LIBRARY OF THE UNIVERSITY OF CALIFORNIA. BIOLOGY R ELEMENTARY TEXT-BOOK OP ZOOLOGY GENERAL PART AND SPECIAL PART: PROTOZOA TO INSECT A. BY DE. C. QLAUS Professor of Zoology and Comparative Anatomy in the University of Vienna Director of the Zoological Station at Triexte TRANSLATED AND EDITED BY ADAM SEDOWICK, M.A., F.R.S. Fellow and Lecturer of Trinity College, Cambridge, and Examiner in Zoology in the University of London WITH THE ASSISTANCE OF F. G. HEATHCOTE, M.A. Trinity College, Cambridge OP THE [USflTBESITT)) SECOND EDITION VOL, I. WITH 706 WOODCUTS, NEW YORK MACMILLAN'& CO. LONDON SWAN SONNENSCHEIN & CO. PEEFAGE TO THE ENGLISH TRANSLATION, r UNDERTOOK the translation of Professor Glaus' excellent * " Lehrbuch der Zoologie " with a view of supplying the want, which has long been felt by teachers as well as students in this country, of a good elementary text-book of Zoology. Professor Glaus' works on zoology are already well known in this country ; and I think it will be generally admitted that they take the first place amongst the zoological text-books of the present day. It has been decided to publish the English translation in two volumes. The second volume, which begins with Mollusca, is in the press, and will, I trust, appear early in the autumn. The German has been, with one or two unimportant exceptions, closely followed throughout. These exceptions, and the few additions which I have thought it necessary to make, have in all cases been indicated by enclosure within brackets. I must ask the indulgence of the reader towards the errors and deficiencies of this translation. I trust that they will be found to be neither numerous nor important. I have to thank Mr. Heathcote for the assistance he has given me in the laborious work of translation. I am also indebted to Professors Newton and Foster, Dr. Gadow, and Mr. W. Heape for advice and assistance. ADAM SEDGWICK. TRINITY COLLEGE, CAMBRIDGE, 1884. TABLE OF CONTENTS. GENERAL PART. CHAPTER I. Page ORGANIZED AND UNOEGANIZED SUBSTANCES . . . 9 14 CHAPTER II. ANIMALS AND PLANTS ......... 1524 CHAPTER III. ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL , 21-131 INDIVIDUAL, ORGAN, STOCK . 24 Repetition of organs and parts of the body . , . . .25 CELLS AND CELL TISSUES 29 Nucleus and Nucleolus 29 Cell-membrane 29 Reproduction of Cells and division of Nucleus .... 30 1. Cells and Cell-aggregates . .32 Isolated cells', 6-. " * Incompleteness of the explanation . . T s 118 T TABLE OF CONTENTS. SPECIAL PART. CHAPTER VI. CHAPTER VIII. Page Page PROTOZOA .... 180 ECHINODERMATA . . 266 RHIZOPODA .... 181 CRINOIDEA . . . 286 Foraminifcra ... 184 Tesselata . . . . 289 Lobosa .... 185 Articulata . . . 289 Eeticularia ... 186 ASTEROIDEA . . . 290 Heliozoa .... Radiolaria 187 189 Stelleridea . Ophiuridea . 292 293 INFUSORIA .... 191 ECIIINOIDEA . 294 Flagellata ... 193 Cidaridea , . 296 Ciliata .... 198 Cypeastridca . . 296 Holotricha ... Heterotricha ... 204 205 Spatangidea . , 297 Hypotricha . . 205 HOLOTHUEOIDEA . . 297 Peritricha Suctoria .... Schizomycetida3 205 265 205 Pedata . Apoda . 299 299 GregarinidEe . . . 207 ENTEEOPNEUSTA . 229 CHAPTER VII. CHAPTER IX. CCELENTERATA 209 VERMES .... 303 "T^Spongiaria = Porifera PLATYHELMINTHES . 309 SPONGIA 221 Turbellaria . . . 309 Myxospongia . . 221 Rhabdoccela . Dendrocoela , . 313 314 Ceraospongia . 221 Trematoda . . 316 Halichondriai . 221 321 Hyalospongia . 221 Polystomea * 322 Calcispongia . . 222 Cestoda . 326 Cnidaria Nemertini . . . 339 Enopla . . . . 342 ANTHOZOA=ACTINOZOA . 223 Anopla . . . 342 Rngosa .... 230 NEMATHELMINTKES . 343 Alcyonaria 231 Nematoda . . 344 Hexactinia = Zoantharia . 231 Cha3tognatha . . 357 POLYPOMEDUSJE = HYDEOZOA 233 Acanthocephala . . 359 Hydromedusse . 236 ANNELIDA . 362 Eleiitheroblastcce Hydrocorallise . . Tubularise 240 240 241 Chcetopoda . . Polychseta 367 374 Campanularise . . . 241 Errantia . . * m 378 Trachymedusae . 242 Sedentaria . . . S80 Siphonophora . 243 Oligochseta . . . 382 Physophoridoe . 248 Terricolae . . t 385 Physalidae 249 Liroicolcs . . 385 Calycophoridee Discoidese 249 250 Gepliyrea, . . . . 386 Scyphomedusa3=Acalepha 251 Chastifera . 389> Calycoxoa 257 Achasta . . 392 Marsupialida . Discophora (Acraspeda) . 258 259 Hiriidinea, . . 394 CTENOPHOEA . . 261 ROTATOEIA . . 400 TABLE OF CONTEXTS CHAPTER X. ARTHROPODA. CRUSTACEA . Entomostraca Phyllopoda Branchiopcxla Cladocera Ostracoda Copepoda . Eucopepoda Branchiura Cirripedia Peduncnlata Operculata A bdominalia Apoda . Rkizooephala Malacostraca Arthrostraca Amphipoda Isopoda . Thoracostraca Cumacea Stomatopoda Schizopoda Decapoda Macrura Brachyura Gigantostraca Merostomata Xiphosura Trilobita . Linguatulida Acarina . Pygnogonida Pago Tardigrada , . . 496 Page Araneida .... 498 4U5 ' Tretrapneumones . . 504 411 Dipneumoiies ... 504, 416 Phalangiidas . . 505 41G Pedipalpi .... Scorpionidea . 506 508 418 Pseudoscorpionidca . 510 419 Solifugse .... 511 423 428 OXYCHOPHOE A 512 435 MYEIAPODA .... 514 43G Chilopoda. . 518 438 Chiloguatha , . . 520 445 HEXAPOD A- INSECT A 521 446 Thysanura . 553 446 446 Oithoptera . . . 534 446 Orthoptera genuina . . 556 447 Ortlioptera Pseudo-Neurop- tera .... 558 449 Neuroptera 562 451 - Planipennia . . 563 4.06 Trichoptera . 564 4GO Strepsiptera . . 565 4C9 Ehynchota 566 470 Aptera .... 567 472 Pliytophthires . 568 475 477 Homoptera-Cicadavia Hemiptera . 570 571 478 470 Diptera . 572 :r i <7 Pupipara . . . 575 479 Braehycera ... 575 480 Nemocera . 577 483 Aphaniptera ... 578 Lepidoptera . . 579 484 Coleoptera . 585 487 Hymenoptera . . . 590 489 Terebrantia . 594 495 Aculeata. . , . 695 GENEEAL PAST. CHAPTER I. ORGANISED AND UNORGANISED SUBSTANCES. IN the world, which is perceptible to our senses, we distinguish between living organised and lifeless unorganised bodies. The former (i.e., animals and plants) are endowed with the power of movement, and they remain the same in spite of manifold changes both of themselves as a whole and of their parts, and in spite of continual change of the matter entering into their composition. Unorganised bodies, on the other hand, are found in a condition of constant rest ; and although this rest is not necessarily fixed and unchangeable, yet they are without that independence of movement which manifests itself in metabolism. In the former we recognize an organisation, a composition of unlike parts (organs), in which the matter exhibits its activity in a fluid and dissolved form; in the latter we meet with a mass which is more uniform, though as far as the position and arrangement of the molecules are concerned, not always homogeneous, and in which the various parts continue in a state of resting equilibrium so long as the unity of the body remains undisturbed. The matter of unorganised bodies (for in- stance, of crystals) is in a state of stable equilibrium, while through the organised being a stream of matter takes place. The properties and changes of living bodies are strictly dependent on the physico-chemical laws of matter, and this is recognized more clearly as science advances; yet it must be admitted that we are entirely ignorant of the molecular arrangement of the material basis of a living organism, and it exists under conditions the nature of which is as yet unexplained. These conditions, which we may designate; as vital, without thereby calling in question their depen- dence on material processes, distinguish organisms from all un- jfO GENERAL PACT. organised bodies. They relate (1) to the mode of origin, (2) to the mode of maintenance, (3) to the form and structure of the organism. Living bodies cannot be manufactured by physico-chemical means from a definite chemical mixture under definite conditions of warmth,, pressure, electricity, etc. ; their existence rather presupposes, accord- ing to our experience, the existence of like or at least very similar beings from which they have originated. It appears that, in the present state of our knowledge, there is no evidence to show that an independent abiogenetic generation, (generatio cequivoca, spontaneous generation) actually takes place, even in the simplest and lowest forms of life ; although very recently some investigators (Pouchet) have been led by results of remarkable but equivocal experiments to the opposite view. The existence of the generatio cequivoca would offer a very important service to our contention for the physico-chemical explanation; it even appears to be a necessary postulate in order to explain the first appearance of organisms. The second and most important characteristic of organisms, and that on w r hich the very maintenance of life depends, is their metabolic poiver, i.e., the power which they possess of continually using up and renewing the matter composing the body. Every phenomenon of growth presupposes the reception and change of material constituents; every movement, secretion, and manifestation of life depend on the exchange of matter, on the breaking down and building up of chemical compounds. On this alternating destruction and renewal of the combinations of the body substance two properties necessary to living things depend, viz., the reception of food and excretion of waste prodiicts. It is the organic substances (so called on account of their occurrence in organisms), i.e., the ternary and quaternary carbon compounds (the former composed of carbon, hydrogen, and oxygen, the latter of these with the addition of nitrogen, and among the latter are included the albumins) which undergo the exchanges characterising metabolism ; they either (in animals) break up under the influence of oxidation into substances of simpler composition ; or (in plants) are built up by substitution from simpler inorganic substances. But just as the general fundamental properties (elasticity, weight, porosity) of organisms agree so closely with those of inorganic bodies, that it was possible to construct a general theory of the constitution of matter, so all the elements (fundamental substances which differ qualitatively, and are chemically incapable of further simplification) of organic matter are again found in inorganic nature. A vital ORGANISED AND UNOEGANISED SUBSTANCES. 11 element, i.e., an element peculiar to organisms no more exists than does a vital force working independently of natural and material processes. Also with reference to the method of arrangement of the atoms, organic and inorganic substances have been erroneously put in sharp contrast ; and the whole of the carbon compounds have been contemplated as the products of organisms only. Now, however, it has been shown for some time not only that the atomic arrangement and constitution of both are explained by the same laws, but also that a great many of the former (urea, alcohol, vinegar, sugar) can be artificially built up by synthesis from their elements. These facts point to the probability that many other organic substances will be synthetically produced, and among them, albumin ; and they also permit us to conclude that in the origination of organised bodies the same forces were in action which are sufficient for the formation of unorganised bodies. The functions peculiar to organisms, viz., metabolism, movement, growth, are accordingly to be referred to the properties of the chemical compounds composing them, and particu- larly to the complicated molecular arrangement of living matter. Nevertheless, this important property of living things, viz., meta- bolic action, may under certain conditions be temporarily suppressed, without thereby depriving the organism of the power of existence. By removal of water or of heat it is possible, in the case of many of the lower organisms and their germs, to suspend the vital processes for months and even years ; and then to restore the apparently life- less body to the full exercise ' of its vital properties by the simple addition of water or warmth (eggs of Apus, Ostracoda, Anguillula tritici, Rotifera frogs, water insects, plant seeds). Finally, the living body is distinguished by its entire form and by the manner in which its various parts are connected together ; in other words, by its organization. The form of a crystal, the in- organic individual, is unchangeable, and is bounded by straight lines meeting at determined angles, and by plane, rarely spherical surfaces, which are capable of mathematical expression. The shape of organisms,* on the other hand, "in consequence of the semifluid con- sistency of the material composing them, is less sharply determinable and is within certain limits variable. Life manifests itself as a con- nected series of ever-changing states ; and the movements of matter are accompanied by growth and change of form. * The fact that there are a number of solid excretion products of organisms (shells) whose form is mathematically determinable does not of course annrl this distinction. 12 GENERAL PART. The organism commencing as a simple cell, the egg or germ, develops by a gradual process of differentiation and change of its parts up to a definite point at which it has the power of reproducing itself ; finally it dies, and breaks up into its elements. The greater part of the substance composing organised bodies is more or less semifluid and liable to osmotic action, a condition which appears to be necessary both for the carrying on of chemical changes (corpora non agunt nisi solutd), and for the modification of the entire form of the organism ; it is not however homogeneous and uniform, but is composed of solid, semifluid, and fluid parts which exist as com- binations of elements of a peculiar form. Crystals do not possess heterogeneous units subordinated to one another, which, like the organs of living bodies, serve as instruments for the performance of different functions, but are composed of molecules of similar atomic constitution ; the absence of uniformity in their structure in differ- ent directions (planes of cleavage) being due to the arrangement of the molecules, and not to any difference in the molecules themselves. Organs again prove, on examination of their finer structure, to be built up of different parts .crt-ri^ix:-. ;'':. . W$A -f*^>K fv or tissues (organs of a ^3 /f^f^& lower order), and these S^' a H&%;? ^J^ & again are composed of the FIG. 1. a, young ova of a Medusa ; b, mother-cells ultimate unit of Cell, the of spermatozoa of a Vertebrate ; one of them pre- ce j^ rp] ie ce jj | ag ^ Q f a |] sented amoeboid movement. is to be traced bac to the germ cell (ovum, spermoblast) (fig 1.) The cell by its properties stands in direct contrast to the crystal, and potentially possesses the properties of the living organism. It consists of a small lump of a semifluid albuminous substance (proto- plasm), containing,- as a rule, a dense or vesicular structure, the nucleus, and is frequently surrounded by a peripheral structureless membrane. If the latter is not developed, the presence of life is indicated by a more or less pronounced amoeboid movement, the fluid protoplasm sending out and drawing in processes of a continually changing form. In this organised fundamental structure, from which all tissues and organs of animals and plants are developed, lie latent all the characters of the organism. The cell is, therefore, in a certain sense the first form of the organism, and indeed the simplest organism. While its origin points to the pre-existence of cells of a similar kind, its maintenance is rendered possible by metabolism. The cell has Its OKGAXISED AND UNORGANISED SUBSTANCES. 13 nourishment and excretion, its growth, movement, change of form, and reproduction. With participation of the nucleus it begets by division or endogenous cell formation new units like itself, and furnishes the material for the construction of tissues, for the for- mation, growth and change of the body. With justice, therefore, is the cell recognised as the special embodiment of life, and life as the activity of the cell. FIG 2,- Amoeba" (Protogenes) porrecta (after Max Schultze)! Nor is this conception of the significance of the cell as the criterion of organisation and as the simplest form of life contradicted by the facts that the nucleus also sometimes fails (so-called cytodes of Hseckel), and that bodies undoubtedly manifesting vital phenomena are known which are structureless under the highest power of the microscope. Many Schizomycetes (Micrococcus) are so small that it is difficult to distinguish them in some cases from the granules of precipitates, especially when they show only molecular motion [Brownean movements] (fig. 3). Consequently, the living protoplasm* with its unknown molecular arrangement, is the only absolute test of the cell and organism in general. While appreciating the essential differences which have been 14 GEXEEAL PAET. expressed in the above discussion of the properties of living things and unorganised bodies, we must not in our criticism of the relations between them lose sight of the fact, that in numerous lower forms of life, metabolism, and all the activities of life can be completely suppressed by the removal of warmth and water, without there- by injuring the capacity of the organism for continuing to live; and further, that in the smallest organisms, which are proved to be such by their capacity of repro- ducing themselves by their meta- bolism, and it is impossible, bv r means of the very strongest powers of the microscope, to detect any organization. Since, moreover, the organic matter composing such forms consist of combinations which can be produced by synthe- sis, independently of organization, \ye must allow that hypothesis a , . . , . _ , . , . . certain justification which asserts that the simplest forms of life have been developed from unorganised matter, in which the same chemical elements occur as are found in organisms. Since no fundamental difference has been shown to hold between the matter and force of crystals and those of organised beings, we might look upon the first appearance of life as essentially only the solution of a difficult mechanical problem (with Du Bois Reymond), were we not obliged to conclude that there is present even in the simplest and most primitive organisms the germs of sensation and consciousness, attributes which we cannot regard as simply the results of the movement of matter. PXG. s.-schizomycetes (after F. Cohn). a, Micrococcus ; I, Bacterium termo, Bacteria found in putrefying bodies both in motile and Zoogicea form. ANIMALS AND PLANTS. 15 CHAPTER II. ANIMALS AND PLANTS. THE division of living bodies into animals and plants rests on a series of ideas early impressed on our minds. In animals we observe free movements and independent manifestations of life, arising from internal states of the organism, which point to the existence of consciousness and sensation. In the majority of plants, which pass their lives fixed in the earth, we miss locomotion and independent activities indicative of sensation. Therefore we ascribe to animals voluntary movement and sensation, and also a mind which is the seat of these. Nevertheless these conceptions apply only to a proportionately narrow circle of organisms, viz., to the highest animals and plants. With the progress of experience, the conviction is forced upon us that the traditional conception of animals and plants needs, so far as science is concerned, to be modified. For although we find no difficulty in distinguishing a vertebrate animal from a phanero- gamous plant, still our conceptions do not suffice when we come to the simpler and lower forms of life. There are numerous instances amongst the lower animals in which power of locomotion and distinct signs of sensation and consciousness are absent ; while, on the other hand, there are plants which possess irritability and the power of free movement. Accordingly the properties of animals and plants have to be compared more closely, and at the same time the question has to be discussed, whether there are any absolute distinctive characters which sharply separate the one kingdom from the other. 1. In their entire form and organization there seems to be an essential contrast between animals and plants. Animals possess a number of internal organs of complicated structure, lodged within a compact outline ; while in plants the nutritive and excretory organs are spread out as external appendages, with a considerable superficial extension. In the one case there is found an inner, and in the other an outer position for the absorbent surface. Animals have a mouth for the entry of solid and fluid nutritive matters, which are digested and absorbed in the interior of an alimentary canal, into which open various glands, (salivary glands, liver, pancreas, etc). The useless solid remains of the food pass out through the anus as faeces. The nitrogenous waste material is excreted by a special urinary 16 GENEEAL PART. organ (kidney), mostly in a fluid form. For the movement and circulation of the fluid carrying the absorbed nutriment, there is a pulsatory pump (heart) and a system of blood vessels, while respira- tion is usually carried on in terrestrial animals by lungs, and in aquatic animals by gills. Finally, animals possess internally placed generative organs, and a nervous system, and sense organs for the production of sensation. In plants, on the contrary, the vegetative organs have a much simpler form. Roots serve to absorb fluid nutriment, while the leaves act as respiratory and assimilating organs, taking in and giv- ing out gas. The complicated systems of organs found in animals are absent, and a more uniform parenchyma of cells and vessels, in which the sap moves, composes the body of plants. The gener- ative organs also are placed in external appendages, and there are no nervous and sense organs. Nevertheless, the above mentioned differences are not universally found, but rather hold only for the higher animals and plants, and gradually disappear with the simplification of the organization. Even among vertebrates, and still more is it the case amongst mollusca, and the lower segmented animals, the respiratory and vascular organs are considerably simplified. The lungs or gills may fail as special organs, and be replaced by the whole outer surface of the body. The blood vessels are simplified, and sometimes they and the heart are absent, the blood being moved in more irregular streams in the body cavity and in the wall-less spaces in the organs. Similarly, the digestive organs are simplified ; salivary glands and liver may no longer be found as glandular appen- dages of the alimentary canal. The alimentary canal may become a blind, branched, or simple sac (Trematoda), or a central cavity, the walls of which are in contact with the body wall (Coelenterata). The mouth and alimentary canal may also fail (Cestodes), nourish- ment being taken in by osmosis through the outer walls of the body as in plants. Finally, nerves FIG. 4. Branch of a Polyparium of Corallium rubrum (after Lacaze Duthiers). P, Polyp. ANIMAL AND VEGETABLE TISSUES. 17 and sense organs are totally absent in many organisms, which are looked upon as animals, e.g., in the whole of the Protozoa. With such reduction of the internal organs it is easy to understand that the simpler lower animals, such as colonies of polyps and the Sipho- nophora, should often in their outer appearance and the manner of their growth resemble plants, with which they were formerly con- founded, especially when they at the same time lacked the power of free locomotion (Polyps, Hy- droids, figs. 4, 5). In these cases it is as difficult to limit the idea of " indi- viduality" as it is in the vegetable kingdom. 2. Between animal and vegetable tissues there exists also generally an important difference. While in the vegetable tissues the cells preserve their original form and independence, in the animal tissues they undergo very various modifications at the expense of their independence. Accordingly vegetable tissues consist of uniform cell - aggregates, the individual cells of which have sharply - marked bounda- ries; while in animal tis- sues the cells give rise to extremely different structures, in which the cells as such do not always remain recognisable. The reason for this unlike condition of the tissues must apparently be sought in the different structure of retained FlG- 5 -~ Pli y s P nora hydrostatica. Pn, Pneuma- tophore ; S, Swimming-bells ; T, Dactylozooid ? P, polypite or stomach with the tentacles, Sf. ; Nk, terminal swellings on the latter provided with thread-cells ; G, Clusters of gonophores ANIMALS AND PLANTS. the cell itself; the vegetable cell being surrounded outside its pri- mordial utricle by a thick non-nitrogenous cuticle, the cellulose capsule ; while the animal cell possesses a very delicate nitrogenous membrane, or instead of this only a more viscous boundary layer of of its own semi-fluid contents. Nevertheless, there are also vegetable cells provided only with a simple naked primordial utricle ; and, on the other hand, animal tissues which resemble vegetable tissues in the fact that the cells remain independent and develop a capsule (chorda dorsalis, cartilage, supporting cells in the tentacles of hydroids, fig. 6) FIG. 6. a, Vegetable parenchyma (after Sachs). I, Axial-cells from the tentacles of Cam- panularia. Neither can we, as has been done by many investigators, regard the multicellular composition of the body as a necessary sign of animal life. For not only are there many unicellular algae and fungi, but also animal organisms which are composed of one simple or complexly differentiated cell (Protozoa). Finally, it is not possible to see any reason why unicellular animals should ;not exist, especially when we consider that the cell forms the starting-point for the development of the animal body. 3. Least, of all can a test be found in the reproductive processes. In plants indeed we find a predominance of the asexual method of increase by spores and buds, but similar methods of increase are widely present amongst the lower and more simply organised ani- mals. Sexual reproduction is effected both in animals and plants by processes which are essentially similar; consisting in both of the fusion of the male element (spermatozoon) with the female element (ovum) ; and the form of these elements presents in both kingdoms a great agreement, at any rate they are in every case derived from cells. The structure and position of 'the generative organs inside the body, or as outer appendages of it, cannot be regarded as a distin- guishing mark, inasmuch as in both kingdoms the greatest difference prevails in this respect. METABOLISM: IN ANIMALS AND PLANTS. 19 4. The chemical constituents and the metabolic processes in animals and plants present, on the whole, important features of difference. Formerly great importance was attached to the fact that plants consist chiefly of ternary (non-nitrogenous) compounds, while animals consist of quaternary nitrogenous compounds ; and a greater impor- tance was attached in the former to the carbon, in the latter to the nitrogen. But ternary compounds are found to be largely present in the animal body, e.g., fats, carbohydrates ; while, on the other hand, quaternary proteids play an important part in those parts of a plant which are especially active in growth. Protoplasm found in the living vegetable cell is richly nitrogenous, and of an albuminous nature; and it agrees in its micro-chemical reactions with sarcode, the contractile substance of the lower animals. In addition, the modifications of egg albumen, known as fibrin, albumen, and casein, are also found in vegetable cells. Finally, it is not possible to mention any substance which is universally and exclusively found either in animals or in plants. Chlorophyll (green colouring matter of leaves) occurs in the lower animals (Stentor, Hydra, Bonellia), while, on the other hand, it is totally absent in Fungi. Cellulose, a peculiar non-nitrogenous substance found in the outer membranes of vegetable cells, occurs in the mantle of Ascidians. Cholesterin, and certain substances especially characteristic of nervous tL c s::e~, are also found in plants (Leguminosse). Of far greater importance is the difference in the nourishment and metabolic processes. Plants take up with certain salts (phosphates and sulphates of the alkalies and earths) more especially water, carbonic dioxide (carbonic acid), and nitrates or ammonia compounds, and build up organic compounds of a higher grade from these binary inorganic substances. Animals, in addition to taking up water and salts, require organic food, especially carbon compounds (fat) and nitrogenous, albuminous substances; which, in the cycle of metabo- lism, break down to nitrogenous waste products (amides and acids), kreatin, tyrosin, leucin, urea, etc.; uric acid, hippuric acid, etc. Plants exhale oxygen, whilst they are decomposing carbon dioxide by means of their chlorophyll under the influence of light, and are forming in their chlorophyll corpuscles organic substances from carbon dioxide and solutions containing combined nitrogen. Animals take up oxygen through their respiratory organs for the maintenance of their meta- bolism. The processes of metabolism and of respiration, therefore, in. the two kingdoms are indeed mutually determinant, but have an exactly opposite result. The life of animals depends on the analysis 20 ANIMALS AXD PLANTS. of complex compounds, and is essentially an oxidation process, by which potential energy is converted into kinetic (movement, produc- tion of heat, light). The vital activity of plants, on the contrary, is based, so far as it relates to assimilation, on synthesis, and is essentially a process of reduction ; under the influence of which the energy of warmth and light is stored up, kinetic energy being converted into potential. Nevertheless, this difference also is not applicable as a test in all cases. Recently the attention of investigators has been turned, especially by Hooker and Darwin,* to the remarkable nutri- tive and digestive processes in a group of plants which were first observed a hundred years ago (Ellis). The plants in question catch, after the manner of animals, small organisms, especially in- Fio.7.-Leafof'Droserarotundifolia, sects > and absorb fl>0m them through with partially contracted tentacles the glandular surface of their leaves the organic matter after a chemical process resembling animal digestion (leaves of the Sun-dew, Drosera rotundifolia, and the fly-catcher, Dioncea muscipula. Figs. 7 & 8). Many parasitic plants and almost all fungi have not, however, in general, the power of making organic substances from inorganic, but suck up organic juices ; and in taking up oxygen and giving out carbonic acid, they present a respi- ratory process resembling that found in animals. It was established by Saussure's observations that all plants require oxygen at certain intervals; that in those parts of plants which are not green, not possessing chlorophyll, and al. c o in the green parts in the absence of sunlight, i.e. at night, a consumption of oxygen and exhalation * Compare especially Ch. Darwin, " Insectivorous Plants." London. 1875. FIG- 8. Leaf of Diongea muscipula in expanded condition (after Darwin). MOVEMENT AND SENSATION AS TEST OF ANIMALS. 21 of carbonic acid goes on. In plants, therefore, together with the characteristic deoxidation process, there is always found a process of oxidation analogous to that occurring in animal me- tabolism; by which a part of the assimilated substances is again destroyed. The growth of plants is impossible without the con- sumption of oxygen and the production of carbonic acid. The more energetic the growth, the more oxygen is consumed, as indeed the germinating seed or the quickly unfolding leaf and flower buds rapidly consume oxygen and excrete carbonic acid. In this con- nection should be mentioned the fact that the movements of proto- plasm depend upon the inspiration of oxygen. The production of heat (in germination), also of light (Agaricus olearius) is accompanied by an active consumption of oxygen. Finally, there are organisms (yeast cells, Schizomycetes) which indeed manufacture both nitro- genous and albuminous compounds, but do not assimilate the carbon of carbonic acid, but rather derive the necessary carbon from pre- pared carbohydrates (Pasteur, Cohn). 5. Voluntary movement and sensation, according to the common view, is the chief characteristic of animal life. Formerly, the power of free locomotion was looked upon as a necessary property of animals ; and as a consequence of this the fixed colonies of Polyps were considered to be plants, until Peyssonnel brought forward proof of their animal nature, a view which by the influence of the great naturalists of the last century has gained general recognition. More recently, on the discovery of the existence of motile spores of algse, it was first recog- nised that plants also, especially at certain stages of their development (fig. 9), possessed the power of free locomotion, so that we are compelled to direct a ^, our attention to the signs v j ^jjj&j? \ by which the voluntary FiG>9 _ Zoosporeg>a|0fp ^ flrKm;6>of ^ nature Of the movement of Ulothrix; d, of Bedogonium; e, of Vaucheria can be decided for a dis- tinction between the respective movements of animals and plants. As such for a long time was regarded the contractile nature of the movement as opposed to the uniform movements of plants carried out with rigid bodies. In the place of muscles, which as a special tissue are absent in the ANIMALS AND PLANTS. FlG. 10. Zoospores of Aeihal'mm septicum after de Bary. a, in condition of hatching ; b, as mastigopods ; c, in the amoeboid stage; d, a piece of plasm-odium. lower animals, there is present an undifferentiated albuminous substance known as sarcode, the contractile matrix of the body. The viscous contents of vegetable cells, kno\vn as protoplasm, possesses likewise the power of contractility, and re- sembles sarcode in its most essential properties. Both present the same chemical reactions and agree in the fre- quent presence of cilia, vacuoles, and streams of granules. Pulsating spaces, the contractile vacuoles, are not ex- clusively a possession of sarcode, but may also occur in the protoplasm of vegetable cells (Gonium, Chlamydo- monas, Chcetophora). The contractility of the protoplasm of vegetable cells is, as a rule, limited by the cellulose membrane, but in the naked cells of Volvocina and Scqirolegnia, and in the aniceba-like forms occurring in the development of Myxomycetes, the contractile pow T er is as intense as in the sarcode of Infusoria and Rhizopoda. The amoeboid move- ments of the plasmodium of Myxomycetes (fig. 10) are not inferior in intensity to those of a genuine %, / Amoeba belonging to the Bhizo- II $ / poda, e.g., Amceba poly podia (prin- \ \\ ..... ,., //.// // ceps), (fig. 11). In these similar phenomena of movement of the lower animals and plants we seek in vain for any test of volition, the interpretation of which will depend upon the individual judgment of the observer. The faculty of sensation, which is inconceivable as a function of matter and which must be always FIG. ii.-Am<*ia Dactyiosphera poiypodia. pre-supposed wherever we have N, nucleus. Pv, contractile vacuole (after to do with voluntary movement, Fr E. Schulze). J ' can by no means be amrmed with certainty in all animal organisms. Many of the lower animals entirely lack a nervous system and sense organs, and, on stimulation, exhibit lEUITABILITY OE PLANTS. 23 but slight movements not more intense than those of plants. This irritability, however, appears widely present among the higher plants. The sensitive plants move their leaves on the application of mechani- cal stimuli (Mimosece), or bend like the sundew (Drosera, fig. 7) small knobbed processes of the leaf surface which are comparable to the tentacles of polyps. The fly-catcher (fiioncea, fig. 8) brings the two halves of the leaf together in a valve-like manner when touched by insects. The stamens of the Centaurea contract along their whole length on mechanical and electrical stimulation, and according to the same laws as do the muscles of the higher 'animals. Many flowers open and shut under the influence of light at certain times of the day. Accordingly irritability as well as contractility appears to be a property both of vegetable tissue and of the protoplasm of vegetable cells; and it is not possible to determine whether volition and sensation, which we exclude from these phenomena in plants, play a part in the similar sensory and motor phenomena of the lower animals. In none of the above-mentioned characteristics of animal and vegetable life, then, do we find any absolute test, and we are not in a position to indicate the presence of a sharp line between the two kingdoms. From the common starting-point of the contractile substance* animals and plants are developed in different directions ; at the beginning of their development they present many kinds of resem- blance, and it is only on their attaining a more complete organization that the full opposition 'between them is apparent. In this sense, without wishing to draw a sharp line between the two series ' of organization, we can define our conception of an animal by putting together all the characteristics distinguishing the direction of animal development. An animal, therefore, is to be defined as an organism provided with the power of free and voluntary movement, and with sensation; whose organs are internal, and are derived from a development of the internal surfaces of the body ; which needs organic food, inspires oxygen, changes potential energy into kinetic under the influence of oxidation processes in metabolism, and excretes carbonic acid and nitrogenous waste products. * The formation of an intermediate kingdom for the simplest forms of life is neither scientifically justified, nor from practical considerations desirable. On the contrary, the acceptance of the Protista would only double the difficulty; f~ determining the limit. 24 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. Zoology is the science which has animals for its subject, and which seeks to examine the phenomena of their structure and life, as well as their relations to one another and to the outer world. CHAPTER III. THE ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. In the foregoing comparison of animals and plants for the establishment of a correct idea of the meaning of the word "animal," the great variety and the numerous grades of animal structure have been hinted at. Just as the complex organism is built up from the ovum by a process of gradual differentiation, and often during its free life passes through conditions which lead in ascending series to an ever higher development of the parts and to a more complete performance of functions; so, if the animal kingdom be examined as a whole, there is apparent a similar law of gradually progressing development, of an ascent from the simple to the complex, manifest both in the form of the body and in the composition of its parts as well as in the completeness of the phenomena of life. It is true that the grades of animal structure do not, like those of the developing individual, follow the one upon the other in a single continuous series ; and the parallel between the developmental gradation of types in the animal kingdom as a whole and the suc- cessive conditions of an individual animal breaks down in so far as we distinguish in the former, as opposed to the latter, a number of types of animal structure often overlapping, but still, in their higher development, essentially different from each other. These we regard as the highest divisions of the system. INDIVIDUAL ORGAN STOCK. The animal organism, when viewed from a physiological and mor- phological stand-point, presents itself as an independent and indivisible unit, as a " complete individual." Amputated limbs or excised parts of the body do not develop into new animals; in fact we cannot usually remove a single piece of the body without thereby endanger- ing the life of the organism, for it is only as a complex of all its parts that the body can retain its full vital energy. With reference to the property of the indivisibility of the individual, we understand INDIVIDUAL. 25 by the term organ every part of the body which as a unit subordi- nate to the higher unit of the organism presents a definite form and structure, and performs a corresponding function ; that is to say, an organ is one of those numerous instruments on the combined work- ing of which the life of the individual depends. There are certainly among the simpler animals many instances in which the term individual in its usual sense cannot be rightly applied. In such cases we have to do with structures which from their development must be termed individuals, and represent indi- viduals, accordingly, in a morphological sense. A great many of them are, however, fused to a common stock, forming what is known as a colony, and are related physiologically to this, as organs are to an organism. They are accordingly incomplete or morphological indivi- duals, which are usually incapable of leading a separate existence ; and, when they differ from each other in form and function, dividing amongst themselves the labours, the performance of which is neces- sary for the maintenance of the whole colony, they always perish if separated from it. Such polymorphous * stocks of animals present the properties of individuals although they are morphologically aggregations of indi- viduals which behave physiologically as organs (fig. 5). On the other hand, groups of organs can acquire individual independence. In the animal body organs do not always remain single, but the same organ may be often repeated. The manner of the repetition is dependent on the kind of symmetry, which may be radiate or bilateral. In animals with radiate symmetry, the Radiata, it is possible to connect two opposite points of the body by an axis, which may be called the chief axis, and to divide the body by sections passing through this axis into a number of equivalent and symmetrical parts known as antimeres. The organs which are not repeated are situated in the chief axis of the body, while the other organs, which are uniformly repeated in each antimere, are situated peripherally. Each antimere contains, therefore, a definite group of organs and represents a secondary unit, which, together with its fellows and the central organs, constitutes the primary unit, i.e., the perfect animal. In a radiate animal a number of lines can be drawn at right angles to the chief axis, corresponding in number to the antimeres, and each passing along the middle of an antimere; such lines are known as radial. Similarly, a corresponding number of inter-radial lines * Vide K. Leuckart, " Ueber den Polymorphismus dor Individuen tmd die Erscheinung der Arbeitstheilung in der Natur." Giessen, 1851. 26 ORGANIZATION AND DEVELOPMENT OP ANIMALS IN GENEEAL. can be drawn, passing between the antimeres. A vertical section through a radial line divides the corresponding antimere into two FIG. I2a. Sea-urchin (diagrammatic). J, inter-radius with, the double row of interambulacral plates and the genital organs G ; E, radii with the double row of ambulacral-plates perforated by the ambulacral pores. A, anas. FIG. 126. Shell of a Sea-urchin seen from above. It, radius with the per- f orated plates ; J, inter-radius with the corresponding generative organs and their pores. equal parts, while a similar section through an inter-radial line divides one antimere from its neighbour. Radiate animals may have two, three, etc., radii; and in animals which possess an uneven number of radii, one radius and one inter-radius always fall in the same vertical plane (fig. I2a, b, and fig. 13). In animals with an even number of radii, on the con- trary, each vertical plane passes through two radii or two inter- radii. A vertical section passing through one radius would, if pro- longed, pass through the radius of the opposite antimere (fig. 14a). For example, an animal with four radii possesses four antimeres, each of which will be divided into two, by two radial vertical sections passing at right angles to each other through the chief axis; while they will all be separated from each other by two similarly directed inter-radial sections. Biradiate forms (the Ctenophora) possess, on the contrary, only two radii, which lie in a common vertical plane. A second vertical plane crossing the first at right angles passes through the inter-radii, and FIG. 13. Star-fish (diagrammatic). .sing process of division of labour ; which results in a clearer and more definite localization of the various functions, necessary for the maintenance of life, in special organs. The greater this specialization the more completely will each organ be able to discharge its special functions, and supposing a proper co-ordination between the working of all the organs, a great advantage accrues to the organism, which is thereby rendered capable of a higher and more complete life. Therefore we find, as a general rule, that the larger the body and the more complex the organization, the higher and more perfect is the life. In this relation, however, the form and arrangement of the organs which characterize the various groups (types), as well as the special conditions of life which are limited by them, must be taken into account as compensating factors. CORRELATION AND CONNECTION OF ORGANS. The organs of the animal body stand in a mutually limiting rela- tion to one another, not only in their form, size, and position, but also in their actions; for since the existence of an organism depends upon the blending of the individual performances of all its organs to a united manifestation, the various parts and organs must all, in * Usually known as segmentation cavity. ED. t Usually known as " body cavity," or " coalom." ED. DCCTKINE OF FINAL CAUSES. 61 a definite and regular manner, be adjusted and subordinated to one another. This relation of dependence, necessarily resulting from the conception of the organism, has been very suitably termed " Corre- lation " of organs ; and many years ago served for the establishment of several principles, the cautious application of which has been of great service to the comparative method. Each organ, in order that it may properly discharge the functions which are requisite for the maintenance of the entire machine, must comprise a certain number of working units, and consequently must have a certain size and possess a form dependent partly on its func- tions and partly on its relation with other organs. If an organ becomes abnormally enlarged it increases at the expense of the sur- rounding organs, and the form, size, and function of the latter become injuriously modified. From this is deduced the principle to which Geoffroy St. Hiliare gave the name if he was not the first to recognise it of the "principe du balancement des organes," and this enabled that investigator to establish the doctrine of " Abnormalites " (Teratology). The organs which are physiologically similar, i.e., organs which per- form in general the same function, as, for instance, the teeth or the alimentary canal or the organs of movement, undergo great and "various modifications; and the particular methods of nutrition and habits of life, as well as the external conditions which must be ful- filled if the life of any particular genus is to continue, depend upon the special arrangement and action of the individual organs. Given therefore the special form and arrangement of a particular organ or part of an organ, it is possible to arrive at conclusions concerning the special structure, not only of many other organs, but even of the entire organism, and to reconstruct to a certain extent the whole animal so far as its essential features are concerned. This was first done by Cuvier for many extinct Mammalia, with the aid of scanty fragments of fossil bones and teeth, in a masterly manner. If we regard the life of the animal and its maintenance, not as the result, but as the end sought, as the aim of all the special arrange- ments and actions of the individual organs and parts, we are led to the "principe des causes finales" (des conditions d' existence) of Cuvier, and consequently to the so-called teleological doctrine by which we certainly do not attain to a mechanico-physical explanation. However that may be, this theory, if it be regarded merely as an expression of the reciprocal relations which necessarily exist between the form and function of the parts and of the whole, and not in the Cuvierian sense as implying the existence of design, renders important and 52 . ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. indispensable service to the understanding of the complicated corre- lations and the harmonious adjustments in the organic world. The same plan of structure and arrangement of the organs is not found, as Geoffroy St. Hilaire asserted in his theory of analogies, in the whole animal kingdom ; but, on the contrary, there are, as Cuvier stated, several plans of organization or types. The term 'Type" was applied by Cuvier to the chief, i.e., the most compre- hensive and general divisions of his system; and each type was distinguished by the sum of the characters of its form and structure. In the essential characteristics of their structure, the higher and lower members of the same type agree, while in the unimportant details they present the most marked differences. The different types themselves do not represent absolutely isolated groups, nor groups which are exactly equivalent to one another, but in a greater or less degree they are related to one another ; this is evident after an examination of the lower forms and a careful comparison of the developmental histories. To morphology belongs the task of pointing out the identity of plan under the most diverse conditions of organization and habits of life, not only among animals of the same group but also between those of different groups. This science has for its object the determination of homologies, as opposed to analogies which concern the similarity of function, i.e., the physiological equivalence of organs found in different groups, e.g., the wing of a bird and that of a butterfly. That is to say, it has to trace back to the same primitive structure parts of organisms belonging to the same or different groups, which with a different structure and under deviating conditions of life discharge different functions ; as, for example, the wing of a bird and the fore-limb of a mammal ; and so to show their morphological equivalence. In the same way the organs of similar structure which are repeated in the body of the same animal, e.g., the fore and hind limbs, are designated as homologous. THE STRUCTURE AND FUNCTION OF THE COMPOUND ORGANS. The vegetative organs comprise the organs of nourishment which are necessary for all living organisms, whether animal or vegetable. In the former, however, they gradually and in the most intimate connection with the progressive development of the animal functions, attain a higher and more complicated structure. In animals, the reception of food is followed by its digestion. The substances to be assimilated, which have been made soluble by digestion, enter a DIGESTIVE ORGANS. 53 nutrient fluid (blood) which permeates the body, and is carried in more or less definite tracts to all the organs. To the latter the blood yields its ingredients, and receives from them such decom- position products as have become useless, and carries them away to be excreted in definite organs. The organs which serve for the performance of the different functions of nutrition and excretion FIG. 41. Rotalia veneta (after M. Schultze) wibh a diatora caught in the pseurtopodial network. consist of the apparatus for the reception of food and for its diges- tion, and for blood formation ; and of the organs of circulation, respiration, and of excretion. Digestive organs. Even animals which have only the value of a single cell (Protozoa) swallow solid particles of food. This is effected 54 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. in the simplest cases, as in the Amcebse and Rhizopoda, by prolon- gations of the sarcode (pseudopodia) surrounding the foreign body (fig. 41). In the Infusoria, which are covered by a firm cuticle, there is a central semi-fluid mass of sarcode (endoplasm), which is distinct from the more compact peripheral layer of sarcode (ecto- plasm), and which receives the nutrient substances through the mouth and digests them. Rows of larger cilia are pretent, which eerve the purpose of procuring food (adoral ciliated zone of the Ciliata) (fig. 42). FIG. 42. Stylonycliia mytilug (after Stein) viewed from the ventral surface ; Wz, adoral zone of cilia; C, contractile vacuole; N, nucleus; JV',nucle- olus (paranucleus) ; A t anus. FIG. 43. Longitudinal section through the body of an Anthozooid (Octactinia). M, stomachic tube with the mouth open- ing in the centre of the feather-like tenta- cles ; Mf, mesenteric folds ; G, genital organs. Among the animals with cellular differentiation (Metazoa\ the internal cavity of the body in the Ccelenterata (morphologically identical with the alimentary cavity and not with the body cavity of other animals) functions as a digestive cavity, and its peripheral adially arranged portions as a system of vascular canals (gastro- ALIMENTARY CAXAL. 55 vascular canals). In the larger Polyps (Anthozoa) a tube derived from an invagination of the oral disc projects into the central part of the digestive cavity. This is known as the stomach of the polyp, although it serves entirely for the introduction of food, and should be called rather the buccal or O3sophageal tube (fig. 43). Organs for the prehension of food are found even with this simple digestive system. For near the mouth are placed radially or bilate- rally arranged appendages or processes of the body, which set up RK FIG. 44. Aurelia aurita seen from the oral surface. MA, the four oral tentacles with the mouth in the centre ; Gk, genital folds; GH, opening of the genital pouches ; Rk, mar- ginal bodies ; KG, radial canals ; T, tentacles at the margin of the disc. currents to convey small particles of food, or as tentacles seize foreign bodies and convey them to the mouth (Polyps, Medusae) (fig. 44). Such appendages serving for the capture of prey may also be placed further from the mouth (tentacles of Medusa, Siphonophora, Ctenophora). When the digestive cavity acquires a wall distinct from the body wall, and usually separated from the latter by the body cavity (ex- cepting the parenchymatous worms), it appears in the simplest cases as a blind tube, which may be either simple, bifurcated, or branched 56 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. (fig. 45), with sharply marked off pharyngeal structures (Trematoda, Turbellaria), or as a tube communicating with the exterior by an anus (fig. 46). In the last case it becomes divided so as to lead to the distinction of three parts (1) of the fore-gut (oesophagus) for the reception of the food, (2) of the mid-gut for the digestion of the food, and (3) of the hind-gut for the expulsion of the undigested remains of the food. Sometimes the alimentary canal aborts ; and, as in the mouthless Protozoa (Opalina), the mouth opening may be absent (Acanthocephala, Cestoda, Rhizoce- phala). In the higher animals, usually, not only is the number of the divisions greater, but their shape and structure becomes more com- plicated. The organs for the seizure of food also become more complicated, and the appendages placed nearest the mouth of ten become modified to subserve this func- tion. A special chamber, the buccal cavity, becomes marked off from the fore-gut, in front of or within which hard structures, such as jaws and teeth, for the seizure and mastication of the food are placed ( Vertebrata, Gastropoda); and into which secretions (salivary) having a digestive function are poured. The masticatory organs are sometimes placed completely outside the body in front of the mouth, and consist of modi- fied limbs ( Arthropoda), which in the parasites are metamorphosed into structures for piercing and sucking ; or they may have shifted so as to lie entirely within the pharynx (Rotifera, errant Annelids.) or in a muscular dilatation of the posterior end of this organ. At this place there is usually developed a widened chamber, the stomach, which by FIG. 45. Alimentary canal of Distomum hepaticum (after R. Leuckart) ; D, alimen- tary canal ; 0, mouth. FIG. 43. Alimentary canal of a young nematode. O, mouth ; Oe, fore-gut (oesophagus) with pharyngeal dilatation, Ph ; D, mid-gut; A, anus. INTESTINE. 57 MI) Al>\ repeated mechanical action (masticatory stomach of Cray-fish) or by the secretion of digestive fluids (pepsin) furthers digestion; or it may, as in birds, subserve both these functions. From the stomach the food passes into the mid-gut. Dilatations and out-growths of the buccal cavity give rise to cheek and throat pouches, of the ceosphagus to the crop, of the stomach to blind sacs which serve as reservoirs for the food (stomach of Ruminants) (figs. 47 & 48). In the middle section of the alimentary ca- nal,or intestine, the digestive processes, al- ready c o m - menced in the mouth by the action of the salivary secre- tion and con- tinued in the stomach by the action of the pepsin of the gastric juice (upon albumins in an acid solution), is completed. The food constituents which have been so far unacted upon (chyme) are in the intestine submitted to the action of the secretions of the liver, pancreas, and intestinal glands, and by them converted into the chyle, \vhich is absorbed by the intestinal walls ; the albumins being converted, as in the stomach, into soluble FIG. 49. Alimentary oanai of modifications by the action of trypsin a butterfly. 7? proboecis (ma- / act i n g however, only in alkaline solutions). xillSB) &2?, Sfilivsxy 2n.Eincls ; ^ * oe, ossophagus; s, sucking The intestine often attains a great length, and becomes divided into regions possessing a different structure ; e.g., in the intestine of mammals three regions can be distinguished duodenum, jejunum, and ileum. Its surface is, as a rule, increased by the develop- ment of folds and villi, and sometimes of outgrowths. Amongst FIG. 47. Alimentary canal and ac- cessory glands of a caterpillar. O, mouth ; Oe, oesophagus ; Sp D, salivary glands; Se, spinning glands ; MD, intestine (mid-gut) ; AD, rectum (hind gut) ; MG, Mal- pighian tubes. stomach ; Mg, Malpighian tubules; Ad, rectum. 58 OBGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEKAL. the Invertebrata it is often possible to distinguish an anterior especially widened portion of the intestine, which receives the hepatic secretion and is called stomach from the posterior, narrower, and longer section, which is known as intestine. The hindermost section of the alimentary canal or hind gut, which is not always sharply marked off from the intestine, is especially concerned with the collection and expulsion of the undigested remains of the food, or faeces. It may also possess csecal appendages attached to its anterior part, and possessing a digestive function. In the lower animals it is a small structure, but in the higher animals it at- tains a much more considerable length, and receives anteriorly one (Mammalia) or two (Birds) caeca, and it may be sub-divided into two parts, known as large intestine and rectum ; in the Vertebrata its hind end receives the ducts of various glands (kid- ney, generative organ*, anal glands). It may in addition dis- charge other functions, e.g., a respiratory (larvae of Libellulidae) or a secretory function (larva of Ant Lion). The salivary glands, liver, and pancreas are to be regarded as outgrowths of the alimentary canal which have become diffe- 0r Fio. 4'J. Alimentary canal of a bird. Of, oesophagus ; A", crop ; Dm, proventriculus ; Km, gizzard ; D, small intestine ; P, pan- creas placed in the loop of the duodenum ; .ff, liver; C, the two cseca; f, ureter; Ov, oviduct; Ad, large intestine; Kl, cloaca. rentiated into glands. The secretion of the salivary glands is poured into the buccal cavity, and there performs two functions (1) it dilutes the food, (2) it has a chemical action upon it, converting the starch into sugar : they are absent in many aquatic animals and are especially developed in herbivorous animals. ORGAXS OF CIRCULATION. 59 Gt, The liver, distinguished in the higher grades of development by its great size, is an appendage of the first part of the small intestine (duodenum). The first trace of it is met with in the lower animals in the form of a characteristically coloured part of the cellular covering of the gastric cavity or intestinal wall (Ccelenterata, worms). In the higher animals it has at first the form of a small blind sac (small Crustacea) ; this, by a process of branching, is con- verted into a complicated struc- ture composed of ducts and folli- cles, which may become connected together in very different ways so as to give rise to an apparently compact organ. Nevertheless, it must be remembered that, in the different groups of animals, glands, which differ both mor- phologically and physiologically, are included under this term, "liver." While in the Verte- brata the liver, as a bile-pro- ducing organ, possesses no known relation to digestion, in the In- vertebrata the secretions of many glands, which are generally called " liver," but which would be more appropriately termed hepato- pancreas, exercise a digestive action upon starch and albumen, and at the same time contain bye-products and colouring mat- ters similar to those found in the bile of Vertebrates (Crustacea, Mollusca). The Organs of Circulation. The nutrient material or chyle re- sulting from digestion is distributed by a system of spaces to all parts of the body. Excluding the Protozoa, in which the distribution of nutrient material is effected in the same manner as in the cell or tissue unit, the simplest form of vascular system in animals with cellular tissues, i.e., in the Metazoa, is found in the Ccelenterata. In these animals the digestive cavity itself extends to the extreme periphery of the body, and serves to distribute the nutritive fluids Coe FIG. 50.- Alimentary canal of Man. Oe, oesophagus; M, stomach; I, spleen; _HT V liver ; Gb, gall bladder ; P, pancreas ; DH, duodenum receiving the bile and pan- creatic ducts ; J7, ileum ; Co, colon ; Coe, caecum with vermiform process, Pv; -B, rectum. 60 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. (gastro-vascular system of Polyps, so-called vessels of Medusae and Ctenophora). The so-called stomach of the Anthozoa is simply an invagination of the body wall into the central cavity of the animal, and functions only as oasophagus. When a distinct alimentary canal is present, the chyle is absorbed by the walls of the gut, and passed through them into the ccelom or space developed between the gut and body walls (into the general FIG. 51. Dapliiiia with simple heart. C, the slit -like opening on one side is seen; Z>, alimentary canal; I, liver; A, anus; G, brain; O, eye; Sd, shell gland; Sr, brood pouch placed dorsally beneath the carapace. tissue of the body in the acoelornate parenchymatous worms), and there gives rise to a fluid, the blood, in which (with some few exceptions) corpuscles (cellular structures produced in the organism) are found. In this space, or in a system of lacunae derived from it, the blood circulates. Primitively its movements are quite irregular, taking place with each movement of the body (as in many worms), and are effected chiefly by the contractions of the somatic muscles HEART OF IXYEUTEBBATES. 61 /Ascaris), but also by the movements of other organs, e.g., the alimentary canal (Cyclops). At a higher stage of development a rudiment of the central organ of the circulation appears, in that a special section of the blood path acquires a muscular investment, and as a pulsating heart, comparable to a force and suction-pump. FIG. 52. Male of Branchipus stagnalis with many- chambered heart or dorsal vessel Sg, the lateral openings in which are repeated in every seg- ment. D, intestine ; M, mandible ; Sd, shell gland ; Sr, branchial appendage of the llth pair of legs ; T, testis. FIG. 53. Heart of a Copepod (Calanella) with an ante- rior artery, A. Os, cstia ; V, valves at the arterial ostium ; M, muscle. maintains a continuous circulation of the blood. The heart is either sac-shaped, with two lateral or one anterior slit-like opening (Daphnia, Calanus) (fig. 51), or elongated and divided into successive chambers and perforated by many pairs of slit-like openings (Insects, Apus) (fig. 52). As a rule, each chamber possesses a pair of laterally placed G2 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. ostia, provided with lip-like valves, which act so as to allow the blood only to enter the organ. From the heart, as central organ of the circulation, well denned canals, the blood vessels, are then developed, which in the Invertebrata may alternate with lacunae not provided with walls. In the simplest cases it is only the tracts along which the blood travels from the heart which are provided with independent walls, and developed into blood vessels (marine Copepoda, Calanella, fig. 53). At a higher stage of development not only do these efferent vessels acquire a more complicated structure, but a part of the lacuna-system, especially in the neighbourhood of the heart, acquires a membranous invest- ment, and gives rise to vessels which carry the blood back to the Accl FIG. 54. Heart and blood vessels and gills of the crayfish. C, heart, in a blood sinus ; with Ps several pairs of ostia; Ac, cephalic aorta; A.ab, abdominal aorta; As, sternal artery. pericardial sinus, from which it passes through the venous ostia into the heart (Scorpions, Decapods) (fig. 54). In other cases (Molluscs) the blood flows directly from the afferent vessels into the heart, the walls of the vessel being directly continuous with the walls of the heart. The heart in such cases consists of two chambers, the one known as auricle serves for the reception of the returning blood, the other known as ventricle for its propulsion (fig. 55). The vessels passing from the ventricle and carrying the blood from the heart are called arteries ; those returning the blood to it are called veins, and, in the higher animals, are distinguished from the arteries by their thinner walls. Between the ends of the arteries and the beginning of the veins the body cavity intervenes either as HEART OF VEBTEBKATES. 63 a blood sinus or as a system of blood-lacunae; or the arteries and veins are connected by a network of delicate vessels, the capillaries. If the connection between arteries and veins is effected by capillaries in all parts of the vascular system, and the body cavity, as in the Vertebrata, no longer functions as a blood sinus, the vascular system is spoken of as being completely closed. In the Vertebrates and segmented worms the vascular system ob- tains a considerable development before a true heart is differentiated in it. At first rhythmically pulsating sections, very frequently the FIG. 55. Nervous system and circulatory organs of Paludina vivipara (after Leydig). F. tentacle ; Oe, oesophagus ; Cg, cerebral ganglion with eye ; Pg, pedal ganglion with adjacent otocyst ; Vg, visceral ganglion ; Phg, pharyngeal ganglion ; A, auricle of heart ; Ve, ventricle ; Aa, abdominal aorta ; Ac, cephalic aorta ; V, vein ; Vc, afferent vessel. r, gill. dorsal vessel, or the lateral vessels connecting this with the ventral vessel (fig. 56), serve for the propulsion of the blood. Similarly amongst the Vertebrata, the lancelet (Amphioxus) possesses no distinctly differentiated muscular heart, the function of that organ being discharged by various parts of the vascular system which are contractile. The arrangement of the vessels supplying the pharyngeal section of the alimentary tract, which has a respiratory function and is known as the branchial sac, admits of a comparison with the vascular arrangement of the segmented worms, and repre- sents the simplest form of the vertebrate vascular system. The longitudinal vessel which runs in the ventral wall of the branchial sac gives off numerous lateral branches, which ascend in the branchial walls. These lateral vessels are contractile at tkeir point of origin (54 OEGANIZATION AND DEVELOPMENT OF AXIMALS IN GEXEIIAL. from the ventral vessel. The anterior pair, placed behind the mouth, unite beneath the notochord to form the root of the median body artery (descending or dorsal aorta) which receives the hinder succes- sive pairs of lateral vessels. This dorsal artery gives off branches to the muscles of the body wall and the viscera, from which the venous blood in part is returned to the ventral pharyn- geal vessel; part of it, however, before reaching the latter, traverses a capillary network in the liver. t \l\J^ From the- hinder part of the ventral pha- ryngeal vessel there is developed, in the higher Yertebrata, the heart, which at first has the shape of an S-shaped tube, but later acquires a conical form and becomes divided into auricle and ventricle. The former receives the blood returning from the body and passes it on into the more powerful ventricle, from which arises an anterior vessel, the ascending or cardiac aorta, presenting a swelling at its root, known as the aortic bulb. This vessel leads, by means of lateral vascular arches, the arterial arches, into the dorsal aorta, which passes backwards beneath the vertebral column, and supplies the body. Yalves placed at the two ostia of the | ventricles regulate the direction of the blood stream ; and they are so arranged as to prevent ^onhe^atc^rTysl'm an y Backward flow of blood from the cardiac ofanOiigochseteworm aorta into the ventricle in diastole, and from (Ssenuris) (after Ge- . . .. . . . . genbaur). in the dor- the ventricle into the auricle in systole,. sal vessel the blood j n consequence of the insertion of the respi- moves from behind forward ; in the ven- ratory organs on to the system oi the arterial f re arches, the latter, and at the same time the rows). H, heart-like structure of the heart, assumes various degrees MertLsse^ nSVerSe of complication. In fishes (fig. 57), four or five pairs of gills are inserted in the course of the arterial arches, which break up into a respiratory capillary net- work in the branchial leaflets. From this network the arterialised blood is collected into efferent branchial arches, the branchial veins, corresponding each to a branchial artery ; and these unite to form the dorsal aorta. In such cases the heart remains simple, and receives venous blood. PULMONARY CIRCULATION. With the appearance of lungs as respiratory organs (Dipnoi, Perennibranchiate Amphibia, larvae of Salamanders and Batra- chians) (fig. 58), the heart obtains a more complicated structure, in that the auricle becomes divided into a right and left division, the latter of which receives the arte- rialised blood, returning from the lungs by the pulmonary veins. The septum between the two divisions of the auricle may, how- ever, remain incomplete (Dipnoi, Proteus). The advehent pulmon- ary vessels, the pulmonary arte- ries, always proceed from the FIG. 57. Diagram of the circulate rf organs of an osseous fish. V, ventricle ; Ea, aortic bulb with the arterial arches which carry the venous blood to the gills ; Ao, dorsal aorta into which open the vessels from the gills or branchial veins Ab. N, kidney ; Z>, alimen- tary canal ; Lk, portal circulation. FIG. 58. Gills (Br) and pulmonary sacs (P) of a perennibranchiate amphibian. Ap, pulmonary artery proceeding from the posterior of the four aortic arches. The other three lead to the three pairs of gills ; D, alimentary tract ; A, aorta. posterior vascular arch, which, as a rule, loses its relation to the branchial respiration. On the disappearance of the gills, which is completed during the metamorphosis in the Salamandrina and Batrachia, the pulmonary 5 66 OEGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEHAL. arteries obtain a much more considerable size and become the direct continuation of the hindermost pair of vascular arches, while the remaining and primitively most important portions of the latter, i.e. the portions leading to the dorsal aorta, are reduced to rudimentary ducts (Ductus Botalli) or completely obliterated. Contemporaneously with these changes there appears a fold in the lumen of the ventral or cardiac aorta, leading to a separation of the posterior vascular arch (pulmonary artery), which now receives through the ventricle venous blood from the right auricle, from the system of anterior arches which give origin to the cephalic vessels and dor- sal aorta and receive arterial blood from the left auricle (mixed, how- ever, with venous blood in the ventricle) (fig. 59). In Reptiles the sepa- ration of the arterial from the venous blood is more complete, in that there is an incomplete ventricular septum which foreshadows the later division of the ventricle into a right and a left half. From \ FIG. 59. Circulatory organs of ike frog. P, left lung, right lung is removed ; Ap, pulmonary artery ; Vp, pulmonary vein ; Vc, vena cava inferior ; Ao, dorsal aorta ; A", kidney ; D, alimentary canal ; Lk t portal circulation. the left division arises the right aortic arch, which gives origin in its further course, to the arteries to the head (carotid arteries). A vessel to the lungs and a left aortic arch may also be distinguished. The left aortic arch and pulmonary artery receive only venous blood, while the right aortic arch, and therefore the carotids which proceed from it, receive principally arterial blood from the left side of the ventricle (fig. 60). The ventricular septum, and consequently the separation of tho right from the left ventricle, is found complete for the first time LYMPHATIC SYSTEM. Ao.s in the Crocodilia, and in these animals the right aortic arch arises from the left ventricle. But the separation of the arterial and venous blood is even now not quite complete, for at the point where the two aortic arches cross one another there is a passage (foramen Panizzse) leading from one into the other, and through which a communication may take place. It is only in Birds and Mammals, in which, as in the Crocodilia, the right and left ventricle are completely separated, that a separation between the two kinds of blood is completely effected (fig. 61). In Birds the right aortic arch persists, and the left entirely disappears ; while in Mammalia the opposite obtains, the left arch per- sisting and giving rise to the dorsal aorta. In these animals the blood is essentially diffe- rent from the chyle both in colour and composition, and there is present a special system of chyle and lymph vessels. This system origi- nates in simple tissue spaces, which are without walls, and its main trunks open into the vascular system. The con- tents are derived from the nutrient material absorbed from the intestine (chyle), and from the fluids which have transuded into the tissues from the capillaries (lymph), and they serve to renovate the blood. In the actual course of the lymph and chyle, i.e., in the lymphatic vessels themselves, are placed peculiar glandular organs, known as lymphatic glands (blood glands), in which the lymph receives its form elements (lymph corpuscles = white blood corpuscles). Organs of Respiration. The blood needs for the retention of its properties not only this continued renovation by the addition of nutrient fluids, but also the constant introduction of oxygen, with the reception of which is closely connected the excretion of carbonic FIG. 60. Heart and great vessels of a Chelouian. Ad, rigfat auricle; .4*, left auricle; Ao.d, right aortic arch ; Ao.g, left aortic arch ; Ao, aorta.; C, carotids ; Ap, pulmonary arteries. 68 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEA.L, acid (and water). The exchange of these two gases between the blood and the external medium is the essential part of the respiratory process, and is effected through organs which are suited for carrying on this process either in air or //V C 2-S > ~(^ V M i- n water. In the simplest cases the exchange of these two gases takes place through the general surface of the body ; and in all cases, even when special respira- tory organs are present, the outer skin also takes part in respiration. FIG. 61. Diagram of the circulation in an animal with a completely separated right and left ventricle, and a double circulation (after Huxley). Ad, right auricle receiv- ing the superior and inferior vense cava3, Vet, and Vci-, Dth, thoracic duct, the main trunk of the lymphatic system ; Ad, right auricle ; Vd, right ventricle ; Ap, pulmonary artery ; P, lung ; Vp, pulmon- ary vein ; As, left auricle ; Vs, left ven- tricle ; Ao, aorta ; D, intestine ; L, liver ; Vp', portal vein ; Lv, hepatic vein. FIG. 62. Diagram of the great arteries of a mammal with, reference to the five embry- onic arterial arches (after Eathke) . c, common carotids ; c', external carotid ; c", inter- nal carotid ; A, aorta. Ap, pulmonary artery ; Aa, aortic arch. Inner surfaces also may be con- cerned in this exchange, especially those of the digestive cavity and intestine, or, as in the Echi- noderms, in which a separate vascular system is developed, the surface of the whole body cavity. Respiration in water obviously takes place under far more un- favourable conditions for the introduction of oxygen than does the direct respiration in air, because it is only the small quantity of EESPIRATO2T ORGANS. 69 Ct oxygen dissolved in water which is available. Hence this form of respiration is found in animals low in the scale of life in which the metabolic processes are less energetic (worms, molluscs, and fishes). Organs of aquatic respiration, or gills, have the form of external appendages possessing as large a surface extension as possible. They consist of simple or antler- shaped or dendritically branched processes (fig. 63 a, &), or of FIG. 63a. Head and anterior body segments of a Eunice, viewed from the dorsal sur- f-ace. T, tentacles. Ct, tentacular cirrus. C, parapodial cirrus. Br, parapodial gill. lancet-shaped closely-packed leaves with a large surface extension (fig. 64). FIG. 61. Transverse section througn the gill of a Teleostean fish. 6, branchial leaf- let with capillaries ; c, branchial artery con- taining venous blood ; d, branohial vein con- taining arterial blood. a, branchial bar. FIG. 636. Transverse section through the body of Eu- nice. r, gill ; C, cirrus ; P, parapodium with a bundle of setae ; D, alimentary canal ; N, nervous system The organs of aerial respiration, on the contrary, are internal. They present likewise the condi- tion favourable for an exchange of gases between the air and the blood, viz., a large extent of surface. They have the form either of lungs or sir-barring tubes. In the first case (Spiders, Vertebrates) they consist of spacious sacs with alveolar or spongy 70 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. St- walls, traversed by numerous septa and folds which bear an extremely rich network of capillaries. The air tubes or tracheae (fig. 65) consti- tute a branched system of canals which extend throughout the whole body, and carry the air to all the organs. Thus instead of the respi- ratory pro- cess being localised, as it is in ani- mals with lungs, it is carried on in all tissues and organs of the body, which are surrounded by a fine tracheal network. Nevertheless, the air tubes in the case of the modification known as fan- tracheae present an approximation in their structures to lungs, in that the main stems, without further branching, give rise to flat hollow leaves. FIG. 6). Tracheje with fine branches (after Leydig). Z, cellular outer wall ; Sp, spiral thread. FIG. GG6. Lateral view of head and body of an Acridium. St, stdgmata ; T, Tympanum. Openings in the body wall are present, placing the organs of aerial respiration in communica- tion with the exterior. These openings may be numerous, and paired, placed symmetrically on the sides FIG. GGa. TracLeal sye tern of a Dipterous larva. Tr, Longitudi- nal stem of the right side with tufts of tra- cheae; St.', and St", anterior and posterior stigmata ; Mh, oral hooks. TEACHER. of the body (fig. 66 a, b) (stigmata of Insects, Spiders), or they may be more restricted in number, and communicate also with cavities of complicated structure which are used for other functions (nasal cavities of Vertebrates). In the aquatic larvae of certain Fro. 67a.- -Larva of an Ephemeral fly \vith seven pairs of trachea! gflis -T/, slightly magnified ; Tk, isolated trachea! gill strongly magnified. /la/ FIG. 676. Tracheal sys- tem at the sides of the alimentary canal of an Agrion larva (after L. Dufour). Tst, main tracheal trunk ; JTf, tracheal gills ; Na, the three simple eyes. Insects (Ephemeridse, Libellulidae) the tracheae may be without any external openings. In such cases processes of the body filled with a close network of trachese, which take up oxygen from the water, and are known as tracheal gills, are developed (fig. 67 a, b). In rare instances tracheal gills are developed on the wall of the rectum, and 72 OEOANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. thus acquire a protected position (rectal respiration of Aeschna, Libellula). In other respects the branchial and pulmonary respiratory pro- cesses are essentially the same. In the pulmonate snails (Lymnseus), the pulmonary cavity may be filled with water, and yet continue to function as a respiratory organ (in the young state and also under special conditions in the adult, the animal remaining permanently in deep water). With this fact before us of an air-breathing surface functioning as a gill, it will not surprise us to find that gills and branching folds of skin, which under normal circumstances serve for breathing in water, can, provided they be protected from shrivelling up and desiccation either by their position in a damp space or by their copious blood supply, function as lungs, and allow their pos- sessors to live and breathe on land (Crabs, Birgus latro, labyrintho- branchiate Fishes). A rapid renewal of the medium which carries the oxygen and surrounds the respiratory surfaces is of the greatest importance for the gaseous exchanges. We find, therefore, very often special arrangements, by which the removal of that part of the respiratory medium which has been deprived of oxygen and saturated with carbonic acid and the introduction of another portion con- taining oxygen and free of carbonic acid, is effected. In the simplest cases this renewal can, although not very efficiently, be brought about by the movements of the body, or by a continuous oscillation of the respiratory surfaces themselves ; a method which is especially common when the gills are placed in the region of the mouth and function also as organs of food prehension, e.g., the tentacles of many attached animals (Polyzoa, Brachiopoda, tubi- colous Worms, etc.) Very frequently the gills appear as appendages of the organs of locomotion, e.g., of the swimming or ambulatory feet (Crustacea, Annelids), the movement of which brings about a renewal of the respiratory medium around the gills. The move- ments become more complicated when the gills are enclosed in special chambers (Decapoda, Pisces), or when the respiratory organs are placed within the body, as happens in the case of tracheae and lungs, in which case also a renewal of the air is effected either by a more or less regular movement of neighbouring parts, or by rhyth- mical contractions and dilatations of the air-chamber, constituting the so-called respiratory movements. The term respiration is now not only applied to these movements so obvious to the eye in air- breathing animal Sj but also to the osmotic processes, secondarily ANIMAL HEAT. 73 dependent upon the entrance and exit of air, which effect the gaseous exchanges. Taken strictly in this sense it is an incorrect term, inasmuch as in the respiratory movements of animals pro- vided with branchial cavities we have to do with the entrance and exit of water. In the higher animals provided with red blood, the difference in the condition of the blood before and after its passage through the respiratory organs is so striking that it is possible to distinguish blood rich in oxygen from blood rich in carbonic acid, by the colour. The latter is dark red, and is known as venous blood ; the former, i.e., blood which has just left the gills or lungs, on the contrary, has a bright red colour, and is known as arterial blood. While the terms venous and arterial are used in an anatomical sense to express the nature of the blood-vessel, those carrying the blood to the heart being called venous, and those carrying it from the heart arterial, they are ako used in a physiological sense as an expression for the two conditions of the blood before and after its passage through the respiratory organs, i.e., to express the quality of the blood. Since, however, the respiratory organs may be inserted in the course of either the venous or arterial vessels, it is obvious that, in the first case, there must be venous vessels carrying arterial blood, (Molluscs and some Vertebrates), and, in the latter, arterial vessels carrying venous blood (Vertebrates). Animal heat. The intensity of respiration stands in direct relation to the energy of the metabolism. Animals which breathe by gills and absorb but little oxygen are not in a position to oxidise a large quantity of organic constituents, and can only transform a small quantity of potential into kinetic energy. They perform, therefore, not only a proportionately smaller amount of muscular and nervous work, but also produce in only a small degree the peculiar molecular movements known as heat. The source of this heat is to be sought, not, as was formerly erroneously supposed, in the respiratory organs, but in the active tissues. Animals in which thermogenic activities are small have no power of keeping independently their own internal heat when exposed to the temperature influences of the surrounding medium. This is also true of those air-breathing animals in which the metabolic and thermogenic activities are great, but which, in consequence of their small size, offer a relatively very large surface for the loss of heat by radiation (Insects). On account of the ex- changes of heat which are continually taking place between the animal body and the surrounding medium, the temperature of the 74 OEGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEBJLL. former must in such animals be largely dependent on that of the latter, falling and rising with it. Hence, most of the lower animals are poikilothermic,* or, as they have less appropriately been called, cold-blooded. The higher animals, on the contrary, in which, on account of their highly developed respiratory organs and energetic metabolism, the thermogenic activity is great, and which are protected from a rapid loss of heat by radiation by the size of their bodies and by the possession of a covering of hairs or feathers, possess the power of maintaining a constant temperature, which is independent of the rising and falling of the temperature of the surrounding medium. Such animals are designated homothermic, or warm-blooded. Since they require a high internal temperature, varying only within small limits, as a necessary condition for the normal course of the vital processes, or one may say for the maintenance of life itself, they must possess within themselves a series of regulators whose function is to keep the body temperature within its proper limits, when the temperature of the surrounding medium is high. This may be effected either by diminishing the production of internal heat (diminishing the metabolism) or by increasing the loss of heat from the surfaces of the body (by radiation, evaporation of secretions, cooling in water) ; and, on the contrary, when the temperature of the outer medium is too low, by increasing the production of internal heat (increasing the metabolic activity by more plentiful food supply, more vigorous movements), or by diminishing the loss of heat by the development of better protective coverings. When the conditions necessary for the action of these regulators are absent (want of food, small and unprotected bodies), we find either the phenomenon of winter sleep, in which life is preserved with a temporary lowering of the metabolic processes ; or, when the metabolic processes of the organism do not enter into abeyance, the remarkable phenomena of migration (migration of birds). Organs of Secretion. The respiratory organs stand to a certain extent intermediate between the organs of nutrition and those of excretion, in that they take in oxygen and excrete carbonic acid. In addition to this gas a number of excrementitious substances, mostly in a fluid form, which have entered the blood from the tissues, pass out by the lungs. The function, ho\vever, of excretion * Comp. Bergmann, " Ueber die Verhaltnisse der Warmeokonomie der Thiere zu ihrer GrBsse," Gottingcr Studicn, 1847; also Bergmann und Leuckart, " Anatomisch-physiologische Uebersicht des Thicrreichs," Stuttgart, 1852. UKIXAEY OEGANS. 75 is mainly discharged by the special secretory organs. These have the form of glands of a simple or complex structure which originate from invaginations of the outer skin or of the intestinal wall, and consist essentially of simple or branched tubes, or of racemose -and lobulated glands. Among the various substances which by the aid of the epithelial lining of the walls of glands are removed from the blood and some- times utilised further for the performance of various functions, the nitrogenous excretory substances are especially important. The organs by which the excretion of these ultimate products of meta- bolism are effected are the kidneys. In the Protozoa they are represented by the contractile vacuoles ; in the Worms they appear as the so-called ivater- vascular vessels, and are constituted of a system of branched canals which take their origin in delicate internal ciliated funnels, which open into the spaces in the parenchymatous tissues or i nto the body cavity. In the latter case the ciliated funnels have a wide opening. In the Platyelminthes (flat worms) the efferent ducts of the system consist of two main lateral trunks (fig. 68, Ex.\ which frequently open together at the hind end of the body by means of a medium terminal contractile vesicle (fig. 68, ep). In the segmented worms the paired kidneys are repeated in every segment, and are known as segmented organs (figs. 69 and 70). The shell-glands of Crustacea are in all probability to be traced back to these segmental organs : as are also the paired kidney (organ of Bojanus) of mussels, and the unpaired renal sac of Snails, both of which communicate by means of an internal opening with the pericardial division of the body cavity. In the air-breathing Arthropods and some Crustacea (Orchestia) the urinary organs are tubular appendages (Malpighian vessels) of the hind gut. In the Yertebrata the urinary organs or kidneys obtain a greater independence, and open to the exterior by special FIG. G9. Young Distormim (after La Valette). Ex, main stems of the excretory system ; Ep, ex- cretory pore ; O, month with sucker; S, sucker in the middle of the ventraf surface ; P, pha rynx ; D, alimentary canal. 76 OEGAMZATIOX JL?V DEVELOPMENT OF ANIMALS IN GENERAL. openings which are usually common to the generative organs ; they consist essentially of a number of coiled tubes, which in the more primitive types of Vertebrates have a ciliated funnel-shaped opening into the body cavity (Dogfish embryo, fig. 71). The individual tubules of which the verfce Wtr F :G> 70. Diagrammatic representation of the segmental organs of a segmented worm (after C. Semper). DJ, dissepi- ment ; Wtr, ciliated funnels which, lead into the coiled tubes. FIG. 69. Longitudinal section through the medicinal Leech (after K. Leuckart). D, ali- mentary canal ; O, brain ; Gk, ventral chain cf ganglia ; Ex, excretory canals (seg- mental organs, water- vascular system). Lrate kidney is composed do not open directly to the exterior, as do the segmental organs of Annelids, but there is present on each side of the body a duct, the kidney duct, which receives the tubules of its own side and opens posteriorly into the cloaca. They also possess an important structure peculiar to the kidney of the Vertebrata known as the " Malpighian body," which consists of a capsular widening of the lumen of each CUTANEOUS GLANDS. 77 tubule, into which projects a coil of arterial blood vessels known as the glomerulus (fig. 72). Very generally the outer body surface is the seat of special secre- tions which frequently play an impor- tant part in the economy of the animal, and are used especially as a means of protection and defence. The same is true also of the secretions of the accessory glands opening into the anterior or posterior end of the ali- mentary canal (salivary glands, poison glands, anal glands) (fig. 73). To the class of cutaneous glands belong, in the first place, the sweat- glands and the sebaceous glands of Mammalia. The fluid secretion of the former, on account of the ease with which it is evaporated, is of special use in keeping the body cool, while that of the latter keeps the integument and FIG. 71. Diagrammatic represen- tation of the kidney (segmental organs) of a dog-fish embryo (after C. Semper). Wtr, ciliated funnels ; Ug, kidney duct. Tr its special coveringsoft and supple. The coccygeal glands of water- birds are derived from an aggre- gation of sebaceous glands ; their secretion by keeping the feathers oiled preserves them from becom- ing saturated with water during swimming. The unicellular and multicell- ular integumentary glands, which are found so widely present in Insects, belong, for the most part, to the category of oil and fat glands. Aggregations of cells whose function is to secrete calcareous matters and pigment are especially widely present in the integu- ment of the Mollusca, and serve for the building up of the beautifully FIG. 72. Ciliated funnel and Malpighian body from the anterior part of the kidney of Proteus (after Spengel). Nr, kidney tubule; Tr, ciliated funnel; Mk, Malpig- hian body. 78 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. Mn coloured and variously shaped shells of these animals. Integumen- tary glands and aggregations of glands may also acquire a relation to the acquisition of food (spinning glands of Spiders). Finally, mucous glands are i*v very widely present in the skin of animals which live in damp localities (Amphibia, Snails) and in water (Fishes, Annelids, Medusae). C ^ ORGANS OF ANIMAL LIFE. Of the so-called animal functions, that of locomotion is the most conspicuous. Animals perform movements for the purpose of procuring food and escaping from their enemies. The muscles used for locomotion are, as a rule, and especially in the simpler forms, intimately united with the skin, and give rise to a muscular body wall (Worms), the alternate shorten- ing and elongation of which brings about a movement of the body. The muscles may also be especially concentrated in parts of the body wall, e.g., in the subum- brellar surface of Medusae beneath the supporting gelatinous tissue, or in the ventral surface of the body giving rise to a foot-like organ (Molluscs), or they may be broken up into a series of successive and similar segments (Annelids, Arthropods, Vertebrates). The latter arrangement prepares the way for the rapid and more complete form of movement found in animals in which the hard parts also, whether exoskeletal (Arthropods) or endoskeletal (Vertebrata), have become divided into a seiies of longitudinally arranged segments or rings, which offer a firm attach- ment to and are moved by the segments of the muscular system. By this arrangement more powerful muscular actions are rendered possible. Thus it becomes indispensable that hard parts should be developed to act as a skeletal support for the soft parts, and also to protect them. The skeletal structures may be external, in which case they have the form either of external shell?, tubes or successive rings, and are Ail FIG. 73. Alimentary canal with its accessory glands of a beetle (Carabus) (after Leon Duf our). Oe, oesophagus ; Jn, crop ; Pv, proventriculus ; Chd, chylific ventricle ; My, Malpighian tu- bules ; S, rectum ; Ad, anal glands with bladder. EN DO SKELE1 OJy . usually products of the external skin (chitin), or they in;iy be internal (cartilage, bone) and give rise to vertelrce (fig. 74 a, b). In either case the body becomes divided at right angles to its long axis into a series of segments, which, in the simpler cases of locomotion, are homonomous (Annelids, Myriapods, Snakes). As development progresses some of the muscles required for locomotion gradually lose their relation to the long axis of the body, and acquire a relation to secondary axes; and in this way conditions are acquired for the accomplishment of more difficult and complete forms of locomotion. The hard parts in the long axis of the body then lose their primitive FIG. 74 a Diagram oi the vertebral column of aTeleostean fish with verte- bral constriction of the notochord. Ch, notochord ; Wk, bony vertebral bodies ; J, membranous intcrvertebral section. FIG. 74 b Vertebra of a fish. K, ver- tebral body. Ob, neural arch (neura- pophysis) ; Ub, haemal arch (haemapo- physis) ; D. neural spine; D', haemal spine ; B, rib. uniform segmentation and partially fuse with one another to form several successive regions, the parts of which are capable of a greater or less amount of movement upon one another (head, neck, thorax, lumbar region, etc.) In this case, however, the parts of the skeleton of the chief axis are usually less movable upon one anot-her, while, on the contrary, a much more perfect locomotion is effected by the extensive movements of the paired extremities or limbs. The limbs likewise possess a solid skeleton, to which the muscles are attached, and which is usually elongated and may be external or internal, and is attached more or less closely to the axial skeleton. The most essential property of animals is that of sensation. This 80 OEGAXIZATION AXD DEVELOPMENT OP ANIMALS E* CE2TERAL. property, like that of movement, resides in definite tissues and organs which constitute the nervous system. For those cases in which a nervous system has not separated from the common contractile basis (sarcode) or from the uniform cell parenchyma of the body, we may suppose that the organism possesses the first beginnings of an irritability serving for perception. This, however, can scarcely be called sensation, for sensation pre-supposes the presence of conscious- ness of the unity of the body, and this we can scarcely attribute to the simplest animals without a. nervous system. The appearance of muscles is coincident with that of the nervous tissues, which are developed in connection with the sense epithe- lium of the surface (Polyps, Medusre, Echinoderms). In such cases the nerve fibres and ganglion cells which all lie mingled together keep their ectodermal position and their connection with the sense epithe- lium. The view that the first diffe- rentiation of the nervous and mus- cular tissues is to be sought in the so-called neuromuscular cells of the fresh-water polyps and Medusas has been shown by later researches to be untenable. The arrangements of the nervous system can be traced back to three distinct types (1) the radial ar- rangement found in the radiate animals; (2) the bilateral arrange- ment found in segmented Worms, Arthropods, and Molluscs; (3) the bilateral arrangement of the Yertebrata. In the first case the central organs are radially repeated ; in the Echinoderms as the so- called ambulacral brains or nerves, which are found in the arms and are connected together by a circumoral nervous commissure contain- ing ganglion cells (fig. 75). In the second type the nervous system, in the simplest cases, consists of an unpaired or paired gangiionic mass placed in the anterior part of the body above the pharynx, and known as the supra-03sophageal ganglion or brain. From this centre radiate in the simplest cases (Turbellaria) nerves which have a bilaterally sym- metrical distribution, and of which two are larger than the others, and take a lateral course (fig. 76). FIG. 75. Diagram of the nervous sys- tem of a star-fish. N, nerve ring which connects together he five am- bulacral centres. NERVOUS SYSTEM. 81 At a higher stage of development a circum-pharyngeal nerve ring is developed. With the commencing segmentation of the body the number of ganglia increases, and in addition to the brain there is present a ventral nervous system consisting either of ventral cord fl'- G FIG. 76. Alimentary canal and nervous system of Mesosto- mum Ehrenbergi (after Graff). G, the paired cerebral ganglia with two eye-spots; St. one of the two main lateral nerves ; Z>,alimentary canalwith mouth and pharynx. FIG. 77. Nervous system of FIG. 78. Nervous system the larva of Coccinella (after Ed. Brandt). G, an- pra-cesopfcageal ganglion or brain; Gfr, frontal ganglion ; Sg, suboeso- phageal ganglion ; Q-',-G", the eleven ganglia of the rentral chain of thorax and abdomen. of adult Coccinella (after Ed. Brandt). Ag, optic ganglion. The other let- ters as in fig. 77. (Gephyrea) or of a ventral chain of ganglia, which may have a homonoinous (Annelids) or heteronomous (Arthropods) arrangement (figs. 77 and 78). The concentration of the nervous system begun 6 82 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. in the latter case may, by the fusion of the brain and ventral oord, be carried to a still further extent, so that in many cases (numerous Arthropods) only a sub-cesophageal ganglion is present. In Molluscs, animals in which segments are not de- veloped, the subo3sophageal ganglion is represented by the pedal ganglion, and there is in addition a third pair of ganglia constituting the visceral ganglia (fig. 55). In Vertebrates, the nervous centres are arranged as a cord, lying on the dorsal side of the skeletal axis, and known as the spinal cord, the segmentation of which is indicated by the regular repetition of the spinal nerves. This cord, which is traversed by a central canal, is anteriorly widened and (except in Amphioxus) differentiated into a complicated ganglionic apparatus, the brain (fig. 79). The so-called sympathetic or visceral nervous system appears in the higher animals (Yertebrata, Arthropoda, Hiru- dinea, etc.) as a comparatively indepen- dent part of the nervous system. It consists of ganglia and plexuses of nerves which stand in connection with the central nervous system, but are not under the direct control of the will of the animal. It innervates the organs of digestion, circulation, respiration, and generation, and it can carry on its functions for a longer or shorter time after destruction of the sensory and motor centres. In the Yertebrata (fig. 80), FIG. 79. Brain and spinal cord the system of visceral nerves consists of a of a pigeon. //, cerebral Double chain of ganglia, placed on each hemispheres; Cb, optic lobes ; ' r c, cerebellum; MO, medulla side of the vertebral column and con- obiongata. s p , spinal nerves. nected w j t h t h e spinal nerves and the spinal-like cranial nerves, by connecting branches, the rami eommunicantes. The ganglia correspond in number with the above- mentioned spinal and cranial nerves, and they send nerves to the SENSE OEGANS. 83 blood vessels and viscera, which there form a complicated network of nervous fibres containing here and there ganglion cells. The nervous sys- tem possesses further > peripheral apparatus, the sense organs, the function of which is to bring about the perception of certain conditions of the outer world as im- pressions of a definite mode of sensation (specific energy of nerves* Joh. Miiller). These peripheral organs usually have the form of peculiarly arranged aggrega- tions of hair-shaped or rod-shaped nerve terminations (hair- cells, rod-cells of sen- sory epithelium) con- nected by fibrillse with ganglion cells, through which under the action of external influences a move- ment of the nervous substance is set up, which travels to the central organ and there affects con- * In opposition to the differences in the quali- ties of the sensations produced by each indi- vidual sense organ (colour, tone). FIG. 80. Nervous system of the frog (after Ecker). Ol olfactory nerves; O, eye ; Op, optic nerve ; Vg, Gasserian ganglion ; Xg, ganglion of vagus ; Spn 1, first spinal nerve ; Br, brachial nerve ; 5^1-10, the ten ganglia of the sym- pathetic system. Js, ischial nerve. 84 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. sciousness as a specific sensation. To these end-cells there are often added cuticular structures, whose function is to communicate the external movement to the nervous substance (retinal rods). The special sensations have quite gradually been developed from the general sensations (comfort, discomfort, pleasure, pain), i.e., nerves of special sense have been derived from sensory nerves which have acquired a special form of peripheral termination, and so become accessible to a special stimulus with which the special sensation is always associated. But it is not till a higher stage of development is reached that the sense-perceptions can be compared according to the nature of the sensations with those of our own body. We can estimate the sense energies of the lower animals exceedingly vaguely, and only by the insufficient method of com- paring them with our own sensations; and it is certain that among the lower ani- mals there are many forms of sensation of which we, in consequence of the spe- cialised nature of our own senses, can have no concep- tion. Probably of all the senses, that of touch is the most widely distributed, and with this we certainly often see a number of special sensations united. It is generally distributed over the whole surface of the body ; frequently, however, it is con- centrated on processes and appendages of it. Probably the tentacular appendages of the Ccelenterata and Echinodermata have this signifi- cance. In the Bilateralia with a differentiated head there are contractile or stiff segmented processes on the head, the antennce or feelers which in the worms are repeated as paired cirri on every segment of the body. It is often possible to trace special nerves to the skin and to find touch organs containing their endings. In the Arthropoda the ganglionic end-swelling of a tactile nerve usually lies beneath a cuticular appendage, such as a bristle, which transmits the mechanical pressure on its point to the nerve (fig. 81). FIG. 81. Nerves with ganglion cells (G) beneath a tactile bristle (TV) from the skin of Corethra larva. AUDITOR r AND VISUAL OEGA5TS. 85 In the Primates amongst the Mammalia there are present papillae in the skin (especially on the volar surface) in which the structures known as touch-bodies, containing the termination of tactile nerves, are placed (fig. 82). In addition to the general sensibility and the tactile sensations, the higher animals possess, as a special form of sensibility, the capacity of distinguishing different temperatures. The sensations of sound are produced through an organ, the auditory organ, which is, in a certain measure, a special modification of a tactile organ. The auditory organ in its simplest form appears as a closed vesicle filled with fluid (endolymph) and one or more calcareous concretions (otoliths) ; and containing in its walls rod OT hair cells in which the nerve fibrilbe end (fig. 83). Sometimes the vesicle lies on a ganglion of the central ner- vous system (Worms), sometimes at the end of a shorter or longer nerve, the auditory nerve (Molluscs, Decapoda). In many aqua- tic animals the vesicle may be open and its contents communicate directly with the exter- nal medium, in which case the otoliths may be represented by small particles such as sand- grains which have entered it from the exterior (Decapod Crustaceans). In Molluscs a deli- cate sensory epithelium (macula acustica, fig. 83 Cz, Hz.\ marks the percipient portion of the inner wall of the vesicle: while in Crus- FlG - 82. -Tactile papilla ,, ~, f ,, ,., , . from the volar surface tacea the fibres of the auditory nerve end in wit h the touch corpuscle cuticular rods or hairs which project from the an(i its nerve N - wall of the vesicle, and, like the olfactory hairs of the antennae, bring about the nervous excitations. In the Vertebrata not only does the auditory vesicle obtain a more complicated form (mem- branous labyrinth), but there are also added to it apparatuses for conducting and magnifying the sound (fig. 84). The tympanum of Acrideidae and Locustidse, which is generally looked upon as an auditory organ, is built upon quite a different type, since here, instead of a vesicle filled with fluid, air cavities serve for the action of the sound waves on the nerve-endings. The visual organs or eyes* are, after the tactile organs, the most widely distributed, and indeed are found in all possible stages * Cf. R. Leuckart, " Organologie des Auges," Graefe and Samisch, Hand- buck der Ophthalmologie, Bd. II. 80 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. of perfection. In the simplest cases they are known as eye-spots, and consist of irritable protoplasm, i.e., nervous substance, containing pig- ment granules ; and in this form they are perhaps scarcely capable of distinguishing light from darkness, but are only susceptible to the warm rays. It is hardly possible to conceive that pigment is indis- pensable for the sensation of light, -because there are many eyes of complicated structure from which pigment may be altogether absent. The view, however, according to which the pigment itself is sensitive to light, i.e., is chemically changed by the light waves and transmits the excitation produced by these movements to the protoplasm or FIG. 83 Auditory vesicle of a Heteropod (Pterotrachea). N, acoustic nerve ; Ot, otolith the fluid of the vesicle ; Wz, ciliated cells on the inner wall of the vesicle ; JIz, auditory cells ; Cz, central cell. the adjacent nervous substance cannot in itself be contradicted, but it is by no mears clear that such changes are produced by the light rays as opposed to the heat rays. Of greater importance in this relation appears the special nature of the nerve endings, through which certain movements, progressing in regular waves, the so-called ether waves, are transmitted to the nerve fibres and give rise to a stimulus which travels to the central organ and is by it perceived as light. In all cases in which in the lower animals specific nerve endings cannot be made out, we have probably only to do with a forerurner of the eye, consisting merely of the pigrnented termina- BEFKACIILE MEDIA AND PIGMENT. 87 C tion of a cutaneous nerve which is sensitive only to gradations of temperature. Although the sensation of light is the function of the nerve centre, the rods and cones at the end of the optic nerve fibres are the elements which convert the external movement of the ether waves into an excitation of the optic nerve fibres adequate for the production of the sensation of light. For the perception of an image refractile apparatuses in front of the terminal expansion of the optic nerve (retina) are necessary; and further, the elements of the latter must be sufficiently isolated to admit of the stimuli set up in them being carried as separate movements to the nerve centre. Instead of a general sensation of light a complex sensation made up of many separate perceptions is produced, which corre- spond in position and I quality with the parts of the exciting source. For the refraction of the light convex and often lens- shaped thickenings of the body covering (cor- nea, corneal lens) through which the rays pass into the eye, are developed ; refractile bodies are also found behind the cornea (lens, crystalline cone). The rays diverging from the various parts of the source of the light are, by means of the refractile media, collected and brought to corresponding foci on the retina or peripheral expansion of the optic nerve, which consists of the rod-shaped ends of the nerve fibres and some more or less complicated ganglionic structures. Lately, in consequence of the discovery of the visual purple* in the outer segments of the rods, it has been attempted to reduce the excitation of the end apparatus of the optic nerve to a photo-chemical process taking place in the retina. The fact that the diffuse pigment (visual purple) of the outer segments of the rods is bleached by the * In addition to the older works of Krobn, H. Muller, M. Schultze, cf. Boll Sitzungsberichte der Akad. Berlin, 1876 and 1877, also Ewald and Kuhne. FIG. 84. Diagram of the auditory labyrinth. I. of , fish. II. of a bird. III. of a mammal (after Wal- deyer). U, utricle with the three semicircular canals ; S, saccule ; US, alveus communis ; C, cochlea ; L, la- gena ; R, aqueductus vestibuli ; Cr, canalis reuniens. ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. action of light is of the highest interest, but it cannot be taken as proving a direct participation of the visual purple in the visual process, inasmuch as the visual purple is not present in those parts of the eye in which alone a distinct image is formed, viz., the macula lutea and, generally, the outer segments of the cones. The pigment of the eye seems to be of importance for absorbing the superfluous rays of light which would be injurious to the per- ception of an image. It is distributed partly immediately outside the retina, forming the choroid. coat of the eye, which extends also inwards between the individual retinal elements ; and partly in front of the lens, giving rise to a transversely placed curtain, the iris which is pierced by an opening, the pupil, capable of contrac- ting and dilating. In the higher grades of development the whole eye is, as a rule, enclosed in a hard, connective tis- sue coat, the sclerotic, and thus marked off as an eye bulb. The arrangements by which the shining points of an object act in regular ar- rangement on corre- sponding points of the optic nerve and so render possible the perception of an image vary, and are closely dependent upon the whole structure of the eye. Leaving out of consideration the simplest eyes, such as we find in Worms and the lower Crustacea, two types of eye are to be distin- guished. 1. The first form occurs in the so-called facetted eyes* (figs. 85 & 86) of Arthropods (Crustacea and Insects). The retina of such eyes has a hemispherical form, the convex surface being directed out- wards, and consists of large compound nerve rods, the retinulse * See Job. Mailer. "Zur vergleichenden Physiologic des Gesichtssinnes," Leipzig, 1826. H. Grenadier, " Untersuchungen iiber das Sehorgan der Arthro- poden," Gottingen, 1879. FIG 85. Diagrammatic representation of the compound eye of a Libellula. C, cornea; K, crystalline cone ; P, pigment ; .K, nerve rods of retina ; Fb, layer of fibres ; Gz, layer of ganglion cells ; Rf t retinal fibres ; Fk, crossing of fibres. UNICOBNEAL EYE. 89 (figs. 85 & 86 Rf & fi), which are separated from one another by pigment sheaths. In front of these rods are placed the strongly refractile crystalline cones (k), and in front of these again the lens- shaped corneal facets (C & F). The eye is enclosed by a firm chitinous layer, which, following the sheath of the entering optic nerve, surrounds its soft parts and reaches as far as the cornea. That part of the eye which is known as optic nerve corresponds in a great measure to the retina itself, and contains a layer of ganglion cells and of nerve fibres. A reversed and reduced picture of the object is thrown behind each convex corneal facet (lying far from the sensitive layer of nervous rods), and only the perpendicular rays can be perceived since all the others are absorbed by the pigment. Ac- cordingly the light impressions caused by these axial rays, whose number corresponds with the separate nerve rods, form a mosaic on the retina which repeats the arrangement of the parts of the external object emitting light. The picture which is here formed lacks, however, brilliancy and dis- tinctness. 2. The second form of eye, which is widely distri- buted in the animal kingdom (the simple eye, Annelids, Insects, Arachnida, Molluscs, Verte- brates) corresponds to a globular camera obscura with collecting lenses (cornea, lens) on its exposed anterior wall on which the light falls and usually with additional dioptric media filling the optic chamber (vitreous humour.) The simple eye of Insects seems to have originated from the simple metamorphosis of part of the integument, beneath which are placed the end organs of the optic nerve (fig. 87). The cuticular covering (CL) projects as a lens- shaped thickening into the subjacent layer of transparent, elongated, hypodermis cells (Gk), within which are placed elongated rod-like nerve- cells with refractile cuticular portions, closely aggregated to form a retina (fig. 87 Rz). The hypodermis cells surrounding the edge of the lens are filled with pigment, and form an iris-like dark ring FIG. 86. Three fa- cets Avith retinulae from the com- pound eye of a cockchafer (after Grenacher) . The pigment has been dissolved away from two of them, F, corneal facet. K, crystalline cone. P, pigment sheath. P-, chief pigment ceils. P", pigment cells of the second order. .R, retinulse. ;0 ORGANIZA1ION AND DEVELOPMENT OF ANIMALS IN GENERAL. through the opening in which the rays of light enter the eye to fall on the terminal segments of the retinal cells (fig. 87). In the more highly developed forms of this type of eye, especially in the Vertebrate eye, the peripheral portion of the optic nerve spreads out so as to form a cup- shaped nervous membrane, the retina, placed immediately behind the refractile media and surrounded by a vascular pigmented membrane, the choroid. The choroid, again, is surrounded by a tough supporting membrane composed of fibrous connective tissue, and known as the sclerotic, which is continued over the anterior part of the eye, i.e., that part through which the light passes, as a thinner transparent membrane. Of the refractile media which are placed behind the cornea and fill the cavity of the optic bulb, viz., the aque- ous humour, the lens (fig. 88 Z), the vitre- ous humcur (Gl), the lens is the most powerful. Grasped by the thickened muscular anterior part of the choroid (the ciliary body (Cc) and ciliary processes), the peripheral part of its anterior face is covered by a forward continuation of tli^ choroid, the iris (Jr), which, as a ring-likj contractile border, forms a kind of diaphragm perforated by a central contractile opening, the pupil, through which the light enters the eye (fig. 88). The reversed image which is formed in the hinder part of the Vertebrate eye on the cup-shaped retina has a very considerable brilliancy and definition. The eyes of many Cephalopods may be looked upon as a modifica- tion of this type of eye. In the eye of Nautilus the lens is absent, and the light enters through a small opening. In this case a reversed, but not brilliant, image is formed on the retina placed on the hinder wall of the eye. To enable the eye to see clearly objects in different directions anJ Rz FIG. 87. Trarsverse section through the simple eye of a beetb L>,rv.i ^>artly after Grenac her). CL, corneal lens ; Gk, the subjacent hypodermis cells, the vitreous humour of Authtrs ; P, pigment in the peripheral cells of the lat- ter ; Rz, r.tiuul cells. St, cuticular rods of the latter. OLFACTORY OKGAX. 