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DPA se LeMNd fh adsbes PEE LN adeg sg pea ed era ee ee OWE Cn ee ee ee awe WA tea ase st a eo rope WIN 3 9088 00013 41 SMITHSONIAN INSTITUTION LIBRARIE oss a se A as Misa Geol”) Yatiynal sett / Se/> A TREATISE ON ZOOLOGY VOLUMES ALREADY ISSUED PART I. (SECOND FASCICLE) INTRODUCTION AND PROTOZOA PART II. PORIFERA AND COELENTERA PART III. THE ECHINODERMA PART IV. MESOZOA, PLATYHELMIA, AND NEMERTINI Demy S8vo, bound in cloth, price 15s. each net. On thin paper, in paper covers, price 12s. Gd. each net. AGENTS America . THE MAcmMILLAN COMPANY 64 & 66 FirtH AVENUE, NEw YORK Canada . THE MacmMILLAN Company OF CANADA, LTD. 27 RICHMOND STREET WEST, TORONTO India . . Macmituan & Company, Lrp. MACMILLAN BuILpInc, BomBay 809 Bow Bazaar STREET, CALCUTTA O05 ro % 449 Moll : TREATISE ON ZOOLOGY EDITED BY HK. RAY LANKESTER M.A., LL.D., F.R.S. HON. FELLOW OF EXETER COLLEGE, OXFORD}; DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS OF THE BRITISH MUSEUM Part V WOLLUSC A/ BY PAUL PELSENEER, D.Sc. POR HSOAT PSM SO NAS f . t 2 ~\ se on LIBRARIES LONDON ADAM & CHARLES 1906 BLACK ~ ~ ye vn or M4 a — y re 7) aa ) oe aiigahe © rs a au ee Ber CU fa ity LRe PREFACE THE manuscript of Dr. Pelseneer’s volume on the Mollusca— now published—was completed nearly two years ago. It has been translated and revised for press by Dr. Gilbert Bourne, of New College, Oxford, to whom the thanks of both the author and editor are due and are cordially tendered. EK. RAY LANKESTER. December 1905. ma mex) i aa; ted) t ee Pree oe are Hixcs hae tt is De CONTENTS CHAPT HE vi THE MOoLLusca ; . ; : : ; 1 CHAPTER Ii Tor AMPHINEURA : i : g j . 40 CHAPTER, (tt THE GASTROPODA : : : 2 : : 66 CHAPEERR IV THE SCAPHOPODA F : ; : 2 , 197 CHAPTER V THe LAMELLIBRANCHIA : : : ; ; 205 CHAPD EER Vi THE CEPHALOPODA ; : Z ; ; ; 285 INDEX ; f : : Lee oar CHAPTER I THE MOLLUSCA PHYLUM MOLLUSCA, Cuvier (=Pavuata, Latreille; Mavacozoa, de Blainville; HETERO- GANGLIATA, Owen; Orocarp!IA, Haeckel ; SaccaTa, Hyatt). GrapvE A. IsopLEuRA (Ray Lankester). Cxass I. AMPHINEURA (von Jhering). Order 1. Polyplacophora. , 2. Aplacophora. GRADE B. PRORHIPIDOGLOSSOMORPHA (Grobben). Cuass I. Gasrropopa (Cuvier). Sus-CLass 1. STREPTONEURA. Order 1. Aspidobranchia. » 2. Pectinibranchia. Sup-CLass 2. EUTHYNEURA. Order 1. Opisthobranchia. » 2. Pulmonata. Cuass H. ScapHoropa (Bronn). (No Orders.) Crass Ii. LAMELLIBRANCHIA (de Blainville). - Order 1. Protobranchia. » 2. Filibranchia. , 3 HEulamellibranchia. , 4. Septibranchia. GRADE ©. SrPHONOPODA (Ray Lankester). Cuass I. CEPHALOPODA (Cuvier). Sus-Cuass 1. TETRABRANCHIA. i 2. DIBRANCHIA. Order 1. Decapoda. » 2. Octopoda. i I i>) THE MOLLUSCA J. INTRODUCTION. FORMERLY a number of very diverse zoological forms, such as Brachiopoda, Tunicata, and even Cirrhipedia, were included among the Mollusca. The last-named were the first to be dissociated from the true Mollusca, after J. Vaughan Thompson had shown, by a study of their larval development and metamorphoses, that they were modified Crustacea. At a later date the Tunicates were shown, also as a result of embryological research, to have affinities with the Vertebrata. The Brachiopoda, both because of their bivalve shell and the supposed resemblance of their superficial anatomy to that of Lamellibranchia, retained a place in the Molluscan phylum for a much longer period. H. Milne-Edwards, it is true, united the Brachiopoda with the Polyzoa under the name Molluscoidea, but he placed this group very close to the Mollusca, and his views were very generally accepted by zoologists. It is only twenty-five years since the phylum Mollusca was_ finally purged of all alien elements, and limited, as in Professor Lankester’s “Mollusca” in the ninth edition of the Encyclopedia Britannica, 1883, to such forms as are demonstrably related to one another. More recently H. von Jhering propounded the view that this assemblage of animals, believed to be closely related to one another, was in fact unnatural, heterogeneous, and polyphyletic. But his hypothesis could not stand the test of criticism, and never ob- tained the support of any reputable malacologist. Since his time the unity of the Molluscan phylum has never been called into question. Closely related as the different forms of the Mollusca are, they exhibit a great variety in external aspect, chiefly because the tegumentary layer, consisting of epithelium, connective tissue, and muscle, is exceedingly plastic, and gives rise to outgrowths, appendages and expansions of the most various kind. ‘The diversity of form is further increased by concrescence of the various out-growths of the body, either with one another, or with adjacent structures; such concrescences being exhibited by the mantle edges, the lobes and margins of the foot, the gills, and other organs. But, however diverse the external configuration of the Molluscan body, the internal organisation, at least in its main features and in young forms, preserves a remarkable uniformity. The group is homogeneous, sharply defined, and its members are easily recognised. The Mollusca also afford a very good instance of the progressive modification and evolution of organic structure. — It would be difficult to name another group of the animal kingdom in which relationships can be more clearly determined and the LHE MOLLUSCA 3 pedigrees of the sub-groups more certainly traced ; and for this reason no phylum, with the possible exception of the Echinoderma, has, in recent years, yielded such fruitful results to the investigator. Il. Tok MorpHoLocy AND Lirre-HIstory OF THE MOLLUSCA. 1. General Description and External Characters.—The Mollusca are Coelomocoela with a distinct coelom and haemocoel. The latter has undergone a great development by phleboedesis (see Professor Lan- kester’s introduction in Part II. of this treatise), and the coelom there- fore is proportionately reduced. In the adult condition there are two recognisable coelomic cavities, the pericardial coelom and the true gonocoel or gonadial cavity. These two may be in communication with one another, but more frequently they are separate. The haemocoel is completely closed, and is probably the remnant of the embryonic blastocoel. The coelom, on the contrary, communicates with the exterior by coelomoducts and coelomopores. The coelomo- ducts are part of the primitive protocoelom ; they first served as gonaducts, but afterwards were adapted to excretory functions and became excretory organs or uroducts. In some cases, however, they retain part of their primitive character and serve the double purpose of uroducts and gonaducts (Fig. 5°, 9, 7, j). The external features of a mollusc, though very variable, nearly always admit of a division of the body into three tegumentary regions or organs. The most anterior division is the head: it bears the mouth, appendages of various kinds, and nearly all the organs of special sense. The second division is ventral, and has the form of a highly developed tegumentary projection of variable shape : this is the foot, the chief organ of locomotion. The third division comprises the dorsal part of the body, covered by a calcified cuticle or protective shell, the shape of which is subject to great variation in the different subdivisions of the phylum. This dorsal region is known as the mantle or pallium. The free surface of the body is covered by an epithelium, which is frequently ciliated. The epithelium is richly supplied with glandular cells which secrete an abundant mucus, serving to keep the skin moist and supple. In some cases, e.g. Phyllirhoé and Pholas, the glandular secretion is phosphorescent. The epithelium is also richly supplied with nerve-endings, and some of the epithelial cells may secrete chitinous or calcareous spicules, which remain embedded in the integument (Amphineura). The greater part of the external, or at least the originally external, pallial epithelium secretes a shell (Fig. 1, sh). The shell consists of a matrix of a chitin-like substance, conchyolin, im- pregnated with mineral salts. The latter may be present in such abundance as to form 95 per cent of the shell substance. ‘The chief / P THE MOLLUSCA mineral constituent is carbonate of lime, but from 1 to 2 per cent of phosphate of lime is also present, and traces (less than 4 per cent) of carbonate of magnesium. The greater part of the thickness of the shell is made up by the ostracum, which consists of two layers : (1) an external layer, frequently coloured, and formed by prisms of calcite ; (2) an internal layer consisting of arragonite, generally in the form of overlapping plates: it is the internal layer that forms, in various species, the nacre or mother-of-pearl. The growth of the shell is effected in two ways. Its extent is increased by the addition of new matter, secreted by the thickened edge of the mantle, to the outer or prismatic layer. Its thickness is increased by addition of new matter, secreted by the whole surface of the mantle, to the inner or nacreous layer. In addition ot Fic. 1. Young embryo of Purpura lapillus, from the left side, x 16. a, anus; f, foot; m, mouth ; ot, otocyst ; p.a.c, post-anal cilia ; re, embryonic kidney ; sh, shell; ve, velum; vi, vitellus. to the two layers of the ostracum already mentioned, there is a third layer, called the hypostracum, on the areas of attachment of the muscles which serve to fasten the animal to its shell. Finally, there is the periostracum or shell epidermis, forming an external covering to most shells: it is formed by the pallial fold at the edge of the mantle. In some Polyplacophora, Gastropoda, and Lamellibranchia, and in most of the Cephalopoda, the free edges of the mantle are reflected over the shell, so as to cover a greater or less part of its outer surface. In some species in which this special feature is developed to its greatest extent, the reflected mantle edges form a completely