Te lh I I nN a en ed cae a fee etme eye eermrn Clarendon YBress Devries FORMS OF ANIMAL ROLLESTON ‘ + meer LIFE London MACMILLAN AND CO. PUBLISHERS TO THE UNIVERSITY OF @xford. | f Ve (oF vy =. Clarendon Press Series FORMS OF ANIMAL LIFE BEING OUTLINES OF ZOOLOGICAL CLASSIFICATION BASED UPON ANATOMICAL INVESTIGATION AND ILLUSTRATED BY DESCRIPTIONS OF SPECIMENS AND OF FIGURES BY GEORGE ROLLESTON, D.M., F.RB.S. LINACRE PROFESSOR OF ANATOMY AND PHYSIOLOGY IN THE UNIVERSITY OF OXFORD Oxford AT THE CLARENDON PRESS M,.DCCC, LXX [All rights reserved ] Aw det pi) Svoxepaivery TaldiKOs THY TEpl TOV atywoTepav CGwv enloxew. ev maou yap Tots guowkols éveorl Te Oavpactov ..... kab 4 X\ / Ae aes an , / ° \ / Tpos THY CyTnoW TEpl ExaoTov TOV CowY TPOTLEVaL de? pr) OvTWTOvPEVOV Os ev dnaow dvtbs @vctkod cal cadod.—ARisTorLE, De Part. Anim. 1. 5. Tlavrds mpocdeivat 7d €\Nettov.— ARISTOTLE, Ethic. Nicom. i. 7. MUSEUM, OXFORD, March 5, 1870. PREFACE. Tuts book is intended to meet certain requirements which, as the writer’s experience has shown him, are felt by students of Comparative Anatomy. It consists of three parts; the first is an introduction, giving a Classification of the animal kingdom, with a Zooto- mical account of its various Sub-kingdoms and their subordinate Divisions and Classes; the second con- sists of descriptions of certain readily procurable spe- cimens which illustrate in the concrete a very large number of the systematic descriptions contained in the introduction; and the third contains descriptions of figures supplementary to the descriptions of speci- mens, and intended to aid them in furnishing that groundwork of particular facts, without which it is impossible to obtain any real knowledge or perma- nent hold of general principles. The distinctive cha- racter of the book consists in its attempting so to combine the concrete facts of Zootomy with the out- lines of systematic Classification as to enable the student to put them for himself into their natural relations of foundation and superstructure. The foun- dation may be made wider, and the superstructure may v1 PREFACE. have its outlines not only filled up, but even considerably altered by subsequent and more extensive labours; but the mutual relations of the one as foundation and of the other as superstructure, which this book particularly aims at illustrating, must always remain the same. It is hoped that this work, though written with a view chiefly to the needs of University students of Comparative Anatomy, and with especial reference to the application of that branch of science as an engine for education, may in some measure meet the require- ments of the now not inconsiderable number of persons who are attracted to the study by seeing the important bearings which it has upon questions not only of theo- retical and philosophical but also of practical interest. The amount of knowledge which is presupposed in all persons who may use this book, may be judged of by the following account of the short preparatory course through which it is the rule that persons entering for the first time upon the study of Anatomy in the Oxford Museum should pass. The first requi- site for a commencing student in this department of knowledge is that he should be taught how much there is to be observed and described in a natural object, and it has been found that such a person can have this lesson impressed upon his mind in an excellent yet easy way, by addressing himself with osteological specimens actually before him to the task of verifying the state- ments made relatively to them in some work specially devoted to the description of them. The vertebral column and the bones of the cranium are the specimens PREFACH. vu selected, and recourse is taken to human rather than to other osteologies, inasmuch as the descriptions they contain are at once more intelligible to beginners, as being couched in less technical language, and more full and precise, and therefore more valuable for the purpose in question, than most of the ordinarily accessible de- scriptions of the bones of the lower animals. Whilst the student is directed not to be dissatisfied at any failure of his memory to retain, in the absence of the natural object, the multitudinous details to which a good descriptive work will have directed his attention during his examination of it, he is warned that he must not acquiesce in any failure of power to verify in such an object, when present, the structural arrangements which he is informed are to be seen in it. When this portion of the preliminary course is com- pleted, a similar study of the principal organs of animal and vegetable life, such as the brain, the heart, the digestive tract, the hepatic, and the renal organs, is entered upon; preparations of these structures pre- served so as to be accessible to manipulation, and also microscopic specimens, being available for comparison with such descriptions as the ordinary works on An- thropotomy give in their chapters on Visceral Ana- tomy. It has been found that after this comparatively small amount of previous preparation a student is competent to follow such a description as is given in this work at pp. 1-4 of a dissection of a mammal; and it is re- commended that in all cases the study of the described vill PREFACE. preparation or specimen should precede that of the accounts in the introduction of the Class and Sub- kingdom to which it belongs, and that the study of the Descriptions of the Plates should be taken up only after the attainment of a considerable familiarity with actual specimens by the practice of dissection. A short statement of the method which has been adopted in the preparation of each specimen has in most cases been prefixed to the description of it; and thus persons who have not, as well as those who have, access to the series in the University Museum, are en- abled to reproduce for themselves the objects described. The specimens themselves, it will be observed, are in the great majority of instances taken from animals which may be found living in inland parts of this country; and even when they have been taken from an exclusively marine Class or Sub-kingdom, such as the Tunicata or the Echinodermata, they are, with an exception or two, readily procurable in places at a distance from the sea-coasta, Small print has been employed in the notes and in other passages, which the student may do well to omit when first reading this book. In some cases, even the beginner will find it necessary a A dissecting microscope will be required for the verification of the Descriptions of many of the Preparations of the Invertebrata, and in these cases the specimens should be affixed to a loaded cork or wax tablet, and dissected under water or spirit. Some of these animals are speedily killed by being placed in a glass-stoppered bottle with a few drops of chloroform ; others by immersion in water several degrees below 140° F, PREFACE. 1X to consult some of the many works referred to in the Descriptions of the Preparations and in the Descriptions of the Plates; but the bibliographical references have been added with a view rather to the wants indicated in the words ‘ Fir Akademische Vorlesungen und zum Selbstudium, so often prefixed to German works on science, than to those of the commencing student. Io . Aon fw ieee ie Diagram of Cephalopod . 5 Section of Brachiopod (Rhychonata psittacea) : : Diagram of Ascidian . . Diagram of Polyzoon . Figure of Rotifer (Hydatina sonitaion . Figure of Turbellarian Worm (Dendro- coelum nausican) . gts Figure of Gregarine (St ijloripoenie olt- cee Plate XII. General account of first six figures . Fig. 1. ee sey ig or an +t & bv Semi-diagrammatic figure of Strobile of Taenia . Immature eae of Strobile of re Mature segment . Segment intermediate in age . . Proscolex of Taenia . BA . Cystic stage of Caenwrus capaci : . Figure of Coelenteratum (Hydra viridis) . Figure of Infusorium (Prorodon teres) . . Figure of Rhizopod (Amoeba radiosa) Errata and Addenda . Index PAGE 167-173 175-180 181-185 187-191 192-198 199-204 205-210 211-216 217-222 223-229 231 232-234 235, 236 237, 238 239, 240 240-243 243, 244 245, 246 246 246-248 249 249, 250 250, 251 251, 252 253-255 255-257 257-259 260 261-268 INTRODUCTION, In several different departments of research, and from many different points of view, we are brought to see that the study of Comparative Anatomy, while raising questions of the highest theoretical importance, throws light at the same time upon pro- blems of great practical interest. Of its twofold bearings, the con- troversies carried on at the present moment as to the Origin of Life and as to the Origin of Species, extending, as they do, on the one side into the provinces of Hygiene and Therapeutics, and on the other into yet higher regions than those, furnish two apposite but not isolated illustrations. It is not within the scope of this work to do more than thus glance® at such practical questions a It may be well here to give a few instances in which light has been thrown upon complex questions of Hygiene and Pathology in the course of investigations ap- parently wholly dissociated from such subjects. Dr. Charlton Bastian has, in the Philosophical Transactions for 1866, vol. 156, pt. ii., pp. 583, 584, put upon record a most instructive account of the production of a spasmodic and catarrhal affection not altogether unlike hay fever, under circumstances, however, which appear to preclude the possibility of any living organisms having been, as has recently been suggested, the cause of it. This affection was invariably produced from the emanations inhaled during the dissection of a particular Nematoid worm, the Ascaris megalocephala, from the Horse, and this not only when the animal was fresh, but ‘after it had been preserved in methylated spirit for two years, and even then macerated in a solution of chloride of lime for several hours before it was submitted to examination.’ It would seem certain that no morphological unit, nor even any cell-like or ‘ cytoid’ body, can have been at work under circumstances such as these. On the other hand, we have no less an authority than Helmholtz for the coexistence of vibrios in the nasal passages with the presence of hay fever (Virchow’s Archiv. xlvi., p. 101, Feb. 1869), and indeed for the causal relation of the former to the latter condition. Chauveau’s experiments, again (Revue des Cours Scientifiques, Jan. 1,1870, p. 77), shew that in the b XVill Introduction. as those relating to the possible modes of origination, and to the available methods for the combating of disease; neither is it advisable here to occupy space in pointing out at length or in detail the various lines along which the results of Comparative Anatomy come to bear upon the more purely speculative questions alluded to. There are, however, certain considerations of greater or less general interest, either as premises or as conclusions, which a eo absence, if not of certain animal cells, still of certain animal ‘ cytoids’ or ‘leucocytes,’ the vaccine poison is inoperative. For the application of such investigations to actual practice see Professor Lister's Introductory Lecture delivered in the University of Edinburgh, Nov. 8, 1869; British Medical Journal, Dec. 4, 1869,—The vexed question of the method in which nerves influence nutritional processes receives considerable elucidation from the facts that not only do certain Holothurioidea (Stichopus and Colo- chirus) possess the power of shedding off the non-muscular elements of their in- tegument as amorphous slimy matter upon irritation, but also that isolated fragments even of their integument, in which it would appear nerve structures are contained, possess the like power, and go through the process of self-dissolution more quickly or more slowly in correspondence with more or less stimulation. (See Semper, Reisen im Archipel der Philippinen, Theil. ii., Bd. i., pp. 72, 171, 172, 200.) The universally acknowledged but often practically ignored influence of changes in the circum- ambient medium are well illustrated by such observations as those of M. Claparéde on the growth of Annelida (see Ann. and Mag. Nat. Hist. Ser. iii., vol. xx., p. 359, 1867), and those of Professor Wyville Thomson on the varying rate of development of certain Echinoderm larvae (see Phil. Trans. vol.155, pt. ii., pp. 514, 515, 532) under varying conditions of light, heat, and aeration. Dr. Charlton Bastian has drawn attention (Linn. Soc. Trans. xxv., p. 84, 1865) to the quantity of large fat globules often seen within the intestinal canal of free Nematodes as being ‘ remark- able, and also interesting in a physiological point of view, as an exemplification of the almost direct conversion of cellulose into fat and other products.’ The facts of Com- parative Anatomy and Physiology as distinct, though not dissociated, from those of Comparative Pathology and Experiment, are appealed to by both sides in the ques- tions ‘Ueber die Fettbildung im Thierkérper,’ and that of the relations of various kinds of food to the various exigencies of the animal body. (See Donders, Nederl. Arch. yoor Genees. en Natuurkunde, Deel. i., Utrecht, 1864; translated, Dublin Quarterly Journal of Medical Science, 1866; Lawes and Gilbert, Phil. Mag., July and December, 1866; Voit. Zeitschrift fiir Biologie, Bd. v., Hft. i., pp. 147-155, 1869.) For the way in which the intimate relations of the fifth nerve to the optic may be illustrated by reference to Comparative Anatomy, see Mooren, Ueber Sympa- thische Gesichtstorungen, pp. 117-119, Berlin, 1869 ; and for numerous illustrations of the fact that the organisms of the lower animals give answers in simple language to what are difficult problems in Anthropotomy, see Schroeder Van der Kolk, on the Spinal Cord and Medulla Oblongata ; New Sydenham Society’s Translation, passim, and especially chapter vi., pp. 170-178, 1859. For other points of connection be- tween Comparative Anatomy and Practical Medicine, see ‘Medicine in Modern Times, pp- 79-91, London, 1869. General Considerations. s X1X contemplation of the subjects here treated of with reference to their bearings upon Classification, is calculated to impress upon the mind; and these it may be well to state in a few words. After some study of the details of Comparative Anatomy we begin to see that the animal kingdom is divisible into a certain number of Sub-kingdoms accordingly as the various structures or organs subserving the functions of animal and vegetable life re- spectively are combined with, separated from, or otherwise arranged relatively to, each other. It is, in the next place, easy to see that whilst in the Sub-kingdom Vertebrata, motor, nervous, vascular, visceral, and perivisceral systems all exist in specialized and differ- entiated forms, no such ‘division of labour’ is recognisable in the structural arrangements of the Sub-kingdom Protozoa ; and that, by a further and detailed reference to the principle just mentioned, we are justified in speaking of the one as the highest and the others as the lowest of the seven animal Sub-kingdoms. It is not easy, however, to assign to the three Sub-kingdoms known as Mollusca, Arthropoda, and Echinodermata their relative rank ¢néer se; and the Sub-kingdom Vermes would appear to underlie each and all of the three obliquely, rather than to be subordinated to any one of them in particular. The Coelenterata, finally, are approximated to the Protozoa by the low degree to which specialization has been carried out in their organization; but they form a more than ordinarily well-cireumscribed group, which we are in no way justified in regarding as forming a transitional stage intermediate between the Protozoa and the other Sub-kingdoms, from which latter it lies far apart. Within the limits of each Sub-kingdom the differentiation of organs, by the assignment of them to the more or less exclusive performance of particular functions, is very often carried out in the different classes to such a different extent as to allow us to speak without violence and without hesitation of such classes as being higher or lower in the scale of existence. Elevation in the scale ‘of life is indirectly entailed in Sub-kingdoms which possess air- breathing representatives, as aerial respiration renders possible a greater activity of function than an organism differing in this, though similarly constituted in all other particulars, can put forth ; whilst the special habit of parasitism, which often renders not merely single organs but even whole systems superfluous, and is 62 xx Introduction. then found to be correlated with the complete or nearly complete disappearance of such structures, must be regarded as entailing a true morphological degradation. Sharply circumscribed outlines are, in the second place, as com- monly wanting in the classifications we have to deal with as are precisely graduated scales of dignity. The boundaries of species, of orders, of classes, and, in more than one instance, even of sub-king- doms, may be closely apposed not only at many single points but even along considerable lengths and depths, so that in not a few cases it is a matter of difficulty to decide whether a particular organism or set of organisms shall be placed within the one or the other of the thus complexly approximated groups. The distances, thirdly, which intervene between the various sub- kingdoms at their points of widest separation from each other are exceedingly unequal. And in particular, it may be said that, in spite of recent discoveries”, it would still appear that the Vertebrate Sub-kingdom lies at a greater distance from the group made up by all the other Sub-kingdoms than that by which any one of these is separated from its nearest neighbour. Groups, fourthly, which would be allowed on all hands to possess the same morphological or qualitative rank are found to differ very widely as to the numbers of the objects they severally include ; and if, by the aid of diagrams, we represent to ourselves the quan- titative relations which the corresponding divisions in almost any two of the animal sub-kingdoms hold to each other as wholes of ‘extension’ or of ‘ denotation,’ we are at once struck by the great inequality of size indicated by the figures thus constituted. A similar result would ensue upon the application of a similar process to many non-biological classifications ; the especial significance which these differences possess in organic classifications depends upon two singular but suggestive facts, actual observation having shown, firstly, that the poorer a species is numerically the more aberrant is it ordinarily found to be from the type of the group to which it is subordinated; and secondly, that with a paucity of individuals or of species, as the case may be, a similar paucity of the localities on the earth’s surface in which they are now to be b For a summary of these discoveries, see the Quarterly Journal of Microscopical Science, January, 1870. General Considerations. Xx1 found living is ordinarily correlated. The Ganoids amongst Fishes, the Perennibranchiata amongst Amphibia, the Crinoids amongst Echinodermata, and the Monotremata amongst Mammals, furnish us with illustrations of these laws for the enunciation of which we are indebted to Von Baer *. A remark of the late Mr. W.S. Macleay, to the effect that xo character 1s natural until it has been proved to be so%, has the merit of at once expressing tersely the necessity of constant recourse to verification when we make deductions from general principles, and of drawing attention to the striking morphological fact of the varying value of class characters. In the face of statements as to the eligibility of particular systems °® as bases of classification, which are only less sweeping and general than they are mutually con- tradictory, it is a satisfaction to be able to quote the following words from the writings of another English naturalist, the late Professor Edward Forbes,—‘no character, whether of structure or form, preserves an equal value in every tribe, but varies in its im- portance, in one group characterizing a class, in another scarcely determining a species ;’ whilst the words of Macleay should be © See Nova Acta, xiii, 2, p.742, 1826, or Professor Huxley’s Translation in * Scientific Memoirs,’ pp. 180, 181, 1853. 4 See Linnaean Society’s Transactions, xxiii., p. 75, 1860. e For the applicability of the nervous system as a basis of classification, see Cuvier, The Animal Kingdom, English Translation, 1854, p. 31; Lacaze Duthiers, Comptes Rendus, 1865, tom. ii., p. 800; Blanchard, Ann. Sci. Nat., Ser. iii., tom. v., pp. 276, 376, 1846 ; Dana, Crustacea, pp. 46, 59 ; Waterbouse, Ann, and Mag, Nat. Hist., vol. xii., p. 399, 1843 ; Professor Owen, Linnaean Society’s Proceedings, 1857. For the applicability of the Reproductive, see Dana, l.c., p. 62; Professor Owen, cit. Darwin, Origin of Species, chap. xiii., p. 490, 4th ed. 1866; Fischer, Orthoptera, p- 62; Stein, Vergleichende Anatomie und Physiologie des Insekten ; erste Mono- graphie ; Die weiblichen Geschlechts-Organe der Kafer, 1847, passim. For the appli- eability of the Respiratory, see Dana, l.c., p. 62. For the value of the changes gone through in development, see Professor Wyville Thomson, Phil. Trans., vol. 155, pt. ii., pp. 514, 532, where attention is drawn to the power which circumstances of light, warmth, aeration and nourishment have in modifying and hurrying over certain stages of larval growth; Oskar Schmidt, Sitzungsbericht, Nat. Wiss. Class. Kais. Akad. Wien. xix., p. 193, 1856; Darwin, Animals and Plants under Domestication, vol. ii., pp. 366-368 ; Origin of Species, p. 494, ébique citata. For the value of the motor system as a basis for classification, in the sub-kingdom Echinodermata, see Brandt, Prodromus, 1835. For that of the Placental system in the class Mammalia, see Zool. Soc. Trans., vol. v., pt. 4, p. 285, 1865 ; H. Milne Edwards et Alphonse Milne Edwards, Recherches pour servir 2 l’Histoire Naturelle des Mammiféres, Livraison i., p. 18, seqq., ibique citata, 1868. Xxli Introduction. borne in mind with reference to certain other statements of even greater generality as to the applicability or imapplicability of phy- siological differences as bases of zoological arrangements. Nothing is easier than to say that by the nervous, or by the reproductive, or by the respiratory systems, or by the history of the changes gone through in development, ‘ characters of the widest bearing in classification are furnished; but nothing is more certain, as a verification of statements referred to below will demonstrate, than that what is true of one of these bases of classification within the limits of one Sub-kingdom, or within the limits of one Class, or even within the limits of yet smaller groups, will not be by any means invariably found to be true within the limits of another similar division. Our knowledge, again, of the power which organisms have of adjusting themselves to their environment, may incline us to think the motor and tegumentary systems to be bad bases for classification, as it is through them that the animal comes mainly and mostly into relation with external influences. Yet, if Seals and Whales exhibit marks of their affinities to the Carnivora and the Artiodactyla respectively, even in such matters as the cha- racter of their placentae, the number of the bronchi in their lungs, and, in spite of the modifications which their motor and tegu- mentary systems have undergone, it is nevertheless true that the specialization of the same systems in Aves and Echinodermata appears to have entailed corresponding variations throughout the entirety of their respective organisms, and in organs of vegetable as well as in organs of animal life. The facts of the varying morphological value of zoological dif- ferentiae ; of the unequal quantitative extent of divisions of equal morphological rank ; and of the unequal distances separating such divisions, go some way towards accounting for the arbitrary way in which the same division has had very different morphological rank assigned to it by different classificatory writers. A pro- visional character however must always attach itself to a greater or smaller part of all our classifications ; if they succeed in pre- f See Erichson, Entomographien, p. 1, 1840, ‘ Dies ist ein physiologischer, kein ‘ zoologischer Character,’ Semper, Reisen in Archipel der Philippinen, Theil. ii., Bd. i., p. 52; Carpenter, Foraminifera, Ray Society, p. 14, 1862 ; Herbert Spencer, Prin- ciples of Biology, vol. i., pp. 306, 307, 1864; Darwin, Origin of Species, 4th ed., P- 490. General Considerations. XX senting to our minds the knowledge we possess at the passing moment in a form which gives it compactness as to the past and availability for use in the future, that is all which in the nature of the case they should be regarded as doing, or expected to do, for us. An increase in our knowledge may confirm, but it may, on the other hand, overthrow the most perfectly symmetrical of systems &. & It is not a little instructive to note that Macleay, to whom Zoology is indebted for the ‘grand principle’ referred to above, should yet have been the inventor of the ‘quinary system,’ with its independent but numerically identical groups arranged in circular series. For the history and for illustrations of the working of this idolon theatri, see Macleay, Horae Entomologicae, vol. i., pt. ii., p. 322, 1821 ; Swainson, Geography and Classification of Animals, p. 202, et passim, 1835; Edward Forbes, Starfishes, p. xvi. 1841; Milne Edwards, Ann. Sci. Nat., Ser. iii., tom. i, p. 79, 1844; Agassiz, Essay on Classification, p. 344, 1859. Bacon’s words are singularly appropriate in relation to these arbitrary assumptions :—‘ Intellectus humanus ex pro- prietate sua facile supponit majorem ordinem et equalitatem in rebus quam invenit ; et quum multa sint in natura monodica, et plena imparitatis, tamen affingit parallela et correspondentia et relativa quae non sunt. Hine commenta illa in coelestibus omnia moveri per circulos perfectos.’ Nov. Organ. xlv. Neither are the words of the modern poet quoted by Sir John Richardson (Introduction, Fishes, Museum Natural History), in relation to a recent attempt to unite Fishes, Amphibia, and Reptiles into one division, the Haematocrya, unworthy of being quoted here :— ‘Our little systems have their day, They have their day and cease to be, They are but broken lights of Thee, And Thou, O Lord, art more than they.’ Tennyson, Jn Memoriam, vi. Striking evidence is borne to the scientific fact of the great difference which exists between the works which are and those which are not of man’s creating, by the singular circumstance that of all the many metaphors which have been used to express the general or picturesque effect produced on the mind by the study of a system of biological classification, those only retain a strong hold upon the imagination which are borrowed from natural objects; whilst those which are borrowed from works of art, or from productions of the arts, are at once felt to be inadequate even when not untrue. In illustration of this, it is sufficient to lay specimens of the two kinds of metaphor mentally alongside of each other. In the latter we have the divisions of the organic world compared to the steps in upward-sloping stairs ; or to a series of columns placed upon a flight of such stairs ; or to the meshes of a net; or to the artificial boundary-lines of neighbouring kingdoms; the more modern and truer comparisons we refer to are drawn from such objects as single stars, each surrounded with its own proper atmosphere ; as aggregations of such stars in constellations ; as trees with stems, branches, twigs and leaves; as hills clothed with woods, and sepa- rated by valleys dipping to various depths, and themselves bestudded with clumps XXIV Introduction. The above-quoted saying of Mr. Macleay’s, by suggesting the question, ‘When is a character to be considered as proved to be natural?’ brings us face to face with the most distinctive pecu- harity of zoological classification, A character is a good basis for classification in zoology, as in every other subject, when its presence enables us to predict the presence of many, or at least of some other characters besides those which its name implies etymolo- gically ; but when we are concerned with species in zoology, these other characters must relate not only to the entirety of the or- ganism as such, but also to the main facts of its life history. When we class two living organisms together in the same species, we include always among the other facts which their common specific name must connote, the particular fact that it is possible for them both to have descended from one ancestor or ancestors, which, either directly, or after certain stages in cyclical metamor- phosis, they could reproduce. For cyclical self-repetition in the way of parentage, being eminently the characteristic of living organisms, as opposed to non-living objects, no classification of such organisms would be either natural or valuable which did not lay that particular part of their history in a compact and manage- able form before the mind, whensoever evidence as to it was ob- tainable. It is true that such evidence is by no means invariably accessible ; and when it is not, we have only likeness to guide us as to saying that it is more or less probable that between any two organisms such prospective and retrospective community in parent- age might or did exist. On the other hand, where this evidence is forthcoming, the question of identity of species is instinctively and at once settled in the affirmative; even when the unlikeness between the individuals compared may be as extreme as that which exists between the well-known larvae of Batrachia and their adult forms, or between the less familiar but even more strikingly differmg larvae and adults of Cirripedia, of other Crustacea, of the Platyelminthes, and of many Hydrozoa (see infra, pp. 162, 245, 252). The theory of evolution with which Mr. Darwin’s name is connected, asks us to deal with species in their relation of trees; as systems of mountain-ranges, more or less connected by outliers; or, happiest metaphor of all—as the islands of an archipelago, sometimes all but conti- nuous through the intermediation of connecting reefs, sometimes sharply separated by unfathomable seas, General Considerations. XXV to genera and still higher divisions, as we deal with individuals in referring them to particular species, and to believe that the ‘secret bond’ which colligates species under larger groups, is of the same genealogical character as that which we look for always, and often find in the case of individuals. Many of the peculiarities which attach to biological classifications would thus receive a reasonable explanation; but where verification is, ea hypo- thesi, impossible, such a theory cannot be held to be advanced out of the region of probability. The acceptance or rejection of the general theory will depend, as does the acceptance or rejection of other views supported merely by probable evidence, upon the par- ticular constitution of each individual mind to which it is presented. But whether the general theory be accepted as a whole or not, it must be allowed that in the face, on the one hand, of our know- ledge of the greatness of the unlikeness, which may be compatible with specific identity ; and, on the other, of our ignorance of the entirety of the geological record, the value of the special ‘ Phylo- genies,’ or hypothetical genealogical pedigrees, reaching far out of modern periods, are likely to remain in the very highest degree arbitrary and problematical. ; XXvl1 Introduction. Tabular View of the System of Classification adopted in this work, shewing the various Sub-kingdoms in some of the relations of mutual affinity and of rank which they have been supposed to hold to each other. In the cases of several names an oblique position would have been truer to nature than the horizontal one which they occupy in the Table. The lines abut upon the names of the Classes or Orders by which the several Sub-kingdoms have been regarded as connected with each other. (Arrangement of Sub-kingdoms after Gegenbaur.) VERTEBRATA (Pharyngobranchii) ARTHROPODA (Crustacea) 4 ECHINODERMATA (Crinoidea) (Holothurioidea) J MOLLUSCA (Polyzoa) (Tunicata) VERMES (Annulata. Tubicolae) (Gephyrea) (Platyelminthes) (Rotifera) COELENTERATA PROTOZOA (Spongiadae) (Infusoria) Introduction. XXVll Tabular View of the System of Classification adopted in this work, giving the various Classes into which the seven Sub- kingdoms are divided. The relative positions of the names of the Classes indicate the relations of affinity and of rank which each Class has been supposed to hold to the other Classes in its own Sub-kingdom. Mammalia Aves Reptilia VERTEBRATA Amphibia Pisces Arachnida Myriopoda Insecta ARTHROPODA Crustacea Holothuriocidea Echinoidea ECHINODERMATA Crinoidea Asteroidea Cephalopoda p; eropoda Gasteropoda MOLLUSCA Lamellibranchiata ; Tunicata Brachiopoda Polyzoa Annulata Gephyrea vine Rotifera Nematelminthes Platyelminthes Ctenophorae COELENTERATA 4 uthozoa Hydrozoa Spongiadae Infusoria PROTOZOA Rhizopoda Gregarinae XXXVI Introduction. Tabular View of the System of Classification adopted in this work, giving the pages at which the characteristics of the various Sub-kingdoms and of the Provinces and Classes subordinated to them ; those at which the Descriptions of the Specimens; and those at which the Descriptions of the Figures in illustration, are to be found. I. SUB-KINGDOM. VERTEBRATA, pp. xxxi-lxxxy. { Mammalia =Class 1. Mammalia pp. xlii-xlix. pp. xlii-xlix. pp. 1-12 Pl. i. pp. 167-173 pp. xlix-ly. pp. 12-29 Allantoidea, p. xl. Subdivisions (a 2. Aves Pl. ii. pp. 175-180 Sauropsida p- xi. DIVISIONS Class 3. Reptilia pp. lv-lxi. pp. 29-35 Class 4. Amphibia pp. lxi-Ixviii. pp. 35-40 Anallantoidea, p. xli-xlii = Pl. iii, pp. 181-185 Salliviaesn. Ichthyopsida pp- xli-xlii. | ——, ee Class 5. Pisces pp- Ixviii-lxxxv. pp. 40-46 II. SUB-KINGDOM. MOLLUSCA, pp. Ixxxy-ciii. if (Class 1. Cephalopoda pp. Ixxxviii-xcii. 1G S06 arly at Odontophora 3 Class 2. Pteropoda Mollusca Proper, pp. lxxxyv-Ixxxvii. p. Ixxxvil. Pp. xeiii—xev. Subdivisions 4 Class 3. Gasteropoda pp. Xcii-xciii. pp. 47-54 L Pl. iv. pp. 187-191 Anodontophora {om 4. Lamellibranchiata pp. X¢v-xeviii. pp. 54-66 onl ee eG Pl. v. pp. 192-198 (Class 5. Brachiopoda pp. xeviii-c. Pl. xi. fig. 2, pp. 232-234 Class 6. Tunicata Molluscoidea, pp. Ixxxvii-Ixxxviii. .. oc OC pp. c-ci. pp. 66-71 Pl. xi. fig. 3, pp. 235, 236 Class 7. Polyzoa pp. ci-ciii. pp. 71-73 L Pl. xi. fig. 4, pp. 237, 238 c— Introduction. XX1x (Tabular View with Pages.) III. SUB-KINGDOM. ARTHROPODA, pp. civ-cxxii. ' Class 1. Insecta pp. evili-cxiii. pp. 73-90 Pl. vi. pp. 199-204 Class 2. Myriopoda Tracheata, pp. ¢v—cvi. : pp. exiv—cxvi. Divis:ons Class 3. Arachnida pp. exvi-ecxviii. pp- exviii-cxxii. pp. 90-119 Pl. vil. pp. 205-210 Class 4. Crustacea Branchiata IV. SUB-KINGDOM. VERMES, pp. exxii-csliii. pp. exxvii-cxxxi. pp. 119-136 if f Class 1. Annulata Proper | Pl. viii. ix. pp. 211-222 Annulata, pp. exxi-cxxiil. .. Class 2. Gephyrea pp. cxxxi-cxxxill. pp.155-157 (Class 3. Nematelminthes Divistons 4 pp. CXxxili-cxxxvil. p. 155 Class 4, Rotifera pp. exxxvili-exl. p. 154 Annuloida, p. exxiii. ac se a: Soe Pl. xi. fig. 5, pp. 239, 240 Class 5. Platyelminthes pp- exl-exliii. pp. 138, 139 Pl. xi. fig. 6. pp. 240-243 i Y Pl. xii. figs. 1-6, 245-252 Class 1. Holothurioidea pp. exlvii-cl. pp. 145-158 Class 2. Echinoidea pp. cl-cliii. V. SUB-KINGDOM. ECHINODERMATA, pp. exliii-clvi. | Class 3. Asteroidea pp. cliii-cliv. pp. 141-145 Pl. x. pp. 223-229 Class 4. Crinoidea pp. cliv-clvi. p, 165 XXX Introduction. (Tabular View with Pages.) Class 1. Ctenophorae pp. elvii-clviil. Class 2. Anthozoa VI. SUB-KINGDOM. COELENTERATA, pp. clvi-clx. pp. clviii-clix. pp. 158-160 Class 3. Hydrozoa pp. clix-clx. pp. 160-163 L —s~Pil. xxii. fig. 7, pp. 253-255 (Class 1. Infusoria pp. clxiv—clxv. Pl. xii. fig.8, pp. 255-257 Class 2. Rhizopoda pp. elxv—clxvi. VII. SUB-KINGDOM. PROTOZOA, p. clx. Pl. xii. fig. 9, pp. 257, 258 Class 3. Spongiadae pp- clxvi-clxvii. pp. 163-166 Class 4. Gregarine pp. clxvii-clxviii. pp. 243, 244. CHARACTERISTICS OF THE SUB-KINGDOM VERTEBRATA. Sus-Kinapom, Vertebrata?. Animas with bilaterally symmetrical bodies, divided internally into two perfectly distinct cavities, one of which is placed dorsally and contains the principal nerve-centres, whilst the other contains the organs of vegetative life. The ventrally-placed cavity of the Vertebrata must be considered to correspond to the entire in- terior of the body of the Invertebrata, and their dorsally-placed cavity, the cerebro-spinal canal, to be without any homologue in the inferior Sub-kingdoms. The motor organs of Vertebrata are directed towards their heart, and point away from their nervous systems, both cerebro-spinal and sympathetic; whilst in Inverte- brata the motor organs are developed upon the neural aspect of their bodies. Thus the arrangement by which the heart of the Invertebrate animal is dorsal and the nerve-system ventral in posi- ® Tn the account here given of the characteristics of each Sub-kingdom and Class, a few general remarks are prefixed to a more detailed zootomical account of each Division. In that account the various organs and systems are treated of very nearly in the same order as that of the ‘ Physiological Series of Comparative Anatomy con- tained in the Museum of the Royal College of Surgeons in London,’ which was fol- lowed by Professor Acland in the arrangement of a large part of the Christ Church Collection now contained in the University Museum. The integumentary and motor organs are first treated of ; then the digestive, circulatory, respiratory and renal; a sketch of the nervous system is then interposed before the account of the reproductive organs. Objection may be taken to this method of arrangement on the ground of the separation it effects between the motor and the other organs of animal life ; but this theoretical drawback is more than compensated for by many practical advantages. A short notice of any peculiarities in the history of Development, which it may have seemed expedient to add, comes next in order; and in some cases an account of its subordinate divisions is prefixed or appended to the description of a larger group. XXXII Introduction. tion, is exactly reversed in the Vertebrate; and the former may consequently be spoken as ‘ neuropodous,’ and the latter as ‘ haema- podous.’ In both cases the digestive tube interposes itself for greater or smaller distances between the haemal and neural systems, but the perforation of the nerve-system, by the anterior segments of the digestive tube, which constitutes the nerve-collar of Inverte- brata, finds no representation in the relations subsisting between the principal or cerebro-spinal nerve-centres of Vertebrata and their digestive tube, the anterior or oral opening of which is always directed towards the ventral, and away from the neural surface of their bodies. The perivisceral cavity of Vertebrata never com- municates with the blood-vascular, though it has recently been shown to communicate with the lymphatic system; nor is it ever prolonged into their limbs, which possess always an internal and segmented skeleton either of cartilage or of bone. The limbs of Vertebrata differ further from the limbs of Arthropoda in never ex- ceeding the number of two pairs. Externally, the Vertebrata show no appearance of seementation, and the segmentation which they do exhibit internally does not affect the organs of vegetative life, but is exemplified only in their skeleton, nerves, and muscles. The axial portion of the internal skeleton, which separates the body of the Vertebrate animal into a neural and haemal cavity, is not always divided by segmentation into the structures whence the Sub-kingdom takes its name. In the Amphioxus, the endo-skeleton is represented simply by the rod-like aggregation of cells known as the chorda dorsalis ; by the sheath surrounding this structure ; and by fibrous arches, which are developed above and below in con- nection with these axial structures, and give attachment laterally to the inter-muscular septa; but it shows no other signs of segmen- tation except by the possession of series of mesially-arranged carti- laginous nodules, which correspond in position to the inter-spinous bones and fin-rays of more highly organized fish. In all other Vertebrata, the endo-skeleton becomes definitely segmented poste- riorly to the head, either by the development of cartilaginous neural arches alone, as in Petromyzon, or by the development of axial, in addition to neural indurations. By the more or less perfect fusion, and, ordinarily, by the calcification of these elements, the structures known as ‘ vertebrae’ are formed. In all Vertebrata, with the exception of Amphioxus, which is Characteristics of the Vertebrata. XXXI11 hence called ‘ Acranial,’ the neural canal widens considerably in the anterior region of the body, in correspondence with the increased size of the neural axis it encloses, and with the organs of special sense to which its walls give support. The superior and the central elements of this portion of the axial skeleton make up the skull, and are differentiated from those of the vertebral series, not only by the greater size of the canal they form, but also by the fact that they undergo no segmentation until the stage of ossification is attained to. In the anterior portion, on the other hand, of the lower of the two cavities of the body, segmentation of a character- istic kind is established at an early period of the development of all Vertebrata, by the formation of the vertical ‘branchial fissures,’ which, in the absence of any anterior prolongations of the peri- visceral cavity, lead directly from the exterior into the digestive tract. The first, and in part the second of these fissures are repre- sented permanently by the Eustachian tube, and the tympanic cavity in all air-breathing Vertebrata possessed of these structures ; the other fissures which are retained in relation with the gill-bearing arches of Fish and Perennibranchiate Amphibia, are, in the higher representatives of the Sub-kingdom, obliterated in the course of their development. The integumentary system of Vertebrata may develope either a dermal or an epidermal skeleton, or both; and muscular fibres are ordinarily interwoven in considerable abundance with its substance. But these structures are never, as in Invertebrata, of primary loco- motor importance, the more deeply-placed skeletal and muscular systems being little less characteristic physiologically than morpho- logically of this sub-kingdom. The jaws of Vertebrata are always modifications of the cephalic parietes, and never, as in Invertebrata, modifications of limbs. No vertebrate animal is aproctous; the digestive tract has the shape of a distinct and independent tube, except in the region of the cephalic parietes, to which, as also to the branchial arches when present, its walls are adherent. In the abdominal region, the digestive tube is suspended by membranous lamellae, which are never fenestrated except as a consequence of absorption in adult fish, but which do occasionally resemble the membranes with similar functions in Invertebrata by possessing muscular fibres. The digestive tract rarely takes a direct antero- posterior course. Its absorbing and secreting surface is often c XXX1V Introduction. increased by the addition to it of coecal diverticula, which may be very numerous, and arranged in whorls in Fishes, but are never so numerous, nor so arranged in higher Vertebrata. Oral salivary glands are often wanting in aquatic Vertebrata, the pancreatic are less frequently, and the hepatic is never absent. Microscopie ab- sorptive, as well as secreting glands, exist in great abundance in the walls of the digestive tube. With the exception of Amphiorus, all Vertebrata possess a lymphatic as well as a blood-vascular system; and the ultimate ramifications of the former of these systems have been recently shown to be continuous with the perivisceral or pleuro-peritoneal cavities. The blood-vascular system, on the other hand, never communicates either with the perivisceral or with the inter- muscular spaces, and the efferent arteries are all but invariably connected with the efferent veins by means of capillaries, with walls distinct from the tissues they pass through. With the exception of Amphioxus, in which animal we find all the main vascular trunks endowed with contractility, all Vertebrata possess a heart of saccular shape, consisting even when most simple of two chambers, one of which receives the blood returned by the veins from the system at large, whilst the other propels that blood into the aerating organs. Thus the heart of the Vertebrata is a respi- ratory, whilst that of the Invertebrate animal is a systemic heart. The formation of retia mirabilia, by the breaking up of arteries into plexuses, in the interstices of which no great amount of interstitial matter is deposited, appears to be a peculiarly verte- brate arrangement ; as is also the so-called ‘ portal system,’ which appears to be formed by the development of retia mirabiha, in the course of the veins returning from the chylopoietic viscera, and the intercalation of the elements of the hepatic glands in the interstices of the plexuses thus formed. The blood of all Vertebrata, except Amphiorus, is red; the colouring matter being contained in corpuscles, which appear to be developed from the white corpuscles which are always found in company with them. The spleen and thymus glands are connected like the lymphatic glands, and many other but smaller bodies of somewhat similar histological character, found in the substance both of mucous and serous membranes, with the process of haemato- poiesis ; and appear to be structures peculiar to Vertebrata. Characteristics of the Vertebrata. XXXV Whether the respiration of Vertebrata be aquatic or aerial, the apparatus by which it is effected is always connected with the commencement, and never, as in some Invertebrata, with the outlet of the digestive tract. The efferent ducts, on the other hand, of the renal organs, are usually confluent and always in near relation with the anal, and also with the generative outlets. In Plagiostomous Fishes, and in all Vertebrata above the Amphibia, a primordial as well as a secondary kidney is developed; and in all cases, ex- cept those of the Cyclostomi and Amphioxus, the renal are closely connected either in their development, or throughout life, with the generative glands. When a primordial kidney, the so-called ‘Wolffian body,’ is replaced by a secondary and persistent kidney, the provisional gland and its efferent ducts are in the male sex partly converted into spermatic ducts, the so-called epididymis and vasa deferentia, and partly remain as the rudimentary ‘ cyst of Morgagni,’ and ‘organ of Giraldés’ of the class Mammalia; whilst in the female sex the primordial kidney and a certain part of its efferent apparatus become atrophied, and are known in Mammals as the ‘organ of Rosenmiiller’ or ‘ parovarium,’ and the ‘ canals of Gaertner’ respectively ; and the remaining part of the efferent apparatus, the so-called ‘duct of Miiller,’ becomes the functional oviduct. In the males of Amphibia, where no secondary kidney is developed, the efferent testicular ducts pass through the anterior part of the substance of their functional kidney, which in higher animals becomes limited to the functions of an epididymis; and these ducts are, on the distal side of the urinary gland, known as ‘vasa uro-spermatica” The posterior part of their functional kidney is exclusively urinary in function, and its ducts may coalesce more or less completely before joining the (Miillerian) duct, into which the uro-spermatie vessels from the anterior part of the gland open; foreshadowing thus the more perfect dif- ferentiation of these structures which we meet with in the air- breathing Vertebrata. According to some authorities, however, the duct of Miller, the parovarium, and the epididymis are deve- loped independently of the Wolffian bodies and their ducts. This appears to be certainly the case in Mammals In the Amphioxus, the brain can scarcely be said to exist at all, being represented merely by the nervous tissue surrounding the open ventricle, which is formed by a slight expansion of ¢ 2 XXXVl1 Introduction. the central canal of their spinal cord, and has an aggregation of pigment granules, the rudimentary eye, placed anteriorly to it. The cerebro-spinal system of other Vertebrata resembles this axial nervous cord of the Amphioxus, in being developed from the uppermost part of the three layers into which the germinal mem- brane divides itself in the embryo, but differs from it in the great size and complete differentiation which its anterior segments attain to in the brain and organs of special sense. The brain consists of three primary vesicles, the anterior one of which is subsequently differentiated into a ‘prosencephalon’ and ‘ dien- cephalon, the latter division corresponding to the parts sur- rounding the ‘third ventricle’ of anthropotomy ; the middle one of which, or ‘mesencephalon,’ remains undivided; whilst the posterior, like the anterior, is ultimately distinguishable into two portions, an anterior corresponding to the cerebellum, and a pos- terior corresponding to the parts bounding the posterior parts of the ‘fourth ventricle’ of anthropotomy, or to the single ventricle of the Amphioxus already mentioned. As in the higher Mollusca, the organs of smell, taste, sight, and hearing are always limited to the head; and with the exceptions of the Amphiorus and Cyclostomi, in which there is but a single nasal opening, and of the asymmetrical Pleuronectidae, these organs always consist of single bilaterally symmetrical pairs. The essential elements of the peripherally-placed portions of the organs of special sense, are mainly, though not exclusively, developed from the epidermic portion of the same uppermost layer of the trifid germinal mem- brane, whence the cerebro-spinal nerve-centres are themselves developed. The so-called olfactory and optic ‘ nerves’ are direct outgrowths of the anterior cerebral vesicle; but in all other cases the central and peripheral factors of the sensory organs are brought into connection through the intermediation of nerves, strictly so called, and developed in the middle one of the three layers of the germinal membrane. In the peripheral apparatus also, certain enveloping and protecting structures, such as the sclerotic coat of the eye, and the skeletal elements in the auditory and olfactory organs are also productions of this intermediate layer; and in the eye the cornea, and in part the lens, are also formed from it. The peripheral apparatus retains its typical character as an involu- tion of the integument in the olfactory, but loses it in the optic Characteristics of the Vertebrata. XXXVI and, with the exception of the Hlasmobranchii, in the auditory organs. Tactile sensibility is possessed in a greater or less degree by the entire cutaneous system. Special tactile organs are developed in many Vertebrata around the region of the mouth, and in some upon the extremities; and we find in Fishes and in the larvae of Amphibia, an additional set of tactile organs in the structures which constitute the system of the lateral line, and are distributed over the walls of the head as well as along the sides of the trunk. Taste may be localized either in the tongue, or in the throat, or in both; or is probably absent altogether, where the epithelium covering this region becomes indurated or spinous. The nerves, as opposed to the nerve-centres of Vertebrata, are developed in the middle, and not in the uppermost layer of the embryo; they are divisible into dorsal, latero-motor, and splanchnic sets, accordingly as they are distributed to the structures formed by the dorsal laminae, by the ventral laminae, and by the visceral factor into which that middle layer divides itself. The sympathetic nervous system is not contained within the cranio-spinal canal, and its branches are mainly, though not exclusively, distributed to the viscera of organic life. It consists, firstly, of bilaterally symme- trical chains of ganglia arranged on either side of the thoracico- abdominal, of the cervical, and occasionally, as in osseous Fishes, also of the caudal vertebrae: and, secondly, of certain great prae- vertebral plexuses, partly lodged in the substance, but for the most part placed upon the exterior of the viscera they supply. With the first of these divisions are to be ranked four pairs of gangha developed in connection with branches of the fifth cranial nerve, and in relation with the cephalic parietes. The entire sympathetic system is developed out of the middle layer of the embryo, and the ereater part, if indeed not the whole of its first division, is a dependency of the similarly developed cerebro-spinal nerves with which it is connected functionally and anatomically in adult life, and which must be taken into account when the nervous systems of Vertebrata and Invertebrata are compared with each other. Certain ganglia developed upon the posterior roots of these spinal nerves in the intervertebral foramina, and upon the roots of certain cranial nerves, in or close to certain cranial canals, resemble the sympathetic ganglia in structure ; but from their very obvious and XXXVIil Introduction. permanent condition of dependency upon the cerebro-spinal nerves, and also from their position, they are often ranked with these latter nerves rather than with the sympathetic system. Though the generative glands of all Vertebrata appear to be hermaphrodite at certain periods of foetal life, they are, with the exceptions of a few Fishes and Amphibians, differentiated as either male or female organs, before the attainment of adult life. In many Fishes, in Amphibia, and in all higher Vertebrata, the ova are impregnated by sexual congress; parthenogenesis and meta- genesis are entirely unknown in this Sub-kingdom, and metamor- phosis has only been observed amongst Amphibia and in a few lower Fishes. In all Vertebrata, except certain osseous Fishes, the ova are set free by dehiscence into the perivisceral cavity, whence they are ordinarily taken up by the infundibuliform orifices of bilateral oviducts, or as in a few Fishes left to find their way into the circumambient water, through an azygos orifice in the abdo- minal walls known as the ‘porus genitalis.”. On the other hand, vasa deferentia, directly continuous with the capsular envelope of the testes, are found in all Vertebrata except the Amphiorus, the Cyclostomi, the Ganoidei, and the Eel. The yolk of the impregnated ovum sometimes undergoes entire, sometimes only partial segmentation. The germinal membrane very early divides itself into three layers, from the uppermost of which the cerebro-spinal nervous centres and the cuticular systems are evolved ; from the lowermost the epithelial structures of the di- gestive tube, and its glands with the exception of the parotid ; and from the intermediate layer all the other structures of the body, the cutis vera, the nerves, muscles, bones, and the various vegetative organs with the exceptions given. The first indication of the forma- tion of the embryo is seen in the appearance of the ‘primitive groove ;’ by the upgrowth of the walls of which, the cranio-spinal canal and the cerebro-spinal nervous axis are both formed as demi-canals at first, and as closed tubes ultimately, by the intermediate, and by the upper layers of the germinal membrane severally. The chorda dorsalis is developed along the infero-median line of these structures ; and at a point corresponding to the level thus marked out, lamellar prolongations are sent off downwards, which form the walls of the inferior cavity of the vertebrate body, and are known as the /aminae ventrales. The intestine in all Vertebrata except Amphioxus (and Characteristics of the Vertebrata. XXX1X Cyclostomi and Amphibia ?) is formed by the junction to the third layer, which has the shape of a groove open towards the. yolk cavity, of an outer fibrous covering, due to the splitting into two portions of the ventral part of the middle layer; and by the sub- sequent conversion of the demi-canal, thus formed, into a tube at its two ends. The space contained between the two layers into which the downward prolongation of the middle layer divides itself, corresponds with the future pleuro-peritoneal cavity of the adult Vertebrate; and the orifice and canal of communication betwen the yolk cavity and the tube which the demi-canal is thus converted into, correspond with the more or less transitory om- phalo-mesenteric duct, which connects the vertebrate intestine with the umbilicus. In no Invertebrate animals are the walls of the perivisceral cavity thus constituted ; and in none does the intestine ever possess any umbilicus. In the Amphiorus, however, (as also in Cyclostomi and Amphibia?) the intestinal tract is said to be formed, as it is in many Invertebrata, by a process of invagination commencing at the future anus; and the larvae of certain Asci- dians have been stated to have their nerve-centre developed similarly to the tubular cerebro-spinal centres of Vertebrata, and to possess within the locomotor caudal appendage, with which they are fur- nished in their larval condition, a structure closely similar to the chorda dorsalis of Vertebrata. In all Vertebrata, with the exceptions just mentioned, a larger or smaller ‘ umbilical vesicle’ is formed by the separation of a distal or extra-abdominal portion of the yolk-sac from an intra-abdominal moiety, at the point where the ventral laminae close upon it in the medio-ventral line, and form the ‘umbilicus.’ The ‘ umbilical ve- sicle’ is usually cast off when the embryo is set free from the egg ; the part of the yolk sae which is intercepted within the abdominal cavity, frequently persists for a considerable period after birth as the ‘ omphalo-mesenteric duct.’ Divisions, Allantoidea and Anallantoidea. Vertebrata are divided into Amniota and Anamniota, accordingly as the dermal and cuticular elements of the ventral laminae are in xl : Introduction. development reflected upwards from the medio-ventral line, so as to meet, along the medio-dorsal line, and form thus the foetal envelope known as the Amnion ; or as no such envelope is superadded to the more or less complex ones, furnished by the maternal organism. In the Vertebrata Amniota, a second foetal envelope, the Allantois, is always developed, originating from the anterior aspect of the poste- rior extremity of the trunk as a body, which is at first bilobed and solid, but which subsequently becomes hollow internally, and covered externally with vascular ramifications, whereby in Reptiles and Birds the respiration, and in Mammals both the respiration and the nutrition of the developing embryo are provided for. From their possession of this structure, the Amniota are also known as ‘Allantoidea ;’ and as gills are never developed upon their branchial arches, they are also called ‘ Abranchiata,’ whilst the Anamniota have in their turn the two additional names ‘ Anallantoidea’ and ‘ Branchiata,’ as never developing an Allantois, at least beyond the stage of a uriary bladder, into which its proximal portion is converted in the higher Vertebrata, and as always developing either deciduous or permanent gills. Drviston, Allantoidea. The Allantoidea comprise the three Classes, Mammalia, Aves, and Reptilia, and possess the following characteristics distinguishing them from the Anallantoidea, in addition to those which their several names given above connote. The axis of their basi-cranial bones always forms a considerable angle with the axis of their vertebral column; the parasphenoid, which is large in the Anallantoidea, is in them rudimentary, whilst the basi-occipital and basi-sphenoid are always well ossified; and the former is never anchylosed with any of the anterior vertebrae, of which more or fewer are always dis- tinguishable as cervical, from a thoracic or thoracico-abdominal series. Inferiorly-placed ‘sternal’ bones ordinarily complete the costal arches. They never have a permanent muscular bulbus arteriosus ; but they always have a trachea, and a secondary kidney. They never have more than five branchial arches ; and it is only in Characteristics of the Vertebrata. xli the three most anteriorly placed of these that cartilaginous supports have been observed to be developed. SuB-DIvIsion, Sauropsida. The two Classes Aves and Reptilia are united into a single province, that of the ‘ Sauropsida,’ by the possession of the following characteristics which distinguish them both from the other sub- division of Allantoidea, the class Mammalia. Their integumentary system always developes either feathers or scales; their skull is articulated by a single occipital condyle to the cervical vertebrae ; they have their ankle-joint interposed between the proximal and distal bones of the tarsus, and not between the distal extremity of the lower leg and the proximal tarsal bones; they have also a single auditory ossicle, the stapes; the malleus of Mammals being represented by their os quadratum, and the incus by their supra- stapedial process. Their blood corpuscles are oval and nucleated. They never have the single aorta turning over the left bronchus, nor a perfect diaphragm, nor a corpus callosum, nor mammae, all of which structural arrangements are found in all Mammals. Drviston, Anallantoidea. The Anallantoidea comprise the two Classes, Amphibia and Pisces, and the province thus constituted is known as that of the ‘Ichthy- opsida,’ as well as by the names of ‘ Branchiata’ and ‘ Anamniota,’ given above. They differ from the Abranchiate province in the following particulars in addition to those which their various names imply. Their integument never developes any epidermic skeleton, except in a few Amphibia (see p. 35, 7/ra), and in some Fishes the bony structures of the cutis may cause the total or almost total disappearance of the cuticle. The axis of the head and vertebral column form one continuous line ; the basicranial bones are, except in some fishes which have not an osseous skeleton, underlaid by a large parasphenoid. The basi-occipital may be rudimentary or xl Introduction. cartilaginous, and may be connected by suture, and not by movable articulation, with the first vertebra of the trunk. The apex of the scapular arch, so far as it is constituted by true endo-skeletal elements, corresponds at its first appearance to the interspace be- tween the second and third vertebrae, marking off thus two cervical vertebrae; but a cervical region is not by any means invariably recognisable in the adult condition of these animals ; when there are two occipital condyles, they are constituted by the ex-occipitals alone. They never possess a series of costal arches completed in- feriorly by sternal bones; and it is only rarely that (in Amphibia) there is any sternum present at all. They always possess two aortic arches at least, and nearly invariably an aortic bulb. They are in many cases competent to the maturation of sexual products, before they attain their full size; and in the case of the Amphibian Axolotl, before the gills characteristic of the larval or tadpole-stage are discarded. No Vertebrata are social, nor are any fixed to one spot. The power of repairing injuries and mutilations is, with possibly a few exceptions, confined to the cold-blooded Amphibia and Reptilia. As in the two higher Sub-kingdoms of the Invertebrata, the Mollusca and the Arthropoda, there are both air-breathing and water-breathing representatives of this Sub-kingdom. As in the Sub-kingdom Mollusca, so in that of Vertebrata, there are very few animals of parasitic habit. All parasitic Vertebrata belong to the class Pisces, and amongst these we may mention the Myxinoids, which are not only ecto-parasitic, but penetrate even into the abdominal cavity of other Fishes, such as the Sturgeon. A Siluroid fish has been found to inhabit the branchial cavity of another fish (P/atystomus) of the same family ; and the invertebrate Asterias discoidea is infested by Oxyheles lumbricoides, and certain Holothurians by a Fierasfer. These latter cases, however, are considered by Van Beneden to be instances of ‘commensalism’ rather than of parasitism strictly so called. See Bulletins de VAcadémie Royale de Belgique, 2™° série, tom. xxvill., no. 12, pp- 624-626, 642, 643, ibique citata. Cuass, Mammalia. Air-breathing, warm-blooded Vertebrata, in which the epidermis developes hairs over a greater or lesser extent of the surface of the Characteristics of the Vertebrata. xi body, either persistently or during foetal life only, as in most of the true Cetacea ; which are always viviparous, and always nourish their young for longer or shorter periods after birth with the secretion of lacteal glands. The anterior pair of limbs is never wanting ; a perfect diaphragm always exists between the thoracic and abdominal cavities ; the aorta is single, and bends over the left bronchus; the red-blood corpuscles are ‘apyrenaematous,’ or ‘ non- nucleated.’ In all Mammalia, with the exception of the Cetacea and Strenia, the abdominal vertebrae are separated into a lumbar and a sacral division, by the abutment of the iliac bones upon the vertebrae immediately anterior to the caudal series. In the Marsupial Perameles, however, there may be but one ‘sacral’ vertebra, whilst in the Edentata, where the ischium as well as the ilium abuts upon the vertebral column, there may be as many as nine. The cervical vertebrae are, with a few exceptions, neither more nor less than seven in number. Of these, the two first arti- culate with each other and with the two occipital condyles by synovial joints, whilst all the other vertebrae have their centra articulated together by fibro-cartilaginous discs, in the axis of which remnants of the chorda dorsalis are to be found. The number of dorsal vertebrae is very frequently thirteen, but it may vary from ten to twenty-four; that of the lumbar is very fre- quently six or seven, but may vary from two to nine; that of the sacral, as already said, varies from one to nine; whilst that of the caudal varies from four, as in certain Simiadae, up to forty-six, as in Manis Macrura. As in Sauropsida, the centres of the vertebrae are always well ossified, but they differ from those of the cold- blooded representatives of that division of the Vertebrate Sub- kingdom, in being always anchylosed with the neural arch in adult life; and from those of both Birds and Reptiles in being during the period of growth provided with epiphyses. There are always two occipital condyles, each of which is constituted by factors from both basi- and ex-occipital. The lower jaw articulates directly with the squamosal element of the cranial walls, the homologue of the os quadratum of Sauropsida having been withdrawn into the cavity of the middle ear, where it is known as the malleus. The lower jaw itself consists always in adult life of a single bone on each side, which in some Mammals does, and in others does not, anchylose with its fellow of the opposite side at the mental xliv Introduction. symphysis. It does not however appear to be always developed, as usually stated, from a single centre of ossification in the membrane covering the distal portion of the cartilage (Meckel’s) of the first branchial arch. In the human subject it has been observed to be developed from as many as four centres of ossification, of which one probably corresponds to the dentary bone of the Crocodile, and the other to the splenial. In the terminal segment of the limbs, the digits never consist of more than three phalanges each, except in the true Cetacea, which order also forms an exception to the rule that the terminal digital phalanges are always in Mammals pro- tected by a nail, a claw, or a hoof. In addition to, and together with the hairs so characteristic of this class, and found even in some adult Cetacea upon the lips, we find the integument developing structures as various as the vibrissae on the snout of Carnivora ; the scales on the body and limbs of the Pangolins, and on the tail of certain Rodents, and of Pttlocercus amongst Jusectivora ; the spines on many members of the two last-mentioned orders; the horns as opposed to the horn-cores of the hollow-horned Ruminants; and the horns of the Rhino- ceros. The scutes of the Armadillo are exclusively dermal pro- ductions. Glands of various kinds are found on very various parts of the body. Some of them are known as sebaceous, sudoriparous, lacteal and lacrymal, according to the character of their secretion ; whilst others, which are usually moditications of the sebaceous type, are, according to the locality in which they are situated, known as anal, inguinal, interungular, and preputial. In all Mammalia, with the exception of the Hare, Lepus timidus, a layer of adipose tissue, the panniculus adiposus, sometimes of great thick- ness, is interposed between the cutis vera and the subjacent muscles or bones. The teeth, which are developments of the mucous mem- brane continuous with the external integument, are normally limited to the lower jaw below, and to the pre-maxillary and maxillary bones above. ‘They may be absent altogether or replaced by horny plates, as in the Ornithorhynchus. Only a certain number of the teeth, the so-called ‘milk teeth, are ever replaced in Mammalia after being shed ; and in many Mammals no such replacement has ever been observed. In the Marsupials, none of which are ever edentulous, there is only a single ‘dent de remplacement ;’ the one, namely, which corresponds to the second human premolar. In 4 Characteristics of the Vertebrata. xlv some Mammals, such as the true Cetacea, which have only a single set of teeth, the pulp atrophies or undergoes calcification ; and a term is thus necessarily put to the duration of the teeth, and of the life of the animal. In others, which are similarly ‘ Monophydont,’ as the Sloths (Lradypoda), amongst the Lruta, the pulp is persistent ; as it 1s also in the ‘ Diphyodont’ Armadillos belonging to the same order, and in the incisors of all, in the molars of some Rodents, and in the permanent incisors, or ‘ tusks’ of the Elephant. It is only in the Mammalian class that teeth have been observed to be implanted by more than a single fang, and the dentinal tissue is ordinarily free from anchylosis with the alveolus in which the tooth is lodged. The digestive tract is always rich in interstitially-placed glands, and of the larger glands appended to it by ducts, none are ever wanting’ except the oral salivary glands in the true Cefacea, and one pair of these glands, the parotid, in the Monotrematous Echidna. There is much variety from order to order, as to the simplicity and complexity of the stomach, and as to the presence or absence of intestinal coeca. It is only in the Ornithodelphia, thence called ‘ Monotremata,’ that the generative and renal ducts are confluent for any great distance with the terminal segment of the intestine, so as to form a true ‘cloaca;’? though in Marsupialia, as also in certain Lodentia, in Centetes amongst the Insectivora, and in certain Bruta, a common sphincter muscle may surround the distal orifices both of urogenital and of the rectal tubes. The red-blood corpuscles of Mammalia differ from those of all other Vertebrata not only in being ‘apyrenaematous,’ but also in being, with the exception of those of the Camelidae, circular. Their heart is always quadrilocular ; their aorta always single, and bent over the left bronchus. The valves, which in other Vertebrata guard the entrance of the great veins into the right auricle, are either absent as usual, or rudimentary as in Bradypus, Hlephas, Simiadae. Correlated with this structural arrangement is the fact that in Mammals the ventricles are the first, the auricles the second in point of time to contract in each systole. In many Rodentia and Insectivora, and in all Marsupialia and Montremata, there are two superior venae cavae. The lymphatic and lacteal glands are always largely developed, as are also the tonsillar and Peyerian aggregations of adenoid substance in the walls of the digestive tube. The entrance to the Jarynx is always protected xlvi Introduction. by an epiglottis, and with the exception of Bradypus tridactylus, the trachea always takes a direct antero-posterior course from the larynx to its bifurcation. The lungs are always freely suspended in pleural cavities, and they are never prolonged into abdominal or other air-sacs. A perfect diaphragm is always present. Portions of this and of other muscles are always interposed between the kidneys and the lower dorsal and upper lumbar vertebrae in the region of which they lie; and their external surfaces are, conse- quently, not conformed, as in other Vertebrata, so as to fit into the sinuosities of the osseous structures in their neighbourhood. The kidneys are provided with a fibrous envelope, surrounded by a panniculus adiposus, the venous system of which is in anastomotic connection with that of the gland; but this connection never attains to the functional importance of a ‘renal-portal’ system. Similar anastomoses, possessed similarly of merely morphological importance, exist between the renal arteries, which bring to the gland the blood upon which its secretion as well as its nutrition is entirely dependent, and certain branches of the lumbar arteries. The substance of the gland is always differentiated into an external cortical secretory, and an internal medullary excretory stratum. A urogenital canal, which is only occasionally found or rudi- mentarily represented in other Vertebrata, is always found in Mammals, except in the females of some Rodentia or Lnsectivora, where the clitoris forms a.closed tube for the urethra. The cerebral hemispheres, as distinct from the corpora striata and optic thalami which they overlie, attain a greater development than in any other class of Vertebrata. Their external surfaces are in many small, and in most large representatives of the Class, convoluted, so as to allow of the ready access of blood to the sub- stance of the hemispheres, at the same time that the amount of the grey matter is greatly imcreased. The cerebral hemispheres are always connected by a more or less extensive ‘corpus callosum,’ and the mesencephalon is always represented by more or less sharply separated ‘ corpora quadrigemina.’ In a few of the true Cetacea the olfactory bulbs are absent, and in certain burrowing Rodentia and Insectivora, the eyes may be absent or rudimentary, but in all other Mammals the organs of special sense are all present. Special organs of tactile sensibility are very ordinarily developed upon the snout, as in the Carnivora and Solidungula. Characteristics of the Vertebrata. xlvil The malleus of Mammalia, though limited to auditory functions, and placed within the cavity of the middle ear, corresponds to the os quadratum, which carries the lower jaw of Sauropsida, being developed out of the proximal elements of the first visceral arch, whilst the stapes and incus hold a similar relation to the second, and represent the columella of those animals and its supra-stapedial appendage. All Mammalia have a urogenital canal independent for a greater or less length, or altogether, of the termination of the intestine ; all male Mammalia have an intromittent organ; in all female Mammalia during the period of gestation, the blood-vessels of the uterus come into intimate relation with those of the foetus, and provide thus for its nutrition aud respiration during a longer or a shorter portion of its developmental life. The reproductive system has furnished a basis for the division of the Class Mammalia into the three Sub-classes, Ornithodelphia, Didelphia, and Monodelphia. ; SuB-cLASS, Ornithodelphia. The Sub-class, Ornithodelphia, is represented by the single order Monotremata, and the two genera, Ornithorhynchus and Echidna. In these animals, as the names Monotremata and Ornithodelphia imply, the urogenital and the rectal canals both open by a common cloacal outlet, and the oviduco-uterine ducts remain distinct up to their points of entry into the urogenital canal. In the males, however, there is a perforated penis, which, though not continuous at its base with the urogenital canal, can be brought into apposition temporarily with the orifices of the vasa deferentia, so as to form a functionally distinct sexual canal. The mammary glands have no nipples ; in Hchidna, the lacteal ducts open into a pouch-like invo- lution of the integument; in the Ornithorhynchus they open upon a plane surface; in both, the embryoes are extruded from the uterine cavities whilst in an exceedingly immature state. In the Monotremata, as in Sauropsida, the coracoid reaches the sternum ; they possess an interclavicle ; and the so-called ‘ marsupial’ bones, which are ossifications of cartilages segmented off from the pubic elements of the pelvis, and which give insertion to a portion of the tendon of the external oblique muscle. The Hehidna is edentulous ; the Ornithorhynchus has horny plates in the place of teeth. xvi Introduction. SUB-cLASS, Didelphia. The Didelphia are represented by the single order JDarsu- pialia, which resembles the Monotremata in the possession of ‘marsupial’? bones, though in few other points besides those common to all Mammalia. The urogenital canal is much more distinct from the rectum than in the Monotremata, but, as is the case also in certain Monodelphia, the external orifices of both canals are embraced by a common sphincter muscle. The testes are never retained in the abdomen, as in the Oruithodelphia and in some Monodelphia, but are suspended in a scrotum placed an- teriorly to the penis. The young are extruded from the uteri in an imperfect condition of development, and whilst going through the further stages necessary for enabling them to provide for themselves, they are attached to a long mammary nipple, which is ordinarily contained within a marsupial pouch. The coracoid never reaches the sternum ; ‘true teeth are never absent ; the angle of the lower jaw is almost always inflected. SuB-CLASS, Monodelphia. The Monodelphia, which are also known as ¢ Placentalia,’ differ from the two other sub-classes in the following points: with a few exceptions, such as the Hare amongst the Rodents, and Orycteropus, amongst the Bruta, their female generative canals form an azygos corpus uteri of greater or less length, which opens into an azygos vagina; which, again, with the exception of Bradypus, opens always by a single orifice into a urogenital canal. In all Mono- delphia the vessels of the allantois come into relation with the vessels of the uterus, and the two sets of vessels form a placenta, which has not been observed in the other two sub-classes. Accord- ingly as portions of the maternal structures come away with the foetal elements of the placenta at birth or not, the Wonodelphia are divided into Deciduata and Non-deciduata, the former of these groups corresponding to the Unguiculata, with the exclusion of Manis and probably also of Rhinoceros; and the latter to the Ungulata and Mutica of Linnaeus. The scrotum is never prepenial as in Marsupials; the testes are, however, sometimes retained within the abdomen as in Monotremata: and in Centetes, in which this is the case, a tendency to develope an inflection at the angle Characteristics of the Vertebrata. xlix of the lower jaw is observable, so. that in the organism of a single Monodelphous animal are combined peculiarities of both the other Sub-classes. Marsupial bones are never present in Monodelphia. Cuass, Aves. Air-breathing’ warm-blooded Vertebrata, which have epidermal appendages of the structure of feathers, and which are always oviparous. Their anterior pair of limbs have the shape of wings, which are formed thus: the two digits of the ulnar side are aborted together with their metacarpals; the remaining three metacarpals, and the os magnum of the carpus, are fused into a single bone, upon which three digits are carried, and which abuts proximally upon two free carpal bones. Of these digits the middle one, corresponding to the index finger, and the carpo-metacarpal bone, carry the ‘primary’ quill feathers, whilst the ulna carries the “secondaries, and the humerus the ‘scapularies’ s, ‘ parapterum ” of pterylography. Most of the peculiarities which distinguish the Avian from the Reptilian organism, are to be correlated more or less directly with their power of flight. The necessity for the possession of the power of exerting great muscular force entails the possession of warm blood; and the immobility of the dorsal, the pliability of the cervical, and the great extent of the sacral vertebral regions, are nearly as directly connected with the function of flight as the great development of the sternum, whence the muscles of flight take origin, or the conformation of the limbs upon which they act. The warm-bloodedness or ‘homoeothermal’ character of Birds, might appear to connect them more closely with Mam- mals than with Reptiles ; but it will be found to be correlated with but few distinctively Mammalian characters, beyond those which may be expressed by saying that in both these homoeothermal classes, the venous and arterial systems are prevented from directly intermingling their blood by the existence of a quadrilocular heart, and of a single systemic aorta; whilst the brain holds a more favourable relation quantitatively to the body and to the spinal cord ; and the spinal cord again is, with perhaps a few exceptions, larger relatively to the body than is observed to be the case in cold- blooded Vertebrata of any Class. On the other hand, the totality of the Avian organization, with the exception of the epidermal d 1 Introduction. system, as observed in existing Birds, and the fossil remains of such transitional forms as are preserved in Archaeopteryx on the one side, and the Dinosauria on the other, show that their more essential morphological affinities are distinctly Reptilian. The aberrant integument of Birds, being, as it is, by virtue of its polished surface, an imperfect radiator, and, by virtue of the layers of air it entangles, an exceedingly bad conductor of heat, is a powerful auxiliary in the economization of the heat generated by - the rapid rate at which their various functions are carried on. Both Reptiles and Birds are favourably conditioned for the conservation of heat, by the semi-solid character of their excreta; and at par- ticular seasons, as has been observed in the case of the incubation of the Python, Reptiles do appear to obtain the power of raising their temperature considerably above that of the medium in which they live. The skeleton of Birds contrasts with those of Reptiles and Mammals generally, by its greater hardness and lightness, and its greater readiness to form anchyloses. The cervical and dorsal vertebrae have their centra articulated by synovial joints, in which cartilaginous menisci are to be found. The anterior surfaces of these centra have the procoelous appearance when looked at in situ and from in front; but when one of these vertebrae is removed from apposition with the one next in front of it, the anterior surface of its centrum is seen to be saddle-shaped or cylin- droidal transversely, whilst the posterior surface, being conformed so as to articulate with an anterior surface of that shape, is, im its turn, convex transversely, but concave from before backwards. On the other hand, the occipital condyle, at least of the more typical Birds, is more perfectly spheroidal as retaining less trace of its trifid composition out of the basi-occipital and the two ex-occipitals than in most Reptiles. The neck vertebrae may vary in number from nine to twenty-four, the dorsal from six to ten, of which the four or five most. anteriorly placed are ordinarily anchylosed with each other, except where, as in the Ratitae and some of the Cari- natae, as the Penguin, the power of flight is lost. The sacral vertebrae vary in number from nine to twenty, the enormously elongated ilia abutting directly upon them without the interposition of any sacral ribs as in Reptiles, or the separate centres of ossifi- cation which represent those ribs in Mammals. There are from eight to ten caudal vertebrae, the last of which forms an ‘os en Characteristics of the Vertebrata. li charrue’ for the support of the ‘rectrices’ feathers. The two anterior ribs having often no sternal element, the character of ‘dorsal’ or ‘cervical’? comes to depend upon the relation these movably articulated appendages hold to the subjacent lung. In the fatitae, the osseous system of which order shows many Rep- tilian affinities, the cervical ribs often remain unanchylosed for considerable periods of their adult life. ‘ Processus Uncinati’ are attached by ligament or anchylosed to the dorsal ribs, with the exception of the first and last. The largely developed sternum gives support to the strong coracoids anteriorly, and to the ossified sternal elements of the costal arches laterally, but it is never pro- longed outwards at its posterior angles into costal processes as in Reptiles. The clavicles are occasionally absent, but ordinarily form a furculum by fusion at their anterior extremities, with which, as also with their upper ends, elements segmented off from the cora- coids are found to anchylose. The iliac bones extend so far forwards as to overlap some of the ribs, so that no distinct lumbar region exists. The ischiac and pubic bones are prolonged backwards, so as to be approximately parallel with each other and with the long axis of the body; except in /#ea, the ischia never form any sym- physis ; nor do the pubic bones, except in Struthio Camelus. The femur moves in the acetabulum in a direction parallel with that of the long axis of the body. The fibula never reaches the ankle joint, which is situated as in Reptiles between the proximal and distal row of the tarsus. In adult Birds, the tibio-tarsus and the tarso-metatarsus are each perfectly anchylosed into a single bone. This is not the case in Reptiles. The external toe is never present in Birds. The hallux is sometimes absent; when present, it is carried upon a metatarsal articulated to the tarso-metatarsus near its distal extremity, and consists of two phalanges. In the Ostrich, both hallux and index are absent, as well as the fifth toe, and the foot is reduced to the didactylous condition, though the tarso- metatarsus retains a rudiment of the third distal articular trochlea. Dental papillae, with caps of dentine, have been observed in the embryoes of Psittacidae ; in adult Birds, the digestive tract is characterized by the absence of teeth, of lips, and of a velum pendulum palati; and by the presence of a horny beak, and of a muscular gizzard placed posteriorly to a glandular proventriculus. With the absence of comminuting organs anteriorly to the gizzard, d 2 hi Introduction. is correlated the width of the oesophagus, which often expands into a crop. The liver ordinarily consists of two lobes, into the fis- sure between which the apex of the heart is received. There are always two, and sometimes three bile-ducts in Birds: they open separately into the intestine; and on one of them a gall-bladder is usually developed. A large and compact pancreas, with two or three ducts, is always to be found in a fold of the duodenum. With few exceptions, two coeca are appended to the intestine at the junction of the ileum to the colon; and a third, representing the omphalo-mesenteric duct of embryonic, and of early life subsequently to hatching, is occasionally present at a poimt higher up in the small intestine. The urinary and genital ducts ordinarily open separately into the cloaca, but there may be a short urogenital cavity distinct from the lower segment of the digestive tube, but opening directly into it. The characters of the beak, tongue, crop, gizzard, and cireum-oral salivary glands, vary much, in correspond- ence with the nature of the food. The heart is quadrilocular, and the right auriculo-ventricular valve muscular in all Birds. The fourth aortic arch of the right side, instead of that of the left, as in Mammals, forms the single systemic aorta; the fourth aortic arch of the left side is converted into the subclavian artery instead of forming a second, or left, sys- temic aorta as in Reptiles, though its homology with this latter vessel is spoken to in many Birds, especially Accipitres, by its retention of a fibrous prolongation onwards to the functional aorta. The aorta and pulmonary artery have each three semilunar valves. ‘The aorta divides after a very short course into three great trunks, by giving off two subequal innominate arteries. In Birds of powerful flight, these trunks are often of larger calibre than the continuation of the aortic trunk itself. There are always two superior venae cavae, which open separately from each other, and from the vena cava inferior, the sinus venosus having disappeared by absorption into the right auricle. The vena cava inferior is formed by the confluence of the efferent renal veins, with which the veins from the lower extremities are, as in Mammals, directly continuous; though, as in Reptiles, the blood which these latter vessels carry can find its way also into the kidney, forming thus a ‘renal portal’ system, as well as into the liver by anastomosis with factors of the true portal system. The trachea in Birds is always of considerable length; it is often Characteristics of the Vertebrata. liu tortuous, and dilated at intervals. Its cartilaginous supports form usually perfect rings, and are not rarely ossified. In most Birds with the exception of the Ratitae, a lower larynx is developed upon the junction of the trachea with the two bronchi. The bronchi lose their cartilaginous rings when they enter the lungs, where they dilate into membranous canals which subsequently become smaller by giving off branches, and finally end by opening into air sacs. The lungs are deeply indented in correspondence with the ribs, but are not otherwise lobed. There are nine air sacs, of which one is placed asymmetrically between the furculum and the trachea, two in the abdomen and pelvis, four in the posterior and lateral parts of the thorax, and one on either side of the azygos interclavicular sac. Processes are prolonged from the anterior and posterior of these sacs into the bones. The bones of the skull are sometimes, as in Mammals, the only pneumatic bones; the vertebrae, humerus and sternum come next in order as to the possession of air cavities ; whilst in some Birds all the bones of the body are said to have been observed to be pneumatic. The bones of the fore-arm, on the other hand, of the lower leg, of the manus and of the foot, are often found to retain their medulla, and to be devoid of pneumatic cavities. The kidneys are divided into three lobes, and have their outlines conformed to the sinuosities of the pelvic bones. There is never any urinary bladder; the ureters open internally to the generative ducts, either directly into a cloaca, or into a urogenital pouch of small antero-posterior extent. The brain is much larger relatively both to the entire body and to the spinal cord than it is in Reptiles, and the spinal cord again holds a more favourable relation to the entire body than in those cold-blooded creatures. It occupies however a greater relative length in the spinal canal than it does in Mammals, and in this resembles the cord of the other Sauropsida. The cerebellum has only rudimentary lateral lobes; its grey matter however is con- siderable in quantity, owing to its transverse lamination. It projects forwards so as to come into relation with the prosen- cephalon, and, as it were, to displace the bigeminal hollow optic or mesencephalic lobes on to either side of its forward prolongation. The cerebral hemispheres are represented by a thin shell of nervous matter, which covers the large corpora striata, and incloses the lateral ventricles. The corpus callosum is absent; and the fornix liv Introduction. can only be considered to be rudimentarily represented by a portion of the inner wall of either lateral ventricle. The anterior com- missure is not, the posterior is largely developed. The optic thalami are smaller than the optic lobes. Tactile sensibility is limited to the beak. Smell and taste are lowly developed. The cochlea of the ear is a much simpler, the tympanum a much more extensive cavity relatively than in Mammalia. The eyes are never absent, and, though small in the Apteryr, are never rudimentary. The globe of the eye consists of two seements, the anterior one of which is more or less obtusely conical, whilst the posterior is spheroidal ; bony plates inlaid in the anterior part of the sclerotica preserve the relative conformation of the two portions. As in many lower Vertebrata, a vascular process is prolonged from the choroid into the interior of the bulb. This structure is known in Birds as the ‘pecten,’ or, from its shape in fatitae, as the ‘marsupium ;’? and in many grallatorial and aquatic Birds it reaches to the lens. It is absent in Apteryx. The vitreous humour is relatively smaller than in Mammals. Except in Owls and aquatic Birds, the lens is flat. The ciliary muscle upon which the bird’s power of accommodating the eye so as to obtain clear vision at very rapidly varying distances depends, is, in correspondence with this need, composed of trans- versely striped muscular fibres. The muscular fibres of the iris are of similar character. A special muscular apparatus and a special (Harderian) gland are developed, in relation with the third eyelid or membrana nictitans. As in the Sub-kingdom Arthropoda, the sexes differ much ex- ternally ; and in the case of the Accipitres, the females, as is so commonly observable in that Sub-kingdom, are larger than the males. The testes are always retained within the abdomen anteriorly to the kidneys; the left is occasionally the larger of the two. The vasa deferentia are often dilated towards their terminations, but in neither sex are there ever any accessory glands, distinct from and appended to the generative canals by ducts, as are the Cowperian, the prostatic glands and the vesiculae seminales of many Mammals. The right ovary is usually atrophied, and when it is persistent, as in some Accipitres, its ova do not come to maturity. In the upper part of the oviduct the albumen, in the lower the calcareous shell of the egg is formed. Many young Birds are, as are also the young Characteristics of the Vertebrata. lv of Chelonia and Ophidia, provided with a hard knob on their upper mandible, for breaking through their shell when ready for hatching. In some Birds the food-yolk is large, and the young are ordinarily more or less entirely competent to provide for themselves when hatched. Where the yolk is relatively small, the young are in- competent to locomotion when hatched, and require to be brooded upon whilst going through further stages of development. Birds which are possessed, immediately after hatching, of the faculty of self-help have been called ‘ Autophagi,’ in opposition to those which require further maternal care, and are called ‘ Insessores.’ Existing Birds are divided into two orders, the Ratitae, in which the sternum has no crest and the wings are rudimentary, and the Caurinatae, in which the sternum has a crest or keel, ossi- fied from an independent median azygos centre, and which have powerful anterior limbs ordinarily organized for flight, though sometimes not, as in the Penguins. ‘The former order includes only the genera Struthio, Dromaeus, Casuarius, Apteryx, and is distin- guished not only by many modifications curtailed by the stunting of their anterior limbs, but also by many morphological points of. affinity to the cold-blooded Sauropsida, amongst which the cha- racters of the osseous system are peculiarly striking. The Ratitae have the barbs of their feathers disconnected, have no inferior larynx, and no angle at the junction of coracoid and scapula. A more perfect diaphragm exists in them than in the Carinatae. This latter order comprises all other existing Birds. The fossil Archaeopteryx appears to have differed from existing Birds by possessing a series of caudal vertebrae equalling the body in length, and in having well-developed non-anchylosed metacarpals. A sepa- rate order, that of Saururae, has been established for the reception of this transitional form. Cuass, Reptilia. Air-breathing cold-blooded Vertebrata, with epidermal struc- tures of the character of scales, into which processes of the ewtis vera are prolonged, but which are not developed like feathers within saccular involutions of the integument. Accordingly as bony scutes are combined with these scales, and constitute an osseous dermal skeleton or not, existing Reptiles are divided into the lvi Introduction. two groups of Loricata and Squamata, the former containing the two orders, Chelonia and Crocodilina ; and the latter the Sauria and the Ophidia. The anterior limbs are sometimes en- tirely absent, together with the scapular arch; they are never modified so as to form wings like those of Birds; the caudal vertebrae very frequently form a series equal in length to the length of the rest of the body; the jaws are usually armed with teeth, which are constantly reproduced during the life of the animal. There are two systemic aortae, which either fuse (Sguamata) or anastomose (Loricata) with each other in front of the dorsal verte- brae; and in no Reptiles, except Crocodilina, is there a complete separation of the ventricular part of the heart into two cavities. And in Crocodilina, the two systemic aortae arising from the two distinct ventricles, communicate with each other at the base of the heart by the foramen Panizzae ; so that in all Reptiles the venous and the arterial blood come to be more or less freely intermingled without the interposition of capillaries, at, at least, two points of the vascular system. Copulatory organs are always present, except in Hatteria ; for the peculiarities of which see Dr. Giinther, Phil. Trans. 1867, p. 595- The skull is less vaulted and less capacious than in Aves. Traces of the entrance of the two exoccipitals into the formation of the occipital condyle are usually persistent. The os quadratum is sometimes movably, sometimes immovably (Loricata and Hatteria) articulated to the cranial walls, a considerable part of the antero- lateral elements of which remain in the condition of fibro-cartilage, except in Ophidia. Amphicoelian vertebrae are found in the existing Geckotidae and Hatteria, where they are connected, as in Mammals, by inter- central cartilages, in the axis of which are persistent masses of substance representing the chorda dorsalis. Vertebrae of similar shape are found in the fossil Hnaliosauria and Teleosauria. The Vertebrae are ordinarily procoelian; and, with the exception of Crocodilina, 1 which a considerable quantity of intervertebral substance remains between the centra of the vertebrae, they are connected with each other simply by synovial joints. In the Chelonia, the vertebral centra vary very much in shape, especially in the neck and tail, where they may either be amphicoelous, biconvex, or procoelous. The neuro-central sutures disappear Characteristics of the Vertebrata. lv in Squamata, but are persistent in Loricata. The number of the vertebrae may amount to several hundreds in the Ophidia, and in the Saurian Amphishaenoidea may be as many as one hundred and thirty. Though ordinarily the number is much smaller in Reptiles provided with limbs, even in the non-serpenti- form Monitor it may be no less than one hundred and forty. There are two cervical vertebrae in Ophidia ; in Sauria their number may amount to ten; in the Loricata it is usually eight. The dorsal vertebrae are movably articulated with each other, except in Chelonia; the sacral vertebrae are seldom more than two in existing Reptiles, though this number was often much exceeded in extinct forms of the Class. Lumbar vertebrae do not exist in Ophidia ; they are present in Chelonia, and in number from four to five, whilst in Sauria they are reduced to two, or even one. The shoulder girdle is entirely absent only in Ophidia, but present in a rudimentary condition in the serpentiform Sawria. The clavicle is wanting in Loricata, Chamaeleonoidea, and Sau- ropterygia. The sternum is wanting in Ophidia, Chelonia, and in. some of the serpentiform Sawria. The ribs in the Chelonia form by fusion with exoskeletal ossifications the expanded lateral or ‘costal’ plates of the carapace. The sternum is absent, and the ventral plates, constituting the ‘ plastron,’ are exclusively dermal ossifications. In the Crocodilina, the ribs of the anterior thoracic vertebrae, and, with the exception of those belonging to the atlas, of the cervical also, articulate with their respective vertebrae by two separate processes, the ‘tuberculum, and the ‘ capitulum.’ The ribs of the Sawria have only a single articular facet, which, however, may show a tendency to bifurcate. The ribs carry pro- cessus uncinati in the Crocodiles and in Hatteria. Many Reptiles have free abdominal ribs, which may be either true endoskeletal elements, or ‘ parostotic’ ossifications of intermuscular fibrous septa, or, as in Hatteria, of the subcutaneous fibrous mesh. In Ophidia, the posterior pair of limbs is sometimes represented by a pair of small bones placed anteriorly to the anus; and in the serpentiform Sauria the pelvic girdle and its appendages are represented merely by a single iliac bone, attached on either side to a single ‘sacral’ vertebra. But in all other Reptiles the three pelvic bones are present, forming pubic and ischiae arches by abutment upon the ossa ilii, which do not extend forwards anteriorly to the acetabulum. K lil Introduction. The number of the phalanges increases in the digits of both extre- mities from the innermost digit outwards, and reaches its maximum in the fourth digit. In the foot of the Orocodilina this digit has no claw on its terminal phalanx, and the fifth digit is altogether lost. Teeth are always present; except in Chelonia, where a horny sheath covers the jaws, as in the bills of Birds. The teeth are limited in Crocodilina to the homologues of the bones which carry teeth in Mammalia; but in many Sauria they are carried upon the pterygoid also; and in Op/idia upon both palatine and pterygoid bones, in addition to the mandibular, maxillary, and premaxillary bones. Teeth are provided with sockets in Crocodilina, but in no other existing Reptiles; they are reproduced, as shed, during the whole period of the life of these animals. The tongue may be either spatula-shaped and immobile, as in Chelonia and Crocodilina, and some Sauria, or bifid, elongated, and protrusible, as in other Reptiles. The wide oesophagus, and the muscular stomach, are ordinarily not unlike those of Birds; and this resemblance is made more striking in the Crocodilina, which, in addition to the muscular gizzard, have a special portio pylorica, such as is developed in many grallatorial and natatorial Birds. But the digestive tract of Reptiles, which are with few exceptions of carnivorous habits, exhibits, in correlation with this uniformity of diet, fewer varia- tions of arrangement than that of Birds. Labial and lingual salivary glands are occasionally present. Of the former of these, the poison-gland of Ophidia is a modification. The liver and pancreas have, as in Birds, two or more excretory ducts; the latter of the two glands is ordinarily perforated by the hepato-enteric ducts; a gall-bladder is always present, but is sometimes developed upon the biliary duct at a distance from the liver. This gland is unilobed in Squamata, bilobed in Loricata. In the Squamate Reptiles and Chelonia, in which the heart has not four distinct and separate cavities, the venous blood returned from the system to the larger right auricle, is kept more or less completely apart from the arterial, returned from the lungs or lung to the left by the non-isochronism of the action of the anterior and posterior parts of the ventricular cavity. The anterior or inferior portion of the ventricular cavity is filled from the right auricle, and empties itself into the pulmonary artery, and partly into the Characteristics of the Vertebrata. lix left aorta, before the posterior part of the ventricular cavity, into which the blood from the left auricle is discharged, commences to contract. When this part of the ventricular mass begins to con- tract upon its arterialized contents, access to the pulmonary artery has been cut off by the closing up of the muscular demi-canal leading to that outlet; and the arterialized blood is consequently thrown into the two systemic aortae. Of these, the one which bends over the left bronchus, or, in Opidia, to the left side of the body, and which is consequently known ordinarily as the left aorta, never gives any branches to the anterior parts of the body; but either as in Sauria and Ophidia, simply joins the right aorta without giving off any branches; or, as in Loricata, distributes itself to the chylo-poietic viscera, and communicates with the right aorta simply by a branch of anastomosis. In the Crocodilina this vessel arises from the right auricle, together with the pulmonary artery, and consequently never carries any arterialized blood. Its com- munication, by the foramen Panizzae, with the right aorta, which supplies the anterior parts of the body, may be held to foreshadow the conversion which the fourth left aortic arch undergoes into a left subclavian artery in Aves. The close proximity of the com- mencement of the left aorta to that of the pulmonary artery, enables it in all Reptiles alike to relieve the pulmonary circulation, when respiration may be put into temporary abeyance. ‘The arterial outlets of Reptiles have only two semilunar-valves. In all Reptiles, as in all Birds, there are two superior as well as one inferior vena eava; but in Reptiles these three vessels open into a pulsatile venous sinus, and have their contents poured through it by an orifice guarded with eyelid-hke valves into the ventricular cavity. In all Reptiles there is a ‘renal portal’ circulation, by which the venous blood returning from parts placed posteriorly to the kidneys finds its way into these organs, at the same time that by means of anastomoses with factors of the true portal system, it may be returned to the heart by way of the hepatic system. The supra- renal bodies are, like the renal, possessed of a system of venous inferent vessels. The lymphatic vessels, which often take the shape of loose sheaths surrounding the large arteries, communicate with the veins both anteriorly in the brachiocephalic, and posteriorly in the caudal regions. Upon their junction with the veins of this latter region, contractile sacs, the so-called ‘lymphatic hearts,’ are lx Introduction. developed. Glands which in Birds are only scantily developed upon the cervical lymphatics, are not represented as distinct from lymphatic plexuses, except by a mesenteric gland in the Crocodilina. The trachea of the Loricata has a more perfect larynx than that of the Squamata, and in some eases it describes a couple of convo- lutions before entermg the lungs. These organs differ in the Lor7- cata from those of other Reptiles in having, in correlation with their non-transpirable integument, a much greater development of internal parenchyma; and in not projecting freely into the general cavity of the body, dissepimental processes of peritoneal membrane separating them from it and foreshadowing thus, as also by their possession of intrinsic muscular fibres, the diaphragm of warm- blooded animals. In the Sguamata the lungs may be prolonged in air-sacs, with little or no reticulation of vessels developed upon them, and these prolongations may be numerous as in Chamae- leonoidea, or simple as in Ophidia. In some of the lower Lizards, again, as Hatteria, the lungs may be nearly as simple as those of the Amphibia. The kidneys are situated posteriorly in the trunk, and, except in the Op/idia, within the pelvic cavity, and close to the cloaca. In the Crocodilina, indications of a separation of the substance of the kidney into a cortical and medullary stratum are not wanting. A urinary bladder is usually present in Sauria and Chelonia, but is absent in Ophidia and Crocodilina. In the Che- lonia, a sinus urogenitalis is present. The kidneys are not con- formed to the sinuosities of the bony structures as in Birds. The cerebral hemispheres are smaller relatively to the rest of the encephalon, and to the spinal chord, than in Aves. The cerebral hemispheres, corpora bigemina, and cerebellum, are larger in the Loricata than in the Sguamata. A tympanic cavity is present except in Ophidia, Amphisbaenoidea, and Hatteria. This latter animal has the commencement of a spiral turn indicated in its cochlea, which in other Reptiles is, as in Birds, merely a flask- shaped cavity; but it differs both from Birds and from other Reptiles in the absence of any intra-ocular structure corresponding with the avian ‘pecten,’ or the ‘processus falciformis’ of other Reptiles. Copulatory organs of two distinct types exist in the Loricata and Syuamata respectively ; those of the former division being Characteristics of the Vertebrata. Ixi developments of the anterior wall of the cloaca, whilst those of the latter consist of two protrusible hollow conical bodies, which open into that cavity from behind. In the Chelonia, two peritoneal canals are prolonged into the penis, in the distal extremity of which they terminate blindly ; two canals, probably homologous with them, and also with the similarly situated pores of the Selachian and Ganoid Fishes, exist in the Crocodilina, but open at the base of the intromittent organ. The testes and ovaries are bilaterally symmetrical, except in the Ophidia, where the right gland is placed anteriorly to the left, and in the females is the larger of the two. The ova often undergo development whilst in the oviducal canals, but the young are not set free from the foetal envelopes before extrusion from the maternal organism. For liberating themselves from these envelopes, the young of the really ovo-viviparous Viper, as also of many other Reptiles, are provided with a temporary premaxillary tooth. All Loricata are oviparous in the strict sense ; and amongst the Squamata, nearly allied forms may vary as to being ovo-viviparous or oviparous. Some lowly organized Lizards, such as Hatteria, possess the power of reproducing lost portions of the tail. The sub-division Loricata, under which are comprised the two orders of Crocodilina and Chelonia, differs from the sub-division Squamata, comprehending the two orders Sawria and Ophidia, in the following particulars besides those already enumerated. Their anal cleft is longitudinal, there is usually some calcareous deposit in the shells of their eggs, their ribs are double-headed in the anterior regions of the body. Setting aside a few points which may be correlated with their aquatic and less active habits, the Zoricata may be considered as more highly specialized, and possessed of nearer affinities to the higher Vertebrata than the other sub- division of this class. Ciass, Amphibia. Cold-blooded Vertebrata, which for longer or shorter periods, or throughout the whole of their lives, are provided with gills for aquatic, in addition to lungs for aerial respiration, and which even when the gills are permanently retained go through some stages of metamorphosis after being set free from the ege. Amongst these lxii Introduction. stages of metamorphosis, the development of limbs never exceeding a pentadactyle division in their terminal segment, and possessing the same segmentation as that seen in the higher Vertebrata, is to be reckoned as an obvious external characteristic, which, together with the absence of scales, differentiates them, with very few ex- ceptions, from Pisces. They never have median fin-rays supported by dermal spines; and, in the absence of an ossified basi-occipital, they always have two condyles formed by the exoccipitals, for articu- lation with the atlas. The heart has always two auricles, perfectly separated ordinarily, and communicating with a single ventricular cavity. Their integumentary system differs from that of Fishes in not having either dermal ossifications or dermal scales developed in the region of the trunk; Ceratophrys, however, and Brachycephalus amongst existing Amphibia, form exceptions to this rule, having dermal ossifications developed in their dorsal region; and the Caeciliae develope dermal scales. In the Salamandra unguiculata again, and in the Dactylethra capensis, a development of nails has been observed, contrary to the rule that in the branchiate Verte- brata there is no epidermal skeleton. The cutaneous system of Amphibia (Zriton) has been observed to possess, during their larval life, rudimentary structures, resembling the sensory organs deve- Joped in Fish, in connection with the ‘lateral line” In adult Am- phibia, the cutaneous glandular system often attains a great deve- lopment as in the ‘parotoids’ and other glands of many Anura. The suspensorium is immovably articulated to the skull, and is continuous with the pterygo-palatine elements of the maxillary apparatus anteriorly, whilst externally it has applied to it a mem- brane bone, homologous probably with the praeoperculum of Tele- ostean Fishes. No Amphibian, however, ever possesses in the cu- taneous opercular flap which it developes, any representatives of the operculum, sub-operculum, inter-operculum, or branchiostegal bones of Fish. The maxillary and praemaxillary bones are never absent, and are ordinarily dentigerous. The vertebrae are very numerous, and amphicoelian in the lower Amphibia; they are few, and show, ordinarily, the procoelian, though, sometimes, the opisthocoeclian arrangement of the articular ends of their centra in the higher orders. The neurocentral suture is usually absent. Except in the serpentiform apodal Caeciliae, the ribs are rudi- Characteristics of the Vertebrata. Ixili mentary in this class. Though there is never any prolongation of costal structures to the medio-ventral line, there is a true sternum developed in relation with the coracoids in most Amphibia except Caeciliae and Proteus. The ilium never abuts upon more than a single vertebra, but the ilium of one side has been observed to abut upon one, whilst the ilium of the other abutted upon another ver- tebra. No ‘parostotic’ bones are ever developed in relation with either limb-girdle. In the highest order of Amphibia, the Anura, the tongue is attached to the front of the mouth and is protrusible; with the exception of Pipa and Dactylethra, where the organ is altogether absent. It is not protrusible in other Amphibia. Amphibia are sometimes edentulous; but usually more or fewer of the bones forming the walls of the mouth, and amongst these, the vomerine, pterygoid, and sphenoid as well as the lower jaw, the maxillary and the praemaxillary bones, are dentigerous. In Proteus, the digestive canal takes a direct antero-posterior course, without any specialization of the stomach as a segment of larger calibre than the intestine ; in other Amphibia a small and a large intestine are ordinarily differentiated as well as a stomach. The small intestine of the larvae of the Anura, which, during that period, feed on vege- table food, is of great length and disposed in numerous coils. At the conclusion of their metamorphoses, the digestive tract has as- sumed a comparatively simple character, though the calibre, direc- tion, mucous and muscular coats of the stomach, small intestine, and colon, severally, are most characteristically developed. A bilobed liver and a compact pancreas are always present, but oral salivary glands are represented only by small glandules impacted in the mucous membrane of the mouth. The heart consists of a sinus venosus, a right and left auricle, a single ventricle, and an arterial bulb. Within this latter portion of the organ, a longitudinal lamellar mdge is developed, which is attached along the dorsal line of the bulb and projects freely into its interior; being connected at either end with a semilunar valve, and describing a curve like that of an italic s, in the interval be- tween those points. This imperfect dissepiment may be held to foreshadow the differentiation of the pulmonary and systemic ar- terial trunks which we find in Reptiles; whilst physiologically, by its relation to the orifices of the branches passing to the anterior lxiv Introduction. and to the posterior parts of the body respectively and to the lungs, it provides for the more or less perfect separation of the streams of arterial and venous blood received from the two auricles. All Am- phibia possess a renal-portal system, the factors of which anastomose freely with those of the true portal system. This latter system always receives, by the intermediation of the epigastric veins, an important factor from the allantoid bladder ; by which connection the connection of the umbilical and placental veins, as seen in Mammals, is very obviously foreshadowed. The transpirable and glandular character of the skin would appear to confer an aerating function upon the vascular ramifications which it contains in great abundance. The lymphatic vessels are greatly developed in the subeutaneous spaces; and lymphatic hearts are present in the Anura, both upon the anterior and upon the posterior junctions of this system to the blood-vascular. In the Urodela, as in Reptiles, the posterior hearts only exist. In the higher Amphibia, two sets of gills are developed. One of these is the external set which corresponds to the permanent gills of the Perennibranchiate Am- phibia, and to the deciduous external gill filaments of the Plagio- stomous Fishes, which latter it resembles in being shed early. The other is the internal set which are developed subsequently to, and retained in the Urodela and Anura longer than the ciliated external set. In certain Amphibia (Menopoma, Amphiuma, Crypto- branchus, thence called Derotremata), a fissure remains in the pha- ryngeal walls after the shedding of the branchiae. This event does not always take place at the same date in the life of the larva. Cartilages representing a larynx are developed round the inlet from the pharynx into the air passages. ‘There is a trachea of con- siderable length in Menopoma, Amphiuma, and the Caecihae; and there are bronchi of considerable length in Pipa and Dactylethra ; but ordinarily, these tubes are only rudimentarily represented in Amphibia. The Amphibia appear to have no secondary kidney developed ; and the products of the urinary and sexual glands are always dis- charged into a cloaca by a single orifice, that of the duct of the Wolffian body, on either side. In Proteus, the transversely running ducts of the primary kidney remain distinct from each other, up to their junctions with the antero-posteriorly running duct of the primary kidney, the so-called ‘ Miiller’s duct.” In other Amphibia, Characteristics of the Vertebrata. lxv the ducts of the Wolffian body form by fusion with each other a secondary duct, which opens into the primitive duct of Miller at its lower end, leaving the upper portion of that duct to serve exclusively as a generative canal. The cerebral hemispheres always contain a lateral ventricle, which is prolonged into the interior of the sessile olfactory lobes. The optic lobes are smaller relatively than in Fish, in correlation with the smaller eyes ; the optic thalami are always differentiated from them, and from the corpora striata in front. The membranes of the brain and spinal cord have an abundance of pigment cells in their visceral laminae, and upon the exterior of these membranes, and especially upon their prolongations upon the spinal nerves, deposits of crystalline carbonate of calcium are commonly observ- able. As in many Fishes, the portio dura often fails to be entirely differentiated from the fifth pair of nerves; as in Lepidosiren, the glossopharyngeal is represented by branches of the vagus, and the hypoglossus by the first spinal nerve. The eye is small in com- parison with that of Fish, but as in that Class the lens is sphe- roidal, and the cornea, except in the Land Salamander, flat. There is no tympanic cavity except in the Axuwra, and no cochlea except in a rudimentary condition in the same order. In the aglossal Anura (Pipa, Dactylethra), there is a single median pharyngeal orifice to the two Eustachian tubes. The two nasal cavities open into the mouth by a canal passing between the bones of the roof of the mouth in Anura, but between those bones and the lips in Perennibranchiata. Rudiments of an ovary have been observed to coexist with the testes in the male Bufo variabilis and cinereus. ‘The sexes are very frequently distinguishable by external differences of colour, size, and conformation, but there are no external copulatory organs in ‘this Class. The ova and spermatozoa come into relation with each other externally to the maternal organism, but by means of congress between the two sexes in the dnura; they come into relation with each either externally to, or within the maternal organism in the Urodela, and probably also in the Perennibran- chiata, but without, at least in the aquatic species, any sexual congress. The Land Salamanders appear to be, under certain circumstances, such as those of the Alpine species living at points of great elevation in the mountains, ovo-viviparous or viviparous, e Ixvi Introduction. the larvae having in some cases shed their external branchiae previously to birth. The ova are small, the yolk undergoes nearly complete segmentation. With a few exceptions, the Amphibia are oviparous. In every case, except possibly that of the Caecilia compressicauda, the embryos very shortly after hatching develope branchiae, or, as in the case of Notodelphys, structures equivalent to them. Existing Amphibia are divisible into three orders. In the most highly organized of these, the swimming tail is discarded in the course of metamorphosis as well as the gills, and they are thence called Anura; in the second order, thence called ‘ Urodela’ the tail is retained, whilst the gills are, in the sub-orders, Sa/amandrina and Derotremata, deciduous ; and in the Perennibranchiata, retained permanently. In these two orders limbs are developed, at least on the pectoral arch; but a third order, that of the Gymnophiona, represented by the single family, Cueci/iae, is constituted by Amphibia in which, though the gills are deciduous, no limbs are developed, and the body remains serpentiform. In development, the body cavity is not formed apart from and around the yolk sac, but the intestine is formed, as in Amphioxus and the Cyclostomi, by a process of invagination, beginning from without at a spot corresponding with the situation of the future anus. The oral opening is not formed when the embryos are first set free from the egg. The Anwra and the Caducibranchiate Urodela have two sets of gills, an external set of three pairs, which is soon lost, and in the land Salamanders partly or wholly before the end of intra-uterine life; and an internal set. After the dis- appearance of the external set an opercular fold, im which however in no Amphibia are bones ever developed, forms over the internal gills, and within the branchial cavity thus produced the anterior extremities first bud forth. When in the course of metamor- phosis the gills disappear, the continuity of the circulation is main- tained, or, in other words, the primitive continuity of the proximal or cardiac with the distal or dorsal elements of the aortic arches is re-established, by the expansion in calibre of a branch of ana- stomosis, which, whilst the branchiae were functionally active, connected the efferent directly with the afferent branchial trunks, but was itself at that time functionally insignificant. The oper- cular structures close up the visceral fissures, except in the Dero- Characteristics of the Vertebrata. Ixvil tremata, and more or fewer of the cartilaginous branchial arches disappear after the disappearance of the branchiae they carried. The Alpine Triton, one of the Caducibranchiate Amphibia, has been observed to attain sexual maturity as indicated not only by external characteristics, but by the maturation of ova and sperma- tozoa, at a time when the branchiae were still in functional activity, and when the characters of the bones in the roof of the mouth, and the presence of a continuous non-constricted cylindriform chorda dorsalis, showed the animal to be really in a larval state. The Axolotl (Siredon pisciformis) has long been known to be competent to sexual functions, whilst organs, regarded as provisional in other Amphibia, were still persistent; and it has consequently been classed with the Perennibranchiata until recently, when it was discovered that its gills are really deciduous, though at varying periods in the life of the animal. Similar instances of larval Ichthyoids maturing sexual products are furnished to us by the immature Lamprey, and the young male Salmon, known as the ‘parr.’ Some Amphibia possess a great power of repairing injuries, and of reproducing destroyed or amputated organs. It has been stated, however, that it is necessary for such reproduction that the basal or some other portion of the mutilated organ or limb should be left zz situ; and it is not certain that the Urodela with well- developed lungs, such as Sa/amandra terrestris, and the Anura generally, possess this power in their adult state, at least to the same extent as they do when larvae, or to the same extent as other Amphibia in which the organs for aerial respiration are less highly evolved. The Amphibia are placed together with the class Pisces in a single group, the Ichthyopsida, s. Anamniota. It is with the more generalized forms of that class, viz., the Ganoidei and the Dipnozi, rather than with those which, as the 7Ze/eoste:, combine in this organization the largest number of specially piscine characteristics, that the Amphibia are allied. The Dipnot indeed have been ranked as a separate order of Amphibia, under the title ‘ Ichthyobatrachia,’ though, if we have regard to the entirety of their organism, we are compelled to regard them as true Fish. The H/asmobranchi resemble certain of the Amphibia in developing external gills in embryonic life, and they were spoken of by Linnaeus as Amphibia nantia. The absence, however, in them of any save an occasional é2 lxvili Introduction. and rudimentary homologue of the pulmonary organs of the Amphibia, appears to put this order of Fishes into a position much farther removed from the higher Vertebrata with which they were thus classed, than that which the Dipnoi, and even the Ganoidei occupy. Cuass, Pisces. Branchiate Vertebrata, with motor organs in the shape of fins, supported by numerous internal rays, and placed along the medio- dorsal and medio-ventral lines, or along these lines and bilaterally also. The endo-skeleton of Fishes takes far more various forms than that of any other vertebrate Class; and their exoskeleton is simi- larly distinguished with reference to all other classes except the Mammalia. The dermal exoskeleton may take the form of scales, as in the great majority of Fishes; of placoid or spiny dentinal formations, as in Mlasmobranchii ; of enamelled scales or of bony plates, as in Ganoidei ; and in Dipnoi, Ganoidei, and Teleostei, it extends into the sub-cutaneous fibrous mesh, and along intermuscular aponeuroses forming ‘splint bones.’ There are no scales in Marsipobranchii, and the Spatularidae, a genus of Ganoidei, have an almost entirely naked skin. There are no splint bones in the HMasmobranchii. The cutaneous system is further distinguished by the possession of the system of the ‘lateral line,’ which has not been detected else- where, except in certain Amphibian larvae, and which is supposed to be sensory in function. The epidermis is ordinarily prolonged as a continuous, even if thin layer, superficially to the various dermal formations, except in the cases of some of the outgrowths deve- loped in the Elasmobranchii, and sometimes of the enamelled scales of the Ganoidei. However various the endoskeletal structures of Fish may be, they all agree in the non-possession of a sternum, the absence of which is connected with the peculiarities of their reproductive processes ; © The low grade of organization to which the Pharyngobranchii, as represented by the Lancelet, have attained, makes it convenient to omit this Order from consideration, whilst detailing the characteristics more or less universally found in the other five Piscine Orders, viz. Marsipobranchti, Teleostei, Ganoidei, Elasmobranchti, and Dipnoi. Characteristics of the Vertebrata. ]xix and in the presence of a largely developed branchial apparatus, which is similarly correlated with their aquatic life. In the Mar- sipobranchii, vertebrae are indicated rather than differentiated by the development of a few cartilaginous neural and haemal arches, the sheath of the chorda dorsalis remaining unsegmented through- out. Indications of the formation of vertebral centra are presented to us in the calcified annuli developed in the sheath of the chorda in Chimaerae. The characters of the axial elements of the endo- skeleton vary much in Plagiostomi, attaining in some represen- tatives of this sub-order to perfect differentiation and partial calei- fication. Greater variety is observable in the same structures in the now numerically much smaller order of Ganoidei, where the centra may be represented by a cylindrical fibro-cartilaginous sheath surrounding the cylindrical notcchord, as in the Sturgeons; or by perfectly ossified opisthocoelian masses connected by anchylosis with perfectly ossified neural arches, as in the Bony Pikes (Lepi- dosteidae). In Teleostei, as the name implies, the vertebrae are differentiated, and, in various degrees, calcified, the amount of lime deposited rarely or never attaining the proportions it assumes in other classes of Vertebrata. The neural arches are in Te/eosted ordinarily, but not always, anchylosed to the centra, without the interposition of any neuro-central suture. ‘The number of the ver- tebrae may be as many as 365 in some Sharks; in some Ganoids, and in some of the Physostomi amongst Teleoste:, 11 may amount to 200; in most Physostomi it is about 80; it falls much lower in Acanthopteri, and may be as low as 15 in the Plectognathi. The trunk is divisible into two main regions, the dorsal and the caudal ; from the former of which a cervical region may be said to be marked off, at least morphologically, inasmuch as the scapular arch makes its first appearance opposite the interval between the second and third vertebrae. The L/asmobranchii and most of the Ganoidei, have their greater geological antiquity spoken to by their retention of the more typical heterocercal form of the tail. This peculiar shape is produced by a disproportionate development of the haemal caudal arches, whereby the tail, which was in the early embryo equilobed, and, as in Marsipobranchii and Dipnoi, a direct continuation of the axis of the dorsal region, is bent upwards. An additional factor im the production of the heterocercal tail, is brought into play in the case of the Holostean Ganoidei, and the Physostomous Te/eoste?, |xx Introduction. which are nearly allied to them, by the stunting of the neural in correspondence with the greater development of the haemal arches. This form of tail may to a superficial examination appear quite equilobed, and it is ordinarily spoken of as ‘homocereal.’ It is, however, morphologically ‘ heterocercal,’ as the haemal and neural arches enter into its composition in very unequal proportions, the chorda dorsalis being really prolonged to the upper angle of the tail fin, and the ‘hypural’ plates being all modified haemal arches, and not half of them haemal, and half of them neural ossifications. A true ‘diphycercal’ tail is finally produced in the Acanthopteri, by a reduction of the disproportionate size of the haemal, and by a simultaneous stunting of the central elements of the terminal vertebrae. The differences in the structural arrangements of the skulls of Fishes are very much greater than those observable in the skulls of members of any other Vertebrate class, relating as they do to points of no less morphological and indeed physiological importance than the absence or presence of cranial bones; of freely movable gill- covers, and suspensoria; of maxillary and premaxillary, and of mandibular bones. In the Hasmobranchii and Marsipobranchit, there are no cranial bones; and with regard to the praemaxillary and maxillary bones, it can only be said, that the sites which those membrane-bones occupy in other fishes may, perhaps, be considered | as marked out in these orders by the presence of certain labial cartilages. The Chimaerae differ from the other Hlasmobranchii, the Sharks and- Rays, in having a movable operculum and an immovable suspensorium, and in this latter particular the non- mandibulate Marsipobranchii more or less closely resemble them. The Zeleoste: and Ganoidei differ from these Fishes by possessing eranial, maxillary, praemaxillary and opercular bones. Their oper- cula and suspensoria are always movable. In the Hasmobranchii the skull is distinctly articulated to the first trunk vertebra. In the Chondrosteal Ganoidei, the largely developed parasphenoid reaches for a considerable distance back- wards underneath the anterior vertebrae ; whilst in the Holostean Ganoidei and many Physostomous 7e/eoste:, the first and some of the following vertebrae may be suturally connected with the basi- occipital. In other osseous Fish the basi-occipital presents a concave conical cavity for apposition with the similar one upon the anterior Characteristics of the Vertebrata. Ibrocet surface of the first vertebra ; and the biconical cavity thus formed is filled with a structure formed by the development of the chorda dorsalis, and of semi-gelatiniform consistence. Fish are very rarely edentulous. Teeth are ordinarily present, and are very variable in number, shape, and situation. Most of the bones of the oral and pharyngeal cavities may be dentigerous; but in Cyprinoids, there may be only a single tooth superiorly, carried by the basi-occipital. The teeth are replaced as often as they are shed, and in the family just mentioned, the inferior pharyngeal are so shed and replaced periodically. It is only in Fish that the dental series is continued in an unbroken row across the middle line, without forming a diastema corresponding to either upper or lower median raphe. Fish have no oral salivary glands, and the tongue is only movable as a part of the hyoid apparatus upon which it is earried. In the Marsipobranchii, the branchial sacs open both in- ternally and externally by the means of larger or smaller ducts, which again may form a common duct before their inner or outer termination respectively. In all other Fishes the branchial inlets and outlets both have alike the form of fissures, the inlets leading directly from the interior of the pharynx, and the outlets opening either directly on to the external surface of the body, as in the Sharks and Rays, or into a branchial cavity covered by the opercular apparatus as in Chimaerae, Dipnoi, Ganoidei, and Teleoste:. The oesophagus is ordinarily short; and it is also, as the food is usually swallowed with little or no comminution, of considerable width. In the Marsipobranchii, the digestive tract takes an antero-posterior course, without any external differentiation into stomach and in- testine. In other Fishes the intestine is readily distinguishable from the siphonal or coecal stomach ; and describes one or two convo- lutions before terminating at the anus through the intermediation of a short rectum, from which a colon can scarcely be said to be differentiated. The length of the entire tract is shorter relatively to that of the entire body than in the air-breathing Vertebrata gene- rally ; it is however not inconsiderable in the species which support themselves upon vegetable diet ; and the absorbing surface of the canal is greatly increased in Dipnoi, Ganoidei, and Elasmobranchi, by the development of internal folds of the mucous membrane into a spiral valve, which appears to be rudimentarily represented in the Marsipobranchii by a longitudinal ridge running along the mternal lxxil Introduction. surface of the intestine. In the three more highly organized of the four orders just mentioned, a duodenal segment is distinguishable in the small intestine anteriorly to its valvular portion. This seg- ment is known as the ‘ Bursa Entiana’ in Elasmobranchii, where it is of considerable size, and marked externally by the entrance of the functional biliary and pancreatic, and the rudimentary omphalo- mesenteric ducts. The rectum always opens anteriorly to the urinary and genital ducts; except when these tubes open upon its dorsal surface near its termination, so as to constitute a cloaca. The suspensory mesenteric laminae often become largely fenestrated, or may disappear altogether in consequence of absorption, in adult Fish. A liver is always present; it is ordinarily unilobar; in some Fish it is multilobar; in the Cyprinoids it is trilobed, and interdi- gitates with the convolutions of their intestine, much as the lobes of the liver do in many of the Gasteropoda. There may be several gall ducts, and a gall bladder is very rarely wanting. Secretory coeca, the so-called ‘pyloric appendages, are developed in many Fish upon the commencement of the intestine. They are very variable in number, and ordinarily simple and distinct, though sometimes ramified and bound together more or less closely. A glandular pancreas of smaller size but more compact structure, coexists some- times with these pyloric appendages. The heart consists of a branchial auricle and ventricle, to the former of which a sinus venosus is superadded, and to the latter, except in Marsipobranchii, an arterial bulb, which breaks up into branches corresponding’ in number to the gill arches. In the Ganoidei and Hlasmobranchii, the arterial bulb has a layer of transversely striped muscular tissue in its walls, and several rows of valves in its interior ; whereby it is enabled, as in Amphibia, to act as an accessory ventricle. The muscular fibre of the arterial bulb of Ze/eostei is not of the striped variety, and the bulb has only two valves internally. In the Dipnoi a second auricle exists, which receives blood brought back to the heart from the pulmonary air sacs. The systemic aorta is formed, in the embryo, by the confluence of the aortic arches into which the bulb divides; and, after the development of the ell fringes, for the supply of which these arches resolve themselves into efferent branches, by the confluence of the efferent branchial veins with which those afferent vessels are continuous through the intermediation of the aerating capillary plexuses. In the Dipnoi, Characteristics of the Vertebrata. [xxl as also in certain Muraenoid 7e/eostei, more or fewer of the branchial arches fail to develope gills, and the direct connections between the sub-branchially placed bulb and the sub-vertebrally placed aorta, which in other Fishes exist only in the foetal state, persist here throughout life. From each of the posterior aortic arches (Lepidosiren paradoza), or from each of the compound factors of the dorsal aorta made up on each side (Rhinocryptis annectens), a branch is given off to the cellular air sac ; and during the period in which these animals live out of the water, the aeration of their blood is dependent upon the ramifications thus formed there. The vein which brings the blood from the pulmonary air sacs back to the heart, instead of opening into the portal or hepatic vein, as the veins from the air-bladders of ordinary Fishes do, or into a vena cava inferior, as does the vein from the air-bladder of the Ganoid Polypterus bichir, opens independently into the ventricular cavity after dilating within the pericardium ; and thus, though diverging but a very little from the arrangements common in (uni-auriculate) Fishes, it constitutes a system analogous to and homologous with the pulmonary veins and auricles of higher Vertebrata. Ordinarily in Fish, the blood from the parts of the body posterior to the heart exclusively of the chylopoietic viscera, is collected into the two subvertebral venae cardinales, which meet the two venae jugulares from the anterior parts of the body, and form with them the trans- verse ductus Cuvieri which open into the sinus venosus. The hepatic veins, which bring the blood of the chylopoietic viscera back to the heart, very ordinarily end by opening into the sinus venosus, with- out receiving any factors from any other than those organs. A true vena cava inferior is constituted in some Fishes, as in the Perch amongst Ze/eostei, and in the Polypterus amongst Ganoider, by the fusion either of veins from the air-bladder with veins from the genital glands as in the former of the two Fishes named, or of a vena cava sub-vertebralis impar with veins from the bifid air-bladder as in the latter. A renal-portal system is present, except in the Marsipobranchii ; it is constituted either by caudal and dorsal veins both or by the latter only ; and anastomoses, though not always, with the hepatic portal system. The Teleostei, Ganoidei, Dipnoi, and Chimaerae have free oper- cular valves covering a more or less extensive branchial cavity. The gills of Ze/eostei are ordinarily four, and are never more than \ Ixxiv Introduction. four in number. They are usually found to form double comb-like rows upon each branchial arch; but the last of the branchial arches very commonly fails to develope more than a single row of gill- processes ; and not rarely is wholly gill-less. This reduction may be accompanied by a similar reduction in the gill arch immediately in front, and we find the third arch carrying a uniserial gill in Malthea, whilst it is gill-less in the Cuchia (Amphipnous). The fifth branchial arch, which is dentigerous in most, and branchiferous in no Teleostet, has a uniserial gill developed upon it in the Dzpnot and in Hexanchus. All the Elasmobranchii, the Dipnot, and the Ganoidei, with the exception of Polypterus and Planirostra, have a uniserial gill developed upon the opercular arch anteriorly to the most anterior of the gill-laminae developed in Zeleostet. In the Sharks and Rays this anterior gill forms the anterior fixed gill lamina of their anterior gill-pouch ; in the Chi- maerae and Ganoidet, it forms the so-called ‘opercular’ gill. In the Dipnoi, the development of the opercular gill appears to have prevented that of the two biserial gills placed next posteriorly in typical fish ; in the American species the gills of the third branchial arch appear to have been lost also, whilst they persist in the African, as do those of the fourth and fifth branchial arches in both species. Except in Hexanchus and Heptanchus, there are only five gill-sacs in the Sharks and Rays, the last of which contains only a single gill-lamina disposed upon its anterior wall. This half-gill is homologous with the posterior row of the biserial gill developed upon the fourth branchial arch of T'e/eostei, but it is not represented in the Chimaerae. The pseudobranchia of osseous Fish is homologous with the spiracular pseudobranchia of Ganoidez and Hlasmo- branchii, and not with their anterior functional half-gill, nor with the thyroid vaso-ganglion, which in many Fish underlies the anterior basi- branchials. In osseous Fish, the pseudobranchia receives arterialized blood from the first branchial efferent vein ; and it serves as a diver- ticular rete mirabile for the eye within which the vessels proceeding from it develope the so-called ‘choroid gland. In the Hlasmobranchii, Ga- noider, and Dipnoi, it serves as a rete mirabile for the brain as well as for the eye, but it has no ‘choroid gland’ developed in connection with it. Accessory aerating organs which enable the fishes possessing them to support respiration when out of the water, are developed in several genera of T'eleostei (Anabas, Saccobranchus, Amphipnous), in relation with the interior of their branchial cavity. The morphological identity of the functionally pulmonary air-sacs of the Dipnoi with the air-bladder of an ordinary Teleostean Fish; which Characteristics of the Vertebrata. xxv is functionally all but exclusively hydrostatic, may be considered to be established by a comparison of those lung-like air-sacs with the air- bladder of the Ganoid Polypterus, which is somewhat similarly bifid, and opens similarly into the pharynx by an air-duct entering it on its ventral surface. From the air-bladder of the Polypterus to that of the Lepidosteus, which however opens into the pharynx from its dorsal side, and which, though divided internally into two longitudinal compartments, is yet externally a single sac, the transition is not abrupt ; nor that from such air-bladders as those of the Lepidosteuws and the Physostomatous Teleostei, to the ductless air-bladders of the Acanthopteri and other bony Fish. The swimming bladder is developed as an outgrowth from the oesophageal portion of the digestive tube, and its ductus pneuma- ticus, when persistent, ordinarily communicates with this portion of the tract. Both bladder and duct are absent in the JMarsipo- branchii, and, except as rudimentary structures in certain Sharks, in all Hlasmobranchii also. The duct is aborted in the majority of Teleoster (the Acanthoptert, Pharyngognathi, Lophobranchu, Plec- tognathi), but is present in the remainder of this order, nearly corresponding to the Malacopterygii of Cuvier, and hence called Physostomi, as also in all Ganoidei and Dipnoi. With the presence or absence of an air-duct to the air-bladder, the presence or ab- sence of bone corpuscles appears to be nearly universally correlated. The shapes which the air-bladder assumes are very various, es- pecially when it is ductless. In many Acanthopteri it sends two prolongations into relation with the caudal muscles, whilst in many Physostomi (Cyprinoideae, Siluroideae, Clupeidae), its ante- rior prolongation is brought into relation with the auditory ap- paratus. : It is only in the Hlasmobranchii that a secondary kidney takes the place of the primordial Wolffian body, which remains as the functional renal organ in other orders of Fishes. This difference is illustrated not only by the difference of form and of compactness of the renal organs in the H/asmobranchii, but also by the facts that in the females of this order the oviducts open separately from the ureters into the cloaca ; that in the males the vasa deferentia are in some species (Mustelus laevis) bestudded with what is probably the remnants of Wolffian bodies for nearly their entire length; and that the ureters are developed mainly along the internal, and not lxxvi Introduction. as in Amphibia along the outer edge, or as in many Te/eostet, along the anterior or inferior surface of the renal glinds. Uro- genital canals are formed in Ganoidei of both sexes, and in the males of Llasmobranchii. In the Teleostei, the ureters often fuse into an azygos duct, which opens above, or behind, or to- _ gether with the generative duct, but always posteriorly to the anus. The urinary bladder may take the shape of a bilateral dilatation, as in the Sharks and Rays; or that of a vesica bi- cornis, as in some Ganoidei ; or of that an azygos sac, as In many Teleostei, The encephalon fills the brain-case in the embryonic Fish, but subsequently, by the disproportionate growth of the cranial walls, it comes to occupy a very small space in the cavity which they inclose, the intervening space between it and the perichondrium or periosteum, as the case may be, of the cranial vault being filled with a mass of loosely compacted tissue, richly laden with fat. The membranes, in relation with the external and internal surfaces of the cerebro-spinal centres, develope pigment cells as in Amphibia. The nerve-centres are smaller in relation to the body in this than in any other vertebrate class; the relation of the encephalon to the body is stated as being on an average as low as 1 to 3000; and the spinal cord of a Sturgeon which weighed 120lbs., has been stated to have been no thicker than that of a Frog. The spinal cord is ordinarily, but not always, devoid of any enlargements, and of uniform diameter throughout its length, which is usually com- mensurate with that of the spinal canal. The cerebellum is very variable in size, but it sometimes, as in Sharks and in the Tunny, attains a greater size relatively to the rest of the brain in this than in any other vertebrate class. It is never bilaterally bilobed, as the divisions of the brain placed anteriorly to it are. The optic lobes are frequently in osseous Fish larger than any other division of the brain, a proportion which they never attain to in any other class. The diencephalon, the homologue of the optic thalami, fails in some Teleostei, as also in the Dipnoi, to be differentiated from the mesencephalon or optic lobes behind, and the prosencephalon in front of it; but in many other Ze/eostei, in the Ganoidei, and Elasmobranchit, this division of the brain is considerably elongated antero-posteriorly, and bounds a ‘ third ventricle’ by its two halves. In the Sharks and Rays, the prosencephalon attains the preponder- Characteristics of the Vertebrata. Ixxvil ance relatively to the other divisions of the brain, which it main- tains in the higher Vertebrata, and developes lateral ventricles in its two halves, which communicate with similar cavities in the rhinencephalon. These two divisions of the brain are solid in most Fishes, the rhinencephalic lobes appear to be attached laterally and by peduncles to the prosencephalic in the Elasmobranchu ; they are pedunculate in many Ze/eostei, but sessile in the Ganoider. Besides developing in Si/wrws and Cyprinoids a supero-median ‘lobus impar,’ or ‘nodulus,’ the medulla oblongata presents in various families certain lateral ganglionic enlargements, which, from their connection with peripheral nerves, are known in Cypri- noids as ‘ vagal,’ as ‘/obi nervi trigemini’ in the Sharks, and as ‘electric lobes’ in the Torpedo. In Dipnoi, and to some extent in Marsipobranchii, the muscles of the eye are supplied by the fifth nerve; and in most Fishes the nervous supply of the superficial structures in the maxillary, hyo- mandibular, and palatine regions supplied in higher Vertebrata, with the exception of the Anurous Amphibia, by the portio dura of the seventh pair, is dependent partly upon factors from the fifth nerve, as well as upon an independent stem. The nervus lateralis which supplies the sensory organs of the lateral line, as well as the medio- dorsal region of the trunk, anastomosing in its course with the spimal nerves externally, much as the sympathetic chain anasto- moses with them within the thoracico-abdominal cavity, is in Elasmobranchii, Ganoidei, and many Physostomous Te/eoste:, con- stituted by the vagus. In some osseous Fish (Gadus), it is formed chiefly by the fifth nerve. The glossopharyngeal is not always differentiated from the vagus, and in some Rays it interchanges fibres with the auditory nerves. The spinal accessory nerve does not exist in Fish, and the place of the hypoglossus is taken by the first spinal nerve. The existence of the sympathetic has not been demonstrated in Marsipobranchii ; in Teleoste: the bilateral gang- hated chain does, in E/asmobranchii it does not, extend into the caudal region. Organs of tactile sensibility are constituted in some Fishes by the development of flexible rays upon their fins; in some others, and more commonly, by that of similar structures, in the shape of barbules upon the snout; but in most cases by the muco-nervous organs developed upon the head, where they are supplied by the lxxvili Introduction. trigeminus, and upon the trunk along the lateral line. The ol- factory organ is an azygos sac in the Marsipobranchii, hence called ‘Monorrhina;’ it ends blindly in the sub-order Petromyzontidae, which are hence called ‘ Hyperoartii,’ but opens into the pharynx in the Myxinoids, hence called ‘ Hyperotreti. All higher Verte- brata have paired nasal sacs, and have consequently been styled ‘Amphirrhina.’ In the Dipnoz, the nasal sacs have valvular poste- rior openings, externally to the pterygo-palatine teeth; in all other amphirrhine Fishes they end blindly. The eyes are relatively large in Fish, the cornea is flat, the lens spheroidal. The L/asmobranchia possess eyelids, and sometimes a membrana nictitans. A peculiarly piscine rete mirabile, the ‘choroid gland,’ exists in most Fishes, except the Hlasmobranchii and Ganoidei, between the layers of the choroid, where it surrounds the entrance of the optic nerve. A structure homologous with the ‘pecten’ of Birds exists in many Teleostei, where it is known as the ‘ processus falciformis.’ Certain structures, consisting of pigment specks with lens-like bodies inlaid in their substance, have been found regularly arranged between the branchio-stegal rays, upon the head, and in two pairs of longitu- dinal rows on the ventral surface of Chauliodes and Stomias, and have been regarded as accessory eyes. The auditory apparatus of the Marsipobranchii consists of a vestibule, with, in Myxinoids one, and in Petromyzontidae two semicircular canals, contained in cartilaginous capsules attached to the skull laterally. In all higher Fishes there are three semicircular canals. In the Sharks and Rays, and in the Dipnoi, the mem- branous labyrinth is entirely surrounded by the cranial walls, but in the Chimaerae, the Ganoidei, and the Teleostei, a median portion is always to be found lying free in the cranial cavity. The air- bladder of some Acanthopteri, and of many Physostomous Ze/eos/ei, comes into relation with the membranous labyrinth, either directly or through the intermediation of ossicula. In Llasmobranchu canals exist, marking the line along which the integument was invaginated, to form the ‘internal ear.” ‘The electric organs of Fishes are not represented in higher Vertebrata. They are most largely developed in the Torpedo and Gymnotus, and in a lower degree in Malapterurus and Mormyrus. They are found in various parts of the body, but consist essentially of prismatic columns, made up by the superposition of flat plates, to which nerves from Characteristics of the Vertebrata. xxix the fifth and eighth pairs, and from the spinal series, are distri- buted. The nerves fuse with one surface of these plates, which is electro-negative, whilst the other is electro-positive. In several species of the genus Serranus, a testis has been ob- served overlying the ovary, and a similar hermaphroditism has been observed occasionally in Cyprinoids, and in some other Fishes. On the other hand, asymmetry is often, as in the Perch, seen to be produced by the stunting of one or other of the (typically sym- metrical) ovaries. The reproductive glands in the two sexes are often so much alike externally, that an examination of their sub- stance is necessary for deciding the sex to which they belong. Sometimes, however, and especially at the breeding season, the sexes may be distinguished by external differences. Fishes are mostly oviparous, but are sometimes viviparous. Rudimentary in- tromittent organs exist in the male Elasmobranchii, as the so-called ‘claspers.’ Sexual congress or contact takes place in many ovi- parous as well as in the viviparous Ze/eostev. The products of the generative glands sometimes find their way into the water by extrusion, by an abdominal pore or pores, as in Marsipobranchiu, Anguilla, and the females of Salmonidae, from the abdominal cavity into which they have been set free by dehis- cence. But in most TZe/eostei, the walls of both the generative glands are directly continuous with their ducts, so that neither ova nor spermatozoa are ever set free into the peritoneal cavity. This is the case also in Lepidosteuws amongst the Ganoidei ; but in the other members of that order, the sexual products of both kinds are taken up after dehiscence by the open mouths of ‘ Fallopian tubes.’ In the Hlasmobranchii, where the ovary is single, and the mouths of the oviducts approximated, the lower parts of the oviduct are specially modified to secrete the shell in the oviparous Seyldium and in the Rays, and to serve as a uterus in the viviparous species of Squalidae. In the males of Llasmobranchii, as of all higher Vertebrata, the testis is continuous on each side, with an epididymis and a vas deferens. The lower segment of the vas deferens is expanded into a vesicula seminalis. The Hasmobranchii have large yolked ova with partial segmentation, and in Mustelus laevis, the vessels on the yolk sac come into such relation with the ma- ternal vessels on the walls of the uterus, as to form a sort of placenta. In osseous Fishes, where the ova are very much Ixxx Introduction. smaller, the segmentation of the yolk is more extensive than in Hasmobranchii, yut less so than in Mammals or Amphibia. In Marsipobranchii, as in Amphibia and Amphiorus, the intes- tinal canal is formed within the yolk sac, as the result of an invagination commencing at the future anus, proceeding from without inwards, and forming thus a tube without any umbilicus, within a cavity which is at once yolk cavity and peritoneal sac. Fishes, hke Amphibia, are competent not rarely to sexual fune- tions before they are mature in other particulars. Their power of repairing injuries, and reproducing lost parts, is confined to the fins. The capacity for growing as long as life lasts, which some Fishes are said to possess, may be explained by the facts that their bodies are, firstly, of very nearly the same specific gravity as the water in which they live; and, secondly, of a temperature which is but a very little higher than that which they are there exposed to. Thus the foree which in other animals is expended in the way of opposition to that of gravity, and in the way of producing heat, is available for sustaining continuous growth. The Class Pisces is divided into six orders—the Dipnoi, the Elas- mobranchit, the Ganoidei, the Teleostei, the Marsipobranchii, and. the Pharyngobranchiit. Of these the Dipnoi are to be considered the highest, as presenting in their organization many points of affinity to the Amphibia; the Hlasmobranchit and the Ganoider have the oldest known geological history of any members of the class ; they possess many characters in common with each other and with the Dipnoi, such as the abdominal position of the posterior pair of limbs; the retention ordinarily of more or less of the axial endoskeleton in a cartilaginous condition; the possession of an anterior functional uniserial gill, which is lost as such in osseous Fishes; and the possession of a spiral intestinal valve. Though coeval in geological time with the Ganoidei, the Llasmobranchii are a distinctly specialized, whilst the Ganoidei are a generalized type of Vertebrata. The Teleostec, and amongst them the Physostomi especially, are linked by many affinities to the Ganoidei. The Mar- sipobranchit may be looked upon as representing a very low grade of development of the type upon which the Elasmobranchit are con- structed ; the superaddition of specializations has however proceeded so far as to leave few points of positive similarity beyond those which an endoskeleton in great part or wholly cartilaginous; a branchial Characteristics of the Vertebrata. Ixxxl apparatus differing in its pouched arrangement and posterior po- sition from those of Ganoidei and Teleostei ; the absence of maxillary and intermaxillary cartilages; and the presence of a raised ridge along the intestine constitute. The sixth order, that of the Pha- ryngobranchii, are the lowest of Vertebrata; their claim to that title resting indeed not upon the possession by them of a vertebral column, but merely upon that of a chorda dorsalis, underlying a membranous neural canal, and overlying a cavity containing the organs of vegetative life. Its digestive tract appears to be formed as in many Invertebrata by an invagination commencing on the exterior of the germinal membrane, and it is to certain of the stages of its metamorphosis that certain similarly transitory phases in the life-history of certain sessile Ascidians have been stated to present a strong resemblance unknown in other Invertebrata. The Dipnot are represented by the Mud-fishes, Lepidosiven and Rhinocryptis, of the South American and West African rivers. They possess, in addition to small external gills, seen elsewhere amongst Fishes only in developing Elasmobranchii, and to func- tional internal gills covered by an operculum, a pulmonary auricle into which blood is returned from two pulmonary sacs. These sacs communicate with the digestive tract by a ventrally-placed opening guarded by cartilage; they receive blood in a venous, and return it in an arterialized state. The Dipnoi differ further from the Ga- noidei, the piscine order with which they are most nearly allied, and resemble the Amphibia in the communication of their paired nasal sacs with the mouth, in the possession of three external branchiae, in the internal structure of their arterial bulb, and in the microscopic characters of their chorda dorsalis. The totality of their organism however shows them to belong to the Sub-kingdom Pisces ; the persistence of the structure last mentioned ; the absence of vertebral centra; the development of eycloid scales; and; more distinctively, of the system of the lateral line; the presence of clavicular, of branchiostegal, of opercular bones, of dermal spines, and of a spiral intestinal valve; constituting a sum of characters which justify us in referring them to that class. The order Dipnot differs from the orders Elasmobranchii and Ganoidei, to which in so many points it appears to be more or less closely allied in the non- heterocercal character of the tail. In this particular it resembles on the one hand the lowest of the Fishes; and on the other, f lxxxil Introduction. the Urodelous and the larvae of the Anurous Amphibia; illus- trating well what is meant by the phrase ‘a generalized type.’ The Dipnoi resemble the Elasmobranchii and Ganoidei in having the posterior pair of limbs placed near the anus, as in all Verte- brata above the Teleostean Fishes in which a posterior pair of limbs is developed. The second order of Fishes, that of the Elasmobranchii, is repre- sented by the Sharks, Rays, and Chimaerae. They differ from the Dipnoi and Ganoidei in the following points besides those which their name connotes. They never have an air-bladder, except occa- sionally as a rudimentary structure; they have no cranial, nor clavicular bones; their exoskeleton has the form of ‘ placoid’ granules, not of scales; and in the males, accessory copulatory organs are developed. They resemble the Ganoidei in the hetero- cercal character of their tail; in the formation of their caudal haemal arches by costal elements; and in the possession of several rows of valves within their arterial bulb; of a coating of transversely striped muscular fibre on the exterior. of this structure; and of an optic chiasma. The order Ganoidei is divisible into two sub-orders—the Chon- drostet represented by the Sturgeons; and the Holostet represented by the Bony Pike, the Polypterus, and the Amia. They always possess-a freely moving operculum, supported by one, as in Stur- geons, or by several bony plates, and an air-bladder provided with an air duct. With a few exceptions, (Polypterus, Amia, Scaphi- rhynchus,) they possess an opercular gill as well as a pseudobranchia ; and a blowing cavity, the remains of the first visceral cleft, may exist together with, or independently of one, or other, or both of these structures. The angular or round enamelled scales, whence their name is taken, are ordinarily but not always present, the skin being sometimes naked and sometimes developing bony plates as in the Sturgeons. The extent to which ossification proceeds in their axial skeleton is, as the two subordinal names above given indicate, very various. he Holostei and especially the genus Amia, make a considerable approximation towards the Physo- stomous division of the Teleostean Fishes, by the distinct speciali- zation of maxillary and intermaxillary bones, and by failing to develope either the enamel on the scales, the fulera on the fins, or the gill on the operculum, so characteristic of Ganoidei generally. Characteristics of the Vertebrata. Ixxxill The Teleostei comprise an immense majority of existing Fishes. They may be subdivided into two great sub-orders: the Physostomi, which possess an air-bladder and an air-duct, and, with the ex- ception of the Pike, bone corpuscles in their skeleton ; and the Physoklisti (Haeckel) in which the air-duct is always absent, the air-bladder sometimes, and in which, with the exception of the Tunny, bone-corpuscles are wanting. The vertebrae vary much in number, and in the extent to which caleificatory deposit takes place in them; but they are always individualized, though the most anteriorly placed of them may be suturally united with each other and with the basi-occipital bone. The gill-fringes may vary in number accordingly, as upon each of four branchial arches a biserial or uniserial gill is developed; but they never exceed the number of four biserial gills, an opercular gill being never developed. They have always more than a single bone in the opercular valve. The cartilaginous cranium may either persist or disappear, but cranial bones are always developed in addition to it. The scapular arch has a clavicular element; the anterior fins are rarely absent ; the position of the posterior, which are much more commonly absent than the anterior, varies from the ‘abdominal’ to the ‘ tho- racic,’ and from the ‘ thoracic’ to the ‘jugular’ region. The aortic bulb is not provided with more than two valves, nor has it a covering’ of transversely striated muscular fibre. The optic nerves decussate, but do not form a chiasma. The fifth order of Fishes, the Marsipobranchii, consists of the two families of Myxinoidei and Petromyzontidae. Their sac-like gills are supported on a cartilaginous framework, which is more superficially placed than the analogous visceral skeleton of higher Fish. They have a single nasal opening, and have been hence called ‘ Monorrhina,’ in contradistinction to all higher Vertebrata. They have no mandible, and higher Vertebrata have, in contra- distinction to them, been on this account spoken of as ‘ Gnatho- stoma.’ They have no traces of air-bladder, of limbs, of limb- girdles, of cranial bones, of scales, of spleen, or of pancreas. Their tail retains the homocercal form characteristic of the early embryo in other Fishes. They have no vertebral centra. The sympathetic system is wanting, and the commencement of their aortic trunk has neither striped nor smooth muscular fibres developed upon it. The Myxinoids are less highly organized, being of parasitic habits, than f 2% lxxxiv Introduction. the Lampreys; their single nasal sac communicates with the pha- rynx, whence they are called ‘Hyperotreti ;’ whilst in the Petremy- zontidae, hence called ‘ Hyperoartii, it ends blindly as in other Fish. The embryos of Petromyzontidae go through a metamor- phosis, being blind and edentulous when set free from the egg. These larvae were formerly supposed to be a distinct species, and were known under the name of Ammocoetes branchialis. Like the larvae of some other Fish and of some Amphibia, they may attain sexual maturity whilst still in one of the stages preparatory to the perfect adult condition. The evolution of the sexual organs appears however to exhaust the powers of such larvae as attain to it, and to be incompatible with the completion of the entire curriculum of metamorphosis. The sixth order of Fishes, the Pharyngobranchi, are represented by a single species, the Lancelet, Amphioxus lanceolatus. These animals are somewhat vermiform in outline, semi-transparent, of small size, being only two inches in length even when adult, without either cranium or brain strictly so called, or any differen- tiation of the axial notochordal, or the primitive membranous neural canal. In this order we have pulsating vessels in the place of a saccular heart, whence the name ‘ Leptocardia’ has been given to it in con- tradistinction to that of ‘ Pachycardia,’ which expresses the condition of the central organ of the circulating system of all other Verte- brata. Another name, ‘ Acrania,’ indicates the fact that in corre- spondence with the absence of any other encephalic nervous centre beyond a dilatation in which the myelon ends, and which may be considered as homologous with the medulla oblongata, no cranial cavity is developed upon the anterior prolongation of the notochord. The mouth is surrounded by a cartilaginous ring, carrying ante- riorly tentacular outgrowths, whence the name ‘ Cirrhostomi’ has been given to this order. The digestive tract immediately pos- teriorly to the mouth is constituted by a multiperforate branchial skeleton, along the bars of which blood is propelled by contractile branchial arteries, and through the fissures of which the inhaled water finds an exit into a cavity homologous with a branchial cavity, and opening by a single orifice on the medio-ventral line, posteriorly to the middle point of the animal’s length. The blood- vessels, which pass from a sub-branchial vessel upwards along the Characteristics of the Mollusca. Ixxxv branchial bars, are collected into a dorsal aorta, which distributes blood to the various organs of the body. A portal system is rudi- mentarily represented by a vessel, which is formed by the veins of the intestine, and sends ramifications to a coecal outgrowth of that tube representing the liver. There is no lymphatic system, nor have any renal organs been discovered in this small Fish. The eye appears to be represented by an azygos pigment speck, sessile upon the anterior prolongation of the nervous axis. No auditory organ has been observed. The generative glands discharge their products by simple dehiscence into the cavity surrounding the branchial sac, whence they escape by the abdominal pore together with the respired water. The ova undergo complete segmentation ; the ciliated embryo is set free before the primitive streak and chorda dorsalis are differentiated, and goes through a peculiar metamorphosis. Sup-Kinapom, Mollusca. Invertebrata, in which the body is bilaterally symmetrical, but often not obviously so; in which it never is segmented nor pro- vided with articulated appendages ; and in which the length is usually less in relation to the bulk than in either Vertebrata, Ar- thropoda, or Vermes. The organs of animal life often attain but an insignificant degree of evolution in this sub-kingdom; whilst those of vegetative, which are ordinarily massed together in a sacciform envelope, may attain a great predominance in point of size, with which their precedence in order of development is to be correlated. The tegumentary envelope of these latter organs is almost always prolonged so as to form a mantle, which may itself entirely surround the body, and which usually furnishes it with an external shell, or shells, or test. A well-developed digestive tract, consisting of oesophagus, stomach, and intestinal segments, and never opening into the perivisceral cavity, though it is occasionally aproc- tous, is always present in Mollusca. It very rarely takes a direct antero-posterior course, but has almost always its terminal segment bent round go as to be approximated to the mouth, and when it is Ixxxvi Introduction. proctuchous, the anal outlet is very usually in close relation to the respiratory inlet. The hepatic organ is very various in shape, but is usually, as in most water-breathing animals, largely developed. A heart is usually but not always present; it is, when present, always systemic, receiving blood, when afferent veins are present, from the aerating and renal organs, or from the general lacunar system when no such vessels exist, and propelling it by an aorta to the main organs of animal and vegetable life respectively.. In many aquatie Mollusca, the external water can find its way by variously situated apertures, so as to become directly intermingled with the blood; in others, a multi-ramified water-vascular system appears to spread itself throughout the body, without becoming directly continuous with the blood-vessels. In some cases no specialized respiratory organs are present; in a few Mollusca aerial respiration is attained to, in most it is aquatie. The renal organ may be represented by a simple non-glandular sac, which communicates internally with the lacunar blood-vascular system, and externally with the circum- ambient medium. When its walls are clothed with glandular cells, it receives an abundant supply of venous blood, some of which is passed onwards to the aerating organs, and some sent directly to the heart. The nervous system may be reduced to a single ganglion, as in Polyzoa and Tunicata, and in the former class organs of special sense are wanting, except occasionally as rudiments. Reproduction may be either sexual or asexual ; and in the Po- lyzoa polymorphic zooids are produced by gemmation. The ova undergo entire segmentation, except in the Cephalopoda; and with the exception of that class, and a few Gasteropoda, of the pulmonate order mostly, the embryos go through metamorphosis subsequently to being set free from the egg. The great majority of Mollusca are water-breathers, and marine in habitat ; some however are fluviatile, or lacustrine; and a few are terrestrial and pulmonate. A few Mollusca are parasitic. Entoconcha mirabilis inhabits the perivisceral cavity of a Synapta; in the genus Hulima, which preys upon Holothurioidea, some species are ento-, others ecto-parasitic. Stylifer lives ecto- or pseudo- parasitically attached to the soft tissues clothing the exterior of Asteriae and Echinoidea and Holothurioidea, as also within their digestive tract. Crenedla infests Tunicata; and Vulsella, Gastro- Characteristics of the Mollusca. Ixxxvil chaena, and Magilus infest certain Coelenterata; but, like certain Polyzoa, such as Lowosoma and Pedicellina, which attach them- selves to Vermes as to other marine objects, are not parasitic in a strict sense. The Sub-kingdom Mollusca contains two great divisions or pro- vinces—the Mollusea proper, under which are comprehended as classes the Cephalopoda, the Gasteropoda, the Pteropoda, and the Lamellibranchiata; and the Molluscoidea, under which are compre- hended the Brachiopoda, the Tunicata, and the Polyzoa. The Mol- lusea proper are distinguished firstly by the great development of their organs of animal life. Their motor organs consist of a ‘ foot,’ which may be of very various shapes, and is divisible morphologically, and sometimes actually, into a ‘ propodium,’ ‘ mesopodium,’ and ‘ me- tapodium;’ and of an ‘epipodium,’ developed by the foot proper along its line of junction with the visceral mass. The names of the three classes, Cephalopoda, Gasteropoda, and Pteropoda, relate to the dif- ferences observable in these motor organs. The nervous system in all four Classes of Mollusca consists of three pairs of ganglia at least, which are sensory, parieto-splanchnic, and motor respectively ; and which, being mutually connected by commissures, form a collar round the commencement of the digestive tract. The organs of vegetative life in the Mollusca contrast with those of the Mollus- coidea in two chief points: firstly, their heart is all but invariably provided with one or two auricles, in correlation with their more perfectly developed and specialized respiratory apparatus, whence they have been called ‘ Otocardia ;’ and secondly, their digestive system is, also all but invariably, proctuchous. The three clagaes! Cephalopoda, Gasteropoda, Pteropoda, are placed together in one sub-division as ‘ odontophorous’ Mollusca, in contradistinction to the ‘bivalve’? Lamellibranchiata, by virtue of their uniformly possessing the peculiar dentigerous rasping organ known as the tongue, and. of their never possessing a bivalved shell. With these differences others are correlated, as will be detailed in the description of the class Lamellibranchiata. The Molluscoidea, as a sub-division, are deaneuished from the Mollusca proper by the following characteristics. They are not only, like the Lamellibranchiata, destitute of any prehensile or masticatory apparatus, and dependent therefore upon ciliary action for the ingestion of alimentary matters, but they are, with the )xxxvlil Introduction. exception of the Nectascidiae and a few Polyzoa, also devoid of organs for motion from place to place, at least in their adult state. The entire sub-division is aquatic, and, with the exception of a part of the Polyzoa, is marme. Most of its members are monoecious, and many are social, which the Mollusca proper never are. They always have a more or less indurated external envelope, which in two of the classes, the Tunicata and the Polyzoa, into which the Molluscoidea are divided, is sacciform ; and in the third, the Bra- chiopoda, takes the form of a bivalve shell. In this latter case the nerve-system attains a higher development in certain species than it ever does in either of the other two classes of Molluscoidea ; but as no Molluscoid has a ‘ foot,’ pedal ganglia are never developed, nor the three pairs of ganglia characteristic of the higher sub- division of the sub-kingdom attained to. Ciass, Cephalopoda. Mollusca, in which the foot proper has its margins split up into tentacles, or into acetabuliferous arms, which are arranged so as to form a corona round the mouth. The epipodia, which in Pteropoda are the principal, remain, in Cephalopoda, important locomotor organs, forming as they do, by their partial or perfect coalescence, the ‘funnel, which is lodged in their capacious neurally-situated mantle cavity, and which by the contraction of the muscular walls of that cavity has water so projected into it as to effect the peculiar backward swimming movement characteristic of the class. Move- ment from place to place in the way of crawling is effected by the multifid foot proper. By virtue of the high evolution of ‘their organs generally, and especially of those of animal life, such as the eyes, the Cephalopoda are by common consent placed at the head of the Molluscan Sub-kingdom; by the retention, however, of a bilateral arrangement relatively to a median antero-posterior plane in many organs, and especially in those of vegetable life, they show indications of affinity to lower Mollusca, which are lost in the inter- mediate classes of Gasteropoda and Pteropoda. The Cephalopoda are divided into two orders, according to the number of their gills; the Tetrabranchiata being the less, and the Débranchiata the more highly organized of the two. All Cephalopoda possess an internal cartilaginous framework which supports and protects their nerve- Characteristics of Cephalopoda. lxexxax collar and their organs of special sense; the Zetrabranchiata, in which the internal skeleton attains much less importance than it does in the Dibranchiata, have an external shell; and the Dzdran- chiata ordinarily possess an internal calcareous shell, as in Sepra, Belemnitidae, and Spirula, or a rigid support of conchiolin, as in Lo- liginidae. The Octopodidae, however, in which locomotion ordinarily is of the crawling kind, are devoid, with the exception of Cirrhoteu- this, of any internal shell distinct from their various internal car- tilaginous supports. The external shell of the female Argonautidae is secreted by the external surface of the expanded ends of their two mesially-placed dorsal arms; the body of the animal is not attached to it by the insertion of any muscles, and it is not homologous with the external shell of the Nautilus, nor indeed with that of any other Molluse. The tegumentary system is distinguished, except in the Tetrabranchiata, by the absence of cilia, and by the presence of chromatophores, and of certain more deeply-placed lamellar cells upon which their well-known power of changing colour depends. The organs of animal life being all highly developed, those of digestion, circulation, and respiration are so also in subservience to them. The entrance to the digestive tract, besides bemg armed with a rasping tongue, is further furnished with a powerful ex- ternally-placed beak resembling that of a parrot, but having its posterior segment the larger of the twa. Though the animals are exclusively carnivorous and marine, they have always, with the exception of the Te¢rabranchiata, a very largely developed salivary system. A crop, and also a spiral stomachal coecum, are usually present; as also glandular appendages, which, as being distinct, at least to the naked eye, from the great mass of the liver, have been regarded as pancreatic. The intestine proper does not describe any complex convolutions in its course to the anus, which opens always in the middle line of the mantle cavity, and contributes thus, with other arrangements, to give these animals their very obvious appearance of bilateral symmetry. The systemic heart consists of a single ventricle, the walls of which, in the higher Cephalopoda at least, are composed of trans- versely-striated muscular tissue. The branchial veins which return the aerated blood to the heart have, in some species of those orders, dilatations developed upon them representing auricles: and in addi- tion to the systemic heart, we find in all the Dibranchiata accessory xe Introduction. branchial hearts, developed upon the great afferent branchial veins. In the Dibranchiata the peripheral circulatory system appears to be closed, consisting of arteries connected by capillaries, in many organs at least, with the veins or great venous sinuses into which the veins expand. In the Zetrabranchiata the blood appears to be more widely distributed throughout the various perivisceral cham- bers than it is, according to Mr. Hancock, in the Dibranchiata ; and as the external water finds in the former free access to the various perivisceral cavities, it would appear that it may thus come, as it does, according to some authorities, in the latter order also, to mix directly with the blood. The gills are in the Dibran- chiate order attached in their entire length to the interior of the mantle cavity, upon the contraction of the muscular walls of which they are, in the absence of any cilia upon their external surface, dependent for fresh supplies of water and aeration. The gills of the Nautili differ from those of the Dibranchiata not only in their number, but also in being attached only at their bases. The renal organs take the shape of bilaterally symmetrical spongy appendages to the stems into which the vena cava divides, and which carry its blood to the similarly bilateral gills. Certain orifices in the bran- chial chamber exist, by means of which the secretion of these organs can more or less directly find its way into the external water. The three typical pairs of excitomotor ganglia are readily recog- nizable in the Cephalopoda as in all other Mollusca proper, the anterior position of the pedal ganglia and of their cerebro-pedal commissure to the visceral or parieto-splanchnie ganglia, and their cerebro-visceral commissure, being as readily demonstrable in these, the highest, as in the Lamellibranchiata, the lowest of the Mollusca proper. The accessory nerve-systems, however, which this latter class does not possess, attain a high development in the paired stomatogastric, parietal, and branchial ganglia, as also in the un- paired stomachal and other visceral ganglia of Cephalopoda. An olfactory organ appears to exist in Cephalopoda in addition to the highly-developed eyes and the auditory organs. The Cephalopoda are always dioecious. The reproductive glands differ from most of their other organs in not being’ bilaterally symmetrical, and they differ from those of all other Invertebrata, except certain of the Vermes, in setting free their respective Characteristics of Cephalopoda. x¢i products into the cavity of a compartment of the perivisceral space, whence they are taken up by the open mouth of the effe- rent generative duct, as the ova in most Vertebrata are taken up by the Fallopian tubes. The oviducts are bilaterally symmetrical in the sub-order Octopoda, and in the genus Ommastrephes ; but both male and female efferent ducts are in all other Cephalopoda unpaired like the glands with which they are in relation. The male and female Cephalopoda are distinguishable from each other by external differences, and most markedly by the modification of one of the arms or tentacles of the males to serve as an intro- mittent organ, the so-called ‘ Hectocotylus,’ which in some species, Argonauta argo, Octopus carena, Tremoctopus violaceus, and Tremoc- topus Quoyanus, is set free from the male animal, and, probably, reproduced after each act of sexual congress. The Cephalopoda differ from other Invertebrata in the very large proportion of the yolk which escapes segmentation; and with the large size of the nutritive yolk we may correlate the fact that the embryos do not undergo any metamorphosis after leaving the ege. The Tetrabranchiate differ from the Dibranchiate Cephalopoda in the following particulars besides those which their name connotes. They have an external shell, to which the body is attached by strong muscles, but no ink-bag; their tentacles are much more numerous, but are not armed with the suckers which gave the Dibranchiata their name of ‘ Acetabulifera;’ their internal cartila- ginous skeleton is limited to the head, and does not there form a perfect ring; the two halves of their ‘funnel’ are not anchylosed, but project by two free edges into the mantle cavity, where they form a tube by mutual apposition; their blood-vascular system ap- pears to be less sharply differentiated from their water-vascular or perivisceral, and their eyes are pedunculate. The families Nawtilidae and Ammonitidae make up the entire order Tetrabranchiata, and are represented in the Silurian formations by numerous genera, species, and individuals, whilst at the present time the order is represented only by the rare Nautili, the living species of which are variously stated to be two, four, or six. The more highly- organized Dibranchiata have attained their greatest development as an order in the modern Period, but make their first appearance in the Triassic formation. They are divided into three sub-orders— the Decapoda calciphora, to which the existing Spirulidae and X¢cll Introduction. Sepiadae, and the extinet Belemnitidae are referred; the Decapoda chondrophora, which do not possess a calcified shell, but a horny ‘pen’ or ‘ gladius;’? and the Octopoda, which, with the exception of Cirrhoteuthis, have no internal shell. Crass, Gasteropoda. Mollusca, distinguished as a class from the Pteropoda and Cepha- lopoda most obviously by the characters of their ‘ foot, which is ordinarily flat and sole-shaped, and adapted for crawling. Usually the foot is not divisible into a propodium, mesopodium, and meta- podium, though the posterior part of the organ is nearly always well developed, and even when no division exists to denote its typically trifid character, the presence of an operculum frequently enables us to differentiate its metapodial portion. In the Hetero- poda however, and in the Stroméidae, the three divisions of the foot are very clearly distinguishable; and the epipodium is occasionally recognizable, as in Aplysia and Turbo. The foot proper may be longitudinally divided for crawling, as in Phasianella, or expanded into lateral lobes for swimming, as in Gasteropteron and Bullidae ; or it may be adapted for the purpose of swimming by being con- verted anteriorly into a vertical fin, whilst it retains its ordinary caudate shape posteriorly, as in the Heteropoda. Finally, the foot may be merely rudimentary, as in Glaucus, Ianthina, and Vermetus. The Gasteropoda count among their number the only representa~ tives of the Sub-kingdom which have attained to aerial respiration, and they form by far the most numerous of all Molluscan, and, with the exception of the Insecta, of all animal Classes. Their digestive tract is almost invariably more or less convoluted, and with the exception of the parasitic Hntoconcha mirabilis, and possibly a few Apneusta (see Baur, Nova Acta, 1864, p. 71), it is always proctuchous. The mouth and anus are ordinarily near to each other, but are never in the same median plane. In certain Ajpneusta and Nudibranchiata, the intestinal tract takes a straight antero-posterior course, but is provided with lateral gastro-hepatic diverticula, which give it much the appearance of the digestive tract of one of the Dendrocoelous Planarian or Trematode Vermes. The heart, which has been supposed to be absent in the Gasteropoda just mentioned, does not seem to be so in any member of the class Characteristics of Pteropoda. xclil except the Hntoconcha and Rhodope ; it is sometimes, as in Chiton, Neritina, Haliotis, perforated by the rectum, as is the case in the Lamellibranchiata, to which some of these Gasteropoda furnish an additional point of resemblance in possessing two auricles. In many, though probably not in all Gasteropoda, the perivisceral cavity is in direct communication with the blood-vascular system. There may be no specialized organ of respiration; gills, however, are ordinarily present, except in the Pwlmonata, where atmospheric air is inhaled into a cavity formed by the mantle. The renal organ is single. The Gasteropoda may be either dioecious or hermaphrodite. In a few dioecious species which are, as Vermetus and Siliquaria, fixed to one spot, there is no sexual congress, but the ova are fertilized by the spermatozoa findmg their way to them after being set free into the water; and in a few of the hermaphrodite species, such as Tergipes Edwardsi and Limnaea auricularis, heautandrous impreg- nation has been observed to take place. But with these exceptions, sexual congress always precedes impregnation, and indeed all re- production, in Gasteropoda. The accessory reproductive apparatus is greatly developed and complex in the hermaphrodite orders, Pu/- monata and Nudibranchiata, whilst in some of the dioecious orders, Cyclobranchiata and Aspidobranchiata, even the intromittent organ may be wanting’, and microscopic examination may be necessary for the distinguishing of the sexes. Gasteropoda are all but universally oviparous, the yolk undergoing segmentation, and manifesting the phaenomenon of rotation whilst within the egg. When the embryo is set free from the egg, it ordinarily goes through a metamorphosis which is marked by the possession of a provisional organ in the shape of a bilobed ciliated locomotor velum. The embryos of the Pu/- monata, in which order the ova may attain a very great size, may possess from the first the form and organization of the adult animal, but provisional organs have been observed in their development (Limax) as in that of Branchiogasteropoda. CLass, Pteropoda. Mollusca of small size varying from 1” to 3” in length, of pelagie habitat, of nocturnal habits, with the head and eyes rudimentary, and with the epipodia largely developed and constituting swimming organs, The foot proper is ordinarily much reduced im size and Xciv Introduction. importance, but its various divisions, propodium, mesopodium, and metapodium, may sometimes be all recognizable in the interspace between the epipodial alae. The processes corresponding to the propodium may be, like the arms of the Cephalopoda, armed with suckers ; and these latter structures may be, as in Clione Borealis, set in great numbers upon certain circumoral retractile upgrowths, which may correspond both to the acetabuliferous arms, and to the buccal membrane, (itself also sometimes, as in Lodigo, acetabuliferous in members) of that highest class of Mollusca. The Pteropoda may further resemble the Cephalopoda by having, as in Cleodora, their ordinarily large mantle cavity opening on the ventral or neural sur- face. This cavity, however, may open upon the dorsal surface, as in Gasteropoda, and it may be absent altogether, as in Clione. The heart consists of a ventricle and auricle, and gives off an anterior aorta which passes forwards through the nerve-collar to supply the epipodial swimming organs. The small size of their bodies enables them to dispense in most cases with branchial organs, both in the families provided with a shell (Zecosomata), and in those destitute of it (Gymnosomata). Their renal organ has the normal internal communication with the pericardial blood-sinus, as well as an opening on to the exterior, but its walls may be either merely hyaline, or con- tractile, without secretory tissue; or thirdly, spongy and glandular, as in the conchiferous families Hyalea and Cleodora. The eyes and, usually, the sensory tentacles are more or less rudimentary. Auditory vesicles are always present, and in relation with the pedal ganglia. The Pteropoda are hermaphrodite. The embryos go through a metamorphosis, being provided, when set free from the egg, with a bilobed ciliated velum, which is replaced by the epipodia. The Gymnosomatous Clionidae and Pneumodermidae go through a second stage of metamorphosis, in which they have three zones of cilia. Most of the points of degradation, or simplicity, observable in the structural arrangements of the Pteropoda, appear to be referrible either to their nocturnal habits, which have entailed a stunting of the cephalic organs, or to their minute size, which has rendered any complex evolution of the circulatory and respiratory organs unneces- sary. They have frequently been classed as an order of Gasteropoda, but the general relations of their motor organs and their mantle cavity appear to approximate them rather to the Cephalopoda, with- out however justifying us in ranking them as an order of that class. Characteristics of Lamellibranchiata. XCV On the other hand, the Pteropoda are closely allied to the Denta- lidae, the Solenoconchae of Lacaze Duthiers, or Prosopocephala of Keferstein ; and this aberrant order, though possessed of a ‘ tongue,’ of cephalic tentacles, and of epipodial lobes, as well as a foot proper, has nevertheless been separated from the Odontophora, on account of the many points of affinity which subsist between it and the Lamellibranchiata. The most important of these appear to be, the bilateral character of the organ of Bojanus, and of the gene- rative gland; the absence of any accessory reproductive organs, either glandular or intromittent; the absence of sexual congress and the consequent extra-corporeal fertilization of the ova; and the singleness of the larval velum. Each one of these points, however, is reproduced either amongst the Cephalopoda or the Gasteropoda, and the sum total of them therefore proves, not that the Dentalidae ought to be dissociated from, but merely that the Lamellibranchiata are rightly associated with the Odontophora, as Mollusca proper, notwithstanding these points of degradation. The organization of the Dentalidae is modified for their special habit of living immersed, during the daylight at least, in the sand; and as many of the points of difference between them and the natatorial Pteropoda may be explained by a reference to this peculiarity, whilst such points of resemblance as the likeness of their larvae to those of Pnumodermon and Clione are of purely morphological value, the two sets of animals may, as suggested by Mr. Huxley, be placed together in a class which would have very generalized affinities on the one hand to the Cephalopoda, and on the other to the non-odontophorous Mollusca s. Lamellibranchiata. Cuass, Lamellibranchiata. Mollusca, which, while agreeing with the other three classes of the Sub-division of Mollusca proper in the properties distinguishing it from the Sub-division of Molluscoidea, differ from them in having a bivalve shell secreted by a medio-dorsally attached and bilaterally symmetrical mantle, in the absence of odontophore, of salivary glands, of stomato-gastric and sympathetic nerve-ganglia, in the ereat size of the. collars formed by the cerebro-pedal and cerebro- visceral nerve-commissures, in the bilaterality of their reproductive glands, and in the absence of any accessory reproductive organs. XCV1 Introduction. In having their organs bilaterally symmetrical in relation to a vertical antero-posterior plane, the Lamellibranchiata differ from the Gasteropoda and Pteropoda, but not from the Cephalopoda. Their bivalve shells differ from those of the Brachiopoda in being placed one on either side right and left of the antero-posterior axis of the body; in being scarcely ever equilateral; in being very fre- quently equivalve, except as regards the hinge; and in having the hinge opened by the action of an elastic ligament, and closed by _ that of one or two transversely-running adductor muscles. Their foot is ordinarily compressed from side to side, so as to be hatchet- or ploughshare-shaped. It may be rudimentary, and not rarely secretes a ‘byssus,’ whereby the animal attaches itself to one spot. It never developes an epipodium, nor presents the trifid division into propodium, mesopodium, and metapodium. Movement is effected ordinarily by means of the foot; but in some instances, as Pecten, by the alternate opening and shutting of the valves. Two or more pairs of retractor, and one pair of protractor muscles, may be present to act upon the foot and visceral mass from bilateral points of attachment to the valves of the shell. In the absence of any pre- hensile or manducatory organs, the Lamellibranchiata are dependent for the ingestion of food upon the currents set up by the cilia covering’ not only all their external organs, except the outer surfaces of their mantle, but also lining their alimentary canal. The mouth is provided with labial tentacles, which are homologous with the arms of the Brachiopoda. The digestive tract has its anterior seements closely and inse- parably connected with the visceral mass made up by the hepatic, and in some cases by the reproductive coeca, after disengaging itself from which it, with some exceptions (Ostrea, Anomia, and Teredo), passes through the ventricle of the heart, before passing over the main adductor muscle of the two valves to end in a cloacal atrium. The ventricle of the heart is, with the exception of Arca, single, whilst the auricles are, with the exception of Anomia, bilaterally symmetrical relatively to a median vertical plane, like the gills and the organs of Bojanus. Gills are uni- versally present, and are in most cases two in number on each side. They take ordinarily the shape of laterally-compressed multi-fene- strated pouches, attached along the upper line of the mantle cavity, much as the leaves of a book are attached to the interior of its Characteristics of Lamellibranchiata. xcvil covers; but in some cases, as Pecten, Spondylus, Trigonia, owing to the absence of the antero-posterior elements of the lattice-work, the gills may be reduced to rows of comb-like processes, as in a Pectini- branchiate Gasteropod, or in an osseous Fish. Ordinarily, there are two gills on each side; there may, however, be only one, as in Lucina and Corbis; and in these cases it is always the external pair which is absent. It is later to be developed, and very often smaller, when present, than the inner gill; and in some cases it serves as a marsupial pouch, in which the ova are impregnated by the spermatozoa brought to them by the inhaled water, and go through certain stages of embryonic development (see p. 65, 7n/fra). The renal organ is always bilaterally symmetrical ; it consists ordi- narily of an excretory sac, which opens into the mantle cavity, and of a secretory lamellar and glandular sac, which opens internally into the pericardial blood-sinus ; but it may consist only of a single sac on either side, which communicates with its fellow, but prob- ably not with the pericardial cavity. The external orifice of the organ of Bojanus may receive the duct of the generative gland of its own side of the body, or that duct may open within the organ, or independently of it, but at a short distance from its external orifice. The Lamellibranchiata never possess any stomato-gastric nor sym- pathetic ganglia; but they may have accessory ganglia developed for the innervation of certain of their organs of animal life when these are largely developed, as in the cases of the siphons of some of the siphonate families, and of the sensory organs developed along the free edge of the mantle lobes. The Lamellibranchiata are, with a few exceptions, such as Os- trea and Cyclas, dioecious. The generative glands are always bilaterally symmetrical, and never possess any accessory glandular or intromittent organs. There is no sexual congress in this class ; the spermatozoa find their way to the ova either in the cir- cumambient water, or in the cavity of the mantle*; or in that of the outer gill; or in the cloacal space; or in the few viviparous species, Kellia, Galeomma, Montacuta, within the ovary itself. The embryos always go through a more or less complex metamorphosis, a See Description of Preparations, pp. 54-66, infra ; and Description of Plate V. pp. 193-198, ibique citata. uy Xevill Introduction. in which they are provided with a unilobar ciliated velum. The fresh-water species, as is often the case, go through less complex . changes than the marine; and in one instance, that of Cyclas Cor- nea, the foot, and not, as usual, the mantle with its shell, has been stated to have been the first organ which differentiated itself in the germinal membrane. The unilobar velum may be armed with a flagellum, and in the marine species come to resemble the homo- logous organ of the Dentalium. The Lamellibranchiata are mostly marine. They may be either fixed or free. They are never social in the sense of being organically connected, but the peculiarities of their reproductive functions render it necessary in their case, as in those of many similarly conditioned creatures, that they should be massed in considerable numbers upon the same spot. CLass, Brachiopoda. Molluscoidea with bivalve shells, which admit of being opened, though usually not widely, either by means of a hinge acted upon by muscles, or by muscles alone, but which are not provided with an elastic ligament as are those of the Lamellibranchiata, to which the term ‘bivalve’ is sometimes exclusively applied. The shell of the Brachiopoda differs from that of the Lamellibranchiata further in being almost always equilateral, but not equivalve, and in having its valves articulated across and not along the dorsal ridge. They are in the adult state always fixed; either, as ordinarily, by a peduncle which is attached to the internal surface of a ‘ ventral’ shell, placed in the living animal superiorly to a shell called, from its relation to the heart, ‘dorsal, or by the attachment of the ventral shell, then placed inferiorly, to some marine object. Larval Brachiopoda have been observed to move from place to place in two ways; viz. either by means of the ciliated epithelium covering their arms, which are then protruded as is the lophophore of a Polyzoon, or by means of spines implanted in the ventral lobe of the mantle. The Brachiopoda are ordinarily said to be dioecious, and in Thecidium the sex can be predicated from an inspection of the shell; but observations exist to show that hermaphroditism also exists in this class, as in some representatives of every molluscan Class, except the Cephalopoda. They are never social, though, as is Characteristics of Brachiopoda. XC1X ordinarily the case with animals which are destitute of the power of moving from place to place, and thus accomplishing sexual congress, they are found frequently placed closely together. They are always marine. They fall into two great Sub-classes, accordingly as they possess, or as they are destitute of an anus. The proctuchous Sub-class is represented by Lingulidae, Discinidae, and Craniadae ; the aproctous by Rhynchonellidae and Terebratulidae. The proctuchous Brachiopoda differ from the aproctous in having no hinge to their shell, in having a vasiform instead of a globular heart; in having a convoluted intestine instead of one describing but a simple curve ; in the much smaller evolution of their nervous system, the existence of which has not, as yet, been fully demonstrated; and in the limitation of their generative glands to their perivisceral chamber. In the existing species of Brachiopoda provided with a hinge, a calcareous process of greater or less length and of various shapes is given off from it for the support of the arms. Some fossil arti- culate Brachiopoda were destitute of these calcified supports, and they are absent in all the hingeless Sub-class. The mouth opens as a simple unarmed transverse slit between the two arms; and it is by the action of the cilia covering their cirri that the ingestion of food, as also the aeration of the blood, is effected. The mantle cavity, a very large part of which is occupied in all Brachiopods, and especially in the aproctous Sub-class, by the arms, is continuous through the oviducts or ‘ pseudo-hearts, with a multiramified sys- tem of interviscerally-placed cavities and canals, which make up the perivisceral system, and in Zerebratulidae are prolonged into the arms. The ‘ pseudo-hearts,’ or oviducts, consist each of them of two segments—the one which opens externally being tubular, and the one which brings the exterior communication with the peri- visceral cavities being of wider calibre. They appear to correspond with the organs of Bojanus in the Lamellibranchiata. They give passage outwards to the products of the generative glands. A nerve-system has been demonstrated in the hinged Brachiopoda, and consists of five ganglia, connected so as to form a collar around the commencement of the oesophagus. Three of these ganglia are placed below the oesophagus, and the other two at the base of the arms. g 2 c Introduction. For a monograph upon the organization of the Brachiopoda, see Hancock, Phil. Trans., 1858 ; see also Lacaze Duthiers, Comptes Rendus, 1865, u1., p. 800. For a monograph of the species Thecidium Mediterraneum, see Lacaze Duthiers, Ann. Sci. Nat., Ser. iv., tom. xv., 1861. For the microscopic structure of the shell, see Carpenter, Palaeon- tographical Society’s Memoirs, 1853, pp. 23-40. For an account of a larval Brachiopod with figures, see Fritz Miller, Reichert und Du-Bois Reymond’s Archiv., 1860, p. 72, Taf.1., figs. 1 and 2. See also pl. xi, fig. 2, and Description, pp. 232-234, i/ra. Cuiass, Tunicata. Molluscoidea, which may be either solitary or social, either fixed or free, but which are exclusively marine and are never aproctous. The animals communicate with the exterior by two orifices, pierced in a sacciform envelope, and here regarded as homologous with the inhalant and exhalant siphons of the siphonate Lamellibranchiata. As in those animals, the inhalant orifice brings into the organism not only food and oxygen, but also spermatozoa, which find their way to the ova by a route homologous to that described as taken from the neural to the haemal surface of the gill, by the male element in the Anodon (see pp. 64, 65, 7fra); and consequently over and along a structure which is regarded as the homologue not of a dilated pharynx, but of the gills of the bivalves. The external envelope of the Tunicata, from the external form of which the name ‘ Ascidiae’ was given to the class by Savigny, is of very various consistency, and of very various histological appearance ; but it always secretes cellulose within its substance, and is made in the way of conversion, and not in that of excretion as is the case in other members of the sub-kingdom. In Tunicata as in Lamelli- branchiata, the anus and generative ducts open into a space lined by the internal tunic, more or less separable from the muscular mantle; but in the cloacal space of the Tunicata there is no pos- terior adductor nor any specialized organ of Bojanus, though there is contained in it their single nerve ganglion, which supplies parts homologous with those supplied by the parieto-splanchnic of the Lamellibranchiata. The heart of the Tunicata is ordinarily elon- Characteristics of Polyzoa. cl gated and vasiform, with one end directly connected with that side of the branchial organ which is opposite to that nearest the rectum. Its action is periodically reversed during life; but this end of the heart may be regarded as the homologue of the vessels which bring blood to the heart, whilst the other end may be considered to represent the systemic aorta of bivalves. The Tunicata are her- maphrodite, but may multiply by gemmation as well as sexually. With the exception of Sa/pa, they all go through a metamorphosis, the larval form being caudate and active. The larvae of certain sessile Ascidians, Phallusia mammillata, Phallusia intestinalis, and Phallusia canina, have been recently described by Kowa- lewsky and Kupffer as possessing in their caudal appendage a structure closely similar to the chorda dorsalis previously held to be a distinctive characteristic of Vertebrata ; as having their nerve-centres formed by the fusion of lamellar upgrowths into tubes, in the manner which had been similarly supposed to be peculiar to the higher Sub-kingdom, thence spoken of as ‘bicavitary ;’ cylinder resembling the vertebrate chorda dorsalis either actually inter- posed between one part of their nerve-centres, or, at least, so placed, that if prolonged, it would come to be so interposed. . . . It may be added that Professor Gegenbaur, in the recently published second edition of his ‘Grundziige der Vergleichenden Anatomie,’ p. 158, 1870, has placed the Tunicata in the Sub-kingdom Vermes, assigning in justification of this step the fact that the peculiar specialization of the anterior segment of their digestive tract as a respiratory organ finds a parallel in the organ- ization of a rare order (or Class) of worms, the Hnteropneusti, represented by two species, the Balanoglossus clavigerus, and the Balanoglossus minutus found on the Neapolitan coast. See Kowalewsky, Mem. Acad. Imp. St. Petersburgh, Ser. vii., Tom. x. 3, 1866. Against this is to be set the close correspondence in the way of homologies which may be shewn (see infra, pp. 66-69, 235, 236) to exist between at least the adult Tunicate and the Lamellibranchiate organism. and finally as having the caudal axis- Cuiass, Polyzoa. Molluscoidea which are always social; and, with the excep- tion of Cristatella and, perhaps, also Lophopus and Selenariadae, always fixed in their adult state, in a ‘polyzoary’ or ‘ coenoe- cium.’ This structure, which is either erect or adnate, and, under cli Introduction. either of these conditions, may be either dendritic or foliaceous, is more or less flexible or rigid, accordingly as the ectocyst of each polypide is more or less hardened by calcareous or siliceous deposit. The animals are never aproctous, but there is only a single orifice in each cell for both mouth and anus, though, when the polypide is protruded, a considerable interval intervenes be- tween these two terminal apertures. The digestive tract is freely suspended in a perivisceral cavity ; which, as these animals possess neither heart nor generative ducts, serves as a receptacle for the blood at all times, and for the products of the generative glands at the periods at which they come to maturity. The mouth opens always between the two lips of a lophophore; both lips being also always, with the exception of Pedicellina, beset with tentacles. The lophophore itself may be circular, as in all marine species, with the exception of the family just named, and of Rhabdopleura ; or it may be prolonged into two arms, extending from the mouth towards the neural or rectal aspect of the animal, as in all fresh- water species, hence called ‘ hippocrepian,’ except Paludicella and Urnatella. In the freshwater species the tentacles are con- nected at their bases by an infundibuliform membrane, known as the ‘calyx ;? and the mouth is guarded by a valvular organ, the ‘epistome,’ by virtue of their possession of which they have been classified as ‘ Phylactolaematous,’ in contradistinction to the ‘Gym- nolaematous’ marine sub-orders. The lophophore, being attached round the mouth, either by its entire circumference, as in the marine Polyzoa, or by the base of its two arms, as in the hippo- crepian representatives of the class, forms a roof to the perivisceral space, with which cavity, the cavities of the lophophore, of the entire series of tentacula which it carries, and of the epistome when present, are freely continuous. The tentacles are not flexible in the Polyzoa, with the exception of the Pedicellineae, and probably some allied forms. Both the external and the internal surfaces of the lophophore and its tentacles are clothed with cilia, the action of which subserves the functions of ingestion of food, and of aeration of the blood. The interior of the perivisceral space is also similarly clothed with cilia; and the movements of the blood between the mutually intereommunicating cavities of the lophophore with its appendages and the general perivisceral system, are further carried out by the contractions of the muscular fibres of the endocyst, and Characteristics of Polyzoa. cli of the retractor and protractor muscles of the entire polypide. The nerve mass situated between rectum and oesophagus, has been figured and described as sending: filaments to the lophophore, ten- tacles, epistome, digestive tract, evaginable endocyst, and retractor muscles, and as also throwing a collar round the oesophagus ; and it may consequently be considered as representing both the parieto- splanchnic and the cerebroid ganglia of higher Molluses. Repro- duction in the Polyzoa is both sexual and asexual. The asexual takes place in the way of gemmation; and in the case of the Fresh-water Polyzoa by means of ‘ statoblasts’ or gemmae, in which the developmental activity remains latent for a period. The Polyzoa are hermaphrodite; the testes being situated near the bottom, the ovary being attached to the parietes of the upper part of the cell. It is by gemmation that the polymorphic organisms. known in Polyzoa as ‘ovicells,’ ‘avicularia,’ and ‘vibracula’ are produced ; and in Serialaria, where the entire colony may have its individual polypide brought into connection by a common nerve-system, we find some cells modified for the discharge of purely passive functions, as ‘stem-’ cells and ‘ root-’ cells. The Polyzoa have, like the Tunicata, been removed from the Sub- kingdom Mollusca by Gegenbaur and Haeckel, and classed with the Vermes. The inosculant form Loxosoma described by Kowalewsky (Mem. Acad. Imp. St. Petersburgh, Ser. vii, Tom. x. 2) has been sup- posed to connect them with this latter Sub-kingdom. Against this view we must set not merely the many structural homologies which can be pointed out as existing between adult individuals of the undoubtedly Molluscoid Classes Brachiopoda and the Polyzoa ; (for which see p. 72, infra, ibique citata), but also the striking similarity which the larval form of a Brachiopod has been observed by Fritz Miiller to present to the Polyzoa with orbicular lophophores such as all the marine sub- orders with the exception of Pedicellinea. See Reichert und Du-Bois Reymond’s Archiv. fiir Anatomie und Physiologie, p. 79, 1860. For an account of the nervous system in Seria/aria, see Fritz Miller, Archiv. fiir Naturgeschichte 1860, p. 311, Taf. xin. ClV Introduction. Sup-Kincpom, Arthropoda. ANIMALS consisting of a series of more or less heteronomous segments, the ‘ Metameren’ or ‘ Folgestiicke ’ of Haeckel, to which jointed appendages are articulated ventrally in pairs, and, ordi- narily, in very different proportions and grades of development in the different regions of the body. These appendages are, in con- tradistinction to those of Vermes, hollow, and have muscles pro- longed into their interior. This external integument is rendered more or less rigid by chitinous deposit, which may be made still more resistent by calcification. Chitinization extends itself from the exterior into the interior, and in many cases an endophragmal skeleton is thus formed, which arches over the ventrally-placed portion of the nervous system. Tubular prolongations of the cuti- cular chitine extend inwards along the various ducts and canals opening on to the exterior, and are shed together with the inte- gument in the moultings which these animals, so long as they continue to grow, must necessarily go through. The chitinous deposit at the commencement of the digestive canal may take the shape of ‘lips,’ or even of non-segmented processes, like the ‘jaws’ of certain Vermes, but the true functional jaws of Arthropoda are always produced by the modification of the hollow segmented appendages of more or fewer of the anterior segments of the body. The organs of special sense are ordinarily confined to the prae-oral segments, and, like the rest of the appendicular skeleton with which they are, either actually or morphologically, connected, contribute at least as much to the heteronomy of the external appearance as the segments upon which they are carried. The antennae, eyes, and auditory organs are all but invariably limited to the prae-oral cephalic segments, and the muscles of the chitinous elements of the segments are never found to form con- tinuous antero-posterior layers, as in Vermes, corresponding with the length and often with the circumference of the body. On the other hand, the chief internally-placed system of animal life, the gangliated nerve-cord, presents a striking resemblance to the homo- logous system in Vermes; and the respiratory system of certain Myriopoda appears to attain in its stigmata an approximation to Characteristics of the Arthropoda. cv correspondence with the number of the segments of the body, which resembles that manifested by the multiple respiratory organs of many Annulata. But the circulatory, depuratory, and reproductive organs are never found to be thus multiplied, such segmentation as they may exhibit being ordinarily limited to one, and that the abdominal region of the body. The digestive tract takes ordinarily a very direct antero-posterior course, rarely presenting any lateral diverticula except in Arachnida, or any convolutions, except in adult Insecta, and some Cladocera. his latter Crustacean family has the anus placed dorsally, and some way anteriorly to the termi- nation of the body segments, and furnishes an exception to the general rule, that the intestine in Arthropoda ends in the last segment of the body. Except in the larvae of Hymenoptera and of \Myrmeleon, the intestine is always proctuchous. But in the suctorial Cirripedia, and in the ‘complementary males’ of the other families of that order, as also in a suctorial Entomostracan, JMJon- strilla Danae, the digestive tract is wanting altogether, and the mouth when, as in the last case, present, leads directly into the general cavity of the body. A heart is very usually present, underlying the dorsal elements of the abdominal segments, and ending in an aorta in the thoracic region. It is usually vasiform and segmented, lateral apertures at the anterior end of each seg- ment serving as venous inlets for the blood filline the pericardial sinus in which the heart is suspended by means of the elastic alae cordis. ‘The circulation is always more or less extensively lacunar ; even arteries may be wanting. Accordingly, as the respiration is aquatic or aerial, the Arthro- poda are divisible into two great groups, one of which is con- stituted by the Crustacea, in which respiration is branchial, or in the absence of branchiae, carried on in water by the general sur- face of the body; and the other by the other three classes, Ara- chnida, Myriopoda, and Insecta, in which respiration is effected by the admission of air into the interior of the body by tracheae, or some modification of those organs. The air-breathing Arthro- poda agree with each other, and differ from the Crustacea in the following points:—they never have two pairs of antennae; and, with the exception of certain Ephemeridae, Strepsiptera, and Diptera amongst Insecta, and certain Hpeirae amongst Arachnida, their eyes are never pedunculate ; their mandibles are not palpate; one evi Introduction. or both pairs of maxillae are more or less completely fused mesially so as to form a functional lower lip; and, with the exception of the lower Myriopoda, their post-abdominal segments, when present, rarely or never carry appendages with locomotor functions in the adult state. The portion of the supra-oesophageal ganglionic mass which corresponds with the eyes, is much larger relatively to that which corresponds with the antennary organs than it is in Crus- tacea; and in exact opposition to what we observe in this latter class, we find the salivary and renal organs largely developed, and the hepatic only represented rudimentarily. The digestive tract is never aborted in air-breathing Arthropoda, nor aproctous in adult individuals. Except in certain lower Crustacea and Arachnida, where the supra-oesophageal nerve-mass is represented simply by a fibrous commissure, the nerve-system consists of supra-oesophageal and of ventrally-placed ganglia, connected with each other so as to form a collar round the oesophagus, and connected with a sympathetic system ordinarily consisting of a ‘stomatogastric’ division and of ‘nervi transversi.’ All Arthropoda, with the exception of the Cirripedia and Tardi- grada, are dioecious, and, with the exception of the Tetradecapodous or Hedriophthalmatous Crustacea, and cornuted Insecta, the males are ordinarily smaller in size than the females. Reproduction is ordinarily sexual, but both parthenogenesis and asexual genesis by means of pseudovaria, if not also by internal metagenesis without the intermediation of such structures, are known to occur in this Sub-kingdom. The Arthropoda are ordinarily oviparous, but are sometimes viviparous, and even pupiparous. Except in the cases of certain of the lower Crustacea and Arachnida, the segmentation of the yolk is always partial, and the first appearance of the embryo takes the shape of a ‘primitive streak.’ Though the embryos of Arthropoda very ordinarily go through more or less numerous stages of metamorphosis, neither larvae nor adults ever possess cilia. In the more usually observable forms of metamorphosis, the embryo leaves the egg not only with its reproductive system, but also with its motor and sensory organs in a less perfect condition than those of the adult; in the less ordinary, or retrogressive metamorphosis, observable in parasitic families, the animal organs of the larva are more perfect than those of the adult. In both cases, change of tegument accompanies metamorphosis. Characteristics of the Arthropoda. evli The most essential difference between the various Classes of the Sub- kingdom Arthropoda, is that which tracheal and branchial breathing re- spectively correspond to, and with this principle of classification in view, we place the Crustacea, the earliest representatives of the Arthropodal type in geological times, apart from the other three Classes. Within the limits of any one of these four Classes, the greater or lesser heteronomy of the several regions of the body, the greater or lesser extent, that is, to which the specialization of segments, and, even more, of appendages, has been carried out, constitutes the most important dif- ference between one order and another, next to that which the actual abortion of segments or appendages entails. The two Classes, Crustacea and Arachnida, differ from the Myriopoda and Insecta in comprehending much more varied forms ; the Myriopoda contrast with the other three Classes by their low degree, whilst the Insecta are distinguished by their high degree of heteronomy. The Crustacea and Arachnida are very closely approximated by such forms as the Cyamidae and the Pycnogonidae. This latter family is re- ferred to the Class Arachnida mainly on account of the lateral diverticula which the digestive tract is furnished with, but there is reason to believe that some of its species possess free and functional antennae, and it should be considered therefore as Crustacean. If the parasitic Hedriophthalmata, such as the Cyamidae, connect the Crustacea with the Arachnida on the one side, they connect them also with the Insecta through Pediculus on the other. A more striking, though perhaps not more real, link be- tween the Crustacea and the Insecta and Myriopoda, is presented by the air-breathing Isopoda, such as Onzscus, on the one side, and the apterous Orthoptera and Glomeris on the other. The Arachnida approximate to the Insecta very obviously by such forms as G‘aleodes ; and though their marked heteronomy and the definite number of their body segments cause them to differ very widely in external appearance from the Myrio- poda, the peculiarities of their reproductive and respiratory systems appear to speak to the existence of a real affinity between them and the Chilognathous division of that class. The Arthropoda have frequently been classed together with more or fewer of the Vermes in one Sub-kingdom, that of the ‘Annulosa;’ and whilst by such highly-organized forms as the Marine Polychaeta an approximation appears to be made to certain of the less specialized of the Crustacea ; or even of the Myriopoda, or the larvae of Insects, amongst the air-breathing Arthropoda: the microscopic Rotifera connect the Vermes, to which Sub-kingdom they are to be referred, very closely to the Crus- tacea. The possession at one period, or, as usual throughout life, of GVill Introduction. hollow articulated and segmented motor organs, into the interior of which transversely striated muscles are prolonged, and the absence at all periods of cilia, are points which distinguish all Arthropoda from all Vermes ; and a third point of nearly equal generality is furnished by the early appearance of a ‘primitive streak’ and the partial segmentation of the yolk in development. Fourthly, whilst in Vermes it is only rarely possible to differentiate the postcephalic segments into several regions, this is always possible in Arthropoda; the history of the development and that of the relation of the internal organs to the external skeleton rendering this possible even in the externally nearly perfectly homo- nomous Myriopoda, and in the most degraded representatives of the Crustacean Class as well as in such homonomous forms as certain of the Isopoda. Fifthly, true metagenesis is unknown in Arthropoda. The various organs and systems of the Crustacean, as being a water-breathing Class, appear to attain a lower degree of evolution than those of the other Arthropoda, and the Vermes may be supposed to approximate to them more closely than to any of the air-breathing classes ; but the points just specified will always serve to differentiate the members of the two Sub- kingdoms, howsoever closely they may at first sight resemble each other. Still it must be said, that the two Sub-kingdoms have their boundaries approximated at many points, if not along great lengths, in space ; and for a concrete illustration of this principle, the student is referred to the description of Echinoderes Dujardinit, an animal which, though classed as a Crustacean, combines with many of the characters of Arthropoda many also of those of such Vermes as the Nematelminthes and the Oh- gochaeta, and has been pointed out by Claparéde, (Anatomie und Entwick- elungsgeschichte Wirbelloser Thiere, 186, p. 92,) as constituting a link between these two Sub-kingdoms. Cuass, Insecta. Air-breathing Arthropoda with well-marked heteronomous divi- sion of the adult body into three distinct regions, the head, thorax, and abdomen. The middle region, or thorax, is composed of three segments, the prothorax, mesothorax, and metathorax, each of which has a pair of jointed appendages, the legs, articulated to it ventrally, whilst each of the two posteriorly-placed segments has also, ordi- narily, a pair of unsegmented appendages, the wings, or the wing- covers, articulated to it dorsally. A post-abdomen is never very obviously marked off from the Characteristics of Insecta. c1x abdomen, but there are not wanting more or less obscure indications of the presence of three segments between the generative outlet and the terminally-placed anus, which may be considered as representing the post-abdomen. The abdomen proper never carries any articu- lated appendages in adult insects, with the single exception of the Coleopterous Spirachtha Eurymedusa, in which the third, fourth, and fifth abdominal segments each carry a pair of biarticulated appen- dages. The post-abdominal segments however may carry segmented appendages both in the adult and in the larval condition, but these organs, though they may attain a considerable development, especially in Orthoptera (Chloeon dimidiatum), do not appear to possess locomotor functions in adult insects. The motor organs are mainly localized in the thoracic, the vegetative in the post-thoracic regions. None of the thoracic segments are ever, except in certain Coccina, fused with the cephalic, nor are any thoracic appendages ever modified so as to serve as manducatory organs. The greater relative size of the eyes gives as distinctive a character to the head in this Class of Arthropoda as its freedom from fusion with the thorax. The mandible has never even a rudiment of a palp; and the second pair of maxillae are always more or less completely soldered together so as to form a functional lower lip, the ‘ labium’ of entomologists. The digestive canal is never aproctous except in the larvae of most Hymenoptera, of the parasitic Diptera, and of Myrmeleo. In these larvae the renal organs open into what is subsequently by moulting brought imto communication with the blind end of the digestive tube, and so converted into a ‘ rectum ;’ the entire apparatus previously to this change bearing a striking resemblance to the so-called ‘ water-vascular’ or excretory system of certain Vermes. The digestive tract presents more numerous and more distinctly distinguishable divisions than in other Arthro- poda ; and it is often, at least in adult insects, arranged in convolu- tions, and is thus longer relatively to the body than in other mem- bers of the Sub-kingdom. ‘The salivary glands may be large and racemose as in Orthoptera, or very small and tubular as in the adult Lepidoptera. The liver appears to be represented by certain coeca which are set round the commencement of the digestive tract in varying numbers in the Orthoptera and Hemiptera, the great development of the respiratory tracheal system appearing to com- pensate for this rudimentary or aborted condition of the hepatic cx Introduction. organ, as in the reverse way the great development of the liver in Arachnida may be supposed to compensate for their less developed aerating organs. The other set of depuratory organs, those, namely, which are charged with the direct elimination of effete nitrogenous substances, are always, with the exception of Aphis, Coccus, and Chermes, present in insects as the ‘ Malpighian vessels.’ The tra- cheae of insects inosculate or anastomose in various parts of their course, but the capillary tracheae in which the spiral thickening of the inner lining membrane may fail to be developed, end blindly in the tissues to which they are distributed. The aquatic larva of one insect, Chloeon dimidiatum, has no tracheae developed in the first three stages of its larval life, but subsequently, like the larvae of many other Orthoptera, Neuroptera, and Diptera, has tracheae developed which are exposed to the action of the oxygen dissolved in outgrowths known as ‘ tracheal gills.’ These organs do not ordi- narily possess any ‘ spiracle’ whereby to come directly into commu- nication with the air of the atmosphere, and must therefore obtain the oxygen they contain as gas from that which is dissolved in the water they live in. They may be said therefore to present us with an instance of an arrangement transitional in character between aquatic and aerial respiration. In a single insect, Péero- narcys regalis, one of the Orthoptera Amphibiotica, which is of lucifugous habits, and mhabits damp localities, tracheal branchiae are retained during adult life, but im other cases, when the insect leaves the water, the external lappets into which the internal tracheae send ramifications fall off, and the ordinary laterally- placed spiracles are formed at the poimts of their separation. The heart is a vasiform organ, consisting ordinarily of eight segments, with as many pairs of venous inlets. It underlies the dorsal elements of the abdominal segments, is ordinarily closed posteriorly, but ends anteriorly at the thorax in an aorta which may be prolonged forwards as far as the cephalic ganglia. In Insects there is never wanting a ventrally-placed ganglionic mass in addition to the first sub-oesophageal centre, which by its commissural junction to the cerebroid mass forms the nerve collar. The first sub-oesophageal ganglia supplies the jaws, and though not so closely apposed to the supra-oesophageal centres as is the case in Arachnida, it is yet so close as often, but mconveniently, to have been spoken of as part of the ‘brain.’ The ganglionic centres Characteristics of Insecta. GX placed posteriorly to it may be-represented by a single continuous mass giving off nerves laterally and posteriorly; or they may take the shape of a chain of ganglia, which are never more than eleven, three being thoracic and eight abdominal, though by fusion or abortion they ordinarily fall below this number. The sympathetic system, both in its stomato-gastric division; and in that part of it which is in connection with the ventral ganglia and supplies the tracheae, attains in insects a large development. The eyes are always confined to the head; in a few instances, of which the Chloeon dimidiatum, one of the Orthoptera Amphibiotica, already mentioned, is one, as also in certain Dipterous, Strepsipterous, and Hemipterous genera, the eyes are elevated upon peduncles or pillars, which however are never movably articulated to the head. In most orders of sects, but most frequently amongst Hymenoptera, Diptera, and Orthoptera, the so-called ‘ simple eyes,’ s. ‘ stemmata,’ s. ‘ocelli,’ coexist with the larger multifacetted eyes. The males and females are ordinarily very different in insects ; the males, except in the cornuted species, being slighter in make, swifter, furnished with larger eyes and antennae, and more brightly coloured. The difference may be so great, especially when the females are apterous and the males winged, as to amount to a kind of Dimorphism. The generative organs of Insects are very varied in the details of their arrangement. The reproductive glands are always double and symmetrical, but the efferent ducts always fuse into a common duct before opening. This they do posteriorly to the eighth abdo- minal segment ; which is homologous with the third caudal segments of Scorpionidae and Crustacea, and therefore posterior by eight seg- ments to the genital sezgment of the Arachnida just named, and to that of Limulus ; and by three to the hinder of the two genital seoments of the Decapodous Crustacea. The female generative organs of insects have often a large number of accessory appendages; the most constant of these is the ‘ receptaculum seminis ;’ but there may be present also an ‘ accessory gland’ appended to the ‘ recepta- culum seminis;’ secondly, a ‘ bursa copulatrix ;’ and thirdly, a num- ber of ‘colleterial’ glands which secrete a glutinous material for fixing the ova to various external objects. The male accessory organs are of two kinds, one of which is considered as analogous to the pro- static organ, and the other to the vesiculae seminales of Mammals. ex Introduction. The segments of the body posterior to the eighth abdominal may be modified so as to serve in either sex as ‘ ovipositors’ or as intro- mittent organs. There are no hermaphrodite insects, and sexual reproduction is the rule in the class. Several forms of agamogenesis have been observed amongst Insects. In one of these, females with a reproductive apparatus provided with a receptaculum seminis produce (without any congress with males), either embryos, as Lecanium hesperidum, Chermes abietis, amongst the Coccina ; or ova, as, amongst Lepidoptera, Psyche helix, Solenobia lichenella, and Solenobia triquetrella, and as, amongst Hymenoptera, Cynips, apterous Queen bees, and normal winged (Queen bees before they leave the hive. In this class of cases sexual may alternate with asexual genesis, and it is to be noted that the male offspring of the Queen bees are only and exclusively due to the agamogenetic process. In a second class of cases, females with a more or less imperfect reproductive apparatus produce either ova, as is the case with the ‘ workers’ amongst the social Hymenoptera, Apis mellifica, Vespa, Bombus, in which the vagina as well as the receptaculum seminis is rudimentary, and which, with, possibly, the exception of the Vespidae, always produce males; or embryos, as is the case with Aphis, in which certain generations without sper- mathecae or colleterial glands are viviparous agamogenetically, whilst others with a perfect sexual apparatus are oviparous gamo- genetically. This form of asexual genesis is called ‘ pseudopartheno- genesis,’ and the reproductive gland a ‘pseudovarium.’ Asexual genesis was supposed to take place metagenetically, that is to say, by a process of internal gemmation in a non-differentiated part of the body, in the larvae of certain Diptera of the family of Ceci- domyidae; but the discovery, by Leuckart, of specialized germ- producing organs in these animals appears to show that the only differences between this process and that observable in Aphis consist in its taking place in forms of a holometabolous order, which, as being larvae, are very different in external appearance from the perfect sexual insect, and in the ‘ pseudovaria’ being destitute of any ‘ pseudoviduct.’ In the development of the ovum the yolk is surrounded by a germinal membrane, in which the first traces of the head and the ventral half of the embryo make their appearance as the so-called ‘primitive streak.’ Insects are ordinarily oviparous, but they may Characteristics of Insecta. exlli be viviparous, and the larva in one sub-order (the so-called Pupi- parae), is so far developed, by means of the nutriment furnished to it by a gland opening within the maternal oviducal canal, as to be nearly ready to enter upon the stage of chrysalis or pupa when set free from the mother’s body. The form which an insect has on leaving the egg always differs more or less from that which it possesses when adult, and capable, as only full-grown insects are, of reproducing its kind by sexual genesis. The larvae of apterous insects, such as certain of the Orthoptera and Hemiptera, differ from the adult, irrespectively of the undeveloped state of the gene- rative organs, only in such points as size, the number of joints in the antennae, and the number of facets in the corneae. It is only in the quantitative increase accruing to these two sets of organs of special sense that the adult after the entire number of its moults comes to differ from the larva in the way of heteronomy. A greater degree of heteronomy is attained to in the families of the two orders specified which are endowed with wings, by the super- addition of those organs, and by the concomitant greater differentia- tion of the thoracic from the abdominal region of the body. Insects which go through either of these two series of metamorphosis are called ‘ametabolous.’ A third kind of metamorphosis is that in which the adult insect, whilst gaining certain organs which the larva does not possess, such as wings, loses certain others, which the larva does possess, such as the provisional structures making up the ‘mask’ of the Libellulidae. Such insects are called ‘ Hemimeta- bolous,’ and in them the heteronomy of the various regions of the body is always well pronounced. Insects, finally, which when adult do not only differ very markedly from their larval forms both by general heteronomy and by the conformation of their particular organs, but also attain to this condition after going through a period of quies- cence known as the ‘ pupa’ or ‘ chrysalis’ stage, preparatory to their final moult and the assumption of the adult condition, are called ‘ Holometabolous.’ A period of quiescence as ‘ pupae,’ in addition to the period of quiescence as ova, gives the Holometabolous orders of Insects an advantage as regards their distribution over the colder regions of the earth, relatively to the orders the pupae of. which are active; and, therefore though certain small Poduridae resist cold well, it is amongst the Holometabola that we find a nearer approach made to cosmopolitanism than is usual elsewhere amongst Insects. h CX1V Introduction. Cuass, Myriopoda. Air-breathing Arthropoda in which the segments and their ap- pendages make a nearer approach to homonomy than in either Insecta or Arachnida, and in which the post-cephalic locomotor appendages, even when least numerous, and amounting to nine pairs only as in Pawropus, are still more numerous than the similar organs in either of the two other classes mentioned, except in the larvae of certain Hymenoptera, Cimber and Tenthredo, which possess eight and seven pairs, respectively, of prolegs, besides the three pairs of true legs. In the homonomy and number of their segments and appendages, the Myriopoda resemble certain of the Crustacea, with which Class they have often been ranked, as also im having the first, or the first two pairs of post-cephalic appendages, subordinated. more or less completely to the manducatory organs, so as in one order, Chilopoda, to form ‘ foot-jaws,’ and in another, Chilognatha, to form ‘labia’ by the partial fusion and other modifications of their coxae, whilst in Pawropus the anterior pair of legs is rudi- mentary. There is however no fusion of segments in the Myrio- poda of the kind which produces a cephalo-thorax in Crustacea, It may be added here that an additional point of similarity to the Crustacea is manifested by the Myriopoda in their mode of growth ; as their larvae instead of leaving the egg, as insect larvae do, with at least as many segments and legs as they ever afterwards possess, leave the egg with a much smaller number of segments and legs than by the periodical addition of segments at successive moultings, they attain in the adult state. The Myriopoda however must be classed with the air-breathing Arthropoda, not only on account of their respiration beg tracheal, except in the case of the diminutive Pauropus, but also on account of the singleness of their antennae ; the sessile position of their eyes; their non-palpigerous mandibles ; the fusion of their maxillae into a labium; the large development of their salivary and renal, and the rudimentary condition of their hepatic glands. The Myriopoda appear to stand midway between the two other classes of air-breathing Arthropoda, as to the mutually correlated and mutual supplementing complexity and simplicity of the circu- latory and respiratory apparatus. Their digestive and nervous- systems are closely similar to those of the larvae of Insects. Characteristics of Myriopoda. CXV The Class Myriopoda is ordinarily divided into two orders—the Chilo- poda and the Chilognatha or Diplopoda, from which the Siphonizantia and the genus Pawropus ought, it is probable, to be separated. The Chilopoda are the most highly organized of the Myriopoda. They are distinguishable externally by the flatness of their bodies; the large size of their antennae, which always possess fourteen joints at least ; by the modification of the two anterior pairs of post-cephalic appendages into foot-jaws, the hinder pair of which is armed with a sickle-shaped unguis and poison-gland ; and by their locomotor legs being attached in single pairs. With these external characters, the following points of internal structure are correlated ; the stigmata for the admission of air to the tracheae do not correspond with the number of segments, and are situated on the sides of the body between the bases of the feet and the dorsal shields ; the generative ducts open at the posterior extremity of the body ; and there is no intromittent organ. It is amongst the Chilo- poda only (in Scutigera) that we meet with compound facetted eyes. In another Chilopodous family (Scolopendridae) we find the generative ducts single, and the tracheae anastomosing as in Insects. The larval Chilo- poda may have as many as six or eight pairs of locomotor appendages when they leave the egg ; and the addition of fresh segments takes place in the way of intercalation at each moult, in the intervals between each pair of older segments. In the Chilognatha the body is sub-cylindriform, the antennae are inconspicuous and do not possess more than seven joints ; the two anterior pairs of post-cephalic appendages, or at least the first of them, may be spoken of as ‘foot-jaws,’ or as forming ‘labia,’ inas- much as they are directed forwards like the operculiform ‘ foot-jaws’ of Crustacea, and have their basal joints or coxae more or less enlarged, apposed mesially, and anchylosed, though they are much less altered in function and structure than their homologues in the Chilopoda; and their legs are, after the first six, or, in the males, seven post-cephalic segments, arranged in double pairs. Differing thus externally from the Chilopoda, they differ from them also in the following points of structure and developmental history, and approximate more closely than they do to the Arachnida and Crustacea, and less closely to the Insecta. The stigmata leading into their tracheae correspond in number with their Segments, and are situated on the anterior border of the ventral plates, under cover of the coxae of the legs, which are articulated to the pos- terior border of these plates ; the tracheae do not anastomose ; the gene- rative ducts are bilaterally symmetrical, having double openings in or upon the borders of the third thoracic segment, which never carries legs, h 2 exvi Introduction. and corresponds precisely with the genital segment of the Scorpion (see p- 116, infra), and with that of the Poecilopodous Crustacea. The seventh post-cephalic segment ordinarily carries a double penis, which may how- ever, as in Glomeris, be removed to the posterior extremity of the body, indicating hereby an approximation to the Chilopoda. The larvae of Chilognatha, when they leave the egg, have ordinarily only three pairs of appendages, which are carried upon three of the four first post-cephalic segments ; and they contrast still further with the Chilopoda, by at- taining their additional segments at each moult by intercalation only in that portion of germinal membrane which is interposed between the penultimate and ante-penultimate segments. Pauropus appears to resemble the Chilognatha in having the generative orifices situated anteriorly instead of posteriorly in the body, and its larvae are hexapodal ; but it differs from them in many points of its external anatomy. The shape of its body as a whole, its dorsal plates, and elongated posterior legs, give it a resemblance to some Chilopoda. As tracheae may be absent in the early developmental stages even of an Insect, Chloeon Dimidiatum, too much weight must not be laid upon their absence in Pawropus ; and it may be safely said that for our present purpose, that, namely, of showing the relationships which subsist between the various classes of Arthropoda, the most important morphological point in this genus (or order ?) is its possession of bifid antennae, carrying multi-articulate flagella, by which peculiarity, as also by the others specified above, a very distinct affinity is shown to exist between Myrio- poda and Crustacea. For the structure and affinities of the Myriopoda, see Sir John Lubbock, on Pauropus, a new type of Centipede, Linn. Soe. Trans., xxvi., 1867, ceque citata; and also Mr. Newport’s Papers on the Myriopoda, in the Transactions of the Royal and Linnaean Societies. Cuass, Arachnida. Air-breathing Arthropoda, with well-marked heteronomy be- tween the several divisions of the body, which are usually only two, a cephalo-thorax to which the limbs are limited, and an abdomen, usually marked off from it by a constriction, a post- abdomen being developed only in the Scorpions. Their antennae are modified so as to serve in the prehension of food; and they Characteristics of Arachnida. exvil have four pairs of limbs, which correspond to the maxillary, and to the labial palps, and to the two anterior pairs of legs in Insects. The fusion of head and thorax approximates the Arachnida to the Crustacea, and puts them into a position of contrast to the other Arthropoda ; the Myriopoda furnishing here, as frequently else- where, an example of a transitional arrangement, by having the two anterior pairs of thoracie appendages subordinated functionally to the oral appendages, though the segments carrying them are not in them actually fused with the head. As the history of the development of the nervous system in the Scorpion appears to show that the first post-oral, which is the cheliferous appendage, corre- sponds to the mandible, and not, as is ordinarily stated, to the first maxilla of other Arthropoda; we may add that the Arachnida resemble the Crustacea in a second point of external anatomy, that of possessing a palp on the mandible, a structure never seen in the air-breathing Arthropoda except as a rudiment in some Chilo- podots Myriopoda. The lesser development of the respiratory apparatus is a point of internal anatomy which distinguishes the Arachnida from the other Arthropoda ; and the large development of the hepatic organ, which may be considered to compensate for this comparative deficiency, is another point of resemblance to Crustacea. As peculiarities which may possibly be correlated with these, and which certainly point in the same direction, we may mention the power of repeatedly moulting ; of reproducing at those periods limbs which have been detached or mutilated ; and of producing offspring repeatedly in the adult state, which the Arach- nida possess in common with Crustacea. The higher Arachnida resemble the Chi/ognatha and the Crustacea, in the bilateral ter- mination of their generative ducts on anteriorly-placed segments of their body ; and they resemble the Cii/ognatha in the non-anasto- mosis of their tracheae. The digestive tract of the Arachnida differs from that of all other Arthropoda in having in many cases lateral coeca appended to it, and prolonged into the interior of the limbs and mandibular palps. Their respiratory system consists either of tracheae alone; or of the so-called ‘lungs, which are sacciform modifications of tracheae, alone; or of both combined ; and in some cases, such as those of certain parasitic families and orders, and of the Zardigrada, a specialized air-breathing apparatus is wholly want- ing. The tracheae when present have very ordinarily a fasciculate eXVill Introduction. rather than an aborescent arrangement, and they not rarely differ also from those seen in Insecta and Myriopoda, by not possessing the internal spiral thickening, so characteristic of the respiratory tubes in those two classes. The limits within which the variations of the circulatory and ner- vous systems may range, are very wide; the arteries and ves may attain, as in Scorpions, a very high grade of evolution and distinct- ness, or both sets of vessels and the heart also may be absent, as im such lower forms as the Acarina and Linguatulina, in which the nerve-system is reduced to a single ganglionic mass perforated by the oesophagus. The supra-oesophageal and the sub-oesophageal ganglia are always closely approximated in Arachnida, in corre- spondence with the assignment of the antennary to act in aid of the manducatory organs, and with the more or less suctorial modi- fieation of their carnivorous habits, with which a small pharynx and oesophagus are correlated. The Arachnida, with the exception of the Zurdigrada, are dioecious ; and with the exception of the order just named, and the Linguatu- lina, the segmentation of the yolk is partial in the class. With the exceptions of Scorpionidae and some » Histoire et 1 PAnatomie des Mollusques, Mémoire sur les Ascidies, pp. 20, 21. The mouth is similarly situated at the bottom of the branchial sac in Ascidia Scabra, which differs from this species, Ascidia Afinis, in being smaller and rougher externally. 23. BROAD-LEAFED Hornwrack (flustra Foliacea). A SEAWEED-LIKE Polyzoon, very common and universal in Euro- pean seas. The Polyzoary is flexible, of silk-like texture and ap- pearance, ordinarily forming erect fronds but occasionally loosely adnate to marine objects. The cells, which by their mutual appo- sition in these social animals form the Polyzoary or Coenoecium, are arranged multiserially in parallel longitudinal rows on both sides of the frond they make up. The individual cells are ovoidal in shape, and have from four to eight spines set round their larger end, in which their mouth, which is crescentic and protected by a lip, is placed subterminally. The avicularium and mandible are semicircular and immersed. There are no vibracula. The polypide itself is, when contained in its cell, bent several times upon itself. Its tentacles are very long. It resembles the great majority of fresh-water Polyzoa in the absence of a gizzard. The ovicell, a sort of marsupial pouch, analogous, in respect of function, if not homologous, with the cloaca of the Ascidians, and continuous with the perivisceral space through a passage at the upper and back part of each cell, is inconspicuous in this species, being deeply immersed. The ova themselves are of a striking colour, and, as in other Polyzoa, are set free by the death and disruption of the parent polypide. For excellent figures of the external and internal anatomy of this animal, see Van Beneden, Recherches sur V Anatomie, la Phy- siologie, et le Développement des Bryozoaires qui habitent la céte d’Ostende, Mem. Acad. Royale de Bruxelles, tom. XVill., For For For Descriptions of Preparations. 1844, pp. 32-34, pl. iv., figs. 11-17. For similar figures of another marine Polyzoon, Acamarchis Avicularia Lmx. Bugula Avicularia, Busk. Brit. Mus. Cat. p. 45; see Bronn’s Klassen und Ordnungen des Thierreichs, iii. 1, Taf. v., fig. 3, A.B.C.D. figures of the Hippocrepian fresh-water species, see Allman, Fresh-water Polyzoa, pl. i. e¢ passim. an account of the zoological characteristics of the class, and especially of the marine subdivision of it, see Busk, ‘ Fossil Polyzoa of the Crag,’ Palaeontographical Society’s Memoirs, 1859, part 12; and British Museum Catalogue of Marine Polyzoa, 1852, where, at pp. 103-108, an account of the struc- tures above mentioned under the names of ‘ vibracula’ and ‘avicularia,’ will be found. the microscopic anatomy of the fresh-water Polyzoa, see Nitsche, Reichert und Dubois Reymond’s Archiy., 1868, p- 465; and for that of the nerve-system especially, see Taf. xi. fig. 23. For similar observations, see Alpheus Hyatt, Proceedings of Essex Institute, Salem, Mass., U. S. A., vol. iv. No. v., 1864-1868. For remarks as to the homologies and affinities of the class to the For Brachiopoda, and also to other Molluscan classes, see Lister, Phil. Trans. 1834, p. 385; Farre, Phil. Trans. 1837, p. 417; Hancock, Phil. Trans. 1857, p. 849; Allman, l. c. pp. 43-55; and Quarterly Journal of Microscopical Science, January, 1869, p- 62; Hyatt, 1. c. vol. v. No. v., pp. 150-157; Fritz Miller, Reichert und Dubois Reymond’s Archiv. 1860, p. 79, where at Taf. 1. fig. 2, a larval Brachiopod is represented with four arms borne upon a retractile proboscis ending in an oval pro- tuberance closely similar to the epistome of the Hippocrepian Polyzoa. the identification of the Polyzoa, as belonging to the sub- kingdom Mollusca, see Audouin and Milne-Edwards, Ann. Sci. Nat. tom. xv. 1828 ; Milne-Edwards, ibid. tom. vi., p. 16, 1836; Recherches Anatomiques, Physiologiques et Zoologiques sur les Polypiers de France, 1841~1844, 8vo. For the literary history of the nomenclature of the class, see Busk, Ann, Nat. Hist. x., 1852. Bugle Coralline. 73 24. Bucte CoRALLINE (Salicornaria Farciminordes). Tue Polyzoary is plant-like, erect, calcareous, dividing dicho- tomously, the internodes articulating by flexible chitinous bands instead of being continuous as in the preceding specimen. It is ordinarily about three inches high, and is attached by a fibrous branching root-like base. ‘The cells are arranged quincuncially round an imaginary stem, and divide the surface of the internodes which they make up, into more or less regularly rhomboidal or hexagonal spaces bounded by the raised borders of the cells. The mouth has a tooth on each side at its orifice within its lowest border. The avicularia are distinct from and placed above the cells, but not regularly.. Their rostrum is immersed, and their mandible semicircular. No vibracula are present in this species. The ovicells, which are immersed as in the preceding specimen, have here their position frequently identifiable by the presence of a perforation above the mouth. For specific characters, see Busk, British Museum Catalogue of Marine Polyzoa, pp. 16-18, pl. Ixiv., fig. 3 ; Fossil Polyzoa of the Crag, p. 23; Johnston’s British Zoophytes, p. 355, 2nd ed.; English Cyclopaedia, article ‘ Polyzoa,’ p. 420, fig. 4; Cam. Heller. Verhand. Zool. Bot. Gesellschaft im Wien, bd. xvii., 1867, p. 85. 25. Larva oF Deratn’s-HEAD MortH (Acherontia Atropos). Tuts and the following five preparations are intended to illustrate the various points of external and internal anatomy, such as the presence of prolegs, the absence of wings, the rudimentary con- dition of the reproductive system, the shortness, large calibre and straightness of the digestive tract, the great development of the salivary glands and of the fat body, in which the larva or pupa, or both differ from the perfect insect. The caterpillar of the Death’s-head Moth is the largest of all European species. The greater or less homonomy of its segments from head to tail, and the fact that the segmentation of its legs and antennae is not very 74 Descriptions of Preparations. obvious to the unassisted eye, give the larva somewhat of a vermi- form appearance ; and together with the absence of wings and of the dense scaly covering clothing both wings and body in the adult Lepidopterous insect, put it into sharp contrast with the imago. Each of the three segments immediately posterior to the head carries with them a pair of quinquearticulate legs. The fourth and fifth post-cephalic segments have no appendages, but, like the first and unlike the second and third, are pierced on each side by a re- spiratory foramen known as a ‘spiracle’ or ‘stigma.’ The sixth, seventh, eighth, and ninth segments possess spiracles, and carry sucker-shaped motor organs, armed with spines, which are known as ‘pedes spur’ or ‘prolegs.? The tenth and eleventh segments are furnished with spiracles but have no prolegs; the eleventh carries on its dorsal surface a tuberculate horn characteristic of the family Sphingidae, with the exception of a few species, one of which is North American; and representing the /unis of the embryo. Posteriorly to this horn and between it and the tri- angular supra-anal valve are two half-ring-shaped ridges, reaching from the level of the spiracle of one side over the dorsum to the level of the spiracle of the other. They appear to be distinct from the ventrally-placed half-ring which carries the posterior or fifth pair of prolegs, and it is possible therefore that the presence of three segments may thus be indicated posteriorly to the eleventh, whereby fourteen, the typical number of post-cephalic segments in Arthropoda, would be made up. The greater part of the covering of the head is made up by two large scales, the ‘parietal scales’ of Lyonet, the ‘procephalic lobes’ of Huxley;’ the ‘ Scheitel- platten’ of the German authors referred to below, corresponding to the ‘epicranium’ of the imago. Anteriorly a triangular plate, the ‘ frontal scale’ of Lyonet, the representative of the ‘labrum?’ and ‘clypeus’ of the perfect insect, is interposed between the pro- cephalic lobes. These lobes or scales are each divided into two nearly equal halves by a dark stripe, on the inferior termination of which are to be found the six ocelli. Mesially to the lower part of the area occupied by the ocelli, the parietal scales give articular origin to the antennae, and more mesially again we have on either side the articulation of the mandible. From the position thus held by the antennae of the larva relatively to that of the organs of the mouth on the one hand, and to that of the antennae of the imago Larva of Death’s-head Moth. 75 on the other, they have been supposed by Zaddach to correspond to the inferior or posterior pair of antennary organs of the Crus- taceans, the so-called ‘ antennae,’ whilst the antennae of the imago correspond with the superior or anterior antennary organs or ‘ an- tennules’ of the Crustaceans. The structures corresponding to the maxillae and labium of such insects as the Coleoptera and Or- thoptera, and to the two pairs of maxillae in Crustaceans, are here more or less fused into a horizontal plate which forms a sort of operculum to the mouth, and carries three segmented organs on its free edge. Of these three organs, the one which is placed mesially is the labium, modified so as to give exit to the common duct of the two silk glands; and the organs placed one on either side of this ‘spinneret’ are the maxillae, modified so as to serve not only in the prehension of food, but also, im many larvae, in the construction of the cocoon. The two pairs of appendages which this compound organ thus represents in the larva, retain more of their typical distinctness in the imago, where they take the shape of a spiral proboscis, and a largely developed and palpigerous labium. On the other hand, the largely developed mandibles of the larva are represented by merely rudimentary organs in the imago, reversing thus the history of the posterior oral appendages. If the eyes be taken as indicating the presence of one segment, the antennae of the larva a second, and those of the imago a third segment, to which three other segments would have to be added for the mandibles, maxillae and labium, the head of the insect will be seen to consist, like that of the typical Ar- thropod, of six segments indicated by as many pairs of appendages ; and the six cephalic segments, together with the three thoracic and eleven abdominal, will make up the entire number of all the seg- ments of the body to twenty. In their possession of prolegs and of bright colours upon the integument, the larvae of Lepidoptera differ from those of Coleoptera and Hymenoptera Genuina, which they resemble, as they do also those of the Diptera and Neuroptera, in passing into a state of perfect quiescence as pupae. For the typical number of segments in the Arthropoda, see Huxley, ‘On the Agamic Reproduction and Morphology of Aphis,’ Linn. Soe. Trans., vol. xxii., 1858, p. 225. For the indication of a distinct cephalic segment which the pre- sence of the eyes furnishes, see Zaddach, Die Entwickelung 76 Descriptions of Preparations. und Bau der Gliederthiere, pp. 78, 87, 88; Rathke, Mor- phologie, pp. 126-127. For the antennae of the larvae in relation to those of the imago, and the antennae and antennules of Crustacea, see Zaddach, I Capps 135 -80,169. For a history of the metamorphoses of Lepidoptera, see Westwood, Introduction to the Modern Classification of Insects, vol. ii., pp. 310-321. For figures of the oral organs of the Larvae of Lepidoptera, see Lyonet, Traité Anatomique de la Chenille qui ronge le bois de Saule, pl. i. 1., and p. 59 for functions. For those of the imago, Savigny, Mémoires sur les Animaux sans Vertébres, vol. i., pl. i. ii. iit. 26. Pupa oF Dratu’s-HEAD Moru (Acherontia Atropos), Showing the form of chrysalis known as ‘ obtected,’ or better, as ‘ larvate’ or ‘ signate.’ Iy this form the external organs of the future perfect insect are more or less obscurely distinguishable beneath the hard elastic membrane in which they are inclosed instead of being free as in the so-called ‘ exarate’ or ‘liberae’ pupae of Coleoptera and Hymen- optera, and which is a product of the hardening of a secretion instead of being merely the dried integument of the maggot, as in the ‘ coarctate’ pupa of many Diptera. The conical form of the pupa case is characteristic of the Heterocerous Lepidoptera, in contradistinction to the angular form of the Rhopalocerous. The apical portion of the cone, the ‘cremaster’ of Kirby and Spence, is made use of by the pupa when it works its way up from the chamber, six inches or so deep in the ground, before entering upon the imago-stage of its existence. In possessing thus a power of motion in the last stages of their pupa-life, the Lepi- doptera resemble the Phryganeodeae or ‘ caddis flies,’ as they do also in many other particulars, though the chrysalis of the family just mentioned differs from that of the Lepidoptera in being ‘free’ or ‘exarate’ like that of the beetles and bees. Seven spiracles are seen on either side upon the abdominal segments ; Pupa of Death’s-head Moth. 77 an eighth, which belongs to the most anteriorly placed of the abdominal segments, is concealed by the wing-case on either side. The ninth abdominal ring is marked by a depression on either side of the middle ventral line, the lines limiting which extend into the interspace between it and the eighth segment, and indicate thus the normal position of the outlet of the generative glands. Posteriorly to this symmetrical depression, and separated from it by the entire breadth of the tenth segment, is seen an azygos depression with an antero-posterior direction indicative of the true position of the anus, which is in relation with the eleventh ab- dominal segment and its appendages, one of which the apical horn may be taken to represent. The dorsal part of the mesothorax or ‘mesonotum’ is largely developed; and the wing-cases are seen to take origin along either side of it, as well as from the much smaller ‘ metanotum,’ which is represented by a dumb-bell-shaped mass, constricted mesially and rugose on the surface. The ‘ pro- notum’ is much larger both relatively and absolutely than in the perfect insect, and forms a transversely elongate oval mesially earimate shield. The head-cover is divided by faintly marked transverse lines into three portions; the most posterior of which gives origin to the ‘ceratothecae,’ and appears to correspond to the ‘parietal scales’ of the larva and the ‘ epicranium’ of the imago, whilst the two anterior portions correspond to the ‘ frontal scale’ of the larva, and the posterior and anterior ‘ clypeus’ of the imago. The middle division of the head cover is the largest, the anterior is minute and the smallest of the three. In the middle line infe- riorly between the ‘ ophthalmothecae’ is seen the ‘ glossotheca’ in which the ‘spirignatha’ or ‘antlia’ of the future imago is lodged ; and externally to it on either side upwards, the ‘ podothecae,’ ‘ ceratothecae,’ and ‘ pterothecae,’ lodging respectively the future feet, antennae, and wings. For the relations of the posterior segments of the abdomen to the generative and anal outlets, see Lacaze Duthiers, Annales des Sciences Nat., 1853, tom. xix., Ser. i., p. 220; Huxley, Linn. Soe. Trans., 1858, vol. xxii., p. 230. For the nomenclature adopted by various writers for the various parts of the external skeleton, see Newport, Cyclopaedia of Anatomy and Physiology, Article ‘Insecta,’ pp. 885,913 ; and 78 Descriptions of Preparations. for a fuller vocabulary, Burmeister’s Manual of Entomology, translated by W. E. Shuckard, chaps. 11. and 11. 27. IMaco oF DeEatTH’s-HEAD Motu (Acherontia Atropos). Tur development of wings and the differentiation of the body into three great heteronomous divisions, the head, the thorax, and the abdomen, are the most prominent external points in which the perfect insect differs from the imago. The scaly covering of the body and wings, the great development of the eyes, the somewhat smaller but still not inconsiderable relative increase of the size of the antennae and of the legs, the replacement of the fused maxillae and labium of the larva by a spiral sucking proboscis, and a labium provided with large palpi, and the reduction of the actively functional mandibles to purely rudimentary structures, are almost equally obvious points of difference between the larva and the imago of a Lepidopterous insect. The maxillary palps are, as in many Hymenoptera, and unlike what we observe in Diptera, very small as compared with the labial. The prothorax is much reduced in size. When viewed from above, the dense covering of scales having been removed, it has the appearance of a narrow ring, whence its technical name of ¢ collar,’ interposed between the head in front and the largely developed mesothorax behind. The pronotum carries laterally a pair of vesicular scales covered with hairs, and known as ‘patagia.? They are characteristic of the order, and distinct from the ‘ tegulae’ or wing-covers, with which they have been sometimes confounded, and which are carried by the mesonotal praescutum, and though very largely developed in the Lepidoptera, are not peculiar to them. As points of more or less classificatory importance, mostly with reference to the differences observable as existing between the diurnal and nocturnal Lepidoptera, may be noted, firstly, the ter- mination of the multi-articulate antennae in a filament, not in a club ; secondly, the existence of a ‘ retinacular’ apparatus, whereby a spinous outgrowth on the under surface of the base of the hinder wing connects it with an annular ligament similarly developed on the under side of the anterior wings ; and thirdly, the two pairs of spurs on the inner side of the posterior tibiae. The family Imago of Death’s-head Moth. 79 Sphingidae have no ocelli, and the genus Acherontia has the spiral proboscis much shorter than other genera belonging to the family. In their possession, when larvae, of provisional organs, of which no traces are left in the perfect insect, the Lepidoptera resemble the Neuroptera and Hymenoptera Phytophaga, amongst the orders dis- tinguished by quiescence in the pupa-stage, and said consequently to have a ‘ perfect metamorphosis,’ as also the Orthoptera Am- phibiotica amongst Ametobolous insects. The true Hymenoptera, on the other hand, and the Coleoptera, with a few exceptions, possess no provisional organs in this larval state, though they pass into perfect quiescence as pupae. This latter condition therefore should be taken as the essential characteristic of a ‘ perfect meta- morphosis.’ For the characteristics of perfect and imperfect metamorphosis, see Gerstaecker, Klassen und Ordnungen des Thierreichs, bd. v., p- 189. 28. Larva oF Goat Morn (Cossus Ligniperda), Dissected so as to show the various internal organs of vegetable life, and the points in which they differ from those observable in the perfect insect. Tue dorsal integuments have been divided down the middle line, and turned outwards on either side, together with the muscles which were in connection with them. The greater part of the body- cavity is occupied by lobulated masses of adipose tissue, known as the ‘fat body, or ‘rete,’ which disappear almost completely in the adult insect of the orders with a perfect metamorphosis. In the middle line we see the digestive tract, which passes, without forming any convolutions at right angles to the long axis of the body, from the mouth to the anus. Its most anterior segment, seen in this Preparation, is the transparent-walled oesophagus upon which is seen the highly developed nervus recurrens. 