91 at different distances, special apparatuses for its movement and accommodation are necessary. They are represented by muscles which can in the former case move the optic bulb and modify the direction of sight in obedience to the will of the animal, and in the latter act upon the refractile media, and vary their relation to the retina. In many compound eyes (Decapod Crustacea) that part of the head on which the eye is placed is prolonged so as to give rise to a movable stalk-like process, which bears the eye at its extremity __ The eyes of Vertebrata possess in addition special protective arrangements, e.g., eyelids, lacrymal glands. The position and number of the eyes present very great variations amongst the lower animals. The paired arrangement on the head appears to be the general rule among the higher animals ; nevertheless visual organs sometimes occur on parts of the body far removed from the brain, as for instance, in Euphausia, Pecten, Spondy- lus, and certain Annelids (Sabellidae). In the Radiata the eyes are repeated at the periphery of the body in each radius. In the star fishes they lie at the extreme end of the ambulacral furrow at the tip of the arms, in the Acalephce as the marginal bodies 011 the edge of the umbrella. The sense of smell appears to be less widely distributed. Its func- tion is to test the quality of gaseous matters rnd to produce in consciousness the special form of sensation known as " Smell." This sense in aquatic animals which breathe through gills cannot be sharply marked off from that of taste. The small pits, standing in connec- tion with nerves and provided with an epithelial lining of hair- bearing sense cells, are to be looked upon as the simplest form of olfactory organ (Medusae, Hetercpoda, Cephalopoda). Nevertheless scattered hair cells (Lamellibranchiata) may also have to do with the same sensation. In the Arthropoda the cuticular appendages of the FIG. 88. Transverse section through the human eye (after Arlt). C, cornea ; L, lens ; Jr, iris with pupil ; Co, ciliary body ; Gl, vitreous humour ; R, retina ; So sclerotic ; Ch, choroid. Ml, macula lutea; Po, papilla optica; 2V'o, optic nerve. 92 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. " antennae in which the gangliated swollen extremities of nerves occur are to be explained as olfactory fibres,.^ In the Yertebrata the olfactory organ usually has the form of a paired pit or cavity placed on the under surface of the head (nasal cavity), on the walls of which the ends of the olfactory nerve are distributed. The higher air- breathing Yertebrata are distinguished by the fact that in them this " cavity communicates with the pharynx, and by the great surface extension (in a confined area) of the much-folded olfactory mucous membrane. The fibres of the olfactory nerve terminate in delicate elongated cells, bearing a rods or hairs and placed between the epithelial cells of this mucous membrane.. The special sense of taste is confined to the mouth and pharynx. Its function, from what we know of the higher organisms, is to test the quality of fluid sub- stances, and to bring about the special sensation of taste. The presence of this sense can be demonstrated with certainty in the Yer- tebrata, and it is connected with the distribution of a special nerve of taste, the glossopharyngeal, which in man supplies the tip, edges, and root of the tongue and also parts of the soft palate, making these parts capable of the taste sensation. The so-called taste-buds found in special papillae (papillae circum- vallatae), with their central fibre-like cells, are explained as the percipient organs of this sense (fig. 89 a, b, c). Taste is, as a rule, connected with the tactile and temperature sensations of the buccal cavity, and also with the olfactory sensations. Finally, special organs of taste appear to be present also in the Molluscs and Arthropods as a specific sensory epithelium at the entrance to the buccal cavity. In the lower animals the taste and olfactory organs are still less FIG. 89. a Transverse section through, a circum- vallate papilla of a calf (after Th. W.Engelmann). If, nerve ; Gk, taste buds in the side-wall of the papilla, PC. b, isolated taste bud from the lateral taste organs of a rabbit, c, isolated supporting cells (Dz) and sense cells (Sz) from the same. PSYCHICAL LIFE AND INSTINCT. 93 clearly distinguishable than in the higher, and there are numerous senses of an intermediate character for the purpose of testing the surrounding medium. The sense-organs of the lateral line of Fishes and Salamanders, and the organs resembling taste-buds of the Hirudinea and Chsetopoda been described as organs of a sixth sense. They probably bring abowNertairi sensations referring to the quality of the water. PSYCHICAL LIFE' 1 ' AND INSTINCT. The higher animals are not only rendered conscious of the unity of their organization by their feelings of comfort and discomfort, pleasure and pain, but also possess the power of retaining residua of the impressions of the outer world conveyed through the. senses, 'and of combining them, with simultaneously perceived conditions of their bodily state. In what manner the irritability of the lower pro- toplasmic organisms leads by gradual transitions and intermediate steps to the first affection of sensation and consciousness is as completely hidden from us as are the nature and essence of the psychical processes which we know are dependent on the movement of -matter. ; We are, however, justified in supposing that a nervous system is indispensable for the development of these internal conditions which may be compared with that condition of our own organization called consciousness. Again, as animals have sense-organs capable of receiving impressions of definite quality from external causes, together with a capacity for retaining in their memory residua of their perceptions, and the power of connecting them with present and with the recollection of past states of bodily sensation so as to form judgments and conclusions, they possess all the conditions essential for the operation of the intelligence; and, as a matter of fact, they do manifest in an elementary form nearly all the phenomena which , distinguish human intelligence. The actions of animals are not only voluntary, the result of experi- ence and intellectual activity, but are also largely determined by internal impulses which work independently of consciousness, and cause numerous, often very complicated, actions useful to the organism. Such impulses tending to the preservation of the individual and the * W. Wundt, " Vorlesungen tiber die Menschen und Thierseele." 2 Bde. Leipzig, 1863. W. Wundt, " Grundziige der physiologischen Psychologic," Leipzig, 1874. 94 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. species are called instincts',* and they are usually regarded as a special property of the lower animals, and contrasted with the conscious reason of Man. But just as the latter must be looked upon as a higher form of the understanding and intellect, and not as something essentially distinct from them, so a closer examination shows that instinct and the conscious understanding do not stand in absolute contrast, but rather in a complex relation, and cannot be sharply marked off from one another. For if, according to the general view, we recognise the essence of instinct in the unconscious and the innate, still we find that actions which were at first performed under the direction of conscious intelligence become, by constant practice, completely instinctive and are performed unconsciously; and that, in accordance with the theory of descent, which the whole connection of natural phenomena renders so probable, instincts have been developed from small beginnings, and have only been able to reach the high and complicated forms which we admire in many of the more highly organised animals (Hymenoptera), when assisted by a certain amount, however small, of intellectual activity. Instinct accordingly may be rightly defined as a mechanism which works unconsciously, and is inherited with the organization, and which, when set in motion by external or internal stimuli, leads to the performance of appropriate actions, which apparently are directed by a conscious purpose. We must not, however, forget that while the intellectual activities are the direct means whereby higher and more complicated instincts arise from simple ones, they themselves depend upon mechinical processes. We may well suppose that the simplest form of instinct is identical with the definite reaction of living matter following a stimulus, or, in other words, with that special form of molecular change which is caused by an external action (as, for instance, the contraction of an Amoeba when brought into contact with a foreign body). By the theory of partly instinctive, partly intellectual processes, we may explain the phenomena of association in societies so often found among the higher animals,t i.e., the association of numerous * Compare H. S. Reimarius, "Allgemeine Betrachtungen iiber die Triebe der Thiere," Hamburg, 1773. P. Flourens, " De Tinstinct et de I'intelligence desanimaux," Paris, 1851. j- The origin of the so-called animal stocks with incomplete or confined individuality among the lower animals is quite different, and merely determined by processes of growth ; at the same time the advantage for the preservation of the spscies gained by the fusion is the same. Cf. the animal stocks of the Vorticellidae, Polyps, and Siphonophora, Bryozoa and Tunicr.ta. REPRODUCTIVE ORGANS. 95 individuals into communities the so-called animal-polities which may be complicated by the division of labour (Bees, Wasps, Ants, Termites). In fact here the combined action appears to be mutually assisting or mutually limiting, as we find in the so-called animal stocks, the individuals of which are bound together by continuity of body. The advantages to be gained by this mutual rendering of service are not merely limited to the greater facilities for nourish- ment and defence, and therefore for the preservation of the in- dividual ; but, above all, tend to the maintenance of the offspring, and hence to the preservation of the species. It is for this reason that the simplest and commonest associations, from which the more complicated communities, subdivided by partition of labour, are derived, are generally communities of both sexes of the same species. REPRODUCTIVE ORGANS. On account of the limit set to the duration of the life of every organ- ism, it appears absolutely necessary for the preservation of the animal and vegetable kingdoms that new life should originate. The forma- tion of new organisms might be due to spontaneous generation (generatio equivoca] ; and formerly this was suppose^ to take place, not only in the simpler and lower organisms, but also in the more complicated and higher. Aristotle thought that Frogs and Eels arose spontaneously from slime ; and the appearance of maggots in putre- fying meat was, till Kedi's time, explained in the same manner. With the progress of science the limits within w r hich this supposition could be applied became ever narrower, so that they soon came to include only the Entozoa and small animals found in infusions. Finally it has been shown by the researches of late years that these organisms also must, for the most part, be withdrawn from the region of the generatio equivoca; so that at present, when the question of spontaneous generation is discussed, it is only the lowest organisms, those found in putrefying infusions, that are considered. The greater number of investigators,* supported by the results of * Of. especially Pasteur, " Memoire sur les corpuscules organises qui existent dans 1'atmosphere " (Ann. des. Sc. Nat.), 1861 ; also "Experiences relatives aux generations dites spontanees " (Compt. rend, de 1'Acad. des Sciences, tome 50). 96 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GEXEEAL. numerous experiments, have rejected, even for the latter animals, the idea of spontaneous generation, which, however, still finds in Pouchet* a prominent and zealous supporter. Biogenesis, as opposed to abiogenesis, or spontaneous generation, must be regarded as the usual and normal form of reproduction. Fundamentally it is nothing else than a growth of the organism beyond the sphere of its own individuality, and can be always reduced to a separation of a part of the body, which develops into an indi- vidual resembling the parent -organism. Nevertheless the nature and method of this process differ extraordinarily ; and various kinds of reproduction can be distinguished, viz., fission, budding (spore- fdrmdtion), sexual reproduction.-}- Reproduction by fission, which, with that by budding and spore- formation, is included under the term monogenous asexual reproduc- tion, is found widely scattered in the lowest animals, and is also of special importance for the reproduction of the cell. It consists simply of a division of the organism into two parts by means of a constriction which gradually becomes deeper, and eventually leads to the separation of the whole body of the organism into two individuals of the same kind. If the division remains permanently incomplete, and its products do not completely separate from each other, con- pound colonies of animals arise. The number of individuals in such colonies increases by a continuation of the process of incomplete and often dichotomous division of the newly-formed individuals (Yorti- cella, Polyp stocks). The division may take place in various direc- tions longitudinal, transverse, or diagonal. Budding differs from fission by a precedent disproportionate and asymmetrical growth of the body, giving rise to a structure not absolutely necessary to the parent organism which is developed to a new individual, and by a process of constriction and division becomes independent. If the buds remain permanently attached to the parent, we have here also the conditions necessary for the formation of a colony (Polyp colonies). Sometimes the budding takes place at various parts of the outer surface of the body, irregularly or obeying definite laws (Ascidians, Polyps) ; sometimes it is localised to a definite part of the body, separated off as a Germ- stock (Salpa, stolo prolifer). The cell-layers distinguished as germinal * Pouchet, " Nouvelles experiences sur la generation spontanee et la resist- ance vitale," Paris, 1864. f Cf. R. Leuckart's article, " Zeugung " in R. Wagner's " HandworterbucL der Physiologic." REPRODUCTION BY SPORES. SEXUAL REPRODUCTION. 97 Ed layers are repeated in the commencing buds, and from them the organs are differentiated. The reproduction by spores is characterised by the production within the organism of cells, which develop into new individuals in situ or after leaving the organism. But this conception of spores, which is taken from the vegetable kingdom, can only be applied to the Protozoa and coincides with endogenous cell-division. The cases of so-called spore-formation amongst the Metazoa (germinal sacs of Trematodes) are probably identical with egg formation, and are to be reduced to a precocious maturation and spontaneous development of ova (Parthenogenesis, Paedogenesis). The digenous or sexual reproduction depends upon the production of two kinds of germinal cells, the combined action of which is necessary for the de- velopment of a new or- ganism. The one form of germ cells contains the material from which the new individual arises, and is known as the egg -cell, or merely egg (ovum). The second form, the sper m-c ell (spermato- zoon), contains the ferti- lising material, semen or sperm, which fuses with the contents of the egg- cell, and in a way which is not understood gives the impetus to the de- velopment of the egg. The cell structures from which the eggs and sperm arise are called sexual organs, for reasons which will be evi- dent in the sequel ; the eggs being produced in the female organ or ovary, and the semen in the male organ or testis. The egg is the female, and the semen the male product. The structure of the sexual organs presents extraordinary diffe- rences and numerous grades of progressive complication. In the simplest cases, both products arise in the body wall, the cells of which give rise at determined places to ova or spermatozoa (Coelenterata). Sometimes they arise in the ectoderm (Hydroid-Medusse), sometimes in the entoderm (Acalepha, Anthozoa). A similar arrangement 7 Rs FIG. 90. Generative organs of a Heteropod (Pterotra- chea) after R. Leuckart. a, Male-organs ; T, testis Vd, vas deferens. b, female organs ; Ov, ovary ; EJ, albumen gland ; Us, receptaculum seminis ; Va, va- gina. 98 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. obtains in the marine Polychseta, in which the ova and spermatozoa are developed from the epithelium of the body-cavity (mesoderm), and dehisced into the body cavity. Usually, however, special glands, the ovaries and testes, are developed, which perform no other function than that of secreting ova and spermatozoa (Echinoderms). As a rule, however, there are found associated with the male and female generative glands accessory structures and a more or less com- plicated arrangement of ducts, which discharge definite functions in connection with the development of the generative products subse- quent to their separation from the glands, and ensure a suitable meeting between the male and female elements (fig 90). The ovaries are provided with ducts, the oviducts, which are not rarely derived FIG. 91, a. The female organs of Pulex (after Stein). Ov, ovarian tubes ; Rs, receptaculum seminis; V, vagina; Gl, accessory gland, b, The male generative organs of a water-bug (Xepa) (after Stein). T, testis ; Vd, vasa deferentia; Gl, accessory glands j D, ductusejacu- latorius. from structures serving quite another purpose (segmental organs). The oviducts, in their course, may receive glandular appendages of various kinds which furnish yolk for the nourishment of the ovum, or albumen to surround it, or material for the formation of a hard egg-shell (chorion). These functions may be sometimes discharged by the ovarian wall (Insects), so that the egg when it enters the oviduct has taken up its accessory yolk and acquired its firm egg- shell. Very often the ducts also discharge these various functions, and are divided into corresponding regions ; they are often dilated at part of their course to form a reservoir for the retention of the HERMAPHRODITISM. 99 eggs or of the developing embryos (uterus). Their terminal section presents differentiations subserving fertilization (reeeptaculum seminis, vagina, copulatory pouch, external generative organs). The efferent ducts of the testis, the vasa deferentia, likewise frequently give rise to reservoirs (vesiculse seminales) and receive glands (pros- tate), the secretion of which mixes with the sperm fluid or surrounds aggregations of the spermatozoa with a firm sheath (spermatophors). The terminal section of the vas deferens becomes exceedingly muscular, and gives rise to a ductus ejaculatorius, which, as a rule, is accompanied by an external organ of copulation to facilitate the conveyance of the semen into the female generative organs. Tha generative organs present a . either a radial (Coaienterata, Zd. Echinodermata) or a bilate- rally symmetrical arrangement (fig. 91), a contrast which is visible in the typical arrange- ment of all the systems of organs. The simplest and most primitive condition of the generative organs is the her- maphrodite. Ova and sper- matozoa are produced in the body of one and the same individual, which thus unites FIG. 92. Sexual organs of a Pteropod (Cymbulia) in itself all the conditions necessary for the preservation of the species, and alone represents the species. Instances of hermaphroditism are found in every group of the animal kingdom. But they are especially nume- rous in the lower groups, and also in animals in which the movements are slow (Land-snails, Flat- worms, Hirudinea, Oligocho3ta), or which live singly (Cestoda, Trematoda), or in attached animals which are without power of changing their position (Cirripedia, Tunicata, Bryozoa, Oysters). The hermaphrodite arrangement of the gene- rative organs presents great variation, which, to a certain extent, forms a gradual series tending towards the separation of the sexes. In the simplest cases, the points of origin of the two kinds of generative products lie close to one another, so that the spermatozoa and ova meet directly in the parent body (Ctenophora, Chrysaora). (after Gegenbaur.) a, Zd, hermaphrodite gland with common duct ; Sg, reeeptaculum seniinis ; U, uterus, b, Acinus of the hermaphrodite gland of the same. 0, ova ; S, spermatozoa. 100 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. The elements of both sexes arise in layers of cells which have a definite position beneath the entodermal lining of the gastro-vascular canals, and can be traced back to growths of the ectoderm. At a higher stage the ovaries and testes are united in one gland, the hermaphrodite gland (Synapta, Pteropoda), provided with a single duct common to the ova and spermatozoa (fig. 92), but which, as in Helix (fig. 93), may partially .separate into vas deferens and oviduct. In other cases the ovaries and testes appear as completely separated glands with separate ducts, which may still open into a common cloaca (Cestoda, Trematoda, rhabdocoele Turbellarians, fig. 94), or may possess separate open- ings (Hirudinea, fig. 95). Two hermaphrodite in- dividuals may, and this appears to be the rule, mutually fertilise each other at the same time, or cases may occur in such hermaphrodites in which self-fertilization is sufficient for the production of off- spring. But this original condition of self-fertiliza- tion appears to be the ex- ception in almost all hermaphrodites. In those animals in which the ovary and testis are not com- pletely separated from one another cross-fertilization is rendered necessary, and self-fertilization prevented by the fact that the male and female elements are matured at different times (Snails, x Salps). From this form of complete hermaphroditism the generative organs pass through a stage of incomplete hermaphroditism, in which, though the organs of both sexes are present, one of them is rudi- mentary, to reach the dioecious condition in which the sexes are completely separated (Distoinumjillicolle and hcemaiobium). Animals in which the sexes are distinct not ^infrequently present traces of an FIG. 93. Sexual organs of the Roman Snail (Helix pomatia). Zd, hermaphrodite gland ; Zg, its duct ; Ed, albumen gland ; Od, oviduct and seminal groove ; Vd, vas deferens ; P, protrusible penis ; Fl, flagellum ; Bn, receptaculum seminis ; D, finger-shaped gland ; L, Spiculum amoris ; Go, common genital opening. SEPARATION OF THE SEXES. 101 hermaphrodite arrangement ; such, for instance, as may be seen in the arrangement of the generative ducts of the Vertebrata. In the Amphibia both male and female generative ducts, which are secondarily derived from the urinary ducts, are developed in each individual. The oviduct (Mullerian duct) in the male atrophies, and is only repre- sented by a small rudiment (fig. 96&, Mg] \ while, on the contrary, in the female, the vas deferens (Wolffian duct) is rudimentary, or, as in Amphibia, functions as the efferent duct for the kidney secre- tion (fig. 96a, kg). With the separation of the male and female gene- rative organs in different indivi- duals the most complete form of sexual reproduc- tion, so far as con- cerns division of labour, is reached ; but at the same time a progressing dimorphism of the male and female individuals be- comes apparent. This is due to the fact that the or- ganization in bi- sexual animals is more and more influenced by the deviating func- tions of the sexual organs, and with the increasing complication of sexual life becomes modified for the performance of special accessory functions connected with the production of ova and spermatozoa. In the first place, the modification of the generative ducts of the two sexes in accordance with the function they have to perform determines the development of secondary sexual characters and of sexual dimorphism. Other organs as well as the generative appa- FIG. 94. Generative appara- tus of a rhabdocoele Tur- bellarian (Vortex viridis) (after M. Schultze). T, tes- tis ; Vd, vas deferens ; Vs, seminal vesicle; P, pro- trusible penis; Ov, ovary; Va, vagina ; M, uterus ; -D, yolk gland ; Rs, recep- taculum seminis. FIG. 95. Generative appa- ratus of the medicinal leech, T, testis ; Vd, vas deferens; Nh, vesicula seminalis ; Pr, prostate ; C, penis ; Ov, ovaries with vagina and female generative opening. 102 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. ratus present differences in the two sexes, being modified for the FIG. 96a. L.-ft urinary and generative or- FIG. 9Ci, Loft urinary and generative organs gans of a female Salamander without the of a male Salamander, more diagrammatic. cloaca. Ov, ovary ; N, kidney ; hg, urin- ary duct corresponding to the Wolfltian duct ; Mj, Muilerian duct as oviduct. T, testis ; Ve, vasa efferentia ; N, kidney with its collecting tubules ; Mg, Miille- rian duct as a rudiment; Wg, Wolffian duct or vas deferens ; Kl, cloaca with ac- cessory glanda Dr, of the left side. performance of special functions in the sexual life. The female is FUNCTIONS OF MALE AND FEMALE. 303 the passive agent in copulation, merely receiving the semen of the male; the female possesses material from which the offspring PIG. Q7a. Male of Aphis platanoides. c, ocelli ; IIr t honey tubes ; P, copulatory organ. develop, and accordingly takes care of the development of the fertilised egg and of the later fate of the offspring. Hence the female usually possesses a less active body and numerous arrangements for the protection and nourishment of her offspring, which develop either from eggs laid by the mother and sometimes carried about with her, or in the maternal body and are born alive. The function of the male is to seek, to excite, and to hold the female during copulation ; hence, as a rule, he possesses greater vigour and power of movement, higher development of the senses, various means of exciting sexual feeling, such as brighter colour- Fl - 976 Apterous oviparous female of the , , same. ing, iouder and richer voice, pre- hensile organs, and external organs for copulation (fig. 97, a, 6). In exceptional cases, the functions relating to the maintenance of 104 ORGANIZATION AXD DEVELOPMENT OF ANIMALS IN GENEEAL. the offspring may be discharged by the male, e.g.. Alytes and the Lophobranchia. Male birds also often share with the female the labour of building the nest, of bringing up and protecting the young. But it is a rare exception to find, as in Cottus and the Stickleback (Gasterosteus), that the care and protection of the young fall exclusively upon the male, that he only bears the brood pouch and alone builds the nest, an exception which bears strong witness to the fact that the sexual differences both in form and function were first acquired by adaptation. In extreme cases, the sexual dimorphism may lead to so great a difference in the sexes that without a knowledge of their development An* J FIG. 98. Chondracanthus gibbosus, magnified about 6 times, a, female from the side, ft, female from the ventral surface with the male (F) attached, c, male isolated, under strong magnification. An 1 , anterior antenna ; An", clasping antennae ; F' and F", the two pairs of feet ; A, eye ; Ov, egg sacs ; Oe, oesophagus ; I), intestine ; M, mouth parts ; T t testis ; Vd, vas def erens ; Sp, spermatophore. and sexual relations, the one sex would be placed in a different family and genus to the other. Such extremes are found in the Rotifera and parasitic Copepoda (Chondracanthus, Lernaeopoda, fig. 98, a, 6, c), and are to be explained as the result of a parasitic mode of life. The difference in the two kinds of individuals representing and maintaining the species, whose copulation and mutual action was known long before it was possible to give a correct account of the real nature of reproduction, has led to the designation "sexes," from which the term sexual has been taken to apply to the organs and manner of reproduction. PARTHENOGENESIS. 105 In reality sexual reproduction is nothing else than a special form of growth. The ova and spermatoblasts represent the two forms of germinal cells which have become free, and which, after a mutual interaction in the process of fertilization, develop into a new organism. Nevertheless under certain conditions the egg can, like the simple germ cell, undergo spontaneous development; numerous instances of this mode of development, which is known as partheno- genesis, are found in Insects. The necessity of fertilization therefore \ Hr FIG. 99. Viviparons form of Aphis platanoides. Oc, ocelli ; Hr, honey tubes. no longer enters into our conception of the egg-cell, and no absolute physiological test is left to enable us to distinguish it from the germ- cell. It is usual to regard the place of origin in the sexual organ and in the female body as a feature distinguishing the ovum from a germ cell, but even with this morphological test we do not in each individual case arrive at the desired result (Bees, Bark-lice, Psychidce). We have already given prominence to the fact that ovaries and testes, in the simplest cases, consist of nothing more than groups of cells of the epithelium of the body cavity or of the outer skin. These, however, do not acquire the character of sexual organs until, at a higher stage of differentiation, the contrast between the two 106 OEGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. sexual elements has made its appearance. When the male elements, and with them the necessity of fertilization, are absent, and when, at the same time, the organ which produces the germ cells possesses, in its full development, a structure similar to that of an ovary, it becomes very difficult to distinguish whether we have to do with a pseudovary (germ-gland), and with an animal which reproduces asexually ; or with an ovary and a true female, whose eggs possess the capacity of developing spontaneously. It is only a comparison with the sexual form of the animal which makes the distinction possible. To take the case of the Plant-lice or Aphides; in these animals we find a generation of viviparous individuals, easily distinguishable from the true oviparous females, which copulate and lay eggs. They resemble the latter in the fact that they are provided with a similar reproductive gland, constructed upon the ovarian type ; but they differ fi'orn. them in this important peculiarity, that they are without organs for copulation and ferti- lization (in correspondence with the absence of the male animal) (fig. 99). The reproductive cells of the organs known as pseudovaries have an origin precisely similar to that of eggs in the ova- ries, and only differ from ova in the very early commencement of the embryonic development. The viviparous individuals will therefore be more correctly regarded as agamic females peculiarly modified in the absence of organs for copulation and fertilization ; and the reproductive cells are by no means to be relegated to the category of germ-cells (as formerly was done by Steenstrup). We must therefore speak of the reproductive pro- cesses in the Aphides as being sexual and partheno- genetic and not sexual and asexual. A comparison of the mode of reproduction of the Bark-lice with that of the Aphides, especially of the species Pem- phigus terebinthi, puts the correctness of this supposition beyond the sphere of doubt. A similar condition is found in the viviparous larva of Cecidomyia. Here the rudiment of the generative glands very early assumes a structure resembling that of the ovary, and produces a number of FIG. 100. Vivipa- rous Cecidomyia (Miastor) larva (after Al. Pagen- stecher). Tl, Daughter larva? developed from the rudimentary ovary. DEVELOPMENT. 107 reproductive cells which resemble ova in their method of origin, and at once develop into larvae. The pseudovary is clearly derived from the rudiment of the sexual gland, but without ever reaching complete development (fig. 100). The ovary acquires to a certain extent the signification of an organ for producing germ-cells, and it is not improbable that many products (Redia, Sporocyst] regarded as spores or germ-cells correspond to embryonic ovaries which produce ova cirable of spontaneous development. FIG. 101. Ovum of Nephelis (after O. Hertwig) . a, the ovum half-an-hour after deposition. a projection of the protoplasm indicates the commencing formation of the first polar body ; the nuclear spindle is visible. 6, The same an hour later, with polar body extruded, and after entrance of the spermatozoon. Sk, male pronucleus. c, The same another hour later without egg membrane, and with two polar bodies and male pronucleus (Sk) d, the same an hour later with approximated female and male pronucleij Bk, pular bodies. DEVELOPMENT. It follows from the facts of sexual reproduction that the simple cell must be regarded as the starting-point for the development of the organism. The contents of the ovum spontaneously or under the influence of fertilization enter upon a series of changes, the final result of which is the rudiment of the body of the embryo. These changes consist essentially in a process of cell division which implicates the whole protoplasm of the ovum, and is known as segmentation. 108 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. For a long time the behaviour of the germinal vesicle at the commencement of segmentation and its relation to the nuclei of the first formed segments were obscure, and the knowledge of the changes and fate of the spermatozoa which enter the ovum in the process of fertilization was, in like manner, in a very unsatisfactory state. Of late years, numerous investigations, especially those of Biitschli, 0. Hertwig, Fol, etc., have thrown some light on these hitherto completely obscure processes. It was supposed that in a ripe ovum preparing itself for segmentation the germinal vesicle disappeared, FIG. 102, a, 1. Parts of the ovum of Asterias glacialis with spermatozoa, embedded in the mucilaginous coat (after H. Fol.) c, upper part of the ovum of Petromyzon (after Calberla). Am, micropyle ; Sp, spermatozoa ; Jm, path of the spermatozoon ; Ek, female pronucleus ; Eh, membrane of ovum ; Ehz, prominences of the same. and a new nucleus was formed quite independently of it ; and that the persistence and the participation of the germinal vesicle in the for- mation of the nuclei of the first segmentation spheres were exceptional (Siphonophora, Entoconcha, etc.) Thorough investigations carried out on the eggs of numerous animals have, however, shown that as a matter of fact the germinal vesicle of the ripe ovum only experi- ences changes in which the greater part of it, together with some of FERTILIZATION. 109 the protoplasm of the ovum, is thrown out of the egg as the so-called directive bodies or polar cells (fig. 101). The part of it, however, which remains in the ovum retains its significance as a nucleus, and is known as the female pronucleus. This fuses with the single spermatozoon (male pronucleus) which has forced its way into the ovum (fig. 102); and the compound structure so formed constitutes the nucleus of the fertilized ovum, or as it is generally called, the first segmentation nucleus. FIG. 103. Development of a Star-fish, Asteracanthion berylinns (after Alex. Agassiz). 1, Commencing segmentation of the flattened egg at one pole are seen the polar bodies ; 2, stage with two segments ; 3, with four ; 4, with eight ; 5, with thirty-two segments ; 6, later stage ; 7, blastosphere with commencing invagination ; 8 and 9, more advanced stages of invagination. The opening of the gastrula cavity becomes the aims. This new nucleus, which divides to give rise to the nuclei of the first segmentation spheres, would appear therefore to be the product -of the fusion or conjugation of the part of the germinal vesicle, which remains behind in the ovum, with the male pronucleus, which is a derivative of the spermatozoon which has entered the ovum. Fertilization would appear, therefore, to depend upon the addition 110 OEGANIZAIION AND DEVELOPMENT OF ANIMALS IN GENERAL. of a neiv element bringing about the regeneration of the primary nucleus of the ovum or germinal vesicle, and would have impressed its influence on the constitution of the conjugated nucleus. The regenerated ovum is therefore the starting-point of the subsequent generations of cells which build up the embryonic body. Both the origin of the polar bodies which takes place in the ripe ovum independently of fertilization, and the division of the segmen- tation nucleus are accompanied by the appearance of the nuclear spindle and star- shaped figures at the poles of the spindle which are so characteristic of the division of nuclei. The male pronucleus, before it fuses with the female pronucleus, also becomes surrounded by a layer of clear protoplasm, around which a star-shaped figure appears (fig. 101). In those cases in which segmentation takes place without a precedent fertilization (parthenogenesis], the female pronucleus appears to possess within itself the properties of the first segmentation nucleus. The fertilization is followed by the process known as segmentation, in which the ovum gradually divides into a greater and greater number of smaller cells. Segmentation may be total, i.e., the whole ovum segments (fig. 103), or it may be partial, in which case only a portion segments (fig. 105). Total segmentation may be regular and equal, the resulting seg- ments being of equal size (fig. 103) ; or it may sooner or later become irregular, the resulting segments being of two kinds the one smaller and containing a preponderating amount of protoplasm, the other larger and containing more fatty matter. In these cases the seg- mentation is said to be unequal. The process of division proceeds much more quickly in the smaller segments, while in the larger and more fatty segments it is much slower, and may eventually come to a complete standstill. The development of the frog's egg will serve as an example of unequal segmentation, of which there are various degrees (fig. 104). In this egg a dark pigmented and protoplasmic portion can be distingirVied from a lighter portion containing much fatty matter or food yolk. The former is always turned uppermost in the water, and is therefore called the upper pole of the egg. The axis which connects the upper pole with the lower is known as the chief axis. The planes of the two first segmentation furrows pass through the chief axis and are at right angles to each other. They divide the egg into four equal parts. The third furrow (fig. 104, 4) is equatorial, taking place in a horizontal plane, and cuttin^ the chief axis at right angles. It lies, however, nearer EOLOBLASTIC AND MEROBLASTIC SEGMENTATION. Ill the upper pole than the lower, and marks the line of division between the upper and smaller portion of the egg from the lower FIG. 104. Unequal segmentation of the Frog's egg (after Eckei) in ten successive stages. and larger portion, in which the segmentation pro2eeds much more slowly than in the former. In partial segmentation we find a sharply marked contrast between the formative and nutritive parts of the egg, inasmuch as the latter does not seg- ment. The terms holoUastie and me- roblastic therefore have been applied to total and partial seg- mentation respec- tively. Nevertheless, in total segmentation also, either groups of segments of a definite quality, or, at any rate, a fluid yolk material may be used for the nourishment of the developing embryo. In fact, the contents of every egg consists of two parts (1) of a viscous albu- and (2) of a fatty granular matter, the FIG. 105. Segmentation of the germinal disc of a Fowl's egg, surface view (after Kolliker). A, germinal disc with the first vertical furrow ; B, the game with two vertical furrows crossing one another at right angles ; C and D t raore ad- vanced stages with small central segments. ininous protoplasm ; deutoplasm, or food yolk. The first is derived from the protoplasm 112 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL, of the original germinal cell, while the yolk is only secondarily developed with the gradual growth of the first ; and not unfrequently it is derived from the secretion of special glands (yolk glands, Trema- todes) ; it may even be added in the form of cells. In the Ctenophora and other Coelenterata we see already in the first-formed segments the separation of the formative matter or peripheral ectoplasm from the nutritive matter or central endoplasm. In eggs undergoing a partial segmentation the formative matter usually lies on one side of the large unsegmenting food yolk. In accordance with this, the segments of such eggs, known as telolecithal, arrange themselves in the form of a flat disc (germinal disc) ; hence this kind of segmentation has been called discoidal (eggs of Aves, Keptilia, Pisces) (fig. 105). The food yolk may, however, have a central position. In such centrolecithal eggs the segmentation is FIG. 106. Unequal segmentation of the centrolecithal egg of Gammarus locusta (in part after Ed. van Ber.edeu). The central yolk mass does not appear till a late stage and undergoes later an " after-segmentation." confined to the periphery, and is sometimes equal (Palsemon) and sometimes unequal (fig. 106). The central yolk mass may at first remain unsegmented, but later it may undergo a kind of after- segmentation and break up into a number of cells (fig. 106). Again, in other cases the food yolk, at the commencement of segmentation, has a peripheral position, so that the cleavage process is at first confined to the inner parts of the egg, and only in Later stages, when the food yolk has gradually shifted into the centre of the egg, appears as a peripheral layer on the surface. This is found especially in the eggs of Spiders (fig. 107). The first processes of segmentation in these at first ectolecithal ova are withdrawn from observation, since they take place in the centre of an egg covered by a superficial layer of food yolk, until the nuclei with their protoplasmic invest BLASTOSPHERE. 113 uient reach the periphery, and the fatty and often darkly-granulai food yolk comes to constitute the central mass of the egg (Insects). As various as the forms of segmentation are the methods by which the segments are applied to the building up of the embryo. Fre- quently in cases of equal segmentation the segments arrange them- selves in the form of a one-layered vesicle, the blastosphere, the central cavity of which not rarely contains fluid elements of the food yolk ; or they are at once divided into two layers around a central cavity containing fluid; or they form a solid mass of cells without FIG. 107. Six stages in the segmentation of a spider's egg (Philodromus limbatus) after Hub Ludwig. A, egg with two deutoplasmic rosette-like masses (segmentation spheres) ; , the rosette-like masses with their centrally placed nucleated protoplasm without egg membrane ; C, egg with a great number of rosette-like masses ; D, the rosette-like masses have the form of polyhedral deutoplasmic columns, each of which has a ceii of the blas- toderm lying immediately superficial to it ; E, stage with blastoderm completely formed ; F, optical section through the same. The yolk columns form wiihin the blastoderm a closed investment to the central space. any central cavity. In numerous cases, especially when the food yolk is relatively abundant (unequal and partial segmentation) or the food supply continuous, the embryonic development is longer and more complicated. The embryonic rudiment in such cases has at first the form of a di*c of cells lying on the yolk ; it soon divides into two layers, and then grows round the yolk. 8 114 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. The two-layered gastrula is, as a rule, developed from the blasto- spliere by invagination (einbolic invagination). In this process the one half (sometimes distinguished by the larger size and more granular nature of its cells) of the cell wall of the blastosphere is pushed in upon the other half (fig. 108), and on the narrowing of the FIG. 108. A, Blastosphere of Amphioxus ; B, invagination of the saint; C, gastrula, invagi- nation completed ; O, blastopore (after B. Hatschek). aperture of invagination (blastopore, mouth of gastrula) becomes the endodermal layer (JiypoUast) lining the gastrula cavity. The outer layer of cells constitutes the ectoderm or epiblast. This mode of formation of the gastrula, which is very common, is found, e.g., in Ascidians, and amongst the Yertebrata in Amphioxus (fig. 108). More rarely the gastrula arises by delamination. This process consists of a concentric splitting of the cells of the blastosphere into an outer layer (epiblast), and an inner (hypoblast) (fig. 109). FIG. 109. Transverse sections through three stages in the segmentation of Geryonia (after H. Fol.) A, stage with thirty-two segments, each segment is divided into an external finely granular protoplasm (ectoplasm) and an inner clearer layer (endoplasm) ; B, later stage ; C, embryo after delamination; with ectoderm slightly separated from the endoderm, which is composed of large cells surrounding the segmentation cavity. c l"he central cavity of the gastrula in this case is derived from the original segmentation cavity, and the gastrula mouth is only secondarily formed by perforation. This method of development PRIMITIVE STREAK. 115 of the gastrula has hitherto only been observed in some hydroid Medusae (Geryonia). finally, when the inequality of the segmentation is very pro- nounced, the gastrula is formed by a process known as epibole. In this process of development the epiblast cells, which are early distin- guishable from the much larger hypoblast cells, spread themselves over the latter as a thin layer (fig. 110); and in this, as in the second method of development of the gastrula, the cavity of the gastrula is, as a rule, a secondary formation in Ihe centre of the closely-packed mass of hypoblast cells. The blastopore is usually found at the point where the complete enclosure of the hypoblast is effected. It sometimes happens that a part of the primary blastosphere is developed more rapidly than the remainder, and gives rise to a FIG. 110. A, Unequal segmentation of the egg of Bouellia; B, epibolic gastrula of the same (after Spengel). bilaterally-symmetrical stripe-like thickening placed on the dorsal or ventral surface of the embryo. Frequently, however, such a germinal or primitive streak is not developed, and the rudiment of the embryo continues to develop uniformly. Formerly great importance was attached to these differences, the one being distinguished as an evolutio ex una parte, and the other an evolutio ex omnibus partibus It is not, however, possible to draw a sharp line between these two methods of development, nor have they the significance which was formerly ascribed to them, for closely allied forms may present great differences in this respect according to the amount of food yolk and the duration of the embryonic development. The Coelenterata, the Echinoderms, the lower Worms and Mol- luscs, Annelids, and even Arthropods and Vertebrates (Amphioxus) present us with examples of regular development of all parts of the 11 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. body of the embryo which, if the yolk membrane fails, has no need of a special protective envelope. In this latter group, however, the formation of the germinal streak, which is in close relation with the formation of the nervous system, is accomplished later, during the post-embryonic development, when the larva is free-swimming and can procure its own food. In like manner many Polychaetes and Arthropods (Branchipus) only acquire a germinal streak in the course of their later growth as larvre. In all cases in which the embryonic development begins by the formation of a germinal streak, the embryo only becomes definitely limited after the yolk has been gradually surrounded, as a result of processes which are connected with the complete entry of the yolk into the body cavity (Frogs, Insects), or with the origin of a yolk sac from which the yolk .passes gradually into the body of the embryo (Birds, Mammals). The progressive organization of this latter, up to its exit from the egg membranes, presents in each group such extraordinary variations that it is not possible to give a general account of them. Of primary importance is the fact that in the rudiment of the germ two cell layers first make their appearance one the ectoderm, which gives rise to the outer integument; and the other the endoderm, 1 from which arises the lining membrane of the digestive cavity and of the glands opening into it. Between these two layers there is formed, either from the outer or the inner layer, or from both layers, an intermediate layer, known as the mesoderm. From the mesoderm arise the muscular system and the connective tissues, the corpuscles of the lymph and blood, and the vascular system. The body cavity may either be derived from the persisting segmentation cavity, i.e., the primitive space between the ectoderm and endoderm (primary body cavity), or it may be developed secondarily as a split in the mesoderm (ccelom), or as outgrowths from the rudiment of the alimentary canal (ar client eron), in which case it is known as an enteroccele body cavity. The nervous system and organs of sense are probably in all cases derived from the ectoderm, very frequently as pit- or groove-like invaginations which are subsequently constricted off. On the other hand, the urinary and generative organs arise both from the outer and inner layers as well as from the middle layer, which is itself derived from one of the primary layers or from, the walls of the primary single -layered blastosphere. Accordingly, as a rule the rudiments of the skin and glandular HOilOLOCJY OE TILE GEEMINAL LAYEES. 117 lining of the alimentary canal are the first differentiations in the embryo ; and many embryos, the so-called Planulae and Gastrulse, on leaving the egg, have only these two layers and an internal cavity, the archenteron. Then follows the development of the nervous and muscular systems, the latter taking place sometimes contem- poraneously with or after the first appearance of the skeleton, especially in cases in which a germinal streak is developed. The urinary organs and various accessory glands, the blood-vessels and respiratory organs do not appear till later. The degree of difference between the offspring on attaining the free condition (i.e., at birth or hatching) and the sexually mature adults, both as regards form and size as well as organization, varies considerably throughout the animal kingdom. It is a very striking fact that an embryo provided with a central cavity and a body wall composed of only two layers of cells appears in different groups of animals as a freely moveable larva capable of leading an independent life. Having recognized this fact, it was not a' great step, especially as Huxley* some time ago had compared the two membranes of the body wall of the Medusae (called later by Allman ectoderm and endoderni) with the outer and inner layers of the vertebrate blastoderm (epiblast and hypoblast), to arrive at. the conclusion that there was a similar phylogenetic origin for the similar larvae of very different animal types, and to trace back the origin of organs functionally resembling each other to the same primitive structure. It was A. Kowalewskit who, by the results of his numerous researches on the development of the lower animals, first gave this conception the groundwork of fact. He not only proved the occur- rence of a two-layered larva in the development of the Co3lenterata, Echinoderms, Worms, Ascidians, and in Amphioxus amongst Verte- brates, but also on the ground of the great agreement in the later developmental stages of the larvae of Ascidians and Amphioxus and in the mode of origin of equivalent organs in the embryos of Worms, Insects, and Vertebrata, protested against the hitherto universally received view implied in Cuvier's conception of types, that the organs of different types could not be homologous with one another. * Th. H. Huxley, " On the Anatomy and Affinities of the family of Medusae." Philosophical Transactions. London, 1849. t Cf. A. Kowalewski's various papers in the " Memoires de 1'Acad. de Peters- bourg," on Ctenophora, Phoronis, Holothurians, Ascidians, and Amphioxus, 1866 and 1867. : o 113 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEEAL. Inasmuch as KowalewL&i,* from the results of his embryological work, drew the Conclusion that the nervous layer and embryonic skin of Insects and Vertebrates are homologous, and that the germinal layers of Amphioxus and Vertebrates correspond with those of Molluscs (Tunicata) or worms, he was in agreement with the long recognised fact that anatomical transitional forms and intermediate links between the different groups or types of animals exist, and that these latter do not represent absolutely isolated planes of organization, but the highest divisions in the system, and he only gave in reality an embryological expression to the claims of the descent theory. In fact, the conclusion which Kowalewski reached was completely correct viz., that the homologies of the germinal layers in the different types afford a scientific basis for comparative anatomy and embryology, and must be recognised as the starting-point for the proper understanding of the relationships of the types. For this position we find amongst the vertebrata proofs at every step. But while his own comprehensive embryological experiences inspired Kowalewski, the founder of the theory of the germinal layers, with a prudent reserve, other investigators, inclined to bold generalization, appeared at once with ready theories, in which the results of embryo- logical investigations were interpreted in accordance with the theory of descent. Among these E. Haeckel's gastrasa theory is especially prominent, which raises no less a claim " than to substitute, in the place of the classification hitherto received, a new system based on phylogeny, of which the main principle is homology of the germinal layers and of the archenteron, and secondarily on the differentiation of bhe axes (bilateral and radial symmetry) and of the ccelom." E. Haeckelf designated the larval form used as the point of depar- ture the Gastrula, and believed to have found in it the repetition in embryonic development of a common primitive form, to which the origin of all Metazoa may be traced back. To this hypothetical prototype, which is supposed to have lived in very early times during the Laurentian period, he gave the name of Gastrcea, and called the ancient group, supposed to be widely scattered and to consist of many families and genera, by the name Gastrceadce. From this sup- position was deduced the complete homology of the outer and inner * A. Kowalewski, "Embryologische Studien an Wiirmcrnund Arthropod en." Petersburg, 1871, p. 58-fiO. f E. Haeckel, " Gastraeatheorie." Jen. nat. Zeitschrifr, 1874.'' For criticism see C. Glaus, " Die Typenlehre und Haeckel's sogenannte Gastrseatheorie," Vienna, 1874. DEVELOPMENT AND METAMORPHOSIS. 119 germinal layers throughout the whole Metazoa ; the one being traced back to the ectoderm and the other to the endoderm of the hypothe- tical Gastraea ; while for the middle layer, which is only secondarily developed from one or both of the primary layers, only an incomplete homology was claimed. It cannot, however, be said that this theory, which is essentially an extension of the Baer-Remak theory of the germinal layers from the Yertebrata to the whole group of Metazoa, with its pretentious and hasty speculation has created a basis for comparative embryology ; such a basis can only be obtained as the result of comprehensive investigations. DIRECT DEVELOPMENT AND METAMORPHOSIS. The more complete the agreement between the just born young and the adult sexual animal, so much the greater, especially in the higher animals, will be the du ration of the embryonic development and the more complicated the developmental processes of the embryo. The post-embryonic develop- ment will, in this case, be confined to simple processes of growth and perfection of the sexual organs. When, how- ever, embryonic life has, relatively to the height of the organization, a quick and simple course ; when, in other words, the embryo is born in an immature condition and at a relatively low stage of organization, the post -embryonic development will be more complicated, and the young animal, in addition to its increase in size, will present various processes of transformation and change of form. In such cases, the just hatched young, as opposed to the adult animal, is called a Larva, and develops gradually to the form of the FIG. 111. Larval stages of the Frog (after Ecker). a, embryo some time before hatching, with wart-like gill papillae on the visceral arches, b, Larva some time after hatching, with external branchiae, c, Older larva, with horny beak and small branchial clefts beneath the integumentary operculum, with internal branchiae ; Jf, nasal pit ; S, sucker ; K, branchiae ; A, eye ; Hz, horny teeth. 120 ORGANIZATION AND DEVELOPMENT OF ANIMALS TN GENEEAL. sexual animal. The development of larvae, however, is by no means direct and uniform, but is complicated by the necessity for special contrivances to enable them to procure food and to protect them- selves ; sometimes taking place in an entirely different medium, under different conditions of life. This kind of post-embryonic development is known as metamorphosis. Well-known examples of metamorphosis are afforded by the deve- lopmental histories of the Insecta.and Amphibia. From the eggs of Frogs and Toads proceed larvae provided with tails, but without limbs, the so-called Tadpoles (fig 111). These, with their laterally compressed tails and their gills, remind one of fishes, and they possess organs of attachment in the form of two small cervical suckers by which they can anchor themselves to plants. The mouth is provided with horny plates ; the spirally coiled intestine is surprisingly long ; the heart is simple; and the vascular arches have the piscine relations. Later, as development proceeds, the external branchiae abort, and are replaced by new branchiae covered by folds of the integument, the caudal fin is enlarged, and the fore and hind limbs sprout out ; the fore limbs remain for some time covered by the integument, and only subsequently break through it to appear on the surface. Meanwhile the lungs have developed as appendages of the anterior part of the alimentary canal, and supplant the gills as respiratory organs, a doable circulation is developed, and the hornv beak is cast off. Finally the tail gradually shrinks and atrophies ; on the completion of which the metamorphosis of the aquatic tadpole into the frog or toad suited for life on land is accomplished (fig. 112). We have then to consider two kinds of development, viz., develop- ment with a metamorphosis and direct development, which in extreme cases are distinctly opposed to each other, but are connected by inter- mediate methods. The size of the egg, or, in other words, the amount of food yolk available for the use of the embryo in proportion to the size of the adult animal appears to be a factor of primary importance in any explanation of these two distinct processes (R. Leuckart). Animals with a direct development require generally in pro- portion to the height of their organization and the size of their bodies that their eggs should be provided with a rich endowment of food yolk, or that the developing embryo should possess a special accessory source of nutriment ; they arise therefore either from relatively large eggs (Birds), or they are developed inside, and in close connection with the maternal body, by which arrangement they have a continual supply of food material (Mammals). Animals, RELATION OF METAMORPHOSIS TO FERTILITY. 121 on the contrary, which pass through a metamorphosis always arise from eggs of relatively small size, are hatched in an immature con- dition as larvae, and obtain independently, by their own activity, the materials which have been withheld from them while in the egg, but which are necessary for their full development. The number of embryos produced in the case of a direct development is, in proportion to the total weight of the material applied by the mother for reproductive purposes, far smaller than in the case of a develop- ment with metamorphosis. The fertility of animals whose young FIG. 112. Later stages in the development of Pelobates fuscus. a, larva without limbs with well developed tail; b, older larva with hind limbs ; c, larva with two pairs of limbs ; d, young frog with caudal stump ; e, young frog after complete atrophy of tail. andergo a metamorphosis, or, in other words, the number of offspring produced from a given mass of formative material, is increased to an extraordinary degree, and has, in the complicated relations of organic life, a great physiological significance, though systematically it is of little importance. Some time ago it was attempted to explain these indirect meta- morphoses, in which both processes of reduction and new development take place, as the result of the necessity which the simply organized 122 OKGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. larva, hatched at an early stage of development, laboured under ol acquiring special arrangements for its protection and nourishment (H. Leuckart). The proof that such relations do exist between the special larval organs and the peculiar methods of nutrition and protection is an important factor for the full understanding of these remarkable processes, but still is by no means an explanation of them. It is only by aid of the Darwinian principles and the theory of descent that we can get nearer to an explanation. According to this theory, the form and structure of larvae are to be considered in relation to the development of the race, i.e. phylogeny, and are to be derived from the various phases of structure through which the latter has passed in its evolution, and in such a way that the younger larval stages would correspond to the primitive, and the older, on the other hand, to the more advanced and more highly organized animals, w r hich have appeared later in the history of the race. In this sense the developmental processes of the individual constitute a more or less complete recapitulation of the developmental history cf the species, complicated, however, by secondary variations due to adaptation, which have been acquired in the struggle for existence * (Fritz Mailer's fundamental principle, called by Haeckel the funda- mental law of biogenesis). The greater the number of stages, therefore, through which the larva passes, the more completely is the ancestral history of the species preserved in the developmental history of the individual ; and it is the more truly preserved the fewer the peculiarities of the larva, whether independently acquired, or shifted back from the later to the earlier periods of life (Copepoda.) On the other hand, there are certain larval forms without any phylogenetic meaning which are to be explained as having been secondarily acquired by adaptation (many Insect larvae). The historical record preserved in the developmental history becomes, however, gradually defaced by simplification and shortening of the free development; for the successive phases of development are gradually more and more shifted back in the life of the embryo, and run their course more rapidly and in an abbreviated form, under the protection of the egg membranes, and at the cost of a rich supply of nutrient material (yolk, albumen, placenta). In animals with a direct development, therefore, the complicated deve- lopment within the egg membranes is a compressed and simplified * Fritz Miiller, " Fur Darwin." Leipzig 1863, p. 7581. ALTERNATION OF GENERATIONS. 123 metamorphosis, and hence the direct development, as opposed to the metamorphosis, is a secondary form of development. ALTERNATION OF GENERATIONS, POLYMORPHISM AND HETEROGAMY. Both in direct development and indirect development by means of a metamorphosis, the successive stages take place in the life- history of the same individual. There are, however, instances of free development, in which the individual only passes through a part of the developmental changes, while the offspring produced by it accomplishes the remaining part. In this case the life-history of the species is represented by two or more generations of indivi- duals, which possess different forms and organization, exist under different conditions of life, and reproduce in different ways. Such a manner of development is known as alternation of genera- tions (metagenesis), and consists of the regular alternation of a sexually differentiated generation with one or more generations reproducing asexually. This phenomenon was first discovered by the poet Chamisso* in the Salpidao ; but the observation remained for more than twenty years unnoticed. It was rediscovered by J. Steenstrup, t and discussed in the reproduction of a series of animals (Medusae, Trematoda) as a law of development. The essence of the process consists in this, that the sexual animals produce offspring, which through their whole life remain different from their parents, but can give rise by an asexual process of reproduction to a gener- ation of animals which resemble in their organization and habits of life the sexual form, or again produce themselves asexually, their offspring assuming the characters of the original sexual animal. So that in the last case the life of the species is composed of three different generations proceeding from one another, viz., sexual form, first asexual form, and second asexual form. The development of the two, three, or more generations may be direct, or may take place by a more or less complicated metamorphosis ; similarly the asexual and the sexual generations sometimes differ but little from each other (e.g. Salpa), and sometimes present relations analogous to those which exist between a larva and the adult animal (e.g. * Adalbert de Chamisso, * De animalibus quibusdam e classe yernrium Linnseana in circumnavigatione terras auspicante comite N. Romanzoff duce Ottone de Kotzebue annis 1815, 1816, 1817, 1818 peracta." Fasc. I. De salpa Berolini 1819. f Joh. Jap. Sm. Steenstrup, " Ueber den Generationswcchsel, etc," ubersetzt von C. H. Lorenzen. Kopenhagen, 1842. 124 OUGANIZATION AND DEVELOPMENT OF ANIMALS IN GENEHAL. Medusae). Accordingly we have to distinguish different forms of alternations of generations, which have genetically a different origin and explanation. The latter form of alternations of generations resembles metamor- phosis ; and we have in most cases to explain it as having arisen in the following way : The asexual form corresponds to a lower stage in the phylogenetic history, from which it has inherited the capacity of asexual reproduction, while the sexual reproduction belongs entirely to the higher form. To take as an example the alternation of generations of the Scyphomedusse. The animal is hatched as a free-swimming ciliated planula (gastrula with closed blastopore) (fig. 113 a). After a certain time it fixes itself by the pole of its body, d Csli FIG. 113. Development of the planula of Chrysaora to the Scyphistoma stage, with eight arms, a, Two layered planula with a narrow gastric cavity; b, the same after its attachment with just-formed mouth (O), and commencing tentacles ; c, four-armed Scy- phistoma polyp ; Cxk, excreted cuticular skeleton ; d, eight-armed Scyphistoma polyp with wide mouth ; M, longitudinal muscles of the gastric ridges ; Csk, excreted cuticular skeleton. which is directed forward in swimming, and acquires at its free ex- tremity a new mouth, round which 1, 2, 4, 8, and finally 16 long tentacles soon make their appearance ; while the broad oral region projects as a contractile cone (fig. 113 b, c, d). Inside the gastric cavity there project four gastric ridges with longitudinal muscular bands extending from the foot or point of attachment to the base of the oral cone. When the polyp, which has now become a Scyphis- toma, has under favourable conditions of nutrition reached a certain size (about 2 to 4 mm.), ring-like constrictions are formed at the SCIPIIISIOMA, STKOBILA, EPHIKA. 125 anterior part of the body, giving rise to a series of segment-like divisions. The anterior part of the body bearing the tentacles is first marked off; and following this a greater or less number of sections, the new segments appearing continuously in the direction from before backward. The hindermost or basal swollen club-shaped end of the polyp's body remains undivided. The Scyphistoma has FIG. 113. e, Stage of Scyphistoma with sixteen arm? (<=1ightly magnified) ; Gw. gastric ridges. /, Commencing strobilization. now become the Strobila, which itself passes through various developmental phases. The tentacles abort ; the successive segments, separated from each other by constrictions and provided with lobe- like continuations and marginal bodies, become transformed into small flat discs, which become separate, and, as Ephyra&, represent the larvae of the Scyphornedusse (fig. 113 b-h). 126 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. In the other cases in which the sexual and asexual forms mor- phologically resemble each other, as in Salpa, the origin of the alternation of generations may, as in the case of the origin of the direcious from the hermaphrodite state, be traced back to the ten- dency towards the establishment of a division of labour acting upon an animal which possessed the capacity of sexual and asexual repro- duction. It was advantageous for the formation of the regular chain of buds (stolo prolifer) that the power of sexual reproduction should be suppressed, and that the generative organs should be- come rudimentary and finally vanish in the budding indivi- duals ; while, on the other hand, in the individuals united in the chain, the gene- rative organs were early de- veloped, and the stolo prolifer was aborted and completely vanished. Special forms of alternation of generations may be dis- tinguished in which colonies are formed as the result of the asexual reproduction by budding from a single animal, the buds remaining attached and developing into individuals which differ considerably in structure and appearance, and each of which performs special functions in maintaining the colony (nutritive, protective, sexual, etc.) Such a form of alternation of generations is known as polymorphism,* and reaches a great complication in the polymorphous colonies of the Siphonophora. A form of reproduction which closely resembles metagenesis, but which genetically has quite a different explanation, is the lately * K. Leuckart, " Ueber den Polymorphismus der Individuen oder die Erscheinung der Arbeitstheilung in der Natur." Giessen, 1851. FIG. 113..;, Fully developed Strobila with sepa- rating Ephyrse. h, Free Ephyra (of about 1 '5 to 2 rnm. diameter. 127 discovered process known as heterogamy. It is characterised bv the succession of differently organized sexual generations living under different nutritive conditions. Heterogamy, which was first discovered in certain small Nematodes (Rhabdonema nigrovenosum and Leptodzra appendiculata), can scarcely be explained otherwise than as an adaptation to changed conditions. For when the embryo is developed as a parasite in conditions favour- able for the acquisition of nutriment, it gives rise to a sexual form so different in size and structure from that which arises if the B. FIG. 114. A, Rhabdonema nigrovenosum of about 35 mm. in length at the stage when the male organs are ripe. G, genital gland; O, mouth ; D, alimentary canal ; A, anus ; A, nerve ring; Drz, gland cells ; Z, isolated spermatozoa. B, Male and female Rhabditis, length from about 1 '5 to 2 mm. ; Ov, ovary; T, testis; F, female genital opening; Sp, spicula. embryo leads a free existence in damp earth or dirty water (i.e., in conditions not so favourable for the acquisition of nutriment), that we should, from the difference in their structure, place the two forms in different genera. Rhabdonema nigrovenosum from the lungs of Batrachians and the free-living Rhabditis follow each other in a strictly alternating manner (fig. 114, A, B). Other cases of hetero- gamy are afforded by the Bark-lice (Chermes), and the Root-lice 128 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. (Phylloxera), in that one or more (winged and apterous) female generations are characterised by parthenogenetic reproduction, and consist only of oviparous females; while the generation of females, which lay fertilised eggs, appears with the males only at certain times of the year, and can be distinguished by their small size, and by the reduction of their mouth parts and digestive apparatus. Such forms of heterogarny lead back apparently to alternations of generations, especially when the parthenogenetic generations present, in the structure of their generative apparatus, essential differences from the females which copulate. The plant-lice and gall-flies afford instances of this. The repro- ductive processes of these animals, on the authority of Steen- strup and V. Siebold, were regarded for a long time as instances of alternations of generations, until the view, which was supported by the reproductive processes of the allied bark-lice, that they came under the head of heterogamy, received general assent. According to this view, the viviparous forms of the plant-lice (Aphides) are merely modified females adapted for parthenogenetic reproduction, and their reproductive gland is nothing more than the modified ovary. There are also cases of heterogamy in which, in the partheno- genetic generations, the development of the egg commences in the ovary of the larva, reproduction being shifted back into larval life. This form of heterogamy, which resembles alternations of genera- tions, was shown to occur in the larva of Cecidomyia-(Miastor) by Nic. Wagner and by 0. Grimm in the larva of a species of Chiro- nomus, and is to be looked upon as a case of precocious development of the egg in the parthenogenetic generation. The morphologically undeveloped larva has acquired the power of reproducing itself by means of its rudimentary ovary, a phenomenon which, following the proposal of C. E. v. Baer, has been designated Pcedogenesis. If the reproductive gland of the Cecidomyia larva be looked upon as a germ-gland, and the cells contained in it as germ cells or spores, the reproduction of the Cecidomyia falls into the category of alterna- tions of generations. But the idea involved in the term " spore " is borrowed from the vegetable kingdom, and there is no reason for looking upon these or any other structures in the Metazoa as spores. The above explanation, therefore, is untenable. The reproductive cells in the Metazoa, which have been regarded in this light, have much more probably originated from masses of cells which represent the rudiment of the ovary, and which are usually visible in early stages of development. DEVELOPMENT OF DISTOilEJE. 129 Further it cannot be doubted that the development of the Distomese, which has hitherto been regarded as a case of alternation of generations really represents a form of heterogamy allied to psedogenesis. After the completion of the segmentation and em- bryonic development, the ciliated embryos (fig 115, a, b) pass from the egg into the water, where they swim about, and eventually make their way into the body of a Snail, in which they give rise to sac-like or branched Sporocysts (fig 115, c) or to Rediae provided with an alimentary canal (fig. 115, d). These stages in the development of Distomum which are apparently FIG. 115. Developmental history of Distomum (in part after R. Leuckart). a, Free- swimming ciliated embryo of the liver fluke. b, the same contracted, with rudiment of alimentary canal D ; and aggregations of cells ; Oo, rudiment of genital gland ; Ex, ciliated apparatus of the excretory system. c, Sporocyst, which has proceeded from Distomum embryo, filled with Cercariae C B, spine of a Cercaria. d, Redia with pharynx Th alimentary canal, D ; Ex, excretory organs; C, contained Cercariae. e, free Cercaria; S, sucker ; D, gut. comparable to larvae, produce by means of the so-called germ granules or spores a generation of offspring known as Cercariae (fig. 115, e), which become free, and then make their way into the body of a new host, and, after the loss of the oral spine and caudal appendage, encyst (fig 115/). Hence they are carried into the body of the permanent host to develop into the sexual adult form. 9 130 ORGANIZATION AND DEVELOPMENT OF ANIMALS. It is, however, extremely probable that the masses of cells from which the Cercarise arise represent the rudiments of ovaries, the elements of which develop parthenogenetically without the addition of spermatozoa. The so-called germ sacs (Sporocysts or Reclise) would in this case be larvae, which possess the power of reproduction; and the development of the Distomese would come tinder the head of heterogamy. The Cercarire, however, represent a second and more advanced larval phase. Provided with a motile tail, frequently with eyes and buccal spine, their organization, save in the absence of developed generative organs, presents great simi- larities to the sexually mature adults into which they develop. This development, however, takes place only in the body of another and usually more highly organized host after the loss of the larval organs. If the conception of a spore as an asexual reproductive product be main- tained, it becomes impossible in practice to draw a sharp line between alterna- tion of generations and heterogamy ; since there is no test which enables us to distinguish between a spore and an ovum which develops parthenogeneti- cally. On the other hand, if we inter- o pret, as we are justified in doing, the so-called spores as precociously developed ova, alternation of generations and heterogamy can be clearly distinguished from one another, since in the former one generation is asexual, and in- creases entirely by budding and division; while in the latter both generations are sexual, though in one of them the ova may possess the power of spontaneous development. An essential characteristic both of heterogamy and alternation of generations depends upon the different form of the individuals appearing in the generations which usually occur in a regularly alternating manner in the life-history of the species. But there are cases in which two methods of reproduction may follow each other in the Iife4ristory of one individual. This form of the FIG. 115. /, Young Distomum (after La Valette). Ex, main trunk of excretory system ; Ep t excre- tory pore ; O, mouth opening with sucker ; S, sucker on middle of ventral surface ; P, pharynx ; J>, limb of alimentary canal. INCOMPLETE HETEROGAMY. 131 reproductive process is of the greatest interest as throwing light upon the way in which the phenomena of alternation of generations and heterogamy may have arisen in that it appears in a certain degree as the precursor of the alternating sequence of two or more genera- tions of individuals. The so-called alternation of generations in the stone-corals (Blastotrochus), which in early life reproduce themselves by budding, without thereby losing the power of acquiring sexual organs at a later period of life, forms an example of this method of reproduction. In this category of incomplete heterogamy should be placed the reproductive processes of the Phyllopoda and Rotifera, in which the female produces summer eggs capable of parthenogenetic develop- ment, and later winter eggs requiring fertilization (Daphnidce). [In the above account the term alternation of generations, or metagenesis is applied to those cases in which sexual and asexual generations alternate ; while heterogamy is applied to those cases in which two sexual generations or a sexual and parthenogenetic generation alternate.] CHAPTER IV. HISTORICAL REVIEW.* THE origin of Zoology extends far back into antiquity. Aristotle (4th century B.C.), who scientifically and in a philosophic spirit worked up the experiences of his predecessors with his own extended observations, must be looked upon as the founder of this science. The most important of his zoological workst treat of the " Repro- duction of Animals," of the " Parts of Animals," and of the " History of Animals." The last and most important work is, unfortunately, only incompletely preserved. We must not expect to find in Aristotle a descriptive zoologist, nor in his works a system of animals followed out into the smallest * Victor Cams, " Geschichte der Zoologie." Munchen, 1872. f Compare Jiirgen Bona Meyer's " Aristoteles' Thierkunde " (Berlin, 1855). Frantzius, " Aristoteles' Theile der Thiere " (Leipzig. 1853). Aubert und Wimmer, " Aristoteles' Fiinf Biicher von der Zeugung und Entwicklung der Thiere, iibersetzt und erlautert" (Leipzig. I860). Aubert und Wimmer, " Aristoteles' Thierkunde." Band I. und II. (Leipsij, 1868). 132 HISTORICAL REVIEW. details; a one-sided treatment of science was not the object of this great thinker. Aristotle contemplated animals as living organisms in all their relations to the external world, according to their development, structure, and vital phenomena, and he created a comparative Zoology, which in several respects constitutes the basis of our science. The distinction of animals into animals with blood (ei/ai^ua) and animals without blood (ai/aijua), which, he in no wise used as a strictly systematic conception, certainly depends, according to the meaning of the word, upon an error, since all animals possess blood; and the red colour can by no means be taken, as Aristotle believed, to be a test of the presence of blood ; but as the possession of a bony verte- bral column was put forward as a character of the animals provided with blood, the two groups established by this distinction coincided in their limits with the two great divisions of Vertebrates and Invertebrates. The eight animal groups of Aristotle are the following : Animals with blood, Vertebrates (1) Viviparous animals (four-footed, ^GJOTOKOWTO. ev avrots), with which as a special yevos was placed the whale. (2) Birds (opwfles). (3) Oviparous four-footed animals (rcTpctTroSa rj airo8a woroKowra). (4) Fishes (ix^'es). Animals without blood, Invertebrates (5) Soft animals (/zaXaKta, Cephalopoda). (6) Soft animals with shells (//,aA.aKo'crrpa/ Nummulite formation k ( of the Paris basin. (Maestricht strata, white chalk, Cretaceous Period -j upper green sand. Gault, lower green sand, Weald. fPurbeck strata, Portland stone, Kimmeridge clay, Coral Bag, | Oxford clay, Great oolite, Lower oolite, Lias (white, ' brown, and black jura). Keuper or upper new red sand- stone, Muschelkalk (upper Muschelkalk, gypsum and anhydrite, Wellenkalk, Bun- ter Sandstein). SECONDARY PERIOD (Mesozoic Formation}. SECONDARY PERIOD ( Mesozuic Formations). Jurassic Period Triassic Period Permian Zechstein, Rothliegendes.- lower new red sandstone. PALEOZOIC PERIOD / (PalcBuzoic Formation*). jCoal Measures of England, Carboniferous Germany, and North Period \ America, Kulm formation, I Carboniferous limestone. Devonian Period (Spiriferenschiefer, Cypridinen- schiefer, Stryngocephalenkalk, etc. old red sand- stone.) Silurian Period (Ludlow, Wenlock, strata, etc.) Cambrian Period (slate, etc.) ( Thonschiefer, Laurentian formations. Mica schist, ( Older Gneiss formations. According to Professor Kamsay the groups of formations in England have a thickness of 72,581 feet, i.e., about 13| English miles ; that is, formations of the Paleozoic period have a thickness of 57.154 1 Secondary 13,190 V 72,584 feet ARCH^AN PERIOD Tertiary 13,190 2.2JO J 166 MEANING OF THE SYSTEM. palseontologically from each other in such a manner as to lend support to the hypothesis of sudden and mighty revolutions and catastrophes destroying the whole living world. We may rather assert with cer- tainty, that the extinction of old species and the appearance of new ones has not taken place at the same time at all points of the surface of the earth, for many species extend from one formation into another, and a number of organisms persist from the tertiary period to the present time, but little altered or even identical. Just as the commencement of the recent epoch is hard to define, and cannot be sharply separated from the diluvial period by the character either of its deposits or of its fossils, so it is with the remoter periods of the earth's history, which are founded, like periods of human history, upon great and important occurrences, and yet are in direct con- tinuity. Lyell has proved in a convincing way on geological grounds that there were no sudden revolutions extending over the whole surface of the earth, but that changes took place slowly, and were confined* to separate localities; in other words, that the past history of the earth consists essentially of a gradual process of development, in which the numerous forces which may be observed in action at the present day have, by their long continued operation, had an enormous total effect in transforming the earth's surface. The reason for the irregular development of strata and for the limitations of formations is principally to be sought in the interrup- tion of depositions, which, though widely distributed, were only of local importance. Were it possible that a single basin of the sea should have persisted during the whole period of sedimentary forma- tion and under singularly favourable circumstances have formed new deposits in persistent continuity, then we should find a progres- sive series of strata interrupted by no gaps, which we should be unable to classify according to formations. Such an ideal basin would include only a single formation, in which we should find representatives of all the other formations of the surface of the earth. * " Every sedimentary formation was extended at the time of deposition over a confined territory, confined on the one hand by the extent of the sea or fresh- water basin, and on the other by the different conditions favourable to the depo- sition inside the basin. At the same time, in other places entirely or at any rate somewhat differently stratified formations (i.e., formations of the same age, but of different composition) resulted. Thus marine, fresh- water, and swamp formations have been deposited at the same time from different rocks and with different fossils, while the land surface has remained free." Comp. B. Cotta, " Die Geologic der Gegenwart." GAPS IN THE GEOLOGICAL EECORD. 167 In reality this ideal continuous series of strata is interrupted by numerous and often large gaps, which determine the petrographical and palaeontological differences, often strongly marked, between successive strata, and correspond to periods of inactivity, or, as may happen, to periods when the results of sedimentary action have been again destroyed. These interruptions of local deposits are explained by the constant alterations of level which the surface of the earth has undergone in every period in consequence of the reaction of the molten contents of the earth against its firm crust. As we see in the present time that wide tracts of country are gradually sinking (west coast of Greenland, coral islands), while others are being slowly elevated (west coast of South America, Sweden) ; that strips of coast line are suddenly submerged beneath the sea by subterranean forces, and that islands as suddenly appear; so it was in earlier periods. Elevation and depression were at work, perhaps uninterruptedly, causing a gradual, more rarely a sudden (and then locally confined) interchange between land and sea. Basins of the sea rising with gradual movement became dry land and rose up first as islands, and afterwards as connected continents, the different deposits of which, with their included fossils, bear witness of the sea which once covered them. On the other hand, great continents sank beneath the sea, leaving perhaps their highest moun- tain peaks appearing as islands, and again became the seat of fresh deposition of strata. In the first case there would be an interruption of deposit, while in the latter there would result, after a longer or shorter period of inactivity, the beginning of a new formation. Since, however, elevations and depressions, even though affecting districts of great extent, must always be locally confined, the commencement and interruption of formations of equal age have not taken place every- where at the same time. Deposits continued a long time on one tract after they had ceased on another; hence the upper and lower boun- dary of equivalent formations may show great want of uniformity, according to the different locality. This explains how it is that for- mations lying one above the other are composed of strata of very variable thickness, and why we can only in rare cases supply the gaps in the series of these strata from strata found in other countries. The whole succession of formations known to us up to the present time is not sufficiently complete to form an entire and uninterrupted series of the sedimentary formations. There are still numerous and important gaps in the geological record which we may expect to 168 MEANING OF THE SYSTEM. see filled in future days, when knowledge has increased, and per- haps only when formations now beneath the sea have become known to us. Imperfection of the Geological Record. After the foregoing dis- cussion we may consider that the continuity of living organisms in the successive periods of the earth's development and their close relationship has been proved partly by geological and partly by palseontological facts. The theory of descent, however, according to which the natural system must be regarded as a genealogical tree, requires still further proof. It requires proof of the presence of numerous forms, transitional not only between the species now existing and those in the more recent formations, but also between the species in all those formations which have immediately succeeded one another in point of time. The theory also demands proof that forms connecting the different groups of plants and animals of the present day have existed. The establishment and limitation of these groups can, according to Darwin, only be explained by the extinction, in the course of the earth's history, of numerous and intimately connected species. Palaeontology is only able imperfectly to comply with these demands ; for the numerous closely graduated series of varieties which, according to the theory of selection, must have existed, are, for the greater number of forms, entirely wanting in the geological record. This want, however, which Darwin himself recognised as an objection to his theory, loses its importance when we consider the circumstances under which organic remains were generally deposited in mud, and preserved for succeeding ages in a fossil form ; when we recognise the facts which indicate the extraordinary incomplete- ness of the geological record, and which show that the intermediate forms must have been in part described as species. First of all we can only expect to find in deposits the remains of those organisms which possessed a firm skeleton supporting the softer parts of the body, since it is only the harder structures of the body, such as the bones and teeth of Vertebrates, the calcareous and silicious shells of Molluscs and Rhizopods, the shells and spines of Echinoderms, the chitinous skeleton of Arthropods, etc., which are able to resist rapid decay, and to undergo gradual petrifaction. Thus the geological record will fail to provide us with any account of the numerous and principally low organisms which are not pro- vided with firm skeletal structures. But also among those organisms which are capable of becoming .IMPERFECTION OF THE GEOLOGICAL BECOBD. 169 fosdlized, there are large groups which have only exceptionally left braces of their existence : these are the animals which lived on land. Fossil remains of land animals can only have survived when, during great floods or inundations, or for some reason or other their carcasses have been carried away by the water, floated hither and thither, and been surrounded finally by hardening mud. This explains not only the relative scarcity of fossil Mammalia, but also the fact that of the most ancient Marsupials (Stonesfield slate), scarcely anything is preserved but the underjaw, which, as the body decayed, was easily detached, and, on account of its weight, offered most resist- ance to the current of the \vater, and was the first part to sink to the bottom. Although it has been shown by such remains that Mammalia existed in the Jurassic period, yet the Eocene forms are the first which give us an insight into the details of their structure. Circumstances must have been more favourable to the preservation of fresh-water animals, and most of all to that of marine animals, since the marine deposits have a much greater extent than the locally confined fresh-water deposits. Thick formations seem in general to have arisen under one of two conditions : either in a very deep sea, protected from the operation of winds and waves, no matter whether the bottom was gradually rising or sinking in this case, however, the strata would be relatively poor in fossils, since only the inhabitants of the deep sea, which is comparatively wanting in animal and vegetable life, would be preserved or in a shallow sea, in which the bottom underwent a gradual and continued depression during long periods of time favourable to the development of a rich and varied fauna and flora. In this case the sea would have retained uninterruptedly its rich fauna so long as the gradual sinking of its bottom was counteracted by the continual supply of sediment deposited upon it. Thick formations, all or most of the strata of which are rich in fossils, must have been deposited in extended and very shallow regions of the sea, during a long period of gradual depression. Thus the great gaps which occur in the series of palseontological remains are explained by a consideration of the mode of origin of deposits. These remains must necessarily be confined to the more recent formations. The lower, more ancient, and very thick succes- sions of strata in which the remains of the oldest fauna and flora must have been buried, seem to have been so completely altered by the heat of the molten interior of the earth, that the organic 170 M EASES' G OF THE SYSTEM. residua which they contain have been completely destroyed, or so altered that they cannot be recognised. In any case it may be regarded as certain, that only a small part of the extinct animal and vegetable world has been preserved in a fossil state, and that of this we only know a small part. Therefore we cannot conclude that, because the fossil remains of intermediate stages cannot be found, they have never existed. It is true that transitional forms are wanting in the strata where they should have occurred, that a species suddenly appears in the middle of a series of strata and suddenly disappears, and that whole groups of species make their appearance and quickly vanish, but the value of these facts as arguments against the theory of selection is diminished by the circumstance that in certain cases series of transitional forms between more or less remotely related organisms have been found, and that many species have been developed in course of time as links between other species and genera ; and again, that species and groups of species not ^infrequently increase very gradually till they attain an unusually wide distribution, extend into later formations, and then gradually di- appear again. Such positive facts have a higher value when we consider the incomplete- ness of fossil remains. It will suffice here to refer to the Ammonites and Gasteropods, such as Valvata multiformis, as examples supplied to us by Palaeon- tology of transitional forms which can be arranged in a gradual series. Relation of Fossil Forms with Living Species. The close rela- tionship of the plants and animals of the present time to the fossil remains of recent formations is a fact of great importance. In particular, we find in the diluvial period and in the different tertiary formations the ancestral forms from which numerous living species are directly descended ; and further the characteristic features of the fauna of any particular geographical province in the present epoch are foreshadowed by the fauna of the epoch immediately preceding in the same region ; a fact which is proved by the fossil remains we find buried in the most recent strata. Many fossil Mammalia from the diluvial period and the most recent (pliocene) tertiary formations of South America belong to types of the order of Edentata which are now distributed in that part of the world. Sloths and Armadillos of immense size (Megatherium, Megalonyx, Glyptodon, Toxodon, etc.) formerly inhabited the same continent, the mammalian fauna of which in the present day is so specially charac- SUCCESSION OF SIMILAR TYP2S. 171 terised by its Sloths, Armadillos, and Anteaters. In addition to these gigantic forms, small and extinct species have been found in the bone caves of Brazil, and some of these are so nearly related to the living forms that we may assume them to have been their ancestors. This law of the " succession of similar types " in the same localities is also exemplified by the Mammalia of New Holland; for in the bone caves of that country are found many species nearly allied to its present Marsupials. The same law holds good for the gigantic birds of New Zealand, and, as Owen and others have shown, for the Mam- malia of the Old World, which, indeed, is continuous by the circum- polar region with North America ; and ancient types were able, in the tertiary period, to pass into North America, and vice versd by that way. The presence of Central American types (Didelphys) in the early and middle tertiary formations of Europe is to be explained in the same way. It is even more difficult to distinguish the regions of distribution of the animals of that time than of those of the later tertiary period. The evolution of the ancient forms into those of the present time was effected in the case of the lower, simply organised animals at a much earlier period than in the case of higher organisms. Rhizopods, indistinguishable from species living at the present time (globigerina ooze) were already living in the Cretaceous period. The deep sea explorations * have accordingly yielded the interesting result, that certain Sponges, Corals, Molluscs, and Echinoderms now living in the deep sea existed in the Cretaceous period. We meet with a number of living species of Molluscs in the oldest tertiary period, though the mammalian fauna of this period differs completely from that of the present day. The greater number of species of Molluscs found in the recent tertiary period resemble those of the present day, but the Insects of that time differed considerably from living species. On the other hand, the Mammalia, even in the post-pliocene (diluvial) deposits, differ in part both in genera and species from those of the present day, although a number of forms have been preserved through the glacial period. On this account, and on account of the relative completeness of the tertiary remains, it is * (RJiizocrinusLofotentis Apiocrinites, Pleurotomaria, Siplionla, Micraster, Pomocaris, etc.) Types of earlier and even of the older geological formations have been found preserved in the depths of the ocean, which, in spite of the great pressure, the want of light and deficiency in gaseous contents of the water, are more suited to the development of animal life than was formerly believed. 172 MEANING OF THE SYSTEM. especially interesting to trace the recent mammalian fauna back through the pleistocene forms to the forms of the oldest tertiary period. It is possible to trace the ancestry of a number of mam- malian species. Riitimeyer was the first to undertake to trace out the ancestral line of the Ungulata, and especially of the Ruminantia, so as to obtain a palseontological developmental history, and succeeded in obtaining results, by means of detailed geological and anatomical (deciduous teeth) comparison, which leave no room to doubt that whole series "of species of existing mammalia are collaterally or directly related with each other and with fossil species. Riitimeyer's investigations have received corroboration in their essential points from the recent comprehensive works of W. Kowalevski, and have resulted in the establishment of a natural classification of the ungulate animals founded on phylogeny. FIG. 117. Bones of the feet of the different genera of the Equidce (after Marsh), a, Foot of Orohippus (Eocene), b, Foot of AncMtkerium (Lower Miocene), c, Foot of Hipparion (Pleiocene). d, Foot of the recent genus Equus. In addition to these works we have the recent researches of Marsh, who has completed to an extraordinary degree our knowledge of the genealogy of the genus Equus, by numerous discoveries (fig. 117) in America (Wyoming, Green River, White River}. The eocene Orohippus, in which the small posterior toes were present as well as the three principal toes which rested on the ground, was succeeded in the Lower Miocene formation by Anchitherium with three hoofs ; and the latter was followed by the Hipparion of the Pleipcene formations ; and this -is the ancestral form of the existing genus Equus. The origin of most orders of Mammalia, such as Rodentia, Cheirop- tera, Proboscidea, Cetacea, etc., cannot be clearly traced out, but for certain orders, as the Prosimice, Carnivora, Ungulata, and Ro- EVOLUTION Ol 1 MAMMALIA. 173 dentia, remarkable transitional forms have been discovered among the remains of extinct types. These also appear most prominently among the tertiary remains of North America. In the Eocene period here (Wyoming) lived the Tillodontia with the genus Tillo- therium* characterized by having a broad skull like a bear, two broad incisor teeth like a rodent, and molar teeth like Palceotherium, and feet having five toes armed with strong claws. It thus united in its skeletal structure peculiarities of Carnivora and Ungulata. The Dinocerata (Dinoceras laticeps mirabile) were powerful Ungulates with five-toed feet with six horns on their heads, without incisors in the praemaxillary bone, with strong sabre-like canine teeth in the upper jaw and with six molars. A third type, that of the Brontotheridce attained elephantine proportions, and was provided with transversely placed horns in front of the eyes. In addition to the foregoing there are a number of other groups of Mammals now completely extinct, the remains of which extend back into far earlier strata. Amongst them are the South American Megatheridce (Mylodon, Megatherium}, which belong to the order Edentata, and the Toxodontia, whose skull and dentition show relations to the Ungulates, Rodents, and Edentates. Many other types, however, especially of the Ungulates, which during the tertiary period inhabited both hemispheres, are now extinct in America, but still exist in the East. Elephants, Mastodonta, Rhinoceridse, and Equidse existed in America in the diluvial but not in recent periods. Of the Perissodactyles the group of Tapirs alone is preserved in America. This group has also been preserved in the Eastern hemisphere in the East Indian species. In the palsearctic region also are found the remains of extinct intermediate groups of Mammals which existed during the tertiary period. In the Phosphorites of Quercyt in the south of France are found the remains of the skulls of Prosimiae (Adapis), the dentition of which is intermediate between the ancient Ungulates and the Lemuridse (Pachylemuridce), so that the question may be raised whether the Prosimiae had not a common ancestry with several * Compare 0. C. Marsh, "Principal Characters of the Tillodontia." Amer. Journal of Science and Art, Vol. xi., 1876. 0. C. Marsh, " Principal Characters of the Dinocerata." Amer. Journal oj Science and Art, Vol. xi., 1876. 0. C. Marsh, " Principal Characters of the Brontotheridae. " Amer. Journal of Science and Art, Vol. xi., 1876. f Compare H. Filhol, " Recherches sur les Phosphorites du Quercy, jfitude des fossils qu'on y rencontre et specialement des Mammiferes." Ann. Science* Vol. vii., 1876. .174 MEANING OF THE SI STEM. eocene Ungulates (Pachydermata). In the same locality are found the well preserved remains of the bones of peculiar Carnivora which are well worthy of remark. These are the Hyaenodonta. It was for a long time doubtful whether they were Marsupials or not, until Filhol showed from the reserve teeth of their permanent dentition that they were probably of the nature of placental Carnivora. The great agreement of the molars of these Hysenodonta with those of the carnivorous Mar- supials, as. well as the small size of the skull cavity and the rela- tively slight develop- ment of the brain, support the view, which is also rendered probable by many other circumstances, that placental Mam- malia have developed from the Marsupials of the mesozoic period. In the oldest strata of the Eocene forma- tions in both hemi- spheres, the higher placental Mammalia already appear in a rich variety of forms, which contrast mark- edly with one another (Artiodactyla, Peris- sodactyla). There is, however, no ground for regarding the immeasurable period from the oldest Eocene to the Keuper, in which the oldest Mammalian remains (the teeth and bones of insectivorous Marsupials) have been found, as the period in which tkis higher development of the Mammalian organism has been effected. In other cases also the science of palaeontology has led to the discovery of intermediate forms between groups and even between FIG. US. Tterodacfyhig cratslrostris (after Goldfuss) about one-third natural size. EVOLUTION OF BIBDS. 175 classes and orders. The Labyrinthodonta, the most ancient of the Amphibia, found as early as the carboniferous period, present many piscine characters (ventral exoskeleton), and have a cartilaginous skeleton. Many fossil orders and sub-orders of Saurians (Halo- sauridce, Dinosauridce, Pterodactylidice (fig. 118), Thecodontidce) have not left a single representative in the present day ; others again are transitional between recent orders. Such a relation has, for example, been recently shown between the " Pythonomorphous " lizards (related to the genus Mosasaurus} from the chalk in America, and serpents so far as the structure of the skull and jaw is concerned. Owen's researches on the fossil Reptiles of the Cape have shown that certain Reptiles (T/ieriodonta) once lived there which showed a close resemblance to carnivorous Mammalia with regard to their dentition and the structure of their feet. The teeth of these animals, though only furnished with one root, can be divided into incisors, canines, and molars, a fact which induces us to believe it possible that the dentition of the most ancient Marsupials hitherto known (Keuper) may have been derived from that of a Theriodon- like Reptile. Even as regards birds, a class so uniform in structure and so sharply defined, a form (Archceopteryx lit/wgraphica) (fig. 119) transitional between them and Reptile has been discovered in the Sohlenhofen slate, although the impression was not perfect. In this form the short tail of the bird is replaced by a long reptilian tail composed of numerous (20) vertebrae and provided with two rows of feathers (Saururce). The articulation of the vertebral column and the structure of the pelvis indicated an affinity to the long-tailed Pterodactyls. The discovery of a second and more perfect specimen of Archceop- teryx has made known to us its dentition. It had sharp-pointed teeth wedged into the jaws. Other types of birds have also been found in the American chalk, which diverge more widely among themseves and from the Saurians than do the birds of any living order. These were defined as Odontornithes by Marsh,* and dis- tinguished as a sub-class j they had teeth in the jaws, which latter were elongated to form a kind of beak. Some of them (Order Ichthyornithes) had biccelous vertebras, a crista sterni, and well * 0. G. Marsh, " On a new sub-class of fossil Birds (Odontornitlie**.'- 9 American Journal of Science and Art, Vol. v., 187;]. 0. C. Marsh, " On the Odontornithes, or birds with teeth.'' American Journal of Science and Art, Vol. x.. 1875. 176 MEANING OF THE SYSTEM. developed wings (Ichthyornis). Others (Odontolcce) had teeth FIG. 110. ArchcEoptcryx lithcgi aplica. bedded in pits, normal vertebra, no keel to the breast-bone, and rudimentary wings. They were not capable of flight PROGRESSIVE PERFECTION. 177 Lestornis). Possibly in future days we shall be able by the dis- covery of new types to establish the connection with the Dino- murians (Compsognathus), the formation of whose pelvis and feet offers a closer relationship to those parts in birds. Advance towards perfection. If we compare the animal and vegetable life of the most ancient formations with that of the sue ceeding periods of the earth's development, it becomes evident that there has been, on the whole, a continual progress from a lower to a higher condition. The oldest formations of the so-called archsean time, the rocks of which are for the most part in a metamorphic state, must from their enormous thickness have occupied immea- surable time in their origin. They contain no fossil remains which can be recognised with certainty as such ; although the presence of bituminous gneiss in the old formations is a proof of the existence of organic bodies at that time. All the organisms of these most ancient periods, which were certainly numerous, have been de- stroyed without leaving any further traces than the Graphite deposits of the crystalline schist. In the most ancient and very extensive groups of strata we find exclusively cryptogamous plants, especially Fuci, which formed extensive forests beneath the sea. The warm seas of the primary period were inhabited by numerous sea animals of very different groups, such as Zoophytes, Molluscs (especially Brachiopoda\ Crustaceans (larva-like Hymenocaris, Trilo- bites), and Fishes whose peculiar armoured forms (Cephalaspidce) indicate a low stage of organization. In the coal formations we meet for the first time with the remains of land animals, Amphibia (Apatheon, Archegosaurus), with a notochord and a cartilaginous skeleton ; we also find Insects and Spiders; and in the Permian formations we meet with large lizard-like reptilian forms (Protero- saurus); while fishes, exclusively Elasmobranchs and Ganoids with a notochord, and vascular cryptogamous plants (Tree-ferns, Lepido- dendra, Calamites, Sigillaria, Stigmaria) still predominate. In the carboniferous period isolated instances of the Lizards amongst Vertebrates and of Coniferse and Cycadiae amongst plants had already made their appearance ; but in the secondary period they obtained such a preponderance that the whole period has been named from them the period of Saurians and Gymnosperms. Amongst the first the colossal Dinosaurians living upon the land, the flying Lizards or Pterodactyls, the Halosaurians, with their best known genera Ichthyosaurus and Plesiosaurus, are entirely peculiar to the secondary period. 12 178 MEANING OF THE SYSTEM. Examples of Mammalia, although scarce, are found in the upper Triassic beds, and also in the Jurassic. Such Mammalia belong without exception to the lowest grade of Marsupials. Flowering plants appear for the first time in the chalk, as do the oldest remains of distinctly bony fishes. Flowering plants and Mammalia and amongst the latter the highest order of Apes is represented so preponderated in the tertiary period that it has been, called the period of leafy forests and Mammalia. The plants and animals of the upper tertiary beds show a gradually increasing resemblance to those of the present time, the higher we ascend in the series. Numerous lower animals and plants are identical, not only generically but also specifically with those now living, and the genera and species of the higher animals have a greater resemblance to those of the present time. With the transition to the diluvial and recent epoch, the number and area of distribution of the higher types of flowering plants increase, and in every order of Mammalia we find forms whose structure is specialized more and more in definite directions, and which therefore appear more perfect. In the diluvial age we find the first unmistakable traces of the existence of Man. His history and the development of his civilization has occupied only the last portion of the recent period which has been relatively so short. Despite its great incompleteness the geological record affords sufficient material to prove the existence of a progressive develop- ment from simple and lower grades of organization to higher, and to confirm the law of a progress towards perfection in the succession of the groups. We are indeed unable to make use of more than a small period of the time that has been occupied in this progress towards perfection of organisms, since the organic world of the most ancient and extensive periods has completely disappeared from the record. If, after the above discussion, we consider the hypothesis of Trans- mutation of Species and of Descent to have a firm foundation on fact, we must concede a high value to Darwin's theory of Selection as an explanation of the manner in which the transmutation of species has been effected. There are yet natural historians who admit the great changes which the animal and vegetable world have undergone, and yet combat the Darwinian principle of Selection, without being able to give any other explanation. The phenomena of gradual progress towards perfection agree very well with the theory of Selection. INCOMPLETENESS OF THE EXPLANATION. 179 Natural Selection leads, on the whole, to a progressive differentiation of organs (division of labour), since it preserves any peculiarities which are of use in the struggle for existence, and thus tends to the perfection of the organism. We can therefore connect the progress of simple types to higher ones with the principle of utility implied by Natural Selection, without being obliged, with Nageli, to have recourse to the obscure notion of an inexplicable tendency towards perfection. It is the latter mystical supposition, and not Natural Selection, which is contradicted by the fact that we find a number of Rhizopods, Molluscs, and Crustacea (e.g., the genera Lingula, Nautilus, Limulus) have existed almost without alteration from the earliest formations through all the geological periods to the present time, and by the observation of a retrogression of organization in the course of development (e.g., retrogressive metamorphosis of Parasites). Nor again can it be objected that on the hypothesis of Natural Selection the lower types should have been long ago suppressed and have become extinct, while, as a matter of fact, there are higher and lower genera in every class, and the lowest organisms are numerous and widely distributed. It is precisely the great variety in the degrees of organization which brings about and is favourable to the greatest development of life, all the forms of which, both the higher and the lower, being best suited to their peculiar circumstances are able, more or less perfectly, to occupy a special place in nature, and in a certain sense to maintain it. Even the most simple organisms occupy a place in the economy of nature which can be filled by no other organisms, and are necessary to the existence of numerous higher grades. However well grounded we admit the theory of Selection to be, we cannot accept it as in itself sufficient to explain the complicated and involved metamorphoses which have taken place in organisms in the course of immeasurable time. If the theory of repeated acts of creation be rejected and the process of natural development be established in its place, there is still the first appearances of organisms to be accounted for, and especially the definite course which the evolution of the complicated and more highly developed organisms has tdfken has to be explained. In the many wonderful phenomena of the organic world, amongst others in the origin of Man in the diluvial or tertiary period, we have a riddle the solution of which must remain for future investigators. SPECIAL PAST CHAPTER VI. PROTOZOA. Animals of simple constitution and small size ; without tissues com- of definite cells. Sexual reproduction by means of ova and spermatozoa unknown. From a morphological point of view the Protozoa have remained at the stage of cells, in the protoplasm of which one or more nuclei may be present. The phenomena of segmentation of the egg and formation of the germinal layers are therefore absent from their development. The body is always composed of a contractile granular substance, filled with vacuoles ; it may also contain a pulsating vacuole } and present the phenomenon of granule currents. The pulsating vacuole consists of a space without walls filled with a clear fluid. This space apparently diminishes and disappears through the contrac- tion of the surrounding plasma., and then re-appears. There exists, however, in the varying differentiations in the interior of the sarcode body, and in the differences in the external boundary, and in the manner of nourishment, a number of modi- fications which we shall use for the foundation of groups. In the simplest cases, the entire body consists of a small lump of sarcode, the contractility of which is confined by no firm external membrane. This lump of sarcode is sometimes semi-fluid, and protrudes and retracts processes. It is sometimes of tougher consistence in parts, and protrudes hair-like rays and threads (JRhizopoda). Nourishment takes place through the intussusception of extraneous bodies, which can be surrounded and enclosed by the protoplasmic substance at any portion whatsoever of the periphery of the body. In other cases the body which sends out slender processes (pseudopodia) secretes fcilicious or calcareous needles, lattice-work shells, or shells perforated RHIZOPODA. 181 by holes, to shelter and protect the body (Foraminifera, Radiolaria). In the Infusoria the sarcode body is bounded by an external mem- brane, and is capable of quick and varied locomotion by means of the movements of the cilia, hairs, bristles, etc., which it possesses. The solid nourishing matter is taken in through a mouth, and the remainder, after digestion, passes out through an anal aperture. CLASS I. RHIZOPODA.* Protozoa without external investing membrane, the parenchyma of which protrudes and retracts processes ; as a rule, a calcareous shell or silicious skeleton is secreted. The body-substance of these animals, the shells of which were described as Foraminifera or Polythalamia, long before their living contents were known, consists of sarcode, and is without any boundary mem- brane. The body- subs tan ce, which is richly granulated and contains pig- ment, contracts slowly and sends out at the same time fine thread -like rays (fig. 120), for FlG 120. Optical section through portion of the sarccde body of the most part of a semi-fluid consistency (pseudopodia] ; and these serve not only as a means of movement but also for the reception of nourishment. The pseudopodia may, how- * Dujardin, "Observations sur les Rhizopodes" {Comptes rendus, 1835). Ehrenberg, " Ubcr noch jetzt zahlreich lebende Thierarten der Kreidebildung und den Organismus der Polythalamien " {AhJiandlung der Akad. zu Berlin, 1839). Max Sigm. Schultze, " Uber den Organismus der Polythalamien" (Leipzig. 1854). Job. Miiller, " Uber die Thalassicolen, Polycystinen und Acan- thometrcn" (1858). E. Haeckel, "Die Kadiolarien " (Eine Monographic. Berlin. 1S62). ActinospJiaerium Eichhornii (after Hertwig and Lesser). N, nuclei in the endosarc, from which the vacuolated ectosarc is clearly dis- tinguishable. In the centre of the pseudopodia the axial thread is visible. 