GENERAL OUTLINE 
 
 THE ANIMAL KINGDOM. 
 
LONDON : 
 
 PRINTED BY SAMUEL BENTLEV, 
 Bangor House, Shoe Lane. 
 
GENERAL OUTLINE 
 
 THE ANIMAL KINGDOM, 
 
 MANUAL OP COMPARATIVE ANATOMY. 
 
 BY THOMAS RYMEB JONES, F.Z.S. 
 
 PROFESSOR OP COMPARATIVE ANATOMY IN KING'S COLLEGE, LONDON} 
 
 FULLERIAN PROFESSOR OF PHYSIOLOGY TO THE ROYAL INSTITUTION OF GREAT BRITAIN, 
 
 &C. &C. 
 
 ILLUSTRATED BY 
 
 THREE HUNDRED AND THIRTY-SIX ENGRAVINGS. 
 
 LONDON: 
 
 JOHN VAN VOORST, ], PATERNOSTER ROW; 
 
 M.DCCC.XLT. 
 
 
 ., 
 
 
K- 
 
 To RICHARD OWEN, ESQ., F.R.S. 
 
 &c. &c. &c. 
 
 THE FOLLOWING PAGES ABE INSCRIBED 
 
 BY HIS SINCERE FRIEND, 
 
 THE AUTHOR. 
 
 M367753 
 
PREFACE. 
 
 THE object of the writer of the present work has been 
 twofold ; first, to lay before the Naturalist a complete view 
 of the organization and physiological relations of every 
 class of living beings ; and secondly, to offer to the Ana- 
 tomical Student a succinct account of the structure and 
 developement of the vital organs through all the modifi- 
 cations that they present in the long series of the animal 
 creation. 
 
 Extensive indeed is the field of study that offers itself 
 to the zealous cultivator of Natural History, if he would 
 step beyond the limits that not unfrequently too narrowly 
 circumscribe his views of animated nature. Needlessly 
 to multiply specific distinctions, or to arrange trivial groups 
 of external forms in imaginary circles, is an easy occupa- 
 tion to the superficial Zoologist, easier perhaps than it 
 would be to one more deeply conversant with the anato- 
 my and intimate composition of the creatures thus sum- 
 marily classified; and, accordingly, it is by no means un- 
 common in the present day to see the most strenuous 
 supporters of this or that theory resolutely shutting their 
 eyes against all evidence deducible from the laws of phy- 
 siology, and stoutly maintaining that outward form is in 
 itself enough for the purpose they have in view, namely, 
 the establishment of some favourite principle or fancied 
 
Ylll PREFACE. 
 
 analogy. Discussions of this kind have been carefully 
 avoided in the following pages : to collect from every 
 available source the ascertained facts connected with 
 anatomical structure, and to arrange the grand divisions 
 of the animal world in conformity with progressive de- 
 velopement as we advance from humbler to more com- 
 plex types of organization, has been the chief aim of the 
 Author; and, if he has at all succeeded in divesting so 
 important a subject of those technicalities which not un- 
 frequently impede the progress of the general reader, 
 his labour has not been thrown away. 
 
 To the Physiologist little apology is necessary for the 
 production of a work intended to exhibit at one view the 
 leading facts of Comparative Anatomy. In this country, 
 unfortunately, so extended a view of Nature is considered 
 as being by no means essential to a correct intelligence 
 of the laws of animal life, and as a branch of professional 
 education has been hitherto completely neglected. Our 
 illustrious countryman John Hunter entertained a dif- 
 ferent opinion. May the fire which he first kindled 
 amongst us, and which has since his time been kept alive 
 by the fostering care of that College, the depository of 
 his invaluable works, soon burst forth, and irradiate the 
 realms of science as brightly as the great founder of 
 Comparative Physiology foresaw that it might ! 
 
PHYSIOLOGICAL INDEX. 
 
 NERVOUS SYSTEM. 
 
 General classification of Animals, in accordance with the condition of 
 ACRITA ........ 
 
 NEMATONEURA ...... . 
 
 Anatomy of the nervous system in 
 
 Linguatula tamioides ..... 
 
 Ascaris lumbricoides . . . . . . 
 
 Notommata clavulata ..... 
 
 Actheres percarum ...... 
 
 Asterias ....... 
 
 Echinus ....... 
 
 Holothuria ...... 
 
 Siponculus ....... 
 
 HOMOGANGLIATA ....... 
 
 Anatomy of the nervous system in 
 
 Hirudo medicinalis . . . . . . 
 
 Myriapoda ...... 
 
 Insecta ....... 
 
 Changes that take place in the condition of the nervous system 
 
 during the metamorphosis of Insects 
 Crustacea ....... 
 
 Motor and Sensitive tracts in the nervous centres of Homogangliata 
 
 HETEROGANGLIATA . . . . . . . 
 
 Anatomy of the nervous system of 
 
 Cirrhopoda . . . . . . . 
 
 Brachiopoda ...... 
 
 Tunicata . . 
 
 Conchifera ...... 
 
 .Gasteropoda ....... 
 
 Pteropoda ...... 
 
 Cephalopoda ....... 
 
 Nautilus Pompilius ..... 
 
 VERTEBRATA . ...... 
 
 Anatomy of the nervous system of 
 
 Fishes ....... 
 
 Reptiles ....... 
 
 Birds 
 
 Mammalia 
 
 SENSE OF TOUCH 
 in Polyps 
 in Holothuria 
 in Siponculus 
 in Leech 
 
 ORGANS OF THE SENSES. 
 
 Sense of touch in Insects 
 
 in Crustacea 
 
 Tentacula of Gasteropoda 
 Pteropoda 
 
 Page Sec. 
 6 8 
 
 6 8 
 99132 
 
 101135 
 103140 
 124163 
 132173 
 158199 
 171211 
 178219 
 183225 
 
 184227 
 
 198240 
 229273 
 270312 
 
 303349 
 336372 
 340375 
 
 351387 
 
 355391 
 367_400 
 372408 
 391425 
 415452 
 427468 
 457499 
 457500 
 
 484520 
 
 521557 
 576633 
 607675 
 691796 
 
 22 28 
 178219 
 180181 
 199_240 
 225267 
 274317 
 343378 
 402439 
 425466 
 
X PHYSIOLOGICAL INDEX, 
 
 Tactile organs of Cephalopoda 
 Sense of touch in Reptiles 
 
 in Birds 
 
 in Mammalia 
 
 SENSE OF TASTE 
 
 in Insects ..... 
 
 in Crustacea ..... 
 
 in Cephalopods ..... 
 
 in Fishes ..... 
 
 in Reptiles ..... 
 
 in Birds ..... 
 
 in Mammals ..... 
 
 SENSE OF SMELL 
 
 in Insects . . 
 
 in Crustacea ..... 
 
 in Nautilus Pompilius .... 
 
 in Fishes ...... 
 
 in Reptiles . . 
 
 in Birds ...... 
 
 in Mammals ..... 
 
 SENSE OF VISION. 
 
 Red specks observable in Acrita 
 
 . in Rotifera 
 
 in Lamproglena pulchella 
 
 Eyes of Leech . 
 
 Simple ocelli of Insects 
 
 Compound eyes of Insects . 
 
 Eyes of Crustacea .... 
 
 the Scallop (Pecten) . 
 
 Snail .... 
 
 other Gasteropoda 
 
 Nautilus Pompilius 
 
 Cuttle-fish . 
 
 Fishes .... 
 
 Reptiles . - . 
 
 Birds .... 
 
 . Mammalia . . . . . 
 
 SENSE OF HEARING 
 in Insects 
 
 in Crustacea . 
 
 in Cuttle-fishes ..... 
 in Fishes ... 
 
 in Reptiles ..... 
 
 in Birds . . . 
 
 in Mammalia ..... 
 
 Page Sec. 
 460501 
 584645 
 608676 
 703825 
 
 275318 
 343_378 
 462503 
 510544 
 555-611 
 608677 
 673752 
 
 275319 
 343_378 
 463-504 
 521558 
 578633 
 608678 
 692800 
 
 64 92 
 124162 
 134177 
 199_241 
 276321 
 277321 
 343379 
 
 391426 
 402439 
 416452 
 464506 
 466507 
 522560 
 578634 
 609679 
 695805 
 
 275319 
 344380 
 470512 
 526568 
 580638 
 614-684 
 699819 
 
 LOCOMOTIVE ORGANS. 
 
 Condition of muscular system in Acrita 
 Coelelmintha 
 
 Bryozoa 
 Rotifera 
 Epizoa 
 
 Suckers of Star-fishes 
 Suckers of Echini 
 Spines of Echini 
 Suckers of Holothuria 
 Muscular system of Siponculus 
 Locomotive organs of the Leech . 
 
 . Earthworm 
 
 Setae of Dorsibranchiate Annelidans 
 
 6 8 
 
 102139 
 111147 
 121159 
 132172 
 149190 
 163204 
 163205 
 173214 
 180221 
 191234 
 201224 
 213258 
 
PHYSIOLOGICAL INDEX. 
 
 Feet of Julus ..... 
 
 Scolopendra . 
 
 Legs of Insects ..... 
 
 Mechanical structure of the feet of Insects 
 
 Wings of Insects ..... 
 
 Muscular system of Insects . . 
 
 Spinning organs of Arachnidans 
 
 Locomotive organs of Crustacea 
 
 Muscles of Cirrhopoda .... 
 
 Arms of Brachiopoda . 
 
 Mantle of Ascidia ..... 
 
 Foot of Conchifera . 
 
 Byssus of Mussel and Pinna 
 
 Apparatus for opening and closing the shells of Conchifera 
 
 Muscular system of Snail .... 
 
 Locomotive organs of Pteropoda 
 
 Tentacula and suckers of Cuttle-fishes 
 
 Sails (so called) of Argonaut . . 
 
 Arms and float of Nautilus Pompilius . . 
 
 Locomotive apparatus of Argonaut 
 
 Fins and muscular system of Fishes 
 
 Limbs of Reptiles . 
 
 Muscular system of Reptiles 
 
 Locomotion of Birds . . . 
 
 Muscular system of Mammalia 
 
 XI 
 
 Page Sec. 
 225268 
 228272 
 240282 
 241283 
 246287 
 250292 
 316363 
 319364 
 356392 
 
 369402 
 381415 
 383417 
 384418 
 395_430 
 424465 
 431474 
 435477 
 437479 
 443485 
 500537 
 542590 
 555610 
 591657 
 660740 
 
 SKELETONS OF INVERTEBRATA. 
 
 Horny and calcareous framework of Sponges 
 Shells of Infusoria .... 
 
 Polyparies of Polyps ...... 
 
 Fungidae .... . 
 
 Cortical Polyps ..... 
 
 Tubiporidae ..... 
 
 Sertularidae . ..... 
 
 Internal plates of Velella and Porpita 
 
 Cells of Bryozoa ...... 
 
 Shells of Rotifera ..... 
 
 Skeletons of Echinodermata. 
 
 Crinoidae ...... 
 
 Asteridae ...... 
 
 Echinidae ...... 
 
 Skeletons of Homogangliata ..... 
 
 Myriapoda 
 
 Insecta . 
 
 Arachnida ..... 
 
 Crustacea ...... 
 
 Structure and growth of the shells of Mollusca : 
 
 Cirrhopoda . 
 
 Brachiopoda ..... 
 
 Tunicata ...... 
 
 Conchifera ..... 
 
 Gasteropoda ...... 
 
 Cephalopoda ..... 
 
 First appearance of an internal skeleton (Endo-skeleton} 
 
 13 16 
 53 74 
 30 42 
 18 21 
 29 40 
 34 48 
 45 63 
 69 97 
 110146 
 118155 
 
 136180 
 147189 
 160202 
 184228 
 224266 
 238279 
 306351 
 319364' 
 
 352389 
 363398 
 369402 
 384419 
 418458 
 440482 
 439481 
 
 SKELETONS OF VERTEBRATA. 
 
 a. Cuticular skeleton, or Exo-skeleton. 
 Dermo-skeleton of Fishes 
 Growth of hair and other epidermic appendages 
 Horns of the Deer 
 
 506541 
 687788 
 688790 
 
Xll 
 
 PHYSIOLOGICAL INDEX. 
 
 b. Osseous skeleton, or Endo- skeleton : 
 
 General view of the skeleton of Vertebrata 
 Osteology of Fishes 
 
 Reptiles 
 
 Birds 
 
 Mammalia . 
 
 Page Sec. 
 477518 
 489522 
 544593 
 592658 
 633710 
 
 NUTRITIVE SYSTEM. 
 DIGESTIVE ORGANS OF ACRITA. 
 
 Sponges ..... 
 
 Fungiae ...... 
 
 Alcyonium ..... 
 
 Hydra viridis ..... 
 
 Cortical Polyps .... 
 
 Tubipora musica .... 
 
 Sertularidae ..... 
 
 Actinia ..... 
 
 Polygastrica .... 
 
 Acalephae ..... 
 
 Hydatid 
 
 Trichina ..... 
 
 Taenia 
 
 Distoma ..... 
 
 Planaria ..... 
 
 Diplozoon . . 
 
 Echinorynchus .... 
 
 DIGESTIVE ORGANS OF NEMATONEURA. 
 
 Linguatula taenioides .... 
 Ascaris lumbricoides . . 
 
 Bryozoa ..... 
 
 Rotifera ..... 
 
 EPIZOA. 
 
 Adheres percarum .... 
 
 Lamproglena pulchella 
 
 ECHINODERMATA . 
 
 Asterias . 
 
 Echinus ..... 
 Holothuria ..... 
 
 Siponculus ..... 
 
 DIGESTIVE ORGANS OF HOMOGANGLIATA. 
 ANNELIDA. 
 
 Leech 
 
 Earthworm .... 
 
 Dorsibranchiata ..... 
 Tubicola ... . 
 
 MVRIAPODA. 
 
 Julus ...... 
 
 Scolopendra .... 
 
 INSECTA. 
 
 Mouths of Insects .... 
 
 Alimentary canal of Insects 
 
 of Arachnid a 
 
 CRUSTACEA 
 
 15 17 
 18 21 
 27 37 
 23 29 
 
 34 46 
 
 35 48 
 45 64 
 40 55 
 56 79 
 71 99 
 81110 
 83114 
 84115 
 87118 
 89119 
 92122 
 95126 
 
 100134 
 103141 
 108145 
 122160 
 
 131171 
 134_177 
 
 151192 
 166207 
 174_215 
 180222 
 
 192235 
 203246 
 215260 
 221265 
 
 226269 
 229274 
 
 254295 
 260301 
 310356 
 
 328367 
 
PHYSIOLOGICAL INDEX, 
 
 Xlll 
 
 DIGESTIVE SYSTEM OF HETEROGANGLIATA. 
 
 Cirrhopoda 
 Brachiopoda 
 Tunicata 
 Conchifera . 
 Gasteropoda. 
 
 Snail 
 
 Mouths of Gasteropoda . 
 
 Alimentary canal, &c. 
 Pteropoda 
 Cephalopoda 
 
 DIGESTIVE SYSTEM OF VERTEBRATA. 
 FISHES. 
 
 Teeth of . 
 Digestive apparatus of 
 
 REPTILES. 
 
 Teeth of ... 
 Alimentary system of 
 
 BIRDS . 
 
 MAMMALIA. 
 
 Teeth of ... 
 
 Alimentary apparatus . , 
 
 Page Sec. 
 356393 
 365399 
 370405 
 378413 
 
 395430 
 410445 
 413448 
 424466 
 445487 
 
 510544 
 515545 
 
 556611 
 561619 
 
 597664 
 
 663744 
 677759 
 
 RESPIRATORY AND CIRCULATORY SYSTEMS. 
 
 Rotifera ........ 125164 
 
 Asterias ....... 155 195 
 
 Echinus ........ 170209 
 
 Holothuria ....... 175 216 
 
 Siponculus . . . . . . . ___ 181 223 
 
 Leech ........ 195237 
 
 Earthworm ........ 204247 
 
 Dorsibranchiate Annelidans ..... 217 262 
 
 Insects . . . . . . . . 264306 
 
 Arachnidans ....... 311358 
 
 Crustacea ........ 329 368 
 
 Cirrhopoda ....... 357394 
 
 Brachiopoda . . . . . . . 366400 
 
 Tunicata ....... 370 403 
 
 Oyster ........ 378412 
 
 Snail 397433 
 
 Gasteropoda ....... 403 440 
 
 Pteropoda ....... 427 467 
 
 Cephalopoda ........ 451 494 
 
 Fishes ........ 517553 
 
 Reptiles ........ 564626 
 
 Birds ........ 602671 
 
 Mammalia ........ 682 778 
 
 GENERATIVE SYSTEM. 
 
 FIISSPAROUS GENERATION 
 in Polygastrica 
 in Annelida . 
 
 GEMMIPAROUS GENERATION 
 in Sponges 
 in Fungia 
 in Hydra viridis . 
 
 59 85 
 211254 
 
 16 19 
 19 23 
 25 33 
 
XIV 
 
 PHYSIOLOGICAL INDEX. 
 
 GENERATIVE SYSTEM IN 
 
 Page Sec. 
 
 Tubipora ....... 
 
 36 49 
 
 Acalephae .... 
 
 78107 
 
 Sterelmintha ...... 
 
 . 82111 
 
 Ccelelmintha. 
 
 
 Ascaris lumbricoides ..... 
 
 . 105142 
 
 Hermaphrodism of Syngamus trachealis 
 Rotifera ..... 
 
 106144 
 . 127166 
 
 Epizoa ....... 
 
 133_174 
 
 Asterias ....... 
 
 . 158198 
 
 Echinus ..... 
 
 172212 
 
 Holothuria ..... 
 
 . 178218 
 
 Siponculus 
 Leech . . 
 
 183226 
 . 200242 
 
 Earthworm 
 
 207249 
 
 Nais 
 
 . 209252 
 
 Dorsibranchiate Annelidans 
 
 219263 
 
 Myriapoda ... . 
 Insects ....... 
 
 . 230275 
 279323 
 
 Arachnidans . . ... 
 
 . 315361 
 
 Crustacea . , . . 
 
 344_381 
 
 Cirrhopoda . . 
 
 . 357395 
 
 Brachiopoda 
 Tunicata ... . 
 
 367401 
 . 403407 
 
 Conchifera ...... 
 
 393427 
 
 Snail 
 
 . 399435 
 
 Gasteropoda 
 
 417453 
 
 Pteropoda ... 
 Cephalopoda ...... 
 
 . 428470 
 472513 
 
 T1- 1 
 
 Fishes ....... 
 
 . 530576 
 
 Reptiles ....... 
 
 585648 
 . 616687 
 
 Mammalia . 
 
 706833 
 
 LYMPHATIC SYSTEM. 
 
 
 In Fishes ....... 
 
 . 517552 
 
 In Reptiles ...... 
 In Birds ...... 
 
 563624 
 . 602670 
 
 In Mammalia ... 
 
 682776 
 
 URINARY SYSTEM. 
 
 
 
 520555 
 
 
 . 584646 
 
 In Birds . 
 
 615685 
 
 In Mammals 
 
 . 704831 
 
 DEVELOPEMENT OF THE EMBRYO. 
 
 
 In Adheres percarum 
 Ova of Earthworm 
 Metamorphoses of Myriapoda 
 Tnfifcts 
 
 133175 
 
 . 209251 
 227271 
 . 288336 
 
 Crustacea 
 
 348386 
 
 
 . 361397 
 475516 
 . 539589 
 572630 
 . 620697 
 707834 
 . 714839 
 728858 
 
 Embryo of Cuttle-fish 
 Metamorphosis of the Tadpole 
 Changes in vascular system of Tadpole 
 Developement of the chick in ovo 
 Anatomy of the ovum of Ornithorynchus paradoxus 
 Anatomy of marsupial ovum 
 Developement of the placental fetus 
 
GENERAL INDEX. 
 
 CLASSIFICATION OF THE ANIMAL KINGDOM. 
 
 ACRITA. Page 
 
 Sponges ........ 12 
 
 Polyps . ..... 17 
 
 Polygastrica . . * . . . .50 
 
 Acalephae ........ 64 
 
 Sterelmintha ...... 79 
 
 NEMATONEURA . .... 99 
 
 Coelelmintha ........ 99 
 
 Bryozoa . . . . . . . . 107 
 
 Rotifera . . . . . . .117 
 
 Epizoa .... ... 128 
 
 Echinoderraata . . . . . . . 135 
 
 HOMOGANGLIATA .... . . 184 
 
 Annelida . . . . . . .188 
 
 Myriapoda ........ 224 
 
 Insecta . . . . . .- . 231 
 
 Arachnida ........ 306 
 
 Crustacea .... ... . 319 
 
 HETEROGANGLIATA . . 351 
 
 Cirrhopoda . . . . . . 352 
 
 Brachiopoda ........ 362 
 
 Tunicata ........ 368 
 
 Conchifera ........ 375 
 
 Gasteropoda ....... 394 
 
 Pteropoda . . . . . . . . 423 
 
 Cephalopoda ....... 430 
 
 VERTEBRATA . .... .476 
 
 Fishes ........ 488 
 
 Reptiles ........ 537 
 
 Birds .... .... 591 
 
 Mammalia . . . . . . .632 
 
A GENERAL OUTLINE 
 
 OF 
 
 THE ANIMAL KINGDOM. 
 
 CHAPTER I. 
 
 ON CLASSIFICATION. 
 
 (1). FROM the earliest periods to the present time, the great 
 desideratum in Zoology has been the establishment of some fun- 
 damental system of arrangement, which, being universal in its 
 application, should distribute the countless beings surrounding us 
 into natural groups or divisions, such as might be subdivided 
 into classes, orders, and genera, by obvious differences of structure 
 in the tribes composing them, and thus enable the Zoologist at 
 once to indicate the position which any unknown animal ought 
 to occupy in the scale of existence, and its relations with other 
 creatures. 
 
 (2.) Aristotle, the father of our science, was the first who at- 
 tempted a scientific division of the animal world ; * the outlines 
 of his system were rude in proportion to the necessarily limited 
 knowledge at his disposal, although his efforts were gigantic, 
 and still excite our warmest admiration. This acute observer ad- 
 mitted but two great sections, in one or other of which all known 
 beings were included, the highest comprehending creatures pos- 
 sessed of blood, (i. e. red blood,) corresponding to the vertebrata 
 of modern authors ; the lowest embracing animals which in his view 
 were exsangueous, or provided with a colourless fluid instead of 
 blood, and corresponding to the invertebrata of more recent 
 Zoologists. 
 
 (3.) Linnaeus, like Aristotle, selected the circulatory system as 
 
 * Historia Animalium. 
 
2 ON CLASSIFICATION. 
 
 the foundation of his arrangement,* dividing the animal creation 
 into three great sections, characterized as follows : 
 
 I. Animals possessed of warm red blood, and provided with a 
 heart containing four compartments, viz. two auricles and two 
 ventricles. Such are the mammalia and birds. 
 
 II. Animals with red cold blood, their heart consisting of but 
 one auricle and one ventricle, as he believed to be the case in 
 reptiles and fishes. 
 
 III. Animals possessed of cold white sanies instead of blood, 
 having a heart consisting of a single cavity which he designates an 
 auricle : under this head he includes insects and all other inverte- 
 brate animals, to which latter he gives the general name of vermes, 
 worms. 
 
 We shall not in this place comment upon the want of anatomi- 
 cal knowledge conspicuous in the above definitions, or the insuffi- 
 cient data afforded by them for the purposes of Zoology. The appa- 
 ratus of circulation, being a system of secondary importance in the 
 animal economy, was soon found to be too variable in its arrange- 
 ment to warrant its being made the basis of zoological classification, 
 and a more permanent criterion was eagerly sought after to supply 
 its place. 
 
 (4.) Among the most earnest in this search was our distinguished 
 countryman John Hunter, who, not satisfied with the results ob- 
 tained from the adoption of any one system, seems to have tried all 
 the more vital organs, tabulating the different groups of animals in 
 accordance with the structure of their apparatus of digestion, of 
 their hearts, of their organs of respiration, of their generative 
 organs, and of their nervous system, balancing the relative im- 
 portance of each, and sketching out with a master hand the 
 outlines of that arrangement since adopted as the most natural 
 and satisfactory. ( 
 
 The result of the labours of this illustrious man cannot but 
 be of dee*p interest to the zoological student, and accordingly an 
 epitome of his ideas upon the present subject is here concisely 
 given. 
 
 The apparatus of digestion appears to be among the least 
 efficient for the purpose of a natural division; as the separation 
 
 * Systema Naturae Vindobonae, 1767. Thirteenth Edition. 
 
 t Descriptive and illustrated Catalogue of the Physiological series of Comparative 
 Anatomy, contained in the Museum of the Royal College of Surgeons in London, 
 Vol. III. Fart I. 1835. 
 
ON CLASSIFICATION. 3 
 
 of animals into such as have a simple digestive cavity, receiving 
 and expelling its contents by the same orifice, and such as have 
 an aperture for the expulsion of the contents of the alimentary 
 canal distinct from that by which food is taken into the stomach, 
 is by no means of practical utility, although this circumstance, as 
 we shall afterwards see, has been much insisted upon. 
 
 Hunter's arrangement of the animal kingdom in conformity 
 with the structure of the heart, was a great improvement upon 
 that of Linnseus, founded upon the same basis. He divides in 
 this manner all animals into five groups. 
 
 I. Creatures whose hearts are divided into four cavities Mam- 
 malia and Birds. 
 
 II. Those having a heart consisting of three cavities Rep- 
 tiles and Amphibia.* 
 
 III. Animals possessing a heart with two cavities Fishes 
 and most Mollusca. 
 
 IV. Animals whose heart consists of a single cavity - Articu- 
 lated Animals. 
 
 V. Creatures in which the functions both of stomach and heart 
 are performed by the same organ, as in Medusce. 
 
 We shall pass over Hunter's sketches of arrangements founded 
 on the respiratory and reproductive organs, as offering little satis- 
 factory ; but the researches of this profound physiologist upon the 
 employment of the nervous system for the purpose of zoological 
 distribution, did much to approximate a more natural method of 
 classification, afterwards carried out with important results. 
 
 (5.) The appearance of the " Animal Kingdom distributed in 
 accordance with its organization" of Cuvier, formed a new and im- 
 portant era in Zoology. In this we find all creatures arranged in 
 four great divisions, VERTEBRATA, MOLLUSCA, ARTICULATA, and 
 R ADI AT A. These divisions, with the exception of the first, are 
 named from the external appearance of the creatures composing 
 them, nevertheless the three first are defined by characters exclu- 
 sively drawn from their internal organization, the arrangement of 
 the nervous system being essentially the primary character of dis- 
 tinction, and have been found to be strictly natural ; whilst the 
 last division, characterized by the appellation of R ADI AT A, in the 
 formation of which the structure of the nervous system has 
 
 * For the important discovery that the heart of the Amphibia is divided into three 
 cavities, instead of being composed of a single auricle and ventricle, we are indebted to 
 Professor Owen. Vide Zool. Trans. Vol. I. 
 
4 ON CLASSIFICATION. 
 
 been allowed to give place in importance to other characters of 
 secondary weight, obviously embraces creatures of very dissimilar 
 and incongruous formation. 
 
 The VERTEBRATA are distinguished by the possession of an 
 internal nervous centre or axis, composed of the brain and spinal 
 cord, which is enclosed in an osseous or cartilaginous case, and placed 
 in the median plane of the body, giving off symmetrical nerves, 
 which are distributed to all parts of the system. This general 
 definition indicates a large division of the animal world, which, 
 by secondary characters drawn from the structure of their organs 
 of respiration and circulation, is separable into mammals, birds, 
 reptiles, amphibia, and fishes. 
 
 The MOLLUSCA have a nervous system constructed upon a very 
 different type, and do not possess any vertebral column or articu- 
 lated skeleton. The nervous centres consist of several detached 
 masses placed in different parts of the body, without regularity 
 of distribution or symmetrical arrangement ; and the entire group 
 is obviously natural, although Cuvier has ranged in it some creatures 
 which, in the structure of their nervous system, differ essentially 
 from those comprised in his own definition. 
 
 The class of ARTICULATED ANIMALS is likewise well cha- 
 racterized by the nervous system, which, in all the members of it, 
 is composed of a double series of ganglia or masses of neurine, 
 arranged in two parallel lines along the abdominal surface of the 
 body, united by communicating cords, and from which nerves are 
 given off to the different segments of which the body consists. 
 
 But the fourth division of Cuvier, namely, that of ZOOPHYTES 
 or RADIATED ANIMALS, is confessedly made up of the most hete- 
 rogeneous materials, comprising animals differing in too many 
 important points to admit of their being associated in the same 
 group ; and the efforts of subsequent Zoologists have been mainly 
 directed to the establishment of something like order in this 
 chaotic assemblage. 
 
 (6.) The evident relation which the perfection of the nervous 
 system bears to that of animal structure, and the success of Cuvier 
 in selecting this as the great point of distinction in the establish- 
 ment of the higher divisions of the animal kingdom, necessarily 
 led succeeding naturalists still to have recourse to this important 
 part of the economy in making a further subdivision of the 
 Radiata of Cuvier. In some of the radiated forms, indeed, 
 nervous filaments are distinctly visible, and such are among the 
 
ON CLASSIFICATION. 5 
 
 more perfectly organized of the group ; these, therefore, have 
 been classed by themselves, and designated by Mr. Owen the 
 NEMATONEUROSE* division of the animal world ; while those 
 which are apparently without the least trace of distinct nervous 
 matter, have been formed by Mr. M'Leay into a group by them- 
 selves, to which he has given the denomination of ACRITA.J- 
 
 (7.) There can be no doubt that the nervous matter must be 
 regarded as the very essence or being of all creatures, with which 
 their sensations, volition, and capability of action are inseparably 
 connected ; and such being the case it is a legitimate inference, 
 that the capacities and powers of the several tribes are in im- 
 mediate relation with the developement and perfection of this 
 supreme part of their organization, and their entire structure must 
 be in accordance with that of the nervous apparatus which they 
 possess. The nature of the limbs and external members, the 
 existence or nonexistence of certain senses, the capability of loco- 
 motion, and the means of procuring food, must be in strict cor- 
 respondence with the powers centred in the nervous masses of 
 the body, or in that arrangement of nervous particles which 
 represents or replaces them. 
 
 Granting the accuracy of the above view, it is obvious, that 
 if exactly acquainted with the structure and elaboration of the 
 nervous apparatus in any animal, we might to a great extent pre- 
 dicate the most important points in its economy, and form a 
 tolerably correct estimate of its powers and general conformation. 
 But, unfortunately, such knowledge is not always at our disposal : 
 in the lower forms of the animal world especially, we are far from 
 being able to avail ourselves of such a guide, and it will probably 
 be long ere our improved means of research permit us to apply to 
 practice the views which Physiology would lead us to adopt. 
 
 The grand divisions of the animal kingdom, grounded upon the 
 principal varieties in the arrangement of the nervous system, we 
 shall, however, proceed to consider, leaving to future occasions 
 those comments which a consideration of the structure of par- 
 ticular groups will force upon our notice. 
 
 , a thread ; N-upov, a nerve. t , priv.; notva, to discern. 
 
ON CLASSIFICATION. 
 
 1st Division. ACRITA* (M'Leay); Cryptoneura, (Rudolphi)-f- 
 Protozoa,]. Oozoa. 
 
 (8.) In animals belonging to this division, no nervous filaments or 
 masses have been discovered, and the neurine or nervous matter is 
 supposed to be diffused in a molecular condition through the body, 
 mixed up with the gelatinous parenchyma of which they consist. 
 Possessing no brain or central mass, to which external impressions 
 can be transmitted, or nervous filaments calculated to conduct 
 sensations to distant points of the system, or associate muscular 
 movements, they are necessarily incapable of possessing those 
 organs which are dependent upon such circumstances ; instruments 
 of the external senses are therefore totally wanting, or their ex- 
 istence at least is extremely doubtful ; the contractile molecules of 
 their bodies are not as yet aggregated into muscular fibre. The 
 alimentary apparatus consists of canals or cavities, permeating the 
 parenchyma of the body, but without distinct walls, as in the 
 higher divisions, where it floats in an abdominal cavity. The 
 vascular system, where at all perceptible, consists of reticulate 
 channels, in which the nutrient fluids move by a kind of cyclosis. 
 Their mode of reproduction is likewise conformable to the diffused 
 state of the nervous and muscular systems ; not only are most 
 of them susceptible of being multiplied by mechanical division, 
 but they generate by spontaneous fissure, as well as by gemmae, 
 ciliated gemmules, and true ova. Many appear to be made up of 
 a repetition of similar parts, forming compound animals of various 
 forms, and different degrees of complexity. In this division are 
 included 
 
 1. Sponges. 
 
 2. Polyps. 
 
 3. Polygastric animalcules. 
 
 4. Acalephse. 
 
 5. Parenchymatous Entozoa or Sterelmintha. 
 
 * Horae Entomologicae, Vol. I. Part II. page 202. We adopt the term, however, 
 according to its improved application by Mr. Owen, viz. to the exclusion of the higher 
 organized Polyps and Entozoa, and the admission of part of the Radiata of Macleay. 
 
 t Beytriige sur Anthropologie. 1812. J U^uros, first ; 2*>ov, animal. 
 
 '(lov, an egg ; 2&Jv, animal, so called by Carus, because they resemble the eggs or 
 rudiments of more perfect forms. 
 
ON CLASSIFICATION. 
 
 Second Division. NEMATONEURA (Owen).* 
 
 (9.) In the second division of the Radiata of Cuvier, the nervous 
 matter is distinctly aggregated into filaments, and in some cases 
 nuclei of neurine, which may be regarded as rudimentary nervous 
 centres, have been noticed. It is to be lamented, however, that in 
 this most interesting group of animals, in which we have the first 
 developement of most of the organs subservient to the vital 
 functions, the extreme minuteness of some genera, and the diffi- 
 culty of distinctly observing the nervous system in the larger 
 species, has prevented our knowledge regarding their organization, 
 in this particular, from being of that satisfactory character which it 
 is to be hoped it will hereafter attain to. 
 
 Owing to the want or imperfect condition of the nervous centres, 
 the nematoneura are necessarily incapable of possessing external 
 organs of the higher senses, the general sense of touch being as yet 
 the only one of which they are indubitably possessed ; yet in their 
 muscular system they are much more efficiently provided than the 
 acrite orders, as the developement of nervous threads of communi- 
 cation renders an association of muscular actions possible ; and 
 therefore, co-apparent with nervous filaments, we distinguish in the 
 structure of the nematoneura distinct fasciculi of muscular fibre, 
 and powers of locomotion of a much more perfect description. 
 
 The digestive apparatus is no longer composed of canals merely 
 excavated in the parenchyma of the body, but is provided with 
 distinct muscular and membranous walls, and loosely attached in 
 an abdominal cavity. 
 
 The circulation of the nutritious fluid is likewise carried on in a 
 separate system of vessels, distinct from the alimentary apparatus, 
 yet still unprovided with a heart, or exhibiting pulsations for the 
 forcible impulsion of the contained blood. 
 
 The fissiparous mode of reproduction is no longer witnessed, 
 an obvious consequence of the increased complexity of struc- 
 ture, and these animals are for the most part androgynous, or 
 capable of producing fertile ova, without the co-operation of two 
 individuals. 
 
 Among the nematoneura, therefore, we include 
 
 * Cyclopaedia of Anatomy and Physiology. Article, ACRITA. 
 
8 ON CLASSIFICATION. 
 
 1. Bryozoa, or Polyps, with ciliated arms. 
 
 2. Rotifera. 
 
 3. Epizoa. 
 
 4. Cavitary Entozoa or Ccelelmintha. 
 
 5. Echinodermata. 
 
 The reader will perceive, that this division, however well sepa- 
 rated from the preceding by physiological characters, is, in a 
 zoological point of view, principally composed of groups detached 
 from the members of other orders. The Bryozoa are evidently 
 dismemberments of the family of Polyps, from which they differ in 
 their more elaborate internal organization. The Coelelmintha are 
 more perfect forms of the Parenchymatous Entozoa. The Roti- 
 fera, formerly confounded with the Infusoria, exhibit manifest 
 analogies with the articulated Crustaceans, as in fact do the 
 Epizoa. The Echinodermata alone appear to form an isolated 
 group, properly belonging to the division under consideration. 
 
 Third Division. HOMOGANGLIATA (Owen) ; Articulata (Cu- 
 vier)*; Annulosa (Macleay) ; Diploneura (Grant). ~f* 
 
 (10.) The articulated division of the animal kingdom is charac- 
 terized by a nervous system, much superior in developement to that 
 possessed by the two preceding, indicated by the superior propor- 
 tionate size which the ganglionic centres bear to the nerves which 
 emanate from them. The presence of these central masses of neurine, 
 admits of the possession of external senses of a higher class than could 
 be expected among the Acrita or Nematoneura, and gives rise to 
 a concentration of nervous power, which allows of the existence of 
 external limbs of various kinds, and of a complex muscular system 
 capable of great energy and power of action. 
 
 The nervous centres are arranged in two parallel lines along the 
 whole length of the body, forming a series of double ganglia or 
 brains, belonging apparently to the individual segments of which 
 the animal is composed. The anterior pair placed invariably in 
 the head above the oesophagus, and consequently upon the dorsal 
 aspect of the body, seems more immediately appropriated to the 
 higher senses, supplying nerves to the antennae, or more special in- 
 struments of touch, to the eyes, which now manifest much com- 
 plexity of structure, to the auditory apparatus where such exists, 
 
 * The Cirripecla are excluded from the Articulata of Cuvier. 
 
 -f- The Entozoa and Rotifera are included in the Diploneura of Dr. Grant. 
 
ON CLASSIFICATION. 9 
 
 and probably to the senses of taste and smell. This dorsal or 
 anterior pair of ganglia, which evidently is in relation with the 
 higher functions of the economy of the creature, is brought into 
 communication with the series of nervous centres placed along the 
 ventral aspect, by means of filaments which embrace the oesophagus, 
 and join the anterior pair placed beneath it ; the whole system 
 may therefore be regarded as a series of independent brains destined 
 to animate the segments of the body in which they are individually 
 placed. Such a multiplication of the central organs of the nervous 
 system, is obviously adapted to the elongated forms of the vermi- 
 form orders, but from the want of concentration which such an 
 arrangement implies, this type of structure is still very inferior in 
 its character. As the articulata become more perfect in their out- 
 ward form, the number of the brains becomes diminished, while 
 their proportionate size increases ; and thus in the carnivorous 
 Insects, Arachnida and Crustacea, they are all united into a few 
 great masses, which, becoming the general centres of the entire 
 system, admit of a perfection in their external senses, a precision 
 in their movements, and an energy of action, of which the detached 
 character of the ganglia in the lower tribes was incapable. 
 
 (11.) This dependence of the perfection of the animal upon the 
 concentration of the central masses of the nervous system, is strik- 
 ingly proved by the changes perceptible in the number and arrange- 
 ment of the ganglia, during the progress of an insect through the 
 different stages of its existence. In the elongated body of the worm- 
 like caterpillar, each segment possesses its appropriate pair of ganglia, 
 and the consequence of such diffusion of its nervous apparatus, is 
 apparent in its imperfect limbs, its rude organs of sense, its sluggish 
 movements, and general apathy, but as it successively attains to 
 more mature forms of existence, passing through the different me- 
 tamorphoses which it undergoes, the nervous ganglia gradually 
 coalesce, increase in power, as they diminish in number, until in 
 the imago or perfect state, having arrived at the greatest concen- 
 tration compatible with the habits of the insect, we find it endued 
 with new and far more exalted attributes, the organs of its senses 
 are more elaborately formed, it possesses limbs which previously it 
 would have been utterly incapable of wielding, its movements are 
 characterized by their activity and precision, and its instincts and 
 capabilities proportionately enlarged and exalted. 
 
 The Homogangliate division of the animal world is extremely 
 natural, and includes the following classes : 
 
10 ON CLASSIFICATION. 
 
 1. Cirripeda. 4. Insecta. 
 
 2. Annelida. 5. Araclmida. 
 
 3. Myriapoda. 6. Crustacea. 
 
 Fourth Division. HETEROGANGLIATA (Owen) ; Mollusca 
 (Cuvier)*; Cyclogangliata (Grant). 
 
 (12.) The characters of this division are well defined, and the irre- 
 gular and unsymmetrical forms of the bodies of most of the genera 
 which compose it, in exact relation with the arrangement of the 
 nervous apparatus. 
 
 As in the articulata there is a large nervous mass placed above 
 the oesophagus, which supplies the principal organs of sense, but 
 the other ganglia are variously dispersed through the body, although 
 always brought into communication with the supracesophageal 
 portion by connecting filaments. Throughout all the forms, we 
 find a distinct relation between the size and developement of the 
 nervous centres, and the perfection of the animal, indicated by the 
 senses and organs of motion with which it is provided. 
 
 This division includes 
 
 1. Tunicata. 4. Gasteropoda. 
 
 2. Conchifera. 5. Pteropoda. 
 
 3. Brachiopoda. 6. Cephalopoda. 
 
 Fifth Division. VERTEBRATA (Cuvier); Myelencephala (Owen); 
 Spinicerebrata (Grant). 
 
 (13.) The arrangement of the nervous centres in the highest or 
 vertebrate division, indicates the greatest possible concentration and 
 developement. The ganglionic masses assume a very great pro- 
 portionate size when compared with the nerves which emanate from 
 them, and are principally united into a long chain, denominated 
 the cerebro-spinal axis or cord, which is enclosed in a cartilaginous 
 or bony canal, occupying the dorsal region of the animal. The 
 anterior extremity of the cerebro-spinal axis is made up of those 
 ganglia which are more especially in relation with the principal senses 
 and the higher powers of intelligence, forming a mass denominated, 
 from its position in the skull which encloses it, the encephalon. 
 It is with the increased proportionate developement of this portion, 
 that the intelligence of the animal becomes augmented ; in the 
 lower tribes, the cerebral masses scarcely exceed in size those 
 
 * The Cirripeda are included in the Mollusca of Cuvier. 
 
ON CLASSIFICATION. 11 
 
 which form the rest of the central chain of ganglia, but as we 
 advance from fishes towards the higher forms of the vertebrata, we 
 observe them to preponderate more and more in bulk, until at 
 last in man they assume that extraordinary developement adapted 
 to the exalted position which he is destined to occupy. It is in 
 the cerebral ganglia, therefore, that we have the representative of 
 the supracesophageal masses of the articulated and molluscous 
 classes, which, as we have already seen, preside especially over the 
 senses, and correspond in their proportions with the capabilities of 
 the tribes of animals included in those divisions. The spinal cord, 
 as the rest of the central axis of the nervous system of vertebrata 
 is denominated, is made up of a succession of ganglia, in communi- 
 cation with symmetrical pairs of nerves connected with them, and 
 which preside over the generally diffused sense of touch, and the 
 voluntary motions of the body. But besides the cerebro-spinal sys- 
 tem, we find in the vertebrated classes another set of nervous centres, 
 to which nothing corresponding has been satisfactorily identified in 
 the lower divisions ; namely, the sympathetic system, which mainly 
 controls the involuntary movements of the body connected with the 
 vital functions. 
 
 The vertebrata are further distinguished by the possession of 
 an internal organized skeleton, either composed of cartilage or 
 bone, which is made up of several pieces, and serves as the general 
 support of the frame, forming a series of levers upon which the 
 muscles act. 
 
 This last division of the animal world embraces the following 
 classes : 
 
 1. Fishes. 4. Birds. 
 
 2. Amphibia. 5. Mammalia. 
 
 3. Reptiles. 
 
 Such will be the classification which we shall adopt in the 
 following pages ; and although, perhaps, the definitions of the five 
 great groups may be considered by the scientific reader as some- 
 what scanty, enough, we trust, has been said to render intelli- 
 gible the terms which we shall hereafter have frequent occasion to 
 employ. 
 
 (14.) A question naturally presents itself in this place which re- 
 quires consideration : May we expect, as we advance from the lower 
 types of organization to such as are more perfect, to be led on 
 through an unbroken and continuous series of creatures, gradually 
 rising in importance and complexity of structure, each succeeding 
 
12 ON CLASSIFICATION. 
 
 tribe of beings presenting an advance upon the preceding, and 
 merging insensibly into that which follows it ? A very slight 
 investigation of this matter will convince us of the contrary. Each 
 group, in fact, will be found to present points of relationship with 
 several others, into all of which it passes by connecting species ; as 
 a circle would, at different points of its circumference, touch others 
 placed around it. This, however, will be best illustrated as we 
 proceed. 
 
 CHAPTER IT. 
 
 ON SPONGES. 
 
 Porifera,) Grant Amorphozoa (Blainville). 
 
 (1 5.) The great circles to which we may compare the animal and 
 vegetable kingdom, like the smaller circles to which allusion was 
 made at the close of the last chapter, touch each other ; or, in 
 other words, there are certain forms of organization so closely 
 allied to both, that it is difficult to say precisely in which they 
 ought to be included. Such are the sponges, which, although by 
 common consent admitted into the animal series, will be found to 
 be excluded, by almost every point of their structure, from all the 
 definitions of an animal hitherto devised. What is an animal ? 
 How are we to distinguish it as contrasted with a mineral or a 
 vegetable ? The concise axiom of Linnaeus upon this subject is 
 well known, " Stones grow ; vegetables grow and live ; animals 
 grow, live, and feel." The capability of feeling, therefore, 
 formed, in the opinion of Linnaeus, the great characteristic sepa- 
 rating the animal from the vegetable kingdom ; yet, in the class 
 before us, no indication of sensation has been witnessed ; contact, 
 however rude, excites no movement or contraction which might 
 indicate its being perceived ; no torture has ever elicited from them 
 an intimation of suffering ; they have been pinched with forceps, 
 lacerated in all directions, bored with hot irons, and attacked with 
 the most energetic chemical stimuli, without shrinking or exhibit- 
 ing the remotest appearance of sensibility. On the other hand, 
 in the vegetable world we have plants which apparently feel in 
 
1'ORIFERA. 13 
 
 this sense cf the word. The sensitive plant, for example, which 
 droops its leaves upon the slightest touch, would have far greater 
 claims to be considered as being an animal than the sponges of 
 which we are speaking. 
 
 The power of voluntary motion has been appealed to as exclusively 
 belonging to the animal economy : yet, setting aside the spontane- 
 ous movements of some vegetables, the sponge, rooted to the rock, 
 seems absolutely incapable of this function, and the most micro- 
 scopic scrutiny has failed to detect its existence. 
 
 The best definition of an animal, as distinguished from a vege- 
 table, which has as yet been given, is, that whereas the latter fixed 
 in the soil by roots, or immersed perpetually in the fluid from 
 which it derives its nourishment, absorbs by its whole surface the 
 nutriment which it requires ; the animal, being generally in a 
 greater or less degree capable of changing its position, is provided 
 with an internal receptacle for food, or stomachal cavity, from 
 which, after undergoing the process of digestion, the nutritious 
 matter is taken up. But in the case of the sponge no such 
 reservoir is found; and in its place we find only anastomosing 
 canals which permeate the whole body, and convey the circumam- 
 bient medium to all parts of the porous mass. 
 
 The last circumstance which we shall allude to as specially 
 appertaining to the animal kingdom, is derived from the chemical 
 composition of organized bodies. Vegetables contain but a 
 small proportion of azote in their substance, whilst in animals this 
 element exists in considerable abundance, causing their tissues 
 when burned to give out a peculiar odour resembling that of 
 burned horn, and in this particular sponges differ from vegetable 
 matter. 
 
 (16.) The common sponge of commerce is, as every one knows, 
 made up of horny, elastic fibres of great delicacy, united with each 
 other in every possible direction, so as to form innumerable canals, 
 which traverse its substance in all directions. To this structure 
 the sponge owes its useful properties, the resiliency of the fibres com- 
 posing it making them, after compression, return to their former 
 state, and leaving the canals which they form open, to suck up 
 surrounding fluids by capillary attraction. 
 
 The dried sponge is, however, only the skeleton of the living 
 animal : in its original state, before it was withdrawn from its native 
 element, every filament of its substance was coated over with a thin 
 film of glairy semifluid matter, composed of aggregated transparent 
 
14 
 
 PORIFERA. 
 
 globules, which was the living 
 part of the sponge, secreting, as 
 it extended itself, the horny 
 fibres which are imbedded in it. 
 The anastomosing filaments which 
 compose the skeleton of such 
 sponges, when examined under a 
 microscope, and highly magnified, 
 appear to be tubular, as represented 
 in fig. 1. c. 
 
 Many species, although exhibit- 
 ing the same porous structure, 
 have none of the elasticity of the 
 officinal sponge, a circumstance 
 which is due to the difference ob- 
 servable in the composition of their 
 skeletons or ramified frame-work. 
 In such the living crust forms 
 
 within its substance not only tenacious bands of animal matter, 
 but great quantities of crystallized spicula, sometimes of a calca- 
 reous, at others of a silicious nature, which are united together by 
 the tenacity of the fibres with which they are surrounded. On 
 destroying the softer portions of these skeletons either by the aid 
 of a blow-pipe or by the caustic acids or alkalies, the spicula re- 
 main, and may readily be examined under a microscope : they are 
 then seen to have determinate forms, which are generally in rela- 
 tion with the natural crystals of the earths of which they consist ; 
 and as the shape of the spicula is found to be similar in all sponges 
 of the same species, and not unfrequently peculiar to each, these 
 minute particles become of use in the identification of these 
 bodies.* 
 
 Crystallized spicula of this description form a feature in the 
 structure of the sponge which is common to that of many vege- 
 tables, resembling the formations called Raphides by botanical 
 writers. Some of the principal forms which they exhibit are de- 
 picted in fig. 1 a b, which likewise will give the reader a general 
 idea of the appearance of the silicious and calcareous sponges, 
 after the destruction of their soft parts has been effected by the 
 means above indicated. The figures d, e, f 9 and g, exhibit 
 detached spicula of different forms highly magnified. The most 
 
 * Savigny (Jules Caesar) Zoologie d'Egypte gr. fol. Paris, 1809. 
 
PORIFERA. 
 
 15 
 
 convenient method of seeing them is simply to scrape off a few 
 particles from the incinerated sponge upon a piece of glass, which, 
 when placed under the microscope, may be examined with ordinary 
 powers. 
 
 (17.) On placing a living sponge of small size in a watch-glass or 
 small glass trough filled with sea-water, and watching it attentively, 
 something like a vital action becomes apparent.* The entire 
 surface is seen to be perforated by innumerable pores and aper- 
 tures, some exceedingly minute, opening on every part of its peri- 
 phery ; others of larger dimensions, placed at intervals, and gene- 
 rally elevated upon prominent portions of the sponge. Through 
 the smaller orifices the surrounding water is continually sucked as it 
 were into the interior of the spongy mass, and it as constantly flows 
 out in continuous streams through the larger openings. This con- 
 tinual influx and efflux of the surrounding fluid is produced by an 
 agency not yet discovered, as no contraction of the walls of the 
 canals, or other cause to which the movement may be referred, has 
 ever been detected ; we are as- 
 sured, however, that it is from 
 the currents, thus continually 
 permeating every portion of 
 its substance, that the general 
 mass is nourished. The annex- 
 ed diagram, fig. 2 a, will give 
 the reader an idea of the most 
 usual direction of the streams : 
 the entering fluid rushes in at 
 the countless pores which occu- 
 py the body of the sponge ; 
 but, in its progress through the 
 canals in the interior, becomes 
 directed into more capacious 
 channels, communicating with 
 the prominent larger orifices, through which it is ultimately ejected 
 in equable and ceaseless currents. Organized particles, which ne- 
 cessarily abound in the water of the ocean, are thus introduced 
 into the sponge on all sides, and are probably employed as nutri- 
 ment, whilst the superfluous or effete matter is continually cast 
 out with the issuing streams as they rush through the fecal ori- 
 fices. The growth of the sponge is thus provided for, the living 
 
 * Dr. Grant, in the New Edinburgh Philosophical Journal, 1827. 
 
16 POHIFERA. 
 
 gelatinous portion continually accumulates, and, as it spreads in 
 every direction, secretes and deposits, in the form peculiar to its 
 species, the fibrous material and earthy spicula which characterise 
 the skeleton. 
 
 (18.) From this description of the structure of a sponge, it will 
 be apparent that all parts of the mass are similarly organized : a 
 necessary consequence will be, that each part is able to carry on, 
 independently of the rest, those functions needful for existence. 
 If therefore a sponge be mechanically divided into several pieces, 
 every portion becomes a distinct animal. 
 
 (19.) The multiplication of sponges, however, is effected in 
 another manner, which is the ordinary mode of their reproduction, 
 and forms a very interesting portion of their history.* At certain 
 seasons of the year, if a living sponge be cut to pieces, the chan- 
 nels in its interior are found to have their walls studded with yel- 
 lowish gelatinous granules, developed in the living parenchyma 
 which lines them ; these granules are the germs or gemmules 
 from which a future race will spring ; they seem to be formed in- 
 differently in all parts of the mass, sprouting as it were from the 
 albuminous crust which coats the skeleton, without the appearance 
 of any organs appropriated to their developement. As they in- 
 crease in size, they are found to project more and more into the 
 canals which ramify through the sponge, and to be provided with 
 an apparatus of locomotion of a description which we shall fre- 
 quently have occasion to mention. The gemmule assumes an 
 ovoid form, fig. 2 B, and a large portion of its surface becomes 
 covered with innumerable vibrating hairs or cilia, as they are de- 
 nominated, which are of inconceivable minuteness, yet individually 
 capable of exercising rapid movements, which produce currents in 
 the surrounding fluid. As soon therefore as a gemmule is suffi- 
 ciently mature, it becomes detached from the nidus where it was 
 formed, and whirled along by the issuing streams which are ex- 
 pelled through the fecal orifices of the parent, it escapes into the 
 water around. Instead, however, of falling to the bottom, as so appa- 
 rently helpless a particle of jelly might be expected to do, the cease- 
 less vibration of the cilia upon its surface propels it rapidly along, 
 until, being removed to a considerable distance from its original, 
 it attaches itself to a proper object, and, losing the locomotive cilia 
 which it at first possessed, it becomes fixed and motionless, and 
 
 * Professor Grant loc. cit. 
 
ON POLYPS. 
 
 developes within its substance the skeleton peculiar to its species, 
 exhibiting by degrees the form of the individual from which it 
 sprung. It is curious to observe the remarkable exception which 
 sponges exhibit to the usual phenomena witnessed in the reproduc- 
 tion of animals, the object of which is evident, as the result is 
 admirable. The parent sponge, deprived of all power of movement, 
 would obviously be incapable of dispersing to a distance the numerous 
 progeny which it furnishes ; they must inevitably have accumulated 
 in the immediate vicinity of their place of birth, without the possi- 
 bility of their distribution to other localities. The seeds of vegetables, 
 sometimes winged and plumed for the purpose, are blown about 
 by the winds, or transported by various agencies to distant places ; 
 but, in the present instance, the still waters in which sponges grow 
 would not have served to transport their progeny elsewhere, and 
 germs so soft and delicate could hardly be removed by other 
 creatures. Instead therefore of being helpless at their birth, the 
 young sponges can, by means of their cilia, row themselves about 
 at pleasure, and enjoy for a period powers of locomotion denied to 
 their adult state. 
 
 CHAPTER III. 
 
 ON POLYPS. 
 
 Zoophytes of old Authors Phytozoa (Ehrenberg). 
 
 (20.) IT is not surprising that many members of the extensive 
 family upon a consideration of which we are now entering, should 
 have been regarded by the earlier naturalists as belonging to the 
 vegetable kingdom, with which, in outward appearance at least, 
 numerous species have many characters in common.* 
 
 Fixed in large arborescent masses to the rocks of tropical seas, 
 or in our own climate attached to shells or other submarine sub- 
 stances, they throw out their ramifications in a thousand beautiful 
 and plant-like forms ; or, incrusting the rocks at the bottom of the 
 ocean with calcareous earth separated from the water which bathes 
 them, they silently build up reefs and shoals, justly dreaded by 
 the navigator, and sometimes giving origin, as they rise to the 
 surface of the sea, to islands which the lapse of ages clothes with 
 
 * Tournefoit, Institutiones Rei Herbaria*, 4to. 1719. 
 
18 
 
 ON POLYPS. 
 
 luxuriant verdure, and peoples with appropriate inhabitants. Va- 
 rious indeed are the forms which these creatures offer to the zoolo- 
 gist ; and the classification of them, even at the present day, is a 
 subject of much doubt and uncertainty. Without entering fur- 
 ther into the subject of their division into groups and families 
 than is connected with our purpose of examining the main features 
 of their economy, we shall select some of the most marked varieties 
 for description, commencing with the simplest and least elabo- 
 rately formed. 
 
 (21.) We have already seen that in the Sponges the living portion 
 of the animal was composed of a gelatinous film, which, without any 
 apparent organization, was possessed of the power of extracting nutri- 
 ment from the water around it, of deriving from the same source ani- 
 malized materials and earthy particles, which were deposited within 
 its texture, and used in constructing a porous frame-work or skele- 
 ton ; and, moreover, that the same semifluid parenchyma could de- 
 velope from its substance germs, which became ultimately expanded 
 into other beings resembling that from which they sprung ; we shall 
 therefore be prepared to find, in the class upon which we are enter- 
 ing, like results produced by equally simple means. 
 
 Among the calcareous 
 structures, derived from 
 the tropical seas, which 
 are usually known by the 
 general terms of Madre- 
 pores, Corals, &c. and 
 which, from the beauty of 
 their structure, form the 
 ornaments of our cabinets, 
 few are more common than 
 those denominated Fun- 
 gise and Meandrinse, 
 animals belonging to the 
 group Madrephyllicea of 
 systematic zoologists. 
 
 These masses consist of thin plates or laminse of various dimensions 
 (fig. 3.) disposed in different directions in different species, but in 
 the Fungia Agariciformis, which we have selected as an example, 
 radiating from a common centre, and forming a circular mass resem- 
 bling a mushroom. When living in its native element, every part of 
 the surface of this stony skeleton was encrusted with a film of animal 
 
 Fig. 3. 
 
ON POLYPS. 19 
 
 matter, dipping down into the interstices of the plates, and cover- 
 ing the whole frame-work. In the figure, the darker portion indi- 
 cates the living crust ; whilst from the lighter parts it has been re- 
 moved, to show the stony skeleton itself. There are no arms or 
 moving parts adapted to the prehension of food, and no separation 
 of organs adapted to the performance of the vital functions has 
 hitherto been described ; the thin membranous film apparently 
 absorbs the materials of its support from the water of the 
 ocean, and deposits within its substance the calcareous par- 
 ticles which it secretes, moulding them into the form peculiar 
 to its skeleton, which it gradually enlarges as its own extent 
 increases. 
 
 (22.) The gelatinous investment, however, gives certain dubious 
 indications of vitality, and possesses the power of contracting itself 
 so as to retire between the laminae of its skeleton when roughly 
 handled, and thus conceal itself from injury. Upon the surface of 
 the soft crust are seen a number of vesicles indicated in the figure, 
 which were regarded formerly as rudimentary tentacula, from the 
 circumstance of their being able to contract and vary their dimen- 
 sions ; recent observations however lead to the belief that they are 
 cavities filled with air, and serving an important purpose in the eco- 
 nomy of the creature, namely, that of preventing it from being 
 turned upside down by the occasional agitation of the ocean, as in 
 such case the animal has been found by experiment to have no power 
 of restoring itself to its former position, and consequently perishes : 
 these air-vessels may therefore be looked upon as floats, which, ren- 
 dering the upper surface more buoyant than the inferior, materially 
 assist in preventing such an accident ; for, as it lies quite loose and 
 unattached upon the surface of the sand, it is subject to be lifted 
 up from its bed by any sudden roll of the sea, and deposited at a 
 considerable distance from its former place. 
 
 (23.) The reproduction of fungise is effected by the developement 
 of sprouts or gemmae, which pullulate from the animal substance as 
 buds issue from a plant, and remain for some time fixed to 
 the parent by a species of foot-stalk, which sustains them until 
 they have attained to a considerable size ; the young fungiae being up- 
 wards of an inch in diameter before they become detached. When 
 mature, they separate from the top of the stony peduncle which hi- 
 therto supported them ; and at this time, the skeleton of the young 
 fungia, when divested of its fleshy part, shows a circular opening 
 beneath, through which the radiating plates of the upper surface 
 
20 ON POLYPS. 
 
 are visible. In a short time a deposit of calcareous matter takes 
 place, which cicatrizes the opening, the marks of which however can 
 be traced for a considerable period, until at length the increase of 
 this secretion continuing with the growth of the animal, entirely 
 obliterates all appearance of its having existed. 
 
 In the earliest period of its developement, the foot-stalk by 
 which the young is united to the parent, as well as its radiating 
 disc, is entirely enveloped with the soft parts of the animal ; but as 
 the upper portion spreads, and assumes its characteristic form, the 
 pedicle is left naked, and the gelatinous coating extends only to the 
 line where the separation afterwards takes place. 
 
 (24.) It is generally supposed that the calcareous matter which 
 forms the skeleton of these madrepores is perfectly external to the liv- 
 ing crust which secretes it, and accordingly is absolutely inorganic, 
 and removed from the future influence of the animal which produced 
 it. Such a supposition appears, however, at variance with the facts 
 above stated, and incompatible with many circumstances connected 
 with the history of the lithophytous polyps. On trying to detach the 
 soft envelope from the surface of the skeleton, the firmness of their 
 adherence would render such a want of connexion improbable, they 
 appear to be, as it were, incorporated with each other ; and besides, 
 the separation of the fungia from the peduncle which joined it to 
 its parent during its earlier growth, necessarily supposes a power of 
 removing the calcareous particles after their deposition. It is 
 therefore almost demonstrable that the earthy matter secreted 
 by the polyp is deposited in the tissue of its substance, and 
 still remains, in a greater or less degree, subject to absorption 
 and removal : of this, however, we shall have fuller evidence 
 hereafter. 
 
 (25.) It is astonishing how nearly the animal and vegetable king- 
 doms approximate each other in the lower orders of these calcareous 
 zoophytes. Admitting the animal nature of fungia, we find calcareous 
 skeletons, essentially similar in their chemical composition, produced 
 by a large tribe of organic forms, long classed with the creatures we 
 are now considering, which modern observations have clearly shown 
 to be of vegetable nature.* 
 
 These are the Corallines, (Linn.) which, although so nearly re- 
 sembling the skeletons of polyps, that Cuvier, Lamarck, and others, 
 scrupled not to admit them into the animal circle, have been proved 
 
 * Schweigger, Anatomische Physiologische Untersuchungen liber Corallen. Berlin, 
 
ON POLYPS. 
 
 by microscopical researches to possess the cellular structure apper- 
 taining to vegetable organization, and are thus placed beyond the 
 limits of our present investigations. 
 
 (26.) We have hitherto spoken of animals which do not appa- 
 rently possess any stomach or oral aperture, any apparatus for 
 the purpose of the digestion or prehension of food. Before describ- 
 ing the more complex forms of polyps, we will now select a group 
 of that class of animals, in which the organs provided for these pur- 
 poses are easily recognisable ; and, as the simplicity of their orga- 
 nization will well exhibit the principal points in the physiology of the 
 acrita,we shall detail at some length the facts known concerning them. 
 
 The HYDR.E, or fresh- water polyps, are common in the ponds and 
 clear waters of our own country ; they are generally found creeping 
 upon confervse which float upon the surface, and may readily be pro- 
 cured in summer for the purpose of investigating the remarkable cir- 
 cumstances connected with their history. p^ 4 
 
 The body of one of these 
 simple animals consists of a 
 delicate gelatinous tube, con- 
 tracted at one extremity, which 
 is terminated by a minute 
 sucker, and furnished at the op- 
 posite end with a variable num- 
 ber of delicate contractile fila- 
 ments, placed around the open- 
 ing which represents the mouth. 
 
 In the Hydra viridis, (jig- 
 4, 1,) the species most common 
 amongst us, the tentacular fila- 
 ments are short, and, when elon- 
 gated to the utmost, are not 
 equal to the length of the body; 
 but in the long-armed species 
 Hydra fusca, (Jig. 4, 2,) they 
 are much prolonged, and of extreme tenuity. If placed in a small glass 
 tube, one side of which is flattened, these animals may readily be sub- 
 mitted to microscopical examination, and, from their transparency, 
 their entire structure is easily made out. When highly magnified, the 
 whole body is seen to consist of a granular substance, generally of a 
 greenish hue, the granules being loosely connected by a semifluid 
 albuminous matter ; but the most minute research reveals no fur- 
 
22 ON POLYPS. 
 
 ther appearances of organization : there is no trace of muscular 
 fibre or of nervous substance, not the slightest indication of vessels 
 of any kind, nor any apparatus destined to the function of repro- 
 duction ; such is the hydra, offering in every particular a good 
 example of the acrite type of structure. 
 
 The young naturalist would scarcely be prepared to see an 
 animal of this description waging continual war with creatures 
 much more perfectly organized than itself; endowed with consi- 
 derable capability of locomotion ; possessed not only of a refined 
 sense of touch, but able to appreciate the presence, and seek the 
 influence of light ; and exhibiting moreover a tenacity of life and 
 power of reproduction almost beyond belief : a little observation, 
 however, will convince him that it possesses all these attributes, 
 and enable him to share in some degree the astonishment with 
 which Trembley, their enthusiastic discoverer, first witnessed and 
 described them.* 
 
 (27.) The hydra is not like most other polyps, fixed and station- 
 ary; but can roam about and change its situation according to circum- 
 stances. Its usual mode of progression is by creeping along the 
 stems of aquatic plants, or upon the sides of the glass in which it 
 is confined : attaching first the little tubercle at its posterior ex- 
 tremity to the surface upon which it moves, it slowly inflects its 
 body (fig. 4, 3), and fixing its oral tentacles, moves along in the 
 manner of a leech, by a succession of similar actions. This method 
 of advancing is, from the small size of the animal, necessarily slow ; 
 and a march of a couple of inches will require several hours for its 
 performance : but, when arrived at the surface of the water, it adopts 
 a more speedy course ; suspending itself by the tail as by a minute 
 float, and hanging with its mouth downwards, it rows itself about 
 with its tentacles, or, wafted by the wind, can travel to a consider- 
 able distance without effort. 
 
 (28.) When left free, the hydrse are found to select positions most 
 exposed to the influence of light, assembling at the surface of the 
 ponds which they inhabit, or seeking that side of the glass in which 
 they are confined, that is most strongly illuminated. That they 
 are able to appreciate the presence of light is therefore indubitable ; 
 yet with what organs do they perceive it ? We are driven to the 
 supposition that, in this case, the sense of touch supplies to a certain 
 extent the want of other senses, and that the hydrse are able, as 
 
 * Trembley, Memoires pour servir a 1'Histoire des Polypes d'eau douce. Leyde, 
 1744. 
 
ON POLYPS. 23 
 
 an Italian author elegantly expresses it, 6C palpare la luce," to feel 
 the light. 
 
 (29.) The tentacles placed around the mouth are eminently sensi- 
 tive, and the smallest particles which impinge upon those organs in 
 their expanded state appear to excite a perception of their presence ; 
 yet their movements, as well as those of the whole body, are extremely 
 slow and languid : it would be difficult therefore to imagine that 
 creatures apparently so helpless should be able to obtain other 
 prey than such as had no power of resistance ; and we could scarcely 
 believe, were it not a matter of continual observation, that the most 
 active little animals, entomostraca, the larvse of insects, and even 
 minute fishes, form their usual food. 
 
 When the hydra is watching for prey, it remains expanded, 
 (fig. 4, 1, 2,5,) its tentacula widely spread and perfectly motionless, 
 waiting patiently till some of the countless beings which populate the 
 stagnant waters it frequents, are brought by accident in contact 
 with them : no sooner does an animal touch one of the filaments 
 than its course is arrested as if by magic ; it appears instantly fixed 
 to the almost invisible threa,d, and in spite of its utmost efforts is 
 unable to escape ; the tentacle then slowly contracts, and others are 
 brought in contact with the struggling prey, which thus seized is 
 gradually dragged towards the orifice of the mouth, that opens to 
 receive it, and slowly forced into the interior of the stomach. 
 
 (30.) We are naturally led to ask, what is the nature of the action 
 by which a passing animal is thus seized ? Trembley supposed that 
 the filamentary arms were besmeared with an adhesive secretion 
 like bird-lime, by which the victim became glued to the tentacle ; 
 this however can hardly be the case, as the exercise of the power of 
 retaining prey seems quite under the control of the hydra : when 
 hungry, seven or eight monoculi* will be captured and swallowed in 
 succession ; but when thus gorged with prey, or when indisposed to 
 take food, although these animals may touch the tentacula again 
 and again, they escape with impunity. 
 
 (31.) Arrived in the stomach of the polyp, the animal which has 
 been swallowed is still distinctly visible through the transparent 
 body of the hydra, which seems like a delicate film spread over it : 
 (Jig* 4, 4,) gradually the outline of the included victim becomes 
 indistinct, and the film which covers it turbid ; the process of diges- 
 tion has begun ; the soft parts are soon dissolved and reduced to a 
 
 * Minute crustaceous animals, possessing considerable strength and agility. 
 
24 OX POLYPS. 
 
 fluid mass, and the shell or hard integument is expelled through the 
 same aperture by which it entered the stomach. 
 
 We will not even hazard a conjecture concerning the process by 
 which digestion is effected in this case, our knowledge of animal 
 physiology is by no means sufficiently advanced to render any 
 attempt at explanation useful ; we will rather pass on, and enquire 
 in what manner the nutritious parts of the food are conveyed into 
 the system of the polyp. We have already observed that no 
 traces of vessels of any kind have as yet been detected in the 
 granular parenchyma of which the creature seems to be composed ; 
 coloured globules are seen floating in a transparent fluid, which, in 
 the Hydra viridis, are green, although in other species they 
 assume different tints. When the food has been composed 
 of coloured substance, as, for example, red larvae, or black 
 planarite, the granules of the body are seen to acquire a simi- 
 lar hue, but the fluid in which they float remains quite trans- 
 parent ; each granule seems like a little vesicle into which 
 the coloured matter is conveyed, and the dispersion of these 
 globules through the body gives to the whole polyp the hue of 
 the prey which it has devoured; sometimes the granules thus 
 tinted are seen to be forced into the tentacula, from whence 
 they are driven again by a sort of reflux into the body, pro- 
 ducing a kind of circulation or rather mixing up of the granular 
 matter which distributes it to all parts. If, after having thus 
 digested coloured prey, the polyp is made to fast for some time, 
 the vesicles gradually lose their deepened hue and become com- 
 paratively transparent. The granules, therefore, would seem to 
 be specially connected with the absorption and distribution of 
 nutriment. 
 
 (32.) Rapid as is the action of the stomach upon food introduced 
 into it, it has no effect upon other parts of the animal when immersed 
 in its cavity : the arms, for example, of the long-armed hydra are 
 frequently coiled around its prey during the process of its solution, 
 without receiving the slightest injury. This circumstance may 
 not appear very remarkable, but it has been found that other 
 polyps of the same species are equally able to resist the solvent 
 action. Trembley once saw a struggle between two of these 
 creatures which had seized upon the same animal ; both had partially 
 succeeded in swallowing it, when the largest put an end to the 
 dispute by swallowing its opponent as well as the subject of con- 
 tention. Trcmbley naturally regarded so tragical a termination 
 
ON POLYPS. 25 
 
 of the affray as the end of the swallowed polyp's existence, but he 
 was mistaken ; after the devourer and his captive had digested 
 the prey between them, the latter was regurgitated safe and sound, 
 and apparently no worse for the imprisonment. 
 
 (33.) We will now proceed to consider the mode of reproduction of 
 these simple animals. When mature and well supplied with food, 
 minute gemmules or buds are seen to become developed from the 
 common substance of the body ; they spring from no particular 
 part, but seem to be formed upon any portion of the general sur- 
 face. These gemmsB appear at first like delicate gelatinous tu- 
 bercles upon the exterior of the parent polyp ; but, as they increase 
 in size, they gradually assume a similar form, become perforated at 
 their unattached extremity, and develope around the oral aperture 
 the tentacula characteristic of their species. 
 
 During the first period of the formation of these sprouts, they 
 are evidently continuous with the general substance from which 
 they arise ; and even when considerably perfected, and possessed of 
 an internal cavity and tentacula, their stomach freely communicates 
 with that of their parent by a distinct opening, so that food 
 digested by the latter passes into the stomach of the young one, 
 and serves to nourish it. As soon as the newly-formed hydra is 
 capable of catching prey, it begins to contribute to the support of 
 its parent ; the food which it captures passing through the aperture 
 at its base into the body of the original polyp. At length, when 
 the young is fully formed and ripe for independent existence, the 
 point of union between the two becomes more and more slender, 
 until a slight effort on the part of either is sufficient to detach 
 them, and the process is completed. 
 
 This mode of increase, when the animals are well supplied with 
 nourishment, and the temperature is favourable, is extremely rapid ; 
 sometimes six or seven gemmse have been observed to sprout at once 
 from the same hydra, and, although the whole process is concluded 
 in twenty-four hours, not unfrequently a third generation may be 
 observed springing from the newly-formed polyps even before 
 their separation from their parent : eighteen have in this manner 
 been seen united into one group, so that, provided each individual 
 when complete exhibited equal fecundity, more than a million 
 might be produced in the course of a month from a single polyp. 
 
 (34.) But perhaps the most remarkable feature in the history 
 of the hydra is its power of being multiplied by mechanical 
 division. If a snip be made with a fine pair of scissors in 
 
ON POLYPS. 
 
 the side of one of these creatures, not only does the wound soon 
 heal, but a young polyp sprouts from the wounded part ; if it be 
 cut into two portions by a transverse incision, each soon deve- 
 lopes the wanting parts of its structure ; if longitudinally di- 
 vided, both portions soon become complete animals ; if even it 
 be cut into several parts, every one of them will rapidly assume the 
 form and functions of the original ; the inversion of its body, by 
 turning it inside out, does not destroy it ; on the contrary, the ex- 
 terior surface assumes the office of a stomachal cavity, and that 
 which was originally internal will give birth to buds, and take 
 upon itself all the properties of the skin. 
 
 (35.) Cortical compound Polyps. From what we have said con- 
 cerning the two preceding families of polyps, one composed of 
 animals consisting entirely of a gelatinous crust which invests a fixed 
 and immoveable skeleton ; the other exhibiting active and hungry 
 creatures, provided with an internal digestive cavity, and endowed 
 with the capability of seizing and devouring living prey, we are 
 prepared to examine the more complex structure of compound 
 polyps, which combine in themselves the characteristics of both 
 families. The compound polyps consist of a mass of gelatinous 
 matter, which indicates, by its power of contraction upon the appli- 
 cation of stimuli, a degree of sensation ; and of a great number of 
 hydrseform polyps, which spring from the surface of the common 
 body, and are individually capable of seizing and digesting prey, 
 the nutriment thus gained being appropriated to the nourishment of 
 the general mass. The animals of this division are provided with 
 numerous mouths and stomachs, each endowed with a power of 
 independent action. 
 
 Although essentially similar in their habits, the compound 
 polyps present various modifications of structure, which natu- 
 rally leads them to be grouped in distinct families. Some- 
 times the central common mass is entirely soft and gelatinous, 
 its surface being covered with minute cells in which the polyps 
 are lodged; such are the Alcyonidas. Sometimes the common 
 body secretes large quantities of calcareous matter in the same man- 
 ner as the Fungia, which, being deposited in its interior, forms 
 arborescent masses, presenting upon their surface multitudes of 
 cells, generally distinguishable after the removal of the outer 
 crust, in each of which when alive a polyp existed : these form 
 the family of Madrepores. The central axis is not unfrequently 
 quite solid and smooth upon the surface, offering no cells for the 
 
ON POLYPS. 
 
 lodgment of the hydrseform mouths ; being sometimes composed of 
 hard and dense calcareous substance, or else flexible and horny in 
 its texture : such are the Corallida or family of corals, properly so 
 called. The internal central axis is, moreover, in another family, 
 composed of several pieces united together by the living crust 
 which secretes them ; and such individuals, being free and unat- 
 tached, are probably able to change their position at pleasure : 
 these form the family of Pennatula. These groups are, however, 
 merely modifications of the same general type of structure, although 
 differing in certain minor points of their organization, so as to render 
 an examination of each form needful for our purpose. 
 
 (36.) Alcyonidce. This family includes several genera, known by 
 the names of Alcyonium, Lobularia, Cydonium, &c., being charac- 
 terized by having no solid axis developed in the interior of the com- 
 mon body. The Cydonium Fig. 5. 
 Mulleri (Jig. 5, 1,) will give t 
 the reader a good idea of the 
 general appearance of one of 
 these compound animals. The 
 central mass, or polypary, is 
 entirely soft, being of a gelati- 
 nous or rather subcartilagi- 
 nous texture. Its density varies 
 with the state of the animal, 
 being more firm when the crea- 
 ture is contracted or hardened 
 by immersion in spirits of 
 wine, than when alive and ex- 
 panded. Upon cutting into 
 it, it is found to be intersected 
 by tough fibrous bands, and 
 not unfrequently contains calcareous spicula dispersed through its 
 substance ; no muscular fibre or nervous matter has ever been de- 
 tected in its composition, and its interior is permeated by nume- 
 rous wide canals variously disposed. The alcyonidse, therefore, may 
 justly be looked upon as intimately related to the sponges in the 
 structure of their common body, differing from them principally in 
 the polyps which occupy the cells upon their surface. 
 
 (37.) The polyps which fill these cells resemble so many hydra in 
 their external configuration, from which, however, they differ in the 
 number of tentacula surrounding the mouth. In the hydra we 
 
28 ON POLYPS. 
 
 find sometimes five, sometimes six, or more of these appendages ; 
 but in all the cortical polyps there are eight. The tentacles, also, 
 are not unfrequently pinnated or slightly fringed on each side, but 
 never provided with moveable cilia. The body of the polyp, when 
 withdrawn from its cell, is somewhat globular, and more complex 
 in its structure than that of the hydra. In Jig. 5,2, a diagram is 
 given, representing the Alcyonium exos, in which the following 
 parts may be distinguished. The stomach* is considerably dilated, 
 and terminates inferiorly in a tubular prolongation, b, which ex- 
 tends into the substance of the common mass, into which it most 
 probably conveys nourishment. But the main difference observ- 
 able between the alcyonidse and the hydra consists in the possession 
 of a reproductive organ or ovary, in which the germs of its progeny 
 are developed. This consists of a tubular filament, c, lodged in 
 the cell which the polyp inhabits, which opens by one extremity 
 into the bottom of the stomach, into which the ova when mature 
 are conveyed, and they are ultimately ejected through the mouth, 
 a, as represented in the figure. 
 
 (38.) Few objects exhibit to the naturalist a more beautiful spec- 
 tacle than the compound animals of which we are speaking. When 
 found upon the shore contracted and deformed, it would be diffi- 
 cult to imagine that they were really organized beings, much less 
 possessed of the elaborate conformation we have described ; yet, on 
 placing one of them in a tumbler of sea-water, and watching it 
 attentively with a magnifying glass, its true nature is gradually re- 
 vealed : the central mass expands in all directions, exhibiting the 
 cells upon its surface, from which in time the countless flower-like 
 polyps are protruded, and, stretching out their arms in all directions, 
 wait for the approach of prey. A scene like this naturally leads us 
 to make a few observations upon some points of physiology con- 
 nected with their economy : several questions obtrude themselves 
 upon us, which, although applicable to the whole group of com- 
 pound polyps, may be well discussed in this place. 
 
 (39.) That there is a community of nutrition, or, in other words, 
 that food taken and digested by the individual polyps is appropriated 
 to the support of the general body, appears to be indisputable, and 
 is generally admitted ; but is there a community of sensation so as to 
 render the entire mass one animal, capable of consentaneous move- 
 ments, or is each polyp independent of the rest in its sensations 
 and actions ? Upon this there are different opinions : some regard- 
 * Spix (Jean), Memoire pour servir a I'histoire de 1'Alcyonium exos. 
 
ON POLYPS. 
 
 ing the whole as a single animal, each part being in communication 
 with the rest, and thus participating in the feelings and movements 
 of the others ; whilst some consider each polyp as a distinct crea- 
 ture, independent of the rest. The solution of this problem is 
 a matter of some difficulty ; but there are several facts recorded by 
 observers, which may in some measure enlighten us upon the sub- 
 ject. From the absolute want of nervous filaments, which 
 might bring into communication distant points of the body, 
 we might theoretically deny the possibility of any combina- 
 tion of actions ; and experiment teaches us that the assumption 
 is correct. 
 
 If when one of these animals is fully expanded, transparent and 
 soft, any point of its surface be rudely touched, the whole body 
 does not immediately shrink, but the point only where the irrita- 
 tion was applied appears to feel the impression ; this part shortly 
 becomes more dense, opaque, and a depression is seen gradually to 
 appear. If the shock be severe, and extensively diffused over the 
 body, the contraction slowly extends to the whole mass ; the most 
 violent local injury, indeed, seems to be totally unperceived at re- 
 mote parts of the body : whilst a general shock, such as striking the 
 vessel which contains the expanded polyp, produces a simultaneous 
 contraction of the whole.* The polyps, however, exhibit much 
 greater irritability, and their movements, from their rapidity, form 
 a striking contrast to the languid contractions of the connecting 
 central mass ; but that they have a community of life appears im- 
 probable : they seem to act quite independently of each other ; 
 when one is touched and suddenly retracts itself within its cell, it 
 is true that those in the neighbourhood will likewise not unfre- 
 quently retire, but this circumstance may be accounted for by the 
 sudden movement of their neighbour ; for, as the polyps often touch 
 each other with their tentacles, there is no cause for urging a com- 
 munity of substance to explain it."f" 
 
 (40.) Madreporidce. Were we to imagine one of the alcyonidse 
 capable of secreting not merely the calcareous spicula which are 
 mixed up with the softer portions of its body, but abundant quan- 
 tities of carbonate of lime, which, being stored up in the centre of 
 its substance, should form a dense calcareous axis encrusted with 
 the uncalcified part of the living animal, and perforated at its sur- 
 
 * Professor Grant, Lectures on Comparative Anatomy, Lancet for 1833-4, 
 vol. ii. p. 261. 
 
 t Quoy et Gaimard, Zoologie du Voyage de I'Uranie. Paris, 1834. 
 
30 ON POLYPS. 
 
 face so as to form innumerable cells or lodges containing the 
 polyps which provide nourishment for the general mass, we should 
 have a good general idea of the structure of the tribe of polyps 
 which now comes beneath our notice. 
 
 The shallower parts of the tropical seas contain countless forms 
 of madrepores, known to us, unfortunately but too often, only by 
 the earthy skeletons which the beauty of their appearance induces 
 the mariner to bring to our shores. These calcareous masses 
 assume more or less an arborescent appearance, spreading to a 
 considerable extent, so as to cover the bottom of large tracts of the 
 ocean, and not unfrequently they play an important part in pro- 
 ducing geological changes which are continually witnessed in the 
 regions where they are abundant. 
 
 (41.) The extent of our knowledge of the animals themselves is, 
 unfortunately, but very limited. That the entire skeleton, whatever 
 its form, is encrusted with living substance ; that the cells contain 
 polyps, resembling more or less those of the aleyonidse, and which 
 provide for the nutrition of the whole, is pretty much the extent 
 of our information concerning them : and should the scientific 
 naturalist ever be placed in circumstances where he can more closely 
 examine them in their living state, there is scarcely a department 
 of science in which his labours could be more beneficially employed 
 than in the investigation of their structure and history. 
 
 (42.) That the madrepores, from the immense masses of chalky 
 material which they accumulate in the regions inhabited by them, not 
 unfrequently become the cause of excessive danger to the mariner, 
 by raising the bottoms of the shallow seas which they frequent, so 
 as to render regions once covered with deep water no longer navi- 
 gable, or filling up by their accumulation the bays and harbours of 
 the South Seas, is undeniable; and a knowledge of this fact justly 
 makes the navigator cautious in passing through the localities where 
 they most abound. Yet the imagination of authors has not seldom 
 far exceeded the truth in detailing the circumstances connected with 
 them. That the harbour of Tinian, so extolled in the Voyages of 
 Lord Anson and others, is now choked up with the skeletons of 
 madreporegynous polyps, is readily credited ; that islands are gra- 
 dually formed, where none existed, by the agency of these creatures, 
 is equally authenticated ; and that madrepores are found in strata 
 much elevated above the level of the seas in the neighbourhood, is 
 a fact attested by many voyagers. Yet when we are told of coral 
 reefs, some hundred miles in length, entirely formed by the agency 
 
ON POLYPS, 31 
 
 of these apparently insignificant creatures, of perpendicular cliffs 
 rising from immense depths, which are altogether the produce of 
 their secretions, we have only to turn to the details in our posses- 
 sion, concerning their habits and mode of increase, to assure us of 
 the inaccuracy of such statements.* In the hot climates in which 
 the saxigenous corals abound, they are found to frequent shallow 
 bays and sheltered spots, where they can enjoy the full influences 
 of light and air, un exposed to the agitation of the ocean, which, 
 were it to beat continually upon them, would infallibly destroy 
 their delicate substance : in such situations, the sub-marine rocks 
 become gradually encrusted with the calcareous skeletons which 
 they produce ; and if undisturbed, in the lapse of years, successive 
 generations will of course deposit such large quantities of calcareous 
 matter as to form beds of considerable thickness. That there are 
 at the bottom of the ocean bold and precipitous cliffs, rising from a 
 depth of 1000 or 1200 feet, their broad tops approximating the 
 surface of the ocean, every one will admit, without having recourse 
 to the labours of madrepores to account for their formation, although 
 the sheltered portions of the summits of such mountain ridges 
 afford an eligible position for their increase. In such situations, 
 therefore, they accumulate, and slowly deposit continually increas- 
 ing masses of earth upon the brow of these sub-marine mountains, 
 until at last the pile approaches the surface of the sea, and even at 
 low water remains uncovered by the waves. The further elevation 
 of the rock, as far as the polyps are concerned in its construction, here 
 ceases ; but a variety of causes tends gradually to heap materials 
 upon the newly appearing island : storms, which tear up the bottom 
 of the sea, perpetually throw to the surface sand and mud ; which 
 becoming entangled among the madrepore, and matted together 
 with sea-weed, forms a solid bed over which the waves have no 
 longer any power. The circumference of the islet is perpetually 
 augmented by the same agency: sea-weeds and vegetable sub- 
 stances cast upon it, by their decay cover its top with vegetable 
 mould ; and if its proximity to other land permit the united action 
 of winds and currents to bring the germs of vegetation from neigh- 
 bouring coasts, they take root in the fresh soil, and soon clothe with 
 verdure a domain thus rescued from the ocean. 
 
 (43.) The coasts described by Cook and Bougainville, whereon 
 strata of coral are found much elevated above the level of the sea, 
 are undoubtedly of volcanic origin. The bottom of the ocean, 
 
 * Quoy etGaimard, Op. cit. 
 
ON POLYPS. 
 
 crusted over by thick masses of madrepore, has been suddenly 
 heaved up by one of those stupendous convulsions of nature, pro- 
 bably produced by the sea finding its way into some sub-marine 
 volcano ; and rocks and corals, raised from their beds by the tre- 
 mendous explosion so produced, give birth to islands and elevated 
 tracts of country, such as are met with in the South Seas. 
 
 CORALLID.E. The Corallidse are compound polyps of appa- 
 rently more perfect organization than those forming the last family. 
 The polypary or central axis, which supports the external or living 
 crust, is solid, without cells, and variously branched ; the larger 
 species resembling shrubs of great beauty, frequently coloured with 
 lovely hues, and studded over their whole surface with living 
 flowers, for such the polyps which nourish them were long consi- 
 dered even by scientific observers. The central stem of these 
 zoophytes differs much in its composition in different families ; 
 sometimes being of stony hardness, in other cases it is soft and 
 flexible, resembling horn ; and not unfrequently it is formed of both 
 kinds of material : it is however always produced by the living 
 cortex, which secretes it in concentric layers, the external being 
 the last deposited. 
 
 The example which we shall select for special description is the 
 Coral of commerce, Corallium rubrum, (Jig. 6.) from which we 
 derive the material so much prized in Fi S- 6 - 
 
 the manufacture of ornaments. 
 
 (44.) The red coral is principally 
 obtained in the Mediterranean. When 
 growing at the bottom of the sea, it 
 consists of small branched stems, en- 
 crusted with a soft living investment, 
 by which the central axis is secreted, 
 and studded at intervals with polyps 
 possessing eight fringed arms, and 
 capable of being contracted into 
 cells contained in the fleshy covering, 
 but not penetrating the stem itself. 
 
 The skeleton or polypary of the coral is of extreme hardness, and 
 susceptible of a high polish ; a circumstance to which the estima- 
 tion in which it is held is principally owing. But in other 
 genera of this family, the central axis, instead of being con- 
 structed of calcareous matter, is formed of concrete albumen, and 
 resembles horn both in appearance and flexibility ; such are the 
 
ON POLYPS. 
 
 Gorgonise of the Indian Ocean. In the Isis Hippuris (jig. 7, B) 
 the central axis is alternately composed of both these substances, 
 exhibiting calcareous masses united at intervals by a flexible mate- 
 rial, allowing the stem to bend freely in every direction. The 
 object of such diversity in the texture of the polypary of the Coral- 
 hdce will be at once apparent when we consider the habits of the 
 different species : the short and stunted trunks of Corallium, 
 composed of hard and brittle Fig. 7. 
 
 substance, are strong enough 
 to resist injuries to which they 
 are exposed ; but in the tall 
 and slender stems of Gor- 
 gonia and Isis, such brittle- 
 ness would render them quite 
 inadequate to occupy the si- 
 tuations in which they are 
 found, and the weight of 
 the waves falling upon their 
 branches would continually 
 break in pieces and destroy 
 them ; this simple modifica- 
 tion, therefore, of the nature 
 of the secretions with which 
 they build up the skeleton 
 which supports them allows, 
 them to bend under the passing waves, and secures them from 
 otherwise inevitable destruction. 
 
 (45.) Upon making a transverse section of one of these poly- 
 paries, (Jig. 7, A,) the solid axis is distinctly seen to be made up 
 of layers arranged in a somewhat undulating manner around the 
 centre, and successively deposited by the living cortex : the growth 
 of the stem, in the harder species at least, is very slow, and several 
 years are necessary to its maturity ; a circumstance whicFlias ren- 
 dered it needful to impose strict laws, forbidding the Mediterranean 
 coral-fishers to disturb too frequently the same localities, which are 
 only visited at stated periods. 
 
 (46.) The deposition of solid matter in the soft bodies of these 
 polyps is not confined to the production of the central stem, but in 
 many even of the Keratophyta * cretaceous particles are extensively 
 
 * An old name for polyps with a horny axis, x'^xf, horn; Qvrov, a stem ; as distin- 
 guishing them from the stony polyps, Lithophyta, *.i0 a{ , a stone ; <f>vrav. 
 
 D 
 
34 ON POLYPS. 
 
 diffused through the cortex, which not unfrequently is likewise 
 gorgeously coloured by secretions of different hues. In the Gor- 
 goniae, a section of one of which (Gorgonia verrucosa) is repre- 
 sented in Jig. 7, A, the earthy matter in the crust is so abundant, 
 that, even when dried, it will retain in some measure its natural 
 form, and exhibit the tints peculiar to the species. 
 
 The structure of the individual polyps of the Corallidse, as far 
 as we are acquainted with their history, resembles that of one 
 of the polyps of the Alcyonidse already described ( 36) ; and the 
 prey obtained by each, goes to the support of the general mass. 
 Their reproduction is undoubtedly from germs developed in in- 
 ternal filamentary ovaria, which escape either through the mouth, 
 as in Alcyonium, or else, as Cavolini* supposed, through apertures 
 placed between the origins of the tentacles. 
 
 (47.) Pennatulidce. This family belongs likewise to the divi- 
 sion of cortical polyps, and agrees with the two last in most points, 
 the principal distinction consisting in the character of the internal 
 axis which supports the body. In some species this part is reduced 
 in fact to a ligamentous mass, interspersed with calcareous granules ; 
 but, in the most typical forms, the skeleton consists of several 
 pieces, capable of moving upon each other. The whole animal, 
 in such cases, resembles a feather, the stem supporting lateral 
 branches, upon which the polyps are arranged. From the circum- 
 stance of these compound animals being unattached to any foreign 
 support, they have been supposed to be capable of swimming at 
 large in the sea, by the voluntary movements of their articulated 
 branches, a fact strongly contested by many modern zoologists ; 
 but, as we can say nothing from our own observation upon this 
 subject, we must leave the question open to future investigation. 
 Many species are eminently phosphoric. 
 
 Tubiporidcc. We now have to speak of a class of polyps very 
 different in their construction from those which have been described. 
 Instead of encrusting an internal solid skeleton, the Tubiporidse are 
 enclosed in a calcareous or coriaceous sheath or tube, from the ori- 
 fice of which the polyp is protruded, when in search of prey : these 
 are named by authors Vaginated Polyps. 
 
 (48.) The Tubipora musica (jig. 8, a) is the species which has 
 been most carefully studied, and the details connected with its or- 
 ganization will be found of the highest importance, as affording a 
 
 * Cavolini (Philippe), Memorie per servire alia storia diPolipi marini. 4to. Naples, 
 1785. 
 
ON POLYPS. 
 
 clue to the investigation of other forms, to be mentioned hereafter.* 
 The Tubiporse live in society, but do not appear to be organically 
 united as the compound polyps; a group of these animals presents 
 
 Fig. 9. 
 
 several stages of tubes, placed one above another ; the tubes are ge- 
 nerally straight, and nearly parallel to each other, but appear 
 slightly to diverge, as ra- 
 diating from a common 
 centre ; they are separated 
 by considerable intervals, 
 and reciprocally support each 
 other by horizontal laminae 
 of the same substance as 
 the tubes themselves, which 
 unite them. From each tube 
 issues a little membranous 
 animal of a brilliant grass- 
 green colour, the mouth 
 being surrounded by eight 
 tentacles, which are furnished 
 along their edges with two or 
 three rows of minute fleshy 
 papillae. Within the mouth 
 of the specimen examined by 
 M. Lamouroux, was found an 
 
 * Anatomic de Tubipore Musical, par M. Lamouroux, in the Zoology of Quoy et 
 Gaimard, Voyage de 1'Uranie. 
 
36 ON POLYPS. 
 
 oval membranous sac, but not in sufficient preservation to be 
 properly described. This was most probably the stomach. 
 
 (49.) Around this sac, alternating with the tentacles, are eight 
 triangular filaments, (Jig. 9 ; 1 e,) which are at first free and 
 floating, but they soon become attached to a membrane which 
 lines the calcareous tube ; and, gradually diminishing in size, they 
 extend through its whole length. These filaments are analogous 
 to the ovaries of the Corallidse and Pennatulidse ; their inner sur- 
 face, in mature individuals, is studded with ova of different sizes 
 attached to them by short pedicles (Jig. 9 ; 8). 
 
 (50.) At the point where the ovigerous filaments reach the ten- 
 tacles, a membrane is observable which assumes the shape of a 
 funnel when the animal retires into its shell, and at the open end 
 of the funnel the membrane is seen to fold outwards, and become 
 continuous with the calcareous tube; (Jig. 9 ; 1, &;) its inner sur- 
 face indeed is prolonged under the form of a thin pellicle over all 
 that part of the interior of the tube which is inhabited by the 
 polyp, terminating at a kind of diaphragm composed of the same 
 hard substance as the tube itself. The remains of these diaphragms 
 are found in the interior of old tubes at various distances from 
 each other. 
 
 The funnel-shaped membrane does not terminate suddenly at its 
 point of junction with the calcareous tube ; the latter, indeed, is a 
 continuation and product of the first, the calcareous substance being 
 evidently deposited in this gelatinous membrane, in the same man- 
 ner as phosphate of lime is deposited in the bones of very young 
 subjects, changing its soft texture into hard, solid substance. The 
 manner, therefore, in which this tube is formed, cannot be compared 
 to the mode of formation of the shells of Serpulce or the shells of 
 mollusca; in the latter case it is a secretion from the skin, almost 
 an epidermic product, but in these polyparies there is a real change 
 of soft into solid substance, which is effected gradually, but not 
 deposited in layers. 
 
 (51.) When the tube has acquired a certain height, the animal 
 forms the calcareous horizontal plate which unites it to those 
 around ; the still membranous upper part of the tube extends 
 itself horizontally outwards around the aperture, (Jig. 9 ; 2, 6,) 
 doubling itself so as to form a circular fold ; this part of the 
 membrane is no longer irritable ; its internal surfaces unite so as 
 not to interrupt the continuity of the tube ; carbonate of lime is 
 gradually deposited within it, and soon a prominent partition, com- 
 posed of two lamellae, soldered together through almost their entire 
 
ON POLYPS. 37 
 
 extent, surrounds the tubular cell. Generally many polyps of the 
 same polypary form these partitions at the same time and upon the 
 same plane. In this case the gelatinous margins of the folded mem- 
 brane unite, no space is left ; and they ultimately become most inti- 
 mately soldered together, and the solid plane or stage (fig. 8) is 
 formed. If the animal constructs its partition against a tube already 
 perfect and solidified, it fixes its collar to its sides, so that the point 
 of junction is imperceptible ; but when it is quite insulated, as at &, 
 Jig. 8, the horizontal collar is still formed, and it then assumes 
 somewhat of an octagonal shape. The tube-forming membrane 
 exhibits no appearance of vessels or other traces of organization. 
 
 When the polyp is withdrawn within its cell, its tentacles form 
 a cylindrical fasciculus {Jig- 9, c) ; the papillae which partially cover 
 them being laid upon each other like the leaflets of some mimosa 
 when asleep. 
 
 The protrusion of the creature from its tube is accomplished by 
 the contraction of the membrane, 6, inserted into its neck. 
 
 (52.) How the eggs formed upon the oviferous filaments issue from 
 the polyp, has not been ascertained : it is most probable, from their 
 size, that they are not expelled during the life of the parent ; but 
 that, when it dies, the eggs all come out of the tube, except one, 
 which developes itself in the old cell ; the rest fixing themselves 
 upon the neighbouring stage, there to form a new story of tubes. 
 The germs, during the first period of their developement, have no 
 organs distinguishable, not even the rudiment of a tube ; each ap- 
 pears to consist of a simple gelatinous membrane folded upon itself, 
 (Jig. 9 ; 4, c,) and forming upon the stage upon which it is fixed a 
 little tubercle resembling a small Zoanthus or other naked zoophyte. 
 This tubercle gradually elongates, and assumes the form of a polyp, 
 provided with all its organs ; but the sac which encloses it is still 
 gelatinous at its upper part, and membranous near the base, 
 (Jig. 9 ; 4, 6,) where it gradually diminishes in thickness, and, 
 becoming calcareous, gives to the animal the general appearance of 
 its original. 
 
 (53.) In Tubularia indivisa the structure of the tentacula around 
 the mouth is different from what has been described in Tubipora mu- 
 sica, although in the principal points of its structure the resemblance 
 between the two is very great ; when the Tubularia is expanded, its 
 protruded portion is seen to be furnished with two circles of arms, 
 one placed around the opening of the mouth, the other at a consi- 
 derable distance beneath it, (Jig. 10 ; 1,) and nearly on a level with 
 the inferior circle a second aperture (Jig> 10 ; 1, a) is observable, 
 
ON POLYPS. 
 
 Fig. 10. 
 
 communicating with that portion of the body which is lodged within 
 the tube, and resembling a second mouth. A remarkable action has 
 been observed to take place in these parts of the polyp, producing a 
 continual variation in their form ;* a fluid appears at intervals to be 
 forced from the lower compartment into the space intervening be- 
 tween the two rows of tentacula, which becomes gradually dilated 
 into a globular form (Jig. 10 ; 2 and 3.) This distension continues 
 for about a minute, when the upper part, contracting in turn, 
 squeezes back the fluid which fills it into the lower compartment 
 through the opening a, which then closes preparatory to a repeti- 
 tion of the operation. The intervals between these actions were, 
 in the specimen observed by Mr. Lister, very evenly eighty 
 seconds. In Tubularia indivisa the sheath or cell, &, which en- 
 closes the polyp, is perfectly diaphanous, allowing its contents to 
 be readily investigated under 
 the microscope. When thus 
 examined, a continual circu- 
 lation of particles was visi- 
 ble, moving in even, steady 
 currents in the direction of 
 the arrows (fig. 10; 1) along 
 slightly spiral lines represent- 
 ed in the drawing. The par- 
 ticles are of various sizes, 
 some very minute, others 
 apparently aggregations of 
 smaller ones ; some were 
 globular, but they had gene- 
 rally no regular form. In 
 fig. 3, d, a series of longitu- 
 dinal lines are perceptible, 
 which most probably are ovi- 
 gerous filaments, resembling 
 those of Tubipora musica. 
 
 Actiniadce. The next family of polyps, from the fibrous 
 character which the substance of their bodies assumes, have been 
 named by zoologists " Fleshy Polyps.' 1 '' They differ indeed re- 
 markably from the soft gelatiniform structures which have hitherto 
 come under our notice, exhibiting traces of muscular fibre which 
 are not to be mistaken. 
 
 * Lister, on the structure and functions of Tubular and Cellular Polypi. Philoso- 
 phical Transactions, 1834. 
 
ON POLYPS. 
 
 Fig. 11. 
 
 Fig. 12. 
 
 Although the genera composing this division are exceedingly 
 numerous, and vary much in their external characters, they will 
 be found more or less to conform in the essential points of their 
 organization with the subject which we have chosen as the type of 
 this extensive tribe, and of which, being common upon our own 
 coasts, the reader will have little difficulty in procuring specimens 
 for examination. 
 
 (54.) The body of an 
 Actinia when moderately 
 expanded, (fig. 11?) is a 
 fleshy cylinder, attached 
 by one extremity to a 
 rock, or some other sub- 
 marine support ; whilst 
 the opposite end is sur- 
 mounted by numerous 
 tentacula, arranged in se- 
 veral rows around the oral 
 aperture (fig. 1) . When 
 these tentacula are expand- 
 ed, they give the animal 
 the appearance of a flower, 
 a resemblance which is 
 rendered more striking by 
 the beautiful colours which 
 they not unfrequently as- 
 sume ; and hence in all 
 countries they have been 
 looked upon by the vulgar 
 as sea-flowers, and distin- 
 guished by names indica- 
 tive of the fancied resem- 
 blance. Their animal na- 
 ture is however soon 
 rendered evident by a little attention to their habits ; when 
 expanded at the bottom of the shallow pools of salt-water left by 
 the retreating tide, they are seen to manifest a degree of sensibility, 
 and power of spontaneous movement, which we should little an- 
 ticipate from their general aspect. A cloud veiling the sun will 
 cause their tentacles to fold, as though apprehensive of danger 
 from the passing shadows : contact, however slight, will make 
 
40 ON POLYPS. 
 
 them shrink from the touch ; and if rudely assailed, they com- 
 pletely contract their bodies so as to take the appearance of a hard 
 coriaceous mass, scarcely distinguishable from the substance to 
 which they are attached. 
 
 (55.) It is in seizing and devouring their prey however that the 
 habits of the Actiniae are best exemplified ; they will remain for 
 hours with their arms fully expanded and motionless, waiting for 
 some passing animal which chance may place at their disposal, and 
 when the opportunity arrives, are little inferior to the Hydrse in their 
 voracity or powers of destroying their victims. Their food generally 
 consists of crabs or shell-fish, animals apparently far superior to 
 themselves in strength and activity, but even these are easily over- 
 powered by the sluggish yet persevering grasp of their assailant. 
 No sooner are the tentacles touched by a passing animal than it is 
 seized, and held with unfailing pertinacity ; the arms gradually 
 close around it ; the mouth, placed in the centre of the disc, ex- 
 pands to an extraordinary size ; and the creature is soon engulph- 
 ed in the digestive bag of the Actinia, where the solution of all its 
 soft parts is rapidly effected, and the hard undigestible remnants 
 speedily cast out at the same orifice. 
 
 The Actiniae, although exceedingly voracious, will bear long 
 fasting :* they may be preserved alive for a whole year, or per- 
 haps longer, in a vessel of sea- water, without any visible food ; but 
 when food is offered, one of them will devour a crab as large as a 
 hen's egg, or two muscles in their shells : in a day or two the 
 shells are voided through the mouth, perfectly cleared of the soft 
 parts which they contained. 
 
 (56.) The Actiniae, like the Hydras, possess the power of chang- 
 ing their position : they often elongate their bodies, and, remaining 
 fixed by the base, stretch from side to side as if seeking food at a 
 distance ; they can even change their place by gliding upon the 
 disc which supports them, or detaching themselves entirely, and 
 swelling themselves with water, they become nearly of the same 
 specific gravity as the element which they inhabit, and the least 
 agitation is sufficient to drive them elsewhere ; Reaumur even 
 asserts that they can turn themselves so as to use their tentacles as 
 feet, crawling upon the bottom of the sea ; but this mode of pro- 
 gression has not been observed by subsequent naturalists : when 
 they wish to fix themselves, they expel the water from their dis- 
 
 * Encyclopaedia Londinensis, art. Actinia. 
 
ON POLYPS. 
 
 tended body, and sinking to the bottom attach themselves again 
 by the disc at their base, which forms a powerful sucker. 
 
 (57.) From this sketch of the outward form and general habits 
 of these polyps, the reader will be prepared to examine their internal 
 economy, and the more minute details of their structure. On ex- 
 amining attentively the external surface of the body, it is seen to 
 be covered with a thick mucous layer resembling a soft epidermis, 
 which extending over the tentacula, and the fold around the aper- 
 ture of the mouth, is found to coat the surface of the stomach 
 itself; this epidermic secretion forms in fact a deciduous tunic 
 which the creature can throw off at intervals. On removing this, 
 the walls of the body are seen to be made up of fasciculi of mus- 
 cular fibres, some running perpendicularly upwards towards the 
 tentacula ; and others, which cross the former at right angles, pass- 
 ing transversely round the body ; the meshes formed by this in- 
 terlacement are occupied by a multitude of granules apparently 
 of a glandular nature, which give the integument a tuberculated 
 aspect : these granules are not seen upon the sucking disc at the 
 base. The tentacula are hollow tubes, composed of fibres of the 
 same description. The stomach is a delicate folded membrane, 
 forming a simple bag within the body ; it seems to be merely an 
 extension of the ex- 
 ternal tegument, some- 
 what modified in tex- 
 ture ; it is closed infe- 
 riorly, the same orifice 
 serving both for the in- 
 troduction of food, and 
 the expulsion of effete 
 or indigestible matter. 
 
 (58.) On making a 
 section of the animal, as 
 represented in jig. 13, 
 the arrangement of these 
 parts is distinctly seen : 
 a being the muscular 
 integument ; b the ten- 
 tacula formed by the 
 same fibrous membrane ; 
 and c the stomach, 
 which is apparently de- 
 
ON POLYPS. 
 
 rived from it. Between the digestive sac c, and the fibrous ex- 
 terior of the body a, is a considerable space d, divided by a great 
 number of perpendicular fibrous partitions, /, into numerous com- 
 partments, which however communicate freely with each other, and 
 likewise with the interior of the tentacula, as seen at e. Every 
 tentacle is perforated at its extremity by a minute aperture , 
 through which the sea-water is freely admitted into these compart- 
 ments, so as to bathe the interior of the body ; and when from 
 alarm the animal contracts itself, the water so admitted is forcibly 
 expelled in fine jets through the holes by which it entered. There 
 can be no doubt that the surrounding fluid, thus copiously taken 
 into the body, is the medium by which respiration is effected ; and 
 every one who has been in the habit of keeping Actiniae in glass 
 vessels for the purpose of watching their proceedings, must have 
 noticed that as the fluid in which they are confined becomes less 
 respirable, from the deficiency of air, the quantity taken into the 
 body is enormous, stretching the animal until it rather resembles 
 an inflated bladder than its original shape. 
 
 (59.) It is in the compartments which are thus at the will of the 
 creature distended with water, that we find the organs of reproduc- 
 tion, which here assume a developement far exceeding what we have 
 noticed in other zoophytes. On raising a portion of the mem- 
 brane which forms the stomach, as aty, we see lodged in each par- 
 tition an immense number of ova attached to a delicate transparent 
 membrane, and arranged in large clusters, g. The ovigerous mem- 
 brane which secretes these eggs is represented unravelled at h ; it is 
 through its whole extent bathed with water admitted into the compart- 
 ment in which it is lodged, a circumstance which provides for the re- 
 spiration of the ova during their developement. The convoluted ovary 
 is seen to terminate by a minute aperture near the bottom of the sto- 
 mach k, into which when mature the young escape. The eggs found in 
 the ovaria are round and of a yellow colour, resembling minute grains 
 of sand : it is probable that sometimes they are hatched after their ex- 
 pulsion, but it is likewise asserted by numerous authorities that the 
 young are not unfrequently born alive. The manner in which the 
 ova are extruded has been long a matter of controversy, and perhaps 
 cannot yet be regarded as definitively ascertained. Our own dissec- 
 tions would lead us to concur with those anatomists who describe 
 them as escaping from the ovaria into the bottom of the stomach, 
 whence they have been seen to escape by the mouth fully formed : 
 it is possible, however, that they may likewise be expelled with the 
 
ON POLYPS. 43 
 
 streams of water forced by the contractions of the animal through 
 the orifices at the extremities of the tentacula. 
 
 The Abbe Dicquemare* relates several curious experiments on 
 the multiplication of these animals by mechanical division. When 
 transversely divided, the upper portion still stretched out its ten- 
 tacles in search of food, which, when seized, sometimes passed 
 through its mutilated body, but was occasionally retained and di- 
 gested. In about two months tentacles grew from the cut ex- 
 tremity of the other portion, which soon afterwards began to seize 
 prey. By similar sections he even succeeded in making an animal 
 with a mouth at each end. 
 
 (60.) The entire organization of the Actinia is evidently very supe- 
 rior to that of any animals which have been described in the preceding 
 pages ; the muscular fasciculi, now for the first time distinctly recog- 
 nisable, give an energy to their contractions very different from the 
 languid movements of the gelatinous polyps. The Actinia can in- 
 deed hardly be classed in the acrite division of the animal kingdom ; 
 the developement of muscular fibre which it presents, presupposes 
 the existence of nervous filaments, and we might a priori infer 
 their existence. Spix, many years ago, described a nervous sys- 
 tem, which he believed he had discovered, in the neighbourhood 
 of the base, or sucking disc by which the animal attaches itself to 
 foreign bodies ; in which situation he was led to look for it, by ob- 
 serving that when galvanic shocks were sent through the body, 
 convulsive movements were excited most distinctly in this part, 
 and also from the supposition that the organ of attachment, here 
 placed, must necessarily be the most abundantly endued with sen- 
 sibility, j* 
 
 Having raised the longitudinal muscles by a slight incision near the 
 middle of the base or disc of attachment, he thought he perceived an 
 interlacement formed by some pairs of nodules, disposed around the 
 centre, which communicated by several cylindrical threads ; from 
 each nodule two filaments ran forwards, one accompanying the lon- 
 gitudinal fleshy fasciculi, the other penetrating to the internal 
 longitudinal septa, which have likewise a muscular character. Suc- 
 ceeding anatomists have, however, totally failed in their endeavours 
 to detect the arrangement here described ; and which indeed, did it 
 exist, would be contrary to every analogy with which we are ac- 
 quainted. It is more probable that the nervous system consists in 
 
 * Philosophical Transactions, 1773. 
 
 t Spix (Jean) Annales du Museum, tome 13. 
 
44 ON POLYPS. 
 
 a delicate thread, which we are pretty well convinced we have de- 
 tected running round the roots of the tentacles, embedded in a 
 strong circular band of muscle which surrounds the orifice of the 
 stomach, and acts the part of a powerful sphincter in closing the 
 aperture. 
 
 (61.) After the account which has been given of the general 
 structure of the Actinia, the mechanism by which the tentacula are 
 expanded and withdrawn will be easily understood : these do not, 
 like the horns of a snail, become inverted and rolled up within the 
 body, but owe their different states of extension entirely to the 
 forcible injection of water into the cavities which they contain. We 
 have seen already that the interior of each tubular arm communi- 
 cates freely with the space which intervenes between the stomach 
 and the external integument, a space which, at the will of the 
 animal, is filled with sea-water drawn through the orifices seen at the 
 extremity of each arm : when these minute orifices are closed, and 
 the body of the creature contracted, the water, being violently forced 
 into the tentacula, distends and erects them, as when watching for 
 prey ; and, on the other hand, when emptied of the fluid thus 
 injected, they shrink and collapse. This circumstance, so easily 
 seen in the Actiniae, will probably enable us to account for similar 
 phenomena observable in other polyps, the internal economy of 
 which is by no means so conspicuous. 
 
 (62.) The next tribe of polyps which presents itself to our notice, 
 differs widely from the preceding families in outward form, as well 
 as in many important features of internal structure. It would seem, 
 indeed, to comprise animals distinguished from each other by so 
 many important circumstances, and yet so intimately related by ex- 
 ternal configuration, that it is difficult to separate them, or to leave 
 them in the same group. 
 
 It was imagined a few years ago, before accurate researches had 
 been made concerning the internal structure of these zoophytes, 
 that in all the compound species the polyps or mouths of the 
 general mass were in their essential structure analogous to the 
 Hydra, being simple digestive sacs, without more complication of 
 structure than we have found those of the cortical polyps to possess. 
 Recent investigations, however, have shown that amongst the 
 species ranged by Cuvier under the head of Tubular Polyps, 
 " Polypes a Tuyaux" many are exceedingly complex in their 
 organization, possessing the outward form of the simpler kinds, but 
 
ON FOLYPS. 45 
 
 furnished with a complete digestive canal, and approximating in 
 their general economy very superior orders of animals. These latter 
 would appear to be distinguishable by the nature of the tenta- 
 cles around the mouth, which, in all the families as yet examined, 
 we have found to be smooth or merely fringed, as they are indeed 
 in some of the tubular polyps hereafter to be noticed ; but, in the 
 more perfect species, the arms are covered with vibratile hairs or 
 cilia, forming important agents in securing prey : such have been 
 separated by Ehrenberg into a distinct class, under the title of 
 BRYOZOA, and have been recently designated by Dr. Arthur Farre, 
 
 ClLIOBRACHIATE POLYPS. 
 
 Further observation is necessary before the boundaries of these 
 important divisions can be accurately laid down ; we shall neverthe- 
 less, without entering upon a question foreign to our present sub- 
 ject, arrange them in conformity with the analogies of their internal 
 structure, rather than of their outward general form, and defer the 
 consideration of the ciliobrachiate division to another place. 
 
 (63.) In the unciliated tubular polyps, the common body of 
 the animal, instead of encrusting a solid skeleton, is enclosed in a 
 horny sheath, which it traverses like the pith of a tree, follow- 
 ing all the ramifications of the branched stem of the polypary : 
 to the central part are attached, at intervals, cells opening exter- 
 nally, in which the polyps which provide nourishment for the whole 
 are lodged. 
 
 Zoophytes of this description are readily found on our own 
 coasts, and the microscopic observer can scarcely enjoy a richer 
 treat than the examination of them affords. In order to study 
 them satisfactorily, it is necessary to be provided with several 
 glass troughs, of different depths, in which the living animals 
 immersed in their native element may be placed : in this situa- 
 tion, if the water be carefully renewed at short intervals, they will 
 live for some time. 
 
 (64.) On examining a piece of one of these polyparies with a good 
 glass, the tubular horny envelope is seen to be filled with granular 
 matter ; and, on attentively watching it, globules will be seen moving 
 in different directions, producing a sort of circulation or cyclosis 
 very much resembling what is observable in some plants. The glo- 
 bules thus moving do not appear to be contained in vessels, but steal 
 in slow currents, ascending along the sides, and returning down the 
 middle in an opposite direction, as represented by the arrows in 
 fig- 14. 
 
46 
 
 ON POLYPS. 
 
 (65.) It has been generally stated that the living pith exuded from 
 its surface the horny matter which, by its concretion, forms the 
 tube or external skeleton investing the whole ; the accuracy of such 
 a supposition, however, may well be questioned. We have already 
 seen, in the Tubipora musica, that the calcareous tube investing that 
 polyp was produced by the interstitial deposit of earthy matter in 
 the membrane which formed originally its outer case. In the tribe 
 of zoophytes which we are now speaking of, we shall find the 
 exterior tube to be formed in a way precisely similar. On referring 
 to the diagram, (fig. 14,) the mode of its growth will be rendered in- 
 telligible: the soft part or living axis of the polypary is seen to be 
 contained in two distinct layers ; the inner one composing the 
 digestive sac of the polyp, and embracing the granular matter, 
 which seems to be the special seat of the nutritive process ; the 
 outer or tegumentary layer, i, after leaving the tentacula, may 
 be traced down the sides of each polyp to the bottom of the cell, 
 where its course is arrested by a slight partition, at which point 
 it turns outwards, lining the interior of the cell as far as its margin, 
 where, as in the Tubipora, it is seen to be continuous with the 
 horny matter itself. It is this tegumentary membrane, then, which 
 forms by its develope- ji. 14. 
 
 ment the entire skele- 
 ton : as it expands, it 
 gives origin to the cells 
 and branches character- 
 istic of the species; and, 
 from being at first quite 
 soft and flexible, it gra- 
 dually acquires hardness 
 and solidity by the de- 
 position of corneous 
 matter in its sub- 
 stance. 
 
 The cells thus formed 
 are inhabited by polyps 
 analogous to those which 
 provide nourishment for 
 the cortical families ; but 
 differing in the number 
 and appearance of the 
 tentacula, which are 
 
ON POLYPS. 47 
 
 here studded with minute tubercles, but never provided with cilia. 
 Few objects are more admirable than these polyps, when watched 
 with a good microscope : protruding themselves beyond the mouths 
 of their cells, they inflect their bodies in all directions in quest of 
 prey, waiting till some passing object impinges upon their tenta- 
 cula, which is at once seized and conveyed into the stomach with 
 a rapidity and dexterity almost beyond belief. 
 
 The multiplication of these singular animals appears to take place 
 in three different modes : 1st, by cuttings, as in plants ; Sndly, 
 by off-shoots, or the formation of new branches bearing polyps ; 
 3dly, by gemmules capable of locomotion. 
 
 (66.) The first mode strikingly resembles what is observed in the 
 vegetable kingdom ; for as every branch of the plant-like body 
 contains all the parts necessary to independent existence, it can 
 hardly be a matter of surprise that any portion, separated from the 
 rest, will continue to grow and perform the functions of the entire 
 animal. 
 
 (67.) The second mode of increase, namely, by the formation of 
 new branches and polyps, seems more like the growth of a plant than 
 the developement of an animal. We will consider it under two 
 points of view : first, as regards the elongation of the stem ; secondly, 
 as relates to the formation of fresh cells containing the nutritive 
 polyps. On examining any growing branch, it will be found to be 
 soft and open at the extremity, and through the terminal orifice, 
 the soft tegumentary membrane above described as forming the 
 tube by its conversion into hard substance is seen to protrude ; the 
 skeleton is not therefore merely secreted by the enclosed living 
 granular matter, but it is the investing membrane, which continually 
 shoots upwards, and deposits hard material in its substance, as it 
 assumes the form and spreads into the ramifications peculiar to 
 its species, 
 
 (68.) Having thus lengthened the stem to a certain distance, the 
 next step is the formation of a cell and a new polyp, which is accom- 
 plished in the following manner :* the newly formed branch has at 
 first precisely the appearance and structure of the rest of the stalk 
 of the zoophyte, (Jig. 15, 1,) being filled with granular matter, 
 and exhibiting in its interior the circulation of globules already 
 described, moving towards the extremity along the sides of the 
 tube, and in an opposite course in the middle ; the end of the 
 branch, however, before soft and rounded, soon becomes perceptibly 
 
 * Lister, Philosophical Transactions, Loc. cit. 
 
ON POLYPS. 
 
 dilated. After a few hours the branch is visibly longer, its 
 extremity more swollen, and the living pith is seen partially to 
 
 Fig. 15. 
 
 f 
 
 have separated itself from the sides of the tube, the boundaries 
 of which become more defined and undulating (2). The growth 
 still proceeding, the extremity is distinctly dilated into a cell, in 
 which the soft substance seems to be swollen out, so as to give a 
 rude outline of the bell-shaped polyp (3), but no tentacula are yet 
 distinguishable ; a rudimentary septum is now visible stretching 
 across the bottom of the cell, through the centre of which the 
 granular matter, now collected into a mass occupying but a portion 
 of the stem, is seen to pass. The polyp and cell gradually grow 
 more defined, (4, 5, 6,) and the tentacula become distinguish- 
 able ; the cell, moreover, is seen to be continued inwards by a mem- 
 branous, infundibular prolongation of its margin (7), which imme- 
 diately reminds us of the funnel-shaped membrane of Tubipora 
 ( 50), and its office is no doubt similar. As the developement 
 proceeds, the tentacles become more perfect (8), and the polyp at 
 length rises from its cell to exercise the functions to which it is 
 destined. 
 
 (69.) The third mode of multiplication, or that by reproductive 
 gemmules, seems to be specially adapted to the diffusion of the 
 
ON POLYPS. 49 
 
 species ; and as it is peculiar to zoophytes of this description, 
 we shall dwell upon it at some length. At certain periods of the 
 year, besides the ordinary cells which contain nutritive polyps, 
 others are developed from different parts of the stem, which may be 
 called female or fertile polyps, although usually simply termed 
 the vesicles. The cells of this kind are much larger than the 
 nutritive cells, and of very different forms ; they are moreover 
 deciduous, falling off after the fulfilment of the office for which 
 they are provided. They are produced in the same manner as 
 the rest of the stem, by an extension of the tegumentary mem- 
 brane, (fg. 14,6,) which, as it expands into the form of the cell, 
 becomes of a horny texture ; it may be traced, however, over the 
 opening of the cavity, where it sometimes forms a moveable oper- 
 culum. The cell being thus formed from the expansion and subse- 
 quent hardening of the tegumentary membrane, it remains to explain 
 the origin of the reproductive germs which soon become developed 
 in its interior.* These are seen to spring from the inner or nutritive 
 layer of the polyp (a), to which they are attached by pedicles, re- 
 garded by authors as fulfilling the office of umbilical cords during 
 their early growth. As the germs expand, they gradually advance 
 towards the opening of the cell, where, as they are protruded, 
 each becomes covered with a layer derived from the tegumentary 
 membrane ( f) which closed the orifice, and protruding externally, 
 has very much the form and appearance of a young polyp, for 
 which indeed it has often been mistaken. We are assured, how- 
 ever, that this supposition is erroneous, and that the polypiform 
 bodies are only external capsules inclosing the real germs (e), 
 from which young polyps are to be formed.^ On tearing open 
 one of these capsules when the included germs are ripe, the latter 
 are seen to be rounded grains of a gelatinous appearance, covered 
 externally with minute cilia, which, like those of the gemmules of 
 the sponge, enable them to swim about at pleasure in search of a 
 proper locality whereon to fix their permanent habitation. These 
 ciliated gemmules are highly irritable, and frequently contract 
 their bodies into different shapes during their progress through the 
 water ; but at length, when about to fix itself, each gemmule becomes 
 flat and circular, and assumes a radiated appearance, resembling a 
 minute grey star, having the interstices between the rays filled with 
 
 * Lcefling. Miiller's Archives, 1826. Lister, Loc. cit. 
 
 t Professor Grant, Edinb. New Philosoph. Journal, 1827. Observations on the 
 spontaneous motions of the Campanularia Dichotoma, &c. 
 
50 POLYGASTKICA. 
 
 a colourless transparent matter, which seems to harden into horn. 
 The grey matter swells in the centre, where the rays meet, and 
 rises perpendicularly upwards, surrounded by the transparent horny 
 substance, so as to form the trunk of the new zoophyte. The rays 
 first formed are obviously the fleshy central substance of the 
 roots ; and the portion of that substance which grows perpendi- 
 cularly upwards forms the fleshy part of the stem, from which in 
 due time polyps become developed. 
 
 CHAPTER IV. 
 
 POLYGASTRICA. 
 
 ANIMALCULA INFUSORIA. Auct. 
 
 (70.) Previous to the discovery of the microscope, it was little sus- 
 pected that animals existed of such minute size as totally to elude 
 the search of unassisted vision ; much less that every drop of water in 
 which animal or vegetable substances have been allowed to decay, 
 swarms with numberless forms of living beings ; that countless 
 millions inhabit every stagnant pool or running stream ; nay, that 
 every drop of the surface of the ocean is in itself a little world, 
 peopled by innumerable active creatures, as various in their out- 
 ward forms as they are elaborately adapted by their internal organi- 
 zation to the circumstances in which they live. 
 
 The terms Infusoria and Animal cula, as first used by the earliest 
 discoverers of these beings, were applied to an immense number of 
 creatures widely differing from each other in every particular except 
 in the minuteness of their size, which had previously concealed 
 them from observation. The germs of embryo polyps, the larvae 
 of insects, and all microscopic forms of being, including the won- 
 derful tribes of living atoms which inhabit various secretions in the 
 interior of other animals, were thus thrown together in one heteroge- 
 neous and chaotic group, without reference to the structure, rela- 
 tions or habits of the creatures so denominated. This motley 
 assemblage has, however, by subsequent laborious investigations, 
 been separated and arranged so as in some measure to enable us to 
 acquire accurate notions concerning the animals formerly confounded 
 under one common designation. 
 
POLYGASTRICA. 51 
 
 (71.) The character which distinguishes the class of microscopic 
 creatures which first offers itself for consideration, is derived from 
 the nature of the digestive apparatus with which the creatures com- 
 posing it are provided ;* this consists of a number of internal sacs 
 generally regarded as stomachs, which are easily distinguishable with 
 the microscope, and form a feature in their economy so peculiar, 
 that they are from this circumstance alone at once recognised as an 
 exceedingly natural and well-defined group, allied with each other in 
 the general details of their history, and exhibiting most astonishing 
 powers, not met with in other forms of being. In order to investigate 
 the facts which will be hereafter stated, connected with the history of 
 these animals, the young naturalist must be provided with a good 
 microscope, furnished with glasses capable of magnifying objects 
 from 200 to 1000 diameters, the last will be seldom needed ; but 
 a power of one-fourth of an inch focus will be indispensable. As 
 some practice and dexterity is requisite in prosecuting researches of 
 this description, a few hints relative to the best methods of procur- 
 ing and observing animalcules will not be improper in this place. 
 It would be needless to advert to the situations in which they are 
 to be found ; every stream and stagnant pool contains some forms 
 in countless numbers ; but, in order to obtain many uncommon 
 species, a little care is necessary. The lemna or duck-weed 
 should be skimmed from the surface of ponds which are exposed 
 to the rays of the sun, or the green film, which not unfrequently 
 covers stagnant waters ; and from these sources examples of most 
 tribes may readily be collected : or else recourse may be had to 
 infusions of various vegetable substances, of hay, chopped straw, 
 or the leaves of plants, which, if left in open glass vessels, and 
 fully exposed in the open air to the influence of the sun, will in a 
 few days swarm with polygastric animals, sometimes not to be pro- 
 cured by other means. 
 
 A drop of water derived from any of these sources, if placed 
 upon a thin plate of glass, and covered with a film of talc, will rea- 
 dily enable the observer to examine the beings which inhabit it ; 
 or if it be deemed advisable to insulate the larger species, they 
 may be separated from the rest with a feather, and placed in small 
 tubes or flat troughs in filtered water, and their developement and 
 mode of increase watched from day to day. 
 
 (72.) We shall now proceed to describe some of the most common 
 forms which the Polygastrica thus procured exhibit. In all water 
 
 * Ehrenberg. 
 
 E 2 
 
POLYGASTRICA. 
 
 containing putrefying vegetable matter, innumerable moving points 
 are visible, scarcely distinguishable except under the highest powers 
 of the microscope, but, when magnified to the utmost, assum- 
 ing the appearance represented at Jig. 16, 1 : these have been 
 termed Monads; and, as they F - lg 
 
 may well be supposed to be 
 the smallest creatures in ex- 
 istence, have been regarded 
 as the limit of the animal 
 world ; their minuteness, in- 
 deed, is incalculable. Dr. 
 Ehrenberg * has described 
 monads which are not larger 
 than from ToW to T^O o of a 
 line, and which appeared to 
 be separated from each other 
 by intervals not greater than 
 their diameter. Each cubic 
 inch of the water in which 
 they are found must contain, 
 therefore, 800,000 millions of 
 these animalcules, estimating 
 them to occupy but one-fourth 
 of its space. A single drop, brought under the field of the micro- 
 scope, and not exceeding one cubic line in diameter, will there- 
 fore contain 500 millions, equal to the whole number of human 
 beings upon the surface of the globe. Well may the mind, 
 overwhelmed with wonder at such an astounding fact, launch 
 into visionary speculations when contemplating it ; and we are 
 little surprised to see the fertile imagination of Buffon figuring all 
 animal and vegetable bodies as composed of aggregations of these 
 living particles, believing them to be the primitive materials of 
 which organized substances are made up. 
 
 (73.) The Proteus, (Am<ebaE.)Jig. 16, 2, is not frequently met 
 with, but affords a singular example of an acrite animal. It ap- 
 pears under a good glass to be an atom of transparent jelly, which 
 perpetually changes its form by contractions of different parts of its 
 body ; at one time being a roundish mass, then expanding into a linear 
 
 * Ehrenberg's valuable researches concerning the Polygastrica are to be found in 
 the Transactions of the Berlin Academy, Abhandlungen der Academic von Berlin. 
 vols.68, 69, and 71. 
 
POLYGASTRICA. 53 
 
 figure, and again shooting out processes of its substance in various 
 directions, so as to assume all kinds of shapes with the greatest 
 facility. 
 
 The Flask animalcule, (Enchelis,) fig. 16, 3; the Trichoda 
 sol, fig. 16, 4 ; the Euglena viridis, fig. 16, 5 ; the Gonium 
 pectorale, fig. 16, 6 ; the Trachelius anas, fig. 16, 7 ; the Para- 
 mecium aurelia, fig. 16, 8 ; the Navicula, fig. 16, 9 ; the Vibrio 
 Spirillum, fig. 16, 10 ; and the Vorticella Stentor, fig. 1 6, 11, will 
 give the reader an idea of the most common species of these crea- 
 tures, the structure of which we shall now proceed to investigate. 
 
 (74.) With regard to their external covering, thePolygastrica may 
 be divided into two parallel groups, in one of which the body is en- 
 tirely soft, whilst in the other the animals are enclosed in a delicate 
 transparent shell : the former are termed nuda, or naked ; the 
 latter loricata, or loricated animalcules. The shells of the lori- 
 cated division vary much in form ; sometimes being mere transparent 
 shields covering the back, as in Euplsea Charon (Jig. 17, 4) ; at 
 others they would seem to be capable of opening, like the bivalve 
 shells of mollusca, as in the minute Naviculse^g. 16, 9. Delicate 
 as these shells are, and requiring the most accurate examination, 
 even with a good microscope, to detect their presence, we shall be 
 surprised to find that they play an important part in nature, mak- 
 ing up by their immense accumulation for their diminutive size. 
 We have before us, while writing this, a specimen of pulverulent 
 matter collected upon the shores of Lake Lettnaggsjon, two 
 miles and a half from Urnea in Sweden, which from its extreme 
 fineness resembles flour : this has long been known by the natives 
 of the region where it is plentiful, under the name of Bergmehl or 
 mountain meal, and is used by them, mixed up with flour, as an 
 article of food ; experience having taught them that it is highly 
 nutritive. On examination with the microscope, the Bergmehl is 
 found to consist entirely of the shells of loricated infusoria, which, 
 having been accumulating from age to age at the bottom of the waters 
 in which the living animals are found, form a stratum of considera- 
 ble thickness. Nor is this all : for, when agglomerated and mixed 
 up with siliceous and calcareous particles, these exuviae become con- 
 solidated by time into masses of flint and marble, in which the 
 shape and characters of the shells are perfectly distinguishable, so 
 that even the species of the animalcules to which they originally 
 belonged is easily made out. 
 
 (75.) The movements of the polygastrica, when seen under the 
 
POLYGASTRICA. 
 
 Fig. 17. 
 
 microscope, are exceedingly vivacious ; and although many of them 
 inhabit a space not larger than the point of a needle, they swim 
 about with great activity, avoiding each other as they pass in their 
 rapid dance, and evidently directing their motions with wonderful 
 precision and accuracy. Our next enquiry therefore must be con- 
 cerning the organs of locomotion which they possess. These are 
 of various kinds, and are arranged differently in different species. 
 In the smallest animalcules, monads, &c. no locomotive organs 
 have been satisfactorily detected ; yet even in some of these 
 Mons. F. Dujardin perceived one or more filaments of extreme 
 tenuity attached to their globular bodies, which he regards as 
 instruments for progression. These filaments he describes as not 
 exceeding -30 j 00 of a millimetre in diameter, and consequently 
 requiring the utmost penetration of the microscope for their detec- 
 tion. Tn Amteba diffluens (Jig. 16, #) organs of locomotion are 
 formed at the pleasure of the animal, by shooting out processes 
 from different parts of its semifluid substance, which may be used 
 as fins or legs, as occasion requires. Some are provided with styli^ 
 or articulated, stiff, bristle-like organs, which are moveable, and 
 perform in some measure the 
 office of feet, and with uncini, 
 or little hooks, serving for at- 
 tachment to foreign bodies ; 
 these are seen in Eupltea 
 Charon (Jig. 17, 4). 
 
 (76.) But the most impor- 
 tant locomotive agents are the 
 cilia,* with which the Poly- 
 gastrica are generally fur- 
 nished (fig. 17; 1, 2, 3). 
 On attentively examining most 
 forms of these creatures, espe- 
 cially those of comparatively 
 large size, the body will be 
 seen in some cases to be en- 
 tirely covered with minute 
 vibrating hairs, or at least 
 furnished with such appen- 
 dages on some part of its surface. The existence of these cilia 
 is readily detected by a practised eye, even when using glasses 
 
 * Cilium, an eye-lash. 
 
POLYGASTRICA. 55 
 
 of no very great magnifying power, by the peculiar tremulous 
 movement which they excite in the surrounding fluid, somewhat 
 resembling the oscillations of the atmosphere in the neighbour- 
 hood of a heated surface ; but on applying higher magnifiers, espe- 
 cially if the animalcule is in a languid state, the motion is 
 seen to be produced by the action of the delicate filaments 
 of which we are speaking. It is extremely difficult accurately 
 to define the motion of the individual cilia ; it is most probable 
 that each forms by its rotation a cone, the apex of which will be 
 at the root of the organ this at least is the opinion of the best ob- 
 servers, and the combination of such movements gives rise to cur- 
 rents in the water, serving a variety of purposes in the economy of 
 these minute creatures. The vibrating organs, notwithstanding 
 their indescribable minuteness, vary considerably in size ; and it is 
 more than probable that in those monads, and other species, in 
 which their existence has not been detected, the apparent want of 
 them is owing to the imperfection of our means of investigation. 
 A few years ago, indeed, some species now distinctly proved to be 
 covered with cilia, were looked upon as being absolutely deprived 
 of locomotive apparatus, as the Volvox globator (Jig. 20) ; and 
 few greater proofs can be given of the superiority of the microscopes 
 now at our disposal, than the fact of our being able, not only to 
 detect with facility their existence on the surface of the parent 
 volvox, but even upon the young volvoces before their birth. 
 
 (77.) The cilia, as has been already observed, are sometimes 
 dispersed over the whole body, either arranged in parallel rows or 
 scattered irregularly ; they are, however, most frequently only met 
 with in the neighbourhood of the mouth, in which position they 
 are always most evident : here they produce, by their vibration, 
 currents in the surrounding fluid which converge to the oral aper- 
 ture, and bring to the mouth smaller animalcules, or particles of 
 vegetable matter, which may be floating in the neighbourhood, and 
 thus ensure by an admirable contrivance an abundant supply of 
 food, which without such assistance it would be almost impossible 
 for these little creatures to obtain. 
 
 (78.) We may be expected, in this place, to make a few obser- 
 vations concerning the agency by which these numberless and 
 almost invisible organs are made to perform their rapid move- 
 ments. The subject is one of no little difficulty, and in the 
 present state of our knowledge probably inexplicable. Ehrenberg 
 indeed asserts, that round the base of every cilium is an appa- 
 
POLYGASTRICA. 
 
 ratus of radiating muscular fibres, to the successive contractions of 
 which the rotation of the cilium is owing. Such an arrangement 
 is, to say the least, hard to be conceived, for in this case we must 
 attribute to these acrite beings an elaboration of structure of infi- 
 nite complexity ; and in creatures so small, how can the human 
 mind imagine the cilia to be wielded by many millions of distinct 
 and independent muscles, as such a supposition would infer ? 
 Some authors attempt to get rid of the difficulty by ascribing the 
 apparent ciliary movement to the rapid undulations of mem- 
 branous fins ; others altogether deny its existence, asserting that 
 the vibratory appearance is caused by the mingling of some secre- 
 tion which exudes from the surface of the animalcule with the sur- 
 rounding fluid, in the same manner as the union of spirit of wine 
 and water gives rise to an oscillation of particles visible to the 
 naked eye : to these suppositions, however, we barely allude, be- 
 cause we are convinced that any one who with a good microscope 
 and an unbiassed mind investigates the subject, will be con- 
 vinced that the cilia are such as we have described above, 
 however unable he may be to conjecture the cause of their 
 movement. 
 
 (79.) The mouth of the polygastrica is generally a simple and 
 extremely dilatable orifice, and, with a few rare exceptions, is un- 
 provided with any masticating organs ; yet in Nassula elegans, 
 (Jig- 17, 1,) and a few kindred species, Ehrenberg describes a 
 dental system of a most extraordinary description : this consists of 
 a prominent cylinder (a), of which an enlarged view is given at , 
 composed of numerous long teeth adapted to seize and bruise 
 materials used as food. 
 
 (80.) The digestive apparatus itself, from the peculiarity of its 
 structure, has given the character usually employed to distinguish 
 the entire class : it is described as consisting essentially of a 
 number of internal sacculi, varying from four to two hundred in 
 number in different species. These sacs are readily distinguishable 
 without any preparation, but are rendered more conspicuous by 
 feeding the animalcules with pure carmine or indigo, the coloured 
 particles of which substances they eagerly swallow. In one large 
 division, called A NEXT ERA, the sacculi or stomachs are said 
 to arise by separate tubular pedicles from the mouth itself 
 (./? 18, 1); whilst in others, ENTERODELA, there is supposed 
 to be a complete intestinal canal, terminated by a mouth and 
 anus, to which the sacculi or stomachs, as they are called, 
 
I'OLYGASTHICA. 
 
 57 
 
 Fig. 18. 
 
 n 
 
 are appended : sometimes the 
 
 mouth and anus are lodged in 
 
 the same fossa, and the intes- 
 tinal canal forms a circle in the 
 
 body (ANOPISTHIA, Ehren.), as 
 
 in the Vorticella (Jig. 18, 2) : or 
 
 else the mouth and anus are placed 
 
 at opposite extremities of the body, 
 
 through which the intestinal tube 
 
 passes either in a straight course, * 
 
 or exhibiting several flexuous curves 
 
 in its passage. (ENANTIOTRETA 
 
 and ALLOTRETA, Ehren.) (fig- 
 
 18, 3 and 4.) When neither the 
 
 mouth nor anus are terminal, as 
 
 in Kolpoda, (Jig. 19 ; 7, a, ,) 
 
 such animals belong to the group 
 denominated KATOTEETA by the 
 same author. 
 
 (81.) However imposing, from their completeness, the views of 
 Ehrenberg concerning the digestive system of the polygastrica may 
 be, and sanctioned as they are by almost general consent, we can- 
 not pass over a subject of so much importance without expressing 
 ourselves as being far from admitting their accuracy in all respects, 
 and we must say that our own observations upon the structure of 
 the polygastrica have led us to very different conclusions.* 
 
 The positions of the mouth and anal aperture we are well 
 assured, by frequent examination, to be such as are indicated by 
 the illustrious Professor of Berlin ; but with regard to the tube 
 named by him intestine, and the stomachs appended thereto, our 
 most patient and long-continued efforts have failed to detect the 
 arrangement depicted in his drawings. In the first place, as re- 
 gards the function of the sacculi, which he looks upon as the organs 
 in which digestion is accomplished ; in carnivorous animalcules 
 which devour other species we might expect, were these the 
 stomachs, that the prey would at once be conveyed into one or 
 other of these cavities ; yet, setting aside the difficulty which must 
 manifestly occur in lodging large animalcules in these microscopic 
 
 * It may be proper to state that the microscope used in these and similar re- 
 searches to which allusion will be made, is a compound achromatic, made by Ross 
 of London ; and the powers employed, of -&, , ^, and $ of an inch focus. 
 
58 POLYGASTRICA. 
 
 sacs, and having recourse to the result of actual experience, we 
 have never in a single instance seen an animalcule, when swallowed, 
 placed in such a position, but have repeatedly traced the prey into 
 what seemed a cavity excavated in the general parenchyma of 
 the body. 
 
 In the second place, the sacculi have no appearance of being 
 pedunculated, and consequently in a certain degree fixed in defi- 
 nite positions : during the last two hours we have been carefully 
 examining some beautiful specimens of Paramecium aurelia, 
 (Jig- 18, 4,) an animalcule which, from its size, is peculiarly 
 adapted to the investigation of these vesicles ; and so far from 
 their having any appearance of connection with a central canal, as 
 represented in the figure copied from Ehrenberg, they are in con- 
 tinual circulation, moving slowly upwards along one side of the 
 body, and in the opposite direction down the other, changing 
 moreover their relative positions with each other, and resembling 
 in every respect the coloured granules which have been described 
 ( 31,) as visible in the gelatinous parenchyma of the hydra. 
 
 With respect to the central canal, (Jig. 18 ; , 3, 4,) we have 
 not in any instance been able to detect it, or even any portion of 
 the tube seen in the figures, much less the branches represented as 
 leading from it to the vesicles or stomachs, as they are called. 
 Even the circumstances attending the prehension of food would 
 lead us to imagine a different structure ; witness for example the 
 changes of form which Enchelis pupa undergoes when taking prey, 
 as shown in fig. 16, 3, where it is represented in the act of devour- 
 ing a large animalcule, almost equal to itself in bulk, and is seen to 
 assume a perfectly different shape as it dilates its mouth to receive 
 the victim, with which its whole body becomes gradually distended. 
 Such a capability of taking in and digesting a prey so dispropor- 
 tionate, would in itself go far to prove that the minute sacculi 
 were not stomachs ; as it evidently cannot be in one of these that 
 digestion is accomplished. 
 
 (82.) Looking at the above facts as a whole, we cannot mistake 
 the analogy which there is between the organization of the so- 
 named Polygastrica and of the Hydra viridis ; there is the same 
 dilatable body in which the solution of food takes place, and the 
 same granular vesicles by which the nutritious portions are ab- 
 sorbed : that the vesicles become coloured by the coloured food 
 given to the animalcule, cannot be considered as a proof of their 
 being stomachs, as in the experiments of Trembley, above nar- 
 
POLYGASTRICA. 
 
 59 
 
 rated, the granules which circulate in the body of the hydra 
 became dyed with the juices of the animals with which it was fed, 
 precisely in a similar manner. 
 
 The reproduction of the polygastric animalcules is effected in 
 various ways, and not unfrequently the same individual would 
 appear to propagate in two or three different modes. 
 
 (83.) The first is by external gemmules or buds, resembling 
 those by which the hydra is multiplied which sprout like minute 
 gelatinous tubercles from the surface of the body, and, gradually 
 attaining the shape of their parent, develope the cilia characteristic 
 of their species, and soon become independent beings, although 
 they do not attain to their full growth until some time after their 
 separation. 
 
 (84.) A second mode of reproduction is witnessed in the 
 Volvox, and others of similar conformation. In these animalcules 
 (Jig- 19, 1,) the parent is a delicate green transparent globe, which 
 
 Ffe.19. 
 
 under a good microscope is seen to 
 be entirely covered with cilia, whose 
 action produces currents in the water, 
 the course of which is represented by 
 the arrows in the figure ; impelled by 
 these cilia, the little globe makes its / j 
 way with a revolving motion through 
 the element which it inhabits. In 
 the interior of the volvox, the observer 
 readily discovers "other smaller globes 
 of a dark green colour, which a little 
 attention will prove to be young vol- 
 voces, exactly resembling the larger 
 one which contains them, and covered 
 in like manner with vibratile cilia, by 
 the assistance of which they swim 
 about in the body of their parent, and seem to have ample 
 space for their motions. At length, when the imprisoned gem- 
 mules are ripe for exclusion, the skin of the original volvox bursts, 
 (Jig. 19, ,) and the young ones, (Jig. 19, 8,) escaping through 
 the fissure, enter upon a wider stage of existence : yet, even before 
 their escape, the gemmules of a third generation are seen within 
 their bodies, which, gradually enlarging, are destined to terminate 
 by their birth the life of the newly liberated beings. 
 
 (85.) The most usual mode of propagation however is by 
 
60 
 
 POLYGASTRICA. 
 
 spontaneous fissure, or division of the body of an adult animalcule 
 into two or more portions, each of which is perfect in all its parts. 
 This singular kind of generation, by which the old animalcule 
 literally becomes converted into two or more young ones, is 
 accomplished in various ways, which will require separate notice. 
 
 In the oval forms of the polygastrica, the line of separation 
 generally divides the body transversely into two equal portions, 
 by a process, the different stages of which are represented in 
 Jig. 20 ; 1, 2, 3. The body 
 of an animalcule about to di- 
 vide in this manner becomes 
 at first slightly elongated, 
 and a line more transparent 
 than the rest of its body is 
 seen to cross its middle por- 
 tion : a constriction becomes 
 gradually apparent at each 
 extremity of the line of divi- 
 sion, which soon grows more 
 decided, and at length the 
 two parts are only united 
 by a narrow isthmus, {Jig. 
 19, 3,) which, getting thinner 
 and thinner, allows a slight 
 effort on the part of either of 
 the now nearly distinct por- 
 tions to tear itself from the other half, and complete the separation. 
 
 In some elongated species {fig. 20, 4) the fissure is effected in 
 a longitudinal direction, the separation gradually proceeding from 
 the posterior to the anterior extremity of the body (fig. 20, 6) ; 
 yet even in these the division is occasionally transverse, the newly 
 formed creature appearing truncated at one end (fig. 19, 5) for 
 some time after the completion of the process. 
 
 (86.) The mode of generation in Convallaria, a group of which 
 is seen at fig. 20, 11, is very curious; and from the different 
 forms which the young assume during the progress of develope- 
 ment much confusion has occurred, each stage of its growth having 
 been described as the permanent appearance of a distinct species. 
 This beautiful animalcule seems to be propagated in several 
 ways : sometimes this is effected by external gemmules, which 
 appear like minute points, scarcely more than y^oo of a l me * n 
 
POLYGASTIUCA. 61 
 
 diameter, upon the pedicles of the adult convallarise ; these in time 
 become pedunculated, and, although still very small, exhibit the 
 cilia upon the margins of their delicate cups ; in this state they 
 were called by Schrank Vorticella monedicce. The Convallarise 
 generally however multiply by fissure, the bell-shaped cup at the 
 extremity of their highly irritable pedicles separating longitudinally 
 into two ; but the progress of this division requires our particular 
 notice, as the unpractised observer might be considerably puzzled 
 on witnessing some of the phenomena attending it. 
 
 The adult animalcule, seen with its pedicle fully extended, 
 (Jig. 20, 9,) when it is alarmed, shrinks by throwing its stem into 
 spiral folds (10) : in the latter figure, the bell or body of the 
 animalcule is seen to have extended considerably in breadth, pre- 
 paratory to its becoming divided into two distinct creatures. At 
 11, the commencement of its division is depicted; the separation 
 gradually extending from the base, or ciliated extremity, to the 
 point where the body is attached to its stem. When the division 
 has extended thus far, (12,) the newly formed portion is seen with 
 surprise to have become furnished with cilia at both ends, and, 
 when finally detached, (13,) only at the opposite extremity to 
 that on which they originally existed ; it then, freed from its pe- 
 dicle, and thus losing the great characteristic of its species, swims 
 about at large, exhibiting forms represented at 14, 15, 16, 17, all 
 of which have been described as distinct species by different 
 writers ; at last it puts forth a new stem, and, assuming the adult 
 form, becomes fixed by its pedicle to some foreign body. 
 
 (87.) This fissiparous mode of reproduction is amazingly pro- 
 ductive, and indeed far surpasses in fertility any other with which 
 we are acquainted, not excepting the most prolific insects or even 
 fishes. Thus the Paramecium aurelia, if well supplied with 
 food, has been observed to divide every twenty-four hours, so that 
 in a fortnight, allowing the product of each division to multiply at 
 the same rate, 16,384 animalcules would be produced from the same 
 stock ; and in four weeks the astonishing number of 268,435,456 
 new beings would result from a continued repetition of the process : 
 we shall feel but little surprise, therefore, that with such powers of 
 increase these minute creatures soon become diffused in countless 
 myriads through the waters adapted to their habits. 
 
 (88.) The capability of spontaneous division is one of the most 
 distinctive attributes of the acrite type of structure ; and was the 
 organization of these animalcules as simple as it was supposed to 
 
POLVGASTR1CA. 
 
 be a few years ago, when they were thought to be mere specks of 
 living gelly, imbibing nourishment at every point of their surface, 
 which became diffused through all parts of the homogeneous tex- 
 ture of their bodies, such a mode of multiplication would be per- 
 fectly intelligible, and every step of the process easily understood : 
 but setting aside the conformation of their digestive apparatus, 
 which, as we have before observed, is in our opinion not satisfac- 
 torily determined, there are many circumstances attending the 
 operation, which would indicate a power of developing new organs 
 in the construction of every fresh individual, which must be looked 
 upon as a very interesting feature in their history. Thus a new 
 oral orifice, surrounded with cilia, must be formed upon the poste- 
 rior segment of each divided animalcule, while an anal aperture is 
 developed upon the anterior half. In Nassula elegans (Jig. 17, 1) 
 the dental apparatus a, complex as its structure seems to be, must 
 be formed upon a new part of the body preparatory to every sepa- 
 ration ; and accordingly, in the plates which Ehrenberg gives of the 
 reproduction of this animalcule, a new mouth or dental cylinder is 
 actually seen to sprout from the hinder half of the creature before 
 its transverse fissure is complete. These structures therefore, and 
 others hereafter to be mentioned, must continually be called into 
 existence at new and distant parts of the system. 
 
 (89.) We have as yet only spoken of those forms of fissiparous 
 generation in which the original animalcule divides either trans- 
 versely or longitudinally into two portions ; yet there are instances 
 where several new beings result from a like process. In Gonium 
 pectorale (Jig- 16, 6) the entire animalcule seems to consist of 
 sixteen globules enclosed in a delicate film or capsule ; which, 
 divides both in a transverse and longitudinal direction, so as to 
 separate into four portions, each composed of one large and three 
 smaller globules, which, after their separation from the rest, swim 
 freely about, and soon develope the parts and assume the appear- 
 ance of the parent. In Gonium pulvinatum the offspring is still 
 more numerous ; the parent resembles a square piece of delicate 
 membrane, and, on assuming its full growth, is seen to be marked 
 by three transverse and as many longitudinal lines, crossing each 
 other at right angles, and dividing the original into sixteen smaller 
 squares, which soon separate from each other, and become as many 
 detached beings. 
 
 (90.) Productive as the above-mentioned modes of increase 
 are, it would seem that they are not the only sources of propagation 
 
POLYGASTRICA. 63 
 
 in the polygastric class of animals ; as many tribes have been 
 observed to be produced from ova or spawn, as well as by fis- 
 sure and gemmation. The Kolpoda cucullus {Jig. 20, 7) is 
 one in which Ehrenberg succeeded most perfectly in detecting this 
 kind of generation, but he has likewise observed it in many others. 
 The ova seem to be produced in the general parenchyma of the 
 body, without the visible existence of any organ specially destined 
 to their formation ; and, when mature, are expelled in a delicate 
 reticulate mass (Jig. 20, 8). Ehrenberg even describes some 
 contractile vesicles discovered to exist in many species, which he 
 regards, though perhaps without sufficient grounds, as being a 
 male apparatus provided for the fertilization of the ova previous to 
 their expulsion. In Paramecium aurelia (Jig. 17, 2) these were 
 two in number, (a, g,) placed at the two extremities of the body, 
 each seeming to consist of a delicate irritable central portion, 
 from which he could see, on gently pressing the animalcule be- 
 tween two plates of glass, eight canals issuing in a radiating manner 
 and diverging toward all parts of the body ; these became gradually 
 enlarged as the vesicle contracted, and, on the contrary, became 
 narrow and disappeared as the vesicle dilated. The contractile 
 organs were detected in twenty-two species belonging to very 
 different families ; but the radiating canals were only seen in two, 
 viz. Paramecium aurelia and Ophryoglena : their appearance in 
 Nassula elegans, Stentor polymorphus, and Euplotes charon, is 
 seen in Jig. 17 ; 1, 3, 4, b. The function of these organs 
 Ehrenberg believes to be connected with the secretion of a fecun- 
 dating fluid, which, being dispersed by their contraction through 
 the body, serves to fertilize the ova. 
 
 (91 .) No circulation, properly so called, has been seen in 
 the polygastrica ; neither have vessels of any kind been satisfac- 
 torily made out. There is however in Paramecium aurelia, as has 
 been already mentioned, a constant sap-like movement in the gra- 
 nular matter of the body, which is easily detected, and was described 
 by Gruithuysen : this appearance Ehrenberg attributes to the 
 movements of the intestine ; but as we have been quite unable to 
 detect the arrangement which he indicates, or to reconcile the ap- 
 parent course of the globules with the supposed direction of the 
 alimentary tube, we are still inclined to regard the flow of particles 
 alluded to as analogous to what has been described as existing in 
 the stems of polyps. Neither do we find any distinct apparatus 
 devoted to respiration in these minute beings : the cilia upon the 
 
AC ALE PH. E. 
 
 surface, by the constant currents which they excite, necessarily 
 ensure a continual supply of aerated water, which bathing the 
 whole body exposes every part to the influence of oxygen, and 
 Ehrenberg thinks that he has even perceived the existence of a 
 delicate net-work of minute canals hollowed out in the periphery 
 of some species, which, if filled with nutritive juices, might be 
 regarded as the first rudiments of a vascular system. 
 
 (92.) The nervous matter, or neurine, which we must suppose 
 to exist in a molecular state mixed up with the tissues of the body, 
 has never been detected in an aggregated form ; nevertheless, upon 
 many species, when observed under good glasses, it is easy to see 
 one or two extremely minute red or brown specks, which have 
 been conjectured to be eyes, though probably without further 
 reason for the supposition than the resemblance which they 
 exhibit, in colour at least, to the visual organs of some ento- 
 mostracous Crustacea : in some cases, these points exist only in 
 the young animalcule prior to its birth ; thus in Eudorina 
 elegans, an animal resembling the Volvox in its mode of gene- 
 ration, the offspring, while confined in the body of their parent, 
 are each seen to be furnished with a red speck, as well as a long 
 bristle, which is exserted through the parent envelope ; but as soon 
 as, by the rupture of the sac, the contained gemmules are set at 
 liberty, a time when we should imagine the faculty of vision to be 
 most useful, the red point disappears ; and, were that the only 
 means of appreciating the presence of light, we might suppose the 
 liberated animalcules to be deprived of the power of seeing when 
 most capable of enjoying it. 
 
 CHAPTER V. 
 
 ACALEPHJE, (CuV.) 
 
 (93.) The fourth class of acrite animals is scarcely inferior to 
 that last described, either in numbers or interest. The ocean in 
 every climate swarms with infinite multitudes of animals, which, 
 from their minuteness and transparency, are almost as impercepti- 
 ble to the casual observer as the infusoria themselves ; their exist- 
 ence being only indicated by the phosphorescence of some species, 
 which, being rendered evident on the slightest agitation, illuminates 
 
ACALEPH^E. 65 
 
 the entire surface of the sea. All however are not equally minute, 
 some grow to a large size ; and their forms are familiar to the inha- 
 bitants of every beach, upon which, when cast up by the waves, 
 they lie like masses of gelly, melting as it were in the sun, inca- 
 pable of motion and exhibiting few traces of organization, or 
 indications of that elaborate structure which more careful examina- 
 tion discovers them to possess. Their uncouth appearance has 
 obtained for them various appellations by which they are fami- 
 liarly known, as sea-gelly, sea-blubber, or gelly- fishes; whilst, 
 from disagreeable sensations produced by handling most of them, 
 they have been called sea-nettles, stingers, or stang-fishes. The 
 faculty of stinging is indeed the most prominent feature in their 
 history, so that their names in almost all languages are derived 
 from this circumstance : they were known to the older naturalists 
 by the title of Urtica marina ; and the word at the head of this 
 chapter, applied by Cuvier to the entire class, and originally used 
 by Aristotle, is of similar import (axaXrjpij, a nettle). 
 
 There are few subjects which come under the observation 
 of the physiologist more calculated to excite his astonishment 
 than the history of these creatures. If he considers, in the first 
 place, the composition of their bodies, what does he find ? -an 
 animated mass of sea-water, for such in an almost literal sense 
 they are. Let him take a medusa of any size, and lay it in a 
 dry place ; it will be found gradually to drain away, leaving nothing 
 behind but a small quantity of transparent cellular matter, almost 
 as delicate as a cobweb, which apparently formed all the solid 
 frame-work of the body, and which, in an animal weighing five or 
 six pounds, will scarcely amount to as many grains ; and even if 
 the water which has escaped from this cellulosity be collected and 
 examined, it will be found to differ in no sensible degree from the 
 element in which the creature lived. The conclusion therefore 
 at which he naturally arrives is, that, in the medusae, the sea-water 
 collected and deposited in the delicate cells of an almost imper- 
 ceptible film becomes in some inscrutable manner instrumental 
 to the exercise of the extraordinary functions with which these 
 creatures are endowed. The Acalephse have been divided by 
 zoologists into groups distinguished by the nature of their means 
 of progression : in describing therefore the organs of locomotion, 
 with which we commence their history, the reader will be made 
 acquainted with the principal modifications of outward fonn which 
 they exhibit. 
 
66 
 
 ACALEPH^. 
 
 (94.) Pulmonigrada. The most ordinary examples of the 
 aealephse found in our climate, when examined in their native 
 element, are seen to be composed of a large mushroom-shaped 
 gelatinous disc, from the inferior surface of which various pro- 
 cesses are pendent, some serving as tentacula, others for the pre- 
 hension of food. In Rhizostoma (fig. 21) the central pedicle 
 resembles in structure 
 and function the root of 
 a plant, being destined 
 to absorb nourishment 
 from the water in which 
 the creature lives. The 
 body of one of these 
 medusae is specifically 
 heavier than the water 
 of the ocean, and would 
 consequently sink but 
 for some effort on the 
 part of the animal. 
 The agent employed 
 to sustain it at the sur- 
 face, and in some mea- 
 sure to row it from place 
 to place, is the um- 
 brella-shaped expansion 
 
 or disc, which is seen continually to perform movements of con- 
 traction and dilatation, repeated at regular intervals about fifteen 
 times in a minute, having some resemblance to the motions of the 
 lungs in respiration, whence the name of the order (pulmo, the 
 lung; gradior, I advance). By these constant movements of the 
 disc, the medusa can strike the water with sufficient force to 
 insure its progression in a certain direction when swimming in 
 smooth water, but of course utterly inefficient in stemming the 
 course of the waves, at the mercy of which these animals float. 
 The tentacula, in such species as are provided with these organs, 
 are likewise capable of contractile efforts, and may in some slight 
 degree assist as agents of impulsion, although they are destined to 
 the exercise of other functions. The locomotive disc, when cut 
 into, seems perfectly homogeneous in its texture, nor is any 
 fibrous appearance recognisable to which its movements could be 
 attributed ; but in the larger species its inferior surface appears 
 
ACALEPH.E. 
 
 67 
 
 corrugated, as it were, into minute radiating plicae, which seem 
 to contract more energetically than the other portions, and re- 
 semble a rudimentary developement of muscular fibre. 
 
 (95.) Ciliograda. In the Ciliograde acalephse, the organs of 
 motion are of a very different description, consisting of narrow 
 bands of vibratile cilia variously disposed upon the surface of 
 the body, which in their motions and office resemble those of 
 the polygastric animalcules. 
 
 In the globular forms of Beroe (fig. 22) the cilia are generally 
 
 arranged in eight longitudinal bands, and appear to be attached to 
 subjacent arches of a firmer consistence than the rest of the body. 
 They are generally quite naked, but in Pandora are lodged 
 between folds of the skin, which will close over and completely 
 conceal them ; their motion is extremely rapid, and sometimes 
 only recognisable by the currents which they produce, or the 
 iridescent hues which play along the arches. The ciliary action 
 seems to be perfectly under the control of the animal, as it can 
 retard or stop their motions at pleasure, sometimes arresting the 
 play of one, two or more rows, whilst the rest continue in rapid 
 vibration, and thus changing its course, or causing its body to 
 revolve in any direction. In some of the Ciliograda, the loco- 
 motive cilia are of considerable size ; and in Cydippe pileus their 
 structure has been particularly examined by Dr. Grant.* In this 
 animal eacli cilium, instead of being a simple filament, seems to 
 be made up of several, arranged side by side, so as to form a flat 
 membranous organ, not unlike the fin of a fish (fig. 22 ; 3, 4) : 
 the individual filaments appear tubular when viewed under a 
 powerful magnifier, and are slightly curved backwards, so that 
 
 * Transact. Zoolog. Society of London, vol. i. 
 
68 
 
 ACALEPH.E. 
 
 the whole apparatus gives not a very bad representation of the 
 paddle-wheel of a steam-boat. The cause of their movements is 
 however as little evident in the Beroeform acalephte as in the 
 minute Polygastrica. Under the arches which support them 
 are vessels containing a fluid, which Dr. Grant imagines may in 
 some manner be injected into the tubular structure, and thus cause 
 them to become erected ; but how their rapid motions are excited, 
 is still far from being explicable. 
 
 But one of the most beautiful examples of a ciliated medusa 
 is seen in the Girdle of Venus (Cesium Veneris) (fig. 23). 
 
 Fig.23. 
 
 This creature is a long, flat, gelatinous riband, the margins of 
 which are fringed with innumerable cilia, tinted with the most 
 lovely iridescent colours during the day, and emitting in the dark 
 a phosphorescent light of great brilliancy : in this animal too, 
 which sometimes attains the length of five or six feet, canals may 
 be traced running beneath each of the ciliated margins, analogous 
 to those which exist in the Beroe, and no doubt answering a 
 similar purpose. 
 
 (96.) Physograda. In the third division of acalephae, de- 
 nominated by Cuvier " Acalephes Hydrostatiques," the body is 
 supported in the water by a very peculiar organ, or set of organs, 
 provided for the purpose. This consists of one or more bladders, 
 capable of being filled with air at the will of the animal, which 
 are appended to the body in various positions, so as to form floats 
 of sufficient buoyancy to sustain the creature upon the surface of 
 the sea when in a state of distension ; but, when partially empty, 
 allowing it to sink, and thus escape the approach of danger. In 
 
ACALEPH.fc 
 
 0'9 
 
 Physalus, (Jig- 24,) known to sailors by the name of the Por- 
 tuguese man-of-war, the swim- p igt 24. 
 in ing-bladder is single, and of 
 great proportionate size, so that 
 when full of air it is exceed- 
 ingly buoyant, and floats con- 
 spicuously upon the waves. The 
 top of this bladder bears a crest, 
 c, of a beautiful purple colour, 
 which, presenting a broad surface 
 to the wind, acts as a sail, by the 
 assistance of which the creature 
 scuds along with some rapidity. 
 The air-bladder is endowed with 
 a considerable power of contrac- 
 tion, and, when carefully exa- 
 mined, two orifices are observ- 
 able, one at each extremity, (a, &,) 
 through which, upon pressure, 
 the contained air readily escapes ; 
 a provision which enables the 
 creature to regulate its specific 
 gravity at pleasure, and, when alarmed, at once to lessen its buoy- 
 ancy by diminishing the capacity of its swimming-bladder, and 
 to sink into the waves. The nature of the air with which the 
 little voyager distends its float has not been accurately deter- 
 mined ; but it is undoubtedly a secretion furnished at pleasure 
 when at a considerable distance from the surface, although the 
 mode of its production is still unknown. 
 
 Among the diversified forms of the Hydrostatic acalephse, few 
 are more elegant than one named by Peron Cuvieria cariso- 
 chroma (Jig. 27). In this beautiful medusa we find the floats 
 arranged like a string of pearls around the margin of its circular 
 body ; which, thus supported, spreads its long and delicate fila- 
 mentary tentacles to a considerable depth, in search of passing 
 food, as it swims upon the tranquil bosom of the ocean. 
 
 (97.) Cirrigrada. The Cirrigrade acalephse form a very 
 remarkable family, peculiarly distinguished by the possession of 
 an internal solid support or skeleton secreted in the substance 
 of their soft and delicate bodies. In For pita (Jig. 25) this 
 consists of a flat plate of semicartilaginous texture, (2,) evi- 
 
70 
 
 ACALEPtLE. 
 
 1. 
 
 Fig. 25. 
 
 dently deposited in 
 thin secondary lami- 
 nae, which gradually 
 increase in size as the 
 animal advances in 
 growth, the inferior 
 being the largest and 
 last formed. When 
 
 examined after its removal from the body, this fragile skeleton is 
 seen to be extremely porous or cellular ; and, the pores being 
 filled with air, it is specifically lighter than water, a circumstance 
 which may contribute to the buoyancy of the animal, even when 
 alive. 
 
 The lower surface of Porpita is furnished with numerous appen- 
 dages called cirri, some of which appear to be organs of prehension, 
 but perform also the office of oars, which in this species are the 
 principal agents in progression ; yet in other Cirrigrada, as Velella 
 and Rataria, besides the horizontal lamella, which forms the whole 
 skeleton of Porpita, there is a second subcartilaginous plate rising 
 at right angles from its upper surface, and supporting a delicate 
 membranous expansion, which rises above the water and exposes a 
 considerable surface to the wind, so as to form a very excellent 
 sail. To perfect so beautiful a contrivance, in Rataria the crest 
 is found, to contain fibrous bands, apparently of a muscular nature, 
 by the contractions of which the sail can be lowered or elevated at 
 pleasure. 
 
 (98.) Diphyda. The last family of acalephse derives its name 
 from the singular appearance of the creatures which compose it : 
 each animal, in fact, seems to consist of two portions so slightly 
 joined together, that it is by no means easy to understand the 
 nature of the con- 
 nection which ex- 
 ists bet ween them; 
 and from the per- 
 fect transparency 
 of their bodies, 
 which is such that 
 it is with great 
 difficulty they are 
 discoverable even 
 in small quanti- > 
 
ACALEPH^E. 
 
 71 
 
 Fix. 27. 
 
 ties of sea-water, our knowledge of their internal structure is at 
 present extremely imperfect. The annexed figure of Diphyes cam- 
 panulifera (^g". 26) will give the reader a general idea of their 
 form. The two bell-shaped portions of which the creature may 
 there be seen to consist, are constantly found united together, and 
 seem to compose but one animal, although they might readily be 
 conceived to be distinct creatures ; the apex of the posterior part 
 is received into a cavity in the other portion, but the connection 
 between the two is so slight, that, when preserved in spirits at 
 least, the slightest touch is sufficient to tear them asunder ; their 
 principal bond of union appears to 
 be a delicate filament, which, arising 
 from the anterior compartment, 
 passes through the whole length 
 of the posterior portion. This 
 strange compound body, concern- 
 ing the structure of which our 
 knowledge is very imperfect, swims 
 through the water with consider- 
 able rapidity, urged forward by the 
 alternate contractions of the two 
 campanulate halves, which con- 
 tinually take in and eject the cir- 
 cumambient fluid, with sufficient 
 force to propel the creature in an 
 equable and uniform course. 
 
 (99.) Interesting as the acalephse 
 may justly be considered when we 
 contemplate the singular beauty of 
 their external configuration, and 
 the wonderful design conspicuous in 
 their locomotive organs, a more in- 
 timate acquaintance with their habits and economy will be found to 
 disclose many facts not less curious in themselves than important in a 
 physiological point of view. In the higher animals we are accustomed 
 to find the nutritive apparatus composed of several distinct systems ; 
 one set of organs being destined to the prehension of food, another 
 to digestion, a third to the absorption of the nutritious parts of the 
 aliment, a fourth provided for its distribution to every part of the 
 body, and a fifth destined to ensure a constant exposure of the cir- 
 culating fluid to atmospherical influence. These vital operations 
 
72 ACALEPH.E. 
 
 are carried on in vessels specially appropriated to each ; but, in the 
 class of animals of which we are now speaking, we find but a 
 single ramified cavity appropriated to the performance of all these 
 functions, and exhibiting in the greatest possible simplicity a 
 rough outline, as it were, of systems afterwards to be more fully 
 developed. 
 
 In the Pulmonigrade acalepha we have the best illustration of 
 this arrangement : in these the stomach or digestive cavity is ex- 
 cavated in the centre of the disc, and is supplied with food by a 
 mechanism which differs in different species. In Rhizostoma, 
 (fig. 21), which receives its name from the nature of the 
 communication between the stomach and the exterior of the 
 body,* the organ destined to take in nourishment consists of a 
 thick pedicle, composed of eight foliated divisions, which hang 
 from the centre of the disc. Each of these appendages is found 
 to contain ramifying canals, opening at one extremity by nu- 
 merous minute apertures upon the external surface, whilst at the 
 opposite they are collected into four large trunks communicating 
 with the stomach ; as the Rhizostoma therefore floats upon the 
 waves, its pendent and root-like pedicle absorbs, by the numerous 
 oscules upon its exterior, such food as may be adapted to its 
 nutrition, finding most probably an ample provision in the mi- 
 croscopic creatures which so abundantly people the waters of the 
 ocean. The materials so absorbed are conveyed through the canals 
 in the interior of the arms into the stomachal cavity, where their 
 solution is effected. 
 
 But it is not upon this humble prey that some of the medusae 
 feed ; many are enabled, in spite of their apparent helplessness, to 
 seize and devour animals which might seem to be far too strong and 
 active to fall victims to such assailants : Crustacea, worms, mollusca, 
 and even small fishes are not unfrequently destroyed by them. In- 
 credible as this may seem when we reflect upon the structure of these 
 feeble beings, observation proves that they are fully competent to 
 such enterprises. The long tentacula or filaments, with which 
 some are provided, form fishing-lines scarcely less formidable in 
 arresting and entangling prey than those of the Hydra ; and, in all 
 probability, the stinging secretion which exudes from the bodies of 
 these medusae speedily paralyzes and kills the animals which fall 
 in their way. The mouth of these acalephse is a simple aperture 
 leading into the gastric cavity, and sometimes surrounded with 
 
 * 'Pi&, a root j frozen, a mouth. 
 
AC ALE PILE. 
 
 tentacula, which probably assist in introducing the food into the 
 stomach. 
 
 In Cassiopea Borbonica, the principal agents in procuring 
 nourishment are numerous retractile suckers, (Jig. 28, a,) terminat- 
 ing in small violet- F/g.28. 
 coloured discs, which 
 are dispersed over the 
 fleshy appendages to 
 the under surface of 
 the body ; the stem 
 of each of these suck- 
 ers is tubular, and 
 conveys into the sto- 
 mach nutritive mate- 
 rials absorbed from 
 animal substances to 
 which they are at- 
 tached during the 
 process of imbibing food. 
 
 (100.) The above examples will suffice to give the reader an idea of 
 the most ordinary provisions for obtaining nourishment met with 
 in the Pulmonigrada : we will therefore return to consider the 
 structure of the stomach itself, and of the canals which issue from 
 it, and convey the digested nutriment through the system. In 
 Cassiopea Borbonica, which will serve to exemplify the general 
 arrangement of these parts in the whole order, the stomach (Jig- 
 28) is a large cavity placed in the centre of the inferior surface of 
 the disc, and is apparently divided into four compartments by a 
 delicate cruciform membrane arising from its inner walls. Into 
 this receptacle all the materials 
 collected by the absorbing suck- 
 ers are conveyed through eight 
 large canals, and by the process of 
 digestion become reduced to a 
 yellowish pulpy matter, which is 
 almost fluid, and which is the 
 pabulum destined to nourish the 
 whole body. From the central 
 stomach sixteen large vessels 
 arise, (Jig. 29, c,) which ra- 
 diate towards the circumference 
 
74 ACALEPH.E. 
 
 of the disc, dividing and subdividing into numerous small branches, 
 which anastomose freely with each other, and ultimately form a 
 perfect plexus of vessels as they reach the margin of the mush- 
 room-shaped body of the creature. The radiating vessels are 
 moreover made to communicate together by means of a circular 
 canal (Jig. 29, e) which runs around the entire animal, so that 
 every provision is made for an equable diffusion of the nutritive 
 fluid derived from the stomach through the entire system. Now, 
 if we come physiologically to investigate the nature of this 
 simple apparatus of converging and diverging canals, we cannot 
 but perceive that it unites in itself the functions of the digestive, 
 the circulatory, and the respiratory systems of higher animals : 
 the radiating canals, which convey the nutritive juices from the 
 stomach through the body, correspond in office with the arteries 
 of more perfectly organized classes ; and the minute vascular 
 ramifications in which these terminate, situated near the thin 
 margins of the locomotive disc, as obviously perform the part of 
 respiratory organs, in as much as the fluids which permeate them 
 are continually exposed to the influence of the air contained in the 
 surrounding water, the constant renewal of which is accomplished 
 by the perpetual contractions of the disc itself. 
 
 (1 01.) Before closing our description of the alimentary system of 
 the Pulmonigrade acalephse, we must mention some accessory organs 
 of recent discovery which are in connection with it. Eschscholtz* 
 describes a series of elongated granular bodies, placed in little de- 
 pressions around the margin of the disc, which seem to be of a 
 glandular nature, and apparently communicate by means of minute 
 tubes with the nutritious canals : these he regards as the rudiments 
 of a biliary system. Other observers assign a similar office to a 
 cluster of blind sacculi or caeca, which are connected in some 
 species with the commencement of the radiating tubes ; it is, 
 however, scarcely necessary to observe that such surmises relative 
 to the function of minute parts are but little satisfactory. 
 
 (102.) The Ciliograde acalephse, although their digestive system 
 varies considerably in its general arrangement from what has been 
 described in the Pulmonigrade division, will be found to exemplify 
 in an equally perfect and perhaps more striking manner the for- 
 mation of the vascular and respiratory systems from an extension 
 of the nutritive canals. In the Beroeform species (Jig. 22) the 
 
 * System der Acalephen. Berlin, 1829. Annales des Sciences Nat. vol. xxviii. 
 p. 251. 
 
ACALEPH.E. 
 
 75 
 
 alimentary canal passes straight through the globular or barrel- 
 shaped body, commencing at one extremity by two prominent and 
 sensitive lips. No apparatus of prehension is here needful ; for, as 
 these animals swim along by the action of their cilia, the water 
 passes freely through this capacious channel, and brings into the 
 stomach materials proper for food. From both extremities of the 
 digestive cavity arise vascular canals which empty themselves into 
 two circular vessels, one surrounding the oral, and the other the 
 anal portions of the body : from these two rings eight double vessels 
 arise, which run longitudinally from one pole to the other of 
 the creature beneath each of the cartilaginous ribs upon which 
 the cilia are placed ; and from these, others more minute arise, 
 which are distributed in a delicate network through the sub- 
 stance of the animal. In the Beroe, therefore, we must regard 
 the vessels which convey the nutritive juices beneath the ciliated 
 arches, not merely as arteries, but as organs of respiration ; for, 
 thus placed close beneath the outer surface of the body, the water, 
 which is perpetually made to rush over them by the ciliary move- 
 ments, will serve to aerate the fluid contained within. 
 
 The Cestum Veneris (fig. 23) is nearly allied to the Beroe in 
 the arrangement of its nutritive apparatus, notwithstanding the 
 difference of form observable in these Ciliograde medusae. In Ces- 
 tum the digestive cavity, which is exceedingly short in comparison 
 with the length of the animal, passes transversely across the body 
 in a straight line from one side to the other, as represented in the 
 engraving (fig. 23) ; but the details of its 
 structure, and the nature of the vessels aris- 
 ing from it, will be best understood by a 
 reference to the enlarged diagram of these 
 parts given in the annexed figure (fig. 30). 
 The mouth (i) is a rhomboidal depression 
 seen near the centre of the body, between 
 the two lateral rows of locomotive cilia 
 which extend from one end of the animal to 
 the other. From the mouth arise two 
 tubes, (/,y,) which terminate in a globular 
 cavity common to both ; these would seem 
 to constitute the digestive apparatus : and 
 a straight and narrow tube (o), prolonged 
 to the margin of the body opposite to that 
 which the mouth occupies, may be regarded 
 
 Fig. 30. 
 
76 ACALEPH.E. 
 
 as an intestine through which the residue of digestion is discharged. 
 From around the oral extremity of the stomach, and from the glo- 
 bular cavity in which the two principal canals terminate, arise ves- 
 sels, (, t, ,) which diverge so as to form a cone at the base of which 
 they all empty themselves into two circular canals, one surrounding 
 the mouth, and the other encircling the anal aperture ; which pre- 
 cisely correspond with the vascular rings already described in the 
 Beroe : and, from these, four long vessels, or branchial arteries as 
 they might be termed, (/?, p ; </, </,) are prolonged beneath the four 
 ciliated margins all around the body. But, besides these four nutri- 
 tive vessels, two others (#, x) arise from the anal ring which run 
 inwards towards the centre of the animal, and afterwards, assuming 
 a longitudinal direction, seem to distribute nourishment to the me- 
 dian portions of the body. The caeca or blind tubes, (w, w,) ap- 
 pended to the intestine, may possibly furnish some secretion use- 
 ful in digestion, although we are perhaps scarcely warranted in 
 saying decidedly that they are the rudiments of biliary organs.* 
 
 Our information concerning the nutritive apparatus of the other 
 orders of acalephse is very limited. In Physalus (Jig. 24) and 
 Porpita (fig. 25), the suckers appended to the body would seem 
 to be the organs by which food is taken into the system ; but, of 
 the internal arrangement of the parts subservient to its digestion 
 and distribution, little has been determined satisfactorily. 
 
 (103.) Extraordinary as must appear the powers which these 
 animals possess of seizing and dissolving other creatures, apparently 
 so disproportioned to their strength, and the delicate tissues which 
 compose their bodies, there are other circumstances of their history 
 equally remarkable, which in the present state of our knowledge 
 are still more inexplicable. If a living medusa be placed in a 
 large vessel of fresh sea-water, it will be found to secrete an abun- 
 dant quantity of glairy matter, which, exuding from the surface 
 of its body, becomes diffused through the element around it so 
 copiously, that it is difficult to conceive whence materials can be 
 derived from which it can be elaborated. Of the origin of this 
 fluid we are ignorant, although certain glandular-looking granules 
 contained in the folds of the pedicle have been looked upon as 
 connected with its production. 
 
 (104.) We are equally at a loss to account for the pro- 
 duction of the irritating secretion in which the power of stinging 
 
 * Delle Chiaje, Memorie per servire alia storia degli Animali senza vertebre del 
 regno di Napoli. 4to. 18231825. 
 
ACALEPHSE. 77 
 
 seems to reside, but it is observed that the tentacuhi seem 
 to be more specially imbued with it than other parts of the 
 body. Perhaps the most remarkable property of the acalephse 
 is their phosphorescence, to which the luminosity of the ocean, 
 an appearance especially beautiful in warm climates, is princi- 
 pally due. We have more than once witnessed this pheno- 
 menon in the Mediterranean, and the contemplation of it is well 
 calculated to impress the mind with a consciousness of the profu- 
 sion of living beings existing around us. The light is not con- 
 stant, but only emitted when agitation of any kind disturbs the 
 microscopic medusse which crowd the surface of the ocean : a pass- 
 ing breeze, as it sweeps over the tranquil bosom of the sea, will 
 call from the waves a flash of brilliancy which may be traced for 
 miles ; the wake of a ship is marked by a long track of splendour ; 
 the oars of your boat are raised dripping with living diamonds ; 
 and, if a little of the water be taken up in the palm of the hand 
 and slightly agitated, luminous points are perceptibly diffused 
 through it, which emanate from innumerable little acalephse scarce- 
 ly perceptible without the assistance of a microscope. All, how- 
 ever, are not equally minute ; the Beroes, in which the cilia would 
 seem to be most vividly phosphorescent, are of considerable size ; 
 the Cestum Veneris, as it glides rapidly along, has the appearance 
 of an undulating riband of flame several feet in length ; and many 
 of the larger Pulmonigrade forms shine with such dazzling bright- 
 ness, that they have been described by navigators as resembling 
 " white-hot shot " visible at some depth beneath the surface. 
 This luminousness is undoubtedly dependent upon some phospho- 
 rescent secretion, but its nature and origin are quite unknown. 
 
 (105.) The principal instruments of sensation in the acalephse are 
 the tentacula and suckers, which, under various forms, are append- 
 ed to different parts of the body, and which are individually capa- 
 ble of contraction and elongation to a considerable extent. In the 
 discophorous forms, these are frequently appended to the margin 
 of the disc (Jig- 27) ; sometimes they are only found around the 
 aperture of the mouth. In Porpita and Physalus they are nu- 
 merous, and hang in clusters from the inferior surface of the body : 
 but the most beautiful tentacular apparatus is that which is met 
 with in the Beroe (Cydippe) pileus; this is represented in Jig. %% ; 
 1, a, a, and consists of two very long and delicate filaments, 
 many times exceeding the length of the body when extended to 
 their full length ; from these arise others of still greater tenuity, 
 
78 ACALEPHJE. 
 
 which are likewise capable of spontaneous elongation. When not 
 in use, these organs are retracted within the body, and lodged in 
 two membranous sheaths visible in the drawing, from which they 
 are protruded at the pleasure of the animal, and, as they expand, 
 gradually uncurl the spiral, secondary tentacula by movements 
 which are singularly graceful and elegant. 
 
 In Medusa aurita there are seen around the circumference of 
 the locomotive disc certain red spots, which Ehrenberg regards as 
 eyes, without however adducing the slightest proof that they 
 possess any claims, derived either from their structure or function, 
 to the name which he is pleased to give them. 
 
 (106.) Most anatomists have failed to detect nervous filaments 
 even in the largest medusae ; nevertheless Ehrenberg is inclined to 
 believe that in some Pulmonigrade species a delicate thread, which 
 encircles the margin of the disc, is to be regarded as nervous, as 
 well as others, which he describes as being visible around the base 
 of the pedicle. In the Beroe (Cydippe) pileus, (Jig. &2) Pro- 
 fessor Grant* regards a double cord which runs around the oral 
 extremity of the alimentary canal, of which an isolated view is 
 given at Jig. %%, 2, as constituting the nervous system ; this ar- 
 rangement, however, has not been confirmed by later observations, 
 and we are inclined to think that the vascular circle which sur- 
 rounds the mouth ( 102) of the Beroeform species has been in 
 this case mistaken for nervous fibre. 
 
 (J 07.) We know little satisfactorily concerning the mode of gene- 
 ration in the acalephse, the opinions of authors upon this subject 
 being in the last degree vague and contradictory. Confining our- 
 selves to the examples which have been selected as best adapted to 
 put the reader in possession of the principal facts known concerning 
 the class under consideration, we find the organs usually regarded 
 as the agents of reproduction assuming very different forms. In 
 Cassiopea Borbonica, the parts which Delle Chiaje describes as 
 ovaria, are four membranous tubes filled with granular matter, and 
 placed above the stomach (Jig. 28, c) ; from each of these a canal 
 issues, which, dividing into several smaller branches, opens by as 
 many minute orifices into four cavities placed around the stomach, 
 into which the sea-water is freely admitted. 
 
 According to Gaede*^ and Eysenhardt,j the ovaria examined 
 
 * Transactions of the Zoological Society, vol. i. 
 
 f Beytrage zur Anatomic und Physiologic der Medusen. Berlin, 1816. 8vo. 
 J Zur Anatomic und Naturgeschichte der Quallen j Rhizostoma Cuvierii. Mem. de 
 1' Academic Leopold des cur. de la Nature. 
 
STERELMINTHA. 
 
 79 
 
 in oilier forms of the Pulmonigrada occupy a similar position, and 
 at certain seasons of Fig.si. 
 
 the year become re- 
 markably distended 
 with ova ; but, from 
 the observations of 
 these writers, it 
 would seem that the 
 young medusae arc 
 hatched in the ova- 
 ria, and afterwards 
 escape in a very per- 
 fect state of deve- 
 lopement. One of 
 the ovaria of Medusa 
 aurita is represented 
 in the annexed figure, 
 (fig. 81, 1,) taken 
 from Ehrenberg's ela- 
 borate plates of the 
 
 anatomy of this animal, in which a, b indicate the extremities of 
 the convoluted organs in which the germs are developed. The 
 gemmules, when mature, are, according to this author, covered with 
 locomotive cilia like those of sponges and polyps (). 
 
 In Physalus the ova would seem to be generated by the 
 long undulating filaments attached to the lower surface of 
 the body, and in Beroe the ovaria are seen to form clusters 
 around the alimentary canal ; but we are ignorant of the mode 
 of their developement, and of the circumstances connected with 
 the exclusion of the young. 
 
 CHAPTER VI. 
 
 STERELMINTHA. 
 
 Parenchymatous Entozoa. (Cuv.) 
 
 The ENTOZOA, as the name implies, are nourished within the 
 bodies of other animals, from the juices of which they derive their 
 sustenance. It may naturally be supposed that living under such 
 
80 
 
 STERELMINTHA. 
 
 circumstances, deprived of all power of locomotion, as is gene- 
 rally a necessary consequence of the localities in which they are 
 found, debarred from the influences of light, and absolutely de- 
 pendent upon the fluids which bathe their bodies for nutriment, 
 the entozoa have little occasion for that elaborate organization 
 needful to animals living in immediate communication with exter- 
 nal objects. 
 
 We find therefore, among these creatures, some whose structure 
 is more simple than that of any other animals, in adaptation to the 
 circumscribed powers of which they are capable. Yet, however ap- 
 parently insignificant some may appear from their diminutive size, 
 they not unfrequently become seriously prejudicial to the animals 
 in which they are found, by the prodigious numbers in which they 
 exist, or from their growth in those organs more especially essential 
 to life, and not a few of them from their dimensions alone some- 
 times prove fatal. The annexed figure (Jig. 32) represents a 
 Ligula developed in the abdominal cavity of a Fig. 32. 
 
 fish. There are probably no races of animals 
 which are not infested with one or more species 
 of these parasites, from the microscopic infu- 
 soria up to man himself, and sometimes several 
 different forms are met with in the same spe- 
 cies, to which they would appear to be peculiar, 
 and even in some cases the entozoa would 
 seem themselves to enclose other species para- 
 sitically dwelling in their own bodies. Neither 
 is their existence confined to any particular 
 parts ; they are met with in the alimentary 
 canal, in the liver, the kidneys, the brain, the 
 arteries, the bronchial passages, the muscles 
 and cellular tissue, and in fact in almost all the 
 organs of the body. 
 