'This nerve is connected, anteriorly, with a series of three ganglia which are placed one behind the other, and correspond with the single ganglion Jrontale of some insects; and, posteriorly, at the junction of the oesophagus and stomach, with a plexus into which the two lateral stomato-gastric nerves enter. The stomato-gastric nerves undergo less change in metamorphosis than perhaps any other system of 80 Descriptions of Preparations. the larva. The stomach succeeds to the oesophagus, from which it is readily distinguished by the opacity of its walls and the tracheae which are distributed to it in great abundance. Bands of oblique muscles are observable decussating superficially, and longitudinal muscles lying at a deeper level in its walls. The tubular renal organs, the so-called ‘Malpighian vessels,’ are seen upon the pos- terior half of the stomach, forming two loops on either side, the mesially placed being shorter than the more externally placed loops, and having its limb which passes towards the anal end of the body bifurcated, whilst the returning limb of each outer loop remains undivided. The two loops on each side thus form three trunks which form an intricate interlacement in the posterior part of the body-cavity, on either side of the intestine. The two stems themselves fuse on either side into a single trunk, which opens into the intestine a short way below the pylorus; and as the product of these tubules is uric acid, the portion of intestine below their opening may be regarded as excretory, and that intercepted between their opening and the pylorus, as corresponding func- tionally with the small intestine. The point however at which these vessels open into the digestive tract may vary, in different orders, from the immediate vicinity of the pylorus to the immediate vicinity of the anus. The looped portions of these organs are of larger calibre than the more complexly convoluted posterior por- tions ; from which they differ also in being smooth exteriorly, and cylindriform, instead of having a moniliform appearance, from being beaded over with sacculi. The rectum, which is considerably longer than the small intestine, has its external surface divided into six longitudinal strips by as many muscular bands; and the spaces thus marked out are again subdivided by a very much larger number of very much smaller transversely running muscular bars. The long convoluted white tubes, the coils of which are seen to commence with a blind end on either side, about opposite the junction of the stomach and intestine, are the silk glands, and they pass to the under surface of the digestive tract, anteriorly, to end ina common duct opening in the modified labium or ‘ spinneret.’ Underneath the coils of the silk gland of the left side, a large trans- parent walled bladder is seen, from the posterior end of which a tubular gland passes off to form the mass of convolutions called the ‘queue du vaisseau dissolvant’ by Lyonet in his elaborate mona- Larva of Goat Moth. 81 graph of the anatomy of this larva, and bent round so as to lie in apposition with the bladder into which it opens, and in the interval between it and the stomach. The bladder, with the pos- terior extremity of which this tubular gland is thus connected, opens anteriorly by means of a wide duct into the mouth ; and the organ thus made up of a duct, a bladder-like receptacle, and a tubular gland, may be seen to correspond with the much smaller salivary glands of the perfect insect. Neither upon the fasciculi of tracheae which are seen passing inwards from the spiracles to dis- tribute themselves to the viscera, nor upon the longitudinal canals connecting the stem whence these fasciculi spring, which may be seen here and there in the intervals left between the lobes of the ‘fat body,’ are there any vesicular dilatations developed in the larval state. This relatively inferior evolution of the respiratory system may be explained upon purely mechanical grounds, when we consider the comparatively sluggish movements of the larva, whilst the physiological necessity which exists during periods of growth and development for an active performance of the renal functions, will account for, the large development of the Malpighian vessels here observable. And the all but complete absorption and disappearance of the ‘fat body’ at the end of the metamorphoses of metabolous insects, is to be explained by the need they have, especially during their period of existence, as pupae, for a large supply of foree and matter, for the carrying out of the complex changes in, and the superadditions to, the larval organism which the arrangements of the muscles and the evolution of the reproductive organs in the imago may be taken as illustrating. Such dif- ferences in the digestive apparatus of the larva as those already spoken of (Prep. 25, p. 75) in the appendages of the oral segments, as the larger calibre and the lesser length of the digestive canal, as the absence of convolutions, and of a crop, and as the much larger size of the salivary glands, are obviously correlated with the dif- ferences existing between its mode of sustenance and that of the butterfly. The presence of a rectal coecum in the perfect insect, is to be noted as an additional point of contrast. The disappear- ance of the silk-glands during the pupa-stage is readily explicable by the fact, that all need for such organs ceases after the forma- tion of the cocoon; and the condition of semi-fluidity to which the various organs of the pupa are reduced in the early stages of the G 82 Descriptions of Preparations. period of quiescence, makes the method of their disappearance easily intelligible. A monograph of great merit and detail has been written upon the anatomy of the larva of the Goat Moth, by P. Lyonet, Traité Anatomique de la Chenille qui ronge le bois de Saule, 1762, in which excellent figures will be found of the digestive system in pl. v. xiii. xviull., of the respiratory in pl. x. x1., of the mus- cular in pl. vi. vil. vull., of the ganglia frontalia of the azygos stomato-gastric system, pl. xvill., for which see also Brandt, Ann. Sci. Nat., Ser. i1., tom. v., 1836, p. 99. For the sources for the production of fat within the animal’s body, see Voit, Zeitschrift fiir Biologie, Bd. v., Hft.i., p. 79, 1869. For the development of the ‘fat body’ in Lepidoptera, see Hermann Meyer, Zeitschrift fur Wissenschaftliche Zoologie, 1. 175. For the absorption of it in the processes of growth and develop- ment, especially of the reproductive organs, see Peters, Carus, and Gerstaecker, Handbuch der Zoologie, p. 120, and Weis- mann, Die Entwickelung der Dipteren, p. 178. For the changes of consistence observable in the tissues and organs of the Lepidopterous pupa, see Newport, Phil. Trans., 1832, p- 390; and for the much more extensive changes in the way of histolysis which appear to furnish an instance of < free cell- formation’ on the one hand, and on the other to approximate the character of the metamorphosis of the coarctate dipterous pupae to that of ‘alternation of generations,’ see Weismann, igs; pp--135,.404,176, 231, 232, 239. the respiration and temperature of insects, see Newport, Phil. Trans., 1836, 1837. 29, Larva or Priver HawK Mors (Sphinx Ligustri), Dissected so as to show its nervous system. Tue dorsal integuments and the various organs of vegetative life have been removed; a black bristle has been passed through the nerve collar, and slips of blue paper placed under various parts of the chain of ventral ganglia. In the nerve system as thus ex- Larva of Privet Hawk Moth. 83 posed and prepared, twelve main ganglionic masses are readily detectible with the naked eye. The first of these is placed above the oesophagus, is divisible into two lobes by a shallow antero- posterior depression, and from its relation to the eyes and antennae, may be called the ‘cerebroid’ ganglion. The first sub-oesophageal ganglion, by the commissural junction of which to the cerebroid, the nerve collar is formed, is in closer proximity to the second than this is to the third, or the third to the fourth, or the fourth to the fifth. These five ganglia resemble each other in being more or less heart-shaped, the nerves they give off being directed forwards ; the first of them supplies the organs of the mouth, and the other four those of the thorax. The first of these ganglia is represented in the developing Crustacean Astacus fluviatilis by three pairs of ganglia corresponding severally to the mandibles, the anterior, and the posterior maxillae, but, so far as is known, it is connate in the developing insect from the earliest periods. The second, third, fourth and fifth pairs of ganglia are distinct in development in both these animals; they are fused into a single ganglionic mass in the adult forms of both; the single mass thus formed may retain more or less distinct indications of its originally composite character, but in the insect it does not, as in the Crustacean spe- cified (see Prep. 34), fuse with the similarly fused mass supplying the three true jaws. Thus the distinctness of the head of the insect from its thorax is preserved and reproduced in its nervous system, whilst the fusion of head and thorax in the Crustacean is similarly reproduced also. The fact so far as relates to the class Insecta is sometimes expressed by speaking of their brain as con- sisting of a sub-oesophageal as well as of a supra-oesophageal portion, or of a ‘cerebellum’ as well as a ‘ cerebrum,’ the former of which is in connexion with a chain of ventral ganglia. As however the serial homology of the various ventrally-placed appendages of the articulate Neuropods is universally recognised, this nomen- clature is less to be recommended than one which by numbering the segments of the nerve cord as is done here, enables us at once to see where correspondence has or has nat existed, or been re- tained between the external and the internal organs. Though the line of division between the head and thorax of the insect, both in its larval and its perfect state, has thus a diastema in the ganglionic chain corresponding to it internally, which is not preserved in the a 2 84 Descriptions of Preparations. sephalo-thoracic ganglion of the Crustacea; it is by no means invariably the case in other parts of the insect’s organism, that a fusion or distinctness of external segments is reproduced internally by a fusion or segmentation of the chain of nerve ganglia. The sixth, seventh, eighth, ninth and tenth ganglia are more or less spheroidal in form, the two first disappear, the three last are re- tained in the adult insect. The eleventh ganglion is ‘distinctly divisible into two lobes by a bilaterally symmetrical construction, representing thus, as also by the distribution of its nerves, the two ganglia, by the fusion of which it is composed. In the larvae of some insects, as, for example, Phalaena neustria, Dorcus paral- lelepipedus, and Corethra plumicornis, these ganglia retain as much or more of their typical distinctness, and even in the larvae of Muscidae, where the ventral cord is not itself seemented, eleven pairs of nerves are given off from it exclusively of those in con- nection with the jaws, indicating thus that the number of post-oral ganglia is twelve. The tenth, and the bilobed eleventh ganglia, appear to correspond to the six post-abdominal ganglia of Astacus fluviatilis ; and the five ganglia from the fifth to the ninth, with the five ganglia in relation with the five pair of ambulatory limbs in the Crustacean. A slip of blue paper has been passed underneath the two diverging cords of commissure of the third and fourth post-oral ganglia, and we see in the intercepted space one of the systems of ‘ respiratory,’ ‘accessory,’ or ‘ transverse’ nerves, connecting itself with the larger ganglia of the ventral in much the same way as the ‘ ganglion frontale’ and the ‘lateral nerve ganglia’ are connected with the cerebroid ganglia. The ‘ transverse nerves’ of each inter-ganglionie space are not only connected with these larger ganglia, but also with each other, so as to form a continuous chain overlying the ventral cord. From this chain, nerves pass to the tracheae and spiracles, and also to the muscles which act upon these organs and upon the wings. One of the large longitudinal tracheae is seen on the right side of the future thorax, in which part of the body the respiratory system attains ultimately its greatest size and importance, and has the system of transverse nerves similarly evolved in correlation with it. One of the diagonal muscles is seen passing through the interval between the cords connecting the second and third ventral ganglia. This and the succeeding interspace are represented in the perfect insect Larva of Privet Hawk Moth. 85 by a single oval foramen, the third post-oral ganglion having dis- appeared, and the mass made up by the fusion of the fourth and fifth, having closely approximated to that representing the second. For a detailed account of the metamorphoses of the nervous system in the Sphinx Ligustri, resulting in the replacement of the eleven ventral ganglia of the larva by one sub-oesophageal, two thoracic and four abdominal in the imago, see Newport, Phil. Trans., 1832 and 1834; or, Cyclopaedia of Anatomy and Physiology, Article ‘ Insecta,’ p. 962; Herold, ‘ Entwickelungs- geschichte der Schmetterlinge,’ pp. 58, 59; and description of Tab. ii., where he speaks of the ventral ganglia of the larva of Papilio Brassicae as being twelve in number; the com- missural cords between the eleventh and twelfth being absent. For accounts of the first appearance of the nerve system, in the developing embryo of various orders of insects, see Weismann, ‘Entwickelung der Dipteren, 1864, pp. 38, 82, 190, 192; Rathke, ‘Zur Morphologie, Reisebemerkungen aus Taurien,’ 1837, pp. 123-127; Léon Dufour, Ann. Sci. Nat., Ser. ii. tom. 18, pl. iv. and v. See also, for the relatively late period at which the nerve system is developed and differentiated from the structures which underlie it, Rathke, ‘ Bildung und Ent- wickelung des Flusskrebses,’ p. 85 ; Zaddach, ‘ Die Entwicke- lung und den Bau der Gliederthiere.’ For development of the first sub-oesophageal ganglion, see Metschni- kow, ‘Embryologische Studien an Insecten,’ p. 79, Taf. xxx., fig. 33; Zeitschrift ftir Wissenschaftliche Zoologie, Bd. xvi. For the ‘nervi transversi,’ see Newport, |. c. 1834, p. 401; Leydig, For Vergleich Anat. p. 205, Taf. vii. fig. 1, Taf. ix. fig. 2. descriptions and figures of the systems of tracheae and of muscles, see Lyonet, Traité Anatomique de la Chenille qui ronge le bois de Saule, 1762; and Newport, Phil. Trans. 1836 ; and for descriptions of the variations in the muscles of the larva of Pygaera Bucephala, see Lubbock, Linn. Soe. Trans., vol. xxii. pt. ii., 1857. For the relations existing between the external and internal struc- tures, see Burmeister’s ‘ Manual of Entomology,’ translated by W. E. Shuckard, p. 281; Blanchard, Ann. Sci. Nat., Ser. ii1., tom. v., 1846, p. 281. 86 Descriptions of Preparations. 30. Common Cockroacu (Periplaneta Orientalis), FEMALE, Dissected so as to show its digestive, renal, nervous, and reproductive systems. THE greater part of the dorsal integumental system has been removed by incisions carried along either side; the short elytron, the only representative of the wings in the females of this species, has been left cm situ on the right side, where it is seen reaching just far enough back to overlap a part of the metanotum; the greater part of the fat body which abounds in the interspaces between the viscera, especially in the abdominal region of these insects even in their adult state, has been removed, and the digestive tract fastened out upon the left side of the body. The upper seg- ment of the digestive canal, seen in this preparation, 1s the crop, which is about three-fourths of the entire length of the body, and is distended with food. The entire length of the digestive tract would be little more than twice that of the body, and this compara- tive shortness may be considered as compensated for partly by the character of the food of this species, and partly by the large quan- tities which, as seen in this preparation, they devour. A muscular subconical gizzard, an organ which is not developed in the larvae of insects with a perfect metamorphosis such as the Coleoptera, even in species which have it when adult, but is developed in the larvae of Orthoptera, including Libellulidae, follows after the crop. Eight coeca are arranged in a whorl round the commencement of the ‘chy- lific stomach,’ and a very much larger number of very much longer and more slender tubes are similarly arranged around its lower end. The gizzard does not open directly into the chylific stomach, a narrow neck of about the same length as the gizzard itself inter- vening between the apex of the gizzard and the zone marked out by the eight coeca just mentioned. These coeca appear, from the facts that they often contain a yellowish fluid, and that they never afford lodgment for particles of food even when the digestive tract is distended, to be analogous to the liver of higher animals, whilst the existence of uric acid in the other set of tubules already men- tioned, the so-called ‘ Malpighian vessels,’ would appear to justify Common Cockroach. 87 us in speaking of them as ‘renal’ organs. The colon, which is bent upon itself, and has its external surface beaded over with granulation-like pouches by the action of its muscular coats, is connected with the lower end of the chylific stomach by a short segment of small calibre, and of similar length to that which connects the upper end of the chylific stomach with the larger end of the gizzard. The colon ends in a rectum, which is divided into six longitudinal areae by as many longitudinal muscular bands, alternating with internally-placed lamelliform projections of the inner coats of the intestine. A somewhat similar arrangement has already been noted in the larva of the Goat-moth (p. 80) ; and in the larvae of certain Libellulidae the supply of tracheae to the ridged surface thus constituted, is so abundant as to convert it into a respiratory organ. On either side of the junction of the crop to the oesophagus is seen the bilobed salivary gland. On the right side in this preparation is seen the salivary recep- tacle, a pellucid bladder, reaching a little farther back than the gland. The duct from this receptacle fuses with that of its fellow of the opposite side, and into the common duct thus formed a second duct, formed by the junction of the ducts of the two glands, is re- ceived, so that all the four ducts find an outlet into the mouth by a short common canal. An azygos nerve, the nervus recurrens, from the ‘ ganglion impar’ or ‘ganglion frontale’ of the stomato-gastric system, is seen passing from before backwards to join a triangular ganglion placed a little way in front of the middle point of the dorsal median line of the crop. From this ganglion a nerve passes off on either side to the posterior extremity of the crop, and may be seen to have an elon- gated thickening developed upon it at the lower third of its length. A third nerve, not seen in this preparation, has been described as passing off from the centrally-placed triangular ganglion to the salivary glands. The ganglion impar, from which the nervus re- ceurrens takes origin, is not seen in this preparation, being situated anteriorly to the cerebral ganglia, with which it is connected by delicate filaments joining it just internally to the large antennary nerves. The paired ganglia of the stomato-gastric system are situated some way posteriorly to the cerebral ganglia; and the short nerve seen on either side of the nervus recurrens, just where the salivary gland abuts upon the crop, is given off by the posterior 88 Descriptions of Preparations. of the two pairs of ganglia, of which the symmetrical portion of the stomatogastric system consists, in this as in most other insects. The paired ganglia are connected with each other, with the cere- bral ganglia, and finally with the nervus recurrens, which struc- ture, however, together with the ganglia in connection with it, constitutes in these and most other insects by far the most im- portant part of the stomato-gastric system. In the abdominal region are seen six ganglia corresponding to the six posterior ganglia of the Lepidopterous larva. The two first of the six, which correspond to the two which become obsolete in the butterfly, are more closely apposed to each other than are any of the succeeding four. The last ganglion is more or less cordiform, and larger than those which precede it, and gives off nerves to the lower portions of the generative and digestive tubes. The ovaries are of the kind called ‘verticillate’? by Muller; and consist of eight moniliform tubes on either side, which are connected anteriorly with the dorsal element of the prothorax by means of a suspensory ligament, made up of the fusion of filaments given off from their apices; and which inferiorly open upon the convex end of a pear-shaped oviducal infundibulum, as ordinarily figured. The infundibula of the two sides which may be seen, when undistended, to have the egg-tubes inserted laterally as in other Orthoptera, pass beneath the terminal nerve structures and the ‘ oviscapt’ to form a common vagina, which opens in the interval between the eighth and ninth abdominal segments. Immediately posteriorly to the last nerve ganglion, in the angle limited by its branches, we may see with a lens the receptacula seminis, which take the shape of two short contorted coeca, one of which is rather larger in calibre than the other, and which open by means of a single short duct in the sternum of the ninth segment. The ‘colleterial’ or ‘sebaceous’ glands, which consist of numerous delicate tubules of much greater length than the receptacula seminis, open by two ducts in an orifice upon the sternum of the tenth segment. The sternum of this segment developes the smaller and inner processes of the ‘oviscapt,’ whilst that of the ninth developes the elongated ex- terior pieces of that apparatus; and as the lateral anal valves re- present an eleventh segment, we have thus the typical number of the segments of the Arthropodous abdomen made up. The recep- taculum seminis is ordinarily in insects an azygos vesicle, and it is Common Cockroach. 89 possible that the aberrant arrangement observable in the Blattinae may foreshadow the more usual one in which a single receptaculum seminis has a gland of a secretory character superadded to it. And, as the number of the ‘ colleterial’ tubules is very considerable, they may be taken, perhaps, to correspond not only to the colleterial glands of other insects, but also to their so-called ‘scent glands.’ The food, and to a considerable extent the habits, of the larvae and of the adult insect being identical in this family, we find little differ- ence existing between their internal structural arrangements beyond that which a greater prominence in the evolution of the reproductive apparatus constitutes. The retention of the ‘fat body’ is obviously correlated with the absence of any period of quiescence and absti- nence from food, such as that of the pupa stage of Metabolous insects, and of the need for a supply of force which the changes gone through by those classes entail. Externally the imperfect insect in the class Orthoptera does not, with the exception of the Orthoptera Amphibiotica, such as the Libellulidae and Ephemeridae, differ from the adult by the possession of any provisional organs of which the perfect insect is destitute, but contrasts with it almost exclusively by inferiority of size, by the smaller number of facets in its corneae, by the absence of wings, and in this family by a greater lightness of colour. Great differences, however, exist as to this latter particular between adult individuals of this species. For a monograph of the order Orthoptera, see the Latin work, ‘Orthoptera Europaea,’ Auctore Leop. Henrico Fischer, Lip- siae, 1853, where a general account of the external and internal anatomy of the entire order will be found, pp. 5-32, and an account of the anatomy of the family Blattinae will be found, pp. 84-88. See also Léon Dufour, Recherches Anatomiques et Physiologiques sur les Orthoptéres, 1834, Mem. Acad. Sci., tom. vii., des Savans Etrangers ; also in 4to, Paris, 1841. At pl. v., figs. 44-47, good figures of the digestive and reproductive systems are given. See also PI. vi. ¢m/ra, with description. For a monograph’ on the digestive and renal systems of this insect, see S. Basch, Sitzungsberichte, Kaiser Akad. Wiss. Wien, vol. 33, 1858, p. 234, Math. Nat. Classe. An account of the natural history, as well as of the anatomy of the common Cockroach, may be found in a short monograph, Descriptions of Preparations. entitled ‘Beitrage zur nahern Kenntniss von Periplaneta (Blatta) Orientalis,’ von C. Cornelius, Elberfeld, 1853. For an account of the various glands superadded to the essential organs of the female reproductive apparatus, see Siebold, in Miiller’s Archiv. for 1837, p. 393 seqq., and for their arrange- ment in Blatta (Periplaneta) Orientalis, p. 408. For figures of a female reproductive apparatus essentially similar to that here described, see Lespés’ account of the Zermes Lucifugum, Ann. Sci. Nat. Ser. iv., Tom. v., Pl. 6, fig. 24-27. For the orifices of the various ducts in the reproductive apparatus, see Hux- ley, Linn. Soe. Trans., vol. xxi. p. 231. For the ‘ suspensory ligament’ of the ovary, see Stein, ‘ Vergleichende Anatomie und Physiologie der Insecten,’ pp: 36, 41-43; Muller, Nova Acta, xii., pt. ii., p. 578. For the composition of the ‘oviscapt’? and the number of the abdominal somites, see Lacaze Duthiers, Ann. Sci. Nat., Ser. iii., tom. xvil., 1852, p. 227; tom. xix., pp. 229-233, and Huxley, Linn. Soc. Trans., vol. xxil., 1858, p. 231. For the development of the fat body independently of the yolk, see For Elias Metschnikow, ‘Embryologische Studien an Insecten,’ p- 73, and for its connection with the production of phospho- rescence in such insects as the Lampyris splendidula, see Leydig, ‘Lehrbuch der Histologie,’ p. 342. r a description, with figures, of the stomatogastric nervous system, see Brandt, Ann. Sci. Nat., Ser. 1, tom. v., 1836, p- 103, pl. iv., figs. 4, 5. Bibliographical references, see Scudder, Smithsonian Institu- tion’s Catalogue of Orthoptera, Washington, 1868, pp. 17-63. 31. Common CrayFisH (Astacus Fluviatilis), FEMALE. Tus Crustacean’s body consists of two great divisions, the so-called ‘ cephalo-thorax,’ covered dorsally and at the sides by a carapace, and carrying fourteen pairs of articulated appendages, and the post-abdomen consisting essentially of six definitely an- nulate and calcified segments, to the posterior one of which a powerful natatorial organ, the ‘swimmeret,’ is articulated. The Common Crayfish. 91 cephalo-thoracie carapace again is divisible into two regions, an anterior and a posterior, by the well-marked curved line with its concavity looking forwards, which is known as the ‘cervical su- ture.” The anterior portion of the carapace is called the ‘ cephalo- stegite ;? and the posterior the ‘omo-stegite ;? inasmuch as an examination of the relation of the inner aspect of the cervical suture to the hindmost of the three pairs of jaws, that is to say, to the most posterior of the cephalic appendages, shews that the anterior portion of the carapace corresponds with the head, and the posterior with the post-cephalic segments. The crayfish furnishes an excellent example of the general law that every segment carries an appendage in the Crustacean, the first post-abdominal segment in this (female) specimen being the only segment in which a distinct pair of appendages is not readily recognizable. The pe- dunculate position of the eyes in the Decapodous Crustaceans makes it easy to understand, even without a reference to the history of development, or to instances of abnormal replacement of the eyes by articulated appendages’, how the eyes may be regarded ~ as homologous with articulated appendages ; and that the eyes and antennae do not really belong to the tergal aspect of the anterior cephalic segment, may be shewn not merely from the history of the reflection upwards and backwards of the developing cephalic blastoderm, but also from the direction and relations of these three pairs of sensory appendages in such Crustaceans as the Squillina. With the history of the relations of these organs in the developing Astacus, or with that of their disposition in the family just mentioned, before the mind, it is easy to see how the oph- thalmic peduncle may be spoken of as the most anterior of the ap- pendages, and as marking out the most anterior of the segments of the body. Next in order to the ophthalmic peduncles come the ‘antennules,’ consisting, as usual in Crustacea, of three basal joints, succeeded by a multi-articulate flagelliform element, which is here double. The ‘antennules’ are said to correspond to the antennae s See A. Milne-Edwards, Comptes Rendus, vol. lix., p. 710, f, 1864. It may be added that the pedunculate position of the two centrally-placed eyes in certain Ephemeridae, for which see Westwood, Modern Classification of Insects, pp. 25, 31, De Geer, Histoire des Insectes, viii., pl. 18, tom. 2, fig. 10; Kirby and Spence, pl. xxvi, fig. 39, is, when we consider the many Crustacean affinities of the order Orthop- tera, not without significance. 92 Descriptions of Preparations. of perfect insects; in some Isopoda, however, which in many points approximate to insects, they are rudimentary. The inner of the two antennulary flagella is the smaller, and correspond to the structure described in other Crustacea as a ‘secondary ap- pendage.’ Posteriorly, and a little externally to the antennules, come the antennae, each of which consists of a single multi- articulate flagellum carried by a series of five basal joints, the second one of which, if we count the sternal or proximal joint as the first, carries the representative of the appendages which are developed early upon this joint, but are subsequently aborted in Carcinus maenas, in the shape of two scales, one much the larger, somewhat of the shape of a short wide knife-blade, the other minute, prolonged into a spinous point externally, and ar- ticulating internally with the fourth basal segment. A com- parison of the five basal joints of the antenna with the five basal joints of such a typical seven-jointed appendage as any one of the four posterior ambulatory legs in the Astacus, will leave no doubt as to their correspondence ; and the multi-articulate flagellum will thus come to be the homologue of the two terminal joints of those appendages which are known as the ‘ propodite’ and ‘ dactylo- podite,’ and are sometimes supposed to correspond to the ‘ tarsus’ of insects. The proximal joint of the antenna has a conical process developed on its inferior surface, internally to the apex of which there exists an orifice leading into the antennary gland. On the triangular space between these two conical processes which is known as the ‘epistoma,’ and is constituted by the sternum of the antennary segment, are seen lying the anterior extremities of the palpiform exopodites of the two anterior maxillipeds, which correspond to the two anterior thoracic legs of insects. The pos- terior pair of maxillipeds have been displaced a little backwards, so as to give a better view of the two other pairs of foot-jaws, and of the three pairs of jaws which they partly conceal; though they never form for them, either in Macrurous or Anomurous Decapods, such a perfect operculum as they do in the Brachyurous. Posteriorly to the ‘epistoma,’ we see the upper lip or ‘ labium,’ and between it and the first pair of thoracic appendages, or ‘ maxillipeds,’ we have the three cephalic appendages essentially concerned with the prehension of food, and assisted in that function in the Hedri- ophthalmatous or fourteen-footed Crustaceans by two, and here in Common Crayfish. 93 the Decapods by all three pairs of thoracic limbs. Of the three true jaws the most anteriorly placed, the so-called ‘mandible,’ carries a tri-articulate palp with an expanded terminal joint, and corresponds as a whole to an ambulatory leg, or to the endopodite of a foot-jaw. The palp, as being of great use in directing floating food towards the mouth, is rarely absent in Crustacea, except in the terrestrial Isopods and Amphipods. The basal portion of the mandibular appendaget appears to correspond to the four basal joints of the ambulatory legs; and it may be remarked that the denticulation and anchylosis of the second and third segments of the third pair of foot-jaws afford an instructive example of transi- tion towards the modification of the basal segments seen in the mandible. The two pairs of foliaceous maxillae, the posterior one of which remains mesially divided, probably in relation to the ingestion of floating food, and does not form a ‘labium’ as in air-breathing Arthropoda, are not seen in this preparation, being closely appressed by the foot-jaws in apposition with them. Of the five pairs of ‘ambulatory’ or ‘ abdominal’ legs, whence the order Decapoda take their name, the first has its two terminal joints or ¢arsus modified, so as to form a large pair of pincers, by having the posterior distal angle of the penultimate joint, or propodite, prolonged so as to be parallel with and commensurate with the dactylopodite. Similar but smaller pincers are developed similarly upon the second and third pairs of feet; the fourth and fifth are not so armed, the penultimate joint not being prolonged beyond its distal articular surface. It may be noted that the chela of the Scorpion, which bears a considerable resemblance to the largest of the three chelae of the Astacus, has its pincer-like portion somewhat differently constituted, the anterior or interior angle of the propodite being produced instead of the posterior or exterior; and the smaller of the two blades of the prehensile organs lying exteriorly, instead of interiorly as in the Crustacean. The large pincers of the scor- pion are homotypical, as representing the two terminal joints of an appendage with the large pincers of the crayfish, but they are not t See figure of edentulous mandible of Matuta Victor in ‘Régne Animal,’ Crustacés, pl. vii. fig. i. c., where the palp has six joints, the three proximal ones of which are very small, whilst the three distal have the proportions of those which make up the ordinary tri-articulate palp. 94 Descriptions of Preparations. its exact homologues, inasmuch as they correspond in strictness with the two terminal joints of its mandibular palp. The four posterior of the five abdominal legs of either side consist each of seven joints, seven being considered by Mr. Spence Bate to be the typical number of the joints in the normally developed appendage of every kind in Crustaceans. The second and third joints are anchylosed in the anterior of these five appendages, as they are in all the five of the Brachyura, so as to reduce the number of separate joints to six. The proximal joint is known as the ‘ coxopodite;’ a black bristle is in this (female) specimen introduced into the oviduct, which opens in Macrurous and Ano- murous Decapods, as also in Hedriophthalmata, in the coxopodite of the third abdominal appendage. The second joint is known as the ‘basipodite,’ or ‘basis.? It is in the interval between the ‘basi-’ and ‘ coxopodite’ that the separation of the limb takes place when a Crustacean throws it off in consequence of fright or injury. The third, or ‘ischiopodite,’ is marked by an annular constriction a little way distally to its articulation with, when it is distinct from, the basipodite. This constriction may perhaps represent the aborted exopodite, which in the three posterior abdominal legs of Squilla is articulated to the third segment of the appendage; by observing its presence we are enabled to identify the various segments in the appendages of the abdomen in Brachyura. The fourth, the longest of all the segments in all the five appendages except the first, is known as the ‘meropodite,’ and has been compared with the ‘femur’ of insects; the fifth is known as the ‘ carpopodite, and the two terminal are known as ‘ propodite’ and ‘ dactylopodite,’ and have been compared to the ‘tibia’ and ‘tarsus’ of insects. The append- ages on the first post-abdominal segment are rudimentary; to the hairs upon the appendages of the succeeding segments, some of the large ova of this fresh-water Decapod may be observed to be attached. The appendages of the second, third, fourth and fifth post-abdominal segments consist of a biarticulate ‘ protopo- dite,” the proximal segment of which is small and annular, and the distal cylindriform ; and of two multiarticulate filaments repre- senting an ‘exopodite’ and an ‘ endopodite,’ the basal segment of the latter of which is much the largest in either series. The appendages of the sixth abdominal segment form the powerful “swimmeret’ of the crayfish. The lateral elements of this organ Common Crayfish. 95 correspond to the appendages already described in the five ante- rior post-abdominal segments, and consist each of an uniarticulate ‘ protopodite,’ which carries on its apex a biarticulate ‘ exopodite’ and a uniarticulate ‘endopodite.’ The mesial element of the ‘swimmeret’ is constituted by the so-called ‘telson, an azygos plate divided in the crayfish into an anterior and posterior portion by a transverse suture, immediately anteriorly to which the anus opens on the ventral surface of the body. The telson has some- times been reckoned as a seventh post-abdominal segment, but as it, with scarcely an exception, is without appendages; as it is generally aborted, or rudimentary, or fused with the sixth segment in Hedriophthalmata ; and as, finally, it is developed after the other segments and from the dorsal surface of the body, it is better to re- gard it as being simply an outgrowth from the sixth segment of the post-abdomen, in the same way as the rostrum may be considered to be an outgrowth from the carapace. The proximal segment of the ‘telson’ is not calcified continuously across its ventral surface, whereas the true post-abdominal segments have each of them a horizontal calcified chitinous chord, connecting, without the inter- position of any suture, the opposed internal surfaces of the are represented by their dorsal wall. At the junction of the chord and are are the articular surfaces for the post-abdominal append- ages already described. The portion of the dorsal wall which is prolonged downwards beyond the level of the junction of the ventral and dorsal portions of the external skeleton of each segment is known as the ‘pleuron.’? There is no such element in the telson. The pleura of the sixth, fifth, fourth and third segments, and the convex tergal surfaces whence the pleurae arise in all the segments, have facets developed upon them anteriorly, which are overlapped by processes of the segments next in front. The pleura, however, of the second and first post-abdominal segments, develope processes which are not overlapped by, but themselves overlap, the one the pleuron of the first post-abdominal segment, and the other the posterior pleural edge of the carapace. A quadrangular area, corresponding pretty accurately with the position of the subjacent heart, is marked off in the posterior portion of the carapace, or ‘omo-stegite, by two linear depressions on either side the middle line, and by an anterior faintly marked line, eurving concentrically with the convexity of the cervical suture, 96 Descriptions of Preparations. and uniting the anterior extremities of the two laterally placed lines. The area on the omo-stegite intercepted between the curved line and the cervical suture represents the terga of the three thoracic segments; the area posteriorly to this line represents the terga of the five abdominal segments. The portions of the omo- stegite which lie laterally to these mesial areae are the connate pleura of all the eight segments just mentioned ; from their function they are called ‘ branchio-stegites.’ Their free border con- sists of a smooth rim, thickly fringed with hairs, arising along its inner edge; between which and the coxopodites of the thoracico- abdominal segments, water can find free access to the branchial chamber. The branchial portions of the carapace may be considered as representing the fused pleura of the eight thoracico-abdominal segments. The cervical suture which separates the omo-stegite from the cephalo-stegite begins anteriorly opposite the middle line of the antennary sternum. From this point it passes at first horizontally backwards ; then it turns almost vertically upwards, bounding a surface of the omo-stegite, which is slightly convex forwards, and beset with from four to five spines ; finally, it bends boldly backwards, describing a curve the mesial portion of which bounds the cardiac area anteriorly. The cephalo-stegite is pro- longed anteriorly into a triangular mesial rostrum, terminating anteriorly in a sharp point, about on a level with the commence- ment of the antennary flagellum. The cephalo-stegite carries a sharp spine on either side, just externally to the basis of the rostrum. Immediately posteriorly to this spine is seen a convex surface, which is conspicuous even in early stages of development, and marks the origin of the powerful adductor mandibulae muscle. Inferiorly the cephalo-stegite is connected, though it is not anchy- losed, with the antennary sternum, as it is in the Brachyura, and indeed in the much more nearly allied species Homarus Vulgaris. For a full description of the external and internal anatomy of Astacus Fluviatilis, see Huxley, Medical Times and Gazette, Feb. 7, 1857 seqq.; and for the tegumentary skeleton and morphology of Decapodous Crustacea generally, see Milne- Edwards, Ann. Sci. Nat., Ser. iii., tom. xvi., p. 221, 1851. For the development, see Rathke’s Monograph, ‘ Ueber die Bildung und Entwickelung des Flusskrebses,’ 1829; and for the de- For For Common Crayfish. 97 velopment of the ‘telson’ in particular, p. 27, and ‘Zur Mor- phologie, Reisebemerkungen aus Taurien,’ 1837, pp. 113-115. In this latter work about fifty pages are devoted to general remarks on the development of Crustacea. the development of other Crustacea, see Spence Bate, Phil. Trans., 1858; Fritz Miiller, Archiv. fiir Naturgeschichte, 1862, 1863; Van Beneden, Recherches sur la Faune Lit- torale de Belgique, Crustacés, 1861; Claparéde, Beobach- tungen uber Anatomie und Entwickelungsgeschichte wirbel- loser Thiere, 1863, cheque citata. the morphology of the appendages, see Savigny, Mémoires sur les Animaux sans Vertébres, 1816, vol. i., p- 48, Mem. ii., pl. i. and iv. ; Erichson, Entomographien, 1840, where, at p. 28, attention is drawn to the fact of the relative prominence of the thoracic appendages in the larval (Zoea) stages of Crustacea which undergo metamorphosis, and to the illustration which this peculiarity in the development of Crustacea affords of their essential affinity to other Arthropoda which possess the same hexapod arrangement permanently as adults in the class Insecta, or, it may be added, pass through a hexapod larval stage, as Iulus among Myriapoda, and Hydrachna among Arachnida. That the prolegs of Insect larvae are rightly con- sidered as homologous with the abdominal and post-abdominal limbs of Crustacea, though the proleg, even when greatly elon- gated as in the anal appendages of the Puss Moth (Cerura Schrank), is still an annulated rather than a segmented and articulated outgrowth, may be seen from the fact that prolegs and true legs may replace each other. In the Coleopterous Insect Spirachtha Eurymedusa, described by Schiddte in the Ann. Sci. Nat., Ser. iv., tom. v., 1856, p- 178, pl.i., fig. 19, we have the first, second, and third prolegs of the Lepidop- terous larva replaced by biarticulate appendages; whilst in the Coleopterous Curculionidae we have the thoracic legs replaced by prolegs. For excellent figures of the appendages, see Brandt and Ratzebure,, ‘Medizinische Zoologie, Bd. ii., Taf. xi., p. 58; or, Victor Carus, ‘Icones Zootomicae,’ Taf. xi. See also Milne-Edwards, ‘Suites 4 Buffon,’ Crustacés, tom, i. ii, ii., and in ‘ Régne Animal,’ Crustacés, Atlas, pl. iv. H 98 Descriptions of Preparations. For generalizations as to the homologies of the appendages in the various orders of Crustacea, see Spence Bate, ‘ History of British Sessile-eyed Crustacea,’ Spence Bate and Westwood, 1868, Introduction, pp. viu—xx. For the bibliography of memoirs upon the anatomy of the Fresh- water Crayfish, see Brandt and Ratzeburg, ‘ Medizinische Zoologie, Bd. ii., p. 65, note 1; or, Leydig, Handbuch der Vergleichenden Anatomie,’ p. 253. For the differences between Macrurous and Brachyurous Crustacea, see Dana, ‘ Crustacea, U. S. Exploring Expedition,’ pt. 1., p. 49- 32. Common Crayrisu (Astacus Fluviatilis), MALE, Dissected so as to show the nervous, circulatory, and digestive systems in situ, and in the relations they hold to each other and to the external tegumentary skeletal system. Tue nerve system underlies the sternal elements of the various segments ; the heart, the dorsal portion of the omo-stegite, giving off both anteriorly and posteriorly an azygos artery which may represent the more elongated and vasiform heart, which is more usual in Arthropoda than the compressed irregularly polygonal organ seen here; and the digestive tract occupies a position be- tween those of the two other systems. A white bristle has been introduced through the mouth into the oesophagus and stomach, and shows that this latter organ is prolonged as far forwards 1n- ternally as the antennary sternum is externally, and to a point, therefore, much in front of the plane of entrance of the oesophagus. - In order to show these points, the external skeleton and its append- ages, with the exception of the eyes, antennule, and antenna, have been removed on the animal’s left side, together with the muscles in connection with them, and together with the two lobes of the liver and the ¢ green’ or ‘antennary’ gland of the same side. A slip of blue paper has been placed under the nerve cord in the post- abdominal region, in the interval between its penultimate and ante- penultimate ganglia; a second has been placed in the same region, but in its dorsal portion, under the azygos caudal artery and above Common Crayfish. 99 the intestine; a third is placed underneath the sternal artery, just at its origin from the bulbus arteriosus, at the posterior extremity of the heart, from which the post-abdominal artery just mentioned is continued directly backwards; the fourth and most anteriorly placed slip of blue paper occupies an interval between the coecal process, the rudiment of the embryonic yelk-sac, which marks the commencement of the intestine, and the hepatic artery of the left side, just as it emerges from under the cover of the testis, and passes down on to the pylorus. The anterior wall of the stomach, finally, has been displaced a little backwards, and the commissural cord between the supra- and the infra-oesophageal ganglia, which was rendered visible by the removal of the antennary gland, has had its various connections made more evident. The twelve post-oral and the supra-oesophageal ganglia are here seen in profile, and the great lengths of the commissural cords passing between the last-named ganglia and the first of the post- oral series whence the three pairs of foot-jaws as well as the three pairs of true jaws are supplied, is well seen, corresponding with the elongated antennary sternum. Visceral nerves are seen passing from the commissural cords and from the supra-oesophageal mass on to the stomach. A sub-circular raised area on the anterior aspect of the stomach as displaced backwards, and about midway between its upper and lower border, marks the position of the so-called ‘eye,’ a circular calcareous dise periodically developed in the Crayfish. A convex protuberance marks the pylorus, imme- diately behind which is seen, the two hepatic lobes having been cut away, the opening of the left ductus choledochus into the commencement of the intestine. The inferior portions of the hepatic lobes of the right side come into view beneath the pyloric portion of the stomach and the duodenum, along the middle line of which they come into the apposition with the homologous portions of the left hepatie lobes. The convolutions of the vas deferens of the left side fill up the space between the two slips of blue paper which are placed under the hepatic and the sternal arteries, and which abut by their upper angles upon the anterior paired and the posterior azygos testicular lobe respectively. Superiorly to the testicular lobes, and, as in all Arthropoda which possess it, immediately underneath the dorsal integument, is seen the heart. In the interior of the post-abdominal region are seen, H 2 100 Descriptions of Preparations. besides the straight intestine, the nerve cord, and the post-abdo- minal artery already mentioned, the powerful and complex flexor muscles of the post-abdominal segments and the ‘swimmeret ;’ fascicles from which are observable passing to find attachment to ‘apodemata,’ as far forwards as the entrance of the oesophagus. It is by these muscles that the more rapid movements of these animals are executed. For their slower crawling movements, the ambulatory legs are employed, and the muscles which act upon the limbs of the right side, may be seen passing upwards through the apodematal cells to take origin from the epimera as seen im Prep. 34. Some muscular fasciculi not ordinarily described pass backwards from the sternal regions, anteriorly to the mouth on to the anterior surface of the stomach, decussating thus with the commissural and stomato-gastric nerve cords. As a sexual peculiarity, the modifications of the first and second - post-abdominal appendages should be noted. But the testis itself does not extend further backwards than the posterior border of the carapace, and the outlet of the vas deferens, as being placed in the basal joint of the last ambulatory leg, justifies the application of the term ‘ post-abdomen’ to the segments placed posteriorly to it. For figures of the Crayfish as thus dissected and described, see plate vil. For a detailed account of the flexor muscles of the post-abdominal segments, see Milne-Edwards, ‘ Suites & Buffon,’ Histoire Na- turelle des Crustacés, tom. i. p. 157, tom. iii. pl. xin. For the late period at which the digestive tract is developed in Arthropoda, and the possibility of thus accounting for its comparative simplicity and the straightness of its course, see Zaddach, Untersuchungen iiber die Entwickelung und den Bau der Gliederthiere, p. 42. 33. Common CrayrisH (Astacus Fluviatilis), Dissected so as to show the heart, its six arteries, and two of its six venous inlets, im situ. Tux cardiac and part of the cephalo-stegal portion of the carapace has been removed, as well as a flattened venous sinus which was Common Crayfish. 101 interposed between the shell and the heart, and the terga of the two anterior post-abdominal segments. The heart in the Deca- podous, as also in some of the lower Crustacea such as Daphnia, differs in its compressed shape from the vasiform structure which is observable in the other classes of Arthropoda, and indeed in such Crustaceans as Squilla and the Hedriophthalmata. From the an- terior border of the heart a single artery is given off in the middle line, and supplies the eyes and antennules. On either side of this artery is given off the trunk which supplies the antennae; and finally, from either outer angle of the front border of the heart, an artery passes downwards, between the testicular lobe of either side and the intestine, over the pylorus to the hepatic lobes. A slip of blue paper has been placed under the post-abdominal artery, which, passing immediately beneath the middle dorsal line and above the intestine, may be taken as representing the posterior segments of the forms of heart more usually seen in Arthropoda. The sternal artery, which is larger than the post-abdominal, and is given off from the same short trunk, is not seen in this Preparation. Two venous inlets are seen in the anterior fourth of the upper surface of the heart ; the two laterally placed and the two inferiorly placed are not seen in this view. The cavity in which the heart is lodged has been sometimes called ‘a pericardium,’ and sometimes an ‘auricle It is formed by a reflection of the membrane which lines the general visceral cavity ; and it receives the blood returned from the branchiae, so as functionally at least to represent a bran- chial auricle. Six elastic ligaments, the ‘a/ae cordis, pass from the cardiac aspect of this ¢ pericardial’ or ‘auricular’? membrane, to attach themselves to the walls of the heart, their main function being probably to reopen by their recoil the six venous orifices which each systole of the ventricle closes. These hgaments may serve also to suspend the heart in the pericardial sinus, but the arteries which pass off from it are probably in these, as in other animals, the chief means whereby the heart is maintained 7x si¢w. The five arteries arising along the anterior edge of the heart, and the sort of bulbus arteriosus into which the posterior end of the heart tapers, give it the polygonal appearance which distin- euishes the heart of the Decapodous Crustaceans from the similarly unilocular and non-vasiform heart of the Entomostracous order which gives off no arteries. The anterior edge of the heart corre- 102 Descriptions of Preparations. sponds more or less exactly with the curved line already described at page 96 supra, as limiting off in the omo-stegite an area repre- senting the coalesced terga of the thoracic segments anteriorly from one similarly representing the coalesced terga of the five abdominal segments posteriorly. In having thus its anterier edge or boundary not prolonged beyond the region of the abdomen, the heart of Crustacea corresponds with the heart of all other Arthro- poda, and furnishes an excellent illustration of the value in mor- phology of identity in the relative positions of organs which may differ very widely in external shape and appearance. For a figure of the heart of a Decapodous Crustacean, see Professor Owen, Comp. Anat. Invert., p. 318. For a discussion as to the venous system, and as to the prolong- ation or non-prolongation of the branchio-cardiac vessels as distinct tubes through the pericardial sinus into the ventricle, see Straus Durckheim, Considérations générales sur Anatomie Comparée des Animaux Articulés, p. 346; Milne-Edwards, Histoire Naturelle des Crustacés, p. 103, 1834; Lecgons sur la Physiologie et Anatomie Comparée, tom. 1ii., p. 183, 1857, where the views of Straus Durckheim are adopted. For the Alae Cordis and their functions, see Verloren, Sur la Circu- lation dans les Insectes Mém. Couronn et Mém. Sav. Etrang. Acad. Roy. Belgique, tom. xix., pp. 68-70, 1844, where the alae cordis are said not to be muscular even in insects. 34, Common CRAYFISH (Astacus Fluviatilis), MALE, Dissected so as to show its stomach, intestine, reproductive and respiratory systems, in situ. THE greater part of the tergal elements of all the seements of the body have been removed, together with the venous sinuses which underlaid them, as also the heart and its arteries. An arcuated plate, the ‘cardiac ossicle,’ is seen crossing the cardiac portion of the stomach, and receiving the insertion of the anterior gastric muscles, which arise from the ventral base of the triangular Common Crayfish. 103 rostrum. Between these gastric muscles anteriorly is seen the azygos stomato-gastric nerve entering a small ganghon. From this ganglion it is continued onwards, after giving off a nerve on either side, across the cardiac ossicle, posteriorly to which it bifur- cates, and joins one of the lateral stomato-gastric nerves to supply the liver lobes. A small ossicle, the ‘ pterocardiac,’ articulates with either outer angle of the cardiac; and from the base thus constituted the supero-lateral ossicles pass backwards so as to form with it anteriorly, and with the ‘pyloric ossicle’ distally, a tr- angular framework, into the apex of which two other muscles are inserted, which take origin posteriorly from the carapace. Imme- diately in apposition with the portion of the stomach thus strength- ened, is seen the end of the adductor mandibulae muscle, separated from its attachment to the carapace ; and exteriorly again to the muscle, are seen on either side the two lobes of the liver. In the middle line between the hepatic lobes are seen the paired lobes of the testis. Where these lobes join an azygos lobe placed pos- teriorly to them in the middle line, and superiorly to the in- testine, the vasa deferentia are seen taking origin as slender tubes, the calibre of which rapidly widens, and the lengthy convolutions formed by which intrude some way into the post-abdominal cavity, before they turn downwards to open in the basal joint of the last abdominal limb on either side. Posteriorly, the comparatively small strata of extensor muscles having been removed, we see the intestine taking a straight course, as always in Crustacea, to the anus. Externally to the vasa deferentia and hepatic lobes are seen the branchial organs, arranged in three rows, the outermost con- sisting of the branchiferous epipodites, which are developed upon the coxopodites of the two posterior maxillipeds and upon the four anterior ambulatory legs; and the two innermost of simple tree-like upgrowths, developed in pairs from the third maxilliped to the fourth ambulatory leg inclusively, and singly upon the second maxilliped and the last ambulatory leg. The branchiferous epipo- dites are in shape like a leaf, with the two halves of the blade or lamina folded backwards, and with the mid-rib looking forwards. Both halves are longitudinally plicated, but the branchial filaments are developed only upon the half which looks outwards. The bran- chiae proper are sessile, internally to the epipodites, upon the epimera, and the membrane intervening between them and the basal joints 104 Descriptions of Preparations. whence the epipodites spring. The seven branchiferous segments, which, it may be remarked, correspond with the seven segments carrying ambulatory legs, in Amphipoda and Isopoda, carry ten branchiae in the pairs which all of them except the first and last support, and a single branchia upon the first and last of their number. To these twelve respiratory organs we may add six, by counting the branchiferous epipodites as such. In the American species of the genus Astacus, with one exception, there is no branchia upon the fifth abdominal leg; and with the absence of this branchia a lesser width of the cardiac area on the carapace has been observed to be correlated. In the genus Homarus, on the other hand, the branchiae are much more numerous than in Astacus, and indeed without counting the epipodites which, as may be seen in the common lobster, are setigerous rather than branchiferous, and act mainly as the scaphognathite does, by changing the water in the neighbourhood of the true branchiae, they out-number all the branchial organs of the Astacus, whilst the cardiac area on the carapace is relatively much less clearly indicated than in the smaller Decapod. Most of the anatomical points upon which weight has been laid in these descriptions of the fresh-water Crayfish, may be illustrated in the structural arrangements of the common lobster, in places where the Astacus may not be procurable. The marine species will however be found to differ from the fluviatile in the following points. Its hepatic coeca are shorter, and the anterior portion of the entire gland is larger, whilst the vasa deferentia are shorter, the testes are very long and only joined by a commissure. The coecum at the commence- ment of the intestine, which has already been spoken of as the rudiment of the yelk-sac, is smaller and bilobed in the lobster, whilst it is simple in the Astacus. The duodenum itself is smooth, and the rectum plicated internally in the lobster, and the duodenum, where it ends in the rectum, has an azygos coecum appended to it dorsally, as in Amphipoda, and most other Decapoda except Astacus. The nervous system differs mainly in having the ganglionic mass, whence the jaws and foot-jaws are inner- vated, more distinctly constricted at the sides, and less in size relatively to the five abdominal ganglia which succeed it, than we find the homologous structures to be in the Crayfish. Of external points of difference, perhaps the two most important are presented by the telson, which is uniarticulate in the lobster, and the second abdominal appendage in the male, which is much less modified, and differs much less in appearance from those which succeed it, than the same appendage does in the male Astacus. Common Crayfish. 105 For the points of difference between Astacus and Homarus, see Milne-Edwards, Histoire des Crustacés, vol. i., pp. 329-333. For the American subgenus. Cambarus, to which the species inhabiting the mammoth cave in Kentucky belongs, see Dana, Crustacea, United States Exploring Expedition, 1852, p. 522. For the nervous systems of the common lobster, see Swan, Comp. Anat. Nerv. System, pl. iti. and iv., where the endophragmal arch formed by the mandibulo-maxillary apodema, and inter- posed in the natural position of the parts between the stomach and the cords of the nerve collar, and the first sub-oesophageal ganglion is well seen. See also Newport, Phil. Trans. 1834, pl. xvii., fig. 40. For an account of the development of the common lobster, Homarus For Vulgaris, see Rathke, Wiegman’s Archiv. fur Naturgeschichte, 1840, p. 241, translated in Annals and Magazine of Natural History for 1841, vol. vi., p. 263, where the embryo on the point of hatching is shown to differ from the adult mainly by the presence on the ambulatory legs of an exopodite, such as the two posterior maxillipeds retain in the adult Decapod, and the ambulatory legs themselves in Mysis and Squilla. the correlation of large size of ova with the completion of development before hatching, see Bergmann and Leuckart, Vergleichende Physiologie und Anatomie, p. 647; and for an exemplification of this law, in the instance of Mysis, where the eyes are few (fifty) in number and large, and where the development is direct and without metamorphosis, as com- pared with such cases as those of the Palinuri and Careini, where the eggs may be from one to three hundred thousand, and are of small size, and where the well-known metamor- phoses with forms known as ‘Zoea’ and ‘Megalopa’ are gone through, see Van Beneden, Recherches sur les Crustacés, PP: 52> 53, 57 The fresh-water congeners of marine species which go through metamorphoses, are very frequently ameta- bolous in the sub-kingdoms of Mollusca and Vermes as well as in that of Arthropoda. In the instances here under com- parison, of the fresh-water Astacus and the marine Homarus, it should be borne in mind that the ova of the former animal are larger than those of the latter, though the adult Crayfish rarely attains one-third of the size of the lobster. 106 Descriptions of Preparations. 35. ComMoN CRAYFISH (Astacus Fluviatilis), Dissected so as to show its nerve system; the greater part of all the terga of the animal, and the viscera of organic life, with the exception of the commencement and the termination of the digestive tract, having been removed. Brstpes the prae-oral or so-called ‘ supra-oesophageal’ ganglionic mass, supplying the eyes, antennules and antennae, there are twelve post-oral ganglia in the Crayfish, of which six belong to the seg- ments anterior to the post abdomen, and six to these terminal segments. The first post-oral ganglion is the largest of the series, and supplies no less than six pairs of appendages, viz. the man- dibles, the two pairs of maxillae, and the three pairs of foot-jaws. In the developing Crayfish, as shown by Rathke®, this mass which is thus fused in the adult is represented by six pairs of white specks. Posteriorly to it we see five ganglia, remaining distinct, and corresponding in the adult as they do in the embryo of the Macrurous Decapods, and also of the Hedriopthalmatous Crustacea, with the five pairs of abdominal feet. Each of these six ganglionic masses presents a perfectly fused and continuous surface, but traces of the primitive antero-posterior bifidity of the nerve chain are still faintly visible, even to the unassisted eye, in the commissural cords passing between the ganglia. The wide opening which is seen in the commissural cord connecting the third and fourth abdominal ganglia, gives passage to the sternal artery seen in Prep. 32, p. 99, and the cord which connects the fourth with the fifth, differs from the cords which connect the pairs anteriorly placed in being shorter than any one of them. There are six post-abdominal ganglia, under the third and fourth of which, as also under the cord of commissure between the fifth and last, slips of blue paper have been placed. Each of the five anterior post-abdominal ganglia gives off two pairs of nerves, the sixth, which is the largest of the series and alone of the six connected with the one preceding it by a double commissure, gives off a considerably larger number of nerves, supplying as it does both the anus and the telson, in addition to the parts homologous with those supplied by the five anterior 4 Ueber die Bildung und Entwickelung des Flusskrebses, pp. 32, 33. Common Crayfish. 