182 PROTOZOA. ever, be broad, lobed, or finger-like processes by means of which a quick and flowing motion can be imparted to the body mass. A tougher, clear homogeneous external layer (Exoplasm) is usually to be distinguished as the peripheral boundary from a more fluid and more granular internal mass (jEndoplasm). During motion the former is projected in processes into which the granules of the latter stream more or less quickly. In the stiffer pseudopodia streams of granules are observable, slow but regular, passing from the base to the extremity and vice versd. The explanation of these movements is to be sought in the contractility of the surrounding portions of sarcode (fig. 120). A pulsating space, the contractile vacuole, is not unfreqently to be found in the sarcode, e.g., Difflugia, Actinophrys, Arcella (fig. 121). Nuclei are also usually present in the sarcode, by w^hich the morpho- logical value of the Khizopod body as cell or as cell aggregate is placed beyond all doubt. There are also forms in the protoplasm of ji 7 / which no trace of a cell nucleus has been found. In such either the protoplasm of the nucleus is not yet \^i^fH^f3^V^ differentiated as a separate structure "" .__, (the Monera of E. Haeekel), or we j have to do with a transient, non- nucleated stage in the life-history. The sarcode usually secretes sili- cious or calcareous structures, either \j \ as fine spicula and hollow spines ' / \\ which are directed from the centre to the periphery in regular order '%?<.S*l3?*& "* numW > or as ^ice-work cieus. PC. pulsating vacuole. chambers (Radiolaria) , which often bear points and spines, or finally as single and many chambered shells with finely perforated walls (Foraminifera) and one larger opening. Through this last (fig. 123), as well as through the countless pores of the small shells (fig. 122), the slender threads of sarcode pass out to the exterior as pseudopodia, changing without intermission in form, size, and number, and often joining themselves together in delicate networks (figs. 122, 123). The pseudopodia, by their slow, creeping movements, afford a means of locomotion, while they also serve for the taking up of nourishment EIITZOrODA. 183 by surrounding and transporting into the interior of the body small vegetable organisms '. Bacillaria. Among the shell-bearing forms, the reception and digestion of food takes place outside the shell in the peripheral threads and networks of sarcode ; for each spot on the surface can for the time being assume the functions of mouth, and v FIG. 122. Rotalia venda (after M. Schultze), with a DIaton. taken in tha network of Pseudopodia. also of anus, by rejecting the undigested remnants. The Rhizopoda live for the most part in the sea, and contribute by the accumulation of their shells to the formation of the sea sand, and even to the deposition of thick strata. An innumerable quantity of fossil forms from various and very ancient formations are known. 184 JMIOTOZOA. Order 1. FORAMINIFERA.* Rhizopoda, either naked or with a shell, the shell almost invariably calcareous and usually pierced ivith fine pores for the exit of the pseudopodia. Only in rare cases, for instance Nonionina and Polymorphina, is the shell substance of a silicious nature; in all other forms it is J FIG. 123. Miliola tenera, with, network of pseudopodia (after M. Schultzc). membranous or consists of a calcareous deposit in a basis of organic matter. The shell is either a simple chamber, usually provided with a large opening, or is many chambered, that is, is composed of numerous chambers arranged upon one another according to definite laws. The spaces of these chambers communicate by means of narrow * Besides D'Orbigny, Max Schultze, 1. c.,. compare W. C. Williamson, " On the recent Foraminifera of Great Britain," London, 1858. Carpenter. " Introduq- tion to the Study of the Foraminifera," London, 1862. Eeuss, "Eutwurf einer system. Zusammenstellung der Foraminiferen," Wien, 1861. 185 passages and large openings in the partition walls. In like manner those portions of the living sarcode body which are enclosed in the individual chambers are in direct communication with one another by means of processes which pass through the passages and openings in the septa, and connect one portion with another. The quality of the body-substance, the mode of movement .and nourishment, agree closely with those which have been depicted as characteristic of the order. Our knowledge of the mode of reproduction is imperfect. Amongst the forms without a shell, fission has been observed as well as fusion, which may perhaps be referred to a species of sexual reproduction (conjugation}. The reproduction of shell-bearing Foraminifera such as Miliola and Rotalia has also been observed. The former produces from the protoplasm of its body single chambered, the latter three-chambered, young. Probably this mode of reproduction is preceded by an increase in the number of nuclei, and the animal divides into as many portions as there are nuclei, each of which becomes a young Foraminifer, and contains but one nucleus. In spite of their small size, the shells of our simple organisms may lay claim to no small consequence, since they not only accumulate in enormous quantity in the sea sand (M. Schultze calculated their number for an ounce of sea sand from Molo di Gaeta at about one and a half millions), but are also found as fossils in different formations (the cretaceous and tertiary), and have yielded an essential material to the construction of rocks. Silicious nodules of Polythalamia are even found in Silurian deposits. The most remarkable, on account of their considerable size, are the Nummulites (fig. 124) in the thick formation of the so-called Nummulite limestone (Pyrenees), A coarse chalk of the Paris basin, which makes a i excellent building stone, contains the Triloculina triyonula (Miliolite chalk). The greater number of Foraminifera are marine, and move by creeping on the bottom of the sea, but Globigerina and Orbulina have been met with on the surface. The bottom of the sea at very consider- able depths is also covered with a rich abundance of forms, especially with Globigerina, the remains of the shells of which give rise to an enduring deposit. 1. Sub-order: Lobosa (Am&biformts). Amceba-like fresh -water Khizopoda, usually with pulsating vacuole, sometimes naked, some- times with a single-chambered firm shell. The sarcode body consists as a rule of a tougher exoplasm and a fluid granular endoplasm. The pseudopodia are lobed or finger-shaped processes of considerable 186 PEOTOZOA. size, occasionally tougher slender processes without granule streams (figs. 125 and 126). Amoeba princeps Ehrbg., A. terricola Greet"., Petalc>i/u.s di&ugiens Clap. Lachm. Here should also be placed the famous BathyMus SaecTteli Huxl., which is found in the' deep sea mud of the Atlantic Ocean, if it is indeed a living organism (and not simply a deposit of Gypsum). Arcella vulgaris Ehrbg., Difflugia proteiformis Ehrbg., Euglyplia globosa Cart, have shells and tough, pointed, dichotomously branching pseudopodia (fig. 125). FIG. 12i. Nunmmlitic Limestone, with horizontal section of N. distant (after Zittell). FIG. 12P. ollonga (after Steiu). v FIG. 125. Euglypla globe fa (after Hei twig and Lessei ). FIG. 127. Acervulina ghboxa (alter M. Schultze). 2. Sub-order : Reticularia (Thalamophora). Principally marine Rhizopods with extremely slender anastomosing pseudopodia, with granule streams in the latter, rarely naked (Protogenes, Lieber- kuhnia), usually with membranous or calcareous shell, which is single-chambered (Monolhalamia) or many-chi-'mbered (Polythalamid) (fig. 127). HELIOZOA. 187 1. Imperfurata. With membranous or calcareous shell, which is without fine pores, but possesses, in one place, an opening, either simple or sieve-like, through which the pseudopodia project. To these belong the Gromidce, with a mem- branous chitinous shell : Gromia oviformis Duj., and Miliolidfe, with a porcellanous shell : Cornuspira planorbis M. Sch., Miliola cyclostoma M. Sch., from the Miliolite chalk. 2. Perforata. The shell, which is usually calcareous, is invariably pierced with innumerable fine pores as well as by one larger opening, and has complicated passages in the partition walls of its chambers. The LagenidcB have a hard shell, with a large opening surrounded by a toothed lip : Lagena vulgaris Williamson. The Globigerinidce on the contrary have a hyaline shell pierced by large pores, and a simple slit-like open- ing : Orbulina, universa D'Orb., Gloligevina bulloides D'Orb., Rotalia D'Orb. , Textularia D'Orb. The greatest size is attained by the Nummulinida, which possess a firm shell and an in- ternal skeleton, which last is pierced by a complicated canal system : Polystomella Nummulina D'Orb. Lam. \ Order 2. HELIOZOA.* Fresh-water Rhizopods usually with pulsating vacu- ole, and one or more nuclei. A radial silicious skeleton sometimes present. The sarcode body sends out in all directions tough radiating pseudopodia (fig. 128). When a skeleton is secreted, it consists either of radially arranged silicious spines (Acanthocystis) or of latticed silicious shells (Clathrulina), and so closely resembles the skeleton of the Radiolaria that the Heliozoa have been actually described as fresh-water Radiolaria. They differ from the Radiolaria in the absence of the complicated * L. Cienkowski, " Ueber Clathrulina." Arcliiv. fur mihrosk. Anatomie, Tom III., 1867. R. Greeff, " Ueber Radiolarien und radiolarienahnliche Rhizopoden des siissen Wassers." Tom V. & XT. R. Hertwig und Lesser, " Uber Rhizopoden und denselben nahe stehende Organismen." Suppl. Tom X., 1874. Also Aroher and F. E. Schultze, etc. 123. Young ActinofpTicenum, stiH with a single nucleus (aftei F. E. Schultze). N, Nucleus. 188 PROTOZOA. differentiations of the sarcode, particularly of the central capsule. One or more nuclei may be present in the central mass. An im- portant distinguishing mark is afforded by the presence of the pulsating vacuoles, which have not been observed in any marine Radiolarian. The reproduction very frequently takes place by fission, occasionally FIG. 129. Thalassicolla pelagica, with central capsule and single large nude us, also numerous alveoli in the protoplasm (after E. Haeckel). after previous conjugation of one or more individuals, also during encystmeiit. Multiplication by spores has also been observed (Clathrulina). In the ActinojjJiryidce there is no skeleton secreted : Actinnsphcerium Eichhornii Ehrbg. The central matter contains numerous nuclei. Actinoplirys sol Ehrbg. of small size, with a single central nucleus. In the Acantliocystidts slender silicious spikes, are found: Acanthocysti* spinifera Greeff. with silicious spikes and needles. In Clathrulina there is a latticed silicious shell, and ihe body has a stalk Clathrulina elegans Cienk. KADIOLARIA. 189 Order 3. RADIOLARIA.* Marine Rhizopoda with complicated differentiation of the sarcode body, with central capsule and radial silicious skeleton. The sarcode body contains a membranous porous capsule (the central capsule), in which is contained a tough slimy protoplasm with vacuoles and granules (intracapsular sarcode), fat and oil globules, and albuminous bodies, and more rarely crystals and con- cretions. The intracapsular mass contains also a single large nucleus or several small nuclei. The sarcode which surrounds the capsule and which emits on all sides simple or anastomosing pseudopodia, contains numerous yellow cells, sometimes pigment masses ; and in some cases delicate trans- parent vesicles, or alveoli, are found in the peripheral layer between the radia- ting pseudopodia (Thalas- sicolla pelayica, fig. 129). Many Radiolaria form colonies, and are composed of numerous individuals. In such colonies the al- veoli are placed in the common protoplasm, which contains in itself, not as in the monozoic -; ; i ; . Radiolaria a single cen- ( tral capsule, but a number FlR iso.Acanthometra mileri (after E. Haeckel). of capsules. Only a few species remain naked and without firm deposits ; as a rule, the soft body possesses a silicious skeleton, which either lies entirely outside the central capsule (Ectolithia) or is partially within it (Entolithia}. In the most simple cases the skeleton consists of small, simple, or toothed silicious needles (spicula) united together, which sometimes give rise to a fine sponge work round the periphery of the proto- plasm, e.g., Physematium. In a higher grade we find stronger hollow silicious spicules, which radiate from the middle point of the body to the periphery in regular number and order, e.g., Acanthometra * Joh. Miiller, " Ueber die Thalassicoilen, Polycystinen und Acanthometren," Abh. dcr Bcrl. Akad. 1858. E. Haeckel, " Die Kadiolarien," Eine Monographic Berlin, 1862. 190 PROTOZOA. (fig. 130). A fine peripheral framework of spicules may be added to these. In other cases simple or compound lattice-works, and pierced shells of various external form (like helmets, bird-cages, shells, etc.) are found, and on the periphery of these, spicules and needles, and even external concentric shells of similar shape may be formed, e.g., Polycystina (figs. 131 and 132). Tip to the present time but little has been made out about the reproduction of these animals.. Besides fission (Polycyttaria), the formation of spores has been observed. These are formed from the contents of the central capsule, and, after the bursting of the latter, become free-swimming mastigopods. Kadiolaria are inhabitants of the sea, and swim at the surface, but are also able to sink to deeper levels. Fossil remains of Ra- diolaria have been made known in great numbers by Ehrenberg, e.g. from the chalky marl and polishing slate found at certain parts of the coast of the Mediterranean (Caltanisetta in Sicily, Zante and ^Egina in Greece), and in particu- lar from the rocks of Barbados and Nikobar, where the Radiolaria have given rise to widely extended rock formations. Samples of sand also from very con- siderable depths have shown themselves rich in Radiolarian shells. I. Radiolaria monozoa. Kadiolaria which remain solitary. 1. Fam. Thalassicollidae. Skeleton absent or consisting of single spicules not joined together. Thalassicolla (without skeleton) nucleata Huxl., Physe- matium Millie ri Schn. 2. Fam. Polycystinidae. The skeleton consists of a simple or divided latticed shell, the long axis of which is bounded by two poles of different structure. Heliosphcera. Eucyrtidium galea E. Haeck. 3. Fam. Acanthometridae. The skeleton consists of several radial spicules which pass through the central capsule and unite in its centre, without forming J FIG. IZl.HeUosplicera echinoides (after E. Haeckel). INFUSORIA. rJl a latticed shell. The extra-capsular cells [yellow bodies] are wanting. Acantlio- inetra pellucida Joh. Mull. II. Polycyttaria. Radiolaria which form colonies with several central capsules- Amongst the Sphaerozoa a skeleton is wanting or consists of single pieces not joined together. Collozoum inerme E. Haeck. Splicer ozoum punctatum Joh. Mull. In Collosplusra the skeleton consists of simple latticed spheres, each of which encloses a central capsule, Collosplicera Huxley i Joh. Mull. \ FIG. 132 Eucyrtidium cranoides (after E. Haeckel). CLASS II. INFUSORIA.* Protozoa with a definite form and provided with an external membrane, bearing either flag ella or cilia. Mouth and anus usually, contractile vacuole and one or more nuclei always present. Infusoria were discovered towards the end of the 17th century * Ehrenberg, " Die Infusionsthierchen als vollkommene Organismen," 183S. Balbiani, "Etudes sur la Reproduction des Protozoaires," Journ. de la Phys., Tom. III. Balbiini, "Recherches sur les phenomenes sexuels des Infusoires," 192 PEOTOZOA. in a vessel of stagnant water by A. von Leeuwenhoek, who made use of a magnifying glass for the examination of small organisms. The name Infusoria, which was at first used to denote all animalculse which appear in infusions and are only visible with the aid of a microscope, was first brought into use by Ledermiiller and Wrisberg in the last century. Later on the Danish naturalist 0. Fr. Miiller made valuable additions to our knowledge of Infusoria. He observed their conjugation and their reproduction by fission and gemmation, \ and wrote the first systematic work on the subject. 0. Fr. Miiller included a much larger number of forms than we do now-a-days, for he placed among the Infusoria all invertebrate water animal- culse without jointed organs of locomotion and of microscopical size. The knowledge of Infusoria received a new impulse from the comprehensive researches of Ehrenberg. The principal work of this investigator, " Die Infusionsthierchen als vollkommene Organismen," discovered a kingdom of organisms hardly thought of. These were observed and portrayed under the highest microscopic powers. Many of Ehrenberg's drawings may even yet be taken as patterns, and are hardly surpassed by later representations, but the significance of the facts observed has been essentially corrected by more recent investi- gations. Ehrenberg also conceded too great an extent to the group of Infusoria, including not only the lowest plants such as Diatomacece, Desmidiacece, under the name of Polygastrica anentera, but also the much more highly organised Rotifera. As he chose the organization of the last-named for the basis of his explanations, he was led into numerous errors. Ehrenberg ascribed to the Infusoria ( mouth and anus, stomach and intestines, testis and ovary, kidneys, sense-organs, and a vascular system, without being able to give reliable proofs of the nature of these organs. There very soon came a reaction in the way of regarding the Infusorian structure ; for the discoverer of the Rhizo})oda } Dujardin, as well as von Siebold and Kolliker (the latter taking into consideration the so-called Nucleus and Nudeolus), referred the Infusorian body to the simple cell. In the subsequent works of Stein, Claparede, Lachmann, and Balbiani numerous differentiations were certainly shown to exist, which, however, can all be referred to differentiation of the body of the cell. This view is supported by Journ. de la Phys., Tom. IV. Claparede und Lachmann. "Etudes sur les Infusoires et les Rhizopodes," 2 vol. Geneve, 1858 1861. E. Haeckel, "Zur Morphologic der Infusorien" Jen Zeitschrift, Tom. VII., 1873. 0- Biitschli, "Studien tiber die ersten Entwickelungsvorgange des Eizelle, die Zelltheilung und die Conjugation des Infusorien," Frankfurt, 1876. FLAGELLATA. 193 the more recent work of Biitschli, who has shown that the repro- duction of these animals is essentially similar to that of the cell. The outer boundary of the body is usually formed by a cuticle, a delicate, transparent membrane, the surface of which is beset with vibratile and moving appendages of various kinds arranged in regular order. In the smallest Infusoria, the Flagellate, we find only one or two long whip-like cilia ; while the more highly differentiated Ciliata are usually richly provided with cilia. According to the varying thickness of the external membrane, which cannot in all cases be isolated, and according to the different condition of the peripheral parenchyma of the body, we get forms which change their shape, forms which have a fixed shape and armoured forms. If the simply organized Flagellata, which present numerous affinities and transitional forms to the Alga3 and Fungi, are not entirely removed from the region of the Infusoria, the two principal groups to be distinguished are the Ciliata and Flagellata. Order 1. FLAGELLATA.* Infusoria of small size, characterised by possessing one or more long whip-like cilia, usually placed at one end of the oval body. A row of cilia sometimes and a nucleus always present. The Flagellata are Infusoria the locomotive organs of which consist of one or more whip-like cilia, rarely with an accessory row of cilia. They pass through an inactive stage, and in their develop- ment as well as in their mode of nourishment are allied to certain Fungi. The reasons for regarding the Flagellata as Protozoa are the perfect contractility of the body, which is not surpassed by Myxomycetes in the mastigopod stage ; also the contractility of the cilia, the apparently purposed and voluntary movements, the occurrence of contmctile vacuoles, and, as has been established in many cases, the reception of solid substances into the body through an opening at the base of the flagellum. Nevertheless these phenomena are by no means a test of animal organization. The Monadince are a large group of Flagellata, found for the most part in putrefying infusions, and are hard to distinguish from the monads usually regarded as fungi. They reproduce themselves by * Besides Ehrenberg, Claparede, and Lachmann, loc. cit., compare Stein, "Organismus der Infusionsthiere," Tom. III., 1878. Biitschli, " Beitrage zur Kenntniss der Flagellaten," Zeitsclir. fur Tf 'iss. ZooL, Tom. XXX. Dallinger and Drysdale, "Researches on the Life-history of the Monads," Monthly Mieroscop. Journal, Tom. X. XIII. 13 194 PROTOZOA. transverse fission, and also by spore formation in an encysted condition; 'the latter method seems in many forms to be preceded by conju- gation. The best known species are Cercomonas Duj. and Trichomonas Donne, of which the first is characterised by the possession of a caudal filament, while Trichomonas has an undulating row of cilia close to the flagella, which are usually two in number (fig. 133). They live principally in the intestines of Vertebrates, but are also found in Invertebrates. Cercomonas intestinalis Lambl. and Trichomonas vayinalis Donne, are found in Man. The Monads* which cannot be sharply separated from the Jfonadince, are simple cells free from chlorophyll, the swarm spores of which usually pass into an amoeboid stage, and after receiving nourish- ment enter upon a motionless stage characterised by the possession of a firm cell-membrane. A number of them (Jfonas, Pseudospora, Colpodella), the so-called Zoospores, are mastigopods resembling the mastigopods (swarm spores) of 3Iyxo- mycetes, and, with the exception of Colpodella, grow up to creeping Amoebae which protrude pointed pseudopodia. In this stage they may also be simply regarded as small plasmodia, especially when, as in Fionas amyli, several masti- FIG. i33.-, Cercomonas intntinaU*. gopods f use together to form the amcoba. i, Trichomonas vaginaiis (after K. They then take in Colpodella without Louckart). . ' first entering the amoeba stage a globu- lar form, their surface develops a membrane, and in this cyst they break up by division of protoplasm into a number of segments which pass out as swarm spores and repeat the course of development (Colpodella puynax to Chlamydomonas, Pseudospora volvocis). Other Monads, the so-called Tetnqdasta (Vampyrella, Nudearia\ do not pass through the mastigopod (swarm spore) stage. Their pro- toplasm during the inactive encysted stage gives rise by division into two or four, to the same number of Actinophrys-like Amoebae, of which some, like Colpodella, suck their nourishment from alga cells (Spirogyra, Oedogonia Diatomacea, etc.), and some envelope ex- traneous bodies. In mode of nourishment and locomotion the monads are allied to the Khizopods, but also to lower fungus forms like Chytridium* * L. Cienkowski, :i Bcitriigc /ur Kcntniss dcr Monadcn," Archin /&> Hfiflrusk. Anatomic, Tom. I., 1805. L. Cienkowski, " Uber Palmellacocn und cinige Flagellatcn," Tom. VI., 1870. E ASTASIADvE. 195 In their whole developmental cycle they agree very closely with uni- cellular algse and fungi; still the analogy to the developmental processes of many Infusoria, Ampliileptus, is not to be passed over. Spumella vulyaris (termo Ehrbg.) of Cienkowski shows a somewhat different development and cyst formation ; it receives solid food (by aid of the food vacuoles) and is fixed by a fibre, as also Chromulina nebulosa Cnk., and Ochracea Ehrbg. A second group nearly allied to the Algae (Protococcacea) is that of the Volvocinidce. These organisms consist of colonies of cells united by a common gelatinous substance, and the following characteristics indicate their close relationship to the Algae: (1) in the inactive stage they possess a cellulose membrane ; (2) they exhale oxygen ; (3) they possess an abundance of chlorophyll and of vegetable red or brown coloured oils. v FIG. 134. TZuglena virldis. a and J,free swimming, in different states of contraction, c, d, e, encysted and in process of division. During the motile stage they, possess the power of reproduction, since the individual cells give rise to daughter colonies inside the mother colony. A sexual reproduction (conjugation) has also been shown. Certain of the mother cells increase in size and divide into numerous microgonidia corresponding to spermatozoa ; others grow to large ovicells, which are impregnated by the former, and then surround themselves with a capsule, and sink to the ground as large star-shaped cells. They also reproduce themselves during their period of inactivity by fission within the cellulose capsule, while at the same time a change of colour takes place. Amongst the best known of the Yolvocina are Volvox globator, Gonium pectorale, Ste- 2)hanosphcera pluvialis. The Astasiadce are contractile unicellular Flagellata, which are allied to the Volvocinidce in their life phenomena, but they take up 196 PROTOZOA. solid nutriment. The best known genus is Euglena, which, according to Stein, has a mouth and gullet. In their inactive stage they secrete a capsule and divide up into parts which pass out as mastigopods. Euglena viridis (fig. 134), E. sanguinolenta. Another genus, also with a mouth, is Astasia Ehrbg. A. trichophora Ehrbg., with rounded posterior end, a very long flagel- lum, and an abruptly terminated anterior end. The genera Salpingoeca and Codosiga described by Clark were included by Biitschli under the name Cylicomastiges, on the ground that they possess a well-marked collar surrounding the basis of the nagellum, and corresponding to the collar on the entoderm cells of the Sponges (hence Clark regarded the Sponges as most nearly related to the Flagellata); Codosiga Botrytis Ehrbg, forming colonies, possessing food vacuoles which contain the solid bodies taken up as nutriment, with nucleus and contractile vacuole. Salpingoeca Clarkii Biitsch. (the individuals of this species possess a shell). ' Another group, the Cilioflagel- lata* is characterised by the posses- sion of a row of cilia, situated in a furrow of the hard cuticular exo- FIG. \tt.-Ceratium tripos (after skeleton (fig. 135), in addition to Nitzsch). the nagellum. The Peridiniw, some of which are of peculiar appearance, with large horned processes of the shell, belong to the group, and are allied, so far as their development is know r n, most nearly to the Euglence. The mouth lies in a depression ; there is sometimes a kind of gullet, at the end of which the nourishing materials pass into a vacuole. In addition to the locomotive and armoured forms, there are also some without shell or organs of locomotion ; and again there are encysted stages in the interior of which a number of small young forms are said to take their origin (Ceratium cornutum Perhg., Peridinium tabulatutn Ehrbg). Finally Noctiluca t is included in this group. It is an inhabitant * R. S. Bergh, " Der Organismus der Cilioflagellaten," Morpli. Jahrb. Tom. TIL L. Cienkowski, " Ucber Noctiluca miliaris" Arclriv. fur microsh. Ana* tomie, 1871 and 1872. NOCTILUCA. 197 of the sea, and possesses a peach shaped body which is surrounded by a cuticular envelope, and bears a tentacle-like appendage. A furrow- like invagination is situate at the base of this appendage, at one end of which is the mouth close to a tooth-like prominence and a slender vibratile nagellum. The soft body consists of a central mass of contractile protoplasm, connected by fine and anastomosing threads with a layer of the same substance which lines the cuticular envelope of the body. In the central protoplasm lies a clear body, the nucleus; and the spaces between the radiating processes, which exhibit the phenomena of granule currents, are filled with fluid. The contractile substance extends into the appendage, and there assumes a cross- striped appearance (fig. 136). N FIG. 136. A'orftfKea miUaris (partly after Cienkowski). N, Nu- cleus, a, Single animal, b, conjugation of two individuals, c and d, swarm spores. The reproduction takes place by means of fission (Bright well), pre- ceded by division of the nucleus ; or by spore formation (Zoospores). In the latter case, the nagellum is absorbed or thrown off, and the Noctiluca assumes a spheroidal shape. After the disappearance of the nucleus, the sarcode contents accumulate on the inner side of one region of the cuticle, divide into from two to four masses which are not sharply separated from one another, and the cuticular envelope is thrust out into a corresponding number of protuberances. These buds increase and form numerous wart-like prominences, the future spores. They arise, therefore, at the expense of the protoplasmic contents of the disc, which is gradually exhausted in their for- 198 PHOTOZOA. mation. The buds separate themselves from the membrane and become free as small spores, with nucleus and cylindrical appendage, to assume the Noctiluca form under circumstances which have as yet not been closely observed. According to Cienkowski, conjugation may take place between normal forms as well as between encysted forms. The Noctiluca owe their name to their power of producing light, a power which they share with numerous sea animals, such as Medusae, Pyrosoma, etc. The light proceeds from the peripheral layer of protoplasm. Under certain conditions they rise from the deep to the surface of the sea in such enor- mous numbers as to cause wide tracts of the sea to give out a reddish light. It is after sunset, and especially in the evening, when the sky is overcast, that we get the beautiful phenomenon of the phosphorescent sea. The species distributed in the North Sea and in the Atlantic Ocean is Noctiluca uiiliaris. Nearly allied is the Mediterranean Leptodiscus medusoides K. Hertwig. Order 2. CILIATA.* Ciliated Infusoria with 'mouth and anus, sarcode body of complicated structure (with endoplasm and exoplasm\ with nucleus and paranucleus (nucleolus}. FIG 137 S 1 / /OH ch'a m-ti'm ^ e l com tive cuticular appendages that (after stein), (seen from ^e most frequently meet with are slender ventral side). Wz, Adoral .,. -, . . /., ,-, T , ,. < zone of cilia; C, contractile clha > whlch ften COVer the whole Surface f vacuoie ; N, nucleus ; N>, the body in close rows, and give it a striped paranucleus; A, anus. -r,, .,. ,, appearance. I he cilia are usually stronger m the region of the mouth, and are here grouped so as to form an adoral zone of large cilia, which, during swimming, causes a whirl- pool, and conducts the matter which serves as nourishment into the mouth (fig. 137). This adoral zone is more highly developed in fixed Infusoria such as the bell animalcule, the surface of which has no uniform coating of cilia. In these animals there are Fr 180 * Besides Ehrenberg, Claparedc, Lachmann. Biitschli, 1. c., compare especially . Stein, " Der Organismus der Infusionsthiere," I. and II., Leipzig, Ib59 and CILIATA. 199 one or more rings of large cilia round the edge of a raised lid- like flap which is capable of being shut down. There is also an in- ferior row of cilia upon this flap running to the mouth. The free-swimming Infusoria often possess in addition to these delicate cilia and zones of cilia, thicker hairs and stiff bristles, and more or less bent hooks, which are em- ployed in locomotion and for attachment. Certain fixed Infusoria as Stentor (fig. 138) and Cothumia secrete external coverings or shells, into which they retract themselves. Nourishment is taken in in a few cases by endosmosis through the whole surface of the body, e.g., the parasitic Opalina.. The Acineta feed themselves by sucking the body of their prey. They are without a mouth, and are incapable of taking in solid food. But they possess a number of long, narrow, contractile tentacles, which radiate from the surface of their bodies, and have the form of delicate tubes, presenting a structureless external wall and a FIG. 133. Stentor semi-fluid granular axis. The Acineta applies ^ <* a * t %k one or more of these organs to the body of an gullet; pv, pulsating , i . -i T , P vacuole : N, nucleus. extraneous organism, when the substance of the latter travels down the interior of the granular axis of the tentacle into the body of the Acineta (fig. 139). By far the greatest num- ber of Infusoria possess an oral aperture, usually near the anterior pole of the body, and a second aperture which acts as anus, and which can be seen in a definite part of the body as a slit during the exit of the excreta. The bodv mrenohvim' FlG ' 139 ^"''' tt /<,.r?;m Ehrbj?., which in eUJina, sucking the body of a small i nfusor i a n (Enchelys) which is bounded by the (after Lachmann). T, sucking tentacle ; V, vacuole ; external membrane, is N> divided into a viscid exoplasm and a more fluid endoplasrn, into 200 PEOTOZOA. which a slender oesophagus, rarely supported by firm rods (Ckilodon, Nassula), often projects (fig. 140). Through this the food stuff passes into the endoplasm, in which it gives rise to food vacuoles. The latter undergo a slow rotating movement round the body in the endoplasm, which is caused by the contractility of the sarcode. During this process the food is digested, and finally the solid, useless remainder is ejected through the anal aperture. A digestive canal, bounded by distinct walls, exists no more than do the numerous stomachs which Ehrenberg, who was deceived by the food vacuoles, . ascribed to his Infusoria polygastrica. In all cases where a digestive canal has been described, we have to do with peculiar strings and trabeculse of the internal parenchyma which enclose spaces filled with a clear fluid. The more viscid exoplasm is pre-eminently to be regarded as the motor and sensory layer of the body. In it we find differentiations resembling muscles (Stentor, the stalk of Vorti- cella). Sometimes small rod-shaped bodies are present (e.g., Bursaria leucas, Nassula), which are comparable to the thread cells of Turbellaria and Coelenterata. The contractile vacuoles appear as further differentiations of the external layer, structures which to the number of one or more are found in quite definite portions of the body. They are clear, mostly spherical spaces filled with a fluid ; they diminish suddenly and then vanish, but gradually reappear and increase to their original size. These pulsating vacuoles are usually connected with one or more vessel- like lacunae, which swell considerably during the contraction of the vacuole. These structures have been compared to the water vascular system of Rotifera and Turbellaria, and have been explained as excretory an interpretation which has in its favour the fact that the contractile vacuoles in certain cases open to the exterior through a fine pore at the surface, through which granules pass to the exterior. Th nucleus and nudeolus lie in the exoplasm of the infusorian body. The nucleus t which ten years ago was compared to the nucleus of the simple cell, is a structure of variable shape but with a definite position in the body. One, or more than one, may be present. It is sometimes round or oval, sometimes elongated, being drawn out FIG. 140. Chilodon cucul- Ins (after Stein), with gullet resembling 1 a fish-basket. Nj nucleus with nucleolus, -.excreta are passing out of the anus. KEPEODUCTION OF CILIATA. 201 to the shape of a horse-shoe or a band, and may be broken up into a number of fragments. It contains a granular viscid substance, is bounded by a delicate membrane, and, according to the erroneous views of Stein and Balbiani, gives rise to ova or to germi- nal spores. The nucleolus or paranucleus also varies in form, position, and number in different species. It is always much smaller than the nucleus, and is strongly refractile ; it usually lies close to the nucleus, or even sunk in a cavity of the latter. Both play an important part in the reproduction of the Infusoria. The most usual method of reproduction in the Infusoria is by j fission. When the forms reproduced remain together and connected with the parent, a colony of Infusoria is formed, e.g., the stocks of Epistylis and Carcliesium. Fission usually takes place by a trans- verse division (at right angles to the long axis), as in the Oxytrichidce, a, Aspidisca lyncaster (after Stein), b, Aspidisca poly sty- la, during fission (after Stein) . * FIG. 1-12. Podoplirya rjemm'ipara (after R. Hertwig). a, with extended suction-tubes and pre- hensile tentacles, with two contractile vacuoles. b, the same with ripe buds, in which processes of the branched nucleus N enter, c, free young form. Stentoridce, etc., and, obeying definite laws, follows conjugation and division on the one hand of the nuclei, and on the other of the nucleoli (fig. 141). Less frequently (Vorticella) the fission takes place through the long axis (fig. 143, a, b), and far more rarely in a diagonal direction. The asexual reproduction is often preceded by encystment, which appears to be of great importance for the 202 PROTOZOA. preservation of the Infusoria from desiccation. The animal retracts its cilia, contracts its body to a globular mass, and then secretes a transparent cyst, which hardens and protects the animal, thus en- abling it to survive in damp air. In the water, the contents of the cyst divide into a number of parts, which attain freedom by the bursting of the cyst, each one becoming a young animal. Moreover, many Infusoria (Acinetce) produce with participation . of the nucleus a number of buds asexually, which separate them- selves from the walls of the parent body (fig. 142). The broods of Sphnerophrya make their way into the interior of other Infusoria, as Parameecium and Styl ony chia, nourish jhemselves at the cost of the enlarged nu- cleus, and form em- bryos by fission. These embryos swarm out, and were for a long time taken by Stein for the embryo broods of Stylonychia (fig. 144, b). The process of con- jugation observed by Leeuwenhoek and O. Fr. M tiller is very general, and is con- nected with changes of the nucleus and nucleolus. These changes, which gave rise to the erroneous interpretation of the two structures as ovary and testis, are in reality simply preparatory to a process of regeneration of the nucleus by parts of the paranu- cleus, a process comparable to the phenomena of the fertilization of the ovum in sexual reproduction. The conjugation of two Infusoria occurs in very different ways, and leads to a more or less complete fusion, which, after regeneration of the nucleus, is followed by an increase in the frequency of fission. Paramcecium, Stentor, Spirostoma, during conjugation, become con- FIG. 143. Vorticella microstoma (after Stein), a, In process of fission ; N, nucleus ; the mouth apparatus in each por- tion is formed afresh, oe, gullet, b, Fission is completed, the smaller product is set free after the formation of a posterior ring of cilia ; w, adoral zone of cilia, c, Vorti- cella in process of bud-like conjugation ; -ST/the bud-like individuals attached. CONJUGATION OF CILIATA. 203 nected by their ventral surfaces ; other Inf usoria with a flat body like Oxytrichina, Chilodon, by their sides ; while Enchelys, Halteria, Coleps, join together the anterior extremi- ties of their bodies, giving the appear- ance of transverse fission. A lateral conjugation also takes place not un- frequently in Vorti- cella, Trichodina, etc., between individuals of unequal size, the smaller one having the appearance of a bud (bud-like conju- gation) (fig. 143, c). The alterations FIG. 144. a, Stylonychia myiihit, in process of conjugation. The nucleus is depicted i uring division (Balbiani's so- Which the nucleus called ova ). the nuc leoli have divided into four spheres (sup- and IXlTCinucleus un- posed spermcapsules). 6,' Stylonychia filled with parasitic Sphatrophrya (after Balbiani). dergo during and after conjugation have been especially worked out in Paramcecium and Stylonychia (fig 144 a, 145). When several nuclei are present they FIG. 145. Stylonychia my fit us in process of conjugation, slightly magnified, (treated with acetic acid), (after Butschli). a, Stage of conjugation with two nucleoli (paranuclei) ; Nl, the four pieces into which the nucleus has divided in each individual, b, Stage of conjuga- tion with four nucleoli, of these N' becomes the nucleus, and ' the two nucleoli ; Nb, tho lour remaining pieces of the old nucleus, c, Stylonychia on the sixth day after conjuga- tion with nucleus and two nucleoli. fuse together to form a single oval body (Balbiani), the substance of which takes a finely fibrous structure previous to further fission, 204 PROTOZOA. like the substance of a true ceil nucleus, when undergoing division. The paranucleus too increases in size and becomes striated, and divides into a number of bodies by a single or re- peated division. Some of these bodies produced by the division of the nucleus and paranucleus disappear or are cast out., and others are employed in the formation of the new nucleus and paranucleus. The processes of regene- ration are for the most part not com- pleted until the conjugating animals have separated. Conjugation is probably followed by a repeated division (fig. 146). The mode of life of the Infusoria, which principally inhabit fresh water, is very various. Most of them lead an independent life, and take up larger or smaller bodies, even Rotifera, as nourishment. Some, as Amphileptus, select fixed Infusoria, as Epistylis and C 'archesium, for their prey, and swallow them down as far as the origin of the stalk ; they then, while fixed on the stalk, secrete a capsule, and divide up into two or more individuals, which pass out. Certain Infu- soria, as the mouthless Opalina, and many Bursa- ridse, are parasitic in the intestine and bladder of Vertebrates. To these belongs the Balantidium coli from the large intestine of Man (fig. 147). 1. Sub-order : Holotricha. Body uniformly covered with cilia, which are arranged in longitu- dinal rows, and are shorter than the body. Longer EiG.147. Balantidium c ^ia ar e sometimes found in the region of the coil with two puisa- mO uth, but these do not form an adoral zone. ting vacuoles (after Stein). Under the Besides the parasitic Opalinse (Opalinee ranarum*), with- nucleus lies a t mouth or aims the f o ii ow i ng families belong to this starch-granule that has been eaten, a group : ball of excrement is Fam. Trachelidae. Body of changeable shape prolonged passing out of the j n to an anterior neck-like process. Mouth ventral, without anus at the poste- longer cilia> Traclielius ovum Ehrbg.. Avwltilentu* fasci- riorend. t . v cola Ehrbg. Fam. Colpodidse. Form of body definite. Mouth ventral, in a depression, FlO. 146. Paramcecium Bttrsaria about one hour after conjugation (after Biitschli). n, nucleolus ; N, nucleus ^ PF, contractile vacuole. Two of the nucleoli have become clear spheres. CILTA.TA. 205 always furnished with long cilia or undulating membranes. Paramcecium Aurclia Fr. Miiller, P. Bursaria Focke, Colpoda cucullus Ehrbg., Glaucoma scintillans Ehrbg. 2. Sub-order: Heterotricha. Body uniformly covered with fine cilia, which are arranged in longitudinal rows, with a distinct adoral zone of cilia. Fam. Bursaridae. The adoral zone of cilia is on the edge usually of the left half of the body. Sursaria truncatella 0. Fr. Mull., Balantidium coli Malmst., parasitic in the colon of man ; Spirostomum ambiguum Ehrbg. Fam. Stentoridae. At the anterior end of the body is a peristomial space with a funnel-shaped depression, without any distinct gullet. Stentor polymorplius, O. Fr. Mull., St. ccarulcus Ehrbg. 3. Sub-order : Hypotricha. Body with sharply defined dorsal and ventral surface. The convex dorsal surface is usually naked, the ventral covered with cilia and beset with styles and processes, mouth on the ventral surface. Fam. Oxytrichidae. Body elongated to an oval. On the left half of the ventral surface is a peristomial region, with an adoral zone of cilia. The ventral surface is beset at either edge by a marginal row of cilia, and also with bristles and hooks. Stylonycliia pustulata Ehrbg., with eight anterior styles, five ventral, and five anal cilia. Oxytriclia gilla, O. Fr. Miiller. Fam. Chilodontidae. Body usually armoured, with gullet in the form of a fish -basket. Chilodon cucullus Ehrbg. 4. Sub-order : Peritricha. Infusoria with cylindrical or bell-shaped partially ciliated body. The cilia are placed on an adoral ciliated disc, and frequently on a ring-like zone. Fam. Vorticellidae. Peritricha with adoral spiral of cilia, without a shell, attached by a stalk, usually forms colonies. Vorticella microstoma Ehrbg., Epistylis plicatilis Ehrbg., Zootliamnium arluscula Ehrbg., Carchesiwn polypinum Ehrbg. Fam. Trichodinidae. Peritricha with adoral spiral of cilia, and circle of cilia as well as an apparatus for attachment at the posterior end. Tricliodinapcdiculus Ehrbg. Fam. Halteriidae. Near the adoral spiral of cilia is an equatorial zone of longer cilia. Haltcria volvox Clap. Lachm. 5. Sub-order : Suctoria. Body usually without cilia, with knobbed tentacle-like processes which serve as sucking tubes. Fam. Acinetidae. Acineta mystacina Ehrbg., Podoplirya cyclopum Clap. Lachm., Splicerophrya Clap. Lachm. As an appendix to the Protozoa we will now proceed to consider the Schizo- mycetidce, which approach more nearly to the Fungi, and the Grcgarlnidte. 206 PROTOZOA. 1. The ScliizomyGtMaa)* (Bacteria) are small globular or rod-shaped bodies which are found in decaying matter, and are especially numerous on the surface of putrefying fluids, where they give rise to a slimy film (fig. 148). They are most nearly allied to the fungus of yeast, with which they also agree in their manner of nourishment, in that they make use of ammonia and organic com- pounds containing carbon. Like the yeast fungus they excite and maintain the fermentation or, as may happen, putrefaction of organic matter by with- drawing its oxygen or by attracting oxygen from the air (reduction or oxyda- tion ferments). But they are clearly separated from the fungi by their deve- lopment, for they increase by dividing into two ha-lct's, while the yeast fungus (Saccharomyces, Hormiscium) forms buds which separate off as spores. The transverse division takes place, after the cell has become elongated, by a con- striction of the protoplasm and by the secretion of a cross partition wall. The daughter-cells either divide at once, or remain united and produce chains of Bacteria (filiform Bacteria) by afresh fission. Sometimes the successive genera- tions of cells remain connected by a gelatinous substance, and so produce irre- gular shaped gelatinous masses (zoogloea). Sometimes they become free and arc dispersed in swarms. They may also settle on the bottom in the form of a FIG. 148. Schizomycetcs (sifter F. Cohn). a, Micrococcus. b, Bacterium termo, bacteria of putrefying fluids, both in the motile and zoogloea form. granular precipitate, as soon as the nourishment in the fluid is exhausted. The greater number have a motile and a motionless stage ; in the first they rotate themselves about their long axis, but are also able to bend and extend, but never to serpentine. Their activity seems to be connected with the presence of oxygen. Owing to the absence of sexual reproduction, the division of Bacteria into genera and species is beset with such difficulty that we must content ourselves with establishing, in an artificial fashion, form species and physiological species and varieties without always being able to demonstrate their independence. F. Cohn distinguishes four groups : (1) Globular Bacteria, Micrococcus (Mona* and My coder ma) ; (2) Rod Bacteria (Bacterium) ; (3) Filiform Bacteria (Bacillus and Vibrio) ; (4) Spiral Bacteria (Sjnrillum and Sjriroch&ta). The Globular Bacteria are the smallest forms, and only exhibit molecular movements. They cause various forms of decomposition, but not putrefaction. * F. Cohn, " Bcitrage zur Biologic tier Pflanzen." Heft 2 and 3, 1872 and 1875. " Untcrsuchungen iiber Baktcricn," 1, 2, and 3 (Bacterium termo). Com- pare further the works of Ebcrth and Klebs. EACTEEIA GREGA.HIUTDJE. 207 They can only be divided, according to their various methods of development, i7ito chromogenous (pigment), zymogcnous (fermentation), and pathogenous (contagion) divisions. The first appear in coloured gelatinous masses and vegetate in the Zoogloeaform, e.g.. M. prodigww* Ehbrg. in potatoes, etc. To the Zymogenous belong M. urea, urine ferment ; to the Pathogenous J/. vaccinat, the Pox Bacteria, Jf. septicus of pyaemia, M. dijpktkcri&t* of diphtheritis. The Rod Bacteria form small chains or threads, and exhibit spontaneous motions, especially in the presence of abundant nourishment and oxyges. Here belongs Bacterium termo Ehrbg. distributed in all animal and vegetable infusions and the necessary ferment in putrefaction, just as yeast is in alcohol fermentation ; also B. Lineola Ehrbg. of considerable size, which exists in spring water and in standing water, in which there are no products of putrefaction, and, as well as the former, has a zoogloea jelly. Another Bacterium form acts as ferment of lactic acid, according to Hoffmann. Of the Filiform Bacteria the motile Bacillus (vibrio) subtilis Ehrbg. occasions butyric acid fermentation, but is also found in infusions together with B. tcrmo. Very nearly allied and hardly to be distinguished is the motionless Bacillus anthracis of inflammation of the spleen. Vibrio ruqula and scrpens are charac- terised by constant undula- tions of the chain. Finally these lead to the spiral forms of which Spirocha&a resembles a long and flexi- ble but closely wound, and fy trillion, a thick, short, and coarse screw. Sj) tril- lion tcnax, 'undula. volutans, the last with a flagellum at each end. 2. The Grcgarinido} * are FIG. 149. Greyarlna (after Stein and Kolliker). a, Sty- lorhynchus oUgacanthus out of the intestine otCallopteryx. b, Gregarina (Clepidrina) poJymorpfia from intestine of the meal beetle, during conjugation, c, The same in process of encystment. d, Encysted Gregarina. e, Stage of formation of Pseudonavicellro. /', Pseudo- navicellacyst with ripe Pseudonavicellaj. unicellular organisms which lire as parasites in the intestine, and in the internal organs of the lower animals. The body is fre- quently elongated like that of a worm, and consists of a granular viscid central mass surrounded by a delicate external membrane (st metimes with a subcuticular layer of muscle stripes). The nucleus, a round or oval clear body, is embedded in * N. Lieberkiihn, {< Evolution des Gregarines," Mem com: de VAcad. de Belf). 1855. N. Lieberkiihn, " Beitrag zur Kcnntniss der Gregarinen." Arclt. fur Anat. mid PhyxioL, 18G5. E van B.cnedcn, "Becherfehea sur 1'evolution des Gregarines." Bulletin de VAcad. roy. de Bt'h/iyiw, 2 Ser. xxxi., 1871. Aime Schneider, " Contributions a 1'histoire des GrOgarines des Invertebres de Paris et dc Koscoff." Arch, dc Zool. Experiment.. Tom IV., 1875. 208 PEOTOZOA. the central mass. The structure of the body may be complicated by the pre- sence of a partition wall which parts off the anterior end from the main mass of the body. The anterior portion of the body gets in this way the appearance of a head, upon which there may be formed here and there prominences in the form of hooks and processes for the purpose of attachment. Nourishment is effected by endosmosis, through the external walls. Motion is confined to slow gliding forward of the feebly contractile body. In their full-grown state the Gregarina are frequently seen fastened to one another, two or more together. This connected state precedes reproduction (fig. 149). The two individuals lying with their long axes in the same straight line contract and surround themselves with a common cyst, and after undergoing a process resembling segmentation, divide into a number of small spore- like balls, which become spindle- shaped bodies (pseudonavicellse). The cyst secreted round the conju- gating individuals, or, as is often the case, round a single individual, be- comes a pseudonavicella cyst, and by its bursting the spindle-shaped bodies reach the exterior. The contents of each Pseudonavicella sometimes gives rise to a small amoeboid body, as may be inferred from Lieberkiihn's obser- vations on the Psorospcrnis of the pike. In other cases (Monocystis, Gonoxjiora, etc.) sickle-shaped bodies arise in the spores, which, without passing through an amoeboid stage, give rise to young Gregarines. Mono- cystis agilis from the testis of the earth-worm. Greyarina L. Duf. (Clcpsidrina Hammersch.) Body with flat partition wall and wart-like head at anterior end. In the young stage the anterior end of Gr. llat- taruni v. Sieb. is fixed in the cells of the intestinal epithelium of Blatta. Gr. polymorpliCL Hammersch. in the meal- worm. [The Gregarines are found mainly in Invertebrata. They may be divided into two main groups, the Polycystidca and the Monocystldea. In the former, which are found for the most part in Arthropods, there is a partition dividing the body into two parts ; in the latter, which are found chiefly in Vermes, there is no such partition.] The structures long known as Psorospcrms from the liver of the rabbit, the slime of the intestine, the gills of fishes, and the muscles of many Mammalia, etc., present a great resemblance to the Psei d jnavicellae ; but we are not yet fully enlightened as to their nature. The cr.se is the same with the structures known as Rainey'sor Mischer's corpuscles from the muscles of, e.g., the pig ; aud FIG. 150. Rainey'g corpuscles from the flesh of a pig. a, An animal inside a mus- cle fibre, b, Posterior end of the same, strongly magnified ; C, cuticular layer ; , spores. LXELENTEKATA. 209 the parasitic animals from various wood-lice and Crustacea, which were assigned by Cienkowski to the fungi, under the name of AmaMdium parcuiticwa, remind us by their reproduction no less of the Grega rinse and their cysts. The Coccidia which we ten ill ^ ::;.> A meet with in the cells of the epithelium of the intes- tine as well as in the bile- ducts of Mammalia should also be regarded as Grega- rin have no external membrane, can protrude and retract processes, and f ake into their interior foreign substances (fig. 157). The framework or skeleton, which we find wanting only in the soft * Literature : Nardo G. D., " System der Schwamme," Isis, 1833 and 1834. Grant, " Observations and Experiments on the Struct, and Funct. of Sponges," Edin. Phil. Journal, 1825 1827. Bowerbank, "On the Anatomy and Physio- logy of the Spongiadag," Pli'dos. Trans., 1858. and 18G2. Lieberkiilm, " Beitrage zur Entwickelungsgeschichte der Spongillen," J\lilUc?'\t Arc-Mr., 1856. Lieber- kiihn, " Zur Anatomic der Spongien," Mutter's ArcJtir., 1857, 1851), 1863, 1865, 1867. O. Schmidt, " Die Spongicn des adriatischen Mceres," Leipzig, W. En g- elmann, 1862, as well as Supplement. Leipzig, W. Engelmann, 18G4, 18(5(5, 1868. E. Haeckel, "Die Kalkschwamme," 3 Bde, Berlin. 1872. FT. E. Schulze, " Untersuchungen iiber den Ban und die Entwickelung der Spongiea," Zeitiiclirlft,fiir vriss. Zool., 1876 1SSO. POKIFEEA. 215 gelatinous Sponges or Myxospongia, is composed of horny fibres or silicious or calcareous spicules. The horny fibres form, without exception, anastomosing networks of varying degrees of thickness, and present a lamellated structure (fig. 158), which indicates that they are formed of a number of layers. They are formed by excretion as hardening portions of sarcode. The calcareous needles (fig. 159) are simple or three- and four- rayed spicules, and take their origin, as do the silicious structures, in the interior of cells. The silicious spicules present, however, an extraordinary variety of form : some of them constitute a connected frame- work of silicious fibres, and others are free silicious bodies with simple or branched central canals (fig. 160). The latter are found in the form of needles, spindles, cylinders, hooks, anchors, wheels, and crosses, and arise in nucleated cells, pro- bably as deposits round a hardening of FIG. 158. Piece of network of organic matter (central fibre). In order to understand the morphology of the Spongiaria we must begin by examining the structure of a young Sponge, which proceeds from the fixed larva. The young Sponge, after the formation of a ciliated gastric cavity and an ex- halent opening or osculum, has the form of a simple hollow tube, the walls of which are pierced by pores for the passage of small food particles suspended in the water (fig. 152). In this stage we can distinguish three layers ( 1 ) an entoderm, formed of elongated flagellated cells; (2) a mesoderm, the skeleto- genous cell layer, the structure of which recalls connective tissue; and (3) an ectoderm, which forms the outer layer of the Sponge, and consists of a flat epithelium. The cylindrical cells of the endo- derm possess at their free ends surrounding the flagellum a delicate horny fibres from Euspongia equina. reous Spicules of Sycon. 216 CCELENTERATA. hyaline marginal membrane, which, derived frc^n a prolongation of the hyaline plasma, projects as a hollow cylinder resembling the protoplasmic collar of certain Flagellata* (Cylicomastiyes). [This FIG. 160. Silex bodies from different silicious Sponges, a, Silex needle from Spongllla, inside the cell. 5, Amphidisc of a gemmule of Spongilla. c, Anchor from Ancorina. d, Hook from Esperia. c, Star from Chondrilla. f, Anchor froTnJSuplcctella asperglllum. g, Ji t needle rays from the same, i, Six-rayed needle from the same, with central canal. structure is commonly known as the collar, and the cells as the collared cells.] The thick layer in which the skeletal spicules are produced consists of a hyaline matrix, in which irregularly branched or spindle-shaped amosboid cells are embedded, and may be regarded, like the gelatinous substance of the Acalepha, as mesoderm, while the external, clearly defined, flat epi- thelium (also in the Asconia, Leucosolenia) is to be considered as ectoderm. The pores or inhalent openings so cha- racteristic of the Sponge body are in reality only intercellular spaces, and are able to close themselves, vanish and be replaced by new pores, which arise by the separation of one cell from another (fig. 161). * Upon this ground Clark declared the Sponges to be nearly allied to the Flaqdlata, and regarded them as great colonies of the latter. FIG. 161. Portion of the exter- nal layer of Spongilla with the pores, P (after Luberkiihn). PORIFERA. 217 Amongst the calcareous Sponges, the simple Sponge with inhalent pores and terminal osculum (Olynthus-iorm) is represented by the stock-forming Leucosolenia (Grantia), which is composed of numerous hollow cylinders. The structure of this sponge has been described by Lieberkiihn. In the Syconidw the body cavity has a more complicated form. The central space opens into secondary peripheral spaces or radial tubes, which are lined by ciliated cells, and open externally through the inhalent pores (fig. 162). In other calcareous Sponges (Leuconidce) the radial canals have the form of irregular parietal canals, giving off branches to the periphery and possessing dilated, ciliated chambers. This form of internal canal system is also found in most of the stock-forming, silicious Sponges (fig. 163). Sponge forms may become more complicated by the formation of stocks ; the originally simple Sponge, which has developed from a single cili- ated larva, gives rise by budding and incomplete fission to a polyzoid sponge body; or several originally separate iriclividu - als, each of which has origi- nated from a single larva, fuse together to form a com- pound sponge stock. Both these methods of growth are repeated in a similar manner in the formation of the stocks of Polyps (fig. 164). In the same way that the fan-like FIG. 1G2. Longitudinal section through Sycon raphanug, slightly mag- nified. 0, Osculum with collar of spicules; Jit, radial tubes which open into the central cavity. FlO. 103. Section of Cort icium candelabrum (after nets of the Fan Coral th dogorgia flaMUm) are formed by the repeated fusion of its branches, the gastrovascular cavities of which anastomose, so also in the case of the branching sponges, as a result of the same pro- cess, reticulate, or coiled or even massive stocks are formed (fig. 165). 218 CCELENTEBATA. In this case the canal system, in which the modifications before described for each individual Sponge are repeated, becomes more complex, partly through the formation of anastomoses, and partly because irregular gaps and winding passages make their appearance between the fused branches of the stock and form spaces which lead into the ciliated cavities. Reproduction takes place mainly asexually by fission and the production of germs or gemmules, but also by the formation of ova and sperm capsules. The gemmules are in the fresh-water jSpongitta masses of cells which are surrounded by a firm shell composed of silicious structures (amphidiscs\ and, like encysted Protozoa, pass through a long period of rest and inac- tivity. After the expiration of the cold and sterile season of the year, the contents pass out of the opening of the capsule and gene- rally surround the latter, and with increasing growth become differentiated into amo3boid cells and all the essential parts of a new small sponge body. Multiplication by means of gemmules is also common among the marine Sponges. The gemmules take their origin under certain conditions as small globules surrounded by a membrane. The contents are essentially formed of sponge cells and spicules, and, after a longer or shorter period of inactivity, reach the exterior by the rupture of the membrane. Sexual reproduction was first demonstrated with certainty by Lieberkiihn for Spongillct, but more recently has been shown to exist in almost every group of Sponges. In most CaS6S the Va and s P ermatozoa seem to reach maturity at different times in the same Sponge. The spermatozoa are needle-shaped, and lie in small spaces lined with cells. The ova, like the mother cells of the spermatozoa, are modified cells of the parenchyma, and are derived from cells of the same tissue layer (mesoderm) in which the needles and skeletal structures take their origin. The ova are naked amoeboid cells, and pass into the canal system, while in the viviparous Sycons they PORIFERA. 219 remain in the mesoderm, and there undergo their development. It is only later that the ciliated embryos or larvse fall into the canal system, pass out, and attach themselves, to de- velop into a young sponge. The embryonic de- velopment among the calcareous sponges is most accurately FIG. 165. Euspongia offldndlis adriatica, with a number of - oscula, O (after Fr. E. Schulze). known for the Syconidce from the investigations of Fr. Schulze and Barrois. FIG. ICG. Development of Sycon rapt amis (after Fr. E. Schul/e). a, Ripe ovum, ft, Stage with four segmentation cells, c, Stage of segmentation with sixteen cells, d, Blastosphere with large dark granular cells at the open pole, e, Free-swimming larva, one-half of the body (entodermal) being formed of long ciliated cells, the other (ectodermal) of large granular cells. 220 CCELENTEBA.TA.. After the completion of the tolerably regular segmentation (fig. 166, a c), Sycon (Sycandra) raplmnus passes through a blastosphere stage, during which the greater half of the ovum consists of clear cylindrical cells, and the smaller half at the still open pole of large dark granular cells (fig. 166, d). The cylindrical cells of the larger half develop cilia, and the embyro passes out of the body cavity and becomes a free-swimming larva, which attaches itself and alters its shape in such a manner that the dark cells grow over the ciliated portion of the globe, which is meanwhile invaginating. The ecto- derm and mesoderrn are derived from the dark granular cells, and the ciliated cells give rise to the entoderm of the gastric cavity. Later on the body of the sponge be- comes cylindrical, the osculum makes its appearance, and calcareous needles appear in the wall, which becomes pierced by pores (fig. 167). With the excep- tion of Spongilla, the sponges are marine, and are met with under very different con- ditions, and covering a wide area of distribution. The horny sponges live in shallow seas, as also the Myxospongice and Chalinece, or siliciceratous Sponges ; while the Hexactinellidce inhabit very considerable depths. Petrified remains of sponges are also found preserved in various formations, for instance in the chalk ; and these remains differ much from the greater number of those living. On the other hand, the hyaline sponges of the deep sea agree so fully with the ancient forms that they seem to be the direct descendants of the latter. Finally, many of the principal groups extend back into the palaeozoic age, in which LithistidcK and Hexactinellidce especially are met with in the most ancient Silurian FIG. 107. Young Sycon (after Fr. E. Schulze). O, Osculum or exhalent aperture ; P., pores of the wall. POKIFEBA. 221 strata. Hence paleontology affords us no facts for determining the phylogenetic development of the Porifera. CLASS I. SPONGIA. (With the characteristics of the Group). Order 1. MYXOSPONGIA (gelatinous sponges). Soft, fleshy sponges, without any skeleton, with a hyaline gelatinous mesoderm, often containing fibrous cords. The ectoderm cells are fairly elongated, and bear flagella. Fam. Halisarcidae. Ilnlisarca Duj. II. lolidaris 0. S., colour dark violet ; encrusts stones ; Sebenico. 77. Dujardinil Johnst., forms a white encrustmeut on the Laminaria of the North Sea. Order 2. CERAOSPONGIA (horny sponges). For the most part branched or massive sponge stocks, with a framework of horny fibres, in which grains of silex and sand are present as foreign bodies. Fam. Spongiadae. Eusponyia 0. S., with very elastic fibrous framework, of equal strength throughout, mostly capable of being used for bath and washing sponges. E. adriatica 0. S., cquina O. S., zimocca O. S., in the Greek Archi- pelago, molissima 0. S., Levantine sponge, cup-shaped. Spongdia elegans Nardo. Order 3. HALICHONDRI.E (siliciceratous sponges). Sponges of very various shapes, with usually uniaxal silicious needles, simple silicious spicula, which are connected by delicate or firmer plasmatic structures, disposed in networks or enclosed in sponge fibres. Of the numerous families the following may be mentioned : Fam. Chrondrosidae. (6rummin< *9), Coriaceous sponges. Clirondrosia rcni- formis Nardo. Fam. Suberitidaa. Sponges of massive form, with knobbed silex spicules, which, as a rule, are arranged in network. Suberites Nardo. S. domuncula Nardo, Adriatic, Mediterranean. Fam. Spongillidae. Massive or branched with simple spicules, connected by investments of sarcode. Spongilla fluviatilis Lk., Sp. lacustris Lk. Order 4. HYALOSPONGIA. Sponges with a firm, often hyaline lattice-work of silex spicules, which present the most perfect form of six-rayed spicules (Hexactinellidce), and may be cemented together by a stratified silicious substance. Fam. Hexactinellidae (hyaline sponges). With connected silicious framework and network of stratified silicious fibres, which join the six-rayed silicious bodies, frequently with isolated spicules and tufts of silex hairs, which serve to attach the sponge. They live for the most part at considerable depths, and are allied to the fossil Ventriculitida;. Dactylocalyx Bbk. Euplcctella, 0\ven, 222 CKELENTERATA. E. aspergillum Owen, Philippines. In the body cavity of the glassy sponge are found Aega spongipliila, and a small Palcemon. Hyalonema Sieboldii Gray, Japan. H. boreale Loven, North Sea. Order 5. CALCISPONGI^E, Calcareous sponges. Usually colour- less, sometimes red-coloured sponges and sponge stocks, the skeletons of which consist of calcareous spicules. These are either simple needles (as they first appear in the embryonic form) or three or four- armed cross spicules. Very often, however, we meet with two or all three forms of spicules in the same sponge. Fam. Asconidse (Leucosolenidee, Ascons). Calcareous sponges, the walls of which are pierced by simple canals. Grantia Lk. (Leucosolenia Bbk.), these are divided by E. Haeckelinto seven genera, Ascyssa, Ascetta, Ascilla, Ascortis, Asculmis, Ascaltis, Ascandra, according to the form of the calcareous needles or spicula. Gr. botry aides Lk. (Ascandra complicata, E. Haeck), Heligoland, nearly allied to Gr- LieberJiultnii O. S. from the Mediterranean and Adriatic. Fain. Leuconidae ( Grantiidcc, Leucons), calcareous sponges, with thick wall, which is pierced by branched channels. Leuconia Grt. , divided by E. Haeckel into seven genera, according to the form of the calcareous spicules Leucyssa, Lcucetta, Leueilla, Leucortis, Leumdmis, Leucaltis, Leucandra. L. (Leucetta) primigenia E. Haeck. Fam. Sycondise (Sycons). Mostly solitary calcareous sponges, with thick walls, which are pierced by straight radial tubes. The latter project on the surface as conical prominences of the wall. Sycon Kisso, divided by E. Haeckel into seven genera Sycyssa, Sycetta, Sycilla, St/cortis, Syculmis, SycaUis, Sycandra, SUB-GROUP II. CNIDARIA (CCELENTERATA, s. str.) Coelenterata, with consistent tissues not pierced by a system of pores ; the osculum is replaced by a mouth ; with thread cells in the epithelial tissues. The Cnidaria represent the Ccelenterata in a more restricted sense ; and in their structure the radial symmetry appears more strongly marked. In them the amoeboid cell, as an independent tissue unit, loses its importance for the functions of locomotion and nourishment, although the entoderm cells often possess the power of absorbing solid particles, after the manner of the amoebae. The gastrovascular apparatus, on the contrary, functions distinctly as a digestive and circulatory body cavity. Pore systems in the skin are not required for the introduction of nourishment, since the mouth, which corre- sponds to the osculum, provides for the reception of food. IsTemato- cysts are very commonly found as productions of the epithelial cells, ACTItfOZOA. 223 principally of the ectoderm, but also of the entoderm. Each cnido- blast, from the contents of which a nematocyst is developed, possesses a fine superficial plasmatic process (cnidocil), which is probably very sensitive to mechanical stimuli, and occasions the bursting of the capsule. Very frequently the cnidoblasts are found thickly grouped to- gether at certain places, and form wart-like swellings or batteries (fig. 168). The differentiation of tissues and organs also appears to have i cached a higher stage in the Cnidaria, in comparison with the Porifera, in which cnidoblasts have not hitherto been discovered. L Sense cells, in particular, a: e found in the ectoderm, and these are not seldom grouped together as specific sense organs. Nerve cells and fibres are also present ; the latter often form a deeper layer of fibrous tracts beneath the superficial layer of the ec- toderm, with FIG. 168. Group of nematocysts at tlu- end of the tentacle of a Scyphist^ma -Stl which they Stand FIG. 169. Longitudinal section through the nerve ring of Charybdea. i n connection Sz> Sense cells in the ectoderm ; Gz, ganglion cells ; Nf, nerve fibres ; Stl, supporting lamella ; E, entoderm cells. through pro- cesses of the sense cells. Amongst many Medusae (Craspedota and Charybdea) we find a single or double nerve ring near the edge of the disc, while in the Polyps (Actinia), the nerve fibres have a more irregular distribution (fig. 169). CLASS I. ANTHOZOA*=ACTINOZOA (Coral polyps). Polyps with cKSOpliageal tube and mesenteric folds, with internal generative organs (no medusoid sexual generation), usually with solid mesodermal calcareous skeleton. The polyps of the Actinozoa are distinguished from the polyps * Ehrenberg, " Beitrage zur physiologischen Kenntniss der Korallenthiere im Allgemeincn und besonders des rothen Meeres." Ehrenberg. " Tiber die Natur und Bildung der Korallcnbanke," Abh. der Berl. Akad, 1832. Ch. Darwin, 224 C(ELEiNTERA.TA. of the Hydromedusre by their larger size and the more com- plicated structure of their gastrovascular cavity (fig. 43). The latter is not a simple cavity in the body, but is divided by numerous vertical partitions, the mesenteric folds, into a system of vertical pouches which communicate with one another at the bottom of the gastric cavity. In addition a system of capillary passages is also frequently present in the body wall. At their upper extremity the pouches are continuous with the canals leading into the hollow tentacles, since the edges of the mesenteries bounding them unite with the wall of the oral tube which hangs from the mouth. An opening may however persist in each mesentery underneath the oral disc, putting the neighbouring chambers in communication. The oral tube has the significance of an oasophagus, and possesses at its internal end, where the peripheral chambers open into the central cavity, an opening capable of being closed, by means of which its cavity stands in communication with the gastrovascular system. The mouth is used not only for the reception of food, but also for the re- jection of excreta. The secretions of the coiled and twisted filaments (mesenteric filaments) at the edge of the mesenteries must be regarded \ as aiding in digestion (fig. 43). The body of the polyp consists of an external coating of cells, an internal layer lining the gastric cavity, and an interposed connective tissue layer of very various thickness and structure (mesoderm). The latter appears rarely as gelatinous tissue, and more frequently as a tough homogeneous connective tissue containing spindle and star-shaped cells (Alcyonidw, Gorgonidce). This tissue may also assume the form of fibrous connective tissue, and become the seat of calcareous deposits. Muscle fibres, which take their origin from the entoderm cells, may also appear in the mesoderm ; while the newly discovered ectodermal sense epithelium and nerve fibrillse keep their superficial position in the region of the oral disc and on the tentacles. The generative products arise on the mesenteries near the mesenteric filaments as band-shaped or folded thickenings, and, according to Hertwig, are products of the entoderm. The sexes are for the most part separate, although hermaphrodite individuals " The Structure and Distribution of Coral Reefs," London, 1842. J. D. Dana, " United States Expl. Expedition, Zoophytes," Philadelphia, 1846. M. Edwards et J. Haimc, " Histoire naturelle des Corailliares," 3 Tom, Paris, 1857 1SGO. Lacaze Duthicrs, ' Histoire naturelle du Corail," Paris, 18(54. Gosse, " Actino- logia britannica," London, 1860. Kolliker, - Anatomisch-systcmatische Bcschrei- bung der Alcyonarien," 1872. Moseley, " The Structure and Relations of the Alcyonarian Heliopora coerulea, etc," Philowjjh. Transactions of the Roy. 8oc. t 1876. ACTIFOZOA. 225 are met with. In rare cases all the individuals are hermaphrodite, e.g., Ceriantlius. The embryos produced from the fertilised ovum, which undergo a complete segmentation, are frequently born alive as ciliated larvae, and possess an internal gastric cavity, and an oral aperture situated at the pole, which is directed backwards during movement. They then fix themselves by the pole opposed to the oral aperture and protrude in the region of the mouth first two, then four, eight, twelve, etc., tentacles ; in the Octactinia eight tentacles at once. In the Polyactinia, the tentacles and mesenteric pouches of which are arranged in multiples of six, it was till recently erroneously believed with M. Edwards that six primary mesenteries were first developed, then six secondary between them ; then twelve were formed, then twenty-four, etc., so that mesenteries of equal size were of equal age and belonged to a cycle formed at one time. Lacaze Duthiers however produced proofs that the increase of mesenteries and of tentacles follows an entirely different law of growth, and that these structures in the first phases of development show a bilateral symmetry; and it is only later that the six radial symmetry appears by the equalization of the alternating elements of unequal age. A remnant of the primitive bilateral symmetry is moreover often preserved in the elongated mouth slit, which falls in the plane of the two primary tentacles. Amongst the Poly actinia the very young larvae of the Actinia (A. mesemhryantkemum, Sagartia, Bunodes) have been most accu- rately investigated. They are small ciliated planulae, one pole of which is somewhat drawn out and bears a tuft of longer cilia. The opposite end of the body is flattened and pierced with a mouth. This leads by a short rcsophageal tube, which arises by invagination, into the narrow gastric cavity. The first differentiation consists in the appearance of two folds placed opposite each other, which divide the gastric cavity into two unequal chambers. The mouth is drawn out in the form of a longitudinal slit symmetrical with and at right angles to these primary mesenteric folds ; so that by means of them the position of the median plane can be determined. Two new folds soon arise in the larger chamber, which we will call the anterior j these lie opposite to one another and symmetrically with the median plane; so that four chambers are now present, an anterior, a posterior, and two smaller lateral ones. A third pair of folds are then developed in the posterior space, and a fourth pair follow quickly in the lateral chambers : the fourth pair are slightly smaller 15 226 CCELENTEBATA. than the preceding ones. After an interval four new folds appear, one- on each side of the two primary mesenteries (fig. 170). The twelve- gastrovascular chambers thus formed gradually become equal in size, and can be separated into two unpaired chambers situated in the median plane, and into five pairs placed symmetrically on cither t-ide of it. FIG. 170. From the history of the development of Actinia mesemlryanfhcmum (after Lacazo Duthiers). a, Larva with eight mesenteries and two coiled bands ; 0, mouth, b, Slightly more advanced larva with the commencement of eight tentacles, c, d, Young Actinia with twenty-four tentacles, two longitudinal sections at right angles to one anothei. e f Mouth and tentacles seen from the oral surface. The tentacles begin to develop before the appearance of the fifth and sixth pairs of mesenteries. They appear at the oral end of the gastrovascular chambers, and the tentacle of the anterior unpaired 227 FIG. 17l^-Bla*totroc?Mt nutrix (after C. Sem- per). LK, Lateral bud. chamber* .appears first, surpassing in size those which follow it. The opposite (posterior) unpaired tentacle and the other paired tentacles then make their first appearance as small wart-like prominences. When the twelve tentacles have been formed, they become alter- nately equalised, so that six larger tentacles, amongst which are reckoned the unpaired ten- tacles of the long axis, alternate with the same number of smaller ones, and we have two circles of six tentacles of the first and the same number of the second order. The asexual reproduction by gemmation and fission is of great significance. Buds can be formed in various positions, even at the oral end, in which case a strobila-like form appears. In Blastotrochus the buds appear at right angles to the axis of the parent animal (fig. 171). If the individuals so produced remain connected with one another, a polyp-stock is formed, which may attain very various forms and great size. As a rule the individuals are imbedded in a common body mass, the ccenenchym, and their gastric cavities communicate more or less directly, so that the juices acquired in the in- dividual polyps penetrate into the collective stock. This stock affords us an excellent example of an animal community built up out of similar members. The formation of the generative products alone is distributed, as a > rule, to different individuals, which, however, unite in dis- charging all animal and vege- tative functions together (fig. 172). The skeletal formations of the FIG. 172. Branch of a Polyparium of CordUi rubrum (after Lacaze Dllthiers )- p > polyps are specially worthy of remark (polyparia). In almost every case, with the exception of Ae- tinia, there is a deposit of solid calcareous matier in the rnesoderm, and * Like the first tentacle of the young Scyphistoma polyp among the Hydvs- Mcdusce. 228 C(ELENTERATA. according to the density of this deposit, there is produced a leathery, chalky, or even stony framework. If isolated needles or toothed rods (fig. 173) of calcareous substance are distributed beneath the epidermis and the crenenchyma, the polyp-stock has a fleshy, leathery nature (Alcyonaria) ; but if, on the contrary, the calcareous structures are fused together or are cemented together in a larger mass, a solid, more or less firm, often stony cal- careous skeleton is developed (Madreporaria). In the individual animals the formation of this sub-epidermic skeleton begins on the foot surface, and advances thence in such a manner that near the calcareous foot-plate there is formed in the under part of the polyp body a more or less cup-shaped theca, from which numerous perpendicular plates, the septa, radiate in- wards. In the cup-shaped cal- careous framework of the individual polyp, the structure of the gastrovascular cavity is repeated, with the exception that the calcareous septa cor- respond to the interspaces of the mesenteries (fig 174). The number of the eepta in- creases as does that of the mesenteries and tentacles with the age of the polyp according to the same laws. At the same time a great number of systematically important modifications of the skeleton are effected by further differentiation. A column-like, calcareous mass sometimes arises in the axis of the cup (columella), and in its neighbourhood a circle of calcareous rods (jyali), which are separate from the septa (fig. 175). There may further be formed between the lateral surfaces of the septa processes of calcareous substance as interseptal rods or horizontal shelves (dissepimenta} ; also on the outer side of the wall of the theca ribs (costce) projecting beyond its external surface, and similar dissepi- ments may be produced between thes-e. FIG. 173. Calcareous bodies (Sclei-oder mites) of Alcyonaria (after Kolliker). , of Plcxaurella. b, of Oorgonia. c t of Alcyonium. ACTINOZOA.. 220 The important diversities of form in the polyp stocks are not only occasioned by the differences of structure of the skeleton of the mm FIG. 175. Vertical section through the cup of Cyathi- na Cyathm (after Milne Edwards). S, Septa ; P, pali ; C, columella. polyp, but are also the resultant of varying methods of growth by FIG. 17L Vertical section through a polyp of Astroides gemmation and impei'- calyoularis (after Lacaze Duthiers). The mouth open- ing and cesophasreal tube are seen as well as the me- senteries fastened to the same ; a 1 so the calcareous septa between the mesenteries, and the columella of the skeleton, Sk. feet fissioa. According to the method, nume- rous modifications of branched stocks are dis- tinguished, e.g., Madre- pores (fig. 176), Oculi- nidce (fig. 177), and the lamellar and massive stocks as Astrcea (fig. 178) and the Mcean- drinidce (fig. 179). The Anthozoa are all inhabitants of the sea, and live mostly in the warmer zones, but certain types of the fleshy FIQ. 176. "Sladtvpora verrtt- cosa after Ed. H. FIG. 177. Branch of Ocu- lina speciota (after Ed. H). 230 C(ELEK TERATA, FiG. 178. Astr&a (Goniastraea) pectlnata Elirbg. (after Klunzinger). Octactinia and Actinia, are distributed in all latitudes. The polyps which build banks and reefs are confined to a zone extending about 28 degrees on either side of the equator, and only here and there extend beyond these bounds. They live for the most part near the coast, and produce there in course of time rocky masses of colossal extent by the accumulations of their stony calcareous frameworks. These masses may form coral reefs (atolls, barrier reefs, fringing reefs], which are perilous to ship- ping, and may also become the foundations of islands. In both cases a gradual alteration of level, the raising of the bottom of the sea, assists the work of tlie coral animals. The presence of the coral banks in the deep sea is, on the other hand, due to a continual sinking of the sea-bottom The part which the Anthozoa take in the alteration of the earth's surface is considerable. In the present time they protect the coast from the consequences of the breaking of the waves and assist in the formation of islands and rocks by producing immense masses of calcareous matter. In earlier geological epochs they have played a still more important part FiG. 179. Mfeandrina (CoelorJa) arallca Klz. (after Klun- iud cr in' from the zinger). fe . , , great thickness or the coral formations of the Palaeozoic period and of the Jurassic formation. Order 1. HUGOSA = TETRAOORALLA. Palaeozoic Corals with numerous symmetrically arranged septa, grouped in multiples of four. To these belong the families of the Cyathophyllida, Stauridce, etc. ACTINOZOA. 231 Order 2. ALCYONARIA == OCTACTINIA. Polyps and polyp stocks with eight plumed tentacles and the same number of uncalcijied mesenteric folds. * The calcareous secretions of the so-called cutis lead to the forma- tion of fle-hy polyparia or of friable crusts surrounding an axial skeleton, which is sometimes horny, sometimes calcareous and stony, or of rigid calcareous tubes (Tubipora). In all cases definite cal- careous bodies, the sclerodermites, form the foundation of the skeleton. The embryos are mostly born as ciliated larvae, without mesenteries or tentacles. The separation of the sexes in different individuals is the rule (fig. 172). 1. Fam. Alcyonidae. Fixed polyp stocks without axial skeleton, usually with a fleshy, leathery polyparium, with only a slight deposition of calcareous matter in the cutis. The colonies arise either through lateral gemmation, when they form lobed and ramified masses, e.g. Alcyonium palmatum, Pall., digitatum L., or the individual animals are connected by basal buds and root- like processes, e.g., Cornularia crassa Edw. 2. Fam. Pennatulidae (Sea feathers). Polyp stocks, the naked free basis of which is embedded in sand and mud, usually with horny, easily bent axial skeleton. There are small sterile polyps as well as the sexual animals. The presence of an opening in the stem for the ejection and reception of water is worthy of remark. The animals sometimes are placed on the side twigs of the stem, and the polyparium is feather-like, e.g., Pennatula rubra Ellis ; some- times they are distributed on all sides of the simple stem, e.g., the dioecious Veret ilium cynoinorium Pall. In other cases the polyparium appears flat and shaped like a kidney, with a bulbous root without an axis, Eenilla violacea Quoy. Gaim., or a kind of umbel is formed by the aggregation of the polyps at the upper end of a long stem, Umlellula Thomsonii Kb'll. 3. Fam. Gorgonidse. The fixed colonies possess a horny or calcareous tree- like branched axial skeleton, which is surrounded by a friable crust, or by a softer parenchyma containing calcareous particles. The body cavities of the individual animals communicate by branched vessel-like tubes which contain the common nutritive fluid. The axis is either horny, flexible, and unjointed, as, e.g., Gorgonia verrucosa Pall., (Rliipidogorgia) flabellum L., or composed of alternating horny and calcareous segments, as, e.g., Isis hippuris Lam., Melithcea ochracea Lam., or stony and formed of calcareous matter. The red coral, Corallium rubrum Lam., falls under the last head, and yields the coral stone which is used in jewellery. This species is found in the Mediterranean, on the rocky coasts of Algiers and Tunis, and there forms an important object of industry. 4. Fam. Tubiporidae, organ coral. The polyparia resembling the pipes of an organ. The animals are placed in parallel calcareous tubes connected by hori- zontal plates. Tubipora Hemprichtii Ehrbg. Order 3. ZOANTHARIA = HEXACTINIA. Polyps and polyp stocks, whose tentacles usually alternate in several circles, and are either six or some multiple of six in nuncler. 232 C(ELEXTEEATA. The body is seldom quite soft, or with a leathery framework ; as a rule it has a calcareous stony polyparium with radial striations. Separated sexes are the rule, but hermaphrodite polyps (Actinia) are not seldom to be met with. The polyps very generally retain their embryos for a long time, so that they are born eight or twelve rayed, with rudimentary tentacles. Many give rise to coral reefs and islands (figs. 175 179). 1. ANTIPATHARIA. Mostly with only six tentacles, and horny skeletal axis. Fam. Antipathidae. Polyp stocks with soft non-calcareous body, but with simple or branched axial skeleton. Only six tentacles surround the mouth, e.g., Antipatlies Pall. 2. ACTIXIARIA, with no hard structure. Fam. Actinidae, with soft body ; sometimes single animals with several alternating circles of tentacles, Actinia L. ; sometimes connected in stolons and aggregated to form stocks, Zoantkus Cuv. The former are able, by means of their contractile foot, to leave their place of attachment and to move freely. Many reach a relatively considerable size, and possess beautiful colours. Under the name of sea anemones they are the ornaments of salt water aquaria. Actinia mesemlryantliemum L. The skin sometimes secretes a glutinous mass filled with nematocysts or a kind of membrane, Cerianthus Delle Ch. 3. MADEEPORAEIA with continuous hard calcareous skeleton. (a) Aporosa. w Fam. Turbinolidae. Mostly single polyps with compact calcareous frame- work, imperforate thecse, and well developed septa, the spaces between which are open to the bottom. Turlinolia Lam., Flaldlum Less., Caryoplnjllia Lam., C. cyatlnts Lam., Blastotrochus Ed. H. Fam. Oculinidse. Polyp stocks with hard usually branched polyparium, with coenenchyma rich in calcareous matter, and but few septa in the cup of the individual. Ocidina virr/inea Less., Indian Ocean. AvyrftiJtelia oculata L. white corals of the Mediterranean. Fam. Astrse'idse, Star corals, Mostly massive polyp stocks with fused thecce, and without coenenchyma. The septa have sometimes cutting edges, sometimes toothed edges. The interseptal spaces are filled with horizontal partition walls. Eusmilia Edw. The single animals are produced by fission and remain connected only at their bases. They produce a cespitous polyparium, the septal edges of the cup being cutting. Galaxea Okeii. The single cups arise by gemmation, are free at the upper edge ; the septa have cutting edges. Astrcea Lam., single cups fused throughout the entire wall. The septal edges of the cup are jagged. Maandrlna Lam., the neighbouring cups fused to form long valleys. M. Crassa Edw. H. Fam. Fungidae. Mushroom corals. Usually with large fiat single cups, some- times polyp stocks ; without thecee, with numerous strongly developed septa, toothed and connected by synapticulse. JFungia discus Dana., JJalomitra Dana., ZtOjjJiosei'is Edw. II. (b) Perforata. Fam. Madreporidae, Madrepores. Polyps and polyp stocks with porous coenenchyma and perforated thecae. Gastric cavity open at the bottom and communicating with the central canal in the axis of the branched polyparium. HYDROZOA. 233 Th Septa but slightly developed. Mzdrepora cervicornis Lam., Dendropliyllia ramea Edw., Mediterranean. Astroides ealycuiaris Pall. CLASS II. POLYPOMEDUSJE.* [HYDROZOA.] Polyps without cesophageal tube, with simple gastrovascular cavity , The generative elements are developed in medusoid forms which may be either free-swimming, or permanently attached to hydroid forms. This class includes the small polyps and polyp stocks, and the Medusce which form the sexual generation. The Polypomedusce have always a simpler structure than the Anthozoa to which they are also usually infe- rior in size. They lack oesophagus, septa, and gastrovas- cular pouches. Only the polyps of the a- sexual generation of the Scyphomedusse [Acraspeda], known Scypldstoma, pos- sess a remnant of the gastric folds as four gastric ridges from which filaments are developed. The polyp stocks develop in rare cases (Mille- poridce) a compact calcareous framework comparable to the polyparium. When skeletal formations are present they con- sist as a rule of more or less horny secre- tions of the ectoderm, which as delicate tubes surround the stem and its ramifications, and sometimes form small cup-like structures surrounding the po^yp, and known as * Escholtz, " System der Acalephen," Berlin, 1821). Th. Huxley, " Memoir on the Anatomy and Affinities of the Medusae," Phil. Trans., London, IS-l'J. FIG. ISO a. Branch of on Obelia-stock (0, ge j atino?a). O, Mouth of a nutritive polyp wi h extended tentacles. M, Medusa buds on the body of a proliferous polyp (blasto- style) ; Th, bell-shaped tup (theca) of a nutritive polyp. 234 CCELENTEEATJL. hydrothecse (fig. 180 a). A more or less stiff mesoderm lamella is also developed in the interior of the body wall, between the ectoderm and the endoderm. This serves to support the soft parts of the animal, and, in the Medusce, is in part represented by the gelatinous connective tissue of the disc. The Medusa (fig. 180 6) is without doubt morphologically higher than the Polyp, since it represents the mature sexual individual, while the Polyp performs the nutritive and vegetative functions. The Medusa, in correspondence with its power of free locomotion, possesses an ectodermal nervous system and sense organs. The nervous system consists of nerve fibres and ganglion cells, and is usually specially concentrated round the edge of the disc, where it forms a double ring of fibres running parallel to the circular vessel. The sense organs are the so-called marginal bodies. The generative pro- ducts of the Medusae either have their origin in the ectoderm, in which case they may be developed on the under surface of the disc (sub- umbrella) in the ecto- derm immediately un- derlying the radial canals" (Eucopidce), or in the ectoderm of the manubrium (Oceanidoe) ; or they may arise from the endoderm of the under surface of the umbrella (Scyphomedusce}. Both Polyps and Medusae frequently remain at a lower grade of morphological differentiation, the former becoming polypoid appen- dages, the latter medusoid buds enclosing the generative products. In either case they are situated on the stem or on some part of the Polyp. The individuality of such appendages appears limited ; the medusoid or polypoid animal sinks, physiologically speaking, to the value of a portion of the body or of an organ, while the entire stock L. Agassiz, " Contribution to the Natural History of the United States, Aca- lephae," vol. iii., 1860, vol. iv., 1862. E. Haeckel, "System der Medusen," Tom. I. and II., Jena, 1880 and 1881. FIG. 180 J. Free Medusa of Obelia gelatinosa, as yet without generative organs; g, auditory vesicles. HYDEOZOA. 235 approaches more nearly to a single organism. The more completely polymorphism and division of labour are impressed upon the polypoid and medusoid appendages, so much higher becomes the unity of the whole which is morphologically a colony of animals. In these cases it is often difficult to distinguish between budding and simple growth. For a long time it was considered as a remarkable circumstance, hardly admitting of a satisfactory explanation, that organisms which differed so widely as Polyps and Medusae they had, indeed, been systematically separated as different classes should only form dif- ferent stages in the life-history of a single cycle of development and thus be united in the closest genetic connection. The theory of "Alternation of Generations" contained only a description of the matter, and offered no explanation. The discovery of the mode of origin of the Medusa as a bud on the body of the Polyp first clearly demonstrated the direct relation of the two forms, for it proved that the Medusa is a flattened, disc-shaped Polyp with a shallow but wide gastric cavity, the peripheral part of which has, by the fusion of its upper and lower walls along four, six, or eiyht radiating areas, become divided into the vascular pouches ((jastric pouches), or, as they are called, radial canah, which correspond to the gastrovascular pouches of the Anthozoa. The differences consist, in connection with the discoidal form, mainly in the position of the gastric tube as an external appendage, the manu- brium, and in the great reduction in height of the radially extended septa (mesenteries), which are traversed by a layer of endoderm cells, the vascular or endoderm lamella. This layer is derived from the fusi9n mentioned above of the aboral with the oral layer of the endoderm of the peripheral part of the gastro-vascular cavity. At the same time the oral disc becomes enlarged and concave to form the cavity of the bell, the ectodermal lining of which gives rise to the muscles of the suburnbrella. The supporting substance of the arched (after it is freed from its attachment) aboral surface of the disc becomes very much thickened and gives rise to the gelatinous substance (mesodermic), which sometimes contains cells ; while that of the oral surface keeps the character of a thin but firm lamella, and serves as a support for the muscles on the under surface of the disc. The tentacles accordingly arise near the edge of the disc, and become the marginal tentacles of the Medusa. In addition to these, four simple or branched oral appendages appear as outgrowths from the manubrium. In addition to the sexual reproduction, asexual multiplication is 236 CCELENTEEATA. widely distributed, especially amongst the polypoid forms, in which it leads to the formation of polymorphous animal stocks. The two forms of reproduction alternate for the most part in regular order, so as to produce different generations. There are, however, Medusce (Aeginopsis, Pelagia) which proceed without alternation of genera- tions and develop directly from the ovum by continuous development with metamorphosis ; but, as a general rule, the egg of the Medusa (phanero-codonic gonophore) or the niedusoid generative bud (adelo- codonic gonophore) produces a Polyp, and this Polyp either at once, by transverse fission (Scyphomedusoa), or later, after a longer period of growth, in which a sessile or free-swimming polyp stock is pro- duced, gives rise to a generation of free-swimming Medusae, or of medusoid buds which never become separate from the polyp stock. The Hydroinedusse. feed entirely on animal substances, and for the most part are inhabitants of the warmer seas. The free-moving Medusce, and Siphonophora are phosphorescent. Order 1. HYDEOMEDUS^E.* Colonial forms, the individual Polyps of which are without wsophageal tube or mesenteric folds. The sexual generation has the form either of small free-swimming Medusce provided with a velum (Craspedote Meduscey or of medusoid generative buds (rudimentary Medusce} which remain attached to the hydroid colony. The Polyps and polypoid forms are the asexual individuals. They form small moss- or tree-like stocks which aro frequently surrounded by chitinous or horny tubes (cuticular skeleton). These exoskeletal structures may become extended into cup-like hydrothecte surrounding the individual Polyps. The stem and ramified branches [cceiiosark] contain a central canal which communicates with the gastric space of each individual Polyp and polypoid appendage and contains the common nourishing fluid. The Polyps have no oesophageal tube, and the ciliated gastric cavity is undivided by mesenteries. As a rule, the ectoderm and entoderm remain simple, and are only separated by a thin interposed supporting lamella which does not contain cells. The presence of elongated muscle fibres as processes of the ectodermal epithelial cells is very general (Hydra, Podocoryne). These muscles may, however, * L. Agassiz, " Contributions to the Natural History of the United States of America/' vol. ii. iv., 186018*52. G. J. Allman, "A Monograph of the Gymnoblastic or Tubularian Hydroids," vol. i. and ii., London, 1871 and 1872. N. Kleinenberg, " Hydra," Leipzig, 1872. 0. and R. Hertwig, "Das Nerven- system und die Sinnesorgane der Medusen," Leipzig, 1878. 1IYDEOZOA.. 237 be separated as an independent layer of nucleated fibre cells below the epithelium. The Polyps are not invariably alike, proliferous Polyps (or Blastostyles) being frequently found as well as the nutritive ones. The proliferous Polyps develop generative buds on their walls. The sterile Polyps may differ from one another in the number of tentacles and in their entire form, so that different kinds of individuals may be found on a single stock. Thus we find the polymorphism of the Siphonophora foreshadowed amongst the Hydroidea (Podocoryne^ Plu'/nularia). The generative products are only exceptionally developed in the Polyp body itself, in which case they are produced in the ecto- derm (Hydra). This exception is probably to be looked upon as an extreme case of degeneration of a medusoid bud. As a rule the generative products are de- veloped in special medusoid buds [gono- phores] formed from both cell-layers. In the most simple cases the budding in- dividuals of the sexual generation contain a diverticuluin of the gastric cavity of the polyp-shaped parent or of the axial cavity of the hydroid stock. The generative products become accumulated around this diverticulum (Hydractinia echinata, Clava squamata). In a more advanced stage we find a mantle-like envelope enclosing the bud, and con- stituting the rudiment of the umbrella, with a continuous vascular lamella or with more or less developed radial vessels (Tubularia coronata, Eudendrium ramosum, Van Ben.) Finally, at the highest stage, the buds develop into small M edusse (Campanularia gelatinosa van Ben., Sarsia tubulosa), which become free, and sooner or later, FIG. 181. Podocoryne cornea (after C. Grobben). P, Polyp ; M, Medusa bud on the proliferating polyp ; 8, spiral- zooid; Sk, skeleton Polyp (compare the free Medusa, fig. 154). 233 CGELENTEEA1 A. often only after a long period of free life, in which they become much larger and undergo a metamorphosis, reach sexual maturity. The Medusae belonging to the order Hydromedusaa are, with but few exceptions, distinguished from the Acalephce (Scyphomedusae) by their smaller size although certain forms, for example Aequorea, may attain such a size as to have a diameter of more than a foot and by their simpler organization. The number of their radial vessels is smaller (4, 6, or 8), their sense organs (marginal bodies) are not covered by folds of membrane (hence G ' ymnophthalmata Forbes), and they have a muscular velum (hence Craspedota Gegenbaur) (fig. 182). The generative products are always formed from the ectoderm, and originate on the walls of the radial canals or of the manubrium, but never, as in the Acalepha, ^/l Rw * n diverticula of the gastric cavity. The hyaline gelatinous substance of our Medusae is, as a rule, structureless, and contains no cellular elements ; there may, how-, ever, be fibres running per- pendicularly through it- (Liriope). These fibres are. probably derived from cell processes of the ecto- derm and entoderm, and have arisen contemporane- ously with the gelatinous disc, which is itself to be looked upon as an excretion product of the adjoining ectoderm and entoderm epithelium. The nerve-ring is placed at the edge of the disc at the point of insertion of the velum. It is covered by a sense epithelium com- posed of small cells bearing sense hairs, and has the form of a double fibrous cord containing ganglion cells. The larger upper nerve-ring runs above the velum, while the weaker nerve-ring, on the other hand, is placed below it. The lower nerve-ring is composed of larger fibres and larger ganglion cells ; bundles of fibrillse pass off from it to supply the muscles of the velum and subumbrella, where they form a sub-epithelial plexus interspersed with ganglion cells, between Ov FI&. 162. Phialadium varialile represented from the underside of the umbrel'a. V, Velum ; O, mouth ; Ov, ovary ; Ob, auditory vesicle ; Ef, tentacles on the margin of the disc ; Rw, marginal swellings. 23D the muscular epithelium and the fibrous layer. The ganglion cells in the upper nerve-ring are smaller, and the fibrillse given off from it pass to the tentacles. The fibrillse of the sense nerves may be derived from both rings. The marginal bodies have long been recognised as sense organs, and are either eye spots (ocelli) or auditory vesicles ; hence the Hydromedusce may be divided into two groups, the Ocellata or Vesiculata. In the Vesiculata the auditory vesicles are situated at the edge of the under side of the umbrella, and contain one or more concretions (otoliths) which are formed in the interior of cells. Peculiar sense cells surround each vesicle-like cell containing a concretion. The curved hairs of these sense cells (auditory hairs) are in contact with the con- cretion vesicle. A nerve fibrilla enters the basis of the auditory cells (fig The audi- tory organs of the Tra- chymedusce are placed above the velum, and are in con- nection with the upper nerve ring ; they have the form of tentacles furnished The FIG. 183. Sense organ on the nerve-ring and circular vessel of Octorchlt (after 0. and R. Hertwig). Bb, Sense organ; O, O', two otoliths ; Hh, audi- tory cilia ; Hz, auditory cells ; No, upper nerve-ring ; Eg, cir- cular vessel. (Type of the audi- tory organ of the Vesiculata.) FIG. 184. Auditory vesicle of Gery- onia (Car marina), seen from the surface (after O. and R. Hertwig). 2f and N', The auditory nerves ; Ot, otolith ; Hz, auditory cells ; Hh, auditory cilia (type of the auditory organ of the Trachy- medugce) . small projecting with otoliths and auditory hairs. tentacle may either project freely on the surface (Trachynema), or, as in Geryonia, it may be placed in a vesicle (fig. 184) which lies in the gelatinous substance of the disc and close to the edge of the latter. Separate sexes are almost invariably the rule, but it is rare to find that the colonies are dioecious, i.e., that male and female medusoids are developed in different colonies (Tubularia). Gemma- tion has occasionally been observed among the Medusa* (Sarsia proliferd) and division (Stomobrachium mirabile). The larvaj of Cunina, which are parasitic on the Genyonidas, may also there give rise to a cluster of Duels. 240 C'CELENTEEATA. The development of the ovum, which is, as a rule, naked (i.e., with- out a vitelline membrane), has hitherto only been completely followed out in a few cases. In every case the segmentation seems to be com- plete, and leads to the formation of a segmentation cavity and a single-layered blastoderm [a single-layered blastosphere]. The latter gives rise to a second endodermal layer of cells, which lines the segmentation cavity. The segmentation cavity thus becomes converted into the gastric cavity of the future polyp. The spherical or oval larva now either attaches itself and gives rise by budding to a small hydroid stock, or swims freely and develops directly into a small Medusa (TrachymeduAce). The Medusa, after becoming free, usually undergoes a more or less fundamental change of form, which concerns not only the alteration caused by the enlargement of the umbrella and manubrium, but also the increase, according to definite laws, of the marginal tentacles, sense organs (Tima), and the radial canals (Aequorea). We must remark, however, that the sexually complete Medusae exhibit very considerable variations in size, number of sense organs and tentacles (Phycdidiwn variabile, Clythia volubilis}. The difficulty of systematic arrangement is augmented by the fact that closely allied Polyp stocks can produce different sexual forms. Thus, for example, Monocaidu* gives rise to sessile generative buds and Corymorpha to free Medusce (Steenstrupici). Medusae of identical structure also, which one would place in the same genus, may form the sexual generations of hydroid stocks belonging to different families (isogonism). There are also cases in which we find Medusa 3 , of closely allied genera, some developed from hydroid stocks by an alternation of generations, and others developed directly. Hence it appears just as little satisfactory to found a classification entirely upon the sexual generations as to pay attention to the asexual generation alone. (1) Sub-order: EleutheroUastece. Simple hydroid Polyps without medusoid buds ; both generative products are developed in the body- wall of the Polyp. Fam. Hydroidoe. Hydra, the fresh- water polyp. II. viridis L., H.fusca L., remarkable for great powers of reproduction. (2) Sub-order : Hydrocorallice. Coral-like hydroid stocks with cal- careous coenenchyma and tubular hydrothecse opening to the exterior by pores. Some of these contain the larger nutritive animals, while others contain animals without a mouth and beset with tentacles. HYDROZOA HTDEOMEDUS2E. 241 The latter are arranged usually in the form of a circle round each of the nutritive animals. The polyparia are found in the fossil state Fam. Milleporidae. JMillepora L. M. alcicornis L. Fam. Stylasteridae. (3) Sub-order: Tubularice (Ocellata). Polyp stocks which are either naked or clothed by a chitinous periderm without cup-shaped hydrothecae surrounding the polyp head. The generative buds arise on the body of the Polyp or on the stock. The Medusce which are set free belong to the genera Oceania, Sarsia, etc., and have ocelli. Fam. Clavidae. Polyp stocks with a chitinous periderm. Polyp club-shaped, with scattered, simple, filiform tentacles. The generative buds arise on the Polyp body and for the most part remain sessile. Cord y lop liora Allm. The stock is branched ; there are stolons which grow over external objects. Oval gonophores covered by the perisarc. The animals are dioecious. In fresh water C. lacustris Allm. albicola Kirchp., Elbe, Schleswig. The following are marine genera Clava 0. Fr. Mliller. Allied are the Eudendridee with Eudendriwn ramosnm. L. Fam. Hydractinidee. Polyp stocks with flat extended coenenchyma and firm encrusted skeletal excretions. The Polyps are club-shaped, with a circle of simple tentacles. In addition to the latter there are large tentacle-shaped Polypoids (Spiralzooids). Hydractinia van. Ben. The medusoid buds sessile on the proliferous animals, which are without tentacles. H. ecliinata Flem. Podocoryne Sars. (fig. 181). The generative buds are freed as Oceanldce. P. carnea, Sars. Fam. Tubularidae. Polyp stocks clothed with a chitinous periderm. The polyps possess a circle of filiform tentacles on the proboscis inside the external circle of tentacles. The generative buds arise between the two circles of tentacles. Tulnlaria L. The hydroid stocks form creeping root-like branches at the bottom, from which arise simple or branched twigs with the terminal polyp heads ; the generative buds are sessile. T. (Thamnocnidia Ag.) coronata Abilg. dioecious. Conjmorpha Sars. The stalk of the solitary polyp is clothed with a gelatinous periderm, attaches itself by root-like processes, and con- tains radial canals which lead into the wide digestive cavity of the Polyp- head. The freed Medusa is bell-shaped, with one marginal tentacle, and bulbous swellings at the end of the other radial canals. C. nutans Sars., C. nana Alder. (4) Sub-order: Campanularice (Vesiculata). The chitinous skeletal tubes widen out round the Polyp-head to form cup-like hydrothecse. The Polyp-head, the oral cone (proboscis), and tentacles can be in most cases completely retracted into these hydrothecse. The generative buds arise almost regularly on the walls of the proliferous individuals, which have neither mouth nor tentacles. The buds are sometimes sessile, and sometimes become separated off 16 242 CCELENTERATA. as small vesiculate Medusce, with generative organs on the radial canals (Eucopidce, Geryonopsidce, Aequoridce). Fam. Plumularidae. The hydrothecae of the branched hydroid-stocks are arranged in single rows ; those of the nutritive Polyp have small accessory calyces rilled with nemntocysts (nematocalyces). Plumularia cristata Lam., Antennularia antcnnina Lam. Fam. Sertularidae. Branched Polyp stocks, the Polyps of which project in flask-shaped hydrothecas on opposite sides of the stem. Dynamena pumila L., Sertularia abietliia, cupressina L. Fam. Campanularidae-Eucopidae. The cup-shaped hydrothecas are placed at the end of ringed stalks. The Polyps possess a circle of tentacles below their conical proboscis. Campanularia Lam. The proliferous individuals are situated on the branches and give rise to free Medusce, bell-shaped, with a short manubrium with four lips, four radial canals, the srire number of marginal tentacles, and eight inter- radial marginal vesicles. After separation the inter-radial tentacles are formed. C. ( Clytliia') Jolinstoni = volulilis Johnst., probably with Eticope variabills Cls. Obelia Per. Les., is distinguished from Campanularia by its Medusce. These are flat, disc-shaped Medusce with numerous marginal tentacles, but with eight inter-radial vesicles. 0. dicliotoma L. = (Campanularia gelatinosa van Ben.), C. geniculata L., Laomedea Lamx. The generative buds remain sessile in the hydrotheca of the proliferous polyps. L. caliculata Hincks. Fam. Aequoridae. Medusce with numerous radial vessels and mat ginal tentacles. Aeqiwrea Forsk. The Qeryonopsidce are allied here. Octorckls E. Haeck. Tim a. (5) Sub-order : Tr achy medusae. Medusce with firm, gelatinous umbrella, supported by cartilaginous ridges with stiff tentacles filled with solid rows of cells ; these may be confined to the young stage (larvae of Geryonidce). Development by metamorphosis without hydroid asexual individual. Fam. Trachyneinidae, with stiff marginal tentacles, which are scarcely capable of motion. The genital organs are developed on vesicle-like swellings of the eight radial canals. Tracliynema cillatum Ggbr. Rhopalonema relatum Ggbr., Messina. Fam. Aeginidae. The hard cartilaginous umbrella has a flat, discoid shape. The extended digestive cavity has pouch-like enlargements in place of the radial vessels. The circular vessel is usually reduced to a row of cells. Cunina albescent Ggbr., Naples. Aegincta flavescens Ggbr. Fam. Geryonidse. Umbrella with cartilaginous mantle ridges and four or six hollow tube-shaped marginal tentacles. The manubrium is long, cylindrical, or conical, with a proboscis-like oral portion, and four or six canals which lead into the radial canal. The generative organs lie on the radial canals ; eight or twelve marginal vesicles. Liriope Less. , with four radial canals, four or eight tentacles and eight vesicles. L. tetraphylla Cham., Indian Ocean. Geryonia Per. Les., with six radial canals without lingual cone. G. umbella E. HaecK. , Cannarina E. Haeck., with six radial canals and a lingual cone, E. Haeck, C. h&stata, Nice. HTDEOZOA SIPHONOPHOttA. 243 Order 2. SIPHONOPHORA.* Free- swimming polymorphous hydroid-stocks with contractile stem, with polypoid nutritive indi- viduals and medusoid buds, usually also with nectocahj- ces, hyrophyllia and dactylo- zooids. Morphologi- cally the Sipho- nophora are directly allied to the hy- droid-stocks; but they possess to a much greater extent than the latter the characters of individuals, in consequence of the highly developed poly- morphism of their polypoid and medusoid appendag es. The functions of the latter seem so inti- mately con- FIG. 185.-Diagram of a colony of Physophonda. St, Stem; Ek, nected and are ectoderm; En, entoderm; Pn, Pneumatophor; Sk, nectocalyx beinpf budded off ; S, nectocalyx ; 2>, hydrophyllium ; battery of n e ma tocysts. tion of the entire colony that we may regard each colony of Sipho- * Besides Kolliker, C. Vogt, Huxley and others, compare C. Gegenbaur, " Beobachtungen liber Siphonophoren," ZeUtchrift fur wit*. ZooL, 1853. C. 244 CffiLEFlERATA. nophora physiologically as an organism and its appendages as organs. In this connection we may mention that the sexual medu- soid generation is so little independent that it only exceptionally (Velellidce) reaches the morphological grade of the free-swimming Medusa. In place of the attached and ramified hydroid-stocks we find in the Siphonophora a free-swimming con- tractile unbranched stem (hydrosoma), which is rarely provided with simple lateral branches. The upper end of the hydro- soma is frequently dilated to the form of a flask (pneumatophore), and contains an air chamber [pneumatocyst] (fig. 185). In every case there is a central space in the axis of the stem in which the nutritive fluids are kept in constant motion by the contractility of the walls and by the move- ments of the cilia. The air sac or pneu- matocyst at the apex of the hydrosoma is connected to the chamber which contains it by radial septa, and in many cases attains a considerable size ( Physalia). It func- tions as a hydrostatic apparatus, and in those forms, which have a long spiral hydrosoma (Pliysoplioridce), serves to keep the body in an upright position. In some cases the gaseous contents can escape freely by one or more openings. The appendages which are attached to the spirally twisted bilaterally symmetrical stem and whose cavities communicate with that of the stem are of at least two kinds (1) The polypoid nutritive animals with their tentacles ; (2) the medusoid sexual buds. The nutritive Polyps (hydranths) are simple tubes provided with a mouth, and never Gegenbaur, " Neue Beitrage zur Kenntniss der Siphonophoren," Nova Acta., Tom. XXVII., 1859. E. Leuckart, " Zoologische Untersuchungen," I., Giessen, 1853. R. Leuckart, " Zur naheren Kenntniss der Siphonophoren von Nizza," Arcliiv. fur Naturgesch, 1854. C. Glaus, "Ueber Halistemma tergestinum n. s. nebst Bemerkungen iiber den feineren Bau der Physophoriden," Arbeit en aus dem Zoologisclien Institnt. der Univ. Wiun, etc., Tom. L, 1878. E. Met- schnikoff, " Studien iiber die Entwickelung der Medusen und Sipho.nophoren," Zeitscli.fur miss. Zool., Tom. XXIV., 1874. FIG. 186. A portion of the stem and appendages of Halistemma tfrgestinum. St, Stem ; D, hy- drophyllium ; T, dactylozooid; Sf, tentacle of the latter ; Wg, female, Mg, male, gonophores. HYDROZOA SIPHONOPHOBA. 245 possess a circle of tentacles. They always, however, have a long tentacle arising from their base. This tentacle can be extended to a considerable length, and be retracted into a spiral coil. It rarely has a simple form, but, as a rule, it bears a number of unbraiiched lateral twigs, which are also very contrac- tile. These tentacles are invariably beset with a great number of nema- tocysts, which in many places are closely packed and have a regular arrangement. These aggregations of thread-cells are especially found on the lateral branches of the tentacles, and give rise to large, brightly-coloured swellings, the batteries of nematocysts. The batteries show considerable variations a I Fio. 187. Group of buds of aPhysophor at the bottom of the pneumatophore. C, Central cavity ; Sk, nectocalyx bud with the ectodcrmal ingrowth. FIG. 1 S3. Development of Agalmopls Sarsii (after Metschnikoff). a, Ciliated larva. 5, Stage with developing hydrophy Ilium (D) . c, Stage with cap-shaped hydrophyllium (D) and developing pneumatophore (Lf). d, Stage with three hydrophyllia, (D, D', D"\ polyp (P), and tentacle. in form in the various species, genera, and families, and such varia- tions afford valuable characters for systematic lacssification. 