closed sac round the shell, so that the latter is internal and concealed. In rare cases the pedal integument may secrete a calcified “shell,” which may be adherent (Hipponyz) or free (Argonauta). The shell was for a long time the criterium of Molluscan classification. But the progress of anatomical study showed that THE MOLLUSCA 5 genera with more or less similar shells might differ considerably from one another in internal organisation, and gradually the structure of the animal, rather than the form of its shell, came to be recognised as the guide to its systematic position. But to this day there are many genera of Gastropods and Lamellibranchia whose anatomy is unknown, and their classification, founded on the characters of their shells alone, is, of course, provisional. The head and foot are fastened to the shell by muscular bundles, which are paired and symmetrical in the Polyplacophora, Scaphopoda (Fig. 181, ¢’), and Lamellibranchia (retractors of the foot), and in the Cephalopoda (retractors of the head and funnel), but in the Gastropoda there is a single asymmetrical so-called “ columellar” muscle (Fig. 45, co). The fibres of these muscles are attached to the epithelium under the shell. The connective tissue layer which lies beneath the tegumentary epithelium is mesodermic in origin, and is extensively developed in the Mollusca. It invades the greater part of the original blastocoel and presents the following varieties : (1) plasmatic or vesicular cells, which sometimes give rise to endoplastic calcareous concretions or even to true sub-epithelial spicules, as in Plewrobranchus and various Nudibranchia ; (2) stellate cells; (3) fibrillar cells. Blood spaces, whose distension causes turgescence of various parts of the body, are frequently found in this connective tissue. On the other hand, the connective tissue may become compact and form supporting structures ; such are the “skeleton” of the gill filaments, the sub-epithelial “shell” of the Cymbuliidae, and the cartilaginous pieces in the Cephalopods and in the buccal mass of all classes except Lamellibranchs. Below, or imbedded in the subcutaneous connective tissue, are muscle fibres forming layers of rectilinear or annular bundles ; but as a rule only a few definite muscular masses can be distinguished. The muscle fibres are of the smooth variety, though in certain cases they appear to be striated, especially in muscles which contract rapidly. Such apparently striated fibres are found in the buccal mass of various Gastropods, in the heart, in the fins of Pteropods and Heteropods, in the siphon of Cephalopods, in the columellar muscle of the larvae of certain Nudibranchs, in the branchial septum (Cuspidaria), in the adductor muscles of various Lamelli- branchs, and especially in the Pectinidae, in which the striation looks almost identical with that of Arthropods and Vertebrates. These fibres, however, are usually regarded as unstriated: they are wholly bi-refringent. The fibrillae are parallel to one another, but in the contracted state are thrown into spirals, which is said to produce the appearance of transverse striation. The subject calls for renewed investigation. The tegumentary layer, composed as described of epithelium, connective tissue, and muscles, may attain to a very considerable 6 THE MOLLUSCA thickness. Certain portions of the tegumentary organs can be spontaneously detached from the body by the reaction of the animal against the incidence of external forces. This phenomenon is known as “autotomy,” and is generally defensive, as, for instance, ~ the loss of portions of the foot (Harpa) or of its appendages ; the loss of the siphons of some Lamellibranchs ; of the dorsal papillae and other parts of the dorsal integument in certain Nudibranchs ; of the cephalic tentacles of Scaphopods, etc. The lost parts are regenerated, just as other tegumentary organs (cephalic tentacles, fins, arms of Cephalopods) that have been accidentally removed, are regenerated with all the complex and differentiated structures that they may possess, such as eyes, suckers, etc. The most remarkable example of regular physiological autotomy is found among the Cephalopods, namely, the hectocotylised arms of the Philonexidae and Argonautidae (Fig. 287). 2. The Digestiwe Tract—The alimentary tract always has two orifices, the mouth and anus, generally situated at the two extremities of the body; but the anus may be brought to an anterior position by a ventral flexure, which may or may not be complicated by a lateral torsion. The anus is absent only in the parasitic genus HLntosiphon ; the alimentary tract is rudimentary in the parasites Hntocolax and Hntoconcha; it is absent altogether in Einteroxenos. In all other forms three essential parts can be recognised in the digestive apparatus. Firstly, the buccal or anterior section of the gut, of ectodermic origin, which comprises the first dilatation or buccal cavity and the oesophagus. Secondly, there is the mid-gut, of endodermic origin, comprising the second dilatation or stomach. Thirdly, there is the hind-gut or intestine. The anterior dilatation or buccal cavity is absent in the Lamellibranchs, with the exception of certain Nuculidae. Cuticular formations are present in different parts of the internal wall of the alimentary tract, and are specially developed in its anterior portion. They occur around the mouth— having the form of a prehensile collar in Doris—but more particularly in the buccal cavity, where two different sorts of cuticular formations are found, the mandibles and the radula. The mandibles are anterior, dorsal, and unpaired in the Dentaliidae, Patellidae, Pulmonates, Aegirus (Fig. 73, B), etc, but paired and lateral in the majority of the Gastropoda. In the Cephalopoda the members of the pair are dorsal and ventral (Fig. 266). These organs are chitinous, and are only calcified in certain Chaeto- ‘dermidae, and partially so in Nautilus. ) ] Me The radula is characteristic of the phylum Mollusca. It exists throughout the series, from the most archaic forms upward, and is only absent in the most specialised types, in which it has evidently been lost, such as certain Neomeniomorpha among the Aplacophora, THE MOLLUSCA 7 the Lamellibranchs, various isolated forms of Gastropoda, and the Cirrhoteuthidae among Cephalopods. The radular apparatus has the form of chitinous teeth, disposed in transverse rows; the number of teeth in each row is sub- ject to variation, but they are always arranged symmetrically on one side 4 and the other of a central tooth (Fig. 2). Thus there are eight lateral teeth on either side of the central tooth in Polyplacophora (8.1.8); two laterals on either side of the central in ‘ . Scaphopoda (2.1.2); three laterals _ ws on either side of the central in almost * fie am 5 = all Cephalopods (3.1.3). In the ao : oe Gastropods the number of teeth in each row varies considerably in the Ket Lays different sub-groups. The radular “rene ribbon issues from a_ pharyngeal \ caecum, in which it is secreted, and es is applied to the surface of paired — qyansverse rows of the radula. A, cartilaginous pieces situated on the Porochiton ruber. B, Natica clausa: C, . se 7 gonum ,; >» 4v0SSia giau floor of the buccal cavity. These copis; all much enlarged. c, central : tooth; J, lateral teeth; m, marginal so-called cartilages have a charac- feeth.’ (After G. 0. Sars.) = teristic vesicular structure quite dif- ferent from that of ordinary cartilage such as is found in Cephalo- pods and Opisthobranchs. Applied to these cartilaginous pieces the radula, by the action of special muscles, executes backward and forward rasping movements. The cuticular lining of the stomach is specially developed in Lamellibranchs and in certain Gastropods in which it is sometimes differentiated into masticatory plates provided with special muscles. The buccal cavity or anterior dilatation of the alimentary tube receives in the Amphineura, Gastropoda, and Cephalopoda, the secretion of the so-called salivary glands, of which one or several pairs may be present. The oesophagus may present various forms of accessory dilatations, known as “gizzards,” glandular regions, ete. - The secretion of an important and voluminous digestive gland is poured into the second primary dilatation of the gut or stomach : this gland is called the liver, but this name must not be taken to imply a physiological identity with the liver of vertebrates. The liver is an acinous glandular organ, the epithelial cells of which are all very similar to one another in Polyplacophora, but in other forms they are generally differentiated into ferment cells and excretory cells. From the physiological point of view this gland is 8 THE MOLLUSCA a hepato-pancreas, since its secretion peptonises albuminoids, converts starches into sugar, and saponifies fats. Absorption of digested food-stuffs is effected, in some forms at least, by the liver itself, and finally this gland has an excretory function in that it secretes waste products of metabolism into the alimentary tube. The stomach (in various Gastropods, in Scaphopods, and Lamellibranchs) is provided with a caecum in which a crystalline style is often secreted. In addition there exists, in some Gastropods and Cephalopods, a caecum coiled in a spiral. These two structures do not appear to be homologous, for in some Gastropods (Vassopsis) the spiral caecum and the sac containing the crystalline style occur together. The intestine, or at least its terminal portion, is furnished, in nearly all groups of Mollusca, with a longitudinal ridge called a typhlosole or with a furrow bordered by two ridges. An anal gland is present in various Gastropods, in Dentaliwm, and in nearly all Cephalopods. 3. Circulation and Respiration.