;ESE LIBRARY": 
 
 OF ' 
 
 ZRSITY OF CALIFORNIA^ 
 
 "Vf-d 
 
 ^cessions No. S^fZ-r Claxs No. 
 
AN ELEMENTARY 
 
 TEXT-BOOK OF BIOLOGY, 
 
STANDARD TEXT-BOOKS. 
 
 WORKS BY WM. STIRLING, M.D., Sc.D., 
 
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 EXAMINER IN THE UNIVERSITIES OF OXFORD, EDINBURGH, AND LONDON ; AND 
 
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 1. HUMAN PHYSIOLOGY (A Text-book of). By Profs. 
 
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AN ELEMENTARY 
 
 TEXT-BOOK OF BIOLOGY: 
 
 COMPRISING 
 
 VEGETABLE AND ANIMAL MORPHOLOGY 
 AND PHYSIOLOGY. 
 
 BY 
 
 J. R. AINSWORTH DAVIS, B.A., 
 
 TRINITY COLLEGE, CAMBRIDGE ; 
 *mOPES80R OF BIOLOGY AND GEOLOGY IN THE UNIVERSITY COLLEGE OF WALKS, ABERY8TWYTH. 
 
 HQlitb numerous $llugtrattons an? <Mossav\\ 
 SECOND EDITION, REVISED AND ENLARGED. 
 
 PART II ANIMAL MORPHOLOGY AND PHYSIOLOGY, 
 
 CHARLES GrRIFFIN tfe V/V^J-TAJ. -n-xi j-j O-IJ.J.U.JL JL *m~r } 
 
 EXETER STREET, STRAND. 
 1893. 
 
 [All Rights Reserved.} 
 
B:OLOGY 
 
 LIBRARY 
 G 
 
TABLE OP CONTENTS. 
 
 INTRODUCTION, . . . . . . .1 
 
 CHAPTER I. PROTOZOA. 
 
 1. Amoeba (Proteus Animalcule), . . . . .7 
 
 2. Vorticella (Bell Animalcule), . . . . .11 
 
 3. Gregarina, . . . . . . .17 
 
 CHAPTER II. CCELENTERATA. 
 
 4. Hydra (Fresh Water Polype), . . . . ,19 
 
 Further remarks on Hydrozoa, ..... 27 
 
 CHAPTER III. PLATYHELMIA (Flat- worms). 
 
 5. Distoma' (Liver-fluke), ...... 28 
 
 Further remarks on Flukes, . .... 39- 
 
 6. Tsenia (Tapeworm), . . . . .39 
 
 Further remarks on Tapeworms, . . . .46 
 
 CHAPTER IV. NEMATHELMIA (Thread-worms). 
 
 7. Ascaris (Round-worm), . . . ... 47 
 
 Other Thread- worms, ...... 53 
 
 CHAPTER V. ANNELIDA (Segmented Worms). 
 
 8. Lumbricus (Earthworm), . . . . .54 
 
 Sexual reproduction, . . . . . .71 
 
 9. Hirudo (Leech), .... . 75 
 
viii CONTENTS. 
 
 CHAPTER VI. ARTHROPOD A. 
 
 VAGK 
 
 10. Astacus (Crayfish), ... .83 
 
 Other Crustacea, ... .107 
 
 CHAPTER Vll. MOLLUSC A. 
 
 11. Anodonta and Unio (Fresh Water Mussels), . .109 
 
 12. Helix (Snail), . . . . . .122 
 
 CHAPTER VIII. VERTEBRATA ACRANIA. 
 13. Amphioxus (Lancelet), .... .134 
 
 CHAPTER IX. PISCES (Fishes). 
 > 14. Scyllium (Dogtish), . .153 
 
 CHAPTER X. AMPHIBIA. 
 15. Raiia (Frog), ....... 174 
 
 CHAPTER XI. AVES (Birds). 
 . 1. Columba livia and Gallus bankiva (Pigeon and Fowl), . . 229 
 
 CHAPTER XII. MAMMALIA. 
 17. Lepus cuniculus (Rabbit), . . . . .268 
 
 CHAPTER XIII. COMPARATIVE ANIMAL MORPHOLOGY AND PHYSIO- 
 LOGY, 310 
 
 CHAPTER XIV. MAN, ...... 321 
 
 CHAPTER XV. CLASSIFICATION AND DISTRIBUTION OF ANIMALS, , 339 
 
LIST OF IL LUST RATIONS. 
 
 (Names in italics indicate the Sources whence derived. ) 
 
 FIGURK PACK 
 
 1. Amoeba and Vorticella (Haddon, after Howes and Stein), . 8 
 
 2. Group of Vorticellse (Marshall and Hurst), . . .12 
 
 3. Gregarines (after Stein and Riitschli), . . . . 17 
 
 4. Hydra (Original), ....... 21 
 
 5. Distoma Gut (from Claus, after Leuckart), . . .29 
 
 6. ,, Excretory, Nervous, and Reproductive Organs (after 
 
 Sommer), . . . . 30 
 
 7. ,, Reproductive Organs (Claus, after Sommer), . . 32 
 
 8. ,, Development (Clans, partly after Leuckart), . . 37 
 
 9. Txnia, (Landois and Stirling), . . . . . .40 
 
 10. ,, Reproductive Organs (after Sommer), . . .42 
 
 11. ,, Ripe Egg (Landois and Stirling), . . . .44 
 
 12. Cysticerci ( ,, ), . . . .44 
 
 13. ,, ,, everted (Landois and Stirling), . . . 45 
 
 14. Ascaris (von Jaksch), ...... 47 
 
 15. ,, (Original, and after Leuckart, Vogt and Yung, Butschli, 
 
 and Van Beneden), ..... 50 
 
 16. Oxyuris (von Jaksch), . . . . . .53 
 
 17. Trichina (),,. . . . . . 53 
 
 18. Lumbricus Gut, Circulatory Organs, Nervous System (Original), 56 
 
 19. ,, Reproductive Organs (Marshall and Hurst), . 63 
 
 20. ,, Development (after Wilson), . . . .69 
 
 21. A sterias Polar Cells (after Fol and Hertwig), ... . .73 
 
 22. ,, Fertilization (after Fol), . . . .74 
 
 23. Hirudo General Dissections (after Leuckart, and Vogt and Fung), 77 
 
 24. Nephridium and Eye (after Vogt and Yung, and Whitman), 77 
 25 and 26. Astacus ^External Characters (Original), . . .85 
 
 27. Astacus Appendages (Original), . . 88 
 
 28. Gut and Kidney (Original), . . 94 
 
 29. ,, Reproductive Organs (Original). . 99 
 
 30. ,, Eye (after Carriere), . . 104 
 
 31. ,, Blastula and Gastrula (after Reichenbach and Huxley), 105 
 
 32. Unio General Dissection (Claus, after Grobben), . .^ 110 
 
 33. Anodonta Nervous System (Claus, aft^r Keber), . . . 112 
 
 2 b 
 
LIST OF ILLUSTRATIONS. 
 
 KlftDKK 
 
 PACE 
 
 34. Anodonta Transverse Sections and Gill (Original), 
 
 35. Helix Digestive Organs and Nervous System (Original), . 124 
 
 36. ,, Buccal Mass (Claus, after Refer stein), . .126 
 
 37. Reproductive Organs (Original), . 
 
 38. Amphioxus (Marshall and Hurst), 
 
 39. Sections (Original), ... .140 
 
 40. ,, Blastula and Gastrula (Glaus, after Hatschek), . 148 
 
 41. ,, Sections of Embryos (Haddon, after Hatschek), . 149 
 
 42. Larval Stages (Claus, after Hatschek), . .150 
 
 43. Scyllium Skull, &c. (Original), . .156 
 
 44. Skeleton of Pectoral Fins (Original), . . .159 
 
 45. ,, Pelvic Fins (Original), . . . 159 
 40. General Dissection (Original), .... 163 
 
 47. ,, Nerves (after Wiedersheim), . . . .170 
 
 48. Diagrams of Membranous Labyrinth (Bell, after Waldeyer), . 173 
 
 49. Rana Skin (after W iedersheim), . . . . .177 
 
 50. ,, Endoskeleton (Original, and after Ecker), . . . 181 
 
 51. ,, General Dissection (Original), .... 190 
 
 52. Unstriated Muscle- Fibres (Landois and Stirling), . .192 
 
 53. Rana Heart (after Ecker), . . . . ,195 
 
 54. ,, Arteries ( ), . . . . .196 
 
 55. ,, Veins ( ,, ), . . . . .199 
 
 56. ,, Posterior Lymph-Hearts (Ecker), . . . .200 
 
 57. ,, Muscle-Fibres from Heart (Landois and Stirling), . 201 
 
 58. Small Artery showing the Goats ( ), .201 
 
 59. Capillaries (Landois and Stirling), .... 202 
 
 60. Rana Female Reproductive Organs (after Ecker and Wieders- 
 
 heim), ........ 207 
 
 61. Histology of Nerve (Landois and Stirling), . . . 214 
 
 62. Rana- Sense Organs (after Ecker and Wiedersheim), . .219 
 
 63. Diagrammatic Horizontal Section of Eye (Landois and Stirling), 220 
 
 64. Diagram of Layers of Retina (Landois and Stirling), . . 221 
 
 65. Rana Cleavage of Oosperm (Haddon, after Ecker), . . 223 
 
 66. Early Stages (Haddon after Gotte), . . . 223 
 
 67. ,, Diagrammatic Longitudinal Section through Embryo 
 (Haddon, after Gotte), . . . . . . 225 
 
 68. Columba Endoskeleton (Original), . . . .235 
 
 69. (),.... 240 
 
 70. ,, General Dissection of Male (Original), . . . 243 
 
 71. ,, Urinogenital Organs (Original), . . . . 250 
 
 72. ,, Diagrams of the Membranous Labyrinth (Bell, after 
 Waldeyer), .... 255 
 
LIST OF ILLUSTRATIONS. XI 
 
 JIGUBK PAGE 
 
 73. Gall us Diagrammatic Longitudinal Section through Uniiicubated 
 
 Egg (Claus, after Balfour and Allen Thomson], . 4 2f>7 
 
 74. ,, Surface Views to showCleavage in t]ieoosperm(Haddon, 
 
 after Coste), ...... 258 
 
 75. Section through part of Unincubated Blastoderm (Haddon, 
 
 after Klein], ...... 259 
 
 76. ,, Transverse Section through Front End of Primitive 
 
 Streak in First Day Chick (Haddon, after Balfour), '259 
 
 77. ,, Surface View of First Day (20 hrs.) Chick (Kolliker), . 260 
 
 78. , , Surface View of Chick, rather later than Fig. 77 ( Kolliker), 261 
 
 79. ,, Surface View of Second Day Chick (Kolliker}, . . 262 
 
 80. ,, Development of the Eye (Haddon, partly after Marshall], 263 
 
 81. Transverse Section through Embryo Duct at Third Day (from 
 
 Haddon, after Balfour), ..... 2t>4 
 
 82. Gallus Diagram to Illustrate the Embryonic Appendages 
 
 (Haddon, after Foster and Balfour), .... 266 
 
 83. Six Stages in the Development of Hair (Had,don, after Wiedersheim), 270 
 
 84. Lepus Endoskeleton (Original), .... 277 
 
 85. ,, General Dissection of Head and Thorax (Original), . 283 
 
 86. ,, Histology of Liver (Landois and Stirling, after Herimj), 289 
 
 87. Muscle-Fibres from Mammalian Heart (Landois and Stirling), . 292 
 
 88. Structure of Mammalian Kidney (Landois and Stirling), . 296 
 
 89. Lepus Urinogenital Organs (Original), .... 297 
 
 90. Histology of Striated Muscle (Landois and Stirling), . . 300 
 
 91. Diagrams of Membranous Labyrinth (Bell, after Waldeyer), . 304 
 
 92. Lepus Formation of Blastocyst (Haddon, after E. Van Beneden), 305 
 
 93. ,, Blastocyst (Haddon, after Kolliker), . . . -307 
 
 94. ,, Head of Ten Day Embryo (Haddon, after Kolliker), . 307 
 
 95. ,, Embryonic Appendages ( Haddon, after Bischo/), . 309 
 
 96. Man Skull (Macalister), . . 324 
 
 97. ,, Sacrum ( ,, ), . . . . 325 
 
 98. Coccyx (,,),. . . . 325 
 
 99. Bones of Hand (,,),. . . 327 
 
 100. ,, Pelvis, ( ,, ), . . . .328 
 
 101. ,, Bones of Foot (,,),. . . .328 
 
 102. ,, Ca-cum, &c. (),'. 329 
 
 103. ,, Aortic Arches (),,. . . . 330 
 
 104. ,, Development of Veins (Macalister), . . . 331 
 
 105. ,, ., Urinogenital Organs (Macalister), . 332 
 
 106. ,, Brain-exterior (Macalister), . . . . 335 
 
 107. section ( ,, ), . . . . 336 
 
 108. Fcetal Membranes (Macalister, after Longet), . . 337 
 
AN ELEMENTARY 
 TEXT-BOOK OP BIOLOGY, 
 
 PART II. ANIMAL MORPHOLOGY AND PHYSIOLOGY. 
 
 INTRODUCTION. 
 
 1. ZOOLOGY, the branch of Biology which deals with animals, 
 is such an immense subject that, like Botany, it is conveniently 
 split up into a number of subdivisions. The most important of 
 these are (1) Animal Morphology, dealing with the structure 
 and form of animals; (2) Animal Physiology, which treats of 
 their actions or functions; (3) Development, the application of 
 morphology and physiology to the study of immature forms ; 
 (4) Classification or arrangement; (5) Distribution, in space and 
 time; and (6) Phylogeny, the province of which is to make out 
 the past history of animal groups (phyla). We are mainly con- 
 cerned in this volume with the first three branches, and, to a 
 much smaller degree, with the questions of classification. 
 
 The range of these subdivisions will be comprehended more 
 clearly if we consider what questions they seek to answer in 
 regard to some particular animal, say, for example, the common 
 Frog. 
 
 (1) Morphology takes note of the external characters, such as 
 shape, colour, divisions of the body, &c., and by means of dissec- 
 tion determines that various systems of organs (digestive, &c., &c.) 
 are present, which have a definite arrangement, and which can 
 2 1 
 
2 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 be more or less divided up into smaller parts visible with the eye 
 or with the aid of a lens. The stomach, for instance, is found to 
 have a wall .consisting of certain layers or coats. So far we have 
 had to do with External Morphology and Anatomy. But, with the 
 assistance of the compound microscope, a further analysis is pos- 
 sible, and the special aim of Histology is to consider minute struc- 
 ture. Such an analysis demonstrates that the body of a Frog is 
 composed of an exceedingly large number of miscroscopic units, 
 cells, differing very much in size, shape, and form, like cells being 
 aggregated into masses known as tissues, such as muscular, 
 nervous, &c. There are, besides, other elements formed by or 
 from cells. It is usual to regard the cell as the morphological 
 unit, but the higher powers of the microscope prove that the cell 
 itself is most wonderfully complex. 
 
 Morphology, however, in the modern sense, is not a mere de- 
 scriptive study, but endeavours to discover not only how things 
 are but also why they are. In the Frog, for example, there is a 
 slender tube, the pineal body, running from the brain to the roof 
 of the skull. In the tadpole it stretches right up to the skin, 
 but the formation of the skull-roof pinches off its end, which 
 remains in the adult frog as a " brow-spot." What, then, is the 
 meaning of the pineal body and brow-spot ? No light is thrown 
 upon this question by the study of the Frog only, but by employ- 
 ing the comparative method a definite answer can be given. It 
 is known that in certain lizards the pineal body has the structure 
 which is characteristic of eyes, and we, therefore, conclude that the 
 Frog's remote ancestors possessed an unpaired eye in the top of 
 the head, which has since disappeared, leaving an insignificant 
 rudiment. In numberless other instances Comparative Morphology 
 (including Comparative Anatomy, &c.) helps to clear up otherwise 
 unintelligible matters. 
 
 (2) From the physiological standpoint, a Frog is a machine 
 capable of performing various kinds of work. Physiology is con- 
 cerned, in fact, with the uses of the different parts of the body. 
 It investigates, for example, the processes by which food is 
 digested, absorbed, and built up into living tissue; the circulation 
 of the blood ; and the functions of the brain. The problems of 
 physiology, like those of morphology, often require comparative 
 treatment, and they are commonly more difficult to solve. 
 
 (3) Development (Embryology, Ontogeny) as applied to the 
 
INTRODUCTION. 3 
 
 Frog traces its life-history from the egg to the adult condition, 
 and is separated from the two preceding branches merely for the 
 sake of convenience. In the solution of many biological pro- 
 blems it is often of the greatest possible use. An animal in the 
 course of its development passes through a series of stages which 
 to some extent indicate its pedigree, or, as it has been put, 
 "climbs up its own genealogical tree." Thus the Frog starts 
 active life as a gill-breathing aquatic tadpole which is practically 
 a fish in structure, and points to descent from fish-like ancestors. 
 (4) Classification refers the Frog to a definite place in a 
 system of grouping, in which animals are best arranged according 
 to those characters which denote blood-relationship. It is found 
 possible to divide the animal kingdom into several large branches 
 or phyla, which are again subdivided, and the process continued 
 until the individual is reached. The relative status of the various 
 groups may be indicated as follows : 
 
 PHYLUM 
 
 SUB-PHYLUM 
 
 CLASS 
 
 ORDER 
 Family 
 
 Genus 
 
 Species 
 
 Variety. 
 
 The Frog is placed in the important phylum CHORDATA, which 
 includes all animals that possess, temporarily or permanently, an 
 elastic supporting rod, the notochord, below the central nervous 
 system, as well as clefts which place the cavity of the throat in 
 communication with the exterior. Mammals, Birds, Eeptiles, 
 Frogs, Fishes, and certain somewhat lower forms are here included. 
 The Frog's sub-phylum, that of the VEETEBEATA, embraces 
 animals among the common characters of which are possession 
 of a more or less complete brain-case and spinal column. It 
 includes the above-mentioned animals except the forms lower 
 than fishes. Vertebrates are subdivided into several classes, one 
 of which, the AMPHIBIA, comprises frogs, toads, newts, sala- 
 manders, and the like, all of which pass through a tadpole-stage. 
 
AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Those Amphibia which, like frogs and toads, have four well- 
 developed limbs, but are tailless, constitute the order ANURA, 
 and this includes a number of families, of which one, Eanidae, 
 comprehends frogs with long hind limbs, webbed hind feet, teeth 
 in the upper jaw, and tongue fixed to the front of the mouth- 
 floor. The most important genus in this family is Rana, to which 
 the common and edible frogs belong, and which is characterized 
 by the rudimentary nature of the thumb, by the presence of teeth 
 on the roof of the mouth, and the deeply forked tongue. Some 
 forty " kinds " or species of frog are included in the genus Rana, 
 and this is a convenient place to explain the principle upon which 
 scientific names are given to animals. On the binominal system , 
 which is universally adopted, each animal receives two names, 
 that placed first being the generic, while the other is the specific 
 name. The common or Grass Frog is known as Rana temporaria, 
 and the Edible Frog as Rana esculenta. The species temporaries is 
 marked by a number of distinctive features, among which may 
 be placed the presence of a dark blotch on each side of the head, 
 and the absence of croaking sacs in the male. It is scarcely 
 possible to say what is actually meant by the term " species," and 
 there is much difference of opinion in certain cases. The follow- 
 ing definition, given by De Candolle, will serve as well as any : 
 " A species is a collection of all the individuals which resemble 
 each other more than they resemble anything else, which can by 
 mutual fecundation produce fertile individuals, and which re- 
 produce themselves by generation, in such a manner that we may 
 from analogy suppose them all to have sprung from one single 
 individual." It is generally found impossible to obtain crosses 
 between different species, or if such crosses (hybrids) are pro- 
 duced these are, as a rule, infertile. 
 
 The Frog is not a very good illustration of varieties, to ex- 
 plain which other animals may be taken. The Clouded Yellow 
 Butterfly (Colias edusa), for instance, is usually orange and black, 
 but a small proportion of yellow and black individuals are found, 
 and these constitute a variety* of the species edusa. Another good 
 example is the Field Snail (Helix hortensis), in which the colour 
 and striping of the shell vary in the most remarkable way, so that 
 the species hortensis has been split up into a large number of 
 varieties. In such a case, however, the varieties are perfectly 
 
 * Hyale. 
 
INTRODUCTION. 5 
 
 fertile among themselves, and the crosses (mongrels) between 
 them are also fertile, though there are exceptions to this among 
 plants. 
 
 The old view as to the " origin of species " was that they were 
 all separately created, but it is now almost universally held by 
 scientists that living species have been evolved from pre-existing 
 ones, and that varieties are to be regarded as species in process 
 of evolution. A brief sketch of the evolution theory will be 
 given in another place. 
 
 (5) Distribution. Rana temporaria is a very widespread species, 
 ranging over the greater part of Europe, N. Africa, N. Asia to 
 Japan, and N. America. It is absent, however, from Iceland and 
 N. Scandinavia. 
 
 We have less definite knowledge as to the range in time of 
 this species, but in this country the bones of a frog closely 
 resembling it have been found in a deposit * accumulated at a time 
 when the British fauna included species of Elephant, Hippopo- 
 tamus, Rhinoceros, and Hyaena. 
 
 (6) Phylogeny (^Etiology) makes use of data supplied by all 
 the other departments to work out the evolution of groups. The 
 Amphibia must be regarded as one branch of a huge genealogical 
 tree, its orders corresponding to subdivisions of this branch, its 
 families and genera to still smaller ramifications, and its species 
 to the ultimate twigs. 
 
 2. Differences between Animals and Plants. No difficulty is 
 experienced in distinguishing a higher animal from a higher 
 plant. A Frog, for instance, differs in the compactness of its 
 form from, say, a tree, and this difference is correlated with the 
 nature of the food. A tree spreads out leaves for the absorption 
 of carbon dioxide, while it takes up by its roots water charged 
 with inorganic salts. Its food is of simple kind and gaseous or 
 liquid in nature ; hence the diffused branching form which offers 
 a large external absorptive surface. A Frog, on the other hand, 
 requires much more complex food, part of which must be albu- 
 minous in nature, and it can only get this by devouring other 
 organisms, in this case insects; while tadpoles chiefly live on 
 plants, upon which, indeed, all animals directly or indirectly 
 depend. This complex organic food being solid the Frog requires 
 an internal digestive cavity for its reception, and there is an obvious 
 * The Cromer Forest-Bed. 
 
6 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 necessity for powers of locomotion, which are unnecessary to 
 higher plants. A compact form is obviously advantageous under 
 the circumstances, and the possession of a well-developed nervous 
 system and sense-organs bringing the various activities of the 
 animal into touch with one another and the outer world becomes 
 readily intelligible. 
 
 Plants and animals, however, must be regarded as of common 
 descent, forming as it were the two diverging limbs of a V, the 
 higher forms being situated at the ends of those limbs, and 
 the lower forms near the point of union. Hence, as we pass 
 down in the scale the differences between the two kingdoms 
 become less and less marked, until, in the simplest cases, it is 
 often scarcely possible to say whether a given organism be plant 
 or animal. 
 
 The distinction which perhaps holds most generally is found in 
 the nature of the food, and plants are also usually characterized 
 by the presence of protective membranes composed of cellulose 
 (C 5 H 10 5 )n, a substance closely allied to starch. It is, indeed, 
 the presence of these membranes which renders it necessary that 
 the food should be in a gaseous or liquid condition. 
 
 3. Distinctions between Living and Non-Living Matter. An 
 organism is bounded by curved surfaces, while masses of non- 
 living matter are either shapeless (amorphous) or else of crystalline 
 form, in which case they are usually limited by flat faces meeting 
 in straight edges. An organism, too, is of excessively compli- 
 cated physical and chemical structure, and its living part is 
 always composed of a substance known as protoplasm, of which 
 more will be said in the sequel. This complexity is related to 
 a process of constant chemical change (metabolism), involving 
 continual loss of substance, which must be compensated by the 
 intaking of food. This is built up into fresh protoplasmic mole- 
 cules, which are intercalated between those already existing. By 
 this process of intussusception growth may be effected, up to a 
 certain limit in the case of each organism. A mineral mass, say, 
 for example, a crystal of copper sulphate, is not of such exceed- 
 ingly complex nature, nor are its molecules subject to constant 
 down-breaking and up-building. It may be kept in an unaltered 
 form for an indefinite period, and since it does not eliminate 
 waste products does not require food. If placed in a saturated 
 solution of copper sulphate it exhibits a kind of growth, by 
 
PROTOZOA. 7 
 
 addition of new layers to its outside (accretion), and such increase 
 may go on indefinitely so long as fresh solution is available. 
 
 An organism, again, has a life-history, passing through a cycle 
 of changes, which either terminate in death or else in loss of 
 individuality (cf. Section on Amoeba). This is not the case with 
 a mineral. 
 
 4. Biogenesis and Abiogenesis. All existing organisms, so far 
 as we know, have been derived from pre-existing individuals by 
 processes of reproduction (biogenesis). It was, however, formerly 
 held that some organisms could spring directly from non-living 
 matter (abiogenesis, spontaneous or equivocal generation). This 
 belief was gradually limited to the lowest forms of life, and even 
 for them has now been disproved. A flask partly filled with 
 broth or hay-infusion soon swarms with such organisms if left 
 freely exposed to the air ; but if all germs are killed by continued 
 boiling, and the entry of fresh ones prevented by plugging the 
 neck of the flask with sterilized cotton-wool, none of them make 
 their appearance. Such experiments, however, do not prove that 
 abiogenesis has not occurred during some former period of the 
 earth's history. 
 
 CHAPTER I. PROTOZOA. 
 1. AMCEBA (Proteus Animalcule). 
 
 THIS is a microscopic animal, varying much in size. It is found 
 on the surface of the mud in fresh-water pools, on damp earth, in 
 organic infusions, and elsewhere. 
 
 MORPHOLOGY. 
 
 1. External Characters. The form of an active Amoeba is 
 constantly changing, but it is always irregular. The semi-fluid, 
 transparent protoplasm of which the body is wholly composed is 
 thrust out into bluntish lobes (pseudopodia), which vary contin- 
 ually in number and shape. In most Amoebae these can be 
 emitted from any part of the body. 
 
8 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 2. Structure (Fig 1, A). An outer perfectly transparent 
 exoplasm can be distinguished from a more granular internal endo- 
 plasm. The exoplasm is apparently stiffer than the endoplasm, 
 but there is no clear line of demarcation, and as part of the body 
 may be outside one moment, and inside next, the apparent differ- 
 ence is probably caused by a tendency of the granules to collect 
 
 Fig. 1. AM(EBA AND VoRTiCELLA. (from ffaddon, after Howes, and Stein], 
 enlarged. A-0, Stages in fission of Amoeba; D and E, fission of other 
 Protozoa; F, conjugation of Vorticella. c.v., Contractile vacuole ; 
 n, nucleus. [ 
 
 in the centre. Some amoebae, however, possess a firmer exoplasm 
 in which a sort of fibrillation can be made out. 
 
 Within the granular portion two important structures are 
 present: (1) The nucleus (n), a rounded or ovoid mass, consist- 
 ing of a modification of protoplasm, and denser than the rest of 
 the body. In the living animal it is inconspicuous, but becomes 
 very obvious on treatment with weak acid or a staining solution. 
 In some cases, at any rate, the nucleus is invested by a delicate 
 membrane, and consists of two substances, one, chromatin, staining 
 readily the other, achromatin, staining with difficulty. The 
 arrangement of the chromatin differs with the species, but part 
 of it is frequently aggregated into a central particle, the nudeolus. 
 (2) The contractile or pulsating vacuole (c.v.), a spherical space 
 
PROTOZOA. 9 
 
 with fluid contents, which alternately increases and diminishes in 
 size, in a rhythmic manner. There may be more than one. 
 
 More or less food, surrounded by fluid, is usually present in 
 the endoplasm, occupying spaces known as food-vacuoles. Gas- 
 containing vacuoles have also been observed in some specimens. 
 
 PHYSIOLOGY. 
 
 The functions carried on by Amoeba and, indeed, by all other 
 organisms may be conveniently considered under five headings. 
 
 1. Nutrition, The food of Amoeba consists of small organisms 
 and organic particles, which its pseudopodia first come into con- 
 tact with, and then flow around. All parts of the body alike 
 serve for the reception of food. The complex chemical composi- 
 tion of the substances utilized, and their ingestion in the solid 
 state are worthy of notice, as typical animal characteristics. 
 Each mass enters the body surrounded by a small quantity of 
 water, and a food-vacuole is thus constituted, the temporary 
 breach in the protoplasm being at once closed up. Within the 
 body, mechanical and chemical influences are brought to bear 
 upon the food, it being subjected, on the one hand, to slow rota- 
 tion in the endoplasm, while on the other, either the protoplasm 
 itself or a digestive juice formed (secreted) by it reduces the 
 digestible portions to a state of solution, or fine division. The 
 food thus digested is then assimilated, that is, built up into living 
 protoplasm, while the indigestible and undigested remnants are 
 thrown out at any convenient point. 
 
 Encystment. If conditions of temperature or food-supply are 
 unfavourable, Amoeba possesses the power of assuming a spherical 
 form, and then secreting a firm structureless coating or cyst, which 
 is possibly of a horny nature, and is a very considerable protec- 
 tion. 
 
 2. Katafoolism. The complex protoplasmic molecules are con- 
 stantly breaking down into simpler substances, and potential 
 energy is thus transformed into kinetic. This process is, as a 
 rule, far more rapid in animals than in plants, and greater activity 
 is consequently displayed by the former. 
 
 The products of Katabolism (Katastates) are : 
 a. Secretions, which are utilized in some way before passing 
 out of the body. It is probable, for example, that Amoeba 
 
10 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 secretes something which acts chemically upon the food, 
 
 and corresponds to the digestive juices of other forms. 
 I. Excretions (waste-products), which pass out of the body 
 
 at once. These are water, carbon dioxide (C0 2 ), and 
 
 compounds of ammonia. 
 
 Katabolism is, practically, a process of oxidation, the result 
 being that animals, like most plants, require a supply of free 
 oxygen, and the term Kespiration, or breathing, is applied to the 
 taking in of oxygen with concomitant excretion of carbon dioxide 
 (and water). 
 
 The contractile vacuole, which is alternately enlarged to a certain 
 maximum size by the gradual aggregation of liquid, and obliter- 
 ated by the contraction of the surrounding protoplasm, appears 
 to communicate with the exterior. It probably serves as a recep- 
 tacle in which can collect, at one time, oxygenated water from 
 the exterior, at another time waste-products. The general surface 
 of the body is also doubtless respiratory, oxygen diffusing in and 
 carbon dioxide diffusing out. 
 
 3. Reproduction (Fig. 1, A-C). This is asexual, and usually 
 effected by binary fission, the animal splitting into two equal parts. 
 The nucleus elongates, becomes dumb-bell-shaped, and separates 
 into two, each half being surrounded by a moiety of the proto- 
 plasm, which has meanwhile been gradually constricted. The 
 two new individuals grow to the adult size, divide again, and so 
 on, there being no known limit to the process. 
 
 An Amoeba, in fact, instead of dying, divides into two new and 
 vigorous individuals. Hence it has been said to be, in a sense, 
 immortal. 
 
 4. Contractility is one of the primary properties of protoplasm, 
 in virtue of which a change of form is effected. The process does 
 not involve diminution in volume, since reduced breadth in one 
 or more directions is made up for by equivalent increase in other 
 directions. In Amoeba there are irregular contractions of the 
 protoplasm leading to the formation of pseudopodia. Where one 
 of these is about to be thrust out, the exoplasm (which is probably 
 specially contractile) is protruded as a clear knob, into which, as 
 it increases in size, the endoplasm enters. An anterior progressing 
 region, actively flowing into pseudopodia, and a more passive 
 following region, can be made out in some Amoebae. These regions 
 are in ordinary cases determined by the direction of movement, 
 
PROTOZOA. 1 1 
 
 and simply correspond to the anterior and posterior ends for the 
 time being. There are, however, some species which can only 
 thrust out pseudopodia from part of the body, and which there- 
 fore possess permanent progressing and following regions. 
 
 It appears probable that a delicate film of firmer nature rapidly 
 forms on the surface of naked protoplasm. The direction of 
 pseudopodia may perhaps, in some Amoebae, be determined by 
 the rupture of such a film at definite points. The movements of 
 Amoeba are so characteristic that the special epithet, " amoeboid," 
 is given to all similar movements, wherever occurring. 
 
 5. Irritability and Spontaneity. That Amoeba is affected by 
 external agents or stimuli may readily be noticed. Pseudopodia 
 which come in contact with food-particles flow around them, but 
 inedible substances are usually rejected. Increase of temperature 
 enhances activity, but as 35 C. is neared, this is diminished, and 
 arrested when that point is reached. Death is caused by a rise 
 of 5 or 10 more. On the other hand, activity is diminished by 
 cooling, and arrested at the freezing-point. Weak electric shocks 
 cause the animal to assume the spherical form, and become 
 quiescent. 
 
 Amoeba is constantly moving, and it cannot be doubted that 
 some of its movements are spontaneous i.e., not directly due 
 to external stimuli, but resulting from internal causes, such, per- 
 haps, as chemical decomposition. 
 
 2. VORTICELLA (Bell Animalcule). 
 
 Vorticella is an animal of microscopic dimensions, which is 
 found attached to marine and fresh-water plants, &c., and may be 
 distinguished by the aid of a lens. 
 
 MORPHOLOGY. 
 
 1. External Characters (Fig. 2). The^ body is shaped some- 
 thing like a pear or rounded cone, and, in most individuals, is 
 attached to some object by an elongated slender stalk, into which 
 its apex is drawn out. It is convenient to speak of the attached 
 end of the body as proximal, the free end as distal. The animal 
 possesses considerable powers of movement, and may be found 
 fully expanded, fully retracted, or in an intermediate condition. 
 
12 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 ,B XI 
 
 y 
 
 2. GROUP OF VORTICELL.E (from Marshall and Hurst). x 220. 
 L, II., and III. show the animal in various positions ; IV. is a much 
 smaller specimen drawn to the same scale ; V. shows a specimen made 
 to contract by action of alcohol ; VI. is detached from its stalk, and 
 swimming away freely, disc forwards ; VII. , VIII. , and IX. show three 
 stages of fission; X., XL, and XII. show the separated individual 
 swimming by means of the aboral circle of cilia ; XL is slightly con- 
 tracted ; XIL strongly contracted after the cover-glass has been tapped. 
 A, Food-vacuole discharging contents at anus; C, cilia of the disc; 
 C F, contractile fibre of stalk ; D, disc ; D', disc contracted ; F V, food- 
 vacuole ; P H, gullet ; P V, pulsating vacuole ; P, peristome ; M, myo- 
 phan striation ; N, nucleus ; V, vestibule. 
 
PROTOZOA. 1 3 
 
 When it is completely expanded the stalk is straight, or slightly 
 curved, while the distal end, or disc, forms a flattish projection 
 bordered by a thickened rim or peristome. Within the peristome 
 is a groove which surrounds the disc and forms on one side a 
 deep depression, the vestibule. In the groove is a row of delicate, 
 hair-like, protoplasmic processes (cilia). The retracted state is 
 initiated by the withdrawal of the disc ; then follows the folding- 
 in of the peristome, so that the body becomes rounded, and, at 
 the same time, the stalk is thrown into a tightly-coiled spiral. 
 
 Smaller free-swimming, stalkless individuals are also met with, 
 simpler in structure and possessing a circlet of cilia near the 
 arboral .end of the body. 
 
 2. Structure. The body is transparent as in Amoeba, and its 
 internal parts can therefore be readily studied. Covering the 
 whole external surface, cilia excepted, is a thin elastic membrane, 
 the cuticle, which may exhibit transverse striations. It is thinnest 
 on the disc and peristome, and thickest on the stalk, of which it 
 forms the sheath. The cuticle is secreted by the underlying pro- 
 toplasm, and owing to its presence the body possesses a constant 
 form, while the protrusion of lobe-like pseudopodia is rendered 
 impossible. The cilia, which may be compared to permanent 
 thread-shaped pseudopodia, pass through holes in the cuticle. 
 The protoplasm is divided into a firm, finely granular, external 
 ectosarc or cortical layer, and a semi-fluid endosarc. The deeper 
 part of the ectosarc exhibits more or less distinct longitudinal 
 striations (myophan striations), probably due to a fluting of the 
 internal surface. This deeper part is produced into a contractile 
 filament, which is slightly twisted in a spiral manner, and traverses 
 the cavity of the hollow stalk, attached here and there to the firm 
 sheath. 
 
 As in Amoeba, a nucleus and contractile vacuole are present. 
 The former is a horse-shoe-shaped band placed in the broad end 
 of the body, just within the ectosarc ; the latter is spherical, and 
 situated nearly the vestibule. There is a small round pamnuchus 
 near the nucleus. 
 
 A rudimentary digestive apparatus can here be distinguished 
 for the first time. The vestibule, which performs the function 
 of a mouth, is continued into a short tube, the pharynx, which is 
 lined by a continuation of the cuticle, and is provided with 
 numerous short cilia. It passes down into the body with a some- 
 
14 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 what curved course, and ends abruptly within the endosarc. A 
 small area in the vestibule, beneath the disc, is devoid of cuticle, 
 and serving, as it does, for the extrusion of remnants of the food, 
 may be termed the anus. Within the endosarc numerous food- 
 vacuoles can usually be distinguished. 
 
 PHYSIOLOGY. 
 
 Vorticella, like Amoeba, is an unicellular animal, but the single 
 cell of which its body is composed is very much specialized or 
 differentiated, since different parts of it are modified for the per- 
 formance of different functions. 
 
 1. Nutrition, The combined action of the cilia produces a 
 current by which minute organisms and organic particles are 
 carried down to the end of the pharynx, and, together with a 
 small amount of water, forced into the endosarc. There, in food- 
 vacuoles, they slowly pass down one side of the body and up the 
 other, the water being gradually absorbed, and the nutritious 
 parts digested as in Amceba. The undigested remnants are 
 ejected from the anus, which is only visible at the moment of 
 extrusion, and are carried out of the vestibule by the ciliary 
 current. 
 
 Under unfavourable conditions Vorticella sometimes detaches 
 itself from its stalk, and swims away by means of its cilia, 
 becoming re-attached, and developing a new stalk, if a suitable 
 spot is reached. As in Amoeba, unfavourable conditions may also 
 lead to encystment, the body, either whilst attached to its stalk or 
 after separation, becoming rounded, and secreting a protective 
 horny cyst. 
 
 In one species of Vorticella, V. viridis, chlorophyll is diffused throughout 
 its body, which no doubt enables it to live, in part, like a green plant, 
 utilizing carbon dioxide as a source of carbon. 
 
 2. Katabolism. As in Amceba, something akin to a digestive 
 secretion is probably formed by the protoplasm. The same waste- 
 products, namely, carbon dioxide, water, and ammonia compounds, 
 result from the breaking-down of the body, and, as before, the 
 contractile vacuole is probably excretory and respiratory, waste- 
 products passing from it into the vestibule, with which it has 
 been observed to communicate, while, on the other hand, oxygen- 
 ated water may be taken up into it from the exterior. The 
 
PROTOZOA. 1 5 
 
 ciliary current brings dissolved oxygen with it, and also carries 
 away waste-products. 
 
 3. Reproduction (Fig. 2). This is asexual, and usually takes 
 place by equal binary fission in a longitudinal direction. The 
 animal broadens, its nucleus elongating, and then a furrow appears, 
 which rapidly deepens so that the animal is cleft down to its 
 stalk, the nucleus and contractile vacuole being halved. Two 
 equal-sized individuals result, one of which remains attached to 
 the stalk, while the other develops a circlet of cilia near its prox- 
 imal end, becomes detached, and swims away, later on becoming 
 fixed by its proximal end and developing a stalk. Thus Vorticella, 
 although a fixed form, can readily spread from place to place, and 
 it is, therefore, not to be wondered at that it has a very wide dis- 
 tribution, especially if it be remembered that the process of fission 
 only takes an hour or two for its completion. 
 
 Small free-swimming individuals (microzooids), similar in struc- 
 ture to the large free forms, may be produced by unequal fission, 
 in which case an ordinary zooid divides into two parts, one large, 
 the other small, or else continued fission may take place in 
 which equal bipartition is immediately followed by rapid division 
 of the half to be detached into eight microzooids. Using large 
 letters for the larger zooids (macrozooids) and small ones for the 
 microzooids, the different kinds of fission may be expressed as 
 follows : 
 
 Equal Fission. Unequal Fission. 
 
 B (fixec 
 B' (free) 
 
 Continued Fission. 
 
 ^ |B (fixed) A _^ /B (fixed) 
 
 C C C C 
 
 A process, known as conjugation, which has an important 
 bearing on the origin of sexual reproduction, also frequently 
 occurs in Vorticella. A microzooid comes into contact, by its 
 ciliated end, with a large fixed macrozooid, at a point near the 
 junction of the stalk. The two gradually fuse together, parts of the 
 
16 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 paranuclei uniting. Increased vigour (rejuvenescence) appears to 
 be imparted by this process, which generally shows itself in greater 
 reproductive energy, as displayed in fission. More rarely, encyst- 
 ment may follow, when the nucleus becomes larger and much 
 longer, ultimately breaking up into a number of spores, oval 
 bodies, each provided with a circlet of cilia at one end. These 
 are liberated by the rupture of the cyst, and becoming attached 
 by their ciliated ends, grow up into adult forms. Before this 
 they may, however, increase by a process of fission. 
 
 4. Contractility. The presence of a firm cuticle prevents the 
 formation of pseudopodia, though protoplasmic currents are observ- 
 able in the endosarc, by which the food-vacuoles are carried round 
 the body, and such streamings are also seen in the firmer ectosarc, 
 though to a much less extent. Locomotion is effected in the free 
 forms by cilia, while the currents that bring food and oxygen, 
 and carry away waste, are also due to ciliary action. Each cilium 
 is a delicate thread of protoplasm, protruded from the ectosarc 
 through a pore in the cuticle. By means of the alternate con- 
 traction of its longitudinal halves, bending and straightening are 
 produced in turn. 
 
 The retraction of the body is due to the ectosarc, and in this 
 case contraction takes place is the direction of the myophan 
 striation, whence it appears probable that the deeper layer is the 
 part mostly concerned in the process. The thread which traverses 
 the stalk contracts in such a definite way, getting shorter and 
 broader, that it deserves to be called a specially contractile or 
 muscle fibre. The spiral direction taken by the fibre causes the 
 stalk to be readily thrown into spiral folds. The much slower 
 process of expansion appears to be largely due to the elasticity of 
 the cuticle, and this is especially true of the stalk. 
 
 5. Irritability and Spontaneity. These phenomena are much 
 more definitely exhibited than in the case of Amoeba. The 
 animals appear sensitive to the slightest touch, which causes 
 them to contract rapidly. The same effect may be produced 
 by irritant solutions, such as weak acetic acid, and by other 
 stimuli. Spontaneity is shown by the way in which the cilia 
 work together to a common end, instead of acting irregularly. 
 Spontaneity is further exemplified by free-swimming individuals 
 in fixing and conjugation. 
 
PROTOZOA. 
 
 17 
 
 3. GREGARINA. 
 
 Gregarines are Protozoa, often of worm-like form, in which a 
 relatively large size may be attained (up to f of an inch long). 
 They are parasitic, living at the expense of other animals, and as 
 they are found within the bodies of these " hosts," may be termed 
 endoparasites. Since they are surrounded by abundance of nutri- 
 tious food, there is no necessity for locomotor or current-producing 
 organs, and, in fact, there are neither pseudopodia nor cilia, and 
 digestive organs are absent as well. 
 
 Fig. 3. GREGARINES (after Stein and Biitschli). Enlarged to various 
 scales. A-E, Stages in the life-history of Monocystis off His; A, adult ; 
 co, cortical layer (dotted) ; n, nucleus ; B, cyst, with developing 
 spores ; C, cyst, with ripe spores ; D, a spore with contained falciform 
 young ; E, one of the falciform young ; F-K, stages in the life-history 
 of Gregarina blattarum ; F, young adult ; ep, epitnerite ; pr, proto- 
 merite ; deu, deutomerite containing nucleus, n ; G, cyst containing 
 two conjugated individuals; H, ripe cyst; g.l, gelatinous layer; 
 f.l, firm stratified layer, within which is a network, still enclosing 
 spores in the centre ; sp, sporoduct ; K, a spore ; L, epithelial cells 
 from intestine of cockroach, with attached stages (1, 2, 3) of developing 
 spore-contents. 
 
 The vesiculse seminales of the earthworm are infested with one 
 
 kind of Gregarine, to which the name of Monocystis has been 
 
 applied. This has a cylindrical body (Fig. 3), which in the 
 
 largest species may be -J- of an inch long. It is covered with a 
 
 2 2 
 
18 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 firm cuticle, within which is a well-marked ectosarc or cortical 
 layer, in which an appearance of longitudinal striation may be 
 observed, probably due to an internal fluting, as in Vorticella. 
 Worm-like movements can be performed by the contraction of 
 this layer. Within the ectosarc is a more fluid endosarc, and 
 there is a large nucleus at one end. There is no contractile 
 vacuole, which is not surprising when the sluggish nature and 
 consequently slow katabolism of the animal is considered. 
 
 Monocystis undergoes encystment as a regular part of its life- 
 history, and this is usually preceded by the conjugation of two 
 individuals, which come into contact by their anterior ends, some- 
 times fuse, but in any case assume a spherical form and become 
 surrounded by a firm cyst, said to be formed from the cuticle and 
 an altered part of the underlying protoplasm. The contents 
 of the cyst now break up into a large number of spindle-shaped 
 spores (pseudonavicellse) invested in firm envelopes, and then, by 
 a process of division, eight nucleated sickle-shaped cells (falciform 
 young) are formed within each spore, a small part of the proto- 
 plasm, however, being left unused (residual core). The falciform 
 young are ultimately liberated by rupture of the cyst and the 
 spore-envelopes. They are capable of movement by alternate 
 bending and straightening, and make their way into those cells 
 (spermatospores) from which the male sex-cells of the earthworm 
 are developed, thus becoming intracellular parasites. After a 
 time they quit these cells and gradually assume the adult form. 
 
 Another common kind of Gregarine is Gregarina (Clepsidrina) 
 folattarum, found in the intestine of the cockroach. A mature 
 individual, when young, possesses an elongated tapering body 
 (Fig. 3), divided into three regions, (a) an anterior epimerite 
 (" cap "), provided with hook-like cuticular processes, and passing 
 into (6) a protomerite, separated by a transverse septum of ecto- 
 sarc from (c) a much larger deutomerite, in which the nucleus is 
 contained. These regions are probably not distinct cells, but 
 merety parts of one cell. Sooner or later the epimerite is thrown 
 off. 
 
 Two individuals unite, the anterior end of one being opposite 
 the posterior end of the other, and a complicated cyst is secreted, 
 consisting of a number of firm layers with an external gelatinous 
 investment. Eepeated nuclear division presumably takes place, 
 and a considerable number of barrel-shaped spores are formed 
 
CCELENTERATA. 1 9 
 
 just within the wall of the cyst, migrating later on to the centre. 
 Part of the protoplasm remains as a kind of network, and a 
 number of tubes (sporoducts) are formed, which are at first 
 directed inwards, but are later on turned inside out (everted), 
 projecting from the cyst, and serving as channels through which 
 the spores escape. This, of course, involves absorption of the 
 firm cyst at points where sporoducts are formed. From each 
 spore a single embryo escapes, which makes its way into one of 
 the epithelial cells lining the intestine of the cockroach. The 
 regions of the body are now gradually developed, the protomerite 
 and deutomerite projecting into the cavity of the intestine, while 
 the epimerite remains imbedded in the cell, and is soon thrown 
 off. The young Gregarina absorbs the digested food with which 
 it is surrounded, and quickly grows to the adult size. 
 
 CHAPTER IL CCELENTERATA. 
 4. HYDRA (Fresh Water Polype). 
 
 THIS is a small animal common in ponds, ditches, and stagnant 
 streams. Extended specimens measure from half an inch in 
 length downwards. There are two common kinds, the Brown 
 Hydra (Hydra fusca), and the rather smaller Green Hydra 
 (Hydra viridis). 
 
 MORPHOLOGY. 
 
 1. External Features (Fig. 4). The body of Hydra, when 
 extended (A), is in the form of a hollow cylinder, usually attached 
 to some object by its closed proximal end, which constitutes an 
 adhesive disc (the "foot"). The distal end is terminated by a con- 
 ical projection, the hypostome, in the centre of which is a rounded 
 opening, the mouth (m). Several (5 to 8) slender prolongations 
 of the body, known as tentacles (hi), project, at regular intervals, 
 from the base of the hypostome. Both body and tentacles may 
 
20 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 undergo various stages of contraction or shortening. In extreme 
 contraction, the entire animal appears (A') like a small, rounded, 
 gelatinous knob, brown or green, according to the species. The 
 external appearance presents certain characteristic features in 
 connection with reproduction (see below). 
 
 By looking down upon the distal end of Hydra, it is seen that 
 a number of radiating lines, all passing through similar parts, can 
 be drawn from the centre of the mouth along the tentacles. This 
 sort of symmetry, common among lower animals, is of the kind 
 termed radial. 
 
 2. Body-wall. Amoeba, Gregarina, and Vorticella are unicellular, 
 each being made up of one cell or morphological unit. These animals 
 therefore possess diverse parts in virtue of the specialization, 
 differentiation, of the protoplasm of single cells. Hydra, on the 
 other hand, is multicellular, being made up of very numerous cells, 
 each of which is morphologically equivalent to an Amoeba. These 
 cells, however, are modified in various ways for the performance 
 of diverse functions. This is the principle of physiological division 
 of labour, arid the accompanying diversity of form is termed 
 morphological differentiation. Aggregates of cells, similar in 
 form and mode of origin, and specially capable of carrying on a 
 particular function or functions (instead of all functions, as in 
 Amoeba), are known as tissues, and these again are interwoven 
 into organs, digestive, reproductive, &c. In Hydra this special- 
 ization is not very complete ; but, as the animal scale is ascended, 
 physiological division of labour and morphological differentiation 
 become more and more marked. 
 
 Histology. The body of Hydra contains a large digestive cavity, 
 prolonged into the hollow tentacles. The wall of this cavity is 
 the body-wall, and the cells composing it are divided into two 
 distinct layers, an external ectoderm (ec), and an internal endoderm 
 (en), about twice as thick. Between the two is a very thin 
 structureless membrane, the mesoglcea (intermediate or supporting 
 lamella) (i.F), not composed of cells. 
 
 The ectoderm (ec) is mainly made up of large somewhat conical 
 cells (C) which are broadest externally, while the narrow internal 
 end of each of them is drawn out into one or more contractile 
 tail-like processes, which may branch. These "tails" take a 
 longitudinal direction, and are closely attached to the mesogloea. 
 Each large ectoderm cell possesses a clear external border, and 
 
CCELENTERATA. 
 
 21 
 
 contains a large nucleus with nucleolus. Adjacent cells touch 
 one another externally, whilst, internally, spaces are left between 
 them which are occupied by interstitial cells (ic). .These are small 
 nucleated cells present in all parts of the body but the foot, and 
 often crowded together so as to obscure their individual outlines. 
 
 / 
 
 ec. 
 
 Fig. 4. HYDRA, various scales. A, Budding specimen of H. fusca 
 extended; A', ditto, retracted; B, tranverse section of H. fusca; 
 B', part of same on larger scale; C, isolated tailed cells; D, isolated 
 thread -cell, from H. viridis; f, foot; ra, mouth; tn, tentacles; 
 ec, ectoderm; en, endoderm; 6, bud; or, typical position, &c., of 
 ovary; t, do., of testes; i.l, intermediate lamella, the dots above this 
 represent the cut ends of "tails;" i.c, interstitial cells; n, thread-cells; 
 /, flagella; fd, organism (in B) in digestive cavity, as food. 
 
22 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Within some of the interstitial cells (cnidoblasts) oval vesicles 
 (nematocysts) are developed, each of which contains a coiled-up 
 filament. Nematocysts are chiefly found in the distal end of the 
 body, especially in the tentacles, where they are aggregated into 
 " batteries," giving rise to an irregular surface. If a little weak 
 acid is added to the water which contains a Hydra, the threads 
 will be rapidly shot out. 
 
 The cnidoblasts are at first situated deeply in the ectoderm, 
 but as their nematocysts (" thread-cells ") develop, force their way 
 to the surface. Several kinds of nematocyst may be distinguished, 
 of which the largest consist of a transparent vesicle containing 
 fluid, and (when examined in the discharged condition) this it 
 seen to be produced (D) into a long tapering neck, which towards 
 its end bears a few large backwardly directed spines, and is 
 continued into an extremely long and delicate hollow filament 
 or thread. In an unused nematocyst, the neck is turned into 
 the vesicle, within which the filament is coiled up. The remains 
 of the cnidoblast persist as a layer of protoplasm surrounding the 
 vesicle and produced externally into a slender sensitive process, 
 the cnidocil, which slopes towards the free end of the body or 
 tentacle, as the case may be. There are also other much smaller 
 nematocysts with shorter, thicker threads, and without barbs. 
 Small star-shaped nerve-cells, connected with the protoplasmic 
 investment of the thread-cells, are said to exist in the ectoderm. 
 
 The endoderm (en) is made up of a single layer of large, irre- 
 gular, granular cells, each containing a big flattened nucleus with 
 nucleolus, and one or more vacuoles, often of great size. The 
 endoderm cells abut at one end upon the supporting lamella (and 
 appear to be here produced into transversely-wrsiRged tails), while 
 the other end projects into the digestive cavity, and can be thrust 
 out into pseudopodia. This end often bears one or more elon- 
 gated protoplasmic threads (flagella*) (/), which are capable of 
 being withdrawn, like pseudopodia. The external half of each 
 cell contains in Hydra viridis numerous small globular bodies, 
 coated with chlorophyll. Hydra fusca possesses small bodies of 
 similar nature, but containing particles. 
 
 Reproductive Organs. Male and female sex-organs are differ- 
 entiated, and, as both occur in the same animal, Hydra is said to 
 
 * Flagella are longer than cilia, capable of more complex movement, and 
 either occur singly or associated in small numbers. 
 
CCELENTERATA. 23 
 
 be hermaphrodite. They are only found, as a rule, during the 
 autumn months. 
 
 (1) The Male Organs consist of a varying number (1 to 20) of 
 spermaries (testes) (t, ), usually placed near the distal end of the 
 body. Each is a conical or rounded elevation, the wall of which 
 is formed by large ectoderm cells, while within is an aggregate 
 of interstitial cells. The spermaries are, in fact, projections 
 caused by the increase of these cells at particular points of the 
 bodj*. These contained germinal cells develop into sperms (sperm- 
 atozoa), minute tadpole-like bodies, with oval heads and long 
 vibratile tails. The head of the sperm is mainly formed from 
 the nucleus of the germinal cell, covered by a thin film of its 
 protoplasm, the rest of which is drawn out into the tail. 
 
 (2) The Female Organs are known as ovaries (ov), and are 
 typically developed at the proximal end in the same manner as 
 the spermaries. Hydra viridis usually has but one ovary; H.fusca 
 may possess from one to eight. Each is a rounded projection, 
 much larger than a spermary, and, when mature, contains a 
 single large egg-cell or ovum. The young ovary contains at first 
 a large number of germinal cells. One of these, occupying a 
 central position, grows more vigorously than the others, becomes 
 amoeboid, and uses them as food, amoeba-fashion. This relatively 
 large cell is the ovum. It assumes a spherical form on attaining 
 its full size, and though resembling ordinary cells in structure, 
 its parts receive special names. The protoplasm is termed 
 vitellus, and contains numerous highly refractive bodies, known 
 as yolk-spherules. The large spherical nucleus, or germinal vesicle 
 contains a nucleolus, the germinal spot. 
 
 PHYSIOLOGY. 
 
 As might naturally be expected, the ectoderm is more espe- 
 cially concerned with the function of irritability and spontaneity, 
 while the encloderm carries on digestion. 
 
 1. Nutrition. The food consists of small animals, often of 
 relatively high organization, such, for example, as the active little 
 Crustacea known as water fleas. The tentacles are the agents by 
 which these are conveyed to the mouth, arid their nematocysts 
 play an important part in this connection. The following -de- 
 scription applies to the large forms. In the quiescent state, the 
 
24 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 neck and filament of the thread-cell are inside the vesicle, which 
 contains a poisonous fluid. If now a small animal touches the 
 cnidocil (trigger-hair), the neck is first turned inside out, everted 
 (d), and then, by means of its spines, becomes fixed in the animal. 
 The thread is now everted within the wound, and the poisonous 
 fluid exerts a paralyzing influence. The mouth of the animal is 
 very extensile, and capable of taking in morsels of considerable 
 size (B/ef). Within the digestive cavity movement of fluids, &c., 
 is mainly effected by the action of the endodermal flagella. The 
 endoderm-cells vary much in size at different times, and can 
 extend themselves so as to almost obliterate the cavity. It is 
 stated that some of these cells are glandular, secreting a fluid 
 which diffuses into the digestive cavity, where it dissolves and 
 breaks down the food; but digestion is also largely infra-cellular, 
 the pseudopodia ingesting solid particles in the same way as in 
 Amoeba. Within these cells the food is reduced to solution, or 
 fine division, and readily passes to the other parts of the body by 
 diffusion. Undigested remnants are passed out through the mouth. 
 In Hydra mridis the presence of chlorophyll probably enables 
 the nutrition to be partly effected as in green plants. 
 
 2. Katabolisin. Secretions are elaborated by glandular cells 
 in various parts of the body. All parts of the body alike give 
 rise to waste-products, which are secreted into the surrounding 
 water, and in the process of Respiration oxygen is taken in 
 (cf. p. 10). 
 
 3. Reproduction is of two kinds, asexual and sexual, the one 
 irrespective of, the other dependent on, the reproductive organs. 
 
 (1) Asexual Reproduction (A and A') is effected by gemmation, 
 and is not limited to any special time of year, but depends upon 
 the food supply and temperature. A small knob grows out from 
 the side of the body, and not only the ectoderm and endoderm but 
 also the digestive cavity of the parent are continued into it. This 
 bud (&) lengthens, develops a mouth and tentacles, and is finally 
 pitched off at its proximal end, which becomes an attachment 
 disc. Several buds in the same or different stages of develop- 
 ment may be present on one individual at the same time, and, 
 under favourable circumstances, these may themselves bear buds 
 before becoming detached. Fission is not known to occur in 
 nature, but a Hydra may be cut into several pieces, each of which 
 can develop into a new and perfect individual. 
 
CCELENTERATA. 25 
 
 (2) Sexual Reproduction. The wall of the ripe ovary bursts, 
 and part of the surface of the now spherical ovum is exposed. 
 By the rupture of the spermary at its apex, the sperms are 
 liberated, and by the action of their tails move rapidly head first 
 through the water. Impregnation or fertilization of the ovum now 
 takes place, that is, a sperm (derived from the same or a different 
 individual) fuses with it to form an oosperm. This union of a 
 small active male cell with a relatively large and passive female 
 one, is the essential part of sexual reproduction. 
 
 4. Contractility. Amoeboid and ciliary movements are seen 
 in the endoderm. Besides these, Hydra is capable of movements 
 on a larger scale. The body and tentacles can be extended and 
 contracted, their appearance varying very much in consequence, 
 and curvings, very complex in the case of the tentacles, can also 
 be effected. These movements may lead to locomotion, either slow 
 by the gradual shifting of the foot, or more rapid by the alternate 
 sucker-like attachment of the foot and the mouth. Hydra has 
 also been seen creeping along on its tentacles, the body being 
 held almost vertical. It can also float passively near the surface 
 of the water, mouth downwards. 
 
 The retraction of the body subserves protection, whilst the ten- 
 tacular movements are mainly concerned with the procuring of 
 food. All these movements are the result of longitudinal and 
 tranverse contractions, separate or variously combined. The tails 
 of the large ectoderm cells are arranged longitudinally, and by 
 their shortening or contraction furnish the retracting element. 
 If the endoderm-cell really possesses traversely-arranged tails, 
 their contraction would give the necessary extending element. 
 If this is not the case, the conical parts of the tailed-cells could 
 effect the same purpose, by contracting traversely, the result being 
 a corresponding increase in length. 
 
 Discharge of a nematocyst is caused by the contraction of the 
 cnidoblast. By this means the contained fluid is put under pres- 
 sure, and everts first the neck, and then the hollow filament. 
 There is no contrivance for effecting the reverse process, and 
 nematocysts, when once used, are therefore discarded. 
 
 5. Irritability and Spontaneity. Hydra is extremely sensitive 
 to external stimuli, and this is especially well seen in the move- 
 ments of retraction and in the discharge of nematocysts. The 
 cnidocils are sensory, that is to say, specially modified for the 
 
26 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 reception of external stimuli, in this case chemical. They are 
 turned in those directions whence food is most likely to approach, 
 i.e., the oral end of body and tips of tentacles. The external sur- 
 faces of the large ectoderm-cells appear to receive those stimuli 
 which lead to movements. 
 
 Spontaneity is best shown by the co-ordination of the cells for 
 the performance of useful movements, such as those of locomotion, 
 which cannot all be directly due to external influences. The co- 
 ordinative power certainly resides in the ectoderm, either in the 
 large cells or nerve-cells, or probably in both. The discharge of 
 the nematocysts also seems to depend on the "will" of the 
 animal. If a cnidocil is touched, an impulse of some sort appears 
 to be transmitted to the connected nerve-cell, which, in the case 
 of food, sends back an impulse leading to the eversion of the cell, 
 while a particle of sand, say, causes no such disturbance. 
 
 DEVELOPMENT. 
 
 In each ovary, as a general rule, only one ovum is developed, 
 which when almost mature projects freely to the exterior, as a 
 result of the rupture of the cells which cover it. Before fertil- 
 ization the ovum divides into two unequal parts, the smaller of 
 which is known as a polar cell. A second polar cell is next 
 formed by further subdivision, and the nucleus of the ovum is 
 now known as the female pronucleus. The two polar cells perish 
 without taking any share in the further development. 
 
 Fertilization now ensues, a single sperm fusing with the ovum, 
 and its nucleus (male pronucleus) uniting with the female pro- 
 nucleus to constitute the nucleus of the oosperm (segmentation 
 nucleus). The oosperm at once commences to develop, and 
 during the earlier stages remains attached to the parent. The 
 first process is that of segmentation or cleavage, consisting of a 
 series of cell-divisions by which the unicellular oosperm is con- 
 verted into a cellular mass. It is, in fact, a case of continued 
 fission, but the products of division, instead of separating and 
 becoming distinct organisms, as in Vorticella and the like, remain 
 connected together and constitute the rudiment of a multicellular 
 animal. The cleavage in Hydra consists of a series of bipartitions, 
 so that the embryo consists of 2, 4, 8, 16, 32, &c., cells succes- 
 sively. Cleavage is here said to be both complete (holoblastic) 
 
CCELENTERATA. 27 
 
 and nearly regular, for the whole of the oosperm divides, and 
 the resultant cells (blastomeres) are of about the same size. At 
 the end of cleavage the embryo is a hollow sphere or blastula 
 (blastosphere), the cavity of which is known as the blastocoele 
 (segmentation cavity). Cells are now budded off into the blasto- 
 coele from the attached side of the blastula, until the embryo 
 becomes a solid mass, consisting of an external layer of cells, the 
 ectoderm (epiblast) covering an internal cellular core, the endoderm 
 (hypoblast). At the same time a double protective investment, 
 the outer layer of which is firm and chitinous, is secreted by the 
 ectoderm. The changes above described occupy about four days, 
 and, after their completion, the embryo falls from the ovary into 
 the mud, where its development is slowly completed during the 
 winter months. 
 
 The further changes consist in the formation of a digestive 
 cavity by absorption of some of the endoderm cells, while the 
 remaining ones constitute a layer surrounding this cavity. The 
 ectoderm at the same time becomes differentiated, and the meso- 
 glcea makes its appearance. Later on the outer membrane is 
 ruptured by increase in size and elongation of the embryo, the 
 mouth is then formed as a perforation, tentacles grow out as hollow 
 processes of the body-wall, and the inner membrane is cast off. 
 
 The development of Hydra has been investigated by several writers, 
 whose accounts are conflicting. The brief outline given above is probably 
 correct in the main. 
 
 Further remarks on Hydra: 
 
 It must be remembered that although Hydra is a simple and readily 
 obtainable type of the lower multicellular animals, it is by no means a 
 typical example of the group, i.e., the HydrOZOa, to which it belongs. 
 These are for the most part colonial, the colonies being produced by bud- 
 ding. If, in Hydra, the buds, instead of becoming detached, remained 
 united together, something resembling one of these " hydroid zoophytes" 
 would be produced. These colonial forms give rise, in a large number of 
 cases, to free-swimming sexual individuals, which are somewhat umbrella- 
 shaped, and are popularly known as "jelly-fish," technically as "medusae." 
 This is a good example of "alternation of generations," where asexual and 
 sexual stages alternate in the life history of the same form. Thus : A, an 
 asexual hydroid colony gives rise to S, sexual medusa;, which again pro- 
 duce A, and so on, indefinitely. By taking a selected series of forms it can 
 be shown that the sexual organs of Hydra are probably morphologically 
 equivalent (homologous) to medusae. From (1) forms with free swimming 
 medusas, we can pass to (2) forms with medusa-like buds, and thence to 
 (3) forms with sexual buds obscurely medusa-like, lastly to (4) Hydra, 
 with sexual buds as mere knobs of ectoderm. If this reasoning be correct, 
 Hydra is a degenerate form i. e, derived from ancestors more highly differ- 
 entiated than itseLf. 
 
28 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 CHAPTER III PLATYHELMIA (Flat-worms). 
 5. DISTOMA (The Liver-fluke). 
 
 THE best-known kind of fluke is Distoma hepaticum, the Liver- 
 fluke. This is an internal parasite (endoparasite) when adult 
 about an inch and a half long, which lives in the bile-ducts of 
 several animals, more especially the sheep, and causes the disease 
 known as liver-rot. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The animal (Fig. 6) is lilaterally sym- 
 metrical, right and left halves, anterior and posterior ends, and 
 upper (dorsal) and lower (ventral) surfaces being distinguishable. 
 The animal can be divided into corresponding halves by one 
 plane only, the median vertical. 
 
 The body is flattened and somewhat leaf-shaped, its broad 
 dorsal and ventral surfaces passing into sharp edges at the sides 
 and behind. The gently curved outline is interrupted at the 
 anterior end by the head-papilla, a projection which tapers to a 
 blunt point, and ends in an adhesive cup or sucker which looks 
 somewhat ventralwards. Behind the head-papilla the sides of 
 the body curve outwards and backwards till the maximum 
 breadth is attained at about the junction of the anterior and 
 middle thirds, while the hinder two-thirds narrow gradually to 
 the posterior end of the body. There is a second sucker (v.s) on 
 the ventral surface, a little way behind the head-papilla. 
 
 Four median apertures are present on the surface of the body. 
 These are: (1) The mouth (m), in the centre of the anterior 
 sucker; the minute excretory pore (ex.p) at the posterior end; (3) 
 the genital aperture (g.o) on the ventral surface between the 
 suckers; and (4) the minute opening of the vagina (Laurer's 
 canal) on the dorsal surface. 
 
 With the exception of the smooth suckers the body surface is 
 rough, owing to the presence of an immense number of minute 
 backwardly directed spines, which project from the cuticle, a firm 
 membrane which invests the body and is secreted by an under- 
 lying epidermis, that consists of a single layer of large granular 
 cells. The hard cuticle protects and supports the body, and its 
 
PLATYHELMIA. 
 
 29 
 
 spines prevent the animal from slipping back as it makes its way 
 along the bile-ducts of its host. 
 
 The digestive and other organs are imbedded in a mass of 
 tissue, which, since it supports the various parts and connects 
 them together, may be termed connective tissue. Polyhedral 
 nucleated cells are the main constituent of this tissue in the 
 Liver-fluke, but there is also a certain amount of non-cellular 
 fibrous material between these. 
 
 2. Digestive Organs (Fig. 5). The mouth leads into a short 
 tube which quickly forks, the two limbs of the fork passing back 
 and giving off numerous branching processes, all of which end 
 blindly. There is no anus. 
 
 The oval mouth (0) is situated in the middle 
 of the anterior sucker, and leads into a small 
 mouth-cavity, which is followed by the oval, 
 thick-walled pharynx that passes into a very 
 short, straight, delicate tube, the gullet or 
 oesophagus, this again opening into a bifurcated 
 intestine. Each half of this is a thin-walled, 
 fairly wide tube (D), running back to the end 
 of the body, and situated near the middle line. 
 A number of small pouches project from its 
 inner side, whilst a large number of pouches, 
 mostly much branched, extend from its outer 
 side to the edge of the body. 
 
 Special muscles i.e., bands of contractile 
 fibres are connected with the pharynx. A 
 sheath of such fibres, the protractor muscle, 
 closely surrounds this organ, and, on the other F - 5 _Ip ISTOMA 
 hand, is connected with the anterior sucker, ( from Claus after 
 while retractor muscles slant back from the 
 pharynx to the dorsal wall of the body. 
 
 Histology. The pharynx is lined by a con- 
 tinuation of the general cuticle. Its wall is very 
 muscular, the fibres taking various directions. 
 The gullet and intestine have very thin walls, 
 consisting of an epithelial layer of cells, external 
 to which is a structureless membrane. The term epithelium is 
 applied to membranes, formed by one or more layers of cells,, 
 which cover external and line internal surfaces. The epithelium 
 
 Leuckart) Ali- 
 mentary canal. 
 O, Mouth, a 
 short distance 
 behind which is 
 ventral sucker. 
 D, right limb of 
 intestine. 
 
30 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
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 pv c o .jS ^ o O 
 O3 03 -I * "8 
 
 g'ill: : !l 
 
 i.tt-. 
 
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 M o 
 
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 ^anii 
 
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 fX I 0> M Q*N 9 
 
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PLATYHELMIA. 3 1 
 
 in question is simple only one cell thick and columnar, the 
 constituent cells being longer than broad. They are amoeboid 
 and contain large nuclei. 
 
 The food consists of the bile of the host, together with blood 
 and disintegrated liver-substance, resulting from the " rot." This 
 is taken in by the action of the pharynx, which acts somewhat 
 like a piston. By the retractor muscles it is drawn back, when 
 the food rushes into and fills the mouth-cavity. The mouth is 
 now closed and the pharynx brought forwards by the protractor 
 muscle. As, meanwhile, its cavity is enlarged by the contraction 
 of radial fibres in its wall, food passes into it, and (the cavity 
 being diminished by the contraction of other fibres), is then 
 squeezed on into the gullet and intestine. These present a large 
 surface which can at once absorb the fluid part of the food. The 
 amoeboid epithelial cells effect intra-cellular digestion, and perhaps 
 also secrete a digestive fluid which, being poured into the gut, can 
 bring solipl food into solution or a fine state of division. Undigested 
 matter is ejected from the mouth. The digested material diffuses 
 through the intestinal wall to the other parts of the body. 
 
 3. Excretory Organs (Fig. 6, A). Those organs are termed 
 " excretory " (in the narrowest sense), the function of which is 
 to get rid of nitrogenous waste. They here form a network of 
 canals ramifying throughout the body. The smallest of these 
 each terminate in a pear-shaped " flame " cell, containing a large 
 vacuole, and named from the flickering appearance it presents in 
 the living state, and which is probably due to the presence of a 
 row of cilia projecting into the vacuole. The cavities of the 
 flame-cells open into the canals where they terminate, and also, 
 perhaps, into the minute spaces in the tissues, which collectively 
 represent the continuous space, or body-cavity, found around the 
 organs of most animals. The small tubes branch freely, and are 
 united into a network. They open into larger tubes, which, in 
 the anterior quarter of the body, are continuous with four still 
 larger longitudinal trunks, two dorsal (d.b) and two ventral (v.b), 
 and in the posterior three-quarters with a median longitudinal 
 trunk, formed by the union of the four anterior trunks. This main 
 duct (m.d), the largest excretory trunk, runs back, just beneath the 
 dorsal wall of the body, to open by the minute excretory pore (ex.p). 
 
 Histology. The delicate walls of the excretory tubes are made 
 up of a single elastic, structureless layer. They contain a clear 
 
32 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 I) 
 
 fluid, in which are numerous highly refracting granules. The 
 
 presence of guanin (C 5 H 5 N 5 O) has been proved. 
 
 4. Keproductive Organs (Fig, 7). Distoma is hermaphrodite, 
 
 and its very complex reproductive organs lie, for the most part, 
 
 ventral to the intestine. The 
 genital aperture (Fig. 6, g.o) is a 
 small oval pore situated in the 
 middle line between the anterior 
 and ventral suckers, and rather 
 nearer the latter. It leads into 
 a shallow pit, the genital sinus (Fig. 
 6, B), on the right of which is the 
 larger male aperture (c/), and on 
 the left the female aperture (od'). 
 
 (1) The Male Organs consist 
 of two spermaries (testes) (T), one 
 behind the other, extending over 
 a considerable area in the middle 
 region of the body. Each is made 
 up of several much-branched tubes, 
 which unite to form a tube or duct 
 of smaller calibre, the spermiduct 
 (vas deferens). The spermiducts 
 run forwards, one on each side of 
 the middle line, to the level of 
 the ventral sucker (S). In the 
 latter part of their course they 
 converge (Fig. 6, B, B'), and at the 
 above level open into a spindle- 
 shaped thick - walled tube, the 
 vesicula seminalis (v. sm\ which 
 tapers into a very delicate con- 
 voluted tube, the ejaculatory duct 
 (ej.d), that again opens into a 
 shorter and stouter tube, the penis 
 (cirrus) (cr), opening at the male 
 aperture. Around the end of the 
 ejaculatory duct a mass of nucle- 
 ated cells is arranged, each of which 
 
 opens by an excessively fine tube into the duct. They are the 
 
 unicellular accessory glands (ac.gl). 
 
 Do 
 
 Fig. 7. DISTOMA HEPATICUM 
 (from Claim after Sommer). O, 
 Mouth ; D, limb of intestine ; S, 
 ventral sucker, in front of which 
 is genital opening ; T, testis, in 
 front of which is the rounded 
 shell - gland ; Do, yolk - gland ; 
 Ov, oviduct ; Dr, ovary. 
 
PLATYHELMIA. 33 
 
 A gland is an organ essentially composed of one or more epithelial-cells, 
 in which some special secretion or excretion is formed. The simple uni- 
 cellular, i.e., one-celled, condition is seen in the accessory glands. 
 
 The vesicula seminalis, ejaculatory duct, accessory glands, and 
 penis are contained in the cirrus-sac (cr.s), a hollow oval body 
 with muscular walls, lying between the ventral sucker and genital 
 opening. 
 
 (2) The Female Organs are made up of the following parts: 
 The unpaired ovary (Dr) lies on the right side, in front of the 
 spermaries. It is composed of several branched tubes, which 
 unite together to form the oviduct (Ov). This is at first very 
 narrow, then gradually enlarges and becomes considerably con- 
 voluted, and finally narrowing, opens by the female aperture 
 (Fig. 6, B, odf). The dilated part of the oviduct (uterus) is 
 generally found full of eggs, in which embryos are beginning to 
 develop. Two glands are connected with the female organs. 
 (1) The yolk-glands (Do), which secrete a nutritive substance 
 (yolk) for the use of the developing embryos, are paired, and 
 each of them is made up of an immense number of minute 
 rounded bodies (acini) of glandular nature, and extends over a 
 lateral strip outside the other reproductive organs. Behind the 
 spermaries the two meet in the middle line. From the acini fine 
 ducts proceed, which unite into larger ones that finally open into 
 a longitudinal duct which runs along the inner side of the gland. 
 Just in front of the anterior spermary a transverse duct arises 
 from this trunk, which unites with its fellow in the middle line 
 to form a small yolk-reservoir, from which the short impaired yolk- 
 dud runs forwards to join the oviduct not far from its commence- 
 ment. Just before their union a fine tube, the vagina (Laurer's 
 canal), through which sperms are introduced into the oviduct, 
 passes to the yolk-duct from the dorsal surface, where it opens 
 by a minute aperture. (2) The shell-gland, by which the egg- 
 shells are secreted, is similar in structure to the accessory gland. 
 It is a rounded mass, the elements of which open into the 
 oviduct near its junction with the yolk-duct. (See Fig. 7, just 
 below convoluted oviduct.) 
 
 Histology. The tubules of the spermary are supported by a 
 
 structureless wall, on the outside of which filamentous contractile 
 
 cells are arranged longitudinally. There appears to be a lining 
 
 of germinal epithelial cells, sperm-mother-cells, some of which 
 
 2 3 
 
34 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 become free, and give rise to tufts of sperms (spermatozoa). 
 Only part of the substance of the mother-cells is used up in 
 this process. Each sperm possesses a small oval head, and long 
 vibratile tail. The walls of the vesicula seminalis, cirrus-sac, 
 and penis contain muscle-fibres variously arranged, and the last 
 is lined by a continuation of the spiny cuticle covering the 
 body. 
 
 The ovarian tubules possess supporting layers, and are lined by 
 germinal epithelium, the cells of which become ova. Each of 
 these has a small vitellus, and large germinal vesicle, with germi- 
 nal spot. In the acini of the yolk-glands a formation of yolk-cells 
 occurs. These contain a large amount of nutritious matter. A 
 yellowish fluid, which can harden into shell substance, is secreted 
 by the shell-glands. 
 
 5. Muscular System. This is made up of bands and sheets of 
 contractile muscle-fibres, by means of which definite movements 
 are effected. When these fibres contract they become shorter 
 and broader, their ends being thus 'brought closer together so 
 that the parts to which they are attached tend to approach. In 
 the case of fibres surrounding a cavity in a circular direction 
 (pharynx, for example), narrowing of the cavity takes place, and 
 the reverse is effected by longitudinal fibres. The movements of 
 locomotion are mainly due to the dermal musculature, a sheet of 
 muscle intimately connected with the skin, and together with it 
 making up the body-wall. The sheet is composed of three layers, 
 external, middle, and internal, the fibres of which take respec- 
 tively transverse (circular), longitudinal, and oblique directions. 
 Closely connected with these are the suckers, which are muscular 
 cups of rather complex structure. There are also a great many 
 muscular bands running through the connective-tissue which fills 
 up the space between the organs. These bands take a dorso- 
 ventral direction, and are also connected together so as to form a 
 close network. 
 
 Locomotion is effected in the following way: The ventral 
 sucker having been fixed, the head-papilla is elongated by the 
 contraction of its circular muscle-layer. The anterior sucker 
 then attaches itself, the ventral sucker being at the same time 
 loosened, and the body is dragged forward by the contraction of 
 its longitudinal muscle-layer. 
 
 6. Nervous System (Fig. 7). Under this term are included 
 
PLATYHELMIA. 35 
 
 those organs which have more especially to do with irritability 
 and spontaneity. 
 
 Around the pharynx is placed a nerve-ring, the plane of which 
 slopes downwards and backwards. In its dorsal part there is a 
 swelling, the cerebral ganglion (c.g) } on either side, and a similar 
 unpaired ventral ganglion (v.g) below. From each cerebral gang- 
 lion two small filaments, nerves, are given off to the head-papilla, 
 in which they branch, whilst a stouter lateral nerve (Ln) runs 
 back almost to the end of the body, giving off branches as it 
 does so. It lies just within the ventral body-wall, below the 
 reproductive organs, and is separated from its fellow by about 
 one-third the breadth of the body. Excessively fine filaments 
 are given off from the ventral ganglion to surrounding parts. 
 
 Histology. Two elements make up the essential part of the 
 nervous system (a) Nerve-cells (ganglion-cells), (b) Nerve-fibres. 
 The nerve-cells are most numerous in the ganglia, but are also 
 present in less abundance in parts of the nerve-ring. They are 
 irregular in shape, with several projections or processes ; their 
 protoplasm is clear and they contain a very distinct refractive 
 nucleus. The nerve-fibres are extremely delicate threads, which 
 make up the nerves and most of the nerve-ring. They are con- 
 tinuous on the one hand with the processes of the nerve-cells, on 
 the other with the various organs of the body. 
 
 The nerve-cells are connected with one another by means of 
 
 their processes. 
 
 
 
 DEVELOPMENT (Fig. 8). 
 
 The life-history of the Liver-fluke, like that of many other 
 parasites, exemplifies alternation of generations, a phenomenon 
 far less general in the case of animals than in the case of plants. 
 
 From the egg a young fluke does not proceed direct, but a 
 number of asexual stages i.e., forms capable of asexual multipli- 
 cation, intervene between it and the sexually mature adult. The 
 sequence of events is as follows: (1) A ciliated embryo escapes 
 from the egg and becomes parasitic within the lung-chamber of 
 a water-snail, there degenerating into (2) a shapeless sac or sporo- 
 cyst. (3) Within the sporocyst numerous cylindrical red-m are 
 produced by a process of internal budding, and these feed upon 
 the liver of the snail. There are usually several generations of 
 
36 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 recline, (4) A number of tadpole-shaped cercarice are formed in 
 the redia by budding. The cercaria makes its way out of the 
 siiail, and after losing its tail, encysts upon grass. (5) A young 
 fluke is formed within the cyst from the remains of the cercaria. 
 (6) If the cyst is now swallowed by a sheep the young fluke 
 emerges, makes its way up the bile-duct into the liver, and be- 
 comes sexually mature. 
 
 Cleavage (segmentation), which occurs within the oviduct, is 
 regular and complete. The ovum, together with a number of 
 yolk-cells, is enclosed in a horny shell to form the egg. This is 
 oval, with a smooth surface. The ovum lies at one end, and a 
 small circular area of the transparent shell is here marked off as 
 the lid or operculum. The further development occurs outside 
 the body of the sheep, the eggs passing to the exterior with the 
 excrement. It leads to the formation of a free embryo (a and b) t 
 which gradually comes to occupy most of the cavity of the egg, 
 as the yolk-cells are used up. When fully developed, a sudden 
 elongation of its body causes the operculurn to fly open, and it is 
 thus liberated. The body is somewhat conical, and its thick an- 
 terior end possesses a short retractile head-papilla. The external 
 layer of the body-wall is formed by flattened ectoderm cells which, 
 except on the head-papilla, bear long locomotor cilia. The 
 deeper layer of the body-wall is granular, with rudimentary 
 muscle-fibres, a pair of excretory funnels, and near the anterior 
 end a pair of eye-spots. These are two small refracting cells, 
 placed close together, and each containing a crescentic mass of 
 pigment. The two crescents placed back to back present a 
 somewhat X- shaped appearance. The eye-spots are imbedded 
 in an ectodermic thickening, the cerebral ganglion. The interior 
 of the body is mostly filled with rounded germinal-cells, but there 
 is also an oval mass of endoderm cells (b, D), representing a rudi- 
 mentary and mouthless gut (digestive tube). The germinal and 
 other cells which come between this and the ectoderm are collec- 
 tively known as the mesoderm (mesoblast). 
 
 If the free embryo finds itself in water or among damp herbage, 
 it moves actively about by means of its cilia, and should it meet 
 with a small water-snail, Limnaea truncatula, within about eight 
 hours development proceeds, but not otherwise. The head-papilla 
 is lengthened, and the embryo, revolving rapidly, bores by its 
 means into the snail. Within this host, generally in the lung- 
 
PLATYHELMIA. 
 
 37 
 
 chamber, it becomes a sporocyst. The ciliated ectoderm-cells 
 are lost, and the body gradually becomes an elongated and rather 
 irregular sac. Its wall is covered externally with a cuticle, below 
 which are feebly developed muscle-fibres, within which is a layer 
 of epithelium lining the body-cavity. Several excretory funnels 
 are present in the body-wall, and the eye-spots, separated from 
 each other, can still be recognised. The sporocyst may multiply 
 by transverse fission, and it produces asexually within it a number 
 
 Fig. 8. DEVELOPMENT OF DISTOMA (from Glaus, partly after Leuckart). 
 a, Free swimming ciliated embryo: b, the same contracted, with 
 rudimentary gut, D, germinal cells, Ov, and excretory funnels, Ex: 
 d, redia; 0, mouth; Ph, pharynx; D, intestine; Ex, excretory tubule ; 
 C, contained cercarise: e, free cercaria ; S, ventral sucker ; D, intestine; 
 Ex, excretory tubule; the little circles in the body represent cysto- 
 genous cells. 
 
 of the next, or redia stage, in the following manner : The body- 
 cavity contains a large number of germinal cells, partly those of 
 the free embryo, partly budded off from the lining epithelium, 
 lying loosely within it. These become aggregated into small 
 
38 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 solid masses, morulce, each of which becomes a gastrula (i.e., a 
 two-layered embryo with a mouth and rudimentary digestive 
 cavity), by an inpushing or imagination of cells on one side. 
 This becomes a redia, which breaks through the wall of the 
 sporocyst, the ruptured place afterwards closing up. 
 
 Redia (d). Body elongated and cylindrical. Near the anterior 
 end is a thickened ring or " collar," while not far from the pos- 
 terior end a pair of blunt processes project, one on each side. 
 The body wall has a structure similar to that of the sporocyst, 
 but the muscle is better developed. A mouth (0) is present at 
 the anterior end of the body, which leads into a muscular pharynx 
 (Ph). This is continued into a simple digestive sac (D). Branched 
 excretory trunks (Ex) commencing in ciliated funnels are pre- 
 sent. 
 
 The redia wanders over the body of the snail and feeds upon 
 its tissues, especially the liver. The posterior processes act as 
 foot-stumps, and the collar serves as a relatively fixed point upon 
 which the anterior end can move when feeding. Within the 
 body-cavity, daughter ^redice, or the next, cercaria stage (c), may 
 be developed, the former only in warm weather. In either case 
 some of the epithelial cells lining the body-cavity enlarge and 
 segment to produce morulse, which become gastrulse, and grad- 
 ually assume the form of daughter-redia3, or cercarise, which 
 escape by a special birth-opening behind the collar. 
 
 The Free Cercaria (e) resembles a minute tadpole. It has a 
 rounded flattened body armed anteriorly with minute spines, and 
 possessing anterior and ventral (S) suckers, and a muscular tail. 
 The body-wall contains numerous large granular lime-secreting 
 cells (cystogenous cells). A mouth, pharynx, gullet, and simple 
 forked intestine (D) are present, as well as excretory organs (Ex). 
 The cercaria makes its way out of the snail, loses its tail, and 
 attaches itself to a grass-stem, the cystogenous cells pouring out 
 a secretion which hardens into a bright white cyst, within which 
 it develops into a young fluke. If this encysted stage is swal- 
 lowed by a sheep, the gastric juice dissolves the cyst, and the 
 young fluke makes its way up the bile duct into the liver, there 
 becoming sexually mature in about six weeks. It is worthy of 
 remark that the adult sexual stage lives in the higher vertebrate 
 host, where it has a better chance of being preserved. 
 
PLATYHELMIA. 39 
 
 The following table summarizes the succession of stages: 
 1. Sexiial Fluke 
 
 ~^r 
 
 In liver of sheep,- <fcc.) 
 
 ^^ce s 
 "~^^^~--~- 
 
 5. Cercaria 
 (first free, then 
 encysted on grass). 
 produces 
 4. Redia 
 
 produces 
 
 2. Free Embryo. 
 | 1 develops 
 
 r m 
 
 3. Srorocvsfc 
 
 (in Limnaea truncatula, <.- (in Limnaea truncatula, 
 
 may produce may produce fresh 
 
 daughter -redice). sporocysts by fission). 
 
 Further Remarks on Flukes. 
 
 "Alternation of Generations" includes a number of by no means equi- 
 valent cases. One of the simplest is that described (p. 27) for certain 
 Hydrozoa, where an asexual hydroid (A) produces a sexual medusa (S) by 
 budding or fission. The sequence is AS, AS, &e., and this simple alterna- 
 tion of asexual and sexual stages may be termed metagenesis. The 
 "internal budding" by which, in the Liver-fluke, redia and cercaria are 
 produced is not, strictly speaking, an asexual process, nor, on the other 
 hand, is it a normal sexual process. The germinal cells appear to be pre- 
 cociously formed ova which can develop without fertilization (partheno- 
 genetically). Such an alternation of normal sexual reproduction with 
 parthenogenesis may be termed heterogamy. Writing S for the sexual 
 fluke, s 1 for the sporocyst, and s 2 for the redia, this particular instance, 
 reduced to its simplest form is s 1 s 2 S, s 1 s 2 S, &c. The ciliated embryo 
 is included in the s 1 , since it develops into the sporocyst, and similarly the 
 cercaria is merged in the S. 
 
 D. hepaticum is but infrequently found parasitic in man, a far more 
 important fluke, from a medical point of view, being D. hsematobium 
 (Bilharzia), which chiefly occurs in Egypt, Abyssinia, and S. Africa. It 
 infests the portal vein and its branches, and is remarkable among flukes in 
 having the sexes separate. The male is elongated and worm-like ; upon its 
 ventral surface is a groove in which the similarly shaped female is carried. 
 Life-history unknown. 
 
 6. TJENIA (The tapeworm). 
 
 Tapeworms are endoparasites, nearly all of which, when sexually 
 mature, inhabit the intestines of vertebrate animals. One of the 
 best known types is TsGnia sol in m, the Common Tapeworm, 
 which during the early stages of its existence is found in the 
 muscles of the pig (intermediate host), and, when mature, in the 
 small intestine of man (final host). 
 
40 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 The tapeworm is bilaterally symmetrical and made up (c/.Fig. 9) 
 of a minute scolex (head and neck), about ^ of an inch long, and 
 
 a body some six to ten feet in length, consisting of 800 to 900 
 joints (proglottides), which near the scolex are extremely small 
 
PLATYHELMIA. 41 
 
 and narrow, while at the other extremity they attain the length 
 of half an inch and about two-thirds that breadth. The scolex 
 is slightly, the proglottides very much flattened dorso-ventrally, 
 but there is no obvious difference between the dorsal and ventral 
 surfaces. The somewhat pear-shaped scolex bears four muscular 
 suckers on its broadest part, and at its free head-end there is a 
 round projection (the rostellum), in which are imbedded some 
 twenty-four chitinous hooks, arranged in a double circlet. By 
 means of these hooks and suckers the tapeworm firmly fixes 
 itself to the wall of the intestine. The difference in size between 
 the proglottides is accounted for by the fact that they are not all 
 of the same age, those next the scolex being youngest. In fact, 
 during the life of the scolex, new joints are continually being 
 developed by the alternate constriction and growth of its narrow 
 neck-end. A proglottis taken from about the middle of the 
 body will be found to possess a complicated set of hermaphrodite 
 reproductive organs, while the oldest proglottides are full of eggs 
 containing embryos. About the middle of one edge of a proglottis 
 is seen a small elevation, the genital papilla. These papillaB are 
 alternately right and left in successive proglottides. As new 
 joints are developed at the head-end old ones become detached 
 and pass out of the body of the host. No sexual organs are 
 found in the scolex, which is often regarded as an asexual indi- 
 vidual from which, by means of budding, a chain of sexual 
 individuals (proglottides) arise. It is, however, more likely 
 that the entire worm is a single individual. 
 
 The tapeworm is entirely devoid of digestive organs, its food 
 consisting of the highly nutritious ready digested material with 
 which it is surrounded, and which can readily diffuse into its 
 body. Although the animal is invested by a complex four- 
 layered cuticle this does not prevent such diffusion, as the two 
 outer layers are traversed by numerous pores. Below the cuticle 
 there is an epidermis composed of a single layer of spindle-shaped 
 cells. The hooks in the head are cuticular thickenings. 
 
 Excretory Organs are present similar to those found in the 
 Liver-fluke. Like the other internal structures these are imbedded 
 in a mass of parenchyma, which serves as a kind of packing-tissue 
 and is made up of variously shaped cells and a granular matrix 
 through which detached nuclei, fat-globules, and calcareous par- 
 ticles are scattered. A main excretory tube runs along each side 
 
42 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 of the body (Fig. 10), not far from its margin, and is connected 
 with its fellow in the head and also by a transverse commissure 
 running across each proglottis near its posterior side. In the 
 young tapeworm, before any proglottides have been detached, the 
 two excretory trunks converge posteriorly and pass to a vesicle 
 which opens to the exterior by a terminal pore. Numerous 
 delicate excretory tubules appear to be present in the parenchyma, 
 and these communicate on the one hand with the main trunks, 
 while on the other they terminate in flame-cells, which probably 
 
 ul. 
 
 Fig. 10. TAPEWORM (after Sommer). Enlarged. Proglottis of T<rnia 
 mediocanel/ata, with developed sexual organs. t, Spermaries (testes) ; 
 v.d, spermiduct (vas deferens) ; p, penis, contained in cirrus sac ; 
 ov, ovary ; y.rj, yolk gland ; sh.g, shell gland ; lit, uterus ; sp, spermo- 
 theca ; v, vagina ; g. a, genital atrium ; ex, main excretory tube, with 
 valves, v; n, lateral nerve-cord. 
 
 communicate with minute spaces in the tissues. These spaces 
 collectively constitute a body-cavity. The main excretory trunks 
 possess valves by which the fluid they contain is prevented from 
 flowing along them towards the front end. Xanthin (C 5 H 4 N 4 O ) 
 and guanin (C 5 H 5 N 5 0) are said to occur in this fluid. 
 
 The complicated hermaphrodite reproductive system (Fig. 10) 
 of the tapeworm bears a general resemblance to that of the Liver- 
 fluke. (1) The male organs consist of an immense number of 
 
PLATYHELMIA. 43 
 
 minute rounded spermaries (f), from which proceed exceedingly 
 delicate ducts that by their continued union form a spermiduct (v.d). 
 This is continuous with a muscular, eversible penis (p) (cirrus), 
 contained in a cirrus-sac (c.s) and opening into a depression, the 
 genital atrium (g.a) which occupies the summit of the genital 
 papilla. 
 
 Each spermary essentially consists of germinal cells (sperm- 
 mother-cells) each of which produces a number of sperms. In 
 this process the nucleus divides repeatedly to form the heads of 
 the sperms, and their vibratile tails are then differentiated from 
 the protoplasm. (2) The female organs consist of two ovaries, 
 an oviduct, uterus, vagina with spermotheca, a yolk-gland, and a 
 shell-gland. 
 
 The ovaries (ov) are collections of much branched tubules situ- 
 ated in the posterior part of the proglottis. These tubules unite 
 to form an oviduct which communicates on the one hand with a 
 blindly ending tube, the uterus (ut), and on the other with a 
 vagina (v), dilated internally into a spermotheca (sp) and opening 
 into the genital atrium. The yolk-gland (yk) is a tubular network 
 situated behind the ovaries and opening into the oviduct, which 
 also receives in this region the numerous minute ducts of the 
 unicellular elements which make up the rounded shell-gland 
 (sh.g). 
 
 Self-fertilization appears to be the rule, and takes place, after 
 closure of the genital atrium, by contractions of the spermiduct 
 and penis the result being that sperms are forced through the 
 vagina to the spermotheca, and thence' to the oviduct, where they 
 meet with and fertilize the ova. Each fertilized ovum, together 
 with a number of yolk-cells, is surrounded by an egg-shell to 
 constitute an egg, and the eggs pass on to the uterus. 
 
 The tapeworm possesses considerable power of movement, being 
 able to elongate or shorten itself, raise or lower its hooks, and 
 attach or detach its suckers. The muscles by which these various 
 movements are made consist of (1) a superficial longitudinal 
 layer by which the body can be shortened, (2) transverse muscle- 
 bands situated more deeply and serving to elongate the body, 
 
 (3) dorso-ventral fibres by which the proglottides can be flattened, 
 
 (4) radial and circular muscles in the suckers, and (5) minute 
 elevator and depressor bands attached to the hooks. 
 
 The muscles are for the most part attached to the firm cuticle, 
 
44 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 and they are made up of exceedingly delicate muscle-cells which 
 are of considerable length and taper at both ends. 
 
 The nervous system of a tapeworm consists of two longitudinal 
 cords, one of which traverses each side of the body near its 
 margin (Fig. 10), and of a transverse brain-commissure by which 
 these two cords are connected in the head. Nerves run from the 
 commissure to the hooks, suckers, and other parts of the scolex. 
 Histologically the nervous system is essentially made up of nerve- 
 cells and nerve-fibres, the former of which are not limited to the 
 cerebral commissure. 
 
 DEVELOPMENT. 
 
 The very numerous eggs pass into the uterus, which, at first a 
 simple tube, becomes much branched (Fig. 9), and fills up the 
 greater part of the ripe proglottis, while at the same time the 
 remaining sexual organs gradually abort. 
 
 The minute oosperm first undergoes 
 complete cleavage, and then is gradu- 
 ally converted into a spherical six- 
 hooked embryo (Fig. 11), in the devel- 
 opment of which the yolk-cells enclosed 
 i in the e SS are gradually used up. 
 
 The ripe proglottides pass out of 
 the body of the host, and gradually 
 decay, the innumerable embryos con- 
 tained being thus liberated. If any 
 of these are now swallowed by a pig 
 (or other warm-blooded animal) the egg 
 shells are dissolved, and the embryos, 
 by means of their hooks, penetrate the 
 walls of the intestine and pass into 
 blood-vessels, being then carried in the 
 circulation to the muscles. In these they pass into the cysticercus 
 or bladder worm stage (Fig. 12), consisting of a fluid-filled vesicle, 
 (proscolex) into which a tapeworm-head (scolex) projects as a 
 hollow bud, the whole being surrounded by a firm cyst developed 
 from the surrounding tissue as a result of irritation. Develop- 
 ment proceeds no further in the pig, but if pork infested by these 
 cysts (" measly " pork) is taken into the stomach of a human 
 
 d 
 
 Fig. 11. TAPEWORM (from 
 Landois and Stirling). 
 Ripe egg from uterus of 
 Tsenia solium : a, albumin- 
 ous envelope; 6, remains 
 of yolk ; c, covering of 
 embryo ; d. embryo with 
 booklets. 
 
PLATYHELMIA. 45 
 
 being the cyst is dissolved, the scolex is everted (Fig. 13), and 
 the proscolex digested. The scolex then passes on into the in- 
 
 Fig. 12. TAPEWORM (from Landois and Stirling).- Cysticerci of Tsenia 
 solium removed from their cysts, (1) natural size, (2) magnified; a, 
 proscolex ; 6, proscolex with hooks and suckers, c. 
 
 testine, attaches itself by means of its hooks and suckers to the 
 mucous membrane, becomes solid, and develops a chain of pro- 
 glottides. The bladder worm was not at first known to be a stage 
 in the life-history of tapeworm, and hence received a special generic 
 
 Fig. 13. TAPEWORM (from Landois and Stirling). Cysticercus of Tsenia 
 solium with everted scolex : a, proscolex ; 6, head with hooks and 
 suckers ; c, neck. 
 
 name, Cysticercus, the particular one belonging to Taenia solium 
 being known as Cysticercus cellulosce. 
 
 Those who regard the tapeworm as an example of alternation 
 of generations, recognise three stages in its life-history, two 
 asexual (proscolex, A; scolex, A'), and one sexual (proglottis, S), 
 the cycle being A A 7 S. 
 
46 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Further Remarks on Tapeworms. 
 
 The following tapeworms are, next to T. solium, of most importance : 
 
 Name. 
 
 Intermediate Host 
 (sheltering Cysticercus). 
 
 Final Host 
 (sheltering adult). 
 
 Tcenia mediocanellata 
 (saginata). No hooks. 
 Very numerous pro- 
 glottides. 
 
 Ox. 
 
 Small intestine 
 of Man. 
 
 T. echinoc.occus. 
 Minute. Numerous 
 very small hooks. 
 Only three or four 
 proglottides. 
 
 Cysticercus (Echinococcus 
 veterinorum). Very large, 
 with numerous tapeworm 
 heads ; in man and domes- 
 tic animals. 
 
 Small intestine 
 of dog. 
 
 Bothrioceplialus latus. 
 Flat head ; no hooks ; 
 two adhesive grooves. 
 Very numerous broad 
 proglottides, with 
 ventral genital and 
 uterine openings. 
 
 Embryo ciliated, passes 
 into first int. host, and 
 thence to muscles of second 
 int. host (pike, or burbot). 
 
 Intestine of Man; 
 rarely cat or 
 dog- 
 
 Tcenia ccenurus. 
 24 to 32 small hooks. 
 Numerous proglot- 
 tides. 
 
 Cysticercus ( = Ccenurus 
 cerebralis) in brain of 
 sheep, causing "staggers." 
 
 Intestine of 
 sheep-dog. 
 
 T. serrata. 
 38 to 48 hooks of two 
 sizes. Numerous pro- 
 glottides, with promi- 
 nent posterior angles. 
 
 Cysticercus pisiformis. 
 Liver and mesentery of 
 rabbit. 
 
 Intestine of dog. 
 
 Certain tapeworms are known (parasitic when mature in the intestines 
 of fishes) which have no proglottides. The scolex in these cases pos- 
 sesses a set of hermaphrodite reproductive organs, and, in many respects, 
 is not unlike a fluke. 
 
NEMATHELMIA. 
 
 47 
 
 CHAPTER IV. NEMATHELMIA (Thread-worms). 
 7. ASCAEJS (The Round- worm). 
 
 THE large group of Nemathelmia or Thread-worms, includes both 
 free and endoparasitic forms. The latter are by far the more 
 numerous, and of these the most convenient type-genus is Ascaris 
 (the round-worm), one species of which A. lumbricoides infests 
 the small intestine of the human subject, while the much larger 
 A. megalocephala commonly occurs in the intestines of the horse. 
 The following description applies to both species, but when 
 measurements are given they refer to A. lumbricoides. 
 
 MORPHOLOGY AND 
 PHYSIOLOGY. 
 
 1. External Characters (Figs. 1 4 
 and 15). The bilaterally symmet- 
 rical body is cylindrical and tapers 
 to a blunt point at each end. The 
 dorsal and ventral surfaces are 
 much alike. Thread -worms are 
 not, as a rule, hermaphrodite, and 
 in Ascaris the two sexes are readily 
 distinguishable, for the male is 
 not only smaller than the female 
 ( $ about 6 inches, $ about 8 
 inches long), but the posterior end 
 of its body is sharply bent up on 
 the ventral side (Fig. 15). 
 
 The colour is whitish, and in 
 the fresh condition the worm is 
 somewhat translucent, there being, 
 however, four more opaque longi- 
 tudinal streaks, named from their 
 relative positions the dorsal, ven- 
 tral, and lateral lines. The mouth, 
 situated at the anterior end, is 
 guarded by three projecting lips, one of which is dorsal, while 
 the other two meet together in the mid-ventral line. The gut 
 lias also a posterior opening, readily seen as a ventral slit, not 
 
 Fig. 14 ASCARIS. a, Female 
 specimen of A. lumbricoides; 
 b, head ; c, egg. From v. Jaksch 
 (Clin. Diagnosis). 
 
48 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 far from the hind end of the body. This aperture is termed 
 anus in the female, but cloacal opening in the male, because it is 
 common to the digestive and reproductive organs. The female 
 possesses a rounded genital aperture, situated in the mid-ventral 
 line about one-third of the way back. In both sexes there is a 
 minute excretory pore, placed mid-ventrally not far from the front 
 end. 
 
 2. The body- wall (Fig. 1 5) consists of a firm, chitinous several- 
 layered cuticle, covering an epidermis, internal to which is a layer 
 of longitudinally directed muscle-cells. 
 
 In a young specimen the cuticle is thin and the underlying 
 epidermis a distinctly cellular layer, but in the adult the formation 
 of a thick complex cuticle (c) seems to have caused degeneration 
 in the epidermis (ep\ which is then a thin granular stratum 
 through which numerous nuclei are scattered, and which is tra- 
 versed by gelatinous fibres. It is, however, much thickened mid- 
 dorsally, mid-ventrally, and, especially, laterally, to form the 
 dorsal (d.F), ventral (v.l), and lateral lines (1.1) to which reference 
 has already been made. Each of these is lined by a layer of 
 cuticle which is folded in so as to nearly divide the line into two. 
 
 The muscle-layer is divided into four parts by the epidermal 
 lines, and is made up of flat muscle-cells. Each of these is about 
 i of an inch long, and consists of a transversely striated contractile 
 fibre, internal to which is a nucleated protoplasmic part produced 
 into a number of threads. The cell is directed longitudinally, 
 with its fibre closely attached to the epidermis, its protoplasm 
 projecting 'into the body-cavity, and its flat sides facing adjacent 
 muscle-cells. The thread-like internal processes rim to the dorsal 
 line in the upper half of the body, and in the lower half of the 
 body to the ventral line. 
 
 3. The Digestive Organs (Fig. 15) consist of a narrow tube 
 which runs straight from mouth to anus or cloacal aperture. 
 This alimentary canal or gut is divided into three well-marked 
 regions (1) the fore-gut (stomodseum), (2) mid-gut (mesenteron), 
 and (3) hind-gut (proctodseum). The essential difference between 
 these is their mode of origin. In the course of development 
 (1) and (3) are formed as infoldings or in-pushings from the 
 exterior, and are therefore lined by ectoderm, while (2) is lined 
 by endoderm. 
 
 The fore-gut consists of a thick-walled gullet (oesophagus) into 
 
NEMATHELMIA. 49 
 
 which the mouth opens. Its wall, starting from the inside, is 
 made up of (a) a thick cuticle, and (b) a layer of epithelium, 
 continuous respectively with cuticle and epidermis of body-wall, 
 while outside these is (c) a muscular layer, the cells of which are 
 radially arranged. The gullet is about J of an inch long, and is 
 sharply marked off by a constriction from the mid-gut. This, 
 consists of an intestine, somewhat flattened dorso-ventrally, and 
 with an exceedingly thin wall made up of a single layer of 
 columnar epithelial cells, lined by a thin cuticle and covered 
 externally by a structureless membrane. The intestine passes 
 into a short hind-gut or rectum, the walls of which are thickened 
 and resemble those of the gullet in structure. In the male, the 
 terminal part of the rectum is a cloaca, since it receives the 
 genital duct. 
 
 A definite body-cavity is found outside the wall of the gut, but 
 it is for the most part reduced to a system of narrow spaces by 
 the projecting parts of the muscle-cells. The body-cavity contains 
 a clear albuminous perivisceral fluid. 
 
 Ascaris lives, for the most part, in the small intestine, and is 
 consequently surrounded by food much of which is digested i.e., 
 in a dissolved or finely-divided state. The gullet acts as a kind 
 of suction-pump, its radial muscle-fibres causing enlargement of 
 its cavity, when food rushes into it, after which the elasticity of 
 the cuticular lining comes into play, and, the lips being approxi- 
 mated, drives the food into the intestine. Here the digested 
 part of it diffuses into the perivisceral fluid. There is no special 
 provision for setting up currents in this, but the general move- 
 ments of the body effect an indefinite kind of circulation. 
 
 4. Excretory Organs are represented by a narrow tube, imbedded 
 in each lateral line (Fig. 15), and ending blindly behind, while the 
 two tubes unite anteriorly to form an unpaired portion which 
 opens by the excretory pore. 
 
 5. Reproductive Organs (Fig. 15). (1) The male organs chiefly 
 consist of a much convoluted tube, some seven or eight times the 
 length of the body, ending blindly at one end and opening by 
 the other end into the ventral side of the cloaca. The greater 
 part of this tube is very slender and constitutes the spermary, which 
 merges into a much shorter thicker portion, the vesicula seminalis, 
 and this again into an extremely short and narrow ejaculatory 
 duct, the walls of which are very muscular. 
 
 2 4 
 
re' so 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Fig. 15. _ ASCARIS ( A, B, C, D, H, a, c, K, G, after Leuckart; E, mainly 
 after Vogt and Yung ; H, b, after Van Beneden ; L, after Butschli). 
 A-D (enlarged), dorsal, ventral, and front views of anterior end, and 
 side view of posterior end of $ ; d.lp and Lip, dorsal and lateral lips, 
 possessing tactile papillae, and surrounding mouth, m; d.l, dorsal line ; 
 ex, excretory pore ; sp y copulatory spicules. E, Part of transverse 
 section of $ , much enlarged ; c, cuticle ; ep, epidermis, thickened into 
 
NEMATHELMIA. 51 
 
 The spermary is lined by nucleated protoplasm, and its cavity is 
 traversed by a cord or rachis from which mother-sperm-cells arise. 
 Each of these divides into two, and each of the halves by further 
 division produces a group of four cells (spermatocytes) which 
 divide once more. Of the eight cells thus originated four are 
 small and four large. The former are in the centre of the group 
 and constitute a sperm-blastophor, the latter are external and 
 become sperms. At first the sperms are spherical, but after 
 transfer to the female become conoidal. They never assume the 
 tadpole-shape seen in so many other cases. The basalpart of the 
 conoidal sperm is protoplasmic and nucleated, while the narrow 
 part is a highly refractive " cap " probably composed of nutritive 
 material analogous to yolk, and covered by a layer of protoplasm 
 external to which is a firm membrane. The consecutive stages 
 in sperm-development (spermatogenesis) can be easily followed 
 in a single spermary by examining its successive portions. 
 
 Accessory male organs are present in the form of two curved 
 chitinous spicules which are contained in a pouch that opens 
 dorsally into tlie cloaca. These spicules can be protruded and 
 retracted by special muscles. 
 
 The vesicula seminalis serves for the storage of sperms, and, 
 by the contraction of the muscular walls which it and the ejacu- 
 latory duct possess, sperms can be ejected into the vagina of the 
 female, this process being aided by the copulatory spicules. 
 
 dorsal line (d.l) traversed by dorsal nerve (d.n), ventral line (v.l) 
 traversed by ventral nerve (v.n), and lateral line (LI) traversed by 
 excretory tube (ex) and strengthened by internal cuticular thickening ; 
 m, layer of muscle-cells, with striated part external and protoplasmic 
 part internal, the oblique lines represent processes of the latter running 
 to median lines ; i, intestine ; ov, ovary, traversed by rachis bearing 
 germ-cells ; ut, ut, uteri. F, Female Ascaris opened from ventral side, 
 and reproductive organs of left side cut short (semidiagrammatic) ; 
 ov, right ovary ; od, right oviduct ; ut, ut, uteri ; v, vagina ; i, intestine ; 
 l.l, lateral line. G, Posterior part of $ reproductive organs, longi- 
 tudinally bisected (enlarged) ; cl, cloacal opening ; ej, ejaculatory duct ; 
 sp, spicule in sac ; r, rectum. H, Stages in sperm-development (much 
 -enlarged) ; a, part of rachis, with mother-sperm-cells ; b, group of four 
 spermatocytes, surrounding a four-celled sperm-blastophor ; c, a sperm, 
 nucleus below and refractile "cap" above. K, A muscle-cell (much 
 enlarged) ; /, contractile fibrous outer part, inner protoplasmic (dotted) 
 part, with nucleus (n), and processes (pr). L, Diagram of nervous 
 system ; v.g, ventral ganglion ; l.g, lateral ganglion ; a. g, anal ganglion ; 
 l.n, lateral nerve ; d.n, dorsal nerve ; v.n, ventral nerve; co, commissural 
 nerves. 
 
52 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 (2) The female organs consist of two convoluted tubes, ten 
 times the length of the body, which unite to form a short 
 unpaired section that opens to the exterior. 
 
 Three regions are distinguishable in each tube, ovary, oviduct, 
 and uterus, while the unpaired part is a vagina. The ovary is ana- 
 logous in structure to the spermary, like it being traversed by a 
 rachis, from which in this case ova arise.. The mature ovum is of 
 ovoid shape, invested by a delicate vitelline membrane except at 
 one point (the micropyle), and consisting of vitellus (protoplasm) 
 with numerous contained yolk particles, nucleus (germinal vesicle), 
 and nucleolus (germinal spot). The wall of the oviduct contains 
 a muscle layer, and so does that of the much wider uterus, which 
 also possesses a lining raised into numerous longitudinal ridges. 
 The wall of the narrower vagina contains internal circular and 
 external longitudinal muscle-layers. 
 
 Ascaris megalocephala presents special facilities for the study 
 of ovum-development (oogenesis) and fertilization, since a single 
 female specimen furnishes all the various stages. 
 
 The sperms, ejected into the vagina, crawl by amoeboid move- 
 ments to the upper ends of the uteri, where they meet and unite 
 with the mature ova. In their upward course the sperms pass 
 along the grooves between the ridges into which the uterine 
 lining is raised, and so escape, being swept back by the descending 
 current of ova, The fertilized ova are surrounded by thick egg- 
 shells secreted by the glandular lining of the uteri, and also by 
 firm membranes developed within the shell by the oosperms 
 themselves. 
 
 6. The Nervous System (Fig. 15) is made up of a ring, which 
 closely surrounds the anterior part of the gullet, and gives off 
 ill-defined longitudinal nerves, six in front and six behind. Two 
 of the former (the largest) run in the lateral lines, and the rest 
 near the median lines, one of the latter is dorsal, one ventral, 
 while the others are sublateral and do not extend far back. The 
 dorsal and ventral nerves are connected by a number of trans- 
 verse commissures. The circumoesophageal ring is somewhat 
 swollen at the origins of the lateral and ventral nerves to form 
 two lateral ganglia and a ventral ganglion. There is also a small 
 anal ganglion in front of the anus (or cloacal aperture). The 
 ganglion-cells are most abundant in these ganglia, but are not 
 limited to them. 
 
NEMATHELMIA. 
 
 53 
 
 7. Sense Organs are only represented by tactile papilla, in which 
 nerves terminate. There are two of these on the dorsal lip, one 
 on each ventral lip, and others near the anus (or cloacal aper- 
 ture). 
 
 LIFE-HISTORY. 
 
 In both Ascaris lumbricoides and A. megalocephala the eggs pass 
 out of the intestine of the host, and embryos develop within 
 them which may be liberated on damp soil, &c. Infection results 
 from the swallowing of these eggs or embryos. A. lumbricoides, 
 however, may perhaps pass into an intermediate host, Julus 
 guttulatus, a small millipede. 
 
 Other Nemathelmia. 
 
 Oxyuris Vermicularis (the thread-worm) is probably the commonest 
 parasite of the kind found in the human subject. It occurs throughout the 
 
 Fig. 16. OXYURIS (from von 
 Jaksch). a, Head; b, female; 
 ' c, male ; d, eggs. 
 
 Fig. 17. TRICHINA (from von 
 Jaksch). a, Male ; b, female ; 
 c, encysted young. 
 
54 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 large intestine, especially in children, its head-quarters being the caecum. 
 The female is rather less than 4 an inch long, and the male about half that 
 length (Fig. 16). The eggs, which are laid in an advanced state of develop- 
 ment, are passed out of the body of the host in vast numbers. There is no 
 intermediate host, and infection is easy, while it is an unusually difficult 
 parasite to get rid of, as its numbers are kept up by self-infection. 
 
 Trichina spiralis (Fig. 17) is a minute parasite ( $ i\ inch, $ ^ inch 
 long), the adult sexual stage of which occurs in the intestines of vertebrates, 
 especially rat, pig, and man. The young are born alive, bore into the wall 
 of gut where they enter blood-vessels, and thus reach the muscles within 
 which they encyst. Infection is caused in the human subject by the eating 
 of "trichinized" pork (i.e., pork containing encysted trichina?) which has 
 not been sufficiently cooked. 
 
 CHAPTER V. ANNELIDA (Segmented Worms). 
 8. LUMBRICUS (Earthworm). 
 
 IN this country there are several species of Earthworm, which 
 differ from one another in comparatively minor details. The 
 largest is Lwribricus herculeus. It and the other kinds are found 
 in damp earth, &c., in which they burrow. The variations in 
 size are very considerable. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The body is much elongated, and 
 sub-cylindrical. The hinder part is somewhat flattened from 
 above downwards. As in crawling animals generally the sym- 
 metry is bilateral, and the dorsal surface is readily distinguishable 
 by its dark-reddish colour from the paler ventral surface. The 
 body is segmented, that is, made up of a series of transverse rings 
 or segments (metameres). These are very numerous (as many as 
 150), and vary much in size. They are largest at the anterior 
 end, where also the shallow grooves, of which one (or more) 
 encircles each segment, are most evident. The front end of the 
 body tapers to a blunt point, the apex of which is formed by the 
 small upper Up (prostomium). This overhangs the transversely 
 crescentic mouth which is mainly bounded by the first or mouth- 
 
ANNELIDA. 55 
 
 segment (peristomium). A small vertical oval opening, the anus, 
 is seen at the posterior end of the body. 
 
 The eleventh, like all succeeding segments, has a minute 
 median dorsal pore, which communicates with the body-cavity, 
 and is placed in the groove separating the segment from the one 
 in front of it. Every segment, except the first three and the 
 last, possesses a pair of extremely small excretory apertures on its 
 ventral surface. 
 
 The worm is hermaphrodite, and the openings of its repro- 
 ductive organs are found on certain of the anterior segments. 
 The dorsal and lateral regions of some of the segments between 
 29 and 36 inclusive (in L. herculeus, 32-37 inclusive) are thick- 
 ened into a band, the clitellum, which varies in size according to 
 the sexual condition. 
 
 Eunning along each side of the body are two double rows of 
 minute, backwardly directed bristles, setce, which can be readily 
 felt by drawing a worm backwards between the fingers. One 
 row is lateral and placed where the pigment of the dorsal surface 
 shades off, the other ventral. Each segment, therefore, except 
 the first few and sometimes the last few, possesses eight setae. 
 
 2. Skin. The body is covered by cuticular and epidermal 
 layers, internal to which come the muscles of the body-wall. 
 The cuticle is a very thin iridescent membrane, traversed by 
 numerous pores and of chitinous nature. It is secreted by the 
 underlying epidermis, which, except in the clitellum, is made up 
 of a single layer of nucleated columnar cells, many of which 
 are unicellular glands, of the type known as goblet-cells. These 
 are oval, and filled with liquid secreted by the cell-protoplasm. 
 The epidermis also lines deep narrow pouches (setigerous sacs), in 
 which are secreted the hard curved setae, which project at the 
 surface for only about one-fifth of their length. Each sac contains 
 one bristle, and when this falls out it is replaced by another 
 developed in the same sac. Muscular bands pass from the sacs 
 to the body-wall. The ventral setae of the genital and clitellar 
 regions are very slender. In the former region some of the 
 ventral setigerous sacs are glandular and much enlarged (capsul- 
 ogenous glands). 
 
 The epidermis is much thickened and very glandular in the 
 clitellum, which also contains a network of blood-vessels. 
 
 3. Digestive Organs (Fig. 18, A). The alimentary canal or gut 
 
56 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 is a straight tube, of varying calibre, traversing the whole length 
 ofjthe body, and separated from the body-wall by a spacious 
 
 A B 
 
 Fig. 18. DIGESTIVE AND CIRCULATORY ORGANS AND NERVOUS SYSTEM 
 OF EARTHWORM. A, Digestive and circulatory organs; b.p, buccal 
 pouch ; ph, pharynx ; >, oesophagus ; ce.gl, O3sophageal pouches and 
 calciferous glands; cr, crop; gz, gizzard; i, intestine; c.g, cerebral 
 ganglia; A, hearts; d.v, dorsal vessel. B, Nervous system ; c.g', cerebral 
 ganglia; c.c, circumcesophageal commissure; g.g, ganglia of ventral 
 cord; n, nerves, from ganglia; n', nerves, from between ganglia; *//, 
 sympathetic nerves. 
 
 or body-cavity, which is divided into compartments corre- 
 sponding to the segments, and separated imperfectly from one 
 another by thin transverse partitions, the mesenteric septa, which 
 are perforated below. These septa are firmly united to the gut, 
 
ANNELIDA. 57. 
 
 which they hold in place. Fore-gut (buccal pouch, pharynx), 
 mid-gut (gullet, crop, gizzard, intestine), and hind-gut (rectum) 
 are distinguishable. 
 
 The mouth, for which the prostomium and peristomium form 
 upper and lower lips, leads into a small, thick-walled eversible 
 buccal pouch (b.p). This is connected by muscle-fibres with the 
 wall of the body in front of it. The walls of the mouth-cavity 
 contained in the pouch are raised into numerous folds. Next 
 follows the oval pharynx (ph) which is placed in segments 3-6. 
 It is very thick- walled, and connected by numerous retractor 
 muscle -fibres with the body- wall. The posterior end of the 
 pharynx is continued into the tubular gullet or cesophagus (ce) 
 which occupies segments 7-14, and bulges out slightly in each 
 of them. Three pairs of swellings (ce.gl) are to be seen on the 
 sides of the gullet in segments 10, 11, and 12 respectively. The 
 anterior pair (oesophageal pouches) are outgrowths from the 
 gullet, while the others (oesophageal or calciferous glands) are 
 glandular thickenings in which carbonate of lime is secreted. 
 The calciferous glands contain a number of small cavities, which 
 communicate with the oesophageal pouches. In 13 to 16, the 
 oesophagus expands into a rounded chamber, the crop (cr), with 
 rather thicker walls. Behind this comes the thick-walled gizzard 
 (gz) of similar shape, extending back to about segment 1 9. The 
 rest of the alimentary canal is almost entirely formed by the 
 thin-walled intestine (i), which is dilated in each segment. Its 
 dorsal wall is pushed in, so to speak, and forms a thick, longitud- 
 inal ridge, the typhlosole, which projects into the intestinal cavity 
 from its dorsal side. Its surface is raised into transverse ridges. 
 The outside of the intestine is covered by a thin layer of yellowish- 
 brown cells (chloragogen cells), which also fill up the cavity of 
 the typhlosole, and form the so-called liver. The gut is com- 
 pleted by a very short thin-walled rectum which occupies the last 
 segment. 
 