246 CGELENTEEATA. The second form of appendage, the gonopJiores, usually possess a bell-shaped mantle containing circular and radial vessels, and surround- ing the central stalk or clapper (manubrium), which is filled with ova or spermatozoa. They usually arise in clusters at the base of the tentacles, more rarely from the nutritive Polyps themselves (e.g. in Velella). The male and female generative products always arise separately in differently shaped buds, but are usually found closely approximated on the scnn stock (fig. 186). There are, however, also dioecious Sipho- nophora, or if the medusoid buds or gonophores be regarded as generative organs, Sipliono- phora of distinct sexes, e.g., ApolemicL uvaria and Diphyes acuminata. The ripe sexual Medusoids frequently become separated from the stock, i.s. after the development of the generative products, and only rarely become liberated as small Medusce (Chrysomitra in the Velellidce), which produce generative products during their free life. Besides the constant nutri- tive Polyps and medusoid gonophores, there are incon- stant appendages, which are also modified Polypoids or Medusoids. These are the mouthless worm-like dactylo- zoids (fig. 186), which, like the Polyps, are provided with a tentacle, which is, however, shorter and simpler, and has no lateral branches or aggregations of nematocysts ; also the leaf -shaped hard cartilaginous hydropJiyllia, which serve to protect the polyps, dactylozoids, a-nd gonophores ; and finally the appendages known as nectocalyces, which are placed beneath the pneumatophore. The nectocalyces have a structure similar to that of the Medusse, though their bilateral symmetry is apparent ; NK FIG. 189. Small larval stock of Agalmopsis after the type of Athorylia. Lf, Pneumatophore ; D, hydrophyllium ; Nk, groups of nemato- cysts ; P, polyp. HTDBOZOA SIPHOXOPHORA. 247 tney are, however, without manubrium, mouth, tentacles, and sense organs. The deeply concave sub-umbrella surface of the nectocalyx is largely developed and has a very powerful muscular covering in rela- tion to its exclusively locomotive function. All the appendages are developed as buds formed of ectoderm and endo- d rm, and containing a central cavity which communicates with the central space of the stem. In the nectocalyces anl gonophores an ecto- dermal ingrowth gives rise to the covering of p. the sub-umbrella and to the generative products respectively v (fig. 187). The ova, of which there is often only one in each female gono- phore, are large, and have no vitelline mem- brane, and, after im- pregnation, undergo a complete and regular segmentation. A nectocalyx (Diphyes) is the first structure formed in the free-swim- ming larva, or the upper part of the body of the larva gives rise to a cap- shaped protective cover or hydrophyllium as well as a pneumato- phore, and the under part becomes the primary nutritive polyp (Agalmopsis, fig. 188). Since new buds give rise to leaf -shaped hydrophyllia, a small stock with FIG. 190. Physophora hydrostatica. Pn, Pnenmatoph,,-e ; S, nectocalyces arranged in double rows on the swim- ming column ; T, dactylozoid ; P, polyp (nutritive individual) with tentacles, 8f; Nk, groups of nemato- cysts on the latter ; G, clusters of generative buds. 243 CCELENTEEATA. Pn S / FIG. 197 . Htulftemma iergtstunim. S. Nectocalyx; P, polyp; JD, provisional appendages is formed which allows us to regard the develop- ment of the Siphono- pliora as a metamorphosis (fig. 188 and 189). The crown of hydro- phyllia, which is com- pleted by the addition of fresh hydrophyllia. after the appearance of a tentacle with provisional groups of nematocysts, persists only in Athory- bia, where a swimming column with nectocalyces is never formed. In Agalmopsis and Physophora the primary hydrophyllia of the larva fall off as the stem be- comes larger, and are replaced by nectocalyces. (1) Sub-order: Physo~ plwridce. Stem short, extended in the form of a sac (fig. 190), or elongated spirally (fig. 191), with a pneumato- phore, usually nectocaly- ces, which are arranged in two or more rows on a swimming column below the pneumatophore. Hydrophyllia and dacty- lozooids are usually present, and alternate with the polyps and gonophores in regular order. The body of the larva usually develops Pn, pneumatophore ; bydrophy Ilium ; Nk, groups of nematocysts. HTDfiOZOA. SIPHOXOPIIOBA. 249 first a polyp with pneumatophore and tentacle beneath aD apical hydrophyllium. The female gonophore has only one egg. Fam. Athorybiadae. With a bunch of hydrophyllia in place of the swim- ming column ; resembling a persistent larval stage. Athorybia rosacca Esch., Mediterranean. Fam. Physophoridae. s. str. Stem short and enlarged to a spiral sac beneath the swimming column with its double row of nectocalyces. No hydrophyllia but instead two outer bunches of dactylozooids with gonoblastidia, nutritive polyps and tentacles lying beneath them. Pltysopliora Forsk., Ph. liydrostatica Forsk., Mediterranean (fig. 190). Fam. Agalmidae. Stem unusually elongated and spirally twisted. Swimming column with two or more rows of nectocalyces. There are both hydrophyllia and tentacles. Forsltalia oontorta M. Edw., Halistemma. Dactylozooids and hydrophyllia directly connected with the stem. In the ciliated larva a pneumatophore is first developed at the upper pole. H. rubriim Yogt, Mediterranean. II. tergestinum Cls. (fig. 191). Agal- mopsis Sarsii Koll., Apolemia uvaria Less., Mediter- ranean. Dioecious. (2) Sub-order : Physalidce. Stem dilated to form a large chamber, the pneumatophore lying almost horizontally, containing a very large pneurnatocyst opening to the exterior. Necto- calyces and hydrophyllia absent. On the ventral line of the sac are situated large and small nutritive polyps with strong and long tentacles. There are also clusters of gonophores attached to the tentacle-like polyps. The female buds seem to become free-swimming Medusce. Fam. Physalidae. With the characteristics of the group Pliysalia Lam., P. carat ell a Esch. (Arethusa Til.'), yelagica, utriculus Esch., Atlantic Ocean. (3) Sub-order : Calycoplwridce. Stem long and without pneumatophore. Swimming column with double row of nectocalyces (Hippopodidae) or with two large opposed nectocalyces, more rarely with only one nectocalyx. There are no dactylozooids. The appendages arise in groups arranged regularly, and can be retracted into a cavity of the nectocalyx (fig. 192). Each group of individuals consists of a small nutritive polyp, a tentacle with naked kidney-shaped groups of nematocysts, and gonophores. FIG. 192. Diphyes acu- minata, magnified about 8 times. Sb f Fluid reservoir in the upper nectocalyx (somatocyst). 250 C(ELENTERATA. To these is usually added a funnel or umbrella-shaped hydrophyl- liurn (fig. 192). These groups of individuals may in some Diphyids become free, and assume a separate existence as Eudoxia (fig. 193). The gonophores contain numerous ova in the manubrium, which often projects as a cone from the aperture of the bell. In the larva the upper nectocalyx is the first formed. Fam. Hippopodidae. The swimming column has two rows of nectocalyces, and is situate on an upper lateral branch of the stem. The male and female gonophores are grouped in clusters and are situate at the base of the nutritive polyp. Glela Hippopus Forsk., Mediterranean. Fam. Diphyidae. With two very large nectocalyces at the upper end of the stem and opposite to each other. Dipliyes acuminata Lkt., dioecious ; with Eudoxia campanulata. Alyla pcntagona Esch., with Eudoxia cuboides, Mediterranean. Spliceronectes J!vixl. MonopJiye8 Cls., Sp. (/racilis Cls. with Diplo- ^Jiysa inermis. Mediterranean. (4) Sub-order : Discoidece. Stem compressed to a flat disc, with a system, of canal-like spaces (central cavity). Above lies the pneurnatocyst in the form of a disc-shaped reservoir of car- tilaginous consistence composed of concentric canals opening to the exterior. The polypoid and medusoid appendages are situate on the under side of the disc. In the centre is a large nutritive Polyp, around which are a number of smaller ones. To the base of these small Polyps FIG. 193. -Part of a T>i- are attached the gonophores. The dactylozooids piiy-.d (after R. Leuck- are no t far from the edfife of the disc. The art). D, Hydropliyl- , lium ; GS, genital gonopnores are set tree as small Medusce (Cliry- nectocaiyx ; p, polyp somitra), which do not produce the generative with tentacles. The . ' . individual groups se- material till long after separation. parate as Eudoxia. Fam. Velellidae. Velolla spirans Esch., Mediter- ranean. Porplta mcdlterranea Esch. Order 3. SCYPHOMEDUS^E = ACALEPHA.* Medusce of considerable size, with gastric filaments. The edge of the umbrella lobed. The sense organs covered. The embryonic stages are not hydroid stocks but Scyphistoma and Strobila forms. The Medusce of this order are distinguished from those of the hydroid group by their considerable size and the great thickness of * Besides the works of Brandt, L. Agassiz, Huxley, Eysenhardt, compare v . Siebold, " Beitrage zur Naturgeschichte der wirbellosen Thiere," 1839. M. HTDEOZOA SCiPIIOMEDUS^E. 251 their umbrella, the gelatinous connective tissue of which is richly developed and contains a quantity of strong fibrillae and a network of elastic fibres, which structures confer upon it a greater firmness and rigidity. Another characteristic of the group is derived from the structure o" the edge of the umbrella. This is divided by a regular number RK FIG. 191. Aurelia aurlta, from the oral surface. MA, The four oral tentacles with the mouth in the centre ; Gk, generative organs ; GH, aperture of sub-genital pit ; Rk, sense organ (marginal body) ; EG, radial vessel ; T, tentacle at edge of the disc. of indentations usually into eight groups of lobes between which the sense organs are contained in special pits (fig. 194). The marginal lobes of the Acalephse, like the continuous velum of the Hydromedusce, appear to be secondary formations at the edge of the disc. In the young stage known as Ephyra, which is common at least to all the Discophora, they are present as eight pairs of Sars, "Ueber die Entwicklung der Medusa aurita und Cyanea capillata," Archir.fiir Naturgescli, 1811. H. J. Clark, ' Prodromus of the History, etc., of the Order Lucernaria" Journ. of Host. Soc. of Nat. Hut.. 1863. C. Claus, " Studien iiber Polypen und Quallcn der Adria," Drnhxeliriften der It. Academic der Wissensck. Wicn, 1877. C. Claus, ' Untersuchungen iiber Charybdea marsupialis," Arleiten aus don Zoul. Imtltut, \\iun, 1878. Also E. Haeckel, 1. c. 252 CGELENTERATA. relatively long tongue-like processes, and grow out from the disc-like segments of the /Strobila as marginal cones. An undivided mar- ginal membrane (the velarium), differing from the velum of the Craspedota [in containing prolongations of the canals of the gastro- vascular system], is present in the Charybdeidoe alone. The Acalepha differ from the Hydromedusce in possessing, as a rule, large oral tentacles at the free end of the wide raanubrium. These may be regarded as being derived from an unequal growth of the edges of the mouth. They grow as four arm-like processes of the manubrium from the angles of the mouth, and are placed radially, FIG. 195. Diagrammatic longitudinal section through a Khizosfoma. V, Umbrella; If, gastric cavity ; S, sub-umbrella ; (?, genital band ; Sh, sub-genital pit ; F, filament ; S3f, muscle system of the sub-umbrella ; Rgf, radial vessels ; Rk, sense organs ; Eg, olfactory pits ; Al, ocular lobe ; Sk, shoulder tufts ; Dk, dorsal tufts ; Vk t ventral tufts of the eight arms ; Z, terminal parts of the arms. i.e. they alternate with the genital organs and gastric filaments. In some cases the arms become forked at an early period, and four pairs of arms are formed, the lobed tufted edges of which may again divide and sub-divide into many branches. In this case, the margins of the mouth and the opposed surfaces of each pair of arms fuse in early life in such a way that the original central mouth becomes obliterated, and in its place there are developed a number of small tufted orifices on the peripheral parts of the arms, through which nutriment is taken in (Rhizostomidce, fig. 195). HTDEOZOA SC YPHOMEDUS JE. 253 The form of the gastrovascular apparatus exhibits considerable differences, which in the Discophora may be considered as modifica- tions of the Ephyra type. The flat disc of the Epliyra, which is split into eight pairs of lobes, contains a central gastric cavity into which the canal of the short, wide, four-cornered manu- brium leads. From this central cavity there diverge eight canal- like peripheral diverticula (radial pouches), between which there are formed sooner or later in the vascular lamella the same number of short intermediate canals (intermediate pouches). The radial and intermediate canals sometimes become enlarged, as in Pelagia and FIG. 106. Section through the olfactory pit, the sense-organ (marginal body) and its nerve centre, of Aurelia aurita. E, Olfactory pit; L, lobe of the umbrella covering the sense organ ; P, eye spot ; Of, otolith of the auditory sac ; Z, cells after solution of the otoliths ; En, entoderm ; He, ectoderm with the underlying layer of nerve fibrillEe, F. Chrysaora, so as to form unusually broad gastric pouches separated by thin septa and without any communication with each other at the periphery. Sometimes, however, they become transformed into narrow vessels, between which, in the broad intervening septa, there is secondarily developed during the subsequent growth by a separa- tion of the two layers of the vascular-lamella, a rich network of anastomosing canals, and near the edge of the disc a circular canal (Aurelia, Rhizostomci). 254 CCELENTERATA. The gastrovascular apparatus of the cup- or bell -t haped Calycozod and Charyldeidce differs from the types above described, and re- sembles that of the more primitive Scyphistoma stage, in that the gastric cavity presents only four peripheral vascular pouches, which are very wide, and separated by extremely thin septa. The worm-like movable tentacles of the gastric cavity, the gastric filaments, which are not found in any Hydromedusce afford an im- portant distinctive mark. They correspond to the so-called mesenteric filaments of the Anthozoa, and afford the same aid to digestion through the secretion of their glandular entodermal covering. In every case they are attached to the sub-umbrella wall of the stomach, and fall in the four radii of the generative organs (radii of the second order), which alternate with the radii of the angles of the mouth, or radii of the first order. They usually follow the inner edge of the generative organs in a simple or convoluted curved line. The existence of the nervous system of the Acalepha has only recently been demonstrated with certainty. It has been proved that the centres of the nervous system are contained in the ectoderm of the stalk and base of the marginal bodies, and consist of a considerable layer of nerve fibrillse deep in the ciliated ectodermal epithelium, the nerve cells of which are elongated in the form of a rod, and bend round at their basal extremities to be continued directly into the nerve fibrillae (fig. 196). There is in addition a widely distributed and important peripheral nerve plexus in the muscles of the sub-umbrella. Up to the present time no investigations have completely elucidated the manner in which this nerve plexus is related to the nerve centres of the marginal bodies, and how the latter are connected with one another. The existence of a nerve ring on the sub- umbrella surface has been proved only for the Charybdeidce, in which the edge of the, disc is not notched (fig. 169). The antimeres of the Acalepha show in nil cases a great degree of individuality, and, when cut off, are rrblb to live for a considerable time. The marginal bodies, as well as the pit-like depressions on the dorsal side of the excavations in which the marginal bodies are placed (olfactory pits), must be considered as sense-organs. The marginal bodies are morphologically the remnants of reduced tentacles. They may be seen on the under side of the umbrella in the stage of the Ephyra, and are overgrown by portions of the edge of the umbrella (Steganophthalmata). [They contain a central canal lined by endoderm and continuous with the gastro- vascular system of the disc, fig. 196], They appear in all cases to unite the functions HTDEOZOA SCYPHOMEDUS.$. 255 of ocular and auditory apparatus. The auditory function is provided for by a large sac containing crystals, which originates from the cells of the entoderm ; while the eye consists of a mass of pigment lying on the dorsal or ventral face, and nearer the end of the stalk. In some exceptional cases (Nau&ithoe) it is provided with a refractile cuticular lens. But it is in the UWrybdeidae that the sense body reaches the highest development ; for m^iem, in addition to the terminal &ac of otoliths, there is also present, in the wall of the dilated vascular- space of the papilla, an extremely complicated visual organ, formed of four small paired and two large unpaired eyes, in which lens, vitreous body, and retina can be distinguished. The four generative organs of the Acalepha can be easily dis- tinguished in consequence of their size and their bright colouring. In some cases, at any rate in the Discophora, they protrude as folded bands into special cavities in the umbrella, the so-called sub-genital pits (hence the term PlianerocarpcK Esch.) In all cases these bands lie on the lower (sub-umbrella) wall of the digestive cavity (figs. 194, 195), from which they originate as leaf -like prominences. The upper surface is covered with gastric epithelium ; the under, which is turned towards the sub-umbrella, with germinal epithelium, the elements of which, in the process of development, pass into the gelatinous substance of the band. The formation of the cavities in the sub-umbrella of the Discophora is due to a local growth of the gelatinous substance of the sub -umbrella; in some cases, however, they may be completely absent (Discomedusa, Nausithoe]. The mature generative products are dehisced into the gastric cavity, and pass out through the mouth; but in many cases the ova undergo their embryonic development either in the ovary ,(Chrysaora) or in the oral tentacles (Aurelia). Separate sexes are the rule. Male and female individuals, however, apart from the colour of their generative organs, have only slight sexual differences, as, for instance, the form and length of the tentacles (Aurelia). Chrysaora is hermaphrodite. In the Discophora he development is .generally accompanied by an alternation of generations ; the asexual generations being repre- sented by the Scyphistoma and Strobila ; but in exceptional cases it is direct (Pelagia). In all cases a complete segmentation leads to the formation of a ciliated larva, the so-called planula, which attaches itself by the pole which is directed forwards in swimming. This pole is, however, opposite to the gastrula mouth, which in the meantime becomes oiosed, while round the mouth, which is 256 CCELEtfTEEATA. formed as a perforation at the free eud, the tentacles appear. As in the embryo Actinia, two opposite tentacles first make their appearance ; not, however, simultaneously, the one appearing after the other, so that the young larva about to develop into the Scyphis- toma presents a bilaterally symmetrical structure. Subsequently the second pair appear in a plane at right angles to the plane of the first tentacles. These four tentacles mark the radii of the first order. Then alternating with these, but in a less regular suc- cession, the third and fourth pairs appear ; and soon after in the plane of these latter four longitudinal folds of the gastric cavity are developed (radii of the second order or of the gastric filaments and genital organs). The eight-armed Scyphistoma soon produces eight fresh tentacles, which succeed one another in irregular succession, and alternate with the tentacles already present. Their position determines the inter- mediate radii of the future young DiscopJwr or Ephyra. After the formation of the circle of tentacles and the secretion of a clear basal periderm (Chrysaora), the Scyphistoma is capable. of reproduction by fission and gemmation. At first the Scyphistoma appears to multiply only by budding ; the second mode of reproduction, the process of stabilization, begins later. This consists essentially in the fission and division of the anterior half of the body into a number of segments, thus changing the Scyphistoma to a Strobila. The separation of the segments progresses continuously from the anterior end to the base of the Strobila, so that after the disappearance of the tentacles, first the terminal segment, then the second, and so forth, attain independent existence. Each segment becomes an Ephyra, developing eight pairs of elongated marginal lobes, with a marginal body in the notch which separates the two lobes of the same pair. It is these marginal lobes which give to the edge of the umbrella of the Ephyra its characteristic appearance. The young Ephyra gradually acquires the special peculiarities of form and organization of the sexually mature animal (vide figs. 113 a A). The number of nematocysts accumulated on the upper surface of the disc and on the tentacles of many Medusce enable them to cause a perceptible stinging sensation on contact. Many, e.g. Pclagia, are phosphorescent. According to Panceri, this phenomena originates in the fat-like contents of certain epithelial cells on the surface. In spite of the delicacy of their tissues, certain large Medusce have left impressions in the lithographic slate of Sohlenhofen (Medusites circularis, etc.) SCYPHOMEDUS.E CALYCCZOA, 5? li) Sub-order: Calycozoa (Cylicozoa). Cup-shaped Acalepha attached by their aboral pole. They have four wide vascular pouches separated by narrow walls, and eight arm- like processes beset with tentacles on the edge of the umbrella. The Calycozoa are best considered in their relation to the Scyhis- toma. They may be looked upon as Ssyphistoma deprived of their tentacles, which indeed are only transitory structures, and elongated so as to assume the form of a cup, and changed in several particulars which are characteristic of the medusa stage. The four septa arise by the fusion of the four gastric folds with the wide oral disc, which becomes drawn in and concave like a sub- umbrella. These four septa separate the same number of gas- FIG. 197. a, A Calycozoon (Luccrnar\a) from the .oral surface magnified about 8 diameters. S, Septa of the four gastric pouches ; L, longitudinal muscle fibres with the genital band ; lit, marginal tentacles, b, The Calycozoon seen from the side ; t gastric fold in the stalk ; at the base is the foot gland. trovascular pouches ; while the margin of the cup is drawn out into eight arm-like processes, from which groups of short, knobbed tentacles arise (fig. 197). The genital organs extend on the oral wall of the umbrella into the arms as eight band-shaped, plicated ridges. They run along in pairs at the lower part of each septum in the gastric cavity. The ovum, according to Fol, undergoes a complete segmentation, which results in a single-layered blastosphere. This becomes an oval, two- layered larva, which becomes ciliated, swims freely about, and finally attaches itself. The further development probably takes place directly without alternation of generations. 17 253 CCELEXTEEATA. Fam. Lucernaridae. Liicernaria 0. Fr. Miiller, Calycozoa with four radial chambers ; without genital pouches, and without the accessory chambers of the digestive cavity alternating with these. L. quadricornis 0. Fr. Miiller, campanulata Lmx. Crateroloj)hus Clark, with genital pouches and four chambers of the gastric cavity alterna- ting with them. Cr. Leuckarti Tsehb. = ltclgolandica Lkt. , Heligoland. The Lucernaria are without exception marine animals, and are remarkable for their great reproductive power. Accord- ing to A. Meyer, if the stalk be cut off, the cup reproduces a new one, and injured individuals, and even excised pieces, can become perfect animals. (2) Sub-order : Marsupialida (Lobophora). Tetra-radiate Acalepha having a four-sided pouch-like form. The velum has a smooth margin, and contains vessels prolongations of the gastro-vascidar systeni\. On the, margin of the disc there are four vertically placed lobe-like appen- dages. There are four covered sense organs, and the same number of vascular pouches separated by nar- row partition walls. The Charybdew are distinguished by the deep bell shape of their body, and were formerly reckoned as " Craspeclota " among the Hydro- medusce, with which they certainly have some characteristics in com- mon. Amongst these character- istics the most striking is the possession of a smooth-edged velum, which, however, contains vessels. FIG. 198. CharyMea marmpialis, natural Q n ^6 Other hand, the presence of size. T, Tentacles ; Ek, marginal bodies . , (sense organs) ; Oo, ovaries. the gastric filaments and ot the large sense organs enclosed in niches points to a relationship with the Acalepha; and this view is supported by the character of their whole structure, in which the peculiarities of the Lucernaridce are perceptible, though greatly SCYPHOMEDUS.E MAESUPIALIDA. 250 modified. As in Lucernaridce, the vascular spaces are wide pouches divided from each other by four narrow septa (figs. 198, 199). The nervous system is allied to that of the Hydromedusce by the presence of a sharply defined nerve-ring. This nerve-ring is placed on the sub-umbrella side of the bell, and, since at the bases of the four sense organs it lies further from the margin than it does at the corners of the bell, it has a sharply marked, zig-zag course. The nerve fibrillae given off from it mostly supply the muscular system of the sub-umbrella, and there give rise to numerous reticula of fibrillse connected with large ganglion cells. Large bundles of fibrillse com- parable to nerves have only been found in the four radii of the mar- ginal bodies. The latter attain a high degree of development, since the knob-like swelling in which they terminate possesses, in addition to the lithocyst, a complicated visual apparatus consisting of two large unpaired median eyes and four small paired lateral eyes. The generative organs have a very peculiar form. They are separated from the gastric filaments and as thin, rather broad plates attached in pairs to the four partition walls, reach the whole length of the vascular pouches. Unfortunately nothing is as yet known of the development. Fam. Charybdeidee. CUavyldea mar- x it j) -I alls Per. Les. (Marsupialis Planci Les.) Mediterranean. (3) Sub-order : Discophora (Acra- speda), Ephyra-medusce. Disc-shaped Acalepha, the margin of whose disc is divided into eight .lobes. They have at least eight sub-marginal sense organs contained in niches, and with the same number of ocular lobes. As a rule there are four great cavities in the umbrella for the generative organs. The Discophora, which are generally known simply as Acalepha, can at once be distinguished from the Calycozoa and the Charybdeidee by the disc-shaped lobed umbrella and usually by the large size of the oral tentacles. The lobes of the umbrella, however much they may differ in detail, can always be reduced to the eight pairs of lobes of the Ephyra, which, as the common starting-point of the Discophora, presents most clearly the eight-rayed symmetry char- Fre. 199. The apicalhalf of a Charyldea divided transversely, seen from the sub-umbrella side. The four oral arms are visible. Ov, Ovaries on the four septa, S; Ost, ostia of the gas- trie pouches ; Gf, gastric filaments. L'60 CCELENTEBATA. acteristic of the group. The striped muscles of the sub-umbrella are strongly developed to correspond with the great size of the body ; and beneath them the supporting lamella is usually thrown into a number of closely aggregated circular folds, thus causing a consider- able increase in the surface on which the muscular epithelium with its circularly arranged fibres are placed. The generative organs have the form of horse-shoe shaped frills which project into four widely open cavities in the sub-umbrella, the sub-genital pits. These cavities are not developed in some ex- ceptional cases (Nausitfwe, Discomedusa). The geiminal epithelium, FIG. 20Q.Aurelia aurita, seen from the oral surface. MA, The four oral arms with the mouth in the centre ; Gk, The genital frills ; G H, Openings of the sub-genital cavities ; Rk, Marginal bodies ; EG, Radial vessels ; T, Tentacles on the margin of the disc. which is always embedded in the gelatinous substance, is covered with an endodermal layer, and is probably itself ari endodermal product (fig. 200). Development takes place by alternation of gene- rations. In rare cases (Pelagia) the development is simplified, and the larva passes directly into the Ephyra, missing out the attached Scyphistoma and the Strobila stage (Krohn). 1. Semceostomece. Discophora with large central mouth sur- rounded by four large often multi-lobed oral arms. The form of the SCYPHOMEDUSJE RniZOSTOMEJE. 261 umbrella edge, the number of lobes and marginal tentacles present great variations. Fam. Ephyropsidae. Epliryopsi*, Ggbr. (Namithrt Koll). Disc small and like that of Epliyra, vith sbrvple gastric sacs, without oral arms, but with eight marginal tentacles. The genital organs (in four pairs) do not lie in umbrella cavities. E. iwlagica Koll., Mediterranean and Adriatic. Fam. Pelagidtf. Pelagia Per. Les. With wide gastric pouches and eight long marginal tentacles in the interradii. No alternation of generations. P. noctiluca Per. Les., Mediterranean. Clirysaora Per. Les., with twenty -four long marginal tentacles. The radial and intermediate gastric pouches are per- ceptibly different. Clir. liysoscclla Esch. Hermaphrodite, North Sea and Adriatic. Fam. Cyaneidae. Cyanea P6r. Les. The tentacles are united in bundles on the under surface of the deeply lobed thick disc. There are sixteen (eight radial and eight intermediate) more or less wide gastric pouches, which break up near the end of the marginal lobes into small ramified vessels. C. capillata Esch. Fam. Aurelidoe. Discomedusa Cls. With large oral arms, with branched vessels and 24 marginal tentacles. Subgenital pits present. D. lobata Cls., Adriatic. Aurelia Per. Les., with branched radial vessels and edge of disc fringed with small tentacles. A. aurita L. (Medusa, aurita L.), Baltic, North Sea, Adriatic, etc. A.flavidula Ag., coast of North America. 2. Rhizostomece. No central mouth, funnel-shaped slits in tho eight oral arms and eight, rarely twelve, marginal bodies on the lobed margin of the disc. There are no marginal tentacles. The central mouth, which is at first present, becomes closed during the larval development by the fusion of the edges of the lips. Funnel-like splits are formed on the folded edges of the four pairs of arms, the so- called suctorial mouths, by means of which microscopic bodies are received into the canal system of the oral arms (fig. 195). Rliizostoma Cuv. The arms end in simple tubular prolongations, and bear accessory tufts at their bases. RJi. Cuvieri Per. Les., Ceplie-a Per. Les. The branched oral arms have groups of nematocysts and long filaments between the terminal tufts. Cepliea Per. Les. (C'assiopca) borbonica Delle Ch., Medi- terranean and Adriatic. CLASS III. CTENOPHORA.* Medusce of spherical or cylindrical, rarely band-shaped form / with eight meridional rows of vibratile plates formed of fused cilia. They * C. Gegenbaur, "Stuclien iiber Organisation und Systematik der Cteno- phorcn." Archiv. fur Naturyesch., 1856. L. Agassiz, " Contributions to the Natural History of the United States of America," vol. iii., Boston, 1860. A. Kowalevski, "Entwickelungsgeschichte der Rippenquallen." Petersburg, 1866. H. Fol, " Ein Beitrag zur Anatomie und Entwicklungsgeschichte einiger Rip- penquallen," Inaugural dissertation. Jena, 1869. A. Agassiz, " Embryology of the Ctenophor," Cambridge, U.S., 1874. C. Chun, "Die ^tenonhoren de's Golt'cs von Neapel," Leipzig. 1880. 262 CCELEN1EEATA. possess an cesophageal tube and a g astro-vascular canal system. Two lateral tentacles, which can be retracted into pouches, are often present. The Ctenophora possess a shape which can in all cases be reduced to a sphere. They are radially symmetrical free-swim- ming Ccelenterata of gelatinous consistence. The body is often bilaterally compressed, so that it is possible to distinguish two planes passing Gf FIG. 201. Cydippe, seen from the through the long axis at right angles to one an- I . to apical pole. S, Sagittal plane ; T, Other ; these transverse plane; E, swimn ing oy.p-f-V.po,, '/ plates; Gf, gastro-vascular system. c s 9 ' tal plane and the transverse plane, and are analogous to the median (longitudinal vertical), and lateral (longitudinal horizontal) planes of bilaterally symmetrical animals (fig. 201). The arrangement of the internal organs bears a relation to these two planes. All parts of the body which occur in pairs, as the two tentacles, the gastric canals, the hepatic bands of the stomach, and the vessels which give origin to the eight lateral canals, all lie in the transverse plane, while the sagittal plane coincides with the longer axis of the O3sophageal (gastric) tube (whence also called the gastric plane), the two so- called pol r- fields, and the terminal vessels of the infundibulum. The infundibulum is so compressed that p IG 202. its longest diameter falls in the lateral piumosa (after Chun) . . . . Mouth. plane, which on this account is sometimes called the infundibular plane. Since these two planes divide the body into halves, which correspond with one another, and since there is no division into dorsal and ventral surfaces, the arrangement of the body may be said to be bi-radially symmetrical, but cannot be called 0, CTENOPHORA. 263 bilaterally symmetrical, although each half possesses this property. The body is divided by these two perpendicular planes into four similar quadrants. Locomotion is principally effected by the regular vibration of the hyaline swimming plates, which are disposed over the surface of the body in eight meridional rows, in such a way that each quadrant possesses two rows of plates, a transverse and a sagittal (fig. 202). Locomotion is also assisted by the contractility of the muscle fibres of the gelatinous tissue ; this contractility in the band-shaped Cestidce causes an undulating motion of the whole body. The mouth, which is sometimes surrounded by umbrella-shaped lobed processes of the gelatinous tissue, leads into a wide (Beroe) or narrow cesophageal tube, which in the latter case soon becomes flattened and broad. The cesophageal tube is furnished with two hepatic bands, and com- municates posteriorly, by an opening capa- ble of being closed by muscles, w T ith the gastric FIG. 2"3. -Aborsvl end of Callianlra bimata (after R. Hertwig). x, The two polar spaces ; to, the beginning of the eight rows of swimming plates, between which the otolith vesicle and the herve plate are seen. monly called, the in- fundibulum. The long cesophageal tube projects and opens freely into the infundibulum, and is completely surrounded by the gelatinous sub- stance, as far as the level of the two longitudinal vessels which accompany the two lateral surfaces in the transverse plane. The infundibulum, which is in all cases compressed in a direction at right angles to the O3sophageal tube, gives off eight vessels to the swimming-plates. These vessels have a bi-radial symmetry. It also gives off two vessels, which are dilated into two terminal sacs ; the latter surround the sense-organ at the aboral pole, which is known as the otolith vesicle, and each of them opens to the exterior by an orifice which is placed in a diagonal plane and is capable of being closed. Two tentacular vessels may arise from the bottom of the infundibulum. The internal surface both of the cerophageal tube and of the infundibulum and its vessels seem to be comnletelv clothed with cilia. 264 CCELENTEKATA. Up to the present time, the nervous system of the Ctenop/iora (fig. 203) is but imperfectly known. There is no doubt that the large vesicle found at the aboral pole, with its clear fluid and vibratile otoliths, is a sense-organ ; it is also exceedingly probable, taking into consideration the organization of the Acalepha, that the central nervous system of the Ctenophora is contained in the thickened base of the vesicle, the Otolith plate, especially as the latter is also closely united with a second sense-organ, the sagittal polar areas, which have already been described by Fol as olfactory organs, and is also directly connected with the swimming plates by eight ciliated grooves. True neniatocysts are but seldom found in the ectoderm of the Ctenophora, but they are represented by peculiar fixing or prehensile cells, the base of which is prolonged into a spirally coiled thread, while the projecting and convex free end (fig. 204) is of a glutinous consistence, and becomes readily attached to any object which touches it. The Ctenophora are hermaphrodite. Both kinds of generative products arise 011 the wall of the vessels of the swimming plates or of blind sac-like diverticula of the same. Some- times their production is localised (Cestum) ; sometimes they originate along the whole length of the canals, one side of the latter being beset with egg-follicles, the other with sperm-sacs (Beroe}. The germ layers, which arise from the ectoderm, are covered by entodermal epithelium, and are separated from one another by a projecting fold. Ova and spermatozoa pass into the gastro- vascular cavity, and are ejected through the apertures of the same. The fertilized ovum, which is enclosed by a loosely fitting membrane, consists, as in the case of many Medusce, of a thin outer layer of finely granular protoplasm (exoplasm) and a central food yolk (endoplasm), containing vacuoles. The segmentation, which is complete, leads to the formation of two, four, eight segmentation spheres, each of which, like the original ovum, consists of a central mass, surrounded by a thin layer of finely granular protoplasm. Ta FIG. 20-1 Smooth muscle fibres, prehensile cells (JcfJ, and tactile cells (b), from the lateral filaments of the tentacle of Euplo- camis stationis (after R. Hertwig). kf, Prolonga- tion of the contractile thread of a prehensile cell. CTENOPIIOKA. 71- the stage with four segments, the segments are so disposed that two perpendicular planes placed between them would correspond to the two principal planes of the fully developed animal. Each of the four spheres gives rise to one of the four quadrants of the' adult animal (Fol.) The whole mass of the finely granular exoplasm now becomes collected at the upper end of the segmentation spheres, where it is separated off and gives rise to eight new small spheres. These, by continued division, break up into a great number of small nucleated cells, which increase rapidly and grow round the eight large seg- mentation spheres or the cells produced from them. The young Ctenopliora sooner or later leave the egg membranes, and at this period differ more or less from the sexually mature animal in the simpler and usually more spherical form of the body, in the small size of the tentacles and swimming plates, and in the differ- ence in the relative size of the O3sophageal tube, infundibulum, and vascular canals. The differences are most striking in the lobed Ctenophora (with the exception of Cestum), the embryos of which have a great similarity to the young of Cydippe, and have no traces of bi-radial structure. It is only after a longer period of larval life that the completely mature form is attained by the unequal growth of the swimming plates and their canals, the out- growth of the tentacle-like processes, and the formation of two lobe-like projections round the mouth from those halves of the body which correspond to the longer rows of swimming plates. The phenomenon remarked by Chun is worthy of notice, that the young of Eucharis, while still in the larval stage, become sexually mature during the hot period of the year. The Ctenophora live in the warmer seas, and, under favourable conditions, often appear in great quantities at the surface. They feed on marine animals of various size, which they capture with their tentacles. Many, as the Beroidce, which do not possess tenta- cles, are compensated for this deficiency by the possession of an unusually large mouth (fig. 205), by means of which they are able FIG. 2-\ tne latter in the larger inter-radial genital plates. The Crinoidea, in addition to the dermal skeleton of the disc, possess a stalk, which i,s composed of pentagonal calcareous masses, arises from the dorsal side of the body, and becomes attached to firm sur- rounding objects. Amongst the appendages of the dermal armour, the numerous and variously shaped spines and the pedicellariae must be mentioned. FIG. 212. Third ambulacrum of a young Toxopnettstes droe- bachemis of 3 mm (after Lcven). Op, Ocu'ar plate ; P, primary plates and tentacle pores. The sutures of the primary plates are visible on the plates ; Sw, the tubercles to which the spines are articulated. FIG. 213.- riei)! P 272 ECniNODEBMATA. The former are moveably articulated to the knobbed tubercles on the shell of the Sea-urchin, and are raised and moved laterally by special muscles developed in a soft superficial dermal layer. The pedicellarise (fig. 213) are stalked, prehensile appendages furnished with two, three, or more rarely four jaws, which are continually snapping together. They are especially collected around the mouth of the Sea-urchin and on the dorsal surface of the Star-fish. Small transparent bodies, spkceridia, are found in the living Sea-urchins, and probably have the value of sense organs. In the Spatanyidce, knobbed and ciliated bristles (clavulce) are found upon the so-called A fascioles. The Echino- dermata are especially cha- racterised by the possession of the peculiar water - vascular system and of the distensible ambulacral feet connected with it (figs. 214, 215). This ambulacral vas- cular system consists of a circular vessel surrounding the oesophagus, and of five radial vessels projecting into the rays. These vessels have ciliated internal walls, and contain a watery fluid. Very frequently a number of vesicles. the Polian vesicles, are connected with the circular vessel, also a number of racemose appendages, the significance of which is no*, fully understood. In connection with the circular vessel there is also a stone canal (in rare cases more than one are present), which permits of communication between the sea water and the n*uia contents of the water vascular system. This canal, which is w FIG. 214. Diagram exhibiting the relations of the different systems of organs in an Echinus (after Huxley). O, mouth ; A, anus ; Z, teeth ; L, lips ; Aur, auriculas of the shell ; re, retractor and pro- tractor muscles of lantern ; Rg, circular ambulacral vessel ; Po, pyuan vesicle ; R, radial vessel of the same, with side branches to the ambulacral feet (Am) ; Sc, stone canal; M, madreporic plate ; St, spine ; Pe, pedicellarise. WA.TEE-YASCULAR SYSTEM. 273 called on account of the calcareous deposits in its walls, either hangs within the body cavity, whence it takes up fluid through the pores in its walls (Holothu- rians), or ends in a porous calca- reous plate, the madreporic plate, which is inserted in the external covering of the body, and through the pores of which the sea water percolates into the lumen of the canal system. The position of the madreporic plate varies con- siderably. In the ClypQastrideci it is at the apical pole ; in the Cidaridea and SpatangidQo, it is interradial, and falls in the an- terior right interradius near the apex ; in the Aster idea it is also interradial and dorsal ; in the Euryalidce and the Ophiuridce it lies on one of the five buccal plates. Some Echinoderms, e,g., species of Ophidiaster and Echi- naster echinites, possess several stone canals and madreporic plates. On the lateral branches of the five or more radial trunks are found the appendages known as the ambulacral feet (fig. 216). These are extensible tubes or sacs, w T hich pass through pores and openings in the dermal FIG. 215. Diagramatic representation of the water-vascular system of a Star-fish. EC, Circular vessel ; Ap, ampullae, or Poliau vesicles ; Sic, stone canal ; A.', madreporic plate ; P, ambulacral feet connected with the side twigs of the radial canals ; Ap', the ampullae of the same. skeleton and project on the surface of the body. They are capable of being swollen out, and are frequently pro- FIG. 21G.-Diagrammatic section through one of -j j -.1 suc kincr disc -it the arms of Ateracanthion (after W. T,fmrt. ' in & C their free extremity. Con- tractile ampullae are placed at the point of junction of the Lube feet with the side branch of the radial vessel ; they force the 18 the arms of Atteracanthion (after W. Lange). N, Nervous system; P, ambulacral fact ; A, calcareous portions of integument ; T, dermal branchia. 274 ECHINODEEMATA. fluid into the feet and cause them to swell, and hence to project. A number of feet so distended affix themselves by means of their sucking discs ; they then contract and draw the body slowly in the direction of the radii. The number and distribution of these appendages are subject to numerous modifications. Sometimes FIG. 217. feca-nrchin divided along the equatorial line (after Tiedemann). D, Digestive canal fixed to the shell by mesentery ; G, generative organs ; J, inter-radial plates. they are arranged in rows along the whole length of the meridian from the oral region to the periproct (Cidaridea and Pentacta). Sometimes they are scattered irregularly over the whole surface of the body, or only over the foot-like ventral surface, as in the Md FIG. 218. Longitudinal section through the arm and disc of Solaster endeca (somewhat altered after G. O. Bars). 0, mouth leading into the wide stomach ; A, anus ; L, radia- hepatic diverticulum of the stomach ; G, genital organs ; Md, madreporic plate ; , inter- radial diverticulum of the rectum ; Af, ambulacral feet Holothurians. In some cases they are confined to the oral surface ? as in all the Asteroidea. We are able therefore to distinguish an ambulacral and an antambulacral zone the first coincidi-ng with the oral and ventral surfaces, the latter with the dorsal surface. Never- theless the ambwlacral feet are variously constructed, and do not in AMBULACRAL APPENDAGES. ALIMENTARY CANAL. 275 Jf- Sc all cases serve for locomotion. In addition to the ambulacral feet, great tentacle-like tubes may be present as appendages of the water- vascular system ; the circle of tentacles round the mouth of Holo- thurians (fig. 209) is composed of such appendages. We also find leaf -like appendages arranged over four or five-leaved rosette- shaped areas, forming the ambulacral gills of the Spatanyidea, and Clypeastridea (figs. 207 and 208). The irregular Sea-urchins all possess in addition ambulacral feet upon the ventral surface. These are in the Cly- peastridea almost mi- croscopic in size ; they are very numerous, and are arranged in branched rows or are irregularly distributed over the surface. The Echinodermatct possess an alimentary canal distinct from the body cavity ; it can be divided into three parts oesopha- gus, stomach, and rectum. The anus is placed usually at the centre of the apical pole rarelvin an inter- FlG< 219 '~ HolotJlur ' a tu.lulca t opened longi udinaily (after J M. Edwards). O, Mouth in the midst of the tentacles Wl Cl radius on the ventral side. The intestine may, however, end blindly, as for example in all the Opkixsrida* and Euryalidce pecten, Ctenodiscus, and Luidia, which have no anus. (T) ; D, digestive canal ; Se, stone canal ; P, Poliaa vesicle ; Rg t circular vessel of the water- vascular system ; Ov, ovaries; Ag, ambulacral vessel; M, 'ungitudinal muscles; with four P airs of noglosius, with one pair of , branchial slits (after Al. branchial slits (after E. Met- l ar Collar. Poste- Agassiz). Letters as in figs, schnikoff), seen from the side. r i or to the collar 242 ' 243 ' So, external branchial open- ing ; p, peritoneal sac ; Vc, there is a longer portion of the body, the branchial region, which may be divided into a median distinctly ringed part (branchiae) and two lobed lateral portions usually filled with yellow glands. At the boundary, between the median portion and the two lateral lobes, there are on either side rows of openings which serve for the exit of the water from the branchial chamber. Then follows a third division of the body, the gastric region, upon the upper side of which there are four rows of yellow glands (generative glands). circular vessel ; O, mouth ; C, hevrt. 302 ENTEEOPNETJSTA. Between these, brownish-green prominences are visible (the hepatic appendages of the intestine), which, towards the posterior extremity where the yellow glands disappear, are larger and more closely aggregated. Finally there follows a distinctly ringed caudal region, at the hind end of which is the anus. The contractile proboscis serves not only as a siphon to maintain respiration, but also as a locomotory organ. It projects above the level of the mud in which the animal is buried, and is said to take in water by a terminal aperture (the existence of this opening has been recently disputed) [and to pass it out into the mouth through a pore at its base]. The mouth lies behind the anterior margin of the so-called collar, and leads into a buccal cavity, the walls of which contain a great number of unicellular mucous glands. The portion of the alimen- tary canal which follows the buccal cavity bears the branchial frame- work, and is divided into a dorsal and ventral part by two longitudinal folds, so that it almost presents in transverse section the appearance of a figure of 8. The intestine does not hang freely in the body cavity, but, except in the region of the tail, is fastened to the body wall by connective tissue; it is, however, always very closely attached in the two median lines. Beneath the dorsal and ventral median lines, where the two principal vascular trunks are visible through the skin, two grooves, beset with strong cilia, run along the whole length of the intestine. From these grooves secondary grooves are given oft', and as it were divide the whole surface of the intestine into islands. Some distance behind the branchial region, on the upper side of the intestine, the peculiar cell masses begin, which gradually assume the form of sac-like diverticula with ciliated internal walls. These " hepatic appendages " are either disposed in a simple row along each side (B. minutus Ivow.), or densely aggregated together (B. clavigerus DelleCh.) The branchial basket-work which is placed at the commencement of the alimentary canal projects on the anterior flattened part of the body in the form of a transversely ringed longitudinal fold, and con- tains a system of chitinous plates, which constitute its framework and are connected in a peculiar manner by transverse rods. The water taken in through the mouth passes through special openings in the wall of the anterior portion of the alimentary canal into the ciliated branchial spaces, to issue thence through the two rows of lateral pores on the dorsal surface of the branchial region. The vascular system consists of two median longitudinal trunks, B-1LA3TOGLOSSUS. TEEMES. 303 which give off numerous transverse branches to the walls of the intestine and body, and of two lateral trunks. The branchire receive their rich vascular supply entirely from the lower trunk. The upper trunk, in which the blood flows from behind forwards, divides at tho posterior end of the branchiae into four branches, of which the two lateral ones pass to the lateral portions of the anterior part of the body. Certain fibrous cords, running directly beneath the epidermis in the dorsal and ventral median lines and branching into a net-work of fine fibrillse, have lately been interpreted as nervous centres. These cords are described as being connected at the posterior end of the collar by a ring-like commissure. The generative organs are arranged in single rows in the branchial region, but posterior to this in double rows. During the breeding season they are extraordinarily developed, and the male and female can be easily, distinguished by the difference in their colour. Each ovum is contained in a capsule, which is provided with nuclei, but is otherwise homogeneous. The eggs are probably laid in strings like those of Nemertines. These animals live in fine sand. They saturate the sand in their immediate vicinity with mucous. They fill their alimentary canal with sand, and move themselves by means of their proboscis, which, alternately elongating and retracting, draws the body after it. Both the species named were found in the Gulf of Naples. A third northern species of Balanoylossus was discovered by Willenioes-Suhm, and described as B. Kupfferi. CHAPTER IX. YERMES. Bilateral animals with unsegmented or uniformly (Jiomonomsus) segmented body. There are no segmented lateral appendages. A dermal muscular system and paired excretory canals (water-vascular system) are present. SINCE the time of Cuvier, a number of groups of animals all characterised by the possession of an elongated laterally symmetrical body and by the absence of articulated limbs have been classed together as Vermes. This group includes such a variety of forms that attempts have already been made to break it up, and it will perhaps be necessary at some future time to separate the unseg- 304 VERMES. Ct mented from the segmented forms, under the respective heads of Vermes and Annelida. The form of the body, which is soft and adapted to live in damp media, is usually elongated, flat, or cylindrical, sometimes without rings, sometimes ringed, and sometimes divided into segments (meta- meres). In every case we can distinguish a ventral and a dorsal surface. It is on the first that the animal moves or attaches itself to foreign objects. The mouth is usually placed ventrally at the end of the body which is directed forward in locomotion. The con- trast between the flat, shorter form of body and the cylindrical and elongated seems, especially in the case of the non-segmentecl worms (Vermes s. str.), to be of importance, so that on this ground we can establish the classes of Platyhelminthes or flat worms, and of Nemathdminthes or round worms. The segmented worms (Annelida) possess a ventral chain of ganglia in addition to the brain, and a segmentation of the organs which corresponds more or less with the external segmentation. The portions of the body which are primitively alike and are* known as segments or metameres do not by any means always re- main homonomous. In the most highly developed segmented worms, the two anterior seg- ments unite to form a division of the body which foreshadows the head of the Arthropoda, and, like the latter, is pierced by the mouth, contains the brain, and bears the sense organs (fig. 245). In the succeeding metameres there are also frequently variations of form which disturb the homonomy. The skin of worms presents very different degrees of consistence, and covers a strongly developed muscular system. In the skin we can distinguish a layer of cells (hypodermis) or. at any rate, a nucleated layer of protoplasm which functions as a matrix, and a superficial homogeneous cuticular layer which is secreted by the first- named layer or matrix and in the lower worms is extremely thin and delicate. In the Nemathelminthes it is often laminated, and can FIG. 245.- Head and anterior segments of Eunice seen from the dorsal surface. T, Tentacles or antennas of the prgestomium ; Ct, tentacular cirri; C, cirri of the parapodia ; Sr, branchial appendages of the parapodia. INTEGUMENT. 805 even be separated into several layers. It is of considerable thickness in many Annelida (Clicetopoda), and may be perforated by pores. Cilia are found principally in the larval stages of Platylielmintlies and Annelida. Where there are no cilia, the superficial cuticular mem- brane, which may project in the form of tubercles or spines, consists of a substance allied to the chitin of the Arthropod skin, like which it may bear cuticular formations of many kinds, such as hairs, bristles, hooks, etc. In many Nemathelminthes, as well as in segmented worms, this firm cuticula gives rise to a kind of exo-skeleton, which opposes the contractions of the dermal muscular envelope. In the Chcetopoda among the Annelida, but also in the Rotifcra, the tough integument is divided into a number of sections lying one behind the other. These, like the segments of Arthropoda, are connected by soft portions of skin and moved by the dermal muscles, which are divided into corresponding groups. The cutaneous segments of the Rotifera are not true metameres, since there is no segmentation of the internal organs. Cutaneous glands are very widely distributed ; they are sometimes unicellular, sometimes poly cellular, and are sometimes situated directly ^beneath the epidermis, sometimes in the deeper tissues of the body. The tissue which lies beneath the hypodermis, and which we may call the cutis, contains in all cases longitudinal and in some cases also circular muscles, and so constitutes a muscular cutaneous envelope, the principal locomotory organ of worms. Taking into consideration the importance of this dermal muscular system in the locomotion of worms, we must attribute a certain systematic value to the special forms which it assumes, a value which, however, we must be careful not to exaggerate. The stratification and the direction of the fibres of this dermal muscular system is most complicated in the Platyhel- minthes and in the Hirudinea amongst the Chcetopoda, for here we find the circular and longitudinal muscles, which are embedded in a basis of connective tissue, crossed by muscle fibres, which run in a dorso-ventral direction (sometimes also by fibres running obliquely). To these may be added groups of muscular fibres, which serve to attach the internal organs to the integument. The suckers of the parasitic worms, the pits and the parapodia with their setae of (7Aeeopo<&,mustbe looked upon as special differentiations of the dermo- muscular envelope. These aids to locomotion are mostly developed upon the ventral surface. The suckers and their accessory hooks, etc., are situated either near the two ends or in the middle of the 20 306 YERMES. body ; the parapodia are distributed in pairs on the individual seg- ments along the whole length of the body, and belong to the dorsal as well as to the ventral surface, so that each segment bears a dorsal and a ventral pair of parapodia. The internal organization of Worms is extraordinarily various. In those flat and round worms which live in the chyme or the other organic juices of the higher animals, as, for instance, the Cestoda and the Acanthocephala, the whole of the digestive apparatus, including the mouth and anus, may be wanting ; the nutrition in such cases taking place by osmosis through the body- wall. When the alimen- tary canal is present, the mouth is usually situated ventrally in the anterior region of the body, while the anus is placed either terminally at the posterior end of the body, or near it on the dorsal surface. The alimentary canal is generally simple, and is only exceptionally divided into numerous portions corresponding to the special functions. A muscular pharynx can most often be distinguished, also a well developed stomach and a short rectum opening at the anus. The nervous system appears in its most simple form as an unpaired ganglion or, when the two parts of which it is composed are separated, as a pair of ganglia (fig, 76), which are placed near the anterior pole of the body above the oesophagus and genetically may be referred to the apical plate of Loven's duetopod larva. The nervous system has more rarely the form of a nerve ring surrounding the oesophagus and connected with groups of ganglion cells {Nemcitodci). The nerves given off from the supra-resophaffeal ganglion are distri- buted symmetrically forwards and laterally ; they supply the sense organs, and form two strong lateral nervous trunks, which run back- wards. In still higher types two larger ganglia appear, which are con- nected by an inferior commissure (Nemertinea). In the Annelids with degenerated metameres (Gepliyrwi) there is in addition to the supra- 03sophageal ganglion (the brain) a ventral nerve cord connected with the supra-oasophageal ganglion by an cesophageal ring. This nerve cord is in all other Annelids divided into a series of paired ganglia which, in most cases, correspond to the segmentation. The lateral nerve trunks approach each other in the middle line below the ali- mentary canal, and constitute, together with their ganglia, which are connected together by transverse commissures, a ventral chain of ganglia, which is connected with the brain by the circum-oasophageal commissures, and is continued to'the hind end of the bcdy, giving off in its course paired nerves to the right and left. The sense organs are represented by eyes, auditory apparatus, and SENSE ORGANS. TASCULAR SYSTEM. 307 Br tactile organs. The latter are joined to nervous expansions and special integumentary appendages (tactile hairs), and are present even in the parasitic Worms as papillae of the outer skin connected with nerves. Iri the free-living worms, these tactile organs fre- quently take the form of filiform, tentacle-like appendages on the head and segments (cirri). Auditory organs are not so generally present, and are represented by auditory vesicles (otocysts) either lying on the brain (some Turbellaria and Nemertinea), or on the cesophageal ring (certain branchiate Worms among the Annelida). The organs of sight are simple pigment spots in connection with nerves (eye-spots), and may be provided with refractive bodies. The ciliated pits of the Nemertinea have been regarded as organs of smell. The cup-shaped organs of the Ilirudinea and Gephyrea are also sense organs. A blood vascular! system is wanting inJ the Nemathelmintlies, the Rotifera, and the Platyhelminthes with the exception of the Nemertinea. In these cases, the nu- tritive fluid passes endosmotically into the body parenchyma or into the body cavi- ty, and penetrates the tissues as a clear chyle, sometimes containing cellular elements. In the Nemertinea a blood vascular system is present, as also in the Gephyrea and Annelida. In the latter it obtains the highest development, and may have the form of a completely closed vascular system provided with pulsating trunks. In most cases a dorsal contractile longitudinal trunk and a ventral vessel can be distinguished; the two being connected in each segment by arched transverse vessels, which are sometimes pulsatile. Where a vascular system is present, the blood does not always appear clear and colourless like the fluids of the body cavity, but sometimes has a yellow, greenish, or more frequently red colour, which is in some cases connected with the presence of blood corpuscles. The function of r^smration is_ usually performed by the general external surface of the body. XXrnong the Annelida, however, we FIG. 246. Section through a body segment of Eunice. Br t branchial appendages ; C, cirri ; P, parapoclia with tuft of bristles ; D, intestine ; -ZV, nervous system. 308 YEEMLS. find in the large marine Chcetopoda filiform or branched gills, which are usually appendages of the parapodia (fig. 246). A respiratory function may also be attributed to the tentacles of the Gephyrea. JPkfi pjRcrqtor.ft oraanty&re represented by the so-called water-vas- cular system, which consists of canals of different sizes, symmetrically arranged and filled with a watery fluid in which granules are sus- pended \ they communicate with the exterior through one or more openings. The canals begin either as small passages in the tissues of the body, or free funnel-shaped openings in the body cavity. In the last case, they may subserve other functions ; for example, they may conduct the generative products out of the body cavity. In the segmented Vermes they are paired, and are repeated in each segment as nephridia or segmented organs (fig. 70). A different arrangement is presented by the two lateral canals of the Nematoda, which lie in the so-called lateral lines or areas, and open by a common excretory pore in the region of the pharynx. In addition to sexual reproduction/ an \asexual multiplication by means of gemmation and fission (rarely by formation of germinal cells) is widely distributed, especially among the lower forms. This asexual reproduction is, however, frequently confined to the larvae, which differ from the sexually mature animal in form and habitation, and play the part of an asexual generation in the cycle of development. Almost all the Platyhelminthes and numerous Annelida are hermaphrodite ; the Nemathelminthes, the Gephyrea, and Rotifera, and also the branchiate Annelids are of separate sexes. Many Worms pass through a metamorphosis ; the larvae are charac- terised by the possession of a praeoral ring of cilia (Loven's larva), or of several rings of cilia. In the Cestoda and Trematoda, which possess in their embryonic stage the capability of asexual reproduc- tion, the metamorphosis assumes the form of a more or less com- plicated alternation of generations which is often characterised by the difference in the habitat of the two successive stages of development and by the alternation of a parasitic and free life. The vital activity of the Worms is in general of a low order, corresponding with their habitat. Many of them (Entozoa) live as parasites in the interior of the organs of other animals, some as ectoparasites on the external surface of the body, and feed on the juices of their hosts. Others live free in damp earth, or in mud others, and these are the most highly organized forms, inhabit fresh and salt water. TUEBELLAEIA. 309 CLASS I. PLATYHELMINTHES Vermes with aflat, more or less elongated body, with cerebral gan- glion. They are often provided with suckers and hooks, and are usually hermaphrodite. The series of forms included under this class are mostly Entozoa, or else live in the mud and beneath stones in the water. In their organization they occupy the lowest place among the worms. Their body is more or less flattened, and is either unsegmented or is divided by transverse constrictions into a number of successive divisions, which, although forming parts of one animal, yet have a strong tendency towards individualisation, and frequently attain to separa- tion and lead an independent life. These segments are products of growth in the direction of the long axis of the body, and stand in a special relation to reproduction. They are by no means to be con- sidered as necessarily indicating a high grade of organization, as does the segmentation of the Annelida. The alimentary canal may be altogether wanting (Cestoda), or, if present, may be without an anus (Trematoda, Turbellaria}J The nervous system is usually composed of a double ganglion above the oesophagus, giving off small nerves anteriorly and laterally, and two stems backwards. In many Platyhelminthes ^eye-spots occur, either with or without refractive bodies, and more rarely there is an auditory vesicle. Blood-vessels and organs of respiration are found only in the Nemertinea. The excretory (water vascular) system is everywhere developed. With the excep- tion of the Microstomidce and Nemertinea, hermaphroditism is the rule. The female generative glands consist of distinct yolk-glands and ovaries. The development very frequently takes place by a very complicated process of metamorphosis connected with alternation of generations. Order 1. Free living Platyhelminthes with oval or leaf-shaped body, with soft skin covered with cilia. They possess a mouth and aproctous * Duges, " Recherches sur Porganisation et les moeurs de Planaires," Ann. des Sc. Nat., Ser. I., Tom XV. A. S. Oerstedt, " Entwurf einer systcinatischen Eintheilung und speciellen Beschreibung der Plattwurmern," Copenhagen, 1844. De Quatrefages, " Memoire sur quelques Planariees marines," Ann. des Sc. Nat., 1845. M. Schultze, " Beitrage zur Naturgeschi elite der Turbellarien," Glreifswald, 1851. L. Graff, " Zur Kenntniss der Turbellarien," ZeiUchnft fur Wig*. Zool., Tom XXIV. L. Graff, "Neue Mittheilungen iiber Turbellarien." Zeitscli. f. n-iss. Zool., xxv., 1875. P. Hallez, " Contributions 4 1'histoire uatnrelle des Turbellarics," Lille, 1879. 310 PIATYHELMINTHES. alimentary canal. Hooks and suckers are absent. A cerebral ganglion is present. The Turbellaria usually possess an oval flattened body, and reach only a small size. The uniform ciliation of the body is connected with their existence in fresh and salt water, beneath stones, in mud, and even in damp earth. Only in exceptional cases do we meet with apparatuses for adhering, viz., small hooks and suckers. The skin consists of a single layer of cells, or of a finely granular layer containing nuclei, which is sup- ported by a stratified basal membrane, and covered externally by a special homogeneous membrane bearing cilia and comparable to a cuticula. Peculiar integumentary structures, which have the form of rods or spindles, and, like the nematocysts in Co2lenterata, take their origin in cells, are not unfre- quently present. Various pigments are also often found embedded in the epi- dermis, and of these pigments the green- coloured vesicles, in Vortex viridis for example, which are identical with chlo- rophyl corpuscles, are specially worthy of remark. Pear-shaped mucous glands are also present. Beneath the conspicu- ous basement membrane which supports the epidermis lies the derniis. It con- tains the strongly developed derma] muscular system embedded in a connec- tive tissue layer formed of round, often branched cells. A body cavity between FIG. 247. Alimentary canal and ner- , , , , ,, , ,, ,. , vous system of Meotomum Ehren. tne body wall and the alimentary canal, berffii (after Graff). &, the two { s as a ru i e absent ; it may, however, cerebral ganglia with two eye spots; st, the two lateral nerve in many cases be recognised as a system trunks ;I> alimentary canal mth of lacume or asa continuous cavity mouth and pharynx. surrounding the alimentary canal. The nervou re^consists of two ganglia connected by a com- missure, and giving off nerve fibres in various directions ; of these, two especially large lateral trunks run backwards, one on either side (fig. 247). The latter are connected at regular intervals by delicate transverse trunks. In a number of dendroccelous Turbellarians a TUEBELLARIA. 311 diverticulum of the stomach runs forward above the transverse commissure in a groove between the two cerebral lobes (Leptoplana). In some genera of Planarians, a ring-shaped double commissure has been shown to exist in the brain (Polycelis), and ganglion-like swellings, from which nerves are given off, have been observed on the lateral nerve- trunks (Sphyrocephalus, Polycladus). With regard to sense organs, eye spots are tolerably widely distri- buted among the Turbellaria. They either lie in pairs upon the cerebral ganglia or are connected with short nerves given off from the latter. More frequently two larger eyes with refractive struc- tues are developed. Otocysts are but rarely present, e.g., in Monocelis among the Rhabdoccela a single one is present lying upon the cerebral ganglion. The integument is without doubt en- dowed with a highly developed tactile sense ; the large hairs and stiff bristles which project between the cilia may possibly be of importance in this relation. Lateral ciliated pits, which may also be explained as sense organs, are in rare cases present at the anterior end of the body (compare the Nemertinea). Mouth and digestive apparatus are never wanting but the former is frequently removed from the ventral surface of the anterior end of the body to the middle or, indeed, even to the posterior region. According to Metschnikoff and Ulianin, a stomach may in some cases be absent (Convoluta, Schizo- prora), and be replaced, as in Infusoria, by a soft internal parenchyma. The mouth leads into a muscular pharynx, which can usually be protruded after the manner of a proboscis. The alimentary canal, of which the internal wall is frequently ciliated, is either forked and then simple or branched (Dendrocoela), or rod-shaped (Ehabdo- ccela). An anus is never present. A peculiar tube capable of being evaginated as a proboscis, and without connection with the pharynx is sometimes also present (Prostomum). The excretory (water-vascular) system consists of two transparent lateral trunks and innumerable side branches, which begin with closed ciliated funnels, and are furnished with vibratile cilia, which FlG. 24S. M'crogfo- mum lineare, after Graff. A chain produced by fis- sion ; O,-0', mouth openings. 312 FLATYHELMINTHES . project here and there freely into the vessels. As a rule, several openings occur on the main trunk of this excretory apparatus. Reproduction may take place asexually by transverse fission, e.g., Derostomea (Catenida) and Microstomea (fig. 248). With the exception of the Microstomea, the Turbellaria are hermaphrodite; but steps intermediate between the hermaphrodite and the dioecious condition seem by no means to be wanting, for, according to MetschnikofF, in Prostomum lineare the male generative organs are sometimes developed, while the female remain rudimentary ; and sometimes, on the other hand, the reverse holds. In Acmostomum dioecum also the sexes are separate. In the her- maphrodite forms the male sexual organs consist of testes, which mostly lie as paired tubes at the sides of the body, also of yesi- cula3 seminales, and of a protru- sible copulatory organ beset with hooks. The female organs con- sist of ovaries, yolk glands (vitellarium), a receptaculum seminis, a vagina, and a uterus (fig. 249). The male copula- tory organ and the vagina open as a rule by a common orifice upon the ventral surface. Some- times, as in the Rhabdoccele genus Macrostomum, the vitella- rium (yolk gland) nnd ovary are united; the ova being produced at the upper blind end of the ovary, and the yolk at the lower end of the same gland. In the marine Dendroccela, on the other hand, the vitellarium is generally absent. After fertilization, a hard, usually reddish-brown shell begins to be formed round the ovum. In such cases, the hard-shelled eggs are laid ; but among the Rhabdoccela, in Schizostomum and certain Mesostomea (M. Ehren- bergii), transparent eggs furnished with thin, colourless capsules, and undergoing development in the body of the parent, are often produced. According to Schneider, the production of these thin* 249. Generative apparatus of Mesotto- mum Ehrenbergil (combined from Graff and Schneider). S, Pharynx ; Go, sexual openings ; Ov, ovary ; Ut, uterus, with winter eggs ; Do, yolk gland ; Dg, duct of yolk gland ; T, testis ;-. Vd, vas deferens ; P, penis ; jR#, receptaculum seminis. TURBELLARIA. 313 shelled or summer eggs invariably precedes that of the hard-shelled or winter eggs, and the summer eggs are normally self-fertilized. In rare cases the hermaphrodite generative organs present a segmentation recalling that of the Cestoda (Alaurina composita). The freshwater Turbellaria, as well as many of the marine forms, undergo a simple direct development, and in the young state are often difficult to distinguish from Infusoria. Other marine Dendrocoela undergo a metamorphosis, the larvae being characterised by the possession of finger-shaped ciliated lobes (fig. 251). (1) Sub-order : Rhabdoccela. The body is round and more or less flat. The intestine is cylindrical, and there is usually a protrusible pharynx. They are usually hermaphrodite. The Rhabdoccelous Turbellarians are the smallest and most simply organised forms. The intestine is cylindrical and elongated, and is sometimes provided with lateral diverticula. The position of the mouth varies exceedingly, and has been employed as a principal characteristic for distinguishing the various families. Sometimes salivary glands are present, opening into the pharynx. According to Ulianin's discovery, which has been several times confirmed, the alimentary canal may be wanting in many forms, and be replaced by a central cavity, filled with a substance containing numerous vacuoles and rich in oil globules (Convoluta, Schizoprora, Nadina). In those Rhabdocoela which possess an alimentary canal, interstices and spaces in the connective tissue parenchyma are often present : these must be related to a body cavity. In some cases (in Prostomum) the body cavity may be recognised as a continuous space filled with fluid and surrounding the alimentary canal. The Rluibdoccda live on the juices of small worms and of the larvae of Entomostraca and Insecta, which they envelop with a cutaneous secretion containing small rods, and afterwards suck. They are mostly inhabitants of fresh water, and only a few of them are to be met with in the sea or upon the land (Geocentrophora sphyrocephcda). Fam. Opisthomidae. The mouth is placed at the posterior end of the body and leads into a . tubular pharynx, which can be protruded like a proboscis. Monocelis agilu M. Sch., Opisthomum pallid-urn O. S. Fam. Derostomidae. Mouth placed slightly behind the anterior margin ; pharynx barrel-shaped. Derostomum Scltmidtiamtm M. Sch., Vortex viridis, M. Sch., Catcnnla lemncc Dnir. Fam. Mesostomidae. Mouth placed nearly in the middle of the body, pharynx ringlike, cylindrical or resembling a sucker. Jfcsostomum Ehreribcryii Oerst., with two eyes. Fam. Convolutidae. (Acoela). Without alimentary canal. The ovaries and 314 PLAT YHELMIN TILES . yolk glands are not separate. Convoluta Oerst. C. yaradoxa Oerst., North Sea, Baltic. ScMzoprora O. S. Fam. Prostomidae. The mouth, which is situate on the ventral surface, leads into a muscular pharynx. At the anterior end there is a protrusible tactile proboscis furnished with papillre. Prortomum Oerst. (Gyrator Ehrbg.), P. lineare Oerst. With pointed penial spine at the posterior end, imperfectly hermaphrodite, living principally in fresh water. Pr. lielgolandicum, Kef., completely hermaphrodite. Fam. Microstomidae. Ithaldoccela with separate sexes. The small but very extensible mouth lies near the anterior end of the body. There are laterally placed ciliated pits near the anterior end of the body. Formation of metameres and transverse fission fre- quently occur. Microsto- iu um lineare Oerst. (fig. 248). f\ (2) 'Sub-order: Den- drocoela. The body is broad and flat, and the lateral margins are often plicated. There are ten- tacle-like processes at the anterior end. There is a branched alimentary canal and a muscular pharynx which is usu- ally protrusible. They are, as a rule, herma- phrodite. The Dendroccda are mostly marine, but also live in fresh water and on land. In their ex- ternal appearance they resemble the Trema- todes, and the branching of their straight or forked intestine is a character common to the larger species of the latter. Compared with the Rhabdoccda, they are distinguished by the greater develop- ment of their bi-lobed cerebral ganglion, as well as by the greater number of their eyes (fig. 250). The rows of papillae, or the tentacle-like' processes at the anterior end of the body have FIG. 250. Anatomy of Poll/cells pallida (after Quatre- fages). G, Cerebral ganglion with the nerves given off from it ; O, mouth ; D, branches of intestine ; Ov> ova; Od, oviduct; F, vagina; W.Goe, female gene- rative opening; T, testes; ZI.Goe, male generative opening. T UEEELLABIA DENDEOCCELA. 315 FIG. 251. Larva of Eurylepta auri- culata, after Hallez. probably the function of tactile organs. The mouth usually lies in the middle of the body, and leads into a wide and protrusible pharynx. The skin is often provided with glands, the secretion of which in certain land Planaria (Bipalium, Rhynchodesmus) hardens to a fibrous web. They are almost always hermaphrodite. The fresh- water forms possess a common generative opening, while in the marine forms the generative openings are usu- ally separate (fig. 250). In the latter case a separate vitellarium is absent. In some marine forms development takes place with metamorphosis, as is shown by the larva discovered by J. Miiller, which possessed six provisional finger-like ciliated lobes (fig. 251). In the fresh- water Planarians develop- ment is direct. The cocoon, when laid, contains four to six small eggs. At the close of segmentation there is developed a layer of cells, which is said to split into two layers, an upper or animal layer, from which are derived the body wall and muscular system, and a lower or vegetative, from which the alimentary canal is formed. The marine Dendrocoda fre- quently deposit their eggs in the form of broad bands. 1. Monogonopora Stimps. Den- droccda with single sexual opening. The land and fresh-water Planaria be- long to this group. Fam. Planariadse. The body is of a long, oval, flattened shape, and is often provided with lobed processes, more rarely with ten- tacles, and, as a rule, with two eyes, which are provided with lenses. Planaria 0. Fr. Miiller, two eyes, no tentacles. PI. torva, M. Sch. (divided by 0. Schmidt into higutris, polycliroa, and torva) (fig. 252). PL dioiea Clap., with separate sexes. Dc-ndrocoelum Oerst. Distinguished by the possession of lobed processes on the head, also by the presence of a copulatory organ placed in a special sheath. D. lacteum Oerst., Poly cells nitjra, brunnea 0. Fr. Mull. Fam. Geoplanidae.* Land Planarians. They are characterised by their * Besides M. Schultze, Stimpson, Metsclmikoff, Grube, etc., compare II. N. a FIG. 252. Planaria polychroa (a), luffubris (b), torva (c), about twice the natural size (after O. Schmidt). 316 PLATYHELMIXTHES. elongated and flattened body, which is provided with a foot-like ventral surface. Geoplana lapidicola Stimps., IthyncJiodesmus terrestris Gm. {Fasciola terrestri*, 0. Fr. Miiller), Europe. Geodesmus biluieatus, Metschn., with thread cells in the integument, found in potter's earth. 2. Digonopora. Dendrocoda with double sexual opening. Almost all are marine. The proboscis is often folded and lies within a special pouch. When protruded, it spreads out like a lobe. Fam. Stylochidae. The body is flat and rather thick, and is provided with two short tentacles on the head. There are usually numerous eyes on the tentacles or on the head. The genital openings are posterior. Stylockus macu- latus Quatr. Fam. Leptoplanidae. Body flat and broad, usually very delicate. Cephalic region not distinct, without tentacles. The eyes are more or less numerous. The mouth is usually placed in front of the middle of the body. The genital openings lie behind it. Leptoplana tremellaris O, Fr. Mull., Mediterranean. Fain. Euryleptidae. Body broad, and either smooth or furnished with papillae. There arc two tentacle-like lobes on the anterior region of the head. The mouth is placed in front of the middle of the body. Numerous eyes are disposed near the anterior margin. Marine. Thysanozoon Diesingii Gr. Mediterranean. Eurylepta aurlculata 0. Fr. Mailer, North Sea. Order 2. TREMATODA.* [ Parasitic Platyhelminthes with unsegmented, usually leaf-sliaped, rarely cylindrical body. TJiey possess a mouth and ventrally placed organ for attachment : the intestine is forked and ivithout an anus. The Trematodes are with great probability to be derived from the Turbellaria, with which group, both in form and organization, they show a close relationship. In connection with their parasitic mode of life they develop special organs for adhering, such as suckers and hooks. Cilia are present only in larval life. The mouth is invariably placed at the anterior end of the body, usually in the middle of a small sucker (fig. 253). It leads into a muscular pharynx with a more or less elongated oesophagus, which is prolonged into a forked intestine ending blindly. Moseley, " Notes on the Structure of Several Forms of Land Planarians," etc. Jovrnal of jllicr. Science, vol. xvii. * A. v. Nordmann. " Mikrographische Beitrage zur Kcnntniss der wirbelloscn Thiere," Berlin, 1832. G. G. Cams, " Beobachtung iibcr Leucochloridium paradoxum. etc.," Nov. Act., vol. xvii., 18:55. Wagener, " Ueber Gyrodactylus elegans." Mullens Archiv., I860. Van Beneden, " Memoire sur les vers intes- tinaux," Paris, 1801. E. Zellcr, " Untcrsuchungen tiber die Entwickelung und den Bau von Polystoma integerrimum, Zeitsclir. f. n-ixs. Zool., vol. xxii., 1872. E. Zeller, "Untcrsuchungen iibcr die Entwickelung .von Diplozoum paradox- um," Hid., vol. xxiii., 1873. E. Zeller, " Ueber Leucochloridium paradoxum und die wcitere Entwickelung seiner Distomumbrut," Hid.. Tom XXIV. E. Zeller, " Weitercr Beitragzur Kenntniss der Poly stomeen," Hid., xxvii., 187G. Compare also the works of G. Wagener and De Filippi. TEEMATODA. 317 The excretory apparatus consists of two large lateral trunks and a network of fine vessels permeating the tissues and beginning with small ciliated lobules. The two large trunks open into a common contractile vesicle, which opens to the exterior at the posterior end of the body (fig. 253, Ep). The excretory system contains a watery fluid with granular concretions. This fluid is probably an excretory product, corresponding to the urine of higher animals. Tli PJ T) f.rvnnff Kflxtqm consists of a double ganglion lying above the oesophagus, and from it several small nerves and two posteriorly directed lateral trunks are said to be given off. Eye spots with refractive bodies are sometimes present in the larvae during their migrations. Locomotion is effected by the dermal muscular system and the organs of attachment, viz., the suckers and hooks, which present numerous modifications in number, form, and arrangement. In general, the size and development of these organs are related to the endo- parasitic or ecto-parasitic mode of life. In the endo-parasitic Trema- todes they are less developed, and usually consist of the oral sucker and a second larger sucker on the ven- tral surface, either near the mouth, as in Distomum, or at the opposite pole of the body (Amphistomum). This large sucker may, however, be absent (Monostomum). The ecto- parasitic Polystomea, on the other hand, are distinguished by a much more powerful armature, for besides two smaller suckers at the sides of the mouth, they possess one or more large suckers at the posterior end of the body (fig. 258), which, moreover, may be supported by rods of chitin. There are often in addition chitinous hooks, and very frequently two larger hooks among the posterior suckers in the middle line (//). The Trematoda are Costly hermaphrodite. As a rule, the male and female generative openings lie side by side, or one behind the other, not far from the middle line of the ventral surface, near the anterior end of the body (fig. 254). The male opening leads into a sac, the FIG. 253. Young Dixtomum (after La Valette). Ex, trunk of the excretory (water vascular) system ; 'Ep, excre- tory pore; O, mouth, with sucker; S, sucker in the middle of the ventral surface; P, pharynx; D, forked in- testine. 318 PULTYHELMINTIIES. JD Dr. Ov cirrus sac, which encloses the protrusible terminal part (cirrus) of the vas deferens. The vas deferens soon divides into two, which lead back to the two large simple or multilobed testes. The supposed third vas deferens, which, according to v. Siebold, runs from one testis to the female sexual apparatus, so as to permit of direct ferti- lization without copulation, has been recognized as a vagina opening to the exterior on the dorsal surface (canal of Laurer). The female organs consist of a convo- luted uterus and of the glands concerned in the preparation of the egg, viz., an ovary and two yolk glands. There is sometimes in ad- dition a special shell gland. The true ovary which produces the pri- mary ova is a round body, and is usually placed in front of the testes. The yolk glands which secrete the yolk are much ramified tubular glands, and fill the sides of the body (fig. 254). The yolk particles come in contact with the primary ova in the first portion of the uterus, and surround them in greater or less quantities. Subsequently each ovum, with its investment of yolk, is surrounded by a strong shell. The ova in their passage along the uterus become packed together, often in great numbers, and undergo the stages of embryonic development in the body of the parent. Most Trematodes lay their eggs ; only a few are viviparous. The just-hatched young either possess (in most Polystomea) the form and organization of the parent; or they present the phenomenon of a complicated alternation of generations (heterogamy) connected with a metamorphosis (Distomea). In the first case, the large eggs become attached in the place where the mother lives; in the last case, the relatively small eggs are deposited in a damp place, usually in the water. After the completion of the segmentation and the em- FiG. 254. Disiomum hcpaticum (after Sommer). O, Mouth ; D, limb of in- testine ; S, sucker; T, testes; Do, vitellarium ; Oo (uterus), oviduct ; Dr, accessory glands. 1.HJSMATODA. 319 bryonic development-, the contractile, usually ciliated embryos* (fig. 255, a), which already possess the first rudiments of an excretory system and more rarely a sucker with a mouth and alimentary canal, leave the egg and wander about independently in search of a new host. The latter is, as a rule, a snail, into the interior of which they pene- trate and there become transformed into simple or branched Sporocysts (without mouth and alimentary canal, fig. 255, c), or into Redice (with mouth and alimentary canal, fig. 255, d). These give rise, by means of the so-called germs [cells lying in the body cavity of the Ov- FIG. 255. Developmental history of Distomum '(partly after E. Leuckart). a, free swimming ciliated embryo of the liver fluke, b, the same in a state of contraction with rudimentary alimentary canal (D) and cell mass (Ov) (rudiments of the genital glands). Ex, ciliated apparatus of the rudimentary excretory system, c, sporocyst developed from a Distomum embryo, filled with Cercarire (C) ; .27. Boring spine of a Cercaria. d Redia with pharynx, (Ph), and alimentary canal (D) ; O, mouth ; Ex, Excretory organ ; C, Cercaria inside Redia. e, Free Cercaria ; S, sucker ; D, alimentary canal. sporocyst or redia], which probably~Teacrespond to the germinal cells (primitive ova) of the rudimentary ovary, to the generation of the * As K. Leuckart has rightly observed, the Dicycmidev, which were regarded as Mesozoa by Ed. v. Beneden, as well as the Orthoncctidat, which have recently been especially investigated by Giard and E. Metschnikoff, and which in the reproductive stage do not rise above a form corresponding to the embryos of Trernatodes, recall these Distomum larvae. 320 PLA.TYIIELMINTHES. tailed Cercarice, or to another generation of Sporocysts or Redice* which then produce the Cercarise. The Cercarice are nothing else than Distomum larvse, which eventually reach (often only after two migrations, an active and a passive one) the final host, where they become sexually mature. They are furnished with an exceedingly motile caudal appendage, frequently with a buccal spine, and occasionally with eyes, and they present in the rest of their organization great resemblances to the adult Distomum, excepting that the generative organs are not developed. In this form they leave independently the body of the Redia or Sporocyst and of the host of the latter, and move about in the water, partly creeping and partly swimming. Here they soon find a new host (Snail, Worm, Insect larva, Crustacean, Fish, Batrachian), into which they penetrate, aided by the powerful vibrations of their tail ; they then lose the latter and encyst. The Cercarice from the interior of the snail thus become distributed amongst a number of hosts, and each of them gives rise to an encysted young Distomum without generative organs. This young Distomum mi- grates passively with the flesh of its host into the stomach of another animal, and thence, freed from its cyst, into the organ (intestine, bladder ^-)> in wnich ^ becomes sexually mature. There are, then, as a rule, three different hosts in the organs of which the different developmental stages (Redia or Sporocyst, encysted form, sexually mature animal) of the Distomum bury themselves. The transitions from one host to another are effected partly by inde- pendent migration (embryos, Cercarise), partly by passive migration (encysted young Distomuni). Modifications of the ordinary course of development may, however, take place ; these may be either complications or simplifications. . The embryo at hatching may contain a single Redia (as in Monostomum * In Cercaria cystoplwra from Planorbis marr/inatus ; according to G. Wagoner, the primaiy asexual individual is a Spc.rocyst, the secondary a Redia. FIG. 256. o, Embryo of subclavatus (after G. Wagener). D, Alimentary canal ; Ex, excre- tory system. I, Embryo of Mo- nostomum mutabile (after v. Sie- bold). P, Pigment spots ; J2, redia in the interior of the embryo. TREHATODA. 321 flavum find mutabile), which it carries about until it enters the first host (fig. 256, b). In other cases the course of development is sim- plified by the omission of the second intermediate host, viz., that which contains the encysted immature Distomum (Cercaria macro- cerca of Distomum cygnoides, also Leucochloridium in the tentacles of Helix succinea). (1) Sub-order : Distomea. Trematodes with at most two suckers, without hooks. They develop with a complicated alternation of generations. The asexual individuals and the larvse live principally in Mollusca, the sexually mature animals in the alimentary canal of Vertebrates. The sexes are completely separated in Distomum hcematolium (from the veins of man); individuals of the two sexes being united in pairs (fig. 257). Dimorphic forms are found in certain species of the genera Monostomum and Distomum in connection with the division of labour of the sexual functions ; one individual develops only male sexual organs, and the other only female, the former producing spermatozoa and the latter ova. The rudiment of the functionless generative gland undergoes in these cases a more or less complete degeneration. Such Distomea are morphologically hermaphrodite, but practically of separate sexes. The complete biology and developmental history is unfortunately only satisfactorily known for a few species which can be fol- lowed through all the stages of development. FiO. 257Dittomum haemato- Hum. Male and female, the latter being in the canalis gynaecophorus of the former. 8, sucker. Fam. Monostomidae. Of an oval, elongated, more or less rounded form, with only one sucker, which surrounds the mouth. Monostomum Zeder. Sucker surrounding the mouth ; pharynx powerful. Sexual openings but slightly removed from the anterior end. M. mutabile Zeder, in the body cavity and in the orbit of various water-birds ; viviparous. M. flavum Mehlis, in water-birds, develops from Cercaria ephemera of Planorbis. M. lentis v. Nordm., the young form without generative organs is found in the lens of the human eye. M. bipartitum Wedl., living in pairs enclosed in a common cyst, the one indi- vidual surrounded by the lobed posterior end of the other ; branchiae of Tunny- fish. Fam. Distomidse. Body lancet-shaped, frequently spread out. more rarely elon- gated and rounded with a large median sucker ; in front of which lie the genital openings, usually close together. 21 322 PLATTHELMINTHES. Distomnm. Median sticker approached to the anterior one. If. licpaticum L, Liver fluke. With conical anterior end. and numerous spine-like prominences on the surface of the broad leaf-shaped body, which is about 30 mm. long. Lives in the bile-clu^ts of sheep and other domestic animals, and produces the liver disease of the sheep. It is occasionally found in Man, and bores its way into the portal vein and into the system of the vena cava. The elongated embryo only develops after the egg has remained a long time in water ; it has a continuous ciliated envelope with an X- shaped eye-spot. E. Leuckart's re- searches have rendered it probable that the development is passed through in the young Limnceits pereyer and truncatulus, that here the embryo becomes a Sporocyst. and that this produces EC dice, in which it is supposed that tailless Distom-ca arise. [The life-history of the liver-fluke has been completely worked out by A. P. Thomas (Quart. Journal of Mic-roscoplcal Set. 1883, pp. 99133). He has shown that the ciliated embryo passes into Limnceits tmncatuliis, and there gives rise to a sporocyst which produces rediae. The redice produce more re dice or Ccrcarice. The Cercaritf. which are provided with long tails, leave the host (Limncens trimcatttlvs), swim about for a short time in the water, and encyst on foreign objects, e.g. blades of grass. In this condition they are eaten by the sheep.] D. crassum Busk., in the alimentary canal of the Chinese, one to two inches in length, and half-inch broad, without spinous prominences, with a simple forked intestine. D. lanceolatum Mehlis. Body elongated into the form of a lancet, 8 9 m.m. long, lives in the same place with D. liepaticum. The embryo develops at first in water, is pear-shaped, and only ciliated on the anterior half of the body, bears a styliform spine on the projecting apex. D. oplithalmoMum Dies. A doubtful species of which'only four specimens have been observed in tho lens capsule of a nine-months' child. D. lieteropliycs Bllh. v Sieb. 1 1'5 mm. long, in the alimentary canal of man in Egypt. D. goliath van Ben., 80 mm. long, in Pterobalesna. Numerous species live in the alimentary canal, lungs, and bladder of the frog. Distomun filicolle Eud. (D. Olieni Roll) in pairs in the mucous sacs in the branchial cavity of Brama Raji. The one individual is cylindrical and narrow, and produces spermatozoa ; the other is swollen in the middle and posterior region of the body, and is filled with eggs. The dissimilar development of the two individuals is probably due to the fact that copulation only leads to the fertilization of one of them, which alone is able to perform the female sexual functions. I), licematobium. Bilh. v. Sieb. (Gynwcopliorus Dies) (fig. 257). Body elongated ; sexes separate. The female is slender and cylindrical. The male has powerful suckers, and the lateral margins of the body arc bent round o as to form a groove, the canalis gynascophorus, for the reception of the female. They live in pairs in the portal vein, and in the veins of the intestine and of the bladder of man in Abyssinia. According to Cobbold, the embryos are ciliated, and possess a tolerably well dereloped excretory system. By the deposition of masses of their eggs in the vessels of the mucous membrane of the ureter, bladder, a ad great intestine, inflammation is set up, which may cause hrcmaturia. (2) Sub-order: Polystomea. Trematodes with two small lateral suckers at the anterior end, and one or more posterior suckers, to which two large cliitinous hooks are often added. In exceptional TKEMATODA. 323 cases (Tristomum coccineum) transverse rows of bristles are found. Paired eyes are frequently present. In some species the elongated body presents a kind of external segmentation. They are for the most part ectoparasitic, to a certain extent like the ffirudinea, and they develop directly without alternation of generations from eggs which are usually hatched in the locality inhabited by the mother. Sometimes the development is a metamorphosis (Polystomum), and the young larva? live in another place. The development of Polystomum integerri- mum from the bladder of the frog is the best known, owing to the researches of E. Zeller (figs. 258, 259). The production of eggs begins in the spring, when the frog awakes from hibernation and proceeds to pair. It lasts from three to four weeks. It is easy then to observe the Polysto- mea in the process of reciprocal copulation. When the FIG. 259. Egg with embryo{),and hatched larva (b) of Polystomum integerrimum ; Dk, operculum (after E. Zeller). eggs being the forces are laid, the anterior end of the body with the genital FlG - 2o8 - ..,/;,. gerrimum (after E. Zeller). opening through the mouth of the bladder o, mouth; GO, genital nearly as far as the anus. The development P enin g; A intestine; . ., ' , . 7F copulatory opening or the embryo takes place in water and occu- (lateral pads) ; Zty, yolk pies a period of many weeks, so that the young larva? are only hatched when the tad- poles have already acquired internal gills. GyrodactyluSj and possess four eyes, a pharynx and alimentary canal, as well as a posterior disc (for attachment), which is surrounded by sixteen hooks. They possess five transverse rows of cilia ; three are ventral and anterior, two dorsal and posterior. There is also a ciliated cell upon the anterior extremity. The larva? now migrate The larvae resemble 324 PLATYHELMrNTIIES. into the branchial cavity of the tadpole, lose their cilia, and are transformed into young Pnlystomea by the formation of the two median hooks and of the three pairs of suckers upon the posterior disc. The young Polystomum, eight weeks after the migration into the branchial cavity, at the time when the latter begins to abort, passes through the stomach and intestine into the bladder, and there FIG. 260. Young Diplozoon (after E. Zeller). c, Two young Dlporpa beginning to attach themselves together, b, After both individuals have attached themselves. O, mouth ; H, fixing apparatus ; Z, papilla ; G, sucker. only becomes sexually mature after three and more years. In some exceptional cases, and always when the larva has passed on to the gills of a very young tadpole, it becomes sexually mature in the branchial cavity of the latter. The forms then remain very small, are without the copulatory canals and uterus, and die after the production of a single egg, without ever to the bladder - Fam. Polystomidae. With seve- ral posterior suckers, which are usually paired and arranged in two lateral rows, and are rein- forced by an armature of hooks. The genital openings are fre- FIG. 261 .-Egg (a) and larva (6) of Diplozoon (after quently surrounded by hooks. E. Zeller). Many species have a length of only a few lines. Polystomum Zed., with .four eyes; with no lateral suckers at the anterior end, but with oral sucker; with six suckers, two large median hooks and sixteen small, hooks at the posterior end. P. intcyerrimnm Eud., in the bladder of Rana temporaria. P. ocellatum in the pharyngeal cavity o Emys. In the formation of the testis and the absence of the uterus it resembles the adult form of P. integerrimum from the branchial cavity of the tadpole. Octobotlirium lanceolatum Duj. Onckocotyle appcndiculata Kuhn, on the gills of Elasmobranchs. Diplozoon v. Nordm. The animal is double, two individuals being fused to TEEMATODA. 325 form an X-shaped double animal, the posterior ends of which are provided with two large suckers divided into four pits. In the young state they live solitarily as Diporpa ; they then possess a ventral sucker and a dorsal papilla (260 a, G and ^). In the double animals the formation of ova is confined to a definite period of the year, usually the spring. The eggs are laid singly after the forma- tion of the thread by which they are attached, and two weeks later the embryo (fig. 261, ), which only differs from Diporpa in the possession of two eye- spots and a ciliated apparatus upon the sides and on the posterior extremity of the body, is hatched. When an oppor- tunity of fixing itself on the gills of a fresh -water fish occurs, the young animal loses its cilia and becomes a Diporpa, which possesses, besides the characteristic apparatus for attachment, the alimentary canal, and the two excretory canals with their openings at the anterior part of the body (at the level of the pharynx), and sucks the branchial blood. The junction of the two Diporpa soon follows ; and this does not take place, as was formerly believed, by the fusion of the two ventral suckers, but in such a manner that the ventral sucker of each animal affixes itself to the dorsal papilla of the other, and fuses with it (fig. 260, ). D.paradoxum, v. Xordm., on the gills of many fresh- water fish. Fam. Gyrodactylidae. Very small Tre- matodes with large terminal caudal disc and powerful hooks. They are viviparous, producing a single young one (first gene- ration) at a time, within which, while still in the body of the parent, another young one (second generation) may be present, and in this yet another (third generation). V. Siebold believed that he had observed a young animal developing from a germ cell of Gyrodactylus, and that this became pregnant during its development. He regarded the Gyro- dactylus as an asexual form, since he failed to find organs for the production of sperm. G. Wagener, however, showed that the reproduction is sexual, and conceived the idea that the germs from which the second and third generations are formed are derived from the remains of the fertilized ovum from which the first generation is formed. MetschnikofE, too, is of the opinion that the individuals of the first and second generations are formed at the same time from a common mass of similar embryonic cells. Gyrodactylus v. Nordm., G. elcgans v. Nordm., from the gills of Cyprinoids and fresh-water fish. FlG.262. Tcenia sag'mata (medlocanellata), natural size (after E. Leuckart). 326 PLATYHELMLS TILES. Order 3. C. STODA.* Elongated, and usually segmented Platyhelminthes without mouth or alimentary canal, with organs for attachment at the anterior extremity. The tape-worms, which may easily be recognised by their band- shaped usually segmented bodies, are parasitic in the alimentary canal of Yertebrata, and were formerly taken for single animals. Steenstrup was the first to introduce a different view, according to which the tape-worm is a colonial animal, a chain of single animals, each segment or proglottis being an individual. There are, however, Cestoda, like Caryophyllceus, which are destitute both of external segmentation and of segmentation of the gene- rative organs ; while in other cases the segments of the body are clearly differentiated, and each is provided with a set of genera- tive organs, but they do not attain individual independence. The proglottides, however, usually become separated off, and in some cases (Echineibothriuni) after their separation from the body of the tape-worm continue to live for a long time independently, and even increase considerably in size ; so that although the individuality of the tape- worm may be justly insisted on, yet the subordinate and morphologically more restricted degree of individuality of the proglottis must also be admitted. This is the only satisfactory mode of regarding the Cestoda ; especially as the entire tape-worm, and not the proglottis alone, corresponds to the Trematode, and is to be derived from the latter by a simplification of organization and loss of the alimentary canal. The anterior part of the tape-worm is narrow, and presents a terminal swelling by which it attaches itself. This anterior swollen part is distinguished as the head of the tape-worm, but it is only its external form which entitles it to this name. In Caryophyttceua * Besides the older works and papers of Pallas, Zeder, Bremser, Kudolphi, Dicsing, and others, compare van Beneden, " Les vers cestoides ou acotyles," Brussels, 1850. Kiichenmeister, " Ueber Cestoden im Allgemeinen und die des Menschen insbesondere," Dresden, 1853. V. Siebold. " Ueber die Band- und Blasen-wiirmer," Leipzig, 1854. G. Wagener, " Die Entwicke- lung, der Cestoden," Nov. Act. Leop.-Car., Tom XXIV., Suppl., 1854. G. Wagener, " Beitrag zur Entwickelungsgeschichte der Eingeweidewiirmer," Haarlem, 1857. B. Leuckart, "Die Blasenbandwurmer und ihre Entwicke- lung," Giessen, 1856. B. Leuckart, " Die menschlichen Parasiten," Bd. I., Leipzig, 1862. F. Sommer and L. Landois, " Ueber den Bau der geschlcchts- reifen Glieder von Bothriocephalus latus," Zeitsckr. f. wiss. ZooL, 1872. F. Sommer, " Ueber den Bau und die Entwickelungsgeschichte der Geschlechts- organe von Taenia mediocanellata und Taenia solium," Ibid., Tom XXIV., 1874. CESTODA. 327 the head armature is very weak, and consists of a lobed fringed expansion. The apex of the head often ends in a conical projection, the rostellum, which is armed with a double circle of hooks, while the lateral surfaces of the head are furnished with four suckers (Tcenia, fig. 263). In other cases only two suckers are present (Bothriocephalus) ; or we find suckers of more complicated structure and beset with hooks (Acanthobothrium), or four protrusible probosces beset with recurved hooks (Tetrarhynchus); while in other genera the head armature presents various special forms. That portion of the animal which follows the head and is dis- tinguished as the neck shows, as a rule, the first traces of com- mencing segmentation. The rings, which are at first faintly marked and very narrow, become more and more distinct and gradually larger the further they are removed from the head. At the pos- terior extremity the segments or pro- glottides are largest, and have the power of becoming detached. After separation they live independently for a long time, and sometimes even in the same medium. The simplicity of the internal or- ganization corresponds with the simple appearance of the external structure. Beneath the delicate external cuticle is a matrix consisting of small cells, , . i T i i i 11 FIG. 263. Head of Tcenia solium, viewed in which are scattered glandular cells. from the front (apical gurfaoe)f with Beneath the matrix there is a delicate rosteiium and double circle of hooks. The four suckers are visible. superficial layer of longitudinal mus- cular fibres, and next a parenchyma of connective tissue, in which strongly-developed bundles of longitudinal muscular fibres, as well as an inner layer of circular muscles, are embedded ; both these muscular layers are traversed, principally at the sides of the body, by groups of dorso-ventral muscular fibres. The power which the proglottis possesses of altering its form is due to the interaction of all these muscles. By means of them it is able to shorten itself considerably, at the same time becoming much broader and thicker, or to elongate to double its normal length, becoming much thinner. In the connective tissue parenchyma of the body, not only the muscles, but all the other organs are embedded. In its peripheral portion, especially in the neigh- bourhood of the head , we find small densely packed calcareous concre- raents, which are generally regarded as calcified connective tissue cells. 328 PLATYHELMINTHES. The nervous system consists of two lateral longitudinal cords passh_g externally to the main trunks of the excretory system. They are somewhat swollen in the head, where they are connected by a trans- verse commissure ; these anterior swellings and the commissure may represent a cephalic ganglion. Distinct sense organs are wanting, but the tactile sense may be ascribed to the skin, especially to that of the head and the suckers. An alimentary canal is also wanting. The nutritive fluid, already prepared for absorption, oasses endosmotically through the body wall into the parenchyma. The excretory apparatus, on the contrary, attains a considerable development as a system of much ramified canals which are dis- tributed throughout the whole bcdy.* It consists primarily of two longitudinal canals (a dorsal and a ventral), running along each side of the body and connected in the head and in each segment by transverse trunks. According to the state of contraction of the muscular system, these longitudinal trunks and cross branches appear sometimes straight and sometimes bent in a wavy or zigzag manner : their breadth also presents consider- able variation, so that the power of contraction has been ascribed to their walls. The longitudinal trunks only serve as the efferent ducts of a system of very fine vessels which ramify throughout the whole paren- chyma and receive numerous long tubes : the latter begin in the parenchyma with closed funnels, which contain a vibratile ciliated lappet (fig. 264). In many cases, as in the Ligulidw and Caryo- phyllcPMS, these longitudinal trunks are broken up into numerous longitudinal vessels, which are connected by transverse anastomoses. In other cases, on the other hand, the two ventral vessels are enlarged at the cost of the two dorsal, which may entirely atrophy. The external opening of the excretory system is, as a rule, placed at the * Compare Th. Pintner, " Untersuchungcn iiber den Bau des Bandwurm- korpers," Wien, 1880. Fio. 26i. A portion of the excretory system of Caryophyllceus mutabilis (after Pintner). Wb, Ciliated funnels with the nucleus of the cell belonging to them. CESTODA. 329 posterior end of the body, i.e., at the hind end of the last segment, in which a small vesicle with an external opening receives the longi- tudinal trunks. According to the observations of Leuckart on Tcenia cucumerina, the posterior transverse canals in the segments immediately preceding the last become, by their gradual shortening and the approach of the longitudinal trunks, transformed into the vesicle, which acquires an external opening when the segment behind it is detached. In rare cases the excretory system possesses additional openings in the anterior part of the body behind the suckers. The generative apparatus is also divided into segments which correspond to the proglottides. Each proglottis possesses its own FIG. 265. Proglottis of Tcenia mediocanellata, with male and female organs (after Sommer). Ov, ovary ; DS, yolk gland (vitellarium) ; Sd, shell gland ; Ut, uterus ; T, testea ; Yd, vas deferens ; Cb, pouch of the cirrus ; J5T, generative cloaca; Va, vagina. male and female generative organs, and can therefore, when separated, be considered as a sexual individual of a lower order. The male apparatus consists of numerous pear-shaped vesicles, the testes (fig. 265, T), which are situated upon the dorsal side, and their vasa efferentia open into a common efferent duct (vas deferens). The coiled end of this duct lies in a muscular pouch (cirrus sheath), whence it can be protruded through the genital opening as the so-called cirrus. This cirrus is frequently beset with spines which are directed back- wards, and serves as a copulatory organ. The female generative organs consist of ovary, yolk gland, shell gland, uterus, receptaculum, and vagina. The vagina and vas deferens usually open into a common 330 PLATTIIELMIXTHES. genital cloaca, which lies either on the ventral surface of the segment (Bothriocepalw), OT on the lateral margin (Tcenia) (fig. 265). In b the last case it is placed alter- nately on the right and on the left side. Nevertheless it may happen that the two. genital openings are widely separate, the male opening being placed at the side, the female on the surface of the segment. As the segments increase in size and become further removed from the head, the contained generative organs gradually reach maturity in such a way that the male generative organs arrive at maturity rather earlier than the female. As soon as the male elements are mature, copulation takes. place, and the receptaculum seminis is filled with sperm, and then only do the female generative organs reach maturity. The ova are fertilized and pass into the uterus, which then assumes its characteristic form and size. As the uterus becomes distended, the testes and then the ovaries and vitellaria are more or less completely absorbed (fig. 266). The posterior proglot- tides, viz., those which are ready for separation, have alone under- gone full development, and the FIG. 20(3. Ripe proglottides ready to separate. a, of Tcenia solium ; b, of Tcenia mcdiocanellata ; Wf! t water- vascu'ar (excretory) canal. eggs in their uterus often contain completely developed embryos. Accordingly we can recognize in a continuous series of the seg- ments the course of development passed through by the sexual organs and products in their origin and gradual progress towards maturity. The number of segments between that with the first trace of the generative organs FIG. 267. Egg with embryo (condary vesicles (fig. 269, a). In such cases the number of tape-worms which arise from one embryo is naturally enormous, and the parent vesicle may reach a very considerable size, being some- times as large as a man's head. In consequence of this enormous growth the vesicles frequently obtain an irregular shape ; while on the other hand, the tape- worms which are developed from them remain very .small, and carry, as a rule, only one ripe proglottis (fig. 370). So long as the tape-worm head (scolex) remains attached to the body of the bladder-worm and in the host of the latter, it never develops into a sexually mature tape-worm ; although in many cases it grows to a considerable length (Cysticercus fasciolaris of the house-mouse). The bladder- worm must enter the alimentary canal of another animal before the head {scolex) can, after separation from the body of the bladder-worm, develop into the sexually mature tape- worm. This transportation is effected passively, the new host eating the flesh or organs of the animal infected with Cysticerci. The tape- worms, therefore, are principally found in the Carnivora, the Insecti- vora, and the Omnivora, which receive the bladder-worms in the flesh of the animals on which they feed. The vesicles are digested in the stomach, and the cestode head becomes free as a scolex. The latter is protected from the too intense action of the gastric juice by its calcareous concretions, and at once enters the small intestine, fastens * In Cysticerci (0. longicollis, tenuicolli?} also sterile daughter vesicles are sometimes budded off. m FIG. 270. Taenia Echinococcus (after R. Leuc- kart), magni- fied 12 to 15 times. 334 PLATYHELMIXTHES. FIG. 271. Cysticercoid of Tcenia cucumarina t magni- fied CO times (after R. Leuckart). itself to the intestinal wall, and grows by gradual segmentation into a tape- worm. From the Scolex the chain of proglottides proceeds as the result of a growth in length accompanied by segmentation, a process which is to be looked upon as a form, of asexual reproduction (bud- ding in the direction of the long axis). Since, however, it is the body of the Scolex which undergoes growth and segmentation, it seems most natural to assume the individuality of the entire chain, and to subordinate to this the individuality of the proglottides. The development of the tape-worm is then to be explained as a metamorphosis, characterised by the individualization of certain stages of the development. It is only in those cases in which the young form produces a number of heads that the development can be ex- plained as a case of alternation of genera- tions. The development of some tape-worms pre- sents considerable simplifications. In the cysticercus stage the vesicle frequently dimin- ishes to an excessively small appendage, and the Cysticercus becomes a cysticercoid form, in which one portion bearing the embryonic hooks is distinct from a larger part which represents the scolex (figs. 271, 272). In other cases the embryo becomes a Scolex directly without passing through a cystic stage, so that the Scolex stage is merely a late stage of the embryo (Bothrio- cephalus). The segments produced from the Scolex also show very different degrees of individuality, and finally are sometimes not deve- loped at all. In the latter case (Caryophyllceus) the head and body cannot be sharply distinguished from one another, and represent only one single individual comparable to a Trematode and characterised by its single generative apparatus. Its development is to be looked upon as a metamorphosis completing itself in one individual. Fam. Taeniadae. The armature of the head consists of four muscular suckers, to which is frequently added a single or double circle of hooks on the rostellwn. a FIG. 272. Hchinococcus-like Cysticercoid from the body cavity of the Earth- worm (after E. Metschnikoff). , Brood- capsules with three' Cysticer- coid. b, Cysticercoid with evaginated head. CESTODA. 