mm t&m. Marine Biological Laboratory Received. Accession No. 58111 Given By Place,_ rs. Washington, D.C. , libris eigs ELEMENTARY TEXT-BOOK OF ZOOLOGY C s ELEMENTARY TEXT-BOOK ' OF ZOOLOGY. SPECIAL PART: MOLLUSCA TO MAN. BY DE. C. GLAUS. of Zoology and Com fin nit in An itomi/ in Hi' University o/ ]'/. j/,; Director of the Zoological Station ut Trieste. TRANSLATED AND EDITED BY ADAM SEDGWICK, M.A., Fflloie nnd Lecturer of Trinity Col/riff, Cnmbriibii , WITH THE ASSISTANCE OF F. G. HEATHCOTE, B.A., Trinity College, Cambridge. WITH 706 WOODCUTS. NEW YORK: MACMILLAN A CO. TABLE OF CONTENTS. Page MOLLUSCA 9 II. BRACHIOPODA . 80 1. Ecardines 84 I. LAMELLIBRANCHIATA 15 2. Testicardincj 85 1. Asipbonia . 25 2. Siphoniata . 27 TUNICATA 85 II. SCAPHOPODA . 28 I. TETHYODEA (Ascidians) . 90 III. GASTROPODA . 30 1. Copelatfe 100 1. Prosobrancbiata . 1. Placophora . 2. Cyclobranchiata . 43 44 2. Ascidite Simplices 3. Ascidise Compositse 4. Ascidiaj Salpteformes . 10(> 101 102 :;. Zeugobraiichiata . 4. Ctenobranuliiata (Aniso- 4:. II. THALIACEA 103 branchiata) . 46 1. Desmomyaria 108 2. Heteropoda . 48 2. Cyclomyaria 109 3. Pulmonata . 50 1. Basommatophora . 51 VERTEBRATA . 109 2. Stylommatophora . 51 4. Opistbobrancbiata 52 1 2/ 1. Tectibranchiata . ;.2 1. Leptocardii (Acrania) . 150 _'. Xudibrancliiata 52 2. Cyclostomi (Marsipo- 3. Saccoglossa . 53 brancbii) . 153 IV. PTEROPODA 53 3. Selachii (Chondro- pterygii) . 157 1. Thecosomata 56 1. Holocephali. 161 2. Gymnosomata 56 2. Plagiostomi . 161 . 1 ffi/ildliiliil 162 V. CEPHALOPODA . 50 2. Rr. Dt'ciduata 318 221 222 1. Proboscidea . 318 223 Lamnungia (Hyra- 225 coidea) 319 8. Rodentia 320 230 9. Insectivora . 322 255 10. Pinnipedia . 323 255 11. Carnivora 324 257 12. Chiroptera . 327 260 1. Frugivora . 32S 261 2. Insectivora . 329 263 13. Prosimiaa (Lemurs) 330 264 14. Primates 332 265 ofi^ 1. Arctopitheci 334 ZOu 2. Platyn-liini . 385 266 3. Catarrhini . 335 266 268 15. Man 339 SPECIAL PAET: MOLLUSC A TO MAN. Vel CHAPTER I. MOLLUSCA.* Bilaterally symmetrical unseymented animals, without a locomotory skeleton; with a a /if ml foot and v.si.illy a calcareous univalve or It! mice shell: fit// hm'nt (supraossophageal yartyHa\circuinaxophayeal i'i inj, and suboesophageal yron /> <>f yamjlia. SIXCE Cuvier several different groups of animals, which were placed amongst the worms by Linnanis, have been included in the Mollusca. Of late years, however, the anatomy and de- velopment of these forms have been more closely examined, and it seems fairly certain that some of them are allied to the Worms. In any case, the group Mollusca must be looked upon as of more limited extent than has for FIG. 492. Older larva of a Gagerqpo<2 (after Gegenbaur). 8, Shell; P, foot ; Tel, velum ; T, tentacles ; Op, operculum for the closure of the shell opening. development stand in closer relationship to the Bryozoa, may be removed from the Mollusca and united with the latter under the head Molluscoidea. The Tunicata also must be constituted an independent group between the Mollusca and the Vertebrata. * G. Cuvier, ' Mrmoires pour servir a 1'histoire et a I'anatoinie des Mol- lusques." Paris. 1817. R. Leuckart, " Ueber die Morphologic mid die Verwandschaftsverhaltnisse der wirbellosen Thiere." Braunschweig, 1848. Huxley, ' On the Morphology of the Cephalous Mollusca, as illustrated by the Anatomv of certain Heteropoda and Pteropoda, etc." Pit II. Trans.* 1853. some time been the case. The bivalved Brachiopoda, which in structure and 10 MOLLL'SCA. Br S The Mollusca are unjoin ted, unsegmented animals, without jointed appendages. The body is covered by a soft slimy skin. They lack both an internal and external locomotory skeleton, and appear there- fore especially suited for life in water. But few of them are terrestrial, and when this is the case the locomotion is always limited and slow ; while the aquatic forms, in correspondence with the far more favourable conditions for locomotion presented by water, may be endowed with the power of rapid swimming. The ilt'rmttl itii'scnlar system plays an important part in the locomotion of these animals, especially that part of it placed on the lower, i.e., ventral, surface of the body. In this region it is greatly developed, and gives rise to a more or less projecting locomotory organ of very various shape, the foot (figs. 492 and 493). The foot always consists of an unpaired median structure, which is some- times divided into several parts and may possess in addition lateral paired portions, the epipodia. Above the foot there very generally exists on the body a shield - shaped thickening of the integu- ment, the so-called mantle, the edges of which, in more advanced develop- ment, grow over the body as a fold of the skin and partially or completely cover it. The surface of this fold of skin secretes calcareous and pigmentary substances, and gives rise to the variously shaped and coloured shells which contain and protect the soft body. In addition to the foot, and mantle, the body generally possesses in the anterior region, on either side of the mouth, a pair of lobe-like appendages, the luccal lobes, which are the remnants of a largely-developed larval structure, known as the velum. In the higher Mollusca (Cephalophora) the anterior part of the body bearing the buccal lobes, and containing the central parts of the nervous system and the sense organs, is more or less sharply marked off as a head. The part of the body behind the head constitutes the main mass of the animal. Its dorsal portion (the visceral sac) contains the viscera and is frequently spirally twisted, as a result of which the bilateral symmetry undergoes externally a FIG. -193. Larva of Termtttts (after Lacaze-Duthiers). S, velum ; Si; gill ; F, tentacle; P, foot; Oc, eye. HEAD AND ITS APPENDAGES. 11 remarkable disturbance. The visceral sac may, however, have a flattened or cylindrical form and retain its symmetry. In this group (the Cepkalophora) the shell may be simply plate-shaped or spirally wound, or remain as a mere flat rudiment hidden under the dorsal integument. In one group of the Cephalophora, viz., the Cephalopoda, a circle of arms is attached to the head around the mouth opening. They serve both for swimming and creeping, and for the capture of nourishment. By Loven and R. Leuckart they were looked upon as modifications of the buccal lobes ; by others, perhaps with greater justice, as tentacles, and by others again as Bm FIG. 494. Male of Carinaria medil'i-ranta (after Gegenbaur). P, F<3ot ; 8, sucker; 0, month ; Bm, buccal mass; M, stomach ; Sj>, salivary gland; X, liver; A, anus; CG, cerebral ganglion ; Tf , tentacle ; Oc, eye ; Of, auditory vesicle ; &, buccal ganglion ; PIJ, pedal ganglion; Mg, mantle ganglion; N, kidney; -Be, gill; At, auricle; T>, ventricle; A,; :K ii-t a ; Z, hinder branch of the same ; T, testis ; TV, vas defereus ; Wp, ciliated furrow ; Pe, penis ; F, flagellum with gland. modifications of the foot. A perforated funnel-shaped cone, through which the excretory products and water which has passed over the gills is expelled from the large mantle cavity, and which thus serves at the same time as a swimming organ, probably corresponds to the fused folds of the epipodia. Amongst the Gastropoda the head is provided with tentacles and buccal lobes, and the ventrally placed foot possesses a large Hat plantar surface ; more rarely it has the form of a vertically placed fin (Heterojwda, fig. 494). In another group, the LaiiielUbranchiata (Acephala], there is 110 independent head, and the laterally compressed body bears two large lateral mantle 12 310I.LUSCA. lobes, each of which secretes a single shell; the two valves so formed are united 011 the dorsal surface by a ligament. The internal organization of the Mbllusca presents as many differences as does the external form. Like the external form, the internal structure also frequently presents surprising devia- tions from the bilateral arrangement. The nervous system :;: (tigs. 495, 496, 497) consists of a dorsal p.-dr of ganglia lying on the oesophagus (only exceptionally tig. 495 dissolved into a general gangiionic investment of the com- missure), the cerebral ganglia (figs. 496, 497, C,j), from which pass off the sense nerves and an oesopha- geal ring, composed of several PaSt fibrous cords. The latter primi- tively gives off two pairs of nerve- truiiks. The nerves of the upper and lateral pair are the pallial nerves (fig. 495, Pa$t) ; they supply the lateral parts of the body and the mantle. The nerves of the ventral pair are placed nearer the middle line, and are known as the pedal nerves (fig. 495, Pe/St) ; they are connected together by transverse commissures (fig. 495) and innervate the muscles of the foot. This arrangement,, found in the simplest form in. Chiton, agrees essentially with that of the Gephyrean-like genus, Neomenia. At a more advanced stage, two large swellings are found FIG. -195. Nervous system of Chiton (after . . B. nailer). Sr, oesophageal ring; s g , at the origin of the pedal nerves j buccal ganglion ; P< st, pedal nerve ; these are the pedal ganylia (figs. PaSt, pallial nerve; Br, gills. _ T1 . T , .. . 496, 497, Pg). Ln addition, a third group of ganglia, known as the visceral ganglia, is also found. The arrangement of the latter ganglia is very various ; they are some- times fused with the cerebral, sometimes with the pedal ganglia, and are sometimes broken up into several groups of ganglia. They are * H. v. Jhering, " Vergleickende Anatomie des Nervensystems and Phylogenie der Mollusken." Leipzig, 1877. SENS:-: oi;.\\s. 13 connected with the cerebral ganglia by a longer or shorter commissure, and give off nerve plexuses to the heart, gills, and generative organs. This third pair of ganglia is, therefore, regarded as the equivalent of the sympathetic, but unjustly, as it also gives off nerves to the skin and muscles. Small ganglia (hi weal ganglia), lying above and below the buccal mass and sending off nerves to the oesophagus and intestine, may more justly be regarded as sympathetic. Tactile organs are present in the more highly-developed Mollusca, as two or four lobes placed near the mouth, the above-mentioned buccal lobes ; in addition to which, tenta- cles round the edge of the mantle are often found in the Awphnla, and in the Cephalophora two or four retractile tentacles on the head. The eyes have almost always a complicated structure, and are provided with lens, iris, choroid, and retina. There are usually two of them oil the head ; in rare cases e.g., in some Lamellibranchs they are more numerous, and are placed 011 the edge of the mantle. Auditory organs are very generally present. They have the form of closed otocysts, provided with hairs on their internal walls. They are usually paired, and lie either on FlG mussel (A noao system of the )(af ter Keber). 0, mouth ; A, anus ; K, gills ; P, foot ; Se, labial palps ; By, cerebral o-anirlion ; P//, pedal ganglion; Vg, splanchnic ganglion; G, generative gland ; Oe', external opening of kidney ; Oe", opening oi' generative gland. the cerebral or pedal ganglia (tig. 497, Of). They are, however, al- ways innervated from the former. In the alimentary canal, three divisions, at least, can be clearly distinguished the oesophagus, the stomach and intestine, and the hindgut or rectum. Of these the middle or digesting division (stomach and intestine) is usually characterized by the possession of a very extensive liver. Kidneys are always present, and are frequently paired and symmetrical in each half of the body. Often, however principally when the body is asymmetrical the kidney of one side is smxller (Patella, Haliotis) or i^ entirely absent ((l- 14 MOLLUSCA. poda\ They usually have the form of sacs with a wide lumen, and open on the one hand into the body cavity (pericardial sinus), and on the other to the exterior by a lateral opening. In all probability the mol- luscan kidney is homologous with an annelidan segniental organ. The internal, funnel- shaped opening is frequently beset with cilia. The anus is very often removed from the middle line, and placed on one side of the body. A compact heart is always present, driving the blood through the vessels into the organs. The vascular system is never completely closed, for, even when the arteries and veins are connected by capillaries, blood sinuses, de- rived from the body cavity, are inserted into the course of the vessels. The heart is always arterial i.e., systemic and receives arterial blood from the respiratory organs. Respiration is in all cases carried on through the general outer surface of the body ; but in addition special respiratory organs, in the form of Iranchiw, more rarely of lungs, are present. The branchiae are ciliated projections of the body sur- FIG. 497. - Nervous system of Cuuidaria (after d usua lly placed Haller). Cg, cerebral ganglion; Pg, pedal r ganglion; pig, pieurai ganglion; Bg, buccai between the mantle and the ganglion; Gp, supraintestinal ganglion; Gib, ^ave the subintestinal ganglion; r./, visceral ganglion; o/.otocyst. form of branched append- ages or of broad lamella (LamcUibrancMata}. The lung, on the other hand, is derived from the mantle cavity, which is tilled wi V LAMELLIBRANCHIATA. 15 aii', and the inner surface of which is thrown into a number of complicated folds, so as to expose a large surface for the respiratory blood-vessels; it communicates by an opening with the extern,! 1 medium. The pulmonary and branchial cavities are, therefore, mor- phologically equivalent. Reproduction is always sexual. The hermaphrodite condition, on the whole, preponderates ; nevertheless, not only many marine Gastropods, but al>o most Lamellibranchs and all Cephalopods are dioecious. Development usually begins with a total segmentation, which is followed by the formation of a blastoderm surrounding the hinder part of the yolk or the whole yolk. The just hatched young often pass through a complicated metamorphosis, and possess an anterior cutaneous expansion bordered with cilia the velum which func- tions as a locomotory organ. In form, disposition of cilia and organisation, many molluscaii larva? permit of a closer comparison with Loven's worm larva. By far the majority of the Mollusca are aquatic animals, especiallv marine ; only a few live on land, and these always seek damp localities. When we consider the extraordinarily wide distribution of the Mollusca in past times, the importance of their fossil remains for the determination of the age of the sedimentary formations becomes intelligible. Class 1. LAMELLIBRANCHIATA.* Laterally compressed Mollusca without separated head, with bilobed mantle and bivalve shell, composed of a riyht and left half and connected by a dorsally -placed ligament ; with large gill plates ; sexes usually separate. The Lamellibranchs were formerly united with the Brachiopoda as Conchifera. Like the latter, they lack a differentiated cephalic region, and possess a large and usually bilobed mantle and a bivalve shell. Nevertheless, the structural differences between these * G. Cuvier, " L' histoire et 1'anatomie des Mollusques." Paris, IS I 7. Bojanus, " Ueber die Athem- und Kreislaufswerkzeuge dor z\veischaligcn Muscheln." Jv/.v, 1817, 1820, 1827. S. Loven, A". Vet. Alui'l . Handlgr. Stockholm, 1848. Translated in the Arch, fur Natwgescli., 1849. Lacaze-Duthiers, Ann. tics Sc. Nat.. 1854 181. H. and A. Adams, "The Genera of the lleeent Mollusca." London, 1853- 1858. T . Reeve. " Conchologia icouica." London, 1846-1858. 16 MOLLUSCA. two groups are so essential, that a close connection between them cannot be maintained. The usually strictly symmetrical body is laterally compressed and of considerable extent, and is surrounded by two lateral mantle lobes, which are continuous across the dorsal middle line and secrete a right and left shell valve. To the sides of the mouth opening are found two pairs of leaf- or tentacle-like buccal lobes the labial palps. On the ventral surface a lai-ge, usually hatchet-shaped foot (fig. 498, F) projects; and two pairs, rarely one pair, of large lamellar gills are always placed in the mantle furrow between the mantle and foot (fig. 498, K}. as FIG. 498. Anatomy of Unio pictorum (after C. Grobben). TS, anterior adductor muscle; HS, posterior adductor muscle ; MS, labial palp ; F, foot ; Mt, Mantle ; , branchiw ; Off, cerebral ganglion ; Pg, pedal ganglion ; My, splanchnic ganglion ; O, mouth ; -V, stomach ; L, liver ; KrS, crystalline style ; D, intestine ; Af, anus ; G, generative organs ; A, region of mantle lobes bounding the exhalent or cloaca! orifice ; E, region of ditto bounding inhalent or branchial orifice ; N, kidney ; Tk, auricle ; Ilk, ventricle ; VA, anterior aorta; HA, posterior aorta; P, pericardial gland (schematic). The hind end of the edges of each mantle lobe almost always presents two slight, contiguous excavations (fig. 498, A and E\ the ventral of which is bordered by numerous papilla?. When the two halves of the mantle are above together, these excavations form, with the corresponding structures of the opposite side, two slit-like openings, placed one behind the other. The upper or dorsal of these two openings functions as the cloacal, or exhalent opening ; the lower or ventral as the inhalent opening. Through the latter, with a slightly gaping shell, the water is driven by the peculiar arrangement and action of the cilia on the inner LAMELLIBRANCHIATA. 17 KIS surface of the mantle and the gills into the mantle and respira- tory chamber. Food materials pass with the water to the labial palps, and so to the mouth. The edges of the mantle lobes do not always remain free through their whole extent, but frequently fuse together, first at the hind end, and then gradually forwards. As a result of this fusion, a posterior opening, including in itself the inhalent and exhalent orifices, becomes separated from the anterior opening into the mantle cavity ; and, further, the exhalent and iuhalent openings become separated from each other by a transverse bridge of tissue. The long anterior opening or foot-deft, in consequence of the progressive fusion of the mantle edges, often becomes gradually so shortened, that the foot, which is correspondingly reduced, can scarcely be protruded. In this case, the mantle comes to have the form of a saccular investment with two openings. The further forward the fusion of the two mantle lobes proceeds, the more marked becomes a peculiar elonga- tion of the posterior mantle region round the inhalent and exhalent openings an elongation of such a nature that two contractile tubes, or siphons, become formed (fig. inn mi i j i FIG. 499. a, Mattra, ellhitica, animal with 499, a). The latter may reach shell . XIS> cloacal or f exh ' aleut siphon . Such a size that they Can no longer KS, branchial or inhalent siphon ; P, foot, i 6. left valve of M. sol Ida ; 1'3f, anterior be drawn between the posterior ad(luc tor muscle ; MH, posterior adductor edges of the gaping valves of muscle ; J//, pallial line ; Mb, pallial indentation. the shell. The two siphons often fuse with one another ; but the two canals, with their openings surrounded by tentacles, remain separate. In the most extreme cases the siphons are enormously enlarged, and the posterior region of the body is peculiarly elongated and uncovered by the rudimen- tary shell; so that the whole animal acquires a vermiform appear- ance, the shell-bearing anterior region of the body constituting the head (Teredo, fig. 505). The mantle and skin consist of a cellular, slimy epidermis, beneath which lies a connective tissue, richly traversed by muscular fibres. The epidermis on the outer surface of the mantle consists of columnar cells ; while on the inner surface of the mantle the cells composing VOL. II. 2 18 MOLLUSCA. it are ciliated. Pigments are present principally upon the edges of the mantle, which are frequently folded or beset by papilla? and tentacles. The outer surface of the mantle secretes a sti-ong calcareous shell, which is constituted of two valves corresponding to the two mantle lobes. The two valves are united dorsally. They are rarely exactly alike. Nevertheless, the term unequivalve is only applied to those shells in which the asymmetry is very marked, and the valves can be distinguished as upper and lower. The lower valve is the larger and more arched, while the upper is smaller and natter, closing up the cavity of the lower after the manner of an operculurn. The edges of the two valves are generally closely applied to one another, still they may gape more or less widely at various points for the exit of the foot, byssus and siphons. The latter is especially the case for those Molluscs which bore in sand, wood, or hard rock. In extreme cases the shell may, by a wide anterior emargination and an extended docking of its posterior part, be re- duced to an annular ru- diment (Teredo), while to its hinder end is applied a calcareous tube, which may intimately fuse with the shell rudiments and receive the latter entirely into itself (Aspergillwm). The two valves of the shell are always connected dorsally by an external or internal ligament, which tends to keep the valves open. The two shell valves are also firmly connected together dorsally by interlocking teeth, which constitute the so-called hinge (canto). The hinge edge with the ligament is therefore to be distinguished from the free edge of the shell, which is divided into an anterior^ inferior (ventral), and posterior or .siphonal edge. The anterior and posterior edge may generally be easily determined by the position of the hinge-ligament with regard to the two umbones (nates), which have the form of two prominencies projecting over the dorsal edge, and indicate the point (apex) where the development of the valves began. The area is behind the apex, and includes the dorsal posterior side of the shell. The part of the dorsal edge in front of Fie. 500. Ai-ifiihi nemiMffitta, the valves are shifted over one another ; M , muscle impression. LAMKLLIBRANCHIATA. 19 the apex is usually shorter, and contains, at least in the equivalve species, an excavation, the lunnla, by means of which the anterior .-e'dge can be at once recognised. While the outer surface of the shell presents various sculpture markings, the inner surface is smooth and shines with the lustre of mother-of-pearl. On a closer examination, impressions and pits become visible on the inner surface. A narrow line, the so-called mantle or paUlal line (the line of attachment of the mantle edge to the shell), is placed near and fairly parallel to the ventral edge of the shell (tig. 499, J//). In the siphoned forms this presents posteriorly a bend directed forwards and upwards (J/7>). the pulUal bay, which is due to the siphons. Impressions are i ^_-^ = _ ===== usually caused by the inser- tion of an anterior and pos- terior adductor muscle which I iiiss through the body of the animal transversely from one side to the other, and are attached to the inner surface of the shell (fig. 499, HM, FJ/). While in the equivalve mussels (pr- tJiaconclia} the two impres- sions are usually of equal size, in the uneq nival ve forms (Pleuroconcha) the anterior adductor is re- T FIG. 501. Vertical section through the shell and duced, and may Completely mantle of Anodonta (after Leydig). Cu, cuticle ; i ,i_ - i S, prismatic layer; SI, laminated (mother-of-pearl) vanish ; the posterior ad- ductor, on the other hand, now a muscle of much larger size, shifts forward to the middle of the shell (fig. 500). Hence the names Dinti/urf// and Monomyaria. According to its chemical composition, the shell consists of carbonate of lime and an organic matrix (conchy oliii), which usually presents a laminated texture. In addition to this laminated layer there is also a thick external calt-areous layer, composed of large, pallisade-like prisms, which are placed side by side and may be compared to the enamel of teeth (fig. 501, S}. Finally, on the outer surface of the shell there is a horny cuticle, the so-called epidermis (Cvi.}. The internal lami- nated layer is secreted by the whole internal surface of the mantle, layer; Ep', external epithelium of mantle; Kd, connective tissue substance : EJI", internal epi- thelium of mantle. 20 MOLLUSCA. while the two outer layers are formed only by the free edge of the mantle. The growth of the shell is effected in two ways; (1) by additions to the internal laminated layer, whereby the shell increaM-s in thickness ; (2) by additions to the prismatic and horny layers, whereby it increases in superficial extent. Accordingly the outer coloured part of the shell, which is composed of vertical prisms and a horny cuticle, when once formed cannot increase in thickness ; while new concentric layers are constantly being added to the internal colourless mother-of-pearl layer during the whole life of the animal. The mantle-secretion gives rise in the so-called pearl-mussel (Melea- yrina, Unio margaritifer), to the formation of pearls. The foot is completely absent in comparatively few of the Lumdll- branchiata, and only in those which have lost the power of locomotion (Ostrea, Anomin). In many forms, principally in the larva (Unio), less frequently in the adult (Mytilus), the foot possesses a byssus gland, which secretes silk-like fibres, by which a temporary or permanent attachment of the animal is effected. The form and size of the foot vary very considerably, according to the special kind of locomotion. The foot is most frequently used for creeping in sand, and then is hatchet-shaped; in other cases it is spread out laterally and its creeping sxirface has the form of a disc. More rarely it is of a large size and bent, in which case it serves for springing movements in the water (Cardiuw). Some Lamellibranchs possess a linear club-shaped or cylindrical foot (Solen, Solenoniya), and move by rapidly retracting the foot and ejecting water through the siphons. Many use the foot for burying themselves in mud ; others bore into wood (Teredo) or hard rock (Pholas, Lithodomus, Saxicava, etc.), for which purpose they push themselves against the rock with their short blunt foot (PJiolas, Teredo), and use the hard and often finely serrated edge of their shell as a grater, giving it a rotatory movement. According to Hancock, the foot and edge of the mantle at the anterior end of the gaping shell are beset with siliceous crystals, and effect the excava- tion of the rock after the manner of a file. The nervous system presents three pairs of ganglia, the cerebral, pedal, and visceral ganglia. The visceral ganglia are connected with the cerebral by a longer or shorter commissure on each side (figs. 496 and 498). Since there is never a distinct head, and sense organs do not appear on the anterior region of the body, the brain (cerebral ganglia) is proportionately little developed. Its nerves supply mainly the region round the mouth and the mantle, to which two large nerves are often distributed. The two halves of the brain LAMELLI BRANCHI ATA. 21 are frequently (Unio) f:ir removed from one another laterally, and are approximated to the anteriorly placed pedal ganglia (Pecten}, whose nerves are distributed 011 the ventral side of the body in the foot. The large visceral yanylia are placed on the ventral side of the posterior adductor muscle, and supply nerves partly to the gills and partly to the viscera and to the mantle; the latter are two large trunks which run in the edge of the mantle and anastomose with the mantle nerves from the brain, often forming plexuses. Large nerves also pass oft" from the visceral ganglia to the siphons, at the base of which they form an accessory pair of ganglia. Sense organs. Auditory organs, eyes, and tactile organs are present. The former have the form of paired auditory vesicles, and lie beneath the oesophagus attached to the pedal ganglia (their nerve, however, arises from the brain) ; they are characterised by the large hair cells which line the wall of the vesicle. Eyes may either be simple pigment spots at the end of the respiratory tube (Solen, \'<-itirs), or be much more highly developed and placed on the edge of the mantle of Area, Pectunculus, Tellina, and especially of Pecten and XjHitK/yf/'s. In the latter genera they are placed .011 stalks between the marginal tentacles, and have an emerald green or brown red colour ; they consist of an eye-bulb with a coriieal lens, choroid, iris, and a well-developed layer of rods into which the optic nerve passes. The sense of touch is provided for by the labial palps, the edges of the respiratory apertures (siphons) with their papilla? and cirri, and also the often numerous tentacles at the edge of the mantle (Lima, Pecten). In all probability the hair cells found in the mantle are the seat of a special olfactory sense (tracking sense). The digestive organs begin with the mouth, which is placed between the labial palps (tig. 498). The mouth leads into a short oesophagus, into which the cilia of the labial palps drive small nutrient particles received into the mantle cavity with the water. Jaws and tongue are always absent. The oesophagus widens into a spherical stomach, at the pyloric end of which a blind sac, which can be closed up, is attached. A rod-like transparent structure (crystalline style) is often found either in the above-mentioned blind diverticulum of the stomach, or in the alimentary canal itself. It is to be regarded as an excretion -product of the alimentary epithelium, and is periodically renewed. The intestine always attains a con- siderable length, is much coiled and is surrounded by the liver and generative glands ; it projects into the foot and then ascends again behind the stomach to the dorsal surface : it then traverses the ~2'2 MOLLUSCA. veiitiicle of the heart, passes over (dorsal to) the posterior adductor muscle to open at the hind end of the body into the mantle cavity at the end of a projecting papilla. The circulation is effected by an arterial heart, which is enclosed in a pericardium and lies in the dorsal middle line slightly in front of the posterior adductor muscle. The heart consists of a median ventricle, which is perforated by the alimentary canal, and of two lateral auricles, through which the blood enters the ventricle. The ventricle of the heart of Area is peculiar in being double- the efferent aorta?, however, unite to form an unpaired vessel. The ramifications of the anterior and posterior aorta lead the blood into a compli- cated system of lacuna? in the mantle and in the interspaces between the viscera. These, which coincide with the body cavity, represent the capillaries and finer venous vessels ; while, by some observers, they have been regarded as a true capillary and venous system. The chief venous sinuses are two lateral sinuses placed at the base of the gills, and a median sinus into which the lacunae of the foot lead. From these part of the blood passes direct into the "'ills; the main part, however, first passes through a network of canals in the walls of the kidney or organ of Bojanus, as through a kind of portal circulation, and thence into the gills, whence it is returned as arterial blood to the auricles of the heart. Watei is .said to enter the circulation through openings in the foot and to become mixed with the blood. Nevertheless the erectile networks of the foot are blood-lacunae. Organs of respiration. There are usually two pairs of branchial leaflets (gills), which begin behind the labial palps and pass back- warcls along the sides of the body. The outer surfaces and the interlamellar water-spaces of these branchial leaflets are covered with cilia, which keep up a continuous flow of water over the gills. The outer gill, viz., that lying next the mantle, is usually con- siderably the smaller of the two. It is often completely absent, so that the number of the gills is reduced to a single pair. Sometimes the gills of the two sides fuse with one another across the middle line in the posterior region, and may in extreme cases represent a sack, like the branchial sack of the Ascidians (ClavageUa). The most important of the excretory organs --the organ of Bojanus, so-called .alter its discoverer is a paired, glandular sac with folded walls, and of an elongated oval form, whose cavity communicates with the pericardium (fig. 498). The substance of this gland, which functions as kidney, is composed of a yellow or LAMELLIBRANCHIATA. 23 spongy tissue, which is covered with a closely ciliated layer of cells, from which concrements containing calcareous matter and uric acid (also ijitanin) are excreted. The simple duct often receives the duct of the generative apparatus, or the two organs open together on a common papilla on either side. In the Siphoniata, on the other hand, the renal and generative openings are almost always separate. Generative organs. The Lamellibranchs are, with a few exceptions (the genera, Cyclas, Pecten,_0strea, Clavayella, Pandora], direcious. Both kinds of sexual organs lie amongst the viscera, and have the form of lobed or racemose glands, which are placed near the liver, surround the windings of the intestine, and extend into the base of the foot. The testis and ovary can usually be distinguished from one another with the unaided eye by their colour ; the ovary being red in consequence of the coloxir of the ova ; the sperm, on the contrary, is milk-white or yellow. The openings of the ducts are placed right and left near the base of the foot. The form, position and opening are exactly the same in the hermaphrodite glands, in which the male and female follicles may be separate and open separately (Pandora] or together (Pecten, Glavagella, Cijclas); or the same follicles may function sometimes as ovary and sometimes us testis (Ostrea, Cardium norwegicum). In the diox-ious forms, the male and female animals may differ in the shape of the shell, as is the case in the fresh water Unionidce. Here the outer gills of the female are used for the reception of the eggs (brood pouch), and the shell is more arched. Hermaphrodite individuals are met with among the freshwater mussels, both in. Unio and in Anodonta. The fertilization of the eggs is probably usually effected in the mantle or branchial cavity of the female. But few Lamellibranchs are viviparous. The fertilized eggs, however, almost always remain for some time between the valves of the shell, or pass into the branchial leaflets, where they undergo the early processes of embryonic development under the protection of the mother. This care of the brood is especially conspicuous in the freshwater forms ; in the Unionidw the eggs pass into the great longitudinal canal of the external gill, whence they are dis- tributed into the gill spaces, which become enormously widened and modified into peculiar brood-pouches. In the emptying of these brood-pouches the contents are expelled through the great longitu- dinal canal as a mass of eggs, united together by mucus and con- taining ciliated embryos, or as a continuous string of eggs. 24 MOLLUSCA. The development* of the embryo' is introduced by an unequal segmentation. The segments arrange themselves in the form of a blastosphere, on which the archenteron often arises by imagination, while the rnesoderrn is developed from two cells which are early En a FIG. 502. Stages in the development of the larva of Teredo (after B. Hatschek). <>/. Institute, etc., Tom. III. Vienna. 1881. LAMELLIBRANCHIATA. afterwards; while the heart, kidney, and gills are still later in making their appearance. Among the provisional arrangements the velum, which proceeds from, the sides of the preeoral ciliated ring, is very generally present, and in the free-swimming larv:v j has the form of a large ciliated ring or collar. The development of the freshwater forms (Cyclas, Unio,Anodonta\ in which the eggs and embryos are contained in well-protected brood pouches, may generally be called direct. The marine Lamelli- branchs, on the other hand, are born at an early stage, and swim about for a long time as larviv with large umbrella-like velum, from which the labial palps are developed (fig. 503). The Lamellibranchs are for the most part marine and live at different depths, sometimes creeping, sometimes swimming and jumping. Many are without the power of changing their position, inasmuch as they fix themselves at an early age by means of the byssus threads to rocks and stones (oysters). Others, as the boring forms, bore passages in the wood of ships and piles and in rocks. The Lamellibranchs had a wide dis- tribution in the earlier periods of the earth's history, and their fossil shells are most excellently preserved ; they FlG. SOS. Larva of Montacida bidentata are therefore of the greatest import- (after Loven). s. velum; s t ,, apical ance as characteristic fossils for the i llate wirtl ^seiium; D intestine; L, liver ; 1 i/mnrphti Fall., has gradually extended over many fi-esh water systems of Germany. Fam. Arcaceae (Archenmscheln). Shell thick, equivalved with well- developed hinge, and covered by hairy epidermis. The two adductors form two equally large anterior and posterior muscle impressions. . I rcn .\oic L., Mediterranean. Pi'ctuitciiln* j/ihisnx L., Mediterranean. The Trigoniadae (Trigoniacea) are allied here. Trigonia jin-t i////f// Lam. Fam. Unionidae (Najades), Freshwater Mussels. With long equivalved but not equisided shells, which are covered externally by a strong smooth usually brown epidermis, and internally by a mother-of-pearl layer. One of the muscle impressions is divided. Foot with cutting edge ; gills fused behind the foot. The outer gill plates also function as brood-pouches for the developing eggs. They live in standing or running water. Anodonta cygiiea Lam., in ponds. A. laidtina L., more in rivers and brooks. 1'n in ji'ictfiniiii L., (Malermuschel). Unio tumid us Retz., batarus Lam. J/ar- yaritdtid, ^nargaritifera Retz. (Flussperlmuschel), in mountain streams of South Germany, especially in Bavaria, Saxony, and Bohemia. II. SIPHONIATA. Part of the mantle edges fused, with elongated tubular siphons. Fam. Chamidae (Chamacea) (Gieumuschelu). Shell uuequivalve, with ^trongly developed cardinal teeth and simple pallial line. The mantle edge fused, except at three points, viz., the opening for the foot, the dorsal (cloaca!) and ventral (inhalent) siphons. C'Jiama Lazurus Lam. The Tridacnidae are closely related to the above. Ti'idacnu ffi'/as L. Hip- pi\pux mdculdtux Lam. Indian Ocean. Fam. Cardiidae (Cardiacea) Cockles. Shell equi valve, fairly thick, heart- shaped and arched, with large incurved umbones, external ligament, and strong hinge formed of several teeth. Siphons short. Foot powerful and bent elbow - like, serves for swimming ; passes out through anterior slit. Curdinw cdule L., North Sea and Mediterranean. Hemicardium cardixsa L.. East Indies. Fam. Lucinidae (Lucinacea). Shell circular, free, closed, with one or two cardinal teeth, and a second quite rudimentary lateral tooth. Pallial line simple. Mantle open in front, prolonged behind into one or two siphons. Lut-lna Idctfd Lam. Mediterranean. Fam. Cycladidae.* Shell equi valve, free, swollen, with external ligament and thick horny epidermis. Mantle with -two (rarely one) more or less fused siphons. Live in fresh water. Ci/flti-xcur/ieu L., Pisidtn-ni Pf. Corbicula Miihlf. Fam. Cyprmidae. Shell regular, equivalve, elongated to an oval, closed, with thick and strong epidermis. One to three principal cardinal teeth, and usually a hinder lateral tooth. Pallial line simple. Mantle edges fused to form two siphonal openings. Cyprina ixJ//nJ/ra Lam., IsocardAa cur L. Mediterranean. Fam. Veneridae. Shell regularly round, or oblong with three diverging car- dinal teeth on each valve. Pallial line bent in. Siphons of unequal size, fused at the base. Venus rerrucosa L., Mediterranean. Ci/thcrca Clilonc L.. edible, Mediterranean. C. Dioiu- L., Atlantic Ocean. Fam. Mactridae (Fig. 499). Shell trigonal, equivalve, closed or slightly * Fr. Levdig, "Anatomic und Entwickelung von Cyclas." Millie r'x An ////, 1835. 28 MOLLUSCA. gaping, with thick epidermis. Two diverging cardinal teeth. Pallial indenta- tion short, rounded. Siphons fused, with fringed openings. Mactra gtultorwm L., Mediterranean. Lutraria Lain. Fam. Tellinidae. With two long, completely separated siphons ; edges of mantle widely orien, bearing tentacles. Triangular foot. Tcllina bait tea Gin. T. I'adiata L. Dona,e tntnculvs L. Fam. Myidae (Gapers). Mantle almost completely closed, with slit for the protrusion of the short or cylindrically elongated foot, and very long fleshy fused siphons. The valves gape at each end and possess a weak hinge. Bury themselves deep in mud and sand. Sub-n rag inn L., razor shell. Mi/a truiieata L. (Gaper). Fam. Gastrochaenidse (Tubicolidae). Shell thin, equivalve. toothless, sometimes inserted in a calcareous tube formed by an excretion of the mantle. Mantle with one small opening anteriorly and prolonged behind into two fused siphons with terminal openings. Gastrocltoena c7ai-a L., 4'lavaf/cUu bacillaris Desh. Aspergillum javantMn Lam., Indian Ocean. Fam. Pholadidae. Boring mussels. The valves of the two sides gaping ; without cardinal teeth and ligament, but with accessory calcareous pieces which lie either on the hinge (Pholas) or on the siphons (Teredo, fig. 505). Mantle with only small opening for the passage of the thick foot. Siphons elongated. Bury themselves in mud and sand, or bore into wood and even into solid stone, calcareous rocks and corals. They form passages, from which they protrude their fused siphons. Phulax dactyl us L. Piddock, Pit* craxaata L. Ten-do nnvalh L. (Fig. 505) Shipworm, was the cause of the famous dam- break in Holland at the beginning of last century. SCAPHOPODA. Dioecious Mollusca without head, eyes, or heart, with tri-lobed foot, and tubular calcareous shell open at the two ends. FIG. 505. Teredo v navatis, removed The Scaphopoda are allied to the Lamellibraiichs. from its calcareous Tne admirable investigations of Lacaze-Duthiers* tube, with elonga- ted siphons (after first cleared up this group of Molluscs, which were Quatrefages). f or a j Qn g t ' me k nowll as C irrobranchiata and grouped amongst the Gastropods. He showed that they are closely related to the Acephala, and constitute forms transitional between the latter and the Cephalophora. The shell is an elongated, somewhat bent, open, conical (with the apex broken off) tube, and contains the animal, which has a similar shape and is fastened by a muscle to the thinner lower edge of the shell * Lacaze-Duthiers. Histoire de 1 'organisation et du developpement du Den- talc." Ann. des Sc. Nat.. 185(i-lS58. SCAP1IOPODA. 29 -Br (fig. 506). The body possesses a saccular mantle, like the shell open at both ends, and a trilobed foot ; the foot is protruded through the larger of the openings of the shell- from the anterior opening of the mantle, the margin of which is thickened. A separated cephalic region is not present, .but there is an egg-shaped projection in the mantle cavity, at the apex of which is placed the mouth, surrounded by eight leaf-like labial appendages. The buccal armature con- sists of a lateral (right and left) rudimentary jaw, and a tongue beset with five rows of plates. The alimentary canal is divided into a buccal cavity, resophagus, stomach with large liver, and an intestine, which after several coils closely pressed together, opens behind the foot into the middle of the mantle cavity. The circulatory organs are reduced to two mantle vessels and a complicated system of wall-less spaces of the body cavity. Respiration is effected by the surface of the mantle and also by the filiform tentacles, which arise from two ridges (cervical collar) behind the head-like buccal prolongation. The kidney lies round the rectum, and opens by two openings placed on the right and left of the anus. The nervous system consists of three groups of ganglia, of which the pedal ganglion bears two otocysts. Eyes are absent. The numerous ciliated tentacles serve as tactile organs. The Sca/pkopoda are dioecious. The ovaries and testes are un- paired finger-shaped lobed glands, which are placed behind the liver and intestine, and open to the exterior with the right kidney. FIG. 50C. Tare nt in urn (after Lacaze- Duthiers). Animal without ' shell from right side. .P.foot; Mt, circular muscle of mantle ; M, longi. tudinal muscle ; BI-, gills ; N, kid- ney; L, liver; G, generative gland. s FIG.. 507. Larva of Dentu- Hi'.m (after Lacaze-Du- thiers). a, young larva with first rudiment of shell (S). I, Older larva seen from the dorsal sur- face ; T, tentacle collar ; Gff, cerebral ganglion ; Oet, oesophagus ; L, liver. 