 The alimentary canal is lined with simple columnar epithelium, 
 the surface of which, except in the intestine, is covered by a 
 cuticle that is especially thick and firm in the gizzard. The 
 glandular cells of the calciferous glands are of epithelial nature, 
 and so are a number of small glands which open into the pharynx. 
 A sub-epithelial layer follows, composed of connective-tissue, in 
 which is a network of blood-vessels. Externally is a muscular 
 
58 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 layer, composed of an internal sheet of circular, and external sheet 
 of longitudinal fibres. The muscle layer is thicker, and has a 
 more complicated arrangement in the pharynx, crop, and gizzard 
 than elsewhere. Outside the muscle there is a layer of delicate 
 flattened peritoneal epithelium. The " hepatic cells " are elon- 
 gated and fusiform, with well-marked nuclei, and granular proto- 
 plasm often containing concretions. They are closely connected 
 with the blood-vessels. 
 
 Earthworms live principally on vegetable food, but animal sub- 
 stances can be used as well. Much earth is swallowed by them, 
 chiefly for the sake of the contained organic matter, but also as a 
 means of excavating burrows. Darwin has shown " that in many 
 parts of England a weight of more than ten tons of dry earth 
 annually passes through their bodies, and is brought to the 
 surface on each acre of land." Pieces of leaf, &c., are partially 
 digested before being taken into the body by a fluid poured on to 
 them from the mouth, and apparently secreted by the pharyngeal 
 glands. Food is taken in by alternate dilatation and contraction 
 of the mouth, aided by a sucking action of the pharynx, and 
 organic acids contained in it are neutralized by the carbonate of 
 lime secreted in the calciferous glands.* 
 
 Food accumulates in the crop, and is then passed on to the 
 gizzard, where the contractions of that organ grind it up. This 
 process is largely helped by small stones which have been swal- 
 lowed and act as millstones. The contractions of the muscular 
 wall of the intestine cause the substances which enter it to be 
 passed slowly backwards. They are meanwhile subjected to -the 
 action of a digestive juice, similar to that poured from the mouth, 
 and probably secreted by the intestinal epithelium. This appa- 
 rently contains ferments^ which bring the starch and proteids 
 into a state of solution, the former being converted into grape- 
 sugar, the latter into peptones. Any fat swallowed is brought 
 into a very fine state of division i.e.. emulsified. The particular 
 ferments which bring about these changes can only work well 
 in an alkaline solution, hence the use of the eesophageal glands. 
 
 * This lime may also be regarded as an excretion. A superabundance of 
 it is taken in with the food, and is thus got rid of. 
 
 t Ferments are bodies which excite chemical changes in other bodies 
 without themselves entering into the reactions. They are (1) Living e.g., 
 Yeast and Bacteria; (2) Non-living e.g., digestive ferments, complex 
 nitrogenous bodies found in digestive fluids. 
 
ANNELIDA. 59 
 
 The undigested remnants are passed out from the anus as 
 cylindrical "worm-castings." These form little heaps on the 
 surface of the ground, and as they are composed of earth brought 
 from below, a mixing of soil is gradually effected. 
 
 The intestine, partly owing to the presence of the typhlosole, 
 offers a large absorbent surface to the digested materials. The 
 products of digestion readily pass into the blood-vessels ramifying 
 in the intestinal wall, and are thence distributed to the body at large, 
 
 4. Circulatory Organs (Fig. 1 8, A). These place the different 
 parts of the body in communication as regards oxygen and the 
 products of digestion and katabolism. They may be divided into 
 (1) Blood System, (2) Ccelom and Ccelomic Fluid. 
 
 (1) Blood System. This is made up of a closed series of 
 tubes containing bright red blood, in which are contained minute 
 colourless nucleated cells, the Hood-corpuscles. The red fluid in 
 which these are suspended is known as plasma. The blood, after 
 death, or on removal from the body, coagulates i.e., sets into a 
 jelly-like mass. There are five chief longitudinal vessels, a large 
 number of transverse vessels, and delicate capillary networks 
 which connect up the various branches. 
 
 Eunning in the median line on the dorsal side of he alimentary 
 canal, and visible through the skin in a fresh specimen, is the 
 dorsal vessel (d.v). This breaks up in front into a network of 
 small vessels on the pharynx. A similar ventral vessel runs 
 longitudinally below the alimentary canal. A longitudinal sub- 
 neural vessel runs below the ventral nerve-cord, and a small lateral 
 neural vessel on each side of it. These longitudinal trunks are 
 connected by transverse lateral vessels, of which the most important 
 are the hearts. These are six pairs of large lateral vessels in 
 segments 6-11, which connect the dorsal and ventral trunks, 
 and are closely attached to the anterior faces of the septa. The 
 typical arrangement of the transverse trunks in a segment of 
 the intestinal region is as follows : (a) A pair of parietal 
 (commissural) vessels, receiving numerous twigs from the body- 
 wall, connect the dorsal and sub-neural trunks; (b) The intestine 
 is supplied by numerous afferent branches from the ventral, 
 which break up into a network, from which the blood returns 
 by two efferent branches to the dorsal; (c) Each nephridium 
 possesses a very rich plexus of vessels, supplied by a branch 
 from the ventral and sending one to the corresponding parietal. 
 
60 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 A large lateral cesopliageal vessel runs along each side of the 
 gullet, opening into the dorsal vessel in segment 10, and return- 
 ing blood from the gullet and pharynx. 
 
 Course of the Circulation. The blood is kept circulating by 
 means of the hearts, which act as force pumps. Their walls are 
 muscular, and they contract rhythmically from above downwards, 
 the hinder ones contracting first. The large vessels also have 
 contractile walls by which the circulation is assisted. The blood 
 flows from back to front in the dorsal vessel, and the contrary 
 way in the ventral one. The parietal vessels return blood puri- 
 fied in the skin and nephridia to the dorsal vessels, which also 
 receives blood from the gut by means of the lateral cesopliageal 
 and efferent intestinal vessels. This blood passes forwards in the 
 dorsal vessel and through the hearts to the ventral vessels, in 
 which the blood flows backwards and passes by afferent trunks 
 to the gut, nephridia, and body-wall. 
 
 The delicate networks of capillary vessels which complete the 
 closed blood-system are of great physiological importance, since 
 their extremely thin walls allow of diffusion. In this way, for 
 example, the tissues are nourished. 
 
 There are no special organs of respiration and this function is 
 performed by the general surface of the body, the carbon dioxide 
 diffusing out of the blood-vessels underlying and penetrating the 
 skin, while oxygen diffuses into them. The red colour of the 
 blood is due to hemoglobin, a complex compound of carbon, 
 hydrogen, oxygen, nitrogen, sulphur, and iron, which enters into 
 loose combination with the oxygen taken into the body, readily 
 parting with it again to the tissues. 
 
 (2) Coelom and Coelomic Fluid. The coslom or body-cavity is 
 imperfectly separated into compartments by the septa, and com- 
 municates with the exterior by the dorsal pores, excretory tubes 
 (nephridia), and oviducts. It contains a milky coagulable coelomic 
 (peri visceral) fluid, in which are suspended numerous irregular 
 nucleated cells (ccelomic corpuscles), with granular protoplasm, 
 capable of amoeboid movements. The body-cavity is lined by 
 coelomic epithelium composed of a single layer of flattened 
 nucleated cells, from which these corpuscles are constantly being 
 budded off. 
 
 5. Excretory Organs. Each segment, with the exception of 
 the first three and the last, contains a pair of nephridia (segment*! 
 
ANNELIDA. 6 1 
 
 organs). Each nephridium is a very long convoluted tube, of 
 varying calibre in its different regions, attached by a membrane 
 to the back of the septum bounding the front of the segment, 
 and placing the coelom in communication with the exterior. It 
 is thrown into three main folds running parallel to the septum in 
 a vertical direction, and forming an internal short loop, a middle 
 long loop, and a wide external end loop. The nephridium com- 
 mences with a ciliated funnel which lies in the preceding segment. 
 The margin of the funnel is formed by a row of elongated ciliated 
 cells, and its back by a very large crescentic cell. The slit-like 
 internal opening (nephrostome) of the nephridium is situated 
 within the funnel. The rest of the tube is divided into four 
 sections : (1) An extremely long and delicate narrow section which 
 runs back from the funnel through the septum, round the short 
 loop, up and down one side of the long loop, and back round the 
 short loop, after which it passes into (2) a much wider middle 
 section, contained entirely in the long loop, and followed by (3) a 
 wide section, which begins with a dilated part, runs along one 
 side of the long loop, round the short loop, and across to the end 
 loop, where it is succeeded by (4) a much larger muscular section 
 ("bladder") which opens to the exterior by a small ventral 
 aperture, the nephridiopore. The greater part of the nephridium 
 (i.e., from the funnel to (4) ) is made up of tubular " drain-pipe 
 cells," placed end to end, and the cavity of this part is therefore 
 intracellular i.e., within and not between cells. The tubular cells 
 differ in size and character in the different regions of the neph- 
 ridium. 
 
 Cilia are found in parts of the narrow section and throughout 
 the middle section, while the cells of the middle and wide sections 
 are very large and full of excretory granules. The muscular 
 section is lined by cells (its cavity being therefore intercellular), 
 and its thick wall contains a network of muscle-fibres. 
 
 The nephridium possesses a very rich network of capillary 
 blood-vessels, supplied from the ventral vessel and returning its 
 blood into one of the parietals. 
 
 The nephridia are specially concerned with the excretion of 
 water and nitrogenous waste, the former entering them by the 
 ciliated funnels, and the latter being probably excreted by the 
 glandular drain-pipe cells of the middle and wide sections. It 
 is not unlikely that the chloragogenous cells have to do with 
 
<62 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 excretion, for they are closely connected with the blood-vessels, 
 resemble excretory cells in their granular character, and are known 
 to break down into the ccelom, the materials thus formed being 
 very probably got rid of by the nephridia. 
 
 The urine, as the excreted substances may be collectively 
 termed, passes down the nephridia by the action of the cilia, 
 and collecting in the dilated muscular section is expelled by its 
 contraction. 
 
 6. Reproductive Organs (Fig. 19). The Earthworm is herma- 
 phrodite, and its sexual organs vary much in size, according 
 to the time of year, being largest in the summer, which is the 
 breeding-season. The segments in which they are placed are 
 anterior to the clitellum. Their colour is white, and they lie 
 below and at the sides of the gut, in its oesophageal region. 
 
 (1) Male Organs. There are two pairs of minute flattened 
 spermaries (T), produced into finger-like processes behind. These 
 are attached, near the nerve-cord, to the back of the septa forming 
 the anterior boundaries of segments 10 and 11. In the sexually 
 mature state they project into the cavities of the seminal reser- 
 voirs. The most conspicuous parts of the male apparatus are the 
 vesiculce seminales, three pairs of large white pouches which may 
 completely overlap the oesophagus, and are situated in segments 
 9-12. The anterior pair (A) lie in segment 9, and are united 
 into a median seminal reservoir (B) in segment 10. This also 
 receives the middle (C) pair of vesiculse situated in segment 11, 
 while the posterior vesicular are situated in segment 12, and unite 
 into a similar reservoir in segment 1 1 . Projecting into the floor 
 of each reservoir is a pair of large plicated seminal funnels (S F) 
 turned towards the testes. From each funnel a delicate tube, the 
 vas efferens, proceeds, which, after forming a coil, takes a backward 
 course. The two vasa efferentia on each side unite together in 
 segment 12 into a straight tube, the s])ermidud (VD), which 
 passes back through segments 13 and 14 to open by the male 
 pore on segment 1 5, just external to the ventral setae. 
 
 The spermary may be regarded as a thickened and specialized 
 part of the epithelium lining the body-cavity. It is made up 
 of numerous germinal-cells which, as mother-sperm-cells, pass into 
 the vesicula3 seminales, the cavities of which are traversed by 
 numerous strands of connective tissue. In the interstices between 
 these the mother-sperm-cells undergo repeated division or seg- 
 
ANNELIDA. 
 
 63 
 
 mentation to produce sperm-morulcr, each of which contains a 
 central sperm-blastophor covered by numerous small cells, sperm- 
 atoci/tes, which become sperms. These possess a long cylindrical 
 
 Fig. 19. EARTHWORM (from Marshall and Hurst}. Plan of the reproduc- 
 tive organs as seen from above after removal of the alimentary canal. 
 The body-wall is pinned down flat. A, Anterior vesicula seminalis, 
 uniting with its fellow to form the anterior seminal reservoir (B) which 
 is cut open on one side to display an anterior spermary (testis) (T) and 
 an anterior seminal funnel. C, Middle vesicula opening into B. In 
 segment 12 is seen one of the posterior vesiculae, which unite to form 
 the posterior reservoir in 11. This is cut open to display a posterior 
 spermary (testis) and posterior seminal funnel (S F). VD, Vas deferens 
 or spermiduct ; 0, ovary ; D, oviduct ; 11, ootheca ; S, spermotheca ; 
 N, nerve-chain ; 9-15, ninth to fifteenth segments. 
 
64 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 head and vibratile tail. They remain for some time attached by 
 their heads to the blastophor, but are finally liberated.* 
 
 (2) Female Organs. The ovaries (0) are two pear-shaped 
 bodies, rather larger than the spermaries, and having a similar 
 position in segment 13. Their narrow ends are directed back- 
 wards. The oviducts (OD) are short, wide tubes, lying mainly in 
 segment 14, on the ventral side of which they open by the 
 female pores, much smaller than the male pores, but occupying a 
 similar position. Each oviduct ends internally in a funnel which 
 pierces the septum between segments 13 and 14, projecting into 
 the cavity of the former. The funnel communicates with a small 
 pouch-like ootheca (E,) (receptaculum ovorum), in which a few 
 ripe ova temporarily accumulate. The spermothecce (receptacula 
 seminis) are two pairs of rounded sacs, lying in segments 9 and 
 10 (S). They open laterally between segments 9 and 10, and 
 10 arid 11, just on a level with the lateral setae. 
 
 The ovaries consist of germinal cells which develop into ova. 
 Each ovary contains many ova in different stages of development, 
 the ripest being at the free end. The ovum is spherical in shape, 
 and covered externally by a delicate vitelline membrane. The 
 granular protoplasm contains a clear germinal vesicle, with germinal 
 spot. The ripe ova burst out of the ovary into the body-cavity r 
 and are taken up by the ciliated funnels of the oviducts. 
 
 Although the Earthworm is hermaphrodite, self-fertilization 
 does not occur. Two individuals copulate and fertilize each 
 other. This takes place on the surface of the ground during 
 the warm spring and summer months. The two. apply them- 
 selves by their ventral surfaces, their heads being in opposite 
 directions. Adhesion is effected by the slender genital setae, 
 the prominent ventral edges of the swollen clitella, and a firm 
 secretion of the clitella and capsulogenous glands. The sperms 
 pass back from the male pores of either worm to the spermo- 
 thecse of the other, along grooves visible at the time. They are 
 aggregated within the spermothecae into thread-like packets 
 (spermatophores), by means of a glutinous secretion. 
 
 The ova are laid in firm capsules, probably formed by the 
 hardening of a- fluid secreted by the clitellum. In L. hercukus 
 many ova are passed into each capsule, together with a few 
 
 * The contents of the vesiculoe commonly contain various stages in the life- 
 history of the Earthworm Gregarine, Monocystis lumbrici (see p. 17). 
 
ANNELIDA. 65 
 
 spermatophores (composed of sperms derived from another indi- 
 vidual) from the spermothecae. The egg-capsule or cocoon is 
 passed forwards over the front end of the worm, and cylindrical 
 to begin with immediately becomes spindle-shaped by closure of 
 its ends. The spermatophores break down within the capsule, 
 and the liberated sperms fertilize the ova, polar cells having pre- 
 viously been formed. 
 
 7. Muscular System. As in the Fluke, most of the muscle is 
 found in the body-wall. Underlying the skin is a continuous 
 circular layer in which the pigment that gives the dorsal surface 
 its characteristic tint is imbedded. Delicate bands, the protractor 
 muscles of the setae, pass from this layer to the inner ends of the 
 setigerous sacs. Beneath the circular layer is a longitudinal layer 
 of about the same thickness, subdivided into longitudinal bands, 
 a broad dorsal band between the two rows of lateral setae, a much 
 narrower ventral band between the ventral setse, a lateral band of 
 about the same width between the lateral and ventral setae on 
 either side, and finally four excessively thin strips (two dorso- 
 lateral and two ventro-lateral), one between the setigerous sacs 
 in each double row. Each band is made up of plates, perpen- 
 dicular to the circular layer, in which the fibres are arranged so 
 as to give a feather-like appearance in cross-section. Connected 
 with the longitudinal layer are delicate retractor muscles of the 
 setae, attached to the setigerous sacs where they reach the middle 
 of the circular layer. 
 
 The septa contain muscular fibres, imbedded in much connective- 
 tissue, and taking various directions. They are covered by the 
 peritoneal epithelium of the body-cavity, with which also the longi- 
 tudinal muscle layer is lined. 
 
 The muscle-fibres are very slender cells, united together by 
 their tapering ends. 
 
 In locomotion the circular layer contracts so as to advance the 
 front part of the body, and the hinder part is then dragged up by 
 contraction of the longitudinal layer. The reverse movement 
 can also be effected, and complex curves described. The setae 
 act as hold-fasts, their direction and amount of protrusion being 
 regulated by their retractor and protractor muscles. 
 
 8. The Nervous System (Fig. 20, B) consists of a ring encircling 
 the gut at the junction of the buccal pouch and pharynx, a ventral 
 cord, and numerous nerves. The dorsal side of the ring is thick - 
 2 5 
 
'66 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 ened into two cerebral ganglia (c.g, A and B), while its sides, the 
 connectives (cc), run downwards and backwards and unite together 
 to form the ventral cord. This dilates slightly into a ganglion (g) 
 in each segment, the ganglia being best marked in the posterior 
 part of the body. The double nature of the cord is indicated by 
 a longitudinal furrow running along its upper surface. 
 
 A nerve passes from each cerebral ganglion to the prostomium 
 and peristomium, numerous nerves run out from the first ventral 
 ganglion, while behind this there are typically three pairs of nerves 
 in each segment, two arising from its ganglion (ft), and one (septal 
 nerves) from the cord in front of this (n r ). 
 
 A number of delicate nerves pass from the inner sides of the 
 connectives to the pharynx, in the walls of which they form a 
 delicate ganglionated network. This arrangement is called the 
 sympathetic nervous system (sy). 
 
 The nervous system is essentially made up of nerve-cells and 
 nerve-fibres. In the nerve-ring and cord there is a very delicate 
 connective-tissue framework (neuroglia) in which these elements 
 are imbedded. The nerve-cells occupy the anterior part of the 
 cerebral ganglia and the under side of the ventral cord both in and 
 between the ganglia. The ventral cord is surrounded by a firm 
 muscular sheath in which the neural vessels run, and imbedded 
 in the dorsal part of the sheath there are three giant-fibres, which 
 perhaps have a supporting function, but in any case are modified 
 nerve-fibres. 
 
 The central organs certainly constitute a correlating apparatus, 
 but scarcely anything is known of their mode of action. 
 
 9. Special Sense Organs appear to be represented only by 
 "goblet-bodies," consisting of aggregates of slender epidermal 
 cells connected with nerve-fibres, and occurring on the prosto- 
 mium, peristomium, and, less abundantly, on the anterior segments. 
 The Earthworm is, however, by no means devoid of special senses. 
 The entire surface of its body is endowed with a delicate sense of 
 touch, while certain kinds of food (e.g., bits of onion) are specially 
 preferred and readily discovered, which seems to prove possession 
 of both smell and taste. The structure and position of the pro- 
 stomial and peristomial goblet-bodies indicate that these are the 
 special organs of taste and smell. Although earthworms possess 
 nothing that can be described as a definite sense of sight, they 
 are sensitive to intense light, which they shun, and thus escape 
 
ANNELIDA. 67 
 
 many enemies. The anterior part of the body is specially sensi- 
 tive to light, which perhaps, as Darwin suggested, passes through 
 the skin and acts directly on the cerebral ganglia. It has, however, 
 been stated that all the pigmented regions of the body are affected 
 by blue, violet, and ultra-violet rays. The sense of hearing is 
 entirely absent. 
 
 DEVELOPMENT (Fig. 20). 
 
 The egg-capsules of the Earthworm are deposited during spring 
 and summer in damp earth, a few inches from the surface. They 
 are olive-green in colour, spindle-shaped, and about J of an inch 
 long. Each capsule contains a mass of slimy albumen and several 
 eggs, of which, however, only one usually comes to maturity. 
 
 Fertilization takes place within the capsule, after which the 
 oosperm undergoes continued cell-division (cleavage, segmentation) 
 to form a hollow sphere (blastula, blastosphere) with a cellular 
 wall. The sphere is then converted into a double-walled bag or 
 gastrula by inpushing of its wall. The inner layer of the gastrula 
 is endoderm, the outer ectoderm. At the same time the third 
 germinal layer, mesoderm, begins to develop by division of two 
 large cells (mesoblasts) found near the posterior end of the body. 
 The embryo gradually becomes more and more elongated, the 
 various organs being at the same time differentiated from the 
 three germinal layers. The surrounding albumen is used as food, 
 and one embryo develops more rapidly than the others which 
 it utilizes in the same way. In the case of capsules which are 
 kept in the laboratory, hatching takes place in from two to three 
 weeks. 
 
 1. Cleavage (Segmentation). This is complete (holoblastic) 
 and irregular, the entire oosperm dividing, but the resultant cells 
 being of unequal size. The divisions take place in a regular way 
 (B, C) until a 7- or 8 -celled embryo is produced, consisting of 
 2 large, 2 medium-sized, and 3 or 4 (probably ectodermic) small 
 cells. Beyond this there seems to be no definite order. The com- 
 pletely segmented oosperm is a blastula (blastosphere) containing 
 a large segmentation-cavity (s.c) (blastocoele), bounded on one side by 
 small and on the other by large cells, which respectively become 
 ectoderm and endoderm (D, E, F). Two large cells (mesoblasts) 
 are also distinguishable (E, M) from which the whole of the 
 
68 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 mesoderm arises later on, and even during the blastula stage they 
 divide to produce mesodermic cells which partly block up the 
 blastoccele (F, m.s). 
 
 2. Gastrulation. This is effected on the third day by a modi- 
 fication of what is known in other more typical cases as emboly 
 or embolic invagination. This is a sort of inpushing, the nature 
 of which may be realised by taking one of the perforated india- 
 rubber balls used by small boys as squirts, and collapsing it so as 
 to form a double-walled cup. The earthworm blastula first of all 
 flattens (F), and becomes an oval plate, with an upper layer of 
 small cells (ec) constituting the ectoderm (epiblast) and a lower 
 layer of clear columnar cells (en) constituting the endoderm 
 (hypoblast). Mesoderm (mesoblast) is also present (ms). The 
 plate next becomes concave below, and its edges approach. 
 The embryo is now a gastrula (G, H, K) with an internal diges- 
 tive cavity, the arclienteron (ar), opening by a longitudinal ventral 
 slit, the blastopore. The embryo is elongated in the direction 
 which correspond to the long axis of the future worm, and the 
 two mesoblasts (M) are at its posterior end. In fact, bilateral 
 symmetry is well established. 
 
 Fig. 20. EARTHWORM DEVELOPMENT (after Wilson). Enlarged to various 
 scales. A, Unsegmented ovum, surrounded by the vitelline membrane, 
 with two cell-groups formed by division of polar cells. B, First 
 cleavage (in the plane of the polar cells). C, Six-celled stage. D, 
 Optical section of young blastula. E, Surface view of young blastula, 
 showing the two mesoblasts. F, Optical section of a flattening blastula, 
 seen from the side. G, Ventral view of early gastrula (anterior end 
 directed upwards), with wide blastopore. H, Similar view of rather 
 older gastrula, with slit-like blastopore. K, Left lateral view (in optical 
 section) of established gastrula, in which mesoderm bands have met 
 above mouth. L, Right lateral view (partly in optical section) of 
 embryo with established germinal bands and fore-gut. M, Ventral 
 view of same embryo. N, Transverse (slightly oblique) section of rather 
 younger embryo, cutting through germinal bands, the left neuroblast, 
 and one of the right nephroblasts. O, Right lateral view (in optical 
 section) of older living embryo, showing fore-gut, mid-gut, septa, 
 sections of body-cavity, and cerebral ganglia. P, Left lateral view of 
 embryo in middle of development, showing segments, prostomium, 
 head-cavity, nerve-ring and cord, setae, nephridia, and lateral vessel. 
 ar, Archenteron; c.g, cerebral ganglia; cce, ccelotn; d, septum; ec, 
 ectoderm; en, endoderm; l.v, lateral vessel; M, primary mesoblast; 
 m, mouth; ms, mesoderm (upper ms in O = migratory mesoderm budded 
 off from main band); N, nephroblast; Nb, neuroblast; n. c, neural cord 
 (nerve-cord in P) ; np, nephridia; np.c, nephric cords; ps, prostomium ; 
 S.c, segmentation cavity; st, fore-gut (stomodaBum). 
 
ANNELIDA. 
 
 69 
 
 4 C 
 
 n. 
 
 Fig. 20. 
 
70 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The blastopore immediately closes up except in front, where it 
 acts as a mouth, and at this stage the swallowing of albumen 
 begins, and the embryo becomes distended and thin-walled as a 
 result (L, 0). 
 
 3. Fate of the Germinal Layers. The ectoderm produces the 
 epidermis with its setigerous sacs, the nervous system, the neph- 
 ridia (except their funnels), and the epithelium lining fore- and 
 hind-guts. The mesoderm gives rise to nearly everything between 
 the epidermis and the epithelium of the gut, including circulatory 
 and reproductive organs, the funnels of the nephridia, and all the 
 muscular and connective tissue. The endodcrm originates the 
 epithelium of the mid-gut. 
 
 Ectoderm. The fore-gut is formed at a comparatively early 
 stage as an ingrowth of ectoderm (st) at the unclosed mouth-end 
 of the blastopore (L, M). Soon after gastrulation cilia are devel- 
 oped along a median ventral strip of the ectoderm, and by their 
 action cause the embryo to rotate in the surrounding albumen. 
 The fore-gut is also ciliated. Not long before hatching the hind- 
 gut is formed as a small ectodermic involution which soon meets 
 and fuses with the mid-gut. 
 
 At the time when the fore-gut is being formed a thickened 
 band can be made out running along each side of the body, and 
 known as a germinal "band. It is partly constituted by three 
 longitudinal rows of ectodermal cells, each of which is derived by 
 constant subdivision from a cell (teloblast) at its posterior end. 
 These rows and their teloblasts are at first superficial, but later 
 on sink in and are covered by other ectodermal cells. The middle 
 region of a fully developed germ-band (L, M, N) consists of three 
 layers 
 
 (a) Outer layer, of ordinary ectodermal cells. 
 
 (b) Middle layers, of cells derived from ectodermal teloblasts. 
 
 (c) Inner layer of mesoderm. 
 
 The internal teloblasts are known as neuroblasts (Nb), and the 
 neural cords (n.c) which they produce thicken and become the 
 right and left halves of the central nervous system, shifting down 
 and uniting ventrally to form the cord and uniting above the 
 mouth to form the nerve-ring (see P). The two external telo- 
 blasts on each side are termed nephroblasts (N), because the 
 nephridia (except funnels) grow out from the nephric cord (np.c) 
 which they originate. The two nephric cords on each side soon 
 
ANNELIDA. 71 
 
 unite together, and the setigerous sacs as well a*s the nephridia 
 grow out from the band thus formed. 
 
 Mesoderm. The whole of this is developed from the primary 
 mesoblasts (M). These lie behind the other teloblasts and give 
 rise to a mesodermal band (ms in K to 0) on each side which 
 forms the middle layer of the germinal bands. From the front 
 ends of these bands stellate cells bud off' in front and form a 
 mass above the mouth (see 0) by which the two bands are 
 connected together. Similar cells are budded off' in the trunk- 
 region, but these do not develop into any adult structures. 
 
 The mesodermic bands gradually broaden and thicken, their 
 posterior ends being smallest because they have only recently been 
 derived from the teloblasts. In each band a series of cavities 
 (cce) appear from before backwards. These become the sections 
 of the adult coelom and indicate the position of the future seg- 
 ments. Where the bands unite an unpaired "head-cavity" (P) 
 is developed. The mesoderm which forms the outer boundary 
 of each cavity gives rise to part of the body-wall, that making 
 up the inner boundary originates part of the gut-wall, while the 
 partitions between adjacent cavities become septa. 
 
 The mesodermal bands gradually get broader by the division 
 of their cells and unite together from before backwards, first 
 ventrally and then dorsally, making their way between the other 
 layers, and ultimately forming a continuous sheet of mesoderm. 
 The corresponding coelomic cavities of the two bands fuse com- 
 pletely together dorsally, but remain separated ventrally by a 
 thin mesentery. The blood-vessels are developed as spaces in 
 the mesoderm which at first (except in the case of the hearts) 
 have no proper walls of their own. The dorsal vessel has a 
 double origin, being formed from two lateral vessels (l.v in P) 
 which gradually shift upwards and fuse together. Each neph- 
 ridial funnel is formed by the subdivision of a large mesodermal 
 cell which soon becomes connected with an ingrowth from the 
 nephric band. 
 
 The endoderm becomes the lining of the mid-gut, including 
 the epithelial part of the cesophageal pouches and calciferous 
 glands. 
 
 Sexual Reproduction. 
 
 There is some difficulty in comparing the reproduction of unicellular 
 animals (Protozoa) and multicellular animals (Metazoa), because in the 
 
72 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 former case all the functions are performed by the same cell, while in 
 the latter there are special reproductive cells. The permanent conjugation 
 of Vorticella, however, where a small active microzoid unites with a larger 
 more passive macrozoid, appears to be equivalent to an act of sexual repro- 
 duction i.e., to the union of a male cell (sperm) with a female one (ovum). 
 The process in Vorticella is in reality a very complicated one, and the 
 paranuclei (micronuclei) are alone concerned in it. The ordinary nuclei 
 (macronuclei) appear to have as their function the regulation of nutrition. 
 In many free-swimming ciliated Protozoa "temporary" conjugation takes 
 place between two equal-sized individuals. They apply themselves closely 
 by their oral surfaces and exchange parts of their paranuclei, after which 
 separation takes place, the nuclear apparatus is reconstructed, and fission 
 is resumed. It has been demonstrated that, in ciliated Protozoa, this 
 process is necessary for the continuance of the species, as without it asexual 
 reproduction cannot take place beyond a certain number of generations. 
 In one of the simplest cases (Colpidium) the changes which take place in 
 the paranucleus are as follows: The division is always of the "indirect" 
 kind (mitosis, karyokinesis), and involves more than simple elongation, 
 constriction, and division; (1) Paranucleus divides into two, n 1 , n 1 , and 
 (2) these subdivide again n 2 , n 2 , n 2 , n 2 . (3) Of these four parts three are 
 absorbed by the protoplasm, while the fourth again divides into two, n 3 , n 3 . 
 (4) One of these migrates into the other individual and fuses with the cor- 
 responding part. (5) Each individual now contains a conjugation nucleus 
 [n 3 + n 3 ] formed by fusion of -|th of one paranucleus with ^th of the other. 
 This compound structure divides twice, two of the quarters passing to 
 one end and two to the other. Meanwhile the original nuclei have been 
 absorbed and the individuals have separated. Transverse fission now takes 
 place, the quarters above-mentioned becoming the nuclei and paranuclei 
 of the daughter forms. The complete process may be graphically repre- 
 sented as follows, where N = nucleus, n paranucleus, and the indices are 
 written above (e.g., n 3 ) for one individual and below (e.g., n 3 ) for the 
 other. Elements enclosed in parentheses are absorbed, v subdivisions 
 of conjugation nucleus. 
 
 INDIVIDUAL 1. INDIVIDUAL 2. 
 
 c 
 
 H v "- i ^2 4 ". n s 1 ' no 
 
 n s / 
 
 (N) 
 
 
 
 + n s ]^- 
 
 I 
 
 (N 
 
 new 
 
 N and n = 
 of 
 
 new = 
 
 fvM v 
 
 Nandn 
 
 The processes of conjugation just described involve complete reconstruc- 
 tion of the nuclear elements by (a) rejection and absorption of parts of the 
 
ANNELIDA. 
 
 73 
 
 old constituents, (6) addition of new constituents from another individual. 
 In Vorticella there is in addition dimorphism, the conjugating elements 
 differing in size and activity. This is a form of physiological division of 
 labour, for a small active cell is best fitted for the mere transfer of nuclear 
 material, and a large cell is a convenient storehouse of nutriment for 
 developmental needs. This is the meaning of the striking differences 
 between sperm and ovum in the sexual reproduction of the Metazoa. 
 Again, in the maturation of both ova and sperms the elimination of nuclear 
 material just described for ciliate Protozoa is paralleled. This is the 
 import of the polar cells or bodies which are separated off from ripening 
 ova. An ovum is commonly invested by a cell- wall, the vitelline membrane, 
 within which are the protoplasm and nucleus (germinal vesicle). The pro- 
 toplasm (vitellus) consists of a delicate living network, the meshes of which 
 enclose different substances, especially nutritive granules or food-yolk, the 
 amount of which varies with the size of the ovum. The nucleus is covered 
 by a delicate nuclear membrane, and it consists of a modification of pro- 
 toplasm roughly divisible into (a) achromatin, staining with difficulty, 
 and traversed by (&) an easily stained convoluted thread or network of 
 chromatin, part or all of which may be condensed into a rounded nucleolus 
 (germinal spot). Fig. 21 represents the stages in the formation of polar 
 
 Fig/21. FORMATION or POLAR CELLS IN A STARFISH (Asterias glacialis). 
 A.K, after Fol ; L, after O. Hertivig. A, Ripe ovum, with excentric 
 germinal vesicle and spot. B-D, Gradual metamorphosis of germinal 
 vesicle and spot, as seen in the living egg, into two asters. F, Forma- 
 tion of first polar cell and withdrawal of remaining part of nuclear 
 spindle within the ovum. G, Surface view of living ovum, with first 
 polar cell. H, Completion of second polar cell. I, A later stage, showing 
 the remaining internal half of the spindle in the form of two clear 
 vesicles. K, Ovum, with two polar cells and radial striae round female 
 pronucleus, as seen in the living egg. [E, F, H, I], From picric acid 
 preparations. L, Expulsion of first polar cell. 
 
 cells in the case of a starfish (Asterias glacialis). In A are seen the 
 excentric germinal vesicle and spot, which become less distinct in B, C, 
 and D. A "nuclear spindle" is then formed, consisting of threads along 
 which half the chromatin passes to one end and half to the other. At each 
 end of the spindle a small "central corpuscle" or centrosoma appears, 
 which is the centre of a radiating sun-like figure, and appears to be the seat 
 of a special sort of protoplasm (archoplasm) that determines the division 
 and movement of the chromatin. The spindle now places itself vertically 
 
74 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 to the surface of the ovum, and part of it, together with a minute quantity 
 of protoplasm, is pinched off as the first polar cell (F, L, G). A second 
 division (H, I, K) leads to the production of a second polar cell, and the 
 nucleus, now reduced by three-fourths, travels back to the centre of the 
 ovum. It is now termed the female pronudeus, and does not contain 
 enough chromatin to enable the ovum to develop further. In certain ova 
 which can develop without fertilization (i.e., are parthenogenetic) only one 
 polar cell is formed. Weismann supposes that the germinal vesicle contains 
 two kinds of protoplasm, (1) ovogenetic substance, which presides over the 
 growth of the ovum, and (2) germ-plasma, which enables it to develop into 
 an embryo. He believes the first polar cell (or only one in cases of par- 
 thenogenesis) to consist of (1), the second of half (2). A certain amount of 
 germ-plasma is imagined to be requisite for development, and when two 
 polar cells are formed too little is left for the purpose. Fertilization 
 according to this would seem to mean the importation of germ-plasma in 
 sufficient quantity to make up the deficit. In Ascaris the polar cells are 
 not formed till after the entry of the sperm. 
 
 In spermatogenesis something akin to the formation of polar cells is to 
 be observed. The whole of a mother-sperm-cell does not become converted 
 into sperms; there is always a residue forming a sperm-blastophor or an 
 equivalent to it. A typical sperm is somewhat tadpole-shaped. The head 
 contains a nucleus rich in chromatin, and covered by a thin layer of pro- 
 toplasm drawn out into the vibratile tail, by means of which the sperm is 
 propelled head first. 
 
 Fig. 22. FERTILIZATION OF OVUM OF A STARFISH (Asterias glacialis) 
 (after Fol). In A-D the sperms are represented as imbedded in the 
 mucilaginous coat of the ovum. In A a small prominence is rising 
 from the surface of the ovum towards the nearest sperm. In B they 
 have nearly met, and in C they have met. D, The sperm has pene- 
 trated the ovum, and a vitelline membrane which prevents the entry of 
 other sperms has been formed. H, Ovum showing polar cells and 
 approach of the $ and $ pronuclei ; the protoplasm is radially 
 striated round the former. E, F, G, Later stages in the coalescence of 
 the two pronuclei. 
 
 Fig. 22 illustrates fertilization (impregnation) as it occurs in a starfish 
 (Asterias glacialis). A single sperm penetrates the ovum, with the proto- 
 plasm of which its protoplasm fuses, while its nucleus, now known as the 
 male pronudeus, unites with the female pronucleus to form the segmentation- 
 nucleus. The oosperm constituted by the union of the male and female 
 cells can now develop into an embryo. The phenomena of fertilization 
 have been studied with great care in Ascaris, and it has been shown that 
 
ANNELIDA. 75 
 
 the chromatin elements of the pronuclei become intimately united, and 
 that when the oosperm undergoes cleavage, the chromatin is halved at each 
 cell- division in a very exact manner. Centrosomata in the protoplasm play 
 an important part in cleavage. 
 
 9. HIRUDO (The Leech). 
 
 The medicinal Leech (Hirudo medicmalis) is a slimy, flattened 
 worm-like animal some 2 to 6 inches long, found abundantly in 
 the freshwater pools and marshes of the Continent. It also 
 occurs in this country. There is a sucker at each end of the 
 body, and by the alternate attachment of these locomotion is 
 usually effected. The animal can also swim by means of wave- 
 like contractions of the body. It is a matter of ordinary know- 
 ledge that the Leech is a blood-sucking ectoparasite. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The bilaterally symmetrical body, 
 when fully extended, is somewhat strap-shaped, broadest about 
 the middle, and with the dorsal surface rather more convex than 
 the ventral. A large amount of contraction can, however, take 
 place, by which the body is much shortened and its shape altered. 
 A number of transverse grooves divide the body into about 
 95 rings or annuli, these, however, being superficial and not 
 corresponding to the true segments, which are 26 in number, 
 as indicated by the structure of the nervous and excretory 
 systems. Except near the ends each segment is made up of five 
 annuli, of which the last is distinguished by special colour- 
 markings, and the first by a transverse series of small white 
 papillae. There is a considerable difference in appearance between 
 the dorsal and ventral surfaces, for the former is much darker 
 and marked on each side by three longitudinal bands, of which 
 the two outer are diversified by dark dots, specially conspicuous 
 in the last annulus of each segment. The segments making up 
 the anterior and posterior ends are shorter than the others and 
 contain fewer annuli. 
 
 An oval ventral sucker (Fig. 23) terminates the front end, and 
 it appears to be formed by fusion of a lip-like prostomium with 
 the first two annuli of the most anterior or peristomial segment. 
 The mouth is placed within this sucker, and round its dorsal 
 
76 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 margin ten minute eyes can be recognized as black spots. A 
 large round sucker (Fig. 23), also facing ventrally, occupies the 
 posterior end of the body, and the small dorsal anus opens just 
 in front of it. There are two other unpaired openings, both in 
 the median ventral line, one, the male aperture, in the second 
 annulus of the 6th segment, the other being the female aperture 
 in the second annulus of the 7th segment. There are also 17 
 pairs of minute excretory pores by which the nephridia open in 
 the hindmost annuli of segments 2-18. The setae of the earth- 
 worm are quite unrepresented in the leech. 
 
 2. The Skin consists of cuticle, epidermis, and dermis. The 
 cuticle is thin, elastic, and frequently cast and renewed. It is 
 secreted by an underlying epidermis, which is mainly made up 
 of a single layer of cells shaped like mallets with the handles 
 turned inward. There are also numerous epidermal glands, each 
 of which is unicellular and opens on the surface by a very narrow 
 tube or duct. These glands are of two kinds (1) mucous glands, 
 scattered all over the body and secreting the slime which makes 
 the body of a leech so slippery, and (2) clitellar glands, occurring 
 in segments 5-7, and secreting the materials from which the 
 cocoons are made. There is no swollen clitellum as in the earth- 
 worm, and a further difference is that the reproductive organs 
 open in, not in front of, the clitellar region. The dermis is a 
 moderately thick gelatinous layer containing a number of branched 
 cells, and traversed by pigmented fibres and a network of capillary 
 vessels, both of which penetrate between the internal " handles " 
 of the epidermal cells. There are also muscle-fibres in the 
 dermis. 
 
 Eespiration is effected by the skin (i.e., is cutaneous), and 
 absorption of oxygen from the exterior with corresponding elimi- 
 nation of carbon dioxide is rendered possible by the superficial 
 position of the capillary network, as described above. 
 
 3. The Digestive Organs (Fig. 23) consist of a tube running 
 straight from mouth to anus, and divisible into fore-gut (buccal 
 cavity and pharynx), mid-gut (gullet, crop, and stomach), and 
 hind-gut (rectum). 
 
 The fore-gut (stomodseum) commences with a conical buccal 
 cavity, situated at the bottom of the anterior sucker with three 
 flat muscular jaws projecting into it. One of these is dorsal, the 
 others ventro-lateral, and they are arranged in a three-rayed 
 
er - 
 
 &-} 
 
 ANNELIDA. 
 
 77 
 
 B 
 
 eg. 
 
 -a/ 
 
 Fig. 23. LEECH. A (slightly altered after Leuckart), Diagram of side- 
 dissection, showing general relation of organs. B (slightly altered 
 after Vogt and Yung), Diagram of dorsal dissection, showing relation 
 of excretory, reproductive, and nervous systems. p. ., Posterior 
 sucker; m, mouth; ph, pharynx; c 1 , first pouch of crop; c 11 , eleventh 
 pouch of crop; st, stomach; r, rectum; a, anus; l.v., lateral vessel;. 
 Ti 1 and 7i 17 , first and seventeenth (last) nephridia ; sp l and sp 9 , first and 
 ninth spermaries (testes); spd, spermiduct (vas deferens); ep, epi- 
 didymis; p, penis; ov, ovary in sac; od, oviduct; v, vagina; e.g., 
 cerebral ganglia ; g, g t g, g, ganglia of ventral chain. 
 
78 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 manner, thus A- The cuticle covering each of them is thick- 
 ened along its margin into a large number of sharp calcified 
 teeth. The remainder of the fore-gut is constituted by an ovoid 
 muscular pharynx, with which the buccal cavity communicates 
 by an extremely small aperture. Its wall is thick, and numerous 
 dilator muscles radiate from it to the body-wall. The pharynx 
 is surrounded by a large number of salivary glands, each of which 
 is a large cell from which a slender duct runs forwards to open 
 on one of the jaws. 
 
 The mid-gut (mesenteron) commences with a short and narrow 
 gullet (oesophagus) leading from the pharynx to a very large crop 
 which constitutes the greater part of the gut. The crop is a 
 thin- walled tube which gives off 11 pairs of lateral pouches, 
 corresponding but not limited to segments 4-14, and increasing 
 in size from before backwards. The last pair are much the 
 largest, and extend backwards by the sides of the intestine. A 
 small rounded stomach terminates the mid-gut. 
 
 The hind-gut (proctodseum) consists of a narrow tube, the 
 rectum or intestine, running from the stomach to the anus. A 
 spiral fold projects into its interior. 
 
 The food consists of blood sucked from a higher animal, attach- 
 ment being effected by the anterior sucker, and a three-ra} r ed cut 
 made by a sawing action of the jaws. Meanwhile a fluid is 
 poured out from the salivary gland by which the blood of the 
 victim is prevented from coagulating. The pharynx acts as a 
 suction-pump, its cavity being alternately enlarged by contraction 
 of the dilator muscles and diminished by contraction of its 
 muscular wall. A very large amount of blood can be sucked 
 at one time, and this is stored up in the capacious crop. Meals 
 are often infrequent and they take a corresponding time to digest, 
 even as much as nine months. This is accounted for by the fact 
 that digestion and absorption take place only in the relatively 
 small stomach. 
 
 4, The Circulatory Organs consist of a blood-system which 
 freely communicates with a reduced coslomic system, both alike 
 containing blood coloured red by haemoglobin. There are numer- 
 ous colourless corpuscles. 
 
 The blood-vessels are distinguished from the ccelomic spaces 
 by the possession of definite muscular walls lined by epithelium. 
 A large lateral vessel runs along each side and is connected with 
 
ANNELIDA. 79 
 
 its fellow by transverse ventral branches. Numerous branches 
 are given off to the gut, excretory organs, and reproductive 
 organs. 
 
 The ccelom or 'body-cavity is largely filled up with connective 
 tissue, which unites the internal organs firmly together. The 
 chief ccelomic spaces are, a dorsal sinus, running above the gut, 
 and a ventral sinus surrounding the nerve-cord and connected with 
 spaces which surround the internal ends of the nephridia. These 
 sinuses have no definite walls and are simply spaces in the con- 
 nective tissue. The vessels and sinuses communicate together 
 by means of capillary networks, the chief of which are found in 
 
 B. 
 
 Fig. 24. LEECH. A (slightly altered after Vogt and Yung enlarged), a 
 nephridium with adjacent organs, seen from above (1) testes lobe, fol- 
 lowed by 2, 2, principal lobe, which again passes into the apical lobe, 
 3, <?; the vesicle duct, 4, arises from junction of 1 and 2, and runs to 
 vesicle 5, which opens to exterior ; sp, one of right spermaries (testes) ; 
 xpd, right spermiduct (vas deferens) ; l.v, lateral vessel of right side; 
 g, one of ventral ganglia. B (after Whitman), longitudinal section of 
 eye, much enlarged ; ep, epidermis ; gl, glandular cells of epidermis ; 
 pg, pigmented sheath; r.c, refracting cells; s.c, sense cells; n, optic 
 
 the skin and surrounding the crop. The latter plexus is made 
 up of irregular tubules, the walls of which are composed of large 
 brown granular cells, and which constitute what is known as the 
 botryoidal tissue. 
 
 There are no hearts as in the earthworm. The course of the 
 circulation is not accurately known. The general movements of 
 the body largely aid in the circulation. 
 
80 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 5. Excretory Organs. Seventeen pairs of complicated neph- 
 ridia succeed one another from the second to the eighteenth 
 segment. Their internal ends lie within, but do not open into, 
 special sections of the body-cavity communicating with the ventral 
 sinus, and their external ends open by ventral pores. 
 
 A nephridium taken from the middle of the series is an up- 
 wardly projecting f*|" sna P e d loop, the limbs of which are anterior 
 and posterior. The walls of the loop are traversed by a compli- 
 cated system of intracellular ducts. The anterior limb commences 
 with a blind cauliflower-shaped end which lies in the special 
 sinus, and then runs upwards to be succeeded by the posterior 
 limb which ends blindly below. A narrow vesicle-duct runs from 
 the anterior limb to a vesicle which opens by a short tube to the 
 exterior. The vesicle is muscular and lined by ciliated epithelium, 
 which also extends into the tube leading from it. As in earth- 
 worm, therefore, the nephridial cavity is mainly intracellular, but 
 its last section is intercellular. The former part is closely asso- 
 ciated with an elaborate network of capillary vessels. 
 
 Nitrogenous waste has been detected in the vesicles. 
 
 6. Reproductive Organs (Fig. 23). The unpaired ventral aper- 
 tures of the hermaphrodite system have already been described. 
 
 The male organs consist of spermaries, ducts, and a protrusible 
 penis. 
 
 There are nine pairs of spherical spermaries (testes) in the ventral 
 region of segments 8 to 16. The testes on each side communicate 
 by means of wavy vasa efferentia with a sinuous spermiduct (vas 
 deferens) which enlarges in the sixth segment into a convoluted 
 epididymis. From this a short duct runs to the base of the pro- 
 trusible penis which lies in the same segment. 
 
 The female organs consist of ovaries, oviducts, and vagina, all 
 of which are placed in the seventh segment. 
 
 The ovaries are two small thread-like structures enclosed in 
 rounded sacs, from which two narrow oviducts proceed. These 
 unite to form an unpaired convoluted tube which is continuous 
 with a muscular sac-like vagina. 
 
 Numerous sperms with rounded heads and vibratile tails are 
 produced in the testes by the division of mother-sperm-cells, and 
 passing down the spermiducts are bound into cylindrical packets 
 (sperm-ropes or spermatophores) by a secretion of the epididymes. 
 The penis is a copulatory organ by which these packets are intro- 
 
ANNELIDA. 81 
 
 duced into the vagina of another individual. In this process two 
 individuals mutually fertilize each other, their ventral surfaces 
 being applied and their anterior ends turned in opposite directions. 
 
 7. Muscular System. The body-wall, within the skin, consists 
 of three muscle-layers, an external, a middle, and an internal. 
 The thin external layer is composed of fibres taking a circular 
 direction, and within this comes the thin middle layer in which 
 the fibres are oblique, while the very much thicker internal layer 
 is made up of numerous bundles of longitudinal fibres. There are 
 also numerous dorso- ventral muscle-bands, the ends of which 
 spread out in a fan-like way within the epidermis. The suckers 
 are made up of radial and circular muscle-fibres. 
 
 The muscular tissue is composed of elongated spindle-shaped 
 muscle-cells, each of which consists of a longitudinally striated 
 external (cortical) part and a granular nucleated internal (medul- 
 lary) part. The former is specially contractile, the latter proto- 
 plasmic. 
 
 Locomotion is chiefly effected by a looping movement or by 
 swimming. In the first method the posterior sucker is attached 
 to some object and the body stretched forwards by contraction 
 of the circular muscle-layer. Then the anterior sucker is attached 
 and the body is dragged forwards by contraction of the longi- 
 tudinal layer. Swimming is a much more complex affair ; in it 
 the body is moved in a wave-like fashion. 
 
 8. The nervous system consists of a very narrow nerve-ring 
 round the pharynx, a ganglionated ventral cord, a sympathetic 
 system, and nerves connected with these. 
 
 The nerve-ring is thickened above into cerebral ganglia, which 
 supply the jaws, sense-organs of the head, and other anterior 
 structures. The sides of the ring are connectives which unite 
 these ganglia with a pair of infra-wsophageal ganglia, from which 
 five pairs of nerves are given off. The ventral cord is made up 
 of two closely united longitudinal halves, which enlarge to form 
 a pair of ganglia in the first annulus of each segment. Of the 
 23 pairs thus constituted the first and largest are the infra- 
 cesophageal ganglia. Then follow 21 much smaller pairs, from 
 each of which two dorsal and two ventral nerves are given off to 
 the corresponding segment, and the cord is terminated by the 
 somewhat larger 23rd pair, which supply the posterior sucker 
 and give origin to a number of nerves. 
 
 6 
 
82 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The sympathetic or visceral system is constituted by a slender 
 nerve running on the under surface of the crop, which it supplies 
 with numerous branches. This nerve is probably connected in 
 front with the ventral cord ; behind it bifurcates to supply the 
 last pair of crop-pouches. 
 
 The large pear-shaped nerve cells make up the external part 
 of the ganglia. 
 
 9. The most important sense-organs are the ten pairs of eyes 
 situated in the dorsal margin of the anterior sucker. Each of 
 these (Fig. 24) is a cylindrical cup, covered by elongated trans- 
 parent epidermal cells and perforated by a nerve near its internal 
 end. The axis of the cup is occupied by slender cells in conti- 
 nuity with nerve fibres, and it is lined with large cells containing 
 refractive masses. A pigment-layer surrounds the eye except on 
 its outer side. 
 
 A large number of tactile organs are found on the upper side 
 of the front part of the body, and there is a ring of tactile papillae 
 on the first annulus of every segment. These all closely resemble 
 the eyes in structure, but are devoid of pigment. It is probable 
 that the eyes in this case are modified tactile organs. The leech 
 possesses a very delicate sense of touch. 
 
 LIFE-HISTORY. 
 
 The breeding-season is spring. The fertilized ova are laid in 
 ellipsoidal cocoons, and these are deposited in the damp earth at 
 the margin of the water. Each cocoon is about an inch long, 
 and has a thick wall composed of a firm inner layer and a spongy 
 outer layer which is supposed to prevent desiccation. The cocoon 
 contains as many as twenty eggs floating freely in an albuminous 
 liquid. The cocoon is made from the hardened secretion of the 
 clitellar glands, and in the first stage of its formation is a cylin- 
 drical band surrounding the clitellar region. The leech draws 
 its body back out of this band, the ends of which then close up. 
 
 The course of development is in many respects similar to that 
 of the earthworm, and germinal bands of the same nature are 
 present. The embryos are soon liberated from the eggs and 
 swim about in the surrounding albumen by which they are nour- 
 ished. The young leeches escape from the cocoon after several 
 weeks have elapsed, 
 
ARTHROPOD A. 83 
 
 CHAPTER VI ARTHROPODA. 
 10. ASTACUS (The Crayfish). 
 
 THE Crayfish is a small greenish lobster-like animal, living in 
 streams and canals, under the banks of which it burrows. An 
 average mature specimen is about five inches long. There is only 
 one British species, Astacus fluviatilis, a large variety of which, 
 A. fluviatilis var. nobilis, is common on the Continent, where it is 
 largely used as food. As the points of difference are but small, 
 the following description will apply to either : 
 
 Crayfishes are mainly carnivorous, devouring water-snails, tad- 
 poles, insect larvae, worms or other animals, dead or alive, but 
 they also feed on vegetable matter. They either walk by means 
 of their four pair of jointed legs, or else swim swiftly by alter- 
 nately bending and straightening their powerful tails, which 
 propel them backwards; they can also employ their large nippers 
 for climbing. 
 
 The sexes are distinct, but there is not much difference exter- 
 nally between the male and female. The most obvious distinction 
 is that the tail of the latter is somewhat broader, and in specimens 
 examined during winter or spring a considerable number of rather 
 large eggs will be found attached to its under side. These are 
 hatched in May or June. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters (Figs. 25, 26, and 27). The bilater- 
 ally symmetrical body is segmented, as in the Earthworm, but the 
 segments are definite in number, and, instead of being nearly all 
 alike, vary much in character, and many of them are fused 
 together. Owing to these differences the body is marked out 
 into regions from before backwards, head, thorax, and abdomen or 
 tail. The two first are united to form the cephalothorax, which 
 is covered by a firm continuous shell, the carapace, dorsally and 
 laterally. The segments of all the regions bear paired, jointed 
 appendages of various kinds, which differ greatly in form and 
 
84 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 function. Since the body is covered by a firm calcified cuticle, 
 segmentation and jointed appendages are a mechanical necessity 
 to an animal of such active habits. 
 
 (1) The abdomen, as the least modified part, affords a con- 
 venient point of departure for study. It is made up of seven 
 segments, movably joined together, the first six of which bear 
 appendages. The abdominal region, like all the rest of the body, 
 is covered by a firm chitinous exoskeleton which is largely calcified, 
 but parts of it remain soft and joints are 'thus formed. The 3rd, 
 4th, and 5th abdominal segments are most typical, and similar 
 in the two sexes. The exoskeleton of each of these segments 
 consists of a calcified ring connected by uncalcified parts with 
 the segments in front and behind. The broad, strongly convex 
 dorsal and lateral part of the segment is the tergum (t). The 
 front part of this is overlapped by the preceding tergum, and its 
 hinder part overlaps the one behind it. Between the two extends 
 an uncalcified intertergal membrane, which is folded when the 
 tail is straight. The sides of the terga of adjacent segments 
 are united by peg and socket joints, allowing of upward and 
 downward movements. The tergum passes down on each side 
 into a small pointed projection (pi), the pleuron (larger in the 
 female), which is V-shaped in transverse section, being made up 
 of an outer and an inner limb. On the under side of the segment 
 is a slender transverse bar, the sternum (st), and broad uncalcified 
 intervals, the intersternal membranes, separate adjacent sterna. The 
 sternum passes on each side into a very short but broader epimeron 
 (epri), the junction between the two being marked by the attach- 
 ment of the appendage. The foregoing parts form a perfectly 
 continuous ring with no sharp lines of demarcation. 
 
 The appendages are swimmerets (Figs. 26 and 27, M), and each 
 of them is a small elongated A' sna P e d limb, consisting of a prox- 
 imal* stalk, the protopodite (pr), and two distal* branches, an 
 internal endopodite and external exopodite (ex). 
 
 The protopodite is made up of a very short proximal and a 
 larger distal joint. The endopodite and exopodite both possess a 
 relatively long proximal joint, and a rather longer distal part 
 imperfectly divided into rings. All parts of the swimmeret are 
 more or less beset with stiff bristles or setce. 
 
 * The proximal and distal ends of an appendage, &c., are the ends respec- 
 tively further from and nearer to its free end. 
 
ARTHROPODA. 
 
 85 
 
 Fig. 25. 
 
 Fig. 26. 
 
 Fig. 25 DORSAL and Fig. 26 VENTRAL VIEW or MALE CRAYFISH. r, Bostrnm; 
 c.gr, cervical groove ; x , placed on branchio-cardiac groove ; br, bran- 
 chiostegite ; t, tergum ; st, sternum ; pi, pleuron ; ep, epimeron ; pr, 
 protopodite ; ex, exopodite ; en, endopodite ; the appendages and parts 
 of certain segments are numbered 1 to 21, but probably the eyestalks 
 (1) are not appendages, therefore subtract one from each number to 
 make it correct; g.y, excretory opening; m, mouth; a, anus; g.o, 
 genital opening. 
 
86 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The 6th abdominal segment (20 in Figs. 25 and 26) differs 
 from the preceding, mainly in the great size of the swimmerets. 
 The protopodite is broad, thick, and undivided, while two broad 
 oval plates fringed with setae represent endopodite and expodite, 
 the latter being two- jointed. The last abdominal segment or 
 telson (21) possesses neither pleura nor appendages. It is divided 
 into two by an imperfect transverse joint, and upon its little- 
 calcified sternal surface the anus (a) opens as a longitudinal slit 
 with thickened edges. The telson and large 6th pair of swim- 
 merets make up together the tail-fin. The 1st and 2nd abdominal 
 segments mainly differ in the character of their appendages, but 
 in addition to this the former is small, possesses no pleura, and 
 hinges on to the cephalothorax in a somewhat complicated manner. 
 In the female, the 2nd pair of abdominal appendages are swim- 
 merets, the 1st pair, when present, rudimentary swimmerets. 
 The appendages of these segments are modified in the male into 
 copulatory organs (Fig. 26, 15 and 16; Fig. 27, K and L). 
 
 In the cephalothorax (Figs. 25 and 26) the tergal and pleural 
 regions are covered by a continuous carapace, produced in front 
 into a sharp spine, the rostrum (r). On the upper surface of the 
 carapace is a transverse groove, which slopes downwards and 
 forwards to its front edge. This cervical groove (c.gr) marks the 
 boundary between the head and thorax. 
 
 (2) The thorax is composed of eight fused segments, the last 
 of which is slightly movable. In many of the lower Crustacea 
 the thoracic segments are freely movable upon one another like 
 the abdominal segments of the crayfish, and particular interest 
 attaches to the genus Nebalia, which is in many ways transitional 
 between the lower and higher forms. This is a small shrimp- 
 like animal with a thorax composed of eight segments and covered 
 by a large fold growing back from the head. The part of the 
 crayfish's carapace behind the cervical groove probably corresponds 
 to such a fold, which in this case, however, has fused closely with 
 the thorax. The tergal region of this fold is rather narrow, and 
 its lateral boundaries are indicated by a branchio -cardiac groove ( x ) 
 running back from the cervical groove. The pleural region of 
 the fold on each side is a large curved plate, the branchiostegUe (br), 
 which bends outwards and downwards to the bases of the thoracic 
 appendages and covers a large gill-chamber. It is united with the 
 head along the cervical groove. The epimera are very large and 
 
ARTHROPODA. 87 
 
 thin, forming on each side a plate sloping steeply downwards, 
 which constitutes the inner wall of the gill-chamber. Grooves 
 converging upwards mark the boundaries of the segments. The 
 thoracic sterna (st) are narrow elongated plates, lying between 
 the bases of the appendages, and, except the last, closely united 
 together. The last four of these appendages are elongated 
 walking-legs (11-14), the two first of which are chelate, i.e., with 
 pincers, and possess no exopodite. The two-jointed protopodite 
 is continuous with a five-jointed endopodite, the last joint but 
 one of which, in the two first, is produced distally alongside the 
 last joint, which works against it to form a claw. The broad 
 proximal joint of the protopodite bears in the first three walking- 
 legs a membranous plate, the epipodite (ep., I, Fig. 27), which 
 projects into the gill-chamber, and on which gill-filaments are 
 arranged in a plume-like way. The male genital pore (g.o) is 
 placed on the inner side of the proximal joint of the protopodite 
 of the last walking-leg. The female genital pore is found in a 
 similar position on the second walking-leg. 
 
 The fourth pair of thoracic appendages are the large j "weeps 
 (10). These are similar in structure to the chelate walking-legs, 
 but their claws are very much larger. The first three pairs of 
 thoracic appendages are relatively small and flattened, and are 
 termed foot-jaws (maxillipedes). They are directed forwards and 
 work against one another from side to side, their inner margins 
 being provided with stout setae. By turning a crayfish on its 
 back the last pair (27, H) will readily be seen, and upon removing 
 or turning back these the smaller second pair (27, G) will come 
 into sight. These similarly conceal the still smaller first pair 
 (27, F). They possess all the typical regions, but there is con- 
 siderable variation in detail as may be gathered from Fig. 27. 
 
 (3) The head (Figs. 25 and 28, B) is probably made up of five 
 segments closely united, and bears five pairs of appendages. That 
 part of the carapace in front of the cervical groove represents the 
 terga. It is produced in front into the rostrum, on either side of 
 which is a deep notch, in which the stalked eye is placed. This 
 region is much broader than the corresponding thoracic one, and 
 bounds the front of each gill-chamber. The pleural region is 
 rudimentary, and represented by the edge of the carapace, while 
 the epimera are narrow and the sterna represented by several 
 small median pieces. On the sternal surface, between the 3rd 
 
88 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Fig. 27. APPENDAGES or ASTACUS, Right side. A and A', Upper and 
 lower views of antennule ; B, antenna ; C, mandible ; D, mx. 1 ; 
 E, mx. 2 ; F, mxpd. 1 ; G, mxpd. 2 ; H, mxpd. 3 ; I, base of third 
 walking-leg; K and L, 1st and 2nd abdominal appendages of male; 
 M, typical swimt.; N, arthrobranchia ; pr, protopodite; en, endopodite; 
 ex, exopodite ; ep, epipodite ; c. s, coxopoditic setse ; sg, scaphognathite ; 
 au, auditory opening. 
 
ARTHROPOUA. 89 
 
 and 4th segments, is the elongated and slit-like mouth (m), with 
 a posterior lip, the metastoma (28 A, mi), from which a pointed 
 lobe grows out on each side, and an overhanging pointed anterior 
 lip, the Idbrum (28 A, lb\ both of which are supported by calca- 
 reous plates. In front of the mouth the sternal region is sharply 
 bent up, and, owing to this cephalic flexure, the anterior append- 
 ages are directed forwards (28, B). The last three pairs of head- 
 appendages are small jaws, covered over by the foot-jaws. The 
 hindmost are the second maxillae (27, E), which resemble the first 
 foot-jaws, but are more delicate. The exopodite and epipodite 
 are fused into a relatively large elongated plate, which lies in 
 the front of the gill-chamber, and has received the special name 
 of scaphognatliite (sg). These appendages overlap the still weaker 
 first maxillae (D), which are devoid of endopodite. Lying at the 
 sides of the mouth are the mandibles (C), in which exopodite and 
 epipodite are absent. The protopodite is a firm, transversely 
 elongated structure, the inner end of which possesses two strongly 
 toothed ridges. The endopodite is a small three-jointed palp. 
 The two segments in front of the mouth bear slender forwardly 
 directed tactile appendages. Those of the 2nd segment are the 
 large feelers or antennce (B). Each of these consists of a proto- 
 podite with two stout cylindrical joints, the proximal of which 
 has a small tubercle on its under surface, upon which is the 
 excretory or renal aperture (28, B). To the protopodite a scale- 
 like exopodite, the "squame," is attached externally, and a very 
 long slender endopodite internally. This is composed of two 
 stout proximal joints and a terminal part made up of a great 
 many small rings, imperfectly jointed together. The small 
 feelers or antennules (A and A') attached to the 1st segment are 
 of much less size. They lie rather internal to the antennae, and 
 are directed forwards. The protopodite is three-jointed, and its 
 proximal joint, which is much the largest, abuts against its fellow 
 in the middle line. It is somewhat trihedral, and on its upper 
 surface is a small longitudinal slit (au), the auditory aperture, over 
 which a horizontal brush of seta? attached to its outer edge 
 projects. The endopodite and exopodite are two short, slender, 
 imperfectly-jointed filaments, of which the latter is rather the 
 longer. 
 
 Between the sterna of the thorax and posterior part of the 
 head a number of cuticular folds project into the body. These 
 
90 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 apodemes are calcified and make up a kind of open framework, the 
 endophragmal system, which imperfectly roofs over a cavity known 
 as the sternal canal, which is traversed by the ventral nerve-cord. 
 
 It will be seen from the foregoing that the body of the cray- 
 fish may be regarded as made up of twenty segments or metameres 
 all serially homologous that is, reducible to the same type. The 
 differences between the several regions are chiefly differences of 
 proportion, while certain parts are suppressed in some segments, 
 and the anterior segments have fused together. These various 
 differences have been brought about by division of physiological 
 labour. The head bears the chief sense-organs and contains the 
 ganglia which supply them. Its three posterior pairs of append- 
 ages are jaws, the last of which help to renew the water in the 
 gill-chambers. The anterior thoracic appendages are jaws, then 
 follow forceps which seize food, serve as weapons, and enable the 
 animal to climb, lastly come walking-legs. The thorax also 
 undertakes the work of respiration, and affords firm points of 
 origin to the powerful muscles which move the tail. This is the 
 swimming organ, and it also has secondary functions in relation 
 to reproduction. 
 
 2. Skin. The true skin is formed by an epidermis with a thin 
 underlying dermis. The former secretes the exoskeleton, a many- 
 layered pigmented cuticle, differing in degree and not in kind 
 from that of a worm, and largely impregnated with salts of lime 
 (seven-eighths carbonate and one-eighth phosphate). The numer- 
 ous setae are cuticular structures. 
 
 The epidermis is a single layer of columnar cells, the outlines 
 of which are indistinct. Slender prolongations of the epidermis 
 traverse the cuticle and end at the bases of the setae. Numerous 
 tubular cement-glands, lined by glandular epidermal cells, open on 
 the ventral surface of the abdomen in the female. The thin 
 dermis is composed of connective tissue, in which delicate blood- 
 vessels and nerves run. The exoskeleton is made up of numerous 
 closely-united layers, which are traversed by an immense number 
 of delicate vertical " pore-canals." Most of the setae are two- 
 jointed pinnate bristles slightly sunk in small pits of the outer 
 surface. Each of these setae is hollow and contains a granular 
 core, which is only separated by a thin transverse cuticular layer 
 from the epidermic process which occupies the underlying pore- 
 canal. 
 
ARTHROPODA. 91 
 
 3. The muscular system is conveniently considered here, since 
 its arrangement is dependent upon the structure of the exoskeleton, 
 to the inside of which the muscles are attached. 
 
 Locomotion consists in swimming, walking, or climbing. The 
 first results from alternate flexion (bending ventralwards), and 
 extension (straightening), of the abdomen. In accordance with 
 this, two great flexor muscles arise from the roof of the sternal 
 canal, and are inserted into the abdominal sterna, and two much 
 smaller extensor muscles have their origin and insertion in the side- 
 walls of the thorax and abdominal terga respectively. During 
 flexion the intertergal membranes are stretched and the inter- 
 sternal ones folded, vice versd during extension. The lateral peg- 
 and-socket joints only permit upward and downward movements, 
 while excessive extension is prevented by the overlapping terga. 
 Movements of the walking-legs and forceps effect the other two 
 kinds of locomotion, and the successive segments of these append- 
 ages are connected by hinge-joints, the axes of which all take 
 different directions, so that the limb can be bent in various planes 
 and execute complex movements. Some of the limb-muscles are 
 extrinsic, taking origin from the exoskeleton of the body ; others 
 are intrinsic, having both origin and insertion within the limb. 
 
 The jaws are moved to and from the middle line by adductor 
 and abductor muscles. The mandibular adductors are easily seen 
 in dissection. The claws of the first three pairs of thoracic limbs 
 are opened and shut by abductor and adductor muscles which 
 work the terminal joint against the produced part of the last 
 joint but one. In many cases it is advantageous for a large 
 muscle to be attached to a small and definite area. This is 
 managed by means of a firm tendon, formed as a cuticular infolding 
 to which the muscle-fibres are connected. 
 
 The muscles are made up of numerous slender muscle-fibres 
 resulting from the modification of cells. Each of these fibres 
 is invested by a delicate membranous sheath (sarcolemma), and, 
 owing to the regular alternation of dark and clear bands, is 
 transversely striated. Hence the term "striped" or "striated" 
 muscle. Longitudinal striations also occur, and along these the 
 fibre can be split, after death, into primitive fibrillce. Beneath 
 the sarcolemma a number of longitudinal rows of muscle-corpuscles 
 are arranged, each of which consists of a nucleus surrounded by 
 a small quantity of protoplasm. 
 
92 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The motor nerve-fibres which supply muscle come into very close 
 relation with its fibres. The primitive-sheath becomes continuous 
 with the sarcolemma, and the axis-cylinder passes into a granular, 
 nucleated end-plate, resting upon the muscle substance. 
 
 4. Digestive Organs (Fig. 28, A). The forceps and clawed 
 walking-legs are accessory to digestion, and the six pairs of jaws 
 overlapping one another outside the mouth are still more closely 
 connected with the same function. But all these are more or less 
 modified appendages, and outside the alimentary canal. This is 
 a tube which runs straight from mouth to anus and consists of a 
 capacious fore-gut (gullet and stomach), a very small mid-gut 
 into which a large digestive gland opens, and an elongated tubular 
 hind-gut (intestine). 
 
 The ventral mouth (m), which possesses anterior and posterior 
 lips (I and mt), leads into the fore-gut (stomodseum). This consists 
 of a short, wide, upwardly-directed gullet (oesophagus) (05), and a 
 large sac, the stomach, into which this opens. The stomach fills 
 most of the cavity in the head, and is divided into a larger 
 cardiac (ca) part in front and a smaller pyloric (py) part behind, 
 the two being separated by a deep constriction. The fore-gut is 
 an ingrowth from the exterior, and it is not, therefore, surprising 
 to find it lined by a firm cuticle, continuous at the mouth with 
 the exoskeleton. The cuticular lining of the stomach is locally 
 thickened and calcified into hard plates and bars (sclerites) which 
 form a chewing-apparatus or gastric mill, situated for the most 
 part in the posterior part of the cardiac division. Numerous 
 projecting setae constitute a strainer in the pyloric part of the 
 c stomach. The sclerites of the gastric mill 
 
 are united together into an elastic hexagonal 
 framework with anterior and posterior sides 
 connected by a jointed rod. These can be 
 diagrammatically represented as in annexed 
 P plan, the arrow pointing to the front. 
 
 A broad cardiac sclerite (c) lies transversely in the dorsal wall of 
 the cardiac division. Attached to the middle of this is a small 
 uro-cardiac sclerite (u), directed downwards and backwards in the 
 front wall of the constriction separating the two regions of the 
 stomach. These two sclerites form a T-shaped arrangement. 
 A second and somewhat similar J_-shaped combination is formed 
 by a pyloric sclerite Q?) placed across the dorsal wall of the pyloric 
 
ARTHROPODA. 93 
 
 part of the stomach. To this is jointed a pre-pyloric sclerite (pr), 
 forming the stem of the J_, which takes a downward and back- 
 ward course in the back wall of the constriction above-mentioned, 
 and joins the end of the uro-cardiac sclerite. At the junction 
 of the two there is a red-coloured median c n 
 
 tooth (*), which projects into the cardiac 
 chamber. The diagram here shown indicates 
 the relation of these five sclerites as seen 
 from the side. 
 
 From the extremity of the cardiac sclerite on either side a 
 small ptero-cardiac sclerite (pt) runs back, and unites with a zy go- 
 cardiac sclerite (z) that runs forwards from the end of the pyloric 
 scleriie. The inner side of each zygo-cardiac sclerite is thickened 
 into a red elongated lateral tooth (f), which projects into the 
 cardiac cavity, and is marked by numerous transverse ridges. 
 
 Two anterior gastric muscles (28, a.g.m) take their origin on the 
 inner side of the carapace, and run backwards and downwards to 
 be inserted into the cardiac sclerite, while two posterior gastric 
 muscles (p.g.m) run downwards and forwards from a similar origin 
 to be inserted into the pyloric sclerite. 
 
 By the contraction of the anterior and posterior gastric muscles 
 the cardiac and pyloric sclerites are pulled away from each other, 
 which involves (1) the conversion of the hexagon into a rect- 
 angle, causing the lateral teeth to approach; (2) the pulling out 
 of the sharp fold made by the urocardiac and prepyloric sclerites, 
 so that the median tooth passes downwards and forwards. Hence 
 the three teeth meet together in the centre, and effectually chew 
 anything that comes between them. The elasticity of the frame- 
 work then comes into play and separates the teeth. 
 
 In addition to the sclerites forming the gastric mill, others of 
 less importance are found in the cardiac wall ; and in summer a 
 round button-like calcareous gastrolith is often seen projecting into 
 the cardiac cavity on either side. 
 
 The communication between the cardiac and pyloric cavities 
 is very narrow, partly owing to the external constriction and 
 partly to hair-fringed projections. This is the commencement of 
 the strainer, the rest of which is formed by hairy cushions project- 
 ing into the pyloric cavity and reducing it to a fissure, anchor- 
 shaped in cross-section. A valve composed of five flaps separates 
 the stomach from the mid-gut. 
 
AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The extremely short mid-gut (m.g) is not lined by cuticle. Its 
 dorsal wall is produced upwards and forwards into a short blind 
 tube, the ccecum (cce). A large brownish three-lobed digestive 
 gland (h.p) (liver, hepato-pancreas) lies on each side within the 
 cephalo-thorax, and opens by a short, wide duct (bile duct) (b.d) 
 into the mid-gut, of which it was originally an outgrowth. 
 
 Fig. 28. ALIMENTARY CANAL AND EXCRETORY ORGANS or CRAYFISH. 
 A, Alimentary canal ; m, mouth ; Ib, labrum ; mt, metastoma ; ce, gullet : 
 ca and py, cardiac and pyloric ends of stomach; c.o, cardiac sclerite; 
 the horizontal shading just below reference-line shows the commence- 
 ment of the ptero-cardiac sclerite, which tapers to a point below; 
 py.o, pyloric sclerite, running into the zy go-cardiac sclerite, which 
 joins the ptero-cardiac ; a.g.m and p.g.m, anterior and posterior 
 gastric muscles; m.g, mid-gut; cce, caecum; h.p, digestive gland; b.d, 
 duct of the same ; t, intestine ; a, anus. B, Left renal organ ; gl, 
 glandular part ; bl, bladder ; st, style passed into renal opening ; 
 an and an', antennule and antenna ; op, eye ; r, rostrum. 
 
 The hind-gut or intestine (i). which succeeds the mid-gut, is a 
 narrow thin-walled tube running back in the middle line, between 
 the abdominal flexor and extensor muscles, to open by the anus (a). 
 It is lined by cuticle, and six slightly-twisted longitudinal ridges, 
 covered by minute elevations (papillae) project into its cavity. 
 
 The alimentary canal is lined throughout by epithelium one 
 layer of cells thick, which in the fore and hind guts secretes a 
 
ARTHROPODA. 95 
 
 cuticle similar to that covering the outside of the body. Outside 
 the epithelium, connective tissue and muscular layers are present. 
 
 Each digestive gland is made up of a very large number of 
 short caeca, lined by glandular epithelium. In each lobe these 
 open into a central duct, and the three central ducts unite to form 
 the main duct. 
 
 The crayfish feeds upon various substances, vegetable and 
 animal, which are seized by the chelate appendages and torn 
 into small fragments. These are passed on to the third foot- 
 jaws, by which, and the other mouth-appendages, they are still 
 further reduced. All the jaws work from side to side, and not 
 up and down, as in backboned animals. Mastication is completed 
 by the gastric mill. The pyloric strainer prevents any but small 
 particles from passing on to the mid-gut, and parts incapable of 
 sufficient reduction are ejected from the mouth. During the 
 action of the gastric mill, probably, and certainly after reaching 
 the mid-gut, the food is acted upon by the secretion of the 
 digestive glands. This is an alkaline fluid, containing ferments 
 which convert starch into sugar, and proteids into peptones, also 
 emulsifying fats (i.e., converting them to a state of fine division). 
 
 The ridged and papillated lining of the intestine affords a large 
 absorptive surface. Owing to the action of the muscle in the 
 wall of the alimentary canal, the food is gradually passed back- 
 wards, and the undigested parts are ejected from the anus. 
 
 The digested parts of the food, which are either dissolved or 
 emulsified, diffuse out of the digestive organs into the blood- 
 system, by which they are distributed over the body. 
 
 5. The Circulatory Organs consist of a blood-system only, 
 which can be divided into heart, arteries, capillaries, and more 
 or less definite channels and spaces (sinuses) in various parts of 
 the body. All these are in continuity, and they contain a nearly 
 colourless blood. In those invertebrates which, like Crustacea, 
 insects, &c., possess jointed lateral appendages and are known as 
 Arthropods, the coelomic system seems to have been almost 
 aborted as a result of exuberant development of the blood- 
 system. 
 
 The blood is of a faint bluish tint, owing to the presence of 
 hcemocyanin, a complex compound of the nature of a proteid and 
 playing the same physiological part that haemoglobin does in red 
 blood. It contains, however, copper instead of iron. The blood 
 
96 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 consists of plasma, in which are suspended numerous colourless cor- 
 puscles, nucleated, and capable of performing amoeboid movements. 
 On the dorsal side of the thorax is a good-sized pericardial sinus, 
 in which the heart is suspended by fibrous cords. This organ is 
 a flattish, thick-walled sac, into which open three chief pairs of 
 valvular apertures (ostia), dorsally, laterally, and ventrally respec- 
 tively. From the heart seven delicate arteries* proceed, five in 
 front and two behind. From the front a small impaired ophthalmic 
 artery runs forwards and divides to supply the eyes, antennules, 
 and cerebral ganglia, while on each side of this a much larger 
 antennary artery arises which supplies the antenna, giving off 
 branches to the stomach during its course. A hepatic artery takes 
 origin a little behind each antennary artery, and supplies the 
 mid-gut and digestive gland. The posterior end of the heart 
 dilates into a kind of bulb which is continued backwards into a 
 dorsal abdominal artery running in the middle plane above the 
 intestine, to which it gives oif numerous branches. Near the 
 point of origin of this vessel a sternal artery leaves the heart, 
 gives a branch to the reproductive organs, and, running down- 
 wards on one side or other of the intestine, pierces the nerve- 
 cord, and divides into an anterior ventral thoracic artery and a 
 posterior ventral abdominal artery, both of which run below the 
 nerve-cord. 
 
 The arteries branch repeatedly, and some of the branches enter 
 into capillary plexuses, as, for example, upon the cerebral ganglia. 
 The finest ramifications end in minute spaces (lacunce) found in 
 all parts of the body and which communicate with larger spaces 
 (sinuses) that are placed around the various organs. The most 
 important of these is the sternal sinus, running along the ventral 
 surface, and with which the others are directly or indirectly 
 connected. There are external channels in the gills which com- 
 municate on the one hand with the sternal sinus, and on the 
 other hand with internal gill-channels opening into branchio-cardiac 
 canals which run up the sides of the thorax into the pericardial 
 sinus. 
 
 The heart is chiefly made up of interlacing muscular cords, 
 which in their turn are aggregates of elongated muscle-cells, the 
 inner sides of which are metamorphosed into transversely striated 
 contractile substance. 
 
 * An artery is a blood-vessel carrying blood away from the heart. 
 
ARTHROPODA. 97 
 
 Circulation of the blood is effected by the rhythmical contrac- 
 tion of the heart, which acts as a central pump. The valves allow 
 the blood to enter the heart, but prevent it from passing out 
 again into the pericardial sinus during contraction. 
 
 Course of the Circulation. The gills are placed in the course of 
 the blood-current returning to the heart, this passing from the 
 internal gill-channels to the branchio-cardiac canals, and thence 
 into the pericardial sinus. The heart in its diastole, i.e., when 
 expanding, sucks in this purified blood through its ostia, and then 
 undergoing systole (contracting) forces it into the arteries. From 
 these it passes into venous spaces, and ultimately reaches the 
 sternal sinus, loaded with carbon dioxide, and poor in oxygen. 
 From the sternal sinus it enters the external gill-channels. A 
 heart, which, like that of the crayfish, distributes oxygenated 
 blood to the body at large is said to be systemic. 
 
 6. Special respiratory organs are present on the thorax in 
 the form of gills (branchiae), adapted for breathing the oxygen 
 dissolved in water. These are vascular outgrowths covered by a 
 very delicate cuticle. Those on each side are contained in a gill- 
 chamber covered over by the branchiostegite, and communicating 
 with the exterior by a narrow slit above the bases of the thoracic 
 limbs. Parasites are particularly fond of fixing upon gills, since 
 these are always delicate structures with an abundant supply of 
 blood and fresh water, and, besides, are usually well sheltered. In 
 this case such unwelcome guests, as well as particles of sand, &c., 
 are largely prevented from entering by long coxopoditic setce pro- 
 jecting from the basal joints of the third foot-jaws, forceps, and 
 first three walking-legs. Each chamber contains 18 perfect, and 
 2 or 3 rudimentary gills. The free ends of all converge upwards. 
 Six of the perfect gills, podobranchice (Fig. 27, G, H, I, ep), are 
 constituted by the lamellar epipodites of the second and third 
 foot-jaws, forceps, and first three walking-legs, which bear a large 
 number of delicate gill-filaments on their anterior arid external 
 surfaces. Eleven more, arthobranchice (Fig. 27, N), are attached 
 to the membranous junctions between the bases of the foregoing 
 appendages and the body. Two are placed on each of these 
 junctions except the first, which possesses only one. These gills 
 are plume-like, with a central stem bearing numerous gill- 
 filaments. The remaining perfect gill, pleurobranchia, similar in 
 structure to one of the arthrobranchise, is attached to the epimeron 
 
98 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 of the last thoracic segment. The two or three rudimentary 
 gills are also pleurobranchise, and are attached to the epimera of 
 the two or three preceding thoracic segments. 
 
 The number and position of the gills can be expressed by a 
 branchial formula, as follows : 
 
 j 
 
 od a 
 
 & f 
 
 P pi 
 
 
 
 VI ( 
 
 )(ep)+ ( 
 
 ) + ( 
 
 ) + 
 
 = 
 
 (ep) 
 
 VII 
 
 + 
 
 + 1 
 
 ) + o 
 
 = 
 
 2 
 
 VIII 
 
 _j_ 
 
 + 
 
 + 
 
 
 
 3 
 
 IX 
 
 + 
 
 + 
 
 -f 
 
 
 
 3 
 
 X 
 
 + 
 
 + 
 
 + o 
 
 
 
 3 
 
 XI 
 
 4- 
 
 -f 
 
 4- r 
 
 
 
 3 + r 
 
 XII 
 
 + 1 
 
 l + 
 
 4- r 
 
 = 
 
 3 + r 
 
 XIII ( 
 
 ) + ( 
 
 ) + ( 
 
 ) + 1 
 
 = 
 
 1 
 
 6 + (ep)+ 6 
 
 [ The numbers refer to the thoracic segments ; pd = podobranchs ; a* = 
 anterior arthrobranchs ; a p = posterior arthrobranchs ; pi = pleurobranchs ; 
 ep = epipodite; r rudiment.] 
 
 The gills are covered with a very thin cuticle, underneath 
 which lies a delicate epithelium. The connective tissue forming 
 the central parts of the filaments is traversed by a network of 
 blood-passages connected with the external and internal channels 
 of the gill-axis. 
 
 The essential part of respiration consists in diffusion of oxygen 
 into the blood contained in the gills, while at the same time carbon 
 dioxide diffuses out into the surrounding water. The hffiinocyanin 
 acts as an oxygen-carrier, since it is able to take a certain amount 
 of that element into loose chemical combination, and parts with 
 it as readily to the tissues. The water in the gill chamber is 
 renewed chiefly by the action of the scaphognathite which bales 
 it out in front, while fresh water enters below and behind. The 
 movements of the thoracic limbs also assist in the production of 
 currents. 
 
 In the young crayfish water is regularly taken into, and ex- 
 pelled from, the intestine by the anus. This anal respiration may 
 possibly also occur in the adult. 
 
 7. Excretory Organs (Fig. 28, B). A pair of kidneys (" green 
 glands ") are situated in the head, one on each side of the 
 oesophageal connectives. Each is a small green body (gl) round 
 and flattened, from the upper surface of which proceeds the ureter, } 
 
ARTHROPODA. 
 
 99 
 
 an oval thin-walled bladder (&/), which opens (st) externally on 
 the basal joint of the antenna. The green part is made up of a 
 single much-coiled tubule, lined by glandular epithelium. 
 
 The kidney is richly supplied with blood, from which it separ- 
 ates nitrogenous waste in the form of guanin (C 5 H 5 N 5 O), and 
 uric acid (C 5 H 4 N 4 3 ), by means of its glandular epithelium. 
 
 8. Reproductive Organs (Fig. 29). The sexes are distinct, 
 and the external differences between them chiefly consist in the 
 greater breadth of the abdomen in the female, and the modification 
 of the two first pairs of abdominal appendages in the male. 
 
 (1) In the male crayfish (A) a single yellowish- white spermary 
 (testis) underlies the pericardial sinus. It possesses two short 
 
 Fig. 29. REPRODUCTIVE ORGANS OF CRAYFISH. A, Male organs ; 
 
 anterior and posterior lobes of spermary (testis); v.d, spermiduct (vas 
 deferens) ; g. o, style inserted into genital aperture. B, Female organs ; 
 ov and ov', anterior and posterior lobes of ovary; od, oviduct; y.o, 
 genital opening. The ovary has been cut open on one side to expose 
 its cavity. 
 
 anterior lobes (t), which broaden behind, and a longer and narrower 
 posterior lobe (t'). A slender spermiduct (vas deferens) (v.d) arises 
 on each side from the junction of the lobes, enlarges considerably, 
 and, after many convolutions, runs downwards to one of the male 
 genital pores (g.o), situated on the proximal joint of the last pair 
 of walking-legs. 
 
 The spermiducts branch repeatedly within the spermary, their 
 finest branches ending in minute lobules, each of which is formed 
 by a small group of vesicles lined by mother-sperm-cells. Each 
 of these divides, before the breeding-season, and gives rise to a 
 number of spermatocytes, which develop into minute nucleated 
 sperms, rounded and somewhat flattened, with a number of delicate. 
 
100 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 stiff processes, all curved in one direction, projecting from their 
 edges. The epithelial lining of the spermiducts is glandular, and 
 secretes a viscid fluid which hardens to form threads (spermato- 
 phores) in which the sperms are imbedded. 
 
 (2) The female (B) possesses an ovary (ov, ov), similar in shape 
 to the spermary, and occupying a similar position, but larger and 
 broader. Its colour is reddish-brown, and its surface is raised up 
 into rounded projections of various sizes, caused by the presence 
 of ova. This is most obvious in the breeding-season, when the 
 ovary becomes considerably larger. Within it is a cavity on 
 either side into which ova project, and from which, near the 
 junction of the lobes, a short, wide oviduct (od) leads to the basal 
 joint of the second walking-leg (g.o). 
 
 The ova are reddish-brown spheres about of an inch in 
 diameter, and enclosed in capsules, the ovarian follicles, which 
 project into the cavities of the ovary. The wall of a follicle is 
 constituted by a structureless membrane, underneath which is a 
 layer of simple epithelium. The large ovum consists of a vitelline 
 membrane, a vitellus containing a considerable quantity of food- 
 yolk, and a germinal vesicle with numerous germinal spots. The 
 ripe ova burst from their follicles, pass into the ovarian cavities, 
 and thence by the oviducts to the exterior. 
 
 In the breeding-season (autumn) the male, by means of the two 
 pairs of copulatory abdominal appendages, deposit spermatophores 
 upon the posterior thoracic sterna of the female. Just before the 
 eggs are laid the abdomen of the female is flexed, and a glairy 
 secretion is poured out from the numerous cement-glands, probably 
 dissolving the substance which unites the sperms together. The 
 eggs are now passed out from the oviducts, fertilized, and each 
 of them enclosed in a sort of capsule formed by this secretion, 
 and fixed by a filament of the same substance to one of the 
 swimmerets. Some two hundred eggs, are thus attached, and 
 during the winter gradually develop, the movements of the 
 swimmerets keeping them surrounded by fresh water. 
 
 9. The nervous system consists of a nerve-ring passing into a 
 ganglionated ventral cord, and of nerves connected with these. 
 The ring is thickened dorsally into a large cerebral ganglion (brain) 
 situated in the head between the origin of the eyestalks. It is 
 divided into lobes, which indicate that it is composed of at least 
 three pairs of ganglia fused together. A very long asophageal 
 
ARTHROPODA. 101 
 
 connective runs down on each side of the gullet to join an elon- 
 gated post-cesophageal ganglion, notched on each side, and repre- 
 senting the six ganglion-pairs of segments 3-8 inclusive. The 
 post-oesophageal ganglion is the first of the ventral chain, the 
 thoracic part of which lies in the sternal canal. The rest of 
 the cord consists of eleven well-marked pairs of ganglia united 
 by double connectives. The first five of these are thoracic ganglia 
 placed at unequal distances, the posterior ones being rather near 
 together. The connectives between the third and fourth diverge 
 to allow the sternal artery to pass between them. The last six 
 are the rather smaller abdominal ganglia placed at regular intervals 
 upon the ventral wall of the abdomen. The last is somewhat larger 
 than the others, and probably represents two pairs fused together. 
 
 The ganglia supply nerves to their own segments. Two pairs 
 run from the cerebral ganglion to the eyestalks, and one pair each 
 to the antennules and antennae. The anterior part of the post- 
 cesophageal ganglion supplies the segments to which the mandibles, 
 maxillae, and first two pairs of foot-jaws belong. Its posterior 
 part (the only partially fused ganglion of the third thoracic 
 segment) supplies the third pair of foot-jaws, and behind it two 
 pairs of interganglionic nerves run to the other parts of the 
 segment. From the following ganglia two pairs of nerves arise 
 in most cases, the anterior of which supply the corresponding 
 pair of appendages. An interganglionic pair of nerves is found 
 (in the majority of segments) behind the ganglion. The sixth 
 abdominal ganglion supplies the last two segments. 
 
 The visceral (sympathetic) nervous system consists of an 
 anterior visceral nerve (formed by the union of three trunks, one 
 running back from the cerebral ganglion, and one arising from 
 each oesophageal commissure), which branches out on the stomach, 
 and a posterior visceral nerve which runs forwards on the ventral 
 surface of the intestine from the last abdominal ganglion. Several 
 small ganglia are present on the branches of the anterior visceral 
 nerve. 
 
 The ganglion-cells, which are here confined to the ganglia, 
 possess the usual parts, and are surrounded by special nucleated 
 sheaths. Each nerve-fibre is invested by a firm primitive -sheath, in 
 which are imbedded at irregular intervals, small nerve-corpuscles, 
 with large nuclei and scanty protoplasm, and within the sheath is 
 a clear axis-cylinder. 
 
102 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The nerve-fibres, considered from the physiological standpoint, 
 are either afferent or efferent, transmitting molecular impulses to 
 and from the ganglion-cells. These are confined to the ganglia, 
 which are consequently the central organs. Most of the afferent 
 nerves are sensory, connecting sense-organs with the ganglia, while 
 a majority of the efferent ones are motoi', running from the ganglia 
 to muscles. Each ganglion has more especially to do with the 
 segment it supplies, but can also work conjointly with others. 
 An abdominal ganglion, for example, if the connectives which 
 unite it with its neighbours are cut, still causes regular move- 
 ments in the corresponding swimmerets. These movements are 
 undoubtedly caused by efferent nerve impulses from the ganglion, 
 as they cease on its extirpation. 
 
 If the nerve-cord is cut at the end of the thorax, the abdominal 
 ganglia, working as a whole, cause all the swimmerets to work 
 regularly together. And by allowing more and more ganglia to 
 remain, connected movements of increasing complexity are 
 rendered possible. The addition of the cerebral ganglion, how- 
 ever, makes far more difference than the addition of any other. 
 Without this the movements are for the most part irregular 
 and lacking in purpose. The cerebral ganglion, in fact, controls 
 the body at large. 
 
 The actions may be reflex or spontaneous. A reflex action 
 starts with an external stimulus, by which one or more afferent 
 fibres are affected. These carry impulses to the central organ, 
 from which other impulses pass along efferent fibres to the parts 
 they supply, causing them, if muscular, to contract. Suppose, 
 for instance, the abdomen, when nervously isolated from the 
 rest of the body, be irritated, say, by tapping, it will " flap 
 vigorously." Here the tapping causes afferent fibres to carry 
 impulses to the abdominal ganglia (central organs). These 
 " reflect " the impulses into motor fibres, down which they pass 
 to the flexor and extensor muscles, and cause these to contract. 
 
 Spontaneous actions are not directly dependent on external 
 stimuli. A crayfish from which the cerebral ganglion is removed 
 exhibits constant movements, to all appearance "spontaneous," 
 as above defined. They are, however, not voluntary, the effect 
 of "will," spontaneous actions of this sort being probably the 
 result of impulses passing from the cerebral ganglion. This, too, 
 is the seat of consciousness and intelligence in so far as these exist.. 
 
ARTHROPODA. 103 
 
 The visceral nerves are concerned with the regulation of the 
 movements of the alimentary canal. As small ganglia are devel- 
 oped upon their course in front, they acquire a certain inde- 
 pendence. 
 
 10. The different sense organs have a certain community in 
 structure. They all consist of elongated " end-organs," belonging 
 to the ectoderm, and connected directly or indirectly with the 
 cerebral ganglion by sensory nerve-fibres. 
 
 (1) Tactile Organs. The numerous setae scattered over the 
 body, and the slender ectodermic processes with which they are 
 connected, serve as end-organs of touch. The antennae and, to a 
 less extent, the antennules, are of great use to the animal in 
 informing it as to the position of external objects, and well 
 deserve the name of " feelers." 
 
 (2) Olfactory Organs. Each joint of the exopodite of the 
 antennule bears below two tufts of flattened, spatula-shaped setae, 
 which probably serve as organs of smell, and are denominated 
 olfactory setce. 
 
 (3) Auditory Organs. The organs of hearing are two small 
 auditory, sacs, lodged one in the basal joint of each antennule, and 
 opening on its upper surface by a three-cornered aperture fringed 
 with setae (Fig. 27, A, au). Each is somewhat pear-shaped, with 
 a backwardly directed narrow end, into which an auditory nerve 
 passes. The floor and posterior wall of the sac bear numerous 
 auditory setw, which project into a gelatinous mass, in which are 
 imbedded numerous foreign particles (sand, &c.), the otoliths, 
 introduced from the exterior. The auditory nerve branches in 
 the wall of the sac, one of its fibres becoming continuous with the 
 granular axis of each auditory seta. 
 
 (4) Visual Organs (Fig. 30). The crayfish possesses a pair of 
 eyes, each of which is placed on a two-jointed stalk traversed by 
 an optic nerve, that dilates at its extremity into a rounded optic 
 ganglion. On the end of the stalk is an oval area, the cornea, 
 where the cuticle is transparent and uncalcified. Owing to under- 
 lying dark pigment it appears black. The corneal surface is 
 divided into a large number of small square facets, each of which 
 corresponds to one of the elements which build up the deeper 
 part of this so-called " compound " eye. These visual elements 
 (oinmatidia, visual pyramids) are the slender, four-sided bodies 
 whose bases are applied to the inner sides of the corneal facets, 
 
104 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 while their slender apices abut against the optic ganglion. Each 
 ommatidium is surrounded by a pigmented sheath, and consists of 
 the following parts, commencing from the outside : (a) A corneal 
 lens, (b) modified epidermic corneal cells by which this is secreted, 
 (c) a group of four crystal cells, which secrete refracting structures 
 constituting a crystal cone, (d) a retinula, constituted by seven 
 slender cells which surround a transversely ridged rhabdom (striated 
 
 Fig. 30. CRAYFISH EYE (after Carriere). Enlarged. A, Longitudinal 
 section; cu, cuticle, and ep, epidermis, of eyestalk; co, cornea; vt, 
 vitreous body, the dark lines in its outer part indicate pigment; 
 rt, retinulse imbedded in pigment, and bounded internally by a base- 
 ment membrane (indicated by a strong line) ; n, nerve-fibres running 
 from retinulse to the optic ganglion, g. B, An ommatidium ; co, corneal 
 lens; co.c, corneal cells; cr.c, crystal cells ; cr, crystal cone; rt, retinula, 
 enclosing rhabdom, rh ; 6, basement membrane ; n, nerve-fibres. 
 
 spindle), secreted by them and continuous with the crystal cone. 
 Fibres of the optic nerve are probably continuous with the cells 
 of the retinula, which appear to be the end-organs for sight, while 
 the corneal lens, crystal cone, and rhabdom are refracting elements. 
 The crystal cones form collectively a " vitreous body." 
 
 The action of the eye is best explained by the theory of "mosaic 
 vision," according to which each ommatidium is only affected by 
 rays which correspond with it in direction, so that if the animal 
 
ARTHROPODA. 
 
 105 
 
 perceives the form of external objects, it must be by the combined 
 action of the ommatidia, which almost certainly do not act like 
 so many simple eyes. 
 
 DEVELOPMENT. 
 
 1. Early Stages (Fig. 31). The ovum is centrolecithal, con- 
 taining a central mass of food-yolk. Cleavage (segmentation) is 
 regular, but incomplete and peripheral, chiefly concerning the 
 external protoplasmic part of the oosperm. This is owing to 
 the food-yolk; but this, though it impedes division, is for the 
 most part affected by the cleavage, being divided into radiating 
 
 Fig. 31. BLASTULA AND GASTRULA OF CRAYFISH (after Reicheribach and 
 Huxley). A, Blastula (segmented ovum); bl, blastoderm; v, yolk. 
 B, Gastrula ; ep.b, ectoderm (epiblast) ; m.g, archenteron (which 
 becomes the mid-gut), bounded by endoderm (hypoblast), shaded 
 darkly ; bp, blastopore. 
 
 yolk-pyramids, continuous at first (A) with the segments of the 
 peripheral protoplasm, but -soon (B) becoming separated. The 
 blastula, at the end of cleavage, consists of a central mass of 
 yolk (v), enveloped by the blastoderm, a single layer of small 
 cells (W), which become thickened over a small oval area, the 
 germinal disc, that marks the ventral surface of the embryo. The 
 posterior part of this is invaginated (B) to form a small pouch 
 (m.g) sunk in the food-yolk. The embryo has now reached the 
 gastrula stage, and is practically a double-walled pouch, the inner 
 wall of which is the endoderm. (hypoblast) and the outer wall the 
 ectoderm (epiblast), while its small cavity is the archenteron, and 
 
106 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 its wide mouth the Uastopore (bp), which soon narrows, and even- 
 tually closes. Owing to the presence of food-yolk, which the 
 ectoderm envelops, this layer is much more extensive than the 
 endoderm. The mesoderm (mesoblast) is recognizable at an early 
 stage as a solid mass of cells arising in front of the archentercm, 
 and derived from its wall. It gradually extends, by division of 
 its elements, until it forms a complete layer surrounding the body 
 within the ectoderm. 
 
 2. General Growth. The germinal disc is the first trace of the 
 ventral surface of the embryo. From its hind end the abdomen 
 grows out as a small knob, and on its front end and sides little 
 elevations appear, the rudiments of the eyes, labrum, and append- 
 ages of the head and thorax. The swollen part containing food- 
 yolk corresponds to the dorsal region of the cephalothorax, and 
 it gradually becomes smaller as its contents are used up in the 
 processes of growth. 
 
 The young crayfish are hatched at or near the commencement 
 of summer. "They resemble the adult in most respects, but the 
 first and last abdominal appendages are wanting, and the ends 
 of the forceps are sharply hooked, thus serving as a means of 
 attachment to the cement with which the swimmerets are more 
 or less covered. 
 
 Owing to the firm exoskeleton, growth cannot take place in 
 the same way as in soft-bodied animals, and the adult size is only 
 reached after a series of moults or ecdyses, by which the cuticle 
 (including the endophragmal system and the linings of the fore- 
 and hind-guts) is thrown off, a fresh one being subsequently 
 secreted. Moulting occurs as often as eight times the first year, 
 five the second, and after that less frequently. 
 
 3. Fate of the Germinal Layers. (1) The ectoderm (epiblast) 
 develops into the epidermis, with the exoskeleton and its various 
 types of seta?. The epithelium and cuticle of the fore- and hind- 
 guts are also derived from this layer. They both arise as deep 
 pits which become connected with the archenteron to form a 
 continuous alimentary canal. The nervous system is formed from 
 ectodermal thickenings, and the auditory sacs from ectodermal 
 pits. Each eye (except the pigment, which is mesodermal) is 
 developed from (1) an ectodermal thickening, and (2) an optic 
 pit or fold of ectoderm internal to this. All external to the 
 retinulse arises from (1), while (2) becomes isolated from the 
 
ARTHROPODA. 107 
 
 surface as a solid mass consisting of an outer layer, from which 
 the retinulse originate, and an inner layer which is converted 
 into nerve-fibres connecting the eye with the optic ganglion. 
 
 (2) The endoderm (hypoblast) is converted into the epithelium 
 of the mid-gut, and of the digestive gland which grows out from 
 each side of this. 
 
 (3) The mesoderm (mesoblast) does not divide into regular 
 mesoblastic somites (except in the tail at a comparatively late 
 period). Irregular spaces are formed in it which become the 
 venous sinuses. The circulatory and respiratory organs (except 
 the epithelium and cuticle), the excretory (?), and reproductive 
 organs, together with the muscular system and the connective 
 tissue uniting the various parts, all arise from this layer. 
 
 Further Remarks on the Development of the Crayfish : 
 
 It is a noteworthy fact that most Invertebrates which inhabit rivers 
 have a direct development, that is the young, when hatched, closely 
 resemble the adults in appearance. Marine forms, on the contrary, are 
 commonly hatched as free-swimming larvce, leading an independent exist- 
 ence for some time, and differing more or less from their parents, which 
 they ultimately come to resemble by passing through a series of changes 
 known as a metamorphosis. This is the case, for example, with crabs and 
 lobsters, and a larval form is of obvious advantage to them since it affords 
 a means of widening their area of distribution. But to most fluviatile 
 animals free-swimming larvae would be a positive disadvantage, since they 
 would be very liable to be swept down to sea by the current and so 
 perish. There is some danger of this even in the case of the young crayfish, 
 but the risk is reduced to a minimum by their attachment immediately 
 after hatching to the swimmerets of the mother, and it is stated that 
 even after this she shelters them for a time under her tail, when danger 
 threatens. 
 
 Other Crustacea. 
 
 The Lobster (Homarus) closely resembles the crayfish in structure, but 
 differs in the following respects: Ext. Chars. Last thoracic segment 
 completely fused with cephalothorax. Telson undivided. 1st abd. app. 
 of $ two-jointed, with spoon-shaped end ; 2nd ditto with plate-like endo- 
 podite. Well-developed swimmerets on 1st abd. segment of $ . Antenna 
 with small squame. Digestive Organs. Mid-gut with small bilobed caecum. 
 Intestine of a smooth anterior and ridged posterior part, with a dorsal 
 caecum at the junction of the two. Digestive gland extends far forwards. 
 Respy. Organs. Podobranchs arranged as in crayfish, but the gill-plume is 
 not fused with the epipodite. Arthrobranchs one less in number, the one 
 found on the second thoracic segment of the crayfish being absent here. 
 Pleurobranchs four in number. Reproductive Organs. Two tubular sper- 
 
108 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 TABLE OF CRAYFISH SEGMENTS. 
 
 No. of 
 Segment. 
 
 Skeleton. 
 
 Appendages. 
 
 Apertures. 
 
 
 Gills 
 
 
 Ganglia. 
 
 Sense- 
 Organs. 
 
 
 
 
 
 Pod. 
 
 Arth 
 
 Pleu 
 
 
 
 Pro-sto- 
 
 
 
 
 
 
 
 
 
 mium 
 
 1 " 
 
 ... 
 
 
 
 ... 
 
 ... 
 
 1 
 
 Eyes 
 
 11. 
 
 
 Antennules 
 Antennae 
 
 Auditory 
 Excretory 
 
 ... 
 
 ... 
 
 
 ! Cerebral 
 | (Gang. 1) 
 
 J 
 
 Tactile ) 
 Olfactory > 
 Auditory) 
 Tactile 
 
 III. 
 
 
 Mandibles 
 
 
 
 
 
 , 
 
 
 
 
 
 Mouth 
 
 
 
 
 
 1 
 
 IV. 
 
 
 MX. 1 
 
 
 
 
 
 
 
 V. 
 
 
 MX. 2 
 
 ... { 
 
 Sca- 
 phog 
 
 ... 
 
 
 ! 
 
 Post- 
 cesopha- 
 
 i| 
 
 r vi. 
 
 Cara- 
 
 Mxpd. 1 
 
 ... { 
 
 Epi- 
 pod 
 
 
 ... 
 
 h geal 
 (Gang. 2) 
 
 P 
 
 o'S 
 
 VII. 
 
 pace. 
 
 Mxpd. 2 
 
 
 1 
 
 1 
 
 ... 
 
 
 Si 
 
 
 
 
 
 
 
 
 
 'S S 
 
 VIII. 
 
 
 Mxpd. 3 
 
 ... 
 
 1 
 
 2 
 
 
 ) 
 
 w O 
 
 eg oo 
 
 IX. 
 
 
 Forceps 
 
 
 1 
 
 2 
 
 
 Gang. 3 
 
 .ii 
 
 
 
 
 
 
 
 
 
 15 
 
 X. 
 
 
 Legl | Chel 
 
 ... 
 
 1 
 
 2 
 
 M 
 
 Gang. 4 
 
 
 XI. 
 
 
 Leg2( ate 
 
 | genital 
 
 1 
 
 2 
 
 r 
 
 Gang. 5 
 
 til 
 
 XII. 
 
 
 Leg 3 
 
 
 1 
 
 2 
 
 r 
 
 Gang. 6 
 
 11 
 
 . XIII. 
 
 J 
 
 Leg 4 
 
 \ genital 
 
 ... 
 
 
 1 
 
 Gang. 7 
 
 l 
 
 
 
 ? * 
 
 
 
 
 
 
 QJI 
 
 XIV. 
 
 >. 
 
 Sw. 1] Cop>' 
 
 
 
 
 
 Gang. 8 
 
 O 
 
 XV. 
 
 
 Sw. 2 A pp. 
 
 
 
 
 
 Ganer 9 
 
 l| 
 
 XVI. 
 
 
 Swmt. 
 
 
 
 
 
 \-J C*i 1 1^ . i/ 
 
 Gang. 10 
 
 l 
 
 XVII. 
 
 } Free. 
 
 Swmt. 
 
 
 
 
 ... 
 
 Gang. 11 
 
 |j 
 
 XVIII. 
 
 
 Swmt. 
 
 
 
 ... 
 
 ... 
 
 Gang. 12 
 
 || 
 
 XIX. 
 
 
 Swmt. 
 (very large) 
 
 
 
 ... 
 
 "i 
 
 Gang. 13 
 
 s| 
 
 I XX. 
 
 J 
 
 
 
 Anus 
 
 
 ... 
 
 ... i 
 
 
 0) 
 
 r = rudiment; [ ] signify present or absent. 
 
MOLLUSCA. 109 
 
 I 
 
 maries united by a transverse commissure ; spermiducts comparatively 
 short. Nervous System. Post-oesophageal ganglion comparatively small. 
 Development. Hatched as a somewhat shrimp-like Mysis larva, the last 
 five pairs of thoracic limbs of which are provided with slender exopodites, 
 afterwards lost, and which has no abdominal appendages. 
 
 The Sea Crayfish or Norway Lobster (Nephrops) closely resembles the 
 common lobster, but the antenna possesses a large squame, and the gill- 
 plume of the first podobranch (that of mxpd. 2) is rudimentary or absent. 
 The number of gills on each side in the three forms is, therefore, as follows, 
 writing p, a, and pi for podo-, arthro-, and pleurobranchs, and omitting 
 rudiments : 
 
 Astacus, 6p + 11 a + I pi = 18. 
 
 Homarus, Qp + 10a + 4 pi = 20. 
 
 Nephrops, 5p + lOot + 4?>Z = 19. 
 
 CHAPTER VII MOLLUSCA. 
 11. ANODONTA and UNIO (Fresh Water Mussels). 
 
 THESE are bivalve molluscs found in considerable numbers in the- 
 mud at the bottom of many ponds, streams, and canals, in this 
 and other countries. Mature specimens may be as much as five 
 or six inches long. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The bilaterally symmetrical body is 
 unsegmented, flattened from side to side, and entirely enclosed 
 in a calcareous bivalve shell, cuticular in nature, and consisting 
 of a right and a left piece (valve). These two valves are hinged 
 together dorsally by the ligament, an uncalcified band of horny 
 elastic fibres, which in the closed shell are on the stretch. In 
 dead specimens there is nothing to keep the valves closed, and 
 they consequently " gape," owing to the elasticity of the ligament, 
 but in the living animal their edges can be closely approximated 
 by means of two strong adductor muscles, running across from 
 valve to valve. Each valve is oval with a rounded anterior and 
 a more pointed posterior end, a strongly curved ventral margin, 
 and a straight dorsal margin near the front end of which is the 
 umbo or oldest part of the shell. Around the umbo lines of growth 
 
110 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 are concentrically disposed, which mark successive additions made 
 during the life of the animal. The outside is olive green in colour, 
 owing to the periostracum, a thin horny membrane, which also 
 forms a flexible margin to the shell. Within the periostracum 
 there is a prismatic layer, and the shell is lined by a pearly layer, 
 marked by a number of muscular impressions. Near the anterior 
 end there is an oval anterior adductor impression, and near the 
 posterior end a similar but larger posterior adductor impression. 
 The two are connected by a pallial line running parallel to the 
 
 KrS 
 
 Fig. 32. GENERAL DISSECTION OF UNIO (from Glaus, after Grobben). 
 V.S and H.S, anterior and posterior adductors; M.S, labial palp; F, 
 foot; Mt, mantle; K, gills; C.g, cerebro-pleural ganglion; P.g, pedal 
 ganglion; M.g, visceral ganglion; 0, mouth; M, stomach; L, digestive 
 gland; Kr.S, crystalline style; D, intestine; Af, anus; G, genital 
 gland; A, exhalent aperture; E, inhalent aperture; N, nephridium; 
 Vh, auricle; Hk, ventricle ; V. A, anterior aorta ; H. A, posterior aorta : 
 P, organ of Keber. 
 
 ventral edge of the shell. Immediately behind the anterior 
 adductor impression is a much smaller anterior retractor impression, 
 behind which again is a small protractor impression. Just in front 
 and above the posterior adductor impression, there is a small 
 posterior retractor impression. From the various places above 
 mentioned lines of shifting converge towards the umbo, indicating 
 the successive positions occupied by the impressions during earlier 
 stages of growth. 
 
MOLLUSCA. Ill 
 
 In Unio the valves are connected at the hinge-line by small projections, 
 teeth, which fit into corresponding sockets. 
 
 In removing the animal from its shell the various muscles 
 attached to the impressions are cut through. They have corre- 
 sponding names. The adductor muscles (Fig. 32, V.S and H.S) 
 are broad bands of fibres which run transversely across from 
 one valve to the other, and by their contraction keep the shell 
 closed. 
 
 Each shell is lined by a nap, the right or left lobe of the 
 mantle. These lobes have thickened edges which are attached 
 to the shell along the pallia! line by means of muscle-fibres 
 (Fig. 32, Mt). They are continuous dorsally with the wall of 
 the body, from which they grow out, are fused together above 
 and behind the posterior adductor (H.S), and immediately beyond 
 this are closely apposed to bound two oval openings. These are 
 a smaller exhalent or cloacal aperture (A) above, and a larger 
 inhalent aperture (E) below, the edges of which are fringed with 
 short tentacles. When at rest the mussel is completely imbedded 
 in the mud, with its posterior end projecting, so that water can 
 pass in at the inhalent and out at the exhalent aperture. In this 
 way the animal is supplied with food and oxygen on the one hand, 
 and gets rid of waste on the other. The mantle-lobes enclose 
 between them a large space, the mantle-cavity, which is divided 
 into two parts, a large branchial chamber below, and a small supra- 
 branchial chamber above. It must not be supposed that the 
 mantle lobes are fused posteriorly to bound the inhalent and 
 exhalent apertures, or ventrally to bound the branchial chamber. 
 If the animal is placed on its back the lobes can be separated 
 without cutting anything, as in Fig. 33, where by this means the 
 contents of the branchial chamber are exposed. In this figure 
 the smooth sides of the exhalent aperture have been separated, 
 and are seen just above A, on either side of which letter are the 
 fringed right and left sides of the inhalent aperture. A large 
 oval visceral mass (mesosoma), compressed from side to side, hangs 
 down into the branchial cavity, but there is no distinct head, nor 
 anything comparable to the lateral appendages of a crayfish. 
 The lower edge of the visceral mass is produced into a yellow 
 ploughshare-shaped muscular expansion, the foot' which projects 
 forwards (Fig. 32, F, and Fig. 33, P), and can be protruded from 
 the shell, serving as a locomotor organ. On either side of the 
 
112 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 visceral mass is a gill (ctenidium), made up of two elongated 
 plates (Figs. 32 and 33, K). These extend behind the visceral 
 mass below the posterior adductor, and in this region the gills of 
 
 opposite sides are united to- 
 gether. In Fig. 33 this union 
 has been cut through in order 
 to expose part of the supra- 
 branchial chamber. At the 
 front end of the visceral mass, 
 and just beneath the anterior 
 adductor, is a transversely 
 elongated mouth (0), on each 
 side of which are two tri- 
 angular folds, the labial palps 
 (Fig. 33, Se), which are united 
 together at their bases to form 
 ridge -like anterior and pos- 
 terior lips. The exhalent 
 aperture opens out of a cloacal 
 chamber, which is the posterior 
 part of the supra -branchial 
 chamber, and is floored by the 
 united gills. The last part of 
 'the intestine or rectum,, which 
 ends in the anus (Fig. 32, Af, 
 and Fig. 33, A), runs dorsal 
 to the posterior adductor, and 
 projects into this chamber. 
 Upon either side of the vis- 
 
 K 
 
 Fig. 33. NERVOUS SYSTEM or ANO- 
 DONTA (from Glaus after Keber}. 
 0, Mouth; A, anus; K, gills; P, 
 foot; Se, labial palp; Gg, cerebro 
 
 pleural ganglion ; Pg, pedal ganglion; ceral mass, near the attach- 
 Vg visceral ganglion ; G, part of t f tl m u j 
 
 mmi-hal fflfl.nH OA' nnp mnrr nf rh+.fn 8 
 
 genital gland ; Oe', opening of ditto ; 
 
 Oe", opening of excretory organ. 
 
 or female genital opening is 
 placed (Fig. 33, Oe'), and 
 close to this is a rather larger excretory or renal opening (Oe"). 
 
 2. Skin. The most important part of this is the mantle, which 
 forms a sort of flap drawn out on either side, and secretes most 
 of the shell. The whole external surface of the mantle and 
 dorsal region of the body can add to the pearly-layer, but the 
 periostracum and prismatic layer can only be increased by the 
 thickened edge of the mantle, and hence if worn away from 
 
MOLLUSCA. 113 
 
 the older part of the shell, as commonly occurs in the region of 
 the umbo, cannot be renewed. 
 
 Pearls are formed by the deposition of matter similar to that making 
 up the pearly-layer around grains of sand, &c., that get into the shell. 
 The pearl-fisheries of Britain were once famous, the pearls being obtained 
 from a species of Unio. In China, small metal images of Buddha are 
 placed within the shells of fresh-water mussels, and thus receive a pearly- 
 coating. 
 
 The mantle is covered externally and internally by a layer of 
 simple columnar epithelium, which on the outer side contains 
 many glandular cells, and on the inside is ciliated. The sub- 
 stance of the mantle between these layers of epithelium is made 
 of connective tissue, traversed by muscle-fibres, blood-channels, 
 and a complex network of nerves. 
 
 The skin covering the visceral mass and foot is very glandular 
 and closely connected with underlying layers of muscle. The 
 labial palps are, like the inside of the mantle, covered by ciliated 
 epithelium. 
 
 The shell consists of an organic basis impregnated (except in 
 the periostracum) with carbonate of lime. The prismatic layer 
 is made up of polygonal prisms packed closely together, and 
 arranged obliquely to the surface. The pearly-layer is composed 
 of numerous thin laminae, the edges of which constitute a series 
 of delicate ridges which by diffraction produce an iridescent 
 appearance. 
 
 3. The digestive organs consist of a convoluted tube running 
 from mouth to anus and of a large digestive gland (Fig. 32). 
 The mouth (0), on each side of which are the transversely striated 
 labial palps (MS), leads into a very short gullet (oesophagus), 
 which runs almost directly upwards, just behind the anterior 
 adductor, and passes into a dilated stomach (M). This is succeeded 
 by a narrow thin-walled intestine (D), which coils about (mostly 
 in the median vertical plane) within the visceral mass, where it 
 is closely surrounded by the genital gland (G), finally curving 
 upwards and running back dorsally as the rectum through the 
 ventricle of the heart, and over the posterior adductor to terminate 
 in the anus. The cavity of the stomach is partially subdivided 
 by irregular folds, and the ventral wall of the rectum is longi- 
 tudinally infolded to form a typhlosole. A lobed digestive gland 
 (L), dark brown in colour and made up of numerous branched 
 2 8 
 
114 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 tubules, closely surrounds the stomach, into which it opens by 
 several ducts. 
 
 The alimentary canal is lined throughout by simple columnar 
 epithelium, which is partly ciliated, partly glandular. External 
 to this are muscular layers. The tubules of which the digestive 
 gland is made up are lined by glandular epithelium, the cells of 
 which are cuboidal with brown granular contents. By the succes- 
 sive unions of these tubules the ducts are ultimately formed. 
 
 The ciliated epithelium, lining the mantle-lobes and covering 
 the gills and labial palps, sets up currents in the mantle-cavity, 
 and causes water to enter the branchial chamber by the inhalent 
 orifice. Some of this is conducted along the groove between each 
 pair of labial palps to the mouth, into which the small organisms 
 it contains are carried. These constitute the food, and by the 
 contraction of the muscular walls of the alimentary canal gradu- 
 ally pass backwards within it. The fluid secreted by the digestive 
 gland contains ferments by the action of which fats are emul- 
 sified, while starch and proteid are respectively converted into 
 grape-sugar and peptone. The length of the intestine increases 
 the surface for absorption, and this is augmented by the typhlosole. 
 The digested parts of the food diffuse into the blood-vessels of 
 the intestinal walls, and the refuse is ejected at the anus, being 
 afterwards carried out of the cloacal chamber by the currents 
 which flow from the exhalent aperture as a result of ciliary 
 action. 
 
 In specimens examined during autumn a transparent elastic rod, 
 the crystalline style, will be found in the stomach. It is of albu- 
 minous nature and probably serves as a store of nutriment, for it 
 is gradually used up during the winter. Some material of similar 
 kind, only less compacted, is found in the intestine at the same 
 period. 
 
 4. Circulatory Organs (Figs. 32 and 34). A blood system 
 alone is present, containing colourless blood in which are sus- 
 pended numerous nucleated amoeboid corpuscles devoid of colour. 
 This system is constituted by heart, arteries, veins, and irregular 
 blood-spaces. The heart, which is contained within a thin-walled 
 pericardial cavity situated on the dorsal side of the body, consists 
 of a central oval muscular ventricle, into which a thin-walled 
 auricle opens on each side. The auricles are funnel-shaped, with 
 the narrow end attached to the ventricle, the broad end to the 
 
MOLLUSCA. 115 
 
 ventro-lateral wall of the pericardial cavity. An auricula-ventricular 
 valve is placed at the point of union of each auricle with the 
 ventricle. It is made up of two small flaps, which permit blood 
 to pass into but not out of the ventricle. 
 