107 ganglia. This ganglion has been said to represent two ganglia, which were separate and distinct in the embryo. Rathke, however, informs us, |. ¢., that he has not been able to observe anything as to the mode of origination of the post-abdominal ganglia; and though the distribution of the nerves of the sixth ganglion may seem to make it probable that it was so developed, the comparative anatomy of the homologous series in other Crustacea would appear to militate against such a view. A system of nerves homologous with the xervi transversi or ‘ brides Epiniéres’ of Lyonet, described under Prep. 29, p. 84, in the insect, is represented by a nerve which arises in each segment, as seen with the naked eye in the third post-abdominal segment over the slip of blue paper placed there, from the commissural cord, and bifurcates into two lateral nerves. The bilaterally symmetrical and the azygos stomato- gastric system of insects are represented in the Crayfish by a system of nerves which arises symmetrically on either side of the oesophagus from a thickening on the commissures of the nerve collar, and by an azygos nerve which arises from the supra-oeso- phageal mass; but which has not any separate prae-cerebroid gan- glion frontale developed upon it as in insects. A slip of blue paper has been placed between the commissural cords of the nerve collar, and the antennary sternum with which they are commensurate in length; and in the interval between the commissural cords, the various trunks of the stomato-gastrie system are seen. The com- missural cords are connected anteriorly to the first post-oral gan- glion by a transverse cord, which is in apposition with the posterior wall of the oesophagus, and represents, probably, an anterior frag- ment of the backwardly displaced ganglionic mass which supplies the jaws and foot-jaws. The prae-oral ganglionic mass, which in embryonic life was seen by Rathke to be made up of two ganglia on each side, of which the posterior or the one more nearly placed to the mouth was the larger, and supplied the antennae and anten- nules, sends nerves to these organs, to the auditory organ lodged in the antennule, to the antennary gland, and finally to the eyes. The ocular portion of the prae-oral mass has not assumed the degree of relative importance which it has in air-breathing Ar- thropoda. The distinctness of the fibrous chords from, and their position superiorly to the ganglionic elements of the ventral chain, can 108 Descriptions of Preparations. be recognized in Astacus as well as in other Arthropoda, when the specimen has been, as in this case, sufficiently hardened in alcohol. The summits of the branchial plumes are well seen in this Prepa- ration, between the omo-stegite and the epimera of the abdominal segments. From the internal aspect of the epimera, the muscles which move the limbs are seen passing downwards and bifureating as they pass through the apodematal cells to their insertions in the upper segments of those appendages. In the cephalo-stegite, the adductor mandibulae is seen taking origin from the internal aspect of the protuberance already described, at page 96, as existing on its outer surface. On the ventral surface a packet of spermatozoa, aggregated in their passage along the convolutions of the vasa deferentia into the so-called ‘spermatophore,’ may be observed adhering to the cox- opodite of the last abdominal segment, in which the vas deferens opens. These structures, which are of comparatively small size as compared with those of some much smaller Crustacea, but which are produced in great numbers in the Crayfish, are by no means found exclusively in the neighbourhood of the generative outlet of the male, but may be seen adhering to various parts of the animal’s body. In the Chilopodous Myriapoda they may be at- tached even to foreign bodies. It may here be noted that though in many Hedriophthalmata, or four- teen-footed Crustacea, the number of post-oral ganglia may be the same, or nearly the same, as in such Macrurous Decapods as the Crayfish or Lobster, it is never made up of the same pre-thoracic, thoracic, abdominal, and post-abdominal factors in the same proportions as in the higher order. The ganglia supplying the ambulatory appendages, which in the Hedriophthalmata correspond with the two posterior maxillipeds or foot-jaws of Decapods, escape fusion with the first post-oral mass con- sisting of the coalesced ganglia belonging to their three pairs of foot- jaws and single pair of foot-jaws ; and maintain their typical distinct- ness, just as the appendages which they supply maintain their primordial locomotor functions. Having thus two more ganglia in the anterior portion of their segmented bodies, the Amphipods and Isopods have fewer than the Decapods in the post-abdominal region ; and by a re- duction of the number of the ganglia of this region from six to five or four, the entire number of their ventral ganglia comes to be thirteen or twelve, as in Homarus or Astacus. In some of the air-breathing Common Crayfish. 109 Isopoda, the post-abdominal may be represented by but a single mass. Though, as already stated, we know that in the earliest periods of de- velopment of the nerve system, at least in the Crayfish and Scorpion, the single ganglionic centre which innervates the first six post-oral segments, consists of an equal number of pairs of ganglia, it has been shown in other cases, as by Weismann in the developing Dipterous larva, and Metschinow in Aphis Rosae, that the nerve centres of many typically distinct segments may from the very earliest periods be connate. As, indeed, the nerve system is specialized in Arthropoda at a very late period as compared with that of the segmentation of the body and the development of the appendages, it may seem that when it does thus come into being, it must adjust itself to any secondary arrangement or disposition which these organs may have assumed in the course of their evolution, rather than to any typical relations of distinctness or of one- ness which they may have manifested in earlier periods. In cases such as those of the larvae of Muscidae, as described by Weismann, where the nerve centres of the entire series of post-maxillary segments are, if no earlier and rapidly transitory period of distinctness has been overlooked, connate from their first appearance, the number of nerves given off from the connate mass may serve to indicate its really compound nature. But though in the larvae specified, as many as eleven pairs of nerves are given off from the single mass corresponding to eleven post-maxillary ganglia of such larvae as Corethra plumicornis or Phalaena neustria, it is well to note that in the perfect insect, even this indication of the typical plurality of nerve ganglia is wanting, and that the ventral cord of the adult fly, exclusively of its first sub-oesophageal mass which supplies the modified jaws, gives off only four pairs of nerves, and one terminal azygos abdominal cord. As in the Myriapoda the jaws are supplied from a single gang- lion, just as in the other three classes of this sub-kingdom, we may say that in all Arthropoda, the first three post-oral segments upon which the mandibles and maxillae are developed, are inner- vated, at least in the adult state, by a single ganglion. In Crustacea and Myriapoda, this, which may be spoken of as the manducatory ganglion, is always fused with more or fewer of the succeeding ganglia accordingly as more or fewer of the thoracic appendages are converted into auxiliary jaws. In the fourteen-footed Hedrioph- thalmata therefore, where only the anterior pair of thoracic limbs is converted into an accessory oral organ, we should say that the 110 Descriptions of Preparations. first post-oral ganglionic mass consists of the manducatory gang- lion fused with one thoracic ganglion; whilst in the Decapoda all three thoracic centres have coalesced with the manducatory. In insects, on the other hand, we should say that even when the nerve ganglia attain the very extreme of concentration, the man- ducatory ganglion is always distinct from the rest of the ventral gangha ; and that the thoracic ganglia, as might be expected from the importance of the parts they supply, have a much greater relative size and independence than the homologous ganglia in Crustacea. The first abdominal ganglion in insects very frequently coalesces with the third thoracic, which is rarely the case in the Crustacea, in which the nerve centres of what Fritz Miiller has called the ‘middle body,’ very ordinarily are the best developed in their entire ganglionic series. The Arachnida resemble, on the one side, Crustacea, in having their manducatory fused with their thoracic ganglia, and on the other, Insecta, in having’ more or fewer of the abdominal ganglia coalesced with the thoracic. The Arthrogastrous Arachnida, as the scorpion, may have as many as four post-abdominal ganglia; Insecta appear never, even in the larval state, to have more than three; whilst Crustacea may have as many as six; or may, in the air-breathing Isopoda, as Oniseus Murarius, have a single ganglionic mass partially coalesced with the last abdominal to represent the entire caudal series, which, together with the post-abdominal segments, may be wholly lost in Laemodipoda. On the other hand, though fusion and connation even may be carried out to the extreme degree witnessed in Diptera, as also in Carcinus Maenas amongst Crustacea, and the Araneae amongst Arachnida, it would be wrong to hold that the nerve system of Arthropoda is in no case a guide towards the determination of the homologies of their seg- ments and appendages, or that the necessity existing in particular in- stances for the establishment of consentaneous muscular action in seg- ments and appendages, entirely obliterates all traces of a common typical arrangement of the elements of this system. The innervation of the so-called ‘mandibles’ or ‘ cheliceres’ in the Arachnida from the supra- oesophageal mass, must be held to prove that these organs are essentially antennae ; and a study of the appended Tables will show, that if we make allowance for the (possible) connation of the three ganglia, which should typically be developed in correspondence with the three manducatory i f fe deer ae Taste oF Post-oraL Nerve Ganewia or Decapopous CrusTAcEAN, oF MacruRous ARACHNIDAN, AND OF LEPIDOPTEROUS INSECTS, AS OBSERVABLE IN DEVELOPING AND IN ADULT INDIVIDUALS OF THE GENERA Astacus, ScoRPIo, AND SPHINX. Developing Astacus. Rathke, 1. c. Post-oral ganglion. Mandible Adult Astacus. Brandt, 1. ¢. ee er a Developing Scorpion. Rathke, 1. c. i. Post-oral ganglion. Cheliferous mandibles Adult Scorpion. Phil. Trans., 1843. Larva of Lepidopterous Insect. Newport, Phil. Trans. 1832. i. Post-oral ganglion. Mandibles, Spinnerets, Imago of Sphina. Phil. Trans., 1834. ” ” 1st Maxilla ii. Fis % 1st pair of legs Salivary gland = » » 2nd Maxilla =i. Ganglion, described | 1. » » 2nd pair of legs =i. Ganglion, laterally » » 1st Maxilliped as two in Lobster | 1V- ” » 8rd pair of legs constricted ii, Post-oral ganglion. 1st leg =a ” ” 2nd sy v » » 4th pair of legs iii. a ny 2nd leg = Aborted ” ” 8rd ” vi. Genital segment iv. ”» » 8rd leg aee ”” ” 1st Abdominal leg vii, Pectiniferous segment Es : ‘ } = iii. Cheliferous =ii. Ganglion ~ : Fs - gndAbdominalleg =iii, ., viii. 1st Pulmoniferous segment = ii, Ganglion observed | vi. > wal = | by Léon Dufour, Ann, Sci. Nat. xv. 1851. Eachtwopairsof nerves, Aborted ” ” 3rd ” = iv. ”» ix. 2nd . & = iii. Ganglion vii. i = one large and one 4 = J ”» ” 4th ” =v. ” x. Srd » » = iv. » viii. 3 » small. = iv. Fi nr 5th ” = vi. ” xi. 4th % “A =v. ” ix. > » =v. - A 1st Post-abdominalleg = vii. —_,, xii. 1st Caudal = vi. io x. rr ” = vi. ” ” 2nd ” = viii ” xiii, 2nd ,, = vii ” xi. Bilobate. Five pairs of nerves, fourof which = vii. 5; 7 8rd 5 =k. nm xiv. 8rd, = > are large. ” ” 4th » =x. ” xv. 4th ,, = ix, ” ” ” 6th ” — ot ” xvi. 5th ., not developed a 7 6th a xi Bf xvii. 6th, » oo” TABLE oF PosT-oRAL Amphipodous Crustacea, Talitrus, Milne-Edwards and Spence Bate, A mphithoe, Bruzelius, Hyperia, Straus Durckheim, Gammarus Pulex, mihi. NERVE GANGLIA OrRTHOPTEROUS INSECTS. Tsopodous Crustacean, Oniscus Asellus, Woodlouse, Leydig, 1. c. Taf. iv. 7. i, Post-oral ganglion gives branches to jaws, is not figured by Straus Durckheim in Mem. du Museum, 1829, tom. xviii, in Hyperia Galba. But see Bruzelius’ figures, Arch, fiir Naturgeschichte, 1859, Taf. x., fig. 18, ii. 1st Ambulatory foot Fused in Hyperia with each other iii, nd, } and with i. approximating De- 7 capodous arrangement. iv. 8rd 5 0 Distinct ganglion v. 4th 7 iY = vi. 5th FA + of vii. 6th a) Oy Ss a viii. 7th ” ” ix. 1st Pleopodos Reed 5, xi. 8rd > » 5 xii. 4th Pleopodos. Distinct ganglion according to Spence Bate in Talitrus Locusta; but in Talitrus, Hyperia, and Amphithoe, as figured by Milne-Edwards, De la Valette, and Straus Durckheim, and in Gamma- rus Pulex where it is much elongated, supplying the 5th and 6th Pleopodos also. xiii. 5th Pleopodos. Distinct ganglion in Talitrus Locusta, Spence Bate, in British Association Report, 1855, p. 56, Pl. xxii. xiv. 6th 5 » ” ” ai i. Post-oral ganglion, very small and ordinarily overlooked. The nerves for the manducatory organs are said to come from the commissures of the collar. Nova Acta, xx., p. 85, in Idothea and Aga, as also in the Scolo- pendra, ii, 1st Ambulatory foot iii. Qnd ,, *y iv. 8rd ” » v. 4th ” ” vi. 5th » ” vii. 6th A) ” Vili. 7th op ” ix. Supplies terminal segments, being itself distinguish- able from the eighth ganglion by a foramen placed mesially. This ganglion represents the free terminal ganglia described by Rathke and Milne-Edwards in the marine species Idothea Entomon, #ga Bicar- inata and Cymothoe, and by Lereboullet in the air- breathing and closely allied Ligidium Persoonii. See Nova Acta, xx., Pt, i. p. 34; Hist. Crustacés, Taf. xi. 2; Ann. Sci. Nat. xx. Pl. v. 24. Orthopterous Insect. Periplaneta Orientalis. See Plate vi. i. Post-oral ganglion supplies mandibles and bifid labium; is closer to supra-oesophageal mass than in Crus- tacea. ii, 1st pair of feet 2nd 7 8rd * v. This ganglion is probably to be considered as having become fused with No. iv. vi. 1st abdominal ganglion vii, 2nd ,, ”» viii, 5rd * » ix. 4th Fj , x. 5th abdominal ganglion, corresponding as the tenth post-oral of the Larvee of Lepidoptera and tenth post- oral of the embryo Scorpion do with the first post- abdominal of the Crustaceans. xi. 6th, bilobed terminal ganglion, corresponding to the three terminal ganglia of Gammarus Pulex. AS OBSERVABLE IN AMPHIPODOUS AND Isopopous CRUSTACEA AND IN (Table to page 111.) Common Crayfish. 11 seements in the insect, a very close, even if not complete, correspondence exists between the arrangements of the ventral ganglionic chain in Insecta, Arachnida, and Crustacea. In this Table the series of ganglia as observable in the developing and in the adult forms respectively of Astacus, Scorpio, and Sphinx, have been placed side by side in six columns, the maximum number of divisions in which is seventeen, the typical number, according to the view here adopted, of the post-oral segments in Arthropoda. Each actually existing ganglion is placed in the particular division of the scale of seventeen which is regarded as its homological relation to the complete series furnished by the developing Astacus. Thus a glance shows both where coalescence has taken place and where ganglia have failed to be developed. In a second Table the ganglionic series of an Amphipodous, of an Tsopodous Crustacean, and of an Orthopterous insect, have been similarly arranged in parallel columns, the Amphipodous Gammarus making the transition from the Decapodous Astacus to the Isopodous Oniscus easy, and the Oniscus in its turn approximating perhaps more closely than most or all other Crustaceans to the insects*. The anatomical points x The order Orthoptera is believed to be the earliest representative of the class Insecta in geological times, see Gerstaecker, Klassen und Ordnungen des Thier-reichs, Bd. v., p, 292; and as an order they are distinguished by the possession of a number of characteristics which approximate them to the Crustacea, the earliest geological representatives of the sub-kingdom Arthropoda. Amongst these may be mentioned the possession of the processes figured at ¢ in pl. vi., and known as ‘cerci anales,’ which appear to be homologous with certain processes which Rathke has spoken of in Crustacea, e.g. Apus, Branchipus, Cyclops (Morphologie, p. 115) ; the retention by the second pair of maxillae of something of their typical distinctness as opposed to fusion, as in other insects, into a ‘labium ;’ the presence of three basal joints as a support to the multiarticulate antenna which thus resembles the antennule of Crustacea; and, lastly, the functional peculiarity of ecdysis, which attaches even to adult Ephemeridae in this order of insects, and the pedunculate position of the central eyes in certain male Ephemeridae, Chlée diptera s. Ephemera bioculata, Linn. The internal structural arrangements of the order Isopoda, irrespective of those of their nervous system, present some points of interesting resemblance to those of Insecta, and especially of Orthoptera, Their long non-ramified hepatic coeca are essentially similar to those seen in the Orthoptera; see above, p. 86, and pl. vi. h, and description; Leydig, Lehrbuch der Histologie, pp. 362, 333, fig. 194; whilst in their air-breathing genera, Oniscus and Tylos, a system of canals has been discovered in the opercula of their branchial plates, which has been supposed to be a rudimentary tracheal apparatus. As these peculiarities do not relate to the nervous system, it is of the more importance to note that a sympathetic 112 Descriptions of Preparations. embodied in this Table can be illustrated by dissection of the readily procurable animals, Gammarus Pulex, Oniscus Murarius, and Peri- planeta Orientalis. Much has been written as to whether twenty or twenty-one is the typical number of segments in the Arthropoda. The great number of homonomous segments which in Myriapoda are developed posteriorly to their thoracic region, enables us to eliminate them from consideration, except so far as the thoracic and cephalic segments are concerned ; but in all other Arthropoda, with the exception of the Trilobites and Phyl- lopoda amongst Crustacea, the number of actually, if not of homologically distinct segments, appears to be very definitely limited. The typical number of segments has been considered here as being twenty, in ac- cordance with the views of Professor Huxley, and in opposition to those of Professors Milne-Edwards and Van Beneden ; inasmuch as the ‘ telson’ or terminal so-called segment of the Crustacea does not appear to possess the characteristics of a true segment. In the Sessile-eyed Crustacea, the telson is, according to Mr. Spence Bate, 1. ¢. p. xxi., who however appears to reckon it as making a twenty-first segment, “ generally an abortive, and frequently a rudimentary part ;” and in the Isopoda, with the excep- tion of two genera, it is always fused with the preceding segment. With one, or perhaps two exceptions, the telson never carries appendages, “ whereas it is a law common to all Crustacea, that every segment has its appendage ;” and Rathke, from whom however Van Beneden differs, describes it as being developed after the other segments, and from the dorsal aspect of the body. Even if it should be proposed to regard it as representing in a rudi- mentary form the very great or all but indefinite number of homo- nomous segments which we meet with in Apus amongst Crustacea, and in the Myriapoda, we should still be justified in eliminating it from the number of the typical segments of Arthropoda ; that is to say, from the number of segments to which some of the best marked representatives of three out of the four great classes into which the sub-kingdom is divided, can all alike be shown to conform. The history of the development, and to a considerable though lesser extent, that of the comparative ganglion corresponding in position and connections to the azygos ‘ ganglion frontale’ of Insecta and Myriapoda has been discovered by Leydig in Oniscus. In other Crustacea, the nervus recurrens has no ganglion frontale developed, but appears to take origin from the supra-oesophageal ganglia. Brandt has figured a lateral paired system of sympathetic ganglia in this Crustacean, see Med. Zool., Bd. ii. Taf. xv. fig. 27 ; but Leydig declares the structures thus described to be merely glands in connection with the stomach, Common Crayfish. 113 anatomy of the antennae and jaws in Arthropoda, prove that they are appendages in just the same sense as any of the ventrally placed append- ages attached to segments posterior to the cephalic ; and with them, most authors, with the exception of Claus and Fritz Miiller, would be inclined to rank the eyes. The facts of the pedunculation of these organs in the Podophthalmatous, and indeed in some other Crustacea ; of the occasional replacement of their facets by a flagellum such as the antennae carry ; of their having a separate pair of lobes developed in connection with them in the supra-oesophageal ganglionic mass in ordinary De- capods, as shown by Rathke y, see p. 108, swpra, in Amphipoda, and also y Bruzelius, Archiv. fiir Naturgeschichte, tom. xxv., 1859, p. 306; Beitrig zur Kenntniss vom innern Baue der Amphipoden, has described the supra-oesophageal mass of an Amphipod, Amphithoe Podoceroides, as consisting of three pairs of ganglia, the most anterior of which is in relation with the eyes, the middle one with the antennules, and the one nearest the mouth with the antennae. Similarly Mr. Newport, Phil. Trans., 1834, p. 422, pl. xvii. fig. 40, a, b, c, has figured and de- scribed the supra-oesophageal nerve-mass in the common Lobster, Homarus Vulgaris, as consisting of three pairs of ganglia in relation with the three pairs of sensory organs specified. Though no air-breathing Arthropod has at any one period of its life more than a single pair of antennary organs, Rathke’s figures of the cerebroid mass in the developing Scorpion, Morphologie, Reise nach Taurien, Taf. i. fig. 10, and his description of it in contrast to the brain of the adult animal, as ‘composed of several pairs of ganglia lying one behind the other,’ and also Metschnikow’s figures, Zeitschrift fiir Wiss. Zool., Bd. xvi. Taf. xxx., figs. 31, 33, though not his description of the brain in Aphis Rosae, lead us to think that the brain, even in these classes, may make its first appearance as a bilaterally trilobed mass, indicating thus the presence of three prae-mandibular segments. Mr. Newport indeed has put on record, Phil. Trans., 1843, p. 245, an observation to the effect that in the embryo of a Chilopodous Myriapod, Geophilus Longicornis, the brain is at the moment of its bursting its shell composed of four double ganglia. But here it is probable that one of the pairs, as Metschnikow l. c. has shown to be actually the case in Aphis Rosae, corresponded to the ‘lobi optici,’ which are lateral outgrowths of the cerebroid ganglia, and do not therefore indicate the presence of a separate segment, though they may have been displaced inwards by lateral com- pression. See Leydig, Vergleich. Anat., p. 183. The brain in adult Myriapoda is very obviously quadrilobular, as has been noted, by Newport, loce. citt., of Scolopendra, Polydesmus, Geophilus Subterraneus when adult, and by Zaddach of Lithobius Foryi- catus. This point is particularly well shown in the brain of Glomeris Marginata, a Myriapod closely resembling the Oniscus in external appearance. It has been figured by Brandt, Miiller’s Archiv., 1837, Taf. xii. fig. 7, p..324, a8 consisting of two irregularly quadrangular masses, prolonged at either outer angle into ocular and antennary nerves respectively, and united at either inner angle to each other by commissures passing over the oesophagus, and inclosing a wide open space between them. For the development of the prae-oral ganglia in Astacus, see Rathke, Fluss- krebs, p. 50, For the segmentation of the head, Rathke, Morphologie, pp. 126, a 114 Descriptions of Preparations. in Myriapoda, Geophilus, Lithobius and Scolopendra ; and finally, that of their having an all but independent annular segment, as well as a pe- duncle, developed for their support in Squilla, appear to justify us in regarding the eyes as either being or, when sessile, as representing ar- ticulated appendages, and, by consequence, a distinct cephalic segment”. The apparent paradox of speaking of the eyes, which ordinarily have a more or less completely dorsal position as homologous not with such dorsal outgrowths as the wings of insects or the shells of certain Crus- tacea, but with the ventrally placed articulated appendages, is to be justified by the history of the development of the pro-cephalic lobes, which at an early period are bent upwards at a right angle to the rest of the blastoderm, and even backwards, so that the roof of the skull, which is really a sternal, appears to be a tergal surface. Taking then the eyes as indicating one segment, and the two pairs of antennae and the three pairs of jaws as indicating five segments, we find that the typical number of segments in the head of the Arthropod amounts to six. The segments anterior to the maxillae, together with that part of the body which ultimately becomes the swimmeret, in the Astacus, Fritz Miiller has called the ‘primitive body,’ as being that which makes up the ‘Nauplius’ form of larva, and which carries the sensorial appa- ratus, as, for example, the ear, which is lodged ordinarily in the scale of the second pair of antennae, but sometimes in the ‘uropodos,’ as in Mysis. The sections of the body which are intermediate to these extreme points, he divides into a ‘fore-body, which corresponds to what is here spoken of as ‘thorax,’ and which is second in order of develop- ment; into a ‘hind-body, the ‘post-abdomen,’ deducting the sixth segment, which is third in order of development ; and finally the ‘ middle body,’ the ‘ abdomen’ in the language here employed, which in Crustacea always puts forth limbs immediately after its segments are developed, 127. The demonstration of the points relating to the brain of Amphipoda, is made much more easy if acetic acid is added to the alcohol employed for hardening the specimens to be dissected. z Two pairs of articulated appendages have been observed in the larval forms of Cirripedia anteriorly to the superior pair of their natatory antennae ; and if the posterior of these be taken as equivalent to the ‘ olfactory filaments’ of the superior antennae, the anterior, the ‘larger antennae’ of Darwin, the so-called ‘ horns of the carapace’ would still indicate the presence of a third pre-mandibular segment. For an account of these outgrowths, see Gerstaecker, Klassen und Ordnungen des Thier- reichs, Bd v., p. 508; Spence Bate, Ann. and Mag. Nat. Hist., Ser. ii., vol. viil., 1851, p. 327; Fritz Miiller, Archiv. fiir Naturgeschichte, 1862, p. 7, 1863, p. 25; note 2; Darwin, Lepadidae, 1851, p. 9; Balanidae, 1854, p. 105. Common Crayfish. 115 and which has a high degree of independence manifested by its nerve ganglia in Podophthalmata and Hedriophthalmata. The number of the prae-oral segments being thus taken as three, and the so-called ‘lips’ of certain Crustacea being eliminated from the enu- meration as not representing appendages, but being merely indurations of the lining membrane of the digestive tract homologous with the ‘jaws’ of the leech, we obtain, by omitting, for the reasons above stated, to count the telson as a segment, seventeen as the typical number of post- oral, and twenty as the typical number of the entire series of segments in Arthropoda. The appended Table shows how these views may be applied to the Insecta, the Arthrogastrous Arachnida, Myriapoda, and to the two above-named orders of Crustacea, as also to the Copepoda ; which, in spite of their small size, with which inferiority of organization has been supposed to be commonly correlated in Crustacea, present many important points of affinity to the highest order in the class. Amongst these may be mentioned the degree to which heteronomy or differentia- tion is carried out in the various regions of the body; and the external similarity which these small animals thus obtain to such Crustacea as Penéus and Mysis is made the more striking, when we recollect that they all alike leave the egg with no other appendages than those of the ‘Nauplius ;’ and that the adult Copepod corresponds very closely, if not exactly, as to the number of articulated appendages on its ‘fore-’ and ‘middle-body,’ with certain ‘ Zoea’ stages in the development of Podoph- thalmata. See Spence Bate, Phil. Trans. 1858, pl. xl. figs. A and B ; Claus Die frei Lebenden Copepoden, 1863, Taf. xxxiii. fig. 6; Dias Longiremis, Taf. xix., fig. 2, Thalestris harpactoides*. The non-seg- mentation of the post-abdomen in many of the parasitic Copepoda, as also in the Cladocera, Daphnis, the Ostracoda, Cypris and the Cirripedia, eliminates them as it does the non-Arthrogastrous Arachnida from con- sideration, except as to the anterior regions of the body. The Myriapoda together with a few Branchiopoda, Apus, and the extinct Trilobites, are similarly eliminated for the opposite reason. The term ‘ Hedriophthalmata, Schiddte, Ann. and Mag. Nat. Hist., Ser. iv., vol. i., 1868, p. 6, is employed in the following Table in the same restricted sense as its etymological equivalent, by Professor West- wood and Mr. Spence Bate, in their work on the Sessile-eyed Crustacea. ® The internal anatomy of the Copepoda is well illustrated in the former of these two figures ; the dorsal opening of the anus being especially noteworthy, as corre- sponding with a condition observed by Rathke, in the early stages of the develop- ment of the Astacus, see p. 97, supra. I2 116 ee eee Number of Insecta. Arachnida. Myriapoda. ° Segment. I. Mandible, never pal- | ‘Chelae’ of Scorpion Mandible, with rudi- pate. are the palps of its | mentary palp in Chilo- mandible. The so-call- | poda; not palpate in ed ‘maxillae’ of Spiders | Chilognatha. arealso palpate. ————— a as Ii. Maxilla, palpate. First pair of legs are | Outer element of ‘ La- the palps of the ‘la- | bium,’ in both orders, | bium.’ as in Lepidopterous larva. vee ae iil. ‘Labium,’ palpate. Second pair of legs. Mesial elements of ‘ Labium.’ pe | IV. First pair of legs. | Third pair of legs. Basal joints forming First spiracle in Cater- a Labium by junction. pillar. Wo Second pair of legs. Fourth pair of legs. Basal joints as in vii, and in Chilopoda arm- ed with claw and poi- son duct. —= | a eee ee = VI. Third pair of legs. Genital segment in| Genital opening in Scorpion. some Chilognatha. Simple pair of legs in Chilopoda. Vil. First abdominal seg- | Pectiniferous seg- Simple pair of legs in ment. Second spiracle | ment in Scorpion. both Chilognatha and in Caterpillar. Chilopoda. VIII. Second abdominal| First pulmoniferous | Ditto, ditto. segment. segment in Scorpion. IX. Third abdominal seg Second pulmoniferous | Ditto, ditto. ment. Carries first pro- | segment in Scorpion. leg of Caterpillar. X. Fourth abdominal) Third pulmoniferous | Simple pair of legs in segment. Second pro- | segment in Scorpion. | Chilopoda and female leg of Caterpillar. Chilognatha. Penis in male Chilognatha. XI. Fifth abdominal seg- | Fourthpulmoniferous Simple pair of legs in Caterpillar. ment. Third proleg of T ABLE OF OF POST-ANTENNARY SEGMENTS segment in Scorpion. Chilopoda. Double pair in Chilognatha. Crustacea. Mandible, ordinarily carrying a tri-articu- late palp, except in terrestrial Isopods and Amphipods. ‘Maxilla’ i. or ‘Siag- onopodos’ i. Westwood and Bate in ‘Sessile- eyed Crustacea,’ p. 3. ‘ Maxilla’ or ‘Siagono- podos’ ii. Bifid, Cyclops. ‘Maxilliped’ i. Auctt. ‘ Siagonopodos’ iii. Westwood and Bate. ‘Maxilliped’ ii. or *Gnathopodos’ i. Last foot of early Zoea Lar- va. ‘Maxilliped’ ‘ Gnathopodos’ Third swimming foot, Cyclops. iil. First ambulatory ap- pendage of Astacus; third of Amphipod. ‘Pereiopodos’ i. West- wood and Bate. ‘ Pereiopodos’ ii. ‘Pereiopodos’ iii. In basal joint of append- age or in sternum of segment we find the fe- male generative outlet. ‘ Pereiopodos’ iv. abort- ed, as also iii. and v. in Copepoda. ‘Pereiopodos’ v. In basal joint of append- age or in sternum of segment male genera- tive outlet in Podoph- thalmata and Hedri- ophthalmata. HOMOLOGIES 117 MARKED BY APPENDAGES IN ARTHROPODA. Number of Insecta. Arachnida. Myriapoda. Crustacea. Segment. Xil. Sixth abdominal seg-| First caudal segment | Simple pair of legs in| First post-abdominal ment. Fourth proleg | in Scorpion. Chilopoda. Double pair | segment. ‘Pleopodos’ of Caterpillar. in Chilognatha. i. Generative outlets in Copepoda. XIiil. Seventh abdominal} Second caudal seg-| Ditto, ditto. ‘ Pleopodos’ ii. segment. Last gang-| ment in Scorpion. lion in larva. XIV. Eighth abdominal] Third caudal seg-| Ditto, ditto. ‘Pleopodos’ iil. segment. Ninth spi- | ment in Scorpion. racle and horn of Sphinx larva. XV. Ninthabdominalseg- | Fourth caudal seg-| Ditto, ditto. ‘Pleopodos’ iv. or ment. Vulva opens in | ment in Scorpion. *Uropodos’ i. front of it and outlet of Spermatheca upon its sternum in Cock- roach. Symmetrical depression on the me- sial ventral line in pupae of Sphingidae. XVI. Tenth abdominal seg-| Fifth caudal segment | Last segmentin Pau-| ‘Pleopodos’ v. or ment. Orifice of col- | in Scorpion. ropus, see Lubbock, | ‘ Uropodos’ ii. leterial glands of Cock- Linn. Soe. Trans. xxvi. roach. pp. 182, 184, XVII. Eleventh abdominal} Sixth caudal segment ‘Pleopodos’? vi. or segment. Anal orifice. The ‘cerci anales’ are carried by it in Panor- pa, and are supposed to belong to it in other insects by Lacaze Du- thiers, Ann. Sci. Nat. 1852, 1853. They are probably homologous with the caudal ap- pendages of Apus and Branchipus, see p. 111, supra. of Scorpion carrying sting on its apex. An appendage homologous probably with mesial element or ‘telson’ of Astacus. ‘Uropodos’ iii. This seg- ment has the lateral elements of the swim- meret articulated to it just as the other post- abdominal appendages are articulated to their respective segments. The mesial portion of the swimmeret or ‘ tel- son’ may be articu- lated to it or fused with it, and may be of very various forms. The ‘furea’ of Cope- poda, Cyclops, p. 111, is held by Claus to repre- sent this segment. Compare trifid append- ages of Chloeon Di- midiatum, Linn. Soe. Trans. xxiv., 1865. 118 Descriptions of Preparations. A very clear account of the nerve system of the various orders of For Crustacea may be found in Frey and Leuckart’s Lehrbuch der Zootomie, 1847, pp- 195, 623. an account of the development of the nervous system of the Crayfish, see Rathke, Ueber die Bildung und Entwickelung des Flusskrebses, 1829, pp- 32, 33> 59 61, 64, 85. For that of the Scorpion, see Rathke, Morphologie Reise nach Taurien, p- 28, cit. Huxley, Linn. Soc. Trans., vol. xxll., pp. 227, 2.28. For a figure of the nervous system in the common Lobster, Homarus Vulgaris, see Newport, Phil. Trans., 1834, pl. xvii. fig. 403 where, however, the evident constriction of the first. post-oral ganglionic mass has caused the writer to count it as two, and to speak of the entire number of ventral ganglia as being thirteen. The relative superiority in size of this first post-oral ~ ganglion is not so marked relatively to those which come posteriorly to it in the marine as it is in the fluviatile species here contrasted. For the nervous system in the Decapodous Crustacea generally, see For For Leydig, Vergleichende Anatomie, Bd. i. p. 253, ibique citata. the stomato-gastric system, see Huxley, Medical Times and Gazette, April 11 1857, p- 3533; Brandt, Ann. Sci. Nat. Ser. ii. tom. v, 1836, p. 87, pl. 4, figs. 1, 2, 3. the nervous system of Myriapoda and Macrurous Arachnida, see Newport, Phil. Trans., 1843, pt. ii. pp. 243-272; and for the structure of the cord, p. 248, and Phil. Trans., 1834, p. 406, pl. xvii. fig. 42; Leydig, Vergleich. Anat., pp. 229- 241; and Helmholtz cit. im loc. ; Carpenter, Comp. Physiology, p- 669. various views as to the homologies of the segments, see Savigny, Mémoires sur les Animaux sans Vertébres, 1816; Milne-Edwards, Histoire Naturelle des Crustacés, 1834, Pp. 505 Ann. Sci. Nat., 1851; Erichson, Entomographien, 1840; Lacaze Duthiers, Ann. Sci. Nat., Ser. 11. tom. Xvil., 1852, pp. 227, 232, 233, tom. xix., pp. 34, 40, 229-233 3 Dana, Crustacea, U. S. Exploring Expedition, 1852, p. 19 seqg.3 Zenker, Archiv. fiir Naturgeschichte, 1854, p. 118; Van der. Hoeven, Handbook of Zoology, English translation, vol. 1., 1856, p. 557, ibique citata; Huxley, Linn. Soe. Proc., vol. Common Earthworm. 119 xxii, 1858, p. 228; Van Beneden, Recherches sur les Crus- tacés, 1861, p. 29; Claus, Copepoden, 1863, pp. 13-18; Gerstaecker, Klassen und Ordnungen des Thier-reichs, 1866, Bd. v., pp. 38, 48, 333, 3393 C. Spence Bate and Westwood, British Sessile Crustacea, 1868, vol. 1. pp. vill.—xxl., 3-7, vol. li. pp. 102-105. For the reckoning of the eyes as appendages indicating the presence of a distinct segment, see Zaddach, Untersuchungen iiber die Entwickelung und den Bau der Gliederthiere, pp. 78, 87; Gerstaecker, Klassen und Ordnungen des Thier-reichs, Bd. v., pp. 202, 343; Alphonse Milne-Edwards, Comptes Rendus, Lixepp-< 7103.1. 36. Common Eartuworm (Lumbricus Terrestris), Prepared so as to show the external organs which subserve locomotion and reproduction. Tue epidermis forms an iridescent capsule for the animal’s body, the tissues of which have shrunk a little away from it under the action of spirit. The integument is at various points to be here- after specified, thickened and intumescent, but these thickened portions are all developed in relation to the function of repro- duction, there being no specialized organs of respiration. A thickened white ring, the ‘clitellus,’ made up of the fusion of the dorsal and lateral portions of about six segments, may be seen in the middle third of the body. The thickened glandular three- fourths of these segments are separated off from the ventrally placed and unthickened fourth, by a hyaline slightly elevated ridge, which is muscular and more constant in its characters from species to species than the glandular portion of the clitellus. On either side of this ridge may be seen the rows of setae, the inner one of which has its spines much lengthened. An orifice with pro- minent tumid lips produced similarly to the clitellus by the de- velopment of the glandular layer of the integument, is seen on the fifteenth segment of the body, and corresponds to the termination of the vas deferens on either side. A somewhat similar but smaller prominence may be observed on either side the middle line of a 120 Descriptions of Preparations. segment sixth in order anteriorly to the clitellus. In this pro- minence there is no foramen, but two spines modified so as to co-operate with the clitellus as an organ of adhesion in the act of copulation may be observed to be implanted in it. These spines belong to the inner series of locomotor spines, which are prolonged from the third or fourth or fifth segment of the body anteriorly, down to the posterior segments, upon the last of which they, as well as the spines of the outer series, fail to be developed. The outer row of spines is very visible along the line where the darker coloured dorsal region shades off into the lighter coloured ventral. Each series is represented in the Lumbricidae by two spines only; the multiple or fasciculate arrangement not being found in this family, which are therefore pre-eminently ‘oligo- chaetous.’ The external series is wanting not rarely upon the anterior segments, and may be wanting even as far back as the clitellus inclusively. The spines of the inner series are modified so as to subserve the mutual adhesion of the allotriandrous Lum- bricus in the act of copulation, not only in the segment already specified, but also in the entire series of segments occupied by the clitellus, and in the tenth and fifteenth segments, where they are thinner and twice as long as in other segments. The oviducts and the vasa deferentia open in the fourteenth and fifteenth seg- ments respectively, just externally to the outer of the two setae of the inner row. In large specimens of Lumbricus communis, an orifice may often be noted in the median dorsal line, in the inter- space between the rings from the tenth segment or so backwards. From this orifice, which opens into the interior of the posterior of the two segments between which it is placed, in a recently killed animal, the peri-gastric fluid may be seen to escape in small jets upon pressure. Much variety is observable in the condition of development of the clitellus, and even the number of segments composing it and interposed between it and the head are by no means uniform within the limits of the same species. For the zoological characters of the family Lumbricidae, see British Museum Catalogue of the British Non-parasitical Worms, by George Johnston, M.D., 1865, pp. 57, 318, and especially p. 323 for the variability in external anatomy just mentioned. For the anatomy of Lumbricus, see E. Ray Lankester, Esq., Quar- Common Earthworm. 121 terly Journal of Microscopical Science, 1864-1865, iique citata. See also D’Ukedem, Mémoires de Academie Royale de Belgique, tom. xxxvi., 1865. A monograph on the natural history and anatomy of the Lum- bricus Terrestris, of considerable merit, was published in Latin by C. F. A. Morren in 1829, under the title ‘De Lumbrici Terrestris Historia Naturali necnon Anatomia Tractatus.’ 37. Common EartHworm (Lumbricus Terrestris), Dissected so as to show its gangliated nervous system consisting of a bilobed supra- oesophageal mass and a ventrally placed nerve-cord, connected with each other by commissures, which give off numerous branches on either side to the large sympathetic ganglionic mass lying upon either side of the pharynx. THE inteeuments having been divided down the middle dorsal line and fastened out on either side, the entire digestive tract with the exception of the commencement of the pharynx, through which a black bristle has been passed, has been removed, together with the pseud-haemal vessels in connection with it; the segmental organs, and the muscular dissepiments dividing the body into compartments. The organs of reproduction have been similarly removed, with the exception of the two receptacula seminis of the right side, two globular white sacs which are seen opening in the line of the outer rows of setae, in the intervals between the ninth and tenth, and between the tenth and eleventh segments respect- ively. The two lobes making up the supra-oesophageal mass are pyriform, and have their broader ends apposed to each other in the middle line. From their outer and narrower ends a thick nerve passes off, bifurcating almost immediately, to supply the pro- boscidiform and tactile anterior segment or upper lip. These nerves would appear to be homologous with those given off from the post-oral ganglia, and the anterior or upper surface of the ganglionic mass whence they are given off to be homologous with the under surface of the ventral ganglia. 'The cords of commissure to the first ventral ganglion pass downwards and form the nerve 122 Descriptions of Preparations. collar in which a part of the pharynx is still left. Upon either side of the pharynx a reticulation of ganglionic masses may be seen with a lens, one of which masses is much larger than the rest, and running parallel with the commissural cords is connected with them by six or more nerve branches. Two distinct strands may be distinguished in the anterior portion of the ventral cord, and they are underlaid by a continuous stratum of vesicular substance, which at intervals is aggregated into more or less distinct ganglia, from each of which a pair of nerves is given off on either side, whilst a single nerve is given off on each side from the portion of the cord interposed between each two pairs of ganglia. These latter nerves may probably be considered as homologous with the nervi transversi of the Arthropoda, and as serially homologous with the branches of the plexus already described as existing upon the pharynx. They are given off in each segment anteriorly to the paired nerves, and take a course outwards in relation with the posterior aspect of the anterior dissepiment of each segment. They are accompanied by a branch from the sub-neurally placed pseud- haemal vessel, whilst the paired nerves are similarly accompanied by a branch from one of the pseud-haemal vessels on either side of the nerve cord. The ventral cord takes the shape of a thick band in which the ganglionic enlargements are difficultly recognizable for a space corresponding with that occupied by pharynx oeso- phagus and reproductive organs; posteriorly to the fifteenth seg- ment it becomes much slenderer, but the ganglia become much more distinguishable, though separated by wide interspaces up to a point a little way posterior to the middle of the entire length of the body. Finally, for a length nearly equal to that of the pos- terior half of the animal, the cord becomes much more distinctly moniliform, its ganglionic enlargements being very plainly marked though very closely apposed. The terminal ganglion of the chain is, contrary to what is seen in some other Annelids, as also in many Arthropoda, smaller than those which precede it. The ganglia do not maintain the same numerical equality with the segments in other Annelids as in Lumbricus, exceeding their number in some, as Aphrodite, and falling below it in others, as Hirudo, see Preps. 41, 42. The two rows of paired setae are well seen on either side of the middle line; the inner setae in the two segments fifth and sixth in order anteriorly to the clitellus are seen together with the Common Earthworm. 123 glandular follicle secreting them to be considerably enlarged in re- lation to their function as accessory generative organs. In the anterior fifteen segments in the interval between the inner row of setae and the nerve cord, a white muscular fascicle is seen passing forwards and finally upwards alongside of the commissural cords of the nerve collar, and dorsally to the nerves given off from the first ventral ganglion, to be inserted partly in the capsule of the cephalic ganglia, and partly in the muscular and tegumentary tissues above them. No mus- cular fibres are developed upon the commissural cords connecting the ventral chain with the supra-oesophageal ganglia, as there are upon the ventral cord itself; and the function of retracting the supra-oesophageal ganglia, together with the structures above them, is performed by the muscle here described, which from its origin and course acts at great advantage. These two muscular bands have at first sight an appearance closely similar to that presented by the two somewhat widely separated halves of the ventral cord of the Tubicolar Annelids, and of Peripatus, or to that of the accessory nerve-chains, developed in the Amphinomidae in relation with the locomotor organs. For an excellent account of the nerve system of the Earthworm, see Lockhart Clark, Royal Society’s Proceedings, 1857, pp. 344-351: For figures of the general arrangement of the nerve system, see pl. viii., and Description. Quatrefages, Régne Animal An- nelés, pl. i. e, fig. 2a, and Ann. Sci. Nat., Ser. iii., tom. viil., 1847, p. 36, for discovery of sympathetic system in Lumbricus. See also D’Ukedem, /. ¢., pl. ili. fig. 4. For the histology, see eae: Tafeln zur Vergleich. Anat., iv., fic. 8, and the various toe cited in the letter-press of that work at pp. 138 seqg., 168 seqg. For figures of the nerve cord as existing in two separated halves, see Grube, in Miiller’s Archiv. for 18 53, Taf. x., 14. Quatre- fages, ‘Suites 4 Buffon, Annelds, pl. ii., figs. 7 and 8; in Peripatus Edwardsii, and Sabella and Serpula. 124 Descriptions of Preparations. 38. ANTERIOR SEGMENTS OF HKARTHWORM (Lumbricus Terrestris), In number about forty, and including three placed posteriorly to the clitellus ; dissected so as to show the reproductive system, the whole of which, together with the various accessory organs, is contained in or constituted by modifications of the structures of these segments ; as also the portions of the pseud-haemal and the digestive system which are contained in this part of the animal’s body. THE integument having been divided down the middle dorsal line and pinned out on either side, the digestive tract is seen to occupy the middle line of the Preparation, and to have in con- nection with it the vascular system, which is called ‘ pseud-haemal,’ because though the fluid which it contains is coloured and prob- ably respiratory in function, it is not corpusculated, and therefore not morphologically blood. The digestive tract manifests a very considerable degree of heteronomy, consisting of a pharynx which extends through the first six segments; an oesophagus which extends through the succeeding ten; a crop which occupies a large space in the sixteenth and seventeenth; a gizzard which is seen in the seventeenth and eighteenth ; and finally, the intestine which is laterally sacculated for its first eight segments, and posteriorly to them more evenly cylindriform. The pharynx has a coarsely villous exterior, owing partly to the breaking away in the dis- section of the muscular bands by which it was connected with the muscular dissepiments and with the body-walls, and partly to the salivary gland-tissue which composes part, and especially the outer part, of its walls. The oesophagus is of much smaller calibre than either of the two segments of the digestive tube, the pharynx and the crop which it connects. The so-called ‘hearts’ are in close connection with it in the anterior segments of its course, and the reproductive and certain oesophageal glands are seen at its sides in the middle and posterior. The crop is considerably distended with dark coloured contents, and forms a larger mass than the thicker coated lighter coloured gizzard which comes next behind it. The dorsal pseud-haemal vessel is well seen along the median dorsal line of the crop and intestine, where owing to the con- traction of its muscular walls it has a moniliform appearance. Anterior Segments of Earthworm. 125 Posteriorly to the gizzard the dorsal vessel is seen to give off two, or sometimes three, vessels in each segment on each side, which pass round the intestine, in close connection with its walls, and indeed invested by the glandular hepatic tissue which forms here the exterior layer of the coats of the tube, to join a sub-intestinal vessel. This vessel is not so closely attached to the digestive tube as is the dorsal vessel, but is loosely suspended between the nerve cord and the intestine. It gives off branches to the segmental organs, and is connected with a third set of longitudinal vessels which are in close relation with the several aspects of the nerve cord, one inferiorly and two laterally, and send branches outwards with the nerves. In possessing this vascular supply to the seg- mental organs, and this third set of longitudinal vessels, the Lumbrici differ from other Oligochaetous worms. The commis- sural vessels connecting the dorsal and the sub-intestinal are reduced in number to a single pair in each segment, anteriorly to the crop and posteriorly to the pharynx; but they are so much enlarged in size as to have been called ‘hearts,’ in about six segments posteriorly to the pharynx. In the first six segments of the body corresponding with the pharynx, both the dorsal vessel and the commissural vessels are resolved into plexuses. Anteriorly to the crop and in the line of the outer row of setae are seen the large pendulous lobes which are the vesiculae seminales, increasing in size from the ninth segment, where the first of the three is attached, backwards. On the left side, the posterior having been displaced a little backwards from the middle vesicula seminalis, the corrugated funnel-shaped opening of the posterior of the two branches of the left vas deferens is seen in the interval between them. Immediately exteriorly to the line of attachment of the vesiculae seminales are the so-called ‘capsulo-genous’ glands, which appear to be due to the development in these segments of the setiparous glands of the inner row of setae; and more ex- teriorly again, in the intervals between the ninth and tenth and the tenth and eleventh segments, are seen the two globular recep- tacula seminis in the line of the external series of locomotor setae. On the walls of the oesophagus, in the segments corresponding to the two posterior vesiculae seminales, may be seen the oeso- phageal or ‘ calciferous’ glands, structures said to attain a great development in the Perichaetous worms. On the internal surface 126 Descriptions of Preparations. of the body-walls are seen the remnants of the muscular dissepi- ments which gave to the body and to the digestive tract their annulate appearance. Near the line of the inner row of setae, a little way exteriorly to which they ordinarily but not invariably have their external outlet, are to be seen the ‘segmental organs,’ which are muciparous glands forming complexly convoluted coils, attached by a sort of mesenteric membrane to the muscular dis- sepimental walls of the segments in which the greater part of their length is lodged, and prolonged through the anterior wall of this segment into the segment next in front, to end by ex- panded and ciliated infundibula near the middle line and the ventral surface. For a description and figure of the reproductive organs of the Lumbricus Terrestris, see pl. vii. infra; and Hering, Zeit- schrift fiir Wiss. Zool. viii., 1857, p. 400. See also D’Ukedem, Mémoires Couronnés Acad. Belg., 1856, tom. xxvil., p. 9 seqg.; Mém. Acad. Roy. Belg., tom. xxxv., 1865, pl. i1, figs. 2 and 3. For the ‘segmental organs,’ see Gegenbaur, Zeitschrift fir Wiss. Zool. iv., 1853, p. 221. See also a note by Hering, J. ec. p- 401, and for the homologies of these organs with the efferent ducts of the reproductive glands, see Claparede, Re- cherches Anatomiques sur les Annélides, Turbellariés, &c., 1861, p. 28; and Lankester, Journal Micr. Soc., 1865, p. 7. For the oesophageal glands, see Lankester, /. c., 1864, p. 265; and D’Ukedem, Mém. Acad. Roy. Belg., tom. xxxv., pl. i. fig. 10, p223: For the Perichaetous Worms, see D’Ukedem, /. c., pp. 30, 31; Schmarda, Neue Wirbellose Thiere, 1861, i. 1, p. 13. For the classification of the Annelids generally, see Grube, Die Familien der Anneliden, 1851; Ehlers, Die Boérstenwiirmer, 1864-1868, vol. i., pp. 52-57; Claparéde, Annals and Maga- zine of Natural History, Ser. iii., vol. xx., 1867, p. 337. Medicinal Leech. 127 39. Mepicinat Leecu (Hirudo Medicinalis), Showing the terminal suckers, the segmentation and annulation of the body, and the distinctively coloured dorsal bands which differentiate the variety Hirudo medicinalis from the variety Hirudo officinalis. Tue number of annuli may be taken as about one hundred ; but these annuli appear to be due merely to secondary corrugation of the primary segments of the body, each of which comprises from three to five of the secondary annuli. The primary segments are not so readily distinguishable as the smaller rings; but in a freshly killed specimen, two white spots on either side the median line and in a line with the central pair of eyes are considered to mark out the anterior boundary of each segment; whilst the posterior boundary is given by the openings of the two muciparous or seg- mental organs on the ventral surface, from which jets of fluid can be made to issue by pressure, especially on the posterior part of the body. The black pigment specks which are seen in this variety upon the outer and middle of the three tawny stripes on either side of the dorsum seem, by attaining a great size and prominence on every fifth annulus, to point in the same direction as those more constant land-marks just specified, and to mark out in each case a segment consisting of five annuli. Fewer annuli are interposed between each pair of the dorsally placed white specks at either extremity of the body, than in the intervening space occupied by the middle regions of the body. Upon the anterior sucker a pair may be found upon almost every one of four half- circles of which it is made up, whilst the posterior sucker appears at certain periods of its development to be made up of no less than seven segments, to which seven ganglia subsequently fused to- gether correspond, just as in the rest of the body each pair of white specks on the dorsal surface corresponds to the nerve ganglia on the ventral. This aggregation of segments at either end of the body corresponds firstly to the externally visible concentra- tion of the animal functions of special sense, prehension of food, and locomotion in the region of either sucker; and secondly to a concentration of nerve ganglia and an abortion of the reproduc- tive and depuratory or muciparous organs which are vegetatively 128 Descriptions of Preparations. repeated in each of the intervening segments of the body’s length. The anterior sucker is perforated centrally by the mouth, and is prolonged superiorly into an obtusely lanceolate lip consisting of four rings. It is not separated by any constriction from the rings immediately succeeding it, whilst the posterior sucker is very markedly so separated, has the anus opening in the line of this constriction, and differs consequently still further from the anterior sucker in being imperforate and having an evenly circular un- interrupted rim. ‘Ten eyes are carried in pairs upon the three first rings of the upper lip-like portion of the anterior suckers, and also upon the fifth and eighth segments, the ten eyes as thus arranged forming an ellipse. The male generative orifice from which the penis is sometimes in this species, and very ordinarily in the common Horse-leech, Aulostoma gulo, protruded when the animal has been killed with chloroform, is visible in the interval between the twenty-fourth and twenty-fifth sezments; and at an interval of five segments posteriorly, the female generative orifice is seen in the interval between the twenty-ninth and the thirtieth segments. A series of raised granular but minute tubercles may be observed crossing the dorsal line in many segments, and representing in miniature the warty exterior of Pontobdella. The external colouration of the Leech is very variable, and hence the more or less strikingly regular development of black patches at intervals of five rings in the rust-coloured line on the dorsal is of the greater morphological importance. The amount of pigment specks on the ventral surface is especially variable, and there does not appear to be any regularity as to their distribution when present. For an excellent monograph of Hirudo Medicinalis, see Brandt and Ratzeburg, Medizinische Zoologie, 1833, Bd. 11., pp. 230-297, Taf. xxvili., xxix. A, xxix. B, xxx. See also Moquin Tandon, Monographie de la Famille des Hirudinées, 1846; Leuckart, Die Menschlichen Parasiten, 1863, pp. 634-739; Claus, Grund- zuge der Zoologie, pp. 154-161; Gratiolet, Ann. Sci. Nat., Ser. iv., tom. xvii., 1862, pp. 177-182, for the general out- lines of the body. For certain organs of which as many as sixty may be found upon Medicinal Leech. 129 the cephalic, and some upon other segments of the body, and which, as resembling the ‘ becher-formige Organe’ of fish, may be supposed to be sensory in function, and concerned possibly with the perception of chemical rather than of other stimuli, see Leydig, Archiv. fiir Anatomie und Physiologie, 1861, p. 599; Tafeln zur Vergleich. Anatomie, 11.1; F. H. Schultze, Zeitschrift Wiss. Zool. xii., 1862, p. 222. 40. MepictnaL Lrsecu (Hirudo Medicinalis), Prepared and dissected so as to show its laterally sacculated stomach and its in- testine, in their natural relations to the ventral chain of ganglia inferiorly, and the pharynx anteriorly. A STIFFENING injection having been thrown into the digestive tube, the specimen was hardened in spirit. After this, the im- tegument having been divided down the middle dorsal line and reflected outwards, the portions of the pseud-haemal system which were interposed between the digestive tract and the dorsal surface were removed, and the entire cavity of the ‘stomach’ and of its diverticula exposed by the removal of its upper wall. Anteriorly to the stomach is seen the pharynx with a villous exterior, much resembling that in the earthworm” as seen by the naked eye, as also when its constituent elements, unicellular gland cells and involuntary muscular fibre, are examined under the microscope. Partly concealed by this villous exterior of the commencement of the digestive tract, may be seen the prae-oral ganglionic mass. The walls of the portion of the digestive tube which comes next after the pharynx, are much thinner than those of the pharynx itself, and consist mainly of a structureless basement membrane and an internal layer of pavement epithelium; its muscular coat being almost wholly aborted, as in the Ophidia (see p. 30), and its func- tions discharged by the muscular layer of the body-walls. This portion of the digestive tube has a much larger calibre than the pharynx, and has lateral diverticula appended to it on either side, which occupy five-sixths of the entire cavity of the body. These b See Plate viii. 6. K 130 Descriptions of Preparations. lateral diverticula are eleven in number, the two anterior being smaller than the nine succeeding ones, and differing from them also in not having their outer angles prolonged backwards. The last pair of diverticula are twice the length of any other pair, and bending sharply back almost immediately at their commencement, so as to become apposed to each other along the middle line, are prolonged backwards up to a point on a level with the commence- ment of the rectum, and nearly up to the termination of the body. The digestive tube is of very small calibre posteriorly to the point of origin of the two last diverticula, and lies in the interval between them superiorly. The diverticulate portion of the di- gestive tract is called a ‘stomach’ by most writers, but it 1s considered to. be homologous and analogous with a crop or dilated oesophagus by Gratiolet, on account of its resemblance to the crop of the Horse-leech (Aulostoma gulo), and on account of its functions, which appear to be merely the squeezing out the watery part of the blood which the animal swallows, and allowing it to be dis- charged by the segmental organs. Dissepiments run transversely across the body, and interpose themselves between the apposed walls of the several diverticula. The central emargination in each of the septa thus formed, corresponds to what was the antero- posterior part of the digestive tube in the region of the diverticula ; the method of preparation has given the shape of an ellipse to what was, in the natural state of the parts, a circular foramen in a diaphragm. A rudimentary dissepiment passes off from the pos- terior aspect of each of the eight larger dissepiments, inwards and backwards, within the cavity of each diverticulum towards the middle line; but it is not prolonged quite up to the line of the chain of nerve-ganglia. An accessory compartment is thus added on to each of the diverticula from the third to the tenth inclu- sively; whilst the eleventh pair has five pairs of accessory im- perfect dissepiments, introdigitating along their interior. The ganglia of the ventral chain are seen towards the posterior part of each compartment, constituted by the median portion of the di- gestive and its lateral appendages ; and in some cases they are in immediate relation with the anterior face of the dissepimental wall. A black bristle has been introduced into the segments of the di- gestive tract, posteriorly to the point where the last diverticula are given off. The ‘ oesophageal’ portion of the tract projects and Medicinal Leech. 131 opens as a nipple-shaped process, into the bilobed commencement of what Gratiolet calls the ‘ gastroileal’ intestine, the mucous membrane of which is prolonged into spirally-arranged valvulat folds. This ‘ gastroileal’ intestine ends in an ovoidal colon; and this again in a short rectum of very small calibre, which terminates in a dorsally-placed anus, as in all Hirudineae except Acanthob- della. For description of digestive tract, see Gratiolet, Ann. Sci. Nat. Ser. iv., vol. xvii., pp. 182, 188, 197; Brandt, Medizin. Zoolog., Bd. ii., p. 246. For figures of the digestive tract of the Horse-leech, see Moquin Tandon, Monographie des Hirudinées; Atlas, pl. v. fig. 11 ; Gervais and Van Beneden, Zoologie Medicale, 1859, p. 186. 41. Mepicinat Leecu (Hirudo Medicinalis), Dissected so as to show its nervous system. A part of the pharynx and the jaws are still left 7 situ, and a black bristle has been passed through the remaining: part of the pharynx, where it is embraced by the nerve collar. There are in the Leech twenty-two ventral ganglia, the most anteriorly placed one of which is connected by commissures with the supra-oeso- phageal mass. This mass is seen above the pharynx, part of the glandular and muscular walls of which have been removed to show it, 7z situ, and immediately posteriorly to the middle one of the three jaws. In the narrow interspace between these two structures is seen a minute mesial stomato-gastrie ganglion, which is con- nected with the supra-oesophageal ganglia, and sends nerves to the semilunar saw-like jaw and its muscles; and a similar gang- lion similarly connected with the supra-oesophageal mass, may be seen on either side, sending nerves similarly to either of the two lateral jaws. Each lobe of the supra-oesophageal mass gives off three other nerves, whence the five eyes of either side and certain other, probably sensory, organs, the ‘ becher-formige Organe’ of Leydig, are supplied. The first sub-oesophageal ganglion is much K 2 132 Descriptions of Preparations. larger than any which come after it; it gives off five pairs of nerves, and is connected by very short commissural cords te the supra-oesophageal ganglia anteriorly, as also to the second ventral ganglion posteriorly. The commissures between the second and third, and the third and fourth ventral ganglia increase in length, though they are shorter than those connecting the ganglia be- longing to the middle region of the body; the ganglia at the posterior extremity of the animal are again closely aggregated together. The last ganglion of the ventral chain is much larger than any of the series except the first, and gives off from seven to nine branches to the posterior sucker; the other ganglia give off each two trunks, which distribute themselves to the muscles of the body, with the exception of the penultimate ganglion, which gives off only a single nerve on either side. ‘The paired nerves ave given off very close to each other, and the one which ramifies nearer to or in connection with the anterior wall of each disse- piment, and takes a dorsal rather than a ventral direction, arises above rather than behind the other. This latter nerve has, just at the point of its bifurcation, a small ganglionic mass developed upon it, which may represent the accessory gangha seen upon the pedal nerves in Nereis, and called ‘ ganglions de renforcement ” by De Quatrefages. With a microscope, a small detached ganglion, probably homologous with the lateral ganglia of the system of the nervi transversi in insects, may be seen apposed to but not inclosed within the capsule of each ventral ganglion, in the interval between the points of origin of these paired nerves. A second element homologous to a portion of the Arthropodous system of mervr transversi is presented to us in the Leech by an ‘intermediary ” nerve, which runs in the interval between the two fibrous strands connecting the several pairs of ganglia, but which does not give off any branches. The bilateral character of the chain of nerve ganglia is as plainly seen in the Leech as in the worm ; but there are no nerves given off from the inter-ganglionic commissural cords in the Hirudineae. A third nerve of the sympathetic class exists in the Leech, in the form of an azygos nerve trunk, with ganglion cells appended to it throughout its course, which corresponds to the ventral aspect of the digestive tract, and has two lateral arms prolonged in relation with the two posterior lateral coeca of the ‘stomach’ or ‘oesophagus.’ The removal of the digestive tract Medicinal Leech. 133 prevents us from seeing this structure in this Preparation. It 1s figured, however, by Brandt, its discoverer, Tab. xxix. B, 7 d. e., where it is seen not to be distinctly prolonged upwards into con- nection with the stomato-gastric or supra-oesophageal ganglia. Its relation would appear to correspond to the nervus recurrens of Arthropoda, but that it is in relation with the ventral rather than with the dorsal aspect of the digestive tube. For the ‘intermediary nerve,’ see the memoir of Faivre, its dis- coverer, in the Ann. Sci. Nat. Ser. iv., tom. vi., p. 29. In this author’s previous memoir, published in the volume of the Annales des Sciences Naturelles, immediately preceding the one just referred to, will be found, at p. 361, an account of the various chemical reagents which may be employed in the microscopic investigation of the nervous system of An- nelids. For methods of preparation of entire specimens for the dissection under a lens, without which much of what is here described cannot be made out by the student for himself, see Leydig, Vergleich. Anatomie, pp. 164, 165; and Gratiolet, Ann. Sci. Nat. iv. 17, pp. 177, 178, 181. For the lateral ganglia in apposition with the ventral ganglia, see Leydig, Vergl. Anat., Taf. it., fig. 3 e. For the lateral ganglia developed upon the inferior pair of nerves, see Leydig 7. c., p. 146; Quatrefages, Histoire Naturelle des Annalés, tom. i., p. 81, pl. i1., fig. 1, 2. &., Nereis regia. 