30 MOLLUSCA. The animals live buried in niud, and creep abcmt slowly by means of the foot. The young s\vim about for some time as larva?, provided with ciliated tuft and ciliated collar ; then acquire a shell, which is almost bivalve, a velum, and foot; the shell subsequently becomes tubular (fig. 507). Fain. Dentalidae. and Indian Ocean. Order. Solenoconchae. Dcntdllvm entalix L., D. elephant/ mini L.. Mediterranean Class II. GASTROPODA. Mollusca with distinct head, often bearing tentacles ; a ventral muscular foot and undivided mantle, which frequently secretes a ximpli' plate-shaped or spirally twisted shell. The anterior part of the body or head usually bears two or four tentacles and two eyes, which are placed sometimes at the apex, usually at the base of a pair of tentacles (fig. 508). The muscular foot projects from the ventral side of the its form presents Pe FIG. 508. Helix poniutiu. 0, Eyes at the extremity of the body : long tentacles ; 1'c, foot. J ' and size numerous modifications. As a rule it has a broad and long plantar surface ; but in the Heteropoda it has the form of a vertically extended fin. The shape of the body depends on the position and form of the mantle. The latter is placed like a cap on the dorsal surface, and consists of a more or less considerable fold of the dorsal integu- ment ; its edge is usually thickened, sometimes also prolonged into * Martini and Chemnitz. Conchylien-Cabinet. 12 Bde. Herausgegeben von Kiister. Niirnberg, 1837-1865. Sowerby. " Thesaurus conchyliorum, or figures and descriptions of shells/' London, 183218(52. Reeve. " Conchologia iconica. etc." London, 1842-1S62. H. and A. Adams. " The genera of the recent Mollusca," 3 vols. London. 1 858. H. Troschel. " Das Gebiss cler Schuecken." Berlin, 1856-1878. Woodward. " Manual of the Mollusca." 2nd ed., London, 1868. Fol. " Etudes sur le developpement des Mollusques." I. and II. C. Eabl, " Ueber die Entwickelung der Tellerschnecke/' Morphol. Jahrbuch. Tom. V. 1819. GASTROPODA. 31 lobes or drawn out into processes. The lower surface of the mantle usually serves as the roof of a cavity, which extends on to the dorsal surface and also on to the sides of the body. This cavity contains the respiratory organ, and opens to the exterior by an aperture or tubular prolongation at the mantle edge. The body cavity is developed on the dorsal surface of the foot,, usually in a visceral sac, which projects like a hernia. The visceral sac tapers gradually at its upper end, and is usually spirally twisted. The mantle and visceral sac are covered by the shell, which to a certain extent repeats the twistings of the latter and can usually completely receive and protect the head and foot when the animal is retracted. The shell is as a rule hard and calcareous, and possesses an internal nacreous layer similar to that of the mother-of-pearl layer of the Lamellibraiich shell. The shell is sometimes delicate, horny, and flexible, or it may have a gelatinous (Tiedmannia) or cartiliginous (Cyinlndiii) consistency. More rarely the shell is so small that it only covers the mantle cavity with the respiratory organs or lies hidden completely within the mantle (Limax, Pleurobranchiata). In other cax-s it is thrown off at an early stage, so that the adult beast is completely without a shell (Nudibranchiata}. The shell differs from that of the LctynelKbranchiata in being composed of a single piece; it is either flat and cup-shaped (Patdhi) and uncoiled, or it is spirally twisted in very different ways, from a flat disc-shaped to the long drawn-out turret-shaped spiral (fig. 509). In the first case it more resembles the embryonic shell, which lies as a delicate, cap-shaped covering 011 the mantle. The growth of the shell keeps pace with that of the animal, the additions being made to the edge of the shell, viz., to that part which lies on the edge of the mantle. In consequence of the inequality of this growth spiral .twistings arise, the diameter of which gradually and continuously increases. .Inasmuch as the unsymmetrical growth of the shell is due to the unequal growth of the body, the position of the openings of the unpaired organs (anus, sexual opening) to one side of the- great external lip of the shell is intelligible. The following parts may be distinguished in a spirally-twisted shell; (1) the apex, as the part of the shell at which the growth began and from which the spiral twistings started; (2) the opening FIG. 509. Section through the shell of II, /i.i- jifiMiitiu. 32 MOLLUSCA. or cqwture, which leads into the last and usually largest turn of the spiral ; its lip (peristoma), swollen in the adult animal, lies on the edge of the mantle. The spiral is twisted to the right or left round an axis which is directed from the apex to the aperture, and is indicated either by a solid spindle (columella) or a hollow canal. When the turns of the spiral are far removed from the axis, this canal may become an almost conical space with a wide opening (Solarium}. The turns are usually closely applied to one another ; more rarely they are separated (Scalaria pretiosct). According to the position of the columella, a columella edge or inner lip and an outer edge or outer lip of the aperture may be distinguished. The latter may be entire (kolostomatous}, or broken by an excavation which is often prolonged into a canal (sijjhonostomatous). In many Gastropods an operculum is added; this is usually placed on the hind end of the foot, and closes the shell aperture when the animal is retracted. Many terres- trial Gastropods secrete before the beginning of the winter sleep an operculum, which is thrown off again in the spring. The slimy integument consists of a superficial layer of cylindrical cells, which are frequently ciliated, and of a connective tissue dermis, which is inseparably connected with the dermal muscles. Cal- careous and pigment glands are placed in the integument ; they are especially numerous at the edge of the shell, where they .contribute to the growth and peculiar colouring of the shell. The shell, which is a cuticular structure, is secreted by the epithelium, like other cuticular structures ; it becomes hard when the calcareous salts which are mixed in the organic basis assume a hard and crystalline condition. The superficial layer of the shell often remains uncalcified as a thin delicate epidermis, while the inner surface is thickened by mother-of- pearl layers (secreted by surface of mantle). The connection of the animal to its shell is effected by a muscle, which on account, of its position on the spindle (columella}, is called the spindle muscle. This muscle arises from the dorsal part of the foot, and is attached to the spindle at the beginning of the last turn of the spiral. The nervous system presents a great resemblance to that of the Lamellibranchiata, but there are many differences in detail. In the Placophora, whose nervous system presents close relations to that of Neomenia and Chcetoderma, the ganglionic swellings are not marked (fig. 495). In all other cases the three typical groups of ganglia are present. * The cerebral ganglia (fig. 497, C y} are * The subjoined account of the nervous system is slightly modified from the Oerman. ED. GASTROPODA. 33 connected together by a transverse band, and each of them gives off a commissure to the pedal ganglia (P g), and a second commissure to a pair of visceral ganglia (Pig}. The latter ganglia, which are known as the commissural or pleura! ganglia, are also connected with the pedal ganglia (fig. 497). There are thus two nervous com- missures round the oesophagus the direct cerebro-pedal, and the cerebro-pedal by way of the pleural or commissural ganglia. The pleural ganglia may lie directly on the cerebral or pedal ganglia. Br- FIG. 510. Nervous system of ffaliotis (diagrammatic, after Spensel). C/, cerebral ganglion ; Pg, pedal ganglion; Pig, pleural ganglion (commissural ganglion); Ag, abdominal ganglion ; O and O', olfactory organs ; PC, pedal cord ; S and -$', lateral nerves ; Br, gills, b, Nervous system of Limnceits (aftei Lacaze-Duthiers). The pleural ganglia are part of the third typical group of ganglia, viz., the visceral group. They are connected with each other by a long commissure, the visceral commissure, which often extends into the hinder part of the body, and contains several ganglia in its course ; the latter ganglia, which also constitute part of the visceral group of ganglia, send off nerves to the sexual organs, kidney, heart, gills, olfactory organs, and mantle (fig. 497, G s b, V g, G sp; fig. 510 a, 0,0', A g; fig. 510 b, A g). The visceral ganglionic system of Gastropods is therefore broken VOL. ii. 3 34 MOLLUSCA. up into several ganglia, and is connected with the pedal (by the pleuro-pedal commissure) as well as with the cerebral. In the Prosobranchiata the position of the visceral commissure, with its ganglia, and nerves presents a peculiar condition (Chiasto- neura) ; the commissure from the right pleural ganglion passes over (dorsal to) the alimentary canal to the left side, and here forms a ganglion the supraintestinal ganglion (fig. 497, G s p] which supplies the left side, while the commissure from the left pleural ganglion passes under (ventral to) the alimentary canal to the right side, and there gives rise to a ganglion, the subintestinal ganglion, which supplies the right side (vide also fig. 510 a). The part of the visceral commissure, which connects the supra- and sub-intestinal ganglia often contains one or more ganglia (V g, A g}. More rarely this crossing is less clearly marked. The cerebral ganglia always give off a pair of nerves, one on each side of the oesophagus, to the buccal ganglia, which give off nerves to the mouth and alimentary canal (fig. 497, B g\ Sense organs. Eyes, auditory vesicles (otocysts), tactile and olfactory organs are present. The eyes are paired, and are usually placed at the end of stalks, which are as a rule fused with the tentacles. The eyes are largest and most developed in the Heteropoda* in which group they are fastened in special transparent capsules and admit of a movement of the bulb. The two otocysts are ciliated internally, and are, except in the Heteropoda, connected with the pedal ganglion (fig. 497, t), although their nerve always arises in the brain. Tactile organs are represented by the tentacles, the edges of the lips which are often folded, and lobe-like prolongations which are found here and there on the hend, mantle and foot. There are usually two tentacles ; t exceptionally they are absent (Pterotrachea, etc.). They consist of simple contractile prolongations of the body wall, which can sometimes (Pulinonata) be invaginated into the interior of the body. Certain peculiar hair cells, from which tufts of hairs project in the aquatic Molluscs, are to be looked upon as the seat of a special sensation. They are scattered over the whole surface of the body, and are especially aggregated upon the parts of the body * V. Hensen. " Ueber das Auge einiger Cephalophoren." Zeit.fiir miss. Zool., Tom. XV., 18H5. f W. Flernminor. " Untersuchungen liber Sinnesepithelien der Mollusken. Arch.fiir. -milt. Anctomle, Tom. VI., 1870. GASTROPODA. 35 serving for the tactile sensation. The antenna? of the terrestrial Gastropods possess on their end-plates a great number of fine sense- cells (club-shaped cells with rods, Flernnring), which are placed between specially-modified epithelial cells, and probably function as olfactory organs. Recently an organ, which was supposed to be a rudi- mentary gill and is innervated from the supraintestinal ganglion, *P \Ir n FIG. 511. Anatomy of Helix pomatia (after Cuvier). The mantle cavity is opened on the left side, and the mantle is turned over to the right. The body cavity has been opened and the viscera are unravelled. Cg, cerebral ganglion ; Sp, salivary gland ; .!/, stomach; D, intestine ; L, liver ; A, anus ; N, kidney ; At, auricle ; C, ventricle ; PI, lung ; Zd, hermaphrodite gland, invested by the lobes of the liver ; Ed, albumen gland ; P*-, prostate ; Ut, uterus ; Us, receptaculum seminis ; Dr, finger-shaped glands ; Ps, dart sac; P, penis ; Fl, flagellum; Mr, retractor muscle; Sp, spindle muscle. has been recognised as a sense organ and explained as an olfactory * organ. In the Zeugobranchiata (Fissurella, Hatiotis), two such organs are present, one on the right and the other 011 the left side, and are indicated by a considerable ganglion. The digestive organs rarely have a straight course ; they are * J. \V. Spengrel, " Die Geruchsorgane und das Nervensystem der ilollusken." Zeit. fur. miss. Zool., Torn. XXXV. MOLLUSCA. usually much coiled, and as a rule bend forwards to open in front on the right side in -the mantle cavity. The anus, however, is some- times on the dorsal surface behind. Many of the higher Gastropoda possess an invaginable proboscis, the invagination beginning at the base ; others possess one which is retractile from the point. The mouth is bounded by lips, and leads into a buccal cavity armed with hard masticating structures, and receiving the ducts of two salivary glands. The buccal cavity leads into the oesophagus, which is followed by a dilated stomach, usually provided with a caecal appendage. The stomach opens into an intestine, which is usually long and much coiled, and surrounded by a very large, multi-lobed liver. The liver occupies nearly all the upper part (upper coils) of the visceral sac, and pours its secretion into the intestine and also into the so-called stomach (fig. 511). The arrangement of the digestive canal and of the liver presents in details many essential modifications ; one of the most remarkable is that offered by the intestine with its hepatic ca?ca of the Phlebenterata (fig. 512). The terminal portion of the intestine is distinguished by its size, and may be called the rectum. Of, The armature of the buccal cavity consists partly of jaws placed on the upper wall, partly of the so-called lingual ribbon (radu- la). placed on a tongue-like pro- FlCT . 513 ._Longitudmai section through the jection of the ventral surface of buccal mass of JfeKa (after W.Keferstein). ' . , . O, mouth; M h, buccal cavity ; M, muscles; tlie DUCCal Cavity. ^ j-a^ig, . Zn, lingual cartilage ; Oe, The jaws consist either of a single oesophagus; i'f, jaws; z, sheath of curved horny plate, placed close behind the edge of the lip, or of two lateral pieces of very different form, between which, in some Pulmonatee, there is an unpaired piece. There are no lower jaws ; but on the floor of the buccal FIG. 512. Alimentary canal of JEo7is papillosa (after Hancock). Bm, buccal mass ; Oe, oesophagus; M, stomach, L, liver sacs, which enter the dorsal appendages ; A, anus. MJi GASTROPODA. 37 cavity there is a ridge, partly muscular and partly cartilaginous, which, from its resemblance to the tongue of the Yertebrata. has received the same name (fig. 513). The surface of this tongue is covered by a tough membrane, known as the lingual ribbon or ,-<> the mantle cavity serves as the respiratory cavity, but it differs from the branchial cavity by containing air, and possessing, instead of a gill, a rich network of blood-spaces and vessels on the inner surface of its roof. Both branchial and' pulmonary cavities communicate by a long slit along the mantle edge or by a small round aperture, capable of being closed, with the external medium. Frequently, however, the edge of the mantle is prolonged into a long respiratory tube of variable length, which is analogous to the siphon of the Lamellibranchiata. This siphon corresponds, as a rule, to a notch or canal of the shell (vide p. 32). N FIG. 516. Anatomy of Cassis cornufa (after Quoy)). -ff, proboscis; Si, siphon; Sr, gill; jy/f, olfactory organ (formerly regarded as a rudimentary gill) ; Spd, salivary gland ; -ZV, kidney ; P, penis. The structure of the respiratory organs has become of importance for the classification of the larger groups. According to the position of the respiratory organs, with regard to the heart and its auricle, two great divisions can, as Milne Edwards has pointed out, be established: (1) the Opist/wbranc/iiata, in which the auricle and gills are placed behind the ventricle ; (2) the Prosobranchiata, in which the auricle, with the branchial vein entering from the front, lies in front of the ventricle. As far as this character is concerned, the* Heteropoda and most Pulmonata are allied to the latter group ; but the Pulmonata, in many features of their organization and in their hermaphroditism, stand closer to the Opistliobran.clii.aia. The kidney (fig. 516) is the most important excretory organ of 40 MOLLUSCA. the Cephalopkura. It corresponds in position and structure to the organ of Bojanus of Lamellibranchs. It is, however, usually un- paired, and lies near the heart as an elongated triangular sac, with spongy (rarely smooth) walls of a yellowish brown colour. The secretion of the gland consists mainly of hard concrements, which arise in the lining cells, and consist of uric acid, calcareous and ammoniacal salts. It opens near the anus into the mantle cavity, either immediately by a slit capable of being closed, or by a special excretory duct running with the rectum. The Gastropoda generally possess, in the roof of the respiratory cavity, a mucous gland, which often pours out an enormous quantity of its secretion through the mantle orifice. The purple gland (Purpura, Murex) lies in the roof of the mantle cavity, near the rectum. It is a long, whitish-yellow glandular mass, the colourless secretion of which, according to the investigations of Lacaze-Duthier, quickly acquires, under the influence of sunlight, a red or violet colour. The secretion of this gland was known to the ancients, and prized by them on account of its permanence. The coloured fluid, which is excreted from pores of the skin of many Opisthobraiichs, e.g., Aplysia, must not be confounded with the genuine purple. Another gland, whose function is not accurately known, is the pedal gland of Limax and Arion. It extends through the whole length of the foot, and consists of unicellular glands, the delicate ducts of which open into the band-shaped main duct. The latter opens to the exterior between the foot and the head. In many naked Pulmonates (Arion) there is, in addition, a gland at the point of the tail, which secretes considerable quantities of mucus with great rapidity. Generative Organs. Some of the Gastropoda are dioecious, some are hermaphrodite. The Pulmonata and Opisthobranchiata are her- maphrodite ; the Prosobranchiata are dioecious. Almost all Gastro- pods lay eggs, usually in strings. Only a few bear living young, which have developed from the fertilised eggs in the uterus. The female organs consist of an ovary, oviduct, albumen gland, uterus (dilated and glandular part of the oviduct), vagina, and receptaculum seminis. The male organs consist of a testis, a vas deferens with seminal vesicle, a ductus ejaculatorius, and external copulatory organs. The hermaphrodite forms are distinguished by the close connection of the male and female generative glands and their ducts ; for not only are the latter in direct communication with each other, GASTROPODA. 41 but the ovaries and testes are, with a few exceptions (Actceon, Janus), united in one hermaphrodite gland, which is usually imbedded among the lobes of the liver. The ova and spermatozoa arise either in different but adjacent follicles of the lobed or branched hermaphrodite gland (Nudibranchiata), the ovarian follicles being placed peripherally to the semeniferous follicles (^Eolis) or the epithelium of the same follicle produces in one part ova, in another part spermatozoa, not however usually at the same time, the maturity of the male element preceding that of the female (terrestrial snails). The efferent duct of the female is nearly always provided with a separated albumen gland, and a re- ceptaculum seminis (fig. 51 7). In the Helicidce the vagina bears two tufts of finger- shaped glandular tubes and a peculiar sac the dart-sac which produces in its interior a dart- like calcareous rod. The latter - - the so-called love-dart is attached to a papilla at the base of the sac ; it is protruded during copulation, and seems to play the part of a stimulating organ. It is. usually broken during use and is replaced Fia. 517. Sexual organs of the Eoman Snail (Helix poinatia). Zd, hermaphrodite gland; Zg, its duct ; EJ, albumen gland ; Od, oviduct and seminal groove ; Vd, vas deferens ; P, protrusible penis ; Fl, flagellum ; Rs, receptaculum seminis ; D, finger-shaped gland ; Z, Spiculum arnoris ; Go, common genital opening. (After Baasen). later by a new one. The male generative opening is always in connection with a protrusible penis, and usually opens with the female into a common lateral cloaca. The structure of the generative organs in the dioacious Gastropods resembles that of the hermaphrodite forms. A receptaculum seminis and an albumen gland may be present in the female (Paludina). The ovaries and testes lie hidden among the lobes of the liver, and the sexual orifices are placed laterally. The males almost always possess a projecting penis, which is either perforated by the terminal part of the vas deferens (Buccinuni) or traversed by a furrow, at the base of which the sexual opening is placed. When 42 5IOLLUSCA. the penis is remote from the sexual opening, a ciliated furrow is present, which conducts the spermatozoa from the opening to the penis (Murex, Dolium, Strombus}. The embryonic* development begins with an unequal segmenta- tion leading to the formation of a blastula or gastrula. Later the embryo acquires a ciliated velum, the first rudiment of the shell, foot, and primitive kidney, and rotates in the fluid albumen of the egg by the vibrations of the cilia. The free development is either direct, the just-hatched anima possessing (excepting for the rudiments of larval organs) the form and organization of the adult (Pulmonatrt), or it takes place by a metamorphosis. Almost all marine Gastropoda develop by meta- Ms FIG. 518. Some stages in the embryonic development of Planorli* (after C. Eabl). a, optical section through a segmenting ovum (24 segments). Sk, polar bodies; Fh, segmentation cavity, b, stage with four mesoderm cells, viewed from the vegetative (lower) pole. Ms, mesoderm cells ; En, endoderm ; EC, ectoderm, c, Oblique optical longitudinal section through the stage with four mesoderm cells, d, Older embryo, in wh'ich the shell gland has shifted to the right. Sdr, shell gland ; S, shell ; O, mouth ; D, alimentary canal ; R, commencing radula ; Sp, apical plate (thickening of praeoral lobe) ; Oc, eyes ; Ot, otolith ; N, primitive kidney ; Ve, velum. rnorphosis, and the larvte possess two large ciliated sails (velum), which serve as locomotory organs in place of the still rudimentary foot. The shell, which is already present on the dorsal surface, is still small and flat with hardly any trace of the spiral twisting, and can usually be closed by an operculum which is attached to the foot. Very often a change of shell is effected, the old embryonic shell being thrown oflf and a new one formed in its place. * Cf. especially. N. Bobretzky, " Studien liber die embryonale Entwickelung der Gastropoden." Archir fur mik. Anat., Tom XIII.. 1876. C. Kabl, ' Ueber die Jiutwickeluug der TellurscLnecke." Moruh. Juhrb. !(,. V. Also Fol, Biitsehli, R. Lanktster, etx'. GASTROPODA PROSOBRANCHIATA. 43 By far the majority of Gastropoda are marine ; the Basommato- pliora and some Prosobranchiata (Paludina, Valvata, M'-lnnm, X i' retina, etc.) inhabit fresh-water. Many Littorina, CV/-/Y///". Mi'lania, etc., live in brackish water. The Cyclostomidce, and the Stylommotophora among the Pulmonates, are terrestrial. Further, many branchiate Gastropods are able to live for some time out of water in dry places; in such circumstances they are withdrawn into their shells, the opening of which is closed by the operculum. Almost all move by creeping ; some, however, as Strombus, jump ; others, as Oliva and Ancillaria, swim excellently by the aid of the lobes of their foot. Some marine forms, as Magilus-, Vermetus, etc., are fixed by their shells; a few only are parasitic, as Ktylifer on sea-urchins and starfishes, Entoconcha mirabilis in Synapta. The method of nutrition differs as much as the habitat. Many, especially the Siphonostomata, are voracious predatory animals, and prey on living animals; some branchiate Gastropods, as Hurex and ^Yuftca, with this object bore into the shells of Molluscs; several (tifrombus, Buctinwm) prefer dead animals. An equally large number, viz., almost all Pulmonates and holostoniatous branchiate Gastropods, feed on plants. Order 1. PROSOBRANCHIATA.* Dioecious branchiate Gastropods with shell, and with gills in front of the heart. Behind the usually distinctly separated head lies the respiratory (mantle) cavity, into which the rectum, kidney, and oviduct open. In rare cases two gills are present, as a rule the right gill is absent. The branchial veins enter the heart from the front. Cerebral, pedal,, pleural and visceral ganglia are present. The males are, as a rule, more slender, and are easily recognized by the large penis placed on the right side of the anterior part of the body. In the generative organs, the accessory glands are usually absent. The eggs are sur- rounded by albumen and laid in capsules, which are frequently fixed to foreign objects ; more rarely they are attached to the foot and carried about (Janthina). * Fr. Leydig, " Ueber Paludina vivipara." Zdt. fur.wiss. Zool., Tom II., 1850. E. Clapar&de, "Anatomic und Entvvickelungsgeschichte dcr Neritina flu- viatilis." Miillrr's Archil-., 1S.~>7 '. H. Lacaze-Duthiers, " M&noire sur le systeme nerv.de 1'Haliotideet Memoire sur la Poupre.'' Ann. (lets tie. A Four nerve trunks pass off from the double oesophageal ring, an upper lateral pair, the pallial nerves, and a ventral pair, the pedal nerves, which latter are connected by transverse commissures. Pedal and visceral ganglia are not separated as ganglionic swellings from the nerve stems. Buccal ganglia, on the contrary, are present. The alimentary canal begins with the mouth, which is placed on a roundish lobe ; it is much coiled, and extends through the whole length of the body, to open by the anus at the hind end. As in * A. Th. Middendorff, " Beitrage zu einer Mnlaoozoologica rossica. 1. Beschreibung und Anatomie neuer oder fur Kussland neuer Clntonen." Mem. Acad. Jii/j).,St. Pcterxlnrg, 1848. S. Loven, " Ueber die Entwickelung der Gattung Chiton." ArcJiiv fur Natwrgescli., 3856. B. Haller, " Die Organisation der Chitonen der Adria." Arleiten a. d. Ziwl lust, in Wicn., Tom IV., 1882. Vide also Tullberg's and Graff's works on Neomenia and Cli(etoderina. GASTROPODA PROSOBRANCHIATA. 45 most Cephalophora (Odontophora) a large muscular mass, the tongue, covered by a hard rhitinous plate, the radula, is found upon the floor of the buccal cavity. The heart, on the other hand, more nearly resembles in structure and position that of the Lameilibranchs, in that it consists of two auricles opening into a median ventricle, which lies over the rectum. The kidneys are paired, and open right and left in the mantle furrow ; [they also open, as in other Molluscs, into the pericardium]. The Placophora are dioecious. Testes and ovaries are simple unpaired glands, which lie im- mediately over the liver and alimentary canal ; their ducts open 011 each side into the mantle cavity in front of the kidneys. The development of the egg begins with an equal segmentation ; subsequently the segments of one-half of the ovum divide le.ss rapidly. This half is invaginated, so that a gastrula arises. The larva which leaves the egg membranes resembles Loven's worm larva in the possession of two eye-spots and a ciliated ring, and develops without a larval shell. Fam. Chitonidae. In place of the shell, eight calcareous pieces are present, which are so arranged that the hinder" edge of one shell piece overlaps the anterior edge of the next following piece. Chiton f/inamosus L., Mediterranean. Cnjptoclilton Stellcri, Midd. Sub-order 2. Cyclobranchiata. Prosobranchiata with flat plate- shaped shell and foliaceous gills, w T hich are arranged in a closed circle under the edge of the mantle round the broad root of the foot. The buccal lobes are little developed. The foot is powerful, and usually flat and broad. The lingual armature, like that of the Placophora, is formed of toothed horny plates, hence the name Docoylossa of Troschel. A cervical gill placed on the right side of the neck is sometimes present (Lottia}. Two kidneys are present. External copulatory organs absent. They feed on plants. Fam. Patellidae. (Limpets). The shell is bowl-shaped, and consists of a single piece, to which the animal is attached by a horse-shoe-shaped muscle. Head with two tentacles, at the swollen base of which are placed the eyes. Tongue extraordinarily long and spirally coiled. The radula is without the median plates, while the intermediate and marginal plates are raised to hooks, and smaller lateral plates appear. Patella L. The apex of the shell is slightly eccentric, and hardly inclined to the front. P. ccendca L., P. tareittina Lain., P. scut/'ll/iris Lam., Adriatic and Mediterranean. Nact-Ua Schurn. Circle of gills broken on the head ; the apex of the pellucid shell, shining internally like mother-of-pearl, bent forwards. N. pellucid a L. Sub-order 3. Zeugobranchiata. Gills bipennate, paired and sym- 46 MOLLUSCA. metrical. Anterior border of mantle deeply cleft, in correspondence with which the shell is perforated or provided with a slit on its outer lip. Kidneys paired, that of the left side rudimentary. Auricle paired; ventricle perforated by rectum. Tongue rhipidoglossal, in that the complicated radula bears in each transverse row, in addition to the median and intermediate plates, a great number of lateral plates which are arranged in a fan-like manner and the upper edges of which are bent into the form of hooks. They are all herbivorous, and are without a retractile proboscis or siphonal tube at the shell aperture. They often possess filiform appendages on the foot. A penis is not developed. Fam. Fissurellidae. Shell cup- or cap-shaped, with an aperture at the apex or an anterior marginal excavation for the entrance of water into the mantle cavity, which contains two symmetrical gills. Mantle edge fringed. The animals resemble the PatdUdte, are provided with tentacles and a large foot. Fissurella, Brug. Shell with longish aperture through the apex, which is placed in front of the middle. F. cfrceca L., Adriatic and Mediterranean. Emargin uln Lam. An excavation at the anterior edge of the deep bowl-shaped shell. E. elvit- !intii Costa, Adriatic and Mediterranean. Scutu* Montf. (Parmoplior-us Blainv.) Australia. FIG. 520. Conus textilig (regne animal). R, proboscis; Fam. Haliotidae. Sea-ears, -Si, siphon ; F, tentacle ; 0, eye. ormers. Shell flat, ear- shaped, internal mother-of- pearl lustre, with a row of holes on the left side. The mantle cavity is on the left side and contains two gills, of which the right is the smaller. Foot fringed, with a broad pedal surface. Head with two long tentacles and short stalked eyes. Hal lot is L. Spiral of shell small and flat. Foot projecting slightly over the shell. //. tubercvlata L., Adriatic and Mediterranean. Sub-order 4. Ctenobranchiata (Anisobranchiata, e.p.). With lar<*e cervical gill of pectinate form on the left side with small olfactory organ (so-called rudimentary gill, fig. 516, J\ T k). A spiral shell is very generally present (fig. 520). The male possesses a penis on the right side. Most are carnivorous and possess a protrusible proboscis. 1. Rhipidoglossa. Each transverse row of the radula with numerous lateral plates arranged in a fan-like manner (fig. 514, &). Fam. Trochidae, (Top shells). With conical shell and spiral oper- culum. Foot prolonged into cirri and lobes. Eyes on short stalks. Turbo L. With roundish (convex) windings, round aperture, and buccal edge somewhat cut off. T. rvgosuis Lam. Trochus L. With angular windings, buccal ecl^e GASTROPODA PROSOBRANCIIIATA. 47 divided above, and outer lip thin. Tr. varlux L., Adriatic and Mediter- ranean. Fain. Neritidse (Neritacea). With thick, hemispherical shell and opcrculum. l-.vs stalked, behind the two long tentacles. Proboscis slmrt. cift.'ii Foot large, triangular. Heart perforated by rectum, with two auricles. L. Shell thick, hemispherical, spiral lateral ; aperture semi-circular. N. Reel.; -V. (.Veriti/t/i') Jtuclatilis L. ; Nuricella Lam.; JV. clliptica Lam., Pacific Ocean. 2. Ptenoglossa. Without siphon, aperture of shell entire, without excavation or canal. Tongue armed with rows of numerous small hooks and without the median plates. Fam. Janthinidbe. Junthina bicolor Menke, Mediterranean. Fani. Solariidse. (Wentle-traps). Scalarla cunt inn nix Lam., 8e. pri'tinxn Larn., East Indies. Solarium perspectiwm Phil., Mediterranean. 3. Rhachiglossa. With long proboscis invaginable from the base. Tongue long and narrow with at most three plates in each transverse row, a toothed median plate and an intermediate plate on each side, which are often reduced to mere hooks, and may be absent. All possess a siphon and are predatory. Fain. Volutidae (Faltenschnecken). Valuta v,i/,eta L. Fam. Tritoniidae, (Tritonshorner). Ti-itoiilum varieyatum Brug. ; RaneUa giijitntca Lam. Fam. Doliidae. Cassis cormtta Lam. ; Dolium galca L.. Mediterranean. Fam. Strombidae (Alata) (Fliigelschnecken). Stromlm* Isabella Lam. ; Pterooeras lam^'ts Lam. ; lioKtellaria rectirostris Lam. Fam. Naticidae. Natica ampiillaria, Lam.; Slgarctus lial'wto'uli'us L. , Atlantic. Farn. Capulidae, (Mlitzenschnecken). Capulus lumgaricus L., Adriatic ; Calyptrcea rugosa Desh. Fam. Ampullariadae, (Doppelathmer). With branchial and pulmonary cavity. In rivers of hot countries. Ampullaria celebensis Quoy. ; ^1. polita Desh. Order 2. HETEROPODA.* Pelagic Gastropoda with Jin-like foot, large projecting head and highly-developed moveable eyes. Divecious. The body (fig. 521) of the Heteropoda is usually cylindrical and elongated and prolonged into a proboscis-like projecting head, which carries large well-developed eyes and tentacles, and encloses a power- fully-armed protrusible tongue (fig. 514 a). The main peculiarity of the body consists in the formation of the foot, the anterior and middle portion (pro- and mesopodiwm) of which is modified to the form of a leaf-shaped fin, often provided with a sucker (fig. 521 S) ; while the hinder section (inetapodiuwi) is considerably elongated and extended far backwards, and seems to form the caudal continuation of the body. The visceral sac is either spirally twisted, and en- closed by a mantle and spiral shell (Atlanta], or has the form of a saccular and projecting mass, which is placed at the limit of the hinder region of the foot, and is likewise covered by the mantle and a hat-shaped shell (Carinaria, fig. 521) ; or finally the visceral sac is reduced to a very small, scarcely -projecting nucleus, which is covered on the front side by a membrane with a metallic lustre and is completely without a shell. The nervous system is more highly developed than that of any other Gastropod. The two large eyes are placed near the tentacles in special capsules, in which they are moved by several muscles. The * Souleyet. " Heteropodes. Yoyage autour du monde execute" pendant les annees 1836 et 1837 sur la corvette la Bonite, etc," Tom II. Paris, 1852. R. Leuckart. " Zoologische Untersuchungeu," Heft III. Giessen, 1854. C. Gegenbaur. " Untersuchungen iiber Pteropoden und Heteropoden." Leipzig. 1854. H. Fol. " Sur le Developpement des Heteropodes." Arch, de Zool. experim. Tom V., 1876. GASTROPODA HETEROPODA. 49 large auditory vesicles each receive a long auditory nerve from the cerebral ganglion, and are characterised not only by the remarkable vibrations of the long tufted cilia of their epithelium, but also by the arrangement of the nerve cells (group of hair cells of the mai-n/d acustica round a large central cell, fig. 83). In addition numerous peculiar nerve-endings in the skin, which appear to serve the tactile sensation, and the so-called ciliated organ on the anterior side of the visceral sac, are present. The latter has the form of a ciliated pit, under which is placed the gaiiglionic swelling of a nerve which Qc Te Bm Fig. 521. Male of Carinaria mediterranea (after Gegenbaur). P, foot ; S, sucker ; O, mouth; Bm, buccal mass; M, stomach; Sp, salivary gland; L, liver; A, anus ; CQ-, cerebral ganglion ; 2V, tentacles ; Oc, eye ; Of, auditory vesicle ; BG, buccal ganglion ; Pg, pedal ganglion; Mg, mantle ganglion; N, kidney; Si-, gills; At, auricle ; TV, ventricle ; As, anterior aorta ; Z, posterior branch of same ; T, testis ; Vd, vas deferens ; \\'p, ciliated furrow ; Pe, penis ; F, flagellum with gland. arises in the visceral ganglion; it has the value of an olfactory organ. The males are distinguished by the possession of a large copulatory organ, which projects freely on the right side of the body : the males of Pterotrachea also possess a sucker on the foot. In All'.intn an 1 Carinaria the sucker is present in both sexes. The te-tes and ovaries fill the posterior part of the visceral sac and are partially imbedded in the liver. The ducts, viz., vas deferens and oviduct, open on the right side of the body ; the former at some distance from the organ of copulation, to which the sperm is conducted from the sexual opening in a ciliated furrow. The copulatory organ consi-ts VOL. II. 4 50 MOLLUSCA. of two parts placed side by side, (1) the penis with the continuation of the ciliated groove ; and (2) the gland rod which encloses a longish gland. The oviduct (fig. 90) is more complicated, inasmuch as a large albumen gland and a receptaculum seminis open into it; its dilated terminal part acts as a vagina. The Heteropoda are exclusively pelagic animals, and they are often found in great numbers in the warmer seas. They are somewhat clumsy in their movements, which are effected with the ventral surface uppermost by oscillations of the whole body and the fin. They are all carnivorous. When the tongue is protruded, the lateral teeth fly apart from one another like the limbs of forceps, and when retracted they again fall together. By means of these prehensile movements small marine animals are seized and drawn into the mouth. Fam. Pterotracheidse. Oirinnrla mcditerranea Lam., PterotraeJiea eoronata Forsk. Mediterranean. Fain. Atlantidae. Atlanta Peronii Less., Mediterranean. Al FIG. 522. Arion empiricoriim (regne animal). Al, respiratory aperture. Order 3. PULMONATA.* Terrestrial and fresh-water Gastropods with lung which is placed in front of the heart. Hermaphrodite. The roof of the mantle cavity, as in the Cyclostomidce, is provided with a network of vessels for aerial respiration. The mantle (pul- monary) cavity opens to the exterior on the right side by a respiratory aperture (fig. 522.) The mantle cavity of the young of the fresh- water Pulmoiiates is at first filled with water, and only later with air. Some species of Planorbis and Limnceus retain, during the whole time of their life, the ability to breathe both in air and water (some Limnaius, with lungs full of water, have been dredged up at * L. Pfeiffer. ' Monographia Heliceorum viventium." Leipzig, 1848-1869; acti ' : Monographia Auriculaceorum viventium." Cassel, 1856. A. Rossmassler, " Iconographie der Land-imd Susswassermolhisken Europas." Leipzig, 1835-1859. Ferussac et Deshaj'es. " Histoire naturelle generate et particuliere des Moliusques terrestres et fluviatiles." Paris, 1829-1851. GASTROPODA PULMONATA. 51 considerable depths in Lake Constance). The anus and renal open- ing are placed near the respiratory aperture, sometimes in tin- respiratory cavity itself. The generative organs open some way in front, but on the same side. In the forms with a left-handed spiral, the respiratory orifice, anus and generative opening are on the left side. Some Pulmonates are naked, or possess only rudiments of the shell in the dorsal integument; others carry a relatively thin and u.Mially right-handed shell. PJtijsa, Pkmorbis, and Clausilin alone present a left-handed spiral. A true operculum is absent. On the other hand, many forms secrete temporarily a winter operculum. While the Pulmonates (with some exceptions) resemble the Proso- branchs in the position of the heart behind the respiratory organs, in the arrangement of other organs, e.g., the nervous system, they more resemble the Opisthobranchs. The dentition consists of an unpaired, horn}", and usually longitudinally-ribbed upper jaw (which, however, may be absent) and of a radula, which is covered with a great number of toothed plates in longitudinal and trans- verse rows. All are hermaphrodite. A few, e.g., species of Clu, buccal mass ; >S/' from the dorsal side (after Hunter) Br, gills ; C, ventricle ; An' and Ao", the anterior and posterior aorta ; V, latei-al vein ; Vc', anterior vena cava ; Vc" , posterior vena cava ; N, renal append- ages of the veins ; Vbr, advehent branchial vessels (branchial arteries) ; Kit, branchial heart; Ap, appendage of the same ; At, At', auricles receiving the revehent branchial vessels (branchial veins). 64 MOLLUSCA. fis (k abdomen. They open into the mantle cavity, each through the apex of a papilla. The anterior walls of the sacs are pushed inwards by csecal appendages of the vense cav* (branchial arteries), so as to give rise to a number of racemose lobules projecting into each renal sac (fig. 536). The renal sacs, as in other Molluscs, communicate with the body cavity, which in Sepia is largely developed and contains the heart, generative organs, etc., but in the Octopoda is reduced to a narrow tubular space (" water - vascular sys- tem " of Krohn) and only contains the sexual glands. An excretory organ very generally present is the ink- sac. It is a piriform sac, whose duct opens to the exterior with the anus, and empties an intensely black fluid, which sur- rounds the body of the animal as in a black cloud, and so protects it from the pursuit of larger marine animals. The Cephalopoda are dioecious. Males and females present external sexual differences which principally concern a particular arm. Accord- FIG. 537. Anatomy of the body of a female Sepia (after C. Grobben). Ov, ovary in its cavity (body cavity) which is laid open ; Od, oviduct ; Oe, opening of the same ; OdD, oviducal gland ; Nd, nidamental gland ; AD, accessory nidamental gland ; JV, kidney ; U, ureter ; Lk, canal of the body cavity (water canal); Kh, branchial heart ; Kha, pericardia! gland (appendage of branchial heart); K, gills; Af, anus ; tfst, stellate ganglion. ing to the discovery of Steenstrup, one of the arms in the male always becomes modified, hectocotylized as it is called, as an intromittent organ. The two sexes of Argonauta differ considerably, inasmuch as the small male has no shell. The sexual glands lie freely in the body cavity. Their products are dehisced into the body cavity, from which they are taken up and conveyed to the exterior by special ducts. The ovary is unpaired and racemose, and the oviduct is a double (Octopoda) or unpaired (usually left) duct opening into the mantle cavity ; it receives in its CEPHALOPODA. 65 course a round gland, and its terminal portion possesses glandular walls. In addition, the so-called nidamental glands (fig. 537) :m> present in the Decapoda and Xmitllus; they open into the mantle cavity near the generative opening and secrete a cementing substance which surrounds and unites together the eggs. The eggs are sur- rounded either singly (Ai-tnti(ta, Octopus) or in great number (N-ynVi) by capsules with long stalks, which are united together in racemose masses (so-called sea-grapes), and fastened to foreign objects in the sea. In other cases the eggs are aggregated in gela- tinous tubes (Loligo, Se- pioln). The male generative apparatu s presents a similar ar- rangement (fig. 538, a). The testis (2*) consists of an unpaired gland formed of long cylin- drical tubes. The duct of the testis is FIG. 53Sa. Male sexual organs of Sepin orhv;,i/;.