 The ventricle (through which the rectum runs) gives off two 
 arteries, an anterior aorta in front running forwards above the 
 rectum, and a posterior aorta behind running backwards below 
 the rectum. The anterior aorta divides into branches, which 
 supply the labial palps, the greater part of the alimentary canal, 
 the foot, the anterior adductor, and adjacent parts; while the 
 posterior aorta supplies the hinder part of the rectum, the posterior 
 adductors, and the greater part of the mantle. The ultimate 
 branches of these arteries end in minute irregular spaces (lacunae) 
 from which veins arise. These are vessels in which the blood is 
 flowing towards the heart. The foot and organs of the visceral 
 mass return their blood to the vena cava, a longitudinal vein lying 
 in the middle line immediately below the floor of the pericardial 
 chamber. The blood passes from the vena cava into the neph- 
 ridium on either side, where it enters a close network of channels. 
 From this network vessels run to the gills, opening on each side 
 into an afferent branchial vein, which runs along the junction of 
 the outer and inner gill-plate. Numerous branches pass into the 
 gill-substance from, this vein. The blood is returned to each 
 auricle by an efferent branchial vein, which takes a course along 
 the attachment of the outer lamella of the outer gill-plate on that 
 side. Efferent veins from the mantle-lobes also enter the efferent 
 branchial veins at each end. 
 
 Course of the Circulation. The heart is systemic, receiving 
 pure blood from the gills and mantle-lobes, which passes into the 
 auricles, and thence into the ventricle. The former contract 
 together, filling the ventricle, which then also contracts in a 
 wave-like manner, and forces the blood through the arteries to 
 the body at large. From the smallest arterial branches the blood 
 passes into the lacunae, and thence into venous channels, which 
 are arranged as above described. The result is that the blood 
 from, the visceral mass and foot is purified in the nephridia, and 
 then in the gills, before reaching the auricles, while the blood 
 from the mantle-lobes is oxygenated there, and returned to the 
 auricles without passing through either nephridia or gills. 
 
 4. Respiratory Organs (Figs. 32, 33, and 34). These consist 
 
116 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Fig. 34. MUSSEL, ? . A, Section passing through pedal ganglia, p.g, 
 showing stomach, s, surrounded by digestive gland, d.g; labial palps, 
 l.p, and foot, /, projecting into branchial chamber, laterally bounded 
 by mantle, m. B, Section passing through heart. Above is seen the 
 ventricle, vn, traversed by rectum, r, with auricle, aw, on each side. 
 Below pericardium are seen ureters, u, with vena cava, v.c, between 
 them ; and kidneys, Jc, with cerebro- visceral connectives (black) be- 
 tween them. Projecting into branchial cavity is visceral mass showing 
 intestine, i, cut through in six places, and foot, /; also inner and outer 
 gill-plates, i.g and o.g, on each side ; ax, gill axis on each side traversed 
 by afferent branchial vessel (black) ; the outer gill-plates are full of 
 Iarva3, and # is placed in each of the outer supra-branchial passages, 
 the smaller inner passages are seen above the inner gill-plates. The 
 branches of the ovary, which fill up the greater part of the visceral 
 mass, are omitted. C, Section passing through visceral ganglia, v.g. 
 The rectum, r, is seen above the posterior adductor, p. add. The inner 
 gill-plates have united together behind the visceral mass ; a # is placed 
 in each outer supra-branchial passage, and in the median passage formed 
 by union of two inner ones. In a section still further back these three 
 channels would be found to have coalesced to form the cloacal chamber. 
 Gill axes as in B. D, Small part of longitudinal section through outer 
 gill (enlarged), showing the two gill-plates formed by union of flattened 
 gill-filaments, f, supported by chitinous rods (dark dots). Between 
 the plates are seen two water-tubes, ic.t, separated by an interlamellar 
 junction, i.l.j, in which is a blood-vessel, b.v. The plates are per- 
 forated by numerous small apertures, |, f , leading into the water- 
 tubes. E, Outer parts of six gill-filaments, further enlarged, showing 
 supporting rods. 
 
MOLLUSCA. 117 
 
 of the mantle and of a gill (ctenidium) on each side, composed of 
 an inner and an outer gill-plate, each of these being again made 
 up of an outer and inner lamella united together ventrally. The 
 outer lamella of the outer gill-plate is attached by its dorsal edge 
 to the inner side of the mantle, close to where it joins the body- 
 wall. The inner lamella of the outer gill is united above with 
 the outer lamella of the inner gill, and the common union of the 
 two (gill-axis) is attached above to the wall of the body. The 
 inner lamella of the inner gill-plate is attached anteriorly to 
 the body-wall, is then free for a short distance, and behind 
 the visceral mass unites with its fellow in the middle line to 
 form the floor of the cloacal chamber. The gill-lamellae are 
 vertically striated, and between the striations numerous minute 
 apertures are present, leading into an interlamellar space present 
 in the interior of each plate, which is divided into a number of 
 vertical water-tubes by the union of the two lamellae along a 
 corresponding number of narrow vertical strips by interlamellar 
 junctions. The visceral mass divides the anterior part of the 
 supra-branchial chamber into right and left halves. Each of these, 
 owing to the dorsal attachment of the gill-axis, is again subdivided 
 into two. There are, therefore, four channels above the gill- 
 plates in this region, into which the four sets of water-tubes 
 open. Behind the visceral mass the two inner channels coalesce 
 with one another, and, finally, in the cloacal region, the supra- 
 branchial chamber is undivided. These various relations will be 
 understood by examining Fig. 34. 
 
 In Fig. 33 the cohering inner plates have been separated so as to expose 
 part of the supra-branchial chamber. 
 
 The gills of Anodon are unusually complicated. They appear to have 
 arisen in the following way : From the gill-axis on either side two longi- 
 tudinal rows of filaments grew out. The ends of the outer row turned 
 sharply outwards and upwards ; those of the inner row inwards and 
 upwards. Thus in cross-section a W-shaped outline would be seen. These 
 filaments then fused into two folded lamellae, numerous apertures being 
 left, however. The descending and ascending halves of each lamella then 
 became connected to form a gill-plate. Union of the plates with one 
 another and with surrounding parts increased the complexity, and brought 
 about the distinction between branchial and supra-branchial chambers. 
 
 Each gill is covered by a single layer of ciliated epithelium. 
 The external ridges (representing gill-filaments), which appear to 
 the naked eye as vertical striae, are supported by slender horny 
 
118 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 rods, two of which run vertically within each ridge. Beneath 
 the epithelium the gills are composed of loose connective tissue, 
 everywhere permeated by blood-containing lacunae. The inter- 
 lamellar junctions are traversed by more definite blood-channels. 
 Respiration is said to be effected more by the mantle than the 
 gills, which are elaborate current-producing organs, and, as usual, 
 essentially consists of gaseous interchange between the blood and 
 the surrounding medium, oxygen being taken up and carbon 
 dioxide eliminated. Water entering the branchial chamber by 
 the inhalent aperture partly passes to the mouth and partly into 
 the water-tubes of the gills through the numerous small apertures 
 in the lamellae. It then runs upwards into the supra-branchial 
 passages, and backwards through the exhalent aperture to the 
 exterior. All the currents are the result of ciliary action. 
 
 6. Excretory Organs (Figs. 32 and 34). A pair of kidneys 
 (organs of Bojanus) are present, each of which is essentially a 
 tube folded upon itself, and communicating on the one hand with 
 the pericardial cavity, which appears to represent a much-reduced 
 coelom, and on the other with the exterior by the renal opening 
 noted above. The tube is divided into a thick-walled glandular 
 part, the lining of which is raised into numerous ridges, and a 
 thin-walled ureter (non-glandular part). The vena cava lies 
 between the two ureters, which open in front by the renal 
 openings, and communicate posteriorly with the glandular parts 
 which underlie them. The glandular part is broadest behind, 
 where it abuts upon the posterior adductor, and narrows in front 
 where it opens into the floor of the pericardium. The kidneys 
 should perhaps be regarded as nephridia, like the excretory organs 
 of earthworm, since they are excretory tubes opening out of a 
 coelomic body-cavity. 
 
 The glandular parts of the kidneys are lined by glandular 
 epithelium, the cells of which are granular, and often contain 
 concretions, in which guanin (C 5 H 5 N 5 0), uric acid (C 5 H 4 N 4 3 ), 
 and urea (CH 4 lSr 2 0), have been stated to occur. The organs of 
 Keber, consisting of glandular tubules, and situated one on each 
 side of the pericardium, into which they have been said to open, 
 may also have an excretory function. 
 
 7. Eeproductive Organs. The sexes are distinct, and the 
 female is somewhat thicker from side to side. The genital 
 glands (spermaries or ovaries, as the case may be) are much- 
 
MOLLUSCA. 119 
 
 branched structures, surrounding the coils of the intestine in 
 the visceral mass (Fig. 32, G). They are yellowish in the male, 
 reddish in the female, and consist of an immense number of 
 blind tubules, from which ducts pass on either side, uniting 
 together into a short spermiduct or oviduct which opens to the 
 exterior by the genital aperture (Fig. 33, Oe'). 
 
 The tubules of the gonads are lined by germinal epithelium. 
 These in the male produce large numbers of sperms, each of 
 which possesses a cylindrical head and motile filiform tail. In 
 the female ova are developed, each of which is covered by a 
 vitelline membrane, which at one point, the micropyle, is incom- 
 plete. The vitellus, which contains a moderate amount of food- 
 yolk, is separated when ripe by albuminous fluid from the 
 vitelline membrane. It contains a large germinal vesicle with a 
 germinal spot. Each ovum while still in the ovary is contained 
 in a follicle, to the wall of which it is attached by a protoplasmic 
 stalk passing through the micropyle. 
 
 The ova pass back from the genital openings to the cloacal 
 chamber, and then forwards into the water-tubes of the outer 
 gill-plates, where they are fertilized by sperms brought in by the 
 inhalent current. The sperm enters the ovum by the micropyle. 
 The breeding season is in the summer. 
 
 8. Muscular System. The skin is intimately connected withx 
 underlying muscle, and there are also definite muscles, of which \ 
 the adductors have already been described. The foot is almost / 
 entirely made up of muscular tissue, and slender protractor, anterior I 
 retractor, and posterior retractor muscles, which take origin from I 
 the corresponding impressions on the shell are inserted into it. 
 
 The muscles are composed of fusiform muscle-cells, exhibiting 
 somewhat indefinite transverse striations. The foot serves as an \ 
 organ of locomotion by which the animal can move forwards in \ 
 the mud, leaving a furrow-like trail behind it. The retractor J 
 muscles by their contraction draw the foot back, and the pro/ 
 tractors pull it forwards. 
 
 9. The nervous system (Figs. 32, 33, and 34) consists of a wide 
 oesophageal nerve-ring, a long visceral loop connected with this 
 on the dorsal side, and numerous nerves. Two pairs of ganglia 
 (cerebro-pleural and pedal) are developed upon the ring, and one 
 pair (visceral) upon the loop. It is convenient to use the term 
 commissure for a nerve-cord connecting ganglia of the same name, 
 
120 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 and the term connective for a nerve-cord connecting ganglia of a 
 different name. Both kinds are here exemplified, but most of the 
 nerve-cords are connectives, not commissures. On each side of the 
 mouth, just beneath the skin, a cerebro-pleural ganglion is situated, 
 and the dorsal part of the nerve-ring constitutes a short com- 
 missure above the mouth connecting these two ganglia. A pair 
 of pedal ganglia lie close together at the junction of the foot and 
 the visceral mass, resting upon the muscle of the former nearer 
 its anterior than its posterior end. Each side of the nerve-ring 
 may be regarded as a cerebro-pedal connective, since it unites a 
 cerebro-pleural ganglion with the pedal ganglion of the same side. 
 The visceral loop runs back along the dorsal side from the cerebro- 
 pleural ganglia to the under side of the posterior adductor, where 
 it thickens into a closely apposed pair of visceral (parieto-splanchnic) 
 ganglia. Each side of the loop constitutes a very long cerebro- 
 visceral connective running back from one cerebro-pleural ganglion 
 to the visceral ganglion of the same side, to reach which it first 
 traverses the digestive glands and then takes a course along the 
 inner side of the kidney. 
 
 The cerebro-pleural ganglia supply the lips, labial palps, anterior 
 adductor, and probably the otocysts. They also give off anterior 
 pallial nerves which break up into a network in the margin of the 
 front part of the mantle. The pedal ganglia supply the muscular 
 tissue of the foot, and from the visceral ganglia three chief pairs 
 of nerves run out to the gills and mantle. These are (1) in front, 
 branchial nerves, then (2) lateral pallial nerves, and (3) posterior 
 pallial nerves, which supply the tentacles of the inhalent aperture, 
 and break up to form a complex nervous network in the margin 
 of the hinder part of the mantle, continuous with the similar 
 network arising from the anterior pallial nerves. The visceral 
 ganglia also send nerves to the posterior adductor and the rectum. 
 
 A visceral or gastric nerve runs to the digestive glarid and 
 stomach from each cerebro-visceral connective, not far from its 
 anterior end. 
 
 As usual, ganglion-cells and nerve-fibres are the essential parts of 
 the nervous system, the former being entirely confined to the 
 outer part of the ganglia and nerve-origins. 
 
 10. Sense Organs. (1) Tactile Organs. The labial palps act 
 as feelers, and their epithelium comes into close relation with 
 fibres from the cerebral ganglia. The tentacles surrounding the 
 
MOLLUSCA. 121 
 
 inhalent aperture are well supplied with fibres from the visceral 
 ganglia, and appear to be specially sensitive. The palps, tentacles, 
 and mantle margin are provided with tactile cells, each of which 
 is elongated and provided at its external end with a bunch of 
 delicate setse. 
 
 (2) Gustatory Organs. The labial palps (?) possibly subserve 
 the function of taste. 
 
 (3) Olfactory Organs. Each of the branchial nerves is covered 
 at its beginning by a patch of sensory epithelium known as an 
 osphradium, and usually considered as a sort of olfactory organ 
 which perhaps tests the quality of the water entering the pallial 
 chamber. 
 
 (4) Auditory Organs. Two minute vesicles, the otocysts, are 
 found just behind the pedal ganglia, each of them being placed 
 at the end of an auditory nerve which comes off from the lower 
 end of the corresponding cerebro-pleural connective, and the 
 fibres of which probably run up the connective to the cerebro- 
 pleural ganglion of the same side. 
 
 The otocysts are lined by ciliated columnar epithelium of 
 sensory nature, and each of them contains a rounded otolith 
 made up of concentric layers of carbonate of lime. 
 
 The otocysts are difficult to study in Anodon, but are readily seen under 
 the microscope in a living specimen of Cyclas, a small freshwater bivalve 
 abundant in many streams and canals. 
 
 The mussel never at any time possesses eyes. 
 
 LIFE-HISTORY. 
 
 The ova are fertilized and the oosperms developed, up to a 
 certain point, in the water-tubes of the outer gills of the female, 
 the interlamellar junctions of which secrete a nutritive substance. 
 It is an interesting fact that the shell commences as a single 
 saddle-shaped plate on the dorsal surface. As the mantle-lobes 
 are formed^this is divided into the two valves, which remain 
 connected by the ligament, so that this must be regarded as an 
 uncalcified part of the shell. Each valve is triangular, and its 
 lower pointed end is bent inwards into a sharp spine. In the 
 hinder part of the body a pit is formed, the lyssus gland, which 
 secretes a long sticky filament or lyssus. 
 
122 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Many shell-fish, e.g., the salt-water Mussel, are attached during life to 
 surrounding objects by threads forming the byssus. 
 
 The embryo now passes out of the gill of the parent, being 
 ejected from a small opening bounded by the coalesced mantle- 
 lobes, and situated some distance above the exhalent aperture. 
 The young mussel is very unlike the adult. It was formerly 
 thought to be a distinct mollusc, and named Glochidium. This, 
 however, was afterwards found to be only a larva i.e., a free- 
 living embryo, very dissimilar to the mature form, and undergoing 
 a series of changes known collectively as a metamorphosis before 
 becoming adult. 
 
 The Glochidium has special larval sense organs, by which it 
 is enabled to detect the presence of fish, and it swims freely by 
 napping the valves of the shell. The long byssus trails behind, 
 and if it comes into contact with the skin of a fish adheres to it, 
 and the sharp spines on the valves then effect a firmer hold. In 
 this position the larva is covered over by outgrowths from the 
 skin of the fish, and undergoes metamorphosis. The byssus and 
 larval sense organs are lost, while the foot, gills, and internal 
 organs are gradually developed. The host is then left. 
 
 This peculiar parasitic habit of the larva prevents it from being 
 washed down to sea by the current (see p. 107). 
 
 12. HELIX (The Snail). 
 
 The two species of Helix most available in Britain for dissec- 
 tion are Helix aspersa, the common snail, and Helix pomatia, the 
 Eoman snail. H. pomatia is characterized by its much larger 
 size, and lighter colour. In the essential features of its organ- 
 ization, however, it differs but little from H. aspersa, which, as 
 the commoner kind, will be described here. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The most striking feature is the pos- 
 session of a shell, into which the animal can entirely withdraw 
 
MOLLUSCA. 123 
 
 itself. It consists of one piece only; in other words, it is uni- 
 valve. If a hollow cone with a very small angle is thought of 
 as wound round and round into a right-handed spiral with 
 closely adherent coils, a good notion will be formed of its 
 structure. By the juxtaposition of the inner edges of the coils 
 or whorls, a hollow pillar, the columella, is produced, which forms 
 the axis of the spiral, and opens to the exterior below. The 
 opening of the shell (mouth, or peristome) has a prominent smooth 
 rim, and the blind end is termed the apex. 
 
 During winter the snail passes into a torpid condition (hyber- 
 nates) when the aperture of the shell is closed by means of a 
 thick calcareous plate, the epiphragm or hylernaculum. When the 
 animal is fully expanded, the part of the body protruding from 
 the shell is bilaterally symmetrical, terminated in front by a 
 distinct head, and produced ventrally into the broad sole-like 
 foot, an elongated muscular expansion, tapering behind to a point, 
 and ending in front just below the mouth. The animal crawls 
 by wave-like contractions of this organ. The dorsal part of the 
 body projects as a spirally coiled visceral hump, always contained 
 within the shell, and attached to the columella by a special 
 muscle (spindle muscle) by the contraction of which the animal 
 can be completely withdrawn into its shell. The anterior boun- 
 dary of the visceral hump is marked by a thickened edge, the 
 collar. 
 
 The head bears two pairs of tentacles or feelers, which are hollow, 
 and can be retracted into the body much as the finger of a glove 
 can be turned into the glove's interior. Each of the posterior 
 longer pair, the optic tentacles, bears a small black dot, the eye, on 
 the outer side of its tip. The anterior shorter pair are the olfactory 
 tentacles. In the front of the head is the mouth, guarded by an 
 inferior and two lateral lips. Below the mouth there is a small 
 pore, the opening of the supra-pedal gland. Not far below the 
 right optic tentacle the rounded genital opening is situated. In 
 the thickened anterior edge of the mantle, on the right side, 
 there is a deep depression, into the left side of which the large 
 valvular respiratory aperture opens, and on the right side of this a 
 smaller anus. The respiratory opening leads into a spacious 
 mantle-cavity, which acts as a lung and is roofed in by the mantle, 
 a vascular flap-like outgrowth of the body-wall. 
 
 2. Skin. The skin is smooth on the under side of the foot, 
 
124 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 and on the visceral hump, where it is so thin and transparent 
 that many of the internal organs can be seen through it. Else- 
 where the surface of the body is corrugated. The skin is very 
 glandular and secretes the characteristic slime. 
 
 The skin consists of an epidermis made up of a single layer of 
 cells, and a connective tissue dermis, closely united with under- 
 lying muscular tissue. The epidermal cells are flat on the visceral 
 
 Fig. 35. DIGESTIVE ORGANS AND NERVOUS SYSTEM or SNAIL. A, General 
 view ; B, left side of stomach, &c. ; C and D, side and hind views of 
 buccal mass; f, foot; t, tentacle; m, mouth; b.m, buccal mass; r.s, 
 radular sac ; ce, gullet ; cr, crop ; st, stomach ; i, intestine ; r, rectum ; 
 a, anus; s.gl, salivary glands; s.d, salivary ducts; LI, Lr, left and 
 right lobes of digestive gland; l.b.d, r.b.d, ducts of ditto; c.g, cerebral 
 ganglion ; v.g, ventral ganglionic mass ; b.g, buccal ganglion ; t.n, 
 tentacular nerve; b.n, buccal nerve; o.t, hermaphrodite gland; h.d, 
 hermaphrodite duct ; g, place from which genitals have been cut away. 
 
 hump, cylindrical elsewhere. Many of them constitute uni- 
 cellular mucous and pigment glands, while few-celled pigment 
 and calcareous glands are also present. These various glands 
 project into the dermis, which is also traversed by muscle-fibres, 
 blood-spaces, and nerves. 
 
MOLLUSCA. 125 
 
 The shell consists of three layers. There is a thin external 
 chitinous periostracum, which is pigmented, and gives colour to 
 the shell. Below this is a dense prismatic layer, and internally a 
 thinner pearly layer, composed of numerous lamina?, and with a 
 smooth and polished internal surface. The last layer can be 
 secreted by all parts of the epidermis covering the visceral hump, 
 but the two others can only be formed by the collar, which, as 
 the animal grows, adds successive increments to the mouth of 
 the shell, the boundaries between which are indicated by lines of 
 growth. 
 
 3. The digestive organs (Figs. 35, 36) consist of a convoluted 
 gut running from the anterior ventral mouth to the unsymmetri- 
 cally placed anus, and receiving the secretions of salivary and 
 digestive glands. The gut is divisible into buccal mass (pharynx), 
 gullet, crop, stomach, intestine, and rectum. 
 
 The mouth leads into a large mouth-cavity, contained in an 
 oval muscular buccal mass. Immediately within the lips, dorsally, 
 is a crescentic, horny, toothed structure, the jaw. But the most 
 important organ connected with the mouth is the odontophore. 
 This consists of an elevation rising up like a tongue from the 
 floor of the mouth, on which .a horny ribbon (the radula), bearing 
 innumerable minute pointed teeth, is spread out from back to- 
 front, passing behind into a pouch, the radular sac, which lies 
 at the back of the buccal mass, and forms a small rounded pro- 
 tuberance of whitish colour. Into the outside of the buccal mass 
 special muscles are inserted, the buccal protractors and retractors. 
 From the upper side of the buccal mass a narrow, thin-walled 
 gullet (oesophagus) passes back, and merges into a spindle- 
 shaped crop, the thin walls of which are marked by longi- 
 tudinal striations. The crop narrows behind, and is succeeded 
 by a rounded stomach with moderately thick walls. This turns 
 sharply upon itself, and is then followed by the narrow, thin- 
 walled intestine, which first bends ventrally, and then, after 
 coiling a little, passes into the rectum, which takes a straight 
 course along the right side of the lung-chamber to open by 
 the anus. Projecting into the intestinal cavitv is a longitudinal 
 fold. 
 
 The salivary glands are paired branching structures, placed one 
 on each side of the crop, to which they are attached by connective^ 
 tissue. A slender salivary duct runs from each of them down the 
 
126 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 side of the gullet, and, dilating slightly, opens into the side of 
 
 the mouth-cavity. 
 
 The digestive gland ("liver") 
 is a large brown organ making 
 up a considerable part of the 
 visceral hump. It is divided 
 into right and left lobes, of 
 which the latter (LI) is deeply 
 three-cleft, and much larger 
 than the other, which occupies 
 the final coils of the visceral 
 hump. Two ducts (bile-ducts) 
 run from the corresponding 
 lobes to the riht and left 
 
 Refer stein).-, Mouth; Mh, mouth- 
 cavity; M, muscles; Rd, radula; 
 
 Kn, s 
 sac 
 
 , supporting cartilage ;Z,radular 
 ; Kf, jaw; Oe, oasophagus. 
 
 stomach> 
 
 f th 
 
 left duct is extremely short, 
 and formed by the union of three branches from the subdivisions 
 of its lobe. 
 
 The gut is lined by a single layer of epithelial cells, which are, 
 for the most part, of the simple columnar type. The radula is a 
 cuticular ribbon, developed by the epithelium lining the radular 
 sac. Upon its upper surface are numerous longitudinal rows of 
 minute pointed, backwardly-projecting "teeth." Teeth of the 
 same age are at the same level, so that a clear arrangement into 
 transverse rows is also seen. The central row contains sym- 
 metrical median teeth (undnf), while the lateral (rachidian) teeth 
 of the other rows are asymmetrical. The arrangement may be 
 expressed by the formula oo . 1 . oo , in which the 1 = the single 
 longitudinal row of median teeth and oo = the numerous longi- 
 tudinal rows of lateral teeth on each side of this. As the radula 
 is worn away in front, it grows forwards (like a finger-nail on its 
 bed) upon, and connected with, the sul-radular membrane, which 
 covers the projection from the floor of the mouth. This membrane 
 is formed by epithelium, together with underlying connective 
 tissue, and is to some extent movable upon the central part of 
 the odontophore, which is supported by two masses of gristle, the 
 odontophoral cartilages. These serve as the origins of minute 
 muscles, which are inserted into the sub-radular membrane in 
 front and behind. The cartilages consist of a clear matrix, in 
 which are imbedded numerous branched cartilage cells. The 
 
MOLLUSCA. 127 
 
 wall of the alimentary canal, outside the epithelium, contains 
 muscular layers, an internal longitudinal and an external circular. 
 The salivary glands are aggregates of unicellular glands, each of 
 which is sharply marked off from its neighbours, and has its 
 own minute duct. The digestive gland is composed of branched 
 tubules, ending blindly, and lined by glandular epithelium, in 
 which three chief types of cell can be distinguished, (1) granular 
 cells (liver-cells), containing yellowish granules, (2) pear-shaped 
 ferment cells, (3) large calcareous cells. 
 
 The snail chiefly feeds upon the fresh leaves, steins, &c., of 
 plants, from which it rasps off small fragments by means of its 
 radula, in the following way : The buccal mass is pulled forwards 
 by means of its protractor muscles, when the front of the radula 
 on its cushion projects a little from the mouth. Appropriate 
 contractions of the small muscles within the cushion move the 
 sub-radular membrane, and with it the radula, backwards and 
 forwards, the jaw meanwhile holding the food firmly, and serving 
 as a relatively fixed part against which the radula works. The 
 particles of food scraped off pass back into the mouth-cavity, 
 partly by the agency of the flexible lips, and partly as a result 
 of the backward movement of the odontophore, which acts to 
 some extent like a suction-pump. The salivary secretion has 
 been stated to contain a ferment which converts starch into 
 sugar, and the acid secretion of the digestive gland is known to 
 bring about fermentative changes of this kind and others involving 
 the conversion of proteids into peptone. The food gets mixed 
 up and gradually passed backwards by the contractions of the 
 muscular walls of the gut, the length of which gives a consider- 
 able absorbing surface, augmented by the longitudinal fold in the 
 intestine. 
 
 The digestive gland has other functions besides that of aiding 
 digestion. The granules in its granular cells are most likely of 
 excretory nature, and the material secreted by its calcareous cells 
 is used in the construction of the epiphragm. 
 
 4. Circulatory Organs. As in the mussel, a blood system alone 
 is present, and the reduced ccelom is represented by the pericardial 
 cavity. Heart, arteries, and venous system can be distinguished. 
 The blood is of a bluish tinge owing to the presence of haemo- 
 cyanin, and consists of plasma and amoeboid colourless corpuscles. 
 
 The muscular heart is situated in the posterior part of the 
 
128 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 lung-chamber, in close proximity to the kidney, and contained in 
 a pericardial cavity bounded by a firm translucent pericardium. 
 It is oval in form, and made up of an anterior thin-walled auricle, 
 which communicates by a valve with a posterior ventricle. 
 
 Arteries. The ventricle is continued into a large artery, the 
 aorta, which almost immediately gives off an important visceral 
 artery to the visceral hump, then runs forwards, supplying the 
 body-wall, muscles, viscera, &c., finally perforating the ventral 
 nerve-mass, and breaking up into branches for the head. 
 
 Venous System. The smallest arteries form networks (? capil- 
 laries), from which the blood passes into minute spaces (lacunae), 
 which communicate on the other hand with large venous sinuses. 
 Of these the most important are the spacious body-cavity sur- 
 rounding those viscera which are not contained in the visceral 
 hump, two lateral sinuses in the foot, a visceral sinus along the 
 inner edge of the coiled visceral hump, and a pulmonary sinus 
 with which this communicates, running round the floor of the 
 lung-chamber. 
 
 From the pulmonary sinus numerous a/erent pulmonary vessels 
 are given off, which branch in the roof of the lung, and from 
 these branches efferent pulmonary vessels arise, which unite together 
 to form the pulmoruary vein opening into the auricle. A number 
 of the afferent trunks enter the kidney, and form a network 
 within it, from which one large and several smaller renal veins run 
 to the pulmonary vein. 
 
 Course of the Circulation. Blood, oxygenated in the lung, and 
 (part of it) purified in the kidney, enters the auricle during its 
 diastole by the pulmonary vein. It then passes into the ventricle 
 during the auricular systole. The ventricle, owing to its muscular 
 walls, contracts more vigorously, and the blood, prevented by the 
 auriculo-ventricular valve from returning to the auricle, is forced 
 into the arteries. From the fine ramifications of these it passes 
 into the lacunae, and thence into the venous sinuses, ultimately 
 reaching the pulmonary sinus. From this the blood, now carbon- 
 ated and loaded with nitrogenous waste, passes by the afferent 
 pulmonary vessels into the roof of the lung. Here it is oxygen- 
 ated, and passes into the efferent pulmonary vessels from which 
 the pulmonary vein arises. Part of the blood traverses the 
 kidney before entering the pulmonary vein, and thus gets rid of 
 nitrogenous waste, some of which has been previously eliminated 
 
MOLLUSCA. 129 
 
 in the digestive gland. The hsemocyanin of the blood is a copper- 
 containing proteid which readily takes up oxygen from the air in 
 the lung into loose chemical combination, and parts with it as 
 readily to the tissues. It acts, therefore, as an oxygen-carrier. 
 
 5. The Respiratory Organs are represented by a true air- 
 breathing lung (pulmonary sac) placed on the upper side of the 
 visceral hump, behind the collar, and communicating with the 
 exterior by a rounded valvular opening on the right side of the 
 body. The delicate roof and side- walls of the lung are formed 
 by the mantle, which presents internally a network of ridges, in 
 which the vessels already described ramify. The floor is thin, but 
 muscular, and immediately overlies the crop and the bulk of the 
 reproductive organs. When at rest it is strongly convex upwards, 
 but it becomes flattened by contraction so that the lung-cavity is 
 increased in size, and air consequently passes in. This is inspiration, 
 the converse of which, expiration, is effected by the floor simply 
 ceasing to contract. The pulmonary opening is valvular, and 
 thus the supply of air is regulated and desiccation prevented. 
 The essential part of respiration consists in carbon dioxide 
 diffusing out of and oxygen diffusing into the vessels ramifying 
 in the lung-roof. The part played by haBmocyanin is explained 
 above. 
 
 6. Excretory Organs. A large, cream-coloured kidney, some- 
 what triangular in form, with the apex forwardly directed, is 
 closely united to the posterior part of the lung-roof. It contains 
 a cavity (the surface of which is increased by the projection into 
 it of numerous lamella) which communicates with the pericardium 
 by a minute opening, and with the exterior by an ureter. This 
 arises from the anterior end of the kidney, passes along its right 
 side, and then runs along the side of the lung above the rectum 
 to open close to the anus. The kidney is equivalent to one of 
 the renal organs in the mussel, and is perhaps to be regarded as 
 homologous with one of the nephridia in such a form as the 
 earth-worm. It is plentifully supplied with blood, from which its 
 glandular epithelium separates nitrogenous waste in the form of 
 ammonium and calcium urates. The digestive gland has also 
 been shown to take part in the work of nitrogenous excretion. 
 
 7. Reproductive Organs (Fig. 37). The snail possesses a very 
 complicated set of hermaphrodite reproductive organs, mostly of a 
 whitish colour. (1) The hermaphrodite gland is a small kidney- 
 
 2 9 
 
130 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 shaped organ imbedded in the inner side of the coiled right liver- 
 lobe. From it a much convoluted hermaphrodite duct proceeds. 
 
 (2) Special Male Organs. The hermaphrodite duct splits as 
 it were into male and female ducts, or spermiduct and oviduct, 
 which convey the sperms and ova respectively. The spermiduct 
 
 o-t 
 
 Fig. 37. REPRODUCTIVE ORGANS OF SNAIL. o-t, Hermaphrodite gland ; 
 h.d, hermaphrodite duct; a.gl, albumen gland; v.d, spermiduct (vas 
 deferens); ov, oviduct; va and vs, upper and lower parts of vagina; 
 d.s, dart-sac; m.gl, mucous glands; g.o, genital opening; sp, spermo- 
 theca; sp' and sp" y left and right branches of ditto; p, penis; r.p, 
 retractor penis; /, flagellum. 
 
 (vas deferens) is a narrow tube running at first along the side of 
 the much larger oviduct, the cavities of the two being incom- 
 pletely separated.* In this part of its course it is beset with 
 numerous small eminences collectively constituting a prostate 
 gland. Further forwards the spermiduct separates from the 
 
 * The two together often receive in this region the name of COmmOU 
 
 duct. 
 
MOLLUSCA. 131 
 
 oviduct, and, after pursuing an independent course for some time, 
 opens into a hollow muscular tube, the penis, which receives at 
 the same point the flagelhim, a long and hollow filament. The 
 penis opens into the genital atrium, a shallow depression common 
 to both male and female ducts, and opening to the exterior below 
 the optic tentacle by the genital opening. A narrow band-like 
 muscle, the retractor penis, takes origin in the lung-floor, and is 
 inserted into the penis. 
 
 (3) Special Female Organs. The oviduct is a wide, somewhat 
 twisted tube, with folded and pouched walls, along one side of 
 which the spermiduct runs. The tongue-shaped albumen-gland, 
 which varies very much in size, according to the time of year, 
 opens into its commencement. Where the spermiduct assumes an 
 independent course, the oviduct merges into a muscular, smooth- 
 walled tube, the vagina, which opens into the genital atrium. A 
 tubular organ, the spermotheca (receptaculum seminis), consisting 
 of right and left branches, opens into the hinder end of the 
 vagina. The right and shorter branch ends in a berry-like 
 dilatation. 
 
 In Helix pomatia the lefVbranch is only represented by a small projection. 
 
 Two tuft-like mucous glands open into the side of the vagina 
 somewhat further forwards, and in front of this an extremely 
 muscular pouch, the dart-sac, which can be everted from the 
 genital opening, communicates with it. This sac contains an 
 elongated calcareous body, the spiculum amoris, which is sharply 
 pointed and possesses four slightly twisted lateral ridges. 
 
 It is doubtful whether the dart-sac really belongs to the female organs, 
 Imt its position would seem to indicate this. 
 
 The hermaphrodite gland is made up of numerous branched 
 tubules lined by germinal epithelium. Some of these germinal 
 cells develop into rounded ova, which possess a well-marked 
 germinal vesicle with germinal spot, but are devoid of a vitelline 
 membrane. Other germinal cells pass into the cavities of the 
 tubules, and as mother-sperm-cells divide repeatedly to produce 
 bunches of sperms (spermatozoa), each of which has an irregularly 
 oval head, and long vibratile tail. 
 
 The breeding season is early summer. As in most hermaphro- 
 dite animals cross-fertilization takes place, and self-fertilization is 
 prevented, in this case by the sperms maturing before the ova. 
 
132 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The ripe sperms pass down the spermiduct and into the Hagellum, 
 by a viscid secretion of which they are bound into a thread-like 
 packet (spermatophore). Two individuals mutually fertilize each 
 other, the eversible penis being used as a copulatory organ, by 
 which the spermatophore is conveyed into the sperm otheca. A 
 preliminary stimulus is given by the ejected darts, which may be 
 found sticking in the skin. After some days the spermatophore 
 disintegrates and the liberated sperms fertilize the ova as they 
 pass down the oviduct. Each oosperm is surrounded by an albu- 
 minous investment secreted by the albumen gland, and, external 
 to this, by a tough calcareous shell, with the formation of which 
 the mucous glands appear to be concerned. The eggs, thus con- 
 stituted, are about a quarter of an inch long in H. pomatia. They 
 are laid in damp earth during June or July. 
 
 8. Muscular System. The foot is almost entirely made up of 
 muscle-bands, arranged in a complicated way, and bringing about 
 creeping movements by their contraction. The spindle-muscle 
 serving to pull the body into the shell is a firm band taking 
 origin in the columella, and, dividing into right and left halves, 
 again subdivided into numerous slips which are inserted into the 
 foot. The retractor of the buccal mass, by which the snail's 
 head is drawn in, is a branch of this muscle. The contrary 
 movement is effected by protractors of the buccal mass which 
 take origin in the foot, and there are also depressors, having a 
 similar origin, which pull the buccal mass down. A branch of 
 the spindle-muscle on each side constitutes a tentacular retractor 
 which bifurcates into two slips traversing the corresponding ten- 
 tacles and inserted into their tips. When these muscles contract 
 they draw the tentacles back into the body-cavity, invaginating 
 them. The retractor penis has been mentioned above (p. 131). 
 
 The muscle-fibres are composed of slender spindle-shaped cells, 
 which, except in the odontophore, are unstriated. 
 
 9. Nervous System (Fig. 35). This is remarkable for its great 
 concentration, and is chiefly localized in the head, where a nerve- 
 ring enclosed in a firm sheath is found 'surrounding the gullet, 
 immediately behind the buccal mass in the extended state. 
 
 When the animal retracts itself, this is drawn backwards through the 
 nerve-ring, which is, therefore, then found further forwards than usual. 
 
 The ring is thickened dorsally into two cerebral ganglia, connected 
 together by a broad commissure, and ventrally into a ganglionic 
 
MOLLUSCA. 133 
 
 mass, formed by the coalescence of several pairs of ganglia. This 
 ventral mass is divisible into postero-dorsal pleuro-visceral ganglia, 
 and antero-ventral pedal ganglia, respectively connected with the 
 cerebral ganglia by a posterior cerebro-pleural connective and an 
 anterior cerebro-pedal connective, on each side. 
 
 The head is innervated by branches from the cerebral ganglia, 
 which give off five pairs of nerves. (1) The tentacular nerves, which 
 supply the optic tentacles. Each runs within the corresponding 
 tentacle, gives off an optic nerve to the eye, and ends in a tentacular 
 ganglion, from which branches run to the skin covering the end 
 of the tentacle. (2) Two pairs of labial nerves, one of which 
 gives off to the short tentacle a tentacular nerve ending in a 
 tentacular ganglion. These nerves supply the lips and neigh- 
 bouring parts. (3) An auditory nerve passes down on each side 
 between the two connectives to the otocyst. (4) A buccal nerve 
 comes off from the front of each cerebral ganglion, and runs 
 forwards to a buccal ganglion placed in the angle where the 
 gullet joins the buccal mass. The buccal ganglia innervate 
 the pharynx, gullet, and salivary glands. They are connected 
 together by a commissure ventral to the gullet. An unpaired 
 nerve runs to the penis from the right cerebral ganglion. The 
 body-walls and viscera are supplied by the pleuro-visceral ganglia, 
 while the nerves of the foot come off from the pedal ganglia. 
 
 The nervous elements are as usual ganglion-cells and nerve-fibres 
 the former are confined to the outer parts of the ganglia, and 
 usually possess only one process. 
 
 10. Sense Organs (1) Tactile Organs. The sense of touch 
 is possessed by the surface of the body generally, but is specially 
 localized in the head, tentacles, and sides of the foot. The tactile 
 cells are narrow cylinders with tapering external ends formed by 
 an aggregation of hair-like processes. 
 
 (2) Olfactory Organs. The snail possesses a keen sense of 
 smell which enables it to detect the presence of various kinds 
 of food and to avoid certain strongly odorous liquids, such as 
 turpentine. This discriminative power is lost if the tentacles 
 are removed, and there is a patch of modified epithelium at the 
 tip of each of them, apparently of olfactory nature and containing 
 numerous flask-shaped cells closely related to the corresponding 
 tentacular ganglion. An olfactory function has also been ascribed 
 to the supra-pedal gland, a tubular organ, lined with columnar 
 
134 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 epithelium, lodged in the foot, and opening to the exterior by a 
 small pore beneath the mouth. 
 
 (3) Auditory Organs. A minute spherical otocijst or auditory 
 sac is placed on each side of the ventral nerve-mass, and is con- 
 nected by an auditory nerve with the corresponding cerebral 
 ganglion. The sac possesses an outer firm investment, and is 
 lined by ciliated columnar epithelium, composed of auditory cells. 
 It is filled with numerous calcareous particles or otolitlis, suspended 
 in fluid. 
 
 (4) Visual Organs. Each optic tentacle bears on the outer side 
 of its tip an eye, which appears as a black dot, and is innervated by 
 the optic nerve. It is placed immediately below a small transparent 
 area of the epidermis, and essentially consists of a spherical vesicle, 
 enclosed in a firm sheath, and containing a large globular lens, 
 devoid of structure. The vesicle is made up of a single layer of 
 cells, which in front are short and transparent, constituting a 
 cornea, while behind they are much more elongated and form a 
 sensitive retina. The retinal cells are of two kinds, unpigmented 
 and pigmented. Each of the former is produced into a flask- 
 shaped visual rod next the cavity of the vesicle, and is surrounded 
 by several of the latter, which are pigmented in their outer parts 
 only, while internally they taper to transparent processes ensheath- 
 ing the visual rod. 
 
 It has been shown that the eyes of the snail can only clearly 
 distinguish the form of external objects when at a distance of from 
 A to JV of an inch- The pigmented skin appears to be sensitive 
 to light, helping the animal to distinguish between light and 
 darkness. 
 
 CHAPTER VIII. VERTEBRATA ACRANIA. 
 13. AMPHIOXUS (The Lancelet). 
 
 AMPHIOXUS is a semi-transparent somewhat fish-like animal, not 
 exceeding two inches in length, and laterally flattened. There is 
 a free-swimming larva, but the adult animal is a shallow water 
 marine form generally found vertically buried in the sand, from 
 which only its anterior end projects, but also capable of swimming: 
 by eel-like movements of its body. It is abundant round many 
 
VERTEBRATA ACRANIA. 
 
 135 
 
 coasts, as, for example, the Mediterranean, and has been found 
 off our own shores. 
 
 All the types hitherto described belong to the Invertebrata, or 
 animals devoid of backbone, while Amphioxus, Dog-fish, Frog, 
 Pigeon, and Rabbit, the remaining animals to be dealt with, are 
 examples of the Vertebrata, or backboned group, using the word 
 in a very broad sense, and by " backbone " understanding a firm 
 rod, not necessarily of bone, underlying and supporting the central 
 nervous system. To avoid confusion it is perhaps advisable to 
 drop the name Vertebrata as used in the broader sense, replacing 
 it by the term Chordata, and styling the Invertebrates Non- 
 Chordata for the sake of uniformity. All Chordate animals 
 possess, temporarily or permanently 
 
 (1) A tubular central nervous system running along the dorsal 
 side of the body, and not perforated by the gut as in many higher 
 Non-Chordates (e.g., Earthworm, Leech, Crayfish). 
 
 (2) A firm elastic rod, the notochord, underlying the central 
 nervous system for part or all of its length. 
 
 (3) [Except in one instance] A laterally perforated pharynx, 
 serving in the lower forms as a respiratory organ, 
 
 The Chordata are classified as follows : 
 
 CHORDATA ( = VERTEBRATA in wider sense). 
 
 I. Heinichorda. Small notochord in anterior 
 part of body. A small group of worm-like 
 forms. 
 
 II. Urochorda. Small notochord in tail of 
 larva, generally absent in adult. A group 
 of degenerate forms, the Ascidians or Sea- 
 Squirts, which are usually fixed when 
 adult. 
 
 III. Cephalochorda. Notochord extending from 
 one end of the body to the other. 
 Amphioxus. 
 
 IV. Vertebrata (in narrower sense). Noto- 
 chord ends anteriorly below the middle of 
 the brain. A more or less complete ver- 
 tebral column ("backbone") in which 
 segmentation is always indicated, and 
 which usually encroaches more or less 
 upon the notochord. -Dogfish, Frog, Lizard, 
 Fowl, Rabbit. 
 
 = VERTEBRATA 
 ACRANIA. 
 
 Nobrain-case,limbs, 
 or jaws. 
 
 = VERTEBRATA 
 
 CRANIOTA. 
 A brain-case. 
 Limbs, when present 
 riot more than two 
 pairs. 
 
136 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters (Fig. 38). The scientific and popular 
 names of Amphioxus are alike derived from the fact that the 
 flattened body is pointed at both ends. There is no distinct 
 division into head, trunk, and tail, as is the case in a fish, and, 
 at the first glance, it does not seem easy to say which is the 
 anterior and which is the posterior end. The former, however, 
 is recognizable on a cursory examination by the presence of the 
 ventral mouth, an oval opening bordered by numerous stiff ciliated 
 processes, the buccal cirri. Further back along the ventral surface 
 is seen another median aperture, the atriopore, situated on a pro- 
 minent papilla. It is the outlet of a large atrial cavity, by which 
 the perforated pharynx is surrounded. A thin, laterally flattened 
 fin runs from the mouth round the front end of the body along 
 the dorsal surface, round the posterior end, and forwards along 
 the ventral surface as far as the atriopore. About the middle 
 of this ventral section of the fin a small opening, the anus, is to 
 be found on the left of the median line. This is one of several 
 particulars in which Amphioxus deviates from strict bilateral 
 symmetry. The fin is rather larger round the posterior end, 
 constituting a caudal fin, while that part of it which runs along 
 the upper side of the body in front of this is known as the dorsal 
 fin, and the part between anus and atriopore as the anal fin. 
 All these are perfectly continuous. The ventral surface between 
 mouth and atriopore is broad, gently convex, and marked by a 
 series of longitudinal ridges. It is bounded on each side by 
 a longitudinal fold (metapleural fold), the lateral fin, which unites 
 with its fellow just behind the atriopore, at the point where the 
 anal fin begins. 
 
 Amphioxus is a segmented animal, and this is indicated exter- 
 nally by a number of > shaped lines on the sides of the body, 
 corresponding to a division of the lateral muscles of the body into 
 muscle-segments (myomeres, myotomes) which in Amphioxus lanceo- 
 latus, the species commonly used in laboratories, are 61 or 62 in 
 number. The atriopore corresponds to the 36th myomere, while 
 the anus is situated between the 51st and 52nd. 
 
 There is a small ciliated pit (? olfactory) on the left side of the 
 head above the anterior end of the mouth. 
 
VERTEBRATA ACRANIA. 
 
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138 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 2. Skin. This consists of the epidermis and dermis. The 
 epidermis is made up of a single layer of columnar cells (ciliated 
 in the larva), among which are a number of scattered sensory 
 cells, each of which is somewhat rod-like and terminates exter- 
 nally in a stiff tapering process, while internally it is continuous 
 with a nerve-fibre. These cells are most numerous in the anterior 
 part of the body. 
 
 The derm-is presents a firm external layer, beneath which is a 
 much thicker gelatinous stratum again succeeded by a very thin 
 nucleated layer. 
 
 3. Skeleton (Figs. 38 and 39). As in all Chordates the most 
 important part of this is internal, constituting an cndoskeleton, 
 which contrasts strongly with the cuticular exoskeletons of such 
 forms as Crayfish and Mussel. Amphioxus, however, possesses 
 only a feeble endoskeleton, of which the most characteristic part 
 is the notochord. This is an elastic rod which runs from one end 
 of the body to the other, above the gut and below the central 
 nqrvous system. It gives a certain amount of firmness to the 
 body, and serves for the attachment of the lateral muscles. The 
 notochord is of cellular nature, as is readily seen in young speci- 
 mens, but most of the constituent cells become, later on, much 
 vacuolated, so that their outlines are obscured. They are arranged 
 so as to form a succession of thin vertical discs. 
 
 The notochord is surrounded by a firm connective-tissue sheath 
 which is continued dorsally into a tube investing the spinal cord, 
 and laterally into septa running between the myomeres and join- 
 ing the dermis. The notochordal sheath resembles the dermis in 
 structure, the dense layer being in this case internal, while the 
 other layers are continued into the neural sheath and septa. 
 
 Amphioxus possesses other skeletal structures besides those 
 already described i.e., a buccal skeleton, a branchial skeleton, 
 and fin-rays. 
 
 The buccal skeleton consists of a series of short rods jointed 
 together so as to form an incomplete ring stiffening the margin 
 of the mouth, with processes extending into the buccal tentacles. 
 These parts resemble the notochord in minute structure. 
 
 The branchial skeleton supports the pharynx, and will be described 
 in the next section. 
 
 The dorsal Jin is supported by a very large number of minute 
 vertical fin-rays, consisting of little columns of gelatinous material 
 
VERTEBRATA ACRANIA. 139 1 
 
 attached below to a ridge running along the top of the neural 
 sheath, and projecting above into box-like spaces full of lymph. 
 The anal fin is supported by a double series of such fin-rays. 
 
 4. Digestive and Respiratory Organs (Figs. 38 and 39). The 
 gut is a straight tube running from mouth to anus, and consisting 
 of buccal cavity, respiratory pharynx, gullet, stomach with liver, 
 and intestine. It is ciliated throughout. 
 
 The buccal cavity, into which the wide jawless mouth opens, is 
 somewhat funnel-shaped, and it is lined by two kinds of epithelium,, 
 the boundary between which is marked by a series of lobes. The 
 kind which occurs in the posterior part of the cavity is distin- 
 guished by the presence of pigment and specially long cilia. At 
 the back of the buccal cavity there is a muscular partition, the 
 velum, which is perforated by an aperture leading into the pharynx 
 and guarded by a circlet of twelve delicate backwardly projecting 
 tentacles. Between buccal cavity and atriopore the gut is sus- 
 pended from the sheath of the notochord in a spacious atrial 
 cavity. 
 
 The pharynx is the largest and most characteristic part of the 
 gut, extending for about half its length as a wide tube laterally 
 perforated by numerous oblique gill-slits, opening into the sur- 
 rounding atrial cavity. The first formed gill-slits in the young 
 larva open at first directly to the exterior, and then into a longi- 
 tudinal groove, the sides of which unite to form a tube open 
 behind. This tube, the opening of which persists as the atriopore, 
 gradually becomes more extensive, sinking into the body, so to 
 speak, and surrounding the gut (except on the dorsal side) behind 
 the buccal cavity. There is also a narrow prolongation of the 
 atrial cavity extending back on the right side of the intestine 
 between atriopore and anus. It is obvious from the above outline 
 of its development, that the atrial cavity is, morphologically, a 
 part of the exterior. 
 
 The cavity of the pharynx is much wider in its anterior than 
 in its posterior portion, where it is somewhat flattened from side 
 to side. A well-marked Abranchial groove runs along the middle 
 of the roof of the pharynx, while in the median line of the floor 
 there is a thickening known as the endostyle, flat or convex ante- 
 riorly, groove-like posteriorly. Both these median regions are 
 characterized by the presence of elongated columnar epithelial 
 cells provided with very long cilia. 
 
140 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Fig. 39. AMPHIOXUS, reduced. Transverse sections through regions of 
 A, olfactory pit ; B, buccal cavity ; C, pharynx and liver; D, atriopore; 
 E, anus. All enlarged to same scale. Lymph-spaces dotted. R and 
 L, right and left sides, a.f, Anal fin; an, anus; at, atrial cavity 
 (atriopore shown diagrammatically in D) ; b. c, buccal cavity (just 
 beginning in A); b.sk, pieces of buccal skeleton (others seen within 
 sections through buccal cirri) ; c.ao, cardiac aorta; c<e, sections of 
 coelom ; cr, buccal cirri; d, dermis; d.ao, dorsal aorta; d.ar, dorsal 
 artery; d.f, dorsal fin; d.gr, dorsal groove of pharynx; d. n, dorsal 
 nerve ; en, endostyle ; ep, epidermis ; ex, excretory tube (brown tube 
 of Lankester) ; f.r, fin ray; g, possible gustatory organ; h.v, hepatic 
 veins; in, intestine; I, liver; l.f, lateral fin; ///, lymph-spaces; m, 
 myomeres and (in B) mouth; m.c, metapleural lymph-canal; my, 
 myoccele, including fin-ray spaces and (in A) spaces connected with 
 myomeres; n, notochord, the dots represent nuclei around it is 
 seen its sheath (left white) continued into septa and neural sheath; 
 n.c, nerve cord; nv, nerves (in A); o, eye; ol, olfactory pit; ov, ovary; 
 p.v, portal veins; sp, septa; tr.m, transverse muscles; v.n, ventral 
 nerve (represented as coming off too high up). 
 
VERTEBRATA ACRANIA. 141 
 
 The gill-slits slope downwards and backwards, so that a number 
 of them are cut through by a single transverse section. They 
 are separated by lath-shaped gill-arches, the flat surfaces of which 
 face one another and are covered by very long cilia. New gill- 
 slits are continually being added, in growing animals, at the 
 posterior end of the series as the pharynx increases in length. 
 Each gill-slit is at first a simple oval aperture, but soon becomes 
 horseshoe-shaped and finally divided into anterior and posterior 
 parts by the downgrowth of a tongue-like secondary gill-arch 
 from its dorsal margin. The 1st, 3rd, 5th, &c., arches are conse- 
 quently secondary, and the alternate ones primary. It is also to 
 be noted that the gill-slits are bridged over by numerous short 
 horizontal bars, so that the lateral walls of the pharynx resemble 
 open basketwork in structure. 
 
 There is a somewhat complex branchial skeleton supporting the 
 parts described, and composed of firm material, conveniently 
 termed chitinoid, since it resembles horn or chitin in physical 
 respects, though its exact chemical nature is not known. Each 
 gill-arch is traversed by an internally grooved rod of this kind, 
 which in the primary arches is solid and forked at both ends, 
 but in the secondary arches hollow and simple ended. These 
 rods are connected by short horizontal pieces which run through 
 the bars that bridge the gill-slits, and ventrally they come into 
 relation with a double series of small chitinoid plates supporting 
 the floor of the pharynx. 
 
 The pharynx is succeeded by an exceedingly short gullet, and 
 this again by a fairly wide stomach, from which a simple blindly 
 ending tube, the liver, runs forwards along the right side of the 
 pharynx, extending further in adult than in young specimens, 
 such as the one drawn in Fig. 38. The stomach passes gradually 
 behind into a tubular intestine running straight to the anus. 
 
 Amphioxus feeds chiefly upon small organisms suspended in 
 the surrounding water, and in the normal position of the animal 
 i.e., vertically imbedded in the sand, with its anterior end 
 projecting, these are swept into the mouth by the currents 
 which the ciliated lining of the gut sets up. A certain amount of 
 sand also appears to be swallowed for the sake of the contained 
 organic matter. Since the anterior part of the Chordate gut has 
 to do with respiration as well as nutrition, it is commonly special- 
 ized so that the food takes a different path from the respiratory 
 
.142 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 current. In this case the epibranchial groove, judging from its 
 contents, serves as a channel along which food passes back to the 
 gullet. 
 
 The ciliated lining of the buccal cavity and pharynx sets up 
 currents which not only bring in food but also the oxygen 
 required in respiration. These currents continually stream into 
 the pharynx, through the gill-slits into the atrial cavity, and 
 out at the atriopore. The blood contained in the vessels of 
 the gill-arches is thus oxygenated and at the same time gets rid 
 of its carbon dioxide. The current emerging from the atriopore 
 .also serves to carry the sperms or ova, as the case may be, out of 
 ,the body. 
 
 5. Circulatory Organs. These are in a degenerate condition. 
 There is no heart, but this is compensated for by the contractile 
 nature of some of the blood-vessels. A distinction can be drawn 
 between blood and lymph-systems, but these appear to com- 
 municate with one another and consequently contain the same 
 .circulatory fluid, which may be termed blood or lymph indiffer- 
 ently. It is colourless, and chiefly consists of coagulable plasma 
 in which a few amoeboid corpuscles are suspended. 
 
 ( 1 ) Blood System. A cardiac aorta runs along the floor of the 
 pharynx, giving off branches, the aortic arches, which traverse 
 the primary gill-arches, uniting above to form a dorsal artery 
 -running along each side of the epibranchial groove. These two 
 arteries are indirectly connected in front, while posteriorly they 
 form by their union a dorsal aorta, which runs below the noto- 
 chord. The aortic arch which is furthest forward on the right 
 side is larger than the rest and supplies the front end of the body. 
 A lateral artery runs along each side of the body, just within the 
 gonads. It is connected by transverse vessels with the correspond- 
 ing dorsal artery. 
 
 The remaining important blood-vessels are the portal and hepatic 
 veins. The first of these run along the under side of the intestine, 
 passing to the liver and breaking up into capillaries from which 
 the hepatic veins arise. These run along the dorsal side of that 
 organ and unite at its origin to form the cardiac aorta. 
 
 Course of the Circulation. This is only imperfectly known, 
 
 but is probably as follows : Impure blood passes from the hepatic 
 
 veins to the cardiac aorta, thence through the aortic arches (and 
 
 connected vessels in the secondary gill-arches), where it is oxygen- 
 
VERTEBRATA ACRANIA. 143 
 
 ated, and on into the dorsal arteries and dorsal aorta for general 
 distribution. There also appears to be an hepatic portal system 
 that is to say, the impure blood from the gut passes by portal 
 veins to the liver and enters a capillary system drained by hepatic 
 veins. 
 
 The motive power by which circulation is effected appears to 
 be the contractility of the chief vascular trunks, especially of the 
 aortic arches, each of which commences in a small contractile 
 bulb which lies in the ventral fork of the corresponding primary 
 gill-bar. 
 
 (2) Lymph System. This consists of a body-cavity or coelom, 
 and of other lymph-spaces. These are continuous with one 
 another and with the blood-system, but their exact relations are 
 complex and but ill understood. 
 
 Coelom (Fig. 39). In a cross-section taken between anus and 
 atriopore this is easily recognised as a fairly wide space sur- 
 rounding the gut, but in front of this region the arrangement 
 is complicated by the large development of the atrial cavity. 
 Between atriopore and pharynx it is seen as a narrow space 
 surrounding the gut and continued round the liver. In the 
 pharyngeal region the most obvious parts of the coelom are the 
 dorsal cwlomic canals which run one on each side of the upper 
 part of the pharynx. The floors of these canals are obliquely 
 fluted to form suspensory folds connected with the primary gill- 
 arches, and each containing a ccelomic pouch running down the 
 outer side of its arch. 
 
 A ventral ccelomic canal runs below the endostyle and receives 
 ccelomic tubes which traverse the chitinoid rods of the secondary 
 gill-arches. Besides this there are special sections of the coelom 
 .surrounding the gonads. 
 
 The most important lymph-spaces, in addition to the coelom, are 
 (1) a metapleural canal running along each lateral fin, (2) spaces 
 round the fin-rays, (3) spaces in the myomeres of the head. 
 
 6. Excretory Organs. It has been shown by experiment that 
 the organs which, under ordinary circumstances, excrete nitro- 
 genous waste, can also get rid of certain pigments artificially 
 introduced into the system. In this way a means is afforded of 
 recognizing such organs in doubtful cases. This method has 
 been employed for Amphioxus. The living animals were kept 
 in sea-water full of suspended carmine until they became pink in 
 
144 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 colour, after which they were transferred to clean sea-water till 
 the colour faded somewhat owing to the action of the excretory 
 tissue. Sections cut at this stage showed the presence of carmine 
 in the cells of (1) the atrial epithelium, more particularly that 
 part of it covering the outside of the secondary gill-arches and 
 the atrial floor, (2) a series of small tubules, previously over- 
 looked, opening (?) from the dorsal coelomic canals into the atrial 
 cavity at the tops of the primary gill-arches. These tubules, and 
 part of the atrial epithelium have probably, therefore, an excretory 
 function. 
 
 Besides this, a pair of atrio-codomic funnels (pigmented canals) 
 occur in the 27th segment, which are possibly of similar nature. 
 Each of them is a short funnel-shaped tube, situated in the dorsal 
 coelomic canal of its side (Fig. 39), opening by its wide posterior 
 end into the atrial cavity and (I) by its narrow front end into the 
 ccelom. Owing to observation being rendered difficult by the 
 abundant pigment naturally found in the walls of these tubes, 
 the carmine method just described gave no positive results in 
 this case. 
 
 7. Reproductive Organs (Fig. 39). Although the sexes are 
 separate there are no distinctive external characters, and the 
 reproductive organs are of the simplest possible kind, consisting 
 of 26 pairs of gonads, spermaries (testes) or ovaries, as the case 
 may be, imbedded in the outer wall of the atrial cavity. Those 
 of one side are not exactly opposite those of the other side. The 
 gonads are squarish sacs, each of which is surrounded by a special 
 section of the ccelom. The ova are just visible to the naked eye, 
 and when mature are dehisced into the atrial cavity, out of which 
 they are carried by the respiratory current flowing through the 
 atriopore. The very much smaller sperms (spermatozoa), which 
 reach the outside of the body in a similar manner, are tadpole- 
 shaped, each of them possessing a short conical head and a 
 vibratile tail. 
 
 8. The muscular system (Figs. 38 and 39) exhibits well-marked 
 segmentation, for the great lateral mass of muscle on each side is 
 divided into a series of (in A. lanceolatus) 61 or 62 > shaped 
 muscle-segments (myomeres, myotomes), separated by connective- 
 tissue septa. Those on opposite sides do not correspond. The 
 constituent muscle-fibres run longitudinally. Swimming move- 
 ments, consisting in bending the body first to one side and then 
 
VERTEBRATA ACRANIA. 145 
 
 to the other, can be effected by alternate contraction of the lateral 
 muscles on each side. 
 
 Transverse muscles run across the floor of the atrial cavity, 
 and these no doubt assist in the expulsion of water through the 
 atriopore. 
 
 The muscle-fibres are transversely striated rhomboidal plates. 
 
 9. The nervous system consists of a dorsal nerve-cord and of 
 nerves connected with this. 
 
 The nerve-cord (spinal cord) constituting the central part of 
 the nervous system is a thick- walled tube exactly fitting the 
 neural sheath above the notochord, and extending the greater 
 part of the length of the body. In front, however, it does not 
 reach so far forwards as the notochord, but terminates bluntly 
 just above the front end of the mouth. The cavity of the nerve- 
 cord forms an exceedingly narrow central canal, except anteriorly, 
 where it dilates into a much larger ventricle which opens to the 
 exterior on the left-hand side within the olfactory pit. 
 
 Behind the ventricle, a narrow slit, the dorsal fissure, divides 
 the upper part of the cord, above the central canal, into right and 
 left halves. 
 
 The nerve-cells are grouped round the central canal and dorsal 
 fissure; in a stained section they appear as a deeply-coloured 
 dorso-ventral streak, readily seen under the low power. As in 
 other cases .they are produced into processes by which union 
 with one another and with nerve-fibres is effected. The smallest 
 nerve-cells have but one process (i.e., are unipolar), the larger ones 
 generally have several processes (i.e., are multipolar^). A double 
 longitudinal series of small irregular masses of black pigment- 
 cells is imbedded in the floor of the central canal. The greater 
 part of the nerve-cord is made up of slender nerve-fibres, most of 
 which take a longitudinal direction, while others pass out into 
 the nerves. 
 
 Numerous segmentally-arranged nerves take origin from the 
 nerve-cord and constitute a peripheral nervous system. Most 
 of them correspond to myomeres, being consequently arranged 
 asymmetrically and not in regular pairs. The nerves are of two 
 kinds (1) single-rooted and (2) multiple-rooted. The single- 
 rooted nerves (except the first two) arise from the dorsal surface of 
 the cord as single bundles of nerve-fibres, and the first six of 
 them constitute three regular pairs. Behind this, however, those 
 2 10 
 
146 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 on one side alternate, like the myomeres, with those on the other 
 side. The first pair have a ventral origin from the extreme front 
 of the nerve-cord, and, together with the second pair, which arise 
 dorsally behind the ventricle supply the parts in front of the 
 mouth, while the third pair supply the mouth-region. These 
 single-rooted nerves are partly sensory, innervating the skin, and 
 partly motor, giving off twigs to the muscles. Their sensory 
 branches divide repeatedly, and their finest ramifications ulti- 
 mately unite together to form a delicate nerve-plexus below the 
 epidermis. Such a nerve-plexus, investing the whole body, is 
 characteristic of certain non-chordates, and must be regarded here 
 as a primitive feature inherited from non-chordate ancestors. 
 
 The multiple-rooted nerves all arise from the ventral side of the 
 nerve-cord for the greater part of its extent, alternating with the 
 dorsal nerves. Each of them consists of a longitudinal series of 
 slender bundles (roots) which remain independent of one another, 
 and branch out in the adjacent muscles. These nerves, therefore, 
 are of motor nature. 
 
 10. The sense-organs of Amphioxus are ill-developed and for 
 the most part of problematical nature. 
 
 A considerable number of the epidermal cells, especially in the 
 anterior part of the body, probably serve as tactile organs. These 
 cells are comparatively slender, continuous internally with sensory 
 nerve-fibres and produced externally into a stiff process. 
 
 A gustatory function has been ascribed to the following struc- 
 tures : ( 1 ) Small aggregates of sense-cells, similar to those 
 described in the last paragraph and situated upon the buccal 
 cirri. The external processes of each group form a conical pro- 
 jection. (2) Circlets of sense-cells occurring in the velar tentacles. 
 (3) A sac lined by sensory epithelium and opening on the left 
 side of the roof of the buccal cavity. 
 
 It is exceeding doubtful whether the so-called olfactory pit, 
 situated on the left side of the head, has anything to do with 
 smell. It is a depression lined with ciliated epithelium and 
 communicating with the ventricle. 
 
 A pigmented mass imbedded in the front wall of the ventricle 
 has received the name of eye. 
 
VERTEBRATA ACRANIA. 147 
 
 DEVELOPMENT. 
 
 The breeding-season commences about the end of March and 
 lasts throughout the summer. The eggs are laid about an hour 
 after sunset, and are fertilized at once by sperms shed over them 
 by the male. Development begins an hour later and at first goes 
 on very rapidly, so that by sunrise next morning free-swimming 
 flagellated embryos escape from the eggs. Twenty-four hours 
 later the flagellated embryo has become an elongated unsym- 
 metrical larva, with mouth, anus, and one gill-slit. This completes 
 what may be termed the embryonic development. 
 
 The larval development which now succeeds extends over a 
 much longer period. The free-swimming larva is for some time 
 extremely unsymmetrical, but gradually becomes less so. At the 
 same time the adult structure is slowly assumed ; ultimately the 
 free-swimming life is given up, and this closes the larval period. 
 
 I. EMBRYONIC DEVELOPMENT. Cleavage (Segmentation). 
 The ovum, in spite of its small size (^Q of an inch in diameter), 
 contains a considerable number of yolk-granules. It is covered 
 by a delicate vitelline membrane, which becomes separated from 
 it as soon as fertilization has been effected. Only one polar body 
 has been observed, and this rests on the upper pole of the 
 oosperm. Cleavage is complete (holoblastic) and nearly regular. 
 It occupies from three to four hours. The first division takes 
 place in a vertical plane and results in two cells of equal size. 
 These are then equally halved by a second vertical division at 
 right angles to the first. The third division is horizontal (equa- 
 torial) and separates four rather smaller upper cells from four 
 rather larger lower cells in which more numerous yolk-granules 
 are present. These eight cells are now bisected by two vertical 
 divisions making angles of 45 with the earlier vertical ones. The 
 16-celled stage so constituted becomes a 32-celled one by two 
 new equatorial divisions, the planes of which are respectively 
 above and below the first equatorial division. From this point 
 cleavage proceeds more irregularly. It ultimately results in a 
 spherical blastula (blastosphere), which may be compared to a 
 hollow ball with a large central cavity (blastoccele, segmentation 
 cavity) and a wall composed of a single layer of cells, which in 
 the upper half are smaller than in the lower half (Fig. 40). The 
 
148 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 former constitute the ectoderm (epiblast), the latter the endoderm 
 (hypoblast). 
 
 G-astrulation (Fig. 40), by which the single-walled blastula is 
 converted into the double-walled gastrnla, follows cleavage and 
 occupies about six hours. The endoderm cells undergo a gradual 
 inpushing or invagination (emboly, embolic invagination) until 
 the blastocoele is obliterated, and the embryo has become cup- 
 shaped, with a central digestive cavity (archenteron) opening by 
 a wide blastopore. The endoderm cells now line the archenteron 
 and are covered by the ectoderm, each cell of which develops a 
 flagellum. The cup-shaped gastrula soon assumes an ovoid shape 
 with a flattened dorsal and a convex ventral surface. Meanwhile 
 
 Fig. 40. BLASTULA AND GASTRULA OF AMPHIOXUS (from Clans, after 
 Hatschek). A, In optical section. A, Blastula with flattened lower 
 pole of larger cells. B, Commencing invagination. C, Gastrulation 
 completed ; the blastopore is still widely open, and one of the ineso- 
 dermic teloblasts is seen at its ventral lip. The flagella of the ecto- 
 derm cells are not represented. 
 
 the blastopore has narrowed to a small rounded aperture, and is 
 now situated at the posterior end towards the dorsal surface. Two 
 endoderm cells on the ventral side of the blastopore are distinguished 
 by their relatively large size. These are the mesodermic telo- 
 blasts, which subsequently originate a part of the mesoderm. 
 
 The completed gastrula escapes from the vitelline membrane and 
 swims freely, front end first, by means of the ectodermal flagella. 
 
 Origin of the Mesoderm, Ccelom, Muscles, Notochord, and 
 Nervous System (Figs. 41 and 42). The foundations of all 
 these are simultaneously laid during the twenty-four hours which 
 succeed hatching. 
 
 The mesoderm in the anterior part of the body is constituted 
 by the walls of myoccelomic pouches which successively grow out 
 
VERTEBRATA ACRANIA. 
 
 149 
 
 from the archenteron. The first of these pouches is unpaired 
 and median, the remainder are paired and lateral. They develop 
 in order from before backwards. All these outgrowths become 
 separated from the gut (which may now be called the mesenteron), 
 and are known as meso- 
 dermic (mesoblastic) 
 somites, since they in- 
 dicate the segmenta- 
 tion of the body. 
 Other such somites 
 are added later as en- 
 dodermic outgrowths, 
 but their cavities 
 never communicate 
 with that of the gut. 
 The mesodermic telo- O 
 blasts give rise to part 
 of the mesoderm of 
 the tail-region. The 
 somites soon become 
 divided into dorsal 
 sections, the cavities 
 of which collectively 
 constitute themyocwle, 
 and ventral sections, CO 
 the cavities of which 
 collectively constitute 
 the splanchnocceh. The 
 outer wall of each sec- 
 tion consists of somatic 
 mesoderm, and its 
 inner wall of splanch- 
 nic mesoderm. The 
 splanchnic walls of 
 the dorsal sections 
 are converted into ^ 
 the lateral muscles, 
 and their somatic 
 
 walls into the dermis. The sheath of the notochord, neural sheath, 
 .and septa are formed from outgrowths of these dorsal sections. 
 The myocoele is mostly obliterated in the adult, exwpt in the 
 
 CNIVEBSITT 
 
150 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Fig. 42. THREE LARVAL STAGES or 
 AMPHIOXUS (from Glaus, after 
 Hatschek). D, Stage with 2 pairs 
 of mesodermic somites, seen in opti- 
 cal longitudinal section, dorsal side 
 to right. E, Stage with 9 pairs of 
 mesodermic somites, seen from above. 
 F, Living larva with mouth and first 
 gill-slit, seen from the left side ; the 
 2nd, 4th, and 6th bent lines represent 
 respectively the posterior boundary 
 of the 1st, 2nd, and 3rd somite of 
 the opposite side. Bl, ventral blood- 
 vessel ; Gh t notochord ; D, intestine ; 
 K, gill-slit ; MF, unsegmented meso- 
 derm fold, behind which one teloblast 
 is seen in D, both in E ; N, neural 
 canal ; 0, mouth ; Oc, anterior open- 
 ing of neural canal ; Us, mesodermic 
 somites. 
 
 head (see Fig. 39), but por- 
 tions of it are converted into- 
 the fin-ray lymph-spaces and 
 the metapleural canals. The 
 ventral sections of the somites 
 grow downwards, ultimately 
 fusing below the gut, the 
 wall of which, outside the- 
 epithelium, is formed from 
 their splanchnic layer. The 
 splanchnocoele becomes the 
 coelom, which is later on 
 split up into sections. A 
 body-cavity, which, like this, 
 is derived by the outgrowth 
 of myocoelomic pouches, is 
 said to be enterocoelic, and 
 may be called an enteroc&h. 
 Such a simple mode of origin 
 is probably a very primitive 
 one. 
 
 The anterior unpaired arch- 
 enteric pouch divides into 
 right and left halves, of which 
 the latter becomes the pro- 
 blematic sense organ that, in 
 the adult, opens on the roof 
 of the mouth. 
 
 The notochord is developed 
 as a longitudinal fold of the 
 archenteric wall in the mid- 
 dorsal line. 
 
 The central nervous sys- 
 tem arises in a way which, 
 in its more general features, 
 is characteristic of all Chor- 
 dates. The ectoderm cover- 
 ing the flattened dorsal sur- 
 face of the completed gastrula 
 becomes marked off by a 
 slight furrow from the lateral 
 
YERTEBRATA ACRANIA. 151 
 
 ectoderm on each side, and constitutes a neural (medullary) plate, 
 which becomes depressed in the centre so as to originate a neural 
 (medullary) groove bounded by neural (medullary) folds. These 
 folds gradually approach each other, and ultimately unite, so that 
 the trough-shaped neural plate, now V-shaped in transverse section, 
 is completely covered. It ultimately folds up into a tube, which 
 is converted into the nerve-cord by thickening of its walls. A 
 small opening, however, is left in front, and this neuropore is appa- 
 rently converted into the olfactory pit of the adult. Posteriorly 
 the union of the neural folds involves roofing over the blastopore 
 with consequent formation of a short neurenteric canal by which 
 the cavity of the nerve-tube communicates with the digestive 
 cavity, which now no longer opens directly to the exterior. 
 
 The embryonic development is brought to a close by the 
 appearance of the larval mouth, anus, and first gill-slit. 
 
 The larval mouth ( = velar opening of adult) appears as a small 
 round ciliated opening on the left side of the head, in the region 
 of the first myomere. The anus develops soon afterwards. The 
 first gill-slit is formed on the right-hand side, close to the median 
 line, as a ciliated rounded aperture leading out of the pharyngeal 
 region. 
 
 II. LARVAL DEVELOPMENT. The appearance of the larva at 
 the beginning of this period may be gathered from Fig. 42, F. 
 The points of most importance in the further history are connected 
 with the development of the adult mouth and buccal cavity, gill- 
 slits, and atrial cavity. 
 
 Adult Mouth and Buccal Cavity. The larval mouth becomes 
 wide and oval, and two folds grow out, one above it, the other 
 below it, which respectively become the left and right boundary 
 walls of the buccal cavity. Later on the mouth shifts round to 
 a median ventral position, while the two folds become at the same 
 time more prominent, fusing together so as to enclose a cavity, 
 the buccal cavity, outside the larval mouth, and provided with 
 an oval opening, the adult mouth, from the margins of which 
 buccal cirri grow out. 
 
 Gill-Slits. It is convenient to classify these, according to the 
 order of their appearance, as primary, secondary, and tertiary. 
 
 (1) Primary Slits. The first of these, already mentioned, is 
 succeeded by 13 others, developed on the right side of the mid- 
 ventral line, and passing well up the right side of the body. 
 
152 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Later on, the first and some of the posterior ones close up, while 
 the others gradually shift round across the mid-ventral line to 
 the left-hand side of the body and become the anterior slits of 
 that side. 
 
 (2) Secondary Slits 7, 8, or 9 in number appear on the 
 right-hand side of the body above the primary ones, the first slit 
 corresponding with the gap between the 2nd and 3rd primaries. 
 So many of the primaries close up as is necessary to make their 
 number equal to that of the secondaries. Thus if there are 8 of 
 these last, 6 of the primaries close, as follows, using Roman 
 numerals for the primaries, arabic numerals for the secondaries, 
 and brackets to indicate closure : 
 
 87 654321 
 
 [XIV] [XIII] [XII] [XI] [X] IX VIII VII VI V IV III II [I] 
 The secondary slits become the anterior slits of the right side. 
 
 (3) Tertiary Slits are formed on each side behind those already 
 developed. New ones are added as long as the animal continues 
 to grow in length. 
 
 Primaries, secondaries, and tertiaries alike become divided into 
 two by the downgrowth of secondary bars, as described on p. 141. 
 
 A trial Cavity. The primary gill-slits at first open directly to 
 the exterior, but later on into a groove which is bounded by a, 
 ridge on each side. The groove is then converted into a narrow 
 canal, open at both ends, by the fusion of two shelf-like subatrial 
 folds which grow out from the ridges. This canal, which becomes 
 the atrial cavity, sinks as it were into the body, gradually extend- 
 ing round the gut so that the new gill-slits open into it. The 
 anterior opening soon closes, but the posterior one remains as the 
 atriopore. 
 
 CHAPTER IX. PISCES (Fishes). 
 
 THE lowest group of Vertebrates, using that term in the more 
 restricted sense (see p. 135), is constituted by Fishes, which are 
 again arranged in smaller subdivisions, as follows : 
 
PISCES. 153 
 
 1. Cydostomata lampreys and hags. 
 
 2. Elasmolmnchii dogfish, shark, skate. 
 
 3. Ganoidei sturgeon. 
 
 4. Teleostei herring, perch, cod, eel. 
 
 5. Dipnoi mudfishes. 
 
 The last group is a small and highly specialized one, including a 
 few fresh-water forms which breathe by gills and also by a lung- 
 like swim-bladder. It includes Ceratodus, in Australia ; Protopterus, 
 in Africa ; and Lepidosiren, in S. America. 
 
 The large majority of recent fishes belong to the Teleostei, some 
 of the most obvious characteristics of which are an externally 
 symmetrical tail, terminal mouth, thin scales, comb-like gills 
 protected by a firm gill-cover, and a well-ossified endoskeleton. 
 
 The Ganoidei are represented at the present time by a small 
 number of genera widely distributed in the fresh waters and 
 estuaries of the globe. The group was once large and important, 
 but is now approaching extinction. The recent Ganoids, of which 
 the best known is the one (Acipenser) including the sturgeon, 
 form a very heterogeneous assemblage, not closely related, and 
 difficult to include in a common definition. 
 
 Cydostomata are limbless, jawless fishes with a suctorial mouth. 
 
 Elasmobranchs are a very ancient type, and though common at 
 the present day are relatively far less abundant than they were 
 in former geological epochs. The skates are a good deal special- 
 ized, but dogfishes and sharks present the features of the fish- 
 type in a comparatively unmodified condition, and are, therefore, 
 better general illustrations of the group of fishes than members 
 of the teleostei. Dogfishes, which may be regarded as small 
 sharks, are represented on the British coasts by several genera, of 
 which Scyllium, the Spotted Dogfish, is perhaps the commonest. 
 S. canicula, the one usually dissected in laboratories, has an 
 average length of about two feet; S. catulus is much larger. 
 The following account will apply to either. 
 
 14. SCYLLIUM (Dogfish). 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The elongated spindle-shaped body, 
 eminently adapted for rapid progression through water, exhibits 
 
154 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 complete bilateral symmetry and is divisible into head, trunk, 
 and tail, between which there are no sharp lines of demarcation. 
 The head is flattened from above downwards, and ends anteriorly 
 in a rounded snout. The trunk and tail are laterally flattened, 
 while the latter is extremely long and very narrow in its posterior 
 part. 
 
 A number of thin flat fins are present, some unpaired and 
 situated in the median plane, others paired and lateral. They 
 are all supported by an internal skeleton. The unpaired fins are 
 four in number two dorsals, a caudal, and an anal. They are to 
 be looked upon as surviving portions of a continuous expansion 
 which in ancestral forms probably ran along the dorsal surface, 
 round the tail, and forwards for some distance along the ventral 
 surface (cf. Amphioxus, p. 136). The first dorsal is a small trian- 
 gular flap commencing about half-way back along the upper 
 surface ; not far behind it is a similar but smaller second dorsal. 
 The caudal fin fringes the tail and is markedly asymmetrical 
 (heterocercal). It consists of a square-ended upper lobe into 
 which the upwardly bent end of the body is continued, and a 
 rather broader lower lobe. The anal fin projects from the ventral 
 surface opposite the space between the first and second dorsals. 
 
 The paired fins are four in number, and are homologous to the 
 fore and hind limbs of terrestrial Vertebrates. They are probably 
 specialized portions of continuous lateral fins which existed in 
 ancestral forms (cf. Amphioxus, p. 136). The anterior pair, or 
 pectoral fins, project horizontally from the sides of the broadest 
 region of the body, and mark the junction of head and trunk. 
 Each is a broad flat plate with dorsal and ventral surfaces, and 
 (when it is pulled slightly outwards) anterior (pre-axial), posterior 
 (post-axial), and external margins. 
 
 The much smaller pelvic fins are attached to the ventral side of 
 the body, half-way between the snout and beginning of the caudal 
 fin. Their post-axial margins touch each other in the female and 
 are fused together in the male. A ready means of distinguishing 
 the sex is thus afforded, and further, in the male, a part of each 
 pelvic fin is converted into a grooved rod or clasper, which func- 
 tions as a copulatory organ. 
 
 Apertures. The mouth is a large crescentic slit on the under 
 side of the head; the cloacal aperture is an elongated opening 
 between the pelvic fins. There is a small abdominal pore on each, 
 
PISCES. 15& 
 
 side of this aperture leading into the body-cavity. The remaining 
 external openings are all in the anterior part of the body. Upon 
 the under side of the snout the external nares or nostrils are seen 
 as large rounded openings, from each of which a groove, covered 
 by a fold of skin, leads back to the mouth. 
 
 The oblique eyes, provided with upper and lower eyelids, are 
 placed on the sides of the head above the posterior corners of 
 the mouth. Just behind each of them is a small round hole, the 
 spiracle, opening out of the pharynx. It is of the same nature as 
 five oblique gill-slits which are seen further back immediately in 
 front of the pectoral fin. 
 
 Two minute apertures on the top of the head communicate 
 with the auditory organs. A large number of regularly-arranged 
 pores can be seen upon the head, especially in its anterior part. 
 They are the openings of sensory tubes (jelly-tubes, mucous canals), 
 which lie under the skin. Another sensory structure underlies 
 the groove-like lateral line which runs along each side of the 
 body. 
 
 The dogfish is of a whitish colour ventrally, grey with dark 
 brown spots dorsally and laterally. The fins are spotted as well 
 as the body. This colouration must make the animal extremely 
 inconspicuous when seen from above in its natural surroundings. 
 
 The body is entirely covered by small sharp, placoid scales, 
 imbedded in the skin, but with projecting, backwardly directed 
 points. The scales near the mouth closely resemble the teeth. 
 
 2. The skin consists of an epidermis composed of stratified epi- 
 thelium, and an underlying dermis made up of connective-tissue 
 traversed by blood-vessels, lymphatics, and nerves. 
 
 The only important glands connected with the skin, if the jelly- 
 tubes are excluded, are the clasper-glands of the male, each of which 
 is a pouch underlying the skin between the pelvic fins and opening 
 backwards into the groove of the corresponding clasper. 
 
 The small placoid scales are developed in the skin. Examined 
 with a powerful lens, or under a low power of the microscope, 
 each of them is seen to consist of a four-rayed basal plate, and of 
 a much larger spine attached to it. The end of the spine is leaf- 
 shaped and directed obliquely backwards with its flat side upper- 
 most. The basal plate is bone-like, the spine composed of hard 
 dentine, capped by exceedingly hard enamel secreted by the epi- 
 dermis. The rest of the scale is developed by the dermis. 
 
156 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The very young scales are covered by the epidermis, through 
 which the spines later on force their way. 
 
 3. Endoskeleton. In an embryo dogfish a firm cellular rod, 
 the notochord, underlies the central nervous system, much as in 
 Amphioxus, but in this case only extending as far forwards as the 
 middle of the brain. A cartilaginous sheath is soon formed round 
 the notochord ; in the head-region the floor of a firm cartilaginous 
 brain-case is developed in connection with this ; in the trunk and 
 tail the sheath is transversely segmented into a series of joints, 
 flexibility being thus much increased. Further modifications and 
 additions result in a complicated endoskeleton, composed almost 
 exclusively of cartilage. 
 
 'Pfi.br. 
 -Jlp. br. 
 
 Fig. 43. DOGFISH. Skull and part of vertebral column (reduced). Au, 
 Auditory capsule; JVa, nasal capsule; //. , ///., /F., <fcc., nerve-exits; 
 /./, upper jaw; L.J, lower jaw; H.m, hyo-mandibular ; Cer.h, cerato- 
 hyal; B.hy, basi-hyal; Ph.br, pharyngo - branchials ; Ep.br, epi- 
 branchials; Cer.br, cerato-branchials ; B.br, basi-branchials ; c, centra, 
 continued up into neural plates; Sp, neural spines; Int, intercalary 
 pieces ; F. d, F. r, foramina tor dorsal and ventral roots of spinal nerves, 
 indicated for two nerves. 
 
 It is convenient to consider the skeleton under two headings : 
 I. Skeleton of the body axial skeleton ; II. Skeleton of the fins 
 appendicular skeleton. 
 
 I. Axial Skeleton (Fig. 43). This is divisible into (1) Skull, 
 (2) Vertebral Column arid Ribs. 
 
 (1) The skull is characteristic of Yertebrata proper (Vertebrata 
 Craniota). It includes a cranium or brain-case olfactory and 
 auditory capsules ; and the visceral skeleton, consisting of jaws 
 and respiratory skeleton. 
 
PISCES. 1ST 
 
 The cranium is a somewhat rectangular box of cartilage enclos- 
 ing the brain, and incomplete dorsally, where there is a large 
 gap or fontanelle closed by membrane. Posteriorly the cranium 
 articulates immovably with the vertebral column by two rounded 
 projections (condyles), between which is a large aperture (foramen 
 magnum), where the spinal cord and brain are united. There are 
 nerve-exits in front and at the sides, while the cranial floor is 
 continued forwards as a median nasal septum bearing in front a 
 slender pointed rod. 
 
 The olfactory capsules are large thin-walled structures sepa- 
 rated from one another by a median septum, open below, and 
 fused with the front of the cranium. The auditory capsules are 
 much firmer. They enclose the organs of hearing, and are fused 
 with the sides of the cranium in its hinder region, each of them 
 appearing as a squarish projection. 
 
 Visceral Skeleton. In the embryo dogfish seven thickenings, 
 visceral arches, appear on each side of the neck, and between them 
 six openings, visceral clefts, placing the cavity of the pharynx in 
 communication with the exterior. The arrangement may be 
 indicated as follows for the left side, using strokes for the arches 
 and numbers for the clefts ; the arrow points to the front. 
 
 \'\'VV\\'\ 
 
 Beginning in front, the arches are termed mandibular, hyoid, 
 1st, 2nd, 3rd, 4:ih, and 5th branchials. The first cleft is the 
 hyomandibular, and becomes the spiracle; the rest are named 
 like the arches which bound them behind, and become the gill- 
 clefts. 
 
 Curved supporting rods of cartilage are developed in the vis- 
 ceral arches, and become converted into the visceral skeleton. 
 
 The mandibular bars are converted into two cartilages which 
 support the lower jaw. From the upper end of each a forward 
 outgrowth is developed, which becomes separated off and supports 
 the corresponding half of the upper jaw. 
 
 The hyoid bars are segmented into upper pieces, the hyo- 
 mandibular cartilages, which suspend the jaw-cartilages from 
 the auditory region of the skull, and lower pieces (cerato-hyals) 
 which unite with a median ventral basi-hyal cartilage. A skull 
 like this, in which the jaws are suspended by means of hyo- 
 
158 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 mandibulars, is said to be hyostylic. The upper jaw is also 
 'Connected with the skull by two strong fibrous bands (ligaments), 
 one in front (ethmopalatine ligament) and one behind (pre- 
 spiracular ligament) running in front of the spiracle and contain- 
 ing a small pre-spiracular cartilage. 
 
 Each of the five branchial rods on each side becomes jointed 
 into a series of segments, named, from above downwards, pJwryngo-, 
 epi-, cerato-, and hypo-lranchials. A median ventral basi-branchial 
 cartilage lies between and connects together the arches of opposite 
 sides. 
 
 Slender cartilaginous gill-rays for the support of the gill-folds 
 radiate backwards from the posterior margins of the cerato-hyals 
 and first four pairs of cerato-branchials. 
 
 The visceral skeleton includes a few other cartilages besides the above. 
 They are (1) a pair of rod-like labials at each corner of the mouth, (2) three 
 flattened rods, the extra-branchials, on each side, external to the three 
 middle branchial arches. 
 
 (2) Vertebral Column and Ribs. The vertebral column con- 
 sists of a series of joints or vertebrae, which are united together 
 to form a flexible rod. The vertebrae are of two kinds, trunk 
 vertebrae and tail vertebras ; the latter are the more typical, and 
 each of them consists of a deeply biconcave (amphiccelous) body or 
 centrum lined by bone, a neural arch under which the spinal cord 
 runs, and a hcemal arch protecting the blood-vessels of the tail, 
 and produced downwards into a hcemal spine. The trunk vertebrae 
 chiefly differ in the absence of complete haemal arches; those in 
 front possess horizontal projecting transverse processes which bear 
 short ribs; those behind have downwardly projecting haemal 
 processes ( = transverse processes of those in front, and sides of 
 haemal arches of tail vertebrae). The neural arches of both kinds 
 of vertebra are similar. Each consists of four pieces, a lateral 
 neural plate projecting from the centrum on each side, and two 
 small rounded dorsal cartilages (neural spines) placed one behind 
 the other. The spaces between the neural plates are filled up by 
 hexagonal intercalary cartilages. 
 
 The notocliord persists throughout the entire extent of the verte- 
 bral column, but by the development of the vertebral centra is 
 deeply constricted at regular intervals, though not quite divided 
 dnto a series of separate sections. 
 
 II. Appendicular Skeleton. Each unpaired fin is in typical cases 
 
PISCES. 159 
 
 supported by a series of cartilaginous rod-like fin-rays, bearing 
 small plates of cartilage at their distal ends. The fin-skeleton is 
 completed by a large number of horny fibres developed in the 
 skin and running in the same direction as the fin-rays. 
 
 The skeleton of either anterior or posterior paired fins is 
 divisible into a proximal part, the limb-girdle, connected with the 
 body, and a distal part which supports the free limb. (1) Pectoral 
 Jins (Fig. 44). Each shoulder girdle is a curved flat cartilage 
 
 Fig. 44. Fig. 45. 
 
 Fig. 44. DOGFISH. Skeleton of pectoral fins seen from below (reduced). 
 Co, Coracoid region; Sc, scapular region; p.pt, propterygium ; me.pt, 
 mesopterygium ; mt.pt, metapterygium ; p.r, me.r, mt.r, corresponding 
 fin-rays. 
 
 Fig. 45. DOGFISH. Skeleton of pelvic fins seen from below (reduced). 
 Pb, Pubic region; il, iliac process; bas.pt ', basipterygium, continued 
 back into Cl, clasper skeleton. Fin-rays seen externally. 
 
 consisting of a dorsal half, the scapular region, and a ventral half, 
 the coracoid region, the junction of the two being marked by the 
 attachment of the free limb. The two girdles are fused together 
 ventrally. The base of the free fin is supported by three cartilages, 
 named from before backwards propterygium, mesopterygium, and 
 metapterygium, the last being much the largest. To these elements 
 a number of fin-rays succeed, one propterygial, one mesopterygial 
 split into two or three distally, and about a dozen metapterygial. 
 The fin- skeleton is completed by rows of polygonal plates and by 
 
160 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 horny fibres like those of the unpaired fins. (2) Pelvic fins 
 (Fig. 45). The two pelvic girdles are fused together into a 
 transverse bar of cartilage lying a little way in front of the 
 cloaca. Most of the bar (pubic region) lies between the attach- 
 ment of the free fins, but there is a small projection (iliac process) 
 external to this on each side. 
 
 The inner side of the free limb is supported by an elongated 
 basipterygium ( = metapterygium) which in the male is continued 
 into the clasper. A series of fin-rays are attached to the outer 
 side of this cartilage, and one ray directly to the girdle. The fin 
 is completed by small plates of cartilage and by horny fibres. 
 
 4. The digestive organs (Fig. 46) consist of the gut or 
 alimentary canal running from mouth to cloacal aperture, and 
 of appended glands. The sections of the gut are mouth-cavity, 
 pharynx, stomach, intestine, arid cloaca. The glands are the 
 liver and pancreas. 
 
 The margins of the mouth are beset with several rows of 
 small, sharply-pointed teeth, which must be regarded as modified 
 placoid scales. The mouth-cavity is spacious, and upon its floor 
 there is an ill-developed tongue, supported by the basi-hyal 
 cartilage, and with a forwardly-directed rounded end. The 
 pharynx or respiratory section of the gut, which next succeeds, 
 communicates with the exterior by means of the spiracles and 
 gill-slits, and merges into a short, wide gullet (oesophagus) which 
 enters the abdominal cavity, and is there continuous with a large 
 U-shaped stomach. This is followed by the intestine, which 
 is divided into (a) a short, moderately-large bursa Entiana; (b) 
 a much larger and longer section, into which a shelf -like spiral 
 valve projects; and (c) a short narrow rectum opening into a 
 good-sized cloaca which also receives the excretory and genital 
 ducts. 
 
 The liver is a large brown organ attached to the front end 
 of the abdominal cavity and divided into two long backwardly- 
 directed lobes. The secretion of the liver (bile) is carried away 
 by a bile-duct which opens into the middle section of the in- 
 testine, on the right side, not far from the beginning of the 
 spiral valve. A large gall-bladder connected with the duct is 
 imbedded in the left lobe of the liver near its origin. 
 
 The pancreas is a small, pale, flattened gland situated in the 
 angle between the stomach and the bursa Entiana. The pan- 
 
PISCES. 161 
 
 creatic duct is a short tube carrying off the pancreatic secretion 
 and opening into the left side of the intestine about the same 
 level as the bile-duct. 
 
 A short tube with thickened walls, the rectal gland, opens 
 into the dorsal side of the rectum. 
 
 The abdominal cavity, in which most of the digestive organs 
 are contained, is lined by a thin membrane, the peritoneum, 
 which leaves the body- wall in the median dorsal line to form 
 a double sheet, the mesentery, the halves of which diverge and 
 wrap round the gut, liver, &c., constituting suspensory folds, 
 which, however, are for the most part very incomplete. 
 
 The dogfish is a very voracious animal, feeding upon other 
 fishes, Crustacea, and molluscs. In some districts, at any rate, 
 it is especially abundant during the herring season. The rows 
 of sharp backwardly-pointed teeth assist in securing the prey. 
 By means of contractions of the muscular walls of the gut the 
 food is gradually passed backwards, and the force expended 
 during this process, combined with the softening and chemical 
 action of the digestive juices, serves to disintegrate it. The 
 chief digestive juices are the gastric juice, pancreatic juice, and 
 bile, of which the first is secreted by small glands in the wall 
 of the stomach and contains a ferment which converts proteids 
 into soluble diffusible peptones. The pancreatic juice, also 
 by ferment action, completes the digestion of proteids, converts 
 starch into sugar, and emulsifies fats. Bile assists in the last 
 kind of digestion. 
 
 The digested food diffuses into the blood-vessels and lym- 
 phatics which ramify in the wall of the gut. An increased 
 absorptive surface is given by the spiral valve, which also 
 prevents the contents of the intestine from passing backwards 
 too rapidly. The comparative shortness of the gut is correlated 
 with the easily digestible animal diet. 
 
 5. The circulatory organs of the dogfish comprise (I.) a blood 
 system, and (II.) a lymphatic system. 
 
 (I.) The "blood system (Fig. 46) is a closed set of tubes con- 
 taining red blood, consisting of coagulable plasma, in which 
 colourless corpuscles and red corpuscles are suspended. The former 
 are amoeboid and nucleated, the latter are oval discs, containing 
 a well-marked nucleus, and coloured red by hemoglobin. 
 
 A heart, arteries, veins, and capillaries can be distinguished. 
 2 11 
 
162 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The heart lies in a pericardial cavity which is separated from 
 the abdominal or peritoneal cavity by a transverse septum, but 
 the two cavities communicate with each other by a pair of 
 pericardio-peritoneal canals. The pericardium is immediately 
 above the ventral portion of the pectoral girdle, and its dorsal 
 wall is supported by the basi-branchial cartilaginous plate. 
 
 The heart, which contains only impure blood (i.e., blood poor 
 in oxygen, and loaded with C0 2 ), consists of sinus venosus, 
 a single auricle, a single ventricle, and a conus arteriosus. 
 The sinus venosus is a transverse tube which receives blood at 
 its two ends from the chief venous trunks. From this the blood 
 passes through a valved aperture into the auricle, which is by 
 far the largest division of the heart, and occupies the dorsal 
 half of the pericardial cavity. The thin walls of the auricle are 
 provided with a plentiful meshwork of muscles, which by their 
 contraction drive the blood through a valved auriculo-ventricular 
 aperture into the ventricle which lies on the ventral wall of the 
 pericardium. The ventricle is a nearly globular sac with a very 
 thick muscular wall, which by its contraction drives the blood 
 forwards into the conus through a valved aperture. The conus 
 arteriosus is a muscular tube running horizontally forward from 
 the ventricle to the anterior wall of the pericardium, from which 
 point it is continued forwards by the cardiac aorta. Within 
 the conus are two series of valves, viz.: the series already 
 referred to guarding the aperture from the ventricle, and a 
 
 Fig. 46. DOGFISH. General dissection of $ , semi-diagrammatic (re- 
 duced). na, Nostrils; s.t, openings of sensory tubes; <jl, gill-slits, 
 widened in both directions by means of scissors ; p.f, right pectoral 
 fin; pl.J, right pelvic fin the left one is cut away; d, cloacal aper- 
 ture ; ab.p, abdominal pore ; the tail has been cut off. The floor of 
 the mouth-cavity and pharynx has been cut through and its left half 
 removed, and the walls of these cavities have been dissected to show 
 blood-vessels; g, cut end of gullet; st, stomach; int, intestine cut open 
 to display spiral valve; ret, rectum; Ir, liver, the bile-duct, b.d, is 
 seen crossing the bursa Entiana; pa, pancreas, the pancreatic duct is 
 seen at x ; rct.gl, rectal gland. Heart, lit, with ventral aorta, v.ao, 
 and afferent branchial arteries (shaded with transverse lines). The 
 dorsal aorta is seen to be formed by the union of efferent branchial 
 arteries (darkly shaded), arising from loops surrounding gill-clefts, 
 x x x x x ; sp, internal opening of spiracle; ca, carotid; a.ca, 
 anterior carotid ; set, subclavian ; cos, cceliac ; a. m, anterior mesenteric. 
 The ovary has been removed ; ovd, right oviduct with oviducal gland, 
 od ; ovd ', common abdominal opening of oviducts. 
 
PISCES. 
 
 163 
 
 Fig. 46. 
 [From a Dissection by S. T. Parkinson.] 
 
164 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 second set about the middle of its length. Each series consists 
 of three pouch-like flaps (pocket-valves) attached to the wall 
 by their posterior edges, their anterior edges being free. All 
 the valves of the heart are so arranged as to allow blood to flow 
 freely in the direction described, but not in the opposite direction. 
 
 The arteries are well-defined tubes with largely muscular 
 walls. The blood leaving the heart passes through a mid- 
 ventral cardiac aorta to be distributed to the gills, where the 
 blood receives a supply of oxygen from the water by which 
 the gills are bathed, and gets rid of its C0 2 . It is then 
 collected by a series of efferent branchial vessels into a median 
 dorsal aorta, from which arise arteries distributing blood to all 
 parts of the body with the exception of the head. 
 
 The head is supplied with blood by arteries arising direct 
 from the foremost of the efferent branchial vessels. 
 
 The blood-vessels of the gills are: (1) the afferent branchial 
 arteries bringing the blood from the cardiac aorta, of which one 
 supplies the gills of each gill-arch, the three hinder pairs arising 
 separately from the cardiac aorta, while those supplying the two 
 foremost pair of arches arise by one pair of vessels, each of which 
 then divides into two. (2) The efferent branchial arteries, carrying 
 pure blood into the dorsal aorta, and arising from loops which 
 surround each of the gill-clefts except the last. The blood from 
 the gill of the last (or fifth) gill-cleft is received by an efferent 
 vessel which opens into the efferent loop of the fourth cleft. 
 Each efferent loop communicates also by means of a short vessel 
 with the loops in front of and behind it. 
 
 The dorsal aorta, formed by the union of the efferent branchial 
 arteries, runs back below the vertebral column to the posterior 
 end of the body, becoming the caudal artery in the tail. It also 
 has a forward continuation which divides into two branches that 
 are connected with the carotid arteries. 
 
 Branches of the Dorsal Aorta. (1) A pair of snbclavian arteries to pectoral 
 fins. (2) A cceliac artery, supplying liver, anterior end of stomach, begin- 
 ning of intestine, liver, and pancreas. (3) An anterior mesenteric artery to 
 intestine and reproductive organs. (4) A lieno-gaztric artery to stomach, 
 spleen, and pancreas. (5) A posterior mesenteric artery to rectal gland. 
 (6) Numerous pairs of small parietal arteries to body walls. (7) Numerous 
 pairs of small renal arteries to kidneys. 
 
 Each half of the head is supplied with pure blood by : (1) a carotid 
 artery, running forwards from the top of the first efferent loop and dividing 
 into (a) external carotid to upper jaw and snout; (b) internal carotid to brain. 
 
PISCES. 165 
 
 (2) A hyoidean artery, running from the middle of the same loop to supply 
 pseudobranch and brain. (3) Small vessels to the floor of the mouth from 
 the ventral ends of the efferent loops. 
 
 The veins are partly regular tubes, partly irregular sinuses, all 
 of which have thin walls. They may be divided into : (1) Sys- 
 temic veins. (2) Portal systems. 
 
 (1) Systemic Veins. The impure blood from the anterior 
 part of the body is brought back on each side by an anterior 
 cardinal sinus running above the gill-clefts to the level of the 
 sinus venosus, where it unites with a much larger posterior 
 cardinal sinus bringing forwards the impure blood from the body 
 behind the pectoral fins. By the union of the anterior and 
 posterior cardinal sinuses on each side a very short Cuvierian 
 sinus is formed, which, after receiving a jugular sinus from the 
 floor of the mouth and pharynx, is merged in the corresponding 
 side of the sinus venosus. 
 
 Factors of Cardinals. An orbital sinus surrounding the eye opens behind 
 into a short post-orbital sinus, which again communicates with the anterior 
 cardinal. A hyoidean sinus opens into the front end of the anterior cardinal. 
 
 The posterior cardinals begin between the kidneys, and each of them, 
 before it unites with the corresponding anterior cardinal, receives a lateral 
 vein from the body-wall, a genital sinus from the gonad, and a subclavian 
 vein from the pectoral fin. 
 
 (2) Portal Systems. Hepatic portal and renal portal systems 
 are present, which respectively supply the liver and kidneys with 
 impure blood. 
 
 Hepatic Portal System. The blood from the abdominal 
 digestive organs and spleen, containing most of the products of 
 digestion, enters the hepatic portal vein, which breaks up into 
 branches in the substance of the liver. This organ returns its 
 impure blood direct to the sinus venosus by means of two hepatic 
 sinuses. 
 
 Renal Portal System. The impure blood of the tail passes 
 into a caudal vein which runs forwards to the posterior ends of 
 the kidneys and divides into right and left renal portal veins, 
 which divide up in the kidneys, from which the blood is returned 
 to the posterior cardinals by numerous small renal veins. 
 
 The capillaries are minute tubes arranged in plexuses, in 
 which the smallest arteries end and the smallest veins begin. 
 
 (II.) The lymphatic system consists of minute spaces, small 
 lymphatic vessels, and large cavities, all containing lymph, 
 
166 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 which resembles blood in many respects but possesses no red 
 corpuscles. There are also certain " ductless glands " connected 
 with the lymphatic system, of which the largest is the spleen, a 
 reddish body attached to the bend and distal limb of the 
 stomach. 
 
 The largest lymph-space is the body-cavity or ccelom, which 
 includes the abdominal and pericardial cavities. 
 
 6. The respiratory organs of the dogfish are gills, adapted for 
 breathing the oxygen dissolved in the surrounding sea- water. 
 They consist of vascular folds arranged upon the posterior side 
 of the hyoid arch, and both sides of the first four branchial 
 arches. Water is taken in at the mouth and expelled through 
 the gill-slits to the exterior, so that a continual stream passes 
 over the gills, in the small vessels of which the blood is purified. 
 The haemoglobin of the red blood-corpuscles acts as an oxygen- 
 carrier, taking up a certain amount of free oxygen from the 
 exterior into a state of loose chemical combination, and parting 
 with it again to the tissues. 
 
 A rudimentary gill (pseudobranch) is found on the anterior 
 wall of the spiracle. 
 
 7. The excretory and reproductive organs are so closely con- 
 nected that it is best to consider them under the common heading 
 of urine-genital organs. 
 
 The male dogfish possesses a pair of elongated narrow kidneys 
 extending nearly the whole length of the abdominal cavity and 
 situated close together below the vertebral column and above the 
 peritoneum. Each kidney is divided into a number of segments, 
 and its anterior half is distinguished as mesonephros (Wolffian 
 body) from its posterior half or metanepkros, the excretory pro- 
 ducts of these being carried off by distinct mesonephric (Wolffian) 
 ducts, and metanephric ducts (ureters). 
 
 Each mesonephric duct, which, since it also acts as a spermi- 
 duct, may be termed urino-genital duct, is a convoluted tube 
 running along the ventral side of the corresponding mesonephros, 
 dilating into a vesicula seminalis, and finally opening into an urino- 
 genital sinus that communicates with the cloaca by a small aperture 
 placed on the end of a dorsally situated urino-genital papilla. 
 
 The metanephric duct on each side is formed by the union of 
 several smaller ducts and opens into the dorsal side of the urino- 
 genital sinus. 
 
PISCES. 167 
 
 The spermaries (testes) are two soft flattened bodies, each 
 connected by a number of small ducts (vasa efferentia) with the 
 front end of the corresponding mesonephros. 
 
 The kidney is made up of numerous glandular tubules, and 
 the sperms have to traverse some of these before they can reach 
 the urino-genital duct. 
 
 The urino-genital sinus is forwardly produced into two blindly- 
 ending sperm sacs situated on the ventral side of the kidneys. 
 
 The daspers serve as copulatory organs by which the sperms 
 are introduced into the oviducts of the female. 
 
 Two short tubes, with a common opening into the abdominal cavity, can 
 be seen on the ventral side of the gullet. These are rudimentary Mullerian 
 ducts, equivalent to the oviducts of female specimens. 
 
 The kidneys in the female exhibit the same regions as in the 
 male, but the mesonephros is not so well developed. The two 
 mesonephric ducts are straight and unite to form a urinary sinus, 
 which receives a number of distinct metanephric ducts and opens 
 into the cloaca on a dorsal urinary papilla. 
 
 The reproductive organs of the female are not so intimately 
 connected with the urinary organs as in the male. There is a 
 large unpaired ovary from which large ova in various stages of 
 development can be seen projecting. When ripe these may 
 exceed half an inch in diameter, their large size being due to 
 the presence of abundant food-yolk. 
 
 The oviducts (Mullerian ducts) have a common anterior open- 
 ing into the abdominal cavity, situated on the ventral side of the 
 gullet in front of the liver. Each of them curves back and soon 
 dilates into an ovoid oviducal gland, after which it runs back as a 
 good-sized tube towards the cloaca, just before reaching which it 
 unites with its fellow to open by a median dorsal aperture. 
 
 The ova are fertilized in the oviduct, after which each of them 
 is surrounded by an albuminous fluid and enclosed in a horny 
 case secreted by the oviducal gland, and with four corners pro- 
 duced into tendril-like threads. In this condition the eggs are 
 laid, the threads serving to attach them to seaweeds, &c. De- 
 velopment takes place at the expense of the food-yolk, which 
 after a time is found stored in a vascular sac, the yolk-sac, 
 attached to the ventral side of the embryo. 
 
 In most dogfishes the entire embryonic development takes place in the 
 oviduct, and in one species (Mustelus Ia3vis) the vascular yolk-sac is thrown 
 
168 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 into folds which interlock in corresponding folds of the oviduct, so that a 
 kind of placenta is formed i.e., an embryonic structure by which the blood- 
 systems of parent and embryo are brought into close relation. Scyllium, 
 therefore, is oviparous, a term applied to cases where most or all of the 
 development takes place external to the body other dogfish are viviparous. 
 
 8. The most obvious part of the muscular system is a great 
 lateral mass extending along each side of the body from the 
 neighbourhood of the spiracle, and segmented into a succession 
 of myomeres, with zigzag boundaries. The lateral muscles are 
 also divisible into dorsal and ventral sections along the boundary 
 between which runs the lateral line. These muscles effect 
 swimming movements, during which the body is not merely 
 bent from side to side but thrown into sinuous curves. There 
 are also special muscles for moving the fins, lower jaw, &c. 
 
 9. The nervous system (Fig. 48) consists of (1) cerebro-spinal 
 axis, (2) cranio-spinal nerves, and (3) sympathetic system. 
 
 (1) The cerebro-spinal axis is a thick- walled tube invested 
 in a delicate vascular membrane (pia mater) and contained in 
 the neural canal of the skull and vertebral column. The canal 
 is lined by a firm membrane (dura mater) between which and 
 the pia mater there is a large lymph-space. The front end of 
 the cerebro-spinal axis is dilated into a brain, lying within the 
 cranium and a spinal cord, running along the spinal canal above 
 the vertebral centra. The cavity of the neural tube constitutes an 
 extremely small central canal in the spinal canal and larger spaces 
 known as ventricles in the brain. 
 
 The brain at an early stage exhibits three successive swellings, 
 the anterior, middle, and posterior cerebral vesicles. These, 
 together with outgrowths from them, become the fore-, mid-, 
 and hind-brains of the adult. 
 
 The fore-brain consists of a central thalamencephalon, with a 
 large antero-dorsal outgrowth, the prosencephalon, with which 
 are connected two olfactory lobes. 
 
 The thalamencephalon is somewhat cylindrical and contains a 
 large cavity (3rd ventricle) with thin roof but thickened floor 
 and side walls. The floor is produced downwards into a pro- 
 jection (infundibulum) in which are two oval swellings (lobi 
 inferiores). Two structures of non-nervous nature are connected 
 with the thalamencephalon. They are known as the pineal and 
 pituitary bodies. The pineal body is a stalk-like structure with 
 
PISCES. 169 
 
 a swollen end, running forwards and upwards from the roof of 
 the 3rd ventricle. It corresponds to what appears to have been 
 an unpaired dorsal eye (pineal eye) in ancestral forms (see p. 2). 
 The pituitary body is a problematic organ attached to the inf un- 
 dibulum, and consisting of two thin- walled sacs (sacci vasculosi) 
 and a central tube. 
 
 The prosencephalon ( = cerebral hemispheres of higher verte- 
 brates) is the largest part of the brain. It is a rounded mass 
 presenting indications of divisions into right and left halves, 
 and containing a ventricle connected with the 3rd ventricle. 
 An expanded olfactory lobe abuts on the posterior wall of each 
 olfactory capsule, and is connected behind with the prosen- 
 cephalon by a short stalk. It contains an olfactory ventricle 
 which communicates with the brain-cavity last mentioned. 
 
 The short, thick mid-brain which next succeeds contains a 
 ventricle (iter or Sylvian aqueduct), the roof of which is raised 
 up into two ovoid optic lobes containing optic ventricles. 
 
 The axis of the hind-brain is constituted by a long cylindrical 
 bulb (medulla oblongata) containing a cavity (4th ventricle) with 
 a thin roof. A large hollow body, the cerebellum, of elongated 
 oval shape is attached by the middle of its length to the dorsal 
 side of the bulb, which is also produced on each side into a 
 conspicuous lobe (restiform body). 
 
 The spinal cord is cylindroidal in shape and somewhat 
 flattened from above downwards. It is deeply furrowed by 
 two median fissures one dorsal, the other ventral. 
 
 (2) Cranio-spinal Nerves. These may be divided into cranial 
 nerves and spinal nerves, which respectively take origin from 
 the brain and spinal cord. 
 
 There are ten pairs of cranial nerves, as follows : 
 
 I. Olfactory, each of which consists of two bundles of fibres 
 arising from the corresponding olfactory lobe and supplying 
 the lining of the olfactory sac on the same side. 
 
 II. Optic, running to the eyeballs. They unite to form an 
 X-shaped chiasma on the ventral side of the thalamencephalon. 
 The posterior limbs of the X (optic tracts) end in the optic lobes. 
 
 The III., IV., and VI. nerves are known as the eye-muscle 
 nerves. 
 
 III. Oculomotor. These arise from the ventral side of the 
 mid-brain and supply most of the eye-muscles. 
 
170 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 IV. The pathetic nerves are the only, cranial ones which have a 
 dorsal origin. They arise nearly in the middle line just behind 
 the optic lobes and supply the superior oblique muscles. 
 
 All the remaining nerves take origin from the bulb. 
 
 Fig. 47. DOGFISH. A, Diagram of cranio-spinal nerves (slightly altered 
 after Wiedersheim). M, Mouth; Or, margin of orbit (indicated by 
 dotted line); Au, auditory capsule ; Sp, spiracle; ttttt, gill-slits; 
 II., optic ; III, oculomotor; IV., pathetic ; V, ophthalmic branch of 
 trigeminal ; *, its course in front of orbit to join VIP ; V 6 and V c , 
 maxillary and mandibular branches of trigeminal ; VI., abducent ; 
 VIP, ophthalmic branch of facial ; VII., main trunk of facial, where 
 palatine branch runs forward and hyomandibular backward behind 
 spiracle, giving off prespiracular branches ; IX. , glossopharyngeal, 
 forking over first gill-slit; X., vagus, giving off branchial branches 
 which fork over gill-slits, a lateral line branch (Lat), and then supply- 
 ing viscera ; 1-14, first fourteen spinal nerves, forming brachial plexus 
 (Br.pl], from which pectoral fin is supplied. B, Dorsal view of brain. 
 C, Ventral view of brain. ol, Olfactory lobes; pr, prosencephalon ; 
 th, thalamencephalon ; pin, pineal body; py, pituitary body; Li, 
 lobi inferiores ; o.l, optic lobes; e&, cerebellum ; r.b, restiform body; 
 b, bulb ; sp, spinal cord ; II. -X., cranial nerves. 
 
PISCES. 1 7 1 
 
 VI. The abducent nerves, which innervate the external rectus 
 muscles, arise almost mid-ventrally from the anterior part of the 
 bulb. [NJB. These nerves are mentioned out of their order 
 for the sake of convenience.] 
 
 V. The trigeminal, which, like all its successors, arises from the 
 side of the bulb, is a large nerve which has 3 chief branches : 
 a. Ophthalmic, to sensory tubes on upper side of snout ; 
 /3. Maxillary, to sensory tubes on under side of snout ; 
 y. Mandibular, to muscles of the lower jaw. 
 
 VII. The facial nerves arise close behind the trigeminals, and 
 like them have three chief branches : 
 
 a. Ophthalmic, which first runs parallel to the similarly named 
 division of the fifth, then fuses with it and has the same distribution ; 
 
 J3. Palatine, to roof of mouth ; 
 
 j. Hyoidean (post-spiracular), which runs down behind the 
 spiracle, supplying muscles, and gives off small pre-spiracular 
 branches. 
 
 VIII. The auditory nerves run into the auditory capsules to 
 supply the membranous labyrinths. 
 
 IX. The gfassopharyngeal nerve on each side arises just behind 
 the eighth, traverses the floor of the auditory capsule, and forks 
 over the first branchial cleft into an anterior (hyoidean) branch 
 and a posterior (branchial) branch. 
 
 X. The vagus (pneumogastric) is a large nerve arising by 
 several roots and taking a backward course. It gives off a 
 lateral line nerve, which supplies the similarly named sense-organs, 
 four branchial nerves, which fork over the last four branchial 
 clefts, and finally divides into branches for the heart and viscera. 
 
 The spinal nerves arise segmentally from the spinal cord, each 
 by two roots, a dorsal (upon which is a small ganglion) and a 
 ventral, which pierce the wall of the spinal canal and then unite 
 together. Each segment is supplied by the corresponding pair 
 of nerves, the fibres of the dorsal root going to the skin, those of 
 the ventral root to the muscles. The regularity is somewhat dis- 
 turbed by the presence of the paired fins, which are supplied from 
 plexuses formed by certain of the anterior and posterior nerves. 
 
 (3) The sympathetic system consists of two longitudinal 
 cords situated ventral to the vertebral column and dilated into 
 segmentally - arranged ganglia which are connected with the 
 adjoining spinal nerves. Each cord is connected in front with 
 
172 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 the corresponding vagus. x The sympathetic ganglia supply the 
 viscera and vascular system. 
 
 Histologically, the nervous system is essentially made up of 
 the two usual elements, 'nerve-cells (ganglion cells) and nerve fibres. 
 In the brain and spinal cord these elements are respectively 
 aggregated into what are known as grey and white matter. 
 The former exists in the spinal cord and bulb as an axial core, in 
 the prosencephalon and cerebellum as an external crust. Masses 
 of it are also found in the optic lobes, side-walls of the thalam- 
 encephalon, basal part of the prosencephalon, and in the olfactory 
 lobes. 
 
 10. The chief sense organs of the dogfish are those connected 
 with the skin, the olfactory sacs, the ears, and the eyes. All 
 of these essentially consist of end-organs connected with nerve- 
 fibres. 
 
 The skin is abundantly provided with groups (end-buds) of 
 projecting sense-cells, probably of tactile nature, and it also 
 possesses lateral line organs and sensory tubes. The indistinct 
 groove termed lateral line in describing the external characters 
 corresponds pretty much in position with a tube which underlies 
 the skin and opens to the exterior at intervals. It is lined by 
 epithelium, many of the cells of which are mucus-secreting goblet 
 cells, while others are sense-cells (hair-cells), each provided with 
 a slender hair-like process. 
 
 The sensory tubes (jelly tubes) which open on the snout under- 
 lie the skin of the head and each of them ends in a rounded 
 sac (ampulla) divided into compartments, and partly lined by 
 hair-cells. These tubes contain a gelatinous substance, secreted 
 by the lining epithelium. The ampullae are supplied by the 
 ophthalmic branches of the fifth and seventh cranial nerves, the 
 fibres of which run to the hair-cells. 
 
 The large olfactory sacs, contained in the olfactory capsules 
 opening ventrally by the nostrils, have their lining raised into 
 numerous transverse folds, the epithelium of which contains 
 elongated olfactory cells, supplied by the olfactory nerve. 
 
 The ear (Fig. 48) on each side is a membranous sac (labyrinth) 
 of complicated shape contained within the auditory capsule, and 
 surrounded by a large lymph-space. It is lined by epithelium, 
 part of which is sensory, and is filled with fluid in which are 
 suspended numerous calcareous particles. The membranous 
 
PISCES. 
 
 173 
 
 labyrinth originates as an ectodermic pit, and in the adult still 
 retains a connection with the exterior by means of a narrow 
 tube (aqueductus vestibuli) opening on the top of the head. 
 
 The labyrinth is divided into a central region (vestibule) and 
 three curved tubes, the semicircular canals. The vestibule is 
 again divided into an anterior utriculus, and a posterior sacculus 
 with which the aqueductus vestibuli communicates and which 
 is produced into a process, the cochlea. The semicircular canals 
 
 Fig. 48. DIAGRAMS or THE MEMBRANOUS LABYRINTH (from Bell, after 
 Waldeyer). A, Fish ; B, Bird ; C, Mammal. Internal side of left 
 labyrinth. us, Utriculus and sacculus ; w, utriculus ; s, sacculus ; 
 c, cochlea. 
 
 are known from their position as anterior vertical, posterior 
 vertical, and external horizontal. They open at both ends into 
 the utriculus, and each has a small swelling (ampulla) at one 
 end. This is anterior in the first and last named, posterior in 
 the horizontal canal. The ampullae and parts of the vestibule 
 possess patches of auditory hair-cells, with which fibres of the 
 auditory nerve are connected. 
 
 Each of the eyes is flattened externally and rounded internally. 
 Its wall consists of three coats, the most external of which is 
 the firm sclerotic, supported by cartilage and exhibiting externally 
 a transparent oval area, the cornea. The middle coat (choroid) 
 is a pigmented vascular membrane lining the rounded part of 
 
174 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 the eye, and continued into a partition, the iris, by which the 
 cavity of the eye is divided into a small outer and a large 
 inner chamber. The iris is perforated by an oval slit (the 
 pupil) for the transmission of light. The innermost coat of the 
 eye is a delicate membrane, the retina, which contains the end- 
 organs for sight (rods and cones). The optic nerve perforates 
 the sclerotic and choroid on the inner side of the eye and 
 branches out in the retina, its fibres becoming indirectly con- 
 nected with the rods and cones. The interior of the eye is 
 occupied by refracting structures, by which the light is focussed 
 on the sensitive retina. These are : a watery fluid (aqueous 
 humour) external to the iris, a jelly-like substance (vitreous 
 humour} occupying the internal chamber, and a spherical trans- 
 parent lens suspended on the inner side of the iris. 
 