—In addition to the cavity of the alimentary tube two other important cavities, completely separated from one another, are found in the Molluscan body. The first, called the coelomic cavity, communicates freely with the exterior, and is generally reduced to the pericardium and the gonadial or genital cavity. The second is very probably the remnant of the blastocoel or segmentation cavity, and is continuous with spaces in the conjunctive mesenchyme of the integuments. It is filled with a fluid blood or haemolymph which is at once nutritive and respiratory in function. ~This cavity constitutes the circulatory apparatus. The circulatory apparatus is provided, for a greater or less part of its extent, with proper endothelial walls; where these are | absent it is lined by connective tissue so that the organs are never brought into direct contact with the blood. The circulatory cavity is, in fact, more or less specialised into arteries and veins of vascular structure, but there are rarely tubular capillary ramifica- tions, except in the integuments of Cephalopods. More usually the capillaries are swollen irregular cavities. The rest of the circulatory system is formed of sinuses ;—irregularly defined spaces in the connective tissue and specially abundant in the integuments. In fact, the phenomenon of phlebcedesis (Ray Lankester) is manifested in a very high degree in the Mollusca, the cavity of the circulatory system being distended and in- sinuated among the organs to such a degree as to push back and diminish the coelom, though no communication is ever estab- lished between the two. The blood-vessels pass abruptly into the: sinuses, and in some cases communication between sinus and blood- vessel is established by orifices in the walls of the latter. Remark- able instances of this form of communication may be seen in the THE MOLLUSCA 9 vena cava of Nautilus, in the auricle of Patella (Fig. 80), and in the afferent branchial vein of Aplysia. The central and pulsatile portion of the circulatory apparatus is well developed, except in the Entoconchidae. It is situated 4 ne C f Noe A E iy ae | i eal ae) Go| | ie is y CS =<) ne \ [ at Se Vr ee a ra; a\ a | f Fic. 3. Diagram to show the relations of the heart in the Mollusca. 4, part of the dorsal vascular trunk and transverse trunks of a Chaetopod worm; B, ventricle and auricles of Nautilus; C, of a Lamellibranch, of Chiton, or of Loligo; D, of Octopus; E, of a Gastropod. a, auricle; a.c, arteria cephalica (aorta); ai, arteria abdominalis ; v, ventricle. The arrows show the direc- tion of the blood-current. (From Lankester, after Gegenbaur.) on the dorsal side in the pericardium, except in Anomia and the Octopods, and originally at the posterior end of the animal. In no case is the pericardium a blood sinus ; it is a portion of the coelom, without communication with the circulatory system, as is shown by the absence of red corpuscles in the pericardium of such Molluses as have red blood (Penrose and Ray Lankester). The heart is entirely arterial, and comprises, firstly, a median ventricle, with muscular walls and internal fleshy columns, the fibres of which give the appearance of , striation: being spongy in texture, this organ has no intrinsic nutritive vessels. Secondly, two (in Nautilus four) paired auricles, disposed symmetrically on either side of the ventricle. The auriculo-ventricular openings are simple, except in the Polyplacophora, where they are frequently multiple (Fig. 4). Each opening is provided with a valve opening towards the cavity of the ventricle and preventing the reflux of blood into the auricle. Frequently one member of the single pair of auricles is much reduced, or may be aborted, as is the case in the majority of Gas- tropods (Fig. 3, E). Primitively a single, morphologically Vil Fic. 4. Heart of Chiton pellis-serpentis, dor- sal aspect. I, left anterior auriculo- ventricular communication; II, ven- tricle; III, right anterior afferent vessel; IV, V, VI, right posterior afferent vessels; VII, left auricle; VIII, left posterior auriculo-ventricu- lar communication. anterior aorta is given off from the ventricle, and this condition persists in the Amphineura and in the archaic Lamellibranchia. fe) THE MOLLUSCA The aorta together with the ventricle forms a dorsal vessel com- parable to that of Annelids. Secondarily a second and morpho- logically posterior aorta may be formed, as in the Gastropods and the majority of Lamellibranchs (Fig. 3, E), and even a third (the genital aorta of certain Cephalopods) may be formed in connection with the first. The ramifications of these aortae carry the blood throughout the body. The kidneys, however, are supplied almost entirely with venous blood, from which their cells extract and excrete the waste products of metabolism. ‘Thus the circulation of the kidneys may be described as a portal system. The blood is generally a colourless fluid containing amoebocytes and sometimes haematids. It may be of a bluish colour, due to the presence of haemocyanin, an albuminoid containing copper (Fredericq). In other cases it is red, owing to the presence of haemoglobin, which may be in solution in the plasma (Planorbis) or may be localised in haematids (red blood corpuscles). These are present in Pectunculus, Arca, Ceratisolen |Lankester], Poromya, and Neomeniomorpha. The musculature of the buccal bulb has been shown by Lankester in Gastropoda to owe its red colour to haemoglobin impregnating the muscular tissue. The density of the blood is always greater than that of water, greater even than that of sea-water in the case of some marine molluscs. The blood of Anodonta contains ten times more salts than the sur- rounding medium: the density of the blood of Octopus is 1,047. The pressure of the blood in the arteries amounts to from 3 to 5 centimetres of water in Anodonta and to 108 centimetres of water in Octopus. The volume of blood in some groups, particularly in the Lamellibranchs and Gastropods, is so great that it plays a very important part in the turgescence of various parts of the integu- ment, by filling the tegumentary sinuses during the relaxation of their muscles. To this end some blood spaces, corresponding to different turgescible organs, are separated by valves which admit of the accumulation of a considerable volume of blood in a definite portion of the body. Examples of this are found in Gastropods and in the valve of Keber in Lamellibranchs. ; Respiration.—The venous blood is oxygenated almost exclusively in the superficial tegumentary sinuses of the mantle, this organ receiving a comparatively feeble supply of arterial blood. A portion of the free or ventral surface of the mantle is specialised to form a respiratory organ, through which passes nearly the whole of the blood that is returned to the auricles. These tegumentary organs, enclosing a part of the vascular system, project into the surrounding water in the form of pallial expansions, normally paired, in which the blood is oxygenated. This special part of the circulatory system is often regarded as a separate organ under THE MOLLUSCA II the name of the “respiratory apparatus.” ‘It is constituted by the ctenidia or branchiae properly so-called, of which there may be one or many pairs. There are two pairs in Nautilus ; from four to eighty pairs in the Polyplacophora, and where a single pair is normally present it may be reduced to a single azygos organ, generally in correlation with the reduction of the auricles. The ctenidia are situated primitively in the posterior or anal region of the mantle, but they may be multiplied and spread anteriorly, or both anteriorly and posteriorly (Polyplacophora, Fig. 28), or without being multiplied they may extend pro- gressively towards the region opposite to their primitive situation, Diagrams of transverse sections of the ctenidia of various Mollusca. I, Chiton; II, Pleurotomaria ; 111, Trochus; 1V, Nucula; V, Nautilus; VI, Chaetoderma ; VII, Haliotis; VLII, Lacuna ; 1X, Solenomya; X, Sepia. a, afferent vessel ; e, efferent vessel ; pa, mantle. as in Gastropods and Lamellibranchs. They are shorter in Nucula than in Arca; shorter in Arca (Fig. 188) than in Avicula (Fig. 236); shorter in Pleurotomaria than in Trochus, and in Trochus than in Fissurella. These ctenidia have exactly the same structure in the archaic members of the different groups: an identical fundamental structure may be recognised in the Polyplacophora, in the Rhipidoglossa among Gastropods, in the Protobranchs among Lamellibranchs, and in the Cephalopods (Fig. 5). Each etenidium consists of an axis containing two vascular trunks. The one, an afferent vessel, in which the blood current is centrifugal, communicates with a “vena cava” or with a simple venous sinus ; the other is the efferent vessel, in which the current is centripetal, and the auricle is nothing more than its specialised terminal portion. The auricle, in fact, has the innervation of a pallial 12 THE MOLLUSCA organ like the ctenidium; the ventricle that of a visceral organ properly so called. Each side of the axis bears a row of respiratory filaments, generally flattened, but of variable shape, whose cavities communicate with the two vascular trunks of the axis. It is in the cavities of these filaments that the blood absorbs oxygen dissolved in the water. The continuous renewal of water on the surface of the ctenidium is provided for by a covering of ciliated epithelium. ‘The ciliated epithelium is absent in Cephalopods, but in this group the powerful musculature of the mantle and siphon is sufficient for the purpose. The whole volume of venous blood, however, is not in all cases passed through the ctenidia: a smaller or larger part may be distributed to the mantle and thence returned directly to the heart. This arrangement is found in a considerable number of Gastropods (Heteropods, Pleurobranchs, and Nudibranchs) and in the majority of Lamellibranchs. Finally, the typical respiratory apparatus may be complicated by specialisation or by reduction, and may disappear altogether, as in the Neomemiidae, the Scaphopoda, the Septibranchia, and a large number of Gastropoda. In such cases the function of oxygenating the blood is wholly transferred to the free surfaces of the pallial integuments, which often form a secondary respiratory organ, especially in «the Gastropoda. In aquatic species this secondary apparatus takes the form of “pallial branchiae,” in terrestrial species of a “Jung.” In certain cases there is a localised blood-gland or lymphatic gland which, from its phagocytic function and the formation of amoebocytes, may be said to have the physiological character of the spleen of Vertebrates. This organ is generally situated on the course of the aorta, instances being found in many Opisthobranchs and in the “white body” of Cephalopods (Fig. 268). It consists of conjunctive tissue in which blood corpuscles are formed at the expense of the conjunctive cells. In other cases the gland is diffuse, that is to say, distributed in a more or less irregular fashion in the conjunctive tissue in the form of plasmatic cells. 