< (after placed On the Duvernoy), modified from 0. Grobben. T, testis, with ^ a piece of peritoneum ; To, opening of the testis into the left Side and Fio body cavity; Vd, vas deferens; O, opening of the vas j s l onar co jl ec [ S per mat o- deferens into the body cavity ; Vs, vesieula seminalis ; phore of Sepia Pi; prostate; S/*, spermatophore reservoir ; Oe, sexual and COmpli - (after M. Ed opeQins ' cated. The wards) - following parts may be distinguished in it : ( 1 ) a much coiled vax deferens (Vd), which opens into the body cavity, (2) a long dilated vesieula seminalis (Vs) with two prostatie glands (Pr) opening into its terminal portion, (3) a spacious sac, known as Needham's sac, in which the spermatophores are formed, and which opens into the mantle cavity at the apex of a papilla placed on the left side. In copulation the large spermatophores (fig. 538, b) are introduced by means of the hectocotylised arm into the female sexual opening. In some Cephalopoda (Tremoctopus violaceus, PhUonexis Carence, and VOL. II. 6 G6 MOLLUSCA. Argonauta argo) the hectocotylised arm of the male appears as an individualized intromittent organ which is filled with spermatophores, then separates from the body of the male, moves about for a time independently, and finally conveys the semen into the mantle cavity of the female (fig. 539). The development" of the egg is introduced by a discoidal (partial) segmentation which takes place at the pointed pole of the egg. As in the bird's egg, the segmented portion of the ovum (formative yolk) gives rise to a germinal disc which in the subsequent growth is raised more and more from the lower part of the blastoderm which forms the yolk sac. Soon several projections appear on the embryonic rudiment (fig. 540) ; first in the centre of the germ a flattened ridge is formed around a cen- tral depression (M) which it soon grows over. This is the mantle [the depression is the so-called shell gland] ; on each side of it the two parts of the funnel appear (Tr), and between these and the mantle the gills (Br). Also laterally but ex- ternal to the folds of the funnel the first traces of the head ap- pear as two pairs of elongated lobes, of which the external an- terior pair bears the eyes. On the outer edge of the disc papilli- form structures are formed, the first rudiments of the arms. In the later growth of this absolutely symmetrical embryo the Cephalopod form becomes more and more apparent : the mantle projects considerably, and grows over the gills and two parts of the funnel, which fuse to form the definitive funnel. The cephalic lobes grow together between the mouth and funnel, and on their oral sides become more sharply constricted oft' from the yolk, which with a few exceptions persists for some time as a yolk sac (fig. 541). The Cephalopods are marine animals, some frequenting the coast and others the high seas. They feed on the flesh of other animals, FlG. 539. Male of Argouauta argo (after H. Miiller). He, hectocotylised arm. * Of. besides van Beneden and KSlliker; Ussow, " Zoologiseh-embryologische Untersuchungen." Archivfur Naturgesch., 1874. CEPHALOPODA. G7 especially Crustacea. Some of them attain a great size. The flesh is Br. ^- eaten, and the colouring matter of the ink-sac (sepia) and the 7r. / dorsal shell (os sepice] are used \^ \ by man. The remains of Cepha- lopods occur in all formations from the oldest Silurian and constitute important charac- teristic fossils (Belcmnites, Am- monites). Order 1. TETRABRANCHIATA.* Cephalopoda with four (/ills in the mantle cavity and nu- merous retractile Ds~ tentacles on the head, with split funnel and many- chambered shell. The append- ages of the head are peculiar. In place of the arms there are a num- ber of filiform tentacles round the mouth. In Nautilus there are on each side of the body (a) nineteen ex- ternal tentacles, of which the dorsal pair constitutes a kind of hood which can close the orifice of the shell ; (lj) two ocular tentacles on each side near the FIG. 541. Almsto ripe embryo of Sejiitt rifticinalis f r< mi thedorsal (an- terior) face (after Kolliker). J)s, yolk sac. FIG. 540. Embryonic development of Sepia offici. nails (after Kolliker). a, View of germinu disc from above, commencing embryo lying on the yolk. Br, gills ; Tr, folds of the funnel ; Oc, eye ; M, mantle. l>. Somewhat older stage, seen from the front. D, yolk ; Kl', anterior ; A"/", posterior cephalic lobe ; 0, mouth, c, later stage from the side. 1-4, first rudiments of the arms, d, older stage from the front. 5, fifth pair of arms, e, Still later stage in lateral view The halves of the funnel have united. * Van der Hoeven, " Beitrage zur Kenntniss von Nautilus " (in Dutch), Amsterdam, 1856. W. Keferstein in Bronn, Classen mul Ordnungen des Thienvii'l's. Dritter Band. Cephalopoda. 18< : 5. G8 MOLLUSCA. eye and (c) twelve internal tentacles, the four ventral of which on the left side are in the male modified to form the spadix, an organ analogous to the hectocotylised arm. Finally, in the female there are on each side, within the latter, fourteen or fifteen ventrally- placed labial tentacles. (Fig. 542.) The cephalic cartilage, instead of forming a complete ring, con- sists of two horse-shoe-shaped limbs on which the central parts of the nervous system lie. The eyes are stalked, and are without a lens or other refractile media. The funnel has the form of a lamina rolled upon itself, but the edges are free and not fused. There is no ink-sac. The branchiae are four in number as are also the branchial vessels and the kidneys. K FIG. 542. Nvut,ilus(regne aniirml). T, tentacles ; P, pupil of the eye ; Ek, terminal chamber ; Tr, funnel ; A", chambers of the shell ; S, siphon ; Ma, mantle ; M, muscle. The hinder part of the thick external shell of the Tetrabranchiata is divided by cross partitions into numerous chambers, which are filled with ail 1 and are traversed by a siphon. The shell consists of an external, frequently coloured calcareous layer, and an internal mother-of-pearl layer. The similar structure of many fossil shells allows us to infer a similar organisation for their unknown inhab'- tants. The position and structure of the siphon, as well as the form of the septa, and the lines of fusion of the latter with the shell are important characters for the classification of the fossil Tetra- branchiata. The small number of living species of the genus Nautilus are found in the Indian and Pacific Oceans. ( Kl'HALOPODA. <>D Fam. Nautilidae. The septa are simply bent and concave towards the anterior chambers. Line of suture simple, with a few large wavy curves or a lateral lobe. Siphon usually central ; shell orifice simple. Ortltnrarfix, shell straight. 0. regularise. Schl., calcareous strata of the North Germ?*! plain. Nautilus, shell coiled. N. pomj>ilii/.-< L., Indian Ocean. Fam. Ammonitidse. The septa much folded at the sides, always with lobe on the outer side, in the middle usually convex forwards. Siphon on the outer side. Contains only fossil forms. Gonintites ri'tnn-xiix v. Iueh., Cn-ti- tites nodosus Bosc., Ammonite* ciqn-iforniis v. Schl. Order 2. DIBRANCHIATA.* Cephalopoda ivith two gills in the mantle cavity, eight arms bearing suckers or hooks, complete f'unnel and ink-sac. The Dibranchiata possess round the mouth eight arms provided FIG. 543. Ai'i/Oiiauta argo (female), swimming. with suckers or hooks ; in the Decapoda there are, in addition, two long tentacles placed between the ventral arms and the mouth. The cephalic cartilage constitutes a completely closed ring surrounding the central parts of the nervous system ; its slightly arched lateral parts serve for the support of the sessile eyes. There are only two gills in the mantle cavity and the same number of branchial vessels and kidneys. The funnel is closed. An ink-sac is usually present. The shell is in many forms completely absent ; in others it is reduced to a horny or calcareous dorsal lamella. A spirally-coiled shell is * Chief works: Ferussac et d'Orbigny I.e., also Verany I.e. 70 MOLLUSCA. rarely present. In the female Argonauta (fig. 543) there is a single- chambered spiral shell with thin walls ; in Spirula (fig. 544) there is a niultilocular spiral shell, the chambers of which are traversed by a siphon. Sub-order 1. Decapoda. In addition to the eight arms, there are two long tentacles between the third and fourth pairs of arms (ventral). The suckers are stalked and provided with a horny rim. The eyes are without a sphincter-like lid. The mantle bears two lateral fins, and at the mantle edge a well-developed apparatus for closing the mantle opening. An internal shell is present. Fam. Spirulidae. Sjnnila Pcronii Lam., Pacific Ocean. Fam. Belemnitidae. JMcmnift-s digitalis Voltz, Upper Lias. Fam. Myopsidae. With closed cornea and covered lens. Sepia officinal is Lam., Loligo vulgaris Lam., Mediterranean (fig. 531). Si'jiioln vvl(j(irix Grant., Mediterranean, Russia niurroxoma Fer. d'Orb., Mediterranean, Fam. Oigopsidae. Eyes with widely-opened cornea, so that the crystalline lens is exposed and bathed by the sea-water. Onychoteuthis Lh-htenstei-m Fer., Ommastrephes t octants d'Orb. Sub-order 2. Octopoda. The two tentacles are not Peronii present. The eight arms bear sessile suckers without a horny ring, and are connected at their base by a membrane. Eyes relatively small, with sphincter-like lid. The short, rounded body is without the internal shell, and usually also the fin-like appendages. Mantle without cartilaginous apparatus for closing mantle opening, and attached to the head by a broad band. Funnel without valve ; oviduct paired FIG. 544. Fam. Octopodae (fig. 530). Octopus vuljaris Lam., 0. man-opus (fig. 535), jLlrdoni' Hiunchatti Lam. Fam. Philonexidae. Plnloni>.ris Carence Ver., Tremoctopu-x rivlacevs Dell. Ch., Argonauta argo L. The small male is without a shell (fig. 539). The large female possesses fin-like expansions of the dorsal arms, and bears a boat- shaped, delicate shell, round the sides of which the arm-fins are spread (fig. 543). BRYOZOA. 71 CHAPTER II. MOLLUSCOIDEA. Attached bilateral unsegmented animals, witli crown of ciliated tentacles or spirally rolled buccal arms; enclosed by a cell or It/ biralve shell, the valves of which are dorsal and ventral: with a sim2)le ganglion or u'ith several ganglia connected by a pharyngeal ring. The two groups, Bryozoa and JBrachiopoda, which are included in the Molluscoidea were formerly placed amongst the Molluscs, to which they do indeed present affinities. With the increase in our knowledge of their developmental history, it appears more and more probable, not only that the two groups are descended from an ances- tral form common to them and the Annelids, but also that in spite of the considerable differences between them in the adult state, they are in reality closely related, a supposition which agrees with the great resemblance of their larvae. Should this view of the close relationship of the Brachiopoda, which are always solitary, with the Bryozoa, which almost always form colonies, turn out to be well grounded, then the tentacular crown and the simple ganglion of the latter would be homologous with the spiral arrn-s and subce.so- phageal ganglion of the former respectively. Class 1.- BRYOZOA * == POLYZOA. Small animals usually united together to form colonies ; with ciliated tentacular crown, horse-shoe-shaped alimentary canal am! simple ganglion. The Bryozoa owe their name to the moss-like dendritic appearance of their colonies, on which the small individual zooids are arranged 7 o in a regular manner. The colonies may, however, have a foliaceous or polyparium-like form, or they may form crusts on the surface of foreign objects. Solitary Bryozoa are rare exceptions (Loxosoma). As a rule the colonies possess a horny or parchment-like, frequently * F. A. Smitt, " Kritisk forteckning ofver Skandinaviens Hafs-Bryozoer Ofvers." Kongl. Vet emit. Jltad. Forhandl., 1865, 1866, 1867. H. Nitsche, " Beitrage zur Kenntniss der Bryozoen." Zcit. fiir /.. ZooL, 1809 and 1871. J. L'arrois, " Recherches stir Pembryologie des Bryozoaires." Paris, 1877. MOLLUSCOIDEA. also calcareous, rarely gelatinous exoskeleton, which arises from the hardening of the cuticle around the individual zooids. Each zooid (zocecium) (fig. 545) is accordingly surrounded by a very regular and symmetrical case the ectocyst or cell ; through the opening of which the anterior part of the soft body of the contained zooid with its tentacular crown can be protruded. The form of the cells, and the manner in which they are connected together, are very different in the different groups, and give rise to a great variety in the form of the colonies composed of them. The cells are usually completely shut off from each other. With regard to their connection, they sometimes project obliquely or at a right angle ; sometimes they are spread out hori- zontally on the same plane ; some- times arranged in rows on a branched axis. Their openings are usually turned towards one side or towards two opposite sides. The soft body wall, or endocyst (fig 545, En) is closely applied to the inner wall of the ectocyst : it consists of an ex- ternal layer of cells (matrix of the ectocyst) and of a network of crossing muscular fibres (the external fibres are transversely, the internal longi- tudinally arranged), which are separated from the first layer by a homogeneous membrane. On the inner side of the muscular layer there is, at least in the fresh-water Bryozoa, a delicate layer of ciliated cells which line the body cavity. At the opening of the cell the soft endocyst is invaginated inwards, and passes thence on to the anterior and extensible part of the body, of which it forms the only investment. In most fresh- water Bryozoa this reduplicature of the endocyst is always present even when the zooid is protruded (fig. 545). The greater part of the anterior region of the body, with its crown of tentacles, can, however, always be protruded from the cell and retracted into it again by special muscles traversing the body cavity (fig. 545). The disc on which the mouth is placed is known as the lophophore. The lophophore is either circular (Stelmatopoda), or it is drawn out FIG. 545. Plciiintilla repens (after Allma.li). T, Tentacles ; L, lophophore ; Oe, oesophagus; Mg, stomach ; A, anus ; F, fuuicuius ; St, statoblasts ; Ts, ten- tacular sheath ; Ek, ectocyst ; En, endocyst; Gg, gangliou ; Priii, parieto- vaginal muscles ; Jim, retractor muscle. BRYOZOA. 1-0 I > into two lobes so as to have a horse-shoe shape (Lop/iopoda, fig. 54."),. and its margins are produced into a number of richly ciliated ten- tacles. The tentacles are simply hollow processes of the body wall ; they are provided with longitudinal muscles, and their cavity com- municates with the body cavity, from which they are filled with blood. They serve both for procuring food (setting up by means of their cilia whirlpools in the water) and for respiration. ,- The digestive organs lie freely in the body cavity, and are attached to the integument by the Mj-called funiculus and by bundles of muscles. The body and tentacular apparatus has been in- correctly regarded as a kind of individual, and opposed to the cell or Cystid, in which it is placed, as the Polypid. The mouth is placed in the centre of the circular or horse-shoe shaped lophopore, and a moveable epiglottis-like process, known as the epistome, often projects over it. The alimentary canal is bent on itself, and consists of (1) an elongated ciliated oesophagus often dilated to a muscular pharynx ; (2) a spacious stomach, with a blind backward prolongation, the hind end of which is attached to the body-wall by a cord (funiculus), and (3) a narrow intestine, which is bent up nearly parallel with the pharynx and is directed forwards. The intestine opens by the dorsally-p laced anus, near but usually outside the buccal disc (Ectoprocta, tig. 545). In a few forms the anus is within the circle of tentacles (Endo- in-octa), e.g.. Pedicellina and Loxosoma (fig. 546). ' FIG. 546. /'. ' ' Heart and vascular system are absent. The ,,!,,, ,*,. ?-,, tentaou- blood fills the whole body cavity, through which ^r crown ; 0, mouth ; MI), alimentary canal; it is circulated chiefly by the cilia of the body- A, anus ; G, ganglion; wall. The whole surface of the anterior protrusible part of the body, and especially of the tentacles, serves as a respiratory organ. The ciliated canal of the Endoprocta is to be regarded as a kidney. The nervous system consists of a ganglion placed on the oeso- phagus between the mouth and the anus. This ganglion in the Lophopoda is contained in the cavity of the lophophore, and is attached to the oesophagus by a delicate circum-cesophageal ring ; it sends oft' numerous nerves to the tentacles and oesophagus. Accord- 74 MOLLUSCOIDEA. ing to Fr. Miiller there is in Serialaria a so-called colonial nervous system which connects the individual zooids of one colony and enables them to co-ordinate their activities. Claparede * describes the same for Vesicularia, also for Scmpocellaria scruposa and Eugula (avicu- laria). Special organs of sense have not been recognised. Many forms of Bryozoa present examples of a well-marked poly- morphism. In Serialaria and its allies the joints of the stalk represent a special form of individual ; they have a considerable size and a simplified organization, and serve as the ramified sub- stratum on which the nutritive individuals are placed. In addition, there are here and there joints of the roots which, under the form of tendril- and stolon-like processes, serve to attach the colony. The peculiar appendages known as avicularia and vibra- cula, which are modified individuals and seem to have the function of food-procuring organs, are found in many marine Bryozoa. The avicularia (fig. 547, Av) resemble birds' heads and consist of two-armed pincers, which are attached to the colony near the openings of the cells and occasionally snap. They may seize small organisms, e.g., worms, and hold them till they are dead ; the de- composing organic remains are swept into the mouth by the currents caused by the cilia of the tentacles. The vibracula have a similar arrangement, but present in place (after Busk). Te, Tentacular o f t } ie snap pi n g b e ak a long and extremely crown ; R, retractor muscle ; D, alimentary canal ; F, funi- moveable flagelliforni filament (fig. 548). Knal ] y there are the Ov icell8 (ooecia), each of which is filled with an egg; they have the form of helmet or dome-shaped appendages and are sessile on the zooecium (fig. 547 Ovz). The reproduction is partly sexual and partly asexual ; in the latter case it may be effected by the so-called statoblasts or by budding. The male and female sexual organs are reduced to groups of cells producing either spermatozoa or ova, which usually arise in FIG. btf.- enlnss Ae, avicularia ; (>,, oesophagus; urz, Ovicells. * Ed. Olapar^de, " Beitrage znr Anatomic und Entwickelungsgeschichte (ier Seebryo/.oeu." Zeit.f. miss. ZooL. Tom. XXL, 1871. BRYOZOA. 75 the same animals, more rarely in different individuals. The ovaries which are filled with many ova are placed on the inner surface of the anterior part of the body wall ; while the testes with their seminal capsules are developed either on the upper part of the funiculus or near the point of attachment of the latter to the body wall. Both kinds of generative products are de- hisced into the body cavity where fertilization takes place. From the body cavity the fertilized egg passes either into a bud of the body wall (AlcyoneUa), or, as in marine Bryozoa, into an external appendage, - - the ocecium. The name statoblast (fig. 549) was given by Allman to certain peculiar re- productive bodies, which were formerly regarded as hard-shelled winter eggs, FIG. 548. s<- /<<,.<-,<, iinna fero.c (after i i i . -, Allman). Vi. Vibracula. but by him were recognised to be germs which are not fertilised. The statoblasts are found only in the fresh- water forms. They arise from masses of cells which appear principally towards the end of summer on the funiculus (fig. 545). They usually possess a lens-like, biconvex form, and are covered by two watchglass-shaped, hard chitinous shells, the edges of which are often enclosed by a flat ring formed of cells containing air (float), and some- times (Cristatell(i) provided with a crown of projecting spines (fig. 549). A very important part of the reproduction is effected by buds which remain permanently attached. The process of budding begins very early in life, before the development of the embryo is completed, and gives rise to the formation of colonies. Parts separated off from the colony are rarely able to produce new colonies (Cristatella, Lophopus). The development is always connected with a metamorphosis. The budding always begins in the embryo. In the fresh-water forms, after the alimentary tract and tentacular apparatus have made their appearance, a second alimentary canal and tentacular apparatus arise, FIG. 549. Statoblasts of Ci-istatdla mucedo (after Allman). a, From the surface; b, from the side. 76 MOLLUSCOIDEA. Cb- Cb so that the ciliated embryo still enclosed in the egg membranes repre- sents a small colony of two individuals. In the marine chilostomatous Bryozoa the fertilized egg passes into the ovicell, which consists of a helmet-shaped capsule and a vesicular operculum. Here the egg segments and develops into an embryo, which passes out as a ciliated larva, and swims about freely in the sea. The irregularly globular larva possesses a ring of cilia (fig. 550, a, b, c). After some time the larva attaches itself and develops the tentacular crown. The primary zooeciuni soon produces new zooecia by budding ; avicularia are developed, and final- ly, but not until after the death of the old- er zooecia, root fila- ments. In the Endoprocta the egg develops in a brood-pouch placed on the oral side of the animal. The segmentation is complete, and leads to the formation of a blasto- sphere ; the endoderm arises by invagina- tion, and gives rise to the lining of the midgut ; the oesophagus and rectum being formed from the ectoderm t'fig. 551). The mesoderm arises from two cells. The larvse of the Endoprocta possess an alimentary J canal bent into the form of a horse-shoe, and a cilkted coikr which is p rot ded at the front end; further, they contain a bud (fig. 551 e, Kn}, as the first rudiment of a second individual, and a cement gland at the hind end (Dr). Other larval forms, which are apparently of a very different 'structure, are reducible to the same type e.g., Cyphonautes (fig. 500, c), a larva which is found in all seas, and is, according to Schneider, the larva of Membranipora pilosa. After the winter the contents of the statoblasts give rise to simple, non-ciliated animals, which possess, when they are hatched, all the parts of the adult animal, at once become attached, and produce new colonies by budding. (after Barrois). b, Larva of Le- in-3. Phimatella rejifim, slightly magnified _and jointed. C risia corn uta Lam., (aftei , Allumil) Lp> Loljhul , hore . DI a ii IU eutun "Mediterranean and North Sea ; canal. C. eburncii L. Fani. Tubuliporidae. The zooecia disposed in continuous rows. Idninnrn atlantica Furl;.. Phalaitydla palmata Wood, Arctic Ocean. Tribe 2. Ctenostomata. Apertures of the cells terminal; when the tentacular sheath is retracted they are closed by a circle of spines as by an operculum. Stem-cells and root-filaments frequently occur Fam. Alcyonidiidae. Zooecia united to form gelatinous stocks of irregular form. Alfijiiitidhnn yrlattnoxum L., Northern Seas. Fam. Vesicularidae. Ihe zooecia project as free tubes on the branched, creeping or erect colonies. Ve&lcularia uva L., Far ell a- pedicellata Aid., Nor- way, Seritiftiria Cmiti/thii, Fr. Miill. Fam. Paludicellidse. Fresh-water forms. Paludicclla Ehrenbergii, Van Ben. Tribe 3. Chilostomata. The apertures of the horny or calcareous 80 BRACHIOPODA. cells can be closed by a movable operculum or by a sphincter muscle Avicularia, vibracula, and ovicells are often present. Fam. Cellulariidae. Dichotomously branched colonies ; zooscia in two or several rows. CMularia Pallas, C. Peacliii Busk, SenqwceUaria Van Ben. S. scrtiposa L. Fam. Bicellariidae. Zocecia conical or quadrangular, bent. Lateral face on which the aperture is placed is elliptical, and placed obliquely to the median plane of the axis. Bitf/ula Oken, B. aricularia L. (fig. 547). Fam. Membraniporidse. Zooecia more calcified and united to form an in- crusting colony. Membranipora Blainv., M. pilosa L., Adriatic ; LcjiTiil'ui pertusa Esp., Adriatic ; Flmtra memlranticca L. Fam. Keteporidae. Zooecia oval-cylindrical, united to a reticulated colony. Jteti'pora Lam., 7?. ccllulosa L., Mediterranean to the Arctic Ocean. T St cc Te Oe FIG. 554. Anatomy of Wctldlieimia australis, seen from the side (after Hancock) Do, Dorsal side; Ve, ventral side of the mantle; St, peduncle; Ma, adductor; Md, divaricator Ar, arms: Vw, anterior body wall; Oe, oesophagus; I), intestine ending blindly: 0, point of opening of the liver (Z) ; Tr, funnel of the oviduct. Class II. BRACHIOPODA.- Fixed Molluscoidea, with anterior (dorsal") and posterior (ventral} shell-valves, with two spirally-coiled buccal arms. The more recent researches into the development have shown that * R. Owen. " On the anatomy of the Brachiopoda." Transact. Zool. &'oc., London, 1835. A. Hancock, " On the organisation of the Brachiopoda." PliiL Trans., Lon- don, 1858. Davidson, "Monograph of the British fossil Brachiopoda." 1858. Lacaze-Duthiers, ''Histoire naturelle des Brachiopodes vivants de la Mediter- ranee." Ann. des. Sc. A'at., 1871, Tom. XV. Kowalevski, " Eussische Abhandlung iiber Brachiopodeii-Entwickelung." Moskau, 1874. W. K. Brooks, " The development of Lingula, and the systematic position of the Brachiopoda," Cht'*aj>eafte Zool. Lab. Sclent. Results. 1878. BRACHIOPODA. 81 the Brachiopoda, which have hitherto been regarded as Molluscs, are closely related to the Bryozoa. The Brachiopoda possess a large body, enclosed in a bivalve shell, of which one valve is anterior (dorsal valve), the other posterior (ventral valve) (fig. 554). Both valves lie upon corresponding fold? of the integument (mantle lobes), and are often connected on the back by a kind of hinge, above which the usually more arched ventral valve projects like a beak. This ventral valve is either directly fused with foreign bodies, or the animal is attached by a peduncle projecting through the opening of the beak (fig. 554 Si). The peduncle may, however, pass out between the two valves (/,/// yula}. The valves of the shell are cuticular structures secreted by the skin and impregnated with cal- careous salts; they are not opened by a ligament, but by special groups of muscles (fig. 554 Md} ; they are closed als-o by muscles which un- placed near the hinge, and p;i>s transversely from the dorsal to the ventral surface through the body cavity (fig. 554 Ma}. The body is bilateral and enclosed by the shell ; it possesses two large reduplications of the integument, the two mantle lobes, which are applied to the inner surface of the p IG . 555. Dorsal valve of shell of Waid- shell The edses of the mantle / """ ; sfr*iw with the brachiai skeleton (after Hancock). lobes are thickened, and carry very regularly-arranged seise. The mantle may also produce within its own substance calcareous spicules or a continuous calcareous network. The mouth is placed between the bases of the two spiral arms and leads into the o?sophagus ; the latter passes into the intestine, which is attached by ligaments and surrounded by large hepatic lobes. The intestine either describes a single bend, or is of considerable length and coiled (Discina, Lingula}. In the latter case it opens into the mantle cavity by an anus placed on one side of the middle line ; while in the hinged Brachiopoda (Terebraluta, Waldheimia) there is no anus, and the intestine ends blindly in the body cavity (fig. 5.~>4). Sometimes the end of the intestine is continued into a string-like organ (Tkecidium}. The two buccal arms are supported by a hard framework, con- VOL. II. G 82 MOLLUSCOIDEA. sisting of calcareous processes of the dorsal valve of the shell (fig. 555). They have the form of long appendages rolled up in a conical spiral on the anterior side of the body ; and they are traversed, as are the labial palps of many Larnellibranch.s, by a groove. The edges of the groove give rise to close-set and long fringes composed of stiff II St' FIG. 556. Development of Argiope (after Kowalevski). a, Larva, the gastric cavity of which has given rise to the drverticula of the body cavity (Lh); D, gut. b, Larva with three regions or segments, c, Larva with four bundles of seta? in the mantle-lobes of the middle segment, d. Later stnge. c, Attached larva with mantle lobes bent anteriorly, f, The tentacles (T) are developed ; St, peduncle. and movable filaments, the ciliated covering of which produces a strong current which leads small particles of food to the mouth opening. The heart is placed on the dorsal side of the anterior part of the intestine (stomach). It receives the blood through a venous trunk BRACHIOPODA. 83 running on the oesophagus, and gives oft' several lateral arterial trunks. The vascular system is not closed, but is in connection with a blood sinus surrounding the alimentary canal, with the lacuna* of the viscera and with a well-developed system of lacuna) in the mantle and arms. In the latter the blood is brought into close osmotic relation with the water, over a large surface ; the inner surface of the mantle and the spiral arms are, therefore, correctly regarded as respiratory organs. Excretory organs. Two, rarely four, canals, which are provided with glandular walls and open on each side of the intestine with a funnel-shaped aperture (fig. 554 T ' r) into the body cavity, and on either side of the mouth to the exterior, are to be regarded as kidneys (corresponding to the segmeiital organs of Annelida.) They function at the same time as generative ducts, and were called oviducts by Hancock. The nervous system consists of a circumoesophageal ring on which two small supi-acesophageal ganglia are in- serted. The subcesophageal ganglionic swelling of the ring is, however, much larger, and from it nerves pass out to the dorsal mantle lobe, the arms and ad- ductor muscles, and to two small ganglia which supply the ventral mantle lobe and the peduncular muscle with nerves. Sense organs are not known with cer- tainty. Generative organs. In all probability most Brachiopoda, as Distinct, Thecidium and Terebratulina are dioecious. The sexual organs consist of thick yellow bands and ridges which have a paired arrange- ment and project fi-om the body cavity into the lacuna? of the mantle, and are there considerably ramified. The eggs pass from the glands into the body cavity, and are conducted to the exterior by the ovi- ducts (excretory organs) whose funnel-shaped internal openings have already been mentioned. Development (fig. 556). After a total segmentation a kind of gastrula is formed, usually by invagination, and the archenteron (Argiope) becomes divided as in SiKjitta, into a median cavity, and two lateral diverticula which are constricted off and give rise to the body cavity (fig. 556 a, b). The oval larva then elongates and becomes divided by constrictions into three segments (fig. 556 b, c), D FIG. 557 a. Larva of Liitf/vla (afte. Brooks). T, Tentacles; 0, mouth; D, alimentary canal ; Af, anus ; L, liver; St, rudiment of peduncle. 84 BRACHIOPODA. of which the anterior becomes umbrella-shaped, and develops cilia and eye-spots ; subsequently it atrophies and gives rise to the upper lip. A fold is formed on the middle segment ; this gives rise to the two mantle lobes, which soon cover the body and a part of the caudal segment (fig. 556, d). Four bundles of long setse, which, as in the Worms, can be drawn in and protruded, make their appearance on the ventral lobe of the mantle of the developing larva. Later the larva becomes attached and the metamorphosis begins. The fixed posterior segment becomes the peduncle ; the mantle lobes bend forward and produce the shell. The bundles of setae are thrown off; the deposition of calcareous matter in the shell begins, and the tentacular filaments (which are at first arranged in a circle) of the later arms make their appearance. In Thecidium the inner layer (mesoderm and endoderm) arises from masses of cells which are budded off into the segmentation cavity. The subsequent meta- morphosis of the larva when provided with tentacles has been most accurately investigated by Brooks for Linyula, the larvae of which are still free-swimming when the tentacles are being developed (fig. 557, a, b). At the present day but few Brachiopods are found in the different seas, as compared with the much larger number in the earlier formations ; certain species of these fossil Brachiopods have great importance as characteristic fossils. The oldest fossils also belong to the Brachiopoda and certain genera which first appeared in the Silurian have persisted to the present day (Lingitla). M- FIG. 557 6. Longitudi- nal section of an older larva (after Brooks). Do, Dorsal; Ve, ven- tral valve of the shell ; Mr, thickened mantle edge ; T, tentacles ; 0, mouth ; Md, stomach ; Ad, intestine; M, pos- terior muscle ; G, gang- lion. Order 1. ECARDINES (INARTICULATA.). Shell without hinge and brachial skeleton. Alimentary canal with laterally-placed anus. Edges of the mantle lobes completely separated. Lin gill a atintina Lam., Indian Ocean, Disc-inn- huni'Uosa Brod., South America. Cra-niti anomala Mull., North Sea; Cr. rostrata Hoev., Fam. Lingulidse. Fam. Discinidse. Fam. Craniadae. Mediterranean ; Cr. antiyva Defr., fossil from the Chalk. TUNICATA. 85 Order 2. TESTICARDINES. The shell is calcareous, with hinge and brachial skeleton. The intestine ends blindly. The exclusively fossil families of the Orthidae and Productidae (Prnditctus Sav.), the edge of the shells which have no hinge, form the transition between the two orders. Fam. Rhynchonellidae. Rhy nchonella psittacca Lam., fossil species found in the Silurian. Pvntamcrits Sow., contains only fossil species from the Silurian and Devonian formations. The fossil 8j)iriferid!.Ze;.adi>vri*(regneanimal), together to form a common somewhat diagrammatic. 0, Mouth ; Sr, gills ; mass End, endostyle ; Oe, oesophagus ; G, nervous centre; MO, stomach; A', cloacal space; A, Beneath the saccular mantle exhalent pore; Af, anus , GD, genital gland; lieg the bo( j wall Q f th anima] Gg, genital duct ; Sj, stolons. J the outer cellular layer of which is applied to the mantle and represents the ectodermal epithelium which has produced the mantle and also the subjacent so-called internal mantle layer. Within the latter all the organs of the * Lacaze-Duthiers, " Sur un nouveau d'Ascidien.'' Ser., Tom. IV., 1865. A /in. dcs So. Nat. V e . TUNIC ATA. 87 body, the muscles, nervous system, the digestive apparatus, the generative and circulatory organs, lie embedded in a kind of body cavity. The nervous system is confined to a simple ganglion, the position of which near the inhalent aperture marks the dorsal surface. The nerves which radiate from the ganglion branch and pass, some to the muscles and viscera, some to the sense organs such as eyes, auditory and tactile organs which are found principally in the free- swimming Tunicates. The muscular system is chiefly developed around the respiratory cavity, and serves for the dilatation and contraction of this space as well as for closing the inhalent and exhalent pores. In the Ascidians there are three layers of muscles, an external and internal longi- Kl Nu. End M(l FIG. 559. Salpa democratica from the side, somewhat diagrammatic. 0, Mouth ; Ph, pharyngeal cavity; Kl, cloaca: A, exhalent opening; Br, gills; N, nervous centre; Ma, mantle; M, muscular rings; Z, languet ; Wb, ciliated arc; End, endostyle; Wr, ciliated groove Nu, nucleus ; C, heart. tudinal and an internal circular layer, while iu the Salps there are band-like rings of muscles embedded in the substance of the body- wall, and effecting not only the renewal of the water used in respiration, but also the movements of the free-swimming barrel- shaped body. A special organ of locomotion is present in the small Appendicularia and the free-swimming Ascidian larvse ; it is placed on the ventral surface as indicated by the position of the heart, and consists of a vibratile whip-like caudal appendage supported by a notochordal rod (urochord). The alimentary canal begins in all cases with a wide pharyngeal cavity, which functions as a respiratory organ. The anterior mantle opening, which must be looked upon as the mouth, leads into this cavity. The cesophageal opening is placed at a distance from the TUNICATA. mouth inside this respiratory cavity, which in the Ascidians has the form of a latticed branchial sac. A ciliated groove bounded by two folds extends along the middle ventral line of the pharyngeal cavity, between the mouth and the opening of the oesophagus. The glandular walls of this ventral groove are distinguished as the endo- style (tigs. 558 and 559, End}. It begins with two lateral ciliated arcs, which unite to form a complete ring near the inhalent aperture (mouth), and somewhat in front of the ganglion pass over a small cone projecting into the pharyngeal cavity. The digestive canal which follows the pharyngeal cavity consists of a ciliated oesophagus, which is usually narrowed into the form of a funnel ; of a stomach, usually provided with a liver ; and of a small intestine, which bends round, forming a loop, and opens into the cloacal cavity. There is always a heart, which is placed on the ventral side of the intestine and is surrounded by a delicate pericardium. The con- tractions, which are active and regular, pass from one end of the heart to the other. The sudden change in the direction of the contractions (discovered in the Salps by Hasselt), by which after a momentary period of rest the direction of the blood stream in the heart is reversed, is worthy of note. The vascular trunks (lacunae) passing from the heart lead into a system of spaces in the body wall through which the blood passes. In the Ascidians there are also vascular loops in the mantle, in that diverticula of the body wall, containing blood and covered with epidermis, project into the mantle. Two principal channels for the blood are placed in the middle line one on the dorsal side, and the other on the ventral beneath the ventral groove ; they are connected by transverse channels placed in the wall of the branchial cavity. The latter communicate with the blood spaces of the variously-shaped branchia, which is formed by the walls of the pharynx, and over the surface of which the water is continually renewed by means of the vibratile cilia which cover it. In the Ascidians almost the entire wall of the pharynx takes part in the formation of the gill. In these animals the pharynx has the form of a sac with net-like walls i.e., its walls are perforated by a number of slits, which lead from the pharynx into a chamber which is de- veloped round it. This chamber is derived from the cloacal cavity, and is known as the peribranchial chamber. The branchial sac or pharynx is fixed to the walls of the peribranchial cavity along the whole length of the endostyle, and by numerous short trabeculse TUNICATA. 89 which pass from the bars of the branchial network to the outer wall of the peribranchial chamber. In other cases, the number of gill- slits is considerably reduced, and the gill is confined to the dorsal part of the pharyngeal wall (Doliolum, Salpa). Generative Organs. The Tunicates are hermaphrodite ; the male and female generative products, however, often attain maturity at different times. The Salps especially, at the time of their birth, have only the female organs, and it is not until later when they are pregnant that the male organs attain maturity. In Perophora the testes become mature first, in the Botryllidce the ova. The testes and ovaries lie, as a rule, among the viscera in the hind part of the body. The ovaries have the form of racemose glands, the testes of blind tubes united in tufts. The generative ducts of both sexes open into the cloacal chamber, in which (rarely in the place where the germs originate) the fertilization of the ovum and the develop- ment of the embryo takes place. The embryo either leaves the cloacal chamber through the exhalent aperture while still enveloped by the egg-membranes, or is nourished by a sort of placenta and born at a more advanced stage of development (Salpa). In addition to the sexual reproduction, the asexual reproduction by means of budding is very general, and frequently leads to the formation of colonies with very characteristic grouping of the indi- viduals. The budding sometimes takes place on different parts of the body, sometimes is confined to definite places or to a germ-stock (stolo prolifer). The colonies thus produced do not by any means always remain fixed ; but, as e.g., Pyrosoma, may possess the power of moving from one place to another, or, as in the Salp-chains, they can swim tolerably rapidly. The embryonic development of the Ascidians presents a great re- semblance to that of the lower Vertebrates, a.nd more especially to that of Amphioxus. After the completion of the total segmentation a two- layered gastrula is formed, from the ectoderm of which the neural tube is developed. At the same time an axial skeletal structure, like the chorda dorsalis, arises from a double row of endoderm cells. The relative positions of the alimentary canal, the nervous system and the notochord are analogous to those of the Vertebrates. The post- embryonic development of the Ascidians is complicated. The embryos leave the egg-membranes as movable larvae (Ascidian tadpoles) provided with a swimming organ (tail) and an eye-spot. They swim about freely for some time, and in many cases produce a small colony by budding before becoming fixed. In the Salps and 90 TUNICATA. Doliolum there is an alternation of generations, which was discovered in the case of Doliolum by Chamisso long before Steenstrup. The solitary Salp, developed from the fertilized ovum of the viviparous sexual form remains asexual all its life, but from its stolo prolifer chains of Salps are produced, the individuals of which differ consider- ably in form from the asexual animals and are sexual. In Doliolum the alternation of generations is much more complicated, inasmuch as several generations succeed one another in the cycle of develop- ment. All the Tunicata are marine animals and feed on Algce, Diatoms, and small Crustacea. Many, and especially the transparent Pyroso- midce and Salpidcn, are phosphorescent, emitting a beautiful and intense light. CLASS I. TETHYODEA* (Ascidians). For the most part fixed Tunicata with saccular bodies. The inhalent and exhalent pores are placed close together, and the branchial sac is large. Development by means of tailed larvae. The body of these animals, as the name Ascidia implies, has the form of a more or less elongated tube or sac with two openings, which are usually close to one another ; of these openings the anterior is the mouth and the posterior the cloacal opening. More rarely, as in the BotryllidcK and the free-swimming Pyrosomidce, the two openings are placed at a considerable distance from one another at the opposite ends of the body. The mouth can be closed by a sphincter muscle, and in many cases by four, six, or eight marginal lobes (fig. 560). The edge of the exhalent opening, which can also be closed, and which is placed behind the mouth on the neural (dorsal) side, is often similarly divided into four to six lobes. The spacious pharynx which, as a rule, has the form of a latticed branchial sac, contains at some * Besides the already quoted works of M. Edwards and Savigny, Cf. J. C. Savigny, ' Tableau systematique des Ascidies, etc." Paris, 1810. Eschricht, " Anatomisk Beskrivelse af Chelyosoma Mac-Ley anum." Kjb'ven- havn, 1842. Van Beneden, " Recherch.es sur 1'Embryogenie, I'Anatomie et la Physiologie des Ascidies simples." Mem. de I' Acad. roy. de Belgiqite, Tom. XX., 1846. A. Krohn, " Ueber die Entwickelung von Phallusia mammillata." Miiller's Archii; 1852. A. Krohn, "Ueber die Fortpflanzimgsverhaltnisse bei den Botrylliden vmd iiber die friiheste Bilduug der Botryllusstocke." Archiv fiir Natwrgesehiehte, Tom. XXXV., 1869. Th. Huxley, " Anatomy and development of Pyrosoma." Trans. Lin. Soc., VoL XXIII.,' 1859. TETHYODEA. 