 The eyelids have already been mentioned (p. 155). Other 
 important accessory parts are the six small band-like muscles 
 by which the eyeball is moved. Four of these take origin from 
 the hinder part of the orbit, and are inserted into the upper, 
 lower, anterior, and posterior sides of the eyeball, being respec- 
 tively known as superior, inferior, internal, and external red us 
 muscles. The other two are known as superior and inferior 
 oblique muscles, taking origin from the front end of the orbit, 
 and inserted respectively into the upper and lower sides of the 
 eyeball. 
 
 CHAPTER X. AMPHIBIA. 
 15. RANA (The Frog). 
 
 THE two commonest kinds of Frog are Rana temporaria, the 
 Common Frog, and Rana escul&nta, the Edible Frog. Both are 
 found on the Continent, but only the former in this country. 
 The following description applies to both, any important dif- 
 ferences being noted : 
 
AMPHIBIA. 175 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The bilaterally symmetrical body 
 exhibits no external trace of segmentation, and is divided into 
 head and trunk, between which no neck intervenes. There is 
 also no tail. Fore and hind limbs are present, and these, unlike 
 the paired fins of dogfish, to which they are homologous, are 
 transversely jointed, and split at their distal ends into digits. 
 The surface of the body is soft and mois", and there is no general 
 investing exoskeleton. Owing to the presence of pigment in the 
 skin the body is of a yellowish-brown, and is mottled dorsally. 
 The ventral surface is much smoother and paler than the dorsal. 
 The colour varies with the surroundings. 
 
 The flattened head is bluntly triangular, with a forwardly- 
 directed apex. The mouth is extremely wide, and extends back- 
 wards to the posterior angles of the head. On the dorsal surface, 
 near the front and widely separated, are two small valvular aper- 
 tures, the nostrils or external nares. Behind these are the large 
 projecting eyes, with small, immobile upper eyelids, and delicate, 
 semi-transparent lower eyelids, capable of considerable movement. 
 
 The space between the eyes is broader in JR. temporaria than in R. exc.u- 
 lenta, and while flat or convex in the former, is concave in the latter. 
 
 Behind each eye is a circular space, the tympanic area (larger in 
 R. esculenta), which in R. temporaria is inside a dark patch of pig- 
 ment, that tapers to a point behind. In the male R. esculenta a 
 pair of vocal sacs are found, which, when inflated, appear as rounded 
 projections near the angles of the mouth. 
 
 The trunk is somewhat oval, tapering to a blunt point behind, 
 where a small rounded cloacal aperture is found. Hard parts can 
 be felt through the skin along the entire dorsal surface, but this 
 is only the case with the anterior part of the ventral surface. In 
 this way a thoracic region in front can be distinguished from an 
 abdominal region behind. 
 
 The fore-limb commences immediately behind the head, and is 
 divided into (1) Brachium (arm), (2) Antebrachium (fore-arm), and 
 (3) Manus (hand). 
 
 If the fore- or hind-limb of an animal is spread out in the primitive 
 position i.e., at right angles to the body, with the "palm" or "sole" side 
 
176 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 downwards, dorsal and ventral surfaces can be distinguished. There are 
 also anterior and posterior edges, which, being in front and behind an axial 
 line running down the centre of the limb, are termed preaxial and postaxial 
 edges. (Cf. dogfish, p. 154.) 
 
 The manus possesses four well-developed digits, and, in addition, 
 a rudimentary one concealed under the skin, and corresponding 
 to the pollex (thumb) or 1st digit of other forms. The remaining 
 fingers are 2nd, 3rd, 4th, and 5th respectively, reckoning from the 
 preaxial side (thumb side). None of the digits possess nails or 
 claws. In the male Frog a thickened pad, especially prominent 
 during the breeding-season, is found on the preaxial side of the 
 palm of the hand. It is black in II. temporaria. 
 
 The hind-limb is also divisible into three parts (1) Femur 
 (thigh), (2) Cms (leg), (3) Pes (foot), consisting of a short cylin- 
 drical tarsus (ankle), and five slender digits, united together by a 
 delicate web. The hallux (great toe), or 1st digit, is preaxial, and 
 on its outer side there is a small, horny elevation, the " calcar," 
 which is a rudimentary " sixth toe " (prahallux). 
 
 All the preceding regions, especially the pes, are much longer 
 than the corresponding parts of the fore-limb, but there is obvious 
 serial homology between them. The typical number of digits 
 for manus and pes in terrestrial Vertebrates is five, so that the 
 pentadactyle pes of the frog must be regarded as more typical 
 than the tetrad actyle manus. Using * for rudiment, the state of 
 things in the frog may be represented by 4 */5 *. 
 
 Position of Body. When at rest the frog assumes a squatting 
 position, with the ventral surface near the ground posteriorly. 
 The back is humped, marking the union of the sacrum and ilia. 
 The elbow is directed backwards and outwards, and the hand 
 rests with its preaxial side turned sharply inwards. In the hind- 
 limb the knee is directed outwards and slightly forwards, while 
 the crus is bent back parallel to the femur, by which the ankle- 
 joint is thrown behind the body. The pes runs outwards and 
 forwards with its preaxial side internal. 
 
 2. Skin (Fig. 49). The skin is thin, and raised on the dorsal 
 surface into an immense number of minute wart-like protuber- 
 ances. It is only loosely united to the body, by bands of con- 
 nective tissue along certain definite lines. The intervening 
 subcutaneous spaces, over which the skin is baggy, are filled with 
 lymph. 
 
AMPHIBIA. 
 
 177 
 
 A superficial epidermis can be distinguished from an underlying 
 dermis, which is considerably thicker. 
 
 The epidermis is made up of several layers of cells, and hence 
 is classified as stratified* epithelium. The most external cells are 
 very flat, without evident nuclei, and make up a horny layer, 
 below which are rounded cells with well-marked nuclei and 
 granular protoplasm. Those abutting upon the dermis, forming 
 the Malpighian layer, are columnar. A small number of irregular 
 pigment cells, containing dark colouring -matter, are scattered 
 through the epidermis. Numerous glands open upon the surface 
 
 Fig. 49. VERTICAL SECTION OF SKIN or FROG (after Wiedersheim), much 
 enlarged. ep, Epidermis; h.l, horny layer; m. I, Malpighian layer; 
 w, warts; gl, cutaneous glands; p.c, pigment cells; De y 1, 2, 3, layers 
 of dermis. 
 
 of the epidermis. They are of two kinds, serous and mucous. The 
 former chiefly occur in the skin of the back, and appear to secrete 
 
 * The chief kinds of Epithelium may be thus classified : 
 
 I. SquamOUS (Pavement). 
 Composed entirely, or mostly, of 
 flattened, cubical, or polyhedral 
 cells. 
 
 II. Columnar. Composed of 
 
 cells more or less elongated at 
 right angles to surface. May be 
 ciliated. 
 
 III. Glandular. Composed 
 
 of spherical or cubical cells, 
 which elaborate a secretion or 
 excretion. 
 9 
 
 1. Simple. One cell thick. Endo- 
 thelium is a variety of this, composed of 
 flattened cells, and lining heart, vessels, 
 body-cavity, &c. 
 
 2. Stratified. More than one cell 
 thick. Epidermis, &c. 
 
 1. Simple. Stomach and intestine. 
 
 2. Stratified. Mouth-cavity of frog. 
 
 For the most part Simple. Peptic 
 glands, kidney tubules, &c., &c. 
 
 12 
 
178 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 a substance of irritant nature. The latter, which are more 
 numerous and widely distributed, elaborate a slimy secretion 
 which makes the skin moist and slippery. These glands are 
 rounded vesicles, lying in the outer part of the dermis, but lined 
 by glandular epidermal cells. They are large and numerous. 
 
 The dermis is mainly composed of fibrous* connective tissue, 
 the fibres of which are mostly parallel to the surface, but also 
 form vertical bands. The glands are imbedded in the external 
 part (1) of the dermis, which also contains a large number of 
 pigment-cells (chromatophores) that give to the skin its charac- 
 teristic colours. These vary owing to the fact that the chroma- 
 tophores contract under the influence of the nervous system. 
 In the fully contracted condition the pigment is limited to a 
 relatively small area, and the skin appears light. The reverse is 
 true when the chromatophores are non-contracted. Since these 
 colour-changes protect a frog by causing it to harmonize with its 
 surroundings, thus making it inconspicuous to its enemies, we 
 have here a case of protective general resemblance. But since also 
 the arrangement conceals the frog from its prey to a greater or 
 less extent, the general resemblance is aggressive as well as 
 protective. 
 
 The glands are surrounded by unstriated muscle-fibres, which 
 also form a layer in the deeper part of the dermis, where also 
 occur networks of blood-vessels, lymphatics, and nerves. Many 
 of the nerve-fibres end in touch-corpuscles; small oval flattened 
 bodies mostly forming groups underneath the epidermal warts. 
 
 3. The endoskeleton in the frog is mainly made up of gristle, 
 or cartilage, and bone, both of which are modifications of connective 
 tissue. The bones are largely connected at the joints by fibrous 
 bands (ligaments), which resemble tendons in structure (see p. 208). 
 Those parts of the endoskeleton belonging to the head and trunk 
 
 * Connective Tissue This permeates the whole body, binding together the 
 other tissues. In higher animals generally it consists of three elements, 
 associated together in different proportions. These are (1) Connective-tissue 
 corpuscles, nucleated cells, often branched (of which pigment-cells are modi- 
 fications), most abundant in young tissues. (2) White fibres delicate, and 
 wavy, yielding gelatin on boiling. (3) Yellow elastic fibres, much branched, 
 or forming networks. Unaffected by boiling. 
 
 The fibres are developed from the cells. All are imbedded in a structure- 
 less ground substance or matrix, which is semifluid and albuminous. 
 
 All these elements are found in the skin and in the bands uniting it with 
 the body- wall. 
 
AMPHIBIA. 179 
 
 may be conveniently termed axial, while those supporting the 
 limbs are appendicular. 
 
 (1) The axial endoskeleton consists of the skull, backbone or 
 vertebral column, and breastbone or sternum. 
 
 (a) The groundwork of the skull is made up of cartilage, 
 constituting the chondrocranium or primordial cranium. With 
 this are connected bones of two kinds, named, from their mode 
 of development, cartilage-bones and membrane-bones. The former 
 replace pre-existing cartilage, the latter pre-existing connective 
 tissue. It is convenient to consider the skull under the separate 
 headings of cranium, sense-capsules, jaws, and hyoid apparatus. 
 The membrane bones are flattened structures investing the other 
 parts, and will be taken last in each section. 
 
 The cranium or brain-case is a narrow cartilaginous tube, the 
 upper side of which is broader than the lower, and possesses three 
 spaces, fontanelles, a larger anterior and two smaller posterior, 
 where cartilage is wanting. These are filled in by connective 
 tissue. The cavity of the brain-case opens behind by the large 
 foramen magnum. The region around this is known as occipital, 
 either side of which is occupied by an ex-occipital bone, upon 
 which is a projection, or occipital condyle, with an oval smooth 
 surface. The two ex-occipitals do not completely bound the 
 foramen magnum, a small cartilaginous strip being left above and 
 below. Each of these bones is perforated by a vagus foramen 
 through which the vasjus and glossopharyngeal nerves leave the 
 skull. 
 
 The cartilaginous side-wall of the brain-case is perforated by 
 an optic foramen, and smaller foramina are also present. The 
 cartilage forming the front end of the brain-case is replaced by a 
 bony ring, the sphenethmoid or girdle bone, which also supports 
 the hinder part of the olfactory capsules that lie in front of the 
 skull. The sphenethmoid somewhat resembles a dice-box in 
 shape, and its cavity is divided into two halves by a transverse 
 partition marking the anterior boundary of the brain-case, and is 
 perforated by an olfactory foramen on each side for the passage of 
 the corresponding nerve. The front half of the bone is divided 
 by a vertical longitudinal partition, into right and left halves. 
 
 Membrane Bones. The roof of the brain-case is invested by two 
 long, flat parieto-frontals, which are bent over behind so as to 
 protect the upper part of its side walls. The floor of the brain- 
 
180 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 case is covered by the pamsphenoid, a dagger-shaped bone, with 
 its " blade " running forwards. 
 
 Sense Capsules. Two pairs of these are fused with the skull, 
 (a) auditory capsules behind and (ft) olfactory capsules in front. 
 
 (a ) The auditory capsules are closely fused with the hind end of 
 the brain-case, one on each side. They are largely cartilaginous, 
 but each is invaded behind by the ex-occipital of its side, while 
 in front the cartilage is replaced by a large pro-otic bone, which 
 also assists to form the side- wall of the brain-case, and is notched 
 below by the trigeminal foramen, through which the trigeminal 
 and facial nerves pass. The auditory capsule contains a complex 
 cavity, in which the essential organs of hearing are contained. 
 On its outer side is a depression, in which is a small opening, the 
 fenestra ovalis, filled up with membrane in the recent state. 
 Another and smaller opening on the hinder border, the fenestra 
 rotunda, is filled up in the same way. 
 
 Fig. 50. ENDOSKELETON or FROG (A, A', and C, after Ecker). Cartilage 
 dotted. A and A', Skull from above and below, membrane bones being 
 stripped off on one side; /, /', fontauelles; f.m, foramen magnum; 
 ex-oc, ex-occipital ; c, condyles ; v.f, vagus foramen ; pr-o, pro-otic ; 
 t.f, trigeminal foramen; op.f, optic foramen; g-b, girdle bone; orb, 
 orbit; ol, nasal capsules ; e-p.b, ethmopalatine bar ; pt. b, pterygoid bar ; 
 sp, suspensorium ; q-j, quadrato-jugal; pt, pterygoid; pa-f. parieto- 
 frontals ; p-s, parasphenoid, half cut away ; sq, squamosal ; na, nasals ; 
 v, vomer; pr-mx, pre-maxilla; mx, maxilla; pi, palatine; e.n, external 
 naris ; i.n, position of internal naris. B, Columella, enlarged. p and d, 
 Ends fitting into fen. ovalis and fixed to tymp. membrane, respectively. 
 C, Left half of Mandible, from outside. m-mk, Mento-meckelian ; c, 
 condyle; a-sp, angulo-splenial ; d, dentary. D, Hyoid apparatus. 
 b-hy, Body of hyoid; a.c, anterior cornua; br, remains of branchial 
 arches. E, Spinal Column and Pelvis (top view). Numbers refer to 
 vertebrae, and are placed near transverse processes. ust, Urostyle; il, 
 ilium; is, ischium; ac, acetabulum. F, Various Vertebrae. 1, Atlas, 
 front view; 2, side view of two adjacent vertebrae; 3, back view of 
 vertebra; c, centrum; n.s, neural spine; t.p, transverse process; a-z, 
 pre-zygapophysis ; p-z, post-zygapophysis ; n. c, neural canal ; i.f, inter- 
 vertebral foramen. G, Side View of Pelvis. il, Ilium; pb, pubis; is, 
 ischium; ac, acetabulum. II, Sternum, Shoulder Girdle, and Fore-limb- 
 (Ventral View). o-s, Omo-sternum; st, sternum proper; x-st, xiphi- 
 sternum; gl, glenoid cavity; s-sc, supra-scapula; ep-co, epi-coracoid ; 
 pr-co, pre-coracoid sheathed by clavicle ; h, humerus ; hd, head of ditto ; 
 d.r, deltoid ridge; r-u, radio-ulna ; ra, radiale; wZ, ulnare; en, centrale,- 
 c 1-5, carpalia; I-V, metacarpals; 1-5, phalanges. I, Hind Limb, dec. 
 (ust, urostyle, &c., as before)./, Femur; hd, head of ditto; t-f, tibio- 
 fibula; as, astragalus; ca, calcaneum; t, 1-3, tarsalia; I-V, metatarsals; 
 1-5, phalanges; *, placed by calcar. 
 
AMPHIBIA. 
 
 181 
 
182 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The olfactory capsules, situated in front of the cranium, are 
 separated from one another by a vertical plate of cartilage con- 
 tinuous with the longitudinal partition of the sphenethmoid. The 
 walls of the capsules are mostly composed of cartilage. 
 
 Membrane Bones. On the upper side of the olfactory capsules 
 are two triangular nasal bones, which form the posterior boundary 
 of the external nares. The cartilaginous floor of each olfactory 
 capsule is partly covered by a somewhat triangular vomer, which 
 is widely separated from its fellow. Each vomer bears a patch 
 of sharp vomerine teeth, and partly bounds the internal naris of its 
 side. 
 
 Jaws. Both upper and lower jaws consist of a cartilaginous 
 basis and of several bones, which in the case of the former are all 
 membrane bones. 
 
 (a) Upper Jaw. Owing to the projection of the sense-capsules 
 a sort of bay, the orbit, in which the eye lies, is left on each side 
 of the brain-case. It is bounded in front by a flat piece of 
 cartilage, the ethmo-palatine bar, which runs out transversely from 
 the floor of the olfactory capsule, sends a process forwards, and 
 becomes continuous with a slender pterygoid bar, which passes 
 back on the outer side of the orbit, and fuses behind with the 
 quadrate, cartilage (suspensorium). This is a cartilaginous rod 
 directed outwards, downwards, and backwards. Its proximal end 
 is forked, the short limbs of the fork being attached, above and 
 below, to the outside of the auditory capsule. The lower jaw is 
 " suspended " to its distal end, which presents an articular hollow. 
 These parts constitute the cartilaginous basis of the upper jaw 
 and its supports. Its actual margin is formed by a series of 
 membrane bones, of which the most anterior are the two pre- 
 maxillce, small tooth-bearing elements meeting in the middle line 
 in front of the olfactory capsules. On each side an elongated 
 curved maxilla, which bears most of the teeth, runs back from 
 the pre-maxilla and unites behind with a narrow quadrato-jugal 
 extending posteriorly to the quadrate cartilage. Three bones on 
 each side connect the upper jaw with the cranium and keep ib 
 firmly in position. These are the palatine, pterygoid, and squa- 
 mosal. 
 
 The palatine is a slender transverse bone moulded on the hinder 
 edge of the ethmo-palatine bar, while the pterygoid bar is largely 
 ensheathed by the anterior ray of the three-rayed pterygoid bone, 
 
AMPHIBIA. 183 
 
 which touches the external end of the palatine in front. The 
 other two rays are shorter. One of them runs inwards, the other 
 along the under side of the quadrate cartilage. A T-shaped bone, 
 the squamosal, the stem of which covers the quadrate cartilage, 
 partly covers the auditory region. This bone supports the annular 
 tympanic cartilage, over which the tympanic membrane is stretched. 
 
 (/5) The lower jaw (mandible) consists of two strongly-curved 
 halves, each of which is traversed by an axial cartilage, Meckel's 
 cartilage, ossified in front into a small mento-meckelian bone, uniting 
 with its fellow in a median symphysis. Behind it presents an 
 oval projection, the condylc, which articulates with the quadrate 
 cartilage. Meckel's cartilage is strengthened below and on its 
 inner side by a long angulo-splenial bone, from the posterior part 
 of which a small elevation, the coronoid process, projects upwards. 
 
 Each half of the mandible possesses a membrane-bone, the 
 dentary, which is a thin splint covering the outside of Meckel's 
 cartilage for rather more than its anterior third. 
 
 A series of structures forming the hyoid apparatus are con- 
 nected with the skull, and usually described with it. They are 
 partly related to the auditory apparatus, and partly to the floor 
 of the mouth. The columella is a small rod, bony in the centre, 
 which is fixed into the fenestra ovalis by one end, while the 
 other is attached to the inside of the tympanic membrane. The 
 remainder of the hyoid consists of a quadrangular plate of cartilage, 
 the body of the hyoid, supporting the floor of the mouth. Its angles 
 are produced into anterior and posterior processes. In front of 
 the former two slender, curved rods of cartilage, the anterior cornua, 
 arise, each of which runs backwards round the angle of the mouth 
 to be attached to the auditory capsule just beneath the fenestra 
 ovalis. From the posterior end of the hyoid body two short bony 
 posterior cornua or thyrohyals run back, which diverge and enclose 
 between them the laryngo-tracheal chamber. 
 
 (7>) The vertebral column is a hollow rod running back from 
 the skull along the dorsal side of the body. The spinal cord lies 
 in its cavity. The anterior part of the column is segmented, 
 being made up of nine rings, the vertebrce, while the posterior 
 part, termed the urostyle, is unsegmented. All are cartilage 
 bones. 
 
 The vertebra are very similar, except the first and last. Each 
 is a ring, the thickened ventral part of which is the body or centrum, 
 
184 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 while the rest forms the neural arch. The successive centra are 
 united firmly together, and are procxlous i.e., concave in front 
 and convex behind. Both surfaces are covered by a thin layer 
 of cartilage. (The 8th vertebra is amphiccelous, concave on both 
 faces.) Dorsal and lateral spaces are left between adjacent arches. 
 The former are filled up by connective tissue, while through the 
 latter, or intervertebral foramina, spinal nerves take exit. From 
 the upper side of each arch a small neural spine projects upwards 
 and backwards in the middle line, while on each side of the arch 
 a stout, cartilage-tipped bar, the transverse process, runs outwards. 
 Four small projections with smooth articular surfaces project 
 from the front and back of the arch. By these articular processes 
 or zygapophyses the adjoining arches are linked together. Two, 
 the pm-zygapophyses, are anterior, and their articular surfaces face 
 upwards and inwards, while the other two, post-zygapophyses, are 
 posterior, and their articular surfaces face downwards and out- 
 wards, overlapping the prse-zygapophyses of the following vertebra. 
 
 The 1st vertebra, or atlas, is devoid of tran verse processes and 
 prse-zygapophyses, and the neural spine is rudimentary. The 
 centrum is somewhat thin, and projects forwards between the 
 occipital condyles, which articulate with two large concave facets 
 on the front of the vertebra. 
 
 The 9th vertebra, the sacrum, has very large and strong trans- 
 verse processes directed outwards and backwards. The centrum 
 is convex in front, and presents a pair of articular tubercles behind, 
 which articulate with corresponding concavities on the front of 
 the urostyle. This is a bony rod, somewhat trihedral, and taper- 
 ing behind to a point tipped with cartilage. It may be regarded 
 as representing a number of vertebrae fused together, of which a 
 ridge running along its dorsal surface corresponds to the united 
 neural spines. Two small foramina open, one on either side, 
 into the canal of the urostyle, a short distance behind its anterior 
 end. Through these the coccygeal nerves take exit, and they, 
 therefore, correspond to intervertebral foramina. The part of the 
 urostyle in front of them is the first of the fused vertebrae, and 
 may possess more or less distinct transverse processes. 
 
 (c) The sternum consists of several cartilage bones and cartilages 
 placed in the middle line on the ventral side of the thoracic region. 
 In the extreme front a flat, narrow bone, the omo-sternum, is found, 
 to the anterior end of which a rounded flap of cartilage (the epi- 
 
AMPHIBIA. 185 
 
 sternum) is attached, while posteriorly it broadens out and abuts 
 upon a pair of narrow cartilaginous epi-coracoids. These are 
 succeeded by the sternum proper, a flattened rod of bone, with a 
 core of cartilage. To its hinder end a large, thin, deeply-notched 
 piece of cartilage, the xiphi-sternum, is attached. 
 
 (2) Appendicular Skeleton. The endoskeleton of either the 
 fore- or hind-limb is divisible into (1) Limb-girdle, which is 
 firmly attached to the trunk, and (2) Free limb, articulated to 
 the girdle. 
 
 (a) Fore-Limb. The two shoulder-girdles form an incomplete 
 ring almost encircling the body just behind the atlas vertebra. 
 They are firmly fused to the epi-coracoids, ventrally, while dorsally 
 they are attached by muscles to the skull and vertebral column. 
 Each girdle is made up of a dorsal and a ventral moiety. At 
 their point of union is a shallow, articular, glenoid cavity, affording 
 attachment to the free limb. The dorsal part is made up of 
 (a) The supra-scapula, a quadrangular plate of cartilage, more or 
 less calcified and ossified, broad above, and narrowing downwards 
 to join (b) the scapula, an hour-glass-shaped bone, the lower end 
 of which partly forms the glenoid cavity. The ventral part is 
 composed of (a) The coracoid bone, similar in shape to the scapula, 
 and completing the glenoid cavity. In front of the coracoid there 
 is an oval space filled with connective-tissue, the coracoid fontanelle. 
 This is bounded in front by (b) the prce-coracoid (pr-co), a trans- 
 verse bar of cartilage largely ensheathed by (c) the clavicle, which 
 is the only membrane bone in the appendicular skeleton. 
 
 The free limb is made up of bones supporting the upper arm, 
 fore-arm, and hand. The humerus is a long bone belonging to 
 the first of these. Like the long bones of the limbs generally, it 
 consists of a hollow marrow-containing shaft, and an enlarged 
 epiphi/sis at each end, covered b}' a thin layer of cartilage. The 
 epiphyses remain for a long time distinct from the shaft, with 
 which, however, they ultimately fuse. The proximal end of the 
 humerus forms a rounded head, articulating with the glenoid 
 cavity. A well-marked deltoid ridge, more prominent in the male, 
 runs from this half way along the anterior (ventral) surface of 
 the bone. The distal end presents a spheroidal surface with 
 which the next bone articulates, and above and below this (pre- 
 and post-axially) are condylar ridges. The ante-brachium is sup- 
 ported by a short, stout radio-ulna. This is a compound bone, 
 
186 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 made up of a pre-axial radius, fused with a post-axial ulna. The 
 boundary between these is marked by a groove at the distal end. 
 The proximal end is excavated to receive the corresponding 
 projection on the humerus, with which it forms the elbow- joint, 
 and produced back behind the last into the olecranon process, 
 belonging to the ulnar half of the bone. There are two articular 
 projections, one radial, the other ulnar, on the distal end, which 
 help to make up the wrist-joint. The endoskeleton of the manus 
 is made up of the wrist or carpus, and the bones of the digits. 
 The typical or theoretical carpus, deduced from comparison of 
 numerous cases, consists of 9 elements, 3 proximal, 1 central, and 
 5 distal, the relative position of which is as follows : [R = radial 
 or pre-axial side ; U = ulnar or post-axial side.] 
 
 R U 
 
 radiale intermedium ulnare 
 
 centrale 
 
 carpale 1 carpale 2 carpale 3 carpale 4 carpale 5 
 
 In the frog there are six small bones in the carpus, three prox- 
 imal and three distal. Two of the former, corresponding to radiale 
 and ulnare, articulate with the radial and ulnar facets respectively. 
 The third proximal bone, the displaced centrale, is on the inner 
 (pre-axial) side of the radiale. The three distal bones correspond 
 to the carpalia. The first supports the rudimentary 1st digit 
 and = carpale 1, the second supports the 2nd digit and = carpale 2, 
 while the much larger third bone represents carpalia 3, 4, 5, fused 
 together, and supports the remaining digits. Following the wrist- 
 bones are five slender metacarpals, one to each digit. The 1st 
 metacarpal is very small, but is all that represents the 1st digit, 
 while digits 2, 3, 4, 5 are terminated by 2, 2, 3, 3 slender phalanges 
 respectively. 
 
 (b) Hind-Limb. The hip-girdles are closely united to form the 
 pelvis, which resembles in shape a two-pronged fork with an 
 extremely short handle. Its posterior part is a rounded plate, 
 laterally compressed, and presenting on either side a deep oval 
 cup, the acetabulum, with a prominent margin. This cup is for 
 the articulation of the free limb. Nearly half of the plate and 
 acetabulum are formed antero-dorsally by the broad hinder ends 
 
AMPHIBIA. 187 
 
 of the two " prongs " or ilia fused in the middle line. Each 
 ilium is continued forwards to the sacrum, to the corresponding 
 transverse process of which its cartilage-tipped end is united. 
 This part of the ilium is laterally flattened, with somewhat 
 concave ventral and convex dorsal edges. Two other elements 
 on either side, pubis and ischium, of which the first is cartilaginous, 
 unite with their fellows to form the middle and posterior parts 
 of the plate and acetabulum. The pubes are triangular, and their 
 apices extend to the upper margin of the acetabulum, above which 
 the ilia and ischia unite. 
 
 The free limb is composed of bones belonging to the thigh, leg, 
 and foot. The first is supported by a long bone, the femur, the 
 slender shaft of which possesses a slight double or sigmoid curve. 
 Its proximal end is enlarged into a rounded head, which articulates 
 with the acetabulum to form the hip- joint, and its distal end also 
 presents an articular expansion. The bone of the leg, tibio-fibula, 
 like that of the fore-arm, is compound. It is made up by the 
 fusion of a pre-axial tibia with a post-axial fibula, the boundaries 
 of which are indicated by grooves and a double marrow-cavity. 
 The shaft is curved, and the ends are expanded into transversely 
 elongated pulleys, which assist in the formation of the knee- and 
 ankle-joints respectively. The bones of the foot are partly those 
 of the ankle, tarsus, and partly those of the digits. The typical 
 or theoretical tarsus contains the same number of elements as the 
 theoretical carpus, and these are similarly arranged, as follows : 
 [T = tibial or pre-axial side ; F = fibular or post-axial side.] 
 
 T F 
 
 tibiale intermedium fibulare 
 
 centrale 
 
 tarsale 1 tarsale 2 tarsale 3 tarsale 4 tarsale 5 
 
 The tarsus of the frog is very much elongated, and composed 
 of four bones, two of which are proximal and two distal. The 
 proximal ones, astragalus and calcaneum ( = tibiale + intermedium, 
 and fibulare), articulate with the tibial and fibular sides of the 
 articular surface on the distal end of the tibio-fibula. They are 
 united to each other at either end by their epiphyses. The distal 
 bones, equivalent to the tarsalia, are extremely small. One, 
 
188 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 representing tarsale 1, supports the calcar and 1st digit, the other 
 represents tarsale '2 + tarsale 3, and supports the 2nd and 3rd 
 digits. Tarsalia 4 and 5 are not distinctly represented, and there 
 is no centrale. The tarsus is succeeded by the metatarsus. The 
 base of the calcar is formed by a minute extra metatarsal, while 
 the slender melatarsals 1-5 belong to the corresponding digits. 
 A small flattened phalanx completes the calcar, and 2, 2, 3, 4, 3 
 slender phalanges terminate digits 1, 2, 3, 4, 5, respectively. 
 
 Cartilage and bone may both be considered as modifications of 
 connective tissue in which the matrix is very plentiful. 
 
 The most typical kind of cartilage is made up of a clear, homo- 
 geneous matrix, in which are numerous small cavities, lacunae, 
 connected with one another by fine channels, and containing 
 nucleated cartilage-cells. By the division of these, and the depo- 
 sition of fresh matrix, cartilage grows, especially near its surface, 
 which is covered by a connective-tissue membrane, the perichon- 
 drium, in which nerves, lymphatics, and blood-vessels run. 
 
 The matrix of bone is densely fibrous connective tissue, impreg- 
 nated with lime salts, principally carbonate and phosphate. In 
 this are imbedded numerous much-branched bone-cells, which lie 
 in lacunae connected by fine tubules, canaliculi, into which the 
 cell-processes are continued. The matrix is traversed by blood- 
 vessels, contained in Haver sian canals. Bone may be either spongy, 
 as in the epiphyses of long bones and the interior of flat and short 
 bones, or compact, as seen in the shafts of long bones and the 
 exterior of flat and short bones. A membrane, the periosteum, 
 similar to perichondrium, covers the outer surface of bones. Its 
 inner part is made up of rounded cells, osteoblasts, which during 
 growth add fresh layers of bone to the outside. Ossification 
 always starts from definite centres. Membrane bones commence 
 as calcified networks of connective-tissue fibres covered by osteo- 
 blasts, while cartilage bones are pre-formed in solid cartilage, 
 covered by periosteum. Into this solid cartilage processes of the 
 osteoblastic part of the periosteum penetrate to form the marrow, 
 which first absorbs the cartilage, and then replaces it by spongy 
 bone. In the shafts of long bones this is absorbed in its turn to 
 form a continuous marrow-cavity. 
 
 Cartilage bones can continue to lengthen by growth at their 
 ends. The new bone is formed in the way just described, from 
 the cartilage found there. 
 
AMPHIBIA. 189 
 
 Bones thicken by the addition of layers to the outside, formed 
 by the periosteum. 
 
 The vertebral centra contain peculiar cellular cores, the last 
 remnant of an important embryonic structure, the notochord. 
 
 4. The digestive organs (Fig. 51) consist of a convoluted tube, 
 the gut or alimentary canal, and of glands connected with this. 
 The gut presents the following regions : mouth-cavity, gullet, 
 stomach, small intestine, and large intestine opening into a cloaca 
 which also receives the excretory and reproductive ducts. The 
 most important annexed glands are the liver and pancreas. 
 
 The wide mouth, which reaches back as far as the tympanic 
 area, and possesses a narrow upper lip, leads into a spacious 
 mouth-cavity, the back part of which is termed the pharynx. 
 More than 100 minute double-pointed teeth are affixed to the 
 inner side of the upper jaw. They are attached to the pre- 
 maxillse and maxillse, and are placed in a furrow bounded by the 
 upper lip externally, and a fold of mucous membrane internally. 
 
 The mucous membrane is a pale, soft, extremely glandular layer which 
 lines the alimentary canal. 
 
 On the roof of the mouth are two small patches of vomerine 
 teeth, forwardly placed, and borne by the vomers. They are 
 similar to the others. No teeth are present in the lower jaw. 
 On the roof of the mouth, in the extreme front, a number of 
 minute pores are present, the openings of the intermaxillary glands. 
 The vomerine teeth are a little way behind this, and external to 
 each patch is a small, transversely oval opening, the internal naris. 
 Still further back two large rounded prominences, caused by the 
 eyes, project into the mouth. Near the angle of the jaw, on each 
 side, is a good-sized opening, that of the Eustachian tube, which 
 leads to the tympanic cavity. On the floor of the mouth is a 
 narrow, elongated muscular tongue attached in front. In the 
 quiescent state its forked end is directed backwards. Numerous 
 small elevations cover its surface, some of which, filiform papillce, 
 are narrow-ended ; others, fungiform papillae, broad-ended. 
 
 Near the angle of the mouth in the male R. esculenta an oval 
 opening is present, which leads into a rounded, dilatable vocal sac. 
 
 Posterior to the end of the tongue there is a longitudinal 
 chink, the glottis, with firm swollen edges. It leads into the 
 respiratory organs. 
 
190 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The mouth-cavity passes behind into a short, wide gullet or 
 oesophagus, and this merges without sensible demarcation into a 
 narrower tube, the stomach. This passes backwards, gradually 
 narrowing as it does so. The lining of both oesophagus and 
 stomach is raised into longitudinal ridges. At the posterior or 
 pyloric end of the latter there is a well-marked constriction 
 
 Fig. 51. SIDE-DISSECTION or MALE FROG. 2, 3, 4, 5, Digits; to, tongue; 
 st, stomach, upon which are blood-vessels; py, pylorus; d, duodenum; 
 i, rest of small intestine ; Li, large intestine ; cl, cloaca, opened ; r.l, and 
 l.l, right and left liver-lobes; g, gall-bladder; x, opening of bile-duct, 
 which is represented by the black line ; p, pancreas, s.v, Sinus venosus, 
 near which is cut end of right precaval ; r. a, right auricle, above which 
 are the cut ends of carotid arch, systemic arch, and cutaneous artery, 
 while the pulmonary artery is seen running along lung ; v. ventricle ; 
 t.a, truncus arteriosus. gl, Glottis; Ig, right lung. A:, Right kidney, 
 the dark space above which represents the subvertebral lymph-sinus ; 
 u-g, right urinogenital duct, which opens on a papilla in the cloaca 
 (just above the I in cl) ; bl, bladder (its opening is seen just below I in 
 cl). t, Spermary (testis) above which the vasa efferentia are seen 
 running in the mesorchium; v.s, vesicula seminalis. ol, Right ol- 
 factory lobe, from which right olfactory nerve is seen running forwards ; 
 c h, right cerebral hemisphere ; o. I, right optic lobe, passing below and 
 in front into optic tract and nerve ; cb, cerebellum ; m.o, medulla 
 oblongata; sp, spinal cord, na, Right nasal sac. 
 
 marking the position of the pylorus or point at which the cavity 
 of the stomach communicates with that of the small intestine. 
 This is a narrow thin-walled tube, the first part of which, the 
 duodenum, forms, together with the stomach, a U-shaped loop, 
 
AMPHIBIA. 191 
 
 while the rest is thrown into several coils. Its lining is raised 
 into transverse folds connected by fainter longitudinal ridges. 
 The end of the small intestine suddenly dilates into a short 
 thin-walled large intestine, which narrows behind and becomes 
 continuous with a chamber, the cloaca, opening externally by 
 the small circular doacal aperture. The cavity of the large 
 intestine is separated by an annular valve from that of the 
 small. Its lining is at first raised into delicate intersecting 
 ridges, and then into longitudinal folds which pass back to the 
 end of the cloaca, the posterior part of which is lined by ordinary 
 skin. 
 
 Two important glands are connected with the alimentary 
 canal the liver, and pancreas. 
 
 The liver is a very large reddish-brown organ, occupying a 
 considerable space near the front of the body-cavity. It arises 
 as an outgrowth from the alimentary canal, which quickly be- 
 comes bilobed. In accordance with this the adult liver is divided 
 into right and left halves, connected by a narrow strip of liver- 
 substance. The left half is again subdivided into two, so that 
 altogether three lobes are present. These are convex ventrally, 
 somewhat concave dorsally, blunt-ended in front, and elsewhere 
 thinning oft* into edges. The liver secretes the bile, a bright 
 yellowish-green fluid. Closely attached to the dorsal surface of 
 the right lobe is a rounded thin-walled sac, the gall-bladder, full 
 of bile, in the fresh state. From it a short tube, the cystic duct, 
 proceeds, which is connected with a fine network of hepatic ducts, 
 arising from the liver. From this a bile-duct is given off, which 
 is reinforced by other hepatic ducts, and runs in the U formed 
 by stomach and duodenum, finally opening into the latter about 
 half an inch beyond the pylorus on the inside of the U. 
 
 The pancreas is an elongated yellowish mass lying in the 
 U-shaped loop, and produced into several tapering processes. 
 With it the bile duct is closely connected, receiving from it a 
 number of small pancreatic ducts. This gland secretes the pan- 
 rreatic juice. 
 
 The digestive and other organs of the frog are contained in 
 the large pleuro-peritoneal- or "body-cavity (coelom). This 
 narrows in front, where it is bounded by the heart in its 
 pericardium, and a kind of muscular partition, the diaphragm,. 
 It also narrows behind. Its dorsal wall is formed bv the back- 
 
192 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 bone and associated muscles, its ventral and lateral walls, in the 
 thoracic region, by hard parts and muscles, by muscles alone in 
 the abdominal region. The body-cavity is lined ventrally and 
 laterally by a thin pigmented membrane, the plcuro-peritoneum, 
 which dorso- laterally becomes free, leaving a space, the sub- 
 vertebral lymph-sinus, beneath the vertebral column. The two 
 lateral halves of the pleuro-peritoneum run to the middle line, 
 forming a floor to this sinus, and then unite to make a double 
 sheet, the mesentery, the halves of which diverge, surround the 
 alimentary canal, and then become continuous. The alimentary 
 canal is thus suspended from the dorsal wall of the body-cavity, 
 and, strictly speaking, is outside it. The same may be said of the 
 other contained organs. 
 
 The walls of the oesophagus, stomach, and intestines are com- 
 posed of four coats, which are, commencing from the outside : 
 (1) serous coat; (2) muscular coat; 
 (3) sub-mucous coat ; (4) mucous mem- 
 brane. 
 
 (1) The serous coat is in reality the 
 pleuro- peritoneal investment of the gut. 
 It consists of a layer of simple squamous 
 epithelium, with a thin underlying stratum 
 of connective tissue in which run the 
 blood-vessels, lymphatics, and nerves 
 that supply the other coats. 
 
 (2) The muscular coat, best developed 
 in the stomach, is divided into an outer 
 longitudinal and an inner circular layer. 
 It is made up of unstriated muscle- 
 fibres. These are spindle-shaped cells 
 (Fig. 52), each containing an elongated 
 
 Fig. 52. UNSTRIATED nucleus > which dovetail together by their 
 MUSCLE - FIBRES (from tapering ends. 
 Landois and Stirling), (3) The sub-mucous coat is also best 
 
 SStatedTuf tools'- devel P ed in *e st mach > and C0nsists 
 section. of loose connective tissue traversed by 
 
 numerous blood-vessels and lymphatics. 
 
 (4) The mucous membrane is the part which is raised into 
 folds internally. It is exceedingly glandular, and is made up of 
 (a) a thin external layer of unstriated muscle, the muscularis 
 
AMPHIBIA. 193 
 
 mucosce ; (b) a layer of connective tissue with glands, blood- 
 vessels, and lymphatics; (c) a layer of simple columnar epi- 
 thelium, adjoining the cavity of the gut. 
 
 The epithelium is of most interest. It is ciliated in the 
 oesophagus and beginning of the stomach, and many of its cells, 
 known from their shape as goblet-cells, are unicellular mucus- 
 secreting glands. Besides this there are tubular multicellular 
 glands lined by the epithelium and lying in the connective- 
 tissue layer of the mucous membrane. They are of three 
 kinds : a, cesophageal glands in the gullet ; j3, peptic or gastric 
 glands in the stomach; -y, glands of Lieberkiihn in the small 
 intestine. 
 
 The deeper parts of the peptic glands are lined by cuboidal 
 cells, which secrete the gastric juice. 
 
 There are several points of interest in the histology of the 
 mucous membrane lining the mouth. Its epithelium is strati- 
 fied near the margins, elsewhere simple, columnar, and ciliated. 
 Numerous goblet-cells are present. The tubules of the inter- 
 maxillary glands are lined by mucus-secreting epithelium. 
 
 The teeth are developed in the mucous membrane of the mouth. 
 The projecting part or crown, which is forked, is separated by a 
 constriction from the rest of the tooth, or socket, which contains 
 a pulp-cavity, in which is the pulp, a small mass of vascular 
 connective tissue. The tooth is mostly made up of dentine, the 
 constituents of which are wavy tubules filled by prolongations of 
 the pulp. The crown is covered by a cap of extremely hard 
 enamel, exhibiting a layered structure, and containing prolon- 
 gations of the dentine tubules. It is secreted by the epithelium 
 of the mouth. The socket is covered by a layer of cement, 
 resembling bone in structure. The teeth are all very similar, 
 and during life are constantly replaced by new ones, which grow 
 up from their bases. 
 
 The liver (cf. Fig. 51) is mostly made up of polyhedral glan- 
 dular hepatic cells, granular, nucleated, and containing fat drops. 
 Between these cells minute tubes, the bile-capillaries, run, forming 
 a complex network from which the ultimate branches of the 
 hepatic ducts arise. The vessels supplying the liver with blood 
 break up into capillaries within it, and in these the branches of 
 the hepatic veins, which carry blood from the liver, take their 
 
194 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The ducts of the pancreas subdivide considerably, and finally 
 terminate in blind tubules lined by glandular epithelium. 
 
 Nutrition. The food of the adult frog consists mainly of 
 insects. These are secured by the tongue, which can be rapidly 
 protruded and retracted. Its peculiar mode of attachment enables 
 it to be put out to some distance, and being covered with a viscid 
 secretion, insects are easily secured. The secretion of the inter- 
 maxillary gland is especially sticky, and the tip of the tongue 
 brushes past its openings when protruded. The teeth are not 
 used for chewing, but to prevent the escape of prey. The cilia 
 of the mouth-cavity work so as to carry the food to the gullet, 
 and from this point the contractions of the muscular wall of the 
 alimentary canal propel it backwards. The chemical agents acting 
 upon the foods are principally (1) Gastric juice; (2) Pancreatic 
 juice; and (3) Bile. 
 
 The gastric juice is secreted by the peptic glands, and in 
 virtue of a ferment, pepsin, which it contains, converts some of 
 the proteids into peptones. The ferment can only act in an 
 acid solution, and the secretion contains a small amount of free 
 hydrochloric acid. The cuboidal cells of the peptic glands 
 secrete pepsin, while the acid is formed by the ovoidal cells. 
 The pancreatic juice contains ferments which (a) convert starch 
 into grape-sugar; (b) proteids into peptones; and (c) split up 
 fats. Alkalinity is necessary for this action, and the bile 
 neutralizes any acid passing over from the stomach. It also 
 emulsifies fats, and facilitates their absorption. 
 
 The ridges and folds into which the lining of the alimentary 
 canal is raised largely increase its absorptive surface. Some of 
 the products of digestion pass at once into the blood-system, 
 others reach it indirectly by way of the lacteals, subvertebral 
 sinus, and lymph-hearts. The refuse is ejected at the cloacal 
 aperture. 
 
 Most of the products of digestion, by way of the portal vein, 
 pass through the liver, and this organ absorbs the carbo-hydrates, 
 stores them up (as glycogen), and returns them to the system as 
 required. 
 
 5. The circulatory organs consist of a closed Hood-system 
 with which a lymph-system communicates. 
 
 (1) Blood System. The blood is a bright-red, coagulable fluid, 
 composed of a clear plasma in which float colourless corpuscles of 
 
AMPHIBIA. 
 
 195 
 
 the usual type, and larger and more numerous red corpuscles, 
 which owe their colour to haemoglobin. They are oval and flat, 
 with a large central nucleus of similar shape, projecting some- 
 what on both surfaces of the corpuscle. The blood circulates in 
 a closed system of tubes, consisting of heart, arteries, veins, and 
 capillaries. 
 
 The heart (Figs. 51 and 53) is situated in the anterior part 
 of the thoracic region, on its ventral side. It is enclosed in a 
 membranous bag, the pericardium, which is composed of an inner 
 layer closely adherent to the heart, and a loose outer layer. A 
 space, the pericardia! cavity, which is a separated part of the 
 co.ilom, is found between the two. The heart is roughly conical 
 
 c.s.d. 
 
 ---A.d. 
 
 ci 
 
 Fig. 53. HEART OF FROG (after Ecker), slightly enlarged. a, Ventral 
 view ; b, dorsal view, siuus venosus opened ; s.v, sinus venosus ; Ap, 
 its opening into Ad, right auricle ; As, left auricle ; V, ventricle ; 
 B, truncus arteriosus ; 1, 2, 3, carotid, systemic, and pulmo- 
 cutaneous arches; c, carotid gland; c.s.d and c.s.s, right and left 
 precavals ; c.i, postcaval ; v.p, pulmonary vein. 
 
 in shape, and its backwardly-directed apex fits into a notch in 
 the liver. A dark coloured triangular sac, the sinus venosus, with 
 thin walls, lies on the dorsal side of the heart, and its base is 
 formed by two thin-walled, dark-red auricles, right and left, while 
 a muscular, paler ventricle makes up its apical region. A 
 muscular tube, the truncus arteriosus, leading from the right side 
 of the ventricle, is closely applied to the ventral surface of the 
 right auricle. 
 
 The cavity of the right auricle is separated by a thin muscular 
 partition, the auricular septum, from that of the left auricle. Into 
 the dorsal Avail of the former cavity, near the septum, the sinus 
 venosus opens by an oval valvular aperture. There is a some- 
 
196 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 what similarly situated rounded aperture in the left auricle, that 
 of the pulmonary veins. The auricles have a common opening 
 
 into the ventricle, guarded 
 by two flaps, a dorsal and 
 a ventral, which project 
 into the ventricular cavity, 
 and are attached to its 
 walls by numerous minute 
 fibrous strings. This 
 auriculo- ventricular valve 
 is imperfectly divided into 
 two by the free posterior 
 edge of the auricular sep- 
 tum, which is attached 
 above and below to the 
 flaps. 
 
 The relatively small 
 cavity of the ventricle is 
 transversely elongated, and 
 the ventricular wall is 
 spongy. The auricles open 
 into the left side, and the 
 truncus arteriosus out of 
 the right side of its front 
 The latter opening 
 three semilunar 
 valve*, small membranous 
 pouches with their con- 
 cavities towards the trun- 
 cus. This is divided into 
 two parts (1) the pylan- 
 gium (into which the aper- 
 ture just mentioned opens) r 
 separated by another set 
 of semilunar valves from 
 (2) the excessively short 
 synangium. The cavity of 
 the pylangium is imperfectly divided into right and left halves 
 by a sinuous longitudinal flap attached to its dorsal wall, and to* 
 one of the anterior semilunar valves, but possessing a free ventral' 
 
 end. 
 
 Fig. 54 AUTERTES OF FROG (after EcJcer). 
 R.A, Right auricle; L.A, left auiicle; 
 V, ventricle; t.a, truncus arteriosns ; 
 c.a, carotid arch ; c.gt, carotid gland ; 
 <, carotid artery; La, lingual artery; 
 II., systemic arch ; o-v, occipito- verte- 
 bral artery ; o<; occipital artery ; vr, 
 vertebral artery ; s.d, subclavian artery ; 
 III., pul mo cutaneous arch; pf, pulmo- 
 nary artery ; ct, cutaneous artery ; d.ao, 
 dorsal aorta; cm-m, cceliaco mesenteric 
 artery ; u-cj, urinogenital arteries ; i/, 
 iliac arteries ; sc, sciatic arteries. 
 
AMPHIBIA. 197 
 
 edge. The passage on the left of this flap leads to a small pulmo- 
 cutaneous aperture just behind the anterior valves, the passage 
 on the right into the synangium. This is continuous on either 
 side with a systemic arch and in front two small carotid aper- 
 tures, placed on a small elevation, open out of it. 
 
 Arteries (Fig. 54). From the truncus arteriosus two ap- 
 parently single trunks arise, one on either side, and form with 
 it a Y-shaped figure. Each of these trunks is in reality triple, 
 its cavity being divided by two longitudinal partitions into 
 three cavities anterior, middle, and posterior. These belong to 
 three corresponding aortic arches carotid, systemic, and pulmo- 
 cutaneous, into which the trunk soon splits. Into the first and 
 last of these the apertures of the same name lead, and the 
 synangial cavity is directly continuous with the cavities of the 
 systemic arches. 
 
 (1) The carotid arches supply the brain, orbit, and walls of 
 the mouth-cavity with pure blood. 
 
 Each gives off a small lingual artery to the tongue, dilates into a small, 
 rounded body, the carotid "gland," and then becomes the carotid artery, 
 which divides into , external carotid supplying the orbit, and roof and 
 side-walls of mouth-cavity ; /3, internal carotid artery supplying the brain. 
 
 (2) The systemic arches supply the rest of the body with 
 partially purified blood. The arch of each side runs upwards 
 and backwards, giving off branches to the larynx, oesophagus, 
 fore-limb, and other parts, and uniting with its fellow, just 
 ventral to the backbone, near the front ends of the kidneys, to 
 form the dorsal aorta, a median trunk running back in the 
 subvertebral lymph sinus. The dorsal aorta gives off branches 
 to the viscera and body-walls, ultimately dividing, at the pos- 
 terior end of the body, into two iliac arteries, continuations of 
 which run into the hind-limbs. 
 
 Chief Branches. (1) From each arch in front of dorsal aorta (a) laryn- 
 geal to larynx ; (6) one or two ozsophageal to oesophagus ; (c) occipito- 
 vertebra 1 , dividing into () occipital for side of head and jaws, (/3) vertebral, 
 running along one side of the vertebral column, supplying adjacent 
 muscles and sending branches to the spinal cord through the interver- 
 tebral foramina ; (d) subclavlan to shoulder and fore-limb. . (2) From dorsal 
 aorta (a) cceliafo-mcsenteric, coming from near junction of two arches, 
 or from left arch before the union. It divides into a, cceliac artery, 
 (which has two branches, 1, gastric artery to stomach, 2, /lepntic artery to 
 liver and gall-bladder), and ft, mesenteric artery, which breaks up intc 
 
198 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 1, anterior mesenteric artery to front part of intestine, 2, posterior mesenteric 
 artery to back part of intestine, 3, splenic artery to spleen ; (b) 4 to 
 6 small urinogenital arteries which at once bifurcate, and run to urinogenital 
 organs and fat-bodies ; (c) small paired lumbar arteries to adjoining muscles ; 
 (d) a small hwmorrhoidal artery to the large intestine. (3) Each iliac 
 artery gives off (a) a hypoc/astric arteri/ to the bladder, and (b) epigastric 
 arteries to the ventral body- wall. It then becomes the sciatic artery of 
 the thigh, which divides into peroneal and tibial arteries for the leg and 
 foot. 
 
 (3) The pulmo-cutaneous arches carry impure blood to the 
 lungs and skin. Each of them quickly divides into a pulmonary 
 artery running down the outer side of the lung and a cutaneous 
 artery which ramifies in the skin. 
 
 The veins (Fig. 55) bring back blood from the various parts 
 of the body to the heart. They may best be considered under 
 the following headings: (1) Caval system; (2) Portal systems ; 
 (3) Pulmonary veins. 
 
 The caval system consists of three caval veins with their 
 branches i.e., two precavals (anterior or superior venae cavse) in 
 front, and a postcaval (posterior or inferior vena cava) behind. 
 These pour their blood into the sinus venosus, which may be 
 regarded as formed by the fusion of their ends (see Fig. 55). 
 The precaval on each side is formed by the union of three veins 
 (1) The external jugular bringing back blood from the lower 
 jaw, floor of the mouth, and tongue ; (2) The innominate formed 
 by the union of the internal jugular and subscapular veins which 
 respectively return blood from the brain, and shoulder with back 
 of arm ; and (3) The subclavian. This is a large vein made up 
 of the brachial vein from the fore-limb, and the musculo-cutaneous 
 vein, which brings back blood from the muscles and skin of the 
 sides and upper surface of the body and head. 
 
 The postcaval lies ventral to the dorsal aorta. It commences 
 between the kidneys, and is made up by the union of several 
 pairs of renal veins from those organs, and veins from the genital 
 glands and fat bodies. Just before entering the sinus venosus 
 it receives two hepatic veins from the liver. 
 
 Portal Systems. A portal vein is one which, instead of pouring 
 its blood into a larger trunk, breaks up into capillaries within 
 the substance of some organ, supplying it with impure blood. 
 Both kidneys and liver in the frog possess such a supply, and in 
 accordance with this, (1) renal portal and (2) hepatic portal systems 
 can be distinguished. 
 
AMPHIBIA. 
 
 199 
 
 (1) Renal Portal The principal veins of the hind-limb are 
 the femoral and sciatic, running 
 
 along the front and back of the 
 thigh. The femoral vein is 
 connected by a cross-branch (*) 
 with the sciatic just before 
 reaching the trunk, and then 
 divides into a pelvic vein which 
 runs to the middle ventral line 
 to unite with its fellow, and a 
 renal portal vein which runs to 
 the outer side of the kidney, 
 and divides into small veins 
 breaking up in the kidney- 
 substance. The renal portal 
 vein receives the sciatic vein, 
 dorso - lumbar veins from the 
 dorsal abdominal walls, and, in 
 the female, small veins from 
 the oviduct. 
 
 (2) Hepatic Portal The liver 
 is supplied with impure blood 
 by two veins, (a) the anterior 
 abdominal and (6) the portal. 
 (a) The anterior abdominal is 
 formed by the union of the two 
 pelvic veins, receives veins from 
 the bladder, and runs forwards 
 in the middle line of the ab- 
 dominal wall as far as the liver. F % 55.-VEINS or FROG (after 
 
 . , . Ecker), semi-dias;rammatic. 8.V. 
 
 Here it bifurcates, the two divi- Sinus venosus ; & A , right auricle ; 
 sions going to the right and left L.A, left auricle ; V, ventricle ; 
 
 halves of the liver. (b) The P r ~ c \ P rec . aval ; , ex.ju t external 
 . , , Y jugular veins ; i.ju t internal jugu- 
 
 vein IS formed by the l ar vein ; s-sc, sub-scapular vein ; 
 
 in, innominate vein ; s-cl, sub- 
 
 clavian vein; br, "brachial vein; m-ct, musculo-cutaneous vein; p-c, post- 
 caval ; sc, sciatic vein ; /, femoral vein ; *, cross-branch connecting sciatic 
 and femoral ; p.v, pelvic veins ; r.p, renal portal vein ; d-l, dorso-lumbar 
 veins; o, veins from oviduct; r.v, renal veins ; a.ab, anterior abdominal 
 vein ; bl, veins from bladder ; + , small vein from truncus arteriosus ; p, 
 portal vein ; h, hepatic veins ; k, kidneys ; i, represents alimentary canal 
 with its capillaries ; I, represents capillaries of liver ; pi, pulmonary veins. 
 
200 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 union of the gastric vein, bringing blood from the stomach, with 
 the lieno-mesenteric vein returning it from the spleen and in- 
 testines. It runs to the left half of the liver, and is connected 
 by a cross-branch with the point of bifurcation of the anterior 
 abdominal. 
 
 A pulmonary vein runs up the inner side of each lung, and 
 unites with its fellow to form a short common trunk, which 
 opens into the left auricle. 
 
 The capillaries are excessively fine tubes forming networks in 
 nearly all parts of the body, by means of which the ultimate 
 branches of veins and arteries are united. A vein commences, an 
 artery ends, and a portal vein both commences and ends, in 
 capillaries. 
 
 (2) Lymph System. The lymph is a colourless fluid which 
 resembles blood, differing, however, in the absence of red cor- 
 
 Fig. 56. POSTERIOR LYMPH-HEARTS or FROG (after Ecker). 
 L, Lymph-heart. 
 
 puscles. The lymph-system consists of lymphatic vessels of larger 
 and smaller size, which ramify in the skin, intestinal wall, and 
 other parts of the body, and lymph-spaces with which these vessels 
 are connected. The lymph-spaces include the irregular lacunae 
 between the tissues, and also larger cavities, such as the pleuro- 
 peritoneal, pericardial, subvertebral, and subcutaneous spaces. 
 The lymphatics of the intestine, which receive the special name 
 of lacteals, traverse the mesentery and open into the subvertebral 
 sinus. The lymph is propelled by two pairs of lymph-hearts, 
 small oval sacs, with rhythmically-contractile walls. The anterior 
 lymph-hearts are situated one on each side between the trans- 
 
AMPHIBIA. 
 
 201 
 
 verse processes of vertebrae 3 and 4, and are connected with the 
 subscapular veins. The posterior lymph-hearts (Fig. 56) are 
 placed one on each side of the urostyle, not far from its posterior 
 end, in a triangular space between the muscles. Each com- 
 municates with a small vein which opens into the cross-branch 
 between the sciatic and femoral veins of its side. 
 
 Fig. 57. Fig. 58. 
 
 Fig. 57. MUSCLE-FIBRES FROM HEART OF FROG (from Landois and 
 Stirling), much enlarged. 
 
 Fig. 58. SMALL ARTKRY SHOWING THE COATS (from Landois and 
 Stir lint/). a, Endothelium ; b, elastic membrane; c, muscular coat; 
 d, connective-tissue coat. 
 
 Closely connected with the circulatory system are several small 
 organs known as ductless glands. These are the spleen and the 
 thymus and thyroid " glands." The spleen is a small rounded body, 
 of dark red colour, lying in the mesentery, near the commence- 
 ment of the large intestine. The thymns glands are two small 
 
202 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 bodies situated one on either side, near the end of the quadrate 
 cartilage, and the thyroid glands are similar structures, two or 
 more in number, placed near the posterior hyoid cornua. 
 
 The cavities of the heart and blood-vessels are lined by endo- 
 thelium, which alone forms the capillary walls (Fig. 59). The 
 large lymph-cavities are similarly lined, and patches of granular 
 germinal epithelial cells occur in them, from which colourless 
 corpuscles are budded off. The heart is mainly composed of 
 unicellular, spindle-shaped muscular fibres (sometimes branched), 
 which are transversely striated, but possess no sarcolemma 
 
 Fig. 59. CAPILLARIES (from Landois and Stirling), much enlarged. 
 The outlines and nuclei of the endothelial cells making up their walls 
 are clearly shown. 
 
 (Fig. 57). The veins and arteries possess three coats outside 
 their endothelial lining (Fig. 58). These are, beginning from the 
 inside (1) a membrane formed by elastic connective tissue; (2) 
 a muscular coat made up for the most part of unstriated muscle- 
 fibres arranged circularly ; and (3) a connective-tissue sheath. 
 These coats are thicker in arteries than in veins, and in large 
 vessels than small. They gradually thin out as capillaries are 
 approached, till at last only endothelium is left (Fig. 59). 
 
 Circulation. The heart receives oxygenated blood from the 
 
AMPHIBIA. 203 
 
 lungs by the pulmonary veins, which open into the left auricle. 
 The caval veins pour impure blood from the general body into 
 the right auricle. 
 
 The blood in the precavals is partly oxygenated, as they receive the 
 cutaneous veins from the skin, while that in the postcaval is largely free 
 from nitrogenous waste. 
 
 The blood is pumped out of the heart by the contraction of its 
 walls. The sinus venosus first undergoes systole, then the auricles 
 together, then the ventricle, and lastly the truncus arteriosus. 
 Systole is followed by diastole, and the various valves prevent 
 regurgitation. 
 
 Although the ventricle is single, and receives both kinds of 
 blood, yet these do not completely mix, and the carotid, systemic, 
 and pulmo-cutaneous arches are supplied by oxygenated, mixed, 
 and impure blood respectively. This is explained as follows : 
 The cavity of the ventricle is transversely elongated. Into its 
 left side the auricles open (their common aperture being rendered 
 practically double by the free edge of the auricular septum), and 
 out of its right side the truncus arteriosus. Moreover, its spongy 
 wall absorbs much of the blood received by the auricular systole, 
 and renders mixing more difficult. Just previous to the ventri- 
 cular systole, the three arches offer different degrees of resistance 
 to the passage of blood the pulmo-cutaneous least, owing to 
 the small extent of their branches, the carotid most, on account of 
 the spongy carotid glands. When the ventricle contracts, the 
 blood nearest the truncus is impure, as the right auricle fills the 
 right side of the ventricle. This blood takes the direction of 
 least resistance i.e., runs on the left of the longitudinal septum 
 of the truncus into the pulmo-cutaneous arches. As these are 
 filled, their resistance increases, and blood (now mixed, as 
 sufficient time has elapsed for mixture to commence in the ven- 
 tricle) flows on the right side of the septum, flapping it over the 
 pulmo-cutaneous aperture, and enters the systemic trunks. Their 
 resistance also increases, and the last portion of blood runs into 
 the carotid arches. This is oxygenated blood from the left 
 auricle, which has been stored up in the spongy wall of the left 
 side of the ventricle. 
 
 The large amount of elastic and muscular tissue in the arterial 
 walls serves two useful purposes. (1) Part of the force of the 
 systole of the ventricle and truncus is expended in dilating the 
 
204: AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 arteries, which subsequently contract, and continue the pumping 
 work during diastole, so that jerking is avoided. (2) The blood- 
 supply to any part can be regulated. Owing to the influence of 
 the sympathetic system the muscle is usually kept in a semi- 
 contracted (tonic) state. The same system can cause them to 
 contract more or to contract less, thus diminishing or increasing 
 their calibre. 
 
 The thin walls of the capillaries readily allow the blood-plasma 
 to soak out of them, and waste products to enter them in the 
 tissues, and leave them in the excretory organs. 
 
 The lymph-hearts pump lymph into the blood-system. Blood- 
 plasma exuding in excess through the capillaries is thus carried 
 back again, and some of the products of digestion also enter the 
 blood in this way. 
 
 6. Kespiratory Organs (Fig. 51). The opening of the glottis 
 leads into a small larynx, which is firmly fixed between the 
 posterior hyoid cornua. Its walls are strengthened by two 
 triangular arytenoid cartilages bounding the glottis, and below 
 these by a ring-like cricoid cartilage with several processes. 
 Projecting from the sides of the cavity into its interior are two 
 elastic folds, the vocal cords, one on each side. The larynx 
 opens behind into the two lungs, which lie freely in the dorsal 
 part of the thoracic region. Each is an elongated thin-walled 
 bag, which first dilates and then tapers to a smooth tip. Its 
 inner surface is raised into a prominent series of ridges, which 
 form a close honeycombing. 
 
 The skin must also be considered as a respiratory organ. 
 
 The larynx is lined by a continuation of the ciliated epithelium 
 of the mouth-cavity, and the lungs, for the most part, by simple 
 squamous epithelium. The basis of these organs is fibrous 
 connective tissue, with many elastic fibres and a good deal of 
 unstriated muscle. A network of capillaries immediately under- 
 lies the epithelium. 
 
 Respiration is said to be " buccal," because inspiration (i.e., 
 intaking of air) is effected by the agency of the mouth-cavity, as 
 follows : The mouth being shut, and the walls of the gullet 
 contracted, appropriate muscles lower the floor of the mouth, and 
 thus cause air to rush in by the nostrils. These are then closed, 
 the floor of the mouth is elevated, and air is thus forced into the 
 lungs. Expiration is mainly brought about by the elasticity of 
 
AMPHIBIA. 205 
 
 these organs, and the contraction of the muscle-fibres they contain. 
 The contraction of the abdominal walls may also assist. 
 
 The thin-walled lung-capillaries are only separated from the 
 air contained in the lung-cavities by a layer of epithelium, and, 
 therefore, carbon dioxide can readily diffuse out of, and oxygen 
 into, the blood which they contain. A similar interchange takes 
 place between the blood in the capillaries of the skin and the 
 oxygen in the surrounding air or water. This cannot take place 
 in air unless the skin is damp. 
 
 The haemoglobin of the red corpuscles plays the usual important 
 part in respiration. 
 
 Voice is produced by the vocal chords, the edges of which can 
 be brought parallel to one another by certain muscles, and then 
 thrown into vibration by the expired air. The vocal sacs in the 
 male, R. esculenta, serve as resonators. 
 
 7. Urinogenital Organs, including excretory and reproductive 
 organs. 
 
 The excretory organs (Figs. 51 and 60) are two elongated,. 
 flattened, reddish-brown kidneys, symmetrically disposed in the 
 posterior part of the subvertebral lymph-sinus, and covered 
 with pleuro-peritoneum on their ventral surfaces only. A 
 slender tube, urinary duct in the female, urinogenital duct in the 
 male, runs from the outer side of each kidney to open into the- 
 dorsal side of the cloaca, close to its fellow, by a minute slit. 
 Directly opposite this there is a rounded aperture in the ventral 
 cloacal wall which leads into the urinary bladder, a large bilobed 
 sac with delicate membranous walls. 
 
 Closely connected with the excretory organs are two anomalous 
 tures, the adrenals and fat-bodies. The former are two narrow bodies, of 
 yellowish colour, one of which is closely imbedded in the ventral surface 
 of each kidney. The fat-body (corpus adiposum) is a bright, orange- 
 coloured tuft of finger-like processes attached to the front end of the 
 kidney of either side. It consists of a network of connective tissue, ia 
 the meshes of which numerous fat-cells are imbedded. These are spherical 
 bodies full of fat, and covered by a thin layer of protoplasm with a nucleus 
 on one side. They result from the metamorphosis of ordinary connective- 
 tissue cells. 
 
 The kidney is mostly made up of a large number of uriniferow 
 tubules. Each of these commences in a thin-walled Bowman's 
 capsule, lined by delicate squamous epithelium, into which has 
 been pushed from the outside, so to speak, a tuft of capillaries-,. 
 
206 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 the glomerulus, formed by the. breaking up of a branch of one of 
 the renal arteries. The capsule and glomerulus together are 
 known as a Malpkigian body. A convoluted tubule in which four 
 regions can be distinguished succeeds Bowman's capsule. These 
 regions are (1) a short neck, lined with ciliated epithelium; (2) a 
 much convoluted glandular, part, lined by columnar epithelium 
 which is pigmented and granular ; (3) a second ciliated section ; 
 and (4) a collecting portion. 
 
 The urinary dud is formed by the union of the collecting 
 portions, and is at first imbedded in the kidney on its outer side. 
 The renal-portal vein breaks up into capillaries which closely 
 surround the glandular parts of the uriniferous tubules, and are 
 joined by the small veins coming off from the glomeruli. 
 
 The nitrogenous waste of the body (as urea, CH 4 N 9 0), together 
 with much water and various salts, is excreted by the kidneys. 
 The water and salts are filtered from the glomeruli into Bowman's 
 capsules, while the urea is excreted by the glandular parts of 
 the kidney-tubules. The urinary bladder serves as a temporary 
 receptacle for the urine. 
 
 Male Reproductive Organs (Fig. 51). An oval, yellowish, 
 spermary (testis), enveloped in pleuro-peritoneum, is closely con- 
 nected by a double fold of the same, the mesorchium, with the 
 inner side of each kidney. In this fold a number of delicate 
 tubules, the vasa efferentia, run from one organ to the other. The 
 two spermaries are commonly unequal in size. In It. esculenta 
 the urinogenital duct is considerably dilated just as it leaves the 
 kidney, and in R. temporaria an oval glandular mass, the vesicula 
 seminalis, is placed on its outer side immediately before it enters 
 the cloaca. 
 
 The male Frog is distinguished externally by the characters 
 mentioned on pp. 175 and 176. 
 
 The spermary is essentially composed of seminiferous tubules, 
 lined by epithelium, and opening into a central cavity. From 
 this the vasa efferentia arise, and, after traversing the mesorchium, 
 enter a longitudinal canal imbedded in the inner edge of the 
 kidney, and giving off numerous transverse tubules, which join 
 the collecting parts of the uriniferous tubules just before they 
 enter the urinary duct.. The sperms (spermatozoa) are thread- 
 like bodies, with narrow cylindrical heads and vibratile tails. 
 They are developed from spindle-shaped sperm -mother -cells, 
 
AMPHIBIA. 
 
 207 
 
 Oct. 1 
 
 which largely make up the epithelial lining of the seminiferous 
 tubules. Each sperm-mother-cell originates a tuft of sperms, an 
 unused stump (sperm-blastophor) being left over. 
 
 Female Reproductive Organs (Fig. 60). The ovaries are two 
 flattened sacs, varying much in size according to the season, and 
 situated similarly to the spermaries. The pleuro-peritoneum 
 invests each of them and forms a double suspensory fold, the 
 mesovarium. Ova, of various sizes, enclosed in follicles, project 
 on the outer surface of the ovary. The oviducts are two much- 
 coiled tubes invested in pleuro-peritoneum, and each with a 
 narrow anterior end opening near the 
 root of the lungs by a ciliated funnel. 
 The two funnels are close together 
 (the organs in the Fig. have been taken out 
 of the body), and open into a common 
 ciliated depression. The oviducts widen 
 behind, and each of them finally dilates 
 into a thin-walled uterus, opening on a 
 prominent papilla on the dorsal wall of 
 the cloaca. The two papillae are situated 
 close together, just in front of the 
 urinary apertures. 
 
 The ovary contains numerous ova 
 enclosed in follicles, by the rupture of 
 which they escape into the body-cavity. 
 The mature ovum is about T V of an inch 
 in diameter. It is covered by a delicate 
 mielline membrane, and possesses gran- 
 ular pigmented vitellus, and a large 
 germinal vesicle with numerous germinal 
 spots. Two polar cells are formed before 
 fertilization. 
 
 The wall of the oviduct contains 
 
 Fig. 60. FEMALE REPRO- 
 DUCTIVE ORGANS OF FROG 
 (after Ecker and Wieder- 
 sheim). Right ovary re- 
 moved. ov, Left ovary; 
 od, oviduct; od', funnel 
 of ditto; ut, uterus; ut', 
 opening of ditto in cloaca ; 
 , kidneys; u,u, openings 
 of ureters ; cl, cloaca. 
 
 numerous branched tubular glands 
 which secrete a glairy substance, cap- 
 able of swelling up immensely by 
 imbibition of water. The wall of the uterus contains numerous 
 unstriated muscle-fibres. 
 
 At the commencement of the breeding-season (early spring for 
 R. temporaria), the males affix themselves to the backs of the 
 
208 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 females, in which process the roughened pads on the hands afford 
 firm attachment. This occurs in the water. The ova burst out 
 from the ovaries, are taken up by the ciliated funnels of the 
 oviducts, and pass down those structures to the uteri, receiving 
 on their way gelatinous investments. Here they are aggregated 
 into " clumps," and expelled by the contraction of the muscle in 
 the uterine and cloacal walls. As they are extruded from the 
 body, sperms are shed over them by the male. Fertilization 
 occurs in the usual way by fusion of a sperm with each ovum. 
 
 8. Muscular System. In a tadpole there are lateral muscles 
 divided into myomeres, as in a fish, but only traces of this seg- 
 mentation are to be found in the adult. The muscles are very 
 numerous, and have a very complicated arrangement. The 
 following table will give a rough notion of their classification 
 (after Huxley) : 
 
 A. Muscles of Head j EpisMetal, superficial to the endoskeleton. 
 and Trunk. \ flyposkeletal, within the enduskeleton. 
 
 B. Muscles of Limbs. 
 
 Intrinsic, taking origin in the limbs themselves 
 
 (including girdles). 
 Extrinsic, taking origin outside the limbs. 
 
 The firm endoskeleton affords points of attachment, and this is 
 often effected by the intermediation of cord-like tendons, almost 
 entirely made up of white connective-tissue fibres. The firm 
 sheaths, aponeuroses, by which muscles are covered, may also 
 serve for the attachment of other muscles. This is best seen in 
 flat muscles, such as some of those forming the abdominal wall. 
 
 The muscles are made up of bundles of transversely striated 
 fibres, each of which is invested by a delicate sarcolemma, and 
 contains numerous muscle-corpuscles i.e., nuclei surrounded by 
 small quantities of protoplasm. These fibres also exhibit longi- 
 tudinal striations. 
 
 From a physiological point of view the muscular tissue of 
 Vertebrates is divided into (1) Involuntary, not under the 
 control of the will, including the unstriated fibres of the viscera 
 and blood-vessels, as well as the striated fibres of the heart ; and 
 (2) Voluntary, under the control of the will, including the 
 striated fibres of the ordinary muscle. 
 
 The minute structure of muscle and its physiological import 
 have long been much vexed questions. The views here adopted 
 
AMPHIBIA. 209 
 
 are those of Melland and C. F. Marshall, as set forth in the 
 following summary given by the latter : 
 
 "1. In all muscles which have to perform rapid and frequent 
 movements, a certain portion of the muscle is differentiated to- 
 perform the function of contraction, and this portion takes on 
 the form of a very regular and highly modified intracellular 
 network. 
 
 " 2. This network, by its regular arrangement, gives rise to 
 certain optical effects, which cause the peculiar appearances of 
 striped muscle. 
 
 " 3. The contraction of the striped muscle-fibre is probably 
 caused by the active contraction of the longitudinal fibrils of the 
 intracellular network ; the transverse networks appear to be pas- 
 sively elastic, and by their elastic rebound cause the muscle to 
 rapidly resume its relaxed condition when the longitudinal fibrils 
 have ceased to contract ; they are possibly also paths for the 
 nervous impulse. 
 
 "4. In some cases where muscle has hitherto been described 
 as striped, but gives no appearance of the network on treatment 
 with the gold and other methods, the apparent striation is due 
 to optical effects, caused by a corrugated outline in the fibre. 
 
 "5. In muscles which do not perform rapid movements, but 
 whose contraction is comparatively slow and peristaltic in nature, 
 this peculiar network is not developed. In most if not all of the 
 invertebrate unstriped muscles there does not appear to be an 
 intracellular network present in any form, but in the vertebrate 
 unstriped muscle a network is present in the form of longitudinal 
 fibrils only ; this possibly represents a form of network inter- 
 mediate between the typical irregular intracellular network of 
 other cells and the highly modified network of striped muscle. 
 
 " 6. The cardiac muscle-cells contain a network similar to that 
 of ordinary striped muscle." 
 
 The motor nerve-fibres may terminate in end-plates (compare 
 Fig. 90), within the sarcolemma of striated muscle-fibres, but 
 more frequently the axis-cylinder breaks into a brush of fibrils 
 which run longitudinally in the muscle- substance. 
 
 10. The nervous system (Fig. 51) may conveniently be sub- 
 divided into (1) cerebro-spinal axis; (2) cranio-spinal nerves ; 
 and (3) sympathetic system. 
 
 (1) The cerebro-spinal axis is made up of the brain and spinal 
 2 14 
 
210 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 cord, contained in the neural canal. They are invested 'by a 
 delicate pigmented vascular membrane, the pia mater, and the 
 neural canal is lined by a firm fibrous membrane, the dura mater, 
 Between the two is a lymphatic arachnoid space, the walls of 
 which are formed by a delicate arachnoid membrane. 
 
 The brain is the anterior enlargement of the cerebro-spinal 
 axis, contained in the cavity of the brain-case. At an early stage 
 of development it consists of three vesicles, anterior, middle, and 
 posterior. The adult parts derived from these constitute the 
 fore-, mid-, and hind-brains. That part of the fore-brain which 
 corresponds to the original anterior vesicle is known as the 
 thalamencephalon, and contains a vertical slit-like cavity, the 
 third ventricle, the anterior boundry of which is a thin lamella of 
 brain-substance, the lamina terminalis. The thin roof of the 
 third ventricle, is covered by a vascular membrane, the choroid 
 plexus, and in the young tadpole is connected with a small 
 rounded body, the pineal "gland," by a hollow pineal stalk, 
 directed upwards and backwards. The formation of the roof of 
 the skull pinches off the pineal gland, which in the adult 
 underlies the skin covering the top of the head. The floor of 
 the third ventricle is produced downwards in its hinder part into 
 a funnel-like projection, the infundibulum, with which a flattened 
 sac, the pituitary body, is connected. The much-thickened side- 
 walls (optic thalami) are connected together behind by a small 
 band, the posterior commissure. A similar anterior commissure 
 runs transversely across through the substance of the lamina 
 terminalis, and connects the corpora striata (see below). 
 
 The rest of the fore-brain is made up of the structures deve- 
 loped from a pair of lateral outgrowths of the anterior cerebral 
 vesicle. These are (1) the cerebral hemispheres continuous with 
 the antero-lateral parts of the thalamencephalon, which structure 
 they partly overlap, and in front of which they extend; and 
 (2) the olfactory lobes into which the hemispheres pass anteriorly. 
 
 The cerebral hemispheres are smooth, ovoid bodies, broadest 
 behind, and closely approximated in the middle line. Each 
 contains a lateral ventricle, the inner wall of which presents an 
 elevation, the corpus striatum, and which communicates with the 
 third ventricle behind by a small aperture, the foramen of Monro. 
 The olfactory lobes are two small bodies in front of and con- 
 tinuous with the cerebral hemispheres, from which they are not 
 
AMPHIBIA. 211 
 
 very clearly marked off. They are closely united in the middle 
 line, and each contains an olfactory ventricle continuous with the 
 lateral ventricle of its side. 
 
 The mid-brain is a small axial part lying immediately behind 
 the thalamencephalon, with which it is directly continuous. It 
 contains a narrow canal, the Sylvian aqueduct, opening in front 
 into the third ventricle, and with roof and side-walls swollen into 
 two large ovoid optic lobes, each of which contains an optic ventricle 
 opening into the aqueduct, while its thickened floor is formed by 
 the crura cerebri, two masses of longitudinal fibres. 
 
 The hind-brain is mainly constituted by the bulb (medulla 
 oblongata) which is continuous in front with the mid-brain, and 
 behind with the spinal cord, which it much resembles in structure. 
 The bulb contains a relatively large fourth ventricle, connected by 
 the aqueduct with the third ventricle. Its roof is shaped like a 
 triangle with forwardly-directed base, and is constituted by a 
 vascular membrane. On the under side of the thickened floor 
 is a median groove, the ventral fissure. The cerebellum is a small, 
 solid, transverse ridge, just behind the optic lobes, which arises 
 as a dorsal outgrowth from the posterior vesicle, and together 
 with the bulb makes up the hind-brain. 
 
 The spinal cord is a thick-walled tube, somewhat flattened 
 from above downwards, which is contained in the spinal canal. 
 It merges into the bulb in front, and from this point gradually 
 tapers backwards (dilating, however, where the limb-nerves come 
 off), and ends in a filament, the filum terminate, which occupies 
 the canal of the urostyle. The small central canal of the spinal 
 cord opens into the fourth ventricle. Dorsally, the cord exhibits 
 a deep cleft, the dorsal fissure, and there is a similar ventral fissure 
 which passes on to the base of the hind-brain. 
 
 (2) There are twenty pairs of cranio-spinal nerves ten cranial 
 belonging to the brain, and ten spinal belonging to the spinal 
 cord. 
 
 Cranial Nerves. The two first pairs belong to the fore-brain. 
 I. The olfactory arise from the outer and front sides of the 
 olfactory lobes, pass through the foramina in the transverse 
 septum of the sphenethmoid, and supply the olfactory epithelium 
 of the nasal sacs. II. The optic nerves. On the ventral side of 
 the thalamencephalon there is an X-shaped structure, the optic 
 chiasma. The posterior thickened limbs of this, the optic tracts, 
 
212 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 curve backwards and upwards to fuse with the optic lobes. The 
 anterior thinner limbs are the optic nerves. They pass through 
 the optic foramina to reach the eyeballs. 
 
 The connection with the optic lobes is a secondary one that is, the optic 
 structures do not originally grow out of them, but fusion occurs later. 
 
 The very small third and fourth pairs belong to the mid-brain. 
 III. The oculo-motor nerves arise, near the middle line, from the 
 front of its floor, and pierce the side-walls of the skull by special 
 foramina to supply most of the eye-muscles. IV. The pathetic 
 (trochlear) nerves are given off from the dorsal surface of the 
 brain just behind the optic lobes. They pass through foramina 
 in the cranial wall, and supply the superior oblique muscles of 
 the eye. 
 
 The remaining six pairs belong to the kind-brain, and, with 
 the exception of the sixth, arise from the sides of the bulb. V. 
 The trigeminal are the largest cranial nerves. Each dilates into 
 a Gasserian ganglion, leaves the skull by the trigeminal foramen, 
 and immediately divides into two (1) The ophthalmic branch, 
 which runs along the inner side of the orbit, and then divides to 
 supply the olfactory capsule and skin of the snout ; and (2) The 
 maxillo-mandibular branch. The latter at once bifurcates into 
 (a) The maxillary nerve, supplying the margin of the upper jaw ; 
 and (&) The mandibular nerve, running round the angle of the 
 mouth and along the outside of the mandible, supplying the skin 
 of that region. Branches from this nerve are also distributed to 
 the muscles of the mouth-floor and to certain muscles which 
 elevate the lower jaw. VI. The very delicate abducent nerves 
 arise close together from the ventral surface of the bulb near its 
 front end. Each comes into close connection with the Gasserian 
 ganglion, separates from it, and leaves the skull by a small aper- 
 ture in front of the trigeminal foramen to supply the external 
 rectus and retractor bulbi muscles of the eye, and also the iris. 
 VII. The facial nerve on each side arises just behind the tri- 
 geminal. and passes out of the skull with it, having previously 
 united closely with the Gasserian ganglion. It divides at once 
 into (1) The palatine nerve, which runs along the floor of the 
 orbit, on its inner side, and supplies the mucous membrane of the 
 mouth-roof ; and (2) The hyomandibular nerve. This runs back 
 round the auditory capsule, crosses the columella, and then 
 descends in the posterior wall of the tympanic cavity to the 
 
AMPHIBIA. 213 
 
 angle of the mouth, supplying the regions of the tympanic mem- 
 brane and jaw-articulation. It then divides into (a) The man- 
 dibular nerve, running along the inner side of the mandible, giving 
 branches to its superficial muscles ; and (6) The hyoid nerve, 
 which passes along the anterior hyoid cornu and innervates its 
 muscles. VIII. The auditory nerves arise immediately posterior 
 to the facials, and enter the auditory capsules to supply the 
 essential organs of hearing. IX. The glossopharyngeal nerve on 
 each side takes origin a little way behind the root of VIII., and 
 in close connection with that of X. After leaving the skull by 
 the vagus-foramen, it is connected by a commissure with the 
 facial, and then runs down to the floor of the mouth, along 
 which it runs with a tortuous course, supplying the mucous 
 membrane of the pharynx and tongue. X. The vagus (pneumo- 
 gastric) nerve of each side arises in close connection with IX., 
 passes through the vagus-foramen and dilates outside the skull 
 into the vagus-ganglion. It takes a downward and backward 
 course, and gives off branches to the larynx, heart, lungs, and 
 stomach. 
 
 The ten pairs of spinal nerves have this in common, that each 
 arises from the spinal cord by two roots a dorsal, upon which 
 is a ganglion, and a ventral. These unite together to form the 
 oerve-trunk in the corresponding intervertebral foramen, which 
 serves as a point of exit. The roots of the anterior nerves pass 
 directly outwards, but the posterior ones slope more or less 
 backwards within the spinal canal before reaching their foramina. 
 The last few roots thus form with the filum terminale ? a brush- 
 like cauda equina. The ganglia on the roots are covered ventrally 
 by calcareous sacs. Each nerve sends off, near its commencement, 
 a small dorsal ramus to part of the muscles and skin of the back, 
 while the remaining part, the ventral ramus, is connected by a 
 delicate commissure, ramus communicans, with a sympathetic 
 ganglion. 
 
 The first or hypoglossal nerves run forwards in the throat- 
 muscles and innervate the muscles of the tongue. The second 
 and third unite to form a brachial nerve, which supplies the fore- 
 limb. Nerves 4, 5, and 6 supply the body-wall in their region, 
 while nerves 7, 8, and 9 unite to form a network, the sciatic 
 plexus, which gives off branches to the posterior viscera, and 
 a very large sciatic nerve to the hind-limb. The small tenth or 
 
214 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Fig. 61. HISTOLOGY or NERVE (from Landois and Stirling. 1, Primi- 
 tive fibrillse. 2, Axis- cylinder. 3, Non-medullated fibres. In their 
 course are seen numerous nerve-corpuscles. 5, 6, Medullated fibres ; 
 c, primitive sheath, internal to which the medulla, b, is seen ; U, 
 nodes of Ranvier between the two a single nerve-corpuscle ; a, axis- 
 cylinder. 7, Eleven medullated fibres in cross-section, surrounded by 
 connective tissue ; axis-cylinders dark, surrounded by white areas re- 
 presenting medulla. 8, Medullated fibre at node of Ranvier ; medulla 
 not shown. I., Multipolar ganglion-cell from spinal cord ; z, process 
 passing into axis-cylinder ; y, branched process to right of this 
 ganglion-cell is a bipolar one. III., Bipolar ganglion-cell from sym- 
 pathetic of Frog, surrounded by sheath, m ;. n, o, the two processes. 
 
AMPHIBIA. 215 
 
 coccygeal nerve proceeds from the foramen in the urostyle, and 
 supplies the posterior viscera. It is also connected with the 
 sciatic plexus. 
 
 (3) The sympathetic system is made up of a slender cord on 
 each side, lying just beneath the backbone. It is dilated at 
 intervals into ten sympathetic ganglia, each connected by one 
 or more rami communicantes with the corresponding spinal nerve. 
 In front it passes through the vagus-foramen, and is united with 
 the Gasserian ganglion, while in the region of the dorsal aorta 
 the two cords are closely bound to the dorsal side of that vessel. 
 The internal organs, including the vascular system, are supplied 
 by nerves coming off from the sympathetic ganglia, and breaking 
 up into plexuses. 
 
 Histology (Fig. 61). The ganglion cells of the cerebro-spinal 
 axis are mostly multipolar. They make up the greater part of 
 the grey matter, which forms a central core to the spinal cord, 
 medulla oblongata, optic lobes, and optic thalami, and an external 
 crust to the cerebral hemispheres. The corpora striata are also 
 composed of grey matter. Bipolar ganglion-cells of peculiar 
 type, in which one process is twisted spirally round the other, 
 have been found in the sympathetic ganglia, and unipolar cells 
 in the spinal ganglia. The processes of the ganglion cells either 
 become continuous with the axis cylinders of nerve-fibres or 
 branch, and form networks. 
 
 The nerve-fibres are either non-medullated or medullated. The 
 non-medullated (3) are made up of axis-cylinder and primitive 
 sheath with nerve-corpuscles. They are the only kind found in 
 the sympathetic system and olfactory nerves, besides which they 
 are common in the other parts of the nervous system. The 
 medullated fibres possess a layer of fatty matter, the medullary 
 sheath, between the axis-cylinder and primitive sheath. It is 
 broken up into short segments at the nodes of Schmidt, and at less 
 frequent intervals nodes of Ranvier occur where the primitive 
 sheath is constricted and touches the axis-cylinder. Each inter- 
 nodal segment, bounded at each end by one of these last, generally 
 possesses a single nerve-corpuscle. Medullated fibres make up 
 most of the white matter of the cerebro-spinal axis, which forms 
 the external part of the spinal cord, medulla oblongata, optic 
 lobes, and optic thalami, and the internal part of the cerebral 
 hemispheres. The crura cerebri are also of white matter. 
 
216 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Both sorts of nerve-fibre are connected centrally, directly or 
 indirectly, with ganglion-cells. Peripherally their axis-cylinders 
 may break up into fine plexuses, or those of medullated fibres 
 may terminate in various end-bodies, such as sense-cells, and, in the 
 case of striated muscle, end-brushes and end-plates (Fig. 90). 
 
 Non-nervous structures are intimately connected with the nervous 
 system, especially connective tissue, which forms the investing membranes, 
 and binds the nerve-fibres into smaller and larger bundles, while the fibres 
 and cells of the central organs are imbedded in an excessively delicate 
 connective-tissue network, the neurogiia. The pineal gland and pituitary 
 body are both non-nervous. The former is a rudimentary eye. 
 
 The nerve-fibres are physiologically divisible into afferent and 
 efferent, along which impulses respectively pass to and from the 
 central organs. The majority of the former are sensory, since 
 they are connected with end-organs, the stimulation of which 
 lead, in many cases, to a sensation, judging from analogy. A 
 large number of efferent fibres, since they supply muscles, are 
 known as motor. The brain and spinal cord are, in the first 
 place, centres for reflex actions i.e., those which are independent 
 of volition, and dependent on external stimuli. The apparatus 
 involved in such an action normally consists of (a) end-organs, 
 (b) an afferent nerve, (c) a nerve-centre, (d) an efferent nerve 
 terminating commonly in (e) muscular or glandular tissue. 
 The spinal cord alone, after the removal of the brain, enables 
 fairly complicated and purposeful movements of the body to be 
 effected, in answer to external stimuli. Thus, for example, 
 pinching a foot causes the corresponding leg to be drawn up, 
 and the placing on the skin of the back a bit of blotting-paper 
 dipped in acid leads to leg-movements directed to its removal. 
 The cord also serves as a channel by which afferent impulses can 
 travel to the brain, and efferent impulses from it. If the 
 cerebral hemispheres only are removed, still more complicated 
 reflex actions can be evoked by external stimuli, such, for 
 example, as swimming, croaking, and leaping. The medulla 
 oblongata, next to the hemispheres, is the most important part 
 of the brain. It regulates respiration, and has much to do 
 (through the sympathetic) with the alimentary canal and circu- 
 latory organs. It is also concerned with the co-ordination of 
 many muscular movements. 
 
 Spontaneity entirely resides in the cerebral hemispheres. 
 When these are removed, movements only occur after the appli- 
 
AMPHIBIA. 
 
 217 
 
 cation of stimuli. They are also the seat of consciousness and 
 intelligence. 
 
 
 
 Afferent. 
 
 Efferent. 
 
 I. 
 
 Olfactory. 
 
 Sensory fibres for 
 smell. 
 
 
 
 II. 
 
 Optic. 
 
 Sensory fibres for 
 
 ... 
 
 
 
 sight. 
 
 
 III. 
 
 IV. 
 VI. 
 
 Oculomotor. } 
 Pathetic. > 
 A bducent. } 
 
 
 
 Motor fibres for eye- 
 ball muscles. 
 
 V. 
 
 Trigeminal. 
 
 Sensory fibres to skin 
 of head and nasal 
 
 Motor fibres to floor 
 of mouth, and cer- 
 
 
 
 sacs. 
 
 tain muscles rais- 
 
 
 
 
 ing mandible. 
 
 VII. 
 
 Facial. 
 
 Sensory fibres to roof 
 of mouth. 
 
 Motor fibres to super- 
 ficial muscles of 
 
 
 
 
 mandible,and some 
 
 
 
 
 hyoid muscles. 
 
 VIII. 
 
 Auditor)/. 
 
 Sensory fibres for 
 
 
 
 
 
 hearing. 
 
 
 IX. 
 
 Glossopharyngcal. 
 
 Sensory fibres for 
 
 ... 
 
 
 
 taste. 
 
 
 X. 
 
 Vagus. 
 
 Afferent fibres (some 
 
 Efferent fibres (some 
 
 
 
 sensory). 
 
 motor). 
 
 
 
 To parts supplied. 
 
 The cranio-spinal nerves are made up of afferent and efferent 
 fibres, of which either or both may occur in the same nerve. The 
 preceding table exhibits the leading features of the cranial nerves. 
 
 All the spinal nerves are of mixed character, the fibres derived 
 from the dorsal roots being sensory, those from the ventral roots 
 motor. The sensory-fibres supply the skin, the motor the 
 voluntary muscles of the body ; in the case of the hypoglossal 
 some of those belonging to the tongue. The preceding facts 
 have been ascertained by cutting the roots and stimulating 
 the ends, it being remembered that fibres only carry impulses 
 one way, and hence no demonstrable results follow on stimulating 
 the peripheral ends of sensory, or the central ends of motor, fibres. 
 
 Therefore, the fibres of the dorsal root are sensory, those of 
 the ventral, motor. (See next page.) 
 
 The sympathetic system supplies and largely regulates the 
 internal organs. By its means involuntary muscular contrac- 
 
218 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Severed. 
 
 Result. 
 
 Central end 
 stimulated. 
 
 Peripheral end 
 stimulated. 
 
 Dorsal Root. 
 
 Loss of sensation in 
 
 Pain (comes to 
 
 No effect. 
 
 
 area supplied, but 
 
 same thing as 
 
 
 
 muscles can be 
 
 over-stimula- 
 
 
 
 moved at will, or 
 
 tion of parts 
 
 
 
 reflexly. 
 
 supplied). 
 
 
 Ventral Root. 
 
 Sensation remains in j No effect. 
 
 Muscles sup- 
 
 
 parts supplied, but 
 
 
 plied con- 
 
 
 muscles cannot be 
 
 
 tract. 
 
 
 moved at will, or 
 
 
 
 
 reflexly. 
 
 
 
 tions, such as those of the alimentary canal, circulatory organs, 
 &c., are mainly effected. It is, however, quite subordinate to 
 the brain and spinal cord. 
 
 Sense Organs. (1) Tactile Organs. The sense of touch is pos- 
 sessed by the skin generally, and the mucous membrane of the 
 olfactory sacs and mouth-cavities. The nerve-fibres connected 
 with this sense are derived from the trigeminal in the head and 
 spinal nerves in the rest of the body. They break up into 
 plexuses, and in the dermis numerous groups of oval flattened 
 touch-corpuscles are present. These are most numerous beneath the 
 wart-like elevations, and nerve-fibres are continuous with them. 
 
 (2) Gustatory Organs. Scattered throughout the mouth-cavity, 
 and especially numerous around the vomerine teeth, and on the 
 fungiform papillae of the tongue, are small groups of elongated 
 forked gustatory cells. They belong to the epithelium, and fibres 
 of the glossopharyngeal nerves terminate in them. 
 
 (3) Olfactory Organs. Two olfactory sacs (Fig. 51), separated 
 by a median partition, the nasal septum, are lodged in the front 
 of the head. Each contains a complicated internal cavity, com- 
 municating with the exterior and mouth-cavity by the external and 
 internal naris respectively, and with glandular walls largely lined 
 by olfactory epithelium, containing numerous spindle-shaped olfac- 
 tory cells (Fig. 62), in which fibres of the olfactory nerve end. 
 From these cells a stiff process or bundle of olfactory hairs projects 
 into the nasal cavity. 
 
 (4) Auditory Organs. The ear on each side is made up of 
 two parts (1) Middle ear, and (2) Internal ear. 
 
AMPHIBIA. 
 
 219 
 
 The middle ear consists of a small tympanic cavity, communicating 
 by the short Eustachian tube with the back of the mouth-cavity, and 
 lined by a continuation of its epithelium. It is closed externally by 
 the rounded tympanic membrane, which is stretched over a cartila- 
 ginous ring connected with the squamosal and covered externally 
 by skin. The rod-like columella (Fig. 50, B) is attached at one 
 end to the tympanic membrane, and stretches across the cavity 
 to the fenestra ovalis, into which its other end is inserted. 
 
 The internal ear is made up of the membranous labyrinth (Fig. 62), 
 contained in the cavity of the auditory capsule which, however, 
 it does not fill. Numerous strands of connective tissue unite it 
 with the walls of this cavity, which is filled by a clear fluid, the 
 perilymph. The labyrinth is of complicated shape, and consists of 
 vestibule and semicircular 
 
 canals: (1) The vestibule A B 
 
 is divided into (a) the utri- 
 culus, an irregular bag, the 
 cavity of which is imper- 
 fectly bisected by a fold 
 and communicates by a 
 small aperture with that of 
 Q3) the sacculus, an under- 
 lying oval bladder. Three 
 small swellings on the pos- 
 terior side of the sacculus 
 receive collectively the 
 name of cochlea. (2) The 
 semicircular canals are three 
 curved tubes anterior 
 vertical, posterior vertical, 
 and external horizontal, 
 connected with the utri- 
 culus. They lie in planes 
 mutually at right angles. 
 The first and last dilate 
 into swellings (ampullae) in 
 front, where they join the 
 utriculus. The posterior vertical unites in front with the anterior 
 vertical to form a common tube opening into the utriculus, and 
 dilates behind into an ampulla. 
 
 Fig. 62. SENSE ORGANS or FROG (after 
 JS fleer and Wiedersheim), various scales. 
 A, Cells from olfactory epithelium; ol.c 
 olfactory -cell. B, Right Membranous 
 Labyrinth, viewed from outside. The 
 arrow points to the front. The branches 
 of the auditory nerve are shown (partly 
 dotted), ut, Utriculus; sc, sacculus; 
 a.v, p.v, and h, anterior vertical, pos- 
 terior vertical, and horizontal semi- 
 circular canals ; ap, ampullae ; co, coch- 
 lea. B', 1, auditory cells, with auditory 
 hairs, a. h; 2, supporting-cells. 
 
220 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The labyrinth is filled with clear endolymph, in which are sus- 
 pended, especially near the sensory patches, a large number of 
 
 \o 
 
 a 
 
 y 
 
 Fig. 63. DIAGRAMMATIC HORIZONTAL SECTION OF MAMMALIAN EYE 
 (from Landois and Stirling). a, Cornea; 6, conjunctiva; c, sclerotic; 
 d, external chamber, with aqueous humour; e, iris; /,/', pupil; h, lens; 
 ky junction of cornea and sclerotic ; m, choroid ; n, retina ; o, vitreous 
 humour; .A^o, optic nerve; q, nerve sheath; p, nerve fibres, piercing 
 outer coats and becoming continuous with retina. 
 
 calcareous otoliths. It is lined throughout by simple epithelium, 
 mostly squamous, but in eight sensory patches, largely made up of 
 
AMPHIBIA. 
 
 221 
 
 elongated auditory-cells, closely con- 
 nected with fibres of the auditory 
 nerve. From each a tapering auditory 
 "hair" projects into the labyrinth- 
 cavity. The sensory patches are 
 disposed as follows : One in each 
 ampulla on a projecting fold, crista 
 acustica,znd the remaining five, macula:, 
 in utriculus, sacculus (2), and three 
 cochlear projections. 
 
 (f>) Visual Organs (Fig. 63). The 
 eye is relatively large, and projects 
 not only externally but also internally 
 into the mouth-cavity. It is lodged 
 in the orbit, on the side of the skull. 
 The eyeball is rounded internally but 
 flattened externally, and its wall is 
 made up of three concentric coatings. 
 The outermost of these, the firm, white 
 sclerotic, strengthened by cartilage, 
 exhibits externally a circular trans- 
 parent area, the cornea. The second 
 much thinner coating, the cJwroid, is 
 pigmented externally and very vas- 
 cular internally. This layer does not 
 line the cornea, but, at its margin, 
 becomes continuous with a vertical 
 partition, the iris, which presents a 
 central perforation, the pupil. By 
 the iris the eye is divided into a 
 small external and a large internal 
 chamber. The latter is lined by the 
 retina, which is the third and most 
 delicate coating. In it eight distinct 
 layers (Fig. 64) can be distinguished. 
 The optic nerve pierces the scler- 
 otic and choroid coats on the inner 
 side of the eyeball to reach the 
 retina, in which it breaks up into 
 a feltwork of fibres. These form a 
 
 JtA 
 
 Fig. 64. DIAGRAM OF 
 LAYERS OF RETINA (from 
 Landois and Stirling). 
 Pi, Pigment -cells ; St, rods 
 and cones continuous by 
 various intermediate struc- 
 tures with Ggl, ganglion- 
 cells connected with o, 
 fibres of optic nerve; Li, 
 internal limiting mem- 
 brane which conies just 
 outside vitreous humour 
 (not shown). 
 
222 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 layer on the internal side of the retina (ie., the side next the eye- 
 chamber), and are connected through various intermediate layers 
 with elongated sense-cells, the rods and cones, which occupy the 
 outside of the retina. Refracting structures are contained within 
 the chambers of the eye. A clear, watery aqueous humour fills the 
 external chamber, while a gelatinous vitreous humour is contained in 
 the internal chamber. Immediately behind the iris and connected 
 with its outer margin is a firm spheroidal body, the lens. 
 
 A number of accessory parts are connnected with the eye, of 
 which the two eyelids have already been mentioned. Continuous 
 with the lining of these is a delicate transparent membrane, the 
 conjunctiva, which closely covers the cornea. A small Harderian 
 gland, which secretes a fatty substance, is situated in front of and 
 below the eye. 
 
 The eye is moved by a number of small muscles, the most im- 
 portant of which take origin in the walls of the orbit, and are 
 inserted into the eyeball. They are (1) The retractor bulbi, u 
 muscular sheath surrounding the optic nerve ; (2) the four recti 
 muscles, superior, inferior, internal, and external rectus, inserted into 
 the upper, lower, anterior, and posterior sides of the eyeball. All 
 the preceding take origin from the inner wall of the orbit, near 
 its posterior end ; (3) the two oblique muscles, superior and in- 
 ferior, are inserted into the upper and lower sides of the eyeball, 
 taking origin close together in the anterior part of the inner wall 
 of the orbit. 
 
 DEVELOPMENT. 
 
 The frog is a good example of an animal in which there is a 
 free-living embryo or larva, very unlike the adult stage, into 
 which it is converted by a gradual metamorphosis. Frog larvae 
 are familiar to every one as fish-like tadpoles, which hatch out 
 during March and April from the frog " spawn," which consists of 
 fertilized ova surrounded by gelatinous matter. 
 
 1. Early Stages. Cleavage (segmentation) (Fig. 65) is com- 
 plete but unequal. The ovum is pigmented on one side which is 
 termed the upper pole, the unpigmented end being the lower pole. 
 Division may therefore be spoken of as " meridional " or " equa- 
 torial." The two first divisions are meridional, dividing the 
 oosperm into two and four. Then division into eight is effected 
 
AMPHIBIA. 
 
 223 
 
 Fig. 65. CLEAVAGE OF OOSPERM OF FROG (from Haddon, after Ecker). 
 The numbers indicate the number of segments. Dotted lines show 
 position of succeeding planes of segmentation. 
 
 Fig. 66. BLASTULA AND GASTRULA OF FROG (after Gotte). All are 
 sections. A, Partly segmented oosperm. B, Completely segmented 
 oosperm. C, D, E, Stages in formation of gastrula ; al, archenteron 
 (mesenteron) ; bl, segmentation cavity ; blp, blastopore ; ep and ep', 
 nervous and superficial layers of ectoderm ; hy t endoderm ; m and m', 
 mesoderm ; y.%, lower layer cells. 
 
224 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 by an equatorial furrow nearer the upper than the lower pole. 
 Divisions of both kinds now proceed, the final result being a 
 blastula (blastosphere) (Fig. 66, B), with a small Uastoccele (seg- 
 mentation cavity) near the upper pole. This is roofed by small 
 cells, while its floor and most of the blastula are made up of large 
 yolk-cells, containing food material. 
 
 Invagination (C, D, E) is partly effected by an inpushing of 
 the small cells at one point, and partly by their growing over the 
 yolk-cells elsewhere, leaving, however, for a long time an un- 
 covered circular area, the blastopore. Meanwhile the blastocoele 
 is gradually pushed aside by the archenteron, which occupies the 
 upper pole of the ovum, and is formed partly by the inpushing 
 of the small cells, as above stated, and partly by an absorption of 
 the yolk-cells to form a cavity, and their differentiation to give 
 it definite walls. The small cells, now almost covering the embryo, 
 may at this juncture be termed ectoderm (epiblast), the contained 
 yolk-cells endoderm (hypoblast). The mesoderm (mesoblast) is 
 formed as a layer several cells thick, commencing at the edges of 
 the blastopore and gradually extending over the rest of the 
 ovum below the ectoderm. It is apparently derived from the 
 endoderm. The notochord is formed at the same time, as a 
 median dorsal thickening of the roof of the archenteron. 
 
 2. General Growth. The ectoderm on the upper side of the 
 embryo thickens into a neural (medullary) plate, broad in front, 
 and narrowing behind to the blastopore. The axis of this plate 
 corresponds to the longitudinal axis of the future tadpole, the 
 blastopore being posterior. A delicate neural (medullary) groove 
 appears on the medullary plate. Its side-walls, the neural (med- 
 ullary) folds, grow up and unite together to form a neural tube, 
 the rudiment of the brain and spinal cord. The dorsal side of 
 the embryo is thus indicated, and its head and tail soon become 
 evident, the former being marked by the dilatation of the neural 
 tube into the three brain vesicles in front. The ventral surface 
 bulges out, owing to the food material contained in the endoderm, 
 but it gradually becomes less and less conspicuous. The blastopore 
 closes up, and the cavities of neural tube and gut are then con- 
 nected by a short neurenteric canal. As growth proceeds, the 
 embryo acquires a strong curve, the dorsal side being concave. 
 The sense organs become established, as also do an oval suctorial 
 mouth with horny beaks, and a cloacal aperture. On each side 
 
AMPHIBIA. 225 
 
 of the throat six thickened bars, the visceral arches, passing from 
 above downward, are developed. These are termed mandibular, 
 hyoid, 1st, 2nd, 3rd, and 4th branchial arches respectively. From 
 branchial arches 1 and 2 a branched tuft-like external gill grows 
 out on either side, and after hatching, which occurs about this 
 period, another proceeds from the third branchial arch. The tail 
 now assumes great size and importance as a locomotor organ. In 
 front of each branchial arch a visceral cleft, leading into the 
 throat, makes its appearance, and a fold of skin, the operculum, 
 grows back from the hyoid arches over the external gills. By 
 
 Fig. 67. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH A FROG EM- 
 BRYO (after Gotte). Ectoderm unshaded, endoderm shaded, mesoderm 
 (ra) darkly shaded. nc, Neural canal contained within neural tube, 
 which on the left is dilated into the rudimentary brain already 
 exhibiting flexure; al, alimentary canal, with mass of yolk (yk) be- 
 neath ; x, placed at blastopore, the reference line runs to posterior end 
 of neural canal, which is here continuous with alimentary. 
 
 the union of this fold with the body-wall a branchial chamber is 
 formed on each side. The right one soon closes, but remains 
 connected by a cross-passage under the throat with the left, 
 which opens to the exterior by a small rounded opening. The 
 external gills now shrink and disappear, being succeeded by inter- 
 nal gills, which are vascular folds on the walls of the clefts. As 
 the lungs develop, these too disappear, and the visceral clefts 
 close up. 
 
 The limbs have been arising meanwhile as bud-like out- 
 growths, the anterior pair being hidden at first by the operculum. 
 They appear at the surface after a shedding of skin which follows 
 
 15 
 
226 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 the atrophy of the gills. At the same time the eyes become 
 evident, and the horny jaws are cast off. The adult form is now 
 rapidly assumed, the tail gradually shrinking, while vegetable 
 food is given up, and exclusively aquatic life abandoned. 
 
 3. Fate of the Germinal Layers. (1) The ectoderm is early 
 differentiated into superficial and nervous layers (Fig. 66). The 
 former gives rise to the horny layer of the epidermis, the deeper 
 part of which is formed from the nervous layer. The epithelium 
 of the mouth-cavity (stomodseum) and posterior part of the 
 cloaca (proctodseum) are also ectodermic, these structures arising 
 as pits of the external surface which ultimately communicate 
 with the mesenteron to form a continuous alimentary canal. 
 
 The neural plate from which the cerebro-spinal axis originates 
 arises as a thickening of the nervous part of the ectoderm. The 
 essential parts of the sense organs are ectodermic. The nasal 
 sacs commence as pits in this layer, while the membranous laby- 
 rinths are originally depressions of the nervous part of it, which 
 are separated off as vesicles and grow into their complicated 
 adult form. The lens of the eye (cf. Fig. 80, I) is formed 
 as a similar vesicle, which becomes solid. An outgrowth from 
 the anterior cerebral vesicle, the optic vesicle, grows towards the 
 embryonic lens, which meets and pushes in its end, forming a 
 double-walled optic cup. The part connecting this with the brain 
 narrows to constitute the optic nerve, while the inner wall of the 
 cup becomes the essential part of the retina, the outer part its 
 pigment layer. The rest of the eye is mesodermic. 
 
 (2) The endoderm gives rise to the epithelium of the mesen- 
 teron and its outgrowths (Fig. 67, at) i.e., lungs, liver, and 
 pancreas. The visceral clefts are also formed as pouches of the 
 mesenteron. Four of them open as above described to the 
 exterior. In front of these is a pouch which never opens on the 
 surface and becomes the tympanic cavity. From the endoderm 
 the first rudiment of the endoskeleton is formed. This is a 
 cellular rod, the notochord, which underlies the nervous system as 
 far forwards as the pituitary body. Remains of it are found in 
 the centra of the adult vertebrae. 
 
 (3) The mesoderm at first forms a sheet on each side of the 
 notochord below the ectoderm, and also extends into the front of 
 the head. Each sheet splits into an outer somatic layer, and an 
 inner splanchnic layer, the two remaining united dorsally. The 
 
AMPHIBIA. 227 
 
 layers of the two sides become continuous ventrally, the split 
 between them forming the body-cavity. The mesoderm on each 
 side becomes divided, posterior to the head, into two longitudinal 
 parts. The upper of these, the vertebral plate, lies alongside the 
 neural tube and notochord, and becomes divided transversely 
 into mesoderm ic somites (protovertebrne). The lower part is known 
 as the lateral plate, the somatic mesoderm of which unites with 
 the ectoderm to form the somatopleure (wall of body), while its 
 splanchnic layer unites with the endoderm to form the splanch- 
 nopleure (wall of alimentary canal). Both mesodermic somites 
 and lateral plate are made up of somatic mesoderm externally, 
 and splanchnic mesoderm internally. 
 
 The dermis is developed from somatic mesoderm, mostly from 
 that of the lateral plates. The axial endoskeleton is formed 
 from splanchnic mesoderm, that of the mesodermic somites giving 
 rise to the vertebral column, which, with the hinder part of the 
 base of the brain-case, is moulded round the notochord. 
 
 The visceral arches become supported by rods of cartilage, 
 similarly named. Their fate is as follows : 
 
 I. Mandibular Suspensoria and cartilaginous basis of the jaws. 
 II. Hyoid, \ /Columellae and anterior 
 
 III. Branchial 1, 
 
 IV. Branchial 2, 
 V. Branchial 3, 
 
 VI. Branchial 4, 
 
 Fuse ventrally to 
 form hyoid ap- 
 paratus. 
 
 cornua. 
 
 f Anterior angles of 
 | hyoid plate. 
 Posterior angles. 
 Posterior cornua. 
 
 The rest of the skeleton is also mesodermic. 
 
 The alimentary canal and its outgrowths are formed (except 
 the epithelium) from the splanchnic layer of the lateral plate. 
 
 Important changes take place in the circulatory organs in con- 
 nection with the successive appearance of gills and lungs. The 
 heart at first possesses an undivided auricle, and pumps impure 
 blood to the gills by afferent branchial arteries corresponding to 
 the last four visceral arches (branchial arches), and breaking up 
 into capillaries. After the blood has been oxygenated in these 
 gill-capillaries it passes into efferent branchial arteries, which open 
 above into a loop from which the dorsal aorta arises. These 
 vessels may be numbered 3, 4, 5, 6, like the visceral arches with 
 
228 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 which they are connected. As the lungs develop they are 
 supplied by branches of the 6th afferent arteries, and, gradually 
 becoming functional, pour their blood into the auricle, which 
 becomes divided. At the same time the afferent and efferent 
 vessels become directly united to form continuous arches. The 
 internal gills meanwhile atrophy, and the 4th arches alone 
 remain connected to form the dorsal aorta. These changes are 
 best exhibited tabularly. 
 
 
 1st Stage. 
 
 2nd Stage. 
 
 3rd (Adult) Stage. 
 
 3rd arches, 
 4th arches, 
 5th arches, 
 Qth arches, 
 
 / Supply ex- 
 C ternal gills. 
 
 I Supply in- 
 f ternal gills. 
 
 Become carotid arches. 
 Become systemic arches. 
 Disappear. 
 Become pulmo-cut. arches. 
 
 The adult kidney is preceded by a rudimentary excretory organ, 
 the pronephros (head-kidney), consisting of a glandular con- 
 voluted tube, with three openings into the body-cavity. A 
 longitudinal pronephric dud ( = archinephric or segmental duct) 
 runs back from this and opens into the cloaca. The adult 
 kidney, more properly termed the Wolffian "body or mesonephros, 
 is developed as a number of tubules, at first comparatively simple, 
 which become connected with the body- cavity on the one hand, 
 and the pronephric duct on the other. This duct becomes the 
 urinogenital duct of the male and the ureter of the female. 
 
 The ovary and spermary are developed as thickenings of the 
 peritoneum lining the body-cavity. The oviduct (Miillerian duct) 
 commences on the dorsal wall of the body-cavity as a groove 
 which is subsequently converted into a tube. 
 
 The voluntary muscles are formed from the somatic layers of 
 the mesodermic somites. 
 
AVES. 229 
 
 CHAPTER XL AVES. 
 16. COLUMBA LIVIA (The Rock-Pigeon). 
 
 The common Rock-Pigeon is here selected for description, but 
 it must be remembered that the very numerous fancy breeds 
 have all been derived from this form. In some few places the 
 structure of the Fowl (G-allus bankiva) is alluded to, where it 
 differs markedly from the Pigeon. 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The bilaterally symmetrical body, in 
 addition to head and trunk, possesses a long flexible neck, and a 
 short stumpy posterior process, the tail (uropygium). Fore- and 
 hind-limbs are present, the former modified into wings, the latter 
 set on to the body very far forwards, thus securing equilibrium, 
 and facilitating bipedal progression. The body is largely, but 
 not entirely, covered with feathers, arranged in definite tracts 
 (pterylce), there being intervening bare spaces (apteria). There 
 are several kinds of feathers, the largest, quill-feathers, present on 
 the wings and tail, are those principally used in flight. The 
 wing-quills (remiges) are 19 in number on each side. They are 
 overlapped, above and below, by smaller wing-coverts. The tail- 
 quills (rectrices), 12 in number, are attached to the uropygium, 
 and are overlapped on both sides by tail-coverts. The small soft 
 feathers, which invest all parts of the body, and confer the 
 characteristic outlines, are contour-feathers. In addition to these 
 a very great number of minute rudimentary feathers are present, 
 the filoplumes. 
 
 The head is well rounded behind, while in front it tapers into 
 the beak, the upper and lower parts of which are encased in horn, 
 and bound the large mouth. A bare elevated area, the cere, is 
 present at the base of the upper division of the beak, and in 
 front of this two slit-like nostrils (external nares). The large 
 eyes possess upper and lower featherless eyelids, and each is 
 provided as well with a thin translucent third eyelid (nictitating 
 membrane) which can be quickly drawn over the eye, or folded 
 
230 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 up in its anterior angle. A little way behind and below the eye 
 is a rounded auditory opening concealed by feathers. It opens 
 into a short tube, the external auditory meatus. 
 
 The trunk is somewhat boat-shaped, presenting a prominent 
 ridge along the middle of its ventral side, except for a small 
 posterior area where soft abdominal walls can be left. A large 
 transverse cloacal aperture with swollen edges, opens ventrally at 
 the base of the tail. Upon the dorsal surface of the latter 
 structure there is a small papilla, upon which the oil-gland opens 
 (Fig. 70, u.gt). 
 
 The fore-limb (cf. Fig. 69) is divided into upper arm, fore- 
 arm, and hand (brachium, antebrachium, and manus), which are 
 of about equal length, and folded closely one upon another when 
 not extended for flight, but, when so extended, approximating to 
 the primitive position. The manus is tridadyle, but the small 
 thumb (pollex} is the only digit well-marked externally. It bears 
 a small tuft of feathers, the bastard wing. Eleven of the remiges 
 are attached to the hand. These are the primary quills. The 
 remaining eight remiges, secondary quills, are attached to the fore- 
 arm. 
 
 The hind-limb (cf. Fig. 69) is divided into thigh, leg, and 
 foot (femur, crus, and pes). The last is made up of a cylindrical 
 tarsometatarsus, about as long as the thigh (the leg is much 
 longer), and four digits, of which the first, or great toe (hallux), 
 is 'directed backwards, the others forwards. The foot is covered 
 by overlapping scales, and the digits are terminated by claws. 
 
 Position of Body. The directions assumed by the divisions of 
 the fore-limb have already been mentioned. In the standing 
 posture the thigh, leg, and tibio-tarsus are arranged in a longi- 
 tudinal vertical plane with the knee directed forwards and the 
 mesotarsal ankle-joint backwards. The great toe is also turned 
 backwards, and owing to its free metatarsal is more mobile 
 than the other forwardly directed digits. 
 
 2. The extremely thin skin is divided into epidermis and 
 dermis, the former possessing horny and deeper layers. The 
 scales and claws are made up of coalesced epidermic cells, and 
 the feathers are also modifications of this layer. A feather 
 consists of a central stem, the proximal part of which is a hollow 
 quill, and the distal part a solid shaft, forming the central part 
 of the expanded vane, the rest of which is made up of a row of 
 
AVES. 231 
 
 narrow barbs on each side, flattened at right angles to the axis 
 of the feather. Each barb possesses a proximal and a distal row 
 of minute barbules. These overlap and hold the barbs together, 
 and, for this purpose, the distal barbules are provided with 
 diminutive booklets. A minute aperture, the inferior umbilicus, 
 leads into the proximal end of the quill, and a similar superior 
 umbilicus into its distal end on the ventral side of the feather. 
 
 Ventral side = below in quill -feathers, next body in the others. The shaft 
 is longitudinally grooved on this side. 
 
 In the fowl, but not in the pigeon, a small after-shaft which 
 resembles the vane in structure is attached near the superior 
 umbilicus. 
 
 The Jiloplumes possess a minute thread-like stem, but the barbs 
 and barbules are only represented by a tuft of disconnected 
 processes. 
 
 The oil-gland belongs to the skin. It is made up of numerous 
 branched tubules, epidermic in origin, and lined by glandular-cells. 
 
 The most important histological point is the way of develop- 
 ment of the feathers. A small papilla is formed on the surface, 
 the base of which sinks down into the dermis and thus becomes 
 enclosed in a pit, the feather-follicle, from which its pointed end 
 grows out. The papilla is known as the feather-germ. It con- 
 tains a vascular core of dermis, and the epidermis covering its 
 surface is gradually moulded into the feather. The quill is 
 formed around the base of the germ, the vane around the free 
 part, from which it splits off and expands. The inferior umbilicus 
 is the point where the vascular core entered the feather, the 
 superior umbilicus shows where it left the unsplit quill-part to 
 form the centre round which the vane was once folded. 
 
 This description refers to the first-formed feathers. The papillse of new 
 feathers are formed in connection with the old follicles, and never project 
 on the free surface. 
 
 The feathers are renewed periodically during life, the old ones 
 being cast off at moulting. 
 
 The dermis contains a network of muscle-fibres attached to the 
 feather-follicles. By the contraction of this the feathers can be 
 erected. Blood-vessels, lymphatics, and nerves are present, and 
 a large number of ovoid touch-corpuscles. 
 
 3. The endoskeleton (Figs. 68 and 69). This, as in the frog, 
 
232 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 is mainly made up of cartilage, cartilage-bones,* and membrane- 
 bones, f 
 
 There are also a few sesamoid bones, e.g., patella, developed in the course 
 of tendons. 
 
 The bones are distinguished by their spongy character, and 
 the shafts of the long bones contain, in the adult, air instead of 
 marrow. The skeletons of the trunk and limbs may be distin- 
 guished as axial and appendicular. 
 