 (109.) It would appear that some of the ordinary secretions of ani- 
 mals are, when in a healthy state, naturally inhabited by innumerable 
 active beings, scarcely equalling in bulk some of the most minute 
 infusoria, and consequently requiring the highest magnifiers to 
 detect even their presence. The best known of these are found in 
 the seminal fluid, and of their size the reader may form some judg- 
 ment by the following calculations upon this subject. Reil esti- 
 mated the length of those found in man at the 3 0*0 o o P ar t of an 
 inch, or at the 25,000th part of a line, and their breadth at the 
 
STERELMINTIIA. 81 
 
 thousandth part of the diameter of a hair ; and Clifton Wintring- 
 ham, in order that our ideas concerning them should be as perfect 
 as possible, recorded his estimate of the weight of one of these 
 animalcules, which he supposed might be about the hundred and 
 forty thousand millionth part of a grain !* Notwithstanding their 
 inconceivable minuteness, however, the Zoosperms have each a 
 definite and symmetrical figure, which is peculiar to their species, 
 so that those taken from different animals may be recognized by 
 their outward form. In quadrupeds they have generally the ap- 
 pearance of minute tadpoles, with flattened globular bodies, termi- 
 nated by long tails of extreme tenuity ; but, in fishes and inverte- 
 brate animals, they are often without tails, sole-shaped, or even 
 globular. Nothing of course is known concerning the internal 
 organization of these living atoms. 
 
 (110.) The Cystiform Sterelmintha, which are generally known 
 by the name of Hydatids, are the simplest in structure ; and with 
 these, therefore, we shall commence our enquiry into the economy 
 of these creatures. The Ccenurus cerebralis, (Jig. 33,) one of 
 
 Fig. 33. 
 
 the most common, is met with in the brains of sheep, and is the 
 cause of a mortal disease but too well known to the farmer ; it is 
 likewise occasionally met with in other ruminating quadrupeds, 
 and, by partially destroying the substance of the brain, soon proves 
 fatal. This entozoon, represented in the figure of its usual size, 
 consists of a delicate transparent bladder, the walls of which, 
 
 * De Blainville, (H. M. D.) Manuel d'Actinologie. Paris, 1834. 8vo. 
 
 G 
 
STERELMINTHA. 
 
 Fig. 34. 
 
 during the life of the creature, are visibly capable of sponta- 
 neous contractions on the application of stimuli. To this bladder, 
 or common body, are appended numerous heads, or rather mouths, 
 which are individually furnished with an apparatus of hooks and 
 suckers, (Jig. 33, 2, a, &,) calculated to fix them to the surrounding 
 tissues, whence they derive nourishment. 
 
 (111.) The Cysticerci, or common hydatids, agree in the main 
 features of their structure with the Ccenurus, but are provided 
 with only one head or oral orifice resembling those of Coenurus 
 (Jig. 34; 2). These 
 animals are found in 
 almost all the viscera of 
 the body ; and not un- 
 frequently, especially in 
 pigs, exist in great num- 
 bers, not only in the 
 liver, which is their most 
 usual seat, but in the 
 cellular texture of the 
 muscles, and even in 
 the eyes themselves. 
 
 The human frame is not 
 
 free from their ravages, 
 
 and, when they abound, 
 
 serious consequences 
 
 frequently result from 
 
 their presence. 
 
 The Cysticercus 
 
 crassicollis is less fre- 
 quently met with than 
 
 the ordinary hydatid (C. tenuicollis). In this animal the head 
 
 is provided with a prehensile apparatus analogous to that found 
 the last described species ; a structure which resembles pre- 
 
 in 
 
 cisely what we shall afterwards find in the Tcenice or tape-worms, 
 with which these creatures are closely related in a zoological point 
 of view. Even in external form they are allied to the cestoid 
 worms, as may be seen in the annexed figure, in which, notwith- 
 standing the vesicular character of the posterior part of the body, 
 the anterior portion is distinctly divided into segments. 
 
 (112.) The mode of reproduction in these entozoa resembles 
 that of the Volvox globator. They propagate by internal gem- 
 
STERKLMINTHA. 83 
 
 mules, which grow from the membranous walls of the sac ; and 
 which, having attained a certain growth, become detached, and are 
 found floating in the glairy fluid contained in the interior of the 
 parent. 
 
 (113.) It is difficult even to conjecture the manner in which 
 these parasites first obtain admission to the localities where they are 
 found, and some zoologists have been content to allow the possi- 
 bility of their being spontaneously generated : but the present 
 state of our knowledge can scarcely sanction the occurrence of 
 such developements. It seems more probable to imagine that 
 the entozoa exist in some other form under other circumstances, 
 but that, when introduced into the body, their eggs may be 
 conveyed by the circulating fluids to a nidus proper for their 
 developement, where their inordinate growth is due to the 
 abundant supply of already animalized food placed within their 
 reach, and the exalted temperature at which they are kept. 
 
 (114.) The Trichina spiralis (fig. 35) is an entozoon hitherto 
 only found in the human body, Fig. 35. 
 
 and, although of recent dis- ii; ;i|lliuilla -M^^ 
 co very, several cases of its oc- | 
 currence are recorded. This 
 minute worm is found in im- 
 mense numbers imbedded in 
 the cellular intervals between 
 the muscular fibres, and in 
 some instances all the vo- 
 luntary muscles seem full of 
 these creatures, exhibiting, 
 when viewed with the naked 
 eye, an appearance imitated 
 in the annexed figure (fig. 35, c.) * On examining the white 
 specks attentively under the microscope, every one of them is 
 seen to be a flask-shaped vesicle, apparently formed of condensed 
 cellular membrane, in which the minute animal is lodged ; and 
 when this outer covering is ruptured, as at (a), the worm escapes. 
 A magnified view of the entozoon is given at (6), coiled up in the 
 position in which it is seen prior to the destruction of the sac 
 which enclosed it. The body seems to be filled with granular 
 
 * For the knowledge which we possess of the anatomy of Trichina, we are princi- 
 pally indebted to the researches of Professor Owen and Dr. Arthur Farre ; though 
 
 it was first discovered by M. Hilton, Vide Zool. Trans, vol. i. 
 
 t-t O 
 
 G <<> 
 
84 
 
 STERELMIXTHA. 
 
 matter, which escapes when the worm is torn asunder (d) ; but 
 whether it possesses a true alimentary tube, is not as yet satis- 
 factorily determined. 
 
 (115.) The Tania., or tape-worms, are among the most inter- 
 esting of the Sterelmintha, whether we consider the great size to 
 which they sometimes attain, or the singular construction of their 
 compound bodies. Several species of these worms infest the human 
 body, and many other forms of them are met with in a variety 
 of animals. They are usually found in the intestinal passages, 
 where, being amply provided with nutritious aliment, they fre- 
 quently grow to enormous dimensions, being not unusually 
 twenty or thirty feet in length, and some have been met with 
 much longer ; it is therefore manifest how prejudicial their pre- 
 sence must prove to the health of the animals in which they 
 reside, and we are little surprised at the emaciation and weak- 
 ness to which they generally give rise. 
 
 The T<znia solium, the species most usually met with in the 
 human subject, at least in our own country, is that which we select 
 for description. The body of this creature consists of a great 
 number of segments united together in a linear series (Jig. 36) : 
 the segments which immediately succeed to the head are very small, 
 and so fragile that it is 
 rarely that this part of 
 the animal is obtained 
 in a perfect state ; they 
 gradually however in- 
 crease in size towards 
 the middle of the body. 
 Each segment of the 
 tape-worm might be re- 
 garded as a distinct ani- 
 mal, for every one of 
 them, with the excep- 
 tion of the smallest, or 
 those in the vicinity of 
 the head, is found to 
 contain a complete ge- 
 nerative apparatus ; yet 
 the alimentary tubes 
 are common to them 
 all, those of each joint 
 
 Fig. 36. 
 
STERELMINTHA. 85 
 
 freely communicating with the nutritive canals of the adjoining 
 segments. The first joint of the Tsenia, which may be called the 
 head, differs materially in structure from all the rest ; it is in fact 
 converted into an apparatus by means of which the entire animal 
 derives its nourishment. This part in the Tsenia solium, when 
 highly magnified, is found to be somewhat of a square shape ; 
 in the centre is seen the mouth, surrounded with a circle of 
 minute spines, so disposed as to secure its retention in a posi- 
 tion favourable for imbibing the chyle in which it is immersed. 
 Around this prominent mouth are placed four suckers, which are 
 no doubt additional provisions for the firm attachment of the head 
 of the worm. In other Tsenise the structure of the oral segment is 
 variously modified : thus in Tania lata the aperture of the mouth 
 has no spines in its vicinity ; in Bothryocephalus there are only 
 two longitudinal sucking discs ; in Floriceps these are replaced 
 by four proboscidiform prolongations, covered with sharp recurved 
 spines, which, being plunged into the coats of the intestine, form 
 effectual and formidable anchors : yet the intention of all these 
 modifications is the same, namely to retain the mouth in a position 
 adapted to ensure an adequate supply of nutritious juices. 
 
 (116.) The alimentary canal, which extends from the mouth, is a 
 double tube, which may be traced through the whole length of the 
 body, without any other perceptible communication with the ex- 
 terior than the oral orifice in the centre of the head : at the com- 
 mencement of every segment, moreover, there is a cross-canal, which 
 communicates with the corresponding canal of the opposite side 
 (fig. 37, a), so as to facilitate a free distribution of the nutrient 
 fluids. In some species a delicate vascular network is perceptible 
 in the parenchyma of the body, which may likewise be connected 
 with the nutritive function. 
 
 (117.) A distinct generative system is found in every segment of 
 these remarkable animals ; and, judging from the number of eggs 
 produced by each, we are at a loss to reconcile the disproportion 
 which exists between the extreme fertility of the Tsenise, and the 
 comparative rareness of their occurrence. The ovaria in which the 
 eggs are produced are of great relative size, occupying the centre 
 of each joint. In the annexed figure (fig. 37), which represents 
 one of the segments of the Tsenia solium highly magnified, the 
 ovigerous organ (&) is seen to consist of a central cavity, from the 
 circumference of which radiate a great number of csecal tubes ; 
 these at certain seasons are filled with granular ova. From 
 
86 
 
 STEEELM1KTHA. 
 
 Fig. 37. 
 
 the central portion of this ramified ovary issues a wide canal or 
 excretory duct (c), which may be traced to a prominent tu- 
 bercle placed on the lateral 
 margin of every segment (e), 
 where it terminates in a mi- 
 nute pore opening externally. 
 This canal, which may be 
 called the oviduct, is seen 
 just before its termination in 
 the external pore to be joined 
 by a delicate tube (d), which 
 appears as a dark line under 
 the microscope, and derives 
 its origin from a small bulb or 
 vesicle, and may be regarded 
 as most probably furnishing a 
 secretion serving to fertilize 
 the ova prior to their expul- 
 sion ; such, at least, is the 
 office generally assigned to it. 
 
 Many thousands of eggs must be produced from such multiplied 
 sources of reproduction ; and yet how are they preserved and 
 replaced in circumstances favourable to their developement ? 
 Fortunately it is rare to meet with more than one of these 
 creatures at the same time, taking up a residence in the same 
 individual ; and, in fact, the species which has been specially the 
 subject of our description is often called, par excellence, " the 
 solitary worm," from this circumstance. Yet what becomes of 
 the reproductive germs furnished in such abundance ? Do they, 
 as was the opinion of Linneus, live in a humbler form in stagnant 
 waters and marshes, until they are casually introduced into the 
 body of some animal, where, being supplied profusely with food 
 and placed in a higher temperature, they attain to an exuberant 
 developement ? Or are the germs thus numerous in proportion to 
 the little likelihood of even a few of them finding admission to a 
 proper nidus ? To these questions we can only reply by conjec- 
 tures ; and, interesting as the subject is, few are more entirely 
 involved in mystery. 
 
 (118.) In the Fluke, Distoma (Fasciola, Linn.) hepaticum, we 
 have an entozoon of more complex and perfect structure ; one of 
 those forms, continually met with, which make the transition from 
 
STERELMINTHA. 
 
 87 
 
 Fig. 38. 
 
 one class of animals to another so insensible, that the naturalist hesi- 
 tates with which to associate it. In the Distoma, in fact, notwith- 
 standing its intimate relationship with the Tsenioid Sterelmintha, 
 the first rudiments of nervous filaments are apparent, and we find 
 its whole organization approximating the nematoneurose type rather 
 than strictly exhibiting the simple structure common to the Acrita. 
 
 The Distoma is commonly found in the liver and biliary ducts 
 of sheep, and other ruminants, deriving nourishment from the 
 fluids in which it is immersed. The body of the creature, 
 which is not quite an inch in length, is flattened, and resembles 
 in some degree a minute sole or flat-fish. At its anterior extre- 
 mity is a circular sucker or disc of attachment, by which it fastens 
 itself to the walls of the cavity in which it dwells, as well as by 
 means of a second sucker of similar form, placed upon the ventral 
 surface of the body. In the annexed diagram (Jig. 38) the 
 posterior sucker has been removed, 
 in order more distinctly to exhibit 
 the internal structure of the animal. 
 The name which this entozoon bears 
 seems to have been given to it from 
 a supposition that it possessed two 
 mouths, one in each sucker ; whereas 
 the anterior or terminal disc (a) only is 
 perforated, the other being merely an 
 instrument of adhesion. The ali- 
 mentary canal (b) takes its origin from 
 the mouth as a single tube, but soon 
 divides into two large branches, from 
 which ramifications arise which are 
 dispersed through the body, each ter- 
 minating in a blind clavate extre- 
 mity. These tubes, from being 
 
 generally filled with dark bilious matter, are readily traced, even 
 without preparation ; or they may be injected with mercury intro- 
 duced through the mouth. 
 
 Through the walls of the ventral surface of the body, two 
 nervous filaments (c) are discoverable, crossing over the root of 
 the anterior sucker or acetabulum, and, gradually diverging, may 
 be observed to run in a serpentine course towards the caudal 
 extremity, where they are lost : it would even seem that on either 
 side of the oesophagus there is a very slight ganglion, from which 
 
88 STERELMINTHA. 
 
 other nervous filaments arise to supply the suckers, and the 
 anterior part of the body. 
 
 The organs of generation in the fluke are very voluminous, 
 occupying with the ramifications of the alimentary tubes the 
 whole of the interior of the animal : in the diagram they are 
 not represented on the right side, in order that the distribution 
 of the intestine may be better seen ; and on the left side the ali- 
 mentary vessels are omitted, to allow the general arrangement of 
 the sexual system to be more clearly intelligible. 
 
 These animals would seem to be completely hermaphrodite, 
 not only possessing distinct ovigerous and seminiferous canals, 
 which open separately at the surface of the body, but even 
 provided with external organs of impregnation, so that most 
 probably the co-operation of two individuals is requisite for mutual 
 fecundity. 
 
 To commence with the female generative system, we find the 
 ovaria (h) occupying the whole circumference of the body. 
 When distended with ova, the ovigerous organ is of a yellow 
 colour ; and, when attentively examined under the microscope, is 
 seen to be made up of delicate branches of vesicles united by 
 minute filaments, so as to have a racemose appearance. From 
 these clusters of ova arise the oviferous canals, which, uniting on 
 each side of the body into two principal trunks, discharge their 
 contents into the large oviducts (g). The oviducts terminate in 
 a capacious receptacle (e), usually called the uterus ; and from 
 this a slender and convoluted tube leads to the external orifice, 
 into which a hair (d) has been inserted. On each side of the 
 uterus we find a large ramified organ, made up of csecal tubes, 
 (/,) which opens into the uterine cavity, and no doubt furnishes 
 some accessory secretion needful for the completion of the ova. 
 
 The male apparatus occupies the centre of the body. The 
 testes (A-), in which the spermatic fluid is secreted, consist of 
 convoluted vessels of small calibre, arranged in close circular 
 folds, and so inextricably involved, that it is difficult to get a 
 clear idea of their arrangement ; but towards the middle of the 
 mesian line they become more parallel, and terminate in two 
 larger trunks (t), (one of which has been removed in the figure,) 
 which are enclosed and hidden in the seminal vessels. These 
 great canals, which run side by side in a longitudinal direction, 
 become gradually much attenuated (/), and terminate in the root 
 or capsule of the penis (m). The external male organ (n) is 
 
STEBELM1NTHA. 
 
 89 
 
 placed a little anterior to the orifice which leads to the female 
 parts ; it is a short spiral filament, distinctly traversed by a canal, 
 and perforate at the extremity, so as indubitably to perform the 
 office of an instrument of intromission. 
 
 (119.) The PLANARI.-E, although they do not inhabit the interior 
 of other animals, are so nearly allied in every part of their organi- 
 zation with, the Flukes, (Distoma,) that their history cannot be 
 more appropriately given than in this place. The Planarise are 
 common in ponds and other stagnant waters ; they are generally 
 found creeping upon the stems of plants, or amongst the healthy 
 confervse which abound in such situations, and wage perpetual 
 war with a variety of animals inhabiting the same localities. The 
 body of one of these minute creatures appears to be entirely 
 gelatinous, without any trace of muscular fibre ; * yet its motions 
 are exceedingly active, and it glides along the plane upon which 
 it moves with a rapid and equable pace, of which the observer 
 would scarcely expect so simple a being to be capable ; or, by 
 means of two terminal suckers, progresses in the manner of a 
 leech. No agglomeration of nervous fibre has hitherto been sa- 
 tisfactorily detected in the Planarise ; nevertheless, many species 
 possess two red specks 
 upon the anterior part 
 of the body, which, as 
 in other cases, have 
 been unhesitatingly 
 pronounced to be eyes, 
 although their claim 
 to such an appellation 
 is not only unsubstan- 
 tiated by any proofs 
 derivable from their 
 structure, but com- 
 pletely negatived by 
 experiments, which go 
 to prove that in the 
 pursuit of prey no 
 power of detecting 
 the proximity of their 
 food by the exercise of 
 sight is possessed by 
 any of them. 
 
 * Duges, Annales des Sciences Nat. 
 
 Fig. 39. 
 
90 STERELMINTHA. 
 
 The phenomena which have been observed connected with the 
 multiplication of the Planarise by division are analogous to those 
 which we have witnessed in other acrite animals ; for it has been 
 proved, that if an individual be cut to pieces, every portion continues 
 to live and feel, from whatever part of the body it may be taken ; 
 and, what is not a little remarkable, each piece, even if it be the 
 end of the tail, as soon as the first moment of pain and irrita- 
 tion has passed, begins to move in the same direction as that in 
 which the entire animal was advancing, as if the body was actuated 
 throughout by the same impulse, and, moreover, every division, 
 even if it is not more than the eighth or tenth part of the crea- 
 ture, will become complete and perfect in all its organs. 
 
 The mouth, in a few species of Planarise, is placed at the an- 
 terior extremity of the body, but generally it is found to occupy the 
 middle part of the ventral surface. Its structure is quite peculiar, 
 and admirably adapted to the exigencies of the creature : it con- 
 sists of a wide, trumpet-shaped proboscis, (fig- 39, 3 and 4,) which 
 can be protruded at pleasure, and applied to the surface of such 
 larvae or red-blooded worms as may come within reach, so as to 
 suck from them the juices which they contain ; or, if the prey be 
 small, animalcules and minute Crustacea are seized by it and con- 
 veyed into the digestive canals. The internal organs appropriated 
 to nutrition resemble in all essential points those of the Distoma ; 
 they consist of a multitude of blind tubes, hollowed out in the 
 parenchyma of the body, which, when distended with coloured 
 substances, are sufficiently distinct. The principal trunk, (fig* 39, 
 1,) which communicates with the proboscidiform mouth, soon di- 
 vides into three primary branches ; one of which runs along the 
 median line of the body towards the anterior extremity, whilst the 
 other two are directed backwards towards the tail. From these 
 central canals secondary ones are given off, which permeate all parts 
 of the body. There is no anal aperture, so that of course the 
 residue of digestion is expelled through the mouth ; but the nature 
 of the process by which defecation is thus effected is curious : 
 the Planaria, slightly bending its body, is seen to pump up through 
 its proboscis a quantity of water, with which all the branches of the 
 alimentary ramifications are filled ; the creature then contracts, 
 and, forcibly ejecting the contained fluid, expels with it all effete 
 or useless matter. 
 
 Besides the arborescent tubes in which digestion is accomplished, 
 a rudimentary vascular system is distinctly visible, by which the 
 
STERELMINTHA. 91 
 
 nutritive juices are dispersed through the system. This consists 
 of a delicate network of vessels, arising from three large trunks, 
 one placed in the centre of the dorsal aspect, and the other two 
 running along the sides of the animal (Jig. 39, 2). 
 
 (120.) The Planarise are perfectly androgenous, as each indi- 
 vidual possesses a distinct male and female generative system ; but 
 they are not apparently self-impregnating, as the co-operation of two 
 individuals has been found needful for the mutual fertilization of 
 their ova. In every one of these animals two distinct apertures 
 are seen to exist upon the ventral surface, at a little distance be- 
 hind the root of the proboscis ; the anterior of which gives issue to 
 the male organ, while the posterior leads to the oviferous or fe- 
 male parts. 
 
 In Planaria tremellaris, the penis, which during copulation is 
 protruded from the anterior orifice, (Jig. 89,* 6,) is a white, con- 
 tractile body, enclosed, when in a retracted state, in a small oval 
 pouch; it is perforated by a minute canal, and receives near its root 
 two flexuous tubes, which gradually decrease in size as they diverge 
 from each other, until they can no longer be traced. These are 
 the seminiferous vessels (Jig. 39, 5, a). The posterior genital 
 orifice, which leads to the female organs, communicates with a small 
 pouch, or uterus, as it might be termed (Jig. 39, 5, b) : into this 
 open two lateral oviducts, which run on each side of the male ap- 
 paratus and of the proboscis ; these are very transparent, and only 
 recognisable under certain circumstances by the ova which they 
 contain. In Planaria lactea the oviduct opens into the uterine 
 cavity by a single tube, which, passing backwards, divides into two 
 equal branches ; and both of these, again subdividing, ramify 
 extensively among the cseca derived from the stomach. We 
 likewise find in this species two accessory vesicles, which pour 
 their secretions into the terminal sac. 
 
 (121.) The Diplozoon paradoxum is another form, which, 
 though it cannot strictly speaking be classed with the entozoa, is 
 so nearly allied to Distoma in its internal structure, that its 
 anatomy will be most conveniently examined in this place.']" 
 
 This remarkable animal, as its name imports, is literally pos- 
 sessed of two bodies, precisely resembling each other in every 
 particular, and united by a narrow communicating band, so as to 
 form but one animal, the nutrient canals of one division commu- 
 
 * This figure represents two Planariae as they appear in the act of sexual inter- 
 course, t Nordmann. 
 
STERELMINTHA. 
 
 40. 
 
 nicating most freely with those of the opposite half. We might 
 be led to imagine such an extraordinary arrangement as the result 
 of some monstrous connexion of two separate creatures, did not 
 observation show that the conformation is perfectly natural and 
 common to all the species. 
 
 Each half of the body of the Diplozoon possesses a mouth and 
 digestive apparatus, 
 a distinct set of vas- 
 cular channels, in 
 which a circulation of 
 the nutritive juices 
 is evident, and more- 
 over contains a com- 
 plete and indepen- 
 dent generative sys- 
 tem ; but in the 
 annexed diagram, 
 (fig. 40,) for the 
 sake of clearness, 
 these are only par- 
 tially shown, the ali- 
 mentary organs alone 
 being seen upon the 
 left portion, whilst 
 in the opposite the 
 organs of reproduc- 
 tion are displayed : 
 the reader, there- 
 fore, will imagine similar parts to exist on both sides of the 
 body. 
 
 These animals, which are of very small size, being not more 
 than two or three lines in length, are found attached to the gills 
 of the bream, (Cyprinus brama,) from which they absorb nutri- 
 ment. They are fixed in this position by two sucking acetabula, 
 resembling those of Distoma, (6, &,) which are seen on each side 
 of the mouths, and also by four oval membranous appendages 
 (m, m) attached to the opposite extremities of the body, upon 
 which likewise suckers are placed, so that at all four extremities 
 the creature is provided with instruments of adhesion. 
 
 (122.) The mouths (a, a) are two orifices of a somewhat semi- 
 circular form, and at the lower margin of each two teeth are per- 
 
STERELMINTHA. 93 
 
 ccptible, which are either merely provisions for fixing the mouth 
 firmly when in the act of imbibing food, or else they may act as 
 lancets, by scarifying the surface from which nourishment is de- 
 rived. From the outer orifice we may trace a canal which extends a 
 little way into the body, and becomes slightly dilated ; into the 
 bottom of this cavity a small tongue-shaped organ (d) is seen to 
 project, having its surface perforated by a number of exceed- 
 ingly minute holes, which indeed might be looked upon as the 
 real mouths destined to imbibe the nutritious juices, and convey 
 them to the stomach. The stomach, (c, c, c, c, c,) which has 
 been partly removed on the right side of the figure, is a wide 
 canal, extending through the whole length of both divisions of 
 the body, and passing by a capacious cross-branch from one half 
 to the other, so that the nutriment taken in by either mouth will 
 pass freely to the opposite side. From these central channels 
 great numbers of blind canals issue, resembling those of Distoma 
 and Planaria, which ramify extensively; there is, however, no 
 anal orifice or outlet for excrementitious matter. 
 
 (123.) But, besides the ramifications of the alimentary canal, 
 other vessels are discernible, running through the parenchyma of 
 the Diplozoon, where nutritious fluids circulate, and which corre- 
 spond to the vascular arrangement met with in Planaria. Of 
 these the main trunks only are represented in the figure; the 
 branches given off from them, which are very numerous, being for 
 the sake of distinctness entirely omitted. Each half of the body 
 contains four of these vessels, (/, /,) which run from one extremity 
 to the other. In these a fluid is observed to move, running in 
 the directions indicated by the course of the arrows in the diagram ; 
 namely, in two of them from the head toward the posterior end of 
 the body, and in the other two in an opposite direction. This ru- 
 dimentary circulation must be for the purpose of more perfectly 
 diffusing through the system the fluids which result from the 
 process of digestion, and which are probably taken up by imme- 
 diate osculation, between the terminations of the branches from 
 the stomach, and the origins of the vascular system. 
 
 Upon the opposite side of the figure is given a diagram of 
 the arrangement of the generative apparatus insulated from sur- 
 rounding parts, so as to give the reader a distinct view of the 
 different organs composing it. 
 
 (124.) As in the two last described species, we find both oviger- 
 ous and impregnating organs constituting complete hermaphrodism, 
 
94 STERELMINTHA. 
 
 and this not on one side only of the creature, but on both ; all 
 the parts being precisely similar in the two lateral halves. 
 
 The ovarium is not distinguishable as a distinct viscus, the 
 gems or granular-looking ova (e) being apparently diffused through 
 the parenchyma of the body around the alimentary channels. 
 From this situation the ova are taken up by two long oviducts, 
 which, turning upon themselves near the mouth, are seen to per- 
 form a long course through the anterior part of the body, until at 
 (/) they unite, and immediately expand into a capacious intestini- 
 form cavity, or uterus, (g), from which the eggs escape when 
 mature through a lateral aperture (A). 
 
 The male or seminiferous apparatus is quite unconnected with 
 the female organs, and its structure is easily distinguishable. The 
 testicle (i) is a small pear-shaped vesicle, from which a duct may 
 be traced, which ends in a long cirrus (Ar), represented in the 
 figure as coiled up in a spiral form ; but when unrolled it is of 
 considerable length, and analogous both in structure and office 
 to the male organ of Distoma. 
 
 (125.) We now arrive at the most perfect type of structure found 
 in the Parenchymatous Entozoa, which leads us by a gradual trans- 
 ition to the more highly organized forms which are possessed of 
 a distinct nervous apparatus. The reader will observe that in 
 all the preceding genera the alimentary canal has consisted en- 
 tirely of nutritive canals excavated in the substance of the body, 
 and unprovided with any outlet distinct from the mouth adapted 
 to the discharge of the residue of digestion. From the nature of 
 their food, indeed, we might be led to infer the reason of such a 
 structure ; for living, as these creatures do, upon juices already 
 completely animalized and prepared for the purposes of nutrition, 
 the assimilation of the materials provided for them constitutes 
 nearly the entire process of alimentation. The same con- 
 formity to one type has been also visible in the nature of the 
 reproductive system ; all the species which we have as yet ex- 
 amined, except perhaps the Planarise, having possessed indepen- 
 dent powers of propagation, either containing no visible organs 
 appropriated to the developement of the germs which they 
 produce, or possessing both an ovigerous and impregnating 
 apparatus combined in the same body. The Entozoa acantho- 
 cephala, of which we are now about to speak, will be found still 
 to exhibit a digestive system analogous in structure to that which 
 exists universally among the Sterelmintha, but in the organs 
 
8TEEELMINTHA. 
 
 95 
 
 of reproduction we find a mani- 
 fest analogy with higher classes in- 
 dicated in the complete separation 
 of the sexes, which we now for 
 the first time meet with, the ovig- 
 erous and impregnating organs be- 
 ing found in separate and distinct 
 individuals. 
 
 The Echinori/nchus gigas is the 
 species which has undergone the most 
 complete investigation,* and will 
 serve as an example of the usual 
 structure of the Acanthocephala. 
 
 (126.) The Echinorynchi inhabit 
 the intestinal canal of various ani- 
 mals, to the walls of which they fasten 
 themselves by a singular contrivance. 
 In the animal under consideration, 
 which is found in the intestines of 
 the hog, the head (a, fig. 41 ; 1, 2, 
 3) is represented by a retractile pro- 
 boscis, armed externally with four 
 circlets of sharp recurved hooks, 
 which, when plunged into the coats 
 of the intestine, serve as secure an- 
 chors by which the creature retains 
 itself in a position favourable to the 
 absorption of food. In Jig. 41, 1, 
 2, this aculeated proboscis is repre- 
 sented of its natural size relative to 
 the body of the entozoon, as it ap- 
 pears when fully protruded ; but, 
 when not in use, the spinous part 
 is retracted, and concealed by the 
 mechanism, of which an enlarged 
 view is given at Jig. 3. When 
 extended, the position of the organ 
 is indicated by the dotted lines ; 
 but in the drawing the whole or- 
 gan is represented as drawn inwards 
 
 * Cloquet, Anatomie des Vers intestinaux. 
 
 Fig. 41, 
 
 \rv 
 
 R 
 
 Paris, 1824. 
 
96 STEKELMIXTHA. 
 
 and lodged in a depression formed by the inversion of the in- 
 tegument, so as completely to hide it within the body. This 
 inversion is produced by the contraction of two muscular bands, 
 (d, e,)* which arise from the inner walls of the body, and are 
 inserted into the root of the proboscis around the oesophagus : 
 two other muscles, (6, 6,) antagonists to the former, arise near 
 the spines themselves ; and these, aided by the contractions of 
 the walls of the body, are the agents by which the protrusion 
 of the head is effected. Although the teeth or spines, which 
 render this organ so formidable, are merely epidermic appendages, 
 they are found to be rendered erect or depressed at the will 
 of the creature ; and it is therefore probable that, minute as they 
 are, they have muscular fibres connected with them serving 
 for their independent motions : these spines, moreover, are not 
 always confined to the head ; but in many intestinal worms are 
 found on various parts of the body, wherever their office as 
 instruments of attachment is by circumstances rendered needful. 
 
 (127.) The digestive system of the Echinorynchus is extremely 
 simple. The mouth is a minute pore placed at the extremity of the 
 proboscis, which communicates with two slender canals, (f,f,) at 
 first of great tenuity, but towards the middle of the body assum- 
 ing something of a sacculated appearance. Towards the tail 
 these vessels gradually diminish in size until they are no longer 
 distinguishable ; but they have not been seen to give off any 
 branches, or to communicate with each other. 
 
 Near the origin of these nutrient tubes are two large caeca, nearly 
 an inch in length, called lemnisci, (fig. 41, 1 and 2, d, d,) which 
 are probably connected with the digestive function. 
 
 (128.) The female Echinorynchus is, as is usually the case in 
 Dioecious Entozoa, considerably larger than the male, as may be 
 seen in the figure. In the former (fig- 41, 1) the ovary (c) is a 
 capacious organ occupying the centre of the body, and extending 
 along its entire length. When minutely examined, it is found to 
 consist of two compartments or distinct sacs, one occupying the 
 dorsal, the other the ventral aspect ; the two tubes being separated 
 by a septum. The dorsal ovary commences near the tail, at g, by 
 a cul-de-sac ; and, enlarging as it runs forward, terminates near the 
 point c, by uniting with the ventral portion. The anterior part 
 of the canal (b) is common to both divisions of the ovary ; and 
 from this the ventral tube runs backwards to the posterior end of 
 
 * These muscles are seen of their natural size in fig. 1 at e, e. 
 
STERELMINTHA. 
 
 97 
 
 the body, where it ends in a narrow duct, which opens externally 
 at h. It would seem therefore that the last-mentioned opening 
 is the only excretory passage from the ovarium ; the connection 
 apparent in the figure, between the common sac (b) and the root 
 of the proboscis, being merely of a ligamentous character. 
 
 (129.) The generative system of the male Echinorynchus is re- 
 presented in fig. 41, 2. The organs which secrete the fecundating 
 fluid (y, g) are two cylindrical vesicles attached at one extremity 
 by minute filaments to the walls of the body : from each of these 
 arises a duct (A), and the two, uniting at t, form a common excretory 
 canal. This canal speedily dilates into a number of sacculated 
 receptacles in which the secretion of the testes accumulates, and 
 from them a duct leads to the root of the penis (m). The penis 
 or organ of intromission, when extended, protrudes through the 
 aperture p, placed at the anal extremity of the body ; but when 
 retracted it is folded up, and lodged in a conical sheath (o). The 
 protrusion and retraction of this part of the male apparatus is 
 effected by a very simple mechanism : two muscles, (/, /,) arising 
 from the inner walls of the body, are inserted into the base of the 
 sheath, (m,) and serve to draw it inwards ; and two others, (w, w,) 
 inserted at the same point, but arising from the posterior ex- 
 tremity of the animal, by their contraction force outwards the 
 intromittent organ, an arrangement precisely corresponding with 
 that by which the movements of the proboscis are provided for. 
 
 (130.) In Distoma perlatum 
 (fig. 42), we have another example 
 of organization intermediate be- 
 tween that which is most usual 
 among the STERELMINTHA, and 
 what we shall afterwards meet 
 with in the more perfect entozoa. 
 The animal in question resembles 
 most closely in its outward form 
 the liver-fluke of which we have 
 already spoken, and possesses a 
 similar suctorial apparatus. In 
 the annexed figure (fig. 42), the 
 oral disc only is seen, the ventral 
 sucker having been removed for 
 the sake of displaying the interior 
 of the animal, as in the diagram of 
 
98 STERELMINTHA. 
 
 Distoma hepaticum already given (Jig. 38). On comparing the two 
 we are at once struck with the superior concentration of all the 
 systems of the body, visible in Distoma perlatum. The ali- 
 mentary canal (Jig. 42, ) commences, as in the former example, 
 by an aperture situated in the oral sucker ; but, instead of ramifying 
 through the parenchyma of the body, is contained in an abdo- 
 minal cavity, in which it floats in common with the other viscera. 
 The oesophagus (a) is a simple flexuous tube terminating 
 abruptly in two lateral and more capacious intestines, (b, b,) 
 terminated by blind dilated extremities, which form the digestive 
 apparatus. 
 
 Two vascular canals (d, d) are seen on each side of the body, 
 which ramify extensively, but of these the principal trunks only 
 are represented. 
 
 (131.) The Distoma perlatum is allied to the STERELMINTHA in 
 the hermaphrodism of its generative organs, and the parts subservient 
 to reproduction will be found analogous in structure and arrange- 
 ment to what we observed to be the usual conformation in that 
 order. The ova would seem to be produced in the parenchyma 
 of the body, as in the fluke ; from this situation they are con- 
 veyed by two canals (e) into a capacious receptacle (/), from 
 which arises the tortuous oviduct (g), represented in the en- 
 graving distended with eggs. Near its termination the oviduct 
 is joined by two secerning vesicles having their interior appa- 
 rently of a villous texture. These vesicles are regarded as 
 being the testes, and are supposed to pour out an impregnat- 
 ing secretion, by which the ova are rendered fertile as they 
 pass out of the body. The external aperture through which 
 the eggs are discharged is placed upon a prominent tubercle 
 (t), which, if mutual impregnation is essential in these animals, 
 may indeed perform the office of an intromittent instrument. 
 
CffiLELMINTHA. 99 
 
 CHAPTER VII. 
 NEMATONEURA. 
 
 CffiLELMINTHA* (Owen). 
 
 Vers Intestinaux cavitaires (Cuv.) ; Nematoidea (Rudolplii). 
 
 The entozoa which belong to the nematoneurose division 
 of the animal kingdom have long been separated in zoological clas- 
 sification from those which have been described in the last chapter, 
 on account of the superiority of their internal organization. In 
 the STERELMINTHA, or parenchymatous forms, we have seen the 
 digestive process carried on in canals simply excavated in the sub- 
 stance of the body, without any anal outlet for the discharge of 
 superfluous matter; the nervous system either perfectly diffused 
 through the tissues, or but obscurely visible even in the most per- 
 fect species, and the muscular tissue, as a necessary consequence, 
 scarcely aggregated into distinct fibres : the sexes, moreover, except 
 in the Echinorynchi, which form the transition from the more im- 
 perfect to the more elevated type of structure, have been invariably 
 combined in the same individual. But we now arrive at a point 
 in the scale of animal developement at which the nervous fibre be- 
 comes for the first time distinctly recognisable, forming a more 
 perfect means of intercourse, if we may be allowed the expression, 
 between the different parts of the body ; the muscular contractions, 
 being thus more intimately associated, assume far greater energy, 
 and muscular fasciculi are distinguishable, arranged in precise and 
 definite directions ; the alimentary canal is visible as a separate 
 and distinct tube, enclosed with other viscera in an abdominal 
 cavity; and the ovigerous and impregnating sexual organs are 
 found to exist in different individuals. Still, however, we find 
 no nervous centres developed, or the ganglia which exist are so 
 extremely minute and rudimentary that in no case can we suspect 
 the existence of organs appropriated to the higher senses ; the 
 sensations of all the tribes composing this division of the animal 
 world are therefore apparently limited to the generally diffused 
 
 * xo7*.o, hollow 'fafuvs-ivfaf, a worm. 
 
 H 
 
100 
 
 CCELELMINTHA. 
 
 Fig. 43. 
 
 sense of touch and its modifications, to which the perception of 
 taste and odours must be referred. 
 
 (133.) The Linguatula teenioides (fig. 43, 1) is the first example 
 which we shall select to illustrate the structure of the Ccelel- 
 mintha. This ento- 
 zoon, which is gene- 
 rally found to inhabit 
 the frontal sinus of 
 quadrupeds, is about 
 three inches in length, 
 and as many lines in 
 breadth, at the broadest 
 part of its body. In 
 external form it has 
 some resemblance to 
 the tape- worm, being 
 divided into slightly im- 
 bricated segments; but 
 in its internal structure 
 it is widely different, 
 especially as relates to 
 the arrangement of 
 the generative organs, 
 which, instead of being 
 multiplied until they 
 
 are nearly as numerous as the segments of the body, ( 117,) 
 form but one continuous system. 
 
 The Linguatula is invested externally with a delicate cuticle, 
 easily separable by maceration, so as to peel off as represented in 
 the figure.* 
 
 (134.) Around the mouth (fig. 43,1, a), are several oval pits or 
 cavities containing as many sharp, recurved hooks by which the an- 
 terior extremity of the body is securely attached to the walls of the 
 frontal sinus, and the mouth retained in a position adapted to 
 secure an adequate supply of nutritive material. 
 
 The mouth itself is a simple aperture, from which a short and 
 narrow ossophagus leads to a dilated cylindrical stomachal cavity, 
 (fig. 43, 2, a,) that forms a somewhat capacious receptacle for 
 food ; to this succeeds a straight intestinal tube (/}> which tra- 
 
 Owen, Transact. Zool. Soc. vol. i. 
 
C(ELELMINTHA. 101 
 
 verses the whole length of the body, and terminates by an anal 
 aperture at the extremity of the tail. 
 
 (135.) The nervous system of the Linguatula is distinctly de- 
 veloped. It consists of a central ganglion, situated beneath the oeso- 
 phagus^ from which eight pairs of nervous filaments proceed in dif- 
 ferent directions : of these the greater number are distributed to the 
 parts immediately around the mouth, but the posterior pair (o, o), 
 which is by far the most considerable in size, runs backwards along the 
 ventral aspect of the body, taking first a wavy or serpentine course, 
 but afterwards becoming straight ; these nerves may be traced for 
 some distance until they are gradually lost in the integuments, to 
 which they are distributed. 
 
 It will be seen that in such a condition of the nervous apparatus, 
 we have a type of structure decidedly superior to what has been 
 observed in any of the parenchymptous entozoa, and adapted to 
 the situation in which the Linguatula is generally found ; a situa- 
 tion which allows of considerable change of position, and of some 
 selection as regards the food which it imbibes. The muscular 
 movements, therefore, being more perfectly associated by the de- 
 velopement of nervous filaments, exhibit a greater energy of action ; 
 and although the nervous matter is not as yet sufficiently concen- 
 trated to allow of the possession of organs appropriated to the 
 higher senses, there is provision made by the developement of the 
 rudimentary sub-oesophageal ganglion for more delicate sensibility 
 in the neighbourhood of the mouth, adequate, no doubt, to the 
 perception and choice of such aliment as may be best adapted to 
 nutrition. 
 
 (136.) The female Linguatula^ as is generally the case among 
 the dioecious entozoa, is considerably larger than the male. The 
 generative organs exhibit a peculiar arrangement, and form nu- 
 merous convolutions in the body, which are visible through the 
 semi-transparent integument (Jig. 43, 1). 
 
 The ovary (Jig. 43, 2, g) is a narrow, minutely granulated 
 body, running along the two anterior thirds of the dorsal aspect of 
 the body. It terminates about half an inch from the head in 
 two capillary tubes (c c), which pass on each side of the stomach 
 and nervous cords, embracing them as in a ring. These two tubes 
 unite behind the mouth into a common canal or oviduct, through 
 which the eggs escape ; but, before their junction, each receives a 
 duct derived from a glandular sacculus (e, e), destined no doubt to 
 furnish some secretion essential to the completion of the ova. 
 
102 CGELELMINTHA. 
 
 The oviduct formed by the junction of the oviferous canals which 
 embrace the oesophagus, is very narrow at its commencement, but 
 after running backwards for some distance it dilates a little, and, 
 becoming much convoluted, it winds around the alimentary tube 
 in numerous and extremely complex gyrations (d). Towards the 
 lower third of the body, the coils become less numerous and more 
 distant from each other, and are seen to contain brown ova in scat- 
 tered masses, until at length the oviduct assumes a course parallel 
 to that of the intestine (e), and accompanies it to the anus, in the 
 vicinity of which it terminates. 
 
 The ova are of a firm resisting texture, and do not lose any 
 of their form or contour by drying ; hence they may preserve their 
 vitality for a long period under very different circumstances, and 
 be ready to assume the actions of developement when deposited in 
 a fit situation. 
 
 (137.) In the male Linguatula, the structure of the generative 
 apparatus is very simple. Two long convoluted tubes, which float 
 loosely in the abdominal cavity, secrete the seminal or impreg- 
 nating fluid ; and these tubes, which may be called the testes, ter- 
 minate by forming a single canal or vas deferens, leading to the 
 external organs appropriated to sexual union, which are two fili- 
 form appendages found in the neighbourhood of the head, through 
 which the fecundating secretion is expelled. 
 
 (138.) The only other example which will be necessary to illustrate 
 the structure of the CCELELMINTHA, is an evident approximation to 
 the annulose type of animal organization. The Ascaris lumbri- 
 coides indeed, as its name imports, so strongly resembles some of 
 the annelida in its external configuration, that the zoologist who 
 should confine his attention to outward form alone, might be 
 tempted to imagine the affinities which unite them much stronger 
 than a comparison of their anatomical relations would sanction. 
 This entozoon is found in the intestines of many animals, and is 
 endowed with some considerable capability of locomotion adapted 
 to the circumstances under which it lives ; for in this case the 
 worm, instead of being closely imprisoned in a circumscribed space, 
 may traverse the entire length of the intestines in search of a con- 
 venient locality and suitable food. 
 
 (139.) In accordance with such an enlarged sphere of existence, 
 we observe muscular fibre distinctly recognisable in the tissue which 
 composes the walls of the body, not as yet indeed exhibiting 
 the complete characteristics of muscle as it is found in higher 
 
CffiLELMINTHA. 103 
 
 animals, but arranged in bundles of contractile filaments, run- 
 ning in determinate directions, and thus capable of acting 
 with greater energy and effect in producing a variety of move- 
 ments. 
 
 In this rudimentary state, the muscular fibre does riot possess 
 the density and firmness which it acquires when completely de- 
 veloped ; it has, when seen under the microscope, a soft gelatinous 
 appearance, apparently resulting from a deficiency of fibrin in its 
 composition ; the transverse striae, usually regarded as characteristic 
 of the muscular tissue of the more perfect animals, are not yet 
 distinguishable, and the individual threads are short, passing over 
 a very small space before they terminate. On examining the 
 arrangement of these fasciculi, they are seen to be disposed in 
 two layers, in each of which they assume a different course ; thus 
 in the outer layer they are principally arranged in a longitudinal 
 direction, while the inner stratum of fibres is placed transversely, 
 affecting a spiral course, so as to encircle the viscera. From this 
 simple structure various movements result ; by the action of 
 the longitudinal fasciculi the whole body is shortened, by the 
 contractions of the spiral layer an opposite effect is produced, 
 or by the exertion of circumscribed portions of the muscular in- 
 tegument lateral flexions of the body are effected in any given 
 direction. These motions in the living worm are vigorous and 
 easily excited by stimuli ; they are therefore abundantly sufficient 
 for the purpose of progression in such situations as those in which 
 the creature lives, and enable it to change its place in the intes- 
 tines with facility. 
 
 (140.) The nervous system of the Ascaris is strictly conformable 
 to the nematoid type. Around the mouth or anterior part of the 
 oesophagus, there appears to be a delicate nervous ring, probably 
 specially connected with the association of such movements of 
 the oral extremity as are essential to the imbibition of nourish- 
 ment. From this oral ring proceed two long nervous filaments, 
 (fig. 44, e, e,) one of which runs backwards along the dorsal 
 aspect of the body, while the other occupies a similar position 
 upon the ventral surface. The last-named filament is described 
 by Cloquet as dividing in the female Ascaris, at the point where 
 the termination of the organs of generation issue from the body 
 (fig. 44, w), so as to enclose the termination of the vagina in a 
 nervous circle. 
 
 (141.) The digestive apparatus in this order of intestinal worms is 
 
104 
 
 CCELELMINTHA. 
 
 very simple. In Ascaris lumbricoides, 
 (Jig. 44, a,) when highly magnified, 
 is seen to be surrounded by three 
 minute rounded tubercles ; into each 
 of these, fasciculi, derived from the 
 longitudinal muscles of the body, 
 are inserted in such a manner as to 
 cause the separation of the tuber- 
 cles, and consequent opening of the 
 mouth, which is again closed by a 
 sphincter muscle provided for the 
 purpose. To the mouth succeeds a 
 short 03sophagus, (Jig. 44, 1 & 2, &,) 
 which is separated by a constriction 
 from the rest of the alimentary 
 canal, and would seem, from the 
 muscularity of its walls, to be an 
 agent employed in sucking in the 
 liquid food upon which the crea- 
 ture lives. The true digestive ca- 
 vity (Jig. 44, 1 & 2, c, c) is a sim- 
 ple and extremely delicate tube, 
 which arises from, the oesophagus, 
 and without presenting any appear- 
 ance indicative of separation into 
 stomach and intestine, gradually en- 
 larges as it proceeds backwards, 
 until it terminates at the hinder 
 extremity of the body by a narrow 
 aperture (Jig. 44, 1 & 2, d.) 
 
 It would seem that the food of 
 these entozoa being already ani- 
 malized by having undergone a pre- 
 vious digestion, requires little further 
 preparation ; and we are little sur- 
 prised at finding in the generality of 
 the Coelelmintha no accessory glan- 
 dular apparatus appended to the di- 
 gestive canals for the purpose Lof 
 furnishing auxiliary secretions. In 
 two species only have tributary 
 
 the aperture of the mouth, 
 Fig. 44. 
 
 f 
 
 k 1/r 
 
 
 K 
 
 I 1 
 
 
CGELELMINTHA. 105 
 
 secreting organs been detected ; in one example, Gnathostoma 
 aculeatum, (Owen,) found in the stomach of the tiger, and which 
 is remarkable as possessing a pair of rudimentary jaws, four slen- 
 der elongated caeca are appended to the mouth, into which they 
 pour a fluid analogous, no doubt, to that of the salivary glands.* 
 In a species of ascaris, found in the stomach of the dugong, Mr. 
 Owen likewise discovered a csecal appendage opening into the ali- 
 mentary tube at some distance from the mouth, and which, without 
 much stretch of imagination, may be regarded as the first and sim- 
 plest rudiment of a biliary system.')' 
 
 In further prosecuting our inquiries concerning the process 
 of nutrition in these entozoa, we must now speak of a peculiar 
 structure first noticed by Cloquet,j and apparently intimately 
 connected with the assimilation of nutriment. Projecting from 
 the inner surface of the abdominal cavity, especially in the dorsal 
 and ventral regions, there is a great number of gelatinous, spongy 
 processes (appendices nourriciers) , which, although they have no 
 apparent central cavity, would seem to be appended to vascular 
 canals seen upon the lateral aspects of the body : it is probable, 
 therefore, that their office is to absorb the nutritive juices, which 
 exude through the delicate walls of the intestine, and convey them 
 into the circulatory apparatus ; or they may be reservoirs for nou- 
 rishment, analogous to the adipose tissue of higher animals. 
 
 (142.) In the Ccelelmintha the sexes are separate, and the genera- 
 tive organs, both of the male and female, exhibit great simplicity 
 of structure. In the female Ascaris, the aperture communicating 
 with the ovigerous apparatus is placed upon the ventral aspect of 
 the body, a little anterior to the middle of the worm (Jig. 44, 1, ra). 
 This opening leads into a wide canal (/), usually called the uterus ; 
 and from the last-mentioned organ arise two long and undulating 
 tubes, which, diminishing in size, run towards the posterio ex- 
 tremity, where they become completely filiform, and turning back 
 upon themselves are wound in innumerable tortuous convolutions 
 around the posterior portion of the alimentary canal, until the 
 termination of each becomes nearly imperceptible from its extreme 
 tenuity. In these tubes, which when unravelled are upwards of 
 four feet in length, the ova are formed in great numbers, and 
 are found to advance in maturity as they approach the dilated 
 
 * Owen, Proceedings of the Zoological Society, Nov. 1836. 
 
 t Preparation, No. 429 A. Mus. Coll. Surg. Phys. Catalogue, p. 121. 
 
 t Cloquet, Anatomic des Vers Intestinaux ; Paris, 1824. 
 
106 CCELELMINTHA. 
 
 terminal receptacle common to both oviducts (/), from which they 
 are ultimately expelled. 
 
 (143.) The male Ascaris lumbricoides is considerably smaller than 
 the female, and the. structure of its generative system remarkably 
 similar to what has been just described in the other sex. The testis 
 or gland, which secretes the impregnating fluid, is a single, delicate, 
 tubular, filament (fig. 44, 2,jf), which when unravelled is found 
 to be nearly three feet in length, and is seen winding in close and 
 almost inextricable folds around the middle and hinder parts of 
 the intestine. The termination of this tube (g) may be traced to 
 the tail or anal extremity of the worm, where it ends in a fila- 
 mentary retractile penis (z), in which the microscope exhibits a 
 minute receptacle wherein the seminal fluid accumulates prepara- 
 tory to its expulsion. During copulation, the penis of the male 
 is introduced into the vulva of the female, by which it is firmly 
 embraced, and the different positions which the external parts 
 occupy in the two sexes is evidently an arrangement favourable 
 to their intercourse. 
 
 (144.) There are few more striking exemplifications of that gra- 
 dual transition by which we are led from one type of structure to 
 another, than we meet with in tracing the progressive separation 
 of the sexes as we advance from the monoecious to the dioecious 
 families of the entozoa. Leaving those forms of hermaphroditism 
 in which the male and female parts are both found in each division 
 of the body, we find in Syngamus trachealis an animal " in which 
 the male is organically blended by its caudal extremity with the 
 female, immediately anterior to the slit-shaped aperture of the 
 vulva, which is situated as usual near the anterior third of the 
 body. By this union a kind of hermaphroditism is produced ; 
 but the male apparatus is furnished with its own peculiar nutrient 
 system, and an individual is constituted distinct in every respect, 
 save in its terminal confluence with the body of the female. This 
 condition of animal life, which was conceived by Hunter as within 
 the circle of physiological possibilities, (see Animal (Economy, 
 p. 46,) has hitherto been only exemplified in this single species 
 of entozoon, the discovery and true nature of which is due to 
 the sagacity and patient research of Dr. Charles Theodore Von 
 Siebold."* 
 
 * Cyclop, of Anat. and Phys. ; article Entozoa, by Professor Owen. Vide Siebold, 
 in Weigmann's Archives, 1835. 
 
BRYOZOA. 
 
 107 
 
 CHAPTER VIII. 
 BRYOZOA* (Ehrenberg) ; CJLIOBRACHIATE POLYPI (Farre). 
 
 (145.) It is only within the last few years that microscopical re- 
 searches have revealed to naturalists the real structure of a series of 
 animals originally confounded with the simpler polyps, with which, 
 as far as external form is concerned, they are indeed intimately 
 related. The observations of Milne Edwards,*f* Audouin, Ehren- 
 berg,^: and Thompson, gradually led the way to more correct 
 and precise ideas concerning the more highly organized genera ; 
 and Dr. Arthur Farre, || by a series of investigations, followed 
 up with exemplary industry and perseverance, seems to have com- 
 pleted our knowledge of the anatomical details of these creatures, 
 in a manner which leaves few points of their economy unknown. 
 
 We shall select an in- 
 dividual, named by Dr. 
 Farre JBowerbankia den- 
 sa 9 as an illustration of 
 the general structure of 
 the BRYOZOA, partly from 
 the complete manner in 
 which its organization has 
 been developed in the me- 
 moir alluded to, and partly 
 because we have had fre- 
 quent opportunities of ve- 
 rifying the accuracy of the 
 descriptions, and the ex- 
 treme fidelity of the draw- 
 ings by which it is illus- 
 trated. 
 
 The animal Bowerban- 
 kia, which is only about 
 a line in length, inhabits a 
 
 Fig. 45. 
 
 sea-moss Zuov, an animal. 
 t Annales des Sciences Naturelles, for Sept. 1828, and July 1836. 
 $ Symbolae Physicae. 
 
 Zoological Researches and Illustrations, Memoir v. ; Cork, 1830. 
 || Philosoph. Trans. Tart 2, for 1837. 
 
108 BRYOZOA. 
 
 delicate and perfectly transparent tube of horny texture, which 
 arises from a repent stem, common to a great many individuals, 
 found aggregated in small patches upon the surface of Flustra 
 foliacea, upon which they are apparently parasitic. 
 
 The mouth is surrounded by ten long and slender tentacula, 
 (Jig. 45,) which, during the expanded state of the animal, are 
 kept quite straight and motionless, as represented in the drawing. 
 Each tentacle is provided upon its outer aspect with a series 
 of stiff and immoveable spines, probably serving to keep off any 
 foreign bodies, which, by their proximity, might interfere with the 
 ciliary movements immediately to be described. 
 
 Besides the stiff spines, the tentacula are covered with an im- 
 mense number of vibrating cilia, which at the will of the animal are 
 thrown into most rapid movement, so as to produce strong and 
 continuous currents in the surrounding fluid, by which particles 
 floating in the neighbourhood are hurried along with great velocity. 
 From the direction of the streams produced by the cilia, namely, 
 towards the mouth, we at once perceive the utility and beauty 
 of the contrivance which compensates to a great extent for the 
 fixed condition of the Bryozoon ; animalcules floating in the vi- 
 cinity no sooner come within the influence of the currents so pro- 
 duced, than they are forced towards the mouth, which is placed 
 at the roots of the tentacula, and, being at once seized, are imme- 
 diately swallowed. 
 
 The tentacula themselves, notwithstanding their immobility dur- 
 ing the process of watching for prey, are highly irritable, and sensi- 
 ble of the slightest contact. No sooner does an animalcule im- 
 pinge upon any part of their surface, than the tentacle touched 
 bends with extraordinary quickness, as if endeavouring to strike it 
 towards the mouth ; and, if the object be sufficiently large to touch 
 several at the same moment, all the tentacula simultaneously co- 
 operate in seizing and retaining it. 
 
 (146.) The existence of the cilia upon the tentacula would seem to 
 be characteristic of the BRYOZOA, and is invariably accompanied, as 
 far as our information extends at present, with a digestive apparatus 
 of far more complex structure than what we have seen in the un- 
 ciliated polyps, for in the class before us, besides the stomach, we 
 find a .distinct intestinal tube and anal outlet. In the specimen 
 under consideration the organization of the alimentary organs is 
 even rendered more elaborate than is usual in the class, from the 
 addition of a gizzard or cavity in which the food is mechanically 
 
BRYOZOA. 109 
 
 bruised before its introduction into the proper stomach. The 
 mouth is placed in the centre of the space enclosed by the tenta- 
 cula ; it appears to be a simple orifice, incapable of much distension, 
 through which the particles of food brought by the ciliary action 
 pass into a capacious oesophagus, (Jig- 45, a, 1, 2,) which, gradually 
 contracting its dimensions, ends in a globular muscular organ to 
 which the name of gizzard has been applied. (8) The walls of this 
 viscus are composed of fibres which radiate from two dark points 
 seen in the figure, and its lining membrane is covered with a great 
 number of hard horny teeth, so disposed as to represent, under the 
 microscope, a tesselated pavement. The contractions of the giz- 
 zard are vigorous ; and, from the structure of its interior, its office 
 cannot be doubtful. 
 
 To the gizzard succeeds a stomach (j^^.45, #, 4,) which is studded 
 with brown specks apparently of a glandular nature, and probably 
 representing a biliary apparatus. The intestine leaves the stomach 
 at its upper portion, close to the gizzard (5) ; and, running parallel 
 with the oesophagus towards the tentacula (6), terminates at the side 
 of the mouth (7), in such a position that excrementitious matter is at 
 once whirled away by the ciliary currents. The whole intestinal 
 apparatus floats freely in a visceral cavity, which contains a transpa- 
 rent fluid, and encloses distinct muscular fasciculi, which we shall 
 speak of in another place. 
 
 The process of digestion in this minute, yet highly organized being, 
 is well described by Dr. Farre in the memoir above mentioned. 
 
 " The little animal, when in vigour, is seen projecting from its cell 
 with the arms extended, and the cilia in full operation ; the upper 
 part of the body being frequently turned from side to side over the 
 edge of the cell, the extremity of which, from its peculiar flexibility, 
 moves along with it. The particles carried to the mouth in the 
 vortex produced by the action of the cilia, after remaining a little 
 while in the pharynx, are swallowed by a vigorous contraction of 
 its parietes, and carried rapidly down the oesophagus and through 
 the cardia to the gizzard, which expands to receive them. Here 
 they are submitted to a sort of crushing operation, the parietes of 
 the organ contracting firmly upon them, and the two dark bodies 
 being brought into opposition. Their residence, however, in this 
 cavity, is only momentary, and they are immediately propelled into 
 the true stomach below, where they become mixed up with its 
 contents, which, during digestion, are always of a dark, rich, brown 
 colour, being tinged with the secretion of its parietal follicles." 
 
110 BRYOZOA. 
 
 The food appears to be retained for a considerable time in the 
 stomach, and may be frequently seen to be regurgitated into the 
 gizzard, whence, after having been again submitted to its opera- 
 tions, it is returned to the stomach. Here it is rolled about by the 
 contraction of its parieties, and at its upper part is frequently sub- 
 mitted to a rotating motion. This rotation of particles is chiefly 
 near the pyloric orifice ; and a mass may be occasionally seen pro- 
 jecting through the pylorus into the intestine, and rotating rapidly 
 in the direction of the axis of the orifice. In an animal having a 
 similar form of pylorus to this, but in which the parts were more 
 transparent, I could distinctly see the cilia by which this rotation 
 is effected surrounding the orifice." 
 
 The granular matter, after rotating for some time at the pylorus, 
 (a provision for preventing its too rapid escape from the stomach,) 
 passes into the intestine, where it accumulates in little pellets, 
 which are rapidly pushed by the contraction of the intestine to- 
 wards the anal orifice, through which they are expelled from the body. 
 
 The tube or cell inhabited by this bryozoon is of exquisite struc- 
 ture, and the mechanism concerned in the protrusion and retraction 
 of the animal of great simplicity and beauty. 
 
 The inferior two-thirds of the cell in the species under considera- 
 tion is hard and corneous, but perfectly transparent : the upper 
 third, on the contrary, is flexible, and so constructed as to form a 
 very complete operculum by which the entrance is guarded. The 
 flexible part consists of two portions, the lower half being a simple 
 continuation of the rest of the cell, while the upper is composed of 
 a circle of delicate bristle-shaped processes or setse, which are ar- 
 ranged parallel to each other around the mouth of the cell, and are 
 prevented from separating beyond a certain distance by a membrane 
 of excessive tenuity which connects them ; this membrane is evi- 
 dently analogous to the infundibular termination of the cells of 
 polyps already described. 
 
 When the bryozoon retires into its abode, the setse and soft ter- 
 mination of the cell are gradually folded inwards in the manner 
 exhibited in the annexed figures (Jig. 46), which represent the 
 various stages of the process. The esophagus surmounted by its 
 tentacula descends first, whilst the integument of the upper part of 
 the body begins to be inverted at the point where it has its insertion 
 around the base of the tentacles (c). As the descent of the tenta- 
 cula proceeds, the inversion of this membrane continues ; and when 
 the extremities of the arms have reached the level of the extremi- 
 
Ill 
 
 4 321 
 
 ties of the setse, it is seen to form a complete sheath around them. 
 The animal being thus retracted, the next part of the process is to 
 draw in the upper portion of the cell after it. The setse are now 
 brought together in a bundle (jig. 46, Q, ), and are gradually 
 drawn inwards, inverting around them the rest of the flexible por- 
 tion of the cell until they form a close fasciculus (fig. 46, 3 & 4, a), 
 occupying the axis of the opening of the tube, and forming a com- 
 plete protection against intrusion from without. 
 
 (147.) The muscular system exhibits the earliest appearance of 
 muscular fibre. The filaments are unconnected by cellular tissue, 
 and have a watery transparency and smooth surface, neither do 
 they exhibit cross markings or a linear arrangement of globules, 
 even when examined under the highest powers of the microscope. 
 
 The muscles may be divided into two sets, one serving for the 
 retraction of the alimentary apparatus, the other acting upon the 
 setse around the mouth of the cell, and serving for the inversion of 
 its flexible portion. The bundles of muscular fibre which act upon 
 the alimentary canal are two in number, and arise from near the 
 bottom of the cell : one of these is inserted into the stomach 
 (fig. 45, a, 8) ; the other passes upwards along the side of the 
 oesophagus (fig. 45, a, 9), to be attached in the vicinity of the 
 tentacula : the latter fasciculus is evidently the great agent in 
 drawing the animal into its retreat, and in doing so it throws the 
 alimentary canal into close sigmoid folds. 
 
 The muscles which close the operculum are arranged in six 
 distinct fasciculi ; they arise from the inner surface of the upper 
 hard part of the cell, and act upon the upper flexible portion of the 
 tube and upon the setse (fig. 46, d, d). 
 
 The mode in which the protrusion of the tentacula is effected is 
 
BRYOZOA. 
 
 not so easily explained ; it would seem that the lining membrane of 
 the shell is furnished with circular muscular fibres, so disposed as by 
 their action to compress the fluid contained in the visceral cavity, and 
 thus tend to elongate the body. Dr. Farre, however, believes the 
 alimentary canal itself to be the great agent in effecting this object, 
 and he conceives it to possess a power of straightening itself from the 
 flexures into which it is thrown during the retracted state of the 
 animal. 
 
 (148.) The FLUSTILE and ESCHARS are intimately allied to 
 Bowerbankia in all the details of their structure, as we are 
 assured by the researches of Dr. Milne Edwards concerning these 
 singularly aggregated forms of Bryozoa.* 
 
 The cells of the Flustrte and Eschara are disposed side by 
 side upon the same plane, so as to form a common skeleton of a 
 coriaceous or horny texture. The individual cells, which are ex- 
 tremely minute, vary in shape in different species ; and the orifice 
 of each is generally defended by projecting spines, or sometimes 
 by a moveable operculuin, or lid, which closes the orifice in the 
 contracted state of the animal. The extension of one of these 
 skeletons is effected by the regular addition of new cells around 
 the circumference of the Flustra, those of the margin being, of 
 course, the most recent; and the latter are not unfrequently found 
 inhabited by healthy animals, whilst in the older or central ones 
 the original occupants have perished. 
 
 The facts which have been observed relative to the formation of 
 these cells possess a high degree of interest, and materially support 
 the views already given concerning the formation of the tubes of 
 zoophytes in general ; proving that the calcareous matter to which 
 their hardness is owing is not a mere exudation from the surface of 
 the animal, but is deposited in an organized tegumentary membrane, 
 from which it can be removed with facility by means of extremely 
 dilute muriatic acid. When so treated, a brisk effervescence is pro- 
 duced, the cells become flexible and are easily separated from each 
 other, but they are not altered in form, and evidently consist of a soft 
 and thick membrane, forming a sac containing the digestive organs of 
 the creature. In this state the opening of the cell is no longer de- 
 fined as it was before, but the membranous cell appears continuous 
 with the tentacular sheath. We see, therefore, that in these crea- 
 tures the cell is an integrant part of the animal itself, not a mere 
 
 * Recherches Anatomiques, Physiologiques, et Zoologiques sur les Eschares. Ann. 
 des Sciences Nat. for 1836. 
 
BRYOZOA. H3 
 
 calcareous crust moulded upon the surface of the body, being a 
 portion of the tegumentary membrane, which, by the molecular 
 deposit of earthy matter in its tissue, ossifies like the cartilage of 
 higher animals without ceasing to be the seat of nutritive move- 
 ment. It is evident, likewise, that what is called the body of the 
 Bryozoon constitutes, in fact, but a small portion of it, principally 
 consisting of the digestive apparatus. 
 
 As to the operculum destined to close the entrance of the 
 tegumentary cell, it is merely a lip-like fold of the skin, the 
 marginal portion of which acquires a horny consistence ; while, at 
 the point where it is continuous with the general envelope, it re- 
 mains sufficiently soft and flexible to obey the action of the mus- 
 cles inserted into it. 
 
 (149.) The tegumentary sac, deprived of its carbonate of lime, 
 seems to be formed of a tomentous membrane, covered, especially 
 upon its outer side, with a multitude of cylindrical filaments disposed 
 perpendicularly to its surface, and very closely crowded together. 
 It is in the interstices left by these fibres that the calcareous 
 matter appears to be deposited ; for, if a transverse section be 
 examined with a microscope, the external wall is seen not to be 
 made up of superposed layers, but of cylinders or irregular prisms 
 arranged perpendicularly to the axis of the body. 
 
 But the above are not the only arguments adduced by Milne 
 Edwards in confirmation of our view of the mode in which these 
 skeletons are held in vital connection with the animal. On ex- 
 amining the cells at different ages, it is found that they undergo 
 material changes of form. 
 
 This examination is easily made, since in many species the 
 young spring from the sides of those first formed, and do not sepa- 
 rate from their parents ; each skeleton, therefore, presents a long 
 series of generations linked to each other, and in each portion of the 
 series the relative ages of the individuals composing it are indicated 
 by the position which they occupy. It is sufficient, therefore, to 
 compare the cells situated at the base, those of the middle portion, 
 those of the young branches, and those placed at the very extremi- 
 ties of the latter. When examined in this manner, it is seen that not 
 only does the general configuration of the cells change with age, but 
 also that these changes are principally produced upon the external 
 surface. For instance, in the young cells of Eschara cervicornis, 
 the subject of these observations, the walls of which are of a stony 
 hardness, the external surface is much inflated, so that the cells are 
 
114 BRYOZOA. 
 
 very distinct, and the borders of their apertures prominent ; but by 
 the progress of age their appearance changes, their free surface rises 
 so as to extend beyond the level of the borders of the cell, and 
 defaces the deep impressions which marked their respective limits. 
 It results that the cells cease to be distinct, and the skeleton pre- 
 sents the appearance of a stony mass in which the apertures of the 
 cells only are visible. 
 
 It appears evident, therefore, that there is vitality in the sub- 
 stance composing these stony walls ; and the facts above narrated 
 appear only explicable by supposing a movement of nutrition like 
 that which is continually going on in bone. 
 
 (150.) The anatomy of these Bryozoa differs slightly from that 
 of Bowerbankia. The crown of ciliated tentacula is inserted into 
 the extremity of a kind of proboscis, which is itself enclosed in a 
 cylindrical retractile sheath. From the margin of the opening of 
 the cell arises a membrane equalling in length the contracted ten- 
 tacles, and serving to enclose them when the animal retires into its 
 abode. These appendages, thus retracted, are not bent upon them- 
 selves, but perfectly straight and united into a fasciculus, the 
 length of which is nevertheless much less than that of the same 
 organs when expanded. 
 
 By the opposite extremity to that fixed to the margin of the 
 opening of the cell, the tentacular sheath unites with a tolerably 
 capacious tube, the walls of which are exceedingly soft and deli- 
 cate ; and near the point of their union we may perceive a 
 fasciculus of fibres running downwards to be inserted upon the 
 lateral walls of the cell : these fibres appear to be striated trans- 
 versely, and are evidently muscular ; their use cannot be doubted : 
 when the animal wishes to expand itself, the membranous sheath 
 above alluded to becomes rolled outwards, everting itself like the 
 finger of a glove as the tentacles advance. The muscular fasciculi 
 are thus placed between the everted sheath and the alimentary 
 canal, and by their contraction they must necessarily retract the 
 whole within the cell. 
 
 The first portion of the alimentary tube is inflated, and much 
 wider than the rest ; it forms a kind of chamber, in which the 
 water set in motion by the vibration of the cilia upon the tentacles 
 appears to circulate freely. The walls of this chamber are ex- 
 tremely delicate ; the soft membrane forming them is puckered, and 
 appears traversed by many longitudinal canals united by minute 
 transverse vessels ; this appearance, however, may be deceptive. 
 
BRYOZOA. 
 
 115 
 
 Beneath the first enlargement, the digestive apparatus becomes 
 narrower, but immediately expands again, and offers at this 
 point a certain number of filiform appendages, which appear to 
 be free and floating in the interior of the cell. To the second 
 cavity succeeds a narrow canal, opening into a third dilatation, 
 generally of a spherical form. From the last-named viscus 
 issues a kind of intestine, which soon bends upon itself and be- 
 comes attached to an organ of a soft and membranous texture, 
 having the appearance of a caecum, and which seems to be con- 
 tinuous superiorly with the digestive tube ; the latter continues 
 its progress towards the upper part of the cell, and ultimately ter- 
 minates by a distinct anal aperture upon the upper aspect of the 
 tentacular sheath. 
 
 The operculum which closes the cell in Flustra and Eschara is 
 moved by two muscular fasciculi inserted into the internal face of 
 this valve by the intermedium of two filaments analogous to ten- 
 dons : by their inferior extremity, these muscles are attached to 
 the walls of the cell ; and when, by its own elasticity, the operculum 
 is turned back, and the mouth of the cell thus opened, they, by 
 their contraction, can close it like a door. 
 
 (151.) A very singular form of Bryozoon is met with in fresh 
 water, of which the Cristatella Mucedo* is an example that has 
 undergone minute investigation. 
 
 The Cristatella (Jig. 47, 3) consists of a common body or enve- 
 lope (d), which is Fig. 47. 
 membranous, and 
 slightly cordiform ; 
 its surface is tubercu- 
 lated,and it is incapa- 
 ble of con traction. In 
 this outer covering 
 several individuals 
 are contained, but, al- 
 though produced from 
 one another, they are 
 only aggregated, be- 
 ing lodged in distinct tubular cells. The body of each animal 
 appears to consist of a digestive canal, constricted once or twice 
 
 * M. Turpin, Etude microscopique de la Cristatella Mucedo, espece de polype 
 d'eau douce. Ann. des Sciences Nat. for 1837. Also, another memoir upon the same 
 subject, by M. P. Gervais. Ibid. 
 
116 BRYOZOA. 
 
 in its course, and terminated by an anal orifice. When these 
 creatures are extended, the upper part of the body protrudes from 
 the cell ; the tentacular apparatus being supported on a kind of 
 neck, whereon the mouth (a) is easily seen, and near it the anus. 
 
 On each side of the mouth the body divides into two arms, 
 which, when spread out, resemble a horse-shoe, being flattened and 
 blunt ; and upon the arms are arranged about a hundred slender, 
 transparent, and retractile tentacles, disposed on each side and 
 upon the summit, like the barbs of a feather ; and all covered with 
 an infinite number of cilia, whose action produces currents directed 
 towards the mouth, hurrying in that direction organized particles 
 contained in the water. 
 
 The three individuals that thus inhabit the same general cover- 
 ing are produced at two distinct generations ; the two lateral 
 being the offspring of the central one, derived from it by a pro- 
 cess of gemmation, but, when complete, they are evidently quite se- 
 parate from and independent of their parent. 
 
 (152.) From what is known concerning the propagation of the 
 Bryozoa, it would appear that their reproduction is effected in 
 several different ways. 
 
 The most ordinary is by the developement of gemmae or buds, 
 that sprout from the parent stem in the branched species, or, as 
 in the Flustra and Eschara, are derived from the sides of con- 
 tiguous cells. 
 
 A. second mode of increase is by the production of ciliated 
 gemmules capable of locomotion. These gemmules have been 
 attentively examined by Dr. Farre in the paper above alluded to, 
 and the nature of the ciliary action by which they are moved most 
 satisfactorily investigated, as we shall elsewhere have occasion to 
 notice more particularly ; but the organs wherein the reproductive 
 gemmules are developed are as yet undescribed. 
 
 The Cristatella seems to be developed in an ovum, provided 
 with a shell of extremely singular construction. In fig. 47, 2, 
 the investment of one of these extraordinary eggs is represented 
 prior to the exclusion of the embryo Bryozoon, its natural size 
 being shown in the same figure (1): the external surface is 
 seen to be covered with numerous long processes arising perpen- 
 dicularly from it, and each terminates in a minute double hook, 
 adapted apparently to fix the egg upon marine plants at the sur- 
 face of the water : but how these hooks become developed is still a 
 mystery ; it would seem impossible that an ovum so formidably 
 
HOTIFERA. 117 
 
 armed could be expelled from the parent animal in the usual 
 way ; we must therefore suppose that the spines grow, or become 
 hardened at least, subsequently to the birth of the ovum. Since the 
 discovery of this microscopic egg in a recent state, similar bodies 
 have been detected in great numbers in a fossil condition im- 
 bedded in flint ; a fact which, in conjunction with what has been 
 already stated ( 74) concerning the occurrence of the shells of 
 loricated infusoria in the same situation, tends materially to show 
 that masses of flint are agglomerations of siliceous particles inclos- 
 ing immense quantities of the debris of organized bodies.* 
 
 That the bryozoa are very far superior to the polyps in 
 all the details of their structure, will now be sufficiently mani- 
 fest. The ciliated tentacula, although selected as affording the 
 most convenient character for the guidance of the Zoologist 
 from the constancy of their coexistence with elaborately or- 
 ganized internal viscera, are probably only organs of secondary 
 importance in a physiological point of view ; for the analogies 
 between this class and that which will form the subject of our 
 next chapter are not to be mistaken, and the transition from one 
 to the other is so gradual, that where observation has failed in com- 
 pletely developing the anatomy of the animals we have been 
 considering, the facts which have been ascertained concerning the 
 Rotiferous Animalcules, will go far towards supplying the defi- 
 ciency. 
 
 CHAPTER IX. 
 
 fRoTiFERA (Ehrenberg). 
 
 
 
 (153.) The class of animals that next presents itself for our 
 consideration was, until very recently, confounded with the chaotic 
 assemblage of minute creatures to which the name of Infusorial 
 Animalcules was indiscriminately applied; but the information at 
 present in our possession concerning their internal structure and 
 general economy, while it exhibits, in a striking manner, the assi- 
 duity of modern observers, and the perfection of our means of ex- 
 ploring microscopic subjects, enables us satisfactorily to define the 
 limits of this interesting group of beings, and assign to them the 
 elevated rank in the scale of zoological classification to which, from 
 their superior organization, they are entitled. 
 
 * Tuipin, Ann. des Sciences Nat. 1837. t Rota, a wheel; fcro, / bear. 
 
118 
 
 ROTIFERA. 
 
 The character whence the class obtains its name is derived from 
 the peculiar organs placed upon the anterior part of the body, 
 which are subservient to locomotion, and assist in the prehension 
 of food ; these consist of circlets of cilia variously disposed in the 
 neighbourhood of the mouth, and having, when in action, the ap- 
 pearance of wheels spinning round with great rapidity, so as to pro- 
 duce strong currents in the surrounding water. Yet, notwithstand- 
 ing this peculiar structure of the locomotive apparatus, the ROTI- 
 FERA present very marked relations with the BRYOZOA, described 
 in the last chapter ; and the conversion of the ciliated tentacula of 
 the latter into the rotatory organs of the present class is effected 
 by several intermediate forms, which would seem to indicate a 
 closer alliance between the two than, from an examination of the 
 more typical genera of each, we should be inclined to suspect. 
 
 (J54.) The annexed engraving of the Stephanoceros Eichornii* 
 
 Fig. 48. 
 
 (jig- 48) exhibits an 
 animal that would seem 
 to be one of the connect- 
 ing links by which this 
 transition is accomplish- 
 ed ; the transparent cell, 
 and ciliated tentacula 
 around the mouth, would 
 indicate this creature to 
 be a BRYOZOON ; but the 
 tentacula are no longer 
 the stiff and slender arms 
 which we have seen in 
 Bowerbankia, but are vi- 
 sibly stunted and thick- 
 ened at their base, thus 
 approximating in character 
 the cilia-bearing lobes of 
 a Rotifer ; while the inter- 
 nal organs, the pharynx, 
 gizzard, and stomach, in 
 this animal conform ex- 
 actly to the type of structure common to the Rotifera properly so 
 called. 
 
 (155.) The body of one of the wheel animalcules is enclosed in 
 
 * Ehrenberg. 
 
ROTIFERA. 
 
 119 
 
 a delicate transparent envelope of considerable consistency, often 
 terminating at the upper extremity in wavy indentations or tooth- 
 like processes, as in Brachionus urceolaris* (Jig. 49, c, c ). This 
 harder integument is essentially analogous to the cell of a Bryo- 
 zoon, but in this case is so constructed as to allow the animals to 
 move at large in the element they inhabit, instead of being per- 
 manently fixed to the same locality. Continuous with the free 
 margin of the shell is a delicate membrane connecting it with the 
 bases of the cilia-bearing lobes around the mouth, so as to allow 
 those organs, when not in use, to be retracted within the cell by a 
 mechanism resembling that provided in Bowerbankia for the re- 
 traction of the tentacula. 
 
 To the posterior extremity of the body is generally appended a 
 pair of forceps composed of two moveable pieces (Jigs. 50 and 
 51), used as anchors or instruments of prehension; and by 
 means of these the little creatures fix themselves to the confervse 
 or aquatic plants amongst which they are usually found. In 
 Brachionus urceolaris the prehensile forceps (fig. 49, o p,) is at- 
 tached to the extremity of 
 a long flexible tail in which 
 the muscular fibres des- 
 tined for its motions are 
 distinctly visible. 
 
 (156.) The cilia, whose 
 action produces the ap- 
 pearance of wheels turn- 
 ing upon the anterior part 
 of the body, are variously 
 disposed, and from their 
 arrangement Ehrenberg 
 has derived the characters 
 whereon he bases the di- 
 vision of the class into 
 orders. The peculiar 
 movements excited by the 
 vibration of these organs, 
 was long a puzzle to the 
 earlier microscopic observers, who, imagining them to be really 
 wheels turning round with great velocity, were utterly unable to 
 
 * The engravings of the Rotifera are all copied from Ehrenberg's papers. Abhand- 
 lungen der Koniglichen Akademie der Wissenchaften zu Berlin, for 1833. 
 
120 ROTIFERA. 
 
 conceive what could be the nature of the connection between such 
 appendages and the body of the animal. The apparent rotation 
 has, however, been long proved to be an optical delusion, and to 
 be produced by the progressive undulations of the cilia placed in 
 the neighbourhood of the mouth. 
 
 (157.) With respect to the agents employed in producing the 
 ciliary movement in the rotifera, we are as much in ignorance as we 
 are concerning the cause of the same phenomenon in the polygastrica. 
 Ehrenberg describes the cilia as arising from a series of lobes as re- 
 presented in Notommata clavulata (Jig. 51 a); these he regards as 
 being muscular, and capable of producing by their contractions the 
 rapid vibrations of the fibrillse attached to them. We confess, 
 however, that such lobes, even was their existence constant, seem 
 very clumsy instruments for effecting the purpose assigned to them, 
 and it is not easy to conceive how the rapid and consecutive undu- 
 lations to which the appearance of rotation is due can be produced 
 by organs of this description. 
 
 The observations of Dr. Arthur Farre* concerning the ciliary 
 movements visible upon the gemnmles of some of the Bryozoa appear 
 best calculated to throw light upon the nature of the action of these 
 wonderful appendages, and to explain the cause of the apparent 
 rotatory motion of the so-called wheels of the rotifera. The very 
 accurate observer alluded to remarks that under high powers, the 
 cilia have the appearance of moving in waves, in the production of 
 each of which from a dozen to twenty cilia are concerned, the 
 highest point of each wave being formed by a cilium extended to 
 its full length, and the lowest point between every two waves by 
 one folded down completely upon itself, the intervening space be- 
 ing completed by others in every degree of extension, so as to pre- 
 sent something of the outline of a cone. As the persistence of 
 each cilium in any one of these positions is of the shortest possible 
 duration, and each takes up in regular succession the action of the 
 adjoining one, that cilium which, by being completely folded up, 
 formed the lowest point between any two waves, in its turn by its 
 complete extension forms the highest point of a wave ; and thus, 
 while the cilia are alternately bending and unbending themselves, 
 each in regular succession after the other, the waves only tra- 
 vel onward, whilst the cilia never change their position in this di- 
 rection, having, in fact, no lateral motion. 
 
 The whole of the ciliary movements are so evidently under the 
 control of the animal as to leave not the slightest doubt in the 
 
 * Phil. Trans, for 1837. 
 
ROTIFERA. 
 
 mind of the observer upon this point. The whole fringe of cilia 
 may be instantly set in motion, and as instantaneously stopped, or 
 their action regulated to every degree of rapidity. Sometimes one 
 or two only of the waves are seen continuing their action, whilst 
 the remainder are at rest ; or isolated cilia may be observed slowly 
 bending and unbending themselves, while the others are quiescent. 
 It is by the constant succession of these movements that the eye is 
 seduced to follow the waves which they seem to produce, and thus 
 the apparent rotation of the wheels is easily understood. 
 
 (158.) Such being,as we conceive, the nature of the ciliary motion, 
 we will proceed to examine the uses to which it is made subservient in 
 the class of animals under consideration. A very slight examina- 
 tion of one of these creatures under the microscope will show that 
 the cilia answer a double purpose : if the Rotifer fixes itself to 
 some stationary object by means of the anal forceps, it is precisely 
 in the position of a Bryozoon ; and the ciliary action, by producing 
 currents in the water all directed towards the oral orifice, ensures 
 a copious supply of food by hurrying to the mouth whatever 
 minute aliment may be brought within the range of the vortex thus 
 caused ; or, on the other hand, if the animal disengages itself from 
 the substance to which it held by its curious anchor, the wheels 
 acting upon the principle of the paddles of a steam-boat carry it 
 rapidly along with an equable and gliding movement. 
 
 (159.) The whole ciliary apparatus when not in use is retracted 
 within the orifice of the shell, and lodged in a kind of sheath formed 
 for it by the inversion of the tegumentary membrane. The muscular 
 fasciculi by which this is effected are very conspicuous ; they arise 
 from the lining membrane of the shell, and run in distinct fasci- 
 culi in a longitudinal direction to be inserted into the lobules 
 whereon the cilia are arranged (^g. 50, A, h). 
 
 But, besides these retractor muscles, other fasciculi of muscular 
 fibres are seen to run transversely, (Jig. 50, z, i 9 ) crossing the for- 
 mer at right angles : these are, most probably, the agents pro- 
 vided for the extrusion of the wheel-like apparatus; for, aris- 
 ing, as they do, from the inner membrane of the hard integument, 
 they will, by their contraction, compress the fluid in which the 
 viscera float, and, forcing it outward towards the orifice of the shell, 
 it will, of course, push before it the wheels, so as to evert the te- 
 gumentary membrane connecting them with the shell, by unrolling 
 it like the finger of a glove, and thus they will cause the rotatory 
 organs to protrude at the pleasure of the animal. 
 
ROTIFERA. 
 
 We have already described the means whereby the Rotifera pro- 
 cure a supply of food, namely, by exciting currents in the surrounding 
 water ; the materials so obtained pass at once into a pharynx, the 
 capacity of which would seem to vary considerably in different 
 species : from the pharyngeal receptacle it is conveyed into a 
 singularly constructed gizzard, to be bruised and broken down 
 by an apparatus provided for that purpose ; thus prepared it is 
 allowed to enter a third cavity, wherein digestion is accomplished, 
 which may be called the stomach, and this, after becoming gradu- 
 ally constricted in its diameter, terminates at the caudal extremity 
 of the body. 
 
 (160.) The usual arrangement of the digestive apparatus will be 
 readily understood on reference to the annexed figures ; thus, in Ste- 
 phanoceros Eichornii, (Jig- 48,) the pharynx (a) is very capacious, 
 receiving readily the materials brought into it by the ciliated 
 arms ; the gizzard (e) is a small globular viscus, containing the 
 instruments of mastication hereafter to be noticed ; while the 
 digestive cavity properly so called (6), which presents no per- 
 ceptible division into stomach and intestine, extends from the 
 gizzard to the anal aperture. 
 
 In Brachionus urceolaris (Jig. 49) the pharynx or oesopha- 
 gus (e) is less capacious ; the gizzard (/) exhibits through its 
 transparent coats the peculiar dental organs placed within it ; 
 and the stomach (g) is seen partially folded upon itself by 
 the retraction of the body. We observe moreover in this 
 animal, appended to the commencement of the stomach, two 
 large csecal appendages (h A), which were scarcely perceptible in 
 the last figure, and which no doubt are of a glandular nature, 
 furnishing some fluid to be mixed up with the bruised aliment 
 contained in the stomach, to assist in the digestive process. To 
 these secreting caeca Ehrenberg has chosen to give the name of 
 pancreas, but for what reason it is difficult to conjecture, since the 
 first rudiments of a pancreas are only met with in animals far 
 higher in the scale of animal existence ; every analogy indeed would 
 lead us to denominate these cseca the first rudiments of a liver, 
 by far the most important and universal of the glandular organs 
 subservient to digestion, and in a variety of creatures we shall 
 afterwards find it presenting equal simplicity of structure. In 
 the Notommata centrum (Jig. 50, g, #), the cseca are merely 
 two pouches opening into the top of the stomach, whereas in 
 Notommata clavulata there are six of these appendages (Jig. 
 
ROTIFERA. 
 
 123 
 
 51, e, e) communicating with that enlarged portion of the 
 digestive canal (c) which may be looked upon as the proper 
 stomach. 
 
 (161.) We must now revert to the consideration of the 
 dental apparatus contained in the gizzard, represented in situ in 
 (fig- 49, /), and exhi- Fig. 50. 
 
 bited on a still larger 
 scale in (fig- 50, 2). 
 This curious masticat- 
 ing instrument consists 
 of three distinct pieces 
 or teeth, which are 
 made to work upon 
 each other by the con- 
 tractions of the gizzard, 
 so as to tear in pieces or 
 bruise all matters made 
 to pass through the 
 cavity containing them. 
 The central piece (Jig. 
 50, 2, 1) may be com- 
 pared to an anvil pre- 
 senting upon its upper 
 surface two flattened 
 facets ; and upon these 
 the other two teeth, that might without much stretch of 
 fancy be compared to two hammers, act. Each of the superior teeth 
 (fig. 50, a, a) may be described as consisting of two portions 
 united at an angle : the larger portion, or handle as it might be 
 called, serves for the attachment of muscles ; whilst the other 
 part is free in the cavity of the gizzard, and works upon the facets 
 of the anvil, the edge being apparently divided into teeth resem- 
 bling those of a comb, and evidently adapted to bruise or tear 
 substances submitted to their action. Such is the transparency 
 of the whole animal, that the effect of these remarkable masti- 
 cating organs upon the animalcules used as food is distinctly 
 visible under a good microscope, and if the Rotifer be compressed 
 between two pieces of glass, so as to break down the soft textures 
 of its body, the teeth may from their hardness be procured in a 
 detached state for minute examination. The whole apparatus 
 described above evidently resembles very closely the kind of 
 
 
ROTIFER A. 
 
 stomach met with in the Crustacea, to which the rotifera will be 
 found gradually to approximate. 
 
 (162.) Notwithstanding the microscopic size of the Rotifera, and 
 the consequent difficulty of detecting the more minute details of 
 their structure, Ehrenberg thinks he has succeeded in discovering 
 filamentary nerves, and even nervous masses, distributed in different 
 parts of their body ; an arrangement which not only would account 
 for the complete association of their voluntary movements, but 
 would, from the presence of ganglia, render these animals capable of 
 possessing some of the local senses ; indeed Ehrenberg imagines he 
 has discovered such to exist in the shape of red specks, to which he 
 gives the name of eyes. The organ alluded to is a minute red 
 spot, indicated in the figures (Jig. 49 and 50, c) ; nevertheless, no 
 organization has been described of such a nature as to entitle us 
 unhesitatingly to designate it an organ of vision, even if it should, 
 as he intimates, invariably be in connection with a nervous mass, 
 which, from examining his drawing of the arrangement of the 
 nerves, we should have little expected to be the case. 
 
 (163.) The nervous system of Notommata clavulata, as describ- 
 ed by this indefatigable observer, is represented in fig. 51. It would 
 seem to consist of several minute nodules, exhibiting a somewhat 
 symmetrical arrangement, and disposed apparently in pairs ; some 
 of these nodules, which are about ten in number, communicate 
 with each other by delicate filaments, whilst others seem to be 
 quite insulated from the rest. 
 
 Every one who is acquainted with the difficulty of conducting 
 microscopical observations, especially with the high powers needful 
 in detecting structures so minute as the nerves of the Rotifera, will 
 be exceedingly cautious in admitting the complete establishment of 
 facts involving important physiological principles ; and we cannot 
 help thinking that Ehrenberg has been misled by some appearances 
 which it is impossible for the most correct observer always to guard 
 against, in assigning to the rotifera an arrangement of the nervous 
 system so totally different from what is met with in any other class 
 of animals, as that represented in his figure from which our engrav- 
 ing has been accurately copied. 
 
 All our ideas of the physiology of the nerves would lead us to 
 suspect some error. The uses of ganglia, as far as we know at 
 present, are either to associate nerves derived from different sources, 
 or to serve as centres for perception, or else they are for the con- 
 centration of nervous energy. The position of the ganglia depicted 
 in the figure as being in relation with the nervous threads would 
 
ROTIFERA. 
 
 125 
 
 scarcely seem to be consistent with either of the above offices, and 
 therefore we cannot but regard the observations which have been 
 hitherto recorded concerning the nervous system of the rotifera as 
 far from being complete. 
 
 (164.) In addition to the elaborate organization described above, 
 the Prussian naturalist conceived that he had discovered a vascular 
 apparatus, consisting of transverse vessels, (Jig. 51, w, w,) in which 
 
 Fig. 51. 
 
 he supposed a circulation of 
 the nutritive fluids occurred. 
 But the vascular character of 
 the transverse striae visible in 
 this position is more than 
 doubtful, as there seems 
 every reason to suppose that 
 the appearance depicted in 
 the figure is due to the 
 existence of the transverse 
 muscular bands whereby the 
 extrusion of the rotatory ap- 
 paratus is effected, analogous 
 to those occupying a similar 
 situation in the Bryozoa : in 
 fig. 50, i, i, these transverse 
 fasciculi are distinctly de- 
 lineated, and their nature 
 is at once evident. 
 
 (1 65.) The mode in which 
 respiration is effected in the 
 class of animals under consi- 
 deration has been a subject of much dispute. Some have supposed 
 the contact of water, applied to the general surface of the body, 
 sufficient for the aeration of the nutritious juices, especially as its 
 constant renewal would be ensured by the ciliary movements. 
 Bory St. Vincent, * on the contrary, regarded the rotatory cilia 
 as real gills, resembling those of fishes ; and mistaking the move- 
 ments of the gizzard for the contractions of a heart, conceived these 
 animalcules to be even superior to insects in the organization of 
 their vascular system. Ehrenberg, moreover, thinks that he has 
 discovered an internal respiratory apparatus of a most extraordinary 
 description. In Notommata centrura (fig. 50 ) he remarked 
 * Diet, des Sciences Naturelles ; art. Rotifera. 
 
 in. 
 
126 ROTIFERA. 
 
 seven vibrating points on one side, and six on the other, attached 
 to two long and undulating viscera, (/, /,) which he elsewhere 
 describes as being the testes of the animal : the above-mentioned 
 points were never at rest, and appeared to be placed in determinate 
 positions opposite to each other. Accurate observations, he says, 
 have shown each to be a peculiar little organ, provided with a tail 
 resembling that of a note in music, and to be thrown into vibration 
 by three little vesicles or folds of their inflated extremity ; these 
 organs floated freely in the abdominal cavity by their enlarged 
 portion, while by their tail they were attached to the long tubular 
 organ above referred to (figs. 49 and 50). 
 
 Ehrenberg's first idea, on seeing these organs, was, that they 
 formed a vascular system, executing movements of pulsation ; but 
 he now considers them as internal branchiae, or organs of respira- 
 tion, to which the external water is freely admitted in the following 
 manner. 
 
 In many species of the rotifera, we find, projecting from the neck 
 of the animal, a horny tubular organ, called by Ehrenberg the Calcar 
 or spur (figs. 49 d, and 50 Z>) ; this he at first considered to be 
 the male organ of sexual excitement, but he now regards it as a 
 syphon or tube of respiration, through which the circumambient 
 water passes freely into the cavity of the body. He thinks, more- 
 over, that the periodical transparency, and the alternate distension 
 and collapse of the animal, seen to occur regularly in almost all the 
 Rotifera, are produced by the introduction of water into the visceral 
 cavity, and its subsequent expulsion therefrom, upon which action 
 the fluctuations observed in the interior of the body would there- 
 fore depend. The supposition that water is injected in this 
 manner into the body seems to be favoured by other appear- 
 ances ; for, when the internal cavity is thus filled, all the viscera 
 appear isolated, so that the boundaries of each can be distinctly 
 seen, but when the water is discharged they approximate each 
 other, their limits become confounded, and the external membrane 
 of the body assumes a crumpled appearance. 
 
 Upon reviewing the above account of the mode of respiration in 
 the rotifera, we must say that we consider that the office assigned 
 to the little organs called internal branchiae is extremely proble- 
 matical, especially as we have but the most vague intimations con- 
 cerning the existence of a circulating system at all, much less of 
 such a double circulation carried on in arteries and veins as the 
 presence of such organs would infer. " I presume," says Ehrenberg, 
 
ROTIFERA. 
 
 fc< that the branchiae possess a vascular system ; for, when the local 
 contractions occur in the body of the animal, we see distinctly a 
 certain number of filaments (vessels ?) loose and delicate." The 
 opinions of the Professor himself concerning the nature of the 
 organs which he describes being so indefinite, we must pause before 
 adopting the physiological views to which their admission would 
 lead ; more especially as, from the very fact of the whole visceral 
 cavity being perpetually filled with aerated water, the existence of any 
 localized organs of respiration could hardly be esteemed necessary. 
 
 (166.) The last subject which we have to consider relative to the 
 internal economy of the rotifera is, the conformation of their gene- 
 rative apparatus, which now assumes a considerable perfection of 
 developement. The reproductive system is composed apparently 
 of two distinct parts : the one subservient to the formation of the 
 ova ; the other destined either to furnish some secretion essential to 
 the completion of the egg, or, as is more probably the case, secret- 
 ing a fertilizing fluid by which the impregnation of the ova is 
 effected prior to their escape from the body. 
 
 The ovary, as we might term it, or female portion of the system, 
 (jigs. 48 c, 49 7n, n 9 50 &, A*, 5iy,) is a transparent sacciform organ, 
 in which, at some seasons, the eggs are distinctly perceptible through 
 the pellucid coverings of the animal, as represented in the figures. 
 
 The male organs, or testes,as we may call them, are two in number 
 (Jigs. 50 /, and 50 h) ; they resemble long wavy cseca, extending 
 nearly the whole length of the animal, and terminating near the oral 
 extremity by closed extremities. It is to these organs that the small 
 appendages mentioned above as organs of respiration are appended ; 
 and, should the latter not perform the office of respiratory branchiae, 
 they are most probably organs of secretion, such as in many other 
 animals we shall see appended to the spermatic tubes. 
 
 Both the ovigerous organ and the two seminiferous vessels 
 terminate in a common receptacle (Jig. 51, g,) that may be named 
 the cloaca ; this consists of a transparent vesicle endowed with 
 great irritability, in which the fertilization of the ova is apparently 
 effected, the eggs being here brought in contact with the secretion 
 of the testes before they escape through the excretory passage 
 (Jig. 51, d). 
 
 The ova of the rotifera, before they are hatched, form very in- 
 teresting objects for the microscope ; as the movements of the in- 
 cluded young, and even the action of the cilia forming their 
 wheel-like organs, may be distinctly seen through the exquisitely 
 transparent investment of the egg. 
 
128 
 
 EPIZOA. 
 
 CHAPTER X. 
 EPIZOA. 
 
 (167.) Not only are the internal parts of living animals occasion- 
 ally made the residence of creatures adapted by their organization to 
 live under such circumstances, but there is an extensive class of 
 beings destined to an equally parasitical life, so constructed as to 
 be capable of attaching themselves to the external parts of other 
 creatures, from which they suck the nourishment suited to their 
 nature. 
 
 These parasites are commonly found to infest Fishes, Crustaceans, 
 and other inhabitants of fresh and salt water ; generally fixing 
 themselves in positions where an abundant supply of animal juices 
 can be readily obtained, and where, at the same time, the water in 
 which they are immersed is perpetually renewed for the purpose of 
 respiration. The gills of fishes, therefore, offer an eligible situa- 
 tion for their developement, as do the branchiae of the lobster ; or 
 they are sometimes found attached in great numbers to the interior 
 of the mouth in various fishes, deriving from its vascular lining, or 
 from the abundant secretions met with in such a locality, a plentiful 
 supply of food, while they are freely exposed to the currents of 
 water which the mode of respiration in the fish brings in contact 
 with them. 
 
 (168.) Allied, however, as these creatures are in the nature of 
 their mode of life to the entozoa, it is easy to perceive that, from 
 their residence upon the surface of the body, they enjoy a far greater 
 capability of action, and a more enlarged intercourse with the ex- 
 ternal world ; so that we are not surprised at finding them possessed 
 of organs which in both the Sterelminthoid and Ccclelminthoid 
 entozoa would have been entirely useless. In none of the indi- 
 viduals of either of those classes, therefore, have we found external 
 organs developed ; but in the Epizoa* we perceive, in a very in- 
 teresting form, the first sproutings as it were of articulated mem- 
 bers, which in higher classes attain their perfect developement. 
 
 The least elaborately organized of these animals exhibit, indeed, 
 exceedingly grotesque and singular shapes, resembling rather im- 
 
 * E*v, upon ; wv, an animal. 
 
EPIZOA. 
 
 129 
 
 perfect embryos than mature beings ; the first buddings of external 
 limbs in the earlier period of foetal developement imitating not 
 very remotely the appearance of Fig. 52. 
 
 the rudimentary appendages re- 
 presented in the annexed figure* 
 (Jig. 52). But this resem- 
 blance is not confined merely to 
 a fancied similarity in outward 
 form ; it exists in the physio- 
 logical relation that there is 
 between the embryo and the 
 Epizoon, and seems dependent 
 upon that great principle which 
 inseparably connects the perfec- 
 tion of an animal with the cha- 
 racter of its nervous system : 
 the nerves of the Epizoa are 
 simple filaments, the ganglia 
 being indistinct or scarcely de- 
 veloped ; and the imperfection 
 of the limbs is a necessary consequence. In the same manner, in 
 the earliest stages of foetal growth, when we know that the nerves are 
 as yet but mere threads, it is interesting to observe the resemblance, 
 even in outward appearance, between the embryo in this transitory 
 stage of its growth, and the permanent condition of the Epizoa 
 which we are considering. 
 
 (1 69.) A great number of species of these parasites, generally de- 
 scribed under the name of Lerneans, have been observed by authors, 
 and it would seem indeed that each is peculiar to a particular kind of 
 fish. The varieties observable in their outward form are, of course, 
 exceedingly great; but the examples depicted in the figure, namely, 
 the Lerneea gobina, found in the branchiae of Coitus Gobio and 
 Lernaa radiata, which infests the mouth of Coryphcena rupestris, 
 will make the reader sufficiently acquainted with their general ap- 
 pearance and external structure. In the former parasite, of which an 
 anterior and posterior view are given in the engraving (a, b), the 
 appendages seen upon the head and sides of the body answer the 
 purpose of hooks or grappling organs, whereby the creature re- 
 tains its position ; and so firm is its hold upon the delicate covering 
 of the gills, that, even after the death of the fish, it is not easily 
 
 * Miiller (Othone Frederico) Zoologia Danica, 1788. 
 
130 
 
 EPIZOA. 
 
 detached. In the second example, (c, d,) besides the rudimentary 
 limbs, the lower surface of the head and ventral aspect of the body 
 (d) are covered with sharp spines calculated to increase very 
 materially the tenacity of its hold upon the surface from which it 
 imbibes food. The sacculi appended to the posterior part of 
 the animal are receptacles for the eggs, and will be explained 
 hereafter. 
 
 These examples, however, are taken from the most imperfectly 
 organized Epizoa ; but, as we ascend to more highly developed 
 species, we shall at once see how gradually an approximation is 
 made to the articulated outward skeleton, and jointed limbs, met 
 with in the homogangliate forms of being, until at last the zoolo- 
 gist remains in doubt whether the more elaborately constructed 
 ought not to be admitted among the crustacean families, which 
 they most resemble. 
 
 (170.) The Adheres percarum (fig. 53) is one of those spe- 
 cies most nearly allied to the ARTICULATA ; and, the details of its 
 anatomy having been fully investigated by Nordmann,* it will 
 serve as a good example of the type of structure which prevails 
 throughout the class. 
 
 The Actheres is found to infest the perch (Percafluviatilis), 
 adhering firmly to the roof of the mouth, to the tongue or some- 
 
 Fig. 53. 
 
 times even to the eyes of that fish ; 
 in which situations it is concealed by 
 a brownish slimy secretion, so that 
 its presence might easily escape the 
 notice of a casual observer. 
 
 The female, which is represent- 
 ed in the figure, is about two lines 
 in length; the male, which differs 
 materially from the other sex in many 
 points, is considerably smaller. 
 
 The outer covering of the body of 
 these little creatures is at once seen to 
 have assumed a horny hardness ap- 
 proximating the density of the cover- 
 ings of the articulated classes, and in- 
 dications are even perceptible of a 
 division into segments : the distinct- 
 tion, moreover, between the trunk 
 (cephalo-thorax), to which the limbs 
 
 * Mikrogvaphische Beitriige zur Naturgeschichte der witbellosen Thiere ; Berlin, 1832. 
 
EPIZOA. 
 
 131 
 
 arc appended, and the abdomen, wherein the viscera are lodged, 
 is obvious. 
 
 The rude and imperfect limbs that we have seen in the Lerneans 
 are visibly more perfect in their entire construction ; and in the fe- 
 male the posterior pair of these appendages is converted into a most 
 singular instrument of attachment, by which it fixes itself to the 
 gums of the fish. The hinder pair of extremities alluded to (Jig. 
 
 53, &, b) are, in fact, enormously developed; they curve forward after 
 their origin from the posterior part of the trunk, and are so much 
 extended that they project considerably beyond the head of the 
 creature, where, becoming considerably attenuated, the two are 
 joined together by a kind of suture, and support, upon the point 
 where they are united, a cup-shaped organ whereby the creature 
 fixes itself. This singular instrument, represented upon an enlarged 
 scale &tjig. 54, 1, is of cartilaginous hardness, and resembles a little 
 bowl, the inside of which is studded with sharp teeth, and calcu- 
 lated not only to act as a powerful sucker, but, from the hooks 
 within its cavity, it is capable of taking a most tenacious hold 
 upon the lining membrane of the mouth. 
 
 The other members (Jig. 53, o) are much less developed, but 
 are nevertheless so constructed as to assist materially in fixing the 
 Epizoon ; they are represented upon a very enlarged scale in Jig. 
 
 54, 2, where the outer pair (a, a) are seen to exhibit in the transverse 
 lines indented upon their surface the first indication of articulated 
 members ; and their extremities, armed with minute hooks, evidently 
 form powerful agents for prehension. Internal to these are two 
 other jointed organs, still more feeble in their construction, the 
 ends of which (6, 6), being armed with three spines, will assist 
 in effecting the same object. 
 
 (171.) The Figm 54 . 
 
 mouth itself (Jig. 
 54, 2, c) is formed 
 upon similar prin- 
 ciples, the exter- 
 nal orifice being 
 surrounded with a 
 circle of minute 
 recurved spines 
 well calculated to 
 ensure its firm ap- 
 plication to the 
 
132 
 
 EPIZOA. 
 
 surface from which nourishment is obtained ; and, within this, 
 rudimentary jaws furnished with strong teeth are visible, adapted, 
 no doubt, to scarify the part upon which the mouth is placed, in 
 order to ensure an adequate supply of food. In the male Aether es, 
 the sucking-bowl possessed by the female does not exist ; the pre- 
 hensile organs being merely four stout articulated extremities, 
 armed at the end with strong prehensile hooks. 
 
 As we might suppose, from the nature of the food upon which 
 this creature lives, the alimentary system is extremely simple. The 
 oesophagus, the course of which is represented by dotted lines in the 
 last figure, terminates in a straight digestive canal (a), which passes 
 through the centre of the abdomen, but no separation between sto- 
 mach and intestine is visible : the entire tube, from the transverse 
 constrictions visible upon its surface, has a sacculated appearance, 
 and is perceptibly dilated towards the centre of the abdominal 
 cavity ; after which it again diminishes in size as it approaches the 
 anal orifice (Z>), situated at the posterior extremity of the body. 
 
 Near the termination of its Fig. 55. 
 
 course, the alimentary canal 
 passes through a loop formed 
 by transverse bands (w, w), and, 
 moreover, seems to be retained 
 in its position by radiating fibres 
 apparently of a ligamentous cha- 
 racter, but which has been de- 
 scribed as representing a biliary 
 apparatus. 
 
 (172.) The muscular system 
 of this animal is far more perfect 
 in its arrangement than in the 
 preceding classes, and the deli- 
 cate fasciculi which move the 
 rudimentary limbs are visible 
 through the transparent integument (fig. 54). In the abdomen, 
 the muscles form longitudinal and transverse bands, which intersect 
 each other at right angles (Jig. 55, d) ; an arrangement not very 
 different from what we have already seen in the rotiferous ani* 
 malcules. 
 
 (173.) The nervous system appears to consist principally of two 
 long filaments (Jig- 55, c), which run beneath the alimentary ca- 
 nal : but it is extremely probable that these communicate with some 
 
EPJZOA. 133 
 
 minute ganglia in the neighbourhood of the head ; at least, the 
 perfect structure of the oral apparatus, and the developement 
 of the limbs, would seem to indicate such a type of structure. 
 
 (174.) The generative organs in the female Adheres consist of 
 two parts ; the ovaria, wherein the eggs are formed, contained in 
 the abdominal cavity (Jig. 53, d, d), and of two external append- 
 ages, or egg-sacs (Jig. 53,/,/), which are attached to the pos- 
 terior extremity of the body for the purpose of containing the 
 eggs until their complete developement is accomplished ; this ar- 
 rangement we shall again have an opportunity of examining in 
 the entomostracous crustaceans. 
 
 The internal ovaria (Jig- 55, /), when distended with ova, 
 occupy a great part of the cavity of the abdomen, and present a 
 racemose appearance ; but when empty, as represented upon the 
 opposite side of the same figure (e), each is found to be a simple 
 blind canal, with sacculated walls, opening externally by an ori- 
 fice (g, g), through which the ova are expelled into the egg-sacs, 
 where their developement is completed. 
 
 (175.) It would seem that, even when the eggs are hatched, the 
 excluded young are far from having attained their perfect or adult 
 form ; but undergo, at least, two preparatory changes or metamor- 
 phoses, during which they become possessed of external organs 
 so totally different from those they were furnished with on leaving 
 the egg, that it would be difficult to imagine them to be merely 
 different states of existence through which the same animal passes. 
 
 On first quitting the egg, the young Adheres is in fact by no 
 means adapted to the parasitical life to which it is subsequently 
 destined ; possessing no organs of prehension like those of the adult, 
 but merely two pairs of swimming-feet, each armed with a brush of 
 minute hairs, and calculated to propel it through the water. Be- 
 fore, however, the first change is effected, another set of feet may 
 be perceived through the transparent external covering, encased 
 as it were in the first ; when these are completely formed, the 
 original skin falls off, displaying, in addition to two new pairs 
 of swimming-feet, three pairs adapted to prehension ; and it is 
 only when the second set of feet is thrown off in a similar manner 
 that the animal assumes its perfect or mature form. 
 
 (176.) The affinities between the more highly organized EPIZOA 
 and the CRUSTACEA are evidently very strong ; yet, independently 
 of the different character of the nervous system, there is another 
 important distinction between them, derived from their compara- 
 
134 
 
 EPIZOA. 
 
 tive anatomy. In the CRUSTACEA, the organs of circulation and 
 respiration are well developed and easily recognisable ; but, in the 
 class we are now considering, no parts adapted to either of those 
 functions have hitherto been satisfactorily discovered : neverthe- 
 less, that the EPIZOA form a gradual transition from the humbler 
 creatures we have hitherto examined to the great division of ar- 
 ticulated animals, must be obvious to the most superficial observer. 
 
 (177.) In Lamproglena pulchella we have a still more decided 
 approximation to the crustacean type of structure, and the rudimen- 
 tary feet arranged in symmetrical pairs are as numerous as the 
 segments of the body. The limbs, however, are as yet only 
 adapted to secure a firm hold upon the structures to which this 
 parasite attaches itself, namely, the gills of the chub (Cyprinus 
 Jeses), in which situation it is most usually found. The two an- 
 terior pairs (fig. 56, b, c) are far more large- Fig. 56. 
 ly developed than those which are placed 
 upon the posterior parts of the animal, and 
 are apparently strengthened by a cruciform 
 cartilaginous frame-work seen through the 
 transparent integument. The first pair of 
 these holding feet consists of two robust 
 and powerful hooks, terminated by simple 
 horny points ; whilst the second, which are 
 likewise unciform, terminate in trifid prongs, 
 and are evidently equally adapted to pre- 
 hension. The four pairs of members which 
 succeed to these are mere rudiments, and 
 can be of little service as organs of attach- 
 ment ; but, to make up for their imperfec- 
 tion, we find at the posterior^ extremity of 
 the body, between the orifices of the ovaria 
 (g), a pair of cartilaginous suckers well cal- 
 culated to fix this part of the animal. 
 
 The muscular system is readily seen 
 through the transparent skin : four longitudinal bands are visible 
 (d), running from one end to the other, and, besides these, broad 
 transverse fasciculi are discernible in the fifth and sixth segments of 
 the body ; from the nature of the feet, however, and general struc- 
 ture of the creature, we must imagine the existence of muscles 
 provided for the movements of each articulated member, although, 
 from their extreme minuteness, they escape detection. 
 
ECHINODERMATA. 135 
 
 The opening of the mouth is placed in the centre of the space 
 bounded by the four anterior prehensile hooks ; and the alimen- 
 tary canal is a simple tube passing straight through the body to 
 the tail, where the anal orifice is distinguishable. The walls of 
 the intestine have a reticulated appearance, being covered with a 
 kind of glandular net- work, which probably constitutes a biliary 
 apparatus. 
 
 (178.) In a creature thus highly organized we may well expect to 
 find senses of proportionate perfection, and in Lamproglena their 
 existence is no longer doubtful. The eyes are distinctly apparent, 
 of a reddish colour ; but as yet, as in the lowest crustaceans, 
 united into one mass. The antennae likewise, which may be re- 
 garded as special instruments of touch, are well developed ; and, 
 both in number and position, resemble those which characterise 
 the crustacean orders, to which we are thus conducted by almost 
 imperceptible gradations. 
 
 The reproductive organs are entirely similar to those of Adheres 
 already described. Those of the female, represented in the figure, 
 consist of sacciform ovaria, in which the ova are secreted : and 
 from these, when mature, the eggs are expelled through two simple 
 triangular orifices situated on each side of the anus. 
 
 CHAPTER XL 
 
 ECHINODERMATA.* (Cuv.) 
 
 (179.) The last class of beings belonging to the Nematoneurose 
 division of the animal world seems, upon a partial survey, to be com- 
 pletely insulated, and distinct from all other forms of living crea- 
 tures ; so peculiar is the external appearance, and even the internal 
 organization of the families which compose it. The casual observer 
 who should, for the first time, examine a star-fish or a sea-urchin, 
 two of the most familiar examples of the ECHINODERMATA 
 met with upon our own shores, would indeed find it a difficult 
 task to associate them with any other class, or to imagine the affi- 
 nities whereby they are related, either to the simpler animals we have 
 already described, or to more perfect forms of existence hereafter to 
 be mentioned : they would seem to stand alone in the creation, 
 
 * "E%ivos , a hedgehog ; $&/*, the skin. 
 
136 ECHJNODERMATA. 
 
 without appearing to form any portion of that series of devclope- 
 ment which we have hitherto been able to trace. 
 
 But this apparent want of conformity to the general laws of 
 developeinent vanishes on more attentive examination ; so that we 
 may not only trace the steps by which every family of this exten- 
 sive class merges insensibly into another, but perceive that, at the 
 two opposite points of the circle, the ECHINODERMATA are inti- 
 mately in relation with the POLYPS on one hand, while on the 
 other they as obviously approximate the annulose animals, to which 
 the most perfectly organized amongst them bear a striking resem- 
 blance. 
 
 It would be impossible within our present limits to do more 
 than lay before the reader the most important types of structure 
 which the Echinodermata exhibit ; it must, nevertheless, be under- 
 stood that innumerable intermediate families connect the different 
 genera ; so that, however dissimilar the examples we have selected 
 for the purpose of exhibiting their general habits and economy 
 may appear, the gradation which leads from one to another is 
 easily traced. 
 
 (180.) Crinoidce. We have already found that many tribes of 
 polyps secrete calcareous matter in large quantities, so as to con- 
 struct the solid skeletons or polyparies, which generally seem to 
 be placed external to their soft and irritable bodies, but occasion- 
 ally, as in Pennatula, within the living substance. Let us for a 
 moment suppose a polyp supported upon a prolonged stem, and 
 that, instead of depositing the earthy particles externally, they 
 should be lodged in the substance of the polyp itself, so as to fill 
 the pedicle, the body, the tentacula around the mouth and all the 
 appendages belonging to the animal with solid pieces, of definite 
 form ; such pieces being connected together by the soft parts, and 
 surrounded on all sides with irritable matter, would thus form a 
 complete internal skeleton, giving strength and support to the 
 entire animal, and at the same time allowing flexure in every di- 
 rection. A polyp so constituted would obviously, when dried, 
 present an appearance similar to what is depicted in the annexed 
 engraving (Jig- 57), representing an Encrinoid Echinoderm in 
 its perfect condition. That animals thus allied to polyps in 
 their outward form have in former times existed in great num- 
 bers upon the surface of our planet is abundantly testified by the 
 immense quantities of their remains which are met with in various 
 calcareous strata, but their occurrence in a living state is at 
 
ECHINODEKMATA. 
 
 137 
 
 Fig. 57. 
 
 present extremely rare : one 
 minute species only has been 
 detected in our own seas ;* 
 while specimens of larger 
 growth, such as that repre- 
 sented in the engraving, deriv- 
 ed from tropical climates, are 
 so seldom met with, that it is 
 fortunate that one or two ex- 
 amples have been found to 
 reveal to us the real structure 
 of a race of animals once so 
 common, but now almost com- 
 pletely extinct. The body of 
 the Encrinus (Jig' 57, a) (or 
 pelvis, as the central portion 
 of the animal is termed by 
 geological writers,) is com- 
 posed of numerous calcareous 
 plates, varying in shape and 
 arrangement, so as to become 
 important guides to the identification of fossil species ; from this 
 central part arise the large rays (b, b), each furnished with a double 
 row of articulated appendages, which, as well as the arms, are, no 
 doubt, instruments for seizing prey and conveying it to the 
 mouth, situated in the centre of the body near the point a. 
 This part of the animal, when found in a fossil state, from its re- 
 semblance to a flower, has received the common name of a " lily- 
 stone." 
 
 The body above described, with the rays proceeding from it, is 
 supported upon a long pedicle (e), composed of numerous pieces ; 
 and, upon the sides of the stem, similarly constructed filamentary 
 branches are fixed (d, d) at equal intervals. The skeleton of an En- 
 crinite consists, therefore, of thousands of regularly shaped masses 
 of calcareous earth kept together by the living and irritable flesh 
 in which they are imbedded, and it is to the contractions of this 
 living investment that the movements of the animal are due ; but 
 after the death of the creature, and the consequent destruction of 
 its soft parts, the pieces of the earthy frame-work become sepa- 
 rated and fall asunder, forming the fossil remains called " Troeki," 
 
 * Thompson (J. W.), Memoir concerning the Pentacrinus Europaeus ; Cork, 1827, 4to. 
 
138 
 
 ECHINODEllMATA. 
 
 Fig. 58. 
 
 and known in the northern districts of our own island, where they 
 are very abundant, as " St. Cuthberfs beads" 
 
 Of the internal structure of the Encrinites nothing is satisfac- 
 torily known. That 
 they possessed a dis- 
 tinct mouth and anal 
 aperture is evident, 
 from the structure of 
 the plates of the body; 
 but this is the extent 
 of our information 
 concerning them.* 
 
 (181.) Asteridce. 
 In order to convert an 
 Encrinus into an ani- 
 mal capable oflocomo- 
 tion, and'able to*crawl 
 about at the bottom 
 of the sea, little fur- 
 ther would be requi- 
 site than to separate 
 
 the body and arms from the fixed pedicle upon which they are sup- 
 ported, and we should have an animal resembling in every particular 
 the star-fishes. The Comatula, for example, (fig. 58,) one of the 
 lowest of the asteroid Echinodermata, might be looked upon as an 
 animal thus detached. The central part, or body, which contains 
 the viscera, is made up of numerous calcareous pieces, having in 
 its centre a stelliform mouth, and near this is a tubular orifice which 
 might be regarded as an anus. Around the margin of the central 
 disc arise five stunted arms which immediately divide into a variable 
 number of long radiating branches, composed, like those of the En- 
 crinus, of innumerable articulated earthy masses enveloped in a liv- 
 ing and irritable integument. We find, moreover, issuing from 
 the sides of every one of the prolonged rays, a double row of se- 
 condary filaments, each containing an internal jointed skeleton, and 
 capable of independent motion. The complicated arms of the Co- 
 matula, therefore, are not, like those of a polyp, merely adapted 
 to seize prey ; but, from their superior firmness, may be used as 
 so many legs, enabling the animal to travel from place to place. 
 
 * For a detailed account of the fossil Encrinites, the reader is referred to " A Natural 
 History of the Crinoidea, or lily-shaped animals, by J.S. Miller ; 4to. Bristol, 1821. 
 
ECHINODERMATA. 
 
 139 
 
 Setting out from this point to trace the gradual developement of 
 organization in the Echinodermata, we shall observe a progressive 
 concentration of their entire structure. The central part, or vis- 
 ceral cavity, so small in the Comatula when compared to the 
 complicated rays derived from it, enlarges in its proportional di- 
 mensions as the viscera contained within it become more perfect 
 in their structure ; whilst, on the other hand, the radiating or po- 
 lyp form, so visible in Encrinus and Comatula, becomes obliterated 
 by degrees, until, at length, almost all vestiges of it are lost, or but 
 obscurely recognisable. 
 
 In the Gorgonocephalus (Jig. 59), the proportionate size of the 
 rays when compared with that of the central disc still preponde- 
 rates very considerably, although even here some concentration is 
 manifest. The secondary articulated filaments appended to the 
 rays of Comatula are F- lgt 59. 
 
 no longer recognis- 
 able, their place be- 
 ing supplied by the 
 continual division 
 and subdivision of 
 the rays themselves ; 
 the same end, how- 
 ever, is obtained in 
 both cases, for the 
 numerous jointed 
 and flexible rays 
 of Gorgonocephalus 
 still form so many 
 legs, enabling the 
 creature to drag it- 
 self along the bottom of the sea, or to entwine itself among the 
 submarine plants, as well as supplying the office of tentacula in 
 securing food. 
 
 Continuing our progress towards more perfect forms of these 
 remarkable animals, we at length arrive at genera in which the 
 rays become divested of all elongated appendages, either in the shape 
 of articulated lateral filaments or dichotomous ramifications. In 
 Ophiurus, for instance (Jig. 60), the rays are long and simple, re- 
 sembling the tails of so many serpents a circumstance from whence 
 the name of the family is derived ; nevertheless, on each side of 
 every ray we still trace moveable lateral spines, which, although 
 
140 ECHINODERMATA. 
 
 but mere rudiments of what we have seen in Comatula, may still 
 assist in locomotion, or perhaps may contribute to retain the prey 
 more firmly when seized by the arms. The rays themselves are 
 composed of many pieces curiously imbricated and joined together 
 by ligaments, so that they are, from their length and tenuity, ex- 
 tremely flexible in all directions, and serve not only for legs adapt- 
 ed to crawl upon the ground, but are occasionally serviceable as 
 fins, able to support the animal in the water for a short distance 
 by a kind of undulatory movement. The body, or central disc, 
 is beautifully constructed, being made up of innumerable pieces ac- 
 curately fitted together. The mouth occupies the centre of the 
 ventral surface, and is surrounded by radiating furrows in which 
 are seen minute apertures that give passage to a set of remark- 
 able prehensile organs, to be described hereafter : these are calcu- 
 lated to act as suckers, and so disposed as either to fix the body of 
 the animal, or to retain food during the process of deglutition. 
 
 Fig. 60. 
 
 Leaving the Ophiuri, we are led through a long series of almost 
 imperceptible gradations to animals apparently of most dissimilar 
 structure. The star-fishes (Asterias) (Jig. 65) form the next step : 
 
ECHINODERMATA. 141 
 
 in these, from the increased size of the body, the rays are united at 
 their origin, and become so much dilated as to contain prolongations 
 of the viscera lodged in their interior ; an arrangement not met with 
 in Ophiuri and other slender-rayed Asteridse. The dilatation of 
 the central part proceeds, and in the same proportion the rays be- 
 come obliterated ; so that at length, the asteroid shape becoming 
 totally lost by the progressive filling up of the interspaces between 
 the rays, we arrive ultimately at completely pentagonal forms, the 
 sides of the pentagon being perfectly straight lines. 
 
 (182.) It is extremely interesting to remark the changes which 
 occur in the nature of the locomotive organs during these diversi- 
 fications of external figure. We have seen that, in the lower 
 Echinodermata possessing long and flexible rays, such organs were 
 fully adequate to perform all movements needful for progression ; 
 but as the mobility of these parts is diminished by their gradual 
 curtailment, and the filling up of the spaces between them, some 
 compensating contrivance becomes indispensably necessary, and 
 accordingly we find an apparatus gradually developed, well cal- 
 culated to meet the exigencies of the case. In Ophiurus 
 we have already mentioned the existence of protrusible suckers 
 around the opening of the mouth, well adapted, from their posi- 
 tion, to take firm hold of food seized by the animal ; and it is by 
 increasing the number of such organs that ample compensation 
 is made for the loss of motion in the rays themselves. On ex- 
 amining the lower surface of an Aster ias, even in those forms 
 which most approximate a right-lined pentagon in their marginal 
 contour, the number of rays will still be found to be distinctly in- 
 dicated by as many furrows radiating from the mouth, and indicat- 
 ing the centre of each division of the body. These ambulacral 
 furrows, as they are termed, exhibit, when examined in a dried 
 specimen, innumerable orifices arranged in parallel rows, through 
 each of which, when alive, the animal could protrude a prehensile 
 sucker, capable of being securely attached to any smooth surface. 
 
 No verbal description can at all do justice to this wonderful 
 mechanism, even leaving out of the question the means by which 
 each individual sucker is wielded, for of this we shall speak here- 
 after ; but let any of our readers, when opportunity offers, pick 
 up from the beach one of these animals, the common star-fish of 
 our coast, which, as it lies upon the sand left by the retiring 
 waves, appears so incapable of movement, so utterly helpless and 
 inanimate ; let him place it in a large glass jar filled with its 
 
ECHINODE11MATA. 
 
 native element, and watch the admirable spectacle which it then 
 presents : slowly he perceives its rays expand to their full stretch, 
 hundreds of feet are gradually protruded through the ambulacral 
 apertures, and each, apparently possessed of independent action, 
 fixes itself to the sides of the vessel as the animal begins its march. 
 The numerous suckers are soon all employed, fixing and detaching 
 themselves alternately, some remaining firmly adherent while others 
 change their position ; and thus, by an equable gliding movement, 
 the star-fish climbs the sides of the glass in which it is confined, 
 or the perpendicular surface of the submarine rock. 
 
 But it is not only as agents in locomotion that the ambulacral 
 suckers are used ; helpless as these creatures appear to be, they 
 are among the most formidable tyrants of the deep, as will be 
 readily admitted by any one who watches them in the act of de- 
 vouring prey. When seizing its food, the rays of the Asterias 
 are bent towards the ventral aspect so as to form a kind of cup, 
 in the centre of which is the opening of the mouth ; the cup thus. 
 formed will, to a certain extent, lay hold of a passing victim, but, 
 without other means of securing it, the grasp would scarcely be 
 very formidable to animals possessed of any strength ; armed, how- 
 ever, as the rays have been found to be, with hundreds of tena- 
 cious suckers, escape is almost impossible, for prey once seized 
 is secured by every part of its surface, and, in spite of its utmost 
 efforts, is speedily dragged into the mouth and engulphed in the 
 capacious stomach, where its soft parts are soon dissolved. 
 
 But to continue our survey of the class before us. Having ar- 
 rived at the point at which, by the diminution of the rays and 
 consequent extension of the central part, the body has assumed 
 a pentagonal outline, we may now advance in an equally gradual 
 manner to those globular species, of which the Echinus, or sea- 
 urchin, is the type or most perfect example. 
 
 (183.) Echinidce. In the Scutellce (fig. 61), we have a flat and 
 shield-like body, in which even the angles of the margin are lost, 
 and the whole circumference acquires a circular form ; but still the 
 five radiating ambulacra are visible upon the centre of the disc, al- 
 though evidently imperfectly developed when compared with those 
 of the Asteridse above-mentioned. The nature of the integument 
 has, in fact, become so changed in its texture, that another modi- 
 fication of the locomotive organs is here imperatively called for, 
 and the means of progression are therefore proportionately altered. 
 In the Asteridse, the integuments, especially upon the dorsal as- 
 
ECHINODE11MATA. 
 Fig. 61. 
 
 143 
 
 pcct, arc always more or less composed of a coriaceous material, or, 
 at least, of solid pieces so articulated together as to permit of con- 
 siderable flexibility ; but in the Echinidso the nature of the external 
 covering is very different, for these creatures are completely en- 
 cased in a dense calcareous shell, composed of numerous angular 
 pieces accurately fitted together and incapable of movement. The 
 Scutellte, moreover, bury themselves beneath the surface of the 
 sand, a situation in which suckers would be of little use, but for 
 which these animals are admirably adapted by a contrivance not less 
 calculated to excite the admiration of the observer. The exterior 
 of the shell is entirely covered with minute appendages, resembling, 
 when seen with the naked eye, delicate hairs, but which, when ex- 
 amined under a microscope, are found to be spines of most elaborate 
 structure, as may be seen from the magnified view of one represent- 
 ed in the annexed figure (Jig. 61). Innumerable as these spines 
 are, every one of them is articulated to the shell by a kind of ball- 
 and-socket joint, and susceptible of being moved in all directions, 
 so that by their combined efforts the Scutella can speedily bury itself, 
 either for the purpose of procuring food, or of eluding observation. 
 (184.) From the flat Scutellcc^ the passage to the globose Echi- 
 nidee is most gradual ; and a beautiful series of connecting forms, 
 many still existing as living species, but a still greater number found 
 only in a fossil state, demonstrate the gradual expansion of the 
 shell, and its conversion into the spherical figure seen in the Echinus 
 esculentus (Jig. 62). The Echinus in shape resembles an orange, 
 
144 
 
 ECHINODERMATA. 
 
 its dense calcareous crust enclosing the viscera within its cavity, 
 while the locomotive apparatus is placed upon the external surface. 
 The mouth is a simple orifice in the shell placed at one extremity 
 of its axis, and through it, as represented in the figure, the points 
 of five singular teeth project externally ; while the anal aperture 
 occupies the opposite pole of the sphere. The instruments of 
 locomotion occupy the entire superficies of the shell, and consist 
 of two distinct sets of organs adapted to different uses. The first 
 consists of a multitude of sharp purple spines, every one of which 
 is articulated to a distinct and prominent tubercle whereon it 
 moves. These numerous spines, therefore, which are essentially 
 similar in their office to those we have already described in Scutella, 
 differing only in proportionate size, are so many inflexible legs 
 upon which the Echinus rolls itself from place to place, or by their 
 assistance it can bury itself in the sand with the greatest facility. 
 But these wonderfully constructed animals are by no means con- 
 fined to this mode of progression ; for, impossible as it might 
 appear from their outward appearance, they are able to climb 
 rocks in search of food, and thus destroy the corallines and 
 shell-fish upon which they principally feed. In order to effect this, 
 we find the shell perforated with ten rows of small orifices so 
 disposed as to form five pairs of ambulacra extending from one 
 pole to the other : through these apertures a system of long 
 suckers is made to pig. 52. 
 
 issue, which protrud- 
 ing, as represented 
 in the figure (jig- 
 62), beyond the 
 points of the spines, 
 can be firmly fixed 
 to any smooth sur- 
 face, and, like the 
 suckers of Asterias, 
 become locomotive 
 agents. 
 
 (185.) Holothu- 
 ridce. Having trac- 
 ed the developement 
 of the Echinodermata from the polypiform Encrinite to the globu- 
 lar Echinus, we now shall find them perceptibly approximate an 
 annulose or worm-like form. In the Holothuria (Jig. 70), the 
 
ECHINODERMATA. 
 
 145 
 
 Fig. 63. 
 
 commencement of this change is perceptible : instead of being com- 
 posed of hard, calcareous pieces, the integuments of the body now 
 become soft and irritable, a few thin laminae of earthy matter 
 around the mouth being the only vestiges of the shell and the 
 spines, of course, are no longer met with ; the suckers, however, 
 remain, and, when protruded through innumerable apertures dis- 
 tributed over the surface of the body, 
 they still form the principal instruments 
 of progression. 
 
 (186.) Fistularidx.At length, in 
 the last division of the class, even the loco- 
 motive suckers are lost, and the only ex- ^ 
 ternal resemblance left between the now 
 worm-like body and the forms above 
 enumerated is met with in the radiating 
 tentacula which surround the mouth. 
 The apodous Echinodermata, " Echino- 
 dermes sans pieds," of Cuvier have 
 indeed been expunged from the list 
 of radiated animals by some modern 
 writers, but in every point of their in- 
 ternal structure we shall find them 
 offer too many points of similarity to 
 permit of their expulsion from the class 
 under consideration, although they evi- 
 dently form the connecting link between 
 the Radiata and the lowest families of 
 the articulated division of the animal 
 kingdom. The genus Fistularia (Jig. 
 63) strikingly exhibits approximation to 
 the outward form of the ANNELIDA ; 
 and the anatomy of these creatures, 
 which we shall afterwards consider, 
 equally indicates the affinities which 
 unite them. 
 
 (187.) We have already, when speak- 
 ing of the general division of the Echino- 
 dermata, put the reader in possession of 
 all that is satisfactorily known concern- 
 ing the structure of the Crinoid* ge- 
 
 * K{/m, a lily'; tfiat, like. 
 
146 ECHINODERMATA. 
 
 nera ; our knowledge of those singular animals being entirely derived 
 from the exterior conformation of two recent species, and from the 
 mutilated skeletons of fossil Encrinites, which exist in such abun- 
 dance in the limestone strata of our own country. 
 
 Commencing, therefore, with the Asteridce,* we shall now enter at 
 once upon the consideration of the anatomy of such species as have 
 been most carefully examined, and merely notice incidentally the 
 modifications which occur in the disposition of various organs in 
 kindred genera. 
 
 (188.) On examining a living Asterias, the outer covering of its 
 body is found to be composed of a dense coriaceous substance, in which 
 numerous calcareous pieces are apparently imbedded. The cori- 
 aceous integument is generally coloured externally with lively tints, 
 and is evidently possessed of considerable irritability, as it readily 
 shrinks under the knife, or upon the application of various stimuli. 
 When cut into, it has a semicartilaginous hardness, and fibrous 
 bands, almost resembling tendon in their aspect, may be seen to 
 radiate from the centre of the body towards the extremities of the 
 rays. There is no doubt that the movements of the rays are 
 effected by the contractions of this fibrous membrane ; and that, 
 especially in the most polyp-like forms, as in Comatula and Gor- 
 gonocephalus, the irritable skin is the principal agent in effecting 
 locomotion. 
 
 Besides the calcareous matter deposited in its interior, this outer 
 covering of the star- fish appears to furnish several secretions of 
 different descriptions. The colouring matter upon its surface is no 
 doubt one of these ; as is a reddish fluid which exudes from the in- 
 tegument of A. rubens, and is of so caustic a quality as occasion- 
 ally to produce great irritation of the skin in persons by whom 
 individuals of this species are incautiously handled : moreover, in 
 A. aranciaca, the whole animal is coated with a thick mucus, so 
 dense and filamentous that it may be raised in thin films resembling 
 a cobweb, and might easily be taken for a cuticular covering. 
 
 The exterior of the body is generally rendered rough and un- 
 even by various structures, either imbedded in the substance of 
 the coriaceous skin or projecting from its external surface. We 
 have already described the articulated pieces attached to the rays of 
 Comatula and others, which seem to be the most perfectly de- 
 veloped forms of these cutaneous appendages. In the common 
 star-fish of our own coast, similar spinous processes, but composed 
 
 * The name of this family, and of its typical genus, is derived from ao-rng, a star. 
 
ECHINODERMATA. 147 
 
 of but one calcareous piece, are attached to the inferior margins of 
 each ray, sometimes in several rows ; and, being still moveable, they 
 may be useful in seizing prey, or even as assisting in progression. 
 Upon the dorsal aspect of the body are other calcareous projec- 
 tions, exhibiting a great variety of forms, so as to render the en- 
 tire surface of the animal uneven and tuberculated. 
 
 But the most remarkable appendages to the integument of the 
 Asterias are minute bodies, which have been named by authors 
 Pedicellarice, and have been looked upon by many naturalists as 
 distinct animals, allied to polyps in structure, and living parasiti- 
 cally upon star-fishes and other ECHINODERMATA. Each of these 
 curious processes consists of a short stem fixed by one extremity to 
 the skin of the Asterias, and terminating at the opposite end in 
 two or three points resembling in some respects the prongs of a 
 fork : the stem itself does not seem to be perforated by any canal ; 
 but, nevertheless, the terminating points are found to be highly 
 irritable, and quickly seize hold of any minute body placed between 
 them. Some writers regard these bodies as organs of prehension, 
 used under certain circumstances for fixing the animals which 
 possess them ; but, from their small size and general appearance, 
 they seem but ill adapted to such an office. 
 
 (189.) The skeleton or calcareous framework imbedded in the 
 skin of the Asteridse is by no means the least remarkable part of 
 their structure : this consists of several hundred pieces variously 
 disposed, and for the most part fitted together with great accuracy; 
 being either firmly soldered to each other, as we have seen them 
 to be in the formation of the calcareous box that constitutes the 
 central portion of Ophiurus, or united by ligaments, so as to allow 
 of a considerable degree of motion to take place between them, as in 
 the rays of Ophiurus, Gorgonocephalus, and other asteroid forms. 
 
 In the generality of star-fishes, the arrangement, and indeed the 
 entire character of the calcareous plates, differs materially in differ- 
 ent parts of the body; and, even in different species, considerable 
 modifications are observable. In the coriaceous integument form- 
 ing the dorsal parietes of the animal, the pieces in many cases 
 seem rather to be represented by calcareous granules disseminated 
 through the interior of the skin, or in other cases they are ar- 
 ranged in lines anastomosing with each other in all directions, so as 
 to represent, when the skin is dried, a rude network of solid par- 
 ticles, upon the exterior of which the various cutaneous appendages 
 already noticed are sustained. 
 
ECHIXODERMATA. 
 
 It is, however, upon the ventral aspect of the Asterias that the 
 skeleton assumes its most perfect developement ; the floor of every 
 ray is made up of a continuous series of detached pieces, or verte- 
 brae, as they are generally called, fitted to each other and united by 
 a strong ligamentous substance, so as to form a succession of joints, 
 upon which the flexibility of the ray depends. The pieces around 
 the mouth constitute a strong circular framework enclosing the oral 
 aperture, from which, as from a centre, the rest of the skeleton 
 radiates. The joints forming the floor of the ray succeed to this ; 
 these are partially represented in Jig. 67, where the soft parts 
 having been removed from the ray marked &, their general arrange- 
 ment is displayed. 
 
 The vertebrae thus exposed are individually composed of 
 several pieces, and each is articulated by oblique facets to those 
 which precede and follow it ; a kind of union which admits of 
 considerable motion, and provides for the flexibility of the ray, 
 so as to render it capable of executing those movements which 
 are requisite for the purpose of progression, or of seizing prey. 
 The connection of the vertebras is effected in such a manner, 
 that between each pair of calcareous plates minute orifices are left, 
 which in the entire state of the ray are seen to be arranged in a 
 quadruple series ; these holes give passage to the locomotive 
 suckers, and from this circumstance have been named the am- 
 bulacral holes, while the furrows seen upon the ventral surface 
 into which they open are designated the ambulacra! grooves 
 (fig- 64). 
 
 (190.) The singular organs which, at the will of the animal, are 
 protruded through the ambulacral apertures, forming the principal 
 agents whereby, in the generality of species, locomotion is effected, 
 next require our notice. In the annexed figure (Jig. 64) they 
 are seen fully extended, projecting for some distance beyond the 
 margins of the ambulacral grooves which occupy the centre of each 
 ray, every one of them being furnished at its extremity with a 
 sucking disc, adapted to take firm hold upon any smooth surface. 
 The mechanism by which these suckers, or feet, as they are usually 
 called, are extended from the body and again retracted, is very 
 simple. That portion of each foot which is external to the shell 
 is a muscular tube, closed at one extremity, namely, that where- 
 unto the sucker is appended ; whilst, by the opposite, it communi- 
 cates through the corresponding ambulacral hole with a globular 
 contractile vesicle situated within the body of the animal. Both 
 
ECH1NODE11MATA. 
 Fig. 64. 
 
 149 
 
 the tubular foot, and the vesicle appended to it, are endowed with 
 a power of independent action, so that, if the vesicle contracts, the 
 fluid within it is forced into the external tubular portion of the 
 organ, which thus becomes distended and rendered erect ; but if, on 
 the other hand, the muscular tube shrinks in turn, the contained 
 fluid is forced back again into the internal vesicle, and the whole 
 foot collapses. The arrangement referred to will be easily intel- 
 ligible on reference to the rough diagram in the next page, which 
 represents a longitudinal section of one of the rays of the Asterias 
 depicted above. The internal vesicles (Jig. 65, 1, h) occupy the 
 floor of each segment of the body, and, when viewed from above, 
 (Jig. 67, d,) the entire series resembles strings of transparent 
 beads placed above the rows of ambulacral apertures, through which 
 they communicate with the tubular feet (fig- 65, 1, g). In fig. 
 65, 2, three of these organs are represented in different states of 
 
150 
 
 ECHINODERMATA. 
 
 extension, and their whole structure is developed. The foot, d, 
 is shown protruded to its full extent; the vesicle, much contracted, 
 has forced the fluid which it contained into the external tube (t), 
 whereby it is rendered tense and prominent. The muscular coats, 
 which invest the exterior of the protruded portion, are likewise de- 
 picted ; the internal layer (&), immediately in contact with the 
 membranous canal continued from the vesicle, is made up of longi- 
 tudinal bands passing from the root of the organ towards the 
 sucker at its extremity, while the outer layer (/) consists of cir- 
 cular fibres, an arrangement evidently adequate to the performance 
 of all required movements. 
 
 The other portions of this diagram represent the feet in differ- 
 ent stages of protrusion : in Jig. 65, 2, c, the vesicle being par- 
 tially contracted, the tubular portion is seen in a medium state of 
 distension ; and at b, the sucker is shown in a still more retracted 
 state, the contained fluid having been completely expelled from 
 the muscular tube, and driven back into the vesicle, which is dis- 
 tended to the utmost. 
 
 Fig. 65. 
 
 The fluid that thus fills the suckers, and performs so important 
 a part in causing all their movements, is not secreted by the vesi- 
 cles in which it is contained, but is conveyed into them by a 
 special vascular apparatus, (g, /, ) from which branches are given 
 off to each tube. The nature of the fluid, however, and the ar- 
 rangement of the vessels through which it flows, will be more 
 properly discussed hereafter. 
 
ECHINODE11MATA. 151 
 
 (191.) The whole inner surface of the elaborately constructed 
 box which forms the skeleton, as well as the integuments of the 
 star-fish, is lined by a thin membrane, aptly enough called the pe- 
 ritoneum ; for, like the serous tunic so named in higher animals, it 
 not only spreads over the walls of the body, but is reflected there- 
 from upon the contained viscera, so that they are completely in- 
 vested by it, each viscus having a distinct mesenteric fold by 
 which it is supported and retained in situ. 
 
 (192.) The mouth of the Asterias occupies the centre of the lower 
 surface of the body (j^g. 65, a). It is usually described as being 
 a simple orifice entirely destitute of teeth, although it is not impro- 
 bable that the osseous ring around it, and the articulated spines 
 thereunto attached, may, to a certain extent, perform the office of 
 a dental apparatus. 
 
 The oesophagus is very muscular, and susceptible of great dila- 
 tation, its parietes being gathered into deep longitudinal folds. 
 The stomach (fig. 65, b) is a wide sacculated bag, occupying the 
 central portion of the body, and, like the oesophagus, is evidently 
 calculated to undergo considerable distension. There is no anal 
 orifice, and consequently, as in the polyps, the indigestible parts 
 of the food are again expelled through the mouth. The walls of 
 the stomach, as well as those of the oesophagus, contain muscular 
 fibres, and are further strengthened by fibrous bands, apparently 
 of a ligamentous character, derived from the peritoneal covering 
 which spreads over its outer surface. Ten narrow canals open by 
 as many distinct orifices into the sides of the stomach ; each of 
 which, after a short course, expands into a capacious caecum 
 (fig. 65, 1, c). 
 
 The whole of the digestive apparatus is displayed in Jig. 66 : 
 every one of the five rays contains two of the caecal prolongations 
 derived from the stomach or central bag (a) ; and in the rays marked 
 c, d, e, these organs are represented in situ, but at /, they are 
 seen raised from their natural position and carefully unravelled, so 
 as to display more distinctly their complicated structure. When 
 thus unfolded, the caeca present an arborescent appearance, the 
 central canal being dilated into numerous lateral sacculi, from 
 which in turn secondary pouches are given off; and in this manner 
 innumerable ramifications are formed, so that the extent of internal 
 surface is enormously increased, as may be seen in the ray g, in 
 which, the upper walls of the caeca having been removed, their 
 sacculated internal structure is rendered visible. 
 
ECHINODERMATA. 
 
 (193.) With respect to the exact office of these capacious ap- 
 pendages to the stomach, there exists some diversity of opinion. 
 
 Fig. 66. 
 
 It is scarcely possible that they can be at all instrumental in the 
 digestion of food, the passages by which they communicate with 
 the central cavity being too narrow to admit any solid substance 
 into their interior ; the digestive process would therefore seem to 
 be entirely accomplished in the receptacle into which the food is 
 first introduced. But there is every evidence to prove that, 
 although they can have little part in digestion, they are inti- 
 mately connected with the absorption of nutriment ; and thus, 
 although possessing no excretory orifice, they must be looked upon 
 as strictly analogous in function to the intestinal canal of other 
 animals : the great extent of surface which they present internally 
 would alone lead to this supposition, even did not the nature of the 
 material usually found in them, namely a pultaceous creamy fluid, 
 evidently a product of digestion, abundantly confirm this view of 
 their nature. The matter seems, however, to be put beyond a 
 doubt by the arrangement of the vascular system connected with 
 these organs, as the veins which ramify so extensively through their 
 walls are here, as in other ECHINODERMATA, the only agents by 
 which the absorption of chyle can be effected ; this will be evident 
 when we examine the organs subservient to the circulation of the 
 nutritious fluids. 
 
 Those physiologists who have adopted a different view of the 
 nature of the csecal appendages to the stomach, consider them to 
 be adapted to the secretion of some fluid, and probably represent- 
 
ECHINODERMATA. 153 
 
 ing a biliary apparatus. Their enormous extent, however, would 
 alone lead us to dissent from such a conclusion ; more especially as 
 another organ has been pointed out to which the functions of a 
 liver have been assigned. This is situated upon the base of the 
 stomach (Jig. 66, Z>), and is a yellow or greenish-yellow racemose 
 sacculus, which opens into the bottom of the digestive sac by a free 
 aperture : the contents of this organ, moreover, resemble bile both 
 in taste and colour.* 
 
 In the slender-rayed genera, such as Ophiuru*, the csecal 
 appendages are not met with ; but their deficiency appears to be 
 supplied by the plicated walls of the stomach itself, the ^nu- 
 merous folds of which resemble lateral leaflets attached to the cen- 
 tral cavity. We are unacquainted with the precise organization of 
 the alimentary canal in Comalula ,- but, from the orifices visible in 
 the shell, it would appear that in this genus, as well as in some 
 Crinoid species, the digestive tube was furnished with an anal 
 aperture. 
 
 (194.) The star-fishes, grossly considered, might be regarded as 
 mere walking stomachs ; and the office assigned to them in the eco- 
 nomy of nature, that of devouring all sorts of garbage and offal which 
 would otherwise accumulate upon our shores. But, as we have 
 already seen, their diet is by no means exclusively limited to such ma- 
 terials, since crustaceans, shell-fish of various kinds, and even small 
 fishes, easily fall victims to their voracity. Delle Chiaje found a 
 human molar tooth in the stomach of an individual which he exa- 
 mined. Neither is the size of the prey upon which they feed so 
 diminutive as we might suppose from a mere inspection of the orifice 
 representing the mouth ; for this is not only extremely dilatable, 
 but, as we have found to be the case in the Actiniae, the stomach 
 is occasionally partially inverted, in order more completely to 
 embrace substances about to be devoured. Shell-fishes are fre- 
 quently swallowed whole ; and a living specimen of Chama anti- 
 quata, Lin., has been taken from the digestive cavity of an Asterias 
 in an entire state. It appears, moreover, that it is not necessary for 
 testaceous mollusca to be absolutely swallowed, shells and all, to 
 enable the Asteridse to obtain possession of the enclosed animal, 
 as they would seem to have the power of attacking large oysters, 
 to which they are generally believed to be peculiarly destructive, 
 and of eating them out of their shells. The ancients believed that, 
 in order to accomplish this, the star-fish, on finding an oyster par* 
 
 * Delle Chiaje, op. cit. 
 
154 ECHINODERMATA. 
 
 tially open, cunningly inserted one of its rays between the valves, 
 and, thus gradually insinuating itself, destroyed its victim.* Mo- 
 dern observations do not, as far as we are aware, fully bear out the 
 above opinion of our ancestors as to the mode in which star-fishes 
 attack oysters ; although the destruction which they cause is pretty 
 generally acknowledged. The observations recorded by M. Eudes 
 Deslongchamps upon this subject are however exceedingly curious.*)* 
 As the waves had receded from the shore, so as to leave only one 
 or two inches of water upon the sand, he saw numbers of Asterias 
 rubens rolling in bunches, five or six being fastened together into 
 a sort of ball by the interlacement of their rays. He examined a 
 great number of such balls, and constantly found in the centre a 
 Bivalve Mollusc (Mactra Stultorum, Lin.) of an inch and a 
 half in length. The valves were invariably opened to the extent 
 of two or three lines, and the star-fishes were always ranged with 
 their mouths in contact with the edges of the valves. 
 
 On detaching them from the shell which they thus imprisoned, 
 he found that they had introduced between the valves large 
 rounded vesicles with very thin walls, and filled with a transparent 
 fluid. Each Asterias had five of these vesicles ranged around 
 its mouth, but they were of very unequal size ; generally there 
 were two larger than the rest, equal in size to large filberts, 
 while the other three were not bigger than small peas. These 
 vesicles appeared to be attached to the Asterias by short pedicles, 
 and at the opposite end of each was a round open aperture, through 
 which the fluid contained in the vesicle flowed out drop by drop. 
 No sooner was the animal detached from the shell that it was thus 
 sucking, than the vesicles collapsed and became no longer distin- 
 guishable. The Mactra were all found to be more or less de- 
 voured, some having only their adductor muscles left; but, however 
 little they had been injured, all had lost the power of closing their 
 
 * This maybe gathered from Aldrorando, who writes as follows : " AHi ostrea- 
 rom bostes soot Stella; marina? moll& cntsti intectae, rer&am crodeltter, (at JElianos, 
 Kb. ix. cap. 22, ait,) iotmicae ot hcc ipsas exedant et confidant Ratio iosidiantm qoas 
 eis molhmter ejosmodi est. Com testacea soas patefaciant conchas, com vel refri- 
 geratioaeegeot,Telotaliqaidpeittnensadirictam iocidat; eae, ooo de sois stve cnmbos 
 sire radii* infra testas ostreae biaotis iosito eas clandi probibens, came implentar." 
 Testae, lib. iiL page 497. Tbos likewise Oppian, 
 
 " Sic strait insidias, sic sobdola fraodes 
 Stella marina para L, sed mil to adjota lapillo 
 Whiter, et pedUms scabris disjuogit Mantes." 
 t Bulletin des Sciences de M. le Baron Ferossac, vol. *. p. 296. 
 
ECHINODERMATA. 
 
 155 
 
 valves and were apparently dead : nevertheless there was nothing 
 to lead to the supposition that only dead shell-fishes were attacked, 
 so that it is difficult to imagine how the delicate vesicles above de- 
 scribed escaped injury from the closing of the valves. M. Deslong- 
 champs thinks that probably the Asterias pours into the shell a 
 torpifying secretion, and thus ensures the death of its victim. 
 
 (195.) The absorption of the nutritious portions of the food in 
 the Echinodermata is entirely accomplished by the veins distributed 
 upon the coats of the digestive cavities, so that the chyle resulting 
 from digestion is at once introduced into the vessels appropriated 
 to circulation. 
 
 In Asterias, the intestinal veins form a fine vascular network, 
 covering the stomach and the ten digestive caeca. The venous 
 trunks derived from all these sources unite to form a circular 
 vessel (Jig. 67, e), which likewise receives branches derived from 
 the ovaria and other sources. 
 
 The circular vein thus formed, which seems to be the common 
 trunk of the venous system, communicates with another vas- 
 cular circle placed around the mouth (s), by means of a dilated 
 
156 ECHINODERMATA. 
 
 vertical tube of communication (/), which, from its muscular ap- 
 pearance and great irritability, Tiedemann regards as being equiva- 
 lent in function to a heart. The circle around the mouth (s) 
 would seem to be arterial in its character ; and from it branches 
 are derived which supply the various viscera of the body. 
 
 But besides the vessels above described, apparently so disposed 
 as to collect and distribute the nutrient fluids, there is another 
 set of canals appropriated to the supply of the numerous vesicles 
 connected with the locomotive suckers ( 190) ; these Tiedemann 
 regards as being totally unconnected with the vascular system 
 properly so called, and considers the fluid contained in them as quite 
 of a different nature. Delle Chiaje, on the contrary, asserts that 
 the two sets of vessels are derived from each other, and describes a 
 peculiar apparatus connected with them as performing an important 
 part in effecting the protrusion of the suckers. 
 
 The circular vessel around the mouth, which forms the central 
 receptacle of the vascular system, resembles a sinus analogous to 
 those of the dura mater in man ; and is lodged in a groove between 
 the oral circle of vertebrae and the pieces of the skeleton articu- 
 lated therewith. Connected with the sinus above mentioned, and 
 placed regularly in the interspaces between the rays, are several 
 oval vesicles (Jig. 67, &, &), filled with a reddish-coloured transpa- 
 rent fluid. These vesicles, which in dsterias aranciaca are seven- 
 teen in number, communicate by distinct ducts with the central 
 sinus, and are regarded by Delle Chiaje as reservoirs in which 
 the nutritive fluids accumulate until expelled by the contraction of 
 the vesicles. Besides the arteries above described as arising from 
 the vascular circle around the mouth, according to the author last 
 mentioned, vessels are given off which communicate with the am- 
 pulls6 connected with the ambulacral suckers, apparently for the 
 purpose of supplying to them the fluid which they contain. These 
 vessels are seen to run along the floor of each ray, and to give off 
 lateral branches communicating with every vesicle, as represented in 
 the enlarged sketch (Jig. 62, 2 g) . By this arrangement it would 
 seem that the contractile organs (Jig. 65, % e.) appended to the 
 vascular sinus f, are in reality antagonists to the tubular structure 
 of the feet, and serve as receptacles for fluid, which, by their con- 
 traction, they can force into the whole system of locomotive suckers 
 whenever the feet are brought into action. 
 
 The above view of the arrangement of the vascular system of 
 Asterias is, however, by no means universally admitted to be cor- 
 
ECHINODERMATA. 157 
 
 rect. Professor Sharpey agrees with Tiedemann in the opinion that 
 the vessels of the feet form a system perfectly distinct from that of 
 the blood-vessels, and even supposes that the fluid by which the 
 ambulacra! tubes become distended is neither more nor less than 
 pure sea-water. 
 
 (196.) Before quitting this part of our subject, we must briefly 
 mention a singular organ, apparently intimately connected with the 
 circular vessel around the mouth, and called by Tiedemann the sand 
 canal. This organ is represented in j#g. 67, enclosed in the same 
 sheath as the dilated vessel (/), upon the right side of which it is 
 placed ; it appears to communicate by one extremity with an isolated 
 calcareous mass of a rounded figure, seen upon the exterior of the 
 dorsal surface of the star-fish, while by its opposite extremity it 
 opens apparently into the circular sinus which surrounds the mouth. 
 The tube itself Dr. Sharpey describes* as being about the thickness 
 of a surgeon's probe, and composed of rings of calcareous substance 
 connected by a membrane, so that viewed externally, it is not unlike 
 the windpipe of a small animal. On cutting it across, it is found to 
 contain two convoluted laminae of the same nature as its calcareous 
 parietes, which are rolled upon themselves in a longitudinal direction 
 in the same manner as the inferior turbinated bones of an ox. The 
 convoluted arrangement becomes more complete towards the upper 
 end of the tube, where the internal laminae, as well as the external 
 articulated portion, join the dorsal disc, appearing gradually to be- 
 come continuous with its substance. The use of this curious organ 
 is quite unknown, although a variety of conjectures have been 
 hazarded upon the subject. The most probable appears to be that 
 of Dr. Sharpey, who suggests that, should the fluid which distends 
 the feet and the vessels connected with them be indeed sea- water, 
 it may be introduced and perhaps again discharged through the 
 pores of the disc by means of the calcareous tube, which will thus 
 serve as a sort of filter to exclude impurities. 
 
 (197.) The Asterias possesses no organs specially appropriated 
 to respiration ; but the sea-water, being freely admitted into the 
 general cavity of the body through a set of minute membranous 
 tubes seen upon the exterior of the animal, bathes all the viscera, 
 and consequently ensures a complete exposure of the circulating 
 fluids to the influence of oxygen, the whole peritoneal surface per- 
 forming the office of a respiratory apparatus. The mechanism by 
 
 * Cyclopaedia of Anatomy and Physiology j art. Echinodermata. 
 
158 ECHINODERMATA. 
 
 which the surrounding element is thus drawn into the body, and 
 the process by which its expulsion is effected, are not accurately 
 known ; nevertheless, apparently with a view to ensure a continual 
 circulation of aerated water through all parts of the system, the 
 entire surface of the membrane which lines the shell, as well as that 
 which forms the external tunic of the digestive organs, has been 
 found to be covered with multitudes of minute cilia, destined by 
 their ceaseless action to produce currents passing over the vascular 
 membranes, and thus to ensure a perpetual supply of oxygenated 
 water to every part.* But it is not only on the peritoneal surfaces 
 that the existence of cilia has been detected, they are found to be 
 extensively distributed over the external surface of the body, within 
 the cavities of the tubular feet, and even over the whole internal 
 lining of the stomach and caeca. 
 
 This amazing apparatus of vibratile cilia must necessarily serve 
 some important purpose in the economy of these creatures ; and 
 Professor Sharpey, to whose observations upon ciliary motion phy- 
 siology is deeply indebted, regards them as being most probably 
 subservient to respiration. 
 
 (198.) The organs belonging to the reproductive system in the 
 Asterida exhibit the greatest possible simplicity of structure : there 
 is no distinction of sex, neither have any parts been discovered in 
 connection with the ovigerous organs, which can be regarded as 
 ministering an accessory secretion. The ovaria (fig. 67, /, /) are 
 slender cseca arranged in bunches around the oasophagus, two -dis- 
 tinct groups being lodged at the origin of each ray. In Asterias 
 aranciaca (fig. 67), the excretory ducts are not easily seen ; but 
 in the twelve-rayed star-fish, especially if examined when these 
 organs are in a gravid state, each ovary may be observed to com- 
 municate externally by a wide aperture, which perforates the osseous 
 circle encompassing the mouth. (Fig. 65, f.) 
 
 (199.) In order to complete the history of the Asterida, we have 
 yet to mention the nervous apparatus with which they are furnished. 
 This consists of a simple circular cord, which runs around the 
 mouth of the animal ; from this ring, three delicate filaments are 
 given off opposite to each ray, one of which, according to Tiede- 
 mann, runs along the centre of the ambulacral groove upon the 
 under surface of the body, and gives minute twigs to the locomo- 
 tive suckers placed on each side of its course ; the other two fila- 
 
 * See the article Cilia by Dr. Sharpey, in the Cyclopaedia of Anatomy and Physiology. 
 
ECHINODERMATA. 159 
 
 ments pass into the visceral cavity, and are probably distributed to 
 the internal organs. There are no ganglia developed on any part 
 of this nervous apparatus ; or at least, if, as some writers assert, 
 ganglionic enlargements are visible at the points whence the ra- 
 diating nerves are given off, they are so extremely minute as not 
 in any degree to merit the appellation of nervous centres. 
 
 (200.) Such an arrangement can only be looked upon as serving 
 to associate the movements performed by the various parts of the 
 animal, for no portion of these simple nervous threads can be re- 
 garded as being peculiarly the seat of sensation or perception. 
 But this inference is not merely deducible from an inspection of 
 the anatomical character of the nerves ; it is based upon actual 
 experiment. We have frequently, when examining these animals 
 in a living state, that is, when with their feet fully developed 
 they were crawling upon the sides of the vessels in which they 
 were confined, cut off with scissars successive portions of the 
 dorsal covering of the body so as to expose the visceral cavity ; but, 
 so far from the rest of the animal appearing to be conscious of the 
 mutilation, not the slightest evidence of suffering was visible : the 
 suckers placed immediately beneath the injured part were inva- 
 riably retracted; but all the rest, even in the same ray, still continued 
 their action, as though perfectly devoid of participation in any 
 suffering caused by the injury inflicted. Such apathy would in- 
 deed seem to be a necessary consequence resulting from the defi- 
 ciency of any central seat of perception, whereunto sensations could 
 be communicated ; nevertheless Ehrenberg insists upon the exist- 
 ence of eyes in some species of star-fish, attributing the function of 
 visual organs to some minute red spots visible at the extremity of 
 each ray, behind each of which he describes the end of the long 
 nerve which runs along the ambulacral groove as expanding into a 
 minute bulb. We must however confess, that the proofs adduced 
 in support of such a view of the nature of these spots, appear to us 
 to be anything but satisfactory; and as we have already stated in 
 the first chapter the physiological objections which may be urged 
 against the possibility of any localised organ of sense being co- 
 existent with a strictly nematoneurose condition of the nervous sys- 
 tem, they need not be repeated here. The general sense of touch in 
 the Asteridse is extremely delicate, serving not only to enable them 
 to seize and secure prey, but even to recognise its presence at some 
 little distance, and thus direct these animals to their food. Any 
 person who has been in the habit of fishing with a line in the 
 
160 
 
 ECHINODERMATA. 
 
 shallow bays frequented by star-fishes, and observed how frequently 
 a bait is taken and devoured by them, will be disposed to admit 
 this; yet to what are we to attribute this power of perceiving exter- 
 nal objects ? It would seem most probably due to some modifi- 
 cation of the general sensibility of the body, allowing of the per- 
 ception of impressions in some degree allied to the sense of smell 
 in higher animals, and related in character to the kind of sensation 
 by which we have already seen the Actiniae and other polyps 
 able to appreciate the presence of light, although absolutely de- 
 prived of visual organs. 
 
 (SOI.) The ECHINI, however they may appear to differ in out- 
 ward form from the Asteridoe, will be found to present so many points 
 of resemblance in their general structure, that the detailed account we 
 have given above, of the organization of the last-mentioned family, 
 will throw considerable light upon the still more elaborately con- 
 structed animals which now present themselves to our notice. 
 
 The Echinida, as we have already observed, differ from the 
 star-shaped Echinodermata in the nature of the integument which 
 encloses their visceral cavity, as well as in the more or less circular 
 or spherical form of their bodies ; so that the locomotive apparatus 
 with which they are furnished is necessarily modified in its cha- 
 racter and arrangement. 
 
 The shell of an Echinus (Jig. 68, 1) is composed of innu- 
 
EOHINODERMATA. 
 
 161 
 
 merable pieces accurately joined together, so as to form a globular 
 box enclosing the internal parts of the animal, but perforated at 
 each extremity of its axis by two large openings, one of which 
 represents the mouth, and the other the anus. 
 
 The calcareous plates entering into the composition of this ex- 
 traordinary shell may be divided into two distinct sets, which differ 
 materially in size, as well as in the uses to which they are subser- 
 vient. The larger pieces are recognisable in the figure by hemisphe- 
 rical tubercles of considerable size attached to their external surface, 
 adapted, as we shall afterwards see, to articulate with the moveable 
 locomotive spines. Each of these larger plates has somewhat of a 
 pentagonal form; those which are situated in the neighbourhood of 
 the mouth and anal aperture being considerably the smallest, and 
 every succeeding plate becoming progressively larger as they ap- 
 proximate the central portion of the shell : the entire series of 
 pieces in each row resembles in figure the shape of the space 
 included between two of the lines which mark the degrees of lon- 
 gitude on a terrestrial globe, broad at the equator, but gradually 
 narrowing as it approaches the poles ; an arrangement, of course, 
 rendered necessary by the spherical form of the creature. There 
 are ten rows of these tuberculated plates ; but as they are disposed 
 in pairs, each row of large pieces being united by a zig-zag suture 
 with another of a similar description, there are in reality only five 
 large segments of the shell, each supporting a double row of 
 tubercles. 
 
 The reader must not, however, conclude that the great central 
 tubercles above mentioned are the only parts of the shell to which 
 spines are affixed ; hundreds of smaller elevations are disseminated 
 over the surface, to which smaller spiculae are appended, although, 
 from their diminutive size, these are of secondary importance in 
 locomotion. 
 
 The five large double segments which thus form the greater por- 
 tion of the calcareous shell are separated from each other by the 
 interposition of ten rows of perforated plates, likewise disposed in 
 pairs, and composed of much smaller pieces than those which sup- 
 port the tubercles ; hundreds of foramina, which pierce these ambu- 
 lacral bands, give passage to as many tubular feet or protrusible 
 suckers, in every respect resembling those of Asterias, and dis- 
 tended by a similar apparatus. 
 
 It is impossible by any verbal description, at all commensurate 
 with the limits of our present undertaking, adequately to explain 
 
 M 
 
162 ECHINODERMATA. 
 
 the more minute contrivances visible in the disposition of every 
 portion of these wonderfully constructed coverings : it is sufficient 
 for our present purpose to observe that the globular crust of an 
 Echinus is made up of several hundred polygonal pieces of 
 different sizes, and, although presenting every variety of outline, 
 generally approximating more or less to a pentagonal form ; that 
 these pieces are so accurately and completely fitted to each other, 
 that the lines which unite them are scarcely to be distinguished 
 even upon the most minute examination ; and that from the union 
 of so many distinct and dissimilar plates results a firm, compact, and 
 beautiful box, similar to that represented in the figure. The first 
 question which naturally suggests itself on examining a shell of this 
 description, is concerning the object to be attained by such remark- 
 able complexity ; it would appear indeed, at first sight, that a simple 
 calcareous crust, had it been allowed to exude from the entire sur- 
 face of the Echinus, would gradually have moulded itself upon the 
 body of the creature, and thus have formed a globular shell with- 
 out suture, but answering every purpose connected either with 
 support or defence. 
 
 (203.) A very little investigation, however, will suffice to show the 
 necessity for the elaborate arrangement to which we have alluded. 
 In the first place, as we shall immediately see, the earthy matter is 
 not deposited upon the surface of the body, but within the soft 
 external integument by which it is secreted ; the interior of the 
 shell being filled with sea-water, in which the viscera are loosely 
 suspended. But a second and more important reason for the em- 
 ployment of so many pieces in the construction of the shell of an 
 Echinus is to be derived from examining the mode in which the 
 animal grows ; was it to retain the same dimensions throughout the 
 whole period of its life, or could it at stated intervals cast off its 
 old investment, and secrete a new and more capacious covering, as 
 growth rendered the change necessary, a simple earthy crust would 
 have been sufficient, without the presence of such an immense 
 number of sutures and joinings. The calcareous plates of the 
 Echinus, it must be remembered, are merely secreted from the 
 soft parts, having no vital action going on within them, by which, 
 as in the bones forming the skeletons of vertebrate animals, a con- 
 tinual deposition of fresh particles could be effected, allowing of 
 extension by interstitial deposit. How, therefore, could the growth 
 of the animal be provided for ? How is the gradual expansion of 
 the entire shell, thus composed of a dense and extravascular crust, 
 
ECHINODERMATA. 163 
 
 to be effected ; and that without ever deranging the proportions of 
 the whole fabric, or necessitating a loosening of its parts ? No 
 other contrivance could apparently have been adequate to the pur- 
 pose : nevertheless, by the structure adopted, we see how admirably 
 the growth of Echinus proceeds in all directions; for the living and 
 vascular membrane which covers the whole external surface of the 
 body dips down between the edges of the various calcareous pieces, 
 and continually deposits around the margin of each, successive 
 layers of earthy particles, which, assuming a semi-crystalline ar- 
 rangement, progressively increase the dimensions of each individual 
 plate. But the continual augmentation in size, which is thus 
 going on, is attended with no change in the mathematical figure of 
 any given piece of the skeleton ; so that, as they all increase in 
 diameter by the unceasing deposition of earthy matter around the 
 circumference of every plate, the spherical shell gradually expands, 
 without in any degree altering its form or relative proportions, 
 until it has acquired the mature dimensions belonging to its 
 species. 
 
 (204.) The tubular suckers or retractile feet, which are pro- 
 truded at the pleasure of the animal from the countless minute 
 apertures seen in the ten rows of ambulacral plates, are so similar 
 in all essential points to those of Asterias already described, 
 that little further need be said concerning their structure, or the 
 mechanism by which their motions are effected. The tubular part 
 of each foot communicates with the interior of the shell by two 
 branches which pass through two apertures, and these branches in 
 some species (as Echinus saxatilis) receive offsets from the ves- 
 sels which run along the centre of each ambulacral groove, and 
 convey to the feet the fluid by which their distension is effected. 
 In Echinus esculentus the feet open into a plexus of vessels, 
 formed in leaf-like membranes, equal in number with the feet, and 
 disposed in double rows upon the inner surface of the ambulacral 
 pieces,* by the intervention of which they are connected with the 
 canals above mentioned. 
 
 (205.) The tubercles upon the external surface of the shell of 
 the Echini support a corresponding number of long spines, which, 
 as well as the apparatus of suckers, are employed as locomotive 
 agents. These spines vary materially in their form and propor- 
 tionate size, and even in their internal structure and mode of 
 
 * Cyclopaedia of Anat. and Phys. art. ECHINODERMATA. 
 
 M 9 
 
 M /< 
 
164 ECHINODERMATA. 
 
 growth, as may be readily seen by a comparison of different 
 species. Thus, in the flattened forms of Scutella and allied 
 genera, they are so minute as to require the employment of a mi- 
 croscope for their investigation ; in Echinus esculentus (Jig. 62) 
 they are sharp, and almost of equal length over the entire surface 
 of the animal; while in the specimen represented in the an- 
 nexed figure (Jig. 69), the shell of which we have already 
 
 Fig. 69. 
 
 examined when divested of these appendages, the length of the 
 spines which are articulated upon the large tubercular plates fully 
 equals the transverse diameter of the body of the creature, and in 
 some cases they are even found much more largely developed. 
 Every spine, examined separately, is seen to be united with the 
 tubercle upon which it is placed by an apparatus of muscular and 
 ligamentous bands, forming a kind of ball-and-socket joint, allow- 
 ing of a considerable extent of motion. In^/zg. 68, 2, the structure 
 of this articulation is exhibited. The large tubercle (a) supports 
 upon its apex a smaller rounded and polished eminence, perforated 
 in the centre by a deep depression : the bottom of the spine, 
 moreover, (c) is terminated by a smooth hemispherical cavity 
 accurately fitted to the projecting tubercle, so that the two form 
 complete articular surfaces. The bonds of union connecting the 
 spine with the shell are of two kinds : in the first place, there is a 
 stout ligament (a, c), extending from the little pit seen upon 
 the centre of the tubercle, to a corresponding depression visible 
 upon the articular surface of the spine, resembling very accurately 
 
ECHINODERMATA. 165 
 
 the round ligament found in the hip-joint, and obviously a provi- 
 sion for the prevention of dislocation. 
 
 The whole joint is moreover enclosed in a muscular capsule, 
 composed of longitudinal fibres (b, b) arising from the circum- 
 ference of each tubercle, and inserted all around the root of the 
 spine : these fibres therefore, which must in fact be regarded as 
 merely derived from the general irritable skin that clothes the shell 
 externally, are the agents which, acting immediately upon the 
 spine, produce all the movements of which it is capable. 
 
 (206.) The next thing to be accounted for in the history of 
 these elaborately constructed animals is the growth of the spines 
 themselves, which, as we have already seen, are completely 
 detached from the rest of the shell, to which they are only 
 secured by the central ligament, and by the muscular capsule 
 enclosing their base. To account, therefore, for the production 
 of organs so completely insulated as the spines appear to be, 
 especially when we consider that there is no vascular communi- 
 cation between them and the body of the Echinus, would appear 
 to be a matter of some difficulty; and in fact r had we not already 
 seen in the polyps the amazing facility with which calcareous 
 matter was secreted by the living textures of those animals, ifc 
 would be almost impossible to conceive by what process their 
 growth was effected. On examining one of these appendages, taken 
 from a species in which they are largely developed, when fresh, 
 before its parts have become dry, every portion of its surface is 
 seen to be invested with a thin coat of soft membrane, derived 
 from that which covers and secretes the whole shell, of which 
 indeed the muscular capsule enclosing its articulation with the 
 tubercle is only a thickened portion. 
 
 The living covering of the spine therefore, like the crust which 
 invests the cortical polyps, is the secreting organ provided for its 
 growth, depositing the earthy particles separated from the waters of 
 the ocean, layer after layer, upon its outer surface, so as to form a 
 succession of concentric laminae, of which the outer one is always 
 the^last formed. The calcareous matter thus deposited has more 
 or less completely a crystallized appearance ; and on a transverse 
 section of the organ being made, and the surface polished by 
 grinding, the whole process of its formation is at once rendered 
 evident. Such sections, indeed, form extremely beautiful and 
 interesting subjects for microscopical examination, as nothing can 
 exceed the minute accuracy and mathematical precision with which 
 
166 ECHINODERMATA. 
 
 each particle of every layer composing them appears to have been 
 deposited in its proper place : indeed, if the zootomist would fully 
 appreciate the minuter details connected with their organization, 
 it is only by the employment of the microscope that he will 
 arrive at adequate ideas concerning them ; for it is not in the num- 
 ber and variety of the pieces entering into the composition of the 
 skeleton of one of these animals, the extraordinary apparatus of 
 prehensile suckers with which they are furnished, or the singular 
 locomotive spines upon the exterior of the shell, that he will find the 
 most remarkable features of the history of the Echini ; it is only by 
 a minute examination of the intimate structure of each of these 
 parts that the mechanism conspicuous throughout can be properly 
 understood. 
 
 (207.) The calcareous pieces which surround the mouth of the 
 Echinus are not so immoveably consolidated as those composing the 
 rest of the shell, but, on the contrary, admit of considerable move- 
 ment, by which the prehension of food is more easily effected. The 
 mouth itself (Jig- 68, 1) is a simple orifice, through which the 
 points of five sharp teeth are seen to protrude. These teeth 
 obviously perform the office of incisors, and, from their sharpness 
 and extreme density, are well calculated to break the hard sub- 
 stances usually employed as food. The points of such incisor 
 teeth, although of enamel-like hardness, would nevertheless be 
 speedily worn away by the constant attrition to which they are 
 necessarily subjected, was there not some provision made to ensure 
 their perpetual renewal ; like the incisor teeth of rodent quadrupeds, 
 they are therefore continually growing, and are thus always pre- 
 served sharp and fit for use. In order to allow of such an arrange- 
 ment, as well as to provide for the movements of the teeth, jaws 
 are provided, which are situated in the interior of the shell ; and 
 these jaws, from their great complexity and unique structure, form 
 perhaps the most admirable masticating apparatus met with in the 
 whole animal kingdom ; we must therefore entreat the patience of 
 our readers while we describe at some length the parts connected 
 therewith. The entire apparatus removed from the shell is repre- 
 sented in (Jig. 70), and consists of the following parts : There are 
 five long teeth, (c, c,) each of which is enclosed in a triangular os- 
 seous piece, (a, a,) that for the sake of brevity we will call the jaws. 
 The five jaws are united to each other by various muscles, 
 (&, &, i, i 9 ) so as to form a pentagonal pyramid, having its apex 
 in contact with the oral orifice of the shell, while its base is con- 
 
ECHINODERMATA. 
 
 167 
 
 nected with several bony levers, by means of numerous mus- 
 cles provided for the movements of the whole. These parts we 
 must now proceed to describe seriatim. The teeth (fig. 71, a) 
 resemble, at the part protruded from the mouth, long three- 
 
 sided prisms, and at this point they are extremely hard and brit- 
 tle : each tooth is fixed in a socket passing through the jaw, 
 (fig. 71, e,) from which it projects by its opposite extremity, 
 (fig. 71, a',) that may be called the root of the tooth, where, instead 
 of being of glassy hardness like the point (a) which issues from the 
 mouth, it is flexible and soft, resembling fibres of asbestos, and 
 is covered by a membrane apparently connected with its secretion. 
 The jaws, which thus support and partially enclose these teeth, are 
 five in number : when examined separately, each is found to 
 resemble in figure a triangular pyramid, the external surface 
 (fig. 71, e,) being smooth, and presenting eminences provided 
 for the attachment of muscles ; while the other two sides 
 (fig. 71, b, b^ are flat, and marked with transverse grooves, 
 so as to have the appearance of a fine file. When the five jaws 
 are fixed together in their natural positions, they form a five- 
 sided conical mass, aptly enough compared by Aristotle to a 
 lantern, and frequently described by modern writers under the 
 name of the " lantern of Aristotle." When thus fitted to 
 each other, the two flat and striated sides of each jaw are in 
 apposition with the corresponding surfaces of two others, so that 
 
168 
 
 ECHINODERMATA. 
 
 there are ten grinding surfaces formed, between which the food 
 must pass preparatory to its introduction into the digestive canal. 
 This arrangement will be easily understood by referring to 
 
 a 
 
 m l 
 
 Jig. 71, 1, in which three of these jaws, each containing its in- 
 cisor tooth, are represented in situ, the two others having been 
 removed. 
 
 The five curious jaws described above are fixed together by a 
 set of muscles, (Jig. 70, &, A:,) consisting of short fibres passing 
 between the external edges of the -contiguous segments of the 
 lantern, and evidently capable of powerfully approximating the 
 grinding surfaces and rubbing them upon each other. The jaws, 
 moreover, are provided with five other osseous pieces (rf, d,) 
 arranged in a radiating manner between the bases of the different 
 segments, with which they are connected by ligaments, and like- 
 wise by the pentagonal muscle (z, i,) which runs from one to 
 the other. 
 
 The above described parts complete the apparatus required for 
 connecting the different portions of this remarkable mouth, but 
 the movements of the whole are effected by a very complicated set 
 of levers and muscles which must next be noticed. 
 
 The levers attached to the jaws are five long and slender pro- 
 cesses, (Jig. 71, 1 d, d,) each arising from the central extremity of 
 one of the radiating osseous pieces, (c, c,) and arching outwards con- 
 siderably beyond the base of the lantern, to terminate by a forked 
 extremity. But there are likewise other processes projecting from 
 the inner surface of the shell ; these, two of which are seen in 
 (Jig. 70, 6, ,) are also five in number, and are placed around the 
 orifice of the mouth : they are generally perforated in the centre, 
 
ECHINODERMATA. 169 
 
 so as to resemble so many bony arches ; and from them, as well as 
 from the spaces which separate them, numerous muscles derive 
 their origin. Of these muscles, ten (/>/->) arise from the spaces 
 between the arches, two being inserted into the outer edge of the base 
 of each jaw ; so that the effect produced by their contraction, when 
 they all act in concert, will be to approximate the whole mass of 
 the mouth to the oral aperture of the shell, and of course cause 
 the points of the incisor teeth to protrude externally ; or, if they 
 act separately, they can draw the base of the lantern in any di- 
 rection, or cause the grinding surfaces of the jaws to work against 
 each other. 
 
 The antagonists to the muscles last mentioned are ten others, 
 (> >) arising from the extremities of the arches themselves, and 
 running in a radiating manner towards the apex of the lantern, so 
 that the point of each piece or jaw receives a muscle from two of 
 those processes. These fasciculi, from the manner in which the 
 arches project into the cavity of the shell, will draw inwards the 
 entire mass ; or, if they act separately upon the jaws to which they 
 are individually fixed, they will produce movements precisely op- 
 posite to those caused by the contractions of the muscles derived 
 from the spaces between the bony processes ; or, if both sets should 
 act in concert, they become the antagonists of the muscles (i,i,k, &,) 
 which connect the jaws to each other, and by causing the separa- 
 tion of the different pieces they necessarily enlarge, not only the 
 opening of the mouth, but all the passage leading to the oesopha- 
 gus through the axis of the lantern. 
 
 Yet even these are not all the muscles which act upon the 
 masticating apparatus ; ten others, (A, A,) arising in pairs from the 
 middle of the interspaces between the arches, are connected with 
 the bifurcated extremities of the slender curved processes, (e, e,) 
 each of which receives a muscle from two contiguous spaces ; and, 
 from the length of the levers upon which these muscles act, we 
 may well conceive the force with which they will influence the 
 motions of the whole mass of the jaws. 
 
 Such is the complex structure of the mouth of Echinus escu- 
 lentus ; a piece of mechanism not less remarkable on account of the 
 singularity of its construction, than as exhibiting an example of 
 the sudden developement of a dental system, of which not a 
 vestige is visible in any other of the Echinoderm families. In 
 others of the Echinida having the shell much depressed, the 
 dental lantern is modified in form, and proportionately flattened, 
 
170 
 
 ECHINODERMATA. 
 
 Fig. 72. 
 
 but the different parts are essentially similar to those we have 
 described. 
 
 (208.) The oesophagus (Jig. 72, d,) is continued from the termi- 
 nation of the central canal, which traverses the axis of the lantern, 
 and after a short course termi- 
 nates in a much wider portion 
 of the digestive tube, into which 
 it opens on the lateral part of 
 its csecal origin in a manner 
 precisely resembling the com- 
 munication between the large 
 and small intestines of man. 
 
 The dilated alimentary tube, 
 (c,) which presents no separa- 
 tion into stomach and intestine, 
 is continued in a winding 
 course around the interior of the 
 shell, which it twice encircles, 
 and, becoming slightly con- 
 stricted, terminates at the anal 
 orifice of the shell (z). The 
 walls of the intestine are ex- 
 tremely delicate ; although they 
 may be distinctly seen to con- 
 tain muscular fibres, and are 
 covered with innumerable vas- 
 cular ramifications. The external tunic of the whole canal is de- 
 rived from the peritoneum, which lines the entire shell, invests the 
 dental lantern, and forms sundry mesenteric folds as it is reflected 
 upon the other viscera. 
 
 (209.) The system of vessels provided for the circulation of the 
 blood has been differently described by different authors, a circum- 
 stance by no means surprising when we consider the great difficulty 
 of tracing such delicate and extensively distributed canals. Ac- 
 cording to Delle Chiaje, the course of the nutritious fluid is as 
 follows. A large vein runs along the whole length of the intes- 
 tine, from the anus to the oesophagus, where it terminates in a 
 vascular ring surrounding the mouth ; into which, as in Asterias, 
 the contractile vesicle, which he considers to be a receptacle for 
 the nutrient fluid, and the antagonist to the tubular x feet, like- 
 wise opens. The intestinal vein he regards as the great agent 
 
ECHINODERMATA. 171 
 
 in absorbing nourishment from the intestine, and conveying it 
 to the vascular circle around the oesophagus, from which the 
 arteries are given off to supply the whole body. These arte- 
 ries are, 1st, a long vessel to the intestine, which runs along 
 its whole length, and anastomoses freely with the branches 
 of the intestinal vein. Sndly, Five arteries to the parts con- 
 nected with the mouth. Srdly, Five dorsal arteries which run 
 along the interior of the shell, between the ambulacral rows 
 as far as the anal orifice, at which point each dorsal artery leaves 
 the osseous box, through an aperture specially provided for its 
 exit, and, arriving upon the outer surface of the shell, supplies 
 the soft external membrane, and in some species may be traced 
 back again between the rows of ambulacral suckers as far as the 
 mouth. These dorsal arteries, like the corresponding vessels in Aste- 
 rias, supply the vascular origins of the innumerable protractile feet. 
 
 (210.) We found in the star-fish that respiration was provided for 
 by the free admission of the external element into the interior of the 
 body ; and in Echinus the aeration of the blood is effected in an 
 equally simple manner. The sea-water is copiously admitted into 
 the peritoneal cavity by a set of membranous tubes provided for 
 the purpose ; and its due circulation over the lining membrane of 
 the shell, as well as over the outer surfaces of the intestine and 
 other viscera, is provided for by ciliary movements visible in all 
 those situations, and likewise upon the vascular laminae connected 
 with the origins of the feet.* 
 
 Nevertheless, besides this diffused respiration, Delle Chiaje re- 
 gards a series of pinnated tentacula in the neighbourhood of the 
 mouth as being in some degree capable of performing the office of 
 branchiae. These organs, which are protruded through a row of dis- 
 tinct orifices placed around the oral aperture of the shell, are emi- 
 nently vascular ; and as they present a large surface to the action of 
 the water, and receive numerous vessels from the circular vessel 
 which surrounds the mouth, they may no doubt very well contri- 
 bute to the complete exposure of the blood to the influence of the 
 surrounding medium. 
 
 (211.) Little is known concerning the nervous system of the 
 Echini : a few delicate filaments have been observed in the neigh- 
 bourhood of the oesophagus, apparently of a nervous character, 
 which renders it probable that a nervous ring is placed in that vici- 
 nity, resembling that already described in Asterias ; its presence, 
 
 * Dr. Sharpey, loc. cit. 
 
172 ECHINODERMATA. 
 
 however, owing to the complexity of the dental apparatus, has not 
 been satisfactorily demonstrated, although analogy would lead us 
 to infer the existence of such an arrangement. 
 
 (21 2.) The Echini, like the star-fishes, exhibit no distinctions of 
 sex : all are fertile, and in the structure of their reproductive organs, 
 display, if possible, greater simplicity of arrangement than even the 
 Asteridce above described. The ovaria are five delicate mem- 
 branous bags, quite distinct from each other, which open exter- 
 nally by as many delicate tubes, or oviducts, as we may term them. 
 The apertures through which the eggs escape are easily seen upon 
 the outer surface of the shell, placed around the anus ; and are re- 
 cognisable not merely by their size, but from the circumstance of 
 each perforation being placed in the middle of a distinct oval 
 plate of the shell, distinguished by zoological writers as the ova- 
 rian pieces. The membranous sacs in which the ova are secreted 
 vary in size, in proportion to the maturity of the eggs contained 
 within them, and at certain times of the year are enormously dis- 
 tended : it is in this state that the " roe of the sea-egg," as the 
 ovaria are commonly called, is used as an article of food ; and in 
 some countries, especially upon the shores of the Mediterranean, 
 they are eagerly sought after, when in season, by divers employed 
 to procure them. 
 