42. Mepicinat LeecH (Hirudo Medicinalis), Dissected so as to show its reproductive and segmental organs in situ, the digestive and pseud-haemal systems having been in great part removed, and the integuments fastened out on either side. At about the point of junction of the first with the second sixth of the body’s length, is seen a globular body partly overhanging and partly projecting to the left of the nerve cord, communicating mesially with a siphon-shaped muscular tube, and receiving on either side two tubes of smaller calibre but similar structure. The globular organ is constituted partly by muscular and partly by 134 Descriptions of Preparations. glandular tissue, and is called consequently the prostatic part of the male intromittent apparatus; the mesial siphon-shaped tube representing a penis, and the lateral ducts being ductus ejaculatori. Tracing the vas deferens of the right side outwards, we see that it passes under the nerve cord, to join a convoluted epididymis-like mass of a yellowish colour, which from its contents appears to be analogous to a vesicula seminalis. A slightly tortuous duct enters the organ from behind forwards, after receiving on its inner side the short transverse ducts passing to it from each of the nine globular testes which are seen close to the nerve cord, arranged one in each of nine segments, beginning with the one next but one in order to that in which the convoluted vesicula seminalis is lodged. The female generative apparatus is lodged in the seg- ment interposed between that which contains the first testis and that which contains the vesicula seminalis; and four secondary annuli are seen to be interposed externally between those in which the outlets of the two sets of generative organs are pierced. The vagina has the form of an oval sac with thick muscular walls. From its apex a single tortuous oviduct arises which has its coils enveloped in loose tissue, the microscopic elements of which furnish us with large and beautiful specimens of unicellular glands dis- charging their secretion by isolated ducts. The oviduct divides into branches, one of which is seen passing under the nerve cord, on the apices of which the ovaries are carried. Externally to the line of the vasa deferentia and alternating in position with the testes, we see a row of globular sacs only a very little less in size than these organs. These sacs communicate with the exterior by the orifices already spoken of, Prep. 39, p. 127, as marking the posterior limit of each of the primary segments of the body. Exteriorly to each of these sacs we see a loop-shaped gland, the outer convex end of which is directed upwards, and in the natural condition of the parts almost vertically so, whilst internally it is connected with the globular sac by a short duct passing from the anterior limb of the loop backwards; and in the region of the _ testes has a coecal process prolonged on to each of those organs. The connection which subsists in the Lumbricidae between the open mouth of a modified segmental organ and the reproductive glands, may be regarded as represented in the Leech by the ar- rangement just described. There are eight of these segmental Medicinal Leech. 135 organs arranged opposite the interspaces of the testes, and two in the two anterior genital segments. Four more are to be seen in the segments anterior to those last named, and the three first of these are in closer proximity than the rest of the series. There are three segmental organs in the segments posterior to that containing the last testis; and they possess a coecal process pro- longed inwards beyond the line of the globular sac, by which their excretion is discharged on the exterior of the body. The coecal process of the most anterior of the three, comes into apposition with the posterior testis, but its homologue is not developed in the six anterior segmental organs. The segmental organs are much larger in the Medicinal Leech than in the Horse-leech ; and Gratiolet connects the greater power which the former animals have of living out of the water with the greater power of moist- ening the skin thus attained. Hirudineae, such as Branchellion, which possess only two pairs of segmental organs, and Nephelis and Clepsine, in which these organs attain but a small develop- ment, appear never to leave the water, as the other genera do, spontaneously ; and in them, it should be added, the segmental organs open, which they do not in either of the Leeches men- tioned, by ciliated infundibula into the general cavity of the body. The various portions of the loop-shaped constituent of the seg- mental organs of the Leech, communicate with each other very freely by lateral branches of anastomosis, which make the gland to be labyrinthiform rather than merely tubular. It is of im- portance both to the morphology and to the physiology of these animals, to observe that the failure of the organs of vegetative life here described to be developed at either end of the body, coincides with an aggregation both of segments and of animal organs in the same two regions. The azygos character of the generative ducts is noteworthy, as is also the development of an intromittent organ; a structure not found in other Annelids, though existing both in Platyelminthes and Nematelminthes. For the segmental organs, see Gratiolet, Ann. Sci. Nat. iv. 17, p- 192, pl. vii., fig. 4; Leuckart, Die Menschlichen Parasiten,1., p. 672. For the reproductive organs, see Leuckart, 7. ¢., p. 673; and for the antagonism which subsists between the evolution of these 136 Descriptions of Preparations. organs and that of those of animal life, 7did., p. 549, and Art. ‘Zeugung’ in Wagner’s Handworterbuch fur Physiologie, Bd. iv., pp. 719-1853. 43, MANY-HEADED BLADDER-WORM (Caenurus Cunicult), Tn its cystic stage, from the region of the masseter muscle of a rabbit (Lepus Cuniculus). Tuis specimen illustrates the cystic stage in the metamorphoses of the true Taeniadae. It belongs probably to the same species as the one individuals from which are, when in the cystic stage, lodged usually in the brain of the sheep, and are the cause of the disease commonly known as the ‘sturdy,’ ‘gid,’ ‘staggers,’ or ‘turn- sick.’ The specimen consists of a white walled semi-transparent sac; and a large part of its walls having been removed, one end of it is seen to be beset on its interior surface with a number of closely apposed but distinet opaque white bud-like bodies, the area occupied by which is prolonged out laterally into lobes indicating the conti- nuing proliferation of the cyst. Two smaller cysts, one of which is similarly bestudded internally, are attached by mere filaments of tissue to the lower parts of the large cyst, to the proliferation of which they may also be considered to be due. For, though it is possible to suppose that these all but perfectly isolated out- growths may have been produced by the pinching off from the mother vesicle of small portions of its walls, the large cyst having been necessarily subjected to much pressure from time to time by the masseter muscle; cysts of this tapeworm showing a ten- deney to form or forming similar accessory vesicles, have been figured from parts such as the brain, or lungs and liver, where no constriction could be effected by muscular pressure; and the analogy of certain of the forms of the proliferating cysts of the Taenia Echinococcus would appear to indicate that the formation of such pedunculate outgrowths is one of the normal modes of self-multiplication in the cystic stage of the Taenioid metamor- phoses. The white gemmules represent the ‘heads,’ or ‘nurses’ Many-headed Bladder-worm. 137 of the cestode many-jointed tape-worms which this cyst might have given rise to if it had found its way into the intestines of a dog; and it is therefore as truly a social animal, or rather, a colony of animals in this its cystic, as it is in its cestode form. Each of these heads is called by helminthological writers a ‘scolex;? and the sac upon which they have developed them- selves, and upon which the remnants of the six hooks of the embryo might be detected, is the result of the growth of such microscopic embryo, or ‘ proscolex,’ as the one figured pl. xu. fig. 6, when by the aid of its hooks it has bored its way from the intes- tinal canal into the blood-vessels of its ‘host.’ The ‘scolices’ possess two sets of organs for adhesion upon their proboscis ; viz. four suckers placed proximally to the sac, and two rows of hooks placed near their free apical extremity. The heads themselves, as well as the parent vesicle, are endowed with considerable contractile power; a layer of muscular tissue existing in their walls by the action of which the heads with their armature can be retracted as in this Preparation, or protruded. The cystic stage of the bladder- worm is passed in the organism of some herbivorous animal, and ordinarily in the brain of the sheep; and it has been shown by actual and repeated experiments with dogs, that when the cystic form of this Taenia is swallowed by them, its various heads will develope in their intestines into cestode worms, attaching themselves by their armed proboscides, and producing sexual hermaphroditie segments, the so-called ‘ proglottides,’ in the interval between the remnants of the embryonic vesicle and the asexual adherent head. The entire colony is called a ‘strobile.? The asexual character of its ‘head’ may remind us of the similar exclusion of the generative organs from the anterior segments of Hirudo Lumbricus ; and the successive repetition of the testes in nine segments, as described in the former of those animals, bears a distant resemblance to the successive antero-posterior development of sexual deuterozoids, as presented to us in the ‘ proglottides’ of the ‘strobile’ in a Taenia. A process, however, all but identical with the budding off of sexual zooids by an asexual ‘head’ or ‘nurse’? as seen in the cestoid stage of the parasitic Taenia, takes place in dwtolytus (Grube), Nereis prolifera (O. F. Miller), Myrianida (M. Edwards), which are Vermes of the most highly organized order of the Polychaeta ; and the resemblance pointed out in the preceding sentence, as 138 Descriptions of Preparations. existing between the Leech and the Tapeworm, must not be taken as justifying the views of writers who would class Hirudineae with the Platyelminthes’. ¢ The class Platyelminthes is here taken as comprehending three orders—the Cestodes, Trematodes, and Turbellarians ; and it is with the Trematodes that the Leeches have been supposed to be so closely allied as to justify the removal of them from the class Annulata, which comprehends the Polychaeta, Gephyrei, and Oli- gochaeta. The principal reasons for this dissociation are those furnished by the absence of external appendiculate organs such as locomotor setae or gills, and the presence of suckers in both Trematodes and Leeches; by the sacculate character of the digestive tract ; by the absence of a body cavity; and by the structure of its skin. In answer it is to be said that the absence or presence of such organs as setae or gills is not to be considered as of such consequence as the similarity or dissimilarity of such systems as the reproductive or nervous ; and that even if only external characters are to be compared together, the definite segmentation of the Hirudineae differentiates them very sharply from the Trematodes, which are not even annulated. With reference to the similarity which the dendritic digestive tract of certain Trematodes presents to the diverticulate tube of the Hirudineae, it must be borne in mind that amongst the Polychaeta, forms with more complexly diver- ticulate intestinal tubes, Aphroditea, are to be found than amongst the Leeches ; whilst the presence of an anal sucker in other members of the same order, Leucodore and Clymene, furnishes a similar answer to the argument for classing the Hirudineae with the Platyelminthes which is based upon their common possession of these organs of adhesion. Another answer is furnished by the fact that the construction of the suckers is, as Leuckart has pointed out, by no means identical in the two classes under comparison ; and that the possession of suckers is a point of physio- logical rather than of morphological importance, is even more clearly shown by their existence on the caudal extremity of the free, and the ventral surface of the para- sitic Nematoids, which belong to a class very distinct from both Annelids and Platyelminthes. Neither are the Hirudineae truly ‘parenchymatous’ or ‘ sterel- minthous’ Vermes in the same sense as the Trematodes. For Leuckart has shown that in all Hirudineae more or less of a perivisceral cavity remains, after the full development of the large digestive tract, and of the ‘ dorso-ventral’ muscles which encroach so much upon it. In Branchiobdella there exists a large perivisceral cavity, as well as a system of vessels, which appear to be homologous with the so-called ‘ pseud-haemal’ vessels of the common Leech and other Annelids, though at the same time they are continuous with, and must be supposed to represent a part of the perivisceral cavity. And by consequence, therefore, the pseud-haemal vessels of other Hirudineae must be taken to represent the remnant of the peri- visceral cavity, when such a space appears to have become obliterated. So that the true way of expressing the facts would be to say, not that the Hirudineae re- semble the Trematodes in not possessing a perivisceral cavity, but that they differ from them in possessing a system of vessels which, as being continuous with a peri- visceral cavity in Branchiobdella, may be regarded as actually being in the species mentioned, and as representing in other species a part of a perivisceral cavity. To this interpretation the fact that in certain Polychaetous Annelids, Glycera and Phoronis Hippocrepia, the pseud-haemal vessels have been observed to contain true Many-headed Bladder-worm. 139 For a further account, with figures of the metamorphoses, of the Taeniadae, see Description of the semi-diagrammatie figures, 1—6, in plate xii. imfra. See also Cobbold’s Entozoa, 1864, pp. 104 segg. et passim ; Leuckart’s Menschlichen Parasiten, pp- 181-220; and p. 251 for the formation of the proglottides by the development of annular constrictions in the vermiform ‘ corpusculated blood, appears to lend considerable probability. On the other hand, the Hirudineae do to a certain extent resemble the Trematodes, in possessing a muscular system which is more complex, and more closely connected with the glandular and epithelial elements of the integument, than is usually the case in other Vermes. It may be suggested however that the changed relations of the contractile and other elements of the integument in the Leeches, may be correlated with the other changes which are ordinarily produced in subordination to the special habit of parasitism ; and which, in this sub-kingdom, appear to entail the loss of the setae, the gills, and the cilia, And the development of an additional transversely crossing set of muscles in addition to the external circularly arranged and the internally longitudinally arranged muscles of other Vermes, seems similarly referrible to com- munity of habits, and not to any morphological affinity subsisting between the Trematodes and Leeches. For a similar layer of muscles has been observed by Dr. Charlton Bastian to exist in the Nematoids (see Phil. Trans., 1866, p. 564) ; and as in all three orders alike, the special need for some such arrangements, for propelling and otherwise acting upon the contents of a digestive tube, altogether or nearly devoid of muscular fibres, may be considered to account for its presence, it cannot be held to furnish a good basis for classification. On the whole, the Hirudineae appear to be rather Annelids degraded by the special habit of parasitism, than to be intermediate forms in a series which should represent the various stages in progression upwards from the lower Platyelminthous Vermes to the highly organized Annelids. The characters which appear to approximate them to the Platyelminthes, relate mainly to such external points as the shape of the body, and the modifications of the tegumentary system ; and whilst these characters are probably to be regarded as explicable by reference to a community of habit, and therefore as devoid of classificatory value, those which connect the Hirudineae with the Annelids possess a real morphological importance. Among these we may mention the segmentation of the body not merely in the way of external annulation, but in that of internal division into more or less completely separated cumpartments by the development of dissepiments ; the possession of a chain of nerve ganglia, and in most cases of a similarly multiple series of segmental organs ; and the presence of the so-called ‘pseud-haemal’ system. And it should be further noted, that whilst in all these points the organizations of the Hirudineae and the setigerous Annelids resemble each other, and differ from those of the Platyelminthes in the direction of greater complexity and perfection, they still further resemble each other but in the reverse direction, and as presenting lesser complexity and importance, when we come to compare their reproductive systems, which never possess either the high degree of morphological differentiation, or the actual bulk relatively to the rest of the body, which distinguishes the generative organs of the Platyelminthes. See pl. viii., ix., and pl. xii., figs. 2 and 4 with descriptions, infra. 140 For Descriptions of Preparations. appendage of the head, and the constant intercalation of new segments formed in the same way between the head and the earlier formed segments. See also Van Beneden, Mémoire sur les Vers Intestinaux, 1858, pp. 235-251; and for an account of similar processes observed in the Polychaeta, see Huxley, Edinburgh New Phil. Journ., Jan. 1855; Ehlers, Die Bérstenwtirmer, Bd. i. 207 seqq., ibique citata ; and for the Oligochaeta, see Lankester, Linn. Soc. Trans. xxvu., Quart. Journ. Microse. Science, 1869. a special history of this Tapeworm, Cuenurus Cerebralis s. Cuniculi, see Van Beneden, Z. ¢., pp. 146-148; Cobbold, 2. ¢., p- 116; Gamgee, Fifth Report of the Medical Officer of the | Privy Council, 1862, pp. 234-237; Thudichum, Seventh Re- port of the Medical Officer of the Privy Council, 1865, p. 3353 Numan, Verhandelingen der eerste Klasse van het Koninklijk. Nederlandsche Instituut, 1850, where many figures, micro- scopic and other, are given of this animal. For the classificatory relations of the Platyelminthes and the Hiru- dineae, see Grube, Die Familien der Anneliden, 1851, pp. 3-8 ; Schneider, Monographie der Nematoden, 1866, p. 329; Leuc- kart, Die Menschlichen Parasiten, pp. 156, 157; Claparéde, Bibliothéque Universelle, tom. xxii. Bull. Sa., pp. 346-355, 1865; Ann. and Mag. Nat. Hist. Ser. iii. xvil., 1866, p. 100; and M. de Quatrefages, p. 108; Claparéde, vol. xx., 1867, p- 337; Wan Beneden, Turbellariés, p. 48, 1860. * the structure of the integument in the Platyelminthes, see Leuckart, 7. c., pp. 459, 645; Schneider, /. ¢., 333. their ‘parenchymatous’ or ‘sterclminthous’ character, see Leuckart, 7. ¢., pp. 157, 666, 713; and for the presence in the pseud-haemal vessels of true corpusculated blood, such as is ordinarily found only in the perivisceral cavity, see Leuc- kart, /.c., p.670; and Dyster, Linn. Soe. Trans., xxil., p.-254, 1858. Common Crossjish. 141 44, Common CrossFisH (Asterias Rubens), Linn. (Dried.) THE animal consists of a central disk which is prolonged into five lobes, the so-called ‘ arms’ or ‘rays.’ One surface of the specimen is hollowed out into a deep central cavity corresponding with the mouth, and made pentagonal by the abutment upon its edge of the rows of spines bounding the five ‘avenues,’ which radiate out from it on the same surface, and, from lodging the locomotor feet, have given this aspect of the animal the name of ‘ ambulacral.’ The other surface is more or less convex, and beset with spines ; and in one of its interradial spaces it carries the concentrically striated disk known as the ‘madreporie tubercle.’ The two surfaces are nearly equally developed in Asteriae and Ophiurae. Along the middle line of each radial avenue there runs a central furrow, formed by and at the junction of the ‘vertebral’ ambulacral os- sicles. In this central furrow were lodged first and most superiorly the water-vascular canal supplying the ambulacral sucker-feet ; then some transverse adductor muscles; and thirdly and most superficially, the ganghated nerve cord, the ‘ Ambulacral-gehirn’ of the German writers. Externally on either side to this central furrow, the lateral processes of the ambulacral ossicles form, by the apposition of their emarginated edges, two alternately placed series of conjugate foramina, for the vessels bringing the sucker-like exteriorly-placed portion of the feet into communication with in- ternally placed ampullae as seen in Preparation 45. These am- pullae are wanting in the Ophiurae, as also in the ambulacral tentacles of certain Holothurioidea, for which see Preparation 47. Each of the five radial avenues tapers up to its distal extremity where the eye was lodged, and where in the fresh specimen the suckers may be observed to attain a considerable relative length. On each side of each avenue we see two sets of spines, one of which is placed internally, and consists of two rows of long and slender spines ; whilst the more externally placed one is made up of three rows of stouter, shorter, and blunter spines. Towards the apex of each ray the external set of spines attains a greater de- velopment relatively to the internal; and out of it is there evolved 142 Descriptions of Preparations. the circlet of specialized spines, which protect the eye and the contractile tactile organ in relation with it. A third set of spines ~ marks the line of junction of the vertical and dorsal surfaces in each ray ; and the middle line of the anti-ambulacral surface has more or less of a keeled appearance, from the more or less regular longitudinal arrangement there of the spines with which the dorsal surface generally is beset. Remnants of the organs known as ‘ pedicellariae,’ which appear to be spines modified so as to be mobile and prehensile, are to be seen in the interspaces between the spines, and some, though of smaller size and not in especial abundance, may be seen also round the bases of the spines. The spines themselves are immobile in the Asteriae, and, though they may carry a coronet of numerous calcified setae on their apices when they are called ‘ paxillae,’ when modified into ‘ pedicellariae,’ they rarely carry more than two terminal processes, which make up a pincer-like organ. In the Echinidae, on the other hand, the spines are themselves mobile, and provided with a muscular apparatus; and the ‘ pedicellariae,’ which are mainly distributed about the oral region, are trivalved. Opposite one of the inter-radial spaces is seen a whitish, circular, raised, concentrically striated disk, the so-called ‘madreporie tubercle.? In a fresh specimen of any one of the Asteriae which is provided with sucker-hke and not with conical feet, the anus may be found near the centre of the dorsal surface a little to the left of a line drawn from this madreporic tubercle, down the longitudinal axis of the ray, oppo- site to the inter-radial space in which it is lodged. The same line will enable us to divide the five rays into a ‘ bivium,’ between which the madreporie tubercle lies, and a ‘trivium,’ the two lateral arms of which lie on either side of the arm which is opposite to that tubercle. But we cannot speak properly of an anterior or posterior radius or inter-radius in these Echinodermata, inas- much as, like Echinidae and Ophiuridae, they move in locomotion indifferently in the direction of any one radius or inter-radius. The radius which lies to the right in the madreporie bivium in this specimen, when the central ray of the trivium is placed so as to point away from the observer, is much shorter than any one of the other four; having been reproduced after some injury, but not having attained the size of its fellows. The power of reproduction of injured parts is very great in these animals, having indeed Common Crossfish. 143 scarcely any limit short of the retention of the stomach, and of at least one coecal appendage uninjured. As the Echinodermata, on the one hand, all go through more or less complex metamorphoses, and, on the other, never when adult multiply by gemmation, it is obvious that the power of repairing injuries cannot be, as it has been held to be, correlated either with the absence of metamor- phosis, or with the power of reproduction by metagenesis strictly so called. For the account of the structure of the Echinodermata generally, see Johannes Miller, Abhandlungen Kon. Akad. Wiss., Berlin, for 1853, translated in part by Professor Huxley in the Annals and Magazine of Natural History for 1854, Ser. i1., vol. xin. ; Professor Sharpey, Article ‘ Echinodermata,’ in Todd’s Cyclo- paedia of Anatomy and Physiology. For a monograph of the Asteroidea, see Miller und Troschel, System der Asteriden, 1842. For an excellent account of the nerve system of the sensory organs, and of the power of reproduction of lost parts in the common Cross-fish (Asterias rubens), as also of that of the So/aster papposa, and Cribella oculata, see Wilson, Linn. Soc. Trans., 1860, vol. xxiii., pt. 1., p. 107. For an analysis of the tegumentary skeleton, see Gaudry, Ann. Sci. Nat. Ser. i1., tom. xvi., 1851. For reviews of Miiller’s researches into the anatomy and develop- ment of the Echinodermata, see Huxley, Ann. and Mag. Nat. Hist., Ser. ii., vol. viii.. 1851; Baur, Nova Acta, 1864, PP: 17, 57: 45. Common CrossFisH (Asterias Rubens), Linn. Dissected so as to show its digestive and motor systems. One of the rays, the central one of the trivium, has been cut short, and more or less of the anti-ambulacral integument removed from each of the other four, and from the central disk. In the inter-radial space which is opposite to the ray which is cut short, 144 Descriptions of Preparations. is seen the madreporic tubercle; and a little to the left of a line producing the long axis of that ray to the centre of the madreporic tubercle, and near the centre of the disk, is seen the small piece of the apical inteeument in which the anus opens. From the intes- tiniform portion of the digestive tract immediately following upon the anus, two diverticula arise, and efflorescing into two or three coecal ampullae, reach a short way into each of the two inter-radial spaces in the disk, which lie on the left of the madreporic or anal inter-radius. In this species there are only these two inter-radial coeca; the one nearest the madreporic inter-radius is the larger of the two; both have their internal surface plicated longitudinally, and from this it may be seen that, like the ‘respiratory trees’ of the Holothuriae, with which they are homologous, they are highly extensible. In a starfish which has died with its stomach pouted out, as it often is during life, these coeca may be observed to be drawn down much farther than the much longer coeca, which are prolonged into the interior of the rays from a lower level in the digestive tract, but are attached to the anti-ambulacral surface by a mesenteric membrane. These latter coeca are seen to take their origin from a much wider portion of the digestive tract as single trunks; and very shortly after entering the rays they break up into two trees, which, with their foliaceous glandular ampullae, fill up, in this specimen in which the generative glands are in a state of quiescence, the greater part of the interior of the cavity of each ray. At a lower level again than the plane whence the stems of these arborescent coeca take origin, the saccular dilatations of the stomach proper are seen bulging for a short distance into each radial space to the vertebral ossicles in which they are braced by ligaments. The Asteriae are the only Echinodermata in which any radial arrangement attaches to the digestive system beyond that of the calcareous apparatus set around the mouth in all of them, and subservient to the prehension or manducation of food in most except the Crinoidea. In the interior of each ray, and between the ramifications of the digestive coeca, which are here and there slightly divaricated to show them, are to be seen the bilaterally symmetrical biserial rows of ambulacral ampullae on either side of the central stem, resembling that formed by the bodies of a true vertebral column, and made up by the apposition of the mesially articulated ossicles called ‘ vertebral’ from this resem- Angular Sea-Cucumber. 145 blance. The feet with which these ampullae communicate are seen to be provided with sucker-like ends, though not with calcareous terminal supports, as in the Echinoidea and Holothurioidea. In the three genera of Asteriae, Astropecten, Ctenodiscus and Luidia, the locomotor feet end by conical and not by sucker-like termina- tions; and with this point of inferiority is correlated also the absence of an anus. In the Ophiuridae, the digestive tract is a simple coecal sac, bulging somewhat like the true stomach of the Cross-fish radially, but not prolonged into the interior of the arms, as in all the Asteriae including the three aproctous genera just mentioned and Brisinga; and with this increase of inferiority in the digestive apparatus, an increase of inferiority in the locomotor 1s found to correspond, as the feet are devoid not only of true suckers but also of ampullae. It is in the Asteroidea alone that the nerve- system lies externally to the ambulacral plates, which form thus an ‘internal skeleton,’ absent in the Crinoidea, and existing in the Echinoidea and, possibly, in the Holothurioidea also, only as ru- diments. The nerve-cord is further protected in Ophiurae by a row of dermal ventral scutes. For a figure of the digestive tract, see pl. x. infra. For figures of the locomotor feet in Ophiurae, see Sars, Norges Echinodermer, 1861, tab. i., fig. 1-5. 46. ANGULAR Sua-CucuMBER (Cucumaria Pentactes), FORBES, Prepared so as to show the external characters of the class Holothurioidea ; and the traces of a bilateral symmetry, the co-existence of which with the more obvious appearance of a radial arrangement is very well seen in these Echinodermata. Tux five rows of ambulacral feet and the ten arborescent circum- oral tentacles, which are merely modifications of ambulacral feet, give the Sea-Cucumbers at first sight a very markedly radiate appearance. But upon looking closely at these structures, both will be seen to admit of being divided into two bilaterally symme- trical halves, each of which is composed of heteronomous elements. The five rows of ambulacral feet are seen to fall naturally into a ventrally placed trivium, the feet in each of the rays of which are more numerous, more perfectly developed, and more regularly L 146 Descriptions of Prenarations. disposed than those of the two rays of the dorsally placed bivium ; and of the ten tentacles the two which are placed immediately opposite the central ray of the dorsal trivium, and one of which is placed therefore on either side of the medio-ventral line, are very much smaller than any of the other eight’. The ventral trivium gives the surface of the body which it occupies a somewhat flatter surface than is possessed by the surface corresponding to the dorsal bivium ; and this, together with the diminution in number and importance of those two rows of ambulacra, appear to constitute a transitional arrangement between the more perfectly pentagonal appearance which nearly allied species may present, and the close adumbration of the form of an ordinary Gasteropod which we note in Psolus (Cuvieria), where the dorsal bivium is wholly aborted. The ten tentacles are seen to be carried upon the outer rim of a cylindriform prolongation of the body-walls, which is transparent and carries no ambulacral feet. The anti-ambulacral surface is reduced in Holothurioidea as it is in Echinoidea to the small region immediately surrounding the anus ; in Cucwmaria communis, indeed, the ambulacra almost abut upon that orifice; and it may be here 4 Systematic zoologists differ as to whether the smaller size of the pair of ambu- lacral tentacles, which are placed opposite the central ray of the ventral bivium, is of generic, of specific, or even of less classificatory importance. Troschel, in the Archiv. fiir Naturgeschichte for 1846, speaks of this difference as being of generic value, and as separating Cladodactyla (Cucumaria) doliolum, Brandt; Cladodactyla Dicquemarii, Cuvier and Brandt, and Cladodactyla Syracusana from the species here described. Forbes, however, in his ‘ History of British Star-fishes,’ 1841, says of Cucumaria pentactes, ‘It is extremely variable in colour; generally of a deep purple, sometimes altogether white, sometimes purplish white. The tentacula and head of both varieties vary equally, either purple or white. It varies also in the pinnation of the tentacula, and in their relative size and number. The Holothuria Montagui of Dr. Fleming, founded on a white variety described by Montagu, has eight full-sized tentacula and two small ones, which are alternately in motion covering the mouth. The tentacula of this form are not so pinnate as in the common or purple state.’ It has been said that the ‘Cuvierian organs,’ certain structures of various forms and doubtful function attached to the stem of the respiratory trees or inserted upon the cloaca, are wanting in all Cucumariae with unequal tentacles; but the readiness with which these organs are ejected by the Holothurians, when they are alarmed or irritated, is such as to make it unsafe to base a conclusion as to a specific difference upon their absence or presence. Semper, on the other hand, Reisen im Archipel der Philippinen, p. 47, assigns this smaller size of the two medio-ventral tentacles as a generic property to the Cucumariae ; but he also specifies the presence of this peculiarity in individual cases of particular species as though it were not universally present. Angular Sea-Cucumber. 147 remarked that the two classes just mentioned, though they may at first sight, owing to the great differences of their external tegu- mentary organs®, appear to be entirely unlike each. other, are in reality more closely allied by structural, if not by developmental history, than any other two classes in this sub-kinedom. The Holothurians with rows of ambulacral feet are divided into two families, according to the shape of their ambulacral tentacles ; those in which the tentacles are, as in the Cucumariae, dendritic in appearance, and carried upon a cylindriform stem of different texture from that of the rest of the body, being called « Dendro- chirotae ;? and those in which the tentacles are shield-, or rather shovel-shaped, and in which the integument is continued without any alteration in its texture up to the tentacles, being called ‘Aspi- dochirotae.” With these external differences a considerable number of points of difference in their internal structures are correlated, for which see description of next Preparation. In all Holo- thurians, but especially in the otherwise apodal Synaptidae, the ambulacral tentacles are used as locomotor organs; and in the Aspidochirotae they are also used for bringing the sand, in which these animals very ordinarily live partly immersed, into their digestive tract. The intestinal tract, on the other hand, of the Dendrochirotae, in which the tentacles could not be used for this purpose, is ordinarily found to contain no sand or stones. For an excellent account of the anatomy of the entire class Holo- thurioidea, see C. Semper’s beautifully illustrated Monograph, Reisen im Archipel der Philippinen, Theil ii.; Wissenschaft- liche Resultate, Bd. i., Hft. i. 1867, pp. 1-6, Hft. iv. 1868, pp: 101-178; Emil Selenka, Zeitschrift fiir Wissenschaftliche Zoologie, Bd. xvii., Hft. 2, 1867. For the anatomy and development of the Synaptidae, see a me- moir by Dr. Albert Baur, Nova Acta, vol. xxxi., 1864; where, at p. 50-60, Ab. il., some valuable remarks will be found upon the ‘ so-called alternations of generations in the Echinoderms ;’ and at p.17, Ab.i., certain less convincing views as to the homologies of the calcareous ring in the Holothurioidea with the auriculae of Echinoidea. © For a note as to the existence of an Echinus with a soft integument, see Semper, L. c., p. 163, citing Grube, L 2 148 Descriptions of Preparations. 47. ANGULAR SEA-CucuMBER (Cucumaria Pentactes), FORBES, Dissected so as to show its motor, digestive, respiratory, and reproductive systems. Tus integument has been divided down the middle line of the inter-radial space of the dorsal bivium, and fastened out on either side. Five double longitudinal muscular bands are seen to divide the body-walls into a corresponding number of antero-posteriorly running zones, upon which the external circular muscular coat is very well seen. In the interval between the two factors of each double band is lodged the longitudinal water-vascular ambu- lacral vessel in all the pneumonophorous Holothurioidea, whether they possess ambulacral feet, or, as the Molpadidae, are devoid of them; and, as in all Holothurioidea without exception, the longi- tudinal nerve-cord is to be found lying in the longitudinal plane corresponding to the interval between the two muscular bands im- mediately beneath the cutis ; and, as in the families which possess longitudinal ambulacral vessels, between the cutis and those vessels. The longitudinal muscles are prolonged from the region of the mouth, where they are inserted into the integument near its junction with the commencement of the digestive tract, down to the anus; and in the Dendrochirotae, to which family the Cucu- mariae belong, each longitudinal muscle gives off a long slip, which passes to insert itself into the corresponding radial ossicle of the calcareous ring. In this specimen the slip given off is much thicker than the radial muscle itself; indeed, the slightness of the radial muscles, as well as the possession of these slips, is one of the many points in which the Dendrochirotae differ from the Aspi- dochirotae. On cither side of the radial muscles the ampullae, which in Dendrochirotae are not usually present in their tentacular ambulacra, are seen arranged alternately. The radial water-vessels with which these ampullae and the sucker-like feet are in con- nection, pass forward to join the circumoral water-ring, through an emargination in the anterior end of each of the radial ossicles in the calcareous ring; and as the radial nerve-cords hold the same relation to these ossicles, they have been viewed as homo- Angular Sea-Cucumber. 149 logous, not, as they really are, with the masticatory apparatus, the so-called ‘ Aristotle’s Lantern, of the Echinoidea, but with the ‘ auriculae’ of these Echinodermata, and with the proximal pair of < vertebral ossicles’ (see p. 144, supra) of Star-fishes. The water-vascular ring surrounds the muscular pharynx a little way posteriorly to the calcareous ring; two long air-bladder-like Polian vesicles are seen hanging down from it, and ending freely in the body cavity on the left side; whilst the madreporic plate and the pedicle upon which it is placed are seen to join it in the medio-dorsal line. The internal position of the madreporic tubercle, characteristic of the Holothurioidea, renders it necessary that the water in the locomotor water-vascular system should be obtained from the fluid in the perivisceral cavity, from which the pores of the madreporic disk are, however, said to be separated by a layer of epithelium, continuous with that lining the perivisceral cavity ; so that the fluid they receive enters them not directly but by diffusion through and by the intermediation of these cells. In immediate relation with the water-vascular ring is seen an annular plexus of pseud-haemal vessels, which represents the circular pseud- haemal sinus of the other Echinodermata. From it two principal vessels pass backwards; one along the dorsal, the other along the ventral line of the digestive tract, in the substance of the walls of which they are connected with each other by plexuses. Of these two vessels, the ventrally-placed one is always comparatively simple and devoid of any ramifications of importance, though the segment of it in connection with the first descending convolution of the intestine communicates with that in connection with the first ascending, by one or more transverse commissural vessels ; whilst the dorsal vessel may have a considerable rete mirabile developed in connection with it, which in Aspidochirotae comes into relation with the left ‘respiratory tree’ arising from the cloaca. This rete mirabile may be seen in this specimen in connection with the dorsal vessel in the first segment of the intestine ; it must not, however, be confounded with the reticular muscular mesentery, the very abundant fenestration of which gives it the appearance of a plexus of blood-vessels. The muscular pharynx is succeeded by a muscular stomach, which is much smaller in calibre and a little shorter in length than the portion of the pharynx which intervenes between the commencement of the stomach and the 150 Descriptions of Preparations. water-vascular ring anteriorly. The commencement of the intes- tine proper is seen to be connected with the convex portion of the second convolution of the tube by a considerable number of vessels passing between the segments of the ventral vessel in connection with each portion of the tract. The first convolution of the in- testine has its concavity looking forwards, its convex aspect being in relation with the posterior extremity of the animal’s body ; the second convolution or the first ascending segment of intestine reaches about as far forwards as the middle of the body, where it turns backwards to end in the ‘cloaca.’ This term may be applied to the terminal segment of the intestine, inasmuch as, though it does not receive the duct of the generative organs, it does receive those which lead from or into the so-called respiratory trees, the functions of which, there is good reason to think, are as much depuratory or renal as respiratory. These organs are seen to take origin on either side of the cloaca as hollow stems carrying somewhat scanty ramifications, and reaching a considerable but varying distance forwards in various specimens into the cavity of the body. They are both attached to the body-walls by mesen- teries, which are, however, reduced by extreme fenestration to mere series of filaments inserted along the left and right borders respect- ively of the ventral trivium. In the Dendrochirotae there is not, as in the Aspidochirotae, any connection between the respiratory tree of the left side and the pseud-haemal plexus developed upon the vessel in connection with the dorsal surface of the intestinal tube ; and in this sense, though not in that in which the word has been applied to them, the Dendrochirotae may be called ‘ Adetopneu- mones.’ The arborescent form of the tentacles of the Dendro- chirotae may, by exposing a greater surface to aeration than the short shield-shaped tentacles of the Aspidochirotae, compensate for this less perfect evolution of the internal aerating apparatus ; and with the greater evolution of the tentacular apparatus and its division into delicate twigs, we may connect again the evolution of the special system of retractor muscles already noticed. Accord- ingly as these respiratory trees are absent or present, the class Holothurioidea is divided into the two orders of Apneumona and Pneumonophora ; the Apneumona, Synaptidae, having, like such of the Gephyraean Vermes, Sipunculidae, as are similarly devoid of respiratory appendages to their cloacae, certain ciliated infundi- Angular Sea-Cucunvber. 151 buliform organs developed upon their mesenteric membranes, the functions of which may be supposed to be identical with those of the organs they replace. With the absence of lungs the pecu- liarity of monoeciousness or hermaphroditism is correlated in the Holothurioidea. On the right side in this Preparation is seen the generative gland, which consists of two bilaterally symmetrical fascicles of coeca, attached on either side of a thickened portion of the dorsal inter-radially placed mesentery. * Te me _ Py eee hia. . i ¥ Pei tt =i 4 - ‘Hk SS on, dirs Hy Sy siner A 1s VE tims i “4 rat ct OA 3) Maer fateh his iva i ae MED the hirer. Sue Wt somes Wid: oP ae 1 i arin oblintds @ Sb five ttt Seater’ ole? ¢ OF an Say. hess. abt gigas iuagieet ahaa et oie en ere Ta iets te it ee wk 24, a Sear ae : a hes: fell! wo pe aerial > +e Se OGl? Xe. De ee 4 ana all oat prey ae ED 2p ve TA ae daphan le Pine lt «ue 4 > LP e=A7 7 eat elach OMe al nese : {aan = : , ci ae o) == ane ree ’ i ie ae : - wae bs : ¥ Po ble ; . = = 7 7 7 a - i a ~ ] / - C7 2. 5 < a a a tye 4 7 Lee aoe at ae Bon a4 on — * aa = PLATE II. G. Crozier, ded. O. Jewitt, sc. Picron, Columba Livia. PLATE II. Common Picron (Columba Invia), Dissected so as to show, firstly, some of the main points of agreement and difference between Aves, Reptilia, and Mammalia respectively ; and, secondly, the arrange- ment of the principal muscles of flight. In the possession of a single aortic trunk, as seen in the figure a little internally to the letter y, and above the letter g, birds re- semble Mammals, as they do also in the physiological peculiarity of being warm blooded, or ‘homoeothermal.’ A few Mammals resemble all Birds in being testicondous, see 4 in figure, and in the possession of two coeca, see,/ in figure, as also in the possession of a coracoid prolonged down to the sternum, see place of origin of muscle w in figure. But all Mammals differ from all Birds in that their single aorta crosses their left and not, as shown at g in this figure of a Bird, the right bronchus; in the absence of any mdent- ations of the lungs’ surface to correspond with the ribs; and in the absence of any external conformation of the kidney in relation to the pelvic bones. In all Mammals there is a sinus wrogenitalis, in none do the genital and urinary ducts open separately, as shown here at 4 and g, into a cloaca common to genital, urinary, and faecal products. These points are as constant as the possession by Mammalia of a hairy integument and of non-nucleated coloured blood corpuscles. The relation of the pancreas to the duodenum, as seen at ¢, is a minor point, but probably equally distinctive of Birds in opposition both to Mammals and Reptiles. In being testicondous; in the absence of differentiation of the structures of the kidney into cortical and medullary portions, and in the supply of blood-vessels to the gland; and in the absence of 176 Description of the Plates. a perfect diaphragm, and also of a corpus callosum,—Birds and Reptiles resemble each other as closely as they do in the micro- scopic character of their blood-corpuscles. In two points of second- ary importance Birds resemble the Loricate and differ from the Squamate Reptiles; in this latter class there is a rudimentary urogenital apparatus, and the genital gland is situated a certain distance anteriorly to the kidney ; whilst in Birds, Crocodiles, and Chelonia, the genital and urinary glands have separate outlets, and the glands themselves are more or less completely in appo- sition with each other. On the other hand, all Birds possess a quadrilocular heart, and a single aorta belonging to the left ven- tricle, an arrangement by which they are secured against any direct admixture of venous with arterial blood, and in which they differ as widely and constantly from Reptiles as in the peculiarity of their integumentary system. No Reptiles possess a true crop, such as is seen at d in the figure, nor two coeca; but these structural arrangements are by no means constant in Birds. a. Right cerebral hemisphere. Its surface is smooth, contrasting herein with that of the transversely laminated cerebellum seen behind in the median line. 4. The crop, which is bilocular in the Columbidae. It is con- tinuous above with an artificially distended oesophagus, and a window has been made in its right wall to show its divi- sion into two compartments. e. Right lobe of liver, on which the right side of the heart rests. d. Heart. The ventricular portion is more acutely conical in most Birds than in Mammals, and the auricles are smaller in relation to it. e. Loop of duodenum in which are contained the longitudinally arranged lobes of the pancreas. Into this loop of intestine three ducts open from the pancreas and two from the liver, which has no gall-bladder in this species. Two of the pan- creatic ducts open near the middle of the distal segment of the duodenum close to each other and to one of the gall- ducts; the third pancreatic duct opens near the distal end of the loop, and the second gall-duct near its proximal end. Common Pigeon. 177 e.1. Terminal segment of small intestine ending in the large intestine at /, which, together with it, has been turned over out of the abdominal cavity, on to the animal’s left. Two long coils of small intestine have been removed between its terminal segment and the distal end of the duodenum; the first coil being a fold of great length spirally arranged, and the second a much shorter one arranged like the duodenal fold, which however it exceeds in length. J. Large intestine, two small coeca marking its commencement. In the small size of the two coeca the Columbidae contrast with the great mass of the Gallinaceae. g. Terminal dilatation of the large intestine which receives the vas deferens and ureter posteriorly and superiorly on each side. In this cloacal arrangement Birds resemble Reptiles and Amphibia; in all mammals there is a sinus urogenitalis developed, into which these ducts open. In the absence of a urinary bladder Birds resemble Snakes and Cartilaginous Fishes, as also many Lizards. h. Testis. 2. Kidney divided into three lobes, which are conformed to the sinuosities of the pelvic bones. Between the lower and middle lobes the large ischiatic artery and some nerves pass out to the lower limb. The artery gives a supply of blood to the gland. Between the middle and upper lobe of the kidney the small femoral artery passes outwards, and a large vein passes inwards. This vein, besides acting as a ‘renal-portal’ vein and supplying the glandular structure of the kidney, communicates directly also with the renal efferent vein. This latter branch is not possessed by cold- blooded Ovipara Jj. Vas deferens, dilating before its termination in the cloaca. k. Ureter. 7. Teres major muscle, the subscapularis and great part of the scapula having been removed. m. Right jugular vein receiving the veins from the oesophagus, and by virtue of these vessels, as also of a branch of anasto- ® See Jourdain, Sur la Veine Porte Rénale, Ann. Sci. Nat. Ser. iv., tom. 12, 1860, pp- 156 and 359, and plate 4, fig. 2. N 178 s Description of the Plates. mosis with the left jugular, attaining, as is usual in birds, a larger size than that vessel. . Right jugular vein in thorax. The junction of the subclavian with the jugular vein is not effected until some way below the point on which this line terminates; a portion of the former vein is seen in connection with the very short vena cava superior just above the right bronchus. Vena cava inferior, entering the auricle to the right of and posteriorly to the entrance of the vena cava superior of. the right side. . Lung, showing on its exterior surface indentations correspond- ing with the ribs. . Right bronchus entering the lung. The right pulmonary artery and the pulmonary veins which held the same relation to the bronchus on this side which in the mammal they hold on the left have been cut away, together with a con- siderable portion of the spongy tissue of the lung on its internal aspect. The aorta is seen arching over the bron- chus, in its singleness contrasting with the aorta of Reptiles, and in its dextral flexure with that of Mammals. Between the bronchus and the vena cava inferior we see a portion of the glandular proventriculus, and immediately above the bronchus and below the arch of the aorta, which has been a little displaced upwards, the junction of the fragment of vein left to represent the subclavian trunk with the jugular. 7. Right innominate artery, which is seen to break up into three main divisions, the common carotid, the axillary and the pectoral arteries. s. Great pectoral muscle, the main depressor of the humerus and wing seen in section on the right side as it arises from the lower portion of the keel of the sternum and from the clavicle. Its origin from the external lateral portion and processes of the sternum is not seen, those parts having been removed in the dissection; its main tendon is seen turned back at #; two other tendons which it gives, one to the long extensor, the other to the short extensor of the alar membrane, are not shown in this figure. /. Second pectoral, the main elevator of the humerus, seen in Common Pigeon. 179 section along the upper part of the keel of the sternum and much of its lateral portion. It tapers anteriorly as it passes along the internal surface of the coracoid to enter the canal formed for it by that bone together with the furculum and scapula. This muscle is homologous with the comparatively insignificant ‘ subclavius’ of anthropotomy. u. Coracobrachialis inferior, a muscle arising from the inferior and outer three-fifths of the distal part of the coracoid, and inserted into the internal and proximal lip of the cup-shaped pneumatic cavity of the humerus. The opposite lip of this cavity receives the tendon of the teres major 7; and from the triangular space between the muscular bellies of these two muscles the subscapularis muscle, together with the upper portion of the scapula, and a small muscle, the ser- ratus anticus, which passed between the fibres of the sub- scapularis to be inserted into the inferior edge of the scapula, have been removed. v. Coracobrachialis superior, a bicipital muscle with a very ex- tensive origin ; arising, superiorly, from the inner surface of the vertebral end of the clavicle; inferiorly, from a facet on the lateral aspect of the upper surface of the sternal rostrum ; and between these two points of origin from the upper and inner surface of the fascia connecting the cora- coid, clavicles, and sternal rostrum. (See Descriptions of Pre- parations, p.22.) Its tendon, which is joined by that of the subscapularis, is inserted proximally and anteriorly to that of the preceding muscle w. The relations which these muscles hold to each other are much the same as those subsisting between the obturator externus and internus, with which these muscles are serially homologous. w. One head of the extensor plicae alaris anterioris longus, arising from the upper end of the clavicle in continuity externally with a head of the extensor brevis. These muscular bellies appear to be divarications of the deltoid, and to be serially homologous with the outer head of the pectineus of anthropotomy. w’. Muscle in connection with the long alar extensor tendons. Its fibres have in the natural condition of the parts much the same direction as those of the muscle w and of the N 2 180 Description of the Plates. deltoid; but its origin is mainly from the fascia which covers the biceps in front, and being interposed between that muscle and the tendon of the great pectoral, it is con- tinued up into the tendinous expanse by which the posterior layer of the tendon of the great pectoral connecting itself more or less intimately with the coracoid head of the biceps obtains an insertion into that bone. The muscle w’ is inserted mainly into the inner of the two tendons at its distal extremity. This tendon is prolonged down to be inserted into the radial process of the carpometacarpal bone which carries the pollex. It is more or less intimately connected with the two other long extensor tendons from the muscle w and from the great pectoral, which are here drawn as one; as also with the short extensor which is not shown in this figure. | z. Tendon of great pectoral muscle turned back and seen to be folded upon itself so as to form a pouch with its con- cavity upwards. The posterior portion of this tendon receives at its lower edge the tendon of a cutaneous muscle which is figured as attached to its outer angle, and higher up it receives the main tendon of origin of muscle w’, and is ultimately prolonged either separately or in connection with the tendon of the biceps up to the coracoid. a. Biceps. Its tendon is seen running upwards to be inserted into the internal anterior process of the upper end of the coracoid; it had a small insertion into the humerus also, which is not shown here. y. Portion of inner tuberosity of humerus which overhangs the pneumatic foramen of the bone. z. Gizzard. For the bibliography of memoirs upon the Anatomy and Physi- ology of Aves, see Selenka in Bronn’s Klassen und Ordnungen des Thier-reichs, Bd. vi. Abtheilung iv. 1, pp. 12-13, 1869. For the homologies of the Muscles of the Shoulder Joint, see Linn. Soc. Trans., vol. xxvi., p. 609, 1869. PLATE III. Common Froe, Rana Temporaria. PLATE III. Common Frog (Rana Temporaria), Injected and dissected so as to show its circulatory organs, and especially its two systems of veins supplying the liver and the kidney, and known as the ‘ portal’ and the ‘renal portal’ systems. THE ramifications of a subcutaneous vein, which must, like the renal and hepatic systems, have a depuratory action on the blood in these animals with transpirable skin; the renal, reproductive, and parts of the muscular, lymphatic, and other glandular systems of the creature are also shown in the figure. An injection having been thrown into the ‘ renal portal’ or renal _afferent vein of the left side, in a direction the reverse of that which the blood took in it during life, that is to say, towards and not away from the lower extremities, the figure shows that by this means the greater part or the whole of the main venous system can be injected. And it shows, secondly, that a very free anasto- mosis exists, not only between the two renal inferent veins of the two sides of the body, but also between each renal inferent vein and the epigastric, one of the main factors of the hepatic inferent, or true portal system in all cold-blooded air-breathing vertebrata. Hence the blood from the deeply-placed parts, muscular and other, whence the radicles of these vessels arise, can return to the heart through the venous system of either liver or kidney, as cireum- stances may require; whilst the blood of the more superficially- placed organs, glandular, cutaneous, and other, is aerated to a con- siderable extent in the vascular network of the musculo-cutaneous vein seen at 7 in the figure. By these arrangements the functions of the lungs, which are lowly developed, and, in correlation with the periodically recurring vast turgescence of the generative organs, of small size in the Amphibia, are efliciently supplemented. 182 Description of the Plates. The integument has been turned back on the right side, together with the musculo-cutaneous vein, the superficial branches of which extend from the knee to the shoulder; part of the muscular wall of the body has been removed on that side, but part has been left in situ; and the main trunk of the musculo-cutaneous vein is seen crossing a slip which the oddiquus externus muscle receives from the scapula; on the left side the muscular and cutaneous elements of the wall have been turned back whilst remaining in their natural connection with each other and with the epigastric vein; the shoulder girdle has been cut through the middle line, and fastened out on either side so as to expose the lungs, heart, and great vessels; the liver has been removed with the exception of a small part of its substance, as have also the stomach and intestines down to the lower end of the rectum. a. Intermandibular space. The skin is left 7w si¢w anteriorly in the symphysial angle; immediately posteriorly to its cut edge is seen part of the mylohyoid or submazxillaris muscle ; and posteriorly again, and at a deeper level, the converging hyoglossi in the middle line, and on either side of them the geniohyoids, with a glandular body resting upon each of them. b. Tetradactyle hand. The thumb has its basal joint more or less tumid in this, a male, specimen. c. Muscles of thigh. The line points to the sartorius, which 1s bordered externally by the vastus internus, and internally by the adductores and recti interni. See Ecker, Die Ana- tomie des Frosches, p. 115. d. Point where the musculo-cutaneous veins, constituted by factors from the regions of the head and face, as also and mainly from those of the back and flanks, turn inwards to pass over a slip going from the scapula to the external oblique muscle and join the axillary vein. See Ecker, /. ¢., p- 81; Gruby, Ann. Sci. Nat., Ser. 1. tom. KVill., p. 224. e. Vein, called ‘ epigastric’ by Rathke, ‘ umbilical’ by Bojanus and Jourdain, ‘ vena portae accessoria,’ and ‘ vena abdominals inferior s. anterior,’ by other authors. This vein is mainly constituted by the convergence of the two descending branches from the femoral veins seen at / in the figure, but it receives twigs also from the abdominal parietes, and Common Frog. 183 a factor of especial significance in the shape of the hypo- gastric vesico-hemorrhoidal vein from the allantois and rectum. The occasional pathological distension in liver diseases of the veins of the anterior abdominal parietes in the human subject shows that an arrangement may exist in a rudimentary condition in the higher vertebrata similar to that shown here to exist functionally between the epigastric and the parietal veins; and its connection with a vesico-hemorrhoidal vein, whilst it may be held to foreshadow the arrangement of the umbilical vein in the foetus of mammals, puts prominently forward the fact that anastomoses exist between the portal and systemic veins. For the ‘renal portal’ of the Frog, see Jourdain, Ann. Sci. Nat., Ser. iv., tom. xii., p. 180. . Point where the descending branch of the femoral vein of either side fuses with its fellow to form the trunk of the epigastric. . . ‘Renal portal,’ or renal inferent vein of the right side, being the other branch of the bifurcating femoral vein, which is thus seen to be freely and indifferently continuous with the portal systems of both liver and kidney. . Bifid allantoid bladder distended, with ramifications upon it of the vesico-hemorrhoidal veins which are seen to have radicles of origin upon . The rectum, which is cut short. Cf. Quain and Sharpey, vol. i1., pp. 478, 479, fig. 325, ed. 7th. . A vesicular dilatation developed upon the duct, by which both testicular and renal products pass down to the cloaca. From it a vein passes directly into the kidney. . Vena cava inferior, constituted mainly by the efferent kidney veins, but receiving also those of the testes and fat bodies. . Testis of left side. It has, together with its fellow and with the kidneys, been displaced a little to the right side. The vasa efferentia of the testes are seen to pass inwards to the internal edge of the kidneys, which they enter, and some veins pass in the same transverse direction inwards to join the vena cava inferior. Between the lower ends of the kidneys we see a reticular appearance produced by a plexus of arterial blood-vessels, each accompanied by two lymph vessels, closely 184 Description of the Plates. apposed to and so appearing to surround it. See Langer, Lymphgefasssystem des Frosches, 1866-1867, Wien. Akad. Wiss. Sitz. Bericht. m. Katty bodies. n. Spleen. To the left and a little above the spleen are seen the cut ends of two vessels, one of which receives a factor from that organ, coming itself from the intestine, and the other of which took its origin in the stomach, and, like the former, joined a branch of the epigastric, and was distri- buted to the liver, a small portion of which is seen as left immediately above them. o. Gall bladder left attached to the epigastric vein by a vein which passes from it to that vessel. p. Lung of left side. The cavity seen on the outer side of either lung has its outer wall constituted by the internal abdominal muscle, homologous with the internal oblique and transver- salis which arches inwards in a dome shape, and is connected with oesophagus, pericardium, and the coracoid and hypo- sternal bones. In the natural condition of the parts these cavities are however mainly occupied by the lobes of the liver, which nearly entirely cover the lungs in an anterior view. gq. Heart. From the base of the ventricle the muscular bulb is seen to take origin, a constriction known as the fretum Hal- devi marking the line of separation of the two organs. The bulb bifurcates into two great divisions, which again are each firstly subdivided by two imperfect internal partitions into three canals, and then subsequently into three perfect tubes, the carotico-lingual, the aortic, and the pulmonary trunks, of which the first is most internal and anterior, and the last the most external and posterior. q. Musculus bulbus arteriosus, with the auricles one on each side. It inclines to the left, and is attached on that side to the ventricle by the /renulum bulbi of Bracke. Denkschrift. Akad. Wien. Bd. i1., p. 355, 1852. 7. Lingual branch of the first of three trunks arising just inter- nally to a caverno-muscular dilatation of the artery known as the ‘carotid gland,’ from the outer side of which the carotid artery, called sometimes the ‘ ascending pharyngeal,’ Common Frog. 185 passes to the back of the oesophagus in close apposition with the second main trunk or aorta, with which it is usually connected by a ductus Botalli. s. Convergence of hyoglossi muscles, which, together with the diverging arterial trunks, enclose a diamond-shaped space, in the anterior angle of which a large glandular mass, and posteriorly in which several smaller masses of similar cha- racter, are lodged. Into the posterior angle of this space the right auricle, which is here, as in all cold-blooded verte- brata, possessed of two auricles, the larger of the two, pro- trudes itself from behind the arterial trunks. Underneath these structures the recurrent laryngeal nerve passes to the larynx. ¢t. Thyroid proper, of which the glandular masses just spoken of may be considered as divarications. It is placed just inter- nally to the jugular vein. The Thymus is not seen in this figure, lying far back as it does near the angle of the jaw. See Ecker’s Icones Physiologicae, tab. vi., fig. 5; Remak, Entwickelungsgeschichte der Wirbelthier, tab. viil., fig. 8.a.; Kolliker, Entwickelungsgeschichte, p. 391. wu. Left jugular vein passing down to receive the subclavian, and thereby constitute the left cava of that side. For the continuity of the lymphatic vessels with the various serous cavities of the body, see V. Recklinghausen, Handbuch der Lehre von den Geweben, herausgegeben von 8S. Stricker, ii. Lieferung, 1869, p. 222; Virchow’s Archiv., 1863, Bd. 26, p-172; Dybkowsky, Schweigger-Seydel, Dogiel, and Ludwig in Ludwig’s Arbeiten aus der Physiologischen Anstalt zu Leipzig, 1867. PLATE IV. Cretiar Siue, Limax Flavus. PLATE IV. CELLAR SiuG (Limax Flavus s. Variegatus), Dissected so as to show its digestive, circulatory, respiratory, nervous, and reproductive systems. Tur muscular envelope has been separated from the foot proper along the left side, and turned over to the right, together with the shield-shaped mantle and the organs it overlies. The buccal mass and nerve collar, together with the salivary glands, have been displaced a little to the left, on which side of the animal’s body the stomach and bilobed liver have been fastened out, as the generative apparatus has been upon the right. Some of the nerves, muscles, and arteries have been cut away, but most of the organs in the animal’s entire system have been displayed in this view. The oesophagus and buccal mass have been pulled a little forward through the nerve collar, and occupy much the same position relatively to it as they do when in life the buccal mass and head is thrust forward. The two first convolutions described by the intes- tine have been uncoiled, and the intestine has thus been drawn as taking a much less sinuous course than it does in nature from its commencement at the pylorus to the point where it comes into relation with the dorsal integument and shield, and hooks round the stem of the muscle which retracts the buccal mass and the tentacles. The generative organs have been detached from their normal connections, and are arranged on the right side of the animal’s head. Their volume, as drawn here, is but small in comparison with that which it attains in the breeding season. The upper tentacles, together with the nerves which supply and the muscles which retract them have been cut through, and turned 188 Description of the Plates. forward so as to lie between the generative apparatus on the right and one of the salivary glands on the left hand. One of the lower tentacles is seen on the right side in the interspace between the right eye-bearing tentacle and the vestibulum of the reproductive system. a. Locomotive disk or ‘ foot’ passing upwards at the sides into the general muscular envelope of the various organs of the animal’s body, from which it is limited off by a furrow. Its internal circular coat is raised into two corrugated ridges along the middle line for the greater part of the length of the body by the underlying mucous gland. This gland has its bilaterally symmetrical halves arranged on either side of a single duct, which again is underlaid by a large venous sinus, very visible in the living animal along the middle line of the foot inferiorly. i. Shield and organs in connection with it projecting out beyond and above the general muscular envelope of the body. c. Stomach arranged, together with the two lobes of the liver, upon the animal’s left. d. Generative apparatus arranged upon the animal’s right. e. Nerve collar, consisting of two ganglia placed above, or rather . at the sides of, the oesophagus, and two pairs of ganglia placed below it, and connected with the upper pair by com- missural cords. The two superiorly placed ganglia are con- nected with each other by a flat commissural band; and with the suboesophageal ganglia by a double commissure, the posterior cord of which joins the upper or parieto- splanchnic part of the mass formed by the fusion of the’ two inferiorly placed pairs of ganglia into a single centrally perforated body, whilst the anterior cord joins the more inferiorly placed or pedal portion from which nerves are seen to pass off to the foot. The functions of the supra-oesopha- geal ganglia may be judged of by the distribution of its nerves to sensory organs. The nerves which the parieto- splanchnic ganglia gave off to the retractor muscles, as well as to the parts their name denotes, have been removed in the dissection. /. Stomatogastric ganglion of right side placed in the angle Cellar Slug. 189 formed by the inferior surface of the oesophagus with the buccal mass just where it enters it, together with the duct of the salivary gland. The ganglion is connected by a long and delicate commissural cord with the supra-oesophageal ganglion of its own side, and it gives off nerves to the buccal mass, to the oesophagus, and to the duct of the salivary gland. g. Salivary gland. hk. Buccal mass containing the ‘ tongue.’ 