 (1) The axial endoskeleton consists of skull, vertebral column, 
 ribs, and sternum. (a) The mature skull contains compara- 
 tively little cartilage, and a chondro-cranium is only to be made 
 out in the embryo. The bones in the adult are fused together 
 so as to make the determination of boundaries a difficult matter. 
 A rounded cranial portion behind may be distinguished from a 
 tapering facial portion in front, the two being connected together 
 by an imperfect joint which permits a small amount of up and 
 down movement. A large rounded orbit is present on each side 
 near the junction of the two. 
 
 The cranial part is mostly made up of the rounded brain-case 
 or cranium. This exhibits a large foramen magnum behind, 
 bounded by the occipital region, to form which four bones are 
 fused together, two ex-occipitals at the sides, a supra-occipital 
 above, and a basi-occipital below. The last bears a median 
 rounded occipital condyle, for articulation with the vertebral 
 column. The roof of the brain-case is completed by two pairs 
 of bones, the parietals behind and the frontals anteriorly. The 
 side-wall of the brain-case is partly formed by the squamosal, 
 below which is a depression, the tympanic cavity, bounded 
 internally by the auditory capsule. 
 
 This is formed by the union of three elements, pro-otic, epi-otic, and 
 opisth-otic, of which the first is most important. They are placed in front, 
 above, and behind respectively. 
 
 About the centre of the capsular wall are two small openings, 
 one above the other, separated by a very narrow interspace. 
 
 * Cartilage-bones : Basi-, ex-, and supra-occipitals, pro-, epi-, and 
 opisth-otics, basi-, pre-, alt-, and orbito- sphenoid*, meftethmoid, quadrate, 
 articular, columella, basi-hyal, basi-branchiaf, posterior cornua of hyoid. 
 Vertebrae. Sternum. Ribs. Appendicular skeleton (except furcula). 
 
 f Membrane-bones : Parietal, frontal, squamosal, parasphenoid, lachry- 
 mal, basi-temporal, vomer, nasal, premaxilla, maxilla, jugal, quadrate- jugal, 
 pterygoid, palatine, angular, supra-angular, dentary, splenial. Furcula. 
 
AVES. 233 
 
 The upper is the fenestra avails, the lower the fenestra rotunda. 
 Into the front of the tympanic cavity the Eustachian tube opens. 
 Further forwards tlie brain-case is bounded laterally by an 
 orbital plate, which also forms the hinder and upper parts of the 
 wall of the orbit, and is made up below by the ali-sphenoid, and 
 above by the orbital process of the frontal. The floor of the brain- 
 case in front of the basi-occipital is formed by the basi-sphenoid. 
 From this a pointed rod, the para-sphenoid (basi-sphenoidal rostrum), 
 projects forwards. It is fused with the lower edge of a thin 
 bony plate, the interorbital septum, continuous behind with the 
 ali-sphenoids. The posterior part of the septum represents three 
 distinct bones, a median pre-sphenoid, and two lateral orbito- 
 sphenoids. The upper and anterior parts of the septum are, in 
 the young bird a distinct bone, the mesethmoid. The anterior 
 margin of the orbit is formed at this point by the lachrymal. 
 The basi-sphenoid is overlapped by a thin plate of bone, the 
 bast-temporal, which forms the lower boundary of the tympanic 
 cavity on either side. It tapers somewhat in front, and between 
 it and the basi-sphenoidal rostrum is a median Eustachian open- 
 ing, from which an Eustachian tube leads back on either side to 
 the corresponding tympanic cavity. 
 
 The basi-temporal is probably equivalent to the posterior part of the 
 frog's para-sphenoid. 
 
 The cavity of the brain-case closely corresponds to the shape 
 of the brain. Its floor is very steep, rapidly ascending towards 
 the front. The foramen magnum looks downwards in accordance 
 with the upright position of the neck. 
 
 Nerve Exits. The olfactory foramen (I.) is in the front of the 
 brain-case. A vacuity in the dry skull at the upper margin 
 of the inter-orbital septum marks the course of the olfactory 
 nerves to the nasal capsules. Below the olfactory foramen is an 
 o/itic foramen (II.), and at this point, in the dried skull, the two 
 orbits are placed in communication by a hole. The oculomotor and 
 pathetic nerves have exit by special small foramina near the optic, 
 the fifth and sixth by a larger aperture behind the ali-sphenoid. 
 The eighth nerve pierces the inner side of the auditory capsule, 
 and, just in front of it, there is a small foramen for the seventh. 
 Behind the tympanic cavity there is a small opening on each 
 side at the posterior angle of the basi-temporal for the ninth, 
 
234 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 tenth, and eleventh (IX. and X.), while the twelfth passes out 
 by a small condylar foramen situated in the ex-occipital near the 
 condyle (XII.) 
 
 The facial part of the skull consists of the nasal capsules and 
 jaws. The nasal capsules contain a good deal of cartilage, and 
 are separated by a cartilaginous nasal septum, which is a con- 
 tinuation of the mesethmoid. A scroll-like fold, the turbinal, 
 projects from it on either side. Below this is a slender vomer, 
 just in front of the basi-sphenoidal rostrum. The capsules are 
 partly roofed in by the nasals, which unite with the frontals 
 behind, and are deeply notched in front. The notches partly 
 bound the external nares. 
 
 The margin of the upper jaw is formed in front by the pre- 
 maxillce, each of which unites behind with a delicate rod-like 
 maxilla, from the anterior end of which a flat maxillo-palat'me 
 process projects towards the middle line. The maxilla fuses 
 behind with a styliform jugal. These two last bones form the 
 greater part of a sub-orbital bar, which is completed posteriorly 
 by a guadrato-jugal, the rounded posterior end of which is united 
 by a fibrous band with the quadrate, a short thickened bone, 
 
 Fig. 68. ENDOSKELETOX OF PIGEON (Cartilage dotted). A and A', Skull, 
 side and under views; s-oc, supra-occipital; ex-oc, ex-occipital; b-oc, 
 basi- occipital ; c, condyle ; pa, parietal ; sq, squamosal ; a-s, ali-spheuoid ; 
 fr, frontal; fr', orbital process of ditto; i-o.s, inter-orbital septum; 
 la, lachrymal; b-t, basi-temporal ; p-s, para-sphenoid; v, vomer; na, 
 nasal ; p-mx, pre-maxilla ; mx, maxilla ; mx-p, maxillo-palatine process ; 
 j, jugal ; q-j, quadrato-jugal ; pi, palatine ; pt, pterygoid ; qd, quadrate ; 
 d, dentary; ar, articular ; an, angular; s-an, supra-angular; ly, tympanic 
 cavity (reference line runs to fenestra ovalis); Eu, Eustachian opening; 
 f-m, foramen magnum. I., II., &c. , Nerve exits. (V., just above for- 
 amen for fifth.) B, Left columella, enlarged; pi, plate fitting into 
 fenestra ovalis. C, Hyoid apparatus, from above ; g-hy, glosso-hyal ; 
 b-ky, basi hyal; b-br, basi-branchial; a.c, anterior cornua; p.c, posterior 
 cornua. D and D', "Sacrum" and pelvis, under and side views, num- 
 bers refer to vertebras ; t, thoracic ; /, lumbar ; S, sacral ; c, caudal ; 
 c', free caudal; p-sh, plough-share bone; r, rib; il, ilium; pb, pubis; 
 is, ischium ; ac, acetabulum ; ant, anti-trochanter ; ob, obturator 
 fissure; i-s.f, ilio-sciatic foramen. E, 1-6, Vertebrae. 1, Atlas: 2, axis: 
 3, two free cervical, from above : 4, ditto, from side : 5, ditto, from 
 front: 6, first thoracic ; c, centrum; n.sp, neural spine; t.p, transverse 
 process ; hy, hypapophysis ; a-z, pre-zygapophyses ; p-z, post-zyga- 
 pophyses; o.p, odontoid peg; i.l, cervical rib; n.c, neural canal; r.c, 
 vertebrarterial canal ; r, vertebral rib ; c.p, head ; tb, tubercle ; un t 
 uncinate process : 7, sclerotic ring. 
 
tt& 
 
236 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 raovably articulated at one end by two convex surfaces with the 
 squamosal and pro-otic, while the other presents a transverse 
 articular condyle for the mandible. Upon the ventral surface 
 of the skull an X-shaped structure is formed by four bones, 
 pterygoids behind and palatines in front. The pterygoid arti- 
 culates behind with a facet on the quadrate, in front with a facet 
 on the side of the parasphenoid, at its base. When the facial 
 part of the skull is moved up and down, the pterygoids readily 
 slide forwards and backwards on these smooth facets. The 
 palatine is a flattened rod, broadest behind, where it meets its 
 fellow and the pterygoid, and tapering to a point in front, where 
 it fuses with the maxillo-palatine process. 
 
 The lower jaw or mandible consists of two almost straight 
 halves (rami), each of which articulates behind with the corre- 
 sponding quadrate, and unites with its fellow in front to form a 
 median symphysis. The axis of the ramus is formed by 
 Meckel's cartilage, which persists, more or less, throughout life, 
 and is ossified proximally into the articular, which is jointed on 
 to the quadrate. Angular and supra-angular elements ensheath 
 the ramus below and above in its proximal half, the latter being 
 produced above into a small coronoid process, while the distal half 
 is covered ventrally and externally by the dentary, internally by 
 the splenial. 
 
 Hyoid and First Branchial Arches. The proximal end of the 
 hyoid arch is formed by the columella, which helps to transmit 
 sound-waves to the internal organs of hearing. Its inner end is 
 bony and expanded into an oval plate fitting into the fenestra 
 ovalis, while its outer cartilaginous end is firmly fixed to the 
 inner side of the tympanic membrane. The " hyoid apparatus " 
 consists of the body of the hyoid, supporting the base of the 
 tongue, and anterior and posterior cornua. The body is composed 
 of three median pieces : (a) A cartilaginous glosso-liyal, shaped 
 like an arrowhead, from which the short anterior cornua also of 
 cartilage, diverge backwards; (6) a short bony basi-hyal; and 
 (c) a styliform bony basi-branchial. Between (b) and (c) the 
 slender three-jointed posterior cornua diverge backwards and 
 upwards. 
 
 The basi-branchial and posterior cornua represent the first branchial 
 arches. 
 
AVES. 
 
 237 
 
 (b) Vertebral Column and Ribs. The vertebral column is 
 divided into regions, arranged as follows : 
 
 
 JV'o. of Vertebrae. 
 
 
 1. Cervical, 
 
 13 or 14 
 
 Free. 
 
 1. Thoracic 
 
 
 
 (a) Anterior, 
 
 4 
 
 Fused. 
 
 (b) Posterior, 
 
 1 
 
 
 3. Lumbar, 
 4. Sacral, . 
 5. Caudal 
 
 2 or 3 
 4 or 3 
 
 Fused to form 
 "Sacrum." 
 
 (a) Anterior, 
 
 6 
 
 
 (b) Middle, . 
 
 6 
 
 Free. 
 
 (c) Posterior, 
 
 Several 
 
 / Fused to form plough- 
 ^ share bone. 
 
 The cervical vertebrae are those supporting the neck. Each is 
 made up of two parts : (a) An elongated centrum, articulating 
 with neighbouring centra by saddle-shaped surfaces conferring 
 great flexibility to this region, and with a median ventral process 
 (hypapopliysis). (b) A neural arch, produced dorsally into a plate- 
 like neural spine, and connected with adjacent arches by pre- and 
 post-zygapophyses in the same way as in the frog. Intervertebral 
 foramina are left between the arches for the transmission of the 
 spinal nerves. 
 
 The last cervical vertebra possesses a strong transverse pi'ocess 
 running out from each side of the neural arch, and bears a pair 
 of cervical ribs, each of which is a small curved bone, with a 
 forked proximal end attached to the vertebra, and a free distal 
 end. From its hinder edge a small flat uncinate process projects. 
 The two limbs of the forked end terminate in articular projections 
 termed head (capitulum) and tubercle. The former articulates 
 with a small capitular facet on each side of the centrum near its 
 front end, the latter with a similar tubercular facet on the under 
 side of the transverse process. The last vertebra but one also 
 bears free ribs, these, however, are devoid of tubercles and 
 uncinate processes. 
 
 In the remaining vertebrae which possess them, the cervical ribs 
 are very short, and completely fused with the transverse process 
 and centrum, an aperture being left, however, which, with those 
 
238 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 of the other vertebrae, forms the vertebrarterial canal in which 
 certain soft structures run. 
 
 The first and second vertebrae, atlas and axis, are very small and 
 possess neither ribs nor transverse processes. The atlas (1) is a 
 ring, without anterior zygapophyses. Over its centrum's upper 
 surface a small peg, the odontoid process, projects from the front 
 end of the centrum of the axis (2). The occipital condyle fits 
 into an articular pit formed above by the odontoid process, and 
 below by the atlas-centrum. 
 
 The odontoid process is at first a distinct bone. It is part of the atlas- 
 centrum which fuses with that of the axis. 
 
 The thoracic vertebrae bear free thoracic ribs, and the commence- 
 ment of the series is marked by the first vertebra bearing ribs 
 which unite ventrally with the sternum. The four anterior 
 vertebra are closly united with one another by their centra and 
 the processes of their arches. The thoracic ribs are made up of 
 two segments, one, the vertebral rib, similar in character and mode 
 of attachment to the last cervical rib, the other, sternal rib, arti- 
 culated distally, with a facet on the sternum. The " sacrum " of 
 the adult bird is made up of vertebras belonging to four regions 
 closely fused together. The single thoracic vertebra is easily le- 
 cognised by its rib. It possesses a large bi laminar hypapophysis, 
 and its stout transverse processes abut against the ilia. The 
 lumbar vertebra have short and strong, the sacral, lamellar trans- 
 verse processes, while the first caudal possesses a ventral caudal 
 rib as well as a dorsal transverse process. 
 
 The free caudal vertebrae are small, and their transverse pro- 
 cesses flattened. 
 
 The ploughshare bone is a laterally flattened plate, bent up 
 sharply on the rest of the vertebral column. 
 
 (c) The sternum (Fig. 69) is a very broad, plate-like bone, 
 concave above, supporting the ventral wall of the thorax and 
 part of the abdomen. It is produced in front into an obtuse 
 process, the manubrium, and behind into a narrow plate, the 
 middle xiphoid process. At the sides are paired internal and 
 external xiphoid processes. On each side of the front of the ster- 
 num there is an excavation for the end of the coracoid, and 
 behind this comes the costal process, bearing four facets for the 
 .articulations of the sternal ribs. The ventral side of the sternum 
 
AYES. 239 
 
 is produced downwards into a prominent vertical plate, the keel, 
 which is deepest in front. 
 
 (2) Appendicular Endoskeleton. The long bones possess epi- 
 physes, as in the frog. Girdle and free limb can be distinguished 
 in both fore- and hind-limbs. 
 
 (a) Fore-Limb Shoulder-girdle (Fig. 69). The scapula is a 
 backwardly-directed, blade-like bone, united closely in front with 
 a rod-like coracoid, the other end of which articulates with the 
 sternum. These two bones make with one another an acute 
 angle, open behind, and the glenoid cavity is situated at their 
 point of union. In front of this the slender clavicle is attached, 
 which curves backwards and downwards, and unites with its 
 fellow in the middle line to form the furcula ("merry-thought"). 
 
 The union is effected (?) through the intermediation of a small inter- 
 clavicle, which forms in the Fowl a small, laterally flattened disc. 
 
 Free Limb (Fig. 69). The humerus possesses a proximal head 
 for articulation with the glenoid, and a distal, pulley-like trochlea, 
 which presents preaxial and postaxial articular surfaces for the 
 radius and ulna. Two distinct bones, radius and ulna, support 
 the antebrachium. The preaxial radius is straight and slender, 
 the postaxial ulna relatively stout. The proximal end is pro- 
 duced into an olecranon process. 
 
 The carpus is made up of two small bones, the radiale and 
 ulnare, which articulate with the radius and ulna respectively. 
 First, second, and third metacarpals are present, closely united 
 proximally. The first is small, and projects but little beyond 
 the fused part. The second is long and stout, and the third long 
 and slender. The three digits are completed by phalanges, the 
 first and third possessing a single small one, while two large 
 phalanges terminate the second digit. 
 
 (1)) Hind-Limb Hip Girdle (Fig. 68). Each half, or os 
 intwminatum, is separate from the other, and made up of three 
 elements, ilium, ischium, and pubis, all three of which contribute 
 to the formation of the acetabulum, a rounded cup, not floored by 
 bone, on the outer side of the girdle. The large ilium extends 
 forwards and backwards above the acetabulum. It meets and 
 fuses with the anterior ends of the ischium and pubis to bound 
 the acetabular cavity, above which it presents a smooth surface, 
 .the anti-trochanter. The " sacrum " is closely connected with the 
 
240 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 inner concave surface of the ilium. The ischium is a flat rod 
 running back from the acetabnlum parallel to the lower edge of 
 
 Fig. 69. ENDOSKELETON OF PIGEON. A, Sternum and shoulder-girdles ; 
 c.st, corpus sterni; k, keel; x.a, x.m, x.p, external, internal, and 
 middle xiphoid processes ; r, sternal ribs ; co, coracoids ; sc, scapulae ;. 
 
 /, furcula ; gl, glenoid cavity. B, Left Wing h, humerus ; hd, head 
 of ditto ; r. t and u. t, radial and ulnar tuberosities ; r, radius ; ul, ulna, 
 showing scars left by quills; ra, radiale; u, ulnare ; I. -III., meta- 
 carpals; 1-3, phalanges. C, Left Leg (patella gone, fibula not seen) 
 
 J\ femur; hd, head; g.t, great trochanter; t-t, tibio-tarsus ; t.p, proxi- 
 mal part of tarsus; t.d, distal part of tarsus; t-mt, tarso-metatarsus j. 
 I. -IV., metatarsals; 1-4, phalanges. 
 
AVES. 241 
 
 the ilium, beyond which it extends. The pubis is a slender rod 
 which, in the acetabulum, fuses with the ilium and ischimn. It 
 runs back below the latter, the obturator fissure separating the 
 two, and extends for some distance behind it. A wide space 
 separates the pubes and ischia of opposite sides. 
 
 Free Limb (Fig. 69). The femur articulates with the acetabu- 
 lum by a preaxial head at right angles to the shaft, while its 
 proximal end is terminated by a facet which works against the 
 anti-trochanter, and on the postaxial side of which is a consider- 
 able elevation, the great trochanter. The distal end of the femur 
 is pulley-shaped. The main bone of the leg is the preaxial tibio- 
 tarsus with which the small rod -like postaxial fibula is partly 
 fused. The tibio-tarsus is a stout bone, much longer than the 
 femur, and with a pulley-shaped distal end. In front of the 
 knee-joint and fibula there is a small irregular bone, the patella. 
 
 In the adult there is no separate tarsus, but in the embryo it 
 is represented by two cartilages, the proximal of which unites 
 with the preaxial tibia and forms the distal end of the tibio- 
 tarsus, while the distal fuses with the metatarsus. The ankle- 
 joint is thus between the two tarsal elements, and is said to be 
 mesotarsal i.e., in the middle of the tarsus. 
 
 Four digits are present first, second, third, and fourth. The 
 metatarsals of the three last fuse with the distal part of the 
 tarsus to form the tarso-metatarsus. This is a rod of bone, the 
 distal end of which possesses three very distinct pulley-like sur- 
 faces for the three corresponding metatarsals. The small first 
 metatarsal is attached to the preaxial side of this end. The four 
 digits, of which the first is directed backwards, are completed 
 by 2, 3, 4, and 5 phalanges respectively. The terminal phalanges 
 support claws. 
 
 4. The digestive organs (Fig. 70) consist of gut and appended 
 glands. The former is divided into mouth-cavity, gullet with 
 crop, proventriculus, gizzard, small intestine, and large intestine 
 opening into a cloaca. The glands are liver and pancreas. 
 
 The mouth is bounded by the horny margins of the beak, 
 and, owing to the double joint by which the mandible is connected 
 with the skull, can be opened very widely. It leads into a large 
 mouth-cavity, upon the roof of which are two narrow slits, the 
 internal nares, largely overlapped by folds of mucous membrane. 
 Behind them is a small median Eustachian aperture, and posterior 
 2 16 
 
242 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 to this the end of the roof is marked by a backwardly directed 
 fringe. The large tongue attached to the floor of the mouth, 
 has a sharply-pointed tip directed forwards, and its hinder part 
 is produced backwards into fringed processes, behind which is 
 the glottis, a narrow slit, with edges also somewhat fringed. The 
 back part of the mouth-cavity, or pharynx, is continued behind 
 into a very long gullet (oesophagus), for the most part with thin 
 walls, which runs back on the ventral side of the neck to reach 
 the thorax. In the posterior part of the neck it dilates into 
 the crop, a very large bilobed sac, with extensible walls. Behind 
 this the gullet narrows, and its walls are much thicker. It 
 passes in the thorax into a small oval chamber, the proventri- 
 culus, of somewhat larger calibre, and with thick soft walls, 
 upon the inner surface of which are a number of small rounded 
 apertures, those of the peptic glands. The proventriculus opens, 
 on the left side, into the dorsal border of the gizzard, a large 
 rounded, somewhat flattened structure with extremely thick 
 hard walls, the lining of which is horny. It contains numerous 
 small pebbles and other foreign bodies which have been 
 swallowed. Proventriculus and gizzard together are equivalent 
 to a stomach. A narrow tube, the small intestine, comes off 
 from the right side of its dorsal border, forms a U-shaped loop, 
 the duodenum, and, after making several loops and coils, merges 
 into the short, straight, large intestine, the junction between the 
 two being marked by a pair of small projections, the intestinal 
 cceca. These are very large in the fowl. The large intestine is 
 continued posteriorly into a small cloaca which opens externally 
 by the cloacal aperture. The cloaca is divided by inwardly pro- 
 jecting folds into three compartments, internal, middle, and 
 external (Fig. 71). The first receives the large intestine, the 
 second the urinary and genital ducts, while into the dorsal wall of 
 the third a small thick-walled pouch, the bursa Fabricii, opens in 
 young birds. The lining of the small intestine is raised into 
 innumerable delicate thread-like processes, the mlli, which gradu- 
 ally die away posteriorly and are replaced by longitudinal ridges. 
 
 The lining of the large intestine and cloaca is smooth. 
 
 The liver is a large, brown organ, lying on the ventral side of 
 the body, and presenting depressions above and in front into 
 which the heart, duodenum, and gizzard fit. It is divided into 
 right and left lobes, of which the first is the larger. There are 
 
AVES. 
 
 243 
 
 Fig. 70. GENERAL DISSECTION OF MALE PIGEON. c, Cere, close to which 
 is external naris, ex.n. ; u.gl, opening of uropygial gland; il, cut edge 
 of ilium ; st, keel of sternum. A large part of this bone has been 
 removed together with ribs, b, Beak ; t, tongue ; p.n, internal nares ; 
 rjl, glottis ; ffi., gullet, which swells into the crop in the middle of its 
 course ; pr, proventriculus ; gz, gizzard ; d, duodenum. Most of 
 ileum has been cut away, at i its junction with large intestine is seen. 
 This point is marked externally by the intestinal caeca, one of which is 
 shown ; cl, cloaca ; /. I, placed on left liver-lobe at point where right 
 lobe was removed ; x , x , placed on points where bile-ducts enter 
 duodenum ; p, pancreas ; ***, placed 011 points where the pancreatic 
 ducts enter duodenum; r.a, right auricle of heart, into which the 
 cavals run ; pr-c, right precaval, formed by the union of (ju) jugular 
 and subclavian, the short vessel just over pr-c. which the brachial 
 ( 1 ) and pectoral (2, 2') veins combine to form ; p-c, postcaval, the 
 other cut end of which is close to t; r.v, right ventricle ; i.a, right 
 innominate artery bifurcating into common carotid above, and sub- 
 clavian, the latter at once dividing into brachial (above) and pectoral 
 (below). The dorsal aorta (d.ao) is seen running back from heart. 
 The cut end of the coeliac artery is just above pr, and that of the 
 anterior mesenteric to the right of t; tr, trachea; k, k', k", anterior, 
 middle, and posterior lobes of right kidney cut through ; v.d, right 
 spermiduct (vas deferens), along inside of which right ureter runs ; t, 
 left spermary (testis) the right is removed ; ol, placed over olfactory 
 lobe, and olfactory nerve which runs forwards from it; cJi, cerebral 
 hemisphere; o.l, optic lobe; cb, cerebellum; m.o, medulla oblongata. 
 II. , Optic nerve, just above which is optic tract; sy, right sympa- 
 thetic ganglia of thorax, between which are cut ends of ribs. The 
 ganglia are connected by double commissures, which, with connected 
 nerve branches, are represented by black lines. 
 
244 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 two bile-ducts, the left short and wide, running into the duodenum 
 near its commencement, while the right, long and narrow, opens 
 into its distal limb near the beginning of its distal third. There 
 is no gall-bladder. 
 
 A gall-bladder is present in the Fowl. The bile and pancreatic ducts are 
 also arranged differently. 
 
 The pancreas is a compact, elongated body, lying in the loop 
 of the duodenum, and sending three pancreatic ducts into its 
 distal limb. 
 
 As in the frog, the alimentary canal is suspended from the 
 dorsal wall of the body-cavity by mesenteric folds. The mem- 
 branous lining of the abdominal region (which, however, is quite 
 continuous with that of the thorax) is the peritoneum. This 
 closely lines the dorsal side of the cavity before leaving its walls 
 to form mesenteric folds. 
 
 The wall of the alimentary canal is made up of the usual four 
 coats mucous, submucous, muscular, and serous. The mucous 
 membrane possesses an epithelial lining varying in the different 
 parts of the canal. That found in the mouth-cavity and parts of 
 the oesophagus is stratified squamous epithelium, and that lining the 
 crop glandular. The lower parts of the gullet, the proventriculus, 
 and the intestines are lined by simple columnar epithelium, con- 
 tinued into the simple tubular peptic glands of the second, and 
 there becoming glandular. Glands of Lieberkiihn are present in 
 the small intestine. The epithelium of the gizzard secretes a 
 thick horny cuticle. 
 
 The muscular coat varies very much in thickness, and typically 
 consists of two layers, an internal circular and an external longi- 
 tudinal, the relative position of these being reversed, however, in 
 the gullet. This coat is immensely thickened in the gizzard, 
 and has there a complicated arrangement. 
 
 The serous coat is an epithelial and connective-tissue layer 
 present from the proventriculus backwards, and formed by the 
 investing mesentery. 
 
 The liver and pancreas present no important deviations from 
 the structure of the same organs in the frog (pp. 193, 194). 
 
 The food, chiefly consisting of grain, accumulates in the crop, 
 from which it passes on through the proventriculus to the gizzard, 
 which grinds it up, the process being aided by the foreign bodies 
 
AVES. 245 
 
 present. The three chief digestive juices are, gastric juice, bile, 
 and pancreatic juice, secreted respectively by the peptic glands, 
 liver, and pancreas, and acting as in the frog. An important 
 addition to the absorptive surface is afforded by the villi. 
 
 5. Circulatory Organs. Blood and lymph systems are present, 
 and well developed. 
 
 I. Blood System. The bright red blood, which coagulates 
 very quickly, is made up of plasma, with amoeboid colourless 
 corpuscles and much more numerous red corpuscles. Both kinds 
 are nucleated, and the latter are small, flattened, and oval, with 
 ends somewhat pointed. The blood circulates in a closed system 
 of tubes made up of heart, arteries, veins, and capillaries. 
 
 The large conical heart (Fig. 70), contained in its pericardium, 
 lies in the anterior part of the thorax, and is made up of four 
 chambers, two auricles and two ventricles. Its forwardly directed 
 base is chiefly made up of the dark thin-walled right and left 
 auricles, its apex by the thick-walled right and left ventricles, the 
 latter being the firmer, and alone reaching the extreme apex. The 
 cavities of the auricles are separated by a thin auricular septum, 
 upon which is a depression, the fossa ovalis, where the septum is 
 thinnest. Within the right auricle are the three openings of the 
 caval veins, that of the postcaval being guarded by a muscular flap, 
 the Eustachian valve, and, posteriorly, the crescentic right auriculo- 
 ventricular opening leading into the right ventricle. From the right 
 side of this opening a muscular flap, the right auriculo-ventricular 
 valve, projects into the ventricular cavity, to the walls of which it 
 is united by fibrous cords (chordce tendinece). The right ventricle is 
 separated from the left by the ventricular septum, which bulges 
 into its cavity, the walls of which are raised into muscular ridges 
 (columnce carnece). The pulmonary artery, which arises from this 
 division of the heart, has its origin guarded by three pulmonary 
 semilunar valves (pocket-valves). Within the left auricle, dorsally, 
 is the small opening of the pulmonary veins, and, posteriorly, the 
 rounded left auriculo-ventricular opening. This is guarded by a 
 mitral or bicuspid valve, made up of two membranous flaps, 
 situated in the cavity of the left ventricle, and connected by 
 chordae tendinese to papillary muscles, conical elevations, which 
 may be considered as modified columnse carnese. The aorta 
 arises from the anterior end of the left ventricle, and its origin 
 is guarded by three aortic semilunar valves (pocket- valves). 
 
246 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Arteries. A single aortic arch is present, the aorta, the first 
 part of which (arch of aorta) curves round to the right, giving 
 off branches which supply the head, neck, wings, and pectoral 
 muscles, and then, reaching the middle dorsal line, becomes the 
 dorsal aorta. This runs straight to the tail, where it becomes the 
 caudal artery, giving off branches on its way to the viscera, hind- 
 limbs, and body-wall. 
 
 From the arch of the aorta, large right and left innominate arteries are 
 given off close to the heart, after which the calibre of the aorta diminishes 
 considerably. Each innominate divides very quickly into common carotid 
 and subclavian arteries. The common carotid runs along the neck, soon 
 giving off the vertebral arteri/ (which supplies the brain and spinal cord, 
 and occupies the vertebrarterial canal), and, at the angle of the jaw, 
 divides into internal and external carotids. The former supplies the brain, 
 the latter the head generally. The subclavian divides almost at once into 
 the small brachial and large pectoral arteries, which respectively supply the 
 wing and muscles of the chest. The dorsal aorta gives off an unpaired 
 cceliac artery, the branches of which run to the proventriculus, gizzard, 
 spleen, duodenum, pancreas, and last loop of the small intestine; while, 
 slightly behind this, an unpaired anterior mesenteric artery comes off, which 
 supplies the rest of the small intestine. Still further back the small 
 anterior renal arteries, for the anterior kidney-lobes ; the femoral arteries, 
 for the extensor muscles of the thigh ; and the sciatic arteries, for the flexor 
 muscles of the thigh and for the rest of the hind-limb, are given off in suc- 
 cession. Branches of the sciatic, the middle and posterior renal arteries, 
 supply the corresponding kidney-lobes. Just behind the kidneys the dorsal 
 aorta gives off an unpaired posterior mesenteric artery to the large intestine 
 and cloaca, and paired internal iliac arteries to the hinder part of the pelvis, 
 and then runs, as the caudal artery, into the tail. 
 
 The pulmonary artery arises from the right ventricle, and soon 
 divides into right and left branches for the right and left lungs. 
 
 Veins. These may be dealt with under the headings of caval 
 system, hepatic portal system, and pulmonary veins. 
 
 (1) Caval System. There are two precavals (superior venae 
 cavse) and a postcaval (posterior vena cava), all opening into the 
 right auricle. Each precaval is a large, short vein, formed by 
 the union of three trunks jugular, brachial, and pectoral, return- 
 ing the blood from one side of head and neck, one wing, and 
 chest-muscles of one side, respectively. 
 
 The jugular runs back from the base of the head (where it is united by 
 a cross-trunk with its fellow), along one side of the neck, and not far from 
 its union with the other two trunks, receives the vertebral vein. 
 
 The postcaval is a large vein returning the blood from the 
 posterior part of the body, formed just in front of the kidneys, 
 
AVKS. 247 
 
 by the union of two iliac veins, and running through the liver, 
 from which it receives two hepatic veins, to the heart. 
 
 The iliac on each side commences between the anterior and middle 
 kidney-lobes where the femoral vein, bringing back blood from the greater 
 part of the hind-limb, imites with the hypoi/astric vein to form it. The 
 latter traverses the substance of the kidney, behind which it is connected 
 with its fellow by a cross-branch, that receives the caudal vein from the 
 tail, and internal iliac veins from the pelvis, and is also united with the 
 hinder end of the posterior mexenteric vein. The sciatic vein carries blood 
 from the hinder part of the leg into the hypogastric, at the junction of the 
 middle and posterior kidney-lobes. These lobes return their blood by a 
 large superficial renal vein to the iliac vein, which also receives a small vein 
 from the anterior lobe. 
 
 (-) Hepatic Portal System. This, the only portal system 
 present in the pigeon, is entirely made up of vessels running to 
 the liver from the alimentary canal and spleen. 
 
 Into the left liver-lobe two small left gastric veins take blood from the 
 left side of the gizzard, while the large portal vein divides into two 
 branches, one for each liver-lobe. This vein is formed by the union of 
 three others gastro-duodenal, returning blood from the right side of the 
 gizzard, duodenum, pancreas, and last loop of the small intestine ; anterior 
 mesenteric, from the rest of the small intestine; and posterior mesenteric 
 from the large intestine and cloaca. (The hypogastric veins receive part of 
 their blood from this vessel. ) The spleen pours its blood directly into the 
 portal trunk. 
 
 (3) One or two short pulmonary veins from each lung unite 
 together and open by a single aperture into the left auricle on 
 its dorsal side. 
 
 Circulation. The two sides of the heart do not directly com- 
 municate, and therefore no mixing of blood occurs, as in the 
 frog. The impure blood from the body is poured into the right 
 auricle by the caval veins, and passes into the right ventricle, by 
 which it is forced into the lungs. Thence the oxygenated blood 
 is returned to the left auricle, and, passing into the left ventricle, 
 is pumped through the aorta to the body at large. 
 
 The movements of the heart are very vigorous. The auricles 
 contract together, and their systole is followed by a ventricular 
 systole, both ventricles contracting together. The auriculo- 
 ventricular valves prevent the blood from passing back into the 
 auricles, and the chordae tendinese prevent the valvular flaps from 
 going too far. The chordae would be slackened during the ven- 
 tricular systole by the approach of the ventricular walls, were 
 this not compensated for by the papillary muscles, which con- 
 
248' AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 tract at the same time and pull the chordae taut. The semilunar 
 valves only allow blood to pass out of the ventricles. 
 
 II. The lymph system mainly differs from that of the frog 
 (p. 200) in the absence of lymph-hearts, and the greater definite- 
 ness of the lymphatic vessels {lymphatics of general body, lacteals 
 of gut). These resemble small veins in structure and ultimately 
 open into two delicate tubes, the thoracic ducts, lying just beneath 
 the vertebral column in the thoracic region, and communicating 
 with the veins at the junction of the jugular and subclavian on 
 each side. Minute lymph-spaces are found in all parts of the 
 body, and there are also large lymph-spaces of which the most 
 important is the cceloxn, which includes the general body-cavity 
 and the pericardial cavity. 
 
 Two cervical lymphatic glands are found at the base of the neck, 
 and a small red ovoid spleen is attached to the right side of the 
 proventriculus. 
 
 6. The respiratory organs (Fig. 70) consist of lungs, to which 
 the air gains access through a trachea, and of accessory structures. 
 An organ of voice results from modification of part of the air- 
 passages. 
 
 The glottis leads into a small larynx, the walls of which are 
 supported by several cartilages, and which is the commencement 
 of the windpipe or trachea, a long tube which runs along the 
 neck to the thorax. Numerous firm rings surround and support 
 the trachea, which bifurcates in the thorax into a right and a left 
 bronchus, one going to each lung. At the point of bifurcation is 
 situated the syrinx, which is here the organ of voice. 
 
 The end of the trachea and commencements of the bronchi enclose the 
 tympanum or syringeal cavity. Into this an elastic fold, the membrana 
 semilunaris, projects from the point of bifurcation, and is supported by a 
 slender bar of cartilage, the pessulus, running dorso-ventrally. The inner 
 side of each bronchus, at its commencement, is membranous, and forms the 
 membrana tympani/ormis interna. Special muscles are connected with the 
 syrinx. 
 
 The lungs are spongy bodies, of dark-red colour, which lie in 
 the anterior part of the thorax. They are closely attached to 
 the ventral side of the vertebral column and ribs, and a thin 
 membrane, the pleura, continuous with the peritoneum, covers 
 their ventral surface. The bronchus which runs to each lung 
 enters it, becomes membranous, and, after dilating into a vestibule, 
 runs towards the external side of its posterior end, bifurcating 
 
AVES. 249 
 
 into two secondary bronchi. Other secondary bronchi come off 
 from the vestibule. All these tubes are placed near the ventral 
 surface of the lung, the dorsal part of which organ is mainly 
 made up of their branches, delicate tubes with blind endings. 
 
 Closely connected with the lungs are a number of thin-walled 
 air-sacs into which the secondary bronchi open. 
 
 On each side of the body, in the abdominal region, between the kidneys 
 and the intestines, there is a large posterior air-sac, communicating with 
 the hinder end of the lung. In front of this are two pairs of intermediate 
 air-sacs, situated on the ventral side of the body-cavity. The posterior 
 intermediate air-sacs overlap the hinder part of the lungs, and communicate 
 with them by openings close to those of the posterior sacs, while the 
 anterior intermediate air-sacs are situated ventral to the anterior two-thirds 
 of the lungs, and open into them near the middle of their length. In the 
 region of the clavicle a large, unpaired inter -clavicular air-sac is present 
 (formed by the fusion of two sub-bronchial air-sacs), communicating with 
 either lung by an aperture near the entrance of the bronchus. This air-sac is 
 bilobed, and each lobe passes out of the body-cavity near the origin of the 
 wing to communicate with the hollow shaft of the humerus, while dorsal to 
 it there is a small prebroncJiial air-sac, connected with the anterior end of 
 the lung. 
 
 The most important histological point to be noticed is the finer 
 structure of the delicate tubules making up the greater part of 
 the lungs. The walls of these are raised up internally into 
 intersecting ridges, which form a complicated honeycombing, 
 traversed by networks of capillaries, and covered by simple 
 squamous epithelium. 
 
 The epithelium lining the bronchi and trachea is largely 
 ciliated. 
 
 The lungs are very immobile and take but little part in the 
 respiratory movements. Expiration is effected by a contraction 
 of the body-walls, by which the highly elastic air-sacs are com- 
 pressed. Inspiration is passively effected by the elasticity of the 
 body-walls, which expand and cause air to rush into the air-sacs. 
 Owing to the presence of these, a large amount of air passes 
 through the main passages of the lung. The essential part of 
 respiration takes place in the small tubes making up the bulk of 
 the lung, the walls of which are raised into folds, and the air is 
 kept pure in them by diffusion. 
 
 Respiration is very vigorous, in accordance with the rapid 
 oxidation (metabolism) of the tissues. A great deal of heat 
 results from this latter process, and the body is maintained at 
 a very high temperature (103- 10 4 F.) 
 
250 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The organ of voice is here the syrinx. 
 
 7. The urinogenital organs (Fig. 71) include the excretory 
 and reproductive organs. 
 
 Excretory Organs. The reddish-brown kidneys, covered ven- 
 trally with peritoneum, are situated just behind the lungs, and 
 closely applied to the under side of the ilia and " sacrum." Each 
 
 Fig. 71. URINOGENITAL ORGANS OF PIGEON. A, female; B, male; 
 k, &',&", anterior, middle, and posterior lobes of kidney; u, ureters; 
 u', openings of ditto; cl, elf, cl", internal, middle, and external divi- 
 sions of the cloaca, which has been cut through on its ventral side and 
 opened out; t, spermaries (testes); v.d, spermiducts (vasa deferentia); 
 v.s, vesiculse seminales; g.p, genital papillae, on the end of which are 
 the male genital openings; ov, ovary; od, oviducts (right a mere rudi- 
 ment); od', funnel of left oviduct; od", openings of oviducts into 
 cloaca; ad, adrenals. 
 
 possesses three lobes, anterior, middle, and posterior. Between 
 the two first, on the ventral side, a small thin- walled ureter arises, 
 which runs to the middle division of the cloaca, into the dorsal 
 side of which it opens. 
 
 The adrenals (Fig. 71, B, ad) are small elongated bodies, of yellowish 
 colour, closely connected with the origin of the iliac vein on either side. 
 
 The urinifcrous tubules are not ciliated. Each of them begins 
 
AVES. 251 
 
 in a glomerulus-containing Bowman's capsule, which passes into 
 a dilated glandular portion, that, after a somewhat convoluted 
 course, is succeeded by a narrow looped part. The terminal 
 portions of the tubules form the ureter by successive unions. 
 
 The water and salts are strained off in Bowman's capsules, 
 while the nitrogenous waste is excreted, mainly as uric acid 
 (C 5 H 4 N 4 8 ) by the glandular parts of the uriniferous tubules. 
 The urine is semi-solid. 
 
 Male Reproductive Organs (Figs. TO and 71). The sper- 
 maries (testes) are two oval, whitish bodies, situated ventral to 
 the kidneys, and near their anterior ends. They are invested 
 and held in place by folds of peritoneum (mesorchia). From the 
 inner side of each an opaque white tube, the spermiduct (vas 
 deferens), repeatedly and sharply bent from side to side, runs on 
 the outer side of the corresponding ureter to the cloaca, dilating 
 at its end into a vesicula seminalis, and opening on a small genital 
 papilla placed just external to the opening of the ureter. 
 
 The spermaries are made up of a large number of much- 
 convoluted seminiferous tubules formed by the continued branch- 
 ing of the spermiduct. The tubules are lined by epithelium, 
 many of the cells of which are sperm-mother-cells, producing 
 sperms (spermatozoa), with cylindrical heads and motile tails. 
 
 Female Reproductive Organs (Fig. 71). These are only 
 developed on the left side. The ovary is a very irregular body 
 (similarly situated to the spermaries), from the outer surface of 
 which globular ova of various sizes project, enclosed in follicles. 
 It is covered by peritoneum, which forms a suspensory fold 
 (mesovarium). The oviduct is a thick- walled convoluted tube, 
 communicating with the body-cavity at one end by a delicate 
 membranous funnel situated near the, ovary, and at the other 
 entering the cloaca by a large aperture external to the opening 
 of the left ureter. The right oviduct may be represented by a 
 short blind tube having a similar situation. 
 
 The cloaca is larger in the female. 
 
 The ovary consists of a connective-tissue framework, the stroma, 
 richly supplied with blood-vessels. The ova are contained in 
 ovarian follicles, lined by follicular epithelium, which is again in- 
 vested by the stroma. 
 
 These ovarian ova are, when ripe, yellow spheres rather less than 
 an inch in diameter. Such an ovum (cf. Fig. 73) is covered by 
 
252 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 a delicate vitelline membrane, within which is the vitellus, contain- 
 ing a germinal vesicle placed close to the surface. That part of 
 the vitellus in which the germinal vesicle is imbedded, the 
 germinal disc, is a small lens-shaped mass of clear protoplasm, 
 while the rest is mainly made up of food-yolk, through which 
 protoplasm is sparingly diffused. The yolk is of two kinds 
 yellow, composed of granular spheres, and white, formed of smaller 
 spheres enclosing highly refracting spherules. The yellow yolk 
 is more abundant, while the white yolk is arranged in a flask- 
 shaped mass running from the germinal disc to the centre of the 
 ovum, and several thin lamella concentric to this. 
 
 The oviducts possess muscular walls, and are lined by glandular 
 and ciliated epithelium. 
 
 The cloacal chambers of the two copulating individuals are 
 partially everted and the sperm passed into the oviduct. The 
 ova burst out of their capsules into the body-cavity, and are 
 taken up by the funnel of the oviduct. Before passing down 
 very far, they are fertilized by the fusion of a single sperm with 
 
 8. Muscular System. The muscles may be classified as in 
 the frog (p. 208), but their arrangement is more complicated. 
 The presence of air-sacs largely increases the surface for attach- 
 ment of the muscles of flight, the most important of which take 
 origin in the sternum and its keel, and are inserted into the 
 humerus. The specific gravity of the body is diminished by the 
 presence of air-sacs, as also by the nature of the bones, and flight 
 is thus indirectly aided. 
 
 Both unstriated and striated muscles are present, as in the 
 frog, and their structure and distribution are substantially the 
 same. 
 
 9. The nervous system (Fig. 70) consists of cerebro-spinal 
 axis, cranio-spinal nerves, and sympathetic system. 
 
 (1) The cerebro-spinal axis consists of brain and spinal cord, 
 enclosed in the neural canal and covered by membranes, but 
 closely fitting the cavities in which they are placed. 
 
 The brain is large and rounded. As before (p. 210), it may 
 be divided into fore-, mid-, and hind-brains : (a) Fore-brain. 
 The thalamenceplidon contains a large slit-like third ventricle, 
 bounded by the lamina terminal-is in front, and the optic thalami 
 at the sides (united behind by a posterior commissure), while a 
 
AVKS. 253 
 
 stalked pineal gland is connected with its thin roof, and a 
 pituitary body with the infundibulum formed by its floor. This 
 part of the fore-brain is overlapped by the large smooth cerebral 
 hemispheres. These are ovoid bodies closely applied to each 
 other in the middle line, broadest behind and bluntly pointed in 
 front. Each contains a large lateral ventricle, communicating 
 with the third ventricle by a foramen of Monro, and having its 
 floor raised into a considerable elevation, the coitus striatum. 
 The two corpora striata are connected by the anterior commissure 
 running in the lamina terminalis. A small pointed olfactory lobe 
 is connected with the anterior end of each hemisphere, close to 
 the middle line on the ventral surface, and it contains a small 
 olfactory ventricle, continuous with the lateral ventricle. 
 
 (b) Mid-brain. The optic lobes are very large. They are widely 
 separated from one another, and situated laterally, but remain 
 united by a dorsal optic commissure. Each contains a good-sized 
 optic ventricle, opening into the Sylvian aqueduct, which connects 
 the third and fourth ventricles, and possesses a thick floor formed 
 by the crura cerebri. 
 
 (c) Hind-brain. The thickened cylindrical bulb (medulla ob- 
 longata) possesses shallow dorsal and ventral fissures, and the roof 
 of the fourth ventricle is extremely thin. The cerebellum is a large 
 rounded projection, flattened laterally, which overlaps the mid- 
 brain and medulla. It is marked by deep transverse furrows, 
 and on each side presents a small rounded elevation, the flocculus. 
 The cerebellum is united with the bulb by a large cylindrical 
 peduncle on each side. 
 
 The spinal cord is continuous in front with the bulb, a sharp 
 ventral flexure marking their union, and tapers gradually back ta 
 the caudal region, exhibiting, however, considerable brachial and 
 lumbar enlargements where the limb-nerves come off. Dorsal and 
 ventral fissures are present, and a central canal, which in the lumbar 
 enlargement expands into a sinus rhomboidalis, the lozenge-shaped 
 roof of which is covered by membrane only. 
 
 (2) Cranio-Spinal Nerves. There are twelve pairs of cranial 
 nerves, the first ten of which correspond in origin and distribution 
 to those of the frog (p. 211). The optic chiasma is very large, 
 and the optic tracts very wide. The (V.) trigeminal nerve arises 
 by two roots, upon the larger of which is the Gasserian ganglion.. 
 Owing to the elongation of the neck, a very long course is taken- 
 
254 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 by the (X.) vagus to reach the heart, lungs, &c. The (XI.) spinal 
 accessory, a nerve not present in the frog, is made up of fibres 
 arising from the side of the spinal cord and bulb, it leaves the 
 skull with the vagus, and supplies some of the neck-muscles. 
 The (XII.) hypoglossal nerve corresponds to the first spinal of the 
 frog, and has a similar distribution, but it arises from the ventral 
 surface of the bulb. 
 
 For the nerve exits see p. 233. 
 
 The spinal nerves arise by dorsal and ventral roots (the former 
 ganglionated) from the spinal cord, and pass transversely outwards 
 by the intervertebral foramina. They are named cervical, thoracic, 
 &c., in the corresponding vertebral regions. The brachial plexus, 
 from which the wing is supplied, is produced by the union of the 
 last three cervical with the first thoracic. A lumbar plexus is 
 formed by the last lumbar and first sacral nerves, and a sciatic 
 plexus by the five succeeding nerves. These two plexuses supply 
 the hind-limbs and their girdles. 
 
 (3) Sympathetic System (Fig. 70, Sy). The main part of 
 this is a delicate ganglionated cord running close to the vertebral 
 column on each side. The ganglia are connected by rami com- 
 municantes with the commencements of the spinal nerves. The 
 two cords unite behind in an unpaired ganglion (ganglion impar), 
 while the anterior part of each of them is double, half of it run- 
 ning in the vertebrarterial canal. 
 
 The same histological elements are present as in the frog, and 
 their structure and arrangement are similiar (cf. Fig. 61). There 
 are, however, no bipolar ganglia in the sympathetic of the peculiar 
 kind described on p. 215. The external part of the cerebellum 
 is composed of grey matter, its internal part and peduncles of 
 white matter. 
 
 The most important advance upon the frog is found in the 
 large size of the cerebral hemispheres, and this is associated with 
 increased intelligence. The large cerebellum has apparently the 
 correlation of muscular movements for its main function. 
 
 10. Sense Organs. (1) Tactile Organs. Many of the nerves 
 ramifying in the skin terminate in ovoid touch-corpuscles. 
 
 (2) Gustatory Organs. Gustatory cells, supplied by the fibres 
 of the glossopharyngeal nerve, are present in the hinder part of 
 the tongue and roof of the mouth. 
 
AYES. 
 
 '255 
 
 (3) Olfactory Organs. The olfactory sac on each side, which 
 communicates by an external naris with the exterior, and by an 
 internal nans with the mouth-cavity, is partly lined by olfactory 
 epithelium. This covers the projecting turbinal, the rolled shape 
 of which increases the surface. The olfactory nerve breaks up 
 below the olfactory epithelium to supply the olfactory cells, of 
 which this is largely made up. 
 
 (4) Auditory Organs. External, middle, and internal ears are 
 present. The external ear consists of a short tube, the external 
 auditory meatus, opening below and behind the eye. It is 
 separated by the tympanic membrane from the middle ear or tym- 
 
 Fig. 72. DIAGRAMS OF THE MEMBRANOUS LABYRINTH (from Haddon}. 
 Internal side of left labyrinth. A, Fish. B, Bird. (7, Mammal; 
 us, utriculus and sacculus ; u, utriculus ; 5, sacculus ; c, cochlea. 
 
 panic cavity. This communicates with the mouth-cavity by an 
 ffustachian tube, while the columella stretches across it, having one 
 end attached to the tympanic membrane and the other inserted 
 into the fenestra walls, below which is the fenestra rotunda. The 
 internal ear is essentially composed of the membranous labyrinth 
 (Fig. 72), enclosed in a somewhat larger cavity (filled with 
 perilympfi) of closely corresponding shape. This cavity is con- 
 tained in the auditory capsule, and is surrounded by a thin, dense 
 layer of bone, forming the bony labyrinth. The utriculus and 
 sacculus are ill-marked off from one another. With the former 
 three semicircular canals are connected, arranged as in the frog, 
 
256 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 with the exception that the posterior vertical takes an outward 
 course, and crosses the horizontal before it dilates into an ampulla. 
 A slightly-curved tube, the cochlea, is connected with the anterior 
 part of the sacculus. The membranous labyrinth contains endo- 
 lymph with otoliths, and is lined by epithelium, patches of which 
 are largely made up of auditory cells, connected with auditory 
 nerve-fibres. 
 
 It has been determined by experiment that the semicircular canals of the 
 ear have to do with the perception of position in space. In this connection 
 the fact that their planes are mutually at right angles deserves notice. 
 
 (5) Visual Organs. The eye agrees in all essential particulars 
 with the description on p. 221, but differs in certain points. 
 The inner half of the eyeball is hemispherical, while its outer 
 part is somewhat conical and terminated by the very convex 
 cornea around which the sclerotic is strengthened by a circlet of 
 small, flat sclerotic plates (Fig. 68). The lens is flattened, and a 
 vascular, pigmented, longitudinally plaited fold, the pecten, pro- 
 jects into the vitreous humour below the entry of the optic 
 nerve. 
 
 The accessory parts connected with the eye are the three eyelids, 
 conjunctiva, two glands, and the eye-muscles. The glands are (1) 
 the Harderian gland in front, and (2) the lachrymal gland behind 
 and above. The eye-muscles are arranged much as in the frog. 
 
 DEVELOPMENT. 
 
 The common fowl has been most studied, and, as birds differ 
 but little in their development, will be here described. 
 
 1. Early Stages. The fertilized ovum, in passing down the 
 oviduct, is covered by several structures secreted by its walls 
 (Fig. 73). These are: (1) The white of the egg, mainly com- 
 posed of semifluid proteid material, and containing a somewhat 
 convoluted cord, the chalaza, at each end, (2) the double-layered 
 shell-membrane, covered by (3) the shell, formed of an organic 
 matrix hardened by salts of lime. The entire egg is elongated, 
 and broader at one end than the other. 
 
 Cleavage (segmentation) (Fig. 74) is unequal and also partial 
 (meroblastic), being confined to the germinal disc. It commences 
 
AYES. 257 
 
 in the lower part of the oviduct, and by a succession of furrows, 
 some at right angles and others parallel to the surface, the 
 germinal disc is converted into a many-celled blastoderm. This 
 is placed on one side (Fig. 73, Bl), and always remains upper- 
 most, the most favourable position for development, which 
 requires a good deal of warmth, supplied in nature by the 
 body of the hen. Before incubation (Fig. 75) the blastoderm 
 consists of a superficial layer, one-cell thick, of columnar ecto- 
 
 Fig. 73. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH UNINCCT BATED 
 HK.N'.S EGG (from Claus, after Balfour and Allen Thomson). Bl, 
 Blastoderm; GD, yellow yolk; WD, white yolk; DM, vitelline 
 membrane; EW, "white;" Ch, chalazae ; S, shell membrane; K8, 
 shell ; LR, air-chamber. 
 
 derm (epi blast), and a more irregular thickened mass of lower 
 layer celk, which are rounded, granular, and of larger size. Below 
 them is a space, the earliest rudiment of the alimentary canal. 
 
 Previous to laying, a blastOCCBle (segmentation cavity) can be seen 
 between ectoderm and lower layer cells. 
 
 The blastoderm is at first circular, and the more transparent 
 central part, known as the area pellucida, is surrounded by a 
 darker rim, the area opaca (cf. Fig. 77). If the egg is placed 
 with its broad end to the right, the diameter of the blastoderm, 
 which is to become the long axis of the embryo, will run across 
 the egg, the posterior end being towards the observer. 
 
 It now remains to describe the formation of the endoderm 
 and mesoderm. These are first clearly differentiated in the 
 2 17 
 
253 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 posterior part of the blastoderm. Many of the lower layer cells 
 here become much flattened and unite to form a thin membrane, 
 
 Fig. 74. SURFACE VIEWS TO SHOW CLEAVAGE IN THE FOWL'S OOSPERM 
 (from Kolliker, after Coste). Cleavage commencing in 1, completed 
 iu 6. 
 
 the endoderm (hypoblast) (Fig. 76, luj). In the hinder part of 
 the area pellucida an opaque longitudinal strip, the primitive 
 
AVKS. 
 
 259 
 
 st-mik (Fig. 77, 7V), appears. This is a local thickening (Fig. 
 76), where ectoderm and endoderm are continuous, and from 
 which a sheet of mesoderm (mesoblast) grows out on each side, 
 
 
 Fig. 75. SECTION THROUGH PART OF UNIXCUBATED FOWL'S BLASTODERM 
 (after Klein"). a, Ectoderm ; b, lower layer cells ; f, archenteron ; 
 below this, yolk. 
 
 Fig. 76. TRANSVERSE SECTION THROUGH FRONT END OF PRIMITIVE 
 STREAK IN FIRST DAY CHICK (see Fig. 77) (after Sal/our). Columnar 
 ectoderm above, two cells thick. Pr, Region of primitive streak, 
 where rounded mesoderm cells are originating from the ectoderm ; hy, 
 endoderm, above it, at the side, are stellate mesoderm cells of endo- 
 dermal origin. N.B. Pv is placed over the middle line. 
 
 being reinforced by those lower layer cells which have not 
 united to form endoderm. 
 
 In the anterior part of the blastoderm, i.e., in front of the 
 primitive streak, the lower layer cell form (1) a thin layer 
 of endoderm (hypoblast), (2) two lateral sheets of mesoderm 
 (mesoblast), (3) an axial rod of cells, the notochord, at first 
 closely united with the hypoblast. 
 
260 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The blastoderm thus comes to be three-layered, both in front 
 and behind. 
 
 The closure of the blastopore in a frog-embryo produces a small primitive 
 streak, in which the germinal layers are continuous. There can be no 
 doubt that the primitive streak in the chick-embryo is equivalent to a 
 closed blastopore of slit-like form. If the slit were to re-open it would 
 lead into the space figured at / in Fig. 75, and which = an archenteron. 
 The gastrula of the fowl, therefore, is very much modified, owing to (1) 
 closure of blastopore, (2) enormous accumulation of yolk on ventral side. 
 
 Ao 
 
 ^Z-SGiZSS&r 
 
 Fig. 77. SURFACE VIEW OF FIRST DAY (20 HRS.) CHICK (from Kolliker). 
 A.o, Area opaca, bounding A.p, area pellucida ; Pr, primitive streak ; 
 Af, head-fold. 
 
 2. General Growth. The blastoderm is at first a watch-glass 
 shaped plate resting upon the yolk. It generally grows in all 
 directions, and ultimately completely encloses the yolk. This 
 enclosure is mainly effected by the area opaca. The body of the 
 embryo is formed in the area pellucida. This elongates (Fig. 77) r 
 
AVKS. 
 
 261 
 
 becoming somewhat pear- 
 shaped, the broad (head) end 
 being anterior. In front of 
 the primitive streak a neural 
 (medullary) plate is formed 
 (cf. p. 224), upon which is a 
 longitudinal neural (medullary) 
 groove. This is bounded at 
 the sides by neural (medullary) 
 folds (Fig. 78, Mil), which 
 unite above to form the neural 
 tube. The folds first unite in 
 the region of the mid-brain. 
 The head now projects from 
 the surface of the yolk, and 
 makes with it, as seen from 
 the left side, an S -shaped 
 head-fold. A similar tall-fold 
 is formed later, and then 
 lateral folds. The embryo, at 
 first flattened out on the 
 curved yolk - surface, thus 
 gradually comes to assume 
 the form of the chick, and 
 the ever diminishing yolk re- 
 mains attached to its ventral 
 surface (Fig. 82). In a chick 
 at the end of the second day 
 of incubation (Fig. 79), the 
 cerebral vesicles (Fh, Mh, and 
 Hli) are present, and the eyes 
 and ears are commencing. 
 The front part of the brain 
 begins to bend round the end 
 of the notochord. At the end 
 of the third day, the front 
 part of the embryo is twisted 
 round so as to lie with its left 
 
 Jiv 
 
 streak ; vAf, head - fold, 
 either side of Rf. 
 
 Fig. 78. SURFACE fc ViE\v OF CHICK, 
 RATHER LATER THAN FIG. 77 
 Magnified 39 diameters (from Kol- 
 
 : liker). Mn, Medullary folds uniting 
 in the head region ; Pi', primitive 
 Three ''mesodermic somites are visible on 
 
AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 side on the yolk, and the cranial flexure round the notochord 
 is well-marked. Five visceral arches and four visceral clefts 
 have made their appearance (Fig. 80), one less than in the 
 frog. The most posterior of these are very small. The pro- 
 minent heart is situated just under the throat, close to the 
 
 n 
 
 Fig. 79. SUKFACK VIK\V OF SECOND DAY CHICK Magnified rather more 
 than 50 diameters (from KSlliker). Ap, Area pellucida ; Vh, Mh, JHh, 
 fore-, mid-, and hind-brains. The neural groove has closed as far back 
 as omr. Pr, Primitive streak. Eight mesodermic somites are shown. 
 
 ventral ends of the visceral arches. The eye and ear are much 
 more advanced, and the olfactory sacs are commencing as pits. 
 On the fourth day the limbs appear as buds. The chick is 
 hatched on about the twentieth day of incubation, breaking the 
 shell with its beak, which possesses a small knob for the purpose. 
 
AYES. 
 
 263 
 
 3. Fate of the Germinal Layers. These give rise to the 
 same organs as in the frog (p. 226), but there are differences 
 which will be here briefly noted. (1) The ectoderm (epiblast) 
 does not become divided into superficial and nervous layers till 
 comparatively late, and the membranous labyrinth commences 
 as a pit open externally. (2) The endoderm (hypoblast) presents 
 no important differences, but the notochord disappears more corn- 
 
 Fig. 80. DEVELOPMENT OF THE EYE (from ffaddon, A after Marshall). 
 A and B sections through head of third day chick. In A the optic 
 vesicle (o.c) from the fore-brain (/.&) is becoming cup-like, I is the 
 developing lens. In B the cup and lens are more distinct. Stalk of the 
 former not cut through. C. Later stage Inner wall of optic cup 
 (o.c) forming most of retina, r outer wall, p, forming pigment layer 
 of ditto; /, leus (quite separated off). These sections incidentally 
 illustrate other points. In all, owing to the cranial flexure, both fore- 
 and hind-brains have been cut through (f.b, h.b). In C, c./i, Lt, and 
 inf, indicate cerebral hemispheres, lamina terminalis, and infundi- 
 bulum. Near the last is the pituitary body, pit. In A and B the 
 pharynx (ph) is cut through, and the first two visceral clefts (v.c' and 
 v.c") are shown, a.a, aortic arches; a.c.v, anterior cardinal vein; 
 nch, notochord ; olj, olfactory pit. 
 
 pletely in the adult. (3) The mesoderm (mesoblast) becomes 
 divided (cf.p. 227) into vertebral and lateral plates in the region of the 
 trunk, the former being again divided into mesodermic (mesoblastic) 
 somites (Figs. 78 and 79). The coelom (Fig. 81) is as before the 
 split between the somatic and splanchnic layers of the lateral 
 plates, the former uniting with the ectoderm to form the body-wall 
 (somatopleure), the latter with the endoderm to form the wall of 
 
AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 the gut (splanchnopleure). When the embryo is spread out flat 
 on the yolk, the somatopleure and splanchnopleure belonging to 
 opposite sides diverge widely, but, as the embryo is folded oft', 
 they gradually approach, unite, and form a continuous boundary 
 to the body and gut respectively. The latter meets in front and 
 behind with inpushings of ectoderm that form the mouth-cavity 
 and posterior part of the cloaca (stomodaeum and proctodseum). 
 
 Fig. 81. TRANSVERSE SECTION THROUGH EMBRYO DUCK AT THIRD DAY 
 (after Balfour}. The external layer is ectoderm; hy, endoderm; meso- 
 derm, a thick layer between the two; am, lateral amniotic fold; -so, 
 somatopleure ; sp, splanchnopleure (the reference letters wd and sb are 
 placed in co3lom); xp.r, spinal cord, at the side of which is section 
 through mesodermic somite; cA, notochord (the reference letters <>. 
 hy, sp are placed in the alimentary canal, the walls of which, at this 
 stage, are widely divergent). 
 
 The first three visceral arches are supported by skeletal struc- 
 tures that become in the adult 
 
 I. Mandibular. Quadrates and Meckel's Cartilages, Palatines and 
 Pterygoids. 
 
 II. Hyoid, ) fuse ventrally f basi-hyal, 
 
 III. Branchial 1, 
 
 to form, 
 
 basi- branchial, 
 
 anterior cornua ; 
 
 columellae. 
 posterior cornua. 
 
 The last two visceral arches, corresponding to branchials 2 and 3 of the 
 frog, are small and have no skeleton. 
 
AVES. 265 
 
 The circulatory organs are not complicated by the presence of 
 gills. The heart at first consists of two longitudinal vessels that 
 fuse to form a simple tube, which first becomes twisted and 
 then chambered. From its front end aortic arches run up the 
 visceral arches (Fig. 80), and unite above to form the dorsal 
 aorta. 
 
 1st and 2nd Arches become (in part) . carotids. 
 
 3rd Arches ,, subclavians. 
 
 (right, . . aorta. 
 
 4th Arches '\ . abo rts. 
 
 5th Arches ,, ... pulmonary arteries. 
 
 The veins of the embryo at first (3rd day) consist of paired 
 anterior cardinals ( = adult jugulars) and posterior cardinals, which 
 bring back blood from the anterior and posterior parts respec- 
 tively (cf. Dogfish, p. 165). The anterior and posterior cardinal 
 of each side unite to form a Cuvierian vein ( = adult precaval), 
 which enters the heart. The posterior cardinals are supplanted 
 later on by the development of a postcaval. 
 
 The course of the embryonic circulation will be discussed 
 below. 
 
 Excretory Organs. A very rudimentary pronephros is first 
 developed, with a pronephric duct (= archinephric or segmental 
 duct) which runs back and opens into the cloaca. It is succeeded 
 by a mesonephros (Wolffian body), the duct of the pronephros 
 becoming the mesonephric (Wolffian) duct. The mesonephros does 
 riot, however, become the excretory organ of the adult, but is 
 succeeded by a metanephros, or true kidney, for which a special 
 metanephric duct (ureter) is developed. The only conspicuous 
 remnant of the mesonephros that persists after embryonic life is 
 its duct, which becomes the spermiduct of the male. 
 
 4. Embryonic Appendages (Fig. 82). These are important 
 structures connected with, but not forming part of, the embryo. 
 To understand them, it is not only necessary to remember that 
 the blastoderm gradually grows round the yolk, but also that the 
 mesoderm splits here, as elsewhere, so that continuations of soma- 
 topleure, splanchnopleure, and ccelom are present. As the embryo 
 is folded off from the yolk, this, with the covering of splanchno- 
 pleure, comes to form a sort of bag, the yolk-sac, attached to the 
 ventral side of the embryo by a stalk continuous with the wall of 
 the gut. The yolk is gradually used up during development, so 
 
266 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Fig. 82. DIAGRAM TO ILLUSTRATE THE DEVELOPMENT OF THE AMNION 
 AND ALLANTOIS (after Foster and Balfour). In A the embryo (e) is 
 being constricted off from the yolk-sac, and the folds of the amnion are 
 seen to be rising up at each end of the embryo, the anterior fold (at) 
 being the larger ; in B (a transverse section) the lateral amniotic folds 
 nearly meet, and in C (also a transverse section) they have entirely 
 coalesced. In D (a rather later stage than A), the allantois (al) is 
 budding out from the alimentary canal ; in E (side-view corresponding 
 to C), the allantois is seen extending round the embryo. In F, the 
 yolk-sac (y) is reduced in size, and in G it is being withdrawn into the 
 embryo's body. Allantois omitted in F and G. These diagrams only 
 roughly indicate the relation of parts. In all, the embryo is repre- 
 sented by horizontal shading, the ccelom and its extension are dotted, 
 and the yolk-sac marked with concentric lines. The dotted line repre- 
 sents the vitelline membrane. 
 
AYES. 267 
 
 that the yolk-sac becomes smaller, and at last passes into the 
 body. The continuation of the somatopleure outside the boundary 
 of the body rises into folds, which grow up, and, finally meeting 
 above the body, fuse together. Their inner layers form the 
 amnion, a membrane enveloping the embryo, while their outer 
 layers (and the somatopleure prolongation in the yolk-sac region) 
 unite with the vitelline membrane. As the somato- and splanch- 
 nopleures are prolonged outside the region of the embryo, the 
 space there present between them must be a continuation of the 
 body-cavity. A flattened sac, the allantois, grows from the 
 posterior part of the alimentary canal into this space, and ex- 
 tends over the embryo. 
 
 The yolk-sac possesses at one time a system of capillaries, and 
 functions as a respiratory organ. As the allantois develops it 
 also becomes very vascular, first assists the yolk-sac in respira- 
 tion, and then carries it on entirely. It also grows round, and 
 absorbs the albumen (' white '). 
 
 The urinary bladder of the frog is a rudimentary allantois. 
 
 Course of the Embryonic Circulation. The dorsal aorta sends 
 vitelline and allantow arteries from its posterior part to the yolk- 
 sac and allantois respectively. These structures return purified 
 blood to the body by vitelline and allanloic * veins. These unite 
 to form, with a vein from the gut, a trunk, the ductus venosus, 
 which traverses the liver (giving off twigs in its course), and 
 enters the now-developed postcaval. This communicates with 
 the right auricle, and its (mostly) purified blood is directed by 
 the Eustachian valve through the foramen ovalefi an aperture 
 existing at this time in the auricular septum, into the left auricle. 
 Thence it passes into the left ventricle, and so to the dorsal aorta. 
 The right auricle also receives impure blood by the Cuvierian 
 ducts. This passes into the right ventricle, whence, by the pul- 
 monary artery, it reaches the lungs and also, to some extent, the 
 dorsal aorta, by a cross branch, the ductus arteriosus. The lungs, 
 at this time functionless, return impure blood to the left auricle. 
 It will be seen that, in the embryo, the comparatively pure blood 
 of the left ventricle is derived from the right side of the heart. 
 As soon as lung-respiration commences, the foramen ovale closes, 
 
 * = Anterior abdominal vein of Frog. 
 
 t Its position is marked by i\\e fossa ovalis of the adult. 
 
268 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 the system of the ductus venosus becomes the hepatic portal system 
 (that vessel being abolished as a continuous trunk), and the 
 ductus arteriosus is reduced to a fibrous cord (ductus Botalli). 
 
 CHAPTER XIL MAMMALIA. 
 17. LEPUS CUNICULUS (The Eabbit). 
 
 THE wild Rabbit, which is here described, forms the parent- 
 stock from which the different kinds of tame Rabbit have sprung, 
 and which differ from it in no essential points of structure. It 
 is, as everyone knows, a gregarious, burrowing animal, of a 
 brownish colour, which harmonizes with the surroundings when 
 it is out feeding, and so serves as a means of protection (protec- 
 tive general resemblance). The short tail is white on its under- 
 side, and is very conspicuous when the animal is moving, pro- 
 bably serving as a " danger signal.'' 
 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 1. External Characters. The bilaterally symmetrical body is 
 divided into the same regions as in the pigeon i.e., head, neck, 
 trunk, and tail. The fore- and hind-limbs are adapted for 
 quadrupedal progression. Almost all the external surface is 
 covered by hair, but a bare perineal space is present on each side 
 near the root of the tail. 
 
 The elongated head tapers in front into the snout, at the end 
 of which is the mouth, a transverse slit bounded by soft mobile 
 upper and lower lips, the former of which is cleft. The external 
 nares are two oblique slits near the tip of the snout, converging 
 in front to the cleft of the upper lip. Long stiff hairs, the 
 whiskers or vibrissce, are present on the sides of the snout as well 
 as in the neighbourhood of the eyes, which are large, and pro- 
 tected by upper, loiver, and third eyelids. Each of the two first is 
 fringed by a row of stiff eyelashes, while the last is a bare opaque 
 
MAMMALIA. 269 
 
 white membrane, usually folded up in the anterior angle of the 
 eye. The auditory aperture on each side is situated some distance 
 behind the eye, and is guarded by a long backwardly and up- 
 wardly directed flap, the pinna, the base of which is supported by 
 cartilage. 
 
 The pinna varies very much in size and position in tame rabbits, 
 especially in lop-eared varieties. 
 
 The short neck forms a connecting region between head and 
 trunk. 
 
 The trunk is somewhat flattened from side to side. It i& 
 divided into a relatively small thorax in front, bounded by hard 
 parts, and a large soft-walled abdomen behind. There are, in the 
 fei mile, five to six pairs of teats on the ventral surface, belonging 
 to the milk glands (mammary glands). Upon each teat are the 
 small openings of the corresponding gland. 
 
 The intestine and urinogenital organs here open separately to 
 the exterior, the former by a rounded anus situated immediately 
 beneath the tail, and the latter by an urinogenital aperture, placed 
 a, little further forwards, and varying in character according to 
 sex. The space between the anus and urinogenital aperture is 
 known as the perineum, and on each side of this there is a bare, 
 pouch-like depression, the perineal space, upon which is a small 
 papilla bearing the aperture of a perineal gland, to the secretion 
 of which the unpleasant odour of rabbits is due. 
 
 The tail is short, but distinct. 
 
 The fore-limb is divided into upper arm, fore-arm, and hand 
 (brachium, antebracldum, and maims}. The much longer hind-limb 
 is divided into thigh, leg, and foot (femur, cms, and pes). The 
 digits are clawed, five in number in the hand, four in the 
 foot. 
 
 Position of Body. In the standing posture the elbow i& 
 directed backwards, the knee forwards, and the ankle-joint back- 
 wards. Both limbs are disposed in longitudinal vertical planes r 
 and the body is lifted well off the ground. 
 
 2. The thick skin is made up of epidermis and dermis, the hairs- 
 being developments of the former. The mammary and perineal 
 glands belong to the skin, and they are imbedded in the under- 
 lying, subcutaneous, connective tissue, which is everywhere abun- 
 dantly present. Beneath and closely connected with this is a 
 
270 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 thin sheet of striated muscle, the panniculw carnosus, on the 
 ventral side of the neck and trunk. 
 
 Each hair commences (in the embryo) as a thickening of the 
 Malpighian layer of the epidermis projecting towards the dermis 
 (Fig. 83). This hair-germ gradually becomes converted into a 
 hair-fotticle, at the bottom of which is a hair-papilla. A special 
 
 .tfjSlgfttf 
 
 * * * t?Z1*.iif4 
 
 C:jy%? m 
 
 Fig. 83. Six STAGES IN THE DEVELOPMENT OF HAIR (from Haddon, after 
 Wiedersheim). Sc, Hori^y layer; SM, Malpighian layer; (7,. dermis; 
 F, hair-follicle ; Dr, sebaceous glands ; CZ, shaft of hair f PZ, hair 
 sheath; HK, hair germ; P' t hair-papilla; P, commencement of ditto. 
 
 investing sheath is formed by the dermis, which also penetrates 
 into the hair-papilla and vascularises it. The hair, developed 
 from the epidermis of the hair-papilla, exhibits an external firmer 
 cortex, covered by a scaly cuticle, and a softer internal air-con- 
 taining medulla, which, in coloured hairs, is pigmented. Small 
 branched sebaceous glands, secreting an oily substance, open into 
 
MAMMALIA. 271 
 
 the follicle near its mouth, and with it are also connected bands 
 of unstriated muscle, by contraction of which the hair can be 
 erected. The hairs are continually being shed, and are replaced 
 by new ones developed on papillae connected with the old hair- 
 follicles. 
 
 The mammary and perineal glands are made up of tubules, 
 dilated at their ends, and lined by granular epithelium continuous 
 with the epidermis. 
 
 The dermis is rich in blood-vessels, lymphatics, and nerves, arid 
 many nerve-fibres end in elongated ovoid touch-corpuscles. One of 
 these is closely connected with the base of each vibrissa. 
 
 3. The endoskeleton (Figs. 84 and 85) is made up of the usual 
 histological elements. The bones are much more compact than 
 those of the pigeon, and the shafts of the long bones contain 
 marrow.* As in other cases a distinction can be drawn between 
 axial and append icular skeletons, belonging respectively to trunk 
 and limbs. 
 
 (1) The axial endoskeleton consists of skull, vertebral column, 
 ribs, and sternum. 
 
 (a) Skull. As in the pigeon, the mature skull is mostly com- 
 posed of bones, but these are comparatively little fused together, 
 many of the boundaries remaining apparent, even in old animals. 
 They are united, in many cases, by finely jagged edges, which 
 interlock. Such unions are called sutures. 
 
 A small posterior cranial portion may be distinguished from a 
 much larger facial portion, the boundary between the two being 
 indicated by the large orbits. 
 
 It is convenient to consider the cranium or brain-case which 
 constitutes most of the cranial region of the skull, as being made 
 up of three rings (not segments), named from behind forwards 
 occipital, parietal, and frontal. These rings fit closely together, 
 ventrally and dorsally, but certain gaps are left laterally. Each 
 possesses an unpaired ventral element, and the floor of the brain- 
 case is largely formed by these ventral elements, the line along 
 which they are arranged being known as the basi-cmnial axis. 
 
 * 1. Cartilage bones: Ex-, supra-, and basi-occipitals ; basi-, pre-, and 
 orbito-sphenolds ; mesethmoid, periotic, malleus, incus, os orbiculare, stapes, 
 turbinals, palatine, pterygoid, hyoids, Vertebrae, Riba, Sternum, Appendicular 
 endoskeleton (except clavicle). 2. Membrane bones: Interparietal, parietal 
 frontal, squamosal, tympanic, vomer, lachrymal, nasal, premaxilla, maxilla, 
 jugal, mandible, Clavicle. 
 
2 1 "2 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 I. Occipital ring, of four bones, surrounding foramen magnum 
 at back of cranium la si-occipital below, an ex-occipital each side, 
 supra-occipital above. 
 
 II. Parietal ring, of six bones basi-sphenoid below, a small 
 ali-sphenoid each side, two large parietals above. 
 
 III. Frontal ring, of six bones pre-splienoid below, a small 
 orHto-sphenoid each side, two large frontah above. 
 
 I. II. III. 
 
 s. occ. pa. pa. fr. fr. 
 
 ex. occ. ex. occ. al. s. al. s. or. s. or. s. 
 b. occ. b. s. pr. s. 
 
 The cranium narrows anteriorly, and its front end is closed by 
 a median mesethmoid, which continues the direction of the basi- 
 cranial axis into the facial region. Cranial axis + facial axis 
 constitute the cranio-facial axis. The mesethmoid also assists in 
 the formation of the olfactory capsules. 
 
 The auditory capsule is wedged in between the occipital and 
 parietal rings, the lateral gap between which is partly filled by a 
 squcwiotal bone. 
 
 There are two smooth oval occipital condyles, one on each side of the 
 foramen magnum, mainly formed by the corresponding ex-occipitals, but 
 partly by the basi- occipital, which is a small, flat bone. Each ex-occipital 
 is produced downwards into a long par-occipital process, closely applied to 
 the hinder part of the tympanic bulla. The large, irregular supra- occipital 
 is raised into a prominent, shield-shaped elevation. The roof of the brain- 
 case is completed by inter-parietal, parietal, and frontal bones. The inter- 
 parietal is a small, unpaired bone, placed transversely, and partly shutting 
 out the parietals from union with the supra-occipital. These are large, 
 flattish bones, united together by a longitudinal sagittal suture, and with 
 the supra-occipital and inter- parietal by the transverse lamboidal suture. 
 A slender process runs downwards from the outer side of each. The 
 frontals, which cover the front of the rapidly-narrowing brain -case, are 
 united with each other by the median frontal suture, and with the parietals 
 by the transverse coronal suture. Each is very irregular in shape, and 
 possesses parts situated in very different planes. That part roofing the 
 brain-case is broadest behind, and tapers anteriorly, to form with its 
 fellow a sharp point. From the side of this part a plate-like orbital process 
 turns sharply downwards and inwards to form the upper part of the inner 
 orbital wall. Where it turns down, a large overhanging supra-orbital 
 process sticks out, which partly roofs the orbit. A process from the frontal 
 runs into the nasal region. The floor of the brain-case rapidly steepens in 
 front of the basi-occipital, and is formed in the middle line by the basi- 
 and pre-sphenoids, on each side by the ali- and orbito-sphenoids. The 
 basi-sphenoid is a small bone with a broad posterior end separated from the 
 
MAMMALIA. 273 
 
 basi-occipital by a thin plate of cartilage, and a narrow anterior end united 
 by cartilage to the pre-sphenoid. Upon its upper surface is a pit, the 
 stlla turcica (for the pituitary body), bounded behind by the posterior 
 clinoid processes. Firmly fused to each side of the basi-sphenoid is a thin 
 wing-like expansion, the ali-sphenoid, from the under side of which a trans- 
 verse lamella, the external pterygoid process, passes vertically downwards. 
 The pre-sphenoid is a vertical plate, the upper surface of which is produced 
 backwards into the anterior cUnoid processes which bound the sella turcica 
 in front. After limiting the optic joramen below, the pre-sphenoid ends in 
 two diverging lamellae which articulate above with the orbital processes of 
 the frontal, and help to form the inner wall of the orbit. A wing-like 
 orbito- sphenoid is firmly fused with the pre-sphenoid on either side, form- 
 ing the hinder and upper boundaries of the optic foramen, and uniting 
 with the orbital process of the frontal above, and the ali-sphenoid behind. 
 The narrow front end of the brain-case is filled in by the cribriform plate, 
 a lamella perforated by numerous holes and forming the party-wall between 
 the cranial and nasal cavities. It is the hinder part of the mesethmoid. 
 The side- wall of the skull is largely formed in its posterior region by the 
 squamosal, which tills up the gap between parietal and ali-sphenoid, unites 
 in front with the frontal and orbito-sphenoid, and behind overlaps the 
 descending process of the parietal. A delicate backward process from the 
 squamosal helps to keep the large, irregular periotic in place, and a large 
 zygomatic process runs outwards and forwards from it just behind the 
 orbit. 
 
 The auditory capsule is formed by the periotic bone which 
 results from the early fusion of pro-, epi-, and opisthotic elements. 
 
 The outer and hinder mastoid portion of this bone is porous, and a 
 tapering mastoid process runs down from it in front of the par-occipital 
 process. The inner side of the mastoid part presents a deep rounded pit, 
 the floccular fossa, for the flocculus of the cerebellum. The petrous portion 
 which forms the rest of the periotic is very dense, and contains the mem- 
 branous labyrinth. Upon its outer surface there is a smooth projection, the 
 promontory, above which is the elliptical fenestra ovalis, and behind it the 
 more irregular fenestra rotunda. 
 
 Closely applied to the outer surface of the periotic is the 
 tympanic, a bone with a dilated lower part (bulla) and a short 
 part directed upwards and backwards. The inner side of both is 
 incomplete, for which the periotic makes up, forming the inner 
 wall of the tympanic cavity, which is contained in the bulla. The 
 tubular part supports the external auditory meatus, and, at its 
 junction with the bulla, the tympanic membrane is stretched over 
 a flattened rim which projects into the latter. Extending across 
 the tympanic cavity are four minute auditory ossicles. 
 
 (1) The malleus, which possesses two slender processes (one, the man- 
 
 ubrium, attached to the tympanic membrane), which are given off from a 
 
 rounded head. This articulates by a saddle-shaped surface with the 
 
 head of (2) the incus which gives off a small process backwards and a 
 
 2 18 
 
274 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 slender one downwards. The latter is bent up at its tip, and connected by 
 a minute disc (3), the os orbicutare, with (4) the stirrup-shaped stapes, the 
 oval base of which fits into the fenestra ovalis. The Eustachian tube enters 
 the tympanic cavity below and in front by a very short canal, formed by 
 the apposition of a groove in the tympanic to the surface of the periotic. 
 The par-occipital and mastoid processes overlap the tympanic behind, and 
 hold it in place. 
 
 The cavity of the brain-case closely corresponds to the shape 
 of the brain, and is divided into a small olfactory fossa in front, 
 ill-marked off from the large cerebral fossa, which extends back 
 to the anterior limit of the periotics and supra-occipital, where a 
 sharp ridge separates it from the cerebellar fossa. 
 
 NERVE-EXITS. 
 
 I. Olfactory. 
 
 Numerous olfactory 
 
 Cribriform plate. 
 
 
 foramina. 
 
 
 II. Optic. 
 
 Optic foramen. 
 
 A large unpaired aper- 
 
 
 
 ture, bounded by pre- 
 
 
 
 and orbito-sphenoids, 
 
 
 
 which places hinder 
 
 
 
 end of orbits in com- 
 
 
 
 munication with each 
 
 
 
 other and the cranial 
 
 
 
 cavity. 
 
 III. Oculomotor. 
 
 \ 
 
 
 IV. Pathetic. 
 VI. Abducent. 
 V. Trigeminal 
 a. Ophthalmic. 
 
 1 Sphenoidal fissure 
 V (foramen lacerum 
 I anterius). 
 
 Between basi- and ali- 
 sphenoid on either side. 
 
 &. Maxillary. 
 
 J 
 
 
 c. Mandibular. 
 
 Foramen lacerum 
 
 Between ali-sphenoid 
 
 
 medium 
 
 and periotic. 
 
 VII. *YwaZ. 
 
 
 
 Enters periotic by 
 
 Aqueductus Fallopii. 
 
 Just below the floccular 
 
 
 
 fossa. 
 
 Leaves skull by 
 
 Stylomastoid foramen. 
 
 Between mastoid pro- 
 
 
 
 cess and tympanic. 
 
 VIII. Auditory 
 
 
 
 Enters periotic by 
 
 Meatus auditorius 
 internus. 
 
 Just behind aqueductus 
 Fallopii, and sunk in 
 
 
 
 a depression with it. 
 
 IX. Glossopharyngeal 
 
 
 
 X. Vagus. 
 
 Foramen lacerum 
 
 Between periotic and 
 
 XI. Spinal 
 
 posterius. 
 
 ex-occipital. 
 
 Accessory. 
 
 
 
 XII. Hypoglossal 
 
 Condylar foramina (2). 
 
 In ex -occipital, near the 
 
 
 
 condyle. 
 
MAMMALIA. 275 
 
 The facial part of the skull consists of the olfactory capsules 
 and jaws with associated parts. The olfactory capsules are 
 separated from the cranial cavity by the cribriform plate, from 
 which a vertical partition, bony behind (lamina perpendicular is), 
 cartilaginous in front (septum nasi), extends forwards and separates 
 the two capsules. This partition, together with the cribriform 
 plate, constitutes the mesethmoid, and its lower edge rests in a 
 deep furrow on the upper surface of the elongated vomer. 
 
 The posterior wall of each capsule is partly formed by the small lachrymal, 
 which also makes up part of the anterior orbital wall. Its outer side is 
 deeply notched to transmit the lachrymal duct. The capsule is partly 
 roofed in behind by the frontal, but mainly by an elongated flat 'nasal, 
 which, with the premaxilla, largely bounds the external naris. The cap- 
 sular side-wall and floor are principally formed by the premaxilla and 
 maxilla. The nasal cavity contains the ethmo-turbinal behind and above, 
 a bone made up of thin lamellae disposed in a complex manner, which is 
 fused with the cribriform plate, and a similarly constructed but more 
 delicate maxillo-turbinal in front. From the nasal bone a delicate curved 
 fold, the naso-turbinal projects into the cavity. 
 
 The margin of the upper jaw is formed by premaxillce and 
 maxillae. With the latter a zygomatic arch, running along the 
 lower side of the orbit, is connected externally, while internally 
 they come into relation with palatine and pterygoid bones. 
 
 The premaxillce contain sockets for the upper incisor teeth. Each sends 
 an elongated nasal process upwards and backwards along the outer edge of 
 the nasal, a delicate palatine process backwards along the roof of the mouth, 
 and a stout maxillary process backwards and outwards to unite with the 
 maxilla. This is a large, extremely irregular bone that forms the jaw- 
 margin with the premaxilla, a little way behind which bone it dilates to 
 contain the sockets of the grinding teeth, and projects into the front part 
 of the orbit. The maxilla also forms a large part of the side-wall of the 
 nasal capsule, and in this region is very loose in texture. From its external 
 side, above the grinding teeth, a stout zygomatic process projects, which is 
 connected by the laterally flattened jugal with the zygomatic process of the 
 squamosal to make up the zygomatic arch, a bony bar forming the lower 
 boundary of the orbit. A small, horizontal palatine process runs from the 
 inner side of the maxilla, and unites with its fellow in the middle line to 
 form the front part of the bony palate, a transverse bridge of bone between 
 the first four grinding teeth of opposite sides. The inner surface of the 
 maxilla behind this is covered by the palatine, a thin vertical plate uniting 
 above with the orbital process of the pre-sphenoid. The bony palate is 
 completed behind by the horizontal palatine process of this bone which 
 unites with its fellow. The posterior nasal chamber is bounded laterally 
 by the palatines, which are united behind with the downward processes of 
 the ali-sphenoids, and with the pterygoids. Each pterygoid is a small 
 plate, behind, and in the same plane as the palatine. It is produced 
 below into a curved hamular process, and connected above with the junction, 
 between basi- and ali-sphenoids. 
 
276 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The lower jaw or mandible consists of two halves or rami, 
 each of which unites in front with its fellow in the mandibular 
 symphysis, and articulates behind by a longitudinally elongated 
 condyle with the glenoid fossa, a smooth hollow on the under side 
 of the zygomatic process of the squamosal. It is laterally flat- 
 tened and composed of an anterior horizontal part bearing sockets 
 for the lower teeth, and a posterior ascending part ending in the 
 condyle above in front of which is the coronoid process and 
 uniting with the horizontal portion in the rounded angle. 
 
 Hyoid and First Branchial Arches. The proximal end of the 
 hyoid arch is formed by the stapes. The "hyoid apparatus" 
 consists of a small lasi-liyal imbedded in the root of the tongue, 
 and with which are connected short anterior and long posterior 
 cornua. The anterior cornua represent the hyoid arches of the 
 embryo, and are connected by ligaments with the skull, close to 
 the mastoid processes. In this region a small part of the hyoid 
 arch (tympanohijal) is fused to the skull. The posterior cornua 
 represent the first branchial arches. 
 
 Fig. -64. ENDOSKELETOX OF RABBIT. A, Skull (jugal bone removed) ; 
 s-oc, supra-occipital ; ex-oc, ex-occipital ; c, condyle ; par, par- 
 occipital process ; s-m.f, stylo -mastoid foramen ; ty, tympanic ; per, 
 periotic ; i-p, inter-parietal ; pa, parietal ; a-s, ali-sphenoid ; sq, squa- 
 mosal ; z.s, zygomatic process of squamosal ; pt, pterygoid ; fr, frontal ; 
 or.s, orbito-sphenoid ; pr-s, pre-sphenoid ; pi, palatine; mx, maxilla; 
 , zygomatic process of ditto (with cut end); p-mx, pre-maxilla ; la, 
 lachrymal ; na, nasal ; op-f, optic foramen ; x placed at junction of 
 basi- and pre-sphenoid. A', Outside of periotic, after removal of 
 tympanic; ma, mastoid portion; m.pr, mastoid process; pr, promon- 
 tory ; f.ov, fenestra ovalis ; f.ro, fenestra rotunda. A", Auditory 
 ossicles from inside ; rn, malleus ; i, incus ; st, stapes. B, Mandible ; 
 c, condyle ; a, angle ; c.pr, coronoid process. C, Hyoid apparatus ; b, 
 body ; a.c, anterior cornu ; p.c, posterior cornu. D, Various vertebrae ; 
 1, atlas (front view); 2, axis ; 3, typical cervical (front view) ; 4, typi- 
 cal lumbar ; c, centrum ; n. s, neural spine ; t. transverse process ; a.f, 
 (in atlas), articular facet for coudyle ; a.z, prezygapophysis ; p.z, post- 
 zygapophysis ; n.c, neural canal ; v.c, vertebrarterial canal ; o.p, odon- 
 toid peg; i.l, cervical rib; ep, epiphysis ; mt, metapophysis ; an, ana- 
 pophysis. E, Hip-girdles and Sacrum. 1, 2, 3, Sacral vertebrae ; s.r, 
 sacral rib ; il, ilium ; pb, pubis ; is, ischium (reference letter placed in 
 obturator foramen) ; ac, acetabulum. F, Right tarsus ; as, astragalus ; 
 ca, calcaneum; en, centrale ; t, 1-5, tarsalia; 2-5, metatarsals ; *, 
 placed by process of met. 2, representing hallux. G, Left Scapula 
 s-sc.b, co.b, gl.b, supra-scapular, coracoid, and glenoid borders; sp, spine; 
 ac, acromion ; mtc, metacromion ; co, coracoid process ; gl, glenoid 
 cavity. H, Left Carpus r, Radiale ; i, intermedium ; w, ulnare ; en, 
 centrale; c, 1-5, carpalia ; 1-5, metacarpals. 
 
MAMMALIA. 
 
 277 
 
 /to 
 
 i -ft 
 
278 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Skull Of the Dog. This agrees in all essential matters with the rabbit's 
 skull, but there are differences in general shape and also in certain details. 
 Most of these variations are correlated with the larger development of the 
 jaw-muscles, as may be seen, for instance, in the presence of strong ridges 
 on the brain-case and the width of the zygomatic arches. The skull is much 
 stronger, and the face is in line with the cranium, whereas in the rabbit it 
 is bent slightly downwards. The spongy areas present in the skull of the 
 rabbit (especially on the outer side of the maxilla) are absent in the dog. 
 Other differences are the following: (1) Cranium. Plane of occipital 
 region vertical, instead of slanting somewhat downwards ; interparietal 
 represented by a process of supra-occipital. (2) Olfactory capsules. Naso- 
 turbinal represented by uppermost lamella of ethmo-turbinal. (3) Bony 
 palate very large and long. (4) Mandible, with short ascending part, well- 
 marked angle, large coronoid, and transverse condyle, articulating with 
 glenoid fossa to form a well-marked hinge-joint. All these last features 
 are connected with the great size of the muscles used in biting. The hinge- 
 joint only allows of snapping movements, giving no lateral play. (5) Nerve- 
 exits. The 2nd and 3rd branches of the trigeminal exit by special openings, 
 foramen rotundum and foramen ovale, situated one behind the other in the 
 ali-sphenoid, between the sphenoidal fissure and the foramen lacerum 
 medium. (6) Teeth, see p. 285. 
 
 (b) Vertebral Column and Ribs (Fig. 84). The vertebral 
 column is divisible into cervical, thoracic, lumbar, sacral, and 
 caudal regions, corresponding to neck, thorax, loins, pelvis, and 
 tail. Except in the sacral region the vertebrae remain distinct 
 from one another, and the more or less flat ends of the centra 
 are connected together by cartilaginous discs, intervertebra3, 
 which come between them. The front and back of each centrum 
 ossify independently as thin bony plates, epiphyses, which fuse 
 later on with the middle part. The spinal nerves exit as in the 
 other types by intervertebral foramina between adjoining arches, 
 and neural spines and zygapophyses of the usual kind are present. 
 
 The cervical vertebrae are seven in number. Their centra are 
 short, and their neural spines small. The cervical ribs are not 
 free but fused, as in most of the pigeon's cervical vertebrae 
 (cf. p. 237). The apparent transverse processes are thus perforated 
 at their bases to form the vertebrarterial canal, and are divided 
 into two parts, the upper of which is true transverse process, the 
 lower (inferior lamina} the projecting part of the fused rib. 
 
 The atlas or first cervical vertebra is ring-like, possesses large 
 transverse processes (but no inferior laminae), and a thin narrow 
 centrum. It presents in front two large oval articular surfaces 
 for the occipital condyles, and behind two smaller concavities for 
 the axis, but there are no true zygapophyses. 
 
MAMMALIA. 279 
 
 The axis or second cervical vertebra has an odontoid peg (which 
 ossifies separately), projecting forwards above the centrum of the 
 atlas. 
 
 A convex articular surface is present on the under side of the peg, which 
 plays upon a corresponding surface on the upper side of the atlas-centrum, 
 and there are also two large convexities on its base which fit into the two 
 shallow cups on the hind end of the atlas. The neural spine of the axis is 
 a prominent ridge which bifurcates behind. 
 
 The last (seventh) cervical vertebra has a half-facet on the 
 side of the centrum, at its hinder end. 
 
 The thoracic vertebrae are 12 (or 13) in number, and are 
 characterized by the possession of free thoracic ribs. 
 
 They increase in size from before backwards, their centra, which are 
 thick from above downwards, elongating. The neural spines of the first 9 
 are slender and backwardly directed, that of the tenth is vertical, and those 
 of the remainder slope forwards like the lumbar spines. From the ninth 
 backwards metapophyses appear, stout processes directed upwards and for- 
 wards in the region of the pre-zygapophyses. The transverse processes of 
 the first 9 possess tubercular facets on the under side of their tips, and 
 capitular half-facets on the sides of their centra, one in front, the other 
 behind. The last 3 (or 4) have entire capitular facets on the sides of their 
 centra, situated near the front. 
 
 The ribs are curved flattened rods, increasing in length up to 
 the sixth, and then shortening. Each consists of a bony vertebral 
 portion, possessing two articular processes (tubercle and capitulum), 
 and a much shorter sternal part of more or less ossified cartilage. 
 
 The tubercles of the ribs articulate with the tubercular facets, and the 
 capitulum of each of the first 9 articulates with a capitular facet, formed in 
 part by the anterior half-facet of its own vertebra, in part by the posterior 
 half-facet of the preceding vertebra (the seventh cervical in the case of the 
 first rib). The last 3 (or 4) possess no tubercles, and their capitula arti- 
 culate with the corresponding facets on their own vertebra. The sternal 
 parts of the first 7 ribs unite distally with the sternum ; those of the remain- 
 ing ones do not. This is the distinction between " true " and " false " ribs. 
 
 The lumbar vertebras are 7 (or 6) in number. They are large, 
 with elongated centra, laterally flattened neural spines, directed 
 forwards, and strong elongated transverse processes running down- 
 wards and forwards. 
 
 They also possess large metapophyses, stout processes overhanging the 
 pre-zygapophyses, and small anapophyses, backwardly directed processes 
 given oft below the post-zygapophyses. The first two also have hypapo- 
 physes, unpaired processes running downwards from the under side of the 
 centra. 
 
280 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The sacral vertebrae are 4 in number, closely fused together. 
 The two first possess sacral ribs, which form lateral wing-like 
 expansions, articulating with the inner sides of the ilia. 
 
 The caudal vertebrae, about 1 5 in number, gradually get smaller 
 towards the end of the tail, losing first their processes, and then 
 their neural arches. 
 
 (c) The sternum is a narrow rod, made up of six laterally com- 
 pressed segments or sternelm, and placed in the mid-ventral line 
 of the thorax. The first segment (manubrium) is much larger 
 than the others, and possesses a prominent ventral ridge. It is 
 composed of two segments completely fused together, and this is 
 indicated in the adult by the attachment of the first sternal ribs 
 to the middle of its length. The remaining six pairs of sternal 
 ribs are connected with the junctions of the sternebrae, one pair 
 each to the first four, and two pairs to the last. The hindmost 
 sternebra is elongated, slender, and terminated by a rounded plate 
 of cartilage, with which it forms the xiphisternum. 
 
 (2) Appendicular Endoskeleton. The long bones are terminated 
 as usual by epiphyses. As in other cases the skeleton of fore- or 
 hind-limb is divisible into girdle and free part. 
 
 (a) Fore-limb (Fig. 84). The shoulder girdle is mainly composed 
 of the triangular scapula, placed external to the anterior ribs, 
 where it is held in place by muscles and ligaments. Its enlarged 
 apex presents a shallow glenoid cavity for the head of the humerus. 
 The base, anterior, and posterior sides of the triangle are termed 
 supra-scapular, coracoid, and glenoid borders respectively. With the 
 first a strip of cartilage, the supra-scapula, is connected. A con- 
 spicuous ridge, the spine, runs along the outer surface of the 
 scapula, and is produced below into a freely projecting process, 
 the acromion (ac), from which a more slender metacromion is 
 given off behind. The coracoid border is continued below into a 
 hook-like coracoid. process. This is originally distinct, and repre- 
 sents the coracoid bone of lower Vertebrates. A ligament, in 
 the centre of which is a slender curved clavicle, runs from the 
 tip of the manubrium to the acromion. To the sternal end of 
 this ligament a minute nodule of cartilage is attached which 
 represents a precoracoid. 
 
 Free Limb. The humerus presents a proximal head, on its 
 upper (dorsal) surface, for articulation with the glenoid cavity, 
 and a distal pulley-like trochlea, which assists to form the elbow- 
 
MAMMALIA. 281 
 
 joint. The radius and ulna, which support the antebrachium, 
 are immovably articulated, but not fused together in the position 
 
 of pronation. 
 
 Where, as in Man, the radius and ulna are movable, they may assume 
 two main positions: () Supijiation, when they are parallel, the palm of 
 the hand is upwards, and the thumb outside (like the radius), (b) Prona- 
 tion, when the radius crosses over the ulna towards the inside, the palm of 
 the hand is downwards, and the thumb inside (like the distal end of the 
 radius). 
 
 The preaxial radius possesses a proximal head for articulation 
 with the trochlea, and two distal concavities for the carpal bones. 
 The postaxial ulna has a proximal sigmoid cavity for articulation 
 with the trochlea, and a convex distal end. Proximally the ulna 
 is produced into the olecranon, a process which, in the extended 
 limb, fits into the olecranon fossa, a pit situated above the trochlea. 
 
 The carpus consists of a proximal and a distal row of small 
 bones, and a diminutive centrale. The proximo! row is made up 
 of four bones, which are (beginning on the inner (preaxial) side) 
 (a) radiale (scaphoid), and (/3) intermedium (lunar), articulating 
 with the concavities on the radius, (y) ulnare (cuneiform), and 
 (S) pisiform (not shown), articulating with the convexity on the 
 ulna. The distal row is made up of four carpalia, which are, 
 beginning as before, carpale 1 (trapezium), carpale 2 (trapezoid), 
 carpale 3 (magnum), carpale 4 -f- carpale 5 (unciform). Five 
 digits are present supported by five metacarpals, articulating 
 with the corresponding carpalia, and completed by phalanges, 
 of which the short pollex (1st digit) possesses 2, the others 
 3 each. The terminal phalanges are conical, and grooved to 
 support the claws. 
 
 (b) Hind-limb. The hip-girdle is formed by an innominate bone 
 on each side, made up of four fused bones, ilium, ischium, pubis, 
 and cotyloid. Upon the outer side of each innominate is a deep 
 cup, the acetabulum, the floor of which is complete, and in the 
 young rabbit, marked by the three-rayed junction of the ilium, 
 ischium, and cotyloid. 
 
 The ilium is placed above and in front. It is laterally flat- 
 tened, and the sacrum articulates with its inner surface. The 
 ischium is placed above and behind. It is separated from the 
 pubis by the oval obturator foramen, and presents posteriorly a 
 rough and thickened tuberosity. A plate-like expansion runs 
 
282 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 from its hinder part towards the mid-ventral line, and unites 
 there with its fellow to form the posterior portion of the ischio- 
 pubic symphysis. 
 
 The cotyloid is a very small bone helping to form the ventral 
 side of the acetabulum, from which it shuts out the pubis. 
 
 The small pubis runs from the cotyloid bone towards the 
 mid-ventral line, and unites with its fellow to form the anterior 
 part of the ischio-pubic symphysis. 
 
 Free Limb. The elongated femur presents a proximal head 
 upon its inner (preaxial) side, which articulates with the aceta- 
 bulum, and two distal condyles which articulate with the tibia to 
 form the knee-joint. The actual proximal end of the femur is a 
 large projection known as the great trochanter. There is* a lesser 
 trochanter below the head, and opposite this on the outer (post- 
 axial) side a third trochanter. 
 
 A large patella is present on the front of the knee-joint, at 
 the back of which are two other sesamoid bones, the fabellae. 
 
 The cms is supported by the large preaxial tibia, which pos- 
 sesses two proximal concavities for the femur, and two distal 
 surfaces for the tarsus. With the tibia a small, postaxial, rod- 
 like fibula, is completely fused distally. 
 
 The ankle-joint in the rabbit is between the distal ends of the 
 above bones and the tarsus. 
 
 The tarsus is made up of proximal and distal rows partly 
 separated by a large centrale (navicular). 
 
 The proximal row contains two bones, the preaxial (a) tibialo- 
 intermedium (astragalus), and postaxial (/3) fibulare (calcaneum) 
 produced into a large projecting heel. The distal row is com- 
 posed of three bones, which are, beginning preaxially, (a) tarsale 2 
 (mesocuneiform), (j3) tarsale 3 (ectocuneiform), and (y) tarsale 
 4 -f tarsale 5 (cuboid). 
 
 There are four digits, the first or hallux being absent. Each 
 possesses a metatarsal, the first of which is produced proximally 
 into a process, originally separate, which may represent the miss- 
 ing hallux. Each digit is completed by three phalanges, similar 
 to those of the manus. 
 
 Small nodular sesamoid bones are developed in the tendons, opposite the 
 joints on the under (ventral) side of manus and pes. 
 
 4. The digestive organs (Fig. 85) consist of an alimentary 
 
MAMMALIA. 
 
 283 
 
 canal (mouth-cavity, pharynx, gullet, stomach, intestine) with 
 appended glands (salivary glands, liver, pancreas, and rectal 
 glands). They begin in the head and thorax, but are contained, 
 
 Fig. 85. GENERAL DISSECTION OF HEAD AND THORAX OF RABBIT 
 (reduced). a, Atlas; ax, axis; 1 to 11, placed on centra of thoracic 
 vertebrae ; b-o, basi-occipital ; pt, is placed on basi-sphenoid, and 2, on 
 pre-sphenoid ; l.p, lamina perpendicularis ; e-t, ethmo-turbinal, and 
 m-t, maxillo-turbinal, of right nasal cavity, the turbinal bones of left 
 cavity having been removed and the septum nasi cut through ; p-mx, 
 pre-maxilla ; b.p, bony palate ; x-st, xiphisternum ; d,d,d, diaphragm ; 
 '/, incisors ; t, tongue ; p.f, papilla foliata, above which is seen a circum- 
 vallate papilla ; * placed just below tonsil ; ph, pharynx ; p.n, internal 
 nares, the opening of p.n.c, the posterior nasal chamber, which is 
 mostly floored by soft palate the letter n is placed just under 
 Eustachian opening ; (?, oesophagus ; La, left auricle ; l.v and r.v, 
 left and right ventricles ; pr-c, left pre-caval ; e.ju, right external 
 jugular, formed in front by union of facial veins, and running back to 
 help to form right pre-caval ; p-c, post caval ; ao, arch of aorta left 
 common carotid is seen running forwards along trachea (tr is placed 
 just above it) ; s-d, left subclavian artery ; ao', dorsal aorta ; pa and 
 pv, pulmonary artery and veins left lung has been removed ; ep, 
 epiglottis ; x , placed on vocal chord ; tr, trachea ; a little way behind 
 ao, opening of right bronchus, end of trachea, and left bronchus cut 
 open, are seen ; (fj, Ig, If], Ig, lobes of right lung ; ol, olfactory lobe, 
 below which is cribriform plate ; c.h, cerebral hemisphere ; s.v, LI, 
 and/, superior vermis, lateral lobe, and flocculus of cerebellum ; m.o, 
 medulla oblongata-in front of these letters are the roots of the eighth, 
 seventh, and fifth cranial nerves ; op, optic nerve ; sp, spinal cord. 
 
284 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 for the most part, in the abdominal cavity, which is separated 
 from the thoracic cavity by a firm partition, the diaphragm^ and 
 lined by the thin peritoneum, which forms suspensory mesenteric 
 folds for the viscera. 
 
 The small mouth, guarded by flexible lips, leads into a large 
 mouth-cavity, the roof of which is elongated, and presents a 
 central part, the palate, bounded by the margin of the upper jaw. 
 The anterior half of the palate, marked by firm transverse ridges, 
 and the soft flexible posterior half, are called respectively hard 
 and soft palates. The latter ends in a free notched edge, on each 
 side of which is a small thickening, the tonsil, indented by a pit. 
 The floor of the mouth, bounded by the margins of the mandible, 
 has the long muscular tongue attached to the greater part of its 
 extent. This exhibits in front a free tip, in the neighbourhood 
 of which are numerous small papillce that also extend back some 
 distance on the upper surface. There is a hard elongated area 
 above and behind, and, on each side of the posterior end of this, 
 a circumvallate papilla, consisting of a small projection encircled 
 by a groove. An oval elevation, the papilla foliata, across which 
 numerous oblique ridges run, is present on each side of the tongue. 
 The hair covering the body is continued into the sides of the 
 mouth-cavity for a short distance.. 
 
 The teeth, definite in number, are imbedded in sockets, or 
 alveoli, and are of three kinds. There are two sets of them, the 
 first, milk teeth, very transitory, and succeeded by permanent teeth, 
 which continue to grow throughout life as they are worn away 
 at their ends. This is called growth from " permanent pulps." 
 The front of the jaws is occupied by cutting teeth (incisors) ; the 
 remainder are grinding teeth (premolars and molars) placed a 
 good deal further back. 
 
 In the front of the upper jaw two strongly curved incisors are found, 
 grooved in front, and with chisel-shaped edges. Two very small incisors 
 of similar shape are placed behind them. All the upper incisors are 
 imbedded in the pre-maxillse. Next follows a gap destitute of teeth 
 (diastema) on each side, posterior -fcc- which are six prismatic grinding 
 teeth, imbedded in the maxilla. The first three, premolars, are preceded 
 by milk-grinders, the last three, molars, have no predecessors. The 
 grinding teeth are much flattened, and, with the exception of the first 
 and last, which are small, each possesses a deep groove on its outside, 
 from the end of which a transverse ridge runs nearly across the flattish 
 grinding surface or crown. 
 
 Two incisors similar to the large upper ones, but less curved and not 
 
MAMMALIA. 285 
 
 grooved, are imbedded in the front of the mandible. Then comes a 
 diastema 011 either side, succeeded by five grinding teeth, of which two 
 are premolarx, and three molar*. They are similar to the upper grinders, 
 but, except the last, more strongly ridged, and grooved internally as well 
 as externally. 
 
 In many animals four pointed canine teeth are present, two above, 
 immediately behind the pre-maxillo-maxillary suture, and two below. 
 There is no trace of these in the Rabbit. 
 
 It is convenient to express the number and kind of teeth by 
 a dental formula. Each kind is indicated by a fraction (preceded 
 by its initial letter), in which the numerator and denominator 
 signify upper and lower teeth, those of opposite sides being 
 separated by dashes. Thus the Rabbit's dental formula is : 
 
 . _ 2 2 _0-0 _3-3 _ 3 3 _ 9 
 
 ~ 1 - 1 ~ - P ' m ' ~ 2~~^~2 m ' ~ 3^-~3 ~ 
 
 Those before the vertical line have predecessors in the milk- 
 dentition. As, however, the teeth of one side only need be ex- 
 pressed, those of the other exactly corresponding, and the kinds 
 are easily remembered, the formula may be simplified to : 
 
 2033 
 1023' 
 
 Two rudimentary incisors have been found in the front of each jaw, 
 which are probably persistent members of the milk dentition. They are 
 not included in the above formulae. 
 
 3 1 42 
 
 The dental formula of the dog is 7777777 The canines are strong, pointed 
 
 teeth, adapted for holding prey. All the premolars and the first lower 
 molars have sharp cutting crowns, which are very large in the last upper 
 premolars and first lower molars. These are known as carnassial teeth, 
 and work against one another like the blades of a pair of scissors. The 
 upper molars and last two lower molars have grinding crowns. 
 
 All the teeth have continuous coveriug of enamel in their crowns, and 
 taper below into pointed " fangs. " They do not continue to grow through- 
 out life as in the rabbit. 
 
 The soft palate hangs down behind, and imperfectly separates 
 the mouth-cavity from the pharynx, a small chamber which 
 passes back into the gullet An unpaired oval opening, the 
 internal naris, opens into it in front, and on its floor, at the root 
 of the tongue, is the glottis, guarded in front by a thin flexible 
 flap, the epiglottis, supported by cartilage. The gullet (oesophagus) 
 is a narrow thick-walled tube, which runs from the pharynx 
 through the neck and thorax, just ventral to the backbone, 
 
286 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 pierces the diaphragm, and enters the stomach, a large trans- 
 versely placed sac, with firm thick walls. 
 
 Its left (cardiac) portion is much dilated, while its right (pyloric) portion 
 is thickened. Posteriorly it presents a convex margin, the greater curva- 
 ture, and anteriorly a concave margin, the lesser curvature, to the left of 
 which is the cardia, or opening of the gullet. The pylorus where the 
 duodenum commences, is at the extreme right of the pyloric end. The 
 mucous membrane lining the stomach is raised into irregular longitudinal 
 ridges, or rugce. Between stomach and duodenum there is an inwardly 
 projecting rim, the pyloric valve. 
 
 The stomach is succeeded by a much convoluted intestine, some 
 15 or 16 times the length of the body, and divided into small 
 and large. The first part of the thin-walled small intestine,* 
 the duodenum, forms a longitudinally directed U-shaped loop 
 nearly the length of the abdominal cavity. It passes insensibly 
 into the much longer ileujti, in the wall of which there are oval 
 thickenings, Peyer's patches, here and there. 
 
 This part of the intestine finally opens into the crecum (see below], and 
 at this point its wall is much thickened to form the sacculus rotundus* 
 The mucous membrane of the small intestine is raised into numerous 
 irregular transverse ridges, the valvulce connivences, from which project an 
 immense number of villi. 
 
 The large intestine is divided into caecum, colon, and rectum. 
 The caecum is a very large thin-walled sac, nearly 2 feet in length, 
 interposed between the ileum and colon. Its wall is marked 
 externally by a spiral groove. One end, near which the ileum 
 opens, is continuous with the colon, while the other terminates- 
 blindly in a thick-walled finger-like vermiform appendix. 
 
 A spiral fold, corresponding to the external groove, projects into the 
 cavity of the caecum, with which cavity the sacculus rotundus com- 
 municates by a small rounded aperture (ileo-colic valve), and which opens, 
 by a larger aperture into the colon. The lining mucous membrane is raised 
 into minute elevations ; in other words, is papillose. 
 
 The colon is a moderate-sized thin-walled tube with baggy 
 walls, along which three smooth longitudinal bands run. It 
 passes insensibly into the narrow rectum, which, after some con- 
 volutions, runs back within the pelvic cavity, below the backbone, 
 and above the urinogenital organs, to the anus. The mucous 
 membrane lining the colon is papillose, that lining the rectum 
 
 * In human anatomy this is divided, somewhat arbitrarily, into three 
 parts duodenum, jejunum, and ileum. The two last are here included in* 
 the term " ileum." 
 
MAMMALIA. 287 
 
 is smooth at first, but raised into prominent longitudinal ridges 
 near the end. 
 
 The following large glands are connected with the alimentary 
 canal salivary glands, liver, pancreas, and rectal glands. 
 
 Four pairs of salivary glands open into the mouth-cavity, 
 parotid, submaxillary, sublingual, and infra-orbital. 
 
 (1) The parotid glands are irregular pinkish masses, extending, on each 
 side, from the origin of the pinna to the higher end of the mandible. From 
 each a delicate (Stenson's) duct runs forwards just below the skin, turns 
 inwards, and opens into the side of the mouth-cavity opposite the last 
 upper molar. (2) The sub-maxillary glands are oval and compact bodies, 
 of reddish colour, lying near together between the rami of the mandible, 
 in front of the larynx. A delicate (Wharton's) duct runs from the outer 
 side of each to the floor of the mouth, in front of the tongue. (3) The small 
 red sub-lingual glands are elongated and flat. They lie in front of and 
 above the sub-maxillary glands among the muscles of the tongue. (4) The 
 infra-orbital glands are irregular and lobulated. They lie, one on each side 
 in front of and below the eye, partly within the orbit. A duct runs down- 
 wards from each and opens into the side of the mouth-cavity, opposite the 
 last upper premolar. 
 
 The liver is a very large reddish-brown organ, closely applied 
 to the concave abdominal side of the diaphragm in front, and 
 largely overlapping the stomach behind. 
 
 Right and left halves may be distinguished in the liver. The former is 
 divided into two lobes, right central, and caudate, hollowed out for, and 
 abutting against, the right kidney. The left half is divided into three lobes, 
 left central, left lateral, and the very small Spigelian, fitting into the an- 
 terior concavity of the stomach. A pear-shaped, thin-walled gall-bladder 
 lies in a slit on the posterior surface of the right central lobe. From it a 
 short cystic duct opens into the bile-duct, a small tube formed by the union 
 of hepatic ducts from the various liver-lobes, and opening into the duodenum 
 a little way beyond the pylorus. 
 
 The pancreas is not compact as -in the frog and pigeon, but 
 diffuse i.e., made up of numerous scattered lobules. These 
 resemble small masses of fat, and are found in the mesentery 
 between the limbs of the U formed by the duodenum. Delicate 
 ducts proceed from the various lobules, and by their successive 
 unions the pancreatic duct is formed, which opens into the distal 
 limb of the duodenum, about 3 inches from the bend. 
 
 The rectal glands are two compact elongated bodies lying 
 alongside and above the rectum near its termination, and opening 
 into it. 
 
 The alimentary canal is lined as usual by mucous membrane. 
 
'288 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 external to which are submucous and muscular coats, and, in the 
 abdominal organs, there is a thin serous layer outside all. 
 
 The muCOUS membrane consists of epithelium internally, which, as far 
 as the stomach, is stratified squamous, but in that organ and the intestines, 
 simple columnar. Goblet cells are everywhere common, peptic glands are 
 found in the stomach, and ylands of Lieberkiihn throughout the intestines. 
 Each peptic gland opens on the surface of the stomach by a narrow neck, 
 lined with columnar epithelium. It branches at its deep end, and the 
 branches are lined by granular cuboid chief cells, among which are scattered 
 (in the glands of the cardiac end) a much smaller number of ovoid cells. 
 Beneath the epithelium is a layer of connective tissue surrounding the 
 glands, and the external limit of the mucous membrane is marked (in the 
 stomach and intestines) by a very thin sheet of unstriated muscle, the 
 muscularis mucosce. 
 
 The SUbmUCOUS COat is made up of loose connective tissue, traversed 
 by vessels and nerves. 
 
 The muscular COat varies very much in thickness, attaining its maxi- 
 mum in the stomach. It consists of an inner circular and an outer longi- 
 tudinal layer in the gullet and succeeding parts. The fibres are striated in 
 the gullet and pharynx, and the tongue is mainly composed of such fibres ; 
 but the muscle in the walls of the stomach and intestines is made up of 
 unstriated fibres. 
 
 The salivary glands and pancreas consist of a number of lobules 
 united together by connective tissue. Each lobule is composed 
 of numerous acini, blindly ending tubes lined by glandular epi- 
 thelium, from each of which a duct, lined by simple columnar 
 epithelium, proceeds. These ducts unite again and again to 
 form the main duct of the gland. The preceding type of 
 structure is termed racemose. 
 
 The liver, as in the frog and pigeon, is mainly made up of 
 polyhedral, granular, hepatic cells (Fig. 86), placed in the meshes 
 of the network formed by the bile-capillaries, from which the 
 hepatic ducts arise. The hepatic cells are aggregated into small 
 lobules, around each of which is an interlobular capillary network 
 formed by the ultimate branches of the portal vein. From this 
 network veinlets pass into the centre of the lobule, and there 
 unite into a small intralobular vein which carries away its blood. 
 By the union of these small vessels sublobular veins are formed, 
 which are the factors of the hepatic veins. 
 
 The food consists of vegetable substances, and the great length 
 of the alimentary canal is correlated with this, an immense 
 absorptive surface, largely augmented by the caecum with its 
 spiral valve, being given. 
 
 The food is divided by the incisor teeth, and ground up by 
 
MAMMALIA. 
 
 289 
 
 the molars and premolars. The hard tongue, working against 
 the ridged palate, assists in this process of mastication. Saliva 
 is poured by the salivary glands into the mouth-cavity, and not 
 only lubricates the food, but also, in virtue of a ferment, ptyalin, 
 which it contains, converts more or less of the starch into soluble 
 grape-sugar. The gastric juice, bile, and pancreatic juice act as in 
 preceding cases (p. 194). 
 
 5. Circulatory Organs. Well developed blood and lymph systems 
 are present. 
 
 (1) Blood System. The blood consists of liquid plasma, in 
 which are suspended colourless corpuscles of the usual type, and 
 
 Bile-capillary. Nucleus of a liver-cell. 
 
 Bile- capillary divided. Bile-capillary. 
 
 Fig. 86. HISTOLOGY OF RABBIT'S LIVER (after Hering). Relation of 
 liver-cells, bile-capillaries, and blood-capillaries. 
 
 a much larger number of smaller red corpuscles, which are bicon- 
 cave, non-nucleated discs. The blood-containing tubes comprise 
 heart, arteries, veins, and capillaries. 
 
 The conical heart (Fig. 85) enclosed in its pericardium, lies 
 between the lungs on the ventral side of the thoracic cavity, with 
 its apex directed backwards. It contains four chambers, two 
 thin-walled auricles, and two thick-walled ventricles. 
 
 The broad base of the heart is chiefly made up of the dark, thin-walled 
 right and left auricles, to each of which is attached a plaited fold, the 
 auricular appendix, while the rest of the heart is made up by the firm 
 2 19 
 
290 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 right and left ventricles. The internal structure of the heart is in most 
 particulars like that of the pigeon (p. 245), but the right auriculo- 
 ventricular valve is not muscular but made up of three membranous flaps 
 (giving the name tricuspid valve), connected by chord* tendinew with 
 papillary muscles in the right ventricle. These muscles are also found in 
 the left ventricle, and are more numerous than is the case in the pigeon. 
 The opening of the postcaval is guarded by a fold, the Eustachian valve, 
 and that of the left precaval by a similar Thtbesian valve. 
 