4. Coelom.—The walls of the coelom of Molluscs are completely covered by a continuous epithelium, partly genital, partly excretory. The coelom is divided into several different cavities, gonadial, pericardial, and renal, the two last named being excretory. The gonadial and reno-pericardial cavities are separate, except in the Cephalopods and aplacophorous Amphineura. It must be assumed . that the ‘ Prorhipidoglossa,” the common ancestors of the Gastropods, Scaphopods, and Lamellibranchs, had also this communication between the pericardium and genital cavity, and it is preserved in the more archaic Gastropods and Lamellibranchs (certain Rhipidoglossa and Protobranchs), in which the gonads THE MOLLUSCA ~ 13 open, not into the pericardium, but in the reno-pericardial duct, uniting the pericardium to the kidney. Such an arrangement is found in T’rochus, Solenomya, ete. (Fig. 5°"’, g, 7); and here we find that the genital and pericardial cavities are united to the kidney by a common duct of double origin, genital and pericardial. As a further differentiation, we find in a fairly large number of Lamelli- branchs and in the Scaphopods that the two distinct branches of this duct become longer (Fig. 5°", 7); then the common duct dis- appears, and the gonad opens directly into the renal sac (Fig. Be iat): The pericardial coelom always surrounds the heart except in the Octopoda and the Anomiidae, or is much reduced or absent. Sometimes prolongations, ramifications, or parts of this pericardial cavity have their walls much specialised to form an excretory apparatus, known as the pericardial glands. The pericardial coelom always communicates with the renal sacs or renal portion of the original coelom: in Nautilus alone the kidneys are no longer continuous with the pericardial cavity, and this latter opens directly to the exterior by ‘“coelomopores,” orifices peculiar to itself. The Cephalopods have a pair of coelomoducts leading directly from the genital cavity to the exterior. In the Aplacophora this genital space only communicates with the exterior through the intermedium of the pericardium and renal sacs. The polyplaco- phorous Amphineura have acquired two special genital canals, through which the sexual products are discharged, but they do not appear to be true primitive coelomoducts (Fig. 5°, e; Fig. 30, D). Finally, in the Lamellibranchs in general and in the Gastropods the genital ducts are formed at the expense of a portion of the renal sacs and ducts (on one side only in Gastropods); but the male ducts of the hermaphrodite Lamellibranchs, the Anatinacea, are neomorphs and an exception to the general rule. 5. Excretory Organs.—The essential organs of excretion are the renal sacs or urocoeles, whose morphological nature requires further elucidation. They consist of paired canals, more or less modified, which open to the exterior on the surface of the body and internally into the pericardium, except in the case of Nautilus, in which, as described above, the pericardial coelom has its own separate orifices, and in Dentaliwm. The reno-pericardial apertures are more or less elongate ciliated funnels whose cilia create a current in the direction of the kidney. In Elysia alone does the kidney possess multiple reno-pericardial apertures, to the number of about ten (Fig. 92). True “nephridia” (Lankester) only occur in the young stages of certain Gastropods (Pulmonates (Fig. 118), Paludina, etc.) and in Lamellibranchs; they are described below under the head of Embryology (p. 136). 14 THE MOLLUSCA In cases in which a single pair of renal sacs is present, one member of the pair is often rudimentary or absent. This condi- tion is found in the majority of Gastropods, where the ctenidium mol Dine: Wt a Fic. 5vis, Transformations of the genital duct in the Mollusca: diagrammatic dorsal views of the peri- cardium, gonad, and kidneys. a, ancestral hypothetical form; b, Cephalopod; c, stock form of Amphineura ; d, Aplacophora ; e, Polyplacophora ; f, Prorhipidoglossum ; g, some Rhipido- glossa (Emarginula, etc.); h, specialised Gastropod ; 7, Protobranch Lamellibranch ; j, Pecten ; k, Eulamellibranch. I, pericardial part of coelom ; II, gonad ; III, kidney ; IV, genital duct of Cephalopoda and Polyplacophora; V, duct leading from the gonad into the pericardium, into the reno-pericardial duct, or into the kidney ; VI, reno-pericardial duct ; VII, secondary genital duct in specialised Gastropoda and Lamellibranchs. THE MOLLUSCA 15 and auricle of the same side (topographically the right side) are also atrophied or have disappeared (Fig. 55). Almost all the venous blood that passes to the ctenidia tra- verses the kidneys, so that there is a renal portal system. The renal sacs are, in fact, irrigated by conduits which lead to the afferent branchial veins, and these conduits may traverse the kidneys, as in Cephalopods (Fig. 273), or may surround them, as in Septibranchs (Fig. 210). Consequently the blood passing through the ctenidia is devoid of the products of excretion. The surface of the excretory sac which forms the kidney may be greatly increased by folds, by the formation of caeca, etc. Its walls are glandular for a greater or less part of their extent, and consist of an excretory epithelium in the cells of which the nitrogenous products of metabolism are accumulated. These products are ejected in the solid or liquid form, and vary from one group to another as regards their chemical constitution. They consist essentially of guanin in the Cephalopods, of uric acid in Gastropods, except in Cyclostoma, where they consist of urea, as is also the case in Lamellibranchs, in which group uric acid is not normally found. The external water does not penetrate into the kidney, nor, a fortiori, does it enter the pericardium. It has, however, been established that water may occasionally enter the kidney of certain Heteropods and of Styliger, an Opisthobranch of the family Hermaeidae. The glandular part of the kidney is not the only region in which a glandular epithelium may be present. The epithelial lining of the pericardium may, in various groups, be specialised to form a pericardial gland (Grobben) whose excretion is more acid than that of the kidney properly so called. Such a gland may be seen on the surfaces of the auricles or in the ramifications of the pericardium in Gastropods, Lamellibranchs (Fig. 212), and in Cephalopods (Fig. 273). This glandular region has a blood supply analogous to that of the kidney, and one may even see, in Nautilus, the renal epithelium and that of the pericardial gland developed at the same level on the same afferent branchial vessel, the one on the one side, the other on the other side. The pericardial gland eliminates the waste products which are excreted by the Malpighian glomeruli of the vertebrate kidney ; the molluscan kidney, properly so called, deals, on the other hand, with the same products of excretion as the tubuli contorti. Certain liver cells also constitute an important organ of excretion, especially in the Opisthobranchs and Pulmonates. In the latter the dorsal wall of the pedal gland is also excretory, and finally veritable accumulatory excretory organs are often formed in the conjunctive tissue by plasmatic cells known as the “cells of Leydig.” True nephridia exist in developmental stages in the form of “larval kidneys.” 16 THE MOLLUSCA 6. Nervous System and Organs of Sense.—In the nervous system of Mollusca a perioesophageal collar is normally present, of which the dorsal moiety is the cerebral and the ventral moiety the labial com- missure. From either side, at the junction of the two moieties of the collar, nerve cords distributed to the integuments take their origin. These latter are differentiated into a dorsal pair, innervat- ing the mantle, and a ventral pair, innervating the foot: they may be ganglionated throughout the whole of their extent, as in the pallial cords of Amphineura and the pedal cords of Amphineura and Aspidobranchs, or they may bear localised ganglia, known as the pleural and pedal ganglia respectively, near their origins. These two paired cords are connected by anastomoses, the most anterior anastomosis being always preserved and known as the pleuro-pedal connective. The pedal cords or centres are united by anastomoses ventrad of the digestive tract, the most anterior and at the same time the largest of the anastomoses being always retained as the pedal commissure. ‘The pallial cords are often united by an anastomosis dorsad of the rectum as in Amphineura, Cephalopods, Lamellibranchs, and various Gastropods. The . nervous system of Molluses is thus characterised by its oesophageal ring, from which issue four, originally parallel, tegumentary nervous cords (Fig. 19). The visceral organs are innervated firstly by trunks given off from the labial commissure. These trunks, uniting under the oesophagus, form an anterior or stomato-gastric visceral