 (213.) Holothuridce. The name applied by naturalists to the 
 animals composing the next family of Echinodermata is derived 
 from a Greek word of uncertain application (oAo0oup*ov). In 
 common language they are generally known by the appellation 
 of " sea-cucumbers ;" and in fact, to a casual observer, the resem- 
 blance which they bear to those productions of the vegetable 
 kingdom, both in shape and general appearance, is sufficiently 
 striking. The surface of these animals is kept moist by a 
 mucus, which continually exudes through innumerable pores, 
 and appears to be secreted by minute follicles imbedded in the 
 substance of the skin. The integument which covers, or rather 
 forms the body, is entirely destitute of those calcareous pieces 
 which encase the Echini and Star-fishes ; but appears to consist of a 
 dense fibrous cutis of considerable thickness, covered externally 
 with a thin epidermic layer. Beneath the cutis is another tunic com- 
 posed of strata of tendinous fibres crossing each other in the midst of 
 a tissue of a semicartilaginous nature, which is capable of very great 
 distension and contraction, and serves by its elasticity to retain the 
 shape of the body. Within this dense covering are seen muscular 
 
ECHINODERMATA. 
 
 173 
 
 Fig. 73. 
 
 bands running in different directions, which by their contraction 
 give rise to the various movements of the creature ; of these muscle 
 five strong fasciculi 
 assume a longitu- 
 dinal course, pass- 
 ing along the entire 
 length of the ani- 
 mal from the mouth 
 to the cloaca, and 
 in the interspaces 
 between these cir- 
 cular and oblique 
 muscles are readi- 
 ly distinguishable. 
 The whole of this 
 muscular case is 
 lined with a deli- 
 cate membrane or 
 peritoneum, from 
 which processes 
 pass inwards, to 
 support the various 
 viscera. 
 
 (214.) But al- 
 though the calca- 
 reous shell of the 
 Echinus is thus to- 
 tally lost, the lo- 
 comotive suckers or 
 feet already de- 
 scribed are still 
 the principal agents employed in progression. In many species, 
 as in that represented in the annexed figure, (Jig. 73,) these organs 
 are distributed over the whole surface of the animal, and are pro- 
 truded through countless minute orifices which perforate the in- 
 tegument. In other cases, as in H. frondosa, they are arranged 
 in five series, resembling the ambulacra of an Echinus ; and in some 
 instances they are only found upon the middle of the ventral sur- 
 face of the body, that forms a flattened disc upon which the ani- 
 mal creeps, somewhat in the manner of a snail. The ambulacral 
 feet themselves, represented on an enlarged scale at (c), pre- 
 
174 ECHIXODERMATA. 
 
 cisely resemble in all the details of their structure those of the 
 Asterias, and their protrusion and retraction are effected in the 
 same manner ; but, in addition to these organs, we find in some 
 genera moveable hooks or spines (Jig. 73, d,) which are likewise 
 retractile, and most probably assist in locomotion. 
 
 (SI 5.) The mouth is a round aperture, as wide as a goose-quill, 
 placed in the centre of a raised ring at the anterior extremity of 
 the body (Jig. 73, a). Around the, oral orifice is placed a circle of 
 tentacula, which are apparently extremely sensible, and serve per- 
 haps not only as instruments of touch, but as prehensile organs 
 used for the capture of prey, or for assisting in deglutition. 
 When the sphincter muscle which closes the mouth contracts, the 
 tentacles are withdrawn, and become no longer visible externally ; 
 in this state, on opening the animal (Jig- 74, &,) they are found 
 to resemble long caeca appended to the commencement of the 
 oesophagus, which have been described by some authors as forming 
 a salivary apparatus. 
 
 The total deficiency of any external skeleton, or calcareous frame- 
 work, precludes, of course, the possibility of the existence of any 
 complex dental apparatus resembling the " lantern of Aristotle ;" 
 the only vestige of the complex teeth of the Echinidse which here 
 remains is a small circle of calcareous pieces, surrounding the opening 
 of the mouth : these plates, from their extreme friability, have been 
 aptly enough likened to laminae of dried paste ; they may indeed 
 in some slight degree be efficient in bruising food taken into the 
 mouth, but it is more probable that they merely form points of 
 insertion to the longitudinal muscles of the body, which, thus fixed 
 around the circumference of the oral orifice, will by their contrac- 
 tion powerfully dilate that aperture for the purpose of taking in 
 nourishment. 
 
 The alimentary canal is of great length, but, like that of the 
 Echinus, presents no stomachal dilatation ; from the mouth, 
 (Jig. 74, a,) in which a bristle is placed, it descends to the anal 
 extremity of the body, where, turning upon itself, it again mounts 
 up towards its commencement, whence turning back again, and 
 forming numerous convolutions, (d, d, rf,) it once more passes 
 backwards, and, becoming restricted near its termination, opens 
 into a large membranous cavity (e) which may be called the 
 cloaca. Throughout the whole of this long course, the alimentary 
 tube is surrounded with a membrane derived from the peritoneal 
 lining of the visceral cavity, which forms delicate mesenteric folds 
 connecting it to the walls of the body, and supporting it through 
 
ECHINODERMATA. 
 
 175 
 
 its entire length. The whole intestine is generally found distended 
 with sand, in which may be detected the debris of corals, algse, 
 fuci, and other marine substances. 
 
 (216.) In the structure of the respiratory apparatus, the Holothu- 
 ridse differ materially from the rest of the Echinodermata, and in 
 fact from all other animals. In the Asterida and Echinida, the 
 reader will remember that respiration was effected by the free 
 admission of sea-water into the interior of the animal, which, thus 
 penetrating to every part of the body, rendered the existence of 
 special respiratory organs unnecessary. In the Holothuria like- 
 wise the aeration of the circulating fluid is provided for by allow- 
 ing the surrounding element freely to enter into the internal parts 
 of the creature ; but in this case, instead of bathing the surfaces of 
 the viscera, the water is confined in a peculiar system of ramifying 
 canals, forming a structure of great beauty, and, from its singularity, 
 extremely interesting in a physiological point of view. We have 
 seen that the intestinal canal terminates in a membranous recep- 
 tacle or cloaca {Jig. 74, e,) contained within the cavity of the 
 
 Fig. 74. 
 
176 ECHINODERMATA, 
 
 abdomen, to the walls of which it is attached by delicate fleshy 
 bands : this cloacal cavity communicates with the exterior 'of the 
 body by a wide orifice twice as large as the aperture of the mouth, 
 through which, in the figure, a bristle (f) has been passed ; it is 
 by this hole that the water required for the purpose of respiration 
 is taken in, and it is then forced by the muscular walls of the cloaca 
 itself through the whole system of respiratory canals by which its 
 distribution is effected. The organs of respiration commence at 
 the upper part of the cloaca, near the termination of the intes- 
 tine, by a large opening leading to a wide membranous tube, which 
 immediately divides into two vessels (g, g,) forming the main 
 trunks of the beautiful arborescent branchiae, which extend to the 
 opposite extremity of the body, giving off in their course numerous 
 lateral branches that divide and subdivide, so as to form what has 
 been not inaptly termed the " respiratory tree," until they ulti- 
 mately terminate in minute vesicular caeca, into which the water 
 derived from the cloaca of course penetrates. One division of this 
 elegant apparatus is maintained in close contact with the walls of 
 the body by a series of delicate tendinous bands, while the other 
 becomes applied to the convolutions of the intestines, with which 
 it is likewise united. It is this last-mentioned division which 
 would appear to be specially provided for the oxygenization of 
 the nutritive fluids taken up by the intestinal veins. 
 
 (217.) The circulation of the blood in the Holothuria, as in 
 the Echinus, is still but imperfectly understood, and considerable 
 difference of opinion upon this subject will be found in the 
 writings of anatomists. According to Tiedemann,* innumerable 
 small veins collect the blood and nutritive products of diges- 
 tion from the intestine, and convey them into a large central 
 vessel, (Jig. 74, i, i,) from whence the circulating fluid passes 
 by other trunks (/, /,) to the respiratory tree ; hence it is re- 
 turned by vessels (partly represented at m) to the intestinal 
 artery (k) 9 by which it is again distributed over the intestinal 
 parietes. 
 
 Delle Chiaje gives a different account of the arrangement of 
 the vascular system in these creatures, which he seems to have 
 investigated with his usual untiring perseverance. According to 
 the last-mentioned anatomist, the blood is taken up from the in- 
 testines by a complicated system of veins, the main trunks of which 
 
 * Anat. der Rohren, Holothuriej fol. 1816. 
 
ECHINODERMATA. 
 
 177 
 
 are indicated in the annexed diagram {fig. 75) by the letters 
 c, e, p, p, </, q ; these communicate with each other not only by 
 the intervention of numerous Fig. 75. 
 
 anastomosing branches, (d, d,) 
 but likewise by means of de- 
 licate vascular plexuses (a) 
 passing between them. All 
 these veins terminate in two 
 large venous canals (o), which 
 convey the blood and nutri- 
 ment absorbed from the in- 
 testine to a vascular circle 
 (g) 9 placed around the com- 
 mencement of the oesopha- 
 gus, which corresponds with 
 the circular vessel around 
 the mouth of the Echinus. 
 This circle Delle Chiaje re- 
 gards as the centre of the 
 arterial system, in communi- 
 cation with which is the con- 
 tractile vesicle (/), which he 
 looks upon as a reservoir for 
 the nutritive fluid. From the circular vessel various arteries are 
 given off; large branches pass into the tentacula around the 
 mouth (z), so that these organs, besides being instruments of touch, 
 from the extent of surface that they present, and their great vas- 
 cularity, are most probably important auxiliaries in respiration. 
 Five other large arteries, derived from the same source, (&, fc, /,) 
 pass backwards to supply the integuments of the body, and also to 
 communicate by small cross branches with the little vesicular 
 organs connected with the locomotive suckers, which in the 
 opinion of Delle Chiaje are distended with the same blood as 
 that which circulates through the rest of the body. The descend- 
 ing arteries, thus destined to supply the integument and distend 
 the prehensile suckers, run in the centre of each of the five lon- 
 gitudinal fasciculi of the muscular tunic of the skin as far as the 
 cloaca, and exhibit in their distribution a remarkable exception to 
 the usual arrangement of the arterial system, which is generally 
 found to divide and subdivide continually into smaller and still 
 smaller canals, but, in the case before us, there would seem to be 
 
 N 
 
178 ECHINODERMATA. 
 
 no diminution in the size of the main trunks as they approach 
 their termination ; and the cross branches given off in their course, 
 instead of ramifying, all end in the minute ambulacral vesicles, to 
 the injection of which they would appear to be subservient. 
 
 (218.) The generative system of the Holothuria is essentially 
 similar to that found in the Asteridse, consisting of long ovigerous 
 caeca, without any superadded parts which might be regarded as con- 
 tributing to the impregnation of the ova. The germs are secreted 
 in slender ramified tubes (Jig. 74, A, h,) which are collected into 
 one great bundle, and open externally by a common canal in the 
 neighbourhood of the mouth, not into the oesophagus as Cuvier 
 supposed, but upon the back of the animal. These generative 
 cseca at certain times of the year become enormously distended, 
 being at least thirty times larger than when not in a gravid state ; 
 if examined at this period, they are found to contain a whitish, 
 yellowish, or reddish fluid, in which the ova are suspended, but 
 nothing is known concerning the mode of the expulsion of the 
 eggs, or their subsequent developement. 
 
 (219.) The special instruments of touch, the only sense allotted 
 to these animals, are the branched tentacula around the mouth, 
 which seem by far the most irritable parts of the body. The 
 nervous system is so obscurely developed that even Delle Chiaje 
 was unable to detect any traces of its existence ; nevertheless 
 there is little doubt of the presence of nervous threads in the 
 muscular envelope of the animal, although, from the dense tissues 
 in which they are imbedded, it is next to impossible to display their 
 course ; most probably, as in the Echinus and Asterias, these com- 
 municate with a circular cord which embraces the oesophagus. No 
 ganglia have as yet been discovered even in the Holothuria ; and 
 consequently, although the muscular actions of the body are no 
 doubt associated by nervous filaments, the movements of these 
 creatures appear due rather to the inherent irritability of the 
 muscular tissues themselves, than to be under the guidance and 
 control of the animal. In many species, the slightest irritation 
 applied to the surface of the body causes such powerful contrac- 
 tions of the integument that the thin membranes of the cloaca, 
 unable to withstand the pressure, become lacerated, and large 
 portions of the intestine and other viscera are forced from the anal 
 aperture. So common indeed is the occurrence of this circum- 
 stance as to have induced the older anatomists to suppose that, by 
 a natural instinct, the animals when seized vomited their own 
 
ECTIINODEIIMATA. 179 
 
 bowels. It is in fact extremely difficult to obtain perfect speci- 
 mens of tlie Holothuridse, from the constant occurrence of this ac- 
 cident : but, although annoying to the naturalist, such a pheno- 
 menon affords the physiologist an important lesson, teaching that 
 here, as in the lower Zoophytes, the muscular system possesses an 
 innate contractile power, which would seem only to be destroyed 
 by incipient putrefaction ; but so little is this contractility under 
 command, that, once excited to an inordinate extent, it becomes 
 totally unmanageable, even though its continuance inevitably causes 
 the destruction of life. 
 
 (220.) Fistularida. In order to complete our account of the 
 organization of the Echinodermata, we have still to investigate the 
 structure of the Fistularid<z ; a group which, from the external 
 appearance of the individuals composing it, and the total absence of 
 the tubular feet met with in other families, has been improperly 
 separated by some modern writers from the class under consideration. 
 Nevertheless, we shall find the position assigned to these animals by 
 Cuvier to be in strict accordance with the character both of their 
 outward form and internal structure ; only, instead of placing them 
 with the lowest of the Echinoderms, they would have been more 
 properly situated at the head of the class, as most nearly ap- 
 proximating the Annelida in all the details of their economy. We 
 have already given a description of the outward form of a Fistu- 
 laria ( 186), and seen the completely annulose condition of its 
 body, although the radiating tentacula around the mouth are evi- 
 dently analogous to those of the Holothuria already described. We 
 are indebted to the patient researches of Pallas and Delle Chiaje* for 
 almost all that is known concerning the anatomical structure of these 
 animals, and the descriptions of the Siponculus phalloides and bala- 
 nophorus have left little to be desired by the systematic zootomist. 
 
 The Siponculus inhabits shallow seas, concealing itself at the 
 bottom in holes which it excavates in the sand. Having once 
 located itself, it is seldom found to quit its concealment, but, re- 
 taining its hold upon the sides of the retreat which it inhabits by 
 dilating the posterior part of its body, it occasionally protrudes its 
 head from the orifice, either for the purpose of procuring food, or 
 of respiring more freely the element in which it lives. 
 
 These animals are much sought after by fishermen, who employ 
 them as baits for their hooks ; and one species, Siponculus edulis, 
 is used in China as an article of food. 
 
 * Storia e Notomia delle Animate senza Vertebre del Regno di Napoli. Napoli, 1823. 
 
 N 2 
 
180 ECHINODERMATA. 
 
 (221.) The body is covered externally with a delicate cuticle, 
 easily separable by maceration or immersion in spirit of wine ; and 
 when thus detached it forms so loose a covering, that Linnseus, 
 deceived by the appearance of an animal thus preserved, applied to 
 it the name of Siponculus saccatus. 
 
 The muscular investment, placed beneath the skin, is composed 
 of strong fasciculi arranged in three distinct layers. The external 
 stratum is disposed in circular rings, beneath which spiral fibres 
 may be observed crossing each other at various angles ; and lastly, 
 the inner coat is made up of about thirty powerful longitudinal 
 bands, extending from one extremity of the body to the other. 
 Such an arrangement is evidently sufficient for the general move- 
 ments of the creature ; but, in order to facilitate the retraction of the 
 tentacular apparatus around the mouth, eight additional muscles 
 surround the oesophagus, and by their action the whole of the oral 
 apparatus is completely inverted and drawn inwards. 
 
 The tentacula around the oral orifice are the principal agents 
 employed in seizing and swallowing food, an office to which they 
 are peculiarly adapted by their great sensibility and power of con- 
 traction ; but, as we have found to be generally the case among 
 the Echinodermata, sand and fragments of shell form the great 
 bulk of the contents of the intestine, so that it is by no means 
 easy to state precisely the nature of the food upon which the 
 Siponculi are nourished. 
 
 (222.) The structure of the alimentary canal, and of the nutrient 
 apparatus, conforms too accurately with what we have already seen 
 in Holothuria to permit of a moment's hesitation concerning the 
 relationship which exists between the apodous Echinodermata 
 and the Holothuridse. The oesophagus (fig. 76, b) is narrow, and 
 soon dilates into a kind of stomachal receptacle (c) ; but, although 
 the diameter of the intestinal tube is at this point perceptibly 
 larger than in any other part of its course, there is no other pecu- 
 liarity to distinguish it from the rest of the intestine. In the 
 ANNELIDA, the digestive apparatus is invariably straight, travers- 
 ing the body from one extremity to the other, a circumstance which 
 distinguishes them remarkably from the Echinoderms we are now 
 considering ; for in Siponculus we find a digestive canal, six or 
 seven times the length of the animal, within which it is folded 
 upon itself in various distinct convolutions. Leaving the stomach, 
 if we may so call the dilatation above alluded to, it passes down 
 (d, J, d,) nearly to the tail, where it is reflected upon itself, and 
 
ECHINODERMATA. 
 
 181 
 
 mounts up again as far as the point where it commenced ; here it 
 again turns back, and, once more reaching the bottom of the tegu- 
 mentary sac, becomes a second 
 time directed upwards, and re- 
 ascends as far as the point (e), 
 where the anus is situated. 
 
 It is easy to account for this 
 extreme . length of the intestine 
 when we consider the nature of 
 the materials used as food, and 
 the small proportion of nutri- 
 ment contained among the sand 
 and broken shells which fill the 
 digestive canal : but the re- 
 markable position of the anal 
 aperture is only explicable by a 
 reference to the peculiar habits of 
 the creature ; for living as it does 
 in a narrow excavation bored in 
 the sand, from which it seldom 
 issues, had the excrements been 
 discharged, as in Holothuria, 
 through a terminal orifice, their 
 accumulation at the bottom of 
 the hole would soon expel the 
 animal from its retreat ; but, by 
 the arrangement adopted, it is 
 only necessary that the anterior 
 part of the body should be pro- 
 truded from its concealment, 
 and the excrementitious matter 
 may be cast out without incon- 
 venience. The intestine is retained in situ, and supported at 
 all points, by innumerable tendinous bands, which arise from the 
 interior of the muscular walls of the body, and form a kind of 
 mesentery. 
 
 (223.) In Sipomulus, the character of the circulating system is in 
 all essential points strictly analogous to that of the other Echinoder- 
 mata; and moreover, from the superior concentration visible in 
 every part, we have the multiplied organs of the other families ex- 
 hibiting so much simplicity of arrangement, that, whatever may 
 
ECHIXODERMATA. 
 
 have appeared obscure or complicated in our description of Echi- 
 nus and Holothuria will receive elucidation from the diagram- 
 matic form in which all the organs connected with the circulation of 
 the blood are represented in the adjoined figure. The intestinal 
 vein (m) may be traced along the entire length of the alimentary 
 canal ; commencing near the anal extremity of the bowel, it fol- 
 lows all its convolutions, and receives from every part the minute 
 vessels which ramify over the intestinal walls. These venous 
 ramifications undoubtedly perform the office assigned to the lac- 
 teals of higher animals, and imbibe the nutritive particles furnished 
 by digestion, which, of course, are conveyed into the great venous 
 trunk (m). Arrived opposite to the termination of the oesopha- 
 gus, the intestinal vein divides into two vessels : one performing 
 the office of a branchial artery, by conveying a part of the blood 
 to the respiratory organs in the neighbourhood of the mouth ; the 
 other, which we may call the aorta, distributing the remainder to 
 all parts of the tegumentary system. The branchial vessel (M) 
 runs from the bifurcation of the intestinal vein to the base of the 
 oral tentacles, where it forms a vascular circle around the com- 
 mencement of the oesophagus, analogous to that which we have seen 
 in Holothuria ; and in connexion with this circular vessel we find 
 the " ampulla Poliana " (A), which Delle Chiaje conceives to be 
 here, as in other cases, a receptacle for the circulating fluid. From 
 the vascular circle around the mouth, vessels are given off, to ramify 
 minutely through the substance of the tentacula (a), so that these 
 appendages may be considered as respiratory organs, like those of 
 Holothuria. The other vessels derived from the oral circle have 
 not been traced ; but we may conclude from analogy that arteries 
 supplying the mouth and alimentary canal are furnished from this 
 source. 
 
 The aorta (o) is the other large vessel derived from the intes- 
 tinal vein, and is seen to pass in a flexuous course from its origin 
 to the posterior extremity of the body, following the median line, 
 and giving off transverse branches on both sides opposite to every 
 ring of the muscular integument. At the commencement of the 
 aorta is a dilated vesicle (/), which may be looked upon as a heart 
 (auricle, Delle Chiaje). The vesicle alluded to is of a conical 
 form, the apex of the cone being directed towards the tail 
 of the animal ; and, from the impossibility of making mercury 
 pass from the aorta through this organ in the direction of the 
 intestinal vein, it is probable that it contains an apparatus 
 
ECHINODERMATA. 183 
 
 of valves so disposed as to prevent any retrograde motion of the 
 blood. At the termination of the aorta there appears to be a 
 second enlargement, to which the name of ventricle has been 
 given, and which is perhaps also capable of contraction, so as 
 to assist in the propulsion of the circulating fluid. The blood 
 of these animals is of a purple colour in the veins, but red in the 
 arterial vessels. 
 
 (224.) We have seen that the tentacula are, from their vascu- 
 larity, well adapted to fulfil the office of a respiratory apparatus ; but 
 it may be presumed that they are not the only agents by which 
 respiration is accomplished. Upon the outer surface of the body, 
 in the neighbourhood of the anal opening, two apertures arc visible, 
 which lead into two long sacculi (jf, j^), the entrance being 
 guarded by muscular fibres (g) : their texture presents transverse 
 and longitudinal striae, and they contract spontaneously even 
 after the animal is dead ; internally they are lined with a mucous 
 membrane. The use of these organs is not precisely known ; 
 Cuvier regarded them as belonging to the generative system, 
 while Delle Chiaje looks upon them as respiratory organs, inter- 
 mediate in structure between the arborescent tubes of Holothuria, 
 and the respiratory vesicles which we shall afterwards find in some 
 of the ANNELIDA. 
 
 (225.) In this elevated form of the Echinodermata, so nearly 
 allied to the Homogangliate type, we may naturally expect a 
 more complete developement of nervous ganglia than we have yet 
 met with in the class ; and accordingly we find, upon the an- 
 terior part of the oesophagus, two little nervous tubercles (t), 
 from which nervous filaments issue to be distributed to different 
 parts of the body ; one of these in particular may be traced 
 along the whole length of the intestine from the mouth to the 
 anus. 
 
 (226.) We are entirely ignorant concerning the mode of repro- 
 duction in these creatures, as no generative apparatus has as yet 
 been distinctly pointed out. Nevertheless, at certain seasons of 
 the year, on opening the visceral cavity, it is found to be filled 
 with a fluid of a reddish tint, in which thousands of minute white 
 bodies resembling millet-seeds are seen to float : should these 
 be ova, they are probably expelled through an orifice which exists 
 in the vicinity of the tail. 
 
184 
 
 CHAPTER XII. 
 
 HOMOGANGLIATA (Owen). 
 ARTICULATA (Cuv.) ; ANNULOSA (Mac Leay). 
 
 ) The third great division of the animal kingdom includes 
 an immense number of living beings adapted by their conforma- 
 tion to exist under a far greater variety of circumstances than any 
 which we have hitherto had an opportunity of examining. The 
 feeble gelatinous bodies of the ACRITA are obviously only adapted 
 to an aquatic life ; and accordingly they are invariably found either 
 to inhabit the waters around us, or to be immersed in the juices of 
 living animals upon which they subsist. The NEMATONEURA, 
 likewise, are all of them too imperfect in their construction to ' 
 admit of their enjoying a terrestrial existence, for, possessing no 
 nervous centres adequate to give force and precision to their move- 
 ments, they are utterly incapable of possessing external limbs 
 endowed with sufficient power and activity to be efficient agents in 
 ensuring progression upon land ; neither are any of them furnished 
 with those organs of sense which would be indispensable for the 
 security of creatures exposed to those innumerable accidents to 
 which the inhabitants of a rarer element are perpetually obnoxious : 
 the NEMATONEURA therefore are, from their organization, neces- 
 sarily confined to a watery medium. 
 
 But the type of structure met with in the HOMOGANGLIATA 
 admits of far higher attributes, and allows the enjoyment of a more 
 extended sphere of existence : senses become developed propor- 
 tionate to the increased perfection of the animal ; limbs are pro- 
 vided endowed with strength and energy commensurate with the 
 developement of the nervous ganglia which direct and control 
 their movements ; and instincts are manifested in relation with the 
 increased capabilities and more exalted powers of the various 
 classes as they gradually rise above each other in the scale of 
 animal developement. 
 
 (228.) The most obvious, though not the most constant, cha- 
 racter which distinguishes the creatures we are now about to de- 
 scribe, is met with in their external conformation ; they are all of 
 them composed of a succession of rings formed by the skin or 
 
HOMOGANGLIATA. 185 
 
 outward integument, which from its hardness constitutes a kind 
 of external skeleton, supporting the body, and giving insertion to 
 the muscles provided for the movements of the animal. In the 
 class CIRRHOPODA alone is this external characteristic wanting, 
 and the Homogangliate organization masked by a tegumentary tes- 
 taceous coat of mail, which they seem to have borrowed from the 
 molluscous type. In the lowest forms of the ARTICULATA the 
 body is extremely elongated, and the rings proportionately nu- 
 merous ; the integument moreover is soft and yielding, and, as a 
 necessary consequence, the limbs appended to the different seg- 
 ments are feeble and imperfect : such is the structure met with in 
 the worms, or ANNELIDANS, properly so called. 
 
 As we advance, we perceive the tegumentary rings to become 
 less numerous, and the skin of a denser and more firm texture, 
 adapted to support the action of stronger and more powerful 
 muscles ; the limbs likewise become more elaborately formed, their 
 movements more free and energetic, and the instruments of sight 
 and touch begin to assume considerable perfection of structure. 
 This state of developement we find in the MYRIAPODA or 
 Centipedes. 
 
 In the INSECTS the concentration of the external skeleton is 
 still more remarkable, and the integument assumes a hardness 
 and solidity proportioned to the vigorous movements of which 
 the limbs are now capable ; the rings or segments of the body, 
 hitherto distinct, become more or less firmly soldered toge- 
 ther in those parts where the greatest strength and firmness are 
 necessary, and scarcely any traces are left to indicate their ex- 
 istence as separate pieces ; so that, instead of exhibiting that 
 succession of similar segments seen in the Centipede, the body 
 is apparently divided into three distinct portions, viz. the head, 
 which contains the organs of the senses and the parts of the 
 mouth ; the thorax, sustaining the limbs or instruments of pro- 
 gression ; and the abdomen, enclosing the viscera subservient to 
 nutrition and reproduction. 
 
 In the fourth division of articulated animals, namely the 
 ARACHNIDANS or Spiders, a still greater consolidation of the 
 external skeleton is visible ; for in them even the separation 
 between the head and the thorax is obliterated, and it is in the 
 abdomen only that the segments of the body are recognisable. 
 
 Lastly, in the CRUSTACEANS we have various modifications of 
 the outward skeleton adapted to the habits of the different tribes ; 
 
186 HOMOGANGLIATA. 
 
 in the least perfect species, which are all aquatic, the rings of the 
 skeleton are perfectly distinct and separate, resembling those of 
 the Myriapoda ; but in the stronger and more predacious tribes, the 
 pieces of the head and thorax become solidly fixed together ; and in 
 those forms most adapted to a terrestrial life, namely, the crabs, 
 almost all traces of distinction between the thoracic segments are 
 lost in the construction of the calcareous shield which covers and 
 protects their whole body. 
 
 (229.) We see therefore in the above rapid sketch of the dif- 
 ferent classes which compose the articulated division of the animal 
 kingdom, that, as their organization assumes greater perfection, 
 the different segments of the external skeleton coalesce and become 
 united together, so as to give greater strength to those parts which 
 are more immediately connected with locomotion or the destruc- 
 tion of prey ; let us now examine the nature of the nervous appa- 
 ratus which characterises the HOMOGANGLIATA, and observe the 
 relation which the outward form of the body bears to the arrange- 
 ment of this primary system of the animal economy. In tracing 
 the developement of animal structure, on the first appearance of 
 any new apparatus, it is by no means unusual to find it repeated 
 again and again in the same creature, divided as it were into 
 distinct portions, prior to its appearance in its more highly organ- 
 ized and perfect condition. Thus in Ccenurus cerebralis, 110, 
 the reader will remember numerous mouths were dispersed over 
 different parts of the simple sac composing the stomach of the 
 animal ; in the compound Polyps, 36, innumerable digestive 
 organs ministered to the support of one common mass ; in the 
 Tape-worm, 117, the generative apparatus was repeated in nearly 
 every segment of its compound body ; and, did we choose to antici- 
 pate, other examples might be adduced, derived from the more per- 
 fect animals, exemplifying the same fact. We shall not be sur- 
 prised, therefore, to find that, on the first developement of a 
 nervous system provided with ganglionic masses, these nervous 
 centres, or brains as we might term them, are very numerous, and, 
 instead of being united, are located in different parts of the system. 
 In the humblest forms of the Annulosa it would seem indeed that 
 every ring of the body contained a complete nervous apparatus, 
 consisting of a pair of ganglia and a set of nerves destined to 
 supply the particular segment in which they are lodged. All these 
 different brains, belonging to the individual segments, communicate 
 with each other by nervous filaments, so that a continuous chain is 
 
HOMOGANGLIATA. 187 
 
 formed, passing along the whole length of the body. With the 
 exception of the anterior pair of ganglia, or that contained in the 
 first ring, which we may call the head of the worm, the nervous 
 centres are arranged along the ventral region of the body, that is, 
 beneath the alimentary canal ; but the anterior pair itself is inva- 
 riably placed upon the dorsal aspect of the animal, and communi- 
 cates with the rest by a nervous collar which embraces the com- 
 mencement of the oesophagus. The nervous masses placed along 
 the belly would seem to preside specially over the movements of 
 the segments to which they belong, and to have little to do with 
 sensation or the perception of external objects ; whilst the anterior 
 or cephalic pair, from the constancy of their communication with 
 the organs of the senses, would appear peculiarly in relation with 
 the perceptive faculties of the creature. 
 
 (230.) It may be taken as a general law, that the perfection of 
 the nervous system of any animal may be estimated by the propor- 
 tionate size of the central ganglia connected with it, upon the 
 developement of which both the energy of the actions of the 
 body and the completeness of perception depend ; and, by follow- 
 ing out this great principle, we shall be easily able to account for 
 the progressive steps by which the Articulata become more and 
 more perfectly organized, as we trace them in the series above in- 
 dicated. In proportion as we have found the segments of the 
 body to become less numerous, the appended limbs stronger, the 
 outward skeleton more dense, and the muscular powers more ener- 
 getic, we shall find the abdominal ganglia to dimmish in number 
 by becoming consolidated into larger masses, increasing in size and 
 energy in accordance with the developement of the limbs over 
 which they preside : and in the same manner we shall observe the 
 senses assume greater perfection of structure, and the instincts 
 become more developed, as we find the cephalic or anterior pair of 
 brains increasing in proportionate bulk. 
 
 These observations will suffice to introduce the student to the 
 Homogangliate division of the animal world, and to direct his at- 
 tention to those physiological points connected with the nature of 
 their nervous system which will be more fully laid before him in 
 the following pages. 
 
188 
 
 CHAPTER XIII. 
 
 ANNELIDA.* Red-blooded Worms. (Cuv.) 
 
 (231.) The lowest class of articulated animals comprehends an ex- 
 tensive series of creatures generally grouped together under the com- 
 mon name of Worms. In the outward form of their bodies many 
 of them resemble some of the more perfect Entozoa, and we need 
 not therefore be surprised that in ordinary language they are not 
 unfrequently confounded together. But whatever may be the 
 similarity in outward appearance between the more perfect intes- 
 tinal worms, and the animals belonging to the class upon the con- 
 sideration of which we are now entering, the examination of their 
 anatomical structure will at once show that they differ widely from 
 each other, and have thus been properly separated by a consi- 
 derable interval in all the more modern systems of zoological 
 arrangement. 
 
 (232.) The principal characters which serve to distinguish the 
 Annelida from other forms of the animal world are readily appre- 
 ciated ; and, when once pointed out, will be found sufficient for the 
 guidance of the most superficial observer. The body is always 
 considerably elongated, and composed of a succession of rings or 
 segments, which, with the exception of the first and last, scarcely 
 differ from each other except in size. Each ring is generally 
 found to be furnished with a set of short spines or setae, calcu- 
 lated to assist in locomotion ; but in no instance are these animals 
 provided with articulated legs. The first segment of the body, 
 which may be called the head, contains the mouth, sometimes 
 provided with a formidable apparatus of jaws ; and is also generally 
 furnished with eyes, and variously shaped tentacula, which are 
 apparently instruments of touch. The last segment also, which 
 is generally the smallest, occasionally presents setiform appen- 
 dages, and occasionally a prehensile sucker, used as an organ of 
 progression. 
 
 Their blood is remarkable for its red colour, and circulates 
 in a double system of arteries and veins ; respiration is effected 
 either in membranous sacculi contained within the body, or by 
 means of arborescent tufts appended to various parts of their ex- 
 
 * Annellus, a little ring. 
 
ANNELIDA. 189 
 
 ternal surface ; they are moreover almost all hermaphrodite, and 
 generally require the congress of two individuals for mutual im- 
 pregnation. 
 
 (233.) These animals are separated by Cuvier into three distinct 
 orders, distinguished by the nature and position of their organs of 
 respiration ; they are as follows : 
 
 ABRANCHIA. In this order there is no respiratory apparatus 
 visible externally, but on each side of the body a series of minute 
 apertures may be detected, whereby the surrounding medium is 
 admitted into numerous internal delicate sacs, over which the 
 blood-vessels are seen to ramify ; these form apparently the re- 
 spiratory system : the sacculi themselves, and the ducts by means 
 of which they communicate with the external apertures, are de- 
 lineated in^g. 80, 2, ra. 
 
 This order comprises two distinct tribes, that differ widely in 
 their habits and external appearance : the first comprehends the 
 LEECHES (Annelida suctoria), distinguished by the existence of 
 a prehensile sucker at each extremity of the body ; while, in 
 the second, instruments of attachment are totally wanting, the 
 only external appendages to the body being a number of minute 
 and almost imperceptible bristles, which project from the different 
 segments and assist in progression : such are the EARTH-WORMS, 
 &c. (Annelida terricola.) 
 
 DORSIBRANCHIATA. In the second order the respiratory appa- 
 ratus consists of numerous vascular tufts, a pair of which is ap- 
 pended to the outer surface of every ring of the body, or, in some 
 cases, only to those near the middle of the animal. The organs of 
 locomotion, which are likewise attached to each segment, assume 
 various forms, but are generally composed of short moveable spines, 
 or packets of retractile bristles, probably destined to perform the 
 office of oars. In the annexed figure, (fig. 77, 1,) which repre- 
 sents the Leodice antennata, the general form of these animals is 
 well seen, as is the most usual arrangement of the branchial tufts 
 and locomotive setae, \nfig. 77, , showing an imaginary trans- 
 verse section of one of the segments, the relative positions of the oars 
 (c, rf, e), and of the branchial appendages (&), are likewise indicated. 
 
 TUBICOLA. The two preceding orders of Annelidans are 
 erratic ; but in the third we find creatures inhabiting a fixed and 
 permanent residence, which encloses and defends them. This is 
 generally an elongated tube, varying in texture in different species. 
 Sometimes it is formed by agglutinating foreign substances, such 
 
190 
 
 ANNELIDA. 
 
 as grains of sand, small shells, or fragments of various materials > by 
 means of a secretion which Fig. 77. 
 
 exudes from the surface of the 
 body, and hardens into a tough 
 membranous substance, such is 
 the case of Terebella Medusa 
 (fig. 96). In other cases, as 
 in the Serpula contortuplicata \ 
 (fig- 78), the tube is ho- 
 mogeneous in its texture, 
 formed of calcareous matter 
 resembling the shells of cer- 
 tain bivalve mollusca, and ap- 
 parently secreted in a similar 
 manner. These tubes are ge- 
 nerally found encrusting the 
 surface of stones or other bo- 
 dies which have been immersed 
 for any length of time at the 
 bottom of the sea ; they are 
 closed at one end, and from the 
 opposite extremity the head of 
 the worm is occasionally pro- 
 truded in search of nourish- 
 ment. It must be evident that, 
 in animals thus encased, the 
 character of the respiratory ap- 
 paratus must be considerably 
 modified ; instead therefore of 
 the numerous branchiae ap- 
 pended to the segments of the 
 body which we have found in 
 the Dorsibranchiate order, the 
 respiratory tufts are all at- 
 tached to the anterior extre- 
 mity of the creature, where 
 they form most elegant arbo- 
 rescent appendages, generally 
 tinted with brilliant colours, 
 and exhibiting, when expanded, 
 a spectacle of great beauty. In 
 some species, as in that repre- 
 
ANNELIDA. 
 
 191 
 
 sen ted in the annexed figure, there is a remarkable provision made 
 for closing the entrance Fig. 78. 
 
 of the tube when the 
 animal retires within its 
 cavity. On each side 
 of the mouth is a fleshy 
 filament resembling a 
 tentacle ; but one of 
 these, sometimes the 
 right and sometimes 
 the left, is found to be 
 considerably prolonged, 
 and expanded into a 
 funnel-shaped opercu- 
 lum, which accurately 
 fits the orifice of the 
 shell, and thus forms 
 a kind of door, well 
 adapted to prevent in- 
 trusion or annoyance 
 from external enemies. 
 
 (234.) Abranchia. The common Leech (Hirudo medicinalis) 
 affords the most interesting example of a suctorial Annelide. The 
 outward form of one of these animals is familiar to every one, and 
 their general habits too well known to require more than a very 
 brief notice. The body is very extensible, and divided by a great 
 number of transverse lines into numerous rings, extremely apparent 
 in the contracted state of the animal, but nearly imperceptible 
 when the body is elongated. The skin is soft, being merely a thin 
 cuticular pellicle separable by maceration ; and the surface is lubri- 
 cated by a copious secretion of mucus. Beneath the cuticle is a 
 layer of coloured pigment, upon which the colours of the animal 
 depend ; but the cutis, or true skin, is so intimately connected with 
 the muscular integument of the body, that its existence as a distinct 
 tunic is scarcely demonstrable. The muscular covering or walls of 
 the body, which form a kind of contractile bag enclosing the 
 viscera, is found, upon accurate dissection, to consist of three 
 distinct strata of fibres running in different directions. The 
 outer layer is composed of circular bands passing transversely ; 
 in the second, the fibres assume a spiral arrangement, decussating 
 each other ; while the internal layer is made up of longitudinal 
 
192 ANNELIDA. 
 
 muscles, extending from one end of the creature towards the oppo- 
 site. Such an arrangement is evidently adequate to the produc- 
 tion of all needful movements, and capable of giving rise to all 
 the motions connected with the elongation, contraction, or lateral 
 inflexions of the body used in progression. 
 
 At each extremity of the animal, the muscular coat expands into 
 a flattened fleshy disc, composed of circular and radiating fasciculi, 
 which, when applied to a smooth surface, perform the office of 
 suckers, and thus become important instruments of prehension. 
 There are no vestiges of external limbs ; nevertheless, with the 
 simple mechanism above described, the leech is able to crawl with 
 considerable rapidity along the surface of subaquatic plants, or even 
 to swim with much facility through the water. The first method 
 of locomotion is accomplished by means of the terminal suckers : 
 supposing the posterior disc to be attached, the animal elongates 
 its body to the utmost, and then fixes the sucker placed at the 
 opposite extremity ; this done, the hinder parts are drawn forward 
 and again fixed, preparatory to a repetition of the process. In 
 swimming, the whole body is elongated, and by some partial con- 
 tractions of the muscular integument, not precisely understood, 
 assumes the appearance of a flattened band, and in this condition 
 the leech makes its way through the element which it inhabits, 
 by successive undulatory movements of the body performed with 
 much grace and elegance. 
 
 (235.) The mouth of the leech is an exceedingly perfect appa- 
 ratus, adapted not only to the destruction of those minute aquatic 
 animals which constitute its usual food, but, as is universally 
 known, admirably fitted to extract blood from the higher animals ; 
 combining, in its operation, the offices both of the cupping-glass 
 and the scarificator. 
 
 The mouth is situated near the centre of the anterior sucker, so 
 that the oral aperture is firmly applied to any surface upon which 
 this part of the animal is fixed. Around the entrance of the 
 oesophagus are disposed three minute cartilaginous teeth, im- 
 bedded in a strong circle of muscular fibres (fig. 79, 1). Each 
 tooth has somewhat of a semicircular form, and, when accurately 
 examined with a microscope, is found to have its free margin sur- 
 mounted with minute denticulations (fig. 79, 2), so as to resem- 
 ble a small semicircular saw. On watching a leech attentively 
 during the process of biting, the action of these teeth is at once 
 evident ; for, as the skin to which the sucker is adherent is 
 
ANNELIDA. 
 
 193 
 
 rendered quite tense, the sharp serrated edges of the teeth are 
 pressed firmly against it, and, a sawing movement being given to 
 each cartilaginous piece by the strong contractions of the muscular 
 fibres around the neck, these instruments soon pierce the cutis to 
 a considerable depth, and lay open the cutaneous vessels, from 
 which the creature sucks the fluid which its instinct prompts it to 
 seek after with so much voracity. The position of the teeth 
 around the opening of the mouth, as represented in the subjoined 
 figure, (fig- 79, A,) will at once explain the cause of the tri-racliate 
 form of the incision which a leech-bite invariably exhibits. 
 
 On contemplating Fig. 79. 
 
 this singular dental ap- 
 paratus found in the / \ 
 medicinal leech, and 
 considering the na- 
 ture of the food upon 
 which it usually lives, 
 it is difficult to avoid 
 arriving at the conclu- 
 sion that such a struc- 
 ture, which is indeed 
 only met with in one 
 or two species, is ra- 3 A 
 ther a provision in- 
 tended to render these creatures subservient to the alleviation of 
 human suffering than necessary to supply the wants of the animals 
 themselves. In the streams and ponds which they usually in- 
 habit, any opportunity of meeting with a supply of the blood of 
 warm-blooded vertebrata must be of rare occurrence, so that 
 comparatively few are ever enabled to indulge the instinct 
 which prompts them to gorge themselves so voraciously when 
 allowed to obtain it : neither does it appear that the blood 
 which they swallow with so much avidity is a material properly 
 suited to afford them nourishment ; for although it is certainly 
 true that it will remain for a considerable time in its stomach, 
 without becoming putrid, yet it is well known that most fre- 
 quently the death of the leech is caused by such inordinate reple- 
 tion, provided the greater portion of what is taken into the body 
 is not speedily regurgitated through the mouth. 
 
 (236.) The internal digestive apparatus is evidently adapted in 
 the construction of all its parts to form a capaciovis reservoir for the 
 
194 ANNELIDA. 
 
 reception of fluids taken in by suction : the stomach indeed, with 
 the numerous lateral appendages opening from it on each side, 
 would seem to fill the whole body ; and, being extremely dilatable, 
 allows the animal to distend itself to a wonderful extent, so that 
 it is not unusual to see a leech, when filled with blood, expanded 
 to five or six times the dimensions which it presented in an empty 
 state. 
 
 The stomach itself (Jig. 80, 1, A, i,) occupies about, two 
 thirds of the visceral cavity ; on opening it, as represented in the 
 figure, it is seen to be divided by delicate septa into nine or 
 ten compartments, which communicate freely with each other. 
 In each compartment we observe two lateral orifices leading into 
 as many wide membranous pouches (&), which although shrunk 
 and flaccid when in an undistended state, as they are seen in the 
 figure, are easily filled with fluid introduced into the stomach, and 
 are then swelled out into very capacious bags. Perhaps the sim- 
 plest way of obtaining a correct idea of the relative sizes and 
 general arrangement of these organs, is to make a cast of their 
 internal cavities when in a state of distension ; this is readily 
 effected by placing a dead leech in warm water until it is slightly 
 heated : in this state the pipe of a small injecting syringe can be 
 introduced into the oesophagus so as to fill the stomach and cseca 
 with common wax injection ; and, if the body be immediately re- 
 moved into a vessel of diluted muriatic acid, the soft parts will 
 be speedily destroyed, leaving an exact model of the interior. 
 It will then be seen that the lateral caeca increase gradually in 
 size as they approximate the posterior extremity of the body, until 
 the last pair (d) become so large as nearly to fill up the space 
 intervening between the end of the stomach and the anal boundary 
 of the visceral cavity. What is the exact nature of these capa- 
 cious sacs which thus open into the stomach of the leech ? Are 
 they prolongations of the digestive surface, or are they glandular 
 cseca provided for the secretion of some auxiliary fluids poured into 
 the stomach ? These are questions which admit of considerable 
 discussion. On the one hand, there can be little doubt that, when 
 the leech is filled with blood, the various csecal pouches become 
 likewise distended, and they are apparently as well calculated to 
 effect the digestion of their contents as the stomach itself. Those 
 physiologists, however, who embrace a different opinion, support their 
 views by referring to the structure of analogous parts found in other 
 ANNELIDANS : in Aphrodita aculeata, for example, the representa- 
 
ANNELIDA. 195 
 
 tives of the wide pouches met with in the leech are narrow and 
 branched tubes terminating in blind extremities, to which it is 
 usual to assign the office of separating a biliary secretion ; and, 
 according to this view, we may regard the caeca of the leech as the 
 simplest rudiments of the assistant chylopoietic glands, the first 
 pair (g, g) 9 from their proximity to the mouth, may be destined 
 to furnish a salivary fluid, and the succeeding ones to perform the 
 functions of biliary follicles. 
 
 The small size of the intestine (e), when compared with the 
 capacious stomach described above, is remarkable : it commences 
 by a minute orifice from the termination of the digestive cavity, 
 and becoming slightly enlarged passes in a straight line, lodged 
 between the two posterior cseca, to the anus, which is an almost 
 imperceptible aperture placed at the root of the posterior sucker ; 
 four small and apparently glandular masses are appended to this 
 short canal, but their nature is unknown. The entire alimentary 
 apparatus is retained in situ by numerous membranous septa, 
 (m, w,) passing between its outer walls and the muscular parietes 
 of the body. 
 
 (237.) It has already been mentioned, that, in the abranchiate 
 Annelidans, the organs provided for respiration are a series of 
 membranous pouches, communicating externally by narrow ducts or 
 spiracles, as they might be termed, into which aerated water is 
 freely admitted. These respiratory sacculi, in the leech, are about 
 thirty-four in number, seventeen being visible on each side of the 
 body : they are extremely vascular ; and in connection with every 
 one of them there is a long glandular-looking appendage, repre- 
 sented in the figure, (Jig. 80, 2, m,) that was looked upon until 
 recently as being intended to furnish some important secretion, 
 but which recent discoveries have shown to be connected with the 
 propulsion of the blood over the walls of the breathing vesicle, in a 
 manner to be explained immediately. It would seem, however, that 
 the respiratory function is not exclusively carried on by the agency 
 of the lateral sacculi : the entire surface of the body is permeated 
 by innumerable delicate vascular ramifications ; and, from the thin- 
 ness of the integument, it is evident that the blood which tra- 
 verses the cutaneous net-work thus extensively distributed must 
 be more or less completely exposed to the influence of oxygen 
 contained in the surrounding medium ; nay, it would even appear 
 from careful examination of the movements of the blood, as seen 
 in the transparent bodies of some of the Hirudinidte, that a kind 
 
 o % 
 
!<)(> .\\\i i u>\. 
 
 ol' \icarious action occurs bet\\eeu the capillary vessels of the skin 
 :md those of the respiratory sacs, So that \\hen the circulation pro- 
 cceds languidly tlin>ii"Ji om- sd of \essels, it is carried on with 
 :ler aeliyitx in the other. 
 
 Fig. 80. 
 1 2 3 
 
 (288.) The vessels appropriated to the distribution of the circu- 
 lating ilnid in the leech are rudely sketched iu.//ir. 80, 8. Then- is 
 no heart, Imt the movements of the blood arc entirely dne to the 
 contractions of the canals in which il Hows. The principal vascu- 
 lar trunks are four in number, which, although they all communi- 
 cate extensively with each other, perform distinct ollices in cllcct- 
 ing the circulation; two of them being specially connected \sith 
 the supply of the general system, while the other two seem sub 
 scnicnt to the distribution of the blood over the respiratory 
 saecnli. 
 
A \NI<: 1.1 1) \. 1 1)7 
 
 The two systemic trunks ( /', g) run along the mcsian line of 
 l.lir body ; one upon the <lors.il, ;in<l llir oi.lirr upon the ventral 
 as|>cet. The dorsal vessel (y) seems to be ;i.rl.eri;i.l in its eha- 
 raetrr, and no doubt corresponds in function with the heart of 
 more |>nfeet forms of the articulata ; receiving the blood from all 
 parts of the system, as'well from the respiratory vessels as from 
 the venous capillaries, and by successive undulatory contractions, 
 uhieh may be observed to proceed from the tail towards the an- 
 terior extremity, propelling it through all the arterial branches 
 derived from it. The ventral vessel (g), on the contrary, seems 
 to be venous, collecting the blood after its passage through I he 
 systemic capillaries, and returning it partly into the dorsal artery 
 from wliieli it set out, and partly to the lateral vessels for the 
 purpose of undergoing respiration. 
 
 The two lateral vessels (a, c) are appropriated to the supply 
 of the respiratory system, and in them the blood moves in a circle 
 quite independent of that formed by the dorsal artery and ventral 
 vein, although they all communicate freely by means of cross 
 branches, those passing from the lateral vessels to the dorsal 
 being called by M. Duges* dor so- lateral , while those which 
 join the lateral trunks to the ventral canal arc the latero-abdo- 
 minal branches of that observer. The movement of, the blood 
 in the lateral or respiratory system of vessels is quite distinct 
 from that which is accomplished in the dorso- ventral or systemic 
 trunks : sometimes it passes down the vessel marked a, from the 
 head towards the tail, and in an opposite direction on the other 
 side of the body ; but in a short time the movement of the cur- 
 rents will be seen to become completely reversed, so that an un- 
 dulatory motion, rather than a complete circulation, is kept up. 
 By this action of the lateral canals the blood is made perpetually 
 to pass and repass the respiratory sacculi ; and, opposite to each 
 of these, branches are given off which form so many independent 
 vascular circles, representing very closely the minor or pulmonary 
 circulation of higher animals. 
 
 (239.) On examining attentively one of the respiratory pouches 
 (Jig. 81, y ), its membranous walls arc seen to be covered with very 
 line vascular ramifications, derived from two sources: the latcro-ab- 
 dominal vessel (d) gives off a branch (c), which is distributed upon 
 the respiratory sacculus ; and there is another very flcxuous vas- 
 
 * Annalcs dcs Sciences Nat. vo). xv. 
 
198 
 
 ANNELIDA. 
 
 cular loop (b) derived from the lateral vessel itself (a), which ter- 
 minates by ramifying upon the vesicle f, in a similar manner. The 
 
 Fig. 81. 
 
 walls of the loop &, are extremely thick and highly irritable ; but, 
 on tearing it across, the internal cavity or canal by which it is 
 perforated is seen to be of comparatively small diameter, so that we 
 are not surprised that, although such appendages to the respira- 
 tory sacs were detected and well delineated by former anatomists,* 
 their nature was unknown, and they were supposed to be glandular 
 bodies appropriated to some undiscovered use. From the ar- 
 rangement above described, it is evident that small circular cur- 
 rents of blood exist, which are independent, to a certain extent, of 
 the general circulation ; since opposite to each membranous bag a 
 portion of the fluid contained in the lateral vessel (a) is given off 
 through the muscular tube (&), which thus resembles a pulmonary 
 heart, and after being distributed over the walls of the respiratory 
 vesicle, and in this manner exposed to the influence of oxygen, 
 the blood returns into the general circulation. 
 
 (240.) The nervous system of the leech (Jig. 80, 2, k) consists of 
 
 * Delle Chiaje, op. cit. Moquin Tandon, Monographic sur la famille des Iliru- 
 dinees, 4to. Montpellier, 1827. 
 
ANNELIDA. 199 
 
 a long scries of minute ganglia joined by connecting filaments ; of 
 these, about twenty-four are situated along the ventral surface of 
 the body. The anterior pair, or that immediately beneath the 
 oesophagus, is larger than the rest, forming a minute heart-shaped 
 mass, which is united, by a delicate nervous collar embracing the 
 gullet, with two small nodules of neurine situated upon the dorsal 
 aspect of the mouth. The two minute ganglia last mentioned 
 form that portion of the nervous system most intimately connected 
 with sensation ; for, while the nervous filaments given off from the 
 abdominal ganglia are distributed to the muscular integuments of 
 the body, the nerves which issue from the supra-oesophageal pair 
 supply the oral sucker, where the organs of the senses are situated. 
 In all the homogangliata, indeed, it is exclusively from this ce- 
 phalic pair of ganglia that the nerves appropriated to the instru- 
 ments of the senses are derived, and we shall therefore not hesitate 
 in the following pages to apply to this part of the nervous system 
 of the articulata the name of brain ; considering it to be strictly 
 analogous, in function at least, with the cerebral masses of more 
 highly organized beings. 
 
 When we regard the minute size of these, as yet rudimentary 
 nervous centres, we cannot, however, expect to find them asso- 
 ciated with any very perfect apparatus of -sensation. The oral 
 sucker, indeed, seems to possess a more delicate sense of touch 
 than the rest of the body, adapting it to examine the surface to 
 which it is about to be fixed ; and probably the leech may enjoy 
 in some measure perceptions corresponding with those of taste and 
 smell. These senses have been found to exist in many of the 
 animals we have already described ; but in the ffirudimdte we 
 have, in addition, distinctly formed organs of vision, exhibiting, 
 indeed, the utmost simplicity of structure, but nevertheless cor- 
 responding in the perfection of their developement with the con- 
 dition of the cerebral masses in relation with them. 
 
 (241.) The eyes of the leech are eight or ten in number, and are 
 easily detected by the assistance of a lens under the form of a semi- 
 circular row of black points, situated above the mouth upon the suck- 
 ing surface of the oral disc ; a position evidently calculated to ren- 
 der them efficient agents in detecting the presence of food. The 
 structure of these simple eyes, according to Professor M tiller,* 
 does not as yet present any apparatus of transparent lenses adapted 
 
 * Annales des Sciences Nat. vol. xxii. 
 
200 ANNELIDA. 
 
 to collect or concentrate the rays of light ; but each ocellus, or vi- 
 sual speck, would seem to be merely an expansion of the terminal 
 extremity of a nerve derived immediately from the brain, spread 
 out beneath a kind of cornea formed by the delicate and transparent 
 cuticle : behind this is a layer of black pigment, to which the dark 
 colour of each ocular point is due. 
 
 (242.) Leeches, like the generality of the Annelida, are herma- 
 phrodite, every one possessing two complete systems of generative 
 organs, one subservient to the impregnation, the other to the produc- 
 tion of the ova; nevertheless these animals are not self-impregnating, 
 but the congress of two individuals is essential to fecundity. 
 
 Commencing with the male organs, we are not surprised to find 
 the testes divided into numerous distinct masses, or rather repeated 
 again and again in conformity with a law to which we have already 
 alluded ( 229). The glands which apparently secrete the semi- 
 nal fluid are about eighteen in number (Jig. 80, 2, e, /), arranged 
 in pairs upon the floor of the visceral cavity. Along the external 
 edge of each series there runs a common canal, or vas defer ens 9 
 which receives the secretion furnished by all the testicular masses 
 placed upon the same side of the mesian line, and conveys it to 
 a receptacle (d), where it accumulates. The two reservoirs, or 
 vesicula seminales, if we may so call them, (d, d,) communicate 
 with a muscular bulb (c) situated at the root of the penis. The 
 penis itself (a) is frequently found protruded from the body after 
 death ; it is a slender tubular filament, which communicates by its 
 origin with the contractile bulb (c), and, when retracted, is lodged 
 in a muscular sheath (5). The male apparatus is thus complete in 
 all its parts : the fecundating secretion derived from the double row 
 of testes is collected by the two vasa deferentia, and lodged in the 
 receptacles (d, d) ; it is thence conveyed into the muscular cavity 
 (c) situated at the root of the male organ of excitement, through 
 which it is ultimately ejected. 
 
 (243.) The ovigerous or female sexual organs of the leech are 
 more simple in their structure than those which constitute the male 
 system ; they open externally by a small orifice situated immediately 
 behind the aperture from which the penis is protruded, the two 
 openings being separated by the intervention of about five of the 
 ventral rings of the body. The vulva, or external canal, leads into 
 a pear-shaped membranous bag (Jig. 80, 2, g), which is usually, 
 but improperly, named the uterus. Appended to the bottom of 
 this organ is a convoluted canal (^), which communicates with two 
 
ANNELIDA. 201 
 
 round, whitish bodies ; these are the ovaria. The germs, there- 
 fore, which are formed in the ovarian corpuscles, escape through the 
 tortuous duct (h) into the uterus (), where they are detained for 
 some time prior to their ultimate expulsion from the body. The 
 exact nature of the uterine sacculus, as it is called, is imperfectly 
 understood : some regard it as a mere receptacle wherein the se- 
 minal fluid of the male is received and retained until the ova come 
 in contact with it as they pass out of the body, and thus are sub- 
 jected to its vivifying influence ; other physiologists believe that the 
 germs escape from the ovaria in a very immature condition, and sup- 
 pose that during their sojourn in this cavity they attain to more com- 
 plete developement before they are ripe for exclusion ; while some 
 writers go so far as to assert that leeches are strictly viviparous, in- 
 asmuch as living young have been detected in the interior of this 
 viscus : but all these suppositions are easily reconcileable with 
 each other ; there is no doubt that the seminal liquor is depo- 
 sited in this reservoir, during the copulation of two individuals, 
 neither would any one dispute that the ova are collected in the 
 same cavity before they are expelled from the body ; as to the 
 discussion whether the young are born alive or not, or, as it is ge- 
 nerally expressed, whether leeches are oviparous or viviparous, it is 
 in this case merely a question of words, for in a physiological point 
 of view it can make not the slightest difference whether the ova 
 are expelled as such, or whether, owing to their being retained by 
 accidental circumstances until they are hatched internally, the 
 young leeches make their appearance in a living state. 
 
 (44.) Abranchia terricola. The second division of those Anne- 
 lidans which possess no external organs of respiration are easily dis- 
 tinguishable from the suctorial worms by the different construction 
 of their instruments of locomotion. They live in general beneath 
 the surface of the ground, either perforating the soil in all direc- 
 tions, as the Earthworms (Lumbrici), or burying themselves in the 
 mud upon the sea-shore, where many of them, called Naides, 
 (Nais, Lin.) live a semi-aquatic life. In conformity with such 
 habits, their entire structure is adapted to a subterranean existence, 
 and their bodies so organized as to enable them to burrow with 
 facility through the dense and unyielding materials in which they 
 are usually found. Whoever has attentively watched the opera- 
 tions of an earthworm when busied in burying itself in the earth, 
 must have been struck with the seeming disproportion between the 
 laborious employment in which it is perpetually engaged, and the 
 
ANNELIDA. 
 
 means provided for enabling it to overcome difficulties apparently 
 insurmountable by any animal unless provided with limbs of extra- 
 ordinary construction, and possessed of enormous muscular power. 
 In the mole and the burrowing cricket we at once recognise in 
 the immense developement of the anterior legs a provision for 
 digging, admirably adapted to their subterranean habits, and cal- 
 culated to throw aside with facility the earth through which they 
 work their way ; but in the worms before us, deprived as they 
 appear to be of all external members, feeble and sluggish even to 
 a proverb, where are we to look for that mechanism which enables 
 them to perforate the surface of the ground, and to make for them- 
 selves, in the hard and trodden mould, the pathways which they 
 traverse with such astonishing facility and quickness ? 
 
 (245.) The structure of the outer fleshy integument of the earth- 
 worm resembles in every respect that of the leech already described, 
 both in the annular arrangement apparent externally, and the disposi- 
 tion of the muscular strata. The suctorial discs, however, which 
 in the leech formed such important instruments of progression, 
 are here totally wanting ; and the annular segments of the body, 
 as they approach the anterior extremity, become gradually dimi- 
 nished in size, so as to terminate when the worm is fully stretched 
 out in a fine point, near the apex of which is the opening of the 
 mouth. But there is another circumstance in which the external 
 anatomy of the terricolous Ann elides differs materially from what 
 we have seen in the suctorial Abranchia : in the latter, the tegu- 
 mentary segments were quite naked upon their outer surface ; but in 
 the Lumbrici, of which we are now speaking, every ring, when ex- 
 amined attentively, is found to support a series of sharp retractile 
 spines or prickles ; these, indeed, are so minute in the earthworm, 
 that, on passing the hand along the body from the head backwards, 
 their presence is scarcely to be detected by the touch, but they are 
 easily felt by rubbing the animal in the opposite direction ; a cir- 
 cumstance which arises from their hooked form, and from their 
 points being all turned towards the tail. These differences be- 
 tween the external structure of the suctorial and setigerous Abran- 
 chia, minute and trivial as they might seem to a superficial ob- 
 server, are however all that are required to convert an aquatic 
 animal into one adapted to a subterranean residence, as will be 
 evident to any one who observes carefully the manner in which the 
 earthworm bores its way through the soil in which it lives. The 
 attenuated rings in the neighbourhood of the mouth are first insi- 
 
ANNELIDA. 
 
 niiated between the particles of the earth, 
 which, from their conical shape, they pene- 
 trate like a sharp wedge ; in this position 
 they are firmly retained by the numerous 
 recurved spines appended to the different 
 segments : the hinder parts of the body are 
 then drawn forwards by a longitudinal con- 
 traction of the whole animal ; a movement 
 which not only prepares the creature for 
 advancing further into the soil, but by swell- 
 ing out the anterior segments forcibly di- 
 lates the passage into which the head had 
 been already thrust : the spines upon the 
 hinder rings then take a firm hold upon the 
 sides of the hole thus formed, and, prevent- 
 ing any retrograde movement, the head is 
 again forced forward through the yielding 
 mould, so that, by a repetition of the pro- 
 cess, the animal is able to advance with the 
 greatest apparent ease through substances 
 which it would at first seem utterly impossi- 
 ble for so helpless a being to penetrate. 
 
 (246.) The alimentary canal of the earth- 
 worm is straight and very capacious. Its great 
 size, indeed, is in accordance with the nature 
 of the materials employed as food, for it is 
 generally found distended with earth ; and, 
 indeed, by the older physiologists these 
 creatures were generally regarded as afford- 
 ing proof that the nourishment of animals 
 was not exclusively derived from animal and 
 vegetable substances, since in this case they 
 supposed nutriment to be obtained from 
 matter belonging to the mineral kingdom. 
 This supposition, however, has been long 
 since exploded, for it is not from the earth 
 that nourishment is afforded, but from the 
 decaying animal and vegetable particles 
 mixed up with the soil taken into the sto- 
 mach ; so that the exception to the general 
 law of nature supposed to exist in the earth- 
 
 Fig. 
 
 
204 
 
 ANNELIDA. 
 
 worm has no foundation in truth. The whole intestinal tract of 
 one of these animals is represented in the figure (Jig. 82) : it con- 
 sists of a wide O3sophagus which terminates in a crop-like dilata- 
 tion ; to this succeeds a muscular gizzard (fc), and a long sacculated 
 intestine (/, /) which passes in a direct line to the anus. 
 
 (247.) The circulation of the blood in the terricolous Annelidans 
 has been the subject of much discussion, and until recently was but 
 very imperfectly understood. In the earth-worm there are three 
 principal trunks connected with the vascular pj g ^ 33. 
 
 system,* the arrangement of which is repre- 
 sented in the annexed diagram (Jig. 83). 
 First, a dorsal vessel (a) runs along the whole 
 length of the back in close contact with the 
 intestine (Jig. 82, o, o), upon which it lies ; 
 this vessel is tortuous, and exhibits constant 
 movements of contraction and dilatation, by 
 which the blood is propelled in continuous 
 undulations from the tail towards the head. 
 Two other large vessels occupy the ventral 
 region of the body : of these, one (Jig. 83, 2>), 
 which we shall call the ventral vessel, runs 
 immediately beneath the alimentary tube ; 
 while the other, which is situated close un- 
 der the skin, and consequently beneath the 
 ventral chain of ganglia composing the nervous 
 system, by which it is separated from the last, 
 may be distinguished as the sub-ganglionic 
 vessel. These three great trunks are united 
 by important branches, and form two distinct 
 systems : one of which is deeply seated, being 
 distributed to internal viscera ; the other is 
 superficial, giving off innumerable vessels to 
 the integuments of the body, which, by rami- 
 fying through the skin, form an extensive vas- 
 cular surface adapted to respiration. 
 
 The ventral vessel (6), like the dorsal (), 
 may be traced quite to the anterior extremity 
 of the worm, where numerous small anastomosing branches unite 
 the two trunks : but these inosculations are of little consequence 
 in describing the circular movement of the blood ; a more impor- 
 
 * M. Duges, Annales des Sciences Nat. vol. xv. 
 
ANNELIDA. 205 
 
 tant communication being established, through which the blood 
 passes freely from one to the other, by the intervention of seven or 
 eight pairs of large canals, situated in the immediate neighbourhood 
 of the generative apparatus, with which indeed they are interwoven. 
 Each of these voluminous vessels (d) is composed of a series of 
 swellings, or rounded bead-like vesicles, endowed with consider- 
 able contractile power ; and they form together a kind of heart of 
 remarkable construction, which propels the blood received from the 
 dorsal trunk into the ventral tube (b). 
 
 Along the rest of the body, the communication between the 
 dorsal and ventral trunks is repeated at each ring by canals which 
 are much smaller than the bead-like or moniliform vessels, and 
 have no vesicular arrangement ; they (g and e) run perpendicu- 
 larly upwards, embracing the alimentary canal, and giving off 
 branches at right angles, which divide into innumerable ramifi- 
 cations so as to cover the whole intestine with a delicate vascular 
 net-work ; these may be called the deep-seated abdomino-dorsal 
 branches. 
 
 The sub-ganglionic vessel (c) may be looked upon as arising 
 from the termination of the dorsal vessel, with which it is evi- 
 dently continuous at the anterior extremity of the body. At the 
 posterior edge of every segment, a delicate branch is given off from 
 this sub-ganglionic tube (/), which, running upwards in the same 
 manner as those derived from the ventral trunk, joins the dorsal, 
 and receives in its course a large anastomosing branch from the 
 deep abdomino-dorsal canal which corresponds to it. From this 
 system of superficial vessels arises a cutaneous net-work, analogous 
 to that described above as covering the digestive viscera which tra- 
 verses the skin in all directions. 
 
 Let us now trace the blood in its circulation through this ela- 
 borate system. In the dorsal vessel (a) the sanguineous fluid 
 passes from the tail towards the head ; at the anterior extremity of 
 the body it passes partly into the sub-ganglionic vessel (c), through 
 the anastomosing branches, and partly into the ventral vessel (Z>), 
 into which it is forcibly driven by the contractions of the monili- 
 form canals. In both the ventral and sub-ganglionic trunks, there- 
 fore, the course of the blood is necessarily from the head towards 
 the tail ; and the circulating fluid is continually returned to the 
 dorsal canal by the deep and superficial abdomino-dorsal vessels 
 (e,/, g), completing the vascular circle. 
 
 On reviewing the above arrangement, we immediately perceive 
 
206 ANNELIDA. 
 
 that, notwithstanding the similarity observable in the distribution 
 of the ventral and sub-ganglionic systems of vessels, in a physio- 
 logical point of view they are subservient to very different func- 
 tions ; the former representing the systemic, the latter the pul- 
 monary circulation. The blood derived from the dorsal trunk by 
 the moniliform hearts (d) is supplied by the ventral vessel, which 
 may be compared to an aorta, over the surface of the viscera, and 
 the remnant of this blood, after furnishing materials for nutrition, 
 is returned to the dorsal canal by the deep vessels e, g ; but that 
 portion of the circulating fluid which passes from the termination 
 of the dorsal tube into the sub-ganglionic trunk, not only serves 
 for the nourishment of the skin and muscular integument, but at 
 the same time is brought in contact with the air as it passes through 
 the cutaneous net-work, and is thus, more or less, replenished 
 with oxygen before it is again returned to the general circulation. 
 The sub-ganglionic canal is, therefore, a kind of pulmonary artery, 
 and the dorsal drives to the moniliform vessels a mixed fluid, 
 composed partly of venous blood derived from the viscera, and 
 partly of arterial derived from the superficial or sub-cutaneous 
 system. 
 
 (248.) We see, therefore, that the extensive diffusion of vascular 
 canals immediately beneath the surface of the skin must undoubtedly 
 contribute materially to effect those changes in the blood which 
 are analogous to those produced by respiration in the higher ani- 
 mals ; but it would seem that this is not the only provision made 
 for the aeration of the circulating fluids. It is long since Willis* 
 described the existence of a series of pores upon the back of the 
 earthworm, which he regarded as stigmata, and had remarked 
 that air blown into these openings is dispersed between the mus- 
 cular integument and the intestine, so that it passes readily from 
 one segment to another. Duges repeated these experiments with 
 the same result, and found that the pores alluded to, instead of 
 terminating in muciparous follicles, as they were supposed to do 
 by many, penetrate into the interior of the body, so that air in- 
 jected into one of them passes freely along the membranous com- 
 partments which surround the intestine, and escapes through other 
 neighbouring orifices. In like manner water is found to be 
 taken into the body through the same apertures, from which it is 
 often given out in great abundance when the animal is too rapidly 
 dried by exposure to the sun, or irritated by external stimuli: 
 
 * De Ahima Brutorum, 4to. 1672. 
 
ANNELIDA. 207 
 
 aerated water thus taken into the system, and brought immediately 
 in contact with the deep-seated vascular net-work dispersed over 
 the intestinal parietes, must therefore necessarily contribute to the 
 respiratory function. Nevertheless, in addition to all this, we find 
 in every segment of the body a pair of membranous vesicles {fig. 
 82, v) communicating externally by lateral orifices, apparently 
 analogous to the respiratory vesicles of the leech ; and, in fact, by 
 many authors they have been described as constituting the breath- 
 ing apparatus.* Their real office, however, is but imperfectly 
 understood ; they evidently have not the same relation with the 
 circulatory system, which the lateral sacculi of the leech have been 
 found to exhibit ; are they then merely secreting follicles destined 
 to furnish a mucosity for lubricating the external surface of the 
 body, or are they aquiferous tubes adapted to introduce water into 
 the interior ? Future observations must determine these ques- 
 tions. 
 
 (249.) Few points connected with the history of the earthworm 
 have given rise to so much speculation as the manner of their repro- 
 duction. The generative organs have long been known to be lodged 
 in the anterior part of the body, their position being indicated 
 externally by a considerable enlargement or swelling which extends 
 from the seventh to about the fourteenth segment, counting from 
 that in which the mouth is situated. On opening this portion of 
 the animal, a variable number of white masses are found attached 
 to the sides of the crop and gizzard (fig. 82, A, ^, A), which have 
 long, by general consent, been looked upon as forming the repro- 
 ductive system ; some having been regarded as representing the 
 testes, others the ovaria : yet so delicate are the connections 
 which unite these glandular masses, and such the difficulty of 
 tracing the ducts whereby they communicate with the exterior 
 of the body, that the functions to which they are individu- 
 ally appropriated have given rise to much discussion. The 
 Lumbrici have been generally acknowledged to be hermaphrodite, 
 that is, possessed of organs adapted both to the formation and 
 fertilization of ova ; and it is likewise well understood that the 
 congress of two individuals is essential to the fecundity of both, 
 as, in the earlier summer months, the mode in which they copulate 
 is a matter of constant observation. At such times two of these 
 animals are found to come partially out of the ground from 
 contiguous holes, and, applying together those segments of their 
 
 * Sir E. Home. Lectures on Comp. Anat. 4 vols. 4to. 1323. 
 
208 
 
 ANNELIDA. 
 
 bodies in which the generative glands are situated, are observed 
 to remain for a considerable time in contact, joined to each other 
 by a quantity of frothy spume which is poured out in the neigh- 
 bourhood of the sexual organs. No organs of intromission, how- 
 ever, have ever been distinguished, neither until recently had the 
 canals communicating between the sexual orifices and the testicular 
 or ovarian masses been satisfactorily traced ; so that Sir Everard 
 Home* was induced to believe that, in the kind of intercourse 
 above alluded to, there was no transmission of impregnating fluid 
 from one animal to the other, but that the excitement produced 
 by mutual contact caused both the ovaria and testes to burst, so 
 that the ova escaping into the cells of the body became there 
 mingled with the spermatic secretion, and being thus fertilized the 
 ova were hatched internally, and the young, having been retained 
 for some time in the cells between the intestine and the skin, 
 were ultimately ejected through apertures which were supposed to 
 exist in the vicinity of the tail. There is, however, little doubt 
 that what Sir E. Home conceived to be young earthworms were 
 in reality parasitical Entozoa, and that, in the mode of their pro- 
 pagation, the animals we are describing exhibit but little deviation 
 from what we have already seen in the leech. 
 
 (250.) According to M. Duges,-f- the arrangement of the sexual 
 parts is represented in the diagram (fig. 84). The testicles (b) are 
 
 placed in successive segments of 
 the body from the seventh back- 
 wards ; they vary in number in 
 different individuals from two to 
 seven : but whether this variety 
 depends upon a difference of 
 species, or is only caused by the 
 posterior pairs becoming atrophied 
 when not in use, is undetermined. 
 Each testis is fixed to the bot- 
 tom of the ring in which it is 
 placed by a short tubular pedicle 
 that opens externally by a very 
 minute pore through which a 
 milky fluid can be squeezed. 
 The testicular vesicles of the 
 same side of the body all com- 
 
 * Lectures on Comp. Anat. vol. iii. 
 
 Fig. 84. 
 
 t Ann. des Sciences Nat. vol. xv. 
 
ANNELIDA. 
 
 209 
 
 municate by a common canal ; and the contained fluid, which like 
 
 the seminal secretion of other animals contains animalcules, can 
 
 readily be made to pass from one to another. 
 
 The ovaria (c) are eight large ' Fig. 85. 
 
 white masses of a granular texture, 
 
 from which arise two delicate tubes 
 
 or oviducts ; these have no connection 
 
 with the testes, but, running back- 
 wards, they become dilated into two 
 
 small vesicles at their termination 
 
 (d), and open by two apertures or 
 
 vulvse seen externally upon the six- 
 teenth segment of the body : in these 
 
 'ducts eggs have been detected as large 
 
 as pins 1 heads. 
 
 (251.) The eggs, when laid, are two 
 
 or three lines in length. In figure 85, 
 
 A, one of them enclosing a mature em- 
 bryo is delineated ; its top is seen to 
 be closed by a peculiar valve-like 
 structure adapted to facilitate the 
 escape of the worm, and opening 
 (Jig. 85, B) to permit its egress. 
 Another remarkable circumstance ob- 
 servable in these eggs is, that they very generally contain double 
 yolks, and consequently two germs, so that a couple of young 
 ones is generally produced from each. 
 
 (252.) The generative system of the Nais presents a somewhat 
 different arrangement to that which exists in the earthworm. The 
 swollen part of the body in which the sexual organs are placed, occu- 
 pies a space of five or six rings, beginning at the eleventh. On each 
 side of the eleventh segment is a minute transverse slit (Jig. 86, b) 
 communicating with a slightly flexuous canal which terminates 
 in a transparent pyriform pouch or vesicle. The latter con- 
 tains a clear fluid, in which minute vermiform bodies are seen 
 to float, and most probably represents the testis. The twelfth 
 segment likewise exhibits two openings, each placed upon the 
 centre of a little nipple (c), these are the orifices leading to 
 the female portions of the sexual system. The ovaria (</, e) 
 are composed of four large and several smaller masses of a 
 granular character, and from them proceed long and tortuous 
 
210 
 
 ANNELIDA. 
 
 oviducts, which just before their termination at the lateral openings 
 (c) become thick and glandular. These animals most likely co- 
 pulate like the earthworm, and lay their 
 eggs in a similar manner. We have al- Fig. 86. 
 
 ready seen in the Lumbricus terrestris 
 ova containing two yolks, and consequently 
 giving birth to two animals ; but in the 
 Nais every egg produces ten or a dozen 
 young ones,* or, perhaps we ought rather 
 to say, that what appears to be a single 
 egg is in fact merely a capsule enclosing 
 several distinct ova from which a numerous 
 progeny arises. The manner in which 
 these compound eggs are formed is 
 easily understood, when we consider the 
 structure of the oviduct described above. 
 The granular germs escape no doubt 
 separately from the ovaria, and remain 
 distinct from each other as they pass 
 along the tortuous canal which leads to 
 the external opening ; but at length, ar- 
 riving at the thick and glandular portion 
 (c) of the oviferous tube, several of them 
 become enclosed in a common investment 
 secreted by the walls of the oviduct, and 
 are expelled from the body with the out- 
 ward appearance of a simple egg. 
 
 (253.) Besides the ordinary mode of pro- 
 pagation by ova, it has long been ascertained 
 that some of the Annelida at least are re- 
 produced by spontaneous division. Bonnet, M tiller, and Duges, all 
 agree that this is the case with certain species of Nais ; and in Nais 
 filiformis the process of separation has been witnessed from its com- 
 mencement to its termination. The division was seen to occur 
 near the middle of the body of the animal, the posterior half re- 
 maining motionless upon the mud of the bottom of the vessel, 
 whilst the anterior portion buried itself as usual ; after some days 
 the truncated extremity of the hinder part was observed to become 
 swollen, transparent, and vascular, and ultimately to assume the 
 complete structure of the mouth of the perfect animal ; it then 
 
 * Duges, loc. cit. 
 
ANNELIDA. 
 
 buried itself in the mud, and no doubt there completed its de- 
 velopement. 
 
 (254,) It is very generally believed, that even the earthworm may 
 be multiplied by mechanical sections, the separated portions repro- 
 ducing such parts as are removed in the experiment, and again 
 becoming perfect. Careful experiments made to ascertain how far the 
 statements of former authors upon this subject are substantiated, 
 prove that the assertion is not entirely without foundation, al- 
 though by no means to the extent indicated in their writings. It 
 would indeed be easily credited that the removal of the hinder 
 part of the body of an earthworm would not necessarily destroy the 
 anterior portion, since no organs absolutely essential to existence 
 are removed by the operation, and even the course of the circu- 
 lating fluids would not be materially interrupted by the mutilation ; 
 but that the hinder moiety should be able to reproduce the mouth, 
 gizzard, and stomach, the complicated apparatus of moniliform 
 vessels and the sexual organs, contained in the anterior segments, 
 could scarcely be deemed possible, and the assertion has been 
 satisfactorily disproved by actual observation. On cutting an 
 earthworm in two, the anterior portion is found in fact generally 
 to survive ; and the wound caused by the operation, becoming 
 gradually constricted, is soon converted into an anal orifice, render- 
 ing the animal again complete in all parts necessary for its ex- 
 istence. This, however, is by no means the case with the posterior 
 portion ; for although it will exhibit, for a very long period, indica- 
 tions of vitality, no signs of reproduction have been witnessed, and 
 it invariably perishes. 
 
 (255.) Nevertheless, although it is thus proved that the earthworm 
 cannot be multiplied by mechanical division, it is undeniably able 
 to reproduce small portions of its body, the removal of which does 
 not implicate organs essential to life. In the experiments of 
 M. Duges,* for example, it was found that four, or even eight, of 
 the anterior rings might be cut off with impunity, although the 
 cephalic pair of ganglia, the mouth, and a part of the oesophagus 
 were necessarily taken away. In worms thus mutilated, after the 
 lapse of from ten to thirty days, a conical vascular protuberance 
 was observed to sprout from the bottom of the wound ; and, in 
 eight or ten days later, this new part had become so far developed, 
 that not only all the lost rings were apparent, but even the upper 
 lip and mouth had assumed their normal form, and the animal 
 again began to eat and bury itself "in the earth. 
 
 * Loc. cit. p 2 
 
212 ANNELIDA. 
 
 (256.) Dorsibranchiata. We have gone too minutely into the 
 anatomy of the two preceding orders of Annelidans to render an 
 equally detailed account of the structure of the Dorsibranchiata ne- 
 cessary ; we must therefore restrict our observations to those points 
 in which remarkable variations from what has already been described 
 present themselves to our notice. These worms are all inhabit- 
 ants of the sea ; and although upon our own coasts they seldom 
 attain to very considerable dimensions, rarely exceeding a few 
 inches in length, in tropical climates some species are found of 
 comparatively gigantic proportions, having their bodies composed 
 of four or five hundred segments, and occasionally measuring four 
 feet from one end to the other. 
 
 We have already seen ( 233) that, in the more perfectly or- 
 ganized forms of these worms, each segment of the body supports 
 certain external, moveable appendages adapted to assist in locomo- 
 tion, which are usually called the feet, or more properly the oars ; 
 they present great diversity of appearance, and, from the nature and 
 arrangement of the different parts composing them, are of material 
 assistance to the systematic zoologist, as they afford important 
 characters for the establishment of generic and specific differences. 
 In the section of Leodicea antennata already given, (Jig. 77, 2,) 
 these parts are seen in a very intelligible form, and are visibly 
 composed of three distinct structures adapted to different uses. 
 The first, which occupies the uppermost position, is the respiratory 
 apparatus (b) ; in Leodicea its structure is extremely simple, 
 being composed of a central stem from which a single series of 
 vascular filaments is sent off, giving the organ a pectinated ap- 
 pearance ; but in other cases the branchial tuft is far more con- 
 siderably developed, dividing and subdividing into minute ramifi- 
 cations, and thus offering a more considerable surface to the 
 surrounding element. In most instances, as in Leodicea (Jig. 
 77, 1), these respiratory arbuscles are placed along the entire 
 length of the body, being appended to every segment, with the 
 exception perhaps of a few of the most anterior ; nevertheless, in 
 some species, their distribution is more partial, and their presence 
 is restricted to a few rings of the animal. 
 
 In Arenicola piscatorum, for instance, (Jig. 87,) a worm 
 met with abundantly upon our own coasts, and eagerly sought 
 after as a bait by fishermen, who dig it from the holes which 
 it excavates in the sand, the branchiae (b) are confined to the 
 central portion of the body, where they form on each side a series 
 
ANNELIDA. 
 
 213 
 
 of bundles which are remarkable during the life of the creature 
 for their beautiful red colour, derived from Fig. 87. 
 
 the crimson blood which circulates copious- 
 ly through them. 
 
 But the organs of respiration in the Dor- 
 sibranchiate Annelidans are not always arbo- 
 rescent ; on the contrary, they are not un- 
 frequently spread out into thin membra- 
 nous lamellee, or resemble fleshy crests or 
 vascular tubercles ; still, whatever their 
 form, their office is the same, and the vessels 
 spread over them, presenting an extensive 
 surface with which the water is brought in 
 contact, the blood is oxygenated as it passes 
 through them. 
 
 (257.) The second class of organs to be 
 enumerated as entering into the composi- 
 tion of the lateral appendages, are soft, fleshy, 
 and sub-articulated processes called cirri 
 (Jig- 77, 2, c, d) ; these are generally two in 
 number, and belong one to the ventral and 
 the other to the dorsal oar : their precise 
 office is not well understood ; but as in 
 some of the segments, especially in the 
 neighbourhood of the head, they assume a 
 tentacular form, they have with some pro- 
 bability been regarded as instruments of 
 touch. 
 
 (258.) The seta (fig. 77, 2, d) are per- 
 haps the most efficient agents in progression. 
 These are long and stiff hairs disposed in 
 bundles and implanted into strong muscular 
 sheaths. Each packet of setse can be retracted 
 within the body to a certain extent, and 
 again protruded by the action of the tubular 
 supports from which they arise, and, being 
 capable of independent action, these organs 
 must be looked upon as so many power- 
 ful fins, well calculated to propel the 
 creature through the element which it in- 
 habits. 
 
ANNELIDA. 
 
 Nothing can exceed the splendour of the colours which orna- 
 ment some of these fasciculi of hairs ; they yield, indeed, in no 
 respect to the most gorgeous tints of tropical birds or to the bril- 
 liant decorations of insects : green, yellow, and orange, blue, 
 purple, and scarlet, all the hues of Iris play upon them with the 
 changing light, and shine .with a metallic effulgence only com- 
 parable to that which adorns the breast of the humming-bird. 
 But it is not for their dazzling beauty merely that these setse are 
 remarkable ; they are not unfrequently important weapons of de- 
 
 Fig. 88, 
 
 fence, and exhibit a com- 
 plexity of structure far be- 
 yond anything to be met 
 with in the hair of higher 
 animals. In the Aphro- 
 dite hispida, for example, 
 (Jig. 88, A,) they are per- 
 fect harpoons ; the point 
 of each being provided 
 with a double series of 
 strong barbs, (fig- 88, B,) 
 so that when the creature 
 erects its bristles, much 
 more formidable than those 
 of the porcupine, the most 
 determined enemy would 
 scarcely venture to attack 
 it. 
 
 But here we cannot help 
 observing an additional 
 provision, rendered neces- 
 sary by the construction of these lance-like spines. We have 
 before noticed that the bundles of setse are all retractile, and can 
 be drawn into the body by the muscular tube from which they 
 spring. It would be superfluous to point out to the reader the 
 danger which would accrue to the animal itself by the presence of 
 such instruments imbedded in its own flesh, as by every movement 
 of the body they would be inextricably forced into the surrounding 
 tissues. The contrivance to obviate such an accident is as beau- 
 tiful as it is simple. Every barbed spine is furnished with a 
 smooth, horny sheath, (fig. 88, a, 6,) composed of two blades, 
 between which it is lodged ; and these, closing upon the barbs when 
 
ANNELIDA. 
 
 215 
 
 they are drawn inwards, effectually protect the neighbouring soft 
 parts from laceration. 
 
 (259.) In the Aphrodite above alluded to we have an additional 
 appendage developed from the upper part of each lateral oar, in the 
 shape of a broad membranous scale, which, arching inwards over 
 
 Fig. 89. 
 
 Fig. 90. 
 
 the back {Jig. 89, c), forms with 
 its fellows a series of imbricated 
 plates, or Elytra, as they are tech- 
 nically named (Jig. 88, A) ; and 
 beneath these the branchial organs 
 are lodged. Each of the elytral 
 scales is formed by a double mem- 
 brane, between the laminae of which 
 at certain seasons the eggs are 
 found to be deposited ; a situation 
 evidently adapted to ensure the ex- 
 posure of the ova to the influence of the surrounding element, 
 and thus to provide for the respiration of the embryo.* 
 
 (260.) The structure of the mouth in the Dorsibranchiate Anne- 
 lidans is very peculiar. The 
 first portion of the alimentary 
 canal or stomach, as it is most 
 erroneously called by some 
 writers, is muscular ; and 
 certainly, when seen in a dead 
 Annelide, it might easily be 
 taken for a digestive cavity. 
 Nevertheless, during life, this 
 part of the alimentary ap- 
 paratus is destined to a widely 
 different office ; for it is so 
 constructed, that at the will 
 of the animal it can be com- 
 pletely everted, turned inside 
 out, and, when thus pro- 
 truded externally, it forms a 
 very singular proboscis, used 
 in seizing food, and frequent- 
 ly armed with powerful teeth of singular construction. The an- 
 nexed figure (Jig. 90, A), representing the head of one of these 
 
 * Milne Edwards, Ann. des Sciences Nat. vol. xxvii. 
 
216 
 
 ANNELIDA. 
 
 worms (Goniada a chevrons, Milne Edwards), will give a good 
 idea of this curious organ when fully displayed; and in Jig. 90, 
 B, the mechanism is exhibited by which its protrusion and re- 
 traction are accomplished. The whole apparatus is there seen to 
 consist of two muscular cylinders, placed one within the other, but 
 continuous at their upper margin (B), or, to use a familiar illustra- 
 tion, the proboscis may be compared to the finger of a glove 
 partially inverted ; it is obvious that in this case, if the inner cylin- 
 der be drawn inwards, that is, into the mouth, the whole 
 structure becomes shortened, until at last it is entirely retracted 
 into the oral cavity ; whereas, on the contrary, if the outer tube 
 is made to protrude, it expands at the expense of the inner one, 
 which is gradually drawn forwards. The internal surface of this 
 remarkable proboscis is, moreover, variously modified in its struc- 
 ture, so as to adapt it to the prehension of different kinds of prey. 
 In Amphinome, for instance, the orifice of the mouth is a thick, 
 fleshy, and callous circle {fig- 93, b, c, d), and the surface of the 
 exserted proboscis is covered with delicate transverse rugae, evi- 
 dently so arranged as to give tenacity to its gripe. In Goniada it 
 supports two distinct sets of horny teeth, provided for very differ- 
 ent uses ; one set, which is exposed when the proboscis is un- 
 rolled to a very small extent, consists of a series of linear horny 
 plates, (Jig. 90, A, d 9 ) and probably forms a kind of file, or ra- 
 ther a scraper, with which the 
 animal excavates the subterra- 
 nean galleries in which it lives. 
 The other set does not make its 
 appearance till the proboscis is 
 more completely expanded, and 
 is evidently an instrument of pre- 
 hension, formed by two horny 
 hooks (Jig. 90, B, a, b) placed 
 upon an elevated ridge near the 
 entrance of the oesophagus, so as 
 to take a secure hold of any vic- 
 tim seized by this curious mouth. 
 In Phyllodoce laminosa the 
 teeth form a circle of semi-carti- 
 laginous beads, encompassing the 
 extremity of the proboscis when 
 that organ is pushed out to its 
 
 Fig.91. 
 
ANNELIDA. 217 
 
 full length (Jig. 91, 6), an arrangement well adapted to hold and 
 perhaps to crush their prey. 
 
 But the most formidable jaws are met with in some of the 
 Nereidiform species, as in Leodicea antennata, of which a figure 
 is given above (fig. 77). When the proboscis of one of these 
 creatures is slightly everted, the extremities of three pairs of 
 strong horny plates emerge from the mouth ; of these, one pair 
 terminates by forming a powerful hooked forceps, while the others 
 present strong denticulated margins (fig. 92, A, a, 6, c). The 
 
 Fig.92. 
 B A 
 
 N 
 
 nature of these teeth will be better seen by a glance at B in the 
 same figure, where they are represented upon an enlarged scale, 
 as they appear when detached from their connections. 
 
 (261.) The alimentary canal of the Dorsibranchiate Annelidans 
 offers little which requires special notice. It invariably passes in a 
 direct line from the termination of the proboscis to the anal extremity 
 of the body. In the Nereidte it is provided with numerous lateral 
 pouches, somewhat resembling those of the leech. In Aphrodite 
 these lateral cseca are very long, slender, and branched at their 
 extremities, so that they have been thought by some to be secret- 
 ing organs, representing the liver. In Arenicola we find at the 
 termination of the oesophagus (fig. 94, f) two large csecal ap- 
 pendages (e) of unknown office, while the rest of the tube (c) is 
 entirely covered with minute sacculi, the walls of which are de- 
 cidedly glandular, and secrete a fluid of a greenish-yellow colour. 
 
 (262.) The course of the principal trunks of the circulating system 
 in the Dorsibranchiata bears a general resemblance to what we have 
 already seen in the Abranchiate order, modified, of course, by the 
 variable position of the branchial tufts ; but with respect to the 
 
218 
 
 ANNELIDA. 
 
 minuter details 
 connected with 
 the arrangement 
 of the vessels our 
 information is but 
 vague and unsa- 
 tisfactory. The 
 investigation, in- 
 deed, is attended 
 with considerable 
 difficulty. The 
 annexed figure of 
 an elaborate 'dis- 
 section of an Am- 
 phinome (-4. ca- 
 pillata)) copied 
 from one of the 
 beautiful draw- 
 ings contained in 
 the Hunterian 
 Collection,* af- 
 fords an example 
 of a circulating 
 system in which 
 the propulsion of 
 the blood is ef- 
 fected entirely by 
 vessels, without 
 the intervention 
 of any muscular 
 cavities or heart. 
 In this animal 
 the respiratory 
 organs are penni- 
 form appendages 
 
 * Descriptive and 
 illustrated Catalogue 
 of the Physiol. Series 
 of Comp. Anat. in the 
 Mus. Royal Coll. Sur- 
 geons, London, vol. ii. 
 pi. xiv. 
 
 Fig. 93. 
 
ANNELIDA. 
 
 placed along the back, and these external vascular tufts communi- 
 cate with delicate plexuses of vessels situated in the interior of the 
 body, called the branchial plexuses. In the figure the branchial 
 plexuses of the left side only are represented (</, </, <?), and of 
 these one marked q' has been turned aside. The blood and nutri- 
 tious fluids derived from the whole alimentary tract are collected 
 by the large ventral intestinal vein (w, w, n), and conveyed to the 
 branchial plexuses through the numerous vessels (o, o, o), some of 
 which (o', o', o') are displaced in the drawing in order that their 
 connections may be better seen. Besides the blood and nutriment 
 thus derived from the intestine, the branchial plexuses receive the 
 circulating fluid from all the segments of the muscular envelope by 
 separate veins (p 9 p), and thus the blood from all parts is brought 
 to the gills and exposed to the influence of oxygen. 
 
 After undergoing respiration, the blood is collected from the 
 branchial plexuses by the lateral veins (r, r, r) ; from which, 
 through communicating vessels (s, s, s), it passes into the aorta 
 or great dorsal vessel (, , ), to be distributed through the body. 
 From the aorta large trunks (v, v) are given off to form the intes- 
 tinal artery (w, w), which, ramifying over the intestine, communi- 
 cates with the intestinal vein (w, w), and thus completes the vas- 
 cular circle.* 
 
 In the JVereidce, the aorta, or dorsal vessel, runs along the whole 
 length of the back, and in each ring offers a perceptible fusiform 
 dilatation, so that it has a beaded appearance ; at every segment it 
 gives off lateral branches, every one of which is furnished with a 
 little rounded vesicle, which Delle Chiaje conceives to be a distinct 
 heart or contractile cavity, calculated to assist in the propulsion of 
 the contained blood. 
 
 In Arenicola the arrangement of the vascular trunks seems to 
 be very nearly similar to that found in the earthworm ; but, instead 
 of the moniliform hearts, ( 247,) two large contractile sinuses 
 communicate between the dorsal and ventral vessels {Jig. 94, 6, b). 
 
 (263.) The reproductive organs of iheDorsibranchiateAnnelidans 
 are, perhaps, less known than those of any other animals. Cuvier-)- 
 
 * The parts indicated in the drawing by letters not referred to in the text are the 
 following : a, a, the ventral surface of the segments of the body ; e, e, the ventral 
 oars or packets of bristles ; /, /, the ventral cirri, or feelers ; g, the anal cirri ; ft, the 
 anus ; i, i, k, k, the bases of the dorsal and ventral oars, with their surrounding mus- 
 cles ; J, /, the dorsal longitudinal muscular bands ; m, m, the ventral longitudinal 
 muscular bands. 
 
 t Le9ons d'Anatomie Comparee, vol. v. p. 186. 
 
220 
 
 ANNELIDA. 
 
 J. 
 
 observed in the anterior part of the body of Arenicola five grey 
 vesicles resembling the ovaria of the earthworm ; and he was led 
 to conclude, in conformity with the Figt 94 
 
 then generally received opinion, that 
 the ova escaped from these vesicles 
 into the cellular structure between 
 the intestine and the walls of the 
 body. It is, however, probable that the 
 granular bodies {Jig. 94, m, m) usu- 
 ally found in that situation are para- 
 sitical Entozoa, as those of the earth- 
 worm have been proved to be. ; { 
 
 In .the Nereis, Delle Chiaje de- 
 scribes the ovaria as two long and ex- ; 
 trernely delicate caeca, occupying the , 
 posterior half of the visceral cavity, ( 
 and offering various constrictions and " 
 dilatations in their course ; these 
 caeca terminated by distinct apertures 
 in the neighbourhood of the anus, 
 and when gravid were found to be 
 filled with granular ova of a greenish 
 colour. 
 
 (264.) In one species of Nereis (N. 
 prolifera), Miiller* observed repro- 
 duction to take place by spontaneous 
 division ; a mode of propagation which, 
 although common among the Naidce, 
 had not previously been seen in any 
 of the Dorsibranchiate families. The 
 process of division is represented in 
 the appended figure (fig. 95); the 
 hinder part of the body, including 
 about seventeen segments, is seen to 
 be gradually separated from the ante- 
 rior or larger portion, and, moreover, 
 at the point of separation a new head 
 with eyes and tentacular cirri is dis- 
 tinctly formed. " In one case," says 
 
 * Ohtho Fred. Mii.Mer, Zoologia Danica, pi. lii. fig. 6, fol. 1788. 
 
ANNELIDA. 
 
 221 
 
 Miiller, u I found a mother to which F/ s- 95 - 
 
 three fetuses of different ages ap- 
 peared in one length. The mother 
 had thirty pedate segments ; the 
 youngest daughter, or that nearest 
 the mother, had eleven, but the head 
 was not yet developed. The most 
 remote had seventeen rings, with both 
 head and eyes, and, moreover, the 
 tail of the mother ; the middle one 
 had seventeen segments, and a head. 
 The two posterior were broken off 
 from the mother by pressure : in the 
 last, or oldest, was found a black sub- 
 stance filled with white spots ; and the 
 white spots, when squeezed from the 
 body, were oval, each marked with a 
 pellucid speck. Were they eggs ? If 
 so, how were they formed in a young 
 one still adhering to the body of its 
 parent ? In the middle one were si- 
 milar spots, but smaller. Were they 
 younger eggs ?" 
 
 Some curious speculations have been entertained by continental 
 writers relative to this mode of propagation. The tail of the ori- 
 ginal Nereis is still the tail of its offspring, and, however often the 
 body may divide, still the same tail remains attached to the hin- 
 der portion, so that this part of the animal may be said to enjoy 
 a kind of immunity from death. 
 
 (265.) Tubicola. Our knowledge of the last, or tubicolous di- 
 vision of the Annelidans, is very limited ; it may, indeed, be said to 
 be confined to an acquaintance with their external configuration, for 
 the few unconnected accounts which are given by authors relative 
 to their internal anatomy are so obviously based upon pure sup- 
 position, that, perhaps, the zootomist who should enjoy favourable 
 opportunities of inspecting the larger species in a fresh state, could 
 hardly make a more valuable contribution to our science than by 
 giving an account of the organization of these interesting animals. 
 We have already described the different kinds of tubes in which these 
 Annelidans live ( 233), and given a representation (Jig. 78) of 
 the calcareous tube secreted by the Serpula contortuplicata : the 
 
ANNELIDA. 
 
 annexed figure represents the 
 curious habitation of the Te- 
 rebella Medusa, constructed 
 by cementing together minute 
 shells and other small bo- 
 dies. In neither case is there 
 any muscular connection be- 
 tween the worm and its abode, 
 so that the creature can be 
 readily drawn out from its 
 residence in order to ex- 
 amine the external appen- 
 dages belonging to the indi- 
 vidual segments of its body. 
 When thus displayed (fig- 
 97), the modifications con- 
 spicuous in the structure of 
 the lateral oars are at once 
 seen to be in relation with 
 their circumscribed move- 
 ments, and offer a wide con- 
 trast to the largely developed 
 spines, setse, and tentacular 
 cirri, met with in the Dorsi- 
 branchiata. In the upper 
 part of the body, rudimentary 
 protractile bunches of hairs 
 are still discernible, but so 
 feebly developed that their 
 use must evidently be restrict- 
 ed to the performance of those 
 motions by which the protru- 
 sion of the head is effected ; 
 while upon the posterior seg- 
 ments even these are oblite- 
 rated, the only organs at- 
 tached to the rings being 
 minute foot -like processes 
 adapted to the same office. 
 The tentacular cirri, which 
 were likewise distributed 
 
 F/2-. 96. 
 
ANNELIDA 
 
 along the entire length of the 
 Dorsibranchiate order, are here 
 transferred to the head, where they 
 form long and delicate instruments 
 of iouch, and, most probably, assist 
 materially in distinguishing and 
 seizing prey ; the branchiae, like- 
 wise, are no longer met with upon 
 the segments enclosed within the 
 tegumentary tube, but are placed 
 only in the immediate vicinity of the 
 head, where they form fan-like ex- 
 pansions, or ramified tufts, so ar- 
 ranged as to be most freely exposed 
 to the surrounding medium. The 
 mouth placed at the origin of the 
 tentacular cirri is a simple orifice 
 closed with a valve-like flap or up- 
 per lip, but is unprovided with any 
 dental structure. The alimentary 
 canal is generally a simple and 
 somewhat capacious tube which tra- 
 verses the axis of the body ; but in 
 some species, as in Sabella pavo- 
 nina, it assumes a spiral course, 
 making close turns upon itself from 
 the mouth to the anal aperture, 
 which is always terminal. The cir- 
 culating system probably resembles, 
 in its general arrangement, that 
 of the Dorsibranchiate worms, the 
 course of the vessels being modified 
 in accordance with the altered posi- 
 tion of the branchiae ; but of this 
 we have no certain knowledge, nei- 
 ther are we acquainted with the na- 
 ture of the generative apparatus, 
 and the scattered remarks of au- 
 thors upon this subject are to the 
 last degree vague and unsatisfac- 
 tory. 
 
 Fig. .97. 
 
224 
 
 CHAPTER XIV. 
 
 MYRIAPODA.* 
 
 (266.) The Annelidans examined in the preceding chapter, with 
 the singular exception of the earthworm, are only adapted to an aqua- 
 tic life ; the soft integument which forms their external skeleton and 
 the setiform and tentacular organs appended to the numerous seg- 
 ments of their elongated bodies, are far too feeble to support them 
 in a less dense and buoyant element, so that when removed from 
 their native waters they are utterly helpless and impotent. Sup- 
 posing, however, that, as a mere matter of speculation, it was in- 
 quired by what means animals of similar form could be rendered 
 capable of assuming a terrestrial existence, so as to seek and obtain 
 prey upon the surface of the earth, and thus represent upon land 
 the Annelidans of the ocean : a little reflection would at once in- 
 dicate the grosser changes required for the attainment of such an 
 object. To convert the water-breathing organs of the aquatic 
 worms into an apparatus adapted to aerial respiration would be the 
 first requisite. The second would be to give greater density and 
 firmness to the tegumentary skeleton, to allow of more power- 
 ful and accurately applied muscular force, by diminishing the num- 
 ber of segments composing the annulose covering, and also by 
 converting the lateral oars into jointed levers of support sufficiently 
 strong to sustain the weight of the whole body, to provide instru- 
 ments of locomotion fitted for progression upon the ground. Yet 
 all these changes would be inefficient without corresponding modi- 
 fications in the character of the nervous system : the lengthened 
 chain of small ganglia found in the aquatic worms would be quite 
 inadequate to wield muscles of strength adapted to such altered cir- 
 cumstances ; the small encephalic brain would be incompetent to 
 correspond with more exalted senses, so that, as a necessary conse- 
 quence of superior organization, the nervous centres must be all 
 increased in their proportionate developement to adapt them to 
 higher functions. 
 
 The changes, which our supposition infers would be requisite 
 for the conversion of an aquatic Annelidan into a land animal, are 
 precisely those which we encounter when we turn our attention 
 from the creatures described in the last chapter to the MYRIA- 
 PODA, upon the consideration of which we are now entering : . 
 
 * (*,v(>ux.S) ten thousand, i.e. many ; vrovs, a foot. 
 
MYRIAPODA. 
 
 225 
 
 they form the transition from the red-blooded worms to the class 
 of insects, and are intermediate between the two in every point of 
 their structure. 
 
 (267.) The body of a Myriapod is composed of a consecutive 
 series of segments of equal dimensions, but, unlike those of 
 the generality of the Annelida, composed of a dense semi-calca- 
 reous, or else of a firm coriaceous substance ; and to every segment 
 is appended one or two pairs of articulated legs, generally termi- 
 nated by simple points. 
 
 The anterior segment or head, besides the organs belonging 
 to the mouth, contains the instruments of sensation, consisting of 
 simple or compound eyes, and of two long and articulated organs 
 called antenna, generally regarded as appropriated to the sense of 
 touch, but which probably are connected with other perceptions less 
 intelligible to us. 
 
 The air required for respiration is taken into the body through 
 a series of minute pores or spiracles placed on each side along the 
 entire length of the animal, and is distributed by innumerable 
 ramifying tubes or tracheae to all parts of the system. 
 
 The number of segments, and consequently of feet, increases 
 progressively with age ; a circumstance which remarkably distin- 
 guishes the Myriapoda from the entire class of insects, properly so 
 called. 
 
 (268.) The Myriapoda may be divided into two families, origin- 
 ally indicated by Linnaeus : the Julidce, or millepedes ; and the Sco- 
 lopendridtf, or centipedes ; each of which will require our notice. 
 
 Julid<. The lowest division, 
 which derives its name from the 
 Julus, or common millepede, is 
 most nearly allied to the Anneli- 
 dans, both in external form, and 
 also in the general arrangement 
 of its different organs ; this, there- 
 fore, we shall first examine, and 
 select the Julus terrestris, one 
 of the species most frequently 
 met with, as an example of the 
 rest. These animals (Jig- 98, A) 
 are generally found concealed un- 
 der stones, or beneath the bark of 
 decaying timber, where they find 
 
 Fig. 98. 
 
MYRIAPODA. 
 
 subsistence by devouring decomposing animal and vegetable sub- 
 stances. The body is long and cylindrical, composed of between 
 forty and fifty hard and brittle rings, which, with the exception of 
 those forming the head and tail, differ but slightly from each other. 
 Every segment supports two pairs of minute feet, arising close to 
 the mesian line upon the under or ventral surface ; but these feet, 
 although distinctly articulated {fig- 98, c), are as yet extremely 
 small in comparison with the bulk of the animal, and are evidently 
 but mere rudiments of the jointed legs developed in more highly 
 organized forms of homogangliate beings ; so that the movements 
 of the Julus are very slow, and the creature seems rather to glide 
 along the ground, supported on its numerous but almost invisible 
 legs, than to walk. When at rest, the body is rolled up in a 
 spiral form (j%. 98, B), the feet being concealed in the con- 
 cavity of the spire, and thus protected from injury. 
 
 (269.) The mouth resembles in structure that of the larva of 
 some insects, and is furnished with a pair of stout horny jaws, mov- 
 ing horizontally, and provided at their cutting edges with sharp den- 
 ticulations, so as to render them effective instruments in dividing 
 the fibres of rotten wood, or the roots and leaves of vegetables, 
 which are usually employed as food ; and the alimentary canal, 
 which is straight and very capacious, is generally found filled with 
 materials of this description. 
 
 (270.) In most points of their internal organization, the Myria- 
 poda resemble insects ; and we should only anticipate the obser- 
 vations which will be more conveniently made hereafter, did we 
 enter into any minute description of their anatomy : we shall, there- 
 fore, in this place, simply confine ourselves to the notice of those pe- 
 culiarities which occur in the animals under consideration, by which 
 they are distinguished from insects, and entitled to rank as a dis- 
 tinct class. We have seen that in such of the Annelida as have 
 been most carefully investigated, the orifices of the sexual organs 
 are situated near the anterior part of the body, not, as is invariably 
 the case among insects, at the caudal extremity : in this particular 
 the JulidfE still present analogies with the red-blooded worms ; 
 for in them the external openings of the male parts are situated im- 
 mediately behind the base of the seventh pair of legs, and are found 
 to be placed upon minute mammillary protuberances, which are 
 each furnished with a sort of hooked scale, adapted to hold the 
 female during the process of impregnation. 
 
 In the female, also, the sexual orifices are advanced very far 
 
MYUIAPODA. 
 
 227 
 
 forward, being situated in the vicinity of the head, between the 
 first and second segments ; the sexes, however, as in insects, are 
 perfectly distinct, and the conformation of the internal organs 
 coincides with that type of structure which is common to the insect 
 orders. 
 
 (271.) Another important distinction between these animals and 
 insects properly so called, is met with in the mode of their growth 
 and developement. Insects, as we shall more fully explain here- 
 after, undergo a more or less complete change in their outward 
 form as they advance through several preparatory stages to their 
 mature state : during the progress of these changes, which consti- 
 tute what is usually called the metamorphosis of insects, they are 
 invariably unable to perpetuate their species ; and it is only in their 
 last or perfect condition, which is ordinarily of very short duration, 
 that the sexual organs attain their perfect developement, and are 
 fit for reproduction. In this state all true insects have six legs, 
 which is one of the most important characters of the class. The 
 Myriapoda, likewise, undergo several changes of form as they ad- 
 vance to maturity ; but these changes principally consist in the 
 repeated acquisition of additional legs, so that in their perfect 
 condition, instead of the limited number of six legs met with 
 in insects, these organs have become extremely numerous. The 
 progress of these transi- Fig. 99. 
 
 tions, from their imma- 
 ture to their fully de- 
 veloped state, has been 
 well observed by De 
 Geer * and Savi ;*f and 
 the result of their ob- 
 servations is here given, 
 in order that the rea- 
 der may compare the 
 different steps of the 
 process with what we 
 shall afterwards meet 
 with in the more highly 
 organized articulata. 
 
 The eggs, (Jig. 99, 
 
 * Memoires pour servir a 1'Histoire des Insectes. 7 vols. 4to. Stockholm, 1778. 
 t Osservazione per servire alia storia di una specie di Julus communissima. Bo- 
 logna, 1817. 
 
MYRIAPODA. 
 
 A, ) which are very minute, are deposited in the earth or vege- 
 table mould in which the Julus is usually met with. When first 
 hatched, the young Myriapod is of course exceedingly diminu- 
 tive ; at that period it resembles a microscopic kidney-bean, and 
 is completely destitute of legs or other external organs. After 
 a few days the embryo Julus changes its skin, and, throwing off 
 its first investment, appears divided into distinct segments, and 
 furnished with a head, a pair of simple eyes, a pair of antennae, 
 and six jointed legs attached to the anterior rings of the body 
 (fig- 99, B, c). Some days subsequent to its first moult, the 
 skin is again cast, and the millepede acquiring larger dimensions is 
 seen to possess seven pairs of ambulatory extremities, which are, 
 however, still placed only upon the anterior segments (Jig. 99, D). 
 When twenty-eight days old, they again throw off their outward 
 covering, and assume, for the first time, their adult form : they 
 then consist of twenty-two rings, and have twenty-six pairs of 
 feet ; but, of these, only the eighteen anterior pairs are used in 
 progression. At the fourth moult the number of legs is increased 
 to thirty-six pairs ; and at the fifth, at which time the body be- 
 comes composed of thirty segments, there pfg m 100. 
 are forty-three pairs of locomotive organs. 
 At last, in the adult state, the male has 
 thirty-nine and the female sixty-four rings 
 developed; but it is not until two years after 
 this period that the sexual organs appear, 
 and the animals become capable of repro- 
 duction. 
 
 (272.) Scolopendrida. In the second 
 family of Myriapoda we have a very striking 
 illustration of the manner in which the de- 
 velopement of the nervous centres proceeds 
 step by step with that of the external limbs. 
 The slow-moving Julidse possess in their 
 rudimentary feet organs adapted to their 
 condition, and their feeble powers of locomo- 
 tion are in relation with their vegetable 
 diet and retiring habits. But in the pre- 
 daceous and carnivorous Scolopendra (Jig. 
 100), which, although it lurks in the 
 same hiding-places as the Julus, obtains 
 its food by pursuing and devouring insects, 
 
MYRTAPODA. 229 
 
 far greater activity is indispensable, and accordingly we find the 
 segments of the body, and the extremities appended to them, ex- 
 hibiting a perfection of structure adapted to greater vivacity and 
 more energetic movements. 
 
 This is at once evident upon a mere inspection of their out- 
 ward form ; the individual segments composing the animal are 
 much increased in their proportionate dimensions, and, instead of 
 being cylindrical, each division of the body is flattened and pre- 
 sents a quadrangular outline. In order to give greater flexibility to 
 the body, instead of the semi-crustaceous hard substance which forms 
 the rings of the Julus, the integument is composed of a tough and 
 horny substance, forming two firm plates, one covering the back, the 
 other the ventral aspect of the segment, while all the lateral part 
 is only incased in a flexible coriaceous membrane with which the 
 individual rings are likewise joined together. Such an external 
 skeleton is obviously calculated to give the greatest possible free- 
 dom of motion, and thus to enable the Scolopendra to wind its 
 way with serpent-like pliancy through the tortuous passages in 
 which it seeks its prey. 
 
 (273.) The ventral chain of ganglia belonging to the nervous 
 system presents a series of nervous centres of dimensions proportioned 
 to the increased bulk of the segments in which they are lodged, and 
 thus fitted to direct the movements of more perfect limbs. The 
 legs, therefore, as a necessary consequence, become proportionably 
 powerful, divided into distinct joints, and provided with muscles 
 calculated to bestow on them that activity essential to the pursuit 
 and capture of active prey. Thus, then, by a simple concentra- 
 tion of the nervous masses composing the abdominal chain of 
 ganglia, we have the slow-moving and worm-like Julus, which we 
 have seen to be, in consequence of its feebleness, restricted to live 
 upon roots and dead substances, converted into the active and 
 powerful Scolopendra, well able to wage successful war with the 
 strongest of the insect tribes, and not unfrequently formidable 
 from its size even to man himself. 
 
 (274.) The mouth of the Scolopendra is a terrible instrument 
 of destruction ; being provided not only with horny jaws resembling 
 those of insects hereafter to be described, but with a tremendous 
 pair of sharp and curved fangs, ending in sharp points, and per- 
 forated near their termination by a minute aperture, through which 
 a poisonous fluid is most probably instilled into the wound in- 
 flicted by them. It is to this structure that the serious conse- 
 
230 MYR1APODA. 
 
 quences, which in hot climates not unfrequently result from the 
 bite of one of these animals, must no doubt be attributed. 
 
 (275.) In their internal anatomy the Scolopendrida resemble 
 insects even more nearly than the Julus. The alimentary canal is 
 straight and intestiniform, but of much smaller diameter than that of 
 the vegetable-eating Myriapoda. It presents an oesophagus, and a 
 small muscular gizzard ; but there is no perceptible division into 
 stomach and intestine. The respiratory and circulating sys- 
 tems, as far as they are understood, seem to correspond with 
 what we shall afterwards find to exist in the larva of insects. In 
 the position and arrangement of the sexual organs the Scolopen- 
 dridse complete the transition between the Annelidans and insects, 
 properly so called ; for, while in Julus we have found them still 
 occupying the anterior part of the body as in the former class, in 
 the Scolopendra they are removed to the tail. The structure of 
 the male organs is remarkable. The testes are seven in number, 
 and, on opening the posterior segments of the animal, they are 
 found closely packed in parallel lines : each testis is composed of 
 two fusiform parts precisely similar to each other, and from both 
 ends of every one of these, which is hollow, arises a narrow duct, 
 so that there are fourteen pairs of ducts arising from the fourteen 
 secreting organs. The ducts all end in a common canal, which 
 gradually becomes enlarged and tortuous, and terminates by a 
 distinct aperture in the vicinity of the anus. Just prior to its ter- 
 mination the common ejaculatory duct communicates with five 
 accessory glands, four of which are intimately united until 
 unravelled, while the fifth is a simple caecum of considerable 
 length.* 
 
 The ovarian system of the female Scolopendra is a single tube, 
 apparently without secondary ramifications. 
 
 Some Scolopendrse (S. phosphorea) emit in the dark a strong 
 phosphorescent light ; and one species (S. electrica) is able to 
 give a powerful electrical shock to the hand of the person who in- 
 advertently seizes it. 
 
 * Vide Cyclop, of Anat. and Phys. art. Generation, organs of. Comp. Anat. 
 
231 
 
 CHAPTER XV. 
 
 INSECTA. 
 
 (276.) The word Insect has at different times been made use of 
 in a very vague and indeterminate manner, and applied indiscrimi- 
 nately to various articulated animals. * In the restricted sense in 
 which we now use it, we include under this title only such of the 
 HOMOGANGLIATA as in their perfect or mature state are recog- 
 nisable by the following characters, by which they are distinguished 
 from all other creatures. 
 
 The body, owing to the coalescence of several of the segments 
 which compose their external skeleton, is divided into three prin- 
 cipal portions ; the Head, the Thorax, and the Abdomen. The 
 Head contains the oral apparatus, and the instruments of the 
 senses, including the antennae or feelers, which are articulated 
 organs presenting great variety of shape, but invariably only two 
 in number. The Thorax, formed by the union of three segments 
 of the skeleton, supports six articulated legs, and sometimes four 
 or two wings ; these last, however, are frequently wanting. The 
 Abdomen is destitute of legs, and contains the viscera connected 
 with nutrition and reproduction. 
 
 (277.) But insects, before arriving at that perfect condition in 
 which they exhibit the above-mentioned characters, undergo a series 
 of change, both in their outward form and internal structure, which 
 constitute what is generally termed their metamorphosis. When 
 this is complete, as for example in the butterfly, the insect, after 
 leaving the egg, passes through two distinct states of existence 
 before it arrives at maturity and assumes its perfect form. The 
 female butterfly lays eggs which when hatched produce, not but- 
 terflies, but caterpillars, animals with elongated worm-like bodies, 
 divided into numerous segments, and covered with a soft coriaceous 
 integument {Jig. 105, A). The head of the caterpillar is provided 
 with horny jaws and several minute eyes ; the legs are very short, 
 six of them which are attached to the anterior rings being horny and 
 pointed, while the rest of variable number appended to the posterior 
 
 * The word Insect, derived from the Latin word Insecta, simply means divided into 
 segments. 
 
232 INSECTA. 
 
 part of the body are soft and membranous. The caterpillars, or 
 larveEj* live for some time in this condition, and frequently change 
 their skin as they increase in size, until at length, the last skin of 
 the larva being thrown off, the animal presents itself in quite 
 a different form, enveloped in an oblong case, without any ex- 
 ternal limbs, and almost incapable of the slightest motion, re- 
 sembling rather a dead substance than a living creature ; it is then 
 called a chrysalis, nymph, or pupa^ (Jig. 105, B). 
 
 On examining attentively the external surface of this pupa, we 
 may discern, in relief, indications of the parts of the butterfly con- 
 cealed beneath it, but in a rudimentary condition. After some time 
 the skin of the pupa bursts, and the imago, or perfect insect, issues 
 forth, moist and soft, with its wings wet and crumpled ; but in a 
 few minutes the body dries, the wings expand and become stiff, 
 and, from being a crawler upon the ground, the creature is con- 
 verted into a gay and active denizen of the air (Jig. 105, c). 
 
 Such is the progress of the metamorphosis when complete ; but 
 all insects do not exhibit the same phenomena. Those genera 
 which, in their mature condition, have no wings, escape from the 
 egg nearly under the same form as they will keep through life ; these 
 form the Insecta Ametabola^ of authors : and even among those 
 tribes which, when perfect, possess instruments of flight, the larva 
 frequently differs from the complete insect only from its wanting 
 wings, and the pupa is recognisable by being possessed of these organs 
 in an undeveloped or rudimentary state ; an example of this is 
 seen in the house-cricket, (Jig. 102,) in which A represents the 
 imago ; B, the pupa ; c, the full-grown larva ; D, the young just 
 hatched ; and E, the eggs. 
 
 (271.) The extensive class of INSECTS has been variously arranged 
 by different entomologists, and distributed into numerous orders. 
 Among the different systems which have been given, we select the 
 following as best calculated to render the reader acquainted with 
 
 * So called by Linnaeus, because in this condition the perfect form of the insect is 
 concealed as it were under a mask. Larva, Lat. a mask. 
 
 t The two first of these names are purely fanciful ; the last is derived from pupa, 
 a baby wrapped up in swaddling bands. 
 
 J , without ; ptruZoXvi) change. 
 
 $ The classification of insects here given is that of Burmeister, which we select 
 without giving any opinion as to its relative merits compared with others adopted by 
 different entomologists, but simply as being most convenient for our present purpose. 
 Manual of Entomology, translated from the German of Dr. Hermann Burmeister by 
 W. E. Shuckard, 8vo. 1836. 
 
INSECTA. 233 
 
 the transformations, as well as the principal forms, to which allu- 
 sion will be made in subsequent pages. 
 
 I. INSECTA AMETABOLA. The larva resembles the perfect 
 insect, but is without wings. The pupae of such species as have 
 wings in their imago state possess rudiments of those organs. 
 The pupa runs about and eats. 
 
 a. With sucking mouths composed of four fine setae lying in 
 a sheath. 
 
 1st Order. Hemiptera* In such insects of this order as pos- 
 sess wings, which when present are always four in number, the 
 anterior or upper pair are generally coriaceous in their texture for 
 one half of their extent, while the posterior portion is thin and 
 membranous ; a circumstance from which the name of the order is 
 derived. The Notonecta or water boatman, {fig' 101) is a 
 
 Fig. 101. 
 
 familiar example ; c and D represent immature, and F mature 
 larvae. The pupa, G, H, differs little in outward form from the 
 perfect insect E, but possesses only the rudiments of wings. 
 
 /3. Having mouths furnished with jaws, or distinct mandibles 
 and maxillae. 
 
 2nd Order. Orthoptera."^ In this order the perfect insect pos- 
 sesses four wings, the posterior pair being the largest ; and, when 
 at rest, these are folded both in a transverse and longitudinal 
 
 * wfjuffus, half ; frtgov, a wing, t O^of, straight, 
 
234 
 
 INSECTA. 
 
 direction. The anterior wings are of a denser texture, resembling 
 leather or parchment. To this order belongs the common house- 
 cricket (Gryllus domesticus), of which, as well as of its eggs, 
 larvae, and pupa, figures are here given (fig- 
 
 Fig. 102. 
 
 3rd Order. Dictyotoptera* This order comprises the cock- 
 roaches, in which the wings are four in number when they exist ; 
 but they are generally of equal size, and never folded. 
 
 II. INSECTA METABOLA. The larva is a worm either 
 with or without legs. The pupa is quiet ; or, if it moves, it does 
 not eat. 
 
 4th Order. Neuroptera.^ Insects having four equally large 
 or equally long wings with reticulated nervures, and mouths pro- 
 vided with strong lateral jaws. The most perfect examples of this 
 order are the dragon-flies (Libellula), the largest of the insect 
 inhabitants of our own country. The perfect insect (Jig. 103), 
 equally remarkable for its beautiful form, powerful flight, and car- 
 nivorous habits, is among the most formidable tyrants of its 
 class ; while the larvae, which abound in our ditches and stagnant 
 pools, are eminently destructive to their aquatic companions. The 
 larva (Jig- 104, B) possesses six articulated legs ; while the 
 pupa A, which certainly forms an exception to the general 
 
 ot, reticulated ; 
 
 a wng. 
 
 a nerve ; <rri(>ov t a wing. 
 
1NSECTA. 
 
 235 
 
 rule given above, is not only furnished with rudimentary wings, 
 but is eminently rapacious, and possesses in the structure of its 
 
 Fig. 103. 
 
 mouth, to be described hereafter, peculiar facilities for gratifying 
 its blood-thirsty disposition. 
 
 In other orders, the wings are always unequal ; the pos- 
 terior, and sometimes both pairs, not unfrequently being wanting. 
 
 . Mouths adapted to sucking. 
 
 5th Order. Diptera* Instead of posterior wings, we find in 
 this order pedunculated appendages called halteres orpoisers. The 
 mouth contains a soft proboscis, and is usually armed with several 
 setse and provided with a pair of palpi ; of such, the common 
 house-fly affords a familiar instance. 
 
 6th Order. Lepidoptera.^ The insects belonging to the lepi- 
 dopterous order are possessed of four wings, which are generally 
 covered with microscopic scales, frequently exhibiting the most 
 beautiful colours : the larvae are provided with feet and a dis- 
 
 * ^iTTi^os (S/-j, wrigflv), with two wings. "T X /?, a scale 
 
236 
 
 INSECTA. 
 
 tinct head ; the mouth of the 
 perfect insect is a long spiral 
 proboscis. 
 
 The butterflies, so conspi- 
 cuous for their beauty, are 
 well-known representatives of 
 this order ; and the usual 
 forms of these insects in the 
 larva, pupa, and imago state 
 are familiar to all (Jig. 105, 
 A, B, c). 
 
 /3. Mouths with distinct 
 biting jaws. 
 
 7th Order. Hymenoptera.* 
 Possessing four naked 
 wings traversed by ramose 
 nervures. Larvae generally 
 without head or feet, but 
 sometimes with both. Wasps, 
 Bees, Sec. 
 
 8th Order. Coleoptera. 
 In this last order, the ante- 
 rior wings are converted into 
 dense horny cases 
 or elytra, be- 
 neath which the 
 posterior pair, a- 
 dapted to flight, 
 are folded up 
 when the insect 
 is at rest. The 
 larvae possess a 
 head, and are 
 sometimes pro- 
 vided with feet, 
 but not always. 
 
 The Coleopte- 
 rous division of 
 the insect world 
 embraces the ex- 
 
 * vprivtvos, a membrane; 
 
 Fig. 104. 
 
INSECTA. 
 
 237 
 
 tensive tribe of beetles, both terricolous and aquatic ; of the 
 former, we have an example in the common cock-chaffer (Melo- 
 lonthci), of which a figure is here given, as well as of the different 
 stages of its developement (fig- 106, A, B, c, D, E).* 
 
 Fig. 106. 
 
 Having thus introduced the reader to the chief orders com- 
 posing the vast class of insects, our next object must be to ex- 
 amine more in detail the principles upon which these animals are 
 constructed, both as regards their external organization, and the 
 nature and arrangement of their internal parts. We shall speak 
 of them in the first place only in their perfect condition, leaving 
 all observations relative to the metamorphosis to which they are 
 subject for subsequent consideration. 
 
 * It would be foreign to our present purpose to do more than enumerate other orders 
 of insects which have been formed by different authors ; of these, the following are 
 the most important. 
 
 Dermaptera (Leach), ^i^x t skin; vrngov) a wing. Earwigs (Forficula). 
 
 Trichoptera (Leach), 6^ rp%os, hair; rrsgav. May-flies (Phryganea). 
 
 Aphaniptera (Kirby), a<pav/jj, invisible ; vrr&gov. Fleas (Pulex). 
 
 Aptera, arr^aj, without wings. Wingless insects. 
 
 Parasita, (Latreille). Lice (Pediculus). 
 
 Thysanoura (Latreille), 0v<rav-euos, bushy-tailed. Spring-tails (Lepismenae). 
 
INSECT A. 
 
 (79.) Insects, examined generally, differ from all other articu- 
 lated beings in one remarkable circumstance they are capable of 
 flight can maintain themselves in the air by means of wings : it is 
 true, indeed, that some species are met with in all the orders de- 
 scribed above, which are apterous, being destitute of such organs ; 
 but these form exceptions to be noticed hereafter. Such a mode of 
 progression, through so rare a medium as that of the atmosphere, 
 necessarily demands an exercise of muscular power of the most 
 vigorous and active description, and a correspondent strength and 
 firmness in the skeleton upon which the muscles act. It is suffi- 
 cient to cast a glance at the external construction of any of the 
 Annelidans or Myriapoda, which have come under our notice, to be 
 convinced that in such animals flight would be impossible under any 
 circumstances : their long and flexible bodies present no point to 
 which efficient wings could be appended ; neither is any part of their 
 divided skeleton possessed of sufficient strength to support the action 
 of muscles so forcible and energetic as would be indispensable to 
 wield the instruments used in flying, or raise the body above the 
 surface of the ground. 
 
 Similar changes, therefore, to those which we found requisite in 
 order to convert the aquatic Annelide into the terrestrial Myriapod, 
 must be still further carried out before the animals last mentioned 
 could be adapted to become inhabitants of the air. The number of 
 segments composing their elongated bodies must be materially re- 
 duced ; certain parts of the skeleton must be strengthened in order 
 to sustain the efforts of muscles sufficiently strong to raise the 
 weight of the animal ; and, in the last place, the nervous ganglia, 
 by a like concentration of hitherto separated parts, must be gather- 
 ed into masses of increased power sufficient to animate the more 
 vigorous muscles with which they are in relation. 
 
 (280.) Such changes are precisely those which are most remark- 
 able when we compare the external appearance of a centipede with 
 that of a winged insect : the entire number of segments, and conse- 
 quently the proportionate length of the latter, is obviously reduced. 
 The head is seen to be more distinct from the rest of the body, to 
 which it is connected by a moveable joint. The three anterior seg- 
 ments of the trunk become largely developed, and, from the density 
 of their substance, form by far the strongest part of the skeleton, 
 constituting what is called the thorax of the insect ; they are, 
 moreover, generally united together, especially the two posterior, 
 so as to be consolidated, as it were, into one piece ; and to these 
 
INSECT A. 239 
 
 rings only the organs of locomotion are appended. The remaining 
 segments of the body are much less firm in their texture, especially 
 in insects with hard or horny wing-covers, in which indeed they are 
 almost of a membranous consistence, so as to increase as far as pos- 
 sible the lightness of the animal in parts where strength is not re- 
 quired. Here then is an annulose skeleton adapted to flight ; 
 dense and unyielding where support is required for the attachment 
 of the locomotive organs, but thin and flexible elsewhere. 
 
 (281.) The above conditions being required in the arrangement 
 of the pieces which compose the outward framework of the body in 
 insects, we may easily conceive that the mode of union between 
 the various segments above described is by no means a matter of 
 indifference, inasmuch as very different degrees of motion are re- 
 quired between the individual rings. In the Annelida and My- 
 riapods a very simple kind of junction was sufficient ; for in them 
 the segments were all united by the mere interposition of a 
 thinner coriaceous membrane, extending between their contiguous 
 margins ; but in insects several kinds of articulation are, met 
 with in the construction of the trunk adapted to the mobility 
 of different regions. 
 
 The first mode of connection is effected by suture, or rather by 
 a species of " harmony" as it is technically termed by anatomists ; 
 two plates of the skeleton being accurately and immoveably fitted 
 to each other, but without being decidedly fastened together by 
 serrated edges. This kind of junction is met with in the thorax, 
 and serves an important purpose ; for at the point of union both 
 plates are bent inwards, and prolonged internally, so as to form 
 numerous partitions and processes from which the muscles mov- 
 ing the wings and legs derive extensive origins. 
 
 A second means whereby the pieces of the thorax are fastened 
 together is by syinphysis, in which a somewhat soft membrane 
 is interposed between two plates, so as to admit of a slight degree 
 of motion. 
 
 More extensive movement is required between the pieces which 
 compose the abdomen ; for in this region that rigidity and firm- 
 ness which are essential in the construction of the thorax, would 
 be highly disadvantageous, inasmuch as the abdominal viscera must 
 be subject to constant variations in bulk, caused either by food 
 taken into the intestines, or, in the case of the female, by the de- 
 velopement of the eggs after impregnation. The rings of the 
 abdomen are, therefore, united by a membrane passing from one 
 
240 INSECTA. 
 
 to another ; but so loosely, that the edges of the individual plates 
 wrap over each other to some extent, and thus may be separated 
 by the slightest pressure from within. 
 
 But in other regions there is an absolute necessity for a mode 
 of communication intermediate in character between the two kinds 
 mentioned above ; having neither the firmness of the one, nor 
 the mobility of the other. This is more especially the case in 
 the junction between the head and the anterior segment of the 
 thorax, and also between the last-named segment and the middle 
 piece of the thorax, in those cases where these two parts are not 
 joined by suture. The joint employed in this case is of very 
 beautiful construction, resembling in some respects that formed 
 by a ball and socket ; a conical prolongation of one segment is 
 admitted into a smooth cavity excavated in the corresponding 
 margin of the other, and secured in this position by muscles and 
 an external ligament. Such an articulation is of course capable of 
 being firmly fixed by muscular action, but at the same time admits 
 of sufficient freedom of motion to allow rotation in all directions. 
 
 (282.) The legs of insects, as we have already stated, are in- 
 variably six in number, one pair being attached to each of the three 
 thoracic segments. Considered separately, every leg may be seen 
 to consist of several pieces, connected together by articula- 
 tions of different kinds, which require our notice. The first di- 
 vision of the leg, or that in immediate connection with the thorax, 
 to which it is united by a kind of ball-and-socket joint, enclosed 
 in a strong membranous capsule, and possessing very various de- 
 grees of motion in different insects, is called the hip (coxa)', and 
 upon this, as upon a centre, the movements of the limb are per- 
 formed. To the extremity of the coxa a small moveable piece is at- 
 tached, called the trochanter ; to which succeeds the thigh (femur), 
 which is the thickest and most robust of all the divisions of the 
 limb. The next piece, called the shank (tibia"), is occasionally of 
 considerable length, and is connected to the last by a hinge ; to its 
 extremity is appended the foot (tarsus), composed of a consecutive 
 series of small segments, varying in number from five to one, the 
 last of which is armed with claws, or other appendages, adapted 
 to different kinds of progression. These divisions of the leg the 
 reader will easily recognise ; they are for the most part united 
 together by articulations so constructed as to allow simply of flexion 
 and extension, which will be best understood by inspecting, in 
 some large insect, the junction between the femur and the tibia, 
 
INSECTA. 
 
 or the knee-joint, as we might term it. Upon the upper ex- 
 tremity of the tibia the observer will find on each side a precise 
 semicircular furrow, behind which is a concentrical but smaller 
 ridge, and still further back a circular depression or fossulet. On 
 examining the corresponding surfaces of the femur, he will detect 
 a ridge accurately corresponding to the above-mentioned furrow ; 
 behind this a furrow corresponding to the preceding ridge, and still 
 further back, a minute elevation adapted to the fossulet of the 
 tibia, wherein it is fastened by a minute but very strong ligament. 
 Such ridges and grooves, when fitted into each other, form a joint 
 evidently admitting of a free and hinge-like motion, while from 
 its structure, dislocation is almost impossible. 
 
 (283.) The above general description of the leg of an insect will 
 prepare us to examine various modifications in outward form and 
 mechanical arrangements by which these simple organs are adapted 
 to progression under a great diversity of circumstances. When, 
 indeed, we reflect how extensively this class of animals is distri- 
 buted, and the variety of situations in which insects live, we are 
 led to expect corresponding adaptations in the construction of their 
 instruments of locomotion ; and in this our expectations will not 
 be disappointed. 
 
 In the generality of terrestrial species, the last segment of the 
 tarsus or foot is provided with a pair of strong horny hooks, which 
 are available for many purposes, being used either for creeping 
 upon a moderately rough surface, for climbing or for clinging to 
 various substances. 
 
 Such simple hooks, however, would not always serve. In the 
 case of the louse (Pediculus) for example, that is destined to 
 climb slender and polished hairs, such prehensile organs could be 
 of little use. The structure of the foot is therefore modified ; the 
 tarsus in this insect terminates in a single moveable claw, which 
 bends back upon a tooth-like process derived from the tibia, and 
 thus forms a pair of forceps fitted to grasp the stem of the hair and 
 secure a firm hold. 
 
 Many insects, especially those of the Dipterous order, are able 
 to ascend the smoothest perpendicular planes, or even to run with 
 facility, suspended by their feet in an inverted position, along sub- 
 stances which, from their polished surfaces, could afford no hold to 
 any apparatus of forceps or booklets. In the common flies (Mus- 
 cidcc), the exercise of this faculty is of such everyday occurrence, 
 that, wonderful as it is, it scarcely attracts the attention of ordinary 
 
 R 
 
242 
 
 INSECT A. 
 
 observers. The foot of the house-fly, nevertheless, is a very curious 
 piece of mechanism ; for, in addition to the recurved hooks pos- 
 sessed by other climbing species, it is furnished with a pair of 
 minute membranous flaps (Jig. 107, c), which, under a good mi- 
 croscope, are seen to be covered with innumerable hairs of the ut- 
 most delicacy : these flaps, or suckers as they might be termed, 
 adhere to any plane surface with sufficient tenacity to support the 
 whole weight of the fly, and thus confer upon it a power of pro- 
 gression denied to insects of ordinary construction. 
 
 Fig. 107. 
 
 In Bibio febrilis (fig. 107, B) the sucking discs appended to 
 the foot are three in number, but in other respects their conforma- 
 tion is the same. 
 
 In Cymbex lutea (fig. 107, D) the arrangement of the suckers 
 is different, one large and spoon-shaped disc being attached to the 
 extremity of each tarsal joint. Moreover, in this case there is 
 another singular structure, two spur-like organs project from each 
 side of the extremity of the tibia, each being is provided with 
 a sucking disc, while the two together form a strong prehensile 
 forceps. 
 
 In some water-beetles (Dytiscidce) the feet are armed with a 
 still more elaborately constructed apparatus of suckers ; but in this 
 case, as they are only met with in the male insect, they perhaps 
 ought rather to be looked upon as a provision made for the purpose 
 
INSKCTA. 24-3 
 
 of securely holding the female during sexual union, than as being 
 specially connected with locomotion. 
 
 In the anterior legs of the male Dytiscus the three first joints of 
 the tarsus are excessively dilated, so as to form a broad circular 
 palette : on examining the inferior surface of this expanded portion 
 under a microscope, it is seen to be covered with an immense num- 
 ber of sucking-cups (Jig. 107, F), two or three being much larger 
 than the rest, but they form collectively a wonderful instrument of 
 adhesion. 
 
 The middle pair of legs of the same beetle (Jig. 107, A) exhibit 
 a somewhat similar structure ; but, in this case, the disc upon which 
 the sucking apparatus is placed is much elongated, and the suckers 
 are all of small dimensions. 
 
 In the female Dytiscus (Jig* 109, c) this configuration of the 
 tarsus is wanting, and, moreover, the surface of the back is marked 
 with deep longitudinal grooves that do not exist in the male insect, 
 but seem to be an additional provision for facilitating the inter- 
 course of the sexes in these powerful aquatic beetles. 
 
 (284.) Another mode of progression common among insects is 
 by leaping, to which, from their extraordinary muscular power, these 
 little beings are admirably adapted. The common flea, for example, 
 (Pulex irritansy) (Jig. 110), will leap two hundred times its own 
 length ; and many Orthoptera possess a power of vaulting through 
 the air scarcely less wonderful, of which the cricket affords a fami- 
 liar instance. In such insects (Jig. 102, A, B) the thighs of the 
 posterior legs are enormously dilated, and the length of these 
 limbs is much greater than that of the anterior pair. When dis- 
 posed to leap, such insects bend each hind-leg, so as to bring the 
 tibia into close contact with the thigh, which has often a longitudi- 
 nal furrow armed on each side with a row of spines, to receive it. 
 The leg being thus bent, they suddenly unbend it with a jerk, 
 when, pushing against the plane of position, they spring into the 
 air.* In many of these saltatorial tribes the tarsus is furnished 
 with very curious appendages, either provided for the purpose 
 of taking off the jar when the animal alights from its lofty 
 leaps,')" or else by their elasticity they may act like firm cushions, 
 adapted to give greater effect to the spring which raises the insect 
 from the ground. In the magnified view of the tarsus of an Abys- 
 
 * Kirby and Spence, Introduction to Entomology, 4 vols. 8vo. 
 t Sir E. Home, Phil. Transact. 1816. 
 
244 
 
 IXSECTA. 
 
 sinian grasshopper (Jig. 107, E) the arrangement of these organs is 
 well exhibited. 
 
 (285.) The next modification in the structure of the legs is met 
 with in such species as burrow beneath the surface of the ground, of 
 which mode of progression the most remarkable example is seen in the 
 mole-cricket (Gryllo-talpa vulgaris) (Jig. 108). In this creature 
 
 Fig. 103. 
 
 the anterior segment of the thorax, whereunto the fore-legs are ap- 
 pended, is wonderfully enlarged, and of great strength, while the 
 legs themselves are equally remarkable for their enormous bulk and 
 muscularity. The tibia is excessively dilated, and terminates ob- 
 liquely in four sharp and strong spines. The whole of the tarsus 
 would, at a first glance, appear to be wanting ; but on inspection it 
 is found to consist of three joints placed upon the inner side of the 
 tibia, the two first being broad and tooth-shaped, while the last 
 piece is very small, and armed with two hooks. The direction and 
 motion of these hands is outwards, thus enabling the animal most 
 effectually to remove the earth when it burrows, and by the help of 
 such powerful instruments it is astonishing how rapidly it buries 
 itself* 
 
 (286.) Similar examples of adaptation in the mechanical structure 
 of the legs of insects might be multiplied indefinitely ; we shall, 
 
 * Kirby and Spence. Introd. to Ent. vol. ii. p. 362. 
 
INSECTA. 
 
 245 
 
 however, select but one other illustration before leaving this part 
 of our subject, namely, the conversion of these organs into instru- 
 ments for swimming, whereby, in aquatic insects, they become adapt- 
 ed to act as oars. Nothing is, perhaps, better calculated to excite 
 the admiration of the student of animated nature than the amazing 
 results .obtained by the slightest deviations from a common type 
 of organization ; and in examining the changes required in order to 
 metamorphose an organ which we have already seen performing 
 such a variety of offices into fins adapted to an aquatic life, this 
 circumstance must strike the mind of the most heedless observer. 
 The limbs used in swimming exhibit the same parts, the same 
 number of joints, and almost the same shape, as those employed for 
 creeping, climbing, leaping, and numerous other purposes ; yet how 
 different is the function assigned to them ! In a common water 
 beetle already referred to, the Dytiscus marginalis (Jig- 109, c), 
 
 Fig-. 109. 
 
 the two anterior pairs of legs, that could be of small service as in- 
 struments of propulsion, are so small as to appear quite dispropor- 
 tionate to the size of the insect, while the hinder pair are of great 
 size and strength ; the last-mentioned limbs are, moreover, removed 
 as far backwards as possible by the developement of the hinder seg- 
 ment of the thorax, in order to approximate their origins to the 
 centre of the body, and the individual segments composing them 
 
246 INSECTA. 
 
 are broad and compressed, so as to present an extensive surface to 
 the water, which is still further enlarged by the presence of flat spines 
 appended to the end of the tibia, as well as of a broad fringe of 
 stiff hairs inserted all around the tarsus. The powerful oars thus 
 formed can open until they form right angles with the axis of the 
 body, and from the strength of their stroke are well adapted to the 
 piratical habits of their possessors, who wage successful war not 
 only with other aquatic insects and worms, but even with small 
 fishes, the co-inhabitants of the ponds wherein they live. 
 
 The same principles are carried out even more perfectly in the 
 construction of the swimming legs of the water-boatman (Noto- 
 necta), a kind of water-bug. The resemblance of this creature 
 (Jig. 101, G, H) to a boat with its oars, cannot escape the most in- 
 attentive examiner ; and the similarity is still further increased by 
 its manner of swimming ; for, as it preys, upon insects that have 
 been accidentally drowned by falling into the water, it usually rows 
 itself about upon its back, because in such a position it can best 
 watch for its victims. 
 
 (287.) The wings of insects, when present, are invariably attached 
 to the two posterior segments of the thorax, which, as we have al- 
 ready seen, are strengthened in every possible manner, so as to afford 
 a support of sufficient density and firmness to sustain the violent ex- 
 ertions of the muscles inserted into the organs of flight. 
 
 In the most perfectly organized families the wings are four 
 in number, as in the Neuroptera (Jig. 103), the Hymenoptera 
 (Jig. 129), the Orthoptera (Jig. 102), the Dictyoptera, the He- 
 miptera (Jig. 101), the Lepidoptera (Jig. 105), and the Cole- 
 optera (Jig. 106). 
 
 In the Dipterous insects there are only two wings, which are 
 fixed upon the central segment of the thorax ; while, in the posi- 
 tion usually occupied by the posterior pair, we find a pair of pe- 
 dunculated globular bodies, usually named the Halteres or poisers, 
 as in the gnat (Culex,) (Jig. 131, F). 
 
 But, in every one of the orders above enumerated, there are 
 certain families which, throughout the whole period of their exist- 
 ence, are never provided with wings at all ; and these by many 
 entomologists have been formed into an order by themselves, under 
 the name of Apterous insects. In the opinion of Burmeister,* 
 whose classification we have adopted, such an arrangement is 
 purely artificial, inasmuch as it must embrace insects of most 
 
 * Manual of Entom. p. 623. 
 
INSECTA. 247 
 
 dissimilar kinds. In proof of this, he adduces the fact, that in the 
 same family we not unfrequently meet with both winged and ap- 
 terous species nearly related to each other ; and in many cases the 
 males possess wings, while the females of the same insect are en- 
 tirely destitute of such appendages. In such cases, the metamor- 
 phosis is necessarily what is called incomplete, inasmuch as the 
 organs which characterize the perfect state are not developed. Thus, 
 in the flea (Pulex irritans) (fig. 110), the wings never become 
 apparent, and the Fig. 110. 
 
 thorax in conse- 
 quence, even in 
 the imago state, 
 does not exhibit 
 that develope- 
 ment and con- 
 solidation of its 
 parts invariably 
 met with in wing- 
 ed genera. The flea, however, cannot on this account be looked 
 upon as any other than the imago or complete insect, for it will 
 be found to have undergone all the preparatory changes. The 
 flea, when it issues from the egg, is in fact a worm-like and foot- 
 less larva, in which condition it lives about twelve days. When 
 about to become a pupa, it spins for itself a little silky cocoon, 
 wherein it conceals itself, until, having thrown off its last skin, 
 it appears in its mature form, deprived indeed of wings, that, under 
 the circumstances in which it lives, would be useless appendages, 
 but still with this exception corresponding in every particular with 
 other insects in their imago state. 
 
 (288.) The wings of insects differ much in texture. In the Neu- 
 roptera, by far the most powerful fliers met with in the insect 
 world, all four wings are of equal size, and consist of a thin mem- 
 branous expansion of great delicacy and of a glassy appearance, 
 supported at all points by a horny network (Jig. 103). Few 
 things are met with in nature more admirable than these struc- 
 tures ; they present indeed a combination of strength and lightness 
 absolutely unequalled by anything of human invention, and as 
 instruments of flight they far surpass the wings of birds, both 
 in the power and precision of their movements, inasmuch as these 
 insects can fly in all directions, backwards, or to the right or left, 
 as well as forwards. Leeuwenhoek* narrates a remarkable instance 
 * Leeuw. Epist. 6, Mart. 1717. 
 
INSECTA. 
 
 in which lie was an eye-witness of the comparative capabilities of 
 the Dragon-fly and the Swallow, as relates to the perfection of their 
 flight. The bird and the insect were both confined in a mena- 
 gerie about a hundred feet long, and apparently their powers were 
 fairly tested. The swallow was in full pursuit, but the little crea- 
 ture flew with such astonishing velocity, that this bird of rapid 
 flight and ready evolution was unable to overtake and entrap it ; 
 the insect eluding every attempt, and being generally six feet 
 before it. " Indeed," say the authors from whom we quote 
 the above anecdote,* " such is the power of the long wings by 
 which the dragon-flies are distinguished, and such the force of the 
 muscles which move them, that they seem never to be wearied with 
 flying. I have observed one of them (Anax Imperator, Leach) 
 sailing for hours over a piece of water, sometimes to and fro, and 
 sometimes wheeling from side to side, and all the while chasing, 
 capturing, and devouring the various insects that came athwart its 
 course, or driving away its competitors, without ever seeming 
 tired or inclined to alight." 
 
 In Hymenopterous insects (Jigs. 128 and 129), the wings are 
 much more feebly organized, but their structure is similar ; the 
 nervures, or horny ribs, supporting the membranous expansion, 
 are comparatively few, and in the Diptera they are still less nu- 
 merous. 
 
 In several orders the anterior pair of wings are converted into 
 shields for the protection of the posterior ; such is the case in the 
 Orthoptera, many of the Hemiptera, and more especially in the 
 Coleopterous genera. In the latter, indeed, they are very dense 
 and hard ; and, being nearly unserviceable in flight, the hinder pair 
 are necessarily developed to such a size as to present a very ex- 
 tensive surface (fig. 106, A), and when in repose are closely 
 folded up beneath the elytra, and thus carefully preserved from 
 injuries to which they would be constantly exposed without such 
 provision for their security. 
 
 (289.) The above observations relate only to the general disposi- 
 tion and connection of the different parts of the skeleton, and loco- 
 motive appendages connected with it; it remains for us now to speak 
 more fully of the texture of the external integument, and those 
 modifications which it presents, adapting it to various purposes. 
 
 The hard covering of an insect, like the skin of vertebrate 
 animals, consists of three distinct layers. The outer stratum or 
 
 * Kuby and Spence, op. cit. p. 351. 
 
1NSECTA. 249 
 
 epidermis is smooth, horny, and generally colourless, so that it 
 forms a dense inorganic film spread over the whole surface of the 
 body. Immediately beneath the epidermis is a soft and delicate 
 film, the rete mucosum, which is frequently painted with the most 
 lively hues, and gives the characteristic colouring to the species. The 
 third and principal layer is the true skin or cutis, which is gener- 
 ally of a leathery texture, and, especially in the elytra of beetles, 
 of considerable thickness : this layer is abundantly supplied with 
 nutritive juices, and in its substance the bulbs of hairs, scales, and 
 similar appendages, to be described hereafter, are embedded and 
 nourished. 
 
 (290.) The wings are mere derivations from this common cover- 
 ing, and are composed of two delicate films of the epidennis, stretch- 
 ed upon a strong and net-like framework. Every membranous wing 
 is in fact a delicate bag formed by the epidermic layer of the in- 
 tegument, and in the recently developed insect can be distinctly 
 proved to be such, by simply immersing the newly escaped imago 
 in spirit of wine, which gradually insinuates itself between the 
 still fresh and soft membranes ; and, filling the cavity enclosed be- 
 tween them, distends the organ until it represents a transparent 
 sacculus in which the ribs or nervures of the wing are enclosed.* 
 This structure, however, is only to be displayed while the wings, 
 after being withdrawn from the pupa-case, are still soft and moist, 
 for they soon become so intimately united with the horny frame- 
 work upon which they are extended, that they seem to form a 
 single membranous expansion. 
 
 The, ribs or nervures, whereby the two plates of the wing are 
 thus supported, are slender hollow tubes, filled with a soft paren- 
 chyma, in the interior of some Burmeister detected an air-vessel 
 recognisable by the texture of its walls, and a minute nervous 
 filament. 
 
 (291.) We have still, in order to complete our descriptioirof the 
 external anatomy of an insect, to describe certain appendages which 
 not unfrequently clothe the exterior of the skeleton, and exhibit 
 great diversity of appearance in different tribes. These may be 
 divided into spines, hairs, and scales ; and, however much they 
 may appear to be distinct structures, all these are essentially very 
 nearly related to each other. 
 
 The spines are horny processes developed from the epidermis ; 
 and sometimes, especially in the Coleopterous order, as in some 
 
 * Heusingcr, System der Hystologie, 2 Heft. Burraeister, op. cit. p. 224. 
 
250 IN SECT A. 
 
 lamellicorn beetles, exhibit considerable dimensions. These spines 
 are sometimes bifurcated or branched ; but, whatever their shape or 
 size they never grow from bulbs implanted in the cutis, but are 
 mere prolongations of the exterior layer of the integument. 
 
 The hairs in their mode of growth appear to resemble those of 
 quadrupeds, inasmuch as they are secreted from roots embedded in 
 the substance of the cutis or true skin : they are fine horny cy- 
 linders, and frequently are found to be branched and divided like 
 the feathers of birds ; but the manner of their formation will be 
 more conveniently discussed hereafter. 
 
 The wings of the Lepidoptera are covered with minute flat 
 scales of various shapes, and not unfrequently tinted with the most 
 beautiful colours ; such scales, nevertheless, are in reality only 
 flattened hairs, into which indeed they frequently degenerate by in- 
 sensible transitions, and, moreover, they grow from bulbs of pre- 
 cisely similar construction. The variety of colours exhibited by 
 the scales of a butterfly depends upon a film of pigment interposed 
 between the two plates of transparent epidermic matter forming 
 each ; but the gorgeous hues derived from this source must not be 
 confounded with the iridescent tints for which they are not un- 
 frequently remarkable, as these have a very different origin : the 
 surface of every scale, that with the changing light reflects 
 evanescent prismatic colours, is seen, when examined under a micro- 
 scope, to be marked with regular parallel striae of exquisite minute- 
 ness ; and such a surface, even when grossly imitated by human art, 
 has been found to give rise to the brilliant appearances exhibited 
 by polarized light. 
 
 (292.) The muscular system of insects has always excited the 
 wonder and astonishment of the naturalist, in whatever point of view 
 he examines this part of their economy, whether he considers the 
 perfection of their movements, the inconceivable minuteness of 
 the parts moved, or the strength, persistence, or velocity of their 
 contractions. Insects are proverbially of small comparative dimen- 
 sions " minims of nature" 
 
 " that wave their limber fans 
 For wings, and smallest lineaments exact, 
 In all the liveries decked of summer's pride j" 
 
 their presence, indeed, around us, is only remarked as conferring 
 additional life and gaiety to the landscape ; and, except when by 
 some inordinate increase in their numbers they make up by their 
 multitude for their diminutive size, the ravages committed by them 
 
INSECTA 251 
 
 are trifling and insignificant. Far otherwise, however, would it be, 
 if they attained to larger growth, and still possessed the extra- 
 ordinary power with which they are now so conspicuously gifted ; 
 they would then, indeed, become truly the tyrants of the creation, 
 monsters such " as fables never feigned or fear conceived," fully 
 adequate to destroy and exterminate from the surface of the earth 
 all that it contains of vegetable or of animal life. 
 
 We have already seen that the flea or the grasshopper will 
 spring two hundred times the length of its own body ; that the 
 dragon-fly possesses such indomitable strength of wing, that for a 
 day together it will sustain itself in the air, and fly with equal 
 facility and swiftness backwards or forwards, to the right or to 
 the left, without turning ; that the beetles are encased in a 
 dense and hard integument, impervious to ordinary violence ; and 
 we might add, that the wasp and the termite ant will penetrate 
 with their jaws the hardest wood. Neither is the velocity of the 
 movements of insects inferior to their prodigious muscular power. 
 An anonymous writer in Nicholson's Journal," say Kirby and 
 Spence, u calculates that in its ordinary flight the common house- 
 fly (Musca domestica) makes with its wings about six hundred 
 strokes, which carry it five feet every second ; but, if alarmed, he 
 states their velocity can be increased six or seven-fold, or to thirty 
 or thirty-five feet in the same period. In this space of time a 
 race-horse could clear only ninety feet, which is at the rate of 
 more than a mile in a minute. Our little fly, in her swiftest 
 flight, will in the same space of time go more than the third of a 
 mile. Now, compare the infinite difference of the size of the two 
 animals (ten millions of the fly would hardly counterpoise one 
 racer), and how wonderful will the velocity of this minute crea- 
 ture appear ! Did the fly equal the race-horse in size, and retain 
 its present powers in the ratio of its magnitude, it would traverse 
 the globe with the rapidity of lightning."* 
 
 Let the reader, therefore, imagine for an instant that great law 
 of nature, which restricts the dimensions of an insect within certain 
 bounds, dispensed with even in a single species. Suppose the 
 wasp or the stag-beetle dilated to the bulk of a tiger or of an 
 elephant cased in impenetrable armour furnished with jaws 
 that would crush the solid trunk of an oak winged, and capable of 
 flight so rapid as to render escape hopeless ; what would resist 
 such destroyers, or how could the world support their ravages ? 
 
 * Kirby and Spence, op. cit. vol.ii. p. 358. 
 
252 1NSECTA. 
 
 Such is the comparative strength of insects. Let us now pro- 
 ceed to examine the muscles to which it is owing their structure 
 and general arrangement. 
 
 (293.) The muscles consist of bundles of delicate fibres, that 
 arise either from the inner surface of the segments composing the 
 skeleton, or else from the internal septa ( 281.) which project into 
 the thorax. The fibres themselves are of a white or yellow colour ; 
 and so loosely are they connected by cellular tissue, that they may 
 be separated by the slightest touch. 
 
 All the muscles of an insect may be arranged in two great 
 divisions; the first including those that unite the different seg- 
 ments of the body ; the second, those appropriated to the move- 
 ments of the limbs, jaws, and other appendages : the former are 
 entirely composed of fleshy fibres ; the latter are provided with 
 tendinous insertions, by which their force is concentrated and made 
 to act with precision upon a given point of the skeleton. 
 
 The connecting muscles are generally arranged in broad parallel 
 bands, arising from the inner surface of a given segment, and 
 passing on to be inserted in a similar manner into another seg- 
 ment, so that by their contraction the cavity in which they are 
 lodged is diminished by the approximation of the different rings : 
 these have no tendons. 
 
 The locomotive muscles of course take their character from the 
 joints of the limb upon which they act ; and, as we have already 
 seen that these movements are generally confined to those of a 
 hinge, the muscular fasciculi may be conveniently grouped into 
 two great classes, the flexor muscles, that bend the joint ; and 
 the extensors, by which it is again straightened, and brought back 
 to its former position. This simple arrangement will be best 
 understood by an inspection of the appended figure (fig. Ill), 
 representing the muscles of the leg of a cockchafer (Melolontha 
 vulgaris), as they are depicted by Strauss Durckheim.* In the 
 thigh, for example, there are two muscles, one of which bends, 
 the other straightens, the tibia. The flexor (fig. Ill, a) arises 
 from the lining m'embrane of the femur, and is inserted by a ten- 
 don into a process of the tibia in such a manner as to flex the 
 leg upon the thigh ; while its antagonist (&), attached to a process 
 derived from the other side of the joint, has an opposite effect, and 
 by its contraction extends the leg. In the tibia there are like- 
 
 * Considerations ge"ne"rales sur 1'Anat. comp. des Animaux Articules, auxquelles on 
 a joint 1' Anatomic descriptive du Hanneton. 1 vol. 4to. Paris, 1828. 
 
INSECTA. 
 
 253 
 
 wise two muscles, so disposed as move the Fig. ill. 
 
 entire tarsus and foot. The extensor (f) of 
 the tarsus is the smallest ; it arises from the 
 lower half of the interior of the tibia, and is 
 inserted into the margin of the first joint of 
 the tarsus : but the flexor of the foot (c), aris- 
 ing from the upper half of the cavity of the 
 tibia, ends in a delicate tendon, which passes 
 through all the tarsal segments, to be fixed to 
 the flexor tendon of the claw-joint upon which 
 it acts ; and, as it traverses the penultimate 
 joint, it receives the fibres of an accessory 
 muscle (d). The extensor of the claw (e) 
 is likewise placed in the penultimate tarsal 
 segment, and strikingly exhibits, by its small 
 comparative size, the feebleness of its action, 
 when compared with the flexors of the same 
 joint. 
 
 It would be superfluous to describe more 
 in detail the disposition of individual muscles, 
 as the above example will abundantly suffice 
 to give the reader an idea of the general ar- 
 rangement of the muscular system, not in in- 
 sects only, but in all the ARTICULATA provided 
 with jointed extremities. 
 
 (294.) The substances employed as food by insects are various, 
 in proportion to the extensive distribution of the class. Some de- 
 vour the leaves of vegetables, or feed upon grasses and succulent 
 plants ; others destroy timber, and the bark or roots of trees ; while 
 some, more delicately organized, are content to extract the juices of 
 the expanding buds, or sip the honeyed fluids from the flowers. 
 Many tribes are carnivorous in their habits, armed with various 
 weapons of destruction, and carry on a perpetual warfare with their 
 own or other species ; and again there are countless swarms ap- 
 pointed in their various spheres to attack all dead and putrefying 
 materials, and thus to assist in the removal of substances which, by 
 their accumulation, might prove a constant source of annoyance 
 and mischief. Such differences in the nature of their food demand 
 of course corresponding diversity in the construction of the in- 
 struments employed for procuring nourishment, and accordingly 
 we find in the structure of the mouths of these little beings innu- 
 
254 
 
 INSECTA. 
 
 merable modifications adapting them to different offices. The 
 mouths of all creatures are constructed upon purely mechanical 
 principles ; and in few classes of the animal world have we more 
 beautiful illustrations of design and contrivance than in that before 
 us : -jaws armed with strong and penetrating hooks for seizing 
 and securing active and struggling prey, sharp and powerful 
 shears for clipping and dividing the softer parts of vegetables, 
 saws, files, and augers for excavating and boring the harder parts 
 of plants, lancets for piercing the skin of living animals, 
 siphons and sucking tubes for imbibing fluid nutriment ; all 
 these, in a thousand forms, are met with in the insect world, 
 and thus provide them with the means of obtaining food adapted 
 to their habits, and even of constructing for themselves edifices 
 of inimitable workmanship. 
 
 (295.) Parts of the mouth. The mouths of insects may be di- 
 vided into two great classes, those which are adapted for biting, 
 forming what is called a perfect or mandibulate mouth ; and those 
 which are so constructed as only to be employed in sucking, consti- 
 tuting the suctorial or haustellate mouth. It is in the former of these 
 divisions that all the parts composing the oral apparatus are most 
 completely developed . we shall therefore commence by describ- 
 ing the different pieces of which a perfect mouth consists, viz. 
 an upper and an under lip, and four horny jaws. We select the 
 dragon-fly (fig 112, A) as an example. The upper lip (labrum, 
 
 Fig, 112. 
 
 B) is a somewhat convex corneous plate, placed transversely across 
 the upper margin of the cavity wherein the jaws are lodged, so that, 
 when the mouth is shut, it folds down to meet the under lip (la- 
 
INSECTA. 55 
 
 bium), and these two pieces more or less completely conceal the 
 proper jaws, which are lodged between them. 
 
 The upper pair of jaws (mandibulfs) are two hard and powerful 
 hooks (c), placed immediately beneath the upper lip, and so ar- 
 ticulated with the cheeks that they move horizontally, opening and 
 shutting like the blades of a pair of scissors. Their concave edge 
 is armed with strong denticulations of various kinds, sometimes fur- 
 nished with cutting edges, that, like sharp shears will clip and di- 
 vide the hardest animal and vegetable substances ; sometimes they 
 form sharp and pointed fangs, adapted to seize and pierce their 
 victims ; and not unfrequently they constitute a series of grinding 
 surfaces, disposed, like the molar teeth of quadrupeds, to triturate 
 and bruise the materials used as food. The variety of uses to which 
 these mandibles can be turned is indeed amazing. In the car- 
 nivorous beetles, their hooked points, more formidable than the 
 teeth of the tiger, penetrate with ease the mailed covering of their 
 stoutest congeners ; and in the dragon-fly they are scarcely less 
 formidable weapons of destruction. In the locust tribes these 
 organs are equally efficient agents in cutting and masticating leaves 
 and vegetable matters adapted to their appetites ; while in the 
 wasps and bees they form the instruments with which these insects 
 build their admirable edifices, and, to use the words of a popular 
 author, supply the place of trowels, spades, pick-axes, saws, scissors, 
 and knives, as the necessity of the case may require. 
 
 Beneath the mandibles is situated another pair of jaws, of similar 
 construction, but generally smaller and less powerful; these are 
 called the maxilla (F). 
 
 The lower lip, or labium (E), which closes the mouth inferiorly, 
 consists of two distinct portions, usually described as separate 
 organs, the chin (mentum), that really forms the inferior border of 
 the mouth ; and a membranaceous or somewhat fleshy organ, repos- 
 ing upon the chin internally, and called the tongue (lingua) of the 
 insect (D). 
 
 All these parts enter into the composition of the perfect mouth 
 of an insect, and, from the numerous varieties that occur in their 
 shape and proportions, they become important guides to the ento- 
 mologist in the determination and distribution of species. For 
 more minute details concerning them, the reader is necessarily re- 
 ferred to authors who have devoted their attention specially to this 
 subject ; we must not, however, omit to mention certain appen- 
 dages or auxiliary instruments inserted upon the maxilla and the 
 labium, usually named the palpi, or feelers, and most probably 
 
256 INSECTA. 
 
 constituting special organs of touch, adapted to facilitate the appre- 
 hension and to examine the nature of the food. The maxillary 
 feelers (palpi maxillares) are attached to the external margin of 
 the maxillae by the intervention of a small scale and very pliant 
 hinge, and consist of several (sometimes six) distinct but ex- 
 tremely minute pieces articulated with each other. The labial 
 feelers (palpi labiates) are inserted into the labium close to the 
 tongue, or occasionally upon the chin (mentum) itself. The joints 
 in the labial palpi are generally fewer than in the maxillary, but in 
 other respects their structure and office appear to be the same. 
 
 In the suctorial orders of insects we have the mouth adapted to 
 the imbibition of fluid nutriment, and consequently constructed 
 upon very opposite principles ; yet, notwithstanding the apparent 
 want of resemblance, it has been satisfactorily demonstrated by Sa- 
 vigny* that the parts composing a suctorial mouth are fundament- 
 ally the same as those met with in the mouth of mandibulate in- 
 sects, but transformed in such a manner as to form a totally differ- 
 ent apparatus. 
 
 According to the distinguished authors of the u Introduction to 
 Entomology,"')' there are five kinds of imperfect mouth adapted to 
 suction, each of which will require a separate notice. 
 
 (29 6.) The first is met with among the Hemiptera, and is 
 to perforate the stalks and buds of vegetables, in order to 
 procure the juices which they contain ; or in some bugs it 
 is employed to puncture the integument of living animals for a 
 similar purpose. This kind of mouth is exhibited in fig. 113 : 
 first, there is a long jointed sheath (d), 1J3 
 
 which is in fact the lower lip (labium), con- 
 siderably elongated, and composed of three 
 or four parts articulated together; second- 
 ly, there is a small conical scale covering the 
 base of the sheath last mentioned, and re- 
 presenting the upper lip ; and between these 
 are four slender and rigid bristles or lancets 
 (scalpella) (c) that, when not in use, are 
 lodged in a groove upon the upper surface 
 of the sheath so as to be concealed from view. 
 These lancets are, in reality, only the man- 
 
 * Savigny (Jules Cesar), Memoires sur les animauxsans vertebres, 8vo. Paris, 1816. 
 t Kirby and Spence, vol. iii. p. 463. 
 
INSECTA. 257 
 
 diblcs and maxillae strangely altered in their form and excessively 
 lengthened, so as not merely to become efficient piercing instru- 
 ments, but so disposed as to form by their union a suctorious tube, 
 through which animal or vegetable fluids may be imbibed. This kind 
 of mouth, when not employed, is usually laid under the thorax be- 
 tween the legs, in which position it is easily seen in most Hemi- 
 ptera : in some families, as, for example, in the plant-lice (Aphides), 
 it is of extraordinary length ; thus, in the aphis of the oak it is three 
 times as long as the whole body of the insect, projecting posteriorly 
 like a tail, and in the fir-aphis it is still longer. 
 
 (297.) The second kind of mouth is that met with among the 
 Diptera, and from its construction in some tribes we may well under- 
 stand how they are enabled to become so seriously annoying. The 
 gnat and the mosquito furnish sufficiently well-known examples of 
 the formidable apparatus in question, which, in the horse-fly (Taba- 
 nus), seems to attain its maximum of developement. The oral 
 organs of the Diptera are composed of a sheath or proboscis, that 
 represents the lower lip of the mandibulate insects ; it is sometimes 
 coriaceous or horny in its texture, or in other cases, as in the com- 
 mon flesh-fly, soft and muscular, and folds up when at rest in such a 
 manner as to form two angles, representing the letter Z. At the 
 base of this sheath or proboscis there is a small upper lip, between 
 which and the sheath are lodged the setae, knives or lancets, which 
 form such terrible instruments for cutting or piercing the skin of 
 their victims. These cutting parts vary in "number from one to 
 five : when they are all present, the upper pair (cultelli^ or knives) 
 represent the mandibles of a perfect mouth, the two lower ones 
 (scalpella, the lancets) are the maxillae, the fifth or middle piece 
 (glossarium) is the tongue, and between them all is the oral 
 opening. The strength of the above piercing instruments varies 
 greatly ; in the ghat they are finer than a hair, very sharp and 
 barbed occasionally on one side ; while in the horse-fly they 
 are flat, like the blades of a lancet or penknife : occasionally 
 they are so constructed as to form a tube by their union, through 
 which the liquid aliment is sucked up and conveyed into the 
 stomach. 
 
 (298.) The mouth of the flea, although described by Kirby and 
 Spence as forming a distinct type of structure, differs very little 
 from that of the Diptera described above, as will be at once evi- 
 dent on inspecting the accompanying figure, reduced from a beau- 
 tiful drawing by Mr. W. Lins Aldous. 
 
258 
 
 In this insect the piercing organs are two sharp and razor-like 
 instruments (Jig- 114, d, d), placed on each side of the elongated 
 tongue (e), and enclosed in a sheath (c, c), probably formed by 
 pieces representing the mandibles of mandibulate insects. Two 
 palpi or feelers (0, a), and a pair of triangular plates (6, i), com- 
 plete this remarkable apparatus. 
 
 (299.) Another kind of mouth adapted to suction, and which seems 
 to differ more widely from the perfect form than any we have as 
 yet examined, is that which we meet with in moths and butterflies. 
 This singular organ is adapted to pump up the nectareous juices 
 from the cups of flowers, and is necessarily of considerable length, in 
 order to enable the insect to reach the recesses wherein the honeyed 
 
 * Head of the flea, as represented by the Solar microscope in Canada balsam ; dedi- 
 cated by permission to the President and Members of the Entomological Society, by 
 W.Lins Aldous. 
 
INSECTA. 
 
 259 
 
 stores are lodged. When unfolded, the apparatus in question repre- 
 sents a long double whip-lash (Jig. 115, a, 5, c, d), and, if carefully 
 examined under the micro- 
 
 scope. 
 
 each division is found 
 
 Fig. 115. 
 
 to be made up of innumer- 
 able rings connected toge- 
 ther, and moved by a dou- 
 ble layer of spiral muscular 
 fibres, that wind in oppo- 
 site directions around its 
 walls. When not in use, 
 the proboscis is coiled up 
 and lodged beneath the 
 head ; but when uncurled 
 its structure is readily ex- 
 amined. Each of the two 
 long filaments composing 
 this trunk, which, in fact, are the representatives of the maxilla: 
 excessively lengthened, is then seen to be tubular ; and, when they 
 are placed in contact, it is found that their edges lock together by 
 means of minute teeth, so as to form a central canal leading to the 
 orifice of the mouth. It is through this central tube, formed by 
 the union of the two lengthened maxillae, that fluids are imbibed. 
 Burmeister, however, asserts that the cavities contained in each divi- 
 sion likewise communicate with the commencement of the oasophagus, 
 so that the Lepidoptera have, as it were, two mouths, or rather two 
 separate methods of imbibing nourishment ; one through the com- 
 mon canal formed by the junction of the whip-like jaws, the other 
 through the cavities of the filiform maxillse themselves : such an 
 arrangement, however, which would be quite anomalous, may rea- 
 sonably be doubted. In this mouth, therefore, all the parts, except 
 the maxillse, would seem at first sight to be wanting ; they may, 
 nevertheless, be detected upon a very careful examination, and 
 rudiments of the upper lip, of the mandibles, of the lower lip, as 
 well as of the labial and maxillary palpi, be distinctly demonstrated. 
 (300.) The last kind of mouth to which we shall advert, is that 
 met with in the louse tribe (Pediculi) ; but, from the extreme mi- 
 nuteness of the parts composing it, the details of its structure are 
 but imperfectly known. It seems to consist of a slender external 
 tube, wherein a sharp sucker, armed with barbs adapted to fix it 
 securely during the act of sucking, is lodged ; when feeding, the 
 
260 INSECTA. 
 
 barbed piercer is denuded and plunged into the skin, where it" is 
 retained until a sufficient supply of nourishment has been obtained. 
 (301.) Inviting as the subject is, we are compelled by the strictly 
 general character of our investigations to abstain from entering upon 
 further details concerning the mouths of perfect insects, and conse- 
 quently to omit noticing innumerable secondary modifications in 
 the mechanical structure of the oral organs of these little animals. 
 When we turn our attention to the consideration of their internal 
 viscera, connected with the preparation and digestion of so many 
 different materials, we may well expect to find equal variety of 
 conformation ; and, in fact, the course, dimensions, and relative 
 proportions of the alimentary canal will be seen to be different to 
 a greater or less extent in almost every species. Considered as a 
 whole, the internal digestive apparatus of insects must be regarded 
 as a delicate membranous tube, in which the digestion of the sub- 
 stances used as food is accomplished, partly by mechanical and 
 partly by chemical agents : for the former purpose, gizzard-like 
 muscular cavities are not unfrequently provided ; and, to fulfil the 
 second, various fluids are poured into the canal in different parts of 
 its course : the arrangement of the cavities, and the nature of the 
 secreting vessels, however, will be modified in conformity with the 
 necessities of the case, and certain parts will be found to exist, or 
 to be deficient, as circumstances may require : it would be absurd, 
 therefore, to attempt to describe particular examples ; our observa- 
 tions must be of general application, and such as will enable the 
 reader to assign its proper functions to any organ which may pre- 
 sent itself to his notice. The first part of the digestive appara- 
 tus is disposed in the same manner in all insects, and is a slender 
 canal, arising from the mouth and passing straight through the tho- 
 rax into the cavity of the abdomen ; this portion represents the 
 oesophagus (fig* 116, a, a; 117, o). t The stomach and intestine 
 succeed to this, and, if the body of the insect be very thin, their 
 course also passes nearly in a direct line to the tail ; but in those 
 families which have the abdomen thick and largely developed, espe- 
 cially if herbivorous, the intestine becomes much elongated, and 
 winds upon itself in various convolutions : nevertheless, however 
 tortuous the canal may be, its windings are never sustained by any 
 mesentery or peritoneal investment ; the air-tubes, that, as we shall 
 afterwards see, permeate the body in all directions, form a sufficient 
 bond of connection, and one which is better adapted to the wants 
 of these animals. 
 
INSECTA. 
 
 We m-ust now examine more minutely the different portions of 
 which the alimentary canal may consist, premising at the same 
 time that the structures mentioned do not invariably exist together, 
 as sometimes one part, and sometimes another, may be entirely 
 wanting, or only found in a very rudimentary condition. They 
 are the Crop, the Gizzard, the Stomach, the Small Intestine, 
 and the Large Intestine. 
 
 (302.) The Crop, or Sucking- Stomach, as it is called by some 
 writers, is only met with in Hymenoptera, Lepidoptera, and Di- 
 ptera, insects which have no gizzard.* In bees, wasps, and other 
 Hymenoptera, it is a simple bladder-like distension of the oesophagus 
 (Jig. 116, b) ; in butterflies and moths it forms a distinct bag, 
 that opens into the side of the Fig. 116. 
 
 gullet (Jig. 117, v, v) ; while in 
 the Diptera it is a detached ve- 
 sicle, appended to the oesophagus 
 by the intervention of a long thin 
 duct. This organ, which in bees 
 is usually called the honey blad- 
 der, is regarded by Burmeister, 
 who founds the opinion upon the 
 result of experiments made by 
 Treviranus upon living insects, as 
 being not merely a receptacle for 
 food resembling the craw of birds, 
 as Ramdohr j- and Meckel con- 
 sider it, but as being a sucking instrument for imbibing liquids, 
 by becoming distended, as he expresses it, and thus, by the rare- 
 faction of the air contained within it, facilitating the rise of the 
 fluids in the proboscis and oesophagus. It must, however, be 
 confessed that there is something very anomalous in the idea of a 
 delicate bag having the power of distending itself ; its muscular 
 walls might indeed contract, but that a thin sacculus should forci- 
 bly expand itself would be a fact new to physiology. 
 
 (303.) The Gizzard is found in insects which possess mandibles, 
 and live upon solid animal or vegetable substances. It is a small 
 round cavity with very strong muscular parietes, situated just above 
 the stomach properly so called, and, like the gizzard of granivorous 
 birds, is employed for the comminution of the food preparatory to 
 
 * Burmeister, op. cit. p. 125. Treviranus, Vermischte Schriften. 
 
 t Ramdohr, iiber die Verdauungswerkzeuge der Insecten. Halle, 1811. 
 
262 
 
 INSECTA. 
 
 its introduction into the digestive stomach. In order to effect this, 
 it is lined internally with a dense cuticular membrane, and occa- 
 sionally studded with hard plates of horn or strong hooked teeth, 
 adapted to crush or tear in pieces whatever is submitted to their 
 action. 
 
 When bruised in the gizzard, the food passes on into the proper 
 stomach, which is generally a long intes Uniform organ (Jig. 116, 
 d, d), extending from the crop or gizzard to the point where the 
 biliary vessels discharge themselves into the intestine. The size 
 and shape of this organ will vary of course with the nature of the 
 food. Thus, in the butterfly (Jig. 117, &), which scarcely eats 
 at all, or sparingly sips the honey from the flowers, it is very mi- 
 nute ; but, in insects which live upon coarse and indigestible mate- 
 rials, it is proportionately elongated and capacious. 
 
 (304.) The stomach generally ends in the Small Intestine (Jig. 
 116, e ; 117, *), but this is occasionally entirely wanting, so that the 
 stomach seems to terminate immediately in the colon or large intes- 
 tine, which is the terminal portion of the alimentary canal : when 
 much developed, the small intestine is sometimes divided by a con- 
 striction into two parts, to which the names of Duodenum and Ilium 
 have been applied by entomological writers. The colon (fig. 
 
 Fig. in. 
 
 116,y; 117, k) is separated 
 from the small intestine by 
 a distinct valve; and, in con- 
 nection with its commence- 
 ment, a wide blind sacculus 
 or caecum is often met with. 
 
 (305.) We may now no- 
 tice the secern ing organs that 
 pour fluids in to different parts 
 of the digestive apparatus ; 
 beginning with those which 
 open into the oesophagus in 
 the vicinity of the mouth, 
 and examining them in the 
 order of their occurrence as 
 we proceed backwards. 
 
 The first are the salivary 
 vessels, which terminate in 
 the neighbourhood of the 
 mouth itself, into which they seem to pour a secretion analogous to 
 
INSECTA. 263 
 
 saliva. These glands are principally met with in suctorial insects, 
 but not unfrequently among the mandibulate orders. Their form 
 varies ; but they are generally simple slender tubes, that float 
 loosely among the juices of the body, from which they separate the 
 salivary fluid. There are, for the most part, only two of these 
 organs (fig. 117, s, s) ; but in fleas (Pulex), and bugs (Cimex), 
 there are four, and in a water-bug (Nepa), there are six such 
 vessels, all of which open into the cavity of the mouth. The 
 fluid supplied by the salivary glands is usually merely intended to 
 facilitate deglutition ; but there are cases in which the saliva is ex- 
 cessively acrid and irritating, acting as a kind of poison when in- 
 fused into a puncture made by the mouth : this is especially re- 
 markable in many bugs and gnats, and is the chief cause of the 
 pain and inflammation frequently occasioned by their bite. 
 
 Besides the proper salivary vessels, there are other glands, or 
 rather caeca, which open into the stomach itself, occasionally cover- 
 ing that organ over its entire surface, as is the case in some water- 
 beetles (Hydrophilus) ; these, no doubt, secrete a fluid subser- 
 vient to digestion ; but whether of a peculiar description, or allied 
 to saliva in its properties, is unknown. 
 
 The third kind of auxiliary vessels connected with the intestinal 
 canal of insects, is supposed to furnish a secretion analogous to 
 the bile of other animals, and consequently to represent the liver. 
 The bile-vessels (fig. 116, A, h; fig. 117,#, g) are generally four, 
 six, or eight in number, but occasionally much more numerous ; 
 they are usually of great length, but exceedingly slender, and wind 
 around the intestine in all directions. When unravelled, they are 
 found to terminate, in the neighbourhood of the pylorus (fig. \ 17, 
 A, w), close to the commencement of the intestine, at which point 
 the secretion produced by them is mixed with the food after it has 
 undergone the process of digestion. 
 
 Appended to the termination of the alimentary tube, close to 
 its anal extremity, other vessels are met with in some insects that 
 are looked upon by authors as being allied in function to the kid- 
 neys of higher animals ; but apparently this opinion rests upon 
 very doubtful grounds. They indubitably furnish some secretion, 
 the use of which is perhaps connected with defecation ; but that it 
 is of the same character as the fluid separated by the renal organs 
 of vertebrata may well be called in question, as no such parts are 
 distinctly recognisable until we arrive at much more elevated forms 
 of life than the insects we are now considering. There is, how- 
 
264 1NSECTA. 
 
 ever, another reason for rejecting the opinion that these accessory 
 vessels secrete urine, and that is, that they are only met with in a 
 few beetles and some species of Orthoptera ; a circumstance that 
 alone would be sufficient to disprove such supposition. 
 
 In the vertebrate animals, as the reader is well aware, the nu- 
 tritious products of digestion are taken up by a system of absorb- 
 ing vessels, that ramify extensively over the coats of the intestine, 
 and the nutriment is thus conveyed into the mass of the circu- 
 lating fluid by ducts appropriated specially to this office ; in 
 animals of less perfect structure than these, such as the Mollusca, 
 the veins themselves absorb the nutritive materials. But in insects, 
 in which we find neither absorbents nor veins, a different arrange- 
 ment is necessary ; and, in the little creatures before us, nutrition 
 appears to be carried on by the simple transudation of the chyle 
 through the coats of the intestine, so that it escapes into the 
 general cavity of the abdomen, where, as we shall see when we 
 examine the arrangement of their circulating organs, it is im- 
 mediately mixed up with the blood. This transudation has in- 
 deed been actually witnessed by Ramdohr and Rengger,* and 
 even analyzed by the last-mentioned physiologist, who found it to 
 consist almost entirely of albumen. 
 
 (306.) The respiratory organs of the INSECT A, as well as their 
 circulatory apparatus, are constructed upon peculiar principles, and 
 are evidently in relation with the capability of flying, which distin- 
 guishes these minute yet exquisitely constructed articulated animals. 
 Any localized instruments for breathing, whether assuming the shape 
 of branchiae or lungs, would materially have added to the weight of 
 the body, and moreover have rendered necessary an elaborate ap- 
 paratus of arteries and veins for conveying the blood to and fro 
 for the purpose of purifying it by securing its exposure to the in- 
 fluence of air. By the plan adopted, however, all these organs are 
 dispensed with ; and the organs of respiration, so far from increasing 
 the weight of the animal, actually diminish its specific gravity to 
 the greatest possible extent. The blood, in fact, in insects is not 
 brought to any given spot to be exposed to oxygen, but the air is 
 conveyed through every part of the system by innumerable tubes 
 provided for that purpose, and thus all the complicated parts 
 usually required to form a vascular system are rendered unnecessary. 
 These observations, however, only apply to the insect in its perfect 
 
 * Physiologische Untersuchungen iiber den thierischen Haushalt der Insekten- 
 8vo. 1817. 
 
1NSECTA. 265 
 
 state; for in tlie larva and pupa condition, where flight is not 
 possible, various additional organs, frequently of considerable bulk, 
 are provided, that we shall speak of in another place. If we 
 examine the external skeleton of any large insect, a beetle for ex- 
 ample, we shall find between the individual segments of the body 
 minute apertures or pores (spiracles) through which the air is 
 freely admitted ; these openings, ten in number, on each side of 
 the body, are situated in the soft membrane interposed between 
 the different rings, and not in the rings themselves, a provision for 
 the purpose of allowing their orifices to be opened or closed at 
 pleasure, instead of being rigid and motionless. The margin of the 
 spiracle is frequently encompassed by thick horny lips, which may 
 be approximated by muscles provided for the purpose, so that the 
 opening can be shut at pleasure, in order to exclude any extraneous 
 substances that might otherwise obtain admission : in many insects 
 indeed, especially in beetles which crawl upon the dusty ground, 
 an additional provision is necessary to prevent the entrance of foreign 
 matter, and in such cases the spiracles are seen to be covered with 
 a dense investment of minute and stiff hairs, so disposed as to 
 form a sieve of exquisite fineness ; a beautiful contrivance, by which 
 the air is filtered, as it were, before it is allowed to pass into 
 the breathing-tubes, and thus freed from all prejudicial particles. 
 From every spiracle is derived a set of extremely delicate tubes 
 (trachea), that pass internally, and become divided and subdi- 
 vided to an indefinite extent, penetrating to every part of the 
 body, and ramifying through all the viscera, so that air is thus 
 supplied to the entire system. Upon more minutely inspecting 
 these air-tubes, they are found to assume various forms in different 
 parts of the body, being sometimes simple tubes of exquisite deli- 
 cacy ; in other cases they present a beaded or vesicular structure, 
 and in many insects they are dilated at intervals into capacious cells 
 or receptacles, wherein air is retained in great abundance. The figure 
 in the following page (Jig. 118), taken from Strauss Durckheim's 
 elaborate work upon the anatomy of the cockchafer, will illustrate 
 this arrangement. The spiracles, situated at the points respectively 
 marked by the letters a, c, e?, e,jf, g, h, i, open into two wide air- 
 trunks, disposed longitudinally along the whole length of the 
 body : from these, innumerable secondary branches are given off, 
 many of them being seen to dilate into oval vesicles, from which 
 smaller tracheae proceed ; while others, without any vesicular en- 
 largement, plunge at once into different textures, and supply the 
 
266 
 
 INSECTA. 
 
 viscera and internal organs. The muscular system, the legs, the 
 wings, the alimentary canal, and even the brain itself, are permeated 
 in all directions by these air- conducting tubes, and thus the 
 oxygen penetrates to every corner of the body. 
 
 (307.) There is one Fig. lie. 
 
 circumstance connected 
 with the tracheae, which 
 is specially deserving 
 of admiration, whether 
 we consider the obvious 
 design of the contriv- 
 ance, or the remarkable 
 beauty of the struc- 
 ture employed. It is 
 evident that the sides 
 of canals, so slender and 
 delicate as the tracheae 
 of insects, would in- 
 evitably collapse and 
 fall together, so as 
 to obstruct the passage 
 of the air they are 
 destined to convey ; 
 and the only plan 
 which would seem cal- 
 culated to obviate this 
 would appear to be, to 
 make their walls stiff 
 and inflexible. In- 
 flexibility and stiffness, 
 however, would never 
 do in this case, where 
 the vessels in question 
 have to be distributed 
 in countless ramifica- 
 tions through so many --:->, 
 soft and distensible viscera ; and the problem, therefore, is, how 
 to maintain them permanently open, in spite of external pres- 
 sure, and still preserve the perfect pliancy and softness of their 
 walls. The mode in which this is effected is as follows : Be- 
 tween the two thin layers of which each air-vessel consists, an 
 
INSECTA. 
 