91 Eml distance from the mouth a circle of usually simple tentacles. On the neural side of the branchial sac is the cloacal cavity which receives not only the water flowing out through the branchial slits, but also the faeces and the generative products. The digestive canal, together with the other viscera, is some- times placed as in all the simple Ascidians rather to the side of the branchial sac or, as in the elongated forms of the compound Ascidians, simply behind the same, and in the latter case often occasions a constriction of the body, so that Milne Edwards was able to distinguish a thorax and abdomen, or even a thorax, abdomen and post-abdomen. The Ascidians either remain solitary, and then usually attain a considerable size (A. solitarice), or by budding and throwing out root -processes they produce branched colonies, the individuals of which are connected together by their body walls, and are not embedded in a common mantle covering (A. societies). In other cases (Synascidice) numerous in- dividuals live in a common man- tle ; they often have a charac- teristic around a common central opening (A. composites), so that each group has its central cavity, into which the exhalent (i.e. atrial) openings lead as into a common cloacal cavity (fig. 561). There are solitary (Appendicularia) as well arrangement FIG. 560. Clacellina lepadiformig (regne ani- mal), somewhat diagrammatic. &, Mouth ; Br, branchiae ; End, endostyle ; Oe, oesophagus ; G, nervous centre ; MD, stomach ; Kl, cloacal chamber; A, exhaleut pore; Af, anus; GD, genital gland ; Off, duct of genital gland ; Sf, stolons. as compound Ascidians (Pyrosoma) which can move freely. The solitary Appendicularice execute the most perfect swimming move- ments. In their external form they resemble the free-swimming Ascidian larva?, and like these they have a whip-like swimming 92 TUNICATA. A tail, which by its undulating movements propels the body forward. In order to understand the structure of the Ascidians, it will be well to start from these simply organised forms. The most striking character of the Appendicularia, next to the possession of the ventrally-placed swimming tail with its notochord-like skeletal axis (urochord), consists in the absence of a cloacal chamber for the reception of the excreta. The anus is placed in the middle line of the ventral surface ; further, there are two funnel-shaped atrial canals which begin on either side with a strongly-ciliated opening into the pharyngeal sac, and open to the exterior right and left, visually rather in front of the anus. These branchial passages arise as invaginations of the ecto- derm, which come into connection with corresponding evaginations of the pharyngeal sac. The in- troduction of nourishment is regulated by two ciliated arcs, which begin at the front end of a short endostyle, surround the entrance of the pharyngeal sac, and run obliquely towards the dorsal surface, where they unite to form a median row of cilia (composed of two rows of ciliated Cells). The latter passes back fc o the opening of the O3SOphagUS, , .,. , opposite a narrow ventral ciliated band, which begins at the hind end of the endostyle (fig. 562). The Ascidian larvae (PhaUusia) also have, as Krohn long ago discovered, two branchial slits with corresponding atrial passages. The latter, according to Kowalevski, arise as invaginations of the ectoderm, and later on unite on the dorsal side, and then open by a common cloacal orifice. The ectodermal lining of the atrial cavity, which grows round the sides of the pharyngeal sac, consists, therefore, of a branchial layer which is applied to the pharynx, and a parietal layer which forms the internal lining of the outer wall of the peri- branchial or atrial cavity. The atrial cavity extends round the pharynx as far as the sides of the endostyle. The wall of the Pio. 561BotryH.w molaceia (after M. Ed- wards). 0, Mouth; A, common cloacal opening of a group of individuals. TETIIYODEA. 93 pharynx becomes perforated by an ever-increasing number of slits, and thus gives rise to the branchial basket-work. The special form of the branchial basket-work presents numerous modifications of systematic value. Not only is the external surface of the branchial sac attached to the body-wall by trabecuke and band-, End GD FIG. 562.Appen&icularia (Fritillaria) fureata. a, From the ventral side with the tail bent for wants. GD, Genital glands ; M, muscles of the tail. 6, From the ventral side after the caudal appendage has been removed. 0, Mouth ; End, endostyle ; Sp, the two ciliated passages of the pharyngeal cavity; DW, the dorsal row of cilia; Oe, oesophagus ; Md, stomach ; Af, anus; Dr, glands ; C, heart; Oa, ovary ; T, testis. through which the blood passes, but the internal surface also often presents folds and projections of varying form. Similarly the branchial openings with which the wall of the pharynx is pierced differ in size, number, and form ; they may be rounded, elliptical, or even spirally coiled. The ciliated arrangements in the perforated branchial sac of the 94 TUNICATA. Ascidians correspond to those of the Appendicularice, and consist of the so-called endostyle with the ventral groove and the two ciliated arches. The ciliated oesophagus is short and funnel-shaped, and leads into a dilated portion distinguished as stomach, whose walls have a layer of large entodermal cells and are complicated by the presence of fold-like projections. Glands, which are sometimes follicular sometimes composed of bundles of tubes, or of tubes united in a network, lie upon and open into the stomach ; they are generally known as * liver, but would be better called hepatopancreas. The small intestine which follows the stomach is of considerable length, is usually bent on itself (haemal curvature), and is continued into a short rectum (piriform in Appendicularia), which opens into the cloacal chamber. Besides the glands already mentioned, a gland-like organ has been found in many Ascidians : as there is no opening to this gland, the concretions found in its lumen are probably not in general removed. It may, perhaps, be regarded as a kidney, since Kupffer f has shown that uric acid is present in the concretions. The heart is placed on the ventral side of the intestinal canal. It is a contractile tube, each end of which is prolonged into a vessel. In the AppendicularioB (Copelata) the heart is placed transversely, and is pierced by only two slits. The so-called vascular system of the Ascidia.ns consists of a rich net-like system of lacunae, which cannot, however, be said to have special walls. The nervous system is reduced to an elongated ganglion (cerebral ganglion) placed on the dorsal side of the branchial cavity. From this ganglion nerves are given off, especially forwards towards the entrance of the pharyngeal sac ; but unpaired sense nerves and lateral and posterior nerves also arise from it. In the Copelata and Ascidian larvae the cerebral ganglion is more complicated. In these animals it has the form of a cord, primitively containing a cavity, and divided later by constrictions into three regions, and is connected with ganglia in the tail (fig. 563). The anterior conical part of the brain gives off paired sensory nerves to the region of entrance into the branchial sac ; on the median globular part are placed the auditory vesicle and a stalked ciliated organ ; while the attenuated posterior part gives off two lateral nerves to the atrial canals, and is prolonged * Th. Chandelon, "Eecherches sur une annexe du tube digestive des Tuniciers." Bull, de Vacad. roy. de Bclyique, Tom. XXXIX., 1875. f Cf. Besides Kowalevski I.e. KupfEer. " Zur Entwickelung der einfachen Ascidien." Arch.fiir miltr. Anat.. Tom. VIII. 1872. Lacaze-Duthiers, Arch, dc Zool. expert m., 1874. TETHYODEA. 95 into a long nerve, which at the base of the tail dilates to a ganglion, and in its further course forms a number of smaller ganglia (tig. 563). The reduction of the central nervous system to the simple ganglion of the Ascidian begins after loss of the tail, and after development of the branchial basket. Of sense organs the processes of the integument which serve for tactile purposes (the lobes of the oral and at rial apertures and the tentacles), and peripheral nerves, ending in epithelial cells, are most widely distributed. The large ciliated cells on the edge of the mouth of the Copdata must be placed in the same category. The ciliated pit is to be regarded as an olfactory organ. It consists of a depression in the wall of the pharynx lined with ciliated cells, and is situated in front of the ganglion. Accord- ing to Julin, it is, to- gether with a gland situated beneath the ganglion, to be regarded as the equivalent of the hypophysis. In the Copdata the ciliated pit is elongated and lies on the right side of the ganglion. There is an auditory vesicle on the left side of the ganglion in the Copdata. This structure, which is developed from a cell of the of the ganglion, is found in the Ascidian larvae, but degenerates soon after the attachment of the larva. Paired auditory vesicles appear in Pyrosonm where they are connected with the ganglion by a short stalk. Masses of pigment which are present with great regularity on the lips of the large openings of the body in the simple and compound Asciclians may be interpreted as eye spots. The eye of the Ascidian larvse, which lies on the ganglion and originates from a part of the neural canal, has a more complicated structure. Later it degenerates, but in Pyrosoma it is retained in the adult condition and possesses a lens-like structure. FIG. 563. Xervous system of A/i/fO x/.V,'/< n-'m fi> rcata (after Fol.). G, Ganglion ; N, body nerve ; lateral nerve ; Ot, otolith vesicle ; Ry, olfactory pit : tactile cells with their nerve ; II7/, arch of cilia. 96 TUNICATA. The generative organs are always united in the same animal. The formation of villi on the surface of the egg-membrane by the follicular cells surrounding the ovum is remarkable. The origin of FIG. 564. Development of Phallusia titcninni/lntf/ (after Kowalevski). a, Blastosphere beginning to invaginate ; Fh, segmentation cavity, b, Gastrula with blastopore (0) ; Ed, endoderm ; Ch, commencing uotochord (urochord). f, Later stage. Ek, Ectoderm ; N, rudiment of the still open neural canal, d, Stage with body and tail ; Ed' , eudodermal layer in the tail ; M, muscular cells iu tail, e, Just hatched larva ; Rg, anterior swelling of the spinal division of the neural tube ; Rm, posterior part of neural tube ; Gb, dilated anterior part of neural tube (cerebral vesicle), with otolith projecting into it; F, opening of Gb ; A, eye; 0, in- vagination of mouth; Pit, pharyngeal cavity; Ed, endostyle ; D, commencing intestine ; Kl, atrial opening; Bl, blood corpuscles; JIji. papilla for attachment. /, Two days' larva (only the beginning of the tail is represented); .Ks, ^Ks, branchial stigmata : Bb, branchial vessel between them ; B, intestine. the so-called test-cells (follicle-cells which have migrated inwards) over the substance of the yolk on the inside of the egg-membrane, is also worthy of note. TETHYODEA. 97 Development. The segmentation is complete, and leads, according to Kowalevski, to the formation of a blastosphere as in Amphi- oxus (tig. 504). The wall of the blastosphere then begins t> invaginate. After the completion of the invagination the blastosphere becomes a gastrula, with the remains of the segmentation cavity between the ectoderm and entoderm (fig. 564, F/t). The mouth of the gastrula is at first wide, but soon becomes narrower and narrower, until finally it becomes transformed into a small opening placed on the dorsal surface at the hind end of the body. A flat median groove on the ectoderm appears along the dorsal side of the already bilaterally symmetrical embryo extending from the blastopore forwards. This groove, into the hind end of which the blastopore opens, is the first rudiment of the central nervous system. It is known as the medullary groove. Its edges project and form the medullary folds which grow round and clo.-e the narrow blastopore, and gradually fuse with one another from this point forwards in such a manner as to convert the groove into a canal, the walls of which separate from the external ectoderm and give rise to the central nervous system. .This canal is known as the medullary canal : behind it is shut off f rorn the exterior, but communicates with the cavity of the gastrula (archenteron) by way of the blastopore (fig. 504 c), which is now known as the neurenteric canal ; while in front it remains open for some time. Before these processes are completed two rows of the endoderm cells of that part of the gastric wall which immediately underlies the neural tube become different from the remaining endoderm cells and give rise to the first rudiment of the notochord. The anterior part of the archenteron only gives rise to the pharynx and intestine (fig. 564, e), while the posterior part furnishes the cell material not only for the notochord, but also for the muscular system and the blood corpuscles. It may accordingly be asserted that the meso- dermal organs in the Ascidians arise from the entoderm, which is as good as saying that the hinder half of the gastral sac has the value of mesoderm. In the further course of development the somewhat elongated spheroidal body grows out at the posterior and inferior end, opposite to the blastopore and rather to the right,* into a tail-like prolonga- tion, the axis of which is formed by the cells of the notochord (at thi* period arranged in a simple row). The neural canal is prolonged into * In A. iiiammillittit, according to Kowalevski. on the contrary, this growth takes plaoe at the other end towards the left, and therefore agrees with that of VOL. n. 98 TUN1CATA. the tail dorsal to the notochord. The tail, thus developed, becomes bent and applies itself to the side of the body opposite to that on which the nervous system is placed (Fig. 564e). Subsequently the skin begins to thicken at the anterior end and gives rise to three papillae, the future papillae for attachment. The rudiment of the nervous system, on which two pigment spots provided with refractive organs make their appearance (eye and auditory organ, fig. 564e,y), is converted at its anterior extremity into a vesicle and is continued above the chorda into the tail (as a cord with a central canal) (A. canina). The branchial sac, still closed and formed of columnar epithelium, lies close to the nervous system : it is separated from the ventral wall of the body by roundish uncoloured cells, which are probably the formative elements of the blood and of the wall of the heart. It has at this period the position and relative size of the future pharynx and its posterior dorsal extremity grows out to form the, at first ca?cal, . rudiment of the digestive canal (fig. 564 e, D). The mouth is formed from an invaginatioii of ectoderm on the dorsal surface immediately in front of the anterior end of the cerebral vesicle (fig. 564 e, 0). The cloaca first appears as a pair of dorsally-placed epiblastic involu- tions (fig. 564 e, A7) : these ingrowths meet and fuse with the wall of the branchial sac so that two perforations are formed. The embryo surrounded by the mantle (formed of gelatinous substance with amoeboid test-cells which have wandered into it) now breaks through the villous egg-membrane and passes into the stage of the free- swimming larva, which presents on the right side of the endostyle the first rudiments of the heart, and possesses all the organs of the later Ascidian except the vessels and the generative glands : in its subsequent development, however, it has to go through a decidedly retrogressive metamorphosis. After the larva has attached itself by means of its papilla;, the tail aborts, the muscles and notochordal sheath degenerate, and the axial string of the notochord contracts. The nervous system with the pigment organs degenerates, and the cavity in it disappears; the branchial sac, on the contrary, increases in size, and the oesophagus, stomach, and intestine proper become more sharply distinct. The mantle then becomes firm, the mouth opening perforates the gelatinous covering and becomes the entrance to the branchial sac; behind the mouth the arch of cilia appears at the anterior end of the ventral furrow, which was formed at an earlier stage and gives rise to the endostyle.. The opening to the oesophagus becomes funnel-shaped and more distinct. The first branchial slits TETHYODEA. 99 soon become visible. The blood with its amoeboid corpuscles i>, already moving in the body cavity beneath the skin, and indeed on the branchial sac. through definite channels in the connective tissue, which connects the walls of the branchial sac with the skin. The water which flows through the slits of the branchial sac is collected in the peribranchial space the opening of which coincides with the cloacal opening. Asexual Reproduction. In addition to the M>.\ual reproduction, multiplication by means of budding plays an important part, particu- larly in the Si/nascidians. According to Krohn, Metschnikoff, and Kowalevski, an entodermal layer (arising in Botryllus from the cover- ing of the atrium) and mesoderrnal cells as well as the ectoderm take part in the formation of the buds. Many Ascidians, as Perophora and Clavellina, produce stolons by budding, and from these new individuals are developed, but the latter are not united together into a compact system. Complex systems of buds are developed in the Synascidians, the individuals of which are embedded in a common cellulose mantle. In some cases the larva may form buds while it is still in the tailed stage (Didemnum). In Botryllus, a genus which is distinguished by the star-like grouping of the individuals round a common cloaca (fig. 561), and by the rich branching of the blood canals, the larva is simple, and does not, as Sars believed, form a colony. MetschnikotF and Krohn, whose accounts agree, have both shown that the eight knob-like buds of the larva are only processes of the ectoderm and contain diverticula of blood spaces. The young Botrijllus produces only one bud (first generation), and before the latter is mature perishes without attaining sexual maturity. The bud of the first generation produces two buds (second generation), and dies without reaching sexual maturity. The buds of the second generation each produce two buds, which arrange themselves in a circle, and after the death of their producers form the first system with a common cloaca. In a similar manner new buds are formed, and the older generation dies; the new systems are, however, as transitory and are replaced by others, so that as the stock increases the old generations are continually being replaced by new. In this continuous process of renewal the first-formed generations have only the provisional value of establishing the colony. The later generations alone become sexually mature, and the female maturity is attained before the male. The ova of the still young hermaphrodite gene- rations are fertilized by the sperm of the older ; and it is not until after the death of the latter that the testes of the former become 100 TUNICATA. fully developed. The young generations, therefore, now have the double ta.sk of caring for their own already fertilized eggs and of fertilizing those of the succeeding generations. Order 1. CopELATyE* (Ascidians with larval tail). Small free-swimming Ascidians of long oval form, with swimming tail ; they resemble in the whole of their organization the larvae of other Ascidians (tig. 502). The anus opens directly to the exterior on the ventral side. The pharyngeal sac is pierced by only two branchial slits. The heart has two slits and no vessels. The ovaries and testes lie in the hind part of the body, close to one another, and are without ducts. The elongated cerebral ganglion is divided by constrictions into three parts ; it is connected with a ciliated pit and an otolithic vesicle, and is prolonged into a nerve- cord of considerable size. The latter is continued into the tail, at the base of which it swells out to a ganglion ; in its further course it forms several small ganglia, whence lateral nerves pass out. In consequence of a torsion of the axis of the tail, the originally dorsally-placed caudal nerve comes to have a lateral position. The segmentation of the nerve-cord in the tail (as shown by the gang- lionic swellings) corresponds to the segmental divisions of the muscles, which recall the myotomes of Am.p/tioxus. The large chorda (uro- chord), which extends along the whole length of the tail, constitutes another point of resemblance to Amphioxus. Some species have a pellucid gelatinous covering, comparable to a shell. The development of these small animals, which were formerly erroneously held to be larvse, has been insufficiently investigated. Fam. Appendicularidse. Uiluyleura Mertens {Appendicidaria Cham.), 01- coplioeerca Gegbr., Oi.fitrrata Gregbr., Fritlllaria Fol. The integument forms a hood-like reduplicature in front ; the tail one and a-half times as long as the elongated body; the endostyle is curved. Fr. fureata C. Vogt., Fr. for mien Fol, Kowalwxkla Fol. Without heart and endostyle. Rectum absent. X. tennis Fol, Messina. Order 2. ASCIDI^E siMPLiCES.f This order comprises solitary forms as well as branched stocks. * Cf. C. Gegenbaur, " Bemerkuugen liber die Organisation der Appendicu- larien.'' Zeitscft. fur /rixs. Zuol., Tom. VI.. 1855. H. Fol, " Etudes sur les Appendiculaires du detroit de Messine." Mem. Sue. dc Plnjx. et n'lllst. Nat. di- Genecc, Tom. XXI.. Ih72. t Of. besides Lacaze-Duthiers I.e., C. Heller, " Untersuchuugen iiber die Tuni eaten des Adriatischen Meeres, I., II., III.," Uenlwhr. der It. Altad. >lcr Wistenxcli. !('/>//, 1874-1877. ASCIDI.E COMPOSITE. 101 " Tlie latter, or social Ascidians, are placed on branched root-processes, and have for a time, or permanently, a common circulation. The mantle-parenchyma is usually of transparent hyaline consistency. The body of the solitary Ascidiaiis is far larger and is surrounded by a hard cartilaginous, very thick and usually completely opaque mantle, the surface of which often has wart-like protuberances and incrustations of various kinds (tig. 560). Fain. Clavellinidae. Social Ascidians, the stalked individuals of which arise from a common branched stolon, or on a common stem. The body is sometimes (C/nr/'l/htti) dividrd into th ee regions, like that of the Pnli/clinidfe. C/ttrrllhia Sav. : (1. IcjHirliformix Sav., North Sea ; Pi-ropluira Lixteri Wiegm., North Sea. Fain. Ascidiadae. Solitary Ascidians, usually of considerable size. The individuals reproduce themselves, as it seems, only occasionally by budding, and are connected, when they are aggregated together, neither by a common mantle covering nor by bloodvessels. Axridia L. {Phrilliixlu Sav.) ; A. tnnm- miUiila Cuv.. Mediterranean; A. (Ciona) intestinalis L. . etc. ; Ci/iif?t!f/ Sav., C. puptlhisa Sav., C. i>iicr<>ri>xiniix Cuv., Chevreulinx Lac-Duth., Mediter- ranean. The deep-sea Ascidians are very remarkable aberrant forms. Hypobi/thiitx ralci/codcx Mos.. and Octacnemns liythinx Mos. Order 3. ASCIDI.* COMPOSITE." Numerous individuals lie in a common mantle layer, and form soft, brightly-coloured colonies, which have a spongy or lobed form, and not unfrequently form crusts round foreign objects. In almost all cases the individuals are grouped in a definite number round a common cloaca (Botryllidce), so that round or star-shaped systems with central openings are formed in the colony (fig. 561). The body is sometimes simple and short, sometimes long and divided into two or three regions, and sends out branched processes contain- ing blood into the common mantle mass, so that the latter is per- meated by vascular canals. Fain. Botryllidse. The viscera of the simple body, which is not divided into thorax and abdomen, lie by the side of the respiratory cavity ; without lobes round tlie inhaleiit opening. Botri/Uus xti-lltitiis. Pall. ; B. riolaci'iix Edw. Fam. Didemnidae. The viscera arc for the most part placed behind the re- spiratory cavity, and the body is divided into two parts, the thorax and abdo- men. Hull 1 in innn Sav. : D. cii/itliihu/i Sav. : D. xf //life rum Kow. Fain. Polyclinidae. The body of the individual is much elongated, and is * Besides Savigny. cf. M. Edwards. Observations sur les Ascidies compo- sees des cotes rle la Blanche.'' Jfem. Arnd. xc.. Tom. XVIII.. Paris. 1S42. A. Giard. " Recherches sur les Synascidies." Arch, (h' Zool. I'.rpt'r., Tom. L, Paris. IS 72. Kowalevski, " Ueber die Knospung dei Ascidien." Arcl. fiir miftr. At/nf. . Taf. X.. 1874. 102 TUNICATA. divided into thorax, abdomen, and postabdomen. The heart lies at the hind end of the body. Amaruciiun, Edw. ; A prolifcrum Edw. Order 4. ASCIDIJE SALPJEFORMES.* Free-swimming colonies, which float on the surface of the sea, and have in general the form of a fir cone, hollowed out like a thimble. They are composed of numerous individuals arranged in the common gelatine-cartilaginous mass in a direction at right angles to the long axis of the colony. The inhalent openings lie in irregular circles on the external surface ; the exhalent openings open opposite to them into the space which serves as a common cloaca. The branchial sac is wide and latticed as in the Ascidians. The intestine and ovary are compressed together, and lie in a rounded prominence like a nucleus N Wb Br FIG. 565. An individual of Pyriixomd, (after Keferstein). 0, Mouth ; A, atrial aperture >' Af, anus ; Of, ovary ; T, test is ; A", ganglion ; End, endostyle; Br, branchial sac ; W/j, ;irch of cilia; C, heart; Si, stolo pvolifer. b, C.yathozoid of Piiroxnntn (after Kowalev&ki). //, Heart ; Kl, cloaca ; D, yolk around which are the four individuals (ascidiozoids). (fig. 565 a) ; near them is the heart. The ovary brings only one ovum to maturity, which is surrounded by a saccular follicle with a long stalk. The stalk constitutes the oviduct, and opens into the cloacal cavity. The eye lies on the ganglion. By the presence of the eye, as well as by the position of the two respiratory openings and of the viscera, by the method of reproduction and the free locomotion, the Pyrof>omidce are allied to the Salps. Budding takes place by means of a stolon, which begins at the hind end of the endostyle, and contains an endodermal process of * Th. Huxley. " Anatomy and development nf Pyrosoma." Trans. Linn. &H-.. 18(30. \V. Keferstein vmd Ehlers. " Zooloo-ische Beit; age." Leipzig 1 . 18f>l. Kowalevski, " Ueber die Entwickelungsge s chichte der Pyrosomen." Arch, fiir m/kr. A-natomie, Tom. XI., 1875. THALIACEA. 103 the latter (endostylic cone). Sexual reproduction and gemmation take place in the same individual. The egg develops within an ovarian sac into an embryo, which has the form of a stunted Ascidian-like individual (ct/athozooid], and produces, by budding from a stolon, a group of four individuals (ascidiozooids). The peculiar mode of origin of these individuals has been minutely described by Huxley and Kowalevski (fig. 565 b}. The process of budding, by which the colony is increased, is no less complicated : it takes place on a germ-stock (stolo prolifer, fig. 565 , *SV.) placed behind the endostyle. Each commencing bud receives a prolongation of the foundation of the ovary,* as well as of the endoderm. The Pyrosomidce derive their name from the bright light which they emit. According to Panceri, this light proceeds from a paired group of cells in the region of the mouth. Fam. Pyrosomidae. These animals were discovered by Peron in the Atlantic Ocean, and were at first regarded as solitary individuals. Pyrosoma Per. ; P. nil antic a in Per. ; P. eleyans and ijiijnnti'tnn Les., from the Mediterranean. Class II. THALIACEA.t Free-swimming transparent Tunicata with cylindrical or cask- shaped bod i/. The mantle apertures are terminal, and at opposite ends of the body. The branchiae are band-shaped or lamellar, and the viscera are compressed together into a nucleus. The Thaliacea (fig. 566 a, b) are transparent, cylindrical or cask- shaped animals, of gelatine-cartilaginous consistency : they are either solitary, or the individuals are united in chains (usually in double rows). They move on the surface of the sea by the rhythmically alternating contraction and dilatation of the branchial cavity. The two openings are placed at opposite ends of the body ; the mouth at the anterior end, the atrial at the posterior end, near the dorsal * [Generative blastema, or indifferent tissue from which the reproductive organs of the parent were developed (Huxley).] f Compare Th. Huxley, " Observations upon the anatomy and physiology of Salpa and Pyrosoma, together with remarks upon Doliolurn and Appendicu- laria." Phil. Trans., London, 1851. E. Leuckart, " Zoologische Untersuchimgen." Heft IT., Gicsson. 1854. C. Gegenbaur. " Ueber den Ent-vvickelungscyklus von Doliolnm nebst Bemerkunsren liber die Larven dieser Thiere." Zritxchr. fiir n-iss Z/ml., Tom. VII. C. Grobben. "Doliolurn und sein Generationswechsel, etc." A >'!>< >tni aits dnn Zool. Institute in Wien, Tom. IV., 1882. . 104 TUNICATA. surface. The mouth has usually the form, of a broad transverse slit, bounded by movable lips, and leads into the large respiratory cavity, which consists of the pharyngeal cavity and the cloaca, and contains the lamellar or band-shaped gill, extended from the dorsal surface obliquely backwards and ventralwards. In Doliolum the gill has the form of an oblique partition, which is pierced by two lateral rows of large transverse slits, through which the water flows Enl A PIG- 566. a, Salpa mncroii/'ta. '>, S. ilemocratica. 0, Mouth; A, cloacal aperture ; N, ganglion ; Br, gill End, endostyle ; Wg. ciliated pit ; Ma, mantle ; Nu, nucleus ; C, heart ; Bmb, embryo ; Stp, stolo prolifei-. from the pharyngeal cavity into the cloacal chamber. In Salpa the transverse slits are represented by one very large gill -slit on each side, so that the branchial wall is reduced to a median band (the median part of the gill of Doliolum}. The two arches of cilia which bound the entrance to the respiratory cavity, and the ventral endo- style (mucous gland) from which a ciliated groove leads to the oesophagus, are placed in' the wall of the pharyngeal cavity. THALIACEA. 105 The digestive canal, together with the other viscera, the heart and the generative organs, are closely packed together in a brightly- coloured mass, the nucleus, at the ventral side of the hind end of the body. The mantle is often thickened round the nucleus so as to form a globular swelling. The nervous system, the sense organs, and the organs of loco- motion, in correspondence with the power of free locomotion, present a higher grade of development than in the Ascidians. The ganglion, with its numerous nerves, lies above the point of attachment of the branchial band, and attains a considerable size. On the ganglion there is usually (Safya) a piriform or spherical process, with a horse- shoe-shaped brownish-red pigment spot and numerous rod-shaped structures, which prove beyond all doubt that this structure is an eye. In other cases (Doliolum] there is on the left side of the body an auditory vesicle connected with the ganglion by a long nerve. The median ciliated pit, too, is placed in the respiratory cavity in front of the ganglion. Peculiar sense organs, probably tactile in function, have been observed in JJofioliun in the lobes of the two mantle apertures and also on other parts of the external skin. These have the form of groups of roundish cells into which nerves enter. Locomotion is effected by means of broad bands of muscles, which span the respiratory cavity like hoops, and by their contraction narrow it. Part of the water is thus driven out of the cloacal aperture, and the body is propelled in the opposite direction. The reproduction of the Snips is alternately sexual and asexual. The solitary Salps are produced sexually, the chains of Salps asexually. The individuals of the chains of Salps are sexual animals, which form no stolon ; the solitary Salps only reproduce themselves asexually by budding on a ventrally-placed stolon. Since these two forms, which differ both in size aiad shape, as well as in the course of their muscular bands, and in certain features of the gills and viscera, alternate regularly in the developmental cycle of the species, the development represents an alternation of generations, which may even be still further complicated (Doliolum}. This alternation of solitary Salps and chains of Salps was discovered long before Steenstrup by the poet Chamisso. The Salps which form the chain are hermaphrodite, but the two kinds of sexual organs are neither developed nor ready to discharge their functions at the same time. Soon after birth the female organs attain maturity, while the testicular cseca are not developed till later, and produce the sperm still later. In Salpa the female 106 TUNICATA. parts are almost always reduced to a capsule enclosing a single egg and surrounded by blood. This capsule opens into the respiratory cavity on the right side, some distance from the nucleus, by a narrow stalk-like duct (tig. 567 b). After fertilization the stalk becomes A Sip El FIG. 5i37. ", Posterior end of Sctlpa democrat ica, seen from the ventral .side. Stp, Stolo prolifer ; jV, nucleus, h, Terminal portion of stolon=young chain, strongly magnified ; 0, mouth ; A, cloacal aperture ; jV, nervous centre (ganglion) ; If';/, ciliated pit ; Tf7>, aroh of cilia ; End, endostyle ; Af, anus ; Br, gill ; Nu-, nucleus; Of, ovary'; C, heart, e, Embryo of Kfil^ri ,], ,,,,11-,-ntlca (after C- Grobben). El, Elasoblast ; PI, placenta ; Ph, pharyngeal cavity ; Kl, cloaoal cavity. shorter, so that the is in- creasing in size, ap- proaches closer and closer to the lining .of the respiratory cavity, and forms with its capsule a projecting cone in which, as in a brood pouch, the embryonic development takes place.* In the course of development a pla- centa is formed be- tween the embryo * Besides E. Leuckart I.e. compare Kowalevski. " Beitrag zur Entwiekelungs- geschichte der Tunioaten." " Entwickelungsgeschichte der Salpen." Xm-Jir. run. (In- lidnii/l. GesclUrli . der WiwnxcJt., Nr.'li), Gottingen, 1868. W. Salensky, " Ueber die embryonale Entwickelungsgeschichte der Salpen," Zcitsclu'.fur'n-UK. Zonl., Tom XXVII.. 1876. W. Salensky, "Ueber die Knospung tier Salpen/' Morpli. JnJirli., Tom. III., 1877. THALIACKA. 107 and the mother, and this structure plays an important part in the nourishment and growth of the embryo. In the further development of the organs, which agrees in its general features with that of the Ascidians, the placenta becomes more sharply marked off from the body of the embryo, at the posterior end of which a structure known as tin- elceoblasttihe equivalent of the notochord makes its appearance (fig. 567 c). It is only after a Relatively long period that the embryo is born as a small fully- developed Xtd/>K, which, however, still possesses the remains of the placenta and the rhi'oblast. This solitary Saljxt, which has been produced sexually, grows considerably during its free life, but always remains asexual, while by budding on its stolon it produces a number of individuals united together in chains. This stolon or germ-stock is a process of the body containing the rudiments of the most important organs. Its central cavity is traversed by a stream of blood, and on its walls the buds sprout out. In Salpa, as in the Ascidians, the stolon lies on the ventral side, and later enters into a special, open excavation of the body covering (fig. 567 a). On account of the extraordinary fertility of the stolon several groups of buds of different ages are always present one behind the other ; they separate successively as independent chains. In Doliolum the reproductive processes are much more complicated, for not only do the sexually produced young undergo a metamorphosis but a new series of generations is introduced into the life history. The eggs are laid, and the larva; which issue from them are provided with tails and resemble Ascidian larva? (fig. 568, e). They develop into asexual forms which differ from the sexual forms, and are pro- vided with a dorsal stolon (fig. 568 b, Std} ; the ventral stolon (stolon of Salpa) is rudimentary (, arch of cilia ; ]!''. znnii-riu Pall, (chain form). Order 2. CYCLOMYARIA. Body cask-shaped, mouth and atrial opening surrounded by lobes, with delicate mantle (tig. 568). The muscles are in the form of closed rings. The dorsal wall of the pharyngeal cavity is formed by a branchial lamella which is pierced by numerous slits, is placed obliquely or is bent and stretched far forwards (D. denticulatnm). The digestive canal is not compressed into a nucleus. The ovaries contain several eggs. The testes attain maturity simultaneously with the ovaries. In the first asexual generation there is a large auditory vesicle on the left side. The development takes place by means of a complicated alternation of generations. Fam. Doliolidae. L>. ih-ntii-ulnt'nin Quoy, Gaim., the gill is bent and is pierced by about forty-five slits. D. Miillcrl Krohn. The gill is straight, with ten to twelve slits on either side. Mediterranean. CHAPTER IV. VERTEBRATA.* Bilaterally symmetrical animals with an internal skeleton (vertebral column), of -which dorsal processes (iqiper vertebral arches) enclose the nervous centres (brain and spinal cord), and ventral processes (ribs) the cavity in which the vegetative oryans are enclosed. There are at most two pairs of limbs. The various animals included in this group were first put together * I'.esides the works of (Juvier, F. Meckcl and J. Miillcr. cum] pare K. Owen. "On the anatomy of Vertebrates." Vol. [., II.. III., London, IHM-tiS. ( '. Gegenbaur, " Gruudziige der verp-leicheii'len Anatomic," 2 Aufl. Leipzig, 187S. Tb. H. Huxley, " A Manual of the Anatomy of vertebrated animals.' Loudoi., 1871. 110 VEETEBRATA. by Aristotle, who called them " animals with blood" (vol. I., p. 132) ; he also put forward the possession of a bony or cartilaginous skeletal axis as a common characteristic. But it was Lamark who first recognised the presence of a vertebral column as the most important character, and introduced before Cuvier the name of Vertebrata into the science. This designation, however, in its strict significance, is only an expression for a definite grade of develop- ment of the skeleton, which may persist in its first unsegmented condition as the notochorcl (Amphioxus, Myxine). The most im- portant characteristics therefore of the Vertebrata do not depend upon the presence of internal vertebrae and of a vertebral column, but upon a combination of characters which have to do with the general relations of posi- "--// \ \ tion, the mutual arrangement of the organs and the mode of embryonic development. We may accordingly define the Vertebrata as laterally symmetrical organisms with an axial skeleton, on the dorsal side of which is placed the central nervous system (brain and spinal cord), while on it's ventral side lie the alimentary canal with its two open- ings (oral and anal) and the rest of the viscera and the heart ; the latter being placed on the ventral side of the alimentary canal. 569,-Transverse section The Skeleton.-The presence of an in- through the chorda dorsalis ternal skeleton is a character of great im- (CA) of the larva of Jinm/ii, mtor ITTI -i ,1 T ignem (after Gotte). c/,s,Noto- P ortance - whll e m the Invertebrates the chordai sheath ; sk, skeietoge- firm supporting structures are almost always nous layer ; N, spinal cord. j , produced by the hardening and segmenta- tion of the external skin, in the Vertebrates the relation of the hard to the soft parts of the body is reversed. The hard parts are ' placed in the axis of the body, and send out processes towards the dorsal and ventral surfaces, which constitute respectively a dorsal canal for the reception of the central nervous system (brain and spinal cord) and a ventral arch over the vascular trunks and the viscera. In the simplest and lowest Vertebrates the axial skeleton remains as an elastic cord the notochord (chorda dorsalis}, which in the higher Vertebrates is present in embryonic life and constitutes the first rudiment of the vertebral column (fig. 569). When the internal skeleton acquires a firmer consistency it, like the external skeleton of the Invertebrates, becomes segmented. This modification is intro- VERTEBRAL COLUMN. Ill (lured l>y alterations in tlie notochordal sheath as well as in the surrounding skeletogenous sheath (rig. 570, a). The latter gives rise to cartilaginous or bony rings, which represent the first rudiments of the vertebral bodies. These rings constrict the notochord till they assume the form of biconcave car- tilaginous or bony discs, and become connected with cartilaginous or bony arches which are developed round the spinal cord and the perivisceral cavity (tig. 570 a, f>). Each vertebra therefbre consists of a principal median portion, the body of the vertebra or centrum, which frequently retains the re- mains of the notochord in its axis ; of a dorsal or neural arch, and a ventral or ha?mal arch. The two limbs of the dorsal arch are called neurapophyses, those of the ventral arch hsemapophyses, and the unpaired median prolongation of each arch is known as the spinous process (tig 570, J), D'}. The trans- verse processes (pleurapophyses) which arise from different parts of the vertebra*, either from the neural arches or from the centra, are not independent structures but merely processes. The ribs, on the other hand, are independent lateral bony or cartilaginous rods which are attached either to the ha-mapophyses (fishes) or to the pleurapophyses, and embrace the part of the body cavity containing the viscera. Regions of the vertebral column. In the higher Vertebrates the primitive homonomous si '-mentation of the skeleton gives place to a heteronomous segmentation which leads to the origin of a number of regions. In this point as in others there is a parallel between the segmented Invertebrates and Vertebrates. In the first place an anterior region or head can always be distinguished from the posterior uniformly segmented region or trunk (fig. 571) ; and this division corresponds with the enlargement of the anterior part of the central nervous system to FIG. 5~0. , Diagram of the vertebral column of a Teleostean with inter- vertebral growth of the notochord. Ch, Noto- chord ; 1T7-, bony verte- bral bodies ; /, mem- branous intervertebral portion, b, Vertebras of fish. A", Body of vertebra, Ob, dorsal arch (mvra- jn>, Jit/sis) ; Ub, ventral arch (JireitKijiiiji //<> t ,<>,,i 5- -3 8 1 i S-.S en - o o S" be - 9 as ventral elements which join their fellows in the middle ventral line, and are known as the pubis ami ischium. The limbs are divided into three segments the two proximal of which are long and contain long hollow bones articulated together, the third segment being shorter and "m-.i * i terminal. These segments are called brachium, antebrachium and maims in the fore-limb: femur, cms and pes in the-- hind-limb. The proximal segments (I.e., the brachium and femur) each contain one bone the humerus (//) and femur (Fe) respectively. The middle segments (i.e., antebrachium and eras) each contain two bones the radius and ulna in the former (, U ), the tibia and fibula (T, F ) in the latter. The distal or terminal segments (i.e., the manus and pes) each contain a large number of elements placed close together. These elements consist of two proximal rows of bones, known in the hand as the carpus, and in ' the foot as the tarsus; of a middle row, known respectively as the meta- carpus and metatarsus; and of a number of distal bones known as the phalanges, and constituting the skeleton of the fingers and toes. The skull varies considerably in form and structure. When the ver- tebral column is membranous and cartilaginous, the skull likewise con- sists of a continuous membrano-car- tilaginous capsule, which in essential points agrees with the embryonic rudiment of the cranium (primor- dial cranium) of the higher Vertebrates (fig. 571). From this primordial cranium the bony .2 a tao 55 & -LJ o FH O _ " M IB 116 VERTEBRATA. skull* is developed partly by ossifications in the cartilaginous capsule or by ossifications proceeding from the membranous peri- chondrium ; partly by the addition of membrane bones, which gradually supplant the cartilaginous parts. Segmentation of the skull. It is only when the cranial capsule is bony that any comparison can be instituted between the arrangement of the hard parts of the skull and that of the parts of a vertebra : this comparison has led to the view that the skull is composed of three or four vertebra? or segments. These are from behind forwards, the occipital, parietal, frontal and ethmoid segments. Each such segment, according to the vertebral theory of (P. Frank) Goethe and Ql FIG. 574. Lateral view of a goat's skull ; O/, exoccipital bone; C, condyle ; Os, supra- occipital; Sq, squamosal ; Ty, tympanic; Pe, petrosal ; Pm, paramastoicl process; Pa, parietal; Fr, frontal, Lti, lachrymal ; -ZV, nasal ; Fo, optic foramen ; MX, maxilla; Jiux, inter-maxilla (pre-maxilla) ; Jn, jugal ; Pa/, palatine ; Ft, pterygoicl. Oken, is supposed to consist of a basal part corresponding to the body of the vertebra, and of a neural arch formed of two lateral pieces and a median dorsal piece (spinous process) (fig. 574). According to this theory the basi-occipital bone would correspond to the body of the vertebra, the two exoccipitals to the lateral parts of the neural arch, and the supra-Occipital to the dorsal median parts or spinous process. The bones of the middle or parietal region of the skull consist of a basal bone, the , basisphenoid, two lateral bones, the alisphenoids and two dorsal bones, the parietals ; the two latter are membrane bones, and complete the arch dorsally. The bones of the * Compare especially Eeichert and Kolliker. Huxley, Parker etc. SKULL. 