 Arteries. The aorta takes origin from the left ventricle, and 
 its arch curves round to the left to form the dorsal aorta, giving 
 off vessels which supply head, neck, and fore-limbs. The dorsal 
 aorta runs back ventral to the backbone, supplying the trunk 
 with its contained viscera, and finally forks into two iliac arteries, 
 which supply adjacent parts and continuations of which run into 
 the hind-limbs. 
 
 The aorta dilates at its origin into the 3 sinuses of Valsalva, situated 
 behind the pouches of the semilunar valves. Two coronary arteries, for 
 the supply of the heart-walls, are given off here. Near the beginning of the 
 arch a short innominate artery runs off, which at once gives off the left 
 carotid, and soon after divides into right subclavian and right carotid 
 arteries. The left subclavian arises from the left side of the arch. Each 
 carotid runs forwards on one side of the trachea, giving off branches to the 
 neck as it does so, and divides in front into internal carotid for the brain, 
 and external carotid for the outside of the head. The subclavian arteries 
 supply the fore-limbs, on entering which they become the brachial arteries. 
 A vertebral artery runs doraalwards from each subclavian near its com- 
 mencement, and enters the vertebrarterial canal to supply the brain and 
 spinal cord. 
 
 The dorsal aorta gives off in the thorax small paired intercostal arteries 
 to the thoracic walls. In the abdomen a large unpaired cwliac artery 
 takes origin a little way behind the diaphragm, and quickly divides into 
 the hepatic artery for the liver, and lieno-gastric artery for the spleen and 
 stomach. Another unpaired artery, the anterior mesenteric, for the small 
 intestine, pancreas, caecum, and colon, arises a short distance posterior to 
 the coeliac. Paired renal and spermatic (or ovarian) arteries are next given 
 off to the kidneys and spermaries (or ovaries), and still further back a small 
 unpaired posterior mesenteric artery to the rectum. The dorsal aorta 
 bifurcates at the posterior end of the abdominal cavity into the iliac 
 arteries, each of which, after giving off an ilio-lumbar artery to the body- 
 wall, divides into an internal iliac artery for the pelvic region and an 
 external iliac artery, which, after giving off a branch that supplies the 
 bladder (and uterus in the female), enters the thigh as the femoral artery 
 for the hind-limb. 
 
 Shortly before the aorta bifurcates, it gives off from its upper surface a 
 small median sacral artery, which runs back into the tail. 
 
 The pulmonary artery arises from a forward prolongation of 
 the right ventricle on the ventral side, and, curving round the 
 
MAMMALIA. 291 
 
 front of the heart, divides into right and left branches for the 
 corresponding lungs. 
 
 Veins. Caval, hepatic portal, and pulmonary systems can be 
 distinguished. 
 
 (a) Caval System. Right and left precavals (anterior venae 
 cavse) and a postcaval (posterior vena cava) carry the impure 
 blood from the general system into the right auricle. The 
 precavals drain the head, neck, and fore-limbs, the postcaval the 
 rest of the body. 
 
 Each precaval is formed by the union of an external jugular, with a 
 subdaviaii vein. The former runs back along the side of the neck from the 
 angle of the jaw, where it is formed by the union of facial veins returning 
 blood from the outside of the head. Just before uniting with the sub- 
 clavian it receives the small internal jugular vein from the brain. The 
 subclavian vein brings back blood from the fore-limb. The right precaval 
 is joined by an unpaired azygos vein, which lies just beneath the vertebral 
 column in the thorax, and carries off blood from a large part of its walls. 
 The left precaval receives a coronary vein from the heart-walls, just before 
 entering the right auricle. 
 
 The postcaval is a very large vein formed at the posterior end of the 
 abdomen by the union of the internal iliac veins from the backs of the 
 thighs. It is joined almost at once by the external iliac veins, which return 
 blood from the hind-limbs and bladder (also uterus in the female). They 
 are direct continuations of the femoral veins of the thighs. The postcaval 
 runs forwards in the abdomen close to and on the right of the aorta, 
 receiving successively ilio-lumbar, spermatic (or ovarian), and renal veins, 
 from the body-walls, spermaries (or ovaries), and kidneys respectively. 
 Before reaching the diaphragm it turns ventralwards, runs through the 
 dorsal part of the liver (from which it receives four chief hepatic veins), and 
 pierces the diaphragm ventral to the gullet. In the thorax it runs forwards 
 between the lungs and finally enters the right auricle. 
 
 (b) Hepatic Portal System. The portal vein is formed by the 
 union of lieno-gaxtric, duodenal, anterior mesenteric, and posterior 
 mesenteric veins, which return blood from the stomach and spleen 
 duodenum and pancreas ileuin and most of large intestines 
 and last part of rectum, respectively. The portal vein soon 
 divides into branches, which break up in the various liver-lobes. 
 
 (c) Pulmonary System. There are two pulmonary veins from 
 each lung. All four open into the dorsal side of the left auricle. 
 
 The muscle of the heart (Fig. 87) is composed of transversely- 
 striated fibres, devoid of sarcolemma, which are united into a 
 close network. This is marked into short lengths corresponding 
 to the constituent cells, and in each of these a muscle-corpuscle, 
 not placed superficially, is imbedded. The arteries and veins are 
 
292 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 constructed as described on p. 202. The veins contain numerous 
 valves, which are flap-like projections of their inner coat. 
 
 The capillaries are networks of fine tubes (cf. p. 202), con- 
 necting the ultimate branches of arteries and veins. 
 
 Course of the Circulation (cf. p. 247). The impure blood of 
 the body is returned by the caval veins to the right auricle, 
 thence passing into the right ventricle and into the lungs through 
 the pulmonary artery. The oxygenated blood is returned to the 
 left auricle by the pulmonary veins, then enters the left ventricle 
 to reach the aorta, the branches which take it to all parts of the 
 body. 
 
 (2) Lymph System. The lymph, as in other cases, resembles 
 blood, were it not for the absence of red blood-corpuscles. It is 
 contained in the minute lymph-spaces found in most of the 
 tissues, larger lymph-cavities, and lymph-vessels opening into a 
 thoracic duct. The lymphatic vessels resemble small veins in 
 structure, and are of two kinds (a) lymphatics, belonging to the 
 body generally; (/5) ladeals, belonging to the gut, and com- 
 mencing in blind branched tubules, one of which is found in 
 
 [Fig. 87. MUSCLE-FIBRES FROM MAMMALIAN HEART (from Landois and 
 Stirling), much enlarged. 8, Side view; 9, cross-section. 
 
 each intestinal villus. The thoracic duct, to which the lacteals and 
 most of the larger lymphatic trunks run, is a slender tube lying 
 above the dorsal aorta in the thorax, and opening anteriorly into 
 the junction between the left subclavian and external jugular 
 veins. Some of the lymphatics unite to form a much smaller 
 trunk, opening similarly on the right side. The most important 
 large lymph-space is the ccelom, here divided up into abdominal, 
 pleural, and pericardial cavities. 
 
MAMMALIA. 293 
 
 Numerous small lymphatic glands, which resemble the cervical 
 glands of the pigeon, are present in various situations. Those 
 belonging to the lacteals are known, from their position, as 
 mesenteric glands. 
 
 An elongated flattened spleen, of a dark-red colour, is attached 
 by a flap of mesentery to the cardiac end of the stomach. 
 
 The thymus gland is a fat-like mass, largest in young animals, 
 closely connected with the base of the heart. The thyroid gland 
 consists of two small elongated bodies of reddish colour, closely 
 applied to the sides of the front end of the trachea, and con- 
 nected together by a ventral bridge of tissue. 
 
 New colourless corpuscles are developed in the lymphatic glands, 
 thymus, and spleen, new red corpuscles in the red marrow of 
 bones, and from pre-existing colourless corpuscles. The worn- 
 out red corpuscles are probably broken down in the spleen. 
 
 6. The respiratory organs (Fig. 85) are lungs contained in 
 the thorax, and communicating with the exterior by a trachea, 
 the front end of which is modified into an organ of voice 
 (larynx). 
 
 The slit-like glottis, situated at the base of the tongue, and 
 guarded in front by an elastic flap (epiglottis), leads into the 
 larynx. This is supported by a broad thyroid cartilage (which is 
 a bent plate, incomplete dorsally), and, posterior to this, by a 
 ring-like cricoid cartilage, the dorsal side of which is thickened. 
 Two elastic folds, the weal chords, project from the sides of the 
 larynx. They are attached below to the thyroid cartilage, above 
 to two small arytenoid cartilages, which articulate dorsally with 
 the front edge of the cricoid. The larynx may be regarded as 
 the modified front end of the windpipe or trachea, which runs 
 along the neck ventral to the oesophagus, and is supported by 
 cartilaginous hoops. The trachea bifurcates within the thorax, 
 just anterior to the base of the heart, into two bronchi. 
 
 The lungs are two spongy bodies, pink in colour, which mainly 
 fill the thoracic cavity, as long as its walls remain intact. The 
 left lung is subdivided into two, the right lung into four lobes of 
 very unequal size. Each lung is enveloped by a delicate mem- 
 branous pleura, which consists (like the peritoneum) of a visceral 
 layer, closely applied to the surface of the lung, and a parietal 
 layer, lining one half of the thorax. The two layers are continuous 
 at the root of the lung. 
 
294 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The parietal layers of the two pleurae meet together in the middle line 
 to form, in the posterior part of the thorax, a longitudinal vertical partition, 
 the mediastinum. The two sheets of which this is composed diverge further 
 forwards, and leave between them the mediastinal space, occupied by the 
 heart in its pericardium. The bronchi enter the anterior end of the lungs, 
 and, like the trachea, are supported by cartilage. Each of them forms 
 a bronchial tree in its lung by giving off alternating right and left 
 branches. 
 
 The diaphragm is a thin partition which forms the posterior 
 boundary of the thorax, and separates it from the abdomen, 
 towards which it is strongly concave when at rest. The centre 
 of the diaphragm is transparent and tendinous (i.e., composed of 
 white connective-tissue fibres), while its margins are muscular, 
 especially on the dorsal side, where they are continued into two 
 muscular pillars, which take origin on the under sides of the 
 lumbar vertebrae. 
 
 Histology. The branches of the bronchial tree divide repeatedly 
 (the supporting cartilages being at the same time gradually lost), 
 to form delicate bronchial tubes. These end in clusters of dilations, 
 the infimdibula, with sacculated walls. They are lined by simple 
 squamous epithelium, beneath which is a very rich network of 
 capillaries. The trachea and larger air-passages are lined by 
 stratified columnar epithelium, ciliated in part. 
 
 The lungs contain a large quantity of elastic connective tissue 
 and unstriated muscle. 
 
 Respiration. Inspiration and expiration are partly effected by 
 movements of the ribs, and partly by movements of the diaphragm, 
 and respiration is hence said to be both costal and diaphragmatic. 
 
 It must be remembered that each lung is enclosed in an air- 
 tight bag, the pleura, and is obliged to follow all the movements 
 of the thoracic walls, or else a vacuum would be formed between 
 the two layers of this. The elastic tissue in the lungs causes 
 them to be always trying to contract, but this is prevented by 
 the pressure of the air in the lung-passages. If, however, the 
 pleura is perforated, this pressure is counterbalanced and the lung 
 at once contracts. 
 
 Inspiration. The ribs and sternum are moved downwards and 
 forwards, and thus increase the dorso-ventral capacity of the 
 thorax. At the same time the muscular parts (especially the 
 pillars) of the diaphragm contract, thus flattening it and increas- 
 ing the antero-posterior capacity of the thorax. 
 
MAMMALIA. 295 
 
 Air consequently rushes into the larger air-passages from the 
 exterior. 
 
 Expiration is the exact converse of this, but is largely passive, 
 the various muscles ceasing to contract. It is aided by the 
 elasticity of the lungs and walls of the thorax. As a result, the 
 air rushes out again. 
 
 The air passes directly in and out of the larger air-passages 
 only. The rest is effected by diffusion, and the essential part of 
 respiration (exchange of gases) is carried on in the infundibula. 
 
 Respiration is less active than in the pigeon, but here also the 
 body is maintained at a temperature (about 100F.) much above 
 that of the surrounding medium. 
 
 7. The urino-genital organs consist of excretory and repro- 
 ductive organs. 
 
 Excretory Organs (Fig. 89). In both sexes two oval, compact, 
 reddish-brown kidneys are closely applied to the dorsal wall of 
 the abdominal cavity, the right rather further forwards than the 
 left. The} 7 are covered ventrally by peritoneum. 
 
 Each kidney presents a notch, the hilus, on its inner margin, 
 from which the ureter, a narrow tube with muscular walls, 
 proceeds. The ureters open obliquely into the dorsal side of 
 the pear-shaped urinary bladder, towards its narrow portion or 
 neck. The walls of the bladder are translucent and muscular. 
 It projects into the body-cavity just in front of the symphysis 
 pubis. 
 
 A median horizontal section of either kidney shows that it is 
 differentiated into a marginal cortex, dark red in colour, with 
 numerous small dots (Malpighian bodies), and a central paler 
 medulla, which presents a striated appearance. The strise con- 
 verge internally towards a conical eminence, the urinary pyramid, 
 which projects into the pelvis, or dilated end of the ureter. 
 
 The kidney is essentially made up of uriniferous tubules 
 (Fig. 88), each commencing with a Bowman's capsule, which with 
 its glomerulus constitutes a Malpighian body, and is situated in the 
 cortex. The neck of the capsule passes into a thickened glandular 
 part, also in the cortex, from which a narrow part runs into the 
 medulla, and then loops back into the cortex to dilate into a 
 second glandular part, which passes into a collecting part. The 
 collecting parts run towards the urinary pyramid, often uniting 
 in their course, and finally open upon it. 
 
Fig. 88. DIAGRAM OF BLOOD-VESSELS AND UIUNIFEROUS TUBULES OF 
 KIDKEY (from Landois and Stirling). A and B, Capillaries of cortexT 
 and medulla. On the left numerous glomeruli are shown with (1) 
 afferent artery ; (2), efferent vein. The glomeruli are enclosed in 
 Bowman's capsules, x, x, x, and n, n, n, glandular parts, and o, o, o, 
 collecting parts of tubules ; O, opening on urinary pyramid. 
 
MAMMALIA. 
 
 297 
 
 The renal artery divides within the kidney, and from its 
 branches small afferent arteries run to Bowman's capsules and 
 break up into glomeruli. A small efferent vein arises from each 
 glomerulus. The efferent veins now break up into a network of 
 capillaries surrounding the glandular parts of the tubules, and 
 the factors of the renal vein take origin in this network. 
 
 ft. 
 
 Fig. 89. URINOGENITAL ORGANS OF EABBIT. A, male; B, female; C, 
 horizontal section of right kidney ; co and md, cortex and medulla of 
 kidney (in C) ; x , placed on urinary pyramid; ur, ureter; u.b, urinary 
 bladder; r, rectum; r.gl, rectal gland; a, anus; p.s., perineal space; 
 p.gl, perineal gland (in A, the aperture is shown by a dot); t, sper- 
 maries (testes); ep and ep', caput and cauda epididymis; gu, guber- 
 naculum; v.d, spermiduct (vas deferens); ut.m., uterus masculinus; 
 pr, pr', and pr", lobes of prostate; u.-g.c, urinogenital canal; c.c, cor- 
 pus cavcrnosum ; gl.p, glans penis ; or, left ovary ; F. t, left Fallopian 
 tube; F.t', funnel of ditto; u,u', left and right uteri, the latter cut 
 short; o.u and o.u', the mouths of the left and right uteri, to show 
 which the vagina, va. has been cut open; vb, vestibule; gl.cl, glans 
 clitoridis. 
 
 Excretion (cf. p. 206). The nitrogenous waste-products are 
 urea (CH 4 N 2 O) and Mppuric acid (C 9 H 9 NO 3 ). 
 
 The male reproductive organs (Fig. 89) consist of spermaries 
 (testes), from which spermiducts (vasa deferentia) proceed. These 
 communicate with a urinogenital canal traversing a cylindrical 
 penis. Other accessory parts are present. 
 
298 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The oval spermaries (testes) are contained in the scrotal sacs, 
 which, in the breeding season, project at the sides of the urino- 
 genital aperture. Each spermary is attached to its sac by a 
 short fibrous cord (gubernaculum), and is also suspended by a 
 mesenteric fold (mesorchium). Attached to the spermary is a 
 compact mass of coiled tubules (epididymis}, divided into the 
 caput epididymis in front, and the cauda epididymis behind. These 
 cap the anterior and posterior ends of the testis, and are con- 
 nected by a tubule running along its surface. 
 
 The spermatic artery and vein are connected with the anterior end of the 
 testis. They form, with nerves, connective tissue, &c., the spermatic cord. 
 
 The spermiduct (vas deferens) proceeds from the cauda epidi- 
 dymis, runs forwards, and then curves over the ureter to enter 
 the uterus masculinus, a large, slightly bilobed sac, which opens 
 into the dorsal side of a urinogenital canal (urethra), a backward 
 continuation of the neck of the bladder. After receiving the 
 uterus masculinus, the ducts of a five-lobed prostate gland, and, 
 further back, the openings of two small Cowpefs glands, the 
 urinogenital canal traverses the penis, an elongated backwardly- 
 directed structure, the ventral side of which is strengthened by 
 two fibrous rods, the corpora cavernosa, attached in front to the 
 ischia. The dorsal side of the penis is made up of a mass of 
 vascular tissue, the corpus spongiosum, through which the urino- 
 genital canal runs, and which projects beyond the corpora caver- 
 nosa as the (flans penis, a soft conical body, upon which is the 
 slit-like urinogenital aperture. 
 
 The spermary is essentially composed of seminiferous tubules 
 lined by germinal epithelium, the cells of which divide frequently 
 to form sperms, each producing several, but not being entirely 
 used up in the process. The srjerms (spermatozoa) have oval 
 flattened heads and vibratile tails. The tubules of the spermary 
 unite to form msa efferentia, which make up part of the epididymis. 
 
 The female reproductive organs (Fig. 89) consist of ovaries, 
 oviducts, vagina, and urinogenital canal, together with accessory 
 parts. 
 
 The ovaries are whitish, oval bodies, placed one on either side 
 of the dorsal abdominal wall, posterior to the kidneys. In a 
 mature female, Graafian (ovarian) follicles appear as clear, rounded 
 projections on their surfaces. Near each ovary is the fringed 
 
MAMMALIA. 299 
 
 funnel-shaped opening of the corresponding oviduct. This con- 
 sists of a narrow convoluted Fallopian tube, which merges into a 
 cylindrical uterus, with thick muscular walls, which may be of 
 very large size in the pregnant female, and then exhibits a series 
 of oval swellings, in each of which an embryo is contained. The 
 two uteri open by separate apertures (ora uterorum) with rounded 
 projecting margins, into the vagina, a large tube which runs back 
 dorsal to the bladder, and becomes continuous with the urino- 
 genital canal (vestibule), a somewhat smaller but still wide tube, 
 which runs back from the bladder in the same relative position 
 as the narrow urinogenital canal of the male. The walls of this 
 tube are very vascular, and it ends in an elongated urinogenital 
 aperture (vulva). Imbedded in the ventral wall of the vestibule 
 is a small elongated body, the clitoris, supported by corpora cavernosa, 
 similar to, but very much smaller than, those of the penis, and 
 similarly situated. The clitoris ends in a soft, flattened glans 
 ditoridis. Small Cowper's glands open into the dorsal wall of the 
 vestibule. 
 
 The ovary consists of Graafian follicles in various states of 
 development imbedded in a connective-tissue basis or stroma. 
 The mature follicles project from the surface of the ovary, and 
 each, when mature, is a fluid-containing vesicle, the wall of which 
 consists of a fibrous coat, internal to which are two or more layers 
 of columnar epithelial cells (membrana granulosa). The ovum is 
 placed on the outer side, and is surrounded by several layers of 
 these cells, with which it forms a mass, the discus proligerus, 
 that projects into the cavity of the follicle. The ripe ovum is 
 invested by a radiately striated membrane, the zona radiata, but 
 no distinct traces remain of the vitelline membrane present in the 
 young ovum. The vitellus contains hardly any food-yolk, and 
 within it is a large germinal vesicle with germinal spot. 
 
 The ova burst from their follicles into the body-cavity, and are 
 taken up by the funnels of the Fallopian tubes. Fertilization is 
 effected in the upper part of these tubes, by fusion with sperms 
 previously ejected by the male into the female passages, the penis 
 being used as a copulatory organ. 
 
 8. Muscular System (c/.p. 208). The muscles are very numerous 
 and arranged in a very complicated manner. The voluntary 
 muscles are from their appearance divided into red and white, the 
 darker colour of the former being due to their richer blood-supply. 
 
300 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The striated muscle-fibres are smaller than those of the frog 
 (cf. p. 208), and the muscle-corpuscles are situated superficially, 
 just beneath the sarcolemma. The fibres of the red muscles are 
 larger than the rest. 
 
 9. The Nervous System (Fig. 85) consists of cerebro-spinal 
 axis, cranio-spinal nerves, and sympathetic system. 
 
 Fig. 90. HISTOLOGY OF STRIATED MUSCLE (from Landois and Stirling), 
 all much enlarged. 1. Part of a fibre Q, transverse striations; F, 
 primitive fibrillae; K, muscle-corpuscles; S, sarcolemma; N, an entering 
 nerve-fibre, with a, axis cylinder, and e, end-plate. 2. Part of a fibre 
 in cross-section K, muscle-corpuscle. 3. Primitive fibrillse. 
 
 (1) The cerebro-spinal axis comprises brain and spinal cord 
 contained in the neural canal and invested by three membranes, 
 pia mater carrying blood-vessels for supply of the nervous 
 tissue, arachnoid, a delicate mesh-work traversed by lymph-spaces, 
 and firm dura mater lining the neural canal. 
 
MAMMALIA. 301 
 
 The brain is elongated, but not particularly well developed. 
 It presents the usual division into fore-, mid-, and hind-brain. 
 
 Fore-Brain. The thalamencephalon possesses two parts not 
 present in preceding types. One is the middle commissure, a 
 broad band of grey matter connecting the side- walls of the third 
 ventricle between the anterior and posterior commissures. The 
 other is a rounded eminence, the corpus mammillare, seen on the 
 under surface immediately behind the pituitary body, which is 
 attached as previously to the infundibulum. With the hinder 
 part of the thin roof of the third ventricle the pineal gland is 
 connected by a hollow bifurcated stalk. 
 
 The cerebral hemispheres are broad behind and taper in front 
 to blunt points. Externally they are almost smooth, but each is 
 divided by grooves into three lobes, frontal, parietal, and temporal, 
 placed respectively in front, postero-dorsally and postero-ventrally. 
 As in the frog and pigeon the hemispheres are closely applied in 
 the middle line, but here, in addition, they are firmly united by 
 an elongated band of transverse fibres, the corpus callosum. Below 
 this and continuous with it behind is another fibrous band, the 
 body of the fornix, which divides in front into four smaller bands, 
 the pillars of the fornix. 
 
 Two of these, the anterior pillars, pass downwards in the lamina 
 terminalis and substance of the optic thalami to reach the corpus 
 mammillare, while the other two, posterior pillars, curve outwards into 
 the hemispheres. Each lateral ventricle is divisible into three parts a 
 narrow anterior cornu in front, and towards the inner side a posterior 
 cornu, similarly placed behind, and a descending cornu, which passes 
 down into the temporal lobe. A prominent oval mass, the hippocampus 
 major, projects into the last-named cornu, and along the anterior edge 
 of this the posterior pillar of the fornix runs. In front of this pillar 
 there is a vascular fold, the choroid plexus, which extends into the ven- 
 tricle from the pia mater. The corpus striatum forms the outer side and 
 floor of the anterior cornu. The cerebral hemispheres fuse where they 
 meet in front of the lamina terminalis, and form a party-wall, the septum, 
 lucidum, to the hinder parts of the anterior cornua, immediately in front 
 of the foramen of Monro on each side. This partition is not solid, but 
 contains a small slit-like fifth ventricle. 
 
 This is not, therefore, like the other ventricles, a part of the cavity of 
 the original neural tube of the embryo. These were originally named 1st 
 and 2nd (i.e., the two lateral), 3rd and 4th ventricles, and when another 
 brain-cavity was discovered it naturally received the name 5th ventricle. 
 
 The olfactory lobes are elongated and dilated at their ends. 
 They are attached to the under sides of the frontal lobes, and 
 run forwards in front of them to rest on the cribriform plate. 
 
302 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Each contains a small olfactory ventricle continuous with the 
 -corresponding anterior cornu. 
 
 The mid-brain is traversed by the Sylvian aqueduct. Above it 
 presents the optic lobes (corpora quadrigemina) which are over- 
 lapped by the cerebral hemispheres. Each of them is subdivided 
 into two, so that there are four elevations, two anterior and larger 
 nates, and two posterior testes. There are no optic ventricles. 
 Two very distinct longitudinal masses of fibres, the crura cerebri, 
 form the floor of the mid-brain. 
 
 Hind-brain. The bulb (medulla oblongata) presents well- 
 marked dorsal and ventral fissures bounded by narrow bands, the 
 dorsal and ventral pyramids. The dorsal pyramids diverge in 
 front and sweep round the sides of the thin roof of the fourth 
 ventricle, on each side of which is a projection, the corpus resti- 
 forme. On the under surface the ventral fissure and pyramids 
 .are interrupted by a broad band of transverse fibres, the pons 
 Varolii, just behind the crura cerebri. Immediately behind this 
 there is a rectangular area, the corpus trapezoideum, on each side 
 of the ventral pyramid, occupied by transverse fibres. 
 
 The cerebellum is very large and made up of a median vermis 
 marked by deep transverse furrows, and a pair of much convoluted 
 lateral lobes, to each of which a small rounded flocculus similarly 
 furrowed, is attached. The cerebellum is united to the rest of 
 the brain by three pairs of commissures or peduncles. The 
 anterior peduncles connect it with the testes, the middle pedun- 
 cles with the pons Varolii, and the posterior peduncles with the 
 corpora restiformia. 
 
 The spinal cord is cylindrical, and possesses dorsal and ventral 
 fissures. There is no sinus rhomboidalis. 
 
 (2) Cranio- Spinal Nerves. There are twelve pairs of cranial 
 nerves, as in the pigeon, which take origin and are distributed 
 in a similar manner. The olfactory lobes send numerous fibres 
 through the pores in the cribriform plate to the olfactory mucous 
 membrane. The optic nerves form a chiasma, but the optic 
 tracts are relatively narrow. The trigeminal nerves arise from 
 the sides of the pons, and the facial and auditory from the sides 
 of the corpora trapezoidea. The abducent nerves come off from 
 the extreme front of the ventral pyramids. The exits of the 
 cranial nerves have already been described (p. 274). Outside 
 the skull it may be noted that the mandibular ramus of the fifth 
 
MAMMALIA. 303 
 
 sends a lingual branch to the tongue. The vagi run back along 
 the neck by the sides of the common carotids. Each gives off to 
 the larynx a superior laryngeal nerve, from which a depressor 
 branch runs, closely united with the sympathetic, to the heart. 
 At the posterior end of the neck a recurrent laryngeal nerve is 
 given off, which curves round the aorta on the left, or the sub- 
 clavian on the right, and runs forwards to the larynx. Behind 
 this the vagi run through the thorax and pierce the diaphragm, 
 finally breaking up into branches for the abdominal viscera. 
 
 The spinal nerves arise by two roots as usual, and are named 
 cervical, thoracic, <fec.. according to the region of the vertebral 
 column to which they correspond. 
 
 The last four cervical and the first thoracic nerves form the 
 orachial plexus, from which the fore-limb is supplied, and from 
 which also arises the phrenic nerve, which runs back to supply 
 the diaphragm. 
 
 The lumbo-sacral plexus for the hind-limb is constituted by the 
 last three lumbar and the first three sacral nerves. 
 
 (3) The sympathetic system is formed by a ganglionated cord 
 on each side (cf. p. 215) of the body, beginning in the head, 
 traversing the neck, and then running ventral to the vertebral 
 column through the thorax and abdomen into the tail. These 
 are connected by rami communicantes with some of the cranial 
 nerves and with the spinal nerves. They are also connected by 
 commissures with each other. In the neck there are only three 
 ganglia, the posterior and middle cervical at the root of the neck, 
 and the anterior cervical placed near and connected with the 
 vagus ganglion. In the thorax two large splanchnic nerves run off 
 from the cords, and, piercing the diaphragm, fuse with a large 
 cosliac ganglion, placed just in front of the origin of the anterior 
 mesenteric artery, and united with an anterior mesenteric ganglion 
 just behind it.* This latter ganglion is again connected with a 
 posterior mesenteric ganglion situated near the origin of the 
 posterior mesenteric artery. From these ganglia numerous 
 branches run off to the abdominal viscera. The sympathetic 
 also supplies the vascular system. 
 
 10. Sense Organs (1) Tactile Organs. Numerous touch-cor- 
 puscles are present in the skin (p. 271), especially at the bases 
 of the vibrissae. 
 
 * Cceliac ganglion + anterior mesenteric ganglion =semilunar ganglion of 
 .human anatomy. 
 
304 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 (2) Gustatory Organs. Imbedded in the sides of the circum- 
 vallate papillae and papillae foliatae are numerous taste-buds, con- 
 taining elongated taste-cells, connected with glossopharyngeal 
 fibres. 
 
 (3) Olfactory Organs. The nasal cavities (Fig. 85) are largely 
 lined by olfactory mucous membrane, which extends over the ethmo- 
 turbinals, and contains elongated olfactory cells (cf. Fig. 62). 
 
 (4) Auditory Organs. (a) The external ear consists of a pinna 
 and an external auditory meatus, closed below by the tympanic 
 membrane. This last also forms the upper and outer boundary 
 of (6) the middle ear or tympanic cavity, which has already been 
 described, (c) The inner ear (Fig. 91,0) is, broadly speaking, 
 
 Fig. 91. DIAGRAMS or THE MEMBRANOUS LABYRINTH (from Haddon). 
 Internal side of left labyrinth. A, Fish, B, Bird. C. Mammal ; us, 
 utriculus and sacculus ; u, utriculus ; s, sacculus ; c, cochlea. 
 
 similar to that of the pigeon, but the semicircular canals are ar- 
 ranged rather differently (the anterior vertical not crossing over 
 the horizontal), the sacculus and utriculus do not communicate 
 directly, and the cochlea is produced into a delicate tube, spirally 
 coiled, and contained within the promontory. A special series of 
 special sense cells (hair-cells) are formed in the cochlea. This 
 also contains a large number of pairs of elastic fibres, of different 
 lengths, constituting the problematical organ of Corti and forming 
 a series of /y-shaped arches projecting into the endolymph. 
 
 (5) Visual Organs see Figs, 63 and 64). The eye and the 
 
MAMMALIA. 
 
 305 
 
 eye-muscles do not differ widely from the condition found in the 
 frog (p. 221). But the sclerotic is not supported by cartilage, 
 and the lens is much flatter (as in Fig. 63). The accessory 
 structures, besides muscles, are the conjunctiva, three eyelids, and 
 lachrymal and Harderian glands. 
 
 cnt. 
 
 Fig. 92. FORMATION OF BLAS- 
 
 TOCYST IN THE RABBIT (after 
 
 E. Van Beneden).a, Bias- 
 tula ; 6, e, d, successive stages 
 in the formation of the blas- 
 tocyst; ect, outer cells; ent, 
 inner cells ; z.p, zona pel- 
 lucida. 
 
 DEVELOPMENT. 
 
 1. Early Stages. Cleavage (segmentation) (Fig. 92) is com- 
 plete and almost regular, there being only a very small quantity 
 of food-yolk in the minute oosperm to impede it. By successive 
 bipartitions eight cells are produced, four of which are larger 
 than the others, and are called outer cells, from their subsequent 
 
 UNIVEBSITT 
 
 V. of 
 
306 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 fate. The other four are termed inner cells, for a similar reason. 
 Both inner and outer cells continue to divide, but the latter 
 increase more rapidly and grow over the others. At the close 
 of segmentation, which takes place in the Fallopian tube, the 
 blastula consists (Fig. 92) of a layer of clear outer cells, which 
 cover a central mass of granular inner cells, except at one point. 
 The embryo is still invested by the zona radiata, external to 
 which is an albuminous coating, the zona pellucida, received from 
 the wall of the Fallopian tube. The changes that follow take 
 place in the uterus, and lead to the formation of the embryonic 
 layers. 
 
 The outer cells first of all grow completely over the inner cells, 
 and then increase and become flattened to form the blastocyst 
 (blastodermic vesicle), an internal cavity forming meanwhile, 
 which gets larger and larger. The blastocyst is a delicate 
 vesicle, the walls of which are mainly formed by outer cells, to 
 which the inner cells adhere over a small internal area. It 
 continues to increase in size, and the inner cells gradually extend 
 at the edges. In the centre, however, of the patch of inner cells 
 a circular thickening appears (Fig. 93), the embryonic area, 
 corresponding to the area pellucida of the Chick. The inner 
 cells here become divided into an upper layer of rounded cells 
 and a lower layer of flattened cells. The former unite with the 
 outer cells to form the ectoderm (epiblast) of the embryonic area, 
 while the latter constitute the endoderm (hypoblast) of the same 
 region. Outside this the epiblast and hypoblast are formed by 
 the outer and inner cells respectively. 
 
 
 Embryonic Area. 
 
 Rest of 
 
 Vesicle. 
 
 Ectoderm, . 
 
 Outer cells, 
 f Rounded inner cell layer, "| 
 
 Outer cells. 
 
 Endoderm, . 
 
 | Flattened inner cell layer, 
 
 I J 
 
 Inner cells. 
 
 The mesoderm (mesoblast) is first formed in the embryonic 
 area, and has a double origin similar to that described for the 
 
MAMMALIA. 
 
 307 
 
 Chick (p. 259). A side view of the blastocyst on the seventh 
 day is shown in Fig. 93.* 
 
 2. General Growth. This is essentially the same as in the 
 case of the Chick (p. 260). The embryo is formed in the 
 
 Fig. 93. Fig. 94. 
 
 Fig. 93. BLASTOCYST OF RABBIT SEVEN DAYS AFTER FERTILIZATION. Side 
 view. Magnified about 10 diameters (after Kolliker). ag, Embryonic 
 area; fje, lower limit of endoderm; below this line the vesicle consists 
 only of a single layer of ectoderm. 
 
 Fig. 94. HEAD OF TEN-DAY RABBIT (after Kolliker}. a, Eye; at, r, 
 and b, atrium, ventricle, and truncus arteriosus of heart; v (upper one) 
 and s, fore- and mid-brains; k', k", k'", mandibular, hyoid, and first 
 branchial arches; o, superior maxillary process of k'; m, mouth. 
 
 embryonic area (area pellucida), and is at first flattened out on 
 the surface of the blastodermic vesicle, just as the Chick is 
 flattened out on the yolk. But the vesicle only contains fluid, 
 
 * The above account of the origin of the germinal layers is the one usually 
 given, but comparison with other forms renders it probable that the wall 
 of the blastocyst outside the embryonic area consists at first of endoderm 
 only, which becomes continuous with the endoderm of that area. If so, 
 the cavity of the blastocyst = an extended archenteron. The lowest mam- 
 mals are developed outside the body of the mother, from large eggs resem- 
 bling those of birds, and there can be no doubt that the rabbit is descended 
 from similar forms, the transition to an intra-uterine mode of development, 
 resulting in loss of the food-yolk. If in a fowl's egg ready for incubation 
 (cf. Fig. 73), we suppose the shell and white removed, and the food-yolk 
 replaced by a much smaller amount of albuminous fluid if, further, we 
 suppose that the lower layer of cells extends right round, and encloses this 
 mass of fluid, then we shall get something resembling the rabbit's blastocyst 
 on the view given in this note. 
 
308 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 there being hardly any food-yolk, and its wall, from the first, 
 is partly formed of ectoderm, the other layers subsequently ex- 
 tending into it. In the Chick all the layers grow round to 
 invest the yolk, which is at first covered only by the vitelline 
 membrane. The embryo is folded off as described previously for 
 the Chick, and it is only at a comparatively late date that special 
 characteristics are developed. It must, however, be remembered 
 that though four visceral clefts (Fig. 94) are present, the last 
 one is not bounded behind by an arch. 
 
 3. Fate of the Germinal Layers. The three layers give rise 
 to the same parts as in the Chick (p. 263), but a few remarks 
 are necessary concerning the mesodermic structures. 
 
 Cartilaginous bars are developed in the first three visceral 
 arches, which develop as follows : 
 
 I. Mandibular. Incus, Malleus, and Meckel's cartilage of either side, 
 Eustachian cartilage, Pterygoid, and Palatine. 
 
 TT ir-v7 ( * use ventrally to form 1 anterior 
 
 \ body of hyoid, / cornua ; stapes. 
 
 - Branchial 1, { P^ 
 
 The aortic arches develop in a similar way to those of the 
 Chick (p. 265), but the left th arch becomes the aorta, and the 
 right Mh the right subclavian, while the rigM 5th arch disappears, 
 and the left 5th forms the pulmonary artery. 
 
 The anterior cardinals become the external jugulars, and the 
 Cuvierian ducts the precavals. 
 
 The history of the excretory organs is much as in the Chick 
 (p. 265), but there is no trace of a pronephros. 
 
 4. Embryonic Appendages (Fig. 95). These are modified in 
 accordance with the important fact, that while in the Chick 
 development mainly goes on outside the parent's body, at the 
 expense of the bulky food-yolk, the embryo Rabbit develops 
 mainly within the body of the mother, and is born " alive." In 
 other words, the Bird is oviparous, the Mammal viviparous. 
 
 It must be borne in mind that the blastocyst is closely invested 
 by the remains of the zona radiata of the ovum. 
 
 The yolk-sac (umbilical vesicle) is formed by that part of the 
 blastocyst which is outside the embryonic area. From the first 
 its wall is formed within the zona radiata by ectoderm, beneath 
 
MAMMALIA. 
 
 309 
 
 which the other layers grow round. As the embryo is folded 
 off, the yolk-sac comes to form a ventral appendage to its body. 
 A yolk-sac blood-circulation is established, and this appendage 
 becomes much flattened and shaped like an umbrella, with the 
 handle attached to the embryo (Fig. 95). 
 
 The amnion is formed as in the Chick (Fig. 82), but there the 
 outer limbs of the fold contain ectoderm and mesoderm, and, 
 with the ectoderm and somatic mesoderm of the yolk-sac, with 
 which they are continuous, fuse with the vitelline membrane. 
 
 '7.7 
 
 Fig. 95. EMBRYONIC APPENDAGES OF THE RABBIT Diagrammatic longi- 
 tudinal section (from Kolliker, after Bischoff). c, Embryo; a, amnion, 
 and stalk of allantois (al); sh, subzonal membrane; pi, placental villi; 
 fd and ed, vascular and hypoblast layers of yolk-sac; ds, placed in 
 narrow cavity of yolk-sac ; r, space filled with fluid. 
 
 Here the outer limbs of the fold contain ectoderm alone (proba- 
 bly), and are continuous with the ectoderm of the yolk-sac, which 
 splits off. This continuous layer of ectoderm forms a subzonal 
 membrane, lining the zona radiata. To this membrane the flattened 
 yolk-sac attaches itself closely over a large area. 
 
 The allantois (cf. Fig. 82) grows out from the hinder end of 
 the alimentary canal, and becomes closely united with the sub- 
 zonal membrane for a small circular area on the dorsal side of 
 the embryo, to which it remains attached by a narrow stalk. From 
 this area numerous slender processes, villi, grow out, which fit 
 
310 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 into depressions in a corresponding area of the uterine mucous 
 membrane, which becomes thickened and vascular. A blood- 
 circulation is developed in the allantois, and blood-vessels extend 
 into the villi. Ultimately, close union takes place between the 
 villi and the wall of the uterus. A circular flattened structure, 
 the placenta, is thus formed, consisting of an embryonic part, 
 mainly formed by the allantois, and a maternal part, constituted 
 by the thickened area of the uterine mucous membrane. The 
 placenta is connected with the embryo by the stalk of the 
 allantois, and certain structures which surround and form with 
 it the umbilical cord. The impure blood of the embryo passes 
 into the embryonic part of the placenta by two allantoic arteries 
 which break up into branches, and, in the villi, come into close 
 relation with the blood-vessels of the mother. There is not, 
 however, an actual union. Waste-products thus pass from the 
 blood of the embryo into the blood of the mother, which, on the 
 other hand, supplies nutritive material and oxygen. The lack of 
 food-yolk is thus compensated for. (For details of the embryonic 
 circulation, see p. 267.) 
 
 Several embryos develop in each uterus at the same time, 
 occupying separate swellings. At birth the embryonic mem- 
 branes are cast off, including the embryonic part of the 
 placenta. 
 
 CHAPTER XIIL COMPARATIVE ANIMAL 
 MORPHOLOGY AND PHYSIOLOGY. 
 
 THE comparison of animals is perhaps best conducted on a 
 physiological basis, taking the headings of nutrition, katabolism, 
 reproduction, contractility, irritability, and spontaneity (see 
 Amoeba) and adding to these the subordinate one of protection 
 and support. 
 
 Amoeba, Vorticella, and Gregarina, unicellular animals, perform 
 all the functions of life, the first being but little differentiated, 
 the second a great deal, the third modified as a result of para- 
 sitism. From this point onwards the multicellular condition leads 
 
COMPARATIVE ANIMAL MORPHOLOGY AND PHYSIOLOGY. 311 
 
 to increasing specialization, different cells performing different 
 functions. Tissues and cellular organs result. 
 
 Amoeba is usually irregular in form, but, when at rest, tends to 
 become spherical. This is simply a physical result of its semi- 
 fluid nature. The firm cuticle possessed by Vorticella and 
 Gregarina necessitates a definite form. 
 
 Bilateral symmetry (exhibited by most of the forms) may be 
 conceived of as derived from radial symmetry (seen in Hydra), 
 by elongation transverse to the long axis, which, at the same 
 time, shortens. Meanwhile, ventral and dorsal surfaces, and 
 anterior and posterior ends, become differentiated, as the result 
 of a creeping mode of progression. The anterior end ultimately 
 becomes the head, in which some of the most important organs 
 are located. 
 
 The higher forms mostly exhibit metameric segmentation, 
 that is, a division from before backwards into segments or meta- 
 meres. These are similar in the Earthworm and Leech, but in 
 the Crayfish are more or less dissimilar, and largely fused. It is 
 thus that distinct body-regions arise. The Fluke and Ascaris are 
 unsegmented, and the Mussel and Snail have lost all traces of 
 segmentation. The last has also become twisted and asymmetrical 
 owing to the development of a spiral shell. Amphioxus is clearly 
 segmented but very unsymmetrical. Segmentation is obvious in 
 the Dogfish, but in the Frog, Pigeon, and Rabbit, is much 
 obscured in the adult. It is best seen in the spinal nerves. The 
 jointing of the backbone appears to be a case of " secondary " 
 segmentation i.e., the segments do not correspond to the primi- 
 tive ones indicated by the mesodermic somites (protovertebrae) 
 of the embryo. 
 
 Homology and Analogy are important kinds of agreement. Homo- 
 logous organs agree in relative position and mode of development, analogous 
 organs correspond merely in function. For example, the quadrate bone of 
 the Pigeon is probably homologous with the incus of the Rabbit, though 
 their functions are different, while the breathing-organs of the Snail, Cray- 
 fish, and Rabbit are analogous, agreeing in function. Homology is, in fact, 
 morphological, analogy physiological equivalence. It must not be forgotten 
 that organs are often both homologous and analogous e.g., the eyes of 
 Dogfish, Frog, Pigeon, and Rabbit. 
 
 Serial homology is agreement in plan of structure and mode of develop- 
 ment between series of structures e.g., the segments of the Earthworm, or 
 spinal nerves and vertebrae of the Frog. 
 
 1. Protection and Support. In Amoeba there is, under ordinary 
 
312 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 conditions, no special modification for this purpose, but in Vorti- 
 cella and Gregarina a firm cuticle is present. All three pass 
 through an encysted stage. A cuticle is also found in Tapeworm, 
 Ascaris, Leech, and Earthworm, and to a more marked extent in the 
 Fluke, where it is much thickened and provided with numerous 
 minute spines. The maximum of cutictilar protection is reached 
 in the Crayfish, Mussel, and Snail, where a firm exoskelelon is 
 produced by the impregnation of a thickened and laminated 
 cuticle with salts of lime. 
 
 In Hydra the thread-cells serve as a very effective protection. 
 The skin of the Dogfish, Frog, Pigeon, and Rabbit serves for 
 protection, and respectively possesses scales, poison glands, 
 feathers, and hairs. The colour of the skin is protective in 
 Frog and Kabbit. From the Fluke upwards, support is 
 largely afforded by what may be termed indifferent tissues, 
 i.e., connective tissue, and its modifications, cartilage and bone. 
 Cartilage first appears in the odontophore of the Snail, and, 
 together with bone, .forms in the Dogfish, Frog, Pigeon, and 
 Eabbit a more or less complete endoskeleton. The most primitive 
 part of this endoskeleton appears to be the backbone, the founda- 
 tion of which is the notocJwrd which, in Amphioxus, persists 
 without modification, except that it extends further forwards 
 than in higher animals. In the Chordate forms, the body is 
 divisible into an upper, smaller, neural tube, contained in the 
 skull and backbone, and a lower larger visceral tube. 
 
 2. Nutrition. The food of Amoeba can be ingested, and refuse 
 egested at any point of the shapeless body, and the pseudopodia 
 are used for overwhelming any minute organisms that may serve 
 as nutriment. Vorticella is usually fixed, and the place of pseudo- 
 podia is taken by cilia, which do not themselves seize food, but 
 cause food-bearing currents to enter the vestibule and gullet. 
 Within the body the food takes a definite course, and the undi- 
 gested parts are cast out at a special anal area. The necessity 
 for definite points at which food may be taken in, and innutri- 
 tions residues ejected is brought about by the presence of the 
 firm cuticle. In Gregarina, however, the ready prepared food 
 is absorbed through the cuticle. 
 
 Hydra presents a great advance upon this state of things. 
 The tentacles can seize small animals (which are first paralyzed 
 by the thread-cells) and convey them to the " mouth." Within 
 
COMPARATIVE ANIMAL MORPHOLOGY AND PHYSIOLOGY. 313 
 
 the large digestive cavity, they are partly taken in amoeba-like 
 by the endoderm cells, and partly reduced to a state of solution 
 by digestive fluids poured out by those cells. The flagella 
 produce currents, which assist in the circulation of food in the 
 cavity, and the rejection of waste by the " mouth." Ascaris, 
 Earthworm, and Leech are far more highly differentiated in this 
 and other respects. The conversion of radial into bilateral 
 symmetry, in the way already indicated, would cause the 
 " mouth " of a hydra-like animal to be pulled out into a long 
 slit. The closure of this, in the middle of its extent, would 
 lead to the formation of two apertures, one at each end, placing 
 the gut in communication with the exterior. 
 
 The mouth and anus of the Earthworm, &c., can be conceived 
 of as derived in this way from the " mouth " of a form like 
 Hydra. The digestive organs of the Earthworm present a 
 number of special contrivances. The pharynx helps to draw 
 in the food, and the gizzard to crush it, while the lining of the 
 alimentary canal is glandular and secretes digestive fluids. The 
 typhlosole increases the absorptive surface. The Leech is 
 specially modified as an ectoparasitic blood-sucker. 
 
 The Fluke is a very much modified worm, adapted for a 
 parasitic life, and the digestive organs are much specialized in 
 accordance with this. The Tapeworm has no gut, and lives 
 by absorption ; but the equally endoparasitic Ascaris retains a 
 well-developed alimentary canal. 
 
 The segments of the Crayfish bear jointed appendages, which, 
 in the anterior part of the body, are adapted for seizing and 
 crushing food, the reduction of which to a fine state of division 
 is completed by the complex gastric mill. The alimentary canal, 
 like that of the Earthworm, exhibits bilateral symmetry, and its 
 absorptive surface is increased by the ridges present in the 
 intestine. Two very large digestive glands are present, which 
 must be regarded, like all such glands, as extremely complicated 
 pouches or diverticula of the alimentary canal, from which, 
 indeed, they grow out, as the study of development shows. 
 
 In the Mussel, although the mouth and anus are in the middle 
 line, the gut is convoluted, as in the higher forms (except 
 Amphioxus), by which absorptive surface is gained, augmented 
 in this case by a typhlosole. The food is procured by the aid of 
 ciliary currents, and digested by the fluid secreted in the diges- 
 tive gland surrounding the stomach. 
 
314 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The asymmetry of the Snail affects the internal organs, includ- 
 ing those of digestion, especially as regards the position of the 
 anus. The odontophore is a very special modification for rasping 
 food, and not only is a large digestive gland present, but also 
 salivary glands, the function of which is, however, doubtful. 
 
 Amphioxus feeds on small organisms carried into the gut by 
 ciliary currents. The nature of the so-called liver is doubtful. 
 
 The Dogfish is carnivorous and possessed of rows of sharp teeth 
 fitted for securing prey. As in all the vertebrate forms there are 
 two digestive glands liver and pancreas. The gut is short, as 
 in all cases where the food is of easily digestible animal nature, 
 but the spiral valve offers a considerable absorptive surface. 
 
 In the Frog, insects are secured as food by means of the 
 tongue, aided by the sticky secretion of numerous small glands. 
 Their escape from the mouth-cavity is prevented by the minute, 
 pointed teeth. The absorptive surface is much increased, not 
 only by the length but by the ridged internal surface of the small 
 intestine. The gut is relatively much longer in the herbivorous 
 tadpole. 
 
 The Pigeon, by means of its horny beak, picks up food, which 
 is temporarily stored up in the crop, and acted upon mechanically 
 in the gizzard. The finger-shaped absorptive projections from 
 the lining of the intestine are here, and in the Rabbit, called 
 villi. 
 
 The Eabbit possesses teeth adapted for cutting and grinding 
 vegetable food. The flexible, fleshy lips largely aid in seizing 
 food. The alimentary canal is here immensely long, as a result 
 of the vegetable food, and its absorptive surface is, in consequence, 
 extremely large. Not only are liver and pancreas present, but 
 also several pairs of salivary glands. 
 
 Circulation. In Amoeba and Vorticella this is aided by the 
 presence of a contractile vacuole, and in the Tapeworm and Fluke 
 one of the functions of a circulatory system i.e., the conveyance 
 of waste-products to organs which get rid of them is rendered 
 superfluous by the large extent of those (excretory) organs them- 
 selves. The general movements of the body effect circulation in 
 Ascaris. 
 
 The Earthworm possesses a well-defined and closed blood 
 system as distinct from a coelomic system. The propulsion of 
 blood is effected by the paired hearts. The Leech exhibits a 
 well-developed blood system in communication with a reduced 
 
COMPARATIVE ANIMAL MORPHOLOGY AND PHYSIOLOGY. 315 
 
 coelomic system. The Crayfish, Mussel, and Snail show no dis- 
 tinction between blood and lymph systems. The blood system 
 in each case is lacunar i.e., the ramifications of the blood-vessels 
 terminate in the lacunse everywhere permeating the tissues. The 
 heart of the Crayfish possesses no auricles ; there are two in the 
 Mussel, but only one (a result of asymmetry) in the Snail. All 
 three hearts are systemic, that is to say, they receive oxygenated 
 blood, which they pump to the body at large. Amphioxus ap- 
 parently possesses freely communicating blood and lymph systems. 
 The absence of a heart is made up for by the contractility of the 
 vessels. In the Dogfish, Frog, Pigeon, and Eabbit, the blood 
 system is closed, owing to the presence of the capillaries, which 
 connect the ultimate ramifications of the arteries and veins. The 
 lymph system is largely lacunar, including also certain large 
 spaces, the coelom, &c., but definite trunks are also present, 
 best marked in the Eabbit and worst in the Dogfish. The Frog 
 possesses propulsive lymph-hearts. In the Dogfish, the heart 
 contains impure blood only, which it pumps to the gills for oxy- 
 genation and elimination of C0 2 . The heart in Frog, Pigeon, and 
 Kabbit is both systemic and pulmonary, supplying the body and 
 also pumping impure blood to the lungs (and in the Frog to the 
 skin also) for purification. Only one ventricle is possessed by. 
 the Frog, which involves complicated mechanical contrivances by 
 which the complete mixing of oxygenated and impure blood in 
 the heart is prevented. The Pigeon and Rabbit have two com- 
 pletely separated ventricles. 
 
 3. Katabolism (1) Respiration. This is aided in Amoeba and 
 Vorticella, by the contractile vacuole. In Gregarina, Hydra, 
 Fluke, Tapeworm, Ascaris, Earthworm, and Leech, it is effected 
 by the general surface of the body, beneath which, in the last 
 two cases, there is a rich supply of blood-vessels. The Crayfish 
 and Mussel possess gills (and the latter mantle-lobes as well) for 
 breathing the oxygen dissolved in water, and in Amphioxus and 
 Dogfish the pharynx is modified for the same purpose, while the 
 Snail, Frog, Pigeon, and Rabbit possess lungs, by means of which 
 the oxygen in the air is utilized. The gills of Crayfish and 
 Mussel are specialized outgrowths of the body ; the mantle lobes 
 of Mussel and lung-roof of Snail may be similarly described ; the 
 lungs of Frog, Pigeon, and Rabbit are ventral outgrowths of 
 the gut. 
 
316 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 Respiratory oxygen-carrying substances are commonly present 
 in the blood, as, for example, hsemocyanin in Crayfish and 
 Snail; haemoglobin in Earthworm, Dogfish, Frog, Pigeon, and 
 Rabbit. In the Crayfish water is renewed in the gill-chamber 
 mainly by the action of the scaphognathite, and in the Mussel 
 the same end is effected by ciliary action. Water streams 
 in at the mouth, and out through the branchial clefts in 
 Amphioxus and Dogfish, partly as a result of ciliary action in 
 the former, where, too, matters are complicated by the presence 
 of an atrial cavity. In the four air-breathing forms inspiration 
 and expiration may be distinguished, and special provisions are 
 made for these the muscular floor of the Snail's lung the 
 buccal respiration of the Frog the contraction and elastic ex- 
 pansion of the body-walls in the Pigeon and costal, together 
 with diaphragmatic respiration, in the Rabbit. An increase of 
 surface is gained in various ways both in the case of lungs 
 and gills. 
 
 (2) Excretion. The contractile vacuole assists this in Amreba 
 and Vorticella. Ascaris possesses two lateral excretory tubes 
 opening anteriorly by a common ventral pore. The branched 
 excretory system of Tapeworm and Fluke is very complicated, 
 and almost every segment in Earthworm and Leech possesses its 
 own pair of complex glandular nephridia. A pair of glandular 
 kidneys (? nephridia) are found in Mussel, and one (another 
 example of asymmetry) in the Snail. The renal function is per- 
 formed in the Crayfish by the paired green glands. Amphioxus 
 appears to possess various excretory structures. The kidneys 
 of the Dogfish, Frog, Pigeon, and Rabbit are very complicated, 
 but essentially consist of glandular tubules, each commencing 
 in a filtering apparatus (Malpighian body). The kidney in 
 the Pigeon and Rabbit is a metanephros, not morphologically 
 equivalent to the kidney of the Frog, but it is preceded in 
 development by a transitory mesonephros, which is homologous. 
 The kidney of the Dogfish is partly mesonephros, partly meta- 
 nephros. In all these forms the mesonephros is at first made 
 up of tubules in which a segmental arrangement can be detected. 
 If the nephridia on each side of the Earthworm communicated 
 with a duct which opened into the posterior part of the gut, a 
 structure would be produced of similar nature. A urinary 
 bladder is present in the Frog and Rabbit, which in one case is 
 
COMPARATIVE ANIMAL MORPHOLOGY AND PHYSIOLOGY. 317 
 
 a rudimentary allantois, and in the other is the proximal end 
 of that structure, and receives the urinary ducts. 
 
 4. Reproduction. This is effected asexually in Amoeba and 
 Vorticella by means of fission, and in Hydra by means of gem- 
 mation. 
 
 Sexual Reproduction is first hinted at in conjugation, which 
 differs somewhat from the same phenomenon as exhibited by 
 plants, in that it is merely a temporary or permanent (as in 
 Vorticella) fusion of two similar or dissimilar individuals which 
 leads to more vigorous asexual reproduction. In Gregarina it is 
 followed by spore-formation. 
 
 In Hydra both male and female reproductive organs, spermaries 
 and ovaries, producing male and female reproductive cells (sperms 
 and ova) respectively, are present in the same individual. Fer- 
 tilization is, probably, preceded in all cases by the formation of 
 two polar cells from the ovum, and in most forms at any rate the 
 germinal cells producing sperms are not entirely used up in the 
 process. 
 
 The spermaries and ovaries may be termed the essential organs, 
 and advance upon the conditions seen in Hydra principally con- 
 sists in the development of various accessory parts, such as ducts, 
 special glands, and copulatory organs. Amphioxus, however^ 
 possesses no such supplementary structures. In Dogfish and 
 Frog the mesonephros performs, in the male, a double function. 
 In the Pigeon and Rabbit the mesonephros aborts, but its duct 
 remains in the male as the spermiduct. A cloaca is present in 
 the Dogfish, Frog, and Pigeon, but, in the Rabbit, the termination 
 of the alimentary canal is quite distinct from that of the urino- 
 genital organs, and opens to the exterior by an anus, while they 
 do so by an urinogenital opening. 
 
 Considerable variations are presented in development, which 
 are largely dependent upon the amount of food-yolk in the egg. 
 In the Rabbit this is present in but very small quantity, and the 
 nutritive material and oxygen required by the embryo are supplied 
 by the mother, the embryonic and maternal blood-vessels becoming 
 closely related in the placenta. Waste is partly carried off in the 
 same manner. 
 
 Hydra differs markedly from the higher forms, in that two 
 germinal layers only, ectoderm and endoderm, are present. This 
 animal is in fact little more than a permanent gastrula. The 
 
318 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 embryos of the higher forms, possess three germinal layers ecto- 
 derm, endoderm, and mesoderm. Alternation of generations is 
 exemplified in the life-history of Fluke, and possibly of Tape- 
 worm. 
 
 5. Contractility. This is exhibited in the three forms of move- 
 ment, amoeboid, ciliary, and muscular. 
 
 Amoeboid movement is typically seen in Amoeba, from which 
 animal its name is derived. It is also observable in the endoderm 
 cells of Hydra and the epithelial cells lining the intestine of the 
 Fluke. From this animal upwards the power of amoeboid move- 
 ment is mainly retained by the colourless corpuscles found in 
 lymph and blood (leucocytes). 
 
 Ciliary movement is first seen in Yorticella. and is also shown 
 by the endodermal cells of Hydra, and the external surface of 
 the ciliated embryo in the Fluke. Cilia are found in the seg- 
 mental organs and oviducts of the Earthworm, and cover the 
 gills, labial palps, and inner side of the mantle-lobes in the Mussel, 
 in which animal they play a very important part in respiration 
 and nutrition, as is also the case in Amphioxus. In the Frog cilia 
 line the mouth-cavity, and are present in the lungs, oviducts, and 
 elsewhere. In the Pigeon and Eabbit ciliary action is mainly 
 exemplified in the trachea and oviducts. Most sperms are pro- 
 pelled by flagella. 
 
 Muscular movement is foreshadowed in the cortical layer of 
 Vorticella and Gregarina, and tailed cells of the ectoderm in 
 Hydra. The muscles are at first largely connected with the skin, 
 as seen in the Fluke, Ascaris, Earthworm, and Leech. The 
 exoskeleton of the Crayfish, Mussel, and Snail, serves for the 
 attachment of muscles, as does the endoskeleton of the Dogfish, 
 Frog, Pigeon, and Eabbit. 
 
 Muscular fibres play an important part in the working of most 
 of the organs of the body, and a distinction arises in the 
 vertebrate forms between unstriated and striated muscle, which 
 belong to the internal organs, and the muscles respectively. 
 These varieties of muscle fibre are distinguished by histological 
 characters (cf. p. 208), and their involuntary and voluntary nature, 
 the latter difference depending upon nerve-supply. 
 
 Locomotion is one of the most important outcomes of con- 
 tractility. It is effected by amoeboid movement in Amoeba, 
 ciliary action in free-swimming Vorticellae, and muscular con- 
 
COMPARATIVE ANIMAL MORPHOLOGY AND PHYSIOLOGY. 319 
 
 tractions in the higher forms. The Earthworm progresses in 
 a characteristic fashion, by contractions of its dermal musculature, 
 while Amphioxus and Dogfish can swim by means of their 
 lateral muscles, aided in the latter by paired fins. The tadpole 
 swims pretty much like a fish, but the Frog is adapted to 
 terrestrial locomotion by means of transversely jointed limbs, 
 which are also effective swimming organs. The limbs of the 
 Rabbit are completely given up to movements on land, and in it, 
 as in the Frog, the hind-limbs are the longer, this being 
 connected with the leaping habit. In the Pigeon the fore-limbs 
 are modified into organs of flight. 
 
 6. Irritability and Spontaneity (1) Nervous System. Un- 
 differentiated in Amreba, Vorticella, and Gregarina, and very 
 diffuse in Hydra. The Fluke and Ascaris possess a fairly well- 
 developed nervous system with ganglia and nerve-cords. The 
 two elements, ganglion-cells and nerve-fibres, are here found, 
 the former being mainly confined to the ganglia. In the Earth- 
 worm the segmentally arranged nervous system consists of a 
 nerve-collar and ganglionated ventral cord, but the ganglia, with 
 the exception of the cerebral, are not very distinct, and the 
 ganglion-cells are not confined to them. Nerve-fibres are afferent 
 and efferent, the former being mainly sensory, the latter mainly 
 motor. The nervous system of the Leech is similar, but the 
 ganglia are very distinct, and this is also the case in the Crayfish, 
 where, however, a good deal of fusion has taken place, especially 
 anteriorly. At the same time a distinct head, containing the 
 main ganglionic masses and with which the chief sense organs 
 are connected, is present. The nervous system of the Mussel is 
 made up of three pairs of widely separated ganglia connected by 
 nerve-cords. Three pairs can also be recognized in the Snail, but 
 here they are very much localized and a distinct head is present. 
 Amphioxus possesses a dorsal nerve-tube contained in a neural 
 canal. The Dogfish, Frog, Pigeon, and Rabbit possess very 
 complicated nervous systems, consisting of brain with spinal cord, 
 contained in the neural canal, cranio-spinal nerves, and sympa- 
 thetic system. The brain becomes more complicated, mainly by 
 the increase in size of the cerebral hemispheres and cerebellum, 
 the former of which are connected together in the Rabbit by the 
 corpus callosum and fornix. At the same time, histological 
 distinction may be drawn between medullated and non-medullated 
 
AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 nerve-fibres. The latter are especially characteristic of the 
 sympathetic system. 
 
 There is reason to believe that the nervous system is derived from the 
 epidermis, with which, in lower forms, it often remains closely connected. 
 The deeper position in higher forms has been assumed for protective 
 purposes. The development of the brain and spinal cord (see Frog) exem- 
 plifies the steps in such a change of position. A nervous plexus underlying 
 the epidermis appears to have preceded definite nerve-cords, which have 
 probably arisen by condensation of parts of such a plexus, with which they 
 may co-exist. In Amphioxus, for example, there is such a plexus. 
 
 The typical form of the nervous system (when differentiated nerves are 
 present) in a radially symmetrical animal, is that of a ring. The assump- 
 tion of bilateral symmetry would pull this out into a long loop, the anterior 
 end of which might thicken into cerebral ganglia. The sides of the loop 
 might remain separate, and even (cf. lateral nerves of Fluke) become dis- 
 connected behind. By the ventral fusion of such lateral nerves a circum- 
 esophageal ring and double ventral cord (Earthworm and Crayfish) might 
 be produced. 
 
 (2) Sense Organs. These are not differentiated in Amoeba, 
 Vorticella, and Gregarina, and are absent in Tapeworm as a 
 result of parasitism. It may be mentioned here that a sense 
 organ essentially consists of one or more usually elongated sense- 
 cells (end-organs), of epithelial nature, and connected on the one 
 hand with the nervous system, while on the other they are 
 adapted to receive impressions from various stimuli coming, in 
 the large majority of cases, from the exterior. 
 
 The function of the lateral line organs and ampullae of Dog- 
 fish are not certainly known. 
 
 (a) Tactile Organs. Under this heading may be classified with 
 more or less certainty cnidocils and palpocils of Hydra, head- 
 papilla of Fluke, tactile papillae of Ascaris, segmental papillae of 
 Leech, setae of Crayfish, labial palps and tentacles round inhalent 
 opening in Mussel. Definite tactile cells are present in the skin 
 of Snail, Amphioxus, Dogfish, Frog, Pigeon, and Rabbit. 
 
 (b) Gustatory Organs. These are not certainly known except 
 in the Frog, Pigeon, and Rabbit, where, as taste-cells, they are 
 supplied by the glosso-pharyngeal nerve. In the last case they 
 occur aggregated into well-marked taste-buds, localized in the 
 circumvallate papillae and papillae foliatae. 
 
 (c) Olfactory Organs. These are probably represented in the 
 Crayfish by olfactory setae, and in the Snail by the epithelium 
 on the tips of the tentacles. The Dogfish, Frog, Pigeon, and 
 
MAX. 321 
 
 Rabbit possess nasal sacs largely lined by olfactory epithelium 
 containing numerous olfactory cells. 
 
 (d) Auditory Organs. These are first recognizable in the Cray- 
 fish, where they exist in the form of small, open, auditory sacs, 
 lodged in the basal joints of the antennules, and lined by sensory 
 epithelium. In the Mussel and Snail closed sacs are found, similar, 
 in essential respects, to the open sacs of the Crayfish. By the 
 growth of such simple vesicles into a complicated shape, the 
 membranous labyrinths found in the Dogfish, Frog, Pigeon, and 
 Rabbit are formed during development. To these may be super- 
 added accessory parts making up middle and external ears. 
 
 The function of the " auditory organs " of Invertebrates is ill understood. 
 In some cases they have been shown to be concerned with the perception of 
 position in space, as is the case with the semicircular canals of Vertebrates. 
 
 (e) Visual Organs. Two eyes in the form of pigment-spots are 
 possessed by the ciliated embryo of the Fluke. In the Earthworm 
 the cerebral ganglia themselves appear to be sensitive to light 
 acting upon them through the translucent skin; and the pigmented 
 part of the skin is sensitive to light (as also in the Snail). The 
 Leech possesses eyes, which appear to be modified tactile organs. 
 The Crayfish possesses compound eyes, to which the theory of 
 "mosaic vision" is applicable, while the simple -eyes of the Snail 
 resemble in principle those of the Frog, Pigeon, and Rabbit, which 
 have a double origin, being partly formed by involutions from 
 the exterior, and partly by outgrowths from the fore-brain. It 
 is doubtful whether the so-called " eye " of Amphioxus has a 
 visual function. 
 
 CHAPTER XIV. MAN. 
 
 THE aim of this chapter is to form a connecting link between the 
 subjects of General Biology and Human Anatomy as successively 
 taken in a medical course, and it mainly consists of a statement 
 of the leading differences between Rabbit and Man, so that a 
 student who has carefully dissected the former will be able to 
 turn the knowledge thus gained to useful account when he comes 
 to dissect the latter. Comparative Anatomy is also of import- 
 ance in relation to therapeutics and pathology. Those characters 
 2 21 
 
322 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 are also given by which Man is distinguished anatomically from 
 the forms most closely related i.e., the higher apes. 
 
 The proportions of the human body and the structure of many 
 of its parts are influenced by two chief factors, (1) the erect 
 attitude, and (2) the mental development. 
 
 (1) Man is the only Mammal in which the erect position is 
 habitual, easy, and maintained without the help of the upper 
 limbs. In accordance with this the lower limbs, which are much 
 the longer, have become specialized as supports and means of 
 progression, with corresponding loss of mobility in the feet. The 
 relatively short upper limbs, on the contrary, are capable of 
 performing exceedingly complex movements, and the hand is 
 capable of the most delicate manipulation as a combined result 
 of extreme flexibility, the presence of a long thumb opposable to 
 the remaining digits, flat nails, and a delicate sense of touch. 
 These characteristics are associated with corresponding features 
 in the structure of the skeletal and muscular systems. 
 
 (2) Omitting psychological characteristics, although these are 
 by far the most distinctive, the relatively great mental develop- 
 ment of Man is associated with exceedingly large cerebral hemi- 
 spheres, and this again profoundly influences the proportions of 
 the skull. 
 
 Comparison with Rabbit. 
 
 In human anatomy the body is supposed to be in a vertical position, so 
 that upper (superior), lower (inferior), front (anterior), back (posterior) 
 are used as the respective equivalents of the terms front (anterior), back 
 (posterior), lower (ventral), upper (dorsal), as used in Comparative Anatomy. 
 The latter set of terms will be employed here. 
 
 1. Skin. The covering of hair is very much reduced as regards 
 strength and thickness, but the only large areas entirely devoid 
 of hair are the palms of the hands and soles of the feet, this being 
 associated in the former case with very great tactile sensibility. 
 
 2. Endoskeleton. 
 
 I. Axial Skeleton. (1) The skull is accurately poised upon 
 the vertebral column, the two occipital condyles being situated 
 about the middle of its base and the occipital plane being hori- 
 zontal. The cranium is of enormous relative size, in correlation 
 with the dimensions of the brain, while the facial region is 
 reduced, owing to the smaller development of the olfactory 
 capsules, and the reduction of the jaws, which are no longer 
 
MAN. 323 
 
 directly used as weapons of offence and defence, nor in procuring 
 food. The facial * and basicranial axes are not, as in the Kabbit, 
 nearly in the same straight line, but the former is bent sharply 
 downwards, so that the craniofacial angle is not more than 120, 
 and in many races may be much less, 90 being the usual inferior 
 limit. Many of the bones of the skull are very strong and thick, 
 and fusion has taken place to a much larger extent than in the 
 Rabbit, (a) Cranium. The four elements of the occipital ring 
 (basi-, ex-, and supra-occipitals) are united into a single occipital 
 bone, and a median sphenoid bone is formed by the fusion of the 
 ventral portions of the parietal and frontal rings. The sphenoid 
 consists of a central body and two pairs of lateral expansions or 
 " wings." The anterior part of the body = presphenoid, and the 
 posterior part (on the dorsal side of which is the sella turcica for 
 the pituitary body) = basisphenoid. The anterior or lesser wings 
 = orbitosphenoids, and the posterior or greater wings, with which 
 the small pterygoids are fused ventrally, = alisphenoids. The 
 parietals are distinct, but the frontals are usually united together 
 into one bone. The ethmoid bone, which completes the morpho- 
 logically anterior end of the cranium and forms a large part of 
 the bony framework of the olfactory capsules, consists of (a) a 
 small horizontally placed cribriform plate, (ft) a vertical bony plate 
 (lamina perpendicularis), which with its cartilaginous continuation 
 (septum nasi) constitutes a party- wall between the olfactory cap- 
 sules, and (y) two lateral masses of the ethmoid ( = ethmoturbinals) 
 projecting into the capsules. In the auditory- region of the cranium 
 a great deal of fusion has taken place leading to the formation of 
 a large temporal bone = periotic + tympanic + squamosal, which 
 are represented by different regions, as follows : Petrous and 
 mastoid regions = periotic, tympanic plate = tympanic, and 
 squamous region =- squamosal. Besides this, the temporal pos- 
 sesses a prominent styloid process mainly formed by the fusion 
 of two small elements (tympano-hyal and stylo-hyal) belonging to 
 the upper end of the hyoid arch. (b) Face. The olfactory 
 capsules are relatively short and deep. The part taken by the 
 ethmoid in their formation has been mentioned above. Each 
 lateral mass of the ethmoid is divided into upper and lower parts, 
 known as the superior and middle turbinate bones. These are 
 
 * The facial axis is a line joining the front of the premaxilke with the 
 anterior end of the basicranial axis. 
 
324 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 much less complex than the corresponding ethmoturbinal of the 
 rabbit, which is also the case with the inferior tnrbinate bone 
 representing the maxilloturbinal. The equivalent of the naso- 
 
 Fig. 96. MAN. Skull in Longitudinal Vertical Section (from Mnc- 
 alisler). A, Frontal; B, parietal; C, occipital; D, squamous part of 
 temporal; E, sphenoid body; F, lamina perpendicularis ; G, vomer; 
 H, nasal ; J, superior maxilla. 2, Suture between frontal and parietal ; 
 3, suture between parietals ; 4, boundary of D ; 5, suture between 
 parietal and occipital ; 9, internal auditory meatus on inner side of 
 petrous part of temporal ; 10, condylar foramen ; 11, sella turcica ; 12, 
 sphenoidal fissure; 14, placed below cribriform plate; 16, external 
 pterygoid process; 17, styloid process. 
 
 turbinal is here found in the uppermost lamella of the superior 
 turbinate. The nasals are small, but the vomer is of considerable 
 size and produced ventrally into a vertical plate which divides, 
 the posterior nasal passage into right and left halves. 
 
MAN. 
 
 325 
 
 The orbits are for \vardly directed and almost completely shut 
 oft' by bone from the temporal fossae. 
 
 The superior maxillary bones ( = premaxillse + maxillae) which 
 support the upper jaw, are of great importance in the formation 
 of the face. Above, they partly wall in the olfactory capsules, 
 and together with the malars, frontal, and lachrymals, form the 
 margins of the orbits. Below, they present a horseshoe-shaped 
 
 ridge excavated by the 
 sockets of the upper teeth, 
 and large palatine pro- 
 cesses,"' making up the 
 greater part of the hard 
 palate, which is relatively 
 much larger than in the 
 rabbit. The hard palate 
 
 Fig. 97. MAX. Dorsal view of Sacrum 
 (from Macalister). 
 
 Fig. 98. MAN. Dorsal 
 view of Coccyx (from 
 MacaUstf.r). 
 
 is completed by palatal bones, and immediately behind it on each 
 side there is a pterygoid plate projecting downwards from the 
 greater wing of the sphenoid ( = alisphenoid) and divided into 
 an external pterygoid plate, and a narrow internal pterygoid 
 plate ( = pterygoid bone) produced into a hook-like process. 
 
 The most noteworthy features in the inferior maxilla or bone 
 of the lower jaw ( = mandible) are the very complete fusion of 
 its two rami and the presence of a chin-projection or mental 
 prominence at the symphysis. The inferior maxilla also presents, 
 in the upper side of its horizontal part, a horseshoe-shaped ridge 
 excavated by the sockets of the lower teeth. 
 
 The vertebral column is both strong and flexible. To support 
 the vertically-placed body great strength is necessary, and in 
 
 * If these processes fail to unite in the middle line cleft palate results. 
 
326 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 accordance with this the column broadens out below, especially 
 in the sacrum which transmits the weight to the innominate 
 bones. Strength and flexibility are both given by the series of 
 gentle curves into which the spine is thrown, and a kind of spring 
 is thus constituted by which the transmission of shocks to the 
 brain is prevented. The convexities of these curves are ventral 
 in the neck and loins. The vertebrae are usually thirty-three 
 in number, as follows : Cervical 7, dorsal ( = thoracic) 1 2, 
 lumbar 5, sacral 5, coccygeal ( = caudal) 4. The sacral vertebra 
 are fused into a large, strong sacrum. The caudal (coccygeal) 
 vertebrae are very much reduced, and, in the adult, generally 
 become anchylosed together into a small triangular coccyx. 
 
 The sternum is relatively broad and flat, nor is it divided into 
 distinct sternebree, although manubrium and xiphisternum com- 
 monly remain distinct. The former does not possess a ventral keel. 
 
 There are twelve pairs of ribs, of which the first seven are 
 " true," their costal cartilages ( = sternal ribs) uniting directly 
 with the sternum. Of the remaining five pairs of " false " ribs, 
 the first three pairs have costal cartilages connected with the 
 preceding ones, while the last two pairs (" floating " ribs) possess 
 free ventral ends. 
 
 II. Appendicular Skeleton (1) Fore -Limb. The most note- 
 worthy point regarding the shoulder girdle is the presence of a 
 strong /-shaped clavicle or collar-bone stretching from sternum 
 to scapula. The presence of clavicles is associated with the 
 power of free lateral movement possessed by the arms, these 
 bones acting as props to keep the shoulders well apart, and 
 giving points of attachment to several muscles. Free Limb. The 
 articulation of the humerus with the very shallow glenoid cavity 
 forms an exceedingly free ball-and-socket joint, contrasting with 
 the hinge-joint at the elbow. 
 
 The radius has a very large distal end which plays the chief part 
 in the support of the hand, and it is capable of rotation upon the 
 ulna at both ends. When the palm is placed upwards (supine 
 position) radius and ulna are parallel, but if it is then turned down- 
 wards (prone position) the radius rotates on the ulna, carrying the 
 hand round with it. In the rabbit the arm is immovably fixed 
 in the prone position. The ulna is larger than the radius, and 
 its large proximal end takes a larger share in forming the elbow 
 joint. The large olecranon process prevents over-extension. 
 
MAN. 
 
 32 
 
 The carpus differs from that of the rabbit in the absence of a 
 distinct centrale, it being fused with the radiale. The propor- 
 tionate size of the different elements is not the same, carpale 3, 
 for example, being relatively very large. The following will give 
 some idea of the method of arrangement, the theoretical names 
 being placed in parentheses : [R = radius ; U = ulna.] 
 
 R U 
 
 scaphoid semilunar cuneiform pisiform 
 
 (radiale + centrale); (intermedium); (ulnare); 
 
 trapezium trapezoid magnum unciform 
 
 (carpale 1) ; (carp. 2) ; (carp. 3) ; (carp. 4 + carp. 5) 
 
 The skeleton of the hand is completed by five metacarpals, and 
 fourteen phalanges, of which two belong to the thumb, and three 
 to each of the fingers. The first 
 metacarpal articulates with a saddle- 
 shaped surface on the trapezium, 
 which allows of very free move- 
 ment, so that the thumb can be 
 readily opposed to the other digits. 
 (2) Hind -Limb. The ossa inno- 
 minata which constitute the hip- 
 girdles are very broad, and together 
 with the sacrum and coccyx make , 
 up the basin -shaped pelvis, by e 
 which the weight of the trunk is 
 supported and transmitted to the 
 legs. Each os innominatum is 
 made up of the same four elements 
 as in the rabbit i.e., ilium, pubis, 
 ischium, and acetabular ( = coty- 
 loid), but the last is very small 
 and fused with the pubis, of which I 
 for all practical purposes it is con- 
 sidered a part. The ilia are very 
 broad and expanded ; the pubes 
 but not the ischia meet in a median 
 ventral symphysis. The large size 
 and strength of the bones supporting the free limb are worthy 
 of notice. The femur is very long, tibia and fibula are well 
 developed and separate, and there is a large patella. The bones 
 
 L99. MAN. Skeleton of 
 ft Hand. Dorsal view (from 
 Macalister). 1 , Scaphoid ; 2, 
 semilunar; 3, cuneiform; ^pisi- 
 form ; 5, trapezium; 6, trapezoid; 
 7, magnum; 8, unciform; 9-13, 
 metacarpals; b,c,d,e, phalanges. 
 
328 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 of the foot are arranged so as to constitute strong arched supports, 
 the parts which touch the ground being the outer sides, heels, 
 and front part of the sole. The tarsal bones are as follows : 
 [T = tibia ; F = fibula.] 
 
 Fig.'lOO. MAN. Ventral view of Pelvis (from Afacalister). 1, Sacrum: 
 2, 5, 6, 7, 8, ilium; 4, 13, pubis; 14, pubic symphysis; 3, 10, ischium : 
 9, acetabulum; 11, obturator foramen. 
 
 5 pi 
 
 Fig. 101. MAN. Outer Side of Right Foot (from Macalitter). Ta, 
 Astralagus ; Ca, calcaneum ; N, navicular ; CI, CII, CHI, internal, 
 middle, and external cuneiforms ; Cb, cuboid ; M5, fifth metatarsal. 
 
 T F 
 
 astragalus (tibiale + intermedium) ; calcaneum (fibulare) 
 
 navicular (centrale) 
 
 \ internal middle external 
 
 cuneiform cuneiform cuneiform cuboid 
 
 (tarsale 1); (tars. 2); (tars. 3); (tars. 4 + tars. f>) 
 
31 AN. 
 
 329 
 
 The foot is completed by five metatarsals, and fourteen 
 phalanges, of which two belong to the great toe and three to each 
 of the other digits. In the rabbit the great toe (hallux) is only 
 represented by a process of the 2nd metatarsal, there being no 
 distinct equivalents of the internal cuneiform (tarsale 1) and 
 1st metatarsal with the two corresponding phalanges, of the 
 human foot. 
 
 3. Digestive Organs. The only parts of the alimentary canal 
 which call for special notice are mouth-cavity, pharynx, and caecum. 
 
 Mouth and Mouth-cavity. The pathological condition known 
 as hare-lip must not be confounded with the cleft upper lip of 
 rabbit and hare. The upper 
 boundary of the mouth is formed 
 to begin with by a median fronto- 
 nasal process and a maxillary pro- 
 cess growing forward on each side 
 (<:f. Fig. 94) from the mandibular 
 arch. This is the permanent 
 condition in a dogfish (Fig. 46), 
 but in chick, rabbit, and man, 
 the fronto-nasal and maxillary 
 processes fuse together and con- 
 stitute a continuous ridge within 
 which premaxillae and maxillae 
 develop. Failure of this union Fig. 102. iM AN. Junction of Small 
 on one side is the cause of single and Large Intestines (from Mac- 
 hare-lip, while failure on both 
 sides results in double hare-lip. 
 The cleft in a rabbit's lip is median, and does not affect the hard 
 parts. 
 
 There are no papilla? foliatae on the tongue, the circumvallate 
 papillae are from 7 to 1 2 in number, and arranged on the pos- 
 terior part of the back of the tongue in the form of a V with 
 backwardly directed apex. 
 
 The upper and lower teeth are arranged in two horseshoe- 
 shaped curves. There are no gaps, and the canines are not dis- 
 proportionately large. The dental formula is 
 
 allster. 1, Colon; 2, caecum ; 3, 
 vermiform appendix ; 4, ileum. 
 
 2 2 
 
 1-1 
 
 2-2 
 
330 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 The premolars are termed bicuspids. 
 
 The caecum and appendix vermiformis are extremely small as 
 compared with the same structures in rabbit. 
 
 Dorsal, aorta, 
 
 Fig. 103. MAN. Diagram to explain fate of Aortic Arches (from 
 Macalister). The parts in black are obliterated. 
 
 The large glands which open into the alimentary canal are sali- 
 vary glands, liver, and pancreas. Infra-orbital salivary glands 
 are not represented, the liver is not so deeply cleft into lobes, 
 
MAN. 
 
 331 
 
 and the duct of the compact pancreas joins the bile duct in the 
 Avail of the duodenum. 
 
 4. Circulatory System. Three arteries come off from the aortic 
 arch, (a) innominate, from which right subclavian and right 
 common carotid arise, (b) left common carotid, (c) left subclavian. 
 The fate of the embryonic aortic arches is shown in Fig. 103. 
 
 1st ( =mandibular) arches become ophthalmic branches of external carotids. 
 
 ( middle 
 " | meningeal 
 
 internal carotids. 
 
 2nd ( = hyoid) 
 
 3rd ( = 1st branchial) 
 
 4th ( = 2nd branchial) 
 
 left 
 right 
 
 5th ( = 3rd branchial) 
 left \ 
 right / 
 
 ( aortic arch 
 
 < represented by a very variable arteria 
 
 f aberrans. 
 
 / pulmonary artery. 
 1 obliterated. 
 
 Veins. The development of the caval system is illustrated by 
 There are to begin with anterior and posterior car- 
 
 Fig. 104. 
 
 Fig. 104. MAN. Diagram to explain Development of Systemic Veins 
 (from Macalister). Three successive stages are represented, R.C. and 
 L.C, Cuvierian veins; R.V.I., L.V.I., vena innominata ; S.V.C., 
 superior vena cava ; sup. *, superior intercostal; h.a~, hemi-azygos. 
 
 dinals, which, as in the adult Dogfish (cf. p. 165),unite together 
 on each side to constitute a Cuvierian vein which opens into the 
 
332 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 heart. The anterior cardinals persist as the external jugulars; 
 internal jugulars and subclavians are developed later on. So far 
 there is agreement with the Rabbit, but in Man an oblique cross- 
 connection is established between the junction of the left jugular 
 and subclavian and the middle of the right Cuvierian vein. This 
 cross-piece becomes the left innominate vein, the part of the right 
 Cuvierian vein distal to it becomes the right innominate, and the 
 part proximal to it becomes the superior vena cava. The left 
 Cuvierian vein partly aborts, but its proximal end persists as a 
 coronary sinus, which receives the coronary veins and opens into 
 the right auricle, while its distal end becomes the superior inter- 
 costal vein. 
 
 Fig. 105. MAN. Development of Urinogenital Organs (from Landois and 
 Stirling). I, Undiffereiitiated condition D, Gonad, resting on tubules 
 of mesonephros, W; M, Miillerian duct; S, urinogenital sinus. II, 
 Transformations in the female F, Funnel, with hydatid (h'), of 
 Fallopian tube, T; U, utero-vaginal region formed by fusion ; O, ovary, 
 with parovarium, P, &c. Ill, Tranformations in male h, Hydatid of 
 Morgagni ; u, uterus masculinus ; H, spermary (testis), with vasa 
 efferentia running to epididymis, E ; a, vas aberrans ; V, spermiduct 
 (vas deferens). 4, Shows bladder (a) and rectum (d) opening into 
 cloaca. 5, Later stage, where bladder (6) and urinogenital sinus (S) 
 are separated from end of rectum (M) by a perineum (m). 
 
 The posterior cardinals atrophy in the middle of their course ; 
 their hinder ends become the internal iliac veins. The anterior 
 part of the right posterior cardinal is converted into the azygos 
 
MAN. 333 
 
 vein, with which is connected ;i hemi-ozygos vein developed from 
 part of the left posterior cardinal. 
 
 The inferior vena cava (posterior v.c.) only becomes important 
 when the hind-limbs have been developed to some extent. It is 
 formed by the union of iliac veins. 
 
 5. Urinogenital System. The excretory organs of the embryo 
 consist, as in the rabbit, of a mesonephros (Wolffian body) on 
 each side, from which a mesonephric duct (Wolffian duct) runs 
 back to open into an urinogenital sinus. The adult kidney is a 
 metanephros, and the ureter (metauephric duct) is an outgrowth 
 from the posterior end of the mesonephric duct. As before, the 
 bladder is the proximal end of the allantois. The reproductive 
 organs at first consist of a pair of gonads and two Mullerian ducts, 
 and later on the excretory organs of the embryo in part become 
 genital ducts, and in part are reduced to rudiments, which are of 
 considerable importance from a medical point of view, since they 
 may enlarge and become the seat of disease. The following table 
 exhibits the most important details regarding the fate of the 
 embryonic excretory organs and Mullerian ducts. Rudiments are 
 italicized. 
 
 As compared with the Rabbit it should be noticed that (1) in 
 the male there are vesicuhie seminales, while the uterus masculinus 
 is relatively small. (2) In the female the most important part is 
 the single uterus, though in abnormal cases the Mullerian ducts 
 may fuse less completely. 
 
 6. Nervous System. The brain (Figs. 106 and 1 07) is exceed- 
 ingly large, one result of which is to profoundly influence the 
 shape and proportions of the skull, as already explained. This 
 increased size is mainly due to the enormously developed cerebral 
 hemispheres, which overlap and largely conceal the other regions, 
 extending in all directions to such an extent that nothing else is 
 visible in a brain viewed from above. In the rabbit the hemi- 
 spheres leave the cerebellum quite uncovered, while they are 
 nearly smooth and a division into lobes is only indicated. In 
 each hemisphere of the human brain, on the contrary, six chief 
 lobes can be distinguished, and its surface is marked by elabor- 
 ately arranged convolutions (gyri) separated from one another by 
 furrows (sulci). In this way the surface is 5| times as great as 
 if it were smooth, and the extent of the cortex is correspondingly 
 increased. It is an established fact that the intelligence of an 
 
334 
 
 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 ADULT MALE. 
 
 EMBRYO. 
 
 ADULT FEMALE. 
 
 Vasa efferentia (coni 
 vasculosi), 
 
 Vasa aberrantia and 
 parepididymis (or- 
 gan of Giraldes). 
 Blindly ending tub- 
 ules connected with 
 the epididymis, 
 
 I. Mesonephros. 
 
 1. Anterior tubules, . 
 2. Posterior tubules, . 
 
 Parovarium (organ of 
 Rosenmuller, epoo- 
 phoron). A series 
 of tubules (some of 
 which may be con- 
 verted into hyda- 
 tids) connected with 
 front end of ovary. 
 Paroophoron; a much 
 smaller rudiment 
 lying near the hind 
 end of the ovary. 
 
 Epididymis, . . . 
 
 Spermiduct(vasdefe- ( 
 rens) and branched < 
 vesicula seminalis, ( 
 
 II. Mesonephric Duct. 
 
 1. Anterior part, . . 
 
 2. Middle part, . 1 
 3. Posterior ,, ) 
 
 Par ovarian duct, ter- 
 minating anteriorly 
 in a *hydatid, and 
 sometimes contin- 
 ued back as 
 
 Gartner's duct. 
 
 *Hydatida ofMorgagni 
 (one more constant 
 and of larger size 
 than rest). Situated 
 between spermary 
 (testis) and caput 
 epididymis, 
 
 Aborts . . . . 
 
 III. Miillerian Duct. 
 
 1. Anterior part, . . 
 2 Middle part 
 
 Fallopian tube, to the 
 fimbriated funnel of 
 which a * hydatid 
 is attached. 
 
 Unites with its fellow 
 
 ? Unites with its fellow 
 to form a small uterus 
 masculinus (sinus 
 prostaticus), 
 
 3. Posterior part, . . 
 
 to form a pyriform 
 uterus. 
 
 Unites with its fellow 
 to form vagina. 
 
 * Hydatids are small stalked pear-shaped bodies. 
 
MAN. 
 
 335 
 
 animal is proportional to (1) the size of its hemispheres, and to 
 (2) the complexity of their convolutions. It must be remembered, 
 however, that the absolute size of the animal has also an influence 
 on these factors, as might be expected, since the hemispheres are 
 
 Fig. 106. MAN. Left Side of Brain, showing convolutions on outer side 
 of left hemisphere (from Macalister}. S, Sylvian fissure, running nearly 
 to P 2 ; c, Rolandian fissure ; A, B, S' S", convolutions of opercular lobe ; 
 F, frontal lobe, including convolutions F 1} F 2 , F 3 ; P, parietal lobe, 
 including convolutions P 1} P 2 , P 2 / ; T, temporal lobe, including con- 
 volutions Tj, To, T 3 ; 0, occipital lobe, including convolutions O 1} O 2 , 
 O 3 . N.B. These lobes also include convolutions on the inner flattened 
 side of the hemisphere (see Fig. 107). The bulb and cerebellum are also 
 shown. 
 
 not concerned with sensation and intelligence alone, but also 
 contain the highest motor centres. In fact, the cortex has been 
 partly mapped out into motor centres, regulating definite groups 
 of muscles, and sensory centres, concerned with specific sensations. 
 
336 
 
 AN ELEMENTARY. TEXT-BOOK OF P.IOLOGY. 
 
 The most important sulcus is the Sylvian fissure (just indicated 
 in the rabbit), which marks oft' the temporal lobe below. Above 
 this another important sulcus, the central or Jtolandian fissure, the 
 
 
 
 . BOO ^ 
 
 " 
 
 11111 
 
MAN. 337 
 
 convolutions bounding which constitute the opercular lobe* The 
 frontal lobe is anterior to this, the parietal lobe posterior to it, and 
 there is an occipital lobe at the extreme back of the hemisphere. 
 Besides this, there is a small central lobe (island of Eeil) which 
 can only be seen by separating the lips of the Sylvian fissure. 
 The opercular lobe has been mapped out into lower, middle, and 
 upper motor areas for the muscles of the face, leg, and arm 
 respectively. The following sensory centres have also been 
 
 Fig. 108. MAN. Embryo in Uterus, showing Foetal Membranes (from 
 Macaiister, after Longet). al, Stalk of allaiitois ; am, amnion ; c, neck 
 of uterus ; ch, chorion ; dr, decidua reflexa ; ds, decidua serotina ; du, 
 decidua vera ; nb, yolk-sac ; z, placental villi ; z 1 , transient villi. 
 
 recognized (with less certainty) in other lobes, (a) Sight, occipital 
 lobe ; (b) Hearing, uppermost convolution of temporal lobe (T) ; 
 (c) Smell, inner side of temporal lobe, just below Sylvian fissure. 
 The corpus callosum is relatively very large, and it is much more 
 strongly curved than in the rabbit. The anterior commissure is 
 smaller, and so are the olfactory lobes. There are two corpora 
 mammillaria (c. albicantia). 
 
 The cerebellum is well-developed, but, in comparison with the 
 
 * Many anatomists do not recognize the opercular lobe as a distinct sub- 
 division, and take the Rolandian fissure as the line of demarcation between 
 frontal and parietal lobes. 
 
 2 22 
 
338 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 hemispheres, smaller than in the rabbit ; its lateral lobes are far 
 larger than the median one, and the flocculi are insignificant. 
 
 There are no corpora trapezoidea. 
 
 7. Placenta. This is of the type known as metadiscoidal, for, 
 although it is circular like that of the Rabbit, yet, to begin with, 
 villi are developed over the entire surface of the chorion, though 
 they only persist over a limited area. These villi, too, are much 
 branched, and their relation to the maternal tissue is complex. 
 It will also be observed that the placenta is opposite the ventral 
 surface of the embryo, the reverse being the case in the Rabbit 
 (Fig. 95). The yolk-sac (umbilical vesicle), again, is of less 
 importance. The thickened mucous membrane lining the uterus 
 is known as the decidua, because it is shed at birth. That part 
 of it which forms the maternal portion of the placenta is the 
 decidua serotina, that lining the rest of the uterus is the decidua 
 vera, and a decidua reflexa surrounding the embryo is formed by 
 the outgrowth and fusion of folds. 
 
 Comparison of Man with the Highest Apes. 
 
 The apes which come nearest to Man in structure are the 
 Gibbons (Hylobates), Orang-outan (Simla satyrus), Chimpanzee 
 (Troglodytes niger), and Gorilla (T. gorilla}. In none of these is 
 the erect attitude maintained without the assistance of the fore- 
 limbs, the easiest and most habitual position. Consequently 
 there are not the same perfect adaptations to this attitude which 
 are formed in Man, and of which the most striking are the 
 following: (1) Double S-shaped curve of the vertebral column, 
 (2) hind-limbs longer than fore-limbs, (3) feet completely special- 
 ized for terrestrial locomotion, (4) pelvis broad and short. Both 
 pollex and hallux are proportionately much larger in Man, but 
 the latter is not opposable as in apes. 
 
 The dental formula of Man and the higher apes is the same, 
 but in Man the teeth form a continuous curve above and below 
 (there being no diastema), and the canines are not so well 
 developed. The canines of apes are disproportionately large 
 when the jaws are closed their points fit into gaps between the 
 incisors and canines above, between the canines and premolars 
 below. 
 
 The most distinctive anatomical features of Man, besides those 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 339 
 
 mentioned, are found in the relatively large cranium and brain. 
 In the Gorilla, for example, which is better developed in these 
 respects than other apes, the brain volume and brain weight are 
 30-35 cubic inches and about 24 oz., as compared with 55-115 
 cubic inches and over 40 oz., in Man. The cerebellum of apes is 
 larger in comparison with the cerebral hemispheres. The cranial 
 capacity of Man is, of course, proportionately large, while the 
 facial part of the skull is relatively small (cf. p. 322), and the 
 cranio-facial angle is less than in apes. The nasal bones of Man, 
 however, project more, and there is a mental prominence (chin) 
 at the mandibular symphysis. 
 
 CHAPTER XV. CLASSIFICATION AND DISTRIBUTION 
 OF ANIMALS. 
 
 THE following is a brief outline of the classification of animals 
 
 (cf. p. 3) :- 
 
 DIVISION A. PROTOZOA. 
 
 Unicellular animals (or if multicellular, as Collozoum, the cells 
 are all similar and independent), not reproducing by means of 
 sperms and ova. 
 
 GROUP 1. RHIZOPODA (Amceba). Protozoa devoid of 
 cuticle, and possessing pseudopodia. 
 
 GROUP 2. INFUSORIA (Torticella). Protozoa covered 
 by a cuticle and possessing flagella or cilia. 
 
 GROUP 3. SPOROZOA (Gregarinida) (Gregarina). 
 Endoparasitic spore-producing Protozoa, covered by a cuticle 
 but devoid of cilia or flagella. 
 
 DIVISION B. METAZOA. 
 
 Multicellular animals, made up of tissues, and reproducing by 
 sperms and ova. 
 
340 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 A. DIPLOBLASTICA. Embryo two-layered. 
 
 PHYLUM I. CCELENTERATA (Hydra}. Radially symmetrical 
 Metazoa with body-wall composed of ectoderm, endoderm, and 
 mesogloea. There is a digestive cavity opening by a mouth, but 
 no body-cavity. 
 
 B. TRIPLOBLASTICA (Ccelomata). Bilaterally symmetrical 
 Metazoa, usually with a body-cavity, and possessing mesoderm 
 in addition to ectoderm and endoderm. 
 
 PHYLUM II. PLATYHELMIA (Distoma, Twnia). Unseg- 
 mented usually flattened worms, without lateral appendages or 
 distinct body-cavity. Nervous system of cerebral ganglia, nerve- 
 cord (not as double ventral cord), and nerve-plexus. Life-history 
 often complex. 
 
 PHYLUM III. NEMATHELMIA (A scans). Elongated cylin- 
 drical unsegmented worms, usually with complete alimentary 
 canal, but no blood-system. Cuticle well developed ; ciliated 
 epithelium absent. Excretory organs as two unbrariched lateral 
 canals opening by a common anterior ventral pore. Sexes distinct. 
 Gullet surrounded by a nerve-ring from which two principal nerves 
 (lateral) run forwards and two (a dorsal and a ventral) backwards. 
 
 PHYLUM IV. ANNELIDA. Elongated segmented worms, 
 with paired nephridia, a nerve-ring, and a ventral ganglionated 
 nerve-cord of double nature. Possess both blood-system and a 
 ccelom. 
 
 Class 1. Chaetopoda (Lumbricus). Annelids possess- 
 ing setae, and with a well-developed coelom. 
 
 Class 2. Hirudinea (Hirudo). Annelids devoid of 
 setae, with segmentation obscured by secondary annu- 
 lation, and with a reduced ccelom communicating with 
 the blood-system. 
 
 PHYLUM V. ARTHROPOD A (Astacus). Segmented animals 
 possessing well-marked body-regions as a result of the differen- 
 tiation of segments. Lateral jointed appendages, and a nervous 
 system of the same type as in Phylum II., but with better- 
 developed ganglia, especially anteriorly. Blood-system largely 
 lacunar, replacing the coelom. 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 341 
 
 PHYLUM VI. MOLLUSCA. Unsegmented animals possessing 
 a mantle and (usually) a shell. The body is ventrally produced 
 into a muscular locomotor appendage, the foot. The blood- 
 system is largely lacunar, and the coelom is reduced to a peri- 
 cardial cavity communicating with the exterior by two tubular 
 kidneys (? nephridia), one of which is often aborted. Nervous 
 system more or less concentrated, and mainly formed of ganglion- 
 ated cesophageal ring. 
 
 GROUP 1. LAMELLIBRANCHIATA (Anodonta, Unio). 
 Molluscs without a distinct head or an odontophore. 
 Shell bivalve and lateral. Nerve-ring long. 
 
 GROUP 8. ODONTOPHORA (Helix}. Molluscs with 
 odontophore, and a distinct head bearing sense-organs and 
 containing a short nerve-ring. Mantle never bilobed. A 
 univalve shell commonly present. 
 
 PHYLUM VII. CHORD AT A. Segmented animals possessing 
 a notochord and visceral clefts, transitorily or permanently. 
 Central nervous system dorsal and (usually) tubular. (See p. 1 35). 
 
 SUB-PHYLUM L HEMICHORDA (Balanoglossus, Cepha- 
 lodiscus,Rhabdopleura). A small group including three genera 
 of worm-like Chordates possessing a proboscis supported by 
 a smaH notochord. [Rhabdopleura has no visceral clefts.] 
 
 SUB-PHYLUM II. UROCHORDA (Ascidians).A. group 
 of degenerate Chordates in which the larva possesses a tail 
 supported by a notochord, both, however, disappearing as a 
 rule before the adult stage is reached. 
 
 SUB-PHYLUM III. CEPHALOCHORDA (Amphioms). 
 A Chordate group containing a single genus, and charac- 
 terized by asymmetry, very complete segmentation, a noto- 
 chord extending from end to end. and the presence of an 
 atrial cavity. 
 
 SUB-PHYLUM IV. FERTEBRATA.ChoTdates with 
 never more than two pairs of limbs, and usually possessing 
 jaws that move up and down and are not constituted by 
 modified appendages. Skin consists of a several-layered 
 epidermis and a connective tissue dermis traversed by vessels, 
 
342 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 nerves, &c. The notochord does not extend further forward 
 than the middle of the ventral side of the brain. It is sup- 
 plemented, or more or less replaced by a well-developed 
 endoskeleton consisting of at least a vertebral column, brain- 
 case, and sense-capsules; also supports for limbs when these 
 are present. The blood contains red as well as colourless 
 corpuscles, and it is enclosed in a system of tubes comprising 
 a ventral heart, arteries, veins, and capillaries. There is a 
 lymph-system, communicating with the blood-vessels, and 
 consisting of the large ccelomic body-cavity, smaller lymphatic 
 spaces, lymphatic vessels, and " ductless " glands, of which 
 the most conspicuous is the spleen. The body may be 
 regarded as made up of two tubes, (a) a smaller dorsal tube 
 enclosing brain and spinal cord, (/3) a larger ventral tube 
 (coelom) containing most of the other organs. Two compact 
 kidneys are present, each provided with a special longitudinal 
 duct. Ova in most cases shed into coelom and are carried off 
 by two oviducts. When the mesonephros persists it not only 
 performs excretory functions, but may also serve as a channel 
 for carrying off the sperms. When entirely replaced by a 
 metanephros it is converted into a conducting-apparatus for 
 sperms. The outlets of the intestine, excretory and repro- 
 ductive organs, are situated close together and ventrally. 
 There is a distinct brain, outgrowths from which develop 
 into the retinae of two eyes, each of which also possesses a 
 lens formed as an ectodermic involution, and a muscular iris 
 of mesodermic origin. Two olfactory sacs and two mem- 
 branous labyrinths are present, all of which are developed 
 from ectodermic involutions. 
 
 A. Anamniot a. Embryo without amnion. Allantois, when 
 present, is not an embryonic appendage. 
 
 GROUP I. ICHTHYOPSID A. Vertebrates with epi- 
 dermic exoskeleton slight or absent. Lateral line sense- 
 organs and a median fin present at some period of life. 
 The notochord often persists, and the vertebrae, when 
 present, are without epiphyses. The cranium always pos- 
 sesses extensive tracts of cartilage, there is never a well- 
 developed basisphenoid, and the cranial membrane bones, 
 when present, include a parasphenoid. The gut either ends 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 343 
 
 in a cloaca or opens by an anus in front of the urinogenital 
 apertures. Blood at about same temperature as surrounding 
 medium, and containing large oval nucleated red corpuscles. 
 Heart two- or three-chambered, and aortic arches never less 
 than two. Gills, and at least four pairs of branchial arches, 
 always present at some period of life. The coelom is not 
 divided into thoracic and abdominal sections by a respiratory 
 diaphragm. The meson ephros persists. The cerebral hemi- 
 spheres are never united by a conspicuous corpus callosum, 
 the hypoglossal nerve does not perforate the brain-case, and 
 the sclerotic coat of eye, when present, is cartilaginous or 
 bony. 
 
 Class 1. Pisces (Scyllium). Ichthyopsida with fin-like 
 limbs, the margins of which are supported by fin-rays, 
 as also are the unpaired fins. A well-developed exo- 
 skeleton mainly of dermal origin. No postcaval vein 
 and no allantois (see p. 153). 
 
 Class 2. Amphibia (Rand). Ichthyopsida in which 
 the unpaired fins always present in the larva and some- 
 times in the adult are not supported by fin-rays. The 
 limbs are transversely jointed and their extremities 
 divided into digits. There is no epidermic exoskeleton, 
 and the skin is very glandular. A cloaca and an allan- 
 toid bladder. 
 
 B. A m n i o t a. Embryo with amnion and respiratory allantois. 
 Gills never present. 
 
 GROUP 2. SA UR OP SID A. Air-breathing Amniota, 
 with epidermic exoskeleton of scales or feathers. The ver- 
 tebrae are without epiphyses, the cranium is well ossified 
 and articulates with the vertebral column by a single occi- 
 pital condyle, partly belonging to the basi- and partly to the 
 ex-occipital region. There is an interorbital septum, the 
 otic bones do not fuse into a periotic before uniting with 
 other elements, there is no separate parasphenoid, and the 
 complex mandible articulates with a quadrate bone. The 
 ankle-joint is between the proximal and distal tarsal bones. 
 The oval nucleated red corpuscles are smaller than those of 
 the Ichthyopsida, the heart possesses two auricles and one 
 
344 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 (physiologically double) or two ventricles, and the aortic 
 arches are seldom more than two. There is never a complete 
 respiratory diaphragm. The kidneys are metanephric, and 
 their ducts open into a cloaca, together with the intestine 
 and sexual ducts. The cerebral hemispheres are not united 
 by a well-marked corpus callosum, and the hypoglossal nerve 
 perforates the brain-case. The sclerotic coat of the eye is 
 supported by cartilage or bone, the cochlea is straight or 
 slightly curved, and there is a columella. The large telole- 
 cithal ova are invested in firm calcareous shells, the cleavage 
 is meroblastic, and most of the development takes place, with 
 few exceptions, outside the body of the parent. 
 
 Class 1. Reptilia (Reptiles). 
 
 Class 2. Aves (Columba). Warm-blooded Sauropsida 
 with fore-limbs modified into (usually) functional wings, 
 and a reduced tail-region (uropygium). There is an 
 epidermic exoskeleton, in the form of feathers. The 
 cervical vertebrae possess saddle-shaped articular surfaces, 
 the true sacral vertebrae are without expanded ribs, and 
 fuse with numerous other vertebrae to form a pseudo- 
 sacrum, and the posterior caudal vertebrae (usually) 
 unite together into a ploughshare-bone. The manus 
 never possesses more than two free carpals nor more 
 than three digits ; there is a carpo-metacarpus. The 
 ilia extend far behind and in front of the perforated 
 acetabulum, and the pubes and ischia are directed 
 backwards, the former rarely, the latter never meeting 
 in a ventral symphysis. The tarsal bones are never 
 separate, but fuse with tibia proximally and metatarsus 
 distally to form a tibio-tarsus and tarso-metatarsus ; 
 digits of pes, never more than four. The jaws are 
 covered by a horny sheath, functional teeth never being 
 present in recent forms ; a bursa Fabricii opens into 
 the cloaca. The heart is four-chambered, and the right 
 auriculo-ventricular valve muscular. There is a single 
 aortic arch, curving to the right. The lungs are immo- 
 bile, and the bronchia communicate with air sacs. The 
 right ovary and oviduct are rudimentary. The optic 
 lobes are displaced to the sides of brain. 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 345 
 
 GROUP 3. MAMMALIA. 
 
 Class 1. Mammalia. Warm-blooded Amniota in 
 which an epidermic exoskeleton, in the form of hair, 
 is always present at some period of life. The vertebrae 
 possess epiphyses, and the cervical vertebras are 
 usually seven. The occipital region is well ossified, 
 and there are two occipital condyles. The otic bones 
 early fuse together into a periotic. The mandible is 
 of two pieces only, and articulates directly with the 
 squamosal. The lips are usually definite and muscular, 
 and the teeth, when present, are only replaceable to a 
 limited extent by new ones. The large intestine is 
 very long, and usually opens independently, behind a 
 urinogenital aperture. The red corpuscles are non- 
 nucleated, the heart four-chambered, the right auriculo- 
 ventricular valve membranous, and there is a single 
 aortic arch, curving to the left. There is an epiglottis, 
 the lungs are mobile, there are no air-sacs, the bronchial 
 tubes end in infundibula, and there is a complete respi- 
 ratory diaphragm. The cerebral hemispheres are united 
 by a corpus callosum, a third commissure and corpus 
 mammillare are present, and the optic lobes are double. 
 The sclerotic coat of eye is fibrous, there are three 
 auditory ossicles, and the cochlea is (almost always) 
 spirally coiled. Usually viviparous, and the young 
 always nourished by milk for some time after birth. 
 
 Sub-Class 1. Prototheria (Ornithodelphia). Mam- 
 mals devoid of functional teeth, and possessing 
 distinct coracoids, epicoracoids, interclavicle, and 
 epipubic (marsupial) bones. There is a cloaca, the 
 young are hatched from large eggs with a calcareous 
 shell and much food-yolk, the cleavage being conse- 
 quently meroblastic. The mammary glands have no 
 teats. 
 
 Order 1. Monotremata. Ornithorhynchus, Echidna, 
 Proechidna. 
 
 The remaining sub-classes of Mammals include vivi- 
 parous animals which usually have functional teeth, 
 
346 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 but do not possess distinct interclavicle, epicoracoids 
 and coracoids, the last being represented by a process 
 of the scapula. There is no cloaca. The mammary 
 glands possess teats. 
 
 Sub-Class #. Metatheria (Didelphia). Mammals 
 with inflected angle to the mandible and epipubic 
 (marsupial) bones. The oviducts are distinct in 
 typical cases, and there is not an allantoic placenta. 
 The female usually possesses a pouch. 
 
 Order 1 . Marsupialia. Pouched animals : Kan- 
 garoo, opossum, wombat, &c. 
 
 Sub-Class 3. Eutheria (Monodelphia). Mammals 
 in which the angle of the jaw is not inflected, and 
 there are no epipubic bones. The oviducts are more 
 or less fused, and there is an allantoic placenta. 
 
 Orders of Eutheria. (1) Edentata Armadillo, sloth, &c. (2) 
 Ungulata (a) Artiodactyla, none of the digits bilaterally sym- 
 metrical Swine, hippopotamus, ruminants ; (b) Perissodactyla, 
 with a bilaterally symmetrical 3rd digit in each manus and pes 
 Tapir, rhinoceros, horse, &c. (3) Sirenia Dugong, manatee. 
 (4) Rodentia Rabbit, rat, porcupine, squirrel, guinea pig, &c. (5) 
 Proboscidea Elephant. (6) Hyracoidea Hyrax. (7) Insectivora 
 Hedgehog, mole, shrew, &c. (8) Cheiroptera Bats. (9) Carnivora 
 Dog, cat, bear, seal, &c. (10) Prosimice Lemurs. (11) Primates 
 (a) Arctopitheci, Marmozets ; (b) Platyrrhini, lower monkeys ; 
 (c) Catarrhini, higher monkeys (Cynomorpha) and man-like apes 
 (Anthropomorpha), see p. 338; (d) Anthropidae Man. 
 
 PRINCIPLES OF DISTRIBUTION. 
 
 Explanatory Theories. 
 
 I. Theory of Special Creations, now abandoned. According to 
 it : 1. Organisms were created where now found. 2. The fauna 
 and flora of any particular region must be better adapted to it 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 347 
 
 than any other fauna and flora. 3. Climate, soil, and position 
 explain all the phenomena of distribution. 
 
 II. Theory of Evolution, generally accepted. Eegards modern 
 distribution as the result of innumerable changes that have 
 affected (1) organisms; (2) the surface of the globe. 
 
 1. Geological history shows that there has been a succession of 
 faunas and floras passing gradually into one another, old species 
 becoming extinct, and new ones being evolved by the combined 
 influence of variation and heredity, which respectively originate 
 and accumulate new characters. Upon the whole a gradual 
 advance in complexity has taken place, but the geological record 
 is extremely imperfect, especially as regards land organisms. The 
 process of change is still going on, and examples of modern 
 extinction (e.g., the gigantic wingless New Zealand bird Dinornis 
 and Sirenian form Rhytina) are well known, but the detection 
 of newly evolved species involves greater difficulties. 
 
 Species once established have extended themselves over smaller 
 or larger areas, according to their powers of migration and sur- 
 rounding conditions i.e., their environment. Physical barriers, 
 such as oceans, mountains, climate, and soil, have played an 
 important part in limiting such extension, but the competition 
 of other forms has had a still greater influence. Introduced 
 forms often increase prodigiously, and even supersede the indi- 
 genous ones, whence it follows that these last are not necessarily 
 the best adapted. Exs. Rabbits in Australia; the brown 
 rat in England, which has almost ousted the indigenous black 
 rat. 
 
 2. Owing to the wearing away or erosion of the land by 
 various agencies (chiefly the different forms of water), and the 
 action of subterranean forces by which upward and downward 
 movements of the earth's crust are produced, the distribution of 
 land and sea has constantly varied. Europe and North America, 
 for example, have most likely been connected at various times 
 by land occupying part of what is now the North Atlantic, and 
 Australia appears to have been once united with Asia. On the 
 other hand, evidence is found on every continental land surface 
 of the former presence of the sea. In spite of what has been 
 said, the theory of " permanence of oceanic and continental 
 areas " finds much support. According to it the great oceans are 
 of extreme antiquity, and, on the whole, more or less land has 
 
348 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 existed from very remote times within the present continental 
 areas. It is perhaps best to accept this theory only for the 
 deeper parts of the great oceans. An accurate knowledge of the 
 contours of the ocean floor is important in this connection, and 
 serves as an important check upon speculations regarding former 
 land-unions. On this basis islands have been divided into oceanic 
 and continental, which are believed respectively to have been 
 always isolated, and to have been connected with an adjoining 
 continent. 
 
 Oceanic Islands are : (a) generally remote from continents ; (&) 
 separated from them by very deep (usually over 1,000 fathoms) 
 water; (c) of volcanic or coral nature; (d) inhabited by forms 
 which possess powers of migration capable of carrying them, 
 actively or passively, over more or less broad ocean tracks ; (e) 
 characterised by numerous peculiar species. Exs. The Azores, 
 St. Helena, Ascension, coral islands of Pacific. 
 
 Continental Islands are: (a) comparatively near a continent; 
 (b) separated from it by comparatively shallow (under 1,000 
 fathoms) water ; (c) of similar geological structure, and not 
 entirely volcanic or coral ; (d) inhabited by similar organisms, 
 irrespective of powers of migration. Such islands are : (1) 
 Ancient continental, separated from the nearest continent by fairly 
 deep (over 100 fathoms) water, and presenting only a general 
 resemblance in the fauna and flora ; many peculiar species. Exs. 
 Madagascar, Celebes. (2) Recent continental, separated from the 
 adjacent continent by shallow (not more than 100 fathoms) 
 water, and with closely similar fauna and flora ; very few peculiar 
 species. Exs. British Islands, Japan. Both (1) and (2) have 
 presumably been united with the adjoining continents, the latter 
 at a recent date, geologically speaking. 
 
 The surface of the globe has also undergone numerous muta- 
 tions as regards climate. The temperate parts of N. America 
 and Europe, for example, were at a geologically recent period 
 passing through a glacial epoch (the " great ice age "), as proved 
 by ice-worn and scratched rock-surfaces and rocks, boulder-clay, 
 &c. On the other hand, fossil plants evidencing subtropical 
 conditions have been found in the Arctic regions. Many theories 
 have been advanced to account for secular changes of climate. 
 The most satisfactory is one by Wallace which attributes them to 
 geographical revolutions (previously suggested by Lyell), influ- 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 349 
 
 enced by astronomical changes (variations in exceritricity of earth's 
 orbit and movements of precession, as advanced by Croll). 
 
 All the preceding changes must have exerted a profound 
 influence upon organisms, and throw light upon many problems 
 of distribution. 
 
 Areas of Distribution. May be mapped out for species, genera, 
 families, and orders. In all cases : (1) Size and nature of bound- 
 aries very variable. (2) Need not be continuous. 
 
 (a) Exs. of Limited Areas. The marmot only found in the 
 Alps. A species of humming-bird confined to the crater of the 
 extinct volcano Chiriqui in Veragua. 
 
 Six genera of Lemurs are peculiar to Madagascar. The family 
 GaleopithecidcB (including the single genus Galeopithecus) is limited 
 to Malacca, Sumatra, Borneo, and the Philippines. The order 
 Monotremata only occurs in Australia, Tasmania, and New Guinea. 
 
 (b) Exs. of Extensive Areas. The Leopard is distributed through 
 the whole of Africa and S. Asia to Borneo and E. China. 
 The genus Felis (cat, lion, leopard, &c.) ranges over most of the 
 globe except Australia, the Pacific Islands, W. Indies, Mada- 
 gascar, and the more northerly parts of North America and Asia. 
 The family Pesperttiionidce, including 200 species of small insect- 
 eating bats, occurs everywhere within the tropical and temperate 
 /ones; while the family Muridce (rats, mice, &c.) is only absent 
 from Polynesia and New Zealand. 2. Discontinuity is generally 
 a sign of antiquity, the two or more parts being remains of a once 
 continuous distributional area, in part of which extinction has 
 occurred. Changes in the distribution of land and sea have 
 broken up many once continuous areas. Examples. The variable 
 hare (Lepus variabilis), Europe and Asia N. of 55; Alps, 
 Pyrenees, and Caucasus. The genus Tapirus, S. America, S. E. 
 Asia. Centetidce (a family of the Insectivora), Madagascar, Cuba. 
 Hayti. 
 
 Ganoid fishes are now represented by genera with the fol- 
 lowing distribution : Acipenser, N. temperate and Arctic regions. 
 Most species marine, others are found in the Caspian Sea, Black 
 Sea, and N. American lakes, with their rivers, also in the 
 Danube, Mississippi, and Columbia. Scaphirhynchus, Mississippi 
 and tributaries. Polyodon, Mississippi and Yang-tse-Kiang. 
 Polypterus, Nile and W. African rivers. Calamoichthys, rivers 
 of Old Calabar. Amia, fresh-water, United 
 
350 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 fresh-water, N. America to Mexico and Cuba. Ganoid fishes 
 are of great geological antiquity, and were formerly a widely 
 spread marine group. Most of the forms now surviving have 
 gradually accommodated themselves to a life in rivers, lakes, &c., 
 where the struggle for existence is less severe. 
 
 The peculiar distribution of the Dipnoi (p. 153) can be explained 
 similarly. 
 
 The Marsupialia and Edentata (p. 354) are also good examples 
 of interrupted areas of distribution. 
 
 Zoological Regions, characterized by the presence of peculiar 
 families and genera, and by the absence of other families and 
 genera, have been formed for sea and land. The most useful 
 division of the latter is chiefly based on the Mammalia, but 
 applies very well to birds and reptiles and fairly to other groups. 
 The regions thus established are six in number. 
 
 I. Palcearctic Region. Temperate Europe and Asia and N. 
 temperate Africa. Extends "W. to Iceland, the Azores, and 
 Cape Verde Islands, and E. to Behring Straits and Japan. 
 Southern boundary somewhat indefinite, tropic of Cancer in 
 Africa and Arabia, river Indus, Himalayas, Nanling mountains. 
 
 II. Ethiopian Region. Africa and Arabia south of the tropic 
 of Cancer, and including Madagascar. 
 
 III. Oriental Region. Asia, S. of Region I., and the western 
 part of the E. Indies. The eastern boundary of this region 
 {Wallaces line] passes between Bali, Borneo, and the Philippines 
 on the one hand, Lombok and Celebes on the other. The 
 former islands are therefore in the Oriental Region, the latter in 
 the Australian Region. 
 
 IV. Australian Region. Australia, New Guinea, New Zealand, 
 with the smaller islands from Wallace's line to the Marquesas and 
 Low Archipelago, and the tropic of Cancer to the Macquarie 
 Islands. 
 
 V. Neotropical Region. S. America, the W. Indies, and tropical 
 N. America, with the exception of the central part of the Mexican 
 table-land. 
 
 VI. Neardic Region. Arctic and temperate N. America, with 
 the central part of the Mexican table-land. 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 351 
 
 DISTRIBUTION OF MAMMALS. 
 
 I. Palcearctic Eegion. Thirty-five families represented. Peculiar 
 Genera. The camel, six deer, the yak, six antelopes (including the 
 chamois), and all wild sheep and goats, except two species. Six 
 p.g. of Muridce (rats and mice), two of mole-rats, and one other ; 
 dormice and pikas (calling hares) are almost confined to this 
 region. Six p.g. of moles ; the remaining two genera of which 
 (Talpa, Urotriclms) extend, respectively, into N. India and N. W. 
 America. Five p.g. of Carnivora, including the racoon-dog, a 
 seal, and the badger ; the last just enters the Oriental region in 
 China. 
 
 II. Ethiopian Region. Fifty families represented, of which nine 
 are peculiar i.e., Onjcteropodidce. Hippopotamidce ; Camelopardidce. 
 Potamogalidcv (including Potamogale, an otter-like Insectivore) ; 
 Chrysocldoridce (golden moles). Cryptoprodidce (Cryptoprocta is a 
 small civet -cat -like form peculiar to Madagascar) ; Protelidce 
 (Proteles, the aard-wolf, is allied to the hyaenas and weasels) ; 
 Cheiromyidce (contains Cheiromys, the aye-aye, peculiar to Mada- 
 gascar). 
 