commissure, bearing on its course two ganglia which are situated near and partially innervate the buccal bulb and also the whole of the oesophagus and stomach. In some cases, e.g. the Cephalopods and certain Tectibranchia, the stomato-gastric commissure _ bears stomachal ganglia. The viscera are innervated, in the second place, by trunks issuing from the pallial cords and distributed to the circulatory, excretory, and genital viscera. In all Molluses except the Amphineura the two most important of these trunks are united below the digestive tube, thus forming an infra-intestinal loop or “ visceral commissure,” provided with one or more ganglionic centres (Fig. 19, v.g). These two visceral loops, the stomato-gastric and the visceral properly so called, are generally united together by anastomoses (Cephalopods and Gastropods). There are, therefore, three kinds of nerve-centres in Molluses : (1) sensory centres, represented by the ganglionated cerebral commissure or differentiated cerebral ganglia; (2) tegumentary centres, represented by the pleural and pedal cords or ganglia ; (3) the visceral centres, represented by the stomato-gastric and the visceral loop properly so called. The nerve-centres consist of a superficial portion, made up of ganglion cells, and a central fibrillar portion which is almost THE MOLLUSCA 17 exclusively composed of prolongations of sensory or centripetal nerve fibres. The prolongations of the superficial ganglion cells are continued into motor or centrifugal nerve fibres. Isolated ganglion cells are to be found in the muscles of the heart and in those of the buccal bulb (Pulmonata). The nervous system, being-in close relation to all the other organs, is of great importance to the morphologist, and the more so because it is the last to be influenced by the modifications under- gone by the organism. At the same time, every modification of an organ is faithfully reflected by the nervous. system. In such forms as are still slightly differentiated, the large nerve cords are uniformly covered with ganglion.cells: in less primitive forms the special development of certain parts of the body has produced a preponderant development of certain nerves corresponding to them, and nerve cells accumulate and give rise to ganglia at the bases of these more highly developed nerves. Accessory ganglia may also be formed at different points of the nervous system, either at the bases of sensory organs (Figs. 94, br.g; 214, os, ete.) or at the origin of important nerve trunks (Fig. 159, 7). The ganglion centres may be shifted along the cords on which they are situated in. consequence of changes in the parts that they innervate. Similarly, a nerve may be shifted along the cord from which it issues until it seems to have changed its place of origin, but its fibres always maintain their connection with their primitive nerve- centre. The approximation or the union of two parts of the body in- volves the approximation or fusion of the corresponding ganglia ; or if one of the two parts is atrophied, its nerve-centre is reduced and may be fused with the adjacent nerve-centre. ‘The various ganglia exhibit a general tendency to centralisation, all the principal sensory organs being aggregated at the anterior part of the body. At first all the sensory and motor nerve - centres, and finally all the others (Cephalopoda, Nudibranchia, many Pulmonata), become localised in the same region and are grouped together. Organs of Sense.—The function of general sensibility is spread over the whole of the free surface of the envelope of the body and the surfaces in continuity with it: included among the latter are the internal surface of the mantle, and especially its glandular tracts, and all invaginations of the ectoderm, such as the pedal glands, the terminal portion of the rectum, the kidneys, ete. On these various surfaces sensory elements are found among the epithelial cells in the form of neuro-epithelial or end-cells, which sometimes traverse a thick calcified cuticle (aesthetes of Chiton, Fig. 24). These elements are particularly numerous in the most exposed parts, such as the cephalic tentacles of Gastropods, the 2 18 THE MOLLUSCA epipodial tentacles of Rhipidoglossa, the pallial tentacles of Lamelli- branchs, etc., which therefore have the more special function of tactile organs. Taste organs in the form of sensory bulbs or cups have been shown to exist in the buccal cavity or round the mouth of several Molluscs. There are several kinds of organs of olfactory or some analogous function; such are the cephalic rhinophores and the pallial osphradia. The rhinophores are situated on the head, and are frequently borne on more or less prominent appendages resembling tentacles (Fig. 163, ¢); or in other cases they have the form of a pit, as in the Cephalopods (Fig. 259, ol). The nerve of each rhinophore is supplied by the corresponding cerebral ganglion, and is sometimes partially united to the optic nerve. The osphradia (Ray Lankester) are situated near the entrance to the pallial cavity (Figs. 58 and 89, os; 99, XVI.), on the course of the branchial nerve, but sometimes, as a result of specialisation, they are situated on separate ganglia. The osphradia have the form of ridges or pits lined by sensory epithelium, and their function is to test the respiratory fluid. It has been demonstrated, in certain Lamelli- branchs at any rate, that the nerve-fibres supplying the osphradia originate in the cerebral ganglia. The otocysts (de Lacaze-Duthiers) are invaginations of the integuments of the foot. In the Protobranchs (Pelseneer) and in Mytilus (List) they are ofocrypts, that is to say, they are still open invaginations ; but in all other Molluscs these organs are closed and contain auditory granules or otoliths suspended in a fluid secreted by the wall of the otocyst, this latter structure being furnished with sensory and ciliated cells. The.otocysts, even when they are attached to the pedal ganglia, are innervated from the cerebral ganglia (Koren and Danielssen, de Lacaze-Duthiers, Leydig; Figs. 123, C; 146). They are absent both in the young and adult Amphineura and in the adult stages of various sessile Molluscs. It is through the agency of these organs that the animal is able to perceive disturbances in the surrounding medium, and the re- sistance offered to the locomotory apparatus: through them the creeping Molluscs preserve their orientation and swimming Molluses their equilibrium. The Eyes are normally cephalic structures, one pair in number, symmetrically placed on or at the bases of the cephalic tentacles. Cephalic eyes are absent in the Scaphopods and in the adult state in Amphineura and the Lamellibranchs (with the exception of the Mytilidae and Avicula). In Molluscs devoid of cephalic eyes, visual organs are often developed on the mantle. Thus among the Amphineura they are found over the whole surface of the mantle in the Chitons; among the Lamellibranchs on the borders of the mantle only in the Arcidae and in numerous Pectinidae ; finally, one THE MOLLUSCA 19 Gastropod, Oncidiwin, possesses, in addition to a pair of normal cephalic eyes, numerous pallial eyes scattered over the whole dorsal surface. The cephalic eyes are pigmented invaginations of the integu- ment: they may be open, without any refractive body, as in Patella and Nuutilus (Fig. 6, A), or with a crystalline lens, as in Plewroto- maria, Trochus, Haliotis, etc. They are closed, and have a cornea and an internal crystalline lens in the majority of Gastropods and in the dibranchiate Cephalopods (Fig. 6, B, C). The pallial eyes may be “compound,” without an internal crystalline lens (Arcidae), or simple. In the latter case they may present one of the following characters :—(1) an internal crystalline lens and a deep retina (Polyplacophora, Fig. 33); (2) an internal crystalline lens and a we Gop Fic. 6. Diagrams of sections of the eyes of Mollusca, A, Nautilus; B, Gastropod (Limaa or Helix) ; C, Dibranchiate Cephalopod (Oigopsid). Co, external cornea; Co.ep, internal cornea; G.op, optic ganglion ; Int, Intl, Int, Int3, different parts of the integuments ; Ir, iris ; /, crystalline lens ; ie outer (extra- corneal) ‘portion of the lens ; N.op, optic nerve ; N.S, nervous stratum of the retina ; Pal, eyelid ; x, inner layer of the retina. (From Lankester, after Grenacher.) superficial retina (Pecten, Fig. 217); (3) an internal crystalline lens, the retinal cells reversed and the nerve traversing the retina (Oncidium). With the exception of the Cephalopods, and possibly also the Heteropods, the vision of Molluscs is limited. In the forms devoid of eyes, as in other groups of the animal kingdom, the general surface of the body is capable of dermatoptic perceptions. 7. Organs of Generation.