335 The proglottides have a marginal sexual opening. The vagina is usually long, separated from the uterus, and enlarged at the end to form a receptaculum seminis (fig. 265). The young stages are Cysticerci or Cysticercoids, rarely quite without caudal vesicle ; parasitic in warm and cold-blooded animals. Tcenia L. ( Cijstotcenia R. Lkt). Development takes place with large vesicles. The heads arise from the embryonic vesicle itself. T. sollum. L. 2 3 metres long. The double circle of hooks is composed of 26 hooks. The ripe proglottides are 8 10 mm. long and 67 mm. broad ; the uterus has 7 10 dendritic branches. It lives in the human intestine. The Bladder- worms belonging to it (Cysticercus celluloses} live principally in the dermal cellular tissue and in the muscles of pigs, but also in the human body (muscles, eyes, brain), in which self-infection with them is possible if a Tcenia is present in the digestive canal ; more rarely in the muscles of the Roe-deer, the Dog, and the Cat. In the human brain the Cysticercus acquires an elongated form, and sometimes does not produce a head. T. stiff inata GoQze=--mediocaneUata Kiichenm., in the intestine of Man, distin- guished by the older helminthologists as a variety of T. sollum. Head without circle of hooks or rostellum, but with four more powerful suckers. The Tape- worm reaches a length of four metres, and becomes much stronger and thicker. The mature proglottides are about 18 mm. long and 7 9 mm. broad. The uterus forms 20 35 dichotomous side branches. The Cysticerffus lives in the muscles of the ox (fig. 273). It appears to be principally distributed in the warmer parts of the Old World, but is often found in great numbers in many places in the north. T.' serrata G-oeze, in the intestinal canal of the dog. The Cysticercus is known as Cysticercus plsclformis in the liver of the Hare and Rabbit. T. crassicollis Rud. in the Cat. with Cysticercus fascwlaris of the common mouse. T. marginata Batsch. of the Dog (butcher's dog) and Wolf with Cysticercus tenuicol- lis from Ruminants and Pigs, and occasionally in Man (Cyst, visceral is}. T. crassiccps Rud. in the Fox with Cysticercus long icollis from the thoracic cavity of the Fieldmouse. T. coenurus v. Sieb. in the intestine of the sheep-dog, with Coenurus cerebralis in the brain of one year old sheep. The presence of Coenurus in other places has been stated, as for instance in the body cavity of the Rabbit. T. tcnuicollis Rud. in the intestine of the Weasel and the Pole-cat, with a Cysticercus which, according to Kiichenmeister, lives in the hepatic ducts of the Field-mouse. EoHinococcifer Weinl. The heads bud on special brood-capsules, in such a way that their invagination is turned towards the lumen of the vesicle (fig. 269). T. echinococcus v. Sieb. (fig. 270) in the intestine of the dog, 3 4 mm. long, forming but few proglottides. The hooks on the head are numerous but small. Its Bladder-worm is distinguished by the great thickness of the stratified cuticula. It lives as Echinococcus principally in the liver and the lungs of Man (#. h-omims} and of domestic animals (E. veterinorum). The first form is also distinguished as E. altricipat'iem on account of the frequent production of primary and secondary vesicles ; it usually reaches a very considerable size and FIG. 273. Cysticercus of Tcenia mediocanellata, magnified about eight times. The head is protruded. 336 YERMES. has a very irregular shape ; while that form which inhabits domestic animals, E. scoliciparicng, more frequently retains the form of the simple vesicle. Finally these echinococcus cysts frequently remain sterile, in which case they are called Acephalocysts. Another and indeed pathological form is the so- called multilocular Echinococcus, which was for a long time taken for a colloid cancer. It is also found in Mammalia (in cattle), and here presents a confusing re- semblance to a mass of tubercles. The echinococcus disease (hydatid plague) was widely spread in Iceland. This disease likewise seems endemic in many places in Australia. T, (Mierotcenia). The Cysticercoid form is small, and has but little fluid in the small portion which corresponds to the vesicle. The head is small, but has a small club- shaped or proboscis-like rostellum, and is furnished with weak hooks. The eggs are provided with several membranes. The embryo is usually furnished with large hooks. The Cysticercoid stages live prin- cipally in Invertebrates (in Slugs, Insects, etc.), and more rarely in cold-blooded Vertebrates (the Tench). T. cucumcrina Bloch, in the intestine of dogs (house dogs). The Cysticercoid is entirely without the caudal vesicle, and lives (according, to Melnikoff and R. Leuckart) in the body cavity of the Dog-louse (Trichodectes canis). The infection with the Cysticercoids takes place when the dog swallows the parasites which are annoying him, while the para- sites swallow the eggs contained in faeces adherent to the hair of the dog. Nearly allied is T. elliptic a Batsch. in the intestine of the Cat, occasionally in that of Man. T. nana Bilh. v. Sieb. in the intestine of the Abyssinians. hardly an inch long. T. flavojt)unctataWcin\. in the human intestine (North America). The ("Jysticercoids of the Meal-worm are probably developed into tape-worms in the intestines of Mice and Rats. In other partially unarmed Tcenias the generative organs and development are as yet not accurately known ; such are T. FIG. 274 a. Bothriocephalus latus (after R. Leuckart). perfoliata Goeze, and T. plicata Rud. in the horse ; T.pectinata Goeze, in the hare ; T. dispar Rud. in the frog ; T. expansa Im. in the ox. Fam. Bothriocephalidae. With only two suckers, which are weak and flat. The generative organs, as a rule, open upon the surface of the proglottis. The proglottides do not become detached singly. Hydatid stage represented by an encysted Scolex. CESTODA. 337 Bothriocephalus Brems. Segmented body. Head with two pits, without hooks. The genital openings are on the middle of the ventral surface. The young stage usually in fishes. B. latus Brems., the largest of the tape-worms parasitic in man, twenty-four to thirty feet in length, principally found in Kussici, Poland, Switzerland, and South France. The sexually mature segments are broader than they are long (about 10 12 mm. broad and 3 5 mm. long). They do not become detached singly, but in groups (fig. 274). The segments of the hindermost portion of the body are, how- ever, narrower and longer. The head is club- shaped, and is provided with two slit-like pits. The cortical parts of the lateral regions of the body contain a number of round masses of granules, the yolJt-glands (fig. 275, Dsf), the contents of which are poured into the shell glands (coiled glands) through the so-called yellow ducts. The genital openings lie close together, one behind the other, in the midst of the segment (fig. 275, #). The anterior and larger belongs to the male generative apparatus, and leads into the muscular terminal portion of the vas deferens, which is enclosed in the cirrus sheath and can be eva- ginated as the cirrus (fig. 275, Cb~). The vas deferens just before its entrance into the cirrus pouch is dilated (fig. 275 5) to form a large muscular swelling (the vesicula seminalis ?). It then becomes coiled, and passes in the direction FIG. 274 J. Larva of a Bofhrio- cephalusfrom the Smelt (after R. Leuckart). FIG. 275. Geaerattve organs of a sexually mature proglottis of SothrioeepAaltu latui (after Sommer and a. Leuckarl) ; a, from the ventral surface, 5, from the dorsal surface. Ov and P, ovary ; Ut, uterus ; Sd, shell gland ; Dst, vitellarium (yolk gland) ; Va, vagina with opening ; T, testis ; Cb, pouch of the cirrus ; Vd, vas deferens. of the long axis of the segment on the dorsal surface and divides into two side branches. These receive the efferent canals of the delicate testicular sacs, which occupy the lateral parts of the middle layer (T). The female genital opening (fig. 275 a) leads into a vagina ( Va) situated behind the pouch of the cirrus, and frequently filled with semen. This vagina runs as a tolerably 22 3t38 PLA.TTHELMINTHES. straight median canal on the ventral surface, and opens by a short, narrow tube into the oviduct. The vagina also functions as a receptaculuin seminis. There is yet a third opening (fig. 275, a), situated at some distance behind the other two ; this is the opening of the tubular uterus (Z7), the convolutions of which give rise to a peculiar rosette-shaped figure in the midst of the segment (Wappenlilie Pallas). Close to the hind end of the segment the ducts of the yolk-glands (JDsf) and of the ovaries ( Ov) unite with each other and open into the uterus ; the cells of the shell-gland (fid) surround and open into the point of junction of these structures. Behind the uterus, and partly among its posterior lateral horns, lie the so-called coiled glands ; and at its sides are the so-called lateral glands (Eschricht). The latter are, according to Eschricht, the ovaries or germaria (formerly held by Leuckart to be the vitellaria). The coiled glands (Leuckart's ovaries), an aggregation of pear-shaped cells, were considered by Stieda, with whom Landois and Sommer are in accord, to be a shell gland (fig. 275). The ova are for the most part developed in water, and escape from the upper pole of the egg-shell through a lid-like valve. The escaped embryo is covered with cilia, by means of which it swims about for a long time. Hence it is probable that the later stages of development take place in an aquatic animal. It is unknown how and in what host the embryo with six hooks becomes a Scolex ; and the question how this tape-worm gets into the human body in spite of the researches of Knoch, who maintained that they appeared there directly and without the intervention of an intermediate host is still un- decided. B. cordatus Lkt. With large, heart-shaped head, without a filiform neck ; with numerous deposits of calcareous bodies in the parenchyma. It attains a length of about three feet and lives in the intestines of man and of the dog in Greenland. Schistocephalm Crepl. Head split, with a sucker on each side. The body of the cestoid form is segmented. S. solidus Crepl. Lives in the body cavity of the stickleback, escapes into the water, and becomes sexually adult in the intestine of water-birds. TricenopTiorus Hud. Head not distinct, with two weak suckers and with two pairs of tridentate t hooks. The body has no external segmentation. The generative openings are marginal. T. nodulosus Kud, In the intestine of the pike. Asexual encysted form in the liver of Cyprinus. Fam. Ligulidae (Pseudopliyllid(B). Without real suckers. Hooks are either present or absent. The Cestoid has no segmentation, but the generative organs are repeated. They live in the body cavity of Teleosteans and in the intestine of birds. Ligula Bloch. Body band-shaped and unsegmented. L. simpli- cissimu Kud., in the body cavity of fishes and in the intestine of aquatic birds, L. tuba v. Sieb., in the intestine of the Tench. The families of the Tetrarhynchidae (TetrarliyncTius lingualis, Guv., passes its young stages in Soles, and is matured in the intestine of Eays and Dog-fish), and Tetraphyllidae (EcMncibothrium minimum van Ben.) are allied here. Fam. Caryophyllaeidae. Body elongated and unsegmented. The anterior margin is plicated. There are no hooks, and there are eight sinuous longitu- dinal canals of the excretory system. Generative organs single. The develop- ment is a simplified metamorphosis. Caryopliyllteus mutabilis Hud., in the intestine of Cyprinoids. The young form possibly lives in TuHfex rivulorwu t if the Helminth observed by d'Udekem was the same. In this worm^ however, there lives another parasite, which was observed by Eatzel and has recently been more closely investigated by R. Leuckart, who has shown that it is 339 a sexually mature Cestoid still fixed by an appendage bearing the embryonic hooks. Archigvtes Sieboldii Lkt. With two weak suckers and a caudal appendage. Order 4. NEMERTINI* = RH YNCHOCgrovenosiim of about 3'5 mm. in length in the stage of maturity of the male products ; G, genital glands ; 0, mouth ; D, intestine ; A, anus ; N, nerve-ring ; Drz, glandular cells ; Z, isolated spermatozoa, b, Male and female Rhubditis forms from about I'o mm. to 2 mm. long ; Oo, ovary ; T, testis ; V, female genital opening ; Sp, spicula. been discovered whether the migration of the Filarian larva into the permanent host (Man, see p. 356) takes place with the body of the Cyclops, or independently after copulating in the free state. The embryos of some Nematoda develop in damp muddy earth, after casting their skin, to small so-called Rhabditis forms with a double * Compare Fedschenko, " Ueber den Bau und Entwicklung der Filaria medinensis," in the Bericltten der Freunde der Naturwissenschaften in 3foskaii, Tom VIII. and X. 350 NEMATHELMIXTHEB. enlargement of the oesophagus and with a pharynx armed with three teeth. They lead an independent life in this habitat, and finally migrate to lead a parasitic life within the permanent host, where, after several ecdyses and alterations of form, they attain the sexually mature condition. This mode of development occurs in Dockmius irigonocephalus from the intestine of the dog, and very probably in the nearly allied D. (Ancylostomum) duodenalis of man, and also in Sderostomum. The offspring of parasitic ISTematodes may, however, attain sexual maturity in damp earth, as free Rkabditis forms, and represent a special generation of forms whose offspring again migrate and become parasites. Such a life history is a case of heterogamy. It occurs in Rhabdonema nigrovenosum, a parasite in the lungs of Batrachians. These parasites, which are about half to three-quarters of an inch long, all have the structure of females, but contain spermatozoa, which are produced (as in the viviparous Pelodytes] in the ovarian tubes, but earlier than the ova. They are viviparous. The embryos make their way into the intestine of their host, and accumulate in the rectum, but finally pass to the exterior in the fseces, and so reach the damp earth or muddy water, where they develop in a short time into the JRkabditis-like forms, which have separate sexes and are barely 1 mm. in length (fig. 282, a and 6). The impregnated females of the latter produce only from two to four embryos, which become free inside the body of the mother, pass into her body cavity, and there feed on her organs, which disintegrate to form a granular detritus. They finally migrate as slender, already tolerably large Nematodes into the lungs of the Batrachia, passing through the buccal cavity and glottis. The Leptodera appendiculata, which lives in the slug Arion empiricorum, also presents in its development a like alternation of heteromorphic generations, which, however, are not strictly alternating, inasmuch as numerous generations of the Rkabditis form may succeed one another. The Leptodera are peculiar in that the form parasitic in the snail is a larva characterised by the absence of a mouth, and by the possession of two long band-shaped caudal appendages ; it quickly attains maturity, but only after a migration into clamp earth and after losing the caudal appendages and casting the skin. The Nematoda feed on organic juices, some of them also on blood, and are enabled by their armed mouth to inflict wounds and to gnaw tissues. They move by bending their body with a rapid nndulatory movement towards the ventral and dorsal surfaces, which thus seem NEMATODA. 351 to be the lateral surfaces of the moving animal. Most Nematoda are parasitic, but lead an independent life in certain stages of their life history. Numerous small Nematoda, however, are never parasitic, but live freely in fresh and salt water and in the earth. Some Nematodes are parasitic in plants, for example, Anguillula tritici, dipsaci, etc. ; some live in decaying vegetable matter, e.g., the vinegar worm in fermenting vinegar and paste. Nevertheless very similar forms occur in the contents of the intestine and in the faeces of different animals and of man (A. intestinalis, stercoralis). The power possessed by small Nematoda of resisting the effects of pro- longed desiccation and of coming to life again on being moistened is very remarkable. Fam. Ascaridse. Body tolerably stout. With three lips furnished with papillee. One of these lips is. directed towards the dorsal surface, while the two others meet together in the ventral 'line. The posterior end of the male is ventrally curved, and usually furnished with two horny spicula. FIG. 283. Axcarii lumbricoides (after R. Leuckart). a, Posterior end of a male with the two spicula (Sp). b, Anterior end from the dorsal side, with the dorsal lip furnished with two papillae, c, The same from the ventral side with the two lateral ventral lips and the excretory pore (P). d, Egg with the external membrane formed of small clear spherules. Ascaris L. Polymyarian, with three strongly developed lips, the edges of which are in the larger species provided with teeth. The pharynx is not sepa- rated as a distinct bulb. The caudal extremity is usually short and conical, and in the male sex invariably provided with two spicula (fig. 283, a). A. luwibricoidcs Cloquet, the human round worm, a smaller variety in the pig (J.. suilla Duj.) The eggs pass into water or damp earth and remain there some months, until the embryonic development is completed ; they are probably carried into the alimentary canal of their later host by means of an inter- mediate host. A. megalocephala Cloquet (horse and ox) ; A. mystax Zed. (cat and dog), sometimes parasitic in man. Oxyuris Eud. Meromyarian ; usually with three lips, which bear small papillge. The posterior end of the oesophagus is enlarged to a spherical bulb provided with a masticatory apparatus. The posterior end of the body of the female is thin and pointed, while that of the male has only two prseanal and few postanal papillae, and a single spiculum (fig. 279). O vcrmicularis L., in the large intestine of man, distributed in all countries. The female is about ten mm. long. 0. curvula Eud., in the caecum of the Horse. 352 NE1IATHELMLNT1IES. Fam. Strongylidae. The male genital opening is placed at the hinder end of the body, at the bottom of an umbrella- or bell-shaped bursa, the margin of which is furnished with a varying number of papillae. JSustrongylus Dies. With six projecting oral papillae, and a row of papillae on either lateral line. The bursa is bell- shaped and completely closed, with regular muscular walls and numerous marginal papillae. There is only one spiculum. The female genital opening is far forward. The larvae live encysted in fishes. (Filaria cystica from Symbranchus'). E. gigas Kud., the body of the female is three feet in length, and only twelve mm. thick. It lives singly in the pelvis of the kidney of the Seal and Otter, and very rarely in Man. Strongylus Rud. With six oral papillae and small mouth. Two conical cervical papillae upon the lateral lines. The pos- terior end of the male has an umbrella-like incom- pletely closed bursa. Two equal spicula, usually with unpaired supporting organ. The female sexual opening is sometimes approached to the posterior end of the body. They live for the most part in the lungs and bronchial tubes. St. longevaginatus Dies. Body 26 mm. long, 5 to 7 mm. thick. The female sexual opening lies directly in front of the anus, and leads into a simple ovarian tube. Only once found in the lung of a six-year old boy, in Klausen- burg. St. paradoxus Mehlis, in the bronchial tubes of the pig. St. Jilaria Rud., in the bronchial tubes of the sheep. St. commutatus Dies., in the trachea and bronchial tubes of the hare and rabbit. St. auricularis Rud., in the small intestine of Batrachia. Doclimius Duj. With wide mouth and horny oral capsule, the edge of which is strongly toothed. Two ventrally placed teeth project at the bottom of the oral capsule, while on the dorsal wall a conical spine projects obliquely forwards. D. duodenalis Dub. (Ancylostomun duodenale Dub.), 10 to 18 mm. long, in the small intestine of Man, discovered in Italy ; very widely distributed in the countries of the Nile (Bilharz and Griesinger). By aid of its strongly armed mouth it wounds the intestinal mucous mem- brane, and sucks the blood from the vessels. The frequent haemorrhages occasioned by these Doclimia are the cause of the illness known by the name of Egyptian chlorosis (fig. 284). It has lately been established that this worm occurs in Brazil, and that, like D. trigonocepl talus, it develops in puddles- of water (Wucherer). D. trigonocephalus Rud., in the Dog. Sclerosto-mum Rud. With characters of Dochmius, but with a different oral capsule, into which two- long glanular sacs open. So. equinum Duj. = armatum Dies. In the intestine and the mesenteric arteries of the horse. Bollinger* has shown that the phenomena of colic in the horse may be referred to embolic processes proceeding from aneurism of the intestinal artery; Each aneurism contains about nine worms * Bollinger, " Die Kolik der Pferde und das Wurmaneurysma der Einge- weidearterien,' Miinchen, 1870. Fio. 284. Dochmiu* du (after E. Leuckart). a, male; O, mouth ; B, bursa. b, Female ; 0, mouth; A, anus; V, vulva. NE3IATODA. 358 Sc. tetracanthwn Mehlis, also in the intestine of the horse. The embryos, after migrating into the intestine, become encysted in the walls of the rectum and caecum, assume within the cyst their definite form, break out from the cyst, and escape again into the intestine. Gacnllanus elegans Zed., in the Perch. Fam. Trichotrachelidae, with long neck-like thin anterior portion of the body. Mouth small, without papillae. (Esophagus very long, traversing a peculiar cord of cells. Tricliocephalus Goeze. Anterior part (fig. 285) of the body elongated and whip shaped : posterior part cylindrical and sharply distinct, enclosing the generative organs, in the male it is coiled up. Lateral lines absent. Main median lines present. The penis is slender and furnished with a sheath, which is turned inside out when the former is protruded. The hard-shelled, lemon-shaped eggs undergo the first part of their development in water. Tr. dispar Bud. In the human colon : these worms do not live free in the intestine, but bury their filiform anterior extremity in the mucous membrane (fig. 285). The eggs pass out of the host with the fasces, as yet without a sign of beginning development, which only takes place after a prolonged sojourn in the water or in a damp place. According to the ex- periments of Leuckart per- formed with Tr. affinis of the sheep and Tr. crenatus of the pig, embryos with the egg membranes, if introduced into the intestine, develop into the adult Tricoceplialus ; and we may therefore conclude that the human Tr. dispar is intro- duced directly, and without an intermediate host either in the drinking water or in uncleaned food. The young Tr. dispar is at first hair-like, and re- sembles a Trichina, and only gradually acquires the considerable thickness of the hind end of the body. Tricliosomum Kud. Body thin, hair-like, but the posterior end of the body in the female is swollen. Lateral lines and the principal median lines are present. The male caudal extremity has a cutaneous fold and a simple penis (spiculum) and sheath. Tr. muris Creplin., in the large intestine of the house-mouse. Tr. crassicauda Bellingh., in the bladder of the rat. According to Leuckart, the dwarfed male lives in the uterus of the female. There are usually two or three, more rarely four or five males in a single female. There is also a second species of Tricliosomum found in the bladder of the rat. Tr. Sclimidtii v. Linst, the larger male of which was formerly taken for that of Tr. crassicauda. Trichina Owen.* Body thin, hair-like. Principal median lines and lateral * Compare the writings of R. Leuckart, Zenker. R. Virchow, Pagenstecher, etc. 23 FlG. 285.Trichoceplialiis dispar (after R. Leuckart). a, Egg ; 6, female ; c, male with the anterior part of the body buried in the mucous membrane; Sp, spiculum. 354 KEMATHELMINTHES. lines arc present. The female generative opening well forward. The posterior end of the body of the male has two terminal cones between which the cloaca is FIG. 286. Trichina spiralis. a, Mature female Trichina from the alimentary canal ; G, genital opening; E, embryos; Ov, ovary, b, Male; T, testis. Embryo8 to be mentioned as the natural strongly magnified, host of the Trichina. This animal does not hesitate to eat the carcase of its own species, and so the Trichina infection is passed on from generation to generation. Carcases in- fected with Trichinas are sometimes eaten by the omnivorous pig, in whose flesh the encysted Trichinas are introduced into the intestine of man, and occasion the well-known disease, Trichinosis, which when the migration takes place in number, often has a fatal result. Fam. Filariidae. Body filiform, elongated, often with six oral papillae, some- 356 NEMATHELMINTHES. times with a horny oral capsule, with four prseanal pairs of papillse, to which an unpaired papilla may be added, with two unequal spicula or with simple spiculum. A'ilaria 0. Fr. Mull. With small mouth and narrow oesophagus. This species, which is sometimes destitute of papillae, lives outside the viscera, usually in connective tissue, frequently beneath the skin (divided by Diesing into numerous genera). F. (Dracunculus) mcdincnsis* Gmel. the Guinea worm, in the subcutaneous cellular tissue of Man in the Tropics of the Old World, reaches a length of two feet or more. The head is provided with two small and two larger papillae. The female is viviparous, and without sexual opening. The male form is unknown. The worm lives in the connective tissue between the muscles and beneath the skin, and after reaching sexual maturity, occasions the formation of an abscess, with the contents of which the embryos escape to the exterior (fig. 287). It has lately been proved (Fedschenko) that the embryos of Filaria migrate into a Cyclops and there undergo an ecdysis. Whether they are then (in the body of the Cyclops) introduced into man in his drinking water, or whether they first escape and copulate in a free state, is not known. F. immitis lives in the right ventricle of the dog, and is very abundant in East Asia. It is viviparous. The embryos pass directly into the blood, where, however, they do not undergo their further development. Similar young Ha3matozoa are also found in the blood of man in the Tropics of the New and Old Worlds (F. sanguinis Jwminis, F. Bancrafti). Since these animals are also found in the urine, their appear- ance seems to have an tetiological connection with hsematuria. In the East Indies, young Filaria also live in the blood of the street dog, and would seem to be related to the brood of Filaria sanguinolenta, since, according to Lewis, knotty swellings on the aorta and oasophagus are invariably found with these Filaria. F. papttloxa Hud. in the peritoneum of the horse. F. loa Guyot., in the conjunctive of negroes on the Congo. F. laMalis Pane. Only once observed at Naples. An immature Filaria described as Filaria lentis (ocnli humani) has been found in the human capsula lentis. Fam. Mermithidae. Aproctous Nernatodes, with very long filiform body, and six oral papillae. The male caudal region is broad, and is provided with two spicula and three rows of numerous papillae. They live in the body cavity of insects, and escape into the damp earth, where they attain sexual maturity and copulate. Mcrmis nigrcscens Duj., was the occasion of the fable of the worm rain. M. alMcans v. Sieb. v. Siebold established by experiment the migration of the embryos into the caterpillars of Tinea cvonynwlla. Sphcerularia boinbi Leon Duf. Fam. Gordiidae. Body elongated and filiform. Without oral papillse and lateral lines, with a ventral cord. The mouth and anterior region of the alimentary canal is obliterated in the adult state. The testes and ovaries are paired and open to the exterior with the anus near the hind end of the body. Uterus unpaired, with receptaculum seminis. The male caudal region is forked, and is destitute of spicula. In the young stage they live in the body cavity of predatory insects, and are provided with a mouth. At the pairing time they pass into the water, where they become sexually mature. The embryos, which are provided with a circle of spines, bore through the egg-membranes and migrate into Insect larvaa (Chironomus-larvte, Epliemerida:}, and there encyst. Water * Compare H. C. Bastian, "On the Structure and Nature of the Dracunculus," Trans. Linn. Society, vol. xxiv., 1863. Fedschenko I. c. CH^TOGNATHA. 357 beetles and other aquatic predatory insects eat with the flesh of the Ephcmcrid larva the encysted young forms, which then develop in the body cavity of their new and larger host to young Gordlidce. Gordius aquaticus Dvj. Fam. Anguillulidae. * Free living Nematodes of small size. Caudal glands are sometimes present. The lateral canals are often replaced by the so-called ventral glands. Some species either live on or are parasitic in plants ; others live in fermenting or decaying matter. The greater number, however, live free in earth or water. Tylenchus Bast. Buccal cavity small, and con- taining a small spine. The female genital opening lies far back. I\ scandens Schn. = tritici Needham, in mildewed wheat grains. When the grains of wheat fall the dried embryos grow in the damp earth, bore through the softened membranes, and make their way on to the growing wheat plant. Here they remain some time, perhaps a whole winter without alteration, until the ears begin to be formed. They then pass into the latter, grow, and become sexually mature, while the ear is ripening. They copulate and deposit their eggs, from which the embryos creep out, and at length constitute the sole con- tents of the wheat grains. T. dipsaoi Kuhn, in heads of thistles (Cardius) T. Davainii Bast, on roots of moss and grass. Heterodera Schachtii Schmidt., roots of the beet-root, also of the cabbage, of wheat, barley, etc. Rhabditis Duj., divided by Schneider into Lcptodera Duj. and Pelodera Schn. Rh. flexilis Duj., head very sharply pointed, mouth with two lips, in the salivary glands of Limax cinereus. Rli. anglostoma Duj. RJi, appendiculata Schn., in damp earth, 3 mm. long. The larva, which is without a mouth, and has two caudal bands, is found in Arion empiricovum. Angnillula aceti = gliitinis 0. Fr. Mull., known as the vinegar worm and pasteworm, 1 to 2 mm. long. Of the many marine Angmllulidce {Enoplidaf), we must mention Dory- lalmus maximus Butschli, D. stagnalis Duj., found in mud everywhere in Europe. Enclielidiwm, marinum, Ehrbg., Enoplus trldentatus Duj. The abberant families Desmoseolecidce and Chcetosomidce are allied to the Nematoda. THE CH^ETOGNATHA. The Chcetognatha, f containing only the genus Sagitta, are allied to the Nematodes. They are elongated round worms, with a pecu- liarly armed mouth and laterally placed horizontal fins, the mem- branous edges of which are supported by rays. The anterior portion of the body is sharply separated off as a head, and bears in * Davaine, " Recherches sur I'Anguillule du ble nielle," Paris, 1857. Kuhn, " Ueber das Vorkommen von Anguillulen in erkrankten Bliithenkopfen von Dipsacus fullonum," Zeltschr.fur wiss Zool., Tom IX., 1859. Bastian, " Mono- graph of the Anguillulidae or free Nematoids, marine, land, and fresh water," London, 1864. O. Butschli, ' Beitrage zur Kentniss der freilebenden Nema- toden," Nov. Acta, Tom XXXVI., 1873. Lad. Oerley, "Monographic der Anguilluliden," Buda-Pest., 1880. f Compare A. Krohn, " Anatomisch-physiologische Beobachtungen liber die Sagitta bipunctata," Hamburg. 1844. R. Wilms, " De Sagitta mare germani- cum circa insulam Helgoland incolente," Berolini. 1846. Kowalevski, "Em- bryologische Studien an Wiirmern und Arthropoden," Mem. de VAcad. St. Petersburg, Tom XVI. 0. Hertwig, " Die Chsetognatha, eine Mono- graphic," Jenr,, 1830. 358 KEMATHELMIXTHES. the region of the mouth two lateral groups of hooks which function as jaws. The nervous system consists, according to Krohn, of a cerebral ganglion on which the eyes are situated, and a ven- tral ganglion placed in about the middle of the body length. There are in addition two ganglia near the mouth, which may be considered as the subcesophageal gan- glia, and are connected with each other and with the cephalic ganglion by oeso- commissures. l^. 288.Sagitta (Spadella) cephalopttra, magnified 30 times, viewed from the dorsal side (after O. Hertwig). F, posterior fin; G, supra- O3sophageal ganglion ; Te, ten- tacles ; R, olfactory organs ; Ov, ovary; Od, oviduct; T, testis; Vd, vas deferens; Sb, vesicula seminalis. [The common view now is that the large ventral ganglion of the middle of the body, which is connected with the cerebral by com- missures, is homologous with the suboesophageal ganglia of other types.] The straight alimentary canal is at- tached to the body wall by a dorsal and ventral mesentery from the oesophagus backwards, and opens to the exterior at the base of the long tail, which terminates in a horizontal fin (fig. 288). [The body cavity is well developed, and divided by the dorsal and ventral mesenteries into two parts, and again by two transverse verti- cal septa into a cephalic section, a section in the body, and finally a caudal section. Vas- cular and excretory organs are absent.] Reproduction. The Chcetognatka are hermaphrodite, and possess paired ovaries, which open by two apertures at the base of the tail and are connected with seminal pouches. The testes also are paired, and situated posteriorly to the ovaries in the tail; their products pass to the exterior by openings at the sides of the tail. Segmentation is complete, and leads to the formation of a blastosphere. One side of this becomes invaginated so that the segmentation cavity is obliterated and a gastrula is formed, in the entoderm CILETOGNATHA.. 359 of which two cells may already be recognised as primitive generative cells. As soon as these make their appearance in the entoderm, the latter becomes folded in such a way that the archenteron is divided into a median and two lateral cavities. The layer of cells lining the lateral cavities becomes the mesoderm, and the contained cavities the two lateral compartments of the body cavity, while that of the middle cavity gives rise to the wall of the mesenteron or alimentary canal. The permanent mouth is formed at the end opposite to that at which the blastopore, w r hich is now closed, was situated. There is but one genus, Sagitta Slab., of which several species, e.g., Sagitta bipunctata Krohn, S. germanica Lkt. Pag. from the Euro- pean seas have been more accurately described. Order 2. ACANTHOCEPHALA.* Elongated round ivorms with protrusible 2^'oboscis furnished with hooks ; without mouth and alimentary canal. The saccular, often transversely wrinkled body begins with a proboscis, which is furnished with recurved hooks and can be retracted into a tube projecting into the body cavity (sheath of the proboscis) (fig. 289, .7? and Us). The posterior end of this sheath is fas- tened to the body wall by a ligament, and by retractor muscles. The nervous system (fig. 289, G) is placed at the base of the proboscis, and consists of a simple ganglion formed of large cells. Nerves are given off from the ganglion anteriorly to the proboscis, and through the lateral retractors (retinacula) to the body wall g (fig. 289, R). The latter supply partly the muscular system of the body, and partly the R genital apparatus, in which there are, princi- pally in the male animal, special nerve centres FIG. 289 Anterior part, consisting of ganglionic enlargements. Sense organs are entirely wanting, as also are mouth, alimentary canal, and anus. The nutritive juices are taken in through the whole outer surface of the body. In the soft granular subcuticular * Besides Dujardin, Diesing, 1. c., compare : K. Leuckart, " Parasiten des Menschen," Tom II., 1876. Greeff, " Untersuchungen liber Echinorbynchus miliaris," Arch, fiir Naturgesch, 1864. A Schneider, a IJeber den Bau der Acanthocephalen," Mutter's Arcltiv., 1868. Also the Sltzungslcrichte der OberJiessischen Gesellscliaft fiir Natur- und Heilkundc, 1871. n of an EchinorJiynchus. B, Proboscis ; Eg, sheath of proboscis; G, ganglion ; Le, lem- nisci ; K, retinacula. 360 NEMATHELMIS THES. layer of the integument lies a complicated system of canals, filled with a clear fluid containing granules. Beneath the internal layer of the integument, which layer is often very extensive and of a yellow colour, is placed the powerful muscular tunic; it is composed of external transverse and internal longitudinal fibres, and bounds the body cavity. Tae complicated ramified system of dermal canals, of which two principal longitu- dinal trunks may be recog- nised, is filled with juices, and probably functions as a nutritive apparatus. The portion of this system which extends into two bodies (the lemnisci, fig. 289, Le) project- ing behind the proboscis through the muscular tunic into the body cavity, probably acts as an excretory organ, since the contents of the fre- quently anastomising canals of these lemnisci is usually of a brown colour, and consists of a cellular mass rich in concretions. According to Schneider, the vessels of the lemnisci open into a circular vessel in the integument, and only communicate with the network of canals in the cephalic region, while the other dermal vessels (nutritive FIG. 290. Male of EcU- norhyncu, angustatu* apparatus), the Contents Of FlG - 291. - Generative (after R. Leuckart). w hiVh difFpr* from that of thp ^ & ^ f female S proboscis Its J&chinorhynchus gigas sheath of the probos! vesselsof the lemnisci, are com- ^'^j. ^^^^ cis; Li, ligament; p l e telv shut off from the latter. sSSdfloccuil. F**F Or, ganglion ; Le, lem- The nisei; T, testes; rd, Generative organs. The ^e^rTutems T proL d tic fer sacs a; Be' bod y Cavit ^ through which vajna ;' S, Patera! ductus ejacuiatorius ; fluids circulate encloses the B, retracted greatly developed generative pouches of the bell ; Gd, dorsal cells at the base of the bell; (?/, lateral cells. , . , , , organs, which are attached to the end of the sheath of the proboscis by a ligament (figs. 290 ACANTHOCEPHALA. 361 FIG. 292. Embryo of Echin- orhynchus gigan enclosed in the egg membranes (after Leuckart) . and 291, Li). The sexes are separate. The male (fig. 290) has two testes (T), and the same number of efferent ducts (Vd). The latter unite behind to form a ductus ejaculatorius (De), which is often fur- nished with six or eight glandular sacs (Pr), and a conical penis (P), at the bottom of a bell-shaped protrusible bursa (B), situated at the posterior pole of the body (fig. 290). The generative organs of the larger females (fig. 291) consist of the ovary developed in the ligament ; of a complicated uterine bell, beginning with a free opening into the body cavity ; of the oviduct and the short vagina, which is divided into several portions and opens at the posterior end of the body (fig. 291). It is only in the young stage that the ovary is a simple body en- closed by the membrane of the above-men- tioned ligament. As the animal increases in size, the ovary grows, and becomes divided into numerous spherical masses of eggs, the pressure of which bursts the membrane of the ligament ; the masses of ova as well as the ripe elliptical eggs, which gradually become free from them, fall into the body cavity. The egg membranes are not formed till rf after seg- mentation, and ought perhapsto be interpreted as embryo- nic mem- branes. The eggs, which already con- tain em- bryos, pass out of the body cavity into the uterine bell, which is continually dilating and contracting, thence into the oviduct, and through the genital opening to the exterior. FlG. 293. Larvae of Echinorfiyncltus profess from Gamniarus (aftei Leuckart). a. Free embryo ; Ek, embryonic nucleus, b, Older stage, with more differentiated embryonic nucleus, c, Young female worm ; Ot>, ovary, d, A young male worm ; T, testes ; Le, lemnisci. 362 ANNELIDA. Development. Segmentation is irregular and complete, and results in the formation of an embryo, which is enclosed in three egg-mem- branes. The embryo has a small, somewhat long body, armed with small spines at the anterior pole, and containing a central granular mass (embryonic nucleus) (fig. 292). It passes into the intestine of Am- phipods (Ech. proteus, polymorphic], or of Isopods (Ech. angustatus), and there becomes free, bores through the wall of the intestine, and after losing the embryonic spines, develops to a small elongated larva, which, like a pupa, lies in the body cavity of the small Crustacean with its proboscis retracted and surrounded by its firm external skin as by a cyst (fig. 293). The skin of the larva gives rise only to the integument, the vessels and the lemnisci of the adult ; while all the other organs enclosed within the dermal muscular envelope, viz., the nervous system, the sheath of the proboscis, and the gene- rative organs, are developed from the so-called embryonic nucleus. It is only after their introduction into the intestine of fishes (Ech. proteus} or of aquatic birds (Ech. polynwrplius}, which feed on these Crustacea, that the larvae attain to sexual maturity, copulate, and reach their full size. The numerous species of the genus Eohinorhyncus 0. F. Mliller live prin- cipally in the alimentary canal of different Vertebrata ; the gut wall may be as it were sown with these animals. Ech. polymorplius Brems., in the intestine of the duck and other birds, also in the crayfish. Ecli. proteus Westrumb., Ecli. angustatus Kud., in fresh- water fish. Ecli. giyas Goeze, as large as an Ascaris lumtricoides, in the small intestine of the pig. According to A. Schneider, the embryo completes its development in the maggot. Lambl found a small sexually immature Echinorhynchus in the small intestine of a child which died of leukaemia. CLASS III. ANNELIDA. Segmented Venues with brain, circum-cesopliageal ring, ventral nerve cord, and vascular system. The larva of Loven and its development seems to throw light upon the organization of the Annelida and their relations to the lower worms and to the JRotifera; and further makes evident the relationship of the Annelida to the Gepliyrea, a group of worms which possess an elongated body devoid alike of external and internal segmentation, and, as an equivalent of the ganglionic chain, a ventral nerve trunk, which is usually uniformly covered with ganglion cells. The body of Loven's larva, from which we must derive the body of Annelids, is unsegmented, and represents mainly the Annelid head. LOTN'S LAEYA. 363 Behind it is continued into an indifferent terminal portion equivalent to the whole body of the adult. At the apical region of the larva (fig. 294, Sp) there is a thickening of the ectoderm, which is called the apical plate. This represents the rudiment of the cerebral ganglion (apical ganglion), and gives off nerves to either side. The wide mouth (0) has a FIG. 291. Development of Polygordiug (after B. Hatschek). a, Young larva ; Sp, apical plate with pigment spot ; frw, prse-oral circle of cilia ; O, mouth ; Poic, post-oral circle of cilia; A, anus; Ms, mesoderm ; JOT. head kidney. 5, Older larva with commencing segmentation of the body, a second limb is developed in the head kidney, c, Older stage. The body is elongated to the form of a worm, and divided into a number of metameres ; HWk t posterior circle of cilia; Af t eye spot; F, tentacle. ventral position, and leads into an alimentary canal, which opens at the posterior end of the body (A). In front of the mouth there is a strongly developed circle (prscoral) of cilia (Prw) ; and behind 364 ANNELIDA. the month a weaker (postoral) circle (Pow) ; to the right and left there is an excretory canal (head kidney), which begins with a ciliated funnel. By the differentiation of the cephalic region of the larva into prsestomial lobe and oral segment, and by the gradual growth in length of the posterior part of the body and the -r, segmentation of the latter into a number of successive metameres, the originally un- segmented larva is transformed into an Annelid (fig. 294, ad). There is, therefore, between the segmented adult and the larva a morphological relation similar to that be- tween the cestoid and the simple scolex, from the posterior end of which the proglottides are developed. The body of the Annelida is sometimes flattened, sometimes completely rounded and cylindrical. It is composed of a number of successive segments, which are usually sepa- rated from each other externally by trans- verse constrictions. The segmentation is generally homonomous^ in that the segments following the head resemble each other not only in external appearance, but also in internal structure, i.e., they repeat similar sections of the internal organization. The terminal segment with the anus, however, has a special structure inasmuch as it retains the primitive, more indifferent char- acter of the posterior end of the body of the larva, and during the development of the worm gives origin to new segments anterior to itself. The homonomy of the preceding segments of the body is, how- ever, never complete, since certain organs are confined to definite segments. The internal segments, which are separated by dissepiments, either correspond with the external segmentation as marked by the annular constrictions of the integument (Chcetopoda), or each internal segment corresponds to a definite number (3, 4, 5, etc.) of the external rings (Hirudinea). FIG. 294 d. The young Polygordius ; G, cerebral ganglion ; Wg, ciliated pit ; D, alimentary canal. JLN1TEL1 DA.. 365 Organs of locomotion. Special organs of locomotion may either have the form of bristle-bearing un jointed appendages (parapodia) on each ring of the body (Chcetopoda), or of terminal suckers (Hirudinea). In the first case each segment may possess a dorsal and ventral pair of appendages (the neuropodia and notopodia), which, however, are sometimes replaced by simple setae embedded in dermal pits. Alimentary canal. The mouth is placed on the ventral surface at the anterior end of the body, and leads into a muscular pharynx, which is often provided with a powerful armature and can be protruded like a proboscis. This is followed by the gastric region of the gut, which occupies the greatest portion of the length of the body, and is either regularly constricted in correspondence with the segments, or possesses lateral diverticula ; it is only coiled in excep- tional cases. The anus is usually dorsal at the hinder end of the body. The nervous system consists of /a cerebral or supra - O3sophageal ganglion, which is derived from the apical plate of the larval prse-oral lobe, of an 03sophageal ring, and of a ventral cord or ganglionic chain, the two halves of which lie more . FIG. 295. Transverse section through or less approached to each other in the body of Protodriiw, (after B. Hat- the median line. The ventral cord s hek >- * s, The two lateral trunks of the nervous system; G, ganglionic arises from two lateral nerve COrds, layer of the same; D, alimentary which probably correspond to the ^'J' nephridium; * muscles; lateral nerve trunks of the Ne- mertines. These two cords are continuous with the cesophageal commissures, and, like the latter, are uniformly covered with ganglionic cells. This form of the nervous system may persist, as may also its ectodermal position (Archiannelida, Protodrilus) (fig. 295). In most Annelida, however, this is only a transitory condition; for at a later stage the lateral cords become separated from the ectoderm, come together in the median line, and acquire a segmentation corresponding to the metameres of the body. The nerves of the sense organs arise from the cerebral ganglion ; the other nerves pass out from the parts of the ventral cord or, as the case may be, from the ganglia of the ventral chain and from the longitudinal commissures between the latter. There is in 366 ANNELIDA. almost all cases a visceral nervous system (sympathetic). The following sense organs are found : paired eye spots with refractive structures, or larger more complicated eyes; also auditory vesicles upon the O3sophageal ring (branchiate worms), and tactile organs. The latter have, in the Chcetopoda, the form of tentacles and tentacular cirri on the head and of cirri on the parapodia, When tentacles and cirri are absent, the anterior end of the body and the region of the mouth seem to function as tactile organ?,. Vascular system. A blood vascular system is very commonly present ; in many cases, however, it seems not to be completely closed, but to communicate with the body cavity, which contains blood. Two main vascular trunks, a dorsal and a ventral, connected with one another by numerous transverse anastomoses, are generally present. The blood is usually coloured (green or red), and its cir- culation is effected by the contractility of the walls of certain vessels ; sometimes the dorsal vessel, sometimes the ventral, and sometimes the transverse connecting vessels are contractile. Lateral longi- tudinal vessels are often present in addition to the above. In the Hirudinea these, as well as the median contractile blood sinus, are probably to be regarded as isolated parts of the body cavity. Special respiratory organs are found amongst the Chcetopoda in the branchiate worms. The excretory organs, corresponding to the water-vascular or excretory system of the Platyhelminthes, have the form of coiled canals (segmental organs or nephriclia), which are repeated in pairs in each segment. Each nephridium usually begins with a ciliated, funnel-shaped opening into the body cavity, and opens to the exterior by a lateral pore (fig. 70). These may assume in certain segments the function of generative ducts, e.g., the nephridia of the Gfepkyrea, which, however, are much reduced *n number. In the cephalic segment or head there is also a segmental organ (head kidney), which in the larva functions as a kidney and later disappears. Reproduction. Considering the independence of the segments, to which we ascribe the value of a subordinate (morphological) indi- viduality, the occurrence of asexual reproduction by fission and gemmation in the long axis (Chcetopoda) is not surprising. Nume- rous Annelida (Oligockccta, Hirudinea) are hermaphrodite ; the marine Glicetopoda, on the contrary, are for the most part of separate sexes. Many lay their eggs in special sacs and cocoons, in which case development is direct, without metamorphosis. The marine worms, on the contrary, undergo a more or less complicated CHJETOPODA. 867 metamorphosis. The Annelida comprise terrestrial and aquatic animals, and they eat, for the most part, animal food. Many of them (flirudinea) are occasionally parasitic. In the group of the Annelida three principal divisions may be distinguished, the Chcetopoda, the unsegmented Gephyrea, and the Hirudinea which are adapted for parasitism. The Hirudinea are not in any degree to be regarded as Annelida of a lower grade of organization, but they rather present, at least in the case of some organs, as alimen- tary canal, circulatory and generative organs, a more complicated structure, and agree most closely with the Oligochreta, from which they may be derived. /Sub-class 1. CH^TOPODA.* Free living Annelida, with paired tufts of setce on the segments, frequently with distinct head, also with tentacles, cirri, and branchice. The Chsetopoda are divided externally into segments, which correspond with the metameres of the internal organs, and are, with the excep- tion of the anterior region, which is distinguished as the head, usually tolerably alike (fig. 296). Parapodia provided with setae are very frequently present on the segments ; their prin- cipal function is that of locomotion, but their va- rious appendages, the branchice and cirri, also discharge tactile and respi- ratory functions (fig. 297). FIG. 296. Grulea fun- fera (after Quatre- fages). Ph. pharynx D, alimentary canal; C, cirri; JF, tentacles. Ac * Besides the older works of Savigny, Audouin et Milne Edwards, and Quatrefages, compare E. Grube, " Die F ami- lien der Anneliden," Archiv fur Naturr/eseJt, 1850 and 1851. E. Claparede, " Eecherches anatomique sur les Ann glides, etc.," Geneve, 1861. E. Cla- parede, " Les Annelides che'to- podes clu golfe de Naples," Geneve et Bale, 1868, also Sup- plement, 1870, and " Eecherches sur la structure des Annelides sedentaires," Geneve, 1873. Fr. Leydig, 1. c.. also " Tafeln zur vergl. Anatomic/' 1864. FIG. 297. Dorsal (DP) and ventral (VP) Para- pcdium with bundles of setaB of Nerds (after Quatrefages). Ac, Aciculum ; Re, dorsal cirrus j Be, ventral cirrus. 368 ANNELIDA. The form of the movable setae varies extremely, and affords a good character for the classification of families and genera. According to the strength, form, and mode of ending (fig. 298), the following a, e f Pia 298. Setse of different Polychata (after Malmgren and Claparcde). a, Hooked seta of Sdbella crassicornis ; b, of Terebella Danielsseni; c, seta with spiral ridge from Sthenelais ; d, lance-shaped seta of Phyllochcetopterus ; e, of Sabella crassicornis ; f, of Sabella pavonis ; g, Composite sickle-shaped seta of Nereis cultrifera. forms can be distinguished : hair-setae, hooked-setae, flat-setae (palece), lance-setae, sickle-shaped setae, etc. When the parapodia and their appendages are com- pletely wanting, the setae are embedded in pits in the integument, and are arranged either in one or two rows on either side, that is, in a lateral ventral row on either side, or in a ven- tral row and a dorsal row on either side. In such cases the number of setae is small (Oligo- chceta}. The setae may, on the contrary, be pre- fiG 2'JO Anterior end of Polynoe extenuata, the first . elytron on the left hand being removed (after Cla- sent in great number, parede). The two setae of the oral segment are visible ; go fa^ t] ie integument .El, Elytra. . , on either side seems to oe covered with long hairs and setae, and a thick felt of hairs shining with a metallic lustre is distributed over the whole dorsal 369 surface (Aphrodite). The appendages of the parapodia present an equally great variety of form and not unfrequently vary in the different parts of the body. They are either simple or ringed tenta- cle-like processes, the cirri, which are distinguishable into dorsal and ventral cirri. The cirri are for the most part filiform, and sometimes jointed or conical, and then are often provided with a special basal joint. In some cases the dorsal cirri are flattened out as broad scales and leaves, the elytra, which constitute a protective covering (Aphro- dite] (fig. 299). In addition to the cirri, branchiae which may be filiform or branched and antler-like, comb- shaped or in the form of tufts, are frequently present ; sometimes they are confined to the middle region of the body, or are extended over almost the whole dorsal surface ; sometimes they are confined to the head or to the anterior segments immediately following the oral segment (cephalic branchiae). The two anterior segments may be regarded as forming the head ; they are fused together, and are, with regard to their appendages, different from the following segments (fig. 245). The anterior segment projects beyond the mouth as the frontal lobe, and bears the tentacles and palps [palps are ten- tacular structures arising from the ventro-lateral sides of the head, vide p. 379] and also the eyes ; the posterior cephalic segment or oral segment bears the tentacular cirri. The last segment (anal segment) bears the anal cirri. The alimentary canal is usually straight, and extends from the mouth to the anus, which is terminal and rarely dorsal; it is divided into oesophagus, intestine, and rectum (fig. 300). There is in most cases a dilated muscular pharyngeal bulb which is armed with papillae or with movable teeth and can be protruded as a proboscis. The intestine usually preserves the same structure in its entire length and is divided by regular constrictions into a number of 24 FIG. 300. Alimentary canal of Aphrodite aculeata (after M. Ed- wards). Ph, pharynx ; D, intes- tine ; L, hepatic appendages. 370 CH^ETOPODA. divisions or chambers, which correspond to the segments and dilate again into lateral cliverticula and caeca. The constrictions are due to filamentous or membranous septa (dissepimenta), which divide the body cavity into the same number of chambers lying one behind another. The vascular system appears to be closed, so that the clear nutri- tive fluid found in the body cavity, which, like the blood, contains amoeboid corpuscles, does not communicate with the usually coloured contents of the vessels. The dorsal and ventral vessels are not only connected at each end by lateral loops, but also in each segment ; and from these connecting vessels proceed peripheral networks, which extend into the integument, the wall of the alimentary canal, and the branchiae. Special organs of respiration are wanting in almost all the Oligo- chceta. In the marine Worms, on the contrary, branchiae are very generally present, usually as appendages of the parapodia. These branchiae are either simple cirri which have delicate ciliated walls and contain blood-vessels, or are branched (Amphinome) or in some cases are pectinate structures (Eunice) which co-exist with special cirri on the notopodia (fig. 246). The branchiae are sometimes confined to the middle segments (Arenicola), and are sometimes developed on almost all the segments on the dorsal surface, being simplified towards the posterior end of the body (Dorsibranchiata). In the Tubicolce the branchiae are confined to the two (Peciinaria,Sabellidce) or three (Terebella) anterior segments. The respiratory function is, however, also shared (Ccqntibranchiata} by a number of elongated tentacles wMch are grouped in tufts on the head. These are, in the /Sabellidce, supported by a special cartilaginous skeleton, and may have secondary twigs developed upon them. They are either simply arranged in a circle round the mouth, or in two fan-like lateral groups (Serpulidce), the base of which is not unfrequently drawn out into a spiral plate. Such branchial structures, however, also function as organs of touch, as organs for procuring nutriment, and even for building the tubes and shells. Excretory organs. There are usually in all the segments paired segmental organs, which serve as excretory organs. They begin, as a rule, with a ciliated funnel in the body cavity ; they possess a glandu- lar wall, are several times coiled upon themselves, and open to the exterior in each segment by a lateral pore. These glandular passages serve in general for the removal of matters from the body cavity, and in the marine Chcetopoda are used during the NERVOUS SYSTEM. 371 breeding season as oviducts or vasa deferentia, and permit of the passage outwards of the generative products., which have been set free in the body cavity. Amongst the special glands in the body of the Chcetopoda, those cutaneous glands of the Oligochceta which give rise to the thickening (extending over several segments) known as the clitellus or girdle, are especially worthy of remark. The secretion of these glands perhaps assists the intimate connection of the Worms during copula- tion. In the Serpulidce there are present two large glands, which open upon the dorsal surface of the anterior portion of the body and furnish a secretion used in the formation of the tubes in which the animals live. FIG. 301. Brain and anterior portion of the ganglionic chain, a, of Serpula 6, of Nereis, (after Quatref ages) ; O, eyes ; ff, cerebral ganglion ; c, cesophageal commissure ; Ug, suboesophageal ganglion ; e e t nerves to the tentacular cirri and the mouth segment. Nervous system. The longitudinal trunks of the ventral cord are often so closely approached that they seem to form a single cord (Oligochceta]. In the Tubicolce (fig. 301), on the contrary, they are very widely separated from one another, especially in the anterior part of the ganglionic chain (Ser}mla). The visceral nervous system consists of paired and unpaired ganglia, which supply the oral region and especially the protrusible proboscis. Sense organs. Paired eyes upon the surface of the frontal (i.e. 372 CEUETOPODA. CT, praeoral or cephalic) lobe are widely distributed. Eye-spots may also be present upon the posterior end of the body (Fabricia), or may be regularly repeated upon the sides of each segment (Polyophthcdmus). In species of Sabella, pigment-spots with refractive bodies are found even upon the branchial filaments. The large cephalic eyes of the genus Alciope* are the most highly 'developed, being provided with a large lens and a complicated retina. The presence of auditory a. organs seems less frequent. They appear as paired otolithic vesicles ; upon the cesophageal ring of Arenicola, Fabricia, some Sabellidce and young Terebellidce, etc. Besides the tentacles, cirri and elytra, other % portions of the surface of the body may be sensi- tive to tactile sensations. On such parts there are either stiff hairs and tactile setae, or, as in Sphcerodorum, special tactile warts with nerve terminations. Reproduction. In the smaller Clicetopoda asexual generation by fission and gemmation may occur. Either (fissiparous reproduction) a large number of segments of the parent be- come separate and give rise to the body of the new worm, as for example in Syllis prolifera, where a series of the posterior segments, which are filled with ova, become separated by a simple transverse fission, after the formation of a head provided with eyes; or (gemmiparous repro- duction) a single segment only, usually the last, becomes the starting-point for the formation of a new individual. In this way Autolytus pro- lifer, one of the Syllidce, asexually reproduces itself, giving rise to a male and female sexual form, known respectively as Polybostrichus Mulleri^ (male) and Sacconereis helgolandica (female). This is a case of alternation of gene- rations, for the asexual form, Autolytus, gives rise by budding in the long axis to the sexual forms (fig. 302). In this case a whole series of segments are developed Pro. 502. Autolytus cor- nutut, with the male animal Polybostrichua (after A. Agassiz). F, Tentacles ; CT, tenta- cular cirri: /, tenta- cles ; ct, tentacular cirri of the male. * Greeff, " Ueberdas Auge der Alciopiden, etc.," Marburg, 1876 ;and " Unter- suchungen iiber die Alciopiden," Nov. Act. der K. Leap. Akad., etc., Tom XXXIX., Nro. 2. j- Compare besides the works of 0. Fr. Miiller, Quatrefages, Leuckart, and Krohn, especially A . Agassiz, J On alternate Generation of Annelids and the embryology of Autolytus cornutus," Boston Jonrn. Nat. Hist., vol. iii., 18G3. GENERATIVE ORGANS. 373 in front of the last segment of the asexual form, and these segments, after the formation of a head, constitute a new individual. As this process is repeated, a chain of connected individuals is formed, and these, as soon as they are separated, represent the sexual individuals. Among the freshwater Naidce, in Chcetogaster, a regular and continued budding in the long axis leads to the formation of chains, consisting of not less than 12 to 16 zooids, each having only four segments, while the sexual individuals consist of a greater number of segments. A similar process occurs in the mode of reproduction observed by O. Fr. Miiller in Nais proboscidea, from the last segment of which a new zooid is produced. Both generations of Nais, however, be s me sexually mature. [For a more complete account of the asexual reproduction of Chsetopoda, vide Balfour, "Comparative Embryology," vol. i., pp. 283, 284.] The Chcetopoda are, with the exception of the her- maphrodite Oligochceta and certain Serpulidce (e.g., Spi- rorbis spirillum, Protula Dysteri) of separate sexes. Male and female individuals seem occasionally so strikingly different in the Structure of FIG. 303. A parapodium of Tomopterii with a their organs of sense and lo- ass f va and one free ovum < after c - Gegenbaur). comotion that they have even been taken for species of distinct genera. Besides the above- mentioned Sacconereis and Polybostrichus, the asexual generation of which is Autolytus, a similar sexual dimorphism has been shown by Malnigren for Heteronereis, a genus of the Lycoridce, in which the males and females differ both in external form and in the number of their segments. A remarkable case of heterogamy is also afforded by this genus, in that a generation of smaller animals swimming upon the surface alternates with a generation of arger forms living upon the bottom. The generative apparatus of the Oligoc/iceta is very highly deve- loped. The ovaries and testes lie in definite segments, and empty their contents by dehiscence of their walls into the body cavity. Special generative ducts often co-exist with segmental organs in the same segment (0. terricolce), while in other cases the segmen- tal organs are wanting in the generative segments (0. limicolce}. In 374 CH.ETOPODA. the marine Chcetopoda, the ova or spermatozoa originate on the body wall (fig. 303) from cells of the peritoneal membrane, either in the anterior segments alone or along the whole length of the body. The generative products then become free in the body cavity, attain maturity, and pass through the segmental organs to the exterior. Only a few Chcetopoda, as Eunice and Syllis vivipara, are viviparous, all the rest are oviparous ; many lay their eggs in connected groups, and carry them about with them, while the Oligochceta lay theirs in cocoons. Development. The segmentation is unequal. A primitive streak is very generally developed, though sometimes not until the embryo has left the egg. It arises on the ventral side in consequence of the development of a middle layer and from neutral plates of the upper layer. Excepting in the Oliyockceta, the young forms undergo a metamor- phosis and after leaving the egg appear as ciliated larvae, which are provided with mouth and alimentary canal, and essentially resemble, with some modifications, Loven's larva. The capability of renewing lost portions of the body, more espe- cially the posterior part of the body and different appendages, seems to be generally distributed. The Lumbricince and certain marine Worms (Diojxitra, Lycaretus) are even able to replace the head and the anterior segments, with the brain, cesophageal ring, and sense apparatus. Fossil remains of Chwtopoda are found from the Silurian onwards in the most different formations. Order 1. POLYCH^ETA.* Marine Chwtopoda, with numerous setae embedded in the parapodia, usually with distinct head, tentacles, cirri, and branchice. They are for the most part dioecious, and develop with metamorphosis. The marine Chcetopoda must be considered as belonging to a higher grade of life, on account of the sharp distinction of the head which is composed of the prsestomiuni (prseoral lobe) and oral segment (in the Amphinomidce several succeeding segments are also included), and of the presence of the tentacles, tentacular cirri and * Audouin ct Milne Edwards, " Classification dcs Ann elides et description des celles qui habitent les cotes do la France," Annalcs dcs Sc. Nat., Tom. XXVII. to XXX., 1832-33. Dclle Chiaje, " Descrizioni e notomia degli animali senza vcrtebre della Sicilia citeriorc," Napoli, 1841. Quatrefages, " Histoire naturelle des Anneles," Tom. I. and II., 1865. Also the numerous writings of E. Grube and E. Clapamlo POLTCELETA. 375 gills, and also of the setae embedded in prominent parapodia, which serve as aids to swimming. The internal organization, however, is in no way more complicated than that of the Oligochceta. Neverthe- less all these distinctive characters may be less and less marked, and, indeed, so 'completely vanish that it is difficult to draw a sharp line between the Oligochceta and the Polychceta. The parapodia (Capitettidce) and also the setae (Fomopteridce) may be wanting. In rare cases, bundles of setae are present on all the segments behind the head ; they are however arranged in a single row and embedded in a single pair of ventral retractile parapodia in each segment. FIG. 30-1. Head and anterior body segments of Nereis Dumerilii (after E. ClaparMe). O, Eyes ; P, palps ; Ct, tentacular cirri ; -BT, pharyngeal jaws. This arrangement, which is found in Saccocirrus and its allies, pro- bably represents the primitive state, especially as in these animals the character of the nervous system, which lies in the ectoderm external to the dermal muscular envelope, and of the sense organs, which are reduced to two simple tentacles upon the cephalic lobe and to ciliated pits, indicates lower and more primitive conditions. In another and very remarkable type, Polygordius Schn. and Protodrilus Hatsch., not only parapodia and setae but also the external segmentation are wanting. The segmentation of this achsetous and externally unsegmented worm is entirely confined 370 CHJETOPODA. to the internal organization and is, as compared with that of all other Annelida, to a certain extent completely homonomous, inasmuch as the oesophagus is confined to the cephalic segment and does not extend into the anterior segments of the body. Further, the nervous system is connected with the ectoderm along its whole length, and the cerebral ganglion maintains its primitive position at the anterior end, corresponding to the apical plate of the larva ; and the ventral cord is without ganglionic swellings. In all the above points these forms seem to have preserved the primitive An- nelidan structure, and they have therefore been united by Hat- schek into a special class, the Archian- nelida. In the Pobj- chceta the vascular system is compli- cated by the ap- pearance of bran- chiae, which are provided with blood-vessels. In the forms with dorsal branchiae the branchial blood is derived from the dorsal trunk and re- turned to the ven- tral by special vessels. When, on the other hand, as in the tubicolous capito-branchiate forms, the respiratory apparatus is concentrated on a few segments, the vascular system of that part undergoes greater modifications. In the Tere- bellidce (fig. 305), the dorsal trunk dilates above the pharynx to a branchial heart from which lateral branches are given off to the branchiae. In the same region the transvers loeops connecting the FIG. 305. Terebella nebulota, opened from the dorsal side (after M. Edwards). T, Tentacles ; K, Branchiae; Dg, dorsal vessel or heart. POLYCH.ETA. 377 dorsal and ventral trunks may perform the function of hearts, as is also frequently the case in the Oligochceta. Finally the vascular system is in many cases considerably reduced, and, according to Claparede, is entirely wanting in Glycera and Capitella, in which the blood is represented by the perivisceral fluid. The generative organs, unlike those of the hermaphrodite Oligo- chceta, are usually placed in different individuals ; and the males and females are sometimes of very different forms. A number of herma- phrodite Polychceta are, however, known ; such principally belong to genera of the Serpulidce, e.g., Spirorbis, Protula. The development, unlike that of the Oligochceta, is invariably con- nected with a metamorphosis. Segmentation is, as in the Hirudi- nea, usually un- equal, and even the first two seg- mentation spheres are of unequal size. The smaller (animal) half, which segments more quickly, gives rise to smaller segments, which grow round and envelope the larger segments proceeding from the segmentation of the larger half. In the subsequent development a primitive streak makes its appearance in all embryos of Polychceta, sometimes, how- ever, not until the embryo has begun to lead a free life as larva. The ganglia become differentiated later into the ventral chain. In the free-swimming Iarva3 the cilia are rarely distributed over the whole surface of the body (Atrocha*). They are usually confined to special rows (ciliated rings) ; sometimes, as in Loven's larva, there is one row placed in front of the mouth at some distance from the * Compare E. Claparede and E. Metschnikoff, " Beitrag* zur Entwickelungs- geschichtc der Chaetopoden," Zeitschr. fur wiss. Zool., Tom. XIX., 1869. FIG. 306. Larvse of Polychaeta (after Busch). a, Larva of Nereis F, tentacle; Oc, eyes; PrW, prseoral circle of cilia: 0, mouth; A, anus, b, Mesotrochal, larva of Ouetopterus ; Wp, circle of cilia. 378 CH^TOPODA. anterior end of the body (Cephalotrocha, e.g., larva of Polynoe). Sometimes there are two rows, one at each end of the body, con- stituting a praeoral and perianal ring (Telotrocha, e.g., Spio-NepMhys- larva). In addition to these two rings of cilia, incomplete rings may also be present on the ventral surface (Gastrotrocha), or both ventrally and dorsally ( Amplii.tr oclici). In other cases one or more rows of cilia surround the middle of the body (Mesotroc/ia), while the terminal rings (pneoral and perianal) are absent (Telepsavus-Clicztop- terus larva) (fig. 306). Many larvse are provided with long pro- visional setae, which are later replaced by the permanent structures (MetachcBta). In spite of their great diversity of form the Chaetopod larvae can in their later development also be reduced to the type of the larva of Loven. Relatively few forms, as for instance the transparent Alciopidce, live at the surface (pelagic animals) ; most JV of them live near the coast. Numerous forms descend into the deep sea. Many have the power of emitting an intense light, especially species of the genus Chce- topterus which emit light from their an- tennae and appendages. The elytra of Polynoe, the tentacles of Polycirrus, arid the integument of certain Syllidce, are also phosphorescent. Panceri* has shown FIG. 3Q7.Nereii margaritacea. r r Head with protruded j;uv that the seat of the phosphorescence is STaol/lCX - unicellular cutaneous glands, which, in M. Edwards). ", Jaws; i\ Polynoe, were proved to be in communi- tentacles; P, palps; Fc. ten- , -,1 tacular cirri. catlOn Wlth nerves. Sub-order 1. Errantia. Free-swim- ming, predacious PolycJiceta. The praestomium always remains in- dependent and forms, with the oral segment, a well-marked head which bears eyes, tentacles, and usually tentacular cirri. The parapodia are much more developed than in the Tubicolce, and, together with their very variously shaped setae, serve as oars. The anterior portion of the pharynx can be protruded as a proboscis and is divided into several portions ; it is either beset with papillae or contains a powerful masticatory apparatus, which appears at its extremity when protruded (fig. 307). Branchiae may be wanting ; when present, they usually appear as comb -shaped or dendritic * Panceri, " La luce e gli organ! luminosi di alcuni annelidi," Atti clclla E. Acad. scicnsz fi. c mat. di Napoli, 1875. POLYCHJETA, EEEANTlA. 379 tubes on the parapodia (Dorsibranchiata). The Errantia are pre- datory in their habits (Rapacia) and swim freely in the sea; but they may also inhabit temporarily thin membranous tubes. Fam. Aphroditidse. Broad scales (elytra) on the notopodia. These are usually placed on alternate segments, often only on the anterior part of the body. Praestomium, with eyes, with one unpaired and usually two lateral tentacles, to which may be added two stronger lateral ventrally placed tentacles (palps). Proboscis cylindrical, protrusible, with two upper and two under jaws. Aphrodite aculeata Lin. (Hystrix marina Redi.) The back has a thick felt of hairs. Eyes sessile. Numerous setee on the neuropodia. Polynoa scolopcndrina Sav. Ocean and 'Mediterranean. Fam. Eunicidse. Body very long, composed of numerous segments. Prsesto- mium with several tentacles. Parapodia usually uniramous, rarely biramous, usually with ventral and dorsal cirri as well as branchiae. One upper jaw composed of several pieces, and a lower consisting of two plates ; both lie in a sac, the jaw-sack, on the dorsal surface of which runs the pharyngeal tube. Stauroceplialus mttatus Gr., Ilalla (Lysidice) parthenopeia Delle Ch., Naples. Diopatra neapolitana Delle Ch. , Naples. Eunice Harassii Aud. Edw. Fam. Nereidae = Lycoridce* The elongated body is composed of numerous segments. The prtestomium has two tentacles, two palps, and four eyes. The parapodia are either uni- or bi-ramous, and are furnished with dorsal and ventral cirri and with composite setre. Proboscis usually possesses spines, and always two jaws. Nereis Dumerilii Aud. Edw., French and English coasts, to which belongs Hetcronereis fucicola Oerst. N. cultrifcra Gr., Mediterranean N. fucata Sav., North Sea. The form formerly distinguished as Hetcronereis Oerst. differs from Nereis in the great size of the prasstomium and of the eyes, also in the extraordinary development of the parapodia, and in the abnormal formation of the hinder end of the body. It belongs, however, to the same cycle of development as Nereis and Nereilepas. Fam. Glyceridse. Body slender, composed of numerous ringed segments. The prrcstomium is conical and. ringed, with four small tentacles at its point and two palps at its base. The proboscis can be protruded to a great length, and is provided with four strong teeth. The hsemal fluid, coloured by red corpuscles, is contained in the body cavity and the branchial sinuses. There is no special vascular system. Glycera capltata Oerst., North Sea. Fam. Syllidse. Body elongated and flattened, head usually with three tentacles and two to four tentacular cirri. The protrusible proboscis consists of a short proboscis tube, a pharyngeal tube lined by stiff cuticular formations, and a portion characterised by annular rows of points. Sexual and asexual individuals, differing in form, are sometimes found in the same species. Many carry their eggs about with them until the young are hatched. Syllis vittata Gr., Mediterranean. Odontosyllis gibla Clap., Normandy, Autolyim prolifer 0. Fr. Mull., asexual form. The male has been described as PolyTiostriclius Mulleri Kef., the female as Sacconereis helyolandica Mull. SpJu&roelorwn, peripatus Gr., Mediterranean. Fam. Alciopidae (Alcwpea). With two large hemispherical projecting eyes. Ventral and dorsal cirri leaf-like. The proboscis is protrusible, the tube of the proboscis being thin walled and its terminal portion thick walled. At * Compare E. Grube, " Die Familie der Lycoridcen," Jahresber. der Schlesis- Gesellschaft, 1873. 380 CH^TOPODA. its aperture are two hook-shaped papillae. The larvae are in part parasitic in the Cydipplilce. Alciopa Cantrainil Delle Ch., Naples. Fam. Tomopteridae {Gynmocopa). Head well marked, two eyes, bifid prffistomium, and four tentacles, of which two in many species are only present in the young. The mouth segment has two long tentacular cirri which are supported by a strong internal seta. The mouth is without proboscis and jaws. The segments are provided with large bi-lobed parapodia without seise. Tomojjteris scolopendra Kef., Mediterranean. T. onisciformls Esch., northern seas, Heligoland. The genus Myzostoma F. S. Lkt., a small group of hermaphrodite worms whose affinities are doubtful and disputed, may be placed here. They are small, disc-shaped animals, parasitic on Comatula. They possess a soft and ciliated skin, four pairs of laterally placed suckers on the ventral surface, and a protrusible proboscis fur- nished with papilla3 at their anterior end, also a branched alimentary canal which opens at the posterior end of the body. On the sides of the bod}- are five pairs of short parapodia, of which each one bears a hook (with one to three supple- mentary hooks) as well as supporting setas. As a rule, double as many cirri or short wart-like protube- rances are found on the margin of the body. M. glabrum, cirrifcrum F. S. Lkt. Ov FIG. 308. Spirorli* l&i-ig (after Claparede). animal removed from its tube, strongly magnified; b, tube ; T, tentacles ; Bn, brood-pouch with oper- Sub-order 2. Seden- taria = Tubicolae. * The With indistinctly sepa- rated head and short, culum; Dr, glands, Ov, ova; Oe, oesophagus; M, usually not protrusible stomach ; D, intestine. proboscis, without jaws. The branchiae may be entirely absent and in many cases are confined to the two or three anterior segments following the head. In exceptional cases they are placed on the dorsal part of the middle of the body (Armicolidce). As a rule, however, they are represented by numerous filiform tentacles and teri- * E. Claparede, " Eecherches sur la structure des Annelides sedcntaires. ' Geneve, 1873. POLYCH.ETA, TUBICOL.E. 381 tacular cirri upon the head (Captiibranchiata), of which one or more may bear an operculum at its apex to close the tube (fig. 308). The parapodia are short, and are never used in swimming; the notopodia usually carry hair-like setae ; the neuropodia are trans- verse ridges with hooked setae or plates. Eyes are very frequently absent ; in other cases they are present in pairs upon the head or on the terminal segment, sometimes even on the branchial tentacles; in the latter case they are very numerous. The body is often divided into two (thorax and abdomen) or three regions, the seg- ments of which are distinguished by their unequal size. The Tubicolce live in more or less firm tubes which they construct for themselves, and feed on vegetable matter which they procure by means of their tentacular apparatus. In the construction of their tubes the animals are assisted in various ways by the long tentacles or branchial filaments of the head ; thus, for example, the Sabelliclce are said to accumulate fine ooze at the funnel-shaped base of the branchial apparatus by means of the cilia of their tentacles, to mix it with a cement secreted by large glands, and then to transfer it to the edge of the tube ; while the Terebellidce procure the grains of sand for the construction of their tubes by their long and very extensible tentacles. There are also boring Annelids, which pierce limestone and mussel shells, like the horny Molluscs ; e.g., Sabetta saxicola, etc. The development is simplest when the mother possesses a kind of brood-pouch for the development of the young, e.g., Spirorbis spirillum Pag., the eggs and larvae of which remain within a dilatation of the opercular stalk until the young animals are able to construct a tube for themselves. The free-swimming larvae of most Tubicolce, on assuming the form of the worm, lose the ciliary apparatus, while tentacles and parapodia make their appearance. In this condition and sometimes surrounded by delicate membranes, they swim about for some time longer, and, having lost their eyes and auditory vesicles, gradually assume the structure and mode of life of the sexual animal (Terebella). Fam. Saccocirridae. With two tentacles on the prac,stomium, two eyes and the same number of ciliated pits. A single row of retractile parapodia, furnished with simple setse, on either side of the segments of the body. Sacco- cirrus papillocercus Bobr., Black Sea and Mediterranean (Marseilles). Fam. Arenicolidae. Prsestomium small and without tentacles. The pro- boscis is beset with papillae. There are branched gills on the median and posterior segments. The animals burrow in sand. Arcnicola marina Lin. (A. piscatorum Lam.), North Sea and Mediterranean. Fam. Spionidae {Spiodcce). The small praestomium sometimes with tentacu- 332 CH^TOPODA. lar processes, usually with small eyes. The oral segment mostly with two long tentacular cirri, which are usually grooved. Cirriform branchiae are present. Poly dor a antennata Clap., Naples. Spio seticornis Fabr., north seas. Fam. Chaetopteridae. Body elongated and separated into several dissimilar regions. Usually two or four very long tentacular cirri. Dorsal appendages of the middle segments have the shape of wings and are often lobed. The}' live in parchment- like tubes. Telepgavus Costarum Clap., Naples. Ghatopteru* perf/aincntaceits Cuv.. West Indies. Fam. Terebellidae. Body vermiform and thicker anteriorly. The thinner posterior portion is sometimes distinctly marked off as an appendage destitute of setoe. The prsestomium is indistinctly separate from the mouth segment. There is frequently a lip above the mouth. Numerous filiform tentacles, usually arranged in two tufts. There are pectinate or branched, rarely filamentous, gills on a few of the anterior segments. Dorsal prominences (notopodia) fur- nished with simple setae, and ventral transverse ridges (neuropodia) with hooked setae. Tcrclclla concliilega Pall., English coast, Mediterranean. Ampliaretc Grille i Malmgr., Greenland and Spitzbergen. Pectinaria auricotna 0. Fr. Mull., North Seas, Mediterranean. Sabdlaria (Hermclla) gpinulosa B. Lkt., Heligoland. Fam. Serpulidae. Body usually distinctly divided into two regions (thorax, abdomen). Praestomium fused with the mouth segment, which as a rule is pro- vided with a collar. The mouth is situated between two semicircular or spirall}- eoiled plates, from the anterior margin of which spring the branchial filaments. These have secondary filaments arranged in single or double rows, and may be supported by a cartilaginous skeleton, and have their bases connected by a membrane. Spirographis Spallanzanii, Naples. Salella penicillus Lin., North Seas. S. Koll Uteri Clap., Mediterranean. Protula Rudolplii Risso, Mediterra- nean. Filly rana implexa Berk., Norwegian and English coasts. Serpula nor- veyica G-unn., North Sea and Mediterranean. Spirorlis spirillum Lin., Ocean. Order 2. Hermaphrodite Choetopoda without pharyngeal armature and para- podia,. There are no tentacles, cirri, or branchice. The development is direct. The cephalic region is composed of the prsestoinium, which projects as an upper lip, and the mouth segment. It does not essentially differ from the following segments so as to form a special region (fig. 309). Tentacles, palps, and tentacular cirri are never found on it, but tactile papillae are present^in great number, as are also peculiar sense organs which resemble taste buds. Eyes either fail or are present as simple pigment spots. Besides the small gland cells of the * Besides the works of W. Hoffmeister, D'Udekem, and others,' compare : E. Claparede, " Kechcrches anatomiques sur les Annelides, etc., observes dans les Hebrides," Geneve, 1860. E. Claparede, "Recherches anatomiques sur les Oligochaitcs," Geneve, 1862. A. Kowalevski. " Embryologische Studien an Wiirmem und Arthropoden (Lumlricns, Evaxes)," Petersburg, 1861. B. Hatschek, " Studien iiber Entwicklungsgeschichte der Anneliden," Wien, 1878. Fr. Vejdovsky, " Bcitrage zur vergleichenden Morphologic der Anneliden. I. Monographic der Enchytraeiden," 1879. OLIGOCH.ITA. 383 hypodernris there is present in the clitellus a deeper glandular layer (Sdulenschicht Clap.), which consists of finely granular cells embedded in a framework of pigmented and vascular connective tissue and situated between the hypodermis and the external muscular layer. There are but few setae present, and they are never disposed on special parapodia, but always in simple pits in the integument, by the cells of which they are secreted. There are small secondary bristles which serve as a reserve. The blood is usually red, as in the Hirudinea. The alimentary canal is often divided into several regions, the relations of which are most complicated in the Lumbricidce. In Lumbricus, the buccal cavity leads into a muscular pharynx, which is probably used for sucking. This is followed by a long oesophagus extending to the 13th segment, and furnished with a thick layer of glandular cells and several glandular dilated ap- pendages (calcareous sacs). The oeso- phagus is succeeded by a crop, a muscular gizzard, and finally by the intestine itself, the dorsal wall of which is pushed inwards so as to form a longi- tudinal fold, the typhlosole (comparable to a spiral valve). In the Limicolce the alimentary canal is simpler by the absence of a muscular stomach: a pharynx and oasophagus are, however, always present. Reproduction. The Oligochceta are hermaphrodite ; they lay their eggs either singly or united in greater num- ber in a capsule; and they develop without a metamorphosis. The testes and ovaries are paired and placed in definite segments, usually near the an- terior end of the body ; they dehisce their products into the body cavity. The generative ducts possess funnel-shaped openings into the body cavity through which the generative products pass, and may FIG. 309. Lumbricus rulellus (after G. Eisen) . a, The whole worm ; Cl, Clitellus. 5, Anterior end of the body from the ventral side, c, Isolated seta. 384 CH^TOPODA. co-exist in the same segment with segmental organs (Lumbricidve). In the earth-worm, whose generative organs were first accurately described by E. Hering, the female apparatus consists of two ovaries in the 13th segment,* and two oviducts, which begin with trumpet- shaped openings into the body cavity, contain several eggs in a dila- tation and open to the exterior on either side on the ventral surface of the 14th segment. There are in addition in the 9th and 10th segments two pairs of receptacula seminis, which open at the junction of the 9th and 10th and 10th and llth segment respectively. They are filled with sperm in copulation (fig. 310). The male genital organs consist of two pairs of testes in the 10th and llth segments, and two vasa defe- rentia, each of which opens inter- nally by two fun- nels and to the exterior in the 15th segment. Copulation takes place in June and July on the sur- face of the earth at night. The worms apply their ventral surfaces to one another and lie in opposite directions, in such a manner that the openings of the re- ceptacula seminis of one worm are opposite the clitellus of the other. During copulation sperm flows out from the openings of the sperm duct and passes backwards in a longitudinal groove to the clitellus, and thence into the receptaculum seminis of the other worm. In Tubifex and Enchytrceus the ovaries may break up into groups of ova which float free in the body cavity. Special albumen glands and also glands which secrete the substance of the shell of the cocoon are often present. In the breeding season the above-mentioned * The head (prgestomium and buccal region) being reckoned as the first segment. FIG. 310. Generative organs of Lumbricus in segments VIII. to XV. (after E. Hering). T, Testes ; St, the two funnels of the vas deferens on either side ; Vd, vas deferens ; OP, ovary ; Od, oviduct ; Re, receptacula seminis. 385 girdle or clitellus, which is formed of a thick glandular layer, is almost always present. The embryonic development of the Oligochceta presents many relations to that of the Hirudinea. . The unequal segmentation, which is very much alike in the two groups, and the similarity in the method of origin of the mesoderm, from two large cells near the blastopore at the posterior end of the embryo, point to a close relation- ship between these two groups of Annelids. A few Oligochceta, as for example Chcetogaster, are parasitic on aquatic animals ; the rest of them live, some free in the earth, some in fresh water, and some in the sea. Sub-order 1. Terricolse. Oligochseta which live principally in the earth. They have segnieiital organs in the genital segments. Fam. Lumbricidae. Large earthworms with compact skin and red blood. Without eyes. Tufts of vessels surround the segmental organs. Their activity in boring into the earth is of the greatest importance, loosening and exposing the soil to the action of the weather. Lumbricu* L., Earthworm. Prasstomium distinct from the mouth segment. The clitellus includes a series of segments, and is situated nearly at the end of the anterior quarter of the body far behind tlie genital openings. Setae elongated, hook-shaped, arranged in four groups in each segment, each group containing two setaa. The earthworm lays its eggs in capsules, into each of which several small ova, with sperm from the recep- tacula seminis, are emptied ; as a rule, however, only one or but a few embryos are developed. The developing embryo takes up with its large ciliated mouth not only the common mass of albumen, but also the other eggs. Z. agricola H. Hatschek, " Ueber Entwickelungsgeschichte des Echiurus*," etc. Wien, 1880. J. W. Spengel, "Beitrage zur Kenntniss der Gephyreen. I. Mittheil, aim der zoolo- fjisclicn station w.i Ncapcl, 1879 ; II. ZcitscUr. fur iviss. Zool., Tom XIV., 1881. GEP1IYEEA. 387 A D and an inner layer of longitudinal fibres. The latter are connected with the former and also amongst themselves by net-like anastomoses. These dermal muscles cause the folds of the cuticle. Internally to the longitudinal muscles there is another layer of circular muscles. In the Chcetifera two hooked setae are present near the genital opening (fig. 311); these assist locomotion. There may also be present one or two circles of setae at the posterior end of the body (Echiurus). In the Chcetifera (fig. 311), the ante- rior part of the body is elongated to form a kind of proboscis, which projects im- movably and cor- responds to the praeoral lobe (prae- stomium) of the Annelida. The mouth is placed ventrally at the base of the probos- cis. In the Acluzta (Sipunculidce) this proboscis is want- ing; the mouth is placed at the ex- tremity of the an- terior region of the body, which is sur- rounded with cili- ated tentacles and FIG. 312. Sipunculus ddlidce), sometimes at the base of a projecting spoon-shaped hood, which resembles a sucker (Gnathobdellidce) (fig. 319). The mouth leads into a muscular pharynx provided with glands. The anterior part of the pharynx, which may be distinguished as the buccal cavity, is armed (Gnathobdelli- dce) with three serrated chiti- nous plates (fig. 319, a, b), or more rarely with a dorsal and ventral plate (Branchi- o'bdellidce), or it is provided with a protru- sible proboscis, which lies free in its anterior part (Rhynchobdellidce). The pharynx leads into a stomach, which forms a straight tube in the axis of the body and sometimes shows con- strictions, which correspond with the segments ; sometimes it is produced into a larger or smaller number of lateral caeca. From the stomach a short rectum, which is sometimes also provided with crcca, leads to the anus. The anus is placed at the posterior pole of the body, dorsal to the sucker. Excretory organs. Segmental organs are pre- sent, one pair to each segment in the middle region of the body. Their number, however, ; and setae, with a a b FIG. 319. Cephalic region of the Medicinal Leech. The three jaws are visible, b, One of the jaws isolated with the finely serrated free edge. FIG. 320. Longitudinal section through the Medicinal Leech (after R. Leuckart). Z>, in- testinal canal ; G, cerebral ganglion ; Gk, ganglionic chain ; Ex, excretory canals or segmental organs (water -vascular sys- tem). 396 ANNELIDA. varies very considerably, since, for instance, Branchiobdella astaci, parasitic on the gills of the cray-fish, has but two pairs, while the Gnathobdellidce usually possess seventeen pairs. Unicellular glands are present in the Hirudinea in great numbers in the skin and in the deeper layers of the connective tissue. The former secrete a finely granular mucous fluid, which covers the skin ; while the more deeply situated glands, which lie beneath the dermal muscular tunic, secrete a clear viscid substance, which quickly hardens outside the body and is used to form the cocoons when the eggs are laid. These glands are espe- cially numerous in the region of the genital openings. A blood-vascular system is always present, but in different degrees of development. Portions of the body cavity are transformed into vessel- like trunks, and as a result of this organs which lie in the body cavity teem to be enclosed in blood sinuses. The two lateral vessels and the me- dian blood sinus, which always en- closes the ventral ganglionic chain and sometimes also the alimentary canal (Clepsine, Piscicola), may be interpreted in this manner. In most of the Gnathobdellidce the blood is red, the colour being due to the fluid part of the blood and not to the corpuscles. Special respiratory organs are wanting, excepting in Branchellion and some allied leeches, which pos- sess leaf -like branchial appendages. The nervous system* in all cases is highly developed. The cerebral ganglia are characterized by a peculiar arrangement of the nerve cells which give rise to swellings on the surface of the ganglia (described by Leydig as a follicular arrangement) (fig. 321). * Hermann, " Das Centralneirensystem von Hirudo mcdicinalis," Munchen, 1875. FIG 321. Anterior end of Hirudo (after Leydig). G, Cerebral ganglion with subcesophageal ganglionic mass ; Sp, sympathetic ; A, eyes ; Sb, sense organs. HIEUDINEA. 397 This is also the case with the ganglia of the ventral cord, and especially with the siib-cesophageal ganglia, on which there are often four longitudinal series of such ganglionic swellings, two median and ventral, and two lateral projecting dorsally. The two longitudinal trunks of the ventral ganglionic chain are invariably closely approached to one another in the middle line, and their ganglia are connected together in pairs by transverse com- missures. In the Gnathobdellidce two nerve trunks are given off to the right and left from each pair of ganglia, while from the brain and the last ganglion, which may be called the caudal ganglion and is formed of several ganglia fused together, a much greater number of nerves pass off. The nerves passing off from the brain supply the sense organs and the mus- cles and skin of the cephalic disc (ancerior sucker) ; the nerves of the ventral chain are distributed in their proper segments, (and those of the terminal ganglion supply the ventral sucker. An unpaired median longitudinal cord (Faivre, Leydig), which passes from ganglion to ganglion between the two halves of the ven. tral cord, most probably corresponds to the unpaired nerve which Newport discovered in insects. A system of visceral nerves was dis- covered by Brandt. It consists of an intestinal nerve, which arises from the brain and runs close to and above the ganglionic chain and sends branches to supply the caeca of the in- testine. Three ganglia, which in the common leech lie in front of the brain and send their nerve plexuses to the jaws and pharynx, are considered by Leydig as enlargements of cere- bral nerves and very likely control the move- ments which occur in swallowing. Almost all leeches possess simple eyes on the dorsal surface of the anterior ring. In addition there are cup-shaped organs (in Hirudo medicinalis about sixty) on the cephalic rings. These probably give rise to a sense perception comparable to the sensation of taste. Generative organs. The Hirudinea, are hermaphrodite. As in many marine Planaria, the openings of the male and female generative organs are placed one behind the other in the middle FIG. 322. Generative apparatus of the Med- icinal Leech. T, Tes- tis ; Vd , vas deferens ; Nk, epididymisj Pr, prostate ; C, cirrus ; Ov, ovaries with vagina and female genital opening. 398 ANNELIDA. line of the anterior region of the body. The male generative opening lies in front of the female and is usually provided with a protrusible cirrus. The testes lie in pairs in several successive segments and are usually present in considerable numbers (fig. 322). In Hirudo there are nine or ten pairs of testicular vesicles, which are connected with a sinuous vas deferens on either side. Each vas deferens is coiled in front to form a kind of epididymis (fig. 322, Nh) and is then prolonged into a muscular portion, the ductus ejaculatorius, which unites with that of the other side to form an unpaired copulatory apparatus. This is in connection with a well- developed prostatic gland (Pr), and can be protruded either as a two-horned sac (RJiyncobdellidce) or as a long filament (Gnathdb- dettidce). The female generative apparatus consists either of two long tubular ovaries with a common opening to the exterior (PJiyncobdellidce), or of two short saccular ovaries, two oviducts, a common duct surrounded by an al- bumin gland, and a dilated vagina with the genital opening (Gnathdb- dellidce) (fig. 323). In copulation a spermatoplwre, passes out of the male genital organs, and is either received into the vagina of the other animal or at least becomes attached within the generative opening, In any case the fertili- zation of tne m takes P lace with - j n he bodv of the mother. The eS J is laid soon after. For this purpose the animals seek suitable places on stones or plants, or leave the water and, as Hirudo medicinalis, burrow in damp earth. At this period the genital rings are swollen out into the form of a saddle, partly by the turgescence of the generative organs and partly by the great development of the cutaneous glands, the secretion of which is of special importance to the fate of the eggs which are about to be laid. When the eggs are about to be laid, the leech attaches itself firmly by its ventral sucker and, twisting itself about, envelops the anterior part of its body with a viscid mass, which covers especially the genital rings like a girdle arid gradually hardens to form a firmer membrane. A number of small eggs and a considerable quantity of albuminous matter then pass out, and the animal with- Pi. 323.-a, Cocoon, 6, female genera- tive apparatus of Jlirudo medicinalis (after R. Leuckart). niEUDIlTEA. 399 draws its anterior end from this barrel-shaped membrane, which is now filled and which, after the animal has left it, becomes in consequence of the narrowing of the terminal openings a tolerably completely closed cocoon. The number of eggs contained in a cocoon varies but is never large. The eggs are small, yet the young leeches when hatched are of considerable size, those of the Hirudo medicinalis, for example, are about 17 mm. long, and, excepting the fact that they are not sexually mature, have essentially the organization of the adult animal. The young of Clepsine alone are hatched at a very early stage, and differ essentially from the sexual animal both as regards the shape of the body and the internal organisation. They have a simple intestine, are without the posterior sucker, and live a long time attached to the ventral surface of the mother ; and it is not until they have received a considerable quantity of newly secreted albuminous matter that they obtain an organization which fits them to lead a free life. The development of the embyro of Clepsine among the Rhyncob- dellidce and Neplidis and Hirudo amongst the Gnathobdellidce is better known. The segmentation is always unequal. The mouth is formed early, and through it, after the formation of the pharynx and intes- tinal canal, the albumen contained in the cocoon is taken into the intestine of the growing embryo by means of swallowing movements of the pharynx. The Leeches live for the most part in water or temporarily in damp earth. They move partly by " looping " with the help of their suckers, and partly by swimming with active undulations of the usually flattened body. Many of them are parasitic on the skin or the gills of aquatic animals, e.g., on fishes and the cray-fish ; most of them, however, are only occasional parasites on the outer skin of warm-blooded animals. Certain forms are predaceous and, as for example Aulastomum gulo, eat snails and earthworms, or, like Clepsine, suck snails. They do not feed exclusively on any special genus of animals, and their diet is not always the same in the different periods of their existence. Hirudo medicinalis in its young stage lives on the blood of insects, then on that of frogs, and only when it has attained sexual maturity is a diet of warm blood necessary to it. Fam. Bhyncobdellidae. Leeches with proboscis. Body elongated, cylindrical, or broad and flat ; with an anterior and posterior sucker, and a powerful pro- trusible proboscis in the buccal cavity : with paired eyes on the anterior sucker. Organs concerned in the formation of blood corpuscles occur (so-called valves) in the dorsal contractile vessel. Piscicola Blainv. (Iclithyol)dellidfc}. P. cjcometra L., on -fresh water fish. P. respirans Tr., with lateral vesicles which dilate as 400 BOTIFERA. the blood enters. Pontoltdella muricata L..on Rays. Branc hellion torpedinis Sav., Clepsine Sav., (Clcpsinidce}, Cl. Uoculata Sav., Cl. complanata Sav., CL marginata 0. Fr. Mull. Hcementaria mexicana de Fil., H. officinalis de Fil., both in the Lagunes of Mexico, the latter used for medicinal purposes. H. GMlanii de Fil., in the river Amazon. Fam. Gnathobdellidae. Leeches with jaws. Pharynx armed with three fre- quently serrated jaws, and folded longitudinally. In front of the mouth there is a ringed, spoon-shaped process, which forms a kind of oral sucker. The cocoon has a spongy shell. Hirudo L. Usually with 95 distinct rings, of which four are upon the spoon-shaped upper lip. The three anterior rings, the fifth and the eighth, bear the five pairs of eyes. The male genital opening lies between the 24th and 25th, the female between the 29th and 30th rings. The three jaws are finely serrated and can be moved like a circular saw in a manner well adapted to inflict a wound, which readily heals, in the external skin of man. The stomach has eleven pairs of lateral casca, of which the last pair is very long. The cocoons are deposited in damp earth. H. medicinalis L., with the variety distinguished as officinalis, possesses 80 to 90 fine teeth on the free edge of the jaws and attains a length of about six inches. They were formerly common in Germany and are still frequently to be found in Hungary ind France. They are cultivated in special ponds and take three years to attain sexual maturity. Ilcemopsis vorax Moq. Tand, the horse-leech. 30 coarse teeth on the edge of the jaws, which enable it to inflict wounds on soft mucous membranes. The horse-leech is indigenous in Europe, and espe- cially North Africa. It attaches itself to the interior of the pharynx of horses, cattle and men. Aiilastomum gulo Moq. Tand. Also known as the horse- leech, feeds on Mollusca, Nephelis Sav., N. vulgaris Moq. Tand. Fam. Brancblobdellidae. The body in the extended condition is nearly cylindrical and is composed of few unequally ringed segments. There is a bilobed cephalic lobe without eyes, with a well -developed sucker at the posterior end of the body. Pharynx without proboscis, with two flat jaws lying one above the other. Branchioldella parasita Henle, B. astaci Odier. CLASS IV. ROTATORIA * = ROTIFERA. With a retractile ciliated apparatus at the anterior end of the body, with cerebral ganglion and excretory canals ; without heart or true vascular system. The sexes are separate. The Rotifera are Worms which can be derived from Loven's larva and have nothing to do with the Arthropoda, since they are without limbs and do not develop metameres. The body of the fiotifera is certainly externally segmented and divided into more or less sharply * Ehrenberg, " Die Infusionsthierchen als vollkommene Organismen," Leipzig, 1838. Dujardin, " Histoire naturelle des Infusoires," Paris, 1841. Dalrymple, Phil. Trans. Roy, Soc. 1844. Fr. Leydig, " Ueber den Bau unddie systematische Stellung der Raderthiere,'' Zcitsclir. fur wiss. ZooL, Bd. VI.. 1854. F. Cohn, "Ueber Raderthiere," Zeitschr.fur wiss. Zool., Bd. VII., 1856, Bd. IX., 1858, Bd. XII., 1862. Gosse, " On the Structure, Functions and Homologies of the Manducatory Organs of the class Rotifera," Phil. Trans., 1856. W. Salensky, " Beitrage zur Entwickelungsgeschichte des Brachionus urceolaris," Zcitsclir. filr wiss. ZooL, Tom. XXII., 1872. EOTIFEEA. 401 defined and very dissimilar regions, but the internal organs show no trace of any corresponding segmentation. There is therefore no true segmentation, i.e., division of the body into metameres. It is usually possible to distinguish an anterior region of the body, in which the whol3 of the viscera are situated, and a posterior movable foot-like region, which terminates in two opposed pincer-like styles and is used both in locomotion and for attachment. The broad anterior portion of the body, as well as the narrow posterior region, is often divided by transverse constrictions into several rings, which can be drawn into one another like the rings of a telescope and can be bent more or less freely upon one another. The anterior cili- ated and usually re- tractile apparatus whieli projects at the anterior end, and is termed the trochal disc, or from its like- ness to a rotating wheel, the wheel or- gan, is an important characteristic of the Rotifera. Very fre- quently, especially in the parasitic forms, this trochal disc is re- duced, and in certain cases entirely aborted (Apsilus). In Notom- mata tardigrada the trochal disc is reduced to a small ciliated lip round the mouth ; in Hydatina (fig. 324) to the margin of the head, the whole circumference of which is ciliated. In other cases the ciliated edge projects over the head and forms the so- called double wheel, e.g., Philodina, Brachionus, or becomes a ciliated cephalic shield, e.g., Megcdotrocha, Tubicolaria. Finally, it may be produced into ciliated processes of various form (Floscularia, Steplianoceros). As a rule, the cilia form a continuous border, starting from the mouth and returning to it. The cilia are chiefly 26 CBl FIG 324. Hydatina senta (after F. Cohn). a. Female; I, male. Wpr, Trochal disc; CBl; contractile vesicle; Wtr t ciliated funnel of the excretory apparatus (Ex) ; K, jaws ; Dr, salvary glands ; Md, stomach, Ov, ovary ; T, testis ; P, penis. 402 EOTIFERA. concerned in locomotion, but in addition they play an important part in attracting small particles of food. There is also a second row of delicate vibratile cilia, extending on either side from the dorsal edge of the trochal disc to the mouth [parts of the continuous border of cilia just mentioned as starting from the mouth], which is placed on the ventral side of the trochal disc. These cilia serve to guide the small food particles which are captured by the trochal disc into the mouth. Alimentary canal. The mouth leads into a dilated pharynx (fig. 324), provided with a special armature. The parts of the armature are in continual movement, and serve for mastication. Following the pharynx there is a short cesophageal tube ; this leads into the digestive sac, which is lined with large ciliated cells. The anterior or gastric part of this cavity is wide, and receives two large glandular tubes, which may sometimes be resolved into unicellular glands. They may be explained from their function as salivary or pancreatic glands. The posterior narrow intestinal part usually opens into a eloacal chamber, which is likewise ciliated and opens on the dorsal surface at the point where the foot-like posterior region joins the anterior part of the body. In some Rotifera, as for example Asco- morpha, Asplanchna, the intestine ends blindly. A blood-vascular system is always wanting, and the body cavity is filled with a clear vascular fluid. The structures, erroneously described by Ehrenberg as vessels, are in reality the transversely striped muscles and muscular networks beneath the integument. Respiration is carried on by the general surface of the body; special organs of respiration are wanting. Excretory organs. The so-called respiratory canals are excretory, and correspond to segmental organs. They consist of two sinuous longitudinal canals with cellular walls and with fluid contents, and they communicate with the body cavity by ciliated funnel-shaped openings placed at the end of short ciliated lateral branches (vibratile organs). They open into the cloaca either directly or by means of a contractile vesicle (respiratory vesicle). The nervous system is allied to that of the Platyhelminthes. The central part of it consists of a simple or bi-lobed cerebral ganglion placed above the oesophagus, and giving off nerves to peculiar cuta- neous sense organs and to the muscles. Eyes are often present, and lie upon the brain either as an x-shaped unpaired pigment body or as pairel pigment spots provided with refractile spheres. The above- mentioned cutaneous sense organs, which are probably tactile, have EOTIFEKA. 403 the f orm of prominences beset with hairs and setae, or even of tubular elongated processes of the skin (respiratory organs of the neck), beneath which the sensory nerves end in ganglionic swellings. Generative organs. The sexes are separate, and are distinguished by a strongly marked dimorphism. The very small males have neither cesophagus nor intestinal canal, which are reduced to a string- like rudiment ; and they leave the egg completely developed. Their generative organs are reduced to a testicular sac filled with spermatozoa, the muscular duct of which opens at the hinder end of the body, sometimes on a papilliform protuberance. The generative organs of the females, which are far larger than the males, consist of a roundish ovary filled with developing ova, and of a short oviduct which contains one or but few ripe ova, and usually opens into the cloaca. Almost all Rotifera are oviparous; and their eggs are distinguishable into thin-shelled summer eggs and thick-shelled winter eggs. They carry both kinds of eggs about on their body, but the summer eggs not unfrequently undergo their embryonic development in the oviduct. The summer eggs probably develop parthogenetically, since at the season of the year when they appear the males are not to be found. The thick-shelled winter eggs, which are often dark coloured, are produced in the autumn and fertilized. Development. As far as the embryonic development is known, it shows a great agreement with that of many Gasteropoda (Calyptrcea). The ova undergo an irregular segmentation. The cells proceeding from the smaller segmentation spheres become accumulated at one pole, and finally enclose the darker coloured yolk cells completely, so that a two-layered embryo is formed. The cells of the outer layer are much poorer in granules than are those of the central entoderm layer, and form the ectoderm. A depression of the ectoderm is formed on the (later) ventral surface, from the side walls of which the two lobes of the trochal disc grow out (like the oral lobes of mollusc embryos). The hinder portion of the depression becomes the posterior part of the body, at the base of which a pit forming the first rudiment of the cloaca makes its appearance. The mouth and the anterior part of the alimentary canal are developed anteriorly at the bottom of the depression. The ganglion arises from the ectoderm in the cephalic region. There are no reliable observations on the formation of the mesoblast. In the male embryo the development takes a different course, the alimentary canal not being completely developed. The free development takes place either 404 EOTIFERA. without or with an inconsiderable and sometimes retrogressive metamorphosis. This latter is most striking in the Floscularidce, which are fixed in the adult state. The Rotifera principally inhabit fresh water, in which they swim about by means of the trochal disc, and sometimes they attach them- selves to foreign objects by means of the forked glandular foot. When thus attached, they extend the anterior part of the body, and the cilia begin to move. The currents set up by the latter convey to the mouth food material, such as small Infusoria, Algse, Diatoms. Some species live in gelatinous sheaths and delicate tubes, others (Conochilus) are fixed by their foot in a common gelatinous mass, and are united to form a free-swimming colony. A relatively small number are parasitic. It seems that many species are able to endure drying, if it be not too prolonged. Fam. Floscularidae. Fixed Rotifera with^a long transversely ringed foot, usually surrounded by gelatinous coverings and tubes. The margin of the head has a lobed or deeply cleft wheel-organ. Floscularia proltoscidea Ehrbg., Steplianoceros Eiclilwrnii Ehrbg., Tubicolaria najas Ehrbg., Mcliccrta ring ens L., Conochilus volvosc, Ehrbg. Fam. Pliilodinidae. Free, often creeping (in a looping manner) Rotifera ; with double-wheeled rotatory organ, and jointed, telescopically retractile foot, without gelatinous investment. Callidina elcgans Ehrbg., Rot'ifer vulgaris Oken (R. rcdivivus Cuv.), Pliilodina crytliroplitlialma Ehrbg. Fam. Brachionidae. Rotifera with bifid or multifid wheel-organ ; with broad, shield-shaped armoured body ; and foot ringed, or with short segments. Brachionus Balteri 0. Fr. Mull., B. militaris Ehrbg., Euchlanis triqiietra Ehrbg. Fam. Hydatinidae. Edge of wheel-organ prolonged into numerous processes (multifid) or only sinuous ; skin delicate, often ringed ; foot short, usually forked, with two setge or pincer -shaped. Ilydatina Ehrbg., II. scuta 0. Fr. Mil", with Entcroplea liydatince Ehrbg., as male. Notommata tardigrada Ldg., N. Brackionus Ehrbg., N. parasita Ehrbg. Farn. Asplanchnidae. The sac-like unarmoured body is destitute of rectum and anus. Asplanclina Sieboldii Ldg., A. myrmeleo Ehrbg., Ascomorplia germanica Ldg. Two groups of small animals are allied to the Rotifera : (1) the Echinoderidse which Dujardin and Greef regarded as connecting links between Vermes and Artliropoda (Echinodercs Dvjardinii Clap., E. setigcra Greef) ; and (2) the Gastrotricha * or Ichthydina ( Chatonotus). * Compare E. MeUclmiTtoff, " Ueber einige wenig bekannte niedere Thier- formen," Zcitschr. fur miss. Zool., Tom. XV., 1865. Also the works of H. Ludwig and 0. Butschli. AETHBOPODA. 4.05 CHAPTER X. ARTHROPODA. Laterally symmetrical animals with heteronomously segmented body and jointed segmental appendages ; with brain (suprao&sophageal ganglia) and ventral nerve cord (ganglionic chain). The most important characteristic which distinguishes the Arthro- poda from the closely allied segmented worms, and is an essential condition of a higher organization and grade of life, is the possession of jointed segmental appendages which serve as organs of locomotion. ~Irf place of the unjointed parapodia of the Chcetopoda, jointed appendages more adapted for locomotion and confined to the ventral surface, are present. Every segment may possess a ventral pair of appendages which, in the simplest case, are short and consist of only a few joints (Peripatus) (fig. 325). While in the Annelida loco- FIG. 325. Peripatus capensis (after Moseley). motion is effected by the movements of the segments and undulatory movements of the whole body, in the Arlhropoda the function of locomotion is removed from the chief axis of the body to the secondary axes, i.e., to the paired appendages, with the result of the possibility of a much more effic.'erit discharge of the function. The appendages enable the Arthropoda not only to swim and creep with much greater ease and speed, but also to execute various kinds of more complicated movement, e.g., running, climbing, springing, and flying. The Arthropoda are, therefore, true terrestrial and aerial animals. The high development of the organs of locomotion as paired appendages leads of necessity to a second essential property, viz., to the lieteronomy of the segmentation, and in connection with this to the hardening of the outer layer of the skin to form a firm exo-skeleton. If the function of the limbs is to be perfectly discharged, there will be need of a considerable mass of muscle, the points of attachment of which can only be furnished by the integument of the body. The insertions of the appendages and their muscles, therefore, require 406 AHTHEOPODA. rigid surfaces, which are obtained partly by the development of internal chitinous tendons and plates, and partly by the hardening of the integument and the fusion of several segments to form larger armoured regions. It is only when the movements are simpler and resemble those of Annelids, that all the segments remain independent and bear similar appendages along the whole length of the body (larvae, Myriapoda). In general, three regions of the body can be distinguished, the head, the thorax, and the abdomen, the appendages of which possess respectively a different structure andfunction(fig.326). The head constitutes the short and compact anterior region of the body, is covered by a hard integument, encloses the 'brain and bears the sense organs and mouth-parts (jaws). The appendages of this region are modified to form the antennae, and jaws. The head of Arthropods, as compared with that of Annelids, contains, besides the frontal (pneoral) or antenna! segment and the oral segment, in FIG. 326. Head, thorax and abdomen of an Acridium, seen from the side. St, Stigmata j T, tympanum. FIG. 327. Squilla mantis. A', A" Antennae ; Ef, Sf" the anterior maxillipeds on the cephalo-thorax ; ', B", E", the three pairs of biramous feet. addition at least one jaw segment, the appendages of which may, in larval life (Nauplius), still function as legs. Usually, however, several of the succeeding segments whose appendages function as jaws form part of the head. The middle portion of the body, or thorax, is likewise distinguished by a relatively intimate fusion of some or all of its segments, as well as by the hardness of its integument. It is sometimes sharply marked off from the head, sometimes fused with the head to form a INTEGUMENT. NERYOUS SYSTEM. 