 Peculiar Genera (besides those in the above families). Potamo- 
 chaerus (river hog), and Phacochaerus (wart hog) ; Hyomoschus 
 (a small deer-like form), twelve p.g. of antelopes. Thirteen p.g. 
 of Muridce; Pedetes (a jerboa or jumping mouse); Anomalums 
 (a flying squirrel) ; three other p.g. of Kodents. Three p.g. of 
 elephant-shrews, and the Insectivorous family Centetidce, except 
 one genus from Cuba and Hayti. Three p.g. of bats. Seventeen 
 p.g. of Viverridce (civets and ichneumons), two p.g. of dogs, and 
 two p.g. of Mustelidce (weasels, otters, &c.) Nine p.g. of Lemurs. 
 Eight p.g. of apes and monkeys, the most important being Trog- 
 lodytes (gorilla and chimpanzee). 
 
 Peculiar Species. Among these are several species of Manis, 
 the two-horned African rhinoceroses, the zebras, African elephant, 
 and lion. 
 
 Absent Palcearctic Forms. The genera Bos (wild ox), and Sus 
 (wild boar), camels, deer, goats and sheep, moles, bears. 
 
 III. Oriental Eegion. Forty-two families represented, of which 
 two are peculiar, and one other almost so i.e., Galeopithecidce 
 (including Graleopithecus, the flying lemur), and Tupaiidw (tree- 
 shrews), among Insectivora. Tarsiidce, a family of lemurs (includ- 
 
352 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 ing only Tarsius spectrum, found in Sumatra, Banca, and Borneo; 
 also outside the Oriental region in Celebes). 
 
 Peculiar Genera (besides those in the above families). Tragulus 
 (chevrotain) ; Cervulus (a deer) ; Bibos (wild cattle) ; three p.g. 
 of antelopes. Platanista (a dolphin found in Ganges and Indus). 
 Three p.g. of Muridce; Pteromys (a flying squirrel) ; Acanthion 
 (a porcupine) ; Gymnura (a hedgehog). Eleven p.g. of bats. 
 Twelve p.g. of V'werridw ; Cuon (a dog); five p.g. of Mustelidce; 
 two p.g. of bears. Loris and Nycticebus (lemurs). Four p.g. of 
 apes, including Simla (orang-utan), and Hylobates (gibbon). 
 
 Peculiar Species. Among these are the Indian tapir, several 
 species of rhinoceros, and the Indian elephant. 
 
 IV. Australian Region. Twenty-eight families represented, of 
 which eight are peculiar i.e., seven out of the eight families o! 
 Marsupials, and the two families of Monotremes. All of these, 
 however, are absent from Polynesia and New Zealand. 
 
 Peculiar Genera (besides those in the above families). Babimsa 
 (a hog), and Anoa (a small kind of cow) in Celebes. Five p.g. of 
 Muridce in Australia, and one of these in Tasmania also. Three 
 p.g. of bats. 
 
 Absent Forms. Australia and New Guinea possess no non- 
 aquatic Mammals higher than Marsupials, except some bats, mice, 
 and rats. This points to extremely long-continued isolation, 
 which has afforded time for the Marsupials to become modified 
 in the most diverse directions, thus enabling them to fill places 
 elsewhere occupied by other orders. New Zealand is remarkable 
 for the absence of all indigenous Mammals, so far as certainly 
 known, with the exception of two bats. 
 
 V. Neotropical Eegion. Thirty-seven families represented, of 
 which seven are peculiar i.e., Bradypodidce (sloths), Dasypodidce 
 (armadilloes), and Myrmecophagidce (true ant-eaters). Chinchillidw 
 (chinchillas) and Camidce (cavies) among Kodents. Cebidce (New 
 World monkeys) ; Hapalidce (marmozets). The Phyllostomidce 
 (leaf-nosed bats) are peculiar, with the exception of a Californiari 
 species. 
 
 Peculiar Genera (besides those in the above families). Chiro- 
 nectes and Hyracodon (opossums). Dicoctyles (peccary, also in 
 Texas) ; Auchenia (llama) ; Elasmognathus (a tapir). Inia (a 
 dolphin, upper part of Amazon basin). Six p.g. of Muridce; six 
 p.g. of Oclodontidce (rat-like forms), two of them peculiar to W. 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 353 
 
 Indies ; eight p.g. of Echimyidce (spiny rats) ; two p.g. of Cercola- 
 bidce (tree porcupines). Solenodon (a hedgehog-like form from 
 Cuba and Hayti). Twenty-six p.g. of bats, including the Vampires. 
 Five p.g. of Canidce; three p.g. of Mustelidce; Nasua (coati) and 
 Cercoleptes (Kinkajou) ; Tremarctos (spectacled bear) ; Otaria 
 (an eared seal). 
 
 Peculiar Species. Among these are twenty species of Didelphys 
 (to which genus most opossums belong). The American tapir. 
 A species of racoon (genus Procyon). 
 
 Absent Forms. Ungulata are scarce, deer and llamas being the 
 only ruminants, tapirs and peccaries the only non-ruminants. 
 The only insectivores are Solenodon and a species of shrew 
 (Sorex). The Viverridce are absent. 
 
 VI. Nearctic Region. Thirty-two families are represented, of 
 which one is peculiar, while one other is almost so i.e., Haploo- 
 dontidce (rat-like forms allied to beavers and marmots), and 
 Saccomyidce (the pouched rats, of which one genus ranges into 
 the N. of the Neotropical region). 
 
 Peculiar Genera (besides those in the above families). Antilo- 
 capra (prong-horned antelope), Aplocems (a goat-like antelope), 
 and Ovibos (the musk-sheep). Three p.g. of Muridce; Jaculus 
 (a jerboa), Cynomys (the so-called prairie dog), and Erethizon 
 (the tree porcupine). Three p.g. of moles; two p.g. of bats; 
 two p.g. of Mustelidce; Eumetopias (an eared seal) ; Halicyon 
 (a seal). 
 
 Peculiar Species. Among these are two of Didelphys, a peccary, 
 several deer, the American bison, racoons, and the grizzly bear 
 (Ursus ferox). 
 
 Absent Forms. Ungulates are ill represented, deer, the American 
 bison, two antelopes, a sheep, and the musk-sheep being the only 
 ruminants, while a peccary (Texas to Red River) is the only 
 non-ruminant. Hedgehogs, Viverridce, and monkeys are all unre- 
 presented. 
 
 Distribution of Orders. 
 
 1. Monotremata. Consists of only three genera, limited to 
 part of the Australian region. Ornithorhynclius, Australia and 
 Tasmania ; Echidna, Australia, Tasmania, and N. New Guinea ; 
 Proechidna, S. New Guinea. 
 
 2 23 
 
354 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 No fossil forms are found elsewhere, so that the place of origin 
 of this order is unknown. 
 
 2. Marsupialia. Consists of eight families (comprising thirty- 
 seven genera), of which only one, the Opossum family (including 
 three genera), occurs outside the Australian region. The Opossums 
 are Neotropical and Nearctic. 
 
 Fossil opossums occur in the Pleistocene of America, and in 
 much older European deposits (Eocene to Miocene). The secondary 
 rocks of Europe contain a number of small forms, which probably 
 resemble the ancestors of the Australian Marsupials. We may 
 therefore suppose that this order originated in the Palsearctic 
 region, and then extended into what is now Australia (at that 
 time united by land with Asia), isolation occurring soon after, 
 followed by specialization in various directions. The Opossums 
 seem first to have existed in Europe, from whence they spread 
 into America by former northerly land-connections. 
 
 3. Edentata. This order is now chiefly limited to S. America, 
 but Orycteropus is peculiar to the Ethiopian region, while Manis 
 is found both in that and the Oriental region. 
 
 The geological evidence is in favour of considerable development 
 in Africa, whence the order would spread north to the Oriental 
 and Palsearctic regions, and thence on to America. The compe- 
 tition with higher forms has caused its extinction in most areas, 
 and Edentates appear to be most abundant in S. America, because 
 the competition with other animals is there comparatively small. 
 The peculiar burrowing or climbing habits of most of the genera 
 also tend to preserve them, and these habits no doubt represent 
 attempts to escape from the severe competition with higher forms. 
 The size of existing Edentates is insignificant compared with that 
 of Pleistocene S. American and European genera. 
 
 4. Ungulata. (a) Artiodactyla. Non-ruminantia. Swine are 
 only represented in America by peccaries (Dicotyles) ; true swine 
 are found in all the other regions, but only extend into the 
 Australian as far as New Guinea. These animals are first known 
 in the European Eocene, and during Miocene and Pliocene times 
 were as common in N. America as Europe, but since then have 
 almost entirely disappeared from the former area. 
 
 The hippopotamus is now limited to the Ethiopian region, but 
 fossil forms occur in Europe (Pliocene and Pleistocene) and India 
 (Miocene). 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 355 
 
 Riimmcintia. Recent Camelidce are only found in the Neotropical 
 and Palaearctic regions, but numerous forms occur in the Miocene 
 and later deposits of N. America, where the group originated. 
 
 Tragulidce or mouse-deer have also a discontinuous area of 
 distribution W. Africa (Hyomoschus) and Oriental region 
 (Tragulus). This is accounted for by the presence of Miocene 
 forms in Europe, whence the family extended south. 
 
 Deer occur in all the regions except the Ethiopian, but do not 
 extend far into the Australian region. They appear to have 
 taken origin in the Old World, from whence they reached 
 N. America in Miocene times, and afterwards passed to S. 
 America. 
 
 Giraffes are at the present time confined to the Ethiopian 
 region, but fossil forms are known from S. Europe and India, 
 and a northern temperate origin is probable. 
 
 Bovidce (oxen, sheep, antelopes, &c.) are present in all the regions 
 except the Neotropical, though they only just pass into the 
 Australian, and are scarce in the Nearctic. The family appears 
 to have originated in the Palsearctic and Oriental regions during 
 Miocene times. 
 
 (b) Perissodactyla. Tapirs present a striking example of dis- 
 continuous distribution, being found, on the one hand, in the 
 Malay peninsula, Sumatra, and Borneo, and on the other, in S. 
 and Central America. True tapirs occur in the W. of Europe as 
 far back as Miocene times, but in America are not found further 
 back than the Pleistocene. Migration from the Palsearctic region 
 is thus indicated. 
 
 Rhinoceroses are now only Ethiopian and Oriental, but they 
 appear to have originated in the Palsearctic region, whece they 
 extend back to the Miocene period. In Pliocene times they also 
 ranged into N. America. 
 
 The genus Equus (horse, ass, zebra) is now limited to the 
 Ethiopian and Palsearctic regions. It appears to have originated 
 in the latter area during Miocene times, and then migrated not 
 only into the Ethiopian, but also into the Oriental, Nearctic, and 
 Neotropical regions, as proved by fossil forms. 
 
 5. Sirenia. Manatus (manatee), E. coast of S. America, and 
 W. coast of Africa. Halicore (dugong), shores of Indian Ocean 
 and Red Sea. 
 
 6. Bodentia. Ver}' widely distributed; occurring in all the 
 
356 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 
 
 regions, but in Madagascar and Australia only represented by 
 Muridce. They attain their largest development in S. America. 
 
 The order is of great geological antiquity, for some living 
 genera extend back to the Eocene. Eodents probably originated 
 in the PalaBarctic region, whence migrations took place at an early 
 date to S. America and S. Africa, allowing time for great special- 
 ization. 
 
 7. Proboscidea. Elephants are now limited to the Ethiopian 
 and Oriental regions, but formerly had a much wider extension. 
 
 Pala3arctic forms occur from Miocene to Pleistocene times, 
 and elephants have lived in India since the Miocene period. 
 Numerous fossil examples occur in the Pliocene and Pleistocene 
 deposits of N. and S. America. 
 
 8. Hyracoidea. Almost entirely limited to the Ethiopian region, 
 but range northwards as far as Syria. 
 
 9. Insectivora. Very widely distributed, and represented by 
 numerous specialized forms. Absent from S. America and 
 Australia. 
 
 This order is a very ancient one, as shown by the fact that 
 Miocene forms mostly belong to existing families. Extinction 
 appears to be slowly taking place, and has led to many cases of 
 discontinuous distribution e.g., Centetidce, represented by Solenodon 
 in the W. Indies, and Centetes, with four other genera, in Mada- 
 gascar. 
 
 10. Cheiroptera. Bats, as might be expected, are found in all 
 the great areas, but the Frugivora are absent from the Nearctic 
 and Neotropical regions, as are the Horse-shoe bats (Rhinolophidce) 
 among insectivorous forms. On the other hand, the Leaf-nosed 
 bats (Phyllostomidce) are almost exclusively Neotropical. 
 
 Fossil bats, very like recent species, date from Eocene times, 
 and the order is undoubtedly one of extreme antiquity. 
 
 1 1. Carnivora. (a) Fissipedia. Occur in all the regions, except, 
 perhaps, the Australian (the " native dog " of Australia is only 
 doubtfully indigenous), but are especially characteristic of the 
 Ethiopian and Oriental, which possess almost all the Fiverridce 
 and HycenidcK, with a great many of the Felidce and Mustelidce. 
 Two genera, Cryptoprocta and Proteles, constituting distinct 
 families, are limited respectively to Madagascar and S. Africa. 
 Bears, however, are absent from the Ethiopian region, and are 
 only represented by one species in the Neotropical region, which 
 
CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 357 
 
 is also very poor in other Carnivora. The Procyonidce are small 
 bear-like forms, found in the Nearctic and Neotropical regions, 
 and include the racoons (Procyon), coatis (Nasua), and kinkajous 
 (Cercoleptes). 
 
 Fossil Carnivores date back to the Lower Eocene, but the recent 
 families were not then differentiated. The order appears to have 
 originated in the northern half of the Old World. 
 
 (b) Pinnipedia. Seals are limited to cold and temperate seas, 
 and are also found in the Caspian, Sea of Aral, and Lake Baikal, 
 all of which, at no very distant epoch, were connected with the 
 Arctic Ocean. 
 
 Walruses characterize the North Polar regions. 
 
 12. Prosimice. (a) Cheiromyini. Only one form, the aye-aye 
 (Cheiromys), which is restricted to Madagascar. 
 
 (b) Lemurini. Practically limited to the Ethiopian and Oriental 
 regions. Indris, Lemur, and four other genera are only found in 
 Madagascar. Tarsius constitutes a distinct family, and is limited 
 to Sumatra, Banca, Borneo, and Celebes. 
 
 Lemurs date back to the Eocene in Europe. 
 
 13. Primates. (a) Arctopitheci and (b) Platyrrhini are confined 
 to the Neotropical region. 
 
 (c) Catarrhini are found only in the Old World. 
 Cynomorpha are especially Ethiopian and Oriental, but also 
 
 extend into the Pataarctic region, and into the Australian region 
 as far as Timor. 
 
 Anthropomorpha present a marked example of discontin- 
 uous distribution. Gibbon S. E. Asia and Malay Archipelago. 
 Orang Borneo and Sumatra. Chimpanzee and Gorilla W. 
 Africa. 
 
 The order dates back to the Eocene. 
 
 Origin and Migrations of the Mammalia. The Class, and most 
 likely all the Orders, originated in the Northern Hemisphere. 
 Australia was isolated at a very early date, and therefore has 
 preserved a very ancient Mammalian fauna, S. America and 
 S. Africa were severed somewhat later, to be afterwards reunited, 
 and they also have preserved some very ancient forms. The 
 northerly connection between the Eastern and Western Hemi- 
 spheres was then broken, not only by submergence of land, but 
 also by a lowering of temperature. The Oriental and Ethiopian 
 regions were also marked off by the formation of the Himalayas 
 and the desert zone stretching from the Sahara to Central Asia. 
 
INDEX-GLOSSARY TO PART II, 
 
 A 
 
 ABDOMEN, Astacus, 83, 84 ; Lepus, 269. 
 
 Abduction (ab, from ; duco, ductum, draw, lead) of appendages Movement 
 
 away from the. middle line, 91. 
 Abiogenesis (-, not ; #/os, life, yt'i'eo-is, birth) Derivation of living from 
 
 non-living matter, 7. 
 Aboral (ab, away from ; os, mouth) Situated at the end further away 
 
 from the mouth, 19. 
 Absorption, 5, 194. 
 Accretion (ad, to ; cresco, cretum, grow) Growth by addition of layers to 
 
 the outside, 7. 
 Acetabulum (acetabulum, properly a vessel for vinegar ; the socket of the 
 
 hip bone) The socket into which the head of the femur fits, 186, 239, 
 
 281, 327. 
 Achromatin (a-, not ; xpw/ma, colouring matter) The part of the nucleus 
 
 which does not readily take up stain, 8, 73. 
 Acinus (ckii/os, acinus, a berry, a grape) of a gland One of the ultimate 
 
 (spherical or tubular) subdivisions, lined by secreting cells, 33, 288. 
 Acipenser, 153, 349. 
 Acrania, 135. 
 Acromion (a K pwuiov, used with the modern meaning) in Mammalia A 
 
 . spine-like process of the scapula, 280. 
 Action, 102. 
 Adduction (ad, to; duco, ductum, draw) of appendages Movement towards 
 
 the middle line, 91. 
 Adrenal, 205, 250. 
 
 Aetiology (aiTiov, a cause ; Xoyos) = Phylogeny, q. r. 
 Afferent (ad, to ; fero, I carry) Of nerve-fibres in conducting impulses to 
 
 a ganglion cell or to the central nervous system, 102, 146, 217 ; of 
 
 vessels carrying impure blood to gills, 164. 
 Africa, 349. 
 After-shaft, in the Fowl A minute vane attached to the superior umbilicus 
 
 of an ordinary feather, 231. 
 
INDEX-GLOSSARY. 359 
 
 Air-sac, 249, 252. 
 
 Alimentary Canal. See Digestive Organs. 
 
 Allantois (aXXas, a\\avr-, a sausage), in the Bird and Mammal An embry- 
 onic appendage which grows out from the posterior part of the intestine, 
 
 309. 
 
 Alps, 349. 
 
 Alternation of Generations, 39 ; Hydra, 27 ; Distoma, 35, 39. 
 Alveolus (alveolus, a little hollow) A socket for a tooth, 284. 
 America North A., 349, 350, 353; South A., 349, 350, 352. 
 Amia, 349. 
 Amnion (apviov, used with the modern meaning), in the Bird and Mammal 
 
 A sac-like appendage by which the embryo is surrounded, 265, 309. 
 Amniota (U/JLVIOV), 342. 
 Amoeba (a/xoi/36s, changing), 7, 11, 311. 
 Amoeboid Resembling an amoeba, especially as regards movement by slow 
 
 protrusion of pseudopodia, 11, 60, 318. 
 
 Amphibia (<V</jo>, both; 0ios, life), 343 ; 3, 4, Chap, x., 174. 
 Amphiccelous (<V<w, both ; /coTXos, hollow) of the centrum of a vertebra 
 
 Biconcave, 158, 184. 
 
 Amphioxus (M<i, on both sides; oi/s, sharp), 341, 134-152. 
 Ampulla (ampulla, a flask, a bottle), in the Vertebrate ear A dilatation 
 
 at one end of each semicircular canal, 173, 219, 256. 
 Anabolism (ava/SaX*:, a heaping up, an ascent) Assimilation, q.v. 
 Analogy Physiological equivalence, 311. 
 Anamniota (av- y negative ; a/jiviov), 343. 
 Anapophysis, in a Vertebra A process situated below the postzyga- 
 
 pophysis, 279. 
 Angle ; of jaw, 276. 
 
 Annelida (annellus, a little ring) Segmented worms, 340 ; Chap, v., 65. 
 Annulus, 75. 
 
 Animals Distinction from plants, 5. 
 Ankle. See Tarsus. 
 
 Antebrachium (ante, before ; brachium) The fore-arm. See Arm. 
 Antenna (antenna, a yard-arm), in Crustacea One of the second pair of 
 
 slender sensory appendages of the head, 89, 103. 
 Antennule (dim. of antenna, a yard-arm), in Crustacea One of the first 
 
 pair of slender sensory appendages of the head, 89, 103. 
 Anti-trochanter (av-ri, against ; trochanter), in the Bird A facet above the 
 
 acetabulum, against which the great trochanter plays, 239. 
 Anodonta (av-, negative; ooous, OOOVT-, a tooth) Fresh-water Mussel, 341; 
 
 109-122. 
 Anthropidje, 346. 
 
360 INDEX-GLOSSARY. 
 
 Anura, 4. 
 
 Anus (anus, in modern sense) The opening by which the undigested pro- 
 ducts are ejected from the food-canal, 14, 29, 48, 86, 94, 113, 123, 269, 
 286, 313. 
 
 Aorta, 128, 164, 197, 227, 246, 265, 308; Anterior, 115; Cardiac, 142; 
 Dorsal, 142 ; Posterior, 115. 
 
 Apertures, pores, &c. Abdominal p., 154; Auditory a., 89, 269; Auriculo- 
 ventricular, 162, 196, 245; Cloacal, 48, 111, 154, 175, 191, 230, 242; 
 Eustachian, 241 ; Excretory, 28, 31, 48, 55, 61, 76, 80, 89, 112 ; 
 Exhalent, 111 ; Genital, 28, 32, 62, 63, 76, 80, 87, 99, 112 ; Renal, 89, 
 112; Urinogenital, 269, 298, 299. 
 
 Apodeme (iirJ^jj/xos, absent from home), in the Crayfish One of the elements 
 of the endophragmal system, 90. 
 
 Aponeurosis (aTroi/ei^otoo-is, used with the modern meaning) The connective 
 tissue sheath of a muscle, 208. 
 
 Appendages, 83, 84, 87, 89, 90, 108. 
 
 Appendicular, of skeleton Belonging to limbs, 178, 239, 280, 326. 
 
 Appendix, Vermiform, 286, 330. 
 
 Apteria (a-, negative ; in-epov, a feather), in the Bird Featherless patches, 
 229. 
 
 Aqueduct, Sylvian, 169. 
 
 Aqueductus vestibuli, 173. 
 
 Arachnoid (apax^X, a spider's web ; i5-El5os, IS-, appearance, 210. 
 
 Archoplasm (PX*J> a beginning; TrXaT/ua, anything formed) The proto- 
 plasm composing the centrosoma, 73. 
 
 Archenteron (apx ? J, the beginning ; ev-repov, an intestine) The digestive 
 cavity of the gastrula, 68, 106, 148, 224, 260, 307. 
 
 Arch Gill a., 141; Hamal a., 158; Neural a., 158, 184. 
 
 Arches Arterial or Aortic, 197, 246, 265, 290, 308 ; Carotid, Pulmo- 
 cutaneous, Systemic, 197. 
 
 Arches, Visceral, in Chordata Thickenings in the wall of the pharynx 
 between which are the visceral clefts, 141, 157, 225, 227, 262, 264, 308 ; 
 Mandibular a. : The first bar of the visceral skeleton, 157, 225, 227, 
 264, 331 ; Hyoid a. : The second bar of the visceral skeleton, 157, 225, 
 227, 236, 264, 276, 331 ; Branchial a. : The third and succeeding bars 
 of the visceral skeleton, 157, 225, 227, 236, 276, 308, 331. 
 
 Area a. opaca, in the Bird and Mammal The part of the blastoderm 
 outside the area pellucida, 257, 260 ; a. pellucida (embryonic area), in 
 the Bird and Mammal That part of the blastoderm from which the 
 body of the embryo is mainly formed, 257, 260, 307. 
 
 Areas of distribution, 349. 
 
 Arm, 175, 230, 269. 
 
INDEX-GLOSSARY. 361 
 
 Artery A blood-vessel carrying blood away from the heart Abdominal, 
 96; Allantoic, 267, 310; Antennary, 96; Aorta, 164, 197, 227, 246, 
 265, 308 ; Brachial, 246, 290 ; Branchial, 164, 227 ; Carotid, 164, 
 197, 246, 265, 290, 331 ; Caudal, 164, 246; Cceliac, 164, 197, 246, 290; 
 Cosliaco-mesenteric, 197 ; Coronary, 290 ; Cutaneous, 198 ; Dorsal, 
 142 ; Femoral, 246, 290 ; Hepatic, 96, 290 ; Hyoidean, 165 ; Iliac, 197, 
 246,290; Ilio-lumbar, 290; Innominate, 246, 290, 331; Intercostal, 
 290 ; Lateral, 142 ; Lieno-gastric, 164, 290 ; Lingual, 197 ; Mesenteric, 
 164, 197, 246, 290; Ophthalmic, 196; Parietal, 164; Pectoral, 246; 
 Pulmonary, 198, 246, 265, 290, 308, 331 ; Renal, 164, 246, 290, 297 ; 
 Sacral, 296 ; Sciatic, 198, 246 ; Sternal, 96 ; Subclavian, 164, 197, 246, 
 265, 290, 331 ; Thoracic, 96 ; Vertebral, 246, 290 ; Vitelline, 267. 
 
 Arthrobranchia (lipdpov, a joint ; braiichia), in the Crayfish) One of the 
 eleven brush-like gills attached on either side to the membranous junc- 
 tions of certain appendages and the body, 97. 
 
 Arthropoda (apQpov, a joint; TTOUS, TTOO-, a foot), 340; Chap, vi., 83. 
 
 Artiodactyla (apTws, even ; octKTiAos, toe), 346, 355. 
 
 Ascaris, 340 ; 47-53, 74. 
 
 Ascension Is., 348. 
 
 Ascidia, 135, 341. 
 
 Asia, 349, 350, 357, 352. 
 
 Assimilation (assimilo, I make like to) The building up of food into proto- 
 plasm, 9. 
 
 Astacus (ioTOKOf, a species of crayfish), (crayfish), 340; 83-109, 135, 138. 
 
 Asterias, 73, 74. 
 
 Atlas The ring-like first vertebra, 184, 238, 278. 
 
 Atrial cavity, in Amphioxus A chamber surrounding the pharynx through 
 which water passes out, 136, 134, 152. 
 
 Atriopore, 136, 139, 142. 
 
 Atrium, genital (atrium, an entrance hall), 42, 131. 
 
 Auditory Organs, 369 ; Astacus, 103 ; Anodonta, Unio, 121 ; Helix, 134 ; 
 Scyllium, 172; Rana, 218; Columba, 255; Lepus, 304 ; Comparison 
 of, 321. 
 
 Auricle (auricula, dim. of auris, the ear) In a two or more chambered 
 heart, the thin walled receptive part, 114, 162, 195, 245, 289. 
 
 Australian region, 350, 352. 
 
 Aves, 344 ; Chap, xi., 229. 
 
 Axial, of skeleton Belonging to the head and trunk, 156, 178. 
 
 Axis, in Bird and Mammal The second vertebra, 238, 279 ; Basi-cranial a. , 
 271; Facial a., 323. 
 
 Axis-cylinder, of nerve-fibre, 215. 
 
 Azores, 348. 
 
362 INDEX-GLOSSARY. 
 
 B 
 
 Backbone. See Vertebral Column. 
 
 Bacteria, 58. 
 
 Balanoglossus, 341. 
 
 Bali, 350. 
 
 Banca, 352. 
 
 Barb, in the feather One of the lateral appendages of the shaft, 231. 
 
 Barbule, in the feather One of the lateral appendages of a barb, 231. 
 
 Basipterygium (basis, the base ; Tn-fpuytov, a fin), 160. 
 
 Bats, 346, 356. 
 
 Bell-animalcule = Vorticella, q.v. 
 
 Bile The secretion of the liver, 160, 161, 191, 194. 
 
 Bile-duct, 94, 126, 160, 191. 
 
 Bilharzia, 39. 
 
 Biogenesis (/3tos, life ; yeveais, birth) The production of life from life, 7. 
 
 Bivalve, 79. 
 
 Black Sea, 349. 
 
 Bladder, Gall b., 160, 191 ; Urinary, 99, 205, 267, 295, 316, 333. 
 
 Bladder-worm, 44. 
 
 Blastoccele (jtfXao-ros, a germ ; /anXos, hollow) The cavity of the blasto- 
 
 sphere (segmentation cavity), 27, 67, 147, 224, 257. 
 Blastoderm (/3\ao-To ; oepjua, the skin), in Meroblastic Ova The cellular 
 
 patch resulting from segmentation, 105. 
 Blastomeres (/3Xao-To ; jue/)o?, a part) Cells resulting from the cleavage of 
 
 the oosperm, 27. 
 
 Blastopore (/3Xa<rr6s ; Tropos, a passage) The orifice by which the archen- 
 teron of a gastrula communicates with the exterior, 68, 70, 106, 148, 
 224, 260. 
 Blastosphere (/3Xacn-os ; <r<pa7pa t a sphere) A hollow blastula, 27. 
 
 Blastula (dim. of j3Xao-Tos, a germ) The embryo at the conclusion of 
 cleavage, 27, 67, 105, 147, 224, 306. 
 
 Blood, 95. 
 
 Blood-corpuscles, 59, 78, 142, 166, 195, 245, 289. 
 
 Blood-system, Lumbricus. See Circulatory System. 
 
 Body (of vertebra). See Centrum. 
 
 Body-cavity A space or system of spaces between the viscera and the 
 body wall, 31, 49 ; Lumbricus, 56, 71 ; Hirudo, 79. See also Ccelom. 
 
 Body-wall Hydra, 20 ; Distoma, 28 ; Ascaris, 48. 
 
 Bojanus, organs of, in Mollusca The kidneys, 118. 
 
 Bone, 312. I. Cartilage b. One replacing pre-existing cartilage, 179, 
 188, 232, 271 ; Acetabular (cotyloid), 327 ; Alisphenoid, 272, 323, 325 ; 
 
INDEX-GLOSSARY. 363 
 
 Articular, 236; Astragalus, 187, 282, 328; Basioccipital, 232, 272; 
 Basisphenoid, 233, 272, 323; Calcaneum, 187. 282, 328; Carpale, 186, 
 281, 327; Centrale, 186, 187, 281, 282, 327, 328; Coccyx, 326; 
 Columella, 183, 236, 255, 264; Coracoid, 185, 239, 280; Cotyloid, 241, 
 327 ; Cuboid, 282, 328 ; Cuneiform, 281, 327 ; Epicoracoid, 185 ; 
 Epiotic, 232; Ethmoid, 323; Ethmoturbinal, 275, 323; Exoccipital, 
 179, 180, 232, 272 ; Femur, 187, 241, 327 ; Fibula, 187, 241, 282, 327 ; 
 Fibulare, 282, 328 ; Humerus, 185, 239, 280, 326 ; Ilium, 187, 239, 
 281, 327; Incus, 273, 311; Innominate, 239, 281, 327; Intermedium, 
 186, 187, 281, 282 ; Ischium, 187, 239, 281, 327 ; Lunar, 281 ; Magnum, 
 281, 327; Malleus, 273; Maxilla (man), 325 ; Maxillo-turbinal, 275; 
 Mento-meckelian, 183 ; Mesethmoid, 233, 272 ; Metacarpal, 186, 239, 
 281, 327; Metatarsal, 188, 241, 282, 328; Nasal, 182; Naso-turbinal, 
 275; Xavicular, 282, 328; Occipital, 323 ; Omosternum, 184; Opisthotic, 
 232 ; Orbiculare, 274 ; Orbitosphenoid, 233, 272, 323 ; Palatal, 325 ; 
 Palatine (rabbit), 275; Periotic, 273, 323; Phalanx, 188, 239, 241, 
 281, 282, 327, 329; Ploughshare b., 237; Precoracoid, 280; Pre- 
 sphenoid, 233, 272, 323 ; Pro-otic, 180, 232 ; Pterygoid (rabbit), 275 ; 
 Pubis, 187, 239, 281, 327; Quadrate, 234, 264, 311; Radiale, 186, 
 239, 281 ; Radio-ulna, 185 ; Radius, 186, 239, 281, 326 ; Sacrum, 237, 
 326 ; Scaphoid, 281, 327 ; Scapula, 185, 239, 280, 326 ; Stapes, 274, 
 276, 308 ; Sternum, 185, 238, 280, 326 ; Sphenethmoid, 179 ; Sphenoid, 
 323; Supraoccipital, 232, 272; Tarsale, 187, 282, 328; Tarso-meta- 
 tarsal, 230, 241 ; Temporal, 323 ; Tibia, 187, 284, 327 ; Tibiale, 187 ; 
 Tibio-fibula, 187 : Tibio- tarsus, 241 ; Trapezium, 281, 327 ; Trapezoid, 
 281, 327; Turbinal, 234; Turbinate, 323; Tympano-hyal, 276; Ulna, 
 186, 237, 281, 326; Ulnare, 186, 239, 281; Uncinate, 281, 327. 
 II. Membrane bone One replacing pre-existing connective tissue, 
 179, 188, 232, 271; Angular, 237; Angulo-splenial, 183; Clavicle, 
 185, 239, 326 ; Dentary, 236 ; Frontal, 232, 272, 323 ; Furcula, 239 ; 
 Iiiterclavicle, 239 ; Jugal (malar), 234, 325 ; Lachrymal, 233, 275, 325 ; 
 Maxilla, 182, 189, 234, 275; Maxillary, 325; Nasal, 182, 234, 275, 
 324; Palatine, 182, 236; Parasphenoid, 180, 233, 236; Parietal, 232, 
 272, 323; Parieto-frontal, 179; Premaxilla, 182, 189, 234, 275; 
 Pterygoid, 182, 236, 264; Quadrato-jugal, 182, 234; Splenial, 236; 
 Squamosal, 183, 232, 272, 323; Tympanic, 273, 323; Vomer, 182, 
 234, 273, 324. III. Sesamoid b.-One developed in a tendon, 232; 
 Fabellfe, 282; Patella, 282, 327; Pisiform, 281. 
 
 Borneo, 349, 350. 
 
 Bothriocephalus, 46. 
 
 Botryoidal (/3oVpus, a bunch of grapes ; $->.T$os, $-, appearance), 79. 
 
 Bovidre, 355. 
 
364 INDEX-GLOSSARY. 
 
 Bowman's Capsule The dilated commencement of a uriniferous tubule, 
 
 into which a glomerulus projects, 205, 251, 295. 
 Brachium (brachium, the arm) The upper arm. See Arm. 
 Brain Scyllium, 168 : Rana, 210; Columba, 252 ; Lepus, 301 ; Homo, 333, 
 
 339 ; Gorilla, 339. 
 Brain case = Cranium, q.v, 
 
 Branchiae ((3pdyx ia > branchice, the gills of a fish). See Gills. 
 Branchio-cardiac-groove, 86. 
 Branchiostegite, in the Crayfish The fused thoracic pleura, which form 
 
 the outer wall of the branchial chamber, 86. 
 British Isles, 348. 
 
 Bronchus One of the main subdivisions of the trachea, 248, 293. 
 Brow-spot, in the Frog, 2. 
 Buccal cavity = Mouth cavity, q.v. 
 Buccal mass, in the Snail The anterior part of the alimentary canal, which 
 
 contains the mouth-cavity and odontophore, 125. 
 Buccal pouch, 57. 
 Buddha, 113. 
 Budding, 39. 
 Bulb (Medulla Oblongata) The axial part of the hind brain, 169, 211, 253, 
 
 302. 
 Bulla (butta, anything swelling up and so becoming round) The dilated 
 
 part of the tympanic bone, in which the tympanic cavity is contained, 
 
 273. 
 
 Bursa ; B. Entiana, 160 ; B. Fabricii, 242. 
 Butterfly, 4. 
 Byssus, in some Lamellibranchs Threads developed by a gland near the 
 
 foot, and subserving attachment to foreign bodies, 121. 
 
 Crecum (ccecus, blind) A pouch of the intestine which ends blindly, 94, 
 
 242, 286, 330. 
 Calamoichthys, 349. 
 Calcar (calcar, a spur), 176, 188. 
 Canal Branchio- cardiac, 96 ; Central c., 253; Coelomic, 143; Neural, 168, 
 
 210, 252, 300; Neurenteric c., 151, 224; Pigmented c., 144 ; Pore c., 
 
 90; Semicircular c., 173, 219, 255, 304; Urinogenital, 298, 299; 
 
 Vertebrarterial, 238, 278. 
 Canaliculi (canaliculus, dim. of canalis, a channel) Minute tubules in bone, 
 
 traversed by processes of the bone-cells, 188. 
 Capillaries, 60, 79, 96, 142, 166, 200, 245, 292. 
 
INDEX-GLOSSARY. 365 
 
 Capitulum (dim. of caput, the head) The head of a rib, 237, 279. 
 
 Capsule Auditory, 157, 180, 232, 273; Xasal c., 234; Olfactory c., 157; 
 179, 182, 275, 323. 
 
 Carapace, 83. 
 
 Carbon dioxide, 10. See Respiration. 
 
 Cardia (/ca/oot'a, used with the modern meaning), 286. 
 
 Cardiac ((ca/cxSta/cos, belonging to the cardia) Belonging to or near the heart. 
 In the stomach : the part nearest the opening of the oasophagus, 92. 
 
 Garni vora, 346, 356. 
 
 Carpus The wrist, 186, 239, 281, 327. 
 
 Cartilage A connective-tissue substance consisting of cells embedded in a 
 clear matrix, 179. 
 
 Cartilages Arytenoid, 204, 293 ; Basi-hyal, 157, 158, 236 ; Basi-branchial, 
 236 ; Cerato-hyal, 157 ; Cricoid, 204, 293 ; Epicoracoid, 185 ; Epi- 
 sternum, 184; Extra-branchial, 158; Glosso-hyal, 236; Hyomandibular, 
 157; Intercalary, 158; Labial, 158; Meckel's c., 183, 236, 264; 
 Pessulus, 248; Quadrate c., 182; Septum nasi, 275, 234, 323 ; Supra- 
 scapular, 185, 280; Thyroid, 273; Tympanic, 183; Xiphi-sternum, 185. 
 
 Caspian, 349. 
 
 Cat, 349. 
 
 Caucasus, 349. 
 
 Cauda equina The filum terminale together with the last few nerve-roots, 
 213. 
 
 Caudal Belonging to the tail, 136. 
 
 Caval system Rana, 198 ; Columba, 246 ; Lepus, 291 ; Man, 331. 
 
 Cavity Abdominal c., 161 ; Atrial c., 136, 139, 152; Buccal or mouth c., 
 29, 57, 76, 136, 139, 151, 160, 189, 204, 241, 284, 329; Glenoid c., 185, 
 239, 280, 326; Pericardial, 195; Peritoneal, 162; Pleuro-peritoneal, 
 191 ; Sigmoid c., 281 ; Tympanic c., 189, 219, 232, 255, 273, 304. 
 
 Celebes, 348. 
 
 Cell The morphological and physiological unit Auditory, 221, 256; 
 Bone c., 188; Calcareous, 127; Chief c., 288; Chloragogen c., 57; 
 Cystogenous, 38 ; Ferment c., 127; Flame c., 31; Ganglion c , 205, 215; 
 Germinal, 20, 33, 36, 62; Goblet c., 55, 193, 288; Gustatory, 254, 
 304; Hair c., 172, 173, 304; Hepatic, 288; Inner, 306; Liver c., 127; 
 Lower layer c., 257 ; Muscle c., 81, 209 ; Nerve c., 35, 145, 172, 205 ; 
 Olfactory, 255, 304; Outer c., 305; Ovoid c., 305; Pigment c. (Chro- 
 matophore), 178; Polar c., 26, 73, 143, 207; Sense c., 216, 320; 
 Sensory, 138; Sperm-mother c., 33; Taste c., 254, 304; Thread c. 
 (Nematocyst), 24, 312; Yolk c., 226. 
 
 Centetidse, 349. 
 
 Centrolecithal, of ovum Containing a central mass of yolk, 105. 
 
366 INDEX-GLOSSARY. 
 
 Centrosoma A specialized part of the cell protoplasm which probably 
 
 determines the division of the nucleus, 73. 
 Centrum The body of a vertebra, 158, 184. 
 Cephalochorda, 341, 135. 
 Cephalothorax, 83, 86. 
 Geratodus, 153. 
 Cercaria, in the Fluke The free tadpole-like stage which, after losing its 
 
 tail, becomes the adult, 36, 38. 
 Cercaria, 338. 
 
 Cere (cera, wax), in the Pigeon A bare patch near each external naris, 229. 
 Cerebellum A dorsal outgrowth of the hind -brain, 169, 211, 253, 254, 302, 
 
 337, 339. 
 Cerebral hemispheres Lateral hollow outgrowths of fore-brain, 169, 210, 
 
 216, 253, 254, 301, 333. 
 Cerebro-spinal axis Scy Ilium, 168; Rana, 209; Columba, 252; Lepus, 300; 
 
 Homo, 333. 
 Cervical groove, 86. 
 
 Chaetopoda (xiTfj, hair ; TTOUS, TTOOOS, a foot), 340. 
 Chalaza (x^a<X hail), in the Bird's egg A cord-like structure traversing 
 
 the white at either end, 256. 
 
 Chamber Branchial, 111; Cloacal, 112; Supra-branchial, 111, 117. 
 Cheiroptera, 346, 356. 
 
 Chelate (xn^i, a cloven hoof, a claw) Provided with pincers (chelse), 87. 
 Chiasma, optic (xio"/ia, the mark of the letter x) The X-shaped structure 
 
 formed by the crossing of the optic nerves on the ventral surface of the 
 
 thalamencephalon, 169, 211, 253, 302. 
 Chick, 256-268. 
 Chimpanzee, 338. 
 China, 349. 
 Chiriqui, 349. 
 Chloragogen, 57, 61. 
 Chlorophyll (x^wpos, green ; 0uX\oi/, a leaf) The characteristic green 
 
 colouring matter of plants, 14, 22, 44. 
 
 Chondrocranium (x'"<Vo s , a cartilage; cranium) The cartilaginous ground- 
 work of the skull ; the primordial cranium, 179, 232. 
 Chordinse tendincse Firm bands of connective tissue uniting the flaps of an 
 
 auriculo-ventricular valve with the wall of the ventricle, 245, 288. 
 Chordata (xP$V, a string), 341 ; 3 ; Chap, vii., 134, et stq. 
 Chorion, 338. 
 Choroid (yopiov, skin, membrane ; t<5o9, to-, appearance), 174, 221 ; c. 
 
 plexus, 210. 
 Chromatin (xpuna-nvos, coloured) The more deeply staining part of a 
 
 nucleus, 8, 73. 
 
INDEX-GLOSSARY. 367 
 
 Chromatophore (xfS/ice, xptafiaT-, colouring matter ; </>o % oos, bearing; <t>epw, 
 I bear) A pigment-bearing cell, 178. 
 
 Cilium (dl'mm, an eyelash) A short vibratile thread of protoplasm on the 
 free surface of a cell, 13, 61, 312. 
 
 Circulatory system Lumbricus, 59; Hirudo, 78; Astacus, 97; Anodonta, 
 Unio, 114; Helix, 127; Amphioxus, 142; Scy Ilium, 161; Rana, 194; 
 202; Tadpole, 227; Columba, 245; Chick, 267; Lepus, 289; Homo, 
 331 ; Comparison of, 314. 
 
 Cirrus, in Distoma and Ttenia The penis, 32, 42 ; buccal c., 136. 
 
 Cirrus-sac, 33. 
 
 Clasper, 154, 167. 
 
 Classification of Animals, 1, 3; Chap. xv. , 339. 
 
 Claw, 176, 230, 241. 
 
 Cleavage (Segmentation) The early stages of cell division occurring in a 
 developing oosperm, 26, 67, 105, 147, 222, 256, 306. 
 
 Clefts, visceral, in Chordata Lateral apertures by which the pharynx com- 
 municates with the exterior, 3, 157, 225, 226, 262, 308. 
 
 Clepsidrina, 18. 
 
 Climate, 348. 
 
 Clitellum (clitella;, a pack-saddle), 55, 64, 76. 
 
 Clitoris, 299. 
 
 Cloaca (cloaca, a sewer) The chamber into which the intestine, genital, 
 and, usually, urinary ducts open, 48, 49, 160, 191, 242. 
 
 Cnemial crest, 290. 
 
 Cnidoblast, 22. 
 
 Cnidocil, 22. 
 
 Coagulation, 165. 
 
 Coats, of Alimentary canal, 192, 244, 288 ; of Artery, 202. 
 
 Coccyx, 326. 
 
 Cockroach, 18. 
 
 Cocoon, 82. 
 
 Cochlea (cochlea, a snail-shell) A posterior outgrowth from the mem- 
 branous labyrinth, coiled in higher forms, 173, 219, 256, 304. 
 
 Cod, 153. 
 
 Ccelenterata, 340; Chap, ii., 19. 
 
 Ccelom (/coIXos, hollow) A body cavity which typically (1) does not contain 
 blood, (2) communicates at some period with the exterior by excretory 
 tubes, (3) has parts of its lining thickened into gonads, (4) arises early 
 in development, 56, 60, 79, 95, 143, 150, 191, 248, 263. 
 
 Coelomata, 340. 
 
 Ccenurus, 46. 
 
 Collozoum, 339. 
 
368 INDEX-GLOSSARY. 
 
 Colon, 286. 
 
 Colpidium, 72. 
 
 Columba, 344 ; 229-268. 
 
 Columbia, 349. 
 
 Columella, 123, 219. 
 
 Columnse carnese, in the heart Internal projections of the ventricular 
 
 wall, 245. 
 Commissure (commissura, a joining together) (1) In Invertebrates: a 
 
 nerve-band uniting transversely two ganglia of the same name, 119; 
 
 (2) in the Vertebrate brain : bands of connecting fibres ; Anterior c., 
 
 253, 301, 337 ; Posterior c., 210, 252, 301; Middle c., 301. 
 Comparative Animal Morphology and Physiology, Chap, xiii., 310. 
 Condyle A rounded projection, 276; Mandibular, 183; Occipital c., 179, 
 
 232, 238, 272, 322. 
 
 Cones Crystal c., 104; of Retina, 174, 221. 
 Conjugation, in Protozoa The temporary or permanent fusion of two 
 
 individuals, 15, 18, 72, 317. 
 
 Conjunctiva (conjungo, conjunct-, join together), in Vertebrates A trans- 
 parent membrane, covering the front of the eyeball, and connecting 
 
 the eyelids, 222, 256, 305. 
 Connective A nerve cord joining ganglia of different name to each other 
 
 or to the main cord, 66, 81, 119. 
 Continental Islands, 348. 
 
 Contractility, 318 ; Amoeba, 10 ; Vorticella, 16 ; Hydra, 25. 
 Conus Arteriosus, in many Fishes A contractile tubular part of the heart 
 
 succeeding the ventricle, 162. 
 Copulatory Organ, 86, 154. 
 Coral Is., 348. 
 Cornea (corneus, horny), in the eye The transparent area forming the front 
 
 part of the sclerotic, 103, 134, 174, 221. 
 Cornua (1) in Brain, of lateral ventricle, 301 ; (2) of hyoid apparatus, 
 
 see Hyoid apparatus. 
 Corpora quadrigemina, in Mammalia The optic lobes, each being divided 
 
 into natis and testis, 302. 
 Corpus albicans = c. mammillare, q.v. 
 Corpora cavernosa, in Mammalia The two firm cylindrical structures 
 
 supporting the clitoris and penis, 298, 299. 
 Corpus adiposum, 205. 
 Corpus callosum, in Mammalia A band of nerve-fibres uniting the cerebral 
 
 hemispheres, 301, 337. 
 Corpus mammillare, in the Rabbit A small rounded projection situated 
 
 on the base of the brain, just behind the infundibulum, 301. 
 
INDEX-GLOSSARY. 369 
 
 Corpus restiforme, in the Rabbit A projection situated on either side of 
 
 the roof of the fourth ventricle, 302. 
 Corpus spongiosum, in Mammalia A mass of vascular tissue making up 
 
 the dorsal part of the penis, and traversed by the urinogenital canal, 
 
 298. 
 Corpus striatum, in the fore-brain A mass of grey matter projecting into 
 
 the front part of either lateral ventricle, 210, 253, 301. 
 Corpus trapezoideum, in the Rabbit A rectangular area situated ventrally 
 
 and anteriorly on either side of the medulla oblongata, 302, 338. 
 Corpuscles Blood c., 59, 78, 161, 195, 245, 289, 293; Central c. (centro- 
 
 soma), 73; Colourless c., 161 ; Muscle c., 208, 291, 300 ; Red c., 161; 
 
 Touch c., 178, 218, 254, 271, 303. 
 Cortex, of kidney, 295 ; of brain, 333. 
 Corti, Organ of, 304. 
 Coverts Wing c., 229 ; Tail c., 229. 
 Cranio-facial angle, 272, 339. 
 Craniota, 135. 
 
 Cranium ( K paviov, the skull) The brain-case, 179, 232, 271, 323. 
 Cranium Primordial. See Chondrocranium. 
 Crayfish = Astacus, q.v. 
 Crista acustica A projection in the ampulla of a semicircular canal, upon 
 
 which is a patch of auditory epithelium, 221. 
 Croll, 349. 
 
 Crop Part of the mid-gut serving for the storage of food, 57, 58, 242. 
 Cross, 4. 
 Crura cerebri Two longitudinal masses of nerve-fibres on the floor of the 
 
 mid-brain, 211, 253, 302. 
 Crus (crus, a leg), in Vertebrates The part of the leg between thigh and 
 
 ankle. See Hind limb. 
 Crustacea, 86. 
 Crystal cone, 104. 
 Crystalline style, 114. 
 Ctenidium (dim. of XTS/J, *Tyy, a comb) The gill of Molluscs, typically 
 
 plume-like, 112. 
 Cuba, 349. 
 Cuticle (cuticula, dim. from cutis, skin) A structureless membrane 
 
 covering the epidermis, 13, 28, 29, 48, 55, 76, 312. 
 Cyclas, 121. 
 Cyclostomata, 153. 
 Cyst A protective case in which some animals are enclosed during a 
 
 dormant stage, 9, 14. 
 Cysticercus, 44, 46. 
 
 2 24 
 
370 INDEX-GLOSSARY. 
 
 D 
 
 Danger signal, 268. 
 
 Danube, 349. 
 
 Dart-sac, 131. 
 
 Darwin, 58. 
 
 Death, 10, 11. 
 
 De Candolle, 4. 
 
 Decidua, 338. 
 
 Deer, 355. 
 
 Delamination Formation of epiblast and hypoblast, by division of the 
 
 segmented ovum parallel to the surface. 
 
 Dentine The part of a tooth or scale developed from the dermis, 155. 
 Dermal Belonging to the dermis, or, in general, to the skin, 34. 
 Dermis The deeper part of the skin derived from mesoderm, 76, 90, 138, 
 
 178, 227, 231. 
 Deutomerite, 17, 18. 
 Development Direct d., 107; Indirect d. = Metamorphosis, q.v. ; of 
 
 nervous system, 150 ; of feather, 231 ; of hair, 270 ; Hydra, 26 ; 
 
 Distoma, 35 ; Tsenia, 43 ; Ascaris, 53 ; Lumbricus, 67 ; Hirudo, 82 ; 
 
 Astacus, 107 ; Anodonta, Unio, 121 ; Amphioxus, 147 ; Scyllium, 167 ; 
 
 Rana, 222; Columba, 256; Lepus, 305; Homo, 338; Comparison 
 
 of, 317. 
 
 Diaphragm, (1) in the Frog The muscular anterior boundary of the body- 
 cavity, 191 ; (2) in Mammalia A muscular and tendinous partition 
 
 separating the thoracic and abdominal cavities, 294. 
 Diastema (Sictrrqua, an interval) A gap between the incisor and pre- 
 
 molar teeth, 284, 329, 338. 
 
 Diastole, in the heart The relaxation which follows each contraction, 97. 
 Didelphia ($/-, two ; t&Qv;, the womb), 346. 
 Differentiation Morphological d., 20. 
 Digestion. See Nutrition. 
 Digestive System Vorticella, 13 ; Hydra, 27 ; Distoma, 29, 36 (embryo), 
 
 38 (cercaria) ; Teenia, 41 ; Ascaris, 48 ; Lumbricus, 55 ; Hirudo, 76 ; 
 
 Astacus, 192; Anodonta, Unio, 113; Helix, 125; Amphioxus, 139; 
 
 Scyllium, 160 ; Rana, 189 ; Columba, 241 ; Eana, 282 ; Homo, 329 ; 
 
 Comparison of, 313. 
 
 Digit, 176, 186, 239, 241, 281, 282, 327, 329. 
 Dimorphism (Bis, doubly ; noptyf], a shape) The occurrence of bi-sexual 
 
 and uni-sexual forms in the life cycle of one animal, 73. 
 Dinornis, 347. 
 
 Diploblastica (SnrXows, double ; /SXao-n/cos, growing), 340. 
 Dipnoi, 153, 350. 
 
INDEX-GLOSSARY. 3 7 1 
 
 Disc, of Vorticella, 13. 
 
 Discontinuity, 349. 
 
 Discus proligerus, in the Rabbit The projection into the cavity of a 
 Graafian follicle, formed by the ovum and several surrounding layers 
 of cells, 299. 
 
 Dissepiment. See. Septum. 
 
 Distal Furthest removed from the main body, 11. 
 
 Distoma (the Liverfluke), 340 ; 28-39. 
 
 Distribution, 1, 5, 346 ; of Mammals, 351 ; of Orders, 353. 
 
 Division of labour, 20. 
 
 Dog, Skull of, 278. 
 
 Dogfish = Scy Ilium, /_/. r. 
 
 Dorsal (dorsum, the back) Upper, 28, 322. 
 
 Duct Archinephric, 228, 265; Bile (hepato-pancreatic), 160, 191, 244, 
 287; Cystic, 191, 287; Hepatic, 191, 287; Lachrymal, 275; Meso- 
 nephric, 167, 265, 333 ; Metanephric, 166, 265 ; Mullerian, 167, 228, 
 333; Pancreatic d., 161, 191, 244, 287; Pronephric, 228; Segmental, 
 228, 265; Stenson's d., 287 ; Sub-lingual, 287 ; Thoracic d., 248, 292; 
 Urinary, 205, 206; Urinogenital, 166, 205, 206; Wharton's d., 287; 
 Wolffiand., 166, 265, 333. 
 
 Ductus D. Botalli, 268 ; in embryos : D. arteriosus A cross branch from 
 the pulmonary artery to the dorsal aorta, 267 ; D. venosus A trunk 
 traversing the liver, formed by the union of a vein from the gut with 
 the vitelline and allantoic veins, 267. 
 
 Duodenum The first part of the small intestine, into which the liver and 
 pancreas open, 191, 242, 286. 
 
 Dura mater A firm fibrous membrane lining the neural canal in Verte- 
 brates, 168, 210. 
 
 E 
 
 Ear, 172, 218, 255, 304. 
 
 Earthworm = Lumbricus, q.v. 
 
 Ecdysis (e/couo-is, the act of putting off, or unclothing) The complete 
 casting-off of an exoskeleton at one time, 166. 
 
 Echidna, 345, 353. 
 
 Echinococcus, 45. 
 
 Ectoderm (e/cros, without ; deppa, the skin) The outer cell-layer of the 
 body, 20, 27, 36, 70, 106, 148, 226, 263, 308. 
 
 Ectoparasite (Uroj, parasite) A parasite living on the exterior of its host, 
 75. 
 
 Ectosarc (e/cros ; <rap%, o-apKos, flesh), in Protozoa The firmer external con- 
 tractile layer of the cell, 13, 16. 
 
372 INDEX-GLOSSARY. 
 
 Edges Pre-axial, 225 ; Post-axial, 225. 
 
 Edentata, 346, 349, 354. 
 
 Eel, 153. 
 
 Efferent (cfferens, carrying out) Of nerve fibres carrying impulses away 
 from a ganglion cell or the central nervous system, 102, 146, 217. 
 
 Egg The fertilized ovum often with nutritive and protective layers, 36, 43, 
 52, 83, 100, 132, 167, 256, 305. 
 
 Egg-capsule, 64, 67. 
 
 Elasmobranchii, 153. 
 
 Elephant, 5, 356. 
 
 Emboly Formation of the gastrula by inpushing of endoderm cells, 68. 
 
 Embryo (see Development), free e., 35, 36. 
 
 Embryology The history of the early stages of development. See, Deve- 
 lopment. 
 
 Embryonic appendages. See Amnion and Allantois. 
 
 Embryonic circulation, 267. 
 
 Emulsion, 58. 
 
 Enamel The part of a tooth or scale developed from the epidermis, 155. 
 
 Encystment The formation of a cyst, 14, 16, 18. 
 
 End-body, 216. 
 
 End-brush, 216. 
 
 Endoderm (evSov, within ; <5e'pM, the skin) The inner cell-layer of the 
 body, 22, 27, 36, 71, 107, 148, 226. 
 
 Endolymph ('iv^ov ; lymph) The fluid contained in the membranous 
 labyrinth, 219, 256, 304. 
 
 Endoparasite (evbov parasite) An internal parasite, 17, 28, 39, 47. 
 
 Endophragmal system, in the Crayfish A series of hard parts, which in- 
 completely roof over the sternal sinus in the thorax, 90. 
 
 Endoplasm (evdov, TrXdvpa, anything formed), in Amoeba The internal 
 granular part of the body, 8. 
 
 Endopodite (evSov; TTOUS, TTO^OS, a foot), in the Crayfish appendages The 
 internal part of the forked end, 84. 
 
 Endosarc (ZvSov, o-ap, o-apxds, flesh), in Protozoa The granular, more 
 fluid, internal part of the protoplasm, 13, 16. 
 
 Endoskeleton An internal skeleton. See Skeleton. 
 
 Endothelium Simple squamous epithelium, lining the heart, vessel, and 
 lymphatic sinuses, 202. 
 
 End-organs, 103, 174. 
 
 End-plate, 92, 209, 216. 
 
 Endostyle A medium ventral thickening in the wall of the pharynx of 
 lower chordates, 139. 
 
 Ends Anterior and posterior, 28, 311 ; Oral and aboral, 19. 
 
INDEX-GLOSSARY. 373 
 
 Energy, 9. 
 
 Enterocoele (evripov, an intestine; K-oiAos, hollow) A body cavity (coelom) 
 
 formed by the outgrowth of pouches from an archenteron, 150. 
 Environment, 347. 
 Epiblast (eirl, upon; j8Xa(rros, a growth) The ectoderm of a developing 
 
 embryo, 27. 
 Epiboly (eTrt, upon; /3o\j, a throwing, casting) Formation of a gastrula 
 
 by overgrowth of ectoderm cells, 148. 
 Epidermis (t^ri, upon; dermis) Simple columnar or stratified squamous 
 
 epithelium covering the external surface. See Skin. 
 Epididymis (eTrt, upon; oi<5v/xo, the testicles) A convoluted region of the 
 
 spermiduct, 80, 298, 334. 
 Epiglottis (t-Tri, upon; glottis), 285. 
 Epimerite, 17, 18. 
 Epimeron (tiri, upon ; M e V s 5 a part), in the Crayfish The part of a segment 
 
 situated between the pleuron and the attachment of the appendage, 
 
 84. 
 
 Epiphragm (<bri, upon; <payM, a fence, a partition), 123. 
 Epiphysis (tirt, upon; </>u<ri?, growth, a growing), in bones A separately 
 
 ossified end, 185, 239, 280. 
 Epipodite (l-ri, upon; TTOUS, TO&OI, a foot), in the Crayfish appendages A 
 
 process which (usually) bears gill-filaments, 178, 185. 
 Episkeletal, of muscles Superficial to the endoskeleton, 208. 
 Episternum, 185. 
 Epithelium Cell-layers covering external and lining internal surfaces, 29, 
 
 177; Ciliated, 113, 117, 193; Germinal, 34, 202; Glandular, 94, 118, 
 
 244; Olfactory, 218; Simple columnar e., 31, 57, 121, 244; Stratified, 
 
 squamous e., 244. 
 Ethiopian region, 350, 351. 
 Ethmo-palatine bar, 180, 182. 
 Europe, 349. 
 
 Eustachian tube, 189, 219, 233, 255, 274; e. valve, 245, 267, 290. 
 Eutheria (cw, well ; Qnpiov, a beast), 346. 
 
 Eversion (evcrto, I turn out) The process of turning a part inside out, 19. 
 Evolution, 347. 
 
 Excretion A waste product cast out by the body, 10, 14, 31. 
 Excretory System Amoeba, 10 ; Vorticella, 14 ; Distoma, 30, 31 ; Tsenia, 
 
 41; Ascaris, 49; Lumbricus, 60; Hirudo, 80; Astacus, 98; Anodonta, 
 
 Unio, 118; Helix, 129; Amphioxus, 143; Scyllium, 166; Rana, 205; 
 
 Columba, 250; Chick, 265; Lepus, 295; Homo, 333; Comparison of, 
 
 316. 
 Exits, of nerves, 233, 274. 
 
374 INDEX-GLOSSARY. 
 
 Exoplasm (g, without ; *-XaV^, a thing formed), in Amoeba The outer 
 
 clearer part of the body, 8. 
 Exopodite ('<%*>, without ; xov;, 'roles, a foot), in the Crayfish appendages 
 
 The outer part of the forked end, 84. 
 Exoskeleton An external skeleton, 84, 109, 122. 
 Expiration The outbreathing of air, 129, 204, 249, 295, 316. 
 External characters Amoeba, 7 ; Vorticella, 11; Hydra, 19; Distoma, 28; 
 
 Tsenia, 40 ; Ascaris, 47 ; Lumbricus, 54 ; Hirudo, 75 ; Astacus, 83 ; 
 
 Anodonta, Unio, 109 ; Helix, 122 ; Amphioxus, 136 ; Scyllium, 153 ; 
 
 Kana, 175 ; Columba, 229 ; Lepus, 268. 
 
 Extrinsic, of muscle of any part Originating outside that part, 91, 208. 
 Eye Compound e., 103 ; Scyllium, 173 ; Rana, 221 ; Columba, 221 ; 
 
 Lepus, 304. See also Visual Organs. 
 Eyelashes, 268. 
 
 Eyelids, 155, 174, 222, 256, 268, 305. 
 Eye-spot, 36. 
 
 Facet Capitular, 237, 279 ; Tubercular, 237, 279. 
 
 Falciform (falx, a sickle ; forma, shape), sickle-shaped, 18. 
 
 Fallopian tube, 299, 334. 
 
 Fang, 285. 
 
 Fat-body (corpus adiposum), 205. 
 
 Feathers, 229, 231. 
 
 Feeler, 103. 
 
 Felis, 349. 
 
 Femur (1) The thigh, or (2) the thigh bone, 176, 230, 241, 2S2. 
 
 Fenestra (fenestra, a window) F. ovalis, 130, 219, 233, 255, 273; 
 f. rotunda, 180, 233, 255, 273. 
 
 Ferment Bodies which excite chemical change without themselves enter- 
 ing into the reaction, 58, 94. 
 
 Fertilization, 74 ; Hydra, 25, 26 ; Tsenia, 43 ; Ascaris, 52 ; Lumbricus, 64 ; 
 Astacus, 100; Auodonta, Unio, 119; Helix, 131; Amphioxus, 147; 
 Scyllium, 167 ; Rana, 207 ; Columba, 252 ; Lepus, 299. 
 
 Fibrilla One of the fine threads into which muscle fibres may be split, 91. 
 
 Filoplume A rudimentary feather, 229, 231. 
 
 Filum terminale The filament in which the spinal cord ends, 211. 
 
 Fins, 136, 154. 
 
 Fin-ray, 138, 159. 
 
 Fish Chap. ix. 
 
 Fission (findo, fissum, split) Reproduction by spliting into two or more 
 equal parts, 10, 15. 
 
INDEX-GLOSSARY. 375 
 
 Fissure Central or Rolandian f., 336; Dorsal f., 145, 169, 211, 253, 302 ; 
 
 Obturator f., 241 ; Sphenoidal f., 274; Ventral f., 169, 211, 253, 302 ; 
 
 Sylvianf., 336. 
 Flagellum (flagellum, a whip, a lash) (1) In Protozoa, an elongated motile 
 
 thread of protoplasm, 22 ; in Snail, 131. 
 Flexure, 262 ; Cephalic f., 89. 
 
 Flocculus A lateral projection of the cerebellum, 253, 302, 338. 
 Fluke = Distoma, q.v. 
 Fold Lateral f., 261 ; Head f., 261 ; Neural (medullary f.), 224, 261 ; Tail 
 
 f., 261. 
 
 Follicle, Ovarian (Graafian) An ovum-containing capsule, 207, 251, 299. 
 Fontanelles, in the endoskeleton Spaces filled with membrane, 179, 180; 
 
 Coracoid f., 185. 
 Food, 5, 6, 9. See Nutrition. 
 
 Foot Hydra, 19 ; Mollusca, 111, 123 ; Vertebrata, = pes, q.r. 
 Foot- jaws = Maxillipedes, 87. 
 Foramen Condylar, 234, 274; Inter vertebral f., 184, 237, 254, 278; f. 
 
 lacerum anterius (Sphenoidal fissure), 274 ; f. lacerum medium, 274 ; 
 
 f. lacerum posterius, 274; f. magnum, 157, 179, 180, 232; f. of 
 
 Munro, 210, 253, 301 ; Obturator f., 281 ; Olfactory f., 179, 233, 274; 
 
 Optic, 179, 180, 233, 274; f. ovale, 267; Stylomastoid f., 274; Tri- 
 
 geminalf., 180; f. of urostyle, 184; Vagus f., 180. 
 Forceps, 87. 
 
 Fore-arm (antebrachium), 175, 230, 269. 
 Fore-brain The part of the brain developed from the first cerebral vesicle, 
 
 168, 210, 252, 301. 
 Fore-gut (Stomodaeum) The anterior part of the alimentary canal, which 
 
 arises as an endodermic pit, 48, 57, 77, 92. 
 Fore-limb, 175, 230, 239, 280, 326. 
 
 Formula Dental, 285 ; Rabbit, 285 ; Dog, 285 ; Man, 329. 
 Fornix, in the Mammalian brain A transverse band of fibres connecting 
 
 the hemispheres and optic thalami, 301. 
 
 Fossa, of brain, 273, 274 ; glenoid f., 276 ; f. ovalis, 245, 267. 
 Fowl, 229. 
 
 Fresh- water Polype = Hydra, q.v. 
 Frog = Rana, q.v. 
 Funnel Atrio-coelomic f., 144; Excretory f., 61, 144; Seminal f., 62. 
 
 G 
 
 Galeopithecus, 349. 
 
 Gall-bladder A swelling on the bile-duct acting as a store for bile, 160, 
 244, 287. 
 
376 INDEX-GLOSSARY. 
 
 Gallus bankiva = Fowl, 229. 
 
 Ganglion (ydyyXioi/, a small tumour) An aggregation of nerve-cells, 35, 
 
 66, 81; Abdominal, 101, 102; Anal, 52; Buccal, 133; Cerebral, 35, 36, 
 
 66, 81,100, 132; Cerebro-pleural, 119; Cervical, 303 ; Cceliac, 303 ; 
 
 Gasserian, 212, 215, 253 ; Infra-cesophageal, 81 ; Lateral, 52 ; Mesen- 
 
 teric, 303; Optic, 103; Parieto-splanchnic, 119; Pedal, 119, 133; 
 
 Pleuro- visceral, 133 ; Post-oesophageal, 101 ; Semilunar, 303 ; Spinal, 
 
 215 ; Sympathetic, 171 ; Thoracic, 101 ; Vagus, 213, 303 ; Ventral, 35, 
 
 52 ; Visceral, 119. 
 Ganoidei, 153, 349. 
 Gastric juice, 194. 
 Gastric mill, 92. 
 
 Gastrolith (yao-rj/p, the stomach ; \i'0os, a stone), 93. 
 Gastrula (dim. from gaster, yao-rj/p) An embryonic stage, the typical form 
 
 of which is a two-layered sac with digestive cavity opening to the 
 
 exterior, 38, 68, 105, 148, 260. 
 
 Gastrulation The formation of the gastrula, 68, 148, 224. 
 Gemmation (gemma, a bud) Asexual reproduction by budding, 24. 
 Generative or Genital Organs. See Reproductive Organs. 
 Genus, 3, 4. 
 Geology, 347. 
 Germinal band, 70. 
 Germinal disc, in the Crayfish A thickening of the blastoderm, which 
 
 indicates the ventral surface of the embryo, 105 ; in the Bird's ovum 
 
 The lenticular mass which contains most of the protoplasm, 252, 256. 
 Germinal layers, in the Embryo Cell-aggregates, which precede the tissues 
 
 in development (see Layers, Germinal, fate of). 
 Germinal spot The nucleolus of the nucleus (germinal vesicle) of an ovum, 
 
 23, 34, 73. 
 
 Germinal vesicle The nucleus of an ovum, 23, 34. 
 Giant-fibres, 66. 
 Gibbon, 338. 
 Gill A respiratory organ adapted for breathing the oxygen dissolved in 
 
 water, 97, 115, 117, 166, 225, 315. 
 Gill-chamber, 86, 117. 
 Gill-filament, 117. 
 Gill slit, 141, 151, 155, 166. 
 Giraffe, 355. 
 Girdle, in the endoskeleton of limbs The part between the body and free 
 
 limb. Shoulder (pectoral), 159, 185, 239, 280, 326; Hip (pelvic), 160, 
 
 186, 239, 281, 327. 
 Gizzard A muscular part of the mid-gut, 57, 58, 242. 
 
INDEX-GLOSSARY. 377 
 
 Glacial epoch, 348. 
 
 Gland An organ essentially formed by one or more epithelial cells, which 
 elaborate a secretion or excretion, 33 ; Accessory g., 32; Albumen g., 
 131 ; Byssus g., 122; Calciferous, 57, 58; Capsulogenous, 55; Cement 
 g., 90; Clasper g., 155; Cowper's g., 298, 299; Digestive, 94, 127; 
 Ductless, 165, 201 ; Gastric, 193; Green g., 98, 316; Harderian, 222, 
 256, 305 ; Hermaphrodite g., 129 ; Intermaxillary, 189 ; Infra-orbital, 
 287 ; Lachrymal, 256, 305 ; g. of Lieberkuhn, 193, 244, 288 ; Lym- 
 phatic, 248, 292; Mesenteric, 292; Milk (mammary) g., 269, 271; 
 Mucus, 76, 131, 177; (Esophageal, 57, 193; Oil g., 230, 231; Ovi- 
 ducal, 167; Parotid, 287; Peptic, 193, 242, 244, 288; Perineal, 269, 
 271 ; Pineal, 2, 168, 210, 216, 253, 301 ; Prostate, 130, 298 ; Rectal, 
 161, 287 ; Salivary, 78, 125, 127, 287, 288 ; Sebaceous, 270 ; Serous, 
 177; Shell g., 33, 43; Sub-lingual, 287; Sub-maxillary, 287; Supra- 
 pedal, 133; Thymus, 201, 293; Thyroid, 201, 293; Yolk g., 33, 43. 
 
 Glans penis, 298 ; g. clitoridis, 299. 
 
 Glochidium (dim. from y\u>x. e<s , the prickles on ears of corn) The free- 
 swimming embryo of Anodonta or Unio, 122. 
 
 Glomerulus (dim. of glomus, -eris, a skein), in the kidney A tuft of capil- 
 laries projecting into Bowman's capsule, 206, 295. 
 
 Glottis (yXwT-rts, used with modern sense), in air-breathing Chordata The 
 chink-like opening into the respiratory organs, 189, 204, 242, 285. 
 
 Glucose Grape-sugar, 58. 
 
 Glycogen, 194. 
 
 Goblet-cell, 55, 66. 
 
 Gonad (yovii, production) A reproductive gland, typically formed by a 
 thickening of the epithelium (and underlying tissue) lining the body- 
 cavity. See Spermary, ovary. 
 
 Gorilla, 338. 
 
 Grape -sugar = Glucose, q.v. 
 
 Great toe = Haltux, q.v. 
 
 Green gland, 98. 
 
 Gregarina, 17-19, 64, 311, 339. 
 
 Gregarinida, 339. 
 
 Grey matter, in the brain and spinal cord The part mainly composed of 
 ganglion -cells, 172, 215. 
 
 Groove Epibranchial g., 139; Neural (medullary) g., 224, 261. 
 
 Guanin, 32, 41, 99, 118. 
 
 Gubernaculum (gubernaculum, a rudder), in the Rabbit A fibrous cord 
 connecting the spermaries with the scrotal sac, 298. 
 
 Gullet The part of the alimentary canal which next succeeds the pharynx ; 
 the resophagus, 29, 49, 57, 92, 242, 284. 
 
378 INDEX-G LOSS ARY. 
 
 Gustatory Organs, 369 ; Anodonta, Unio, 121 ; Amphioxus, 146 ; Rana, 
 218 ; Columba, 255 ; Lepus, 304 ; comparison of, 320. 
 
 Gut The alimentary canal, composed of fore-gut, mid-gut, and hind-gut. 
 See Digestive System In Human Anatomy : the small intestine. 
 
 H 
 
 Heemal arch, 158. 
 
 Haemal spine, 158. 
 
 Hsemocyaniii (xJ/xet, blood ; xvuvtos, blue), 95, 98. 
 
 Hemoglobin (aT^a) The red colouring-matter of blood, (50, 78, 95, 166. 
 
 Hag, 153. 
 
 Hair, 270. 
 
 Hair-follicle The capsule in which the base of a hair is ensheathed, 270. 
 
 Hair-germ The first rudiment of a hair in the embryo, consisting of a 
 
 thickening of the Malpighian layer of the epidermis, 270. 
 Hair-papilla The projection at the bottom of a hair-follicle, upon which 
 
 the hair is moulded, 270. 
 Half-facets, Capitular, 279. 
 Hallux The great toe, 176, 230, 329. 
 Hand = Manus, q.v. 
 Hare-lip, 329. 
 
 Haversian canals The cavities in bone tissue in which the small blood- 
 vessels run, 188. 
 Haversian system An Haversian canal with concentric lamellae of bone 
 
 surrounding it, 291. 
 Hayti, 349. 
 Head Astacus, 83, 87 ; Helix, 123 ; of Ribs = Capitulum, q.v. ; Scyllium, 
 
 154 ; Rana, 175 ; Columba, 229 ; Lepus, 268. 
 Head kidney, in Vertebrata = Pronephros, q.v. 
 Heart Astacus, 96; Anodonta, Unio, 115; Helix, 127; Scyllium, 161; 
 
 Rana, 195 ; Columba, 245 ; Chick, 265 ; Lepus, 289. 
 Hearts, of Lumbricus, 60. 
 Heel, 282, 328. 
 Hemichorda, 135,^341. 
 Hepatic Belonging to the liver. 
 Herring, 153, 161. 
 Heterocercal, of tail-fin Asymmetrical both externally and internally, 
 
 154. 
 Heterogamy (sngoi, another; yajuos, a marriage) An alternation of normal 
 
 sexual reproduction with parthenogenesis, 39. 
 Helix (Snail), 4, 122-134, 341. 
 
INDEX-GLOSSARY. 379 
 
 Hepato-pancreas, 94. 
 
 Hepatic portal system Rana, 143, 165, 199, 268. 
 
 Hermaphrodite Bi-sexual, 23. 55. 80. 12Q. 
 
 Hilus, in Mammalia The point at which the ureter leaves the kidney, 295. 
 
 Hind-brain The part of the brain developed from the third cerebral 
 
 vesicle, 169, 211, 253, 302. 
 Hind-gut (Proctodeeum) The posterior part of the alimentary canal which 
 
 arises as an ectodermic pit, 48, 57, 78, 94. 
 Hind-limb, 176, 230, 241, 269, 281, 327. 
 Hinge- joints, 91, 326. 
 Hippocampus major, 301. 
 Hippopotamus, 5, 354. 
 Hippuric acid, 297. 
 Hirudo (Leech), 75-82, 135, 340. 
 Hirudinea, 340. 
 
 Histology (lords, a thing woven; Xoyos, speech, discourse) The mor- 
 phology of minute structure, 2. 
 Homarus = Lobster, q.v. 
 Homo, Chap, xiv., 321. 
 
 Homology Morphological equivalence, 27, 90, 311. 
 Holoblastic (o\os, whole; /SXao-ros, a germ) of cleavage Affecting the 
 
 whole oosperm, 26, 44, 67. 
 
 Host An organism preyed on by a parasite, 34. 
 Humming bird, 349. 
 
 Humour Aqueous, 174, 222; Vitreous, 174, 222. 
 Hyaena, 356. 
 
 Hybernaculum (hibernaculum, a winter abode), 123. 
 Hybernation (hiberno, I winter) A state of torpidity during winter ; 
 
 Helix, 123. 
 Hybrid, 4. 
 
 Hydra (ufym, a water-serpent), 19-27, 340. 
 Hydroid Resembling Hydra, 27. 
 Hydrozoa, 27, 
 Hylobates, 338. 
 Hyoid H. apparatus: (1) Strictly speaking, structures derived from the 
 
 hyoid arch or in connection with such ; (2) The above + elements from 
 
 the branchial arches, 183, 236, 276. See Arches. 
 Hyomandibular, 157. 
 Hyostylic, of the Skull With the lower jaw attached with the aid of 
 
 hyoid elements, 158. 
 Hypapophysis (UTTO, under ; ebro^i/o-is, a process) A downward process 
 
 from the centrum of a vertebra, 238. 
 
380 INDEX-GLOSSARY. 
 
 Hypoblast (vvo; /SXao-ros, a growth) The endoderm of a developing em- 
 bryo, 27. 
 
 Hyposkeletal, of muscles Taking origin within the endoskeleton, 208. 
 
 Hypostome (UTTO; <rro/ia, the mouth), in Hydra The conical projection at 
 the end of which the mouth is placed, 19. 
 
 Hyracoidea, 346. 
 
 I 
 
 Ice age, 348. 
 
 Ichthyopsida (ix^ s a fish j ovjns, an appearance), 342. 
 
 Ileum (<\\o>, I twist; iXeos, eiXtos, colic), in the small intestine The part 
 succeeding the duodenum, 286. 
 
 Impregnation. See Fertilization. 
 
 Incubation, 257. 
 
 Infundibulum (infundibulum, a funnel) (1) A ventral projection of the 
 thalamencephalon, to the end of which the pituitary body is united, 
 168, 210, 253, 301 ; (2) in Mammalia One of the vesicles in which the 
 bronchial tubes end, 294. 
 
 Infusoria, 339. 
 
 Ingestion (ingero, ingestum, carry in) The taking-in of solid food-particles, 9. 
 
 Insectivora, 346, 349. 
 
 Insertion, ~6f muscle The end attached to a relatively movable part, 91. 
 
 Inspiration The in-breathing of air, 129, 204, 249, 294, 316. 
 
 Intelligence, 333. 
 
 Intercellular Situated between cells, 61. 
 
 Interstitial In the interstices between cells, 21. 
 
 Intestine The part of the alimentary canal in which* digestion is completed, 
 29, 49, 57, 78, 94, 113, 125, 141, 160, 190, 242, 286. 
 
 Intracellular Within the cell, 24, 31, 61, 80, 209. 
 
 Intrinsic, of muscle of any part With origin and insertion within that 
 part, 91, 208. 
 
 Intussiisception (intus, inside ; suscipio, susceptum, take up) The inter- 
 calation of new particles between pre-existing ones, 6. 
 
 Invagination The process by which a part originally external becomes 
 internal, 38, 148, 224. 
 
 Invertebrata, 135. 
 
 Iris, 174, 221. 
 
 Irritability, 319 Amceba, 11 ; Vorticella, 16 ; Hydra, 25 ; 319. 
 
 Islands, 348. 
 
 Island of Reil, 338. 
 
 Iter The ventricle of the mid-brain ; the Sylvian aqueduct, 169. 
 
INDEX-GLOSSARY. 381 
 
 J 
 
 Japan, 348. 
 
 Jaws, 125; Upper j., 182, 236, 275, 325; Lower j. = mandible, q.v. 
 Jejunum, in human anatomy The part of the small intestine whicli imme- 
 diately succeeds the duodenum, and is followed by the ileum, 286. 
 Jelly-fish, 27. 
 
 K 
 
 Karyokinesis (xapvov, a kernel ; /averts, movement) A method of cell- 
 division in which the nucleus undergoes complex changes, 72. 
 
 Katabolism (/ca-ra/SoXr), a casting down) The breaking down of complex 
 substances into simple ones, 9, 315. 
 
 Keber, organs of, 118. 
 
 Keel, 239. 
 
 Kidney, 98, 118, 129, 166, 228, 250, 265, 295, 316, 333. 
 
 Knee, 176, 230, 269. 
 
 Labial palps, 112. 
 
 Labrum (labrum, a lip), in Astacus The upper lip, 89. 
 
 Labyrinth, Membranous, in VertebratesThe sac which forms the essential 
 part of the auditory organ, 172, 219, 255, 273 ; Bony 1. The compact 
 layer of bone which, in higher vertebrates, surrounds the membran- 
 ous 1., 255. 
 
 Lacteal A lymph-vessel belonging to the gut, 248. 
 
 Lacuna (lacuna, a cavity) An interstice between the constituents of a 
 tissue, 188. 
 
 Lamella (dim. of lamina, a plate), 117. 
 
 Lamellibranchiata (lamella ; fipdyxia, branchiae, gills of fish), 341. 
 
 Lamina inferior, 328 ; 1. perpendicularis, 275, 323 ; 1. terminalis, 225. 
 
 Lamprey, 153. 
 
 Lancelet = Amphioxus, q.v. 
 
 Larva A free-living embryo differing from the adult in form, 107, 122, 
 151, 222. 
 
 Larynx (^f>i>7, used with the modern meaning), in Vertebrate The 
 modified top of the trachea, usually serving as an organ of voice, 204, 
 248, 293. 
 
 Lateral line, 155. 
 
 Laurer's canal, in the Fluke A tube by which the oviduct opens on the 
 dorsal surface, 28, 33. 
 
382 INDEX-GLOSSARY. 
 
 Leech = Hirudo, q. e. 
 Lemurs, 349, 357. 
 
 Lens, in the Eye A firm refracting structure, 104, 134, 174, 222, 256, 305. 
 Leopard, 349. 
 Lepidosiren, 153. 
 Lepidosteus, 349. 
 
 Lepus (Rabbit), 135, 268-310, 347 ; L. variabilis, 349. 
 Life History, 7. See Development. 
 Ligament, 109, 178. 
 Light. See Eye. 
 Limb-girdle. See Girdle. 
 
 Limbs Eana, 185 ; Columba, 239 ; Lepus, 280. 
 Lime, 90, 113, 121, 188. 
 
 Limnaea (Xi/xyaTos, living in a Xi/j-un or marsh), 36. 
 Line, pallial, 110. 
 Lion, 349. 
 
 Liver A gland, usually digestive, derived from and opening into the mid- 
 gut, 57, 94, 126, 141, 160, 191, 242, 287, 288. 
 Liver-rot, 28. 
 Lobes Of Liver, 160, 191, 244, 287, 330; of cerebral hemispheres, 301, 
 
 337; Olfactory 1., 168, 210, 252, 301 ; Optic, 169, 211, 253, 302. 
 Lobi inferiores, in Scyllium Two oval swellings on the ventral surface of 
 
 the thalameiicephalon, 168. 
 Lobster, 107. 
 Lobules, 288. 
 Locomotion Amoeba, 10 ; Hydra, 25 ; Distoma, 34 ; Lumbricus, 65 ; 
 
 Hirudo, 81 ; Astacus, 91 ; Anodonta, Unio, 119; Comparison of, 318. 
 Lombok, 350. 
 
 Lumbricus (Earthworm), 17, 54-71, 135, 340. 
 Lung A respiratory organ adapted for breathing ordinary air, 129, 204, 
 
 248,293,315. 
 Lyell, 348. 
 Lymph, 165. 
 Lymphatics A system of vessels by which (1) Part of the digested food, 
 
 (2) Plasma and white corpuscles exuded in excess through the capillaries 
 
 are carried into the blood-system, 200, 248, 292. 
 Lymph-heart, 200, 204. 
 Lymph-sinus, 192, 200. 
 Lymph-space, 150, 168, 172, 210, 248, 292. 
 Lymph-system; Amphioxus, 142; Scyllium, 165, Rana, 200; Columba, 
 
 248 ; Lepus, 292 ; Comparison of, 314. 
 
INDEX-GLOSSARY. 383 
 
 Macronucleus (/xa/cpd, large ; nucleus), 72. 
 
 Macrozooid (M^'POS; woi/, a living creature), 15, 72. 
 
 Macula (macula, a spot), in the membranous labyrinth One of several 
 
 sensory patches situated in the utriculus, sacculus, and (when rudi- 
 mentary) the cochlea, 221. 
 Madagascar, 348, 349. 
 Malacca, 349. 
 Malpighian Body, in the Kidney A Bowman's capsule with its glomerulus, 
 
 206, 295. 
 
 Malpighian layer, 177. 
 Mammalia, 345; Chap, xii., 268, et seq. : Distribution of, 357; Origin of, 
 
 357. The lower jaw, 183, 236, 276, 325. 
 Man = Homo, q.v. 
 Mandible In Crustacea : the third pair of head appendages, which act as 
 
 jaws, 89. 
 Mantle, in Mollusca A flap-like outgrowth of the body- wall which usually 
 
 shelters the gills, 111. 
 Manubrium-(l) A process of the sternum, 238, 280, 326; (2) a process 
 
 of the mallens, 273. 
 
 Manus The hand, 176, 186, 230, 239, 281. 
 Marmot, 349. 
 
 Marrow The central soft tissue contained within bone, 188, 293. 
 Marsupialia, 346, 349, 352, 354. 
 
 Mastoid A term applied to the spongy part of the periotic, 32, 273. 
 Matrix Intercellular substance in which tissue elements are imbedded, 
 
 126, 188. 
 Maxilla (maxilla, a jaw) (1) In Crustacea : one of the second or third 
 
 jaw-like appendages belonging to the head, 89 ; (2) In Vertebrata : one 
 
 of the membrane bones of the upper jaw, 182, 234, 275, 325. 
 Maxillipede A flattened jaw-like appendage belonging to the head, 89. 
 Meatus (meatus, a passage) External auditory m., 230, 255. 
 Mediastinum A median partition in the thorax, formed by the apposition 
 
 of the parietal layers of the two pleurae, 294. 
 Medulla In nerve fibre : the fatty layer surrounding the axis cylinder, 
 
 81 ; m. of hair, 270 ; m. of kidney, 295. 
 Medulla oblongata The axial part of the hind-brain ; the bulb, 169, 211, 
 
 216, 253, 302. 
 Medusa, 27. 
 Membrane Arachnoid, 210; m. granulosa, 299; Mucous, 189, 192,244, 
 
384 INDEX-GLOSSARY. 
 
 289; Nictitating, 229 ; m. semilunaris, 248; Shell m., 256; Subzonal, 
 
 309; Tympanic, 219, 255, 273, 304; m. tympaniformis interna, 248; 
 
 Vitelline, 73, 252, 299. 
 Mesenteron (/xeo-os, middle ; eWtpoz/, a bowel) That part of the alimentary 
 
 tube which is lined by epithelium of hypoblastic origin ; the mid-gut, 48. 
 Mesentery (/xeVos ; 4Wpos, a bowel) (1) In Earthworm (.see Septum ; (2) in 
 
 Vertebrates, a fold of peritoneum by which the alimentary canal is 
 
 suspended, 161, 192. 
 Mesoblast (jue'cros ; /3\ao-Tos, properly anything grown; /W<rraj/w, I grow) 
 
 The mesoderm of a developing embryo, 36. 
 Mesoblastic bands, 71. 
 Mesoblastic somites, 227, 263. 
 
 Mesoblasts Cells in the embryo which gives rise to the mesoderm, 67. 
 Mesoderm (/xe'o-os ; oe'p/xct, the skin) The middle germinal layer and parts 
 
 derived from it, 36, 68, 71, 106, 107, 149, 224, 226, 259, 263, 306, 308. 
 Mesoglrea, 20. 
 Mesonephros (/j.e<ros ; i></>po, a kidney), in Vertebrates The second-formed 
 
 excretory organ, which, as in the Frog, may persist throughout life, 
 
 166, 216, 265, 333, 334. 
 Mesopterygium, 159. 
 Mesorchium (jue'o-os ; o/>x ts , a testicle) A fold of peritoneum by which the 
 
 testis is suspended, 206, 251, 298. 
 
 Mesosoma (jueo-os ; au>/j.a, a body), in Molluscs The main body-mass, 111. 
 Mesotarsal, applied to an ankle-joint situated in the middle of the tarsus, 
 
 241. 
 
 Mesovarium (AKJO-OS ;* ovarius, adjective from ovum, an egg) -A fold of peri- 
 toneum by which the ovary is suspended, 207, 251. 
 Metabolism (/xETa/3o\7/, change) The sum total of the chemical changes 
 
 which constantly occur in protoplasm, 6. 
 Metacromion, 280. 
 Metadiscoidal, 338. 
 
 Metagenesis Simple alternation of sexual and asexual stages, 39. 
 Metamere = Segment, q.v. 
 Metamorphosis The series of changes by which a larval form becomes 
 
 adult, 107, 122. 
 Metanephros (M eT , behind ; vt^pos, a kidney) The third-formed excretory 
 
 organ typically developed in the Pigeon and Rabbit, 265, 316, 333, 334. 
 Metapleural, 136. 
 Metapophysis (fJ-era, in addition; a7ro<u<ris, a projecting part), in Vertebrae 
 
 A process on the anterior end of the arch, above the prsezygapophysis, 
 273. 
 Metapterygium (M T "J after ; TTTsplyiov, a fin), 159, 160. 
 
INDEX-GLOSSARY. 385 
 
 Metastoma (/tira, behind ; errata, a mouth), in the Crayfish The lower lip, 
 
 89. 
 
 Metatarsus, 188. 
 Metatheria, 346. 
 Metazoa (pira,, after, later ; &/, living creatures) Animals consisting of 
 
 more than one cell, 339, Chap. ii. to end, 7 1 . 
 Micronucleus, 72. 
 
 Micropyle (tumps, little ; -rvXti, door), 119. 
 Microzooid, 15, 72. 
 Mid-brain The part of the brain developed from the second cerebral 
 
 vesicle, 169, 211, 253, 302. 
 Mid-gut (Mesenteron) That part of the alimentary canal which is lined by 
 
 epithelium of endodermic origin, 48, 57, 78, 94. 
 Mitosis (PITO;, a thread) = Karyokinesis, q.v. 
 Mississippi, 349. 
 
 Mollusca (mollis, soft), 340; Chap, vii., 109, 161. 
 Monocystis, 17, 18, 64. 
 Monodelphia, 346. 
 Monotremata, 345, 349, 352, 353, 
 Morphology (pitfii, a shape ; xya,-, speech, discourse), 1,2; Amoeba, 7 ; 
 
 Vorticella, 11; Hydra, 19; Distomum, 28; Tsenia, 40; Ascaris, 47; 
 
 Lumbricus, 54 ; Hirudo, 75 ; Astacus, 83 ; Anodonta, Unio, 109 ; 
 
 Helix, 122 ; Amphioxus, 136 ; Scyllium, 153 ; Eana, 175 ; Columba, 
 
 229 ; Lepus, 268 ; Homo, 322. 
 
 Morula (dim. of morum, a mulberry) A solid blastula, 38. 
 Mosaic vision, 104. 
 Motor, of Nerves Supplying muscular tissue and conveying impulse 
 
 leading to its contraction, 102, 146, 209, 216. 
 Moults, 106. 
 Mouth, 19, 29, 38, 47, 54, 57, 70, 76, 92, 113, 125, 157, 241, 268, 284, 313, 
 
 329. 
 
 Mouth-cavity = Cavity, buccal, q.v. 
 Mud-fish, 153. 
 Multipolar, 145, 214. 
 Muridae, 349. 
 Muscle, 209; Involuntary m.,208; Striped or striated m., 91, 145, 202, 
 
 208, 209; Unstriped m., 132, 192: Voluntary m., 208; Abductor, 91 ; 
 
 Adductor, 91, 109 ; Circular, 65, 81 ; of Eye, 174, 222, 256, 305 ; Ex- 
 tensor, 91 ; Flexor, 91 ; Gastric, 93 ; of Heart, 291 ; Longitudinal, 65, 
 
 81; Oblique, 81, 174, 222; Papillary, 245; Protractor, 29, 65, 119; 
 
 Rectus, 174, 222; Retractor, 29, 81, 119; Spindle m., 123, 132. 
 Muscle-cell, 81. 
 
 2 25 
 
386 INDEX-GLOSSARY. 
 
 Muscle-corpuscle, 91. 
 
 Muscle-fibre, 91, 192, 201, 209. 
 
 Muscularis mucosse, in Vertebrates A thin layer of unstriated muscle 
 
 traversing the mucous membrane of the stomach and intestines, 192, 
 
 288. 
 Muscular system Distoma, 34; Tsenia, 43; Ascaris, 48; Lumbricus, 58, 
 
 64; Hirudo, 81; Astacus, 91; Anodonta, Unio, 119; Helix, 122; 
 
 Amphioxus, 144; Scyllium, 168; Rana, 208; Columba, 252; Lepus, 
 
 299. 
 
 Musculature The muscle system, 34. 
 Mussel (salt-water), 122. 
 Mussel (fresh- water), 100-122. 
 Mustelus, 167. 
 Myocoele (/xus, a muscle ; /coTXos, hollow) The cavities of the mesodermic 
 
 somites, 149. 
 Myoccelomic, 149. 
 
 Myophan striations (M^S; 0a/o/x<, 0ai/- } appear), 13, 16. 
 Myomere = Segment, muscle, q.v. 
 Myotome = Segment, muscle, q.v. 
 Mysis, 109. 
 
 N 
 
 Nail, 176. 
 Nares (nares, the nostrils) External (anterior), 175, 218, 229, 268, 275 ; 
 
 Internal (posterior), 189, 218, 241, 285. 
 Nates, 302. 
 Nearctic, 350, 353. 
 Nebalia, 86. 
 Nemathelmia (v*ina, a thread ; e\/>uvs, intestinal worm) Thread worms, 
 
 340 ; Chap, iv., 47. 
 
 Nematocyst (Thread-cell), 22, 24, 25, 312. 
 Neotropical, 350, 352. 
 
 Nephridiopore The external opening of a nephridium, 61. 
 Nephridium (dim. of i/e^/oos, a kidney) An excretory tube by which waste 
 
 products are carried from the coelom, or a section of it, to the exterior, 
 
 60, 70, 80, 118, 129, 316. 
 Nephrops, 109. 
 
 Nephrostome (e0pos; O-TO/XO, a mouth) The internal opening of a nephri- 
 dium, 61. 
 Nerve Nerve-exits, 233, 274; Cranio-spinal nerves, 319; Scyllium, 169; 
 
 Eana, 211; Columba, 253; Lepus, 302; Abducent (vi.), 170, 212; 
 
 Auditory (viii.), 133, 171, 213; Brachial, 213; Branchial, 171; Buccal, 
 
INDEX-GLOSSARY. 387 
 
 133; Coccygeal, 184, 213; Cranial, 169, 211, 217; Facial (vii.), 171, 
 
 212; Glossopharyiigeal (ix.), 171,213; Hyoid, see Facial; Hyoman- 
 
 dibular, see Facial; Hypoglossal (xii.), 254; Labial, 133; Lateral, 35; 
 
 Lateral line n., 213; Mandibular, see Trigeminal and Facial; Maxillary, 
 
 see Trigeminal; Oculomotor (iii.), 169, 212; Olfactory (i.), 169, 211; 
 
 Ophthalmic, see Trigeminal and Facial; Optic (ii.), 103, 133, 169, 174, 
 
 211, 221; Palatine, see Facial; Pathetic (iv.), 170, 212; Phrenic, 303; 
 
 Pneumogastric (x.) = Vagus, q.v.; Post-spiracular = Hyoid, q.v.; 
 
 Sciatic, 213; Spinal, 171, 213, 217; Spinal accessory (XL), 254; 
 
 Splanchnic, 303; Tentacular, 133; Trigeminal (v.), 171, 212, 253; 
 
 Trochlear (iv.) = Pathetic, q.v.; Unpaired n. (impar), 254; Vagus (x., 
 
 Pneumogastric), 171, 213, 254; Visceral, 101, 103. 
 Nerve-cell, 35, 145, 172, 205. 
 Nerve-cord, 145; ventral n.-c., 66, 81. 
 Nerve-corpuscle, 101. 
 Nerve-fibre, 35, 92, 101, 145, 209, 215. 
 Nerve-ring, 35, 65, 81, 119. 
 Nervous system Development of, 150, 320; Distoma, 34; Tsenia, 43; 
 
 Ascaris, 52; Lumbricus, 65; Hirudo, 81; Astacus, 100; Anodonta, 
 
 Unio, 119; Helix, 132; Amphioxus, 145; Scyllium, 169; Rana, 209 ; 
 
 Columba, 252 ; Lepus, 300 ; Homo, 333 ; Comparison of, 319. 
 Neural arch, 158. 
 Neural fold, 151, 224. 
 Neural groove, 151, 224. 
 Neural plate, 151, 224. 
 Neuroglia (veupov, a nerve; y\/a, glue) The delicate connective- tissue 
 
 framework of the nervous system, 66, 216. 
 New Zealand, 347, 349. 
 Nile, 349. 
 
 Nodes Of Ranvier, 215 ; of Schmidt, 215. 
 Non-chordata, 135. 
 Norway Lobster (Nephrops), 109. 
 Nostrils (see Narea, external). 
 Notochord (VUTOV, the back ; xP^'/, a string), in the Chordata A cellular 
 
 rod which prefigures the vertebral column, 3, 135, 138, 150, 156, 158, 
 
 189, 226, 259, 263, 312. 
 Nucleolus (dim. of nucleus, a nut, a kernel) A dense particle within a 
 
 nucleus, 8. 
 Nucleus (nucleus, a nut, a kernel) A more highly differentiated part of the 
 
 protoplasm occurring in most cells, 8 ; Segmentation n. The nucleus 
 
 of the oosperm, 26, 74. 
 Nutrition Amoeba, 9; Vorticella, 14; Hydra, 23; Distoma, 31; Astacus, 
 
388 INDEX-GLOSSARY. 
 
 83; Anodonta, Unio, 114; Helix, 127; Amphioxus, 141; Seyllium, 
 161; Rana, 194; Columba, 244; Lepus, 288; Comparative, 312. 
 
 
 
 Oceanic Is. , 348. 
 
 Occipital (occiput, the back of the head) Belonging to the hinder region 
 of the skull, 179. 
 
 Odontophora, 341. 
 
 Odontophore (6<5ous. oSov-r-, a tooth; (pepw, I bear; 0o/oo?, bearing), in the 
 Snail A rasping structure which projects into the floor of the mouth 
 cavity, 125. 
 
 Odontophoral cartilages, 215. 
 
 Odours, 369. 
 
 (Esophagus. See Gullet. 
 
 Old Calabar, 349. 
 
 Olfactory Organs, 66; Astacus, 103; Anodonta, Unio, 121; Helix, 123, 
 133; Scyllium, 172; Rana, 218; Columba, 255; Lepus, 304; Com- 
 parison of, 320. 
 
 Ommatidium (dim. of o/^ua-r;oi/, a little eye) One of the elements of a com- 
 pound eye, 103, 104. 
 
 Omo-sternum (w/xos, the shoulcter ; crTcpvov, the breast), 184. 
 
 Ontogeny (ov-ra, beings ; yei/j/aco, I produce) The development of indi- 
 viduals, 2. 
 
 Operculum (operculum, a lid, a cover), 36, 225. 
 
 Ob'genesis (wov, an egg; yivwis, birth) The development of the ovum, 52. 
 
 Ob'sperm (u'v ; ov'ippa., seed) The sexual cell produced by fertilization of 
 the ovum, 25, 74. 
 
 Obtheca (a' ; 0jxti, a cover, a case) A female organ for the storage of ova 
 (receptaculum ovorum), 64. 
 
 Opossum, 354. 
 
 Optic thalami The thickened side-walls of the thalamencephalon, 210, 
 252.; 
 
 Orang-outan, 338. 
 
 Orbit, 182, 232, 271, 325. 
 
 Organ, 1. 
 
 Organic acids, 58. 
 
 Oriental Region, 350, 351. 
 
 Origin of species, 5; of muscle The end attached to a relatively fixed 
 part, 91. 
 
 Ornithodelphia, 1345. 
 
 Ornithorhynchus, 345, 353. 
 
INDEX-GLOSSARY. 389 
 
 Osphradium (6<r<pd<koi;, anything sharp-smelling ; vfr^paivo^ai, I smell) 
 
 The olfactory organ of Molluscs, probably serving to test the respira- 
 
 tory quality of water, 121. 
 
 Ossicle Auditory o. = malleus, incus, stapes, and os orbiculare, 273. 
 Ossification, 188. 
 Osteoblast (oo-Teoi/, a bone ; /3\ao-Tya>, I grow ; /3\a<rr6s, something that 
 
 grows) A bone-forming cell, which becomes modified into a bone- 
 
 corpuscle, 188. 
 Ostium (ostium, a door, an entrance), in the Crayfish One of six valvular 
 
 slits in the wall of the heart, 97. 
 Otocyst (ous, WTOS, the ear; KU<TTIS, a bag, a bladder) The auditory sac, 
 
 121, 134. 
 Otoliths (ous, tores, the ear ; Xi0oe, a stone) Concretions (or foreign particles) 
 
 found within an auditory sac or membranous labyrinth, 121, 134, 219. 
 Ovary (ovum, an egg) The organ producing ova; Hydra, 23; Distoma, 33; 
 
 Taenia, 42; Ascaris, 52; Lumbricus, 64; Hirudo, 80; Astacus, 100; 
 
 Anodonta, Unio, 118; Amphioxus, 144; Scyllium, 167; Rana, 207; 
 
 Columba, 251 ; Lepus, 298. 
 Oviduct The duct conducting the ova to the exterior or into the urino- 
 
 genital canal, 33, 64, 80, 100, 119, 131, 167, 207, 251, 299, 333. 
 Oviparous (ovum, an egg; pario, I produce) Laying eggs, 168, 308. 
 Ovogenetic, 74. 
 Ovum The female sexual cell, 23, 34, 72, 73, 80, 100, 131, 144, 167, 207, 
 
 251, 299. 
 
 Oxidation, 10. See Respiration. 
 Oxygen, 10. 
 Oxyuris, 53. 
 
 P 
 
 Pacific islands, 349. 
 
 Palsearctic, 350, 351. 
 
 Palate, 275, 284, 325 ; cleft p., 325. 
 
 Pallial Belonging to the mantle, 110. 
 
 Palp, labial, 112, 113, 120. 
 
 Pancreas (Tray /ejects, the sweet bread) A digestive gland opening into the 
 
 intestine, and secreting a fluid which converts starch into sugar, 
 
 proteid into peptone, &c., 160, 191, 244, 287, 288. 
 Pancreatic juice, 161, 194, 245, 289. 
 Panniculus carnosus, 270. 
 Papilla A small projection ; Head p. , 28, 36 ; Circumvallate p. , 284, 329 ; 
 
 Filiform p., 189; p. Foliata, 284, 329; Fungiform p., 189; Genital p., 
 
 41, 207, 251; Tactile p., 53; Urinary p., 167. 
 
390 INDEX-GLOSSARY. 
 
 Papillose Covered with small papilla?, 286. 
 
 Paranucleus (micronucleus) A small reproductive nuclear structure by the 
 side of the main nucleus, 13/16, 72. 
 
 Parasite An organism living in, or upon, another organism and deriving 
 nourishment from it, 17, 313 ; endoparasite, 17, 28, 39, 47, 313 ; 
 intracellular p., 18. 
 
 Parenchyma (Trapevxyp-", the spongyj-oubstance of'the lungs) Tissue com- 
 posed of cells which are fairly equal in their different dimensions, 41. 
 
 Parthenogenesis (irapdevos, a maiden ; yevvaw, I produce) Development of 
 an ovum without fertilisation, 39, 74. 
 
 Pearls, 113. 
 
 Pearly layer, 110, 125. 
 
 Pecten (pecten, a comb), in the Pigeon A plaited vascular fold projecting 
 into the vitreous humour of the eye, 256. 
 
 Peduncle (pedunculus, a little stalk) One of the bands of fibres uniting 
 the cerebellum with the rest of the brain, 253, 302. 
 
 Pelvis = (1) The hip-girdle + the sacrum. See Hip-girdle. (2) The dilated 
 end of the ureter, within the kidney, 295. 
 
 Penis A copulatory organ, 32, 42, 80, 131. 
 
 Pentadactyle (irevre, five ; SUKTU\OS, a finger) With five digits, 176. 
 
 Pepsin A proteid-digesting ferment found in the gastric juice, 194. 
 
 Peptone A soluble form of proteid matter, 58. 
 
 Perch, 153. 
 
 Pericardial cavity, 195. 
 
 Pericardium (u-eps around ; /capita, the heart) The space surrounding the 
 heart, 245, 289. 
 
 Perichondrium (Trepl ; x"^Ps, cartilage) The fibrous membrane which 
 invests cartilage, 188. 
 
 Perilymph (trepl lympha, water) A clear fluid surrounding the mem- 
 branous labyrinth, 219, 255, 304. 
 
 Perineum, in the Rabbit The area between the anus and urinogenital 
 aperture, 269. 
 
 Periosteum (^repl ; 6<rreov, a bone) The fibrous membrane investing bone, 
 
 188. 
 Periostracum (irepi; oaTpaKov, a shell), in the Mussel and Snail The pig- 
 
 mented horny membrane which covers the shell, 110, 125. 
 Perissodactyla (-jrepio-o-os, odd ; SCIKTV\O<:, toe), 346, 355. 
 Peristaltic action The wave-like contraction of muscle or of the muscular 
 
 wall of a tube, 209. 
 
 Peristome (irtpl ; cro/ma, the mouth), 13, 123. 
 Peristomium (Trepi ; o-To/za, the mouth), 55, 75. 
 Peritoneum (-ntptTovfiov, used with modern meaning ; irepi, around ; 
 
IXDEX-GLOSSARY. 391 
 
 Ttv-, TOV-, stretch), in Vertebrates The membrane lining the abdominal 
 
 cavity, 161, 244, 293. 
 
 Perivisceral Surrounding the viscera, 60. 
 Permanence, of areas, 347. 
 
 Fes, in Vertebrata The foot, 176, 230, 241, 269, 282. 
 
 Pessulus (pessulus, a bolt), in the syrinx A slender bar of cartilage run- 
 ning dorso-ventrally, 248. 
 Petrous part (of periotic), 273. 
 Peyer's patches, in the Rabbit Lymphatic thickenings in the wall of the 
 
 small intestine, 286. 
 
 Phalanx A joint of a digit, 188, 239, 241, 281, 282, 327, 329. 
 Pharynx ($<ipuyl, used in modern sense) The part of the alimentary canal 
 
 next succeeding the mouth-cavity, 13, 28, 38, 57, 76, 139, 160, 189, 
 
 242, 285. 
 Phillipines, 349. 
 Phylogeny (pwXav, a tribe ; ytwcia, I produce) The development of groups 
 
 (phyla), 1. 
 
 Phylum (p;uv) One of the main groups of organisms, 1. 
 Physiology (Quri;, nature ; Ayo;, a discourse), 1, 2; Amoeba, 9; Vorticella, 
 
 14; Hydra, 23; Astacus, 83; Anodonta, Unio, 109; Helix, 122; 
 
 Amphioxus, 136 ; Scyllium, 153 ; Rana, 175 ; Columba, 229 ; Lepus, 
 
 268 ; Homo, Chap. xiv. 
 Pia mater A delicate vascular membrane investing the cerebro-spinal axis, 
 
 168, 210. 
 
 Pigeon = Columba, q.v. 
 Pillar, of Fornix, 301. 
 Pineal body, 2, 168, 210, 216, 253, 301. 
 Pinna (pinna, a feather), in the Rabbit The external flap of the ear, 
 
 319. 
 
 Pisces (pisces, fishes) Fishes, 343 ; Chap, ix., 152. 
 Pituitary body, in the brain A rounded non-nervous structure connected 
 
 with the infundibulum, 169, 210, 253, 273, 301. 
 Placenta (placenta, a cake) in Mammals A vascular structure, bringing 
 
 the embryo into relation with the mother, 168, 310, 338. 
 Placoid (<rXaJ, anything flat and broad ; ^;, /$-, appearance), of Scale- 
 Developed both from epidermal and dermal elements, 155. 
 Plants, 5. 
 Plasma (Xaoy*, anything which has been formed) The liquid part of the 
 
 blood or lymph, 78 ; germ Plasma The part of the nuclear protoplasm 
 
 of a sexual cell, which enables it to develop into an embryo, 74. 
 Plate Cribriform p., 275, 323; Neural (Medullary) p., 151, 224, 261; 
 
 Orbital p. 233 ; Sclerotic p., 256. 
 
392 INDEX-GLOSSARY. 
 
 Platyhelmia (-TrXaTus, flat; e/\/uivs, eX/ui/dos, a worm) Flat worms, 340; 
 
 Chap, iii., 28. 
 Pleura (rXsw/>a, a rib), in Vertebrates The membrane lining the thorax, 
 
 293. 
 Pleuro-branchia (<r*.fupov, a rib ; branchia), in the Crayfish A gill attached 
 
 to an epimeron, 97. 
 Pleuron (**.'. vpov), a rib, 84. 
 Pleuro-peritoneum, in the Frog The membrane lining the body-cavity, 
 
 191. 
 
 Pleuro- peritoneal cavity, in the Frog The body-cavity, 191. 
 Plexus A network ; Brachial p., 254, 303 ; Choroid p., 210, 301 ; Lumbar 
 p., 254; Lumbo-sacral, 303; Nerve-p , 146, 171, 215, 320; Sciatic p., 
 213, 254. 
 Podobranchia (ruj, *obos, a foot ; branchia), in the Crayfish One of the 
 
 gills attached to the bases of the appendages, 97. 
 Polar-cell The cell, or one of the cells cut off from the ovum before it 
 
 develops into the embryo, 26, 73, 143, 207. 
 Pollex The thumb, 176, 230, 281, 338. 
 Polynesia, 349. 
 Polyodon, 349. 
 
 Polype, fresh water = Hydra, q.v. 
 Polypterus, 349. 
 Pons Varolii A band of fibres running transversely across the ventral 
 
 surface of the medulla, at its front end, 302. 
 Pore Excretory p., 31 ; Genital pore, see Aperture ; Dorsal p., 65 ; Ven- 
 
 tral p., 80; Abdominal, 155. 
 Pore-Canal, 90. 
 Portal System A meshwork of capillaries interposed in the course of a 
 
 vein, 143, 165, 199, 247, 291. 
 Position of body, 176, 230, 269, 322; Erect p., 338; p. of fore-limb, 281, 
 
 326; Primitive p., 175. 
 
 Post-axial Lying posterior to the axis, 154, 176. 
 Postzygapophysis An articular process projecting from the posterior end 
 
 of a vertebra's neural arch, 184, 237. 
 Prsezygapophysis An articular process projecting from the anterior side 
 
 of a vertebra's neural arch, 184, 237. 
 Pre-axial Lying anterior to the axis, 154, 176. 
 Prehallux, 176. 
 
 Premolars, in the Rabbit Grinding teeth which succeed the milk molars, 284. 
 Primates, 346, 357. 
 
 Primitive fibrillse Longitudinal elements into which a muscle-fibre or 
 nerve-fibre may break up, 214, 300. 
 
INDEX-GLOSSARY. 393 
 
 Primitive .sheath The delicate membranous investment of a nerve-fibre, 215. 
 
 Prismatic layer, 110, 125. 
 
 Proboscidea, 346, 356. 
 
 Process Acromion p., 250; Articular, 184; Clinoid, 273; Coracoid, 
 Coronoid, 183, 276 ; Costal, 238 ; Fronto-nasal, 329 ; Harnular, 275 ; 
 Iliac, 160; Mastoid p., 273; Maxillary p., 329; Maxillo- palatine, 
 234 ; Odontoid, 238, 279 ; Olecranon p., 186, 239, 281, 326 ; Orbital p., 
 233, 272; Palatine, 275; Par-occipital p., 272; Pterygoid p., 273; 
 Styloid p., 323 ; Supra-orbital p., 272; Transverse, 158, 184, 237, 278; 
 Uncinate p., 237 ; Xiphoid, 238 ; Zygomatic, 273, 275. 
 
 Procoelous (irpo, before ; KoiXos, hollow), of the centra of vertebrae Con- 
 cave only in front, 184. 
 
 Pro-echidna, 345, 353. 
 
 Proctodeeum (TTPWKTOS, the rectum, the anus) The posterior part of the 
 alimentary canal which arises as an epiblastic pit ; the hind-gut, 48. 
 
 Proglottis, 40-44. 
 
 Promontory, 273. 
 
 Pronation, of the fore-limb The position in which the palm is downwards 
 and the radius crosses the ulna, so that its distal end is inwards, 281, 
 326. 
 
 Pronephros (TT/OO, before; ve^pos, a kidney), in Vertebrates The first- 
 formed excretory organ, which is usually very transitory ; the head 
 kidney, 166, 228, 265, 308. 
 
 Pronucleus Male p., The name given to the nucleus of the sperm after it 
 enters the ovum, 74; female p. The nucleus of the ovum after the 
 formation of polar cells, 26, 74. 
 
 Propterygium (TT/UO, before ; Tnepvyiov, a fin), 159. 
 
 Prosencephalon (irpos, in addition ; cy/ce'0a\os, the brain) An outgrowth 
 or two lateral outgrowths of the fore-brain. See Fore-brain. 
 
 Pro-scolex, 44. 
 
 Prosimia-, 346, 357. 
 
 Prostate An accessory gland on the male organs, 130. 
 
 Prostomium (irpo ; CTTO'/LI, the mouth), 54, 75. 
 
 Protection, 25, 178, 268, 312. 
 
 Proteids (Ilpou-reus, a sea-god with remarkable power of changing his form) 
 Complex compounds of C, 0, N and H with small amounts of S and P, 
 58. 
 
 Proteus animalcule = Amoeba, q.v. 
 
 Protomerite, 17, 18. 
 
 Protoplasm (Tr^w-ros. first ; TrXdoyxa, that which has been formed) An 
 extremely complex substance upon which life-manifestations depend, 6. 
 
 Protopodite, in the CrayfishThe basal, undivided part of an appendage, 84. 
 
394 INDEX-GLOSSARY. 
 
 Protopterus, 153. 
 
 Prototheria (Trpiros, first ; 0ijpt'oi>, a beast), 345. 
 
 Protovertebne = Somites, mesodermic, q.v. 
 
 Protozoa (Trpwrot , first ; tyov, a living creature) The simplest animals, 
 consisting each of one cell, 339 ; Chap. i. 7, 71. 
 
 Proventriculus (pro, in front ; ventriculus, dim. of venter, the belly), in the 
 Pigeon The part of the stomach which secretes the gastric juice. It 
 precedes the gizzard, 242. 
 
 Proximal (proximus, nearest, next) Nearest to the main body, 1 1 . 
 
 Pseudobranch (-^'.t^tif, false; jSpay^/a, the gills of a fish), 166. 
 
 Pseudonavicellse (^<vlfa ; navicella, dim. of navis, a ship), 18. 
 
 Pseudopodium ($Mt ; veoliov, dim. of vroiis, a foot) A temporarily project- 
 ing, blunt lobe of protoplasm, 7, 10, 312. 
 
 Pterygoid bar, 182. 
 
 Pterylse, 229. 
 
 Ptyalin (<r<rvKXov, spittle) A ferment, found in saliva, which converts 
 starch into grape-sugar, 289. 
 
 Pulmonary Belonging to the lungs. See Respiration. 
 
 Pupil, 174, 221. 
 
 Pylangium (vuXv, a gate; ayyiiov, a vessel), in the Frog That part of the 
 truncus arteriosus which immediately succeeds the ventricle, 196. 
 
 Pyloric Stomach : next the intestine, 91. 
 
 Pylorus The valve between stomach and intestine, 190, 286. 
 
 Pyramid Urinary, 295 ; of Brain, 302. 
 
 Pyrenees, 349. 
 
 Quill, 229, 230. 
 
 R 
 
 Rabbit Lepus, q.v. 
 
 Racemose (racemus, a bunch or cluster of berries), 288. 
 
 Radula (radula, a scraper) A horny, tooth-bearing ribbon, which forms 
 
 part of the odontophore, 125. 
 Ramus (ramus, a branch) Of Nerves, 213, 215; of Mandible, 236, 276, 
 
 325 ; r. communicans, 213, 215, 254, 303. 
 Rana, 343; 1-5, 135, 175-228. 
 Ranidse, 4. 
 Rat, 347, 349. 
 
 Receptaculum R. ovorum = Ootheca, q.v. ; r. seminis = Spermotheca, q.v. 
 Rectrices (rectrix, fern, of reef or, a ruler, a steersman) Quill-feathers of 
 
 the tail, 229. 
 
INDEX-GLOSSARY. 395 
 
 Rectum (rectus, straight) The last part of the intestine, 49, 57, 78, 112, 
 
 160, 286. 
 Redia, 36, 37. 
 
 Reflex, of action Not directly under the control of the will, 62, 216. 
 Regions Zoological, 350. 
 Regular, of segmentation, 27. 
 
 Remiges (remex, remigis, an oarsman) Quill-feathers of the wing, 229, 230. 
 Renal Portal System, 199. 
 Reproduction 
 
 (1) Asexual Amoeba, 10; Vorticella, 15; Hydra, 24; Distoma, 
 
 37; Comparison of, 317. 
 
 (2) Sexual, 71; Protozoa, 72; Metazoa, 73; Vorticella, 15, 72; 
 
 Hydra, 25. See Reproductive Organs. 
 Reproductive Organs Hydra, 22; Distoma, 32; Tsenia, 42; Ascaris, 49; 
 
 Lumbricus, 62; Hirudo, 80; Astacus, 199; Anodonta, Unio, 118; 
 
 Helix, 129; Amphioxus, 144; Scyllium, 166; Rana, 206; Columba, 
 
 251 ; Lepus, 297 ; Homo, 333 ; Comparison of, 317. 
 Reptiles, 344. 
 Resemblance, 178. 
 Respiration, 10, 141; Amoeba, 10; Vorticella, 14; Lumbricus, 60; Hirudo, 
 
 76; Astacus, 98; Anodonta, Unio, 115; Helix, 129; Amphioxus, 139; 
 
 Scyllium, 166; Rana, 204; Columba, 248; Lepus, 293; Comparison 
 
 of, 315. 
 
 Respiration Anal, 98. 
 
 Restiform bodies Lateral lobes of the medulla oblongata, 169. 
 Retina (rete, a net), in the eye The layer which contains sense-cells, 134, 
 
 174, 221. 
 Retinula, 104. 
 Rhabdom, 104. 
 Rhabdopleura, 341. 
 Rhinoceros, 5, 355. 
 Rhizopoda, 339. 
 Rhytina, 347. 
 
 Ribs Scyllium, 158; Columba, 237; Lepus, 278; Homo, 326. 
 Ridge Condylarr., 185; Deltoid r., 185. 
 Rodentia, 346, 355. 
 
 Rods Certain of the retinal sense-cells, 174, 221. 
 
 Rostrum (rostrum, a beak), 86, 87 ; parisphenoidal r. = parasphenoid, 233. 
 Round-worm = Ascaris, q.v. 
 Rugae (ruga, a wrinkle), in the Rabbit Longitudinal folds into which the 
 
 mucous membrane of the stomach is thrown, 286. 
 Ruminantia, 355. 
 
396 INDEX-GLOSSARY. 
 
 Sac Air, 249, 252; Dart, 131; Scrotal, 298; Vocal s., 175, 189; Yolk s., 
 
 167, 265, 308, 338. 
 Sacculus (dim. of saccus, a bag), in Vertebrates The lower part of the 
 
 membranous labyrinth, with which the cochlea is connected, 173, 219, 
 
 255, 304. 
 
 Sacculus rotundus, 285. 
 Sacrum That part of the vertebral column with which the hip-girdles are 
 
 connected, 184, 238, 325. 
 Saliva, 289. 
 Salts, 206. 
 Sarcolemma (ffa.p,, <rp*o;, flesh ; Xr/p/tK, used here in the sense of that 
 
 which receives, a sheath) The delicate membranous sheath of a 
 
 striated muscle-fibre, 91. 
 
 Sauropsida (a-xvpos, a lizard ; o^n, sight, appearance), 343. 
 Scales, 155, 230. 
 Scaphirhynchus, 349. 
 Scaphognathite (rxcifas, a boat ; yvddof, a jaw), in the Crayfish The large 
 
 epipodite of the second maxilla, 89, 98. 
 
 Sclerite (fxXnpis, hard) A definite cuticular plate or band, 92. 
 Sclerotic coat (<r>.npo;) The firm outer coat of the eyeball, 173, 221, 305 ; 
 
 sclerotic plate, 256. 
 Scolex, 40, 44. 
 Scyllium (Dogfish) (ZgyXXa, a monster barking like a dog), 343 ; 135, 
 
 152-174. 
 Secretion A katastate which performs some definite functions before it 
 
 is excreted, 9. 
 Segment One of a series of transverse divisions into which all or part of 
 
 the body may be divided, 54, 75, 83, 90, 136, 311 ; muscle s. (myotome, 
 
 myomere), 136, 145, 168, 208. 
 Segmentation, of embryo = Cleavage, q.v. 
 Segmentation, of body Division mto_originally similar parts (segments) 
 
 from before backwards, 311 ; secondary s., 311. 
 Segmentation-cavity = Blastoccele, q.v. 
 Segtnental Organ = Nephridium, q.v. 
 Self-fertilization, 43. 
 Sella turcica, 273, 323. 
 Sensation. See Sense Organs. 
 Sense organs Ascaris, 53; Lumbricus, 66; Hirudo, 82; Astacus, 103; 
 
 Anodonta, Unio, 121 ; Helix, 133 ; Amphioxus, 146 ; Scyllium, 172 ; 
 
 Rana, 218, 226 ; Columba, 254 ; Lepus, 303 ; Comparison of, 320. 
 