—Among Molluscs in general the sexes are separate, and this is the case in the most archaic forms of the different groups of the phylum. Hermaphroditism, on the contrary, is always a sign of specialisation, and is only found as a normal condition in one sub-order of Amphineura (Neomeniomorpha), in one sub-class of Gastropoda (Kuthyneura), in some genera of Streptoneura, in one order (Anatinacea), and in some isolated species of Lamelli- 20 THE MOLLUSCA branchia. In the forms with separate sexes there is often a definite sexual dimorphism, which is exhibited not only by the presence of a copulatory organ (Cephalopods and the majority of Gastropods), but also in the breadth and even in the greater size of the females (Fig. 7, f). It has been shown that in the Cephalopods hyperpolygyny is the rule, and in certain Aflantae and American Unionidae, hyperpolyandry. The gonads are primitively paired and developed from the coelomic wall, but they are only in direct communication with the remainder of the coelom (the pericardium) in the Aplacophora (Figs. 5°, d; 30, C) and the Cephalopoda (Fig. 5%, 6). In the former case the genital products fall into the peri- cardium and are carried to the exterior by the renal ducts, which thus act as gonaducts. In other cases the genital products may be dis- charged into the reno-pericardial duct (Zrochus, Fig. 55 ; Solenomya), and are thence expelled through the kidneys, or they may be discharged directly into the kidneys, more or less close to the external renal orifice (various archaic Lamellibranchs, the majority of Rhipidoglossa, Scaphopods). Otherwise, in all groups, the gonads open to the exterior by their proper pores, which are nearly always adjacent to the renal openings ; they may, however, be more or less removed to a distance from the latter, and in certain hermaphrodite forms (Pulmonates and Nudibranchs) the renal orifice is near the anus and the genital aperture is secondarily separated from it and shifted towards the penis. Accessory glands are often developed on the course of the genital duct, especially in the female. The male and female elements are formed from the epithelium of the gonad: each oogonium gives rise to a single ovum with its polar bodies, while ™ each spermatogonium gives rise to several sperma- tozoa. The eggs of Cephalopods, of the majority Diie Seine of Polyplacophora, and of the Lamellibranch The male in sity on Pseudokellya (Fig. 220) are invested by a continuous the shell-aperture of Cellular follicle. In hermaphrodite Molluscs the Palen male,” Spermatozoa ripen before the ova; the herma- phroditism is therefore protandric. The herma- phroditism also is not self-sufficient, and the ova of one individual must normally be fertilised by the spermatozoa of another individual. The ‘ parthenogenesis” observed in hermaphrodite Pulmonata (Arion, Limnaea), which have been isolated from the time of their birth, is possibly due to an abnormal autofertilisation. “Progenesis” has only been observed in one Gymnosome (Clione), in which the larval characters are preserved for a long time. Copulation only takes place in such Gastropods, whether monoecious or dioecious, as are provided with a penis, and in the Cephalopoda. In several members of the latter class the copulatory organ, or Fia. 7. LHe, MOLLUOSCA 21 = hectocotylus, is caducous and travels independently in search of the female. In those Molluscs which do not copulate the eggs are fertilised after oviposition. The eggs are laid separately in the Amphineura, in the more archaic Gastropoda, in the Scaphopoda, and in almost all the Lamellibranchia (that is to say, generally, in the forms that do not copulate), but in the majority of aquatic Gastro- pods and in the Cephalopods the eggs when laid are united into a gelatinous or coriaceous nidus, which may be attached (benthos) or floating (plankton). As a rule, Molluscs do not nurture their progeny, and when once the eggs are laid they take no further heed of them. Some of them, however, retain their eggs till the time of hatching, and are therefore called incubatory forms (Fig. 8). Examples of incubatory forms occur among the Lamellibranchs, especially the specialised eulamellibranchiate Submytilacea ; among marine Gastropods (/ermetus, etc.), among freshwater Gastropods (Melania, etc.), and even among the octopodous Cephalopods (47rgo- nauta), but the number of truly viviparous forms is very small. Callistochiton among the Amphi- neura and several genera of aquatic and pulmonate Gastro- Sah pods are the only instances. Fie. 8. The number of eggs laid is very “gy amit et ide iow, with ou variable. It is always greater in the case of those marine Molluses which abandon their eggs to the mercy of the waves than in those which deposit them in a nidus, agglomerated together in ribands or in shells in which the embryos are naturally protected. Thus Ostraca may lay as many as 60,000,000 eggs, Chiton 200,000. On the other hand, numerous eggs are found in the nidus of certain Nudibranchs (50,000 in the case of Doris), Cephalopods (Loligo, 40,000), and pelagic Gastropods (Cymbulia, 1200). In all cases in which numerous eggs are laid free larval forms are developed, but when the whole of the develop- mental stages are passed through within the egg-membranes, and when the young individual is hatched with the characters of its parents and undergoes no metamorphoses, the number of eggs is generally small (Cenia, 4-12), or the greater number of the eggs laid is absorbed and furnishes nutriment for a few embryos (Buccinum, Purpura, etc.). In the following cases also eggs are laid in small numbers :—(1) In incubatory forms, such as Vermetus, where from 120-240 eggs are incubated in the pallial cavity, under the protection of the shell; (2) in terrestrial and fluviatile species, in which the number of eggs is always smaller than in marine forms. In this case caenogenesis or embryonic condensation is the rule ; the young animal quits the egg in the adult form, and there is no need for a large number of embryos. Instances in point are— 22 THE MOLLUSCA Limnaea, 20-100 eggs; felix, 40-100; Ancylus, 5 or 6; Valvata, 17; Neritina, 50-60. Lastly, the number of eggs is small in viviparous forms: in Paludina there are about 15; in Subulina (Fig. 8) there are 4. III. Empryo.oey. In the Mollusca the segmentation of the egg is unequal. In some primitive forms, it is true, the first two or three divisions are regular (Patella, Fig. 9, A; Chiton), and the two first blastomeres are often equal in size, but it is frequently the case that even the first division is unequal (many Lamellibranchs, Rachiglossa, ete.). From the first phases of segmentation up to the blastula stage one may distinguish two kinds of cells or blastomeres: the ectodermic cells, called ectomeres or micromeres; and the endodermic cells, called endomeres or macromeres. In the more primitive forms, however, such as Patella (Fig. 9, A), and the Protobranchia, there is uaavea Mma Fig. 9. A me ap owe) Eggs of various Mollusca, at the same stage, with 4 micromeres. A, Patella (Patten); B, Lacuna; C, Teredo (Hatschek); D, Sepia (Kolliker). ma, macromeres ; mi, micromeres. scarcely any difference in size between the two kinds of blastomeres, but in proportion as the endodermic cells are charged with food-yolk so does the difference in size become accentuated, as may be seen in the Taenioglossa (Fig. 9, B), and particularly in the Lamellibranchs (Fig. 9, C) and Rachiglossa. In the last-named group the irregu- larity of segmentation reaches its maximum, leading to the stage of incomplete or meroblastic segmentation characteristic of the Cephalopods (Fig. 9, D). It is quite exceptional for the segmenta- tion to become secondarily regular, as in Paludina, where this condition is due to the diminution of the yolk (Fig. 110). The separation of the ectodermic from the endodermic elements of the embryo follows a constant rule, similar to that which obtains among the Annelida. After the formation of the four primary micromeres two new series or quartettes of micromeres are formed at the expense of the large endodermic cells, and all the ectodermic organs are formed from these three quartettes. The micromeres multiply more rapidly than the macromeres, and there are even cases, such as Dentalium (Fig. 184), certain Rachiglossa, and Lamellibranchs (7eredo, Fig. 9, C, Cyclas, Unionidae), in which there THE MOLLUSCA 23 is only a single macromere during the early stages of segmentation. The segmentation sphere or blastula is thus formed of two more or less unequal moieties, respectively known as the formative (ectodermic) and nutritive (endodermic) moieties. Internally there is a segmentation cavity or blastocoele, generally much reduced (Fig. 10, A), except in certain Lamellibranchs (Cyclas, Dreissensia, etc.) and stylommatophorous Pulmonates. The animal or formative pole of the egg is indicated by the presence of the polar bodies ; the vegetative or nutritive pole is opposite, and at this point the blastopore or orifice of the digestive cavity will be formed (Fig. 110, A, 2). Formation of the Digestive Cavity and of the Diblastula or Gastrula. —The final result of the segmentation is that the micromeres form a more or less complete envelope to the segmented ovum, covering over the macromeres which remain within to form the endoderm. But the formation of this double-walled sphere, the diblastula or Fic. 10. Two types of gastrulae. 4, invaginate or embolic (Chiton : after Kowalewsky) ; B, epibolic (Crepidula y after Conklin). 1, blastopore ; ec, ectoderm ; en, entoderm. gastrula, may be effected in one or the other of two apparently different methods, invagination or epiboly. Invagination or emboly is certainly the more primitive method, and is realised in ova with a relatively small amount of food-yolk. In this case the nutritive moiety of the blastula is doubled back within the formative moiety, muchas one half of a deflated hollow indiarubber ball may be pushed by the finger within the other half. These two halves are separated by a remnant of the original segmentation cavity, which is invariably much reduced by the process. The invagination thus produced gives rise’ to the digestive cavity or archenteron, lined by the endoderm and communicating with the exterior by the blastopore. As examples of this mode of formation one may cite Chiton (Fig. 10, A), Paludina, the Pulmonata, the Nudibranchia, the Pteropoda, the Gymnosomata and Limacinidae, the Scaphopoda, Nucula, Ostraca, Pisidium, and the Unionidae. The gastrula is formed by epiboly when the nutritive cells or macromeres have become so much distended with food-yolk as to be too large to be invaginated into the layer of micromeres. In such case the micromeres as they multiply grow round the 24 THE MOLLUSCA endoderm and gradually surround it, leaving at the nutritive pole an orifice, which is the blastopore. Examples of this mode of formation are—Many streptoneurous Gastropoda (7rochus, Vermetus, Crepidula, Fig. 11, Janthina), the majority of the Rachiglossa (Columbella, Fusus, Nassa, Purpura, Urosalpinz), the