 267 
 
 elastic spiral thread is interposed {Jig. 119, a), so as to form by 
 its revolutions a firm cylinder of sufficient strength to insure the 
 calibre of the vessel from being diminished, but not at all inter- 
 fering with its flexibility, or obstructing its movements ; and this 
 fibre, delicate as it is, may be traced with the microscope, even 
 through the utmost ramifications of the tracheae, a character 
 whereby these tubes may be readily distinguished. 
 
 (308.) We must now consider Fi 119> 
 
 the mechanism by which air is per- 
 petually drawn into the body of 
 the insect, and again expelled. If 
 the abdomen of a living insect be 
 carefully watched, it will be found 
 continually performing movements 
 of expansion and contraction that 
 succeed each other at regular in- 
 tervals, varying in frequency, in 
 different species, from twenty to 
 fifty or sixty in a minute,* but 
 occurring more rapidly when the 
 insect is in a state of activity than 
 when at rest. At each expansion 
 of the abdomen, therefore, air is 
 sucked in through all the spiracles, 
 and rushes to every part of the o/^ 
 body ; but, when the abdomen 
 contracts, it is forcibly expelled through the same openings. 
 Burmeister even supposes that the humming noises produced 
 by many insects during their flight, must be referred to the vi- 
 bration caused by the air streaming rapidly in and out of the 
 spiracular orifices. Insects which live in water are obliged, at short 
 intervals, to come to the surface to breathe, at which time they 
 take in a sufficient quantity of air to last them during the period 
 of their immersion ; but if the spiracles are closed by any acci- 
 dent, or by the simple application of any greasy fluid to the ex- 
 terior of their body, speedy death, produced by suffocation, is the 
 inevitable result. 
 
 (309.) A moment's reflection upon the facts above stated, con- 
 cerning the respiration of insects, will suggest other interesting views 
 connected with the physiology of these little creatures. It is evident, 
 
 * Sorg, Disquisitio Phys. circa Resp. Insectorum et Verminum. 
 
268 1NSECTA. 
 
 in the first place, that their blood is all arterial ; they can have no 
 occasion for veins, as they have no venous blood, the whole of the 
 circulating fluid being continually oxygenized as its principles be- 
 come deteriorated. The perfection of their muscular power, their 
 great strength and indomitable activity, are likewise intimately 
 related to the completeness of their respiration ; so that the vital 
 energies of the muscular system are developed to the utmost, en- 
 dowing them with that vigorous flight and strength of limb which 
 we have already seen them to possess. It must likewise become 
 apparent, that, as the blood is freely exposed to the influence of 
 oxygen in every portion of the insect to which the air-tubes reach, 
 one great necessity for the existence of a circulatory apparatus is 
 entirely done away with, and as we have observed before, all those 
 parts of the vascular system required in other animals for the pro- 
 pulsion of the vitiated blood through pulmonary or branchial organs, 
 are no longer requisite ; so that, by dispensing with the compli- 
 cated structures usually provided for this purpose, the body is 
 considerably lightened. The circulation of the nutritive fluids is 
 in fact limited to their free diffusion amongst all the internal 
 viscera, and is effected in the following manner: If we ex- 
 amine the back of a silkworm, or of any transparent larva, a long 
 pulsating tube is seen running beneath the skin of the back, from 
 one end of the body to the other ; its contractions may readily be 
 watched ; they are found to begin at the posterior extremity, and 
 are gradually continued forwards, so that the vessel presents a 
 continual undulatory movement, by which the fluid contained in 
 its interior is pushed from the tail towards the head. This dorsal 
 vessel, which may be so well observed in the thin-skinned larva, 
 exists likewise in the perfect insect, although from the opacity of 
 the integument, its movement is no longer apparent, except by the 
 vivisection of the animal. 
 
 (310.) This dorsal vessel, or heart as we shall call it for the sake 
 of brevity, is organized in a very singular manner ; for, instead of 
 being a closed viscus, it communicates most freely, through several 
 wide lateral apertures, with the cavity of the abdomen, and from 
 thence derives the blood with which it is filled. The dorsal vessel 
 is widest in the abdominal region ; but is continued, nevertheless, 
 through the thorax into the head, where it terminates as a simple 
 or furcate tube, that is not closed, but open at the extremity. 
 
 The structure of this remarkable heart has been fully investi- 
 gated by Strauss Durckhcim,* and is extremely curious ; it con- 
 
 * Op. cit 
 
INSECT A. 
 
 269 
 
 sists, in the cockchafer, of eight distinct compartments, sepa- 
 rated from each other by as many valves formed by productions 
 from the lining membrane, and so disposed that the blood passes 
 freely from the hinder chambers into those which are placed more 
 anteriorly, but is prevented from returning in the opposite di- 
 rection. 
 
 Each compartment of the dorsal vessel communicates by two 
 wide slits, likewise guarded by valves, with the cavity of the 
 belly, so that fluids derived from thence will readily pass into the 
 different chambers, but cannot .again escape through the same 
 channel. The arrangement of these valves will, however, be best 
 understood by reference to the accompanying Fig. 120. 
 figure (Jig. 120), representing a magnified view 
 of the interior of a portion of the heart of the 
 cockchafer, as depicted by the celebrated en- 
 tomotomist above alluded to. The organ has 
 been divided longitudinally, so that one half only 
 is represented in the figure upon a very large 
 scale. The compartments (a, a, a) are distinctly 
 composed of circular muscular fibres ; the large 
 valves (d, d) separate the individual chambers, 
 allowing the blood to pass in one direction only, 
 viz. towards the head ; while the openings (c), 
 likewise closed by semilunar membranous valves, 
 admit blood from the cavity of the abdomen, but 
 effectually prevent its return. 
 
 (311.) Let us now consider the movements of 
 the circulating fluids produced by the contractions 
 of this apparatus. The chyle or nutritive material 
 extracted by the food, eludes, as we have already seen, by a species 
 of percolation through the walls of the intestine, and escapes into 
 the cavity of the abdomen, where it is mixed up with the mass of the 
 blood, which is not contained in any system of vessels, but bathes 
 the surfaces of the viscera immersed in it. When any compartment 
 of the heart relaxes, the blood rushes into it from the abdomen, 
 through the lateral valvular apertures ; and as it cannot re- 
 turn through that opening on account of the valves (c) that 
 guard the entrance, nor escape into the posterior divisions of the 
 heart by reason of the valves (c?), the contraction of the dorsal 
 vessel necessarily forces it on towards the head. When it arrives 
 there, it of course issues from the perforated termination of the 
 
270 INSECTA. 
 
 heart, but does not appear to be received by any vessels, and 
 therefore becomes again diffused through the body. The diffused 
 character of the circulation met with in insects may easily be made 
 a matter of observation in many of the transparent aquatic larvae 
 that are readily to be met with. When any of the limbs of these 
 larvae are examined under a powerful microscope, continual cur- 
 rents of minute globules are everywhere distinguishable, moving 
 slowly in little streams ; some passing in one direction, others in 
 the opposite : but that these streams are not contained in vascular 
 canals is quite obvious, from the continual changes which occur in 
 the course of the globules ; their movements, indeed, rather re- 
 semble those of the sap in chara, and other transparent vegetables, 
 in which the circulation of that fluid is visible under a microscope. 
 
 The organs appropriated to furnish the different secretions met 
 with in the economy of insects, are modified in their structure to 
 correspond with the character of the circulation, and are invariably 
 simple tubes or vesicles of various forms immersed in the fluids of 
 the body, from which they separate their peculiar products. The 
 poisonous saliva of bugs, and the innoxious salivary fluid of other 
 insects ; the bile and auxiliary secretions subservient to digestion ; 
 the venom which arms the sting of the wasp, and the silky en- 
 velope of the caterpillar, are all derived from the same source, and 
 in some mysterious manner elaborated from the blood by variously 
 formed vessels : but of this we have already given many examples, 
 and others will present themselves in the following pages. 
 
 (312.) In the nervous system of the INSECTA, we have many 
 interesting illustrations of that gradual concentration of the parts 
 composing it, and consequently of increased proportionate deve- 
 lopement of the nervous centres, corresponding with the more active 
 movements and higher faculties by which the class before us is so 
 remarkably distinguished from those forms of articulated animals 
 that we have hitherto had an opportunity of examining. The su- 
 pra-O2Sophageal ganglion, or brain, assumes a preponderance of size 
 in relation to more perfect organs of sense, and to instincts of 
 more exalted character ; the chain of ganglia placed along the floor 
 of the abdomen, is composed of a few large masses of sufficient 
 power to animate the strong and energetic muscles of the limbs ; 
 and, moreover, anatomists have detected the existence of an addi- 
 tional nervous apparatus, apparently representing the sympathetic 
 system of vertebrate animals, which is distributed to the viscera ap- 
 propriated to digestion : each of these divisions will therefore re- 
 quire a separate notice. 
 
INSECTA. 
 
 271 
 
 The brain, or encephalic ganglion (Jig. 121, 1), is a nervous 
 mass of considerable size placed above the gullet ; it consists es- 
 
 Fig. 121. 
 
 sentially of two ganglia united into one mass, and from it all the 
 nerves appropriated to the special instruments of the senses are de- 
 rived, so that it may naturally be regarded as the chief seat of sens- 
 ation and intelligence. The nerves originating from this common 
 sensorium are seen upon an enlarged scale in Jig. 122 : they are the 
 optic (Jig- 122, a), supplying the eyes, and the antennal (Jig. 
 122; e), which run to the special instruments of touch, or antenna',, 
 
272 INSECTA. 
 
 organs of a very singular character that we shall examine more mi- 
 nutely hereafter. Two other cords of variable length {Jig- 122, 
 g, g) are given off from the inferior aspect of the brain, and serve 
 to connect it with the anterior ganglion of the ventral chain (j%. 
 122, A), to which some writers have thought proper to give the 
 name of cerebellum, though upon what grounds it is difficult to 
 conjecture ; the mass last mentioned gives off various nerves to 
 supply the parts connected with the mandibles, maxilla, and other 
 organs of the mouth. 
 
 The rest of the ventral chain of ganglia forms a continuous series 
 (fig. 121, 2, 3, 4, 5, 6, 7, 8) of nervous centres arranged in pairs, 
 and united to each other by double cords of communication, but they 
 vary much in number and relative magnitude in different families. 
 Those situated in the thorax are usually of the greatest proportion- 
 ate size, inasmuch as they furnish the nerves that supply the mus- 
 cles of the wings and legs ; the succeeding ganglia give branches to 
 the abdominal segments ; and the last, which is commonly of consi- 
 derable bulk, supplies the sexual organs and the extremity of the 
 colon. 
 
 (313.) It is the general opinion of modern physiologists that the 
 intimate composition of the nervous apparatus described above is by 
 no means so simple as it appears to ordinary observation ; and, since 
 the experiments of Sir Charles Bell and Majendie demonstrated 
 the existence of distinct columns or tracts in the spinal axis of ver- 
 tebrate animals, various anatomists have endeavoured to show that 
 corresponding parts may be pointed out in the ventral chain of ar- 
 ticulated animals. There can, indeed, be no doubt that this por- 
 tion of the nervous system of an insect corresponds in every parti- 
 cular with the medulla spinalis ; and if, in the one case, the nerves 
 which preside over the general muscular movements arise from a 
 different column to that whence the nerves that correspond with 
 the periphery of the body originate, while those which regulate the 
 motions of respiration emanate from a distinct tract, we might rea- 
 sonably suppose a similar arrangement to exist in the structure of 
 the nervous system we are now examining. It has, in fact, been 
 well ascertained that the nerves given off to the muscular system of 
 the Homogangliata are not derived from the ganglionic masses them- 
 selves, but from the cords which connect them together, while the 
 nerves distributed to the integument and external parts of the body 
 communicate immediately with the ganglia. These different modes 
 of origin give presumptive evidence that at least two distinct tracts 
 
INSECTA. 273 
 
 exist in the central axis of insects ; but, from the extreme minute- 
 ness of the different parts, it is not easy satisfactorily to demonstrate 
 them separately. In the larger ARTICULATA, however, as for 
 example in the CRUSTACEANS, two distinct columns of nervous 
 matter are readily detected: it will, therefore, be more convenient 
 to defer the investigation of this interesting subject until we have 
 an opportunity of describing these parts upon an enlarged scale ; 
 enough has been said at present to enable the reader to compare 
 the nervous axis of an insect with that of a lobster, and draw correct 
 conclusions from the comparison. 
 
 (314.) The last division of the nervous apparatus, which we have 
 already mentioned as being the representative of the sympathetic 
 system, consists of two portions ; one corresponding, in distribution 
 at least, with the nervus vagus of VERTEBRATA, while the other 
 represents, apparently, the sympathetic ganglia. The nervus vagus , 
 as we shall call it, and which has been named by Swammerdam* 
 and Cuvier the recurrent nerve, arises (Jig* 122, i, b) by two roots 
 from the opposite extremities of pi ff , 122. 
 
 the brain close to the origins of 
 the antennal nerves. The nervous 
 cords thus derived soon unite to 
 form a minute central ganglion 
 (Jig- 122, i), from which proceeds 
 a single nerve (fig. 122, /, *), 
 that runs with the gullet (/) be- 
 neath the brain, and spreads in deli- 
 cate ramifications upon the oesopha- 
 gus as far as the muscular stomach (Jig. 121, 9, 9), or to the gizzard, 
 when that organ exists. 
 
 (315.) The Sympathetic system, properly so called, consists 
 of four small ganglia (Jig. 121, c, c, /, /), the two anterior of 
 which communicate with the brain, and with each other by 
 means of connecting filaments. These ganglia are closely applied 
 to the commencement of the resophagus, and supply it with minute 
 nerves. 
 
 (316.) Various are the conjectures entertained by different au- 
 thors concerning the senses possessed by the members of the insect 
 world, and^ the organs subservient thereunto. The possession of 
 certain sources of perception has been alternately granted and denied, 
 
 * Biblia Naturaj, 
 
INSECTA. 
 
 the nature of their sensations has been a fruitful subject of inquiry, 
 and some physiologists have even gone so far as to deny the corre- 
 spondence of the impressions derived by insects through the medium 
 of their senses with those which we ourselves receive. It would 
 lead us far out of our course did we even advert to the multiplicity 
 of opinions and conjectures promulgated from various sources rela- 
 tive to these inquiries, and, perhaps, with little addition to our 
 real knowledge. It is true that we cannot deny the possibility of 
 the existence of other modes of sensation than those familiar to us ; 
 but it is likewise evident that, as we can never have the most remote 
 conceptions concerning their nature, speculations respecting them 
 are calculated to lead to very unsatisfactory conclusions. We must 
 from necessity take our own senses as the standard of comparison, 
 limiting our inquiries to examine how far insects possess means of 
 intercourse with the external world similar to those which we enjoy, 
 and, when we find certain faculties to exist, to investigate the struc- 
 ture of the organs by which they are exercised. 
 
 (317.) The sense of touch is indubitably bestowed upon all in- 
 sects ; and, to judge from the perfection of the edifices which they 
 build, and the precision of their usual operations, this must be ex- 
 tremely delicate. It is sufficient, however, to look at the external 
 construction of the skeletons of ARTICULATA, to perceive that the 
 hard and insensible integument spread over the entire surface of 
 their bodies is but little calculated to receive tactile impressions. 
 The antennae, or feelers as they are popularly called, have been 
 very generally regarded as being peculiarly instruments of touch ; 
 and whoever watches the proceedings of an insect in which these 
 appendages are largely developed, will, we apprehend, easily con- 
 vince himself that they are employed to investigate surrounding 
 objects by contact, Strauss Durckheim regards the feet as being 
 specially appropriated to the sense of feeling, but this opinion 
 seems quite inadmissible. Burmeister places the exercise of touch 
 exclusively in the palpi attached to the maxillae and labium, and 
 observes that in the larger insects, such as the predatory beetles, 
 the grasshoppers, humble-bees, and many others, the apex of the 
 palpus is dilated into a white transparent and distended bladder, 
 which, after the death of the insect, dries up, and is no longer 
 visible. This bladder he looks upon as the true seat of the sense 
 in question, and remarks that the main nerve of the maxillae 
 and of the tongue spreads to it, and distributes itself upon its 
 superior surface in minute ramifications. 
 
INSECTA. 275 
 
 (318.) Whether taste exists in insects as a distinct sense may 
 admit of dispute ; the tongue, already described, seems but little 
 adapted to appreciate savours, and, seeing this, it is obvious that 
 all opinions assigning the function of tasting to other parts are 
 purely conjectural. 
 
 (319.) Many insects are certainly capable of perceiving odours ; 
 of this we have continual proof in the flesh-fly and other species, 
 that are evidently guided to their food, or select the position in which 
 to deposit their eggs, by smell ; but where the olfactory apparatus 
 is lodged is still a matter of doubt. The antenna and the palpi 
 have each had the power of smelling assigned to them, but without 
 much plausibility. The respiratory stigmata have been pointed 
 out as performing the office of examining the air admitted for the 
 purpose of breathing ; yet other authors, with equal probability, 
 look upon the ultimate ramifications of the trachese as forming one 
 extensive nose. The interior of the mouth has been indicated by 
 Treviranus ; * while Kirby and Spence find in the Necrophori, and 
 other insects remarkable for acuteness of smell, an organ in close 
 connection with the mouth, to which they attribute the perception 
 of odoriferous particles : this is a cavity situated in the upper lip, 
 containing a pair of circular pulpy cushions covered by a membrane 
 transversely striated or gathered into delicate folds. 
 
 (320.) We are scarcely better informed concerning the organs of 
 hearing, but that insects are capable of perceiving sounds is proved 
 by the fact of many tribes being capable of producing audible noises 
 by which they communicate. There seems, indeed, to be little 
 doubt that the auditory apparatus is in some way or other con- 
 nected with the antennae. Some have supposed that these slender 
 and jointed organs, supplied, as they are, with large nerves, are 
 themselves capable of appreciating sonorous vibrations. Bur- 
 meister j- thinks that, as in crabs and lobsters, it is at the base 
 of the antenna that the ear is situated, and observes that if we 
 examine the insertion of these appendages we shall detect there 
 a soft articulating membrane which lies exposed, and is rendered 
 tense by the movements of the antenna, this he looks upon 
 as representing the drum of the ear, and conceives that it is so 
 placed as to receive impressions of sound, increased by the vibratory 
 movements communicated to the antennas by the sonorous undula- 
 tions of the atmosphere. 
 
 * Vermischte Schriften, vol. ii. t Op. cit. p. 296. 
 
 T 2 
 
276 INSECTA. 
 
 In some moths, Treviranus* has discovered structures which 
 would seem to be indubitably real auditory organs. He found in 
 front of the base of each antenna a thin membranous drum, behind 
 which, large nerves, derived from those supplied to the antennse, 
 spread themselves out ; but this apparatus has not been detected 
 in other insects. 
 
 (321.) The eyes of insects are of two kinds, simple and com- 
 pound ; the former being insulated visual specks, while the latter 
 consist of agglomerations of numerous distinct eyes, united so as to 
 form most elaborate and complex instruments of sight. 
 
 Some insects, as the Dictyotoptera and Thysanoura, only 
 possess simple eyes ; others, as for example the Coleoptera, have 
 only compound eyes ; but in general both kinds exist together. 
 In the Sir ex gigas (Jig. 128), for instance, besides the large 
 hemispherical organs of sight, situated at the sides of the head, 
 three simple spots are seen upon the vertex, which are likewise 
 appropriated to vision. 
 
 The structure of the eyes has been most minutely investigated 
 by several distinguished entomotomists, and the labours of Marcel 
 de Serres,j- Joh. M tiller, J Strauss Durckheim, and Duges,|| have 
 done much to dispel the mistaken notions entertained by preceding 
 anatomists. 
 
 The simple eyes consist of a minute, smooth, convex, transpa- 
 rent cornea, in close contact with which is a small globular lens ; 
 behind this lens is placed the representative of the vitreous humour, 
 upon which a nervous filament spreads out, so as to form a retina : 
 the whole is enclosed in a layer of brown, red, or black pigment, 
 which, bending round the anterior surface of the eye, forms a dis- 
 tinct-coloured iris and pupillary aperture. Such an arrangement 
 evidently resembles what is met with in higher animals, and is 
 remarkable for its simplicity ; but it is far otherwise with the com- 
 pound eyes of insects, for these are constructed upon principles so 
 elaborate and complex, that we feel little surprise at the amaze- 
 ment expressed by early writers who examined them, although 
 their ideas concerning their real structure came far short of the 
 truth. 
 
 * G. R. Treviranus, Annalen der Wetterau. Qesel. f. d. Ges. Naturk. vol. i. 1809. 
 t Mem. sur les Yeux composes, et les Yeux lisses des Insectes. Montpel. 8vo. 
 1813. 
 
 t Zur Vergleichenden Physiologie des Gesichtssinnes, 8vo. 1826. 
 
 Annales des Sciences Nat. torn, xviii. || Ibid. torn. xx. 
 
INSECTA. 
 
 277 
 
 A 
 
 The compound eyes of insects are two in number, situated on 
 the lateral aspects of the head, the form of each being more or less 
 hemispherical. When examined with a microscope, their surface 
 is seen to be divided into a multitude of hexagonal facets, between 
 which, minute hairs are generally conspicuous. The number of 
 facets or cornese, for such in fact they are, varies in different 
 genera : thus, in the ant (Formica) there are 50 ; in the common 
 house-fly (Musca domestica), 4000 ; in some dragon-flies (Libel- 
 Ma), upwards of 12,000. In butterflies (Papilio) 17,355 have 
 been counted, and some Coleoptera (Mordella) possess the as- 
 tonishing number of 25,088 distinct cornese. 
 
 But in order to appreciate the wonderful organization of these 
 remarkable organs of sight, it is necessary to examine their internal 
 structure : every cornea is then found to belong to a distinct eye, 
 provided with a perfect nervous apparatus, and exhibiting its pe- 
 culiar lens, iris, and pupil ; thus being completely entitled to be 
 considered a distinct instrument of vision. 
 
 By attentively examining & 123 
 
 the annexed figure, repre- 
 senting a section of the eye 
 of the cockchafer (Melolon- 
 tha), as displayed by Strauss 
 Durckheim, the whole struc- 
 ture of the organ will be 
 readily understood. The 
 optic nerve (Jig. 123, a), 
 derived immediately from 
 the supra-cesophageal mass 
 of nervous matter, swells 
 soon after . its origin into a 
 rounded ganglion, nearly 
 half as large as the brain it- 
 self. From the periphery 
 of the ganglion so formed 
 arise a considerable number of secondary nerves (6), which are 
 very short, and soon come in contact with a layer of pigment (d) ; 
 that in the cockchafer is of a brilliant red colour, and is placed 
 concentrically with the convex outer surface of the eye. Behind 
 this membrane, called by Strauss the common choroid, the second- 
 ary optic nerves (b) unite to form a membranous expansion of 
 nervous matter (c) which may be denominated the general retina. 
 
278 INSECTA. 
 
 From the nervous expansion so formed arise the proper optic 
 nerves (e), appropriated to the individual eyes or ocelli, as we shall 
 term them. These nervous filaments are as numerous as the 
 facets of the cornea, and traverse the common choroid to radiate to- 
 wards the individual eyes whereunto they are respectively destined, 
 and the structure of which we must now proceed to examine. 
 In fig. 123, B, a portion of the circumference of the compound 
 eye is represented upon a very large scale, in order to show the 
 construction of the hexagonal ocelli that enter into its composi- 
 tion. Each cornea (i) is a double convex lens, adapted by its 
 shape to bring to a focus the rays passing through it. Behind 
 every lens so constituted is placed an hexaedral transparent prism 
 (A), which from its office may be compared to the vitreous hu- 
 mour of the human eye ; and it is upon the posterior extremity 
 of these prisms that the proper optic nerves (jig- 1 23, A, e) spread 
 themselves out, so as to form so many distinct retinae. When we 
 reflect upon the extreme minuteness of the parts above alluded to, 
 we may well expect slight discrepancies to occur between the ac- 
 counts given of them by different anatomists. Strauss Durckheim 
 represents every optic nerve as terminating in a minute pyriform 
 bulb (fig. 123, B,/), and points out a dark layer of pigment (g), 
 which forms a choroid tunic proper to each ocellus ; while, accord- 
 ing to Muller and Duges, the vitreous humours (h) are conical, and 
 terminate posteriorly in a sharp point, upon which the terminal 
 expansion of the optic nerve spreads out without any pyriform 
 enlargement : they likewise deny the existence of the proper 
 choroid (g) in the situation indicated by Strauss, but find a black 
 pigment situated immediately behind the cornea, that at first sight 
 would appear to be continuous over the whole surface of the eye. 
 Even Cuvier seems at one time to have adopted this opinion ; 
 Muller, however, found that, upon carefully removing the internal 
 structures of the organ, leaving the pigment untouched, the dark 
 varnish in question, although very thick at the lines of union of 
 the different facets, where it is continuous with a choroid that 
 separates the individual ocelli, yet towards the centre of each facet 
 it becomes exceedingly thin, and at the very centre is quite want- 
 ing, so that a minute perforation or pupil is thus left, through 
 which the rays of light enter. The existence of the secondary 
 optic nerves (b) and common retina (c) is likewise disputed by 
 Muller and Duges, who consider the proper optic nerves to arise 
 immediately from the surface of the brain. 
 
INSECTA. 
 
 279 
 
 With regard to the wonderfully complex structure of these 
 organs, Strauss Durckheim suggests, that, the eyes of insects being 
 fixed, nature has made up for their want of mobility by their 
 number, and by turning them in all directions ; so that it might be 
 said that these little animals have a distinct eye for every object. 
 But here we are naturally tempted to inquire, whether insects see 
 at the same time distinctly with every one of these eyes, or if they 
 distinguish with one eye only. Upon this point Strauss Durck- 
 heim observes, that, if they saw clearly with all, the great number 
 of images would necessarily produce confusion, and would prevent 
 creatures so organized from paying special attention to any deter- 
 minate point. It is probable, therefore, that one ocellus only is at 
 any given time placed in circumstances precisely adapted to the 
 complete examination of an object, the animal seeing things imper- 
 fectly with the rest, in the same manner as we see objects situated 
 nearer to us or further off than that upon which we fix our atten- 
 tion ; so that, according to this supposition, insects would see very 
 distinctly with one eye only, exactly as we see confusedly an ex- 
 tensive landscape, although we only distinguish a small part of it. 
 
 (323.) In all insects the sexes are quite distinct, and the genera- 
 tive apparatus, both of the male and female, consists of various se- 
 creting organs with their excretory ducts : in the male, such glands 
 furnish the impregnating secretions ; and, in the female, give origin 
 to the ova, and pro- 
 vide the covering 
 wherein the eggs are 
 enveloped. 
 e (324.) Commenc- 
 ing with a descrip- 
 tion of the male or- 
 gans, we find in the 
 cockchafer various 
 parts represented in 
 the accompanying 
 figure, taken from 
 the admirable work 
 of Strauss already so 
 often quoted. The 
 testicles of Melolon- 
 tha (fig. 124, a, a) 
 are six in number 
 on each side of the 
 
 Fig. 124. 
 
280 INSECTA. 
 
 body ; but, in the engraving, those of one side only are delineated. 
 Every testis consists of a vesicular organ, hollow internally, which, 
 being immersed in the juices of the insect, separates therefrom 
 the seminal fluid. Six ducts (5, b, b) may be called Vasa 
 deferentia, and convey the spermatic liquor into a common 
 canal (c, c), of considerable length and much convoluted. 
 Although slender at its commencement, this tube ultimately 
 expands into a wider portion (d), wherein, no doubt, the semen 
 accumulates, and which has been called by authors the vesica 
 seminalis. 
 
 The canal (d) terminates by joining the corresponding duct 
 from the opposite side (d?) to form a common tube (g), but just 
 at the point of junction they are joined by two long auxiliary 
 vessels (y, f) that have been named sperm-vessels, gluten-vessels, 
 and gum-vessels, by different authors, but which appear to be 
 appropriated to the production of some fluid, perhaps analogous to 
 the prostatic fluid of mammalia, whereby the bulk of the seminal 
 liquor is increased in order to facilitate its expulsion. Each of 
 these auxiliary vessels consists of two parts, a long and much con- 
 voluted portion (e, e, e), forming the secreting organ ; and a dila- 
 tation (f), that must be looked upon as a reservoir for the fluid 
 elaborated. The common canal (g) receives all these secretions ; 
 it is at first enclosed in a kind of sheath (A), but, soon becom- 
 ing muscular, it dilates into a strong contractile canal (g, z), called 
 the ductus ejaculatorius, which is continued to the extremity of 
 the penis. 
 
 The intromittent organ itself is composed of two parts ; a pro- 
 trusible corneous tube (/, /), and an external horny sheath (n, n), 
 in which the former is usually concealed and protected. 
 
 (325.) Great variety, of course, exists in the number, form, and 
 general arrangement of all the parts alluded to in the above descrip- 
 tion, when examined in different insects.* In the hive-bee, for 
 example, the testes (Jig. 125, a) are only two in number, and 
 are simple oval vesicles ; the vasa defer entia (b, b) are short ; and 
 the seminal receptacles (c) form membranous sacculi. The aux- 
 iliary secreting organs (d), although placed in the same position 
 as in Melolontha, are represented by capacious cseca ; while the 
 common excretory duct (e) swells into a strong and muscular bag 
 
 * For more ample details relative to the various forms of the testis in insects, the 
 reader is referred to the Cyclop, of Anat. and Phys. ; art. GENERATION, ORGANS 
 
INSECTA. 
 
 281 
 
 ( f ), which constitutes the ejaculatory F *8 
 
 apparatus. Still, however, it is easy to 
 see that, although diversified in appearance, 
 the parts here found are essentially similar 
 to those met with in the cockchafer, and 
 represent respectively the same organs. 
 
 (326.) The female apparatus of reproduc- 
 tion presents a general correspondence, both 
 in form and arrangement, with the sexual 
 parts of the male insect. The ovaria are 
 simple secreting sacculi, or elongated tubes, 
 in which the germs or ova are produced, 
 instead of the seminal liquor ; and the 
 excretory canals, or egg-passages, with the 
 organs appended to them, although appro- 
 priated to different functions, strikingly re- 
 semble the organs met with in the other 
 sex. 
 
 In the female of Melolontha the ovaria are long tubes, form- 
 ing two distinct fasciculi, symmetrically situated on the two sides 
 of the body. At their commencement (Jig> 126, w, u) the ovi- 
 gerous tubes are slender, and the ova which they contain at this 
 point are in a very rudimentary state of developement ; they ge- 
 nerally dilate, however (, , t, i), and, as they expand, the ova are 
 seen to attain larger dimensions. Near its termination each ova- 
 rian tube assumes a granulated texture (s 9 *), and they all ulti- 
 mately open into the corresponding excretory canal (r, r). 
 
 All the ovarian tubes of one side are united into a bundle, by 
 a ligament (v 9 #), which Joh. Miiller* traced to the dorsal vessel, 
 and believed to be a vascular canal adapted to bring blood imme- 
 diately into the tubes wherein the ova are formed ; but no satis- 
 factory evidence has been adduced in proof of the existence of such 
 an extraordinary communication, and the thread in question is most 
 probably a mere ligamentous connection. 
 
 (327.) Taking the higher animals as a standard of comparison, we 
 may suppose the formation of the eggs in these tubes to be accom- 
 plished in the following manner : In the upper part of the tube (u) 
 is formed the yolk, enclosed in its peculiar membrane, and provided 
 with that wonderful germ from which after impregnation the future 
 being is to be developed ; as the yolk slowly descends to the more 
 
 * Nova Acta Phys. Med, n. c. vol. xii. part ii. 
 
INSECTA. 
 
 dilated parts of the canal *"* 126 - 
 
 (, ), it becomes clothed 
 with the albumen which 
 constitutes the white of 
 the egg ; and ultimately, 
 before quitting the nidus 
 of its formation, receives 
 from the granular termi- 
 nation of the ovary its J 
 last integument or shell. 
 Thus completed, it passes 
 into the excretory canal 
 (r, r) ; and this, meeting 
 the corresponding tube 
 derived from the ovaries 
 of the opposite side, joins 
 it to form the common 
 oviduct {I) through which 
 the egg is conducted out 
 of the body. 
 
 (328.) But we must 
 now advert to certain ap- 
 pendages connected with 
 the common oviduct. 
 These are of two kinds ; the gluten-secretors and the spermalheca. 
 
 The gluten-secretors (Jig- 126, p, p ) are glandular caeca 
 opening into the common egg-canal, and are apparently destined 
 to furnish a glutinous fluid with which the eggs become invested 
 before they are expelled from the body and thus they are fre- 
 quently united into long chains and variously shaped masses ; or 
 else the adhesive varnish thus secreted serves to glue the ova in 
 situations favourable to the developement of the embryo. 
 
 The other organ, or spermatheca (Jig. 126, w, o), has a widely 
 different office, being a receptacle provided to receive the seminal 
 secretion of the male during copulation : it is always situated upon 
 the upper aspect of the oviduct, into which it opens by a small ori- 
 fice surrounded by a thickened margin or sphincter, embracing the 
 neck of the bag, and so disposed as either to retain the enclosed fluid,, 
 or to allow it to escape into the oviduct. That this organ really does 
 receive and retain the seminal liquor is proved by the presence of 
 seminal animalcules in its contents ; but the matter has been placed 
 
INSECTA, 283 
 
 beyond a doubt by the experiment of John Hunter,* who actually 
 succeeded in fecundating the eggs of an unimpregnated female, by 
 applying to them a little of the fluid contained in its cavity : but 
 that the reader may comprehend fully the reason of such an arrange- 
 ment, it is necessary to consider the circumstances under which 
 insects propagate. 
 
 In most animals, sexual union may be repeated several times 
 during the life of individuals, but, in insects, intercourse between 
 the sexes is permitted to take place but once ; and this solitary 
 congress must suffice for the impregnation of all the ova, however 
 numerous, and however imperfect may be the developement of 
 some of them at the time when the embrace occurs. 
 
 Let us take the hive-bee as an example ; in the females of this 
 insect the ovigerous tubes (fig. 127, a, a) are excessively numerous, 
 and the eggs produced in them may amount to between 20,000 and 
 30,000 : these eggs, of course, arrive at maturity in succession, 
 and not all at once ; so that at the moment when the queen-bee 
 meets her selected mate, perhaps the majority of the ova are not 
 in a sufficiently mature condition to be rendered fertile. Never- 
 theless, the meeting of the sexes cannot be repeated ; for no sooner 
 has copulation taken place than the favoured male dies, and 
 by a simultaneous butchery all the other males, or drones as 
 they are commonly designated, are F,v. 127. 
 
 destroyed by the working inhabit- 
 ants of the hive. The quantity 
 of the fecundating liquor, there- 
 fore, supplied by one connection, 
 must serve to fertilize all the eggs 
 produced during the lifetime of the 
 queen-bee ; and for this purpose it 
 is stored up in the spermatheca 
 (Jig. 127, c), so that, how numer- 
 ous soever may be the eggs formed, 
 
 they are all vivified as they pass out through the oviducts (5, e), 
 and thus come in contact with the orifice of the reservoir of semen. 
 
 In Meloe variegatus (Jig. 121) the ovaria (d) consist of 
 wide and capacious sacs, covered externally with innumerable 
 glandiform vesicles, opening into the cavity of the ovary (e). The 
 gluten-secretor (h) and the spermatheca (g) are seen as in 
 Melolontha, appended to the common oviduct (f) ; but the sperma- 
 
 * Home's Lectures on Comp. Anat. vol. iii. p. 370. 
 
284 
 
 1NSECTA. 
 
 theca has a small accessory vesicle (i) connected with it, not found 
 in the former examples. 
 
 (329.) In many insects, especially of the Hymenopterous order, 
 the generative apparatus is terminated externally by peculiar instru- 
 ments provided for the purpose of introducing the eggs into a 
 proper situation. This is particularly remarkable in the Ichneu- 
 mons, which deposit their ova in living caterpillars ; and in the 
 saw-flies (Tenthredo), whose eggs are insinuated into the sub- 
 stance of the leaves, or even of the branches of trees. To describe 
 all the contrivances employed for this purpose would lead us far 
 beyond our prescribed limits : one example of an organ of this 
 description must suffice. 
 
 In the Sir ex gigas (Jig. 128) the ovipositor consists appa- 
 
 Fig. 128. 
 
 rently of three pieces of considerable length, seen in the figure to 
 project from the inferior margin of the abdomen. Of these pieces, 
 two form a sheath enclosing a third, called the terebra, or borer, which 
 in the Tenthredo contains two saws of extremely beautiful construc- 
 tion, as we learn from an account of them given by Professor Peck, 
 and quoted by Kirby and Spence :* the original description, which 
 it would be unpardonable to abbreviate, is as follows : " This in- 
 strument," says Professor Peck, " is a very curious object ; and, in 
 order to describe it, it will be proper to compare it with the tenon- 
 saw used by cabinet-makers, which, being made of a very thin plate of 
 steel, is fitted with a back to prevent its bending. The back is a piece 
 
 * Introd. to Entom. vol. iv. p. 161 . 
 
1NSECTA. 285 
 
 of iron, in which a narrow and deep groove is cut to receive the plate, 
 which is fixed : the saw of the Tenthredo is also furnished with a 
 back, but the groove is in the plate, and receives a prominent ridge 
 of the back, which is not fixed (to the saw), but permits the saw 
 to slide forward and backward as it is thrown out and retracted. 
 The saw of artificers is single, but that of the Tenthredo is double, 
 and consists of two distinct saws with their backs : the insect, in 
 using them, first throws out one, and while it is returning pushes 
 forward the other ; this alternate motion is continued till the inci- 
 sion is effected, when the two saws, receding from each other, con- 
 duct the egg between them into its place." 
 
 (830.) With respect to the number of eggs laid by insects it 
 varies in different species ; the flea, for example, lays about twelve, 
 and many Diptera and Coleoptera average perhaps fifty : but others 
 are far more prolific ; among moths, for example, the silkworm pro- 
 duces 500, and some from 1000 to 000 : the wasp ( Vespa vulgaris) 
 deposits 3000 ; the ant (Formica), from 4000 to 5000. The 
 queen-bee is said by Burmeister to lay from 5000 to 6000 ; but 
 Kirby and Spence consider that in one season the number may 
 amount to 40,000 or 50,000, or more. Yet, surprising as this 
 latter statement may appear, the fecundity of the queen-bee is far 
 inferior to that of the white-ant (Termes fatalis) ; for the female 
 of this insect extrudes from her enormous matrix innumerable eggs 
 at the rate of sixty in a minute, which gives 3600 in an hour, 
 86,400 in a day, and 2,419,200 in a lunar month : how long the 
 process of oviposition continues in the termite is unknown ; but, if 
 it were prolonged through the entire year, the amazing number of 
 211 ,449,600 eggs would proceed from one individual ; setting, how- 
 ever, the number as low as possible, it will exceed that produced by 
 any known animal in the creation. 
 
 (331.) The Aphides, or plant- lice, furnish a remarkable instance 
 of fecundity. In these insects it has been satisfactorily ascertained 
 by Bonnet, Lyonnet, and Reaumur, that a single sexual intercourse 
 is sufficient to impregnate not only the female parent, but all her 
 progeny down to the ninth generation ! The original insect still 
 continues to lay when the ninth family of her descendants is capa- 
 ble of reproduction ; and Reaumur estimated that even at the fifth 
 generation, a single Aphis might be the great-great-grandmother of 
 5,904,000,000 young ones. 
 
 (332.) Innumerable are the means employed by nature to keep 
 the balance between the increase and destruction of the insect tribes, 
 
INSECTA. 
 
 and countless enemies are provided for the purpose of checking 
 their inordinate accumulation. 
 
 Fig. 129. 
 A 
 
 (333.) Among the most remarkable provisions for preventing su- 
 perabundant fertility, is that law which compels the most prolific 
 insects to live in large societies, and permits but one female out of 
 a multitude to lay eggs. As an example of this, we may take the 
 hive-bees,* so remarkable for their elevated instincts and industri- 
 ous habits. A swarm of bees consists, first of females, whose sex- 
 ual organs remain permanently in an undeveloped condition, usu- 
 ally called the Workers (Jig- 129, A) ; secondly, of perfect males or 
 drones (c) ; and thirdly, of a solitary fertile female, called the Queen 
 (B), which gives birth to all the progeny of the hive ; and thus, 
 instead of 20,000 or 30,000 eggs being furnished by every one of 
 as many females, one female only is permitted to be instrumental 
 in perpetuating the species. 
 
 (334.) The termite ants likewise, were it not for a similar restric- 
 tion, would soon, by their overwhelming increase, depopulate whole 
 regions of the earth, and render the countries in which they are 
 met with absolutely uninhabitable by their extreme voracity. A 
 community of termites is said to consist of five different members, 
 namely, winged males and females (Jig. 130, A) ; apterous neu- 
 ters, or soldiers, which have large heads furnished with strong pro- 
 jecting mandibles (B) ; uriwinged pupse, having a smaller head, and 
 the rudiments of wings only (c) ; and, lastly, of similarly formed 
 larvte, or workers (D), differing from the latter only in wanting 
 the rudiments of wings. The following is a brief history of the 
 establishment and growth of a colony of these insects, as narrated 
 by Burin eister.f At the termination of the hot season, the young 
 
 * For ample details concerning the habits of these interesting creatures, the reader is 
 referred to Dr. Bevan's work on the Honey -Bee, its Natural History, Physiology, and 
 Management, vol. I, 12mo. Lond. t Op. cit. p. 535. 
 
INSECTA. 
 
 287 
 
 males and females disclosed in a nest quit it, and appear upon the 
 surface of the earth, where they swarm in innumerable hosts and pair. 
 The busied workers then convey a chosen male and a female back 
 into the dwelling, and imprison them in the central royal cell, the 
 entrances to which they decrease and guard ; through these apertures 
 the imprisoned pair then receive the nutriment they require. The 
 male now, as amongst all other insects, speedily dies after the im- 
 pregnation of the female has been effected ; but the female from this 
 period begins to swell enormously from the developement of her 
 countless eggs, and, by the time she is ready to commence laying, 
 her abdomen is about 1 500 or 000 times larger than all the rest 
 of her body (fig. 130, E). During the period of this swelling the 
 
 Fig. 130. 
 
 - 
 
 workers remove the walls of the royal apartment, uniting the nearest 
 cells to it, so that, in proportion to the increase of the body of the 
 queen, the size of the abode she inhabits is also increased. She 
 
288 INSECTA. 
 
 now commences laying eggs, and, during the process, the abdomen 
 exhibits a continual undulatory motion, produced by the peristaltic 
 movement of the egg-ducts ; while the workers convey away the 
 eggs as they are laid, and deposit them in the distant rearing-cells 
 of their wonderful habitation. The reader will be able to form 
 some idea of the relative proportions and outward appearance of 
 the edifices erected by these comparatively minute beings by the 
 group of their citadels represented in the back-ground of the figure ; 
 but to describe them more minutely would lead us into details 
 unconnected with our subject.* 
 
 (335.) The eggs of these little animals vary much in shape and 
 external configuration ; so that, from the beauty of their forms and 
 exquisite sculpture, some of them are interesting objects for the 
 microscope. 
 
 (336.) We have already spoken concerning the metamorphosis 
 which insects undergo during the progress of their developement from 
 the form under which they first leave the egg to their mature con- 
 dition, when they become fertile, and, in most instances, acquire 
 those instruments of flight so generally characteristic of their perfect 
 state. Before entering upon a more minute inquiry concerning 
 the physiological principles upon which the important changes in 
 question depend, and the phenomena attending the process, it will 
 be advisable to cite a few more examples illustrative of the most 
 interesting varieties of metamorphosis signalized by authors. Fa- 
 bricius distinguishes five different kinds of metamorphosis, and has 
 applied a different name to each. 
 
 The first class comprises all insects of which the larva is a mag- 
 got entirely deprived of legs, that after having changed its skin, or 
 moulted, a certain number of times, becomes, previous to its last 
 change, incased in an oval horny sheath, or pupa-case, whereon not 
 the least trace of the limbs of the mature insect is to be detected ; 
 such pupse are absolutely without the power of motion, and are 
 distinguished by the name of coarctate : examples of this sort of 
 metamorphosis are met with in the common house-flies (Muscida), 
 and the forms of their larvae and pupse are familiar to every one. 
 
 Of the second kind, technically named obtected, the Lepido- 
 ptera furnish well-known instances. The changes which occur in 
 the developement of the silkworm, represented in the annexed 
 figure (Jig- 131), may readily be witnessed. In such insects the 
 full-grown caterpillar, having enclosed itself in a silken ball, throws 
 
 * Vide Smeathman, Phil. Trans, vol.lxxi. 1781. 
 
INSECTA. 
 
 289 
 
 off its last skin, and becomes a quiescent pupa ; but while in tins 
 state the position of the rudiments of the wings and other appen- 
 
 Fi,J3l. 
 
 dages of the perfect insect is strongly indicated upon the exterior of 
 the chrysalis (A), though these parts are still closely wrapped up in 
 the external covering. 
 
 (337.) The third form of metamorphosis, called incomplete, is 
 seen in the Hymenoptera, and in many Coleopterous insects. The 
 maggot, in such tribes as exhibit this kind of change, is sometimes a 
 simple worm deprived of feet or other external organs, or in other 
 species these parts exist in a very imperfect condition ; in the pupa, 
 however, the form of the legs and antennae is perfectly distinct, and 
 even the wings may be seen as rudiments projecting from the thorax. 
 This kind of chrysalis we have seen in the cockchafer (fig. 106, B), 
 in which the grub (c) possessed feebly developed legs ; and in the 
 hive-bee, although the larva (Jig. 132, a, c, d, e,f) has no legs or 
 exterior appendages, in the pupa (b) all the limbs of the perfect 
 bee are recognised with the utmost facility. Yet all these organs 
 are still enclosed in distinct cases (thecte), to each of which names 
 have been applied by entomological writers ; and it is only on 
 throwing off the integument which thus imprisons the mature in- 
 sect, that the bee makes its appearance in a capacity to begin its 
 active and industrious existence in the winged state. 
 
 u 
 
290 INSECTA. 
 
 Those insects whose larva only differs from the imago in not 
 being possessed of wings (Jig. 102), Fabricius regarded as under- 
 going a semi-complete metamorpho- pig. 132. 
 sis ; and when the perfect insect did 
 not acquire wings at all, but pre- 
 cisely resembled the pupa, he called 
 the latter complete. 
 
 (338.) But there are innumer- 
 able examples of metamorphosis 
 which will not conform to any of 
 the above definitions, and in some 
 of them the phenomena exhibited 
 are not a little remarkable. We 
 have already mentioned the changes 
 which the dragon-fly undergoes 
 (figs. 103, 104), and have seen 
 that in this case there is no very 
 striking resemblance between the 
 
 pupa and the adult creature, but, on the contrary, that very won- 
 derful changes occur during the last stage of the metamorphosis. 
 The pupa lives in water ; and, besides six jointed legs adapted to 
 climb the stems of subaquatic plants in search of prey, is pos- 
 sessed of a very peculiar locomotive apparatus, whereby it can 
 propel itself through the element which it inhabits. Appended to 
 the posterior extremity of the abdomen we find three or five leaf- 
 like appendages, which the creature continually opens and closes, 
 and at the same time takes in a quantity of water, sufficient to 
 fill the muscular termination of the rectum, which is expanded for 
 the purpose ; this water is, at intervals, forcibly expelled, mingled 
 with bubbles of air, and thus effects the propulsion of the animal 
 by a mechanism which human ingenuity has imperfectly attempted 
 to imitate, 
 
 But the contrivance above mentioned is also made subservient to 
 respiration ; for, from the observations of Cuvier,* it appears that 
 the interior of the rectum exhibits to the naked eye twelve longi- 
 tudinal lines of black spots arranged in pairs ; and these, when ex- 
 amined under the microscope, are found to be composed of little 
 conical tubes, from which branches go off to join the principal 
 longitudinal tracheae that distribute air through the body. 
 
 Another remarkable peculiarity is met with in the structure of 
 
 * M6m. de la SociSte d'Histoire Nat. p. 48. 
 
INSECTA. 291 
 
 the mouth of these aquatic larvae, for the oral apparatus here forms 
 an instrument of prehension adapted to seize prey at a distance, 
 and constitutes, in fact, a kind of projectile forceps of a very 
 curious construction. Let the reader contrast the following de- 
 scription with that already given of the oral organs of the dragon- 
 fly ( 295), and observe the remarkable difference : a Conceive," 
 say Kirby and Spence,* " your under lip to be horny instead of 
 fleshy, and to be elongated perpendicularly downwards, so as to 
 wrap over your chin and extend to its bottom ; that this elonga- 
 tion is then expanded into a triangular convex plate attached to it 
 by a joint, so as to bend upwards again, and fold over the face as 
 high as the nose, concealing not only the chin and the first-men- 
 tioned elongation, but the mouth and part of the cheeks : conceive, 
 moreover, that to the end of this last-mentioned plate are fixed two 
 other convex ones, so broad as to cover the whole nose and temples ; 
 that these can open at pleasure, transversely, like a pair of jaws, so 
 as to expose the nose and mouth, and that their inner edges, 
 where they meet, are cut into numerous sharp teeth or spines, or 
 armed with one or more long and sharp claws : you will then 
 have as accurate an idea as my powers of description can give of 
 the strange conformation of the lip in the larvae in question, which 
 conceals the mouth and face precisely as I have supposed a similar 
 construction of your lip would do yours. You will probably 
 admit that your own visage would present an appearance not very 
 engaging while concealed by such a mask : but it would strike 
 still more awe into the spectators were they to see you first open 
 the two upper jaw-like plates, which would project from each 
 temple like the blinders of a horse ; and next, having by means 
 of the joint at your chin let down the whole apparatus, and un- 
 covered your face, employ them in seizing any food that presented 
 itself, and conveying it to your mouth. Yet this procedure is 
 that adopted by the larvae provided with this strange organ. 
 While it is at rest, it applies close to and covers the face. 
 When the insects would make use of it, they unfold it like an 
 arm, catch the prey at which they aim by means of the mandibu- 
 liform plates (Jig. 101), and then partly refold it so as to hold 
 the prey to the mouth in a convenient position for the operation 
 of the two pairs of jaws with which they are provided." 
 
 (339.) The metamorphoses of the gnat (Culex) are not less 
 interesting. The female deposits her eggs upon the surface of the 
 
 * Introd. to Entom. vol. iii. p. 126. 
 
INSECTA. 
 
 water, in which her offspring are destined to pass the earlier pe- 
 riods of their existence, gluing the ova together at the moment of 
 their extrusion, so as to unite them into a boat-like mass (Jig. 
 133, A) of such beautiful construction that the little bark swims 
 secure from injury, even during the roughest weather. The in- 
 dividual eggs are of a conical form (fig. 133, B, a, 6, c), and are 
 closed at their inferior extremity by a kind of lid (rf), provided 
 to give egress to the mature embryo. The larva (c), represented 
 upon a magnified scale at E, bears not the slightest resemblance 
 to the perfect insect, and is provided with a singular modification 
 of the respiratory apparatus adapted to its habits. The head is 
 large, and carries two ciliated organs (g, g), which by their 
 movements bring food towards the mouth ; the thorax is even 
 larger than the head, and is furnished with fin-like bunches of 
 minute hairs, as likewise are the segments of the abdomen. To 
 the extremity of the tail is appended a group of moveable leaflets 
 or fins, so disposed that by their action they sustain the larva at 
 the top of the water, where it generally remains suspended with 
 its head downwards. Such a position would obviously render 
 respiration impossible, was there not a corresponding arrangement 
 of the breathing organs to allow of free communication with the 
 air. For this purpose, the respiratory trachese are found to be 
 connected with a tube appended to the antepenultimate segment 
 of the abdomen, the perforated extremity of which, being raised 
 above the water, procures from the atmosphere the oxygen re- 
 quired for respiration. After several moults, the larva, having 
 attained its full growth, enters the pupa state, and in this con- 
 dition still remains an inhabitant of the water, and occupies a 
 position near the surface. A remarkable change, however, is visible 
 in all parts of its structure : the head and thorax (Jig. 133, D) 
 are consolidated into one large mass, under which the lineaments 
 of the mature insect may be detected ; while the tail still con- 
 tinues to be the agent employed in natation. The condition of 
 the respiratory organs is, moreover, completely altered : the tube 
 fixed upon the antepenultimate segment of the larva has totally 
 disappeared, and, instead of it, we find two tubes appended to the 
 back of the thorax ; these, although they perform the same office 
 as the anal pipe of the larva, are thus displaced, in order to cor- 
 respond with the altered position in which the animal now swims ; 
 the back of the thorax, and not the tail, being nearest to the 
 surface, as represented in the drawing (D). The necessity for 
 
293 
 
 this change of posture, and consequent removal of the apparatus 
 for taking in air from one part of the body to another, will be at 
 once obvious when we consider the circumstances under which 
 the perfect insect, having completed its developement, emerges 
 from its pupa investments and enters upon an aerial existence. 
 The problem to be solved is, how shall the mature gnat escape 
 from the water without being wetted ? and, when we consider 
 that neither the larva nor the pupa possesses instruments of lo- 
 comotion capable of enabling it to leave its native element by 
 crawling on shore, the difficulties attending the change appear 
 almost insurmountable. It is evident that, while swimming in 
 the position in which the larva floats (.fig- 133, c), the last 
 
 Fig. 133. 
 
 change could not by possibility be accomplished, as the bursting 
 of the integument would at once admit the water to the sub- 
 merged gnat, and drown it at the moment of its birth ; but by 
 the new arrangement the metamorphosis is easily effected, and 
 that in a manner so beautiful, that it is hard to say which is 
 most admirable, the simplicity of the contrivance, or the perfection 
 with which the object is accomplished. No sooner has the en- 
 cased imago become fitted for its escape, than the pupa, rendered 
 more buoyant, raises its back above the surface : the protruded 
 portion of the pupa-case soon dries, and gradually begins to split 
 in a longitudinal direction, so as to form by its expansion a boat 
 
294 
 
 INSECTA. 
 
 wherein the gnat swims upon the top of its native pond ; and sus- 
 tained in this frail bark, formed by its late skin, it gradually ex- 
 Fig. 134. 
 
 tricates its legs and wings from their coverings, and is kept per- 
 fectly dry until the expansion of its instruments of flight enables 
 
INSECTA. 295 
 
 it to soar into the air and quit for ever the raft so singularly pro- 
 vided for its use. 
 
 (340.) Having thus become acquainted with the various con- 
 ditions under which insects arrive at maturity, and the principal 
 forms that they exhibit during the different stages of the meta- 
 morphosis, the reader will be prepared to investigate more mi- 
 nutely the changes in progress during the process, and the gradual 
 developement of the organs which successively make their appear- 
 ance. On examining the viscera of a Caterpillar, they are found 
 scarcely at all to resemble those of the butterfly or moth, into 
 which a larva of this description is ultimately matured. The 
 jaws (Jig. 136, i, 6), widely different both in structure and 
 office from the proboscis which represents them in the perfect 
 insect (Jig. 115), are strong and horny shears adapted to cut 
 the leaves of vegetables and other coarse materials used as food ; 
 the oesophagus (j%. 134, g, h) is strong, muscular, and capa- 
 cious ; and the stomach (A, i), in capacity corresponding with 
 the extraordinary voracity exhibited by the larva, passes insen- 
 sibly into a wide intestine (i, w), the line of separation being 
 only indicated by the entrance of the biliary vessels (k) that wind 
 in numerous convolutions around the posterior half of the alimen- 
 tary canal. It is sufficient to contrast this arrangement of the 
 digestive organs with what we have already described in the but- 
 terfly (Jig. 117), to appreciate the amazing dissimilarity: it would 
 be difficult indeed to imagine, did not anatomy convince us of the 
 fact, that the digestive apparatus of the imago, with its slender 
 oesophagus, dilated crop, short sacculated stomach, long and con- 
 voluted small intestine, and capacious colon, was derived from a 
 gradual modification of such viscera as those we have just been 
 considering. The salivary glands of the caterpillar (Jig. 134, q, r) 
 are large cylindrical caeca, and their ducts (p) pour into the 
 mouth an abundance of saliva proportioned to the coarse nature 
 of the materials used as food. 
 
 The sides of the body are traversed by the wide longitudinal 
 tracheae, a, 6, c, that communicate on the one hand with the 
 lateral spiracles, and on the other give off at regular intervals 
 the air-tubes (d, e, e, e, e), which ramify most minutely over all 
 the viscera, and convey the atmospheric air throughout the entire 
 system. 
 
 Besides the above organs, there are other viscera, which, al- 
 though of considerable importance to the caterpillar, would be 
 
296 
 
 INSECTA. 
 
 utterly useless to the imago, and consequently are more or less 
 completely wanting in the mature state. 
 
 The whole body of the larva is filled with a peculiar fatty 
 tissue (Jig. 134,/,/,/) called by entomologists the rete, epiploon, 
 or fat-mass. This material, found in great abundance in mature 
 and well-fed larvse, consists of an oily or greasy substance enveloped 
 in a most delicate cellulosity, and seems to correspond to the fat of 
 higher animals, like which it is indubitably a product of digestion, 
 and a repository of superabundant nourishment, stored up, no 
 doubt, for the sustenance of the animal during its helpless con- 
 dition in the dormant or pupa state serving like the fat of hiber- 
 nating quadrupeds, for food during the confinement of the imago. 
 
 (341 .) But the most re- Fig. 135. 
 
 markable peculiarity of the 
 larvse under consideration, 
 is the presence of an appa- 
 ratus employed for produc- 
 ing a tenacious thread of 
 extreme delicacy, appro- 
 priated by different species 
 to various purposes. In 
 many cases (fig. 105), it 
 is made subservient to lo- 
 comotion ; and by its assist- 
 ance, as by a rope, the 
 larva can suspend itself 
 from any object, or let it- 
 self down from one branch 
 to another in search of 
 food. The most import- 
 ant uses however to which 
 this thread is applied are connected with the concealment and pro- 
 tection of the quiescent and defenceless pupa ; either furnishing the 
 means of suspending the chrysalis in a place of safety* (fig. 135), 
 or, as is the case with the silk-worm (fig. 131), supplying the 
 material with which the caterpillar encases itself preparatory to 
 
 * For a most amusing account of the manner in which some chrysalides manage with- 
 out any external limbs to suspend themselves by the tail in a position of security, the rea- 
 der is referred to Kirby and Spence, vol. iii. page 207. The figure above given illustrates 
 the different steps attending the process. The larva, A, having spun some loose silk, and 
 fixed it upon the under side of a leaf or other suitable object, suspends itself therefrom 
 
 C 
 
INSECTA. 297 
 
 throwing off the last skin of the larva. The thread of the last- 
 named insect, the silk-worm, is of great tenacity ; and, notwith- 
 standing its fineness, may be wound off from the cocoon in a con- 
 tinuous thread, forming the important article of commerce, silk. 
 
 (342.) Nothing can be more simple than the apparatus provided 
 in caterpillars for the production of this valuable commodity : 
 Placed on each side of the intestine are two long and tortuous se- 
 creting cseca (Jig. 134, v, x 9 y)> that separate from the surrounding 
 juices of the body a tenacious viscid fluid which is liquid silk. The 
 viscid secretion thus formed is in the silk-worm of a golden yellow 
 colour, and is conveyed by the excretory ducts of the secerning 
 organs (t>, z) to the labium or under-lip, where the ducts terminate 
 at the base of a tubular instrument, the fusulus or spinnaret^ 
 through which the silk is drawn (Jig. 136, c). The fusulus of 
 the silk-worm, represented in the Fi s- 13 6. 
 
 annexed figure upon an enlarged 
 scale, is a simple nipple-shaped pro- 
 minence, perforated at its extre- 
 mity, and surrounded by four rudi- 
 mentary palpi. When about to 
 spin, the larva, by placing the ex- 
 tremity of its spinnaret in contact 
 with some neighbouring object, al- 
 lows a minute drop of the glutin- 
 ous secretion to exude from its ex- 
 tremity, which, of course, adheres 
 to the surface upon which it is 
 placed : the head of the silk-worm 
 being then slowly withdrawn, the 
 fluid silk is drawn out in a delicate 
 thread through the aperture of the spinnaret, its thickness being 
 regulated by the size of the orifice, and, immediately hardening 
 by the evaporation of its fluid parts, forms a filament of silk which 
 can be prolonged at the pleasure of the animal until the contents 
 of its silk reservoirs are completely exhausted. 
 
 (343.) Such is the structure of the larva of a Lepidopterous insect, 
 
 by its hind-legs. The skin of the caterpillar then gradually splits down the back (B, c), 
 and is slowly pushed upwards towards the tail of the chrysalis. The pupa now lays 
 hold of the old skin, nipping it between the rings of the abdomen, and hanging in this 
 posture inserts the apex of the tail, which is covered with hooks for the purpose, into 
 the silk previously deposited, and thus remains fixed in safety (D.) 
 
298 INSECTA. 
 
 and the arrangement of its internal viscera, when arrived at maturity, 
 has been already described. We have yet, however, to mention 
 the series of phenomena observable during the progress of its 
 growth, and the mode of its expansion from the minute size that 
 it exhibits on leaving the egg to the full dimensions which it ulti- 
 mately acquires. In order fully to understand the circumstances 
 connected with this part of our subject, it is necessary to premise 
 that the outer integument of most larvae is of a dense corneous tex- 
 ture, coriaceous in some parts, but quite hard and horny in others. 
 In the second place, it is but very slightly extensible ; and more- 
 over, as is always the case with epidermic structures, is not per- 
 meated by any vascular apparatus, and consequently is absolutely 
 incapable of growth when once formed. This epidermis encases 
 every portion of the larva; the body, the legs, the antennae, the 
 jaws, and all external organs are closely invested with a cuticular en- 
 velope, such as, from its want of extensibility, would form an insu- 
 perable obstacle to developement was there not some extraordinary 
 provision made to meet the necessity of the case. The plan adopt- 
 ed is to cast off at intervals the old cuticle by a process termed 
 moulting ; an operation which is repeated several times during the 
 life of the insect in its larva condition, and is accomplished in the 
 following manner : The caterpillar becomes for a few days slug- 
 gish and inactive, leaves off eating, and endeavours to conceal it- 
 self from observation. The skin, or more properly the cuticle, 
 becomes loosened from the subjacent tissues, and soon a rent ap- 
 pears upon the back of the animal, which gradually enlarges in a 
 longitudinal direction, and the imprisoned insect, after a long series 
 of efforts, at length succeeds in extricating itself from its old cover- 
 ing, and appears in a new skin of larger dimensions than the one it 
 replaces, which however in all other particulars it closely resembles. 
 With the old epidermis the larva throws off all external appendages 
 to the cuticle : the horny coverings of the jaws, the cornese of the 
 eyes, the cases of the claws are all removed ; and many writers have 
 even found attached to the exuviae an epidermic pellicle that had 
 formed a lining to the rectum, and delicate prolongations of the 
 cuticle derived from the interior of the larger ramifications of the 
 air-tubes. Absurd, indeed, have been the explanations given by 
 various writers of the nature of the process under consideration. 
 Swammerdam and Bonnet, nay, even our own illustrious entomo- 
 logists Kirby and Spence, believed that even at the birth of the ca- 
 terpillar all these skins existed ready formed one beneath the other, 
 
INSECT A. 299 
 
 and that the most external being removed at intervals displayed in 
 succession the skins placed underneath. Surely the advocates of 
 this extraordinary theory could scarcely have reflected upon the real 
 object of the moults in question namely, to provide a succession of 
 larger coverings proportioned to the continually increasing bulk of 
 the larva, when they advocated this strange doctrine, alike at vari- 
 ance with observation and sound physiological principles : the epi- 
 dermis and all cuticular structures are mere secretions from the sub- 
 jacent cutis or true skin ; and it can be no more necessary to suppose 
 the pre-existence of so many skins in order to explain the moults of 
 a larva, than to imagine that because, when in our own persons the 
 cuticle is removed by the application of a blister, a new layer of epi- 
 dermis is again and again produced, man should possess as many 
 skins one beneath the other. Nothing, in fact, can be more simple 
 and free from the miraculous than the whole process : at certain pe- 
 riods, when the old cuticle becomes too small for the rapidly enlarg- 
 ing dimensions of the insect, it becomes gradually loosened and se- 
 parated from the vascular and living skin or cutis by which it was 
 originally secreted, and, a new secretion of corneous matter taking 
 place, a fresh and more extensive layer of cuticle is slowly formed, 
 and then the old, dry, and dead epidermis being quite detached, is 
 split by the exertions of the larva, and the newly secreted layer placed 
 beneath it appears ; when the old skin is at length completely 
 thrown off, the newly formed one soon hardens by exposure, and the 
 re-clothed caterpillar assumes again its former activity and habits. 
 
 (344.) Neither is the change from the larva to the pupa or chry- 
 salis less easily explained, although regarded by our forefathers as 
 being so mysterious and astonishing a phenomenon. According 
 to the hypothesis above alluded to, after removing three or four 
 skins in the embryo larva, the anatomist ought to have arrived at 
 the totally different pupa-case ready formed, and only waiting for 
 the removal of the coats above it to exhibit its characteristic form. 
 Leaving however such visionary notions, let us examine the real 
 nature of this portion of the metamorphosis. The reader will 
 bear in mind, that, whatever the form of the exterior or epidermic 
 crust, it is merely a dead and extra-vascular secretion, unchange- 
 able when once deposited. But the living skin or cutis, beneath 
 it, is, during the whole process of the metamorphosis, undergoing 
 great and important changes, increasing in size only, during the 
 larva condition ; but, when perfectly organized, developing itself 
 at different points, and expanding into variously shaped organs 
 
300 INSECTA. 
 
 which did not previously exist. In the dragon-fly, for example 
 (Jig- 104), when the cutis had become expanded to its mature 
 larva condition, it secreted from its surface the external epidermic 
 crust which gives form to the larva, B ; this outward integument 
 remains, of course, unchanged when once formed, and retains the 
 same appearance during the whole period of the existence of the 
 insect in its larva state : but underneath this cuticle, and con- 
 sequently concealed from observation, the growth of the living 
 dermis still goes on, and important organs begin to appear, which 
 had no existence when the last larva-investment was secreted. 
 The wings have sprouted as it were from the shoulders, and 
 already have attained to a certain growth ; the old integument of 
 the larva becomes useless, and a new one is wanted; the process 
 already described is repeated, the old cuticle becomes detached 
 from the surface of the body, and the cutis begins to secrete for it- 
 self a new covering moulded upon its own shape : the newly form- 
 ed wings, therefore, and other newly developed processes of the 
 dermis, secrete horny coverings for themselves in the same manner 
 as other parts of the surface of the body ; and thus, when the in- 
 sect leaves its old skin, and once more escapes from confinement, 
 it presents to view the wing-cases which distinguish the pupa. 
 
 Whatever may be the form of the pupa, its covering is secreted 
 in a similar way ; it is the living and vascular skin which, though 
 concealed, continually grows more perfect in its parts, and the 
 cases secreted by it at distant intervals correspond in shape with 
 the different phases of its developement. 
 
 (345.) After having attained the pupa state, the last steps of the 
 process are completed, and the dermic system becomes fully de- 
 veloped in all its parts. The oral apparatus attains its perfect con- 
 dition ; the wonderfully elaborate structure of the eyes is com- 
 pleted ; the antennae assume their full developement ; the legs en- 
 closed in those of the pupa attain their mature form ; and the 
 wings, which have been continually growing, although concealed in 
 the wing-cases of the pupa, acquire their ultimate size : the per- 
 fect insect is ready for liberation, and, enclosed in its last covering, 
 creeps out of the water in which it has so long resided to enter 
 upon a new state of existence. Fixing itself upon some plant in 
 the neighbourhood of its birth-place, the imprisoned dragon-fly splits 
 its pupa-case along the back (jig. 137, A), and slowly extricates 
 its head and body ; draws its wings from their coverings, and 
 its legs from those of the pupa as from cast-off boots ; and at 
 
INSECTA. 
 
 301 
 
 length (fig. 137, B), getting its body from its now useless cover- 
 ing, it becomes entirely free. The wings, before soft and crumpled, 
 slowly expand (Jig. 137, c) ; the nervures harden, the extended 
 membranes dry, and Fig. 137. 
 
 in a short time the 
 winged tyrant of the 
 insect world (fig. 
 103) commences his 
 aerial career. 
 
 (346.) A strong 
 argument in favour 
 of the above views 
 concerning the pro- 
 duction of successive 
 skins from the der- 
 mis, is derived from 
 the phenomena at- 
 tending the cure of 
 wounds in insects. 
 If a perfect insect 
 be wounded, the 
 wound is never heal- 
 ed at all ; and, if a 
 larva or pupa is 
 similarly injured, the 
 wound remains un- 
 cicatrised until the 
 next moult, when 
 the newly formed in- 
 tegument is found 
 to exhibit no traces 
 of the injury : the 
 secreted and extra- 
 vascular cuticle can 
 not cicatrise ; but the 
 
 living and vascular dermis is not only able to repair injuries in- 
 flicted upon itself, but, in secreting the next investment, to obliter- 
 ate all indications of their occurrence. 
 
 (347.) The changes above described are produced by the pro- 
 gressive developement of the dermic or tegumentary system ; the 
 parts of which, as we have already seen, becoming strengthened and 
 
302 INSECTA. 
 
 consolidated by degrees, ultimately acquire that density of struc- 
 ture which the external skeleton of the insect exhibits in its 
 perfect or imago state. But, while this extraordinary metamor- 
 phosis is going on externally, other changes not less important 
 are in progress in the interior of the body. The size of the 
 alimentary canal, and the shape, proportionate dimensions, and 
 general arrangement of the different parts composing it, are se- 
 cretly and imperceptibly undergoing variations in accordance with 
 the altered necessities of the animal. We have already seen a 
 conspicuous example of this in Lepidopterous insects, 340 ; and, 
 in other orders, equally striking instances might easily be selected. 
 One of the most remarkable is met with in many Hymenoptera^ 
 as, for example, in bees (Apis), wasps (Vespa), and ant-lions 
 (Formica- leo), as well as in most of the Ichneumonidtz. In all 
 these genera, the larva being concealed in a close cell during its 
 developement, under circumstances which would render the evacu- 
 ation of excreinentitious matter an obvious inconvenience, both 
 the larva and pupa (Jig. 132) are entirely without either intes- 
 tinal canal or anal orifice : what little excrement is produced by 
 the digestion of the highly nutritive substances wherewith these 
 larvae are fed being collected in a blind cavity or caecum placed 
 behind the stomach, until the accomplishment of the last change ; 
 at which period the insect, liberated from its confinement, becomes 
 provided with a pervious intestine, and able to get rid of feculent 
 matter. 
 
 The fat-mass ( 340), which at the close of the larva state has 
 reached its maximum of developement, is gradually absorbed du- 
 ring the concealment of the insect in its pupa-case, its nutritive 
 portions being no doubt appropriated to the nourishment of the 
 pupa ; so that in the mature insect the fatty material has almost 
 entirely disappeared, nothing being left in its place but the dense 
 cellular web in which the fat had been deposited. 
 
 The silk-secreting apparatus of such genera as possess the means 
 of spinning a silken thread is peculiar to the larvae ; and, after 
 the commencement of the pupa state, no traces of its previous exist- 
 ence are to be detected. 
 
 (348.) But, while the above-mentioned organs disappear, others 
 become developed ; and the perfect insect is found to possess vis- 
 cera, for which a skilful anatomist might seek in vain in the earlier 
 stages of its existence. The generative system appears, at first, to 
 be absolutely wanting in the larva ; but Herold,* after much 
 
 * Entwickelungsgeschichte der Schmetterlinge, 1815, 4to. 
 
INSECTA. 303 
 
 patient investigation, succeeded in detecting the undeveloped ru- 
 diments of the future sexual organs both of the male and female. 
 It is during the maturation of the pupa that these important parts 
 expand ; and, before the disclosure of the imago, they are found to 
 have attained their complete proportions, so as to be ready to per- 
 form their functions as soon as the expansion of the wings endows 
 the insect with means of locomotion sufficiently perfect to ensure 
 the due dispersion of the species. 
 
 (349.) It is in the nervous system, however, that the most in- 
 teresting phenomena are observable ; and in the lessons afforded by 
 watching the correspondence between the state of the animal during 
 the several phases of its existence and the developement of the ner- 
 vous ganglia, the physiologist cannot fail to recognise those great 
 and general principles upon which our arrangement of the animal 
 creation is based. In the worm-like larva the ganglia are numerous 
 but of small dimensions ; too feeble to be capable of animating 
 powerful limbs, or of appreciating impressions from the organs of 
 the higher senses : the animal is, in fact, precisely in the condition 
 of an ANNELID AN, which it would seem to represent. External 
 limbs are therefore absolutely wanting in many larvae ; in others 
 they are represented by short and stunted appendages ; and even in 
 the most perfect, or hexapod larvae, they are feeble instruments in 
 comparison with those of the mature imago. The senses exhibit 
 equal imperfection ; and eyes are either entirely wanting, or are mere 
 ocelli, simple specks, exhibiting the lowest possible organization 
 of a visual apparatus. But, as the growth of the larva goes on, a 
 change in the arrangement of the nervous system is perpetually in 
 progress. The series of nervous cords connecting the different pairs 
 of ventral ganglia in the larva (Jig. 138, A) become flexuous as the 
 insect attains the pupa state ; the whole chain becomes shorter ; the 
 brain, or encephalic ganglion, increases in its proportionate dimen- 
 sions ; and, moreover, several ganglia, originally distinct, coalesce, 
 and form larger and more powerful masses (Jig. 138, B). This co- 
 alescence of the ganglia, which takes place more especially in the 
 thoracic region, is evidently a preparation for the concentration of 
 greater power and activity in this part of the body ; and although in 
 inactive chrysalides this change is not as yet visible by its effects, 
 in the active forms even the pupa is distinguished from the larva 
 by a considerable increase of vigour and energy in its movements. 
 In the imago the concentration of the nervous centres is carried to 
 that extent which is adapted to the necessities of the mature state ; 
 
304 
 
 INSECTA. 
 
 their number is still further reduced (Jig. 138, c); their size, in the 
 thorax especially, considerably increased ; and the brain, now ar- 
 rived at its maximum of developement, is furnished with the won- 
 derful apparatus of eyes and other instruments of the senses, 
 which heretofore would have been absolutely useless, but now, with 
 the expansion of the brain, have become suited to the more ex- 
 alted faculties of the insect. 
 
 Fig. 138. 
 B C A 
 
 Many insects are capable of producing audible sounds ; and some- 
 times the noises they make are exceedingly shrill, and may be heard 
 at some distance. Such sounds originate from various causes in 
 different tribes, and it is not always easy to detect the mode of 
 their production. In many beetles they are caused by rubbing 
 different parts of their dense integument against each other, and 
 the chirping of several Orthoptera seems to have a similar origin ; 
 the acute note that these insects utter is apparently produced by 
 friction, the edges of their hard pergamentaceous wings being 
 
INSECTA. 
 
 305 
 
 Fig. 139. 
 
 either scraped against each other, or against the long and serrated 
 edges of their thighs. The buzzing and humming noises heard 
 during the flight of many genera results from the forcible expul- 
 sion of the air as it streams through the respiratory spiracles, whose 
 orifices Burmeister imagines are furnished with vibratory lami- 
 nae, to the rapid movements of which the noise may be due. In 
 the genera Gri/llus and Cicada among the Orthoptera, however, 
 there is a peculiar apparatus specially provided for the production 
 of the loud chirping to which such insects give utterance. Upon 
 the first segment of the abdomen, covered by a broad moveable 
 plate (fig. 139 ), there is a large aperture, wherein a tense plicated 
 membrane is observable. This membrane is acted upon internally 
 by certain muscles able to throw it into rapid vibration, and thus 
 give rise to the sound in question. 
 
 (350.) One other point connected with this 
 interesting class of animals requires brief notice. 
 Many insects are endowed with the faculty 
 of emitting phosphorescent light, which is 
 in some species exceedingly brilliant. The 
 Elateridse among beetles are pre-eminently lu- 
 minous, and in them the light seems to be 
 principally given out by two oval spaces upon 
 the thorax, which in the dead insect are of 
 a greenish hue ; during life, some species 
 (Elater noctilucus) are so strongly phospho- 
 rescent as to enable a person to read a book 
 by passing the animal over the lines. The Lampyri emit a light 
 of great brilliancy ; and in Italy, during the summer nights, the 
 groves, illuminated by their incessant scintillations, exhibit a scene 
 equally strange and beautiful. Such insects appear to have a 
 power of obscuring or exhibiting their light at pleasure ; but the 
 nature of the luminous secretion, if such it be, upon which their 
 luminosity depends, has as yet escaped detection.* 
 
 * An interesting account of this subject is to be found in the article LUMINOUSNESS, 
 ANIMAL, by Dr. Coldstream, in the Cyclopaedia of Anatomy and Physiology. 
 
306 
 
 CHAPTER XVI. 
 ARACHNIDA.* 
 
 (351.) THE Arachnidans long confounded with INSECTS, and 
 described as such even by recent entomologists, are distinguished 
 by characters of so much importance from the animals described 
 in the last chapter, that the necessity of considering them as a 
 distinct class is now no longer a matter of speculation. In IN- 
 SECTS, the external skeleton presents three principal divisions, 
 the head, the thorax, and the abdomen : but in the spider tribes, 
 the blood-thirsty destroyers of the insect-world, the separation of 
 the head from the thorax, which, by increasing the flexibility, ne- 
 cessarily diminishes the strength of the skeleton, is no longer admis- 
 sible ; and the process of concentration being carried a step fur- 
 ther, the head and thorax coalesce, leaving only two divisions of the 
 body recognizable externally, viz. the cep halo-thorax and the ab- 
 domen. Insects in their mature forms were found to be invariably 
 furnished with only six legs, but in the adult Arachnidans eight of 
 these limbs are developed. These characters in themselves would 
 be sufficient to discriminate between the two orders ; but when to 
 these we add, that in the Arachnidans the eyes are invariably 
 smooth, the antennae of insects represented by organs of a totally 
 different description, that the sexual apertures are either situated 
 beneath the thorax, or at the base of the abdomen, and, moreover, 
 that in the greater number of Arachnidans, respiration is carried on 
 in localized lungs (pulmonibranchia), instead of by tracheae as in 
 insects, we need not enlarge further in the present place upon 
 the propriety of ranking the Arachnida as a separate class. These 
 animals may be grouped under three principal divisions ; the first 
 of which is evidently an intermediate type of organization, com- 
 bining many of the characters of the Insecta with the external 
 limbs and palpi of proper Arachnida. 
 
 (352.) The ARACHNIDA TRACHEAREA, in fact, breathe by 
 means of tracheae resembling those of insects, which are so ar- 
 ranged as to convey air to every part of the system ; and we may 
 therefore suppose that their circulatory apparatus, as well as their 
 
 a spider. 
 
ARACHNIDA. 
 
 307 
 
 secerning organs, conform more or less to the type of structure 
 met with in the class last described. The Mites (Acaridat) belong 
 to this division, and form a very numerous family, which is exten- 
 sively distributed. Some are parasitic in their habits, infesting 
 the bodies of insects ; and one, the itch-insect (Acarus Scabiei), 
 is found occasionally upon the human skin. Many live in cheese 
 and other provisions, where they multiply prodigiously ; and not 
 a few inhabit leaves, or are found under stones, or beneath the 
 bark of trees. Some (Hydrachna) are aquatic ; but unfortunately 
 in all, from their extremely minute size, the investigation of their 
 internal viscera presents so many difficulties, that but little is 
 satisfactorily known concerning their anatomy : even the pseudo- 
 Scorpionida, which are of larger growth, and, although still 
 breathing by tracheae, approximate most closely to the outward 
 form of the next group, hive been very imperfectly examined. 
 The rest of the Arachnidans breathe by means of lungs, or, as 
 they are more properly designated, pulmonary branchiae; and 
 consequently, in contradistinction to the last-mentioned, are called 
 by zoologists ARACHNIDA PULMONARIA : such are the Scor- 
 pions and Spiders. 
 
 (Fig. 140.) 
 
 The PEDIPALPI, forming the second division, are at once re- 
 cognised by the peculiarity of their external configuration. Their 
 palpi, the representatives apparently of the maxillary palpi of 
 insects, are exceedingly strong, and furnished at their extremity 
 with a prehensile forceps ; the hinder part of the body, correspond- 
 ing with the abdomen of insects, is much prolonged, and composed 
 
308 ARACHNIDA. 
 
 of numerous articulated segments, terminated in the scorpion tribe 
 by a sharp unciform sting (fig> 140), armed with a venomous se- 
 cretion. 
 
 The third section embraces the AIIANEID^E, or Spiders, distin- 
 guished by having the abdomen short and globular, and furnished, 
 moreover, near its posterior termination with spinnerets, by means 
 of which these animals manufacture silken filaments applicable to a 
 great number of purposes, and especially employed in constructing 
 what is usually named the spider's web. The maxillary palpi in 
 the females are simple, and more or less resemble feet ; but in the 
 males they often form a remarkable apparatus, to be described in 
 another place : the jaws are also armed with sharp and hooked fangs, 
 and perforated near their points for the emission of a poisonous 
 secretion provided for the destruction of their prey. 
 
 (353.) Beginning with the first cfivision, we shall now proceed 
 to place before the reader such facts as have been ascertained, con- 
 nected with the anatomical structure of the class under considera- 
 tion. In the Acaridse, or Mites, the skin of the entire body is so 
 soft that any annulose structure is scarcely distinguishable; the 
 division, however, into cep halo-thorax and abdomen is sufficiently 
 evident. The eyes are minute black points, never exceeding four 
 in number and resembling the ocelli of insects. Eight feeble legs 
 are articulated with the thorax, properly so called. The mouth 
 seems adapted to suction, and the jaws form a piercing instrument 
 barbed at the extremity. The structure of the respiratory stig- 
 mata or spiracles would seem to differ very considerably from those 
 of insects. According to Dr. Auduoin, in the species which he 
 examined (Ixodes Erinacei),* each spiracle resembles a spherical 
 tubercle perforated by an infinite number of small holes, in the 
 centre of which may be remarked a larger circular plate ; and it 
 is through these numerous foramina that the air enters the body, 
 and gets into the tracheae. 
 
 (354.) The Pulmonary Arachnidans, both of the pedipalp and 
 spinning divisions, are strictly carnivorous in their habits, living 
 upon the juices of the insects they destroy; and we may consequent- 
 ly expect, in the construction of their alimentary apparatus, a sim- 
 plicity proportioned to the facility with which highly nutritive food 
 composed of already anhnalized materials is capable of being assi- 
 milated. The mouth varies somewhat in its conformation, and, if 
 we compare the pieces composing it with those that we have found 
 
 * Cyclop, of Anat. and Phys. art. ARACHNIDA. 
 
ARACHNIDA. 309 
 
 manclibulate insects to possess, we shall have good reason for surprise 
 in noticing the strange uses to which some parts of the oral appara- 
 tus are converted. In scorpions (fig. 140), the apparent repre- 
 sentatives of the mandibles of an insect are transformed into a pair 
 of small forceps, each being provided with a moveable claw ; these 
 therefore form of themselves prehensile organs adapted to seize prey, 
 and hold it in contact with the mouth. But it is in the maxilla 
 that we find the most extraordinary metamorphosis ; for the maxil- 
 lary palpi, so small in insects, are found to be developed to such 
 prodigious dimensions, that they far surpass in size and strength 
 any of the ambulatory extremities, and, from their resemblance to 
 the claws of Crustaceans, have given the character from which the 
 name of the division is derived.* Each of these formidable organs 
 is terminated by a strong pair of pincers, and thus the maxillary 
 palpi become converted into potent instruments either for attack 
 or defence. The representative of the labium of an insect in the 
 Arachnidans has no palpi connected with it. 
 
 (355.) In spiders the organization of the mouth is altogether dif- 
 ferent. The mandibles (fig. 142, o, o) are each terminated with a 
 moveable fang (c), which ends in a sharp point, and is perforated near 
 its extremity by a minute orifice, from which, when the spider bites, 
 a venomous fluid of great potency is instilled into the wound in- 
 flicted ; such, indeed, is the malignity of this poisonous secretion 
 that its effects in destroying the life of a wounded insect are al- 
 most instantaneous, and in some of the large American species even 
 small birds fall victims to its virulence. The organ in which the 
 poison is elaborated is represented in the figure above referred to : 
 it is a long and slender bag, from which an attenuated duct may 
 be traced through the body of the mandible as far as the perforated 
 extremity of the fang. 
 
 The palpi connected with the maxillse of the spider are termi- 
 nated in the female by a simple hook ; but in the males of many 
 species they exhibit a conformation slightly resembling the forceps 
 of the scorpion, although provided for a very different purpose. 
 When closed (fig. 141, B), the terminal part of the palpus pre- 
 sents a club-like dilatation, which, however, on close inspection 
 will be found to consist of several pieces (fig. 141, A, a,,c, </, e), 
 connected with each other by articulations, and capable of being 
 opened out in the manner represented in the figure. This strange 
 instrument was formerly imagined to be the penis of the male spi- 
 * Pes, a foot ; palpus, a feeler. 
 
310 
 
 ARACHNIDA. 
 
 der, and was thought to contain the terminations of the seminal 
 ducts : the supposition, however, has Fi &' 
 
 been proved to be erroneous, for the 
 palpus is imperforate, and the sexual 
 apertures of the male are situated else- 
 where, but the organ in question is 
 nevertheless apparently used in the 
 process of impregnation, in a manner 
 to be explained hereafter. 
 
 (356.) Both in scorpions and spiders the alimentary canal is ex- 
 ceedingly narrow, presenting scarcely any of those dilatations met 
 with in the digestive organs of insects. This is a natural consequence 
 of the nature of their food ; for, as they live entirely upon animal 
 juices sucked from the bodies of their victims, there could be little 
 necessity for the presence of capacious receptacles for nutritious 
 matter, or for any reservoirs for the accumulation of effete ma- 
 terial. 
 
 In the Scorpionidce there is no stomachal dilatation what- 
 ever : a straight intestine passes directly from the mouth to the 
 anus, situated at the extremity of the abdomen ; and the insertion 
 of the biliary vessels forms the 
 only distinction between its ven- 
 tricular and intestinal divisions. 
 Five delicate caeca are derived 
 from each side of the ventricu- 
 lar portion, and plunge into the 
 centre of a fatty substance in 
 which the alimentary canal is em- 
 bedded. In Spiders, likewise, 
 caeca are appended to the com- 
 mencement of the digestive ap- 
 paratus, and a slight enlargement 
 (Jig. 142, b) may be said to repre- 
 sent the stomach, from which a 
 slender intestine (g) is continued 
 to the anus. As in the scorpion, 
 a large quantity of fat (A) sur- 
 rounds the nutrient organs, and 
 fills up a great proportion of the 
 cavity of the abdomen. Like 
 the fat-mass of the larvae of insects, this substance must, no 
 
 Fig. 142. 
 
ARACHNIDA. 
 
 311 
 
 doubt, be regarded as a reservoir of nutriment ; and when the ha- 
 bits of these animals are considered, the precarious supply of food, 
 and the frequent necessity for long-protracted fasts, when a scar- 
 city of insects deprives them of their accustomed prey, such a 
 provision is evidently essential to their preservation. 
 
 (357.) One peculiarity connected with the arrangement of the 
 chylo-poietic viscera of the spider is the manner in which the biliary 
 organs terminate in the intestine ; for instead of entering in the 
 usual position, namely, close to the termination of the stomach, 
 they seem to pour their secretion into the rectum immediately in 
 the vicinity of the anus. At this point, a kind of sacculus (figs. 
 142 and 143, f) joins the intestine, into Fig. 143. 
 
 which the branched tubes (fig. 143^ o, o ; 
 fig. 142, s) empty themselves. This cir- 
 cumstance has long been a subject of in- 
 teresting inquiry to the comparative phy- 
 siologist. If the fluid secreted by these 
 tubes be really bile, in what manner 
 does it accomplish those purposes usually 
 supposed to be effected by the biliary 
 secretion ? It would seem to be, in this 
 case, merely an excrementitious produc- 
 tion. Are the caeca appended to the 
 stomach biliary organs ? If so, the apparatus in question may be 
 of totally distinct character, and its product only furnished to be 
 expelled from the system. In conformity with the last supposi- 
 tion, many antaomists have been induced to regard these vessels 
 as -being analogous to the urinary secernents of more highly 
 organized animals, and have not scrupled to apply to them the 
 appellation of renal vessels : but this hasty application of names 
 we have already animadverted upon as being highly prejudicial 
 to the interests of science ; and in this instance, as in many others, 
 to wait for the results of future investigations is far more advisable 
 than rashly to assign a definite function to a part, the real nature 
 of which is a matter of speculation. 
 
 (358.) The respiratory system of the Pulmonary Arachnidans is 
 constructed upon very peculiar principles, being neither composed of 
 gills adapted to breathe water, nor lungs like those of other air-breath- 
 ing animals, but presenting a combination of the characters of both. 
 The pulmo-branchite are, in fact, hollow viscera resembling bags ; 
 the walls of which are so folded and arranged in laminae, that a 
 
312 ARACHNJDA. 
 
 considerable surface is presented to the influence of oxygen. It 
 is, indeed, highly probable that these organs are intermediate in 
 function as well as in structure between an aquatic and air-breath- 
 ing respiratory apparatus ; for, as both the pedipalp and spinning 
 Arachnidans frequent moist situations, the dampness of the atmo- 
 sphere may be favourable to the due action of the air upon the 
 circulating fluids of these creatures. Each pulmo-branchia opens 
 externally by a distinct orifice, resembling the spiracle of an in- 
 sect, and is closed in a similar manner by moveable horny lips. 
 In the scorpion (fig. 140) the spiracles are eight in number, 
 placed upon the ventral aspect of the body; and just in front of 
 the first pair of breathing-holes are two remarkable organs repre- 
 sented in the figure, resembling a pair of combs, which are appa- 
 rently adapted to keep the spiracular orifices free from dirt, and 
 thus prevent any obstructions to the free ingress and egress of the 
 air. 
 
 In the Araneidse^ the form and arrangement of the spiracles is 
 somewhat different : according to Treviranus, there are four pairs 
 on each side of the cephalo-thorax, situated immediately above the 
 insertions of the legs ; and in addition to these there is one pair 
 constantly found on the under surface of the abdomen, and four 
 pairs of smaller apertures of less importance on its upper part. 
 
 In order to understand the manner in which respiration takes 
 place in pulmo-branchice of the structure above described, it is 
 necessary to suppose the existence of a vascular apparatus, by 
 means of which the circulating fluid is continually spread over the 
 laminae of the respiratory sacculi, and afterwards returned to the 
 circulation in a purified condition. It is true, that, owing to the 
 extreme difficulty of tracing vessels of such small dimensions, the ' 
 continuity of the entire system is rather an inference deducible 
 from agen eral review of the facts ascertained, than absolutely a 
 matter of demonstration. We will, therefore, briefly lay before 
 the reader the data upon which physiologists found the opinions 
 entertained at the present day relative to the means whereby the 
 circulation of Arachnidans is accomplished. 
 
 (359.) According to Treviranus, spiders are provided with a long 
 contractile vessel, which runs along the mesial line of the back, and 
 resembles in form the dorsal vessel of insects, although in struc- 
 ture it is widely different. In insects, it will be remembered, the 
 dorsal vessel communicated freely with the abdominal cavity by 
 numerous valvular apertures, and neither arteries nor veins were 
 
ARACHNIDA. 
 
 necessary for diffusing the blood through the system ; but in the 
 Pulmonary Arachnidans numerous vascular trunks are given off 
 from both sides of the dorsal heart, and are dispersed in all direc- 
 tions. All the branches proceeding from the sides of the dorsal 
 vessel are presumed to be of an arterial character, with the excep- 
 tion of a few large canals situated near the junction of the anterior 
 and middle thirds of its length, and these are supposed to be 
 veins* (branchio- cardiac vessels) destined to return the aerated 
 blood from the pulmo-branchite into the general circulation. 
 Whoever watches the movements of the blood in one of the limbs 
 of these creatures, will perceive that under the microscope its 
 motion bears little resemblance to that observable in the foot of a 
 frog, or in animals possessed of an arterial and venous system 
 completely developed. So irregular, indeed, is the course of the 
 globules, that it would be difficult to conceive them to be confined 
 in vessels at all ; the whole appearance resembles rather the dif- 
 fused circulation seen in the larva of an insect, than that of a crea- 
 ture possessing vascular canals arranged in definite directions. 
 The only probable way of accounting for such a phenomenon is 
 by supposing that, in this first sketch of a vascular system, if we 
 may be pardoned the expression, the veins are mere sinuses or 
 wide cavities formed in the interstices of the muscles, through - 
 which the blood slowly finds a passage. From a review of the 
 above-mentioned facts we are at liberty to deduce the following 
 conclusions relative to the circulation of Arachnidans : The 
 pulmo-branchite being apparently the only organs of respiration, 
 the blood must be perpetually brought to these structures from 
 all parts of the system, to receive the influences of oxygen, and 
 again distributed through the body : such a circulation could 
 only be accomplished in circumscribed channels ; some destined to 
 propel it through all parts ; others to collect it after its distribu- 
 tion, and bring it to the respiratory organs ; and a third set to 
 return it in a renovated condition to the heart. The circuit of the 
 blood may therefore be presumed to be completed in one or other 
 of the following modes. The dorsal vessel, or heart, by its con- 
 traction drives the blood through numerous arterial canals to the 
 periphery of the system : the blood so distributed gradually finds 
 its way into capacious sinuses, through which it flows to the 
 branchial organs, and from hence it re-enters the heart by the 
 branchio-cardiac vessels above referred to : or else the action of 
 
 * Dr. Audouin, Cyclop, of Anat. and Phys. art. AIIACHNIDA. 
 
314 
 
 ARACHNIDA. 
 
 the heart drives a portion of the circulating fluid into the pulmo- 
 branchifE by the same effort which supplies the rest of the system, 
 and the blood so impelled to the respiratory organs becomes, after 
 being purified, again mixed up with the contents of the veins 
 which return it to the heart. 
 
 (360.) In the nervous system of spiders we observe that pro- 
 gressive concentration of the nervous centres, which we have traced 
 through the lower forms of the HOMOGANGLIATA, carried to 
 the utmost extent. Spiders are appointed destroyers of insects, 
 with which they maintain cruel and unremitting warfare. That 
 the destroyer should be more powerful than the victim, is essen- 
 tial to its position ; that it should excel its prey in cunning and 
 sagacity, is likewise a necessary consequence ; and by following 
 out the same principles, which have already been so often insisted 
 upon, concerning the inseparable connexion that exists between the 
 perfection of an animal and the centralization of its nervous gan- 
 glia, we find in the class before us an additional confirmation of 
 this law. In scorpions, indeed, the nervous masses composing 
 the ventral chain of ganglia are still widely separated, especially 
 those situated in the segments of the pig. 144. 
 
 tail : in the cephalo- thorax they 
 are of proportionately larger dimen- 
 sions ; and, moreover, exhibit this 
 remarkable peculiarity, that, instead 
 of being united by two cords of 
 communication, there are three inter- 
 ganglionic nerves connecting each di- 
 vision. It is in spiders that the con- 
 centration of the nervous system 
 reaches its climax ; for in them we 
 find the whole series of ganglia, en- 
 cephalic, thoracic, and abdominal, ag- 
 gregated together, and fused, as 
 it were, into one great central brain, 
 from whence nerves radiate to all 
 parts of the body. The extent to 
 which centralization is here carried 
 will be at once appreciated by refer- 
 ence to the annexed figure (Jig- 144) : the encephalic masses 
 ja, a, whence the optic nerves distributed to the ocelli are de- 
 rived, are in close contact with the anterior part of a large 
 
ARACHNIDA. 315 
 
 ganglion, c, that represents all the abdominal ganglia collected 
 into one mass ; and from the posterior part of this, nerves, w, w, 
 destined to supply the parts contained in the abdomen, derive 
 their origin. The thoracic ganglia, e, e, are fusiform, and placed 
 on each side of the mass c, with which they are apparently 
 amalgamated at one extremity, while from the opposite they give 
 off the nerves appropriated to the legs. 
 
 The ocelli or eyes of Arachnidans have been minutely investi- 
 gated by M tiller,* and seem to present a type of structure very far 
 superior to that of insects. In the Scorpion this distinguished anato- 
 mist succeeded in detecting most of the parts which enter into the 
 construction of the eye of a vertebrate animal ; and, moreover, 
 a great similarity in their arrangement. The cornea, a globular 
 lens, the aqueous and vitreous humours, the retina and choroid 
 were all found nearly in their usual relative positions ; so that the 
 sense of vision in these animals must be extremely perfect. 
 
 (361 .) The sexual organs of the male and female Fig. 145. 
 
 Arachnidans exhibit very great simplicity in their 
 structure. The testes, or secreting vessels of the 
 male spider, are two long cseca (Jig. 145, 6), lodg- 
 ed in the abdomen, and terminating by simple 
 orifices at the ventral surface. No external in- 
 tromittent organ is perceptible ; and it was on 
 this account that the peculiar apparatus above re- 
 ferred to, situated at the extremity of the maxil- 
 lary palpus, was so long considered as giving pas- 
 sage to the impregnating secretion. The singular 
 instrument already described ( 355), would seem, 
 indeed, to be in some manner really subservient 
 to the fecundating process ; being used most probably as an exciting 
 agent preparatory to the intercourse between the sexes. 
 
 (362.) The ovigerous system of the female is equally devoid of 
 complication, and, like the male testes, consists of two elongated 
 membranous sacculi, in which the eggs are formed and brought 
 to maturity. The impregnation of the ova is evidently effected by 
 the simple juxta-position of the external orifices of the two sexes : 
 yet such is the ferocity of the female spider, that the accomplish- 
 ment of this is by no means without risk to her paramour; for the 
 former being far superior to the male, both in size and strength 
 (Jig. 146, A, B), would infallibly devour him, either before or after 
 * Annales des Sciences Nat. tom.xvii. 
 
316 
 
 ARACHNIDA. 
 
 the consummation of his purpose, did he not exercise the most 
 guarded caution and circumspection in making his advances. 
 
 Fig. 146. 
 
 (363.) One peculiar characteristic of the Araneida is the posses- 
 sion of a spinning apparatus, whereby the threads composing their 
 web are manufactured. The instruments employed for this purpose 
 
 F iff. 147. 
 
 are situated near the posterior extremity of the abdomen, and 
 consist externally of four spinnerets, and twopalpiform organs (fig. 
 147 A, B). Each spinner 'et, when highly magnified, is found to 
 be perforated at its extremity by innumerable orifices of extreme 
 minuteness (^/zg.147, c), through which the filaments are drawn ; so 
 that, unlike the silk of the caterpillar, the thread of the spider, 
 delicate as it is, is composed of hundreds of smaller cords, some- 
 
ARACHNIDA. 
 
 317 
 
 times woven together by zig-zag lines, and thus exhibiting a 
 structure of exquisite and most elaborate composition. The fluid 
 silk, which, when it is drawn through the microscopic apertures 
 of the spinneret, affords the material whereof the web is con- 
 structed, is secreted in a set of glands represented in the sub- 
 joined engraving (Jig. 148). The secerning extremities of the 
 glandular tubes are composed of branched cseca (&), whence arise 
 long and tortuous Fi 148 
 
 ducts (a, a, a), 
 that become dilat- 
 ed in their course 
 into reservoirs for 
 the secreted fluid, 
 and terminate by 
 several canals at 
 the base of the 
 external spinning 
 tubuli. Various 
 are the purposes 
 to which the dif- 
 ferent species of 
 
 the Araneidse convert the delicate threads thus produced. Some 
 construct for themselves silken tubes or cells, in which to conceal 
 themselves from pursuit, and from this retreat they issue to hunt 
 for prey in the vicinity of their abode ; others strew their fila- 
 ments about at random, apparently to entangle passing insects ; 
 many make nets composed of regular meshes, and spread them out 
 in favourable situations to entrap their victims (Jig. 146) ; while 
 a few species, enveloping their eggs in bags of curious construction, 
 carry them about attached to their bodies, and defend them with 
 the utmost courage and pertinacity : even in water these webs are 
 turned to* many singular uses ; and ropes, nets, and even diving- 
 bells are at the disposal of aquatic species furnished with this 
 extraordinary spinning machinery. 
 
 A few only of the most remarkable applications of this de- 
 licate material can be noticed in this place. The mason-spiders 
 (Mi/gale) excavate for themselves subterranean caverns, in which 
 these marauders lurk secure from detection, even by the most 
 watchful foe : nor could any robber's den, which ever existed in 
 the wild regions of romance, boast more sure concealment from 
 pursuit, or immunity from observation. The construction of these 
 
318 ARACHNIDA. 
 
 singular abodes has long excited the admiration of the naturalist : 
 a deep pit is first dug by the spider, often to the depth of one 
 or two feet, which, being carefully lined throughout with silken 
 tapestry, affords a warm and ample lodging ; the entrance to 
 this excavation is carefully guarded by a lid or door, which moves 
 upon a hinge, and accurately closes the mouth of the pit. In 
 order to form the door in question, the Mygale first spins a web 
 which exactly covers the mouth of the hole, but which is attached 
 to the margin of the aperture by one point only of its circum- 
 ference, this point of course forming the hinge. The spider then 
 proceeds to lay upon the web a thin layer of the soil collected in 
 the neighbourhood of her dwelling, which she fastens with another 
 layer of silk ; layer after layer is thus laid on, until at length the 
 door acquires sufficient strength and thickness : when perfected, 
 the concealment afforded is complete ; for, as the outer layer of 
 the lid is formed of earth precisely similar to that which surrounds 
 the hole, the strictest search will scarcely reveal to the most 
 practised eye the retreat so singularly defended. 
 
 Another spider (Clotho Durandii) constructs a dwelling equally 
 artificial and ingenious, a kind of tent in which it lives and rears 
 its young. This tent is composed of several superposed sheets of 
 the finest taffeta, and its contour presents seven or eight prominent 
 angles, which are fixed to the surface of the ground by silken cords. 
 The young Clotho at first lays down only two sheets thus secured, 
 between which she hides herself ; but, as she grows older, she con- 
 tinually lays down additional coverings, until the period when she 
 begins to lay her eggs, at which time she constructs an apartment, 
 soft, downy, and warm, specially devoted to their reception. The 
 exterior sheet of the tent is purposely dirtied for the purpose of con- 
 cealment ; but within, everything is beautifully clean and white. 
 The most admirable part of the contrivance, however, is the per- 
 fect safety afforded to the young when the parent leaves her tent in 
 search of food ; some of the superposed sheets are fastened toge- 
 ther at their edges, others are simply laid upon each other, and, 
 as- the parent herself alone possesses the secret which enables her 
 to raise those layers by which entrance is to be obtained, no 
 other animal can find its way into her impenetrable abode. 
 
319 
 
 CHAPTER XVII. 
 
 CRUSTACEA. 
 
 INSECTS and Arachnidans are air-breathing animals ; and, even 
 in such species of these two extensive classes as inhabit fresh 
 water, respiration is strictly aerial. No insects or spiders are 
 marine ; and consequently the waters of the ocean would be utterly 
 un tenanted by corresponding forms of Articulata, was there not 
 a class of beings belonging to this great division of the animal 
 world so organized as to be capable of respiring a watery medium, 
 and thus adapted to a residence in the recesses of the deep. 
 Examined on a large scale, the Crustaceans, upon the considera- 
 tion of which we are now entering, are marine creatures : many 
 species, it is true, are found abundantly in the lakes and ponds 
 around us, but these form rather exceptions to the general rule ; 
 and we may fairly regard this extensive group of beings as the 
 aquatic representatives of the insects and spiders, with which they 
 form a collateral series. 
 
 (364.) The tegumentary system of the CRUSTACEA corresponds 
 in its essential structure with that of insects, and consists of a 
 vascular dermis, a coloured pigment, and a cuticular secreted 
 layer which forms the external shell or skeleton : the latter, 
 or epidermic covering, however, differs materially in texture from 
 that of other Articulata, inasmuch as it contains calcareous matter 
 in considerable abundance, and thus acquires in the larger species 
 great density and hardness. Figt 149 
 
 As regards the mechanical arrangement 
 of the skeleton, we shall find the same 
 general laws in operation as we have ob- 
 served throughout all the annulose orders, 
 a continual centralization and progressive 
 coalescence of the different rings or ele- 
 ments composing the external integument, 
 and a strict correspondence between the 
 degree to which this consolidation is car- 
 ried and the state of the nervous system 
 within. 
 
 In the lowest forms of the Crustacea 
 
CRUSTACEA. 
 
 we have in fact a repetition of the condition of the skeleton 
 met with in the Myriapoda, or in the larva state of many in- 
 sects ; the whole body being composed of a series of similar 
 segments, to which are appended external articulated members of 
 the simplest construction (Jig. 149). 
 
 The number of rings or segments composing the body varies 
 in different species ; but such variation would seem, from the inter- 
 esting researches of Milne Edwards and Audouin, concerning the 
 real organization of articulated tegumentary skeletons, to be rather 
 apparent than real, inasmuch as the discoveries of these distinguished 
 naturalists go far to prove that, whatever the state of consolidation 
 in which the integument is found, the same number of elements 
 or rings may be proved to have originally existed before, by their 
 union, they became no longer distinguishable as separate seg- 
 ments. 
 
 The normal number of these elements Milne Edwards considers 
 to be twenty-one, seven of which enter into the composition of the 
 head, seven belong to the thorax, and as many appertain to the ab- 
 dominal region of the body. 
 
 To illustrate this important doctrine let us select a few examples, 
 in order to show the manner in which the progressive coalescence 
 of the segments is effected. 
 
 In Talitra (Jig. 150) the cephalic elements are completely 
 united, their existence being Fi S- 15 * 
 
 only indicated by the several 
 pairs of appendages ; one pair, 
 of course, belonging to each 
 ring. The first ring of the 
 cephalic region, in this in- 
 stance, has no external articu- 
 lated member ; but in higher 
 
 orders the eyes are supported upon long peduncles connected with 
 this element of the skeleton, that may be regarded as the represen- 
 tatives of those limbs which take different names in different regions 
 of the body. The second and third rings support jointed organs 
 here called antennae ; while the several pairs of jaws appertaining to 
 the mouth indicate the existence of so many elements united toge- 
 ther in the composition of the head. 
 
 The seven segments of the thorax are still distinct, and each 
 supports a pair of jointed organs, which, being used in locomotion, 
 are called legs ; the abdominal elements, likewise, are equally free, 
 
CRUSTACEA. 
 
 321 
 
 and have natatory extremities developed from the five posterior 
 rings. 
 
 In the lobster (Astacus Marinus) we find not only the cephalic 
 segments anchylosed together, but those of the thorax also ; and al- 
 though the lines of demarcation between them are still recognisable 
 upon the ventral aspect of the body, superiorly the entire thorax 
 and head are consolidated into one great shield (cephalo-thorax) , 
 the abdominal segments only remaining distinct and moveable. 
 
 In the Crabs the centralization of the external skeleton is carried 
 to still greater lengths, so as to enable this tribe of Crustaceans to 
 become more or less capable of leaving their native element, and 
 walking upon the shores of the sea, or even in some instances of 
 leading a terrestrial existence, as in the case of the land- crab of the 
 West India islands. The abdominal segments, however, still re- 
 main free, though proportionately of very small dimensions ; and, 
 being no longer useful in swimming, the abdomen is folded beneath 
 the enormously developed thoracic portion of the body. 
 
 In the King-Crab (Limulus Polyphemus; Jig. 151) even the 
 divisions of the abdomen are obli- Fig. 151. 
 
 terated, the whole body being co- 
 vered by two enormous shields, and 
 the tail prolonged into a formidable 
 serrated spine, of such density and 
 sharpness that in the hands of sa- 
 vages it becomes a dreadful weapon, 
 and is used to point their spears 
 either for the chase or war. 
 
 The reader will at once perceive 
 the strict parallelism that may be 
 traced between the changes which 
 occur during* the metamorphosis of 
 insects, and those observable as we 
 thus advance from the lowest to 
 the most highly organized Crusta- 
 cean genera; and even the steps 
 whereby we pass from the Anneli- 
 dan to the Myriapod, and from 
 thence to the Insect, the Scorpion, and the Spider, seem to be re- 
 peated as we thus review the progressive developement of the class 
 before us. 
 
 Having thus found that the annuli, or rings, which compose the 
 
 Y 
 
322 CRUSTACEA. 
 
 annulose skeleton may be detected even in the most compactly 
 formed CRUSTACEA, it remains for us to inquire, in the next 
 place, what are the principal modifications observable in the arti- 
 culated appendages developed from the individual segments. This 
 inquiry is one of considerable interest, inasmuch as it goes to prove 
 that, however dissimilar in outward form, or even in function, the 
 limbs of Crustaceans are mere developements of the same elements, 
 which, as they remain in a rudimentary condition or assume larger 
 dimensions, become converted into instruments of sensation, legs, 
 jaws, or fins, as the circumstances of the case may render needful. 
 In the lower, or more completely annulose forms (figs. 14$ and 
 152), these members are pretty equally developed from all the seg- 
 ments of the body, and are subservient to locomotion, being gene- 
 rally terminated by prehensile hooks, or provided with fin-like ex- 
 pansions ; but, as we advance to the more perfect genera, the limbs 
 assume such various appearances, and become convertible to so many 
 distinct uses, that they are no longer to be recognised as consisting 
 of similar elements, modified only in their forms and relative pro- 
 portions. To notice Fig. 152. 
 all the varieties which 
 occur in the extensive 
 class before us, would 
 be to weary the reader 
 with tedious and unne- 
 cessary details ; we shall 
 therefore select the De- 
 capod* division of these 
 animals, as abundantly sufficient for the illustration of this part of 
 our subject. This division, which includes the most highly organ- 
 ized forms, has been divided by writers into three extensive fami- 
 lies, the Macroura, or swimming Decapods ; the Anomoura, which 
 inhabit the empty shells of Mollusca ; and the Brachyura, or short- 
 tailed species, of which the crab is a familiar specimen. If we take 
 the common lobster as an example of the first of these groups, we 
 shall find that there are five pairs of articulated limbs placed upon 
 each side of the mouth, which are evidently adapted to assist in 
 seizing and conveying into the stomach substances used as food. 
 These singular organs, which, although entitled to be considered as 
 jaws so far as their use would indicate the name belonging to them, 
 
 * So called from the circumstance of their having five pairs of limbs so largely de- 
 veloped as to become ambulatory or prehensile organs. 
 
CRUSTACEA. 323 
 
 arc no less obviously merely modifications of articulated feet ; and 
 the term foot-jaws has now, by common consent, become the appel- 
 lation by which they are distinguished. 
 
 The pair of legs which succeeds to the remarkable members last 
 referred to, is appropriated to widely different offices. The organs 
 in question are developed to a size far surpassing that attained by 
 any of the other limbs and are endowed with proportionate strength. 
 Each of these robust extremities is terminated by a pair of strong 
 pincers (chelee) ; but the two are found to differ in their structure, 
 and are appropriated to distinct uses. That of one side of the 
 body has the opposed edges of its terminal forceps provided with 
 large blunt tubercles, while the opposite claw is armed with small 
 sharp teeth. One, in fact, is used as an anchor, by which the lob- 
 ster holds fast by some submarine fixed object, and thus prevents 
 itself from being tossed about in an agitated sea ; the other is ap- 
 parently a cutting instrument for tearing or dividing prey. 
 
 To the chela succeed four pairs of slender legs, scarcely at 
 all serviceable for the purposes of locomotion ; but, the two ante- 
 rior being terminated by feeble forceps, they become auxiliary 
 instruments of prehension. 
 
 The articulated appendages belonging to all the abdominal 
 segments are so rudimentary that they are no longer recognisable 
 as assistants in progression ; and it is at once evident, when 
 we examine the manner in which the Macroura use their tails 
 in swimming, that the developement of large organs in this 
 position would materially impede the progress of animals pre- 
 senting such a construction : the false feet, as these organs are 
 called, are therefore merely available as a means of fixing the 
 ova which the female lobster carries about with her attached be- 
 neath her abdomen. 
 
 The tail is the great agent of locomotion in all the Macroura 
 or large-tailed Decapods, and for this purpose it is terminated 
 by a fin formed of broad calcareous lamellae, so arranged, that 
 while they will close together during the extension of the tail, 
 and thus present the least possible surface to the water, they 
 are brought out to their full expansion by the down-stroke of the 
 abdomen ; and such is the impulse thus given, that, as we are 
 credibly informed, a lobster will dart itself backwards to a dis- 
 tance of eighteen or twenty feet by one sweep of this remarkable 
 locomotive instrument. 
 
 If we now pass on to the consideration of the Anomourous De- 
 
CRUSTACEA. 
 
 capods, we find that the external organs above enumerated, 
 although existing in precisely similar situations, are so far modified 
 in their construction and relative proportions as to become suited 
 to a mode of life widely different from that led by the members 
 of the last division. The Anomoura^ as their name imports, 
 have tails of very unusual conformation : instead of being en- 
 cased in a hard coat of mail as in the Macroura, the hinder part 
 of the body is soft and coriaceous, possessing only a few detached 
 calcareous pieces, analogous it is true to those found in the lobster, 
 but strangely altered in structure. 
 
 These animals (Jig- 153), usually known by the name of 
 Soldier-Crabs or Hermit-Crabs, frequent level and sandy shores, 
 
 Fig. 153. 
 
 and, from their defenceless condition, are obliged to resort to 
 artificial protection. This they do by selecting an empty tur- 
 binated shell of proportionate size, deserted by some gasteropod 
 mollusc, into which they insinuate their tail ; and, retreating 
 
CRUSTACEA. 
 
 325 
 
 within the recesses of their selected abode, obtain a secure retreat, 
 which they drag after them wherever they go, until, by growing 
 larger, they are compelled to leave it in search of a more capacious 
 lodging. The wonderful adaptation of all the limbs to a residence 
 in such a dwelling cannot fail to strike the most incurious ob- 
 server. The chela, or large claws, differ remarkably in size ; 
 so that, when the animal retires into its concealment, the smaller 
 one may be entirely withdrawn, while the larger closes and guards 
 the orifice. The two succeeding pairs of legs, unlike those of 
 the lobster, are of great size and strength ; and, instead of being 
 terminated by pincers, end in strong pointed levers, whereby 
 the animal can not only crawl, but drag after it its heavy habit- 
 ation. Behind these locomotive legs are two feeble pairs, barely 
 strong enough to enable the soldier-crab to shift his position in the 
 shell he has chosen ; and the false feet attached to the abdomen 
 are even still more rudimentary in their deyelopement. But the 
 most singularly altered portion of the skeleton is the fin of the 
 tail, which here becomes transformed into a kind of holding ap- 
 paratus, by which the creature retains a firm grasp upon the bottom 
 of his residence. Fig. 154. 
 
 In the Brachyura,) or Crabs, we have at once, in the concentra- 
 tion observable in all parts of the skeleton, an indication of its 
 
CRUSTACEA. 
 
 being formed for progression on land, or, at least, for creeping at 
 the bottom of the sea. The tail, the great instrument of loco- 
 motion in the lobster, is here reduced to a rudiment, and the fin 
 at its extremity entirely obliterated ; the chela still continue 
 to be the most powerfully developed of the extremities ; while the 
 legs, the principal locomotive agents, are either terminated by 
 simple points, as in those species which are most decidedly ter- 
 restrial in their habits, or else, in the swimming crabs, the pos- 
 terior pair become expanded into flattened oars useful in nata- 
 tion (fig. 154). 
 
 (365.) From the extreme hardness and unyielding character of 
 the tegumentary skeleton in Crustaceans, a person unacquainted 
 with the history of these animals would be at a loss to conceive the 
 manner in which their growth could be effected. In insects we 
 have seen that all increase of size occurs prior to the attainment 
 of the perfect condition, and expansion is provided for by the 
 moults or changes of" skin which take place during the develope- 
 ment of the larva ; but the Crustacean, having acquired its mature 
 form, still continues to grow, and that until it acquires in many 
 instances a size far larger than that which any insect is permitted 
 to arrive at. 
 
 The plan adopted in the case before us, whereby growth is 
 permitted, is attended with many extraordinary phenomena. At 
 certain intervals the entire shell is cast off, leaving the body for 
 the time unfettered indeed as regards the capability of expansion, 
 but comparatively helpless and impotent, until such time as a new 
 shell becomes secreted by the dermis, and by hardening assumes 
 the form and efficiency of its predecessor. 
 
 We are indebted to Reaumur,* who watched the process in 
 the Cray-fish (Astacusfluviatilis)^ for what little is known con- 
 cerning the mode in which the change of shell is effected. In the 
 animal above mentioned, towards the commencement of autumn, 
 the approaching moult is indicated by the retirement of the cray- 
 fish into some secluded position, where it remains for some time 
 without eating. While in this condition, the old shell becomes 
 gradually detached from the surface of the body, and a new and 
 soft cuticle is formed underneath it, accurately representing of 
 course all the parts of the old covering which is to be removed ; 
 but as yet little calcareous matter is deposited in the newly formed 
 integument. The creature now becomes violently agitated, and 
 
 * Me"m. de la Acad. des Sciences, 1718. 
 
CRUSTACEA. 327 
 
 by various contortions of its body seems to be employed in 
 loosening thoroughly every part of its worn-out covering from 
 all connection with the recently secreted investment. This being 
 accomplished, it remains to extricate itself from its imprisonment ; 
 an operation of some difficulty ; and, when the nature of the ar- 
 mour to be removed is considered, we may well conceive that not 
 a little exertion will be required before its completion. As soon 
 as the old case of the cephalo-thorax has become quite detached 
 from the cutis by the interposition of the newly formed epidermic 
 layer, it is thrown off in one piece after great and violent exertion ; 
 the legs are then withdrawn from their cases after much strug- 
 gling ; and, to complete the process, the tail is ultimately by long- 
 continued efforts extricated from its calcareous covering, and the 
 entire coat of mail which previously defended the body is discarded 
 and left upon the sand. The phenomena which attend this reno- 
 vation of the external skeleton are so unimaginable, that it is 
 really extraordinary how little is accurately known concerning the 
 nature of the operation. The first question which presents itself 
 is, how are the limbs liberated from their confinement ? for, won- 
 derful as it may appear, the joints even of the massive chela of 
 the lobster do not separate from each other, but, notwithstanding 
 the great size of some of the segments of the claw, and the slender 
 dimensions of the joints that connect the different pieces, the 
 cast-off skeleton of the limb presents exactly the same appearance 
 as if it still encased the living member. The only way of ex- 
 plaining the circumstance, is to suppose that the individual pieces 
 of the skeleton, as well as the soft articulations connecting them, 
 split in a longitudinal direction, and that, after the abstraction 
 of the limb, the fissured parts close again with so much accuracy 
 that even the traces of the division are imperceptible. But this 
 is not the only part of the process which is calculated to excite our 
 astonishment : the internal calcareous septa from which the mus- 
 cles derive their origins, and the tendons whereby they are inserted 
 into the moveable portions of the outer shell, are likewise stated 
 to be found attached to the exuvise ; even the singular dental 
 apparatus situated in the stomach, of which we shall speak here- 
 after, is cast off and re-formed ! And yet, how is all this accom- 
 plished ? how do such parts become detached ? how are they 
 renewed ? We apprehend that more puzzling questions than 
 these can scarcely be propounded to the physiologist, nor could 
 more interesting subjects of inquiry be pointed out to those 
 
CRUSTACEA. 
 
 whose opportunities enable them to prosecute researches connected 
 with their elucidation.* 
 
 (366.) The structure of the articulations which unite the differ- 
 ent segments of the skeletons of the Articulata, and the general ar- 
 rangement of their muscular system, have already been described ; 
 and, in the class before us, these parts of their economy offer no 
 peculiarities worthy of special notice. 
 
 (367.) Throughout all the Crustacean families the alimentary 
 canal exhibits great simplicity of arrangement, and consists of a short 
 but capacious resophagus, a stomachal dilatation or cavity in which 
 is contained a singular masticatory apparatus, and a straight and 
 
 * Since writing the above, I have been fortunate in procuring a very good specimen 
 of Astacusfluviatilis, obtained soon after casting its shell, and also its newly cast-off 
 covering, both of which are in excellent preservation. The following is a description 
 of the appearances observed in each : All the pieces of the exuvium are connected 
 together by the old articulations, and accurately represent the external form of the 
 complete animal j the carapace, or dorsal shield of the cephalo-thorax, alone being de- 
 tached, having been thrown off in one piece. The pedicles of the eyes and external 
 corneae, as well as the antennae, remain in situ, the corresponding parts having been 
 drawn out from them as the finger from a glove ; and no fissure of the shell or rupture 
 of the ligaments connecting the joints is anywhere visible in these portions of the skele- 
 ton. The auditory tubercles, and the membrane stretched over the orifice of the ear, 
 occupy the same position as in the living cray-fish. The jaws, foot-jaws, and ambu- 
 latory feet retain their original connections, with the exception of the right chela, which 
 had been thrown off before the moult began ; and the segments of the abdomen, false 
 feet, and tail-fin exactly resembled those of the perfect creature; even the internal 
 processes derived from the thoracic segments (apodemata) rather seemed to have had 
 the flesh most carefully picked out from among them, than to have been cast away from 
 a living animal : but perhaps the most curious circumstance observable was, that 
 attached to the base of each leg was the skin which had formerly covered the branchial 
 tufts, and which, when floated in water, spread out into accurate representations of those 
 exquisitely delicate organs. No fissure was perceptible in any of the articulations 
 of the small claws j but in the chela each segment was split in the neighbourhood 
 of the joints, and the articulating ligaments ruptured. The lining membrane of the 
 stomach was found in the thorax, having the stomachal teeth connected with it ; from 
 its position, it would seem that the animal had dropped it into the place where it lay 
 before the extrication of its limbs was quite accomplished. The internal tendons were 
 all attached to the moveable joint of each pair of forceps, both in the chela and in 
 the two anterior pairs of smaller ambulatory legs. 
 
 On examining the animal, which had extricated itself from the exuvium described 
 above, the shell was found soft and flexible, but contained a sufficiency of calcareous 
 matter to give it some firmness, especially in the claws. The tendons of the forceps 
 were still perfectly membranous, presenting a very decided contrast when compared 
 with the old ones affixed to the discarded shell. The stump of the lost chela had not 
 as yet begun to sprout, and the extremity was covered by a soft black membrane. The 
 jaws were quite hard and calcified, as likewise were the teeth coutained in the sto- 
 mach. 
 
CRUSTACEA. 329 
 
 simple intestinal tube, which passes in a direct line from the sto- 
 mach to the last segment of the abdomen, where it terminates. 
 
 The description of these parts, as they exist in the lobster, 
 will give the reader a sufficiently correct idea of their general 
 disposition and structure ; nor are we acquainted with any class 
 of animals in which so little variety in the conformation of this 
 portion of the system is to be met with. 
 
 The oesophagus is covered at its origin by the several pairs of 
 foot-jaws already alluded to ; the most internal of which forms 
 a decided cutting apparatus, resembling a pair of strong shears, 
 while the rest are only instruments of prehension, or, perhaps, of 
 sensation also. From the mouth, the oesophagus runs directly up- 
 wards to the stomach, which is a considerable viscus (Jig. 157, a), 
 a large portion of it being situated in that region of the cephalo- 
 thorax which we should be tempted to consider as the head of the 
 animal. The pyloric extremity of the stomach is strengthened 
 with a curious frame-work of calcareous pieces imbedded in its 
 walls, and so disposed as to support three large teeth placed near 
 the orifice of the pylorus ; and, being moved by strong muscles, 
 teeth so disposed, no doubt, form an efficient apparatus for bruis- 
 ing the food before it is admitted into the intestine. 
 
 The intestine itself (, b, I) runs in a direct course to the 
 tail, imbedded between the two great lateral muscular masses that 
 move the abdominal segments ; and terminates upon the ventral 
 surface of the central lamella of the terminal fin in a rounded ori- 
 fice closed by a sphincter muscle. 
 
 The liver (c, c, c), one half of which has been removed in the 
 engraving, consists of two large symmetrical masses, enclosing be- 
 tween them the pyloric portion of the stomach, and a third part of 
 the length of the intestine. When unravelled, the minute struc- 
 ture of the liver exhibits an immense assemblage of secerning caeca 
 agglomerated into clusters, from each of which a duct emanates, 
 and the continued union of the ducts so formed ultimately gives 
 origin to the common hepatic canal (d), which pours the bile de- 
 rived from that division of the liver to which it belongs into the 
 intestine at a very short distance from its commencement at the 
 pylorus. A little below the insertion of the two bile-ducts, a so- 
 litary long and slender caecum enters the intestine, but the nature 
 of the secretion furnished by this organ is unknown. 
 
 (368.) Before tracing the course of the circulation in the Crus- 
 tacea, it will be necessary to consider the character of the apparatus 
 
- i nri i 
 
332 
 
 CRUSTACEA. 
 
 The branchial chambers are in free communication with the ex- 
 ternal medium by means of two large apertures, through one of 
 which the water enters, while it as constantly flows out through the 
 other. The afferent canal is generally a wide slit that allows the 
 water freely to penetrate to the interior of the branchial cavity; but 
 the passage whereby the respired fluid escapes after passing over the 
 branchiae is provided with a valvular apparatus so disposed as to 
 produce a continual current in the water contained in the chamber, 
 and thus, by insuring its perpetual agitation, effectually provides 
 for its constant renewal. The mechanism is as follows : The 
 aperture by which the water issues is in the neighbourhood of the 
 mouth, and is closed by a broad semi-membranous plate (flabel- 
 lum) derived from the root of the second pair of foot-jaws ; so that 
 every motion of these foot-jaws impresses a corresponding move- 
 ment upon the valve-like flabellum, and in this manner urges on the 
 passage of the water out of the cavity in which the branchiae are 
 lodged. 
 
 But there are other means whereby the action of the limbs is 
 made to assist in the perfection of the respiratory process. Thus, 
 in the lobster, the third pair of foot-jaws, and each pair of ambula- 
 tory legs, except the last, supports a flabelliform plate (Jig. 159, n); 
 the movements of which must likewise keep the fluid respired 
 in a state of agitation, and moreover, by gently squeezing and com- 
 pressing the respiratory tufts, powerfully contribute to the per- 
 fect renovation of the water in contact with the surfaces of the 
 branchi*. 
 
 In the crab genera the 
 arrangement is slightly mo- 
 dified, for here there are 
 three flabella derived ex- 
 clusively from the roots of 
 the foot-jaws (Jig. 156, b, 
 c, d) : of these, two are im- 
 bedded among the bran- 
 chiae ; while the third, as 
 represented in the figure, 
 extends in a crescentic 
 form over the external 
 surface of the whole series 
 of those organs. The 
 end answered in this case is obviously the same as that accom- 
 
 
CRUSTACEA. 
 
 plished in the lobster, in a different, and, perhaps, more efficient 
 manner. Fig. 157. 
 
 (370.) In the 
 lowest Crustacea the 
 heart is a long dor- 
 sal vessel, not very 
 dissimilar in form 
 and disposition from 
 that of insects; but 
 of course giving off 
 arteries for the distri- 
 bution of the blood, 
 and receiving veins 
 through which the 
 blood, having ac- 
 complished its cir- 
 cuit, is returned. 
 
 In tie Decapoda 
 the organ becomes 
 more centralized, and 
 in the lobster (Jig. 
 157, e) the heart is 
 found to be an oval 
 viscus, situated in 
 the mesial line of 
 the body, beneath 
 the posterior part 
 of the cephalo-tho- 
 rax; it is composed 
 of strong muscular 
 bands, and contains 
 a single cavity of 
 considerable size. 
 The contractions of 
 this heart are very 
 vigorous, and may 
 readily be witnessed 
 by raising the super- 
 jacent shell in the 
 living animal. 
 
 Several large arte- 
 
334 
 
 CRUSTACEA. 
 
 ries are derived form the above-mentioned simple heart. A consider- 
 able trunk (Jig. 157, g,) Fig. 158. 
 goes from its anterior 
 extremity to supply the 
 eyes, antennae, stomach, 
 and neighbouring or- 
 gans : another, the he- 
 patic (i), which is 
 sometimes double, sup- 
 plies the two lobes of 
 the liver : a third large 
 vessel (A) supplies the 
 abdominal or caudal re- 
 gion : and a fourth, the 
 sternal , derived from 
 the posterior apex of 
 the heart, bends down 
 to the ventral aspect of 
 the body, where it di- 
 vides ; the posterior di- 
 vision (/, /) supplying 
 the lower parts of the 
 abdomen, while the an- 
 terior and larger divi- 
 sion (m) gives off 
 branches to the legs 
 and foot-jaws (w, n, n, 
 w); it likewise furnishes 
 other vessels (o, o, o, 
 o) which are distribut- 
 ed through the bran- 
 chiae. 
 
 The venous system 
 is made up of large and 
 delicate sinuses that 
 communicate freely 
 with each other, and 
 receive the blood from 
 all parts of the body. 
 Those of the dorsal re- 
 gion are represented in the annexed figure: (.fig. 158), a large 
 
CRUSTACEA. 335 
 
 venous sinus (a) occupies the cephalic region, and covers the sto- 
 mach ; another cavity (b) lies immediately above the heart ; and a 
 series of smaller chambers (c, c, c, c) are situated above the muscles 
 of the caudal region. These cavities, notwithstanding their appa- 
 rent extent, are very shallow ; so that, upon a transverse section, 
 their dimensions are by no means so great as a superficial view 
 would indicate. The sinus (Z>), or that placed immediately over 
 the heart, communicates with that viscus by short trunks, the termi- 
 nations of which in the heart are guarded by valves (fig. 157, 
 /,/,/) so disposed as to allow the blood to pass from the sinus 
 into the heart, but prevent its return in an opposite direction. 
 
 (371.) Such is the apparatus provided in the lobster for the cir- 
 culation of the blood. Our next inquiry must be concerning the 
 course that it pursues during its circuit through the body. 
 
 Messrs. Audouin and Milne Edwards,* after very minutely 
 examining this subject, came to the conclusion that the heart is 
 purely of a systemic character, being only instrumental in propel- 
 ling the blood through the body, but having nothing to do with 
 the branchial circulation ; they conceived that the circulating fluid, 
 having been collected in the venous sinuses, was brought to the 
 roots of the branchiae, over which it was distributed by venous 
 tubes, and then returned to the heart by vessels which they call 
 branchio-cardiac to recommence the same course. The appended 
 figures, however, which are accurately copied from engravings of 
 the Hunterian drawings in the collection of the Royal College of 
 Surgeons,-)- wou ^ seem to gi ye great reason to doubt the accuracy 
 of the conclusions arrived at by the eminent naturalists referred 
 to ; and to show that the heart, instead of being purely systemic, is 
 partly branchial, and impels the blood, not through the body only, 
 but also to the respiratory organs. This view of the subject, 
 which we are disposed to consider as the most correct, is exhibited 
 in the diagram annexed. Setting out from the heart, we find that 
 the blood goes to all parts of the body through the different 
 arterial trunks, and by the great sternal artery (Jig. 157, k) is con- 
 veyed to the legs, foot-jaws, and false feet. But from this same 
 artery (m), vessels, o, o, o, o, are furnished to the branchiae. The 
 branchial arteries so derived (Jig. 159, g) subdivide into secondary 
 
 * Recherches Anatomiques et Physiologiques sur la Circulation dans les Crustaces. 
 Annales des Sciences Nat. tora.ii. 
 
 t Catalogue of the Physiological Series of Comparative Anatomy contained in the 
 Museum of the Royal College of Surgeons ; vol. ii. 
 
336 
 
 CRUSTACEA. 
 
 trunks (h, h, h), which ramify through the individual branchise, and 
 supply all their appended filaments. Having undergone exposure to 
 
 the respired medium, the blood is again collected from the branchiae 
 by branchial veins (&, k, k) represented on the opposite side of 
 the body, and conveyed by the large vessel, /, to the dorsal sinus 
 (Jig. 158, 5), where, being mixed up with the general mass of 
 blood contained in the sinus, the circulating fluid is admitted into 
 the heart through the valvular orifices (d, d), to recommence the 
 same track. 
 
 (372.) As might be anticipated from an examination of the ex- 
 ternal configuration of the different families comprised in the exten- 
 sive class we are now considering, the nervous system is found to 
 pass through all those gradations of developement which we have 
 found gradually to present themselves as we have traced the Homo- 
 gangliata from the lowest to the most highly organized types of 
 structure. In the most imperfect Crustacea, indeed, we find a 
 simplicity of arrangement greater than any hitherto pointed out 
 even in the humblest Annelida ; a disposition of parts which the- 
 oretically might have been expected to exist, but has only been 
 distinctly recognised in the class before us. 
 
 We have all along spoken of the nervous centres of the Arti- 
 culata as arranged in symmetrical pairs, although in no example 
 
CRUSTACEA. 337 
 
 which lias yet occurred to our notice have we been able strictly to 
 point out the accuracy of such a view of the subject. The two 
 lateral masses of the supra-cesophageal ganglion are found united 
 into one brain in the humblest forms of annulose animals, and even 
 in the ganglia forming the ventral series, although we might pre- 
 sume each to be composed of two symmetrical halves, the divisions 
 are most frequently so intimately blended, that their distinctness 
 is not susceptible of anatomical demonstration. In some of the 
 Crustacea, however, among those species which have the segments 
 of their external skeleton most perfectly separate and distinct, the 
 nervous system is found to present itself in such a condition that 
 the division into lateral halves is perfectly evident ; and from this 
 condition their progressive coalescence may be traced step by 
 step until we arrive at a state of concentration as remarkable 
 as that already noticed in the most elevated of the Arachnidans. 
 It is to Milne Edwards and Audouin that we are indebted for 
 the interesting particulars connected with this part of our sub- 
 ject ; and the results of their investigations are of such great 
 physiological importance,* that the following condensed ac- 
 count of their labours cannot be omitted in this place. In 
 Talitrus every pair of ganglia consists of two separate nuclei of 
 nervous substance, united by a transverse band so disposed as to 
 bring them into communication with each other, while an anterior 
 and posterior nervous filament derived from each unites it with the 
 preceding and following ganglia of the same side of the body ; 
 even the encephalic mass is composed of two lateral portions united 
 by a cord passing between them : all these pairs of ganglia, thir- 
 teen in number, corresponding with the number of the segments 
 of the body, are exact counterparts of each other both in size and 
 figure, so that none seems to preponderate in energy over the rest ; 
 but the anterior or encephalic pair alone communicates with the 
 eyes and antennae, the only organs of the senses as yet discernible. 
 In Oniscus Asellus a concentration of the elements composing 
 the nervous system above described is discernible, and this is found 
 to be indicated by incipient approximation, which takes place in 
 two directions, one longitudinal, the other acting transversely. In 
 the first place, the entire number of pairs of ganglia is reduced to 
 ten, three pairs having become obliterated by coalescence ; and, 
 moreover, while the central portions still consist of two lateral 
 
 * Recherches Anatomiques sur le Systeme Nerveux des Crustacea. Annales des 
 Sciences Nat. torn. xiv. 
 
 z 
 
'338 
 
 CRUSTACEA. 
 
 masses each, the first and last pairs are united into single ganglia. 
 "As we rise to higher forms the coalescence still proceeds : all the 
 pairs of ganglia soon become united in a transverse direction, and 
 gradually the whole chain becomes shorter by the confusion of 
 several pairs into larger and more powerful masses. 
 
 In the Crab, which, from its terrestrial habits, holds a position 
 among the Crustacea equivalent to that which Spiders occupy 
 among other Articulata, this centralization is carried to the utmost 
 extent ; and all the abdominal and thoracic ganglia become agglo- 
 merated into one great centre, from which nerves radiate to the 
 parts of the mouth and instruments of locomotion (Jig. 160). 
 
 (373.) But this change pig. 160. 
 
 in the condition of 
 the nervous system 
 is not only observ- 
 able as we proceed 
 from species to spe- 
 cies, as they rise 
 higher in the scale 
 of developement ; si- 
 milar phenomena are 
 met with in watch- 
 ing the progress of 
 any individual be- 
 longing to the more 
 perfect families, as it advances from the embryo to its ma- 
 ture condition. Thus in the Cray-fish (Astacus fluviatilis), 
 Rathke* observed, that, when first perceptible, the nervous system 
 consisted of eleven pairs of ganglia, perfectly distinct from each 
 other, and situated on each side of the mesial line of the body. 
 The six first pairs then unite transversely, so as to form as many 
 single masses, from which the nerves of the mandibles and foot- 
 jaws emanate ; while the five posterior, from which the nerves of 
 the ambulatory extremities are given off, remain separate. Such is 
 the state at birth, or on leaving the egg ; but further changes occur 
 before the Cray-fish arrives at maturity. The four anterior gan- 
 glia, which supply nerves to the mandibles and foot-jaws, are, by 
 degrees, all consolidated into one mass, and the fifth and sixth 
 likewise coalesce, while the other pairs continue permanently dis- 
 
 * Untersuchungen liber die Bildung des Flusskrebses in the Annales des Sciences 
 Nat. torn. xx. 
 
CRUSTACEA. 
 
 339 
 
 tinct. The reader will at once recognise the resemblance be- 
 tween these changes and those already described as taking place 
 during the progress of evolution in the caterpillar: the same 
 great law is, in fact, in operation in both cases, and the same 
 results are obtained from the completion of the process.* 
 
 From a review of the above facts, Milne Edwards and Au- 
 douin arrived at the following conclusions : 1st. That the ner- 
 vous system of Crustacea consists uniformly of medullary nuclei 
 (ganglions), the normal number of which is the same as that of 
 the segments or rings of the body. #. That all the modifications 
 encountered, whether at different periods of the developement or 
 in different species of the series, depend especially on the more or 
 less complete approximation of these nuclei, and to an arrest of 
 developement in some of their number. 3. That approximation 
 takes place from the sides towards the mesian line, as well as in a 
 longitudinal direction. 
 
 Fig. 161. 
 
 (374.) In the Crab the distribution of the nerves is briefly as 
 follows : The encephalic mass, or brain, which still occupies its 
 
 * For a minute account of the arrangement of the nervous system in these animals, 
 the reader is referred to the Cyclop, of Anat. and Phys. art. CRUSTACEA ; by Dr. Milne 
 Edwards. 
 
 z 2 
 
340 CRUSTACEA. 
 
 position above the oesophagus, and joins the abdominal centre by 
 two long cords of connection (j%. 161), gives off nerves to the 
 eyes and muscles connected with them, as well as to the antennae 
 and neighbouring parts. 
 
 Near the centre of each division of the nervous collar that 
 surrounds the oesophagus is a ganglionic enlargement, from which 
 arises a nerve that runs to the mandibles, and also a very import- 
 ant branch, apparently the representative of the nervus vagus of 
 insects. This, after ramifying largely upon the coats of the sto- 
 mach, joins that of the opposite side ; and, assuming a ganglionic 
 structure, is ultimately lost upon the intestine. 
 
 The nerves of the extremities, derived from the central abdo- 
 minal ganglion, are represented in the preceding figure (fig. 161), 
 which requires no explanation.* 
 
 (375.) We have already ($ 313), when describing the nervous 
 system of insects, hinted at the probable existence in the HOMO- 
 GANGLIATA of distinct tracts of nervous matter in the composition 
 of the central chain of ganglia, and in the filaments whereby they 
 are connected with each other : reasoning therefore from analogy, 
 it seems fair to presume that, if this be the case, such tracts corre- 
 spond with the sensitive and motor columns which have been dis- 
 tinctly proved to exist in the spinal axis of vertebrate animals. 
 It is to Mr. Newport that we are indebted for the first indication 
 of this interesting fact ;^ and the accuracy of his observations is 
 readily demonstrable by a careful examination of the ganglionic 
 chain of the lobster and other large Crustacean species. Each 
 ganglionic enlargement is, upon close inspection, clearly seen to 
 consist of two portions ; first of a mass of cineritious nervous sub- 
 stance forming the inferior aspect of the ganglion, and of a cord of 
 medullary or fibrous matter which passes over the dorsal or 
 superior aspect, and appears to be distinct from the grey substance 
 over which it passes : supposing, therefore, the longitudinal chain 
 to consist of anterior and posterior fasciculi, as in the medulla 
 spinalis, we have the anterior columns communicating with grey 
 substance, while the posterior are unconnected therewith, but are 
 continued over the ganglion instead of becoming amalgamated with 
 its substance. Another fact, which favours Mr. Newport's view of 
 this subject, is derived from an examination of the manner in 
 which the nerves given off from the central axis take their origin ; 
 
 * Vide Swan ; Comparative Anat. of the Nervous System. London, 4to. 
 t Phil. Transact. 1834. 
 
CRUSTACEA. 341 
 
 for some of them undoubtedly proceed from the cineritious portion 
 of the ganglionic swelling, while others, derived from the upper 
 column, not only have no connection with the grey matter, but 
 arise at some distance from the ganglion (fig. 138) : judging, 
 therefore, by the laws at present established in physiology, there 
 seems reason to suppose that the anterior or rather inferior fasciculi 
 are connected with sensation, while the superior constitute the 
 motor tract. 
 
 The reader who is conversant with human physiology will at 
 once perceive that this arrangement is precisely the reverse of 
 that met with in man and other VERTEBRATA : and this consi- 
 deration, apparently of little importance, has given rise to a va- 
 riety of curious speculations ; some anatomists having even gone 
 so far as to assert that all the organs of articulated animals are 
 in reality placed in a similar inverted position. 
 
 (376.) A more interesting inquiry connected with this part of 
 our subject is, concerning the extent to whrch the ARTICULATA 
 are susceptible of pain. Is it really true in philosophy, as it 
 has become a standing axiom in poetry, that 
 
 " the poor beetle, that we tread upon, 
 
 In corporal sufferance feels a pang as great 
 
 As when a giant dies" ? 
 
 This is a question upon which modern discoveries in science 
 entitle us to offer an opinion, and the result of the investigation 
 would seem to afford more enlarged views relative to the benefi- 
 cence displayed in the construction of animals than the assertion of 
 the poet would lead us to anticipate. Pain, " Nature's kind 
 harbinger of mischief," is only inflicted for wise and important 
 purposes, either to give warning of the existence of disease, or as 
 a powerful stimulus prompting to escape from danger. Acute 
 perceptions of pain could scarcely, therefore, be supposed to exist 
 in animals deprived of all power of remedying the one or of 
 avoiding the other. In man the power of feeling pain indubitably 
 is placed exclusively in the brain ; and, if communication be cut off 
 between this organ and any part of the body, pain is no longer 
 felt, whatever mutilations may be inflicted. 
 
 The medulla spinalis, which, as we shall see hereafter, corre- 
 sponds to the ventral chain of ganglia in articulated animals, can 
 perceive external impressions and originate motions, but not feel 
 pain ; hence we may justly conclude that in the Homogangliata, 
 likewise, the supra-oesophageal ganglia, the representatives of the 
 
342 CRUSTACEA. 
 
 brain, and the sole correspondents with the instruments of the 
 higher senses, are alone capable of appreciating sensations of a 
 painful character. Thus, then, we arrive at a very important con- 
 clusion, namely, that the perception of pain depends upon the 
 developement of the encephalic masses ; and consequently, that, as 
 this part of the nervous system becomes more perfect, the power 
 of feeling painful impressions increases in the same ratio : or, 
 in other words, that, inasmuch as the strength, activity, and intel- 
 ligence of an animal, by which it can escape from pain, depends 
 upon the perfection of the brain, so does the perception of torture 
 depend upon the condition of the same organ. How far the feel- 
 ing of pain is acutely developed in the animals we are now consi- 
 dering is deducible from every-day observation. The fly seized 
 by the leg will leave its limb behind, and alight with apparent 
 unconcern to regale upon the nearest sweets within^ its reach : 
 the caterpillar enjoys, to all appearance, a tranquil existence 
 while the larvae of the Ichneumon, hatched in its body, devour its 
 very viscera : and in the Crustacea before us, of so little import- 
 ance is the loss of a leg, that the lobster will throw off its claws 
 if alarmed by the report of a cannon. 
 
 (377.) The singular power of breaking off their own limbs, 
 alluded to in the last paragraph, is possessed by many Crustacea, 
 and is a very indispensable provision in their economy. We have 
 already found the blood-vessels of these animals to be of a delicate 
 structure ; and, the veins being wide sinuses whose walls possess 
 little contractility, the fracture of a limb would inevitably produce 
 an abundant and speedily fatal haemorrhage was there not some con- 
 trivance to remedy the otherwise unavoidable results of such a catas- 
 trophe. Should the claw of a lobster, for example, be accidentally 
 damaged by accidents to which creatures encased in such brittle 
 armour must be perpetually exposed, the animal at once breaks 
 off the injured member at a particular part, namely, at a point 
 in the second piece from the body ; and by this operation, which 
 seems to produce no pain, the bleeding is effectually staunched. 
 
 But the most remarkable part of the phenomenon remains to be 
 noticed : after this extraordinary amputation has been effected, 
 another leg begins to sprout from the stump, which soon grows to 
 be an efficient substitute for the lost extremity, and gradually, 
 though slowly, acquires the pristine form and dimensions of its pre- 
 decessor. A beautiful example of this curious mode of reprodu- 
 cing a lost organ is preserved in the Museum of Comparative Ana- 
 
CRUSTACEA. 343 
 
 tomy in King's College, London, in which the new limb (one of the 
 cheliferous claws) has already attained the form of the old chela, but 
 still remains soft and uncovered by calcareous integument. The pro- 
 cess of reproduction is as follows : The broken extremity of the 
 second joint skins over, and presents a smooth vascular membrane, 
 at first flat, but soon becoming conical as the limb begins to grow. 
 As the growth advances, the shape of the new member becomes 
 apparent, and constrictions appear, indicating the position of the 
 articulation ; but the whole remains unprotected by any hard cover- 
 ing until the next change of shell, after which it appears in a pro- 
 per case, being, however, still considerably smaller than the cor- 
 responding claw on the opposite side of the body, although equally 
 perfect in all its parts. 
 
 (378.) The observations made in a former chapter relative to the 
 organs by which the senses of touch, taste, and smell are exercised 
 in insects, are equally applicable to the animals composing the 
 class before us ; for in the Crustacea, although we are compelled to 
 admit the possession of the above faculties, we are utterly ignorant 
 of the mode in which they are exercised, and therefore it would be 
 only an unprofitable waste of time to enter at any length into a 
 discussion from which no satisfactory conclusions are, in the pre- 
 sent state of our knowledge, to be deduced. 
 
 (379.) The eyes of Crustaceans are of three kinds, simple, ag- 
 glomerated, and compound. 
 
 The simple eyes (ocelli, stemmata) resemble those of spiders, and, 
 like them, are said to consist of a cornea, a spherical lens, a gelatin- 
 ous vitreous humour, a retina and deeply-coloured choroid, all occu- 
 pying their usual relative positions. These eyes never exceed two 
 or three in number. 
 
 In the agglomerated eyes, such as those of Daphnia (Jig. 155), 
 the organ seems to be composed of a number of simple eyes placed 
 behind one common cornea ; such eyes are moveable, and, in the 
 animal depicted in the figure, the muscles acting upon the visual 
 apparatus, which in this case is single, are arranged so as to form a 
 cone the base of which is formed by the eye and may be distinctly 
 seen under a good microscope. 
 
 The compound eyes appear to be constructed upon the same prin- 
 ciples as those of insects. The cornese are extremely numerous 
 and generally hexagonal ; but sometimes, as in the lobster, they are 
 square. The vitreous humours equal the cornese in number, and 
 behind each of these a distinct retina would seem to be expanded. 
 
344 CRUSTACEA. 
 
 The compound eyes of Crustaceans have not, however, as yet been 
 examined with the same patient diligence as those of the cock- 
 chaffer ; so that, as relates to their minute anatomy, much is still left 
 to conjecture and uncertainty. One peculiarity connected with 
 these organs is, that in the two highest orders of Crustacea, hence 
 called Podophthalmia, the eyes are placed at the extremity of 
 moveable pedicles articulated with the first cephalic ring of the ex- 
 ternal skeleton, and thus they may be turned in various directions 
 without moving the whole body at the same time. This provision 
 was not required in insects, owing to the mobility of the head in 
 those animals; but is absolutely indispensable in the case before us, 
 where, the head and thorax being consolidated into one mass, the 
 extent of vision commanded by sessile eyes would have been ex- 
 ceedingly limited, and inadequate to the security of creatures ex- 
 posed to such innumerable enemies. 
 
 (380.) It is in the higher Crustacea that we, for the first time, 
 indubitably find a distinct auditory apparatus ; and, from the 
 simplicity which the organ of hearing presents in this its earliest 
 appearance, an inquiry concerning its structure becomes of great 
 physiological interest. In the lobster the ears are situated upon 
 the under surface of the basal joints of the second pair of antennae. 
 On looking carefully in this situation the student will find a pro- 
 minent tubercle formed by the shell, the top of which is perforated 
 by a small circular opening covered with a tense membrane. Be- 
 hind this orifice is placed a minute vesicle filled with fluid, upon 
 which a delicate branch of the antennary nerve is distributed. 
 This constitutes the whole apparatus : the vibration of the water 
 strikes upon the external membrane, the water in the sacculus 
 participates in the tremor, and the expanded nerve conveys to the 
 brain the sensation thus produced. 
 
 In the Brachyura, or crabs, the membrane covering the external 
 orifice of the ear is converted into a moveable calcareous lamella, 
 from which, in some genera, a furcate process is continued inter- 
 nally ; so that the whole, when removed by maceration, has no 
 very distant resemblance to the stapes of the human ear, and, like 
 it, seems to be acted upon by muscular fasciculi, so disposed as to 
 regulate the tension of the vibratile membrane, and thus adapt it to 
 receive impressions of variable intensity. 
 
 (381.) One of the first circumstances calculated to attract the 
 notice of the anatomist who turns his attention to the structure of 
 the generative system both in male and female Crustacea, is the 
 
CRUSTACEA. 
 
 345 
 
 complete separation which exists between the organs belonging to the 
 two sides of the body; for not Fig. 162. 
 
 only are the internal secret- 
 ing viscera for the most part 
 perfectly distinct from each 
 other, but even the external 
 sexual orifices are equally se- 
 parate and unconnected. 
 
 (382.) Beginning with the 
 parts observable in the male, 
 we will take the cray-fish ( As- 
 tacusjluviatilis)as a standard 
 of comparison, and briefly 
 notice the principal variations 
 from the type of structure, 
 observable in that species, 
 met with in other genera. 
 
 In the cray-fish and also 
 in the lobster, the secerning 
 organs or testes, when exa- 
 mined in situ, are found to occupy the dorsal region of the thorax, 
 lying upon the posterior part of the stomach. 
 
 Examined superficially, the testes would seem to form but one 
 mass consisting of three lobes (fig. 162, a, a, b) ; but, on investi- 
 gating the minute structure of the organ, it is found to be made up 
 of very delicate -secreting tubes that give origin to two excretory 
 ducts (c, c). After numerous convolutions, which form a kind of 
 epididymis (c?), each duct, becoming slightly dilated, terminates by 
 a distinct orifice (/), seen upon the basal articulations of the last 
 pair of ambulatory legs. There is no intromittent apparatus visible ; 
 but, according to Milne Edwards,* the extremity of the excretory 
 duct, by undergoing a kind of tumefaction, may be protruded exter- 
 nally, so as to become efficient in directing the course of the fecun- 
 dating fluid. 
 
 In crabs the mass of the testis is exceedingly large, but in its 
 essential structure similar to that of the cray-fish, and the external 
 opening of its excretory duct is found to occupy the same situation : 
 in some genera, however, instead of being placed upon the first 
 joint of the last pair of legs, the orifices of the male organs are 
 found upon the abdominal surface of the last thoracic ring itself. 
 
 * Cyclop, of Anat. and Phys. art. CRUSTACFA. 
 
346 
 
 CRUSTACEA. 
 
 (383.) The female generative organs of Crustacea very accurately 
 resemble those of the male ; and in the unimpregnated condition it 
 is not always easy, from a superficial survey of the internal viscera, 
 to determine the sex. In Astacus Fig. 163. 
 
 Jluviatilis, the ovaria (Jig. 163, a) 
 occupy a position analogous to that 
 of the male testis, and a simple 
 canal derived from each side (6, c) 
 conducts the eggs to the external 
 apertures found upon the first joint 
 of the third pair of legs. 
 
 In crabs an important addition 
 is made to the female generative 
 system : -prior to the termination 
 of each oviduct it is found to com- 
 municate with a wide sacculus, the 
 function of which is apparently ana- 
 logous to that of the spermatheca 
 of insects ( 328), inasmuch as it seems to form a receptacle for the 
 fecundating secretion of the male, in which the seminal fluid re- 
 mains ready to impregnate the ova as they successively pass its 
 orifice during their expulsion from the body. 
 
 It is not precisely known in what manner copulation is effected 
 by these animals ; neither, indeed, is it positively ascertained in 
 many species whether the ova are impregnated prior to their 
 expulsion or afterwards, although the latter supposition seems by 
 far the most probable. 
 
 (384.) The eggs are almost invariably carried about by the female 
 until they are hatched, and in order to effect this various means 
 are provided. In the Decapoda they are fastened by a stringy 
 secretion to the false feet under the abdomen, and a female crab 
 may generally be readily distinguished from a male of the same 
 species by the greater proportionate size of this part of their body. 
 In Asellus, a small Crustacean very common in stagnant water, 
 the male may be observed during the breeding season to carry the 
 female about with him for many days ; after which her eggs are 
 found impregnated, and enclosed in a membranous sac placed under 
 the thorax, from which when the young are hatched they escape 
 through a longitudinal fissure provided for the purpose. In many 
 genera, broad laminse, or scaly plates, are found upon the under 
 surface of the body, beneath which the eggs are lodged. 
 
CRUSTACEA. 347 
 
 The more minute Crustacea, or Entomostraca, as they are 
 called by zoologists, in their mode of reproduction, offer several 
 remarkable variations from what has been described above ; and a 
 brief account of their most interesting peculiarities is therefore 
 still wanting to complete this part of our subject. These little 
 creatures, in fact, seem to form a transition between the class we 
 are now considering and the Epizoa, which many of them re- 
 semble so nearly that they are still confounded together by many 
 authors. The female Entomostraca frequently carry their ova in 
 two transparent sacculi attached to the hinder part of the body, 
 and it is in these egg-bags that the oviducts terminate ; so that 
 the ova, as they are formed, are expelled into the singular re- 
 ceptacles thus provided. Without such a provision, indeed, it 
 would be difficult to conceive how the ova could possibly remain 
 attached to the parent, as they far surpass in their aggregate bulk 
 the size of her entire body, and could not, therefore, by any con- 
 trivance be developed internally without bursting the crustaceous 
 covering that invests the mother. J urine,* Ramdohr,*)" and other 
 authors, have carefully watched the generative process in several 
 genera, and brought to light many important and curious facts 
 connected therewith. In Cyclops, a species to be met with in 
 every ditch, the impregnation of the ova is undoubtedly effected 
 in the body of the parent, and the eggs when formed are expelled 
 into two oval sacs placed on each side of the tail, which Jurine calls 
 external ovaries. The number of eggs contained in these sacs 
 gradually increases, and they exhibit a brown or deep red colour, 
 until a short period before the growth of the embryo is completed, 
 when they become more transparent. In about ten days the eggs 
 are hatched and the young escape ; but such is the prodigious 
 fertility of these little beings, that a single female will, in the 
 course of three months, produce ten successive families, each con- 
 sisting of from thirty to forty young ones. 
 
 In the genus Apus, another plan is resorted to for the protec- 
 tion of the ova: the eleventh pair of legs, called by Schcefer\. 
 " womb-legs," have their first joints expanded into two circular 
 valves, which shut together like a bivalve shell, and thus form a 
 receptacle in which the eggs are contained until they arrive at 
 maturity. 
 
 * Histoire des Monocles. 1 vol. 4to. Gen. 1820. 
 
 f- Materiaux pour 1'Histoire de quelques Monocles A Demands. 4to. 1805, 
 
 $ Apus pisciformis, insecti aquatic! species noviter delectae. 4to. Ratisbonne, 1757. 
 
348 CRUSTACEA. 
 
 In Daphnia (Jig. 155) the ovariaare easily distinguished through 
 the exquisitely transparent shell, especially when in a gravid state ; 
 and the eggs after extrusion are lodged in a cavity situated be- 
 tween the shell and the exterior of the body, where they remain 
 until the embryo attains its full growth. 
 
 (385.) One fact connected with the reproduction of the Entomos- 
 traca is so remarkable, that, had we not already had an instance of the 
 occurrence of a similar phenomenon in the insect world (Aphides), 
 the enunciation of it would cause no little surprise to the reader ; 
 and, had its reality been less firmly substantiated by the concur- 
 rent testimony of numerous observers who have witnessed it in 
 many different genera (Cyclops, Daphnia, &c.), it might still be 
 admitted with suspicion. In the genera above mentioned it has 
 been ascertained by careful experiments that a single intercourse 
 between the sexes is sufficient to render fertile the eggs of several 
 (at least six, according to Jurine) distinct and successive gene- 
 rations. 
 
 Some authors have supposed, from the circumstance of all the 
 individuals which have been met with belonging to some genera 
 being females, that some of these little beings were hermaphrodite, 
 or self-impregnating ; but such an opinion rests on very doubtful 
 grounds, especially as there seems good reason to believe that in 
 many instances the forms of the male and female of the same 
 species are so different that they might easily be mistaken for 
 totally distinct animals. 
 
 (386.) The last point which we have to notice, in connection with 
 the history of the Crustacea, is, the progress of their developement 
 from the embryo condition to their mature state. This is a sub- 
 ject which has given rise to considerable discussion, especially as 
 relates to the changes which occur during the growth of the more 
 highly organized forms ; some authors contending that they leave 
 the egg complete in all their parts, and presenting their adult con- 
 figuration, while others assert that they undergo changes so import- 
 ant as only to be comparable with the metamorphosis of insects. 
 
 Among the Entomostraca such changes have been again and 
 again witnessed, and the appearances observed during their growth 
 carefully recorded. From these observations very important results 
 have been obtained, inasmuch as many forms previously described 
 as distinct species have been found to be merely the same animal 
 in different stages of developement. In Cyclops, for example, 
 the newly hatched embryo possesses only four legs, and its body 
 
CRUSTACEA. 
 
 349 
 
 is round, having as yet no appearance of caudal appendages ; of 
 young animals in this condition Muller had formed a distinct 
 genus (Amymonc) :* in about a fortnight they get another pair 
 of legs, and form the genus Nauplius of the same author. They 
 then change their skin for the first time, and present the form of 
 the adult, but with antennae and feet smaller and more slender 
 than in the perfectly mature state. After two other changes of 
 skin they become capable of reproduction. 
 
 Many of the Entomostraca, as for example Daphnia, do not 
 seem to undergo material alterations of form, but simply moult at 
 certain intervals, throwing off their old integument and acquiring a 
 new covering. Nevertheless, even in the Decapoda it is pretty 
 certain that great metamorphoses take place in the external ap- 
 pearance of the young animals, though many contradictory opi- 
 nions concerning their nature are entertained by naturalists. 
 Much confusion, indeed, still exists connected with this important 
 subject. Cavolini long since announced that the embryo of Can- 
 cer depressus exhibited at birth a singular and uncouth appear- 
 ance, of which he gave a very tolerable representation;")" and Mr. 
 Thompson, in a late number of the Philosophical Transactions, 
 has rendered it certain that even 
 in the developement of the com- 
 mon crab, so different is the out- 
 ward form of the newly-hatched 
 embryo from that of the adult, 
 that the former has been describ- 
 ed as a distinct species, and even 
 grouped among the ENTOMOS- 
 TRACA, under the name of Zoea 
 pelagica. On leaving the egg, 
 according to the author alluded 
 to, the young crab presents a cu- 
 rious and grotesque figure (Jig. 
 164) : its body is hemispherical, 
 and its back prolonged upwards 
 into a horn-like appendage ; the 
 feet are scarcely visible, with the 
 
 exception of the two last pairs, which are ciliated like those of a 
 Branchiopod, and formed for swimming. The tail is longer than 
 
 Fig. 164. 
 
 * Latreille, Regne Animal, vol. iv. 
 
 t Sulla Generazione del Pesci edei Granchi. 4to. Naples, 1787. 
 
350 
 
 CRUSTACEA. 
 
 Fig. 165. 
 
 the body, possesses no 
 false feet ; and the ter- 
 minal joint is crescent- 
 shaped, and covered 
 with long spines. The 
 eyes are very large, and 
 a long beak projects 
 from the lower surface 
 of the head. 
 
 In a more advanced 
 stage of growth the 
 creature assumes a to- 
 tally different shape, 
 (Jig- 165,) under which 
 form it has been known 
 to naturalists by the 
 name of Megalopa. 
 The eyes become pe- 
 
 dunculated, the cepha- 
 
 lo-thorax rounded, the 
 tail flat and provided 
 
 with false feet, 
 
 and the chelae 
 
 and ambulatory 
 
 extremities well 
 
 developed. 
 A subsequent 
 
 moult gives it 
 
 the appearance 
 
 of a perfect 
 
 crab ; and then 
 
 only does the 
 
 abdomen become 
 
 folded under the 
 
 thorax, and the 
 
 normal form of the species recognisable (fig. 166), 
 
 Fig. 166. 
 
351 
 
 CHAPTER XVIII. 
 
 HETEROGANGLIATA* (Owen) ; MOLLUSCA. (Cuv.) 
 
 (387.) THE term MOLLUSCA, employed by Cuvierto designate 
 the fourth grand division of the animal world, is obviously derived 
 from a very unimportant circumstance of their organization, which 
 the tribes included in it possess in common with innumerable forms 
 both of Acrite and Nematoneurose beings, whose soft bodies are 
 unsupported by any internal or tegumentary framework of sufficient 
 density to merit the name of a skeleton. Subsequent anatomists 
 have therefore, however unwillingly, been compelled to substitute 
 another name for that given by the illustrious French zoologist to 
 this extensive class, the boundaries and relations of which, as at 
 present admitted, remaining precisely as they were first established 
 by his patient and unwearied investigations relative to the anatomi- 
 cal structure of the animals comprised within its limits. 
 
 It is to the arrangement of the nervous system that we must 
 again have recourse in order to discover a distinctive appella- 
 tion ; nor in this shall we be disappointed, for here we at once find 
 a character peculiar to this great section of animated nature, and 
 generally applicable to the various classes composing it. All the 
 Mollusca present nervous ganglia, which, in the more highly organ- 
 ized forms, attain considerable developement and consequent per- 
 fection ; but these nervous centres, instead of being arranged in a 
 longitudinal series of symmetrical pairs, are variously distributed in 
 different parts of the body ; an arrangement exactly correspondent to 
 the want of symmetry observable both in the external configuration 
 of these creatures, and in the anatomical disposition of their internal 
 viscera. Still, however, one large ganglionic mass occupies a posi- 
 tion above the oesophagus, and it is with this that the nerves of the 
 existing senses invariably communicate ; so that we are naturally 
 induced to regard this as the sentient brain, corresponding with the 
 supra-eesophageal ganglion of the ABTICULATA both in position 
 and office. The other ganglia vary considerably both in number 
 and in situation, but, wherever placed, they all communicate with 
 the supra-cesophageal mass ; while the branches derived from them 
 are distributed to the viscera, or to the locomotive organs. 
 
 (388.) Various are the forms, and widely different the relative 
 
 s, dissimilar ; yyyX/v, a ganglion. 
 
352 CIRRHOPODA. 
 
 perfection of the Mollusca, as regards their endowments and capabili- 
 ties. Some, as the Barnacles (CIRRHOPOUA), fixed to the surface of 
 various submarine bodies, either immoveably or by the intervention 
 of a flexible pedicle, entirely deprived of organs connected with the 
 higher senses, and unable to change their position, are content to 
 cast out at intervals their ciliated arms, which form a net of Na- 
 ture's own contrivance, and thus entrap such passing prey as suits 
 their appetite. Others, equally incapable' of locomotion, but fur- 
 nished with arms of different construction, (BRACHIOPODA,) catch 
 their food by similar efforts. The TUNICATA, enclosed in coria- 
 ceous bags, are firmly rooted to the rocks ; or, aggregated into 
 singular compound masses, float at the mercy of the waves. The 
 CONCHIFERA inhabit bivalve shells ; while the GASTEROPOD or- 
 ders, likewise defended in most cases by a shelly covering, creep upon 
 a broad and fleshy ventral disc, and, thus endowed with a locomotive 
 apparatus, exhibit senses of proportionate perfection. The PTE- 
 ROPODA swim in myriads through the sea, supported on two fleshy 
 fins ; while the CEPHALOPOD MOLLUSCA, the most active and 
 highly organized of this large and important division of animated 
 nature, furnished with both eyes and ears, and armed with formidable 
 means of destroying prey, become tyrants of the deep, and gradu- 
 ally conduct us to the most exalted type of animal existence. 
 
 These different sections, which constitute, in fact, so many dis- 
 tinct classes into which the HETEROGANGLTATA have been divided 
 by zoologists, we shall now proceed to examine seriatim ; beginning, 
 as heretofore, with the most imperfectly organized, and gradually 
 tracing the developement of superior attributes and more exalted 
 faculties as the nervous centres attain greater magnitude and con- 
 centration. 
 
 CHAPTER XIX. 
 
 ClRRHOPOUA.* 
 
 (389.) HOWEVER distinct in outward appearance, and even in 
 their internal economy, the creatures composing the primary divisions 
 of animated nature may seem to be when superficially examined, 
 closer investigation invariably reveals to the zoologist gradations of 
 structure connecting most dissimilar types of organization, and lead- 
 
 * xtppof, a cirrus ; -rov;, -rolog, a foot. 
 
CIRRHOPODA. 353 
 
 ing so insensibly from one to another, that the precise boundary- 
 line which separates them is not always easily defined. The CIR- 
 RHOPODS, or Barnacles, upon the consideration of which we are 
 now entering, present a remarkable exemplification of this import- 
 ant fact ; and are found to be so strictly intermediate, both in 
 external configuration, and even in their anatomical construction, 
 between the HOMOGANGLIATA, which have recently occupied 
 our attention, and the great class of beings that next presents itself 
 for investigation, that these animals might, with almost equal pro- 
 priety, be located either among the Articulated or Molluscous 
 tribes of Invertebrata ; and it will not be surprising, if, after read- 
 ing the details connected with their structure, some naturalists 
 should prefer to regard them as belonging to the former rather 
 than to the latter division. The CIRRHOPODA, indeed, present a 
 strange combination of articulated limbs, united with many of the 
 external characters of a Mollusk, as will be at once evident from 
 the examination of any species of Barnacle whether sessile or pe- 
 dunculated. We select a common form, Pentalasmis vitrea, as 
 an example of the kind last mentioned. The animal in question 
 is enclosed in a shell resembling in some respects that of the com- 
 mon mussel, but composed of five distinct pieces, united together 
 by a dense intervening membrane : of these, four pieces are lateral, 
 and disposed in pairs ; while a fifth, which is single, is interposed 
 between the posterior edges of the two valves, so as to unite them 
 along the whole length of the back. Along the anterior margin 
 the valves are only partially connected by membrane, so that a long 
 fissure is left through which the articulated extremities may be 
 protruded. In place of the hinge that joins the two shells of the 
 mussel, we find the tough coriaceous membrane that unites the dif- 
 ferent shelly pieces of the integument of Pentalasmis, prolonged 
 into a cylindrical pedicle (Jig. 169, /), which is in some species 
 many inches in length, and, being attached by its extremity to any 
 submarine body, fixes the animal permanently to the same locality. 
 The external layer of this pedicle is coriaceous or almost corneous 
 in its appearance, being evidently an epidermic structure ; but, in- 
 ternally, the tube is lined with a layer of strong muscular fibres 
 arranged longitudinally (Jig. 169, m, n), which, by their contrac- 
 tion, are no doubt able to bend the flexible stem in any given 
 direction, and thus confer upon the animal a limited power of 
 changing its position when necessary. On removing one half of 
 the shelly covering, as in Jig. 167, <z, a, we expose the body of the 
 
354 
 
 CIRRHOPODA. 
 
 Cirrhopod, and discern the following particulars. The lower por- 
 tion of the body, which encloses the principal viscera (6, Z>), is soft 
 and much dilated, especi- Fig. 167. 
 
 ally towards the dorsal re- 
 gion ; this part of the ani- 
 mal is covered with a de- 
 licate membrane, beneath 
 which is a layer of whitish 
 granular substance. The 
 mouth (g) is seen upon the 
 ventral aspect, situated 
 immediately at the inferior 
 extremity of that longi- 
 tudinal fissure in the man- 
 tle through which the 
 arms are protruded : the 
 oral aperture appears to be 
 raised upon a prominent 
 tubercle, and, when atten- 
 tively examined, is found 
 to be provided with a ru- 
 dimentary apparatus of 
 jaws, presenting a distinct 
 lip furnished with minute 
 palpi, and three pairs of 
 
 mandibles, of which the two external are horny and serrated, while 
 the third remains permanently soft and membranous. Immediately 
 behind the mouth we find on each side certain pyramidal fleshy 
 appendages (d, d, d), resembling, as Hunter expressed it, a minute 
 star-fish, which no doubt constitute the branchial or respiratory 
 organs. Commencing above the mouth, we further notice on each 
 side six pairs of articulated and flexible arms, or cirrhi (Jig. 167, 
 c, c), each being composed of a series of semi-corneous pieces, and 
 exhibiting at each joint long and stiff hairs. Every pair of cirrhi 
 arises from a single prominent stem ; and those most distant from 
 the mouth being the longest and most extensile, the whole appara- 
 tus, consisting of twenty-four cirrhi, forms, when protruded from 
 the body, a kind of net of exquisite contrivance, in which passing 
 particles of nourishment are easily entangled, and thus conveyed to 
 the mouth. Lastly, on separating the cirrhiferous pedicles, we find, 
 terminating the body, and forming, as it were, a kind of tail, a long, 
 soft, and flexible organ (Jig. 169, &), the extremity of which is 
 
CIRRHOPODA. 
 
 355 
 
 perforated by a minute aperture ; but the real nature of this instru- 
 ment we shall examine by and by. 
 
 (390.) On reviewing this general description of the external con- 
 struction of Pentalasmis, the reader cannot but be struck with 
 the singular combination of characters which it exhibits. Judging 
 from its shell alone, its right to be considered as a Mollusk would 
 seem to be at once demonstrable, for, in fact, most conchologists 
 agree in claiming these animals as belonging to their own de- 
 partment ; and yet, if after removing the shell we compare the 
 animal with a Crustacean, its alliance with that class is equally 
 evident. Suppose the body (Jig. 167, &, b) to Tepresent the 
 thoracic portion of a Crustacean slightly bent upon itself, and 
 enclosed in an extensively developed thorax ;* the valves of the 
 shell would represent this thorax, which would be divided into five 
 pieces ; the first pair of cirrhi arising from the body would then 
 represent the true feet of a Crustacean ; the branchiae would 
 occupy the same position in both ; the rest of the body of the 
 Barnacle, namely, that which supports the five other pairs of feet, 
 would represent the tail of the Crustacean, and the ciliated, nata- 
 tory feet, generally connected with that part of the external skele- 
 ton : even the mouth, as the author referred to might have 
 added, with its triple series of jaws, is more nearly allied in 
 structure to that of the Crustaceans Ffc.168. 
 
 than to anything we shall meet with 
 in the structure of the oral organs of 
 true Mollusca. 
 
 (391.) But the affinity which unites 
 the Cirrhopoda to the Homogangliata 
 is not merely exemplified in the analo- 
 gies that can be pointed out between 
 the external configuration of Pentalas- 
 mis and some Crustacean forms ; the 
 nervous system even, as we might be 
 led to anticipate from the symmetrical 
 arrangement of the articulated cirrhi, 
 still exhibits the Homogangliate con- 
 dition, and, besides the supra-cesopha- 
 geal masses, forms a longitudinal chain 
 of double ganglia arranged along the 
 
 * Cuvier, MSmoire sur les Animaux des Anatifes et des Balanes, et sur leur 
 Anatomic, p. 6. 
 
 2 A2 
 
356 CIRRHOPODA. 
 
 ventral surface of the body, from which the nerves supplying the cir- 
 rhiferous arms take their origins. Four small tubercles (jig. 168),* 
 placed transversely above the oesophagus, represent the brain, and 
 give origin to four principal nerves (/?/,//), which are distribut- 
 ed to the muscles and viscera, for in such a situation organs of sense 
 would evidently be useless. Two lateral cords, derived from the 
 above, surround the oesophagus, from each of which a nerve (o, o) 
 is given off. Below the oesophagus the nervous collar terminates 
 in a pair of ganglia (A), that gives origin to the nerves supplied to 
 the first pair of arms ; and then succeeds a parallel series of double 
 ganglia (i, A:,*/, m), exactly resembling those of articulated animals, 
 from which nerves emanate that are destined to the cirrhi and sur- 
 rounding parts. 
 
 (392.) The muscular system of Pentalasmis is partly appropriat- 
 ed to the movements of the shell, and partly to the general motions 
 of the body. The shell is closed by a single transverse fasciculus 
 of muscular fibres, whereof a section is seen at e,j#g\ 167, placed 
 immediately beneath that fissure in the mantle through which the 
 arms are protruded ; it passes directly across from one valve to the 
 other, and approximates them by its contraction. 
 
 A large muscle, whose origin is seen 'm jig. 167, f, arises from 
 the interior of the mantle, and, as its fibres diverge, spreads over 
 the entire mass of the viscera ; this will evidently draw the body 
 forward, and cause the protrusion of the tentacula, while various 
 muscular slips derived from it scarcely need further description, 
 being destined to move the numerous arms with their jointed 
 cirrhi and the fleshy tubular prolongation (jig' 169, A:) already 
 noticed. 
 
 (393.) The food devoured by the Cirrhopoda would seem to con- 
 sist of various minute animals, such as small Mollusks and micros- 
 copic Crustacea, caught in the water around them by a mechanism at 
 once simple and elegant. Any one who watches the movements of 
 a living Cirrhopod will perceive that its arms, with their appended 
 cirrhi, are in perpetual movement, being alternately thrown out and 
 retracted with great rapidity ; and that, when fully expanded, the 
 plumose and flexible stems form an exquisitely beautiful apparatus, 
 admirably adapted to entangle any nutritious molecules, or minute 
 living creatures, that may happen to be present in the circum- 
 scribed space over which this singular casting-net is thrown, and 
 
 * Cuvier, Ice. cit. 
 
CIRRHOPODA. 357 
 
 drag tli em down into the vicinity of the mouth, where, being 
 seized by the jaws, they are crushed and prepared for digestion. 
 No sense but that of touch is required for the success of this 
 singular mode of fishing ; and the delicacy with which the tentacula 
 perceive the slightest contact of a foreign body, shows that they 
 are eminently sensible to tactile impressions. As regards the 
 digestive organs, we have already described the prominent mouth 
 (Jig- 169, b) 9 with its horny palpiferous lip and three pairs of 
 lateral jaws. The oesophagus (Jig. 169, c) is short, and firm in 
 its texture ; it receives the excretory ducts of two salivary glands 
 of considerable size (fig- 168, d, d), and soon terminates in a 
 capacious stomachal receptacle, the walls of which are deeply 
 sacculated and surrounded by a mass of glandular caeca (Jig. 169, d) 
 that represent the liver, and pour their secretion through numerous 
 wide apertures into the cavity of the stomach itself. The intes- 
 tine (e,/) is a simple tube, and runs along the dorsal aspect of 
 the animal, wide at its commencement, but gradually tapering 
 towards its anal extremity ; it terminates at the root of the tubular 
 prolongation (k) by a narrow orifice, into which a small bristle (g) 
 has been inserted. 
 
 (394.) Little is satisfactorily known relative to the arrangement 
 of the blood-vessels and course of the circulation in these animals. 
 Poli imagined that he had discovered a contractile dorsal vessel, 
 intimating that he had perceived its pulsations in the vicinity of 
 the anal extremity of the body ; and, although his observations upon 
 this subject have not been confirmed by subsequent investigations, 
 analogy would lead us to anticipate the existence of the heart in 
 the position indicated by the indefatigable Neapolitan zootomist. 
 The lateral appendages (Jig. 167, d, d, d) are most probably 
 proper branchial organs, but, perhaps, not exclusively the instru- 
 ments of respiration ; since the numerous cirrhi no doubt co-ope- 
 rate in exposing the blood to the action of the surrounding 
 medium, a function to which they are well-adapted by their struc- 
 ture and incessant movements; especially, as each cirrhus is seen 
 under the microscope to be traversed throughout its whole length 
 by two large vascular trunks, one apparently arterial, and the other 
 of a venous character. 
 
 (395.) With respect to the organization of the reproductive sys- 
 tem in these creatures, the most discordant opinions are expressed 
 by different writers ; no two authors agreeing either concerning the 
 names or offices which ought to be assigned to different parts of 
 
358 
 
 CIRRHOPODA. 
 
 the generative apparatus. It must therefore be our endeavour, 
 in considering this part of their economy, to separate as far as 
 practicable all conjecture and hypothetical reasoning from the 
 simple facts which anatomy has placed at our disposal, and leave 
 disputed questions to be solved by careful experiment and re- 
 search. According to the dissection of John Hunter, the internal 
 generative apparatus is double, occupying both sides of the ali- 
 mentary canal. Covering the liver (Jig. 169, d), there is found 
 a vascular substance, which Fig. 169. 
 
 the above-named illustri- 
 ous anatomist regarded as 
 probably constituting the 
 tubular parts of the testi- 
 cle, from which a tortuous 
 canal with very thick walls 
 (vas deferens) runs up- 
 wards, along the side of 
 the intestine to the root 
 of the fleshy prolongation 
 A:, at which point it is 
 joined by the correspond- 
 ing tube from the oppo- 
 site side of the body. 
 The common canal thus 
 formed is extremely slen- 
 der, and passes in a flexu- 
 ous manner through the 
 whole length of the tubu- 
 lar organ (&), named by 
 Hunter, apparently for the sake of brevity, the penis, to terminate 
 by a minute orifice at its extremity. Yet, notwithstanding the 
 name applied to the termination of the sexual canals, Hunter was 
 well convinced that the Cirripeds were hermaphrodites ; as he ex- 
 pressly says,* " It is most probable that all Barnacles are of both 
 sexes and self-impregnators ; for I could never find two kinds of 
 parts, so as to be able to say, or even suppose, the one was a 
 female, the other male." 
 
 Cuvier found the vascular mass, considered by Hunter as being 
 the tubular portion of the testis, to be composed of granules which 
 
 * Descriptive and illustrated Catalogue of the Physical Series of Comp. Anat. in 
 the Mus. of the Royal Coll. of Surgeons in London, vol. i. p. 259. 
 
CIRRHOPODA. 359 
 
 he deemed to be ova ; and conceived tlic delicate white vessel 
 seen to ramify through the ovarian mass, as represented in the 
 figure, to be the oviduct whereby the eggs were taken up and 
 conveyed into the thick and glandular canal A, from the walls 
 of which he imagined that a fecundating liquor might be secreted 
 for the impregnation of the ova in transitu. He, therefore, re- 
 garded the proboscidiform tube, Ar, as an ovipositor, whereby the 
 ova derived from both sides of the body are expelled. Before 
 scattering them abroad, as Cuvier noticed, the animal retains 
 them for a considerable length of time concealed between the 
 body and the mantle, where they form two or three irregularly 
 shaped layers. When the eggs are found in this situation, he 
 observed that the ovaria were empty and the testicles much less 
 tumid, circumstances which indicate the season of oviposition to 
 be at an end. 
 
 In opposition to the views entertained by Cuvier concerning 
 the generative process in the class before us, various continental 
 writers consider the true ovary to be contained in the cavity of 
 the tubular fleshy pedicle, which in Pentalasmis serves to fix 
 the body to the substance whereunto it is attached. This, indeed, 
 at certain periods, is found to be filled with oval granular bodies 
 of regular shape, which are apparently real ova diffused through 
 the loose cellulosity enclosed within it ; and these ova, being 
 found in different states of maturity, are apparently secreted in the 
 pedicle itself, although some authors contend that, having been 
 formed and impregnated in the manner indicated by Cuvier, they 
 are conveyed into this situation by the ovipositor, as upon this 
 assumption the prolonged organ (fig- 169, k) would be named. 
 Other anatomists, again, regard the instrument last mentioned 
 as being a real penis, and suggest that from its length it might 
 even be introduced into the peduncular cavity itself, and thus 
 effect the impregnation of the ova contained therein. 
 
 The observations of Mr. Thompson* relative to the progress 
 of the ova after their escape from the pedicle, throw much addi- 
 tional light upon this portion of our subject. " In the whole 
 tribe of Cirripeds," says this industrious naturalist, " the ova, 
 after their expulsion from the ovarium, appear to be conveyed by 
 the ovipositor into the cellular texture of the pedicle, just beneath 
 the body of the animal, which they fill to the distance of about 
 an inch. When first placed in this position, they seem to be 
 
 * Phil. Trans, for 1835, page 356. 
 
360 CIRRHOPODA. 
 
 amorphous, and inseparable from the pulpy substance in which they 
 are imbedded ; but, as they approach to maturity, they become 
 of an oval shape, pointed at both ends, and are easily detached. 
 Sir Everard Home has given a very good representation of them 
 at this stage of their progress, in his Lectures on Comparative 
 Anatomy, from the elegant pencil of Mr. Bauer." 
 
 " During the stay of the ova in the pedicle, they render this 
 part more opaque and of a bluish tint ; the ova themselves, and 
 the cellular texture in which they are surrounded, being of a pale or 
 azure blue colour. It is difficult to conceive in what manner the 
 ova are extricated from the situation above indicated ; but it is 
 certainly not by the means suggested by Sir E. Home in the 
 above-mentioned lecture, viz. by piercing outwards through the 
 membranes of the pedicle, for the ova are subsequently found 
 forming a pair of leaf-like expansions, placed between either side 
 of the body of the animal and the lining membrane of the shells. 
 These leaves have each a separate attachment at the sides of the 
 animal to the septum which divides the cavity occupied by the 
 animal from that of the pedicle : they are at first comparatively 
 small, have a rounded outline, and possess the same bluish colour 
 which the ova had in the pedicle ; but, as the ova advance in 
 progress, these leaves extend in every dimension, and lap over 
 each other on the back, passing through various lighter shades of 
 colour into pale pink, and finally, when ready to hatch, become 
 nearly white. These leaves appear to be composed of a layer 
 of ova, irregularly placed and imbedded in a kind of parenchy- 
 matous texture, out of which they readily fall, when about to hatch, 
 on its substance being torn asunder ; indeed, it appears at length 
 to become so tender as to fall entirely away, so that, after the 
 period of gestation is passed, no vestige of these leafy conceptacles 
 is to be found." 
 
 (3.96.) In the second form of CIRRHOPODA (Balani), the 
 animals, instead of being appended to foreign substances by elastic 
 and flexible pedicles, are sessile ; the shelly investment of the body 
 being in immediate contact with the rock, or other submarine 
 body, to which the Barnacle adheres. The soft tube of Penta- 
 lasmis is, in this case, represented by a strong testaceous cone 
 composed of various pieces accurately joined together, and generally 
 closed inferiorly by a calcareous plate ; while the representatives of 
 the valves of the pedunculated species form a singular opercu- 
 lum, which is moved by special muscles, and accurately shuts the 
 
CIRRHOPODA. 361 
 
 entrance of the shell when the animal retires into its abode. In 
 their general structure, however, the Balaniform Cirrhopods accord 
 with the description above given ; and, from the similarity of their 
 habits and economy, a more elaborate account of the peculiari- 
 ties which they exhibit would be superfluous in this place. 
 
 (397.) One of the most remarkable circumstances connected with 
 the history of the CIRRHOPODA, is the recently discovered fact of 
 their undergoing a distinct metamorphosis ; so that, in the earliest 
 periods of their existence, instead of being rooted by means of a 
 pedicle or otherwise, the newly hatched young are endowed with lo- 
 comotive organs, calculated to enable them to swim freely about, and 
 giving them rather the appearance of Entomostracous Crustacea, 
 than of animals of their own class. This singular fact was first 
 announced by Mr. J. V. Thompson, of Cork ;* and its correctness 
 has since been admitted by various anatomists who have devoted 
 their attention to this subject. Mr. Thompson's first observations 
 were made upon minute animals, which, although at first actually 
 taken for Crustaceans, turned out to be the young fry of Balanus 
 pusillus ; and the following is that gentleman's account of their 
 appearance and subsequent change. The young Cirrhopod is a 
 small translucent animal one-tenth of an inch long, of a somewhat 
 elliptic form, but very slightly compressed laterally, and of a brown- 
 ish tint. When in a state of repose, it resembles a very minute 
 mussel, and lies upon one of its sides at the bottom of the vessel 
 of sea-water in which it is placed ; at this time, all the members 
 of the animal are withdrawn within the shell, which appears to be 
 composed of two valves, united by a hinge along the upper part of 
 the back, and capable of opening from one end to the other along 
 the front, to give occasional exit to the limbs. The limbs are of 
 two descriptions : viz. anteriorly, a large and very strong pair pro- 
 vided with a cup-like sucker and hooks, serving solely to attach 
 the animal to rocks, stones, &c. ; and posteriorly, six pairs of na- 
 tatory members, so articulated as to act in concert, and to give a 
 very forcible stroke to the water, causing the animal, when swim- 
 ming, to advance by a succession of bounds after the same manner 
 as the water-flea (Daphnia) and other Monoculi, but particularly 
 Cyclops, whose swimming-feet are extremely analogous. The 
 tail, which is usually bent up under the belly, is short, composed 
 of two joints, and terminates in four setae, forming an instrument 
 of progression. The animal, moreover, is furnished with large 
 * Zoological Researches, 4th Memoir, 1830. 
 
362 BRACHIOPODA. 
 
 pedunculated eyes. After keeping several of the above for some 
 days in sea- water, they threw off their exuvia, and, becoming firmly 
 adherent to the bottom of the vessel, were changed into young 
 Barnacles ; and the peculiarly formed shells with their opercula 
 were soon distinctly formed, while the movements of the cirrhi, 
 although as yet imperfect, were visible. As the shell becomes 
 more complete, the eyes gradually disappear, the arms become 
 perfectly ciliated, and an animal originally natatory and locomotive, 
 and provided with a distinct organ of sight, becomes permanently 
 and immoveably fixed, and its optic apparatus obliterated. 
 
 Similar results were obtained by watching the developement of 
 the pedunculated type of Cirripeds* (Lepades), many of which 
 were proved in their earliest form to resemble different kinds of 
 Monoculi, and to be possessed of the capability of locomotion. 
 
 CHAPTER XX. 
 