INDEX-GLOSSARY. 397 
 
 Sensory, of nerves Conveying impulses from sense-cells, 102, 146, 209, 216. 
 
 Sensory tubes, 155. 
 
 Septum (saeptum, septum, a partition) A partition, 18, 56 ; Auricular s., 
 
 245; Interorbital s., 233; S. lucidum, 301; Nasal s., 218; S. nasi, 
 
 271, 323 ; Ventricular s., 245. 
 Serous coat, 192. 
 Seta (seta, a bristle) A bristle or hair-like cuticular structure, 55, 84, 90 ; 
 
 Auditory, 103; Coxopoditic, 97; Olfactory, 103; Tactile, 103. 
 Sex, or Sexual Organs. See Reproductive Organs. 
 Shaft, of bone, 185; of feather, 230. 
 Shark, 153. 
 
 Shell, 109, 113, 121, 122, 256. 
 Shoulder s. girdle, 159, 185, 239, 280, 326. 
 Sight. See Eye. 
 Sigmoidal cavity, 281. 
 Simia, 338. 
 
 Simple s. epithelium, 177. 
 Sinus (sinus, a curve, a bay) (1) An irregular space, or (2) a much dilated 
 
 blood-vessel, 95,96, 128; Cardinals., 165; Coronary s., 332; Cuvierian 
 
 s., 165 ; Genital s., 324 ; Lymph s., 192 ; Pericardial s., 95 ; s. rhom- 
 
 boidalis, 253; Urinary, 167; Urinogenital s., 166; s. of Valsalva, 
 
 290, 333. 
 Sinus Venosus The receptacle for impure blood entering the heart of a 
 
 lower vertebrate, 162, 195. 
 Sirenia, 346, 355. 
 Skate, 153. 
 Skeleton Amphioxus, 138 ; Scyllium, 156 ; Rana, 178 ; Columba, 231 ; 
 
 Lepus, 271 ; Homo, 322; Visceral or branchial s. The skeleton sup- 
 porting the respiratory part of the pharynx. See Arches. 
 Skin Lumbricus, 55 ; Hirudo, 76; Astacus, 90; Anodonta, Unio, 112; 
 
 Helix, 123; Amphioxus, 138; Scyllium, 155; Rana, 176, 204; Columba, 
 
 230 ; Lepus, 269 ; Homo, 322. 
 Skull, 156 ; Scyllium, 156 ; Rana, 179 ; Columba, 232 ; Lepus, 271 ; Dog, 
 
 278; Homo, 322. 
 Smell. See Olfactory Organs. 
 Snail = Helix, q.v. 
 
 Somatic (o-w/xa, a CO/AUTOS, a body) Relating to the body -wall, 149, 226. 
 Somatopleure (<ro>/xa, <TWjucn-os; TrXtvpov, a side) The body-wall of certain 
 
 embryos, formed by epiblast, together with somatic mesoderm, 227, 
 
 263. 
 Somites, mesodermic, in certain embryos Transverse segments into which 
 
 the mesoderm (or part of it) is divided, 107, 149, 227, 263. 
 
398 INDEX-GLOSSARY. 
 
 Sound-waves, 271. 
 
 Space. (See Sinus), perineal, 268. 
 
 Special creations, 346. 
 
 Species, 3, 4. 
 
 Sperm (tnrep/iu, seed) A male sex-cell (= spermatozoon), 23, 51, 63, 72, 73, 
 
 99, 119, 206, 251, 298. 
 Sperm-blastophor, 51, 63, 74, 207. 
 Spermary (o-Trep/xa) [ = Testis] The organ producing sperms, 23 ; Hydra, 
 
 23; Distoma, 32; Toenia, 42; Ascaris, 51; Lumbricus, 62 ; Hirudo, 80; 
 
 Astacus, 99; Anodonta, Unio, 119; Amphioxus, 144; Scyllium, 167; 
 
 Rana, 206; Columba, 251; Lepus, 298. 
 
 Spermatocyte (o-Trep/xa ; KVTOS, anything that contains) A cell which pro- 
 duces sperms directly or by division, 51, 63, 99. 
 
 Spermatogenesis (o-irep/xa; yeWis, birth) Sperm development, 51, 74. 
 Spermatophore (o-Tre'p/xa ; 0opos, bearing) An aggregation of sperms, 64, 80, 
 
 102, 132. 
 Spermatospore (o-irt/oMa, o-Trc-p/xaTos, seed; crTro/oa, seed) A cell from which 
 
 several spermatozoa are produced, 18. 
 
 Spermatozoon (tnrep/ia, o-Tre'p/xaT-os ; a>oi/ } a living creature) Sperm, q.v. 
 Spermiduct The duct by which the sperms are carried to the exterior, or 
 
 into the urinogenital canal [= vas deferens], 32, 42, 62, 80, 119, 130, 
 
 199, 251, 265, 298, 334. 
 Sperm-morula, 63. 
 Spermotheca (o-Trep/xa ; ^/cj, a cover, a case) In certain female organs The 
 
 sac in which sperms are stored; the receptaculum seminis, 64, 131. 
 Sperm-sac, 167. 
 Sphenoidal fissure, 274. 
 Spiculum amor is, 131. 
 Spinal cord, in Vertebrates The posterior part of the cerebro-spinal axis, 
 
 145, 169, 211, 253, 302. 
 Spindle; Nuclear s. A form assumed by threads of cell protoplasm in 
 
 process of karyokinesis, 73. 
 Spine, of scapula, 280; in a Vertebra A median dorsal process of the 
 
 arch, 158, 184, 237, 278. 
 Spiracle (spiraculum, an air-hole), (1) in the Tadpole: the opening of the 
 
 gill-chambers to the exterior, 155; (2) in many fishes : the opening of 
 
 the hyomandibular cleft to the exterior, 153. 
 Splanchnic (o-TrXayxva, the viscera) Relating to the gut or viscera, 149, 
 
 226. 
 
 Splanchnoccele (crir\a.y^va, the viscera; KolXov, a hollow), 149. 
 Splanchnopleure The wall of the alimentary canal of certain embryos, 
 
 formed by hypoblast and splanchnic mesoderm, 227, 264. 
 

 INDEX-GLOSSARY. 399 
 
 Spleen, 248, 292. 
 
 Spontaneity Amoeba, 11; Vorticella, 16; Hydra, 26; Rana, 216, 319. 
 Spontaneous, of action Not directly dependent 011 external stimuli, 102. 
 Spore (vTTopa, seed), in Protozoa One of many minute individuals into 
 
 which the encysted individual may break up, 
 Sporocyst (oTropa } seed ; KUO-TIS, a bag, a bladder), in the Fluke A sac-like 
 
 asexual stage, 35, 37. 
 Sporoduct, 19. 
 Sporozoa, 339. 
 
 Spot, germinal The nucleolus of the ovum, 7. r. 
 Squama (squama, a scale), 89. 
 Squamous Scale-like, 177. 
 Starch, 58. 
 Sternebne(<rre'pi'j>, the breast), in Mammalia The segments of the sternum, 
 
 280. 
 
 Sternum In Crayfish, 84 ; in Vertebrata, the breastbone. See Bones. 
 Stomach, 42, 141, 160, 190, 286. 
 Stomodteum (o-ro^ct, the mouth) The anterior part of the alimentary canal 
 
 originating as an epiblastic pit ; the fore-gut, 48. 
 Strainer, 92, 93. 
 Stratified, 177. 
 Streak, Primitive A mesodermic thickening in the posterior part of the 
 
 embryonic area, which represents the blastopore of other forms, 256. 
 Stroma (<n-pwjua, anything which is spread out) The connective-tissue 
 
 framework of an ovary, 251, 299. 
 Structure Amoeba, 8; Vorticella, 13. 
 Sturgeon, 153. 
 
 Subcutaneous Lying beneath the skin, 269. 
 Sucker, 28, 34, 75. 
 Sumatra, 349. 
 Supination (supinus, bent backwards, lying on its back), of the fore-arm 
 
 The position in which the palm is upwards and the radius and ulna 
 
 parallel, 281, 326. 
 Support, 311. 
 
 Supra-scapula A cartilage united to the upper edge of the scapula, 185, 280. 
 Supra-scapular border The upper edge of the scapula, 280. 
 Suspensorium (suspendo, suspensum, hang up) The arrangement by which 
 
 the lower jaw is suspended to the skull, 182. 
 Suture, in the Skull A jagged union between two bones, 271 ; Coronal s., 
 
 272; Frontal s., 272; Lambdoidal, 272; Sagittal, 272.: 
 Swimbladder, 153. 
 Swimmeret, 84. 
 Swimming, 318, 319. 
 
400 INDEX-GLOSSARY. 
 
 Swine, 354. 
 
 Sylvian aqueduct, 169, 211, 253, 302. 
 
 Sylvian fissure, 336. 
 
 Symmetry Bilateral s., 28, 54, 75, 154, 311 ; Radial s., 20, 311. 
 
 Sympathetic system A special set of nerves supplying the internal organs, 
 
 82, 101, 104, 171, 215; Columba, 254; Lepus, 303. 
 Symphysis (a-i/v, together ; <t>v<ri; t a growth) A median fusion of two bones ; 
 
 Ischio-pubic, 18, 282 ; Mandibular, 183, 236, 276, 325; Pubic s., 327. 
 Synangium (avv, together ; uyytTtv, a vessel), in the Frog That part of the 
 
 truncus arteriosus from which the aortic arches arise, 196. 
 Syrinx (ffupiy%> a reed-pipe) The vocal organ of birds, situated at the 
 
 bifurcation of the trachea, 248. 
 Systemic, of heart Distributing oxygenated blood to the body in general, 
 
 97, 115, 128, 315. 
 Systole (<7t/<rToA, used with the modern meaning) The contraction of a 
 
 heart, or the chamber of a heart, 97. 
 
 Tactile Organs Hirudo, 82 ; Astacus, 103 ; Anodonta, Uiiio, 120 ; Helix, 
 
 133 ; Amphioxus, 146 ; Scyllium, 172 ; Rana, 218 ; Columba, 254 ; 
 
 Lepus, 303 ; Comparison of, 320. 
 Tsenia, 340 ; 39-45. 
 Tail, 229, 269. 
 Tapeworm = Ta3nia, q.v. 
 Tapir, 349, 355. 
 Tarsometatarsus, in the Pigeon A bone formed by the union of the distal 
 
 part of the tarsus with three of the metatarsals, 241. 
 Tarsus (rap<ros, the sole of the foot) The ankle or the ankle bone, 176, l!S7, 
 
 241, 282, 328. 
 
 Taste. See Gustatory Organs. 
 Teats, 269. 
 Teloblast (<ri>.of, the end ; /3Xao-Tf, a germ) An embryonic cell which by 
 
 division gives rise to a cellular band, 70, 148. 
 Teleostei, 153. 
 Telson (rUo-ov, the termination, the end), in the Crayfish The last segment 
 
 of the body, 86. 
 
 Tendon A fibrous cord by which muscle is attached, 91, 178, 208. 
 Tentacles A small projecting finger-like part of the body, usually 
 
 sensory, 19, 312. 
 Tergum (tergum, the back), in the Crayfish The dorsal part of the exo- 
 
 skeleton in each segment, 84. 
 
INDEX-GLOSSARY. 401 
 
 Testis (1) The Spermary, q.r.- (2) the posterior half of a divided optic 
 
 lobe, 302. 
 Tetradactyle (<ricnrap<f, r&rpet-, four; ^rix.Tv\ti, a finger) With four digits, 
 
 176. 
 Thalamencephalon The axial part of the fore-brain, containing the 3rd 
 
 ventricle, the side-walls of which are formed by the optic thalami. 
 
 See Fore-brain. 
 Thalamus, Optic A mass of grey matter in the thalamencephalon, forming 
 
 either side-wall of the 3rd ventricle, 210, 252. 
 Thigh (Femur), 176. 
 
 Thorax (0/>g, the chest), the chest, 83, 86, 269. 
 Thumb (Pollex), 176, 230, 281, 338. 
 Thyrohyals The posterior cornua of the hyoid, 183. 
 Tissue An aggregate of similar cells adapted for the performance of some 
 
 special function, 20; Connective t., 29, 188 ; Botryoidal, 29. 
 Tongue, 160, 189, 194, 242, 284, 329. 
 
 Tonsil A thickening of the free edge of the soft palate, 284. 
 Tooth, of Crayfish, 93 ; Helix, 126 ; Scyllium, 160 ; Rana, 182, 189, 193 ; 
 
 Lepus, 284 ; Homo, 329. 
 Touch Lumbricus, 66. See Tactile Organs. 
 Touch corpuscles, 178. 
 
 Trachea (r^y,-, r^^s7a, rough) The windpipe, 248, 293. 
 Transverse process, 158. 
 Tragulidae, 355. 
 Tracts, Optic The posterior limbs of the X-shaped optic chiasma, 169, 
 
 211, 253, 302. 
 Tree, Bronchial, 343. 
 Trichina, 54. 
 
 Tridactyle (TP<HS, T?I-, three; SaKTuXos, a finger) With three digits, 230. 
 Triploblastica (-rpiTrXous, triple; /SXao-ros, a germ), 340. 
 Trochanter, 241, 282. 
 Trochlea (trochlea, a set of blocks and pulleys ; <rpo%f, a wheel) The 
 
 pulley-like articular surface on the distal end of the humerus, 239, 
 
 280. 
 
 Troglodytes, 338. 
 Truncus arteriosus, in the Frog The tubular part of the heart which 
 
 succeeds the ventricle, and from which the arterial arches take origin, 
 
 195, 203. 
 Trunk, 
 Tube Eustachian, 189, 219, 233, 255, 274; Fallopian, 299, 334; Neural, 
 
 151, 224, 261. 
 Tubercle, of rib, 237, 279. 
 
 2 26 
 
402 INDEX- GLOSSARY. 
 
 Tubules Uriniferous, 167, 205, 250, 295. 
 
 Tympanic area, 175. 
 
 Tympanic cavity, 189. 
 
 Tympanum (TU/JLTTUVOV, tympanum, a drum) The cavity of the middle ear, 
 
 219, 255, 304. 
 Typhlosole (rw0A.flf, blind ; O-AXV, a channel, a fold), in some Invertebrates 
 
 A longitudinal fold of the intestinal wall which projects inwards, 57, 
 
 133, 313. 
 
 U 
 
 Umbilical cord, 310. 
 
 Umbilicus, 231. 
 
 Umbo (umbo, the boss in the centre of a shield) A projection constituted 
 
 by the oldest part of the shell, 109. 
 
 Uncinus (oyKtvos), uncinus, a small hook), in the Snail One of the symme- 
 trical median teeth of the radula, 126. 
 Ungulata, 346, 354. 
 Unicellular, 20, 310. 
 
 Unio (Fresh-water Mussel), 109-122, 341. 
 Unipolar, 145. 
 United States, 349. 
 Univalve, 123. 
 Urea, 118, 206, 297. 
 
 Ureter The kidney-duct, 98, 118, 129, 166, 250, 265, 295, 333, 334. 
 Urethra The urinogenital canal of the male Rabbit, 298. 
 Uric acid, 99, 118, 251. 
 Urine, 62, 251. 
 Urinogenital system Rana, 205 ; Scyllium, 166 ; Columba, 250 ; Lepus, 
 
 293 ; Homo, 233. 
 
 Urochorda (wpa, the tail ; %oplv, a string), 341, 135. 
 Uropygium (olpovvyiov, oppovvytov, the tail of a bird or fish) The stumpy tail 
 
 of the Pigeon, 229. 
 Urostyle (ovpa, a tail ; rrvXos, a pillar), in the Frog A bony unsegmented 
 
 rod, forming the posterior part of the backbone, 183, 184. 
 Uterus The dilated part of an oviduct, 33, 43, 52, 207, 299, 334. 
 Uterus masculinus, in the male Rabbit A pouch on the dorsal side of the 
 
 bladder, into which the vasa deferentia open, 298. 
 Utriculus (dim. of liter, a bag or vessel of skin) A sac-like central part of 
 
 the membranous labyrinth, from which the semicircular canals take 
 
 origin, 173, 219, 255, 304. 
 
INDEX-GLOSSARY. 403 
 
 V. 
 
 Vacuole (dim. of vacuum, an empty space) A fluid-containing space in the 
 protoplasm of a cell, 8, 31; contractile v., 8, 10, 13, 314, 315, 316; 
 food v., 9, 14. 
 
 Vagina The lower part of the oviduct leading from the uterus to the 
 exterior, or into the urinogenital canal or the cloaca, 43, 52, 80, 131, 
 299. 
 
 Valve; of Shell, 109; of Heart, 162, 164, 196; Auriculo-ventricular, 
 115, 162, 196, 245; Bicuspid (mitral), 245; Eustachian, 245, 290; 
 Semilunar, 196, 245 ; Spiral v., 160, 161 ; Thebesian v., 290. 
 
 Valvulse conniventes, 285. 
 
 Vane The expanded part of a feather, 230. 
 
 Variety, 4. 
 
 Vas deferens = Spermiduct, q.v. 
 
 Vas efferens A duct leading from spermary (testis) to spermiduct, 62, 80, 
 298, 334. 
 
 Vein A vessel carrying blood to or towards the heart, 115; Allantoic, 
 267 ; Anterior abdominal, 199, 297 ; Azygos, 291, 332 ; Brachial, 246 ; 
 Branchial (Afferent and Efferent), 115; Cardinal, 265, 331; Caudal, 
 247 ; Caval, 198 ; Coronary, 291 ; Cuvierian, 265, 331 ; Facial, 291 ; 
 Femoral, 197, 247, 291 ; Gastric, 247 ; Hepatic, 142, 193, 198, 247, 
 291 ; Hepatic portal, 165 ; Hypogastric, 247 ; Iliac, 247, 291, 332 ; 
 Innominate, 198, 331 ; Intercostal, 332 ; Jugular, 198, 246, 265, 291, 
 332 ; Lieno-gastric, 292 ; Mesenteric, 247, 291 ; Pectoral, 246 ; Pelvic, 
 199 ; Portal, 142, 198, 199, 247, 291 ; Postcaval (Posterior vena cava), 
 198, 246, 291, 333 ; Precaval (Superior vena cava), 198, 246, 265, 291 ; 
 Pulmonary, 200, 247, 291 ; Renal, 128, 165, 198, 247, 297 ; Renal 
 portal, 165, 291 ; Sciatic, 199, 247 ; Subclavian, 198, 291, 331 ; Sub- 
 scapular, 198 ; Vence cavse (Caval veins), 198, 246, 291. 
 
 Velum, 139. 
 
 Vena cava, 198, 246, 291. 
 
 Ventral (venter, the stomach) Lower, 28, 322. 
 
 Ventricle (ventriculus, used with the modern meaning), in the heart In 
 the two or more chambered heart a muscular propulsive chamber, 162, 
 195, 245, 290, 315. 
 
 Ventricle, of nerve-cord, 145, 168; of brain, 160, 252, 301. 
 
 Veragua, 349. 
 
 Vertebra (vertebra, a joint, especially of the backbone) A joint of the 
 backbone, 158, 183; Atlas, 184. 
 
 Vertebral Column Scyllium, 158; Rana, 183; Columba, 257; Lepus, 
 278; Homo, 325. 
 
404 INDEX-GLOSSARY. 
 
 Vertebrata (vertebratus, fitted with vertebra-, or joints), 3, 135, 152, 341. 
 Vesicle, Auditory (see Sacs, Auditory) Brain (Cerebral), 168, 210, 260; 
 
 Germinal, 23, 24; Optic, 226; Umbilical v. = yolk sac. 
 Vesicula semiualis A part of the spermiduct (vas deferens) which serves 
 
 for the storage of sperms, 17, 33, 43, 51, 62, 166, 206, 251, 333. 
 Vespertilionidre, 349. 
 Vessel, 59; Dorsal v., 59; Lateral, 59, 78; Lateral -neural, 59; Parietal 
 
 (commissural), 59 ; Subneural, 59. 
 Vestibule, in Vorticella A ciliated depression on one side of the disc, which 
 
 leads to the gullet, 13; in the vertebrate ear The central part of the 
 
 membranous labyrinth, 173, 219. 
 
 Vibrissje (vibro, I vibrate), in the Rabbit The whiskers^ 268, 271. 
 Villus (villus, shaggy hair) A minute, finger-like projection, 242, 286, 309. 
 Visceral-mass, 111. 
 Vision, mosaic, 104. 
 Visual Organs Hirudo, 76 ; Astacus, 103; Helix, 134; Scyllium, 173; 
 
 Rana, 221 ; Columba, 256 ; Lepus, 304 ; Comparison of, 321. 
 Visual- pyramids, 103. 
 
 Vitelline membrane The cell-wall of an ovum, 73. 
 Vitellus (vitellus, the yolk of an egg) The protoplasm of an ovum, 23, 
 
 34, 73. 
 
 Vitreous body, 104. 
 Viviparous Bringing forth well-developed young, as opposed to eggs, 08, 
 
 308. 
 Vocal Cords, in the Larynx Two elastic folds, the edges of which can be 
 
 brought parallel and thrown into vibrations, 204. 
 Vocal Sac, 175, 189. 
 Voice, 205. 
 Volition, 102, 216. 
 Voluntary, 102. 
 
 Vorticella (dim. of vortex, a whirlpool), 339 ; 8, 11-16, 311. 
 Vulva, in the Rabbit The female urinogenital aperture, 299. 
 
 w 
 
 Walking, 83, 229, 268. 
 
 Walking-legs, 87. 
 
 Wallace, 348. 
 
 Wallace's line, 350. 
 
 Waste products, 10, 14, 61, 80. 
 
 Water Flea, 23. 
 
 Water Snail, 82. 
 
 Weismann, 74. 
 
INDEX-GLOSSARY. 405 
 
 Whiskers, 268, 271. 
 
 White matter, of Brain and Spinal Cord The part mainly composed of 
 
 nerve fibres, 172, 215. 
 Will, 102. 
 
 Wind-pipe (Trachea), 248, 293. 
 Wing, 230 Bastard w., 230. 
 Wolffian body = Mesonephros, q.v. 
 Wolffian duct = Duct, mesooephric, q.v. 
 W T orm -castings, 59. 
 Wrist Carpus, q.v. 
 
 X 
 
 Xanthin, 41. 
 
 Xiphisternuni The posterior, more or less cartilaginous part of the 
 sternum, 185. 
 
 Yang-tse-Kiang, 34. 
 Yeast, 58. 
 Yolk, 23, 252. 
 Yolk-gland, 33, 43. 
 Yolk-reservoir, 33. 
 Yolk-sac, 167, 265, 308, 338. 
 
 Zona radiata, in Mammalia A radiately striated membrane which invests 
 the ovum, 299, 306, 308. 
 
 Zooid (*, a living creature) ; in Protozoa and colonies of other groups 
 The individual, 15. 
 
 Zoology (&ov; *.i>yo;, a speech, discourse), 1. 
 
 Zoological Regions, 350. 
 
 Zoophyte (<2<9v ; <t>vrev, a plant), 27. 
 
 Zonitic constrictions, in the Earthworm Shallow grooves, of which one 
 or more encircle each segment, 54. 
 
 Zygapophysis (%vyov, a yoke; <<;, a process) A process projecting 
 from the front or back of a neural arch, and assisting in the articu- 
 lation of adjacent vertebrae, 184, 237, 278. 
 
 Zygoma (^uyupa,, a bar or bolt), in the Mammalian skull A bony bar below 
 the orbit and temporal fossa, 272. 
 
 BKLL AND BAIN, LIMITED, PRINTERS, GLA$O^J N I V K R8IV1? 
 
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A 
 
 CATALOGUE 
 
 OF 
 
 STANDARD WORKS 
 
 PUBLISHED BY 
 
 CHARLES GRIFFIN & COMPANY, 
 
 LIMITED. 
 
 PAGE 
 
 I. Religious Works, 4 
 
 II. Works on Medicine and the Allied Sciences, 9 
 III. General Scientific and Technical Works, . 23 
 
 IV. Educational Works, 54 
 
 V. Works in General Literature, . . .62 
 
 LONDON: 
 12 EXETER STREET, STRAND. 
 
INDEX TO AUTHORS. 
 
 
 PAGE 
 
 AITKEN(SirW., M.D.), Science and Practice 
 of Medicine, 
 
 ANDERSON^M'Call) on Skin Diseases] 
 ANGLIN (S.), Design of Structures, 
 BELL (R.), Golden Leaves, 
 BERINGER (J. J. and C), Assaying, . 
 BLYTH (A. WA Hygiene and Public Health, 
 
 Foods and Poisons, 10 
 
 BROTHERS (A.), Photography, ... 25 
 BROUGH (B. H.), Mine-Surveying, . . 26 
 BROWNE (W. R.) ( Works .... 26 
 B RYCE (A. H.), Works of Virgil, ... 55 
 BUN VAN'S Pilgrim's Progress (Alason), . 4 
 
 BURNET (Dr.), Foods and Dietaries, . .n 
 CAIRO and CATHCART, Surgical Handbook, 12 
 CHEEVER'S (Dr.), Religious Anecdotes, . 4 
 CLARK (Sir A.), Fibroid Disease of Lung, . 16 
 COBBETT (Wm.), Works. ... 55, 63 
 COBBIN'S Mangnall's Questions, . .55 
 
 COLE (Prof.). Practical Geology, . 
 COLERIDGE on Method, .... 55 
 CRAI K (G. ), . History of English Literature, . 56 
 
 Manual of do., . 56 
 
 CRIMP (W. S.), Sewage Disposal Works, . 28 
 CROOM (Halliday), Gynaecology, . . .16 
 CRUDEN'S CONCORDANCE, by Eadie, . 6 
 CRUTTWELL'S History of Roman Literature, 57 
 
 Specimens of do., 
 
 Early Christian Literature, 
 
 CURRIE (J.), Works of Horace, 
 
 DAVIS (J. R. A.), An Introduction to Biology, 
 
 The Flowering Plant, .... 
 
 Zoological Pocket-Book, 
 
 DICK (Dr.), Celestial Scenery, 
 DOERING and GRAEME'S Hellas, 
 D'ORSEY (A. J.), Spelling by Dictation. 
 DUCKWORTH (Sir D., M.D.), Gout, . 
 DUPRfi & HAKE, Manual of Chemistry, . 
 EADIE (Rev. Dr.), Biblical Cyclopaedia, 
 
 Cruden's Concordance, .... 
 
 Classified Bible, 
 
 Ecclesiastical Cyclopaedia, 
 
 Dictionary of the Bible, 
 
 ELBORNE(W.), Pharmacy and MateriaMedica,is 
 EMERALD SERIES OF POETS, . 
 ETHERIDGE (R.), Stratigraphical Geology, 
 EWART (Prof), The Preservation of Fish, . 
 FIDLER (T. Claxton), Bridge-Construction, . 
 FLEMING (Prof.), Vocabulary of Philosophy, 
 FOSTER (Chas.), Story of the Bible, 
 FOSTER (C. Le N.), Ore and Stone Mining, . 
 GARROD (Dr. A. E.), Rheumatism, 
 GILMER (R.), Interest Tables, . . 
 GRAEME (Elliott), Beethoven, .... 
 
 Novel with Two Heroes, . 
 
 GRIFFIN'S ELECTRICAL PRICE-BOOK, 
 GRIFFIN (J. I.), Chemical Recreations, 
 GURDEN (R.1, Traverse Tables, . 
 GUTTMANN (O.), Rock Blasting, 
 HADDON (Prof), Embryology. . 
 HORSLEY (Victor), Brain and Spinal Cord, . 
 HUGHES (H. W.), Coal-Mining, ... 36 
 HUMPHRY, Manual of Nursing, . . . 18 
 HURST (G. H,), Colours and Varnishes, . 35 
 JAKSCH (v.) and CAGNEY, Clinical Diagnosis, 14 
 JAMES (W. P.), From Source to Sea, . . 58 
 JAMIESON (A.), Manual of the Steam Engine 37 
 
 Steam and the Steam Engine Elementary, 37 
 
 Applied Mechanics, . . . .38 
 
 rMagnetism and Electricity, , .38 
 
 PAGE 
 
 JEVONS (F. B.), AHistory of Greek Literature, 59 
 
 Athenian Democracy 59 
 
 Journal of Anatomy and Physiology, . . 67 
 Journal of State Medicine, . . . .67 
 
 KEBLE'S Christian Year 4 
 
 KNECHT and RAWSON, Dyeing, . . 35 
 
 LANDIS (Dr.), Management of Labour, . . 18 
 
 LANDOIS and STIRLING'S Physiology, . 13 
 
 LEWIS (W. B.), Mental Diseases, ... 15 
 
 LINN (Dr.), On the Teeth, . 18 
 
 LONGMORE (Prof.), Sanitary Contrasts, . 19 
 
 MACALISTFR (Prof.), Human Anatomy, . 13 
 
 M AC R EADY (J. F. C), on Ruptures, . . 16 
 
 MANN (Prof), Forensic Medicine, . . 16 
 
 MACKEY (A. G.), Lexicon of Freemasonry, . 65 
 
 MAYHEW (H.), London Labour, ... 65 
 
 M'BURNEY (Dr.), Ovid's Metamorphoses, . 60 
 
 MEYER AND FERGUS' Ophthalmology, . 14 
 
 M I LLER (W. G.), Philosophy of Law, . . 60 
 
 M'MILLAN (W. G.), Electro- Metallurgy, . 39 
 
 MUNRO (R. D.), Steam Boilers, ... 38 
 MUNRO and JAMIESON'S Electrical 
 
 Pocket-Book, - 40 
 
 NYSTROM'S Pocket-Book for Engineers, . 40 
 OBERSTEINER and HILL, Central Nervous 
 
 Organs 15 
 
 PAGE (H.W.), Railway Injuries, . . . 16 
 
 PARKER (Prof.). Mammalian Descent. . . 19 
 
 PHILLIPS and BAUERMAN, Metallurgy, . 43 
 
 POE (Edgar), Poetical Works of, . . 64 
 PORTER (Surg.-Maj.), Surgeon's Pocket-Book, 19 
 
 
 RAMSAY (Prof.), Roman Antiquities, 
 Do. Elementary, 
 
 Latin Prosody, 
 
 Do. Elementary, .... 
 
 RANKINE'S ENGINEERING WORKS, 
 REED (Sir E. J.), Stability of Ships, 
 REID (Geo.), Practical Sanitation, . 
 ROBERTS-AUSTEN (Prof.), Metallurgy, . 
 ROBINSON (Prof.), Hydraulics, . 
 SANSOM (A. E.), Diseases of the Heart, 
 SCHRADER and JEVONS, The Prehistoric 
 
 Antiquities of the Aryan Peoples, 
 SCHWACKHOFER and BROWNE, Fuel 
 
 and Water, 
 
 SEATON (A. E.), Marine Engineering, . 
 SEELEY (Prof.), Physical Geology, 
 SENIOR (Prof.), Political Economy, 
 SEXTON (Prof.), Quantitative Analysis, 
 
 Qualitative Analysis 
 
 SHELTON-BEY (W. V.), Mechanic's Guide,. 
 SOUTHGATE (H.), Many Thoughts of Many 
 
 Minds, 
 
 Suggestive Thoughts, .... 
 
 (Mrs.), Christian Life, 
 
 60 
 . 60 
 . 60 
 . 60 
 44-45 
 . 6 
 
 STIRLING (William), Human Physiology, 
 
 Outlines of Practical Physiology, . 
 
 Outlines of Practical Histology, . 
 
 TAIT (Rev. J.), Mind in Matter, 
 
 THE MASSES : How shall we reach them? . 8 
 
 THOMSON (Dr. Spencer), Domestic Medicine, 68 
 
 THOMSON'S Seasons, 62 
 
 THORBURN (Wm), Surgery of the Spine, . 15 
 
 THORNTON (J. K.), Surgery of the Kidneys, 16 
 
 TRAILLfW.). Boilers, Land and Marine, . 51 
 
 WESTLAND (A.), Wife and Mother, . . 22 
 
 WHAT ELY (Archbishop), Logic, and Rhetoric, 62 
 
 WORDS AND WORKS OF OUR LORD, 8 
 
 WRIGHT (Alder), The Threshold of Science, . 52 
 
 YEAR-BOOK OF SCIENTIFIC SOCIETIES, 53 
 
INDEX TO SUBJECTS, 
 
 PAGE 
 
 ANATOMY, Human, 13 
 
 Journal of , 67 
 
 ANECDOTES, Cyclopaedia of, ... 4 
 ANTIQUITIES, Prehistoric, . . . .61 
 
 Greek, 59 
 
 Roman 60 
 
 ARYAN PEOPLES, 61 
 
 ASSAYING, 24 
 
 BIBLE (The Holy), Classified, ... 6 
 ^Concordance to, . . . . . .6 
 
 Cyclopaedia of, 6 
 
 Dictionary of, ...... 6 
 
 Story of, 5 
 
 BIOLOGY, 29 
 
 BOILERS, Marine and Land, . . . .51 
 
 Management of, 38 
 
 BOTANY 29 
 
 BRAIN, The, 15 
 
 BRIDGE-CONSTRUCTION, . . 23, 31 
 CHEMISTRY, Inorganic, .... 30 
 
 Experiments in, ..... 32, 52 
 
 Qualitative Analysis 49 
 
 1 Quantitative ,,..... 49 
 
 Recreations in, 32 
 
 CLINICAL Diagnosis, .... 14 
 
 DAILY Readings, . , 7, 8 
 
 DICTIONARY of Anecdotes, . ... 4 
 
 of the Holy Bible, 6 
 
 ^Ecclesiastical, ...... 6 
 
 of Medicine (Domestic), . . . .68 
 
 of Philosophical Terms, . . . .58 
 
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 of ,, (Religious), .... 7 
 
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 Physical 41 
 
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 GOUT, 14 
 
 GRAMMARS, 55 
 
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 HORACE, Works of, . . . . .55 
 
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 26 
 
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 Boapteo to tbe Stubs of tbe ffiritisb pharmacopoeia ano tbe tRequirements 
 of tbe {private Student. 
 
 BY W. ELBORNE, F.L.S., F.C.S., 
 
 Late Assistant-Lecturer in Matfria Medica and Pharmacy in the 
 Owens College, Manchester. 
 
 " A work which we can very highly recommend to the perusal of all Students of Medicine. 
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MEDICINE AND THE ALLIED SCIENCES. 13 
 
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 HUMAN ANATOMY. 
 
 BY ALEXANDER MACALISTER, M.A., M.D., F.R.S., F.S.A., 
 
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 BY PROFESSOR LANDOIS OF GREIFSWALD 
 
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 r&c Gbcmical, Microscopical, ani Bacteriological JEvtoence of Disease. 
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MEDICINE AND THE ALLIED SCIENCES. 15 
 
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 DISEASES OF THE HEART 
 
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 BY A. ERNEST SANSOM, M.D., F.E.O P., 
 
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 THEIR STRUCTURE AND FUNCTIONS. 
 
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 THE SURGERY OF THE KIDNEYS. 
 
 Being the Harveian Lectures, 1889. 
 BY J. KNOWSLEY THORNTON, M.B., M.C, 
 
 Surgeon to the Samaritan Free Hospital, c. 
 In Demy %vo, with Illustrations, Cloth, $s. 
 
 "The name and experience of the Author confer on the Lectures the stamp of authority." 
 British Medical Journal. 
 
 READY SHORTLY. 
 
 ON FIBROID DISEASE OF THE LUNG 
 
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 With numerous full-page coloured Illustrations. 
 
 RUPTURES (A Treatise on). By J. F. C. 
 
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 FORENSIC MEDICINE AND TOXI- 
 
 COLOGY. By J. DIXON MANN, M.D., F.R.C.P., Professor of Medical 
 Jurisprudence and Toxicology, Owens College, Manchester ; Examiner 
 in Forensic Medicine, London University, and Victoria University, 
 Manchester. 
 
 GYN^COLOGY (A Practical Treatise on): 
 
 by JOHN HALLIDAY GROOM, M.D., F.R.C.P.E., F.R.C.S.E., Physician 
 to the Royal Infirmary and Royal Maternity Hospital, Edinburgh ; 
 Examiner in Midwifery, R.C.P. , Edinburgh; Lecturer, Edinburgh 
 School of Medicine, &c., &c., with the Collaboration of MM. JOHNSON 
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 %* Volumes on other subjects in active preparation. 
 
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MEDICINE AND THE ALLIED SCIENCES. 
 
 Griffin's Medical Students' Text-Books. 
 
 Anatomy, . 
 
 Biology, 
 
 Botany (Elementary), 
 
 Brain and SpinaJ Cord, 
 Central Nervous 
 
 Organs, 
 Mental Diseases, . 
 
 Chemistry, Inorganic, 
 Qualitative Analysis, 
 Quantitative 
 
 Electricity, . 
 
 Embryology, 
 
 Eye, Diseases of the, 
 
 Foods, Analysis of, . 
 
 Foods and Dietaries, 
 
 Gynaecology, 
 
 Histology, . 
 
 Medicine, 
 
 Nursing, . 
 
 Obstetrics, . 
 
 Pharmacy, . 
 
 Physiology, Human, 
 Practical, . 
 
 Poisons, Detection of, 
 
 Sanitation, Practical, 
 
 Skin, Diseases of the, 
 
 Surgery- 
 Civil, 
 Military, . 
 
 Zoology, 
 
 PROF. MACALISTER, 
 AINSWORTH DAVIS, 
 AINSWORTH DAVIS, 
 VICTOR HORSLEY, 
 
 OBERSTEINER AND HILL, 
 BEVAN LEWIS, . 
 DUPRE AND HAKK, 
 PROF. SEXTON, . 
 PROF. SEXTON, . 
 PROF. JAMIESON, 
 PROF. HADDON, 
 MEYER AND FERGUS, 
 WYNTER BLYTII, 
 
 B. W. BURNET, 
 
 HALLIDAY CROOM, 
 PROF. STIRLING, 
 SIR WM. AITKEN, 
 L. HUMPHRY, 
 H. G. LANDIS, . 
 W. ELBORNE, 
 LANDOIS AND STIRLING, 
 PROF. STIRLING, 
 WYNTER BLYTH, 
 DR. GEORGE REID, . 
 PROF. ANDERSON, 
 
 CAIRD AND CATHCART, 
 PORTER-GODWIN, 
 SELENKA AND DAVIS, 
 
 PAGE 
 
 13 
 29 
 29 
 15 
 
 15 
 15 
 30 
 49 
 49 
 38 
 13 
 14 
 10 
 11 
 16 
 21 
 9 
 
 18 
 18 
 12 
 13 
 21 
 10 
 20 
 14 
 
 12 
 19 
 30 
 
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i8 CHARLES GRIFFIN & CO.'S PUBLICATIONS. 
 
 EIGHTH EDITION. In Extra Crown &vo, iu:th Numerous 
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 NURSING (A Manual of): 
 
 anfc Surgical. 
 
 BY LAURENCE HUMPHRY, M.A., M.B, M.R.C.S, 
 
 Assistant-Physician to, and Lecturer to Probationers at, Addenbrookes 
 Hospital, Cambridge. 
 
 GENERAL CONTENTS. 
 
 The General Management of the Sick Room in Private Houses General 
 Plan of the Human Body Diseases of the Nervous System Respiratory 
 System Heart and Blood-Vessels Digestive System Skin and Kidneys 
 Fevers Diseases of Children Wounds and Fractures Management of Child- 
 Bed Sick-Room Cookery, c., &c. 
 
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MEDICINE AND THE ALLIED SCIENCES. 19 
 
 LONGMORE (Surgeon-General, C.B., Q.H.S., 
 
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 THE SANITARY CONTRASTS OF THE CRIMEAN WAR, 
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 "A most valuable contribution to Military Medicine." British Medical Journal. 
 
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 PARKER (Prof. W. Kitchen, F.R.S., Hunterian 
 
 Professor, Royal College of Surgeons): 
 
 MAMMALIAN DESCENT: being the Hunterian Lectures for 1884. 
 Adapted for General Readers. With Illustrations. In 8vo, cloth, 10/6. 
 
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 and Folding-plate. 8s. 6d. 
 
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 BY SURGEON-MAJOR J. H. PORTER. 
 
 Revised and in great part rewritten 
 
 BY BRIGADE-SURGEON C. H. Y. GODWIN, 
 
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 PRACTICAL SANITATION: 
 
 HAND-BOOK FOR SANITARY INSPECTORS AND OTHERS 
 INTERESTED IN SANITATION. 
 
 BY 
 
 GEORGE REID, M.D., D.P.H., 
 
 Fellow of the Sanitary Institute of Great Britain, and Medical Officer, 
 Staffordshire County Council. 
 
 TKftftb an appen&fj on Sanitary Xaw 
 
 BY 
 
 HERBERT MAN LEY, M.A., M.B., D.P.H., 
 
 Medical Officer of Health for the County Borough of West Bromivich. 
 
 In Large Crown Svo. , -with Illustrations. Price 6s. 
 
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 trated digest of Sanitary Science. 
 
 GENERAL CONTENTS. 
 
 Introduction Water Supply: Drinking Water, Pollution of Water 
 Ventilation and Warming Principles of Sewage Removal Details of 
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 and Appliances Details of Plumbers' Work House Construction Infec- 
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MEDICINE AND THE ALLIED SCIENCES. 21 
 
 WORKS 
 
 BY WILLIAM STIRLING, M.D., Sc.D., 
 
 Professor in the Victoria University, Brackenbury Professor of Physiology and Histology 
 in the Owens College, Manchester ; and Examiner in the University of Oxford. 
 
 SECOND EDITION. In Extra Crown 8vo, with 234 Illustrations, Cloth, 9s. 
 
 PRACTICAL PHYSIOLOGY (Outlines of): 
 
 Being- a Manual for the Physiological Laboratory, including 
 
 Chemical and Experimental Physiology, with 
 
 Reference to Practical Medicine. 
 
 PART I. CHEMICAL PHYSIOLOGY. 
 
 PART II. EXPERIMENTAL PHYSIOLOGY. 
 
 %* In the Second Edition, revised and enlarged, the number of Illustra- 
 tions has been increased from 142 to 234. 
 
 " A VERT EXCELLENT and COMPLETE TREATISE." Lancet. 
 
 "Tne student is enabled to perform for himself most of the experiments usually shown in 
 a systematic course of lectures on physiology, and the practice thus obtained must prove 
 INVAL' ABLE. . . . May be confidently recommended as a guide to the student of 
 physiology, and, we doubt not, will also find its way into the hands of many of our scieminc 
 anil medical practitioners." Glasgow Medical Journal. 
 
 "This valuable little manual. . . . The GENERAL CONCEPTION of the book is EXCKLLKNT; 
 the arrangement of the exercises is all that can be desired ; the descriptions of experiments 
 are CLEAR, CONCISE, and to the point." British Medical Journal. 
 
 In Extra Crown Svo, with 344 Illustrations, Cloth, 12s. Gd. 
 
 PRACTICAL HISTOLOGY (Outlines of): 
 
 A Manual for Students. 
 
 %* Dr. Stirling's " Outlines of Practical Histology" is a compact Hand- 
 book for studerts, providing a COMPLETE LABORATORY COURSE, in which 
 almost every exercise is accompanied by a drawing. Very many of the 
 illustrations have been prepared expressly for the work. 
 
 " The general plan of the work is ADMIRABLE . . . It is very evident that the sug- 
 gestions given are the outcome of a PROLONGED EXPERIENCE in teaching Practical Histology, 
 combined with a REMARKABLE JUDGMENT in the selection of METHODS. . . . Merits the 
 highest praise for the ILLUSTRATIONS, which are at once clear and faithful." British Medical 
 Journal. 
 
 " We can confidently recommend this small but CONCISELY-WRITTEN and ADMIRABLY 
 ILLUSTRATED work to students. They will find it to be a VERY USEFUL and RELIABLE GUIDE 
 in the laboratory, or in their own room. All the principal METHODS of preparing tissues for 
 pection are given, with such precise directions that little or no difficulty can be felt in fol- 
 lowing them in their most minute details. . . . The volume proceeds from a MASTER in 
 his craft." Lancet. 
 
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22 CHARLES GRIFFIN A CO.'S PUBLICATIONS. 
 
 In large Crown Sv0. Handsome Cloth. Price $s. Post free. 
 
 THE WIFE AND MOTHER: 
 
 a flfeebical (Buibe 
 
 TO THE CARE OF HER HEALTH AND THE 
 MANAGEMENT OF HER CHILDREN. 
 
 BY 
 
 ALBERT WESTLAND, M.A., M.D., C.M. 
 
 \* This work is addressed to women who are desirous of 
 fulfilling properly their duties as wives and mothers, and is 
 designed to assist them in exercising an intelligent supervision 
 over their own and their children's health. 
 
 GENERAL CONTENTS. 
 PART I. Early Married Life. 
 PART II. Early Motherhood. 
 PART III. The Child, in Health and Sickness. 
 PART IV. Later Married Life. 
 
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 conscientiously and with perfect good taste. . . . The work is what it pro- 
 fesses to be a guide and help, giving all that is most essential to know of the life- 
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SCIENTIFIC AND TECHNICAL WORKS. 23 
 
 GENERAL SCIENTIFIC WORKS 
 
 RELATING TO 
 
 CHEMISTRY (THEORETICAL AND APPLIED) ; ELECTRICAL 
 
 SCIENCE; ENGINEERING (CiviL AND MECHANICAL); 
 
 GEOLOGY, &c. 
 
 THE DESIGN OF STRUCTURES: 
 
 A Practical Treatise on the Building: of Bridges, Roofs, &s. 
 
 BY S. ANGLIN, C.E., 
 
 Master of Engineering, Royal University of Ireland, late Whitworth Scholar, &c. 
 
 With very numerous Diagrams, Examples, and Tables. 
 
 Large Crown 8vo. Cloth, i6s. 
 
 The leading features in Mr. Anglin's carefully-planned " Design of Struc- 
 tures " may be briefly summarised as follows : 
 
 1. It supplies the want, long felt among Students of Engineering and 
 Architecture, of a concise Text- book on Structures, requiring on the part of 
 the reader a knowledge of ELEMENTARY MATHEMATICS only. 
 
 2. The subject of GRAPHIC STATICS has only of recent years been generally 
 applied in this country to determine the Stresses on Framed Structures ; and 
 in too many cases this is done without a knowledge of the principles upon 
 which the science is founded. In Mr. Anglin's work the system is explained 
 from FIRST PRINCIPLES, and the Student will find in it a valuable aid in 
 determining the stresses on all irregularly- framed structures. 
 
 3. A large number of PRACTICAL EXAMPLES, such as occur in the every-day 
 experience of the Engineer, are given and carefully worked out, some being 
 solved both analytically and graphically, as a guide to the Student. 
 
 4. The chapters devoted to the practical side of the subject, the Strength of 
 Joints, Punching, Drilling, Rivetting, and other processes connected with the 
 manufacture of Bridges, Roofs, and Structural work generally, are the result 
 of MANY YEARS' EXPERIENCE in the bridge-yard ; and the information given 
 on this branch of the subject will be found of great value to the practical 
 bridge-builder. 
 
 "Students of Engineering will find this Text-Book INVALUABLE." Architect. 
 
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 Book. '' Builder. 
 
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 VALUABLE book of reference." Mechanical World. 
 
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 chosen to use as little of the higher mathematics as possible, and has thus made his book of 
 REAL USE TO THE PRACTICAL ENGINEER. . . . After careful perusal, we have nothing but 
 praise for the work." Nature. 
 
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24 CHARLES GRIFFIN <k CO:S PUBLICATIONS. 
 
 With numerous Tables and Illustrations. Crown 8vo. Cloth, 10/6. 
 Second Edition ; Revised. 
 
 ASSAYING (A Text-Book 
 
 For the use of Students, Mine Managers, Assayers, &c. 
 
 C. BERINGER, F.I.C., F.C.S., 
 
 Late Chief Assayer to the Rio Tinto Copper Company, London, 
 
 J. J. BERINGER, F.I.C., F.C.S., 
 
 Public Analyst for, and Lecturer to the Mining Association of, Cornwall. 
 
 General Contents. 
 
 PART I. INTRODUCTORY ; MANIPULATION: Sampling; Drying; Calculation of Re- 
 sults Laboratory-books and Reports METHODS: Dry Gravimetric; Wet Gravimetric- 
 Volumetric Assays : Titrometric, Colorimetric, Gasometric Weighing and Measuring 
 Reagents Formulae, Equations, &c. Specific Gravity. 
 
 PART IT. METALS : Detection and Assay of Silver, Gold, Platinum, Mercury, Copper, 
 Lead, Thallium, Bismuth, Antimony, Iron, Nickel, Cobalt, Zinc, Cadmium, Tin, Tungsten, 
 Titanium, Manganese, Chromium, &c. Earths, Alkalies. 
 
 PART III. NON-METALS : Oxygen and Oxides; The Halogens Sulphur and Sul- 
 phates Arsenic, Phosphorus, Nitrogen Silicon, Carbon, Boron. 
 
 Appendix. Various Tables useful to the Analyst. 
 
 "A REALLY MERITORIOUS WORK, that may be safely depended upon either for systematic 
 instruction or for reference." Nature. 
 
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 tion. . . . Their book ADMIRABLY FULFILS ITS PURPOSE. . . . The results given of 
 an exhaustive series of experiments made by the authors, showing the effects of VARYING 
 CONDITIONS on the accuracy of the method employed, are of THE UTMOST IMPORTANCE." 
 Industries. 
 
 "A very good feature of the book is that the authors give reliable information, mostly 
 based on practical experience." Engineering. 
 
 " This work is one of the BEST of its kind. . . . Essentially of a practical character. 
 . . . Contains all the information that the Assayer will find necessary in the examination 
 of minerals. " Engineer. 
 
 LONDON: EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 25 
 
 In 8vo, Handsome Cloth. Price iSs. 
 
 PHOTOGRAPHY: 
 
 HISTORY, PROCESSES, APPARATUS, AND MATERIALS. 
 
 COMPRISING 
 
 WORKING DETAILS OF ALL THE MORE IMPORTANT METHODS, 
 BY A. BROTHERS, F.R.A.S. 
 
 WITH TWENTY-FOUR FULL PAGE PLATES BY MANY OF THE PRO- 
 CESSES DESCRIBED, AND ILLUSTRATIONS IN THE TEXT. 
 
 GENERAL CONTENTS. 
 
 PART. I. INTRODUCTORY Historical Sketch; Chemistry and Optics 
 of Photography ; Artificial Light (Electric and Oxyhydrogen Light, 
 Compressed Gas, Ethexo-Limelight, Magnesium Light, c.) 
 
 PART II. Photographic Processes, New and Old, with special 
 reference to their relative Practical Usefulness. 
 
 PART III. Apparatus em-ployed in Photography. 
 
 PART IV. Materials employed in Photography. 
 
 PART V. Applications of Photography ; Practical Hints. 
 
 " Mr. Brothers has had an experience in Photography so large and varied that any work 
 by him cannot fail to he interesting and valuable. ... A MOST COMPREHENSIVE volume, 
 entering with full details into the various processes, and VERY FULLY illustrated. The 
 PRACTICAL HINTS are of GREAT VALUE. . . . Admirably got up." Brit. Jour. ofPhotograpJiy. 
 
 " For the Illustrations alone, the book is most interesting ; but, apart from these, the 
 volume is valuable, brightly and pleasantly written, and MOST ADMIRABLY ARRANGED." 
 Photographic News. 
 
 " Certainly the FINEST ILLUSTRATED HANDBOOK to Photography which has ever been 
 published. We have three Photogravures, four Collotypes, one Chromo- Collotype, numerous 
 Blocks, Photo-Chromo-Typograph, Chromo-Lithograph, Woodbury-Type, and Woodbury- 
 Gravure Prints, besides many others. ... A work which should be on the reference 
 shelves of every Photographic Society." Amateur Photographer. 
 
 "This really IMPORTANT handbook of Photography . . . the result of wide 
 experience ... a manual of the best class. . . . As an album of examples of 
 photographic reproduction alone, the book is not dear at the price. ... A handbook so 
 far in advance of most others, that the Photographer must not fail to obtain a copy as a 
 reference work." Photographic Work. 
 
 "The COMPLETEST HANDBOOK of the art which has yet been published. There is no 
 process or form of apparatus which is not described and explained. The beautiful plates 
 given as examples of the different processes are a special feature." Scotsman. 
 
 " Processes are described which cannot be found elsewhere, at all events in so convenient 
 and complete a form." English Mechanic. 
 
 " The chapter on PRACTICAL HINTS will prove INVALUABLE. Mr. Brothers is certainly 
 to be congratulated on the THOROUGHNESS of his work." Daily Chronicle. 
 
 LONDON : EXETER STREET, STRAND. 
 
26 CHARLES GRIFFIN & OO.'S PUBLICATIONS. 
 
 MINE-SURVEYING (A Text-Book of): 
 
 For the use of Managers of Mines and Colleries, Students 
 at the Royal School of Mines, dc. 
 
 BY BENNETT H. BROUGH, F.G.S., 
 
 Instructor of Mine-Surveying, Royal School of Mines. 
 
 With Diagrams. THIRD EDITION. Crown 8vo. Cloth, 73. 6d. 
 
 GENERAL CONTENTS. 
 
 General Explanations Measurement of Distances Miner's Dial Variation of 
 the Magnetic-Needle Surveying with the Magnetic-Needle in presence of Iron 
 Surveying With the Fixed Needle German Dial Theodolite Traversing Under- 
 ground Surface-Surveys with Theodolite Plotting the Survey Calculation of 
 Areas Levelling Connection of Underground- and Surface-Surveys Measuring 
 Distances by Telescope Setting-out Mine-Surveying Problems Mine Plans 
 Applications of Magnetic-Needle in Mining Appendices. 
 
 " It is the kind of book which has long been wanted, and no English-speaking Mine Agent 
 or Mining Student will consider his technical library complete without it.' 1 Nature. 
 
 " Supplies a long-felt want." Iron. 
 
 "A valuable accessory to Surveyors in every department of commercial enterprise." 
 ColU fry Guardian. 
 
 WO R K S 
 
 BY WALTER R. BROWNE, M.A., M. INST. C.E., 
 
 Late Fellow of Trinity College, Cambridge. 
 
 THE STUDENT'S MECHANICS 
 
 An Introduction to the Study of Force and Motion. 
 
 With Diagrams. Crown 8vo. Cloth, 43. 6d. 
 
 " Clear in style and practical in method, 'THE STUDENT'S MECHANICS' is cordially to 
 recommended from all points of view. " A thentzum. 
 
 FOUNDATIONS OF MECHANICS, 
 
 Papers reprinted from the Engineer. In Crown 8vo, is. 
 
 FUEL AND WATER: 
 
 A Manual for Users of Steam and Water. 
 BY PROF. SCHWACKIiOFER AND W. R. BROWNE, M.A. (See p. 49). 
 
 DLONDON: EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 
 
 PRACTICAL GEOLOGY 
 
 DS IIST): 
 
 WITH A SECTION ON PALAEONTOLOGY. 
 
 GRENVILLE A. J. COLE, F. G. S., 
 
 Professor of Geology in the Royal College of Science for Ireland. 
 With Numerous Illustrations and Tables. Large Crown 8vo. Cloth, IDS. 6d. 
 
 GENERAL CONTENTS. 
 
 PART I. SAMPLING OF THE EARTH'S CRUST. 
 
 Observations in the field. | Collection and packing of specimens. 
 
 PART II. EXAMINATION OF MINERALS. 
 
 Some physical characters of minerals. 
 Simple tests with wet reagents. 
 Examination of minerals with the blowpipe. 
 Simple and characteristic reactions. 
 
 Blowpipe-tests. 
 
 Quantitative flame reactions of the felspars 
 
 and their allies. 
 Examination of the optical properties of 
 
 minerals. 
 
 PART III. EXAMINATION OF ROCKS. 
 
 Introductory. 
 
 Rock-structures easily distinguished. 
 Some physical characters of rocks/ 
 Chemical examination of rocks. 
 Isolation of the constituents of rocks. 
 The petrological microscope and microscopic 
 preparations. 
 
 The more prominent characters to be ob- 
 served in minerals in rock-sections. 
 
 Characters of the chief rock-forming minerals 
 in the rock -mass and in thin sections. 
 
 Sedimentary rocks. 
 
 Igneous rocks. 
 
 Metamorphic rocks. 
 
 PART IV. EXAMINATION OF FOSSILS. 
 
 Introductory. 
 
 Fossil generic types. Rhizopoda ; Spongiae 
 
 Hydrozoa ; Actinozoa. 
 Polyzoa ; Brachiopoda. 
 Lamellibranchiata. 
 
 Scaphopoda ; Gastropoda ; Pteropoda 
 
 Cephalopoda. 
 Echinodermata ; Vermes. 
 Anthropoda. 
 Suggested list of characteristic invertebrate 
 
 fossils. 
 
 " Prof. Cole treats of the examination of minerals and rocks in a way that has never 
 been attempted before . . . DESERVING OF THE HIGHEST PRAISE. Here indeed are 
 'aids' INNUMERABLE and INVALUABLE. All the directions are given with the utmost clear- 
 ness and precision. Prof. Cole is not only an accomplished Petrologist, he is evidently also 
 a thoroughly sympathetic teacher, and seems to know intuitively what are stumbling-blocks 
 to learners a rare and priceless quality." Atkerxeum. 
 
 "To the younger workers in Geology, Prof. Cole's book will be as INDISPENSABLE as a 
 dictionary to the learners of a language." Saturday Review. 
 
 "That the work deserves its title, that it is full of ' AIDS,' and in the highest degree 
 'PRACTICAL,' will be the verdict of all who use it." Nature. 
 
 " A MOST VALUABLE and welcome book . . . the subject is treated on lines wholly 
 different from those in any other Manual, and is therefore very ORIGINAL." Science Gossip. 
 
 " A more useful work for the practical geologist has not appeared in handy forin." - 
 Scottish Geographical Magazine. 
 
 " This EXCELLENT MANUAL . . . will be A VERY GREAT HELP. . . . The sectidn 
 on the Examination of Fossils is probably the BEST of its kind yet published. . . . FULL 
 of well-digested information from the newest sources and from personal research." Annals 
 of Nat. History. 
 
 LONDON : EXETER STREET, STRAND, 
 
28 
 
 CHARLES GRIFFIN <k CO.'S PUBLICATIONS. 
 
 SEWAGE DISPOSAL WORKS 
 
 A GUIDE TO THE CONSTRUCTION OF WORKS FOR 
 
 THE PREVENTION OF THE POLLUTION BY 
 
 SEWAGE OF RIVERS AND ESTUARIES. 
 
 BY 
 
 W. SANTO CRIMP, M.lNST.C.E., F.G.S., 
 
 Assistant-Engineer, London County Council. 
 
 With Tables, Illustrations in the Text, and 33 Lithographic Plates. 
 Medium 8vo. Handsome Cloth, 255. 
 
 PART I. INTRODUCTORY. 
 
 Introduction. 
 
 Details of River Pollutions and Recommenda- 
 tions of Various Commissions. 
 
 Hourly and Daily Flow of Sewage. 
 
 The Pail System as Affecting Sewage. 
 
 The Separation of Rain-water from the Sewage 
 Proper. 
 
 Settling Tanks. 
 Chemical Processes. 
 The Disposal of Sewage-sludge. 
 The Preparation of Land for Sewage Dis- 
 posal. 
 Table of Sewage Farm Management. 
 
 PART II. SEWAGE DISPOSAL WORKS IN OPERATION THEIR 
 CONSTRUCTION, MAINTENANCE AND COST. 
 
 Illustrated by Plates showing the General Plan and Arrangement adopted 
 in each District. 
 
 Doncaster Irrigation Farm. 
 
 Beddington Irrigation Farm, Borough of 
 Croydon. 
 
 Bedford Sewage Farm Irrigation. 
 
 Dewsbury and Hitchin Intermittent Fil- 
 tration. 
 
 Merton, Croydon Rural Sanitary Autho- 
 rity. 
 
 Swanwick, Derbyshire. 
 
 The Ealing Sewage Works. 
 
 Chiswick. 
 
 Kingston-on-Thames, A. B. C. Process. 
 
 Salford Sewage Works. 
 
 Bradford, Precipitation. 
 
 12. New Maiden, Chemical Treatment and 
 
 Small Filters. 
 
 13. Friern Barnet. 
 
 14. Acton, Ferozone and Polarite Process. 
 
 15. Ilford, Chadwell, and Dagenham Sewage 
 
 Disposal Works. 
 
 16. Coventry. 
 
 17. Wimbledon. 
 
 18. Birmingham. 
 
 19. Newhaven. 
 
 20. Portsmouth. 
 
 21. Sewage Precipitation Works, Dortmund 
 
 (Germany). 
 
 22. Treatment of Sewage by Electrolysis. 
 
 "All persons interested in Sanitary Science owe a debt of gratitude to Mr. Crimp. . . 
 His work will be especially useful to SANITARY AUTHORITIES and their advisers . . . 
 EMINENTLY PRACTICAL AND USEFUL . . . gives plans and descriptions of MANY OF THE 
 MOST IMPORTANT SEWAGE WORKS of England . . . with very valuable information as to 
 the COST of construction and working of each. . . . The carefully-prepared drawings per- 
 mit of an easy comparison between the different systems." Lancet. 
 
 "Probably the MOST COMPLETE AND BEST TREATISE on the subject which has appeared 
 in our language. . . . Will prove of the greatest use to all who have the problem of 
 Sewage Disposal to face. . . . The general construction, drawings, and type are all 
 excellent." Edinburgh. Medical Journal. 
 
 LONDON: EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 29 
 
 TV O E K S 
 
 BY J. R. AINSWORTH DAVIS, B.A, 
 
 PROFESSOR OF BIOLOGY, UNIVERSITY COLLEGE, ABERYSTWYTH. 
 
 BIOLOGY (A Text-Book of): 
 
 Comprising Vegetable and Animal Morphology and Physiology. In Large 
 Crown 8vo, with 158 Illustrations. Cloth. 
 
 [Second Edition in preparation.} 
 
 GENERAL CONTENTS. 
 
 PART I. VEGETABLE MORPHOLOGY AND PHYSIOLOGY. Fungi Algae The 
 
 Moss The Fern Gymnosperms Angiosperms. 
 Comparative Vegetable Morphology and Physiology Classification of Plants. 
 
 PART II. ANIMAL MORPHOLOGY AND PHYSIOLOGY. Protozoa Coelenterata 
 
 Vermes Arthropoda Mollusca Amphibia Aves Mammalia. 
 Comparative Animal Morphology and Physiology Classification of Animals. 
 With Bibliography, Exam.-Questions, complete Glossary, and 158 Illustrations. 
 
 "As a general work of reference, Mr. Davis's manual will be HIGHLY SERVICEABLE to 
 medical men. ' British Medical Journal. 
 
 " Furnishes a clear and comprehensive exposition of the subject in a systematic form." 
 Saturday Review. 
 
 " Literally PACKED with information." Glasgow Medical Journal. 
 
 THE FLOWERING PLANT, 
 
 AS ILLUSTRATING- THE FIRST PRINCIPLES OF BOTANY. 
 
 Specially adapted for London Matriculation, S. Kensington, and University Local 
 Examinations in Botany. Large Crown 8vo, with numerous Illustrations. 33. 6d. 
 SECOND EDITION. 
 
 " It would be hard to find a Text-book which would better guide the student to an accurate 
 knowledge of modern discoveries in Botany. . . . The SCIENTIFIC ACCURACY of statement, 
 and the concise exposition of FIRST PRINCIPLES make it valuable for educational purposes. In 
 the chapter on the Physiology of Flowers, an admirable resume is given, drawn from Darwin, 
 Hermann Miiller, Kerner, and Lubbock, of what is known of the Fertilization of Flowers." 
 Journal of the Linnean Society. 
 
 "We are much pleased with this volume . . . the author's style is MOST CLEAR, and 
 his treatment that of a PRACTISED INSTRUCTOR. . . . The Illustrations are very good, 
 suitable and helpful. The Appendix on Practical Work will be INVALUABLE to the private 
 student. . . . We heartily commend the work." ScJwolmaster. 
 
 *** Recommended by the National Home-Reading Union ; and also for use in the 
 University Correspondence Classes. 
 
 LONDON : EXETER STREET, STRAND. 
 
30 CHARLES GRIFFIN efc CO.'S PUBLICATIONS. 
 
 PROF. DAVIS'S WORKS Continued. 
 
 A ZOOLOGICAL POCKET-BOOK; 
 
 OP, Synopsis of Animal Classification. 
 
 Comprising Definitions of the Phyla, Classes, and Orders, with explanatory 
 Remarks and Tables. 
 
 BY DR. EMIL SELENKA, 
 
 Professor in the University of Erlangen. 
 
 Authorised English translation from the Third German Edition. In Small 
 Post 8vo, Interleaved for the use of Students. Limp Covers, 45. 
 
 "Dr. Selenka's Manual will be found useful by all Students of Zoology. It is a COMPRE- 
 HENSIVE and SUCCESSFUL attempt to present us with a scheme of the natural arrangement of 
 the animal world." Edin. Med. Journal. 
 
 " Will prove very serviceable to those who are attending Biology Lectures. . . . The 
 translation is accurate and clear." Lancet. 
 
 INORGANIC CHEMISTRY (A Short Manual of), 
 
 BY A. DUPRE, Ph.D., F. R. S., AND WILSON HAKE, 
 
 Ph.D., F.I.C., F.C.S., of the Westminster Hospital Medical School. 
 
 SECOND EDITION, Revised. Crown 8vo. Cloth, 7s. 6d. 
 
 "A well-written, clear and accurate Elementary Manual of Inorganic Chemistry. 
 We agree heartily in the system adopted by Drs. Dupre and Hake. WILL MAKE EXPERI- 
 MENTAL WORK TREBLY INTERESTING BECAUSE INTELLIGIBLE." Saturday Review. 
 
 "There is no question that, given the PERFECT GROUNDING of the Student in his Science, 
 the remainder comes afterwards to him in a manner much more simple and easily acquired. 
 The work is AN EXAMPLE OF THE ADVANTAGES OF THE SYSTEMATIC TREATMENT of a 
 Science over the fragmentary style so generally followed. BY A LONG WAY THE BEST of the 
 small Manuals for Students." Analyst. 
 
 HINTS ON THE PRESERVATION OF FISH, 
 
 IN REFERENCE TO FOOD SUPPLY. 
 
 BY J. COSSAR EWART, M. D., F. R. S. E., 
 
 Regius Professor of Natural History, University of Edinburgh. 
 In Crown 8vo. Wrapper, 6d. 
 
 LONDON: EXETER STREET, STRAJSD. 
 
STAND A ED P UBLIGA TIONS. 3 1 
 
 Royal 8zw. With numerous Illustrations and 17 Lithographic Plates. 
 Handsome Cloth. Price 305. 
 
 BRIDGE-CONSTRUCTION 
 
 (A PRACTICAL TREATISE ON): 
 
 Being a Text-Book on the Construction of Bridges in 
 Iron and Steel. 
 
 FOR THE USE OF STUDENTS, DRAUGHTSMEN, AND ENGINEERS, 
 
 BY 
 
 T. CLAXTON FIDLER, M. INST. C.E., 
 
 Prof, of Engineering, University College, Dundee. 
 
 "Of late years the American treatises on Practical and Applied Mechanics 
 have taken the lead . . . since the opening up of a vast continent has 
 given the American engineer a number of new bridge -problems to solve 
 . . . but we look to the PRESENT TREATISE ON BRIDGE-CONSTRUCTION, and 
 the Forth Bridge, to bring us to the front again." Engineer. 
 
 " One of the VERY BEST RECENT WORKS on the Strength of Materials and its 
 application to Bridge-Construction. . . . Well repays a careful Study." 
 Engineering. 
 
 "An INDISPENSABLE HANDBOOK for the practical Engineer." Nature. 
 
 " The science is progressive, and as an exposition of its LATEST ADVANCES 
 we are glad to welcome Mr. Fidler's well -written treatise." Architect. 
 
 "An admirable account of "the theory and process of bridge-design, AT ONCE 
 SCIENTIFIC AND THOROUGHLY PRACTICAL. It is a book such as we have a right 
 to expect from one who is himself a substantial contributor to the theory of 
 the subject, as well as a bridge-builder of repute." Saturday Review. 
 
 "This book is a model of what an engineering treatise ought to be." 
 Industries. 
 
 "A SCIENTIFIC TREATISE OF GREAT MERIT." Westminster Review. 
 
 "Of recent text-books on subjects of mechanical science, there has 
 appeared no one more ABLE, EXHAUSTIVE, or USEFUL than Mr. Claxton 
 Fidler's work on Bridge-Construction." Scotsman. 
 
 LONDON: EXETER STREET, STRAND. 
 
32 CHARLES GRIFFIN 6 CO.'S PUBLICATIONS, 
 
 FOSTER (C. Le Neve, D.Sc., Professor of Mining, 
 
 Royal College of Science; H.M. Inspector of Mines, Llandudno) : 
 
 ORE AND STONE MINING (A Text-Book of). With numerous 
 Illustrations. Large Crown 8vo. Cloth. [Shortly. 
 
 GRIFFIN'S ELECTRICAL PRICE-BOOK : 
 
 For the Use of Electrical, Civil, Marine, and Borough Engineers, Local 
 Authorities, Architects, Railway Contractors, &c., &c. Edited by 
 H. J. DOWSING, M.lNST.E.E., &c. In Crown 8vo. Cloth. [At Press. 
 
 GRIFFIN (John Joseph, F.CS.) : 
 
 CHEMICAL RECREATIONS : A Popular Manual of Experimental 
 Chemistry. With 540 Engravings of Apparatus. Tenth Edition. Crown 
 4to. Cloth. 
 
 Part I. Elementary Chemistry, 2/. 
 
 Part II. The Chemistry of the Non-Metallic Elements, including a 
 
 Comprehensive Course of Class Experiments, 10/6. 
 Or, complete in one volume, cloth, gilt top, . . 12/6. 
 
 GURDEN (Richard Lloyd, Authorised Surveyor 
 
 for the Governments of New South Wales and Victoria) : 
 
 TRAVERSE TABLES : computed to Four Places Decimals for every 
 Minute of Angle up to 100 of Distance. For the use of Surveyors and 
 Engineers. Second Edition. Folio, strongly .half-bound, 2I/. 
 
 %* Published with Concurrence of the Surveyors- General for New South 
 Wales and Victoria. 
 
 " Those who have experience in exact SURVEY-WORK will best know how to appreciate 
 the enormous amount of labour represented by this valuable book. The computations 
 enable the user to ascertain the sines and cosines for a distance of twelve miles to within 
 half an inch, and this BY REFERENCE TO BUT ONE TABLE, in place of the usual Fifteen 
 minute computations required. This alone is evidence of the assistance which the Tables 
 ensure to every user, and as every Surveyor in active practice has felt the want of such 
 assistance, few knowing of their publication will remain without them." Engineer. 
 
 LONDON: EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 
 
 33 
 
 Griffin's Standard Publications 
 
 FOR 
 
 ENGINEERS, ELECTRICIANS, ARCHITECTS, BUILDERS, 
 NAVAL CONSTRUCTORS, AND SURVEYORS. 
 
 Applied Mechanics, . 
 
 (Student's), . 
 Civil Engineering, . 
 
 Bridge-Construction, . 
 
 Design of Structures, . 
 
 Sewage Disposal Works, 
 
 Traverse Tables, . 
 Marine Engineering 1 , 
 
 Stability of Ships, 
 The Steam-Engine, . 
 
 (Student's), 
 Boiler Construction, 
 
 Management, 
 Fuel and Water (for 
 
 Steam Users), 
 Machinery and Millwork, 
 
 Hydraulic Machinery, . 
 Useful Rules and Tables 
 for Engineers, &e., . 
 
 Electrical Poeket-Book, 
 
 Nystrom's Pocket-Book, 
 
 Electrical Price-Book, . 
 
 PROF. RANKINE, 
 BROWNE, JAMIESON, 
 PROF. RANKINE, 
 PROF. FIDLER, 
 S. ANGLIN, . 
 SANTO CRIMP, 
 R. GURDEN, 
 A. E. SEATON, 
 SIR E. J. REED, 
 PROF. RANKINE, 
 PROF. JAMIESON, 
 T. W. TRAILL, . 
 R. D. MUNRO, . 
 
 f SCHWACKHOFER AND ) 
 
 \ BROWNE, . j 
 
 PROF. RANKINE, 
 
 PROF. ROBINSON, 
 ( PROFS. RANKINE AND ) 
 | JAMIESON, . j 
 
 MUNRO AND JAMIESON, 
 
 DENNIS MARKS, . 
 
 H. J. DOWSING, . 
 
 PAGE 
 
 44, 45 
 26, 38 
 44 
 
 31 
 23 
 28 
 32 
 50 
 40 
 45 
 37 
 51 
 38 
 
 49 
 
 44 
 
 48 
 
 45 
 
 40 
 40 
 32 
 
 For a COMPLETE RECORD of the PAPERS read before 
 the ENGINEERING, ARCHITECTURAL, and ELECTRICAL 
 SOCIETIES throughout the United Kingdom during each year, 
 uide "THE OFFICIAL YEAR-BOOK OF THE SCIENTIFIC 
 AND LEARNED SOCIETIES OF GREAT BRITAIN AND 
 IRELAND" (page 53). 
 
 LONDON : EXETER STREET, STRAND. 
 
34 CHARLES GRIFFIN ie CO. 'S PUBLICATIONS. 
 
 Griffin's Standard Publications 
 
 FOB 
 
 MINE OWNERS AND MANAGERS, GEOLOGISTS, 
 METALLURGISTS, AND MANUFACTURERS, 
 
 Geology (Stratigraphical), 
 (Physical), . 
 
 ,, (Practical), . 
 
 Mine-Surveying-, 
 Mining", Coal . 
 
 ,, Ore and Stone, . 
 Blasting- and Explosives, 
 Metallurgy, 
 
 ,, (Introduction to), 
 Assaying-, . 
 Electro-Metallurgy, 
 
 PAGE 
 
 42 
 41 
 27 
 26 
 36 
 
 E. ETHERIDGE, . 
 PROF. SEELEY, 
 PROF. COLE, 
 
 B. H. BROUGH, . 
 H. W. HUGHES, 
 
 PROF. LE NEVE FOSTER, 32 
 O. GUTTMANN, . . 35 
 PHILLIPS AND BAUERMAN, 43 
 PROF. ROBERTS- AUSTEN, 47 
 
 C. & J. J. BERINGER, 24 
 
 W. M'MlLLAN, . . 39 
 
 OTHER VOLUMES IN PREPARATION. 
 
 Griffin's Students' Text-Books. 
 
 PAGE 
 
 Biology,. . . Davis, 29 
 Botany, . . . Davis, 29 
 
 Chemistry- 
 Inorganic, Dupre&Hake, 30 
 Qual. Analysis, Sexton, 49 
 
 Quant. 
 
 49 
 
 Recreations, Griffin, .32 
 Experiments, Wright, 52 
 
 Magnetism and Electricity, 
 
 Jamieson, 38 
 
 Mechanics, . Rankine, 45 
 
 Physics (Experiments), 
 
 Wright, 52 
 
 Physiology, . Stirling, 21 
 
 Steam-Engine, Jamieson, 37 
 
 ZOOlOgy, . Davis, 30 
 
 LONDON : EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 35 
 
 In Large Svc, with Numerous Illustrations and Folding Plates, 
 Cloth, los. 6d. 
 
 B LAST I N G: 
 
 A Handbook for the Use of Engineers and others Engaged in 
 Mining, Tunnelling, Quarrying, &c. 
 
 BY 
 
 OSCAR GUTTMANN, Assoc. M. INST. C.E. 
 
 Member of the Societies of Civil Engineers and A rchitects of Vienna and Budapest, 
 Corresponding Member of the Imp. Roy. Geological Institution of Austria, &c. 
 
 %* Mr. GUTTMANN'S Blasting'^ the ONLY work on the subject which gives at once full 
 information as to the NEW METHODS adopted since the introduction of Dynamite, and, at the 
 same time, the results of MANY YEARS PRACTICAL EXPERIENCE both in Mining Work and in 
 the Manufacture of Explosives. It therefore presents in concise form all that has been proved 
 good in the various methods of procedure. The Illustrations form a special and valuable 
 feature of the work. 
 
 GENERAL CONTENTS. Historical Sketch Blasting Materials Blasting Pow- 
 der Various Powder-mixtures Gun-cotton Nitro-glycerine and Dynamite 
 Other Nitro-compounds Sprengel's Liquid (acid) Explosives Other Means of 
 Blasting Qualities, Dangers, and Handling of Explosives Choice of Blasting 
 Materials Apparatus for Measuring Force Blasting in Fiery Mines Means of 
 Igniting Charges Preparation of Blasts Bore-holes Machine-drilling Chamber 
 Mines Charging of Bore-holes Determination of the Charge Blasting in Bore- 
 holes Firing Straw and Fuze Firing Electrical Firing Substitutes for Electrical 
 Firing Results of Working Various Blasting Operations Quarrying Blasting 
 Masonry, Iron Structures, Wooden Objects Blasting in earth, under water, of ice, 
 &c., &c. 
 
 "This ADMIRABLE work." Colliery Guardian. 
 
 " Should prove a vade-mecum, to Mining Engineers and all engaged in practical work." 
 Iron and Coal Trades Review. 
 
 HURST (GEO. H., F.CS.) : 
 
 PAINTERS' COLOURS, OILS, AND VARNISHES : A Text-book 
 for Students and Practical Men. With Numerous Illustrations. (Griffin's 
 Technological Series). Crown 8vo, Cloth, I2s. 6d. 
 
 KNECHT .(DR.), RAWSON (Chr., F.C.S.), AND 
 
 LOEWENTHAL (DR.) : 
 
 A MANUAL OF DYEING. With Numerous Illustrations and 
 Specimens of Dyed Fabrics. (Griffin's Technological Series.) 
 
 [At Press. 
 
 LONDON: EXETER STREET, STRAND. 
 
36 CHARLES GRIFFIN & CO:S PUBLICATIONS. 
 
 COAL-MINING (A Text-Book of) 
 
 FOR THE USE OF COLLIERY MANAGERS AND OTHERS 
 ENGAGED IN COAL-MINING. 
 
 HERBERT WILLIAM HUGHES, F.G.S., 
 
 Assoc. Royal School of Mines, Certificated Colliery Manager. 
 
 In Demy Svo, Handsome Cloth. With very Numerous Illustrations, mostly 
 reduced from Working Drawings. i8j. 
 
 GENERAL CONTENTS. 
 
 Geology : Rocks P'aults Order of Succession Carboniferous System in Britain. 
 Coal : Definition and Formation of Coal Classification and Commercial Value of Coals. 
 Search for Coal : Boring various appliances used Devices employed to meet Difficulties 
 of deep Boring Special methods of Boring Mather & Platt's, American, and Diamond 
 systems Accidents in Boring Cost of Boring Use of Boreholes. Breaking Ground; 
 Tools Transmission of Power : Compressed Air, Electricity Power Machine Drills Coal 
 Cutting by Machinery Cost of Coal Cutting Explosives Blasting in Dry and Dusty 
 Mines Blasting by Electricity Various methods to supersede Blasting. Sinking: 
 Position, Form, and Size of shaft Operation of getting down to " Stone-head" Method of 
 proceeding afterward-^-Lining shafts Keeping out Water by Tubbing Cost of Tubbing 
 Sinking by Boring -Kind - Chaudron, and Lipmann methods Sinking through Quicksands 
 Cost of Sinking. Preliminary Operations : Driving underground Roads Supporting 
 Roof: Timbering, Chocks or Cogs, Iron and Steel Supports and Masonry Arrangement of 
 Inset. Methods of Working : Shaft, Pillar, and Subsidence Bord and Pillar System- 
 Lancashire Method Longwall Method Double Stall Method Working Steep Seams 
 Working Thick Seams Working Seams lying near together Spontaneous Combustion. 
 Haulage: Rails Tubs Haulage by Horses Self-acting Inclines Direct-acting Haulage 
 Main and Tail Rope Endless Chain- Endless Rope Comparison. Winding; Pit 
 Frames Pulleys Cages Ropes Guides Engines Drums Brakes Counterbalancing 
 Expansion Condensation Compound Engines Prevention of Overwinding Catches at pit 
 top Changing Tubs Tub Controllers Signalling. Pumping: Bucket and Plunger 
 Pumps Supporting Pipes in Shaft Valves Suspended lifts for Sinking Cornish and 
 Bull Engines Davey Differential Engine Worthington Pump Calculations as to size of 
 Pumps Draining Deep Workings Dams. Ventilation: Quantity of air required 
 Gases met with in Mines Coal-dust Laws of Friction Production of Air-currents 
 Natural Ventilation Furnace Ventilation Mechanical Ventilators Efficiency of Fans 
 Comparison of Furnaces and Fans Distribution of the Air-current Measurement of Air- 
 currents. Lighting: Naked Lights Safety Lamps Modern Lamps Conclusions 
 Locking and Cleaning Lamps Electric Light Underground Delicate Indicators. Works 
 at Surface; Boilers Mechanical Stoking Coal Conveyors Workshops. Preparation 
 of Coal for Market: General Considerations Tipplers Screens Varying the Sizes made 
 by Screens Belts Revolving Tables Loading Shoots Typical Illustrations of the arrange- 
 ment of Various Screening Establishments Coal Washing Dry Coal Cleaning Briquettes. 
 
 V* A Novel and Important Feature will be found in the BIBLIOGRAPHY given at the end 
 of each Chapter. 
 
 " A Text-book on Coal-Mining is a great desideratum, and Mr. HUGHES possesses 
 ADMIRABLE QUALIFICATIONS for supplying it. . . . We cordially recommend the work." 
 Colliery Guardian. 
 
 LONDON : EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 37 
 
 "W O E K S 
 
 BY ANDREW JAMIESON, M.lNST.C.E, F.R.S.E., 
 
 Professor of Engineering, Glasgow and West of Scotland Technical College. 
 
 SEVENTH EDITION, Revised and Enlarged. Crown 8vo, Cloth, 8s. 6d. 
 
 A TEXT-BOOK ON STEAM AND STEAM-ENGINES 
 
 WITH OVER 200 ILLUSTRATIONS, FOLDING-PLATES, AND 
 EXAMINATION QUESTIONS. 
 
 " Professor Jamieson fascinates the reader by his CLEARNESS OF CONCEPTION AND 
 SIMFLIC TY OF EXPRESSION. His treatment recalls the lecturing of Faraday." Athenaeum. 
 " The BEST BOOK yet published for the use of Students." Engineer, 
 " Undoubtedly the MOST VALUABLE AND MOST COMPLETE Hand-book on the subject 
 that now exists. " Marine Engineer. 
 
 A POCKET-BOOK of ELECTRICAL RULES and TABLES. 
 
 FOR THE USE OF ELECTRICIANS AND ENGINEERS. 
 
 Pocket Size. Leather, 8s. 6d. Ninth Edition, revised and enlarged, 
 (See under Mtmro and Jamieson.} 
 
 ELECTRICITY & MAGNETISM (An Advanced Text-Book on) 
 
 ce and Art, City and Guilds 
 Students. With Illustrations. 
 
 For the Use of Science and Art, City and Guilds of London, and other 
 
 th 
 
 [Shortly. 
 
 PROF. JAMIESON'S ELEMENTARY MANUALS FOR 
 FIRST-YEAR STUDENTS. 
 
 1. STEAM AND THE STEAM-ENGINE 
 
 (AN ELEMENTARY MANUAL ON): 
 
 Forming an Introduction to the larger Work by the same Author. With very 
 numerous Illustrations and Examination Questions* Third Edition. 
 Crown 8vo. Cloth, 35. 6d. 
 
 " Quite the right sort of Book . . . well illustrated with good diagrams and drawings 
 of real engines and details, all clearly and accurately lettered. . . . CANNOT FAIL To BE 
 A MOST SATISFACTORY GUIDE to the apprentice and Student." Engineer. 
 
 " Should be in the hands of EVERY engineering apprentice." Practical Engine ir. 
 
 LONDON : EXETER STREET, STRAND. 
 
38 CHARLES GRIFFIN & CO.'S PUBLICATIONS. 
 
 PROF. JAMIESON'S ELEMENTARY MANUALS Continued. 
 
 SECOND EDITION. Crown 8vo, with very numerous Illustrations. 
 
 2. MAGNETISM AND ELECTRICITY 
 
 (AN ELEMENTARY MANUAL ON). 
 With very Numerous Diagrams and Examination Questions. 
 
 Part I. Magnetism. Part II. Voltaic Electricity. Part III 
 
 Electro-Statics, or Frietional Electricity. 
 
 Complete in One Volume, 3s. 6d. 
 
 "The arrangement is as good as it well can be, . . . the diagrams are EXCELLENT. 
 . . . The subject treated as an essentially practical one, and very clear instructions 
 given. Teachers are to be congratulated on having such a THOROUGHLY TRUSTWOKTUY 
 TEXT- BOOK at their disposal." Nature. 
 
 " An excellent and very PRACTICAL elementary treatise." Electrical Review. 
 
 "An ADMIRABLE Introduction to Magnetism and Electricity . . . the production 
 of a skilled and experienced teacher. . . . Explained at every point by simple 
 experiments, rendered easier by admirable illustrations." British Medical Journal. 
 
 "A CAPITAL TEXT-BOOK. . . . The diagrams are an important ieature." 
 Schoolmaster. 
 
 3. APPLIED MECHANICS (An Elementary Manual on). 
 
 With very numerous Illustrations drawn "expressly for the work, and 
 Examination Questions. Crown 8vo. 3-s, (Jd. 
 
 SECOND EDITION. Enlarjed, and very fully Illustrated. Cloth, 4s. Qd. 
 
 STEAM - BOILERS: 
 
 THEIR DEFECTS, MANAGEMENT, AND CONSTRUCTION. 
 BY R. D. MUNKO, 
 
 Engineer of the Scottish Boiler Insurance and Engine Inspection Company. 
 This work, written chiefly to mest the wants of Mechanics, Engine 
 keepers, and Boiler-attendants, also contains information of the first import- 
 ance to every user of Steam-power. It is a PRACTICAL work written for PRAC- 
 TICAL men, the language and rules being throughout of the simplest nature. 
 
 GENERAL CONTENTS. Explosions caused by Overheating of Plates: (a) 
 Shortness of Water : (b) Deposit Explosions caused by Defective and 
 Overloaded Safety-Valves Area of Safety-Valves Explosions caused by 
 Corrosion Explosions caused by Defective Design and Construction. 
 
 %* To the SECOND EDITION, a Section on the Management of Upright 
 Internally-fired Boilers, and a Specification and detailed Drawing of a Lan- 
 cashire Boiler for a working pressure of 200 Ibs. per sq. in., have been added. 
 
 " A valuable companion for workmen and engineers engaged about Steam 
 Boilers, ought to be carefully studied, and ALWAYS AT HAND." Coil. Guardian. 
 
 " The subjects referred to are handled in a trustworthy, clear, and practical 
 manner. . . . The book is VERY USEFUL, especially to steam users, 
 artisans, and young engineers." Engineer. 
 
 LONDON : EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 
 
 39 
 
 ELECTRO-METALLURGY (A Treatise on): 
 
 Embracing the Application of Electrolysis to the Plating, Depositing, 
 Smelting, and Refining of various Metals, and to the Repro- 
 duction of Printing Surfaces and Art-Work, &c. 
 
 BY WALTER G. M'MILLAN, F.I.C., F.C.S., 
 
 Chemist and Metallurgist to the Cossipore Foundry and Shell-Factory; Late Demonstrator 
 of Metallurgy in King's College, London. 
 
 With numerous Illustrations. Large Crown 8vo. Cloth, 10s. 6d. 
 
 GENERAL CONTENTS. 
 
 Introductory and Historical Theoreti- 
 cal and General Sources of Current 
 General Conditions to be observed in 
 Electro-Plating Plating Adjuncts and 
 Disposition of Plant Cleansing and Pre- 
 paration of Work for the Depositing- Vat, 
 and Subsequent Polishing of Plated Goods 
 Electro-Deposition of Copper Electro- 
 typing Electro-Deposition of Silver of 
 Gold of Kickel and Cobalt of Iron of 
 Platinum, Zinc, Cadmium, Tin, Lead, 
 Antimony, and Bismuth; Electro-chromy 
 
 Electro-Deposition of Alloys Electro- 
 Metallurgical Extraction and Eefining 
 Processes Recovery of certain Metals 
 from their Solutions or Waste Substances 
 Determination of the Proportion of 
 Metal in certain Depositing Solutions 
 Glossary of Substances commonly em- 
 ployed in Electro-Metallurgy Addenda : 
 Various useful Tables The Bronzing ot 
 Copper and Brass Surfaces Antidotes to 
 Poisons. 
 
 " This excellent treatise, . . . one of the BEST and MOST COMPLETE 
 manuals hitherto published on Electro-Metallurgy." Electrical Review. 
 
 "Well brought up to date, including descriptions such as that of 
 Elmore's recent process for the manufacture of seamless copper tubes of 
 extraordinary strength and tenacity by electro-deposition of the pure 
 metal. . . . Illustrated by well-executed and effective engravings." 
 Journal of Soc. of Che.m. Industry. 
 
 " This work will be a STANDARD." Jeweller. 
 
 "Any metallurgical process which REDUCES the COST of production 
 must of necessity prove of great commercial importance. . . . We 
 recommend this manual to ALL who are interested in the PRACTICAL 
 APPLICATION of electrolytic processes." Nature. 
 
 LONDON: EXETER STREET, STRAND. 
 
4 o CHARLES GRIFFIN & COSS PUBLICATIONS. 
 
 MUNRO & JAMIESON'S ELECTRICAL POCKET-BOOK. 
 
 NINTH EDITION, Revised and Enlarged. 
 
 A POCKET-BOOK 
 
 OF 
 
 ELECTRICAL RULES & TABLES 
 
 FOR THE USE OF ELECTRICIANS AND ENGINEERS. 
 BY 
 
 JOHN MUNRO, C.E., & PROF. JAMIESON, M.lNST.C.E., F.R.S.E. 
 With Numerous Diagrams. Pocket Size. Leather, 83. 6d. 
 
 This work is fully illustrated, and forms an extremely convenient POCKET 
 COMPANION for reference on important points essential to ELECTRICIANS AND 
 ELECTRICAL ENGINEERS. 
 
 GENERAL CONTENTS. 
 
 UNITS OF MEASUREMENT. 
 
 MEASURES. 
 
 TESTING. 
 
 CONDUCTORS. 
 
 DIELECTRICS. 
 
 SUBMARINE CABLES. 
 
 TELEGRAPHY. 
 
 ELECTRO-CHEMISTRY. 
 
 ELECTRO-METALLURGY. 
 
 BATTERIES. 
 
 DYNAMOS AND MOTORS. 
 
 TRANSFORMERS. 
 
 ELECTRIC LIGHTING 
 
 MISCELLANEOUS. 
 
 LOGARITHMS. 
 
 APPENDICES. 
 
 " WONDERFULLY PERFECT. . . . Worthy of the highest commendation we can 
 give it." Electrician. 
 
 "The STERLING VALUE of Messrs. MUNRO and JAMIESON'S POCKET-BOOK." 
 Electrical Review. 
 
 NYSTEOM'S POCKET-BOOK 
 
 OF 
 
 MECHANICS & ENGINEERING. 
 
 REVISED AND CORRECTED BY 
 
 W. DENNIS MARKS, Pn.B., C.E. (YALE s.s.s.), 
 
 Whitney Professor of Dynamical Engineering, University of Pennsylvania. 
 
 Pocket Size. Leather, 155. TWENTIETH EDITION. Revised and greatly 
 
 enlarged. 
 
 LONDON: EXETER STREET, STRAND, 
 
SCIENTIFIC AND TECHNICAL WORKS. 41 
 
 Demy 8vo, Handsome cloth, 18s. 
 
 PHYSICAL GEOLOGY AND 
 PALEONTOLOGY, 
 
 ON THE BASIS OF PHILLIPS. 
 
 BY 
 
 HARRY GOVIER SEELEY, F.R.S., 
 
 PROFESSOR OF GEOGRAPHY IN KING'S COLLEGE, LONDON. 
 
 Witb ^frontispiece in GbromosTLitbograpbE, anD 5Uustrations. 
 
 " It is impossible to praise too highly the research which PROFESSOR SEELEY'S 
 1 PHYSICAL GEOLOGY ' evidences. IT is FAR MORE THAN A TEXT-BOOK it is 
 a DIRECTORY to the Student in prosecuting his researches." Extract from the. 
 Presidential Address to the Geological Society, 1885, by Rev. Professor Bonney^ 
 D.Sc., LL.D., F.R.S. 
 
 " PROFESSOR SEELEY maintains in his ' PHYSICAL GEOLOGY ' the high 
 reputation he already deservedly bears as a Teacher. . . . It is difficult, 
 in the space at our command, to do fitting justice to so large a work. . . . 
 The final chapters, which are replete with interest, deal with the Biological 
 aspect of Palaeontology. Here we find discussed the origin, the extinction, 
 succession, migration, persistence, distribution, relation, and variation of species 
 with other considerations, such as the Identification of Strata by Fossils, 
 Homotaxis, Local Faunas, Natural History Provinces, and the relation of 
 Living to Extinct forms." Dr. Henry Woodward, F.R.S., in the " Geological 
 Magazine. ' ' 
 
 " A deeply interesting volume, dealing with Physical Geology as a whole, 
 and also presenting us with an animated summary of the leading doctrines -and 
 facts of Palaeontology, as looked at from a modern standpoint." Scotsman. 
 
 " PROFESSOR SEELEY'S work includes one of the most satisfactory Treatises 
 on Lithology in the English language. ... So much that is not accessible 
 in other works is presented in this volume, that no Student of Geology can 
 afford to be without it." American Journal of Engineering. 
 
 " Geology from the point of view of Evolution." Westminster Review. 
 
 " PROFESSOR SEELEY'S PHYSICAL GEOLOGY is full of instructive matter, 
 whilst the philosophical spirit which it displays will charm many a reader. 
 From early days the author gave evidence of a powerful and eminently original 
 genius. No one has shown more convincingly than the author that, in all 
 ways, the past contains within itself the interpretation of the existing world, " 
 Annals of Natural History. 
 
 LONDON: EXETER STREET, STRAND. 
 
42 CHARLES GRIFFIN & CO.'S PUBLICATIONS. 
 
 Demy 8vo, Handsome cloth, 34s. 
 
 STRATIGRAPHICAL GEOLOGY 
 AND PALEONTOLOGY, 
 
 ON 
 
 THE BASIS OF PHILLIPS. 
 
 BY 
 
 ROBERT ETHERIDGE, F. R. S., 
 
 OF THE NATURAL HIST. DEPARTMENT, BRITISH MUSEUM, LATE PALEONTOLOGIST TO THE 
 
 GEOLOGICAL SURVEY OF GREAT BRITAIN, PAST PRESIDENT OF THE 
 
 GEOLOGICAL SOCIETY, ETC. 
 
 TOtb /IRap, Numerous Gables, anfc Gbirtg*01j BMates. 
 
 "In 1854 Prof. JOHN MORRIS published the Second Edition of his 'Catalogue 
 of British Fossils,' then numbering 1,280 genera and 4,000 species. Since 
 that date 3,000 genera and nearly 12,000 new species have been described, 
 thus bringing up the muster-roll of extinct life in the British Islands alone to 
 3,680 genera and 16,000 known and described species. 
 
 "Numerous TABLES of ORGANIC REMAINS have been prepared and 
 brought down to 1884, embracing the accumulated wealth of the labours of 
 past and present investigators during the last thirty years. Eleven of these 
 Tables contain every known British genus, zoologically or systematically placed, 
 with the number of species in each, showing their broad distribution through 
 time. The remaining 105 Tables are devoted to the analysis, relation, 
 historical value, and distribution of specific life through each group of strata. 
 These tabular deductions, as well as the Palseontological Analyses through the 
 text, are, for the first time, fully prepared for English students. " Extract from 
 Author's Preface. 
 
 %* PROSPECTUS of the above important work perhaps the MOST ELABORATE of 
 its kind ever written, and one calculated to give a new strength to the study 
 of Geology in Bi itain may be had on application to the Publishers. 
 
 It is not too much to say that the work will be found to occupy a place 
 entirely its own, and will become an indispensable guide to every British 
 Geologist. 
 
 " No such compendium of geological knowledge has ever been brought together before." 
 Westminster Review. 
 
 " If PROF. SKELEY'S volume was remarkable for its originality and the breadth of its views, 
 Mr. ETHERIDGE fully justifies the assertion made in his preface that his book differs in con- 
 struction and detail from any known manual. . . . Must take HIGH RANK AMONG WORKS 
 OF REFERENCE." Athenceum. 
 
 LONDON: EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 43 
 
 THIRD EDITION, Revised by Mr. H. Bauerman, F.G.S. 
 
 ELEMENTS OP METALLURGY; 
 
 A PRACTICAL TREATISE ON THE ART OF EXTRACTING METALS 
 FROM THEIR ORES, 
 
 BY J. ARTHUR PHILLIPS, M.lNST.C.K, F.C.S F.G.S., <tc., 
 
 AND 
 
 H. BAUERMAlsr, Y.P.G.S. 
 
 With Folding Plates and many Illustrations. Med. Svo. 
 Handsome Cloth, 36s. 
 
 GENERAL CONTENTS. 
 
 Refractory Materials. 
 
 Fire-Clays. 
 
 Fuels, &c. 
 
 Aluminium. 
 
 Copper. 
 
 Tin. 
 
 Antimony. 
 
 Arsenic. 
 
 Zinc. 
 
 Mercury. 
 
 Bismuth. 
 
 Lead. 
 
 Iron. 
 
 Cobalt. 
 
 Nickel. 
 
 Silver. 
 
 Gold. 
 
 Platinum. 
 
 *** Many NOTABLE ADDITIONS, dealing with new Processes and Developments 
 will be found in the Third Edition. 
 
 " Of the THIRD EDITION, we are still able to say that, as a Text-book of 
 Metallurgy, it is THE BEST with which we are acquainted." Engineer. 
 
 "The value of this work is almost inestimable. There can be no question 
 that the amount of time and labour bestowed on it is enormous. . . . There 
 is certainly no Metallurgical Treatise in the language calculated to prove of 
 such general utility." Mining Journal. 
 
 '"Elements of Metallurgy ' possesses intrinsic merits of the highest degree. 
 Such a work is precisely wanted by the great majority of students and 
 practical workers, and its very compactness is in itself a first-rate recom- 
 mendation. The author has treated with great skill the metallurgical opera- 
 tions relating to all the principal metals. The methods are described with 
 surprising clearness and exactness, placing an easily intelligible picture of each 
 process even before men of less practical experience, and illustrating the most 
 important contrivances in an excellent and perspicuous manner. ... In 
 our opinion the best work ever written on the subject with a view to its 
 practical treatment." Westminster Review. 
 
 " In this most useful and handsome volume is condensed a large amount of 
 valuable practical knowledge. A careful study of the first division of the 
 book, on Fuels, will be found to be of great value to every one in training for 
 the practical applications of our scientific knowledge to any of our metallurgi- 
 cal operations." Atkenceum. 
 
 " A work which is equally valuable to the Student as a Text-book, and to 
 the practical Smelter as a Standard Work of Reference. . . . The Illustra- 
 tions are admirable examples of Wood Engraving." Chemical News. 
 
 LONDON: EXETER STREET, STRAND. 
 
44 CHARLES GRIFFIN & CO. '8 PUBLICATIONS. 
 
 SCIENTIFIC MANUALS 
 
 BY 
 
 W. J. MACQUORN RANKINE, C.E., LLD., F.R S., 
 
 Late Regius Professor of Civil Engineering in the University of Glasgow. 
 
 THOROUGHLY REVISED BY W. J. MILLAR, C.E., 
 
 Secretary to the Institute of Engineers and Shipbuilders in Scotland. 
 In Crown 8vo. Cloth. 
 
 I. RANKINE (Prof.): APPLIED MECHANICS: 
 
 comprising the Principles of Statics and Cinematics, and Theory of Struc- 
 tures, Mechanism, and Machines. With numerous Diagrams. Thirteenth 
 Edition, 12/6. 
 
 " Cannot fail to be adopted as a text-book. . . . The whole of the information is so 
 admirably arranged that there is every facility for reference." Mining Journal. 
 
 II. RANKINE (Prof.): CIVIL ENGINEERING: 
 
 comprising Engineering Surveys, Earthwork, Foundations, Masonry, 
 Carpentry, Metal-work, Roads, Railways, Canals, Rivers, Water-works, 
 Harbours, &c. With numerous Tables and Illustrations. Eighteenth 
 Edition, i6/. 
 
 " Far surpasses in merit every existing work of the kind. As a manual for the hands 
 of the professional Civil Engineer it is sufficient and unrivalled, and even when we say 
 this, we fall short of that high appreciation of Dr. Rankine's labours which we should 
 like to express." The Engineer. 
 
 III. RANKINE (Prof.): MACHINERY AND 
 
 MILLWORK : comprising the Geometry, Motions, Work, Strength, 
 Construction, and Objects of Machines, &c. Illustrated with nearly 300 
 Woodcuts. Sixth Edition, 12/6. 
 
 "Professor Rankine's ' Manual of Machinery and Millwork ' fully maintains the high 
 reputation which he enjoys as a scientific author ; higher praise it is difficult to award 10 
 any book. It cannot fail to be a lantern to the feet of every engineer. ' The Engineer. 
 
 LONDON : EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 45 
 
 PROF. RANKINE'S WORKS (Continued). 
 
 IV. RANKINE (Prof.): THE STEAM EN- 
 
 GINE and OTHER PRIME MOVERS. With Diagram of the 
 Mechanical Properties of Steam, Folding- Plates, numerous Tables and 
 Illustrations. Thirteenth Edition, 12/6. 
 
 V. RANKINE (Prof.): USEFUL RULES and 
 
 TABLES for Engineer? and others. With Appendix : TABLES, TESTS, 
 and FORMULAE for the. use of ELECTRICAL ENGINEERS ; comprising 
 Submarine Electrical Engineering, Electric Lighting, and Transmission 
 of Power. By ANDREW JAMIESON, C.E., F.R. S.E. Seventh Edition, 10/6. 
 
 " Undoubtedly the most useful collection of engineering data hitherto produced." 
 
 Mining Journal, 
 
 " Every Electrician will consult it with profit" Engineering. 
 
 VI. RANKINE (Prof.): A MECHANICAL 
 
 TEXT-BOOK, by Prof. MACQUORN RANKINE and E. F. BAMBKR, 
 C.E. With numerous Illustrations. Fourth Edition, g/. 
 
 " The work, as a whole, is very complete, and likely to prove invaluable for furnishing 
 a useful and reliable outline of the subjects treated of." Mining Journal. 
 
 %* THE MECHANICAL TEXT-BOOK forms a simple introduction to PROFESSOR RANKINE'S 
 SERIES of MANUALS on ENGINEERING and MECHANICS. 
 
 VII. RANKINE (Prof.): MISCELLANEOUS 
 
 SCIENTIFIC PAPERS. Royal 8vo. Cloth, 31/6. 
 
 Part I. Papers relating to Temperature, Elasticity, and Expansion of 
 Vapours, Liquids, and Solids. Part II. Papers on Energy and its Trans- 
 formations. Part III. Papers on Wave- Forms, Propulsion of Vessels, &c. 
 
 With Memoir by Professor TAIT, M. A. Edited by W. J. MILLAR, C.E. 
 With fine Portrait on Steel, Plates, and Diagrams. 
 
 " No more enduring Memorial of Professor Rankine could be devised than the publica- 
 tion of these papers in an accessible form. . . . The Collection is most valuable on 
 account of the nature of his discoveries, and the beauty and completeness of his analysis. 
 . . . The Volume exceeds in importance any work in the same department published 
 in our time " Architect. 
 
 LONDON: EXETER STREET, STRAND. 
 
46 CHARLES GRIFFIN & CO.'S PUBLICATIONS. 
 
 Royal 8uo, Handsome Cloth, 25s. 
 
 THE STABILITY OF SHIPS. 
 
 BY 
 
 SIR EDWARD J. REED, K.C.B., F.R.S., M.P., 
 
 KNIGHT OF THE IMPERIAL ORDERS OF ST. STANILAUS OF RUSSIA; FRANCIS JOSEPH OF 
 AUSTRIA J MEDJIDIE OF TURKEY ; AND RISING SUN OF JAPAN ; VICE- 
 PRESIDENT OF THE INSTITUTION OF NAVAL ARCHITECTS. 
 
 With numerous Illustrations and Tables. 
 
 THIS work has been written for the purpose of placing in the hands of Naval Constructors, 
 Shipbuilders, Officers of the Royal and Mercantile Marines, and all Students of Naval Science, 
 a complete Treatise upon the Stability of Ships, and is the only work in the English 
 Language dealing exhaustively with the subject. 
 
 The plan upon which it has been designed is that of deriving the fundamental principles 
 and definitions from the most elementary forms of floating bodies, so that they may be 
 clearly understood without the aid of mathematics : advancing thence to all the higher and 
 more mathematical developments of the subject. 
 
 The work also embodies a very full account of the historical rise and progress of the 
 Stability question, setting forth the results of the labours of BOUGUER, BERNOULLI, DON 
 JUAN D'ULLOA, EULER, CHAPMAN, and ROMME, together with those of our own Countrymen, 
 ATWOOD, MOSELEY, and a number of others. 
 
 The modern developments of the subject, both home and foreign, are likewise treated 
 with much fulness, and brought down to the very latest date, so as to include the labours not 
 only of DARGMES, REECH (whose famous Memoire, hitherto a sealed book to the majority 
 of English naval architects, has been reproduced in the present work), RISBEC, FERRANTY, 
 DUPIN, GUYOU, and DAYMARD, in France, but also those of RANKINE. WOOLLEY, ELGAR, 
 JOHN, WHITE, GRAY, DENNY, INGLIS, and BENJAMIN, in Great Britain. 
 
 In order to render the work complete for the purposes of the Shipbuilder, whether at 
 home or abroad, the Methods of Calculation introduced by Mr. F. K. BARNES, Mr. GRAY, 
 M. REECH, M. DAYMARD, and Mr. BENJAMIN, are all given separately, illustrated by 
 Tables and worked-out examples. The book contains more than 200 Diagrams, and is 
 illustrated by a large number of actual cases, derived from ships of all descriptions, but 
 especially from ships of the Mercantile Marine. 
 
 The work will thus be found to constitute the most comprehensive and exhaustive Treatise 
 hitherto presented to the Profession on the Science of the STABILITY OF SHIPS. 
 
 " Sir EDWARD REED'S ' STABILITY OF SHIPS ' is INVALUABLE. In it the STUDENT, new 
 to the subject, will find the path prepared for him, and all difficulties explained with the 
 utmost care and accuracy ; the SHIP-DRAUGHTSMAN will find all the methods of calculation at 
 present in use fully explained and illustrated, and accompanied by the Tables and Forms 
 employed ; the SHIPOWNER will find the variations in the Stability of Ships due to differences 
 in forms and dimensions fully discussed, and the devices by which the state of his ships under 
 all conditions may be graphically represented and easily understood ; the NAVAL ARCHITECT 
 will find brought together and ready to his hand, a mass of information which he would other- 
 wise have to seek in an almost endless variety of publications, and some of which he would 
 possibly not be able to obtain at all elsewhere." Steamship. 
 
 "This IMPORTANT AND VALUABLE WORK . . cannot be too highly recommended to 
 all connected with shipping interests." Iron. 
 
 " This VERY IMPORTANT TREATISE, . . . the MOST INTELLIGIBLE, INSTRUCTIVE, and 
 
 COMPLETE that has ever appeared." Nature. 
 
 "The volume is an ESSENTIAL ONE for the shipbuilding profession." Westminster 
 Review. 
 
 LONDON: EXETER STREET, STRAND. 
 
 
SCIENTIFIC AND TECHNICAL WORKS. 47 
 
 In Large Crown 8uo, Handsome Cloth, with Numerous 
 Illustrations, 7s. 6d. Second Edition. 
 
 M ETALLURGY 
 
 (AN INTRODUCTION TO THE STUDY OF). 
 
 BY 
 
 W. C. ROBERTS-AUSTEN, C.B., F.R.S., 
 
 CHEMIST AND ASSAYER OF THE ROYAL MINT ; PROFESSOR OF METALLURGY IN 
 THE ROYAL COLLEGE OF SCIENCE. 
 
 GENERAL CONTENTS. 
 
 RELATION OF METALLURGY TO 
 
 CHEMISTRY. 
 PHYSICAL PROPERTIES OF 
 
 METALS. 
 ALLOYS. 
 THE THERMAL TREATMENT 
 
 OF METALS. 
 FUEL. 
 
 MATERIALS AND PRODUCTS OF 
 METALLURGICAL PROCESSES. 
 
 FURNACES. 
 
 MEANS OF SUPPLYING AIR TO 
 FURNACES. 
 
 TYPICAL METALLURGICAL 
 PROCESSES. 
 
 ECONOMIC CONSIDERATIONS. 
 
 " No English text-book at all approaches this one either in its method of 
 treatment, its general arrangement, or in the COMPLETENESS with which the most 
 modern views on the subject are dealt with. Professor Austen's volume will be 
 INVALUABLE, not only to the student, but also to those whose knowledge of the 
 art is far advanced." Chemical News. 
 
 " INVALUABLE to the student. . . . Rich in matter not to be readily found 
 elsewhere. " Athenazum. 
 
 ' ' This volume amply realises the expectations formed as to the result of the 
 labours of so eminent an authority. It is remarkable for its ORIGINALITY of con- 
 ception and for the large amount of information which it contains. . . . The 
 enormous amount of care and trouble expended upon it. ... We recom- 
 mend every one who desires information not only to consult, but to STUDY this 
 work. " Engineering. 
 
 " Will at once take FRONT RANK as a text-book. Science and Art. 
 
 " Prof. ROBERTS-AUSTEN'S book marks an epoch in the history of the teaching 
 of metallurgy in this country." Industries. 
 
 LONDON: EXETER STREET, STRAND. 
 
CHARLES GRIFFIN & COSS PUBLICATIONS. 
 
 Medium 8vo, Handsome cloth, 
 
 HYDRAULIC POWER 
 
 AND 
 
 HYDRAULIC MACHINERY. 
 
 BY 
 
 HENRY ROBINSON, M. INST. C.E., F.G.S., 
 
 FELLOW OF KING'S COLLEGE, LONDON; PROF. OF CIVIL ENGINEERING, 
 KING'S COLLEGE, ETC., ETC. 
 
 TOtb numerous TKIloo&cuts, anD 43 Xitbo. plates. 
 
 GENERAL CONTENTS. 
 
 The Flow of Water under Pressure. 
 
 General Observations. 
 
 Waterwheels. 
 
 Turbines. 
 
 Centrifugal Pumps. 
 
 Water-pressure Pumps. 
 
 The Accumulator. 
 
 Hydraulic Pumping-Engine. 
 
 Three- Cylinder Engines and 
 
 Capstans. 
 
 Motors with Variable Power. 
 Hydraulic Presses and Lifts. 
 Movable Jigger Hoist. 
 Hydraulic Waggon Drop. 
 The Flow of Solids. 
 Shop Tools. 
 Cranes. 
 
 Hydraulic Power applied to Bridges. 
 Dock- Gate Machinery. 
 
 Hydraulic Coal-discharging 
 
 Machines. 
 Hydraulic Machinery on board 
 
 Ship. 
 
 Hydraulic Pile Driver. 
 Hydraulic Excavator. 
 Hydraulic Drill. 
 Hydraulic Brake. 
 Hydraulic Gun -Carriages. 
 Jets. 
 
 Hydraulic Ram. 
 Packing. 
 
 Power Co-operation. 
 Cost of Hydraulic Power. 
 Tapping Pressure Mains. 
 Meters. 
 
 Waste Water Meter. 
 Pressure Reducing Valves. 
 Pressure Regulator. 
 
 "A Book of great Professional Usefulness." Iron. 
 
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 Plates may be had on application to the Publishers. 
 
 LONDON: EXETER STREET, STRAND. 
 
 
SCIENTIFIC AND TECHNICAL WORKS. 49 
 
 SCHWACKHOFER and BROWNE: 
 
 FUEL AND WATER : A Manual for Users of Steam and Water. 
 By Prof. FRANZ SCHWACKHOFER of Vienna, and WALTER 
 R. BROWNE, M.A., C.E., late Fellow of Trinity College, Cambridge. 
 Demy 8vo, with Numerous Illustrations, $/. 
 
 GENERAL CONTENTS. Heat and Combustion Fuel, Varieties of Firing Arrange- 
 ments : Furnace, Flues, Chimney The Boiler, Choice of Varieties Feed-water 
 Heaters Steam Pipes Water : Composition, Purification Prevention of Scale, &c., &c. 
 
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 " Contains a vast amount of useful know ledge. . . . Cannot fail to be valuable to 
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 THE MECHANIC'S GUIDE : A Hand-Book for Engineers and 
 Artizans. With Copious Tables and Valuable Recipes for Practical Use. 
 Illustrated. Second Edition. Crown 8vo. Cloth, 7/6. 
 
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 Recipes The Steam Engine The Locomotive Appendix : Tables for Practical Use. 
 
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50 CHARLES GRIFFIN cfe CO.'S PUBLICATIONS. 
 
 Now Ready, Tenth Edition, Revised and Enlarged, Price 18s. 
 
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 A M A N U A L 
 
 OF 
 
 MARINE ENGINEERING: 
 
 COMPRISING 
 
 THE DESIGNING, CONSTRUCTION, AND WORKING OF 
 MARINE MACHINERY. 
 
 B-y .A.. E. SIE^-TODST, 
 
 Lecturer on Marine Engineering to the Royal Naval College^ Greenwich ; Member of the 
 
 Inst. of Civil Engineers; Member of Council of the Inst. of Naval Architects; 
 
 Member of the Inst. of Mech. 'Engineer?; <tc. 
 
 GENERAL CONTENTS. 
 
 Part I. Principles of Marine 
 Propulsion. 
 
 Part II.-Prineiples of Steam 
 
 Engineering. Part IV. -Propellers. 
 
 Part III. Details of Marine 
 Engines: Design and Cal- 
 culations for Cylinders, 
 
 Pistons, Valves, Expansion 
 Valves, &c. 
 
 Part V.-Boilers. 
 
 Part VI. Miscellaneous, 
 
 "In the three-fold capacity of enabling a Student to learn how to design, constiuct, 
 and work a modern Marine Steam-Engine, Mr. Seaton's Manual has NO RIVAL as 
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 results of mucn close study and 'practical work." Engineering. 
 
 " By far the BEST MANUAL in existence. . . . Gives a complete account of the 
 methods of solving, with the utmost possible economy, the problems before the Marine 
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 "The Student, Draughtsman, and Engineer will find this work the MOST VALUABLE 
 HANDBOOK of Reference on the Marine Engine now in existence." Marine Engineer. 
 
 LONDON: EXETER STREET, STRAND. 
 
SCIENTIFIC AND TECHNICAL WORKS. 51 
 
 SECOND EDITION, Revised and Enlarged. Pocket-Size, Leather, also for Office Use, Cloth, 12t 
 
 BOILERS, MARINE AND LAND; 
 
 THEIR CONSTRUCTION AND STRENGTH. 
 
 A HANDBOOK or RULES, FORMULA, TABLES, &c., RELATIVE TO MATERIAL, 
 
 SCANTLINGS, AND PRESSURES, SAFETY VALVES, SPRINGS, 
 
 FITTINGS AND MOUNTINGS, &c. 
 
 3foc tbe THse of all 
 BY T. W. TRAILL, M. INST. C. E., F. E. R K, 
 
 Engineer Snrveyor-in-Chief to the Board of Trade. 
 
 * # * In the New Issue the subject-matter has been considerably extended ; 
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 have been introduced, which have been specially prepared and computed for 
 the SECOND EDITION. 
 
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 " By such an authority cannot but prove a welcome addition to the literature of the subject. In the 
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 subject." Marine Engineer. 
 
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 Practical Engineer. 
 
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52 CHARLES GRIFFIN & CO.'S PUBLICATIONS. 
 
 SECOND EDITIOX. With very Numerous Illustrations. Handsome Cloth, 6a. 
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 THE THRESHOLD OF SCIENCE: 
 
 A VARIETY OF EXPERIMENTS (Over 400) 
 
 ILLUSTRATING 
 
 SOME OF THE CHIEF PHYSICAL AND CHEMICAL PROPERTIES OF SURROUNDING OBJECTS, 
 AND THE EFFECTS UPON THEM OF LIGHT AND HEAT, 
 
 BY 
 
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SCIENTIFIC AND TECHNICAL WORKS. 
 
 53 
 
 Tenth Annual Issue. Now Ready. 
 THE OFFICIAL YEAR-BOOK 
 
 OF THE 
 
 SCIENTIFIC AND LEARNED SOCIETIES OF GREAT 
 BRITAIN AND IRELAND. PRICE 7/6. 
 
 COMPILED FROM OFFICIAL SOURCES. 
 
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54 
 
 CHARLES GRIFFIN & CO.'S PUBLICATIONS. 
 
 EDUCATIONAL WORKS. 
 
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 PAGE 
 
 61 
 
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 60 
 60 
 
 59 
 
 57 
 
 SCHRADER and JEVONS, 
 
 F. B. JEVONS, . 
 
 Prof. RAMSAY, 
 
 Prof. RAMSAY, 
 
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 Rev. C. T. CRUTTWELL, 
 
 CRUTTWELL and BANTON, 57 
 
 DOERING and GRAEME, . 58 
 Prof. RAMSAY, . . 60 
 
 Prof. RAMSAY, . . 60 
 
 Dr. BRYCE, . . -55 
 Jos. CURRIE, . . -55 
 
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 TATION ON THE SCIENCE OF METHOD. (Encyclopedia 
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 C U R R I E (Joseph, formerly Head Classical 
 
 Master of Glasgow Academy) : 
 
 THE WORKS OF HORACE: Text from ORELLIUS. English 
 Notes, original, and selected from the best Commentators. Illustrations 
 from the antique. Complete in One Volume. Fcap Svo. Cloth, 5/. 
 Or in Two Parts : 
 
 Part I. CARMINA, 3/. 
 
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56 CHARLES GRIFFIN & CO.'S PUBLICATION'S. 
 
 CRAIK'S ENGLISH LITERATURE. 
 A COMPENDIOUS HISTORY OF 
 
 ENGLISH LITERATURE AND OF THE ENGLISH LANGUAGE 
 FROM THE NORMAN CONQUEST. With numerous Specimens. 
 By GEORGE LILLIE CRAIK, LL.D., late Professor of History and 
 English Literature, Queen's College, Belfast. New Edition. In two 
 vols. Royal 8vo. Handsomely bound in cloth, 25/. 
 
 GENERAL CONTENTS. 
 
 INTRODUCTORY. 
 
 I. THE NORMAN PERIOD The Conquest. 
 II. SECOND ENGLISH Commonly called Semi-Saxon. 
 
 III. THIRD ENGLISH Mixed, or Compound English. 
 
 IV. MIDDLE AND LATTER PART OF THE SEVENTEENTH CENTURY. 
 V. THE CENTURY BETWEEN THE ENGLISH REVOLUTION AND 
 
 THE FRENCH REVOLUTION. 
 
 VI. THE LATTER PART OF THE EIGHTEENTH CENTURY. 
 VII. THE NINETEENTH CENTURY (a) THE LAST AGE OF THE 
 GEORGES, (b) THE VICTORIAN AGE. 
 
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EDUCATIONAL WORKS. 57 
 
 WORKS BY REV. C. T. CRUTTWELL, M.A., 
 
 Late Fellow of Merton College, Oxford. 
 
 A HISTORY OF ROMAN LITERATURE: 
 
 From the Earliest Period to the Times of the Antonines. 
 
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 Companion Volume. Second Edition. 
 
 SPECIMENS OF ROMAN LITERATURE: 
 
 From the Earliest Period to the Times of the Antonines. 
 
 Passages from the Works of Latin Authors, Prose Writers, and Poets : 
 
 Part I. ROMAN THOUGHT : Religion, Philosophy and Science, Art 
 
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 Part II. ROMAN STYLE : Descriptive, Rhetorical, and Humorous 
 
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 ** KEY to PART II., PERIOD II. (being a complete TRANSLATION of 
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 A HISTORY OF EARLY CHRISTIAN LITERATURE: 
 
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58 CHARLES GRIFFIN & CO.'S PUBLICATIONS. 
 
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EDUCATIONAL WORKS. 59 
 
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 A HISTORY OF GREEK LITERATURE, 
 
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 BY FRANK BYRON JEVONS, M.A., 
 
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