117 anterior or frontal region likewise consist of the basal praesphenoid, the two lateral orbitosphenoids, and the two dorsal frontal bones, which are membrane bones and complete the arch dorsally. The ethmoid may be regarded as representing the body of a fourth or anterior vertebra ; it is covered above by the nasal bones and below by the vomer. Finally, between these different bones other bones are intercalated, e.g., the mastoid and petrosal between the occipital and sphenoidal. Recently essential objections to this vertebral theory have been raised by Huxley and Gegenbaur ; and the.-e objections have proved fatal to the theory. According to Gegenbaur, the skull is composed FIG. 575. Median longitudinal section of a sheep's skull seen from the inside. Ob, basi- occipital ; O7, exoccipital ; Os, supraoccipital ; Pe, petrous bone ; Spb, basisphenoid ; Px, praesphenoid ; Ah, alisphenoid ; On, orbitosphenoid ; Pa, parietal; Fr, frontal; Sf, frontal sinus ; Na, nasal ; C, tnrbinal ; Ci, interior turbinal ; Ft, pterygoid ; Pal, palatine; I'o, vomer ; MX, maxilla ; JW-, inter-maxi!la (pre-maxilla). of a much greater number of segments corresponding to the primary visceral arches, and the resemblances between the cranial bones, especially of the median and anterior regions of the skull, and the parts of a vertebra are entirely secondary. The rest of the hard parts, which are more or less intimately connected with the skull, consist of a number of arches lying one behind the other, and surrounding the entrance into the visceral cavity. The anterior of these the maxillo-palatine apparatus forms the facial region. In its simplest form it consists of two moveable pieces (palato- quadrate and lower jaw), which are attached by the hyoman- dibular (the dorsal element of the second arch) to the auditory region 118 VERTEBRATA. of the skull (tig. 571, //). The upper piece of the first arch, like- wise, is sometimes more or less firmly applied along its whole length to the skull, and when ossification takes place it becomes divided on either side into an outer and inner series of pieces, the first including the jugal, the maxilla, and praemaxilla, the latter the pterygoid and palatine (fig. 575). These series of bones form the upper jaw and the roof of the mouth. The lower jaw, which is primitively a simple cartilaginous arch (Meckel's cartilage), also becomes replaced on either side by a number of bones (articulare, angulare, clentary, etc.), of which the clentary usually bears teeth and is the largest. The visceral arches which follow the mandibular arch and are also connected with the skull are developed in the wall of the pharynx, to which they bear the same relation that the ribs do to the thorax and body cavity. The anterior arch (hyoid arch), the upper portion of which in the lower Vertebrates serves as the suspensorium of the jaw (hyomandibular), forms a support for the tongue, and the arch of each side meets a median basal piece (os linyuale). The latter is followed by a series of median unpaired bones (copulce), which connect the following arches (branchial arches). The branchial arches are most developed in the aquatic Vertebrates, in which they are separated by the pharyngeal slits, and serve to bear the gills. In the air- breathing Vertebrates they become more and more reduced, and finally are only discernible in imperfect number as embryonic struc- tures. The remains of the whole apparatus form the body and cornua of the hyoid bone. Integument. The external skin of the Vertebrates is divided into two very distinct layers, the epidermis externally and the cutis internally. The latter is principally composed of a fibrous connective tissue, with which muscular elements come into relation, without however forming a complete dermal-muscular envelope as in the Annelids.- When the dermal muscles have a considerable extension over large surfaces, they serve exclusively to move the skin and its manifold appendages, but are not used for the movements of the trunk, which are produced by a highly -developed muscular system surrounding the skeleton. The cutis is continued into a deeper, more or less loose layer, the, subcutaneous connective tissue, but its more superficial part is tolerably compact, and contains not only various pigments, but also blood-vessels and nerves. At its upper surface the cutis is raised into small conical papilla^, which are covered by the epidermis and NERVOUS SYSTEM. 119 are of importance not only as special sense organs (tactile organs), but also for the production of various hard structures (scales, teeth). The epidermis is composed of several layers of cells, of which the upper and older layers are cast off, while the lower layers (stratum Malpi(jhi) are actively growing and serve as a matrix for the con- tinual renewal of the upper layers, and sometimes contain the cutaneous pigments. Some of the appendages of the skin are epidermal structures, in which case they arise as the result of peculiar and independent growths of the epidermis (hairs and feathers). Some are de- rived from ossifications of the dermal papillae which sometimes may even give rise to a hard and complete dermal armour (scales of Fishes and Reptiles, carapace of Armadillos and Tortoises). The central nervous system is placed in the dorsal cavity formed by the upper arches of the vertebrae ; it consists essen- tially of a cord the spinal cord the anterior enlarged and more differentiated part of which is distinguished as the brain. The spinal cord con- tains a narrow central canal, FIG. 576. Embryo chick at end of second day the (after Kolliker). TVi, Fore-brain; Mh, mid- which is continued into brain, where it widens out and forms the ventricles of the brain. The brain and spinal cord are, therefore, parts of the same organ. brain ; Hh, hind-brain ; Ab, optic vesicle ; MR, medullary canal ; UW, protovertebrse ; StZ, vertebral plates of the mesoderm ; SP, lateral mesoblastic plates ; H, heart. The brain seems to be the seat of the intellectual faculties and the central organ of the sensory apparatuses ; while the spinal cord conducts the impulses to and from the brain, and in particular is the centre of reflex move- ments, but it also contains the centres of certain automatic actions. The mass of the brain and that of the spinal cord increase as might be expected, as the grade of life is higher. They increase, however, in an unequal ratio, for the brain soon preponderates over the spinal 120 VERTEBRATA. cord. The lower Vertebrates with cold bloocl have a relatively small brain, the mass of which is still considerably smaller than that of the spinal cord. In the warm-blooded Vertebrates, on the other hand, this proportion is reversed, and the more markedly, the higher the organisation and grade of life of the animal in question. The spinal nerves arise in pairs from the spinal cord : each nerve has two roots a dorsal sensory root and a ventral motor root. They correspond in number with the vertebne, between which they pass out, so that the spinal cord repeats in a general manner the seg- mentation of the vertebral column. In the brain the arrangement of the nerves presents several com- plications which are further increased by the origin of two sensory nerves the olfactory and optic. In spite of the differences in form MO FIG. 577. a. Brain and anterior part of the spinal cord of a human embryo seen from the side (after Kolliker). Vh, Fore-brain; Zh, thalamencephalon ; Mh, mid-brain: Hh, hind-brain ; Nh, medulla oblongata ; T, anterior ventral end of the thalamencephalon ; NO, optic nerve. 1. Diagrammatic longitudinal section through a vertebrate brain (after Huxley). Hs, Hemispheres; LO, olfactory lobes ; Olf, olfactory nerve; ThO, optic thalamus; T7, third ventricle ; No, optic nerve; H, pituitary body (hypophysis); Gp, pineal gland ; CQ, corpora quadrigemina ; Cb, cerebellum ; MO, medulla oblongata ; P V, pons Varolii. and structure presented by the brain, three principal regions which correspond to the three vesicles found in the embryo can always be distinguished (fig. 576). The anterior vesicle (fore-brain, fig. 576, Vh} corresponds to the cerebral hemispheres and the optic thalami (fig. 577, Hs, ThO), the middle vesicle (mid-brain, Mh) to the corpora quadri- gemina (fig. 577, C Q), and the posterior vesicle (hind-brain, fig. 576, flh) to the cerebellum and medulla oblongata (fig. 577, Cb, MO). The anterior vesicle, however, is again divided into two parts an anterior bilobed part, which constitutes the cerebral hemispheres and contains the lateral ventricles, and a posterior unpaired part which constitutes the so-called thalamencephalon with the thalami optici and the parts surrounding the third ventricle (fig. 577). The third cerebral vesicle is also divided into two parts anteriorly the cerebellum, and pos- teriorly the medulla oblongata. SENSE ORGANS. 121 The sense organs present the following arrangement. The anterior is the olfactory organ, which consists of a pit usually paired, excep- tionally unpaired (Cyclostornes) ; the nerves which pass to these pits arise from the fore-brain and are often swollen at their origin into special lobes (olfactory lobes). In aquatic animals which breathe by gills the nasal cavity consists with rare exceptions (Mi/.i-lne] of a blind sac. In all lung-breathing Vertebrates, on the contrary, it communicates with the cavity of the mouth by the nasal passages, and serves for the entrance and exit of the pulmonary air. Next come the eyes with the optic nerves which arise from the thalamencephalon and mid-brain. They are always paired (for the structure of the eye vide p. 73, vol. i.). In Am- phioxus alone they are represented by an un- paired pigment spot placed on the anterior end of the central nervous system. The auditory organ, the nerve of which belongs to the hind- brain (probably derivecl from the sensory root of a spinal- like cranial nerve), is entirely absent in AmphioXUS. In its simplest Fi& 578 _ Dia?ram of the auditory labyrinth (after Waldeyer). I, of fish ; II, of bird ; ///, of mammal ; U, utricle with the three semicircular canals ; S, saccule ; US, alveus communis ; C, cochlea ; L, lagena; Cr, caualis reuniens ; R, aquteductus vesti- bull. form it is a membranous sac (membranous labyrinth) containing fluid and oto- liths. The posterior part of this sac is usually prolonged into three semi-circular canals, while the anterior part, which in many cases is separated as the saccule, gives off a prolongation which forms the cochlea (fig. 578, />', C.). The sense of taste is located in the palate and the root of the tongue. The organs of taste consist of peculiarly-modified groups of epithelial cells (taste buds), and are supplied by a spinal- like cerebral nerve (glossopharyngeaC). The general sensibility, which is distri- buted over the whole surface of the body, and the tactile sense are also connected with the terminations of the sensory fibres of spinal nerves. In addition to the cerebro-spinal nervous system there is (except in Amphioxus and the Cydostomes) a special visceral nervous system 122 VERTEBRATA. the sympathetic. This is formed by special branches of the spinal nerves and spinal-like cranial nerves, which are connected with special ganglia and give off nervous plexuses to the viscera (fig. 80). The organs of nourishment, circulation, and reproduction are placed in the body cavity \^jiich extends beneath (ventral to) the skeletal axis. The digestive canal is a more or less elongated tube which in the region of the skull is encircled by the visceral arches ; it begins with the mouth and ends with the anus, which latter is placed on the ventral surface at various distances from the hinder end of the body (according to the length of the caudal region of the verte- bral column). The alimentary canal is invested in the greater part of its course by a fold of the peritoneum which lines the body cavity, and is fastened to the under surface of the vertebral column by the two lamella? of this fold, which are closely applied to one another and form the mesentery. As a rule the alimentary canal is much longer than the distance between the mouth and anus, and therefore forms more or less numerous coils in the body cavi y. The digestive canal is almost always divided into three regions, the oesophagus and stomach, the small intestine with liver and pancreas, and the large intestine. The oesophagus always begins with a buccal cavity, on the floor of which a muscular fold, the tongue, projects. Although this organ, which is richly supplied with nerves, is in general rightly regarded as an organ of taste, it nevertheless plays a considerable part in the reception of the food, and may even in some cases altogether lose its importance as an organ of taste. The buccal cavity, except in Amphioxus and the C'yclostomes, is enclosed by the skeletal arch known as the maxillo-palatine apparatus and the lower jaw, of which the latter is always . capable of powerful movements, while the parts of the former are either more or less firmly united together and attached to the bones of the skull, or are capable of movement on the latter. The two jaws, unlike those of the Arthro- poda, work upon one another in the direction from below upwards. They are usually furnished with teeth. The teeth are derived from ossified papillae (dentine) of the mucous membrane of the mouth (fig. 579), which are covered with an epidermal structure the enamel ; they are either directly fused with the bones of the jaw or inserted into special alveoli in the latter. The teeth in the higher Vertebrates are confined to the upper and lower jaws, but in the lower Vertebrates they may appear on all the bones which surround the buccal cavity. Teeth are, however, often altogether absent. In Birds and Tortoises they are replaced by a horny covering of the sharp edges of the jaws ALIMENTARY CANAL. I L':; a (beak), and certain toothless Whales bear horny plates (the so-called whalebone) on their palate. In almost all cases the alimentary canal is provided in its different regions with independent glands which mix their secretion with its contents. In the cavity of the mouth the saliva secreted by a greater or less number of salivary glands is mingled with the food. In many aquatic animals these salivary glands may be reduced or be wholly absent. Into the first part of the small intestine the bile and the secretion of the pancreas, which is of great importance for the digestion of the food, is poured. The bile is secreted by the liver a, large gland through which the venous blood returning from the viscera passes on its course to the heart (portal circu- la t i on). I n A mphioxus the liver is repre- sented by a simple ca?cal di- verticulum of the intestine. In Ampliioxus and some other fishes the pan- p IG . 579. creas is want- ing. The small intestine i n which the juices are absorbed is distinguished not only by its great length- it is in fact this portion of the alimentary canal which is arranged in coils but also by the presence of internal folds and papillae which considerably increase the extent of absorbing surface. The terminal region (large intestine, rectum) of the digestive canal is principally distinguished by its width and its powerful muscles. Special respiratory organs, as lungs or gills, are always present. The gills usually consist of double rows of Iniicet-shaped lamella?, which are arranged on the sides of the pharynx behind the rnandibu- lar arch, and except in the Cydostomes are borne by visceral art-lies. Between these arches there are always narrower or wider slit-like openings, which lead directly into the pharynx and allow the water The development of the tooth in Triton (after 0. Hertwig). , The first stages of the development of a tooth ; on the right hand is the earliest rudiment. l>, Later stage of development. DK, papilla of the cut is which later becomes the dentine of the tooth MS, enamel membrane (epithelial growth which forms the enamel) ; D, dentine; S, enamel; Ep, epithelium of the mouth. 124 VERTEBRATA. which bathes the gills and serves for respiration to pass from the pharynx into the branchial cavity. On the external side the gills are often protected by a cutaneous fold or by an operculum, at the lower or posterior margin of which there is a long slit for the passage outwards of the water from the branchial cavity. The gills may, however, project as uncovered external appendages (external gills of Amphibians and Selachian embryos). In the lower Vertebrata lungs and gills may coexist in the same animal, and in fishes the lungs are represented by a morphologically equivalent organ the swimming bladder. Lungs, however, in their more complete development are only found in the higher and for the most part warm-blooded Vertebrates. In their simplest form they appear as two sacs filled with air and opening by a common air passage (trachea) into the pharynx. The walls of the pulmonary sacs contain the respiratory capillaries ; their surface is usually increased by folds and projections which give them the appearance of a spongy organ or of an organ traversed by tubes. The two lungs often extend far into the body cavity, but in the higher Vertebrates they are confined to the anterior part of the latter which may be more or less completely separated off from the hinder part of the body cavity by a transverse partition the diaphragm and is then called the thoracic cavity. Aerial respiration also requires a continual change of the medium serving for respiration ; the exchange of the used-up air saturated with carbonic acid gas for the atmospheric air rich in oxygen. This exchange is effected by various mechanical arrangements on which the so-called respii-atory movements are dependent. These move- ments take place in all those Vertebrates which breathe by means of lungs, but are most complete in the Mammalia, in which they con- sist in alternating rhythmical contractions and dilatations of the thorax. At the entrance of the trachea and in connection with the organs of respiration is the vocal organ (larynx), which is usually formed by a modification of the upper portion of the trachea. The larynx contains vocal chords, and opens into the pharynx by a narrow slit (glottis) which is usually capable of being closed by an epiglottis. The circulatory organs are in close relation with the respiratory organs. The vascular system is always closed and contains red blood (except in Amphioxus and the Leptocephalida, where the blood is white). The red colour of the blood, which was formerly held to be the essential character of blood (Aristotle), is due to the presence of an VASCULAR SYSTEM. enormous number of red blood corpuscles, which are fiat, disc-shaped globules, contain the colouring matter (haemoglobin) and carry the oxygen to the tissues. In addition to the red blood-corpuscles there are small colourless cells in the blood the amoeboid white blood-corpuscles (vol. i., fig. 19). Except in A/iiju/t/o.i'/iv, in which the larger vascular trunks pulsate, a definite part of the vascular system is always developed to form a heart. The heart lies in the anterior part of the body cavity, and is primitively placed exactly in the middle line. It has a conical shape and is enclosed in a pericardium. The position of the principal vessels arid their connection with the heart are in the simplest case as follows : A large artery the dorsal aorta runs along the verte- bral column and gives off numerous lateral branches, corresponding to the segmentation of the vertebral column, to the right and left. Beneath this there is in the caudal region, an unpaired vein the caudal vein, in the body cavity on the contrary a pair of veins the inferior cardinal veins. These veins receive their blood from lateral venous branches which proceed directly from the capillary network of the arterial branches. Another principal vein the vena cava inferior separated from the cardinal veins by the hepatic portal system, and connected with two superior cardinal veins, conveys the venous blood back to that portion of the heart which is known as the auricle. From the auricle the blood flows into the the muscular ven- tricle and is forced thence into an ascending artery (aorta ascendens or cardiac aorta). The latter divides into lateral arterial arches which pass towards the dorsal side and unite beneath the vertebral column to form the anterior part of the dorsal aorta (aorta descendens) (vol. i., fig. 57). This system of the aortic arches is, however, complicated in various ways by the insertion of the respiratory organs in the course of the circulation (compare vol. i., p. 63 et seq). In all Vertebrates there is a system of lymphatic vessels. These are a special part of the vascular system and contain a clear nutritive fluid (chyle and lymph) which is filled with colourless corpuscles (lymph corpuscles). They conduct the lymph (containing plastic materials for the renewal of the parts of the blood which have been consumed in metabolism ) to the blood. The principal trunk of the lymphatic system (the thoracic duct) runs along the vertebral column and in the higher Vertebrates opens into the upper part of the vena cava superior. In the lower Vertebrates there are several communica- tions between the lymphatic and vascular systems. Special gland- 126 VERTEBRATA. like organs the so-called vascular glands, spleen are inserted into the course of the lymphatic vessels. Urinary organs or kidneys are generally present. They have the form of paired glands and lie beneath the vertebral column. The first rudiments of the kidneys appeal- in the form of organs resem- Lc TJ: 'Ilk FIG. 580. Diagrammatic longitudinal section through aii ideal vertebrate embryo (after Balfour). of the embryonic development and in the absence of the embryonic organs characteristic of the higher Vertebrates the amnion and the allantois. On these grounds, and in consideration of the many relations between Reptiles and Birds, Huxley distinguishes three principal groups of Vertebra ta -the Ichthyopsida (Pisces and Am- phibia), the Sauropsida (Reptilia and Aves), and the Mammalia. Among the Fishes there are certainly such wide differences of organi- sation that we are justified in dividing them into several classes. The Leptocardia might be separated not only from all the Fishes but also from all other classes of Vertebrates as Acraniata ; also the Selachians, the Cyclostomes and the Dipnoi might be regarded as separate classes if it were not more convenient to preserve the unity of the class Pisces. CHAPTER V. Class I. PISCES.* Cold-blooded, generally scaly, aquatic animals with unpaired fins and paired pectoral and pelvic fins. They breathe exclusively by means of yills, and have a simple heart consisting of auricle and ventricle. They are without anterior urinary bladder. The peculiarities which the structure and internal organisation of these animals present result in general from the requirements of their * Cuvier ct Valenciennes, " Histoire Nature lie des Poissons." 22 Vol?.. Paris, 1828-49. Job. Mliller, " Vergleichende Anatomic der Myxinoiden." Berlin, 1835-45. L. Agassiz, " Recherches sur les poissons fossiles." Neufchatel, 1833-44. Gunther, "Catalogue of the fishes in the British Museum." London. C. E. v. Baer, " Ent \vickelungsgeschichte der Fische." Leipzig, 1835. VOL. II. 9 130 PISCES. aquatic habits. Although there are in all classes of Vertebrates forms which move and live in water, yet nowhere is the whole organi- sation so completely adapted to an aquatic life as in Fishes. The body is in general spindle-shaped and more or less compressed, but in details presents numerous modifications. There are cylindrical, .snake-like fishes (Lampreys) as well as fishes with a spherical, balloon- like form (Gymnodontct). Others are elongated and band-shaped, and others again are very short, flat and unsymuietrical (Pleiironectidif). Finally a dorsoventral flattening may lead to a flat discoidal form(]ays). Locomotion is effected mainly by lateral flexions of the vertebral column, which are caused by the powerful body muscles. The effect of these movements may be greatly increased by the unpaired dorsal and ventral fins, which are capable of being elevated and depressed. The two pairs of extremities the pectoral and pelvic fins appear, on the contrary, to be used more as rudders to direct the course of , ' i- /<*"> Wl FIG. 583. Pereajluviatilis (regiie animal). the animal. The structure of the vertebral column, which is not divided into many regions, corrresponds to the mode of locomotion. The head is directly attached to the trunk, and is usually rigidly connected with it. A moveable cervical region, which would be a hindrance in swimming, is completely absent. The anterior part of the body is rigid, but behind it becomes more flexible and passes gradually into the the tail, the vertebrae of which permit of the most complete movements on one another, and which on that account constitutes the principal organ of locomotion. Fins. The system of unpaired fins is developed from a median cutaneous fold of the embryo, extending over the back and tail as far as the anus. Subsequently this fold becomes broken up into parts, the definite unpaired fins. There are usually three such parts, constituting the dorsal fin (pinna dor satis), the caudal fin (pinna caudalis), and anal fin (pinna (mails) (fig. 583). These ridges of skin are supported as a rule by firm rays the fin-rays ; in the Teleosteans either by hard, FINS INTEGUMENT. 1 .'U bony, pointed spines the so-called spine-rays (Acant/wpteri) or by soft jointed rays (Malacopteri). The caudal tin is as a rule composed of a part of the dorsal and a part of the ventral fin-fold, but it varies much in its form. When the dorsal and ventral lobes are symmetries] the caudal fin is said to be homocercal ; when the ventral lobe is the larger, in which case the caudal part of the vertebral column is usually bent dorsalwards, the caudal fin is said to be heterocercal. It some- times happens, however, that while the caudal fin is externally horno- cercal the axial skeleton is bent dorsalwards so that the fin is internally heterocercal. The paired pectoral and pelvic fins correspond to the anterior and posterior limbs of other Vertebrates. The former are attached to the head immediately behind the gills by means of an arched shoulder- girdle, while the two pelvic fins are approached to the middle line and placed further back, usually on the abdomen (ventral fins) ; sometimes, however, they lie between the pectoral fins (thoracic fin-s), and more rarely in front of the latter on the throat (jugular fins). The integument of fishes is seldom completely naked (Cydostomi). ^ a rule scales ossifications of dermal papilla 1 , which are completely covered by epidermis are embedded in it. The scales are often so small that they are hidden beneath the skin and seem to be completely absent (Eels). As a rule, however, they are present as firm, more or less flexible plates, which are covered with a number of concentric lines and radial striations and lie on one another like slates on a roof. Scales may be distinguished according to the structure of their free edges as cycloid scales with smooth edges, ;md Ctenoid scales with serrated edges. Scales, which overlap but little and are generally rhomboidal, more rarely cycloidal in shape, and have an outer layer of enamel, are called ganoid scales, while the term placoid scale is applied to the small bony granules (composed of enamel and dentine) of different shapes, which lend to the surface of the skin the appearance of shagreen (these are the primitive form of teeth). Agassiz divided the Fishes according to the shape of their scales into Cycloids, Ctenoids, Ganoids, and Placoid s. In the skin there are peculiar cutaneous canals communicating Avith the exterior by lateral rows of pores. These are called the lateral lines and were considered to be slime-secreting glands till Ley dig* discovered that they contain a sense organ. * Compare Leydig, " Ueber das Organ eines sechsten Sinnes." Dresden, lsi;s Fr. E. Schulze, ' Ueber die Sinnesorgane der Seitenlinie bei Fischen und Amphibian." Arch, fur miJtrosk. Anatomie, Tom. VI., 1S70. 132 PISCES. In the Myxinoids and Acipenseridct; these organs have the form of short sacs- in the Rays, Skates, and Chimaeras they are simple tubes, which begin as ampullae and extend also over the head in several rows. In the Teleostei there are branching tubes which pierce the scales of the lateral lines as pores, and are also present on the head in several rows (fig. 583). Nerves run in the walls of these tubes and end in knob-like swellings. The epithelial covering of the latter contains in the centre short piriform cells, which at the free end are prolonged into a fine stiff hair, while at the base they pass into a varicose process the axis cylinder of a nerve fibre (fig. 584). The skeleton in its simplest form consists only of the notochord (Amphioxus). The notochord also persists in the Myxinoids, which possess a cartilagino-mern- branous cranial capsule. In the Petromyzontida* there appear for the first time, above the notochord, cartilaginous neural arches, and similarly beneath it paired cartilaginous bands. These are the first rudi- ments of the dorsal and ventral vertebral arches. These vertebral arches are more perfect in sturgeons (Acipenser), and in the FIG. 584. a, Lateral organ in the tail of a fish (roach); /7 N, nerve, b, lateral organ in the head of a young sea - cats (ChimCBrct), 111 fish (bream) (after P. B. Schulze). whi(}h the noto chord per- sists, surrounded by a very compact connective-tissue sheath. A differentiation of the axial skeleton into separate vertebrae is first found in the Skates and Rays, where dorsal and ventral arches are united with annular portions of the notochordal sheath which become cartilaginous vertebral bodies. The notochord is constricted by the growth of the latter in the centre of each vertebra, in such a manner that biconcave (cmvphiccdous) vertebral bodies are formed, * Compare Job. Muller I.e., Reichert, " Ueber die Visceralbb'gen im Allgemeiuen, etc." Mailer's Archir, 1837. A. KSlliker, " Ueber die Beziehungen der Chorda dorsalis zur Bildung der Wirbel der Selachier und einiger anderer Fische." Wiirzburg, 1866. C. Gegenbaur, " Ueber die Entwickelung der Wirbel saiile des Lepidostens mit vergleichenden anatomischen Bemerkungen.'' Jot. natwrcissensch. Zeitschr., Tom. III. SKULL. 133 the conical cavities of which contain a part of the remains of the notochord. The notochord as a rule persists also in the centre of the vertebral body as a thin cord (connecting the dilated inter- vertebral portions, fig. 570 ). In the bony Ganoids and the Teleosteans the biconcave :;: vertebral bodies are completely ossified and fuse with the corresponding upper and lower bony arches, so as to form a complete vertebra. In some parts of the trunk ribs are attached to the pieces of the ventral arches (hsemapophyses) which here diverge from one another; and there are often in addition ossifications of the inter-muscular ligaments. The structure of the skull in Fishes presents a series of grades of development culminating in the complicated skull of the Teleostei. The primordial skull of the Cydostomes is the simplest. It consists of a cartilagino-membranous cranial capsule, in the hard basilar part Q FIG. 585. Cephalic skeleton of the Sturgeon (after Wiedersheim). So, rostrum ; C, nasa\ pit ; O, orbit; Hrn, hyomandibular ; S, symplectic ; Pq, palatoquadrate ; Mil, lower jaw; Hy, hyoid bone ; V, foramen for the vagus ; R, ribs. of which the notochord ends. Two bony capsules lateral appendages of the bony basilar region enclose the auditory organ, while two anterior pieces are connected with the complicated apparatus of the facial and palatal cartilages. The primordial skull of the Selachians (fig. 571) shows a further advance in development. It has the form of a simple cartilaginous capsule which is not further divided into separate pieces. The notochord ends in its base. In the sturgeon (tig. 585), there are bony pieces as well as the cartilaginous cranial capsule. These consist of a flat basilar bone the parasphenoid and a system of dermal membrane bones. A true bony cranial invest- ment is first developed round the primordial skull of the Dipnoi. In the bony skulls of the Ganoidei and Teleostei there still remain continuous portions of the primordial cartilaginous cranium (Pike * In the genus Lrpidosteus alone is there an anterior articular surface on the vertebral bodies ; the centra being convex in front and concave behind. 13 i PISCES. and Salmon). The remains of cartilage are retained longest in the ethmoid region (tiilurus, Cyprinus), while on the roof and base of the skull all remains of cartilage are replaced, partly by membrane bones and partly by the primarily ossifying oecipitals (basi- and exoccipital) and petrosals (periotic) as well as by the alisphenoids. The posterior part of the skull is connected with the vertebral column without any special articulation (except in the Rays and Os Par Ethl Ssc SOp Cl FIG. 586. Cephalic skeleton of Perca fluvuMUs (regne animal). Os, supraoccipital ; Oeo-, epiotic ; Par, parietal ; Sij, squamosal (pterotic) ; Fr, frontal ; Frp, poslf rental (sphenotic) ; PrO, prootic ; Ah, alisphenoid ; Ps, parasphenoid ; Sthi, median ethmoid; Ethl, lateral ethmoid (prse -frontal); Hm, hyorcandibular ; S, symplectic; Q, quadrate; Mtp, metapterygoid ; Enp, endopterygoid ; Ekp, ectopterygoid ; Pal, palatine; Vo, vomer; Jm, intermaxillary (premaxillary) ; MX, maxillary; D, dentary ; Ar, articulare ; An, angulare ; O^,.operculum ; POp, prse-operculum ; SOp, sub-opercuhim ; JOp, inter- op^rculum ; Hi/, hyoid arch ; Brs, branchiostegal rays ; Cl, clavicle ; Sc, scapula Cor, coracoid ; Ssc, supraclavicle ; Ac, accessory bone. Chirntera), the os basilare having the conical depression and form of a vertebral body. Between the exoccipitals (which contain the fora- mina for the exit of the vagus and glosso-pharyngeal nerves) and the supra -occipital, which is distinguished by a strong ridge, an epiotic bone (occipitale externum) is inserted on either side (fig. 586, Oex). Close to the epiotic bone is the opisthotic (Huxley), which varies greatly in size and form (being very large in Gadus and small in SKri.i,. 135 , and the prootic (PrO), which surrounds the anterior semi- circular canal and is pierced for the exit of the trigeminal nerve. There is also an external bone, the squamosal (pterotic) (], while the remaining arches are the branchial arches and serve for the support of the branchial lamella? (fig. 587). In the Teleosteans four (seldom three) arches bear gills, while the posterior arch is reduced so that only its ventral PAIRED FINS NERVOUS SYSTEM. 137 part (ceratobranchial) remains and forms the so-called inferior pharyngeal bones (pharyngealia inferiora). The upper segments of the branchial arches, which are applied to the base of the skull, are distinguished as the superior pharyngeal bones (pharyngobranchials or phanjnyealia superiora). Paired Fins.* The pectoral fins are in the Teleosteans attached to the skull by means of the shoulder girdle. In the cartilaginous fishes the shoulder girdle is a simple cartilaginous arch, which unites with that of the other side in the middle ventral line. In the cartilaginous Ganoids the shoulder-girdle is transitional between this primary form and the secondary form, which is characteristic of the Teleosteans (fig. 586), inasmuch as membrane bones (clavicle) are applied to the primary cartilaginous girdle. Ossifications also arise in the cartilage itself and give rise to bones known as the scapula and coracoid, or the praecoracoid. The skeleton of the fins, which is articulated to the shoulder- girdle, can be derived from the primitive form of fin known as the archipterygiurn, which still persists in Ceratodus as an axial row of cartilaginous pieces beset with jointed lateral rays (radii}. The nervous system (fig. 588) presents the lowest and simplest form found in any Vertebrate. In general the brain is small and consists of several swellings lying one behind another. Of these the small anterior, as the lobi olfactorii, pass into the olfactory nerves. The larger anterior lobes correspond to the hemispheres, the median globular swellings to the lobe of the third ventricle with the corpora quadrigemina. From this part of the brain the optic nerves are given off anteriorly, while on its lower surface the infundibulum, to which the pituitary body is attached, arises from the floor of the third ventricle. The posterior region corresponds to the cerebellum and the medulla oblongata. The cerebellum, which varies considerably in size and form, constitutes a transverse bridge, which covers the anterior part of the fourth ventricle. Lateral swellings the so-called lobi j)os- teriores are often developed in this region ; in the Sturgeons and Squalidse at the origin of the trigeminal nerve, as the lobi nervi trigemini ; in Torpedo as the large lobi electrici, projecting over the fourth ventricle. A separate visceral (sympathetic) nervous system is absent in the * Compare C. Gegenbaur, " Untersuchungen zur vergleichenden Anatomie der Wirbeltlriere." 2 Heft, Leipzig, 1865. C. Gegenbaur, " Ueberdas Skelet der Gliedmassen." Jen. naturwiss. Zeitsch.. Tom. V. 138 PISCES. Cyclostomes "alone, where it is represented by the vagus and by fibres of the spinal nerves. The spinal cord, the mass of which is con- -Fa FIG. 588. Brain and anterior part of the spinal cord and nerves of Hexanchus grisews (after Gegenbaur). The nerves are dissected out on the right side ; the right eye removed. A, Anterior cavity of the skull ; N, nasal capsule ; Vh, fore-brain (cerebral hemispheres) ; Mh, mid-brain (optic lobes); Ce, cerebellum ; Mo, medulla oblongata; Bo, olfactory bulb ; tr, trochlear nerve (fourth nerve) ; Tr' , first (ophthalmic) branch of the trigeminal or fifth ; a, terminal branches of the same in the ethmoid region; Tr", second branch Tr'", third branch ; Fa, facial (seventh); Gp, glossopharyngeal (ninth); Vg, vagus (tenth) ; L, lateral branch of vagus (to lateral line) ; J, intestinal branch ; Os, superior oblique muscle of eye ; Hi, internal rectus muscle ; Se, external rectus ; Rs, superior rectus ; S, spiracle ; Pq, palatoquadrate ; Hm, hyomandibular ; jR, branchial rays ; / VI, branchial arches ; Br, branchife ; P, spinal nerves. siderably greater than that of the brain, extends tolerably uniformly throughout the whole length of the neural canal, and usually does not form a so-called cauda equina. Rarely its upper part presents SKXSK oIKiANS. paired or unpaired swellings ( 7 V /,< us) consists only of the labyrinth (tig. 578, /), and in Teleosteans, Ganoids, and Chimcera lies partly in the cranial cavity, surrounded by fatty tissue. It is worthy of notice that in Cyprinoidce Characince, Siluridce, and others, the labyrinth is connected with the swimming bladder by a chain of small bones. The olfactory organ in Amphioxus consists of a simple unsymmetrical pit at the anterior end of the nervous centre. In Cyclostomes also it FIG, sso. - Horizontal . section through, the consists of a simple tube, with an unpaired median e ye of Esox Indus. opening. All other fishes possess double, and o, cornea; i.iene; Pf, processus falci- indeed with the exception of the Dipnoi blindly- closed nasal cavities, the internal surface of which is considerably increased by folds of the mucous membrane. The sense of taste seems to be less developed, the buccal cavity, and especially in the richly innervated part of the soft palate. For the tactile sense, lips and their appendages the frequently appealing barbules probably serve. Certain isolated rays of the ventral fin may also, on account of their rich nerve supply, be regarded as tactile organs (Trigla). The nervous organs of the so-called mucous canals, which we have before mentioned, constitute an organ of a special sense. f orniis ; CH, cam- panula Halleri; No, optic nerve ; Sc, ossification* of the sclerotic. It is located in * Compare E. H. Weber, " Be aure et auditu hominis et animalium." P. I., " De aure animalium aquatilium. " Lipsise, 1820. C. Hasse, " Anatomische Studien." Heft 3 : ' Das Gehororgan der Fische." Leipzig, 1872. 140 PISCES. The electrical organs* may be mentioned as a peripheral appendage of the nervous system (Torpedo, Gymnotus, Malapternrus, Mor- myrys). They are nervous apparatuses which in the arrangement of their parts may be compared to a Voltaic pile. They develop elec- tricity, and give electrical discharges when their opposite poles are FIG. 590. Torpedo with electric organ dissected out (EO) (after Gegenbaur). On the right side the dorsal surface only of the organ is exposed ; on the left side the nerves which go to it are shown. Le, electric lobe ; Tr, trigeminal nerve ; V, vagus nerve ; O, eye ; Br, gills ; on the left the individual branchial sacs ; on the right the latter are shown covered with a common muscular layer. Gr, Gelatinous tubes of the skin (sense canals). connected. In Torpedo these organs are situated (fig. 590) between * Compare Savi, " Recherches anatomiques sur le systems nerveux et sur 1'orgaiie electrique de la torpille." Paris, 1844. Bilharz, "Das elektrische Organ des Zitterwelses." Leipzig, 1857. Max Schultze, " Zur Kenntniss des elektrischen Organs der Fisclie." 1, 2. Halle, 1858 and 1859. Max Schultze, "Zur Kenntniss des den elektrischen Orgauen verwaudten Schwanzorganes von Raja clavata." Mailer's Archiv, 1858. Sachs, ' Untersuchungen am Zitteraal." Leipzig, 1881. ELECTRICAL ORGANS. 