 BRACHIOPODA-J" (Cuv.) ; PALLIOBRANCHIATAJ (Owen). 
 
 (398.) THE next class of Mollusca which presents itself for our 
 consideration was named by Cuvier on account of the remarkable 
 character of the organs by means of which the animals composing 
 it procure the food destined to their support. These instruments 
 consist of two long spiral arms placed on each side of the mouth, 
 that in many species can be unrolled to a considerable length, 
 and protruded to some distance, in search of aliment. The above 
 character, however, taken by itself, would scarcely warrant us in 
 considering the creatures before us as forming a separate class of 
 Mollusca ; but when, in addition to this remarkable feature in 
 their organization, we find that they possess a respiratory appa- 
 ratus peculiar to themselves, and differ widely from all other bi- 
 valves in almost every part of their structure, we feel little hesita- 
 tion in continuing to regard them as distinct, and devoting the 
 present chapter to an investigation of their anatomy. 
 
 * Phil. Trans, for 1835, page 355. 
 
 j- BgctX'*" 1 ) an arm ; jrayj, xobot, afoot. 
 
 $ Pallium, a mantle ; branchiae, gills. This name, originally proposed by Mons. 
 de Blainville, notwithstanding his belief that the spiral arms were the organs of respira- 
 tion, has since been proved by the researches of Professor Owen to be strictly appro- 
 priate to the class. 
 
JJRACHIOPODA. 363 
 
 The BRACHIOPODA inhabit bivalve shells, and for the most 
 part are suspended by a fleshy tubular pedicle, resembling that 
 of the Cirrhopods, to various submarine bodies. Such, at least, 
 is the case in Lingula and Terebratula ; Fig. 170. 
 
 but in the third genus belonging to this 
 class, namely, Orbicula, the pedicle is // .AV.^fe, \ 
 
 wanting, the lower valve of the shell be- 
 ing fixed immediately to the rock where- 
 unto the animal is attached. 
 
 On separating the testaceous valves, 
 the body of the Brachiopod is found to 
 be enclosed between two delicate mem- 
 branes, which exactly line the shell ; and 
 to these membranes, as in the case of 
 other Mollusks, the name of mantle has 
 by common consent been appropriated. 
 The mantle itself is thin and semi-transparent ; but its margins are 
 thickened, and fringed with delicate cilia, the uses of which will 
 shortly become evident. 
 
 When the two lobes of the mantle are widely divaricated, as 
 in Lingula (fig. 170), we perceive the prominent orifice of 
 the mouth (b) placed deeply between them : on each side of 
 the mouth are the two fleshy fringed arms, which in this case 
 can be protruded to a distance out of the shell, and, as Cuvier* 
 supposes, may act as oars, and thus enable the animal slightly 
 to alter the position of its body, or else, as they are most pro- 
 bably delicate organs of touch, they may perform the office of 
 highly sensible tentacula. 
 
 In Terebratula psittacea the arms are enormously developed, 
 fringed upon their outer margins, and quite free except at their 
 origins : when completely contracted, they are disposed in six or 
 seven spiral folds, and, when unfolded, they extend beyond the shell 
 twice its longitudinal diameter. The mechanism by which they 
 are unfolded is described by Professor Owen~[* as being extremely 
 simple and beautiful. The principal stem of each arm is hollow 
 from one end to the other, and contains a fluid, which, being acted 
 upon by the spirally disposed muscles forming the parietes of the 
 canal, is forcibly injected towards the extremity of the arm, and 
 the organ is thus expanded and protruded outwards. 
 
 * M6moire sur 1* Animal de la Lingule. 
 
 f Transactions of the Zoological Society, vol. i. 
 
364 BRACHIOPODA. 
 
 In Terebratula Chilensis, on the contrary, the movements of 
 the arms are extremely limited, and they can no longer be protrud- 
 ed from the shell as in the preceding species ; being connected 
 throughout their whole length with a peculiar complex testaceous 
 apparatus attached to the internal surface of the imperforate valve 
 of the shell (Jig- 171, B), the arrangement and uses of which are 
 thus described in the memoir above-mentioned. The principal 
 part of the internal framework alluded to consists of a slender flat- 
 tened, calcareous loop (y, f), the extremities of which are attached 
 to the lateral elevated ridges of the hinge : the crura of the loop di- 
 verge, but again approximate each other as they advance for a greater 
 or less distance towards the opposite margin of the valve; the loop 
 then suddenly turns towards the imperforate valve, and is bent back 
 
 Fig. 171. 
 
 upon itself for a greater or less extent in different species. The 
 loop, besides being fixed by its origins, or crura, is commonly 
 attached to two processes (</, d) going off at right angles from 
 the sides, or formed by a bifurcation of the extremity of a central 
 process (c), which is continued forwards from the hinge, but it is 
 sometimes entirely free except at its origins. The arches of the 
 loop are so slender, that, notwithstanding their calcareous nature, 
 they possess a slight degree of elasticity, and yield a little to pres- 
 sure. The interspace between the two folds of the calcareous loop 
 is filled up by a strong but extensile membrane, which binds them 
 together, and forms a protecting wall to the viscera ; the space be- 
 tween the bifurcated processes in T. Chilensis is also similarly occu- 
 pied by a strong aponeurosis. In this species the muscular stem 
 of each arm is attached to the outer sides of the loop and the inter- 
 vening membrane. They commence at the pointed processes at the 
 origin of the loop, advance along the lower portion, turn round 
 upon the upper one, are continued along it till they reach the 
 
BRACHIOPODA. 
 
 365 
 
 transverse connecting bar, where they again advance forwards, and 
 terminate by making a half-spiral twist in front of the mouth. 
 
 One use assignable to the spiral arms of the BRACHIOPODA 
 is no doubt connected with the opening of the shell, which, in 
 species provided with muscular and retractile organs of this descrip- 
 tion, is mainly effected by their forcible protrusion. In Terebra- 
 tula Chilensis, however, and other species in which the arms are 
 not extensile, Mr. Owen conceives that the elaborate internal 
 framework above described answers a similar purpose ; observing, 
 that the muscular stem, by means of its attachment to the calcareous 
 loop, has the power of acting upon that part to the extent its elasti- 
 city admits of, which is sufficient to produce such a degree of convex- 
 ity in the reflected portion of the loop as to cause it to press upon 
 the perforated valve and separate it slightly from the opposite one.* 
 
 (399.) The most obvious function, nevertheless, attributable to 
 the tentacular organs of the animals composing this class is connected 
 with the procurement of food ; for, being utterly deprived of pre- 
 hensile instruments, without some adequate contrivance these help- 
 less creatures, imprisoned in their testaceous covering, and fixed 
 immovably in one locality, would be utterly unable to obtain the 
 nourishment necessary for their support. The provision for this 
 purpose is found in the arms, whether they be extensible or attach- 
 ed to calcareous loops ; for these 
 organs, being covered by cilia, pro- 
 duce powerful currents in the sur- 
 rounding medium, which, being di- 
 rected towards the mouth as to a 
 focus, hurry into the oral aperture 
 whatever nutritive particles may 
 chance to be in the vicinity. The 
 mouth itself is a simple orifice with 
 prominent fleshy lips (Jig. 170, I), 
 but unprovided with any dental ap- 
 paratus. The alimentary canal in 
 Lingula is a long and convoluted 
 tube, but without a perceptible sto- 
 machal dilatation ; in Terebratula, A 
 however, there is a large oval stomach (fig. 172, A, d), into which 
 
 * Innumerable shells of extinct species of Brachiopoda occur in a fossil state ; and in 
 many of them (Spirifera, &c.) an internal framework, analogous in some respects to 
 that described in Terebratula Chilensis, is discernible. 
 
 Fi 
 
366 
 
 BRACHIOPODA. 
 
 numerous ducts derived from the hepatic follicles open by large 
 orifices. The structure of the liver in these animals is displayed 
 by Professor Owen in the memoir from which the annexed figures 
 are taken, and the simplicity of its organization affords an interest- 
 ing lesson to the physiologist. The hepatic organ (Jig- 172, a, c) 
 consists essentially of numerous secerning caeca (Jig. 172, B), as yet 
 easily separable from each other ; over which the visceral blood-ves- 
 sels ramify, and bring to the secreting sacculi the circulating fluid 
 from which the bile is elaborated. 
 
 (400.) The greatest peculiarity observable in the structure 
 of the Brachiopoda is seen in the arrangement of the respiratory 
 system ; for these animals, instead of possessing proper branchial 
 organs as is the case with all other Mollusca, have the mantle 
 itself converted into a respiratory surface, and traversed by the 
 ramifications of large blood-vessels, which form an elaborate arbor- 
 escence spreading through its texture, so that it is obviously well 
 adapted to perform the office assigned to it ; more especially as its 
 circumference is thickly studded with vibratile cilia, disposed in such 
 a manner that by their ceaseless movements they impel continued 
 supplies of aerated water Fig. 173. 
 
 over the whole of this vas- 
 cular membrane. The 
 lobe of the mantle which 
 lines the perforate valve 
 of Terebratula Chilensis 
 (fig> 173, c) contains four 
 large longitudinal venous 
 trunks (m, m), and two 
 others of similar dimen- 
 sions are seen in the op- 
 posite lobe a. These veins 
 take their origin by innumerable radicles from a circular canal of 
 great delicacy which encompasses the entire circumference of the 
 mantle (d) ; and it is in this canal that Mr. Owen supposes the 
 branchial arteries that may be seen to accompany the veins above 
 described terminate. The four veins which are placed in the per- 
 forated lobe of the mantle form two trunks near the visceral mass ; 
 and these, joining those of the opposite lobe, terminate in two dis- 
 tinct contractile cavities, or hearts, seen near the exterior margin of 
 the liver. The arms of the Brachiopoda, notwithstanding their 
 gill-like structure, seem to have nothing to do with the renovation 
 
BRACHIOPODA. 367 
 
 of the circulating fluids, since the cilia which fringe the margin of 
 the central stem (fig. 173, k, k) present, under the microscope, a 
 horny texture, instead of being of a vascular character, and the 
 muscular stem itself contains no blood-vessels of sufficient size to 
 indicate that the brachia are at all efficient as respiratory organs. 
 
 The course of the circulation has not been actually demonstrated, 
 but from analogy there is no room to doubt that the two hearts 
 are systemic, receiving the purified blood from the lobes of the 
 mantle, and distributing it through the body. 
 
 The nervous system of the Brachiopoda is but imperfectly 
 known. Cuvier conceived the brain of Lingula to be represented by 
 some small ganglia visible near the mouth (Jig. 170, a), but was 
 unable to follow the nerves ; and Professor Owen, in dissecting Or- 
 bicula, detected two small ganglia on each side of the oesophagus. 
 
 (401.) The muscular system in the class before us differs very 
 materially from that exhibited by any other bivalve Mollusca. 
 
 In Terebratulct) two pairs of muscles arise from each valve :* 
 those of the imperforate valve arise at a distance from each other ; 
 the anterior pair (Jig. 173, /*, f) come off fleshy just behind the 
 middle of the valve (fig- 171, B, g, g) ; they soon diminish to 
 thin shining tendons, which converge and unite below the stomach ; 
 they then again separate, and pass through the foramen of the per- 
 forate valve to be inserted into the pedicle. 
 
 The posterior pair are very short, and wholly carneous : they 
 arise from the lateral depressions in the base of the central portion 
 of the hinge (Jig- 171, B, A), and are inserted into the pedicle. 
 
 The muscles of the perforated valve arise close together, so as 
 to leave only a single muscular impression on each side (fig. 
 171, A, c) ; the anterior pair soon diminish to slender tendons, 
 and are inserted into the base of the imperforate valve ; the pos- 
 terior pass exclusively into the pedicle. 
 
 The pedicle itself consists of a peculiar tendinous-looking struc- 
 ture, enveloped in a tubular prolongation derived from the mantle. 
 
 Little is known concerning the reproduction of the Brachiopoda. 
 The ova, when present, have invariably been found lodged be- 
 tween the layers of the two lobes of the mantle ; a position analo- 
 gous to that in which we have already seen them deposited in the 
 Cirripeds ( 395) preparatory to their expulsion. No internal 
 generative system has as yet been detected ; but, notwithstanding 
 this, we are by no means prepared to assume, as some writers do, 
 
 * Professor Owen, loc. cit. 
 
368 TUNICATA. 
 
 that the ova are formed by the mantle itself in the localities where 
 they are generally met with. Future investigations, conducted 
 under more favourable circumstances, will no doubt reveal the 
 existence of some internal ovarian nidus, in which the eggs are 
 first developed, and from whence they are subsequently removed 
 to the branchial membranes ; as we shall find hereafter to be the 
 usual arrangement in other forms of bivalve Mollusca. 
 
 CHAPTER XXI. 
 
 TUNICATA.* 
 
 THE singular class of Mollusca to which the name at the head 
 of this chapter has been applied, is at once distinguished by the 
 remarkable character afforded in the texture of the external invest- 
 ment of the body. In their general organization the Tunicata 
 are very nearly allied to the ordinary inhabitants of bivalve shells, 
 with which, both in the structure and arrangement of their viscera, 
 they correspond in many particulars ; but, instead of being enclosed 
 in any calcareous covering, a strong flexible cartilaginous or coria- 
 ceous integument forms a kind of bag encasing their entire body, 
 and only presenting two comparatively narrow orifices, through 
 which a communication with the exterior is maintained. 
 
 Various are the forms under which these animals present them- 
 selves to the eye of the naturalist ; but the enumeration of them 
 will be more conveniently entered upon hereafter. We shall, 
 therefore, at once lay before the reader the principal points con- 
 nected with the structure and habits of an Ascidia belonging to 
 one of the most perfectly organized families ; and, after examining 
 this attentively, our descriptions of allied genera will be rendered 
 more simple and intelligible. The Ascidians are abundantly met 
 with upon the shores of the ocean, especially at certain seasons of 
 the year. In their natural condition they are found fixed to the 
 surfaces of rocks, sea- weed, or other submarine bodies ; frequently, 
 indeed, they are glued together in bunches, but in this case in- 
 dividuals are simply agglomerated without organic union. In- 
 capable of locomotion, and deprived of any external organs of sense, 
 few animals seem more helpless or apathetic than these apparently 
 
 * Tunicatus, clad in a tunic. 
 
TUNICATA. 
 
 369 
 
 shapeless beings ; and the anatomist is surprised to find how re- 
 markably the beauty and delicacy pig. 174t 
 of their interior contrasts with 
 their rude external appearance. 
 In the species selected for special 
 description (Phallusia mgra),the 
 external envelope (jig. 174, a, 
 a, a) is soft and gelatinous in its 
 texture, fixed at its base to a 
 piece of coral (/), and exhibiting 
 at its opposite extremity two ori- 
 fices (A, y), placed upon pro- 
 minent portions of the body. 
 Through the most elevated of 
 these orifices (h) the water re- 
 quired for respiration, and the 
 materials used as food, are taken 
 in ; while the other (f) gives 
 egress to the ova and excremen- 
 titious matter. The soft outer 
 covering is permeated by blood- 
 vessels which ramify extensively 
 in it ; it is moreover covered ex- 
 ternally with an epidermic layer, 
 and lined within by a serous vas- 
 cular membrane, which, in the 
 neighbourhood of the two orifices, 
 is reflected from it on to the 
 body of the animal lodged inside. 
 The creature hangs loosely in its 
 outer covering, to which it is only connected at the two apertures 
 by means of the reflection of the peritoneal membrane above men- 
 tioned. 
 
 (402.) On removing a portion of the exterior tunic, that in 
 reality represents the shells of a bivalve Mollusk, the soft parts of 
 the Ascidian are displayed. The body is seen to be covered with a 
 muscular investment (the mantle) (Jig. 174, b, b, c), composed of 
 longitudinal, circular, and oblique fibres, which cross each other in 
 various directions, so as to compress by their contraction the viscera 
 contained within ; and this so forcibly, that, when alarmed, the 
 animal can expel the water from its branchial sac, immediately to 
 
370 TUNICATA. 
 
 be described, in a thin continuous stream, sometimes projected to 
 a distance of many inches. 
 
 (403.) Respiration is effected in an apparatus of very peculiar 
 contrivance ; to the examination of which we must now request the 
 attention of the student. A considerable portion of the interior 
 of the body is occupied by a circumscribed cavity, that opens 
 externally by the orifice h ; into this bag a bristle has been intro- 
 duced, in the dissection represented in the figure (Jig. 174) : its 
 walls are seen to be composed of a thin but very vascular mem- 
 brane (dj d, d), that has been partially turned back, so as to dis- 
 play the interior of the respiratory sac. The membrane (Jig. 174, 
 d, d, d ; Jig. 175, e), when examined with a microscope, is found 
 to be covered with a magnificent network of blood-vessels, formed 
 by innumerable canals uniting with each other at right angles ; 
 and moreover, when seen in a living state, its surface is dis- 
 covered to be densely studded with vibratile cilia, whose rapid 
 action constantly diffuses fresh supplies of water over the whole 
 vascular membrane. The respiratory cavity has but one orifice 
 for the admission of water (Jig. 175, a) ; and this is guarded by 
 a fringe of delicate and highly sensible tentacula (fig. 175, b) ; so 
 that the water, as it is drawn into the body, having necessarily 
 to pass these tactile organs, any foreign substances which it might 
 contain of a prejudicial character are at once detected and denied 
 admission. All the vascular ramifications spread over the lining 
 membrane of the branchial chamber, are connected with two sets 
 of large vessels ; one of which, receiving the blood from the body, 
 disperses it over the spacious respiratory surface ; while the 
 other, collecting it after it has undergone exposure to the respired 
 medium, conveys it in a pure state to the heart. 
 
 (404.) The heart itself presents the simplest possible form ; be- 
 ing generally a delicate elongated contractile tube, receiving at one 
 extremity the blood derived from the numerous vessels that ramify 
 over the interior of the branchial sac, whilst at the opposite end 
 it becomes gradually attenuated into the aorta, through which it 
 impels the circulating fluid, and disperses it through the system. 
 
 The heart, above described, is extremely thin and transparent, 
 and is lodged in a distinct pericardium, which separates it from 
 the other viscera. 
 
 (405.) When we consider the fixed and immoveable condi- 
 tion of an Ascidian, and its absolute deprivation of all prehen- 
 sile instruments adapted to seize prey, it is by no means evident, 
 
TUNICATA. 
 
 371 
 
 at first sight, how it is able to subsist, or secure a supply of nour- 
 ishment adequate to its support ; neither is the structure of the 
 mouth itself, or the strange position which it occupies, at all calcu- 
 lated to lessen the surprise of the naturalist who enters upon the 
 consideration of this part of their economy. The mouth, in fact, 
 is a simple orifice, quite destitute of lips or other extensible parts, 
 and situated, not at the exterior of the body, but at the very 
 bottom of the respiratory sac (Jig. 174 and Jig. 175, g). It is 
 obvious, then, that, whatever materials are used as aliment, they 
 must be brought into the body with the water required for respi- 
 ration ; but, even when thus introduced into the branchial cavity, 
 the process by which they are conveyed to the mouth and swal- 
 lowed still requires explanation. We have before noticed that 
 the interior of the branchial chamber is covered with multitudes of 
 vibratile and closely set cilia, well described by Mr. Lister ;* 
 which, by their motion, cause currents in the water. When these 
 are in full activity, observes that gentleman in the paper referred 
 to, the effect upon the eye is that of delicately toothed oval wheels 
 revolving continually in a direction ascending on the right, and 
 descending on the left of each oval, as viewed from with- 
 out ; but the cilia themselves are very 
 much closer than the apparent teeth ; 
 and the illusion seems to be caused 
 by a fanning motion given to them in 
 regular and quick succession, which 
 will produce the appearance of waves, 
 and each wave answers here to a 
 tooth. 
 
 Whatever little substances, alive or 
 inanimate, the current of water brings 
 into the branchial sac, if not rejected 
 as unsuitable, lodge somewhere on the 
 respiratory surface, along which each 
 particle travels horizontally with a 
 steady, slow, course to the front of 
 the cavity, where it reaches a down- 
 ward stream of similar materials ; and 
 they proceed together, receiving acces- 
 sions from both sides, and enter at 
 last the 03sophagus placed at the bot- 
 
 * Phil. Trans, for 1834. page 378. 
 
 Fig. 175. 
 
372 TUNICATA. 
 
 torn (fig- 175, g), which carries them, without any effort of swal- 
 lowing, towards the stomach. 
 
 (406.) The oesophagus (Jig- 175, h) is short, and internally 
 gathered into longitudinal folds. The stomach (i) is simple, mode- 
 rately dilated, and has its walls perforated by several orifices, through 
 which the biliary secretion enters its cavity. The liver is a glandular 
 mass intimately adherent to the exterior of the stomach and the 
 intestinal canal (Jig. 174, e, e), of variable length and more or 
 less convoluted in different species, after one or two folds, termi- 
 nates in the rectum, which, emerging from the peritoneal invest- 
 ment covering the intestine, has its extremity loosely floating in the 
 cavity communicating with the second orifice (f) : into the latter a 
 bristle is introduced in the figure, having its extremity inserted into 
 the anal extremity of the digestive tube. Excrementitious matter, 
 therefore, when discharged from the rectum, escapes from the body 
 through the common excretory aperture generally situated upon 
 the least elevated protuberance of the outer covering.* It would 
 seem that the food of Ascidians consists of very minute particles 
 of organized matter ; for, although small Crustacea and other animal 
 remains have been occasionally met with in the branchial cham- 
 ber, nothing of this nature has been observed in the stomach 
 itself, and, as must be obvious to the reader, the oral aperture 
 seems but little adapted to the deglutition of bulky substances. 
 
 (407.) The reproductive system in these humble forms of Mol- 
 lusca presents the utmost simplicity of parts ; being composed of 
 an .ovarian nidus, in which the germs of their progeny are ela- 
 borated, and a duct, through which their expulsion is accomplished. 
 Nothing resembling a male apparatus has been satisfactorily indi- 
 cated ; and consequently, if in this form of hermaphrodism the 
 provision of an impregnating fluid be really indispensable to the 
 fertility of the ova, we must suppose it to be furnished by the 
 walls of the egg-passages themselves. The ovary is a whitish 
 glandular mass embedded with the liver among the folds of the 
 intestine : its position injtfg. 174 is indicated by the letter m ; and 
 at o, Jig. 175, it is seen separated from the surrounding struc- 
 tures. The oviduct, which is occasionally very tortuous, accom- 
 panies the rectum, and terminates near the anal aperture {Jig- 174, 
 m, Jig. 175, o), so that the ova ultimately escape through the 
 common excretory orifice. 
 
 (408.) Deprived as these animals are of any of the higher organs 
 
 * Cuvier ; M6moire sur les Ascidies, p. 14. 
 
TUNICATA. 373 
 
 of sense, and almost cut off from all relation with the external world, 
 we can look for no very great developement of the nervous cen- 
 tres. There is one ganglion, however, lodged in the substance of 
 the mantle, distinctly recognizable, situate in the space between the 
 branchial and excretory openings, from which large nerves are given 
 off; but of other details connected with the nervous system of 
 the TUNICATA little has been made out. 
 
 (409.) Many forms of Tunicated Mollusca are met with abun- 
 dantly in the seas of tropical latitudes, which, although allied to 
 Ascidians in the main points of their economy, present certain 
 peculiarities of structure that require brief notice in this place. 
 These, grouped by authors under the general name of Salpa, 
 are many of them so transparent that their presence in a quantity 
 of sea-water is not easily detected ; and their viscera, if coloured, 
 are readily distinguishable through their translucent integument, 
 which in texture seems to be intermediate between cartilage and 
 jelly. The body is oblong, and open at both extremities, the pos- 
 terior opening being very wide, and furnished with a crescentic valve 
 so disposed that water is freely drawn into the interior through 
 this aperture, but cannot again be expelled by the same channel ; 
 so that, being forced by the contractions of the body in powerful 
 gushes from the opposite end, it not only supplies the material for 
 respiration, but impels the delicate animal through the water in 
 a backward direction. The branchial chamber of Ascidia is con- 
 sequently in this case represented by a wide membranous canal, 
 which traverses the body from end to end ; but, instead of the 
 network of vessels lining the respiratory sac of Ascidians, a sin- 
 gular kind of branchial organ is placed within it. This consists 
 of a long vascular riband attached by both its extremities to the 
 walls of the canal through which the water rushes, and of course, 
 being freely exposed to the influence of the surrounding medium, 
 the blood contained in this curious branchial apparatus is perpe- 
 tually renovated, and afterwards distributed, by a heart resembling 
 that met with in the genus last described, to all parts of the body. 
 
 The viscera, which occupy comparatively a very small space, 
 are lodged in a distinct compartment between the membranous 
 respiratory channel and the external gelatinous investment, or soft 
 shell, as we might properly term it. The mouth is a simple 
 aperture, situated near the upper extremity of the branchial organ ; 
 and probably, as in Ascidia, ciliary currents rushing over the re- 
 spiratory surface bring into it a sufficient supply of nutritive mole- 
 
374 
 
 TUNICATA. 
 
 cules : the stomach is capacious, and covered with parallel rows of 
 large white filaments, that seemingly represent the liver ; and 
 the alimentary canal, which is perfectly simple, runs to the pos- 
 terior extremity of the animal, and terminates there by a wide 
 opening.* Two oblong bodies, each consisting of a granular 
 substance, are seen upon the ventral surface of the body lodged 
 between the external and internal membranes, which no doubt 
 are the ovaria, and form a reproductive system as devoid of com- 
 plication as that of the sessile Ascidians. 
 
 (410.) A very remarkable feature in the history of these animals 
 is, that many species are found swimming together in long chains, 
 apparently adhering to each other by little suckers, but without 
 organic connexion ; and, what is still more strange, it would appear, 
 from the observations of M. de Chamisso,'j" that such aggregated 
 animals give birth to insulated individuals of very different ap- 
 pearance, which in their turn reproduce concatenated forms re- 
 sembling their progenitors, so that the alternate generations are 
 quite dissimilar both in conformation and habits. 
 
 The last families of TUNICATA which we have to notice, would 
 seem to constitute a connecting link between the MOLLUSCA 
 and the BRYOZOA, which latter in many points of their anatomy 
 they much resemble. These animals generally are exceedingly 
 minute, and individually present an organization analogous to that 
 of Ascidians. At first it would appear that they are detached 
 from each other, and, like Salpa, are endowed with a power of 
 locomotion ; but subsequently they become aggregated in groups, 
 either incrusting foreign bodies, or else, uniting together to form a 
 mass of definite shape, they seem to enjoy to a certain extent a com- 
 munity of action. They are arranged by Cuvier^: in three princi- 
 pal groups, distinguished by the following characters. In the first 
 (Botryllus), the little bodies of the individual animals are ovoid ; 
 but they fix themselves upon the exterior of sea-weed or other 
 substances in regular bunches, consisting of ten or twelve, arranged 
 like the rays of a star around a common centre. The branchial 
 orifices in such are all placed around the circumference of the star, 
 while the excretory apertures open into a common cavity in the 
 
 * For excellent drawings, representing the anatomy of various Salpae, the reader 
 is referred to the Descriptive and Illustrated Catalogue of the Physiol. Series of Comp. 
 Anat. contained in the Mus. of the Royal Coll. of Surgeons, London, vol. i. plates 
 6 and 7. f Dissert, de Salp&, Berlin, 1830. 
 
 t Regne Animal, vol. iii. p. 168. Bar^t/f, bunch of grapes. 
 
CONCHIFERA. 375 
 
 centre. If tlie external orifice is irritated, the animal to which 
 it belongs alone contracts ; but, if the centre be touched, they 
 all shrink at once. 
 
 In Pyrosoma,* the second family, the animals are aggregated 
 together in great numbers, so as to form a hollow cylinder, open 
 at one end but closed at the opposite, which swims in the sea by 
 the combined contractions and dilatations of all the individuals 
 composing it. The branchial sacs here open upon the exterior 
 of the cylinder, while the anal orifices are in its internal cavity. 
 Thus, a Pyrosoma might be described as consisting of a great 
 number of stars of Botrylli piled one above the other, the whole 
 mass remaining free and capable of locomotion. Many of these 
 moving aggregations of Tunicata emit in the dark a most brilliant 
 phosphorescent light, whence the derivation of the name by which 
 they are distinguished. 
 
 In all other forms of these aggregated Mollusca, which are desig- 
 nated by the general name of Polyclinum^ as in ordinary Ascidi- 
 ans, the anus and branchial orifices are approximated, and placed at 
 the same extremity of the body. They are all fixed; some spreading 
 like fleshy crusts over submarine substances, others forming conical 
 or globular masses, or occasionally so grouped as to produce an 
 expanded disc resembling a flower or an Actinia ; but, whatever 
 the general arrangement of the common mass, it is composed of 
 numerous associated individuals, every one of them corresponding 
 more or less closely as regards their internal structure with the de- 
 scription above given of the organization of Salpse and Ascidians. 
 
 CHAPTER XXII. 
 
 CONCHIFERA (Lamarck) ; ACEPHALES TEST ACES (Cuv.) 
 
 THE great majority of Mollusks which inhabit bivalve shells con- 
 stitute a very numerous and extensive class, distinguished by certain 
 characters possessed by them in common. Encased in dense and 
 massive coverings of such construction as to preclude the possi- 
 bility of their .maintaining more than a very imperfect intercourse 
 
 * ri/, -9s t jire ; ffuftai, a body. -f- vol.vs, many ; xXivn, a bed. 
 
376 
 
 CONCHIFERA. 
 
 with the external world, and deprived even of the means of com- 
 munication with each other, we might naturally expect their or- 
 ganization to correspond in its general feebleness with the cir- 
 cumscribed means of enjoyment and limited capabilities of loco- 
 motion allotted to them. Numerous species, indeed, are from the 
 period of their birth firmly fixed to the rock which gives them 
 support, by a calcareous exudation that cements their shells to its 
 surface, as is familiarly exemplified in the case of the common 
 Oyster ; or else, as the Mussels, anchor themselves securely and 
 immoveably by unyielding cables of their own construction. The 
 Scallop, unattached, but scarcely better adapted for changing its 
 position, rudely flaps together the valves of its expanded shell, 
 and thus by repeated jerks succeeds in effecting a retrogressive 
 movement ; while the Cockles, destined to burrow in the sand, 
 are furnished with a tongue-like foot, by which they dig the holes 
 wherein they lie concealed, and crawl, or even leap about, upon 
 the shore. Many, as the Pholades, penetrate the solid rocks and 
 stones, and excavate therein the caverns that they inhabit ; or, 
 in the case of the Teredo, with dangerous industry bore into the 
 bottoms of ships or submerged wood of any description, and 
 silently destroy by their insidious ravages the piers or dikes which 
 human labour has erected. 
 
 (411.) Following our usual custom, we shall select for examina- 
 tion one of the most simply organized bivalves for the purpose of 
 illustrating the general structure which characterizes the class ; 
 and in the common Scallop (Pecten Jacobtea) we have a species 
 well adapted to exhibit the principal features of their economy. 
 On separating the two valves of the shell in the animal before us, 
 we at once perceive that each is lined internally with a thin and 
 semitransparent membrane (fig- 176, a, A), which, like the shells, 
 encloses the body of the Mollusk in the same way that the leaves 
 of a book are contained between its covers. The circumference 
 of these outer membranes, which form the mantle, is, in this case, 
 quite free and unconnected, except in the immediate vicinity 
 of the hinge that unites the two valves. The borders of the 
 mantle are thickened, and surrounded with a delicate fringe of 
 retractile filaments ; they moreover present a decided glandular 
 appearance, and secrete colouring matter of various tints, similar 
 to those seen upon the exterior of the shell : the glandular 
 margins of the mantle form in fact the apparatus by which 
 the extension of the shell is effected, and by them its outer 
 
CONCHIFERA. 
 
 377 
 
 layer is secreted, and in many cases painted with gorgeous hues, 
 as will be explained more at large hereafter. 
 
 Fig. 176. 
 
 Between the lobes of the mantle are seen the branchiae (b, g) 9 
 always consisting of four delicate leaves, composed of radiating 
 fibres of exquisite structure, and generally attached to the circum- 
 ference of the body by their fixed extremities, but elsewhere per- 
 fectly free, so as to float loosely in the water, which finds free 
 admission to them. The mouth (/) is situated between the two 
 inner laminae of the branchiae, in a kind of hood formed by the 
 union of the gills at their origin ; it is a simple orifice, without any 
 kind of dental apparatus, but bordered by four thin and mem- 
 branous lips (k) placed on each side of the aperture. 
 
 The valves, which are opened by the elasticity of a compressible 
 ligament interposed between them at the hinge, are closed by 
 the contraction of a powerful muscle (c), which passes directly 
 from one to the other, and around this adductor muscle the viscera 
 of the body are disposed : the stomach, liver, and generative 
 system are imbedded in the mass, d, e,y ; the convolutions of the 
 intestine may be traced occasionally (w, o) ; and the termination 
 of the rectum, m, is visible externally, situated upon that side of 
 the adductor muscle which is opposite to the mouth. In the 
 neighbourhood of the oral aperture is placed a retractile fleshy 
 
378 CONCHIFERA. 
 
 organ (i), which, although in Pecten it exhibits very rudimentary 
 dimensions, expands in other species to such a size as richly to 
 merit the name of foot usually applied to it. 
 
 (412.) Whoever for a moment reflects upon the arrangement of 
 the branchial apparatus, and the position of the oral orifice, consist- 
 ing, as it does, of a simple aperture unprovided with any prehensile 
 organs, must perceive that there are two circumstances connected 
 with the economy of a conchiferous Mollusk, and those not of 
 secondary importance, by no means easily accounted for. It is, 
 in the first place, absolutely essential to the existence of these 
 animals that the element in immediate contact with the respiratory 
 surfaces should be renewed as rapidly as it becomes deteriorated, 
 or suffocation would inevitably be the speedy result of an in- 
 adequate supply of fresh and aerated water ; to secure which, 
 especially when the valves of the shell are closed, no adequate 
 provision seems to exist. Secondly, it is natural to enquire, 
 how is food conveyed into the mouth ? for in an animal, itself 
 fixed and motionless, and at the same time, as in the case of the 
 creature we are now considering, quite deprived of any means 
 of seizing prey, or even of protruding any part of its body beyond 
 the margins of its abode in search of provision, it is not easy to 
 imagine by what procedure a due supply of nutriment is secured. 
 Wonderful, indeed, is the elaborate mechanism employed to effect 
 the double purpose of renewing the respired fluid, and feeding 
 the helpless inhabitant of these shells. Every filament of the 
 branchial fringe, examined under a powerful microscope, is found 
 to be covered with countless cilia in constant vibration, causing 
 by their united efforts powerful and rapid currents, which, sweep- 
 ing over the entire surface of the gills, hurry towards the mouth 
 whatever floating animalcules or nutritious particles may be brought 
 within the limits of their action, and thus bring streams of nu- 
 tritive molecules to the very aperture through which they are 
 conveyed into the stomach, the lips and labial fringes acting as 
 sentinels to admit or refuse entrance as the matter supplied be 
 of a wholesome or pernicious character. So energetic, indeed, 
 is the ciliary movement over the entire extent of the branchial 
 organs, that, if any portion of the gills be cut off with a pair of 
 scissors, it immediately swims away, and continues to row itself 
 in a given direction as long as the cilia upon its surface continue 
 their mysterious movements. 
 
 (413.) Our next investigations must be concerning the internal 
 
CONCHIFERA. 
 
 379 
 
 anatomy of tlie CONCHIFEROUS MOLLUSCA. In the Oyster, the 
 general disposition of the body resembles that of the Pecten 
 described above ; and the mouth, enclosed between two pairs of 
 delicate lips, occupies a similar position at the termination of the 
 branchial lamellae. In this well-known Mollusk the (esophagus 
 is extremely short, so that the mouth appears to open at once 
 into the stomachal cavity (Jig. 177, a), which is imbedded in the 
 substance of the liver (d), ; the biliary secretion being poured into 
 the stomach itself through several large orifices represented in 
 the figure. A very peculiar arrangement exists in the stomachs 
 of many genera, the digestive cavity being prolonged in one di- 
 rection, so as to form a lengthened caecum, or blind sacculus, 
 wherein is lodged a cartilaginous styliform body, the use of which 
 it is not easy to conjecture, although its office is no doubt con- 
 nected in some way or other with the preparation of the food. 
 
 Fig. 177. 
 
 The liver is propor- 
 
 tionately of large di- 
 
 mensions, and is at 
 
 once recognized by 
 
 its greenish, or, in 
 
 some cases, dark cho- 
 
 colate colour ; it is 
 
 entirely separable in- 
 
 to masses of secern- 
 
 ing follicles loosely 
 
 connected together 
 
 by a delicate cellu- 
 
 losity. The intes- 
 
 tine varies consider- 
 
 ably in extent, and, 
 
 as a necessary con- 
 
 sequence, in the ar- 
 
 rangement and num- 
 
 ber of its convolutions. In the Oyster it is comparatively short, 
 
 bending twice upon itself, and winding around the stomach and 
 
 adductor muscle (6, c, d,f) ; its termination (g) projecting between 
 
 the folds of the mantle upon the opposite side of the body to that 
 
 where the mouth is situated, and so disposed that excrementitious 
 
 matter is cast out beyond the influence of the ciliary currents. In 
 
 Pecten we have already noticed that it performs sundry gyrations 
 
 through the visceral mass, as well as about the muscle that closes 
 
380 
 
 CONCHIFERA. 
 
 the shell (Jig. 176, o, w, m) ; while in the cockle tribes it even 
 penetrates the base of the foot, and winds extensively through its 
 muscular substance (fig. 182). In the greater number of the 
 Conchifera, but not in the Oyster tribe, there is a very remarkable 
 circumstance connected with the course of the intestine, the object 
 of which is involved in obscurity ; the rectum, at some distance from 
 its termination, passes right through the centre of the ventricle of 
 the heart, its coats being tightly embraced by the muscular parietes 
 of that viscus. 
 
 (414.) The position of the branchiae in the Ostracean family has 
 been already described ; it now remains, therefore, to notice their inti- 
 mate structure, and the arrangement of the vessels connected with 
 respiration and the circulation of the blood. The branchial fringes 
 are of course essentially vascular in their composition ; being, in 
 fact, made up of innumerable delicate parallel vessels enclosed in 
 cellular tissue of extreme delicacy, and exposing a very extensive 
 surface to the influence of the respired medium. The countless 
 branchial canals through which the blood is thus distributed termi- 
 nate in large vessels enclosed in the stems to which the fixed extremi- 
 ties of the vascular fringe are attached (fig. 178,/, g, A, i) ; these 
 communicate extensively with each other, and, ultimately uniting in 
 two principal trunks (e, &), pour the purified blood derived from 
 the whole branchial apparatus into the auricle of the heart. 
 
 The heart in the Oyster Figf 178> 
 
 (fig. 177, n-> o) is situat- 
 ed in a cavity between the 
 folds of the intestine and 
 the adductor muscle ; in 
 which position, from the 
 dark purple colour which it 
 exhibits, it is at once dis- 
 tinguished. It consists, in 
 the species we are more 
 particularly describing, of 
 two distinct chambers, an 
 auricle and a ventricle. The 
 auricular cavity (fig. 178, 
 b), the walls of which are 
 extremely thin, and com- 
 posed of most delicate fas- 
 ciculi of muscular fibres, re- 
 
CONCHIFERA. 381 
 
 ceives the blood from the respiratory apparatus, and by its con- 
 traction transmits it through two intermediate canals (c) into the 
 more muscular ventricle (d), whence it is propelled through the 
 body by the ramifications of the arterial system (w, o, p). 
 
 The above description of the circulatory apparatus as it exists 
 in the Oyster is applicable in all essential points to every family of 
 conchiferous Mollusca ; but there are important modifications in 
 the structure of the heart and arrangement of the blood-vessels, 
 met with in different genera, which now demand our attention. 
 Most generally, in consequence of the broad and dilated form of 
 the animals, instead of a single auricle, such as the Oyster has, 
 there are two auricular cavities, one appropriated to each pair of 
 branchial lamellae, and placed symmetrically on the two sides of 
 an elongated fusiform ventricle, into which both the auricles empty 
 themselves, still the course of the blood is similar to what we have 
 described above. 
 
 A still greater modification is found to exist in those species 
 most remarkable for their breadth. In Area, for example, there 
 are not only two auricles, but two ventricles likewise, placed upon 
 the opposite sides of the body ; that is, there is a distinct heart 
 appropriated to each pair of gills, each receiving the blood from the 
 branchiae to which it belongs, and propelling it through vessels 
 common to both hearts, to all parts of the system. 
 
 (415.) We must now, before entering upon the description of 
 other families of Conchifera, examine the character of the locomotive 
 apparatus with which those possessed of the power of moving about 
 are furnished. The instrument employed for this purpose is a 
 fleshy organ appended to the anterior part of the body, called the 
 foot ; but of this apparatus, for obvious reasons, no vestige is met 
 with in the fixed and immoveable Oyster, and even in the Scallop 
 we have seen only a rudiment of such an appendage. When 
 largely developed, as in Mactra (figs. 179, 180), the foot forms a 
 very important part of the animal, and becomes useful for various 
 and widely different purposes. In structure it almost exactly 
 resembles the tongue of a quadruped, being entirely made up of 
 layers of muscles crossing each other at various angles ; the ex- 
 ternal layers being circular or oblique in their disposition, while 
 the internal strata are disposed longitudinally. In the Cockle tribe 
 (Cardium) this organ attains to a very great size, and on inspect- 
 ing the figure given in a subsequent page, representing a dissection 
 of the foot of Cardium rusticum (Jig. 182), the complexity of 
 
CONCHIFERA. 
 
 its muscular structure will be at once evident, and the disposition 
 of the several layers composing it more easily understood than 
 from the most elaborate verbal description. 
 
 (416.) Diverse are the uses to which the foot may be turned. 
 It is generally used for burrowing in the sand or soft mud ; and, 
 by its constant and worm-like action, those species in which it is 
 largely developed can bury themselves with facility, and make 
 their way beneath the sand with a dexterity not a little remark- 
 able. Perhaps, the most efficient burro wers met with upon our 
 own shores are the Razor-shells (*$WewzW<z), in which family the 
 fleshy foot attains to enormous proportions ; and the rapidity of 
 their movements beneath the soil will be best appreciated by those 
 who may have watched the manner in which the fishermen effect 
 their capture. 
 
 The Solen excavates for itself a very deep hole in the sand, bor- 
 ing its way by means of its foot to a depth of some feet ; and re- 
 mains concealed in this retreat, usually occupying a position within 
 a few inches from the surface. The fisherman, armed with a slen- 
 der iron rod, furnished with a barbed head, resembling a harpoon, 
 treads carefully backwards over the beach left bare by the retreat- 
 ing tide, and finds the holes in which Solen lodges, by watching 
 the little jet of water thrown out by the animal, when, being alarm- 
 ed by the shaking of the sand, it contracts its body. Guided by 
 the orifice through which the water is thrown, he plunges his rod 
 into the sand, and generally succeeds in piercing the animal with 
 the barbed extremity, and dragging it from its concealment ; but, 
 should he fail in his first attempt, he well knows that to try again 
 would be unavailing, for the animal instantly works its way down 
 to such a distance as to render pursuit hopeless. 
 
 But, however efficient, as a means of burrowing, the foot may 
 be, it can be turned to other purposes. The Pholades, for, example, 
 by some means, either of a mechanical or chemical nature, not 
 as yet precisely determined, excavate the solid rocks, and form 
 therein chambers, in which they pass their lives. In such genera, 
 the foot, which would be useless as a boring instrument, by being 
 simply transformed into a broad and flat disc, becomes a powerful 
 sucker, whereby the Pholas fixes itself to the walls of its apart- 
 ment in any convenient situation. 
 
 In many of the Cockle tribe we find the foot converted into 
 an instrument of locomotion, of a very singular description, en- 
 abling the cardiaceous Conchifera to leap by bounds we should 
 
CONCHIFERA. 883 
 
 scarcely expect animals so unwieldy to be capable of executing. 
 For this purpose the end of the foot is bent, and placed firmly 
 against the plane of support in the position represented in 
 Jig. 181 ; when thus fixed, a sudden spring-like action of the 
 muscles of the foot throws the cockle into the air, and, by a repe- 
 tition of these exertions, the creature can skip about with surpris- 
 ing agility. 
 
 (417.) But the most extraordinary office assigned to the foot in 
 the class under consideration, is the manufacture of horny threads, 
 whereby, as by so many anchors, the Mollusca thus provided 
 fix themselves securely to foreign bodies, and that so firmly, that 
 extraordinary violence is requisite to wrench such animals from the 
 place where they have fixed their cables. The marine Mussel is a 
 well-known example of a byssiferous Mollusk, and from this species, 
 therefore, we shall draw our description of the organs by which the 
 tough filaments referred to are secreted. 
 
 The foot in the Mussel is of small dimensions, being useless 
 as an instrument of progression. By its inferior aspect it gives 
 attachment to the horny threads of the byssus, which are individu- 
 ally about half an inch in length, or as long as the foot itself, 
 by which, in fact, they are formed, in a manner quite peculiar to 
 certain families of Conchifera ; no other animals presenting a se- 
 creting apparatus at all analogous, either in structure or office, to 
 that with which these creatures are provided. The manner in 
 which the manufacture of the byssus is accomplished is as fol- 
 lows : A deep groove runs along the under surface of the foot, 
 at the bottom of which thin horny filaments are formed by an 
 exudation of a peculiar substance, that soon hardens and assumes 
 the requisite tenacity and firmness. While still soft, the Mussel, 
 by means of its foot, applies the extremity of the filament, which 
 is dilated into a kind of little sucker, to the foreign substance 
 whereunto it wishes to adhere, and fastens it securely. Having 
 accomplished this, the foot is retracted ; and the thread, of course, 
 being drawn out of the furrow where it was secreted, is added to 
 the bundle of byssus previously existing, all of which owed its 
 origin to a similar process. 
 
 Sometimes, instead of the numerous thin filaments met with 
 in the Mussel, the byssus consists of a single, thick, horny stem ; 
 while in other cases, as, for example, in Pinna, the threads are so 
 numerous, soft, and delicate, that they are not unfrequently spun 
 like silk, and manufactured into gloves and other small articles 
 
384 CONCHIFERA. 
 
 of dress, not unfrequently met with in the cabinets of concho- 
 logists. 
 
 (418.) Taking a more general view of the Conchiferous Mollusca 
 than we have hitherto done, we shall now proceed to consider the me- 
 chanism for opening and closing the valves of the shell in which 
 they reside ; an operation effected in a very simple and elegant 
 manner. 
 
 The shells are connected posteriorly by means of a hinge 
 differently constructed in different species. In the Oyster we have 
 an instance of the most simple kind of junction. In these Mol- 
 lusca a mass of elastic ligament, composed of perpendicular and 
 parallel fibres, is interposed between the posterior edges of the 
 shell, and so disposed, that by closing the shell the ligamentous 
 mass is forcibly compressed while at the same time its resiliancy 
 is such, that, immediately the compressing power is withdrawn, it 
 expands, and thus forms a simple spring calculated to keep the 
 valves apart, and cause their separation to a greater or less extent. 
 
 The antagonist to this elastic force is the adductor muscle 
 (jig. 176, c), a fleshy mass of very great strength, the fibres of 
 which pass directly from one valve to the opposite. The adductor 
 muscle, although in this case single, consists of two portions of dif- 
 ferent texture (Jig. 177, /, m) ; so that it would appear to be formed 
 by two muscles closely approximated, so as to compose a single power- 
 ful mass adapted to keep the valves in contact with a force propor- 
 tioned to its massive size. All those species having a single muscular 
 mass, such as the Oyster and Pecten, have been grouped together 
 by conchologists under the general name MONOMYARIA, while 
 another and more numerous division DIMYARIA, is characterized by 
 having two adductor muscles distinct and widely removed from 
 each other. The Mussel tribe and many others are examples of 
 this arrangement which is represented in subsequent figures. 
 
 Simple as the structure of the hinge is in the Ostracea, in other 
 Bivalves it frequently exhibits far greater complexity, and the op- 
 posed valves present prominent elevations and deep fossse which 
 lock into each other, and thus form a very secure articulation of 
 great strength and solidity. In such cases the arrangement of the 
 elastic ligament for opening the valves is slightly modified, being 
 placed externally instead of within the shell, but its action in 
 antagonizing the adductor muscles is still equally efficacious. 
 
 (419.) We must, in the next place, solicit the attention of the 
 reader to a very important subject connected with the economy of this 
 
CONCHIFERA. 385 
 
 class of Mollusks, viz. the growth and formation of their shells. 
 Infinitely diversified are the forms presented by their testaceous 
 valves, and equally various the colours which not unfrequently adorn 
 their external surfaces. Some exhibit a beauty and delicacy of 
 sculpture of a most exquisite character ; others, covered with large 
 spines, or festoons of calcareous plates, puzzle the beholder to 
 comprehend how the growth of such parts, in the situations which 
 they occupy, can be effected with so much regularity of arrange- 
 ment. The shells themselves are absolutely deprived of vitality, 
 permeated by no vessels, and as incapable of expansion by any 
 internal power as the rocks to which they are not uncommonly 
 attached ; so that the young naturalist is necessarily at a loss to 
 conceive either the mode of their formation, or the origin of all 
 the gaudy tints and external decorations that render them the 
 ornaments of our cabinets. 
 
 The simple apparatus by means of which shells are constructed 
 is the external membranous layer that invests the body of the 
 mollusk, the mantle, as it has been termed ; and, whatever the 
 form of the shell, it owes its origin entirely to this delicate organ. 
 
 In order to simplify as much as possible our description of 
 the process whereby the shell is formed, it will be necessary to 
 consider it under two points of view : first, as relates to the en- 
 largement of the valves in length and breadth ; and secondly, as 
 regards their increase in thickness, very different parts of the 
 mantle being employed in the attainment of these two ends. 
 
 It is the circumference, or thickened margin of the mantle, 
 alone, which provides for the increase of the shell in superficial 
 extent. On examining this part (Jig. 176, hfjig. 177, e), it is found 
 to be of a glandular character, and moreover not unfrequently pro- 
 vided with a delicate and highly sensitive fringe of minute ten- 
 tacula. Considered more attentively, it is seen to contain in its sub- 
 stance patches of different colours, corresponding both in tint and 
 relative position with those that decorate the exterior of the shell. 
 
 When the animal is engaged in increasing the dimensions of 
 its abode, the margin of the mantle is protruded, and firmly ad- 
 herent all round to the circumference of the valve with which it 
 corresponds. Thus circumstanced, it secretes calcareous matter, and 
 deposits it in a soft state upon the extreme edge of the shell, where 
 the secretion hardens and becomes converted into a layer of solid 
 testaceous substance. At intervals this process is repeated, and 
 every newly-formed layer enlarges the diameter of the valve. The 
 
386 CONCHIFERA. 
 
 concentric strata thus deposited remain distinguishable externally, 
 and thus the lines of growth marking the progressive increase of 
 size may easily be traced (fig> 179). 
 
 It appears that at certain times the deposition of calcareous sub- 
 stance from the fringed circumference of the mantle is much more 
 abundant than at others : in this case ridges are formed at distinct 
 intervals ; or, if the border of the mantle at such periods shoots out 
 beyond its usual position, broad plates of shell, or spines of differ- 
 ent lengths, are secreted, which, remaining permanent, indicate, by 
 the interspaces separating successively deposited growths of this 
 description, the periodical stimulus to increased action that caused 
 their formation. 
 
 (420.) Whatever thickness the shell may subsequently attain, 
 the external surface is thus exclusively composed of layers de- 
 posited in succession by the margin of the mantle ; and, seeing 
 that this is the case, nothing is more easy than to understand how 
 the colours seen upon the exterior of the shell are deposited, and 
 assume that definite arrangement characteristic of the species. 
 We have already said that the border of the mantle contains, in 
 its substance, coloured spots : these, when minutely examined, are 
 found to be of a glandular character, and to owe their peculiar 
 colours to a pigment secreted by themselves ; the pigment so fur- 
 nished being therefore mixed up with the calcareous matter at the 
 time of its deposition, coloured lines are formed upon the exterior 
 of the shell wherever these glandular organs exist. If the deposi- 
 tion of colour from the glands be kept up without remission during 
 the enlargement of the shell, the lines upon its surface are continu- 
 ous and unbroken; but if the pigment be furnished only at intervals, 
 spots or coloured patches of regular form, and gradually increasing 
 in size with the growth of the mantle, recur in a longitudinal 
 series wherever the paint-secreting glands are met with. 
 
 (421.) The carbonate of lime, for such is the earth whereof the 
 shells of bivalves are principally composed, is, at the moment of 
 its deposition, embedded in a viscid secretion that forms a kind of 
 cement ; and on dissolving the shell in a dilute acid, the animal 
 material thus produced remains in the shape of a delicate cellu- 
 losity, in the interstices of which the chalky particles had been 
 entangled. If the proportion of the above-mentioned secretion be 
 abundant, it not unfrequently, by hardening on the exterior of the 
 shell, constitutes what has been very inaptly termed its epidermis, 
 representing a comparatively soft external skin of semicorneous 
 
CONCHIFERA. 387 
 
 texture. If exceedingly thick, the epidermic layer thus formed 
 becomes loose and shaggy, giving the shell a hirsute appearance ; 
 but, both in its structure and origin, such pilose investment has no 
 claim to be considered analogous to the hair of animals possessing 
 an epidermis properly so called. 
 
 While the margin of the mantle is thus the sole agent in en- 
 larging the circumference of the shell, its growth in thickness is 
 accomplished by a secretion of a kind of calcareous varnish, derived 
 from the external surface of the mantle generally ; which, being 
 deposited layer by layer over the whole interior of the previously 
 existing shell, progressively adds to its weight and solidity. There 
 is, moreover, a remarkable difference between the character of the 
 material secreted by the marginal fringe, and that furnished by the 
 general surface of the pallial membrane ; the former we have found 
 to be more or less coloured by glands appointed for the purpose, 
 situated in the circumference of the mantle ; but as these glands do 
 not exist elsewhere, no colouring matter is ever mixed with the layers 
 that increase the thickness of the shell, so that the latter always re- 
 main of a delicate white hue, and form the well-known iridescent ma- 
 terial usually distinguished by the name of nacre, or mother of pearl. 
 
 (422.) Local irritation of various kinds is found to stimulate the 
 mantle to increased action, so as to cause the pearly matter to be 
 secreted more abundantly at the part irritated. Thus there are 
 various minute boring annelidans that, in the exercise of their usual 
 habits, perforate the shells of oysters, and penetrate even to the 
 soft parts of their bodies. Stimulated by the presence of these 
 intruders, the mantle beneath the place attacked secretes nacre in 
 inordinate quantities to repair the injured portion of the shell, and 
 prominent nuclei are soon formed, which, enlarging by the addition 
 of continually added layers of nacreous matter, become so many 
 pearls adherent to the interior of the shelly valves. 
 
 Or pearls may owe their origin to another cause : It not unfre- 
 quently happens that sharp angular substances, such as grains of 
 sand or fragments of stone, are conveyed between the valves, and 
 become embedded in the delicate tissue of the mantle. Thus irri- 
 tated, the mantle throws out copiously the peculiar iridescent mate- 
 rial which it secretes, and with it coats over the cause of annoyance, 
 wrapping it in numerous concentric laminae of nacre, and thus form- 
 ing the detached and globular pearls so valuable in commerce. 
 
 (423.) One other circumstance connected with the growth of 
 bivalve shells requires explanation. From the earliest appearance 
 
388 CONCHIFEllA. 
 
 of the shelly valves until the period when the included mollusks 
 arrive at their mature size, the adductor muscle or muscles have 
 been of necessity perpetually changing their position, advancing 
 gradually forward as the enlargement of the shells was accomplished, 
 so as to maintain in the adult precisely the same relative situations 
 as they originally did in the young and as yet minute animal. 
 Taking the Oyster for an example, it is quite obvious that the 
 adductor muscle, which at first was connected with the thin and 
 minute lamellae forming the earliest shell, has, during the entire 
 growth of the animal, become further removed from the hinge, and 
 transferred from layer to layer as the shell increased in thickness, 
 till it arrives at the position occupied by it in connection with the 
 last-formed stratum that lines the interior of the ponderous valves 
 of the full-grown oyster. The manner in which this progressive 
 advance of the adductor muscle is effected is not at first easily 
 accounted for, seeing that it is always fixed and firmly adherent at 
 all points of its attachment. In order to understand the circum- 
 stances connected with its apparent removal, it is necessary to 
 premise that a thin layer of the mantle itself is interposed between 
 the extremities of the muscle and the inner surface of the shell, 
 forming the bond of connection between the two, and, like the rest 
 of the pallia! membrane, assisting in increasing the thickness of the 
 shell by adding layers of nacre to its inner surface. Particle after 
 particle is laid on by a kind of interstitial deposit between the 
 mantle and the extremity of the adductor muscle, but so gradually, 
 that the firm attachment between the muscle and the shell is not 
 at all interfered with ; and as the animal grows the transference of 
 the muscle from layer to layer is thus slowly and imperceptibly 
 effected. 
 
 (424.) We have, as yet, limited ourselves almost exclusively to 
 a description of the simplest forms of CONCHIFERA, namely, those 
 belonging to the Ostracean family, which, being generally inca- 
 pable of locomotion, are deprived of a foot, and are recognisable 
 by having the two lobes of the mantle unconnected w^th each other 
 around their entire circumference. On turning our attention to 
 the organization of the mantle in other families, we find that 
 in them it no longer offers the same simple arrangement ; but, 
 the two lobes becoming gradually more and more completely 
 united along their edges, the bodies of the mollusks are by de- 
 grees enclosed by the pallial membranes, and seem, as it were, 
 sacculated ; moreover, sometimes the mantle is prolonged into 
 
CONCHIFERA. 389 
 
 membranous tubes of considerable length called syphons, through 
 which the water is conveyed to the gills, and excrementitious mat- 
 ters expelled from the body. In the Mussels (Mytilacea) the 
 edges of the mantle are partially joined so as to present two aper- 
 tures, through one of which the foot is protruded, while the other, 
 the smaller of the two, gives issue to the excrement. A third family 
 (Camacea) has the circumference of the two divisions of the mantle 
 still more intimately united, leaving three distinct fissures, one 
 for the passage of the foot, another for the entrance of water to the 
 
 Fig. 179. 
 
 branchise, and a third for the ejection of matter from the rectum. 
 Of these, some are of gigantic dimensions, and fix themselves by 
 a strong byssus. One species, indeed, (Tridacne gigas,) is so 
 enormous in its size, that its shells alone not unfrequently weigh 
 upwards of two hundred pounds, and hatchets are employed to 
 chop its thick and tendinous cables from the rock to which it holds. 
 The Cockle family (Cardiacea) is recognised by having the 
 mantle open anteriorly, but prolonged at one extremity into two 
 tubes, one of which admits the water for respiration, while the 
 other discharges effete matter. In the Cockle (Cardium) the tubes 
 are short, and scarcely reach beyond the shell (Jig. 181, a) ; but in 
 other genera, as, for example, Mactra (Jig' 179, &, c), they are of 
 such length, that, when extended, they protrude to a considerable 
 distance. We at once perceive the use of the tubular arrangement 
 of the mantle here referred to, when we reflect upon the already 
 mentioned habits of this extensive division of the Conchifera, and 
 consider how, by means of their largely developed foot, they burrow 
 into the sand or mud of the shore. Had their mantle been open, 
 
390 
 
 CONCHIFERA. 
 
 Fig. 180. 
 
 like that of the oyster, respiration would have been impossible 
 under the circumstances in which they live ; but, by the modifi- 
 cation of structure thus provided, their tubes being prolonged to 
 the mouth of the excavation 
 wherein they reside, water 
 is freely admitted to the 
 branchiae through one of the 
 passages so formed, and ex- 
 crement ejected through the 
 other (fig. 180). 
 
 Whoever watches these 
 syphoniferous bivalves in a 
 living state will readily ap- 
 preciate the importance of 
 the pallial prolongations 
 forming this tubular appa- 
 ratus ; especially if minute 
 floating particles are placed 
 in the water wherein they 
 are confined. It will then 
 be perceived that powerful 
 currents are perpetually 
 rushing through the extre- 
 mities of each syphon, caused 
 by the rapid action of cilia 
 placed within ; and the 
 streams thus produced not 
 only form a provision for 
 constantly changing the water in which the branchiae (fig. 180, g) 
 are immersed, but forcibly convey floating molecules to the aper- 
 ture of the mouth, which is situated in the position indicated in 
 the figure by the letter h, and thus supply abundance of nutritive 
 materials that could, apparently, in animals so destitute of prehen- 
 sile organs, have been procured by no other contrivance.* 
 
 The last family of this class includes those species which, like the 
 Pholas and Teredo, bore in stone or wood ; or, like the Solen, pene- 
 trate deeply into the sand. In such, the mantle is prolonged into 
 terminal tubes of great length, and their shells remain always open 
 
 * The parts represented in the above figure (fig. 180) which are not particularly 
 pointed out in the text are, the anterior adductor muscle, c ; the posterior adductor 
 muscle, d ; the elastic ligament of the hinge, e ; and the largely developed foot,/. 
 
CONCHIFERA. 
 
 391 
 
 at the extremities ; these constitute the division to which Cuvier 
 has applied the name " Enfermes," on account of the very com- 
 plete union of the two sides of the mantle ; and from such forms 
 of CONCHIFERA the transition to the TUNICATA, described in 
 the last chapter, is by no means difficult. 
 
 (425.) In animals circumstanced as the CONCHIFERA, it would be 
 vain to expect any high developement of the nervous system, or senses 
 of an elevated character : nevertheless, a few small ganglia are percep- 
 tible in different parts, and nervous threads of extreme tenuity are 
 seen to arise from them, and to be distributed in various directions. 
 
 One pair of ganglia is, in the Dimyaria, easily distinguished, 
 occupying the ordinary position of the brain, namely above the oeso- 
 phagus. Hence is derived a supply of nerves to the sensitive labial 
 appendages, to the oral orifice, and other neighbouring parts. Two 
 other ganglionic masses, of larger size than the brains properly so 
 called, are placed near the posterior retractor muscle ; and a fifth 
 small ganglion, in those species provided with syphons, is found 
 in the vicinity of the breathing-tube, the muscular walls of which 
 receive nerves from this source. Fig. 181. 
 
 In the Mono- 
 myaria the nervous 
 centres are still 
 more feebly deve- 
 loped, and the pos- 
 terior ganglia pro- 
 portionately smaller 
 than those found in 
 species possessed of 
 two adductor mus- 
 cles. 
 
 (426.) No or- 
 gans of sense, other 
 than those already 
 noticed, are met 
 within any of the 
 Conchifera, except 
 in one remarkable 
 instance. In the 
 Scallops (Pecten) 
 the edges of the 
 mantle are studded with numerous pearl-like points, interspersed 
 
392 
 
 CONCHIFERA. 
 
 among the retractile tentacula placed around its circumference. 
 These, which are represented in the figure of Pecten already 
 given (j#g.l76), are considered by Poli* to be so many distinct 
 eyes thus singu- fig, 132. 
 
 larly situated ; 
 and, from the 
 circumstance of 
 their being fur- 
 nished with so 
 many organs of 
 vision, he applied 
 the name of Argus 
 to the Mollusca 
 possessing them. 
 Should the bril- 
 liant specks in 
 question be really 
 ocelli, they cer- 
 tainly are placed 
 in the only posi- 
 tion where they 
 could have been 
 efficient as instru- 
 ments of sight, 
 inasmuch as the 
 margin of the 
 mantle is, in such 
 animals, the only 
 portion of the 
 body capable of 
 being protruded 
 beyond the boun- 
 daries of the shell 
 to a sufficient dis- 
 tance to allow the 
 creature to peep 
 into the world 
 around it. 
 
 (427.) All the 
 CONCHIFERA are 
 hermaphrodite as relates to the organization of their generative ap- 
 
 * Poll, Testacea utriusque Sicilian, eorumque Historia et Anatome, 3 vols. fol. 
 
CONCHIFEBA. 
 
 paratus ; or perhaps it would be more strictly in accordance with 
 what is known concerning their mode of reproduction to say that 
 they are all females ; no organ that can be regarded as belong- 
 ing to a male system having, as yet, been pointed out.* 
 
 The ovary, which in fact is the only viscus distinguishable as 
 being connected with the propagation of these animals, is generally 
 a wide glandular sacculus, occupying a considerable portion of the 
 visceral mass. In the Oyster it is, when full of spawn, largely 
 spread through the body ; and if at such seasons its delicate walls 
 are ruptured, countless ova of microscopic dimensions escape from 
 the lacerated part. In Pecten the ovary is very conspicuous from 
 the brilliant colour of the eggs contained in its interior ; it con- 
 stitutes the greater part of the bulk of that prominent tongue-like 
 organ which projects between the branchiae (fig. 176,/) : or, in 
 genera where the foot is very largely developed, as in Cardium 
 rusticum, a great part of the base of that organ is hollowed out 
 into a capacious cavity, enclosed by its muscular walls, wherein 
 the delicate folds of the ovarium (Jig. 182, a) are partially em- 
 bedded, together with a portion of the intestinal canal (c). 
 
 (428.) The course of the oviduct has not as yet been satisfac- 
 torily traced, and, consequently, the precise passage by which the 
 eggs are excluded is still a matter of discussion. There is, how- 
 ever, one very remarkable arrangement observable connected with 
 the reproduction of conchiferous Mollusca, the object of which 
 is sufficiently evident. 
 
 When we consider the position of the ovary in these bivalves, 
 placed as it is in the substance of the body, and reflect upon the 
 immense numbers of eggs to which they give birth, for thousands 
 of ova are generated by every one of these prolific beings, we 
 perceive that, without some special provision, the imprisoned animals 
 would, when gravid, be seriously inconvenienced and exposed to 
 continual danger, as the inordinate enlargement of the ovary would 
 preclude the possibility of bringing the valves of the shell in con- 
 tact with each other. In order to obviate the difficulty referred 
 to, the ova are expelled from the ovarian nidus in an immature 
 
 * At a late meeting of the Zoological Society, a communication from M. Rudolph 
 Wagner was laid before the meeting, from which it would appear that that gentleman 
 has satisfied himself that in many of the lower classes of animals hitherto regarded as 
 being Monoecious, as for example, in many tribes of Polyps, Acalephae, Tunicata, 
 Conchifera, and Gasteropoda, in some individuals the organ generally looked upon as 
 being an ovary, contains Spermatozoa, or Seminal Animalcules j and thus there is reason 
 to suppose, that in such species a difference of sex exists, and that there are males 
 which supply a fecundating secretion. 
 
394 GASTEROPODA. 
 
 condition, and complete their growth in a situation where, being 
 diffused over a larger surface, the shells may be closely approxi- 
 mated ; and, moreover, the eggs and their contained offspring are 
 by this contrivance freely exposed to the influence of the medium 
 around, so as to allow a kind of respiration to be enjoyed by the 
 unhatched young. The situation chosen is the branchial fringes, 
 over which the imperfect spawn, or spat, as it is technically 
 termed, is found widely spread towards the close of gestation, 
 still retained beneath the shelter of the shell of the parent, and 
 thus preserved from destruction ; but at the same time, being in 
 such a position freely washed by the ciliary currents, the respiration 
 of the included embryo is adequately provided for. 
 
 CHAPTER XXIII. 
 
 GASTEROPODA.* (Cuv.) 
 
 (429.) EXTENSIVELY distributed over the surface of the land, or 
 inhabiting the waters either fresh or salt, there exists a very nu- 
 merous body of Mollusca, differing widely among themselves in 
 construction and habits, but distinguished by a peculiar locomotive 
 apparatus common to the entire class, by means of which they are 
 able to fix themselves to plane surfaces, and to move from place to 
 place by a slow and gliding motion. The slug, the snail, the 
 limpet, and the welk, afford familiar examples of their general 
 form and external appearance ; but species of different kinds are 
 so common in every situation, that it would be wasting the time 
 of the reader to dwell at any considerable length upon their ordi- 
 nary configuration and usual mode of progression. 
 
 The bodies of the GASTEROPODA are frequently entirely soft, 
 and devoid of other covering than a thick and slimy skin ; but 
 more generally they are protected by a shell of very diverse form 
 and shape, into which they can retire for protection. Feeble and 
 languid as are the sluggish movements of these creatures, they 
 nevertheless present to the eye of the anatomist a type of or- 
 ganization considerably superior to any that we have had an oppor- 
 tunity of considering in such forms of the HETEROGANGLIATA as 
 have been described in the preceding chapters. From the supe- 
 riority of their mode of progression, it is evident that they are 
 adapted to enjoy a less limited intercourse with external objects 
 than even the most highly gifted of the burrowing CONCHIFERA ; 
 
 * yaffT*i, the belly ; wawj, a foot. 
 
GASTEROPODA. 395 
 
 and accordingly we find in them a nervous system exhibiting a 
 more complete developement, senses of a higher character, and, 
 in the organization of their internal viscera, a complexity of parts 
 such as has not heretofore fallen under our notice, every indica- 
 tion, in fact, that they are animals of a higher grade and more 
 elaborate structure. The GASTEROPODA, for instance, exhibit a 
 distinct head, in which is lodged a supra-oesophageal ganglion of 
 large proportionate size ; and upon the head are found retractile 
 instruments of sensation of peculiar structure, and not unfrequently 
 perfectly formed organs of vision. 
 
 Let us, however, select one species for particular description ; 
 and, after having become acquainted with the details of its ana- 
 tomy, we shall be better prepared to examine such modifications of 
 the various organs ; as are found in other orders destined to exist 
 under different circumstances. 
 
 (430.) The common Snails (Helix) are well known as far as 
 relates to their external appearance ; and, insignificant as they might 
 be thought by those unacquainted with their habits, they not un- 
 frequently become formidable pests to the horticulturist, from the 
 ravages caused by their voracity. On examining a snail more 
 attentively we find its body partially enclosed in a thick muscular 
 envelope composed of transverse and longitudinal fibres, which, 
 being unsupported by any skeleton, allows the shape of the animal 
 to vary at pleasure, as it is shortened or elongated by the con- 
 tractions of the muscles composing it. The foot, or ventral disc 
 is equally composed of an interlacement of muscular fibres ; and not 
 only forms an extensive sucker, but, by the successive action of 
 various portions of its substance, a slow and gliding progressive 
 motion is produced. 
 
 From the head of the snail when its body is expanded, as when 
 in the act of seeking food, four tentacula are protruded, (Jig. 
 195, c, a) which, besides being exquisitely sensitive organs of touch, 
 carry at the extremities of the superior pair two minute but per- 
 fect eyes. When the creature is at rest, the tentacula as well as 
 the eyes are retracted into the visceral cavity by a mechanism 
 hereafter to be noticed. A large proportion of the viscera is en- 
 closed in a turbinated calcareous shell, of sufficient capacity to 
 allow the whole body of the animal to be withdrawn from observa- 
 tion and lodged in its interior. 
 
 The mouth is situated upon the under-part of the head, and, 
 when widely opened, exhibits a cutting instrument of singular 
 
3.96 GASTEROPODA. 
 
 contrivance. Attached to the upper part of the muscular cavity 
 that contains the oral apparatus, there is a broad horny plate, the 
 lower edge of which is free, very sharp, and slightly curved, form- 
 ing in fact a knife (Jig. 195, y), admirably adapted to divide the 
 leaves and soft parts of vegetables when they are pressed by the 
 action of the lips against its cutting edge. 
 
 The floor of the mouth is provided with a small cartilaginous 
 tongue, covered with delicate transverse striae, and so disposed 
 that by its movements it is well calculated to assist in propelling 
 the food into the cesophagus. In many species of Gasteropoda 
 the tongue is indeed even still more efficient as an agent in deglu- 
 tition, being studded all over with minute and recurved hooks, evi- 
 dently intended to take a firmer hold of the substances swallowed. 
 
 (431.) The cesophagus (jig* 183, e) is continued from the 
 muscular cavity (c') that encloses the dental plate, and soon dilates 
 into a wide stomachal receptacle, v 9 r, the posterior portion of which 
 is when in situ imbedded among the viscera contained in the 
 shell ; but in the figure all these parts are unfolded and separated 
 from each other. At the termination of the stomach, biliary 
 vessels (c) are inserted, and the intestine commences ; the latter 
 being a simple tube (a, e) intervolved among the masses of the 
 liver, nearly of equal diameter throughout, and presenting inter- 
 nally neither valves nor any other remarkable appearance. Ex- 
 ternally the intestine is intimately connected with the lobes of the 
 liver among which it lies imbedded, by means of a delicate cellu- 
 losity and vascular twigs passing from one to the other. The anal 
 aperture (o), when undisturbed by dissection, is placed upon the 
 right side of the neck, in the immediate vicinity of the orifice 
 (fig. 195, e ) that leads into the respiratory cavity. 
 
 (432.) Two sets of auxiliary glands are subservient to diges- 
 tion, the salivary and the hepatic, both of which are of consider- 
 able size. 
 
 The salivary glands are semi-transparent and of a whitish colour ; 
 they form two irregular broad ribands, which extend along the 
 sides of the stomach (v), spreading out so as to embrace a con- 
 siderable portion of its extent, and they are occasionally joined 
 together by intercommunicating processes. Two ducts, one de- 
 rived from each gland, run along the sides of the cesophagus, and 
 open into that canal close to the mouth. 
 
 The liver is of large proportionate dimensions, and is made up 
 of four lobes (b, d) of a dark brown colour, and composed of an 
 
GASTEROPODA. 397 
 
 infinite number of minute lobules, every one of winch produces 
 a biliary vessel ; and these, joining continually with each other, 
 form four large hepatic ducts, one proper to every lobe of the liver. 
 The four hepatic ducts ultimately unite into one great central 
 vessel (c), that opens into the alimentary canal in the immediate 
 vicinity of the pyloric extremity of the stomach. 
 
 (433.) The genus of Gasteropoda to which the Snail belongs 
 is composed of air-breathing animals, and we must accordingly ex- 
 pect to find these mollusca provided with a respiratory system 
 specially adapted to the mode of life to which they are destined. 
 The mechanism adopted is as follows : A capacious chamber, of a 
 somewhat triangular form, is found placed beneath the dorsal sur- 
 face of the body, and separated from the visceral cavity by a broad 
 muscular septum forming its floor. Into this chamber a wide 
 orifice (j%. 195, e ), placed upon the right side of the body near 
 the margin of the shell, allows the atmospheric air to enter. 
 The roof of the respiratory cavity is covered with a most intricate 
 arborescence of blood-vessels rudely sketched in Jig. 183, Ar, in 
 which the blood is freely exposed to the air therein contained ; 
 while the muscular floor, performing alternate movements analogous 
 to those of the human diaphragm, continually draws in and expels 
 the air, so as to ensure its constant renewal. The manner in 
 which respiration is effected, and the general disposition of the cir- 
 culatory apparatus, is therefore briefly this : The blood derived 
 from all parts of the body is brought to the respiratory chamber by 
 large veins provided for the purpose ; arrived there, it is dis- 
 persed through the countless ramifications of delicate vessels spread 
 over the entire roof of the breathing cavity, and thus becomes ex- 
 posed to the purifying influence of oxygen. The renovated blood 
 is then re-collected by the large pulmonary vein (k) ; and being 
 conveyed to the heart, which is composed of a single auricle (h) that 
 communicates with a strong ventricular cavity (g), it is propelled 
 through the entire arterial system derived from the aorta (f). 
 
 (434.) The whole of that part of the body of the snail which is 
 not permanently covered by the shell is defended by a thick skin, 
 the surface of which is irregularly furrowed, and continually moist- 
 ened by a viscid secretion that exudes from glands apparently 
 imbedded in the substance of the integument ; and the tenacious 
 slime so furnished, if the creature be irritated, is poured forth in 
 astonishing abundance. 
 
 Nevertheless, besides the slimy material thus copiously supplied 
 
398 GASTEROPODA. 
 
 by the tegumentary glands, there is in the interior of the animal a 
 special apparatus apparently destined to furnish a viscid fluid of 
 a similar character. The gland alluded to, called by Cuvier,* 
 par excellence, " the secerning organ of the viscosity," is in the 
 snail a triangular viscus (Jig. 183, ) placed in immediate con- 
 tiguity with the pericardium. On opening it, it is found to be 
 filled with an infinite number of very thin laminae that adhere to 
 the walls of its cavity by one of their edges, and become joined to 
 
 Fig. 183. 
 
 each other as if by communicating branches. The excretory duct 
 of this slime-secretor, which, we may observe, is found to exist in 
 many other genera of Gasteropods, accompanies the rectum to its 
 
 * Histoire des Mollusques ; M6moire sur la Limace et le Colima^on. 
 
GASTEROPODA. 399 
 
 termination, where it opens externally in the immediate vicinity of 
 the orifice leading into the respiratory chamber. 
 
 (435.) Before we enter upon a description of the somewhat 
 complex generative system of a Snail, it will be proper to advert 
 to one or two remarkable circumstances connected with the procrea- 
 tion of these singular animals. We must first premise that every 
 individual is hermaphrodite, and, moreover, presents a kind of her- 
 maphrodism of the most perfect and complete description, possess- 
 ing elaborately constructed male and female organs, which are dis- 
 tinct and separate from each other ; but, nevertheless, the coopera- 
 tion of two individuals is essential to the mutual impregnation of 
 both. The manner in which they copulate is not a little curious ; 
 their union being accompanied by preparatory blandishments of a 
 very extraordinary kind, that to a spectator would seem rather like 
 a combat between mortal foes, than the tender advances of two 
 lovers. After sundry caresses between the parties, during which 
 they exhibit an animation quite foreign to them at other times, 
 one of the snails unfolds from the right side of its neck, where the 
 generative orifice is situated, a wide sacculus, which, by becoming 
 everted, displays a sharp dagger-like spiculum or dart attached to 
 its walls. Having bared this singular weapon, it endeavours, if 
 possible, to strike it into some exposed part of the body of its 
 paramour ; who, on the other hand, uses every precaution to avoid 
 the blow, by speedily retreating into its shell. But, at length 
 having received the love-inspiring wound, the smitten snail pre- 
 pares to retaliate, and in turn uses every effort to puncture its 
 assailant in a similar manner. The darts are generally broken off 
 in this encounter ; and either fall to the ground, or else remain fixed 
 in the wounds they have inflicted. After these preparatory stimu- 
 lations, the snails proceed to more effective advances. The sac of 
 the dart is withdrawn into the body, and another sacculus is by 
 a like process protruded from the common generative aperture. 
 Upon the last-named organ two orifices are seen, one of which leads 
 to the female generative system ; while from the other a long and 
 whip-like penis is slowly unfolded, being gradually everted like 
 the finger of a glove, until it attains the length of an inch or more ; 
 and then each of the two snails, by inserting its penis into the 
 female aperture of the other, impregnates its partner, and is itself 
 impregnated at the same time. Such is the peculiar manner in 
 which the amours of snails are conducted : let us now examine the 
 internal viscera connected with the process. 
 
400 
 
 GASTEROPODA. 
 
 (436.) The sac of the dart first requires our attention. This 
 viscus, when unin verted, for it must be turned inside out in order 
 to expose the we t apon within it, is a thick muscular bag (Jig. 183, 
 a?) ; and, on opening it, it is found to contain the dart attached to 
 a nipple-like protuberance at the bottom of the sac. The dart 
 itself is four-sided ; and as it grows by the constant addition of cal- 
 careous particles deposited at its base from the surface of the 
 vascular protuberance to which it is fixed, so, if broken off, it is 
 speedily reproduced in a similar manner. 
 
 (437.) The male part of the generative system is composed of 
 a testicle, vas deferens, and the whip-like penis above described. 
 
 The testicle is considered by Cuvier* to consist of two distinct 
 portions: one, a soft whitish oval mass (Jig. 183, p) ; while the 
 other is elongated, thin and granular (y) 9 being imbedded among 
 the convolutions of the oviduct (z*?). The vas defer ens forms the 
 excretory duct of both these portions, and terminates in the side of 
 the penis ; its orifice becoming of course external when that organ 
 is protruded by evolution. The intromittent organ itself, as seen 
 when lodged within the body of the snail, consists of two parts, 
 a muscular bag which forms its body (b') 9 and a long whip-like 
 portion z ; the latter is hollow, but not perforated. The reader 
 will now have little difficulty in understanding how this remarkable 
 apparatus is protruded. The generative sac, common to both the 
 male and female organs, first becomes inverted ; the body of the 
 penis (>') then undergoes inversion in a similar manner, so that the 
 orifice of the vas deferens appears externally ; and lastly, the long 
 appendage to the penis, z 9 being likewise turned inside out by the 
 action of the muscles that compose its walls, completes this strange- 
 ly constructed instrument. Its subsequent retraction into the 
 visceral cavity is effected partly by the assistance of a special re- 
 tractor muscle (a), which acts upon the body of the penis, but 
 principally by the same contractility that accomplished its evo- 
 lution. 
 
 (438.) The female system next demands our notice ; and this 
 will be found to present for our investigation an ovary and lengthy 
 oviduct, to which are appended certain auxiliary organs, namely, 
 the spermatheca and the multifid vesicles. 
 
 The ovary (Jig. 183, s) is found situated in the inmost recesses 
 of the shell, and partially imbedded in the substance of one of 
 the lobes of the liver. From the ovary a long oviduct (g) is de- 
 
 * Loc. cit. 
 
GASTEROPODA. 401 
 
 rived, which is at first thin and slender, but, soon becoming wider 
 and more capacious (M), it gradually expands into an extremely 
 convoluted intestiniform viscus, to which the name of uterus has 
 been improperly given, and ultimately terminates in a canal de- 
 rived from the spermatheca, to be described hereafter. It is during 
 their passage through this enormous oviduct that the eggs attain 
 their full growth preparatory to their expulsion from the body. 
 
 Another viscus, called by Cuvier simply " the bladder," is, from 
 the constancy of its occurrence, evidently an organ of importance ; 
 and there seems to be little room to doubt that it is intended to 
 be a receptacle for the seminal fluid, analogous in function to the 
 copulatory pouches we have already met with in Insects and some 
 Crustacea. The reservoir in question, which we have called sper- 
 matheca (Jig- 183, t), is in the snail placed above the stomach; 
 and the canal derived from it accompanies the sacculated oviduct, 
 which it ultimately joins near its termination, in such a manner 
 that the ova must pass the orifice of its duct as they are expelled 
 from the body. It must nevertheless be confessed that the office 
 here assigned to the "bladder" is rather probable than positively 
 established ; for in the Slug, so nearly allied to the snail in its 
 general organization, the excretory duct of this organ opens into 
 the common generative sac by an aperture distinct from that which 
 leads into the oviduct, although even here the two are closely 
 approximated. Cuvier suggests that perhaps it may furnish some 
 material useful in forming an envelope for the ova, but experiments 
 are still wanting upon this subject. 
 
 There is still another set of organs connected with the canal by 
 which the eggs escape from the oviduct of the snail ; and these, 
 although peculiar to the genus we are examining, no doubt furnish 
 a secretion of importance to their economy. They are called the 
 multifid vesicles (fig. 183,^), and are composed of a series of 
 branched cseca derived from two excretory ducts by which a milky 
 fluid, secreted by the caeca, is poured into the egg-passage prior to 
 its termination. 
 
 (439.) Although it will be convenient to speak in more general 
 terms concerning the nervous system of the GASTEROPODA than 
 the examination of a particular species would permit, we deem it 
 necessary, before closing our description of the snail, to describe 
 with some minuteness the senses possessed by these terrestrial mol- 
 lusks, and more especially the extraordinary mechanism provided 
 for withdrawing the most important instruments of sensation into 
 
 2 D 
 
402 
 
 GASTEROPODA. 
 
 the interior of the body when they are not in actual employ- 
 ment. 
 
 The only senses that we can expect to meet with in animals 
 deprived of either an external or internal skeleton, are those of 
 taste, smell, vision, and touch ; any auditory apparatus being of 
 course deficient. 
 
 The sense of taste, judging from the structure of their tongue, 
 must be extremely obtuse ; and, although these creatures are evi- 
 dently possessed of smell, it is not easy to point out where their 
 olfactory apparatus is placed. The eyes, however, are now found 
 to present a perfection of structure correspondent with the enlarged 
 brain, and occupy a singular position, being situated at the ex- 
 tremities of the two superior tentacula appended to the head ; 
 while the inferior pair, adapted, as it would seem, more exclusively 
 
 Jty.184. 
 
 to the perception of tactile 
 impressions, are deprived of 
 visual organs. Both the up- 
 per and lower tentacula are 
 retractile, and can be com- 
 pletely inverted so as to 
 be withdrawn into the in- 
 terior of the body. To 
 effect the inversion by which 
 this end is attained, the plan 
 represented in the accompa- 
 nying figure is had recourse 
 to. Each tentacle is a hol- 
 low flexible cylinder, the 
 walls of which are muscular, 
 and composed of circular fibres. When partially retracted, as in 
 the tentacle marked c in the figure (fig- 184), the extremity of the 
 organ is drawn inwards, and two cylinders are thus formed, one 
 within the other : if the outer cylinder is elongated, as in pro- 
 truding the tentacle, it is at the expense of the inner one ; and, on 
 the contrary, the inner cylinder, when the organ is retracted, is 
 lengthened as the other becomes shorter. To evert the tentacle 
 the contraction of the circular muscles that form its walls is suffi- 
 cient, as they can gradually unroll the whole by squeezing out, 
 as it were, the inner portion ; but to effect its inversion a spe- 
 cial retractor muscle is required, which is represented in the ten- 
 tacle indicated in the figure by the letter b. This muscle (g) 
 
GASTEROPODA. 403 
 
 arises from the general muscular mass composing the foot and re- 
 tractile apparatus provided for drawing the snail into its shell : the 
 long slip of muscular fibres so derived, accompanied by the optic 
 nerve (/), traverses the interior of the cylindrical tentacle quite to 
 its extremity, where it is attached ; and thus, as the reader will 
 easily conceive, is quite competent to cause its inversion. The 
 lower feeler (d) is represented in the figure as partly retracted by 
 the action of its appropriate muscle k ; while the corresponding 
 one (a), being completely turned inside out, is fully withdrawn 
 and securely packed among the viscera. 
 
 One circumstance connected with the contrivance above describ- 
 ed cannot but excite attention ; and this is the peculiar arrange- 
 ment of the tentacular nerves, whereby they are adapted to 
 changes of position so extensive: the optic nerve (jf), for ex- 
 ample, must not be stretched even when the eye-bearing tentacula 
 are protruded to the uttermost ; and in order to provide for this, 
 when the feelers are not extended, the nerves become thrown into 
 close folds (A), and lodged within the cavity of the body. 
 
 (440.) From the above somewhat lengthened account of the ana- 
 tomy of the snail, the reader will at least have been able to become 
 acquainted with the general features of an organization which is 
 more or less common to all the members of the extensive class 
 under consideration. We must now, however, enter upon a 
 more enlarged survey of the GASTEROPODA, and divide them 
 into such groups as will facilitate our further investigations 
 concerning their structure and habits. The most convenient 
 character by which the different orders composing the class are 
 distinguished has been found to be derived from the nature 
 and arrangement of the respiratory apparatus, which of course 
 varies both in construction and position, according to the circum- 
 stances under which particular tribes or families are destined to 
 exist. 
 
 We have already found that terrestrial species, such as the 
 snail, breathe air, which is alternately drawn into and expelled 
 from a cavity lined with a vascular net-work ; and these, from 
 the resemblance between such a mode of breathing and that of 
 animals possessed of proper lungs, have been formed into an 
 order distinguished by the name of PULMOBRANOHIATA. Ne- 
 vertheless, all the pulmobranchiate Gasteropoda are not terres- 
 trial ; our fresh waters abound with various species that respire 
 air by a similar contrivance, and are consequently obliged, in 
 
 2 D 2 
 
404 
 
 GASTEROPODA. 
 
 order to breathe, to come continually to the surface of the shal- 
 low pools wherein they are found. The Planorbis and Limnceus 
 are examples of this mode of respiration ; and are met with in 
 every ditch, where they voraciously devour the subaquatic vege- 
 tables upon which they feed. 
 
 (441.) It is at once evident that in marine Gasteropods another 
 mode of aerating the blood must be resorted to, and branchiae of 
 some description or other pig. 185. 
 
 substituted for a pulmo- 
 nary cavity. 
 
 The branchiae given 
 for this purpose are 
 variously constructed ; 
 sometimes appearing as 
 extensively branched 
 and arborescent appen- 
 dages to the skin, or 
 else they form broad 
 and thin lamellae at- 
 tached to the exterior 
 of the body ; but more 
 frequently the respi- 
 ratory apparatus con- 
 sists of vascular fila- 
 ments arranged in a pec- 
 tinated manner along a 
 central stem : whatever 
 their form, however, 
 their office is the same, 
 namely, to present a 
 sufficient surface to the 
 
 surrounding medium, in order adequately to expose the blood that 
 circulates abundantly through them to the influence of oxygen. 
 
 It is from the position and arrangement of the branchial organs 
 that the branchiferous Gasteropoda have been classified by zoolo- 
 gists. Thus in the second order, called from this circumstance 
 NUDIBRANCHIATA, they are naked and placed upon some part of 
 the back ; sometimes, as in Tritonia, extending along its entire 
 length; but at others, as for example in Doris (Jig- 185), they 
 are confined to its posterior part, and form a circle around the anal 
 orifice of exquisite beauty, and not inaptly comparable to a flower 
 in appearance and disposition. 
 
GASTEROPODA. 405 
 
 In the INFEROBRANCHIATA the branchiae resemble two long 
 rows of leaflets, placed on the two sides of the body, under a 
 projecting edge formed by the mantle. 
 
 The TECTIBRANCHIATA have respiratory organs upon one side 
 of the body only, and concealed by a flap derived from the 
 mantle. Such, for instance, is the case with Pleurobranchus and 
 Aplysia ; in the former of which the elegant branchial fringe is 
 situated in a deep sulcus between the edge of the mantle and 
 the prominent margin of the foot (Jig. 186, d). 
 
 But by far the most numerous order of the marine Gasteropoda, 
 (PECTINIBRANCHIATA,) which, in fact, includes all the inhabit- 
 ants of spiral univalve sea-shells, have their branchiae placed inter- 
 nally in a capacious cavity, whereinto the water is freely admitted 
 (Jig. 196, a). This cavity is situated in the last or widest turn of 
 
 Fig. 186. 
 
 the shell, and communicates with the exterior of the body by 
 a very wide slit, to which in some genera a long syphon (Jig. 
 196, /), formed by a fold of the mantle or general covering of the 
 animal, conducts the respired fluid. The branchiae themselves, 
 as the name of the order indicates, are pectinated and form a 
 single, double, or triple series of gills suspended from the roof 
 of the branchial chamber, answering the same intention as the 
 pulmonary net-work of the snail, but deriving their supply of air 
 from the water, in which they are perpetually immersed. In the 
 figure referred to, representing a species of Pterocera, the position 
 of the branchial chamber is seen through the shell and mantle, 
 which the reader must suppose to be transparent; and the 
 branchial organ (a), in this case single, is likewise represented 
 in situ, suspended from the roof of the cavity that contains it. 
 In Jig. 198, the roof of the respiratory cavity (x) has been 
 
406 
 
 GASTEROPODA. 
 
 reflected, and the three rows of branchial fringes (n) suspended 
 therefrom are well seen. 
 
 A sixth order of Gasteropods has been formed by Cuvier, 
 under the name of TUBULIBRANCHIATA, remarkable from the 
 shape of their shells, which are long and irregular tubes usually 
 fixed to foreign bodies, but still they have the earliest formed 
 portion twisted into a few spiral curves. To this order belongs 
 Vermetus (Jig. 187), the shells of which, agglomerated into masses, 
 might be taken for pi gf 137, 
 
 those of certain Serpu- 
 I<E. As locomotion is 
 here out of the ques- 
 tion, owing to the im- 
 moveable condition of 
 the habitations of such 
 genera, the foot would 
 seem at first to be al- 
 together deficient, but 
 upon close inspection it 
 is found to be convert- 
 ed into a fleshy organ 
 that bends forward and 
 projects beyond the 
 head, where its extre- 
 mity expands into a disc furnished with a small operculum ; so 
 that, when the animal retires into its abode, a lid is formed 
 adapted to close the aperture, and thus prevent intrusion and 
 annoyance from without. Nevertheless, even in these the bran- 
 chiae are pectiniform, forming a single row attached to the roof of 
 a branchial chamber. 
 
 The SCUTIBRANCHIATA likewise have pectinated gills dis- 
 posed in a special cavity, but their shells are very wide, and 
 scarcely ever turbinated ; a circumstance which, combined with 
 other features of their economy, renders it convenient to consider 
 them as forming an order by themselves. 
 
 An eighth division of this extensive class takes the name of 
 CYCLOBRANCHIATA, because the branchiae form a fringe around 
 the body of the animal, between the edge of the body and the 
 foot (fig. 194, c ; fig. 197, a). 
 
 Lastly, a distinct order has been established to embrace certain 
 families in which the foot is so much compressed as to constitute 
 
GASTEROPODA. 407 
 
 a vertical muscular lamella, that presents merely a remnant of tlic 
 ventral sucker, so characteristic of the entire class, and \vhich can 
 only be serviceable in performing the office of a fin used in swim- 
 ming ; hence these mollusks have been called HETEROPODA. 
 Their branchise are placed upon the back (Jig- 188, d), and 
 resemble small detached tufts. The form of these heteropod Gas- 
 teropoda the reader will gather from an inspection of the accom- 
 panying figure, representing a species of Pterotrachea ; but the 
 details connected with their anatomy therein delineated, will be 
 explained hereafter. 
 
 Fig. 188. 
 
 (442.) It would be useless to weary the student by describing 
 the course of the blood-vessels in all the orders we have just enume- 
 rated ; their distribution necessarily varies with the changes ob- 
 servable in the position of the branchise ; still, whatever the situation 
 of the respiratory organs, the general course of the circulation is 
 the same, and essentially similar to what has been already described 
 in the snail : one or two examples will therefore answer our pur- 
 pose. In the Pectimbranchiata, as for instance in Buccinum (fig. 
 193), the heart (r, s), enveloped in a distinct pericardium, is placed 
 at the posterior extremity of the branchial chamber, and consists, 
 as in all the GASTEROPODA, of two cavities, a thin membranous 
 auricle, and a more muscular and powerful ventricle. It receives 
 the blood from the organs of respiration by a large branchial vein 
 (Jig. 193, q), that communicates with the auricle (s). The con- 
 traction of the auricle forces the circulating fluid into the ventricle 
 
408 GASTEROPODA. 
 
 (r), which, in turn, drives it into the aortic or arterial system of 
 vessels. The aorta, in the case before us, divides into two princi- 
 pal trunks ; of which one (TO) is directed forwards to supply the foot 
 and anterior part of the body, while the other (t) winds among the 
 mass of viscera contained in the shell, to which it distributes its 
 ramifications. The blood thus dispersed through the system is 
 taken up by the commencements of the veins, to be re-convey- 
 ed to the branchiae, there to begin again the circuit we have 
 described. 
 
 When the branchiae are external, and largely distributed over the 
 surface of the body, as for instance in Tritonia, the purified blood 
 is brought from the branchiae to the heart by capacious veins which 
 run beneath each branchial fringe and collect it from the numerous 
 respiratory tufts ; or if, as in Doris (Jig* 185), the branchiae en- 
 circle the anus, a large circular vein placed at the base of the 
 branchial apparatus receives the blood and pours it into the auricle. 
 In all cases, however, the course of the blood is essentially the 
 same, and the heart is systemic. 
 
 (443.) In Aplysia, one of the tectibranchiate Gasteropods, the 
 branchiae (Jig. 189, a, b) consist of delicate lamellae minutely 
 subdivided ; and the vessel (c), which brings the blood derived from 
 all parts of the body to be distributed over the extensive surface 
 thus formed, presents a structure of no ordinary interest to the 
 physiologist.* At some distance before it arrives at the respiratory 
 organs it divides into two main branches, and the coats of each vessel 
 so formed appear to be made up of transverse and oblique muscular 
 bands that cross each other in all directions, so as to leave between 
 them very perceptible apertures, through which injections of any 
 kind readily escape into the abdominal cavity, and, of course, fluids 
 derived from the abdomen as easily penetrate into the interior of 
 the veins. At some points, indeed, these veins seem absolutely 
 confounded with the visceral cavity ; a few muscular bands widely 
 separated from each other, and not at all interrupting a free 
 communication, being alone interposed. The result of Cuvier's 
 anxious researches concerning this remarkable feature in the or- 
 ganization of these Mollusca led him to the following important 
 conclusions, which are no doubt extensively applicable to the GAS- 
 TEROPODA generally: 1. That in Aplysia there are no other 
 vessels appointed to convey the blood to the branchiae than the two 
 above described. 2. That all the veins of the body terminate in 
 
 Cuv. Memoire sur le genre Aplysia. 
 
GASTEROPODA. 
 
 409 
 
 these two canals. Now as tlieir communication with the abdomi- 
 nal cavity is evident and palpable, whether we call them vena 
 cava, or cavities analogous to a right ventricle, or branchial 
 arteries, for it is evident that they fulfil the functions of these 
 three organs, the inevitable conclusion is, that fluids poured into 
 the abdominal cavity can become directly mixed with the mass of 
 the blood and thus conveyed to the branchiae, and that the veins 
 perform the office of absorbent vessels. 
 
 This extensive communication is undoubtedly a first step to- 
 wards the establishment of that, still more complete, which nature 
 has established in insects, where, as we have seen, there are not 
 even distinct vessels of any kind appointed for taking up the nutri- 
 tive fluid. From these facts Cuvier concludes that no proper 
 absorbent system exists in the Mollusca, still less in animals 
 inferior to them in the scale of creation. 
 
 The vein ^.189. 
 
 appointed to 
 convey the re- 
 novated blood 
 from the bran- 
 chiae to the 
 heart, when slit 
 open (./zg.189, 
 d), exhibits the 
 orifices of the 
 smaller vessels 
 derived from 
 the respiratory 
 laminae arrang- 
 ed in circles. The auricle of the heart is made up of reticulated 
 fibres (e), and when laid open it is seen to be separated from 
 the more muscular ventricle (g) by a valve (/), whereby any 
 retrograde movement of the blood is prevented. 
 
 (444.) Such is the construction of the heart in a great majority 
 of the GASTEROPODA ; but in a few of the lowest orders, namely, 
 those most nearly allied to the CONCHIFERA, slight modifications 
 are met with. Thus in Chiton (Jig. 197), so remarkable from 
 the singularity of its shelly covering, the heart is situated in the 
 middle of the posterior region of the back, and is furnished with 
 two auricles, one appropriated to each lateral series of branchiae ; 
 
410 GASTEROPODA. 
 
 and, what is still more remarkable, each auricle would seem to com- 
 municate with the ventricle by two distinct orifices. In Haliotis, 
 Fissurelld) and others of the Scutibranchiate and Cyclobranchiate 
 orders, the resemblance to the arrangement generally met with 
 among the CONCHIFERA is even more striking ; for in such genera 
 not only are there two distinct auricles, but the ventricle embraces 
 the rectum, so that, when superficially examined, it seems to be 
 perforated for the passage of the intestine. 
 
 In Pterotrachea (Jig. 188), the branchiae (e) are placed upon 
 the back, and the blood derived from the tufts composing the 
 branchial apparatus is received into a two-chambered heart (e), 
 whence it is distributed to the body through the aorta, which is at 
 first double, but, after surrounding the visceral sac and supplying 
 the viscera, the two vessels unite to form one large trunk (w), 
 which traverses the body as far as the head. 
 
 (445.) The digestive system of the Gasteropoda, as we might 
 be led to expect from the numerous and widely different forms of 
 the animals belonging to the class under consideration, presents 
 endless diversity of structure; and, did we not strictly refrain 
 from noticing any but the most important modifications, it would 
 be easy to overwhelm the most patient reader with accumulated 
 details. 
 
 The mouth we shall consider as exhibiting four distinct types of 
 organization ; one of which, namely that met with in the Snail 
 and the generality of pulmonated Gasteropoda, has been already 
 described ( 430). 
 
 The second form of mouth, that for instance of Pleurobranchus 
 (fig. 186, a, and of Pterotrachea, fig. 188, >), consists of a simple 
 muscular proboscis, or fleshy tube, which is capable of considerable 
 elongation and contraction : such an oral apparatus is entirely de- 
 void of teeth or any cutting instrument, but is, nevertheless, fully 
 able to seize and force into the stomach such materials as are used 
 for food. 
 
 (446.) A third kind of mouth, by no means so frequently met 
 with as the last, is not a little extraordinary, and forms a more 
 efficient cutting instrument than even that of the snail. We shall 
 offer, as an example of this remarkable organ, that of the Tritonia 
 ffombergii, represented in the annexed figure (fig- 190), whereof 
 Cuvier gives the following graphic description.* In this animal the 
 mouth forms a large, oval, and fleshy mass enclosing the jaws and 
 
 * M6moire sur le Tritonia. 
 
GASTEROrODA. 411 
 
 their muscles, as well as a tongue covered with spines, and its 
 opening is guarded by two fleshy lips. The jaws form the basis of 
 all this apparatus : their substance is horny ; pi gt 190. 
 
 their colour a yellowish brown ; and their form, 
 very extraordinary for an organ of this kind, 
 cannot be better described than by comparing 
 them to the shears used in shearing sheep. 
 They differ, however, in the following par- 
 ticulars : instead of playing upon a common 
 spring, the two blades are found to work 
 upon a joint, and, instead of being flat, they 
 are slightly curved. 
 
 These two blades are very sharp, and there 
 
 is nothing that has life that they cannot cut when the animal 
 causes the cutting edges to glide over each other. For this 
 purpose muscles of great strength are provided, the fibres of which 
 are transverse ; and their office is to approximate the two blades, 
 that are again separated by the natural elasticity of the articulation 
 whereby they are united at one extremity. 
 
 The aliment, once cut by the jaws, is immediately seized by the 
 papillae of the tongue ; which, being sharp and directed backwards, 
 continually drag, by a kind of peristaltic movement, the alimentary 
 materials into the oesophagus. 
 
 (447.) The fourth and most complicated form of the mouth is 
 found in the pectinibranchiate Gasteropods, and with its assistance 
 these animals can bore through the hardest shells in search of food ; 
 making a hole as round and smooth as if it had been made by a 
 drill of human contrivance. It is from Cuvier we again borrow 
 the subjoined description of this unique apparatus.* 
 
 The proboscis of Buccinum is organized with marvellous arti- 
 fice : it is not simply provided, like that of the elephant, with the 
 means of flexion and extension, joined with a limited power of 
 contraction and elongation ; but it can be entirely retracted into 
 the body by drawing itself into itself in such a manner that half of 
 it which forms its base contains and encloses the half nearest its 
 point ; and it can protrude itself from its sheath thus formed, by 
 unrolling itself like the finger of a glove, or like the horns of the 
 garden snail, only it is never completely retracted, but always re- 
 mains more or less folded upon itself. 
 
 It may be represented as being composed of two flexible cylin- 
 
 * M6moire sur le grand Buccin (Buccinum undatum), et sur son Anatomic. 
 
GASTEROPODA. 
 
 ders, one contained within the other, as shown in the annexed figure 
 (Jig. 191), the upper edges (z, z) of the two cylinders being con- 
 tinuous in such a manner, that, by drawing Fig. 191. 
 out the inner cylinder (i, 6), it becomes 
 elongated at the expense of the other, and, 
 on pushing it in again, it becomes shorter, 
 while the outer cylinder (k) is lengthened 
 by adding to its upper margin. 
 
 The reader must now imagine a multitude 
 of longitudinal muscles (d, d), all very much 
 divided at both their extremities, and attach- 
 ed by one end to the parietes of the body, 
 whilst by the opposite they are fixed to the 
 interior of the inner cylinder of the proboscis 
 (b) along its entire length, and as far as its 
 extremity. It is evident that the action of 
 these muscles will retract this cylinder, and 
 consequently the entire proboscis, into the 
 body. 
 
 When thus retracted, a great part of the inner surface of the 
 internal cylinder (b) will necessarily become a portion of the ex- 
 ternal surface of the outer cylinder (k) ; and the contrary when the 
 proboscis is protruded. It is in consequence of this that the in- 
 sertions of the muscles (d, d) vary in position. 
 
 The protrusion of this proboscis is effected by the action of the 
 intrinsic circular muscles that form its walls. 
 
 When the proboscis is extended, the retractor muscles (d, d), if 
 they do not act all together, serve to bend it in any direction, 
 thus becoming the antagonists to each other. 
 
 In the internal cylinder are contained the tongue, with all its 
 apparatus (e, e) ; the salivary ducts (/), and the greater part of 
 the esophagus (g) : but the principal use of the proboscis is to 
 apply the end of the tongue to the surface of bodies that the Buc- 
 cinum wishes to erode and suck. The tongue itself (e) is a car- 
 tilaginous membrane armed with hooked and very sharp spines. 
 It is sustained by two long cartilages, the extremities of which 
 form two lips (c), that can be separated or approximated ; or the 
 cartilages can be made to move upon each other by the mass of 
 muscles in which they are imbedded. When these cartilages 
 move, the spines that cover the tongue are alternately depressed 
 and elevated ; and by a repetition of similar movements, aided per- 
 
GASTEROPODA. 
 
 413 
 
 haps by some solvent quality in the saliva, the hardest shells are 
 soon perforated by this singular file. 
 
 (448.) The salivary glands are lodged in the visceral cavity, 
 and are composed of numerous secerning cseca enclosed in a mem- 
 branous capsule (Jig. 192, A, A:) : their ducts (g, e) 9 which are ne- 
 cessarily as long as the proboscis when extended to the utmost, 
 open by two apertures placed at the sides of the spinous tongue (b). 
 The oesophagus (fig. 191, g, g) runs along the centre of the 
 proboscis throughout its entire length, and, when that organ is pro- 
 truded, becomes nearly straight ; but, when the proboscis is drawn 
 in, the oesophagus is folded upon itself among the viscera. 
 
 Just at the commencement of Fig. 192. 
 
 the stomach there is a small 
 crop (Jig. 192, /), and the 
 stomach itself is single, with- 
 out anything in its texture re- 
 quiring special notice ; its lin- 
 ing membrane being soft, and 
 gathered into longitudinal folds 
 
 (0- 
 
 Equally simple is the alimen- 
 tary apparatus of the Hetero- 
 poda. In these the stomach 
 (jig. 188, f) is a mere dilata- 
 tion of an intestiniform tube. 
 The intestine is not lodged in 
 the general cavity of the body ; 
 but, with the mass of the liver, 
 is contained in a kind of bag 
 attached to the back of these 
 singularly formed animals, and 
 in some genera, as for example 
 Carinaria, defended by a de- 
 licate transparent shell, which 
 in appearance offers a miniature 
 
 resemblance of that of the Argonaut. It is in this visceral sac 
 that the heart and generative apparatus are likewise generally en- 
 closed ; but in many forms of the Heteropoda, both the append- 
 ed sacculus and shell are wanting, in which case the viscera are of 
 course lodged in the general cavity of the body. 
 
 (449.) But although in Buccinum, Pterotrachea, and kindred 
 
414 GASTEROPODA. 
 
 genera, the stomach is thus devoid of complication, it is by no 
 means unfrequently found to be provided with a powerful crushing 
 apparatus, that forms a strong gizzard adapted to bruise, cut, or 
 tear the food introduced into it. In Scyllaa, for example, this 
 gizzard, situated at the entrance to the stomach, contains twelve 
 horny cutting blades disposed around its interior, and arranged in 
 a longitudinal direction ; their sharp edges, therefore, meeting in 
 the centre, efficiently divide whatever passes between them to- 
 wards the proper digestive stomach. In Aplysia there is first 
 a capacious crop, then a strong gizzard studded internally with 
 pyramidal blunt teeth, and to this succeeds a third cavity armed 
 with sharp pointed hooks attached to one side of its walls, and so 
 disposed as to form a kind of carding machine by which the food 
 is still more effectually torn to pieces. 
 
 Various modifications in the form and structure of these sto- 
 machal teeth are met with in the different genera of the GASTE- 
 ROPODA that possess such an apparatus; but whatever their 
 shape, size, number, or position, the office assigned to them i& 
 the same. 
 
 (450.) The liver is proportionately of very large size in the 
 Mollusca we are now describing. Its composition is similar in all ; 
 being made up of bunches of secreting follicles united by the 
 branches of their excretory ducts, and kept together by means of 
 a delicate cellulosity and the ramifications of blood-vessels. We 
 have already described the hepatic viscera of the snail ; and the 
 liver of Buccinum, unravelled so as to show its intimate structure, 
 is represented in the preceding figure (j^g. 192, n, o, p), which 
 requires no additional explanation. 
 
 But if the structure of the liver is similar in all the Gasteropod 
 Mollusca, the manner in which the bile is poured into the intes- 
 tine varies remarkably. The most ordinary position of the orifices 
 of the hepatic ducts is at the termination of the stomach, in the 
 vicinity of the pylorus ; as is the case in the majority of other 
 animals : but many exceptions to this rule are met with in the 
 class before us. 
 
 In Scyllcea the bile is poured into the oesophagus just before it 
 terminates in the gizzard. In many genera the biliary canals open 
 into the stomach itself; and in one remarkable genus, Onchidium, 
 there are three distinct livers, each provided with its proper excre- 
 tory duct ; and, what is still more anomalous, these three glands, 
 which in every particular strictly resemble each other, unless per- 
 
GASTEROPODA. 415 
 
 haps in size, pour the secretion that they furnish into three dif- 
 ferent situations : the first into the esophagus, the second into the 
 oesophagus likewise, and the third into the gizzard, which forms the 
 first of three stomachal cavities. 
 
 In Doris, a figure of which is given above, a still more extra- 
 ordinary arrangement is met with. One set of ducts derived from 
 the liver penetrate the stomach, and pour the bile into that cavity ; 
 while another large canal, equally given off from the liver, terminates 
 at the exterior of the body by an orifice situated in the vicinity of 
 the anus (fig- 185) ; and thus a part of the bile secreted would 
 seem to be expelled from the system as excrementitious matter, 
 a fact of no ordinary importance to the physiologist, as it would 
 itself go far to prove that the function of the liver is not merely 
 limited to the supply of a secretion of importance in the digestion 
 of food, but that it powerfully co-operates with the respiratory 
 system in purifying the circulating fluids by decarbonizing the 
 blood. 
 
 (451.) Other secretions, apparently of an excrementitious cha- 
 racter, are furnished by many Gasteropods. Thus, in Aplysia a 
 glandular mass is imbedded in the opercular flap that protects the 
 gills ; from which, at the pleasure of the animal, a reddish liquor is 
 made to exude in sufficient abundance to obscure the water around 
 it, and thus conceal it from pursuit. Another gland furnishes an 
 acrid limpid fluid, that distils from an orifice near the oviduct ; 
 but the use of this last secretion is as yet unknown. 
 
 (45#.) The scattered condition of the nervous ganglia, charac- 
 teristic of the HETEROGANGLIATA, is well exhibited in the pec- 
 tinibranchiate Gasteropods ; more especially as it not unfrequently 
 happens that the ganglionic centres themselves are of an orange or 
 reddish colour, while the nerves derived from them present their 
 usual appearance. 
 
 In Buccinum the brain still occupies its usual position above 
 the oesophagus (Jig. 193, d), and gives off nerves to the organs of 
 sensation, and largfc twigs (c, c) to the eminently sensitive pro- 
 boscis. A large nervous mass placed beneath the oesophagus (*) 
 is connected with the former by several communicating nerves, that 
 embrace the oesophageal tube. Other ganglia, of smaller size (&, /, 
 w),are distributed in distant parts of the body, and supply the vis- 
 cera to which they are contiguous ; whilst they are connected among 
 themselves, and with the brain, by nervous cords passing from one 
 to another. 
 
416 
 
 GASTEROPODA. 
 
 In Pterotrachea Fi ff- 193. 
 
 the same dispersion 
 of the central gan- 
 glia of the nervous 
 system is equally 
 evident. The brain 
 and nervous collar 
 around the oesopha- 
 gus occupy their 
 usual situation, and 
 give nerves to the 
 tentacles, eyes, and 
 parts around the 
 mouth ; while four 
 smaller ganglia 
 (Jig. 188, f) are 
 placed in the imme- 
 diate vicinity of the 
 foot, to which, and 
 to the neighbour- 
 ing viscera, they 
 distribute their 
 branches. 
 
 But in the most 
 elevated Gastero- 
 pods the ganglia 
 assume greater con- 
 centration, and the brain exhibits much larger dimensions as 
 compared with the size of the body. Thus in the snail (Jig. 
 184) we find only two great nervous masses : the brain (7), a large 
 ganglion placed above the oesophagus, and supplying the nerves 
 connected with sensation ; and an equally large suboesophageal 
 mass (m) 9 whence proceed nerves to all the viscera and locomotive 
 organs. Here, therefore, we have another example of the great 
 law that we have already so often illustrated the diminution in 
 number, and the increase in size, of the nervous centres as we rise 
 from lower to more exalted types of animal organization. 
 
 The tentacula (Jig. 193,/,/) in the marine GASTEROPODA are 
 generally not retractile, and the eyes are frequently situated at the 
 outer side of the base of each tentacle, instead of at their apex, as 
 in the figure referred to ; but, with these exceptions, we can add 
 
GASTEROPODA. 417 
 
 nothing to what has been said concerning the senses of these Mol- 
 lusca in the description of the snail, already given as an example 
 of the general structure of the entire class. 
 
 (453.) We now approach an inquiry of much interest as con- 
 cerns the economy of the animals before us ; namely, the varied 
 forms of their organs of reproduction, and the character of the gene- 
 rative system belonging to each order. This investigation, however, 
 is one of no ordinary difficulty ; for so numerous are the modifica- 
 tions of structure observable in almost every genus, that, were we 
 not strictly to confine ourselves to the study of the most prominent 
 and important features of this portion of their history, the patience 
 of the student would be severely put to the test in following us 
 through all the details connected with so extensive a subject. 
 
 (454.) The three lowest orders of the Gasteropoda are still, in 
 many particulars, more or less allied to the CONCHIFERA ; but 
 more especially this is the case in the organization of their gene- 
 rative apparatus. The Cyclobranchiata, Scutibranchiata, and 
 Tubulibranchiata, like the inhabitants of bivalve shells, are all 
 hermaphrodite and self-impregnating.* A large granular ovary 
 is in all these orders imbedded in the mass of the liver, and 
 from this a duct leads to an external orifice situated in the vicinity 
 of the anus : if impregnation is in such animals essential to fecun- 
 dity, the fertilizing secretion must be furnished by the glandular 
 walls of the oviduct, as no male organs have as yet been disco- 
 vered. 
 
 (455.) The Pectinibranchiata, on the contrary, are all dioeci- 
 ous ; the sexes being distinct, and intercourse between the male 
 and female necessary for the impregnation of the latter. 
 
 The male is generally at once distinguished by the penis appended 
 to the right side of the neck (Jig. 193, g), an organ which is fre- 
 quently of enormous proportions ; so large, indeed, that, it being 
 impossible that it should be retracted into the body, it is generally 
 simply folded back into the branchial chamber. The testicle is 
 imbedded in the mass of the liver, and lodged in the inmost recesses 
 of the shell. It gives origin to a long and very tortuous vas de- 
 ferens, which is at first extremely slender, but on emerging from 
 the mass of the viscera it becomes thicker, running along the right 
 side of the body until it enters the penis, and, having made many 
 
 * The announcement of the discovery of Spermatozoa in individuals belonging to 
 these orders, mentioned in a former page, will, perhaps, materially modify the opinions 
 of physiologists upon this point. 
 
418 GASTEROPODA. 
 
 zig-zag folds, it reaches the extremity of that organ, where it ter- 
 minates by a small orifice. 
 
 Equally simple is the structure of the generative system in the 
 females of the PECTINIBRANCHIATE Gasteropods. A large ovary 
 occupies the same position as the testis of the male, and shares with 
 the liver the interior of the windings of the shell. The oviduct 
 generally follows the same course as the vas deferens of the other 
 sex, and is provided with thick and glandular walls. The eggs, 
 which are very numerous, are arranged in long gelatinous ribands, 
 and, after extrusion, are glued in various ways to the surface of 
 rocks, sea-weed, or even to the shells of other Mollusca. Some- 
 times in the siphoniferous tribes, as for example in the common 
 welk (Buccinum), the ova are enclosed in tough coriaceous capsules 
 secreted by a glandular organ in the vicinity of the oviduct. These 
 capsules contain several eggs a-piece, and are joined together in large 
 bunches, such as the waves continually cast up upon every beach. 
 
 (456.) The HETEROPOD Gasteropoda are hermaphrodite. In 
 Pterotrachea the female organs consist of a distinct ovary, uterus, 
 spermatheca, and an auxiliary gland, all lodged in the visceral sac- 
 culus appended to the back. The ovary (Jig. 188, p) is of con- 
 siderable, size, and gives origin to a slender oviduct, which near its 
 termination communicates with the receptacle for the ova, called the 
 uterus (g). The spermatheca (r) joins the canal leading from the 
 uterine cavity to the exterior of the body, which likewise receives 
 the secretion of two small glandular sacs (k) apparently destined 
 to furnish some investment to the eggs prior to their expulsion. 
 
 The male parts are situated in the general cavity of the body, 
 quite apart from the female apparatus. The testicles seem to be 
 represented by two wavy cseca (Jig- 188, <), which terminate at 
 the root of a small intromittent organ (s) placed at a short distance 
 behind the opening of the vulva. 
 
 (457.) All the TECTIBRANCHIATA, INFEROBRANCHIATA, 
 NUDIBRANCHIATA, and the PULMONATED GASTEROPODS are 
 hermaphrodite, having both a male and female generative apparatus 
 arranged upon the same principles as those of the snail, which 
 have already been described at length ; and to enumerate the 
 variations which occur in the relative position and organization of 
 different parts of the reproductive system in all the genera com- 
 posing these extensive orders would scarcely answer any useful pur- 
 pose, even were it practicable within the limits of this work. 
 
 (458.) Many families of Gasteropoda, as for example the Nu- 
 
GASTEROPODA. 419 
 
 DIBRANCHIATA (Jig. 185), are absolutely deprived of any shelly 
 defence, the investment of their bodies being entirely soft and 
 contractile. In others, as the slug (Limax), a thin calcareous 
 plate is imbedded in the substance of their muscular covering. 
 This little shell is contained in a cavity within the mantle, and is 
 quite loose and unattached to the walls of the cell wherein it is 
 lodged. The mode of its formation and growth is exceedingly 
 simple, and from its very simplicity is well calculated to illustrate 
 the formation of shells of more complex character. The floor of 
 the cavity containing the calcareous plate is vascular, and secretes 
 cretaceous particles mixed up with a viscid animal secretion. The 
 material thus furnished in a semi-fluid state is applied like a layer 
 of varnish to the lower surface of the shell already formed by the 
 same process ; and the added layer, soon hardening, increases the 
 thickness of the original plate, while at the same time, as a necessary 
 consequence of the progressive extension of the secreting membrane, 
 which enlarges with the growth of the slug, each successive lamina 
 of shell is larger than that which preceded it. Thus the extension 
 of the shell in diameter, as well as its increase in thickness, is easily 
 explained. In these internal shells, however, there is no colouring 
 matter ; so that they are uniformly white, and present the same tex- 
 ture throughout. 
 
 (459.) As external shells are generally painted upon their outer 
 surface with colours of different kinds variously disposed, in such 
 the process of growth is somewhat more complicated, and in every 
 essential particular resembles that already described, whereby the 
 shells of the CONCHIFERA are extended in size and thickness. 
 
 We choose, as an illustration of the manner in which the exter- 
 nal shells of univalves are manufactured, one of the least complex 
 forms, as being best adapted to elucidate this part of our subject. 
 The Patella, or common limpet, is covered with a simple conical 
 shell that extends over the whole of the dorsal surface of the mol- 
 lusk. The testaceous shield that thus protects these animals is 
 generally variegated externally with sundry markings of diverse 
 colours, while within it is lined with a smooth and white nacre. 
 
 On making a perpendicular section of one of these Gasteropods, 
 the entire mechanism by which such shells are constructed and 
 painted is at once rendered intelligible. The whole of the back of 
 the animal covered by the shell is invested with a membranous 
 mantle, like that of a conchiferous mollusk ; but different parts of 
 this mantle are appointed to different offices. The extension of the 
 
420 
 
 GASTEROPODA. 
 
 Fig. 194. 
 
 shell is entirely effected by the margin of the mantle (fig. 194, 6), 
 which is thick, vascular, and studded with glands appointed to 
 secrete the colouring material that paints the exterior. This 
 thickened fringe of the mantle is firmly glued to the circumference 
 of the opening of the shelly cone : the earthy matter produced by 
 it is added, layer by layer, to the edge of the shell ; and, wherever 
 coloured glands are situated, this earthy secretion is coloured with 
 a corresponding pigment : in this manner is the shell gradually 
 enlarged, and every additional stratum of calcareous deposit is 
 thus painted at the moment 
 of its formation. 
 
 The growth of the shell in 
 thickness is a subsequent 
 process. After the formation 
 of the outer layer (g) by the 
 edge of the mantle, the ge- 
 neral surface of the pallial 
 membrane (a) adds fresh la- 
 minae of pearly matter (/) 
 
 to the whole interior of the testaceous shield, and it is by the 
 accumulation of such colourless depositions that the thickening of 
 the entire fabric is provided for. 
 
 (460.) When the manner in which the limpet constructs its 
 habitation is understood, the formation of a turbinated or spiral shell 
 is explained with the utmost facility. On extracting a snail from 
 its abode, all that portion of its body which was covered by the shell 
 is seen to be 
 invested with 
 a thin mantle 
 (fig. 195, a) 
 precisely ana- 
 logous to that 
 of the limpet : 
 from this pal- 
 lial membrane 
 the nacreous 
 lining of the 
 shell exudes. 
 But around 
 
 the aperture the mantle swells into a thick glandular collar (), cor- 
 respondent in function with the margin of the mantle in Patella, 
 
 Fig. 195. 
 
GASTEROPODA. 
 
 421 
 
 and in like manner provided with glands adapted to furnish colour- 
 ing matter. From the collar, therefore, those layers are secreted 
 by which the extension of the shell is accomplished ; and, as the 
 deposit is in this case far more abundant in one direction than 
 in another, the shell, as it expands, assumes more or less com- 
 pletely a spiral shape. Wherever glands for secreting coloured 
 pigment exist, corresponding bands or coloured patches are pro- 
 duced as the layers of growth are formed, and the exterior of the 
 shell is thus painted with the tints peculiar to the species. 
 
 (461.) In many marine Gasteropods, spines and various external 
 processes are found projecting from the outer surface of the shell, 
 the production of which depends upon the shape of the margin of 
 the mantle. Let the reader imagine one of these ornamented shells 
 to be transparent, so as to permit the contained animal to be de- 
 lineated in situ, as in the annexed sketch of Pterocera (Jig. 196) ; 
 
 Fig. 196. 
 
 and the collar, which forms the layers of growth, will be found to 
 exhibit fringes or processes precisely resembling those upon the 
 shell itself. But it is only at intervals that, as the growth of 
 the mollusk proceeds, these pallial appendages encase themselves in 
 a calcareous covering, every such interval being distinctly indicated 
 upon the exterior of the shell by the spaces between the successive 
 rows of spinous projections that mark the terminations of so many 
 distinct periods in its formation ; so that the number of ridges 
 or rows of spines is, of course, correspondent with the age of the 
 creature within. 
 
 (462.) Several of the Pectinibranchiate genera are provided with 
 
422 
 
 GASTEROPODA. 
 
 a very complete defence against the assaults of foes that might 
 attack them while they are concealed in their habitations, and, in 
 such a posture, necessarily helpless and incapable of resistance. 
 The provision for their protection is sufficiently simple : attached 
 to the posterior extremity of the body, which is the part last drawn 
 into its abode, is a broad horny or calcareous plate (fig- 196, g), 
 called the operculum ; this is of variable dimensions in different 
 species, but always in shape accurately corresponding with the 
 contour of the mouth of the shell. By this elegant contrivance 
 a door is closely fitted to the aperture of its retreat whenever the 
 mollusk retracts itself within its citadel; and, thus defended, it 
 may safely defy external violence of any ordinary description. 
 
 (463.) A most remarkable exception to the usual univalve con- 
 dition of the shells in the GASTEROPODA, is observable in one 
 solitary genus belonging to the Cyclobranchiate order. In Chi- 
 ton (fig. 197) we find, instead of a turbinated or shield-like 
 
 Fig. 197. 
 
 covering formed of one piece, a kind of armour composed of 
 several distinct plates, arranged in a longitudinal series along the 
 centre of the back, and overlapping each other like the tiles of 
 a house. 
 
 In these curious animals the whole back is invested with a 
 
PTEROFODA. 
 
 dense leatliery mantle of an oval form, and considerably more 
 extensive than the cavity containing the viscera. Where not 
 covered by the calcareous laminae, the exterior of the mantle forms 
 a broad edge variously sculptured in different species : but along 
 its central part the shelly plates, generally eight in number, are 
 partially imbedded in its substance ; being, no doubt, secreted by 
 the surface whereunto they are attached. These mollusks, not- 
 withstanding the singularity of their covering, which almost re- 
 minds us of the armour of many ARTICULATA, in their internal 
 anatomy conform exactly to the type of structure common to the 
 Gasteropod orders, and offer no peculiarities of organization worthy 
 of special notice. 
 
 CHAPTER XXIV. 
 
 PTEROPODA* (Cuv.) 
 
 (464.) NEARLY allied to the Gasteropods in their internal or- 
 ganization, but differing from them remarkably in the character 
 and position of their locomotive apparatus, are the PTEROFODA ; 
 a class of mollusks of small dimensions, but met with in astonish- 
 ing quantities, at certain seasons, in various parts of the ocean. 
 So numberless indeed are these little beings in those regions where 
 they are common, that the surface of the sea seems literally alive 
 with their gambolings ; and thus the store of provisions necessary to 
 render the waters of the ocean habitable to animals of higher grade 
 in the scale of life is still further increased. The great character 
 that distinguishes the members of the class upon the investigation 
 of which we are now entering, is derived from the structure of their 
 organs of locomotion. These are only adapted for swimming, and 
 consist of two broad and fleshy expansions, attached like a pair of 
 wings to the sides of the neck, and forming moveable fins ; enabling 
 the little beings to dance merrily among the foamy waves, now 
 sinking, and again rising to the surface, until some passing whale, 
 opening its enormous jaws, engulphs multitudes of such tiny vic- 
 tims, and hence derives the materials for its subsistence. 
 
 (465.) Several distinct genera of Pteropoda have been esta- 
 
 a wing ; vovs, vobos, a foot. 
 
424 
 
 PTEROPODA. 
 
 blished by zoologists, and some important modifications have 
 been detected in their organization ; although, in all of them, the 
 lateral alee form the instruments of progression. 
 
 The Clio borealis, anatomized by Cuvier,* and more recently 
 and completely investigated by Professor Eschricht of Copen- 
 hagen,'!' is one of the species best known, as well as most abun- 
 dantly met with ; it is, therefore, by a description of this Ptero- 
 pod that we shall proceed to introduce the reader to the general 
 facts connected with the history of the animals under consideration. 
 
 The body of the Clio is about an inch in length, of an oblong 
 shape, and terminating posteriorly in a point ; while at the oppo- 
 site extremity there is a little head supported upon a short neck, 
 and furnished with delicate retractile tentacles, apparently instru- 
 ments of touch. The locomotive organs, as the name of the class 
 imports, consist of two delicate wing-like appendages (Jtg> 198, a, a) 
 attached to the two sides of the neck ; by means of which, as by a 
 pair of broad fins, the Pteropod rows itself about with facility. 
 But the two aliform membranes, although externally they appear 
 separate instruments, are, as we are assured by the observations of 
 Professor Eschricht, but one organ ; being made up entirely of 
 muscular fasciculi, which pass right through the neck, and spread 
 out on each side in the substance of the wing, forming an appara- 
 tus exactly comparable to the double-paddled oar with which the 
 Greenlander so dexterously steers his kajac, or canoe, through the 
 very seas inhabited by the little Clio we are describing. 
 
 (466.) The head of one of these animals is surmounted by va- 
 
 Fig. 198. 
 
 A B C 
 
 * Memoire sur le Clio borealis. 
 
 f- Anatomische Untersuchungen iiber die Clione Borealis, von D. F. Eschricht. 
 Kopenhagen, 1838, 4to. 
 
PTEROPOUA. 425 
 
 rious organs appropriated to different offices, and some of them not 
 a little remarkable from the amazing complication of structure which 
 they exhibit. On each side of the oral opening are three conical 
 appendages (^/zg.198, c, s), that to a superficial examiner might ap- 
 pear to be mere fleshy tentacula, but, in reality, they are instruments 
 of prehension of unparalleled beauty and astonishing construction. 
 Each of these six appendages, when examined attentively, is seen 
 to be of a reddish tint ; and this colour under the microscope is 
 found to be dependent upon the presence of numerous minute 
 isolated red points distributed over its surface. When still fur- 
 ther magnified, these detached points are evidently distinct organs, 
 placed with great regularity so as to give a speckled appearance to 
 the whole of the conical appendage ; and their number at a rough 
 guess may be estimated at about three thousand. Every one of these 
 minute specks is in fact, when more closely examined, a transpa- 
 rent cylinder, resembling the cell of a Polyp, and containing within 
 its cavity about twenty pedunculated discs, which may be protruded 
 from the orifice of their sheath {fig. 199, c), and form so many 
 prehensile suckers adapted to seize and hold minute prey. Thus, 
 therefore, there will be (3000 x 20 x 6) 360,000 of these micro- 
 scopic suckers upon the head of one Clio ; an apparatus for prehen- 
 sion perhaps unparalleled in the creation. 
 
 When not in use, the appendages referred to are withdrawn, and 
 concealed by two hood-like fleshy expansions, which, meeting each 
 other in the mesial line, completely cover and protect the whole of 
 this delicate mechanism, as represented in fig. 198, A. 
 
 Still, however, even when the hoods are drawn over the parts 
 they are intended to defend, the Clio is not left without tactile 
 organs wherewith to examine external objects ; for each valve of the 
 hood is perforated near its centre, and, through the apertures so 
 formed, two slender filiform tentacula {fig- 198, c, &), somewhat 
 resembling the feelers of a snail, are protruded at the will of the 
 animal ; and by means of these it is informed of the presence of food, 
 and instructed when to uncover the elaborately organized suctorial 
 apparatus destined to seize it and convey it into the mouth. 
 
 The mouth itself is described by Cuvier as being a simple trian- 
 gular opening, resembling the wound inflicted by a trocar ; and in 
 the solitary specimen at his disposal he did not succeed in detect- 
 ing any dental structures. Eschricht, however, with superior oppor- 
 tunities, was more successful in displaying the oral organs ; and 
 found the Clio to possess jaws of very singular conformation, and a 
 
426 
 
 PTEJIOPODA. 
 
 tongue covered, as in many other Mollusca, with sharp horny 
 spines. 
 
 One of the jaws removed from the body, and magnified twenty- 
 eight diameters, is represented in the subjoined figure (Jig. 
 199, A). It consists of a series of sharp horny teeth of unequal 
 length, fixed to the sides of a lateral pedicle in such a manner 
 that their points are all nearly at the same level. The teeth them- 
 selves have a golden metallic lustre, and, when examined in the 
 sunshine under water by means of a lens, are especially beautiful 
 objects. The basis to which they are fixed is apparently of a 
 fleshy character, and if smashed by being squeezed between two 
 plates of glass, and then placed under the microscope, it would 
 seem to be made up of a multitude of regularly disposed fibres that 
 cross each other in two principal directions. 
 
 The jaws thus constructed are placed on each side of the mouth, 
 contained in two hollow curved cylinders, the walls of which are 
 muscular ; and, if one of these muscular capsules be snipped by 
 means of a pair of very fine scissors, the strangely-formed jaw, 
 with its teeth, is found lodged within it. 
 
 The manner in which the Clio uses these dental organs is ob- 
 vious from their anatomical position. The curved muscular cylin- 
 ders, by the contraction of their walls, force out the teeth, so that 
 they then project from the mouth, and are ready to seize and drag 
 into the oral orifice whatever food presents itself. 
 
 Once conveyed by the jaws into the interior of the mouth, the 
 prey seized is taken hold of by the tongue ; the free extremity and 
 
 Fig. 199. 
 
PTEROPODA. 427 
 
 upper surface of which is seen, when highly magnified, to be cover- 
 ed with regular rows of spiny booklets, all directed backwards, and 
 evidently intended to assist in deglutition (Jig. 199, B). 
 
 The structure of the alimentary canal is extremely simple. The 
 oesophagus (Jig. 200, t) gradually dilates into a wide stomachal 
 cavity that is surrounded on all sides by the mass of the liver ; 
 while the intestine (u), in which the stomach terminates, mounting 
 towards the left side of the neck, ends by an external anal orifice. 
 Two long and slender salivary glands (w) are placed at the sides 
 of the oesophagus, and furnish a secretion that is poured into the 
 mouth. The precise character of the bile-ducts has not been satis- 
 factorily determined in Clio ; but in Pneumodermon, another 
 Pteropod very nearly allied to the genus we are describing, the 
 stomach itself, which is enveloped on all sides by the liver, receives 
 the biliary secretion through a multitude of minute pores. 
 
 (467.) With respect to the real nature of the respiratory appa- 
 ratus in C/zo, much doubt exists. Cuvier regarded the aliform fins 
 as being subservient to respiration, as well as forming locomotive 
 organs ; and observes, that the surfaces of these appendages seen 
 with the microscope present a network of vessels so regular, so close, 
 and so delicate, that it is not possible to doubt but that they are 
 intended to perform the functions of a respiratory apparatus, and 
 states, moreover, that their connection with the internal vessels and 
 the heart confirms this view of the nature of these membranes. 
 
 Eschricht, on the contrary, denies altogether the existence of any 
 such vascular ramifications as Cuvier describes ; asserting that the 
 appearance alluded to is entirely produced by the spreading out of 
 the muscular fibres above mentioned, and that the only vessels 
 visible in the alar processes are a few arterial branches derived from 
 the aorta. 
 
 We are still, therefore, in ignorance as to the respiratory organs 
 of Clio ; the heart, however, is very apparent : it is composed of a 
 single auricle and ventricle, enclosed in a pericardium (Jig. 200, 
 m), and gives off at one extremity a large vessel (w), which Cuvier 
 regarded as a pulmonary vein, but which Eschricht has proved to 
 be the aorta, inasmuch as he has traced its branches to the liver 
 and the other internal viscera of the body. 
 
 (468.) The nervous system of this mollusk is easily distinguish- 
 ed, not only on account of the large proportionate size of the ganglia, 
 but from the circumstance of the nerves being of a pale red colour. 
 The ganglia form a ring (Jig. 200, y) placed around the cesopha- 
 
428 PTEROPODA. 
 
 gus near the middle of the neck. There are eight large and two 
 smaller ganglionic masses closely aggregated in this situation, and 
 from these sources all the nerves of the body are given off. 
 
 (469.) From the large dimensions of the nervous centres we may 
 be prepared to expect senses of correspondent perfection of structure. 
 We have already mentioned the sensitive tentacula protruded from 
 the hood-like covers that protect the oral apparatus ; but, in addi- 
 tion to these, organs of vision are provided, apparently of a very 
 complete character. These eyes are two in number, and are placed 
 on the back of the neck. Each eye has the form of a somewhat 
 bent cylinder, having its two extremities rounded off. The anterior 
 end of the cylinder is the transparent cornea ; and when the eye is 
 removed from the body of the animal, and examined under the 
 microscope by transmitted light, sundry parts may be detected in 
 its interior, sufficient, indeed, to indicate the existence of a choroid 
 membrane, a vitreous humour, and a distinct lens, occupying the 
 ordinary positions of these parts of the visual apparatus. 
 
 (470.) The generative system of Clio resembles in all essential 
 particulars that of the most highly organized Gasteropoda ; and, as 
 in them, is composed of a complete set of male organs as well as of 
 ovigerous viscera. According to the views which Cuvier was led to 
 entertain from the dissection of a single specimen, he supposed that 
 the ovary (fig. 200, ri) gave off a slender oviduct (o) terminating 
 in a thick glandular canal, the testicle (k) ; which, beginning by a 
 csecal prolongation, and gradually diminishing in diameter until it 
 became attenuated into a slender vas deferens (p), ultimately 
 emptied itself into a small round sac (q) situated in one side of the 
 neck where it communicated with the exterior. Close to the sac 
 (q) the illustrious French anatomist pointed out another vesicle 
 (r), which he compared to the bladder (spermatheca) of Gasteropod 
 Mollusks. The more complete researches of Professor Eschricht 
 have, however, rendered considerable modifications of the above 
 description requisite ; inasmuch as that gentleman has succeeded 
 not only in detecting a testis quite distinct from the oviferous canal, 
 but also a very complete intromittent apparatus. The testis, in 
 fact, in a fresh specimen is so large as to occupy a great portion of 
 the visceral cavity ; and, no doubt, in the individual examined by 
 Cuvier, which had been kept in spirits of wine, it formed a large 
 portion of the mass (Jig. 200, i), which he thought to be entirely 
 made up of the liver. The duct from this testis communicates with 
 the receptacle (</), so that the glandular canal (k) must be regarded 
 
CEPHALOPODA. 
 
 429 
 
 as a part of the oviduct analogous to what has been called the ute- 
 rus in the snail. Figt 2 oo. 
 
 Another important 
 discovery, for which 
 science is indebted to 
 the Danish Professor, 
 is, that the Clio pos- 
 sesses a long and sin- 
 gularly - formed penis 
 (fig. 198, c, A), lodged, 
 when retracted, in the 
 interior of the head of 
 the Pteropod ; but 
 which, together with 
 the bladder (g), in 
 which it was contained, 
 can be extruded from 
 the right side of the 
 neck to such an extent that it nearly equals in length the whole 
 body of the little creature. 
 
 The mass formed by the viscera occupies but a small space in the 
 general cavity of the body. The external investment of the visceral 
 sac is a thin semi-transparent skin (f) of soft texture ; and within 
 this is a second covering (g), thicker than the first, and exhibiting 
 very distinct muscular fibres, principally distributed in a longitu- 
 dinal direction, so that their action would seem to shorten the 
 animal and make its shape more spherical. 
 
 What fills up the space that intervenes between the muscular 
 tunic and the viscera is as yet undetermined ; but Cuvier, in the 
 memoir above referred to, suggests that it may possibly contain air, 
 which, as it should be compressed or allowed to expand, would 
 form a kind of swimming-bladder, and allow the animal to mount 
 to the surface, or sink into the recesses of the sea, with little effort 
 or exertion of muscular power. 
 
 (471.) The other genera included in this class agree in their 
 general form, and in the arrangement of their digestive and repro- 
 ductive organs, with Clio above described ; but present a few im- 
 portant modifications in the disposition of their branchiae, and other 
 minor circumstances. 
 
 In Hyalaa the mantle contains a shell composed of two unequal 
 plates ; one of which is dorsal, and the other ventral : and the 
 
430 CEPHALOPODA. 
 
 branchiae, which are here distinctly recognisable, form a circle of 
 of vascular leaflets enclosed in a cavity of the mantle situated 
 between the divisions of the shell, and so disposed that the water 
 has free admission to them through the two lateral fissures of its 
 testaceous defence. 
 
 In Pneumodermon, again, the branchise occupy a totally different 
 situation ; the branchial leaflets being arranged in semicircular lines 
 upon the posterior extremity of the animal : but such modifications 
 of a general type of structure are of more interest to the zoologist 
 than to the physiological reader. 
 
 CHAPTER XXV. 
 
 CEPHALOPODA* (Cuv.) 
 
 (472.) WE now arrive at the highest order of Mollusca, com- 
 posed of animals distinguished by most strange and paradoxical 
 characters, and exhibiting forms so uncouth that the young zoolo- 
 gist, who for the first time encounters one of these creatures, may 
 well be startled at the anomalous appearance presented by beings so 
 remote in their external construction from everything with which 
 he has been familiar. 
 
 Let him conceive an animal whose body is a closed bag con- 
 taining the viscera connected with digestion, circulation, and repro- 
 duction, furnished with a head and staring eyes ; that upon the 
 head are supported numerous and complex organs of locomotion, 
 used as feet or instruments of prehension ; moreover, that in the 
 centre of the locomotive apparatus, thus singularly situated, is a 
 strong and sharp horny beak resembling that of a parrot ; and he 
 will rudely picture to himself a Cephalopod, such as we are now 
 about to describe. 
 
 (473.) The Octopus vulgaris, or common Poulpe, represent- 
 ed in the next figure, will serve as an example calculated to 
 prove, we apprehend, that the above is no exaggerated statement ; 
 and, should the student unexpectedly observe an animal of this 
 kind walking towards him upon the beach in the position there de- 
 lineated, his curiosity would doubtless be excited to learn some- 
 thing of its habits and economy. 
 
 * xs<|)a>.>j, the head ; -rovs, wo^oj, the foot. 
 
CEPHALOPODA. 431 
 
 Yet not only can the Poulpc walk in the manner exhibited in 
 the subjoined figure {Jig- 201), but it is well able to*swim, if occa- 
 sion require, the broad fleshy expansion that connects the bases 
 of its eight legs being fully adequate to enable it to adopt such 
 a mode of progression ; for, by vigorous flappings of this exten- 
 sive organ, the animal actively impels itself through the water 
 in a backward direction, and shoots along witlf wonderful facility. 
 
 (474.) The feet or tentacula appended to the head are not, how- 
 
 201. 
 
 ever, exclusively destined to effect locomotion ; they are used, if 
 required, as agents in seizing prey ; and of so terrible a charac- 
 ter, that, armed with these formidable organs, the Poulpe be- 
 comes one of the most destructive inhabitants of the sea; for 
 neither superior strength nor activity, nor even defensive armour, 
 is sufficient to save its victims from the ruthless ferocity of such a 
 foe. A hundred and twenty pairs of suckers, more perfect and 
 efficacious than the cupping-glasses of human contrivance, crowd 
 
432 
 
 CEPHALOPODA. 
 
 the lower surface of every one of the eight flexible arms. If the 
 Poulpe but touch its prey, it is enough : once a few of these tena- 
 cious suckers get firm hold, the swiftness of the fish is unavailing, 
 as it is soon trammelled on all sides by the firmly holding tenta- 
 cula, and dragged to the mouth of its destroyer ; the shell of the 
 lobster or of the crab is a vain protection, for the hard and crooked 
 beak of the Cephalopod easily breaks to pieces the frail armour ; 
 and even man himself, while bathing, has been entwined by the 
 strong arms of gigantic species, and struggled in vain against a 
 grasp so pertinacious. 
 
 (475.) In the genus Octopus the arms are only eight in num- 
 ber, and nearly of equal length ; but to the Calamaries (Loligo) 
 and other genera an additional pair is given, which, being pro- 
 longed considerably beyond the rest, are not merely useful for seiz- 
 ing prey at a distance, but become convertible to other purposes, 
 and may be employed as cables whereby the Cephalopods so fur- 
 nished ride securely at anchor in a tempestuous sea ; the suckers 
 being placed upon an expanded disc situated {Jig. 214) at the 
 extremity of the elongated tentacula, and thus rendered capable of 
 taking firm hold of the surface of a rock or other fit support. 
 The posterior extremity of the body is in such forms generally 
 provided with two broad muscular and fin-like expansions {Jig. 
 214), evidently adapted to assist in sculling the animal along. 
 
 Wonderful as are the provisions above described for insuring 
 food and safety to these formidable inhabitants of the sea, it is 
 only by an attentive examination of the individual suckers, so 
 numerously distributed over the tentacula, that the reader will 
 fully appreciate the mechanism we are so inadequately describing. 
 Machines of human construction admit of being variously esti- 
 mated, as they are found to be more or less adapted to accomplish 
 the object of the contriver : but in estimating the works of the 
 DEITY all degrees of comparison are merged in the superlative ; 
 everything is best, completest, perfect. 
 
 Examine any one of these thousand suckers, it is an admirably 
 arranged pneumatic apparatus, an air-pump. The adhesive disc 
 {Jig. 202, A) is composed of a muscular membrane, its circum- 
 ference being thick and fleshy, and in many species supported by a 
 cartilaginous circlet, so that it can be applied most accurately to 
 any foreign body. In the centre of the fleshy membrane is an 
 aperture leading into a deep cavity (6), at the bottom of which is 
 placed a prominent piston (c), that may be retracted by muscular 
 
CEPHALOPODA. 
 
 Fig. 202. 
 
 fibres provided for the pur- 
 pose. No sooner, therefore, 
 is the circumference of the 
 disc placed in close and air- 
 tight contact with the sur- 
 face of an object, than the 
 muscular piston is strongly- 
 drawn inwards ; and, a va- 
 cuum being thus produced, 
 the adhesion of the sucker is 
 rendered as firm as mechan- 
 ism could make it. 
 
 (476.) Yet even this ela- 
 borate and wonderful system 
 of prehensile organs would 
 seem, in some cases, to be 
 insufficient for the purposes 
 of nature. In the powerful 
 and rapacious Onychoteuthis 
 (fig. 203 ) the cupping- 
 glasses which arm the ex- 
 tremities of their long pair 
 
 of muscular arms are rendered still more formidable ; for from 
 the centre of each sucking-cup projects a strong and sharp hook, 
 which is plunged by the action of the sucker deeply into the 
 flesh of struggling or slippery prey, and thus a firm and most 
 efficient hold upon the seized victim is secured. Nor is this all 
 that claims our admiration in the organization of the arms of 
 Onychoteuthis : at the base of each fleshy expansion that sup- 
 ports the tenacious and fanged suckers above described is a small 
 group of simple adhesive discs, by the assistance of which the 
 two arms can be locked together (fig. 203, A), and thus be made 
 to co-operate in dragging to the mouth such powerful or refractory 
 prey as, singly, the arms might be unable to subdue ; an arrange- 
 ment which has been rudely imitated in the construction of the 
 obstetric forceps.* 
 
 * Cyclop, of Anat. and Physiol. art. CEPHALOPODA. 
 
 2 F 
 
434 
 
 CEPHALOPODA, 
 Ff^.203. 
 
 A B 
 
 (477.) The Argonaut constitutes another family of the CEPHA- 
 LOPODA, and is remarkable as being the inhabitant of a shell of 
 exquisite beauty, familiarly known as that of the Paper-Nautilus ; 
 a shell which from remote antiquity has been decorated with all 
 the ornaments of fiction, and celebrated alike by Poetry and her 
 sister Arts. 
 
 It was, indeed, to this CEPHALOPOD, that the ancients assigned 
 the honour of having first suggested to mankind the possibility of 
 traversing the sea in ships ; and nothing could be more elegant than 
 the little barque in which the Argonaut was supposed to skim 
 
CEPHALOPODA 
 
 Fig. 204. 
 
 435 
 
 over the waves, hoisting little sails to the breeze, and steering its 
 course by the assistance of oars provided for the purpose. 
 
 The figure annexed (fig. 204), given by Poll in his magnificent 
 work already referred to,* was in perfect accordance with the gene- 
 rally received opinion ; and on such respectable authority we are not 
 surprised to find Cuvier assenting to and sanctioning the statement, 
 that, when the sea is calm, fleets of these little sailors might be 
 seen navigating its surface, employing six of their tentacula or 
 arms instead of oars, and at the same time spreading out two, 
 which are broadly expanded for the purpose, instead of sails. 
 Should the waves become agitated, or danger threaten, the Argo- 
 naut, as we are told, draws in his arms, lowers his sail, and, set- 
 tling to the bottom of his shell, disappears beneath the waters. 
 * Testacea utriusque Siciliw. 
 
436 
 
 CEPHALOPODA. 
 
 It is a thankless office to dispel the pleasant dreams of imagina- 
 tion ; yet such becomes our disagreeable duty upon this occasion. 
 M. Sander Rang, in a recently published memoir upon this sub- 
 ject,* has, from actual observation, apparently established the fol- 
 lowing facts : 1 st, That the belief, more or less generally enter- 
 tained since the time of Aristotle, respecting the skilful manoeuvres 
 of the Poulpe of the Argonaut in progressing by the help of sails 
 and oars on the surface of the water, is erroneous. 2nd, The arms 
 which are expanded into membranes have no other function than 
 that of enveloping the shell in which the animal lives, and that for a 
 determinate object to be explained hereafter. 3rd, The Poulpe, 
 with its shell, progresses in the open sea in the same manner as other 
 Cephalopods. And lastly, That, when at the bottom of the ocean, 
 the Argonaut, covered with its shell, creeps upon an infundibuli- 
 form disc, formed by the junction of the arms at their base, and 
 presenting (alas !) the appearance of a Gasteropod mollusk. 
 
 (478.) It is not a little remarkable that the same animal should, 
 even in these days, be the subject of the extremes of credulity and 
 scepticism ; yet such has been the case with the Argonaut. While 
 zoologists were contented to allow the creature in question the 
 reputation of being an active and skilful navigator, it has been very 
 generally stigmatised as a pirate, which, having forcibly possessed 
 itself of the shell of another animal, lived therein, and made use of 
 it for its own purposes. It was in vain to urge, in opposition to this 
 calumny, that the Argonaut was never found in any other shell 
 than the beautiful one represented in the preceding figure ; that no 
 other creature had been pointed out as the real fabricator of its 
 abode ; that, whatever the size of the Poulpe, it occupied a re- 
 sidence precisely corresponding in dimensions with those of the 
 possessor. The apparent want of resemblance between the out- 
 ward form of the animal {fig' 206) and that of its fragile covering, 
 together with the absence of any muscular connection between the 
 two, were looked upon as furnishing sufficient evidence of its para- 
 sitical habits. The recent observations of Madame Jeannette 
 Power, to be noticed more at length hereafter, and those of M. 
 Sander Rang, above alluded to, have, however, completely settled 
 the so long agitated question ; and, the Argonaut having been 
 watched carefully from the state in which it leaves the egg until 
 it arrives at maturity, the manner in which it forms and repairs its 
 frail shell is now satisfactorily understood. 
 
 * Guerin's Magasin de Zoologie, translated into the Magazine of Natural History, 
 vol. iii. New Series, p. 521. 
 
CEPHALOPODA. 
 
 437 
 
 . (479.) A still more interesting group of CEPHALOPODS, and 
 one which in former periods of the world has been extensively 
 disseminated, inhabited chambered shells ; but of all the varied 
 forms of these creatures, whose remains are so abundantly met with 
 in a fossil state, and known by the names of Ammonites, Belem- 
 nttes, Nummulites, Sec. two species only have been found to be at 
 present in existence, the Spirula, an animal as yet imperfectly 
 known ; and the Nautilus Pompilius, of which the only specimen 
 obtained in modern times* has been the subject of a monograph 
 by Professor Owen, who has most completely investigated its gene- 
 ral organization and relations with other families of the Cephalo- 
 poda. The shell of the Pearly Nautilus (N. Pompilius) is extreme- 
 ly common, and may be met with in every conchological collection, 
 
 Fig. 205. 
 
 notwithstanding the extreme rarity of the mollusk that inhabits 
 it ; a circumstance, perhaps, to be explained by the fact that the 
 
 * For this invaluable addition to zoological knowledge science is indebted to George 
 Bennet, Esq. who obtained the living animal near the island of Erromanga, New 
 Hebrides. " It was found in Marekini bay, floating on the surface of the water not 
 far distant from the ship, and resembling, as the sailors expressed it, a dead tortoise- 
 shell cat in the water. It was captured, but not before the upper part of the shell 
 had been broken by the boat-hook in the eagerness to take it, as the animal was sink- 
 ing when caught." Mr. Rennet's Journal. 
 
438 
 
 CEPHALOPODA- 
 
 living animal dwells in deep water, and when it comes to the 
 surface is so vigilant against surprise, that at the slightest alarm it 
 sinks to the bottom. On making a section of the shell its cavity 
 is found to be partitioned off by numerous shelly septa into various 
 chambers (Jig. 205, s, s), in the last of which the body of the 
 animal is situated. A long tube, or siphuncle (A, A), partly cal- 
 careous and partly membraneous, passes through all the compart- 
 ments quite to the end of the series. The membranous siphuncle 
 is continued into the animal, and terminates in a cavity contained 
 within its body, hereafter to be described, which is in free com- 
 munication with the exterior. 
 
 Various conjectures have been indulged in concerning the 
 end answered by the camerated condition of the shell in these 
 MOLLUSCA. Dr. Hooke* suggested the idea that the chambers 
 might be filled with air generated by the Nautilus, and thus made 
 so buoyant that the specific gravity of the animal and its shell 
 should correspond with that of the surrounding medium, and 
 that, acting in the same manner as the swimming-bladder of a 
 fish, the creature would float or sink, as the air in its shell was 
 alternately compressed and rarefied. Should this supposition be 
 correct, it would seem probable, as Dr. Buckland has pointed out, 
 that the simple retraction of the head, by injecting water from 
 the chamber within its body (pericardium) into the membranous 
 siphuncle, would cause the needful condensation of the air con- 
 tained in this singular float, and allow the Nautilus to sink to 
 the bottom ; while the protrusion of its arms, by taking off the 
 pressure, and thus allowing of the expansion of the confined air, 
 would give every needful degree of buoyancy, even sufficient to 
 permit the mollusk to rise like a balloon to the top of the sea. 
 
 The body of this Cephalopod is covered with a thin mantle 
 (a, a), of which a large fold (b) is reflected on the exterior of the 
 shell. It is securely fixed to its residence by two lateral muscles, 
 the insertion of one of which is seen at g. A large coriaceous 
 hood (n) covers the head, and, when the creature retreats into its 
 habitation, closes the entrance like a door ; while through the infun- 
 dibulum (i) the ova and excrementitious matters are expelled from 
 the body. The most remarkable feature, however, exhibited in 
 the external conformation of Nautilus, is the conversion of the 
 sucker-bearing arms of other Cephalopods into an elaborate appara- 
 tus of tentacular organs appended to the head (o, o) ; but these, as 
 well as the eye (wi), will be more minutely described as we proceed. 
 
 * Philosophical Experiments and Observations, 8vo. 1726. 
 
CEPHALOPODA. 439 
 
 (480.) Turning our attention to the anatomical structure of the 
 CEPHALOPODA, we find that in all of them the exterior of the 
 body is entirely formed by an intricate interlacement of muscular 
 fibres. The sac that contains the viscera, itself muscular, is united to 
 the head by strong and largely-developed fasciculi ; the funnel (fig. 
 206, a) through which, as through a fleshy pipe, the products of 
 excretion, as well as the eggs or seminal fluid, are ejected, is form- 
 ed of a tissue similarly endowed with contractility ; while the arms 
 are composed externally of muscles disposed in various directions, 
 and moreover have their central portion occupied by strong bands, 
 which traverse them longitudinally from end to end, so that they 
 are thus gifted with all needful powers of motion, and may be 
 shortened, elongated, or bent in any direction at pleasure. 
 
 In those species which, like Loligopsis (fig. SI 4), or Onycho- 
 teuthis (Jig. 203), have fins appended to the sides of the visceral 
 sac, these organs likewise are made up of muscular substance ; 
 and, being thus converted into broad moveable paddles, they also 
 form efficient locomotive agents. 
 
 (481.) One important circumstance observable in the class be- 
 fore us must not be forgotten in connection with this portion of 
 the history of the Cephalopods. We may remind the student, 
 that in the vertebrate division of animated nature, to which these 
 creatures immediately lead us, the locomotive system is support- 
 ed by an internal vascular and living skeleton, composed either 
 of cartilage, as is the case in the most imperfect vertebrated genera, 
 or, in the more highly organized forms, of bones articulated with 
 each other, and possessing within themselves the means of growth 
 and renovation derived from the blood which permeates them in 
 every part. The reader will remember that, in all the classes that 
 have offered themselves to our notice, we have not hitherto observed 
 anything at all comparable to an internal osseous framework such 
 as man possesses ; dead, extra vascular shells, formed by successive 
 depositions of layers of calcareous material, or jointed cuticular ar- 
 mour equally incapable of growth, having as yet represented the ske- 
 leton, and formed the only levers upon which the muscular system 
 could act in producing the movements connected with locomotion. 
 
 Having, however, already had abundant opportunities of seeing 
 how gradually nature proceeds in effecting the developement of a 
 new series of organs, we might naturally be led to expect in the 
 creatures before us some faint indications, at least, of our approach 
 to animals possessed of an internal bony framework, and our ex- 
 
440 
 
 CEPHALOPODA. 
 
 pectations in this particular will be found on investigation to be 
 well-grounded. It is, in fact, in the CEPHALOPODA, the highest 
 of the molluscous classes, that the rudiments of an osseous sys- 
 tem for the first time make their appearance ; not, indeed, as yet 
 composed of perfect bone, but formed of cartilaginous pieces, 
 some being so disposed as to protect the ganglionic mass above 
 the oesophagus, which now from its size well deserves the name of 
 brain, whilst others serve to afford bases of attachment to the mus- 
 cular system in different regions of the body. 
 
 The most important piece met with in the cartilaginous skeleton 
 of the Cuttle-fish encloses and defends the brain, and therefore is 
 most appropriately called the cranial cartilage, being the corre- 
 spondent both in position and office with the cranium of a vertebrate 
 animal. This rudimentary cranium (fig. 215) embraces the oeso- 
 phagus with a cartilaginous ring, encases the brain, affords passage 
 to the optic nerves, and gives off orbital plates for the protection of 
 the eyes. This cartilage likewise gives a firm origin to the muscles 
 of the locomotive tentacula appended to the head, and, moreover, 
 contains within its substance an auditory apparatus, presenting the 
 earliest condition of an organ of hearing such as is met with in the 
 vertebrate division of the animal kingdom ; in every respect, there- 
 fore, it claims to be considered as the first appearance of a skull. 
 Another broad cartilage is imbedded among the muscles at the base 
 of the funnel ; and two distinct plates situated in the lateral fins of 
 such species as possess appendages of that description offer, un- 
 doubtedly, the rudiments of those portions of the skeleton that 
 sustain the locomotive limbs of quadrupeds. 
 
 (482.) But while we thus see in the CEPHALOPODA the earliest 
 form of an internal osseous skeleton, we cannot be surprised to find 
 these mollusks still retaining, at the same time, the tegumentary 
 calcareous shell or epidermic skeleton of inferior animals. 
 
 On slitting up the mantle of a Calamary (Loligo) along the me- 
 sial line of the back, it is found to contain a large cavity, wherein 
 is lodged a long plate of horn, called the gladius, which in shape 
 might be not inaptly compared to the head of a Roman spear. 
 This enclosed horny substance, notwithstanding the dissimilarity 
 of texture, is, in fact, strictly analogous to the enclosed shell of the 
 Slug, described in a former page ; and its growth is effected in the 
 same manner, namely, by an exudation of corneous material from 
 the floor of the chamber that contains it, and this horny secretion, 
 hardening as it is deposited layer by layer, adds to the dimensions 
 
CEPHALOPODA. 441 
 
 of the gladius as the growth of the animal proceeds. Several of 
 these plates may be produced in succession, and in old individuals 
 it is not uncommon to find two or three enclosed in the same 
 cavity, and placed one behind the other ; that nearest the visceral 
 aspect of the chamber being the most recently formed. These 
 rudimentary shells have no connection whatever with the soft parts 
 of the Calamary, to which, in fact, they are so little adherent that 
 they fall out as soon as the sac wherein they are secreted is laid 
 open. 
 
 In the Cuttle-fish (Sepia officinalis} the dorsal plate (os Sepia) 
 is found in the same situation as the gladius of the Calamary, from 
 which, however, it differs remarkably both in texture and compo- 
 sition. The cuttle-bone, with the appearance of which every one 
 is familiar, is principally composed of calcareous substance ; and, 
 were we to judge of its weight from its bulk, would seem calculated 
 materially to interfere with the movements of an aquatic animal, 
 destined to swim about, and consequently needing whatever assist- 
 ance might be derived from lightness and buoyancy. Did a crea- 
 ture so apparently destitute of natatory organs possess a swim- 
 ming-bladder like that of a fish, to assist in supporting it in the 
 water, we should conceive such an apparatus to be far more adapted 
 to its predatory habits than a shell so bulky as that which it is 
 destined to carry. 
 
 (488.) We have, however, already seen in the case of the Nauti- 
 lus that it would be by no means impracticable to convert a shell into 
 a float nearly equalling a swimming-bladder in efficiency ; and on 
 more accurate examination it becomes obvious that even in the 
 bone of the Cuttle we have a provision of a similar nature, though 
 the end arrived at is obtained in a very different manner. On 
 making a section of a cuttle-bone, it will be found to be composed 
 of numerous stages of very thin calcareous plates placed at some 
 distance above each other, and kept apart by the interposition of mil- 
 lions of microscopic pillars. Thus organized, the shell in question 
 becomes sufficiently light to float in water ; and consequently, from 
 its buoyancy, no doubt assists, instead of impeding, the movements 
 of the mollusk. This admirable float, like the horny gladius of 
 Loligo, is lodged in a membranous capsule, and enclosed in the 
 back of the Sepia, having no connection whatever with the sides 
 of the cavity wherein it is placed, but so loose that it readily falls 
 out on opening the sac. 
 
 (484.) The cuttle-bone is formed in the same manner as other 
 
442 
 
 CEPHALOPODA. 
 
 Fig. 206. 
 
 shells, by the continued addition of calcareous laminae secreted by 
 that side of the containing capsule which is interposed between the 
 shell and the abdominal viscera ; and these layers, being successively 
 added to the ventral surface of the shell, thus gradually increase its 
 bulk as the Cuttle-fish advances to maturity. Neither in the mode 
 of its growth nor in its texture, therefore, does the os Sepice resem- 
 ble bone, properly so called ; it receives neither vessels nor nerves, 
 but is in all respects a dermal secretion, imbedded in the mantle, 
 and formed in the same manner as the dorsal plate of the Slug. 
 
 (485.) We 
 now come to 
 consider the 
 long disput- 
 ed question 
 relative to the 
 nature of the 
 shell of the 
 Argonaut. 
 The Poulpe 
 that inhabits 
 the elegant 
 abode repre- 
 sented in a 
 preceding fi- 
 gure ( Jig. 
 204), when 
 removed from 
 its testaceous 
 covering, has 
 the general 
 form of an 
 Octopus. Its 
 body (Jig. 
 206) is en- 
 closed in an 
 ovoid mus- 
 cular sac (d), 
 and the head 
 
 is surmounted by eight long sucker-bearing arms, of which six 
 (e,/)taper gradually from their origins to their extremities, while 
 the other two, formerly regarded as sails, and which we shall con- 
 
 d 
 
CEPHALOPODA. 443 
 
 tinue to designate by their ordinary name, vela, expand into 
 broad membranes (b). 
 
 M. Sander Rang, who, during a residence at Algiers, had ample 
 opportunity of studying the living Argonaut, ascertained that in the 
 figure copied from Poli, which we have given in a preceding page, 
 the animal is placed in its shell in a reversed position ; and that, 
 when alive, the creature is always found with its veliferous arms 
 turned towards the spire of its shell, instead of in the opposite 
 direction, as represented in the drawing referred to. Moreover, 
 the vela, instead of forming sails, are invariably tightly spread 
 out over the external surface of the shell (Jig. 207), which they 
 cover and entirely conceal from view. With its veliferous arms 
 thus firmly embracing its abode, the Argonaut has two modes 
 of progression. It can certainly raise itself from the bottom, and 
 sport about at the surface of the water ; but this is simply effected 
 by the ordinary means used by Calamaries and Cephalopods in 
 general, namely, by admitting the sea-water into its body and then 
 ejecting it in forcible streams from its funnel, so as to produce a 
 retrograde motion, which is sometimes very rapid. Its usual 
 movements are, however, confined to crawling at the bottom with 
 its head downwards ; and in this way it creeps, carrying its shell 
 upon its back. 
 
 The reader will obtain a better idea of the real appearance of 
 the Argonaut in its shell by inspecting the annexed copy of 
 M. Ranges figure than from any verbal description, and we borrow 
 that gentleman's own account of its general appearance.* The 
 membranous portions of the expanded arms, dilated beyond any- 
 thing we could have pictured to ourselves while knowing the 
 animal merely by specimens preserved in spirits of wine, are 
 spread over the two lateral surfaces of the shell in such a manner 
 as to cover it completely from the base of the hard edge to the 
 anterior extremity of the edge of the opening, and consequently 
 the keel. The application of these membranes is direct, and with- 
 out any puckering or irregularity whatever : the lower part of the 
 two large arms being completely stretched, so as to form a kind of 
 bridge over the cavity left between the back of the mollusk and 
 the retreating portion of the spire. When the mollusk contracts 
 itself, it frequently draws in more or less completely its large arms 
 
 * For more ample details upon this subject, the reader is referred to an excellent 
 translation of M. Rang's paper contained in Mr. Charlesworth's Magazine of Natural 
 History. New Series, vol. iii. 
 
444 
 
 CEPHALOPODA. 
 
 and their membranes, so as partially to uncover the shell in front, 
 as is represented in the figure (Jig- 207). 
 
 Fig. 207. 
 
 There is little doubt that the vela of the Argonaut, which thus 
 envelope its abode, are the organs employed in constructing the 
 brittle fabric, and the agents whereby fractures and wounds in the 
 shell are repaired and filled up. 
 
 The positive experiments of Madame Power* leave no doubts 
 upon the subject ; for not only did that lady, by rearing young 
 Argonauts from the egg, watch the first appearance and earliest 
 growth of the shell, but, by breaking the testaceous covering of 
 adult specimens, she found that they could readily repair the 
 damage inflicted. Being desirous of observing the manner in 
 which this operation was accomplished, the lady to whom science 
 is indebted for these interesting researches examined an individual 
 on the day after its shell had been intentionally broken, and found 
 that the aperture was already covered by a thin glutinous lamella, 
 which, although as yet as delicate as a cobweb, united the margins 
 of the fracture. The next day the lamina had become thickened 
 to a certain degree and more opaque ; till at length, at the end of 
 ten or twelve days, the new piece had become quite calcareous. 
 Madame Power is likewise certain that, while in the act of mend- 
 ing the fractures, the Argonaut applied its vela to the exterior of 
 the shell, and wrinkled them upon it ; whence they may naturally 
 be regarded as being the source from which the glutinous secretion 
 that finally became hardened into shell proceeded. 
 
 * Magazine of Natural History, April 1839. Observations on the Poulpe of the 
 Argonaut, by Madame Jeannelte Power. 
 
CEPHALOPODA. 445 
 
 (486.) In order to understand the manner in which the remark- 
 ably constructed camerated shells, such as those of Nautilus, are 
 produced, it is not necessary to imagine any deviation from the 
 simple mode of procedure adopted in all the cases we have as yet 
 considered. The continual elongation of the spiral cone is, as is 
 evident from the lines of growth visible upon its outer surface, 
 effected by the addition of successive layers to the margin of the 
 aperture of the last-formed chamber, wherein the animal resides ; 
 and as the production of the calcareous secretion whereby the shell 
 is enlarged is most rapidly effected upon that side of the body 
 where the funnel (Jig. 205, i) is situated, the gradually expand- 
 ing shell naturally revolves around an eccentric axis. While the 
 growth of the shell continues, the animal is constantly advancing 
 forwards, and thus leaves the first-formed portions of the shell un- 
 occupied. At intervals, as the Nautilus thus removes itself fur- 
 ther and further from the bottom of its abode, that portion of its 
 mantle which covers the general surface of its visceral sac (fig. 
 205, d) secretes floors of shelly substance behind it ; and thus the 
 septa, s, 5, are formed whereby the shell is separated into chambers, 
 every chamber having in turn been occupied by the body of the 
 Nautilus. The gradual prolongation of the fleshy siphon (h) is 
 easily understood, because it naturally increases in length with the 
 growth of the animal : but how the two muscles (fig. 205, g), 
 that fix the body to the shell, progressively advance their points of 
 attachment as the shell enlarges, is not so readily explained ; nei- 
 ther are we prepared to account satisfactorily for the accomplish- 
 ment of this part of the process. 
 
 (487.) It has been already stated that in all Cephalopods the 
 aperture of the mouth is situated in the centre of the disc formed 
 by the union of the origins of the feet (Jigs. 210, 214). The 
 oral orifice is generally surrounded by a broad circular lip (Jig. 
 208, A, a), which being not unfrequently fringed or papillose, 
 there is little doubt of its possessing sufficient sensibility to render 
 it of material assistance in manducation. 
 
 The circular lip partially conceals a pair of strong horny man- 
 dibles, not unlike the beak of a parrot, but differing in this parti- 
 cular, that in the Cephalopod the upper mandible is the shorter 
 of the two, and is overlapped by the lower jaw. - The mandibles 
 detached from the soft part are represented in fig. 208, B, a, b. 
 There is likewise another important difference between the struc- 
 ture of the beak of the Cuttle-fish and that of the bird, inasmuch 
 
446 
 
 CEPHALOPODA. 
 
 as in the former there is no bony support to the horny jaws, and 
 consequently some other means of sustaining them must be had 
 recourse to. We accordingly find the place of the jaw-bones sup- 
 plied by a fibro-cartilaginous substance (fig. 209, c) that fills the 
 interior of each mandible, and thus gives it sufficient solidity for 
 all required purposes. Externally, the jaws are imbedded to a 
 considerable depth in a strong mass Fig. 208. 
 
 of muscle (fig. 08, &), composed 
 of several layers of fibres variously 
 disposed, so as to open or close the 
 jaws with a degree of force propor- 
 tioned to their large size. Here, 
 therefore, is an apparatus fully ade- 
 quate to co-operate with the elabo- 
 rately constructed prehensile arms 
 whereby these predatory animals 
 seize their prey ; and a victim once 
 involved in the tenacious grasp of 
 the tentacula, and dragged to this 
 powerful beak, can have but little 
 chance of resisting means of destruc- 
 tion so formidable as those granted 
 to the Cephalopoda. 
 
 The mandibles of Nautilus Pom- 
 pilius, instead of being entirely 
 composed of horn, as is invariably 
 the case in these genera that, being 
 provided with tentacula armed with 
 suckers, are thus capable of seizing 
 active and slippery animals, would 
 seem to be rather calculated to break 
 to pieces the testaceous coverings of Mollusca or the armour of 
 the Crustacea. They possess indeed the shape of the jaws al- 
 ready described, but are blunt at their extremities (Jig. 10, w, o), 
 and thickened by a covering of a dense calcareous substance ; so 
 that they appear manifestly adapted to crush hard substances, 
 rather than to cut or lacerate the tender bodies of fishes.* The 
 jaws of the Nautilus, like those of the Octopus above described, 
 are embedded in a powerful mass of muscles (p) whereby they are 
 opened and shut with great force, and are also provided with a 
 
 * Owen. Memoir on the Pearly Nautilus ; London, 1832, 4to. 
 
CEPHALOPODA. 447 
 
 distinct muscular apparatus destined to protrude them when in use, 
 and again to retract the whole mass of the mouth deeply into the 
 body when unemployed. The mechanism provided for the pro- 
 trusion of the mandibles is a strong semicircular muscle (Jig- 210, 
 r, r), which firmly embraces the base of the oral apparatus, and 
 by its contraction pushes it outwards among the labial tentacula 
 (A, k) ; while, on the other hand, four retractor muscles, the upper 
 pair of which are represented in the figure referred to (<?, <?), arise 
 from the extremities of the cranial cartilage, and, running forwards 
 to be inserted into the oral mass, are the agents whereby the whole 
 is again withdrawn and thus concealed from view. 
 
 (488.) The tongue of the CEPHALOPODA, as in the Mollusca 
 described in the two last chapters, is an exceedingly important in- 
 strument, and from its construction would here seem to be an 
 organ of taste, as well as a necessary assistant in deglutition. Tn 
 the annexed figure, representing a vertical section of the beak of a 
 very large Onychoteuthis, the shape and disposition of the differ- 
 ent parts of the tongue are well seen. The substance of the 
 
 Fig. 209. 
 
 a 
 
 tongue itself is fleshy (fig. 209, e, i), and its movements are 
 principally performed by the action of its own intrinsic muscular 
 
448 CEPHALOPODA. 
 
 fibres : its surface is divided into several lobes (/, g, A), partially 
 invested with a delicate and papillose membrane ; but a large 
 portion of tlie organ is covered with sharp recurved horny hook- 
 lets, so disposed that, with their assistance, the morsels of food 
 taken int# the mouth are seized and dragged backwards by a kind 
 of peristaltic motion to the commencement of the ffisophagus (z). 
 The necessity of the provision thus made for enabling the Cepha- 
 lopods to swallow the substances upon which they feed, must be at 
 once apparent ; for, seeing that the walls of the mouth are formed 
 entirely by the hard and inflexible horny beak, it is difficult to 
 conceive how deglutition could have been accomplished by any 
 other contrivance. 
 
 (489.) Four salivary glands pour a copious supply of saliva into 
 the oral chamber : of these, two, situated on the sides of the root of 
 the tongue, give off distinct ducts, which terminate near the com- 
 mencement of the O3sophagus ; while the other pair, generally 
 larger than the superior, is lodged in the visceral sac on each side 
 of the upper part of the crop. The inferior salivary glands each 
 furnish an excretory canal ; but their two ducts soon unite into a 
 single tube (wi), which, with the oesophagus, passes through the 
 ring formed by the cranial cartilage, and, piercing the fleshy mass 
 of the mouth, opens in the neighbourhood of the spiny portion of 
 the tongue, so that the secretion furnished at this point serves to 
 moisten the aliment as it is taken up by the lingual hooks to be 
 swallowed. In Onychoteuthis two salivary glands (fig* 09, &) 
 are situated at the root of the tongue, and their ducts are pointed 
 out in the drawing by pins introduced into their orifices. 
 
 (490.) The alimentary canal presents the same general struc- 
 ture in all the Cephalopod families. The oesophagus (fig. 208, 
 A, d',jig. 10, s), derived from the posterior part of the fleshy 
 mass of the mouth, passes through a ring formed in the cranial 
 cartilage ; or else, as in Nautiluses partially embraced by processes 
 derived therefrom. It soon dilates into a capacious crop (fig- 
 210, ), the walls of which are glandular; and, being lined with a 
 mucous membrane that is gathered into longitudinal plicae, this 
 organ readily admits of considerable dilatation. 
 
 From the crop, a short passage (u) leads into a strong muscular 
 gizzard (v) resembling that of a granivorous bird, and lined in the 
 same manner by a thick coriaceous cuticular layer : in this gizzard, 
 therefore, the food is gradually bruised and reduced to a pultaceous 
 magma. 
 
CEPHALOPODA. 
 
 449 
 
 (491.) At a little distance from the gizzard there is in the 
 Nautilus, appended to the side of the intestine, a globular viscus 
 (fig. 10, 3/), which is hollow, and its cavity communicates freely 
 with the intestinal canal. The interior of this organ Professor 
 Owen found to be occupied by broad parallel laminae, puckered 
 transversely so as to offer a great extent of surface ; and, when 
 examined under a lens, their structure was seen to be follicular, and 
 
 F. 210. 
 
 evidently fitted for secretion. The bile is poured into this cavity 
 at the extremity farthest from the intestine, by a duct large enough 
 to admit a common probe. 
 
450 CEPHALOPODA. 
 
 In other genera this laminated viscus is represented by a csecal 
 appendage to the intestine, placed precisely in the same situation ; 
 and, on opening it, its internal surface is found to be increased by 
 a spiral lamella that winds closely upon itself from one end to the 
 other. In such cases it is near the apex of the spire that the 
 bile is received from the liver, so that in all essential particulars 
 this spiriform viscus is precisely analogous to the laminated cavity 
 of the Nautilus. There can be little doubt that this apparatus re- 
 presents a capacious duodenum, and that it is by the extensive 
 surface afforded in its interior that the nutritious portions of the 
 food are separated ; as neither the gizzard nor the intestine itself 
 present an organization adapted to such a purpose. With respect 
 to its other uses Professor Owen remarks, that its reception of 
 the biliary secretion renders it in some measure analogous to a 
 gall-bladder ; but most probably its chief office is to pour into 
 the commencement of the intestinal canal a fluid which is neces- 
 sary for the completion of digestion, so that, like the pyloric ap- 
 pendages of fishes, it might be considered to be the representative 
 of a pancreas. 
 
 The remainder of the intestine is a simple tube, which, after one 
 or two turns upon itself, mounts up to the base of the funnel, into 
 which it opens ; and thus allows the excrement to be ejected to a 
 distance from the body. 
 
 (492.) The liver (fig- 210, z) is of very great bulk when com- 
 pared with the rest of the digestive apparatus. In Nautilus it is 
 divided into four distinct lobes, which are themselves made up of 
 numerous lobules of an angular form, each being invested with a 
 very delicate capsule. On removing the capsule every lobule is 
 seen to be composed of numerous acini, which with a needle may 
 be readily separated into clusters connected by the ramifications of 
 their excretory duct. In other genera, such as Octopus, wherein 
 these acini have been minutely examined, they have proved to be 
 delicate cells or secerning cseca wherein the bile is elaborated. 
 The excretory canals derived from all the lobules of the liver 
 unite by repeated anastomoses, and thus form two main trunks, 
 which ultimately join, and pour the biliary secretion into the lami- 
 nated or pancreatic cavity (y). 
 
 In the Cephalopods, as in all the Mollusca, the bile is separated 
 from arterial blood supplied by large vessels derived immediately 
 from the aorta ; no system of veins analogous to the vena porta of 
 higher animals being as yet developed. 
 
CEPHALOPODA. 451 
 
 In the Dibranchiatc genera the liver is either undivided or pre- 
 sents only two lobes, but in other respects its composition and 
 minute structure is similar to that of the Nautilus t 
 
 (493.) In all the CEPHALOPODA, with the exception of the 
 Nautilus Pompilius, there is an orifice in the immediate vicinity 
 of the anus, through which a coloured secretion, generally of a 
 deep brown or intense black colour, can be poured in astonishing 
 abundance, and, becoming rapidly diffused through the surround- 
 ing water, a means of defence is thus provided ; for no sooner does 
 danger threaten, or a foe appear in the vicinity of the Cuttle- 
 fish, than this ink is copiously ejected, and the element around 
 rendered so opaque and cloudy, that the Cephalopod remains 
 completely concealed from its pursuer, and not unfrequently en- 
 sures its escape by this simple artifice. The organ wherein the 
 inky secretion is elaborated, is a capacious pouch variously situated 
 in different genera. In Octopus it is enclosed in the mass of the 
 liver; in Loligo it is located in the immediate vicinity of the 
 anus ; and in Sepia (Jig- 21 1, q) the ink-bag is lodged near the 
 bottom of the visceral sac. On opening it and carefully washing 
 away by copious ablution the ink within, the cavity of the ink-bag 
 is seen to be filled up with a spongy cellulosity; wherein the black- 
 ing material had been entangled ; and from this cellular chamber a 
 duct leads to the outward orifice, through which the dark secretion 
 is ejected at the will of the animal, and squirted from the extremity 
 of the funnel. 
 
 (494.) The CEPHALOPODA breathe by means of branchiae, and 
 possess a complex and elaborate circulatory system, organized upon 
 very extraordinary principles, to the consideration of which we now 
 invite the attention of the reader. 
 
 The branchiae (Jig. 211, g, g) in all the genera now known to 
 exist, with the exception of the Nautilus, are two in number, one 
 situated on each side of the body ; but in the Nautilus Pompilius 
 there are four branchial organs, two on each side : and hence Pro- 
 fessor Owen has divided the class into two great orders, under the 
 names of Dibranchiata and Tetrabranckiata , the former em- 
 bracing all the ordinary genera, while the latter is, as far as we 
 know, only represented in modern times by the Pearly Nautilus, 
 depicted in a preceding figure. 
 
 In both the Dibranchiate and Tetr 'abranchiate orders, each bran- 
 chia consists of a broad central stem, to which is appended a series 
 of vascular lamellae seen in the figure given below (Jig. 211, g) ; 
 
 O r. Q 
 Xi G << 
 
452 CEPHALOPODA. 
 
 by this arrangement a very extensive surface is obtained, over 
 which the blood is diffused for the purpose of respiration. The 
 respiratory apparatus is lodged within the visceral sac, but sepa- 
 rated from the other viscera by a membranous septum (Jig. 211, t) ; 
 so that a distinct chamber is formed to contain the branchiae, where- 
 unto the water is freely admitted ; the surrounding element being 
 alternately drawn into the branchial cavity by the action of its 
 muscular walls, through a valvular aperture provided for the pur- 
 pose, and again expelled in powerful streams through the orifice of 
 the funnel. Such, indeed, is the force with which the water is 
 ejaculated through the funnel, that it not only serves to expel from 
 the body excrementitious matter derived from the termination of 
 the rectum (Jig. 211, s), which opens into the respiratory cavity, 
 but becomes one of the ordinary agents in locomotion. This mode 
 of progression, although in fact common to most of the Cepha- 
 lopod tribes, is remarkably exemplified in the Argonaut, which, 
 instead of navigating the surface of the sea, as has been already 
 stated, simply darts itself from place to place by sudden and oft- 
 repeated jets thus violently spouted forth ; while with its arms 
 stretched out and closely approximated, and its vela tightly ex- 
 panded over the outward surface of its delicate shell, it shoots 
 backwards like an arrow through the water. 
 
 (495.) Separated from the chamber in which the branchiae are 
 lodged, by the. membranous partition already mentioned (Jig. 
 11, ), and likewise distinct from the peritoneum containing 
 the viscera, is a considerable cavity, divided by a membranous 
 partition into two compartments, wherein are placed the great 
 trunks of the venous system (d, d). These chambers, named 
 by Cuvier* the " great venous cavities," are very remarkable ; in 
 as much as, although they contain the vena cava, which here pre- 
 sent a truly anomalous structure, they are lined with a mucous 
 membrane derived from the branchial chamber, with which they 
 are in free communication, and from whence the external element 
 has free admission to their interior. 
 
 It is in this " great venous cavity" called by Professor Owen 
 the " pericardium" that, in the Pearly Nautilus, the syphon 
 which traverses the partitions of its camerated shell (Jig. 205) 
 terminates ; and the reader will now perceive by what mechanism 
 water received from the branchial chamber may, in that animal, 
 be injected into its partitioned shell for the purpose already referred 
 to (479). 
 
 * M6moire sur le Poulpe. 
 
CEPHALOPODA. 
 
 453 
 
 (496.) In the "great venous cavities" or "pericardium" thus 
 formed, are lodged the principal venous trunks (fig. 211, rf, d), 
 whereunto the blood derived from all parts of the body is brought 
 by capacious vessels (6, c, c) that may be called the vena cavte. 
 The great central receptacles of the venous blood (d, d), whilst 
 they are contained in the pericardium, (or rather project into its 
 interior, being partially covered with the mucous membrane that 
 lines its walls,) are enveloped by a mass of spongy appendages of 
 a most remarkable and peculiar description. These spongy masses 
 
 Fig. 211. 
 
454 CEPHALOPODA. 
 
 are of a yellow colour, and, when squeezed, they give out an opaque 
 yellowish mucosity ; * but the most interesting circumstance con- 
 nected with these bodies is, that they communicate by large and 
 patulous apertures with the interior of the veins to which they are 
 adherent. The short canals derived from these apertures are 
 themselves pierced by very numerous orifices, and so on succes- 
 sively, until each of the spongy bodies referred to is permeated 
 internally by a multitude of short vessels leading one into another, 
 and ultimately into the vein itself. Cuvier supposes, that, seeing 
 it is impossible that these vessels should not be filled with blood, 
 they might themselves be considered as veins; but then their extent, 
 when compared with the very small arteries of the spongy bodies, 
 forbids us to believe that they have no other office than that of 
 bringing back into the general current of the venous circulation 
 blood derived from these arterial ramifications. He suggests, 
 therefore, that they more probably form diverticula, in which the 
 venous blood may become diffused in order to receive, through the 
 intervention of their spongy walls, the influence of the surrounding 
 medium, so that in this way they may be rendered subservient 
 to respiration ; or else it is possible that the orifices in the veins 
 are the openings of excretory canals derived from these appendages, 
 through which they may pour into the vein some substance derived 
 from the water in which they float. Lastly, it is conjectured that 
 they may be emunctories, through which some principle separated 
 from the blood is discharged from the body through the pores upon 
 their surface ; a supposition rendered more probable, seeing the 
 abundant mucous secretion that may be extracted from them by 
 pressure. " However this may be," observes Cuvier, " it is cer- 
 tain that the communication between these bodies and the exterior 
 is very open, for, on blowing into or injecting the vein, the air or 
 injection passes very readily into the cavity that the vein tra- 
 verses ; and, on the other hand, on inflating the cavity from the 
 branchial chamber, it often happens that the vein becomes filled 
 with air."" 
 
 Mayer-[- not only adopts the last of the above-mentioned sug- 
 gestions relative to the nature of these spongy appendages to the 
 great veins of the CEPHALOPODA, but ventures to bring forward an 
 opinion that they perform the office of the kidneys of higher 
 animals, and separate from the blood a fluid analogous to the 
 
 * Cuvier, M6moire sur le Poulpe, p. 18. 
 
 f- Analekten fur Vergleichenden Anatomic, 4to. 1835. 
 
CEPHALOPODA. 455 
 
 urinary secretion ; so that, according to this view, the anatomist 
 referred to does not scruple to designate the chamber called by 
 Professor Owen " the pericardium " as a urinary bladder, and to 
 the two orifices leading from thence to the cavity in which the 
 branchiae are lodged he would assign the name of urethra. Pro- 
 fessor Owen has suggested that, in addition to their subserviency 
 to secretion, these appendages to the veins of Cephalopods may 
 be provisions for enabling their sanguiferous system to accommo- 
 date itself to those vicissitudes of pressure to which it must be 
 constantly subjected, and that they bear a relation to the power 
 possessed by these animals of descending to great depths in the 
 ocean, thus answering the same purpose as the capacious auricle, 
 and the large venous sinuses that terminate in the heart of 
 fishes. According to this view, these follicles relieve the vascular 
 system, by affording a temporary receptacle for the blood when- 
 ever it accumulates in the vessels, owing to a partial impediment 
 to its course through the respiratory organs, serving in this man- 
 ner to regulate the quantity of blood sent to the branchiae.* 
 
 (497.) In Nautilus Professor Owen found, in addition to the 
 spungoid appendages connected with the veins, lodged in what he 
 denominates the " pericardium" that the great trunk of the vena 
 cava itself presents a structure precisely analogous to what has been 
 already described when speaking of the venous system of Aptysia 
 among the GASTEROPODA (^ 443), namely, a free communication 
 between the interior of the vein and the cavity of the peritoneum. ~f* 
 The vein is of a flattened form, being included between a strong 
 membrane on the lower or ventral aspect, and a layer of transverse 
 muscular fibres which decussate each other on the upper or dorsal 
 aspect. The adhesion of the coats of the vein to the muscular 
 fibres is very strong, and these fibres form in consequence part of 
 the parietes of the vein itself throughout its whole course. But 
 there are several small intervals left between the muscular fasciculi 
 and corresponding round apertures both in the vein and in the 
 peritoneum, so that the latter membrane at these points seems to 
 be continuous with the lining membrane of the vena cava. The 
 distinguished anatomist referred to counted as many as fifteen of 
 these openings, and most of them were sufficiently large to admit 
 the head of an eye-probe. Here, therefore, as in Aplysia, there 
 are direct communications between the interior of the vena cava and 
 the great serous cavity of the abdomen ; and, moreover, in both in- 
 
 * Mem. on Nautilus Pomp. p. 34. f Mem. on the Pearly Nautilus, p. 72. 
 