Tectibranchs (deera, Philine, Aplysia, Thecosomata), and many Lamellibranchs (Pecten, Modiolaria, Cardium, Teredo, ete.). The two processes, however, differ only in appearance, and there are intermediate stages which form an insensible passage from one method to the other. In fact, complete invagination only occurs when the segmentation is quite or very nearly regular (Paludina, Chiton, ete., Figs. 10, A, and 110, A), but in consequence of the progressive increase of the amount of food-yolk contained in them, the macro- meres become larger and larger and are only able to be invaginated at a late stage of development. That is to say, in certain embolic gastrulae there is a commencement of epiboly, followed eventually by an invagination of the macromeres (Firoloida, Clione, Nucula). In the various cases enumerated above the segmentation of the ovum is complete or holoblastic. In the Cephalopods the case is different, for the segmentation is incomplete or meroblastic (Fig. 289), a large part of the egg being formed of food-yolk which takes no part in the division. But it must be remarked that in various types, such as the specialised Gastropods (Rachiglossa: Nuassa, Purpura, Fusus, ete. ; Tectibranchia: Aceru, Aplysia, Cavolinia, ete.), there is a sort of quasi-distinct yolk, formed by the granular portion of the macromeres. Hence the meroblastic or “ discoidal ” segmentation of the Cephalopods is not absolutely distinct from the total segmentation observed in other Molluscs: it is only an exaggeration of epiboly. In fact, as the yolk forms the principal part of the ovum and the protoplasm is concentrated at the formative pole, the ectoderm is formed over a limited region of the yolk (the “ germinal disc” or “embryonic area”), and is unable to envelop it entirely, so that development proceeds as if the process of epiboly had been left incomplete, the blastopore remaining very large and leaving all that part of the yolk which could not be covered by the ectoderm outside the embryo. Under these circumstances the endoderm is essentially an embryonic tissue, exclusively employed in the constitution of the vitelline mass, and degenerates in the adult, a great part of the digestive tract of the latter, a long stomodaeum and a long proctodaeum, being formed by the ectoderm. The passage to this condition is presented by some Gastropods with an abundant yolk: in Massa a part of the primitive endoderm degenerates in the adult, and in Fusus the four macromeres of the primitive endoderm seem to form a provisional embryonic organ, and it is the ectoderm that forms nearly the whole digestive tube. In the different groups of Molluses the liver THE MOLLUSCA 25 is formed from the wall of the enteron, generally as a pair of diverticula given off from its middle region (Fig. 116), and com- posed exclusively of cells of a fatty nature, while nutrition is effected by the absorption of the yolk. Formation of the Orifices of the Digestive Tube-—The gastrula mouth or blastopore, at a given period of the development at any rate, has very often the form of an elongated slit. This condition is shown in Patella (Fig. 113, IIL), Bithynia, various Opisthobranchs, such as Aplysia and Nudibranchs, in basommatophorous Pulmonates, Cyclas, etc. This slit gradually closes up from behind forwards, its two margins forming the ventral pedal prominence. In other cases this aperture may be more or less elongated, oval in shape, with an Fie. 11, ’ ° Eggs of Crepidula, showing the origin of the first mesodermic cell. mca, macromeres 3 nies, first mesodermic cell; mi, micromeres. (After Conklin.) anterior groove running forward as far as the velum, as is seen in Paludina. Or again, the blastopore may be circular, and be gradually displaced from behind forwards, suggesting a specialised condition of the slit-like blastopore which closes in the same direction. The linear or circular blastopore is totally closed in a large number of cases; such are, Aspidobranchs: Patella, Trochus, and Neritina; Pectinibranchs: Bithynia, Nassa, Purpura, Nautica, Lamellaria, and Crepidula; Opisthobranchs: Aplysia, various Pteropods and Nudibranchs ; Lamellibranchs: Cyrenidae, Unionidae, Dreissensia, Teredo. In other forms the blastopore, though it may contract so much as to be scarcely visible, remains open ; if it is a linear blastopore it is the anterior end that persists. Examples are, Chiton; several marine Streptoneura, including Vermetus, Fusus, and Heteropods ; Pulmonata ; Dentalinin ; Nucula ; Ostraca. 26 THE MOLLUSCA An invagination of the ectoderm at the place where the blastopore closed, or surrounding the blastopore if it remains open, places the digestive cavity (enteron) of the gastrula in communica- tion with the exterior. This invagination constitutes the stomodaeum, from which the pharynx and _ oesophagus with all their accessory ap- paratus, the salivary glands, radula, ete., are formed. Thus the blastopore, if it remains open, does not become the mouth of the adult. Puludina, however, is an exception, in that the whole of the blasto- pore remains open and be- ae comes the anus (Ray Lan- Trochosphere of Patella, sagittal section. 61, blasto- kester), whilst the stomo- pore ; me, mesoderm ; sh.g, shell-gland; the twodorsal, Gaeum is formed at the ve, and the two ventral ciliated cells are the velar : cells. (After Patten.) anterior end of the embryo (Fig. 110, F, m). Later, in Molluscs in general, the proctodaeum is formed as a very short anal invagination, at the posterior end of the original blastoporic groove. Its position is generally indicated by the presence of two prominent ectodermic cells, and it perforates the posterior part of the archen- teron, establishing a com- munication between the in- testine and the exterior. Eetodermic Organs. —The embryo, then, has an endo- dermic digestive cavity and a general ectodermic en- velope from which the oesophagus and the anal invagination are derived. But the ectoderm is prin- cipally concerned in the production of the permanent tegumentary organs proper Bre obi Se seats) 200); erly Trochosphere of Dreissensia, median sagittal section. so called, such as the foot, 1%, blastopore; f, flagellum; in, intestine; p.a.c, - 4.” post-anal cilia; sk, shell; ve, velum. (After Meisen- the mantle, and the ctenidia, fame.) = ti a and those organs which, al- though deeply placed, originate from the surface, such as the nervous system and the organs of sensation. The ectoderm further gives rise to the embryonic locomotory organs which result from a special Fic. 13. THE MOLLUSCA 27 adaptation to larval life. The most important of these embryonic organs is the velum; primitively a preoral ciliated ring, characteristic of the Trochosphere (Ray Lankester), which delimits an area known as the prostomium or “velar area.” Towards the centre of this area there is often a ciliated tuft or a flagellum, as in the larvae of Amphineura (Figs. 14, 17), Patella (Figs. 14, 113), Dentalium Fig. 14. Three Trochospheres of Mollusea. 4, [schnochiton (Heath); B, Patella (Patten) ; C, Dreissensia (Meisenheiiner). a, anus; f, foot; fl, flagellum; m, mouth; p.a.c, post-anal cilia ; sh, shell; ve, velum. (Fig. 15), and various Lamellibranchs (Figs. 14, C; 16). It is on the buccal side of this tuft, when it exists, that the apical plate is situated, probably the remains of a sensory organ from which the cerebral nerve-centres take their origin. The velum may be differ- entiated in one of two ways :—(1) The preoral ciliated ring may extend itself by growing outwards at all parts of its circumference : the trochosphere larva is thus transformed into a “ veliger ” (Ray Lankester), a larval form highly characteristic of Molluscs (Fig. 18). The velum may be divided into two lateral lobes (Fig. 18, v), which in their turn may be divided into two or three secondary lobes (Fig. 121). (2) The velum may retreat for a greater or less distance Fic. 15. towards the posterior end — trochosphere of Dentativm,sagittal median section. of the embryo, becoming ¥%Qsstopore:#,fayetium; i intestine: yo, mantle attached to it in such a manner as to form a more or less extensive superficial investment furnished with multiple ciliated rings, as in Dentaliwm (Figs. 15, 28 _ THE MOLLUSCA 185), Neomeniomorpha (Fig. 17), Nuculidae (Figs. 16, 225). The embryo may in this manner be nearly completely invested by a “test” extending posteriorly to an orifice which, however, is only a false blastopore. In both cases the velum eventually atrophies when the animal assumes the definitive habits of the adult. When the whole course of the development is undergone within the egg-membranes, there is either no veliger stage (Cephalopods, Figs. 119, D; 257, 290, 291; Cyclas, Entovalva, etc.) or there is no free veliger, but a more or less rudimentary velum, postero-dorsally atrophied, may be observed, which persists nearly to the time of hatching (viviparous Gastropods, Purpura, Fig. 1, Pulmonata). A post-anal ciliated area is not uncommonly found, as, for example, in Purpura (Fig. 1), among Gastropods, and Dreissensia Fic. 16, Trochosphere of Yoldia, median sagittal section. a.a, anterior adductor muscle; ap, apical plate ; bl, blastopore ; c.g, cerebral ganglion ; jl, flagellum ; h.a, posterior adductor ; in, intes- tine; li, liver ; sd, stomodaeum ; ¢, “test” or reflected velum, with 3 circlets of cilia. (After Drew.) (Figs. 13, 14, p.