141 the branchial pouches and the anterior cartilages of the pectoral fins, and consist of a number of perpendicular columns enclosed by walls of connective tissue. The columns are divided by a great number of membranous transverse partitions into a series of com- partments placed one above another. Each of the latter contains a layer of gelatinous tissue, and a finely granular plate containing nerve endings and large nuclei (electrical plate). The latter corre- sponds in a certain degree to the copper and zinc elements of the Voltaic pile, the former to the moist intermediate layers ; while the connective tissue framework seems to serve only to carry the nerves and blood-vessels. Each transverse partition contains a rich network of nerves, which is distributed on the electrical plates. The face on which the nerves ramify is the same in all the columns of the same FIG. 591. Alimentary canal and generative organs of Clupea Harengus (at'cer Brandt). Si; gills ; Oe, cesophagus ; T", stomach ; Ap, pyloric appendages ; D, intestine ; A, anus ; Vn, swimming bladder; Dp, pneumatic duct; S, spleen; T, testis; I'd, vas (leferens; Gp, genital pore. organ, and is always electro-negative, the opposite free surface being positive. In Malapterurus, the other surface of the plate (the posterior surface) on which the nerves enter is electro-positive, but this apparent exception is explained by the fact that the nerves pass through the plate and are distributed on the anterior surface, which is electro- negative. In the electric Eel (Gymnotus electricus] the electric organ lies at the side of the tail and consists of long horizon- tal columns; in Malapterurus it lies along the body beneath the skin. Similar organs in Mormyrus are distinguished as pseudelectric organs, since although they have a similar structure, they give rise to no electric phenomena. The digestive organs vary much in structure. The mouth, which is placed at the anterior end of the head, usually has the form of a transverse slit, and can sometimes be extended forward by means of 142 PISCES. the moveable supporting bones of the upper and lower jaws (Labroidert). The buccal cavity is distinguished by its width, and by the great number of teeth it contains, which are developed from the papilla? of the mucous membrane by dentinal ossification. There are often two curved parallel rows of teeth on the upper jaw ; an outer row on the prenmxilla, and an inner row on the palatine, and there may also be a median unpaired row on the vomer. On the lower jaw there is only one curved row of teeth. There may also be teeth on the hyoid arch and on the upper jaw (maxilla?) and para- sphenoid, and, as a rule, on the branchial arches also, especially on the upper and lower pharyngeal bones. The teeth are distinguished according to their shape into pointed conical prehensile teeth and grinding teeth. A small, hardly moveable tongue is developed on the floor of the buccal cavity, and the At lateral walls of the pharynx are pierced by the gill slits. Fol- lowing the pharyn- geal cavity, there is a usually short, funnel- FIG. 592,-Dia.urammatic longitudinal section through the Sna P ecl WSOphagUS, and head of a larva of Pttromyzon (after Balfour). N, nervous a large stomach, which system; (', nutochord; Ot, auditory vesicle (represented J Q f j-i i as visible) ; O, month ; T>, velum ; H, thyroid involution ; eC l 11 ' ILS, lirnnchial pouches; C, heart; A.I, optic vesicle; out into a CftX'lim of Ol, olfactory pit. n , considerable size (fig 501). Ctt'cal appendages (pyloric appendages] are not unfrequently met with at the entrance to the longer mid-gut (small intestine) which is marked off by a valve ; they probably serve the purpose of increasing the extent of the secreting surface of the alimentary canal. The intestine is usually several times coiled, and its internal surface is remarkable for the longitudinal folds of the mucous mem- brane ; villi such as are found in the higher Vertebrates are only rarely present ; but in the Selachians, Ganoids, and Dipnoi there is a peculiar spirally-coiled longitudinal fold the so-called spiral valve which contributes essentially to the enlargement of the absorbent surfaces. A rectum is not always clearly marked oft', and when present is always short, and in the Selachians it is furnished with a ca?cal appendage. The anus is usually situated far back, and is always ventral and in front of the urinary and generative openings. In fishes with jugular fins, and in some Teleosteans without ventral 01 swiMMtN<; BLADDER. 143 fins, it is situated very fai forward, and may even be on the throat. Salivary glands are absent in Fishes, but there i> a large liver which is rich in fat and is usually provided with a gall-bladder; there is also usually a pancreas, which is by no means replaced by the pyloric appendages as was formerly believed. In many tishes the swimming bladder, an organ which by its mode of origin corresponds to the lungs, is developed as a diverticuhim of the alimentary canal. It is almost always an unpaired sac filled with air and placed on the ventral side of the vertebral column, dorsal to the alimentary canal : it is sometimes closed and sometimes lla FIG. 593. Hcmzontal section through the branchial cavity showing the roof, n, of one of the Sqitalidce, b, of a Teleostean, (altered from Gegenbaur). Nal, nasal aperture ; 3L', mandible; Zlg, hyoid arch; El, branchial arches; Oe, oesophagus ; Spl, spiracle ; -Be, gills ; Sp, gill slits ; Se, septa of branchial pouches ; Psb, pseudobranch of the branchial operculum (hyoid pseudobranch) ; Oj>, operculum. communicates by an air tube the pneumatic duct with the interior of the alimentary canal (Physostomi) (fig. 591 Vn). Its walls are formed of an external elastic membrane which is sometimes invested with muscles, and an internal mucous membrane. Glandular structures are sometimes present in the internal coat, and these may exert an influence on the enclosed air. The internal surface is usually smooth, but sometimes is provided with reticulated pro- jections which lead to the origin of cellular cavities (Ganoidei). Physiologically the swimming bladder is a hydrostatic apparatus, the function of which seems to consist essentially in rendering the specific weight of the fish variable, and in facilitating the rapid change in the position of the centre of gravity. The fact that many fishes 144 PISCES. which swim very well are without the swimming bladder is by no means favourable to the interpretation of its function. When it is present the fish must have the power of compressing it, partly by the muscles in its walls and partly by the muscles of the body, and thus rendering the body specifically heavier so that it sinks. When the compression of the muscles is removed the compressed air will again expand, the specific gravity diminish and the fish will rise. If the pressure is unequal on the anterior and posterior parts then that half of the fish which is rendered specifically heavier will sink. Still more complicated relations, however, seem to exist according to the investigations of Bergmann.* Respiration is in all cases effected by gills. In the Cyclostomes (fig. 592) which have no visceral arches there are six or seven pairs of branchial pouches. These open into the oeso- phagus either by internal branchial passages or (Petromyzon) by a com- mon canal which receives all the branchial passages. The water is expelled through external branchial passages round which a network of cartilaginous rods is developed. In the Plagiostomes (fig. 593 a) there are saccular spaces the walls FIG. 59*. Head of Anabas seandens o f which are supported by car- (regne animal). The operculum . i rri l V,i n l has been removed to shew the tilaginous rods. These branchial spacious upper pharyngeal bones sacs communicate with the exterior (pharyngo-branchials). . , , . , by lateral openings and contain the branchial leaflets which are attached to their walls : they are separated from one another by partition walls which are placed between the two rows of leaflets of each arch, and they are supported by an external framework of cartilaginous rods. In the Selachians there are, as a rule, five pairs of branchial sacs, of which the last has a row of leaflets on its anterior wall only, i.e., on the posterior side of the fourth true branchial arch ; while the first pouch has, in addition to the anterior gill of the first branchial arch, a gill on the hyoid arch corresponding to the accessory gill of Chimera and the Ganoidei. The mandibular arch, however, sometimes bears a * Compare Bergmann and Leuckart, " Anat. Phys. Uebersicht des Thier- rcichs." Stuttgart, 1852. RESPIRATORY ORGANS. 145 remnant of a gill the pseudobranch of the spii-acle the vessels of which belong to the arterial circulation and form a rete mirabile. In the Teleosteans (fig. 593 6) and the Ganoids the lancet-shaped lamella? are arranged in double rows on the four visceral arches which func- tion as branchial arches, and they form four comb-shaped gills on either side. These gills lie in a spacious branchial cavity covered by the branchial oper- culum and the branchial membrane. There is, however, an accessory gill on the inner side of the branchial oper- culum ; this in many Ganoids and Ohimsera functions as a gill, but in the Teleosteans has lost its respiratory function, and is then known as the pseudobranch of the operculum or of the hyoid arch. External gills projecting from the slits of the branchial pouches are found only in the embryos of the Plagiostomes. Rudiments of external gills are found in Rhinocryptis annectens. Finally the secondary cavities, which are sometimes found annexed to the branchial cavity and increase the re- spiratory surfaces by the development of a capillary network, must be regarded as accessory organs of respiration. They consist either of labyrinthine cavities in the superior pharyngeal bones (fig. 594) or of saccular appendages of the FlG . 595 ._ Diafframofthe circulation branchial cavity (Saccobranchus, Am- phipnous). True lungs derived from the swimming bladder, with internal cellular spaces, a short air-tube and glottis-like opening into the pharynx, are only found in the Dipnoi (according to Hyrtl the swimming bladder of Gijmnarchus is also a lung). Vascular system. The blood is generally red; it is white only in A mphioxus and the LeptocephaMdce ; it circulates in a closed VOL. II. 10 of aTeleostean. I', ventricle ; Ba, bulbus arteriosus with the arterial arches which carry the blood to the gills ; Ab, arterial arches ; Ao, aorta descenclens into which the epibranchial arteries passing out from the gills unite ; N, kidneys ; D, intestine; Lk, portal circulation. 146 PISCES. vascular system, in which, except in Amphioxus, a muscular pulsating region or heart is present. The heart (fig. 595) is placed far forward on the throat, ventral to the branchial framework, and is enclosed in a pericardium, the cavity of which communicates with the body cavity in some Plagiostomes, Chimcera, Acipenser, etc. It is a simple venous branchial heart, and is composed of a thin-walled large auricle and a very powerful muscular ventricle. The auricle receives the venous blood returning from the body, and the ventricle forces it through an ascending aorta to the respiratory organs. The aorta begins with a bulbous swelling (bulbus arteriosus), which in the Ganoids, Plagiostomes, and Dipnoi is replaced by an independently pulsating part of the heart with rows of semi-lunar valves (conn* arteriosus}. While the fishes with a simple non-muscular bulbiis arteriosus have but two semi-lunar valves at its origin, the above mentioned orders usually have two to four, or rarely five rows of three, four or more valves each in the conus arteriosus. The aorta at once divides into a number of paired vascular arches corresponding to the embryonic aortic arches. These are the branchial arteries ; they pass into the branchial arches and give oft' branches to form the capillary networks of the gills. From the capillary networks small vessels pass out which unite to form a larger branchial vein in each branchial arch (epibranchial artery). The arrangement of these veins corresponds to that of the branchial arteries ; they unite to form the large aorta descendens or dorsal aorta. Before they unite the cephalic arteries pass off from the epibranchial arteries of the anterior arch. The arrangement of the principal venous trunks in fishes is most nearly related to the embryonic condition. Correspond- ing to the four cardinal veins of the embryo, two anterior and two posterior vertebral* veins (jugular and cardinal veins) bring back the blood from the anterior and posterior part of the body re spectively. These veins unite on each side to form two transverse veins the ductus Cuvieri which enter the sinus venosus of the heart. The course of the returning venous blood is complicated by the insertion of a double portal circulation. The caudal vein passes directly into the posterior cardinal veins only in Cyclostomes and Selachians : in all other fishes there is a renal-portal circulation, in that the caudal vein breaks up into capillaries in the kidneys, from which the blood passes into the posterior cardinal veins. For the hepatic portal circulation on the other hand the venous blood of the * Often called the anterior and posterior cardinal veins. URINARY AND GENERATIVE ORGANS. 147 n Vs. n intestine is used ; this blood after passing through the capillaries of the liver is returned to the heart by one or more veins which cor- iv- pond to the inferior vena, cava and open into the sinus venosus between the two ductus Cuvieri. Such capillary systems must be a considerable hindrance to the circulation of the blood and explain the development of the so-called accessory hearts on the caudal vein of the eel and on the portal vein of Myxine, The urinary organs of Fishes (fig. 596) consist of paired kidneys extending along the backbone from the head to the end of the body cavity, and giving off two ureters which unite into a common duct on which a bladder is usually developed. The urinary bladder and its duct always lie be- hind the intestinal canal. In most Teleo- steans the efferent duct of the bladder opens by a common orifice with the sexual opening, or on a special papilla behind the sexual opening. In the Flagiostomes and Dipnoi on the other hand a cloaca is developed ; in the former the ureters and the generative ducts open into the dilated terminal part of the intestine i.e., the cloaca behind the rectum ; while in the latter the ureters open into the cloaca separately on each side. Generative organs. Excepting in certain forms, such as Serranus and Ohrysophrys, which are hermaphrodite (also some carps), Fishes are of separate sexes ; the two sexes ,, FIG. 596. Kidneys of Sulmo often present more (Jlacropodus) or less f ar io (after Hyrti). R, ki/iin.r//x Ynrrel (Branchiostoma Cnsta) including a single species distributed on the sandy coasts of the North Sea, of the Mediterranean, and of South America. A. l<>!/if/ without jaws. FIG. 599. My .'dm i/lnt iiicmu (regne animal). The Cj/clostomi have a cylindrical vermiform shape (fig. 599), and * Joh. Muller. " Vergleichendc Anatomic der Myxinoiden." Berlin. lS3.~>-4:.. Aug. Miiller. " Ueber die Entwickelung der Neunaugen." J/w/Yr ?'.<; . I rrliic.. 1 s.">r. Max Schultze, "Die Entwickelungsgeschichte von P. Planeri." Haarlem. 1S5C. P. Langerhans, " Untersuchungen iiber Petromyzon Planeri.'' Freiburg. 1S7.'!. W. Miiller. " Ueber das Urogenitalsystem des Amphioxus und der Cyclosto- men." Jen. Htiturn-'ixx. Zritxcln'.. Tom. IX., 1875. A. Schneider. ' Beitrage ziir vergleichenden Anatomic und Entwickelungs- geschichte der Wirbelthiere." Berlin, 1879. Calberla, ' Zur Entwickelung des Medullarrohrs und der Chorda dorsalis der Teleostier und der Petromyzonten." Moriiliol. Jaltrb,, Tom. III., 1877. 154 PISCES. B their skin is without scales. They have no paired fins but the system of vertical fins is developed over the whole length of the dorsal surface and of the tail, and is usually supported by cartilaginous rays. The skeleton is confined to a cartilaginous rudiment of the vertebral column and skull. The notochord persists as the axial skeleton : its sheath presents traces of segmentation in the presence of rudimentary cartilaginous neural arches (fig. 600, I), and in the caudal region (Petromyzon) of the lower vertebral arches also. At the anterior end of the notochord there is a cartilagino- membranous cranial capsule enclosing the brain. It has a bony 'basal region and lateral cartilaginous vesicles in which the auditory organs are enclosed (fig. 600). In place of the visceral skeleton there are cartilaginous pieces surrounding the palate and pha- rynx, various labial cartilages and a complicated frame work of cartilaginous rods, which form the so-called branchial basket round the branchial sacs, and are in part attached to the vertebral column. The Cydostomi possess a brain of the piscine type with three principal sense nerves and a reduced number of spinal-like nerves. Two eyes are always present, but they may be hidden under the skin or even covered by muscles (Myxine, larva of Petromyzon}. The olfactory organ is an unpaired sac opening in the median line between the eyes. In the Myxinoids the olfactory capsule has in addition a posterior opening which pierces the palate and can be closed by a valvular apparatus. This communication between the nasal and pharyngeal cavities serves for the introduction of water into the branchial sac : for the mouth when performing its function as a suctorial organ is closed so far as the passage of water is concerned. The auditory organ is reduced to a simple membranous labyrinth which consists of the vestibulum and one or two semicircular canals. Alimentary canal. The mouth, which is surrounded by fleshy FIG. 600. Skull and beginning of the verte- bral column of Petromyzon mnrin/m (after Joh. Miiller). a, In longitudinal vertical section. I, Seen from above. A, noto- chord ; -B, neural canal ; C, rudimentary vertebral arches ; D, cartilaginous part, and D', membranous part of the cranial roof ; .E, base of skull ; F, auditory cap- sule; G, nasal capsule; l>ril9). Bi-, on the ventral surface of the body. In the Chimceridce llie lirandiial pouches open on either side into a r< numon gill-slit, over which a cutaneous fold, arising from the suspensorium of the jaw and serving as a branchial operculum, is spread. The dentition presents many variations. Sometimes (Ile.'-anchus, Acamthias) the whole of the buccal cavity as far as the entrance to the oesophagus is covered with small teeth of the mucous membrane (placoid scales ''') ; sometimes there are larger teeth, which also always belong to the mucous membrane, and are arranged in rows on the rounded edge of the jaw in such a manner that the younger posterioi- rows of teeth have their points turned inwards, while the teeth of the anterior rows, which are older and more or less worn, have their points turned upwards and outwards. In the Sqi'iili'l' 1 *, dagger-shaped or saw-shaped serrated teeth pre- ponderate, while conical or flat pavement-like molar teeth are characteristic of the greater number of Raiides. Spiracles are frequently present on the upper surface of the head behind the eyes ; they are used for the expulsion of the water from the pharyngeal cavity. The digestive canal is dilated to a spacious stomach, but is relatively short ; the small intestine is furnished with a spirally coiled fold of the mucous membrane the so-called spiral valve which considerably increases the extent of the absorbing surface. A swimming bladder is always absent, though the rudiment of it is often discernible. The heart* has a muscular conus arteriosus ; it contains two to five rows of valves, and represents a part of the ventricle which has become independent. In the structure of the brain and of the sense organs, the Selachians hold the highest place amongst the fishes (fig. 588). The hemispheres are of relatively considerable size, present longitudinal and transverse impressions, and traces of convolutions on their surface. The cerebellum, also, may be so well developed that the fourth ventricle is almost entirely covered by it. The two optic nerves always form a chiasma and some of their fibres cross. The eyes in the Squalides are not only protected by free lids, but often also by a moveable nictitating membrane. * 0. Hcrtwig, Ji it. iidtunriax. Zritxi-hr. Tom. VIII., 1874. * C. Gegenbaur, ' Zur vergleichendeii Anatomic des Herzen^." Jen. nat>/r- iciss. Zritxrlir. Tom. II. 160 PISCES. The urinary organs of the Plagiostomi are paired kidneys, which sometimes retain the ciliated funnels (nephrostomata). The sexes can be easily distinguished by the form of the pelvic fins. A true copulation always takes place. The female genital organs consist of a large, single or double ovary and paired glandular oviducts, which are separate from the ovaries and begin with a common funnel-shaped ostium, and in their further course each of them possesses a uterus-like dilatation. The two oviducts open by a common aperture (in the Ckiinceridce only by separate orifices) into the cloaca. The ova have a large amount of food-yolk, and are enclosed by a mass of albumen, and sometimes by a thin membranous folded chorion, sometimes by a tough, pai-chrnent-like, flat shell, which is prolonged into four horns, or into twisted strings, which serve to attach it to marine plants. In the latter case the eggs are laid (the true Rays and Dogfish) : in the former (elec- tric Rays and viviparous Squa- lides), on the other hand, they develop in the uterus. In this case the eggs are closely applied to the walls of the uterus during the development, the folds of the chorion interlocking with the ridges of the uterine walls. Thus the addition of nutriment is rendered possible. Sometimes the connection between the mother and the embryo is more intimate, and is effected by means of a true umbilical placenta, which was known to Aristotle in Mustelus Icevis (fig. 604). As Joh. Miiller * has shown, the long-stalked yolk-sac of the embryos of Mustelis Icevis and species of Carcharias develops a great number of villi, which are covered by the delicate egg mem- brane, and like the cotyledons of Ruminants fit into corresponding depressions in the uterine mucous membrane. In other respects, * Compare Job. Miiller, " Ueber den glatteu Hai des Aristoteles." Alhandl. der JBerlini-r Alitid., 1840. FIG. 604. Embryo of Mnstelus Iceois, connected with the uterus by the umbilical placenta (Dp) (after Joh. Miiller). SELACHII. 161 also, the embryos of the Plagiostomes exhibit notable peculiarities, especially in the possession of external branchial filaments (tig. 605), which are lost long before birth. Almost all the Plagiostomes are marine ; only a few of them are found in the larger rivers of America and India. They are all carnivorous, and feed on large fishes, or Crustacea and mollusca. Some few (Torpedo] possess an electric organ. "With the exception of Pleur acanthus, remains of spines and teeth only are preserved in the Palaeozoic formations. From the secondary period onwards the remains are more complete and numerous. Sub-order 1. Holocephali. Selachians with maadllopalatine apparatus firmly fused to the, skull, with single external gill slit on each side and small opercular membrane. The thick strangely formed head is provided with large eyes which Sp FIG. 005. Embryo of Acanthvis with external gills. Sp, spiracle; M, mouth; Nb, stalk of yolk-sac. are without lids. The mouth is small and lies on the under surface of the snout. The maxillo-palatine (palato-quadrate) bar is firmly fused with the skull, while the lower jaw articulates with a styliform process of the skull (hyomandibular). The mandible has but few teeth (four above, two below). The naked skin is traversed by the large passages of the lateral sense organs. There are no spiracles. The vertebral bodies are replaced by thin calcareous annular incrusta- tions in the sheath of the notochord. They lay eggs with horny shells. Fam. Chimaeridse (Sea-cats). fl/imcrr,/ nnntxtroxa L. (fig. (iOfi), Northern Seas and Mediterranean ; fullm-liiim-liux tintun-ticiix Lac., Cape and Pacific. Sub-order 2. Plagiostomi. Selachians with wide transverse mouth, which is placed far back, separate vertebral bodies, and a more or less reduced notochord. There are Jive (exceptionally six or seven) external gill slits on each side. The nasal apertures are placed on the under surface of the snout, VOL. II. 11 1G2 PISCES. a little in front of the transversely arched mouth. The skin is rarely naked ; it is usually shagreen-like in consequence of the osseous bodies which are embedded in it, or it may also be covered with osseous plates and scutes. The palato-quadrate bax- is moveable and is separate from the cartilaginous cranial capsule. Tribe 1. Squalides (Sharks). Spindle-shaped Plagiostomes, with lateral gill slits ; eyelids with free edges ; incomplete shoulder girdle, without cranial fin cartilages. The body is spindle-shaped, carries the pectoral fins more or less vertically, and ends with a powerful tail, which is bent dorsalwards at the end. There are, however, forms which, with regard to their body shape, are allied to the Rays, and constitute forms of transition to the latter group, e.g., the genus Squatina. The teeth are usually pointed and dagger-shaped, and placed in numerous rows. The FIG. 606. Chimcera monstrotu (regne animal). families are distinguished principally by the number and position of the fins, by the presence or absence of spiracles and of a nictitating membrane, and also by the form and structure of the teeth. Fain. Scyllidse ( Dog-fishes). Scyllium canicula L., the coasts of Europe. Fam. Cestraciontidae. Ccntntcinn PJtilijtjn Blainv. Fam. Lamnidae (Porbeagles). Lainna ijlauca Mull., Henle ; Selaclie maxima Gunn. , reaches a length of thirty-two feet. Fam. Carchariidae. Carclwu-ias i/lauciis Rond. the Blue Shark, with umbilical placenta. C. lamia Risso. These two last are found in the Mediter- ranean and the Ocean. Zi/fja-nn maUrua Risso. the Hammer-headed shark. Fam. Galeidae (Topes). Galen* runis Rond., European seas ; JfuxteJux rtili/arte and laris Rond.. with umbilical placenta, both are found in the Mediterranean. Fam. Notidanidae. Xotidanits (Sexanehus) yrixens Gm. and .V. (Hrjitan- i-hitx) cinereus Gm., Mediterranean and Ocean. Fam. Spinacidae (Spiny Dog-fishes). Aeantkias i-i/It/tir/x Risso (fig. found from the northern seas to the South Sea. Fam. Squatinidae (Angel- or Monk-fishes). Sonatina rnh/ar : s Risso squat inu L.) European seas. CANOIDEI. Tribe 2. Rajides (Skates and Ears). Plagiostomes, with li.-it bodies ; with five gill slits opening on the ventral surface internal t.<> the pectoral fins ; with complete pectoral girdle and cranial fin cartilages, without anal fins. In consequence of the size and horizontal expansion of the thoracic tins the fiat body presents the form of a large disc, prolonged behind into the long thin tail, which is frequently armed with spines, rarely with one or two serrated stings. The mandibles are short and stout, and are furnished with teeth which may be either small and conical, and arranged near one another in rows, or broad and plate-like. The Rays live for the most part at the bottom of the sea, and feed principally on Crustaceans and Molluscs. The Torpedos have an electrical apparatus between the fin cartilages and the branchial pouches. By means of this organ (fig. 590) they can stun even larger fishes. Many Rays reach the considerable size of ten to twelve feet. Fam. Squatinorajidae. Pristis a nti/j !/<>? m Lath. Sawfish, Ocean and Mediterranean : TUiinobatits grawulatiis <'uv. Fam. Torpedidse. Electric Rays. Torpedo niarmuruta Uiso. Mediterranean and Ocean : jYarr/t/r lirdxilii-tisis v. Ott. Fam. Rajidae. Skates and Rays. Raja clt/vaftt L. ; B. niimlrtiix L. Fam. Trygonidae. Sting Rays. Tri/r/oit j/n.^f/fiaca L. (Paxthmcn iinirimi I'.cll). Atlantic Ocean. Fam. Myliobatidae. Eagle Rays or Sea Devils. Mi/liobati* nquillu L., Mediterranean. Order 4. GANOIDEI.* Cartilaginous and bony Fishes, with enamelled scales, or with osseous dermal plates and fulcra, with muscular conus arteriosus contain in ij rows of valves; witJi comb-shaped gills and S'pii'fiJ ruin- In flie intestine. In former periods of the world's history this order was richly and variously represented (Sauroidce, Lepidoidai, Pt/cnodonta), while at the present day it contains only a few forms (Lepidosteus, Polypterus, Calamoicfithys, Amia, Acipenser, $caphirhynchus, Sj>liunfi'>-us bichir. the biconcave form of the Teleostean vertebra?, and in Lepidosteus reach a phase of development in which, by the presence of an anterior articulating head, they resemble the opisthocrclous vertebrae of Amphibia. Bony ribs, also, are fairly frequently present. The caudal fin is usually heterocercal, and the end of the vertebral column is sometimes continued into its superior lobe ; there are, however, forms which are transitional in this respect, and lead to the homocercal (diphycercal) form. The spine-like splints known as fulcra, which are arranged in a single or double row on the upper edge and the first ray of the fins, particularly the caudal fin, are peculiar to Ganoids. (" Every fish with fulcra on the anterior edge of one or more fins is a Ganoid." Joh. Miiller.) Anatomically the Ganoids present many points of resemblance to the Selachians. The anterior region of the ventricle is separated off as a rhythmically contractile conus arteriosus, and contains several longitudinal rows of valves, which extend as far as the anterior limit of the muscular investment, and prevent the blood flowing back from the artery into the conus during the diastole. The comb-shaped GANOIDEI. 165 gills, on the other hand, lie, as in the Teleosteans, freely in a branchial cavity beneath a branchial operculum, to which a large gill containing venous blood is often attached. This respiratory accessory gill (opercular gill) is wanting in Amia and Spatula/ria, and must be distinguished from the pseudobranch of the spiracle, which may be present together with it. All the Ganoids possess a swimming bladder with a ductus pneu- maticus and two peritoneal canals (abdominal pores), which open at the sides of the anus (as in Ghimcera and Playiostomi}. The optic nerves do not simply cross over one another, but form a chiasma with partial exchange of the fibres. The generative organs present many noteworthy peculiarities. There are two ovaries and the ripe eggs escape into the abdominal cavity. Thence they pass into an oviduct [Miilleriaii duct] which begins with a funnel-shaped opening into the body cavity and opens behind into the urinary duct or into the corresponding cornu of the urinary bladder (Spatularia, Lepi. FIG. 608. Acipenser rufheims (after Heckel and Kner). dosteiis), or unites with the oviduct of the opposite side and opens behind the anus by a single genital pore into which the short urethra also opens. (Hyrtl.) In the two first cases a urogenital canal leads from the bladder to a urogenital pore placed behind the anus. In the male it is remarkable that the same abdominal funnels [Miillerian ducts] also function as seminal ducts. [It has been shown by Balfour and Parker (Structure and Development of Lepidosteus, Phil. Trans., 1882), that in Lepidosteus at any rate the testis is connected with the Wolffian body by a testicular network.] Tribe 1. Chondrostei. Cartilaginous Ganoids with persistent notochord. Branchiostegal rays scanty or absent. Caudal fin heterocercal, with fulcra. Cranium cartilaginous, covered by dermal bones. The teeth are small or altogether absent. The skin is naked or has osseous plates instead of scales. Fam. Acipenseridae (Sturgeons). Arij)i'//xrr xf >/>/<> L.. Sturgeon; A. L., Sterlet (fig. . yhtiJiitx Martens. Yaiitr. Mediterranean. Sub-order 2. Plectognathi. Globular or laterally compressed Teleosteans, with immovably fused maxilla and praemaxilla, and narrow mouth. The dermal armour is strong and often bears spines. There are usually no pelvic fins. The gills are comb-shaped. 168 PISCES. Tribe 1. Sclerodermi. Jaws with separated teeth. Fam. Ostracionidae (Trunk-fishes). Body coffer-like, triangular or quad- rangular, often prolonged into horn-like processes : with firm dermal armour consisting of polyhedral bony plates, on which only the fins and tail are movable. Oxtracwn triqtieter L. (fig. 610), West Indies ; 0. quadricornix L., West Africa, Fam. Balistidae (File-fishes). The body is laterally compressed, and the skin is covered with rough granules, or with hard rhomboid scales, and is oftei beautifully coloured. Salistcs mat-Hiatus L., Atlantic and Indian Oceans. Tribe 2. Gymnodontes. The jaws modified into a beak, with cutting undivided or double dental plate. Dorsal spines absent. Fam. Molidae. OrtlitKjoriscus moln- Bl. Sunfish. Fam. Tetrodontidae [Globefishes, Sea-Hedgehogs.] D'wdon lujstrir L., Atlantic and Indian Oceans ; Tetrodon cut/metis Gthr., St. Helena. Sub-order 3. Physostomi. With soft fins (malacopterygians), with FIG. 610. Oitracioii triquetcr (regne animal). comb-shaped -gills and separated jaw bones. Pelvic fins abdominal or absent. Swimming bladder always with a ductus pneumaticus. Fam. Muraenidae (Eels). Muva-nn livlcna L. ; Ani/uilla anguilla L. (rut- garis"), Europe. At the breeding season in autumn they migrate from the rivers into the sea, and there first attain sexual maturity. The reproductive processes are not perfectly known, though male and female have been dis- tinguished from one another, and the presence of both kinds of sexual organs has been shown. In the spring the young eels migrate from the sea into the rivers. Congrr vulgar Is Guv. . coasts of Europe. Fam. Gymnotidae. Gynmutus electricus L. (Electric eel). Lives in the swamps and rivers of South America, attains a length of six feet, and can, by means of its electric discharge, knock down even large animals, c.ff., horses. Celebrated by the experiments of A. v. Humboldt. Fam. Clupeidae (Herrings). With tolerably compressed body, which with the exception of the head is covered by large, thin, easily-detached scales. Cltipea harenf/nx L., the Herring of the northern seas. It appears every year at certain times, in enormous shoals, on the Scottish and Norwegian coasts. The principal takes occur in September and October. C. (Harengula) sprnffug L., the Sprat, North Sea and Baltic ; Enr/raulis cncraxirlmlus Kond., Anchovy ; TELEOSTEI. 11)1) Alauxa rulyaris Cuv.. Yal., the Shnd ; migrates in May at the spanning sens. .11 from the sea into the rivers, r.//., up the Rhine to Basel, and in the Main t<> \Viirxburg. Attains a length of t'nree feet. .1. /nl<-/iar/l//x Bloch. Sardine. .Mediterranean. Fam. Esocidse (Pikes). The head is broad and depressed : the dorsal tins are placed far back. Pseudobranch glandular, hidden. Voracious carnivorous fish, with wide throat and powerful dental armature. Exo.r lin-iux L.. 1'ike : f'/i/brti Kntnicri Job. Miill. Fain. Salmonidse. \Vith adipose fin. simple swimming bladder, and numerous pyloric appendages. The ovaries are sacs from which the eggs la 1 1 into the abdominal cavity. At spawning time, which is usually in the winter months, the two sexes often exhibit striking dif- ferences. They are large predatory fishes. and belong principally to the rivers, moun- tain streams, and lakes of the northern regions. They like clear cold waters with stony bottom ; but they have, also, repre- sentatives in the sea, which ascend the rivers and their tributaries to spawn, fort't/nnvx \\~a-rtmninii Bloch. Blaufelchen ; in the Alpine lakes. Th>/maU>is rulr/tirix Nilss. (vexillifer'), Grayling : t?almn salvelimis L.. Saibling : /S. Jnicho L., Hucheu. in the region of the Danube, a large predatory fish. S. xal/i>\, Salmon : ,S'. Itieuxtri* L. (Seeforelle, Schwebforelle), in the lakes of the Alps of Central Europe. S. tnitta L., Salmon or Sea trout ; ti.fu-rio L.. Trout. Fam. Cyprinidae (Carps). Fresh-water fish, with narrow mouth, often provided with barbules. The jaws are weak and without teeth, but the lower pharyngeal bones are abundantly furnished with teeth (fig. (ill). Cyprinvs t-iirp'ui L., the Carp ; Caraxxiu* ndyaris Nilss., Crucian and Prussian C'arjis (Karausche) ; Tinea vulgari* Cuv., Tench ; Jiarliisjliifitttilix Ag., the Barbel ; FIG. Oil. Lower pbaryngeal bones with the teeth of a carp (after Heckel and Kner). FIG. 612. Rhodeus amarus. Female (after v. Siebold). Gnlhi Jltu-'uitilix Flem., the Gudgeon ; Rhodi-ux amarus Bloch. (Bitterliug). The female has an ovipositor with which she deposits the ova in the gills of the fresh-water mussel (fig. 612). Allnrrniis lucldiix Heck. Kner, the Bleak ; Li'i/riwitx rutilux L., the Roach ; L. cepJ>nlvs L., the Chub : Chondrostoma iinxim L., (Xasling) ; Arlrainix bruma Flem., Bream ; Phoxinus Ueris L. Ag., Minnow. Fam. Acanthopsidae. The swimming bladder is contained in a bony capsule. Cubitix fusxilist L. ; C. IxtrlMtula L., Loach; (', ta'tihi L.. Spiued Loach or Groundling. 170 PISCES. Fam. Cyprinodontidae (Toothed Carps). Viviparous. Oyprinodan (Li-bins Guv.) caJarltniiiix (.'uv., South Europe : Amililt-jix tetrophtlial/nvus Bl.. Guiana. Fam. Siluridse. Fresh-water fish, usually with broad depressed head, strong dental armature, and skin naked or covered with an armour of bony plates. Silwrus glanis L. (VVels, Waller). The largest river fish of Europe. Hypostovius Lac. (Panzerwels) : Mnlaptcrurux i-lcctricus L. (Zitterwells). Nile. FIG. 613.--i>oforfs XundeMii (after Cuvier and Valenciennes). Sub-order 4. Anacanthini. Malacopterygians (soft tins), which with regard to their internal anatomy are allied to the Acaiitho- pteri bv the absence of a ductus pneumaticus ; usually with jugular pelvic fins. Fam. OpMdiidce. Opliidhtin In rluiiuiii L.. Mediterranean; Ammodytes toliiunux L., Sand-eel, North Sea. Fain. Gadidae, Gndu-s murrliua (the Cod). In Germany dried cod is called Stockfisch, salted cod Laberdan. Cod-liver oil is prepared from its liver. Its PIG. 614. Gasterosteim acitleafus (after Heckel and Kner). young- (Dorsch) were for a long time considered as a separate species (G. callariux). (*. eefflcfinux L. Haddock, with a black spot behind the pectoral fin. G. merlani/itx L., Whiting, coasts of North Europe ; Mt-rhircius ntl///""//""- riih/tirifi, Flem. the . I lolibut, coasts of North Europe; L'linnilux iiKi.r'uinix L.. the Turbot \ lih. leevis l;<>nix L., the Flounder, ascends rivei^ : iSWea ruli/nrix (Juens., the Sole. Fam. Scomberesocidae. Marine Malacopterygians, with cycloid sculps. The lower pharyngeal bones are fused (P/n/ri/^/in/natlu). lielnn- cit-nx Komi.. Gar-pike: Scomberesox gaums Wall'.: Ewcetus ernlans'L.. the Flyinu- fish. The pectoral tins are strengthened SO as to form flying- organs. A', exiliens L.. European Seas : A'. Hoii/lrlrtH * 'uv. Val., Mediterranean (fig. (1 3). Sub-order 5. Acanthopteri. Spii\y-rayed fishes with comb- shaped gills; lower pharyn- geal bones usually separate : thoracic, rarely jugular or ab- dominal pelvic fins. Swim- ming bladder closed, without ductus pneumaticus. Tribe 1. Pharyngognathi. The lower pharyngeal bones are fused. Fam. Pomacentridae. Aiitjiki- pr'wit bifuxcitifnx Bl., New Guinea; Pomtii-rntfiix f a *< in tux Bloch., East Indies. Fam. Labridae. The Wra,-^ - (Lippfische). Brightly - colom-ed fish, with fleshy protrusible lips. L'/lirux iiiacii/tifua Bl., coasts of Europe: Cri-uilnbrux pavo Bru'ivn : llx JHIVO Hassij.. Mediterranean ; ci'rteiixix Aldx., Parrot-fish, FIG. 615. Nest of Gasffrosteim punyitius (after Mediterranean. Landois) . Tribe 2. Acanthopteri (s. str.). The lower pharyngeal bones are not fused. Fam. Percidae. Perches. Fiiis thoracic : scales ctenoid : edge of branchial operculuin or prsBOpercultun serrated or spinous. There are teeth on the prte- maxilla, lower jaw, vomer and palatine. Pa-en tfiiriiitilix Bond., Common Peivh (rig. 583). A voracious fish, especially pursues small Cyprinoids. Lalra.i- lupus Cuv., the Bass, Mediterranean : Accrina cerium L.. the Pope, river fish ; Litrii^im-ti smtdni Guv., river fish of South Europe ; ^crriiitux xc/'ilm L., hermaphrodite. Mediterranean ; Gasterostem iiciilctttux L., the Stickleback (fig. (ili), remarkable for forming a nest and protecting the eggs and young; G. jtiimjitiux L., teu-spined Stickleback (the Tinker) (fig. 615) ; G. spinacliia L., fifteen-spined Stickleback. 172 PISCES. erij - Fam. Mullidse. Mullets. MnUiis l>art,itnx L., red Mullet. Fam. Sparidae. Sea-breams, tin-tins Eondch:tn Cuv. Val. ; Pagi-Uu* thriitux L. ; Chrysophrys nurtita L., Mediterranean. Fam. Triglidae. ( 'aft it* yoliio L.. River Bullhead or Miller's Thumb. A small fish found in clear brooks and streams. It hides beneath stones, and defends itself by expanding- its branchial operculum. The male undertakes the care of the brood. ('. .worphis L.. Sea-scorpion; Ti-u/la rjunardux L.. Grey FIG. 616. Zoarces ch-ijifn-un. A, anus; T", uroo-enital opening. Gurnard ; D/x rolitanx L., Flying Gurnard ; Uranoscopiix sealer L. (Sternsehcr), Mediterranean ; Sfnrpaina jwcus L. : Tracliinm draco L. Fam. Sciaenidae (Umberfische). l^iiilrina. cirrltoxa L., Mediterranean ; ('<- vina nigrti Salv., Mediterranean ; Scieana itqiiilla, Risso., Mediterranean. Fam. Scomberidae. Mackerels. Body elongated, more or less compressed, sometimes very high. The skin is often silvery, and sometimes naked, sonic- times covered with small scales. There are keeled bony plates :in FIG. 617. Lophius pisnttoriiu (after Cuvier and Valenciennes). especially near the lateral line. The caudal fin usually has a semilunar shape. They constitute, on account of their tasteful flesh, an important object of the fishing industry the Mackerel in the North Sea and the Channel, the Tunny Fish in the Mediterranean, ti-oiiifa-r seomln'Hx L.. Mackerel ; Zen* falter L., tbe Dory ; Tl/yiuiiix rnlijaris Cuv., Val., Tunny Fish ; Pi-lami/x xarda Bl., Mediter- ranean ; Cartinj- trai-lntrux L., Horse-Mackerel, coasts of Europe; Xipkia* ylad'ms L., Sword-fish ; Ecliencix imurruti-x L., Sucking-fish. TELEOSTEI DIPNOI. 173 Fam. Gobiidae. Gobies. (Inlnut nii/rr llond. : (T.rtiiriutilix 1'all.. Rivers of Italy and of South-west Russia. Fain. Blenniidae. Blennies. AtmarJiichnx /////w.s- L.. Wolf-fish : Jileiiniux IXT/IIII-IX L., Butterfly-fish, Mediterranean: /nan'fx riri/mfttx ( 'uv. (tig. (ill!;, viviparous. Fain. Taenioidae. Silvery marine-fish, with compres-el. ribbon-like, elon- u; i ted-like body. Triicluiptcriix ftil.r ( 'uv.. Val. = Tr. ttrnia P.I.. Sdin., Nice ; (', /mlii nilii-xi-i-nx L., r.aud-tish. coasts nf Europe. Fain. Labyrinthici. The upper pharyngeal bones are hollowed out so as to have the form of coiled (meandering') lamclhe (fig. 594). in the spaces between which the water required to keep the gills moist is retained. Aintlmx xr/i/tt/r/i* Dald.. Climbing Perch, East Indies. Fain. Pediculati. Of stout clumsy shape. The skin is naked, or covered with rough prominences. The pelvic fins, which are small and placed on the throat (jugular), have their so-called carpal pieces elongated, so that they form movable arm-like supports for the body, and are in fact used for hopping and creeping. Lojihhix pixetttor'uix L., Angler. Frog-fish, etc. (/Scirpaxos of the Greeks), coasts of Europe (fig. lil") : Chironectes pictus Cuv. Order (3. DIPNOI.* Scaly Fishes with branchial and pulmonary respiration, with per- sistent notoc/tord, muscular conus arteriosus and spiral valve in the intestine. The Dipnoi (fig. 618) form a group so strikingly transitional between Fishes and Amphibians that their first discoverer regarded FIG. 618. Pr/if//r). The valves in the conns arteriosus rather resemble those of the Ganoids. 'XSfessstss? : , , rt FIG. 619. a, Cera tod us miolepls. b, its pectoral fin (after Giinther). dental plates of Cei-atodits Fortteri (after Krefft). c, lower jaw with Branchial apparatus formed of five cartilaginous arches and four gills. Pseudobranchs (hyoidean) are present. The lung is composed of two symmetrical cellular halves. The two ureters open on the dorsal side of the cloaca by a common opening. There is a pair of wide peritoneal slits (abdominal pores) behind the anus. The Jfono- pneumona feed on leaves, which they tear off with their incisor teeth and masticate with their molars. They make use of the lungs in re- spiration principally when the muddy water is saturated with gases from organic matter. They have existed since the Triassic period. Fam. Ceratodidae. with the .single genus Cn-atmlx* Ag. C. Forsti-ri Krefft, (and Htio/rjtix Giiuth.). the Barramnnda, Queensland; reaches a length of six feet. Its flesh is salmon-like and much esteemed as food. Sub-order 2. Dipneumona. Fins narrow, with jointed cartilaginous 17'i AMPHIBIA. shaft and rays only on one side. Gills more reduced. Valvular arrangement of conus arteriosus like that in the Batrachians. Lungs paired. Fam. Lepidosirenidae. Pnttoptrrus ininrcttns (fig. 618) Owen, tropical Africa ; iri'n jtaradoxtix Fitz.tr., P.razil. CHAPTER VI. Class II. AMPHIBIA. * Cold-Hooded animals w&ually with a naked skin, with pulmonary and branchial respiration, and incompletely double circulation. The embryos have neither amnion nor allantois. The external form of the body is adapted both for an aquatic and a terrestrial life. It presents, however, considerable variations lead- Ms FIG. 620. Larva of Salamandra muculata (after Malbranc). M*, median, Us, lower lateral line. ing to the creeping, climbing, and jumping land animals. An elongated, cylindrical, or more compressed form is the most frequent, and the body often ends with a large compressed swimming tail. Limbs may be absent, as in the cylindrical Cceciliidce, which live underground in damp earth. In other cases there are only short anterior limbs (Siren], or anterior and posterior stumps, which have a reduced number of toes and are unable to raise the serpentining body from the ground. Even when the extremities have, a con- siderable size and end with four or five digits, they act rather as pushing organs in the movement of the elongated and flexible body. The Batrachians, which have short and stout bodies and are without a tail in the adult state, alone possess powerful limbs adapted for running and jumping, and even for climbing. The skin,* which is of great importance not only as a secretory * Wagner, ' Natiirlicues System der Amphibien." Munich, 1830. Dumeril et Bibrou. " Erpetologie general e. etc." Paris, 1834-1854. * Fr. K. Sc.hulze, " Epithel-imd Drilsenzellen. I. Die Oberhaut der Fische nnd Amphibien." Arr/i.fiir nilliroslt. An/ttinnic. Tom. III. SKELETON. but also as a respiratory organ, is as a rule naked arid slimy. The Ccetiliidce alone possess thickened cutaneous rings, in which scales are imbedded. The sense organs of the lateral line (tig. 620) also are present in the aquatic forms, especially in the larval condition. Glands and pigments are very generally present in the integu- ment. The former often secrete strongly smelling and caustic juices, which act as poisons on other or- ganisms (parotid glands, as well as glands on the sides and posterior extremities). The various colourings of the skin are principally due to branched pigment cells of the cutis. The change of colour in the Frogs a phenomenon which has been known for some time is caused by changes in the form of these cells. Skeleton. -Although a notochord may persist (Cosciliidce, Proteus], yet bony, at tirst biconcave vertebrae,* are always developed, and are separated by intervertebral cartilages. In the Salamandrina the cartilage in the intervertebral regions grows con- siderably and gradually supplants the notochord, the remains of which be- come cartilaginous. As the result of further differentiation of the inter- vertebral cartilages, the rudiments of an articular head and an articular cup are developed, which, however, are only completely separated in the Batrachians provided with proccelous 177 R * Compare especially < '. Gegenbaur, " Un- tersuchungen zur vergleichenden Anatomie dcr \Virbdsaiiir bei Amphibian und Repti- lien," Leipzig, LSi',2. VOL. II. FIG. 621. Skeleton of Menopoma aJ- leghanitnse. Ocl, Exoccipital ; P, pari- etal ; F, frontal ; Ty, tympanic ; Pe, petrous (prootic); MX, maxilla; Jin.r, \ iv; i 'maxilla ; N, nasal; T'o, vomer; Et, girdle bone (sphen-ethmoid) ; Ft, pterygoid ; Sc, pectoral arch; Jl, pel- vic arch ; 8, sacral vertebra; R, ribs. I, hyoid aparatus (remains of liyni.l (Zl) and branchial arches (El). 