456 CEPHALOPODA. 
 
 stances, from the peculiar muscular structure of the vein at the part 
 where these orifices occur, their use appears to depend on, or to be 
 in connection with, a power of regulating their diameters.* 
 
 (498.) The blood derived from the great venous receptacles 
 (d, d) is at once conveyed to the branchiae, and distributed through 
 all the lamellae (g, g) which enter into the composition of the 
 respiratory apparatus. Two distinct hearts, one placed on each 
 side of the body, are interposed between the branchiae and the great 
 trunks of the venous system ; serving by their action forcibly to 
 drive the blood through the ramifications of the branchial arteries. 
 These lateral hearts (Jig. 211, e, e) are of a blackish colour, and 
 their walls moderately thick : internally, their cavities are filled 
 with intercommunicating cells, and, moreover, a strong mitral 
 valve is placed at the orifice through which they receive blood from 
 the veins, as well as smaller valvules at the origin of the branchial 
 arteries ; the latter enter the principal stem of the branchiae, and, 
 running beneath the ligament (/)? divide and subdivide, so as to 
 be dispersed over all the branchial leaflets. 
 
 In Sepia there is appended to each lateral heart a fleshy appen- 
 dage (TTI, w), which, however, is not met with in the generality of 
 Dibranchiate Cephalopods. These bodies are attached to the 
 hearts by narrow pedicles, and Professor Owen considers them to 
 be rudiments of the additional pair of branchiae met with in the 
 Pearly Nautilus. 
 
 In Nautilus Pompilius the hearts just mentioned do not exist ; 
 doubtless, because the greater extent of surface afforded by the 
 four branchiae of this Cephalopod renders the presence of extra- 
 ordinary agents for impelling the blood through them, in order 
 to ensure efficient respiration, unnecessary. 
 
 After undergoing exposure to the surrounding medium in the 
 extensive ramifications of the branchial arteries, the purified blood 
 is returned to the organs belonging to the systemic circulation. 
 In Sepia it is first received from the branchiae by two dilated 
 sinuses (z, t), which might almost be regarded as systemic auricles ; 
 and from these it passes into a strong muscular cavity (/r), which 
 corresponds in function with the left ventricle of the human heart, 
 and by its pulsations forcibly propels the blood through all the 
 arterial ramifications of the vascular system. Two aortae, one de- 
 rived from each of its extremities, arise from the systemic ventricle, 
 the commencement of each being guarded by strong valves so dis- 
 
 * Opuscit. p. 30. . . :>'.* 
 
CEPHALOPODA. 457 
 
 posed as to prevent all reflux towards this central heart ; and thus 
 the circuit of the blood, accomplished in this complicated system of 
 blood-vessels, is completed. In Nautilus the lateral sinuses (w, n) 
 are wanting, and the systemic ventricle is of a square shape ; but 
 in other respects the course of the circulation is the same as is 
 above described. 
 
 (499.) In the nervous system of the CEPHALOPODA we may 
 naturally expect to find not only a superiority in the developement 
 of the nervous centres, as compared with the condition of these 
 important masses in the lower Mollusca, but some indications at 
 least of an approximation to that arrangement so eminently cha- 
 racteristic of the vertebrate division of the animal world, to the 
 confines of which we are now gradually approaching ; more espe- 
 cially as in the activity of the movements of these creatures, and in 
 the increased perfection of their senses, we have abundant evidence 
 of the elevated position assigned to them, when contrasted with 
 other mollusks of less carnivorous and rapacious habits. 
 
 The nervous ganglia from whence the muscles and viscera derive 
 their supply are still numerous and widely scattered ; but their size 
 is considerable, and proportioned to the importance of the organs 
 over which they preside. It is to the encephalic portions of the 
 nervous system, however, that we must principally turn our atten- 
 tion if we would rightly estimate this part of their economy ; and 
 these, we at once perceive, have in the class before us attained to 
 such magnitude and importance that they no longer dubiously 
 emulate the brain of a fish, with which it is not difficult to com- 
 pare them. 
 
 In a Cephalopod, the encephalon for so we now may truly call 
 it is enclosed, as has been already noticed, in a distinct cartila- 
 ginous skull, which embraces it on all sides, and defends it from 
 injury. The capacity of the cranial cavity is however more than 
 sufficient to contain the brain ; and, as is the case in fishes, the 
 interspace is filled up with a semigelatinous substance. The 
 brain, however, still forms a ring through which the oesophagus 
 passes ; so that we might with propriety preserve the terms supra- 
 oesophageal and infra-oesophageal ganglia, were these parts not now 
 become so intimately united to each other that they seem fused 
 into a single mass (Jig. 215, a, &), from different portions of which, 
 nerves, serving very different offices, take their origin. 
 
 (500.) In Nautilus the nervous system has been most minutely 
 and critically examined ; and the important deductions to which the 
 
458 CEPHALOPODA. 
 
 researches of Professor Owen, relative to the analogies that may be 
 traced between the encephalon of these creatures and the brain of 
 higher animals, have served to attach an interest to the study of 
 this part of the economy of the CEPHALOPODA, which has scarcely 
 as yet been sufficiently appreciated by physiologists. 
 
 In the Nautilus Pompilius, the supra-cesophageal ganglion of 
 the GASTEROPODA is represented by a thick round cord of nervous 
 matter (Jig. 212, N), which is in communication with two nervous 
 collars (3, 4) that surround the oesophagus, and likewise with two 
 large ganglia (2) from which the optic nerves take their origin ; 
 but in the Cuttle-fish the same portion of the nervous system 
 (Jig. 215, a) is much more largely developed, and presents a gan- 
 glionic mass of considerable size. If we inquire the reason of 
 this want of correspondence in magnitude presented by the same 
 organ in these two cases, we must necessarily examine the relations 
 in which this part of the brain stands with other circumstances in 
 the economy of the two animals in question ; and we perceive, as 
 Professor Owen has most satisfactorily demonstrated,* that the 
 brain is here developed in accordance wLh the relative complexity 
 of the organ of vision, and also with the perfection of the loco- 
 motive faculties possessed by the Cephalopods under consideration. 
 With the exception of sundry small twigs given off to the mouth 
 and pharynx, the optic nerves (figs. 212, 2; 215, e) are the only 
 ones derived from this part of the encephalon, and, as we shall 
 afterwards see, both the simply constructed eye of the Nautilus 
 and the complicated visual organs of the Sepia are correspondent 
 to the developement of the supra-cesophageal brain ; so that conse- 
 quently the latter may, with every show of reason, be looked upon 
 as the representative of the optic lobes found in the encephalon of 
 fishes,']" and the analogues of the bigeminal bodies in the brains of 
 the higher Vertebrata. 
 
 The ganglia connected with the inferior aspect of the supra- 
 cesophageal mass form two distinct collars embracing the oeso- 
 phagus, an arrangement of which we have already met with an 
 example in Clio borealis among the Pteropod Mollusca. The 
 anterior ring of nervous substance, which no doubt ought rather 
 to be considered as an agglomeration of ganglia than as a simple 
 
 * Descriptive and Illustrated Catalogue of the Physiological series of Comp. Anal, 
 contained in the Museum of the Royal College of Surgeons in London, vol. iii. part i. 
 p. 187. 
 
 f- Cyclopaedia of Anat. and Physiol. ; art. CEPHALOPODA. 
 
CEPHALOPODA. 459 
 
 ganglionic mass, in Nautilus gives off nerves, 1st, to the ophthalmic 
 tentacles (fig. 212, 5*) ; 2ndly, to the digital tentacles (6). 
 Srdly, there arises from near the ventral aspect of the ganglionic 
 collar a pair of nerves (7), each of which soon dilates into a large 
 ganglion (8), from whence are derived the nerves of the internal 
 labial tentacles (9), and also other gangliform nerves (10), distri- 
 buted to what Professor Owen regards as the olfactory apparatus. 
 Lastly, the anterior collar gives off nerves (11) which penetrate 
 the muscular integument and supply the infundibulum. 
 
 In the Dibranchiate Cephalopods the nerves derived from that 
 portion of the brain that may be regarded as analogous to the an- 
 terior collar of Nautilus, supply the locomotive sucker-bearing 
 arms, the labial apparatus, and also the auditory organs (fig. 215, 
 c, d) ; but the latter have not been found to exist in Nautilus 
 Pompilius. 
 
 There is no possibility of doubting that the above nerves, dis- 
 tributed as they are to the complex sensitive tentacula connected 
 with the head and parts of the mouth, represent the fifth pair 
 of Vertebrata ; their general distribution and semiganglionic cha- 
 racter being, ccteris paribus, precisely similar : so that those por- 
 tions of the brain of vertebrate animals from whence the tri- 
 facial and auditory nerves originate, may reasonably be compared 
 with the anterior sub-cesophageal collar of the Cephalopoda. 
 
 The posterior sub-cesophageal ganglionic ring (fig. 212, 4), 
 may be compared to the medulla oblongata of quadrupeds ; in 
 Nautilus it gives origin, 1st, to numerous nerves (13) which, after 
 a short course, plunge into the muscular parietes of the body to 
 which they are distributed : 2ndly, to two large cords (14), which 
 terminate by becoming gangliform (15), and supply the branchial 
 apparatus and the viscera ; thus representing the par vagum in their 
 distribution, and in like manner communicating with branches ap- 
 parently corresponding with the sympathetic nerves that are spread 
 out over the heart and ramifications of the vascular system. Lastly, 
 slender nerves (17), allied to the sympathetic, accompany the vena 
 cava into the abdomen. 
 
 (501.) Such being the arrangement of the principal nervous 
 ganglia, and the general distribution of the nerves, we must now 
 turn our attention to the instruments of sensation possessed by 
 these comparatively highly gifted animals ; and these, as we shall 
 soon perceive, are in all respects correspondent in the perfection 
 of their structure with the exalted condition of the brain. 
 
460 CEPHALOPODA. 
 
 The sense of touch, as might naturally be expected, resides 
 principally in the tentacula, or feet, as they are generally termed, 
 placed around the mouth, and forming, as we have already seen, 
 instruments of locomotion as well as prehensile organs. In the 
 Dibranchiate Cephalopods these tentacula are armed with the tena- 
 cious suckers described in a former page ; but in the Nautilus 
 they are so peculiar both in structure and office, that a more 
 elaborate description of them becomes requisite in this place, for 
 which of course we are necessarily indebted to the same source 
 from whence we have derived all our information relative to this 
 extraordinary animal. 
 
 The head of Nautilus (fig. 205) is of a conical form, and of a 
 much denser texture than the analogous part in the Dibranchiate 
 Cephalopods : it is excavated in such a manner as to form a re- 
 ceptacle or sheath, into which the mouth and its more immediate 
 appendages can be wholly retracted, and so completely concealed 
 as to require the aid of dissection before they can be submitted to 
 examination. The orifice of this great oral sheath is anterior, its 
 superior parietes being formed by a thick triangular hood (fig* 
 205, n) with a wrinkled and papillose exterior ; while the sides 
 give off numerous conical and triedral processes (o, o, o) : the in- 
 ferior portion of the cone is thin, smooth, and concave, and rests 
 upon the funnel (z). From the disposition of the hood, and the 
 tough coriaceous texture of its substance, it is evident that this 
 part is calculated to perform the office of an operculum by closing 
 the aperture of the shell when the body of the animal is retracted. 
 
 The lateral processes (o, o, o) are thirty-eight in number, nine- 
 teen on either side, irregularly disposed one upon another, and all 
 converging towards the oral sheath ; but, as the hood itself con- 
 sists apparently of two very broad digitations conjoined along the 
 mesial line, twenty pairs of these lateral appendages may be enu- 
 merated. There is not the slightest appearance of acetabula, or 
 suckers, upon any of these cephalic appendages ; but their exterior 
 surface is more or less rugose : each is traversed longitudinally by 
 a canal, in which is lodged an annulated cirrus or tentacle (Jig. 
 205,^. 212), which is about a line in diameter, and from two 
 inches to two inches and a half in length. In the specimen ex- 
 amined, a few of these cirri were protruded from their sheaths to 
 the extent of half an inch, but the rest were completely retracted 
 so as not to be visible externally ; and, on laying open some of the 
 canals, the extremities of several were found as far as a quarter of 
 
CEPHALOPODA. 
 
 461 
 
 an inch from the apertures, so that they appear to possess con- 
 siderable projectile and retractile powers. 
 
 To the above forty tentacula must be added four others of a 
 different construction, which project immediately beneath the mar- 
 
 gin of the hood, like antennae, one before and one behind each eye 
 (Jig. 212, r). These tentacles would seem at first sight to be 
 constructed upon the same principles as the last ; but, on examining 
 
462 CEPHALOPODA. 
 
 them attentively, they are found to be composed of a number of 
 flattened circular discs appended to a lateral stem. Yet even all 
 these organs of touch form but a small part of the tactile apparatus 
 of the Nautilus Pompilius ; for the mouth, lodged within the oral 
 sheath, is surrounded with a series of tentacula even more nume- 
 rous than those appended to the exterior of the head. Around the 
 circular lip (Jig- SIS, m) which encloses the beak (w, o), are situ- 
 ated four labial processes (g 9 g, i, i) : each of these processes is 
 pierced by twelve canals, the orifices of which are disposed in a 
 single but rather irregular series along their anterior margin ; and 
 every one of these canals contains a tentacle similar to, but rather 
 smaller than, those of the external digitations (h, A, A-, A;), although 
 their structure is precisely similar. These cirri, like the former, 
 receive large nerves ; those supplying the external labial tentacles 
 being derived immediately from the brain (Jig. SIS, 6, 6), while 
 those distributed to the internal labial tentacles proceed from a 
 large ganglion (8) that is in communication with the cesophageal 
 ring through the intervention of a considerable nervous trunk (7). 
 
 (502.) In the Dibranchiate Cephalopods none of the above- 
 described cirriferous processes are found to exist ; but there is every 
 evidence that the prehensile arms, and most probably the indivi- 
 dual suckers appended to them, are highly sensitive to tactile im- 
 pressions. Every one of the arms receives a large nerve, derived 
 from the same portion of the oesophageal collar as that which gives 
 origin to the tentacular nerves of Nautilus, which traverses its whole 
 length, lodged in the same canal as the great artery of the limb 
 (Jig- SOS). During this course the nerve becomes slightly dilated 
 at short distances, and gives off from each enlargement numerous 
 small nervous twigs which penetrate into the fleshy substance of the 
 foot. Immediately after entering the arm and producing the dila- 
 tations above alluded to, every nerve furnishes two large branches, 
 one from each side, which traverse the fleshy substance connecting 
 the bases of the arms, to unite with the nerves of the two conti- 
 guous arms, so that all the nerves of the feet are connected near 
 their origins by a nervous zone ;* an arrangement intended, no 
 doubt, to associate the movements of the organs to which these 
 nerves are appropriated. 
 
 (503.) There is little doubt, from the character of the soft and 
 papillose membrane which forms a considerable portion of the sur- 
 face of the tongue, that in both the Nautilus and in the Dibran- 
 * Cuvier, M6moire sur le Poulpe, p. 36. 
 
CEPHALOPODA. 463 
 
 chiate Cephalopoda the sense of taste is sufficiently acute ; far supe- 
 rior, indeed, to what is enjoyed by any of the Gasteropod Mollusca, 
 and possibly even excelling that conferred upon fishes, and others 
 of the lowest Vertebrata that obtain their food under circumstances 
 such as render mastication impossible, and the perception of savours 
 a superfluous boon. 
 
 (504.) That the Cephalopoda are provided with a delicate sense 
 of smell, and attracted by odorous substances, is a fact established 
 by the concurrent testimony of many authors, although in the most 
 highly organized genera nothing analogous to an olfactory apparatus 
 has as yet been pointed out : nevertheless, in Nautilus, Professor 
 Owen discovered a structure which he regards, with every show of 
 probability, as being a distinct organ of passive smell, exhibiting the 
 same type of structure that is met with in the nose of fishes ; and, 
 from the circumstance of its being the first appearance of an organ 
 specially appropriated to the perception of odours, well deserving 
 the attention of the physiologist. We may here premise, that the 
 exercise of this function in creatures continually immersed in water 
 must depend upon conditions widely differing from those which 
 confer the power of smelling upon air-breathing animals. In the 
 latter, the odorant particles, wafted by the breeze to a distance and 
 drawn in by the breath, are made to pass, by the act of inspiration, 
 over the nasal passages ; and, being thus examined with a minute- 
 ness of appreciation proportionate to the extent of the olfactory 
 membrane, give intimations of the existence of distant bodies 
 scarcely inferior to those obtained from sight and sound. But, in 
 an aquatic medium, information derived from this sense must be 
 restricted within far narrower limits ; inasmuch as the dissemination 
 of odoriferous particles must necessarily be extremely slow, and the 
 power of perceiving their presence comparatively of little import- 
 ance, seeing that the extent to which it can be exercised is so 
 materially circumscribed. Smell, in aquatic animals, is therefore 
 apparently reduced to a mere perception of the casual qualities of 
 the surrounding element, without any power of inhaling odours 
 from a distance. Simple contact between a sufficiently extensive 
 sentient surface, and the water in which it is immediately immersed, 
 is all that is requisite in the case before us ; and if an organ can be 
 pointed out, constructed in such a manner as to adapt it to fulfil 
 the above intention, there can be little hesitation in assigning to it 
 the office of an olfactory apparatus. 
 
 (505.) In Nautilus, the part indicated by Professor Owen* as 
 
 * Loc. cit. p. 41. 
 
464 CEPHALOPODA. 
 
 appropriated to the sense of smell, consists of a series of soft 
 membranous laminae (Jig. 210, I ; fig. 212, g) compactly arranged 
 in the longitudinal direction, and situated at the entry of the 
 mouth, between the internal labial processes. These laminae are 
 twenty in number, and are from one to two lines in breadth, and 
 from four to five in length, but they diminish in this respect to- 
 wards the sides. They are supplied by nerves (Jig. 212, 10) from 
 the small ganglions (8) which are connected to the ventral extremi- 
 ties of the anterior sub-cesophageal ganglia, and from whence the 
 nerves of the internal labial tentacula are likewise given off. 
 
 (506.) The structure of the eyes in the two divisions of the 
 Cephalopoda differs remarkably, and in both is so entirely dissimi- 
 lar from the usual organization met with in other classes of animals, 
 that we must invite the special attention of the reader to this por- 
 tion of their economy. 
 
 In the TETRABRANCHIATA, of which the Nautilus is the only 
 example hitherto satisfactorily investigated, according to Professor 
 Owen's observations* the eye appears to be reduced to the simplest 
 condition that an organ of vision can assume without departing 
 altogether from the type which prevails throughout the higher 
 classes ; for although the light is admitted by a single orifice into 
 a globular cavity, or camera obscura, and a nerve of ample size 
 is appropriated to receive the impression, yet the parts which re- 
 gulate the admission, and modify the direction of the impinging 
 rays, were, in the specimen examined, entirely deficient. In this 
 structure of the eye, observes Professor Owen,*f- the Nautilus ap- 
 proximates the Gasteropods, numerous genera of which, and espe- 
 cially the PECTINIBRANCHIATA of Cuvier, present examples analo- 
 gous in simplicity of structure, and in a pedicellate mode of support 
 and attachment to the head. Moreover, as the Pearly Nautilus, 
 like the latter group of mollusks, is also attached to a heavy shell, 
 and participates with them in the deprivation of the ordinary lo- 
 comotive instruments of the Cephalopods, the anatomist whose 
 remarks we quote hence deduces the more immediate principle of 
 their reciprocal inferiority with respect to their visual organ, observ- 
 ing that it would little avail an animal to discern distant objects, 
 when it could neither overtake them if necessary for food, nor avoid 
 them if inimical to its existence. 
 
 The eyes of Nautilus (Jig. 205, m) are not contained in orbits, 
 but are attached each by a pedicle to the side of the head, im- 
 
 * Mem. on Nautilus, p. 39, et seq. f Op. cit. p. 51. 
 
CEPHALOPODA. 465 
 
 mediately below the posterior lobes of the hood. The ball of the 
 eye is about eight lines in diameter ; and, although contracted and 
 wrinkled in the specimen examined, it appeared to have been natu- 
 rally of a globular form, rather flattened anteriorly. The pupil was 
 a circular aperture, less than a line in diameter, situated in the centre 
 of the anterior surface of the eye. This small size of the pupil in 
 Nautilus, which contrasts so remarkably with the magnitude of 
 that aperture in the Dibranchiate Cephalopods, Professor Owen 
 suggests is most probably dependent on the great degree of mobility 
 conferred upon the eye of the Nautilus, in consequence of its 
 attachment to a muscular pedicle which enables it to be brought to 
 bear with ease in a variety of directions ; whilst, in the higher 
 Cephalopoda, corresponding motions of the head and body, on 
 account of the more fixed condition of the eye in them, would have 
 been perpetually required, had not the range of vision been ex- 
 tended to the utmost by enlarging the pupillary aperture. 
 
 The principal tunic of the eye is a tough exterior membrane 
 or sclerotic {Jig- 212), thickest posteriorly, where it is continued 
 from the pedicle, and becoming gradually thinner to the margins of 
 the pupil. The optic nerves, after leaving the optic ganglions (2), 
 traverse the centre of the ocular pedicles, and, entering the eye, 
 spread out into a tough pulpy mass which extends as far forwards 
 as the semidiameter of the globe. This nervous tissue, as well 
 as the whole interior of the cavity, is covered with a black pigment 
 which is apparently interposed between the impinging rays of light 
 and the sentient membrane. The contents of the eye-ball, of what- 
 ever nature they had been, had escaped by the pupil. If the eye 
 had ever contained a crystalline lens, that body must have been very 
 small ; as otherwise, from the well-known effect of ardent spirits 
 in coagulating it, it would have been readily perceived. What 
 adds, however, to the probability of this eye being destitute of 
 a crystalline humour is the total absence of ciliary plicae, or any 
 structure analogous to them. In some parts of the cavity a mem- 
 brane could be distinguished which had enveloped the fluid contents 
 of the eye ; but it had entirely disappeared at the pupil, which had 
 in consequence freely admitted the preserving liquid into the in- 
 terior of the globe. 
 
 However much is still left to be ascertained by future observa- 
 tions, we learn from the above able exposition of the appearances 
 detected on examining the solitary example of a visual organ of this 
 description hitherto met with, that the eye of the Nautilus exhibits 
 
 9 TT 
 
 <V II 
 
466 CEPHALOPODA. 
 
 every indication of inferiority of construction when compared with 
 that of the Dibranchiate tribes. Encased in no orbital cavity, and 
 consequently unprovided with any other muscular apparatus than 
 the fleshy pedicle whereby it is connected with the head ; unpro- 
 tected by eyelids and devoid of lachrymal appendages ; without 
 either transparent cornea, aqueous humour, iris, or crystalline lens ; 
 and, moreover, coated internally with a dark pigment, apparently 
 situated in front of the nervous expansion which represents the 
 retina, instead of behind it in the usual position of the choroid 
 tunic, all these are facts calculated to arrest the attention of the 
 physiologist, and excite the surprise of every observer who studies 
 on a large scale this part of the animal economy. 
 
 (507.) The eyes of the Dibranchiate Cephalopoda are not less 
 remarkable in their construction than those of the Nautilus, and 
 from their greater complexity will require a more elaborate descrip- 
 tion. In order to simplify the details connected with this portion 
 of our subject as much as possible, we shall describe separately, as 
 forming distinct parts of the ocular apparatus met with in the com- 
 mon Cuttle-fish (Sepia cfficinalis), first, the orbit ; secondly, the 
 globe of the eye ; thirdly, the chamber of the optic ganglion ; and 
 fourthly, the muscles of the visual organ. 
 
 (508.) The orbit differs from that of all other classes of ani- 
 mals, inasmuch as it is a cavity circumscribed on all sides and 
 covering even the front of the eye.* The bottom of the orbital 
 cavity is cartilaginous, being partially formed by a process derived 
 from the cranial cartilage ; but elsewhere it is made up of the com- 
 mon fleshy integument of the body (fig. 13, d, d, e) : becoming 
 gradually attenuated, the skin (b) passes over the anterior portion 
 of the eye, where, being transparent (/), it represents the cornea, 
 although it has no connection with the eye-ball itself. Beneath 
 the cornea the integument again becomes opaque, and forms a 
 thickened fold (a), which might be considered as the rudiment of 
 an under eyelid. The orbit, therefore, forms a complete capsule, 
 enclosing the whole of the apparatus of vision. 
 
 (509.) The globe of the eye fills up the anterior part of the 
 orbital chamber, and is remarkable from having no cornea properly 
 so called ; so that, on raising the transparent skin (/) which forms 
 the exterior wall of the orbit and supplies the place of the cornea, the 
 
 * Descriptive and Illustrated Catalogue of the Physiological series of Comparative 
 Anatomy contained in the Museum of the Royal College of Surgeons, London, vol. iii. 
 part i. plate 52. 
 
CEPHALOPODA. 
 
 467 
 
 Fig. 213. 
 
 prominent surface of the crystalline lens (o) is found quite naked 
 beneath it ; neither an aqueous humour, nor an iris properly so called, 
 being present. The outer coat of the eye (g, g) represents the scle- 
 rotic tunic in man: 
 it is tough, fibrous, 
 and of a silvery 
 lustre ; perforated 
 anteriorly by a 
 large round aper- 
 ture representing 
 that which con- 
 tains the cornea 
 in the human eye, 
 and pierced pos- 
 teriorly by nu- 
 merous foramina, 
 through which 
 the multitudinous 
 branches derived 
 from the optic ganglion (k) enter. 
 
 The second tunic is usually regarded as the retina, occupying 
 a singular situation and presenting a very anomalous structure. 
 No choroid intervenes between this retina and the sclerotic, as is 
 the case in the eye of man ; but numerous nervous branches given 
 from the optic ganglion (&), having penetrated into the interior of 
 the eye through the cribriform sclerotic, immediately expand into a 
 thick nervous membrane which lines the sclerotic tunic, and is 
 continued forward to a deep groove in the substance of the crystal- 
 line lens, wherein it is implanted so as to form a kind of ciliary zone 
 (m), which is slightly plicated, and obviously assists in keeping the 
 lens in situ. 
 
 Between the retina and the vitreous humour is interposed a thick 
 layer of black pigment, which, being thus strangely situated, has 
 very naturally puzzled all physiological inquirers, inasmuch as it 
 would apparently form an insurmountable barrier between the rays 
 of light and the retinal membrane. The researches of Professor 
 Owen would seem, however, to have removed the difficulty pre- 
 sented by this hitherto incomprehensible and anomalous arrange- 
 ment ; as he has succeeded in discovering, in addition to the thick 
 post-pigmental nervous expansion, a delicate lamella in front of the 
 pigmentum nigrum, correspondent in position at least with the 
 
468 
 
 CEPHALOPODA. 
 
 retina of vertebrate animals. " In the eyes of different Sepice 
 which we had immersed in alcohol preparatory to dissection, we 
 have, however, invariably found between the pigment and the hya- 
 loid coat a distinct layer of opaque white pulpy matter, of sufficient 
 consistence to be detached in large flakes, and easily preserved and 
 demonstrated in preparations. We confess, however, that we can 
 discover no connection between this layer and the thick nervous 
 expansion behind the pigment ; but, nevertheless, we cannot but 
 regard it as being composed of the fine pulpy matter of the optic 
 nerve, and as constituting a true pree-pigmental retina." * 
 
 It has been already stated that there are no chambers of aqueous 
 humour ; and we are but little surprised that, in animals destined 
 to see objects contained in water, the existence of a refracting 
 medium scarcely at all differing in density from the surrounding 
 element should be dispensed with. To compensate, however, for 
 this deficiency, the crystalline, as is the case in all the aquatic 
 Vertebrata, is of short focus and great power ; being, in fact, not 
 merely, as it is generally described, a double convex lens, which 
 is the usual shape of this important piece of the optic apparatus, 
 but exhibiting that form of a simple magnifier most approved of 
 by opticians as being best adapted to ensure a large field of 
 view. Whoever is conversant with the principles upon which 
 the well-known " Coddington lens " is constructed, will have 
 little difficulty in appreciating the advantages derived by intro- 
 ducing a precisely similar instrument in the eye of the Cuttle-fish. 
 The Coddington lens is a sphere of glass divided into two portions 
 by a deeply cut circular groove, which is filled up with opaque 
 matter. The lens of the Cuttle-fish is in like manner divided into 
 two parts of unequal size (o, o') by a circular indentation, wherein 
 the post-pigmental retina with its coat of dark varnish (m) is 
 fixed, and thus a picture of the most perfect character is ensured. 
 The crystalline penetrates deeply into the vitreous humour : the 
 latter, enclosed in a delicate hyaloid membrane, fills up, as in man, 
 the posterior part of the eye-ball ; while the small space that 
 intervenes between the posterior surface of the crystalline and the 
 back of the ocular chamber sufficiently attests the shortness of the 
 focus of so powerful a lens. 
 
 (510.) The posterior portion of the orbital capsule is occupied 
 by a large cavity quite distinct from the globe of the eye, although 
 its walls are derivations from the sclerotic tunic, wherein is lodged 
 
 * Cyclopaedia of Anatomy and Physiology, art. CEPHALOPODA. 
 
CEPHALOPODA. 469 
 
 the great ganglion of the optic nerve (&) imbedded in a mass of 
 soft white substance. This supplementary chamber is formed by 
 a separation of the sclerotic into two layers ; of which one, already 
 
 Fig. 214. 
 
 described ('), forms the posterior boundary of the eye-ball, while 
 the other (h) passing backwards circumscribes the cavity in ques- 
 tion. On entering the compartment thus formed the optic nerve 
 (/>) dilates into a large reniform ganglion, almost equal in size to the 
 brain itself ; and from the periphery of the optic ganglion arise the 
 
470 CEPHALOPODA. 
 
 numerous nervous filaments, which, after perforating the poste- 
 rior part of the globe of the eye, expand into the post-pigmental 
 retina. 
 
 Between the globe of the eye (g) and the cornea (/) is a 
 capacious serous cavity, which extends to a considerable distance 
 towards the posterior part of the orbital chamber ; and holds the 
 same relation to the visual apparatus, and the cavity in which it is 
 lodged, as the serous lining of the human pericardium does to the 
 heart, and the fibrous capsule in which that viscus is lodged, evi- 
 dently forming an arrangement for facilitating the movements of 
 the eye. The serous membrane which lines this cavity, after in- 
 vesting the inner surface of the cornea and the interior of the orbit, 
 is reflected upon the outer surface of the sclerotic tunic of the eye, 
 which it likewise covers ; and moreover, at the front of the eye- 
 ball, enters the aperture which in the eye of a vertebrate animal 
 would be occupied by the cornea, lines the chamber corresponding 
 with that of the aqueous humour, and passes over even the anterior 
 surface of the crystalline. This serous membrane Cuvier very 
 improperly named the " conjunctiva ;" but, as Professor Owen has 
 suggested,* it is evidently rather analogous to the membrane of 
 the aqueous humour, here excessively developed in consequence of 
 the want of a cornea in the sclerotic aperture. This serous cavity is 
 not, however, a completely closed sac ; but, as is frequently the 
 case with the serous membranes of fishes and reptiles, is in com- 
 munication with the surrounding medium, through the interven- 
 tion of a minute orifice visible in the transparent tegumentary 
 cornea. 
 
 (511.) Four muscular slips are appropriated for the movements 
 of this remarkable eye, and serve to direct the axis of the organ 
 so as to ensure distinct vision : they arise principally from the 
 orbital prolongations of the cranial cartilage, and are inserted into 
 the sclerotic tunic. 
 
 (512.) It is always interesting to the physiologist to observe 
 the earliest appearance of a new system of organs, and witness the 
 gradual developement of additional parts, becoming more and 
 more complicated as we advance from humbler to more elevated 
 grades of the animal creation. The progressive steps by which 
 the auditory apparatus of the Vertebrata attains to that elaborate 
 organization met with in the structure of the human ear are not a 
 little curious. In the simplest aquatic fonns the central portion 
 
 * Cyclop, of Anat. and Phys. loc. cit. p. 552. 
 
CEPHALOPODA. 471 
 
 of the internal ear alone exists, imbedded in the as yet cartilagi- 
 nous cranium. Gradually, as in fishes, semicircular canals, pro- 
 longed from the central part, increase the auditory surface, but 
 still have no communication with the exterior of the body. In 
 reptiles and birds destined to perceive sonorous impressions in an 
 aerial medium, a tympanic cavity and drum are superadded ; and 
 lastly, in the Mammiferous orders, external appendages for collect- 
 ing and conveying sound to the parts within, complete the most 
 complex and perfect form of the acoustic instrument. 
 
 As far as is yet known, the Tetrabranchiate Cephalopods have 
 no distinct organ of hearing ; but in the Dibranchiata an ear lodged 
 in an internal cranium for the first time presents itself to our 
 notice, and at the same time exhibits the lowest possible condi- 
 tion of a localized apparatus adapted to receive sounds. 
 
 In the anterior and broadest part of the cartilaginous cranium,* 
 where its walls are thickest and most dense, are excavated two 
 nearly spherical cavities (Jig. SI 5, rf), which in themselves constitute 
 
 Fig. 215. 
 
 the osseous labyrinth of both ears. A vesicle or membranous sac- 
 culus (c), likewise nearly of a spherical form, is suspended in the 
 centre of each of these cartilaginous cells by a great number of 
 filaments that are probably minute vessels. The two auditory 
 nerves derived from the encephalon enter these cavities through 
 special canals ; and each, dividing into two or three branches, spreads 
 out over the vesicle to which it is destined. The auditory vesicle 
 itself is filled with a transparent glairy fluid ; and contains, attached 
 
 * Cuv. MSmoire sur le Poulpe, p. 41. 
 
472 
 
 CEPHALOPODA. 
 
 Fig. 216. 
 
 to its posterior part, a minute otolithe (1, 2, 3), a calcareous 
 body of variable shape in different genera, the oscillations of 
 which doubtless increase the impulses whereupon the production 
 of sound depends. 
 
 Such is the simplest form of an ear ; and if the reader will com- 
 pare the organ above described with that possessed by the highest 
 Articulata, as, for example, the lobster ($ 380), the similarity of 
 the arrangement will be at once manifest. 
 
 (513.) All the CEPHALOPODA are dio3cious, and the structure 
 of the sexual organs both of the males and females is remarkable, 
 inasmuch as it is peculiar to the class. 
 
 In the females, the ovarian receptacle is lodged at the bottom of 
 the visceral sac (Jig. 211, p, p), enclosed in a distinct peritoneal 
 pouch. The ovary itself is a large bag, the walls of which are 
 tolerably thick ; 
 and, on opening 
 it, it is found to 
 contain a bunch 
 of vesicular bo- 
 dies, attached by 
 short vascular pe- 
 dicles to a cir- 
 cumscribed por- 
 tion of its internal 
 surface (Jig. 216, 
 a). These vesi- 
 cles, the ovisacs 
 or calyces, as they 
 are called by com- 
 parative anato- 
 mists, are, in fact, 
 the nidi wherein 
 the ova are se- 
 creted ; and, if 
 examined shortly 
 before ovi position 
 commences, every 
 one of them is 
 seen to contain an ovum in a more or less advanced stage of deve- 
 lopement. In this condition the walls of the ovisacs are thick and 
 spongy; and their lining membrane, which constitutes the vas- 
 
 d 
 
CEPHALOPODA. 473 
 
 cular surface that really secretes the egg, presents a beautiful reti- 
 culate appearance. 
 
 If the contained ova be examined when nearly ripe for exclusion, 
 each is found to be composed of a yolk or vitellus enclosed in a 
 delicate vitelline membrane, and covered externally by a thicker 
 investment the chorion. When the ovum has attained complete 
 maturity, the ovisac enclosing it becomes gradually thinned by 
 absorption, and ultimately bursts ; allowing the egg, now complete 
 with the exception of its shell, to escape into the general cavity of 
 the ovarium (c). The oviduct (e) communicates immediately 
 with the interior of the ovarium by a wide orifice, the dimensions 
 of which are proportioned to the size of the mature ova. It is 
 generally single ; but in some genera, as Loligo and the Octopoda, 
 the canal derived from the ovary soon divides into two(d, e). The 
 walls of the oviferous duct are thin and membranous until near the 
 external outlet, where they suddenly become thick and glandular, 
 and, in many genera, surrounded with a very large laminated gland 
 (/), through the centre of which the eggs have to pass before they 
 issue from the body. It is the gland last mentioned that secretes 
 the external horny covering of the egg ; a defence which seems to 
 be deposited in successive layers upon the outer surface of the pre- 
 viously existing chorion, and, when completed, forms a thick flex- 
 ible case made up of concentric lamellae of a dark-coloured corneous 
 substance. 
 
 (514.) After extrusion the ova of the different families of Ce- 
 phalopoda are found agglutinated and fastened together into masses 
 of very diverse appearance. The eggs of the common Cuttle-fish, 
 frequently found upon the shore, are not inaptly compared by those 
 ignorant of their real nature to a bunch of black grapes ; to which 
 indeed they bear no very distant resemblance, being generally ag- 
 gregated in large clusters, and fastened by long pedicles either to 
 each other or to some foreign body. The Argonaut carries its 
 eggs, which are comparatively of small size, securely lodged in the 
 recesses of its shell ; while the ova of the Calamary, encased in 
 numerous long gelatinous cylinders that conjointly contain many 
 hundreds of eggs, are fixed to various submarine substances, and 
 thus protected from casualties. The form and arrangement of these 
 bunches are no doubt dependent upon the peculiar character of the 
 terminal gland found in the oviduct of the parent, whereby the last 
 covering to the ova is furnished. 
 
 (515.) Cuvier remarks that the male Poulpes must be less nu- 
 
474 
 
 CEPHALOPODA. 
 
 merously met with than the female, as among the numerous speci- 
 mens dissected by him scarcely one fifth were of the former sex. 
 
 The various parts of the male generative apparatus are remark- 
 ably similar both in structure and arrangement to the corresponding 
 portions of the sexual organs of the female. The testicle strikingly 
 resembles the ovary both in its outward form and internal arrange- 
 ment : like that viscus, it consists of a capacious membranous sac 
 (Jig. 217, b) ; and, on opening this, there is found attached to a 
 small portion of its inner surface a large bundle of branched cseca 
 (a), in which no doubt the seminal fluid is elaborated. These 
 strangely disposed seminiferous cseca have apparently no proper 
 excretory ducts ; but the impregnating fluid secreted by them is, as 
 it would seem, poured into the general cavity of the sac, exactly in 
 the same manner as the ova do in the other sex, and, being allowed 
 to escape from this reservoir through a wide orifice (c), it enters 
 the vas deferens. The canal last mentioned (d) is long, slender, 
 and very tortuous, but after many convolutions it enters a wider 
 canal (e), called by 
 
 Cuvier vesicula se- Fi g* 217 - 
 
 minalis, the interior 
 of which is divided 
 by imperfect septa ; 
 and, its texture be- 
 ing apparently mus- 
 cular, this part of 
 the excretory appa- 
 ratus may possibly 
 by its contractions 
 expel the spermatic 
 fluid from the body. 
 On issuing from the 
 seminal vesicle, the 
 semen passes the ex- 
 tremity of an oblong 
 gland (/), which 
 Cuvier denominates 
 the prostate : its 
 structure is compact 
 and granular, and it 
 seems to be destined 
 to furnish some ac- 
 
CEPHALOPODA. 475 
 
 cessory fluid subservient to impregnation. Having passed the 
 prostate, the ejaculatory duct communicates with a large muscular 
 sacculus (g), the contents of which are very extraordinary. This 
 sacculus is in fact filled with innumerable white filaments, each 
 about half an inch in length, arranged parallel to each other, and 
 disposed with much regularity. There are three or four rows of 
 them, one above another, entirely filling the sac ; and they are 
 maintained in situ by a delicate spiral membrane, but are quite 
 unconnected with the sac itself. The filaments when taken out, 
 even long after the death of the Cephalopod, exhibit, when mois- 
 tened, various contortions, and by some have been regarded as En- 
 tozoa ; but their real nature is entirely unknown, although from 
 the time of Needham,* their first discoverer, to the present day, 
 various speculations and conjectures have been entertained con- 
 cerning them. 
 
 From the pouch of Needham a short canal leads to the penis 
 (A), a short, hollow, muscular tube, through which the fecundating 
 fluid is expelled. It is most probable that the ova of the female 
 are impregnated by the aspersion of the male fluid either during 
 their extrusion, as in frogs, or after they are deposited, as is the 
 case in the generality of fishes ; but this part of the economy of 
 the Cephalopoda is still involved in obscurity. 
 
 (516.) Although we mean to defer any minute account of the deve- 
 lopement of the embryo in ovo until an examination of the eggs 
 of oviparous Vertebrata shall afford more ample materials for eluci- 
 
 dating this important subject, it will be as well in this place briefly 
 to notice the condition of the young Cephalopods previous to their 
 escape from the egg, wherein the first part of their growth is 
 accomplished. Before the egg is hatched, the foetal Cuttle-fish 
 already presents all the organs essential to its support and pre- 
 
 * Needham. An Account of some new Microscopical Discoveries, 8vo. 1745- 
 
476 VERTEBRATA. 
 
 servation : the tentacula upon the head, the eyes, the respiratory 
 apparatus, and even the ink-bag, which in the earlier stages of 
 growth were quite undistinguishable in the germ of the future 
 being (fig- &18, 1), slowly make their appearance ; and, even before 
 birth, the little creature presents most of the peculiarities which 
 characterize the species to which it belongs. But the most pro- 
 minent feature that strikes the attention of the physiologist is 
 the remarkable position of the duct communicating between the 
 yolk of the egg, the great reservoir of nourishment provided by 
 nature for the support of the foetus whilst retained in the egg, and 
 the alimentary canal of the as yet imperfect Sepia. This commu- 
 nication, whicli in vertebrate animals is invariably effected through 
 an opening in the walls of the abdomen, whereby the vitelline duct 
 penetrates to the alimentary canal, here occupies a very unusual 
 situation ; being inserted into the head, through which it pene- 
 trates, by an aperture situated in the front of the mouth, to the 
 oesophagus, where it terminates (Jig- &18, 3). 
 
 Leaving the Cephalopod Mollusca, we must bid adieu to the 
 fourth grand division of the animal kingdom, and proceed in the next 
 chapter to introduce the reader to beings organized according to a 
 different type, embracing the most highly-gifted and intelligent 
 occupants of the planet to which we belong. 
 
 CHAPTER XXVI. 
 
 VERTEBRATA. 
 
 (517.) THE fifth division of the animal kingdom is composed of 
 four great classes of animals, closely allied to each other in the grand 
 features of their organization, and possessing in common a general 
 type of structure clearly recognizable in every member of the exten- 
 sive series, although of course modified in accordance with the 
 endless diversity of circumstances under which particular races 
 are destined to exist. The immeasurable realms of the ocean, 
 the rivers, lakes, and streams, the fens and marshy places of the 
 
VERTEBRATA. 477 
 
 earth, the frozen precincts of the poles, and the torrid regions of 
 the equator, have all appropriate occupants, more favoured as 
 regards their capacities for enjoyment, and more largely endowed 
 with strength and intelligence, than any which have hitherto occu- 
 pied our attention, and gradually rising higher and higher in their 
 attributes, until they conduct us at last to Man himself. FISHES, 
 restricted by their organization to an aquatic life, are connected by 
 amphibious beings, that present almost imperceptible gradations of 
 developement, with terrestrial and air-breathing REPTILES : these, 
 progressively attaining greater perfection of structure and increased 
 powers, slowly conduct us to the active, hot-blooded BIRDS, fitted 
 by their strength, and by the vigour of their movements, to an 
 aerial existence. From the feathered tribes of Vertebrata, the 
 transition to the still more intelligent and highly- endowed MAM- 
 MALIA is effected with equal facility ; so that the anatomist finds, 
 to his astonishment, that throughout this division of animated 
 nature, composed of creatures widely differing among themselves 
 in form and habits, an unbroken series of beings is distinctly 
 traceable. 
 
 (518.) The first grand character that distinguishes the vertebrate 
 classes, is the possession of an internal jointed skeleton, which is 
 not, as in the preceding classes, extravascular and incapable of 
 increase, except by the successive deposition of calcareous laminae 
 applied to its external surface; but endowed with vitality, nou- 
 rished by blood-vessels and supplied with nerves, capable of 
 growth, and undergoing a perpetual renovation by the removal 
 and replacement of the substances that enter into its compo- 
 sition. 
 
 In the lowest tribes of aquatic Vertebrata the texture of the 
 internal framework of the body is permanently cartilaginous, 
 and it continues through life in a flexible and consequently 
 feeble condition ; but as greater strength becomes needful, in 
 order to sustain more active and forcible movements, calcareous 
 particles are found to be deposited in the interstices of the carti- 
 laginous substance, and, in proportion as these accumulate, addi- 
 tional firmness is bestowed upon the skeleton, until it assumes, 
 at length, hardness and solidity proportioned to the quantity of 
 the contained earthy matter, and becomes converted into perfect 
 bone. 
 
 (519.) Phenomena precisely similar are observable in tracing the 
 formation and developement of the osseous system, even in those 
 
478 VERTEBRATA. 
 
 genera possessed, when arrived at maturity, of the most com- 
 pletely organized skeletons. 
 
 In the very young animal the bones consist exclusively of 
 cartilage ; but as growth proceeds, earth becomes deposited by the 
 blood-vessels in the as yet soft and flexible pieces of the skeleton, 
 until by degrees they acquire density and strength as the animal 
 advances towards its adult condition. 
 
 The complete skeleton of a vertebrate animal may be considered 
 as being composed of several sets of bones employed for very 
 different purposes ; consisting of a central portion, the basis and 
 support of the rest, and of various appendages derived from or 
 connected with the central part. The centre of the whole os- 
 seous fabric is generally made up of a series of distinct pieces 
 arranged along the axis of the body, and this part of the skeleton 
 is invariably present ; but the superadded appendages, being em- 
 ployed in different animals for various and distinct purposes, pre- 
 sent the greatest possible diversity of form, and are many of them 
 wanting in any given genus : "so that a really complete skeleton, 
 that is, a skeleton made up of all the pieces or elements which 
 might, philosophically speaking, enter into its composition, does 
 not exist in nature ; inasmuch as it is owing to the deficiency of 
 some portions, and the developement of others in particular races, 
 that we must ascribe all the endless diversity of form and me- 
 chanism so conspicuously met with in this division of the animal 
 world. 
 
 Nevertheless, although there is no such a thing in Creation as 
 a fully developed skeleton, it will be necessary, in order to prepare 
 the student for the contemplation of the numerous modifications 
 met with in this portion of the animal economy, hereafter to be 
 described, briefly to enumerate the component parts which might 
 theoretically be supposed to enter into the construction of the 
 framework of an animal ; and thus by comparison he will be 
 enabled, as we proceed, to appreciate more readily the variations 
 from a general type apparent throughout the vertebrate classes. 
 It may, likewise, be as well thus early to caution the anatomist 
 who has confined his studies to the contemplation of the human 
 body, against taking the skeleton of Man as a standard whereby 
 to direct his judgment; for Man, so highly raised by his 
 intelligence and mental powers above all other beings, is, so 
 to speak, a monstrosity in the creation ; and, so far from 
 finding in the human frame the means of elucidating the laws 
 
VEKTEBRATA. 479 
 
 of animal organization, it is found to have been constructed upon 
 principles the most aberrant and remote from those which an 
 extensive investigation of the lower animals has revealed to the 
 physiologist. 
 
 (520.) A skeleton, described generally, is made up of the fol- 
 lowing portions : 1st. of a chain of bones, placed in a longitudinal 
 series along the mesial line of the back, and more or less firmly 
 articulated with each other, so as to permit certain degrees of 
 flexure. These bones, examined individually, present various 
 additional parts destined to very different ends : some defend the 
 central axis of the nervous system from external violence ; others, 
 when present, guard and enclose the main blood-vessels ; and the 
 rest, either acting as prominent levers, serve to give insertion to 
 the muscles which move the spine, or afford additional security to 
 the articulations between the vertebral pieces. Those vertebrae 
 which defend the posterior portions of the nervous axis, usually 
 called the spinal core/, constitute the spine ; while those enclosing 
 the anterior extremity of the nervous axis, which, for reasons 
 hereafter to be explained, becomes dilated into large masses 
 forming collectively the brain, is by the human anatomist distin- 
 guished as the cranium or skull. 
 
 Secondly, we find appended to the cranial or cephalic portion 
 of the spine, a set of bones disposed symmetrically, and forming 
 the framework of the face : these bones, it is true, have by many 
 Continental writers been regarded as constituting additional ver- 
 tebrae, the parts of which are still recognizable, although amazingly 
 modified in shape, so as to enclose the different cavities wherein 
 the senses of vision and smell, as well as the organs of mastication, 
 are situated. We shall not, however, waste the time of the stu- 
 dent by considering in this place the as yet unsettled and vague 
 opinions of transcendental anatomists upon this subject ; it is 
 sufficient for our present purpose to indicate the facial bones as 
 appendages to the cranial vertebrae, avoiding for the present fur- 
 ther discussion concerning them. 
 
 Another most important addition to the central axis of the 
 skeleton is obtained by the provision of lateral prolongations, 
 derived from the transverse processes of the vertebrae, which form 
 a series of arches largely developed at certain points, so as more 
 or less completely to embrace the principal viscera, and give 
 extensive attachment to muscles serving for the movements of the 
 body. 
 
480 VERTEBRATA. 
 
 The first set of arches is appended to the lateral portions of 
 the cranial vertebrae, and the bones thus derived enter largely 
 into the composition of the respiratory apparatus. In Man this 
 important portion of the skeleton is reduced to a mere rudiment, 
 distinguished by the name of the os hyoides ; and in the human 
 subject its relations and connexions with the surrounding parts 
 are so obscurely visible, that the student is scarcely prepared 
 to witness the magnitude and importance of the hyoid framework 
 in other classes, or the amazing metamorphoses which, as we shall 
 afterwards see, it undergoes. 
 
 Behind the hyoid apparatus, other arches are attached to the 
 transverse processes of the spinal vertebrae, called ribs ; and the 
 study of these appendages to the spine is one of the most in- 
 teresting points in the whole range of osteology. In Fishes, 
 wherein respiration is effected entirely by the movements of largely 
 developed hyoid bones, the ribs are mere immoveable derivations 
 from the transverse processes of the vertebrae, and serve exclusively 
 for the attachment of muscles. In Reptiles, respiration is still 
 accomplished by the os hyoides ; and the ribs, thus performing a 
 secondary office, become convertible to different uses, and assume 
 various forms and proportions. In the Amphibious Reptiles, the 
 most nearly approximated to Fishes, they either do not exist at all, 
 as being needed neither for respiration nor locomotion, or they are 
 represented by minute and almost imperceptible rudiments ap- 
 pended to the extremities of the transverse processes of the verte- 
 bras. In Serpents the ribs are wanted for locomotion, and are 
 accordingly developed from the head nearly to the tail, forming a 
 series of strong arches, articulated at one extremity with the ver- 
 tebral column by a very complete joint ; but at the opposite ex- 
 tremity they are loose and unconnected. In proportion, however, 
 as the hyoid bones, with the larynx, of which they form an impor- 
 tant part, become converted into a vocal apparatus, as they gradu- 
 ally do, the ribs assuming more complete developement in a certain 
 region of the spine, and, being augmented by the addition of a 
 sternal apparatus, form a complete thoracic cavity, and thus become 
 the basis of those movements of the body which in hot blooded 
 animals are subservient to respiration. 
 
 The next additions required to complete the skeleton, are two 
 pairs of locomotive limbs, representing the legs and arms of Man. 
 Infinitely diversified as are these members both in form and office, 
 they are, when philosophically considered, found to be constructed 
 
VEKTEBltATA. 481 
 
 after tlie same type. Both the anterior and posterior limbs, when 
 fully organized, consist of similar parts, most of which are met 
 with in the limbs of the human skeleton. Three bones constitute 
 the shoulder, called respectively the Scapula, the Clavicle, and 
 the Coracoid bone. Three bones in like manner sustain the hinder 
 extremity, the Ilium, the Ischium, and the Pubis ; and these evi- 
 dently represent individually the corresponding pieces found in the 
 shoulder, but differently named. The formation of the limbs is 
 likewise strictly parallel ; a single bone articulates with the osseous 
 framework of the shoulder, or of the hip, called in one case the 
 Humerus, in the other the Femur : two bones form the arm, 
 the Radius and Ulna ; and two likewise enter into the composition 
 of the leg, the Tibia and Fibula : the hand and foot are each 
 supported by a double series of small bones, forming the Carpus 
 of the one and the Tarsus of the other ; and in like manner con- 
 sist of similar pieces, five in number, called the Metacarpal or 
 Metatarsal bones, and of the Phalanges, or joints of the fingers 
 and toes. 
 
 A perfect or typical skeleton must therefore be supposed to 
 consist of all the before-named portions, namely, 1. the cranial 
 and spinal vertebrae ; 2. the face ; 3. an elaborately-formed 
 hyoid framework ; 4. the ribs ; 5. a sternal system of bones, con- 
 stituting, in conjunction with some of the ribs, a thorax ; and 
 Gthly, of four locomotive extremities, made up of the parts above 
 enumerated as entering into their composition. Seldom, indeed, 
 is it that the student will find even the majority of these portions 
 of the osseous apparatus coexistent in the same skeleton ; but, 
 whatever forms of animals may hereafter present themselves for 
 investigation, let the above description be taken as a general 
 standard of comparison, and let all variations from it be considered 
 as modifications of one grand and general type. 
 
 We must, however, proceed one step further in this our prepa- 
 ratory analysis of the skeleton ; and, instead of regarding the indi- 
 vidual pieces of the osseous framework of an adult animal as so 
 many simple bones, be prepared to find them resolvable into 
 several distinct^rts or elements, all or only a part of which may 
 be developed in any given portion of the osseous system. 
 
 In order to simplify as much as possible this important subject, 
 we will select first, what is generally considered as a single bone, 
 one of the most complex vertebra of a fish for instance, and 
 examine its real composition. 
 
 2 i 
 
482 VEHTEBRATA. 
 
 This bone (Jig. 219) is found to consist of a central portion 
 (a), and of sundry processes derived therefrom, some of which the 
 younger student of human anatomy would at once be able to call 
 by their appropriate names : to the body of the bone (a) he finds 
 appended the arch (6) which encloses the spinal cord, surmounted 
 by its spinous process (c), and with equal facility he recognises in 
 the lateral processes (d, d) the analogues of the transverse pro- 
 cesses of the human spine ; but here his knowledge fails him, inas- 
 much as he finds another arch (e) formed beneath the body of the 
 bone, and moreover an inferior spinous process (g), neither of 
 which have any representatives in the human body. 
 
 It is evident, therefore, that the human vertebrae are imperfectly 
 developed bones, and do not possess all the parts or elements 
 met with in the corresponding portion of the skeleton of a fish. 
 
 The question, therefore, to be solved is this, how many 
 elements exist in the most perfect vertebra known ? and this being 
 once satisfactorily settled, it is easy to detect the deficiencies of 
 such as are less completely developed. 
 
 Taking the example F/g.219. 
 
 above given as a speci- 
 men of a fully formed 
 vertebra, it has been 
 found to be divisible in- 
 to the following pieces, 
 all or only a part of 
 which may be present 
 in other vertebrae, even 
 belonging to the same 
 skeleton ; and these 
 parts are represented 
 detached from each 
 other in the diagram which accompanies the figure (Jig. 219, B). 
 They are 1st. the centre or body of the bone ; 2dly. two elements 
 (6, >), which embrace the spinal marrow ; 3dly. the superior spinous 
 process (c) ; 4thly. the two transverse processes (d) ; othly. two 
 elements forming the inferior arch, and enclosing the principal 
 blood-vessels (e) ; and 6thly. an inferior spinous process (g). 
 
 With this key before us, we are able with the utmost ease to 
 comprehend the structure of any form of vertebra that may offer 
 itself. Thus, in different regions of the back of the same fish, 
 the composition of the vertebrae is totally different ; near the tail 
 
VERTEBRATA. 483 
 
 the vertebrae consist of the body (a), the superior arch (b) and 
 spinous process (c), and the inferior arch ( e) and spinous pro- 
 cess (g). In the neighbourhood of the head, however, neither 
 the inferior arch nor spinous process are at all developed ; but 
 the transverse processes, which were deficient in the former case, 
 are here of great size and strength. It is obvious, therefore, that 
 the form of a vertebra may be modified to any extent, by the 
 simple arrest of the developement of certain elements, and the 
 disproportionate expansion of others, until at length it becomes 
 scarcely recognisable as constituting the same piece of the ske- 
 leton. 
 
 Who would be prepared to expect, for example, that the occi- 
 pital bone of the human head was merely a modification of a few 
 of the elements of the fish's vertebra above described enormously 
 expanded, in order to become adapted to altered circumstances ? 
 And yet how simple is the transition ! By removing the inferior 
 arch (e) and spinous process (g), and slightly reducing the pro- 
 portionate length of the transverse processes (W), we arrive at 
 the form of a human vertebra, which exhibits precisely similar 
 elements : enlarge the arches (6, b) that surround the spinal 
 axis of the nervous system, increase the size of the superior spinous 
 element (c), and we have the occipital bone of a fish : and from 
 hence, through a few intermediate links, we arrive almost imper- 
 ceptibly at the occipital bone of the human cranium ; the main 
 differences being that the body is in Man divided into two lateral 
 halves, while the superior arches (b) become spread out so as 
 adequately to defend the prodigiously developed masses of the 
 brain, to which in the human body they correspond. 
 
 One other illustration of this interesting subject. What bones 
 compose a completely formed thorax ? In man we find, as every 
 tyro knows, 1st. the dorsal vertebra; 2dly. the ribs, with their 
 cartilages ; and 3dly. the sternum. But it is not in man that we 
 must expect a perfectly developed thoracic framework ; it is in the 
 birds that are destined to rise in the air by the assistance of their 
 proportionately powerful thoracic extremities. If therefore we 
 examine the thorax of a bird, we find it composed of pieces which 
 in man are absolutely wanting: we see 1st. the vertebra; #dly. 
 the dorsal ribs, firmly articulated on each side both with their 
 bodies and transverse processes ; 3dly. the sternal ribs, extending 
 from the ribs last mentioned to the sternum ; and, lastly, the 
 sternum, itself composed, as we shall afterwards see, of various 
 
 2 i 2 
 
484 VERTEBRATA. 
 
 elements not found in the human body. If we prosecute our sur- 
 vey a little further, we shall find this portion of the skeleton offer- 
 ing the greatest possible variety as regards the presence or absence 
 of the elements above enumerated : thus in the Frog we have 
 vertebrae and sternum, but no ribs ; in the Serpent, vertebrae and 
 dorsal ribs, but no sternum or sternal ribs ; in Man the sternal 
 ribs are represented by the costal cartilages ; and thus a thorax of 
 every required description is constructed by adding or taking away, 
 expanding or contracting certain elements, all of which a typical 
 skeleton might be supposed to contain developed in a medium 
 condition. 
 
 The nervous system of the Vertebrata is by far more complex 
 and elaborately organized than that of any of the four preceding 
 divisions of the animal world ; and consists, in fact, of several dis- 
 tinct systems differently disposed and appropriated to different 
 offices. Certain largely developed ganglia situated in the cavity 
 of the cranium, generally considered by themselves on account of 
 their disproportionate size when compared with the other nervous 
 centres, are commonly grouped together under one common de- 
 signation, and form what is called the brain or encephalon : these 
 masses, however, as we shall hereafter see, preside over various and 
 widely different functions ; and with them perception, volition, 
 and intelligence are essentially connected. 
 
 Continued from the brain, and lodged in a canal formed by the 
 superior arches of the vertebral column, is a long chain of gan- 
 gl ionic centres, so intimately united that they appear confused 
 into a long medullary cord usually denominated the spinal marrow 
 (medulla spinalis). 
 
 The spinal medulla in reality consists of two double series or 
 columns, composed of symmetrical and parallel ganglia ; one pair 
 of columns, the anterior, presiding over those muscular movements 
 which are under the control of the will, while the posterior are 
 destined to receive impressions derived from the exterior of the 
 body : these columns, therefore, are denominated respectively the 
 motor and sensitive tracts of the spinal cord. 
 
 From the lateral aspects of the medulla spinalis are derived at 
 intervals symmetrical pairs of nerves, which escape from the spinal 
 canal by appropriate orifices situated between the different bones 
 of the vertebral column, and are distributed to the voluntary mus- 
 cles and integument of the two sides of the body. 
 
 The spinal nerves, however, are not so simple in their conipo- 
 
VERTEBRATA. 485 
 
 sition as they were considered to be by the older anatomists : each 
 of them has, in fact, been found to arise from the spinal cord by 
 two distinct roots, one derived from the anterior, the other from 
 the posterior column of the corresponding side ; so that each nerve 
 is evidently made up of two distinct sets of filaments, one set 
 communicating with the motor, the other with the sensitive tracts ; 
 and thus every nerve derived from the spinal cord is a compound 
 structure, being composed of filaments distinct in office, although 
 enclosed in the same sheath, some being connected with the mus- 
 cular movements, the others with sensation. But in addition to 
 the cerebro-spinal ganglia and the symmetrically arranged nerves 
 emanating therefrom, that are distributed to the organs of sensa- 
 tion and movement, there exists in the Vertebrata a distinct system 
 of nervous centres lodged among the viscera, appropriated to the 
 performance of the automatic functions, and presiding over those 
 involuntary movements of the body upon which depend the ope- 
 rations connected with nutrition. These ganglia are variously 
 distributed, being situated in the head, the neck, the thorax, and 
 the abdomen ; and from them arise large plexuses of nerves, des- 
 tined to supply the organs belonging to digestion, circulation, and 
 secretion ; thus forming extensive ramifications, formerly distin- 
 guished by the name of the sympathetic nerve, but now more pro- 
 perly considered as a distinct system presiding over organic life, 
 as the former is connected with the phenomena of animal life. 
 
 With the increased developement of the nervous system in the 
 vertebrate classes we find the organs of the senses assume a pro- 
 portionate perfection of structure and regularity of arrangement. 
 The auditory apparatus, of which we have seen only rudiments in 
 the lower animals, gradually becomes more and more elaborately 
 organized : the eyes, now invariably two in number* are lodged in 
 cavities formed for their reception by the osseous framework of the 
 face ; and exhibit, in the simplicity of their structure, a higher type 
 of organization than any we have hitherto examined. Organs of 
 smell, also double, but of very variable construction, are likewise 
 constantly present. The tongue becomes slowly adapted to ap- 
 preciate and discriminate savours; and the sense of touch, the most 
 generally diffused of all, is especially conferred upon organs of 
 different kinds peculiarly adapted to exercise this faculty. Thus 
 with increased intelligence higher capabilities of enjoyment are 
 allotted, and sagacity developes itself in proportion as the nervous 
 centres expand. But there are minor points, characteristic of the 
 
486 VERTEBRATA. 
 
 vertebrate division of the animal world, which must not be omitted 
 in this preparatory survey of their organization. Their organs of 
 digestion and nutrition are constructed according to a different type, 
 and upon a more enlarged plan than in any of the classes enumerated 
 in the preceding chapter ; and parts are superadded to the digestive 
 apparatus which in lower tribes had no existence. In addition to 
 the usual subsidiary glands, namely, the salivary and the hepatic, 
 a third secretion is poured into the intestine along with the bile 
 derived from the pancreas, a viscus which we have not as yet met 
 with. Throughout all the MOLLUSCA we have found the bile 
 secreted by the liver to be separated from arterial blood, as are 
 the other secretions of the body ; but in the VERTEBRATA it is 
 from venous blood that the bile is formed, and in consequence an 
 elaborate system of vessels is provided, distinct from the general 
 circulation, by which a large supply of deoxygenized blood is con- 
 veyed to and distributed through the liver, constituting what is 
 termed by anatomists the system of the vena portte : nay, more, 
 in connexion with this arrangement we find another remarkable 
 viscus make its appearance, the spleen; from which venous blood is 
 copiously supplied to the portal vein, and added to that derived 
 from other sources. 
 
 A still more important and interesting circumstance, which 
 strikes the anatomist on comparing the Vertebrata with lower 
 forms of existence, is the sudden appearance of an entirely new sys- 
 tem of vessels, destined to absorb from the intestines the nutritious 
 products of the digestive process, and to convey them, as well as 
 fluids derived from other parts of the body, directly into the veins, 
 there to be mixed with the mass of the circulating blood. These 
 vessels, of which no traces have been detected in any of the INVER- 
 TEBRATA, ara called lymphatics and lacteals, but their structure 
 and distribution will occupy our attention hereafter. 
 
 The blood of all the VERTEBRATA is red, and is composed of 
 microscopic globules of variable form and dimensions in different 
 animals. In the class of Fishes, owing to the as yet imperfect con- 
 dition of the respiratory apparatus, the temperature of the body is 
 scarcely higher than that of the surrounding medium ; and, even in 
 Reptiles, such is the languid condition of the circulation, and the 
 incomplete manner in which the blood is exposed to the renovating 
 influence of the oxygen derived from the atmosphere, that the 
 standard of animal heat is still extremely slow. But in the higher 
 classes, the Birds and Mammalia, owing to the total separation of 
 
VERTEBRATA. 487 
 
 the systemic and pulmonary circulation, the effect of respiration is 
 increased to the utmost ; and, pure arterial blood being thus abun- 
 dantly distributed through all parts, heat is more rapidly generated, 
 the warmth of the body becomes considerably increased, and such 
 animals are permanently maintained at an invariable temperature, 
 considerably higher than that of the medium in which they live. 
 Hence the distinction generally made between the hot-blooded 
 and cold-blooded Vertebrata. 
 
 The variations in the temperature of the blood, above alluded 
 to, are, moreover, the cause of other important differences observable 
 in the clothing, habits, and instincts of these creatures. To retain 
 a high degree of animal heat necessarily requires a warm and thick 
 covering of some non-conducting material ; and consequently in the 
 hair, wool, and feathers of the warm-blooded tribes we at once 
 recognise the provision made by Nature for preventing an undue ex- 
 penditure of the caloric generated in the body. Such investments, 
 however, would be but ill adapted to the inhabitants of a watery 
 medium ; and consequently the fish destined to an aquatic life, or 
 the amphibious reptile doomed to frequent the mud and slime upon 
 the shores, are deprived of such incumbrances, and clothed in a 
 scaly or slippery covering more fitted to their habits, and equally in 
 accordance with the diminished temperature of their blood. 
 
 Still more remarkable is the effect of a mere exaltation of animal 
 heat upon the instincts and affections of the different races of the 
 Vertebrata. The fishes, absolutely unable to assist in the matura- 
 tion of their offspring, are content to cast their spawn into the 
 water, and remain utterly careless of the progeny to be derived from 
 it. The reptile, equally incapable of appreciating the pleasures 
 connected with maternal care, is content to leave her eggs exposed 
 to the genial warmth of the sun until the included young escape. 
 But no sooner does the vital heat of the parent become sufficient 
 for the purposes designed by Nature, than all the sympathies of 
 parental fondness become developed, all the delights connected 
 with paternity and maternity are superadded to other enjoyments ; 
 and the bird, as she patiently performs the business of incubation, 
 or tenderly watches over her newly hatched brood, derives a 
 pleasure -from the performance of the duties imposed upon her, 
 second only to that enjoyed by the mammiferous mother, who 
 from her own breast supplies the nutriment prepared for the sup- 
 port of her infant progeny. 
 
488 
 CHAPTER XXVII. 
 
 PISCES FISHES. 
 
 (521.) To whatever portion of the animal world we turn our 
 attention, we find the lowest and least perfectly organized tribes 
 to be inhabitants of the water. To dwell upon the land ne- 
 cessarily demands no inconsiderable share of strength and activity, 
 limbs sufficiently strong to support the weight of the body, mus- 
 cles possessed of great power and energy of action, acute and 
 vigilant organs of sense, and, moreover, intelligence and cunning 
 proportioned to the dangers or necessities connected with a terres- 
 trial existence. 
 
 The inhabitant of the waters, on the contrary, although less 
 highly gifted, may be fully competent to enjoy the position it is 
 destined to occupy. Being constantly buoyed up on all sides by 
 a dense element, it is easily supported at any required altitude 
 without much muscular effort ; but feeble limbs are needed to 
 guide its path through the water, and slight impulses suffice to 
 impel it forward. Thus, therefore, in Fishes we are prepared to 
 expect a priori, that, as far as strength and compactness of struc- 
 ture are concerned, they will be found inferior to other Vertebrata. 
 
 We are likewise justified in anticipating that in intelligence, 
 and in the relative perfection of their senses, fishes should be less 
 highly endowed than the other vertebrate classes. Plunged in 
 the immeasurable depths of the ocean, whereunto no sound can 
 ever penetrate, dwellers in the realms of eternal silence, where 
 even the roar of the storm is lost, vivid and distinct perceptions 
 of sound can be little needed. Surrounded by a turbid element, 
 through which the rays of light with difficulty make their way, the 
 sphere of vision must necessarily be extremely limited. Immersed 
 in a fluid but little adapted to distribute odorous particles, a 
 refined sense of smell would be a useless provision. Taste, if it 
 exists at all, must be blunted to the utmost, 'from the circum- 
 stances under which fishes seize and swallow prey ; and even the 
 sense of touch, in animals encased in scales and deprived of pre- 
 hensile limbs, can only be exercised in a vague and imperfect 
 manner. 
 
PISCES FISHES. 489 
 
 With such inferiority in their powers of communication with 
 the external world, and with faculties so circumscribed, we might 
 justly infer that, as relates to their intellectual powers, fishes hold 
 a position equally debased and degraded. Destitute of the means 
 of social intercourse, deprived of all sympathy even with indivi- 
 duals of their own species, friendless and mateless, the fish is 
 denied even the privileges of sexual attachment ; the female for the 
 most part ejects her countless eggs into the sea, heedless of the 
 male that blindly fecundates them as she is careless of the progeny 
 to which they give birth : thus, to pursue and destroy their prey 
 constitutes their chief enjoyment during life, and to be devoured 
 at last is the great end of their existence. 
 
 (522.) We shall commence our account of the anatomy of fishes 
 by an examination of the internal skeleton which forms the frame- 
 work of their bodies. The reader has already seen in the CEPHA- 
 LOPODA the first appearance of an osseous system in the carti- 
 laginous pieces described in the last chapter, and will neces- 
 sarily expect that between the rudimental condition which cha- 
 racterizes the cephalic ring of the Cuttle-fish, and the complete 
 and perfect skeleton of the fish, various gradations of developement 
 will occur as we advance progressively from lower to more elevated 
 forms of the finny race. Nor in this will he be deceived. The 
 lowest tribes of fish possess a skeleton but little superior in its 
 organization to that of the Cephalopod : in the Myxine and 
 Lamprey the cranium is still cartilaginous ; and even the spinal 
 column, not yet divided into vertebrae, resembles a cartilaginous 
 cord extending from the head to the tail. Even in the Sturgeon, 
 the Skate, and the Shark, the skeleton is but very partially ossi- 
 fied ; and thus we are gradually and almost imperceptibly conducted 
 to the strong and bony framework of the typical fishes. 
 
 (528.) Even in tracing the modifications observable in the 
 construction of the vertebral column, we have a beautiful illus- 
 tration of the progressive advances of ossification in this the 
 central portion of the osseous system. The spine of the Lam- 
 prey, although at first sight apparently entirely soft and cartila- 
 ginous, presents already in the arches which compose the spinal 
 canal, and in the soft cord that represents the bodies of the ver- 
 tebrse, slight indications of an incipient division into distinct 
 pieces : rings of ossific matter are distinguishable, encircling at 
 intervals the soft spinal cartilage upon which they perceptibly 
 encroach, so that on making a longitudinal section of the cord it 
 
490 PISCES FISHES. 
 
 offers an appearance sketched in the adjoined figure (fig. 220, A). 
 In a more advanced form of a fish's skeleton, as for example in the 
 
 Sturgeon, these ossified rings are 
 
 P j , , & ., Fig. wo. 
 
 found to have enlarged consider- 
 
 ably, and penetrate still more * - - *- - * i 
 
 deeply into the cartilaginous mass 
 (^g.220, B). As the bony rings 
 thus developed approximate the 
 centre, it becomes more and more 
 evident that they represent the 
 bodies of so many vertebrae ; but 
 even in the majority of fishes the 
 central part remains permanently 
 unossified ; so that a cartilaginous 
 axis traverses the vertebral co- 
 lumn from one end to the other 
 (Jig. 220, c), and it is not usual 
 
 to find the central aperture perfectly obliterated, as delineated in 
 the fourth sketch, D. 
 
 (524.) Fishes, being continually resident in an element nearly 
 of the same specific gravity as their own bodies, require little firm- 
 ness or solidity in the construction of their spinal column : a free 
 and unfettered power of flexion in certain directions so as to 
 permit an ample sweep of their expanded tail, which forms the 
 principal agent in propelling them forwards, is far more essential 
 to their habits. Thus the cartilaginous spine of the feeble Lam- 
 prey is sufficient for all needful purposes ; and even in the most 
 perfectly ossified fishes, from the manner in which the vertebrae 
 are united to each other, the greatest possible flexibility is ensured. 
 The body of each vertebra presents two conical cups, the apices 
 of which are nearly or quite continuous ; the margin of each cup- 
 like depression is united by elastic ligament to the corresponding 
 margin of the contiguous vertebra, and thus between the bodies of 
 each pair of vertebrae a wide cavity is formed (D), which is filled 
 up with a semi-gelatinous substance; so that, by this beautiful con- 
 trivance, the mobility of the whole chain is abundantly provided 
 for. 
 
 (525.) There are only two kinds of vertebrae recognizable in 
 the skeleton of a fish, viz. the abdominal and the caudal. The 
 abdominal vertebrae support the ribs, for in these animals the ribs 
 do not constitute a thorax, or contain any of the viscera called 
 
thoracic in the 
 human body : 
 they extend 
 from the head 
 to the com- 
 mencement of 
 the tail, and 
 are at once re- 
 cognizable by 
 the nature of 
 the elements 
 which enter in- 
 to their com- 
 position ; each 
 vertebra being 
 provided with 
 a superior arch 
 (fig. 219, b), 
 through which 
 passes the spi- 
 nal cord, a su- 
 perior spinous 
 process (c), 
 and two trans- 
 verse processes 
 (d), to the ex- 
 tremities of 
 which the ribs 
 are generally 
 attached. The 
 caudal verte- 
 brae are com- 
 posed, as we 
 have already 
 seen, of differ- 
 ent elements: 
 the transverse 
 processes ei- 
 ther do not 
 exist, or are 
 very feebly de- 
 
 PISOES FISHES. 
 
 Fff.221. 
 
 491 
 
492 PISCES FISHES. 
 
 veloped ; but beneath the body an inferior arch is formed, and 
 from this an inferior spinous process, equalling the superior in 
 length, is prolonged in the opposite direction (Jig- 221, b). 
 
 (526.) As the vertebrae approach the tail, they become some- 
 what modified in structure to support the caudal fin ; their spines 
 become shorter and thicker, the canals formed by their superior 
 and inferior arches smaller or nearly obliterated, and at length 
 the spines become, as it were, soldered to each other, and to the 
 interspinous bones hereafter to be noticed ; so that they form a 
 broad vertical plate, to the posterior margins of which the rays of 
 the tail-fin are articulated (Jig. 221. 70). 
 
 (527.) The ribs of fishes are slender bones, appended either 
 to the extremities of each transverse process of the abdominal 
 vertebrae, or else to the body of the vertebra itself : every rib is 
 connected with but one vertebra, and that only at a single point. 
 They do not, as we have already said, form a thoracic cavity ; but 
 enclose the abdomen, and are embedded among the lateral muscles 
 of the trunk, to which they give support. From each rib arises a 
 long styliform process (78), which, inclining backwards, is likewise 
 plunged among the muscular fasciculi ; and in some fishes, such as 
 the Herring and Carp tribes, similar appendages are derived from the 
 bodies of the vertebrae themselves, so that the bones of such fishes 
 appear to be extraordinarily numerous. On the other hand, many 
 tribes have but the rudiments of ribs ; and in some, as for example 
 in the Skate, they are altogether wanting. 
 
 (528.) No sternum, properly so called, exists in fishes ; but 
 the extremities of the ribs are sometimes connected with ossified 
 plates belonging to the tegumentary system, which cover the abdo- 
 men, and which by some authors have been regarded as a sternal 
 apparatus. 
 
 (529.) We have now to request the attention of the reader to 
 certain supplementary organs which are peculiar to the class before 
 us. These consist in sundry appendages to both the superior and 
 inferior spinous processes of the vertebrae, which are generally pro- 
 longed into fins situated along the mesial line of the body. These 
 azygos fins, which must be by no means confounded with the pairs 
 of fins that represent the arms and legs, are very variable in 
 their position, and in many cases are altogether wanting. When 
 fully developed, one of them is situated along the mesian line of 
 the back, and in the Perch (Jig- 221) this dor sal Jin is separated 
 into two distinct portions (75) : another, denominated the caudal 
 
PISCES FISHES. 493 
 
 Jin, forms the tail ; and a third, likewise situated in the median 
 line at a short distance behind the anal orifice, is called the anal 
 Jin from that circumstance. 
 
 These fins present two sets of bones : the interspinous bones, 
 which form the basis to which they are affixed ; and (he Jin-rays. 
 
 The interspinous bones (Jig. 21. 74) form a series of strong 
 dagger-like bones, deeply implanted in the flesh along the mesial 
 line of the body, between the two great masses of lateral muscles : 
 their points generally penetrate to a little distance between the 
 spinous processes of the Vertebrse, to which they are connected by a 
 ligamentous attachment ; whilst to their opposite extremity, which 
 may be compared to the hilt of the dagger, the corresponding fin- 
 rays are affixed by a beautiful articulation. There is generally 
 only one interspinous bone affixed to a vertebral spinous process, 
 but in the Flat-fishes (Pleuronectida) there are two ; and, more- 
 over, in that remarkable family, the, inferior spinous process of 
 the first caudal vertebra, which j as we have already seen, is of 
 enormous size, frequently has not fewer than six or seven interspi- 
 nous bones appended to its extremity. 
 
 Each interspinous bone consists of two pieces united by a 
 suture ; one portion representing the blade, the other the handle 
 of the dagger, to which we have compared it. 
 
 The fin-rays of fishes are of two kinds, being either solid and 
 apparently composed of one strong piece, like those which sup- 
 port the anterior half of the dorsal fin of the Perch (Jig. 75), in 
 which case they are called spinous rays ; or else they are composed 
 of several slender stems derived from one common root, every one 
 of which is made up of numerous pieces : these, which bear the 
 name of soft rays, are found in the posterior portions both of the 
 dorsal and anal fin of the perch, and are invariably met with in 
 the tail of all fishes possessed of a caudal fin. This difference in 
 the structure of the fin-rays, trivial as it might appear, is a circum- 
 stance to which much importance is attached by icthyologists, who 
 hence derive the means of separating osseous fishes into two great 
 groups, the Acanthopterygii, or such as possess spinous rays in 
 the composition of their dorsal fin ; and the Malacopterygii, in 
 which all the fin-rays are soft. Every fin-ray, whether spinous or 
 soft, is in reality made up of two lateral halves placed side by side : 
 in the soft rays these are easily separable ; but in the spinous rays 
 they are firmly united along the median line, so as to represent but 
 one bone. 
 
494* PISCES FISHES. 
 
 The articulation between every fin-ray and the corresponding 
 interspinous bone forms a hinge-joint, so as to allow of the eleva- 
 tion or depression of the fin. The structure of this joint is very 
 beautiful, the two lateral halves of the ray separate so as to form 
 two branches, which firmly embrace the sides of the head of the 
 interspinous bone, and terminate in little prominent tubercles, 
 which are received into corresponding lateral depressions in the 
 bone to which the ray is attached. Sometimes, indeed, the head 
 of the interspinous bone is completely perforated, and then the two 
 branches of the fin-ray passing through the opening become firmly 
 united with each other, forming a kind of joint which is peculiar 
 to fishes, and exactly resembles the mode of union between two 
 links of a chain. This structure is beautifully exhibited in the 
 articulation of the elongated rays attached to the head of Lophius 
 piscatorius.* 
 
 (530.) The composition of the skull of fishes is one of the 
 most difficult studies connected with their history ; nevertheless, 
 it is a subject of very considerable importance, and has recently 
 occupied the attention of the most celebrated Continental anato- 
 mists. It is not by any means our intention to engage our readers 
 in discussing all the conflicting and, sometimes, visionary opinions 
 entertained by different authors relative to the exact homology of 
 the individual bones forming this part of the skeleton ; and we 
 shall, therefore, content ourselves by placing before them, divested 
 as far as possible of superfluous argumentation, Cuvier's*!* masterly 
 analysis of the labours of the principal enquirers concerning this 
 intricate piece of anatomy, taking the Perch as a standard of com- 
 parison.^: 
 
 The head of a fish may be conveniently divided, for the pur- 
 pose of description, into several distinct regions, each of which will 
 require separate notice. 
 
 (531.) The Cranium, which forms the central portion of the 
 skull, contains the brain and auditory apparatus, and constitutes 
 the basis whereunto the other parts are connected. It is remark- 
 able from the number of distinct pieces of which it consists, inas- 
 much as in fishes the elements, or ossific centres, of which the 
 
 * Vide YarrelPs History of British Fishes ; vol. i. p. 271. 8vo. 
 
 t Cuvier et Valenciennes, Histoire des Poissons. 4to. vol. i. 
 
 $ Those who would enter more fully into the discussions relative to the essential 
 composition of the skull, are referred to the works of Geoffroy St. Hilaire, Spix, 
 Rosenthal, Meckel, Bakker, Bojanus, and Oken, the great disputants upon this 
 subject. 
 
PISCES FISHES. 495 
 
 cranial bones of higher animals are composed, remain here per- 
 manently separated, overlapping each other so as to form squamous 
 sutures ; but never becoming fused together, as the elements of the 
 human skull invariably do at a very early period. 
 
 No fewer than twenty-six bones enter into the composition of 
 the cranium we are now considering ; to which, as is now generally 
 allowed, the following names are applicable. 
 
 The Frontal bones are each divided into three portions, called 
 respectively the Principal frontal (1),* the Anterior frontal (2), 
 and the Posterior frontal (4). 
 
 Between the anterior frontal bones is the Ethmoid, a simple 
 vertical lamella, which is often merely a cartilaginous plate. 
 
 The middle of the base of the cranium is made up of two bones : 
 the Basitar (Jig. %$. 5), a portion of the occipital forming the 
 body of the occipital vert'ebra ; and the body of the Sphenoid (6), 
 a distinct bone, which is prolonged anteriorly into a lengthened 
 process, which serves as the base of the membranous septum be- 
 tween the orbits. 
 
 The Parietal bones (7) are placed behind the posterior frontal, 
 but they do not generally touch each other, being separated by an 
 interposed bone called the Interparietal (8) . 
 
 The Occipital bone is made up of five portions, namely, two 
 External Occipitals (9), two Lateral Occipitals (10), and the 
 Basilar bone (5), already noticed, by which the head is articulated 
 with the first vertebra of the spine. 
 
 Two detached bones, which represent the great or temporal ala 
 of the Sphenoid, fill up the space between the body of the Sphe- 
 noid and the posterior frontal. 
 
 Two other pairs of bones, which are elements of the temporal 
 bone in man, likewise assist in forming the cranium : these are 
 called the M astoid bones (12), and the Petrous bones (13). 
 
 A single bone, analogous to the anterior portion of the body 
 of the human Sphenoid, and which, as will be fully evident here- 
 after, is essentially distinct from the posterior portion, bears the 
 name of the Anterior Sphenoid, while the orbital ala of the 
 Sphenoid are found in the two bones marked 14. 
 
 These, therefore, together with the representative of the Vomer 
 (16), complete the cranial portion of the skull ; no fewer than six 
 azygos and twenty pairs of bones entering into its composition. 
 
 * In order lo simplify the subject as much as possible, and prevent unnecessary 
 repetition, the reader will observe that, throughout all the figures connected with the 
 osteology of the Vertebrata, corresponding bones are indicated by the same numbers. 
 
496 
 
 PISCES FISHES. 
 
 (532.) Bones composing the upper jaw. The upper jaw con- 
 sists of two pairs of bones, which, from the looseness of their 
 connexion with the other bones of the face, are endowed with con- 
 siderable mobility. 
 
 The Intermaxillary bones (17) form the greater part of the 
 margin of the jaw, and are attached by a moveable articulation to 
 the anterior extremity of the vomer. These bones are armed with 
 numerous sharp teeth. 
 
 The Maxillary bones (18) are moveably articulated with the 
 last, and generally are in like manner furnished with teeth. In 
 some cases they are divided into two or three pieces. 
 
 Bones of the face. The bones of the face in fishes are very 
 numerous ; but, as they are of little importance to the osteologist, 
 a bare enumeration of them will answer our present purpose, and 
 enable the student to recognize them with facility. We have 
 first the Nasal bones (20) ; then a chain of bones of variable size 
 and number (19), so disposed as to form the lower boundary of 
 the orbit, and hence named Sub-orbital bones. Behind these, 
 again, a similar chain of ossicles is not unfrequently met with, 
 arching over the temporal fossa ; and these, which are apparently 
 peculiar to fishes, are named the Supra-temporal (21). 
 
 Ptery go-palatine and temporal system of bones. Upon each 
 side of the head is situated a somewhat complex apparatus con- 
 
PISCES FISHES. 497 
 
 nected on the one hand with the articulation of the lower jaw, and 
 on the other with the opercula or gill-covers. These bones are 
 seven in number on each side. 
 
 The Palatine (22) are easily recognizable, forming part of the 
 roof of the mouth, and generally armed with teeth. 
 
 Two bones are connected with the posterior edge of each palate 
 bone : one, situated externally, becomes in reptiles a very impor- 
 tant element, it is called the Transverse bone (24) ; the second 
 (25) is named the Internal Pterygoid. 
 
 The other pieces belonging to this part of the skeleton are not a 
 little interesting on account of their remarkable arrangement ; 
 and, perhaps, the anatomical student will be somewhat startled at 
 the position which some of them occupy. In the first place, the 
 squamous portions of the temporal, instead of entering into the 
 formation of the cranium, are here slightly displaced, and, although 
 still called the Temporal bones (23), are articulated by a hinge- 
 joint with the posterior frontal and mastoid bones, and thus 
 form a moveable basis to which the opercular apparatus is at- 
 tached. 
 
 Connected with the Temporal we have the broad and flat 
 piece (27) which is the Tympanic bone, and to these the pieces 
 forming the opercula are appended. 
 
 Lastly, supporting the lower jaw we find the Jugal bones ; 
 and connecting these with the rest of the temporal apparatus are 
 two small ossicles (31), which complete this portion of the ske- 
 leton. 
 
 The seven bones above enumerated are almost immoveably con- 
 nected with each other by the interposition of cartilage between 
 their edges, a mode of articulation distinguished by the name of 
 synchondrosis ; but the whole apparatus moves readily upon the 
 two hinges, one formed by the articulation of the palate bone with 
 the maxillary and vomer, and the other by the joint which unites 
 the temporal bone to the posterior frontal. This movement, by 
 opening the gill-covers, enlarges the cavity of the mouth when 
 the fish wishes to take in the water necessary for respiration ; or 
 else, by acting in a contrary direction, again expels it. 
 
 (533.) Opercular bones. The great flap, which in osseous 
 fishes closes the gill openings externally, is composed of four 
 pieces, to which the following names have been given. The Pra- 
 operculum (30) is attached to the posterior edge or angle of 
 the palato-temporal apparatus last described, and its borders often 
 
 2 K 
 
498 
 
 PISCES FISHES. 
 
 present spines and indentations, which, being visible externally, are 
 of much importance to the icthyologist, as they afford a good 
 character of distinction between allied genera. The second piece 
 (28), which from its size is called par excellence the Operculum, 
 together with the Sub-operculum (32) and the Inter-operculum 
 (33), form a flap which covers the gill-opening like a great valve, 
 opening and shutting continually to give exit to the water used in 
 respiration. 
 
 (534.) Lower Jaw. The lower jaw of fishes consists of two 
 lateral halves united by a symphysis in the mesian line, each 
 branch being articulated with the jugal bone of its corresponding 
 side. Each division is separable by maceration into four or even 
 five pieces : viz. the Dental (34), which supports the teeth; the 
 Articular ($5), bearing the articulating facet ; the Angular (36), 
 forming the angle of the jaw ; and a fourth, placed upon the inner 
 surface of the articular, called the Opercular, because it corre- 
 sponds with a bone met with in the lower jaw of reptiles, to which 
 the same name has been applied. The fifth, when present, is very 
 small and unimportant. 
 
 aides and Bran- 
 chiostegous Rays. 
 The Os Hy- 
 oides of a fish 
 is situated as in 
 other vertebrate 
 animals ; it is 
 composed of two 
 branches, each 
 made up of seve- 
 ral pieces (37, 
 38, 39, 40), and 
 is always suspend- 
 ed from the tem- 
 poral by means of 
 two small ossi- 
 cles (59), which, 
 as they represent 
 the styloid pro- 
 cess of man, are 
 called the Styloid bones. 
 
PISCES FISHES. 499 
 
 Between the two branches of the os hyoides is placed a single 
 central piece (42), which becomes of great importance in reptiles 
 and birds, and upon this is the bone which supports the tongue, or 
 the Lingual bone (41). 
 
 The great fissure that exists on each side between the head and 
 shoulder of an osseous fish, wherein the gills are situated, is not 
 closed merely by the opercular bones, but likewise by a broad 
 membranous expansion called the Branchiostegous membrane, 
 which is adherent to the os hyoides, and assists in forming the 
 great valve of the operculum. This membrane is supported by a 
 series of slender bones derived from the external margin of each 
 branch of the os hyoides, and these are named from their office the 
 .Branchiostegous Rays (43). 
 
 (536.) Branchial apparatus. Fishes breathe by taking water 
 into their mouths, and forcing it out again through the apertures 
 situated upon each side of the neck ; it is thus made to pass be- 
 tween their gills, which form a series of pectiniform vascular fringes 
 supported upon a system of bones called the Branchial arches. 
 The branchial arches, which are generally four in number on each 
 side, are attached by one extremity to an intermediate chain of 
 bones (53, 54, 55) situated in the mesial line behind the os 
 hyoides, whilst by their opposite extremity they are connected by 
 ligaments to the under surface of the cranium. 
 
 Every branchial arch consists of several pieces (57, 58, 59, 60, 
 61), so joined together by ligaments that the whole is perfectly 
 flexible, and their edges are studded with little osseous plates, 
 generally armed with teeth, and so disposed as to prevent food 
 taken into the mouth from being forced out through the branchial 
 fissures with the issuing streams of water ; so that, in reality, these 
 pieces fulfil in their way the same office as the epiglottis of Mam- 
 malia. 
 
 (537.) Pharyngeal bones.' -The last parts found to enter into 
 the composition of this portion of a fish's skeleton, are called from 
 their position the Pharyngeal bones. They are placed imme- 
 diately behind the branchial apparatus, and form a second set of 
 masticatory organs, generally even more efficient than the jaws 
 themselves, being for the most part provided with very strong 
 teeth. 
 
 In the Perch there are eight of these bones situated just at 
 the entrance to the oesophagus, two inferior (56), and six above 
 
500 PISCES FISHES. 
 
 (62) ; their office and efficiency as organs of mastication must be 
 obvious to the most superficial observer. 
 
 Upon reviewing the general disposition of the skeleton in one of 
 the osseous fishes, it is at once apparent that the great instru- 
 ment of locomotion is the tail, which by extensive and vigorous 
 lateral movements sculls the body rapidly along through the 
 yielding element in which these creatures live. In the construc- 
 tion of the caudal extremity of the skeleton, every precaution has 
 evidently been taken to convert this part of the body into a broad 
 and expanded oar, possessed of the utmost possible flexibility in 
 the lateral direction. No pelvis, therefore, trammels the move- 
 ments of the spine, neither do any transverse processes limit the 
 extent of flexion from side to side ; while, on the contrary, the 
 extraordinary developement of the spinous processes both above 
 and below, and more especially the vertical caudal fin, give an 
 extent of surface proportioned to the wants of the animal. 
 
 The dorsal and anal fins, situated upon the mesian plane, 
 steady, and perhaps in some measure direct, the movements of the 
 body ; while the arms and legs, or rather the pectoral and ventral 
 fins, which are in this case of secondary importance as locomotive 
 instruments, exhibit a very rudimentary condition, and are but 
 feeble agents in progression. 
 
 The posterior extremities, or ventral fins, are even less efficient 
 than the pectoral in this respect ; and their position is found to vary 
 remarkably in different orders. In the Perch these organs are, 
 as we have seen, attached to the bony framework of the shoulders. 
 In the Carp tribe (Cyprinidse) they are removed far back towards 
 the commencement of the tail, and the bones supporting them are 
 merely embedded in the muscles of the abdomen. In the Cod 
 (Gadidse) the legs are absolutely in front of the arms, being sus- 
 pended under the throat ; and in the Anguilliform fishes, the Eel 
 for instance, the ventral extremities are altogether wanting. 
 
 (538.) Such being the imperfect developement of the usual 
 locomotive organs, we are quite prepared to expect a corresponding 
 modification in the disposition and efficiency of different parts of 
 the muscular system. When we compare the muscles of a fish 
 with those of any of the higher Vertebrata, the contrast is indeed 
 very striking. 
 
 Delicate muscles (Jig. 224) are provided for the erection or de- 
 pression of the different rays sustaining the dorsal and ventral fins, 
 and thus the fins themselves are expanded or folded up at pleasure. 
 
PISCES 
 
 FISHES. 
 
 501 
 
 Similar fasciculi spread out or approximate the rays of the tail, 
 increasing or contracting at will the extent of surface presented 
 by that organ. The muscles of the pectoral and ventral limbs are 
 small in proportion to the feebleness of these extremities ; the 
 muscles of the trunk alone constitute the great bulk of the body, 
 and form the efficient agents in progression. 
 
 Fig. 224. 
 
 These great lateral masses commence at the back of the head, 
 where they take an extensive attachment to the largely developed 
 cranium : from this point backwards, they fill up the entire space 
 intervening between the skin and the vertebral column, with both 
 of which they are intimately connected, reaching even to the origin 
 of the tail fin. The whole force of these powerful muscles is 
 evidently exerted in bending the spine from side to side, and in 
 effecting those vigorous lateral movements of the tail whereby the 
 fish is propelled through its liquid element. We need, therefore, 
 feel little surprise at the strength with which this part of the body 
 of fishes is not unfrequently endowed, or at the velocity of their 
 movement ; at seeing how easily their speed outstrips our fleetest 
 ships ; how the Flying-fish (Exocetus), urged on by fear, darts like 
 an arrow to a distance through the air; or how the Salmon, in 
 obedience to an imperious instinct, defies even the thundering 
 cataract to stop its course towards the locality where it is in- 
 structed by Nature to deposit its eggs. 
 
 (539.) There are sundry tribes of fishes, which, being destined 
 to remain at the bottom of the sea, present certain peculiarities of 
 structure, whereby they are not only distinguished from all others 
 
502 PISCES FISHES. 
 
 of the class, but form most remarkable exceptions to the general 
 law in accordance with which the Vertebrata are organized. 
 
 The animals presenting this anomalous configuration are the 
 PlcurontctuLe, or Flat-fishes, as they are generally termed, which 
 when at rest lie quietly upon the ground, where, from the colour 
 of the upper part of their bodies, they are scarcely distinguish- 
 able. To an ordinary observer the Pleuronectidse would seem to 
 have their bodies flattened and spread out horizontally, so that, 
 while resting upon their broad and expanded bellies, their eyes, 
 situated upon the back of the head, are thus disposed for the pur- 
 pose of watching what passes in the water above them ; and this, 
 the vulgarly received opinion, is considerably strengthened by the 
 fact, that what is usually called the belly is white and colourless, 
 while the back is darkly coloured and sometimes even richly varie- 
 gated. The very name used in scientific language to distinguish this 
 extensive family (Pleuronectes*) is calculated to propagate the error ; 
 and few imagine that, in applying the terms back and belly to the 
 upper and under surfaces of a Plaice or a Turbot, they are adopting 
 a phraseology quite inadmissible in an anatomical point of view. 
 
 On examining the skeleton of a Flat-fish, we at once see that 
 what we supposed to be the dorsal and ventral regions are in 
 reality the two sides, which are thus strangely different in colour ; 
 and that the great peculiarity of their structure is the want of 
 symmetry between the lateral halves of the body, arising from the 
 anomalous circumstance that both the eyes are placed upon the 
 same side of the head. Their cranium, indeed, is composed of the 
 same bones as that of an ordinary fish, but the two lateral halves 
 are not equally developed ; and the result is such a distortion of the 
 whole framework of the face, that both the orbits are transferred to 
 the same side of the mesial line of the back. 
 
 The position of the pectoral and ventral fins slightly participates 
 in this want of symmetry, but in other respects the skeleton (Jig. 225) 
 precisely corresponds with that of the generality of osseous fishes. 
 The superior and inferior spinous processes of the vertebrae are 
 amazingly developed, and the interspinous bones (74) of inordi- 
 nate length, so that the vertical diameter of the body is dispro- 
 portionately increased, and the animal is obliged to swim and rest 
 upon one side. The dorsal Jin (75) runs along the whole length 
 of the back ; the anal Jin (a) reaches from the large spines that 
 form the posterior boundary of the abdom'en to the tail, which 
 latter holds the same position as in other tribes ; so that the reader 
 
 a, the side ; vjjx'w, a fin. 
 
PISCES FISHES. 
 
 503 
 
 will have little diffi- Fig- 225. 
 
 culty in comparing 
 
 the different pieces 
 
 of the skeleton of the 
 
 Flounder (Pleuro- 
 
 nectes flesus) with 
 
 the corresponding 
 
 bones of the Perch 
 
 already described. 
 
 (540.) The ske- 
 letons of the Car- 
 tilaginous Fishes 
 (Chondropterygii *) 
 will require a dis- 
 tinct notice, inas- 
 much as they pre- 
 sent very remarkable 
 peculiarities of no 
 inconsiderable inter- 
 est. In the Sharks, 
 Skates, and other 
 genera belonging to 
 this important divi- 
 sion of the great 
 class we are now con- 
 sidering, the interior 
 of the bones remains 
 permanently cartila- 
 ginous, but the ske- 
 leton is in some re- 
 gions encrusted, as it were, with osseous granules. No centres of 
 ossification, from which radiating fibres of bony matter progressively 
 extend themselves, as is the case in the osseous fishes, are ever de- 
 veloped ; and consequently the skull, although it presents exter- 
 nally the same regions, eminences, and apertures that are usually 
 met with, is never divided into separate bones, but is formed of a 
 single mass of cartilage, in which no sutures or lines of division are 
 ever distinguishable. 
 
 The face is likewise much more simple in its structure ; for, 
 instead of the numerous pieces composing the palato-temporal 
 region of the Perch (j 532), two bones only are met with, one of 
 
 * ^avSga;, cartilage ; x-Ttpuyiav, a fin. 
 
504 
 
 PISCES FISHES. 
 
 which, the palatine, performs the office of an upper jaw and 
 supports the teeth, while the other connects the lower jaw with 
 
 the cranium. The lower jaw 
 itself, moreover, consists of 
 but one piece on each side, 
 to which the teeth are at- 
 tached. 
 
 From the peculiar con- 
 formation of the respiratory 
 apparatus, which will be ex- 
 plained hereafter, there is no 
 occasion for any opercular 
 flap ; this, therefore, is not 
 present : nevertheless, the hy- 
 oid and branchial arches re- 
 
 semble pretty much those of 
 osseous fishes; only the latter 
 are situated further back- 
 wards, being placed quite be- 
 hind the skull, under the 
 commencement of the spine. 
 
 The bones of the shoulder 
 are represented by a strong 
 cartilaginous zone, which in 
 Sharks is quite unconnected 
 with the vertebral column, 
 but in the Skates (Raia) it 
 is fixed to two large lateral 
 
PISCES FISHES. 505 
 
 apophyses derived from the spine (Jig. 226). The zone, represent- 
 ing the scapulary apparatus, consists of a single piece, which surrounds 
 the body, and on each side supports the bones of the fore-arm. The 
 enormously developed pectoral fin is composed of the carpus, amaz- 
 ingly augmented in size, and of the no less remarkable hand which 
 in the Skate is made up of an immense number of fingers or rays, 
 and forms by itself nearly half the circumference of the body. 
 
 The pelvis, or cartilaginous framework that supports the hinder 
 extremities, i. e. the ventral fins, is a single transverse piece of 
 cartilage quite detached from the rest of the skeleton : it expands 
 on each side into a broad plate, to which the fin, the representative 
 of the foot of higher animals, is appended, and likewise in the male 
 it gives attachment to additional organs called claspers, the use of 
 which will be explained in another place. 
 
 The anterior portion of the spine in the Skate is not as yet 
 divided into distinct pieces ; and, even in the posterior part, the 
 number of vertebral arches is twice as great as that of the separate 
 bodies of the vertebrse. 
 
 In all the Chondropterygii the ribs are mere rudiments, and in 
 some cases can scarcely be said to exist at all. 
 
 The Sturgeons (Sturionidai) form a kind of connecting link 
 between the osseous and cartilaginous fishes, and in them a 
 large swimming-bladder exists, from which is obtained the va- 
 luable material called isinglass : but in the Sharks and Rays this 
 organ is not found ; consequently, especially in the tribe last men- 
 tioned, it is xmly by means of the vigorous flappings of their enor- 
 mous hands that these ground-fishes are able to raise themselves 
 from the bottom. The disposition and relative importance of 
 different parts of the muscular system, is, therefore, necessarily 
 changed to meet these altered circumstances : the muscles of the 
 trunk, which in osseous fishes formed the great agents in loco- 
 motion, become now of secondary importance ; while those of the 
 pectoral fins, so feebly developed in the Perch, are massive and 
 powerful in proportion to the unwieldy size of the anterior extre- 
 mities. Another peculiarity in the skeleton of the Chondro- 
 pterygii is observable in the construction of the caudal fin, which 
 even in the Sturgeon and the Shark, notwithstanding the import- 
 ance which this organ still maintains in those genera as an instru- 
 ment of locomotion, begins to differ very remarkably from the tail 
 of an osseous fish. It is true that it still exhibits great expansion 
 in a vertical direction, and to a superficial observer, if examined 
 
506 PISCES FISHES. 
 
 without dissection, might seem to be constructed on the same prin- 
 ciples ; but, on examining the skeleton of one of these cartilaginous 
 fishes, it will be found that the vertebral column is continued 
 uninterruptedly into the upper half of the generally furcate tail ; 
 whilst the lower division of the caudal fin is entirely made up of 
 supplementary rays, appended to the inferior aspect of the caudal 
 vertebrae. Possessing this form of the tail the transition is by no 
 means abrupt from these highly organized fishes to the Saurian 
 Reptiles, with which, as we shall afterwards see, they exhibit 
 many remarkable affinities. 
 
 (541.) If in the highest HETEROGANGLIATA we found, that in 
 addition to the tegumentary skeleton, or shelly covering, so exten- 
 sively met with among the Mollusca, the first appearances of an 
 internal osseous system became recognizable, we are not on that 
 account to imagine that, as soon as bones become developed inter- 
 nally, the cuticular secretions hitherto denominated shell at once 
 disappear, but, on the contrary, must be prepared to expect that in 
 some form or other calcareous armour deposited by the skin should 
 still be met with. In fishes the coexistence of an internal and of an 
 external skeleton is undeniable ; and having already described the 
 former, which has been aptly enough called the endoskeleton, it 
 remains for us in the next place to examine the latter or exoske- 
 leton, which, as we shall soon perceive, forms no unimportant part 
 of the anatomy of the class under consideration. 
 
 The most usual form of the cuticular covering of fishes is that of 
 imbricated scales, with which the whole exterior of the body is 
 compactly encased, as in a suit of armour. Such an investment 
 is admirably adapted to their habits and economy. The dense and 
 corneous texture of the scales, impermeable to water, defends their 
 soft bodies from maceration, while from their smooth polished exte- 
 rior and beautiful arrangement they ensure the least possible resist- 
 ance from the surrounding medium as the fish glides along. 
 
 (54.) Examined separately, each scale is found to be partially 
 embedded in a minute fold of the living and vascular cutis, to which 
 its under surface is adherent. Every scale is, in fact, made up of 
 superimposed laminae of horny matter secreted by the cutis, pre- 
 cisely in the same way as the shelly covering of a mollusk, and 
 by maceration the different layers may readily be separated, the 
 smallest and most superficial being of course the first formed, while 
 the largest and most recent are those nearest to the surface of the 
 living skin : as far as relates to the mode of growth, therefore, there 
 
PISCES FISHES. 507 
 
 is the strictest analogy between the scale of a fish and shell. Va- 
 rious are the forms under which these scales present themselves to 
 the icthyologist : sometimes, as in the Eel, they are thinly scat- 
 tered over the surface of a thick and slimy cutis, more generally 
 they form a close and compact imbricated mail ; in the Pipe- 
 fishes (Syngnathidee) the whole body is covered with a strong 
 armour composed of broad and thick calcareous plates ; and in the 
 Coffin-fishes (OstracionidtE) the integument is converted into a 
 strong box made up of polygonal pieces anchylosed together, so 
 that the tail and fins alone remain moveable. 
 
 The Sturgeon is covered with broad shield-like plates. The 
 skin of the Sharks is densely studded with minute sharp spines of 
 almost crystalline hardness ; and in many Skates, as in the Thorn- 
 back, similar cuticular appendages, but of more considerable 
 dimensions, are distributed over the back and tail, forming very 
 efficient defensive weapons. 
 
 But cutaneous spines, although while in a rudimentary condi- 
 tion they are obviously mere extraordinary developements of scales, 
 may occasionally become of sufficient size and importance to make 
 them convertible to various unexpected uses ; and when thus 
 exaggerated in their dimensions, and appropriated to distinct offices, 
 they assume so much of the character of true bone, that it is no 
 longer easy to demonstrate their real nature, more especially as 
 they then become in many cases really articulated by means of very 
 perfect joints with different pieces of the endoskeleton properly so 
 called. 
 
 Let us examine this important subject with a little attention, 
 and we shall soon perceive how closely the endoskeleton and the 
 exoskeleton may become connected, not to say interchangeable, with 
 each other. There is no possibility of mistaking the spines and 
 tubercles upon the back of a common Skate for anything but cuti- 
 cular appendages secreted in the same manner as scales from the 
 surface of a vascular pulp ; but in the Fire Flaire (Trygon pasti- 
 naca), where, instead of the scattered hooks of the former species, 
 we find a single sharp and serrated spine projecting like a bayonet 
 from the upper surface of the root of the tail, the analogy between 
 this formidable and bone-like organ and an epidermic structure 
 becomes apparently more remote, and, did we not know that the 
 fish possessing such a weapon had no ossified bones internally, we 
 might be tempted to regard this appendage as a process derived 
 from the endoskeleton. 
 
508 PISCES FISHES. 
 
 The spines of the common Stickleback (Gasterosteus) are indu- 
 bitable derivations from the cuticle ; but here they become fixed by 
 moveable articulations to the sides of the body, and are raised 
 or depressed by means of muscles inserted into their bases. Ad- 
 vancing one step further, we find in Silurus the first ray of the 
 pectoral fin, enormously developed and forming a strong serrated 
 weapon of a very formidable description, which, although both in 
 shape and structure exactly comparable to the spine upon the tail of 
 the Fire Flaire, are nevertheless connected by most beautiful and 
 perfect joints with the bones of the shoulder, so that they might 
 easily be regarded as forming pieces of the endoskeleton, did not 
 their peculiar structure indicate their real nature. 
 
 We thus arrive at the important conclusion, that different por- 
 tions of the exoskeleton become approximated in character to those 
 of the endoskeleton, or in truth really convertible into true bone ; 
 and, with this fact before us, it becomes easy to understand the 
 nature of various parts of the skeleton of a fish, which upon any 
 other supposition would be not a little puzzling to the comparative 
 osteologist. 
 
 The nature of the rays of the dorsal and anal fin of the Perch, 
 for example, together with the interspinous bones upon which they 
 are sustained, is quite unintelligible if they are regarded as belong- 
 ing to the endoskeleton ; and no dismemberments of the osseous 
 system as yet imagined, or supposed subdivisions of the vertebrae 
 into a greater number of elemental pieces than we have enume- 
 rated, has been able to solve the difficulty; but, if they are regarded 
 as ossified derivations from the exoskeleton^ all difficulties at once 
 vanish. 
 
 Again, the opercular bones (28, 30, 32, 33) forming the gill- 
 covers of an osseous fish have been a fruitful source of discus- 
 sion, and M. Geoffroy St. Hilaire* was reduced to the necessity 
 of recognizing in these broad plates the ossicles of the human ear, 
 which, after dwindling to a rudiment in the descending scale of ver- 
 tebrate animals, suddenly reappeared in a new and exaggerated 
 form. " J'ai peu vu dans la srie des etres de ces resurrections 
 d'organes se remontrant subitement dans une classe apr&s avoir dis- 
 paru dans une ou deux de celles qui la precede dans Techelle," 
 are the impressive words of Cuvier upon a similar occasion ; and 
 it is certainly far more simple to imagine the epidermic plates 
 
 * Philosophie Anatomique des pieces osseuses des organes respiratoires. 8vo. Paris, 
 1818. 
 
PISCES FISHES. 509 
 
 of the Sturgeon ossified and converted into bone, than to be com- 
 pelled to have recourse to the bold speculations of the French 
 anatomist regarding the real nature of these opercular portions of 
 a fish's skeleton.* 
 
 (543.) In connection with the locomotive organs we must 
 here notice one of the most elegant contrivances met with in the 
 whole range of animated nature, by which the generality of fishes 
 are enabled to ascend towards the surface, or to sink to any re- 
 quired depth without exertion. 
 
 The apparatus given for this purpose is called the swimming- 
 bladder, and consists of a reservoir of air (Jig. 227, p) placed 
 beneath the spine; in which position it is firmly bound down by 
 the peritoneum. The outer coat of this bladder is very strong, and 
 composed of a peculiar fibrous substance from which isinglass is 
 obtained, but it is lined internally with a thin and delicate mem- 
 brane. The shape of the swimming-bladder varies considerably in 
 different tribes. In the Perch it is a simple cylinder closed at both 
 extremities : sometimes it gives off branched appendages ; some- 
 times, as in the Cyprinid&i it is divided into two portions, one 
 anterior and the other posterior, by a deep central constriction ; 
 but, whatever its shape, its office is the same, namely, to alter the 
 specific gravity of the fish, and thus to cause it to rise or sink in 
 the medium it inhabits. By simply compressing this bladder by 
 approximating the walls of the abdomen, or occasionally by means 
 of a muscular apparatus provided for the purpose, upon a principle 
 with which every one is familiar, the fish sinks in proportion to the 
 degree of pressure to which the contained air is subjected ; and, 
 
 * The different opinions on the nature or homology of the opercular bones may be 
 reduced to two principles : first, that they are modifications of parts of the ordinary 
 skeleton ; secondly, that they are superadded bones peculiar to fishes : the latter view 
 is that taken by Cuvier. According to the former, which is the more philosophical mode 
 of considering them, three opinions have been offered ; the first by Spix and Geoffrey, 
 that they are gigantic representatives of the ossicles of the ear, otherwise absent in the 
 skeleton of fishes, this view has been adopted by Professor Grant ; secondly, that they 
 are dismemberments of the lower jaw, which by the detachment of the opercular bones 
 from the ramus is rendered more simple in its composition than in reptiles, a view 
 proposed by M. de Blainville and temporarily adopted by Bojanus and Oken, but refuted 
 by the complicated structure of the lower jaw in certain sauroid fishes, as the Lepi- 
 dosteus, which likewise possesses the opercular bones; thirdly, that they are parts of 
 the dermal skeleton, in short, scales modified in subserviency to the breathing func- 
 tion ; an opinion first proposed by Professor Owen, in his Lectures on Comparative 
 Anatomy at St. Bartholomew's Hospital in 1835, and which is the view here adopted. 
 
510 PISCES FISHES. 
 
 as the compressed air is again permitted to expand, the creature 
 becoming more buoyant rises towards the surface. 
 
 In the Perch, and many other fishes, this organ is entirely 
 closed, so that there is no escape for the contained air; and in such 
 it has been found that if they are suddenly brought up by means 
 of a line from any great depth, the gas being no longer compressed 
 by the weight of the column of water above, and having no exit, 
 bursts the swimming-bladder, and sometimes distends the abdomen 
 to such an extent, that it pushes the stomach and oesophagus into 
 the fish's mouth. 
 
 In other cases, however, a provision is made apparently with a 
 view of obviating such an accident, and a kind of safety-valve pro- 
 vided, through which the air may be permitted to escape : thus, in 
 the Carps a tube communicates between the interior of the air- 
 bladder and the oesophagus, and in the Herring a similar commu- 
 nication is met with between this organ and the stomach. 
 
 The gas which fills the air-bladder has been found in many 
 cases to be nearly pure nitrogen, but in fishes that live at a great 
 depth Messrs. Configliacchi * and Biot ascertained that oxygen 
 was substituted, whence it has been presumed that this apparatus 
 was in some way or other an auxiliary in respiration ; and some 
 authors have even gone so far as to see in the swimming-bladder 
 the representative of the lungs of aerial Vertebrata. But, however 
 this may be, the gas enclosed is indubitably a product of secretion, 
 being derived either from the lining membrane of the viscus, or 
 from a glandular structure which may frequently be distinctly 
 pointed out in its interior. 
 
 Cuvier justly observes, that, whatever opinions may be enter- 
 tained relative to the use of the air-bladder, it is difficult to 
 explain how so considerable an organ has been refused to so many 
 fishes, not only to those which ordinarily remain quiet at the bot- 
 tom of the water, as Skates and Flat-fishes, but to many others 
 that apparently yield to none either in the rapidity or facility of 
 their movements, such as the Mackerel, for instance ; yet even 
 while the common Mackerel (Scomber scomber) has no air-blad- 
 der, a very nearly allied species (Scomber pneumatophorus) is 
 provided with one, and of this many other instances might be 
 adduced. 
 
 (544.) From the circumstances under which fishes seize and 
 swallow their prey, it must be evident that they are incapable of 
 
 * Suir analisi dell' aria contenuta nella vesica natatoria del Pesci. Pavia, 1809. 4to. 
 
PISCES FISHES. 511 
 
 enjoying any very refined sense of taste. Those species which are 
 carnivorous are of necessity compelled to catch with their mouths, 
 and retain a firm hold of the active and slippery food they are 
 destined to devour : to divide or masticate their aliment would be 
 impracticable ; and, even were they permitted so to do, the water 
 which perpetually washes over the interior of their mouths would 
 obviously preclude the possibility of appreciating savours. In the 
 construction of the mouth of a fish we therefore find, generally 
 speaking, that every part has been made subservient to prehen- 
 sion : teeth, sometimes in the form of delicate spines, or else pre- 
 senting the appearance of sharp recurved hooks, have been fixed 
 in every possible situation where they could be made available as 
 prehensile organs ; not only are the jaws densely studded with these 
 penetrating points, but they are occasionally placed on every bone 
 which surrounds the oral cavity, or supports the entrance of the 
 pharynx. The intermaxillary, the maxillary, and the palatine 
 bones, the vomer, the branchial arches, the pharyngeal bones, and 
 even the tongue itself, may all support a dental apparatus, either of 
 the same description or composed of teeth of different shapes ; 
 generally, however, some of these bones are unarmed, and occa- 
 sionally teeth of any kind are altogether wanting. 
 
 But if such is the most usual arrangement of the dental appa- 
 ratus in fishes, we must be prepared to find, in a class so extensive 
 as that we are now investigating, various modifications both in the 
 form and arrangement of the teeth, adapting them to the diverse 
 habits and necessities of individual species ; and a few of these we 
 must not omit to notice in this place. 
 
 The Myxine, or Hag-fish, one of the lowest of the entire class, 
 possesses no osseous framework whereunto teeth could be attached ; 
 and yet, from the parasitical life which this creature leads, it has 
 need of dental organs of considerable efficiency. The Myxine, 
 feeble and helpless as the casual observer might suppose it, is in 
 reality one of the most formidable assailants with which the larger 
 fishes have to contend, since neither strength nor activity avail 
 aught in defending them against a foe apparently so despicable : 
 fixing its mouth firmly to the skin of its comparatively gigantic 
 victim, the Myxine bores its way into its flesh by means of a dental 
 apparatus of a very extraordinary description. A single fang-like 
 tooth is fixed to the median line of the palate, and the tongue is 
 armed on each side with two horny plates deeply serrated : thus 
 provided, the Myxine, when it attacks its prey, plunges its palatine 
 
512 PISCES FISHES. 
 
 hook into its flesh ; and, thus securing a firm hold, the lingual 
 saws, aided by the suctorial action of the mouth, tear their way to 
 its very vitals.* 
 
 In the Lamprey the whole interior of the mouth is studded 
 with horny teeth, not merely fixed to the palate and tongue, but to 
 the cartilaginous representative of the inferior maxilla, and to the 
 inner surface of the lips. 
 
 In the Carp tribe (Cyprinidte) the jaws are destitute of teeth, 
 but in the throat there is a singular apparatus serving for the masti- 
 cation of their food. The basilar bone at the base of the skull sup- 
 ports a broad three-sided dental plate, which might be compared to an 
 anvil ; while the two inferior pharyngeal bones are each armed with 
 four or five large teeth, so disposed, that, by working upon the 
 piece first-mentioned, they bruise and triturate the aliment before 
 it is permitted to pass into the digestive cavity. 
 
 In Skates (Raidte) the internal surface both of the upper and 
 lower jaws are so covered with teeth, that they have the appearance 
 of a tesselated pavement : these teeth are sometimes flat and 
 smooth, so as to be merely useful in crushing prey ; but in many 
 species they are prolonged into sharp hooks adapted to prehension. 
 
 In the Sharks a beautiful provision is met with. Several rows 
 of teeth placed one behind the other are found laid flat, and con- 
 cealed behind the jaw. One row only, composed of triangular cut- 
 ting teeth, stands erect and ready for use ; but when these fall off, 
 blunted and unfit for service, the next row rises to take their place ; 
 and thus a succession of efficient weapons are given to these terrific 
 monsters of the ocean. 
 
 We will not enlarge further upon this portion of our subject ; 
 enough has been said for our present purpose, and the reader will 
 find elsewhere abundant information. -f- 
 
 The teeth of osseous fishes are generally firmly anchylosed to 
 the bones ^that support them, although in a few instances they 
 are found fixed in sockets, as in the rostral teeth of the Saw-fish 
 (Pristis), and in the mouth of Sphyrfena, Acanthurus, Dicty- 
 odus, &c4 But there are other modes of attachment only met 
 with among fishes, some of which are not a little curious ; and 
 
 X 
 
 * Professor Owen. " ODONTOGRAPHY, or a Treatise on the Comparative Anatomy 
 of the Teeth, their physiological relations, mode of developement, and microscopic 
 structure," &c. 4to. Bailliere, 1840. 
 
 f Vide Yarrell's British Fishes. 8vo. 2 vols. J Owen. Odontography, p. 6. 
 
PISCES FISHES. 513 
 
 Professor Owen, in his truly splendid work above referred to, 
 thus describes the most important. 
 
 " In the Cod-fish, Wolf-fish, and some other species, in propor- 
 tion as the ossification of the tooth advances towards its base and 
 along the connecting ligamentous substance, the subjacent portion 
 of the jaw-bone receives a stimulus, and developes a process cor- 
 responding in size and form with the solidified base of the tooth. 
 In this case the inequalities of the opposed surfaces of the tooth 
 and maxillary dental process fit into each other, and for some time 
 they are firmly attached together by a thin layer of ligamentous 
 substance ; but in general anchylosis takes place to a greater or less 
 extent before the tooth is shed. The small anterior teeth of the 
 Angler (Lophtus) are thus attached to the jaw, but the large pos- 
 terior ones remain always moveably connected by highly elastic, 
 glistening ligaments, which pass from the inner side of the base of 
 the tooth to the jaw-bone. These ligaments do not permit the 
 tooth to be bent outwards beyond the vertical position, when the 
 hollow base of the tooth rests upon a circular ridge growing from 
 the alveolar margin of the jaw ; but the ligaments yield to pressure 
 upon the tooth in the contrary direction, and its point may thus 
 be directed towards the back of the mouth ; the instant, however, 
 that the pressure is remitted, the tooth flies back, as by the action 
 of a spring, into its usual erect position ; the deglutition of the 
 prey of this voracious fish is thus facilitated, and its escape pre- 
 vented. ' 
 
 " The broad and generally bifurcate osseous base of the teeth of 
 Sharks is attached by ligaments to the ossified or semi-ossified 
 crust of the cartilaginous jaws. The teeth of the Salarias and 
 certain Mugiloids are simply attached to the gum. The small 
 and closely crowded teeth of the Rays are also connected by 
 ligaments to the subjacent maxillary membrane. The broad tesse- 
 lated teeth of the Eagle-Rays have their attached surface longi- 
 tudinally grooved to afford them better holdfast, and the sides of 
 the contiguous teeth are articulated together by true serrated or 
 finely undulating sutures; which mode of fixation of the dental 
 apparatus is unique in the animal kingdom. 
 
 " If the engineer would study the model of a dome of unusual 
 strength, and so supported as to relieve from its pressure the floor 
 of a vaulted chamber beneath, let him make a longitudinal section 
 of one of the pharyngeal teeth of a Wrasse (Labrus). The base 
 of this tooth is slightly contracted, and is implanted in a shallow 
 
514 PISCES FISHES. 
 
 circular cavity, the rounded margin of which is adapted to a circular 
 groove in the contracted part of the base ; the margin of the tooth 
 which immediately transmits the pressure to the bone is strength- 
 ened by an inwardly projecting convex ridge. The masonry of 
 this internal buttress, and of the dome itself, is composed of hollow 
 columns, every one of which is placed so as to transmit in the 
 due direction the superincumbent pressure. 
 
 " In another case, in which long and powerful piercing and 
 lacerating teeth were evidently destined, from the strength of the 
 jaws, to master the death-struggles of a resisting prey, we find the 
 broad base of the tooth divided into a number of long and slender 
 processes, which are implanted like piles in the coarse osseous 
 substance of the jaw ; they diverge as they descend, and their 
 extremities bend and subdivide like the roots of a tree, and are 
 ultimately lost in the bony tissue. This mode of implantation, 
 which I have detected in a large extinct Sauroid fish (Rhizodus), 
 is, perhaps, the most complicated which has yet been observed in 
 the animal kingdom." 
 
 For a full account of the growth and developement of the teeth 
 of fishes, we must refer the reader to the same source from which 
 we have extracted the preceding paragraphs ; nevertheless, the 
 following is a brief abstract of Professor Owen's views upon this 
 subject. 
 
 In all fishes the first step in the formation of a tooth is the 
 production of a simple papilla from the surface either of the soft 
 external integument, as in the formation of the rostral teeth of the 
 Saw-fish (Pristis), or of the mucous membrane of the mouth, as in 
 the rest of the class. In these primitive papillae there can be very 
 early distinguished a cavity containing fluid, and a dense membrane 
 (membrana propria) surrounding the cavity, and itself covered by 
 the thin buccal mucous membrane, which gradually becomes more 
 and more attenuated as the papilla increases in size. The pulp- 
 substance, or contents of the membrana propria, remains for some 
 period in a fluid or semi-fluid condition ; granules are ultimately 
 developed in it, which at first float loosely, or in small aggregated 
 groups, in the sanguineo-serous contents of the pulp. These gra- 
 nules soon attach themselves to the inner surface of the membrana 
 propria^ if they be not originally developed from that surface. 
 The whole of the contents of the growing pulp becomes soon after 
 condensed by the numerous additional granules, which are rapidly 
 developed in it after it has become permeated by the capillary 
 
PISCES FISHES. 515 
 
 vessels and nerves. The particles become arranged into linear 
 series or fibres ; an appearance which is first apparent at the super- 
 ficies of the pulp, to which the fibres are vertical. At this period 
 ossification commences in the dense and smooth membrana propria 
 of the pulp, and is thence continued centripetally in the course of 
 the above-mentioned lines towards the base of the pulp. Lastly, 
 around the capillaries of the pulp the granules become condensed 
 into concentric layers, which then form the walls of minute tubes, 
 visible on a microscopic examination of the substance of the tooth. 
 
 In some genera, as Balistes and CAryaopry*, an enamel-pulp is 
 developed from the inner surface of the capsule which surrounds 
 the bone-pulp, and by this organ the surface of the teeth of such 
 fishes is coated with enamel in a manner to be described more at 
 large hereafter. 
 
 In most osseous fishes, in addition to the lips, which even when 
 fleshy, being destitute of proper muscles, would be unable to retain 
 food in the mouth, 'there is generally behind the front teeth in 
 each jaw a valve formed by a fold of the lining membrane of the 
 mouth, and directed backwards so as efficiently to prevent the 
 alimerjt, and more especially the water swallowed for the purpose 
 of respiration, to escape again from the oral orifice.* 
 
 (545.) Fishes have no salivary glands, as saliva to them would 
 be entirely useless : their esophagus (Jig. 227, g ; Jig- 236, d) is 
 capacious ; and, from the circumstance of their having neither neck 
 nor thorax, extremely short, so that the food when seized is con- 
 veyed at once into the stomach. 
 
 (546.) The stomach itself is generally a wide cul-de-sac 
 (fig- 227, A), the shape and proportionate size of which varies 
 of course in different species. Its walls are most frequently thin, 
 and the lining membrane gathered into large longitudinal folds 
 (Jig. 286, e), so as to admit of considerable distension ; but occa- 
 sionally, as for example in the Mullets, its muscular walls are 
 so thick that it might almost deserve the name of gizzard, and 
 in such fishes its power of crushing the food is no doubt consi- 
 derable. 
 
 (547.) The intestinal canal in the osseous fishes is a simple tube 
 (Jig. 227, ) folded in sundry gyrations proportioned to its length ; 
 but in the cartilaginous families, such as the Sharks, the Rays, and 
 the Sturgeons, it presents internally a very remarkable arrange- 
 ment, evidently intended to increase the extent of surface over 
 
 * Cuv. et Valenciennes, op. cit. p. 367. 
 
516 
 
 PISCES FISHES. 
 
 winch the digested aliment may be spread, for the purpose of 
 absorbing its nutritive portions. In these tribes a spiral valve 
 (Jig' 236, A) winds in close turns from the pyloric to the anal 
 extremity of the capacious intestine ; so that, although externally 
 the intestine appears short in proportion to the size of the animal, 
 its mucous lining is exceedingly extensive. 
 
 Fis- 227. 
 
 (548.) In addition to the biliary secretion which we have met 
 with in the lower animals, another system of chylopoietic glands for 
 the first time makes its appearance in the class before us, from which 
 a fluid termed the pancreatic is poured into the intestine. In the 
 osseous fishes this viscus presents the simplest condition of a gland, 
 consisting of simple caeca (fig. 227, n, n) ; sometimes, as in the 
 Perch, only three in number ; at others, as for instance in the 
 Salmonida, extremely numerous. From these appendages a glairy 
 fluid, resembling saliva in composition, is abundantly secreted, 
 and becomes mixed with the bile immediately upon its entrance 
 into the intestine. 
 
 In the cartilaginous fishes, such as Sharks and Rays, the pan- 
 creas exhibits a more perfect developement, and already presents 
 the appearance of a conglomerate gland (fig. 236, /), from which 
 the pancreatic fluid is conveyed into the intestine through a com- 
 mon duct. 
 
PISCES FISHES. 517 
 
 (549.) The liver of fishes is proportionately very large, and 
 generally contains abundance of oil. The bile derived from it is 
 received into a gall-bladder (Jig. 227, c), from which a duct of 
 variable length in different species conveys it into the intestine, in 
 the immediate vicinity of the pylorus. 
 
 (550.) It is in these animals that we for the first time find the 
 biliary secretion separated from venous blood; and consequently 
 they are provided with a new arrangement of the blood-vessels of the 
 abdomen, which they possess in common with the other Vertebrata, 
 forming what is termed by anatomists the system of the Vena 
 Porta. The veins derived from the stomach, the intestines, and 
 the spleen, which last viscus now makes its appearance, instead of 
 conveying their contents to the heart, plunge into the substance of 
 the liver, and there again subdivide into capillary tubes ; thus fur- 
 nishing to the liver abundance of venous blood from which the 
 hepatic secretion is elaborated. 
 
 (551.) The Spleen, now for the first time met with in the 
 animal creation, is a highly vascular organ, generally enclosed in 
 the mesentery between two folds of the intestine (Jig. 227, m ; Jig. 
 236, x), and evidently, in position, presenting no precise relations 
 with the stomach. It receives a large supply of arterial blood, 
 which becomes converted into venous as it circulates through this 
 organ, and in that state is transmitted to the liver through the 
 portal system of veins. 
 
 (552.) Another important addition to the animal economy, pe- 
 culiar to the Vertebrate division of animals, is the lymphatic or ab- 
 sorbent system of vessels, which in fishes are abundantly distributed 
 through the body, and ramify like a rich net- work over the walls of 
 the intestines. These pour the materials absorbed from the body, 
 and the products of digestion, into the principal venous trunks, to 
 be mixed up with the circulating blood.* 
 
 (558.) The circulation of the blood in fishes is carried on by 
 the assistance of a heart composed of two cavities only, which re- 
 ceives the vitiated blood after it has circulated through the system, 
 and propels it through the branchise, where it is exposed to the 
 influence of the oxygen contained in the surrounding medium. 
 After being thus purified, the blood is collected from the respiratory 
 organs by the radicles of the branchial veins ; and these latter ves- 
 
 * For a detailed account of the lymphatic system of fishes the reader is referred to 
 the following authors Monro, Anat. and Physiol. of Fishes, fol. ; Hewson, Phil. 
 Trans. 1769 ; Fohman, Hist. Generate des Lymphatiques des Verteb. ; Heidelberg and 
 Leipzig, fol. 1827. 
 
518 PISCES FISHES. 
 
 sels, by their union, form the aorta. There is, therefore, no sys- 
 temic heart in fishes, the aorta itself serving to propel the slow- 
 moving blood in its course through the arterial system. 
 
 Fig. 228. 
 
 (554.) The heart (Jig. 227, o) is enclosed in a pericardium, and 
 situated beneath the pharyngeal bones and branchial apparatus ; 
 the cavity in which it is lodged being separated from the peri- 
 toneum by a kind of tendinous diaphragm, and also by a capacious 
 sinus, in which the venous blood derived from all parts of the 
 body is collected preparatory to its admission into the heart. 
 
 The auricle of the heart (Jig. 228, B, b) is contained within 
 the pericardium : it varies greatly in form in different fishes, but 
 its capacity is generally considerably greater than that of the ven- 
 tricle ; and its walls are thin, but, nevertheless, present distinct 
 fleshy columns. 
 
 The blood derived from the great sinus before mentioned enters 
 the posterior part of the auricle of the heart by a large orifice, 
 which is guarded by two membranous valves so disposed as to pre- 
 vent the reflux of the blood during the contraction of the auricular 
 chamber. The ventricle is strong and fleshy, and at its communi- 
 cation with the auricle there is a strong mitral valve. The com- 
 mencement of the branchial artery (Jig. 228, A, d), is so muscular 
 and capacious, that it might almost be considered as forming a 
 second ventricular chamber : this portion, which has been distin- 
 guished by the name of the bulb (bulbus arteriosus), is separated 
 from the ventricle by strong valves ; and in the cartilaginous fishes, 
 as, for instance, in the Shark (Jig. 228, B, e), there are several 
 rows of semilunar valves so disposed as most efficiently to prevent 
 
PISCES FISHES. 519 
 
 the blood from being driven back again into the ventricle. In the 
 heart of Lophius (Jig. 228, A), the conformation of the cavities is 
 very peculiar. The auricle (b) is large and pyriform, and the ven- 
 tricle (c) of a globular shape ; but the most singular feature in its 
 structure is the valve between the ventricle and the bulb (d). This 
 is a soft fleshy protuberance (e), perforated in the centre, which 
 projects into the cavity of the bulb, and allows the blood to pass 
 freely in one direction ; but the sides of the canal collapse, and 
 close the orifice, if the blood is forced back from the bulb towards 
 the ventricle. 
 
 Issuing from the pericardium, the branchial artery runs beneath 
 the centre of the branchial apparatus, dividing into as many 
 trunks as there are branchial arches, to each of which a vessel is 
 given off. 
 
 To each branchial arch are attached a great number of vascular 
 lamellae placed parallel to each other, like the teeth of a comb. 
 The branchial artery, which runs in a groove situated upon the con- 
 vexity of the corresponding arch, sends off a twig to every one of 
 these laminae ; and this vessel, after twice bifurcating, divides into 
 an infinite number of little ramuscules, which run across both sur? 
 faces of the branchial fringe, and terminate by becoming converted 
 into capillary veins. 
 
 The radicles of the branchial veins all open into a venous canal 
 which runs along the internal margin of each lamella, and these last 
 terminate in the great vein of the corresponding branchial arch, 
 which runs in the same groove as the artery, but is more deeply 
 situated, and, moreover, runs in the opposite direction ; that is to 
 say, that the branchial artery derived from the heart, and coming 
 from the ventral aspect of the body, diminishes in size as it mounts 
 towards the back, and gives off twigs to the branchial fringe, 
 whereas the branchial vein, on the contrary, receiving blood from 
 the lamellae of the branchia, increases in diameter as it approaches 
 the dorsal region. 
 
 On leaving the gills, the branchial veins assume the appearance 
 and perform the function of arteries. The anterior, even before 
 escaping from the branchial arch, gives off ramifications to different 
 parts of the head, and the heart and parts adjacent likewise receive 
 their supply of arterial blood from a branchial vein. 
 
 The veins derived from all the branchial arches ultimately unite 
 and form the aorta, which evidently corresponds to the aorta of 
 Mammalia, although it has neither auricle nor ventricle at its com- 
 mencement. 
 
520 
 
 PISCES FISHES. 
 
 The aorta, while in the abdomen, runs beneath the spine, and 
 gives arteries to the viscera in the usual manner ; but at the com- 
 mencement of the tail it becomes enclosed in the inferior vertebral 
 arches, by which it is defended to its termination. 
 
 (555.) There is yet another set of organs, which, as we ascend 
 from inferior to higher forms of animal life, we encounter for the 
 first time in the class before us ; an apparatus for elaborating the 
 urinary secretion, which is peculiar to the Vertebrate classes. 
 
 The kidneys in fishes are very voluminous : they are situated on 
 each side of the mesial line, immediately beneath the bodies of the 
 vertebrae ; and extend along the whole length of the abdomen, not 
 unfrequently reaching to the base of the skull, where their anterior 
 portion (Jig. 27, e) lies above the branchial apparatus. The ure- 
 ters (Jig. 27, f) generally terminate in a kind of bladder-like di- 
 latation, the orifice of which is found behind that of the vulva (s). 
 
 Examined minutely, the substance of the kidney is found to be 
 entirely composed of microscopic tubules, which terminate in the 
 ureters : these uriniferous tubes are variously contorted, but of 
 equable diameter throughout ; and they end towards the periphery 
 of the kidney by blind extremities. 
 
 (556.) The skin of these aquatic animals is perpetually lubri- 
 cated by an abundant mucous secretion furnished by muciparous 
 follicles, or secreted in long tubular organs placed beneath the 
 skin. In the Skate the vessels last mentioned are remarkably large, 
 and their distribution very extensive. 
 
 Fig. 229. 
 
PISCES FISHES. 
 
 521 
 
 (557.) The brain of an adult fish occupies but a small portion of 
 the cranial cavity ; the space between the pia mater , which invests 
 the brain, and the dura mater, which lines the skull, being occu- 
 pied by a loose cellular tissue filled with fluid : there is consequently 
 no serous or arachnoid cavity, such as exists in man. It has been 
 remarked, that the interval between the cranium and the brain is 
 considerably less in young than in mature fishes ; a fact which 
 sufficiently proves that in them the brain does not grow in the 
 same proportion as the rest of the body ; and, indeed, the size of 
 the brain is nearly equal in individuals of the same species, even 
 although the body of one be twice as large as that of the other.* 
 
 In these, the lowest forms of Vertebrata, the brain consists of 
 several masses placed one behind the other, either in pairs or singly; 
 these masses in fact may be regarded as so many distinct ganglia, the 
 complexity and perfection of which we must expect to become gra- 
 dually increased as we proceed upwards towards mammiferous 
 quadrupeds. 
 
 The anterior pair of ganglia (figs. 229 and 234, c ; Jig. 232, a) 
 invariably give origin to the olfactory nerves, and consequently may 
 be justly looked upon as presiding over the sense of smell. These 
 ganglia are, in fact, the representatives of those masses which in man 
 are erroneously called the " olfactory nerves ;" for even in the 
 human subject, although their real nature is obscured by the enor- 
 mous developement of other parts of the encephalon, the so-called 
 nerves are not nerves at all, but really lobes of the brain from which 
 the true nerves emanate. Fig. 230. 
 
 (558.) The olfactory nerves of 
 fishes, derived from the lobes al- 
 luded to, vary greatly in composi- 
 tion and proportionate size : some- 
 times they are quite capillary ; 
 sometimes thick, though still sim- 
 ple ; occasionally they are double 
 or triple, and in some cases 
 are composed of numerous fibres 
 bound up in fasciculi. 
 
 (559.) The organs of smell to 
 which these nerves are destined are 
 of very simple structure : Two 
 excavations are found near the an- 
 terior part of the snout, lined with 
 
 * Cuv. et Val. op. cit. 
 
522 PISCES FISHES. 
 
 a delicate pituitary membrane, which is variously folded, in order 
 to increase the extent of the sentient surface (Jig- 230) ; and it 
 may be presumed, that from the number of plicse, which varies 
 amazingly, some estimate may be formed of the relative perfection 
 of the sense of smell in different genera. Into each olfactory 
 chamber the water is freely admitted by two distinct orifices, while 
 behind the pituitary membrane the olfactory nerve swells out into 
 a ganglion (Jig. 232, 1), from which nervous fibrils radiate, to be 
 distributed over the plicated lining of the nose (). 
 
 (560.) The second pair of ganglia met with in the brain of a 
 fish (Jig. 232, b) give origin to the optic nerves (2), and may 
 therefore very properly be regarded as representing the tubercula 
 quadrigemina of the mammiferous brain. The nerves of vision 
 derived therefrom have no commissure, and present in many species 
 a peculiar structure which is not a little remarkable ; each nerve 
 being composed of a broad band of nervous substance, folded up 
 like a fan, and enclosed in a dense membrane, so that when un- 
 folded it presents the appearance delineated at fig. 231, A. 
 
 (561.) The eye itself differs in many points of structure from 
 that of terrestrial Vertebrata, its organization being of course ad- 
 apted to bring the rays of light to a focus upon the retina in the 
 denser element in which the fish resides ; the power of the crystal- 
 line lens is therefore increased to the utmost extent, and the 
 antero-posterior diameter of the eye-ball necessarily contracted in 
 the same ratio, in order that the retina may be placed exactly in 
 the extremely short focus of the powerful lens. 
 
 The eyes of all the Vertebrata are constructed upon principles 
 essentially similar, and present the same tunics and lenses as are 
 met with in the human eye, and, generally speaking, arranged in 
 the same manner as in man. It is not our intention, therefore, in 
 the following pages minutely to describe the anatomy of the eye in 
 every class which will come under our notice ; but taking the human 
 eye, with the construction of which we presume our readers to be 
 intimately acquainted, as a standard of comparison, point out those 
 modifications of the general type of structure common to this divi- 
 sion of animated nature. 
 
 The first thing which strikes the attention of the anatomist, 
 when examining the eye of a fish, is the size of the crystalline lens, 
 and its spherical form. This shape, and the extreme density of 
 texture which the lens exhibits, are, indeed, perfectly indispens- 
 able. The aqueous humour, being nearly of the same density 
 
PISCES FISHES. 
 
 523 
 
 as the external element, would have no power in deflecting the 
 rays of light towards a focus, and consequently the aqueous 
 fluid in fishes is barely sufficient in quantity to allow the free sus- 
 pension of the iris : the vitreous humour, from the same reason, 
 would be scarcely more efficient than the aqueous in changing the 
 course of rays entering the eye, and hence the necessity for that 
 extraordinary magnifying power conferred upon the lens. 
 B Fig. 231. C 
 
 But the focus of the crystalline will be short in proportion as its 
 power is increased ; every arrangement has therefore been made 
 to approximate the retina to the posterior surface of the lens : 
 the eye-ball is flattened, by diminishing the relative quantity of 
 the vitreous humour ; and a section of the eye (Jig. 231 , B, c) 
 shows that its shape is very far from that of a perfect sphere. This 
 flattened form could not, however, have been maintained in fishes, 
 had not special provision been made for the purpose in the con- 
 struction of the sclerotic ; the outer tunic of the eye, therefore, 
 generally contains two cartilaginous plates imbedded in its tissue, 
 which are sufficiently firm in their texture to prevent any alteration 
 in the shape of the eye-ball ; and in some of the large fishes the 
 sclerotic is actually converted into a cup of bone presenting orifices 
 at the opposed extremities, one for the insertion of the trans- 
 parent cornea, the other for the admission of the optic nerve. 
 
 The vitreous humour and crystalline lens in many fishes are 
 kept in situ by a ligament placed for the purpose. This is a deli- 
 cate falciform membrane derived from the retina (Jig- 331, B, c), 
 which plunges into the vitreous humour, and, being continued along 
 
524 PISCES FISHES. 
 
 the internal concavity of tlie eye, is fixed to the capsule of the 
 lens. In some fishes, as the Salmon, this ligament is of a dark 
 colour ; and in the Conger, there are two such bands, by which the 
 crystalline is suspended as by its opposite poles. 
 
 Another peculiarity in the structure of the visual apparatus of 
 osseous fishes is the existence of a vascular organ placed at the 
 back of the eye-ball, and interposed between the choroid tunic and 
 a brilliant metallic-coloured membrane which invests the choroid 
 externally. This organ, generally called the " choroid gland " by 
 the older anatomists (Jig* 231, A,g, g), is of a crescentic form, and 
 always of a deep red colour. It is principally made up of blood- 
 vessels, which run parallel to each other ; and from it issue other 
 vessels, frequently very tortuous, and always much ramified, which 
 form a vascular net-work in the choroid. The nature of this organ 
 it is not very easy to determine. Some have believed it muscular ; 
 but the strise perceptible in it are vascular, and not fibrous : others 
 have thought it to be glandular, but it has no excretory duct. 
 Most probably it is an erectile tissue analogous to that of the 
 corpus cavernosum, and has some influence in accommodating 
 the form of the eye to distances, or to the density of the surround- 
 ing medium.* 
 
 The pupil of the eye in the animals we are describing is very 
 large, so as to take in as much light as possible ; but generally 
 motionless. In some genera the shape of the aperture is curious : 
 thus in the Rays a broad palmate veil hangs in front of the pupillary 
 aperture ; and in one case, the Anableps, there are two pupils to 
 each eye. 
 
 (562.) The eyes of osseous fishes are lodged in the bony orbits 
 of the face, imbedded in a soft glairy cellulosity ; but in many of 
 the cartilaginous tribes, such as the Sharks and Rays, each eye-ball 
 is moveably articulated to the extremity of a cartilaginous pedicle 
 fixed to the bottom of the orbital cavity (Jigs. 232, t, and 231, c). 
 
 (563.) Six muscles serve to turn the eye in different directions : 
 namely, four recti, arising, as in man, from the margin of the optic 
 foramen ; and two oblique muscles, derived from the anterior part of 
 the orbit, and inserted transversely into the globe. These muscles 
 are well represented in Jig.%3l 9 wherein the reader will observe 
 that the superior oblique (g) does not pass through a pulley, as is 
 the case in the human subject. 
 
 (564.) It is extremely remarkable, that even in fishes the muscles 
 
 * Cuv. et Val. op. cit. p. 338. 
 
PISCES FISHES. 
 
 525 
 
 of the eye have special nerves appropriated to them, and those pre- 
 cisely the same as in the highest Mammalia. The third pair of 
 
 Fig. 232. 
 
 nerves animates them all, except the external rectus and the superior 
 oblique ; and also sends off filaments to be distributed to the cho- 
 roid, although no ophthalmic ganglion has yet been discovered. 
 The fourth pair is exclusively appropriated to the superior oblique ; 
 and the external rectus, or abductor muscle, invariably receives its 
 supply from the sixth pair. 
 
 (565.) To animals whose eyes are constantly washed by the 
 water in which they live any lachrymal apparatus would obviously 
 be superfluous ; and consequently, in the class before us, neither 
 lachrymal gland, nor lachrymal puncta, nor even eyelids properly so 
 called, are ever met with. 
 
 (566.) Behind the optic lobes of a fish's brain the ganglia from 
 which the other cerebral nerves emanate become confused into one 
 mass, so that they are no longer distinguishable from each other. 
 The nerves themselves, however, are easily recognised, and, with 
 the exception of the ninth pair (the lingual or hi/poglossal nerves), 
 which are not met with in fishes, both in their distribution and 
 
526 PISCES FJSHES. 
 
 number precisely accord with those with which the human ana- 
 tomist is familiar. We have already traced the third, fourth, 
 and sixth pairs to the muscles of the eye. The fifth issues through 
 the great ala of the sphenoid, and divides, as in man, into an oph- 
 thalmic branch (fig. 229, a), which runs through the orbit to be 
 distributed to the parts about the nose ; a superior maxillary 
 branch (|3), that supplies the parts about the upper jaw ; and an 
 inferior maxillary branch (^), destined to the lower jaw : the ge- 
 neral distribution of the nerve, as far as regards the face, is in fact 
 exactly similar to that of the same nerve in man ; but in fishes it is 
 found to give off other branches not met with in the human subject, 
 one of which (p) is destined to the operculum. Another () 
 takes a very remarkable course : it mounts up to the top of the 
 skull, joins a large branch of the eighth pair (0), and, issuing from 
 the cranium through a hole in the parietal and interparietal bones, 
 passes along the whole length of the back on each side of the 
 dorsal fin, receiving twigs from all the intercostal nerves, and sup- 
 plying the muscles of the fin and the fin-rays themselves. 
 
 This branch is superficial until it reaches the little muscles that 
 move the fin. It has, sometimes, other branches equally superfi- 
 cial, which descend to the anterior parts of the muscles of the trunk 
 above the pectoral fins ; and others, which run as far as the anal fin, 
 where they form a longitudinal nerve similar to that of the back. 
 
 (567.) The seventh pair of cerebral nerves (fig* 229, s, *) in 
 fishes, as in all other Vertebrata, is devoted to the organ of hearing, 
 and brings to the sensorium the impressions of sound. 
 
 (568.) The sense of hearing in these creatures must necessarily 
 be very imperfect ; they have neither an external ear nor a tym- 
 panic cavity, and consequently are entirely destitute of a membrana 
 tympani, and of the ossicles of hearing : they have neither Eusta- 
 chian tube nor fenestra ovalis ; the labyrinth alone, and that more 
 simple in its composition than the labyrinth of the human ear, is 
 all that the anatomist meets with in this first appearance of an 
 auditory apparatus among the Vertebrate classes. 
 
 The accompanying figure (fig. 233) represents the ear of a very 
 large fish, the Lophius piscatorius ; and the student will have little 
 difficulty in at once recognising all the parts of which it consists. 
 The soft parts of this simple ear are not enclosed in bony canals, as 
 in the human subject ; but the membranous labyrinth is lodged in 
 a wide cavity on each side of the cranium : so that little dissection 
 is necessary to expose the entire organ, which is surrounded on all 
 
PISCES FISHES. 527 
 
 sides with the same kind of oily or mucilaginous fluid, which filte 
 up the wide interspace that exists between the brain and the dura 
 mater lining the inner surface of the skull. 
 
 Fig. 233. 
 
 As in all other Vertebrata, there are three semicircular canals, 
 disposed nearly as in the human ear, and each dilated in like man- 
 ner into an ampulla which receives the filaments of the acoustic 
 nerve. Two of the semicircular canals coalesce before they open 
 into the vestibule, so that there are only five orifices whereby the 
 three semicircular canals communicate with the vestibular cavity. 
 
 The membranous vestibule (supported in the figure by two pins), 
 is of variable shape, and its walls are very delicate. Its cavity, as 
 well as the interior of the semicircular canals, is filled with a trans- 
 parent glairy fluid ; and it moreover encloses certain hard bodies 
 (otolitkt*), generally three in number, suspended by delicate fila- 
 ments in its interior. 
 
 The otolithes of osseous fishes are of a stony hardness, resembling 
 shells, and their structure is nothing at all like that of bone. 
 Their shape varies in different species, but, nevertheless, is so con- 
 stantly the same in fishes of the same kind, that the forms of these 
 pieces might be employed as an important zoological character. 
 
 In the cartilaginous fishes the otolithes are quite soft, resembling 
 starch : in both classes they are composed principally of chalk, and 
 effervesce strongly when dissolved in acids. 
 
 The auditory nerve gives a filament to each of the semicircular 
 canals, which penetrates into the ampulla of the canal to which it is 
 destined, and there spreads out ; but the larger portion of the nerve 
 
528 PISCES FISHES. 
 
 iS distributed over the vestibular sacculus, where it forms a beauti- 
 ful net-work. 
 
 There is.no Cochlea, although some writers imagine that they 
 can distinguish a rudiment of this part of the ear in a slight pro- 
 jection from the walls of the vestibule. 
 
 (569.) The ears of fishes are, therefore, much less perfect than 
 those of other Vertebrata : * deprived of tympanum, of ossicles, 
 and of Eustachian tube, they can scarcely receive the impressions 
 produced by the vibrations of the ambient element, except by those 
 vibrations being communicated through the cranium ; and, more- 
 over, the membranous labyrinth not being enclosed in bone, the 
 skull can only transmit these movements in a very feeble and im- 
 perfect manner. The absence of a cochlea would go far to prove 
 that the ear of fishes cannot appreciate the differences of tones. All 
 that it offers to the physiologist is a membranous apparatus en- 
 dowed with great sensibility, in which the nervous filaments distri- 
 buted in the ampullae of the semicircular canals must necessarily 
 partake of all the movements of the fluid in which they are 
 plunged, and where those appropriated to the vestibule must be 
 still more strongly agitated by the shocks that these movements 
 give to the otolithes contained in its cavities. 
 
 It is probable, therefore, that fishes hear ; that noise produces in 
 them a powerful sensation ; but that they cannot distinguish or 
 appreciate differences of tone, as the higher animals are enabled 
 to do. 
 
 (570.) The nerves composing the eighth pair, preside over the 
 same functions in all the Vertebrata. The glosso-pharyngeal sends 
 twigs to the first branchial arch, the fauces, and the tongue. The 
 nervus vagus (Jig. 222, t) supplies the three posterior branchiae, 
 and the lower part of the pharynx; it is then continued along the 
 (oesophagus to the stomach, where it terminates : it thus presides 
 over the same functions in all the Vertebrate classes ; and it is not 
 a little interesting to see it even in fishes distributed to the organs 
 of respiration, notwithstanding the peculiarity of their structure 
 and position. In these creatures, however, it likewise furnishes 
 nerves to other parts of the body, and sends a long branch, 
 which generally runs in the substance of the lateral muscles of the 
 trunk, communicating with the spinal nerves, and giving off fila- 
 ments to the skin ; an arrangement the physiology of which is not 
 as yet understood. The next pair of cerebral nerves in the ani- 
 
 * Cuv. et Val. op. cit. p. 347. 
 
PISCES FISHES. 
 
 529 
 
 mals under consideration would seem to represent the spinal recur- 
 rent of the human subject ; it supplies the swimming-bladder and 
 the muscles of the shoulder. 
 
 (571.) All the above nerves posterior to the optic arise from a 
 chain of ganglia constituting the medulla oblongata ; but above these 
 are situated other important masses entering into the composition 
 of the encephalon, from which no nerves take their origin, viz. the 
 cerebral hemispheres and the cerebellum. 
 
 (572.) The cerebral hemispheres in all the Vertebrata are un- 
 doubtedly the seat of the mental powers; and, as this portion of 
 the brain becomes developed and perfected, brutality and stupidity 
 give place to sagacity and intelligence. 
 
 In the higher quadrupeds, and more especially in man, the pro- 
 portionate size of the hemispheres of the brain is so enormous that 
 they overlap and conceal all the parts we have been describing ; 
 but, as we descend to lower forms, their relative dimensions become 
 gradually smaller and their structure less complicated, until in 
 fishes, the least intelligent of all the creatures belonging to this 
 great division of the animal kingdom, they are found in such a 
 rudimentary condition that they are frequently far inferior in size 
 even to the olfactory or optic ganglia (Jig. 232, c). 
 
 The lobes representing the hemispheres in fishes (Jig- 284, b) 
 are quite smooth externally, and within are hollowed into a large 
 ventricle, in the floor of which is seen the upper surface of the optic 
 ganglia (fig. 234, B, d). They present none of that complica- 
 tion of parts met with in the brains of higher orders : their 
 inner surface is lined with transverse fibres (A), and a simple com- 
 missure passes pi^ 234. 
 
 across the an- 
 terior part of 
 the ventricle, 
 bringing the 
 two sides into 
 
 kA 
 
 communication 
 
 with each other; 
 
 behind the com- 
 
 missure a pas- 
 
 sage leads to the 
 
 third ventricle, ABC 
 
 the infundibulum, and the pituitary gland. 
 
 (573,) The cerebellum (Jig. 234, a) is at (/nee recognisable from 
 
530 PISCES FISHES. 
 
 its position and singleness. In the Perch its form is that of a 
 blunted cone, with the summit directed slightly backward, but the 
 shape and relative dimensions of this part of the brain are extremely 
 variable. It consists, in fishes, only of the central portion (pj'o- 
 cessus vermiformis), so that there are neither lateral lobes nor pons 
 Varolii : its surface is composed of cineritious substance, and in its 
 centre is a ramified medullary axis containing a ventricle that com- 
 municates with the fourth. 
 
 One very remarkable feature in the structure of the encephalon 
 of fishes is the existence of supplementary lobes (Jig. 234, g) 
 placed behind the cerebellum, which sometimes are united by a 
 commissure : occasionally, as in the Trigla, there are as many as 
 five pairs of such supplementary masses ; but probably, instead of 
 regarding these as belonging to the brain, it would be more proper 
 to consider them as being merely the first ganglia composing the 
 spinal cord enormously developed in proportion to the importance 
 of the nerves which they give off to the pectoral fins. 
 
 (574.) The spinal nerves of fishes arise by double roots from the 
 sides of the medulla spinalis, which generally extends from one 
 end of the canal formed by the superior vertebral arches, to the 
 other. The posterior roots are dilated into ganglia soon after 
 their origin, but the ganglia are extremely minute. The spinal 
 cord of the Moon-fish (Orthagoriscus Mold) is, however, an 
 exception to the usual conformation : in this remarkable fish the 
 spinal ganglia are all collected into a stunted mass placed imme- 
 diately behind the brain ; and from this all the spinal nerves are 
 given off, in the same manner as those forming the cauda equina 
 in the human subject. 
 
 (575.) The Sympathetic system in the creatures we are now 
 examining is of very small size, when compared with that met 
 with in the higher Vertebrata ; nevertheless, it occupies the usual 
 position, and communicates as in man with the commencements 
 of the spinal nerves. 
 
 (576.) There are few subjects more calculated to arrest the 
 attention of the physiologist than the progressive developement of 
 the generative system in the Vertebrate classes ; and it is not a 
 little interesting to watch the gradual appearance of additional 
 organs, both in the male and female, as we advance upwards in 
 the series of animated beings from the cold-blooded and apathetic 
 fishes. In its simplest condition, the whole generative apparatus, 
 even of a vertebrate animal, is in both sexes merely a capacious 
 
PISCES FISHES. 531 
 
 gland provided with an excretory duct, wherein, in the female, ova are 
 secreted, and in the male a fecundating fluid is elaborated from the 
 blood. The eggs of the female when mature are expelled from the 
 nidus in which they were formed, and cast out into the surround- 
 ing water. The male, urged apparently rather by the necessity of 
 getting rid of a troublesome burden than by any other feeling, 
 ejects the seminal secretion in the same manner; and the fecun- 
 dating fluid, becoming diffused through the waves, vivifies the eggs 
 with which it is casually brought into contact. Such is the whole 
 process of reproduction in the osseous fishes. 
 
 (577.) In the females of such fishes, the ovary, or roe as it is 
 generally called, consists of a wide membranous bag, ordinarily 
 divided into two lobes, but sometimes, as in the Perch, single 
 (fig. 227, q). This extensive organ, when distended with ova, 
 fills a large proportion of the abdominal cavity, and its lining 
 membrane is folded into broad festoons, wherein the ova are 
 formed, and lodged until sufficiently mature for expulsion. When 
 ripe, the eggs escape into the cavity of the ovary, and are expelled 
 in countless thousands into the surrounding element through the 
 orifice of the ovarian sac (Jig. 227, r), which is situated imme- 
 diately behind the anus (&), and in front of the urinary canal (Y). 
 
 (578.) Generally, as has been already stated, the ova of fishes 
 are fecundated after their expulsion ; but there are a few instances, 
 as for example the Viviparous Blenny (Zoarcus viviparus) of our 
 own shores, in which the young are hatched in the ovary, and grow 
 to a considerable size before they are born : in such cases impreg- 
 nation must take place internally, and the males in these species 
 have, in fact, a nipple-like prolongation of the orifice of the duct, 
 through which the semen escapes, probably for the purpose of 
 introducing the seminal fluid into the interior of the ovary of the 
 females. Nevertheless, even in these the ovaria present the same 
 structure as in ordinary fishes ; the only difference being that their 
 eggs are retained until the embryo is far advanced in its develope- 
 ment, instead of being prematurely extruded. 
 
 (579.) The testicle in the males of osseous fishes, generally 
 named " the milt," equals in bulk the ovary of the other sex, and 
 the quantity of the secretion furnished by it must be exceedingly 
 great. The entire organ is composed of slender and very delicate 
 convoluted caeca, in which the semen is elaborated. These tubes 
 towards the circumference of the testis all terminate in blind 
 extremities, but by their opposite ends they communicate with the 
 
532 PISCES FISHES. 
 
 general excretory duct ; so that, by blowing air into the latter, the 
 entire organ becomes amazingly distended. In some cases the 
 seminiferous tubules run parallel to each other, and become fur- 
 cate as they approach the exterior of the testis : in others, after 
 dividing and subdividing to some extent, as they diverge from the 
 common duct, they become converted into innumerable anastomos- 
 ing ramifications ; so that the whole substance of the testis appears 
 to be made up of reticulate tubes, which during the spawning sea- 
 son, when they are filled with the creamy fluid that they secrete, 
 are visible even with the naked eye.* 
 
 (580.) It will be observed by the anatomical reader, that while 
 in the OSSEOUS FISHES the ova escape into the interior of the 
 ovary, and are expelled through an excretory orifice resembling 
 the duct of an ordinary gland, in the CARTILAGINOUS FISHES 
 and in all other VERTEBRATA the germs burst from the exterior of 
 the ovarium, where they are generally seized by Fallopian tubes, 
 and either conveyed out of the body as eggs, or, being hatched 
 internally, the offspring are nourished in receptacles provided for 
 the purpose, until they arrive at a considerably advanced state of 
 developement. 
 
 But it is only by degrees that these more perfect ovigerous 
 organs make their appearance, and we would particularly solicit the 
 attention of the student to the different gradations of structure met 
 with in this part of the animal economy. 
 
 In the Eel and the Lamprey we have the first appearance of 
 an ovary, such as is common to the higher Vertebrata. It consists 
 of a very extensive vascular membrane covered by the peritoneum, 
 and attached in broad folds beneath the spine, extending nearly 
 from one end of the abdomen to the other (fig- 235). This viscus 
 is not hollow, neither has it any excretory duct, so that naturalists 
 were long at a loss to explain how the ova of these creatures were 
 expelled. 
 
 The extensive membrane above alluded to, as is now sufficiently 
 well determined, produces in its substance the germs of the future 
 progeny ; and these, as they become mature, break loose from the 
 nidus wherein they were generated into the interior of the peri- 
 toneal cavity of the Eel, and float loosely in the abdomen : there is 
 no Fallopian tube as yet developed ; but two simple orifices, placed 
 on each side of the anal opening, serve to give exit to the countless 
 eggs, which thus escape into the surrounding water. 
 
 The male organs of the Lamprey and Eel, together with the 
 
 * Miiller, de Glandularum structura penitiori. Lipsiae, fol. 1830. 
 
PISCES FISHES. 
 
 538 
 
 ovaria of the female, and the kidneys and ureters, were accurately 
 described by Hunter, in the Catalogue 
 of his Collection, and their form and 
 structure are illustrated by the pre- 
 parations and drawings still preserved 
 in the College of Surgeons ;* but in 
 such fishes the testis of the male so 
 exactly resembles the female ovary, 
 that it was even imagined by Sir E. 
 Home that no males existed, or that 
 the females were themselves herma- 
 phrodite : according to Rathke,*f* how- 
 ever, the testes of the male are com- 
 posed of solid granules precisely like 
 the female ova ; and the secretion de- 
 rived from them is in like manner al- 
 lowed to escape into the abdomen, 
 from which it is expelled through si- 
 milar openings in the peritoneum. 
 
 (581.) In the Sharks and Rays 
 we meet with a very important addi- 
 tion to the female sexual apparatus, 
 namely, an oviduct, by which the germ 
 is seized on its escape from the ova- 
 rium, and furnished . with additional 
 coverings necessary in such fishes for 
 the security of the fetus. 
 
 In these genera the folds of the 
 ovarian membrane become less exten- 
 sively spread out; and, from the size of the yolks of the eggs 
 formed therein, the organ assumes a racemose appearance. The 
 ovaries now form two large bunches placed on each side of the 
 spine; and the ova when mature would necessarily escape into the 
 abdominal cavity, as those of the Lamprey and Eel do, were they 
 not seized by the patulous orifices of the two long and membranous 
 oviducts whereby they are conveyed out of the body. 
 
 (582.) There is, moreover, in the CHONDROPTERYGIOUS 
 FISHES a necessity for defending the young during the earlier 
 stages of their growth, by means which it would have been quite 
 foreign to the purposes of Nature to have adopted in the other 
 
 * See Physiol. Catalogue, vol. iv. pp. 48. 129, pi. 59 and 60. 
 
 t Neueste Schriften der Naturforschenden Gesellschaft zu Danzig. Halle, 1824. 
 
534 
 
 PISCES FISHES. 
 
 division of this extensive class. The earth is peopled only at its 
 surface, and the vegetable banquet there spread is abundantly suffi- 
 cient for the support of terrestrial beings. The ocean, however, 
 being densely populated at every assignable depth, could never 
 have supplied vegetable food to anything like the extent required 
 to satisfy her progeny ; hence, therefore, the necessity for that 
 astonishing fertility so remarkable in the osseous fishes nine mil- 
 lions of ova have been calculated to be spawned at a birth by a 
 single cod-fish : such spawn, being naked and unprotected, is 
 eagerly devoured by thousands of hungry mouths, or the feeble 
 young soon fall a prey to countless voracious persecutors. If, how- 
 ever, it was obviously requisite that the progeny of osseous fishes 
 should be thus multitudinous, in order to provide a sufficiency of 
 needful food, it is equally clear that it would have been incom- 
 patible with the design of the Creator that the ravenous Sharks 
 should be endowed with equal fecundity : their eggs are conse- 
 quently few in number ; and, in proportion to their scarcity, jealous 
 precaution must be taken to insure the safety of the included 
 young, in order to prevent the complete extinction of the race. 
 
 The means employed for this Fig. 236. 
 
 end are simple and beautiful. 
 About the middle of the ovi- 
 duct of the female there is a 
 thick glandular mass, destined to 
 secrete a horny shell in which the 
 yolk and white of the egg be- 
 come encased. The egg when 
 complete has somewhat the 
 shape of a pillow-case, with the 
 four corners lengthened out 
 into long tendril-like cords 
 (fig. 236), whereby the egg is 
 entangled amongst the sea-weed 
 at the bottom of the ocean. A 
 brittle egg-shell would soon be 
 destroyed by the beating of the 
 waves, hence the necessity for 
 the corneous nature of the envelope ; and yet how is the feeble 
 embryo to escape from such a tough and leather-like cradle ? This 
 likewise has been provided for: the egg remains permanently open 
 at one extremity, or, to carry out our humble simile, one end of 
 the pillow-case is left unsewn ; the slightest pressure from within, 
 
PISCES FISHES. 
 
 535 
 
 therefore, separates the valvular lips of the opening, and no sooner 
 has the little Shark thus extricated itself from its confinement than 
 the two sides close again so accurately that the fissure is not at all 
 
 perceptible.* 
 
 Fig. 237. 
 
 * According to Cuvier, in those Sharks which are viviparous, that is, whose young 
 are hatched in the oviduct prior to their expulsion, this egg-shell is never formed, 
 and the investments of the fetus remain permanently membranous. Loc. cit. p. 397. 
 
536 PISCES FISHES. 
 
 (583.) The sexual organs of the male Chondropterygii ate very 
 remarkable, and their real character is not properly understood. 
 The testicle (fig. 237, n) is large, and occupies the same posi- 
 tion as the ovary of the female ; but the singularity of this 
 testis consists in its being made up of two portions, one of which 
 has an excretory duct, while the other, although equally bulky, has 
 none. 
 
 The former portion, when minutely examined, is composed of an 
 immense assemblage of flexuous secerning vessels, that pour their 
 secretion into a long and tortuous vas deferens (o), which, after run- 
 ning in a zig-zag course nearly the whole length of the abdomen, 
 dilates into a capacious reservoir of semen (/?), and ultimately ter- 
 minates with its fellow of the opposite side in a conical fleshy 
 organ (&), which may be presumed to answer the purpose of an 
 intromittent apparatus. 
 
 The second portion of the testis appears to consist of globular 
 bodies having no excretory duct whatever ; and it is not impossible 
 that this is an organ analogous to the testis of the Lamprey, and 
 that its secretion escapes into the abdominal cavity, to be ex- 
 pelled through two orifices (s, s) situated on each side of the anus, 
 whereby a free communication exists between the interior of the 
 peritoneal sac and the external surface of the body. 
 
 (584.) In these highly organized genera impregnation takes 
 place internally, and the male is furnished with two strong prehen- 
 sile organs called claspers (/), by means of which he seizes and 
 securely holds the female during copulation. 
 
537 
 
 CHAPTER XXVIII. 
 
 REPTILIA. 
 
 (585.) THE globe that we inhabit is usually said to be made up 
 of land and water, and, perhaps, for the purposes of the geogra- 
 pher, such a division of the surface of our planet is all that is 
 requisite. A slight investigation of this subject, however, is 
 sufficient to convince the naturalist, that a very considerable pro- 
 portion of the world around us can scarcely be strictly referred to 
 either one or the other of the geographical sections referred to ; 
 that there are extensive marshes, for instance, equally ill-adapted to 
 be the habitation of aquatic animals, or of creatures organized for a 
 purely terrestrial existence ; that some localities may be alternately 
 deluged with water and parched with drought ; that the margins of 
 our lakes, the banks of our rivers, and the shallow ponds and stream- 
 lets of warm climates, could only be adequately populated by beings 
 of an amphibious character, alike capable of living in an aquatic or 
 in an aerial medium, and combining in their structure the condi- 
 tions necessary for enabling them to reside in either element. 
 
 Aquatic animals, strictly so called, breathe by means of gills ; 
 for a vertebrate animal to respire air, it must be provided with lungs : 
 but if a creature is destined to live both in air and water, it must 
 obviously have both gills and lungs coexistent, either of which may 
 be employed in conformity with the changing necessities and altered 
 circumstances. We cannot, therefore, be surprised to find that in 
 the lowest Reptiles this is literally the arrangement adopted ; that 
 they respire like fishes by means of branchiae while in the water, 
 whereas on emerging into the air they have lungs ready for use. 
 
 (586.) The AMPHIBIA (Batrachia Cuv.) are to the anatomist 
 amongst the most interesting animals in the whole range of zoo- 
 logy, as we trust will be made sufficiently evident when we come to 
 investigate their internal economy ; but it is to their outward 
 forms and habits that we must first introduce the reader, leaving the 
 details of their organization to be discussed in the sequel. 
 
 From whatever form or race of animals the zoologist advances 
 
538 REPTILIA. 
 
 towards the next succeeding it in the great scale of Nature, he will 
 
 find himself insensibly led on by such gentle gradations that the 
 transition from any one class to another is almost imperceptible. 
 Nihil per saltum is one of the most obvious laws in Creation ; 
 and of this, perhaps, we could not select a more striking illustration 
 than is afforded by the Lepidosiren (Jig. 238). 
 
 Two distinct species of this most remarkable animal have been 
 met with : one, the Lepidosiren paradoxa, discovered by Dr. Nat- 
 terer in the river Amazon ; the other, Lepidosiren annectans, was 
 found by T. C. B. Weir, Esq. and is a native of the African con- 
 tinent, inhabiting the river Gambia. An individual of the species 
 last mentioned has been minutely anatomized by Professor Owen,* 
 and both in its outward form and internal organization is so pre- 
 cisely intermediate between a Reptile and a Fish, that, while Dr. 
 Natterer regards it as an Amphibian, Professor Owen considers 
 that, notwithstanding that it possesses lungs, the icthyic characters 
 predominate, and it ought rather to be ranked among the Fishes. 
 
 The body of the Lepidosiren annectans (Jig. 238) is about a foot 
 long, and covered with scales, resembling those of the cycloid fishes : 
 the tail gradually tapers to a point, but is fringed above and below 
 with a membranous fin, supported by numerous soft, elastic, trans- 
 parent rays, articulated to the superior and inferior spines of the 
 caudal vertebrae ; the gills are covered by opercula, not being 
 exposed, as in the proper Amphibia ; and, moreover, it has four 
 rudimentary fins, or legs, as the reader may choose to call them. 
 These rudimental extremities are round, filiform, and gradually 
 attenuated to an undivided point ; being supported internally by a 
 single-jointed soft or cartilaginous ray. The nostrils of the Lepi- 
 dosiren, however, are merely two blind sacs as in fishes, and do not 
 communicate with the mouth or fauces ; a character which Professor 
 Owen regards as the only decided evidence that the animal ought 
 in preference to be ranked among the class Pisces. 
 
 * Transactions of the Linnean Society for 1840. 
 
REPTIL1A. 539 
 
 (587.) The Siren lacertina, a creature which inhabits the 
 marshes of Carolina, is another amphibious animal, scarcely further 
 removed from the fishes than the last. The Siren attains the 
 length of two or three feet ; it has a body very nearly resembling that 
 of an eel ; but instead of pectoral fins it has two rudimentary feet, 
 each provided with four fingers, its hind feet, the representatives of 
 the ventral fins, being entirely wanting ; it is, moreover, furnished 
 with gills placed on each side of the neck, while internally it 
 possesses two capacious membranous lungs adapted to aerial respi- 
 ration. 
 
 (588.) In the Proteus anguinus, an animal only met with in the 
 subterranean waters of Carniola, the body, of which a figure is given 
 in a subsequent page (Jig. 254), is equally anguilliform ; but the legs 
 are now four in number, although still very imperfectly developed. 
 Its gills are fringes of blood vessels placed externally upon the sides 
 of the neck, and its thin, and delicate lungs (, z) extend nearly the 
 whole length of the abdomen. 
 
 The Amphibia above-mentioned, as well as the Menobranchus 
 and the Axolotle, both animals of very similar construction, pre- 
 serve their branchiae through the whole period of their lives, and 
 are for this reason denominated Amphibia perennibranchiata : but 
 there are other genera which, although in the early part of their exist- 
 ence they are equally provided with both gills and lungs, ultimately 
 become sufficiently perfect in their organization to enable them to 
 enjoy a more or less complete terrestrial existence ; and, conse- 
 quently, their branchiae become obliterated as the lungs grow more 
 efficient, until at length no vestiges of the former remain percep- 
 tible. These are called A. caducibranchiata. 
 
 (589.) The most remarkable examples of the CADUCI BRAN- 
 CHIATE AMPHIBIA are the Frogs, the Toads, and the Newts, so 
 common in our own country ; and the metamorphosis of these 
 creatures from the tadpole, or fish-condition under which they leave 
 the egg, to their perfect air-breathing and four-footed state, is a 
 matter of common observation. We select the Newt (Triton 
 cristatus) as an example of the changes which these amphibians 
 undergo as they advance towards maturity. 
 
 Immediately before leaving the egg, the tadpole of the Salaman- 
 der, or Water-Newt (Jig. 239, A), presents both the outward form 
 and internal structure of a fish. The flattened and vertical tail, 
 fringed with abroad dorsal and anal fin, the shape of the body, and 
 the gills appended to the sides of the neck, are all apparent ; so 
 
540 
 
 REPTILIA. 
 
 that, were the creature to preserve this form throughout its life, the 
 naturalist would scarcely hesitate in classing it with fishes properly 
 so called. 
 
 When first hatched (fig. 239, B),* it presents the same fish-like 
 
 Fig. 239. 
 
 body, and rows 
 itself through 
 the water by 
 the lateral 
 movements of 
 the caudal fin. 
 The only ap- 
 pearance of legs 
 as yet visible 
 consists in two 
 minute tuber- j 
 
 cles, which C 
 
 seem to be sprouting out from the skin immediately behind the 
 branchial tufts, and which are, in fact, the first buddings of ante- 
 rior extremities. Nevertheless, to compensate to a certain extent 
 for this total want of those prehensile limbs which afterwards 
 become developed, two supernumerary organs are provisionally 
 furnished, in the shape of two minute claspers, seen in the figure, 
 situated on each side of the mouth ; by means of these the little 
 being holds on to the subaquatic leaves, and thus prevents itself 
 from being washed away by the slightest current. 
 
 Twelve days after issuing from the egg, the two fore-legs, which 
 at first resembled two little nipples, have become much elongated, 
 and are divided at their extremity into two or three rudiments of 
 fingers (fig. 239, c). The eyes, which were before scarcely visi- 
 ble, and covered by a membrane, distinctly appear. The branchiae, 
 at first simple, are divided into fringes, wherein red blood now cir- 
 culates ; the mouth has grown very large, and the whole body is so 
 transparent as to reveal the position of the viscera within. Its 
 activity is likewise much increased ; it swims with rapidity, and 
 darts upon minute aquatic insects, which it seizes and devours. 
 
 About the twenty-second day (fig. 240, u) the Tadpole, for 
 the first time, begins to emit air from its mouth ; showing that 
 the lungs have begun to be developed. The branchiae are still 
 large. The fingers upon the fore-legs are completely formed ; 
 
 * Vide Rusconi, Amours des Salamandres Aquatiques, et developpement du Tetard de 
 ces Salamandres depuisl'ceuf jusqu'a 1'animal parfait. 4to. Milan. 1821. 
 
REPTILIA. 
 
 541 
 
 the hind-legs begin to sprout beneath the skin ; and the creature 
 presents in a transitory condition the same external form as that 
 which the Siren tacertina permanently exhibits. 
 
 Fig. 240. 
 
 By the thirty-sixth day the young Salamander (Jig. 240, E) 
 has arrived at the developement of the Proteus anguinus ; its hind- 
 legs are nearly completed, its lungs have become half as long 
 as the trunk x>f its body, and its branchise more complicated in 
 structure. 
 
 At about the forty-second day the tadpole begins to assume the 
 form of an adult Triton (Jig- 240, F) : the whole body becomes 
 shorter, the fringes of the branchise are rapidly obliterated, so that 
 in five days they are reduced to simple prominences covered by 
 the skin of the head ; and the gill-openings at the sides of the neck, 
 which, as in fishes, allowed the water to escape from the mouth, 
 and were in like manner covered with an operculum formed by a 
 fold of the integument, are gradually closed : the membranous fin 
 of the tail contracts, the skin becomes thicker and more deeply 
 coloured, and the creature ultimately assumes the form and habits 
 of the perfect Newt (Jig. 241), no longer possessing branchiae at 
 all, but breathing air, and in every particular completely converted 
 into a Reptile. 
 
 But, however curious the phenomena attending the developement 
 of the tadpoles of the amphibious Reptiles may be to the observer 
 
542 REPTILIA. 
 
 who merely watches the changes perceptible from day to day in 
 their external form, they acquire a tenfold interest to the physio- 
 Fig. 241 . 
 
 logist who traces the progressive evolution of their internal viscera ; 
 more especially when he finds that in these creatures he has an 
 opportunity afforded him of contemplating, displayed before his 
 eyes, as it were, upon an enlarged scale, those phases of develope- 
 ment through which the embryo of every air-breathing vertebrate 
 animal must pass while concealed within the egg. The division, 
 therefore, of Reptiles into such as undergo a metamorphosis, and 
 such as do not, is by no means philosophical, although convenient 
 to the zoologist : all Reptiles undergo a metamorphosis, though 
 not to the same extent. In the PERENNIBRANCHIATA the change 
 from the aquatic to the air-breathing animal is never fully com- 
 pleted ; in the CADUCIBRANCHIATA the change is accomplished 
 after the embryo has escaped from the ovum ; and in the REP- 
 TILIA proper, as well as in BIRDS and MAMMALS, which are gene- 
 rally said to undergo no metamorphosis, the changes referred to 
 are accomplished in ovo during the earliest periods of the formation 
 of the fetus. 
 
 (590.) The second order of Reptiles (OPHIDIA) includes the 
 Serpent tribes, animals entirely deprived of external locomotive ex- 
 tremities, and nevertheless endowed with attributes at once formid- 
 able and surprising. Absolutely without limbs or any apparent 
 means of progression, the scale-clad Serpent makes its way in either 
 element with equal facility ; and walks or leaps, or climbs or swims, 
 at will. Destitute of any prehensile members, it seizes and devours 
 the strongest and most active prey : it binds its victim in a living 
 rope ; or, with a single scratch inflicted by its venomed fangs, 
 speedily destroys the stoutest assailant. 
 
 (591.)The transition from the OPHIDIA to the Lizards (SAURIA), 
 composing the third order of Reptiles, is very gradually accom- 
 plished by several intermediate forms, in which the first buddings 
 
REPTILIA. 
 
 543 
 
 of legs make their appearance ; and these locomotive organs, be- 
 coming more and more completely developed in other genera, at 
 
 Fig. 242. 
 
 length conduct us from the flexible and apodous Serpents to the 
 strong and four-footed Reptiles which are the types of the Saurian 
 division (fig. 243). The progressive developement of the locomo- 
 tive extremities is not a little curious : even among some of the Ser- 
 pents properly so called, as, for example, in the Anguis fragilis 
 of our own country, the rudiments of these limbs may be detected 
 beneath the skin ; more especially those of the hinder extremity, 
 wherein a little pelvis and femur mav be distinctly recognised, 
 while a minute sternum, clavicle, and scapula indicate the first 
 appearance of the thoracic legs. 
 
 In Bimanes, the lowest of the Saurian genera, two little feet, 
 each provided with four toes, are appended to the framework of the 
 shoulder; and in Seps, which equally possesses the body of a 
 
544 
 
 REPTILIA. 
 
 serpent, all four extremities first make their appearance externally. 
 As the legs become increased in their relative size and importance, 
 
 Fig. 243. 
 
 the trunk is proportionately shortened and its flexibility diminished 
 (Jig. 243), until at length we are conducted almost by impercep- 
 tible gradations to the strong and voracious Crocodiles, the most 
 perfect of the Reptile families. 
 
 (592.) The fourth order of Reptiles (CHELONIA) comprises a 
 series of animals of most anomalous conformation, in which the 
 greater part of the skeleton is brought quite to the exterior of the 
 body, and the limbs are absolutely enclosed within the cavity form- 
 ed by the ribs. Such are the Tortoises and the Turtles (Jig. 244) ; 
 but, as we shall describe the anatomy of these animals more at 
 length hereafter, we need only in this place point out to the reader 
 their outward form and general appearance. 
 
 (593.) Commencing our researches concerning the internal organ- 
 ization of this extensive class by examining the osteology of the 
 Reptilia, we shall, as we have hitherto done, select one skeleton for 
 special examination ; and afterwards, taking that as a standard of 
 comparison, observe the most conspicuous modifications of struc- 
 ture met with in the different divisions of this important group. 
 
REPTILIA. 545 
 
 Fig. 244. 
 
 (594.) The skeleton we choose for particular description is that 
 of the Crocodile, one of the most interesting that can possibly be 
 offered to the contemplation of the comparative anatomist ; inas- 
 much as it exhibits, developed to a medium extent, a greater num- 
 ber of the elements which we have supposed to enter into the 
 composition of a perfect or typical skeleton than any other with 
 which we are acquainted : we, therefore, beg the attention of the 
 student while we investigate this important piece of osteology. 
 
 (595.) A glance at the skeleton of the Crocodile (jg. 245) 
 at once shows us that in consequence of the addition of a thorax, 
 and the connection which now necessarily exists between the pelvis 
 and the spine, the vertebral column becomes- divisible into dis- 
 tinct regions : viz. the cervical, containing seven vertebrae ; the 
 dorsal, formed by those vertebrae which support the thoracic ribs ; 
 and the lumbar vertebrae intervening between these and the sa- 
 crum. The number of bones entering into the composition of the 
 sacrum, that is, which are connected with the ossa ilii of the pelvis, 
 are in this case two in number; while, behind these, six and thirty 
 vertebrae enter into the composition of the tail. 
 
 In the cervical, dorsal, lumbar, and sacral regions, no inferior 
 spinous processes exist ; but in the caudal portion of the vertebral 
 column these elements are found greatly developed, as in fishes, 
 and obviously with the same intention, namely, to increase as much 
 as possible the vertical extent of the tail, and thus convert this 
 
546 
 
 REPTILIA. 
 
 part of the body, which is here of extraordinary length and great 
 flexibility, into a powerful instrument of propulsion. 
 
 (596.) The transverse processes of the cervical vertebrae are re- 
 markably large, and so extended that they materially interfere 
 with the lateral movements of the neck ; an arrangement evidently 
 designed to afford a sufficient extent of insertion for the powerful 
 muscles of the cervical region. 
 
 (597.) The thorax is com- Fi s- 245. 
 
 posed of a Sternum and two 
 sets of ribs ; one set being ar- 
 ticulated with the transverse 
 processes of the dorsal verte- 
 brae, and hence called dorsal 
 ribs; while the others, being 
 fixed to the sides of the ster- 
 num, are named sternal ribs : 
 the contiguous extremities of 
 the dorsal and sternal ribs are, 
 moreover, united by inter- 
 vening cartilages, which, as 
 they are generally more or 
 less perfectly ossified in the 
 adult Crocodile, might almost 
 be regarded as additional ele- 
 ments of the thorax. 
 
 The posterior dorsal ribs 
 are far less perfectly deve- 
 loped than those situated 
 more anteriorly; and it is 
 not a little interesting to 
 observe how gradually, even 
 in the same skeleton, the 
 transition is effected from 
 the simple condition already 
 noticed in the ribs of fishes, 
 in which each rib is merely 
 appended to the extremity of 
 the transverse process of a ver- 
 tebra, to ribs perfectly adapt- 
 ed to enter into the compo- 
 sition of a true thoracic 
 
REPTJLIA. 547 
 
 cavity, and united by a double articulation both with the trans- 
 verse processes and the bodies of the vertebra. The head of the 
 last rib of the Crocodile is, in fact, simple, and merely articulated 
 with the apex of the transverse process of the corresponding verte- 
 brae ; the next is slightly bifid at its origin, but both the divisions 
 are still connected with the transverse process : as we advance still 
 further forwards, the division of the origin of the rib becomes more 
 and more decided, until at length, at about the fifth rib, we have two 
 distinct heads, one firmly articulated with the body of the vertebra, 
 the other with the transverse process ; presenting an arrangement pre- 
 cisely similar to that met with in the structure of the thorax of a bird. 
 (598.) The sternal apparatus is not less interesting to the osteo- 
 logist. The anterior extremity of the sternum is osseous, and 
 considerably prolonged forwards, to be articulated with the clavi- 
 cles, and thus afford a support to the anterior extremity. Behind 
 this it becomes cartilaginous, and affords attachment to the sternal 
 ribs, which enter into the composition of the thorax : it does not, 
 however, terminate at the posterior margin of the thoracic cavity, 
 but is continued along the mesial line of the abdomen quite to the 
 pubis, and gives off eight abdominal sternal ribs, to which no 
 dorsal correspondents are met with. These abdominal ribs serve 
 to support the muscles of the abdomen, and here present their 
 maximum of developement : rudiments of them are, however, still 
 met with in the higher animals, and even in the human subject 
 we find, in the transverse tendinous bands which intersect the 
 substance of the rectus muscle of the abdomen, the last remains 
 of these appendages to the sternal portion of the skeleton. 
 
 (599.) In the anterior extremity of the Crocodile we have most 
 of the parts enumerated as entering into the composition of a per- 
 fect or typical skeleton ; the shoulder, however, is composed of only 
 two pieces, the Scapula and the Clavicle, the last of which articu- 
 lates with the sternum : the bones of the arm, fore-arm, and hand, 
 are completely developed. 
 
 (600.) The posterior extremities are fully formed, the pelvis 
 being connected by means of the ossa ilii to the transverse pro- 
 cesses of two vertebrae, which therefore, as we have seen, constitute 
 the Sacrum. 
 
 (601 s ) In examining the bones which enter into the composi- 
 tion of the head of the Crocodile, or indeed of most Reptiles, 
 the anatomist finds his studies much facilitated by the circumstance 
 that the sutures separating the individual bones never become 
 
548 
 
 REPTILIA. 
 
 obliterated, so that the elements of this portion of their skeleton 
 remain permanently detached and separate ; and for this reason 
 we shall take the present opportunity of going a little into detail 
 concerning the composition of the skull of the Crocodile, as it is 
 well calculated to illustrate the real structure of the cranium in the 
 Vertebrata generally. 
 