407 region of the body called the cephalothorax (fig. 327). The thorax bears the appendages which are of most importance in locomotion. The posterior portion of the body, or abdomen, is composed of distinctly separate rings, and is, as a rule, without appendages. When the latter are present, they serve partly as aids to locomotion (abdominal feet), partly for respiration, or for carrying the eggs and for copulation. More rarely, as for example in the scorpions, the abdomen is divided into a broad anterior region, the proedbdomen, and a narrow movable posterior region, the postabdomen. ' The skin, as in the Annelida, consists of two different layers,- 1 an external firm, usually homogeneous chitinous layer, and an internal soft layer, which is composed of polygonal cells (matrix, hypodermis) and secretes in layers the at first soft chitinous cuticle (fig. 22). The latter usually becomes hardened by the deposition of calcareous salts in the chitinous basis, so as to form the firm exoskeletal armour, which, however, is interrupted between each segment by thin connecting membranes. The various cuticular appendages of the skin (fig. 22, a, 6, c), which may have the form of simple or pennate hairs, of filaments, setae, spines and hooks, originate as processes and outgrowths of the cellular matrix. The chitinous cuticle together with its appendages is from time to time, principally in the young stage during the period of growth, renewed, the old cuticle being cast off as a continuous membrane (ecdysis, or moult). The muscular system never constitutes a continuous envelope, but the muscles are usually broken up into segments which corre- spond with the segmentation of the animal. The muscles of the body are arranged in longitudinal and transverse bundles in the different segments, and are frequently interrupted. There are in addition large groups of muscles, which move the' appendages. The muscular fibres are always cross-striped. The internal organization is allied to that of the Annelida, but does not present such a well-marked internal segmentation. The nervous system consists of brain, ossophageal commissures and a ventral cord. The latter usually has the form of a ganglionic chain (fig. 328), arid is placed beneath the alimentary canal. Some- times, however, it exhibits great concentration, and may have the form of an unsegmented ganglionic mass beneath the oesophagus. The segmentation of the ventral ganglionic chain presents in details the greatest variations; in general, however, it corresponds to the heteronomous segmentation of the animal, in that in the larger regions of the bodv, which have arisen by fusion of several segments, 408 AETIIEOPODA. aii approximation or fusion of the corresponding ganglia has taken place. In one case only, viz., in the Pentastomidce, which in form and grade of life resemble the intestinal worms, the dorsal part of the oesophageal commissure is not swollen out to form a cerebral ganglion, and the central parts of the nervous system are com- pressed together into a common gangli- onic mass beneath the 03sophagus. In all other cases the brain is a large gangli- onic mass lying above the oesophagus? and connected by means of the cesophageal ring with the anterior ganglion of the ventral chain, which is usually placed in the head and is known as the suboeso- phageal ganglion (fig. 328). The sense nerves arise from the brain, while the ganglia of the ventral chain send nerves to the muscles, organs of locomotion and the body covering. Visceral nervous system. In addition to the brain and ventral ganglionic chain, which are comparable to the cerebro- spinal system of Vertebrata, we can distinguish in the larger and more highly organised Arthropods a visceral nervous system (sympathetic], which consists of special ganglia and plexuses connected with the other system and specially distributed to the alimentary canal. In the higher Ar- thropoda, paired and unpaired visceral nerves are very generally present, both of which have their origin in the brain. Sense organs. Eyes are most generally FIG. 328. Nervous system of distributed, and are only absent in a few paragitic f orms . J n their simplest 'form r _ " they are paired or unpaired structures p ia ~ d p n the bi - ain ' ^-^ with re - fractive bodies, and with or without a \v the larva of Coccinella (after Ed. Brandt,). Ofr, Frontal ganglion ; G, brain ; Sg, sub- chain in the thorax and simple lens (stemmata, or simple eyes). The compound eyes, which are always paired, are much more complicated. They are distinguished by the presence of nervous rods and crystalline cone?-, and may be divided into faceted eyes ALIMENTARY CANAL. EXCBETORY OUGANS. 409 and eyes with smooth cornea (Claaocera). The former possess numerous lenses, and are sometimes placed on movable stalks (Decapoda). Occasionally accessory eyes are found on other parts of the body, on the jaws and between the legs of the abdomen (Eupliausia). Auditory organs are found most frequently in the Crustacea as auditory vesicles with otoliths in the basal joint of the anterior antennae, or rarely in the appendage of the abdomen known as the fan (tail of Mysis). In Insecta, auditory organs of a very different structure have been discovered. Olfactory organs are also widely distributed. They are situated on the surface of the antennae, and consist of delicate tubes or peculiar conical projections, beneath which the sense nerves end in ganglionic swellings. Tactile organs. The antennae and palps of the oral appendages and the ends of the limbs have a tactile function. These parts are provided with peculiar hairs and seta?, beneath which nerves end in ganglionic swellings. Alimentary canal. An independent digestive apparatus is always present, but its structure and degree of development are very various. The alimentary canal is only exceptionally degenerated and absent (Rhizocephala). The mouth is placed on the ventral surface of the head. It is furnished with a projecting upper lip, and usually with paired appendages, which are used either for masticating or for piercing and sucking. A narrow or wide oasophagus leads into the intestine, which either simply traverses the axis of the body or is disposed in several coils. The oasophagus and midgut (chyle stomach) may even be divided into several regions, and may possess salivary glands and hepatic appendages of various size. Excretory organs. Urinary organs are widely distributed. In the simplest form they appear as cells on the surface of the intestine (lower Crustacea), in a more highly developed state as tubular filiform diverticula of the hindgut (Malpighian tubes) (fig. 329). In the Crustacea, glands are present in the shell (shell glands') and in the base of the posterior antenna*; they are regarded as the morphological equivalents of segmental organs. The circulatory and respiratory organs present the greatest differences in the various groups of the Arthropoda. In the simplest case the clear, more rarely coloured blood fluid, which is often corpusculated, fills the body cavity and the interstices of all 410 AETHROPODA. the organs, and is circulated in an irregular manner by the move- ments of the different parts of the body. Not unfrequently (Achtheres and Cyclops] the circulation is effected by the regularly repeated movements of certain organs (intestine, vibratile plates, etc.) ; in other cases, a short saccular heart is present dorsally above the intestine ; or a long vascular tube (the dorsal vessel), divided into chambers, serves as a propelling organ. From this, vessels (arteries) may arise, which conduct the blood in definite directions. Vessels for returning the blood (veins) may also be present. These either begin in the body cavity, or are connected with the ends of the arteries by capillary vessels. The vascular system seems never to be completely closed, since even when the circulation is most complete, lacunar spaces of the body cavity are found inserted in the course of the vessels. Respiration is very frequently effected, especially in the smaller and more deli- cate species of Arihropoda, by means of the entire surface of the body. In the larger aquatic forms, the function of respi- ration is assumed by special tubular, usually branched appendages of the limbs (branchiae) ; while in the air-breathing Insects, Centipedes, Scorpions, and fyiiders, respiration is performed by means of in- ternal branched tubes filled with air (trachece) or by pulmonary sacs (fan trachece). The reproduction of the Artliropoda is usually sexual, but sometimes takes place by the development of unfertilized ova (parthenogenesis). Ovaries and testes are in their origin paired, as are also the gene- rative ducts, which often have a common terminal portion and open by a median generative aperture (Insecta, Arachnoidea). With a few exceptions (Cirripedia, Tardigrada), the sexes are separate. Males and females frequently differ essentially in their entire form and organization. In rare cases, for example in the parasitic Fio. 329. Alimentary canal of Pontia bragsicce (after 2Vew- port). JE, Proboscis (Maxillae) ; Sp, salivary glands ; Oe t oeso- phagus ; S, sucking stomach ; 3fff, Malpighian tubes; Ad, rectum. CRUSTACEA. 411 % Crustacea, there is such a marked sexual dimorphism that the males remain small and dwarfed, and are attached like parasites to the body of the female. During the act of copulation, which is often limited to the external union of the two sexes, the spermatophores are fastened to the female genital segment or thrust into the vagina by the organ of copulation, whence they sometimes pass into a ' special receptaculum seminis. Most Arthropod** are oviparous, but in almost every group there are viviparous forms. The eggs are frequently carried about by the mother, or deposited in protected places where food may easily be obtained. The embryonic development (i.e., development within the egg) is characterised, except in the case of the small stout embryos of the Cydopidce, Pentastomidce and Acarina, by the presence of a ventrally placed primitive streak, from which especially the ganglionic chain and the ventral parts of the segments proceed. The more or less complex embryonic development is usually followed by a complicated metamorphosis, during which the young form as larva undergoes several ecdyses. Numerous seg- ments and parts present in the adult are not ^infrequently wanting in the just-hatched larva ; in other cases, all the segments of the adult are indeed present, but are not as yet fused together to form regions. In such cases, the larvae resemble the Annelida in their homonomous segmentation, and in their locomotion and mode of life. The meta- morphosis may however be retrogressive ; the larvae are hatched with sense organs and appendages, but in the further course of develop- ment they become parasitic, lose their eyes and organs of locomotion, and develop into strange unsegrnented (Lerncece) or entozoon-like (Pentastomidce) forms. The Arthropoda are no exception to the general rule that the aquatic forms which breathe by gills are lower and, from a genetic point of view, older than the air-breathing members of the same group, inasmuch as the Branchiata or Crustacea are the older, the Tracheata the younger types. CLASS I. CRUSTACEA.* Aquatic Arthropoda, ivhich breathe by means of gills. They have two pairs of antennce ; numerous paired legs on the thorax t and usually also on the abdomen. * Milne Edwards, " Histoire naturelle des Crustaces," 3 vol. and atlas. 1838- 18-40. C. Glaus, " Untersuchunqren zur Erforschung dcr geneulogischen Grund- lage des Crustaceensystems," Wien, 1876. ilTYB 412 ARTIIEOPODA. The Crustacea, whose name is derived from the body-covering (which is often hardened), are principally aquatic animals. Some forms, however, can live on land, and possess respiratory organs adapted for breathing air. An important character of the group is the great number of paired appendages. The appendages of all the segments, even those of the head, may be used in locomotion (fig. 330). As a rule, the head fuses with the thorax, or at any rate with one or more of the thoracic segments, to form a cephalothorax ; which is followed by the remaining free thoracic segments. Some- times, however, these two regions of the body remain distinct. The head and thorax are seldom so sharply marked off from one another as, for example, in the Insecta : usually certain appendages, the so-called maxillipeds, occupy an, intermediate position between legs and jaws, and being placed at the boundary between the two regions may be rec- koned either as be- longing to the head or the thorax. The fusion of the seg- ments may be very extensive ; not only may the head and thorax be united, but the boundary be- tween thorax and abdomen may vanish, and the segmentation may even disappear. As a general rule, the form of the body presents extraordinary differences in the various groups. A redupli- cature of the skin arching over the thorax and covering the body as a shell is frequently present. This fold of the integument constitutes, in extreme cases, a mantle-like investment, which may develop calcareous plates and occasion a certain resemblance to Lamelli- branchs (Cirripedia). In other cases the body has quite lost its segmentation, and the animal resembles a worm (Lerncece, Sacculina). On the head there are usually two pairs of antennae, which function as sense organs and sometimes also as organs of locomotion or of prehension. There is a pair of large jaws (the mandibles), one on each side of the mouth, over which a small plate, known as the upper lip, often projects. The mandibles are simple but very rigid and hard masticating plates, which are usually toothed and correspond Fis. 330. Gammarus neglectus (after G. O, Sars). A', A*, The two antennae ; Ef, maxilliped ; F F\ first to seventh thoracic feet ; Sf, anterior swimming feet. CEUSTACEA. 413 R morphologically to the coxal joint of a limb, the following joints developing into a palp-like appendage (mandibular palp). Then follow one or more pairs of weaker jaws (maxillce), and one or more pairs of maxillipeds, which more or less resemble the legs and, in parasitic forms, are often used for adhering (fig. 331). In parasitic forms, the upper and under lips not unfrequently give rise to a suctorial proboscis, in which the styliform mandibles are placed. The appendages of the thorax, of which at least three pairs are present (Ostracoda), present an extremely various structure, in accordance with the mode of life and the use made of them. They are either broad leaf - shaped swimming feet (PhyUopoda), or bi- ramous appendages (Copepoda) ; they may serve to produce currents in the water like the feet of the Girripedia, or they may be used for crawling, walking, and running (Isopoda, Deca- poda). In the latter case, some of them end with hooks or chelae. Finally the appendages of the abdomen, which frequently itself moves in toto and assists in locomotion, are either exclusively locomotory as jumping or swim- ming feet (Ampkipoda), in which case they usually differ from the appendages of the thorax ; or -they serve with their appendages for respiration, as well as for carrying the eggs, and for copulation (Decapodct). The internal organization is not less varied than is the external form. In the lower forms, the nervous system often consists of a ganglionic mass, which surrounds the oasophagus and is not further FIG. 331. Young stage (larva) of the Lobster (after G. O. Sars). a, The larva seen from the side ; R, ros- trum ; A', A", antennae ; Kf" third maxilliped ; .F, anterior ambulatory leg. b, mandible with palp ; c. anterior maxilla with two blades and palp ; d, pos- terior maxilla with vibratile plate (scaphognathite) ; e, first, f, second maxilliped. 414 AUTIIEOPODA. segmented. This ganglionic mass corresponds to the brain and ventral cord and gives off all the nerves. In the higher Crustacea, a distinct brain and ventral ganglionic chain, which is usually elongated and of very varied form, as well as a rich plexus of visceral nerves and ganglia of the sympathetic system are always present. Of sense organs, eyes are the most widely distributed. They may have the form either of simple eyes (paired or unpaired), or compound eyes with smooth or faceted cornea ; in the latter case they are often placed on movable stalks, which are attached to the lateral regions of the head. Auditory organs are also present usually in the basal joint of the anterior antenna, rarely in the caudal plate at the posterior end of the body (My sis). The delicate hairs and filaments of the anterior antenna are probably olfactory organs. The digestive canal is, as a rule, straight, extending from the mouth to the anus at the posterior end of the body. In the higher forms the oesophagus is usually dilated in front of the mesenteron (midgut) into a stomach or crop, which is armed with chitinous plates. The mesenteron is provided with simple or ramified hepatic creca. Excretory organs. The so-called shell glands of the lower Crustacea are regarded as urinary organs, as are also the glands opening at the base of the posterior antenna in the Malacostraca. In the Entomostraca the latter are only preserved during larval life. Short tubes, which correspond to the Malpighian tubes of the Tracheata, may also be present on the rectum (Amphipoda). The circulatory organs present every possible degree of perfection, from the greatest simplicity to the highest complication of an almost closed system of arterial and venous vessels. The blood is usually colourless, but is sometimes green or even red, and as a rule contains cellular blood corpuscles. Respiratory organs are either entirely wanting, or are repre-. sented by- branchial tubes on the thoracic or abdominal appendages. In the first case they are often contained in a special branchial cavity at the sides of the cephalothorax. Generative organs. With the exception of the hermaphrodite Cirripedia and Isopoda, all Crustacea are of separate sexes. The male and female generative organs usually open on the boundary of the thorax and abdomen, either on the last or the antepenultimate thoracic ring, or on the first abdominal segment. The two sexes are very often distinguished by a number of external characteristics. CETJSTACEA. 415 The males are smaller, sometimes even dwarfed, and then attached to the females like parasites. They almost always possess appa- ratuses for holding the females and for transferring the spermato- phores during copulation. The larger females, on the other hand, frequently carry the eggs about with them in sacs, the membranes of which are secreted by the so-called cement glands. Development takes place either directly or by metamorphosis. The metamorphosis is sometimes retrogressive. "When the develop- ment is direct, the young animals, on leaving the egg, already have the body form of the adult. The larva known as the Nauplius (fig. 332) is of great importance as a point of departure. This larva possesses an oval body, on the ventral side of which are present three pairs of appendages for the sense of taste, the prehension of food, and for locomotion. These appendages correspond to the two pairs of antennae and mandibles respectively. Parthenogenesis is said to occur in certain groups (Phyllo- poda). Almost all Crustacea are carnivorous. Some of them suck the juices of living animals on which they are parasitic. For the systematic review of this heterogeneous group, it is convenient to divide the numerous orders into two \ / /&7^m f series. 1. The small simply organized Cms- FlG . 332 ._ NaupUus larva of tacea, the number and form of whose Baianus, seen from the side. appendages is very various, will be in- eluded as EntomOStraCa (0. Fr. Miiller). (second antenna) ; Mdf, third m , -, . , , ,, , T>T TT appendage (mandible); Ob, To this group belong the orders Phyllo- upper lip ; z>, intestine. poda, Ostracoda, Copepoda, and Cirripedia. 2. The higher Crustacea, characterised by a definite number of segments and appendages, may be grouped together as Malacostraca (Aristotle). In this group are included the orders of Arthrostraca (Amphipoda and Isopoda), and Thoracostraca (Cumacea Slomatopoda, Sckizopoda, and Decapoda). In addition there is the genus Nebalia, whicn has been hitherto erroneously placed with the Phyllopoda, but which is to be regarded as the representative of an ancient group connecting the PhyUopoda with the Malacostraca, and may be opposed to the latter as Lept- ostraca. Finally, in addition to these chief divisions, there is a number 4 J ti AETIIROPOPA. ENTOMOSTEACA. of Crustacean orders, for the most part fossil and belonging to the oldest formations, which present in their development no certain trace of the Nauplius form so characteristic of the true Crustacea, and are in all probability related to the Arachnoidea. These orders, which may be grouped together as the Gigantostraca, are the Merostomata and Xipkosura, to which the Trilobita are possibly allied. 1 . ENTOMOSTRAC A. Order 1. PHYLLOPODA.* Crustacea with elongated and often distinctly segmented body ; usually with a flat , shield-like carapace, or laterally compressed bivalve shell, formed by a reduplicature of the skin. There are, at least, four pairs of leaf -like, lobed swimming feet , The animals belonging to this order differ very considerably in form and size, in the number of their segments and appendages, as well as in their internal structure. They all, however, agree in the structure of their lobed, leaf -like feet. In their form, internal organization and development they appear to be the most primitive of Crustacea, and may be regarded as the least modified descendants of ancient types. The body is either cylindrical, elongated and clearly segmented, without free reduplicature of the skin, e.g. Branchi2ms (fig. 333), or it may be covered by a broad and flattened shield, which only allows the posterior part of the body to project uncovered, e.g. Apus. In other cases the body is laterally compressed and is enclosed by a bivalve shell, from which the anterior part of the head projects (Cladocera) ; or finally the laterally compressed body is completely covered by a bivalve shell (Estheridce). Sometimes the head is more sharply distinct, while the thorax and abdomen are not so clearly distinguishable from each other. As a rule, the posterior segments only are without appendages. The hind end of the abdomen is very often curved ventralwards and forwards, and bears two rows of posteriorly directed claws, the two last of which arise at the point of the caudal appendage, and are by far the * Besides the works of O. Fr. Miiller, Jurine, M. Edwards, Dana, compare Zaddach, " De Apodis cancriformis anatome et historia evolutionis," Bonnas, 1841. E. Grube, " Bemerkungen liber die Phyilopoden," Archivfur Naturgesch, 1853 and 1855. Fr. Leydig, " Monographic der Daphniden," Tubingen, 1860. P1ITLLOPODA. 417 strongest. In other cases a pair of fin-like appendages are present constituting the caudal fork (Branchipus'). Appendages. On the head there are two pairs of antennae, which however, in the adult animal, may be rudimentary or peculiarly modified. The anterior antennae are small, and bear the delicate olfactory hairs. The posterior antennae frequently have the form of large biramous swimming appendages, but in the male may also have a prehensile function, e.g., Branchipus. In other cases (Apus) they are rudi- mentary and may even be enirely absent. Two large mandibles are always present beneath the well developed upper lip; they possess a toothed, biting edge, and in the fully developed condition are invariably destitute of palps. The mandibles are followed by one or two pairs of slightly developed maxillae. A kind of under- lip is in many cases present, in the form of two promi- nences behind the mandibles The legs, which are placed on the thorax, are usually very numerous, and are smaller towards the poste- rior end of the body. They are lobed, leaf-like, bira- mous structures, and func- tion as swimming feet ; they also assist in procuring food. They consist of the following parts: a short basal portion, which is usually provided with a masticatory process and is followed by a long foliaceous stem with setae on its inner edge ; this is continued into the multilobed internal branch [endopodite] of the biramous limb, while it bears on its outer de the external ramus [exopodite] with marginal setee, and nearer 27 FIG. 333. Male of Branchipus stagnallg. Eg, Heart or dorsal vessel with a pair of slit-like openings in each segment ; D, intestine ; M t mandible ; Sd, shell gland; Br, branchial appendages of the eleven pairs of legs ; T, testis. 418 CRUSTACEA. its base a vesicular branchial appendage. The anterior, or even all the legs (Leptodora) Eaay have the form of prehensile feet, and be destitute of branchial appendages. The Phyllopods possess a large pair of eyes, which are sometimes fused together in the median line. In addition a small median simple eye (Entomostracan eye) may persist. They have a saccular or chambered heart, which controls the regular circulation. Coiled excretory organs, known as shell glands, are sometimes present; they open to the exterior by a special aperture on the posterior maxilla. The function of respiration is performed by the entire surface of the body, the area of which is much increased by the reduplicature of the skin forming the carapace ; also by the folia - ceous swimming feet, and especially by the surface of the branchial appendages. Reproduction. The Pliyllopoda are of separate sexes. The males are distinguished from the females by the structure of the first pair of antennae which are larger and more richly provided ivith olfactory hairs, and also by their anterior swimming feet whicSi are armed with prehensile hooks. In general the males are iess fre- quently met with than are the females, and, as a rule, only at definite seasons of the year. The females of the smaller Pliyllopoda (Clado- cera) are able to produce eggs without copulation and fertilisation ; and these eggs, the so-called summer eggs, develop spontaneously and produce generations containing no males. In certain genera of the Brancliiopoda, e.g., Artemia and Apus, parthenogenesis is the rule ; the males, indeed, have only been known a few years. The females usually carry the eggs about with them on special appendages, or in a brood pouch beneath the shell on the dorsal surface. The just hatched young either possess the form of the sexually mature animal (Cladocera), or undergo a complicated metamorphosis, leaving the egg membranes as a nauplius larva with three pairs of appendages (Bran- chiopoda). A few of the Pliyllopoda live in the sea, the greater number inhabit stagnant freshwater ; some of them are found in brine pools. Sub-order 1. Branchiopoda.* Pliyllopoda, with clearly seg- mented body, often enclosed in a flat, shield-shaped, or laterally compressed bivalved shell, with from ten to about thirty or more pairs of foliaceous swimming feet. * Schaffer, " Dcr krebsartige Kieferfuss," etc. Regensburg, 1756. A. Kozu bowski. ;; Ueber den mannlichen Apus cancriformis," Archt'r fur Naturcjescli, Tom XXIII., 1857. C. Claus. " Zur Kenntniss dcs Baucs und der Entwickelung von Branchipus und Apus," etc., Gottingen, 1873. PniLLOPODA. BEANCHIOPODA. 419 The alimentary canal is provided with two lateral hepatic appen- dages, which are, as a rule, branched and racemose and only excep- tionally short and simple. The heart appears as an extended dorsal vessel with numerous paired lateral slits, and may extend throughout the whole length of the thorax and abdomen (Branchipus). The genital organs, which are always paired, are placed by the side of the alimentary canal, and open at the boundary between the thorax and abdomen. In the females the genital openings are small slits ; in the male there may be protrusible copulatory organs at the openings (Branchipus}. The males are distinguished from the females principally by the fact that the anterior, or two anterior pairs of legs, are armed with hooks (Ustkeridce), or by the modification of the posterior antennae to form a prehensile apparatus (Branchipus). Hemarkable is the rare occurrence of the males ; they seem only to appear under certain conditions and in definite generations, which alternate with parthe- nogenetic generations. The eggs during development are generally protected within the body of the mother, and are carried about either in a saccular brood-pouch of the abdomen or between the valves of the shell on filiform (Estheria, Branchipus), or in vesicular (Apus) appendages of different pairs of legs (9th to llth). Tho eggs, so far as is known, undergo a complete segmentation. When hatched, the young animal has the form of a Nauplius larva with three pairs of appendages, of which the anterior (which become the anterior antennre) are in the Estheridce only represented by slightly de- veloped setigerous prominences. On the other hand, in Apus the third pair is small and rudimentary. Almost all the Branckiopoda belong to inland waters, and prin- cipally inhabit shallow fresh-water pools. When the latter dry up,, the eggs, preserved in dry mud, remain capable of development. Some species, as Artemia salina, are found in brine pools. Brancliipus pisciformis Schaff = B. stagnalis L., without a shell, found in the lakes of Germany, together with Apus' cancriformis. B. diapJianws Pre>., France. Artemia salina L., in salt pools, near Trieste. Montpellier. They sometimes lay eggs with a hard shell, sometimes they are viviparous. Ajw* cancriformis Schaff, with shield-shaped shell, Germany. The males, which are rare, can be recognized by the normal formation of the eleventh pair of appen- dages. They live in puddles and fresh- water lakes, together with Brancliipus. Estlicria cycladoides Joly L., with perfect shell. Sub-order 2. Cladocera.* Water-fleas. Small laterally com- * Besides the- works already quoted, compare H. E. Strauss, "Memoire sur les Daphina dc la classe des Crustaces," Mem. du Mus. d'Jiist nat., Tom V. and 420 CHUSTACEA. pressed Phyllopoda, whose body, with the exception of the head, which projects freely, is usually enclosed in a bivalve shell. They have two large antennae, which are used in swimming, and four to six pairs of swimming feet. The Cladocera are small simply organized Phyllopods, whose resemblance to the larvae of . the shelled Branchiopoda, particularly to the larva of Estheria with its six pairs of legs, gives the best indica- tion of the probable origin of the group. Unlike the anterior antennas, which are short, the posterior are modified to form biramous swimming appendages beset with numerous long setae. The four to six pairs of legs are not always foliaceous swimming feet, but in many cases have the form of cylindrical ambulatory or prehensile appendages. The abdomen, which is ventrally flexed, develops on its dorsal side several prominences, which serve to close the brood pouch. It usually consists of three free segments, as well as the terminal anal portion, which is beset with rows of hooks. The anal portion begins with two dorsal tactile setae and ends with two hooks or styles, representing the caudal fork (fig. 334). The internal organization is simple in correspondence with the small size of the body. The compound eyes fuse together in the middle line to form a large, continually trembling, frontal eye, be- neath which the unpaired simple eye usually remains. A special sense apparatus, whose function is not quite clear, appears in the region of the neck, in the form of an aggregation of ganglion cells. The heart has the form of an oval sac, with two transverse lateral venous ostia and an anterior arterial opening. Its pulsations are rhythmic, and succeed one another quickly. In spite of the want of arteries and veins, the circulation of the blood, which contains amoeboid cells, is completed in definite tracts marked out by lacunae and spaces in the body. The looped and coiled shell gland is always present. The cervical gland, which functions as an organ of attachment, is less widely distributed. The \ sexual glands lie in the thorax as paired VI, 1819 and 1820, Leydig. " Naturgeschichte der Daphniden," Tubingen, 1860. P. E. Miiller, "Bidrag til Cladocerernes Fortplantings historic," Kjobenhavn, 1868. Gr. 0. Sars, " Om en dimorph Udvikling samt Generations vexel hos Leptodora," Vidensk. Selsk. Fork., 1873. A Weismann, " Beitrage zur Kenntiss der Daphnoiden," I IV.. Leipzig, 1876 and 1877. C. Claus, " Zur Kenntiss der Organisation und des feineren Baues der Daphniden, Zeit. f. miss, tool, Tom XXVII, 1876. C. Claus, " Zur Kenntniss des Baues und der Organi- saton der Polyphemiden," Wien, 1877. C. Grobben, " Die Embryonalentwick- elung von Moina rectirostris," Arleiten aus dem zool. vergl. anatom. Institut. 1 1 Band, Wien, 1879. TIIYLLOPODA. CLA.DOCERA. 421 tubes by the side of the alimentary canal. In the ovaries groups of four cells are separated ; one cell of each group becomes an ovum, while the rest are employed as nutritive cells for the nourishment of the ovum, which increases in size and absorbs fat globules. The ovary is directly continuous with the oviduct, which opens dorsally beneath the shell into the brood-pouch. The testes, like the ovaries, lie at the sides of the intestine and are continuous with the vasa def erentia, FIG. 331. "DapTinia. C, Heart the slit-like opening of one side is visible ; D, alimentary canal; L, hepatic diverticulum ; A, anus ; G, cerebral ganglion ; O, eye ; Sd, shell gland ; Br, brood-pouch beneath the dorsal reduplicature of the shell. which open to the exterior ventrally behind the last pair of appen- dages or at the extreme end of the body, the openings being some- times situated on small slightly protrusible prominences. The smaller males usually appear in the autumn ; they may, however, also be present at any other time of the year, and, as recent investi- gations have proved in a tolerably satisfactory manner, always when 422 CETJSTACEA. the conditions of life and nourishment are unfavourable. Before the appearance of the males, hermaphrodite forms * sometimes make their appearance with an organization which is half male and half female. At the season when males are not present, normally in the spring and summer, the females produce the so-called summer eggs, which contain a large quantity of oil globules and are surrounded by a delicate vitelline membrane. They develop rapidly within the brood- pouch between the shell and the dorsal surface of the mother, and after the space of only a few days give rise to a fresh generation of young Cladocera, which escape from the brood-pouch. The embryonic development takes place accordingly under extremely favourable conditions, which depend upon the rich supply of food yolk in the large eggs, and are sometimes favoured by the secretion of additional food material within the brood-pouch. At the season when the males appear, the females, under the like influence of unfavourable nourishment and independently of copu- lation, begin to produce so-called winter eggs, which are incapable of developing without fertilization. The number of these hard-shelled winter eggs is always relatively small. They are, therefore, distin- guished from the summer eggs by their larger size and the greater quantity of food yolk ; and their origin in the ovary is accompanied by much more extensive processes of absorption. The Daphnidce live for the most part in fresh water. Certain species inhabit deep inland lakes, brackish water, and the sea. They swim quickly, and usually with a jumping movement. Some of them attach themselves to solid surrounding objects by means of a dorsally placed organ of attachment, the cervical gland. When the body is thus fixed, the swimming feet seem to be able by their vibrations to set up currents in which small food particles are swept towards the animal. Sida crystallina 0. Fr. Mviller. The six pairs of lamellar legs beset with long swimming setas. The rami of the swimming antennae two- to three-jointed. Daplmia pulex De Geer. D. sima Liev. Five pairs of legs, of which the anterior are more or less adapted for prehension. One ramus of the swimming antennas is three-jointed, the other four-jointed. Polyphemus pedicvlus De Geer. In the lakes of Switzerland, Austria, and Scandinavia. Ecadne Nordmanni Lov6n, North Sea and Mediterranean. Leptodora, Jiyalina Lillj., in lakes. * Compare especially W. Kurz, " Ueber androgyne Missbildung bei Clado- ceren," Sitzungsber der Altad. der Wisscnsch. Wien. 1874. Also Schmanke- witsch. OSTEACODA. 423 Order 2. OSTRACODA.* Small, usually laterally compressed Entomostraca, with a "bivalve shell and seven pairs of appendages, which function as antennce, jaws, creeping and swimming legs. There is a pediform mandibular palp, and a short abdomen. The body of these small Crustacea is nnsegmented and is completely enclosed in a bivalve shell, which gives the animal a resemblance to a mussel. The two valves of the shell join together in the middle line, and are fastened together by an elastic ligament along the middle third of the back. The action of this ligament is opposed by a two- headed adductor muscle, which passes from one valve of the shell to the other and causes impressions discernible from without. The common tendon of the two heads of this muscle lies nearly in the F' MX" SM. MX' Md, Ob FIG. 335. Female Cypris before sexual maturity ; the right valve of the sneil has been removed, A', A", first and second pair of antennae ;. Ob, upper lip ; Md, mandible with pediform palp ; G, cerebral ganglion with unpaired eye ; SM, adductor muscle ; MX', MX", first and second pair of maxillae ; F 1 , F", first and second pair of feet ; Fu, caudal fork ; M, stomach ; D, intestine ; L, hepatic tube ; Ge, rudimentary genital organs. middle of the body. The edges of the valves are free at both ends and along the ventral side. In the marine Cypridinidce there is a deep indentation in the edges of the valves, to allow the antennae to pass out. When the valves of the shell are open, several pediform appendages can be protruded on the ventral side, which enable the animal to move in the water either by crawling or by swimming. * H. E. Strauss-Diirkheim, " Memoire sur les Cypris de la classe des Crus- taces," Mem. du Mug d'hixt. not., Tom VII., 1821. W. Zenker, " Monographic der Ostracoden," Arckiv.fiir NaturgesoK., Tom. XX.. 1854. C. Glaus, "Beitragc zur Kentniss dcr Ostracoden. Entwickelungsgcschichte von Cypris." Marburg. 1868. C. Glaus. " Neue Beobachtungen fiber Cypridinen," Zeitschr. fiir miss. Zool. t Tom XXIII. C. Claus, "Die Familic dcr Halocypridcn." Sckriften toologiscTien Inhalt<, cement glands, d, The smaller male seen from the side ; Mxf, Mxf", maxillipeds. Many forms of parasitic Copepoda, for example Lemanthropus and Chondracanthus, do not get beyond this stage of body segmenta- tion, and obtain neither the swimming feet of the third and fourth pairs, nor a fifth thoracic segment separate from the stump-like abdomen; others, for example Achtheres, by the loss of the two anterior pairs of swimming feet, sink back to a still lower stage (fig. 344). All the non -parasitic and many of the parasitic Copepoda pass in the successive moults through a larger or smaller number of de- velopmental stages, in which the still undeveloped segments and appendages make their appearance, and the appendages already 434 CEUSTAOEA. present undergo further segmentation. Many parasitic Copepoda, however, pass over the series of Nauplius forms, and the larva, as soon as hatched, undergoes a moult, and appears at once in the youngest Cyclops form, with antennae adapted for adhering and mouth parts for piercing (fig. 344). From this stage they undergo a retrogressive metamorphosis, in which they become attached to a host, lose more or less com- pletely the segmentation of the .* body which grows irregular in shape, cast off their swim- ming feet, and even lose the eye, which was originally pre- sent (Lernceopoda). The males, however, in such cases often remain small and dwarfed, and adhere (fre- quently more than one) firmly to the body of the female in the region of the genital open- ing (fig. 345). In the Lerncea (fig. 346) such pigmy males were for a long time vainly sought for upon the very peculiarly shaped body of the large female (fig. 346, c, d) which carries egg tubes. At last it was discovered that the small cyclops-like males (fig. 346, a), lead an independent life, and swim about freely by means of their four pairs of swim- ming feet; and that the fe- males (fig. 436, 6), in the copulatory stage resemble the males, and that it is only after copulation that they (the females) become parasitic and undergo the considerable increase in size and modification of form which characterises the female with egg-tubes. FIG. 345. The t\vo sexual animals of Chandra, canthus gibbosm magnified about six diameters. a, Female seen from the side; b, from the ventral surface with adhering male ; c, male strongly magnified. An', Anterior antennae ; An'', antennae for attachment; F', F", the two pairs of feet; A, eye; Ov, egg-tubes; Oe, oesophagus ; D, intestine ; M, mouth parts ; T, testis ; Vd, vas deferens ; Sp, spennatophore. COPEPODA. 435 1. Sub-order: Eucopepoda. Copepoda with swimming feet, the rami of which are two or three jointed. They have biting or piercing and sucking mouth parts. 1. Gnathostomata. For the most part non-parasitic; oral apparatus adapted for mastication ; fully segmented body. Fam. Cyclopidae. Mostly fresh- water animals, without a heart, and with a simple eye. The second pair of antenna? are four-jointed and never biramous. The feet of the fifth pair are rudi- mentary in both sexes. The male employs the anterior antennae for prehension. Cyclops coronatus Cls., Cantlwc ampins minutus Cls., liarpactlcus clidlfer 0. Fr. Mull., North Sea. Fam. Calanidae. The anterior antennas are very long, only one of them is modified for prehension. The posterior antenna? are bira- mous. Heart always present. The feet of the fifth pair are, in the male, modified to assist in copula- tion. Cetoclillus SL'ptentrionalis Goods., Diaptomus castor Jur. IrencBiis Patersonii Tempi. Fam. Notodelphyidae. Structure of body like that of the Cyclopidcc. The posterior antenna? modified for attachment. The two last tho- racic segments are fused in the female and form a brood cavity for the reception of the eggs. They live in the branchial cavity of As- cidians. Notodclpliys agilis Thor. 2. Parasita* (Siphonosto- mata). Mouth parts adapted for piercing and sucking, usually with incomplete seg- mentation of the body and reduced abdomen. The posterior antennae and niaxillipeds end with hooks for attachment. Some of GoJm FIG. 34,6. Lcrnaa branckialii. a, Male (abotif, 2 to 3 mm. long). Oe, Eye; G t brain; T, testis ; M, stomach ; F 1 to F ir , the four pairs of swimming feet ; Sp, spermatophore sac. b, Female (5 to 6 mm. long at the time of copulation). A', A", the two pairs of an- tennas; Z>, intestine; R, proboscis; Mxf, maxilliped. c, Female of Lerneea branchialis after copulation undergoing metamorphosis ; d, the same with egg sacs, natural size. * Besides Steenstrup and Liitken I.e. compare A.v. Nordmann, " Mikro- graphische Beitrage zur Naturgeschichte der wirbellosen Thiere," Berlin, 1832. H. Burmeister, " Beschreibung einiger neuen und wenig bekannten Schmarot- 436 CBFSTACEA. them still swim freely, but most of them live on the gills, in the pharynx, and on the outer skin of fishes. Some live within the tissues of their host (Penella), and nourish themselves on the blood and juices of the latter. Fam. Corycaeidse. Anterior antcnnse short, few jointed, and similar in both sexes. The posterior antennae unbranched, with clasping hooks, usually differ- ent according to the sex. Mouth parts often arranged for piercing. Median eye and lateral eyes often present. They live partly as temporary parasites. Coryctsus elongatus Cls., Sappliirina fulgens Thomps. Fam. Chondracantliidae. Body elongated, often without distinct segmenta- tion, and furnished with pointed outgrowths. Abdomen stump-like. The two anterior pair of swimming feet are represented by bifid lobes, the others are wanting. There is no suctorial proboscis, the mandibles are sickle-shaped. The pear-shaped males are small and dwarfed, and attached, often in pairs, to the body of the female. Chondracanthm gibbosns Kr. (on Lophius). Ch. cornutus O. Fr. Mull., on flat fish (Pleuroncctidce) (fig. 345). Fam. Caligidas. Body flat, with shield-like cepkalothorax, and very large genital segment which in the female is especially swollen. Abdomen, on the contrary, is small and more or less reduced. There is a suctorial tube and styliform mandibles. Four paired biramous swimming feet enable the animal to swim rapidly. They live on the gills and the skin of marine fish, and the females have long string-like egg tubes. Caligus rapav Edw., Cccrops Latreillil Leach. Fam. Lernaeidse. The body of the female vermiform or rod-shaped ; unseg- mented, with outgrowths and processes on the head. Mouth parts piercing with suctorial tube. There are four pairs of small swimming feet. The females become attached to fishes, in which the anterior part of their body is buried. Lcrnceocera cyprinacea L., Penella sagitta L., Lerncea brancMalis L. (fig. 346). Fam. Lernaeopodidae. Body separated into head and thorax, abdomen rudimentary. Mouth parts piercing with suctorial tube. The external maxilli- peds attain a considerable size, and in the female unite at their points so as to form a single organ of attachment, by means of which the animal adheres permanently. Swimming feet completely absent. The males, which are more or less dwarfed, have large free clasping feet, and are, like the females, without swimming feet. Aclitliercs percarum Nordm. (fig. 344). Ancliorella uncinata 0. Fr. Mull, (on species of Gadus). 2. Sub-order: Branchiura.* Carp-lice. With large compound eyes, and long protrusible spine in front of the suctorial tube of the mouth ; with four pairs of elon- gated biramous swimming feet. zerkrebse," Nova acta Ac. Cces. Leop., Tom XVII., 1835. C. Glaus, " Ueber den Bau und die Entwickelung von Achtheres percarum," Zeitschr fiir wisx. Zool., 1861. C. Glaus, " Beobachtungen iiber Lernaeocera, etc., Marburg, 1868. * Jurine, " Memoire sur 1'Argule foliace," Annales du Museum d'hist. nat., Tom. VII., 1806. Fr. Leydig, " Ueber Argulus foliaceus," Zeitsclirfilr n-iss. Zool., Tom II., 1850. E. Cornalia, " Sopra una nuova specie di crostacei sifonos- tomi," Milano, 1860. C. Glaus, " Ueber die Entwickelung, Organization und systematische Stellung der Arguliden," Zeitsclirfiirrviss. Zool., Tom XXV., 1875. COPEPODA. BRANCHIURA. 437 The Brancldura are often placed near the Caligidce, but they differ from them and from the true Copepoda in several essential particulars. In the general body form they certainly resemble the Caligida except in the hind part of the body, which is split into two plates (caudal fins). Their internal structure, however, and the structure of the appendages distinguish them from the above-mentioned parasitic Crustacea. A large suctorial tube projects above the mouth, and in it are concealed finely serrated mandibles and styliform maxillae. A little above this proboscis there is inserted a long cylindrical tube, which terminates in a retractile styliform spine, and contains the ducts of a St pair of glandular tubes said to be poison glands. Powerful organs of attach- ment are placed on each side of and beneath the mouth they consist of two parts (1) of an an- terior pair of appendages which correspond to the anterior maxillipeds and are in Argulus modified into large sucking discs, the hook-bearing terminal por- tion being reduced ; and (2) of a posterior pair, which corresponds to the second pair of maxillipeds, and is provided with numerous spines on its broad basal portion, a tactile protube- rance and tw r o curved termi- nal claws at its extremity. Next to these come the four paired swimming feet of the thoracic re- gion, which, with the exception of the last, are, as a rule, covered by the sides of the cephalo-thoracic shield. Each of these consists of a large many-jointed basal portion, and two much narrower rami, which are beset with long swimming setaa and in their form and setigerous investment are not unlike the biramous appendages of the Cirripedia, being like them derived from the Copepod-like feet of the larva (fig. 347). FIG. 347. Young male of Argulus foliaceug. A', Anterior antennae ; Sg, sucker (anterior maxilli- ped); Kf", maxilliped; Sf, swimming feet, It, rostrum ; St, spine ; D, intestine ; T, testes. 438 CEL'STAGEA. ] The internal organization recalls that of the Phyllopoda. The nervous system is distinguished by the great size of the cerebral ganglion, and by the ventral chain composed of six closely approxi- mated ganglia. In addition to two large compound lateral eyes, there is present an unpaired tri-lobed median eye. The alimentary canal consists of a short arched ascending O3sophagus, a wide stomach with two lateral ramified appendages, and a rectum which runs directly backwards and opens to the exterior in the median indenta- tion of the caudal fin above the two plates, which correspond to the caudal fork. There are two lateral slit-like apertures in the heart, and a long aorta. The entire surface of the cephalothorax functions as a respiratory organ. There seems, however, always to be a specially strong current of blood in the caudal fin, so that this part of the body may be regarded as a sort of gill. Reproduction. The small, more agile male possesses peculiar copu- latory appendages on the posterior swimming feet. The females do not carry their eggs about in sacs in the typical Copepod manner, but fasten them to surrounding objects. The vitelline membrane of the deposited eggs acquires a vesicular consistence. The young are hatched as larvae, and undergo a metamorphosis. Fam. Argulidae, Carp-lice. Argulus O. Fr. Mull. The anterior pair of maxillipeds modified into large suckers. There is a styliform spine apparatus. A.foliaceus L. (Pou de poissons, Baldner) parasitic on Carps and Sticklebacks. A. corcgoni Thor., A gig ant ens Luc., Gyropeltis Hell. The maxillipeds end in a claw ; styliform spine absent. G. Kollari Hell, parasitic on the branchiae of Ilydrocyon, Brazil. G. Doradis Corn. Order 4. CIRRIPEDIA.* Fixed, and for the most part hermaphrodite Crustacea with indis- tinctly segmented body enclosed by a reduplication of the skin, and a calcareous valved shell. As a rule, there are six pairs of biramous thoracic appendages. On account of the resemblance .of their shell to that of the mussels, the Cirripedia were held to be Molluscs until Thompson and Burmeister, by the discovery of their larva?, satisfactorily proved that they belong to the Entomostraca. They are enclosed in a mussel- * Compare S. V. Thompson, " Zoological researches," Tom. I., 1829. H. Burmeister, "Beitrage zur Naturgeschichte der Raukenf ussier." 1832. Ch. Darwin, "A monograph of the Sub-Class Cirripedia," 2 vol., London, 1851-1854. A Krohn, " Beobachtungen iiber die Entwickelung der Cirripedien," Archiv fiir Natwgesch I860. C. Glaus, " Die Cypris-iihnliche Larve der Cirripedien, etc," Marburg, 1869. K. Kossmann, " Suctoria und Lepadina," Wiirzburg, 1873. CIEEIPEDIA. 439 like shell composed of several (4, 5 or more) pieces. These pieces, which originate by the deposition of calcareous matter in the chi- tinous covering of a large reduplicature of the skin (mantle), are distinguished as scuta, terga, and carina. The animal is invariably fixed by the anterior end of the head, which in the Lepadidce, (fig. 348, a) may be drawn out into a long stalk projecting freely from the shell. In the Balanidce, which are without the stalk (fig. 348, 5), the body is surrounded by an external calcareous tube, usually com- posed of six pieces ; the aperture of the tube is closed by a sort of operculum formed of calcareous plates lying inside (fig. 348, b). In Te FIG. 348 a, Lepas after removal of the right shell. A', Anterior antennae at the end of the stalk ; C, carina ; Te, tergum ; Sc, scutum ; Mk, oral cone ; F,. caudal fork ; P* cirrus or penis ; M, muscle, b, Balanut tintinnabulum (after Ch. Darwin), one-half of the shell has been removed; Tu, Section of the outer shell ; Oo, ovary; Od, oviduct; Oe, opening of oviduct ; Ad, adductor muscle ; Sc, scutum ; Te, tergum ; A', anterior antenna. both cases the attachment is effected principally by the hardening of the secretion of the so-called cement gland, which opens on the penultimate joint of the small and delicate anterior antennae; this joint being dilated to form a sort of sucker. The body, which is surrounded by the mantle and its shell-plates, lies with its hinder region stretched upwards so that the appendages, which are used to cause currents in the water, may be protruded from the slit -like space left on the ventral side between the paired scuta and terga. Appendages and external features. A head with antennae and 440 CRUSTACEA. jaws can be distinguished from the region of the body (thorax) bearing the biramous appendages, but there is no distinct boundary between N these two regions. The anus is situated at the extremity of the small stump-like abdomen, which succeeds the thorax and is often only indicated by two caudal appendages. Posterior antennae are in- variably absent, while the anterior pair persists, even in the adult, as small organs of attachment. The oral apparatus is situated on a ventral prominence of the cephalic region, and consists of an upper lip with palps, two mandibles and four maxillae, of which the two last unite to form a sort of under lip. On the thorax there are usually six pairs of many- jointed biramous appendages, the elongated cirriform rami of which are richly beset with hairs and setae and serve to set up currents in the water in which the particles of food are brought to the animal. The stump -shaped abdomen bears an elongated cirrus, which is bent to- wards the ventral surface between the thoracic appendages, and con- stitutes the male copulatory organ. There are numerous and very pecu- liar variations in the shape of the whole body. Not only may the de- position of calcareous matter in the mantle be wanting, and the bira- mous thoracic appendages be reduced in number or even absent, but the mouth parts and the appendages may also be lost (Peltogastridce), and the body may be reduced to the form of an unsegmented tube, sac, or lobed disc. Nervous system and sense organs. The Cirripedia possess a paired cerebral ganglion and a ventral chain of ganglia, of which there are usually five pairs, but which are sometimes fused to a common ganglion mass (Balanidce). There is a double eye, which, although rudimentary, corresponds to the unpaired Nauplius eye. An alimentary canal is absent only in the Rhizocephala. In the FIG. 349. The organization of Lepas, after removal of the integument. Cd, Cement gland and duct; - L, liver ; T, testis ; Vd, vas deferens ; Ov, ovary ; Od , oviduct ; Cf t thoracic appendages. Other letters as in fig. 348. C.TRRIPEDIA. 441 Lepadidce and the Balanidce, the alimentary canal consists of a narrow oesophagus, a saccular dilated stomach provided with several csecal (hepatic) diverticula, an elongated chyle-forming intestine, and a short rectum, which is only sometimes clearly marked off from the intestine (fig. 349). The Rhizocephala (fig. 354, a), which are with- out an alimentary canal, possess root-like processes of the paren- chyma, which ramify in the viscera, especially the liver of Decapods, and absorb from them endosmotically the nutritive juices (as in Anelasma). Special glandular organs, the so-called cement glands (peculiar to the Cirripedia), open on the sucker of the persistent (anterior) antennae ; the animal is fixed by their secretion, and the Rhizocephala alone seem to be en- tirely without * them. A heart and vascular sys- tem seem to be wanting in all cases. The tubes which are present on seve- ral thoracic ap- pendages o f many Lepadidce are regarded as branchiae, as are also two plicated lamel- lae on the inte- rior of the mantle of the BalanidcB. Generative organs. The Cirripedia are, with a few exceptions, hermaphrodite. The testes are branched glandular tubes, and lie at the sides of the alimentary canal (fig. 349, T). The vasa deferentia which dilate into vesiculae seminales reach to the base of the cirri- form penis, in which they unite to form a common ductus ejacula- torius opening at the point of the penis (Vd). The ovaries in the Balanidce lie in the basal part of the body cavity (fig. 348, Ov) ; in the Lepadidce (fig. 349) they are moved into the prolongation of the head, which is known as the stalk. The oviducts, according to FIG. 350. Aleippe lampat (after Ch. Darwin.) a, Male, very strongly magnified; ^'.antennae; T, testis ; V, seminal vesicle ; D, redu- plicature of the skin ; 0, eye ; P, penis. 6, Longitudinal section through female; F, maxilliped ; Cf, the three pairs of legs; Ov> ovary. 442 CETJSTACEA. a H FIG. 351. a Lntcr'Nauplius larva. A, arms ; 07, proboscis with mouth ; H, frontal horns ; D, intestine ; A', A", 1st and 2nd antenna;; Mdf, mandibular foot (third pair of appendages). I, Metanauplius larva of Salanns befoie the moult. Beneath the skin are the rudiments of the lateral eyes (0) and all the appendages F 1 to -F 1 " of the Cypris stage ; Ff, frontal filament ; ff, unpaired eye ; Dr, gland cells of the anterior horns ; A*~, the antenna? with suctorial disc ; MX rudiment of maxilla.-"" Krohn, open on a prominence on the basal joint of the anterior pair of thoracic appen- dages. The eggs accumulate in the cavity between the mantle and the body in large thin - walled flat- tened sacs, which, in the Lepadidce. are attached to a fold of the mantle and are packed to- gether on the dor- fcal surface of the animal. In spite of the hermaphrodit i s m, there are, accord- ing to Darwin, in certain genera (Ibla, Scalpdlum) very simply orga- nised dwarfed males of peculiar form, the so-called comp I em ent al males, which are attached like para- sites to the body of the hermaphro- dite. There are also dioecious Cir- ripedes with a strongly marked dimorphism of the sexes. This is the case with Scalpel- CIRB1PEDI.L. 443 lum ornatum and Ilia Cuminyii ; also with the remarkable genera Cryptophialus and Alcippe (fig. 350). The males of these forms are not only small and dwarfed, but also, according to Darwin, have neither mouth, digestive canal, nor thoracic appendages. As a rule, two or sometimes more attach themselves to the body of the female. Development. The eggs, while still within the brood-pouch, undergo an irregular segmentation. The clear cells arrange them- selves around the food yolk in the form of a blastoderm, the ventral side of which soon becomes considerably thickened in consequence of the appearance of the mesodermic layer. The larvae leave the egg as Nauplii (fig. 351, a, 6), of oval or pear-shaped form, with unpaired frontal eye, lateral frontal horns,, and three pairs of appendages, of which the anterior is simple, the two next biramous and closely beset with swimming seta3. After several moults, the larva, which has grown to a considerable size, enters on a new stage of de-' velopment, the so-called Cypris stage (pupa) (fig. 352). The reduplica- ture of the skin has the form of a bivalve mussel-like shell, through the gaping ventral edges of which the appendages can .be protruded. While the form of the shell recalls that of the Ostracoda, the structure of the body, so far as the segmenta- tion and form of the appendages are concerned, approximates to that of the Copepoda. The anterior ap- pendage of the Nauplius larva has given rise to a four-jointed antenna, the penultimate joint of Avhich has become large and disc-shaped and contains the opening of the cement gland, while the terminal joint bears in addition to tactile setre one or two delicate lancet-shaped olfactory hairs. The frontal horns are transformed into two conical prominences near the an- terior margin. Of the two pairs of biramous appendages, those which correspond to the second pair of antennae arc cast off, while FIG. 352. Median section through a pupa of Lepag. A' Attaching antenna ; C, carina; Te, tergum; Sc, scutum; Ov, ovary ; G, cerebral ganglion ; Off, ganglionic chain ; D, alimentary canal ; Cd, cement gland ; Mk, oral cone ; Ab, abdomen ; P, rudiment of the penis ; M, muscle. 444 CRUSTACEA. Te the posterior pair becomes the rudiment of the anterior jaws (mandibles) of the oral cone, which is still closed and on which the first rudiments of the maxillae and under lip are already visible. The oral cone is followed by the thoracic region with six pairs of biramous Copepod-like swimming feet, and a minute three- jointed abdomen, which terminates in two caudal appendages and caudal setae. The pupa has a large pair of compound eyes at the sides of the un- paired eye-spot, and swims about by means of its swimming feet. It appears not to take in food. The material necessary for its further changes is stored up principally in the cephalic and dorsal regions in the form of a largely-developed fat body. After swimming about for a longer or shorter time, the pupa fixes itself by the suctorial disc of its bent antennae to some foreign body. The parts of the adult Cirripede are now visible beneath the skin, and the cement gland begins to secrete a cement, which hardens and so brings about the permanent attachment of the young animal. In the Lepadidae, the region of the head above and be- tween the antennae grows so much that it projects from the pupal integument, beneath which the calcareous pieces of the shell of the Cirripede can be seen, and after the moulting of the chitinous skin of the pupa constitutes the fleshy peduncle by which the animal is attached, and into which the rudiments of the ova- ries project (fig. 353). The paired eyes of the free-swimming Cypris larva disappear, while the unpaired pigment spot remains. The mouth parts become fully differen- tiated, and the biramous swimming feet become short, many-jointed cirriform appendages. The Cirripedia are marine animals. They attach themselves to various foreign objects. They are found fixed, usually in groups, to logs of wood, rocks, mussel shells, Crustacea, the skin of whales, etc. Some, as Lithotrya, Alcippe, and the Cryptopialidce, are able to bore into Lammellibranch shells and Corals, while the Rhizocephala are parasitic on Crustacea. In the RliizoceplialcL the body is saccular, FIG. 353. Young Lepas after disappearance of the two horny valves of the shell and the straightening of the anterior part of the head (stalk) , which in the pupa stage is bent. Letters as in fig. 349. CIEEIPEDIA.. 445 and the animal loses all its appendages and its alimentary canal, and extracts the juices of its host (Decapoda) by means of root -like processes (fig. 354). 1. Pedunculata. There is a peduncle and six pairs of biramous feet ; the mantle has usually carina, scuta, and terga. Fam. Lepadidae. Peduncle well marked, and not provided with calcareous plates. There is a membranous mantle, which, as a rule, is provided with five shell plates, of which the scuta and terga lie behind one another (fig. 348, a). Lepas L. (Anatifa Brug.), L. fascicularis Ellis, (vitrea Lam.) Found from the Northern Seas to the South Sea. L. anatifera L., cosmopolitan. Cbnohoderma Fio. 354. , Sacculina purpurea (after Fr. Muller). Oe, Aperture of the mantle sac; IP, root-like processes ; JT, genital aperture. 6, Nauplius larva of Sacculina. A', A", Mdf, appendages, c, Pupa of Lerneeodiscus porcellance (after Fr. Muller). F, The six pairs of legs ; Ab, abdomen j A', attaching antennee ; O, eye. Olf. (Otion, Cineras Leach.), C. virgata Spengl., frequently attached to ships. C. aurita L., Anelasma Darwin. The stalk is provided with root-like processes, which grow into the skin of Squalida. A. squalicola Loven. Fam. Pollicipedidae. Peduncle not sharply distinct, scaly or hairy. The shell plates very strong, numerous. The scuta and terga lie close to one another. There are sometimes complemental males. Pollicipes cornucopia Leach., Ocean and Mediterranean. Scalpellnm vulgare~Lench., North Sea and Mediterranean. Sc. ornatum Gray, South Africa. Ibla quadrivalvis Cuv., South Australia. J. Cumingii Darw., Philippines. 446 CHUSTACEA. 2. Operculata. The peduncle is absent or rudimentary. The body is surrounded by an external ring of plates at the extremity of which the scuta and terga form an operculum, which is usually freely movable and provided with depressor muscles (fig. 348, b). Fam. Balanidae. Scuta and terga freely movable and articulating with one another. The gills are formed each of a fold. Balanm tintinnalulum L. Widely distributed and found in a fossil form. B. improvisus Darw. Found in brackish water. Fam. Coronulidae. Scuta and terga freely movable, but not articulating with one another. The two gills formed each of two folds. Tullcinella trachcalis Shaw., South Sea, Coromda lalcenaris L., Antarctic Ocean. C. diadcnla L., Arctic Ocean. 3. Abdcminalia. The irregularly segmented body is enclosed in a flask-shaped mantle, and bears on its terminal portion three pairs of cirriform feet. Mouth parts and alimentary canal completely developed. The sexes are separate. They live as parasites buried in the calcareous shell of Cirripedia and Mollusca. Fam. Alcippidae. With four pairs of feet, of which the first pair is palpiform, and the two last are uniramous and composed of few elongated joints. The sexes are separate. The female bores into Mollusc shells. The male is dwarfed, and is without mouth, stomach, or feet. Alcippe lampas Hanc., bores into the columella of the shells of Fnsus and Buccinum. Found on the coast of England. Fam. Cryptophialidae. They have three pairs of feet at the posterior end of the body. Cryptopliialus Darw., sexes separate. Cr. minutus Darw., in the shell of Concholepas Peruviana, found on the west coast of South America. Kocldorine liamata Noll, lives in excavations in the shell of Ilaliotis. 4. Apoda. The body is segmented, and is composed of eleven rings. There is no special reduplicature of the mantle. The shape resembles that of a maggot. The attaching antennae are elongated to the form of a band. The mouth is adapted for sucking, and has mandibles and maxillae. Feet absent. The digestive canal is rudi- mentary. They live parasitically in the mantle of other Cirripedia. They are hermaphrodite. Fam. Proteolepadidse -with the single genus Proteolepas Darw., Pr. Uvincta Darw., West Indies. 5. RMzocephala* (Suctoria). Body tubular or saccular, without segmentation or appendages; with narrow, short peduncle for attachment, from which branched, root-like filaments arise. The * W. Lilljeborg, "Les genres Liriope et Peltogaster, " Nova acta rcg. soc. scicn. Upsal,, Ser. 3, vol. Hi., 1860. Fr. Miiller, " Die Rhizocephalen," Archiv fur Naturgesch.. 1862 and 1863. R. Kossmaun, " Beitrage zur Anatomic der schmarotzenden Rankenf ussier," Verh. der med.-pliys. Gesellsch, Wurzburg, Neuc Folge, Tom. IV. MALACOSTBACA. 447 Jatter pierce the body of the host, and carry nourishment to the parasite. Mantle saccular, and without calcareous plates, with narrow aperture which can be closed. Mouth and alimentary canal absent. The testes are usually paired, lie between the ovaries, and open into the brood-pouch. The EhizocepJiala live principally as parasites on the abdomen of the Decapoda, and wind their root-like filaments around the viscera of the latter. Fam. Peltogastridae. Peltog aster pay uri Eathke. Sacculina carcini Tliomps., LerncBodiscus porcellana Fr. Mull., Brazil. II. MALACOSTRACA. The Malacostraca differ from the Entomostraca in possessing a constant number of segments and paired appendages. The boundary between the head and thorax cannot be absolutely fixed on account of the varying number of anterior pairs of legs which are modified to form jaws. These regions are composed of thirteen segments altogether, and bear the same number of pairs of appendages, while the abdomen, which is always distinct, includes six segments and the same number of paired limbs and terminates with an anal plate (telson) derived from the terminal portion of the body. Amongst the living Malacostraca there is, however, a single group of forms (Nebalia) (fig. 355, a, b), which differ in having a larger number of abdominal segments. They have, in addition to the six abdominal segments with appendages, two segments without appen- dages, and an elongated Phyllopod-like caudal fork. This remarkable form was for a long time regarded as a Phyllopod, and in many of its characters represents a connecting link between the Phyttopoda and the Malacostraca. The structure and segmentation of the head and thorax resembles that of the Malacostraca, but the terminal region of the abdomen does not present the special form of a caudal plate or telson. In Nebalia we probably have to do with an offshoot of the Phyllopod-like ancestors of the Malacostraca, which has persisted to the present time. The head includes in all cases, behind the mandibular segment on which two paragnathi form a kind of underlip, the segments of two pairs of maxillae. The latter preserve more or less the characters of Phyllopod feet. The head, therefore, consists of five segments, each with its pah* of appendages, viz., two pairs of antennae, one pair of mandibles, and two pairs of maxillae. It is followed by the thorax, 448 CRUSTACEA. which is composed of eight segments. The eight pairs of thoracic appendages may have an exactly similar shape, and possess two separate and many-jointed rami. This form of thoracic appendage is characteristic of the Schizopoda ; in Nebalia* the thoracic appen- FIG. 3?C. Nebalia Geoffroyi, strongly magnified, a, Female; 8, male; E, rostrum; O, stalked eye ; M, crop ; D, intestine ; S, shell G, vas deferens. * Nebalia is best placed in a special group, Leptostraca, between the Entomos- traca and Malacostraca. The palaeozoic fossil genera Hymenocaris, Peltocaris, etc., would have to be placed in such a group. AETIIEOSTEACA. 44 f ) closely resemble the typical Phyllopod limb. As a rule, how- ever, some of the anterior thoracic legs take part in preparing the food and have a form intermediate between maxillae and thoracic legs. Such are called foot- jaws or maxillipeds. In the Arthrostraca the anterior pair of thoracic appendages only are so modified, and the segment bearing them joins the head ; the thorax is, therefore, in this group composed of seven segments, each with its pair of appen- dages. In other groups of Malacostraca the next or two next pairs of thoracic legs have the form of maxillipeds, so that there is no sharp division between the head and thorax. The latter is, at least partially, covered by a shield-like reduplicature of the skin, which morphologically corresponds to the Phyllopod shell and forms a more or less extensive carapace, which fuses with the back of the thorax, and under which the posterior, rarely all the thoracic seg- ments may remain separate as free rings. Order 1. AETHEOSTEACA.* Malacostraca with lateral sessile eyes, usually with seven, 'more rarely with six or fewer separate thoracic segments, and the same number of pairs of leys. Without a reduplicaturQ of the skin. The head bears four antennae, the two mandibles, four maxillae, and a pair of maxillipeds ; in all six pairs of appendages. A small bilobed plate, distinguished as the under-lip, behind the pair of mandibles, marks the boundary of the primary region of the head. The two pairs of maxillae as well as the maxillipeds are secondary cephalic appendages derived from the thoracic region of the body. Behind the head there are usually seven free thoracic rings with the same number of pairs of appendages, which are adapted for creeping or swimming. The number of distinct thoracic segments is in rare cases reduced to six (Tanais) or five (Anceus}, the anterior or the two anterior segments of the thorax becoming intimately con- nected with the head. In the latter case a more or less extensive cephalothoracic carapace is formed. The abdomen which follows the thorax includes, as a rule, six segments bearing limbs, and a simple or split plate without appendages and representing the terminal segment. The number of the abdominal segments and appendages may, however, be reduced (Isopoda), and the entire abdomen may * Besides the works of Latreille, M. Edwards, Dana, and others, compare Spence Bate and J. 0. Westwood, "A History of the British sessile-eyed Crustacea," Tom. I. and II., London, 1863-1868. G. 0. Sars, " Histoiro naturelle des Crustacea d'eau douce de Norvege," Christiania, 1867. 29 450 CEUSTACEA. even be reduced to an unsegmented stump-shaped appendage ( Lcemodipoda) . The nervous system consists of a cerebral ganglion and a ventral gan- glionic chain, which is most distinctly composed of two lateral halves. In the Isopoda there is also an unpaired visceral nerve. The two eyes are always sessile, compound eyes, with smooth or facetted cornea; they are never stalked. Delicate olfactory fibres are often present on the anterior antennae, and are especially numerous in the male sex. The alimentary canal begins with a short O3sophagus, which passes upwards to open into a wide crop, supported by firm horny bands and often armed with strong chitinous plates. The crop leads into a long intestine provided with two or three pairs of tubular hepatic glands. The rectum, which may possess one or two tubular appen- dages (probably urinary), opens at the posterior end of the body. The antennal gland opens on the basal segment of the posterior antenna, often upon a conical protuberance. Vascular system. A heart is always present as the central organ of the circulation. It may either have the form of a tube extending along the whole length of the thorax (Amphipoda) ; or it may be saccular and placed in the abdomen (Isopoda). In the first case the gills are placed on the thoracic feet as tubular appendages ; in the latter, on the other hand, they are placed on the abdomen. From the heart the blood passes through an anterior and posterior aorta, and usually through lateral arteries. The vessels conduct the blood into the body cavity, whence it returns in regular streams to the lateral paired slits of the heart. Generative organs. The Arthrostraca, are of separate sexes. The males are frequently distinguished from the females by the modifica- tion of certain parts of the appendages to form prehensile organs, by a greater development of olfactory hairs on the anterior antennae, and by the position of the sexual and copulatory organs. It is rare to find a strongly marked dimorphism of the sexes (Bopyrus, Praniza). The generative organs open either at the posterior part of the thorax or at the base of, the abdomen ; the female always on the ante- penultimate pair, the male on the last pair of the thoracic appen- dages or between the first of the abdomen (Iso%)oda). The ovaries are two simple or branched tubes with the same number of oviducts. The testes similarly seem to be composed of one (Amphi%)oda) or more (3) pairs of tubes (Isopoda), the efferent ducts of which (vasa deferentia) either remain separate or unite to form a copulatory AMP1IIPODA. 451 organ. Appendages of the legs may also be present as additional aids to copulation. The mature ova are, as a rule, carried about by the female in brood pouches formed by the lamellar appendages of the thoracic feet (oostegites). Development as a rule takes place without metamorphosis, but the form and appendages of the young animal not unfrequently differ from those of the adult animal (Phronima). The segments and the appendages may even be incom- plete in number after birth (Isopoda). Fossil Arthrostraca are found in the Oolite (Archceoniscus). Pro- soponiscus occurs in the Permian, Ampliipdtis in the Devonian. 1. Sub order. Amphipoda.* Arthrostraca with later ally compressed body, ivith gills on thoracic feet, and an elongated abdomen, of which the three anterior segments bear the swimming feet, while the three posterior bear posteriorly di- rected feet adapted for springing (fig. 356). The Ampldpoda, *are small animals, being only in rare cases several inches long (Lysianassa magellanica}. They move in the water principally by spring- ing and by swim- ming. The head, which is sometimes small (Crevettina, fig. 356), sometimes large and then much swollen (Hyperina, fig. 357), is sharply distinct from the thorax and is fused with the first of the seven thoracic segments only in the aberrant group of the Loemodipoda. The two pairs of antennae usually consist of a short strong shaft * Besides the older works of De Geer, Kosel. M. Edwards, etc.. compare C. Spence Bate, " On the Morphology of some Amphipoda of the Division Hyper- ina," Ann. of Nat. Hist., Ser. 2. vol. xix., 1857. C. Spence Bate, "On the nidification of Crustacea," Ann. of Nat. Hist., Ser. 3, vol. i. C. Spence Bate. " Catalogue of the specimens of Amphipodous Crustacea in the collection of the British Museum," London, 1862. E. van Beneden et Em Bessels, " Memoirc sur la formation du Blastoderme chez les Amphipodes, etc," Bruxelles. 1868. C. Claus, " Der Organismus der Phronimiden, Arlcitcn auz dem Zool. Institut. dcr UnivertitW Wien, Tom II.. ]879. the | ior ^J FIG. 356. Oammarus nrglectus (after G. O. Sars), with egj? between the brood lamella?, (oostegites) on the thorax. A', A", the two antenna? ; f, maxilliped ; JF> to F\ the seven pairs of thoracic appendages ; Sf, the first swim- ming foot of the abdomen. CRUSTACEA, and a long mnltiarticulate flagellum, which, however, may bo more or less rudimentary. The anterior antennae, which are always longer in the male, often bear a short accessory flagellum and present numerous modifications in their special form. In the Hyperina they are very short in the female ; while in the male they are of consider- able length and are closely beset with olfactory hairs. The posterior antenna? are frequently longer than the anterior : in the male Typhidce they are folded in a zigzag fashion, and in the Corophiidce I* v a, 857. TJironima sedentaria, a, female; J, male. O, eyes; A', A", the two prnrs of fin tennse ; Kf, jaws ; D, intestine ; JET, heart and aorta ; K, gills ; Ov, ovary ; -A", nervous system ; Dr, glands in the chela of the fifth pair of legs ; G, genital opening. are modified to form strong pediform appendages. In the female, on the contrary, they may be degenerated and represented only by the basal joint (Phronima) (fig. 357, a and b). The mandibles are powerful biting plates with a sharp, usually toothed edge and a lower masticating process. They usually possess a three-jointed palp, which is occasionally reduced. The anterior bi- AMPHIPODA. 453 lobed maxillae also have as a rule a short, two-jointed palp, while the maxillae of the second pair are reduced to two lamellae of considerable size attached to a common base. The maxillipeds fuse to form a sort of underlip, which is either tri-lobed (Hyperina} or bears upon a com- mon basal portion an internal and external pair of lamellae, of which the latter may be considered as the basal joint of a large multiar- ticulate and frequently pediform palp (Crevettina and Lcemodipoda). Delicate lamellae or tubes, which are attached to the coxal joints of the thoracic legs, function as gills ; the active movements of the abdominal swimming feet cause a constant renewal of the water around them. In the female there are in addition to the gills lamellar plates (oostegites), which are applied together under the thorax to form a brood-pouch. The males are distinguished from the females not only by the absence of the oostegites, but chiefly by the stronger development of the prehensile hooks on the anterior thoracic feet and the different formation of the antennae. The eggs pass into the brood-pouch and there develop. The yolk sometimes (G. locusta and other marine species) undergoes a com- plete segmentation. Sometimes (G. pulex), after a superficial seg- mentation, a peripheral cell-layer is separated, which develops into a delicate blastoderm beneath the egg membrane. A ventral primitive streak is then formed, and on the dorsal side, beneath a differentiation which has been erroneously taken for a micropyle, a peculiar globular organ makes its appearance ; this is the first rudi- ment of the cervical gland (dorsal organ), which is confined to em- bryonic life. The appendages are developed from before backwards on the ventrally flexed body of the embryo. The young animals usually possess at hatching all their appendages and in all essential points have the structure of the adult animal, but the number of joints of the antennae and the special form of the legs still present differences. In the Hyperina alone the just hatched young may be without abdominal feet and differ so much in their form from the adult that they may be said to undergo a metamorphosis. The Amphipoda for the most part live in fresh and salt water and lead an independent life (the presence of Arctic species in the Swedish and Norwegian seas is very interesting). Some, however, live in tubes (Cerapus), others in holes gnawed in wood (Chelura). The large size of the deep-sea forms is of special interest ; amongst these a Gammarid, allied to the genus Ipkimedia, and Cystosoma Neptuni (Hyperidce) become several inches in length. The Hyperina 454 CRUSTACEA. live principally in transparent marine animals, especially in Medusas, and may, as the female Phronima sedentaria, take up their abode with their entire brood in transparent Pyrosoma, whose internal parts they eat up. The Cyamidce among the Lcemodipoda are parasitic on the skin of whales. Tribe 1. Laemodipoda. Amphipoda with cervically placed anterior legs and rudimentary apodal abdomen. The anterior thoracic segment is more or less closely fused with the head and the anterior pair of legs shifted on to the neck. The maxillipecls are modified to form a quadripartite under-lip with long palps. The branchiae are usually confined to the third and fourth thoracic segments, the legs of which are often rudimentary or are altogether wanting. The feet end with hooks for attachment. The abdomen is small and reduced to a short protuberance destitute of appendages. Caprdla linearis L. Body elongated and thin. They are parasitic on Hydroids and colonies of Bryozoa. Cyamus ceti L. Body broad and flat ; abdomen quite rudimentary ; parasitic on the skin of Cetacea. Tribe 2. Crevettina. Ampldpoda with small head, small eyes, and midtiarticulate pediform maxillipeds. Both pairs of antennae are long and multiarticulate ; in the male they are larger than in the female. The upper or anterior antenna are usually, as in Gammarus, the longer \ their shaft is composed of several joints and bears a small accessory flagellum as well as the principal one. The contrary may, however, occur, as in Corophium, where the posterior antennae are elongated and pediform. The maxillipeds in all cases fuse together at their base and form a large under-lip, usually with four lamellae and two jointed pediform palps. The coxal joints of the thoracic legs have the form of broad and large epimeral plates. The abdomen has always the full number of segments. The three posterior pairs of abdominal feet (uropoda) are well developed and often much elongated. This group, which includes an astonishing variety of forms, is principally distributed in the colder seas. Fam. Corophiidae. The body is not laterally compressed. The posterior antennas are more or less pediform. The coxal joints of the legs are frequently very small They move rather by walking. Corophium lon<]icorne Fabr., dig AMPHIPODA. 455 passages in mud. Cerapus tubularis Say., lives in tubes. Pvdocerus variegatus Leach., English coast. Chelura, terebrans Phil, is allied here, gnaws, with Liminorla lignorum, wood-work in the sea. North Sea and Mediterranean. Fam. Orchestiidae. Anterior antennae usually short, always without accessory ramus. The posterior pair of uropoda are unbranched and are shorter than the preceding pairs. They live on the shore, especially on sandy beaches, and move by springing. Talitrns saltator Mont. = T. locusta Latr. On the sandy coasts of Europe. Orcliestla littorea Mont., North Sea. Fam. Gammaridae. The anterior antennas often have a second ramus, which is always longer than the shaft of the posterior. The coxal plates of the four anterior pairs of legs are very broad. They move more by swimming than by springing. Gammarus pulex L., G.fluviatilis Eos., G. marinas Leach. In the blind Niphargus Schiodte the crystalline cones and eye pigment are wanting. N. puteaniis Koch., in deep springs and lakes (Lake of Geneva). Lysianasia Costa Edw., Mediterranean. L. atlantica Edw. L. magellanica Lillj. Tribe 3. Hyperina. Amphipoda with large swollen head and large eyes, usually divided into frontal and lateral eyes. They have a pair of rudimentary maxillipeds functioning as underlip. The antennae are sometimes short and rudimentary, sometimes of considerable size, and in the male are elongated into a multiarticulate flagellum (Hyperidce). The posterior antennae may in the female be reduced to the basal joint enclosing the glandular tube (Phromina) ; in the male, on the contrary, they are folded in a zigzag, after the manner of a carpenter's rule (Platyscelince). A paired auditory vesicle may be present above the brain (Oxycephalus, Ehabdosoma). The maxillipeds form a small bi- or tri-lobed under-lip. The paired legs end in some cases in a powerful chela. The caudal styles are sometimes lamellar and fin-like, sometimes styliform. Development takes place by metamorphosis. They live principally in jelly-fish, and swim very rapidly. Fam. Hyperidee. Head globular, almost entirely occupied by the eyes. The two pairs of antennas have a multiarticulate shaft ; the flagellum longer in the male. The mandible has a three-jointed palp. The fifth pair of feet is gener- ally formed like the sixth and seventh, with claw-like terminal joint. Hyperia (Lestrigonus Edw.) medusarum O. Fr. Mull. (7 galba Mont. = H. Latreilli Ed\v.) with Lestrigonus exulans Kr. as male, North Seas. Fam. Phronimidae. Head large, with projecting rostrum and large divided eye. The anterior antennae are short in the female, with only two or three joints, in the male with long multiarticulate flageilum and a shaft closely beset with olfactory hairs. The thoracic limbs have in some cases powerful chelae. Phrosina nicceensis Edw., Phronima sedentaria Forsk. The female lives with its offspring in Pyrosoma and Diphyidce, Mediterranean. Fam. Platyscelidae. Both pairs of antennae hidden beneath the head ; the anterior are small ; in the male with much swollen bushy shaft, and short, 456 CEUSTACEA. slender flagellum composed of few joints. The posterior antennae are in the male very long and folded three to four times together in a zigzag fashion ; in the female they are short and straight, sometimes quite reduced. The basal joints of the fifth and sixth pairs of legs are usually enlarged into great lamella?, which cover the thorax. The seventh pair is generally rudimentary. Eutyi)his (Typhis Risso) ovoides Eisso (Platyscelus serratus Sp. Bate), Mediter- ranean,. Oxijcejjkalus piscator Edw., Indian Ocean. 2. Sub-order : Isopoda.* Arthrostraca with usually broad, mare or less arched body, with seven free tho- racic rings, with lamellar legs function- ing as branchice on the short-ringed, often reduced abdomen. The structure of the body, which is flat in shape and covered by a hard, usually encrusted integument, presents a great agreement with that of the Amphipoda, to which the in many respects peculiar Tanaidce are most nearly allied. The abdomen of the Isopods is, however, usually much short- ened and composed of six short seg- ments, which are often fused with one another j it terminates with a large ciudal lamella. The abdominal legs are only exceptionally (Tanaidce) swimming feet ; as a rule they have the form of branchial lamellse. The sixth pair may be fin-like or styliform. The anterior antennae are, with a few exceptions, shorter than the posterior and external antennae ; in rare cases (Oniscidce) they become so much reduced that they are hidden beneath the cephalic carapace. In exceptional cases only (Apseudes) * H. Rathke, " Untersuchungen liber die Bildung und Entwickclung der AVasserassel," Leipzig, 1832. Lereboullet, <; Sur les Crustaces de la famille ces Cloportides. etc." Mem. du Museum d' hist. nat. de Strasbourg, Tom. IV., IS-'O. N. Wagner. " Recherches sur le systeme circulatoirc et les organ es de la respiration chez le Porcellion elanri," Ann. des sc. nat., Ser. 5, Tom. IV., 1865. A. Dohrn, " Die Embryonalentwickelune: des Asellus aquations," Zeitschr fur n-iss. Zool.,Tom. XVIL, 1867. N. Bobretzky, ' Zur Embryologie des Oniscus murarius," Zeitxclir. fur wiss. Zool., Tom. XXIV., 1874. FIG. 858. Asellus aquaticu (after G. O. Sars). Female with brood pouch, seen from the ventral side- ISOPODA. 457 they bear two flagella. As in the Amphipoda, pale, plumous setae and olfactory cones are present on the antennae. The mouth parts are in some parasitic Isopoda modified for piercing and sucking. The mandibles (except in Bopyridce and Oniscidce) often bear a three- jointed palp. On the other hand, the two pairs of maxillse, which are usually bi- or tri-lobed, are in general without the palpiform appendage. The maxillipeds form a sort of underlip,^but present great differences in the arrangement of their parts (fig. 358). As a rule the seven pairs of thoracic legs are adapted for walking .or attachment, and in the female some of them are provided with delicate membranous plates (oostegites) which form a brood pouch. They never bear gills. The branchial function is dis- charged by the delicate inter- nal rami or endopodites of the abdominal limbs (pleo- pods), the anterior pair of which is frequently modified to form a large operculum overlying the following pairs. In certain of the terrestrial Isopods (Porcellio and Arma- dillo) the opercular plates of the two anterior pairs of abdominal limbs contain a system of air spaces which ap- pear to assist respiration. The heart, unlike that in Amphi- pods, lies (except in Tandidce) in the posterior thoracic seg- ments or in the abdomen. The sexes are (except in Cymothoidce) separate, and the position and. arrangement of the generative organs correspond in general with those of the Amphipoda. The sexes are distinguished by external sexual characters, which in some cases (Bopyridai) may lead to a strongly-marked dimorphism (fig. 359, a, b). In the male three tubular testes unite on either side to form a dilated seminal vesicle, from which the vasa deferentia are given off. The latter are frequently separate along their whole length and, at the end of the last thoracic segment, each of them enters a cylindrical appendage FIG. 359. Gyge Iranchlalis (after Cornalia and Panceri). a, Female seen from the ventral side ; Sri, oostegite ; JT, branchiae, b, Abdomen of the same strongly magnified, with adhering male. 453 CRUSTACEA. (Asellus) or they unite together into a common median penis which lies at the base of the abdomen (Oniscidce). A pair of styliform or complicated, hook-bearing appendages of the anterior abdominal feet are to be looked upon as accessory copulatory organs \ in addition to these a pair of outwardly turned chitinous rods on the inner side of the second pair of feet may also be present (Oniscidce). The Cymothoidce are hermaphrodite* (Bullar), but the sexual organs become ripe at different times. In the young stage these animals function as males, and possess three pairs of testes, two rudimentary ovaries internal to the testes, and a paired copulatory organ into which the two vasa deferentia ^ open (fig. 360). After a subse- quent ecdysis and after the fe- male glands have developed at the expense of the gradually diminishing male glands, the oostegites, which in the meantime have been developed, become free on the thoracic legs and the copu- latory organs are thrown off. Henceforward the animal func- tions only as a female. The embryonic development begins after the entry of the eggs into the brood pouch and is in- troduced by a centro-lecithal seg- mentation, the central part of the egg (food yolk) remaining at first unsegmented. The blasto- derm soon consists of a periphe- ral layer of naked nucleated cells and produces by a rapid growth of its constituent cells the ventrally placed germinal bands, at the anterior end of which the cephalic lobes are first marked off. The rudiments of the trifoliate appendages (dorsal organ) of the Isopod embryos are next formed as two prominences on the cephalic lobes. The physiological and morphological meaning of these structures has not yet been explained. Of the appendages the two pairs of antennae * J. Bullar, " The generative organs of the Parasitic Isopoda," Jovrn. Anat. Pky?iol.. 1876. P. Mayer, "Ueber den Hermaphroditismus einiger Isopoden," Mittheil. aus der Zool. Stat. Nt>apcl, 1879. FIG. 300. a, S emale of Cymothoa Amiti (after M. Edwards). Brl, oostegite. b, Sexual organs from a Cymothoa cestridet, 13 mm. in length (after P. Mayer). T, The three testes ; Oo, ovary ; Od, oviduct j Vd, vaa def erens ; P, penis. ISOPODA. 459 are the first formed. After these have made their appearance, a new cuticle, the larval skin corresponding to the Nauplius stage, is formed (as also is the case in Ligia according to Fr. Miiller). While the other appendages are successively developed, the caudal region of the embryo becomes bent towards the dorsal surface. Of the embryonic membranes the chorion is the first to disappear, then the cuticle of the blastoderm, and finally, when the embryo is fully developed, the ISTauplius skin. The young animals, when they become free in the brood-chamber (fig. 361), are still without the last pair of thoracic legs; in the Tanaidce the abdominal feet are also wanting. They undergo not inconsiderable changes in the form of the appendages until the attainment of sexual maturity. The Isopoda may therefore be said to undergo a metamorphosis which is most complete in Ta- nais, Praniza (Anceus) and the Bopyridcs. The Isopoda live some in the sea, some in fresh waters, and some on land (Oniscidce). They nourish themselves on animal matters ; many of them are para- sitic (seldom complete enclopara- sites, Entoniscus) principally on the skin and in the buccal and branchial cavities of fishes (Cy- mothoidce) or in the branchial cavity of prawns (Bopyridce). Tribe 1. Anisopoda.* Body more or less resembling that of an Ampldpod. The abdomen with biramous swimming feet (Tanais), which do not function as gills, or with fin-like feet (Anceus). Fam. Tanaidae. Tanais dulius Kr., Brazil. Two kinds of males, "smellers and claspers." T. gracilis Kr., Spitzbergen. Fam. Pranizidae, Anceidas. Anceus maxillaris Mont. (Pr. cccrulcata Dcsm.), North and West coasts of Europe. * Compare Spence Bate, "On Praniza and Anceus, etc," Ann. of Nat. Hist., Ser. 3, Vol. II., 1858. Hesse, " M&noire sur les Pranizes et les Ancees." Ann. d. Scien. Nat., Scr. IV., Tom IX., 1864. Fr. Miiller, " Ueber den Bau der Scheerenasseln," Areliiv. fiir Natnrgcsck, Tom XXX., 1864. A. Dohrn, " Entwickelung und Organisation von Praniza maxillaris sowie zur Krfintniss des Baues von Paranthura costana " Zcitsclir. fiir vriss. ZooL, Tom. XX., 1870. FIG. 381. Larva of Bopyrus virbii, with six pairs of thoracic le#s (after R Walz). Ul, Under lip ; Abs, first abdominal seg- ment ; A', A", two pairs of antenna?; Mdb. mandible. 460 CRUSTACEA. Tribe 2. Euispoda. Body with seven free thoracic segments and as many pairs of appendages. Abdomen relatively short and broad, with abdominal feet modified to form branchial lamellce. Fam. Cymothoidae. With biting and sucking mouth parts, broad abdomen with short segments and shield-like caudal plate. The last maxillipeds in the form of an operculum. They live partly as parasites on fish, and partly as free-living animals. Cymotkoa oestrum Leach., C. cestroides Risso, Mediter- ranean. Anilocra meditcrranea Leach., ^Ega licaritiata Leach., Scrolls paradoxa Fabr. Fam. Sphaeromidae. Free-living Isopoda with broad head and short, very convex body, which can often be rolled up in a ball towards the ventral side. Splweroma fossarwn Mont, in the Pontine marshes; nearly allied is the 8. granulatum of the Mediterranean. S. serratum Fabr., Ocean and Mediterranean. It also lives in brackish water. Fam. Idoteidae. Free-living Isopoda with elongated body, biting mouth parts, and a long caudal shield formed of several segments fused together. The last pair of abdominal feet is modified to form a wing-shaped operculum for the protection of the preceding branchial feet. Idotea entomon L.. Baltic. Fam. Asellidae. Body flattened ; the last pair of abdominal feet (pleopods) are stylif orm (not shaped like an operculum). Jeera albifrons Mont. . British seas. Asellus aquatlcus L., fresh-water form. A. cavaticus Schibdte, in deep springs. Limnoria tcrcbrans Leach. L. lignorum, gnaws wood-work in the sea. Fam. Bopyridae. Parasitic in the branchial chamber of prawns ; the body of the female is disc-shaped, unsymmetrical, and without eyes. The males are very small and elongated, with distinctly separated segments and eyes. Bopyrus sqidllarum Batr., on Palcemon squilla. Here are allied the Entoniscidoe, which are parasitic in the body cavity of other Crustacea (Clrripedia, Pagv-ridts, and Crabs), Cryptoniseus planarioidea Fr. Mull., parasitic on Sacculina purpurea of a Pagurus, Brazil. Or. pyymcem Rathke, parasitic on Peltogastcr. JSntonigcus Porccllance Fr. Mull., lives between the heart and the intestine of a species of Porccllana in Brazil. Fam. Oniscidae. Land Isopods. Only the internal lamellae (endopodites) of the abdominal feet are modified to form delicate branchiae, the exopodites constituting firm opercula. The two anterior abdominal feet are sometimes provided with air chambers. The mandibles are without palps. They live mostly in damp places on land. Ligia occanica L., on stones and rocks on the sea coast. Onlsciis tmirarius Cuv., Porccllio sealer Leach., Armadillo culfjarls Latr., A. officinarum Brdt. Order 2. THORACOSTRACA.* Malacostraca with compound eyes which are usually placed on movable stalks, with a dorsal shield which connects all or at least the anterior thoracic segments with the head. * Besides the larger works of Herbst, M. Edwards, Dana, and the essays of Duvernoy, Audouin and M. Edwards, Joly, Couch, etc. compare Leach, THOEACOSTBACA. 461 The Thoracostraca, like the Arthrostraca, possess a cephalo-thorax composed of thirteen segments and an abdomen composed of six segments, as well as a caudal plate (telson) ; but the body is stouter and adapted to a more perfect locomotion and a higher grade of life. The thorax, instead of being composed of seven distinctly separate segments, is covered by a dorsal carapace which effects a firm and intimate fusion between the head and thorax. The degrees of development of this dorsal carapace are various. When most highly developed, it forms the dorsal integument of the anterior or of almost all the thoracic segments; and its lateral portions only, which have the form of wings and are bent towards the ventral surface, consist of a free reduplicature. The application of the appendages differs from that in the Arthrostraca, and, indeed, varies in the different groups of the Thoracostraca. The cephalothorax has thirteen pairs, and the abdomen seven. The facetted eyes are born on two movably separated stalks. These were for a long time considered as the anterior pair of appendages, while in fact they are merely lateral portions of the head which have become jointed. Both pairs of antennae belong to the anterior region of the head. The anterior antennae or antennules as a rule bear on a common shaft two or three flagella as the peripheral multiarticulate filaments are called and are pre-eminently sense organs. In the Decapoda the auditory vesicles are placed in the basal joint, and on one of the flagella there are delicate hairs and fibres, which are in connection with nerves and are to be looked on as olfactory organs. The second antennae are attached externally to and somewhat beneath the antennules. They bear a long flagellum and in the macrurous Decapoda are often provided with a more or less considerable scale. A gland (the green or antenna! gland) usually opens on a conical process of their basal joint. The following three pairs of appendages function as jaws; the powerful mandibles, which are furnished with palps, lie at the side of the upper lip ; further backwards are the two pairs of lobed maxillae, in front of which and behind the mouth is the small bilobed underlip. The following eight pairs of appendages present a very " Malacostraca podophthalma Britanniae," London, 1817 1821. V. Thompson, " On the metamorphosis of Decapodous Crustacea." Zool. Journ., vol. ii., 1831, also 7m, 1834, 1836, 1838. H. Bathke, " Untersuchungen tiber die Bildung und die Entwickelung des Flusskrebses,'' Leipzig, 1829. Th. Bell, "A history of the British stalk-eyed Crustacea," London, 1853. Lereboullet, ' Eecherches d'embryologie comparee sur le developpement du Brochct, de la Perch e et de PEcrevisse," Paris. 18G2. V. Hensen, " Studien iiber das Gchororgan der Decapoden." Leipzig, 1863. 462 CRUSTACEA. different form and adaptation in the various groups. As a rule, the anterior pairs are modified to assist in taking up food and are moved nearer the mouth ; these are the maxillipeds, which, with regard to their structure, hold an intermediate position between jaws and feet. In the Deccipoda (fig. 3G2) three pairs of appendages have the form FIG. 362. Male and female of Antaeus Jluvlatilis seen from the ventral side. In the male the ambulatory and abdominal leet of the left side have been removed; in the female the am- bulatory feet of the right side and the maxillipeds of both sides. A' antennules ; A", antenna? ; PI, scale of antenna ; Md, mandible with palp ; MX', MX", first and second maxillse JUTr/ 1 to Mxf, the three pairs of maxillipeds ; Goe, genital opening ; Doe, opening of the green gland; F' t F", first and second abdominal foot ; Ov, eggs ; A, anus. of maxillipeds, so that there are only five pairs of legs left on the thorax. In the Stomatopoda the first five pairs of thoracic append- ages are modified to form maxillipeds and there are only three pairs TnOfcACOSTKACA. 463 of biramous swimming feet, which arise from the three posterior free segments of the thorax. The thoracic legs are either, at least in part, biramous (with swimming ramus), or as in the Decapods the exopodite is absent and the legs have the form of ambulatory appendages. They then terminate with simple claws ; the anterior frequently with large chelae. The terminal joints may however be broad plates, in which case they can be used as swimming feet. The biramous legs of the sixth abdominal segment are, as a rule, broad and fin-like and form, together with the last abdominal segment which is transformed into a large plate (telson), the caudal fin. The feet of the five anterior abdominal segments, on the other hand, are sometimes swimming feet (Stomatopoda), sometimes serve to carry the eggs, or the anterior may assist in copulation (in the male). They may however be more or less rudimentary and some of them absent. With rare excep- tions (Mysidce) all the Thoracostraca possess gills, which are either tufted or composed of regular lancet-shaped leaves. The gills are appen- dages of the limbs: in the Stomatopoda FIG. 363. Cephalothornx of Aefacusfluviatiiit, after removal they are attached to O f the branchiostegite (after Huxley). K, Gills ; K, ros- the abdominal feet, in tram ' ?, stalked eye ; Up scaphognathite (of the second maxilla) ; Mxf", third maxilhped. the Schizopoda and Decapoda to the maxillipeds and ambulatory feet. The Cumacea are without gills, except for a single pair on the second pair of maxil- lipeds. In the Decapods they are contained in a special branchial chamber beneath lateral expansions of the carapace (branchiostegite) (fig. 363). The organs of circulation also attain a high degree of development, the highest not only among the Crustacea, but in general amongst all Arthropods. A heart and vessels are always present. In the Stomatopoda the heart has the form of an elongated tube, which extends through the thorax and abdomen, possesses numerous paired slits, 'and in addition to an anterior and a posterior aorta gives off to the right and left several branching arterial trunks. In the Cumacea, Schizopoda and Decapoda the heart has a saccular form and lies in the posterior region of the cephalo-thorax. More rarely, 464 CETJSTAOEA. as in the youngest larvae of the Decapoda, only one pair of slits is present and the arterial system has but few branches. In the fully- developed Decapoda the number of paired slits is increased by the addition of a dorsal and a ventral pair, and the vascular system is considerably perfected. An anterior cephalic aorta supplies the brain, the antennae and eyes. Two lateral pairs of arteries send branches to the stomach, liver and generative organs. The posterior abdominal aorta usually divides into a dorsal and a ventral artery, of which the first supplies the muscles of the tail, the latter (known as sternal artery) sends branches to the appendages of the thorax and abdomen (fig. 364). From the ramifications (often capillary-like) the blood flows into larger or smaller canals with connective tissue walls which may be regarded as veins, and from thence into a wide blood space situated at the base of the gills. It thence passes through F" F' Fro. 364. Longitudinal section through Asfacus Jluviatilis (after Huxley). C, Heart; Ac, cephalic aorta; Act, abdominal aorta, the sternal artery (Sta) is given off close to its origin; Km, masticatory stomach; J>, intestine; i, liver; T, testis; Vd, vas deferens; Go, genital opening ; <, brain ; 2V, ganglionic cord ; Sf, lateral plate of the caudal fin. the gills and, having become arterial, passes into other vascular tracts (branchial veins containing arterial blood), which conduct it to a receptacle surrounding the heart, the pericardial sinus : from the latter the blood enters the heart through the slits which are provided with valves. The alimentary canal consists of a short esophagus, a wide saccular crop and an elongated intestine which opens by the anus beneath the median plate (telson) of the caudal fin. The wide crop or masticatory stomach is supported by a firm chitinous framework, to which are affixed several pairs of masticatory plates (derived from thickenings of the chitinous lining). In the Decapoda two round concretions of carbonate of lime (Cray-fish) may be deposited in the walls of the masticatory stomach beneath the chitinous lining ; these are the so-called " eyes," and are found in the spring and summer. TIIOEACOSTEACA. 465 The ducts of the very numerous, multilobed hepatic caeca open into the anterior part of the elongated intestine. A simple or looped glandular tube (the green gland} opens on the basal joint of the posterior antenna. A shell gland is not developed. / The nervous system is distinguished by the size of the brain, fwhich is placed far forwards and gives off nerves to the eyes and [antennae. The ventral cord, which is connected with the supra- i O3sophageal ganglion (brain) by very long commissures, presents very different degrees of concentration. In the brachyurous Decapods this concentration reaches its highest point, all the ganglia being fused together to form one great thoracic ganglionic mass. The system of visceral nerves is also very highly developed. Sense organs. The eyes are large and facetted. Except in the Ov FIG. 365. Generative organs of Astacug. a, Female ; b, male. Ov, ovaries; Od t oviduct; Va, vulva on the basal joint of the third pair of ambulatory legs (-F'"); 2 1 , testis; Vd, vasdeferens; Oe, genital openings on the basal joint of the fifth pair of ambulatory legs I?*). Cumacea, in which the eyes are sessile, they are borne on movable stalks, which morphologically are to be regarded as the lateral parts of the anterior region of the head which have been segmented off. In the larva a median simple eye, equivalent to the unpaired Ento- mostracan eye, may appear between the stalked facetted eyes. In exceptional cases the adult animal may have paired eyes at the sides of the thoracic appendages, and unpaired eyes between the abdominal feet (Euphausia). Auditory organs are wanting in the Cumacea and Stomatopoda. In the Decapoda they are present as vesicles containing otoliths in the basal joint of the anterior antenna, and in many Schizopoda in the lamellae of the caudal fin. The delicate 30 466 CEUSTACEA. filaments and hairs on the surface of the anterior antennae have the value of olfactory organs; the antennas function as tactile or gam, as do also the palps of the jaws, the maxillipeds and the legs. The generative organs are paired and lie in the thorax or in the abdomen (Stomatopoda}, and, as a rule, are connected across the middle line by a median portion. The female organs consist of two ovaries and two oviducts, which open on the basal joint of the antepen- ultimate pair of ambulatory legs or on the sternal region between these appendages (fig. 365, a). The testes (fig. 365, b) are composed of numerous sacs and blind tubes, and, like the ovaries, are connected by a median portion; there are two vasa deferentia, often much coiled, which open on the basal joint of the last pair of ambulatory legs, more rarely on the sternum, and occasionally on a special copulatory organ (Schi- zojwda). The first, or the first and second, pair of abdominal feet act as intromittent or- gans. The eggs either FIG. 866. Crab zoeea (Thia), after the first moult. ZS, Zoa-a spine on the back ; Kf, Kf 1 ', the two pairs of "biramous appendages corresponding to the first and second pairs of maxillipeds. pass into a brood-pouch formed by lamellar ap- pendages of the thoracic legs (Cumacea, ScMzo- poda\ or become at- tached by means of the cementing secretion of special glands to the hairy abdominal feet of the female, where they remain until they are hatched (Deccqwdci). Development. Most of the Thoracostraca undergo a metamor- phosis which may be more or less complicated. The Cumacea, some ticldzopoda (Mysidea} and the fresh- water Decapoda (Astacus) leave the egg membranes with the fall number of segments and appen- dages. All the Stomatopoda, on the contrary, as well as most of the Decapoda, are hatched as larvae ; the latter in the so-called Zocea form with only seven pairs of appendages in the anterior region of the body (there are two pairs of antenna?, mandibles, two pairs of maxilla?, and two pairs of maxillipeds), without the last six thoracic segments and with a long abdomen destitute of appendages (fig. 366). The two pairs of antenna? of the Zocea are short and destitute of flagella. The mandibles are without a palp ; the maxillae are already TUOEACOSTEACA. 467 lobed and used as jaws ; the four anterior maxillipeds are biramous and act as biramous swimming feet ; and behind them, in the macru- rous Decapods, the maxilliped of the third pair also appears as a biramous swimming foot. Gills are as yet wanting, being repre- FIQ. 367. Larva of Penaeus (after Fr. Muller). a, Nanplius form seen from the dorsal sur- face. 5, Metanauplius stage seen from the left side; 3Ix', anterior maxillae; Mx' 1 ', pos- terior maxillee; 61, sixth and seventh pairs of appendages or first and second maxillipeds* c, Zoaea stage ; 0, eyes. sented by the thin surfaces of the sides of the cephalo-thoracic shield, beneath which a continual current of water flowing from behind forwards is kept up. A short heart with one or two pairs 468 CRUSTACEA. of slits is present. The facetted eyes are of considerable size, but are not stalked. Between the facetted eyes there is in addition an unpaired simple eye, the Entomoslracan eye. The Zocea larvaa of the short-tailed Decapoda (Crabs) are, as a rule, armed with spinous processes. They usually have one frontal spine, a long, curved dorsal spine, and two lateral spinous processes of the cephalo-thoracic shield. The Zosea, however, is not by any means always the earliest larval stage. Passing over those cases in which the larva has the Zosea form but is without the middle maxillipeds, there are Podophthal- mata (Pen&us), which leave the egg as Nauplii (fig. 367). Thus i'iG.3C8. OfZoeea of Inachus in advanced stage with rudiments of the third maxilliped (1T^") and the five pairs of ambulatory feet (oBp) ; C, heart ; L, liver. I, Megalopa stage of Portunus; Ab, abdomen. F 1 to -F v first to fifth ambulatory legs. the developmental history proves that the series of forms of Ento- mostraca and Malacostraca are continuous. During the growth of the Zorea, the subsequent metamorphosis of which is quite gradual and always different, the six (five) pairs of thoracic legs, which are as yet absent, sprout out beneath the cephalo-thoracic shield. The abdominal feet also make their appear- ance on the abdomen, and the larvae finally enter the Schizopod-like stage, from which the adult form proceeds. The Crab Zocea, how- ever, after a later ecdysis, enters upon a new larval stage, that of the Megalopci (fig. 368, b) ; in this stage it already presents the cha- racters of the Brachyura, but still possesses a large abdomen, which is indeed ventrally flexed, but provided with a caudal fin. CUMACEA. 469 The Thoracostraca are for the most part marine, and feed on dead animal matter or capture living prey. Most of them are good swimmers ; others, e.g. numerous species of crabs, walk and run and sometimes move sideways or backwards with great agility. The chelae of the first pair of ambulatory legs (fourth thoracic appendages) constitute powerful weapons of defence. Besides the frequent ecdyses of the larval stages, the sexually adult animals cast their shell once or several times in the year (Decapodci). They then live with the new and still soft skin for some time in protected hiding-places. Some Brachyura are able to live for a long time in holes in the earth away from the sea. These land crabs undertake, usually at the breeding season, common migrations to the sea and return later to the land with their fully developed offspring (Gecarcinus ruricola). The most ancient fossil Podophthalmia hitherto known are the mac- rurous Decapoda and Scliizopoda, from the carboniferous formations (Palceocrangon, Palceocarabus, Pygocephalus). (1) Sub-order : Cumacea.* Thoracostraca with a small cephalo-thoracic shield, (four to) five free thoracic segments, two pairs of maxillipeds, and six pairs of legs, of which at least the two anterior pairs have the biramous Schizopod form. The abdomen is elongated and, composed of six segments, and bears, in the male, two, three or Jive pairs of swimming feet in addition to the caudal aj)pendages. The Cumacea, the systematic position of which was formerly very differently estimated, have a superficial resemblance to Decapod larvae, which they also recall in the simplicity of their organization ; while in many of their characters, such as the formation of the brood-pouch and their embyronic development, they approach the Arthrostraca. A cephalo-thoracic shield is always present and includes, besides the segments of the head, the anterior thoracic segments and their appendages ; the four or five posterior thoracic segments, however, remain free. The anterior antennae are small and consist of a three-jointed basal portion, to the end of which, especially in the male, tufts of olfactory hairs are attached, and of a short nagellum and secondary flagellum * H. Kroyer, " Fire nye Arter af slasgten Cuma," Naturh. Tidssltr., Tom III., 1841. H. Kroyer, "Om Cumaceernes Familie," Naturli. Tuhslir. N. B., Tom III., 1846. G. 0. Sars, " Beskrivelse af de paa Fregatten Josephines Exped. fundne Cumaceer," Stockholm, 1871. A. Dohrn, " Ueber den Bau und die Entwickelung der Cumaceen," Jen. naturmiss. Zeitschr. Tom V., 1870. 470 CEUSTACEA. In the female the posterior antennae are short and rudimentary, while in the adult male they, together with their multiarticulate flagellum, may be as long as the body (as in Nebalia). The upper-lip is usually small, while the deeply cleft under-lip is of considerable size. The mandibles are without palps, and possess a comb of bristles and a powerful masticatory process below their strongly toothed extremity. The anterior maxilla consist of two toothed blades and a cylindrical, flagellate appendage directed backwards. The unpalped maxilla of the second pair is composed of several pairs of masticatory plates lying one above another. The two following pairs of appendages may be distinguished as maxillipeds. The anterior, which corresponds to the palped under-lip of the Isopoda, is five- jointed and may be recognised by the process of the basal joint ; the posterior, which is also usually five-jointed, is of considerable length and the basal joint is cylindrical and elongated. They also bear the large pinnate gill and a peculiar plate. Of the remaining six pairs of thoracic appendages, the two anterior are always formed like the feet of the Schizopoda ; they consist of a six- jointed leg, the basal joint being strongly developed and lamellar, and of a multiarticulate accessory ramus (exopodite) beset with long swimming setae. The four last pairs of appendages are also six- jointed, but are shorter ; they bear in many cases, with the invariable exception of the last pair, a larger or smaller swimming appendage as exopodite. The very narrow and elongated abdomen is, in the female, entirely without swimming feet, but bears on the large sixth segment at the sides of the caudal plate long-stalked biramous caudal styles; while in the male two, three or five pairs of swimming feet may in addition be present on the preceding segments. Fam. Diastylidae. Diastylis Rathkii Kr., North Sea. D. Edwardsii Kr. Lcucon nasicus Kr. , Norway. (2) Sub-order: Stomatopoda. * Elongated Thoracostraca icit/i short cephalo-thoracic shield wJiich does not cover the thoracic segments. There are Jive pair of maxilli- peds and three pair of biramous thoracic feet. The swimming feet on the strongly developed abdomen bear branchial tufts. * Besides Dana, M. Edwards and others, compare 0. Fr. Miiller, " Bruch- stuck aus der Entwickelungsgeschichte der Maulfiisser," I. and II., Archiv fur Naturgcxcli., Tom XXVIIL, 1862, and Tom XXIX., 18G3. C. _ Glaus, " Dia Metamorphose der Squilliden," Abliandl. der Oottinger Societat, 1872. C. Grobben, " Die Geschlechtsorgane von Squilla mantis," Sitzungsbcr. der 7i Aliad. der Wtisenssh., Wien, 1876. STOMATOPODA. 