2. Semper’s organ; a structure consisting of cells like those of a salivary gland, but devoid of a duct, and very richly sup- plied with nerves from the supra-oesophageal mass, and supposed by its discoverer to be, possibly, an olfactory organ. See Semper, ‘ Beitrage zur Anatomie und Physio- logie der Pulmonaten,’ in the Zeitschrift fiir Wissenschaft- liche Zoologie, Bd. viii., 1857, p. 366. It is large in Li- maces, though small in the other air-breathing Gastero- poda. jy» Coecal projection at pyloric end of stomach. k. Liver, consisting of two main lobes opening each by a single duct into the digestive tube along the line of the opening of the stomach into the intestine. Z. Intestine passing from pylorus to end close by the respiratory inlet, but a little in front and above it. Its two first convo- lutions have been uncoiled in separating it from the liver and reproductive apparatus, but as it approaches the dorsal integument and shield it describes a curve like that of an Italic S. In the first concavity of this curve we see the stem of origin for the retractor muscles of the buccal mass and labial tentacles, and at its opposite extremity we see a straight coecum y pass off and extend nearly to the posterior extremity of the body. m. Respiratory orifice, with the ‘ rectum’ curving round it to open a little above and anteriorly to it. To the right of the rectum again is seen the duct of the renal organ. nm. Portion of dorsal integument, by making an incision imme- diately to the right of which the shell would be found. Internally to it we see the respiratory sac, with the rami- 190 Moe ere Description of the Plates. fications of the pulmonary veins. The cavity of the respi- ratory sac is seen to be formed simply by the divarication of the two layers of the general muscular envelope of the viscera. . Renal organ, placed to the right of the heart in the natural position of the parts, and giving off a duct which passes backwards and curves round, inclosing between itself and its gland a portion of the pulmonary sac, to run in company with the rectum to open near the anus. See enlarged figure by Professor Leidy in Binney’s Terrestrial Molluscs of the United States, vol. i., pl. 1., fig. iv. . Ventricle of bilocular heart. . Hermaphrodite gland. . Hermaphrodite duct. . Albuminiparous gland. . Vas deferens becoming distinct from oviduct v sooner than in Helix or Arion, and richly beset with prostatic glan- dules. . Penis, with part of its retractor muscle left attached to it; the origin of the muscle having been at a spot on the under surface of the muscular envelope of the viscera, close to the arterial outlet of the heart. . Oviduct, like the vas deferens, glandular above, and membra- nous below; and opening into a dilated vagina. Receptaculum seminis, opening in this species, though not in the closely allied Liman Cinereus into the vagina. . Pedal portion of the suboesophageal nerve mass, enclosing, together with the parieto-splanchnic, an orifice through which the anterior aorta passes. The line is drawn to a spot where in Helicidae the otie vesicle is readily found, but where in Limax it is not easy to convince oneself that it exists, even as a rudimentary organ, without the use of reagents, such as the oxalic acid recommended by Lacaze Duthiers. . Coecum passing off from intestine just before it passes into rela- tion with the pulmonary cavity, and reaching down nearly to the termination of the body cavity. . Retractor muscle of the buccal mass and the tentacles. Its fascicles distributed to the parts ,mentioned passed with the Cellar Slug. 191 oesophagus through the nerve collar, being separated from the aorta by the parieto-splanchnic portion of the suboeso- phageal mass. They have been cut away in this Prepar- ation. For the anatomy of the Pulmonate Gasteropoda generally, see Semper, in Zeitschrift fiir Wiss. Zoologie, Bd. viii., 1857. For figures of the anatomy of Limax, see Leidy, in vol. i. of ‘Binney’s Terrestrial Molluses of the United States, pl. i. For the reproductive system, see Baudelot, Ann. Sci. Nat., fom. ax... pl, tis..17, 1609: For the essential connection of the acoustic nerve with the supra- oesophageal ganglia, which has been overlooked on account of the close apposition to the pedal ganglia of the vesicles ap- pended to those nerves, see Lacaze Duthiers, L’Institut, No. 1821, translated in Monthly Microscopical Journal, Feb. 1, 1869; and for instances of the otic vesicle and its nerve maintaining in actuality those morphological relations undis- guised by approximation to the pedal ganglia, see Gegenbaur’s and Souleyet’s figures of the Heteropodous Carinaria and Pte- rotrachea in V. Carus’ Icones Zootomicae, tab. xx., fig. 12; Gegenbaur, Untersuchungen tiber Pteropoden, und Heteropo- den, 1855, tab. vu., fig.1; Vergleichende Anatomie, p. 325, fig. 83. The two sets of organs of special sense, the auditory and the ophthalmic, are thus seen in Gasteropoda to be both in connection with the same nerve-centres. The attachment, however, of the otic vesicle and nerve can scarcely be different in reality from what it is in appearance in the Lamellibranchiata (for which see pl. v. 7’) ; and the multiplicity of the ‘eyes’ in Pecten and Spondylus set along the border of the mantle, to the nervous supply of which both cephalic and parieto-splanchnie ganglia contribute, would lead us to expect variability rather than fixity in the connections of the organs of special sense in Mollusca. The varying allocation of the organs of special sense in the two sub-kingdoms, Arthropoda and Vernus, would appear to point in the same direction. ian bei, ara: i ’ PLATE V. +8 Fresu-water Musset, Anodonta Cygnea. PLATE °V: FREsH-wATER Musset (Anodonta Cygnea), Dissected so as to show its muscular and nervous systems, as well as certain other organs in relation with them. THE animal has been taken out of the shell; the gills have been removed on the left side, as also the mantle, together with the labial tentacles and parts of the pericardium, and of the organ of Bojanus of the same side. a. Right mantle lobe, free along its ventral edge. a. Fimbriated portion of mantle corresponding to the inlet by which water is drawn into the branchial cavity. a’. Dorsal raphe along which the two halves of the mantle meet, and are more or less united. 6. Foot. e. Gills of right side. c’. Process passing from external gill to join the mantle, just where its fimbriae cease and its anal region commences. d. Anterior adductor. e. Posterior adductor. J Posterior retractor of the foot, passing to be inserted. into either valve, anteriorly and superiorly to the posterior ad- ductor, the scar or muscular impression of the two being more or less confluent. Its muscular expansion in the foot is especially well developed along the free or ventral edge of the foot, but it inter-digitates very freely with the pro- tractor pedis, though it lies for the most part at a lower level than that muscle. ) 194 Description of the Plates. g. Protractor of the foot. This fan-shaped muscle spreads over the external surface of the foot, from an insertion into the shell, a little superiorly to the point where the pallial line joins the impression for the anterior adductor. It must act consequently, as an antagonist to the preceding and suc- ceeding muscles. Its impression is distinct in this animal from that of the adductor. i. Anterior retractor of the foot. The fibres of this muscle take origin from a point in the shell, towards the dorsal aspect of the anterior adductor, though some way from its dorsal border. They spread thence into the foot especially along its anterior edge, and down as far as its anterior angle, oc- cupying for the most part a deeper level than the preceding muscle. Some of its fibres, however, spread superficially over the liver region dorsally. Its action is that of a powerful retractor of the foot mass. 2’, Smaller retractor muscles with insertions just anteriorly to the umbones, whence they radiate over the regions of the stomach, and towards the pericardium. i. Labial ganglion lying upon the anterior retractor, and in the angle between that muscle, the anterior adductor, and the protractor pedis, above the entrance to the mouth. j. Cord of commissure passing from labial ganglion to pedal. The pedal ganglion of each side gives off twelve nerves, six from its neural, and six, more slender, from its lateral surface. They are not figured in this plate. j’. Auditory vesicle appended to pedal ganglion. This vesicle is ordinarily found to be appended to a branch given off from the most backwardly-placed but one of the posterior branches given off from the pedal ganglion. It is not always to be found symmetrically developed on both sides, and, when found on one side only, it has been found to con- tain two otoliths. It is situated in a part of the foot narrow from side to side, at the junction of its anterior two-thirds to its posterior third, and near to the purely muscular portion of the foot, into which the viscera do not enter. Cf. Moquin Tandon, Hist. Mollus. 1., p. 136; Duvernoy, Mémoires de l'Institut, tom. xxiv., p. 96. i. Cord of commissure between labial and parieto-splanchnic Fresh-water Mussel. 195 ganglia. It passes between the fibres of the retractor pedis anterior and those of the protractor through the upper part of the foot, just internally or inferiorly to the generative orifice, ¢; then through the glandular portion of the organ of Bojanus, s; and across the tendon of the retractor pedis posterior just where it bifurcates for insertion into either shell, to end in the parieto-splanchnic ganglion. /. Parieto-splanchnic ganglion. The two ganglia of the two sides of the body are closely apposed, so as to form a trans- versely oblong mass, which however still retains an in- dication of its morphological duality in the bilobed con- formation, which is somewhat exaggerated in this figure, and is much less definite than that of the pedal centres between 7 and yj’. Two nerves are figured in connection with it, one, a parietal nerve, going to the mantle, the other, a splanchnic nerve going to the gill. m. Rectum ending in the anal compartment of the mantle, a little beyond the posterior free edge of the posterior ad- ductor. A delicate nerve is figured by Duvernoy, 7. ¢., as passing to it from the parieto-splanchnic ganglion. m. Heart; the letter pointing to the slit left by removal of the left auricle. The rectum passes through the heart, having commenced by emerging from the foot-mass, in close con- nection with the aorta anterior, which lies above it and below the mantle raphe, at a point corresponding to the vertical plane of the orifices of the generative gland and of the organ of Bojanus. 0. Pericardial space into which open the glandular portions of the organ of Bojanus, as also certain orifices belonging to the vas- cular system ; see V. Hessling, ‘ Die Perlmuscheln,’ p. 239. p. Opening by which the excretory portion of the organ of Bojanus communicates with the branchial cavity. q- Opening by which the excretory portion of the organ of Bojanus communicates with the secretory. 7, Wide opening by which the excretory portion of the organ of Bojanus of one side communicates with that of the other. This opening does not exist in Unio margaritifer. The two secretory sacs are similarly connected at a deep level in the same plane. 0 2 196 Description of the Plates. s. Secretory or glandular portion of the organ of Bojanus, reaching from the level of the anterior end of the peri- cardial space to the under surface of the posterior adductor. It opens into the pericardium by a canal along which a bristle has been drawn as passing. It is seen to be covered by the excretory half of the bisacculate organ for a space corresponding with the under surface of the pericardium. With this sac it is seen to communicate by a very fine orifice at g. Posteriorly to this point it is prolonged into a convolutionary mass, roughly drawn here in section as sub-triangular, in relation with the posterior adductor and the tendon of the posterior retractor. These glandular lamellar sacs communicate freely with each other, as do also the excretory sacs in this species. ¢. Orifice leading to ramifications of the duct of the generative gland. ‘This orifice is in the Anodon, though not in the Unios, concealed by the attachment of the inner gill-lamina to the visceral mass. See V. Baer, Meckel’s Archiv., 1830, P2916: From this semi-diagrammatic figure, the course which the ova take in passing from the generative orifice, ¢, to the external gill-cavity, where they meet with the spermatozoa inhaled with the water they breathe, and where they go through certain stages of development, may be understood. The ova are extruded from the orifice specified by the contraction of the several muscles, g, 4, 2’, and f; the shell valves being appressed by the adductors, d and e. When they pass out from this orifice, they pass along a canal, which for the first part of its course corresponds in direction with the nerve cord seen passing through the organ of Bojanus to the parieto-splanchnic ganglion, 7. This first part of the canal is divided into three portions. The first of these is formed by the attachment of the innermost gill-lamina to the vis- ceral mass, and into it the orifice ¢ opens. The second is under ordinary circumstances only a demi-canal, but is completed during the act of the extrusion of the ova, by the close apposition of the inner gill-lamina to the side of the visceral mass, which under these circumstances becomes more globular superiorly than when quiescent. The third Fresh-water Mussel. 197 portion begins immediately posteriorly to the tendon of the posterior retractor pedis, and extends as far back as the entrance of the branchial nerves into the gill. It is bounded below by the commissure of the two internal gills of the two opposite sides of the body, and above, like the rest of the canal, by the organ of Bojanus. Just beyond the line of entrance of the gill-nerves, the canal thus made up of three segments opens into a space, into which the ex- ternal gill’s cavity also opens; a canal having been left along the dorsal attached border of that gill by the failure of the dissepimental bands which connect the lower three- fourths of its two lamellae together, to be developed there. And as the rectum m also opens into this space, it may be called a ‘cloaca.’ Now it is easy to see how, under the extruding action of the foot muscles, the ova will succes- sively be pressed through the canal described into this small cloacal space. When there, if the shell or the mantle lobes are kept appressed posteriorly, or, as in the natural position of the animal, superiorly, it is plain that they must regurgitate, as additional relays of ova find their way into the cavity, into the external gill-cavity from the point ¢’ forwards. In this figure the nerve system is of a somewhat smaller size than it is seen to possess, except when viewed in strict profile, in nature ; and it has been owing to the necessity for maintaining this position, which the demonstration of the relations of the pericardium, and the two sacs of the organ of Bojanus involved, that the distinction between the muscular free border and the main mass of the mantle has not been shown. The muscular portion of the foot is figured in a condition of extreme contraction. For excellent figures of the nerve ganglia seen from below, with their branches and commissural cords, see Duvernoy, Mem. Acad. des Sciences, tom. xxiv., 1854, pl. 7, fig. 2, pl. 8 and 9, figs. 1 and 2. For a diagrammatic figure of the organ of Bojanus, see Lacaze Duthiers, Ann. Sci. Nat., Ser. iv., tom. iv., 1855, reproduced by V. Hessling, /.c., pl. v., fig. 6. 198 Description of the Plates. For a full account of the anatomy of the organ, see Langer, Denkschriften Akad. Wiss. Wien. xii., Bd. 1856, p. 39, Taf. 1., figs. 3 and 4. For figures of the muscular system, see Poli, Testacea Utriusque Siciliae, tab. ix., fig. 2; and for the heart and rectum, the same plate, fig. 12; and Langer, /.c., Taf. 11., fig. 8. For an explanation of the route taken by the ova and spermatozoa, in these dioecious animals, see V. Baer, Meckel’s Archiv., 1830, p. 313; and also V. Hessling, Zeitschrift Wissenschaft Zoologie, x., 1860, p. 358. For the various parts of the Lamellibranchiate organism, which in different species may be modified so as to serve as marsupia for the lodgment of ova and embryos, see Bronn, Klassen und Ordnungen des Thier-reichs, Bd. iil., p. 442, cbeque citata. at ee Te ee ee ee PLATE VI. NE O JEWITT.S¢ Cocxroacu, Periplaneta Orientalis. PLATE VI. Common Cockxroacu (Periplaneta Orientalis), FEMALE, Dissected so as to show its digestive, nervous, and reproductive apparatus; the ‘fat body,’ and a considerable portion of the dorsal integuments having been removed. Or the external organs are seen the multi-articulate antennae, the segmented anal appendages or ‘ cerci,’ the compound eyes, por- tions of the epicranium, of the pronotal, mesonotal, and metanotal elements of the thoracic segments, and of the eight dorsal elements of the abdominal segments; and finally, the three legs articulated to the three thoracic segments on either side, and consisting each of a proximal segment known as the cova, a second and much smaller segment, distinct in these, though not in the saltatorial Orthoptera, from the coxa, and known as the ¢rochanter ; a third, the femur, beset below with spines; a fourth, the ¢i4ia, more richly armed with spines than the femur ; and the fifth, the ¢arsus itself, which is quinque-articulate. a. Antennae consisting of three elongated basal segments, and a multi-articulate appendage made up of as many as ninety- two jomts. The antennae of Insects correspond to the so-called ‘ antennules’ of Crustacea, and they are here made up of large and small joints in similar proportions, see p- 111, supra. 6. 1,6. 2,6. 3. Tibiae, sub-quadrangular in shape, and beset along their two narrower sides with spines. ce. §Cerci anales,’ consisting of twelve segments, the terminal one conical, the others thickly beset with hairs. As sexual characters may be noted the absence of the sub-anal styles 200 Description of the Plates. possessed by the males, and the median emargination of the supra-anal dorsal plate with which the cerci articulate. These cerci appear to represent the processes which the last segment of the post-abdomen so frequently gives off in certain lower Crustacea, as e.g. Apus, Cyclops, Lynceus, Caligus; and, like the line of fission between the second pair of maxillae and the three basal joints supporting the antennary flagellum, to be structures by possessing which the Orthoptera resemble the Crustacea, see p. 111, supra; and Rathke, Morphologie, p. 115. d. Nerve ganglion developed upon the nervus recurrens, and seen to give off a nerve on either side, which passes back- wards upon the crop and has itself fusiform dilatations of a ganglionic character developed upon it. From the tri- angular ganglion, d, a nerve has been figured and described as passing off to the salivary glands. e. Common duct communicating with the two lobes of the dendritic salivary gland. The ducts of the two salivary glands fuse mesially with each other, in the angle formed by the convergence of the ducts of the two salivary bladders or reservoirs; and the common duct thus formed by the ducts from the two glands, fuses subsequently with the common duct from the two reservoirs, so that the two compound ducts find an outlet into the mouth by means of a short common canal. The figure does not accurately reproduce this arrangement, which cannot be demonstrated to the unassisted eye. All the four ducts and the compound ducts have their internal chitinized coat spirally thickened so as to resemble tracheae. J. Salivary bladder. g- Gizzard communicating inferiorly with the chylifie stomach, é, through the intermediation of a short segment of small calibre. h. Whorl of eight coeca, analogous probably to a liver, arranged round the commencement of the chylific stomach, and re- sembling the simple hepatic coeca of Hedriophthalmatous Crustacea. 2. Chylific stomach, smooth externally as is the upper half of the homologous segment in the Gryllotalpa, and limited \ Common Cockroach. 201 inferiorly by the insertion of the Malpighian tubules in a circle around the digestive canal. Jj» Malpighian tubules, in number from twenty-four to thirty ; and by their insertion in a zone around the lower end of the chylific stomach, marking the commencement of the short segment which may be spoken of as the small in- testine. k. Small intestine. Z. Large intestine or colon; found ordinarily to be in its upper part distended with the refuse of the ingesta, and to be below of smaller calibre, and corrugated so as to present a beaded appearance. m. Rectum divided into longitudinal areae by muscular bands, which alternate with internally placed lamelliform produc- tions of the intestinal walls. The ridges thus developed upon the rectum receive in the larvae of certain of the Libellulidae a very rich supply of tracheae, and, together with a valvular apparatus developed from the caudal tegu- mentary skeleton, constitute their aerating organ. m. First abdominal ganglion, closely approximated to the third thoracic, and placed at a little greater distance from the second abdominal ganglion posteriorly. The sixth abdo- minal ganglion should have been drawn as somewhat heart- shaped, but laterally constricted so as to have the appearance of being made up, as the history of its development, of its comparative anatomy, and of the distribution of its nerves shows it to be, of two distinct ganglia. The two oviducts pass to their point of fusion from the outside of the angle bounded by the nerves, seen to pass off from this ganglion ; the receptacula seminis, which are small, and not given in this figure, are situated within that angle and at its apex ; distally to them, but within the angle, the two ducts of the numerous colleterial glands pass to the orifice within which they open on the sternum of the tenth segment. The first sub-oesophageal ganglion is not seen in this figure, being, as always in insects, in such close apposition to the supra-oeso- phageal or cerebroid ganglia, as to have been sometimes, but inconveniently, described, as together with them making up a‘ brain.” Counting however this ganglion whence the 202 Description of the Plates. mandibles, maxillae and labium receive their nerve supply, we find that the entire ventral cord is made up of ten ganglia, the last of which may be taken as representing two. This number is less by one than that of the Lepi- dopterous larva, and, on account of the large size of the third thoracic ganglion, we may suppose that in the Cock- roach, the ganglion homologous with the fifth post-oral ganglion of the Caterpillar has become fused, if it was not originally connate, with the posterior thoracic ganglion. Thus the thoracic ganglia of the Orthopterous insect, which remain always as distinct masses in this order as also in the Coleoptera, will correspond, as to the elements out of which they are composed, with the bilobular centrally per- forated mass whence the three pairs of legs and the wings are innervated in Lepidoptera. The six posteriorly placed ganglia of the Orthoptera and of the Caterpillar will corre- spond with each other; and, allowing for the disappearance in the butterfly of the sixth and seventh post-oral ganglia of the larva, with the four posterior ganglia of the perfect Lepidopterous insect. o. ‘ Verticillate’ ovary of right side, consisting of eight egg- tubes, connected by a suspensory ligament, which is made up by the fusion of filaments given off from their respective apices, and prolonged up to an attachment in the dorsal region of the thorax. ‘The ovarian tubules are here figured as opening into the convex end of a pear-shaped oviducal infundibulum ; and this apical insertion has been supposed by Léon Dufour and Fischer to constitute an important difference between the arrangements of the female repro- ductive apparatus, as existing in the Blattinae and in other Orthoptera. The pyriform shape however of the oviducal infundibula depends merely upon temporary distension ; and when these receptacles are not in this condition, the egg-tubes may be seen to have the same lateral insertion as those of other Orthoptera; as, for example, the Forficula, as figured by Fischer in his work, Orthoptera Europaea, tab. 1., fig. 4; or the Mantis Religiosa figured by Léon Dufour in his work, Recherches Anatomiques et Physiolo- giques sur les Orthoptéres, les Hymenoptéres et les Neurop- Common Cockroach. 203 téres, pl. iv., fig. 42. The two infundibula pass ventrally to the terminal nerve structures and oviscapt, to form a common vagina, which opens between the sterna of the eighth and ninth abdominal segments. Colleterial’ or ‘sebaceous’ glands of the left side. These glands consist of long delicate tubules, the contents of which are by no means always uniform in colour. The very numerous tubules of either side join a single stem, and the two ducts thus formed pass down near the middle line, and within the angle bounded by the nerves of the last abdominal ganglion, to end within a single orifice on the sternum of the tenth abdominal segment. Anteriorly to the two colleterial ducts, and oceupying the apical portion of the angular space limited by the nerve structures, may be found the receptacula seminis, which consist of two short tortuous coeca, opening by a very short common duct upon the sternum of the ninth segment. Spermatozoa are said by Siebold to be found in both these coeca; otherwise, as one is of smaller calibre than the other, we might have considered one to be a receptaculum seminis and unpaired, as usual in insects, and the other to be a ‘ glandula appendi- cularis,’ such as is so frequently attached to the recepta- culum seminis in other insects. In thus possessing two receptacula seminis instead of one, as also in having eight ovarian tubuli instead of twelve, as is usually the case in Orthoptera, the Cockroach presents us with more or less aberrant arrangements. Figures of the various forms which the female generative organs may assume in the Orthop- terous Termes Lucifugum, may be found in the plates ap- pended to M. Lespes’ memoir upon that species, in the Annales des Sciences Naturelles, Ser. iv., tom. v., pl. 6, figs. 24-27, where the colleterial glands and receptaculum seminis will be seen to present much the same arrangement as that which has here been described in the Cockroach. S For the morphology, anatomy, and development of Insecta, the numerous memoirs by Sir John Lubbock, in the Transactions of the Royal and Linnaean Societies from 1857 onwards, should be consulted. Amongst these, see for Parthenogenesis 204 For Description of the Plates. in the Articulata generally, Phil. Trans., for 1857, vol. 147, Pp. 95-99; for the structure of the ova, pseud-ova, ovaria, and pseud-ovaria of Insects, 2did., 1858, vol. 148, pp. 341-360, 1861, vol. 151, pp. 620-623; for the functions and structure of the tracheae, Linn. Soc. Trans., 1865, vol. xxv., p. 480; and for the subject of insect-metamorphosis generally, 2did., pp- 485-491. the asexual propagation of Diptera, which takes place in larvae, and was at first supposed to do so by metagenesis inde- pendently of any ovarium or pseud-ovarium, see N. Wagener, Zeitschrift fiir Wiss. Zool., xiii., 1863, p. 513; Pagenstecher, l.c., xiv., 1864, p. 410; Leuckart, Wiegman’s Archiv., 1865, p. 286, translated in the Ann. and Mag. Nat. Hist., il, 7 March, 1866. For an account of the internal and external anatomy of the order Orthoptera and of the family Blattinae, see Fischer, Orthop- tera Europea, pp. 5-32, pp. 84-88, pls. i., ii., and vii. For an account of the receptacula seminis, see Siebold in Miiller’s Archiv., 1837, p. 408. For the opening of these and the other ducts of the reproductive apparatus, see Huxley, Linn. Soe. Trans. ii., vol. xxii, p. 231, 1858. For number of joints in antennules of Crustaceans, see Spenc: Bate, British Sessile-eyed Crustacea, Introduction, p- xl.; and for correspondence of the antennae of Insects, with imperfect metamorphosis both in the larval and in the adult state with the antennules of Crustacea, see Zaddach, Die Entwickelung des Phryganiden Hies, p. 86. For the anal respiratory apparatus of the Libellulidae, which may be considered to be foreshadowed in the longitudinal folds developed upon the rectum of the Cockroach, see Dufour, Ann. Sci. Nat., Ser. iii., tom. xvii., 1852, p. 65, pls. iii., iv., v.s Leydig, Lehrbuch der Histologie, p. 337. ‘syynUM snonjsp “HSIAKVAQ) NONWOS) Vo 1p ? us 431Z045.5 oS NG TIA HLVId PLATE VII. Common CrayvrisH (Astacus Fluviatilis), MALE, Dissected so as to show its nervous, digestive, circulatory, and reproductive systems in situ ; the various organs having been exposed in an antero-posterior vertical view, by the removal of the tegumentary skeleton, the muscles, and the hepatic lobes of the left side. a. OrsopHacus leading vertically upwards from the mouth into the stomach. The labrum, the free edges of the mandibles, and of the two maxillae, are faintly indicated on the right side of the mouth anteriorly to the three foot-jaws. 4. Cardiac portion of stomach. Superiorly and anteriorly the stomach is still retained in its natural position a long way anteriorly to the line of the entrance of the oesophagus, the anterior gastric muscles which took origin superiorly to the supra-oesophageal ganglia, 0, from the under surface of the ventral wall of the ollow rostrum, and attached them- selves to the cardiac plate, having been left intact; whilst the anterior wall of the stomach has been displaced a little backwards in order to give a better view of the stomato- gastric nerves. c. Lateral valvular prominence of pyloric portion of stomach. d. Hepatic lobes of right side where they came into apposition with those of the left side which have been now removed along the infero-median line. e. Orifice by which the hepatic lobes of the left side opened into the digestive tract immediately posteriorly to the pylorus, and below the coecal process, 2. jf Intestine passing with the straight course characteristic of Crustacea, with the exception of Lynceus, to the anus. 206 Description of the Plates. g. Anus, opening on the inferior surface of the ‘ telson’ in uncal- cified membrane, just anteriorly to the line of junction of its anterior and posterior halves. h. Heart, showing one of the lateral venous orifices, and its posteriorly placed bulbus arteriosus dividing into two main branches, the larger one of which passes vertically down- wards at 7, and is known as the sternal artery; whilst the other passes along the dorsal surface of the intestine at z, and may be called the post-abdominal artery, and taken to represent the posterior chambers of the elongated vasiform heart seen in many lower Crustacea. 2. Post-abdominal artery, taking a course superiorly to the intes- tine, and inferiorly to the extensor muscles of the posterior segments. j. Sternal artery passing down towards the orifice in the com- missural cord connecting the third and the fourth abdominal ganglia. k. Hepatic artery of the left side, passing down from the heart on to the pylorus towards the hepatic lobes of that side which have been removed. /. Anterior left lobe of testis. ’. Azygos lobe of testis placed posteriorly to the paired lobes of the two sides with which it is continuous. m. Convolutions of vas deferens of left side, in length equal to that of the entire body. They probably secrete the agglu- tinating matter of the spermatophores. ‘Phere are in most, if not all, Crustacea and Myriapoda, and in the higher Arachnida, two separate outlets for the vasa deferentia, one on either side of the body, howsoever much intercommuni- cation of the glands or ducts may take place distally to the outlets. The Insecta, on the other hand, have ordinarily a single ductus ejaculatorius, as also a single vagina, into which the generative ducts of both sides of the body open. In both Decapodous and Hedriophthalmatous Crustacea, the male generative outlet is to be found in relation with the last segments, and the female with the last but two of the ambulatory or abdominal segments. n. Coecal sac, the rudiment of the yolk-sac of the embryo. This sac is apparently the homologue of the two coeca, which in Common Crayfish. 207 Brachyura open into the upper part of the pyloric part of the stomach, just posteriorly to its valvular apparatus, and close to its opening into the duodenum. In Brachyura there is a third sac homologous with the single sac observable in some, and the two sacs observable in other Amphipoda as opening into the duodenum just before its junction with the rectum, and sometimes called a ‘renal organ. It is not found in the Fresh-water Crayfish, though it is in the Lobster. o. Supra-oesophageal ganglionic mass, immediately posteriorly to the scaphocerite or squamiform exopodite of the inferior or externally placed pair of antennae, the ‘antennae’ properly so called. The likeness which this ‘scale’ of the antennae bears to the exopodite of the sixth abdominal segment is, as Fritz Miller has remarked, curiously illustrated by the fact that its ordinary function of lodging the auditory organ is sometimes, as in Mysis, transferred from it to that appendage. Both facts find their explanation in the view which regards both segments and both sets of appendages as belonging to a ‘primitive body’ corresponding with that which the Naupliiform larvae of Cirripedia, Copepoda, and Phyllopoda bring with them out of the egg. The greater relative size of the scaphocerite is one of the external points of difference between the Crayfish and the common Lobster. p. First post-oral ganglion, supplying the mandibles, the two pairs of maxillae, and the three pairs of foot-jaws, or thoracic appendages. In the developing Astacus this mass consists of six pairs of ganglia, in correspondence with the six sets of appendages it innervates. In Insects, the first post-oral ganglion is always distinct from the thoracic ganglia, whilst in all other Arthropoda it is fused with more or fewer of them. g. Nervus recurrens, formed by the junction to an azygos nerve, homologous to the nervus recurrens of Insects, and repre- sented by the single trunk 4’, of two pairs of nerves, which arise from the nerve-collar on either side of the oesophagus. This compound nervus recurrens of the Crayfish passes up the anterior face of the oesophagus and stomach, and on the angle formed by the junction of this anterior with the dorsal wall of the organ, it has a ganglion developed upon 208. Description of the Plates. it between the anterior gastric muscles, from which, as also from its posterior prolongation, nerves are given off down- wards on either side of the stomach. q. Azygos nerve, passing downwards from the middle of the posterior edge of the supra-oesophageal mass to meet two pairs of nerves given off from the thickenings developed upon the commissural cords of the nerve collar as they cross the oesophagus, and form with them the compound nervus recurrens, g. The forward position of the supra-oesophageal ganglionic mass would appear to render it impossible for the Crayfish to have any ganglion frontale developed upon such as Insects possess. Leydig, however, appears to have discovered such a ganglion in the Oniscus. This nerve, ¢/, seems to correspond with the nerve-cord passing backwards from the ganglion frontale in Insects before it receives any branches of communication from the paired ganglia; the compound nerve, g, would then correspond to the similarly compounded nerve of Insects, upon which ganglia are frequently developed successively from before backwards in relation with the digestive tract, whilst the ganglion frontale must be considered to have coalesced with the supra-oesophageal mass. r. Fifth abdominal, or sixth post-oral ganglion. It is more closely approximated to the ganglion next in front of it than any of the ganglia either in front of or behind it are to each other. Posteriorly to it are the six post-abdominal ganglia. From this ganglion and the two in front of it, long nerves pass off upwards to the reproductive organs and the superiorly placed muscles, s. Multi-articulate flagellum of inferior or outer pair of antennae, the ‘antennae,’ strictly so called, supported by a peduncle consisting of five joints, to which the scaphocerite and a smaller calcified nodule are laterally articulated. ¢. Paired flagella of upper pair of antennae, or antennules, carried by a triarticulate peduncle, as are the antennae of Orthop- tera. On the larger of these two flagella certain delicate membranous cilia are to be found, which, though of very various forms, are yet constant in Crustacea, and are sup- posed to be olfactory organs by many authors. Common Crayfish. 209 u. Second joint of posterior thoracic appendage, or ‘ maxilliped,’ or ‘foot-jaw.’ This joint, as in the large cheliferous append- age v I, next behind it, represents two joints, the basipodite and the ischiopodite of the normal seven-jointed endopodite, as seen In V2, 03,04,v5. Its antero-internal edge is den- ticulate, as in the Lobster, but its serratures are concealed by a fringe of setae. v1. First abdominal appendage, modified terminally by the pro- duction of the distal outer angle of its penultimate joint or propodite so as to form a pair of pincers with the opposed last joint, or dactylopodite. Two other joints, the ‘ carpo- podite’ and ‘meropodite,’ are shown in this figure; the two basal joints are not seen. The two first abdominal legs are not symmetrically developed in the Crayfish, nor in the Marine Lobster, foreshadowing thus the extreme inequality seen in the Hermit-Crabs. v2 and v3. Second and third pairs of abdominal or ambulatory legs, differing from v 1 in their smaller size, and in not having the second and third joints fused. It is at the interval between the first and second joints, the ‘ coxopodite’ and the ‘basipodite,’ that the power of casting off a limb, in conse- quence of a fright or injury, is put in play by Crustacea. v4and v5. Fourth and fifth pairs of the ambulatory legs of the Decapod. The two terminal joints do not form pincers, otherwise they resemble v 2 and v3. The vas deferens opens in the coxopodite or basal joint of v 5. wand w2. The appendages of the two first post-abdominal seg- ments modified so as to form an accessory copulatory organ. w 3, 4, and w 5. Appendages of the third, fourth, and fifth post- abdominal segments, consisting each of two basal joints, which serve as a pedicle to two multiarticulate filaments representing an exopodite and an endopodite. The inner of these two filaments has its first joint longer and larger than the other joints in either filament. This greater relative importance of the endopodite is more plainly seen in the antennae and thoracic limbs, where the exopodite is markedly smaller than the endopodite, and most plainly in the abdo- minal limbs where it is absent, or only represented by the constriction marking the third joint, or ‘ ischiopodite.’ P 210 Description of the Plates. w 6. Appendage of sixth post-abdominal segment, forming the right lateral element of the swimmeret. It consists of a single basal joint, supporting a biarticulate squamiform exo- podite and a uniarticulate endopodite, which reverse thus the positions of relative size held by these elements in the segments anterior to the swimmeret. The telson is interposed mesially between the two appendages of the sixth post- abdominal segment. z. Flexor muscles acting on the swimmeret and post-abdominal segments in the animal’s rapid movements; its slower movements being dependent upon the ambulatory feet. y. Extensor muscles, in two layers like the flexors, but of much smaller size. For a full account of the anatomy of the Crayfish, see Huxley, Medical Times and Gazette, Feb. 7, 1857, et seqq. For figures of the various systems and organs of the animal, see Brandt, Medizinische Zoologie, Bd. ii., tab. xi., pp. 62-64. For the stomatogastric system, see Brandt, Ann. Sci. Nat., Ser. 11, tom. v., 1836, pl. iv., figs. 1, 2, pp. 87-91. For the olfactory (auditory?) organ, as carried by the internal or superior pair of antennae, see Gerstaecker, Bd. v., p. 357, and La Valette, Leydig, and Fritz Miller, cit. im loc. See also Spence Bate, Sessile-Eyed Crustacea, vol. 1., p. ix. For the formation of the coecal sac opening into the commencement of the duodenum out of the yolk-sac, see Rathke, Entwick- elungsgeschichte der Flusskrebses, p. 64. For other coecal appendages to the digestive tract of Crustacea, see Milne Ed- wards, Hist. Nat. des Crustacés, 1834, pp. 76,77; and for the formation of the liver by a bilateral out-pouching of the yolk- sac, see Rathke, 7. c. p.4g9, and Abhandlungen zur Buldungs-und Entwickelungsgeschichte, Theil. 1., 1832, p. 15; Theil. ii., 1833, p- 78, in which latter memoir the relation of intestinal tract and yolk-sac is shown to be different in Oniscus and Astacus. PLATE VIII. Earth Worm, Lumbricys Terrestris. PLATE VIII. Karta Worm (Lumbricus Terrestris). The fifteen anterior segments of an Earth Worm (Lumbricus Terrestris), numbered from before backwards, the upper lip counting as the first segment. TuE integument has been divided, except in the first segment, down the middle dorsal line, and the greater part of the digestive tract has been removed, together with the pseud-haemal vessels, so as to show the nervous, muciparous, and reproductive organs. a1. Bilobed supra-oesophageal ganglionic mass; giving off from a2. a 3. either outer angle a nerve which bifurcates very soon after its origin, and passes to distribute itself in the tactile upper lip. Visceral or stomatogastric system of the right side, con- sisting of a long ganglion lying upon the lateral wall of the pharynx, and running parallel with the cord of commissure between the supra-oesophageal and the sub-oesophageal gan- glia, with which it communicates by several roots anteriorly, as it does posteriorly with a reticulate ganglionic plexus upon the posterior part of the pharynx. This plexus lies imme- diately externally to the mucous lining of the pharynx, and some of the glandular and muscular tissues of its outer walls must be cleared away in order to demonstrate it clearly. Figured roughly by Morren, /. c. Tabs. xix.—xxi., figs. 1 and 2 &./.; and described more accurately by Qua- trefages, Ann. Sci. Nat., Ser. iii., tom. viii., 1847, p. 36. Commencement of chain of ventral ganglia. The ventral chain consists here, as in Arthropoda, of fibrous elements PY 2 Description of the Plates. placed superiorly, and vesicular placed inferiorly. The latter form a continuous stratum with aggregations at intervals corresponding to the middle of each segment, which are called ganglia, and give off two pairs of nerves on either side. The nerve-cord gives off in each segment anteriorly to the two pairs arising from the ganglioniform imtumes- cence a single pair, which distributes itself along the line of the anterior dissepiment of each segment, and appears to correspond to the Nervi transversi of the Arthropoda, The four nerves given off in the middle of each segment are accompanied by branches from the pseud-haemal vessels which run on either side of the nerve-cord; the two nerves given off anteriorly to them are similarly accompanied by branches from the azygos pseud-haemal vessel which under- lies the nerve-cord. ‘These nervous and vascular branches are not given in this Plate. 6. Pharynx, turned aside to the left, the right half of the organ, except the small portion upon which the right stomato- gastric plexus, a@2, is seen, having been removed. The walls of the pharynx are of great thickness superiorly, glandular tissue forming the exterior, and muscular the middle layers, whilst the mucous membrane forms the inner- most, and attains a considerable thickness where it lines the saucer- or sucker-shaped cavity which opens from above into the cavity of the tube. ei. First muciparous gland, or ‘ segmental organ,’ opening externally in segment iv. Ordinarily the thickened mus- cular portion of the tube of the convolutions of which these glands are made, opens externally in the segment imme- diately posterior to that in which its internal funnel- shaped opening is situated, this internal funnel-shaped opening being carried upon a short hollow stalk prolonged through the anterior muscular dissepiment of each posterior segment of the two with which each segmental organ is connected. But as segment iv. is not limited off from seg- ment ii. by any such perfect or nearly perfect dissepiment as limits the segments after segment v. from the seg- ments next in front of them, the anterior funnel-shaped termination is not seen so distinctly to be in a different Earth Worm. 213 segment from the one in which the mass of the coils of the eland are lodged. e2. Segmental organ similarly modified to ¢ 1. e3,¢4,¢5. Normal segmental organs, the opening on to the exterior being usually close to the inner row of setae, and in the anterior portion of each segment, though it may vary considerably, and even come to lie exteriorly and superiorly to the outer row of locomotor spines. The funnel-shaped internal opening is seen a short way from the outer edge of the nerve-cord, and near the ventral surface in the segment anterior to that in which the gland communicates with the exterior. The coils of the posterior, which is much the larger part of these organs, are connected by a mesentery-like lamina to each other and to the disse- piments of the segments. d. Muscle passing up from one of the ventral muscles to attach itself to the capsule of the supra-oesophageal ganglia and the cireumjacent parts, to which it stands in the relation of a powerful retractor. el, €2, €3, e4, e5. ‘Capsulogenous glands.’ These bodies appear to be specially-modified and greatly-developed seti- parous glands, which attain this prominence in the segments connected with the essential, and with the accessory organs of generation ; amongst the latter of which the inner setae of many segments may be reckoned, besides those here lettered e1toe5. Ate2weseeaslip of muscle passing across the glandular mass, and connecting the inner with the outer row of setae. Over the capsulogenous gland lettered e 4 is seen the vas deferens passing forward and through the dissepi- ment separating segment x1. from segment x., to end in an infundibulum closely similar in form, relations, and connec- tions to the more delicate tubular stalk carrying the funnel- shaped ending of an ordinary segmental organ. On the capsulogenous gland labelled e 5 are seen the junction of the stem of a second vas deferens with the anterior one seen at e4, and the commencement of the common duet. ji. Outer row of setae. Each seta is secreted by a separate gland, and has a separate insertion. The setae of the aquatic Oligochaeta are, on the contrary, ‘ fasciculate’ in their inser- 214 gl. Al. h2. h 3. at. 42. 23. 4. Description of the Plates. tion. The outer row of setae is often wanting in the anterior segments; in the others it is usually connected with the inner row by a transverse muscular slip, such as that seen here, or at ¢2. In the region of the clitellus the outer row of setae may be adapted to serve as accessory copulatory organs; elsewhere they are purely locomotor. . Inner -row of setae. The spines are solitary in their inser- tion as in the outer row, but they are in many segments, as, for example, in the tenth and fifteenth, besides the seements constituting the clitellus, modified so as to serve as organs of adhesion. Anterior receptaculum seminis of the left side, opening in the interval between the ninth and tenth segments, and between the lateral and dorsal muscles in the line of the outer row of setae. . Posterior receptaculum seminis, opening in the interval between the tenth and eleventh segments. These organs are very variable in size, and have had their existence over- looked and denied. Their outer opening is marked by a small elongated papilla; but their development is not always exactly correlated with that of the rest of the gene- rative apparatus. Anterior vesicula seminalis of the left side, attached to the posterior dissepiment of the ninth segment, and communi- eating, as does the middle vesicula seminalis / 2, with the anterior compartment of a sac with delicate walls which occupied a space in the tenth and eleventh segments cor- responding to that underlaid by the azygos ventral muscle, and received the openings of the vesiculae of both sides. Middle vesicula seminalis of left side. Posterior and largest vesicula seminalis, opening into the posterior compartment of the azygos central atrial sae just described. Funnel-shaped orifice of vas deferens anterior of left side. Similar orifice of vas deferens posterior of left side. Similar orifice of vas deferens anterior of right side. Similar orifice of vas deferens posterior of right side. Ex- ternally and interiorly to each of these infundibula there exists in each of these segments a segmental organ’s Earth Worm. 215 posterior and larger portion; and posteriorly to each of these infundibula there exists also in each of these segments the funnel-shaped opening of the segmental organ of the segment next behind it. The coexistence therefore of the vasa deferentia with the very similarly constructed seg- mental organs would appear to be inconsistent with a view which should regard them as modifications of those glands. Still the great development and increase of mass observable in other organs in these segments may, as suggested by Mr. Lankester, induce us to hold that the typical number of segmental organs in any one segment is four, and that this number is attained to in those generative segments only on account of their superabundant nutrition. Upon this view the vasa deferentia, as also the oviducts x, would be serially homologous with the segmental organs. ji. Vas deferens from anterior spermatic infundibulum of left side. j2. Vas deferens from posterior spermatic infundibulum of left side. The junction of the two vasa deferentia to form one common canal is well seen in the twelfth segment on the right side, and the ending of the common canal there formed is well shown on both sides in the fifteenth seg- ment. The external opening of the common vas deferens has the shape of an oval slit, with its long axis transverse to that of the animal’s body, guarded at the breeding season by prominent tumid lips. k1. Anterior testis of right side. k 2. Posterior testis of right side. 1. The single ovary of the right side, occupying the same posi- tion relatively to the nerve-cord and the inner row of setae as the testes. m. Infundibular ciliated mouth of oviduct, holding a similar position to that held by the infundibulum of the segmental organ ¢ 5, which opens both internally and externally in the same segments. n. Oviduct in the posterior of the two segments in which its various parts are found. After passing through the dissepi- ment separating the thirteenth from the fourteenth segment, the oviduct has a saccular dilatation, ordinarily found to 216 Description of the Plates. contain ova, appended to it. It then passes outwards in relation with the dissepiment, to end by opening externally immediately externally to the internal row of setae. It is crossed just before its termination by a part of one of the tubular muciparous or segmental organs which is passing forwards to pierce the dissepiment, and end in its infundi- bulum in the segment next in front. For the nerve system, see Lockhart Clarke, Royal Society’s Pro- ceedings, vol. viil., 1857, p. 343; see also Quatrefages, Ann. Sci. Nat., Ser. iii., tom. viii., 1847, p. 36; Morren, De Lumbrici Terrestris Historia Naturali necnon Anatomia Tractatus, 1829, tabs. xix.-xxi., figs. 1 and 2, 4./., p. 119; and Leydig, Hand- buch Vergleich. Anatomie, tab. iv., p. 168. the reproductive system, see Hering, Zeitschrift Wiss. Zool., vol. vill., 1857; Lankester, Quarterly Journal of Microscopical Society, vol. v., 1865, p. 10. the segmental organs, see Gegenbaur, Zeitschrift Wiss. Zool., vol. iv., 1853, p. 221; Hering, /.c., p.401; Ehlers, Die Bors- tenwurmer, 1., pp. 37-45, 1864; Claparéde, Introduction to work on Annelids of Bay of Naples, translated by W. S. Dallas, Ann. and Mag. Nat. Hist., Ser. iii., vol. xx., 1867, p. 355. PLATE Ix. MepicinaL Lercu, Hirudo Medicinalis. PLATE IX. Fiaure oF Mepricinat Leecu (Hirudo Medicinalis), Dissected so as to show its nervous, digestive, reproductive and segmental organs, as seen from below ; slightly altered from Moquin Tandon’s figure, pl. viii., fig. 10, Monographie des Hirudinées, 1846. Tur integuments are drawn as divided down the middle ventral line, from the posterior border of the anterior sucker to the an- terior border of the posterior sucker; two of the testes and two of the segmental organs have been displaced outwards in the segment, lettered d3,¢2; the rest of the organs have been left undisturbed én situ, after the fastening out of the integuments on either side. ai. a2. Anterior sucker, formed by the proboscidiform upper lip, which is made up of four incomplete annuli, representing however probably at least as many segments, and by the first complete annulus surrounding the mouth. The mouth opens in the middle of this sucker; six of the eyes are carried by the first, second, and third of the rays of the upper lip. Posterior sucker, formed by the fusion of seven distinct annuli, to which seven distinct ganglia subsequently fused into the single posterior ganglion of the ventral chain, corresponded at one period of the animal’s development. The stellate spot in the centre of the sucker must not be taken as representing the opening of the anus, which is situated anteriorly to the sucker in the line of constriction marking it off from the posterior annuli, which are not similarly modified. The anus does however open in the centre of the anal sucker in Acanthobdella, as also in the Polychaetous Annelid, Leucodore 218 er. c 2. C 3. Description of the Plates. . First and second pairs of sub-oesophageal ganglia, very closely apposed to each other. From the first sub-oeso- phageal ganglion, five pairs of nerves are given off; from the second only two, as from all the other twenty ganglia placed posteriorly to it, with the exception of the two last. . Last ganglion, the twenty-second of the ventral chain. This ganglion gives off from five to nine pairs of nerves, which are distributed to the posterior sucker. The penulti- mate ganglion gives off only one pair of nerves. The supra- oesophageal ganglion, with the three stomato-gastric gang- lia connected with it and supplying the jaws, is not shown here; nor the azygos sympathetic nerves with a course above the ventral nerve-chain, and between it and the digestive tract upon which it forms gangliated plexuses, and sends branches along its lateral diverticula. First lateral diverticulum of the portion of the digestive tract, which comes next after the pharynx, and which is called ‘ oesophageal’ by Gratiolet, inasmuch as its functions are, according to him, merely those of a reservoir for the more solid parts of the animal’s food, from which the watery part is squeezed out by the muscular contractions of the body-walls whilst it is contained there; and which, after remaining there thus condensed for several months, still retains the faculty of reddening, when exposed to the oxygen of the air. ‘Small intestine’? of most authors, ‘ gastroiléal’ portion of digestive tube of Gratiolet, in which the blood undergoes the alterations ordinarily effected in it by digestion. It ends posteriorly in a short ovoidal colon, which again ends in a short rectum, which turns slightly upwards to end at the anus. The small intestine is a little dilated at its commencement in the interval between the two terminal sacculi c 3; this dilatation representing the much larger bilobed dilatation, with which the homologous segment of the digestive tract commences in the Horse-leech (Awlostoma Gulo). Eleventh lateral diverticulum of right side prolonged down- wards on either side of the small intestine and colon, as far as the point where the rectum begins. The calibre of either d 2. a 3. ChE. e2. Medicinal Leech. 219 of these terminal coeca is much larger than that of the segment of the digestive tube which hes between them, and which further differs from the homologous segment in the Horse-leech, in not possessing any lateral sacculations. . The most anteriorly placed of the nine testes of either side, communicating by a short transverse duct passing outwards, with a common vas deferens, which receives posteriorly the secretion of the eight posterior testes, and anteriorly leads into a convoluted epidymis-like vesicula seminalis, which is seen in this figure in the space bounded by the lines lettered z and f. Last testis of right side. The segments between this one and the most anterior of the genital segments /, have their cutaneous glands greatly enlarged at the time of ovi- position, and secrete the external chitinous shell of the ‘cocoon’ in which the eggs are lodged; whilst the glands of the female generative apparatus secrete the albuminous matter which fills the shell and surrounds the eggs. Sixth testis, displaced outwards so as to show its own con- nection with the vas deferens, and the relation of apposition with it, into which a coecal process from one of the seg- mental organs, e 2, comes. Seemental organs consisting of one portion, which is tu- bular and loop-shaped to the naked eye, but so mutually inter-communicating when examined with the microscope as to be really labyrinthiform ; of a second portion, which is vesicular and opens on to the exterior; of a third, which, as a slender but resistent duct, connects the loop-shaped with the vesicular portions; and, in the eleven posterior segments, of a fourth portion, in the shape of a coecal process, which is prolonged inwards in the two most pos- terior up to the nerve-cord ; in the ante-penultimate up to the vas deferens from the last testis; and in the eight others up to the eight anterior testes. Segmental organ, shown with all the four constituent por- tions just mentioned; the testis with which its coecal process comes into apposition, though not into any tubular continuity, having been displaced outwards. The vesicular part of the segmental organ lies in every case posteriorly 220 Descruption of the Plates. to the looped portion, with the anterior element of which it is connected by the duct; and in the segmental organs, which are in the relation mentioned with the testes, the vesicular portions occupy the angle bounded by the vasa deferentia and the inner parts of the looped portions, and alternate in position with the testes. The coecal process constituting a fourth portion in the segmental organs in relation with the nine testes, is always brought into relation with the anterior one of the two testes, with which the segmental organ alternates, except in the case of the last testis, in which the coecal process appears only to reach the vas deferens of that last gland. In this figure four seg- mental organs are represented as existing posteriorly to the last testis; in nature there.are only three, the most ante- riorly placed one of which is connected with the male organs as just mentioned; whilst the two posterior ones have their coecal processes prolonged nearly up to the middle ventral line occupied by the nerve-cord. The seven seg- mental organs situated anteriorly to the most anterior testis, are represented in this figure by four. None of these seven possess the inwardly prolonged coecal process, but consist of a simple loop-shaped portion, the outer and larger end of which lies almost vertically in the natural condition, whilst the inner and smaller is prolonged inwards, and more or less horizontally, beneath the digestive tube, as in the other segmental organs, a duct and a vesicle open exteriorly. The coecal process when present may be taken to be homologous with the open infundibulum of the ovi- ducts, and vasa deferentia of the Lumbricidae (see pl. viii., @3,74, m). In some Hirudineae, the segmental organs may resemble those of other Annelids, in opening by ciliated infundibula into the general cavity of the body (Branchio- bdella), or into the interior of one of the pseud-haemal canals (Clepsine), but they never are subordinated, as in those orders, to the function of conveying the generative products. In the middle regions of the body, the segmental organs are repeated at regular intervals, five annuli being interposed between the outlets of each pair; and the annulus imme- diately posterior to these outlets carries a nerve ganglion on Medicinal Leech. 221 its inferior and inner, and a pair of white spots on its supe- rior outer surface. The colouration also, it may be observed, of some varieties of the true Medicinal Leech, as also and more markedly of Hirudo troctina, a distinct but closely- allied species, appears to indicate similarly that five smaller or secondary annuli enter into the composition of the primary segments, by the aggregation of which the middle body is made up. At the anterior part of the body the segmental organs are arranged with less regularity. The segmental organs of one family of marine Annelids, the Capitelleae, are said to resemble those of the Leech in having no inner orifice; and in a few Annelids they may be absent, or represented simply by apertures in the body- walls, J. Muscular ductus ejaculatorius of left side, leading from the convoluted vesicula seminalis into the base of the flask- shaped intromittent organ. It is by the secretion of the vesicula seminalis that the spermatozoa are agglutinated into a spermatophore. g. Club-shaped end of intromittent apparatus, glandular at its coecal convex end, and tapering off into the muscular penis below. h. Penis, surrounded where it passes out of the integument by a strong sphincter. This orifice is separated by an interval of five secondary annuli from that of the female organs. i. Ovary of left side, carried upon one of the short oviducts. The ovary of the other side is seen on the farther side the nerve-cord, underneath which its oviduct passed. j. Muscular vagina, in which after sexual congress the sperma- tophore is found. Between the vagina and the two oviducts, a common oviduct intervenes, which takes a tortuous course, and has its coils surrounded by a mass of loose tissue, com- posed of unicellular glands, which are probably the main agents in the secretion of the albumen which envelopes the eges in the cocoon. The azygos character of the two gene- rative outlets is especially noteworthy. In all other Annelids the generative glands discharge their products by dehiscence into the perivisceral cavity, whence they are taken up by the open mouths of infundibular ducts, as in Ganoid Fishes, Description of the Plates. and in the females of all higher Vertebrata; but in the Hirudineae the walls of the generative glands are continuous with the capsules of the generative glands; and, with the exceptions above stated, p. 220, the segmental organs have no opening internally. In the possession of accessory sexual organs, the Hirudineae and Oligochaeta resemble each other, and differ from the other Annelids. For the general anatomy of the Leech, see Brandt, Medizinische For For Zoologie, Bd. ii., pp. 239-253; or Leuckart, Die Mensch- lichen Parasiten, Bd. i., pp. 634-720. the ‘segmental’ organs, see Gratiolet, Ann. Sci. Nat., Ser. iv., tom. xvu., 1862, p. 192, pl. vii., fig. 4. the nervous system, see Leydig, Vergleichende Anatomie, p. 162, ibique citata ; and Taf.i., figs. 4 and 6; Taf. ii., figs. 1, 2, 3,53 Taf. in, fig. 1; Taf. iv., fig. 1; and for the sensory organs called by him ‘ Becherformige Sinnesorgane,’ see Archiv. fiir Anatomie und Physiologie, 1861, p.601. For the ‘ ganglions de renforcement’ developed upon the inferior pair of nerves given off by each ganglia of the ventral chain, except the first and the two last, see, in addition to the references given at p. 133 supra, G. R. Treviranus, Zeitschrift fiir Physiologie, Bd. u., Hft. 2, 1829, pp. 157-172; cited by Claparede, JZ. c., Pp. 356: the development, see Leuckart, 2. c., 686; and Rathke, Bei- trage zur Entwickelungsgeschichte der Hirudineen (Nephelis, Clepsine), cit. in loco. For the existence of blood-corpuscles in the pseudhaemal system, see For Quatrefages, Hist. Nat. Annalés, 1865, i., p: 63. i, paloss where Sy//idea armata is stated to possess blood-corpuscles in those vessels; and the statement as to Glycera made in the Ann. Sci. Nat., 1850, iii. 14, p. 288, appears to be withdrawn. a statement as to their presence in the ‘ pseudhaemal’ system of some other Annelids, see Claparéde, Ann. and Mag. Nat. Hist., Ser. i, vol. xx., 1867, p. 350, where Glycera is stated to be devoid of the vascular system in question. For the pro- priety, however, of classing Phoronis as an Annelid, as is done at p. 138 supra, see Allman, Fresh-water Polyzoa, pp. 5 5-575 and Dyster, cit., p. 138. 4 et eral Py aehy iH + ata ras | east ASE if | , met 7 (Va i eta) . -, 4 “