 The bones of the face are easily recognised ; the Intermaxillary 
 (fig. 246, 17), the Maxillary (18), and the Nasal (20), the Zy- 
 gomatic (b) and the Lacrymal (c), all occupy their usual relative 
 positions. The roof of the mouth is formed, as in Man, anteriorly 
 by a process of the upper jaw (Jig- 246, A, 18), and posteriorly 
 
 by the palate-bone (22). 
 J Fig. 246. A 
 
 The Frontal consists of five pieces ; viz. the Principal Frontal 
 (1), which probably in the fetus consisted of two lateral halves, 
 the Anterior Frontal (2, 2), and the Posterior Frontal (4, 4). 
 
 The Parietal (7) is, as is generally the case in Reptiles, repre- 
 sented by a single bone. 
 
 The Occipital consists of four pieces, which remain permanently 
 detached; namely, the Basilar (5), the two Lateral Occipital (10), 
 and the Superior Occipital placed above the foramen magnum. 
 
REPTILIA. 549 
 
 The Sphenoid, which in Man is regarded as a single bone, is 
 here represented by several distinct parts. The body is divided 
 into two portions {fig. 246, A, 6), called respectively the Anterior 
 and the Posterior Sphenoids. The great or Temporal Ala (11) 
 are also separate bones, as also are the Internal Pterygoids (25). 
 
 A bone (24), which is not met with either in Mammalia or 
 Birds, passes from the Internal Pterygoid to the point of junction 
 between the Zygomatic, the Maxillary, and the Posterior Fron- 
 tal : this has been named by Cuvier the Transverse bone. 
 
 The Ethmoid and the Vomer (16) are but very imperfectly 
 ossified, so that the septum between the nostrils is in the skeleton 
 extremely incomplete, and the sense of smell of course propor- 
 tionately obtuse. 
 
 But the most interesting of the cranial bones is the Tem- 
 poral, which, although considered as one bone by the human osteo- 
 logist, is in Reptiles evidently composed of at least four distinct 
 and separate parts. These are, 1st, the Petrous bone (fig. 246, 
 A, e), which partially encloses the organ of hearing ; 2dly, the Tym- 
 panic bone (a), which supports the membrana tympani ; 3dly, the 
 Mastoid bone (12), which is the homologue of the Mastoid process 
 of Man ; and 4thly, the Temporal bone, properly so called (23), 
 which represents the squamous portion of the human Temporal 
 bone. 
 
 (602.) Each lateral division of the inferior maxilla of Reptiles 
 is separable into at least five and generally six pieces, which are 
 united together by suture; these are named the dental (84), which 
 support the teeth, the angular (36), the opercular (37), the arti- 
 cular (35), and two small pieces seen upon the inner surface of the 
 jaw. 
 
 Having thus described at some length the composition of the 
 skeleton in the Crocodile, which we have chosen for minute ana- 
 lysis, as being the type of the Saurian Reptiles, we shall now pro- 
 ceed to examine the osteology of the other orders, so as to appre- 
 ciate more correctly the peculiarities of structure that they indivi- 
 dually exhibit. 
 
 (603.) In the AMPHIBIA, as for example in the Frog, one of 
 the most striking circumstances connected with their history is the 
 extraordinary change which takes place in the condition of every 
 part of the framework of the body during the evolution of the tad- 
 pole, and its metamorphosis into the perfect frog. 
 
 The skeleton of a Tadpole is, in every particular, that of a fish : 
 
550 
 
 REPTILIA. 
 
 its texture is soft and cartilaginous, the caudal portion of the spine 
 prolonged and flexible ; neither are there any external limbs con- 
 nected with the vertebral column, so as to trammel the lateral 
 movements of the tail; and yet in the mature frog (jig. 247) 
 let the reader observe the amazing difference. The head, it is 
 true, still preserves somewhat of the character of that of the fish, 
 especially in the disproportionate developement of the face, when 
 compared with the size of the cranial cavity ; but all the bones of 
 the spine have become consolidated into ten vertebrae, firmly con- 
 nected together by strong articulations, while the flexible tail of 
 the tadpole has become converted into a strong and immoveable os 
 coccygis, composed of a single piece. 
 
 No ribs whatever are met with in the Frog ; and, even in those 
 Amphibia which are Fig. 247. 
 
 possessed of these 
 elements of the ske- 
 leton, they are mere 
 rudiments appended 
 to the extremities of 
 the transverse pro- 
 cesses of the verte- 
 brae. The sternum, 
 however, is largely 
 developed, and gives 
 extensive attachment 
 to the muscles of the 
 abdomen. The an- 
 terior extremities are 
 
 supported by a semicartilaginous zone, in which the three elements 
 of the shoulder the scapula, the clavicle, and the coracoid bone, 
 are distinctly recognisable ; and the bones of the arm, fore-arm, 
 and hand, are very perfectly formed. 
 
 The pelvis is large, and firmly ossified in correspondence with 
 the strength and magnitude of the hinder extremity ; the ossa ilii 
 being articulated to the ends of the transverse processes of the last 
 vertebra, which from this circumstance may be called the sacrum. 
 The tibia and fibula are consolidated into one bone ; while two of 
 the bones of the tarsus, the astragalus and the os calcis, are so 
 excessively elongated, that they might almost be taken for a second 
 tibia and fibula, did not their position indicate their real nature. 
 
 One circumstance is remarkable in the construction of the 
 
BEPTILIA. 551 
 
 shoulder-joint of these reptiles, which are found to have a strong 
 ligament passing between the head of the humerus and the scapula, 
 exactly in the same manner as the ligamentum teres of the human 
 hip-joint. The use of such a deviation from the ordinary structure 
 of the articulation is obvious ; the frog, as it alights from those 
 long and vigorous leaps which form its ordinary mode of progres- 
 sion, receives the whole shock of its fall upon its fore-legs, and thus 
 this ligament becomes needful as an additional security to the ar- 
 ticulation in question. 
 
 (604.) The skeleton of an Ophidian Reptile presents a strange 
 contrast to that of the Batrachian last described. Taking the Boa 
 Constrictor as an example of this order, we find the spine of this 
 enormous serpent composed of three hundred and four distinct 
 vertebrae, of which two hundred and fifty-two support ribs : flexi- 
 bility is, therefore, abundantly provided for in the construction of 
 these lithe and elegant beings, inasmuch as the division of their 
 spinal column into so many pieces allows the utmost pliancy in any 
 required direction. Flexibility, however, is not the only condition 
 requisite in this case ; strength and precision of movement are 
 equally indispensable, and the question is, how are these apparently 
 opposite qualities to be so combined and associated as not in the 
 slightest degree to interfere with each other. The mechanism con- 
 spicuous in the construction of the spine of a serpent is in this re- 
 spect truly admirable. The anterior extremity of the body of every 
 vertebra is rounded into a smooth and polished ball (Jig' 248, c), 
 which exactly fits into a hemispherical cup excavated in the sub- 
 stance of the vertebra next succeeding : a perfect ball-and-socket joint 
 is thus formed between every vertebra and that which precedes or 
 follows it; and thus the spine is rendered capable of the utmost lati- 
 tude of movement, and offers, at the same time, a firm purchase to 
 the muscles acting upon the vertebral column. To provide, how- 
 ever, against undue extent of motion in certain directions, we now 
 meet with other processes derived from the vertebral arches : in addi- 
 tion to those given Fig. 248. 
 merely as levers for 
 the attachment of 
 muscles,secondary 
 apophyses, called 
 oblique or articu- 
 lating processes, 
 become develop- 
 
552 REPTILIA. 
 
 ed ; and, contiguous vertebrse being likewise mo veably connected 
 together by means of these appendages, unnecessary flexure is 
 not allowed, and all danger of dislocation prevented. 
 
 (605.) Serpents, being entirely deprived of external limbs, have 
 neither shoulder nor pelvis ; their ribs alone affording them the 
 means of progression. These extend on each side in an uninter- 
 rupted series from the first vertebra behind the head to the origin 
 of the tail, so that the division of the spine into regions is here out 
 of the question. Every rib (fig. 248, a) is attached at its origin 
 by a kind of ball-and-socket joint to the extremity of the correspond- 
 ing transverse process of a vertebra (6), and is therefore freely move- 
 able. There is no sternum here, neither are there sternal ribs ; but 
 the dorsal ribs, wielded as they are by innumerable and powerful 
 muscles connected with them, literally perform the office of inter- 
 nal legs, and materially assist the creature in progression. 
 
 (606.) Having already enumerated the bones which enter into 
 the composition of the cranium of a Saurian Reptile, it would be 
 superfluous again to mention in detail those met with in the skull 
 of a serpent, more especially as they will be easily recognised by 
 a glance at the annexed figure, in which the corresponding bones 
 are all indicated by the same references : one peculiarity only re- 
 
 quires special notice, namely, the extreme mobility of the principal 
 bones of the face, and more particularly of the pieces composing the 
 lower jaw, by which provision these reptiles are enabled to swallow 
 entire animals of astonishingly large dimensions when compared 
 with the size of their mouths. 
 
 In order to allow of this, the bones composing the superior 
 maxilla (17, 18) are only loosely joined together by ligamentous 
 
REPTILTA. 553 
 
 bands, and even the arches of the palate are moveable. The 
 two halves of the lower jaw (34, 34) are connected together at the 
 symphysis by a ligament so loose and elastic that separation to a 
 great extent is easily allowed ; and, moreover, those two elements 
 of the temporal, the Mastoid (12), and the Tympanic (a), which 
 form the bond of connection between the inferior maxilla and the 
 cranium, are here lengthened out into long pedicles, so that by 
 their mobility the entrance to the throat can be dilated in a sur- 
 prising manner, and prey of apparently very disproportionate bulk 
 thus introduced into the stomach. 
 
 (607.) The most extraordinary skeleton met with among Rep- 
 tiles, and, indeed, among the Vertebrata generally, is that of the 
 Chelonia ; in which the ribs and sternum are both placed quite 
 at the exterior of the body, so as to form a broad dorsal shield 
 called the Carapax, and an equally strong ventral plate named the 
 Plastrum, between which the limbs and the head can be more or 
 less completely retracted. 
 
 Yet, notwithstanding this apparent total inversion of the osseous 
 system in the creatures before us, it is interesting to observe by 
 what slight modifications in the arrangement of the elements of the 
 skeleton such prodigious changes are accomplished. This is well 
 exemplified in the construction of the Carapax of the common Tor- 
 toise (EmysEuropaus). In this well-known animal (Jig. 250) the 
 vertebrae of the neck, and of the tail, present nothing particu- 
 larly remarkable in their structure ; but, being connected together 
 in the ordinary manner, the neck and caudal region of the spine 
 present their usual flexibility. The dorsal vertebrae, however, are 
 strangely distorted ; the elements of the upper arch being dispropor- 
 tionately developed, while the bodies remain almost in a rudimen- 
 tary condition. The superior spinous processes of these vertebras 
 are flattened, and converted into broad osseous plates, which form a 
 longitudinal series along the centre of the back, and are connected 
 together by sutures resembling those of the human cranium. The 
 ribs are changed into broad flat bones, firmly united by suture to 
 each other, and also to the lateral margins of the spinous processes 
 of the vertebrae, so that they all form, as it were, a single broad 
 plate : the heads of the ribs are very feebly developed, and the 
 intervals 'between them and the bodies of the vertebrae filled up 
 with ligament. The margin of the shield thus formed by the dorsal 
 ribs is further enlarged by a third set of flat bones, apparently 
 representing the sternal ribs of the Crocodile, fixed by suture 
 
554 
 
 REPTILIA. 
 
 around the whole circumference of the Carapax, which they assist 
 in completing. p . g ^ 
 
 (608.) The Plastrum, or Sternum, is made up of nine pieces, 
 which have been proved by M. Geoffroy St. Hilaire to be the ele- 
 ments of this portion of the skeleton in the most complete state of 
 developement in which they are met with. Of these nine elements, 
 eight are disposed in pairs ; but the ninth, which is always placed 
 between the four pieces composing the two anterior pairs, is single, 
 and occupies the mesial line: in birds we shall afterwards find 
 this element of the sternum performing a very important office. 
 
 (609.) The bones of the shoulder, and of the hip, in the Tor- 
 toise (fig- ^50), are absolutely placed within the thorax, and articu- 
 lated to the sides of the vertebral column. The precise homology 
 
REPTILIA. 555 
 
 of the scapular apparatus has not been as yet decidedly pointed out ; 
 there are, however, three branches, probably representing the Sca- 
 pula, the Clavicle, and the Coracoid bone ; but, in the construction 
 of the pelvis, the Ilium, the Ischium, and the Pubis are identified 
 with facility. 
 
 (610.) The muscular movements of Reptiles are ordinarily 
 slow and languid, a circumstance which no doubt depends upon 
 the impurity of their blood consequent on the imperfect manner in 
 which the circulating fluid is exposed to the influences of respir- 
 ation. The muscles of these animals are, however, peculiarly tena- 
 cious of life, and preserve their irritability and power of contraction 
 for an astonishing length of time after they have even been separated 
 from the body. The muscles of a Turtle will continue to live for 
 days after the creature has been decapitated ; and the heart will 
 still contract, when irritated, even many hours after its removal. 
 
 But, perhaps, the most interesting phenomenon connected with 
 the muscular system of the Reptilia, is the progressive develope- 
 ment of entirely different sets of muscles as the metamorphosis 
 goes on by which they are converted from their earliest fish- condi- 
 tion to their mature and perfect state. This series of changes, 
 which doubtless takes place in all the higher Vertebrata, is well 
 exemplified in the tadpole of the Frog or Toad, and the different 
 phases of developement are in such creatures easily investigated. 
 At first the tadpole presents the muscular structure of a fish, both in 
 the muscles of the expanded and vertical tail, and in those of the 
 branchial apparatus. As growth proceeds, the broad muscles of 
 the abdomen become developed, and ultimately those of the 
 limbs are superadded as those members successively make their ap- 
 pearance ; the muscles of the shoulder and pelvic region being first 
 recognisable, and subsequently those of the legs and feet. In the 
 mean time, as the abdominal muscles, and those of the extremities, 
 become gradually perfected, those peculiar to the fish-state are 
 rapidly removed : the broad tail becomes atrophied and absorbed, 
 diminishing in length nearly at the rate of a line a day ; the 
 flaky lateral muscles of the caudal region disappear altogether ; 
 and, moreover, the entire muscular apparatus of the branchial and 
 hyoid systems is altered as the character of the respiratory organs 
 becomes changed, in a manner to be explained hereafter, from 
 the aquatic to the aerial condition. 
 
 (611.) As Reptiles, for the most part, must from necessity 
 swallow their prey entire, organs of taste would be scarcely more 
 
556 REPTILIA. 
 
 useful to them than to the fishes described in the last chapter ; 
 and we are, therefore, not at all surprised to find the tongue in 
 almost every family appropriated to a totally different use, and not 
 unfrequently converted into an apparatus of prehension, whereby 
 the food is seized and conveyed into the mouth. 
 
 In the Batracoid Amphibia, for instance, we have a remarkable 
 example of this provision. The Frog and the Toad, notwith- 
 standing their slow and clumsy movements, are destined to feed 
 upon insects, and consequently must be provided with some instru- 
 ment by which such active prey may be caught. The organ pro- 
 vided for this purpose is the tongue, which, by a slight modifica- 
 tion in its structure, becomes changed into a prehensile forceps, 
 admirably adapted to such an office. The tongue of the Frog, 
 instead of presenting the usual arrangement, is found to be fixed 
 to the symphysis of the lower jaw, and folded back upon itself, so 
 that its point, which is free and bifid, is lodged in the throat. 
 Thus provided, the Frog is enabled to seize its victim with the 
 greatest ease. No sooner does a fly approach sufficiently near than 
 this living forceps is rapidly everted ; and the insect, being seized 
 by its furcate extremity, is as speedily brought between the jaws of 
 its destroyer. The teeth of the Batrachia very much resemble those 
 of the generality of fishes ; being simple points soldered to the sur- 
 face of the jaws, but not implanted in sockets, sufficient to give a 
 secure hold of their food, but quite unadapted to mastication. 
 
 (612.) The Cameleon is another curious example of a reptile 
 obliged to employ its tongue in securing insect prey. The Came- 
 leon is arboreal in its habits : its feet, cleft, as it were, into two por- 
 tions, firmly grasp the boughs upon which it climbs ; while its well- 
 known power of changing the colour of its skin, so as to imitate 
 that of the branches around it, efficiently conceals it from obser- 
 vation. The tongue of this creature, when extended, is as long as 
 its whole body, and is terminated by a club-shaped extremity, 
 smeared over with a viscid secretion : when an insect comes within 
 a distance of five or six inches from the Cameleon, the end of this 
 tongue is first slowly protruded to the distance of about an inch, 
 and then, with the rapidity of lightning, launched out with uner- 
 ring aim ; the fly, glued to its extremity, is with equal velocity 
 conveyed into the mouth. 
 
 (613.) The jaws of the Chelonian Reptiles are not armed with 
 teeth, but cased in horny coverings so as to resemble the beak of a 
 bird, with which they crop the vegetable aliment upon which they 
 generally subsist. 
 
REPTILIA. 557 
 
 Serpents, as regards their means of destroying prey, may be di- 
 vided into two great groups ; the first including those which are not 
 venomous, the second embracing such as are armed with poison-teeth. 
 
 (614.) In the non-venomous serpents, as for example in the 
 Boa constrictor, the upper jaws and the palate-bones are all lined 
 with sharp teeth, so that there are four rows of dental organs, two 
 placed along the margins of the maxilla, and two projecting from 
 the roof of the mouth : all these teeth are simple, very sharp, and 
 point backwards. Each division of the lower jaw is likewise armed 
 with a single row, which are also directed towards the back of the 
 mouth. It must be evident, from a mere inspection of these teeth, 
 that they can be of little use in holding, much less in destroying, 
 such strong and large animals as the Boa devours ; and upon a little 
 consideration we shall find that they are intended for a very diffe- 
 rent office. These serpents kill their victims by coiling their lengthy 
 bodies around the chest, and then by strong muscular contraction 
 they compress the thorax of their prey so firmly, that, its move- 
 ments being completely prevented, respiration is put a stop to, and 
 the animal so seized speedily perishes from suffocation. But, hav- 
 ing succeeded in extinguishing life, the most difficult task still re- 
 mains to be accomplished : how is the serpent, utterly destitute 
 as it is of all external limbs, to force down its throat the carcase of 
 a creature many times thicker than its own body ? The mode 
 adopted is as follows : Once more winding itself around the 
 slain animal, it commences at the head, which by main force it 
 thrusts into its mouth ; the elastic ligament at the symphysis of its 
 lower jaw gives way, and the branches of the inferior maxilla be- 
 come widely separated, so that the mouth is stretched enormously 
 as the food is thus forced into it. Deglutition is here a very 
 lengthy and laborious process ; and, was there not some special con- 
 trivance to guard against such an accident, no sooner were the 
 efforts of the snake relaxed in the slightest degree, than the mus- 
 cles of the throat and jaws, being in a state of extreme tension, 
 would force out of the mouth what had already been partially 
 swallowed. To provide against this, the teeth are in this case con- 
 verted into a sort of valve : pointing backwards as they all do, they 
 permit the bulky food to pass into the fauces, but at the same time, 
 their sharp points being directed towards the throat, efficiently pre- 
 vent it from being pushed back again in the opposite direction.* 
 
 * In the collection of Professor Bell there is a small snake, which having by mis- 
 hap attempted to swallow a mouse of too large size, and being quite unable, in conse- 
 
558 REPTILIA. 
 
 (615.) In the venomous serpents those teeth, which are fixed to 
 the margin of the superior maxillary bone of the innoxious genera, 
 are generally deficient ; and instead of them there is found an appa- 
 ratus of poison-fangs, constituting perhaps the most terrible weapons 
 of attack met with in the animal creation. The poison-teeth (fig. 
 251, a) are two in number, one fixed to each superior maxillary bone : 
 when not in use, they are laid flat upon the roof of the mouth, and 
 
 Fig. 251. 
 
 covered by a kind of sheath formed by the mucous membrane of 
 the palate ; but when the animal is irritated, or about to strike its 
 prey, they are plucked up from their concealment by muscles in- 
 serted into the upper maxillary bone, and stand out like two long 
 lancets attached to the upper jaw. Each fang is traversed by a canal ; 
 not, as it is generally described, excavated in the substance of the 
 tooth, but formed by bending as it were the tooth upon itself, so 
 as to enclose a narrow channel through which the poison flows. 
 The canal so formed opens towards the base of the tooth by a 
 large triangular orifice, but at the opposite extremity it terminates 
 near the point of the fang by a narrow longitudinal fissure. The 
 gland wherein the poison is elaborated occupies the greater part 
 of the temporal fossa, and is enclosed in a white and tendinous 
 capsule (Jig. 251, ); the substance of the organ is spongy, and 
 composed of cells communicating with its excretory duct (c), by 
 which the venom is conveyed to the opening at the base of the 
 fang.* The poison-gland is covered by a strong process of the tem- 
 
 quence of the mechanism referred to, to disgorge it, was found dead, and the skin and 
 muscles of its neck absolutely rent from excessive stretching. 
 
 * M6moire sur les caracteres tir6s de 1'Anatomie pour distinguer les Serpens venimeux 
 des Serpens non-venimeux ; par M. Duvernoy, D. M. Annales des Sc. Nat. torn. xxvi. 
 
KEPTILIA. 559 
 
 poral muscle (d) 9 which is attached to a thin aponeurotic line (e). 
 The greater portion of the fibres of this muscle take their origin 
 from the capsule of the secreting apparatus, which they partially 
 envelope ; and then winding round all the posterior part of the 
 gland, and passing behind the commissure of the lips, the lower 
 part of the muscle is firmly implanted into the lower jaw very far 
 anterior to the angle of the mouth. The process of the temporal 
 muscle which thus surrounds the gland is very thick and strong, so 
 that it is easy to imagine with what force the poison will by this 
 mechanism be injected into the wounds inflicted by the fangs, seeing 
 that the same muscles which close the jaw at the same time com- 
 press the bag of venom with proportionate energy. 
 
 Behind the large poison-fang in use, the capsule that encloses it 
 generally contains the germs of several others, ready to supply its 
 place should the former be broken off; and, on the event of such 
 an accident, one of these supplementary teeth soon becomes consoli- 
 dated with the superior maxilla, and adapted in all respects to take 
 upon itself the terrible office of its predecessor. 
 
 (616.) Dreadful as are the means of offence thus conferred 
 upon the poisonous serpents, it is impossible to avoid noticing in 
 this place that admirable provision of Nature, which, in one genus 
 at least, serves to give timely warning of the vicinity of such dan- 
 gerous assailants. We need merely mention the rattle of the 
 Rattle-snakes (Crotalus) ; an organ, the intention of which is so 
 obvious, that the most obtuse cannot contemplate it without at 
 once appreciating the beauty of the contrivance. This singular 
 rattle is formed of numerous horny lings, that are in fact merely 
 modifications of the general scaly covering of the reptile, so loosely 
 articulated together, that the slightest movement of their formida- 
 ble possessor is betrayed by the startling noise produced by the 
 collision of the different pieces composing the organ ; even when 
 at rest, the creature announces by rapid vibrations of the tail the 
 place of its concealment, apparently to caution the inadvertent in- 
 truder against too near an approach. 
 
 (617.) In the grand police of Nature, the scavengers are by no 
 means the least important agents. In hot climates especially, 
 where putrefaction advances with so much rapidity, were there not 
 efficient and active officers continually employed in speedily re- 
 moving all dead carcases and carrion, the air would be perpetually 
 contaminated with pestilential effluvia, and entire regions rendered 
 
560 REPTILIA. 
 
 uninhabitable by the accumulation of putrefying flesh. Perhaps, 
 however, no localities could be pointed out more obnoxious to such 
 a frightful cause of pestilence than the banks of tropical rivers ; 
 those gigantic streams, which, pouring their waters from realm to 
 realm, daily roll down towards the sea the bloated remains of 
 thousands of creatures which taint the atmosphere by their decom- 
 position. 
 
 Such are precisely the situations inhabited, by Crocodiles and 
 Alligators, the largest of the Saurian Reptiles now in existence, 
 animals in every way designed by Nature to feed upon putrefying 
 materials : their tongue (Jig- 252, d) scarcely projects from the 
 lining membrane of the mouth, and its surface (e) is studded with 
 large glands ; the whole interior of the mouth is in fact, from its 
 construction, little adapted to gustation. 
 
 The Crocodile nevertheless likewise kills living prey, which, 
 from the structure of its teeth, it is obliged to effect by dragging 
 
 Fig. 252. 
 
 its victim into the water and there drowning it. This mode of pro- 
 ceeding, however, simple as it might appear, involves many difficul- 
 ties : as the reptile has no other instruments of prehension besides its 
 mouth, and is obliged to hold its struggling prey submersed by 
 the strength of its formidable jaws, it is manifest that, without some 
 special contrivance, the water rushing into the throat of the Cro- 
 codile would prevent it from breathing quite as effectually as the 
 
REPTILIA. 561 
 
 animal it endeavours to drown ; it might therefore become a 
 question which of the two would survive immersion longest. The 
 mechanism employed under these circumstances to give the Cro- 
 codile the advantage over its prey is very complete : A broad 
 cartilaginous plate (fig. 25, f) stands vertically from the os 
 hyoides, and projects upwards into the back part of the mouth ; 
 a similar valve (g) hangs down from the back of the palate, so 
 that the two together form a kind of flood-gate, which, when the 
 mouth is widely opened, effect a complete partition between the 
 cavity of the mouth and the fauces, where the aperture of the 
 larynx (h) is situated. The nostrils, moreover, are placed quite 
 at the extremity of the snout, and the nasal passages leading from 
 them are prolonged through the whole length of the upper jaw 
 until they communicate with the fauces behind the velum of the 
 palate (g). Such being the arrangement, it is immediately ob- 
 vious, that, when the communication between the mouth and the 
 fauces is cut off by means of the two valves (gjO, the Crocodile, 
 by merely keeping the tip of its snout above the water, breathes 
 with the utmost facility, and it is thus enabled to keep its prey 
 submerged for any length of time that may be requisite to extin- 
 guish life. 
 
 (618.) The teeth of the Crocodile, and of the higher Saurians 
 are not merely consolidated with the bones of the skull to which 
 they are appended, but are implanted in sockets formed in the 
 bones composing the upper and lower jaws. Each tooth is a 
 simple hollow cone, and encloses a vascular pulp, from the surface 
 of which the bony matter of the tooth was formed. When a tooth 
 becomes old and worn, a second is secreted by the same pulp 
 within, the cavity of the first, and the original one is shed, so 
 that a succession of teeth thus make their appearance. 
 
 (619.) The alimentary canal of Reptiles offers little that requires 
 special description. The oesophagus (Jig. 257,jf, f) is generally 
 extremely capacious, and the stomach of very variable shape and 
 capacity. The latter viscus is for the most part pyriform, tapering 
 gradually towards the pylorus ; such is the case in the CHELONIA 
 and in the BATRACOJD AMPHIBIA : in SERPENTS it resembles 
 a long bowel, and is capable of extraordinary dilatation ; and in the 
 PERENNIBRANCHIATE AMPHIBIA, as in the Proteus /?g.254,z) 
 and the Menopoma (Jig. 257, g), it looks like a mere dilatation of 
 the intestine. 
 
 The stomach of the Crocodile is remarkable as affording ano- 
 
562 
 
 REPT1LIA. 
 
 tlier among the innumerable instances that might be adduced of 
 that gradual transition everywhere observable as we pass from one 
 class of animals to Fig. 253. 
 
 that which next suc- 
 ceeds it in the series 
 of creation. The 
 Crocodile is the con- 
 necting link be- 
 tween REPTILES 
 and BIRDS, and in 
 almost every part of 
 its body it presents 
 a type of structure 
 almost intermediate 
 between the two. 
 
 The stomach of 
 this creature (Jig. 
 253) might in fact 
 be almost mistaken 
 for the gizzard of a 
 rapacious bird. The 
 oesophagus (c) terminates in a globular receptacle, the walls of 
 which are very muscular, and the muscular fibres (a) radiate from a 
 central tendon (b) precisely in the same manner as those of a bird. 
 The pyloric orifice is closely approximated to the termination of 
 the oesophagus, and the commencement of the duodenum dilated 
 into a round cavity (d) ; an arrangement which, as we shall see in 
 the next chapter, exactly resembles that met with in the feathered 
 tribes. 
 
 In the neighbourhood of the pylorus, the walls of the stomach in 
 all the REPTILIA become perceptibly thickened : the intestine is 
 generally short and usually divided into two portions, representing 
 the small intestines and the colon, the division between the two 
 being marked by a prominent valve analogous in function and posi- 
 tion to the ileo-colic valve in the human subject ; and sometimes, 
 moreover, as, for instance, in the Iguana, there is a distinct ceecum 
 developed at the commencement of the large intestine. 
 
 The auxiliary secretions subservient to digestion in the class 
 before us, are the Salivary, the Hepatic, and the Pancreatic. 
 
 (620.) The Salivary glands are of very peculiar construction.* 
 
 * Cuvier, Le9ons d'Anatomie Compare, torn. iii. p. 223. 
 
REPTILIA. 563 
 
 In theCHELONiAN,the SAURIAN, and tlieBATiiACHiAN orders, tlie 
 substance of the tongue seems to be principally made up of a thick 
 glandular mass, formed by a multitude of little tubes united at 
 their bases, but, becoming separate towards the surface of the 
 tongue, they give the whole organ a papillose or velvety appear- 
 ance. This glandular apparatus rests immediately on the muscles 
 of the tongue, and upon its sides a multitude of pores are visible 
 through which the salivary secretion exudes. 
 
 (621.) In the OPHIDIAN REPTILES, from the manner in which 
 they swallow their prey, the bulk of the tongue is necessarily re- 
 duced to the utmost extent ; the whole organ seems converted into 
 a slender bifid instrument of touch, and is covered with a delicate 
 membrane. Instead of the salivary apparatus described in the last 
 paragragh, two glandular organs (Jig. 251, s, ), placed immediately 
 beneath the skin of the gums, surround the margins both of the 
 upper and lower jaws ; and from these an abundant salivary secre- 
 tion is poured into the mouth, through orifices situated externally 
 to the bases of the teeth. 
 
 (622.) The Liver of Reptiles (Jig. 254, h) requires no parti- 
 cular description : its secretion, as well as that of the pancreas 
 (Jig. 254, o), is poured into the intestine in the usual manner at a 
 little distance from the pylorus. 
 
 (623.) The Spleen, and system of the Vena Porta^ are dis- 
 posed in the same manner as in other Vertebrata. The spleen 
 (Jig- 254, /) is generally more or less closely connected with the 
 stomach ; and the large vein derived from it, being joined by those 
 proceeding from the other viscera of the abdomen, forms the trunk 
 of the portal vein (wi), which soon divides again into numerous 
 branches that ramify in the substance of the liver. 
 
 (624.) The Lymphatic and Lacteal systems are very im- 
 portant parts of the economy of these creatures ; and, from the 
 large size of the absorbent vessels, their disposition is more easily 
 traced in the class before us than in any other. The principal 
 trunks surround the aorta and other large blood-vessels, and com- 
 municate very extensively with the veins in different parts of the 
 body. From the imperfect condition of the valves in their inte- 
 rior, the lacteals of many tribes may be readily injected from 
 trunk to branch ; and, when thus filled with mercury, they are 
 found to spread out between the coats of the intestines like a 
 dense network of silver. 
 
 2 o 2 
 
564 REPTILTA. 
 
 (625.) But the most remarkable circumstance connected with 
 the absorbents of this class of animals is the discovery, made by 
 Professor M tiller of Berlin,* of a system of lymphatic hearts 
 destined to propel the products of absorption from the chief lym- 
 phatic trunks into the veins. In the Frog four of these pulsating 
 cavities are easily displayed by simply raising the skin covering the 
 regions of the body where they are situated. The posterior pair 
 of hearts are appendages to the lymphatic trunks which convey 
 the absorbed fluids derived from the hinder extremities into the 
 ischiadic veins : they are situated on each side midway between the 
 extremity of the long bone which represents the os coccygis and 
 the hip-joint, and are placed immediately beneath the integument. 
 They each consist of a single cellular cavity, and pulsate regularly ; 
 but their pulsations are quite independent of those of the heart, 
 neither are the contractions of the two lymph-hearts synchronous 
 with each other. 
 
 Another pair of these contractile cavities is situated beneath the 
 posterior margin of the scapula close to the transverse process of 
 the third vertebra : this pair forces the contents of the lymphatics 
 of the anterior portions of the body into the jugular veins. 
 
 (626.) Fishes respire water by means of gills. Reptiles, 
 breathing a lighter medium, are provided with lungs, membra- 
 nous bags into which the external element is freely admitted, and 
 again expelled in a vitiated condition, its oxygen having been em- 
 ployed in renovating the blood which circulates in an exquisite 
 network of delicate vessels, that ramify in rich profusion over the 
 walls of the pulmonary chamber. 
 
 This important difference between Fishes and Reptiles as 
 relates to their mod^ of respiration would seem, at first sight, to 
 draw such a distinct line of demarcation between these two great 
 classes of Vertebrata that it would be impossible for the most 
 superficial zoologist to confound one with the other, or to be for 
 a single moment at a loss in attempting to assign to any creature 
 belonging to either of these divisions of the animal world its pro- 
 per position ; indeed, to mistake an air-breathing Reptile for a Fish 
 properly so called, would appear to be an error which the most 
 ignorant naturalist could hardly be in danger of committing. 
 
 We have, however, again and again had opportunities of observ- 
 ing how nearly animals of neighbouring classes approximate each 
 
 * V r ide Berlin Annals for 1832; and also Panizza, sopra il sistema linfatico dei Ret- 
 tili. Fol. Pav. 1833. 
 
HKPTILIA. 
 
 565 
 
 other, not only in their outward form, but in their anatomical con- 
 struction ; and, in considering this portion of our subject, we shall 
 have another most striking illustration of Fig. 254. 
 
 this great law in zoology. 
 
 The perfect and typical Reptile, as the 
 Lizard, the Tortoise, and the Serpent, 
 breathes air and air only, and is there- 
 fore only provided with lungs adapted to 
 this kind of respiration : but the Peren- 
 nibranchiate Amphibia, possessing both 
 lungs and gills, participate to a greater 
 or less degree in the characters of Fishes, 
 so that in some, as, for example, in the 
 Lepidosireu (Jig. 238), so near is the 
 approximation, that it becomes almost 
 impracticable for the most accomplished 
 anatomist precisely to determine whether 
 the animal ought rather to be called a 
 Reptile or a Fish ; and lastly, in the 
 Batrachian Amphibia, as we have al- 
 ready seen, we have the same animal 
 gradually changed from a Fish into a 
 complete and perfect Reptile. 
 
 In considering the apparatus provided 
 for circulation and respiration in the ani- 
 mals comprised in the class before us, we 
 shall therefore first describe the organiza- 
 tion of these viscera in Reptiles furnished 
 with lungs only ; secondly, of those hav- 
 ing permanent gills as well as lungs ; and 
 thirdly, the metamorphoses that take 
 place in the construction of the breath- 
 ing organs during the developement of 
 the lungs, and the obliteration of the 
 branchiae in those forms in which the 
 branchiae are not persistent. 
 
 (627.) The lungs of Reptiles are two 
 capacious membranous sacs occupying 
 a considerable portion of the visceral 
 cavity which, as there is no diaphragm as 
 yet developed, cannot properly be di- 
 
 
566 
 
 REPTILIA. 
 
 vided into thorax and abdomen, as it is in Mammalia. From 
 the internal surface of the walls of each lung membranous septa 
 project inwards, so as partially to divide the interior of the organ 
 into numerous polygonal cells, which are themselves subdivided 
 into smaller compartments in a similar manner. This structure is 
 well seen in the lung of the Tortoise (Jig. 255). 
 
 The pulmonary Fig. 255. 
 
 cells are most nume- 
 rous and complete 
 towards the anterior 
 extremity of the 
 lung, and it is here 
 that the pulmonary 
 vessels principally 
 ramify : towards the 
 hinder part of the 
 viscus the cells be- 
 come larger, and 
 the breathing sur- 
 face proportionately 
 less extensive, until 
 in some cases, as in 
 Serpents, the cells 
 being quite oblite- 
 rated, the lung ter- 
 minates posteriorly 
 in a simple mem- 
 branous bladder. 
 
 The air is brought 
 into the lungs 
 through a long tra- 
 chea composed, as 
 in other Vertebrata, 
 
 of a series of cartilaginous rings ; but there is this peculiarity in 
 the construction of the Reptile lung, the trachea never divides into 
 bronchial ramifications, but terminates abruptly by one or more 
 orifices, which open at once into the general pulmonary cavity. 
 
 It must be evident, from the whole construction of a lung of 
 this description, that, owing to the comparatively limited surface 
 that it presents internally, it is far less adapted efficiently to expose 
 the circulating fluid to the influence of the atmosphere than the 
 
REPTILIA. 567 
 
 more complex apparatus of Birds and Mammalia: the respiration 
 of Reptiles is consequently proportionately imperfect ; and hence 
 that coldness of their blood, and feebleness of muscular movement, 
 which are so characteristic of the entire class. 
 
 The air required for purifying the blood is, of course, conti- 
 nually changed ; being alternately takeu into the lungs, and again 
 expelled in a deteriorated condition, by a mechanism which will be 
 found to vary in different Reptiles in accordance with the peculia- 
 rities of their organization. No Reptile possesses a diaphragm, 
 and, being destitute of this important muscle, the movements 
 whereby inspiration and expiration are accomplished are, in such 
 genera as are furnished with moveable ribs, entirely dependent upon 
 the mobility of the framework of the chest : the dilatations and con- 
 tractions of the thorax consequent upon the alternate elevation and 
 depression of the ribs being sufficient to ensure the inhalation and 
 expulsion of air, such is the case in the Serpent and the Lizard. 
 
 In the AMPHIBIA, however, there are not even ribs developed, 
 or, if they exist at all, they are such mere rudiments as to be quite 
 useless as instruments of respiration ; and on the other hand, in 
 the CHELONIAN REPTILES, the large and expanded bones of the 
 thorax are so consolidated together, and so immoveably fixed to the 
 broad and osseous sternum, that respiration in the ordinary manner 
 F would be altogether impracticable. Under these circumstances, as 
 a compensation for the want of mobility in the chest, the os hyoides 
 and the muscles of the throat are converted into a kind of bellows, 
 by which the air is forced mechanically into the lungs, and they 
 are thus distended at pleasure. 
 
 Any one who watches a Frog or a Tortoise with a little attention 
 will at once understand the mechanism by which this is effected. 
 The mouth is kept closely shut ; and the nostrils, which open 
 immediately into its cavity, are each provided with a muscular 
 valve so disposed as freely to permit the entrance of air into the 
 mouth, but also effectually preventing its return by the same chan- 
 nel. By this arrangement the descent of the hyoid apparatus fills 
 the mouth with air ; and the subsequent contraction of the broad 
 muscles of the throat, the nostrils and the pharynx being of course 
 both closed, forces the air into the opening of the larynx, and 
 distends the lungs, from which it ig again expelled by the pressure 
 of the abdominal muscles. 
 
 The structure of the heart and the course of the circulation in 
 Reptiles afford interesting subjects for investigation. The heart 
 
568 
 
 REPTILIA. 
 
 consists of three cavities, namely, a strong and muscular ventricle 
 (Jig- 256, a), and two membranous and very capacious auricles, 
 both of which communicate by valvular openings with the ventri- 
 cular cavity. The right auricle (b) receives the venous blood from 
 all parts of the body through the venae cavse (/, o,j?), the termina- 
 tions of which are guarded by strong valves ; the left auricle (c) 
 is appropriated exclusively to the lungs, from which it receives arte- 
 rial blood through the pulmonary veins (w, m). It is obvious, 
 therefore, that the ventricle receives two kinds of blood from the 
 two auricles, venous blood from the systemic auricle, and arterial 
 blood from the pulmonic auricle ; and as the interior of the ventri- 
 cular cavity is crossed by innumerable column earner, giving it 
 almost a spungoid appearance, the vitiated and purified blood derived 
 from these two sources are more or less completely mixed together, 
 and blood only partially arterialized is distributed to the system. 
 
 Fig. 256. 
 
 Two sets of vessels take their origin from the single ventricle, 
 viz. the pulmonary and aortic. The pulmonary artery soon di- 
 vides into two trunks (/,/), one destined to each lung ; so that a 
 
KEPTILIA. 569 
 
 part of the impure blood expelled from the ventricle is at once 
 driven to the organs of respiration to be further oxygenized. The 
 aorta) immediately after its origin, likewise separates into two 
 trunks (d, e), the right and the left ; which, winding backwards, 
 ultimately join to form one great vessel (/), from which the arteries 
 of the viscera (i, A:), and those destined to the posterior parts of 
 the body, are given off. From the commencement of the right 
 aortic trunk a very large vessel is furnished, "which bifurcates to 
 form two arteria innominate (g*, g), from which the carotid and 
 subclavian arteries take their origin. 
 
 (628.) Although the above description refers more immediately 
 to the construction of the heart of the Tortoise, in all essential par- 
 ticulars it is equally applicable to all Reptiles of the Saurian, Che- 
 Ionian, and Ophidian orders ; and when we thus see that, in addition 
 to the comparatively imperfect condition of their lungs, the blood 
 which circulates through the body is in these creatures a mixed and 
 semi- venous fluid, we need not be surprised at the contrast which 
 they offer when compared with the hot-blooded and vigorous ani- 
 mals to be described in the subsequent chapters of this work. 
 
 Cuvier committed a serious error in describing the Batrachian 
 Reptiles as having a heart composed but of two cavities : our illus- 
 trious countryman John Hunter had already ascertained that, in 
 Frogs, Toads, and Salamanders, the heart possessed a pulmonary 
 as well as a systemic auricle ; and his observations have since been 
 abundantly confirmed by Dr. Davy, Dr. Martin St. Ange, and 
 Professor Owen. The pulmonic auricle in these creatures is in- 
 deed comparatively of small size ; but it exists as a perfectly distinct 
 chamber, and receives the blood from the lungs preparatory to its 
 admission into the common ventricle. 
 
 With regard to the use of the additional auricle in the Reptilia, 
 Professor Owen has well remarked,* that from the impediments which 
 frequently occur to a free and regular circulation of blood in these 
 cold-blooded and slow-breathing creatures, the venous side of the 
 heart is subject to great distension ; hence the large size of the auri- 
 cles, and of the sinus which receives the systemic veins, and also the 
 perfect developement of the valves intervening between the venae 
 cavse and the auricle, of which the Eustachian valve of the Mammi- 
 ferous heart still presents a rudiment. Had the pulmonary veins 
 terminated along with the systemic in the same cavity, their orifices 
 would have been subjected to the pressure of the accumulated con- 
 tents of that cavity, and there would have been a disproportionate 
 
 * Transactions of the Zoological Society of London, vol. i. p. 217. 
 
570 
 
 REPTILIA. 
 
 Fig. 257. 
 
 obstacle to the passage of the aerated blood into the ventricle. 
 This is obviated by providing the pulmonary veins with a distinct 
 receptacle, which is equally ready with the right auricle to render 
 its contents into the ventricle during the diastole of that cavity. 
 
 (629.) Passing from the consideration of the more perfect 
 Reptile circulation as it exists in those genera which in their 
 adult condition possess lungs only, to those which may pro- 
 perly be called Amphibious, and are provided with both lungs 
 and gills throughout the whole period of their lives, we must still 
 pause to notice one or two in- 
 termediate forms, which, not- 
 withstanding that they lose 
 their branchiae at an early 
 stage of their growth, are evi- 
 dently closely related to the 
 Perennibranchiata, as may be 
 gathered from the arrange- 
 ment which their blood-ves- 
 sels permanently exhibit ; 
 such is the Menopoma, or 
 Great South American Sala- 
 mander, an animal met with 
 in the rivers and lakes of the 
 South American continent. 
 In the annexed figure, taken 
 from the Catalogue of the 
 Hunterian Collection, the 
 principal vessels of this crea- 
 ture are delineated as seen 
 from the dorsal aspect. The 
 lower jaw (a) has been re- 
 moved from the head, so that 
 in the drawing are exposed 
 the cut edge of the masseter 
 muscle (6), the tongue (c), 
 and the opening of the larynx, 
 into which a bristle (d) has 
 been introduced, one end of 
 which is seen passing into the 
 cavity of the right lung : the 
 bag of the pharynx (/,/) has been left entire, and upon this the 
 
REPTILIA. 571 
 
 main vascular trunks are supported. From the heart, situated upon 
 the opposite side of the oesophagus, is given off a large vessel 
 representing the bulbus arteriosus of fishes, which terminates by 
 dividing into four branchial arteries ; but, as in the adult Meno- 
 poma there are no branchiae, these vessels (o, o, o) wind round each 
 side of the neck, and again unite into two trunks (r, r) which by 
 their union form the aorta (t, t). It will easily be perceived that 
 this arrangement is precisely that met with in fishes ; only that, as 
 there are here no gills intervening between the terminations of the 
 branchial arteries and the commencements of the branchial veins, 
 these vessels are immediately continuous with each other. Moreover, 
 from the lowest branchial arch (o) a pulmonary artery is given off, 
 which ramifies over the surface of the as yet rudimentary lung (e), 
 and thus gives rise to a distinct pulmonary circulation. 
 
 Having carefully considered the disposition of the vessels in the 
 Menopoma above described, the reader will be able to appreciate 
 the arrangement of the vascular system in those Amphibia which, 
 being provided both with gills and lungs through the whole of their 
 lives, literally combine the blood-vessels of a fish with those of an 
 air-breathing reptile. 
 
 In the PERENNIBRANCHIATA, as, for example, in the Proteus, 
 instead of the bulbus arteriosus being immediately continuous with 
 the aorta, as it is in the Menopoma, through the interposition of 
 the vessels o, o, o, (Jig. 257,) the blood derived from the heart 
 is obliged to pass more or less completely through gills appended 
 to the sides of the neck before it arrives in the vessels (r, r), 
 which may be said to represent the branchial veins of fishes. 
 
 The branchiae are either vascular tufts or pectiniform organs, 
 (fig. 258, b, b,) essentially analogous in structure to those of a fish. 
 The blood, however, which is propelled from the heart is not here 
 entirely venous, but consists of a mixed fluid, partially derived 
 from the systemic and p- lg , 253. 
 
 partially from the pul- 
 monary auricle, the two 
 having of course been 
 mingled together in the 
 common ventricle of the 
 tripartite heart. The con- 
 traction of the heart forces 
 
 the blood into the bulbus arteriosus, from which it is in great part 
 driven into the branchiae : arrived there, it passes along the great 
 
572 
 
 KEPTIL1A. 
 
 branchial artery (Jig.Q58, ), is made to circulate over the branchial 
 fringes (&), and, being again collected into the branchial vein (c), 
 in a purified condition, it is poured into those large trunks, the re- 
 presentatives of the vessels r, r, (Jig. 257,) which form the aorta. 
 
 But, besides the branchial circulation, these creatures likewise 
 possess lungs (Jig. 254, z 9 t), and a pulmonary circulation of 
 greater or less importance in different genera. Nevertheless, the 
 pulmonary artery is merely a small twig given off from the aortic 
 system of vessels, through which semi-arterial ized blood passes to 
 the lungs, to be returned in a still purer condition to the left 
 auricle of the heart. 
 
 (630.) If the student has fully comprehended the permanent 
 condition of the blood-vessels as it exists in the perfect Reptile 
 and in the Perennibranchiate Amphibian, he will have little 
 difficulty in understanding the changes which occur in the dis- 
 tribution of the vascular system during the metamorphosis of the 
 CADUCIBRANCHIATA. 
 
 In the Salamander, when the lungs begin to be developed and 
 are co-existent with the branchial apparatus, the arrangement of 
 the circulating system is precisely similar to that described as being 
 permanent in the Perennibranchiata ; as may be seen by a reference 
 to the appended diagram, which would equally illustrate the dis- 
 tribution of the blood-vessels in both cases. 
 
 In this early stage of the tadpole's life, the contraction of the 
 heart and bulbus arteriosus drives the greater part of the blood through 
 the branchial veins (Jig. 259, 
 a, a, a) to the gills, from which 
 it is returned in a purified con- 
 dition by the branchial veins 
 (f, y,y, ), which by their union 
 at length form the aorta, as 
 in fishes. At this period the 
 pulmonary artery (b), which is 
 very small in correspondence with 
 the as yet rudimentary condition 
 of the lungs, is merely a branch 
 derived from the aortic system, 
 and reinforced by a vessel (c) 
 given off from the bulbus arte- 
 riosus. The greater propor- 
 tion of the blood, therefore, 
 
 Fig. 259. 
 
REPTILIA. 573 
 
 evidently goes to the branchiae, and a very small part to the 
 lungs. 
 
 The reader must, however, here remark, that there are small 
 anastomosing vessels (e, e, e), uniting the branchial arteries with 
 the trunks of the branchial veins, and that these are situated 
 just at the roots of the gills, since these vessels become of the 
 utmost importance during the subsequent stages of the metamor- 
 phosis. 
 
 The branchise gradually become diminished in size, and a smaller 
 quantity of blood passes through them, and as this goes on the vessels 
 (a, a, a ; f,f->f) shrink in the same proportion. Meanwhile the 
 lungs are progressively more and more developed, and the pulmo- 
 nary artery (b) expands in an equal ratio. As the blood forces 
 its way with more difficulty through the branchise, the anastomos- 
 ing vessels (e, e, e) dilate, and a freer supply of blood is poured 
 into the pulmonary system ; until at last, when the lungs are fully 
 formed, and the branchial arteries (a, , a) and veins (/,/,/) 
 quite obliterated, all the blood necessarily passes immediately 
 through the anastomotic trunks (e, e, e), which of course then 
 represent the vessels (0,0, o) of the Menopoma (Jig- 257), and 
 the mode of respiration is thus completely converted from that 
 of a Fish into that of a true Reptile. 
 
 (631.) But, during the progress of these changes in the dispo- 
 sition of the vascular system, others not less wonderful take place 
 in the form and uses of the entire hyoid apparatus, and, in those 
 muscles of the throat which are connected with the function of 
 respiration. 
 
 The hyoid apparatus of the tadpole is, in fact, a very compli- 
 cated structure,* and, like that of the fish, supports the branchise, 
 and facilitates the entrance and expulsion of the water ; moreover, 
 by opening or closing at pleasure the communication which exists 
 through the branchial apertures between the mouth and the ex- 
 terior of the body, it thus allows air to be taken into the lungs at 
 pleasure. 
 
 The os hyoides of the tadpole, at an early period of its deve- 
 lopem en t, supports four branchial arches (Jig. 260, A, 1, 2, 3, 4), 
 which bound three branchial fissures, through which, as in a fish, 
 the water escapes from the mouth. The branchial arches 2 and 3 
 
 * Recherches anatomiques et physiologiques sur les organes transitoires et la meta- 
 morphose des Batraciens ; par J.G. Martin St. Ange. Annales des Sciences Naturelles, 
 vol. xxiv. 
 
574 
 
 REPTILIA. 
 
 are studded on eaeli side with cartilaginous points ; and the arches 
 1 and 4 have similar points on one side only, so that when the 
 arches are approximated, as they can be by an elaborate temporary 
 set of muscles provided for the purpose, the cartilaginous teeth 
 lock into each other so accurately, that the branchial fissures are 
 completely and firmly closed ; a provision which is evidently 
 indispensable, in order to allow the tadpole to fill its lungs with 
 air. 
 
 The above is the condition of the branchial portion of the hyoid 
 apparatus before the metamorphosis of the tadpole has made much 
 progress ; and from this time a series of changes begin of a most 
 curious and interesting description. 
 
 When the me- rig. 260. 
 
 tamorphosis has 
 commenced, the 
 os hyoides and 
 branchial arches 
 assume the ap- 
 pearance repre- 
 sented at Jig. 
 260, B. The 
 pieces 8 and 9 
 are no longer 
 both cartilagi- 
 nous, the latter 
 having become 
 entirely ossified. The branchial arch 1 is likewise converted into 
 bone ; and its upper surface, being considerably enlarged, is now 
 connected with both the pieces marked 10 and 11. The three 
 cartilaginous pieces 5, 6, 7, in Jig. 260, A, are consolidated into 
 one, while the branchial arches 2, 3, 4, become much reduced in 
 size, the branchiae approach each other, and the cartilaginous points 
 with which they are provided adhere together, so that from hour to 
 hour, so to speak, the mass (2, 3, 4) composed of the three united 
 branchial arches becomes insensibly obliterated, and in a very few 
 days is entirely absorbed. While this absorption is going on, the 
 branchial arch 1 assumes greater consistency, its inferior extremity 
 becomes directed outwards, and it loses the little cartilaginous 
 teeth previously appended to it ; the os hyoides thus assumes the 
 simple form represented in Jig. 260, c. Lastly, the cartilage 6 
 disappears, and the complex branchial apparatus of the tadpole be- 
 
REPTILIA. 
 
 575 
 
 Fir.261. 
 
 comes converted into the permanent and comparatively simple os 
 hyoides of the Salamander, depicted in Jig. 260, D. 
 
 The branchial arches 2, 3, 4, Dr. St. Ange remarks, are ab- 
 sorbed in proportion as the circulation becomes modified, their 
 atrophy depending upon the change which takes place in the 
 course of the blood, owing to the dilatation of the anastomotic ves- 
 sels (Jig. 259, e, e, e), and the enlargement of the pulmonary arte- 
 ries (b). It is, therefore, owing to a kind of revulsion produced 
 by the afflux of the blood towards the pulmonary organ, instead of 
 towards the branchiae, that the atrophy of the branchial capillaries, 
 and subsequently of the whole branchial apparatus, is produced. 
 
 (632.) We must, 
 in the last place, before 
 leaving the considera- 
 tion of the circulating 
 system of the REP- 
 TILIA, describe that of 
 the Lepidosiren, a crea- 
 ture so exactly interme- 
 diate between the two 
 classes, that it is really 
 difficult to determine 
 whether it ought most 
 properly to be called 
 a fish provided with 
 lungs, or a reptile with 
 the circulatory organs 
 of a fish. 
 
 The heart resembles 
 that of a fish, and con- 
 sists of a single auricle 
 (fg. 261, a), a ventri- 
 cle (6), and bulbus 
 arteriosus (c). The 
 vena cava (e), bringing 
 the vitiated blood from 
 the system, terminates 
 
 at once in the auricle, which is represented in the figure as laid 
 open ; but the pulmonary vein (/), whereby the aerated blood 
 is brought from the lungs (w, m), passes along as far as the 
 auriculo-ventricular opening, where it empties its contents into the 
 
576 KEPT ILIA. 
 
 ventricle by a distinct orifice, protected by a cartilaginous valvular 
 tubercle. 
 
 It is, therefore, only necessary in this case to dilate the pulmo- 
 nary vein previous to its termination, to make a heart with two 
 auricles ; but, as Professor Owen observes, the same advantage is 
 secured to the Lepidosiren in a different manner, for, while it still 
 retains the diccelous type of the heart of the fish, the continuation 
 of the pulmonary vein prevents the admixture of the respired with 
 the venous blood until both have arrived in the ventricle. 
 
 The aorta, or rather the bulbus arteriosus (g), in this interesting 
 creature, fulfils at once the office of a systemic, a branchial, and a 
 pulmonary artery. It gives off on each side six vessels, which 
 correspond to the six cartilaginous branchial arches : of these arches 
 four, namely, the 1st, 4th, 5th, and 6th, support gills, so that 
 the arteries belonging to them (1, 4, 5, 6) are, as in fishes, 
 distributed over the branchial fringes, and are thus true or func- 
 tional branchial vessels. But the 2nd and 3d arches have no gills 
 appended to them, so that the arteries (2, 3) belonging to these 
 arches do not divide, but are continued round to the dorsal region, 
 where they unite to form an aorta, as in Menopoma (Jig. 257) ; 
 moreover, before their union to form the systemic trunk, they give 
 off the pulmonary arteries (/, m) by which the pulmonary circula- 
 tion is supplied. Thus each contraction of the ventricle of the 
 heart drives the mixed blood derived from the verise cavse and 
 pulmonary veins, first, to the gills ; secondly, to the aorta, through 
 the vascular trunks (2, 3) ; and, thirdly, to the lungs through the 
 pulmonary artery (/, m) ; so that from this arrangement, whether 
 the creature be placed in water or in air, respiration is carried on 
 efficaciously either by the pulmonary or branchial apparatus vica- 
 riously. 
 
 (633.) The principal difference observable between the brain 
 of Reptiles and of Fishes, is the increased proportionate size of 
 the cerebral hemispheres (Jig. 261, 5), but they are still ex- 
 tremely small when compared with the bulk of the body. The 
 appended figure, which represents the brain of the Tortoise in 
 three different aspects, may easily be compared with that of the 
 fish already given. The olfactory lobes (c) might now be mis- 
 taken -for prolongations of the anterior extremity of the hemi- 
 spheres ; they contain distinct ventricles, and of course give origin 
 to the olfactory nerves (o, o). The hemispheres (b) are much 
 more developed than in the last class ; their surface is always 
 
KEPTILIA. 
 
 577 
 
 smooth and without convolutions; and they are hollowed out into 
 capacious ventricular chambers, in which are contained the corpus 
 striatum and choroid plexus (j#g. 262, c), and the two sides are 
 moreover brought into communication by an anterior and posterior 
 commissure. 
 
 The optic lobes (e) are as yet uncovered by the extension of 
 the hemisphere backwards ; and each, when laid open, is found to 
 enclose a ventricle {Jig. 262, c). The cerebellum (a) is still 
 small, and consists but of the median portion : behind it is a sup- 
 plementary lobe (g), extending over the fourth ventricle, as in 
 Fishes. The student will easily recognise the pituitary body (f) ; 
 but neither this, nor the origins of the nerves, present any pecu- 
 liarity worthy of more particular description. 
 
 Fig. 262. 
 
 Taking the cerebral nerves in the order in which they arise, we 
 will now proceed briefly to trace their general distribution ; and 
 this we shall find to correspond most exactly in all essential points 
 throughout the different classes of Vertebrata. 
 
 The olfactory nerves leave the olfactory lobes of the brain as 
 single round cords ; and are not, as in the Mammalia, divided into 
 
 2 p 
 
578 REPTILIA. 
 
 numerous filaments : there is, consequently, no cribriform plate to 
 the ethmoid bone ; but the nerve of each side (Jig. 264, e) 
 is received into a simple canal, partly osseous and partly car- 
 tilaginous, through which it is conducted to the cavity of the 
 nose. 
 
 The nasal apparatus of Reptiles differs from that of Fishes in 
 one important particular. Breathing air as these creatures do, 
 the sense of smell now becomes connected with the respiratory 
 function; and, a communication being established between the 
 nasal cavities and the larynx, the air which passes through this 
 channel into the lungs must necessarily come in contact with 
 the sentient surface formed by those portions of the lining mem- 
 brane of the nose to which the nerves of smell are distributed; 
 and, in proportion as the extent of that surface becomes developed, 
 the power of appreciating the presence of odorous particles in 
 the atmosphere will necessarily be increased. The physiologist 
 is thus enabled to estimate with great exactness the relative per- 
 fection of the sense of smell in different classes, or even in dif- 
 ferent families of the air-breathing Vertebrata, simply by observing 
 the complication and extent of surface presented by the lining 
 membrane of the olfactory organ. 
 
 Taking this as our guide, we must suppose that in all Rep- 
 tiles the sense in question is extremely obtuse, since in these 
 creatures there are neither turbinated bones nor ethmoidal plates 
 as yet distinguishable ; a few folds of the membrane lining the 
 nose, even in those species which are most highly gifted in 
 this particular, being the only provision for extending the olfac- 
 tory surface ; and in many cases, as for example in the Am- 
 phibia, the nose seems merely a simple canal leading into the 
 mouth. 
 
 On reaching the nasal cavity, the olfactory nerve spreads out 
 into delicate filaments (Jig. 264, d), which are distributed to the 
 Schneiderean membrane covering the septum and upper part of 
 the nose. 
 
 (634.) The optic nerves of Reptiles (Jig. 262, n), soon after 
 their origin, become confounded together by a commissure, in 
 the same way as in the human subject; and, again separating, they 
 are continued through the optic foramina to the eyes. 
 
 The eye-ball itself presents few peculiarities in its structure. 
 In the Tortoise, and many Lizards, the sclerotic contains a circle 
 of bony plates imbedded in its substance, and surrounding its 
 
REPTILIA. 579 
 
 anterior margin : these are obviously the rudiments of that os- 
 seous zone which in the class of Birds, as we shall find, performs 
 a very important office. The ciliary processes of the choroid 
 are generally very feebly developed. The pupil is frequently 
 round, but it is sometimes of a rhomboidal figure, as for example 
 in the Gecko ; and in the Crocodile and some serpents the pupil- 
 lary aperture is a vertical fissure like that of a Cat. 
 
 The optic nerve enters the eye in the same way as in qua- 
 drupeds, and, having passed the choroid, it terminates in a round 
 papilla, from the margin of which the retina spreads out : as to 
 the rest, the eye of a Reptile differs so little in any essential cir- 
 cumstance from that of Man as to render any more elaborate 
 description superfluous. 
 
 The eye-ball is moved by six muscles, disposed as in Fishes ; the 
 four recti arising from the margin of the optic foramen, while the 
 two obliqui are derived from its anterior margin. 
 
 In Fishes, from the circumstances under which they live, there 
 is no occasion for the presence of any lacrymal apparatus, or for 
 eyelids adapted to defend and moisten the surface of the cornea ; 
 but in the class before us, especially in the more elevated tribes, 
 these appendages to the eye make their appearance, and gradually 
 assume a complexity of structure even greater than that which they 
 present in the human subject. 
 
 In Serpents, and in some of those Lizards which are most 
 nearly allied to the Ophidians, there are still no eyelids ; and con- 
 sequently in such genera there can be neither any lacrymal appa- 
 ratus, nor a conjunctiva, properly so called : the skin of the head 
 merely passes like a delicate film over the transparent cornea, 
 offering no fold worthy of the name of an eyelid. 
 
 In ordinary Lizards* the skin forms a kind of veil stretched 
 over the orbit, and pierced by a horizontal fissure, which is closed 
 by a sphincter muscle. The lower eyelid is the most moveable, 
 and encloses a small cartilaginous plate; and there is besides ge- 
 nerally a fold of the conjunctiva at the inner canthus of the 
 eye, which is the first appearance of a third eyelid or membrana 
 nictitans. 
 
 In the Chelonian Reptiles, and in the Crocodiles, the upper 
 and lower eyelids are sufficiently perfect accurately to close the 
 eye ; but there are no eyelashes as yet present. Moreover, these 
 
 * Cuv. Le9<>ns d'Anat. Comp. vol. ii. p. 433. 
 
580 REPTILIA. 
 
 animals possess an additional eyelid or nictitating membrane, si- 
 milar to that of Birds, which can be drawn at pleasure over the 
 front of the eye, so as entirely to conceal it. This is effected 
 by a special muscle provided for the purpose, which arises from the 
 posterior part of the globe of the eye, and, after winding round the 
 optic nerve, passes beneath the eye-ball, to be inserted into the 
 free margin of the membrana nictitans. In Frogs and Toads 
 the upper and lower eyelids are nearly motionless ; but the third 
 is largely developed, and moved in the same way as that of the 
 Crocodile. 
 
 In the higher Reptilia a distinct lacrymal gland and puncta 
 lacrymalia are met with, occupying the same positions as those of 
 the human subject. 
 
 (635.) The third, fourth, and sixth pairs of the cerebral nerves, 
 have the same distribution in all the Vertebrata; and represent 
 respectively the oculo-muscular, the pathetici, and the abducentes 
 of man. 
 
 (636.) The nerves belonging to the fifth pair likewise corre- 
 spond both in their distribution and office with the trifacial nerves 
 of mammiferous Vertebrata. 
 
 (637.) The facial nerve, or portio dura of the seventh pair, 
 is small in proportion to the limited developement of the soft 
 parts of the face ; but it is constantly present. 
 
 (638.) The auditory nerve of course is destined to the ear, 
 and its distribution is almost the same as in Fishes ; nevertheless, 
 in the general construction of the organ of hearing, Reptiles present 
 very important and interesting advances towards a higher form of 
 the acoustic apparatus, which we must proceed to notice. 
 
 The ear of Fishes, being only adapted to hear sounds conveyed 
 through a watery medium, was found to consist only of the mem- 
 branous labyrinth, enclosed in the cavity of the skull, and without 
 any communication with the exterior of the body. Reptiles, on 
 the contrary, living in air, must be enabled to appreciate the sono- 
 rous vibrations of the atmosphere, and are consequently provided 
 with an auditory apparatus, capable of responding to pulsations of 
 sound of far greater delicacy than those transmitted through the 
 denser element. 
 
 The first great improvement therefore which the anatomist 
 notices in the composition of the ear of a Reptile, is the addition 
 of a tympanic cavity, and of a tense and delicate membranous 
 drum, the vibrations of which are communicated to the labyrinth 
 
REPTILIA, 
 
 581 
 
 or internal ear through the intervention of an ossicle that represents 
 the stapes of Mammalia. 
 
 The drum of the ear is situated immediately beneath the skin, 
 the parts composing 
 
 the external ear of Fig. 263. 
 
 quadrupeds being as 
 yet entirely deficient. 
 The membrana tym- 
 pani, that now for 
 the first time makes 
 its appearance in the 
 series of animals, is 
 tensely stretched across 
 the tympanic aperture; 
 being covered exter- 
 nally by the integu- 
 ment of the head. In 
 the Turtle (Jig. 263) 
 the tympanic mem- 
 brane is represented by a cartilaginous plate (a). The ossicle, or 
 columnella as it is here called, is single and trumpet-shaped : it 
 passes quite across the tympanic cavity (b), its external extremity 
 being inserted into the drum ; while at its opposite end it expands 
 into a disc (c), which closes an aperture (foramen ovale) that com- 
 municates with the membranous vestibule of the internal ear. It 
 is obvious therefore that every tremor impressed upon the mem- 
 Irana tympani will be conveyed by the columnella to the fora- 
 men ovale, and thus communicated to the fluid contained in the 
 labyrinth, upon which, as in Fishes, the auditory nerve is dis- 
 tributed. 
 
 The cavity of the tympanum communicates with the interior 
 of the mouth by a wide opening, that represents the Eustachian 
 tube ; a circumstance evidently intended to prevent air or fluid 
 from being pent up in the tympanic chamber, and thus interfering 
 with the free vibration of the drum. 
 
 In Serpents, on account of the peculiar disposition of the 
 pieces of the temporal bone before described (J 606), there is no 
 tympanic cavity, and the columnella (Jig. 249, v) is absolutely im- 
 bedded in the flesh ; the arrangement, however, in other respects is 
 the same as in the generality of Reptiles. 
 
 The lower tribes of Amphibia, as we might be led to expect 
 
582 REPTJLIA. 
 
 from their close approximation to Fishes, have neither tympanum 
 nor columnella ; and thus, like Fishes, can only hear in an aquatic 
 medium. 
 
 (639.) The membranous labyrinth of Reptiles (jig> 264, #, &, c) 
 corresponds in its general conformation with that of Fishes, pre- 
 senting the same semicircular canals, ampullse,and vestibular cavity ; 
 
 Fig. 264. 
 
 and moreover, the sacculus contains cretaceous concretions, or oto- 
 lithes of a similar character. But in this class the membranous 
 canals become enclosed in a bony sheath, moulded as it were upon 
 their outer surface ; which is another very important step towards 
 perfecting the auditory apparatus. 
 
 (640.) Neither must we omit to mention, that in the highest 
 of the Reptilia, as for example in the Crocodile, the first rudiment 
 of a cochlea makes its appearance, although as yet in a form of 
 extreme simplicity. This portion of the organ of hearing, which, 
 from the elaborate structure that it presents in the higher Verte- 
 brata, must be regarded as being importantly connected with cor- 
 rect audition, is seen in this, the earliest stage of its developement, 
 to be a simple conical appendage to the sac of the vestibule ; and, 
 on opening it, it is found to be divided by a central cartilaginous 
 septum into two compartments, which are however continuous 
 with each other at the apex of the cone. One of these com- 
 partments or canals opens at one extremity into the vestibule, 
 while the other communicates with the tympanic cavity by a 
 very small aperture closed with a thin membrane. Thus, there- 
 fore, although the entire organ resembles a simple canal bent 
 
REPTILIA. 
 
 583 
 
 upon itself, the representatives of the scala vestibuli, of the scala 
 tympani, and of iliefenestra rotunda of the human ear can be dis- 
 tinctly identified. 
 
 (641.) The glosso-pharyngeal and pneumogastric nerves in Rep- 
 tiles supply the same or- Fig. 265. 
 gans to which they are dis- 
 tributed in the human sub- 
 ject ; the former being 
 destined to the base of the 
 tongue and the muscles of 
 the pharynx; while the lat- 
 ter, assuming a plexiform 
 arrangement, are appro- 
 priated to the lungs and 
 heart, as well as to the 
 oesophagus and the sto- 
 mach. 
 
 (642.) The hypoglossal 
 pair of the cerebral nerves, 
 which was not met with in 
 Fishes, now becomes dis- 
 tinctly apparent ; and, as 
 in the higher Vertebrata, 
 may be traced in the mus- 
 cles of the tongue. 
 
 (643.) The spinal system 
 of nerves offers no peculia- 
 rity worthy of special de- 
 scription. In the annexed 
 figure, taken from Boja- 
 nus, the nerves derived 
 from the medulla spinalis 
 are seen to issue in the 
 usual manner from the 
 intervertebral foramina ; 
 and they evidently essen- 
 tially correspond with the 
 grand type of structure 
 common to the vertebrate classes. In the apodous Reptilia, as 
 for example in the Serpents, to attempt to divide them into the 
 usual regions is clearly absurd ; but in quadrupedal forms, as 
 
584 
 
 REPTILIA. 
 
 for instance in the Tortoise, the cervical nerves, the brachial 
 plexus, from which are derived the nerves of the anterior extre- 
 mity, the intercostal nerves, and those forming the lumbar and 
 sacral plexuses, are at once distinguishable ; and the correspond- 
 ence between their distribution in the reptile and in the human 
 subject must forcibly strike the student who makes the com- 
 parison. 
 
 (644.) Neither does the sympathetic system of the Reptilla offer 
 any important aberration from that arrangement with which the 
 human anatomist is familiar. The ganglia are smaller in their pro- 
 portionate size; those of the neck and face are, indeed, scarcely per- 
 ceptible : but the thoracic ganglia are found in their usual positions, 
 communicating on the one hand with the spinal nerves, and on the 
 other giving off filaments which form plexuses around the arterial 
 trunks, and ramify extensively to be distributed to the viscera of 
 organic life. 
 
 (645.) The sense of touch in all the members of the class under 
 consideration must, from the nature of their integument, be extremely 
 imperfect : many of them, as for example the Serpent tribes, are, 
 in fact, absolutely deprived of any limbs which can be regarded as 
 tactile organs ; and, even in those forms which are provided with 
 efficient locomotive extremities, they are but ill adapted to exercise 
 the functions of an apparatus of touch. 
 
 The cuticular investments of the body are formed of dense and 
 unyielding materials, consisting, in the higher Reptiles, of broad 
 horny plates, or of imbricated scales. In the Amphibia, indeed, 
 the skin is smooth, and the epidermis only forms a delicate cor- 
 neous film ; yet even in these the cuticle is thrown off at certain 
 seasons of the year, as the old coat becomes too small for the in- 
 creasing size of the animal: a phenomenon which in the Lizard and 
 Serpent tribes is still more remarkably witnessed ; for these animals 
 strip themselves of their old scales as the hand would be drawn out 
 of a glove, and cast away in one piece the entire epidermic inte-. 
 gument, even to the film which covers the transparent cornea of 
 the eye. 
 
 (646.) The urinary excretion in Reptiles becomes of very consi- 
 derable importance, and the structure of the kidneys and excretory 
 ducts proportionately elaborate. The kidneys (fig- 267, o, p) are 
 generally situated very far back, even within the cavity of the pelvis 
 where a sacrum exists, as in the Chelonian and Saurian orders ; and 
 in these tribes they are very partially covered by the peritoneum 
 
REPTILIA. 585 
 
 being firmly imbedded in the sacral region. But in the Serpents, in 
 consequence of the elongated form of the body, and the complete 
 flexibility of every portion of the spine, the kidneys are peculiar 
 both in their position and general structure. Instead of being 
 placed upon the same level as in other Vertebrata, the right kidney 
 of an Ophidian is situated much more anteriorly than the left ; a 
 circumstance which much facilitates the packing of the abdominal 
 viscera, and contributes greatly to ensure the free movements of 
 the vertebral column at this place. For the same reason, the 
 kidneys of a serpent are divided into numerous lobes, placed in a 
 longitudinal series upon the outer side of the commencement of the 
 ureter, and loosely connected to each other and to the spine by 
 cellular tissue and a fold of the peritoneum. 
 
 As relates to the minute structure of the kidneys in the Rep- 
 tilia, these viscera are invariably composed of convoluted tubes, 
 which pour their secretion into the commencement of the cor- 
 responding ureter. The ureters of course vary in length accord- 
 ing to the position of the renal organs ; they ultimately terminate 
 in the cloaca (Jig. 267, u) ; a cavity or general outlet through 
 which, in the female, the ova, the fseces, and the urine are dis- 
 charged, and which in the male gives passage to the contents of 
 the rectum, the secretion of the kidneys, and the semen. 
 
 (647.) In connection with the urinary apparatus of Reptiles, it 
 will be convenient to mention a bladder that exists in Chelonian 
 and Amphibious Reptiles, and is also found in some Saurian tribes, 
 to which the name " urinary bladder"" has been erroneously applied. 
 This bladder, in the Tortoise (Jig. 267, A) and Proteus (Jig. 
 254, q) is of considerable size, and in the Frog forms a very capa- 
 cious receptacle, having its upper part divided into two cornua. 
 It is generally filled with a clear limpid fluid, which in the case of 
 the Frog is forcibly ejected if the animal be alarmed : but that this 
 fluid is not urine is obvious from the fact already stated, that the 
 ureters open into the cloaca (Jig. 267, u), and not into the bag 
 referred to ; the latter, in fact, is the unobliterated remains of the 
 ALLANTOIS of the embryo, concerning which further particulars 
 will be given in the next chapter, and the fluid contained in it is 
 most probably the product of cutaneous absorption.* 
 
 (648.) In tracing the developement of the generative apparatus 
 
 * Vide Cyclopaedia of Anatomy and Physic, art. AMPHIBIA, by Professor Bell, 
 p. 104. 
 
586 EEPTILIA. 
 
 through the different orders of Reptiles, the student will not fail to 
 observe many beautiful illustrations of progressive improvement. 
 
 The finny tribes, incapable of social intercourse, were content 
 with the simple extrusion of their eggs into the sea, leaving them 
 to be impregnated by the casual approach of a male of the same 
 species : but even in the Amphibious Reptiles some steps are 
 gained in associating the sexes with each other ; and although the 
 eggs are still impregnated out of the body of the mother, in the 
 Frog this is accomplished in exitu, and not subsequent to their 
 expulsion. 
 
 Frogs, during the breeding season, are found to pair, and the 
 male having selected his mate mounts upon her back, clinging to 
 her with unwearying pertinacity during the whole period of 
 oviposition, and vivifying her eggs by the aspersion of the seminal 
 secretion as they are successively expelled in long gelatinous chains. 
 During this protracted embrace the male Frog is assisted in 
 retaining his hold by the developement of a peculiar papillose 
 structure upon the first toes of the fore-feet, which disappears at 
 the end of the time appropriated to reproduction. Of course no 
 intromittent apparatus is as yet required, and we may naturally 
 expect to find the male organs still exhibiting great simplicity of 
 construction. 
 
 (649.) The testes and their excretory ducts are, in fact, the only 
 parts as yet met with ; but the anatomy of these parts, although most 
 accurately investigated by Swammerdam upwards of a century ago, 
 is still very generally misunderstood. The testicles are situated 
 in the loins, surrounded by several tongue-like masses of fat, pre- 
 senting a peculiar granulated appearance. Each testis is invested 
 by a delicate capsule, and, on removing this very carefully, the 
 entire viscus is seen to be made up of short caeca ; the blind 
 extremities of which alone appearing at the periphery of the 
 organ caused Cuvier to describe it as being " an agglomeration of 
 little whitish grains interwoven with blood-vessels." The semen 
 elaborated by these caeca is taken up by several small excretory 
 ducts that pierce the kidney, in the immediate vicinity of which 
 the testis lies, and open into the ureter, that here forms the com- 
 mon excretory duct, whereby the urine as well as the seminal fluid 
 is discharged, both escaping into the cloaca at a little distance from 
 the orifice of the allantoid bladder, to be ultimately ejected through 
 the vent. 
 
 (650.) Neither is the generative system of the female Frog less 
 
EEPTILIA. 587 
 
 worthy of notice. The ovaria resemble in their essential structure 
 those of the Lamprey ( 580), only they are much less extensive ; 
 consisting of a few festoons of the highly vascular membrane 
 wherein the ova are secreted, fixed at the pelvic extremity of the 
 abdominal cavity. On each side of the body is a long and very 
 tortuous oviduct, which when unravelled is found to be many times 
 the length of the animal. The fimbriated commencement of this 
 oviduct is firmly bound down by folds of peritoneum in the imme- 
 diate vicinity of the pericardium, and, of course, as remote as 
 possible from the ovary ; it therefore becomes a question of no 
 inconsiderable interest to determine the manner in which the ova 
 are conveyed from the ovarian nidus to the orifice of the oviduct : it 
 is obvious that they must first break loose into the abdominal cavity, 
 as we found them to do in the Lamprey and the Eel, and that at 
 length, having made their way into the neighbourhood of the 
 pericardium, they are seized by the patulous extremity of the 
 Fallopian tube, and thus conveyed out of the body. As the ova 
 make their transit through the oviduct, they become imbedded in a 
 tenacious albuminous secretion, "and are at length lodged in a dilated 
 portion of the tube, to which the name of uterus has been very im- 
 properly given, preparatory to their expulsion through the cloaca. 
 After the eggs have been discharged into the surrounding water, the 
 albuminous mass in which they are imbedded swells considerably; 
 and, when the young tadpoles are hatched, this material no doubt 
 serves to nourish them during the earlier period of their existence. 
 (651.) In the Newt (Triton) impregnation takes place internally, 
 although the male is still without any rudiment of an intromittent 
 apparatus, so that we are compelled to believe that in the case of 
 these Amphibia the simple ejection of the male fluid into the water 
 in the vicinity of the female is sufficient to ensure its admission to 
 the ova while still in the oviduct. An improvement is likewise 
 visible in the construction of the internal viscera subservient to 
 generation ; and a vas deferens, quite distinct from the ureter, makes 
 its appearance. In the male Salamander (Triton cristatus) the 
 testis -during the breeding season consists of two pyriform masses, 
 from which the seminal ducts (Jig* 266, c, c) are derived. These 
 soon unite to form a single convoluted tube (d), through which the 
 semen is conveyed into the cloaca. The kidneys (w), and their 
 excretory ducts (i 9 i), are here placed considerably further back ; 
 but the ureters terminate in the cloaca at the same point (m) 
 as the vasa deferentia. Two other large glands (o, o) are appa- 
 
588 
 
 REPTILIA. 
 
 rently connected with the generative functions, and their excretory 
 ducts likewise open into the cloacal outlet. 
 
 (652.) In the female Triton, as Fi s> 266. 
 
 also in the Proteus and Siren, the 
 ovaria and oviducts offer precisely 
 the same arrangement as that met 
 with in the Frog already de- 
 scribed.* 
 
 (653.) In the Ophidian, Chelo- 
 nian, and Saurian orders, the testes 
 of the male sex are situated in the 
 loins ; and, in fact, they occupy 
 the same position throughout the 
 oviparous Vertebrata : they offer 
 no peculiarity of structure ; only 
 differing from those of the Frog 
 in the increased length of the now 
 contorted seminal cseca of which 
 they are essentially composed. 
 From each testis a long and flexu- 
 ous vas deferens conducts the se- 
 men into the cloaca. Here, how- 
 ever, in these more elevated forms 
 of theReptilia,we have another im- 
 portant addition to the male sexual 
 apparatus ; instruments beinggiven 
 to facilitate the impregnation of 
 the female during that union of the sexes which now becomes es- 
 sential to fecundity. The earliest appearance of the copulatory 
 organ is seen in Serpents and in the Lizard tribes ; and in such rep- 
 tiles it will be observed, that the penis is rather a provision for 
 securing the juxta-position of the sexual apertures of the male and 
 female than an instrument of intromission. The two lateral halves 
 of the penis, or corpora cavernosa, as we shall have to call them 
 hereafter when they become conjoined in the mesial line, are as yet 
 quite separate, and placed at each side of the cloacal fissure, from 
 which they protrude when in a state of erection ; so that there ap- 
 pear to be two distinct organs of excitement, or, more properly 
 speaking, of prehension ; for each division, being of course im- 
 
 * Vide Rusconi. Observations Anatomiques sur la Sirene mise en parallele avec Je 
 Protee et le tetard de la Salamandre Aquatique. A Pavie, 1837. 
 
RErTTMA. 589 
 
 perforate, is covered with sharp spines, and is obviously rather 
 adapted to take firm hold of the cloaca of the female than to form 
 a channel for the introduction of the seminal fluid. 
 
 (654.) In the Chelonian Reptiles the penis is much more perfectly 
 developed, and really constitutes a very efficient intromittent in- 
 strument. The two corpora cavernosa, after commencing separately, 
 approach each other, and become united along the mesial line so as 
 to form a single organ of considerable size, terminated at its ex- 
 tremity by a glans-like dilatation. There is, however, no corpus 
 spongiosum, or urethral canal, properly so called : the latter is re- 
 presented by a deep groove, which runs along the upper surface of 
 the penis from the cloaca to the extremity of the organ ; and it is 
 along this groove that the spermatic fluid is conveyed during coitus. 
 
 On making a section of this strange apparatus, two canals are dis- 
 covered, running one on each side of the central furrow, along the 
 whole length of the organ as far as the glans, where they terminate, 
 without at all communicating with the exterior ; but, on tracing 
 them in the opposite direction, they are found to be derived from 
 the peritoneal cavity, into which they open by distinct orifices.* 
 
 Two retractor muscles, derived from the pelvis, and extending 
 along the under surface of the penis quite to its extremity, fold the 
 whole organ back into the cloaca, where it lies concealed when not 
 in use. 
 
 In the Crocodiles and higher Saurians the penis in its structure 
 resembles that of the Tortoise ; and, instead of an urethra, there is 
 merely a deep groove traversing the upper surface of the organ, 
 along which the semen trickles out of the cloaca. 
 
 (655.) Throughout all the Reptile families the organization of the 
 female generative system is so extremely similar, that one example 
 will be abundantly sufficient for our purpose ; the same description 
 in fact being equally applicable to the Saurian, the Chelonian, and 
 the Ophidian orders. The ovaries occupy their ordinary position 
 in the lumbar region of the abdomen, where they are attached on 
 each side of the vertebral column by a broad fold of peritoneum : 
 their structure is in all essential pojnts precisely similar to those of 
 the Amphibia ; but, owing to the increased proportionate size of the 
 individual ova formed by their vascular membrane, they resemble a 
 string of beads, or assume somewhat of a racemose appearance. 
 The oviducts are long and flexuous ; they commence by a wide 
 orifice {Jig. 267, b M), by which the germs are taken up from the 
 * Cuv. Anat. Comp. torn. v. p. 115. 
 
590 
 
 REPTILIA. 
 
 ruptured ovisacs of the ovaria in the same way as those of Mam- 
 malia are seized by the fimbriated extremities of the Fallopian 
 tubes. The first portion of the Fig. 267. 
 
 oviduct is thin and intestini- 
 form; but lower down, where the 
 investments of the egg are form- 
 ed, its walls become thicker, and 
 assume a glandular character 
 (n> o, p) : they finally open into 
 the cloaca; and the mode of their 
 termination in the Tortoise is ex- 
 hibited in the accompanying fi- 
 gure, where (M, m, e M) indicate 
 the terminal portion of the right 
 oviduct laid open ; the left (a M, 
 b M) being shown through its 
 entire length. 
 
 (656.) The formation of the 
 egg and the developementof the 
 embryo is similar in all the ovi- 
 parous Vertebrata ; it will there- 
 fore be more convenient, and 
 prevent unnecessary repetition, 
 if we defer the consideration of 
 this important subject to the 
 
 next chapter ; the reader bearing in mind that in all essential par- 
 ticulars the details which will be given there, when we come to 
 consider the growth of the bird in ovo, are equally applicable to 
 the Chelonian, Ophidian, and Saurian Reptiles. 
 
591 
 
 CHAPTER XXIX. 
 
 AVES BIRDS. 
 
 (657.) THE class of Vertebrate animals which now offers itself to 
 our notice contrasts remarkably with the cold-blooded and apathetic 
 inhabitants of the water ; and even with the slow-moving Reptile, 
 that languidly crawls upon the surface of the ground, or drags on 
 an amphibious existence in the marsh or on the shore. The Bird, 
 ordained to soar into the regions of the air, and not only to sustain 
 itself in that thin medium but to skim from place to place with 
 astonishing rapidity, needs a strength of muscle and activity of 
 limb even greater than that conferred upon the mammiferous qua- 
 druped. Senses of the utmost acuteness are now requisite, com- 
 bined with instinct and intelligence of a high order ; and accord- 
 ingly, both as regards their faculties and enjoyments, the feathered 
 tribes far surpass the other oviparous Vertebrata. 
 
 Next to that improvement in the condition of the nervous 
 system, which we have all along been able to trace advancing 
 part passu with the increase of sagacity and the expansion 
 of the bodily faculties, the most remarkable circumstance observ- 
 able in the economy of Birds is the elevated temperature of their 
 bodies and the heat of their circulating fluids. In the Reptile an 
 impure and semi-oxigenized blood was slowly propelled through 
 the system from the undivided ventricle of their trilocular heart ; 
 and we found their energies, their instincts, and their affections 
 proportionately feeble and obtuse : but now, not only does the 
 heart become divided into four cavities, one ventricle being appro- 
 priated to transmit venous blood to the lungs, while the other 
 drives a pure and highly arterialized fluid in copious gushes to the 
 remotest regions of the body; but, as though even this was not suf- 
 ficient tomeet the necessities of the case, the whole interior of the 
 bird is permeated by the atmospheric air, which penetrates even 
 into the bones ; and the respiratory function being thus rendered as 
 complete as possible, all parts of the muscular system are abun- 
 dantly supplied with blood arterialized to the utmost, and every 
 fibre, quivering with life intense, is ready to exert that vigorous 
 
592 AVES BIRDS. 
 
 activity which brings down the falcon upon his quarry like a thun- 
 derbolt from the clouds, or sustains the migratory bird through 
 long and perilous journey ings. 
 
 But increase of muscular energy is by no means the only conse- 
 quence resulting from more perfect respiration, and a consequently 
 increased temperature of the blood : the clothing of the body must 
 now be changed for a warmer covering than scales or horny plates; 
 feathers are therefore at once provided as the lightest, warmest blan- 
 ket that could be given : maternal care, which to the cold-blooded 
 Ovipara would have been a useless boon, can now be beneficially ex- 
 ercised ; the eggs, no longer left to chance, are cherished by the vital 
 heat of the parent ; and the callow brood, during the first period of 
 their lives, are dependent for support upon the watchful attentions 
 of the beings from whom they derived their existence. 
 
 (658.) The skeleton of a vertebrate animal formed for flight must 
 obviously be constructed upon mechanical principles widely different 
 from any that have yet come under our notice. The utmost lightness 
 is indispensable ; but still, in a frame-work which has to sustain the 
 action of muscles so vigorous, strength and firmness are equally es- 
 sential : it is in combining these two opposite qualities that the 
 human mechanician displays the highest efforts of ingenuity, and by 
 the scientific disposition of his materials exhibits the extent of 
 his resources and the accuracy of his knowledge ; but let the best 
 informed and most ingenious mechanic carefully and rigidly investi- 
 gate the skeleton of a bird, and we doubt not that in it he will find 
 all his art surpassed, and derive not a little instruction from the 
 survey. 
 
 In the spinal column of a bird we find three principal regions, 
 each of which will merit distinct notice. 
 
 The anterior or cervical region is exceedingly variable in its pro- 
 portionate length, and forms the only flexible portion of the spine : 
 it performs, indeed, the office of an arm, at the extremity of which 
 the beak, the chief instrument of prehension, is situated. The 
 number of vertebrae entering into the composition of this part of the 
 spinal column is very variable : in the Swan there are as many as 
 twenty-three ; in the Crane, nineteen ; while in the little Sparrow 
 nine only are met with : their bodies are joined together by articu- 
 lating facets inclosed in synovial capsules, and not by the interposi- 
 tion of intervertebral substance ; an interarticular cartilage, however, 
 is generally met with, by which the movements of the chain are 
 facilitated. The spinous and transverse processes are short ; while 
 
AVES BIRDS. 593 
 
 the oblique processes, united by articulating surfaces, limit the mo- 
 bility of the neck. 
 
 Although this portion of the spine is very properly designated 
 the " cervical region," we are not on that account to imagine that 
 the vertebrae composing it are unprovided with ribs : on the con- 
 trary, rudimentary costal appendages are generally found connected 
 with their transverse processes, which, in the young bird, are obvi- 
 ously separate elements, although they afterwards become united by 
 anchylosis. 
 
 (659.) But if flexibility is thus abundantly provided for in the 
 cervical portion of the vertebral column, it is quite evident that in the 
 thoracic portion of the skeleton, which has to support the framework 
 of the wings, and sustain the efforts of the muscles connected with 
 flight, firmness and rigidity become essential requisites ; and accord- 
 ingly everything has been done to prevent those movements which 
 in the neck were so advantageously permitted. The bodies and 
 spinous processes of the contiguous vertebrae are therefore here 
 firmly consolidated together by anchylosis ; and, moreover, splints of 
 bone, derived from the transverse processes, overlap each other, and 
 still further add to the stability and strength of the back. 
 
 The ribs appended to the dorsal vertebrae may be called the 
 true ribs; these enter into the composition of the thorax, and mate- 
 rially assist in strengthening that region. Each rib, as in the Croco- 
 dile, presents a dorsal and a sternal portion connected together by a 
 joint : the former are attached to the vertebrae by a double articula- 
 tion, their spinal extremity being furcate; while the latter are articu- 
 lated to the sides of the sternum. A thorax is thus formed, 
 possessing sufficient mobility to perform the movements connected 
 with respiration, but still affording a strong basis to support mus- 
 cular action ; and, in order to give the greatest possible strength, 
 from the posterior margin of each dorsal rib a broad flat process is 
 prolonged backwards and upwards to overlap the rib next behind, so 
 as in this manner to bind the whole together into one strong frame- 
 work. 
 
 The sternum itself is developed in proportion to the enormous 
 size of the three pectoral muscles which constitute the great agents 
 in flight : it is principally composed of the central azygos element 
 before noticed in the Tortoise, which is here remarkably dilated, 
 and in birds of flight prolonged inferiorly into a deep keel-like pro- 
 cess, so as to increase materially the extent of surface from which 
 the muscles of the breast take their origin ; but in the cursorial 
 
594 
 
 AVES BIRDS. 
 
 Fig. 268. 
 
 genera, such as the Ostrich, the Emeu, &c. where the wings are 
 not available for flying, the keel is entirely wanting, and the sternum 
 forms merely a kind of osseous shield, covering comparatively a very 
 small portion of the breast. 
 
 (660.) Whoever considers the position of the hip-joint in the fea- 
 thered tribes, and reflects how far it is necessarily removed behind the 
 centre of gravity when the bird walks, carrying its body in a horizon- 
 tal position, will at once 
 perceive that the pelvic 
 portion of the spine, 
 having to sustain the 
 whole weight of the 
 trunk under the most 
 unfavourable circum- 
 stances, and at the same 
 time to give origin to 
 the strong and massive 
 muscles wielding the 
 thigh, must be consoli- 
 dated and strengthened 
 in every possible man- 
 ner; and that even the 
 slight degree of move- 
 ment permitted in the 
 dorsal region would here be inadmissible. The lumbar and the sacral 
 vertebrae, and the entire pelvis, are therefore at an early period 
 solidly united together by anchylosis into one bone, and the num- 
 ber of the vertebrae composing this part of the skeleton is only 
 distinguishable from the situation of the intervertebral foramina 
 through which the spinal nerves are given off. In very young 
 birds the pelvis is evidently formed by the three elements that 
 usually enter into its composition ; and the ilium, the ischium, and 
 ihepubes, as well as the ischiadic notch and obturator foramen, 
 will all be at once recognised by the anatomist, occupying their 
 usual relative positions ; although he will not fail to notice one re- 
 markable circumstance, namely, that except in one instance, the 
 Ostrich, the ossa pubis do not meet in front, so that there is no 
 pubic arch or symphysis. 
 
 (661.) The anterior extremity of a bird, although an instrument 
 of flight, is found, when stripped of those feathers and long quills 
 that form the extensive surface presented by this member during 
 
AVES BIRDS. 
 
 595 
 
 life, still closely to adhere to die general type in accordance with 
 which this part of the skeleton is invariably constructed. The 
 framework of the shoulder exhibits the scapula (fig. 269, 6), the 
 clavicle (of), and the coracoid element (c) ; notwithstanding that 
 these bones, form- Fig. 269. 
 
 ing, as they do, 
 the basis of a limb 
 so vigorous, and 
 wielded by such 
 powerful muscles, 
 are necessarily mo- 
 dified in their form 
 and general ar- 
 ran gement, so as to 
 constitute strong 
 buttresses adapted 
 to keep the shoul- 
 der-joint firm and steady during flight. The scapula (b) is a long 
 and slender bone placed upon the ribs, and lying parallel to the 
 spine along the dorsal region of the thorax, imbedded in the mus- 
 cles to which it gives attachment, while at its fixed extremity it 
 assists in forming the cavity of the shoulder-joint. The coracoid 
 bone (c) is the great support of the shoulder ; for, while at one ex- 
 tremity it sustains the wing, at the opposite it is firmly and securely 
 united to the sternum by a broad articulation. But the most pecu- 
 liar element of this apparatus is the/wrcM/wra, or forked bone (d), 
 composed of the conjoined clavicles; which, being anchylosed to- 
 gether in the mesial line, and also strongly connected with the 
 shoulder-joint, materially add to the stability of the whole. 
 
 In the wing itself the humerus (f) is at once recognised, as 
 also the ulna (g) and the radius (h) ; but in some birds, as in the 
 Penguin, the student might be at a loss to identify one or two 
 small bones (/?), forming a kind of patella to the elbow-joint ; 
 these appear to be the representatives of the olecranon process de- 
 tached from the ulna. The carpus (i) consists of only two 
 small bones. The metacarpus is formed of two pieces (, /), 
 anchylosed together at their two extremities ; and these, with two, 
 or in some cases three, rudimental fingers complete the wing. The 
 largest finger consists of two, or sometimes three, phalanges (m, o) : 
 a second (n) offers but a single joint ; and the third, which is a 
 
 a 2 
 
596 AVES BIRDS. 
 
 mere rudiment when present, is an appendage to tlie radial side of 
 the carpus. 
 
 In the pelvic extremity (Jig. 268) the femur is a short and strong 
 bone : to this succeeds the tibia, upon the outer side of which is 
 fixed a rudiinental^fttf/a. The tarsus can scarcely be said to exist, 
 being at a very early age confused with the metatarsus ; the whole 
 forming a single tarso-metatarsal bone, which, in the Wading Birds 
 especially, is of very great length : at its distal extremity are 
 three articular surfaces that support the three anterior toes, while 
 a fourth toe, the hallux, directed backwards, is attached to it 
 posteriorly by the intervention of a small accessory piece ; and in 
 Gallinaceous Birds an osseous spur, consolidated with the posterior 
 face of the tarso-metatarsal bone, is generally considered as a fifth 
 toe. 
 
 The number of toes varies in different tribes of birds. Thus, in 
 the Ostrich there are only two ; in many genera there are three ; in 
 by far the greater number, four ; and in the Gallinacea, five. But 
 whatever the number of toes may be, the number of phalanges pe- 
 culiar to each is remarkably constant : thus, the outermost toe 
 always consists of five phalanges; the fourth toe invariably of four; 
 the third as constantly of three ; the second, when it exists, has 
 only two ; and, lastly, in the spur or innermost toe there is but a 
 single piece. 
 
 (662.) So rapidly is the progress of ossification accomplished in 
 the skeleton of a bird, that it is only in very young animals the indi- 
 
 Fig. 270. 
 
 vidual bones or elements composing the cranium can be identified, 
 as the sutures speedily become obliterated : when, however, they 
 
AVES BIRDS. 597 
 
 are examined under very favourable circumstances, as for example in 
 the skull of a young Ostrich, it is by no means difficult to distin- 
 guish them, and by comparing them with those of other Vertebrata, 
 to observe the modifications they have undergone both in form and 
 position. In the annexed figure the principal pieces, both of the 
 cranium and face, have been indicated by the same figures as were 
 used to point out the correspondent bones in the skulls of the Cro- 
 codile (Jig. 246) and the Serpent (Jig. 249), so that it would be 
 needless again to enumerate them in this place. 
 
 (663.) The muscular system of the feathered tribes, as far as acti- 
 vity and energy of motion is concerned, contrasts strikingly with that 
 of the Vertebrata we have as yet considered ; for, with the exception 
 of Insects, no animals in creation are comparable to Birds, either in 
 the vigour or velocity of their movements. 
 
 This perfection of muscular power, which is obviously essential to 
 enable the bird to sustain itself in the air, and there perform the 
 varied evolutions connected with flight, is no doubt mainly con- 
 nected with the highly arterialized condition of the blood, and the 
 completeness of the respiratory apparatus. Neither is it uninterest- 
 ing to observe, that while in the Insect respiration was effected by 
 the admission of air to every part of the system by means of tra- 
 cheal tubes, in Birds likewise the air freely penetrates to the interior 
 of the body, and, as we shall afterwards find, is there most exten- 
 sively diffused. 
 
 (664.) In the construction of the alimentary system there are 
 many interesting peculiarities to invite our notice. Their mouth 
 constitutes the apparatus whereby the prehension of food is ac- 
 complished ; it is in no instance provided with teeth, or adapted to 
 masticate food, but forms a beak encased in a dense, horny sheath, 
 which, from the varieties of form that it assumes in different genera, 
 becomes adapted to very various purposes. 
 
 In the Rapacious tribes, for instance, the bill is a strong and for- 
 midable hook, calculated to tear in pieces the animals devoured. In 
 Granivorous Birds it is a simple forceps for picking up the seeds of 
 vegetables. In the Snipe and the Curlew it forms a probe, whereby 
 insects are extracted from the soft and marshy ground. In the 
 Parrot it is partially an assistant in climbing, as well as an organ 
 for seizing food ; and, not to mention innumerable other modifica- 
 tions, in the Flamingo and Duck tribes it constitutes a shovel, by 
 the aid of which alimentary matters are obtained. 
 
 (665.) The sense of taste, even in these highly gifted animals, is 
 
598 AVES BIRDS. 
 
 as yet but very imperfectly developed ; and their tongue, instead 
 of being soft and flexible, as in the Mammalia, is supported 
 by one or two bony pieces, derived from the os hyoides (Jig. 271), 
 and covered with a horny sheath, obviously ill adapted to gus- 
 tation, but simply assisting in the deglutition of food. We 
 
 Fig. 271. 
 
 must not, therefore, be at all surprised if even in birds the 
 tongue is convertible into various instruments assisting in the 
 apprehension or preparation of nourishment : thus, in the Parrot 
 it is a thumb opposable to the upper mandible, and eminently 
 serviceable in holding and turning nuts or morsels of fruit: 
 in the honey-eating tribes the tongue is armed at its extremity with 
 a tuft of horny filaments, resembling a camel-hair pencil, which, be- 
 ing plunged into the bell of a flower, sucks up the nectar from the 
 bottom ; and in the Woodpecker it is absolutely converted into a 
 harpoon, whereby the insect is speared in its lurking-place, and 
 dragged into the mouth. 
 
 (666.) In most birds, in consequence of the very small size of the 
 cavity of the stomach, or gizzard as it is generally called, some other 
 receptacle for the aliment becomes indispensable ; and accordingly 
 various provisions have been made for lodging food in sufficient 
 quantities in situations where it may be retained until the gizzard is 
 ready to receive it. In birds that catch insects on the wing, this is 
 most conveniently effected by dilating the fauces and upper part of 
 the throat into a capacious chamber, wherein the insects as they are 
 seized accumulate : this is remarkably the case in the Swifts. In 
 the Pelican a very peculiar plan is adopted ; the beak is amazingly 
 prolonged, and beneath the lower jaw is suspended a wide pouch, 
 formed by the skin of the throat, wherein large quantities of fish may 
 be contained and carried about. In other fishing birds the whole 
 esophagus is extraordinarily capacious, and will hold a considerable 
 supply ; but the most usual arrangement in birds requiring such a 
 
AVES BIHDS. 
 
 599 
 
 Fig. 272. 
 
 reservoir, is the existence of a crop, or dilatation of some part of the 
 gullet into a wide bag (tngluvict), wherein grain or other sub- 
 stances hastily picked up may be stored preparatory to digestion. 
 After expanding into the crop in those birds that possess this 
 cavity, the oesophagus again contracts to its former dimensions 
 (Jig. 21%, a) ; but just before terminating in the gizzard it again 
 dilates to form a second but smaller cavity (6), called the proven- 
 triculuS) or bulbus glandulosus^ in which the food undergoes further 
 preparation. The walls of the proventiculus are thickly studded 
 with large glandular follicles, variously disposed ; from whence a 
 copious secretion of " gastric juice? as it is called, is poured out 
 and mixed with the aliment. Having, therefore, undergone mace- 
 ration in the juices of the crop, and become subsequently saturated 
 with the gastric fluid, that constitutes so important an agent in 
 digestion, alimentary substances are at length received into the giz- 
 zard (c), where further preparation is necessary. 
 
 (667.) The gizzard in such birds as feed upon vegetable substances 
 is an organ possessing immense strength ; and constitutes, in fact, a 
 crushing mill, wherein nutritive materials are bruised and triturated : 
 its cavity is very small, and lined 
 with a dense, coriaceous cuticu- 
 lar stratum ; and its substance is 
 almost entirely made up of two 
 dense and enormously powerful 
 masses of muscle, the fibres of 
 which radiate from two central 
 tendons (fig. 272, c), situated 
 upon the opposite sides of the 
 viscus. The action of these late- 
 ral muscles will obviously grind 
 and crush with great force what- 
 ever is placed in the central ca- 
 vity ; a process that is materially 
 expedited by the presence of hard 
 and angular pebbles, swallowed 
 for the purpose, by the assistance 
 of which the contained food is 
 speedily comminuted. 
 
 Another and much feebler set of muscles (d) bounds the cavity 
 of the gizzard in the intervals between the great lateral masses, 
 which, receiving the food from the proventriculus, perpetually feed 
 
600 
 
 AVES BIRDS. 
 
 this living mill, and retain the material to be ground within the in- 
 fluence of the crushers until it is properly prepared, when other 
 fibres, acting the part of a pylorus, allow it pass on into the duode- 
 num (e). 
 
 (668.) The intestinal canal of Birds is, as in other classes, very 
 variable in its relative length as compared with that of the body: its 
 calibre is pretty equal throughout, and the division into large and 
 small intestines can scarcely be said to exist. Commencing from the 
 pylorus, the duodenum (Jig- 273, rf, A) is always found to make a long 
 and very characteristic loop, embracing the lobes of the pancreas 
 (e, e), and then, after sundry convolutions, the intestine is con- 
 tinued to its termination in the cloaca. The division between 
 the large and small intestines is indicated by the presence of one, 
 or more generally two, csecal appendages, which communicate with 
 the cavity of the gut at no great distance from its cloacal extremity. 
 
 (669.) In Birds, the auxiliary secretions subservient to the 
 digestive process are the salivary, the gastric, the hepatic, and 
 the pancreatic. 
 
 The salivary apparatus varies much in structure and disposition in 
 different tribes. In its simplest form it consists of distinct secerning 
 follicles, placed immediately beneath the mucous membrane of the 
 mouth, into which the secretion is poured by numerous orifices. 
 In the Gallinaceous Birds the glands assume a conglomerate cha- 
 racter. In the Turkey there are two pairs :* the first pair forms 
 a cone, having its apex directed towards the extremity of the 
 beak ; and the two glands of the opposite sides touch each other 
 along the mesial line through almost their entire length, filling up 
 anteriorly the angle of the lower jaw. These glands are situated 
 immediately beneath the skin, but in front they touch the mucous 
 membrane of the rnouth ; and their secretion is poured into the 
 buccal cavity by several orifices. The second pair of glands is 
 smaller, of an elongated form, and is placed above the posterior 
 third of the former, this is immediately in contact with the 
 mucous lining of the mouth. 
 
 In the Woodpeckers the glands that secrete the fluid whereby 
 the tongue is lubricated are of very considerable size. They pass 
 further back than the angle of the lower jaw, extending even to 
 beneath the occiput ; and their secretion, which is viscid and 
 tenacious, enters the mouth by a single orifice situated under the 
 point of the tongue. 
 
 * Cuvier, Leyons d'Anat. Comp. torn. iii. p. 221. 
 
AVES BIRDS. 
 
 601 
 
 In the generality of birds, however, there is only one pair of 
 salivary glands; and these, in many cases, seem to be united into a 
 single mass, separated posteriorly into two lobes, and situated 
 beneath the palatine membrane, behind the angle of the rami of 
 the lower jaw. From these glands a thick, white, and viscid fluid 
 is poured into the mouth through numerous orifices, principally 
 disposed along the mesial line, which separates the two glands. 
 
 (670.) We have already spoken of the gastric glands which 
 densely stud the coats of the proventriculus, and furnish the "gastric 
 juice ;" and therefore pass on to notice the other subsidiary chylo- 
 poietic viscera, namely, the liver, the pancreas, and the spleen. 
 
 The liver is a viscus of considerable magnitude, consisting of 
 two principal lobes, and firmly suspended in situ by broad liga- 
 ments and membranous processes. The vena portse, supplying 
 that venous blood from which the bile is elaborated, is formed 
 by vessels derived from numerous sources, receiving not only the 
 veins of the stomach, spleen, and intestines, as in Mammalia, 
 but likewise Fig. 273. 
 
 the renal and 
 sacral veins ; 
 another proof, 
 if any were 
 wanting, that 
 no arrange- 
 ment by which 
 the decarbon- 
 ization of the 
 blood can be 
 facilitated has 
 been omitted 
 in the organ- 
 ization of the 
 class before us. 
 Thehepatic ar- 
 teries and the 
 hepatic veins 
 present no- 
 thing remark- 
 able in their 
 disposition, but 
 the course of the bile from the liver into the intestine merits our 
 
602 
 
 AVES BIRDS. 
 
 notice. Two sets of ducts are provided for this purpose : the 
 first (Jig. 73, i) carries the bile directly from the liver into the 
 gall-bladder (g), from which another duct conveys the bilious fluid 
 into the duodenum ; but the second set of bile-vessels conducts 
 the secretion of the liver at once into the intestine by a wide 
 canal (o), that has no communication whatever with the gall- 
 bladder, there is, therefore, no arrangement like that of the 
 " ductus communis choledochus" of Mammals : if the bile is want- 
 ed immediately, it passes at once into the intestine through the 
 duct o ; but, if digestion is not going on, it is conveyed into the 
 gall-bladder through the duct i, to be there retained until needed. 
 The pancreas (Jig. 218, e, e) is a conglomerate gland of con- 
 siderable size, situated in the elongated loop formed by the duo- 
 denum : it generally consists of two portions more or less inti- 
 mately connected, and from each portion an excretory duct (n) is 
 given off; these two ducts terminate separately in the intestine, in 
 the immediate vicinity of the openings of the biliary canals. In 
 some birds even three pancreatic ducts are met with, as is the case 
 in the common fowl ; but under such circumstances the third duct, 
 instead of opening into the intestine at the same point as the 
 other two, issues from the opposite extremity of the pancreas, and 
 enters the middle of the duodenum at the place where the gut 
 turns upon itself. 
 
 The spleen (Jig. 273, f) is of very small size in all birds ; it is 
 situated near the anterior extremity of the pancreas, and is loosely 
 connected to the side of the proventriculus (b). The distribu- 
 tion of its vessels, and its general structure, is the same as in 
 Mammalia. 
 
 The lymphatic system is well developed, and the course of 
 the lymphatic vessels has been investigated with great care by 
 various anatomists. The vessels themselves are thin, and have but 
 few valves ; they principally accompany the larger blood-vessels 
 from all parts of the body to the aorta, around which they form a 
 plexus, and ultimately join to give rise to two principal trunks or 
 thoracic ducts: these terminate severally in the right and left 
 jugular veins, and into these vessels the greater proportion of the 
 lymph and chyle absorbed is of course poured, to be mixed with 
 the circulating blood. 
 
 (671.) Before describing the circulatory apparatus of birds, it will 
 be advisable in the next place to consider the nature and disposition 
 of their organs of respiration ; which, from what has been already 
 
AVES BIRDS. 
 
 603 
 
 stated concerning the heat and purity of the blood in these crea- 
 tures, we are prepared to find presenting the highest possible con- 
 dition of developement. Birds, in fact, breathe not only with 
 their lungs, but the vital element penetrates every part of the 
 interior of their bodies, bathing the surfaces of their viscera and 
 entering the very cavities of their bones ; so that the blood is 
 most extensively subjected to its influence. The lungs, in fact, 
 are no longer closed bags as those of Reptiles are, but rather 
 resemble spongy masses of extreme vascularity, firmly bound 
 down in contact with the dorsal aspect of the thorax ; their poste- 
 rior surface being fixed to the ribs on each side of the vertebral 
 column, and entering deeply into the intercostal spaces. Such 
 
 lungs are obviously incapable of alternate dilatation and contrac- 
 tion, so that inspiration and expiration must be provided for by a 
 mechanism specially adapted to the emergency. From an exa- 
 
604 AVES BIRDS. 
 
 mination of Jig. 274, the arrangement adopted will easily be under- 
 stood : the bronchi derived from the bifurcated inferior extremity 
 of the trachea plunge into the anterior face of the lungs (c, c), and 
 by innumerable canals distribute air throughout their spungoid 
 substance ; but the main trunks of the bronchial tubes, passing 
 right through the pulmonary organs, open by wide mouths, repre- 
 sented in the figure, into the cavity of the thorax, into which the 
 air likewise freely penetrates. The whole thoracico-abdominal 
 cavity is moreover divided by septa of serous membrane into 
 numerous intercommunicating cells, all of which are freely per- 
 meated by the atmospheric fluid, which in most instances is 
 admitted into the very bones themselves, and even penetrates to 
 the interspaces between the muscles of the neck and limbs ; thus, 
 in some birds of powerful flight, gaining free access to almost every 
 part of the system. 
 
 The mechanism by which the air is drawn into, and then expelled 
 from, this extended series of respiratory cells, is sufficiently simple ; 
 the whole being accomplished by the movements of the expanded 
 sternum, assisted slightly by the abdominal muscles. The descent 
 of the sternum from the vertebral column necessarily enlarges the 
 capacity of the chest, and, acting like a great bellows, sucks in air 
 through the trachea, which not only fills all the spongy substance of 
 the lungs, but penetrates to all parts whereunto air is admitted; 
 while the ascent of the sternum, and consequent contraction of the 
 thoracico-abdominal space, alternately effects its expulsion. 
 
 The results obtained by this unusual arrangement are of great 
 importance in the economy of the feathered races. In the first 
 place, the perfect oxygenization of the blood is abundantly secured. 
 Secondly, from the high temperature of the blood, the air drawn in 
 becomes greatly rarified, and thus materially diminishes the specific 
 gravity of the bird. Thirdly, from the inflation of the whole body, 
 the muscles, more especially those of flight, act with better lever- 
 age and firmer purchase ; so that their efforts are materially favoured. 
 And, lastly, it is owing to the capacity of the air-cells that the Sing- 
 ing Birds are enabled to prolong their notes to that extent which 
 renders them pre-eminent among the vocalists of creation. 
 
 (67&.) In connection, therefore, with the respiratory system of 
 the feathered races, it will be advisable, in the next place, to con- 
 sider the construction of the air passages, whereby the atmospheric 
 fluid passes into and out of the body; and more especially of the 
 organs of voice connected with them. 
 
AVES BIRDS. 
 
 605 
 
 A. 
 
 The trachea is of very great proportionate length in correspond- 
 ence with the elongated neck ; commencing at the root of the 
 tongue, and extending into the thoracic cavity, where it divides 
 into two bronchial tubes, one appropriated to each lung 
 (Jig. 274, /, /). The trachea of birds is composed of cartilaginous 
 rings, which are very generally ossified ; each ring, with the excep- 
 tion of two or three immediately beneath the upper larynx, forming a 
 complete circle (Jig. 275, A) surrounding the tracheal tube : these 
 rings are enclosed between the soft membranes of the trachea, and 
 thus keep the air-passages constantly permeable to the atmosphere. 
 
 In many birds, especially among the web- footed tribes, the 
 trachea suddenly dilates into wide chambers, or cavities of different 
 forms and dimensions ; a circum- Fig. 275. 
 
 stance the object of which has not 
 as yet been satisfactorily explained: 
 and, what is still more inexplica- 
 ble, in some genera, and those too 
 with the longest necks, as for ex- 
 ample the Wild Swan, and many 
 of the Wading Birds, the lower 
 part of the trachea is lengthened 
 out and variously contorted before 
 it terminates in the chest. This 
 long trachea is provided with mus- 
 cles whereby the rings may be approximated, and thus the 
 length of the tube is considerably modified : these muscles 
 (fig. 274, A, B, h) arise from the sternum, and sometimes also from 
 the furcula, and are continued along the sides of the windpipe 
 throughout its whole length. 
 
 The upper larynx, or rima glottidis, is in birds but of secondary 
 importance in the production of vocal sounds ; it is a simple fissure 
 bounded by two osseous pieces (Jig. 275, A, B,/) corresponding with 
 the aryienoid cartilages of Mammalia : these, however, in the Bird 
 are not connected with chorda vacates ; but simply, as they are se- 
 parated or approximated, open or close the fissure of the glottis. 
 When, therefore, we compare the framework of this organ with the 
 cartilaginous pieces found in the larynx of Mammalia, considerable 
 difference is perceptible, insomuch that it is not easy positively to 
 recognise the analogous portions, more especially as in the Bird the 
 cartilages are more or less completely ossified. If the broad an- 
 terior plate (Jig. 275, b) be considered as the thyroid cartilage, we 
 
606 AVES BIRDS. 
 
 must suppose the cricoid to be represented by three distinct ossicles, 
 two of which (c, c) are lateral, while the third or central portion 
 (e) supports the arytenoid bones (/,/), which are moveably arti- 
 culated with its anterior margin. The arytenoid bones themselves 
 are of an elongated form, and each presents a long process (g, g) 
 for the insertion of the muscles that act upon them. These 
 arytenoid bones are moved by two pairs of muscles ; the superficial 
 pair (thyro-arytenoidei, Jig. 276, B) serving to pull asunder, 
 while the more deeply seated (constrictores glottidis^Jig. 276, A) 
 bring together the lips of the glottis. 
 
 (673.) It is the lower larynx, 
 situated at the opposite extremity of 
 the trachea, at the point where that 
 tube gives off the bronchi, that 
 the real vocal apparatus of birds is 
 situated ; and in the more perfect 
 Singing Birds a very important 
 set of muscles is appropriated to 
 perform those delicate movements 
 that regulate the condition of the 
 air-passages at this part, and thus 
 give rise to all the varieties of 
 tone of which the voice is ca- 
 pable- 
 
 In the Insessorial Birds, by 
 far the most accomplished song- 
 sters, five pairs of muscles are connected with the inferior larynx ; 
 and so disposed as to influence both the diameter and length of the 
 bronchial tubes (Jig. 274, A, B, n, o, z 9 s, h). In the Parrots, three 
 pairs only are met with ;* some of the Natatores have two ; other 
 natatorial birds, as well as the Rasores and Grallatores, only one ; 
 and in a few, as the King of the Vultures and the Condor, the 
 vocal muscles are quite deficient. 
 
 (674.) Not only is the respiration of these highly gifted Vertebrata 
 thus abundantly provided for, but, as an immediate consequence of the 
 necessity for supplying the system with pure and highly oxygenized 
 blood, the heart, hitherto but imperfectly divided, becomes now 
 separated into two distinct sets of cavities, each composed of an au- 
 ricle and of a strong ventricular chamber. The right side of the 
 heart receives the vitiated blood from all parts of the system, 
 * Vide Yarrell on the Organs of Voice in Birds. Linn. Trans, vol. xvi. 
 
AVES BIRDS. 607 
 
 which is poured into the corresponding auricle by three large veins, 
 viz. one inferior and two superior vena? cavce. The contraction 
 of this auricle drives the blood into the right ventricle ; theauriculo- 
 ventricular opening being guarded by a broad fleshy valve, formed 
 by the muscular substance of the heart itself; and hence the venous 
 blood is forced through all the ramifications of the pulmonary arteries. 
 
 The aerated blood is then returned from the lungs by two veins, 
 which pour it into the left auricle ; and the left ventricle, now en- 
 tirely appropriated to the systemic circulation, diffuses it through 
 the body ; thus all mixture of the venous and arterial fluids 
 being prevented, the system is supplied by the left side of the heart 
 with pure and highly vitalized blood. 
 
 (675.) In the nervous system of Birds there is a very perceptible 
 improvement when compared with that of Reptiles, more especially 
 in the increased proportional developement of the cerebral hemi- 
 spheres : still, however, there are no convolutions seen upon the 
 surface of the cerebrum ; neither are those extensive communica- 
 tions between the lateral halves as yet developed, which in the 
 higher Mammalia assume such size and importance : the corpus 
 callosum and fornix are both wanting, a simple commissure being 
 still sufficient. Neither has the cerebellum in these animals as- 
 sumed its complete developement, presenting only the central por- 
 tion ; so that the pons Varolii^ or the great commissure, which in 
 Man unites the lateral cerebellic lobes, is of course deficient. The 
 olfactory and optic lobes are even here recognisable as distinct ele- 
 ments of the cerebral mass, and the origins of the nerves strictly 
 conform to the arrangement already described in the brain of Rep- 
 tiles. The rest of the cerebro-spinal axis presents no peculiarity 
 worthy of special notice ; and the general distribution of the cere- 
 bral and spinal nerves is so similar in all the Vertebrata, that it 
 would be useless again to describe them in this place. 
 
 The sympathetic system in Birds is well developed, and its ar- 
 rangement differs in no essential particular from what is seen in the 
 human body ; the situation of the cervical ganglia is, however, 
 peculiar, inasmuch as they are lodged in the bony canal formed by 
 the transverse processes of the vertebrae of the neck for the recep- 
 tion of the vertebral artery, and are thus securely protected in spite 
 of the unusual length and slenderness which the neck not unfre- 
 quently exhibits. 
 
 But if in the general arrangement of the nervous system of 
 the feathered races there is little to arrest our notice, we shall find 
 
608 AVES BIRDS. 
 
 in the construction of the organs of their senses many circumstances 
 of considerable interest to the physiological reader ; and, conse- 
 quently, these will require a more extended description. 
 
 (676.) The sense of touch must obviously be extremely imperfect 
 in these animals : their body, enveloped in feathers, can be little 
 sensible to impressions produced by the contact of external objects ; 
 and their limbs, covered as they are with plumes, or cased in horny 
 scales, are but little adapted to exercise the sense in question. The 
 beak alone offers itself as calculated to be a tactile instrument ; but 
 even this, enclosed as it is in the generality of birds by a dense 
 corneous case, must be very inefficient in investigating the outward 
 surfaces of substances : nevertheless, in some tribes the beak is un- 
 doubtedly extremely sensible, and is used to search for food in 
 marshy soils, or to find it in the mud at the bottom of shallow 
 waters ; this is the case, for instance, in many of the long-billed 
 Wading Birds, and also in the flat-billed aquatic families, such as 
 the Goose and Swan ; in these, in fact, the covering of the beak is 
 comparatively soft, and the nerves that supply it, derived from the 
 fifth pair, are of very considerable size. 
 
 (677-) Taste is evidently one of the last indulgences granted, as 
 we advance from the lower to the more highly gifted races of the 
 animal creation ; and even in birds it is only necessary to inspect 
 the structure of the tongue in order to be convinced that they can 
 derive but small enjoyment from this source. The skin of the 
 tongue in these creatures is totally devoid of gustatory papillae, and 
 frequently, indeed, enveloped in a horny sheath; so that, if the sense 
 of taste exists at all, it must be, to the last degree, limited and 
 obtuse. 
 
 (678.) In return, however, for the imperfection of the above 
 senses, the olfactory apparatus in this class of animals begins to 
 assume far greater importance than in the cold-blooded Vertebrata ; 
 
 Fig. 277. ." : -- ;; 
 
AVES BIRDS. (j()9 
 
 and the nasal cavity indicates, by its extent, that it is now 
 well adapted to investigate the odorous properties of the air 
 taken in for respiration. The septum narium completely divides 
 the nose into two lateral chambers of considerable extent, which 
 individually communicate with the pharynx (fig- 277, c) ; and, 
 upon the outer wall of each compartment, three convoluted 
 laminae, covered with a most delicate Schneiderian membrane, re- 
 present the turbinated bones of Mammalia, and increase the olfactory 
 surface. Of these, the middle turbinated bone (jig* 277, a) is the 
 largest ; but the superior appears to be the most important, as it is 
 upon this that the olfactory nerve is principally distributed, inso- 
 much that Scarpa considered that the comparative powers of smell 
 possessed by different birds might be estimated by the develope- 
 ment of this portion of the olfactory organ. The olfactory nerves 
 (Jig. 277, i), as in Reptiles, still enter the nose without dividing, 
 so that there is no cribriform plate to the ethmoid bone. The 
 nostrils are simple apertures, perforating some part of the horny 
 beak covering the upper mandible, and are never provided with 
 moveable cartilages or muscles, as those of Mammalia will be found 
 to be. 
 
 (679.) The eye of a Bird is an optical instrument of such ad- 
 mirable construction, that, did not the nature of this work compel 
 us to adopt the strictest brevity in our descriptions, it might well 
 tempt us to indulge in lengthened details relative to the adaptation 
 and uses of its various parts. If we contrast the Bird with the 
 Reptile, or more especially with the Fish, and consider the totally 
 different circumstances under which these animals exercise the sense 
 of vision, we might well expect extraordinary modifications in the 
 structure of their organs of sight. The Fish, immersed in a dense 
 medium, can see but to a very limited distance around it ; and the 
 sphericity of the crystalline lens, with the consequent contracted 
 antero-posterior diameter of the eye-ball, at once testifies how small 
 is the sphere of vision commanded by the finny tribes. The Bird, 
 on the contrary, dwelling in the thin air, and not unfrequently soar- 
 ing into regions where that air is still further rarified, must sur- 
 vey an horizon even more extensive than that enjoyed by the 
 terrestrial Mammal ; while, from the rapid movements of the 
 feathered races, it becomes absolutely requisite that the focus of the 
 eye shall continually vary between the extremes of long and short 
 sighted vision. The birds of prey, as they fan the air at an altitude 
 which places them almost beyond the reach of human sight, or sail 
 
610 AVES BIRDS. 
 
 in broad gyrations through the sky, are scanning from that height 
 the surface of the ground, and looking out for mice or other little 
 animals on which to feed : but when the prey is seen, and the bird, 
 shooting down with the rapidity of a thunderbolt, stoops upon 
 the quarry, it must obviously be indispensable that it should 
 see with equal clearness and distinctness when close to its victim, 
 as it did when far remote; and to enable it to do this special 
 provisions have been made in the structure of the eye-ball. 
 
 A glance at figure 279, exhibiting a section of the eye of 
 an Owl, will show the anatomist that in its general composition 
 the organ is similar to that of Man. The sclerotic and the 
 choroid tunics present the same arrangement, the transparent hu- 
 mours of the eye occupy the same relative positions, and the iris 
 and ciliary folds exist as in the human subject. Descending from 
 generalities, however, he will find many points in the organization 
 of a bmTs eye eminently deserving separate examination, and it is 
 to these we would specially invite his notice. First, the shape of 
 the eye-ball is peculiar : it is not spherical, as in man, nor flattened 
 anteriorly, as in fishes and aquatic reptiles ; but, on the contrary, 
 the cornea is rendered extremely prominent, and the antero-pos- 
 terior axis of the eye considerably lengthened. This is remark- 
 ably exemplified in the Owl ; in which bird, as Dr. Macartney* 
 pointed out, such is the disproportion between the anterior and 
 posterior spheres of the eye, that the axis of the anterior portion 
 is twice as great as that of the other. The obvious consequence 
 of this figure of the globe of the eye is to allow room for a greater 
 proportion of aqueous fluid, and for the removal of the crystalline 
 lens from the seat of sensation, and thus produce a greater con- 
 vergence of the rays of light, by which the animal is enabled to 
 discern the objects placed near it, and to see with a weaker light ; 
 and hence Owls, which require this sort of vision so much, possess 
 the structure fitted to effect it in so remarkable a degree. 
 
 (680.) But it is evident, that, in order to retain this conical 
 shape of the eye-ball, some further mechanical arrangements are ne- 
 cessary, which in the spherical form of the human eye are not requi- 
 site. In Fishes, where the eye-ball is constructed upon entirely 
 opposite principles, being compressed anteriorly, cartilaginous sup- 
 ports are found imbedded in the sclerotic tunic, which, in some 
 cases, is absolutely ossified into a bony cup. In many Reptiles 
 the same end is obtained by placing a circle of bony plates around 
 
 * Rees's Cyclopaedia, art. Birds. 
 
AVES BIRDS. 611 
 
 the cornea ; and this latter plan is again adopted in Birds, to main- 
 tain their eyes in a shape precisely the converse of the former. In 
 the Owls these ossicles are F*x 278. 
 
 most largely developed; in 
 such birds they form a broad 
 zone (Jig. 278), extending 
 from the margin of the cor- 
 nea, embracing the anterior 
 conical portion of the eye, and 
 imbedded between two fi- 
 brous layers of the sclerotic. 
 The figure which is thus 
 given to the eye, from the in- 
 creased space obtained, is evi- 
 dently calculated to allow the 
 
 humours, forming the refracting media whereby the rays of light 
 are brought to a focus upon the retina, to become materially 
 changed in shape ; and both the convexity of the cornea, and the 
 position of the lens, may thus be altered so as to adjust them in cor- 
 respondence with the distance at which an object is viewed. The 
 cornea is rendered more convex, and the shape of the aqueous humour 
 consequently adapted to examine objects close at hand, by the simple 
 action of the muscles that move the eye-ball ; for these, seeing that 
 the edges of the pieces composing the bony circle overlap each 
 other so as to be slightly moveable, as they compress the globe of 
 the eye, cause the protrusion of the aqueous humour, and the 
 cornea becomes prominent ; or, if the bird surveys things that are 
 remote, the cornea recedes, and becomes flattened, an effect caused 
 by the recession of the aqueous humour, and, as some authors 
 assert,* by muscular fibres disposed around the circumference of 
 the cornea, and attached to its inner layer, which draw back the 
 cornea in a manner analogous to the action of the muscles of the 
 diaphragm upon its tendinous centre. 
 
 But the most beautiful piece of mechanism, if we may be par- 
 doned the expression, met with in the eye of a bird, is destined to 
 regulate the focal distance between the crystalline lens and the 
 sentient surface of the retina, in order to insure the clearest pos- 
 sible delineation either of near or distant objects. The provision 
 for this purpose is peculiar to the class under our notice ; and con- 
 sists of a vascular organ, called the marsupium, or pecten, which is 
 
 * Vide Cyclop, of Anat. and Phys. p. 304. 
 
 2 R 2 
 
612 AVES BIRDS. 
 
 lodged in the posterior part of the vitreous humour (Jig- 279 a). 
 This organ is composed of folds of a membrane resembling 
 the choroid coat of the eye, and, Fig. 279. 
 
 being in like manner covered with 
 pigment, might easily be mistaken 
 for a process derived from that tunic ; 
 with which, in fact, it has no connec- 
 tion, being attached to the optic 
 nerve just at the point where it ex- 
 pands into the retina. Its substance 
 seems to be made up of erectile tis- 
 sue, and it is most copiously supplied 
 with blood derived from an arterial 
 plexus formed by the arteria centralis retinae ;* so that there is 
 little doubt that, being like the iris endowed with an involuntary 
 power of dilatation and contraction, as it enlarges from the injection 
 of blood, it distends the chamber of the vitreous humour, and 
 pushes forward the lens ; while, as it again collapses, the crystalline 
 is allowed to approach nearer to the retina, and thus the focus of 
 the eye is adjusted upon the same principle as that of a telescope. 
 Four recti and two obliqui muscles preside over the movements 
 of the eye-ball ; but, as in the Reptilia, the superior oblique arises 
 from the anterior part of the orbit, as well as the obliquus inferior, 
 and its tendon is not reflected over a trochlea. 
 
 (681.) Birds have three eye-lids : an upper and a lower, resem- 
 bling those of mammalia ; and a third, which, when unemployed, 
 is concealed in the inner canthus of the eye, but can be drawn 
 down vertically by muscles specially appropriated to its motions, 
 so as to sweep over the entire cornea, which it then covers like a 
 curtain. 
 
 The upper and the lower eye-lids differ but little in their struc- 
 ture from those of Man ; nevertheless, a few trivial circumstances 
 are worthy of the notice of the student. In the first place, there 
 are seldom any eye-lashes attached to the palpebral margins ; and, 
 secondly, the lower eye-lid is the most moveable of the two, and 
 not only contains a distinct tarsal cartilage, but is provided with a 
 special depressor muscle, which arises from the bottom of the orbit 
 like the levator palpebra superioris of the human subject : the ele- 
 vator of the upper eye-lid, and orbicularis palpebrarum, are like- 
 wise well developed. 
 
 * Vide Barkow, in Meckel's Archiven, Band xii". 
 
AVES BIRDS. 
 
 618 
 
 The third eye-lid, or nictitating membrane, is represented in 
 fig. 280, A, e ; the upper and the lower eye-lids having been divided 
 through the middle, and turned back to display it: it is necessarily, 
 to a certain extent, transparent, for birds sometimes look through it ; 
 as for instance, when the eagle looks at the sun :* it is, therefore, of a 
 membranous texture ; and a Fig. 280. 
 
 most admirable and peculiar 
 muscular apparatus is given, 
 by which its movements are 
 effected. This is placed at 
 the back of the eye-ball, and 
 may easily be displayed by 
 turning aside the recti and 
 obliqui muscles, as in Jig. 
 280, B. Two muscles are 
 then perceived arising from 
 the globe of the eye, taking 
 their origin from the outside 
 of the sclerotic coat : one of 
 these (c), named the quad- 
 ratus membrane nictitantis, 
 arising from near the upper 
 aspect of the eye, descends 
 towards the optic nerve ; but 
 instead of being inserted into 
 anything, as muscles usually 
 are, it terminates in a most remarkable manner, ending in a tendi- 
 nous sheath or pully, through which the tendon of the next muscle 
 passes as it winds around the optic nerve. The second muscle (d) 9 
 called the pyramidalis memb. nictitantis, arises from the inner 
 aspect of the eye-ball ; and its fibres are collected into a long, 
 slender tendon, which, as it turns round the optic nerve, passes 
 through the tendinous sheath formed by the quadratus, as a rope 
 through a pully, and then is continued in a cellular sheath formed 
 by the sclerotic, underneath the eye, to the lower angle of the third 
 eye-lid, into which it is inserted. The reader will at once perceive 
 how beautifully these two muscles, acting simultaneously, cause the 
 nictitating membrane to sweep over the cornea, which returns again 
 into the inner canthus of the eye by its own elasticity. 
 
 (682.) Being thus provided with moveable eye-lids, a lacrymal 
 
 * Cuv. Lemons, d'Anat. Comp. torn. ii. p. 431. 
 
614 AVES BIRDS. 
 
 apparatus is, of course, indispensable ; and, accordingly, birds are 
 supplied with two distinct glands, one being appropriated to the 
 secretion of tears, while the other furnishes a lubricating fluid, appa- 
 rently destined to facilitate the movements of the membrana nic- 
 titans. 
 
 The lacrymal gland is situated, as in Man, at the outer angle 
 of the eye, and its duct pours the lacrymal secretion upon the eye- 
 ball near the external canthus. The lacrymal canal, whereby the 
 tears, after moistening the cornea, are discharged into the nose, 
 commences by two orifices (j^g*. 280, A, c) situated just behind the 
 internal commissure of the eye-lids ; and is continued, into the nasal 
 cavity, where it terminates in front of the representative of the 
 middle turbinated bone. 
 
 The second gland, the glandula Harden, seems to supply the 
 place of the Meibomian glands of the human eye-lids : it forms 
 a considerable glandular mass, situated behind the conjunctiva at 
 the nasal angle of the eye-lids ; and through its excretory duct, 
 which opens behind the nictitating membrane, the lubricating secre- 
 tion that it furnishes is poured out. 
 
 (683.) Besides the secreting organs above described, a third very 
 large gland is found, generally lodged in a depression beneath 
 the vault of the orbit, although in some genera it is situated 
 external to that cavity : the secretion of this gland is, however, 
 poured into the nose by one or more ducts, and thus serves copi- 
 ously to moisten the Schneiderian membrane. 
 
 (684.) The auditory apparatus of a Bird is almost precisely si- 
 milar in its structure to that of one of the more perfect Reptiles, 
 such as the Crocodile. There is still no external ear, or osseous 
 canal worthy of being called an external meatus, yet in a few 
 rare instances, such as the Bustard, the feathers around the ear are 
 so disposed as to collect faint impressions of sound ; and in the 
 Owls, besides possessing a broad opercular flap, that forms a kind 
 of external ear, there are sinuosities, external to the membrana tym- 
 pani, which resemble, not very distantly, those found in the ear 
 of Man. 
 
 Entering into the composition of the organ of hearing in the 
 class before us, we have the membrana tympani (Jig. 281, a), and 
 tympanic cavity, from which a wide Eustachian tube (d) leads to the 
 posterior nares. The labyrinth presents the vestibule (c), the semi- 
 circular canals (b), and the rudimentary cochlea (e); all of which 
 so exactly correspond in structure with what has already been de- 
 
AVES BIRDS. 615 
 
 scribed when speaking of the ear of Reptiles ( 639, 640), as to 
 render repetition needless. A single trumpet-shaped bone, the 
 representative of the stapes, fig. 281. 
 
 communicates immediately 
 between the mem bran a tym- 
 pani and iliefenestra ovalis ; 
 but two or three minute car- 
 tilaginous appendages, con- 
 nected with the membranous 
 drum of the ear, are regard- 
 ed as being the rudiments of 
 the malleus, incus, and os 
 orbiculare met with in the 
 next class. 
 
 (685.) The kidneys in the Bird (Jig. 282, e, e, e) are very large : 
 they are lodged in deep depressions, situated on each side of the 
 spine in the lumbar and pelvic regions ; their posterior aspects being 
 moulded into all the cavities formed by the bones in that situation. 
 In their essential structure each kidney is made up of innumerable 
 microscopic flexuous tubes ; which, joining again and again into 
 larger and still larger trunks, ultimately terminate in the ureter, 
 without the interposition of any infundibular cavity analogous to 
 the pelvis of the human kidney. 
 
 From the manner in which the kidneys are imbedded, the ureters 
 are necessarily derived from their anterior aspect. After receiving all 
 the terminations of the urinary tubules, they pass behind the rectum 
 to the cloaca, into which they discharge the urinary secretion. 
 The cloaca, therefore, receives the terminations of the rectum, of the 
 ureters, and also, as we shall immediately see, of the sexual pas- 
 sages : no urinary bladder is as yet developed, nevertheless vestiges 
 of its appearance begin to become visible. The cloaca is, in fact, 
 in some birds divided into two compartments, distinct both in their 
 appearance and in their office ; they are, moreover, separated by a 
 constriction, more or less well defined in different species. It is 
 into one of these compartments that the rectum opens, while the 
 other (Jig. 282, TO, m) contains the orifices of the ureters and genera- 
 tive canals ; the latter is, therefore, generally distinguished by the 
 name of urethro-sexual portion of the cloaca, and is in truth a 
 remnant of the allantois, and a rudiment of a bladder for the ac- 
 cumulation of the urine. 
 
 (686.) An unctuous secretion, peculiar to the class under 
 
616 
 
 AVES BIRDS. 
 
 Fi*. 282. 
 
 consideration, has been provided for the purpose of oiling the 
 feathers ; and in water birds the fluid alluded to becomes of very 
 great importance to their welfare, as it causes their plumy covering 
 to repel moisture so efficiently that it is never wet. The gland 
 given for this purpose is called the " uropygium" and is situated 
 upon the back of the os coccygis ; from this source the bird dis- 
 tributes the oily material thus afforded to all parts of its plumage. 
 
 (687.) The male 
 generative organs 
 in Birds are fully 
 as simple in their 
 structure as those 
 of the Reptilia. 
 The testes are 
 two oval bodies 
 (/g. 282, g), in- 
 variably situated 
 in the lumbar re- 
 gion, lying upon 
 the anterior por- 
 tion of the kid- 
 ney. In their 
 intimate structure 
 they consist of 
 contorted and ex- 
 tremely slender 
 tubes, wherein the 
 semen is elabo- 
 rated, contained 
 in a strong cap- 
 sule. The sperm- 
 secreting tubules 
 of each testis 
 terminate in a 
 slightly flexuous 
 vas defer ens (A, 
 i), that opens into 
 the cloaca by a simple orifice (m, m). In most birds it can scarcely 
 be said that a penis exists at all, two simple rudimentary vascular 
 papillae at the termination of the vasa deferentia constituting the 
 entire intromittent apparatus ; so that copulation between the male 
 
AVES BIRDS. 617 
 
 and female must, in the generality of species, be effected by a sim- 
 ple juxta-position of the sexual orifices : nevertheless, in the web- 
 footed tribes, which copulate in the water, and in the Ostrich, the 
 penis of the male is much more perfectly organized, as will be seen 
 by the following description extracted from Cuvier.* 
 
 The structure of the penis is far from being the same in all birds 
 provided with such an organ : it offers, in fact, two types extremely 
 different from each other; whereof the Ostrich and Drake may 
 be taken as examples. The penis of the Ostrich is of a size pro- 
 portioned to that of the bird. Its form is conical ; and a deep, 
 narrow groove runs along its upper surface from the base to the 
 point. The vasa deferentia open into the cloaca opposite to the 
 commencement of the groove; so that the semen flows directly into 
 this furrow. This penis consists, first, of two solid conical bodies, 
 entirely composed of fibrous substance, supported at their base 
 within the sphincter of the cloaca upon its inferior wall. The 
 fibrous cones are placed side by side, but not confounded together ; 
 and the right is smaller than the left, no doubt to allow this organ, 
 which never becomes soft as that of quadrupeds, to be more easily 
 folded back into the cloaca. Secondly, of a fibro- vascular body, which 
 constitutes the bulk of the inferior aspect of the penis, and is con- 
 tinued to its extremity. Thirdly, of a cellular portion, capable of 
 erection, placed beneath the skin lining the urethral groove. This 
 last is doubtless the first appearance of the corpus spongiosum, 
 which in Mammifers completely encloses the canal of the urethra; 
 while the two others represent the corpus cavernosum. The whole 
 apparatus, when not in use, is drawn into the cloaca by two pairs of 
 retractor muscles. 
 
 (688.) In Geese, Ducks, and many wading birds, such as the 
 Stork, the structure of the male intromittent organ is totally dif- 
 ferent. When in a state of repose, it is lodged in a pouch under 
 the extremity of the rectum, and curved, so as to describe three 
 parts of a circle. When the penis is opened in this condition, it is 
 found to be made up of two portions, each composing half of its 
 substance. The parietes of one half are thick, elastic, and slightly 
 glandular. The other presents internally a great number of trans- 
 verse grooves and folds. This latter portion during erection unrols 
 itself outwards like a glove ; and, at the same time, the half first 
 mentioned introducing itself into the hollow cylinder formed by the 
 
 * Lejons d'Anat. Comp. torn. v. p. 108. 
 
618 
 
 AVES BIRDS. 
 
 Fig. 283. 
 
 second, fills it up, and constitutes the firmest part of the organ. 
 Most of the grooves and folds visible during non-erection become 
 much less apparent when the penis is protruded ; and their direc- 
 tion being oblique, they prevent it from stretching out in a straight 
 line, but oblige it to assume a cork-screw appearance. A deep 
 groove runs along the whole length of this singular organ ; and it 
 is into the commencement of this groove that the vasa deferentia 
 pour the seminal secretion. 
 
 (689.) The females of species whose males possess a large 
 penis, are provided with a rudimentary clitoris of similar con- 
 struction. 
 
 (690.) The female ge- 
 nerative system in the fea- 
 thered tribes offers a remark- 
 able exception to what we 
 have as yet seen in the ver- 
 tebrate Ovipara. Instead of 
 being symmetrically develop- 
 ed upon the two sides of the 
 body, the right oviduct, and 
 most frequently the corre- 
 sponding ovarium, remain 
 permanently atrophied ; and, 
 although they do exist in a 
 rudimentary condition, they 
 never arrive at such dimen- 
 sions as to allow them to 
 assist in the reproductive 
 process. 
 
 (691.) The fertile ova- 
 rium presents in all essen- 
 tial circumstances the same 
 organization as those of the 
 Reptilia ; and is in the same 
 Avay attached by folds of 
 peritonaeum in the vicinity of the spine (fig. 283, /). The 
 contained ova are found in all stages of maturity ; and, being con- 
 nected together by narrow pedicles, the viscus assumes a distinctly 
 racemose appearance. 
 
 The oviduct (d, e) commences by a wide funnel-shaped aperture, 
 and soon assumes the appearance of a convoluted intestine. Its 
 
AVES BIRDS. 619 
 
 lining membrane varies in texture in different parts : near the in- 
 fundibular orifice it is thin and smooth ; further down it becomes 
 thicker and corrugated ; and at last, near the termination of the 
 canal, where the egg is completed by the calcification of its out- 
 ward covering (g), it presents a villose texture. The oviduct 
 ultimately opens into the corresponding side of the urethro-sexual 
 compartment of the cloaca. 
 
 (692.) We must, in the next place, proceed to describe, with as 
 much brevity as is consistent with the importance of the subject, 
 first, the nidus, or ovisac, in which the rudiment of the future being 
 is produced; secondly, the structure of the germ (ovulum) when 
 it escapes from the ovary ; thirdly, the additions made to the 
 ovulum as it passes through the oviduct ; and, lastly, the pheno- 
 mena that take place during the developement of the embryo by 
 incubation. 
 
 (693.) If the ovarium of a bird be examined whilst in functional 
 activity, such of the pedunculated ovisacs (calyces, Jig. 283, f) as 
 have within them ovula ripe for exclusion, will be found to consist 
 of two membranes.* Of these, the exterior is very vascular, and 
 is surrounded with a pale zon& (stigma) , occupying the centre of the 
 calyx. The lining membrane of the ovisac, on the contrary, is thin 
 and pellucid, but studded with minute corpuscles, which are probably 
 glandular, or perhaps little plexuses of vessels. Within this 
 ovisac the basis of the future egg (ovulum) is formed. 
 
 (694.) The ovulum produced in the ovisac, when mature, is 
 made up of the following parts. The bulk of it consists of an 
 orange-coloured oleaginous material, enclosed in a most delicate and 
 pellucid membrane (membrana vitelli ) ; this is the yolk of the 
 future egg. Upon the surface of the yolk there is visible a slightly 
 elevated opaque spot (cicatricula), wherein is lodged the repro- 
 ductive germ : this last, which is apparently the most important 
 part of the ovulum, is a minute pellucid globule ; and has been 
 named after its discoverer the " vesicle of Purkinje" or the 
 germinal vesicle. 
 
 (695.) The phenomena attending conception are therefore sim- 
 ply these : The membranes of the ovisac are gradually thinned by 
 absorption ; and, being embraced and squeezed by the infundibular 
 commencement of the oviduct, the transparent zone or stigma gives 
 way, allowing the ovulum, covered only by its membrana vitelli, to 
 escape into the oviductus. The rent ovisac is soon removed by 
 * Vide Purkinje, Symbolae ad ovi Avium historiam ante incubationera. 4lo. Lipsise,1830. 
 
620 AVES BIRDS. 
 
 absorption ; and the ovulum, with its cicatricula, is left to be 
 clothed with other investments : but the germinal vesicle is now no 
 longer to be seen ; its delicate covering having been, as Ptirkinje 
 supposes, ruptured by the violence to which it has been subjected. 
 
 (696.) It is during the passage of the ovulum through the canal 
 of the oviduct that it becomes enclosed in the other parts entering 
 into the composition of the egg : these are, the albumen, the 
 chalazas, the membrana putamim's, and the calcareous shell. 
 
 The albumen, or glairy fluid forming the white of the egg, is 
 secreted by the mucous membrane that lines the commencement of 
 the oviduct ; and being laid on, layer upon layer, gradually coats 
 the membrana vitelli. Some of the albumen meanwhile becomes 
 inspissated so as to form an almost invisible membrane, the chalaza, 
 which being twisted by the revolutions of the yolk, as it is pushed 
 forward in the oviduct, is gathered into two delicate and spiral 
 cords (Jig- 285, c, c), whereby the yolk is retained in situ after the 
 egg is completed. 
 
 The ovulum, now covered with a thick coating of albumen, 
 and furnished with the chalaza, at length approaches the terminal 
 extremity of the oviduct, where a more tenacious material is poured 
 out : it is here that the whole becomes encased in a dense mem- 
 brane resembling very thin parchment, called " membrana puta- 
 minis ;" and ultimately, on arriving in the last dilated portion of 
 the canal (Jig. 283, g), the lining membrane of which secretes cre- 
 taceous matter, the shell is formed by the gradual accumulation 
 of extremely minute, polygonal, calcareous particles, so disposed 
 upon the surface of the egg that imperceptible interstices are left 
 between them for the purpose of transpiration. 
 
 Thus, as the oviduct is traced from its infundibular commence- 
 ment, the different portions of it are seen successively to discharge 
 the following functions : the orifice of the infundibulum receives 
 the ovulum from the ovisac ; the succeeding portion, extending 
 nearly three fourths of its entire length, secretes the albumen and 
 the chalazas ; it in the next tract furnishes the membrana putami- 
 nis ; and in the last place, the shell ; after which, the complete 
 egg is expelled through the cloaca. 
 
 (697.) The anatomy of the egg prior to the commencement of 
 incubation is therefore sufficiently simple. Immediately beneath 
 the shell is the membrana putaminis ; which, however, we must 
 here remark consists of two layers ; and at the larger end of the 
 egg these layers separate, leaving a space (Jig. 284, a, 6), called 
 
AVKS BIRDS. 
 
 621 
 
 the vesicula aeris , 
 so formed is filled 
 with air containing 
 an unusual propor- 
 tion of oxygen, des- 
 tined to serve for the 
 respiration of the 
 future embryo. En- 
 closed in the mem- 
 brana putaminis the 
 student next finds 
 the albumen and 
 chalazas (Jig. 285, 
 c) ; and lastly, the 
 
 we may further notice, that the chamber 
 
 Fig. 284. 
 
 the 
 
 mem- 
 
 yolk, enclosed in its proper membrane (Jig. 284, c), 
 brana vitelli. 
 
 (698.) We must, however, dwell a little more at length upon 
 the composition of the yolk. The cicatricula (Jig. 284, g) is made 
 up of a thin membrane, which originally enclosed the vesicle of 
 Purkinje (/); but this latter, although introduced into the diagram 
 for the purpose of illustration, is in reality, as we have already seen, 
 no longer visible ; and we must now change the word cicatricula 
 for that of blastoderm, which may be presumed to consist of the 
 original cicatricula and the ruptured vesicle of Purkinje : it is from 
 this blastoderm, or germinal membrane, as it is sometimes called, 
 that the future being is developed. 
 
 Immediately over the blastoderm the membrana vitelli is slightly 
 thickened (Jig. 284, F^.285. 
 
 h) ; and beneath it 
 is a canal (e), which 
 leads to a chamber (d) 
 placed in the centre of 
 the yolk; this cavity 
 is filled with a whitish 
 granular substance. 
 
 (699.) Such is the 
 composition of the 
 complete egg of a 
 Fowl ; and with the 
 exception of trifling circumstances, hereafter to be noticed, of 
 that of vertebrate animals in general. The develppement of the 
 embryo is accomplished in the following manner. 
 
622 
 
 AVES BIRDS. 
 
 Fig. 286. 
 
 No sooner has incubation* commenced, than the blastoderm be- 
 comes distinctly separate from the yolk and the membrana vitelli; 
 and, as it begins to spread, assumes the form of a central pellucid 
 spot, surrounded by a broad dark ring (Jig. 285, g, h) : it at the 
 same time becomes thickened and prominent, and is soon separable 
 into three layers; of these, the exterior (Jig. 286, c) is a serous 
 layer ; the internal, or that next the yolk (A), a mucous layer ; 
 and between the two is situated a vascular layer, B, in which vessels 
 soon become apparent. These three layers are of the utmost im- 
 portance ; as from the first mentioned, all the serous structures, 
 from the second all the mucous structures, and from the third 
 the entire vascular system of the embryo originate. 
 
 (700.) Towards the close of the first day of incubation the 
 blastoderm has 
 already begun to 
 change its appear- 
 ance, and two 
 white filaments are 
 apparent in the 
 middle of the cen- 
 tral pellucid cir- 
 cle. Supposing a 
 longitudinal sec- 
 tion of it at this 
 period, the mem- 
 brana vitelli will 
 be found to have 
 become more pro- 
 minent where it passes over the germinal space (Jig. 286, 1, p). 
 The outer layer of the blastoderm (c) has become thickened at e 
 into the first rudiment of the dorsal portion of the embryo ; but the 
 mucous layer A, and the vascular layer B, have as yet undergone 
 little alteration. 
 
 At the commencement of the second day (Jig. 286, 2), the an- 
 terior portion of the embryo is dilated, and bent down so as to 
 inflect the three membranes of the blastoderm at this point. 
 
 At the conclusion of the second day this inflection is carried still 
 further; and from the vascular layer, a single pulsating cavity 
 (Jig. 286, 3, A), the punctum saliens, the first appearance of a 
 
 * Dr. Karl Ernst v. Baer iiber Entwickelungsgeschichte der Thiere. Beobachtung 
 und Reflexion. 4to. 1837. 
 
AVES BIRDS. 
 
 heart lias become developed : so that considerable advance is 
 already made towards that disposition of the fetus and its membra- 
 nous investments represented in the next figure, to which we now 
 beg the reader's attention. 
 
 (701.) The serous membrane (Jig. 287, c) has at the third day 
 become reflected to a considerable distance over the back of . the 
 fetus ; at one extremity investing the head with a serous covering, 
 while at the opposite it in like manner covers the tail : it is this 
 reflection of the serous layer which forms the amnion^ as will be 
 observed infig. 288, where the amniotic sac, C, is completed. 
 
 The mucous layer, A, is now seen to line the as yet open space 
 which is to form 
 
 the abdominal ca- F ^ 287 ' 
 
 vity ; and by its 
 inflections gives 
 birth to the rudi- 
 ments of the ab- 
 dominal viscera. 
 
 From the vascu- 
 lar layer, B, has 
 been developed the heart, now composed of two chambers (a, Z>), 
 and the branchial arteries (c), which join to form the aorta (w), 
 exactly as in the Menopoma (fig. 257). The allantois (p), the 
 uses of which will be described hereafter, likewise begins to make 
 its appearance.* 
 
 (702.) At the fifth day (fig. 288) the lineaments of the viscera 
 become tolerably distinct. The sac of the amnios, c, is completed; 
 the liver ', and the lungs e, begin to show themselves ; and the 
 bag of the allantois (/?) is largely developed : still, however, the 
 heart (a, b) is that of a fish, and the aorta (ra) formed by the 
 union of the branchial arches (c) ; so we have yet to trace how, as 
 the lungs increase in size, the circulatory apparatus becomes 
 changed, and the branchial organs obliterated. 
 
 On the third day of incubation there exist four vascular arches 
 (fig. 287, c) on each side, having a common origin from the bulb 
 (6), which obviously represents the bulbus arteriosus of Fishes and 
 Reptiles (vide figs. 259, 261) ; these encircle the neck, and join 
 on arriving in the dorsal region to form the aorta, which com- 
 mences by two roots, each made up of the union of the four bran- 
 
 * Des Branchies et des Vaisseaux branchiaux dans les Embryons des animaux ver- 
 tebres, par Prof. Ch. Ernst v. Baer. Annales des Sciences Nat. torn. xv. 
 
624 
 
 AVES BIRDS. 
 
 chial vessels of the corresponding side. The vascular arches are 
 developed one after the other, the most anterior being visible 
 even on the second day: shortly, a second appears behind the first, 
 the former in the mean time becoming considerably larger ; and at 
 length the third and the fourth are formed, the fourth being still 
 very small at the commencement of the third day. 
 
 At this period three fissures are perceptible between the bran- 
 chial arches, and in front of the first pair is the first appearance of 
 the oral orifice ; which, however, is not, properly speaking, the 
 aperture of the mouth, since at this epoch the jaws and buccal 
 cavity are not as yet formed ; but, physiologically considered, it 
 rather represents the pharynx. 
 
 At the close of the third day this branchial apparatus is already 
 slightly changed ; the branchial fissures are wider, and the fourth 
 vascular arch is become nearly as large as the others. On the 
 fourth day the first vascular arch is almost imperceptible, and that 
 for two reasons : in the first place, it becomes covered up with cel- 
 lular tissue ; and, secondly, it is so much diminished in size 
 towards the second half of the fourth day, that it merely gives 
 passage to a most slender stream of nearly colourless blood. By 
 the close of the fourth day it is no longer recognisable ; but, before 
 its disappearance, it is seen to have given off from its most convex 
 point a vessel, which becomes the carotid artery, so that, when the 
 arch itself is atrophied, that portion of it which was connected with 
 the bulb of the aorta becomes the trunk of the carotid. 
 
 The second arch then becomes diminished in size, insomuch that 
 the third and fourth receive the greater part of the blood ; while in 
 the meanwhile a fifth arch makes its appearance behind the fourth, 
 so that in this way there are still four permeable arches. 
 
 While these changes are going on in the vascular canals, the 
 first branchial fissure gradually closes ; and, to make up for this,' a 
 new one is formed between the arch which originally was the fourth, 
 and that last developed. 
 
 At the commencement of the fifth day there are consequently 
 again four vascular arches and three branchial fissures on each side ; 
 but not the same as those of the third day, since one arch and one 
 fissure have disappeared, and have been replaced by similar parts. 
 During the fifth day the vascular arch, which at first was the 
 second, is obliterated, and the two succeeding ones become increased 
 in size ; but at the end of the fifth day all the branchial fissures are 
 effaced, being filled up with cellular tissue, and no trace of them is 
 
AVES BIRDS. 
 
 625 
 
 left. The remainder of the metamorphosis seems to depend 
 principally upon changes that occur in the bulbus arteriosus (b) 9 
 which is by degrees converted into the bulb of the aorta. This 
 part of the arterial system, from being a single cavity, about the 
 fifth day divides into two canals, which become gradually more and 
 more separated, and bent upon themselves. The separation of 
 the bulbus arteriosus into two vessels is, in the opinion of Pro- 
 fessor Baer, owing to the circumstance that the ventricles gradu- 
 ally become separated by a septum, which, as it becomes more 
 complete, causes two distinct currents of blood to be propelled from 
 the heart. The current coming from the right ventricle arrives 
 sooner than the other at the vascular arches, and rushes through the 
 two posterior and through the middle arch of the left side ; while 
 the gush of blood from the left ventricle fills the two anterior arches, 
 and the middle arch of the right side ; a circumstance depending 
 upon the course impressed upon the currents derived from the two 
 ventricles. Each current becomes more and more distinct ; and at 
 last each is provided with a proper channel, forming the trunks of 
 the future pulmonary artery and of the future aorta. 
 
 It will be seen, that as yet the real aorta does not exist ; for at 
 
 Fig. 288. 
 
 this period of the metamorphosis all the blood passes through 
 the vascular arches that remain into the dorsal vessel ( fig. 288, m), 
 which is formed in the same manner as the aorta of Fishes by the 
 union of the branchial vessels. 
 
 While the branchial fissures penetrated into the pharyngeal 
 cavity, the branchial vessels were contained in the corresponding 
 branchial arches ; but, as soon as these fissures disappear, the vas- 
 cular trunks abandon the neighbourhood of the pharynx, and begin 
 to assume the character that they afterwards present. 
 
 The most posterior arch of the left side gradually disappears, 
 
 2 s 
 
626 
 
 AVES BIRDS. 
 
 and on the seventh day of incubation is no longer recognisable ; 
 whilst in the mean time the current of blood from the right ven- 
 tricle is directed in such a manner as to pass in front of this arch, 
 and enters the posterior arch of the right side, and the last but 
 one on the left. 
 
 As, moreover, the two arches, that were formerly the most 
 anterior, have become obliterated, while the third and fourth, on 
 the contrary, are increased in size, the blood, passing backwards 
 through these arches into the roots of the aorta, enters also the 
 carotid artery, which now resembles a prolongation of the com- 
 mencement of the aorta towards the head. Thus, one part of the 
 primitive root of the aorta becomes the trunk of the carotid artery. 
 
 There exist, consequently? on the eighth day three vascular 
 arches on the right side, and only two on the left ; and these five 
 arches are derived from the heart, as are also two small vascular 
 trunks now quite distinct, which have been formed from the bulb. 
 
 The anterior arch of both sides and the middle arch of the right 
 side proceed from the left ventricle ; the posterior arches issue 
 from the right : but all of them as yet unite to form the two roots 
 of the aorta, which are still of pretty equal size, and each root 
 gives off a carotid artery. At the point where the anterior arches 
 join the roots of the aorta, they are now seen to give off newly- 
 formed trunks, which go to the anterior extremity of their respec- 
 tive sides ; and as these limbs and the head increase in size, and 
 require more blood, the anterior arch propels a greater proportion 
 of blood in that direction, and insensibly less and less into the 
 aorta. The consequence is, that the anterior arch becomes more 
 and more decidedly the brachio-cephalic trunk ; and in short, on the 
 thirteenth day, it only communicates with the dorsal aorta by a 
 small vessel, and ultimately becomes quite detached, forming the 
 arteria innominata of the corresponding side. 
 
 Meanwhile the posterior arches on both sides send out branches 
 destined to the contiguous lungs. On the eighth day these vessels 
 are still very small, and difficult to find ; but they soon grow larger, 
 and, during the last half of the period of incubation, they show 
 themselves as the immediate continuations of the arches from which 
 they are derived ; their junctions with the aorta becoming more 
 and more imperfect, and constituting the two ductus arteriosi. 
 These canals are of very unequal size ; that of the right side is 
 much shorter than that of the left, which is now the only remnant 
 of the original root of the aorta on that side, and considerably 
 
AVKS BIRDS. G27 
 
 narrower than the root of the aorta on the right side. On the 
 right side, in fact, the middle arch now becomes of great import- 
 ance, and really constitutes the commencement of the descending 
 aorta, receiving the other communications as subordinate parts. 
 
 The bird having escaped from the egg, and having breathed for 
 some time, all the blood from the right ventricle passes into the 
 lungs, the ductus arteriosi become totally imperforate, and two dis- 
 tinct circulations are thus established; one proceeding from the right 
 side of the heart through the lungs into the left side of the heart, 
 the other from the left side of the heart through the system into 
 the left side of the heart. 
 
 We see, therefore, that of the five pairs of vascular branchial 
 arches which at first by their union formed the aorta as in Fishes, 
 those of the first pair on both sides and of the fifth on the left side 
 speedily disappear. The third on each side become the brachio- 
 cephalic trunks, the fourth of the right side becomes the descending 
 aorta, while the fifth of the right side and the fourth of the left side 
 are converted into the pulmonary arteries. The very short trunk 
 common to the two pulmonary arteries, as well as the equally 
 short trunk of the aorta, properly so called, are produced by the 
 transformation of the single cavity of the original " bulbus arte- 
 riosus" into two distinct canals, and thus this wonderful meta- 
 morphosis is accomplished. 
 
 (703.) About the hundred and twentieth hour from the com- 
 mencement of incubation, the vascular layer of the blastoderm has 
 spread extensively over the yolk (Jig. 289, b ) ; and, as the vessels 
 formed by it become perfected, they are found to converge to the 
 
 Fig. 289. 
 
 
628 
 
 AVES BIRDS. 
 
 fig. 290. 
 
 navel of the embryo, and to constitute a distinct system of arteries 
 and veins (omphalo-mesenteric), communicating with the aorta and 
 with the heart of the fetus, and forming a vascular circle surrounding 
 the yolk. The omphalo-mesenteric arteries, (Jig. 291, b, c,) which 
 thus ramify over the vitelline sac, are derived from the mesenteric 
 arteries ; and the blood distributed through them is returned, by the 
 omphalo-mesenteric veins, to the superior vena cava of the young 
 chick. 
 
 (704.) As soon as the intestinal system of the embryo bird is 
 distinctly formed, the membrane enclosing the yolk (vitellicle) is 
 seen to communicate with the intestine by a wide duct (ductus 
 vitello-intestinalis), whereby 
 the nutritive substance of the 
 yolk enters the alimentary 
 canal to serve as food, and 
 the mucous membrane lin- 
 ing the vitellicle becomes 
 thrown into close wavy folds, 
 so as to present a very ex- 
 tensive surface. Gradually, as 
 growth advances, the yolk di- 
 minishes in size ; and at length, 
 before the young bird is hatch- 
 ed, the remains of it are entirely 
 withdrawn into the abdominal 
 cavity, (Jigs. 292, 293,) where 
 its absorption is completed : 
 but even in the adult bird 
 a little caecal appendage, or 
 diverticulum, still indicates 
 the place formerly occupied by the ductus vitello-intestinalis. 
 
 (705.) While the above phenomena are in progress, another 
 important system of vessels provided for the respiration of the bird 
 in ovo are developed, and obliterated before the egg is hatched. 
 
 At about the period represented in Jig. 288, the sides of 
 the abdominal cavity, which is still open anteriorly, are occupied 
 by transitory secreting organs, named corpora Woifiana ; these, 
 apparently, are the rudiments of the genito-urinary system : and, 
 to receive their secretion, a bladder is developed, called the allan- 
 toid sac, a viscus which is moreover destined to play an impor- 
 tant part in the economy of the embryo, and soon becomes 
 
AVES BIRDS. 
 
 629 
 
 its principal respiratory organ. The allantois first makes its ap- 
 pearance as a delicate bag (Jig. 288, p), derived from the anterior 
 surface of the rectum, but Fiv 29 i 
 
 it expands rapidly, and 
 soon occupies a very con- 
 siderable portion of the 
 interior of the egg (Jig. 
 289, c), until at last "it 
 lines nearly the whole ex- 
 tent of the mcmbrana 
 putaminis, and, becoming 
 thus extensively exposed 
 to the influence of the air 
 that penetrates the egg- 
 shell, it ultimately takes 
 upon itself the respiratory 
 function. When fully de- 
 veloped (Jig. 290), it is 
 covered with a rich net work 
 of arteries and veins (a, b) 
 spread upon its surface. 
 The arteries (fig. 291, a) 
 are derived from the com- 
 mon iliac trunks of the em- 
 bryo, and of course repre- 
 sent the umbilical arteries 
 of the human fetus ; the 
 vein enters the umbilicus, 
 
 and, passing through the fissure of the liver, pours the blood, which 
 it returns from the allantois in an arterialized condition, into the 
 inferior cava, as does the umbilical vein of Mammalia. 
 
 About the nineteenth day of incubation, the air-vessel at the 
 large extremity of the egg (Jig. 290, c) is ruptured, and the lungs 
 begin to assume their function, by breathing the air that this 
 vesicle contains. The circulation through the allantois then gra- 
 dually diminishes, and it is slowly obliterated, until merely a liga- 
 mentous remnant, called the urachus, is left. In Reptiles, how- 
 ever, as we have already seen, a portion of the allantoid bag re- 
 mains even in the adult creature (fig. 254, q); and in Birds 
 that compartment of the cloaca in which the genital and urinary 
 passages terminate are vestiges of the same organ. 
 
630 
 
 AVES KIHDS. 
 
 Fig. 292, 
 
 in 
 
 293. 
 
 (706.) Although the above description gives the reader a ge- 
 neral view of the process 
 of oviparous generation 
 in its most perfect and 
 consequently most com- 
 plex form, the reader, in 
 applying it to the deve- 
 lopement of the ovum in 
 the inferior OVIPARA, 
 must bear in mind the 
 following important dif- 
 ferences : 1st. That in 
 the air-breathing REPTI- 
 LIA the white of the egg 
 is almost, if not entirely, 
 wanting; but the other 
 phenomena are similar to 
 those witnessed in the 
 Bird. 2dly. That 
 FISHES not only 
 is there no white 
 formed, but for ob- 
 vious reasons the 
 allantoid apparatus 
 is not developed. 
 The egg in these 
 lower tribes con- 
 tains only the yolk 
 and the cicatricu- 
 la ; it swells from 
 absorbing the sur- 
 rounding water, 
 and the fetus is 
 developed upon 
 the surface of the 
 yolk ; the latter, 
 which, as in Birds, 
 communicates with 
 the intestine, be- 
 ing slowly received 
 into the abdomi- 
 nal cavity. 
 
AVES BIRDS. 631 
 
 (707.) The subsequent changes that occur in the circulatory 
 system of a Bird, namely, the obliteration of the foramen ovale, 
 and of the ductus arteriosi, whereby the pulmonary and systemic 
 circulations become quite distinct, are similar to those which take 
 place in the Mammiferous fetus, and will be described in the next 
 chapter. 
 
632 
 
 CHAPTER XXX. 
 
 MAMMALIA. 
 
 THE highest boon conferred upon the lower animals, " Hea- 
 ven's last best gift," is parental affection. The cold-blooded 
 Ovipara, unable in any manner to assist in the maturation of 
 their offspring, were necessarily compelled to leave their eggs 
 to be hatched by the agency of external circumstances ; and their 
 progeny, even from the moment of their birth, were abandoned 
 to chance and to their own resources for a supply of nourish- 
 ment. In Birds, the duties and the pleasures inseparable from 
 the necessity of incubating their ova, and of providing nutriment for 
 their callow brood, are indeed manifested to an extent unparalleled 
 in the preceding orders of Vertebrata ; but it is to the Mammalia 
 alone, the most sagacious and intelligent of all the inhabitants 
 of this world, that the Creator has permitted the full enjoyment 
 of paternal and maternal love, has thrown the offspring absolutely 
 helpless and dependent upon a mother's care and solicitude, and 
 thus confers upon the parent the joys and comforts that a mother 
 only knows, the dearest, purest, sweetest, bestowed upon the 
 animal creation. 
 
 (708.) The grand circumstance whereby the entire class of 
 beings generally designated under the name of QUADRUPEDS may 
 be distinguished from all other members of the animal kingdom 
 is, that the females of every species are furnished with mammary 
 glands, secerning organs appointed to supply a secretion called 
 milk, whereby the young are nourished from the moment of 
 their birth, until they have reached a sufficient age to enable 
 them to live upon such animal or vegetable substances as are 
 adapted to their maturer condition. The possession of these 
 lactiferous glands would indeed be in itself a sufficiently decisive 
 characteristic of the whole group ; and if to this we add that their 
 visceral cavity is separated into a thorax and abdomen by a mus- 
 cular diaphragm^ and that they breathe by means of lungs pre- 
 cisely similar to our own, we need not in this place dwell upon 
 any more minute definition of the Mammiferous Vertebrata. 
 
MAMMALIA. 633 
 
 (709.) The MAMMALIA, as we might be prepared to antici- 
 pate from their importance, are extensively distributed. The 
 generality of them are terrestrial in their habits, either browsing 
 the herbage from the ground, or, if of carnivorous propensities, 
 leading a life of rapine, by carrying on a blood-thirsty warfare 
 against animals inferior to themselves in strength or ferocity. 
 Many inhabit the trees ; some burrow beneath the surface of 
 the soil ; a few can raise themselves into the air and flit about 
 in search of insect prey; the Otter and the Seal persecute the 
 fishes even in their own element ; and the gigantic Whales, wal- 
 lowing upon the surface of the sea, " tempest the ocean" in their 
 fury. 
 
 (710.) With habits so diverse, we may well expect correspond- 
 ing diversity in their forms, or in the structure of their limbs ; and, 
 in fact, did we not compress our description of these particulars 
 into reasonable limits, we might easily test the perseverance of the 
 most patient reader in following us through the mass of details 
 connected with this part of our subject. We shall, therefore, 
 commencing as we have hitherto done, with the osteology of the 
 class, first describe, in general terms, the characters of a Mam- 
 miferous skeleton ; and then, as we arrange the Mammalia under 
 the various orders into which they have been distributed, speak of 
 the most important aberrations from the given type. 
 
 (711.) The vertebral column of all Mammals, with the remark- 
 able exception of the Cetacea, is divisible into the same regions as 
 in the human skeleton, viz. the cervical, dorsal, lumbar, sacral, and 
 coccygeal or caudal portions. 
 
 The cervical vertebrae are invariably seven in number. The 
 Sloth (Bradypus tridactylus) was, until recently, regarded as 
 forming a solitary exception, it having been supposed to possess 
 nine cervical vertebrae ; the researches of Professor Bell, however, 
 show, that even this animal conforms to the general law. The dis- 
 tinguished naturalist referred to* has demonstrated, " that the pos- 
 terior two of these vertebrae have attached to them the rudiments 
 of two pairs of ribs, in the form of small elongated bones articulated 
 to their transverse processes ; they must, therefore, be considered 
 as truly dorsal vertebrae, modified into a cervical form and function 
 suited to the peculiar wants of the animal/ 1 Professor Bell fur- 
 ther observes, that " the object of the increased number of ver- 
 
 * Cyclop, of Anat. and Phys. art. EULNTATA. 
 
634 MAMMALIA. 
 
 tebrse in the neck of the Sloth is evidently to allow of a more ex- 
 tensive rotation of the head ; for, as each of the bones turns to a 
 small extent upon the succeeding one, it is clear that the degree of 
 rotation of the extreme point will be in proportion to the number 
 of pieces in the whole series. When the habits of this extra- 
 ordinary animal are considered, hanging as it does from the under 
 surface of boughs, with the back downwards, it is obvious that the 
 only means by which it could look towards the ground must be by 
 rotation of the neck ; and as it was necessary, to effect this without 
 diminishing the firmness of the cervical portion of the vertebral 
 column, to add certain moveable points to the number possessed 
 by the rest of the class, the additional motion was acquired by mo- 
 difying the two superior dorsal vertebrae, and giving them the 
 office of cervical, rather than by infringing on a rule, which is thus 
 preserved entire, without a single known exception." 
 
 (712.) The occipital bone articulates with the atlas by two 
 lateral condyles, instead of by a single central articulating surface ; 
 a circumstance which depends upon the greatly increased develope- 
 ment of the encephalon, and the consequent expansion of the 
 cranium. 
 
 (713.) The number of dorsal vertebrae depends upon that of the 
 ribs : thus, in the Bat tribe there are only eleven ; while in some 
 of the Pachydermata, as, for example, in the Elephant and Tapir, 
 as many as twenty dorsal vertebrae may be counted. The lumbar 
 and sacral vertebrae will likewise be more or less numerous in dif- 
 ferent genera ; and in the number of pieces composing the coccyx, 
 or tail, there is every variety, from four to five and forty. 
 
 (714.) The thorax is enclosed by ribs, that in structure, and 
 in their mode of connection with the dorsal vertebrae, resemble 
 those of Man. At its dorsal extremity each rib is articulated by 
 its head to the bodies of the vertebrae, and to the intervertebral 
 substance ; while its tubercle, or the representative of the second 
 head of the rib of a Bird, is moveably connected with the corre- 
 sponding vertebral transverse process. There are no sternal ribs ; 
 but these are represented by cartilaginous pieces, whereby towards 
 the anterior part of the thorax each rib is attached to the side of 
 the sternum ; posteriorly, however, this connection does not exist. 
 The anterior ribs are therefore called true ribs, and the posterior, 
 false or floating ribs, precisely as in the human skeleton. 
 
 (715.) The sternum is composed of several narrow pieces, 
 placed in a line behind each other along the middle of the breast. 
 
MAMMALIA. 635 
 
 These pieces are generally consolidated : by their lateral margins 
 they give attachment anteriorly to the clavicles, if these bones be 
 present ; and, behind these, to the costal cartilages of the true ribs. 
 
 From the whole arrangement of the thorax, it is evident that 
 the ribs are capable of extensive movements of elevation and de- 
 pression, whereby the capacity of the whole thoracic cavity may be 
 increased or diminished ; movements which, aided by those of the 
 diaphragm, draw in and expel the air used for respiration. 
 
 (716.) The anterior extremity is appended to a broad scapula, 
 generally unconnected with the rest of the skeleton except by 
 muscular attachments. In quadrupeds that use this extremity as 
 an instrument of prehension or of flight, a clavicle is interposed 
 between the scapula and the sternum ; but most frequently this ele- 
 ment of the shoulder is deficient, and even the coracoid bone, if a 
 vestige of it remains at all, is reduced to a mere appendage to the 
 scapula, known to the human anatomist as the coracoid process. 
 The rest of the limb presents the arm, the fore-arm, the carpus, 
 metacarpus, and phalanges ; but these are so altered in appearance 
 in different orders, that no general description will suffice, and we 
 must therefore defer this part of our inquiry ^frr tho present. 
 
 (717.) In the posterior extremity there is equal dissimilarity in 
 the construction of the distal portions of the limb ; but the pelvis, 
 although much modified in form, consists of the same pieces as in 
 the human subject, and in like manner has the pubic arch and fora- 
 mina fully completed. 
 
 (718.) The cranium and face are made up of numerous bones, 
 easily recognizable, as they correspond in their general arrangement 
 with those composing this part of the skeleton in the lower Verte- 
 brata. Their developement in the facial region is large in propor- 
 tion to the strength of the muscles moving the lower jaw; and they 
 are so disposed as to form buttresses to resist the powerful pressure 
 of the teeth, as well as to enclose cavities wherein are lodged the 
 organs connected with the senses of smell and of vision. One 
 example will answer our present purpose, and we have selected the 
 skull of the Pig as one calculated to show a medium develope- 
 ment of the whole series. 
 
 In the face we find on each side two bones entering into the 
 composition of the upper jaw, into which teeth are implanted ; 
 these are the superior maxillary (fig- 94, 18), and the intermaxil- 
 lary (17). These bones, moreover, bound extensively the cavity of 
 the nose ; and, together with the palatine process of the palate 
 
636 
 
 MAMMALIA. 
 
 bone (Jig. 295, 22), constitute the bony palate, or roof of the mouth. 
 The nasal bones (20, 20) complete the upper part of the face; and, 
 being in contact along the mesial line, arch over the nasal chamber. 
 
 Fig. 294. 
 
 The orbit is boundeci anteriorly by the lacrymal bone (c), and 
 ihejugal or malar bone (6). Its posterior boundary is generally 
 wanting, as the external angular processes of the jugal and frontal 
 bones do not meet. 
 
 The orbital cavity is principally formed by processes derived 
 from the os frontis, the sphenoid, the lacrymal, and the malar 
 bone ; the ethmoid and the palatine rarely entering into its com- 
 position. 
 
 The os ethmoides, the vomer, and the turbinated bones will 
 be described minutely when we speak of the olfactory apparatus, 
 which they contribute to form. 
 
 The inferior maxilla in Mammals is characterized by two cir- 
 cumstances, which distinguish it from that of other Vertebrata. It 
 consists, in the first place, of only two lateral pieces, exactly similar 
 to each other, joined together at the chin by a symphysis in many 
 orders, but in others even this symphysis is obliterated at an early 
 age, and in the adult the two lateral halves would seem to form 
 but one piece. 
 
 Another character peculiar to the lower jaw of a Mammal is, 
 that it is moveably articulated with the temporal bone by means of 
 a convex and undivided condyle. These marks, identifying the 
 
MAMMALIA. 637 
 
 Mammiferous lower jaw, ought to be well remembered by the 
 geologist. 
 
 We shall hereafter have occasion to describe the teeth that arm 
 the jaws of the different tribes of quadrupeds ; and therefore now 
 
 Fig. 295. 
 
 proceed to examine their cranial cavity, and the bones that enter 
 into its formation. 
 
 The frontal bones (Jigs. 294, 295, 1, 1) are generally two in 
 number ; and even when, as in Man, they seem to form but one 
 bone, the two lateral halves are produced from separate points of 
 ossification, and only coalesce as age advances: sometimes, indeed, 
 even in the adult, they remain permanently separated by suture. 
 
 The parietal bones (7, 7) occupy their usual position ; and, 
 although generally double, as in the human skeleton, they are not 
 unfrequently consolidated together, even at an early age, so as to 
 represent but a single bone. 
 
 The occipital bone consists primarily of the same pieces as in the 
 Reptile ; but in the Mammifer these are at an early period conso- 
 lidated into one mass, situated at the back of the cranium. Its 
 basilar portion (5) articulates with the atlas by two condyles ; while 
 the lateral wings (10) and the superior arch (8) surround the 
 foramen magnum, and protect the cerebellic regions of the 
 encephalon. 
 
 The sphenoid (6), although composed of fewer separate pieces 
 than in the Reptilia, and even regarded by the human anatomist 
 as a single bone, is still distinctly divisible, especially in young 
 animals, into two very important portions, one anterior, and the 
 other posterior ; each, as we shall soon see, forming the body of a 
 distinct cranial vertebra. The posterior half (6) consists of the 
 
638 
 
 MAMMALIA. 
 
 body, including the posterior clinoid processes, and of the greater 
 alse and pterygoid processes (Jig. 295, 25). The anterior half 
 is formed by the anterior clinoid processes and alse minores 
 (Jig- 295, 11). These two halves may therefore be called, respec- 
 tively, the anterior and posterior sphenoids. 
 
 Lastly, we have the temporal bone, exhibiting but one piece, 
 although made up of all the parts which in the Reptile were so 
 obviously distinct elements. The petrous portion wedged into 
 the base of the cranium, still encloses the internal car. The 
 tympanic element (Jig* 294, a) supports the membrana tympani. 
 The mastoid process (Jig. 295, 12) is the homologue of the mas- 
 toid bone of the Crocodile ; and, lastly, the squamous element 
 with which the lower jaw is articulated (Jig. 294, 23) in the 
 Reptilia, was visibly a distinct bone. Even to these may be added 
 the zygomatic process, which Professor Owen regards as an inde- 
 pendent elemental part. 
 
 (719.) Reviewing, therefore, all that has been said relative to 
 the composition of the skull in the different classes of Vertebrata, 
 the following deductions may be arrived at.* 
 
 1. That, as we advance from lower to higher forms, the propor- 
 tionate size of the cranium relative to that of the face becomes 
 greater. 
 
 2. That the number of bones met with upon the inferior and 
 lateral aspects of the head gradually diminishes : for in Mammalia 
 the pterygoid and tympanic bones which even in Birds are sepa- 
 rate pieces, become very generally confounded with the sphenoid 
 and the temporal ; and also the petrous and squamous portions of 
 the temporal become blended together. 
 
 3. The number of bones normally entering into the composition 
 of the cranium of adult Mammalia varies considerably. When most 
 numerous, there are twenty-eight, eleven in the cranium, and 
 seventeen in the face. In this case the cranial bones are the follow- 
 ing, one occipital, one sphenoid, the two squamous portions of 
 the temporal, the two tympano-petrous portions of the temporal, the 
 two parietal, the two frontal, and the ethmoid. 
 
 The bones of the face are, two superior maxillary, two inter- 
 maxillary, two nasal, two lacrymal, the vomer, two inferior turbi- 
 nated bones, two palate bones, two jugal bones, and, lastly, the two 
 halves of the lower jaw. 
 
 It is true that some slight exceptions occur : thus, for example, 
 
 * Meckel, Trait6 G6nerale d'Anatomie Comparee, torn. iii. seconde partie, p. 195. 
 
MAMMALIA. 639 
 
 in the Cetacea the pterygoid bones remain detached; in the Ro- 
 dentia the occipital is divided into a superior and inferior portion ; 
 but, in the latter, the two frontal and the two parietal become con- 
 solidated into one bone. 
 
 In Man the bones of the cranium become much less numerous, 
 inasmuch as all the elements of the occipital, of the temporal, of the 
 frontal, the intermaxillary, and the maxillary, composing the upper 
 jaw, and the two halves of the lower jaw, respectively coalesce ; and 
 the skull consists of but one-and-twenty bones, seven in the cra- 
 nium, and fourteen in the face. 
 
 Even this number is not the smallest ; for in some Monkeys the 
 nasal bones unite and become consolidated into one piece. 
 
 (720.) Having thus enumerated the different osseous pieces 
 forming the crania of all classes of vertebrate animals, we must next 
 consider them in another point of view, namely, as being continua- 
 tions of the spinal chain of bones, or real vertebrae modified in form 
 and proportions in conformity with the increased volume of the 
 nervous masses they are destined to enclose. We must, however, 
 premise that it is by no means our intention to adopt unreservedly 
 the theoretical opinions of those Continental writers who find verte- 
 bral elements in the bones of the face, and even in the nasal carti- 
 lages ; still, without overstraining the facts, it is easy to demonstrate 
 very satisfactorily, that the cranial pieces that immediately enclose 
 the cerebral masses are strictly vertebrae, and present the same 
 essential structure as those of the spinal region. 
 
 That this is the case in the skull of a Reptile, no one, indeed, 
 who examines the subject, can hesitate to admit ; but even in the 
 Mammiferous cranium, where, from the enormous proportionate 
 size of the encephalon, the cranium is most distorted, it is not diffi- 
 cult to perceive the relationship. 
 
 The cranial vertebrae are three in number, the occipital, the 
 parietal, and the frontal : these are exhibited in the subjoined 
 diagram, after Carus, representing those of the Sheep. 
 
 The occipital vertebra (Jig. 296, A) has for its body thebasilar 
 portion ; the arches bound the foramen magnum laterally ; and 
 above, the spinous process, flattened out and expanded in proportion 
 to the size of those lobes of the brain and cerebellum which it de- 
 fends, forms the posterior portion of the skull. 
 
 The body of the second or parietal vertebra (B) is the body 
 of the sphenoid; that is, more properly speaking, the poste- 
 rior sphenoid bone, whose large alse, curving upwards, meet the 
 
640 
 
 MAMMALIA. 
 
 parietal, and thus an arcli is formed of sufficient span to cover the 
 middle lobes of the cerebrum. 
 
 The anterior, or frontal vertebra, Fig. 296. 
 
 has for its body the anterior sphenoid 
 (al<E minores) ; its arch being com- 
 pleted by the cavity of the os frontis, 
 which encloses anteriorly the cribriform 
 plate of the ethmoid bone. 
 
 From this analysis of the compo- 
 sition of the cranium, it is apparent 
 that the temporal bones, although in 
 Man they assist so materially in com- 
 pleting the cranial cavity, are only 
 intercalated between the real vertebral 
 elements ; as indeed might almost have 
 been anticipated, seeing how different- 
 ly the pieces belonging to this bone 
 are arranged in different classes of 
 Vertebrata. 
 
 (721.) Such is the general organ- 
 ization of the Mammiferous skeleton. 
 Let us now proceed to consider the 
 osteology of the different orders into 
 which the Mammalia have been dis- 
 tributed, and observe in what respects 
 they individually differ from each 
 other. 
 
 The transition from Birds to Qua- 
 drupeds, remotely separated as they 
 
 might appear to be, is effected by gentle gradations of struc- 
 ture ; and the MONOTREMATA, notwithstanding their quadru- 
 pedal form and hairy covering, are so nearly allied to the feathered 
 Ovipara in many points of their organization, that they evidently 
 form a connecting link between these two great classes of animals. 
 
 It is true that they have mammary glands, and must therefore 
 be supposed to give suck to their offspring ; but it is not even yet 
 satisfactorily determined whether they lay eggs, or produce living 
 young. The structure of their generative apparatus would seem, in 
 fact, to be rather allied to the Oviparous than the Mammiferous 
 type; and, as in Birds, the rectum, the urinary passages, and the 
 sexual organs, all discharge themselves into a common cloacal 
 
MAMMALIA. 641 
 
 chamber, so that there is still but a single vent, a circumstance 
 from which the name of the order is derived. 
 
 Even their skeleton, in many points, presents a very close affinity 
 to that of a Bird, as will be evident on examining the osseous sys- 
 tem of the Ornithorhynchus paradoxus (Jig. 297). 
 
 Fig. 297. 
 
 The mouth of this quadruped indeed resembles that of a Duck, 
 whence the name of " Duck-bill," whereby it is usually distin- 
 guished. It has, moreover, a distinct furcular bone in addition to 
 what would seem to be the ordinary clavicles ; but in reality these 
 are the coracoid bones still largely developed. Moreover, the an- 
 terior or sternal ribs are ossified, and a spur is attached to the hind 
 foot of the male, not remotely resembling that of a Cock : this last 
 appendage is perforated by a duct, and has a gland connected with 
 it, situated on the inner side of the thigh, by which a poisonous 
 secretion was formerly supposed to be elaborated. 
 
 (722.) The MARSUPIALIA, it will be afterwards explained, as 
 regards the conformation of their generative system, are organized 
 in accordance with a type intermediate between that common to 
 Birds and that which characterizes Mammalia properly so called. 
 
 The Marsupial quadrupeds bring forth their young alive, but in 
 such an imperfect condition, that at the period of their birth 
 scarcely the vestiges of their limbs have become apparent ; and in 
 this state they are conveyed into a pouch formed by the skin of the 
 female's abdomen, where they fix themselves by their mouths to 
 the nipples of their mother, and, sucking milk, derive from this 
 source the materials for their growth. These animals are peculiar 
 to the Australian and American continents; nay, in Australia, so 
 anomalous in all its productions, with one or two exceptions, and 
 those perhaps brought there by accidental importation, all the 
 quadrupeds are constructed after the Marsupial type. The great 
 characteristic whereby to distinguish the skeleton of a Marsupial 
 
642 
 
 MAMMALIA. 
 
 Mammifer, is the existence of two peculiar bones attached to the 
 anterior margin of the pubis, which in the living animal are im- 
 bedded in the muscular walls of the abdomen, and thus support the 
 pouch of the female. The marsupial bones, however, exist in the 
 male likewise ; and even in the MONOTREMATA, that are evidently 
 nearly allied to the proper MARSUPIALS, although no pouch is 
 met with even in the female sex, the bones alluded to are found 
 connected with the pubis. 
 