12 178 AMPHIBIA. vertebra?.* The number of vertebrae is usually considerable, in accordance with the elongated form of body ; but in the Batrachia the vertebral column consists of only ten vertebrae with very long transverse processes, which usually at the same time represent the ribs ; while, with the exception of the first vertebra which is modified to form the atlas, almost all the vertebra? of the trunk possess small cartilaginous rudiments of ribs. The sacral region is formed by a single vertebra (fig. 621). Skull. The primordial cartilaginous cranium persists, but usually loses its roof and floor, and is partly replaced by bony pieces, some of which are ossifications of the cartilaginous capsule (exoccipitals, auditory capsules, sphen-ethmoid, quadrate), while others are Jnix Jmx N Et Od p e Pe p s Od ft FIG. 622. Skull of Sana esculenta (after Ecker). a, from the dorsal, b, from the ventral side ; [Membrane bones of one side removed in each case]. Od, exoccipital ; Pe, petrosal (prootic) ; Et, girdle-bone or sphen-ethmoid ; Ty, tympanic ; Fp, fronto-parietal ; J, quadrato-jugal (juga!) ; MX, maxillary ; Jmx, prsemaxillary ; N, nasal ; Ps, para- sphenoid ; Ft, pterygoid ; PI, palatine ; V, vomer. investing bones (parietals, frontals, nasals, vomer, parasphenoid) (fig. 622). As in Lepidosiren the basi- and supra -occipital remain as small cartilaginous tracts. There is also a parasphenoid on the base of the skull (fig. 622, Ps). The large exoccipitals (Od) (fused with the opistliotic) articulate by means of two condyles with the first vertebra, as in the Mammalia. The projecting auditory region is pierced by the fenestra ovalis, and the bone in its anterior part corresponds to the prootic (Pe). The lateral walls of the skull remain cartilaginous, but in the ethmoid region there is a ring- shaped bone the girdle bone, or sphen-ethmoid. * [For a fuller account of the development of the Amphibian vertebral column, vide Balfour, " Comparative Embryology." vol. ii.. p. 45(5 ft seq.] SKULL NERVOUS SYSTEM. 179 As in Lepidosiren the mandilmlar arch is firmly connected with the skull. The mandibular susjiensoriiitii and the palato-quadrate are in direct connection with the cartilaginous cranium, and form on either side a wide outstanding infra-orbital arch, the anterior end of which either remains free or fuses with the ethmoid cartilage. The ossification appearing at the end of the suspensorium gives rise to the quadrate, while a membrane bone, almost hammer-shaped and overlying the suspensorial cartilage, is called the squamosal or perhaps more correctly tympanic (Ty). Two membrane bones extend forward along the lower side of the palato-quadrate bar the pt&rygoid (Pi] behind and the palatine (PI) in front. The palatine is transversely placed behind the vomer. The outer arch of the upper jaw, formed l>v the prannaxillary and maxillary bones (Jmx, MX) may by means of a third posterior bone the quadrato-jugal (J) be continued back to the quadrate, but in many Perennibranchiata it is incomplete, the maxillaries being absent. The skeleton of the visceral arches is more or less considerably reduced in correspondence with the retrogression of branchial respiration. In the perennibranehiate Amphibia (Am- phibia with gills throughout life) the visceral arches are more numerous, and present an arrangement similar to that found only transitorily in the larvfe of the other forms. In the Salamandrina, in addition to the hyoid arch, the remains of two branchial arches persist ; while in adult Batrachians only a single pair of arches is retained on the hyoid bone. This branchial rudiment is attached to the posterior edge of the body of the hyoid bone, and serves as a suspensormm for the larynx. In the pectoral girdle three parts may be distinguished the scapula, the prcecoracoid, and the coracoid, to which a dorsal cartila- ginous supra-scapula is added. While in the tailed Amphibia ( Urodela), the arch is interrupted below, in the Batrachia the two halves are joined to each other in the middle ventral line, as well as to a posterior plate which has the value of a sternum, and an anterior plate known as the episternum. The pelvic girdle is characterised by the narrow form of the iliac bones, which are attached to the strong transverse processes of a single vertebra, and at their posterior end are fused with the ischiac and pubic bones. The nervous system is higher in several respects than that of the fishes. The brain (vol. i., fig. 80) is certainly in all cases small, but the hemispheres are large and the differentiation of the thalamen- cephalon and mesencephalon is further advanced. The optic lobes reach a considerable size, and the medulla oblongata encloses a wide 180 AMPHIBIA. fourth ventricle. The cranial nerves have the same relations as in the Fishes, since not only are the facial nerves and the nerves supply- ing the muscles of the eye often connected with the trigem/mal, but the glossopharyngeal and the spinal accessory are represented by branches of the vayiis. The hypoglossal is, as in the Fishes, the first spinal nerve. With regard to the sense organs the two eyes may be rudimentary and concealed beneath the skin (Proteus, C'ceciliidai}. In the Peren- nibranchia ta eye-lids are completely absent, while the Salamandrina have an upper and lower eye-lid, and the Batrachians, except Pipa, have, besides the upper eye-lid, a large very movable nictitating membrane, with which a rudimentary lower eye-lid co-exists only in Bufo. In the Batrachians there is a retractor muscle by means of which the large bulb of the eye can be drawn back. The structure of the auditory organ * of the Amphibia resembles that of Fishes. It is usually confined to the labyrinth with three semi-circular canals ; in the Batrachians alone there is a tympanic cavity, which communicates with the pharynx by means of a wide Eustachian tube, and is closed externally by a tympanic membrane, which is sometimes freely exposed on the surface and sometimes covered by the skin. The tympanic membrane is connected with the fenestra ovalis by a small cartilaginous rod (remains of the hyomandibular) with a cartila- ginous plate (columella with operculuni). When there is no tympanic cavity these structures are covered by muscles and skin. The cochlea, which was first discovered by Deiters in the frog, is probably present in all Amphibia. The olfactory organs are always paired nasal cavities, which are provided with folds of the mucous membrane and open internally either anteriorly within the lips, or, in the Batrachians and Salamandrines, further back between the maxillaries and palatines. The external skin, which is richly supplied with nerves, is to be regarded as the seat of the tactile sense. The posses- sion of the sense of taste is indicated by the presence of taste papillje on the tongue of the Batrachians. The Amphibia certainly swallow their food unnmsticated, and the tongiie also subserves other func- tions ; for instance, in the Batrachia it is used as a prehensile organ . Alimentary canal. The mouth is a wide slit. The vomers, palatines, and jaws are usually armed with sharp backwardly curved teeth, which are used not for mastication, but for holding the prey. Teeth are seldom absent, as in Pipa and some Toads ; but in the Frogs they are always present on the upper jaw and palate. * Compare especially the works of Deiters. Has.se, and Retzius. ORGANS OF RESPIRATION. 181 The respiratory and circulatory organs resemble, in essential points, those of the Dipnoi, and stamp the Ampldblu as connecting links between the aquatic animals which breathe by gills and the higher Vertebrates with pulmonary respiration. In all cases there are two lung sacs, either simple or provided with cellular spaces; but in addition to these there are, either in the larva or in the adult animal (Perennibranchiata, fig. 58), three (or four) pairs of gills, which sometimes lie in a cavity covered by a reduplication of the skin and provided with an external opening, and sometimes project freely on the neck as branched or tufted cutaneous appendages. The respiratory movements are effected, in the absence of a thorax capable of distension and contraction, by the muscles of the hyoid bone and by the abdominal muscles. The unpaired air-tube (trachea), which is supported by cartilaginous rods, is usually ex- ceedingly short and wide, like a larynx, and in the Anura alone is developed to form a vocal organ, which pro- duces loud croak- ing sounds and is in the male sex fre- quently reinforced by a resonating ap- paratus, consisting of one or two sacs communicating with the buccal cavity. As long as the respiration is carried on entirely by means of gills the structure of the heart and the arrangement of the principal arterial trunks are the same as in Fishes. Later, when the pulmonary respiration begins, the circulation becomes double and the auricle becomes divided by a septum into a right and left chamber, of which the right receives the veins from the body, the left those from the lungs. The ventricle, 011 the contrary, still remains single, and therefore contains mixed blood. It leads by a muscular rhythmically pulsating conus arteriosus into the ascending aorta with the reduced vascular arches. In the first period of larval life there are four pairs of vascular arches, which surround the pharynx without dividing into capillaries FIG. 623. Aortic arches of an old frog larva (from Bergmaun aucl Leuckart). An, the aortic arches uniting into the descending aorta (Ad) ; Ap, pulmonary artery ; JTps iiii'.i'icana Bum. Bibr. (tig. G2S) ; ,S. aniinl/itu Wagl., Brazil : Epii-rium Wagl.. Ceylon. The extinct Labyrinthodonta of the Triassic, the Permian, and the Carboniferous formations must be regarded as a special order of Amp/tibia. They unite in a remarkable manner the characters of the Ganoids and those of the urodele Amphibians. They possessed an external dermal skeleton, consisting of three broad bony thoracic plates and small scutes on the abdomen, amphiccelous vertebra; and peculiar folded teeth (hence the name of the group) in the Crocodile- like jaws. It has also been shown that they possessed branchial arches in the young state (Archegosaurus). The footmarks of gigantic animals (Chirotherium), which have been discovered in the Bunter- sandstein in England and Germany (Hildburghausen), and which some have ascribed to Chelonia and others to Marsupials, are pro- bably due to the Labi/rinthodonta. Owen has distinguished the oldest forms with armoured skull as Ganocephala. Archegosaurus Dechenii Goldf., Labijrinthodon Rutimeyeri Wied. Order 2. CAUDATA * (URODELA). Elongated Atnj)hibia with naked skin, usually with four short limbs and persistent tail, with or without external gills. The body, which is naked, ends with a long, usually laterally compressed, swimming tail, and possesses as a rule two pairs of short extremities far removed from one another. These limbs effect the relatively clumsy movements of the animals on land, but in swim- ming are used in. a much more effective manner as oars. The posterioi- limbs are completely absent only in exceptional cases (Siren) while the anterior limbs remain as short stumps. Some Urodeles (Perennibranchiata) possess throughout life three pairs of branched external gills, in addition to the lungs. Others indeed cast off the gills in the course of their development, but retain throughout life an external gill slit on each side of the neck * Daudin, ' Histohv naturelle gen. et partic. des Reptiles." Paris. 1802 to 1804. Aug. Bnmeril, "Observations sur la reproduction dans la menagerie de- Reptiles du Musee d : hist. nat. des Axolots, etc.. sur leur developpemeut et sur leurs metamorphoses," .\<>nr. Arch, (hi Musec d'hixt. nut. d<- Paris, II., 186U. Alex. Strauch, " Revision cler Salamandrideugattuugen." Petersburg. 1X70. URODELA. 189 (Derotrenia). Many, however, even completely lose the latter, ami -sho\v themselves by their whole organisation to be the highest mem- bers of the order (Salamandrina). In the two first cases the vertebrae are biconcave, like those of the Fishes, and enclose well-preserved remains of the notochord. The fully-developed Salamandrina, on the contrary, have vertebrae with an articular head in front and a concavity behind (i.e., are opisthoccelous). The eyes, which are small and sometimes rudimentary, are placed beneath the transparent skin, and except in the Salamandrina are without distinct lids. In all cases the auditory organ is without a tympanic membrane and tympanic cavity. The nasal apertures are placed at the end of the projecting snout, and lead into slightly developed nasal cavities, which communicate with the buccal cavity by openings placed far forward in the roof of the mouth immediately behind the maxillae. The buccal cavity is armed with small sharp hooked teeth, which on the lower jaw are arranged in single rows, but on the upper jaw and often on the palatine bone are in double rows. Almost the whole lower surface of the tongue is attached to the floor of the buccal cavity. The life history of the Axolotl, which was taken by Baird, Cuvier, and others for the larva of a Salamandrine, is very remarkable. According to the observations which were made by Dumeiil in the Jardin des Plantes at Paris, the young reared from the eggs of the Axolotl under suitable conditions lose the gill tufts and develop into a form which agrees with the Salamandrine genus Amblystoma, while the specimens which were originally introduced from Mexico preserve the Perennibranchiate form in the sexually adult condition. Species of Triton also have occasionally been found with perfectly developed gill tufts in the sexually adult state. Sub-order 1. Ichthyoidea.* Urodela with three pairs of external gills or without them, but with persisting branchial aperture ; with Jish-like biconcave vertebral and well-preserved notochord. The Ichthyoidea represent the lowest grade among the f r rodela with regard to their respiration, the structure of their skeleton, and their whole organisation ; and to a certain extent represent persistent developmental stages of the Salamandrina. The eyes are small, and * C'ontiwliachi and RuM_'i>L.\$~>&. Fr. Leydig. " Ueber die Molche der wu'rtembergischen Fauna," Archie fit r Naturgesch., 18(57. R. Wiedersheim, "Salamandrina perspicillata und Geotriton fuscus, etc., Genua. 1875. 192 AMPHIBIA. Order 3. BATRACHIA*=ANURA. Amphibia of stout form, with naked skin, without tail, with pro- ccelous vertebrce and well-developed extremities. The body is short and stout and is without a tail. On the head are the wide mouth and the large eyes, the iris of which has usually a golden lustre. The eye-lids are well developed, and the lower, which is transparent, can be drawn as a nictitating membrane completely over the eye. The nasal apertures are placed far forward on the extremity of the snout, and can be closed by membranous valves. In the auditory organ there is generally a tympanic cavity, which communicates with the buccal cavity by means of a .short wide Eusta- chian tube and is bound externally by a large tympanic membrane, which is sometimes free and is sometimes concealed beneath the skin. Only a few of the Batrachia are without teeth (Pipa, Eufo) ; as a rule there are small hooked teeth arranged in simple rows at least on the vomer, in the Frogs and Pelobatidce, on the maxillaries and pr?e- maxillaries also. The tongue is absent only in a small group of exotic forms ; it is usually attached between the rami of the lower jaw in such a way that its posterior part is completely free, and can be protruded as a prehensile organ from the wide mouth. Ribs are, as a rule, absent, but the transverse processes of the dorsal vertebrae attain a considerable length. A pectoral and pelvic girdle is in all cases present. The former is distinguished by firm connection with the sternum, the latter by the styliform elongation of the ilium. The hyoid bone in its definitive form is considerably simplified ; the body, is supported by large anterior horns, while the branchial arches on each side are reduced to a single posterior horn. In the skin, which is usually naked, glands with an acrid milky secretion are often aggregated in many places, especially in the region of the ear, where they form large glandular projections (parotid). Glandular aggregations occur also on the middle division of the hind legs (Bufo calamita) and on the sides of the body. * Rosel von Rosenhof, " Historia naturalis ranarum riostratium," Niiruberg 1758. Dauclin. " Histoire naturelle des Raiuettes, des Grenouilles et des Crapauds." Paris, 1 -SOI'. Rusconi, ' Developpement de ]a grcnouille commune," Milano, 182H. ( '. I'.vuch, " Beitrage znr Naturgeschichte and Classification der nacktc-n Amphibien." Wurzb. naturwiss. ZeitscTvr., !S3U) ; MyobatracJi-us paradoxua Schleg. FIG. Gso.- Tribe 2. Oxydactylia. Batrachia and pointed fingers and toes. with freely movable tongue Fain. Eanidae. "Water-Frogs. Batrachians with long hind limbs, which are adapted for jumping, and the toes of which are usually connected by entire swimming membranes. There are small hooked teeth on the maxillaries. prse. BATRACHIA. 195 maxillaries, .and usually also on the vomcr. Rana i-xciilc-ntu L., the green Frog. Green with dark spots and yellow longitudinal streaks on the back. The male has two vocal sacs. Leaves its place of concealment at the end of April, and spawns at the end of May or the beginning of June. On the banks of stagnant water. 7'. ti-mpoi-nrhi L., the brown frog, with dark spots on the head in the auditory region. It appears very early, and copulates in March; but only remains in the water to spawn, and then frequents meadows and field-. Steen- strup has divided this frog, which is widely divided over Europe, into two species (7?. .///;// ina, phiti/rltlna'). B. mugicnx Daud., Bull-frog, North America ; Pxcudlx paraiJod'n L., South America, distinguished by the size of its larvae. Fam. Pelobatidse. Laud-frogs T< >ad-frogs. With more or less warty, rough, and richly glandular skin, and clumsy toad-like form ; with teeth on the maxillaries. Alyti'x olisti-tricans Laur. (rig. G2G) ; Pdolatcs fuscirs Laur. ; Boiiibiiiatin- iijm-ux lib's. (Unke, Feuerkrbte). Fam. Bufonidae. Toads. Of clumsy build, with warty glandular skin (ear- glands) and toothless jaws. The posterior feet have five digits, and are but little longer than the anterior, so that the animal is unable to spring with the same agility as the Frogs ; but they can in many cases run with great speed. Bufo vulgitris Laur., the common Toad ; B.virulis Laur. (variabilis), the green Toad ; B. cnlnmltn Laur. (Kreuzkrb'te). Tribe 3. Discodactylia. Batrachians with tongue and with broad digits, the points of which are provided with suctorial discs. Fam. Hylidae. Tree-frogs. With maxillary teeth and without parotids. Hi/In rl>i>rca L., Tree-frog, cosmopolitan ; Notodelphys ovifrrn Weinl., Mexico. The female has a brood-pouch on the posterior part of the back. The larvee have bell-shaped external branchial vesicles. Pit t/Homedusa Incolor Bocld., South America; De-nil rolmti'x iliu-torius Schn,, Cayenne. CHAPTER VII. Class III. REPTILIA.* Scaly or armoured cold-blooded animals with exclusively pulmonary respiration and two ventricles incompletely separated from one another. Embryos with an amnion and an allantois. The body-form of the Reptilia varies far more than does that of the J iDjthibid, but repeats on the whole the types described for the latter class. The trunk still plays the principal part in locomotion, and accordingly the vertebral column presents a uniform segmenta- tion adapted for serpentine movements. The body, except in the * J. G. Schneider, " Historia Amphibiorum naturalis et literaria." 171)9 to 1801. A. Giinther, " The Reptiles of British India," London. 18C4. E. Schreiber, ' Herpetologia europtt-a," Braunschweig. 1875. 19G- EEPTILIA. Tortoises, is elongated and more or less cylindrical, and is eitlier altogether apodal, as in the Snakes, or is provided with two or four extremities, which as a rule serve only to support and push on the body which glides along the ground on its belly. In correspondence with this mode of locomotion a cervical region is scarcely at all marked, and even when more developed is always relatively rigid ; the tail on the other hand is long and movable. The skin, as opposed to the predominating soft and naked skin of the Amphibia, is tough and firm, in consequence of ossifications of the cut is as well as of a cornitication of the epidermis. The former may give rise to bony scutes, overlapping one another in a tectiform manner (ftcincoidea), or to larger bony plates, which constitute a hard, more or less continuous, dermal armour (Crocodiles, Tortoises). In general pigments are present in the dermis as well as in the deeper layer of the epidermis ; they determine the diverse colouring of the skin, and sometimes cause a true change of colour (green Tree Snake, Chamceleon). Cutaneous glands are also widely distri- buted among the Reptilia. Many Lizards in particular possess rows of glands on the inside of the femur and in the anal region, which open by distinct pores sometimes on wart-like protuberances (femoral pores, anal pores). In the Crocodiles, too, larger groups of glands are placed beneath the dermal armour both at the sides of the anus and on the sides of the rami of the lower jaw. The skeleton only exceptionally presents the embryonic form of a cartilaginous cranial base and persistent notochord. The vertebral column is more distinctly divided into regions than is that of the Amphifiitt, although the thoracic and lumbar regions still allow of no sharp limitation. In the cervical region the first vertebra becomes the atlas and the second the axis. While fossil Hydrosaurians and the Ascalabota possess biconcave vertebra?, the vertebral bodies of other Reptiles are always bony and generally proccelous. Ribs are very generally present, often along the whole length of the trunk. In the Snakes and the snake-like Lizards, in which a sternum is absent, all the vertebra* of the trunk with the exception of the atlas bear ribs, which, to compensate for the absence of limbs, are capable of free movements. In the Lizards and Crocodiles (fig. 573) there are short cervical ribs. The thoracic ribs are joined to a sternum by means of special sternocostal pieces. In the Crocodiles there is in addition an abdominal sternum, which extends over the belly to the pelvic region, and is composed of a number of ventral ribs (without dorsal part). The sacral T1IK SKULI,. vertebrre, of which there are usually two, have very large t ran -verse processes and ribs. The skull (tig. G31) articulates Avith the atlas by means of an un- paired, often tritid condyle of the occipital bone, and presents a complete ossitication of nearly all its parts, the primordial cranium being almost completely replaced. In the occipital region all four elements are present as bones ; but the j m v j m t basi-occipital (Tortoises) and the supra-occipital (Croco- diles and Snakes) may be excluded from the boundary of the foramen magnum. In the periotic capsule there is a fenestra rotunda, as well as the fenestra ovalis with the columella. The opisthotic, which usually fuses with the exoccipital, takes part in bounding the fenestra ovalis (in the Tortoises the exocci- pital and the opisthotic are separate). The prootic, on the other hand, is separate in all Rep- tiles; at its anterior there is in front of the lateral parts of the occipital region a separate prootic, at the front margin of which is the foramen for the third branch of the tri- geminus. The epiotic is fused with the supra-occipi- tal. The anterior expansion of the cranial capsule, and the development of the sphenoidal region, present considerable differences. At the base of the skull there is a basisp/tenoid in place of the parasplienoid. The alisplienoids and the orbitosphenoids are as a rule wanting, and are often replaced by pro- cesses of the parietals (Ghelonia) or of the fronto-parietals (Ophidla}. In the Chelonia and Lizards there is a large membranous interorbital septum, which may also contain ossifications. The bones of the roof of the cranium are always very large sometimes paired, sometimes FIG. 631.- Skull of Monitor (after Gegenbaur). a, from above, b, from below. C, occipital condyle ; Ocx, supra-occipital ; Ocl, exoccipital ; Ocb, basi- occipital ; P, parietal ; Ft; frontal ; Pf, post- frontal ; Prf, pra>f rontal ; L, lacrymal ; N, nasal; Sq, squamosal ; Q, quadrate ; Qi, qnadratojugal ; J, jugal ; JIx, maxillary; Jinx, prremaxillary ; Co, cohimella ; Us, basi-sphenoid ; Pt, pterygoid ; Pal, palatine ; Vo, vomer ; TV, os transversum. 198 REPTILIA. unpaired. The frontal bone in many cases takes no part in the formation of the roof of the cranial cavity, and only lies on the interorbital septum. Behind the lateral parts of the frontal in the temporal region are the postfrontals (Pf). In the ethmoidal region the median part remains in part cartilaginous, and is covered above by the paired nasal bones (N), and at the base by the vomer (Fo), which in the Snakes and Lizards is paired. The lateral parts are always separate from the median, and are known as the lateral ethmoids or prsefrontals (Prf). In the Lizards and Crocodiles lachrymals (L) are present on the outer side of the prsefrontals, bounding the anterior margin of the orbits. The squamosal (Sq) is more intimately applied to the cranium, and the quadrate (Q) is always a strongly developed bone. In Clidonia and Crocodilia the quadrate and maxillo-palatine apparatus are im- movably united with the wall of the skull : in Snakes and Lizards, on the other hand, they are more or less freely movable. In the first case not only are the large pterygoid and palatine bones fused with the sphenoid, but the quadrate bone is very firmly connected with the superior maxillary (i.e. jugal) arcade. In the Crocodiles a transverse bone (os transversum} is developed between the pterygoid and maxillary, and also a superior temporal arcade by which the squamosal is connected with the postfrontal on either side. In the Lizards, in which the maxillo-palatine apparatus and quadrate are movably articulated to the skull, the jugal arch is completely absent [i.e., the jugal is not connected with the quadrate by bone]. On the other hand, these 'animals possess not only a transverse bone (os transversum) (fig. 631, Tr), already mentioned for the Crocodiles, but also a column-like bone the columella which extends between the parietal and pterygoid. The facial bones are, however, most movable upon one another in the Ophidia, which are without the jugal arcade, but present a large os transversum. The two rami of the mandible, which in all Kept ilia and lower Vertebrates are com- posed of several pieces, are in these animals connected at the symphysis by an elastic band, an arrangement which permits of considerable extension towards the sides. The visceral skeleton is reduced to the hyoid bone, from the anterior arch of which the dorsal element (Jiyomcmdibular) is separated off, enters into relation with the auditory apparatus, and is known as the columella. The hyoid bone is most reduced in the Snakes. The limbs and their girdles are completely absent in most Snakes. In the Peropoda and Tortricidce, however, traces of hind limbs are THE NERVOUS SYSTEM. 1U9 found in the anal region, but they are hidden beneath the skin, except the terminal part, which bears a claw. In the Lacertilia the extremities present very various grades of development ; while the pectoral and pelvic girdles are without exception present, though they are sometimes very rudimentary, the anterior and posterior limbs may be com- pletely absent (Blindwonns), or the one pair may be present without the other as MIUI 11 rudiments. In most cases, however, both pairs of extremities are completely developed, and provided with live digits. Sometimes the digits are connected by swimming membranes (Crocodiles), or the extremities are modified to form flat swimming fins (fossil Hydrosaurians and Turtles). The nervous system (fig. 632) is de-C& cidedly higher than that of the Arityhilid. The hemispheres are distinguished by j^ _j their considerable size, and begin to cover the me>encephalon. The cerebellum shows various grades of development progressing from the Snakes to the Crocodiles, and in tin- latter recalls that of Birds by the contrast of its large median lobe and its small lateral appendages. Of the cranial nerves the facial is no longer united with FIG _ 632 _ Brain of the Al!i( , (lfoi . the trigeniinal, and the giossopharyngeal seen from above (after Rabl- . , -!~. , Ruckhard). T7i. prosencephalon appears as an independent nerve, which (Pcrebval hem i sp heres) ; Mh, me- lias. however, several connections with the ^ncephaiou (corpora bigemina); , . Cb, cerebellum; Mo, medulla vagus. Ihe spinal accessory also arises O biougata ; i, olfactory nerve; independently except in the Snakes. */, optic ; JF, troehiear (fourth); 1 / I", trigerninus (fifth) ; TT/7, audi- Filially the nypOglOSSal, which passes Out tory nerve ; IX, giossopharyngeal through a single or double opening in the ( ninth ); x < va ^ s (tenth); xi, spinal accessory (eleventh); 1C, skull, enters the category of the cranial first spinal nerve; -ic, second nerves. spinal nerve. The eyes are without lids in the Snakes, Geckos, and Amphisbsenas, but are protected in these animals by a transparent capsule, which is separated from the cornea by a. space filled with lachrymal fluid. In all other cases there is an upper and lower eyelid. An independent, nictitating membrane at the inner angle of the eye is always acconi- 200 REPTILIA. pa nied by the appearance of a special gland (Harderian ijliml}. Peculiar folds of the choroid, which correspond to the processus falciformis of the eyes of Fishes and to the so-called pecten of the eye of Birds, are present in the eye of Lizards. The auditory organ has a simple tubular cochlea and a corre- sponding fenestra (fenestra rotunda). A tympanic cavity with Eustachian tube and tympanic membrane is wanting only in the Snakes and apodal Lizards. In these cases the operculum, which covers the fenestra ova? is, and the columella which is attached to the operculum, are buried among the muscles, as in numerous An/ji/tibia. When a tympanic cavity is present, the columella is applied by its cartilaginous end to the tympanic membrane, which in many Lizards is still concealed beneath the skin, while a wide Eustachian tube leads into the pharynx. A cutaneous fold above the tympanic membrane of the Crocodiles may be regarded as the first rudiment of an ex- ternal ear. The olfactory organ of the ReptiUa shows, principally in the Chelonia and Crocodilia, a considerable augmentation of the surface of the mucous membrane, the folds of which are supported by carti- laginous turbinals. The external nares can be closed only in the Water- Snakes and the Crocodiles by an arrangement of valves. In the Crocodiles and Chelonians the internal nares open far back on the palatal part of the mouth. In the Snakes and Saurians there is also a second olfactory organ embedded between the turbinals and the vomer (nasal glands, Rathke, Jacobson's organ, Leydig), the nerve of which arises at the end of the olfactory lobe, and is spread out like a cup around a cartilaginous papilla. The sense of taste is by no means always located in the tongue, since in Snakes and many Lizards this organ serves for feeling, and in other cases e.g., the Chameleon is used as a prehensile organ. Leydig* has recently discovered cup- shaped sense-organs in the buccal cavity of Snakes and Saurians. In the Snakes they are arranged alongside the rows of maxillary teeth, in Saurians they are embedded in small pits of the connective tissue. Alimentary canal. Excepting in the Chelonia, Avhose jaws possess a horny cutting investment, which constitutes a kind of beak, the jaws are provided with conical or hooked prehen- sile teeth, which hold fast the prey, but cannot masticate it. As a rule, the teeth are confined to the jaws, and are always arranged * Fr. Leydig, " Zur Kcnntniss cler Sinnesorganc der Schlangen," Arcli. far miltr. Anatomic, Bonn, 1872. THE ALIMENTARY CANAL. 201 in a single row; .sometimes they are fastened to the upper (acrodont], sometimes to an external, strongly projecting li'din- of the flat dental groove (pleurodont), rarely, as in Crocodiles, they are wedged into special alveoli. Hooked teeth may also be present on the palatine and pterygoid bones, and in this case they frequently (e.g., in non-poisonous Snakes) form an inner arched row on the roof of the mouth. In the poisonous Snakes special teeth of the upper jaw are traversed by a groove or canal, and enter into close relation with the ducts of poison glands, the secretion of which passes into the wound through the groove or canal in the poison teeth. Salivary glands are found in Snakes and Lizards, both in the lips and 011 the lower jaw, and a sublingual gland may also be present. The possession of the latter is charac- teristic of the Chelonia. The oesophagus is very long, and is capable of an extraordinary degree of dilatation. Its walls are usually folded longitudinally, but they may also be beset with large papilla?, as in the Turtles. The .stomach is usually arranged longitudinally, except in the Cli<'l7. 206 REPTILIA. Sh a Thus it happens that the central digestive canal, which at first has the form of a shallow groove, becomes converted into a tube which remains for some time connected with the yolk at the umbilicus by a narrow duct. The appearance of a membrane enclosing the embryo and known as the amnion (fig. 635) is characteristic. The amnion arises in the following way. The outer layer (somatopleure) of the blastoderm is raised at the anterior and posterior end of the embryo, and forms two folds covering the head and tail end. These folds soon extend over the lateral por- tions, and fuse over the body of the em- bryo, so as to form a closed sac filled with fluid. Another organ which is cha- racteristic of the higher vertebrates is the allantois. This arises at the pos- terior end of the body as a vesicular evagination of the ventral wall of the alimentary canal, and grows out to a sac of considera- ble size. The walls of this sac, which is filled with fluid, PIG. 635. Two stages in the development of the chick (after v. Baer) to show the development of the amnioii and the allautois. a, The two folds of the amnion are still widely separate from one another ; only the first rudiments of the allautois are visible. b, Later stage with closed amnion. E, embryo ; D, vitelline membrane ; Am, amnion ; 8h, Serous membrane ; Dh, alimentary cavity ; Dg, umbilical passage ; T,' Yolk ; C, heart ; A/, allantois. are, unlike those of the amnion which is entirely without vessels, extraordinarily vascular and represent an embryonic respiratory organ, which in the long duration and complicated developmental processes of embryonic life is of great importance. The appearance of the allantois is correlated, not only? with the disappearance of branchial respiration, but also with the complete absence of a metamorphosis; the young animal being completely organised when it leaves the egg. Some Snakes and Lizards extend far north, while the Crocodilia are confined to the tori id zone, and only isolated examples of the Chelonia belong to the torrid zone. PLAUIOTREMATA OPIIIDIA. 207 The Reptilia of the cold and temperate regions fall into a sort, of winter sleep, and in the hot climates there is a summer sleep which comes to an end with the beginning of the rainy season. Most Reptiles are very tenacious of life, and can exist a long time without food and with limited respiration, and are capable, though in a less degree than the Amphibia, of reproducing injured or lost parts of the body. The oldest fossil remains of Reptiles belong to the Primary period, but appear only very sparingly in this period, being confined to the Kupferschiefer formation (Proterosaurus Speneri}. The Secondary period (Trias and Jura) can show a far greater variety of forms. At this time the Saurians and Hydrosaurians were predominant. The scaly Lizards first appear in the upper strata of the Jura, and are most abundant in the Tertiary period, which also presents a few remains of Snakes. Chelonia first appear excepting the doubtful footprints of the Trias in the Jura. Land-Tortoises are first met with in the Tertiary formations. Sub-class 1. PLAGIOTREMATA (LEPIDOSAURIA). Reptiles with scales and dermal shields, either apodal or provided with extremities. They have a transverse anal slit and a double penis. Order 1. OPHIDIA* (SNAKES). Apodal Plafjiostremata without pectoral girdle ; with bifid prof/-i'si- ble tongue ; usutdly with freely movable, always displaced bb 1 , ,/'.>/?- la >')/ and palatine bones ; without urinary bladder. The Snakes are chiefly characterized by the absence of extremities, and by the distensibility, sometimes extraordinary, of the mouth and pharynx. They cannot, however, be sharply separated from the Lizards. Formerly the limitations of this order rested entirely on the absence of extremities, and thus not only were the Cwc'di>l parietal scute; /, rostral scute; , tem- poral scutes ; o, chin scute ; j>, lower labial scutes ; q, mental scute ; r, cervical scutes ; *, cervical scales ; /, ventral scutes. the death of the victim. The hard structures of the integument, which have the form of scales, scutes, and splints, vary much in form, number, and arrangement. While the dorsal surface of the trunk is always covered with smooth or keeled scales ; the head is covered with scales as well as with scutes and plates, which, like those of the Lizards, are distin- guished according to their special position as frontal, parietal, and occipital scutes; also as rostral, nasal, temporal, and labial scutes, etc. VOL. ii. 14 210 OPHIDIA. (fig. 637). The mental scutes i.e., the scutes in the mental groove on the ventral surface between the rami of the lower jaw (fig. 637, q) may be mentioned as peculiar to most snakes ; in front of these two accessory labial scutes on either side form with the median labial scute (o) the anterior boundary of the mental groove. The scutes on the abdomen are for the most part broad, and invest the trunk like transverse bands (fig. 637 b, t) ; but scales and small median scutes may also be present here. The ventral surface of the tail, on the other hand, is, as a rule, covered by a double, or rarely by a single, row of scutes. Snakes moult several times in the course of the year : they strip off the whole of the epidermis on which the sculpture of the cutis is repeated. The internal organisation corresponds with the requirements of the elongated form of the body, as well as with the mode of locomo- tion and nourishment. A long and extensible gullet with thin walls leads into the dilated saccular stomach, which is followed by a rela- tively short small intestine. The larynx is placed extraordinarily far forward, and can be projected into the mouth during the long and difficult act of swallowing. The trachea is extremely long, and often contains respiratory air-cells in its course. The left lung is usually entirely rudimentary, while the right lung is correspondingly large, and is transformed at its posterior end into a vesicular air- reservoir. The auditory organ is without an apparatus for conducting sound, and the eyes have no movable lids. The eye-ball, with its usually vertical pupil, is covered by the skin, which is here transparent, and behind which it is bathed by the lacrymal fluid. The nasal apertures are usually placed quite at the apex or on the lateral margins of the snout. The forked horny tongue serves not as an organ of taste, but as a tactile organ, and is enclosed in a sheath, from which it can be protruded through an indentation of the extremity of the snout, even when the mouth is closed. The Snakes move principally by means of lateral flexions of the vertebral column. The vertebrae are very numerous, and almost always bear ribs in the region of the trunk. The centra are concave in front and convex behind ; they are connected with one another by free ball and socket joints, and by horizontal articular surfaces of the transverse processes in such a manner that dorso-ventral move- ments are impossible. The ribs are also freely articulated with the vertebral bodies, and can be moved backwards and forwards, move- ments which are of cn'eat use in assisting locomotion. The Snakes OPOTERODONTA COLUBRIFORMIA. 211 run in a certain sense on the extreme points of their ribs, which are a 1 1 ached to dermal scutes ; for they move by alternately pushing the ribs forward, and drawing after them the ventral scutes, which are attached to one another and to the ribs by muscles. The Snakes feed exclusively on living animals, both warm-blooded and cold-blooded, which they attack suddenly, kill and swallow whole without mastication. Swallowing is effected thus : the teeth on the jaws are alternately hooked further and further forwards into the body of the prey, as a result of which the mouth and pharynx of the snake are in a sense gradually drawn over the animal, whose surface is at the same time made slippery by the abundant secretion of the salivary glands. During this process the larynx is projected forward between the rami of the jaws, so that respiration can be maintained. After the completion of this laborious operation of swallowing, the animal appears entirely prostrated, and passes a long period in inactivity, during which the very slow but complete digestion takes place. Snakes copulate, and are for the most part oviparous. They lay a small number of large eggs, in which the embryonic development may be already far advanced. There are, however, also viviparous Snakes; for example, the sea-snakes (Hyd/rophidae) and the vipers (Pelias berus}. Most of the species distinguished by size and beauty of colour belong to the warmer zones, only the smaller forms extend into northern temperate climates. Many Snakes are fond of the water and are truly amphibious. Others live for the most part on trees and shrubs, or on sandy ground; others exclusively in the sea. In the temperate countries they fall into a kind of winter sleep, in the hot countries they undergo a summer sleep in the dry season. Sub-order 1. Opoterodoilta. With narrow, non-distensible, slit- like mouth, and immovably connected facial bones, without or with only a short tail. They have solid hooked teeth only in the upper jaw or in the lower jaw. Posterior limbs present as rudiments. They live beneath stones, or in passages in the earth, and feed on insects. Fam. Typhlopidae. Typlilopx lumbrieit-li* Merr. (fig. 638), Antilles. T. ver- L., Greece. Stenoxtama nigricann Dum. Bihr., South Africa. Sub-order 2. Colubriformia. Both jaws armed with solid hooked teeth. In the upper jaw the last tooth may be grooved, and then may be either without poison glands, or may be connected with the 212 OPHIDIA. duct of a small poison gland. This sub-order includes the Agly- phodonta and the Opisthoglypha. Fam. TTropeltidae. With short pointed head, mouth not distensible, but with teeth in both jaws. TTi'Opeltis philippinus C'uv. Fam. Tortricidae. With small hardly discernible head and short conical tail. The teeth are small, and there are teeth on the palatine bones. They have a rudiment of the pelvis with small anal claws. Turtrl.r *<-ytale Hmpr., South America ; Cijlindroplris ni /'a Gray. Java. Fam. Pythonidae. With long oval heads covered with scutes or scales, with rudiments of hind limbs which terminate with an anal claw at the sides of the cloaca. Eryx jnculvst Wagl., South Europe ; Bon constrictor L.. Brazil ; Python retictilatiis Schn., Sumatra. Fam. Colubridae. The head is not very broad, and is distinct : it is covered with scutes. The dentition is complete. The tail has a double row of scutes on the under surface. Cwtntclla nvstriucu Laur.