471 The sub-order Stomatopoda, with which formerly the Schizopoda, the genus Leucifer and the Phyllosomata (which are now known to be the larvae of Scyllarus and Palinurus) were united, is confined at the present day to the small and well-defined group of forms included in the Squillidce. They are Thoracostraca of considerable size and of elongated shape, with a broad, well-developed abdomen, which is much more extensive than the anterior part of the body and terminates in an extraordinarily large caudal fin. The cephalo-thoracic shield, which is formed of comparatively soft integument, is short and leaves at least the three large posterior thoracic segments to which the biramous swimming feet belong quite uncovered. The short segments of the maxillipeds also are not fused with the carapace. Appendages. The anterior part of the head with the eyes and antennae is movable, and the ventral portions of the following segments covered by the cephalo-thoracic shield are capable of limited movements upon one another (fig. 369). The anterior A' FIGL 300. Squilla mantis. A', J", antennae ; Kf, Kf, the anterior maxillipeds on the cephalothorax ; B', B", B"', the three pairs of biramous legs. internal antennae consist of a long three-jointed shaft, bearing three multiarticulate flagella. The second pair of antennae has a large scale on the outer side of the multiarticulate flagellum (fig. 369). The mandibles, which are placed far back, are provided with a slender three-jointed palp. The maxillae are relatively small and weak. The five following pairs of pediform appendages are crowded together close to the mouth, and on this account have been appro- priately described as oral feet. They all bear at their base a discoidal plate, which, in the case of the two anterior pairs, attains a considerable size. The anterior pair alone (first maxilliped) is slender and palpiform ; it ends, however, in a small chela, which serves to seize the prey. The chela in this and all the other maxillipeds of the Stomatopoda is formed by the terminal joint turning back and biting on the penultimate joint. The maxillipeds 472 CRUSTACEA. J" of the second pair are by far the largest ; they are moved more or less outwards and are provided with a very large chela. The three following pairs resemble each other in size and structure, each ending in a smaller rounded chela. Accordingly there remain for locomotion only the three pairs of legs of the last three uncovered thoracic segments ; they have the form of biramous swimming feet. The abdominal swimming feet, however, are much more developed and bear the branchial tufts on their external lamellae. The two sexes are only slightly different. The male is, however, easily to be recognised by the possession of the pair of rods at the base of the last pair of thoracic feet, and also by the slightly modified form of the first pair of abdominal feet. Me t amorphosis. The post - embryonic development consists of a complicated metamorphosis, which, unfor- tunately, is as yet not com- pletely known to us. The youngest larvae observed (about 2 mm. long) already possess all the segments of the tho- rax ; but the abdomen, except the caudal plate, is still un- developed. They are thus very different from the Zosea of the Decapoda. Later larval stages are described as Alima and Erichthus (fig. 370). FIG. 370. Young Alima larva, Af. Abdominal The Stomatopoda are found feet (pieopods) ; Mxf, anterior maxiiiipeds ; exclusively in the warmer Mxf, the large maxiiiipeds (second pair). seas. They are excellent swimmers and live by preying on other marine animals. Fam. Squillidae. Mediterranean. Sgitilla mantis Rond., Sq. Desmarestil Risso, Adriatic and (3) Sub-order: Schizopoda.* Small Thoracostraca with large, usually soft cephalo-thoracic shield and eight pairs of biramous thoracic feet, ivhich are similarly formed and frequently bear freely-projecting gills. * G. 0. Sars, " Hist. nat. des Crustaces d'eau douce de Norvege," Chrislianm SCHIZOPODA. 473 In their outward appearance the Schizopoda resemble the long- tailed Decapods, inasmuch as they possess an elongated and usually compressed body, a large cephalo- thoracic shield covering the thoracic segments more or less completely and a well-developed abdomen. In the structure of their nmxillipeds and thoracic legs, however, they differ essentially from the Decapods and approach the more advanced larvae of the prawns, which they also resemble in their simpler internal organization. Further, in all the deep sea forms the cephalo- thoracic shield leaves a greater number of the thoracic segments free (Siriella), and in the early larval stages all the thoracic seg- ments are free as in Nebalia. A* larger or smaller number of these free segments subsequently fuse on the dorsal side with the carapace ( Gnathophausici). Appendages. The first three pairs of thoracic appendages (the homologues of the maxillipeds of the JDecapoda) are biramous ambulatory legs and resemble in structure the following thoracic legs, which, by the possession of a multi&rticulate setigerous exopodite, are adapted both for swimming and for producing currents in the water. The two anterior pairs, however, show a closer relation to the oral appendages by their shorter and stouter form and by the presence of processes on the basal joint (Mysis, SirieUa). The principal ranms (endopodite) of the leg is always relatively slender and ends with a simple weak claw or with a multiarticulate tarsal flagellum. Rarely (Euphausia) the two last pairs of thoracic legs are entirely rudimentary, except as regards the largely developed bran- chial appendages. The abdominal legs are usually small and delicate in the female, but are strongly developed in the male. Sometimes they are of abnormal size and form (to assist in copula- tion), but only exceptionally (male of SirieUa) bear gills. The appendages of the sixth segment, which is usually very much elongated, are always lamellar, biramous structures and form with the telson a powerful caudal fin (fig. 371). The inner lamella or endopodite of this pair of limbs frequently contains an auditory vesicle. The differences between the males and females are so great that formerly they were placed in distinct genera. The former possess, on the anterior antennae, a comb- shaped prominence bearing a great number of olfactory hairs; and, owing to the larger size of the 1867. G. 0. Sars, " Carcinologiske Bidrag til Norges Fauna. Mysider," Christiania, 1870 and 1872. R. v. Willcmoes-Suhm, " On some Atlant. Crus- tacea," cf. Trans. Lin. Soc., 1875. 474 CUUSTACEA. abdominal feet, of which the anterior may, moreover, be provided with copulatory appendages, they are capable of a more rapid and perfect locomotion than the females, to which fact corresponds again the greater respiratory requirements and the possession of branchial appendages in Siriella. Development. The females bear on the two posterior (Mysis) or at the same time also on the median and anterior (Lo})hogaster) pairs of thoracic limbs lamella?, which form a brood pouch, in which, as in the Arthrostraca, the large eggs undergo their embryonic development. In other cases (Eup/uwtsia), the development proceeds by meta- morphosis. The young Eu- phausia is hatched as a Nau- plius larva, on which the three following pairs of appendages (maxilla? and first maxillipeds) soon appear as small promi- nences. The large carapace of the Nauplius, which is curved forwards round the base of the antenna? w r here it has a serrated edge, is the first rudiment of the cephalo- tho- racic shield, and beneath it, at the sides of the unpaired eye, the rudiments of the late- ral eyes are visible. The larva then, having moulted, assumes first the form of the Proto- zoa?a and then of the Zoa?a (described by Dana as Calyp- topis), which is however pro- vided with only six pairs of appendages and a long, already fully segmented, apodal abdomen. In the numerous succeeding larval stages (Furcilia, Cyrtopia) the remaining appendages are successively developed. FIG. 371. Mysis ccutata. Female with brood lamellae (after G. O. Sars). Gb, Auditory vesicle. Fam, Mysidw. My Eaetht, Northern seas x wtlyaris Thomps., M.flexuosa O. Fr. Mull., M. inermte Siriella Edwardsii Cls. DECAPOD A. 475 Fam. Euphausidae. EupJiausia splendcns Dana, Atl. Ocean. Tliysanopoda norwcgica Sars. Fam. Lophogastridae. Lopliogaster typicus Sars, Norway. (4) Sub-order: Decapoda.* Podophthalmia with large dorsal cephalo-thoracic shield, which is usually fused with all the segments of the head and thorax. They have three (two) pairs of maxillipeds and ten (twelve) ambulatory limbs, some of ivhich are armed with chelce. The head and thorax are completely covered by the dorsal carapace, the lateral expansions of which cover the basal joints of the maxil- lipeds and legs, forming a branchial chamber on either side, in which the gills are concealed. Only the last thoracic segment may retain its independence and be more or less movable. The shell is pro- longed into a frontal spine (the rostrum) between the eyes. The firm, calcined integument of the dorsal carapace presents, especially in the larger forms, symmetrical prominences caused by the sub- jacent internal organs : these may be distinguished as regions and named in accordance with the internal organs. The abdomen presents considerable differences both of size and form throughout the sub-order. In the Macrura it is of considerable size, possesses a hard exoskeleton, and, in addition to the five pairs of feet of which the anterior are often aborted in the female, is provided with a large swimming fin (the telson and the pair of large swimming feet of the sixth segment). In the Brachyura the abdomen is without a caudal fin and is reduced to a broad (female) or a narrow triangular (male) plate, which is bent up against the concave sternal surface of the thorax. The abdominal feet also are slender and styliform, and in the male are only developed on the two anterior segments. Appendages. The anterior antennae in the Brachyura are often concealed in lateral pits; they usually arise beneath the movably articulated eye-stalks, and consist of a three-jointed basal portion bearing two or three multiarticulate flagella. The posterior antennae * Herbst, "Versuch einer Naturgeschichte dcr Krabben und Krebse," 3 Bde., Berlin, 1782-1801. Leach. " Malacostraca podophthalma Britannise," London 1817 to 1821. Th. Bell, " A history of the British stalk-eyed Crustacea," London, 1853. H. Eathke, " Untersuchungen iiber die Bildung und Entwick- elung des Flusskrebses," Leipzig, 1829. *S pence Bate, " On the development If Decapod Crustacea," Plril. Trans, of the Boy. Soc., London, 1859. C. Glaus, " Zur Kcnntniss der Malacostrakenlarvcn," Wiirzb. natum-iss. Zcitsclir., Tom II., 1861. Fr. Miiller, " Die Vcrwandlung der Garneclen," Archiv fur NaturgescJi., Tom XIX., 18G3. Fr. Miiller, " FUr Darwin," Leipzig, 1864. 476 CEUSTACEA. are usually inserted externally and somewhat ventrally to the first pair on a flat plate placed in front of the mouth (epistom or oral shield) : they frequently possess a scale-like lamellar appendage. At their base there is always a protuberance with a pore at its end, through which the duct of the antennal gland (green gland) opens. The mandibles vary considerably in shape in the different forms, but have, as a rule, a two or three- jointed palp, which, however, is absent in many prawns (Candidas). They are either straight and strongly toothed on their thickened anterior edge (Brachyura), or are slender and much bent (Crangon), or else forked at the ends (Palcemonidce and Alplieidce}. The anterior maxillae always consist of two lamella? and a palp, which is usually simple. The posterior maxilla?, on which there are usually four lamellae (two double lamella?) as well as palps, bear a large respiratory plate with setose edges (scaphognathite). These are followed by three pairs of maxillipeds, which, as a rule, have a flagellate appendage. There remain, therefore, only five pairs of thoracic appendages for use as legs; of these the two last are sometimes re- duced or may even be entirely absent (Leuci- f&r) as the result of Fio. 372. -Young form (larva) of the lobster (after G. retrogressive changes. O. Bars). E, rostrum; A', A", antennae; K"'. third mi ,-. maxilUpedjJF' anterior ambulatory leg. Tlie thoracic segments to which the ambulatory legs belong are, as a rule, all or all but the last fused together and form on the ventral side a continuous plate, which in all the Brachyura is broad. The legs consist of seven joints, which corre- spond to those of the Arthrostraca, and frequently end with a chela or prehensile hand. Development. The greater number of marine Decapoda leave the egg membranes in the zoaea form ; in Homarus, amongst the Macrura, the metamorphosis is much reduced and the just-hatched young possesses all the thoracic legs, which are, however, provided with external swimming rami, but it is still without the abdominal feet (fig. 372). Embryonic development. In addition to the classical researches of Rathke * on the crayfish, more recent works, especially those of * Besides Rathke 1. c. and Lereboullet 1. c., and a Russian paper of Bobretzky, DECAPODA MACRURA. 477 Bobretzky (prawns and cray-fish) and Reichenbach (cray-fish) have yielded important results. The segmentation seems (in all cases?) to be superficial (centrolecithal), that is, to be confined to the peripheral yolk (formative yolk). This divides successively into two, four, eight, and an increasing number of segmentation cells, while the central granular food yolk, which is rich in oil globules, remains unsegmented. The young of Astactw, when hatched, resemble the adult animal, excepting that the caudal fin is still rudimentary. I. MACRURA. The abdomen is strongly developed and is at least as long as the anterior part of the body \ there are four or five pairs of abdominal feet and a broad, well-developed caudal fin. The antennules bear two or three flagella, the antennae have one simple nagellum and frequently bear a scale at the base. The maxillipeds of the third pair are long and pediform and do not completely cover the pre- ceding ones. The Zocea larva, when hatched, is elongated and has usually three pair of biramous feet. Fam. Carididae. Prawns. Body laterally compressed, with a thin shell, which is often provided with a median ridge and prolonged into a saw-like frontal process. The posterior (external) antennae are inserted beneath the anterior (internal) and have a large scale projecting over the stalk. The long and slender anterior pairs of ambulatory legs frequently end in chelae. They live in shoals near the coast. Some genera (Penceus) possess a rudimentary swimming ramus. Palcsmon squilla L., Crangon vulgaris Fabr., Pontonia tyrrliena Risso. lives between the shells of bivalves. Sergcstes atlanticiis Edw. Fam. Astacidae. Tolerably large, usually with a hard shell. The cephalo- thorax is slightly compressed, the abdomen flattened. The antennas are attached near the antennules, and bear a small or quite reduced scale at their base. The first pair of ambulatory feet ends with large chelae, as do in many cases the weaker and smaller second and third pairs. Some soft -skinned forms bury themselves in the mud or sand. Astacus fluviatilis Rond., Crayfish. Homarns vulgaris Bel., Lobster. JVephrops norwegicus L., Grcbia Leach., Thalassina Latr., Callianaxsa subtcrranea Mont., buries itself in sand on the sea-shore. Fam. Loricata. With very hard, rough armour, and large broad abdomen The antennules end with two short flagella ; all five pairs of ambulatory feet with simple claws. The larvae are described as species of Phyllosoma. Palinurus qvadriccrnis Latr. ScyHarus latus Latr. Fam. Galatheidao. With broad, rather large abdomen, and well-developed caudal fin. The first pair of legs is chelate, the last is weak and reduced. GalatJica strigosa L. Fam. Hippidae. Cephalo-thoracic shield long ; end of the abdomen curved. The first pair of legs usually with a finger-shaped terminal joint ; the last is Kiew, 1873, compare H. Reichenbach, " Die Embryonalanlage und erste Ent- wickelung des Flusskrcbses," Zeitschr.fur wiss. Zool., Tom XXIX., 1877. 478 CRUSTACEA. \vcak. Ilippa eremita L., lives buried in the sea sand, Brazil. Albiincs, sy/irnista Fabr., Mediterranean. Fam. Paguridae. Hermit crabs. Abdomen long, usually covered with a soft skin and distorted, with narrow anal fin and rudimentary abdominal feet. The first pair of feet ends with powerful chela; , the two last are reduced. Some of them seek shelter in empty snail shells, to protect their soft-skinned abdo- minal region. Pag urns Bernhardus L., CcenolAta rugosa Edw., Birgus latro Herbst, said to climb palm-trees. II. BRACHYURA. With pits for the reception of the short internal (anterior) antennae and so-called orbits, i.e., cavities for the reception of the stalked eyes. Abdomen short and reduced, without caudal fin, curved round against the excavated ventral surface of the thorax ; in the male narrow and pointed, with only one, more rarely two pairs of abdominal feet ; in the female broad, with four pairs of abdominal feet. In the female each oviduct dilates to form a bursa copulatrix. The third pair of maxillipeds have broad flat joints and completely cover the anterior mouth parts. The just -hatched Zocea larvae of stout shape, with only two pairs of biramous feet and a dorsal spine ; later they assume the Megalopa form. Many Brachyura live on land. Fam. Notopoda. Transitional between the Brachyura and Macrura. The two or four posterior thoracic feet are articulated higher up than the four or three posterior pairs, and shifted on to the back. The first pair of feet has large chelae, the last is often modified to swimming feet. Porcellana platy elides Penn, Dromia vulgar is Edw., Litliodes. Latr. Farn. Oxystomata. With rounded cephalo-thorax. The frontal region does not project. The buccal frame is triangular. The male genital openings are on the basal joint of the last pair of thoracic legs. Calappa granulata L., Ilia nucleus Herbst, Mediterranean. Fam. Oxyrhyncha. Cephalo-thorax usually triangular, with projecting pointed rostrum. There are nine gills on either side. The male genital opening is on the basal joint of the last pair of thoracic legs. The thoracic ganglia are united into one mass. They do not swim but crawl. In-achvs scorpio Fabr.. Maja squinado Eond.. Pisa armata, Latr., Stenorliynclnis Lam. Fam. Cyclometopa. With broad, short cephalo-thorax, rounded anteriorly. Without projecting frontal rostrum. There are nine gills on either side. The male genital opening is on the basal joint of the last pair of thoracic legs. Some of them are good swimmers. Cancer pagurm L., Xawtho rivulosus Eisso, Mediterranean. Carcitvus mamas L., Portunus pubcr L. Fam. Catometopa. Quadrilatera. Cephalo-thorax quadrilateral. Frontal region is curved downwards. There are fewer than nine gills. The male genital openings usually lie on the sternum. Some of them live for a long time away from the water. Some live in holes in the earth, as land crabs. Pinnotheres pi*nni L., in the shells of Mytilus. P. vetcrum Bosc., in the shells of Pinna ; known to the ancients, who thought that there was a relation of mutual assistance between the crab and the mollusk. Ocypoda cursor Bel., GIGAtfTOSTKACA MEROSTOMATA. 479 Gela$inni8 forceps Latr., Grapsus varlus Latr., Gecarcinus rurlcola L., Land Crabs. Water is retained for a long time in the branchial cavities, owing to the presence of secondary spaces around the branchial plates, which are thus pre- vented from sticking together. They live in holes in the earth in the Antilles. III. GIGANTOSTKACA. The Xiphosura or Pcecilopoda, represented by the living genus Limulus and the orders of the fossil Merostomata, may be united under this head, as opposed to the Entomostraca and Malacostraca. They are principally characterised by the possession of a single pair of appendages placed in front of the mouth and innervated from the cerebral ganglion, also by the presence of four or five pairs of legs, which are placed round the mouth and whose basal joints are modified to form large mandible-like masticatory organs. Behind the last pair of legs there is a simple or cleft prominence, forming a sort of underlip. The region of the body which bears these appen- dages is to be considered as an unsegmented cephalo- thorax ; it is shield-shaped and may be drawn out into projecting wing- shaped lateral portions. On its upper surface two small median frontal eyes as well asttwo large lateral eyes can be distinguished. Following the cephalo -thorax there is an abdomen, which is usually elongated and composed of a greater number of segments. The abdomen tapers posteriorly and terminates in a telson, which may be flat or drawn out into the form of a spine. Order 1. MEROSTOMATA.* Gigantostraca 'with five pairs of appendages on the, ceplialo-tliorax which is relatively short ; with an elongated apodal abdomen, usually composed of twelve segments and ending in aflat or styliform telson. The powerful body of the Eurypteridce (included with the Pcecilo- poda by "Woodward), as the most important family of the Merostomata is named after the genus Eurypterus, consists of a cephalo-thoracic shield with median ocelli as well as large projecting marginal eyes, also of an abdomen with numerous (usually twelve) segments which become longer posteriorly, and of a caudal shield, which is prolonged into a spine. Round the mouth on the underside of the cephalo- thorax * Woodward, " Monograph of the Brit, fossil Crustacea belonging to the order of Merostomata." P. I., % II., Palceont. Soc. of London, 1866-1869. Wood- ward, " On some points in the structure of the Xiphosura, having reference to their relationship with the Eurypteridas," Quarterly Jour*. Geol.Soc. of London, 1867 and 1871. 480 CRUSTACEA. there are five pairs of long spiny legs, of which the last is much the largest and ends in a broad swimming-fin. Some of the anterior appendages may be armed with a chela, The resemblance of the true EurypteridcB (in the general shape of their body) to the Scorpionidce is very striking, while the genus Hemiaspis presents affinities to the Pcecilopoda. The most important forms are: Eurypterus pygmceus Saft., Devonian strata, Pterygotus anglicus Ag., four feet long, from the upper Silurian (fig. 373). FIG. 373. Eurypterus remtpes after Nieszkowski. a, Dorsal view ; b, ventral view; O, eyes; St. caudal spine ; -ff, hypostome. Order 2. XIPHOSURA.* Gigantostraca whose body is divided into three parts, which are movably articulated together ; a large shield-shaped cephalo-thorax, an abdomen ivithfive pairs of lamellar feet and a long movable caudal spine. The large body of these Crustacea is covered with a strong chiti- * C. Gegeiibaur, " Anatomische Untersuchung cincs Limulus, mit besonderer Beriicksichtigung der Gewebe," Alliandl. der naturforsch. Gesellschaft zu Halle, IV., 1858. Packard. ' ; The Development of Limulus Polyphemus," Svc. of Nat. Hist., 1870. A. M. Edwards, " Rechcrches sur 1' anatomic des Limules," .4n7?,. xc. nat. V c Ser. Tom. XVII.. 1872-1873. [E. E. Lankester, "Limulus an Arachnid." Quart. Journ. Mic. Soc., vol. xxi.J XIPHOSUEA. 481 Se- armour and is divided into an arched cephnlo-thorax and a flat, almost hexagonal abdomen, which ends in a movable sword-like caudal spine. The cephalo-thorax (fig. 374) forms by far the larger part of the body; it bears on its arched dorsal surface two large compound eyes, and further forwards, nearer the middle line, two smaller simple eyes ; while on its ventral surface there are six pairs of appendages, of which the anterior pair is slender and may, on account of its position in front of the mouth, be re- garded as a pair of antennae, although it ends, like the others, with a chela. The latter are placed to the right and left of the mouth, and their coxal joints serve as organs for the mastication of the food. At the end of the cephalo-thorax there is a pair of lamellar appendages, which are connected in the middle line and form a kind of operculurn for the branchial ap- pendages of the abdomen. It seems of interest that the form of this branchial operculum in the Asiatic and American species presents constant differences, in that the median portion in the former is undivided, and hi the latter consists of two joints. The shield-shaped abdomen which, by means of a transverse joint, is movable on the cephalic shield in a dorso- ventral direction, is armed on either side with movable spines, and bears on its ven- tral surface five pairs of lamellar feet, which are almost completely covered by the operculum. These abdominal feet assist both in swimming and in respira- tion, since the respiratory lamellaa are placed on them (fig. 374, a, b). The internal organization attains a re- latively high development in correspondence with the large size of the body. In the ( nervous system the following parts can be distinguished : a broad Desophageal ring, the anterior part of which constitutes the brain ind gives off the optic nerves, while from the lateral parts the 31 FiG. 374. a Limit? ut moluccanus, seen from the dorsal side (after Huxley). O, eyes; St, caudal spine. I, L. rotitndi- cauda (after M. Edwards), seen from the ventral side. A Antennae; B, the feet with their coxal jaws ; K, gills ; Op, operculum. 482 CRUSTACEA. six pairs of nerves to the antennae and legs take their origin : a subcesophageal ganglionic mass with three transverse commissures ; and a double ganglionic cord, which gives off branches to the ventral feet and ends with a double ganglion in the abdomen. The alimen- tary canal consists of oesophagus, masticatory stomach, and a straight intestine communicating with a liver and opening by the anus, which is placed immediately in front of the base of the caudal spine. The heart is elongated and tubular, and is pierced by eight pairs of slits, which can be closed with valves; it is also provided with arteries, which, after a short course, pass into lacunar blood paths. From the base of the gills, two spaces, returning the blood, extend to the pericardial sinus. Five pairs of appendages of the abdominal feet function as gills. These are composed of a very large number of delicate lamella 3 , lying one on another like the leaves of a book. Generative organs. The branched ovaries unite to form two oviducts, which open by separate openings on the under side of the operculum (first pair of abdominal limbs) ; in the male the openings of the two seminal ducts are placed in the same position. In Fi G .3W.-EmbryoofZi.z,inthe the male tlie an t er ior thoracic feet Trilobite stage (after A. Dohrn). m > > end in simple claws. Development. It is known that the young leave the egg without the caudal spine and often without the three posterior pairs of gill- bearing feet. This stage has been suitably named the Trilobite stage, on account of the resemblance which the larva presents to a Trilobite (fig. 375). On the cephalic shield there is a median keel- like ridge, which is also found on the abdominal segments. The last abdominal segment includes between its lateral portions the short rudiment of the caudal spine. In the next stage the segmen- tation of the abdomen becomes less obvious (the caudal shield becomes consolidated) and the caudal spine developed. The adult animals reach a length of several feet, and live exclusively in the warm seas, in the Indian Archipelago and on the east coast of America. They exist at a depth of two to six fathoms and move about in the mud by the alternating bending and straightening of the cephalic and abdominal shields and the caudal spine. Their food consists chiefly of Nereids. They are found in a TEILOBITA. 483 fossil state, especially in the Sohlenhofen lithographic slate, but also in older formations as far back as the Uebergangsgebirge (Cambrian, Silurian, etc.) formation. Limulus moluccanus Latr., East Indies. L. polypJicmus L., East Coast of North America. TRILOBITA.* In connection with the Merostomata and the Xiphosura, the Trilobites may be considered. Their systematic position cannot as yet be denned with certainty. They lived only in the most an- cient periods of the earth's his- tory, and their fossil remains are found in great numbers and are excellently preserved; but, un- fortunately, the conditions under which they were fossilised were such that the under side of the body, and, consequently, the structure of the appendages, that is the very characters which would enable us to decide their affinities, remain unknown to us. We may probably infer from this absence of any trace of appendages * in the fossils, that the legs were soft and delicate ; but Burmeister's conclusion that they resembled the legs of the Phyllopoda is not justified. The body, which is frequently found rolled up, is covered with a thick shell, which is divided by two parallel longitudinal furrows into an elevated median portion (rhachis) and two lateral portions- pleura): it rarely attains any considerable size. There is an * Burmeister, " Die Organisation der Trilobiten," etc., Berlin, 1843. Beyrich, "Untersucmmgen liber Trilobiten," Berlin, 1845, 1846. J. Barrande, "Systeme silurien du centre de la Boheme," Prague, 1852. S. W. Salter, "A monograph of the British Trilobites," London, 1864-1866. * Portions of appendages have been recently observed on the ventral surface of an Asaplins ( k< Notes on some Specimens of Lower Silurian Trilobites, " by E. Billings : also "Note on the Palpus and other appendages of Asaphus," etc., by H. Woodward, Quart. Jmirn. of the Gcolog. Soc., London, 1870), which are said to point to the affinity of Trilobites with the Isopoda. FIG. 376. Din gram of Dalmat\tv* (after Pictet). 61, Glabellum ; Sf, great suture (ocular suture); 0,eyes; GP, separable gena (cheeks) ; Kh, rhachis (tergum) ; PI, pleu- ron ; Pg, pygidium. 4S4 TEILOBITA AKACHXIDA. anterior arched, semicircular region, which may be regarded as head or perhaps as cephalo-thorax, and a number of sharply dis- tinct segments, which belong partly to the thorax and partly to the abdomen and are terminated by a larger shield -shaped caudal portion, the pygidium (fig. 376). At the edge of the pygidium, the armour of the upper surface is folded round on to the ventral side and leaves only the middle part of the latter uncovered. The lateral regions of the head, the median part of which especially projects as the " glabellum ," bear usually upon two protuberances large compound facetted eyes, and are often prolonged into two very long backwardly directed spines; they are also folded inwards on to the ventral surface. With the exception of a plate (hypostoma) comparable to the under-lip of Apiis, no trace of mouth parts has been observed for certain on the ventral surface of the head. The number of thoracic (trunk) segments varies considerably, but is tolerably definite for the adults of each species. Their lateral portions are likewise folded inwards on to the ventral surface, and present variously shaped wing-like processes and long pointed spines. The Trilobites lived in the sea, probably in shoals in shallow water near the coast. Their fossils are amongst the most ancient remains of animal life, and are found principally in Bohemia, Russia, Sweden etc., in the lowest strata of the Uebergangsgebirge (Cambrian, Silurian, etc.) They have been divided into numerous families according to the structure of the head (especially of the glabellum), the form of the pygidium and the number of segments. The most important genera are Calymene Blumenbachii Brogn ; Olenus gibbosus Wahlb., Ellipsocephalus Hoffii Schlotth. Class II, ARACHNIDA * Air-breathing Arthropoda with fused head and thorax, with two pairs of jaws, four pairs of ambulatory legs and apodal abdomen. The Arachnida include animals of extraordinarily different form. The head and thorax are almost invariably fused to form a short cepholo-thorax ; but the condition of the abdomen presents very great variations. * C. A. Walekenaer et P. Gervais. " Histoire naturelle des Insectes Apt&res," 8 Vols., Paris, 1837-1844. Hahn und Koch, " Die Arachniden, getreu nach der Natur abgebildet und beschrieben," Nurnberg, 1831-1849. E. Blanchard, " Organisation du regne animal. Arachnides," Paris, 1860. ABACHNIDA. 485 Tn the Spiders (Araneida) the abdomen is swollen and is joined to the cephalo-thorax by a short stalk. In the Scorpionidce, on the contrary, the long abdomen is joined to the cephalo-thorax by its whole breadth, and is divided into a broad segmented prse-abdomen and a narrow, very movable post-abdomen, which is also seg- mented. In the Mites LAcarina) the abdomen is unsegmented and fused with the cephalo-tjiorax. In the Pentastomida the entire body is elongated, ringed and vermiform, with four (two pairs -of) hooks in place of the appendages; these animals are known as * Linguatulida, and might be placed, on account of their parasitism, amongst the intestinal worms. The marked reduction of the cephalic region, which is without true antennae and possesses only two pair of oral appendages, is characteristic of the Arachnida. The anterior pair of cephalic appendages (chelicerae), which are used as jaws, have been regarded as modified antennae ; but it is perhaps more natural to regard them as morphologically equivalent to the mandibles of Crustaceans and Insects. These anterior jaws or chelicerse are either chelate, in which case the claw-like terminal joint can be moved against a process of the preceding joint (Scorpions, many Acarina), or sub- chelate, when the last joint is folded down upon the next like the blade of a pocket-knife upon the handle (Spiders). The chelicerse may also have the form of stylets, which are enclosed in a tube formed by the second pair of jaws (Mites). The latter, which constitute the second pair of appendages of the head or the pedipalpi, consist of a stout basal joint and a palp, which has fre- quently the form and segmentation of a leg. This either ends with or without a claw or with a chela (Scorpions). In the true Spiders there is an unpaired plate, the lower lip, between the basal joints of the two pedipalpi and belonging to the same segment as the latter. The four following pairs of appendages of the thorax are ambulatory legs. The first of them is sometimes modified in form and elongated like a palp ; its basal joint may function as a jaw. The legs consist of six or seven joints, which, in the higher forms, have been called by the same names as the analogous regions of the Insect leg. The internal organization of the Araclinida shows hardly fewer differences than does that of the Crustacea. The nervous system may have the form of a common ganglionic mass around the oeso- phagus (Mites), and may even possess only a simple commissure above the oesophagus (Pentastomida). As a rule, however, there is a distinct separation between brain and ventral cord, the latter showing 436 ARACIINIDA. very different grades of development. Yisceral nerves have been shown to exist in the Spiders and Scorpions. The sense organs are, as a rule, not so highly developed as in the Crustacea, and, putting on one side the tactile function of the extremities, are confined to eyes. The eyes are simple and immovable, and never possess a facetted cornea ; they are from two to tAvelve in number, and are sym- metrically arranged on the anterior surface of the cephalo-thoracic shield. Auditory organs have not yet been discovered, but there are tactile and olfactory organs. The alimentary canal runs straight from the mouth to the hind end of the body, and is divided into a narrow oesophagus and a wide intestine, which is, as a rule, provided with lateral creca. The intes- tine is, in the Spiders and Scorpions, divided into an anterior dilated portion the so-called stomach and the intestine proper. The glandular appendages of the digestive canal are salivary glands ; in Spiders and Scorpions, a liver, composed of a number of branched canals ; and, with a few exceptions, Malpighian tubes, which function as urinary organs and open into the hind end of the intestine. The organs of circulation and respiration also show very different degrees of development and are only absent in the lowest Mites. The heart lies in the abdomen, and is a long, many-chambered dorsal vessel with lateral slits through which the blood enters. It is fre- quently continued into an anterior and posterior aorta, and in Scorpions gives off in addition lateral branching arteries. The organs of respiration are internal air chambers, which have the form either of ramified tubes (trachece), or of hollow lamellae (fan-trachece, lungs) placed upon one another in great number like the leaves of a book and connected together by trabeculse so as to have the form of a sac. The air chambers are always kept open by a firm internal chitinous membrane, so that the air can enter by the paired openings (stig- mata) of the tracheae or lungs at the beginning of the abdomen, and be distributed to the finest ramifications. The chitinous lining may become thickened so as to give rise to a spiral fibre. Generative organs. With the exception of the hermaphrodite Tardigrada, all the Arachnida are of separate sexes. The males are frequently distinguished by external characteristics, as for example by their smaller size, by the possession of organs of attachment (Mites), or by the modification of certain appendages. Their genera- tive organs consist of paired testicular tubes, and the vasa deferentia often receive the contents of accessory glands before opening to the exterior by a single or double aperture at the base (anterior end) of LIXGUATULIDA. 487 the abdomen. Special copulatory organs in the region of the genital openings are, as a rule, wanting, but appendages far removed from the genital openings (e.g., pedipalpi of Spiders) often serve to transfer the sperm from the male to the female. The female sexual organs are also paired, usually racemose glands, with two oviducts, which usually dilate to a receptaculum seminis before their single or double opening at the beginning of the abdomen. They are also connected with accessory glands. Rarely (Phalangium) there is a long pro- trusible ovipositor. Only a few of the Arachnida are viviparous (Scorpions and some Mites) ; the greater number lay eggs, wilich they sometimes carry about with them in sacs till the young are hatched. As a rule, the just -hatched young have the form of the adult ; but in most Mites two or more rarely four legs are wanting, and appear only Avith the succeeding moults. The development of the Pygnogonida Pentas- tomida and Hydrachnea (water-mites) (which latter pass through a pupa-like inactive stage) consists of a complicated metamorphosis. Almost all Arachnida live on animals, a few on vegetable juices. The lowest forms are parasitic. The larger and more highly orga- nised forms prey on living animals, principally on Insects and Spiders, and are usually furnished with poison weapons, with which they kill their prey. Many of them, by means of the secretion of spinning glands, spin webs, in which their prey becomes entangled. Most of them remain during the daytime beneath stones and in hiding-places, and come out to catch their prey only in the evening and at night. Order 1. LINGUATULIDA,* PENTASTOMIDA. Parasitic Arachnida with ringed, elongated, vermiform body, with two pairs of hooks in the neighbourhood of the jawless mouth. The vermiform ringed body of these parasites, which were for a long time taken for intestinal w^ornis, is to be regarded as being principally formed of the extremely enlarged and elongated abdomen, the cephalo-thorax being much reduced ; an interpretation which the form of the body of the Dermatophili seems to support. In the adult, jaws are completely wanting, but there are four curved hooks (two on each side of the mouth, fig. 377), which can be protruded from pouches in the skin and are attached to special chitinous rods. These may correspond to the terminal claws of the two posterior pairs of legs, since the two pairs of legs of the larva, which are to * B. Lcuckart, "Ban und Eiitwickelungsgeschichte der Pcntastomiden," Leipzig und Heidelberg, 1860. 488 ARACIIXLDA. H be regarded as the anterior appendages, are lost in the course of development. The nervous system is confined to a simple suboesophageal nervous mass, with cesophageal ring and giving off numerous ner- vous trunks. Eyes and organs of respiration and circulation are wanting. The alimentary tract is a simple canal in the middle of the body, which opens by an anus at the posterior end. Special cutaneous glands are present in great numbers and strongly developed. Male and female are distinguished by considerable differences in size and by the different position of the genital openings. While the genita opening of the surprisingly small male lies not far behind the mouth, that of the female is situ- ated near the anus, at the hinder end of the body. The Linguatulida, when sexually adult, in- habit the air chambers of warm-blooded animals and Amphibia. The developmental history of Pentastomum tcenioides, which lives in the nasal cavities and in the frontal sinuses of dogs and wolves, is known from the researches of Leuck- art. The embryos of this species, while still enveloped in the egg-membranes, pass out the nasal mucus on to plants, and thence into the stomach of Rabbits and Hares, more rarely into that of Man. When freed from the egg- membranes, they pierce the walls of the in- FIG. 377. Peiitfii 502 AliACIIXIDA. The males are distinguished from the females by the smaller size of the abdomen. The females are always oviparous, and frequently carry their eggs about in special webs (Theridium, Dolomedes). In the male the pedipalpus is modified to form a copulatory organ ; the thickened and excavated terminal joint is spoon-shaped, and possesses a vesicular copulatory appendage with a spirally-twisted fibre (fig. 403). Before copulation the male fills this appendage with sperm, and at the moment of coitus introduces the terminal fibre into the female genital opening (fig. 404). Sometimes the two sexes live peacefully near each other on neighbouring webs, or even for a time on the same web ; in other cases the female, which is the stronger animal, lies in wait for the male in the same way as she does for all animals weaker than herself, and does not spare him even during or after copulation ; the male, therefore, only approaches her with the greatest caution. Development. The segmenta- ^sssssa^ tion of the ovum is centrolecithal (fig. 107). The em- bryos possess, in addition to the ^\^^^^^3 AF thoracic appen- dages, the rucli- FIG. 404. Male and female of ments of abdomi- FIG. 405. Spider embryo (after Linyphia, during copulation ] f pp ^ -.^MoVi Balfour). AF, Rudiments of (after O. Herman). Gl > abdominal feet. subsequently abort (fig. 405). The young, when hatched, already possess the form and appendages of the adult. They are not, however, sufficiently de- veloped before the first moult to spin or to capture prey. It is only after the moult that they become capable of performing these functions, leave the web of the egg membranes, and begin to spin threads and to capture small insects. The threads which we find floating in the air in great numbers in autumn and are known as gossamer threads are the work of young Spiders, which raise them- selves in the air by their means, and pass the winter in sheltered places. The habits of spiders are so remarkable that they have for a long time excited the interest of observers. All spiders are predacious, and suck the juices of other insects ; nevertheless, the manner in which they get possession of their prey varies much, and often AIIANEIDA. 503 indicates the possession of highly-developed instincts. The so-called vagrant spiders do not, as a rule, form nets to catch their prey, but use the secretion of the spinning glands only to line their hiding- places and to make their ovisacs. They catch their prey either by running after it (fig. 406, a), or by springing on it (fig. 406, b). Other Spiders (fig. 406, c) are indeed able to run quickly, but they render the task of catching prey easier by making webs and nets, on which they move about with great dexterity, while other animals, especially insects, become very easily entangled. The webs them- selves are of various kinds, and constructed with more or less skill ; Salti Tegnearla domestic^ O they are either delicate and thin and formed of irregularly arranged threads, or they are of a felt-like quality and extended horizontally or again, they may have the form of vertically placed wheel-shaped nets ; in this case they consist of concentric and radial threads, which are arranged with wonderful regularity, the radial threads meeting in a central point. Tubular or funnel-shaped hiding-places for the spider are often found near the webs. Most spiders rest in the daytime, and go out for prey in the dusk or in the night-time Many vagrant spiders, however, hunt in the day-time, even when the sun is shining. 504 AEACIES'IBA. 1. Tetrapneumones. With four lungs and usually with four spinning mammillae. Fam. Mygalidae. Large spiders thickly covered with hairs, with four lungs and four spinning mammillae, of which two are very small. They do not construct true webs, but prepare long tubes in the earth, or line their hiding- places (in clefts in trees or in holes in the earth) with a thick web ; they lie in wait for their prey (at the entrance of their homes), or they may catch it in the open by springing. The claw joints of the chelicerae are bent downwards. My gale aricularia L., the large Bird Spider of South America, lives in a tubular web between stones and in crevices in the bark of trees. Cteniza cccmentaria Latr. The trap-door spider in South Europe, lives in tubular holes in the earth, the entrance to which is closed with an operculum, as with a sort of trap-door. Atypus Sulzeri Latr., in Central Germany, with six spinning mammillae. 2. Dipneumones. With two lungs and six spinning mammillae. Fam. Saltigradae. Springing spiders (fig. 406, J) with a large arched cephalo-thorax and eight eyes of unequal size, which are grouped almost in a square. The anterior legs with stout femoral joints serve with the following legs for making the leaps by which these animals catch their prey. They do not construct webs, but spin fine saccular structures in which they remain at night, and later on keep guard over their egg-sacs. Salticus cupreus, formicarius Koch. Myrmecia Latr., in Brazil, resemble ants in form. Fam. Citigradse = Lycosidae. Wolf-spiders. With long oval cephalo-thorax, which is narrow anteriorly, but is strongly arched. There are eight eyes, which are usually arranged in three transverse rows. They run about with their long strong legs in pursuit of their prey. By day they are usually concealed beneath stones, in hiding-places, which they line with their webs. The females frequently sit on their egg-sacs, or carry them about on the abdomen, and usually protect the young for some time after they are hatched. Dolomedes mirabilis Walk. (fig. 406, ). Lycosa saccata L., tarantula L., the Tarantula Spider of Spain and Italy. It lives in holes in the ground, and its bite, accord- ing to the erroneous popular belief, occasions the dancing madness. Fam. Laterigradse=Thoinisidae. Crab-spiders. With rounded cephalo-thorax and flattened abdomen. The two anterior pairs of legs are longer than the following legs. They only spin isolated threads. They hunt insects beneath leaves running sideways and backwards. Micrommata smaragdina Fabr., Thomuus citrcm Geoffr. (fig. 406, d~). Fam. Tubitelae. Tube spinners. With six or eight eyes arranged in two transverse rows, which are usually curved. The two middle pairs of legs are the shortest, the hindermost pair often the longest. They spin for the capture of their prey horizontal webs with tubes in which they lie in wait. Tegenaria domcstica L. (fig. 406, thorax and abdcmen of an Acrldium 8ee7] ten segments. from the side. St, Stigmata ; T, tympanic organ. * J. 'Swammerdam, " Historia Insectorum generalis," Utrecht, 1669. J. Swammerdam, " Bijbel der natuure," 1737-1738. Reaumur, " Memoires pour servir a 1'histoire des lusectes," 12 vols.. Paris, 1734-1742. Ch. Bonnet, 'Traite d'Insectologie." 2 vols., Paris, 1740. A. Rb'sel von Rosenhof, "In- sectenbelustigungen," Niirnberg, 1746 to 1761. Ch.de Geer, "Me"moires pour servir a 1'histoire des Insectes," 8 vols., 1752 to 1776. H. Burmeister, " Hand- buch der Entomologie," Halle, 1832 522 INSECTA The separation of the body into the three regions known as head, thorax and abdomen is more distinctly marked in Insects than in any other of the Articulata. The number of somites and appendages appears to be constant ; the head, with its four pairs of appendages, being composed of four segments, the thorax of three, the abdomen usually of nine or ten (eleven) (Orthoptera) (fig. 428). The anterior abdominal segment, however, not unfrequently takes part in the formation of the thorax. The head, which is al- most always sharply marked off from the tho- rax, is formed of an unseg- mented capsule, in which different regions may be distinguished. These re- gions have been named, face, forehead, cheeks, throat, skull, etc. alter the parts of the Vertebrate head. The upper side of the head bears the eyes laterally, and the antenna?, while on the under part the three pairs of oral appendages are inserted round the mouth. The anterior appendages, the antenna?, are in Insects formed of a simple row of segments, but vary miicll in form and size. m-, 11 ' -f 1 ne 7 u SUaiiy arise the frontal region, and 1 serve not only as tactile orUnS but also as Or- gans or smell. We can distinguish between regular antennae (where all the joints are alike) and irregular antennre (fig. 429). The first may be bristle-like, filiform, moniliform, dentate, or pectinate; the irregular antennae, in which the second joint and terminal joints are especially liable to modification, are most frequently club-shaped, knobbed, Fio. 429. Different forms of antenna 1 (af:cr Bur- meister). a, .bristle-like antenna of Locu*ia ; I, filiform antenna of Carabus ; c, moniliform antenna of Tcnc-lrio; d, dentate of Elatcr ; e, pectinate antenna of Ctenicera : f, crooked antenna of Apis ; ff, club-shaped of Silpha ; h, knobbed of Necro- pJiorus ; i, lamellated of Melolontha ; k t antenna with. l)ristle from Saryu*. INSECTA JAWS. 523 L.in lobed, or crooked. In the last case the first or second joint is elon- gated forming the shaft, to which the distal and shorter joints are attached at an angle as the flagellum (Apis). The following structures enter into the formation of the mouth parts : the upper lip (labrum), the upper jaws (mandibles), the first pair of maxillae or lower jaws, the second pair of maxillae or lower lip (labium). The upper lip is a plate, w T hich is usually movably articulated to the cephalic shield and covers the mouth from above. Beneath the upper lip to the right and left are the mandibles or upper jaws, in the form of two palpless biting plates; they are un jointed, and therefore more powerful as masticatory organs. The first pair of maxillae or lower jaws have a more complicated structure. They are composed of several joints, and are, there- fore, adapted for less powerful but more varied move- ments in aid of the masticatory process. The maxillae of the first pair (fig. 430) are made up of the following parts.: a short basal joint (cardo, C), a longer se- cond joint or shaft (stilus, St) with an external scale (squama palpigera), to which is attached a many- jointed palp (palpus maxillaris, Mxt.). Two blades, an internal and external, are attached to the distal end of the second joint [and known respectively as lacinia and galea] (lobus externus, internus, L. in, L. ex). The maxillae of the second pair arise from the throat, and are partially fused together across the middle line so as to form the unpaired lower lip or labium. It is rarely the case that all the parts of the fir;t maxillae are discernible in the labium, the fusion being generally accompanied by the reduction and dis- appearance of certain parts. There are, however, cases in which all the elements of the first maxillae can be shown to exist (Orthop- FIG. 430. Mouth parts of a 'Blatta (nftor Savigny). a, Head seen from, the front: Oe, ocelli; Mxt, maxillary palp; Lt, labial palp, b, Upper lip (labrum, Lr). c, Mandible (Md). d, 1st maxilla : C, Cardo ; St, stipes ; L. in, lobus internus ; L. ex, Lobus externus. e, 2nd maxilla; or labium (lower lip), clearly composed of two halves. 524 tera, fig. 430). While the labium is usually reduced to a simple plate with two lateral palps (palpi labiales), in the Orthoptera we can distinguish a proximal piece (wbmentum), fixed to the throat, from a second piece, bearing the two palps (mentum), at the point of which there is a piece, the tongue (glossa) (fig. 430, e, L. in), and omebimes secondary pieces, the paraglossce (L. ex). The sub- mentum evidently corresponds to the fused basal joints (cardo), the mentum to the fused shafts (stipes), the simple or bifid glossa to the lobus internus, and the paraglossse to the lobus externus of the first maxillae. Median projections on the internal surface of the upper and lower lips are distinguished as epipharynx and hypo- pharynx respectively. The above description refers to insects which gnaw or bite their food. * When the food is fluid, the mouth parts, either in whole or part, become so remarkably modi- fied that it required the penetration of Savigny to establish their morphological relations. The biting mouth parts found in the orders of the Coleoptera, the Neuroptera and the Orthoptera are most nearly allied to the mouth parts of the ffi/menojytera, which may be described as a licking apparatus (fig. 431). The upper lip and mandibles agree with those of the biting apparatus, but the maxillae and la- bium are more or less elongated and modi- fied, to admit of licking and sucking up fluids. Mouth parts adapted for sucking are found in the Lepidoptera, where the first maxillae are united to form a sucking tube, while the other parts are more or less aborted (fig. 432). Finally the piercing mouth parts of the Diptera and Rhynchota also possess a sucking apparatus, which is usually formed of the labium ; but there are also styliform wea- pons, by means of which access is gained to the nourishing fluid, which is to be sucked up (figs. 433, 434). These weapons may be formed by the mandibles, and also by the maxillae, and even the hypopharynx and epipharynx may be used, undergoing numerous modifications. Since the piercing part of the apparatus may be FIG. 431. Moiun parts of Anthophora retitta (after Newport) A, Antennae; Oc, ocelli ; M d, mandibles ; MX, maxillae ; Mxi, max- illary palp ; Lt, labial palp ; Gl, glossa ; Pg, paraglossse. THORAX. 525 totally aborted, or, at any rate, become functionless, it is obvious Lr a FIG. 432. Oral apparatus of Butterflies (after Savigny). a, Of Zygaena; b, of Noctua. A, Antennae; Oc, eyes; Lr, upper lip ; Md, mandible ; Mxt, maxillary palp ; MX, maxilla (first) ; Lt, labial palp, cut away. that no sharp line can be drawn between the piercing and sucking forms of oral apparatus (fig. 434). The next principal region of the body in Insects is the thorax, which is con- nected with the head by a slender neck. It consists of three segments, and bears three pairs of legs and usually two pairs of wings on the dorsal surface. These three segments, the prothorax, the meso- t/wrax and the metathorax are rarely simple horny rings, but are usually com- posed of several parts united by sutures. In each segment a dorsal plate, lateral regions and a ventral plate can be dis- tinguished. These may be termed notum, pleura and sternum respectively, and they may further be described, according to the segments in which they occur, as pro-, meso- and meta-notum, and pro-, meso-, and meta- sternum. The lateral regions are divided into an anterior piece (episternum) and a posterior (epimerum), FIG. 433. Mcuth parts o< Nepa cinerea (after Sa-, vigny). Z77, Lower lip ( abium) or rostrum ; Lr upper lip ; M.I, mandible ; MX, maxilla (first). FIG. 434. Houth parts of Culex memoroxus ^ (after Becher). Lbr, Upper lip ; Lb, lower lip (proboscis) ; Lt, labial palp ; Md, mandibles; MX, maxilla; (first) ; H. hypopharynx (pierc- ing weapon). 526 IXSECTA. while on the mesonotum there is a median triangular plate (the scutellum), and on the metanotum there is not rarely a similar but smaller shield (the postscutettum). The manner in which the three regions of the thorax are connected with one another varies in the different orders. In the Coleoptera, Neuroptera, Orthoptera and in many Ehynchota, the pro-thorax is freely movable, while in all other cases it is a relatively small ring and is fused with the folio win <*. segments. The three pairs of legs are articulated in excavations of the chitinous integument of the ventral surface between the sterna and pleura. The number and size of the joints of the legs seem FIG. 435. Different form of legs (r&gne animal), a, Mantis with predatory leg; b, leg of Carabus used in running; c, of Acrldium used in springing; d, of Gryllotalpa used iu digging ; e, swimming leg of Dytiscus. more constant in the Insecta than in any other group of the Arth- ropoda, so that it is possible to distinguish five regions (fig. 435). The basal joint (coxa), which is either spherical or cylindrical, is articulated to the thorax and permits of free movement of the limb. The coxa is followed by a second very short ring, constituting the trochanter, which is sometimes divided into two parts or in other cases is fused with the next joint. The third joint, which is con- spicuous on account of its size and strength, is the \ongfemur. The next joint is the likewise long but slender tibia, which is armed at LEGS WIXGS. 527 the point with movable spines. Finally the last joint, or tarsus, is less movably articulated. It is simple only in rare cases ; generally it is composed of a number of joints (usually five), of which the last is terminated by movable claws, and sometimes also by lobed appendages. Of course the special form of the legs varies according to the mode of locomotion and the special needs of each insect. Legs adapted for running, walking, burrowing, leaping, prehension can be dis- tinguished (fig. 435). The anterior pair only is used for predatory purposes, and in such a leg the tibia and tarsus are bent backward against the femur in the same way that the blade of a pocket-knife folds back against its handle (Mantis, Nepa). The legs used in springing are the posterior pair (Acridium), and they are charac- terised by the powerful femur. Those used in digging are usually the anterior pair, and they may be recognised by the broad, shovel- like tibia (GryUotalpa}. In the swimming legs all the parts are flat, and closely beset with long swimming hairs (Naucoris). The legs used in walking may be distinguished from the ordinary running legs by the broad hairy lower surface of the tarsus (Lamia). Wings are only found in the fully de- veloped, sexually adult animals, which are re- latively rarely without them. They are attached to the dorsal surface of the meso- and meta-thorax, being articulated between the notum and pleura. The anterior wings are attached to the meso-thorax, and the posterior wings to the meta-thorax. As regards their form and structure they are thin, superficially expanded plates, consisting of two membranes firmly adhering to one another and continuously connected at the edges. They are usually delicate and transparent, and are traversed by various strongly chitinised bands, the nervures or veins or ribs (fig. 436). These nervures, which have a very definite and systematically important course, consist of canals, placed between the two layers of the wing, surrounded by chitin and containing Uood, nerves and especially trachece, the distribution of which corresponds with the FIG. 436. Wing of Tipula (after Fr. Brauer). H, Sub- costa; 1, first longitudinal nervure (costa mecliana) ; 2, radial rib (radius or sector) ; 3, cubital rib ; 4, dis- coidal rib (or cubitus anticus); 5, submedian (or cubitus posticus) ; 6, anal rib (or postcosta) ; 7, axillar rib ; E, marginal cell ; U, submarginal cell. D, discoidal cell ; I V, posterior marginal cells ; VB, anterior basal cell ; HB, posterior basal cell ; AZ t anal cell. 528 IXSECTA. course of the nervures. The nervures, therefore, always start from the root of the wing as two or three principal stems, and distribute their branches more especially to the upper half. The first (fig. 436) of the main trunks which runs beneath the upper margin of the wing is called the costa, and often ends in a horny dilatation. Be- neath the costa there is a second main stem, the radius, and behind this a third, the cubitus, which rarely remains simple, but usually bifurcates before the middle of its course into branches, which are often further divided so that a more or less complicated network is formed in the upper half of the wing. The spaces of this network may be distinguished as marginal spaces or radial cells, and as sub- marginal spaces or cubital cells. Not rarely there may also be present one or more lower nervures (anal, axillar nervures). The form and structure of the wings present various modifications. The anterior wings may become coriaceous by the stronger chitinisation of their substance, as for instance in the Ortlioptera and Rhyncl.ota ; or, as in the Coleoptera, they may have a firm horny structure (teg- mina or elytra), and be used less for flight than as a protection of the back, the skin of which is soft. The anterior wings in the Rhynchota group of the Hemiptera are mostly horny and only membranous at the tip, while the posterior wings are membranous. When both pairs of wings are of a membranous structure, their surface is either thickly covered with scales, LepidopUra and Phry- ganidce (group of Neuroptera), or remains naked and is marked out into a number of very conspicuous spaces, which may not unfrequently have the form of a close net-like mesh-work, as in the Ncuroptera. In general the two pairs of wings differ in size. Those insects which have coriaceous anterior wings and half or whole wing covers, have much larger posterior wings, while in the insects with membranous wings the anterior wings are, as a rule, the largest. In many of the Neuroptera, the wings are pretty nearly the same size, while in the Diptera the posterior wings are aborted and reduced to small knobs (kalteres). Finally we find in all the orders of insects examples of a complete absence of wings either in both sexes, or in the female sex alone. The third region of the body, which contains most of the vegeta- tive organs, as well as the organs of reproduction, is the elongated and well-segmented abdomen. In the adult insect this region is destitute of appendages, although very often in larval life, and as an exception in the sexually adult animal (Japyx), short appendages are present. The abdominal segments are very definitely separated ABDOMEN AND ITS APPENDAGES. 529 St FIG. 437. Posterior end of body of a Beetle. (Pterostichus $ ) (after Stein). 8, 9, Dorsal plates 8' &, ventral plates; St, Btigma ; A, anus; G, genital opening. from one another by soft connecting membranes. They are com- posed of simple dorsal and ventral plates, which are also connected laterally by soft membranes. This structure of the abdomen, which contains the respiratory and genital organs, permits of its being dilated and contracted (respiratory movements, distension of the ovary). Very often the posterior segments have a special struc- ture, owing to the various appendages which are con- nected with the processes of copulation and of depo- sition of the eggs. The anus is usually placed on the last abdominal ring, while the generative open- ing which is separate from the anal aperture opens on the ventral surface of the preceding segment (fig. 437). Terminal appendages, such as jointed filaments, etc., are present on the anal segment. The ap- pendices genitalcs, forming the genital armature, are, on the con- trary, placed on the ventral side around the genital open- ing. Developed in the male as valves and in the female in the form of ovipositors, gtings, etc., they arise from the imaginal discs (growths of the hypodermis), in the Hymenoptera and Orthop- tera on the eighth (first pair) and ninth (second pair) segments of the ab- domen (fig. 438). The ovipositors of the Diptera, on the other hand, are to be derived from the re- tracted posterior segments. Alimentary canal (figs. 439, 440). The mouth, which is covered by the upper lip, usually leads into a narrow resopha- gus, into the anterior portion of which, distinguished as the buccal 34 FIG. 438. a, Hind end of abdomen of a young female Locusta with the protuberances of the ovipositor and the anal styles ; C' and C"', the internal and external protuberances of the penulti- mate ; C"', the same of the antepenultimate seg- ment, b, slightly older stage, c, Nympha ; A, anus with anal styles (after Dewitz). 030 INSECTA. cavity, open one or more pairs of tubular or racemose salivary glands (Sp). In many of the suctorial insects, the end of the oesophagus is dilated into a sack with thin membranous walls and a short stalk, the suctorial stomach ; in others into a more uniform dilatation, known as the crop (fig. 439, Oe). The intestine which follows the oesophagus is sometimes straight and sometimes coiled ; it varies exceedingly in accordance with the mode of life. It is always at least divisible into a longer portion, which is concerned in di- gestion, the mesenteron or cliylijic ventricle (M, Chd} } and a terminal portion, which is concerned with the ejection of the faeces (figs. 439, 440). The number of regions may, however, be larger. In predaceous Insects, especially in the orders of Coleoptera and Neuroptera, a masticatory stomach or proventriculus (fig. 440, Pv) is inserted between the crop and chylific ven- tricle ; this is of globular form, and has powerful muscular walls. It is lined by a specially thick chitin- ous cuticle, which is beset with strong bands, teeth, and bristles. The chylific ventricle also, on which especially the digestive glandular layer is developed at the expense of the mus- cular layer, is sometimes divided into several re- gions, as for example in some Beetles the anterior part has a shaggy appearance from the numerous cseca which project from it (fig. 440 Chd\ and is sharply marked off from FIG. 439. Digestive apparatus of A pit melUfica (after L<5on Duf our). Sp, Salivary glands; Oe, oeso- phagus with crop-like dilatation ; M, chylific ven- tricle ; Re, Malpighian vessels ; R, rectum with so-called rectal glands ; G. Dr, poison glands. ALIMENTARY CANAL. 531 the simple narrower portion which follows it. Larger caeca, too, after the manner of hepatic glands, may be inserted at the com- mencement of the chylific ventricle (Orthoptera). The commencement of the hind gut or posterior portion of the alimentary canal is indicated by the opening of filiform csecal tubes, the Malpighian vessels. It is divided into two or more rarely three .regions, which are distinguished as the small intestine, the large intestine and the rectum. The last region is provided with a strong layer of muscles, and contains in its walls four, six or more longitudinal ridges, the so-called rectal glands (fig. 439, R). Sometimes two glands, the so-called anal glands (G.Dr, Ad), open into the rectum immediately in front of the anus. Their secretion, on account of its irritating qualities and dis- agreeable smell, seems to serve as a pro- tection to the animal. In exceptional cases the larva alone takes up nutriment, the sexually mature apterous form being without a mouth (Ephemera). Finally the stomach of the larva in a few cases ends blindly, and does, not communicate with the hind gut (larvae of Hymenoptera, Pupipara, Ant-lion). The Malpighian vessels already men- tioned, which \vere formerly erroneously held to be bile organs, undoubtedly func- tion as urinary organs. Their contents, secreted by the large nucleated cells of their walls, are usually of a brownish yellow or white colour, and consist of an aggregation of small granules and con- cretions, which, for the most part, consist of uric acid. Crystals of oxalate of lime and taurin have also been found. The numbers and grouping of these filiform tubes, which are usually very long and wound round about the chy- lific ventricle, varies very much. As a rule there are four or six, or more rarely eight of them opening into the intestine, but in the Hymenoptera and Orthoptera the number is much larger; in the latter there may even be a common duct into which the tubes are united (Gryllotalpa). FIG. 440. Alimentary canal and glandular appendages of a Beetle (Carabus) (after L. Da- four). Oe, oesophagus; Jn, crop ; Pv, proventriculus ; CM, chylific ventricle; My, Malpighian tubes ; R, rectum ; Ad, anal glands with vesicle. 532 INSECTA. Amongst the secretory glands of insects the glandules odoriferce, the wax-glands, spinning -glands and poison glands are to be mentioned. Of these, the first, to which belong the anal glands which we have already mentioned (fig. 440), lie beneath the covering of the body and secrete, usually between the articulations, strongly smelling fluids. In the bugs there is an unpaired piriform gland in the metathorax, which pours out its secretion by an opening between the hind legs and gives rise to the notorious smell. Unicellular cutaneous glands have been shewn to exist in different parts of the body of insects, and, like the sebacious glands of vertebrates, seem to secrete an oily liquid, which serves to lubricate the joints. Similar glandular tubes of the integument, which may be called wax-glands, secrete white threads and flakes, which cover the body as with a kind of powder or wool (Plant lice, etc., fig. 441). /Spinning -glands occur exclusively in larvae and serve for the produc- tion of webs and cases. When these glands have the form of two or more less swollen and elongated tubes (s e r i c t e r i a ) opening behind the mouth, they may be com- pared to a special form of salivary gland, which they also resemble in their structure. The larva of the ant- lion has its spinning organs at the opposite end of the body; the wall of the rectum, which is shut off from the chylific ventricle, taking the place of the sericteria. The poison glands, which are present in the female Hymenoptera, consist of two simple or branched tubes, the common duct of which is dilated to form a vesicular reservoir for the secreted fluid, which consists of formic acid. The end of this reservoir is connected with the poison spine. Vascular system. The blood, which is usually colourless but not FIG. 441. The wax glands and the prominences on which they open of an Aphide (Schizoneura Lonicerae). a, Pupa seen from dorsal surface; Wh, prominences on which the wax glands open; b, the unicellular wax glands (WD) beneath the cuticular facets (C/) of the skin. VASCULAR RESPIRATORY ORGANS. At unfrequently has a green tinge, always contains amoeboid blood cells and travels along definite tracts of the body cavity. The simplification of the circulatory apparatus, which is confined to a dorsal vessel, is correlated with the richly branched respiratory apparatus, the air- conducting trachece, which are distributed to all the organs and carry oxygen to the blood. The heart, which has the form of a dorsal vessel (fig. 442), runs in the middle line of the abdomen, and is divided by transverse constrictions into numerous (up to eight) chambers corresponding to the seg- ments. These chambers are attached to the integument of the dorsal sur- face by triangular muscles (alary muscles). During the diastole of the chambers the blood streams through as many paired lateral slits into the heart, which contracts gradually from before backwards and drives the blood in the same direction. The anterior chamber is prolonged into a median aorta, which runs forward to the head. From this aorta the blood flows freely into the body cavity and returns to the heart in four prin- cipal streams, two lateral, one dorsal beneath the dorsal vessel, and one ventral above the ganglionic chain, giving off numerous branches to the extremities, etc. It is only in ex- ceptional cases (e.g., in the caudal filaments of the larvae of Ephemera} FIG. 442. Longitudinal section through . , r> -i the body of Sphinx liqustri (after that arterial vessels are found pass- Newport). MX, maxiiise forming the ing out from the heart. Respiration is effected by branched trachece, which take in their supply of air through paired slit-like open- ings, the stigmata. The latter are usually situated in the membranes connecting the sterna and terga (fig. 428), and the exchange of air is determined by the distinct respiratory movements of the abdomen. The number of stigmata is very various, but there are rarely more than nine or fewer proboscis ; t, palp ; At, antenna ; 445) j thi re m O n a tracheal trunk leg Of Locmta > viridissima (after dilates between two lateral membranes so as to form tympani? mem! a ves i c H on which are spread out the end cells, pro- branewithopcr- vided with so-called nerve rods, of a nerve springing from the first thoracic ganglion (fig. 447). Peculiar sense organs have also been discovered in the posterior wings of beetles and in the halteres of flies. Sliming nerve rods have been found by Ley dig in the nerves of * Compare especially Leydig, " Zum feineren Ban der Arthropoden, sowie Geruclis-und Gehororgane der Krebse und Insectcn." Midler's Archiv, 1855 and 1860. H. Grcnacher, " Untersuchungen iiber das Senorgan der Arthropoden." Gottingcn, 1879. Also V. Grabcr, "Die tympanalcn Sinnesorgane der Orthopteren." Wien, 1875. REPRODUCTION. 539 the antennae, the palps, and legs, under conditions which render it possible that these nerves have the value of tactile nerves, and this is the more probable since the sense of touch is principally discharged by the antennae and the palps of the oral apparatus, as well as by the tarsal joints of the legs. Olfactory organs are very generally distributed, as might have been expected from the developed capability of tracking which many insects possess. It may be regarded as fairly certain that the surface of the antennae is the seat of the olfactory sense. Formerly, in accordance with the views of Erichson, the numerous pits which are found, for instance, on the leaf -shaped antennas of the Lamelli- cornia, were interpreted as olfac- tory pits ; but it is more correct to regard with Leydig the peculiar cones and knobs of the antennae which are connected with gangliated nerve endings as olfactory organs. The reproduction of insects is principally sexual. The male and female generative organs are always placed in different individuals; but they correspond in their position and parts, and in their opening on the ventral surface of the hind end of the body. The testes and ovaries are provided with paired ducts end- ing in an unpaired portion (fig. 91). The first rudiments of the genital organs may be traced back to a very early stage of the embryonic development. Their development, however, is only completed in the latest period of larval life, or in insects with complete metamorphosis during the pupal stage. In rare cases the full development and maturity of the sexual organs is never completed, as in the so-called sexless Hymenoptera (working bees, ants) and termites, which are incapable of reproduction. The males and females are distinguished by more or less important external differences in various parts of the body ; sometimes these differences lead to a marked sexual dimorphism. The males are almost always more slenderly formed, and are capable of quicker and FIG. 4i7. A portion of the nerve termina- tion in the anterior leg of Locusta viri' dlssima (after V. Graber). N, nerve; Gz, ganglion cells; St, rods in the terminal cells. 540 INSECTA. Be easier movement. They have larger eyes and antennae, and their colours are brighter and more striking. When there is a pronounced dimorphism the females are apterous, and their form approximates to that of the larva (Coccidce, Psychidce, Strepsiptera, Lampyris), while the males are provided with wings. The female generative organs are composed of paired ovaries and oviducts, the unpaired oviduct, the vagina and the external genital apparatus. The ovaries are elongated tubes, in which the eggs originate. The ova lie one behind another in a single row like a string of pearls, increasing in size from the blind end to the opening into the oviducts (fig. 91, a). The arrangement of these ovarian tubes presents extraordinary variations, and there thus ori- ginates a great number of dif- ferent forms of ovary, which have been described principally in the beetles by Stein. The number of the ovarian tubes also varies exceedingly, being least in some Rhynchota, and then in the butterflies, the latter having on each side only four very long ovarian tubes, which are many times folded (fig. 448). At their lower ends the ovarian tubes on either side open into the dilated commence- ment of the oviduct, which joins with that of the other side to form a median oviduct. The lower end of the latter repre- sents the vagina, and often receives, near the genital aperture, the ducts of special cement and sebaceous glands (glandulce sebacece), the secretion of which is used to surround and fasten the eggs which are about to be laid. In addition to these glands, the unpaired efferent duct of the genital apparatus is very commonly furnished with one or several usually stalked reccptacula seminis (fig. 449), in which the semen, often introduced in the form of epermatopkores, retains its fertilizing properties for a long time, sometimes for years, under the in- FIG. 448. Female sexual organs of Vanetga urticce (after Stein). Oc, The ovarian tubes cut off ; EC, receptaculum seminis and accessory glands ; Fa, vagina ; Be, bursa copulatrix with duct leading to the oviduct ; Dr, glandular appendage ; Dr ', glandulas sebaceas ; B, rectum. GENERATIVE ORGANS. 541 ttl fluence of the secretion of an accessory gland. Beneath the recepta- culum seminis, a large pouch-like diverticulum, the bursa copulatrix, which assumes the function of the vagina, is sometimes separated from the vagina. In the butterflies (fig. 448) a narrow duct serves to convey the sperm from this bursa, which opens separately, to the receptaculum. The male generative organs consist of paired testes and their vasa deferentia, of a common ductus ejaculatorius and of the external copulatory organ (fig. 450). The testes are long blind tubes, which are present either singly or in number on either side, and are often coiled together so as to form a seemingly compact brightly-coloured body. They may also be united to form an unpaired organ in the middle line. The testicular tubes are prolonged on either side into a usually coiled efferent duct or vas deferens, the lower end of which dilates considerably, and may even swell out to the form of a vesicle (vesicula seminalis). At the point where the two vasa deferentia join to form the muscular ductus ejaculatorius, one or more glandular tubes often pour their coagulable secretion into the latter ; the secretion serving to form a case The transference of the spermato- phores into the body of the female is effected by a horny tube or groove which surrounds the end of the ductus ejaculatorius. This tube, when not in use, usually lies retracted in the abdomen, and when protruded is surrounded by external organs for attachment (valves or pincers), as by a sheath. In exceptional cases (Libellula) the copulatory apparatus which serves to transfer the sperm is remote from the generative opening, as in the male spiders, being placed on the ventral side of the enlarged second abdominal segment. Almost all insects are oviparous, and only a few, as the TachincR, JBl FIG. 449. Terminal region of the female generative organs of Musca domextica (after Stein). Od, Oviduct, EC, the three receptacula seminis ; Dr, glandular appendages of the vagina; SI. blind sac-like appendage. round the balls of spermatozoa. U FIG. 450. Male generative organs of the Cockchafer ; (after Gegenbaur). T, Tes- tes; Vd, dilated portion of the seminal duct ; Dr coiled accessory gland. 542 INSECTA. Dr some of the (Estridce and of the Pupipara, are viviparous. As a rule, the eggs are laid shortly after fertilization, and before the commencement of the development of the embryo. In rare cases the embryo is already formed when the egg is laid. In the last case the segmentation and formation of the embryo take place in the vagina (fig. 451). The fertilization of the egg usually takes place during its passage through the oviduct, at the place where the receptaculum seminis opens. Since the eggs become invested with their resistant chorion in the ovarian tubes, from the epithelial cells of which they originate for the most part during the larval life, it is necessary that there should be special arrangements which render possible the entry of the spermatozoa and the fertilization of the ovum. For this object there exist on the upper pole of the egg (the pole turned towards the egg-tubes during the passage of the egg) one or more pores known as micropyles* which pierce the chorion and present a characteristic form and arrangement (fig. 452). The ova originate in the narrow terminal portion of the egg-tubes, which is often prolonged into a thin thread. Here the growth of the egg-tube takes place, as well as the differentiation of its contents into egg cells and ovarian epithelium. The ovarian tubes increase continuously in diameter towards the oviduct, in correspondence with the gradual increase of size undergone by the eggs, which are arranged one behind another in its lumen. Each egg occupies a chamber, and obtains an external resistant mem- brane (chorion), which is secreted by the epithelium which lines the chamber. The chorion shows in its external markings the pecu- liarities of the epithelium from which it was formed. Besides this type, which is found in Pulex and in many of the Neuroptera and Ortlwptera, there is a second type of ovarian tube, distinguished from the first by a more complicated structure of the ovarian chambers. The lumen of such egg-tubes encloses above the .FiG. 451. Female generative organs of the viviparous Melophagus ovinus (Pupipara) (after R. Leuckart). Oc, Egg in the ovarian tube of one side; lit, uterus ; Dr, the glands opening into the uterus ; Va, vagina. * Compare R. Leuckart, " Ueber die Mikropyle und den feineren Bau der Schalenhaut bei den Insecten." Miiller's Archie., 1855. PARTHENOGENESIS HETEROGAMY. 543 ovum a single (Forficula), or a number of yolk-forming cells (nutri- tive cells), so that we can distinguish in the egg-tube alternate yolk and germ compartments (fig. 453, a and b). In rare cases (Aphides) there is at the end of each egg-tube a common larger chamber of yolk cells, which are connected with the egg-chambers by means of " yolk- cords " (fig. 453 c). Parthenogenesis and Heterogamy. In certain insects, partheno- genesis, i.e., spontaneous development of unfertilized ova, has been shown to obtain ; this occurs in the Psychidce (Psyche), Tineidce (Solenobia), Ccccidce (Lecanium, Aspidiotus) and Chermes ; also in numerous Hymenop- tera, especially in Bees, Wasps, Cynipidce, and Tenthredinidce (Nematus). In the HymenopUra which live together in the so-called animal communities, male forms only are produced from the unfer- tilized ova (arrenotokia). Chermes affords an example of Heterogamy, in that two different oviparous generations follow one another; a slender and winged summer generation, and an apterous generation which is found in autumn and spring and lives through the winter : the males are, in most cases, not yet known. The closely-allied Aphides (plant- lice), which were formerly supposed to present the phenomenon of an alterna- tion of generations, behave in a similar manner. In them the summer genera- tions are very numerous, and are suc- ceeded by a sexually-developed autumn ...... FIG. 452. Micropyles (Mk) of insect generation, which includes winged males e ggs (after R, Leuckart). o, as well as the oviparous and often ap- J terous females (fig. 97, a, b). In the spring, viviparous Aphides are developed from the fertilized eggs. These are mostly winged (fig. 99), and in their organisation closely resemble true females. Their reproduc- tive organs are, however, differently constructed, and are without the receptaculum seminis. Since they never copulate, they have often been regarded as asexual forms provided with gerrn tubes. upper pnrt ot ' the e g- she11 of Anthomyia; b, egg of Drosophila ceiiaru ; c, stalked egg of PUMC, te * taceug - 544 INSECTA. The germ apparatus, however, of the so-called Aphide asexual generation not only has a very great resemblance to the female generative apparatus of insects, but the structure and mode of origin of the germ seems to agree so closely with that of the ovum that the viviparous Aphides must be considered as a peculiarly organised generation of females, the genital apparatus of which has undergone some simplifications adapted to parthenogenesis. However that may be, it will be convenient in this case to call the ovary the pseud&vary, and the ova which originate in it and are incapable of fertilization, the pseudova. From this point of view the reproduction of some FIG. 453. a, Egg tube of Forficula. Nz, Nutritive cells ; E-, ovum ; OE, epithelium of the wall of the egg tube, ft, Median part of the egg tube of a Moth. Nz, nutritive cells of the yolk-chamber ; Ez, ovum in the germ-chamber ; H, connective tissue investment, so-called serosa. c, Egg-tube of Aphis platanoideg with three ovarian chambers (Ez Ez") and the terminal nutritive chamber with its cells Ne. Dx, yolk cord. Diptera (Cecidomyia, Miastor, fig. 100), which can reproduce them- selves while still in the larval stage, may be explained. The development of the embryo takes place as a rule outside the body of the mother, and occupies a longer or shorter period of time, according to the temperature and the time of the year. The centro- iecithal segmentation leads to the formation of a superficial blastoderm, which surrounds the ovum, and always consists of a single layer of ceils. A part of this blastoderm, on that side ot the ovum which the later history shows to be ventral, becomes thickened and sharply EMBRYONIC DEVELOPMENT. 545 marked off from the rest, and forms the structure known as the ventral plate, which constitutes the first rudiment of the head and ventral half of the embryo. In many cases (Rhynchota Libettula) the ventral plate grows out from a hill-like thickening of the blastoderm (fig. 454) into the interior of the yolk, so that an internal ventral plate arises, in the formation of which a portion, though a small one, of the external blastoderm participates. The ventral thickening, which gives rise to the ventral plate, is caused by long columnar cells, and is at first confined to a small portion of the egg ; in Hydrophilus the posterior end (fig. 455, a). Inasmuch as its lateral edges become elevated a Fra. 454. Embryonic development of dtloptpryx vlrgo (after Al. Brandt) . a, Commencing involution of the ventral plate. The blastoderm was at first one-layered and thickened at the poles. G, edge of ventral plate. 5, Later stage of the involution, c, The embryonic membranes are developed ; Lp, parietal (serosa); Lv, visceral (amnion) layer of the latter. d, The appendages have sprouted out on the ventral plate. A, Antenna ; Md, mandible ; MX', first maxilla ; MX, second maxilla (labium or lower lip). Then follow three pairs of legs, e, Eversion of the embryo which is protruded from the sheath of the visceral layer. d, Completion of the inversion ; the hind end of the body is free ; the yolk sac is on the dorsal surface. and grow towards one another (fig. 455, 6, c), the thickened ventral plate first assumes the form of a groove, and then, after the fusion of the lateral edges, becomes a canal, the lumen of which is soon obliterated. The roof only of this canal corresponds to the epiblast, while the cells of its floor and its sides give rise to the first rudiment of the mesoblast. At the edge of the so-called ventral plate, fresh 35 546 INSECTA. folds are then formed ; these lead to the formation of the embryonic membranes, which are so characteristic of insect development. In . 455. Development of the embryo of Hydrophilus piceus (after Kowalevski). a, Shield- like ventral plate with raised edges, b, The edges are already growing together in the middle, c, The groove is almost entirely closed, d, The tail fold of the embryonic membranes has grown over the posterior end of the closed groove and is gradually extending forward ; Am, Amnion. e, The embryonic membranes have almost entirely grown over the embryo, f, The embryonic rudiment beneath the completely closed mem- branes ; with seventeen primitive segments : Kl, Procephalic lobes ; A, antennae, g, The ventral plate extends along the whole length of the ventral surface. The bi-lobed upper lip is present, also the antennae, (A) the jaws, and the first rudiments of the legs; rudimentary appendages are present on the seventh segment as prominences. On the abdominal segments there are round invagiuations, the first rudiments of tracheae ; there is a longitudinal groove from mouth to anus, h, The ventral plate covers the whole ventral surface of the ovum ; the openings of the invaginations (stigmata) have become small ; rudimentary extremities are still present on the first abdominal segment. The ganglia of the ventral chain have appeared, i, Viewed from the dorsal surface the so-called dorsal plate has closed up to a tube; Oe is its opening, k, The embryo just before hatching seen from the ventral side. Hydropldlus these folds grow together over the ventral plate from behind forwards, and fuse with one another, so as to give rise to an LARVAL DEVELOPMENT. 547 external and internal membrane, the former being called the serous membrane, and the latter the amnion (fig. 455, d, e). Simultaneously with the above-mentioned appearance of the membranes (in other cases at an earlier stage of development) the ventral plate becomes divided into two symmetrical halves, the germinal bands, which become divided by transverse constrictions into segments (up to 17). First of all three cephalic segments, on which the oral appendages are subsequently developed, make their appear- ance behind the procephalic lobes, which bear the first rudiments of the antennae. Behind these the rest of the primitive segments (mesoblastic somites} are successively marked off. Inasmuch as the germinal bands become strongly contracted, their dorsally bent round, terminal portion becomes drawn more and more towards the lower part of the egg, while their lateral parts gradually grow round the yolk to form the dorsal surface of the embryo (fig. 455, f, g, h). With these changes the body of the embryo has assumed a closed form ; it now possssses mouth and anus, the first rudiments of the internal organs and the external appen- dages of the segments, and is soon ready to escape from the egg and begin its independent life. In Hydrophilus and the Phry- FIG. 456. JEmchna larva with rudimentary ganidcBj peculiar differentiations appear on the dorsal surface, giving rise to a dorsal plate, which later on becomes folded, so as to form a dorsal canal (fig. 455, i). The post-embryonic development takes place, as a rule, by means of metamorphosis, the form, organization and mode of life of the young animal, after hatching, being different from that of the sexually adult animal. It is only in the lowest forms, the partly parasitic Aptera, both sexes of which are without wings, that the young leave the egg as perfect animals (Insecta ametabola). In those insects which pass through a metamorphosis, the manner and degree of the transformation differs greatly, so that the dis- tinction of a complete and an incomplete metamorphosis, which was formerly employed, seems to be in a certain degree justified. In the case of the incomplete metamorphosis (Rkynchota, Orthoptera) the development of the larva into the perfect winged insect presents a number of stages, during which the larva is capable of free locomo- tion and of nourishing itself. During these stages, which are marked by successive ecdyses, it gradually acquires wings and increases in size, 548 INSECTA. the rudiments of the generative organs are further developed, and it becomes moro and more like the winged insect. In the simplest case- the mode of life and the organization of the young larvae closely resemble those of the sexually adult animal, as for instance in the Hemiptera and Orthoptera genuina, but in other cases the adult and larva may differ considerably, although not so much so as in insects with complete metamorphosis ; for instance, the larvae of the Ephemeridae and the Libellulidae live in another medium and increase in size under different conditions of nourishment (fig. 456). The metamorphosis is only said to be complete in those forms in \vhich the larva passes through a quiescent stage, in which it is known as a pupa and does not take nourishment. With this stage FIG. 457. Metamorphosis of Sitaris kumeralii (after Pabre). a, First larval form, b, Second larval form, c, Pseudo-pupa, d, Third larval form, e, Pupa. the larval life ends and the life of the winged insect (Imago) begins. The larvae of insects with complete metamorphosis differ from the sexual animal to such an extent in mode of life and nourishment, in the form of the body and in the whole organization, that though the parfes of the body peculiar to the winged insect are prepared and established in larval life, yet a longer or shorter period of quiescence, in a certain sense a second embryonic period, seems necessary, during which the essential alterations of the internal organs, as well as the consolidation of the newly-established external parts, are effected (hypermetamorpliosis, Meloidae, fig. 457). In the form of their body and the homonomous segmentation, the larva; recall Annelids, with which they also often have in LARVAL DEVELOPMENT. 549 common the uniform segmentation of the ganglionic chain. Never- theless, it is probable that only a proportionately few of the larval forms have preserved the primitive form, and have a phylo- genetic significance (Orthoptera). In most cases the insect larvae owe their special peculiarities to secondary adaptations. In exceptional cases, the metamorphosis may be distinguished by quite special larval forms, as for instance in the Pteromalina (Platygaster, Teleas), the eggs of which are laid in other insect larvae (fig. 458). The lowest, usually parasitic larvae are quite vermiform, and are without limbs or a separate head, the latter being represented by the anterior rings of the body (maggots of Diptera and of numerous Fio. 4o3. Larval forms of three species of Platyyaiter (after Ganin). a, b, <, Cyclops-like larval stages with claw-like jaws, cephalothoracic shield and abdomen, d. Second larval stage, e, Third larval stage. Hymenoptera, fig. 66, a). In other cases there is indeed a cephalic region, but the following thoracic and abdominal segments are entirely without appendages. The larvae of the Weuroptera, of many beetles, of the Tenthredinidce and butterflies (caterpillars), have, on the contrary, jointed appendages on their three free thoracic seg- ments, and frequently also a greater or less number of rudimentary appendages, the so-called prolegs, on their abdomen. There are two rudimentary antennae on the heads of these larvae, and a varying number of simple eyes. The mouth parts are, as a rule, adapted for biting, even when the adult animal has a suctorial tube, but, with the exception of the mandibles, they are usually rudimentary. The 550 INSECTA. mode of nourishment of the larvae varies very greatly ; but their diet consists mainly of vegetable substances, which stand in great abund- ance at the disposal of the quickly-growing body. The larva usually undergoes four or five, rarely a greater number of moults, and in the course of its growth gradually assumes the form of the winged insect, not in all cases by the direct transformation of parts already present, but sometimes only after essential processes of new formation. In this respect, however, there are considerable differences, the extremes of which are represented in the Diptera by the genera Coretkra and Musca. In the case of CoretJira, the larval segments and the appendages of the head are transformed directly into the corresponding parts of the perfect insect, while after the last larval ecdysis the limbs and wings are formed from the imagined discs. The imaginal discs are derived from the hypodermis of the larva. The muscles of the abdomen and the other systems of organs pass unaltered, or with but little alteration, into those of the adult animal. The thoracic muscles, on the contrary, originate as fresh formations from rows of cells already established in the egg. With these slight changes, the FIG. 458/-imago of piatygaxter active life of the pupa and the small de- (after Ganin). . velopment or the tat body are in necessary correlation. In Musca, on the contrary, the pupa of which is quiescent and enclosed in a firm barrel-shaped membrane and contains a large fat body, the body of the adult animal, with the exception of the abdomen, arises by extensive transformations of the larva. The head and thorax are developed from imaginal discs, which, already established in the egg, become developed in the larva on the investing membrane of the nerves or trachea?. It is not until the pupal stage that these discs grow together, and give rise to the head and thorax. Every thoracic segment is composed of two pairs of discs (a dorsal and a ventral), the appendages of which represent the later wings and legs. All the systems of organs of the larvae are said to undergo a disruption during the protracted pupal stage as a result of the (recently, however, contested) process of so-called histolysis, and are replaced by new formations by aid of the fat body and the granular spheres arising from the latter. When the larva has attained a certain size and degree of develop- ment, i.e., when it is fully grown and provided with the food INSTINCT. 551 material required for its future changes, in the form of the enormously developed fat body, it is ready to enter on the pupal stage. The larvae of many insects prepare above or below the ground, by means of their spinning glands, a protective web, in which, after casting their skin, they enter the pupal stage (Chrysalis). The external parts of the body of the winged insect either lie against the common horny skin of the pupa, so that they are recognizable as such (Lepidoptera, pupa obtecta), or they already stand out freely from the body (Coleoptera, pupa libera). This distinction is, however, an un- important one, since in the first case the limbs are free just after the ecdysis, and are only cemented afterwards by the hardening cuticular layer. If the pupa remains enclosed by the last larval skin (Mus- cidce) it is termed pupa coarctata. In all cases the body of the winged insect lies with its external parts sharply marked in the pupa, and the special object of the pupal life is to complete the changes of the internal organisation and the maturity of the sexual organs. When this is accomplished the winged insect bursts the pupal skin, forces its way out by means cf antennae, wings and legs, and expands those parts which have been folded together, under the influence of violent inspirations, by which the tracheae become filled with air. The chitinous covering becomes harder and harder, the urinary secretion which has accumulated during the pupal sleep is ejected from the rectum, and the insect is capable of performing all the functions of the sexually adult animal. The mode of life of insects is so varied that it is hardly possible to give a general account of it. The diet is both animal and vege- table, and is taken in the most varied forms, either solid or fluid, and fresh or decaying. Plants are especially, subject to the attacks of insects and their larvae, and there exists, perhaps, no Phanerogam which does not afford nourishment to one or more species of insects. On the other hand, insects seem useful or even necessary to the well- being of the vegetable world, for in many cases e.g., many flies, bees, and butterflies they bring about fertilization by carrying the pollen to the stigmata of flowers. The complex, often marvellous, and apparently intelligent actions performed by insects correspond to the perfection with which the vegetative organs discharge their functions. Such actions are largely carried out instinctively by the mechanism of the organi- sation, but they certainly in part depend upon psychical processes, since they presuppose memory and judgment, in connection with 552 INSECTA. the highly-developed perceptive powers of the sense organs. The animal enters the world with instinct, but, in order to perform acts depending on memory and judgment, it must first acquire the necessary psychical conditions by sense perceptions and experience (bees}. In the inherited organisation are latent all those capabilities which have been acquired in the gradual processes of phylogenetic modifications and at the expense of psychical forces, and have^ at last, as the result of frequent use, become automatic and a pure mechanical property of the organism. The instinctive and psychical manifestations tend directly to the preservation of the individual by providing ways and means for the acquisition of food and for protection, but there is a special instinct tending to the preservation of the species and the care of the young. The most simple example of the latter is to be found in the judicious deposition of the eggs in protected localities, and on plants suitable for the nourishment of the just-hatched animal. The actions of the mother become more complicated in those cases in which the larvae develop in specially prepared places, and have, as soon as hatched, to meet with the requisite amount of suitable nutritive material (S2)hex sabulosa). But most wonderful are the instincts of some of the Ort/ioptera and Hijmenoptera, which concern themselves about the fate of their young after they are hatched and carry nourishment to them during their growth. In such cases a great number of indivi- duals become associated together for the common welfare in the so-called animal communities, in which there is a marked division 'of labour among the different members; males, females and sexually aborted forms or neuters (termites, ants, wasps, bees). Some insects are capable of producing sounds,* which we must in part regard as the expression of an internal disposition. We cannot, however, thus regard the buzzing sounds produced during flight by Hymenoptera and Diptera (vibration of wings and of the foHaceous appendages within the trachere), or the sounds like those of a rattle which are produced in numerous beetles by the friction of certain body segments against one another (pronotum and mesonotum of the Laniellicornici) or with Ihe inner sides of the wing-covers, although it is possible that such sounds are of some use for defence against hostile attacks. Peculiar vocal organs, which produce sounds for the purpose of attracting the females, are found in the male Cicada on the abdomen, and in the males of the Gryllidce and * IT. Landois, " Die Ton-nnd Stimmapparate der Insecten." Leipzig, 1867. THYSANURA. 553 Locustidce, at the base of the anterior wings. Both sexes of the Acrididce also produce similar though feebler chirping sounds, by rubbing the femora of the posterior legs against the edge of the wing- covers. Insects are almost universally distributed, from the equator to the extreme limits of vegetation ; certainly with a considerable diminu- tion in the number of species, and in their size and beauty of colour. Some forms are truly cosmopolitan, e.g., Vanessa cardui. Fossil insects are found in increasing numbers of species, from the car- boniferous formation to the tertiary period. The best preserved are those enclosed in amber and the impressions in the lithographic slate. Order 1. THYSANURA* (including COLLEM- BOLA). Wingless insects, with hairy or scaly body cover- ing ; with rudimentary masticating mouth parts and setiform anal fila- ments, which may serve as a springing appara- tus, at the end of the ten-segmented abdomen. Development without metamorphosis. The Thysanura seem to have preserved most completely the primitive character of the oldest insect forms. The elongated Campodidce particularly recall certain Myriapods, especially since they may have rudimentary feet on the abdomen (fig. 459, a, b). On this account the Campodidce have been regarded as ancestral FIG. 459. a, Campodea stapTtyUnnt (after J. LobbOCk). b, Anterior half of the body of C. fragilU (after PalmtSn). Tr, Trachea; S, stigmata; P, legs; P' t rudi- mentary abdominal feet; A, antenna?. * John Lubbock, '' Monograph of the 'Collembola and -Thysanura." Londor, 1873. 554 INSECTA. forms of the insects. The head bears tolerably long setiform an tennaa, and, as a rule, aggregated ocelli, in place of the facetted eyes. The mouth-parts consist of mandibles and maxillae, which can be retracted into a sort of atrium. In this case an apparatus for attachment with gland is often present on the ventral side of the first abdominal segment. Tracheae are completely absent in many Collembola (Podura), while in Campodea they present very simple relations. There are only three pairs of stigmata, and the trunks which spring from them do not anastomose. On the penultimate abdominal segment there are often setiform filaments, which when forcibly bent ventralwards serve as a a TERA STREPSIPTERA. 5G5 HIJ dropsy die and fflnjacopliila, are fastened to stones. In the walls of these cases there are sand grains, bits of plants and empty snail shells. The larvae have biting mouth parts and filiform tracheal gills on the body segments. They project their horny head and thoracic segments, with their three pairs of legs, from these tubes and crawl about. The pupa leaves the case, which serves also as a pupal skin, and develops into the winged insect out of the water. The per- fect insect resembles the Lepidoptera in many respects, and lives near water on leaves, and the stems of trees. The female lays her eggs in clumps enclosed in a gelatinous case on stones and leaves near water. Pliryganea striata L. (fig. 469). Mijstacides quadrifasciatus Fabr., Hydropsyohe varlabilis Pict. Order 4. Strepsiptera.* Insects with rudimentary anterior wings rolled up at the points and large, hind wings which can be folded longitudinally. The mouth parts are rudimentary. In the female there are neither wings nor legs. The larvce are parasitic in the body of Hymenoptera. The mouth parts are reduced in the adult sexual animal, and CL FIG-. 469. a, Pltryganea strlata. b, The larva freed from its case (regne animal). consist of two pointed mandibles which overlap one another, and small maxillae, which are fused with the lower lip and are provided with two-jointed palps. The prothorax and mesothorax are two very short rings, but the metathorax is unusually elongated, and covers the base of the abdomen, which consists of nine segments. The males possess small rolled-up wing covers, and very large hind wings, which can be folded longitudinally like a fan. The females have no eyes, and remain through life without wrings or legs like maggots ; they never leave their pupal skin nor their parasitic * W. Kirby, "Strepsiptera, a new order of Insects/' Transact. Linn. Soc., Tom X. v. Siebold, "Ueber Xenos sphecidarum und dessen Schmarotzer," Beitrage zur Naturgeschichte der wirbellosen Thiere, 1839. ruv. Siebold, "Ueber Strepsiptera," Archiv fiir Xaturgesch., Tom IX., 1843. Ctis, " British Entomology," London, 1849. 566 INSECTA. habitat in the abdomen of wasps and humble bees (Bombyliidce) from which they only protrude the anterior part of their body. In copu- lation the males are said to open by means of their copulatory organ the dorsal tube of the female, which is at first closed. The ovaries have no oviduct, and continue as it seems at an earlier stage of development, since they probably like those of the viviparous Cecidomyia larva? produce eggs. The eggs fall freely into the body cavity, are fertilized and develop (perhaps sometimes parthenogene- tically) into larvse, which pass out through the above-mentioned dorsal canal and become attached to larvre of bees and wasps (fig. 470). In this larval state they are able to move about and possess, like the young larva? of Cantheridce, three well-developed pairs of legs, and two caudal setae on the abdo:nen. They bore their way into the body of their new host. About eight days later they undergo an ecdysis, and Change to an apodal cylindrical maggot, which becomes a pupa within the Hymenopteran pupa, and as such bores its way out with its head from the abdomen of the latter. The males leave the pupal skin and seek the females. They seem to live only a short time. Fam. Stylopidse. Xcnos Rossii Ivirb. (_Y. vcsparum Ross.) parasitic in Polistes gallica. Stylojts melittcn Kirb. FIG. 47Q.Stylops Cli ildreni (after Kirby). a, Larva. I, Female, c, Male. Order 5. Rhynchota* = Hemiptera. Insects with jointed rostrum, piercing (exceptionally biting) mouth parts. With usually free prothorax and incomplete metamorphosis. The mouth parts are almost without exception arranged for taking up fluid nourishment, and are usually represented by a rostrum, in which the mandibles and maxillre, as four rigid styles, are moved backwards and forwards. The rostrum, which is formed * Burmcister, " Handbuch der Entomologie." II. Bd., Berlin 1835. J. Halm, "Die wanzenartigen Insectcn." isiirnberg, 1831-184'J. Continued by H. Schiiffcr. F. X. Fiebcr,"Dic europaischcn Hemipteren nach dcr analytischen Methode." Wien, 1800. EHYNCHOTA. 567 by the labium, is a three- or four- jointed almost closed tube, which is narrowed towards the point, and is covered at the larger open base by the elongated three-cornered upper lip. The antennae are either short and three-jointed with a setiform terminal joint, or are many- jointed and often elongated. The eyes are small and usually facetted, but they are sometimes ocelli with a simple cornea. Frequently two ocelli are found between the facetted eyes. The prothorax is usually large and freely moveable, but all the thoracic segments may be fused together. Wings are sometimes quite absent ; usually four, rarely two, are present. In the first case the front wings are horny at the base and membranous at the tip (Hemiptera), or the front and hind wings are similarly formed and are membran- ous (Homoptera), though the anterior are often stiffer and coriaceous. The legs are, as a rule, adapted for walking, but sometimes they serve for clinging or swimming. In other cases the front legs are used to capture prey, or the posterior for springing. The alimentary canal is distinguished by the numerous salivary glands, and by the complicated chylific ventricle, which is often divided into three regions ; behind the chylific ventricle usually four Malpighian tubes open into the hindgut. The ventral cord is concentrated into three, usually into two thoracic ganglia. With exception of the. Cicada, the female genital organs have only four to eight egg-tubes, a simple receptaculum seminis and no bursa copulatrix. The testes are com- posed of two or more tubes, the ducts of which are usually dilated at the lower end. Many (bugs) emit an offensive smell, which pro- ceeds from the secretion of a gland placed in the mesothorax or metathorax, in the latter case opening between the hind limbs. Others (Homoptera) secrete by means of numerous cutaneous glands a white waxy film which covers the surface of their body. They all live on vegetable or animal juices, to which they obtain access by means of the piercing styles of their rostrum. Many of them, by their appearance in great numbers on young plants, are harmful, and sometimes cause gall-like outgrowths; others are parasitic on animals. The young, when hatched, possess the form and habits of the sexually mature animal. They have, however, no wings, which make their appearance as small stumps after one of the first moults. The true Cicada need several years to effect their metamorphosis. The male Coccidce change inside a cocoon to quiescent pupae, and undergo accordingly a complete metamorphosis. Sub -order 1. Aptera=Parasitica, Wingless Rhynckota, with short fleshy rostrum and broad cutting styles. Sometimes they have 568 IXSECTA. rudimentary biting mouth parts, an indistinctly segmented thorax, and an abdomen which usually consists of nine segments. Fam. Pedicuiidse. Lice. With fleshy proboscis-sheath armed with recurved hooks, protrusible suctorial tube, and two protrusible knife-like stylets. The antennae have five joints. The feet, which are adapted for clinging, have hooked terminal joints. The eyes are small and not facetted. The animals live on the skin of Mammalia, and suck their blood, and lay their pear-shaped eggs in the roots of the hair. The young, when hatched, do not undergo a metamorphosis, and the louse which infects the human head, is fully developed and capable of reproduction in eighteen days. Pedlcultis cap'itls Deg. Head- louse of man. P. vestimenti Burm. (larger and of pale colour). Phthirms pubu L. (fig. 471). Fam. Mallophaga (Anoplura) (Pelzfrcsscr). Lice-like in form, with three- to five-jointed antennas, and biting mouth parts, no fleshy proboscis, but a sort of suctorial tube. They live on the skin of Mammalia and Birds, and feed on young hairs and feathers, but also on blood. Trichodcctes cants Deg. Pliilopterus FIG. 471. Phthiriug publs (after Landois) St, Stigma; Tr, Trachea. anseris Sulz. Menopon Nitsch, M. pallidum Nitsch, on fowls. Sub-order 2. Phy- tophthires. * Rhyn- cJiota with two pairs of membranous wings. The female is usually apterous. The surface of the skin is very often covered with a dense waxy deposit, the product of cuta- neous glands which are placed in groups beneath warty prominences of the segments. Fam. Coccidae (Schildlause). The large females have a shield-shaped body, and are wingless. The males are much smaller, and have large front wings, and sometimes also rudimentary hind wings. The fully-developed males have no proboscis or piercing weapons, and do not take in nourishment, while the unwieldy, often unsymmetrical females, which may even have lost the segmentation, insert their long rostrum into the parenchyma of plants and remain motionless. The eggs are deposited beneath the shield-shaped body * C. Bonnet, "Traite d'Insectologie," Tom. L, Paris 1745. J. F. Kyber," Erfahrungen und Bemerkungen iiber die Blattlause." Germans Magaz. der EntomoL Tom. I., 1815. J. H. Kaltenbach, " Monographic der Familie der Pflanzcnlause." Aachen, 1843. K. Leuckart, " Die Fortpflanzung der Rindcnlause." Arcldvfiir Naturgesch., 1859. RIIYXCHOTA. 539 and develop, protected by the drying-up body of the mother. They are generally fertilized (Coccus'), but sometimes develop parthenogenetically (Lecanlum , Aftpidiotus). Unlike the female (and forming a single exception to what otherwise obtains in the order), the males undergo a complete metamorphosis ; the apterous larvae surround themselves with a cocoon, and are transformed into quiescent pupre. Many Coccidcs cause great damage in conservatories. Others are useful in industry, in that they produce a colouring matter (cochineal), while others are useful in causing, by their puncture, an outflow of vegetable juices which when dried, are used by man (lac, manna). A.yidiotus nerii. Bouche, found on the Oleander, Lecanlum lieKperidum L., L. persicce Bouch6. Kermcs ilicis L., on Quercus coccifera, also K, 1 (Coccus) lacca Kerr., on Ficus religiosa in the East Indies. Coccus cacti L., (fig. 472) lives on Opuntia coccinellifera, Mexico, gives cochineal. C. adonidum L., C. (?) inanniparus Ehbg.. on Tamarix (manna). Fam. Aphidae,* plant-lice. As a rule, there are four transparent wings, with a scanty venation. The wings may, however, be absent in the female, and rarely in the male. The Aphides live on vegetable juices, and are found on roots, leaves and buds of quite definite plants. They frequently live in the spaces of gall-like swellings or deformities of leaves, which are produced by the punctures of the plant-lice. Many of them possess, on the dorsal surface of the antepenultimate segment, two "honey tubes," from which is secreted a sweet fluid the honcydew which is eagerly sought for by ants. In addition to the usually apterous females, which, as a rule, only appear in autumn with the winged males and lay fertilized eggs after copulation, there are also viviparous, usuall3 r winged generations, which appear principally in the spring and in summer, and which produce their living brood without the assistance of males. Bon- net observed nine generations of viviparous aphides succeed one another. They are distin- guished from the true oviparous females, not only by their form and colour, and. in many cases, by the possession of wings, but also by essential peculiarities in the generative apparatus and the eggs (iJseudova, germs). The receptaculum seminis is absent, and the eggs undergo their embryonic development in the very long egg-tubes. Viviparous and oviparous aphides usually succeed one another in regular alternation, since the females lay fertilized eggs in the autumn, which survive the winter and in the spring give birth to viviparous aphides, the descendants of which are also viviparous, and produce viviparous forms through a number of generations. It is only in the autumn that the males and the oviparous females are born which copulate. Viviparous individuals of many forms seem to pass the winter in ant-hills. Sexual forms (at time of birth already mature, wingless and without proboscis) are sometimes found in the spring ; they arc in all probability produced by such viviparous forms which have persisted through the winter. This has been shown to be the case for FlG. 472. Coecut cacti, a, Female. I, Male (after Burineister). * Derbes, "Notes sur les Aphides du pistachier terebinthe." Ann. dcs Sc. Nat. 1872. 570 INSECTA. Pemphigus tcrebintlii by Derbes. Here the sexual animals are succeeded by apterous asexual animals, which produce the galls, and the descendants of which are the winged asexual generations which are dispersed and pass through the winter. The reproduction of Chermes and Phylloxera is different, in that in place of^the viviparous generations there is a special oviparous sexual form, which also produces eggs capable of developing parthenogenetically. The apterous females of the fir-tree lice pass the winter at the base of the young buds, increase in size in spring in the same place, undergo several moults, and lay a number of eggs. The young, when hatched, pierce the swollen pointed leaves of the young shoots and produce galls. They develop later into winged females. In Phylloxera quercus, besides the two generations, there is another genera- tion, which appears in autumn and consists of very small movable males and females (without suctorial proboscis or alimentary canal). These animals arise from two kinds of eggs which are laid on the roots. The female, after copula- tion, lays only a single egg. It is the same with the famous vine-lice (PA. vastatrix), the larvae of which pass the winter on the roots of the vine (fig. 473). The principal enemies of the Aphides are the larvae of the Ichneumonidce (Aphidius}, SyrpJiidce, Coccinellce and Heine- robidce. a. Leaf -lice, s. st. ScJiizoneura lanigera Hartg., on apple trees. Lachnus pini L., L. jiifjlandis L., L.fagi L., Aphis brassicce L., A. rosce L. 5. Bark-lice. Chermes dbictis L., Ch. laricis Hartg., Phyl- loxera quercus v. Heyd., on oak leaves. Ph. vastatrix, vine- lice, with winged and apterous generations. Fam. Psyllidae (Psyllodes}, leaf -fleas. Antennae long, with ten joints. In the fully -developed stage always winged. The hind legs serve for springing. Their puncture often occasions deformities of flowers and leaves. Psylla alni L., Livia juncoruin Latr. Sub-order 3. Homoptera-Cicadaria. Both pairs of wings are, as a rule, membranous. Sometimes the front' pair is coriaceous, not transparent and coloured. They lie, when at rest, obliquely on the body. The head is relatively large, and often prolonged into pro- cesses. The rostrum always arises low down, and apparently between the front legs ; it has three joints. In many species the hind legs are springing legs, with which the animal jumps before flight. The females have an ovipositor, and often lay the eggs beneath the bark and in the twigs of plants. The larvre of larger species may live several years (fig. 474). FIG. 473. Phylloxera vastatrix. a, Wingless root-louse seen from the back, b, from the ventral surface. c. Winged form. RHYNCHOTA. 