 This great section of the Vertebrate creation, which, perhaps, 
 ought rather to be regarded as a class by itself, is composed of 
 numerous families, of diverse forms and very opposite habits. The 
 Opossums (Didelphis) of the American continent live in trees, and 
 devour birds, insects, or even fruits : in these, the thumb of the 
 hind foot is opposable to the other fingers, and adapted for grasp- 
 ing the boughs, whence they are called Pedimanes; their tail is like- 
 wise prehensile. Others are terrestrial in their habits, wanting the 
 prehensile thumb. 
 
 Fig. 298. 
 
 The Kangaroo Rat, or Potoroo (Hypsiprymnus), of whose ske- 
 leton we have given a drawing (fg. 298), is remarkable for the dis- 
 proportionate size of its hind legs: these, moreover, have no thumb, 
 and the two innermost toes are joined together as far as the nails; 
 so that there appear to be but three toes, the inner one being fur- 
 nished with two claws. Such legs are well adapted to make strong 
 
MAMMALIA. 643 
 
 and vigorous leaps over a level plain ; and in the Kangaroos 
 (Macropus) the extraordinary developement of the posterior extre- 
 mities is even yet more wonderful. In other respects, the skeletons 
 of the Marsupialia conform to the general description already given. 
 
 (723.) All other Mammiferous Vertebrata produce their young 
 alive, and not until they have attained a considerably advanced state 
 of developement during their intra-uterine existence. The con- 
 nection between the maternal and fetal systems in these orders is 
 maintained during the latter periods of gestation by the develope- 
 ment of a peculiar viscus, called the placenta: nevertheless, after 
 birth, the young animals are still dependent upon the mother for 
 support, and live upon the milk supplied by her mammary organs. 
 
 (724.) The lowest order of PLACENTAL MAMMALIA com- 
 prises those forms which, although they breathe air by means of 
 lungs, and have hot blood like ourselves, are appointed to inhabit 
 the waters of the ocean, wherein they pass their lives, and even 
 bring forth and suckle their young. In order to live under such 
 circumstances as these, the CETACEA must necessarily, in many 
 points of their structure, be organized after the model of fishes ; 
 and we cannot be surprised, if in their outward form, and even in 
 the disposition of their limbs, they strikingly resemble the finny 
 tribes. Their head is large, frequently indeed of enormous propor- 
 tions : there is no neck apparent externally ; the head and trunk, as 
 in fishes, appearing continuous. The anterior extremities are con- 
 verted into broad fins, or paddles ; whilst the pelvic extremities are 
 absolutely wanting : posteriorly, the body tapers off towards the 
 tail, and terminates in a broad, horizontal fin, which latter, however, 
 is not supported by bony rays, as in the fish, but is entirely of a 
 cartilaginous and fleshy structure. Frequently there is even a ver- 
 tical dorsal fin ; but this, too, is entirely soft and cartilaginous, so 
 that in the skeleton no vestiges of it are apparent.* 
 
 In the Whalebone- Whale (Bal&na mysticetus) the peculiari- 
 ties of the Cetaceous skeleton are well exhibited. In this gigantic 
 animal (fig. 299), which sometimes measures upwards of a hun- 
 dred feet from the snout to the tail, the head forms nearly a fourth 
 part of the entire length of its stupendous carcass ; so enormously 
 developed are the bones of the face that form the upper and 
 the lower jaws. The cranial cavity, wherein the brain is lodged, 
 does not of course participate in this excessive dilatation, but 
 
 * It is interesting to see these fins still formed by the skin (exoskeleton,) where the 
 osseous system could not enter into their composition without deviating altogether 
 from the Mammiferous type. 
 
 2x2 
 
644 
 
 MAMMALIA. 
 
 corresponds to the size of the brain lodged within it. It, however, 
 presents one point of physiological in- Fig. 299. 
 
 terest, serving to prove still more de- 
 monstratively, that the temporal bone is 
 merely an adjunct to, and not essentially 
 a constituent part of, the cranium ; for 
 here the petrous portion of the temporal 
 bone, wherein is lodged the organ of 
 hearing, is entirely detached from the 
 skull, to which it is only fastened by a 
 ligamentous connection. This remarkable 
 arrangement is no doubt intended to pre- 
 vent the stunning noises that would else 
 be conveyed from every side to the ear, 
 by cutting off all immediate communica- 
 tion between the auditory apparatus and 
 the osseous framework of the head. 
 
 The cervical vertebrae, in conformity 
 with the shortness of the neck, are exceed- 
 ingly thin ; and some of them are not 
 unfrequently anchylosed into one piece. 
 
 The thorax is composed in the ordinary 
 manner ; but the posterior ribs are only 
 fixed to the transverse processes of the 
 corresponding vertebras. Behind the tho- 
 rax the whole spine is flexible, its move- 
 ments being untrammeled by any pelvic 
 framework, or posterior extremity ; so that, 
 
 as in fishes, the broadly expanded tail is 
 
 the great agent in locomotion ; and, from 
 
 the horizontal position of this mighty oar, 
 
 it is better adapted to enable the animal 
 
 to plunge headlong into the depth, and to 
 
 rise again to the surface, with all expedi- 
 tion, than if it had been placed vertically, 
 
 as it is in fishes. 
 
 The only vestiges of a pelvis met with 
 
 in the Whale are, the rudimentary ossa 
 
 pubis represented in the figure. These are 
 
 imbedded in the abdominal muscles, and 
 
 serve to support the external organs of 
 
MAMMALIA. 
 
 645 
 
 generation : tlie caudal vertebrse are, however, distinguishable 
 by the inferior spinous processes, developed from their under 
 surfaces. As to the construction of the anterior extremity, the 
 shoulder is composed of the scapula alone. The arm and fore-arm 
 are much stunted, and are not moveable at the elbow ; therefore the 
 muscles for pronating and supinating the arm do not exist, but are 
 represented by aponeurotic expansions spread over the surfaces of 
 the bones. The bones of the carpus are flattened, and more or 
 less consolidated together. The fingers, likewise, are flat; and the 
 whole limb so covered with tendinous bands, and enveloped in skin, 
 as to form merely a fin, whereby the creature guides its course 
 through the water. 
 
 (725.) In the Herbivorous Cetacea, as the Manatus and Du- 
 gong, the head is smaller in proportion to the sides of the body, 
 and the hands better developed, so as to be useful in creeping 
 on land, or in carrying their young. These genera inhabit the 
 mouths of tropical rivers. 
 
 (726.) The relationship between the Cetacea and the next order 
 that offers itself to our notice is too evident not to be immediately 
 appreciated. The thick and naked skin, the gigantic body, 
 the massive bones, the bulky head, and even the variable and 
 irregular teeth that arm the ponderous jaws, are all again conspi- 
 cuous in the PACHYDERMATA; and the river and the marsh, the 
 localities frequented by the latter, as obviously indicate the inter- 
 mediate position which these animals occupy between the aquatic 
 and the terrestrial Mammalia. 
 
 Ffc. 300. 
 
646 
 
 MAMMALIA. 
 
 Fig. 301. 
 
 The skeleton of the Hippopotamus (Jig. 300) offers a good ex- 
 ample of the general disposition of the osseous system in the Pachy- 
 dermata. The spinous processes of the last cervical and anterior 
 dorsal vertebrae are necessarily of prodigious strength, giving origin 
 as they do to the muscles that support the weighty skull : the ribs 
 are numerous, broad, and flat ; they extend nearly along the entire 
 length of the trunk, and thus assist in sustaining the bulky viscera 
 of the abdomen. The pelvis is massive in proportion to the weight 
 of the body ; and both the thoracic and pelvic extremities short, 
 thick, and strong, forming, as it were, pillars upon which the trunk 
 is raised. 
 
 The most important differences ob- 
 servable between the different genera of 
 Pachydermatous Mammalia are found in 
 the structure of their feet, and in the num- 
 ber and disposition of their toes. In 
 the Elephant there are five to each foot ; 
 but in the living state they are so encased 
 in the callous skin which forms a sort of 
 hoof to the foot of this monstrous animal, 
 that they are scarcely perceptible exter- 
 nally. In the Hippopotamus above de- 
 lineated there are four, and also in the 
 Hog tribes; but in the latter the two 
 middle toes are disproportionately large. 
 The Rhinoceros has only three toes to 
 each foot ; and other varieties in this 
 respect might easily be pointed out. 
 
 (727.) In the SOLIDUNGULA, or So- 
 LIPEDS, regarded by Cuvier as a family 
 belonging to the order last mentioned, 
 we have a tribe of animals quite peculiar 
 as relates to the construction of their loco- 
 motive extremities. 
 
 In the Horse, for example, a creature 
 obviously formed to be an assistant to 
 the human race, so completely has every 
 other consideration been sacrificed, in 
 order to ensure the utmost possible 
 strength and solidity in the structure of 
 the foot, that all the toes appear exter- 
 
MAMMALIA. 647 
 
 nally to have been solidified into one bony mass; which, being 
 encased in a single dense and horny hoof, is not only strong 
 enough to support the weight of the quadruped, and to sustain 
 the shock produced by its most active and vigorous leaps, but 
 becomes abundantly efficient to carry additional burdens, or to 
 draw heavy loads in the service of mankind. 
 
 In the anterior extremity of a Soliped (Jig. 301) the shoulder 
 consists only of the scapula, there being no clavicle to connect it 
 with the sternum. The humerus is short and very strong: the 
 radius and ulna are partially consolidated together, so that all 
 movements of pronation and supination are impossible. The car- 
 pus is composed of seven short bones disposed in two rows. The 
 metacarpus is a single bone (the cannon bone), which, from its 
 length and size, is commonly called the " fore-leg" of the horse ; 
 the carpo-metacarpal articulation being looked upon as the " knee." 
 Lastly, the foot consists of three great phalanges ; whereof the 
 proximal is named the " pastern" the second the "coronary" and 
 the distal phalanx the " coffin bone" In the macerated skeleton, 
 however, the vestiges of two other toes are visible ; but they 
 are merely rudiments resembling osseous splints attached to each 
 side of the metacarpus or cannon bone. 
 
 In the posterior limbs of the Horse the same peculiarities are 
 observable, both in the construction of the leg and foot. 
 
 (728.) The RUMINANTIA constitute another order of qua- 
 drupeds of very great importance to mankind, distinguished by 
 their remarkable habit of chewing the cud ; that is, of bringing 
 up the food again from the stomach into the mouth, for the pur- 
 pose of undergoing a second process of mastication. They all 
 have well-developed incisor teeth in the lower jaw, but none in the 
 upper. The patient and thirst-enduring Camel, the stately Giraffe, 
 the Ox, the Sheep, the Goat, the nimble Antelope, and the fleet and 
 elegant Stag, are all examples of this extensive order ; but it is the 
 skeleton of the last-mentioned alone that we shall select for de- 
 lineation Og. 302). 
 
 The most remarkable feature observable in the Ruminant order 
 of quadrupeds is, that, with the exception of the Camel tribe and 
 the Musk-deer, the males, and sometimes the females, are provided 
 with two horns attached to the os frontis, appendages not met 
 with in any other Vertebrata. In some, as the Giraffe, these 
 horns consist merely of a bony protuberance developed from each 
 frontal bone, which is coated with a hairy skin derived from the 
 
648 
 
 MAMMALIA. 
 
 common integument of the head. In others, as in the Ox, Goat, 
 Antelope, Sec. the Fig. 302- 
 
 bony nucleus of the 
 horn is covered over 
 with a sheath of cor- 
 neous matter, giving 
 it a hard and smooth 
 surface. 
 
 Both the above 
 kinds of horns are 
 persistent; but in the 
 Deer tribe the de- 
 fences of the head, 
 which are large and 
 branched, are deci- 
 duous, being formed 
 every year from a 
 vascular skin that 
 covers them exter- 
 nally during the pe- 
 riod of their growth, 
 but shrivels up and 
 dries when they are 
 completed. These 
 horns fall off after a 
 certain time, to be 
 renewed again the 
 
 following season ; the mode of their formation will, however, be 
 examined in another place. 
 
 (729.) In consequence of the weight of the horns in such spe- 
 cies as possess weapons of this description, the head is necessarily 
 extremely heavy ; and in genera where the horns are wanting or 
 feebly developed, as in the Camel or the Giraffe, such is the length 
 of the neck, that, even with a disproportionately small head attach- 
 ed to the extremity of so long a lever, incessant and violent mus- 
 cular exertion would be needed to sustain or to raise it from the 
 ground. This difficulty is obviated by a very simple and elegant 
 contrivance : a broad band of ligament, composed of the same 
 elastic tissue as that composing the ligamenta sub/lava of the 
 human spine, is extended from the tips of the elongated spinous 
 processes of the back, and sometimes even as far backwards as the 
 
MAMMALIA. 649 
 
 lumbar and sacral regions. This ligament, strengthened by addi- 
 tions derived from most of the vertebral processes over which it 
 passes, runs forward to be fixed anteriorly to the crest of the 
 occipital bone, and to the most anterior of the cervical vertebrae. 
 The whole weight of the cranium and neck being therefore fully 
 counterbalanced by the elasticity of this suspensory ligament, the 
 muscles of the neck act with every possible advantage ; and all 
 the movements of the head are effected with the utmost grace and 
 facility. 
 
 The RUMINANT i A are generally distinguished as having " cloven 
 feet ;" and, in fact, both the hind and fore feet present a very cha- 
 racteristic formation. The bones of the fore-arms, as well as the 
 tibia and fibula, are more or less completely consolidated, espe- 
 cially towards their distal extremities. The carpal and tarsal 
 bones resemble those of the Horse, and are similarly situated. 
 The metacarpal and metatarsal or cannon bones are respectively 
 composed of two lateral halves united along the mesian line ; and 
 to each of these halves is attached a toe composed of three pha- 
 langes, the last phalanx of each being encased in a strong hoof. 
 In some genera two rudimentary lateral toes are also distinctly 
 recognisable, but these are too small to be used in locomotion. 
 
 fig. 303. 
 
 (730.) The EDENTATA, forming the next order of quadrupeds, 
 are so called from the deficiency of teeth observable in the fore 
 part of their mouth. In the most perfect tribes, as, for example, 
 in the Armadillo (Jig. 308), the skeleton is well developed in all 
 its parts, and presents nothing to attract our special notice, except, 
 perhaps, the large proportionate size of the distal joints and claws 
 that arm the toes ; but in the Sloths (Bradypus) so unusual is 
 
650 MAMMALIA. 
 
 the conformation of the limbs, that it had at one time become 
 quite the fashion for naturalists to bestow a passing expression of 
 sympathy in alluding to these, so called, miserable and imperfect 
 members of the animal creation. 
 
 " The Sloths," says Cuvier,* u derive their name from their exces- 
 sive slowness, the result of a structure truly heteroclite, where Na- 
 ture seems to have wished to amuse herself by producing something 
 imperfect and grotesque. These animals have their fingers joined 
 together by the skin, and only indicated externally by enormous 
 compressed and hooked claws, which are bent when in repose to- 
 wards the palms of the hands or the soles of the feet. The hind 
 feet are articulated obliquely with the leg, and only rest upon 
 their external edge ; the phalanges of the fingers are articulated by 
 tight hinge-joints, and the proximal ones become consolidated at a 
 certain age with the bones of the metacarpus or metatarsus, even 
 these last become anchylosed with each other for want of use. To 
 this inconvenience in the organization of the extremities may 
 be added one equally great, consequent upon their proportions. 
 The arms and the fore-arms are much longer than the thighs 
 and the legs^ so that when these creatures walk they are obliged to 
 drag themselves upon their elbows ; their pelvis too is so wide, so 
 much directed sideways, that they cannot approximate their knees. 
 Their deportment is the natural consequence of such dispropor- 
 tionate structure. They remain upon trees, and never quit one 
 till they have stripped it of its leaves, so difficult is it for them 
 to get to another ; nay, it is even asserted that they let them- 
 selves fall from their branch to avoid the trouble of crawling 
 down." 
 
 Well may humanity pause before it ventures to accuse Nature 
 of having " wished to amuse herself by producing something im- 
 perfect and grotesque ;" and we should not have inflicted upon 
 ourselves the task of quoting so painful a passage, did it not 
 emanate from such a source, and had not ample opportunities of 
 observation shown that the very structure so accurately described 
 by Cuvier is better than any other adapted to the arboreal life 
 for which the Sloth is destined. It is not upon the ground, but 
 in the tree, that this animal must be criticized; and there, as we 
 learn, among its native branches, hanging securely by means of 
 its hooked toes and peculiarly organized hind legs, it feeds in 
 situations which otherwise would be left unoccupied ; or, using its 
 
 * Regne Animal, vol. i. p. 223, etseq. 
 
MAMMALIA. 
 
 651 
 
 Fig. 304. 
 
 long arms, it swings from bough to bough with a facility little 
 to be expected from its appearance. 
 
 (731.) The herbage that covers the plain, or the foliage of the 
 trees, are not, however, the only vegetable materials that have 
 been made available for the support of Mammiferous quadrupeds. 
 The RODENTIA are furnished with teeth adapted to gnaw even 
 the wood and the bark, or to crack nuts and other hard fruits, 
 from which they derive nourishment. 
 
 This order of Mammals is, therefore, distinguished by the 
 possession of two incisor teeth in each jaw, so constructed as 
 to erode hard 
 substances, and 
 which moreover 
 by a peculiar 
 mechanism, to 
 be described in 
 another place, 
 are always kept 
 sharp and tren- 
 chant: such are 
 the incisor teeth 
 of the Beaver 
 or of the Hare 
 (fig. 304). 
 
 The skeletons of the RODENTIA are slight and feeble, adapted 
 to the bird-like activity of their habits. Their fingers and toes 
 are well developed, and the bones of the leg and fore-arm free 
 throughout their whole length, although the movements of pro- 
 nation and supination are as yet very limited. In many genera, 
 more especially in such as climb trees like the Squirrels, the 
 clavicles are very perfectly formed, so that the fore legs can 
 be employed to a certain extent as hands, for conveying food to 
 the mouth. 
 
 Very generally, the hind legs of the RODENTIA are consider- 
 ably longer than their anterior extremities ; hence such genera 
 run by bounds or leaps, and their course is very rapid. In the 
 Jerboa (Dipus) (Jig. 305) this disproportionate size of the hind 
 legs is excessive, insomuch that the creature moves by leaps, like 
 a Kangaroo ; and, the metatarsal bones of the three middle toes 
 being consolidated into one bone, the whole limb resembles more 
 that of a bird than of a quadruped. 
 
652 
 
 MAMMALIA. 
 
 Fig. 305. 
 
 (732.) Araong 
 all the countless 
 races of the ani- 
 mal kingdom, Man 
 alone is permitted, 
 in a state of na- 
 ture, to arrive at 
 old age; that is 
 to say, at such an 
 age as to allow fee- 
 bleness and decre- 
 pitude to usurp the 
 place of strength 
 and activity. Man 
 only is capable of 
 such a privilege, 
 because he alone 
 possesses that fore- 
 sight which ena- 
 bles him to prepare 
 in youth against 
 the decline of his 
 faculties, and is 
 endowed with sym- 
 pathies and af- 
 fections directing 
 the young and the vigorous to maintain the aged and the 
 infirm. 
 
 Among the lower animals, sickness and decay are not permitted 
 to exist. Activity and health alone are conspicuous throughout the 
 broad creation : disease and decline are banished from the world. 
 Does any creature lack but for a brief period its accustomed powers 
 of escape, the destroyer is at hand instantly to remove it from its 
 appointed sphere of action. Butchers are placed on all sides ready 
 to perform their office ; and nothing is permitted to live but what 
 possesses its faculties and its strength unimpaired and unen- 
 feebled. 
 
 The great character that distinguishes the Carnivorous quadru- 
 peds is, the high degree of intelligence and activity for which they 
 
MAMMALIA. 653 
 
 are so remarkable. The perfection of their limbs, and the acute- 
 ness of their senses, at once indicate their superiority over the Herb- 
 ivorous races ; and their jaws, armed with powerful fangs, usually 
 distinguished by the name of canine teeth, show at a glance the na- 
 ture of their appointed food, and their murderous propensities. 
 
 The distribution of these tyrants of the animal creation we shall 
 find to be coextensive with that of the victims they are appointed to 
 destroy. 
 
 (733.) The aquatic tribes of the Carnivora (Amphibia, Cuv.) 
 are obviously constructed for swimming. Their bodies, covered 
 over with short, close, and polished hair, taper off towards each 
 extremity, resembling in form those of the CETACEANS. The 
 cervical, thoracic, and lumbar regions of the spine are light and 
 flexible ; and the pelvis contracted and placed as far back as possi- 
 ble. Both the anterior and posterior extremities, although com- 
 
 Fig. 306. 
 
 pletely formed, are short ; and in the living animal are only free 
 externally as far as the carpal and tarsal joints. The feet, more- 
 over, are broadly webbed, and thus become converted into most 
 efficient paddles, by the aid of which these creatures swim with 
 astonishing ease and elegance, the hinder pair performing at once 
 the functions of oars and rudder. Upon land, however, their 
 movements are, as might be supposed, extremely clumsy : it is 
 true that they not unfrequently scramble on to the beach, there to 
 bask in the sun, or to suckle their little ones ; but, if danger 
 threatens, they immediately take to the water, and fall easy victims 
 if their retreat towards the sea be intercepted. 
 
 Such being the helplessness of the Seals when they quit the 
 water for the shore, it is not surprising that, in some of the larger 
 
654 MAMMALIA. 
 
 and more unwieldy forms, assistant locomotive organs have been 
 given, derived from unlocked for sources. Thus, in the Walrus 
 (Trichecus rosmarus), which apparently obtains nourishment 
 from the fuci of the shore, as well as by destroying living prey, 
 even the canine teeth of the upper jaw are converted into instru- 
 ments of progression, and serve as crutches to drag the animal 
 along. In these creatures the upper jaw is extremely dilated and 
 massive, and the canine teeth implanted in it not unfrequently 
 project downwards to a distance of from one to two feet from the 
 mouth. The strength of the tusks so formed is proportionate to 
 the bulk of this gigantic Seal, and by their aid the Walrus is en- 
 abled to climb on to the rock in order to repose after its labours in 
 the ocean. 
 
 (734.) The Terrestrial Carnivora, that live upon flesh, are na- 
 turally divisible into two great sections. Of these, the most cruel 
 and blood-thirsty, called from this circumstance " Digitigrada," 
 walk only upon their toes, and bound along with an elasticity and 
 swiftness that are abundantly provided for in the construction of 
 every part of their osseous system. In this section are classed the 
 extensive tribes of Weasels (Jig. 307), and of Civets, the Hyenas, 
 
 and the race of Cats, the most formidable and ravenous of 
 quadrupeds. 
 
 In the Feline Carnivora, indeed, to which belong the Lion and 
 the Tiger, so justly celebrated for their strength and ferocity, a 
 peculiar and beautiful provision is visible in the construction of the 
 foot, whereby the claws that arm the last phalanges of the toes are 
 kept constantly sharp, their points never being allowed to become 
 worn by touching the ground ; hence they are in these crea- 
 tures terrific instruments of attack. The mechanism provided for 
 effecting this is as follows : three elastic ligaments, derived from 
 
MAMMALIA. 655 
 
 the penultimate joint of the toe, are inserted into the last phalanx 
 in such a manner that, by their elasticity, under ordinary circum- 
 stances, they keep the claw laid back upon the upper aspect of the 
 foot ; so that, the soft cushions beneath the toes being the only 
 parts brought in contact with the ground, these creatures always 
 walk with a stealthy and noiseless tread. But when the Tiger 
 springs upon his prey, the tendons of the flexor muscle of the toes, 
 implanted into the opposite surface of the phalanx, overcoming the 
 elasticity of the retractile ligaments, pluck forward the curved claws, 
 and, burying them deeply into the flesh of the victim, the strongest 
 animals struggle vainly to shake off a gripe so tenacious. 
 
 But, among the Digitigrade Carnivora, none are of so much 
 importance as the Dog ; an animal specially provided for the use 
 of mankind, to be his companion in the field, and his assistant 
 at the chase. Nor has Nature, in the case of the Dog, merely 
 given to man a servant endowed with sagacity and zeal : man has 
 need of help in various ways, and under very different circum- 
 stances. In bodily strength he is unable to cope with ferocious 
 enemies that surround him on all sides ; his senses are imperfect, 
 when compared with those of some of the lower animals ; in speed 
 he is outstripped by the very creatures appointed to be his food 
 how then are all these deficiencies to be compensated ? The Dog 
 has been placed at man^s disposal : its instincts, its size, its form, 
 its senses, and its corporeal attributes, are all subjugated to his 
 control; and thus whatever aid he may require, is to be obtained 
 by the cultivation of its faculties. 
 
 (735.) The PLANTIGRADE CARNIVORA, as their name indi- 
 cates, in walking apply the entire sole of the foot to the ground, as 
 far back as the end of the os calcis : such are the Bear (Ursus), the 
 Glutton (GWo), the Badger (J/e/es), and others of similar organ- 
 ization. These tribes are less exclusively carnivorous in their 
 habits than the preceding, and their nails are not retractile, so 
 that their points are blunted by dragging upon the ground. 
 
 (736.) The INSECTIVORA form another section of these de- 
 structive quadrupeds, distinguished by their molar teeth being 
 studded with sharp points, and thus calculated to devour insect 
 prey : the Hedgehog (Erinaceus), the Shrew (Sorex), and the 
 Mole (Talpd), are well-known examples of this division, and 
 their habits are known to all. We need scarcely mention the 
 peculiar circumstances under which the Mole passes its subter- 
 ranean existence, or the extraordinary conformation of its anterior 
 
656 
 
 MAMMALIA. 
 
 extremities, whereby they are converted into most efficient instru- 
 ments for digging beneath the soil. The extended scapula, the 
 strong and well-developed clavicle, the square and massive hume- 
 rus, and, moreover, the broad and rake-like hand, all proclaim 
 the office of this strange limb ; while the long and carinated ster- 
 num indicates with equal plainness the size and power of those 
 muscles by which the apparatus is wielded.* 
 
 (737.) The CHEIROPTERA, or family of BATS, present a 
 striking contrast to the Mole both in form and habits : neither 
 would it be easy to conceive that a skeleton, consisting almost of 
 precisely the same elements, could be converted to uses so diame- 
 trically opposite. 
 
 Fig. 308. 
 
 In these Mammalia the anterior extremities are converted into 
 wings, enabling them to emulate the very birds in their powers 
 of flight, and in the velocity of their movements, when upon the 
 wing pursuing insect prey. In creatures destined to such a life, 
 the whole skeleton must of course be lightened, and the bones 
 attenuated to the utmost. The skull, the spine, the thorax, 
 the pelvis, and the hind extremities, all testify by the delicacy 
 of their structure that no unnecessary weight is here permitted. 
 It is, however, in the construction of the anterior limbs that 
 the Cheiroptera present the most remarkable peculiarities. The 
 scapulae are broad and expanded, covering a considerable portion 
 of the back of the thorax, thus giving a firm basis to the wing. 
 The clavicles are large and perfectly formed, in order to resist 
 the powerful action of the pectoral muscles used in depressing 
 
 * For an admirable history of the habits of the Mole, the reader is referred to Bell's 
 British Quadrupeds, page 85. 
 
MAMMALIA. 657 
 
 the wings during flight ; and, in order to give those muscles a 
 sufficient extent of origin, the sternum, although exhibiting the 
 general characters of that of a quadruped, is deeply carinated 
 along the mesial line. The hurnerus is of moderate length, but 
 the fore-arm prolonged and slender; it consists, in fact, of but 
 one bone, so that all movements of pronation and supination 
 are necessarily impracticable. The carpal bones present their 
 usual structure and arrangement at the base of the hand ; but 
 those of the metacarpus, excepting that of the thumb, are so 
 extraordinarily lengthened, that they themselves form a consider- 
 able portion of the framework of the wing, which is completed 
 by the phalanges of the fingers appended to their extremities. 
 All these wire-like fingers are connected together by a broad 
 duplicature of skin, derived from the sides of the body, which is 
 continued along the whole length of the hind legs, and even fills 
 up the interspace between these last and the tail ; this membrane 
 forms an expansion sufficiently extensive to become converted into 
 an organ of flight. The fingers composing this strange hand 
 are obviously incapable of closing towards the palm, as ours do 
 when grasping an object : their only movements are such as fold 
 up the wing against the side of the body, by laying the fingers 
 close along the side of the fore-arm, as in closing a fan. The 
 thumb alone is left free; and this being short, and armed with a 
 strong nail, is employed in enabling the creature to cling to some 
 elevated object in those gloomy lurking-places wherein it hides 
 during the day. 
 
 (738.) The QUADRUMANA, next to mankind the most ele- 
 vated members of the animal creation, are, as is evident from every 
 point of their organization, the destined inhabitants of the trees ; 
 neither will it appear astonishing, when we consider the extensive 
 provision that has been made for the support of animal life amid 
 the dense and pathless forests of tropical climates, that animals so 
 intelligent, and capable of enjoyment, should have been widely 
 disseminated through extensive regions of our globe. 
 
 The great distinction characteristic of the Quadrumana is found 
 in the organization of their feet, all of which are converted into 
 prehensile instruments, whereby they can seize the boughs of the 
 trees wherein they reside, and thus securely swing themselves from 
 branch to branch, or even leap from one tree to another, with won- 
 derful activity and precision. Their hands are constructed upon 
 the same principle as those of Man ; their thumbs, although less 
 
658 MAMMALIA. 
 
 perfectly formed than our own, being opposable to the other fingers, 
 and thus secure a firm and steady grasp. The bones of the fore- 
 arm are free, and accurately articulated with each other ; the pro- 
 nation and supination of the hand are, therefore, now accomplished 
 with, facility. In the construction of the feet the same provisions 
 have been made to enable them to take a firm grasp : the toes, 
 like the fingers of the hand, are long and flexible, and the repre- 
 sentative of the great toe is converted into a very perfect thumb, 
 easily opposable to the rest ; the foot, or posterior hand, therefore, 
 equals, or even surpasses in its powers of prehension, the hand 
 which terminates the anterior limb. For many of the American 
 monkeys a fifth hand has been provided, formed by their long and 
 muscular tail, which, from its extreme flexibility, can be forcibly 
 twisted around any foreign object, and holds it with a tenacious 
 grasp. Thus abundantly furnished with prehensile instruments, 
 the Quadrumana are obviously most excellent and accomplished 
 climbers ; springing fearlessly through the forest by strong and 
 vigorous leaps, or chasing their prey even to the topmost branches 
 of the trees wherein they live. 
 
 (739.) But, however grotesquely some of the more anthropoid 
 Quadrumana resemble the human race, the approximation, even in 
 their outward form, is at best exceedingly remote. The lower 
 tribes, such as the Lemurs of Madagascar, walk on all fours like 
 cats, and are still remarkable for their long and fox-like muzzle. 
 The brutal and ferocious Baboons are scarcely more human in their 
 appearance ; and even in the most elevated species, called by the 
 vulgar ' wild men of the woods," the interval that separates them 
 from humanity is wide indeed ! 
 
 Taking the skeleton of the Orang-Outang (Simia Satyrus) as 
 one of the most perfect examples met with in the class under con- 
 sideration, it is at once evident that such an animal is by no means 
 adapted to walk in an erect position, although well fitted to main- 
 tain a semi-upright attitude, such as is best calculated for climb- 
 ing. The skull, whose very outline indicates brutal ferocity, is 
 armed with canine teeth, scarcely less formidable than those of 
 the Tiger ; and the massive jaws of this creature are moved 
 by muscles almost equally powerful. It is true that the protu- 
 berance of the face is considerably diminished, and the facial 
 angle thus materially enlarged ; but to make up for the feeble- 
 ness of the upper jaw, consequent upon this reduced size of 
 the bones composing it, additional strength is needed to re- 
 
MAMMALIA. 
 
 659 
 
 Fig. 309. 
 
 sist the strong pressure of the enormous temporal muscles. 
 This is given by adding strong buttresses to the outer angle of 
 the orbit formed by the union 
 of the frontal and the jugal 
 bones, and thus the whole out- 
 line of the face becomes more 
 humanized. 
 
 Another advance towards the 
 condition of the human skull is 
 apparent in the position of the 
 foramen magnum, and of the 
 condyles of the occipital bone, 
 which are now considerably ad- 
 vanced forwards beneath the 
 base of the cranium, thus allow- 
 ing the head to be articulated to 
 the atlas at a very considerable 
 angle with a line drawn through 
 the axis of the spine ; a condi- 
 tion evidently favourable to the 
 erect posture. 
 
 The thorax is well formed 
 and capacious, giving great free- 
 dom of respiration ; but the spi- 1 
 nal column is short and clumsy, 
 neither does it present those 
 graceful sigmoid curves that con- 
 vert the human spine into a per- 
 fect spring, upon the top of 
 which the head is carried. 
 
 The arms are of inordinate 
 length and extremely powerful ; 
 
 the joints perfect, and the clavicle well formed. But in the con- 
 struction of the pelvic extremities the differences between this and 
 the human skeleton become strikingly apparent. The pelvis is 
 long, and the ossa ilii narrow ; the thighs and legs so short, that, 
 when the creature stands erect, the tips of the fingers almost touch 
 the ground. The protuberance of the os calcis is very slight ; and 
 thus the posterior hands, although well adapted for taking hold of 
 any object, are but ill calculated to sustain the weight of the body 
 in an upright posture. Upon the ground, indeed, the living 
 
660 MAMMALIA. 
 
 animal puts the spectator in mind of a human being crippled in the 
 lower extremities; but, in its native trees, these members, like those 
 of the Sloth, are admirably suited to the circumstances under which 
 the Orang is ordained to live. 
 
 (740.) Having thus introduced the reader to the different orders 
 of Mammalia, as well as to the principal differences observable in 
 the arrangement of their osseous system, we must briefly glance at 
 some few points connected with their myology, selecting those that 
 seem most worthy of being specially pointed out to the notice of 
 the anatomical student. 
 
 To enumerate all the varieties that occur in the disposition of 
 the muscular system in vertebrate animals, would, of course, be 
 incompatible with the extent of this work ; and perhaps, even were 
 it practicable, the details would scarcely possess much interest to 
 the beginner in comparative anatomy. Considered generally, in- 
 deed, the muscular system of quadrupeds conforms very accurately 
 in its arrangement to that of the human subject ; and for the most 
 part the same names are applicable to the individual muscles, al- 
 lowance being made for such modifications in the manner of their 
 origins and insertions as are rendered necessary by the disposition 
 of the skeleton, or in order to accommodate them to the perform- 
 ance of special functions. To enumerate, therefore, the muscles of 
 the jaws, of the neck, of the spine, of the chest, of the abdomen, 
 or even of the extremities, in such genera as have the members last 
 mentioned completely developed, would only be to repeat cir- 
 cumstances with which the human anatomist is already familiar : 
 nevertheless, there are some points of practical importance con- 
 nected with this part of our subject that must not be altogether 
 passed over in silence. 
 
 (741.) The diaphragm is a muscle only met with in the 
 class before us, and in all Mammalia it forms the great agent in 
 respiration ; dividing the thoracic from the abdominal cavity by a 
 broad musculo-tendinous septum, and presenting a disposition in 
 all essential particulars similar to that of Man. 
 
 (742.) Another muscle of considerable anatomical interest is 
 the cutaneous muscle provided for the movements of the inte- 
 gument. In many tribes, more especially those which, like the 
 Hedgehog, the Echidne, and the Porcupine, have the skin 
 covered with spines, this muscle is extremely developed, invest- 
 ing the greater part of the body with a thick layer of muscular 
 fibres, called not improperly the panniculus carnosus. In Man, 
 
MAMMALIA. 661 
 
 too, this muscle exists, but under a very different aspect ; being 
 only found in certain regions of the body, where it forms nume- 
 rous cutaneous muscles adapted to different offices. In the 
 neck, where it is principally developed, it is called the platysma 
 myoides : in the facial region it is likewise of great importance ; 
 the occipito-frontalis, the corrugator supcrcilii^ and other mus- 
 cles connected with the expression of the countenance, being indu- 
 bitably but portions of the fleshy pannicle. In the palm of the 
 hand it is slightly visible, forming the palmaris brevis ; and even 
 the little muscles connected with the external ear may be referred 
 to the same series. 
 
 (743.) In Whales no pelvis or posterior extremities exist ; it is 
 needless, therefore, to remark, that the whole of the muscular 
 system appropriated to those parts in higher animals must be 
 totally wanting : but, in return, the muscles connected with the 
 caudal portion of the spine are amazingly powerful, so as to render 
 the horizontally expanded tail an instrument of propulsion, ade- 
 quate to the necessities of these unwieldy animals. A large tri- 
 angular muscle is found in the CETACEA, apparently replacing the 
 quadratus lumborum, the psoas, and the iliacus, which arises from 
 the lower surface of the last rib, from the last dorsal vertebra, and 
 also from those of the loins and sacrum : from this powerful assem- 
 blage of muscular fasciculi tendons are given off, to be inserted 
 into the lower surface of the bones that support the tail, converting 
 this organ into a mighty oar, adapted by its position to bring the 
 creature with all speed to the top of the ocean in search of air. 
 It is, as might be supposed, in the muscles of the limbs that the 
 most important differences exist. In the anterior extremities, for 
 example, the presence or absence of a clavicle will materially affect 
 the disposition of the muscles of the shoulder, as will also the ex- 
 istence of a coracoid process to the scapula ; nevertheless in their 
 general arrangement they conform to those of Man. The rhom- 
 boid muscles, which to creatures walking on all fours must be im- 
 portant agents, are generally found in quadrupeds to take their 
 origin as far forward as the head ; the serrati magni likewise, 
 whereby in the prone position the weight of the body is as it were 
 suspended from the scapula, must be immensely strong. 
 
 The muscles acting upon the arm are similar in all the Mam- 
 malia; but in the fore-arm, as might be expected from the very 
 variable condition of this part of the skeleton, the disposition of 
 the muscular system varies too, and even the existence of many 
 
662 MAMMALIA. 
 
 muscles could not be expected : thus as the movements of pro- 
 nation and supination are, from the immovable condition of the 
 bones of the fore-arm, impracticable in the CETACEANS, the RU- 
 MINANTS, the SOLIPEDS, and others, the pronators and supina- 
 tors are denied; or, if their representatives exist, they become 
 simply assistants in flexion and extension. The flexors and exten- 
 sors of the wrist are pretty constant, but the muscles devoted to 
 the hand and fingers will vary in almost every order. The pal- 
 maris longus, although generally present where the hand is flexi- 
 ble, is wanting where its action upon the palmar fascia would be 
 useless, as, for example, in the ungulate tribes. 
 
 In quadrupeds there are two extensor tendons appropriated to 
 each of the fingers that correspond to the four outer fingers of the 
 human hand ; whilst in Man the index and little fingers only have 
 auxiliary extensors. 
 
 The abductor and extensor muscles of the thumb are not so per- 
 fectly developed in any animals as they are in the human hand. 
 The short extensor is, in fact, wanting even in Monkeys ; and in 
 the lower orders of quadrupeds even the extensor longus and 
 abductor are blended together, or totally wanting. 
 
 The deep and superficial flexors of the fingers are very generally 
 met with, the number of tendons furnished by each corresponding 
 of course to that of the fingers themselves ; but in the Solipeds 
 the two muscles are almost blended together. Even in the Rumi- 
 nants, although these muscles remain separate, their tendons be- 
 come confounded together, and divide again, to be inserted into 
 the phalanges to which they are appropriated. In these Ungu- 
 lata too, as we need scarcely say, the lumbricales and mterossei 
 are quite deficient; and the short muscles of the thumb are com- 
 pletely developed only in Man and in the Quadrumana. 
 
 It is in the human species only that the lower extremities are 
 organized so as to maintain the body in the erect position, and, in 
 consequence, the glutsei muscles in the human body are enormously 
 developed when compared with those of the lower animals ; but the 
 other muscles derived from the pelvis and thigh present but slight 
 differences throughout the whole class under consideration. In the 
 leg and foot likewise it is not difficult to identify the muscles that 
 correspond to those found in the human subject, but, as in the an- 
 terior extremity, modified in their disposition and mode of insertion 
 in accordance with the construction of the skeleton. 
 
 The articulations whereby the different pieces composing the 
 
MAMMALIA. 
 
 663 
 
 Mammifcrous skeleton are connected to each other are constructed 
 upon the same principles as in the human body, insomuch that to 
 describe them even in general terms would be useless. 
 
 The bones of the cranium and face, as in Man, are joined toge- 
 ther by harmony or by suture. The articulations of the lower jaw 
 are double, each presenting an interarticular cartilage ; except in the 
 Cetacea, where, instead of such a structure, a very thick matted 
 ligamentous substance, having its interstices filled with oil, passes 
 directly from the condyles of the jaw to the temporal bones. 
 
 The joints of the spine, thorax, and pelvis are all constructed 
 upon the same principles as the corresponding articulations in the 
 human subject ; and the same may, with slight exceptions, be said 
 of those of the extremities. The chief differences will be found in 
 the connection between the radius and ulna, the movements of 
 rotation becoming gradually less manifest as we descend from Man : 
 the tibia and fibula, too, ultimately become completely anchy- 
 losed to each other. The hip-joint contains an internal liga- 
 mentum teres ; but in a few instances, e. g. the Ornithorhyncus, the 
 Echidne, the Sloths, the Elephant, the Seals, and the Orang 
 Outang, this round ligament is deficient. The arrangement of the 
 other articulations will be at once apparent, on reference to the 
 figures of the different skeletons already given. 
 
 (744.) Turning to the digestive system of Mammiferous ani- 
 mals, their 
 
 teeth first in- Fi s- 310. 
 
 vite our at- 
 tention. We 
 have already, 
 when describ- 
 ing the os- 
 seous frame- 
 work of these 
 elevated be- 
 ings, exposed 
 their general 
 arrangement 
 in the jaws 
 of the diffe- 
 rent orders ; 
 but it still 
 remains for us 
 
664 MAMMALIA. 
 
 to explain the varieties of their structure and the mode of their 
 formation. 
 
 The most remarkable form of teeth, one indeed that is unique, 
 is met with in the Whalebone Whale (Balana mysticetus). The 
 teeth in this Cetacean are -not, indeed, instruments of mastication ; 
 but form a very curious apparatus, adapted to strain the waves 
 of sea as through a sieve, and thus obtain from the ocean a suffi- 
 ciency of food for the sustenance of its monstrous body. 
 
 The whalebone (as it is improperly called) is attached to the 
 gums of the upper jaw, being arranged in thin flat plates of some 
 breadth, and varying in length according to the size of the whale.* 
 These plates are placed in several rows, similar to teeth in other 
 animals; they stand parallel to each other, having one edge di- 
 rected towards the circumference of the mouth. The outer row 
 is composed of the longest plates, and these are in proportion to 
 the varying distances between the two jaws, some being fourteen 
 or fifteen feet long, and twelve or fifteen inches broad, but towards 
 the anterior and posterior part of the mouth they are very short. 
 
 Tnferiorly each plate of whalebone is terminated by a broad 
 fringe of horny fibres resembling hair ; and, seeing that in some 
 whales there are above three hundred plates composing the outer 
 row on each side of the mouth, the reader may form some idea of 
 the extent of this enormous strainer, whereby the little Clio 
 Borealis, and other small Mollusca, that swarm so abundantly in 
 the Northern ocean, are caught by shoals preparatory to their being 
 swallowed. 
 
 For what is known concerning the growth of whalebone, we are 
 indebted to John Hunter ; and, as it would be difficult to curtail 
 his clear and concise description of the process, it is here given in 
 his own words. -f- 
 
 " The formation of whalebone is extremely curious, being in 
 one respect similar to that of hair, horns, spurs, &c. ; but it has 
 besides another mode of growth and decay, equally singular." 
 
 " These plates form upon a thin vascular substance, not imme- 
 diately adhering to the jaw-bone, but having a more dense sub- 
 stance between, which is also vascular. This substance, which 
 may be called the nidus of the whalebone, sends out thin, broad 
 processes answering to each plate, on which the plate is formed, as 
 the cock^s spur or the bulPs horn on the bony core, or a tooth on 
 
 * J. Hunter, on the Structure and (Economy of Whales. Philos. Trans. 1787. 
 t Vide supra. 
 
MAMMALIA. 665 
 
 its pulp ; so that each plate is necessarily hollow at its growing 
 end, the first part of the growth taking place on the inside of this 
 hollow." 
 
 " Besides this mode of growth, which is common to all such 
 substances, it receives additional layers on the outside, formed 
 from the above-mentioned vascular substance, extended along the 
 surface of the jaw. This part also forms upon it a semi-horny 
 substance between each plate, which is very white, rises with the 
 whalebone, and becomes even with the outer edge of the jaw. This 
 intermediate substance fills up the spaces between the plates as 
 high as the jaw ; acts as abutments to the whalebone; or is similar 
 to the alveolar processes of the teeth, keeping them firm in their 
 places. 1 ' 
 
 "As both the whalebone and intermediate substance are con- 
 stantly growing, and as we must suppose a determined length ne- 
 cessary, a regular mode of decay must be established, not depend- 
 ing entirely on chance, or the use it is put to. In its growth, 
 three parts appear to be formed : one from the rising cone, which 
 is the centre ; a second on the outside ; and a third, being the in- 
 termediate substance. These appear to have three stages of dura- 
 tion ; for that which forms on the cone, I believe, makes the hair, 
 and that on the outside makes principally the plate of whalebone : 
 this, when got a certain length, breaks off, leaving the hair project- 
 ing, becoming at the termination very brittle : and the third, or 
 intermediate* substance, by the time it rises as high as the edge of 
 the skin of the jaw, decays and softens away like the old cuticle of 
 the sole of the foot when steeped in water." 
 
 (745.) Other kinds of teeth, met with among Mammals, are com- 
 posed of calcareous earths deposited in a nidus of animal matter, and 
 consequently resemble bones in 
 the hardness of their texture. In F 'g- 31 * 
 
 their simplest form these teeth 
 consist of but one kind of mate- 
 rial, called ivory; and in such 
 cases there' is no distinction into 
 classes as in the human sub- 
 ject, every tooth being conical, 
 and formed upon a simple pulp. 
 Such are the teeth of the Por- 
 
 * Mr. FTunter means, by " intermediate," interposed between the contiguous plates, 
 not between the " hair" and the laminated whalebone. 
 
666 MAMMALIA. 
 
 poises (Delphinidte), and of tlie Caclielot Whales (Physeler). The 
 example selected to illustrate their structure and mode of growth is 
 a preparation of a portion of the jaw of the Bottle-nose Whale 
 (Delphinus Tursio) contained in the Hunterian collection.* 
 From this it is seen (Jig. 311) that each tooth of the Cetaceans in 
 question is a hollow cone of ivory (a, >, c, d), which, on being split 
 longitudinally, is found to contain a vascular pulp, exactly filling 
 up its internal cavity. Tt is upon the surface of this pulp that the 
 ivory matter is produced and deposited, stratum inter stratum, 
 within the tooth, thus gradually adding to its substance as growth 
 proceeds. In animals possessing a dental apparatus of this descrip- 
 tion, Mr. Hunter observed that the teeth are not at first developed 
 in the jaw, but appear to form in the gum upon the edge of the 
 maxillary bones ; and that they either sink into the jaw as they 
 lengthen, or, as is more probably the case, the alveoli rise to en- 
 close their roots as growth advances. It would moreover appear 
 that these creatures do not shed their teeth ; but that, as the jaw 
 enlarges, new teeth are constantly produced from behind, while 
 those towards the symphysis fall off, and their sockets become 
 absorbed : thus the size of the teeth is made to keep pace with the 
 increasing dimensions of the jaw.-)- The exact number of teeth 
 met with in any species of these Whales will evidently be un- 
 certain. 
 
 In the male Narwal (Monodon) there are no teeth implanted 
 along the margins of the jaws ; but from the intermaxillary bone of 
 the left side of the face there projects a single tusk of great strength, 
 which sometimes attains the length of eight or ten feet. This 
 formidable weapon is fully developed only upon one side of the 
 body ; nevertheless, the corresponding tooth exists in a rudimentary 
 condition, enclosed in the opposite intermaxillary bone. 
 
 In the Elephant, a creature which so obviously forms a connect- 
 ing link between the gigantic Cetacea and terrestrial quadrupeds, 
 tusks, more ponderous even than that of the Narwal, project 
 from both intermaxillary bones : but these, as well as the tusks 
 of other PACHYDERM AT A, grow upon a simple pulp, such as that 
 which forms the teeth of the Bottle-nose Whale; are formed of 
 ivory, without any enamel ; and their growth is only limited by the 
 abrasion to which they are subject. 
 
 * Preps. No. 327 and 328. 
 
 t The Animal CEconomy, by John Hunter, with notes by Richard Owen, Esq. F.R.S. 
 p. 353. London, 1837. 
 
MAMMALIA. 667 
 
 In by far the greater number of quadrupeds the teeth pre- 
 sent a more complex structure, and consist of two distinct sub- 
 stances of very different texture : the one analogous to the ivory of 
 the simple teeth described in the last paragraph ; the other called 
 enamel, of crystalline texture, and such extreme density as to 
 withstand being worn away by acting upon the hardest materials 
 used as food. Teeth of this description may be advantageously 
 divided into two principal groups : first, those whose growth is 
 continuous during the entire lifetime of the animal ; and, second, 
 those which are completed at an early period, and then cease 
 to grow. 
 
 The first division includes the incisor teeth of the Rodentia, or 
 denies scalprarii, as they have been termed. Such teeth are, in 
 fact, chisels of most admirable construction, destined to gnaw the 
 hardest kinds of food, and yet never to all appearance wearing 
 away or becoming blunted by use. 
 
 The annexed figure (312) represents a section of the incisor 
 tooth, and of the left ramus of the lower jaw of a Porcupine 
 
 Fig. 312. 
 
 (Hystrix cristatd), and from this example the structure of such 
 teeth will be readily understood. The bulk of the tooth consists 
 of solid ivory (a), which in its texture and mode of growth 
 resembles that of a simple tusk, being continually growing from 
 behind by the addition of new matter produced from the vas- 
 cular pulp (c), so that, were such a tooth not worn away constantly 
 at the point, it would curl up over the face like the tusk of the 
 Babiroussa ; and if by accident the opposing tooth in the upper 
 jaw should be broken off, this circumstance in fact really takes 
 place. 
 
 But, besides the ivory-forming pulp (c), there is a vascular 
 membrane (e) which exists only upon the anterior surface of the 
 
GC8 MAMMALIA. 
 
 socket, its limits on each side being distinctly marked by a defined 
 line. This membrane secretes enamel, and coats the convex 
 surface of the tooth with a thin layer (b) of that dense substance. 
 From this beautiful arrangement it results, that while the ante- 
 rior end of the tooth is perpetually worn away by attrition against 
 hard substances, the ivory is abraded more rapidly than the 
 enamel that coats it in front ; thus, therefore, the tooth constantly 
 preserves its chisel-like shape, and presents the sharp cutting 
 edge formed by the layer of enamel. 
 
 (746.) The second kind of teeth, composed of bone and enamel, 
 are limited in their growth ; and the entire crown or projecting 
 portion is invested with enamel covering its surface. The teeth 
 of all the CARNIVORA, of the QUADRUMAXA, and also of MAN, 
 are of this description. From marked differences in their form 
 in different regions of the mouth, such teeth are conveniently 
 divisible into different groups, called respectively incisores, lani- 
 ares or canine teeth, pseudo-molar es or false grinders, and 
 molar es or grinding teeth. 
 
 Whatever may be the shape of teeth of this class, their mode 
 of growth is similar to that observed in those of our own species. 
 We have chosen, in order to illustrate this, the growing perma- 
 
 Fi^.313. 
 
 nent teeth of a young Lion, wherein the different organs employed 
 in their formation are easily distinguishable. The ivory that forms 
 the bulk of the tooth (Jig. 318, b) is formed by the surface of an 
 internal pulp (a) ; and as it slowly accumulates, encroaching upon 
 the central cavity, and penetrating more deeply into the socket, 
 the fang is gradually formed, and the central pulp shrinks until, in 
 the fully formed tooth, it becomes reduced to a thin membrane, 
 richly supplied with vessels and nerves, which lines the small cen- 
 tral cavitv that remains. 
 
MAMMALIA. 
 
 669 
 
 Before the progressively advancing tooth issues from the nidus 
 wherein it is produced, the enamel is deposited upon the surface of 
 the ivory by the lining membrane of the capsule (c), and becomes 
 arranged in crystalline fibres placed perpendicularly to the surface 
 of the ivory, until the whole crown of the tooth is adequately 
 coated with this important additional substance. Meanwhile the 
 growth of the tooth still proceeds by the lengthening of its root, 
 until at last the crown issues from the jaw, and the enamel-secreting 
 membrane (c) becomes obliterated. 
 
 (747.) The most complex condition of the dental organs is 
 that found in the molar teeth of herbivorous quadrupeds, which, 
 being destined to act the part of mill-stones in grinding down 
 and comminuting vegetable substances, must necessarily, like 
 the mill-stones of human contrivance, have a grinding surface, 
 presenting prominent edges and deep sulci, not liable to become 
 worn even by the continual abrasion to which they are subjected. 
 In order to obtain this end, the ivory and enamel indigitate, as it 
 'were, in the substance of the tooth ; and are, moreover, imbedded 
 in a third material, not met with in the simpler forms, called the 
 cementum or crusta petrosa. In consequence of this arrangement, 
 seeing that the plates of ivory, of enamel, and of cement, are all 
 of different degrees of hardness, the softer substances are most 
 easily worn away; and thus these compound teeth always offer an 
 efficient grinding surface. 
 
 By inspecting the accompanying figure (fig. 314), representing 
 a section of the tooth 
 
 of an Elephant, the Fig.3\4. 
 
 disposition referred 
 to will be better un- 
 derstood : the layers 
 of enamel are seen 
 to alternate with 
 plates of ivory, while 
 all the interstices are 
 filled up by the cir- 
 cum fused cementum. 
 
 During the growth 
 of a compound 
 tooth of this descrip- 
 tion, the enamel- 
 secreting membranes derived from the capsule of the tooth, of 
 
670 
 
 MAMMALIA. 
 
 course, intercligitate with the ivory-forming pulps that arise from 
 the bottom of the sockets, and thus the hard materials formed by 
 them take the same arrangement. After these structures have been 
 completed, one or other of the sets of pulps, most probably the 
 enamel pulps, changing their action, fill up all the intervening 
 spaces with the crusta petrosa. 
 
 (748.) As during the growth of a quadruped the size of the 
 jaws is continually increasing, a necessity exists for changing the 
 teeth once or oftener during the life of the animal, in order to 
 adapt these organs to the altered conditions required : hence the 
 necessity for shedding the teeth of young animals, and replacing 
 them with others of larger dimensions or more numerous than the 
 first set. 
 
 This is effected in two different ways, each of which demands 
 our separate notice. 
 
 In most quadrupeds, as, for example, in the Carmvora, the 
 Quadrumana, and the greater number of herbivorous genera, 
 the succession of the teeth is provided for precisely in the same 
 way as in our own persons, namely, by the formation of a new 
 tooth below each of the deciduous ones (fig- 313, d, d) ; so that, 
 when the latter falls out in consequence of the absorption of its 
 fangs, the former is ready to take its place. The germ of the second 
 tooth is at first found imbedded in the jaw-bone, in the immediate 
 vicinity of the roots of the one which it is destined to replace ; 
 and, as its growth advances, the old and used tooth is gradually 
 removed to make way for the new comer. The steps of this pro- 
 cess are exactly similar to those by which the milk-teeth of a child 
 are changed, and the details connected with it are familiar to every 
 anatomist. 
 
 But in the Elephant, and some other genera of PACHYDER- 
 MATA, the succession of the teeth is effected in a different man- 
 ner ; the place of the first formed being supplied by others that 
 advance from behind as the former become used. Animals exhi- 
 biting this mcde of dentition have the grinding surfaces of their 
 molar teeth placed obliquely ;* so that, if they were to issue 
 altogether from the gum, the anterior portion would be much more 
 prominent than the posterior, notwithstanding that the opposed 
 teeth act upon each other in a horizontal plane. The consequence 
 of this arrangement is, that the anterior portion of these teeth is 
 ground down to the roots, and worn away sooner than the poste- 
 
 * Cuv. Lemons d'Anat. Comp. torn. iii. p. 122. 
 
MAMMALIA. 671 
 
 rior portion. Moreover, the posterior part of the tooth is consi- 
 derably wider than the anterior ; so that, as the succeeding tooth 
 advances from behind, there is always sufficient room to receive 
 it ; and in this way, by the time that the first tooth is quite 
 destroyed and falls out, a new one from behind has already taken 
 its office. There is, therefore, no absorption of the roots of these 
 teeth, but they are ground down from the crown to the stump. 
 
 The new tooth that thus advances from behind is always of 
 larger dimensions than that to which it succeeds ; because the 
 animal itself has grown in the interval, and the jaws have become 
 proportionally developed. 
 
 The Elephant in this way may have a succession of seven or 
 eight teeth on each side in both jaws, or from twenty-eight to 
 thirty-two in all ; and nevertheless, seeing that the anterior ones 
 successively fall out, there are never more than two visible at once 
 above the gums on each side, or eight in all : generally, indeed, 
 there is only one visible at a time. Every successive tooth is 
 composed of more laminae than that which immediately preceded 
 it, and a longer time is required to perfect its growth. 
 
 Nearly the same account of this process was found in the 
 Manuscripts of John Hunter,* who lucidly accounts for such an 
 aberration from the ordinary course of proceeding. " These crea- 
 tures," says that distinguished observer of Nature, " do not shed 
 their teeth as other animals do that have more than one ; for those 
 that have more than one tooth can afford to be for some time 
 without some of their teeth : therefore the young tooth comes up 
 in many nearly in the same place with its predecessor, and some 
 exactly underneath ; so that the shedding tooth falls sometimes 
 before the succeeding tooth can supply its uses. But this would 
 not have answered in the Elephant ; for if the succeeding tooth had 
 formed in the same situation with respect to the first, the animal 
 would have been for some time entirely deprived of a tooth on 
 one side, or, at least, if it had one on the same side in the oppo- 
 site jaw, that one could have been of no use ; and if this process 
 took place in both sides of the same jaw, and in either jaw, the 
 animal would have been entirely deprived of any use of the two 
 remaining." 
 
 (749.) The teeth" of Mammalia being thus adapted to so many 
 various offices, and serving under different circumstances to hold, 
 
 * Descriptive and Illustrated Catalogue of the Physiol. Series of Comp. Anat. in the 
 Mus. Roy. Coll. Surg. Lond. Part i. p. 100. 
 
672 MAMMALIA. 
 
 to bruise, to cut, to tear, or to grind alimentary substances, we 
 must naturally expect the movements of which the lower jaw is 
 capable, to be in correspondence with the nature of the dental 
 apparatus. 
 
 In MAN, as the student well knows, in consequence of the 
 laxity of the ligaments that connect the inferior maxilla with the 
 temporal bone, and the thickness of the articular cartilage that 
 is interposed between the convex surface of the condyle and the 
 shallow glenoid cavity, every kind of motion is permitted in con- 
 formity with the omnivorous habits of the human race; and the 
 temporo-maxillary articulation is no longer a mere hinge, but 
 the teeth can be made to act upon each other by rubbing their 
 grinding surfaces in all needful directions. In the Herbivorous 
 quadrupeds these triturating motions are likewise extensive. In 
 the RODENTIA the movements of the lower jaw are principally 
 backwards and forwards, thus giving free play to their chisel-like 
 teeth whilst employed in eroding hard substances ; and in the 
 CARNTVORA, where there is no necessity for any grinding motion, 
 the condyle is so locked into a deep and transverse glenoid cavity, 
 that the movements of a hinge only are permitted. 
 
 (750.) But, whatever the degree of motion conferred upon the 
 lower jaw, the muscles that act upon it are exactly comparable to 
 those of the human subject. The masseter is strengthened in 
 proportion to the hardness of the substances used for food ; the 
 temporal covers a greater or less extent of the cranium, as the 
 jaws are stronger or more feeble; and even the pterygoid muscles 
 differ only in relative size and form from those of Man. 
 
 The digastric muscle, however, which is an important agent 
 in depressing the lower maxilla, does not preserve the same ar- 
 rangement in the lower quadrupeds that it presents in the human 
 species. In Monkeys indeed it still exhibits two fleshy bellies, 
 and a central tendon that traverses the stylo-hyoideus ; but in 
 general it is a single fleshy muscle, arising from the neighbourhood 
 of the mastoid process, and inserted near the angle of the jaw. 
 
 (751.) The tongue in nearly all the Mammifera is composed 
 of the same muscles as in Man ; and their disposition is so similar, 
 as to render any detailed enumeration of them quite unnecessary. 
 The only exceptions worthy of notice are found in the Ant-eaters 
 (Myrmecophaga), and in the Echidna, animals possessing tongues 
 of remarkable length and slenderness, by means of which they 
 secure their insect prey. 
 
MAMMALIA. 673 
 
 In botli these animals the tongue suddenly becomes much con- 
 tracted at the place where it begins to be free from the surround- 
 ing parts. It then appears to be made up of two very long and 
 slender muscular cones, laid one upon the back of the other, their 
 apices being at the end of the tongue.* Each of these cones 
 consists of two muscles: one external, composed of a multitude of 
 distinct fasciculi investing the internal muscle in a circular manner, 
 and forming around it numerous little rings resembling the annelli 
 of an earth-worm. The internal muscle, on the contrary, is of 
 great length ; it arises from the middle and upper part of the 
 sternum, runs forward along the neck, passes between two layers 
 of the mylo-glossus, and afterwards becomes surrounded by the 
 annular muscle. It is composed of distinct fasciculi, rolled upon 
 themselves in an elongated spiral ; the external fibres terminate at 
 the first rings, those beneath attain the rings that succeed, and so 
 on until the innermost fibres reach quite to the extremity of the 
 tongue. It is easy to perceive that, by its action, this muscle 
 will shorten the tongue until it lies in a very small compass, or 
 bend it in any direction ; whilst the annular muscle will lengthen 
 it, exactly in the same way as the body of a leech is extended or 
 contracted. 
 
 In the Ant-eater the annular muscle does not appear so dis- 
 tinctly double as it does in the Echidna; but it forms by itself 
 almost all the substance of the tongue, which is thus capable of 
 being elongated to a wonderful extent. 
 
 (752.) Regarding the tongue with reference to the sense of 
 taste, the Mammalia may be looked upon as the only animals 
 capable of receiving much enjoyment from this source, since in 
 them alone the lingual mucous lining seems to be perfectly 
 adapted to gustation. Even among these highly endowed crea- 
 tures, it is only in Man, and those Herbivorous orders that pre- 
 pare their food in the mouth by a prolonged mastication, that 
 the sense in question exhibits much delicacy of perception ; for 
 the Carnivorous quadrupeds, seeing that they tear to pieces and 
 swallow their food in large morsels, can scarcely be supposed to 
 pay much attention to its sapid qualities. 
 
 In the Cat tribe (Felida), indeed, all the middle portion of the 
 surface of tongue is covered over with sharp, recurved, and horny 
 spines, adapted as it were to file off remnants of soft flesh from the 
 
 * Cuv. Le9ons d'Anat. Comp. torn. iii. p. 264. 
 
674 MAMMALIA. 
 
 bones of their victims ; and the gustatory papillae are elsewhere of 
 small dimensions. The tongue of the Porcupine, likewise, is 
 armed on each side near its extremity with broad, horny, and sharp 
 scales ; but, with these exceptions, the mucous covering of the 
 tongue, the various kinds of papillae upon different parts of its sur- 
 face, and, moreover, the distribution of the nerves supplied to it, 
 differ in no important circumstance from what is observed in the 
 human organ of taste. 
 
 (753.) Importantly connected with the perfection of the sense 
 of taste, and materially assisting in the mastication of food, is the 
 salivary apparatus, which, throughout all the Mammalia, is made up 
 of the glands, that offer the same general arrangement as in Man. 
 
 The parotids vary principally in their proportionate size, and 
 their ducts always perforate the lining membrane of the mouth in 
 the vicinity of the molar teeth. 
 
 The submaxillary and the sublingual glands are also very ge- 
 nerally present ; and, as in the human subject, the saliva that they 
 furnish enters the mouth beneath the under surface of the tongue. 
 
 The mucous lining of the lips and cheeks is likewise studded 
 with muciparous follicles, called from their situation buccal, molar, 
 or labial glands ; these likewise serve to lubricate the oral cavity. 
 
 In the Seals (Phocida) there are no parotids, neither are these 
 glands found in the Echidna hystrix, or in the Ant-eater (Myrme- 
 cophaga) ; but in the last-named genus their place is supplied by 
 two other secreting organs, of which Cuvier gives the following de- 
 scription.* One is in contact inferiorly with the upper edge of the 
 masseter muscle, and fills up a great part of the space that repre- 
 sents the temporal, zygomatic, and orbital fossae, where it partially 
 embraces the globe of the eye : the excretory duct derived from 
 this gland opens into the mouth, behind the superior maxillary 
 bone. The other, which is probably destined to furnish the viscid 
 secretion that coats the worm-like tongue of this animal, is oval 
 and flat, lying in front of the tendon of the masseter behind the 
 angle of the lips, and then running along the edge of the lower lip 
 as far as its middle. Its canal opens externally in a groove at the 
 commissure of the lips, and a white, thick, and tenacious fluid may 
 be pressed out, from the cells of which the gland seems to be 
 made up. 
 
 In a few species, in addition to the salivary glands met with in 
 
 * Lefons d'Anat. Comp. torn. iii. p. 215. 
 
MAMMALIA. 075 
 
 Man,* there is a group, apparently a continuation of the molar, 
 which mounts up along the superior maxillary bone, beneath the 
 zygoma, even to behind the globe of the eye. The excretory ducts 
 derived from this group pierce the mucous membrane near the 
 posterior margin of the superior alveolar ridge; such an arrange- 
 ment is met with in the Ox, the Sheep, and the Horse. 
 
 In the AMPHIBIOUS MAMMALIA the salivary system is very 
 feebly developed ; and in the GET ACE A, as might be expected 
 from their habits, no salivary glands whatever are to be detected. 
 
 (754.) Before considering the mechanism of deglutition in the 
 Mammalia, we must, in the next place, briefly describe their hyoid 
 apparatus ; more especially as this remarkable system of bones, 
 which in the lower Vertebrata was so importantly connected with 
 the respiratory function, is now reduced to an extremely simple 
 condition, and, although it is still intimately connected with the 
 larynx, is more particularly remarkable, as forming a centre of 
 attachment for almost all the muscles of the throat. 
 
 Perhaps there is no part of the bony framework of the body 
 that exemplifies more strongly than the os hyoides the impossi- 
 bility of attaining correct physiological views relative to the compo- 
 sition of the skeleton by the mere examination of the human sub- 
 ject. Let the student, for instance, compare for a moment the os 
 hyoides of Man with that of the Fish, or of the Amphibious Rep- 
 tile, and endeavour, in the simple segment of a circle presented by 
 the one, to find the analogues of the body and complicated arches 
 of the others; then, doubtless, he will find that, without some inter- 
 mediate gradations of form, it is not easy to trace the slightest rela- 
 tionship between them. 
 
 The human os hyoides consists of a central portion and two cor- 
 nua; but these are generally so completely consolidated as to form 
 but one bone, which is connected by the interposition of a broad 
 ligament with the upper margin of the thyroid cartilage ; moreover, 
 two smaller appendages, called the lesser cornua, are articulated with 
 the upper surface of the hyoid bone, close to the point of junction 
 between the cornua majora and the body; from whence ligaments, 
 called the stylo-hyoid, pass upwards and backwards to the styloid 
 processes of the temporal bone. 
 
 All the apparatus of hyoid arches passing between the body 
 of the bone and the base of the cranium, which were so largely 
 
 * Le9ons d'Anat. Comp. torn. iii. p. 210. 
 
 2x2 
 
676 MAMMALIA. 
 
 developed in the lower Vertebrata, have therefore totally disap- 
 peared ; and the question to be solved is, how we may identify the 
 remaining portions with any of the elements of the more complex 
 structures that have come under our notice. 
 
 (755.) Difficult as this would be to the student who had con- 
 fined his attention to the human body, on referring to the os 
 hyoides of a quadruped, one of the Carnivora for instance, the 
 analogies become at once perceptible. The body (jig- 315, a) 
 
 is evidently the representative of the 
 
 J . Fig. 315. 
 
 central portion of the hyoid apparatus 
 
 in Fishes (Jig. 221, 42), in Reptiles 
 (fig. 260, 5), and in Birds (fig. 271). 
 The lingual elements found even in 
 birds are quite obliterated ; but two 
 arches still remain. The posterior of 
 these (fig. 315, <f), which represent 
 the larger cornua of the human os 
 hyoides, do not reach the cranium, but, 
 as in Man, are attached by muscle and 
 ligament to the thyroid cartilage ; 
 while the anterior cornua, so small in 
 Man, are in quadrupeds by far the 
 largest, each consisting of two pieces, 
 
 of which the second are articulated with the extremities of the 
 styloid bones (c, c), and these last are in turn joined to the tem- 
 poral bones by means of articulating surfaces. In Man the styloid 
 bones (c) become anchylosed with the temporal, giving rise to the 
 i( styloid processes ;" and the intermediate pieces of the anterior 
 cornua (b) have their places supplied by ligaments (the stylo- 
 hyoid) : in this way, therefore, the hyoid apparatus attains the 
 form that it exhibits in the human skeleton. 
 
 (756.) The muscles connected with the os hyoides in quadru- 
 peds correspond with those met with in the human body ; and 
 their action in effecting the deglutition of food is well known to 
 the anatomical reader. 
 
 (757.) The passage of the fauces in the Mammalia presents an 
 organization peculiar to the class, and exhibits structures adapted 
 to prevent alimentary materials from entering the air-passages 
 during the operation of swallowing. The most remarkable of these 
 is the epiglottis, forming a valvular fibre-cartilaginous lid, that 
 accurately closes the opening of the larynx during the transit of 
 
MAMMALIA. 677 
 
 food into the throat. The communication between the posterior 
 nares and the faucial cavity is likewise protected by a musculo- 
 membranous valve, called the velum pendulum palati ; but as, 
 with the exception of the CETACEA hereafter to be noticed, the 
 arrangement of these parts exactly resembles what is seen in the 
 human subject, it would be superfluous to describe them more 
 minutely in this place. 
 
 (758.) The bag of the pharynx in all the Mammalia is similar 
 in its structure to that of Man ; and its muscles, namely, the 
 stylo-pharyngeus, and the three constrictors, although stronger 
 than in our own species, offer no differences worthy of more parti- 
 cular notice. 
 
 (759.) The oesophagus, leading from the termination of the 
 pharynx into the stomach, is a long muscular tube, that traverses 
 the chest in front of the bodies of the dorsal vertebrae, and, having 
 pierced the diaphragm, reaches the abdominal cavity. Its lining 
 membrane is loose and much plicated, so as to allow of consider- 
 able dilatation ; but externally its walls are very muscular, the 
 surrounding muscles being arranged in two distinct layers. In 
 Man the outer stratum of muscular fibres is disposed longitudi- 
 nally, while the inner layer consists of circular fibres ; but in 
 most other Mammalia both these layers assume a spiral course, 
 and cross each other obliquely as they embrace the cesophageal tube. 
 
 (760.) The stomach itself presents such endless diversity of 
 form, that merely to enumerate all the details that have been 
 amassed relative to this part of our subject would fill many vo- 
 lumes, without perhaps at all advancing our real knowledge con- 
 cerning the process of digestion ; we must, therefore, content our- 
 selves with a very general view of the organization of this important 
 viscus, and regard the Mammalia as possessing either simple, 
 complex, or compound stomachs, each of which will deserve a 
 distinct notice. 
 
 (761.) In the simple form of stomach the organ consists of a 
 single cavity, as is the case in the human species, let the shape 
 of the viscus be elongated, pyriform, or globular; for in this 
 respect there is every possible variety ; but whatever its form, or 
 the relative positions of the cardiac and pyloric orifices, its struc- 
 ture corresponds with that of Man in all essential particulars. This 
 kind of stomach exists in by far the greater number of Mammals. 
 
 (762.) In the complex stomach the viscus is made up of several 
 compartments communicating with each other, but without pre- 
 
678 
 
 MAMMALIA. 
 
 sen ting any difference of organization, such as in the present state 
 of physiological knowledge would lead us to suppose them to pos- 
 sess different functions: neither are we at all able to find any con- 
 nection between such an arrangement and the nature of the sub- 
 stances used as food. The Kangaroo (Macropus major), the 
 Kangaroo Rat (Hypsiprymnus), the Porcupine (Hystrix), and 
 the Hi/rax, are amongst the most striking examples. 
 
 (763.) The compound stomach is that possessed by the Ru- 
 MINANTIA, or animals that chew the cud ; and consists of four 
 distinct cavities, differing very materially both in their size and 
 in the arrangement of their lining membranes. The first and by 
 far the largest cavity (Jig. 316, d) is called the paunch (rwwiew), 
 and is of very great 
 size, occupying a 
 considerable portion 
 of the abdominal 
 cavity, and forming 
 the great receptacle 
 into which the crude 
 vegetable aliment 
 is received when 
 first swallowed : this 
 chamber is lined with 
 shaggy villi. The 
 second cavity (reti- 
 culum) (c) is much 
 smaller, and its walls 
 are covered with 
 numerous polygonal 
 cells, from whence 
 
 it derives the name it bears. The third chamber (e), called 
 the psalterium^ has its lining membrane disposed so as to form 
 deep lamellse, arranged longitudinally in alternating large and 
 small layers, and thus presenting a most extensive surface. The 
 fourth stomach (abomasus) (f) also exhibits very numerous 
 folds of mucous membrane : it is of a pyriform shape, and by 
 its smaller end terminates at the pylorus (g). The three first 
 stomachs are lined internally with a thin cuticular investment ; 
 but the last, apparently the representative of the single stomach 
 of those quadrupeds that have but one stomachal cavity, is 
 coated with a soft membrane that furnishes abundantly the ordi- 
 
MAMMALIA. 679 
 
 nary gastric secretions, and appears to be more especially the di- 
 gestive stomach. 
 
 The passage of the food through these different chambers will 
 be easily understood on referring to the preceding figure, in which 
 the course of the aliment before and after rumination is indicated 
 by the direction of the probes a, b. The oesophagus, it will be 
 observed, communicates on the one hand with the paunch d, and 
 on the other with the cavities c, e,jf; and, moreover, by means 
 of a muscular fold formed by the walls of the second cavity, a pas- 
 sage may be formed leading directly into the third stomach (e) 
 without communicating with the second (c). The process of 
 rumination would, therefore, seem to be effected in the following 
 manner. The herbage when first swallowed in an unmasticated 
 condition passes into the capacious paunch (rf), where it accu- 
 mulates, and undergoes, no doubt, a kind of preliminary mace- 
 ration. When the RUMINANT has done grazing, and is at lei- 
 sure, the food is again regurgitated into the mouth, to undergo 
 more careful and complete mastication : for this purpose, a part of 
 it is admitted into the reticulum (c), and there formed into a 
 smooth and lubricated bolus ; which, being expelled into the oeso- 
 phagus, is immediately seized by the spiral muscles surrounding 
 that canal, and forced forwards into the mouth. After undergoing 
 a thorough triturition, the aliment is once more swallowed, and 
 it then enters into the third stomach e, passing along the muscular 
 fold that leads from the oesophagus into that compartment. 
 Here it is spread out over the extensive surface formed by the 
 laminated walls of the psalterium, and is prepared for admission 
 into the last cavity f, which, as has been said, is the true digestive 
 stomach. 
 
 (764.) While the young Ruminant continues to be nourished by 
 its mother's milk, the three first cavities are undeveloped and com- 
 paratively very small ; so that the milk passes on immediately 
 into the fourth stomach, to be at once appropriated as aliment. 
 
 (765.) In the Camel, the Dromedary, and the Llama, the 
 walls of the reticulum and of a portion of the paunch are ex- 
 cavated into deep cells or reservoirs bounded by muscular fasci- 
 culi, wherein water may be retained in considerable abundance, un- 
 mixed with the contents of the stomach ; it is in consequence of 
 this arrangement that these animals are able to subsist for many 
 days without needing a fresh supply of water even during long 
 journeys in a tropical climate. 
 
680 MAMMALIA. 
 
 (766.) In the CETACEA the stomach consists of several bags 
 that communicate with each other. These bags vary from five 
 to seven in number ; but in the present state of our knowledge 
 concerning the physiology of digestion it is difficult to divine what 
 is the purpose of such an arrangement, more especially as rumina- 
 tion is here out of the question. The first stomach of the Whale 
 is, however, no longer merely a reservoir,* as the food under- 
 goes a considerable change in it. The flesh of its prey is entirely 
 separated from the bones, which proves that the secretion of this 
 cavity has a solvent power. This was found to be the case in 
 the Bottle-nose Porpoise and in the large Bottle-nose Whale ; in 
 both of which several handfuls of bones were contained in the first 
 cavity, without the smallest remains of the fish to which they had 
 belonged. In others the earth had been dissolved, so that only 
 the soft parts remained ; and, indeed, it is only partially digested 
 materials that can be conveyed into the second and third cavities, 
 the orifices being too small to permit bones to pass. 
 
 (767.) The rest of the alimentary canal in most quadrupeds, 
 like that of Man, is divisible into the small and the large in- 
 testines ; the division between the two being marked by one or even 
 two appendages, called respectively the ctecum and the appendix 
 vermiformis. 
 
 The small intestines require no particular description, as in all 
 minor circumstances, such as their proportionate length and diame- 
 ter, or in the number and arrangement of the valvula conniventes, 
 they do not differ from the human. The large intestines, how- 
 ever, offer very great variations of structure, and will therefore merit 
 our more attentive consideration ; we shall accordingly lay before 
 the reader the following resume of the principal facts connected 
 with this subject, as given by the indefatigable Cuvier.'J' 
 
 (768.) In Man, the Orangs (Simia), and the Wombat (Phas- 
 colomys), both caecum and vermiform appendage are met with. 
 
 (769.) In the other QUADRUMANA, the DIGITIGRADE CAR- 
 NIVORA, the MARSUPIALIA, the RODENTIA, the PACHYDER- 
 MATA, the RUMINANTIA, the SOLIPEDS, and the AMPHIBIOUS 
 MAMMALS, there is a csecum without any vermiform appendage. 
 
 (770.) Neither ceecum nor appendix vermiformis are found in 
 the EDENTATA, the PLANTIGRADE CARNIVORA, nor in the CE- 
 TACEA. 
 
 * Sir E. Home, Lectures on Comp. Anat. vol. i. p. 225. 
 t Lejons d' Anatomic Comparee, torn. iii. p. 465. 
 
MAMMALIA. 681 
 
 Numerous exceptions, of course, occur to the above summary ; 
 but it would be useless to notice them in a survey so general as 
 the present. 
 
 Even where no caecum exists, the separation between the large 
 and small intestines is generally indicated by a valve (ileo-cotic) 
 formed by the lining membrane of the bowel : this, for example, 
 is the case in the Sloths and Armadillos. 
 
 (771.) In all the Mammalia that possess a caecum, this organ 
 appears to be a prolongation of the colon beyond the point at 
 which the small intestine enters its cavity. The caecum thus 
 formed varies materially, both as relates to its size, shape, and 
 structure : in animals that live upon vegetables, and even in some 
 that are omnivorous, it is generally very large, gathered into sac- 
 culi, and often distinctly glandular ; but in such as live upon flesh 
 it is always small, and its cavity smooth, resembling a small intes- 
 tine. 
 
 (772.) The assistant chylopoietic viscera, namely, the liver, 
 the pancreas, and the spleen, are constructed upon the same prin- 
 ciples as in the human subject, and, except in a few minor circum- 
 stances, offer little to arrest our particular notice. 
 
 (773.) The liver occupies the same position as in Man, being 
 principally situated in the right hypochondrium, where it is se- 
 curely suspended by broad folds of peritonaeum connecting it to 
 the abdominal surface of the diaphragm and to the circumjacent 
 parts. It is most frequently, especially in the more active carni- 
 vorous families, divided by deep fissures into several lobes ; a dis- 
 position whereby the free movement of this part of the body is 
 evidently facilitated. The gall-bladder, when present, which is 
 not invariably the case, receives the bile indirectly through a cystic 
 duct derived from the hepatic, so that the biliary fluid, poured 
 into the duodenum through a ductus communis choledochus, is de- 
 rived either immediately from the liver, or is regurgitated from the 
 gall-bladder as occasion requires. 
 
 The pancreas resembles the human in every particular, and its 
 secretion enters the duodenum at the same point as that of the 
 liver. 
 
 The spleen is always attached to the stomach by a duplicature 
 of the peritonaeal lining of the abdomen, and is organized in the 
 same manner as that of Man, except in the CETACEA, where this 
 viscus is divided into several small portions quite distinct from each 
 other. 
 
682 MAMMALIA. 
 
 (774.) The system of the vena port<p is made up of the ve- 
 nous trunks derived from the spleen, the stomach, the pancreas, 
 and the intestinal canal : these all unite to form one large cen- 
 tral trunk, which after entering the liver again divides and sub- 
 divides minutely in that viscus, and furnishes the venous blood, 
 from which the bile is principally if not entirely elaborated. 
 
 (775.) The peritonaeum, or the serous membrane lining the 
 abdominal cavity, forms in the Mammalia a shut sac, and by its 
 numerous inflexions invests all the chylopoietic viscera, forming 
 broad mesenteric folds to support the intestines ; it thus encloses 
 between its laminae the entire system of mesenteric vessels, and 
 also the lacteals derived from the alimentary canal : as to the rest, 
 its structure and disposition, even to the formation of the omental 
 sacs, differ in no important respect from what is found in the hu- 
 man body. 
 
 (776.) The chyle, the result of the digestive process, is taken 
 up from the mucous lining of the intestinal canal by innumerable 
 microscopic orifices that form the commencement of the lacteal 
 system, which in the Mammalia seems to assume its most perfect 
 developement. This important system of absorbent vessels con- 
 sists of slender canals enclosed between the two layers of the me- 
 sentery, to the root of which they converge from all the tract of 
 the intestine. The valves formed by the lining membrane of 
 these tubes are in Mammals so numerous and perfect that it is no 
 longer possible to inject them from trunk to branch. Before ter- 
 minating in the thoracic duct, these vessels permeate numerous 
 4t mesenteric glands," as they are called, by means whereof they 
 appear to communicate freely with the venous system ; but the 
 bulk of the matter absorbed enters a kind of reservoir called the 
 " receptaculum chyli" whence, by means of the thoracic duct, the 
 chyle is conveyed to be mixed up with the mass of the circulating 
 fluid, and is ultimately poured into the vena innominata at the 
 junction of the jugular and subclavian veins of the left side of the 
 body. 
 
 (777.) The lymphatic system of Mammals, as far as it has 
 been studied, conforms in its arrangement to that of Man. 
 
 (778.) Neither will it be at all necessary to describe at any 
 length the construction of the respiratory and circulatory organs 
 in the class now under consideration ; seeing that the structure of 
 the lungs, the mechanism of respiration, the arrangement of the 
 pulmonary vessels, the cavities of the heart, and the general dis- 
 
MAMMALIA. 683 
 
 position of the arteries and veins of the systemic circulation differ 
 in no material circumstance from what is met with in our own per- 
 sons. 
 
 The lungs, occupying the two sides of the chest, are each con- 
 tained in a distinct chamber, formed by the ribs and diaphragm, 
 without in any part adhering to its walls. Each lung is enclosed 
 in a serous cavity formed by the pleura, which, after lining the 
 ribs, the intercostal muscles, and the thoracic surface of the dia- 
 phragm, is reflected on to the lung itself at the point occupied by 
 the roots of the pulmonic vessels, and invests the entire surface 
 of the viscus ; it moreover passes deeply into those fissures that 
 separate the lung into several distinct lobes. 
 
 In the interspace between the two pleurae, called the medias- 
 tina, is lodged the heart, contained in a fibro-serous envelope (the 
 pericardium) ; and behind this the oesophagus, accompanied by the 
 principal trunks of the vascular system, passes through the thorax 
 into the abdomen. 
 
 (779.) Each lung is a closed bag, composed of innumerable 
 cells that communicate with the terminations of the bronchial 
 tubes, and collectively present an immense surface, over which the 
 blood contained in the capillaries of the pulmonary vessels is made 
 to circulate. 
 
 The inspiration and expiration of air are effected by the alter- 
 nate movements of the diaphragm and of the walls of the thora- 
 cic cavity, whereby the atmospheric fluid is drawn into and ex- 
 pelled from the pulmonary cellules, and is thus constantly renewed 
 as it becomes deteriorated by the abstraction of the oxygen con- 
 sumed during the process of converting the venous into arterial 
 blood. 
 
 The purified blood, after passing through the pulmonary capil- 
 laries, is collected in an arterialized condition by the pulmonary 
 veins, and conveyed to the systemic side of the heart, which offers 
 the same arrangement throughout the entire class, consisting of an 
 auricular chamber (Jig. 317, c), and of a very muscular ventricle, 
 a, the auricula-ventricular opening being guarded by mitral valves 
 and columns earner similar to those found in the human heart. 
 From the left ventricle the blood is driven into the aorta, e, the 
 commencement of which is guarded by three semilunar valves, and 
 thus it passes through the entire system. 
 
 When again collected from the periphery of the body, the now 
 vitiated fluid is returned to the heart by the venous system, and 
 
684 
 
 MAMMALIA. 
 
 Fig. 317. 
 
 poured through the vena cavte into the right or pulmonic auricle ; 
 and hence it passes into the right ventricle (Jig. 317, b), to be 
 again returned through the pulmonary artery to the lungs, thus 
 completing the circulation. 
 
 (780.) But although the general arrangement of the circulatory 
 and respiratory organs in all Mammals thus in every respect re- 
 sembles that which exists in the human body, there are of ne- 
 cessity variations in the distribution of certain parts of the san- 
 guiferous system, adapted to the peculiarities of organization pre- 
 sented by the different orders and even families of this great class, 
 which must not be wholly passed over in silence. 
 
 (781.) In the GET ACE A, for instance, many interesting circum- 
 stances are observable in 
 the arrangement of the 
 vascular system. 
 
 In the herbivorous ge- 
 nera, as for example in 
 the Dugong, the two 
 sides of the heart are 
 separated to a consider- 
 able extent by a deep 
 fissure (Jig. 317, cr, &), 
 so that the pulmonary 
 and systemic hearts are 
 much more evidently dis- 
 tinct viscera than they ap- 
 pear to be in the quadru- 
 pedal forms ; neverthe- 
 less, in the Whalebone and Spermaceti Whales the heart assumes 
 the usual appearance, and is only remarkable for its amazing size ; 
 this, indeed, may well have attracted the notice of Hunter,* while 
 investigating such gigantic beings. " In our examination of par- 
 ticular parts," says that eminent anatomist, " the size of which is 
 generally regulated by that of the whole animal, if we have only 
 been accustomed to see them in those which are small or middle- 
 sized, we behold them with astonishment in animals so far exceed- 
 ing the common bulk as the Whale. Thus the heart and aorta 
 of the Spermaceti Whale appeared prodigious, being too large to 
 be contained in a wide tub, the aorta measuring a foot in diameter. 
 
 * The Animal (Economy, by J. Hunter, with Notes by Professor Owen, p. 366. 
 
 a 
 
MAMMALIA. 685 
 
 When we consider these as applied to the circulation, and figure 
 to ourselves that probably ten or fifteen gallons of blood are 
 thrown out at one stroke, and moved with an immense velocity 
 through a tube of a foot in diameter, the whole idea fills the mind 
 with wonder." 
 
 (782.) In the arrangement of the blood-vessels of the CETA- 
 CEA many interesting peculiarities are met with.* The general 
 structure of the arteries, indeed, resembles that of other Mam- 
 mals, and where parts are nearly similar their distribution is 
 likewise similar. But these animals have a greater proportion of 
 blood than any others known, and there are many arteries appa- 
 rently intended as reservoirs, wherein a large quantity of arterial 
 blood may accumulate, apparently for important purposes, where 
 vascularity could not be the only object. Thus the intercostal 
 arteries divide into a vast number of branches, which run in a ser- 
 pentine course between the pleura and the ribs, and penetrate 
 the intercostal muscles, everywhere lining the walls of the thorax. 
 These plexiform vessels, moreover, pass in between the ribs near 
 their articulation, and anastomose extensively with each other. 
 The medulla spinalis is likewise surrounded with a net-work of 
 arteries in the same manner, more especially as it comes out from 
 the brain, where a thick substance is formed by their ramifications 
 and convolutions, and these vessels most probably anastomose with 
 those of the thorax. The precise function assigned to this ex- 
 tensive plexus of arteries has not been as yet satisfactorily deter- 
 mined, although it is doubtless a receptacle wherein arterial blood 
 is stored up during the long-continued submersion to which these 
 animals are so frequently subjected. 
 
 (783.) As the GET ACE A have no pelvic extremities, the aorta, 
 instead of bifurcating into iliac arteries, is entirely appropriated to 
 supply the enormous tail beneath which it is continued, enclosed 
 in a canal formed by the roots of the inferior spinous processes 
 of the caudal vertebrae, that are here again developed as in fishes. 
 
 (784.) The venous system in the Cetacean order is equally 
 remarkable for the plexuses formed by it in different parts of the 
 body ; of these the most important communicates with the abdo- 
 minal cava, and is of immense extent. The veins of these crea- 
 tures, moreover, are almost entirely deprived of valves, so that 
 every possible arrangement has been made to delay the course of 
 * Hunter, ut supra, p. 365. 
 
686 MAMMALIA. 
 
 the circulating blood during the temporary suspension of respira- 
 tion that occurs whenever the animal plunges beneath the surface 
 of the water. 
 
 (785.) In other aquatic Mammals that dive, and are thus sub- 
 jected to prolonged immersion, large dilatations are found con- 
 nected with the principal trunks of the venous system in the 
 neighbourhood of the heart, in order to prevent a dangerous dis- 
 tension of these veins while the circulation is impeded and re- 
 spiration put a stop to. This is particularly remarkable in the Seal 
 tribe ; and in these Carnivora we are assured by good authorities 
 that it is not uncommon to find the foramen ovale of the heart, 
 and the ductus arttriosus, which in the fetus allows blood to pass 
 from the pulmonary artery directly to the aorta, still open even in 
 the adult animal ; but this arrangement, as we are well satisfied, 
 is by no means to be regarded as the normal structure of the heart 
 in a Seal. 
 
 (786.) In many of the long-necked herbivorous quadrupeds a 
 peculiar provision has been made in the disposition of the internal 
 carotid arteries, apparently intended to equalize the force of the 
 blood supplied to the brain in different positions of the head: for 
 this purpose the arteries referred to, just as they enter the skull, 
 divide into several branches, which again unite so as to assume a 
 kind of plexiform arrangement, forming what is called the rete 
 mirabile of old authors. The effect of this subdivision of the 
 main trunk into so many smaller channels will evidently be to 
 moderate the rapidity with which the blood would otherwise enter 
 the cranium, and thus preserve the brain from those sudden in- 
 fluxions to which it would otherwise be constantly liable. 
 
 (787.) We must likewise notice a structure, in some respects 
 similar to the above, that exists in the arteries both of the an- 
 terior and posterior extremities of the Sloths (Bradypus). In 
 these slow-moving animals, the axillary and iliac arteries, just be- 
 fore entering the limbs to which they are respectively destined, 
 suddenly divide into numerous small channels, which again unite 
 into one trunk before the arteries of the member are given off. 
 No doubt such an arrangement will very materially retard the 
 course of the blood as it flows through these multiplied canals, and 
 perhaps is materially connected with the long-enduring strength of 
 muscle that enables these creatures to cling without fatigue to 
 the branches whereby they suspend themselves. 
 
 Innumerable other minor differences in the course and distribu- 
 
MAMMALIA. 
 
 687 
 
 tion of the blood-vessels might of course be pointed out, a few 
 of which may require notice elsewhere ; but, generally speaking, the 
 arrangement of the vascular system in all quadrupeds is so similar, 
 that the anatomical student who may push his researches thus far 
 will never be at a loss in identifying the different vessels, and com- 
 paring them with those found in the human body. 
 
 (788.) Although the respiration of Mammalia is inferior, as 
 regards the extent to which their blood is exposed to the influ- 
 ence of the atmosphere, to the perfection of this process in Birds, 
 nevertheless, such is the elevated temperature of the body in these 
 hot-blooded animals, that a warm covering of some non-conduct- 
 ing material is here absolutely requisite to retain the vital warmth, 
 and defend them against the thermometrical changes of the ele- 
 ment they inhabit. Their skin is generally, therefore, clothed 
 with a warm covering of hair ; a cuticular structure, the nature 
 and growth of which it behoves us now to examine. We must first, 
 however, notice the organization of the skin itself, and then the 
 nature of the various structures employed to defend it will be 
 readily understood. 
 
 The skin of all Mammals, like that of the human body, con- 
 sists of the cutis, or vascular 
 true skin ; of the epidermis, 
 or cuticle ; and of a thin 
 layer of pigment interposed 
 between the two, which is a 
 diversely coloured secretion, 
 deposited like the cuticle 
 upon the surface of the cutis. 
 
 The hairs that cover the 
 quadruped, whatever be their 
 form or thickness, are cylin- 
 ders of horny or cuticular 
 substance, that grow upon 
 so many minute vascular 
 pulps, from the surface of 
 which the corneous mate- 
 rial is perpetually secreted. 
 Some kinds of hair are per- 
 manent, and, if constantly 
 cut, will continue to grow 
 during the whole life of the 
 
 318. 
 
688 MAMMALIA. 
 
 animal ; such is the hair of Man, and that which forms the mane 
 and tail of the Horse : but generally the hair is shed at stated 
 periods, to be replaced by a fresh growth. For the most part, 
 these structures are so minute, that the apparatus employed in 
 forming them escapes observation ; but in very large hairs, such 
 as those that compose the whiskers of the Seal, or of the Lion, 
 it is not difficult to display the organs by which they are secreted. 
 The appended figure, taken from one of the drawings in the 
 Hunterian collection, represents a section of the lip of a young 
 Lion, and in it all the parts connected with the growth of the 
 larger hairs are beautifully displayed. A bulb or sacculus, formed 
 by an inward reflection of the cutis (Jig- 318, B, e), and lined 
 by a similar inflection of the cuticle (/), contains in its fundus a 
 vascular pulp (g, g, $), well supplied with large vessels and nerves 
 (h). It is from the surface of the pulps (g), exhibited upon a mag- 
 nified scale at A, that the horny stem of the hair is gradually se- 
 creted, and its length of course increases in proportion to the 
 accumulation of corneous matter continually added to the root. 
 
 (789.) Various are the appearances, and widely different the 
 uses, to which epidermic appendages, in every way analogous to hair, 
 both as relates to their composition and mode of growth, may be 
 converted : the wool of the Sheep, the fur of the Rabbit, the spines 
 of the Hedgehog, the quills of the Porcupine, the scaly covering 
 of the Manis, and even the armour that defends the back of the 
 Armadillo, are all of them but modifications of the same struc- 
 tures, adapted to altered conditions under which the creatures live. 
 Even the horn upon the snout of the Rhinoceros is but an ag- 
 glomeration of hairy filaments, formed upon a broad and com- 
 pound pulp. The nails and claws that arm the fingers and toes, 
 the corneous sheath that invests the horns of the Ox and Ante- 
 lope, nay, the hoofs of herbivorous quadrupeds, are all epidermic 
 secretions from the vascular cutis ; or, in other words, are hairs 
 altered in their form and extent, according to the exigencies of the 
 case. 
 
 (790.) Widely different, however, are the so-called horns of 
 the Deer tribe, which in reality consist of bone, and, being deci- 
 duous, have to be reproduced from year to year by a most pecu- 
 liar and interesting process. No sooner does the return of genial 
 weather again call forth the dormant reproductive energies of the 
 system, than the budding antlers begin to sprout from the forehead 
 of the Stag, and rapidly expand in their dimensions from day to 
 
MAMMALIA. 689 
 
 day. On making a longitudinal section of the young horn, it is 
 found to be continuous with the os frontis, having its outer sur- 
 face covered with a vascular periosteal membrane derived from 
 the pericranium, which in turn is protected by a fine velvety skin. 
 Moreover, when a growing antler is injected minutely, and its 
 earthy matter removed by means of an acid, vessels derived from 
 the periosteum are found to traverse it in all directions, proving its 
 identity with real bone. As growth goes on, the external carotid 
 arteries, thus called upon rapidly to furnish a prodigious supply of 
 materials, dilate in a remarkable 'manner, and soon the palm and 
 the antlers of the horn have acquired their full dimensions. No 
 sooner is this accomplished, than a prominent ring or burr is 
 formed around the base ; which, projecting outwards, compresses 
 and soon obliterates the vessels that have hitherto supplied the 
 growing defences. The circulation being thus put a stop to, the 
 soft teguments and periosteum peel off in strips ; and the bone, 
 denuded of its covering, becomes a formidable weapon. 
 
 At the close of the breeding season the removal of the horns is 
 speedily effected : the connection between their bases and the os 
 frontis is gradually weakened by interstitial absorption, until at 
 length a slight effort is sufficient to detach the branching honours 
 of the Stag, and they fall off, leaving a broad cicatrix ; this soon 
 skins over, and the succeeding year calls forth a repetition of the 
 process.* 
 
 (791.) The CETACEA form a very remarkable group among 
 the hot-blooded Mammifers, as relates to the external covering of 
 their bodies. No covering of hair or wool would have been effi- 
 cient in retaining the vital heat under the circumstances in which 
 these creatures live ; and, even if such clothing could have been 
 made available, it would have seriously impeded their progress 
 through the water. Another kind of blanket has therefore been 
 adopted : the cuticle is left perfectly smooth and polished, with- 
 out any vestige of hair upon its surface ; but, beneath the skin, 
 fat has been accumulated in prodigious quantities, and, enveloped 
 in this non-conducting material, the Whales are fully prepared to 
 inhabit an aquatic medium, and to maintain their temperature even 
 in the Polar Seas. 
 
 * In a physiological point of view this rapid production of osseous matter is truly 
 wonderful. The horns of the Wapiti Deer, thus annually reproduced, will weigh up- 
 wards of thirty pounds ; and in the fossil Irish Elk the weight of these deciduous 
 defences must have been greater than that of the entire skeleton. 
 
 2 Y 
 
690 
 
 MAMMALIA. 
 
 (792.) The skin of all quadrupeds contains innumerable se- 
 cerning follicles, whereby lubricating fluids are continually furnish- 
 ed for the purpose of maintaining the surface in a moist or supple 
 condition ; but not unfrequently these glandular follicles are ag- 
 gregated together in considerable numbers, so as to form secreting 
 pouches. In many species of Stags and Antelopes, for example, 
 large pouches of this description are found below the margin of the 
 orbit, that furnish a secretion vulgarly regarded as the Stag's 
 " tears." In most instances some of the cutaneous glands secrete a 
 highly odorous material, especially in the vicinity of the parts of 
 generation ; and their secretion being most abundant during the 
 rutting season, it is not without reason that these organs are 
 looked upon as destined to attract the sexes, and perhaps to stimu- 
 late the sexual passions. The preputial glands, so called because 
 they furnish an odoriferous fluid that lubricates the prepuce and 
 glans of the penis in the male, and of the clitoris in the female, are 
 of this kind.* For the most part, these are simple sebaceous folli- 
 cles contained in the thickness of the prepuce ; but occasionally 
 they are replaced by true conglomerate glands, formed of lobes and 
 lobules, and having but a single excretory duct, that opens upon 
 
 Fig. 319. 
 
 the sides of the 
 glans penis or 
 clitoridis be- 
 neath the pre- 
 puce. Many 
 of the Roden- 
 tia are furnish- 
 ed with glands 
 of this descrip- 
 tion, and they 
 are situated on 
 each side of 
 the penis, im- 
 mediately be- 
 neath the skin 
 that covers the 
 pubic region. 
 
 (793.) It is 
 with the pre- 
 putial glands that we must notice the still more elaborately de- 
 
 * Cuv. Lemons d'Anat. Comp. torn. v. p. 252 et seq. 
 
MAMMALIA. 691 
 
 veloped secreting organs of the Beaver, that furnish the drug 
 called " castor" These organs, represented in the annexed figure 
 (Jig. 319), consist of large glandular pouches, g, A, that discharge 
 their contents in the vicinity of the anal and preputial apertures ; 
 but of what the importance of the material thus abundantly se- 
 creted may be in the economy of the animals so provided, it is not 
 easy to conjecture. 
 
 (794.) The secreting apparatus of the Musk Deer, (Moschus 
 moschiferus,) which produces musk, is of analogous conforma- 
 tion. This is an oval pouch situated beneath the skin of the 
 lower part of the belly : its walls are thin and apparently 
 membranous, but the membrane that lines them is rugose and 
 plicated. The orifice leading to this pouch is small, and opens 
 in front of the prepuce. 
 
 (795.) Lastly, in connection with these odoriferous glands 
 we may mention the " temporal glands" of the Elephant, from 
 the duct of which, situated on each side midway between 
 the eye and the ear, there flows a viscid and fetid liquid ; 
 and likewise the u anal glands" met with in most CARNIVORA. 
 The ducts of the glands last mentioned open near the margin of the 
 anus ; and in some genera, as the Skunk and the Polecat, the 
 stench produced by the fluid poured from these sources is so into- 
 lerable as to become a most efficient defence against a foreign enemy. 
 
 (796.) We now come to consider the nervous system of the 
 MAMMALIA, and are of course prepared to anticipate that in pro- 
 portion as they surpass all other animals in intelligence, so will the 
 encephalic masses assume a complexity and perfection of structure 
 such as we have not hitherto witnessed in the whole series of 
 the animal creation . Their senses likewise may be presumed to 
 have attained the utmost delicacy of organization in correspond- 
 ence with the exalted attributes conferred upon this important 
 class, and consequently to exhibit appendages and accessory parts, 
 adapting them most accurately to repeat to the sensorium impres- 
 sions derived from without. 
 
 (797.) Abstruse as the study of the brain has been rendered by 
 the chaotic assemblage of names applied by the earlier anatomists 
 in their bewilderment to every definable portion of its substance, 
 we have little doubt that, when the grand laws that have hitherto 
 guided us in investigating the nervous system of the lower animals 
 are had recourse to, the student will soon perceive how little diffi- 
 culty there is in comparing even the brain of Man with the ence- 
 
 2 Y 2 
 
692 MAMMALIA. 
 
 phalon of the humbler Vertebrata examined in preceding pages, 
 and thus tracing the progressive advances from simple to more 
 complex organization. 
 
 (798.) The great lessons deducible from all that we have as yet 
 seen relative to the essential organization of the nervous system 
 are obvious enough. First, that all nerves, whether connected 
 with sensation or the movements of the body, emanate from or 
 are in communication with nervous masses called ganglia, which 
 are in fact so many brains presiding over the functions attributa- 
 ble to the individual nerves. Secondly, that in the lower animals 
 where these ganglia exist, they are comparatively small, and more 
 or less completely detached from each other ; but that in the Ver- 
 tebrata such is the increased developement of the central masses 
 of the nervous system, that they coalesce, as it were, into one great 
 organ called the cerebro-spinal axis ; and thus that the encephalon 
 and medulla spinalis are both made up of symmetrical pairs of 
 ganglia appointed to different functions, but so intimately blended 
 together that they are no longer distinguishable, except from the 
 pairs of nerves with which they are connected. 
 
 (799.) Taking the above for axioms, and they are incontro- 
 vertible, let us proceed to analyze the cerebro-spinal axis of the 
 Mammalia, and to compare it in simple terms with that of Birds, 
 Reptiles, and Fishes already examined. 
 
 (800.) Commencing at the anterior extremity of the series, the 
 first encephalic masses that present themselves are the " olfactory 
 nerves^ as the human anatomist has been pleased to call them, 
 although in every one of the details connected with their anato- 
 mical structure and relations they confessedly differ from every 
 nerve in the body. They are, in truth, not nerves at all, but 
 brains, the ganglia or brains of smell, from which the olfactory 
 nerves properly so called invariably emanate. In Fishes ( 557) 
 they were found to equal, or even to surpass in size, the hemi- 
 spheres themselves. In Reptiles and Birds they became gradually 
 concealed by the developement of the hemispherical masses ; and 
 in the Mammalia such is their diminutive appearance when com- 
 pared with the cerebrum, that they are scarcely recognized as ele- 
 ments of the encephalon at all. 
 
 In all the oviparous Vertebrata the nerves of smell were two 
 simple cords, one derived from each of the olfactory ganglia, from 
 which they proceeded through osseous canals to the nose. But in 
 the Mammifers these nerves are extremely numerous in proportion to 
 
MAMMALIA. 
 
 693 
 
 the extent of tlie surface to be supplied, and escape from the skull 
 through the cranial plate of the ethmoid bone, which, from the 
 number of apertures that it offers for their passage into the nose, 
 richly merits the name of " cribriform," more especially in the 
 carnivorous quadrupeds possessed of the most acute smell. 
 
 (801.) The interior of the nasal cavity is divided by a median 
 septum into chambers, in each of which a very large surface is pro- 
 duced by the complicated convolutions of the thin nasal plates of the 
 ethmoid (Jig .230, F ig. 320. 
 
 a), and of the in- 
 ferior turbinated 
 bone (6), over 
 which the air is 
 made to pass in 
 its progress to the 
 lungs before it 
 arrives at the pos- 
 terior nares (c). 
 The whole of this 
 complication of 
 bony lamellae is 
 covered with a de- 
 licate and highly 
 
 lubricated mucous membrane, wherein the olfactory nerves termi- 
 nate ; and from the figure given, representing the left nasal cavity 
 of a Lion, some idea may be formed of the acuteness of the sense 
 in question conferred upon the predaceous Garni vora. 
 
 (802.) With this perfection of the olfactory sense a corre- 
 sponding mobility of the outer nostrils is permitted to the Mam- 
 miferous races. In the Reptiles and Birds the external apertures 
 leading to the nose were merely immoveable perforations in the horny 
 or scaly covering of the upper mandible ; but now the nostrils 
 become surrounded with moveable cartilages, and appropriate mus- 
 cles, adapted to dilate or contract the passages leading to the nose, 
 or even to perform more important and unexpected duties, as, for 
 example, in the proboscis of the Elephant. 
 
 (803.) The CETACEA, as regards the conformation of their 
 nostrils, and indeed of the whole of their nasal apparatus, form a 
 remarkable exception to the above description. Inhabiting the 
 water as these creatures do, they are compelled to breathe atmo- 
 spheric air. Are they then to smell through the intervention of 
 
694 MAMMALIA. 
 
 an aquatic or aerial medium ? To smell in water would require 
 the nose of a fish, which could not be granted without infringing 
 upon the laws that regulate the progression of animal organiza- 
 tion. To smell in air would be useless to the Whale ; and, more- 
 over, its nasal passages are required for another function, with 
 which the exercise of smell would apparently be incompatible. 
 
 Thus circumstanced, we find the whole nasal apparatus com- 
 pletely metamorphosed, and so disposed as to answer two impor- 
 tant purposes : viz. first, to allow the Cetacean to breathe air 
 whilst its mouth is immersed in water ; and, secondly, to provide 
 an outlet whereby the water that is necessarily taken into the 
 mouth may escape without being swallowed. 
 
 The arrangement adopted to attain both these ends is very 
 beautiful. The nostrils, instead of occupying their usual position, 
 are situated quite upon the top of the head (Jig. 321, a), so that, 
 as soon as the vertex reaches the surface, air is freely obtained. 
 But another difficulty remains to be overcome : how is the 
 Cetacean to breathe air while its mouth is full of water ? 
 
 To allow this, the upper extremity of the larynx is prolonged, 
 so as to form a thick cartilaginous plug (c). When the creature 
 breathes, this elongated larynx is introduced into the posterior nares, 
 as represented in the figure ; and, being firmly embraced by a 
 sphincter muscle whilst in that situation, the air is admitted into 
 
 Fig. 321. 
 
 the trachea through the passages a, 6, without ever entering the 
 oral cavity. 
 
MAMMALIA. 695 
 
 It only remains to be seen how the Cetacean gets rid of the 
 water taken into the mouth, without being obliged to swallow it ; 
 and the same figure, representing a vertical section of the head of a 
 Porpoise, will enable us to understand the mechanism whereby 
 this is accomplished. The two canals forming the posterior nares 
 (b) are defended superiorly by a fleshy valve,* which is closed by 
 means of a very strong muscle placed above the intermaxillary 
 bones. To open this valve the force must be applied from below ; 
 and, when the valve is shut, all communication is cut off between 
 the posterior nares and the capacious cavities placed above them. 
 
 These cavities are two large membranous pouches lined with a 
 black skin, which, when they are empty, as represented in the 
 figure, falls into deep folds ; but, when full, the walls are distended 
 so as to form capacious oval receptacles. Externally these cham- 
 bers are enveloped by a very strong expansion of muscular fibres, 
 by which they can be violently compressed. 
 
 Let us now suppose that the Cetacean has taken into its mouth 
 a quantity of water that it wishes to expel : it moves its tongue 
 and its jaws as though it would swallow ; but, at the same time 
 closing its pharynx, the water is forced upwards through the pos- 
 terior nares (b), till it opens the interposed valve, and distends the 
 pouches placed above. Once in these reservoirs, the water may 
 remain there until the creature chooses to expel it, or in other 
 words " to blow." In order to do this, the valve between the 
 pouches and the posterior nares being firmly closed, the sacs are 
 forcibly compressed by the muscles that embrace them, and the 
 water is then spouted up through the " blow-holes," or nostrils, 
 to a height corresponding to the violence of the pressure. 
 
 (804.) It must be evident that it would be impossible that a 
 nose, through which salt water is thus continually and violently 
 forced,, could be lined with a Schneiderian membrane of sufficient 
 delicacy to be capable of receiving odorous impressions. In the 
 CETACEANS therefore the nerves of smell, and even the olfactory 
 lobes of the brain, are totally deficient. 
 
 (805.) The second pair of ganglia entering into the composi- 
 tion of the encephalon, and giving origin to nerves, are the optic 
 lobes ; from which are derived the nerves of vision. In the Fish 
 and in the Reptile these were at once recognizable as primary ele- 
 ments of the brain ; but in the Mammifer, owing to the excessive 
 developement of the surrounding parts, they are quite overlapped 
 
 * Cuvier, Le9ons d'Anat. Comp. torn. ii. p. 673. 
 
696 
 
 MAMMALIA. 
 
 and concealed by the hemispheres. Nevertheless the " tubercnla 
 quadrigemina (Jig. 322, rf, d) occupy the same relative position 
 as in the Tortoise, (vide Jig. 262, B, c, e,) and in like manner 
 still give origin to the nerves appropriated to the instruments of 
 sight, of which they are the proper ganglia. 
 
 (806.) The two optic nerves before passing to their final des- 
 tination partially decussate each other, as in the human subject, 
 they then proceed forward into the orbit, and penetrating the 
 globe of the eye expand into the retinae. 
 
 (807.) Minutely to describe the Fi^.322. 
 
 construction of the eye-ball in the 
 Mammalia would be quite super- 
 fluous, seeing that in every essen- 
 tial particular it exactly corresponds 
 with that of Man. The disposi- 
 tion of the sclerotic and choroid 
 coats, the structure of the cornea, 
 the arrangement of the humours 
 and of the retina, the organization 
 of the iris 9 in short, the whole 
 economy of the eye is the same 
 throughout the entire class. Ne- 
 vertheless, there are a few points 
 of secondary importance deserving 
 our attention, whereby the organ 
 is adapted to peculiarities of cir- 
 cumstance in which different tribes are placed. 
 
 In the Cetacea 9 and also in the amphibious Garni vora that 
 catch their prey in the water, the shape of the lens is nearly sphe- 
 rical as in Fishes ; and the antero-posterior diameter of the eye 
 is in consequence considerably diminished by the extraordinary 
 thickness of the sclerotic at the posterior aspect of the eye-ball, 
 an arrangement approaching very nearly to that already described 
 (560). 
 
 (808.) Instead of the dark brown paint which lines the choroid 
 of the human eye, in many Mammals the Ruyschian tunic secretes 
 a pigmentum of various brilliant hues, that shines with metallic 
 splendour. This membrane, called the " tapetum" partially lines 
 the bottom of the eye-ball, but its use has not as yet been satis- 
 factorily pointed out. 
 
 (809.) The shape of the pupil likewise varies in different 
 
MAMMALIA. 
 
 697 
 
 quadrupeds : for the most part, indeed, the pupillary aperture is 
 round, as it is in Man ; but in Ruminants, and many other Her- 
 bivora, it is transversely oblong. In the Cats (Felida), that hunt 
 in the gloom, and consequently require every ray of light that can 
 be made available, the pupil is a long vertical fissure ; but this 
 only obtains among the smaller genera, for in those Feline Car- 
 nivora that surpass the Ocelot in size, such as the Leopard, the 
 Lion, and the Tiger, the pupil again assumes a round form. 
 
 (810.) The eyes of Mammalia are lodged in bony orbits, as in 
 the oviparous Vertebrata, and in like manner are supported in 
 their movements by a quantity of semifluid fat, with which the 
 orbital cavities are filled up. In Man, as in Birds, Reptiles, and 
 Fishes, six muscles are appropriated to the movements of each 
 eye-ball, viz. four recti and two obliqui. The four recti mus- 
 cles have the Fig.3-23. 
 same disposi- 
 tion in Mam- 
 malia as in 
 Birds ; that is, 
 they arise from 
 the margin of 
 the optic fora- 
 men, and run 
 forward to be 
 inserted oppo- 
 site to each 
 other upon the 
 
 superior, 
 
 infe- 
 
 rior, and late- 
 ral surfaces of 
 
 the sclerotic coat. The inferior oblique likewise offers a similar 
 arrangement in all the Vertebrata, arising from the margin of the 
 internal wall of the orbit, and running outwards to be attached to 
 the external surface of the globe of the eye. But the superior 
 oblique, in the class before us, takes a very peculiar course. Aris- 
 ing like the rest, it passes forward to the upper and inner margin 
 of the orbit, where its tendon is reflected over a little cartilaginous 
 pulley (fig. 323, c), and turns back again to be inserted into the 
 external and posterior aspect of the eye-ball. 
 
 (811.) In addition to the six muscles appointed for the 
 movements of the eye in MAN and the QUADUUMANA, other 
 
698 MAMMALIA. 
 
 Mammalia have a seventh, called the choanoid or funnel-shaped 
 muscle. This likewise arises from the borders of the optic fora- 
 men, and, gradually expanding, forms a hollow cone interposed be- 
 tween the recti muscles and the optic nerve ; the base of the cone 
 being attached to the sclerotic, behind the insertion of the recti. 
 Frequently, indeed, this choanoid, or suspensory muscle, is di- 
 vided into four portions, in which case the animals so provided 
 would seem to have eight recti muscles. 
 
 (812.) The eye-lids of Mammalia resemble the human in every 
 respect, excepting that in the lower orders a remnant of the nicti- 
 tating membrane is still met with ; but it is of small dimensions, 
 and unprovided with muscles. 
 
 (813.) The lacrymal apparatus exists in all quadrupeds, and 
 the lacrymal gland occupies the same situation as in Man; the tears 
 being poured on to the conjunctiva near the external canthus of 
 the eye-lids. The lacrymal ducts, likewise, whereby the tears are 
 conveyed into the nose, so nearly resemble the human as to re- 
 quire no particular description. The carunculte, lacrymales are 
 also met with at the inner canthus of the eye-lids. In some 
 quadrupeds, indeed, an additional gland exists, called the glandula 
 Harderi : this is situated behind the internal angle of the eye, 
 and secretes a lubricating fluid, that is discharged beneath the 
 rudiment of the third or nictitating eye-lid. 
 
 (814.) In Whales, as might be expected from their aquatic 
 Jhabits, no vestige of a lacrymal apparatus is to be seen. 
 
 (815.) Behind the optic lobes of the encephalon the nervous 
 centres, from whence the other cerebral nerves take their origin, 
 are so intimately blended together, that the anatomist is no longer 
 able to distinguish them from each other. They form, in fact, 
 the " medulla oblongata" and are the commencement of that 
 long series of sentient and of motor ganglia that forms the spinal 
 cord. 
 
 All the nerves derived from the medulla oblongata, and from 
 the spinal cord, are throughout the Mammiferous class exactly 
 comparable to those met with in our own species, and therefore 
 will require but brief notice. 
 
 (816.) The third, fourth, and sixth pairs are destined to the 
 muscles of the eye, and their distribution is the same as in Man. 
 
 (817.) The fifth pair, or trigeminal nerves, consist of both 
 motor and sentient fasciculi, both of which are distributed to the 
 different parts of the face exactly as in the human subject ; allow- 
 
MAMMALIA. 6'99 
 
 ance of course being made for the varying form of the jaws, and 
 for the proportionate size of the different organs connected with 
 mastication. 
 
 (818.) The seventh, or facial nerve, as also the glosso-pharyn- 
 geal, the pneumogastric, and the lingual, have the same origin 
 and general distribution throughout the whole class. 
 
 (819.) The eighth pair of nerves are here, as in all the Verte- 
 brata, devoted to the sense of hearing, which in the Mammifera 
 attains its highest developement and perfection. The sensitive por- 
 tion of the auditory apparatus, or the internal ear, is now enclosed in 
 the petrous portion of the temporal bone, and imbedded in osseous 
 substance of such stony hardness, that, except in very young sub- 
 jects, it is by no means easy to display its different parts. 
 
 As in Fishes and Reptiles, it consists of several membranous 
 chambers or canals, filled with a limpid fluid, over which the 
 filaments of the auditory nerve spread out. The whole apparatus, 
 indeed, except in its proportionate size, very accurately resembles 
 the auditory organ of the lower Vertebrata : the semicircular canals 
 exhibit nearly the same arrangement, and in like manner commu- 
 nicate with the vestibule by five orifices. The vestibule itself is 
 small, and no longer contains any chalky concretions : it commu- 
 nicates on the one hand with the cavity of the tympanum, by 
 means of the foramen ovale ; and on the other sends off a canal 
 (scala) to form the cochlea, an organ which in the Mammifer 
 assumes its full developement and perfection. 
 
 In the Reptilia and Birds, as the reader will remember, the 
 cochlea was a simple canal bent upon itself (Jig> 281, e), one end 
 of which (scala vestibuli) opened into the vestibule, while the 
 other (scala tympani) terminated at the tympanic cavity, from 
 which it was separated by the membrane of the fenestra rotunda ; 
 but in the Mammalia the two scalse of the cochlea are consi- 
 derably elongated, and wind in a spiral direction around a central 
 axis (modiolus), so as very accurately to resemble the whorls in 
 the shell of a snail, whence the name of the organ is derived.* 
 
 It is in the increased complexity of the cochlea, therefore, 
 that the chief character of the labyrinth of the Mammal consists ; 
 but in the tympanic cavity the differences between the Mammi- 
 
 * In Man, and by far the greater number of Mammals, the scalae of the cochlea 
 make two turns and a-half around the modiolus; but in a few Rodent quadrupeds, as, 
 for example, in the Guinea-pig, the Cavy, and the Porcupine, there are as many as 
 three turns and a-half. 
 
700 MAMMALIA. 
 
 ferous car and that of the Bird are still more striking and de- 
 cided. 
 
 The cavity of the tympanum in the class before us is very 
 extensive, and not unfrequently its extent is considerably enlarged 
 by the addition of capacious mastoid cells. By means of the 
 Eustachian tube it communicates freely with the throat. Upon 
 its inner wall it offers the fenestra ovalis and the fenestra rotunda, 
 closed by their respective membranes ; and externally is the mem- 
 brana tympani, the vibrations of which are to be conveyed to the 
 labyrinth. 
 
 In Reptiles and Birds the communication between the drum of 
 the ear and the membrane of the fenestra ovalis was effected by 
 the interposition of a single ossicle, called the " columnella ;" but 
 in Mammals a chain of four ossicles, named respectively the mal- 
 leus, the incus, the os orbiculare, and the stapes, intervenes be- 
 tween the labyrinth and the membrana tympani : these ossicles, 
 both in their disposition and connections, are precisely similar to 
 those of Man, and, moreover, are acted upon by little muscles in 
 every respect comparable to those of the human subject. 
 
 However remote the structure of the tympanic chain of ossicles 
 in the Mammal may appear to be from that of the simple co- 
 lumnella of the Bird, it is interesting to see how gradually the 
 transition is effected from one class to another even in this par- 
 ticular of their economy ; for in the Ornithorynchus, the Echidna, 
 and the Kangaroo, so bird-like is the form of the stapes, that it 
 might easily be mistaken for the ossicle" of one of the feathered 
 tribes,* and every intermediate shape is met with as we advance 
 from this point towards the stirrup-shaped bone of the most per- 
 fect quadrupeds. 
 
 It is in the class under consideration, that for the first time an 
 external ear properly so called makes its appearance, for the fea- 
 thered appendages of the Owl or of the Bustard ( 684) are scarce- 
 ly entitled to such an appellation. In the Mammifera, however, 
 with a very few exceptions, such as the CETACEA, Moles, and the 
 Seal tribe, a moveable cartilaginous concha is appended to the 
 exterior of the head, adapted by its form and mobility to collect 
 the pulses of sound and convey them inwards towards the drum of 
 the ear. The basis of this external auricle is composed of fibro- 
 cartilage covered with a delicate skin, and its cavity is moulded 
 
 * Vide Sir Anthony Carlisle, " on the Physiology of the Stapes" Phil. Trans, for 
 1805. 
 
MAMMALIA. 701 
 
 into various sinuosities, so disposed, no doubt, as to concentrate 
 sonorous impressions. In Man, as the anatomist is aware, nume- 
 rous small muscles act upon the auricular cartilages ; but in quad- 
 rupeds possessed of moveable ears the number and size of these 
 muscles are prodigiously increased, and the ears are thus directed 
 with facility in any required direction. 
 
 (820.) More minutely to describe the structure of the auditory 
 apparatus in the Mammiferous class would be foreign to our pre- 
 sent purpose : nevertheless, we must not omit to notice one most 
 remarkable provision whereby the Whales, strangely circumstanced 
 as those creatures are, are permitted to hear either through the me- 
 dium of the air they breathe, or of the water in which they pass 
 their lives. The reader will at once appreciate the difficulties of 
 the case : the ear of a fish, without any external communication, 
 although best adapted to receive the stunning concussions convey- 
 ed through the denser element, could never appreciate the more 
 delicate vibrations of the air, and the ordinary Mammiferous ear 
 would be perpetually deafened by the thundering of the water. 
 How is the Whale to hear what is going on in either the sea or 
 the atmosphere ? 
 
 The plan adopted is simple and efficacious: The external 
 meatus of the ear is reduced to the smallest possible diameter, the 
 canal being barely wide enough to admit a small probe ; this is 
 the hydrophonic apparatus, and is all that is exposed for the recep- 
 tion of aquatic sounds. The Eustachian tube, on the contrary, is 
 very large, and opens into the blow-hole through which the Whale 
 respires atmospheric air : if, therefore, the Cetacean comes to the 
 top of the water to breathe, it is the Eustachian tube that conveys 
 aerial sounds to the ear, and thus it hears sufficiently under both 
 conditions. 
 
 (821.) So far, as the student will have perceived, the different 
 portions of the encephalon to which we have adverted correspond 
 most exactly to similar parts met with even in the brain of a 
 reptile : where then are we to look for those grand differences 
 whereby the Mammiferous brain is peculiarly characterized ? The 
 peculiarities of the brain of a Mammal are entirely due, first, to 
 the increased proportional developement of the cerebral hemi- 
 spheres ; and, secondly, to the existence of lateral cerebellic lobes, 
 in connection with both of which additional structures become re- 
 quisite. 
 
 In those Marsupial tribes that form the connecting links 
 
702 
 
 MAMMALIA. 
 
 Fie. 324. 
 
 between the Oviparous and Placenta! Vertebrata, the brain still 
 exhibits a conformation nearly allied to that of the Bird, and the 
 great commissures required in the more perfect encephalon are 
 even yet deficient ; but in the simplest brain of a Placental Mam- 
 mifer the characteristic differences are at once apparent. 
 
 In the Rabbit, for example, (Jig. 322), the cerebral hemispheres 
 (b) are found very materially to have increased in their propor- 
 tionate dimensions ; and although, even as yet, convolutions 
 upon the surface of the cerebrum are scarcely indicated, additional 
 means of intercommunication 
 between the hemispheric 
 masses become indispensable. 
 The corpus callosum there- 
 fore, or great transverse com- 
 missure of the hemispheres, 
 (fig. 322, c,) is now super- 
 added to those previously in 
 existence; while other medul- 
 lary layers, called by various 
 ridiculous names, bring into 
 unison remote portions of 
 the cerebral lobes. 
 
 In proportion as intelli- 
 gence advances, the surface 
 of the cerebral hemispheres 
 becoming more extensive is 
 thrown into numerous con- 
 volutions separated by deep 
 
 sulci ; until at length in the Carnivora, as, for instance, in the 
 Lion, (Jig. 324,) the cerebrum (e, e) attains such enormous di- 
 mensions that the other elements of the encephalon are, as it 
 were, hidden among its folds. 
 
 (823.) But, in addition to this increased complexity of the cere- 
 brum, the cerebellum likewise has assumed a proportionate im- 
 portance. In the Oviparous races this important element of the 
 brain consisted only of the mesian portion, so that no cerebellic 
 commissure was requisite ; but in the Mammal it exhibits in addi- 
 tion two large lateral lobes (Jig. 324, c, c), and co-existent with 
 these the pons Varolii (Jig. 324, d) makes its appearance, em- 
 bracing the medulla oblongata and uniting the opposite sides of the 
 cerebellum. 
 
MAMMALIA. 703 
 
 (824.) The structure of the spinal cord and the origins of the 
 spinal nerves throughout all the Mammalia are precisely similar, 
 and exactly correspond with what occurs in the human body ; nei- 
 ther does the anatomical distribution of the individual nerves de- 
 rived from this source require any special notice, since, generally 
 speaking, it differs in no important particular from the arrangement 
 with which every anatomist is familiar. 
 
 (825.) The sense of touch in Mammalia is diffused over the 
 whole surface of the body ; its perfection in different parts being 
 of course influenced by the nature of the integument, and the 
 number of sentient nerves appropriated to any given region. All 
 the nerves derived from the sensitive tract of the spinal medulla, 
 and the three divisions of the fifth pair of encephalic nerves, are 
 equally susceptible of tactile impressions ; so that, in a class so 
 extensively distributed as that before us, we need not be sur- 
 prised to find a special apparatus of touch developed in very 
 different and remote parts adapted to particular exigencies. Thus 
 the whiskers of the Seals and of nocturnal Carnivora, the lips of 
 the Horse, the trunk of the Elephant, the hands of Man, the hind 
 feet of the Quadrumana, and even the extremity of the tail 
 where that organ is prehensile, are all in turn made available as 
 tactile instruments, and exercise the sense in question with the 
 utmost delicacy. 
 
 In the Bats, where the sense of vision becomes inadequate to 
 guide them through the dark recesses where they lurk, that of 
 touch assumes its utmost developement, and every part of the 
 body that could by possibility be furnished with it has been 
 abundantly provided for in this respect. Not only is the broad 
 expanse of the wing acutely sensible, but the very ears have been 
 converted into delicate feelers ; nay, from the tip of the nose in 
 some species, membranes of equal sensibility have been largely 
 developed, so that the Bats, as was ascertained by Spallanzani, even 
 when deprived of sight and hearing, will fly fearlessly along, and 
 avoid every obstacle with wonderful precision, guided apparently 
 by the sense of touch alone. 
 
 (826.) The sympathetic system of the Mammifera differs in no 
 important particular from the human, the arrangement of the gan- 
 glia and the distribution of the plexuses being in all respects the 
 same. 
 
 (827.) In the conformation of the genito-urinary apparatus in 
 Mammalia the physiologist will find many circumstances of ex- 
 treme interest. 
 
704 MAMMALIA. 
 
 (828.) Even in Birds, as the reader will remember, the secre- 
 tions of the testes and of the kidneys were both poured into the 
 common cavity of the cloaca, and discharged through the anal 
 orifice. No bladder was provided for the reception of the urine ; 
 and a simple, grooved but imperforate penis, even where that 
 organ was most fully developed, was sufficient for the purposes of 
 impregnation. 
 
 (829.) Widely different, however, is the arrangement of the 
 male genito-urinary system in the class we are now considering. 
 The cloacal cavity is no longer met with, the terminations of the 
 rectum and of the sexual ducts being now remotely separated ; the 
 penis is traversed by a complete urethral canal, through which the 
 seminal fluid is forcibly ejaculated ; and, moreover, subsidiary 
 glands, not met with in any of the preceding classes, add their se- 
 cretions to that of the testes, and thus facilitate the intromission 
 of the fecundating fluid. A urinary bladder is now superadded 
 to the renal apparatus, wherein the urine is permitted to accumu- 
 late in considerable quantities, prior to its expulsion through the 
 urethra, the excretory duct common to both the urinary and 
 generative organs. 
 
 (830.) Not less remarkable are the corresponding changes ob- 
 servable in the disposition of the female reproductive organs. The 
 Mammifers are appointed to bring forth living young ; a uterine 
 receptacle is, therefore, necessarily provided for the reception of 
 the foetus, and mammary glands are given to support the tender 
 offspring during the earlier portion of its existence : but the history 
 of these organs cannot be laid before the reader at a glance, and 
 we must therefore patiently trace out their developement step by 
 step, and gradually ascend from the Oviparous type up to the most 
 complete forms of the genito-urinary system. 
 
 (831.) Commencing with the urinary apparatus, the first parts 
 that offer themselves to our notice are the kidneys, the ureters, 
 and the bladder ; in describing which the same remarks will be 
 found applicable to both sexes. 
 
 The kidneys in all the Mammiferous orders occupy a similar 
 position, being situated in the loins on each side of the aorta, from 
 whence they receive a copious supply of arterial blood by the renal 
 arteries, which, after having supplied the urinary secretion, is re- 
 turned to the circulation by the emulgent veins that empty them- 
 selves into the inferior cava. 
 
 As relates to their intimate structure, the kidneys of all qua- 
 
MAMMALIA. 705 
 
 drupeds are essentially similar to those of our own species, each of 
 these organs being composed of uriniferous tubules of extreme te- 
 nuity that terminate in central papillae from which the urine flows. 
 These tubules, as they advance into the medullary substance of the 
 kidney, bifurcate again and again, until they arrive at the cortical 
 or external portion, where they spread out on all sides, and, be- 
 coming exceedingly flexuous, are inextricably intervolved among 
 each other, so that the entire cortex is composed of their gyra- 
 tions. At last all the uriniferous vessels terminate in blind ex- 
 tremities, and according to M tiller* have no immediate communi- 
 cation with the vascular system. 
 
 In form the kidneys of Mammals more or less resemble the 
 human ; but there is one important circumstance, observable in many 
 tribes, which is well calculated to show that these organs, even when 
 they appear most simple, are in reality formed by the coalescence 
 of several distinct glands. In the human fetus the kidneys pre- 
 sent a lobulated appearance ; that is to say, they are evidently 
 composed of numerous divisions, each having the same structure : 
 but in the adult the lines of demarcation between these lobes be- 
 come entirely obliterated. In many genera, however, this division 
 into lobes remains permanent during the whole lifetime of the crea- 
 ture ; such, for example, is remarkably the case in amphibious CAR- 
 NIVORA, as the Otter and the Seal tribes, and still more strikingly 
 in the CETACEANS, where the kidneys are not inaptly comparable 
 to large bunches of grapes. But whatever the form of the organ, 
 or the number of lobules entering into its composition, the urine 
 secreted by each kidney is received into a common excretory duct 
 called the ureter, and is thus conveyed into the bladder prepared 
 for its reception. 
 
 The urinary bladder exists in all the Mammalia, and receives 
 the ureters by valvular orifices in precisely the same manner as in 
 the human subject. In the male its excretory duct, the urethra, 
 is common to the urinary and generative systems, and terminates 
 at the extremity of the penis ; but in the female the urethral canal 
 is of much simpler structure, opening by a distinct orifice into the 
 vulva.-)- 
 
 (832.) We have preferred laying before the reader the above gene- 
 
 De Gland. Structura, p. 102. 
 
 t The Lemurs and the Mole form remarkable exceptions, for in these creatures the 
 female urethra traverses the clitoris precisely as in the other sex. 
 
 2 z 
 
706 MAMMALIA. 
 
 ral view of the urinary system of Mammalia, to noticing in detail 
 those varieties that occur in the disposition of the bladder and ure- 
 thra of some of the lower tribes, in conformity with the different 
 types of organization presented by their sexual organs ; these, how- 
 ever, must not be lost sight of in following out the developement of 
 the reproductive apparatus, from the oviparous races to the most 
 perfect and highly gifted members of the animal creation. It is to 
 this important subject that we must now invite the attention of the 
 reader. 
 
 (833.) The oviparous Vertebrata lay eggs, and their young are 
 perfected without further nourishment derived from the maternal 
 system than is contained within the egg itself. In our own species, 
 and throughout all the races of Mammalia found on the European 
 continent, the females produce their young alive and fully formed, 
 capable of independent existence, but, nevertheless, nourished for 
 a considerable period by milk derived from the breast of the 
 mother. The distinction, therefore, between an oviparous and a 
 viviparous creature would appear to be sufficiently broad, and the 
 physiological relations between them as remote as possible. 
 
 The student, however, who has followed us thus far through 
 the long series of living beings that have successively presented 
 themselves to our notice, must naturally expect that between ani- 
 mals so dissimilar in their economy as the Bird and the Mammal, 
 intermediate types of organization must occur, and that the trans- 
 ition from one to the other is here, as elsewhere, gradually ac- 
 complished. 
 
 In this respect his expectations will be by no means disap- 
 pointed. The Ornithorynchus paradoxus and the Echidna, ani- 
 mals met with only in the continent of New Holland, are most 
 obviously connecting links between these two grand classes ; and 
 it is, therefore, with the history of these strange animals that we 
 must commence our examination of the Mammiferous generative 
 system. 
 
 The Ornithorynchus paradoxus well deserves the specific epi- 
 thet applied to it by zoologists. It has, indeed, the form of a 
 quadruped, and its body is covered with hair, and not with feathers; 
 but its mouth is the beak of a duck, and upon its hind feet, which 
 are broadly webbed, the male carries a spur not unlike that of a 
 barn-door fowl. Having the beak of a bird, how is the creature 
 to suck ? Nevertheless the females have mammary glands well 
 developed, but destitute of prominent nipples, so that the mode in 
 
MAMMALIA. 
 
 707 
 
 Fig. 325. 
 
 which the young animal obtains the milk provided for it is even yet a 
 puzzling question. Does the Ornithorynchus lay eggs, or produce 
 living young ones ? This is a query that has not been satisfacto- 
 rily answered ; and its generative apparatus is so nearly related to 
 that of an oviparous animal, that even anatomy throws but little 
 light upon the subject. 
 
 Both in the male and female there is, in fact, but one vent, 
 that leads to a cloacal chamber resembling that of a bird, and the 
 entire organization of the sexual organs is 
 rather that of an egg-laying than of a vivi- 
 parous creature, as will be evident from 
 the following details respecting them. 
 
 The penis of the male Ornithorynchus 
 is perforated by a urethral canal, through 
 which the semen passes, but not the urine; 
 its extremity, moreover, is terminated by 
 two tubercles, giving it almost a bifid ap- 
 pearance. This penis when in a relaxed 
 state is lodged in a little pouch in the floor 
 of the cloaca, from which it projects when 
 erected. 
 
 The cloacal cavity, as in birds, gives pas- 
 sage to the feces and to the urine. The tes- 
 tes (a) and the vasa deferentia (b) resemble 
 those of an oviparous animal ; but, on the 
 other hand, there is a complete urinary 
 bladder (c), and moreover a pair of auxi- 
 liary (Cowpers) glands (d, d), organs 
 never met with except in the Mammiferous 
 class. 
 
 (834.) The anatomy of the female or- 
 gans is not less singular. The ovaria 
 (Jig. 327, a, a) are large and racemose, 
 like those of a bird ; while the two oviducts 
 
 or uteri (Jig. 326, a, a), as the reader may choose to call them, 
 open into the cloaca by two distinct orifices (c, c), situated on 
 each side of the urethra, derived from the bladder (b). 
 
 It is to Professor Owen that science is indebted for all that is 
 known relative to the anatomy of the female Ornithorynchus 
 when in a gravid state, and his researches upon this subject 
 appear to establish the following interesting particulars. First, 
 
708 
 
 MAMMALIA. 
 
 Fig. 326. 
 
 a 
 
 that the ovaria, notwithstanding their racemose appearance, ex- 
 
 hibit all the essential characters of the Mammiferous type of struc- 
 
 ture ; and corpora lutea were formed where the reproductive germs 
 
 had escaped from them. Secondly, that the eggs contained in 
 
 the uterine cavities (Jig. 
 
 327, c, e) had no con- 
 
 nection whatever with the 
 
 walls of the uterus. 
 
 Thirdly, that each ovum 
 
 exhibited the usual parts 
 
 of an egg, viz. the cor- 
 
 tical membrane, the al- 
 
 bumen, and the yolk ; and 
 
 that upon the latter a 
 
 membrana vitelli and the 
 
 blastoderm or germinative 
 
 membrane were plainly 
 
 perceptible. Fourthly, 
 
 that the uterine walls 
 
 assume an increased thick- 
 
 ness when in an impreg- 
 
 nated state, but that not 
 
 the slightest trace of a 
 
 decidual or adventitious 
 
 membrane is apparent in 
 
 the cavity of the womb. 
 
 From all these circumstances, the distinguished author of the 
 
 paper referred to* was led to adopt the subjoined train of rea- 
 
 soning as to the probability of the Ornithorynchus being a vi- 
 
 viparous Mammal. The form, the structure, and the detached 
 
 condition of the ova, observes Professor Owen, may still be re- 
 
 garded as compatible with, and perhaps favourable to, the opinion 
 
 that they are excluded as such, and that the embryo is developed 
 
 out of the parent's body. But the following objections present 
 
 themselves to this conclusion : the only part of the efferent tube 
 
 of the generative apparatus which can be compared in structure or 
 
 relative position with the shell-secreting uterus of the Fowl, is the 
 
 dilated terminal cavity in which, in all the specimens examined, 
 
 the ova were situated ; and upon the oviparous theory it must be 
 
 * On the Ova of the Ornithorynchus paradoxus, by Richard Owen, Esq. Phil. 
 Trans. Part II. for 1834, page 563. 
 
MAMMALIA. 709 
 
 supposed either that the parietes of this cavity, after having secre- 
 ted the requisite quantity of soft material, suddenly assume a new 
 function, and complete the ovum by providing it with the calca- 
 reous covering necessary to enable it to sustain the superincum- 
 bent weight of the mother during incubation ; or that this is 
 effected by a rapid deposition from the cuticular surface of the 
 external passages ; or lastly, according to a more recent but still 
 more improbable supposition, by a calcareous secretion of the ab- 
 dominal glands poured out upon the ovum after its exclusion. 
 
 Fig. 327.* 
 
 But granting that the egg is provided in any of these ways with 
 the necessary external covering, yet, from the evidence afforded by 
 the specimens examined, the ovum is deficient in those parts of its 
 organization which appear to be essential to successful incubation, 
 viz. a voluminous yolk to support the germinal membrane, and the 
 mechanism for bringing the cicatricula into contiguity with the body 
 of the parent. Add to this, that such a mode of developement of 
 the fetus requires that all the necessary nutritive material be accu- 
 mulated in the ovum prior to its exclusion. Now the bony pelvis 
 of the Bird is expressly modified to allow of the escape of an egg, 
 both large from the quantity of its contents, and unyielding from its 
 necessary defensive covering ; but, whatever affinities of structure 
 
 * Owing to an error on the part of the draughtsman, who has neglected to reverse 
 the drawing, the left uterus in the above figure is represented on the right side, and 
 vice versa. 
 
7JO 
 
 MAMMALIA. 
 
 may exist in other parts of the Ornithorynchus, it is most import- 
 ant to the question of its generation to bear in mind that it mani- 
 fests no resemblance to the Bird in the disposition of its pubic 
 bones. 
 
 From the above considerations it is therefore probable. that the 
 young Ornithorynchi are produced alive ; yet still the reader will 
 perceive by the closeness of the reasoning brought to bear upon 
 the subject, how nearly the oviparous and mammiferous modes of 
 generation are approximated by the interposition of these con- 
 necting forms of Vertebrata. 
 
 (835.) But if from these arguments, derived from the anato- 
 mical construction of the female parts, it is allowable to conjecture 
 that the Ornithorynchus is ovo-viviparous, using that term in a 
 strictly philosophical sense, the difficulties of the case are by no 
 means removed ; and granting that the contents of the ovum are 
 barely sufficient to nourish the embryo during the very earliest 
 stages of its developement, we have yet to learn how the fetus is 
 matured after the exhaustion of this supply. There is no reason 
 whatever to suppose that a placenta exists at any period of uterine 
 gestation ; neither is there a marsupial pouch in which the pre- 
 maturely born young can be carried about and supplied with milk ; 
 so that whether the young Monotreme be developed in the uterus, 
 or out of the uterus, we are equally at a loss to understand how its 
 nutrition is provided for. 
 
 In this state of uncertainty, the 
 anatomy of the young Ornithorynchus, 
 examined at as early a period as pos- 
 sible, becomes a subject of extreme 
 interest ; and fortunately Professor 
 Owen has been enabled to add obser- 
 vations upon this subject to his other 
 valuable researches relative to the 
 generation of these creatures.* The 
 annexed figure (Jig- 328) is a por- 
 trait of one of the specimens dissected, 
 and from every appearance it could 
 not have been more than a few days 
 old, that is, supposing it to have been 
 born at an advanced period of its de- 
 velopement. It was as yet blind, and the situation of the eyes was 
 
 * Owen, on the Young of the Ornithorynchus paradoxus. Trans. Zool. Society, vol. i. 
 
 Fig. 328. 
 
MAMMALIA. 711 
 
 only indicated by the convergence of a few wrinkles to one point ; 
 but, when these were put upon the stretch, the integument was 
 found entire, and completely shrouding or covering the eye-ball 
 anteriorly : its skeleton was, moreover, quite in a cartilaginous 
 condition, and it was obviously in every respect helpless, and still 
 dependent upon its mother for sustenance. 
 
 The stomach was found filled with milk, a sufficient proof that 
 at that period, at least, it was nourished by the lacteal secretion ; 
 but, with regard to its previous fetal condition, the difficulties that 
 have been above alluded to remained in their full force. No trace 
 of an umbilical cicatrix was visible upon the ventral surface of the 
 body, even when examined with a lens, a sure proof that no pla- 
 centa had existed. The ileum was carefully examined, but there 
 was no appearance of the pedicle of the vitelline vesicle ; neverthe- 
 less, the other vestiges of fetal organization were more obvious 
 than in the ordinary marsupial or ovo-viviparous Mammalia. The 
 umbilical vein was seen extending from a linear cicatrix of the 
 peritoneum, opposite the middle of the abdomen, along the ante- 
 rior margin of the suspensory ligament to the liver. It was re- 
 duced to a mere filamentary tube filled with coagulum. From the 
 same cicatrix the remains of the umbilical arteries extended down- 
 wards, and near the urinary bladder were contained within a dupli- 
 cature of peritoneum, having between them a small flat oval vesicle, 
 the remains of an allantois, which was attached by a contracted 
 pedicle to the fundus of the bladder ; but still as both the em- 
 bryo of a Bird and that of the ovo-viviparous Reptile have an 
 allantois and umbilical vessels developed, no certain inference can 
 be drawn from the above appearances as to the oviparous or vivi- 
 parous nature of the generation of the Ornithorynchus. 
 
 (836.) Such is the present state of our knowledge relative to 
 the first type of Mammiferous generation, viz. that met with 
 among the MONOTREMATA. In the second, or MARSUPIAL 
 TYPE, the phenomena, although equally strange, are better under- 
 stood, and to these we must now beg the attention of the student. 
 
 The MARSUPIALIA, from the variety of their forms and exten- 
 sive distribution, constitute a most important section of Mammi- 
 ferous quadrupeds, distinguished by the peculiarities that occur in 
 the organization of their generative apparatus, and by the singular 
 mode in which they produce and suckle their young. Animals of 
 this kind are only met with in the American and Australian 
 regions of our globe ; and so widely do they differ, as far as their 
 
MAMMALIA. 
 
 reproduction is concerned, from all the Mammiferous inhabitants of 
 the Old World, that they might even be regarded as forming 
 quite a distinct and separate group in the animal creation, serv- 
 ing to accomplish another step in that grand transition by which 
 the physiologist is conducted from the oviparous to the placental 
 Vertebrata. 
 
 The Marsupialia are, strictly speakingj ovo-viviparous, that is 
 to say, the uterine ovum never forms any vascular connection with 
 the maternal system, but after a very brief intra-uterine gestation the 
 embryo is expelled in a very rudimentary and imperfect condition, 
 even its extremities being as yet but partially developed ; and in 
 this helpless state the fetus is conveyed from the uterus into a pouch 
 or marsupium,) formed by the integument of the abdomen, there 
 to be nourished by milk sucked from the mammary glands, until 
 it arrives at such a state of maturity as enables it to assume an 
 independent existence. 
 
 We may naturally expect, therefore, that, with habits so remark- 
 able, the structure of the generative apparatus, both in the male 
 and female Marsupial, will offer important peculiarities, and these 
 accordingly first present themselves for description. 
 
 (837.) We select the Kangaroo as an example of the entire 
 group ; beginning, as we have hitherto done, with the organization 
 of the male organs of generation. 
 
 The first circumstance that strikes the attention of the anatomist 
 in a male Marsupial is the extraordinary position of the testes, 
 which, instead of being situated behind the penis, as in most pla- 
 cental Mammals, are placed in front of that organ in a kind of 
 scrotum that occupies the same place as the pouch of the female, 
 and is in like manner supported by two marsupial bones derived 
 from the pubes, around which the cremaster muscle winds in such 
 a manner as to enable it powerfully to compress the testicles 
 during the congress of the sexes. The vasa deferentia derived 
 from the testes open into the commencement of the urethra, which 
 now, for the first time, forms a complete canal leading from the 
 bladder to the extremity of the penis. The auxiliary glands that 
 pour additional secretions into the urethra are of great size, and 
 more numerous than those met with in the human subject. In 
 the first place, the commencement of the urethral tube is em- 
 braced by a bulky and conical prostate^ to which succeed three 
 pairs of large secreting organs (Cowper's glands), each enveloped 
 in a musculo-membranous sheath, apparently intended to compress 
 
MAMMALIA. 
 
 713 
 
 their substance, and thus efficiently discharge their secretion into 
 the canal of the urethra, there to be mixed up with the seminal 
 fluid. 
 
 But, perhaps, the most decided peculiarities that characterize 
 the males of Marsupial quadrupeds are met with in the construc- 
 tion of the penis itself. The two roots or crura of the corpora 
 cavernosa are not, as in the higher Mammals, attached to the 
 branches of the ischium by ligamentous bands, but each swells into 
 a large bulb enclosed F . g29 
 
 in a powerful mus- 
 cular envelope. The 
 bulbous portion of 
 the urethra is like- 
 wise double, and em- 
 braced by powerful 
 muscles. In the 
 Kangaroo, more- 
 over, the spongy 
 erectile tissue that 
 encloses the urethra 
 passes with that ca- 
 nal through the cen- 
 tre of the body of 
 the penis, formed by 
 the corpora caverno- 
 sa, so that a glans 
 can scarcely be said 
 to exist ; but in 
 other Marsupials, as, 
 for example, in the 
 Opossums (Didel- 
 phis), the extremity 
 of the intromittent 
 organ is bifid, thus 
 forming another ap- 
 proximation to the 
 oviparous type. 
 
 (838). In the female Kangaroo, and other Marsupials, there are 
 still two distinct uteri, opening into the vagina by distinct orifices ; 
 and even the vagina itself is double, exhibiting a very peculiar 
 and interesting arrangement, represented in the preceding figure 
 
714 MAMMALIA. 
 
 (jig. 329). The ovaria (a, a) are now reduced to compara- 
 tively small dimensions when compared with those of the Ovipara; 
 a circumstance that depends upon the reduced size of the ovarian 
 ovules, which no longer present the bulky yolks peculiar to ovipa- 
 rous generation, the necessity for the existence of such a large store 
 of food being now superseded by the provision of another kind of 
 nourishment derived from the mammary glands. The Fallopian 
 tubes commence by wide fimbriated apertures, and each leads into 
 a separate uterine canal (6), in which the first part of gestation is 
 accomplished. The two uteri open by two orifices (e, f) into 
 the two vaginae (g, g), which remain quite distinct from each other 
 from their commencement to their termination in the urethro- 
 sexual canal (A), a kind of cloaca into which both the vaginae and 
 the urethra empty themselves. 
 
 (839.) Such being the arrangement of the generative apparatus 
 of the female Kangaroo, we are prepared, in the next place, to con- 
 sider the structure of the Marsupial ovum, and to trace its progress 
 from the ovary, where it is first formed, into the marsupial pouch, 
 where the developement of the fetus is ultimately completed. 
 
 The ovary of a Marsupial animal, as has been already observed, 
 resembles that of ordinary Mammalia, and presents the same dense 
 structure. But the ovarian ovules, although characterized by the 
 paucity of yolk as compared with the oviparous classes, yet have 
 a larger proportion than exists in the placental Mammalia. When 
 impregnation is effected in the Marsupial animal, the Graqfian 
 vesicle or ovisac is ruptured, and the little ovulum escapes into the 
 Fallopian tube, whereby it passes into the uterine cavity ; from 
 whence of course it must absorb the materials destined to support 
 the future embryo, in the same manner as the egg is furnished in 
 the oviduct with the albumen that invests the yolk. The deve- 
 lopement of the embryo from the blastoderm or germinal membrane 
 is, no doubt, accomplished in the same manner in all Mammalia 
 as it is in Birds, up to a certain stage of maturity ; but at that 
 stage of growth, when, in the case of the Bird, the yolk is required 
 to contribute to the nourishment of the newly-formed being, in 
 the Mammifera where no adequate supply of yolk exists other means 
 must be resorted to ; and accordingly the Marsupial embryo is 
 born prematurely, in order to supply it with milk, and in the or- 
 dinary Mammal a placenta is developed, forming a means of vascular 
 communication between the mother and the fetus. 
 
 (840.) The important investigations of Professor Owen upon 
 
MAMMALIA. 715 
 
 this subject* cannot be too highly appreciated. In the gravid 
 uterus of a Kangaroo, examined by this indefatigable labourer in 
 the cause of science, a fetus was met with that had apparently 
 arrived very nearly at the term of its intra-uterine existence ; and 
 the following is a summary of its anatomy at this period. 
 
 The ovum (Jig- 330, c) was lodged in one of the uterine cavi- 
 ties, and the fetus was about an inch and four lines in length. The 
 walls of the gravid uterus were obviously dilated, and its parietes 
 varied in thickness from one to two lines, being in the unimpreg- 
 nated state about half a line ; but this increase was not in the mus- 
 cular coat, but in the lining membrane, which was thrown into irre- 
 gular folds and wrinkles. There was, however, not the slightest 
 trace of any vascular connection between the uterus and the ovum, 
 neither placenta nor villi, nor any determination of vessels to a 
 given point on either of the opposed surfaces of the chorion or 
 uterus : on the contrary, the external membrane of the ovum (cho- 
 rion) exhibited not the slightest trace of vascularity, even under 
 the microscope, and seemed in every respect to resemble the mem- 
 brana putaminis that lines the egg-shell. 
 
 (841.) The body of the fetus itself was immediately enclosed 
 in a transparent membrane Fig. 330. 
 
 (/;), the amnios. 
 
 (842.) Between the 
 chorion (a) and the am- 
 nios (b) was an extensive 
 vascular membrane (c, d, 
 d, c, e) ; its figure seemed 
 to have been that of a 
 cone, of which the apex 
 was at the umbilicus of 
 the fetus. 
 
 Three vessels could be 
 distinguished diverging 
 from the umbilical cord, 
 and ramifying over it. 
 Two of these trunks con- 
 tained coagulated blood ; 
 while the third was smaller, empty, and evidently the arterial 
 trunk. No trace of any other membrane could be seen extending 
 
 * On the Generation of Marsupial animals, with a description of the impregnated 
 uterus of the Kangaroo, by Richard Owen, Esq. Phil. Trans. 1834. 
 
716 MAMMALIA. 
 
 from the fetus besides the three above mentioned, the chorion 
 (a), the amnios (i), and the interposed vascular membrane, the 
 nature of which becomes the next subject of inquiry. 
 
 (843.) On tracing the three vessels above alluded to, as ramify- 
 ing over the vascular membrane, through the umbilicus into the 
 abdomen, the two larger ones, filled with coagulated blood, were 
 found to unite, and after being joined by the mesenteric vein pene- 
 trated the liver : these, consequently, were the representatives of 
 the omphalo-mesenteric or vitelline vein of the embryo bird 
 ( 703). The third vessel passed between the convolutions of the 
 small intestine along the mesentery to the abdominal aorta, corre- 
 sponding to an omphalo-mesenteric or vitelline artery. The mem- 
 brane, therefore, upon which they ramified answers to the vascular 
 layer of the germinal membrane which spreads over the yolk in 
 the Oviparous animals, or to the vitelline vesicle of the embryo of 
 ordinary Mammalia. 
 
 A filamentary pedicle connected this membrane to the intestine 
 near the termination of the ileum, thus completing the resem- 
 blance between this apparatus and the vitelline system of Birds. 
 But here we must caution the student not to be misled on one im- 
 portant point : the contents of the vitelline sac in the Marsupials, 
 although doubtless intended to afford nourishment to the embryo 
 animal, and thus representing the yolk of the bird's egg, differs 
 from it in one very essential circumstance. The yolk of the Ovi- 
 parous ovum is ready formed in the ovary and exists prior to con- 
 ception ; but in the Mammal, where the ovarian yolk is met with 
 in extremely small quantities, the contents of the vitellicle must 
 obviously be derived from some other source, most probably from 
 absorption from the uterine cavity. 
 
 (844). In the Marsupial ovum the vascular membrane of the 
 vitellicle is doubtless sufficient for the respiration of the little 
 creature up to the time of its birth, and, accordingly, the allan- 
 toic system ( 705) is but very partially developed. In the ovum 
 delineated in the last figure, there was, as yet, no perceptible trace 
 either of an allantois or of a urinary bladder ; but, as has been 
 proved by another dissection, during the latter week of uterine ges- 
 tation, the urinary bladder is prolonged beyond the umbilicus so 
 as to form a small allantois destined to receive the renal secretion, 
 which becomes more abundant as the little fetus increases in size 
 and completeness.* 
 
 * See Proceedings of the Zool. Society for August, 1837. 
 
MAMMALIA. 717 
 
 In the mammary fetus of a Kangaroo a fortnight old, Profes- 
 sor Owen detected both an urachus and umbilical arteries, but 
 these only extended from the bladder and iliac vessels as far as the 
 umbilicus ; neither could any umbilical vein be found penetrating 
 the liver. It is in the placental Mammals that we shall find 
 these vessels assuming their full importance, and developing them- 
 selves into a new system, whereby the communication between the 
 mother and her offspring is still more effectually provided for. 
 
 (845.) When we consider the very early period at which the 
 young Kangaroo is born, namely, at about the thirty-ninth day 
 after conception, it is only reasonable to suppose that the organs most 
 immediately connected with the vital actions are precociously ma- 
 tured ; and accordingly, even in the embryo above delineated (fig. 
 330), the intestines, the liver, the kidneys, and the testes were all 
 conspicuous, and the diaphragm, the heart, and the lungs were in 
 such an advanced condition as to show that they would soon be 
 capable of prematurely taking upon themselves the exercise of the 
 circulatory and respiratory functions. 
 
 (846.) This rapid developement of the viscera connected with 
 circulation and respiration, is in truth essentially requisite ; for no 
 sooner has the embryo arrived at the size represented in the next 
 figure (Jig. 331, A), and while the limbs are still in a most rudi- 
 mentary condition, the embryo is transferred from the uterus into 
 the marsupial pouch, where it is found attached by its mouth to one 
 of the nipples, from whence the materials of its support are to be 
 obtained, until it has acquired sufficient strength and size to leave 
 the strange portable nest in which its fetal growth is accomplished, 
 and procure food adapted to a maturer condition. 
 
 (847.) A very beautiful provision is met with in the construc- 
 tion of the respiratory passages of the young Marsupial, intended 
 to obviate the possibility of suffocation consequent upon the admis- 
 sion of milk into the trachea, a circumstance that without some 
 peculiar arrangement might easily happen ; but of this we must 
 quote the original description, extracted from the paper already re- 
 ferred to.* '" The new-born Kangaroo," observes Professor Owen, 
 " possesses greater powers of action than the same sized embryo 
 of a Sheep, and approximates more nearly in this respect to the new- 
 born young of the Rat; yet it is evidently inferior to the latter. 
 For although it is enabled by the muscular power of its lips to grasp 
 and adhere firmly to the nipple, it seems to be unable to draw sus- 
 
 * Page 348. 
 
718 
 
 MAMMALIA. 
 
 /A 
 
 tenance therefrom by its own unaided efforts. The mother, as 
 Professor Geoffroy* and Mr. Morgan -f* have shown, is therefore 
 provided with a peculiar adaptation of a muscle (analogous to the 
 cremaster) to the mammary gland, for the evident purpose of in- 
 jecting the milk from the nipple into the mouth of the adherent 
 fetus. Now it can scarcely be supposed that the fetal efforts of 
 suction should always be coincident with the maternal act of injec- 
 tion ; and, if at any time this should not be the case, a fatal acci- 
 dent might happen from the milk being forcibly injected into the 
 larynx. Professor Geoffroy first described the modification by 
 which this purpose is effected, and Mr. Hunter appears to have 
 foreseen the necessity for such a structure, for he has dissected 
 two small fetuses of the Kangaroo for the especial purpose of 
 showing the relation of the larynx to the posterior nares. J The 
 epiglottis and arytenoid cartilages are elongated and approximated, 
 so that the rima glottidis is thus situated at the apex of a cone- 
 shaped larynx (Jig. 331, B, a), which projects, as in the CE- 
 TACEA, into the posterior nares, Fig. 331. 
 
 where it is closely embraced by the 
 muscles of the soft palate. The air- 
 passage is thus completely separated 
 from the fauces, and the injected 
 milk passes in a divided stream, on 
 either side of the larynx, into the 
 oesophagus." 
 
 " Thus aided and protected by 
 modifications of structure, both in 
 the system of the mother and in its 
 own, designed with especial refer- 
 ence to each other's peculiar condi- 
 tion, and affording therefore the 
 
 most irrefragable evidence of creative foresight, the feeble off- 
 spring continues to increase from sustenance, exclusively derived 
 from the mother, for a period of about eight months. The young 
 Kangaroo may then be seen frequently to protrude its head from 
 the mouth of the pouch, and to crop the grass at the same time 
 
 * Memoires du Muse~e, torn. xxv. p. 48. .f Trans. Lin. Society, vol. xvi. p. 61. 
 
 t " See Nos. 3731, 3734, 3735, in the Physiological series of the Hunterian Mu- 
 seum, in which there are evidences that Mr. Hunter had anticipated most of the 
 anatomical discoveries which have subsequently been made upon the embryo of the 
 Kangaroo." 
 
MAMMALIA. 719 
 
 that the mother is browsing. Having thus acquired additional 
 strength, it quits the pouch, and hops at first with a feeble and 
 vacillating gait ; but continues to return to the pouch for occa- 
 sional shelter and supplies of food, till it has attained the weight 
 of ten pounds. After this it will occasionally insert its head for 
 the purpose of sucking, notwithstanding another fetus may have 
 been deposited in the pouch ; for the latter, as we have seen, 
 attaches itself to a different nipple from the one which had pre- 
 viously been in use." 
 
 Thus therefore are we conducted by the Ovo-vivipara, as the 
 MAIISUPIALIA are properly called, to the most perfect or pla- 
 cental type of the generative system. 
 
 (848.) Commencing our account of the reproductive organs of 
 VIVIPAROUS MAMMALIA, by examining those of the male sex, 
 we have another striking example of the insufficiency of the no- 
 menclature employed by the anatomist who confines his studies 
 to the human body, when it becomes necessary to describe cor- 
 responding organs even in animals organized after the same type. 
 
 True it is, that there is the same general arrangement of the 
 generative apparatus ; and it is convenient, as far as possible, to 
 apply the same names to structures that apparently represent each 
 other : but a very superficial examination of the facts will serve to 
 show that great differences exist between them ; and, accordingly, 
 we are not surprised to find the utmost perplexity and confusion in 
 the descriptions of these parts, arising from the indiscriminate 
 application of the terms employed in human anatomy to totally 
 dissimilar structures. 
 
 It is not, however, our business here to criticise the labours of 
 authors upon this subject; we must content ourselves with select- 
 ing an example of one of the more complex forms under which 
 the male genitals present themselves, and leave the reader to 
 contrast the various organs with those met with in the human 
 subject. 
 
 The annexed figure (Jig. 332, A) represents the generative 
 viscera of the male Hedgehog. The rectum (a) and the neck of 
 the bladder (h) remain in situ ; but the rest of the latter viscus has 
 been removed, and the first portion of the urethra (e) slit open, 
 in order to show the relations of the surrounding parts. 
 
 The testes (&, b) present the same structure in all the class, and 
 consist essentially of an immense assemblage of extremely delicate 
 tubuli semi?iiferi, enclosed in a dense albugineous tunic from 
 
720 
 
 MAMMALIA. 
 
 which septa pass internally, whereby the seminiferous tubes are 
 
 divided into several fasciculi : after piercing the proper fibrous 
 
 tunic of the testes, the sperm-secreting tubes are collected into an 
 
 extremely tortuous 
 
 duct, that by its F'g- 332. 
 
 convolutions forms 
 
 the epididymis, as 
 
 in Man, and is then 
 
 continued, under the 
 
 name of vas defe- 
 
 rens, to the com- 
 
 mencement of the 
 urethra, into which 
 the two ducts open 
 (B, 6, b). In the 
 Horse, and many 
 Ruminants, the vas 
 deferens presents a 
 remarkable struc- 
 ture : before its ter- 
 mination it suddenly 
 swells to a consider- 
 able diameter, de- 
 pending upon the 
 increased thickness of the walls of the canal, which at the same 
 time become cellular, and secrete a gelatinous fluid that escapes 
 into the cavity of the duct. 
 
 (849.) In their situation the testes of placental Mammals are 
 found to offer very striking differences. In the Cetacea, the 
 Elephant, and the Seal tribes, they remain permanently in the 
 abdomen, bound down by a process of the peritoneum. In Man, 
 and most quadrupeds, on the contrary, they pass out of the abdo- 
 minal cavity through the inguinal rings, and are suspended in a 
 scrotal pouch formed by the skin, and a cremaster muscle, and 
 lined by a serous prolongation of the peritoneal sac. The sper- 
 matic cords, therefore, formed by the vessels and excretory canal 
 of the testes will take a different course, in conformity with the 
 variable position of these organs, and, where a scrotum exists, must 
 enter the abdomen through an inguinal canal. Still, from their 
 horizontal posture, quadrupeds are but little liable to hernise, 
 
MAMMALIA. 721 
 
 even where the inguinal passages are much more open than in the 
 human subject. 
 
 (850.) The quantity of the seminal fluid furnished by the 
 testes is very small, as must be evident from the extreme narrow- 
 ness of the duct through which it passes into the urethra. Ne- 
 vertheless, as the impregnation of the female now requires the 
 forcible injection of this fluid, it is absolutely requisite to increase 
 the bulk of the vivifying secretion, in order to enable the muscles 
 that embrace the urethral "tube efficiently to expel it. For this 
 purpose additional glands are given, whereby different fluids are 
 poured into the urethral cavity, apparently for the sole purpose of 
 diluting the spermatic liquor, and thus forming a vehicle for 
 its expulsion. These succenturiate glands, as they are named, 
 are not found in any oviparous animal ; but in the Mammal such 
 is their size and importance, that there may be just reason for 
 supposing them to exercise a more important office than that 
 usually assigned to them by physiologists ; and this supposition 
 seems to obtain additional weight when we consider the great 
 diversity of structure that they exhibit in different quadrupeds. 
 
 (851.) The vesicultE seminales are the first of these accessory 
 secreting organs that require our notice. In Man the seminal 
 vesicles, as they are erroneously termed, resemble two membranous 
 reservoirs, situated beneath the neck of the bladder, and were once 
 supposed to be receptacles for containing the semen. When 
 opened, however, they are found to be composed of the windings 
 of a very sinuous secreting surface ; and, as their excretory ducts 
 open into the urethra in common with the vasa deferentia, they 
 obviously add the fluid that they elaborate to the secretion of the 
 testes. 
 
 But, notwithstanding their apparent importance in the human 
 species, these organs do not exist at all in by far the greater num- 
 ber of CARNIVOUA ; neither are they found in the RUMINANTS, 
 nor in the cetaceous Mammals. 
 
 In other quadrupeds, on the contrary, they are found ; and 
 their proportionate size is extremely remarkable. This is spe- 
 cially the case in the Rodent tribes, and among the INSECTIVORA. 
 In the Hedgehog, for example, their bulk is enormous. In this 
 creature they form two large masses (Jig. 33, A, c, c), each com- 
 posed of four or five bundles of long and tortuous secerning ves- 
 sels folded upon themselves in all directions, and pouring the 
 
 3 A 
 
722 MAMMALIA. 
 
 product of their secretion into the urethra by two ducts (Jig. 332, 
 B, c, c), quite distinct from the vasa defer entia. 
 
 (852.) The prostates are the next succenturiate glands, super- 
 added to the essential generative organs of the placental Mam- 
 mals ; and so diverse is their structure in different tribes, that it 
 is not always easy to recognise them under the varied forms that 
 they assume. 
 
 In Man the prostate is a solid glandular mass, that embraces 
 the commencement of the urethra, into which it discharges its 
 secretion by numerous small ducts ; and this is the most common 
 arrangement throughout the Mammiferous orders. 
 
 In RUMINANTS, SOLIPEDS, and in the Elephant, there are 
 two or even four prostates of a very different kind ; each gland 
 having a central cavity, into which smaller cavities open by wide 
 orifices. In these creatures, therefore, the prostatic secretion accu- 
 mulates in the interior of the gland, from whence it is conveyed 
 into the urethra by appropriate excretory canals. 
 
 In most of the RODE NT i A, in the Mole and in the Hedgehog, 
 the structure of the prostate is so peculiar, that many distinguished 
 comparative anatomists refuse to apply the same name to organs 
 that obviously represent the gland we are describing, preferring 
 with Cuvier to call them " accessory vesicles.' 1 '' 
 
 In the Hedgehog, the prostate is replaced by two large masses 
 (Jig. 332, A, d, d), each composed of parallel, flexuous, and branch- 
 ed tubes, all of which unite into ducts common to the whole group, 
 whereby the fluid elaborated is conveyed into the urethra through 
 minute orifices (Jig. 332, B, e, e). 
 
 (853.) A third set of auxiliary secreting bodies, very generally 
 met with, are called by the name of" Cowper's glands." These 
 in our own species are very small, not exceeding the size of a pea ; 
 but in many quadrupeds they are much more largely developed. 
 In the Hedgehog (Jig. 332, A,/) they are obviously composed of 
 convoluted tubes, and their ducts open by distinct apertures 
 (B, g, g) into the floor of the urethra. 
 
 (854.) The canal of the urethra, through which the urine as well 
 as the generative secretions are expelled from the body of the male 
 Mammal, is a complete tube, and no longer a mere furrow, as we 
 have seen it to be in all the Ovipara possessed of an intromittent ap- 
 paratus. It extends from the neck of the bladder to the extremity 
 of the penis; but in this course, owing to its relations with the sur- 
 rounding parts, it will be necessary to consider it as divisible into two 
 
MAMMALIA. 723 
 
 or three distinct portions, each of which offers peculiarities worthy 
 of remark. The first part of the urethral tube is not unfrequently, 
 as in the human subject, more or less completely surrounded by 
 the prostate gland, and in such cases merits the name of " pro- 
 static portion;" but where, as in the Hedgehog, the prostates do 
 not enclose the commencement of the canal, this division of the 
 urethra does not exist. 
 
 The second is the " muscular portion," extending from the 
 prostate to the root of the penis, and it is into this part that all 
 the generative secretions are poured from their respective ducts 
 (Jig. 33%, B, b, c, e, g, h). Externally, this division of the 
 urethra is enclosed by strong muscles (Jig. 332, A, i, i), which 
 by their convulsive contractions forcibly ejaculate the different 
 fluids concerned in impregnation, and thus secure an efficient in- 
 tromission of the seminal liquor into the female organs. 
 
 The third portion of the urethra is enclosed in the body of the 
 penis, and surrounded by the erectile tissue, of which that organ 
 essentially consists ; but in all quadrupeds this part of the canal 
 is not so decidedly continuous with the muscular portion as it 
 appears to be in Man and the generality of Mammalia. In many 
 RUMINANTS, and in some of the Hog tribe, the muscular division 
 of the canal opens into the upper part of the third or vascular 
 division, in such a manner that a cul-de-sac occupies the com- 
 mencement of the vascular bulb of the urethra, as it is called by 
 anatomists, into which the secretion of Cowper's glands is poured, 
 without having been previously mixed with the seminal or prostatic 
 fluids. In some RODENTS, as, for example, in the Squirrel and 
 the Marmot, the arrangement is still more curious ; for the cul- 
 de-sac of the bulb of the urethra in these creatures, which receives 
 the secretion of Cowper's glands, is lengthened out into a long tube 
 that runs for some distance beneath the proper urethra, and only 
 joins that canal near the extremity of the penis. 
 
 (855.) The body of the penis in the Mammalia, as in all other 
 Vertebrata possessed of such an organ, is composed of vascular 
 erectile tissue ; but now, besides the corpora cavernosa, which in 
 Reptiles and Birds formed the entire organ, another portion is 
 superadded, destined to enclose the canal of the urethra in a thick 
 erectile sheath, and, moreover, to form the glans or most sensitive 
 part of the intromittent apparatus. 
 
 The corpora cavernosa are now securely fixed to the bones of 
 the pelvis by two roots or crura ; and even in the CETACEA,where 
 
 3 A 2 
 
MAMMALIA. 
 
 no pelvis is met \vith, the ossa ischii exist, apparently only for the 
 purpose of giving firm support to the origin of the parts in ques- 
 tion. The size of the corpora cavernosa in Man, and many other 
 animals, is of itself sufficient to give the needful rigidity to the parts 
 during sexual excitement ; but in some tribes an additional provision 
 is required to ensure adequate firmness. Thus in Monkeys, Bats., 
 the CARNIVORA, the RODENTIA, and the Baltenidte among CETA- 
 CEANS, a bone is embedded in the substance of the male organ, of 
 which it forms a considerable part. Where this bone exists, the 
 corpora cavernosa are proportionately small, and the fibrous walls 
 of the penis are confounded with its periosteal covering. 
 
 The corpus spongiosum, likewise composed of erectile tissue, is 
 quite distinct from the cavernous bodies, and, as we have said 
 before, is only found in the Mammifera. It commences by a bulb- 
 ous origin that embraces the urethra, and it accompanies that 
 canal quite to the extremity of the penis, where it dilates into the 
 glans. 
 
 The size and shape of the male organ varies of course in every 
 genus of quadrupeds, as does the form and texture of the glans. 
 To describe these would lead us into details of too little import- 
 ance to be noticed in a survey so general as that we are now 
 taking ; nevertheless, we cannot entirely omit to notice the strange 
 and unaccountable structure met with in some of the Rodent tribes, 
 whereby the penis is rendered a most formidable-looking apparatus, 
 the object of which it is not easy to conjecture ; although as an 
 instrument of excitement no one will be disposed to deny its 
 efficiency. 
 
 Thus, in the Guinea-pig tribe (Cavia, Ilig.) the penis is 
 strengthened by a flat bone that reaches forward as far as the 
 extremity of the gland beneath which is the termination of the 
 urethra ; but behind and below the orifice of this canal is the 
 opening of a pouch, wherein are lodged two long horny spikes. 
 When the member is erect, the pouch alluded to becomes everted, 
 and the spikes (Jig. 333, d) are protruded externally to a consi- 
 derable length. Both the evected pouch (b) and the entire sur- 
 face of the glans are, moreover, covered densely with sharp spines 
 or hooklets ; and, as though even all this were not sufficient to 
 produce the needful irritation, still further back there are, in some 
 species, two sharp and strong horny saws (c, c) appended to the 
 sides of the organ. From this terrible armature of the male 
 
MAMMALIA. -") 
 
 Cavys, it would be only natural to expect some corresponding 
 peculiarity in the female parts ; but, however inexplicable it may 
 appear, the female vagina offers no uncommon structure. 
 
 (856.) We have in the Hfft 333> 
 
 last place to examine the 
 generative system of the 
 female placental Mamma- 
 lia, and thus to trace the 
 developement of this im- 
 portant system to its most j 
 complete and highest form. 
 In theMARSupiALiA,as 
 the reader will remember, 
 there were still two dis- 
 tinct uteri, that were ob- 
 viously the representatives 
 
 of the oviducts of the oviparous classes. In the human female, 
 on the contrary, the uterus is a single central viscus, into which 
 the germs derived from the ovaria are introduced through the two 
 " Fallopian tubes" as the oviducts are now designated ; but we 
 shall soon see that the viviparous Mammals offer in the anatomical 
 structure of the generative system of the female so many inter- 
 mediate gradations of form, that we are almost insensibly con- 
 ducted even from the divided uteri of the Ornithorynchus up to 
 the most elevated and concentrated condition that the uterine 
 apparatus ultimately attains in our own species. 
 
 In the female Rabbit, for example, we have a placental Mam- 
 mal that in every part of the organization of its reproductive organs 
 testifies its near affinity to the Marsupial type. The .ovaria 
 (Jig' 334, A:, /), although widely different as regards the size of the 
 contained ovules from those of oviparous animals, still retain faint 
 traces of a botryoidal or racemose appearance. 
 
 The oviducts (w, o,) or the Fallopian tubes as we must now 
 call them, are reduced in their diameter to very small dimen- 
 sions, and testify by their tenuity how minute must be the ovule 
 to which they give passage. To these succeed the uteri (e, f) 9 
 still entirely distinct from each other throughout their whole ex- 
 tent, and even opening into the vagina (g) by separate orifices, into 
 which the probes i, A, have been introduced. As far as its anato- 
 my is concerned, such a uterine apparatus might belong to a mar- 
 
726 MAMMALIA. 
 
 supial Maramifer ; and even in the rest of the sexual parts obvious 
 relations may be traced between the rodent we are describing and 
 the ovo-viviparous quadrupeds. 
 
 It is true that there are no longer two vaginae terminating in a 
 single cloacal cavity, but let the reader observe how nearly the va- 
 gina of the Rabbit (a, b) approximates the condition of a cloacal 
 chamber. Anteriorly it receives the contents of the bladder (d, m) ; 
 while the rectum (s) terminates by an anal orifice (r), so closely 
 conjoined with the aperture of the vulva, that the anatomist is 
 almost in doubt whether the external opening might not be de- 
 scribed as common both to the vagina and intestine. Advancing 
 from this lowest form of a placental uterine system, it is found 
 that the two uteri before their termination become united so as to 
 form a central portion common to both, called the body of the 
 uterus, through the intervention of which they communicate with the 
 
 Fig. 334. 
 
 vagina by a single passage named the os tinea ; still, however, 
 the cornua uteri, especially in those tribes that are most remark- 
 able for their fecundity, become during gestation far more capaci- 
 ous than the mesial portion of which they appear to be prolonga- 
 tions. It is, in fact, in the cornua that the numerous progenv of 
 such animals are lodged during the whole time of their retention 
 in the uterus ; and consequently such an arrangement is absolutely 
 requisite, as must be evident from simply inspecting the gravid 
 uterus of a Sow (fig. 335), where the cornua uteri (c, c,) are of 
 remarkable dimensions. 
 
MAMMALIA. 
 
 727 
 
 As we ascend from the more prolific inferior races to the Qua- 
 drumana and the Human species, the proportionate size of the body 
 of the uterus becomes materially increased, and that of the cornua 
 diminishes in the same ratio, until in the Monkeys and in Woman 
 the latter become quite "lost, and the now pyriform central part 
 appears to compose the entire' viscus, into the cavity of which the 
 Fallopian tubes seem immediately to discharge themselves. Thus 
 gradually, therefore, does the oviparous sexual apparatus assume the 
 viviparous type ; and then, passing through numerous intermediate 
 forms, ultimately attains its most concentrated condition in the 
 uterus of the human female. 
 
 (857.) In every other part of the generative system we shall 
 likewise find the characters of the type at length completely estab- 
 lished. The ovaria (Jig. 335, a) entirely lose all traces of their 
 original racemose condition, for now the quantity of granular matter 
 enclosed along with the germ in each Graafian vesicle, the last rein- 
 Fig. 335. 
 
 nant of the yolk, has become almost inappreciable, and the little 
 ovarian ovules are enclosed in a dense parenchymatous substance 
 
728 MAMMALIA. 
 
 enveloped by a smooth albugineous tunic. The Fallopian tubes 
 (b) correspond, in the smallness of their diameter, with the minute- 
 ness of the globules they are destined to convey from the ovaries 
 into the uterine receptacle ; and lastly, the excretory canal of the 
 bladder (cf) becomes quite separated from the vagina (e), and the 
 anal and generative apertures are found completely distinct from 
 each other. 
 
 (858.) After the above brief sketch of the anatomy of the or- 
 gans of generation in the higher Mammalia, it now remains for us 
 to trace the developement of the germ from the moment of im- 
 pregnation to the birth of the fetus, and observe in what particu- 
 lars placental generation differs from the oviparous and ovo-vivipa- 
 rous types already described. In the viviparous or placental Mam- 
 mifer, the effect of impregnation is the bursting of one or more of 
 the Graqfian vesicles, and the escape of the contained germs from 
 the ovisacs wherein they were formed. In the Ovipara, owing to 
 the delicacy of the ovisacs, the vascular membranes composing them 
 when once ruptured are speedily removed by absorption ; but in 
 the Mammal this is not the case, and a cicatrix remains perma- 
 nently visible upon the surface of the ovary, indicating where the 
 rupture has occurred : such cicatrices are known by the name of 
 corpora lutea. 
 
 (859.) On the rupture of the ovarian ovisac, the vesicle of Pur- 
 kinje, or the essential germ, accompanied only by a most minute 
 quantity of granular fluid, or yolk, is taken up by the fimbriated 
 extremity of the Fallopian tube, and conveyed into the interior of 
 the uterus, where its developement commences. Observations are 
 wanting to teach us precisely what are the first appearances of the 
 embryo ; but there is not the least doubt that the materials for its 
 earliest growth are absorbed in the cavity of the womb, and that 
 its formation from a blastoderm, or germinal membrane, is ex- 
 actly comparable to what occurs in the egg of the Bird, already 
 minutely described in the last chapter ( 699 et seq.), and that 
 in every particular, as relates to the growth and functions of the 
 vitelline or omphalo-mesenteric as well as of the amniotic systems, 
 the phenomena are the same as in the marsupial Mammal up to 
 the period when the young Marsupian is prematurely born, to be 
 afterwards nourished in the pouch of its mother from materials de- 
 rived from the breast. 
 
 But precisely at that point of developement where the Marsu- 
 pial embryo is expelled from the uterus of its parent, namely, when 
 
MA MM ALT A. 
 
 729 
 
 the functions both of the vitellicle and of the allantoic apparatus 
 become no longer efficient either for nutrition or respiration, a 
 third system of organs is developed in the placental Mammifer, 
 whereby a vascular intercommunication is established between the 
 fetus and the uterine vessels of the mother, forming what has been 
 named by human embryologists the Placenta. 
 
 In the ovum of a Sheep, at that period of the growth of the fetus 
 which nearly corresponds with the end of utero-gestation in the 
 prematurely born Kangaroo, all the three systems alluded to are 
 coexistent and easily distinguishable, as will be seen in the accom- 
 panying figure (j&\ 336). The fetus (0), enclosed in its amnio- 
 tic membrane (7>), has its limbs as yet but very imperfectly formed, 
 exhibiting pretty nearly the condition of a nascent Marsupial (vide 
 Jig. 331) ; but here it will be seen that the umbilical systems exhi- 
 bit very striking differences in the two races. The vitellicle (f), 
 
 Fig. 336. 
 
 with its pedicle (e), are of very small dimensions ; the allantoid 
 sac (g), on the contrary, is of considerable bulk, and, having ceased 
 to act as a respiratory organ, becomes adapted to receive the urinary 
 secretion through the canal of the urachus. The most important 
 feature, however, is the" rapid extension of the umbilical vessels (rf), 
 which in BIRDS and MARSUPIALS were distributed only to the 
 allantois ; but in the placental Mammals these vessels rapidly spread 
 over the chorion (A), and, coming in contact with the vascular sur- 
 face of the womb, they soon form a new bond of communication be- 
 tween the mother and the fetus, constituting the placenta ; and thus 
 the offspring is nourished, until, its intra-uterine growth being ac- 
 complished, it is born in an advanced condition of developement, 
 and becomes the object of maternal care during that period in 
 which it is dependent upon the breast of its mother for support. 
 
730 MAMMALIA. 
 
 (860.) The appearance of the placenta varies much in different 
 tribes : thus, in the Sheep and other RUMINANTS it consists 
 of numerous detached masses of villi (z, z), that indigitate with 
 corresponding processes derived from the maternal womb ; in 
 the Mare it covers the whole surface of the chorion ; but in the 
 greater numbers of Mammals, and in the Human female, it forms a 
 single vascular cake, whence is derived the name appropriated by 
 anatomists to this important viscus. 
 
 (861.) After the developement of the placental system, it is 
 obvious that the arteries derived from the common iliac trunks of 
 the fetus, which at first were distributed only to the allantois, as 
 in the case of the Bird ( 705), on the developement of the pla- 
 centa become transferred to the latter viscus, and form the umbili- 
 cal arteries of the navel-string. The vein likewise, notwithstand- 
 ing its prodigiously increased extent of origin after the placenta 
 has been formed, takes the same course on entering the umbilicus 
 of the fetus as it did when it was derived only from the allantois ; 
 so that, although the placenta completely usurps the place of the 
 allantois, both the allantoic and placental circulations are carried 
 on through the same umbilical arteries and veins. 
 
 (862.) In order to complete our history of fetal developement 
 up to the full establishment of the permanent double circulation 
 that characterises all the hot-blooded Vertebrata after birth, it 
 only remains for us to notice the changes that occur in the vessels 
 of the fetus, whereby, on the cessation of the functions of the pla- 
 centa, the pulmonary circulation is at length brought into action. 
 
 Up to the period of birth the arrangement of the fetal circula- 
 tion remains essentially that of a Reptile, inasmuch as both the 
 venous blood derived from the system and the arterialized blood 
 that comes from the placenta, are mixed together in the as yet im- 
 perfectly separated chambers of the heart. Under these circum- 
 stances the arrangement of the vascular system is as follows : Pure 
 blood, supplied from the placenta is brought into the body by the 
 umbilical vein, which passes partly into the portal system of the 
 liver, but principally through the ductus venosus into the inferior 
 cava, and thence into the heart. From the construction of the 
 heart during this portion of fetal existence it is obvious, that, in 
 that viscus, all the blood derived from the placenta, from the ve- 
 nous system of the fetus, and also from the as yet inactive lungs, is 
 mingled together prior to its distribution through the arterial sys- 
 tem. The two auricles communicate freely with each other through 
 
MAMMALIA. 731 
 
 the foramen ovale ; and by means of the ductus arteriosus the 
 greater portion of the blood driven from the right ventricle during 
 the systole of that cavity passes into the aorta, a very small pro- 
 portion only finding its way into the pulmonary arteries. Such a 
 heart therefore supplies a mixed fluid to the fetal system ; of which 
 a portion, having passed through the arterial trunks, finds its way 
 back to the placenta through the two umbilical arteries, there to 
 recommence the same circle. 
 
 (863.) Immediately after birth, however, the whole arrangement 
 is altered, and the adult condition fully established. The lungs 
 assume their functions, and the pulmonary arteries attain their full 
 proportions ; while the placenta at once ceases from its office, and 
 all the umbilical vessels become obliterated. The ductus venosus 
 is no longer permeable, so that the portal system and that of the 
 vena; cava are quite separated : the foramen ovale closes, thus 
 completely separating the right from the left auricle : the ductus 
 arteriosus is reduced to a mere ligament ; all the blood, therefore, 
 driven from the right side of the heart must now pass into the ex- 
 panded lungs, and be returned through the pulmonary veins to the 
 left side of the heart. Thus the pulmonary and systemic circula- 
 tions being rendered totally distinct, arterialized blood alone enters 
 the arterial system, to be distributed through the body ; and, the 
 umbilical arteries disappearing, the highest form of the circula- 
 tory apparatus is fully established. 
 
 (864.) After birth the mammary glands supply the first nutri- 
 ment to the still helpless offspring. These vary in number and 
 position in different species of placental Mammifers, their number 
 being of course greatest in the most prolific races. Where the arms 
 or anterior limbs can be used for supporting or clasping the feeble 
 young, as in the QUADRUMANA, the BATS, and the females of our 
 own species, it is upon the breast that these nutrient founts are 
 placed ; but in less gifted tribes the mammte are situated beneath 
 the abdomen or in the inguinal region. Their structure, however, 
 is similar throughout the entire class ; each gland consisting of in- 
 numerable minute secreting cells, grouped together in lobules and 
 in lobes. Delicate excretory ducts, derived from all these ultimate 
 cells, unite together again and again until they form capacious 
 ducts, or rather reservoirs for milk. In the Human female the lac- 
 tiferous canals terminate by numerous orifices upon the extremity 
 of the nipple ; but, where the nipples are of large size, they gene- 
 rally contain a wide cavity wherein the milk accumulates in consi- 
 
10% MAMMALIA. 
 
 derable quantities, to be discharged through one or two orifices 
 only. Such are the modes by which Supreme Beneficence has 
 provided for the infant progeny of Mammiferous beings, and con- 
 ferred the endearments of maternity where He has bestowed intel- 
 ligence to appreciate affection. But even this is not all : from the 
 superabundance of the store provided there may be yet to spare ; 
 and Man is privileged to bid his lowing herds yield him their 
 milk for food, and Ihus obtains no slight addition to the bounteous 
 table spread for his enjoyment. 
 
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