^C". Icevis Lac., widely distributed in Europe; Lio2)ltix coljclla L. Brazil ; Tropidonot'us natrir Gesn., Ringed snake. With obliquely keeled scutes. The species is widely distributed in Europe. Tr. tesselatux Meyr. ; Coluber (Calopeltis) uEsciiliipii Gesn.= C. Jiarescens Gm.. the snake of ^Esculapius. South Europe, Schlangenbad, Austria ; Zatiu'nis nfrariri-Hx Shaw, South Europe ; Herpetodrya* cfii'inutux L.. Brazil. Fam. Dendrophidae. Tree snakes. Body thin and slender, head usually long, flat and distinct from the neck. The ventral scutes usually with two keels. Ventral caudal scutes in two rows. Drndropliix pu-ta Gm., East Indies; Alia-tnlln smaragdina Boie, West Aji'ica. Fam. Dryophidae. Body very long and slender, as is the head ; snout thin and sometimes prolonged into a flexible appendage. Dryophis argentea Daud.. Cayenne. Fam. Psammophidae. Sand snakes. The posterior tooth of the upper jaw is grooved. Psamtnophis linratus Dum. Bibr., Mexico ; Ccelopi'lt'ix lai-rrtina Wagl., Egypt, Fam. Dipsadidse. The body tolerably slender, strongly compressed ; with short tail, broad at the end. and very distinct. There are usually posterior grooved teeth. Dipsas dcndropJiila Reinw., East Indies ; D. fasciata Fisch., West Africa. Fam. Scytalidae. The hindmost tooth in the upper jaw is the longest, and is grooved. Scytale conmatitm Dum. Bibr., Brazil. O.ryrhojmx j)lvmbrnx Wied.. South America. Sub-order 3. Proteroglypha. Poisonous snakes with large grooved FlG. 638. Typhlops lumbri- calis (regne animal). SOLENOGLYPHA. 213 teeth, which are placed anteriorly in the upper jaw, and behind which there are usually solid hooked teeth. The pnlatine and pterygoid bones, as well as the lower jaw, are armed with hooked teeth. Fam. Elapidae. Resemble the Col nitride. Head covered with scales ; usually f vrith two rows of sub-caudal scutes. ^'"ji< tripudiang Merr., the Cobra, Bengal; N. fiaje L. Cleopatra's Snake. Egypt; Elups corallinus L., the coral Snake, South America. (Fig. 63!-.) Fam. Hydrophidae, Sea-Snakes. With scarcely distinct head which is covered with scutes, and compressed body which is prolonged into a strongly compressed FIG. 639. Elaps corallinus (regne animal). swimming-tail. They are viviparous. Platurus fasciat'us Baud., Indian Ocean phix (Pela/nix*) bicolor Baud. (fig. <5-iO), Indian Ocean. Sub order 4. Solenoglypha. Snakes with triangular head and relatively short tail. The small upper jaw has a hollow poison tooth on either side, and one or more reserve teeth. Small solid hooked teeth are also present on the palate and in the under jaw. Fam. Viperidae (Vipers). Head strongly marked off and broad, without pits between the nares and eyes. There are usually two rows of scales on the under side of the short tail. I "ipcra a*/m Merr. In wooded mountain regions of South Europe. V. ammndytes Dum. Bibr. The sand viper, with a soft horny prominence on the tip of the snout. Italy and Dalmatia. Pel MS Imt*. 214 LACERTILJA. (Kreuzottcr). Common Viper, distinguished by the black-brown zigzag band on the back. Found in the mountain forests of Europe. Fain. Crotalidee. With a pit between the eyes and nose. Crotahm dim**//* L.. Kattlcsnake of south-east of North America ; C. Itorridus L. South America Bothrops atrox L. Brazil. FIG. 640. SydropUx bicolor (regne FIG. 641. Pygopus (Bipes) Jepidopits (regne animal). animal) . Order 2. SAUEII * (LACERTILIA) LIZARDS. Plagiotrema with pectoral girdle and sternum, usually with tympanic cavity and movable, eyelids ; with a, non-extensible mouth and with urinary bladder. The Lizards always have an elongated and sometimes a snake-like body. As a rule there are four extremities, which, however, scarcely * Tiedemann, " Anatomie und Naturgeschichte der Drachen. " Niirnbei'g. 1 S 1 1 . J. E. Gray, " Catalogue of the specimens of Lizards in the Collection of the British Museum/' London. 1845. Fr. Leydig, " Die in Deutschlaud Icbenden Arten der Saurier." Tubingen, 1872 THE SKELETON. 215 carrv the body raised from the ground ; but in locomotion art- used principally for pushing- the body forward ; they may alx> be used for clinging (Chauifelion), climbing (Geckos), and digging. They usually end with live clawed digits. They are .sometimes so short and rudi- mentary, that they have the appearance of stumps applied to the serpent-like body, and are without separated digits (Cha/incesaura). In other oases rudiments of the posterior limbs alone exist ( Pseudopus) (fig. 041), or anterior limbs only are present (Ghirotes) ; or finally external limbs may be entirely absent (A-IKJHI*. A rout ins. Ophi- suu.rt.is). The pectoral and pelvic girdles are however present, and in all Lizards except Amphisboena there is at least a rudiment of the sternum, which increases in size as the anterior limb* become more developed, and then serves for the attachment of a correspond- ingly greater number of ribs. The ribs are only wanting on the most anterior cervical vertebra^, and sometimes on some of the lumbar as well as on the caudal vertebras. The anterior ribs present a peculiar modification in Draco, being extremely long and serving to support lateral expansions of the skin, which can be used as wings. The crania] capsule (fig. 631) does not usually extend into the orbital region, behind which it is imperfectly closed by membranous structures (membranous interorbital septum). The squamosal is firmly attached to a strongly projecting process (parotic jn^ocess} of the posterior temporal region. The hinder end of the maxilla is frequently connected with the postfrontral (Pf) by a bony bridge, the jugal (fig. 631 J), which encloses the orbit; while a bone (quadrato- jugal) passes from the jugal to the quadrate, bridging over the temporal region. An important character of the Lizards as opposed to the Snakes consists in the fact that the bones of the jaws are not movable upon one another. Parts of the maxillo-palatine apparatus are indeed movably connected with the skull (Ratteria = Sphenodon excepted), especially the ptery golds, which are applied to the articular processes of the basisphenoid, and usually articulate with the quadrate : but the individual bones of the maxillo-palatine apparatus are firmly connected with one another, and with the anterior part of the skull. The pterygoids are firmly attached to the maxillaries by a transverse bone, and serve to support the parietal bones by a rod-shaped colum&lla [a bone which extends from the parietal to the pterygoid on each side]. On the top of the skull the parietal bones and the occipital segment are connected by fibrous tissue, and in consequence are slightly movable upon one another. The quadrate bone is '216 LACERTILIA. movably articulated with the parotic process of the temporal region and supports the lower jaw, the ranai of which are firmly connected at the syniphy^s. The dentition of the Lizards in form, structure and mode of fixture of the teeth, presents far greater diversity than does that of the Snakes ; it is however not so complete since the palate has never an inner row of teeth, but only small lateral groups on the pterygoids. The teeth are almost always attached directly to the bone, either on the edge of the jaw (Acrodont), or on the inner side of the jaw (Pleurodont). This distinction corresponds to the geographical dis- tribution of the Iguanas, those found in the eastern hemisphere being Acrodonts, and those in the western Pleurodonts. The shape of the tongue seems important, and the principal groups are distin- guished and named according to this characteristic. Most Lizards have eyelids, an exposed tympanic membrane and a tympanic cavity. Only the Amphisbcenas and Geckos are without eyelids, and have the same arrangement for covering the eyes as have the Snakes. In the Scincoideoi the lower eyelid can be raised like a transparent curtain without hindering the sight. In the Clianicelion- idce the single eyelid is a muscular cutaneous ring of skin with circular opening. The integument of Lizards resembles in its general features that of Snakes, but presents much greater variety. Sometimes there are fiat or keeled scales, sometimes scutes and larger plates, for the distri- bution of which on the head the terminology already described for Snakes is used. In addition, more irregular hardenings of the skin may occur warty protuberances which give the skin an appear- ance similar to that of the Toads (Geckonidcu). On the other hand there are often cutaneous lobes on the throat, crests on the back and on the top of the head, also folds of skin on the sides of the trunk, on the neck, etc. Although the skin of Lizards is in general poor in glands, yet in many forms cutaneous glands and corresponding rows of pores along the inner side of the thigh (fig. 634, >SP) and in front of the anus are constantly present. As a rule, the females after copulation (which in temperate regions takes place in summer) lay a small number of eggs ; some genera are viviparous (Anguis, Seps). Most are harmless, and are useful by destroying Insects and Worms ; larger species, as the Iguana, are hunted for the sake of their flesh. By far the greater number, and all the larger and more beautifully coloured species inhabit the warmer and ho f . countries. ANNULATA VERMILINGUIA. 217 Fossil remains of Lizards have been found in great numbers, the oldest from the uppermost strata of the Jura. The Lizards of the chalk (Mosasaurus, etc.), which are most nearly related to the Moni- tors, were of gigantic size. Sub-order 1. Annulata. Body snake-like, with hard scaleless skin, which is divided into rings by transverse furrows (fig. 642). These rings are again crossed by longitudinal furrows in such a way that the surface has an elegantly plated, mosaic-like ap- pearance. There are large sciites only on the head ;ind throat. There is no sternum, and the pectoral girdle, except in C/iirotes, remains very rudimentary. Rudiments of a pelvis are in all cases present. As a rule extremities are wanting, but small front feet (Ghirotes) may be present. Eye-lids and tympanic membrane are absent the small eyes are covered by the integument. A columella is also absent. The tongue is short and thick, without sheath, and the dentition, as in the scaly Lizards, is either acrodont or pleurodont. They are harmless animals, and live for the most part in America, like the Cceciliadce, beneath the ground, usually in ant-hills, and feed 011 Insects and Worms. Fain. Amphisbaenidae. Amjrftislia'iui allti L., Brazil ; A. fidlfjlnoxa L., South America (fig. ;i i-uri/mt,/ Gray. Cuba ; Haxiliftcuts niitratux Daucl., South America. The following belong to the eastern hemisphere, and arc acrodont : Calt>'--< ophiomaehux Merr., East Indies; Druc>> rolanx L..Java: Lojttiium ainl>oi>i< n*i* Schloss. The New Zealand genus, llnth i-'nt = Xji//< //m/n//, which was formerly reckoaed among the Iguanidte. shows such considerable differences in its organization that (iiinther established for it a third order of sealy Reptiles under the name of Rhynchocephalia, * which Huxley hoi, Is to be allied to the extinct Triassic, Lacertilian genera Hypn-ndnju'don and Ifhi/Hchoxttunix. Fam. Humivagse. Lizards with broad Hat body, supported by shorter limbs; of almost toad-like aspect. The skin is not uufrequently covered with spiny scales. They live on the ground in stony and sandy places, where they hide themselves in pits and holes. To the Ifn m ii'ii/j cc of America, which are all pleurodont. Ic'iong Phry>n>x-<> : TriijinJui'iix i-i/i-lnni* \Vied., Urazil. FIG. 6ii. S'(-;c.v i>ffi<-i,i veifiie animal). To the Ilinnicagie of East India and Afnea. which are acrodont. and possess canine teeth. li.-long Pfirynecfplialitx fir/i^xrojn/s Kp.. Siberia : Uromuxti-i- xpinijtrx Merr., Egypt ; Af/ania colon orinn Daud.. Egypt : SfcU'm nihjarix Latr., Hardun, Egypt. Sub-order 4. Brevilinguia. Scaly lizards, with elongated, often snake-like body. The limits are very diversely developed. The tongue is short and thick, without sheath, more or less indented at the thinner anterior end, and but slightly protrusible. Eyelids are, as a rule, present. The tympanic membrane is often concealed beneath the skin. Fam. Scincoidese. Saud-LizanU. The more or less snake-like body is covered with smooth bony scales. The crown of the head is invested with larger scutes. Ani/iiix fragilis L., Blindworm, Europe : Si-'nicux otKcintili* Laur. (tig. G44) Egypt; Seps chalcidica Merr., Dalmatia : Acontuis mulcagrix Cuv.. Cape. A. C- thither. ' Contribution of the Anatomy of Hatteria {Rhynrhoce- Cray.'' Phil. Trans. lfy. Xnr.. London, vol. 157. ii.. 18(57. 220 LACERTILIA. Fam. Ptychopleurae. The body is provided with two lateral folds of skin, covered with small scales. These folds extend from the region of the ear to near the amis, and form the boundary between the dorsal and ventral surfaces. Zonurnx Curdylus Merr. = f/risnus Cuv., South Africa; Pseudupu* Pall as ii, Guv., South-east Europe, and in lower Austria ; Pij/jopus (Bijjcs) lepidopus Lacep., New Holland (rig. 641) ; CJiamcexain-n any succeeding supplementary teeth. Ribs are present in great numbers, not only in the very long thoracic reyion, but also in the cervical and o abdominal regions. In the Crocodiles there is, in the abdominal region, a narrow stern n m abdoDiinale, which is prolonged to the pelvic girdle, and bears on its sides, a number of abdominal ribs, the upper ends of which do not reach the vertebral column (fig. 645). The internal organisation probably presented different grades of per- fection in the various groups, of which only the highest viz., that found in living Crocodiles can be known to us. Order 1. ENALIOSAURIA. If i/dro.^i n ri<(. with naked leathery xk'ui, biconcave vertebra <-< n/i/< ///y a tin. The snout, pointed and elongated like a beak, is principally formed by the praemaxillary bones. The teeth present a striated and folded surface, and are closely crowded together. They arc found principally in the Jura, rarely in the chalk. lelifhyotaatrus i-mininm'tit De la Beche. etc. Order 2. CKGCODILIA (LORICATA). ETydrosauria, n-itli fttnt// il^nn/d plates ami teeth wedyed into the bones of the jaws, tow/tic// tlci/ tir>l : with four partly clawed feet and long, keeled s/i-n// />//,/;/ The extremities no longer have the form of swimming tins, but of freely articulated legs and feet with separated digits. The integu- ment is granular and leathery, and contains, especially on the dorsal surface, large and in part keeled, osseous plates. On the tail these plates form a den ta ted crest, paired in front, but in its hinder part simple. The broad flat skull is distinguished by the corroded appear- ance of the surface of the bones, and possesses separated alisphenoids, and above the maxillo-jugal arcade a supra-temporal arcade, which is separated from the orbit by a bony bridge (process of the post- frontal and jugal). The roof of the skull is formed by an impaired parietal and frontal, to which are joined the paired nasal bones. The upper jaws are firmly united with the skull and are elongated so as to form a long snout, at the end of which the paired pnvmnxillary bones are wedged in. The sides of the snout are formed by the maxillary bones which are very large. The praemaxillaries, which bound the nasal apertures, and the maxillaries develop huri/.ontal palatal plates, which meet in the middle line and form the anterior part of the hard palate. The lacrymal is always of con.sidei-able size. Behind, the palatine and ptervgoid develop palatal plates which unite suturally in the median line, and constitute a comph-U-lv closed 224 HVDROSAUKIA. roof for the buccal cavity. The posterior nares which are surrounded by the paired vomers open at the posterior margin of the buccal cavity. The conical teeth, which are completely confined to the bones of the jaws [preemaxilhe, maxilla?, and mandible], are deeply wedged into alveoli, and they present slightly compressed striated crowns. The fourth tooth of the mandible is usually distinguished by its great size as a prehensile tooth, and, when the jaws are shut, fits into a gap or an excavation in the upper jaw. In the Teleo- sauria the vertebrae are amphiccelous in the Steneosauria, which are also extinct, they are opisthocoelous, and in the Crocodiles of the pre- sent day proccelous. The internal organisation of the living Crocodiles is the highest amongst all Reptiles. The eyes have vertical pupils and two lids as well as a nictitating membrane. The nasal openings lie far forward 011 the point of the snout, and, as well as the ears which are placed far back, can be closed by cutaneous valves. The buccal cavity, to the floor of which is attached a flat non-protractile tongue, is without salivary glands, and leads by a wide oesophagus into the rounded muscular stomach, which resembles that of Birds in form and .struc- ture, and specially in the aponeurotic discs of its internal lining. The stomach is followed by a thin-walled duodenum, which is beset with papilla?, and passes into the small intestine, which is folded in a zigzag fashion. There is no ca?cal appendage to the short wide large intestine. The latter becomes narrow and almost funnel- shaped, before it opens into the cloaca, from the anterior wall of which arises the erectile cppulatory organ. The structure of the heart is the most perfect found in all Reptiles, and, in the com- plete separation of a right venous and a left arterial portion, affords a direct transition to that of the warm-blooded animals. Finally, the free communication of the body cavity by openings of the so-called peritoneal canals, which recall the abdominal pores of the Ganoids and Selachians, deserves to be mentioned as peculiarities of the Crocodilia. Three groups of Crocodiles are to be distinguished : two of these the Teleosauria (AmpMca-lia) and Steneosauria (OpistJioccvlia) are extinct. The former with the genera Mystriosaurus Kp. and Teleo- saurus Geoffr. are confined to the Jurassic formation, the latter with Steneosaurus Geoffr. Cetiosaurus Owen, etc., occur in the Jura and in the chalk. Only the third group of the Crocodiles or Proccelia has persisted from the chalk onwards through the tertiary period to our own time. CHELOMA. '2-~> Sub-order Proccelia = Crocodilia, $.fi-. With proccelous vertebrae and long compressed swimming tall, tin- dorsal side of which bears a double cutaneous crest, which becomes single at the posterior end. The anterior feet with five free digits ; the posterior with four digits, which are more or less united by webs. Live in the mouths and lagoons of great rivers in the warmer climates of the Old and New Worlds, and seek their prey by night. The hard-shelled eggs are laid in the sand and in holes on the banks. Fain. Crocodilidae. The so-called canine teeth (fourth tooth of the lower j;i\v) fit into a notch of the margin of the upper ja\v. Hind feet with com- plete swimming membram-. (.'rncot/ih/x n/ii/i/rix (.,'uv., Xile. ('. rhoiiibifrr ( 'uv,. i 'uba. Kam. Alligatoridae. The snout is broad and without notch for the so-called canines of the mandible. Swimming membranes only partially developed or rudimentary. [Found only in America.] ARiijutor lucius CUT. ; Caiman (J/ic/ii'/') xdt >-oj>x Schn. Fam. Gavialidae. Rhamj}1ixtion of wings and feathers of the class Aves. The shield-like, dermal, armour (fig. 646) beneath which the head extremities and tail can often be retracted, owes its origin partly to osseous parts of the vertebral column and partly to the accessory der- mal bones, which are intimately connected with the former. The flat plastron contains nine more or less developed osseous pieces, an anterior unpaired interclavicular, and four pairs of lateral pieces (the anterior being distinguished as clavicularia) between which there * H. Rathke, " Ueber die Entwickelung der Sdiildkrb'ten," Braunschweig. 184s. Gray, " Catalogue of the Shield Reptiles in the Collection of the British MiiM'iim. I'art L. London IS.")."). Suppl., ISTu. Append.. 1S72. L. Agassiz, " Embryology of the Turtle." Natural History of the United States, Vol. 111., part III., 1857. VOL. II. 15 226 REPTILIA. may be left a median space, closed by skin or cartilage (Triort IHHU. V, vertebral (neural) plates; C, ensta plates ; M, marginal plates ; Nu, nuchal plate ; Py, pygal plate ; B, plastron (ventral shield) ; Cl, clavicle ; Jcl, inter-clavicle ; Sc, scapula ; Co, coracoid ; Pco, acromial process (pro-coracoid); PI, pubis ; ./, ischimn ; Jl, ilium; //, hurnerus ; E, radius; U, ulna; Fe, femur; T, tibia; F, fibula. in the median line in the neck (nuchal plate), and in the sacral region (pygal plate), and partly laterally at the edge of the shield (22 mar- ginal plates). While the spinous processes of eight of the thoracic vertebra? (2nd CHELON1A. 227 to 9th) appear in the median line as horizontal plates [neural plates], the ribs of the same vertebrae (2nd to 9th, these rib.> arc dis- tinguished from the first and last ribs by their greater length) .-ire transformed into broad transverse plates [cost n I /i/nte8~], which are joined with one another by indented sutures, and present the special peculiarity of giving off broad processes, which arch over the muscles of the back, and are connected with the neural plates (expanded spinous processes). In addition, larger plates, which owe their origin to cornifications of the epidermis, are usually present. They are applied to the outer surface of both the dorsal and ventral shields and are used, in the case of some of the larger species, as tortoise- shell. They by no means correspond with the subjacent bony pieces, but are very regularly arranged in such a manner, that in the dorsal shield a median and two lateral rows of plates can be distinguished, and round the periphery a circle of marginal plates. On the ventral surface, on the other hand, there is a double row of such plates. Unlike the middle (thoracic) region of the vertebral column, the vertebra? of which are firmly connected with the dorsal shield, the cervical and caudal vertebra? are always movable upon one another. The cervical region is exceedingly flexible, and can be more or less completely retracted within the shell ; it consists of eight long ver- tebrae, which are without ribs. The ten rib-bearing vertebra? are followed by two or three sacral vertebra?, which project beneath the carapace, and by a considerable number of very movable caudal vertebrae. The head is tolerably arched: the bones of the skull are firmly united to one another by sutures, and form a broad roof, which is prolonged into a strongly developed occipital crest. The skull is characterised by the possession of a pair of parietal bones and of large anterior frontals. Descending lamellar processes of the parietal bones extend along the sides of the cartilaginous cranial capsule as far as the short basisphenoid. The temporal fossa is most completely roofed in in the marine Chelonia by broad osseous plates which are formed by the postf rental, jugal, quadrato-jugal, and the squamosal. The opisthotic remains as an independent bone behind the prootic, which forms the lateral walls of the cranial cavity. All the parts of the maxillo-palatine apparatus as well as the quadrate are firmly connected with the bones of the skull, and are marked off from one another by serrated sutures. The facial parts of the skull are strikingly short, and the nasal bones are absent. The bony palate is formed by the broad palatine and the unpaired vomer, behind the 228 REPTILIA. palatine plates of which the posterior nare.> open. The pterygoids are very broad and lamellar. Teeth are completely absent, both on the palatal bones and on the high, relatively short bones of the jaws, but the edges of the latter are covered, like the beak of a bird, by sharp cutting, serrated horny plates, which enable certain species to bite with great vigour and to inflict sensible wounds. The four limbs enable the Chelonia to creep and run on land : in the aquatic forms, however, they are swimming feet or fins. The position of the pectoral and pelvic girdles, and of the corresponding- muscles, between the dorsal and ventral shields, is remarkable ; but is fully explained developmentally by the growth of the anterior and posterior ribs. The scapula is formed of an ascending rod-like bone, the upper end of which is attached to the transverse process of the anterior thoracic vertebra by a ligamentous or cartilaginous connec- tion. A strong acromial process (procoracoid) reaches from the scapula to the unpaired portion of the ventral shield, to which it is likewise attached by a ligamentous or cartilaginous connection. The pelvis closely resembles that of the Saurians, and except in the Land Tortoises is not firmly connected with the carapace. In the organs of digestion and reproduction Chelonians partly resemble Crocodiles and partly Birds. They especially resemble the former in the structure of the male generative organs, and in the possession of peritoneal canals, which are, however, closed. The opening of the genital ducts and the ureters into the neck of the urinary bladder, which accordingly functions as a urogenital sinus, is worthy of remark. The eyes are placed in closed orbits, and have lids and a nicticating membrane. There is always a tympanic cavity with a wide Eustachian tube, a long columella and a tym- panic membrane, which is visible externally. The tongue is attached to the floor of the buccal cavity, and is not protrusible ; in the Land Tortoises it is beset with long papilla?. The copulation lasts a day, and during that time the male is carried on the back of the female. The eggs are laid in small number, except in the marine Chelonia, in which they are more numerous. They contain within the shell a layer of albumen, sur- rounding the yolk, and are buried in the earth, in the aquatic Chelonians near the shore. According to Agassiz the North American Marsh Tortoises lay eggs only once in the year, while they copulate twice (in the spring and autumn). The first copulation, according to this investigator, takes place in Ennjs picta in the seventh year, the first deposition of eggs in the eleventh year of the animal's life. CHELONIA. 229 These facts agree with the slow growth of the hotly of the Tortoises, and the great age which they attain. The Chelonians belong mainly to warmer climates, and live prin- cipally on vegetables; many of them, however, also live on Mollnsca, ( Yustacea, and Fishes. Fossil remains are first found, but rarely, in the upper white Jura. More numerous remains are found in the Tertiary period. Fam. Cheloniadae. Turtles. With flat dorsal and often cartilaginous ventral shield, between which the head and extremities cannot be retracted. The latter are fin-like feet, with immovably connected digits, which are usually without nails, and are covered by a common skin. The anterior limbs are much lunger than the posterior. Chrltnita cxfiilrtitu .Merr. ; Cli. (Carcttu) hnbr'n-nta FIG. 647. Thalassochelyg caretta (regne animal). L.. Atlantic and Indian Ocean; Tludaawclicli^ caretta L. = /nrf/ritfa Kond. (fig. fill), Atlantic Ocean and Mediterranean; Spliarylx mrir/c/'ti Gray. Rare in the Mediterranean, more common in the Atlantic Ocean and South Sea. Fam. Trionycidae. Soft or Mud Tortoises. With flat, oval, incompletely ossified dorsal shield, and long retractile neck. Jaws with cutting edges, sur- rounded by fleshy lips. The head and feet are not retractile. The nasal openings are on the long snout. Triuinj.i' fi-rn.r Merr. A fierce animal. Found in the rivers of Georgia and Carolina. Good to eat. Fam. Chelydse. Head and feet not retractile. Latter end with free digits, which are webbed and furnished with claws. Clu-lyx Jimlriatit, Schweig., Matamata. South America. Fam. Emydae. Freshwater Tortoises. Dorsal shield flat, plastron usually small. Feet thick, with freely movable digits, which are connected by a weK They swim excellently, and move also with great facility on land. They prin- l'.".U AYES. ripally inhabit sluggish rivers and ponds. Cixtudx r // rojifra Schneid. = (ir-n.. the common Tortoise of South Europe and East Germany ; Ennjs dii the Caspian Sea. in Dalmatia and Greece ; Clniijilru serpent iua L.. with very sliarp jaws, in North America. Fam. Chersidse. Land Tortoises. With high, arched, ossified carapace; head and feet retractile. The digits are immovably connected as far as the nails to thick club-feet, with indurated soles. They live in damp and shady localities in warm and hot climates, and feed on plants. Trxturfo grcrca L. r Alclr.. = nninjinata. South Italy : T. tnlniluta Baud., in America. CHAPTER VIII. Class IV. AVES* BIRDS. Warm-blooded oviparous animals, covered with feathers. The cham- bers of the heart are completely separated. The rlyht aortic arcJi persists. There is a single occipital condole, and the anterior limbs are transformed into winys. As opposed to the poikilothermic Vertebrates (i.e., Vertebrates whose temperature varies with that of the external medium) the blood of Ares and Mammalia possesses a high temperature, which remains tolerably constant in .spite of the changing temperature of the external medium. This maintenance of a constant temperature demands above everything a great energy of metabolism. The sur- face of all the vegetative organs, especially of the lungs, kidneys, and alimentary canal, has a relatively greater extension in the warm- Wooded than in the cold-blooded animals. The operations of diges- tion, preparation of blood, circulation and respiration are carried on with much greater energy. With the need of a richer nourishment, the processes of vegetative life take a disproportionately more rapid course, and as the high and uniform temperature of the blood is a Joh. F. Naumann, ' Xaturgeschichte der Vogel Deutschlands," 13 Bde.,, Stuttgart. 1822-lsr.n. " Naumanuia. Archiv t'iir Oruithologie," Herausgegeben von Ed. Baldamus. Kothen, 1841). " Journal fiir Ornithologies' Herausgegeben von J. Cabanis. Cassel. 1853 . "The Ibis," 1859. Tiedernann. " Anatomie und Naturgeschichte der Vogel." Heidelberg. 1810- 1814. C. E. v. Baer. " Entwickelungsgeschichte der Thiere.'' I. und II., 1828-1837. Rernak. " Untersuch. iiber die Entwick. der Wirbelthieiv." I'.crlin. 1850-5."). Huxley, " On the Classification of Birds." Proceed. Zool. Soc.. Gray and Mitchell. "The Genera of Birds," London, 1841-1'.). C. Sundevall. ' Tentamen." Stockholm, 1872-73. REGULATION' OK TEMPERATURE. L'.". I condition necessary to their very maintenance, they seem to be the principal source of warmth produced. Since the loss of heat is gn i ;iter when the temperature of the external medium is lowered, the activity of the vegetative organs must considerably increase in the colder season of the year, and in the northern climates. In addition to the continual addition of new quantities of heat, a second cause contributes to the maintenance of the constant tempera- ture of the warm-blooded animals. This is the protection afforded by tin- special nature of the covering of the body. While the Ver- tebrates with a variable temperature have a naked or armoured skin, Birds and Mammals have a more or less close covering of hairs or ft -at lu-rs, which limits to a great extent the loss of heat by radiation. The large aquatic animals, on the other hand, have a scanty covering of hair, but they develop thick layers of fat beneath the cutis, which srrve for the retention of heat, and at the same time for hydrostatic purposes. There is in all cases a mutual relation of a complicated kind be- tween the factors which favour the withdrawal of heat and the conditions of the retention and the formation of heat, a relation which in spite of many variations in its individual factors results in the equalization of the heat generated and the heat lost. Some Mam- mals are able to maintain their proper temperature only within certain limits of the external temperature ; these animals are to a certain extent incompletely homothermic, and when the temperature sinks below a certain point they fall into the so-called winter-sleep (hibernation), i.e., a state of rest characterised by an almost com- plete absence of movement, and by a diminution in the energy of all the, vital processes. In the class of Birds, whose higher temperature permits of no interruption or limitation of the vital functions, there is no example of hibernation. But these animals have numerous iiit-ans of heat adjustment at their disposal; in particular, the swift- ness of their flight enables them to leave their homes at the approach of the cold season, and to betake themselves to warmer climates, where food is abundant. The common migrations of the migratory birds, migrations which sometimes extend over great distances, to a certain extent take the place of the winter-sleep of the hibernating animals ; in the Mammalia whose organisation permits of hibernation migrations like those of Birds are very rare. The most essential peculiarity of Birds, and one with which many characteristics both of external appearance and of internal organi- sation are correlated, is their power of flight. This peculiarity in 232 AVES. connection with these characters determines the sharp definition as well as the relatively great uniformity of the class, which, indeed, is descended from the Saurians, but exists at the present day without any forms transitional to other groups. On the other hand, the remains of a group of Saurians (Archceopteryx litlioyraphicri) have been discovered in the Sohlenhofen lithogi-aphic- slate which combine characters of the Pterodactyls with those of the Birds. The entire structure of the body of Birds corresponds with the two principal modes of locomotion on the one hand flight, and on the other walking and hopping on the earth. The trunk, which is oval, is supported in an obliquely horizontal position on the two hind legs, the pedal surface of which stretches over a relatively large area. Posteriorly the body is prolonged into a short rudimentary tail, the last vertebra of which serves for the support of a group of stiff steering, or tail feathers (rectrices). In front it is prolonged into a movable neck, on which is balanced a light, rounded head, with a projecting, horny beak. The anterior extremities, which are trans- formed into wings, lie folded together at the sides of the body. Arrangements for lessening the weight of the body are discernible in the special structure of all the systems of organs; these are especially noticeable in the structure of the osseous skeleton. The bones contain air-spaces (pneumaticity}, which communicate with the air-sacs of the body through openings in the dense and firm osseous substance, which is however confined to a relatively thin layer. This pneumaticity is most highly developed in those birds which combine a quick and enduring power of flight, with a consider- able size of body (Albatross, Hornbill, Pelican). In these cases all the bones except the quadrato-jugal and the scapula appear to be pneumatic, while on the other hand in the fintito' (Ostrich), which have lost the power of flight, all the bones except some of the cranial bones are filled with marrow. The Skeleton. Except in the Ostrich-like birds, the cranial bones very early fuse together to form a light and firm skull, which articu- lates with the atlas by means of a single condyle. The squamosal and periotic bones (prootic, epiotic and opisthotic) fuse to form a single bone which is united with the occipital and with which the quadrate articulates. The large frontal bones take the principal part in the formation of the cranial roof. Almost the whole of the upper edge of the large orbit, which in the Parrots is closed by a lower ring, is formed by the frontal bones. An independent lachry- TIIK SKULL. a mal is pre- sent at the an t eri or margin of the orbit. The eth- 111 o i d r e- gion and the cranial capsule are widely separated by an in- terobital septum of considerable size. The latter, sometimes together with the remains of the fused orbitosphenoids, frequently remains membranous and unossitied in its median part, and rests on an elongated bony rod corresponding to the basisphenoid. At the base of the temporal region there are two bones- the basitemporals (Parker) which arc ankylosed with one another, and a im- probably to be referred to a parasphe- iioid. In all cases independent alisphe- noids are present. The ethmoid region is composed of a vertically placed, 1111- paire.l ethmoid, situated in the anterior prolongation of the interorbital septum, and of lateral ethmoids which separate the eyes and nasal cavities, and through which the olfactory nerves pass into the nasal cavities. The lateral ethmoids may be swollen and contain ethmoidal cells. In front of them are developed the two nasal cavities with their bony or carti- laginous septum, which is the prolonga- tion of the unpaired ethmoid, and affords a support to the rolled-np turbinal bones, which are sometimes also attached to the vomer. The facial bones unite to form a projecting beak, the margins of which are covered with horny substance, and which is often movably connected with the FIG. 648. Skull of O/i* fa,;la (bust- ard), a, From the side; It, from i MK-ath. Ob, basi-occipital ; C, iMiidyle; Ol, ex-occipital; Ox, supra-occipital; c)i- tuni ; Et, median ethmoid ; P,i, parietal ; Fr, frontal ; -l/.c, maxil- lary : J.ii.r, prsemaxillary ; .\', ii:i>:il ; L, lachrymal ; /. jiiLCal ; V /, 'Hiai!rnt'i-jiiL::il ; Q, r|uadrute ; P/, ptrryD'iid ; /'"/, jialiitinc ; I", vorner; D, deutary : Art, articu- larc ; Any, aiiKulare. skull. The suspeiisorium 23 I AVES. Ent Co of the lower jaw and the maxillo-palatine apparatus are enabled by special articular arrangements to move on the temporal bone and on corresponding processes of the basisphenoid. The quadrate, which i; articulated to the temporal bone, has, besides the articular surface of the lower jaw, movable connections with the long rod-like quudrato-jugal, and with the usually styliform pterygoid which runs obliquely inwards, while the base of the upper beak presents a thin elastic place below the frontal bone, or is separated from the frontal bone by a transverse movable suture. When the beak is opened, and the lower jaw is moved downwards, the pressure on the quadrate bone is transferred to the rod-like quadrate -jugal and the pterygoid bones, and from these is transmitted partly directly and partly by means of the palatine bones to the upper beak, so that the latter must be more or less raised at that point. Therefore, when the mouth is opened, the end of the beak is raised. The greater part of the upper beak is formed by the unpaired prajmaxilla, with the sides of which the maxilla? are fused, while an upper median process ascends between the nares and unites with the frontal on the inside of the nasal bones. The hyoid bone (fig. 649) is prolonged into a posterior rod ; its anterior * cornua are usually two-jointed and are not con- nected with the skull, but in some cases they are much elongated and arch over the skull as far as the forehead (Woodpecker). They then consti- tute in connection with the muscles of their sheath a mechanism for the protrusion of the tongue. In the vertebral column (tig. 650), a very long movable cervical region, a rigid dorsal and pelvic region and a rudimentary, only slightly movable caudal region can be distinguished. In Birds there is no separation of thoracic and lumbar regions as in Mammals, since all the dorsal vertebrae bear ribs and the region corresponding with the lumbar region takes a share in the formation of the sacrum. The cervical and dorsal regions also are not sharply distinct from Fig. 049. Hyoid apparatus of Coi'vua comix. Co, body of hyoid ; Zh, cornua ; Ent, ento- glossal bone. * Usually described as the posterior cornua. Ed. THE VERTEBRAL COLUMN. -"'"' one another, since the cervical vertebra?, us in the Crocodiles, bear rin>. \\-Jiicli unite with the transverse processes to form a foramen fcransversarium. The neck is long and always freely movable, and contains 9 to 23 vertebra? (Swan). The shorter dorsal vertebra- are always less numerous ; they have superior and inferior spinous pro- cc-^es and all bear ribs, to the ventral ends of which sterno-costal bones are articulated at an angle which projects backwards (fig. 650, 8tc]. The sternocostals also articulate with the margin of the sternum, and serve when they are extended to increase the distance between the latter and the vertebral column. But, since the ribs are firmly applied to one another by means of posterior processes (iD'ocessus uncinati), the movement of the sternocostal ribs must necessarily a fleet the thorax as a whole, and dilate it (inspiration). The sternum is a broad flat bone which covers not only the thorax but a great part of the abdomen, and bears a projecting keel-like crest which serves for the attachment of the muscles of flight (Ccvrinatce). The sternal crest is reduced or obsolete only when the power of flight is feeble or entirely absent (Ratitce). The rib-bearing dorsal vertebra? are followed by a tolerably exten- sive division of the vertebral column, which corresponds to the lumbar and sacral regions, and which, by the fusion of a number of vertebrae with each other, and with the long iliac bones of the pelvic girdle, presents the characters of the sacrum. The sacrum is much elon- gated, and includes sixteen to twenty and more vertebrae ; of these a certain number can be shown to be lumbar (prsesacral), and are almost always preceded by two to three rib- bearing dorsal vertebra--. Then follows the true sacrum; it consists of two vertebrae, which are equivalent to the sacral vertebrae of Lizards and Crocodiles, and constitute by means of their transverse processes (with fused ribs) the main support of the pelvis near the cup of the hip-joint (acetabular vertebrae). Finally the true sacrum is followed by a postsacral region, which is composed of from three to seven of the anterior caudal vertebra-. The short caudal region, which succeeds the postsacral, consists, as a rule, of from seven to eight movable vertebra?, of which the last is represented by a vertical, laterally compressed plate the pyyustyle to which the muscles for the move- ment of the steering feathers (rectrices) of the tail are attached. This deep ploughshare-shaped terminal body is composed of from four to six vertebra?, so that the reduction of the number of the caudal vertebrae, as compared with that of the Sanrnrii' (ArcliHMpteryx), is bv no means so considerable. 236 PIG. 650. Skeleton of Nco/ihroii p/-iT,io/if'>'/in, HA, cervical rib* ; Du , inferior spiuous pro- cess of the thoracic vertebras; Cl, clavicle; Co, coracoid ; Sc, scapula; St, sternum; Stc, steruocostal limies (sternal ribs); f/i, unciiia.te process of the thoracic ribs; Jl, ilium; JH, ischium ; Pb, pubis; H, humerns ; li, radius; U, ulna; C C', carpus; Jl/e, metacarpus ; P' P" f", phalanges of the three fingers ; l"e, femur; T, tibia ; F, fibula.; Tin, tarsi >-met:itnrsus ; Z, toes. TIIK M.MIis. l'.">7 Shoulder girdle and wings. The peculiarities of the anterior ex- tremities are connected with their transformation into wings. Their connection with the thorax is always ;i firm one, since flying org.-ins. whose movement pre-supposes a great expenditure of niusculai- p<>\\ er, require the necessary support on the trunk. While the scapula, which is a long, sabre-shaped bone, lies along the dorsal side of the thoracic framework, the clavicle and coracoid, as pillar-like supports for the shoulder-joint, are attached to the sternum. The two clavicles are fused so as to form a fork (fvn:nl