571 Fam. Cicadellidse (Klcinzirpen). Jassus T)>guttatns Fabr., Lcdra aurita L., Tettigonia 'dttata L. Aplirophora. The prothorax is trapezoidal (seven- cornered). The larva) eject a bubbly foam out of the anus (cuckoo-spittle), and envelop themselves in it. The wing covers are' coriaceous. Posterior tibire have three strong spines. A. sjmmaria L. Fam. Membracidae (Buckelzirpen). Coitrotus cormitus L., M-smbracis later alls Fabr. Fam. Fulgoridae (Leuchtzirpen). In many species the abdomen is thickly covered with long strings and flakes of wax, which in one species (Plata, linibata) is so richly secreted that it is collected and sold as Chinese wax. Fulgora laternaria L., the lantern carrier of Surinam, is erroneously said by Merian to emit light from its lantern-shaped frontal process. F. candelaria L., Chinese lantern-carrier. Lystra lanata L., and other American species. Flata limbata Fabr., China. Fam. Cicadidae = Stridulantia (Singcicaden). The thick abdomen of the male is provided with a voice organ, which produces loud, shrill, chirping sounds (fig. 474). They are very shy, and remain concealed between leaves in the day time. They feed on the juices of young shoots, and their puncture causes a flow of sweet plant juices, which harden and become manna ( Cicada orni L., Sicily). The females have a saw-like ovi- positor placed be- tween two jointed valves. The larvae, when hatched, crawl on the earth, into which they burrow with their shovel-like front legs, and suck the juice of roots. Cicada orni L., South Europe. C. septemdecim Fabr., Brazil. C. liamatodes L., South Germany. Sub-order 4. Hemiptera (Bugs). The wings of the front pair are half horny and half membranous (hemielytra), and lie horizontally on the body. Many species are apterous, as are the females of some species of which the males have wings. The first thoracic segment is large* and freely moveable. The proboscis arises from the frontal region, and when at rest usually lies folded beneath the thorax. Some species of the Reduvidce produce a shrill sound, as Pirates stridulus, by the movement of the neck on the prothorax. Tribe 1. Hydrocores = Hydrocorisae (Water-bugs). The antennae are shorter than the head, having only three or four joints, and are Fio. 471. Cicada orni (after Packard), a, Larva. J, Pupa. c, Male, Ty, Stridulating apparatus. 572 IXSECTA. more or less hidden from view. The rostrum is short. They feed on animal juices. Fam. Notonectidae (Riickenschwimmer). Corlxa striata L., Nutonecta glauca L., water-bug. Fam. Nepidae, water- scorpions (fig. 475). Naucoris cimicoides L., Nepa cincrea L., water-scorpion. Ranatra linear Is L. Tribe 2. Geocores (Land-bugs). Antennae directed forwards, and of medium length, having four or five joints. The rostrum is usually long. Fam. Hydrometridae (Plater es) (Wasserlaufer). Hydromctra lacustris L., Limnobates stagnorum L., Velia riculorum Latr. Fam. Reduvidse (Reduvini) (Schreitwanzen). Reduvius personatu-s L., Pirates stridulus Fabr., South Europe. Fam. Acanthiadae (Membranacei), skin-bugs. Acanthia lectularia L., bed- bug. Aradus depressus Fabr. (corticalis L.). Fam. Capsidae (Blindwanzen), Capsus trifasciatus L., Miris erraticiis L. Fam. Lygaeidae (Lygaodes) (Langwanzen). Lygceiis equestris L., Pyrrliocoris apterus L. (Feuerwanze). Fam. Coreidae (Corcodcs) (Randwanzen). Coreus vnarginatiis L., Alydus calcaratns L. Fam. Pentatomidae (Schildwanzen). Pentatomajuni- pera L., P. rvfipes L., P. olcracea. Order 6. Diptera * (Antliata). Insects with piercing and sucking mouth parts, with membranous front wings. The hind wings reduced to small knobs (halteres). The metamor- 2)hosis is complete. The designation of this order, which is de- rived from the apparent number of the wings, does not correspond accurately to the actual Two pairs of wings are present, the front pair always as large glassy and transparent plates, the hind pair in a rudimentary condition as stalked knobs (halteres). On the inner margin of the front wings two lobes are marked off by indentations ; an ou'.er lobe (alula], and an inner one (squama) which may cover * J. W. Mcigen, " Systematische Beschreibung der bekanntcn europaischen, zweifliigeligen Inscctcn," 7 Theile. Aachen, 1818-1838. Wiedemann, " Aussereuropaische zweifltigelige Insecten," 2 Theile. Hamm. 1828-1830. N. Wagner, " Ueber die viviparcn Gallmiickenlarven," Zcitschr. fiir. wiss. Zool., Tom. XV., 1SG5. A. Weissmann, " Die Entwickelung der Dipteren," Lcipsig. 1864. A. AVeissmann. " Die Metamorphose der Corcthra plumicornis," 1806. FIG. 475. ]\~epa cincrea, (regne animal). state of matters. DIPTERA. 573 the hind wings. The latter are composed of a spherical head at the end of a thin stalk. Leydig described at the base of the halteres a ganglion with nervous rods, which he concluded was an auditory apparatus. The head is freely moveable, and usually spherical in form. It is articulated to a short and narrow neck, and is dis- tinguished by the large facetted eyes, which in the male sex may meet in the median line of the face and frontal region. There are as a rule three ocelli. The antennae are constructed on two different types ; they may either be very short and composed of three joints, frequently bearing a tactile hair at the extremity (arista), or they may be filiform and of considerable length and composed of a great number of joints. But since in the first case the terminal joint is again divided into a number of smaller joints, and the tactile hair may be also jointed, it is impossible to draw a sharp distinction between the two types. The mouth parts form the kind of suctorial tube known as a proboscis (haustellum), in which the jaws (mandibles and maxillae) and an unpaired rod (epipharynx) attached to the upper lip may appear as horny, setiform or knife- shaped piercing organs. When the maxillae only are present as paired rods, the unpaired piercing stylet seems to correspond to the fused mandibles. The proboscis, which is principally formed by the labium, ends with a swollen spongy tongue, and is without labial palps, while the maxillae are provided with palps, which, in cases of fusion with the labium, are situated on the proboscis. The abdomen is frequently stalked, and consists of five to nine segments. The legs have five- jointed tarsuses, which end with claws and usually with sole-like lobes for attachment. The nervous system presents very different degrees of concentra- tion according to the length of the body. While in flies of very stout build, the ganglia of the abdomen and thorax fuse together to form a common thoracic ganglion; in the Diptera with longer bodies, not only are the three thoracic ganglia distinct, but several, even five or six, separate abdominal ganglia are present. With regard to the alimentary canal, the presence of a stalked suctorial stomach as an appendage of the oesophagus and the number four of the Malpighian tubes may be mentioned. The two tracheal trunks are dilated to two great vesicular sacs at the base of the abdomen. This is correlated with the power of active flight possessed by these insects. The male genital organs consist of two oval testes with short vasa deferentia, to which are added firm copulatory appendages. The 574 IXSECTA. ovaries are not connected with any special bursa copulatrix, but have three receptacula seminis in connection with the vagina (fig. 449), and often end with a retractile ovipositor. There is rarely a striking difference between the two sexes. The males have as a rule larger eyes, which in some cases meet each other in the middle line ; their abdomen also is frequently differently shaped to that of the female, and in exceptional cases the colouring is different (Bibio}. The mouth-parts, too, may differ ; for example, the male gad-flies (Tabanidce) are without the knife-shaped mandi- bles, which form the principal part of the female armature. The males of the Culicidce also are without the piercing weapons, and have multiarticulate hairy antennae, while the antennae of the female are filiform, and are composed of fewer joints. The metamorphosis is complete, and the larvae, which are usually apodal, have either a clearly separate head with antennae and ocelli (most Nemo- cera), or a short, usually retracted, 1f^lff\ cephalic region, without antennae or J \, \f eyes (at most with an X-shaped pig- ment spot), with quite rudimentary mouth parts, sometimes with two oral hooks, serving for attachment. In the first case the larvae have masticating mouth-parts and feed on other animals ; in the latter case they are known as maggots and suck up fluids or semi-liquid substances. After several moults the larvae either change within the hardened larval skin to pupae (P. coarctata), or casting the larval skin are transformed into moving pupae (P. obtecta), which often swim freely in water, and may be provided with tracheal gills. The differences which the development of the winged insect from the larval organism presents in the two groups have been already mentioned (p. 550). Many Diptera when flying give rise to buzzing sounds. This is caused by the vibrations of various parts of the body; partly of the wings and partly of the segments of the abdomen, with participation of the voice apparatus on the four stigmata of the thorax. Here, beneath the margins of the stigmata, the tracheal trunk forms a vesicle with two delicately folded leaflets, which FlG. 7G. pobosca equ'tna (after Packard). DIPTERA. 575 are set in vibration beneath two external valves by the expiration of air. Sub-order 1. Pupipara* (fig. 476). Lice flies. The body is stout ; the three thoracic segments are fused together, the abdomen is broad and often flattened. The antennae are short, and often consist of but two joints. The suctorial proboscis is formed by the upper lip (labruin) and the maxillae. The legs are provided with toothed clasping claws, and the wings may be rudimentary or absent. The development of the embryo and of the larva takes place in the uterus-like vagina. The maggot which issues from the egg (without pharyngeal framework or buccal hooks) swallows the secretion of large glandular appendages of the uterus (fig. 451) ; it undergoes several moults, and is completely developed when it is born, which occurs just before it enters the pupal stage. They are parasitic, like lice, on the skin of warm-blooded animals, rarely of insects. Braula cosea, Nitzsch., Bee louse. Nyctcrilia Latrcillci Curt., without eyes and is parasitic on species of Vespertilio. MglopkaffUt ovinvs L., Sheeptick. Anapcra pallida Meig.. parasitic on Swallows. IRppobosca equina, L., horse-louse. Sub-order 2. Brachycera (Flies). Body of very various shape, frequently thick and FIG. ^i7.Gastrophllus equl (after F. Urautr). StOUt, With an abdomen COm- a, Larva. i.Male. posed of from five to eight segments. Antennae short, and usually composed of three joints with large, usually secondarily ringed terminal joint, to which is attached a simple or ringed bristle. Wings are almost always present. The larvae live in decaying matter in earth and water, partly also as parasites; they are, in great part, maggots with hooked jaws, and pass into the pupal stage within the moulted cask-shaped larval skin (fig. 477). Many of them have the form of a pupa obtecta. Tribe 1. Muscaria. With frontal vesicle; proboscis usually with fleshy terminal lobe ; maxillae as a rule aborted ; larvae without jaw * L. Dufour. " Etudes anatomiques et physiologiques sur les Insectes Dipteres de la famille des Pupipares." Ann. de* Sc. A r at., II. ser., Tom. III., 1843.' R. Lenckart, ' Die Fortpflanzung und Entwickelung der Pupiparen." A bhand. der naturf. GeselUckaft zu Halle, Tom. IV. 57G INSECTA. capsule and as a rule with two or four oral hooks. The pupre are always barrel-shaped. Fam. Phoridae. Phora incrassata Meig. Live as larvae in Bee hives. Fain. Acalyptera. Trypeta Cardul L., Tr. signata Meig., in cherries. Cldorops lincata Fabr. (Weizenfliege), Larvae in blades of grass. Scatopkaga stcrcoraria L., dung-flies, on dung heaps. PiopMla casei L., cheese-flies. Fam. Muscidae. Nmca domestlca L., house-fly. M. Ccc.mr L. (Goldfliege). J/. vomit oria L., the abdomen is of a shining blue colour. M. cadaver ina L.. (Aasfliege). Sarcopliaga carnarla L. (Fleischfliege), viviparous. Tachina puparuni Fabr., T. {Chrysosoma') viridis Fall., T. grossa L., T. larvarum~L. The larvae are parasitic, principally in caterpillars. Fam. Conopidae. Conops flampes L., the larvae live in the abdomen of Ilymcnoptera. C. rvfipes Fabr. (in CEdlpoda). Fam. Stomoxyidae. Stomoxys calcitrans L. (Stechfliege), resembles the house-fly. Fam. (Estridae* (Biesfliegen). The proboscis is aborted. The females have an ovipositor and lay their eggs or their living larvae (in which case the ovipositor is absent) on ceitain places on Mammalia, e.g., in the nostrils of Stags, or on the breast of the Horse. The larvae with dentated body rings r and frequently with oral hooks, live in the frontal sinuses, beneath the skim and even in the stomach of certain Mammalia. Under the skin they produce boils. Hypoderma bovis L. If. Actaon Br., on the Stag. H. tarandi L. Dermatolia hominis Goudot, on Ruminants, Fdidce (Jaguar) and Men in South America. (Estrus auribarbis Wied. The larvae are brought by the flies into the nasal cavities of the Stag. Gastrus (Gastropliilus) cqui Fabr. (fig. 477). The egg is deposited on the breast of the Horse, and licked off by the latter. The larva, when hatched, attaches itself to the T\ alls of the stomach by its oral hooks, undergoes several moults, and is passed with the excrements before the pupal stage. Fam. Syrphidae (Schwebfliegen). Syrpkvt pirastri L., Eristalis tenax L., E. (BHCV.S Fabr. Larvae with respiratory tube, in sewers and stagnant water. Fam. Platypezidae (Pilzfliegen). PI. boletina Fall. Tribe 2. Tanystomata. The proboscis is usually long and has styliform predatory jaws. Larvae with jaw sheath and hooked jaws. Fam. Dolichopodidae. Doliclwpm pennatus Meig. D. nobilitatus L. Fam. Empidae (Tanzfliegen). Empis tessclata Fabr. Fam. Asilidae (Raubfliegen). Asilus germanicus L., A. cralroniformis L. ? LapUria gibbosa Fabr. L.flava Fabr. Fam. Bombyliidae (Hummelfliegen). Anthrax morio Fabr. (sinuatm Fall.). The larvae live in the nests of Megacliile muraria and Own-ia tricorn'ns. Bombyl'ms major L., B. mcdius L. Fam. Henopiidae. Hennps gibbosus L. (Mundhornfliege). Lasla flavitarsis Wied. Fam. Therevidae (Xylotomai), (Stilettfliegen). TJwrcva anmdata Fabr, Tli.plclcja L., Scenopinus fencstrcdis L. Fam. Tabanidae (Gadflies). Proboscis short, horizontally projecting, and provided with six or four (male) stylets and two-jointed palp. In the male * F. Braucr, " Monographic dcr QEstridcn." Wicn. 18G3. DIPTERA. the knife-shaped mandibles are wanting. Their puncture is severe, and they suck blood. Ckrysops ccecutiens L., Talanus bovinus L. (Linderbremse). Hamatopota pluvialis L. (Regenbremse). Fam. Leptidse (Schnepfenfliegen). Leptis scolopacea L., L. vcrmileo L., South Europe. The larva digs holes in the sand, and there, like the Ant-lion, captures insects. Fam. Xylophagidae (Holzfliegen). Xylophagus maculatus Fabr. The larvre live in beech wood. Bcris clavipes L. Fam. Stratiomyidae (Waffenfliegen). Stratiomys chamcclcon L., St. Odon- tomyia hydrolcon L., Sargus cuprarius L. Sub-order 3. Nemocera (Tipulariae). Longhorns (fig. 478). Diptera of elongated form, with many-jointed, usually filiform, antennae, which in the males are sometimes tufted. They have long slender legs, and large, naked or hairy wings. The palps are usually of considerable length, and with four or five joints. The proboscis is short and fleshy, and often armed with The The larvae have usually a perfectly differentiated head (Eucep/iala),more rarely a retractile jaw ^^ n capsule (Tipulidce,Ceci- domyia)', they live in water, in earth, and in vegetable matter (galls and fungi), and some of them have a respiratory tube. After moulting the larval skin the eucephalous larvae become quies- cent or freely moveable pupae ; the latter are provided with tracheal gills on the neck and tail, The insect when hatched swims, till the wings are hard, on the burst pupal skin as on a boat. The females of many species suck blood (gnats), and become a veritable pest in certain districts where they appear in swarms. Fam. BiMonidse (Musci formes}. Body fly-like ; antennae six- to eleven- jointed. The abdomen has seven segments. JSibio viarci L., B. hortulamis L. The males are black, the females brick red with a black head. Simulia reptans L., S. columbacsckensis Fabr. (Kolumbaczer Mucke). Suck blood. In flun- gary they attack the herds of cattle in swarms. 7 piercing setae, halteres are free. FIG. 478. Ceridomyia tritici (after Wagner), a, Female with protruded ovipositor. 6, Larva, c, Pupa. 578 INSECTA. Fam. Fungicolae (Pilzmucken). The larvae, which are without rudimentary feet on the second segment, live in fungi. Sciara To ma L. The larvse before entering the pupal stage come together in great numbers, and wander about in long sinuous chains. Myccto^lnla fusca Meig., (Pilzmucke), Scinphila macu- lata Fair. (Schattenmiicke). Fam. Noctuiformes (owl-like gnats). Psyclioda plialcenoidcs ~L.) Ptychoptera contaminata L. (Faltenmiicke). Fam. Culiciformes. The larva? live in water, in rotten wood, or in earth. Chironomvs plumosus L., Coreilira plu^icormst t Fabr. The larvae have four tracheal vesicles and a circle of setJe on the anal segment ; live in water. Fam. Culicidae (gnats). The larvas live in water and have respiratory tube and appendages at the posterior end of the body. Culexpipiens L. (Singmiicke). The palp of the male is tufted and longer than the proboscis. The females sting. Fam. Gallicolae (gall-flies). The larvae live in galls. Cecidomyia destructor FIG. 479. a, Pulcx avium J (after Taschenberg) . A Antenna; Mt. Maxillary pulp. J,Larva of Pulex irritant. Say, Hessian fly. Notorious in the United States as a destroyer of crops since the year 1778. Imported (?) into the country in straw by the Hessian troops. C. tritlci Kirb., in wheat. C. sec.alina Loew. C. sallcis Schrk. etc. The vivi- parous larvae belong to the genus Jfiastor. Fam, LinmoMidae (Schnaken). The larvae are found in earth or rotten wood. Tipula oleracea, L., (Kohlschnakcn,. Ctenoplwra atrataL. (Kamm- miicke). Sub-order 4. Aphaniptera (Fleas). Dijrtera, with laterally com- pressed body and distinctly separated thoracic rings. Wings are absent, but there are two lateral plate-like appendages on the meso- and meta-thorax. The antennas are very short and arise in a depression behind the simple ocelli. The mandibles have the form of toothed saw-like stylets, the maxilla are broad plates with four- jointed palps. The under lip (labium) is three-jointed and forms LEPIDOPTERA. 579 the proboscis sheath. The larvae have a distinct head and jaws (fig. 479). Fam. Pulicidse. Pulex irritanx L., flea of man. The dorsal surface of the male is concave and serves for the reception of the larger female. The large apodal larvae have a distinctly separated head, and live in sawdust and between boards, where the elongated oval eggs are deposited. Sarcopsylla penetram L., sand-flea (Chigoe), lives free in South America in the sand (fig. 480). The female however bores into the skin of the human foot and of various Mammalia, and there deposits the eggs. The escaping larvae give rise to ulcers. Order 7. Lepidoptera* (Butterflies and Moths). Insects with suctorial mouth parts, which form a spirally rolled, proboscis, ivith four similar wings which are completely covered with scales, with fused prothorax and complete metamorphosis. The head is moveably articulated and thickly covered with hairs. It bears semi- circular facetted eyes and some- times two ocelli. The antennae are always straight aiidmany- J V'|H1HH|B|BV T ^ > jointed, but vary much ill form, FIG. 480. a, Gravid female of Sarcopylla penetrans. b, Foot of a beino 1 often seti- fieM m USe Y?lth ^r 110110 ? 1 11 attached (after H. Karsten). form or filiform, or even club-shaped, and not rarely denticulate or pectinate. The mouth parts are modified for sucking up fluid nourishment, especially the nectar of flowers, but are occasionally very short and hardly capable of being used. The upper lip and mandibles are reduced to rudiments, but the maxillae are elongated and closely jointed, and their inner sides are grooved, so that when applied together they form a tube the spirally rolled proboscis (fig. 481). The proboscis is furnished with small spines used for tearing the nectaries of flowers ; while the nectar ascends through it into the mouth, being sucked up by pumping movements of the * E. J. C. Esper, " Die europaischen Schmetterlinge in Abbildungen nach der Natur, mit Beschreibungen." 7 Bde. Erlangen, 1777 1805. F. Ochsenheimer und F. Treitschke, " Die Schmetterlinge von Europa." 10 Bde. Leipzig, 1807-1835. W. Herrich-Schaffer, " Systematische Beschreibung der Schmetterlinge voa Europa." 5 Bde. Eegensburg, 1843-1S55. W. Herrich-Schaffer, " Lepidopterorum exoticorum species novas aut minus cognitaj. Kegensburg. 1850-1865. 580 INSECTA. oesophagus. The maxillary palps are as a rule rudimentary (except in the Tineidce). When at rest the proboscis lies rolled up beneath the mouth, and on either side of it are placed the large three- jointed labial palps, which are often tufted with hairs and are situated on the rudimentary triangular lower lip. The three thoracic rings are intimately fused with one another, and like almost all external parts of the body are thickly covered with hairs. The wings are in most cases very large, but in rare cases are quite rudimentary (female Geometridce) ; the anterior are the largest, and are distinguished by their partial or complete covering of scale-like hairs which overlap one another in a tectiform manner, and cause the extremely various colouring, tracing, and iridescence of the wings. These scales consist of small, usually finely ribbed and toothed plates, which -A ^ Md \ are attached by styli- form roots in pores of the integument of the wings, and are com- parable to flattened out hairs. They arise during the pupal period. The arrange- ment of the nervures is of systematic value. The essential arrange- ment is a large median cell near the root of the wing, from which six to eight radial nervures pass to the external lateral edges, while above and below the middle cell single independent nervures run parallel to the upper or lower fringed margin. The two pairs of wings are frequently connected with one another by retinacula, the upper edge of the hind wings being covered by spines or setae, which catch in a band of the anterior wings. The legs are delicate and weak, their tibi are armed with spurs of considerable size. The tarsuses are in general five-jointed. The abdomen has six or seven segments and is thickly covered with hairs, and ends not unfrequently with a strongly projecting tuft of hairs. Nervous system. The brain is bi-lobed, and is provided with large FIG. 481. Mouth-parts of butterflies, (after Savigny) ; a, of Zygcena ; I, of Noctua. A, Antennae ; Oc eyes ; Md, mandibles ; Mxt maxillary palp ; MX, maxilla ; Lt, labial palp ; Lr, labrum. LEPIDOPTERA. 581 optic lobes, and special swellings for the origin of the antennal nerves. The ventral ganglionic chain is reduced, leaving the subceso- phageal ganglion out of consideration, to two thoracic ganglia (of which the larger second ganglion shows traces of constrictions and arises from the fusion of four ganglia) and four or five ganglia in the abdomen. In the larval condition, on the other hand, there are eleven pairs of ventral ganglia. The alimentary canal possesses a long oesophagus, which is connected with a stalked suctorial stomach, and usually six much coiled Malpighian tubes, of which the three on either side open by a common duct (figs. 47 and 48). Generative organs. The ovaries consist on either side of four very long many-chambered egg-tubes, which contain a great quantity of eggs, and have, in consequence, a moniliform appearance. The duct apparatus always possesses a long-stalked receptaculum seminis with glandular appendages, and a large bursa copulatrix which opens indepen- dently beneath the genital opening. The T two long testicular canals are packed to- * gether so as to form an unpaired, usually brightly coloured body, from which pass off the two vasa deferentia, which are much convoluted and receive the con- tents of two accessory glandular tubes before Uniting to form a ductllS ejaCU- FIG. 482. a, Female of Psyche helix. latorius. The two sexes are often so 6 > Male - c Case of the male ' d > of the female caterpillar. different in size, colour, and the struc- ture of the wings, that there is a sexual dimorphism. The males are often more brightly and beautifully coloured (a means of exciting the females). The dimorphism, or even polymorphism (seasonal dimorphism), found in the female sex of many butterflies, -is worthy of remark. Parthenogenesis occurs exceptionally in silk- worms (Bombyx mori), in many Psychidce, and some moths (Soleno- bia), the larva-like females of which have no wings (fig. 482). Development. The larvae when hatched (caterpillars) possess masticating mouth parts and feed principally on plants, leaves and wood. On the head, which is large and covered with hard skin, there are a pair of three- jointed antennae and six ocelli, each of which is divided into three parts. In all cases there are abdominal feet behind the three pairs of conical five-jointed thoracic legs. There may be only two pairs of such legs, as in the caterpillars of the 582 IXSECTA. Geometridce, or five pairs, which then belong to the third to the sixth and the last abdominal segments. The caterpillars establish them- selves before passing into the pupal stage in some protected place, or they spin cocoons and become transformed into pupae, obtectcv*, from which the winged insects issue either in a few weeks or in the following year. The winged insects, as a rule, live only for a short time, and die after copulating and laying their eggs. Some of them, however, pass the winter in sheltered localities (Rhopalocera). Some very widely distributed species of caterpillars cause great damage to forests and cultivated plants, a damage which is, however, limited by the persecution which they suffer from certain Ichneumonidce and Tachinaria. Fossil remains of butterflies have been found in tertiary formations and in amber. Linnseus' classification of the Lepidoptzra into diurnal, twilight, and nocturnal butterflies has been superseded by the establishment of several groups and a number of families. Tribe 1. Microlepidoptera. Very small and delicately formed Lepidoptera, usually with long setiform antennae. The caterpillars have as a rule sixteen legs, of which the abdominal feet are provided with a circle of hooks round the sole. Many of them bore passages in the parenchyma of leaves, others live in leaves folded together, and others in buds. Some few are found in water, e.g., Nymplmla and other Pyralidce, The greater number remain hidden during the day. Fam. Pterophoridae (Fcdergeistchen). Plume-moths. PtcropUorus penta- dactylus L., Pt. pterodactylus L., Alucita hexadactyla L. Fam. Tineidae Yponomcuta evonyinclla L., spindle-tree moth. The cater- pillars live together in cocoons ; several species live on fruit trees. Sdlenobia 2nneti=lichenella L., S. rtg3ttfg22a)Fisch., E., the female is apterous. The caterpillars (sac-bearers) live in short sacs. Some of them reproduce partheno- genetically. Tinea granella L., (Kornmotte). Lays its eggs in grain. The caterpillars (known as grain worms) eat the grain. T.pdlionella L., (Pelzmotte) T. tapczclla, L. (Tapetenmotte). Clothes-moth. Fam. Tortricidae (Wicklcr). Tortrix viridana'L., in he oak. Graytliolitlia fwicbvana Tr., in plums. Gr. (Carpocapsa) pomonella L., in apples. Fam. Pyralidae (Zunsler). Crainbus pas.cu.dlus L , Botys urticalis L., Galleria mcllionella, L., in bee-hives. Pyralis pingmaalis L. (Fettschabe). Tabby-moth. Scopula friimentalis~L. (Saatmotte). Tribe 2. Geometrina. Loopers. For the most part of slender build and with large wings, which in repose are tectiform. The antennae are setiform and the basal joint is thickened. The caterpillars have ten to twelve feet ; they move in a looping manner. "When at rest * Compare M. Herold, " Entwickelungsgeschichte der Schmetterlinge. " Cassel und Marburg, 1815. LEPIDOPTERA. 583 they cling with the posterior feet. Many species are hurtful to fruit trees. Fam. Phytometridae. Larentia popidata L., Clicimatolia Iriimata L., winter moths. The females, which have rudimentary wings, lay their eggs on the trunks of fruit trees in late autumn. Fam. Dendrometridae. Acidalia oclircata Scop., Gcomctra papilwnaria L., Abraxas (Zercne) grossularlata L.,Harlequin, Magpie Moth. Tribe 3. Noctuina (Eulen). Nocturnal Lepidoptera with broad body which is narrower behind, and dull coloured wings. The antennae are long and setiform, in the male sometimes pectinate. The wings when at rest are tectiform. The legs are long and have strong spurs on the tibiae. The caterpillars, which are sometimes naked, sometimes covered with hairs, have usually sixteen, more rarely, in consequence of the reduction or absence of the anterior legs, fourteen or twelve legs. The greater number pass the pupal stage in the earth. Fam. Ophlusidae (Ordcnsbander). Catocala paranymplia L. (gelbes Ordens-. band). C. fraxini L. (blaues Ordensband). C. nupta L., C sponsa L., C. promissa Esp. (rothe Ordcnsbiindcr). Fam. Plusiadae (Goldeulen). Plusia gamma L., PI. ckrysitis'L. Fam. Agrotidae. Agrotis scgetuin tr. A. tritlci L., Tripliana pronuba L. Fam. Ortliosiadae. Ortliosiajota'L. Fam. Cuculliadae. Cucullia verbasci L., C. absynthii L. Fam. Acronyctidae. Acronycta 2)si L.. A. rumicis L., Diloba cocruleocepJiala L. The caterpillar is harmful to fruit tress. Tribe 4. Bombycina (Spinner). Nocturnal Lepidoptera, of clumsy build, with body thickly covered with hairs so as often to have a woolly appearance. The antennae are setiform, and in the male pectinate. The wings are tolerably broad and tectiform when at rest. The larger and clumsier females fly but little ; but the males, which are often brightly coloured, move with greater rapidity. In some cases the wings are reduced (Orgyia) or are absent (Psyche) in the female sex. The eggs, which are often laid in groups and are covered with a woolly mass, give origin to caterpillars with sixteen legs and a thick covering of hairs ; the caterpillars spin complete cocoons in which they become pupae above ground. The caterpillars of some species live together in common cocoons ; some (Psychidce) prepare a sac in which they conceal their bodies. Parthenogenesis occurs. Fam. Euprepiadae (Barenspinner). The caterpillars with very long hairs, are known as woolly bears. Euprepia caja L., E plantayinis, etc, Fam. Liparidae. Liparis monaclia L., the caterpillar is very harmful to leafy trees and Coniferae. L. dixpar L., Orgyia antiqua L. The female is apterous. O. (JDasycldra) pudibunda L. 584 INSECTA. Fam. Notodontidae. Notodonta ziczac L., N. dromedarius L. Cncthocampn processionea L., the caterpillars live on oaks. Harpyia vinula L. (Gabel- schwanz). The caterpillar has pharyngeal gland and two protrusible anal filaments. Fam. Bombycidae. Gastropacha guercifolia L. (Kupferglucke). G. potatoria L.. G ?'ubi L., G. pini L., Clisiocampa neustria L. ; Bonibyx inori L. Silk- spinner originally from South Asia, but now bred in South Europe and China on account of the silk obtained from its cocoons. The caterpillar (silkworm) lives on the leaves of the mulberry. (The disease of silkworms, the muscardine, is produced by Botnjtis Bassiana). Fam. Saturnidee. Saturnia pyri Borkh. S. carpini, spini Borkh., Attamvt eynthia, Yamaniai, cecropia cultivated for silk. Aglia tau L. Fam. Psychidae. The caterpillars carry about sacks in which they are trans- formed into pupae. Psyche atra L., Ps. helix L. The sacs are spirally coiled and have a second lateral opening, and are different in the two sexes. Fumea nitidella Hb. Fam. Zygaenidae. Zygoma filipendulce L. Fam. Cossidae. The caterpillars live mostly in the medulla of plants. Cossmt lifjniperda Fabr., cesculi L., Hepialus liumuli L. The caterpillar lives in hop roots. Tribe 5. Sphingina (Sch warmer). Lepidoptera with elongated body, pointed at the end, and usually a very long rolled proboscis. The anterior wings are long and narrow. The hind wings are short. The antennae are short, and, as a rule, taper at the points. The wings lie when at rest horizontally on the body and always have a retina- culum. The caterpillars are flat, and provided with an anal horn and sixteen legs. They pass their pupal stage in the earth. The adult insects fly about in the twilight, some species also in the day (Macroglossci). Fam. Sesiadae. Sesia apiformis L., 8. bembeciformis Hb. Fam. Sphingidae. Hawk-moths. Macroglossa stellatarum L. (Tauben- schwanz), Humming-bird Hawk-moths. Sphinx elpenor L., S. porcellus L. (Weinschwarmer), S. Nerii (Oleanderschwarmer), S. comolvuli L., Aclicrontia atropos L., death-head. The caterpillar lives on potatoes. Snierinthus populi L. (Pappelschwarmer), S. tiliee L. (Lindensch warmer), S. occllatns L. (Nacht- pfauenauge), Eyed Hawk-moth. Tribe 6. Rhopalocera. Butterflies. Lepidoptera of slender build, usually with brightly coloured wings. The antennae are club- shaped, or knobbed at the end. The legs are slender. The tibiae of the front legs are short, and sometimes reduced. The Rhopalocera fly by day, and when at rest hold the wings upright, often applied together. The caterpillars have sixteen feet, and are either naked or thickly covered with hairs and spines. They develop, for the most part without cocoons and attached to extraneous objects by fibres, into the pupa, which is often of a shining metallic colour. COLEOPTERA. 585 Fam. Hesperidae. Ilesperin comma L., H. sylvanm Schn. Fam. Lycsenidee (PolytmmatidaT), (Blaulinge). Polyommatus Arion L., P. Damon Fabr. P. virgaurece L., Thecla ruli L., green hairstreak. T. qucrcus L., purple hair streak. T. to etui a L. Fam. Satyridae. Satyrus JJriseis L., S. Ilermione L., Erebia Bsdv. (Ilip- parcliia Fabr.), E. Janira L., etc. Fam. Nymphalidae. The caterpillars have spiny outgrowths, rarely covered with fine hairs. The pupa is attached by its posterior extremity. Apatura iris L. (purple emperor). Limenitis populi L. (Eisvogel). Vanessa prorsa L. (F. levana is the spring generation). V. cardni L., painted lady. V. atalanta L., Admiral. V. antiopa L. (Camberwell beauty). V. io L., peacock. V. urticce L.. (Kleiner Fuchs), small tortoiseshell. Aryynnis papUia L., silver-washed Fritillary. A. afjlaia L. (dark green Fritillary), Mi'littea cinxia L. Fam. Pieridae (Weisslinge). Pierig crata-gi L. Blackveined white. P. bracsicce L., large white (Kohl- weissling). P. napi L., green- veined white. P. rapes L., small white. Colias liyalc L., C. rhamni L. (Citronenvogel). Fam. Equitidae. Papilio Poda- T^SSK Ail lii ^iritis L., P. MacJiaon L. (Swallow- tail). Doritis Apollo L. The temales have a pouch-like ap- pendago at the posterior end of the body. Or^er 8. Coleoptera.* Inlets with masticating mouth-parts and horny front wings (tegmina). Prothorax freely moveable. The meta- FlG . 4S\Hydrophilus piceus (rcgne animal), a, morptosis is complete. , Beetle - b > Larva, c, Pupa. The chief characters of this large, but tolerably well-defined, group of infects depend upon the structure of the wings. In the state of rest the anterior wings, as wing-covers (elytra), cover the posterior membranous wings which are transversely and longitudinally folded, and lie horizontally on the abdomen (fig. 483). The hind wing? aloue are used in flight, while the front wings are modified to perform a protective function, and usually correspond in size and form to the soft-skinned dorsal surface of the abdominal region, of * W. E. Erichson, "Zur systematischen Kenntniss der Insectenlarven," Arckivfur Naturgesch., Tom. VII., VIII., and XIII. Th. Lacordaire, ' ; Genera des Cole"opteres," Paris, 1854-1860. L. Kedteubacher, "Fauna Austriaca, die Kafer," 3 Ann. Wien., 1873. Gemminger und Harold, " Catalogus Colcopterorum, etc.." Miinchen, 1868. Kowalevski I.e., " Entwickelungsgeschichte des Hydrophilus, etc." 586 INSECTA. which, however, they leave in some cases the last segment (pygidium), or in other cases (StaphylinoR) several segments, exposed. As a rule, when the insects are at rest, the straight internal edges of both wing- covers are shut closely together, while the outer edges are bent round the sides of the abdomen. Sometimes the inner edges of the wings are fused together, so that the power of flight is abolished. In rare cases the wings are altogether absent. The head is seldom free, but as a rule is sunk into the freely moveable prothorax, and bears very variously shaped, usually eleven-jointed, antennae. In the male the latter are of considerable size and have a considerable extent of surface. Ocelli are with few exceptions absent, but the facetted eyes are only absent in certain blind species, which live in caves. The mouth parts are adapted for masticating and biting, and sometimes show transi- tional forms to those of the Hymenoptera. The maxillary palps are usually four- jointed and the labial palps three-jointed. In the predatory beetles, the external lobe of the maxilla has a palp -like form and articulation. The labium, which is sim- plified by the reduction of its parts, is in rare cases elongated to form a divided tongue. The large prothorax (cervical shield) is moveably articulated with the mesothorax, which is usually w T eakly de- veloped ; and on it, as well as on the FiG. 481. a. Cicindela, campestrit , b, c, its larva with the two dorsal other thoracic segments, the pleura ex- hooks on the fifth abdominal tend on to the sternal surface. The segment (regne animal). . legs vary very much in shape, but usually end with a five-, rarely with a four-jointed tarsus. The tarsus is rarely composed of a smaller number (from one to three) of joints. The abdomen is attached to the metathorax by its broad base, and always possesses a greater number of dorsal than of ventral plates, of which some may fuse with one another. The smaller terminal segments are usually retracted and concealed by the preceding. The nervous system of the Coleoptera varies in the greater or less concentration of the ventral ganglionic cord. The subccsophageal ganglion is followed by two or three thoracic ganglia, with the posterior of which one or two abdominal ganglia may be fused. In COLEOPTERA. 587 the abdomen there are usually a series of separate ganglia (2 to 7). The latter may, however, fuse together to form a long mass or be drawn into the thoracic ganglia. The long coiled alimentary canal dilates in the carnivorous beetles to form a gizzard, which is followed by a shaggy chylific ventricle. The number of Malpighian tubes is, as in Lepidoptera, confined to four or six. The males and females are easily distinguished by the form and size of the antennae, the structure of the tarsal joints, and by special relations of size, form and colour. In the female the numerous egg- tubes unite in very various arrangements, and a bursa copulatrix is often present. The males possess a large horny penis, which, when at rest, is retracted into the abdomen and is protruded by means of a powerful muscular apparatus. Almost all the larvae have mouth parts adapted for biting, rarely suctorial pincers. They feed under the most different conditions, as a rule concealed and removed from the light, and usually in the same way as the perfect insect. They are either grub-like and apodal, but with a distinctly developed head (Curculionidce), or they possess, in addition to the three pairs of legs on the thorax, also stumps on the last abdominal segments. Many larvae, as those of the Cicindelce, have a peculiar apparatus for capturing their prey (fig. 484). In place of the facetted eyes, which have not yet appeared, ocelli are present in varying number and position. Some beetle larvae, like the larvae of the Dipterci and Ilymenoptera, live as parasites and feed inside bees nests on the eggs and honey (Meloe, Sitaris) (fig. 485). The pupa? of beetles, which are either suspended and attached to objects or lie on the earth or in holes, have their limbs freely projecting. Fossil Coleoptera, are found in coal formations and are specially numerous in amber. Tribe 1. Cryptotetramera = Pseudotrimera. The tarsuses are com- posed of four joints, of which one joint is rudimentary. Latreille considered them to be three-jointed. Fam. Coccinellidae (Lady Birds). Coco India septempunctata L. The larvae feed on Aphides. Chllacorm liipmtulatus L. 5. a) burrow, and present the peculiarity of using their excrements to prepare cases which they carry about with them (^Clythra^ Cryptoccplialus). Before entering the pupal stage they attach themselves to leaves by the hind end of their body. Ilaltica oleracea Fabr. Harmful to cabbage leaves. Lina popnli L. Chrysomela varians Fabr. Fam. Cerambycidae (Longicorn\a) (Bockkafer). Some species (Lamia) pro- duce a peculiar sound by rubbing the head against the prothorax. The elongated grub-like larvaj have a horny head with powerful mandibles, short antennae, and usually no legs or ocelli. They live in wood, in which they bore passages and sometimes cause great damage. Lamia textor L., Cerambyx heros Scop., C. cerdo Fabr., Prlonus coriarius Fabr. Fam. Bostrychidae (Borkenkafer). Coleeptcra of small size and cylindrical body shape. The larvae are of stout cylindrical shape and without legs, the place of which is taken by ridges covered with hairs like those of the Curcv- lionidce. The adult insects and larvae bore passages in wood, on which they feed. They live in companies, and belong to the most dreaded destroyers of forests of conifers. The way in which they eat into the bark is very peculiar, being characteristic of the individual species and indica j ive of their mode of life. The two sexes meet in the superficial passages, which the female, after copulation, continues and lengthens in order to lay her eggs in pits, which she hollows out for that purpose at the end of them. The larvae when hatched eat out lateral passages, which, as the larvae increase in size and get further from the main passage, become larger and give rise to the characteristic markings on the inside of the bark. Bostrychus cJialcograjrtius L., B. typography* L., under the bark of pine-trees. B. stenographies Duft. Fam. Curculionidae (Riisselkafer). Weevils. Head prolonged into a proboscis in front. Larvae cylindrical, without or with very rudimentary legs and ocelli ; they are almost entirely phytophagous ; and indeed they live under the most various conditions, some inside buds and fruit, others under bark, or on leaves, or in wood. Calandra granaria L., in grain known as black grain- worms. Balanlnus nuciim L., Nut-weevil. Ifylobius alictis Fabr., Apioti fnimcntarium L. Tribe 3. Heteromera. The tarsuses of the two anterior pairs of legs are five- jointed, of the posterior pair four- jointed. Fam. Oedemeridae. Oedcmera vircscens L. Fam. Meloidae (Cantharidae). They furnish a substance used in the prepara- tion of vesicants. The larvae live partly parasitically on insects, partly free under the bark of trees, and some of them pass through a complicated meta- morphosis called by Fabre hypermctamorphosis ; they possess at first three pairs of legs ; in later stages they lose these, and the body acquires a cylindrical COLEOPTERA. 589 form (fig. 457). Mdoe L. The beetles live in grass, and when touched they give oat an acrid pungent fluid between the joints of the legs. The larvae creep on the stalks of plants, penetrate into the flowers of Asclepiadae, Primulacese, etc., and attach themselves fast to the body of bees (Pcdiculus melittce Kirby), in order to be carried to the bees' nest, in which they nourish themselves chiefly on honey. M. proscardbceus L., M. violaceus Marsh. Lytta veslcatoria L., Spanish fly. Sitaris hwneralis Fabr., South Europe (fig. 485). Fam. Khipiphoridae. The larvae live in wasp nests (Metoecus), or in the abdomen of cockroaches (JUilpidius). Rliipipliorus bimaculatus Fabr. Fam. Cistelidse. Cistcla fulvipes Fabr.. C. murina L. Fam. Tenebrionidae. Tenebrio molitor L., Larva known as meal-worm. Blaps mortisaga L. Tribe 4. Pentamera. Tarsus usually five-jointed. Fam. Xylophaga. Tarsus sometimes only four-jointed. The larvae some- times feed on dead animal matters, sometimes bore cylindrical horizontal passages in wood, and are therefore destructive to furniture and wooden material as well as to living trees. Lymexylon navale L., on docks in oak. Anobium pcrtinax L., death watch, produces a ticking noise in wood. Ptinus fur L., Ft. rnjipes Fabr. Fam. Cleridae. The variegated larvae live under bark and for the most part on other insects. Clerus formicaries L., Tricliodcs apiarius L. The larva is parasitic in bee-hives. Fam. Malacodermata. Jfalachins ceneus Fabr. Cantharis (Iklepkorwi) violacea Payk., C. fusca L. Lampyris Geoffr., Glow-worm. Female apterous, or only with two small scales. Light organs in the abdomen L. noctUvca L.. L. gplendidula L. Female with two small scales instead of wing-covers. Fam. Elateridae (Springk'afer). The elongated body is distinguished by the very free articulation between the prothorax and mesothorax ; and by the pos- session of a spine upon the prothorax which fits into a pit on the mesothorax. These two arrangements enable the beetle to jump up when lying on its back. The larvae live under the bark of trees on the wood, sometimes in the roots of grain and turnips, and may be very destructive. Agriotes line-atvs L., Lacon murinus L., Elater sanguineus L., Pyrophorus noctilucus L., in Cuba, prothorax dilated to the form of a vesicle and phosphorescent. Fam. Buprestidae (Prachtkafer). Body elongated, pointed behind, often brightly coloured, with a metallic lustre. The elongated vermiform larvae are without ocelli and, as a rule, legs ; and possess a very broadened prothorax. They live like the larvae of the Cerambycidcc, to which they present a general resemblance, in wood, and bore flat ellipsoidal passages. Trachys minuta L., Agrilus biguttatus Fabr., Bu-prestis rustica Fabr.. B . flavomaculata Fabr. Fam. Lamellicornia (Blatthornkafer). The antennae are seven- to eleven- jointed ; the basal joint is large, and the terminal joints (three to seven) are widened to a fan shape. In many the anterior legs are adapted for digging- The soft-skinned larvae possess a horny head, moderately long legs, and a curved abdomen, which is dilated behind to the form of a sac ; they feed sometimes on leaves and roots, sometimes on putrefying vegetable and animal substances, and enter into the pupal stage after two or three years sojourn in a cocoon beneath the earth. Lucanus ccrvns L., stag beetle. Larvae in rotten wood of old oaks. The beetle feeds on the sap which comes from the oak. L. paralldipipcdus L., 590 INSECTA. Copris lunar is L., ApJiodius subterraneus Fabr., Gcotrupes vernnlis L., 6r. stercorarius L., Rhizotrogus solstitialis L., Melolontlia vulgar Is Fabr.. Cock- chafer. The larvae at first live together and feed on fresh vegetable substances, later (in the second and third years) on roots, which they destroy, doing great damage. Towards the end of the fourth summer the beetle is usually developed from the pupa, which lies in a smooth round hole, but it remains in the earth till the next spring. 31. Kifpooastani Fabr., Cetonia aurata L., Atcuchm saccr L., Oryctes nasicornis L. Fam. Derniestidae (Speckkafer). Attagoius pcllio L. (Pelzkafer). Dermestes lardarius L., (Speckkafer). Fam. Histeridae (Stutzkafer). Ulster maculatus L., Ontopliilm strlatus Fabr. Fam. Silphidae (Aaskafer). Beetles and larvfe live on and lay their eggs in decomposing animal and vegetable matters ; some of them even attack living insects and larvre. When .attacked many defend themselves by the ejection of a stinking anal excretion. Silpha thoraclca Fabr., S. obscura Fabr. Necro- 2)lionts vcspillo Fabr., N. germanicus Fabr. (Todtengraber). Fam. Pselaphidae. Live in the dark under stones and in colonies of ants. Pselaj)Jtus Ilcisei Herbst, Claviger tcstaceus Pr. Fam. Staphylinidae (Kurzdeckflligler). Myrmcdonia canaliculata Fabr. Live among ants. Staphylinus max'dlosus L., Omalluni rlvulare Payk. Fam. HydropMlidse (Palpicornia). Swimming beetles with short club-shaped antenna and long maxillary palps, which often project beyond the antennas. Feed on plants. Ilydropliilus plceus L., IIydro~b'msfusclpc,s L. Fam. Dytiscidae. Swimming-beetles, with filiform, ten- or eleven-jointed antenna and broad swimming legs beset with setae ; the hind legs project back and are especially adapted for swimming by the possession of a close covering of swimming-hairs. Colymbetesfnscus L.. Dytiscus marginal! s, Sturm. Fam. Carabidae.* Running beetles, with eleven-jointed filiform antennae, power- ful pincer-shapcd mandibles, and running legs. The elongated larvae possess four-jointed antennas, four to five ocelli on each side, sickle-shaped projecting pincers, and fairly long five-jointed -legs Harpalm ceneus Fabr., Bracliiim* ercjritans K. (Bombardirkafer). Carabus anratus L., 'Procrustes coriaccus L. Fam. Cicindelidae. Tiger-beetles. Mandibles with three teeth. The larvae form subterranean passages, possess a broad head, very large sickle-shaped curved jaws, and bear on the dorsal surface of the eighth segment of the body two horny hooks for attachment in the passage, at the opening of which they lie in wait for prey. Clcindela campestris L. (fig. 484). Order 9. Insects with biting and licking mouth parts, fused prothorax, /our membranous wings with only few nervures. Metamorphosis complete. The body has as a rule an elongated form, and possesses a freely * Dejean, "Species general des Coleopteres, etc." Tom I.-V., Paris, 1825- 1831. f L. Jurine, " Nouvelle methode de classer les Hymenopteres et les Dipteres/ Tom. L, Hymenopteres. Geneva, 1807. C. Gravenhorst, " Ichneumologia Europasa," Vratislavias, 1829. J. Th. C. Ratzeburg, ' Die Ichneumonen der Forstinsecten." 3 Bde. Berlin, 1844-1852. G-. Dahlbom, " Hymenoptcra Europsea, praecipue borealia." Lund. 1845. v. Siebold, " Beitrage zur Parthenogenesis der Arthropoden." Leipzig, 1871. HYMEXOPTERA. 591 moveable- head with large facetted eyes which in the male are almost in contact, and three ocelli (fig. 486). In the antennae a large basal joint (shaft) and eleven to twelve shorter joints can usually be distinguished, or they are not crooked, in which case they consist of a greater number of joints. The mouth parts are biting and licking ; the upper lip and man- dibles are constructed as in beetles and Orthoptera; the maxillae and labium, on the other hand, are elongated and adapted for licking, and when at rest are frequently bent round. In bees the tongue can be considerably elongated and assume the form of a proboscis ; in this case the lobes of the jaws also become considerably extended, and form a kind of sheath around the tongue. The maxillary palps are usually six-jointed ; the labial palps on the other hand only four- jointed, but the number of joints may be reduced. As in the Lepidoptera and Diptera, the prothorax is firmly con- nected with the following thoracic segments, inasmuch as the ti FIG. 480. Apis mellifica. a, Queen, b, Worker, c, Drone. pronotum at least (excepting in the leaf- and wood-wasps) is fused with the mesonotum, while the rudimentary prosternum remains freely moveable. On the mesothorax two small moveable scales (tegulce) are found over the base of the forewing, and behind the scutellum the anterior part of the metanotum is developed into the posterior shield (postscutettum). Both pairs of wings are membranous, transparent, and traversed by but few nervures ; the anterior are considerably larger than the posterior. From the outer edge of the latter small hooks arise, which are attached to the inferior edge of the anterior pair, thus bringing about the connection between the two pairs of wings. Sometimes the wings are absent in one of the two sexes, or in the workers amongst many social Hymenoptera. The legs possess five-jointed, usually broadened tarsuses with long first tarsal joint. The ab- domen is rarely attached to the thorax by its whole breadth (sessile) ; as a rule the first or the two first segments of the abdomen are narrowed to a thin stalk, bringing about the connection with the 592 tr thorax (stalked). In the female sex the abdomen ends with an ovipositor (terebra), which as a rule is retracted, or with a poison spine (aculeus). The latter develops from six warts, of which four belong to the ventral side of the penultimate, tw r o to that of the antepenultimate segment. The sting (fig. 487) consists of the grooved piece (sting-groove), two piercing stylets and two sting- sheaths (with oblong plates) and is retracted when at rest. The grooved piece, the furrow of which is directed downwards, arises from the inner pair of warts of the penultimate segment, while the piercing stylets on the edge of the grooved piece correspond to the pair of warts of the antepenulti- mate segment. Finally the segments also take part in the formation of this apparatus, inas- much as they furnish powerful supporting plates for the sting (quadratic plate and angular piece). The nervous- system consists of a large com- plicated brain, an in- fra- oesophageal ganglion, two thoracic ganglia (the ganglia of the mesothorax and meta- thorax are fused with the anterior abdominal ganglion), and five to six ganglia in the ab- domen. The alimentary canal frequently attains to a considerable length, especially in those Hymenoptera which with a longer life cumber themselves with the care and nourishment of the young. Large salivary glands are present. The narrow oesophagus usually dilates to a suctorial stomach, more rarely to a spherical gizzard (ants). A considerable number of short Malpighian tubules open into the intestine (hindgut). FIG. 487. Stinging apparatus of the honey bee from the dorsal side (after Kraepelin). GD, poison gland ; Gb, poison reservoir ; &, gland; Sir, grooved piece with the two stylets ; Ba, swollen base of the grooved piece ; S, curved root of the same ; W, angular piece ; Sh, sheath of spine ; O, oblong plate ; Q, quadratic plate ; Stb', Stl", the two piercing spines on the ventral side of the grooved piece. HYMENOPTERA. 593 In connection with the great power of flight, the longitudinal trached. trunks give rise to vesicular dilatations, of which two at the base of the abdomen are conspicuous by their size. The female sexual organs usually possess very numerous (up to one hundred) many- chambered egg tubes, and a large receptaculum seminis with accessory glands. A special bursa copulatrix is absent (fig. 488). When a sting is developed, filiform or branched poison glands with a common reservoir and a duct opening into the sheath of the sting, are present. In the male sex the ducts of the two testes are connected with two accessory glands, while the common ductus ejaculatorius ends with a large protrusible penis. With the exception of the leaf -wasps (Tenthredinidce), and wood- wasps ( Uroceridce), the larvae are apodal and live either parasitically in the body of insects (the Pteromalince pass through various larval stages, undergo- ing a kind of hypermetamor- phosis) or in plants, or in brood spaces (cells) formed of animal and vege- table substances. The former, like the cater illars FIG. 488. The viscera in the abdomen of the queen bee (after of the butterflies, R. Leuckart). D, alimentary canal ; .R, rectum with rectal glands V>Acirlac and anus 5 Gfc > chain of Ranglia; Or, ovary; So, receptaculum . ' seminis ; Gl, reservoir of poison gland ; St, sting. the six thoracic legs, six to eight pairs of abdominal legs, and live free on leaves ; the latter are grub-like, find the nutritive material in their cells, and are in part fed during their growth. Almost all e.g., the larvae of bees and wasps possess a small retractile head with short mandibles and pointed pieces (maxillae and labium). The anus is not developed, for the stomach is blind and does not communicate with the hindgut, which receives the Malpighian tubules. Most of the larvae, when they enter the pupal stage, spin an irregular invest- ment or a firmer cocoon of silk-like fibres. The larvae of bees and wasps then soon undergo a moult (when they get rid of their excrementitious matters), and enter upon a stage which precedes that of the pupa and is called by v. Siebold the pseudo- pupa (fig. 489). 38 594 1NSECTA. Sub-order 1. Terebrantia. Female with ovipositor as tube or borer (terebra), which projects freely at the end of the abdomen, and is sometimes retractile. Tribe 1. Phytophaga. Abdomen sessile. Trochanter composed of two rings. Larvae phytophagous, resemble caterpillars. Fam. Tenthredinidae (Leaf-wasps). Saw-flics. Abdomen sessile with short borer. The larvse have rarely three, usually nine to eleven pairs of legs, and resemble caterpillars. The females lay their eggs in the epidermis of leaves, the puncture causes the flow of .sap. which the egg imbibes and thereby increases in size. The young larvae feed on leaves, often in early stages live in societies, and become pupre in a cocoon. They are distinguished from the caterpillars by the greater number of legs, and by the two ocelli on the horny head. Lyda letvlce L., Tenthredo (Atlialia) spino.rum Fabr.. larvre sometimes on roses. Nematus ventricosus Klg., larvae on gooseberries. Civile x femorata L. Fam. Uroceridee (Wood- wasps). Abdomen with first tergum split, and usually long, freely projecting oviposi- tor (egg-borer). The females bore holes in wood and deposit their eggs therein. The larvae bore further into the wood and live a long time. Sirex gig as L. M>-' * i ^^ FIG. 489.- a, Larva of the bumble bee about to become Tribe 2. GalliCOla. Ab- a pupa, b, Pseudo-pupa (Semi-pupa), c, pupa (after domen stalked. LarV83 apodal and aproctous, usually living in vegetable cells. Fam. Cynipidae (Gall-wasps). Thorax humped. Abdomen usually short, laterally compressed. The ovipositor (egg-borer) arises on the ventral side, and is as a rule retracted. The females bore into plant tissues and cause, by the irritation of an acrid fluid, an abnormal flow of vegetable fluids, thus giving rise to the outgrowths known as galls, on which either one or several apodal larvae feed. Certain galls, especially those of the oaks of Asia Minor (Aleppo), contain tannic acid, and are on this account used in industry. In many species the females only are at present known ; the eggs in such cases develop parthenogenetically. Many larvae are parasitic in Diptera and Apliides. Cynips qucrcus folii L., Rhodites ros.ce L.. produces the bedeguar of roses. Figites scutellaris Latr., parasitic on the grubs of Sarcophaga. Tribe 3. Entomophaga. Abdomen stalked. Female with freely projecting ovipositor (spine). Larvae apodal and without anus, usually parasitic in the larvae of other insects. Fam. Pteromalidae. The larva? are parasitic in all possible insect larva?, frequently in parasites, and pass through a complicated metamorphosis, ex- tremely remarkable for the succession of very different stages. Ptcromalits pnparum L., Teleas clavicornis Latr., Platygastcr Latr., (fig. 458). HYMEXOPTERA. Fam. Braccnidee. They principally persecute caterpillars, as well as beetle larvre living in dead wood. Microgaster glommcratus L., in caterpillars, Bracon impostor Scop., Br.palpebrator Katzbg. Fam. Ichneumonidae. Iclincunwn incubitor L. Z (Trogus) Intorius Ratzbg., P'nnpla (Eplnaltes) manifestator L., OpUion luteus L. Fam. Evaniadse. Ecania appendlg aster L., Foenus jaculator L. Sub-order 2. Aculeata. With retractile perforated sting and poison gland in the female sex. Abdomen always stalked ; the antennae of male usual thirteen- jointed, of the female twelve-jointed. The larvae arc apodal and without anus. Fam. Formicidse* (Ants) (fig. 490). They live together in communities, which contain, besides the winged males and females, a great excess of small apterous workers with stronger prothorax. The latter are sometimes of two kinds, known as soldiers and true workers, distinguished by the size of the head and jaws. The workers are aborted females and re- semble the true females in possessing a poison gland, the acid secre- tion (formic acid) of which they either pour out with the help of the sting or, in the absence of the latter, eject into the wound made by the mandibles. The dwellings of the ants consist of passages and cavities, which are placed in rotten wood, in the earth, or in hill- like heaps which they Fjfl< m _ Fori)j;ca (Camponotu*) lureulanea. a, Female, b, Male. throw up. Winter pro- c> Worker, d. Larva of Formica rnfa. e, pupa with! case, so- visions are not carried called ant egg. /, ,g, Pupa liberated from the case. into these spaces, since the ant-workers, which with the queens alone survive the winter, fal! into a kind of winter sleep. In the spring queens are found in addition to the workers. From the eggs of the queens larvse proceed, which are carefully reared and protected by the workers. The larvae in egg-shaped cocoons become puprc (ants' eggs) and develop, some of them to workers and some to winged sexual animals, which appear with us sooner or later in the course of the summer, and copulate in the flight. After copulation the males die, the females lose their wings and are carried back by * P. Huber, " Recherches sur les mceurs des Fourmis indigenes." Geneva, 1810. LatreUle, " Histoire naturelle des Fourmis." Paris, 1802. A. Forcl, " Les Fourmis de la Suisse." Zurich, 1874. 596 INSECTA. the workers into their dwellings, to deposit their eggs, or found with some of the workers new societies. In the tropics the ants undertake migrations in great numbers, and may become a regular plague when they enter houses and destroy all eatables. Many forms ( Oecodoma species) are especially destructive to young trees and plants, which they strip of foliage. Some species, however, render service in attacking Termites and in destroying other pernicious insects, such as the cock- roaches, even in the dwellings of man. Many species, especially of the genus Uciton, are predatory ants and destroy, other ant colonies. Certain species are said to make war with foreign ant states and to carry off their young, which they bring up for service in their own colony (Amazon colonies. F. rufa, rufescens). The relatively high psychical activity of these insects is undeni- able ; many instances of it have been disclosed by the thorough observations of P. Huber. They keep Aphides as we do milch cows ; they carry provisions into their dwellings ; they go out to battle in regular columns, and offer up their lives bravely for the community. In contrast to the war -like features of the slave-states are the friendly relations of the ants to other insects, which, as Myrmecopkila, live in the ant dwellings (larvte of Cetonia, Myrmecopliila^ic,.'). Formica lierculanea L., F. rvfa L., Myrmica acervorum Fabr., with sting. Fam. Chrysididae (Gold wasps). The females lay their eggs in the nests of other Hymenoptera, especially of the digging wasps (Fossoria), with which they have on this occasion to carry on war. Chrysis ignita L. Fam. Heterogyna (Mutillidce, Scoliadee). Males and females very different in form, size and structure of antennae. The females, with shortened wings or apterous, live solitarily and lay their eggs on other insects or in bees' nests, and do not trouble themselves with the nourishment and care of their young. Mutilla europaca L.. Scolia (Scoliadce) liortorum Fabr. The larva lives parasitically on that of the nasicorn beetle. Fam. Fossoria* (Digging wasps). Solitary Hymenoptera, with unbent antennas and elongated legs; the tibiae are armed with long spines. The females, which live on honey and pollen, dig passages and tubes usually in sand and in earth and in dry wood, and deposit at the end of them their cells, each of which contains an egg and animal nutritive matter for the future larva. Some (Bembex) carry fresh food daily to their growing larvse, contained in open cells ; others place in the closed cell as many insects as the larva requires for its de- velopment. In the last cases the introduced insects are not completely killed, but merely crippled by a sting in the ventral nerve cord. The individual species usually capture quite definite insects (caterpillars, Curculionida, Buprestlda, Acridies, etc.), which they overpower and paralyse in a very remarkable manner. For example, Ceroeris Imprcsticida attacks JSuprestig, while C. Dvfourli chooses Cleonus oplitlialmicm. The digging wasp seizes the head of the beetle with its mandibles and inserts its sting into the thoracic ganglia between the articulation of the prothorax. Sphex flaviptnni&, which constructs three cells at the end of a horizontal passage, two or three inches long, attacks Grylla, and Spliex alMsccta species of (Edipoda. Ammophila liolosericca supplies each of its brood cells with four or five caterpillars ; A. salvlom and argentata only with one very large caterpillar, which is paralysed * Fabre, " Observations sur les moeurs des Cerceris ; " also " Etudes sur 1'instinct et les metamoi'Dhoses des Sphegiens," Ann. des Sc. Nat., ser. 4, Tom IV. and VI. HYMENOPTERA. 597 by a sting in a median apodal body segment. Pompilug viaticus L., Anunophila sdbulosa L., Crabro cribarius L. Fam. Vespidae* (Wasps). Body slender, smooth. Anterior wings are narrow and can be folded together longitudinally. They are sometimes solitary, sometimes they live in societies ; in the last case the workers also are winged. The females of the solitary wasps build their brood-cells in sand or on the stalks of plants with sand and clay, and fill them rarely with honey, usually with insects, especially caterpillars and spiders ; they thus approach the Fossoria in their mode of life. The social wasps approximate to bees in the organization of their society. They construct their nests of gnawed wood, which they manufacture into lamella resembling paper, and fasten together into regularly hexagonal cells. The combs, which are composed of a simple layer of cells attached to one another, are either suspended freely on the branches of trees, or in holes in the earth and in hollow trees, or surrounded by a common leafy investment, on the under surface of which the holes for exit are placed. In the latter case the internal structure frequently consists of several horizon- tally-suspended combs which are placed one above the other, like the floors of a house, and are connected by buttresses. The openings of the hexagonal vertically placed cells look downwards. The foundation of each wasp nest is laid in the spring by a single female, which was fertilized in the preceding autumn and has survived the winter. She begets, in the course of the spring and summer, workers, which help to increase the size of the nest and to rear the offspring, and of which the larger forms produced in the summer not rarely lay eggs, which develop parthenogenetically into males. The larvte are fed with insects which have been well chewed, and are transformed in a delicate case into pupae in the closed cells. The perfect insects feed as a rule on sweet substances and honey juices, which they are said occasionally to gather in (Polities'). Males and females first appear in late summer and copulate in the flight high up in the air. The males soon die and the whole colony is generally dissolved in the autumn ; the fertilized females, on the other hand, survive the winter under stones and moss in order to found new societies in the following year. Odynerus parictum L., Polistes gallica L. Nests are without investment of leaves and consist of a stalked comb. The fertilized females, which have survived the winter, produce according to v. Siebold at first only female offspring, whose eggs remain unfertilized and develop parthenogenetically into males. Vespa crabro L., hornets. V. vtdgaris L. Fam. Apidaef (Bees). Tibia and tarsus, especially of the hind legs, broadened ; the first tarsal joint, especially of the hinder legs, covered with hairs like a brush. Anterior wings cannot be folded together. Body hairy. The hairs on the hind legs or on the belly serve as a collecting apparatus for the pollen. The labium and maxillae often reach a very considerable length. The latter are applied as a sheath to the tongue, and bear only rudimentary palps. The bees are solitary and social, and place their nests in walls, under earth and in hollow trees, and feed their larvae with honey and pollen. Some do not build nests, but lay their eggs in the filled cells of other bees (parasitic bees). Andrcna cineraria L., Dasypoda Mrtipes Fabr., Nomada ruficornis Kirb., * H. de Saussure, " Etudes sur la famille des Vespidcs." 3 vols. Paris, 1852 to 1857. f F. Tlubcr, " Nouvellcs observations sur les Abcillcs." 2 vols. Paris, 1811. 598 1NSECTA. Megachilc (Chalicodoma) mnraria Fabr., Osmia bicorms L., AnfkopTiora pillpcs Fabr., Xi/loeopa Malacca Fabr. "VVood-bees construct perpendicular passages in wood, and divide them by transverse walls into cells. Bovibm Latr. Bumble bee. Body heavy ; hairy like fur. The nests are usually placed in holes under the earth, and include only a small number, about fifty to two hundred, rarely as many as five hundred workers, in addition to the fertilized [female. They do not construct combs, but pile up irregular masses of pollen, in which the eggs are deposited, and which serve as food for the hatching grubs. The latter eat out cellular cavities in the pollen masses and form oval cocoons, which are free but irregularly placed by the side of one another. The nest is founded by a single female which has survived the winter. She at first alone has the burden of rearing the brood ; subsequently, however, this is shared by the hatched workers of different size, which themselves lay unfertilized eggs. B. laphlarlus Fabr., muscorum 111., terrestris, 111., liypnorwM 111. Apis L.. honey-bee. The workers with lateral separated eyes, with one-jointed maxillary palps. The external surface of the hinder tibiae is pressed into the form of a pit, and is surrounded by simple marginal setae (basket, fig. 491, K) ; the inner surface of the tarsus is beset with regular rows of seta3 (brush, fig. 491 B, &). The female (queen) with shorter tongue, longer abdomen, with- out brush. The male (drone), with large eyes in contact, broad abdomen, and short mouth parts, without basket and brush. A. mdl'ifica L., honey bee, distributed over Europe and Asia as far as Africa. The workers build perpendicular combs in hollow trees, or in other protected places ; under the in- fluence of human cultivation, in suitably arranged baskets or hives. The wax used in the construction of the comb is produced in the organism as a result of metabolism (honey being the source), and is exuded in the form of small tablets between the segments of the abdomen. The combs consist of two layers of horizontal hexagonal cells, the bases of which are formed of three rhomboidal plates. The smaller cells serve lor the reception of provisions (honey and pollen) and for the brood of workers, the larger for the reception of honey and the drone brood. Outside, at the edge of the comb, there are at definite times a small number of large irregular queen cells, in which the female larvra are brought up. When the cells are filled with honey, or the larvae contained in them have reached the stage of pupre, they are closed up. A small opening at the bottom of the hive serves for entry and exit ; all other clefts and fissures are closed with wax, and no light enters the interior of the nest. In no other Hymcnopteran society is the division of labour so strictly carried out as in that of the bees. There is only one fertilized queen, and she alone lays the eggs (she may lay more than three thousand eggs in one day). The working bees divide amongst themselves the business of collecting honey, preparing wax, and feeding the brood, and the completion of the nest. The drones, which exist only at the swarming time, and then only in pro- portionately small numbers (two hundred to three hundred in a society of twenty FIG. 491. a, Hind leg of a worker of Apis meWJica. IL, basket on the tibia; B, enlarged tarsal joint with brush on the under side. b t brush, more strongly magnified. HYSfENOPTERA. 599 thousand to thirty thousand workers) have the privilege of enjoying themselves and of doing no kind of work in the hive ; they arise from unfertilised eggs and are killed in the autumn (slaughter of drones). The queen and the workers live through the winter consuming the stored-up provisions, and kept warm by the heat produced by the dense population of the hive. In the first days of spring the queen deposits eggs, first in the workers' cells and later in the drone cells. Some royal cells are then constructed, and at intervals she deposits a fertilised egg in each of them. The larvae in the royal cells receive a richer nourishment and royal food, and become sexually mature females (queens), capable of copulating. Before the oldest of the young queens is hatched sixteen days from the deposition of the egg is required for this, while the workers develop in twenty days, the drones in twenty-four the queen-mother leaves the hive with a part of the inhabitants (first swarm). The young queen either kills all the other royal larvae and remains in the old hive, or if she is prevented from doing this by the workers, and the population is still large enough, she also leaves the old hive with a part of the workers before the appearance of a second queen (second swarm). Soon after her metamorphosis the young queen makes her marriage flight, and returns after impregnation to the hive. The queen is only impregnated once in the course of her life, which lasts four or five years ; she is henceforward able to produce male and female offspring. If the wings of the queen are paralysed and she is unable to copulate, she lays eggs which only give rise to drones ; the same is the case with the fertilised queen in her old age, when the contents of the receptacu- lum seminis is exhausted. Workers also may lay eggs which develop into drones ; the Iarva3 destined to develop into workers may. if the food supply at any early stage be abundant, become queens. As parasites in bee-nests may be mentioned the death's head moth, the wax moth, the larva of the bee-wolf, {Tricliodes apwrms), and the bee-louse (Braula CCBCO). The genera Melipona 111., Trigona Jur., comprise small American species of bees ; they appear, however, to be less closely related to the genus Apis than has been hitherto believed. With regard to the economy of the society, one of the most striking deviations they present, is that the brood-cells are filled with honey before the deposition of the eggs and afterwards closed, so that the just- hatched grub is provided beforehand with all the food material (Fr. Miiller).. The workers also prepare large reservoirs for the storage of the honey. Among the former there are forms as in Bomlus t that do not build nests, but lay their eggs in the nests of other species. INDEX. Aasfliege, 576. Aaskafer, 590. Abdominalia, 446. Abiogenesis, 96. Abraxas, 583. Abyla, 250. Acalepha, 250. Acalyptera, 576. Acanthia, 572. 'Acanthobothrium, 327. 'Acanthocephala,359,343. Acanthometra, 191. Acarina, 489. Acephalocysts, 336. Achseta, 392. Acherontia, 584. 'Achtheres, 436. Acidalia, 583. Acineta, 205. Acmostomum, 312. Accela, 313. Acraspeda, 233. Acridium, 527, 558. AcrocJadia, 295, 296. Acronycta, 583. Acrophalli, 347. Actinaria, 232. Actinia, 230, 232. Actinometra, 286, 289. Actinophrys, 188. Actinosphgerium, 188. Actinotrocha, 389. Actinozoa, 223. Aculeatn, 595. Aculeus, 592. Adambulacral plates, 291. Adapis, 173. Adaptation, 145. Adaptions of embryos and larva?, 157. Adelo-codonic gono- phore, 236. Adenoid connective tis- sue, 38. Admiral, 5S5. 222, 460. yEgineta, 242. ^Eginopsis, 236. uEquorea, 238, 242. ^Eschna, 562. ^Eschna rectal, Respira- tion of, 72. Agalmidse, 249. Agalmopsis, 247, 248,249. Agassiz, L, 139. Agelena, 504. Aglia, 584. Agrilus, 589. Agrion, 562. Agriotes, 589. Agrotis, 583. Alary muscles, 533. Alaurina composita, 313. Albertus Magnus, 133. Albunea, 478. Alcinoe, 266. Alciopa, 380. Alciopea, 379. Alcippe, 446. Alcyonaria, 228, 231. Alcyonium, 231. Aldrovandus, 133. Alima, 472. Alpheidae, 476. Alternation of genera- tions, 123. Alucita, 582. Alula, 572. Alydus, 572. Ambulacral brains, 277. Ambula'cral branchiae, 277. Ambulacral feet, 273. Ambulacral Gills, 275. Ambulacral groove, 291. Ambulacral ossicles, 271, 290. Ambulacral plates, 271. Ambulacral surface, 261). Ambulacral vascular sybtem, 272. Ametabola, 547. Ammophila, 596. Ammothea, 496. Amceba, 186. Amcebidium, 209. Ampharete, 382. Amphibia, Vascular sys- tem of, 65. Amphibiotica, 561. Amphidiscs, 218. Amphihelia, 232. Amphileptus, 195, 204. Amphinomidse, 374. Amphioxus, Vascular system of, 63. Amphipeltis, 451. Amphipoda, 451. Amphipods, Parasites of, 362. Amphiporus, 342, 340. Amphistomum, 317. Amphitrocha, 878. Amphiura, 278, 279, 285, 294. Anal, vesicles of Chseti- fera, 388. Analogy, 52. Anapera, 575. Anatifa, 445. Anceus. 459. Anchitherium, 172. Anchorella, 436. Ancylostomum, 352. Andoctonus, 510. Andrena, 597. Anelasma, 445. Anguilla, 351. Anguillula, 357. Anilocra, 460. Animals and plants, 15. Anisopoda, 459. Annelida, 362. Anobium, 589. Anochanu?, 279. Anopla, 342, 339, 341. Anoplotermes, 560. 602 IXDE5. Anoplura, 568. Antedon, 289. Antennas, 84. Antennal Gland of Thoracostraca, 461 Antennularia, 242. Antbophora, 698. Anthozoa, 223, 229, 230. Anthrax. 570. Antimere, 25. Antipatharia, 232. Antipathes, 232. Antliata, 572. Ant- lion, 564. Ants, 595. Apatheon, 177. Apatura, 585. Aphalaspida3, 177. Aphaniptera, 578. Aphides, Reproduction of, 106, 128. Aphis, 569, 570. Aphodius, 590. Aphrodite, 379. ' Aphrophora, 571. Apical plate of Annelids, 363. Apical pole of Echinder- mata, 268. Apiocrinus, 289. Apiocystites, 289. k ^ Apion. 588. Apis, 598. Apoda, 299, 446. Apolemia, 246, 249. Aporosa, 232. Apseudes, 456. Apsilus, 401. Aptcra, 567. A pus, 419. Arachnida, 484. Aradus, 572. Araneida, 498. Arcella, 136. Archasoniscus, 451. Archffiopteryx, 175. Archegosaurus, 177. Archenteron, 116, 117. Archiannelida, 365, 376. Archigetes, 339. Arenicola, 381. Arethusa, 249. Anras, 495. Argulus, 438. Argynnis, 585. Argyroneta, 499, 504. Arista, 573. Aristotle, classification of, 132. Aristotle's lantern, 276. Armadillo, 457, 460. Arrcnotokia, 543. Artemia, 419. Arterial, 73. Artery, 62. Arthropoda, 405. Arthrostraca, 449. Articulata, 289. Ascalaphus, 564. Ascaltis, 222. Ascanclrn, 222. A scans, 347, 346, 351. Ascetta, 222. Ascilla. 222. Ascomorpha, 404. Ascon, 222. Ascortis, 222. v Asculmis. 222. Ascyssa, 222. Asellus, 460. ; Asilus, 576. Aspidochirotre, 298, 209. Aspidiotus, 543, 569. Asplanchna, 404. Astacus. 477. Astasia,'l69. Asteracanthion, ' 285, 293. Asteriadae, 293, 279. Asterias, 293. Asteridea, 279, 292. Asteroidea, 279, 290. Asterope, 427. Astrrea, 229, 232. AstrsBidae, 232. Astroides, 233. -J Astronyx, 294. Astropecten, 275, 292, 293. Astrophyton, 294. Atax, 495. Ateuchus. 590. Athalia, 594. Athorybia, 248, 249. Atolls, 230. Atrocha, 377. Attacus, 584. Attagenus, 590. Atypus, 504. Auditory organs, 85. Aulastcnvam, 400. Aurelia, 261. Aurelio Severino, 133. Auricularia, 281, 282, 283, 298. Autolytus, 372, 379. Aves, vascular system of, 67. Bacillus, 206. Bacteria, 206, 557. Baer, C. E. von, 137. Balaninus, 588. Baianoglossus, 299, 302. Balantidium, 205. Balanus, 446. Bark lice, 127, 570. Barrier reefs, 230. Bathybius, 186. Bathycrinus, 289. Bdella, 495. Bear-caterpillars, 583. Bed-bug, 572. Bedeguar of TOSQS, 594. Bee-louse, 575, 599. - Bees, 697. Beetle-mites, 495. Bee-wolf, 599. Bell Animalcule, 198. Bembex, 596. Boris, 577. Beroe, 264, 266. Bibio, 574, 577. Biesfliegen, 576. Biogenesis, 96. Bipalium, 315. . Bipinnaria, 281, 283, 292, 293. Bird spider, 504. Birgus, 478. Bittacus, 563. Bivium, 269. Bladder- Worm, 332. Blaps, 589. Blastoidea, 289. Blastopore, 114. Blastosphere, 113. Blastostyle, 236. Blastotrochus, 227, 232. Blatta, 557. Blatthornkafer, 589. Blattkafer, 588. Blaulinge, 585. Blendwanzen, 572. Blood-corpuscles, 32. Bockkafer, 588. Body cavity, 50. Body cavity, primary, 50, 116. Bombardirkafer, 590. Bombus, 598. Bombycina, 583. Bombylius, 576. Bombyx, 581, 584. Bone, development of, 40, 42. Bonellia, 392. Bonnet, 133. Book-lice, 559. Bopyrus, 460. Borkenkafer, 588. Borlasia, 340, 342, 343. Eos taurus, origin of, 143. INDEX. G03 Bostrychus, 588. Bothriocephalidse, 33G. Bothriocephalus, 330, 331, 337, 334, 327. Botrytis, 534. Botys, 582. Brachinjis, 590. Brachiolaria, 281, 292, 298. Brachionus, 404. Brachycera, 575. Brach.yura. 478. Bracon, 595. Brain, 80, 82. Branchellion, 400. Branchiae, 69. Branchiae of Chaetopods. 367. Branchiobdella, 400. ; Branchiopoda, 418. Branchiostegite, 463, Branchipus, 419. Branchiura, 436. Braula, 575, 599. Brisinga, 293. Brissus, 297. Brittle stars, 293. Brontotheridas, 173. Brown tubes of Gephy- rrca, 388. Buckelzirpen, 571. Budding, 96. Buflon, 139. Bugs. 571, 567. Bunodes, 225. Buprestis, 589. Bursae of Ophiuridea, 294. Bursaria, 205. Butterflies, 579. Calandrse, 588. Calanidae, 435. Calappa, 478. Calcareous sacs of Lum- bricus, 383. > Calcareous sponges, 222. Calcispongiaa, 222. Callidma, 404, Caligus. 436. Callianassa, 477. Calopteryx, 5f'2. Calotermes, 559, 501. Calycophoridae, 249. Calycozoa, 254, 257. Calymene, 484. Calyptopis, 474. Camberwell beauty, 535. Camel-neck flies, 563. Campanularia, 242. Campauulariaj, 241. Camp odea, 554. Cancer, 478. Cantharidae, 583. Cantharis, 539. Canthocamptus, 435. Capillary, 63. Capitella, 377. Capitellidae, 375. Capitibranchiata, 381. Caprella, 454. Capsus, 572. Carabus, 590. Carchesium, 205. Carcinus, 478. Cardo, 523. Candida, 477 Carina of Cirripedia, 439. Carmarina, 242. Carotid arteries, 66. Carp-lice, 438. Cartilage, 39. Cartilage calcified, 40. Caryocrinus, 289. Caryophyllaeus, 326, 328, 334, 338. Caryophyllia, 232. Catenula, 312. 313. Caterpillar. 549, 581. Catocala, 583. Catometopa, 478. Cecidomyia, 578. Cecidomyia, reproduc- tion of, 106, 128, 544. Cecrops, 436. Cell, 12, 29. Cellular tissue, 37. Central plate, 271. Centrolecithal, 112. Centrotus, 571. Cephalic branchiae of chaetoporla. 369. Cephalopoda, eye of, 90. Cephalothorax of Arth- ropoda, 407. Cephalotrichidae. 343. Cephalothrix, 343. Cephalotrocha, 378. Cephea, 261. Cerambyx, 588. Ceraospongia, 221. Cerapus, 453. 455. Ccratium, 196. Cercaria, 129. 320. Cercaria macroccrca, 321. Cerceris, 596. Cercomonas, 194. Cerebratulus, 343. Cerianthas, 225, 232. Cestidre, 263. Cestoda, 32 J. Cestum, 264, 265. 266. Cetochilus, 435. Cetonia, 590. 51 6. Chsetifera, 389. Chastogaster, 356. Chastognatha, 357. Chastouotus, 404. Chaetopoda, 367. Chsetopterus, 382. Chaetosomidae, 357. Chalicodoma, 598. Chalineae, 220. Chary bdea, 259. Charybdeidse, 2;2, 251, Cheese-flies, 576. Cheese-mites, 492. Cheimatobia, 583. Cheiracanthus, 345. Chelicerae, 484. Chelifer, 511. Chelura, 453, 455. Chermes, 543, 570 Chermes, reproduction of, 127. Chernetidse, 511. Chiaja, 266. Chigoe. 579. Chilocorus, 587. Chilodon, 205. Chilognatha, 520. Chilopoda, 518. Chirodota, 299. Chironomus, 578. Chitin, 79. Chlamydomonas, 19i. Chloeon, 561. Chlorophyll, 20, 21. Chlorops, 576. Chondracanthus, 435. Chorion, 93, 542. Choroid of eye, 88. Chromulina, 195. Chrondrosia, 221. Chrysaora, 261. Chrysididas, 596. Chrysis, 596. Chrysomela, 588. Chrysomitra, 246, 250. Chrysopa, 564. Chrysops, 577. Chrysosoma, 576. Chthonius, 511. Chyle, 57, 67. Chylific ventricle, 53D. Chyme, 57. Cicada, 567, 571. Cicadellidae, 571. Cicadidaj, 571. Cidaridsa, 273. 274, 295. 296. Cidaris. 293. 604 INDEX. Ciliary body, 90. Ciliata, 196. Cilioflagellata, 196. Cimbex, 594. Cincindela, 590. Cineras, 445. Cirri of Chsetopods, 367. Cirri of Vermes, 307. Cirripedia, 438. Cirrus, sac of Trema- todes. 318. Cirrus, sheath of Cestoda, 329. Cirrus of Trematodes, 318. Cistela, 589. Citigradae, 504. Citronvogel, 585. Cladocera, 419. Claspers of Tanaidas, 459 Clathrulina, 188. Clava. 241. Clavidse, 241. Claviger, 590. Clavulae, 272. Clavulae of Echinoidea. 296. Claw, 34. Clepsidrina, 208. Clepsine, 400. Clerus, 589. Climate, influence of, 148. Climate in relation to fauna, 160. Clisiocampa, 584. Clitellus of Lumbricus, 323, 385. Clothes moth, 582. Clubiona, 504. Clypeaster, 297. Clypeastridas, 295, 296. Clypeastridea, 268, 273, 296. Clythia, 242. Clythra, 588. Cnethocampa, 584. Cnidaria, 222. Cnidoblast, 212, 223. Cnidocil, 223. Coccidaj, 567, 568. Coccidia, 209. Coccinella, 587. Coccus, 569. Coccygeal glands, 77. Cochineal. 569. Cockchafer, 590. Cockroach, 557. Codosiga, 196. Coelenterata, 209. Co2lom,50. Coenenchym, 227. Ccenobita, 478. CcEnurus, 331, 333 Cold-blooded, 74. Coleoptera, 585. Colias, 585. Collembola, 553. Collosphaera, 191. Collozoum, 191. Colpodella, 194. Colpoda, 205. Columella of Actinozoa, 228. Colymbetes, 590. Comatula, 276, 286, 288, 289. Complemental males of Cirripedia, 442. Compsognathus, 177. Conchoderma, 445. Conjugation, 202. Connective tissues, 37. Conochilus. 404. Conops, 576. Contractile Vacuole, 180. Convoluta, 311,314.313. Convolutidag, 313. Copepoda, 428. Copris, 590. Coral, mushroom, 232. Coral organ, 231. Coral Polyps, 223. Coral, red, 231. Coral reefs, 230. Coral, star, 232. Coral, white, 232. Corallium, 231. Cordylophora, 241 Corethra, 578. Coreus, 572. Corixa, 572. Cornea, 87. Cornularia, 231. Cornuspira, 187. Coronula, 446. Corophium, 454. Correlation, 51. Corrodentia, 559. Corycaeus, 436. Corydalis, 563. Corymorpha, 240, 241. Cossus, 584. Costa, 528. Costa of Actinozoa, 228. Coxa, 526. Crabro, 597. Crab-spiders, 504. Crambus, 582. Crangon, 477. Craspedota, 238. Craspedota, 258. Craterolophus. 258. Crayfish, 477. Crevettina, 454. Cribrellum, 499. Crickets, 558. Crinoidea, 279, 286. Crinoids, 289. Criodrilus, 385. Crocodilia, heart of, 67. Crop, 57, 530. Crustacea, 411. Cryptocephalus, 588. Cryptoniscus, 460. Cryptopentamera, 588. Cryptophialus, 446. Crystalline cone, 87. Cteniza, 504. Ctenodiscus, 275, 293. Ctenophora, 261, 578. Ctenophor type, 211. Cubitus, 528. Cuckoo-spittle, 571. Cucullanus, 348, 353. Cucullia, 583. Cucumaria, 299. Culex, 578. Culicidse, 574. Culiciformes, 578. Cumacea, 469. Cunina, 239, 242. Curculionidffi, 588. Cursoria, 556. Cutaneous gland, 77. Cuticle, 35. Cuvier, 135. Cuvieria, 297. Cuvier, organs of, in Holothuroidea, 298. Cyamus, 454. Cyanea, 261. Cyathophyllidge, 230. Cyclometopa, 478. Cyclops, 435. Cydippe. 265, 266. Cylicomastiges, 196. Cylicozoa, 257. Cymothoa, 460. Cynipidas, 594. Cynips, 594. Cyphophthalmus, 506. Cypridina. 427. Cypris, 428. Cypris-stage of Cirri- pedia, 443. Cyrtopia, 474. Cysticercus, 332. 335. Cystic-worm, 332. Cystidea, 289. Cystosoma, 453. Cystotagnia, 335. Cy there, 427. INDEX. 605 Dactylocalyx, 221. Dactylozooids, 216. Daphnia, 422. Darwin, 145. Dasychira, 583. Dasypoda, 597. Death-head moth, 584. Death-watch, 589. Decapoda, 475. Deep sea Fauna, 163. De Gteer, 133. Degradation, 158. Delamination, 114. Demodex, 492. Dendrochirotae, 299. Dendroccela, 311, 314. Dendroccelum. 315. Dendrometridge, 583. Dcndrophyllia, 233. Dentine, 41. Dermal branchiae, 277. Dermanyssus. 495. Dermatobia. 576. Dermatodectes. 492. Dermatophili, 492 Dermatoptera, 556 Dermestes, 590 Derostomea, 312. Derostomum. 313. Descent, evidence in fa- vour of theory of. 151. Desrnoscolecidge. 357. Desor. Type of, 341 Deutoplasm, 111. Development. 107. Diaptomus, 435. Diastylis, 470. Difflugia, 186. Digenous reproduction, 97. Digging- wasps, 596. Digonopora, 316. Diloba, 583. Dimorphism, facts of, in favour of theory of descent 152, sexual 101, 153. Dinoceras, 173. Dinosauridaa, 175. Dioecious, 100. Diopatra, 374, 379. Diphyes, 246, 250. Diplophysa, 250. Diplozoon, 324. Dipneumones, 504. Diporpa, 325. Diptera, 572. Direct development, 120. Directive body, 109. Discoidal segmentation, 112. Discoideas, 250. Discomedusa, 260, 261. Disco phora (Ccelente- rate), 259, 394. Discophora, see Hiru- dinea. Dissepimenta of Actin- ozoa, 228. Dissepiments of Anne- lida, 364. Distomea, 318, 321. Distomum, 317, 322. Distomum cygnoides, 321. Distomum hrematobium, 321. Dochmius, 350, 352. Dolichopus, 576. Dolomedcs, 502, 504. Doritis, 585. Dorsibranchiata, 370, 379 Dorylaimus, 357. Dracunculus, 356. Dragon-fly, ,562. Dromia, 478. Drone, 598. Ductus Botalli, 66, Dung-flies, 576. Duodenum, 57. Dynamena, 242. Dysdera, 499. Dytiscus, 590. Earwigs, 556. Ecdysis of Arthropoda, 407. Echinaster, 273, 293. Echineibothrium, 338, 326. Echiniscus, 497. Echinococcifer, 335. Echinococcus, 336, 331, 333. Echinocucumis, 297. Echinocyamus, 297. Echinoderidae, 404. Echinodermata, 266. Echinoidea, 294. Echinometra, 295, 296. Echinorhynchus, 302. Echinus, 296. Echiuroidea, 389. Echiurus, 387, 392. Eciton. 596. Ectoderm, 213, 49, 116. Ectolecithal, 112. Ectolithia, 189. Ectoplasm, 54. Eisvogel, 585. Elastic fibres, 39. Elater, 589. Eleutheroblastese, 240. Ellipsocephalus, 484. Elytron, 369, 528. Embolic invagination, 114. Embryology in relation to descent theory, 157. Embryonicdevelopment, 119. Empidae, 576. Enchelidium, 357. Enchytraeus, 384. Encrinus, 289. Endoderm, 116. 49, 213. Endogenous cell formao tion, 30, 31. Endomychidai, 588. Endoplasm, 54. End-organs, 47. Endoskeleton, 79. Endothelium, 34. Enopla, 339, 342. Enoplus, 357. Enteroccele, 116. Enteroplea, 404. Enteropneusta, 299. Entoconcha, 299. Entolithia, 189. Entomophaga, 594. Entomostraca, 416. Entoniscus, 459, 460. Entozoa, 308. Epeira, 505. Ephemera, 531, 562. Ephemeridge. 561. Ephialtes, 595. Ephippigera, 558. Ephryopsis, 261. Ephyra, 125, 253, 251. Ephyra-MedussB, 259. Epiblast, 114. Epibole, 115. Epimerum, 525. Epipharynx, 524. E pi sternum, 525. Epistom of Decapoda, 476. Epistylis, 205. Epithelium, 34. Equitidae. 585. Equus,phylogeny of, 1 72. Erebia, 585. Erichthus, 472. Eristalis, 576. Errantia, 378. Erythraaus, 495. Eschscholtzia, 26G. Estheria, 419. Eucephala, 577. Eucharis, 266. Euchlanis, 404. COG IXDEX. Eucope, 242. Eucopepoda. 435. Eucopidaj. 234, 224, 242. Eucyrtidium, 190. Eudcndrium, 241. Eudoxia, 250. Eusrlena. 196. Euglypha, 186. Euisopoda, 460. Eunice, 379. Euphausia, 475. Eupliausia, eyes of, 409. Euplectella, 221. Euprepia, 583. Eurhamphsea, 266. Euryalidae. 273, 275, 294. Eurylepta, 316. Eurypterus. 480. Eusmilia, 232. Euspongia, 221. Eustrongylus, 352. Eutermes, 559. Eutvphis, 456. Evadne, 422. Evania, 595. Exoskeleton, 78. Eyes, 85. Fabricia.372. Facetted eye, 88. Faltenmiicke, 578. Fan of Arthropod a. 409. Fan-tracheae, 70. 410. Fasciola, 316. Fasciolcs, 272, 296. Fat, 39. Fauna of deep sen, 163. Fauna, relation of to re- cent fossil forms, 170. Feathers, Sea, 231. Federgeistch.cn, 582. Femur, 526. Fertilisation of ovum, 109. Fettschabe, 582. Feuerwanze, 572. Fibrillar tissue, 38. Field cricket, 558. Figitcs, 594. Filaria. 347,349,352,356. ,, host of, 356. Filariida?. 355. Filigrana, 382. Final causes, doctrine of, 51. Fir-tree lice, 570. Fission, 96. Flabcllum, 232. Flacrellata, 193. Flata, 571. Flea, 579. Fleischfliege, 576. Flies, 575. Floscularia. 404. Floscularidae, 404. Foenus, 595. Foramen Panizzte. 67. Foraminifera, 184. Fore-gut, 56. Forficula. 556. Formica, 596. Formicid.se, 595. Forskalia, 249. Fossils, Conditions of formation of, 168 ; De- lation of, to living species, 170. Fossoria. 596. Free cell formation, 30. Fringing reefs, 230. Fritillary, 585. Frost-butterflies, 583. Fulgora, 571. Fumea. 584. Fungia, 232. Fungicolae, 578. Fungidai. 232. . Furcilia, 474. Gabelschwanz, 584. Gadflies, 576. Galathca, 477. Galaxea, 232. Galea. 523. Galeodes. 512. Galleria, 582. Gall flics, 578. Gall-flies, Reproduction of. 128. Gallicola, 594. Gallicolse, 578. Galls, 594. Gall-wasps, 594 Gamasus, 495. Gammarus, 455. Ganglion cells, 45. Gastraea theory, 118. Gastropacha, 584. Gastrophilus, 576. Gastrotricha, 404. Gastsotrocha, 378. Gastrovascular space of Coclcnterata, 209. ! Gastro- vascular system, 60. 1 Gastrula, 49, 114, 118. Gastrus, 576. Gcbia. 477. Gecarcinus, 469, 479. Gclasimus, 479. Gelatinous sponges, 221 Gemmules 218. Genera, Origin of, 149. Generatio equivoca. 10. Geocentrophora, 313. Geocores, 572. Geodesmus, 316. Geographical distribu- tion, 159. Geological periods, Cha- racteristics of 177. Geological record. Im- perfection of, 168. Geological table, 165. Geometra, 583. Geometridas, 580. Geometrina, 582. Geophilus, 519. Geoplana, 316. Geoplauidaa, 315. Geotrupes, 590. Gephyrea, 386. Germ-cell, 105. Germinal bands, 547. Germinal disc, 112. Germinal streak, 115. Germinal vesicle, 110. Germs of Trematodcs, 319. Germ-stock, 96. Geryonia, 239, 242. Geryonopsidas, 242. Gessncr 133. Gibocellum, 506. Gigantostraca, 479. Gills 69, Tracbeal, 70. Glabellum, 484. Gland, 36. Glands, cutaneous, 77. Glassy sponges, 221. Glaucoma, 205. Gleba, 250. Globigerina, 187. Glomeris, 516, 521. Glomcrulus, 77. Glossa, 524. Glow-worm, 589. Glyccra, 377, 379. Glyciphagus, 493. Glyptodon, 170. Gnat, 578. Gnathobdellidre. 400. Gnathostoma, 345. Gnathostomata, 435. Goethe, 137. Goldfliege, 576. Gold-wasps, 696. Gonium, 195. Gonophore, 237. Gonophorcs of Siphonc- phora, 246. Gonospora, 208. Gonylcptus, 506. INDEX. 007 Gorcliidse, 350. Gordius, 310. 315, 318, 357. Gorgonia, 231. Gorgonidas, 22 1. Grain-worms, 582. Grant ia, 217, 222. Grapholitha, 582. Grapssv, 479. Grasshoppers. 557. Gregarinidae, 207. Gressoria, 557. Gromia, 187. Gryllotalpa, 527, 558. Gryllus, 558. Gymnocopa, 380. Gymnophthalmata, 238. Oynsecophorufl, 322. Gyrator, 314. Gyrodactylus, 325. Gyropeltis, 438. Heematopota. 577. HEematozoa, 356. Hsementaria, 400. Haemoglobin, 33. Hasmopsis, 400. Hairstreak butterflies, 585. Halichondrire, 221. Halicryptus, 394. Halisarca, 221. Halistemma, 249. Halla, 379. Halocypris, 427. Halomitra, 232. Halosanridae, 175. Halteres, 528, 572. Halteria, 205. Haltica, 588. Hamm, 133 Harlequin, 583. Harpacticus, 435 Harpalus, 590. Harpyia, 584. Harvey, 133. Haustellum, 573. Haversian canals, 41. Hawk-moths, 58 J. Heart of vertebrata. Evolution of, 64. Heat, animal, 73. Heliaster, 293. Heliosphaera, 190. Heliozoa, 187. Hemerobidse, 504. Hemerobius, 504. Hemiaspis, 480. Hemiaster, 279. Hemielytra, 571. Hemiptera, 506. 571. Henops, 570. Hepato-pancreas. 59. Hepialus, 584. Herbert on fertility of Hybrids, 142. Heredity, 145. Hcrmaphroditism 99, in- complete, 100. Herrnella, 382. Hermit Crabs, 478. Hcsperia, 585. Hesperornis. 170. Plessian fly, 578. Heterodera, 357. Heterogamia, 555, 557. Heterosjamy, 127. 130, 131, 543. Heterogamy, incom- plete, 131. Heterogyna, 596. Heteromera, 588. Heteronereis, 373, 379. Heterotricha, 205. Heuschrecken, 557. HexactinellidaB, 220. Hexactinia, 231. Hexapoda, 521. Hibernation. 74. Hilaire, E. G-. St., 137. ,. ,, on mu- tability of species, 1 44. Hindgut, 56. Hippa, 478. Hipparchia, 585. Hipparion, 172. Hippidae, 477. Hippobosca, 575. Hippodidas, 249. Hirudinca, 394. Hirudo, 400. His pa, 588. Histcr, 590. Histolysis, 550. History of Zoology, 131. Holoblastic, 111. Holopus, 289. Holothuria, 299*. Holothurians, 279. Holothuroidea, 297. Holotricha, 204. Holzfliegen. 577. Homarus. 477. Homolog}', 52. Homoptera, 570. Homothermic, 74. Honey-dew, 509. Hoof, 34. Hormiphora. 200. Hormiscium, 200. Hornets, 597. Horny sponges, 221. Horse -louse, 575. House-fly, 570. Humble "bee, 598. Hummelfliegcn, 670. Humming-bird Hawk- moth, 584. Hyalonema, 222. Hyalospongia, 221. Hybrid 142, Fertility of, 142. Hydatid plague, 330. Hydatina, 404 Hydra, 240. Hydrachna, 495. Hydractinia, 241. Hydranth, 244. Hydrobius, 590. Hydrocoralliae, 240. Hydrocores, 571. HydromedusEE, 236, Hydrometra, 572. Hydrophilus, 590. Hydrophilus, develop ment of, 545. Hydrophyllia, 246. Hydropsyche, 565. Hydrosoma, 244. Hydrotheca, 241, 234. Hydrozoa, 233. Hylobius, 588. Hymenocaris, 448. Hymenoptera, 590. Hyperia, 455. Hyperidje, 455. Hypcrina, 455. Hyp c r m et a m o r p hosis, 548, 588. Hypoblast, 114. Hypoderma. 576. Hypodermis Arthropoda, 407. Hypodermis of Vermcs, 303. Hypodermis or Nema- toda, 345. Hypopharynx, 524. Hypopus, 493. Hypotricha, 205. Hystrix, 379. Ibla, 445. Ichneumon, 595 Ichthydina, 40 L Ichthyobdellidse, 399. Ichthyomithca, 175. Idotca, 460. Idyopsis, 266. Ilia, 478. Ileum, 57. Imaginal disc, 550. I Imago, 548. 608 INDEX. Imperforata, 187. Inachus, 478. Insequitelas, 504. Individual, 24, 25. Infundibulum of Cteno- phora, 263. Infusoria, 191. Insecta. 521. Instinct, 94. Iphimedia, 453. Irenaeus, 435. Iris, 88. Irregular Sea-urchins, 268. Isidor of Seville, 133 Isis, 231 Isogonisra, 240. Isopoda, 456. Isopods, Parasites of, 362. Itch-mites, 492. Ixodes, 493. Japyx, 528, 554. Jassus, 571. Jejunum, 57. Jera, 460. Julus, 521. Kammmiicke, 578. Kermes, 569. Kidneys, 75. Kleinzirpen, 571. Kochlorine, 446. Kohlschnaken. 578. Kolumbaczer, 577. Kornmotte, 582. Kupferglucke, 584. Kurzdeckflugler, 90. Labidura, 556. Labium, 523. Labrum, 523. Lac, 569. Lachnus, 570. Lacinia, 523. Lacon, 589. Lady-bird, 587. Lsemodipoda, 454. Lagena, 187. Lamark, 144. Lamellicornia, 589. Lamia, 527, 588. Lampyris, 536, 589. Land-bugs, 572. Land Crabs, 479. Langwanzen. 572. Lantern-carrier, 571. Laomedea, 242. Laphria, 576. Larentia, 583. Larva, 119. Larva of Loven, 362. Lasia, 576. Lateral lines of Nema- toda, 346. Laterigradse, 504. Laurer's canal, 318. Leaf-flea, 570. Leaf -lice, 570. Leaf -wasps, 594. Lecanium,. 543, 569. Ledermuller, 133. Ledra, 571. Leech, 394. Leeuwenhoek, 133. Lemnisci of Acanthoce- phala, 360. Lens, 87. Lepadidie, 445. Lepas. 445. Lepidocentrus, 295. Lepidoptera, 579. Lepisma, 554. Leptidffi, 577. Leptodera, 350, 357. Leptodiscus, 198. Leptodora, 422. Leptoplana, 311, 316. Leptostraca, 448. Leptus, 495 Lernrea, 436. Lernreocera, 436. Lermcodiscus, 447., Lernreopodidre, 436. Lestornis, 177. Lestrigonus, 455. Leucaltis, 222. Leucandra, 222. Leucetta, 222. Lcuchtzirpen, 571. Leucifer, 471, 476.. Leucilla, 222. Leucochloridium, 321. Leucon, 470. Leuconia, 222. Leuconidse, 217. Leucorfs. 222. Leucortis, 222. Leucosolenia, 217, 222. Leuculmis, 222. Leucyssa, 222. Levantine sponges, 221. Libellula, 541, 562. Libellula, Development of, 545. Libellula, Rectal respi- ration of. 72. Lice. 568. Lice-flies, 575. Ligia, 459, 460. Ligula, 338. Ligulidae, 328. Limenitis, 585. Limexylon, 589. Limicolns, 385. Limnobates, 572. Limnobiidre, 578. Limnochares, 495. Limnodrilus, 385. Limnoria, 455, 460. Limulus, 483. Lina, 588. Linckia, 292, 293 Linens, 343. Linguatulida, 487. Linnaeus, 134. Liotheuni, 568. Liparis, 583. Liriope, 242. Lithistidaa, 220. Lithobius, 520. Lithodes, 478. Lithotrya, 444. Liver, 59. Liver Fluke, 317, 322. Livia, 570. Lobophora.,258, 297. Lobosa. 185. Lobster, 477. Locusta, 558. Longhorns, 577. Longicornia, 588. Loopers, 582. Lophogaster, 475. Lophoseris, 232. Loricata; 477. Loven's larva, 308, 362. Lucanus, 589. Lucernaria, 258. Luidia, 275, 293. Lumbriculus, 385. Lumbricus, 385. Lungs, 69. Lungs, Effect of ap- pearance of, on vascu- lar system, 65. Lycgenidaa, 585. Lycaretus, 374. Lycoridaa, 379. Lycosa, 504. Lyda, 594. Lyell, 144. Ly ell's doctrine of gra- dual changes, 166. Lygseus, 572. Lymnajus, Pulmonary cavity of, 72. Lymph, 67. Lymphatic system, 67. Lysianassa, 451, 455. Lysidice, 379. Lystra, 571. INDEX. 609 Lytta, 589. Machilis, 654. Macrobiotus, 497. Macroglossa, 584. Macrostomum, 312. Macrura, 477. Macula acustica, 85. Madrepora, 233. Madreporaria, 228, 232. Madrepores, 229. Madreporic plate. 273. Madreporidas, 233. Mseandrina, 232. Masandrinidas, 229. Maggot, 549. Magpiemoth, 583. Maja, 478. Malachius, 589. Malacobdella, 342, 343. Malacodermata, 589. Malacostraca, 447. Mallophaga, 568. Malpighi, 133. Malpighian body, 76. Malpighian tubes, Arth- ropoda, 409. Malpighian tubules, 75. Mammalia, Vascular system of, 67. Man, First traces of, 178 Mandibles of Crustacea, 412. Manna, 569. Mantis, 527, 557. Mantispa, 564. Manubrium, 211. Marginal bodies, 234, 239, 254. Marine Fauna, 162. Marrow, 41. Marsupialida, 258. Marsupialis, 252. Mask, 562. Masticatory organs, 56. Maxilla of Crustacea, 413. May Flies, 661. Meal-worm, 589. Meckelia, 343. Medusa aurita, 261. Medusas, 236. Medusa, Relation of to Polyp, 236. Medusa type, 211. Medusites circularis,256. Medusoids, 211. Megachile, 598. Megalonyx, 170. Megalotrocha, 401. Megatherium, 170, 173. Melicerta, 404. Melipona, 590. Mclitsea, 585. Melithsea, 231. Melofe, 589 Melolontha, 590. Melophagus, 575. Membracis, 571. Membranacei, 572. Membranous labyrinth, 85. Menopon, 568. Mentum, 524. Mermis, 345, 356. Mermithidas, 356. Meroblastic, 111. Meromyaria, 345. Merostomata, 479. Mesenteric filaments, 224. Mesoderm, 116. 213. Mesostomea, 3i3. Mesostomum, 313. Mesothorax, 525. Mesotrocha, 378. Metabolism, 10. Metachseta, 378. Metagenesis, 123, 130, 131. Metamere, 27, 305. Metamorphosis, 126. Metamorphosis retro- gressive, 158. Metanauplius, 432. Metathorax, 525. Metazoa, 54. Metcecus, 589. Miastor, 578. Miastor, Pasdogenesis of. 544. Micrococcus, 206. Microgaster, 595. Microlepidoptera, 582. Micrommata, 504. Microstomea, 312. Microstomidae, 309. Microstomum, 314. Microtasnia, 336i Micrura, 343. Midgut, 66. Migration, 74. Miliola, 187. Millepora, 241. Milleporidae, 233. Milnesium, 497. Mimicry, 155. Miris, 572. Mites, 489. Mole cricket, 558, Molpadia, 299. Monadinse, 193. Monads, 194. Monas, 194, 206. Monera, 182. Mongrels, Sterility of, 143. Monocaulus, 240. Monocelis,311, 313. Monocystidea, 208. Monocystis, 208. Monogenous reproduc- tion, 97. Monogonopora, 315. Monophyes, 250. Monostomum, 317. 321. Monothalamia, 186. Morphology, 52. Morphology, Evidence of, for descent theory 151. Mososaurus, 175. Mucous connective tis- sue, 37. Miillerian duct, 101. Mundhorn-fliege, 576. Musca, 576. Muscardine, 584. Muscaria, 575. Musciformes, 577. Muscle-epithelium, 43. Muscular tissue, 43. Mushroom coral, 232. Mutilla, 596. Mycetophila, 578. Mygale, 504. Mygalidaa, 499, 504. Mylodon, 173. Myoblast, 43. Myriapoda, 514. Myrmecia, 504. Myrmecophila, 696. Myrmedonia, 590. Myrmeleon, 564. Myrmica, 596. Mysis, 474. Mysis, Auditory organ of, 414. Mystacides, 565. Myxospongia, 221. Myxospongise, 220. Myzostoma, 380. Nadina, 313. Naideae, 385. Nail, 34. Nais, 386. Natural selection, 145. Natural system, 150. Naucoris, 527, 572. Nauplius, 406, 415. Nausithoe, 260, 261. Nausithoe, Eye of, 255. 39 010 INDEX. Nautilus, Eye of, 90. Nebalia, 448. Necrophorus, 590. Nectocalyces, 246. Nemathelminthes, 343. Nematocalyccs, 242. Nematocysts, 212. Nematus, 543, 594. Nemertes, 342, 343. Nemertini, 339. Nemocera, 577. Nemoptera, 564. Nemura, 561. Ncpa, 527, 534, 572. Nephelis, 400. Nephridia, 308. Nephrops, 477. Nereilepas, 379. Nereis, 379. Nerve fibre, 46. Nerve tissue, 45.. Nervous system, Grada- tions of, 80. Nervures, 528. Neuromuscular cells, 80. Neuropodia of Annelids, 365. Neuroptera, 562. Niphargus, 455. Noctiluca, 196. Noctuiformes, 578. Noctuina, 583. Nomada, 597. Nonionina, 184. Notodelphys, 435. Notodonta, 584. Notodromus, 428. Notommata, 401, 404. Notonecta, 572. Notopoda, 478. Notopodia of Annelids, 365. Notum, 525 Nuclear fluid, 29. Nuclearia, 194. Nuclear plate, 30. Nuclear substance, 29. Nucleolus, 29. Nucleus, 12, 13, 29. Nucleus, Division of, 30. Nummulina, 187. Nutritive polyp, .236. Nut- weevil, 588. Nycteribia, 575 Nymphaliadas, 585. Nymphula, 582. Obelia, 242. Obisium, 511. Oceanidse, 234. Ocellata, 239, 241. Ocliracca, 195. Octactinia, 230, 231. Octobothrium, 324. Octorchis, 242. Ocular plates, 278. Oculina, 232. Oculinidae, 229. Ocypoda, 478. Odontolcas, 176. Odontornithes, 175 Odontosyllis, 379. Odynerus, 597. (Ecodoma, 596. CEdemera, 588. (Edipoda, 558. (Erstedtia, 340. CEsophagus of Antliozoa, 60. (Estridae, 542, 576. (Estropsidas, 564. Oken, 137. Olenus, 484. Olfactory organs, 91. Oligochseta, 382. Olynthus, 217. Omalium, 590. Onchocotyle, 324. Oniscus, 460. Ontophilus, 590. Onychophora, 512. Oostegitcs of Arthros- traca, 451. Opalinae, 204. Operculata, 446. Ophiactis, 292. Ophidiaster, 273, 293. Ophioderma, 294. Ophioglypha, 291. Ophiolepis, 294. Ophion, 595. Ophiothrix, 294. Ophiura, 294. Ophiuridas, 273, 275.279. Ophiuridea, 291, 293. Ophiusidge, 583. Opisthomum, 313. Oral pole of Echinoder- mata, 268. Orbitelas, 505. Orbulina, 187. Orchestia, 455. Ordensbander, 583. Organ, 25. Organ coral, 231. Oribates, 495. Orohippus, 172. Orthoptera, 554. Orthosia, 583. Oryctes, 590. Orygia, 583. Osculum, 210. Osmia, 598. Osmylus, 564. Osteoblasts, 42. Ostracoda, 423. Otion, 445. Otolith, 85, 239. Otolith plate of Cteno- phora, 264. Ovary, 97. Ovipositors, 529. Ovum, 33, 97. Ovum, fertilization" of 109. Oxycephalus, 456. Oxyrhyncha, 478. Oxystomata, 478. Oxytricha, 205. Oxyuris, 344, 348, 351. Pasdogenesis, 128 Pagurus, 478. Painted Lady, 585. Paljeaster, 292. Palaamon, 220, 477. Palasocarabus, 469.; Palseocrangon, 49. Palaeontology, Evidence in favour of descent theory, 163 Palese of Annelids, 368 Palingcnia, 562. Palinurus, 477. Pali of Actinozoa, 228 Pallas on domestic hy- brids, 143 Palp, 413, 523. Palpares, 564. Palpicornia, 590. Palps of Chsetopoda, 369. Pandora, 266. Panorpidre, 563. Papilio, 585. Paraglossa, 524. ParaniEeccium, 205. Paramere, 27. Paranucleus. 201. Parapodia, 305, 365. Parasita, 435. Parasitica, 567 Parthenogenesis, 105, 410, 543. Parthenogenesis of Phyl- lopoda, 418. Paste- worm, 357. Pauropus, 521. Peacock butterfly, 585. Pectinaria, 382. " Pedal ganglion, 82. Pedata, 299. Pedicellarirc, 271. Pediculus, 568, 589. INDEX. 611 Pedipalpi, 506. Pedipalpus, 484. Pedunculata, 445. Pelagia, 236, 260, 261 Pelodera, 357. Pelodytes, 346, 350. Peltocaris, 448. Peltogaster, 447, 460 Pelzfresser, 568. Pelzkafer, 590. Pelzmotte, 582. Pemphigus, 570. Penaeus, 477. Penella, 436. Pennatula, 231. Peunatulidas, 231. Pentacrinus, 289. Pentacta, 274. Pentamera, 589. Pentastomidas, 408. Pentastomum, 488. Pentatoma, 572. Pentatrematites, 289. Perforata, 181, 232. Perichondrium, 39 Peridinium, 196. Periosteum, 41. Peripatus, 514. Periplaneta, 557. PerischEechinidse, 295. Peritricha, 205. Perla, 561. Perlidas, 561. Petalopus, 180. Phalaugiida. 505. Phanerocarpse, 255. Phanero-codonic gono- phore, 236. Phascolosoma, 394. Phasma, 557. Philodina, 404. Philopterus, 568. Pholcus, 505. Phora, 576. Phoronis, 389. Phosphorescent organs of insect, 536. PhoxichiMdium, 496. Phreoryctes. 385. Phronima. 455. Phrosina, 455. Phryganea, 565. Phryganidse, 564. Phrynus, 507. Phthirius, 568. Phyllacanthus. 296. Phy Ilium, 557. Phyllophorus, 278. Phyllopoda, 416. Phyllosomata. 471. Phylloxera, 570, Phylloxera, Reproduc- tion of, 128. Phylogeny, 122. Physalia, 244, 249. Physematium, 194. Physometridge, 583. Physophora, 248, 249. Physophoridae, 244, 248. Physopoda, 559. Phytophaga, 594. Phytophthires, 568. Pieris, 585. Pigment of eye, 86, 88. Piiidium, 341. Pilzfliegen, 576. Pilzkafer, 588. Pilzmucken, 578. Pimpla, 595. Pinnotheres, 478. Pinnulge, 270, 288. Piophila, 576. Pirates, 572. Pisa, 478. Pisces, vascular system of, 64. Piscicola, 399. Planaria, 315. Plane, median, 27 ; sa- gittal, 27 ; transverse, 27. Planipennia, 563. Plant-lice, 569. Plants and animals, 15 Planula, 117, 124, 255. PLasmodium, 30. Platygaster, 594. Platygastcr, larvjeof .549. Platyhelminthes, 309. Platypezidre, 576. Platyscelus, 456. Pleopods of Isopoda, 457. Pleuron, 483, 525. Pliny, system of, 132. Ploteres, 572. Plume-moths. 582. Plumularia, 237, 242. Plusiadte, 583. Pluteus, 281, 282, 292, 294, 296. Pneumatocyst, 244. Pneumatophore, 214. Pneumora, 555. Podocerus, 455. Podocoryne, 237, 241. Podophora, 296. Podophrya, 205. Podura, 554. Poikilothermic, 74. Poison glands, 532. Polar areas of Ctcno- j phora, 264, Polar body, 104. Polian vesicles, 272. Polistes, 566, 597. Pollicipes, 445. Polyactinia, 225, Polybostrichus, 372,379. Polycelis, 311, 315. Polychaeta, 374. 1'olycirrus, 378. Polycladus, 311. Polycystidea, 208. Polycystinidse, 190. Polycyttaria, 196. Polydesmus, 521. Polydora, 382. Polygastrica, 192. Polygordius, 375. Polymorphina, 180. Polymorphism, 23, 126. Polymorphism, Facts of, in favour of Theory of Descent, 152. Polymorphism of social insects, 155. Polymyaria, 345. Polynoe, 379. Polyommatidae, 585. Polyophthalmus, 372. Polyparia, 227. Polyphemus, 422. . Polypoid, 211. Polypomedusse, 233. Polyp type, 210. Polystomea, 317, 318,322 Polystornella, 187. Polystomum, 323, 324. Polythalamia, 186. Polyxenus, 521. Polyzonium, 515, 521. Pompilus, 597. Pontobdella, 400. Pontonia, 477. Porcellana, 460, 478. Porcellio, 457, 460. Porifera, 214. Porpita, 250. Portunus,. 478. Postabdomen of Arthro- poda, 407. Postscutellum, 526, 591. Pou de poissons, 438. Prachtkafer, 589. Prseabdomen of Arthro poda, 407. Prrestomium of Chnsti- fera, 387. Praniza, 459. Prawns, 477. Praying insect, 557. Priapulus, 394. Primitive streak, 115, 612 INDEX. Prionus, 588. Procrustes, 590. Proglottisofcestoda,326. Proleg, 519. Pronucleus, 109. Prosoponiscus, 451. Prosorochmus, 340, 341. Prostate, 99. Prostomum,311,312,314. Protaster, 292. Proterosaurus, 177. Prothorax, 525. Protodrilus, 365, 375. Protolepas, 446. Protoplasm, 12. Prototracheata, 512. Protozoa, 182. Protula, 372, 382. Proventriculus, 530. Pselaphus, 590. Pseudonavicellas, 208. Pseudophyllidse, 338. Pseudopodia, 54, 186. Pseudopupa, 593. Pseudoscorpionidea, 510. Pseudospora, 194. Pseudotetramera, 588. Pseudova, 544. Pseudovaries of Aphides, 106. Psocus, 559. Psolus, 299. Psorosperms, 208. Psyche, 543, 584. Psychidas, 581. Psychoda, 578. Psylla, 570. Psyllidfe, 570. Psyllodes, 570. Pteraster militaris. 284. Pterodactylicire, 175. Pteromalus, 594. Pteronarcys, 561. I'terophorus, 582. Pteroptus, 495. Pterygotus, 480. Ptinus, 589. Ptychoptera, 578. Pulex, 579. Pupa, 548. Pupa coarctata, 551, 574. Pupa libera, 551. Pupa obtecta, 551, 574, 575. Pupa of Cirrpcdia, 443. Pupil, 88. Pupipara, 542, 575. Purple, visual, 87. Pygidium, 484. Pygidium of Colcoptera, 586. Pygnogonida, 495. Pygocephalus, 469. Pyralis, 582. Pyrophorus, 589. Pyrrhocoris, 572. Quadrilatera, 478. Radial vessels, 272. Radiata, 266. Radii of Echinodermata, 267. Radiolaria, 189. Radius, 528. Rami communicantes, 82. Ranatra, 534, 572. Randwaiizen, 572. Rapacia, 379. Raphidia, 563. Raubfliegen, 576 Ray, 134. Reaumur, 133. Receptaculum seminis, 99. Eedi, 133. Redia, 129, 319. Reduvidge, 572. Regeubremse, 577. Renilla, 231. Reptiles, Vascular sys- tem of, 66. Respiration, Renewal of .external medium, 72. Respiratory organs, 67. Respiratory trees, 277. Reticular connective tissue, 38. Reticularia, 186. Retina, 87. Retinacula of Acantho- cephala, 359. Retinulae,'S8. Rhabditis, 344, 349, 357. Rhabdoccela, 311, 313. Rhabdonema, 346, 350. Rhabdosoma, 455. Rhachis, 483. Rhipidius, 589. Rhipidogorgia, 231. Rhipiphorus, 589. Rhizocephala, 446. Rhizocrinus, 289. Rhizoglyphus, 492. Rhizopoda, 181. Rhizostoma, 261. Rhizostomea:, 261. RhizostomidEe, 252. Rhizotrogus, 590. Rhodites, 594. Rhopalocera, 582. 584. Rhopalonema, 242. Rhyacophila, 565. Rhynchoccela, 339. Rhynchodesmus, 315 316. Rhynchota, 566. Rhyncobdellidas, 399. Ribs, 528. Rinderbremse, 577. Root-lice, 127. Rosel von Rosenhof, 133. Rosette of Echinoidea. 296. Rostellum of Cestoda, 327. Rotalia, 187. Rotatoria, 400. Rotifer, 404. Rotifera, 400. Rotula, 297. Roux, Breeding experi- ments, 142. Riickenschwimmer, 572. Rudimentary organs, Meaning of, 156. Rugosa, 230. Rutimeyer, on origin of ox, 143. Sabella, 382. Sabellaria, 382. Sac-bearers, 582. Saccharomyces, 206. Saccocirrus, 381. Sacconereis, 372, 379. Sacculina, 447. Sasnurus, 385. Sagartia, 225. Sagitta, 357. Sagittal plane of Cteno- phora, 262. Salivary gland, 58. Salpingceca, 196. Saltatoria, 557. Salticus, 504. Saltigradas, 501. Sapphirina, 436. Sarcode, 19, 22. Sarcolemma, 45. Sarcophaga, 576. Sarcopsylla, 579. Sarcoptidas, 492. Sargus, 577. Sarsia prolifera, 239. Saturnia, 584. Satyrus, 585. Saw-flies, 594. Scalpellum, 445. Scaphognathite of Deca- poda, 476. Scatophaga, 576, INDEX. 613 Scenopius, 576. Schaeffer, 133. Schattenmlicke, 578. Schelling, 137. Schildlause, 568. Schildwanzen, 572. Schistocephalus, 338. Schizaster, 297. Schizomycetes, 206. Schizoneura, 570. Schizopoda, 472. Schizoprora, 311, 313, 314. Schizostomum, 312. Schnabelfliegen, 563. Schnaken, 578. Schnepfenfliegen, 577. Sohreitwanzen, 572. Schwarmer, 584. Schwebfliegen, 576. Sciara, 57g. Sciophila, 578. Sclater on Zoological Provinces, 160. Sclerodermites, 231. Sclerostomum, 350, 352. Sclerotic, 88. Scolex, 333. Scolia, 596. Scolopendra, 519. Scopula, 582. Scorpion, 510. Scorpionidea, 508. Scorpion-spiders, 506. Scuta of Cirripedia, 439. Scutellidfe, 297. Scutellum, 526. Scutigera, 518, 520. Scyllarus, 477. Scyphistoma, 125, 233 255. Scyphomedusae, 231 , 236, 250. Sea feathers, 231. Sea long-worm, 343. Sea-urchins. 294 ; Regu- lar, 296. Sebaceous glands, 77. Secretory organs, 74. Sedentaria, 380. Sedimentary forma- tions : Conditions of forma- tion of, 166, 169. Determination of age of, 164. Table of, 165. Segment, 27. Segmental organs,75,308. Segmentation cavity. 116, Segmentation of ovum, 110. Selection, Artificial, 145. Selection, Sexual, 152. Semaeostomeae, 260. Semen, 97. Semites of Echinoidea , 296. Sense organs, 83. Septa of Actinozoa, 228. Sergestes, 477. Sericteria, 532. Serolis, 460. Serpula, 382. Sertularia, 242. Sesia, 584. Sex, 104. Sexual reproduction, 97. Sexual selection, 152. Sheeptick, 575. Shell glands, 75. Shell glands, Crustacea, 410. Sialis, 563. Sida, 422. Silkworm, 584. Silpha, 590. Simonea, 492. Simple eye, 89. Simulia, 577. Singcicaden, 571. Singmucke, 578. Siphonophora, 236, 243. Siphonostomata,, 435. Sipunculoidea, 392. Sipunculus, 394. Sirex, 594. Siriella, 474. Sitaris, 589. Skeleton, 78. Smellers of Tanaidae, 459. Smerinthus, 584. Smynthurus, 554. Solaster, 293. Solenobia, 543, 581, 582. Solifugas, 511. Solpuga, 512. Spanish fly, 589. Spatangidse, 296, 279, 295. Spatangidea, 273. 297. Spatangus, 297. Species, 140. Species : Cuvier's defi- nition of, 149 ; Muta- bility of, 144 ; Origin of, 144, 149. Species, Kelation of to genera. 149. Speckkafer, 590\ Sperm, 97. Spermatophores, 99. Spermatozoon, 33, 97. Sphaeridia, 272. Sphjerodorum, 372, 379. Sphasroma, 460. SphaBronectes 250. Sphasronites, 289. Sphaarophyra, 205. Sphasrotherium, 521. Sphasrozoum, 191. Sphaerularia, 356. Sphex, 552, 596. Sphingina, 584. Sphinx, 584. Sphyrocephalus, 311. Spicula of Nematoda. 347. Spiders, 498. Spindle-tree moth, 382. Spinning glands, 532. Spinning mite, 495. Spio, 382. Spiodeas, 381. Spio-Nephthys larva, 378. Spionidas, 381. Spiralzooids, 241. Spirillum, 206. Spirochasta, 206. Spirographis, 382. Spiroptera, 348. Spirorbis, 372, 382, Spirostomum, 205. Sponges calcareous, 222 ; glassy, 221; gelatin- ous, 221; horny, 222; levantine, 221. Sponge type, 210. Spongia, 221. Spongiadae, 221. Spongiaria, 214. Spongilla, 218, 221. Spontaneous generation, 10. Spores, 97. Spores 128; of Trema- toda, 129. Sporocyst, 129, 319. Spring-flies 564. Springkiifer, 589. Spring-tails, 554. Spumella, 195. Squama, 572. Squilla, 472. Stag-beetle, 689. Staphylinus, 590. Star coral, 232. Star-fishes, 290. 292. Stauridae, 230. ' Staurocephalus, 379, 614 INDEX. Stechfliege. 576. Stelleridea,' 292. Stemmata Arthropoda, 408. Stenorhynchus, 478. Stentor, 205. Stephanoceros, 404. Stephanosphasra, 195. Sterile polyp, 237. Sternum, 525. Stigmata, 71. Stilettfliegen, 576. Sting, 592. Stipes, 523. Stomatopoda, 470. Stomobrachium mira- bile, 239. Stornoxys, 576. Stone canal, 272. Stratiomys, 577. Strepsiptera, 565. Stridulantia, 571. Strobila, 125, 255, 256. Strongylidse, 347. Strongylocentrotus, 296. Strongylus, 352. Struggle for existence, 145. Stutzkafer, 590. Stylaria, 386. Stylasteridae, 241. Stylochus, 316. Stylonychia. 205. Stylops, 566. Suberites, 229. Subgenital pits of Dis- cophora, 260. Subme'ntum, 524. Suboesophageal gang- lion, 82. Sub-species, 141. Succession of similar types, 171. Suctoria, 205, 446. Summer eggs of Phyl- lopoda, 418. Summer eggs of Koti- fera, 403. Summer eggs of Turbcl- laria, 313. Supra-oesophageal gang- lion, 80. Swallow tail, 585. Swammerdam, 133. Sweat glands, 77. Sycaltis, 222. Sycandra, 222. Sycetta, 220. Sycilla, 222. Sycon, 221, 222. Syconidje, 212, 217, 222. I Sycortis, 222. I Syculmis, 222. I Sycyssa, 220. Syllis, 379. Syllis prolifera, 372. Symbiotes, 492. Sympathetic, 82. Synapta, 278, 283, 298, 299. Synaptida3,.283. Syrphus, 576. System, Meaning of, 150. System of Aristotle, 132. Cuvier, 136. Linnaeus, 135. Pliny, 132. Present day, 138. Tabanida3, 574, 576. Tabanus, 577. Tachina, 576. Tachinse, 541. Tactile corpuscles, 47. Tajnia, 327, 330, 331. 335. Tasnia cucumerina, 329. Taeniadae, 334. Talitrus, 455. Tanais, 459. Tanystomata, 576. Tanzfliegen, 570. Tapetenmotte, 582. Tapeworm 326. Tarantula, 504. Tardigrada, 496. Tarsus, 527. Taste, 92. Tegenaria. 504. Tegmina, 528. Tegulse, 591. Teleas, 594. Teleas, larva of, 549. Telephorus, 589. Telepsavus, 382. Telepsavus- Chsetopterus larva, 378. Telolecithal, 112. Telotrocha, 378. Telson of thoracostraca 461. Tenebrio, 589. Tenthredo, 594. Teratology, 51. Terebella, 382. Terebra, 592. Terebrantia, 594. Terga of Cirripedia, -139. Termes, 561. Termites, 5.~9. Tcrricolae, 385. Tcsselata, 289, Tesfo, 97. Tetracoralla, 230. Tetra'nychus, 495. Tetraphyllidge. 338. Tetraplasta, 194. Tetrapncumones. 504. Tetrarhynchus, 327. 338. Tetrastemma, 341, :)!2. Tettigonia, 571. Tettix, 558 Textularia, 187. Thalamophora, 180. Thalassema, 392. Thalassicolla, 190, Thalassina, 477. Thamnocnidia, 241. Theca of Actinozca J 228. Thecla, 585. Thecodontidse, 175. Thelyphonus, 508. Thereva, 576. Theridium, 502, GOG Theriodonta, 175. Thomisus, 504. Thoracostraca. 460 Thread cells, 212. Threadworms, 344 Thrips, 559. Thysanopoda, 475 Thysanozoon, 316. Thysanura, 553. Tibiu, 526. Ticks, 493. Tiger-beetles, 590. Tillodontia, 173. Tillotherium, 173 Tima, 242. Tinea, 582. Tipula, 578. Tipulariae, 577. Tissue, 29. Todtengraber, 590. Tomopteris, 380. Tornaria, 300. Tortoiseshell butterfl v. 585. Tortrix, 582. Touch, 84. ' Toxodon, 170. Toxodontia, 173. Toxopneustes, 296. Tracheae, 70, 410. Trachelius, 204. Trachymedusee 239,212. Trachynema, 239, 2-J2. Ti-achys, 589. Transverse plane of Ctenophora, 262. Trap-door spider, 504. Trematoda, 316. Trcpang. 299, INDEX. 615 Trifenophorus, 338. Trichina, 347, 348, 353, 354, 355. Trichocephalus, 348, 353. Trichodectes, 336, 568. Trichodes, 589, 599. Trichodina, 205. Trichomonas, 194. Trichoptera, 56i. Tricliosomum, 353. Trichotrachelidge, 353. Trigonia, 599. Trilobita, 483. Triphaena, 583. Tristomum coccineurn, 323 Trivium, 269. Trochal disc of Rotifers, 401. Trochanter, 526. Troctes, 559. Trogus, 595. Trombidium, 495. Trypeta, 576. Tube-spinners, 504 Tubicinella, 446. Tubicolas, 380. Tubicolaria, 401, 404. Tubifex, 385. Tubipora, 231. Tubitelae, 504. Tubularia, 239. 241. Tubulariaa, 241. Turbellaria, 309. Turbinolia, 232. Tylenchus, 357. Type, 52. Type of Desor, 341. Typhis, 456. Typhlosole of Lumbri- cus, 383. Tyroglyphus, 492. Umbellula, 231. Upper lip of Crustacea, 412. Uroceridas, 594. Uropoda of Crevettina, 454. Uterine bell of Acantho- cephala, 361. Uterus, 99. Vagina, 99. Vampyrella, 194. Vanessa. 553, 585. Variability, 145. Varieties, 141. Variety,. Relation of to species, 149. Vascular pore of Nema- toda, 346. Vascular system, 59. Vas deferens, 99. Vein, 62. Veins, 528. Velarium, 252. Velarium of Scypbo- medusae, 252. Velella, 246, 250. Velellid33, 244. Velia, 572. Venous, 73. Ventral plate, 545. Ventriculitidse, 221. . Veretillum, 231. Vermes, 302. Vesiculas seminales, 99. Vesiculata, 239, 241. Vespa, 597. Vexillum, 266. Vibrio, 206. Vine-lice, 570. Vinegar worm, 357. Visceral nerves, 82. Vitellarium of Turbel- laria, 312. Vocal organs, 552. Volvox, 195. Vortex, 313. Vortex viridis, 310. Vorticella, 205. Waffenfliegen, 577. Wallace, 147. Warm-blooded, 74. Wasps, 597. Wasserlaufer, 572. Water-bugs, 571. . Water-fleas, 419. Watermites, 495. Water-scorpions, 572. Water-spiders, 504. Water-vascular system. 308, 311. Water-vascular vessels of Platyhelminthes 75. Wax glands, 532. Weevils, 588. Weizenfliege, 576. White ants, 559. White butterflies, 585. White coral, 232. Wickler, 582. Wings, 528. Wiiikelspinne, 504. Winter eggs of Rotifera, 403. Winter eggs of Turbel- laria, 313. Winter-sleep, 74. Wolf-spider, 504. Wood-bees, 598. Wood-wasps, 594. Worm, Paste, 357. Worm, Vinegar, 357. Wotton, 133. Xantho, 478. Xenos, 566. Xiphosura, 480. Xylocopa, 698. Xylophaga, 589. Xylophagus, 577. Xylotomse, 576. Yolk, 111. Yolk-cord, 543. Yolk, Effect of, on de- velopment, 120. Yponomeuta, 582. Zerene, 583. Zoeea, 466. Zoantharia, 231. Zoanthus, 232. Zoogloca, 200. Zoological provinces, 1 60. Zoophytes, 209. Zoosperms, 209. Zoospores, 194, 197. Zoothammium, 205. Ziinsler, 582. Zygaena, 584. Printed by Hazell, Wataon, & Viney, Ld. London THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. BIOLOGY LIBRARY DEC 13 19* JUL 17 195K No26'57GH 11961 LD 21-5m-7,'37 Vr \ Al ^~- THE UNIVERSITY OF CALIFORNIA LIBRARY