«.c) among Lamellibranchs. Finally, post-oral ciliated rings, secondarily acquired, are found in the larvae of certain Opis- thobranchs, Gymnosomata (Fig. 120). The foot is nothing more than a projection of the integument between the mouth and the anus. Its earliest rudiment is evidently paired, since it is formed by the union of the lips of the (commonly) elongated blastopore (Fig. 113). It is only at a late stage of development that it attains its complete development ; during the early stages it is very small and functionless, the velum serving as the sole organ of locomotion (Fig. 112). An ectodermic invagination, bounded by a ridge, makes its appearance at an early period on the dorsal face of the embryo, near the formative pole. This invagination, known as the “shell- gland” (Ray Lankester) or preconchylian invagination (Fig. 110, E, F, sh.gl), is also the precursor of the mantle, since the edge of the latter structure is formed by the ridge. The shell-gland THE MOLLUSCA 29 spreads from its point of origin in the form of a pallial thickening, which may be only slightly concave, or it may be deeply invagin- ated and afterwards evaginated. The invagination is caused by the very rapid proliferation of the epithelial tissue in the neighbour- hood of the pallial ridge. When evaginated these epithelial cells, having again become external, begin to seerete the shell. The branchiae or ctenidia originate on the inner surface of the mantle as tegumentary projections in the form of papillae or of filaments arranged in series (Fig. 229). The Nervous System and Organs of Sensation.—The various pairs of nerve-centres arise separately, and usually as thickenings of the ectoderm at the points where they are formed. In certain cases, however, the nerve-centres are developed by the more primitive process of invagina- tion, as may be seen in the case of the cerebral ganglia of Den- 2) Fig. 18. Fie. 17. Veliger of Littorina, ventral view, x 80. Trochosphere of Myzomenia banyulensis. e, eye; f, foot; m, mouth; ma, mantle; A, after 36 hours; B, after 100 hours. jl, pa.e, pallial cavity ; 7.7, right liver lobe; s, flagellum ; v, velum. (After Pruvot.) stomach ; ¢, tentacle ; v, velum. talium, Vermetus, Cavolinia (paired invaginations), Yoldia (Fig. 16, c.g), and Dreissensia (an unpaired invagination), a portion of the cerebral centres in Pulmonates, and the cerebral, pedal, and visceral ganglia of the Unionidae. When the cerebral ganglia are formed by invagination, a single pit, or a pair of pits, is formed on the oral side of the apical plate, from the bottom of which ganglion cells are budded off; the remainder of the invagination goes to form the labial palps, ete., of Lamellibranchs, and probably the rhinophores of Gastropods. The eyes also, including the pallial eyes of the Pectinidae, and the otocysts are sometimes developed from ectodermic thickenings ; but in many cases these organs are formed by invagination, for ex- ample, in various Cephalopoda (Fig. 119, D) ; in Gastropoda: in the Aspidobranchs, Paludina, bithynia, Calyptraea, Crepidula, Nassa, the Heteropoda, and the Pulmonata. The otocysts only are formed 30 THE MOLLUSCA by invagination in some other Gastropods (/'usus), and in Dentaliwm and various Lamellibranchs. Mesoderm and Mesodermic Organs.—A third intermediate cellular layer is formed, generally at an early stage, between the external ectodermic envelope and the endodermic wall of the digestive tube. This is the mesoderm, from which all the organs situated between the digestive tube and the integuments are produced. The origin of this layer is often difficult to determine, especially in highly specialised forms, but in all cases in which the origin is distinct there is no doubt about the matter, the mesoderm is derived from the endoderm. ‘This derivation is shown in the Polyplacophora, the Aspidobranchs (Patella, Fig. 12, me; Trochus, Neritina), the Pectini- branchs (Paludina, Bithynia, Crepidula, Fulgur, etc., and seemingly the Heteropoda), the Opisthobranchs (Philine, Umbrella, Aplysia, Clione, Chromodoris, etc.), the basommatophorous and stylommatophor- ous Pulmonates, the Scaphopods, the Lamellibranchs (Piszdium, Unionidae, Dreissensia, Teredo, etc.). Nevertheless we find scattered mesodermic cells, giving rise to unicellular muscular fibres of the integument (Unio, Crepidula), which are derived from the ectoderm. The principal result of the development of the mesoderm is the formation of another cavity in the embryo, the coelom. In the Mollusca the coelom does not originate by the invagination of enterocoelic pouches (Ténniges has shown the inaccuracy of Erlanger’s description of enterocoelic coelomic pouches in Paludina), but, as a result of specialisation, this primitive method is supplanted by solid mesoblastic masses, generally paired, which may be con- sidered as the cardio-genito-renal rudiments. These mesoblastic masses take their origin from the macromeres. As a rule, at the stage when four macromeres are present, it is the most posterior of the four that gives rise, by successive divisions, to the two first mesomeres or primary mesodermic cells (Fig. 11). From these the two mesodermic bands, which constitute the third layer, are produced as solid, or,in some cases discontinuous masses. The coelomic cavity or series of cavities are formed by more or less regular fission or delamination of the mesoblastic bands,—evidently a secondarily acquired mode of development. The coelom is therefore physio- logically a schizocoele. Eventually it is placed in communication with the exterior by ectodermic invaginations. The order in which the different parts of the primitive coelomic cavity make their appearance is not constant. The pericardium, in particular, may originate as two symmetrical cavities, which unite more or less rapidly (Puludina, Cyclas, Cephalopoda), or directly, as a single azygos cavity (Dreissensia, Pulmonata). ‘The extension of the mesodermic elements evidently narrows the primitive segmentation cavity or blastocoele, which becomes the cavity of the circulatory system. These elements spread between the ectoderm and endo- THE MOLLUSCA 31 derm, and become specialised to form the internal lining of the circulatory cavity in particular, and may even fill almost entirely the remainder of the blastocoele in the form of a false mesenchyme (caenogenetic or secondary mesenchyme), which constitutes the connective tissue. This naturally restricts the extension of the coelom properly so called, so that it is commonly reduced to the pericardial cavity. Since the mesodermic tissue gives rise, in this manner, to the epithelial wall of the coelomic cavity, to the lining of the circulatory cavity, and to the conjunctive tissue filling up the spaces between the organs, one must recognise it as sharing in the evolution, firstly, of the coelom and the excretory and repro- ductive organs derived from the coelom ; secondly, of the circulatory apparatus—the heart, ete. The coelom, of which the formation has been described above, is essentially a cavity communicating with the exterior, and its epithelial wall may be differentiated in two special ways—into excretory or renal elements, and into reproductive, and therefore caducous elements. In the most primitive process the kidneys are formed in connection with a portion of the coelom, with which they remain in complete continuity (Paludina). In other cases they are formed by a hollowing out of a portion of the mesoderm in contact with the pericardium (Bithynia, Limax, Cyclus, Dreissensia, etc.), or they may be formed independently in their definitive position (Cephalopoda). Eventually each kidney acquires a com- munication with the pericardium, and in all cases makes a connection with the exterior by an ectodermic invagination. The genital organs or gonads originate either from the wall of the coelom or pericardium (Paludina, Dreissensia), or in contact with the coelomic wall (Cyclas), or from a rudiment common to themselves, the pericardium and the kidney, or, finally, from distinct mesodermic elements. The continuity of the pericardium and gonads is well preserved only in the Aplacophora (Fig. 30, C) and adult Cephalopoda (Fig. 252, coe) ; in all other Molluses the genital organs are separated from the pericardial cavity and acquire communica- tions either with the kidneys or directly with the exterior. In the latter case the terminal portions of the gonaducts, together with the accessory genital glands, are ectodermic in origin. The heart may arise from a portion of the wall of the peri- cardium itself (Paludina), or a common rudiment may give rise to the wall of the pericardium and the heart (Pulmonata, Cyclas, Dreissensia; ete.), and in the latter case the origin of the heart may be paired (Cyclas, Cephalopoda) like that of the pericardium itself. The larvae of such Molluses as lay their eggs singly and free in the sea are hatched out very rapidly ; a few hours suffice in the case of Dentalium among the Scaphopoda ; twenty hours in 7vochus among the Aspidobranchs ; fourteen hours in Yoldia among the THE MOLLUSCA Los) Ww Lamellibranchs ; twenty-four hours in Pholas, ete. The eggs of Gleba, aggregated into a nidus, are hatched after three or four days, those of Ischnochiton after seven days ; but in the majority of Gastropods and the Cephalopods the time required is much longer. The marine larvae of temperate seas are intolerant of a rise of temperature, and generally perish when it approaches 30° C. IV. DEFINITION OF THE MOLLUSCA. From what precedes, it results that in each of the five classes the same lines of specialisation may be observed—viz. the loss of the shell, of the foot, of the ctenidia, of the radula, ete. Thus the general morphological characters are obviously those of the most primitive of the different classes (Fig. 19), and the following diagnosis may be proposed for the phylum :— 1. The Mollusca are originally bilateral organisms, in which signs of primitive segmentation are no longer evident. Fic. 19. Scheme of a primitive Mollusc, viewed from the left side. a, anus ; c.g, cerebral ganglion ; f, foot ; g, gill, in the pallial cavity ; go, gonad; h, heart; k, kidney ; la.c, labial commissure ; m, mouth; pa, mantle; pa.n, pallial nerve; pe, pericardiuin ; p.g, pedal ganglion; pl.g, pleural ganglion ; ra, radula; r.p.o, reno-pericardial orifice ; st, stomach ; st.g, stomato-gastric ganglion ; v.g, visceral ganglion. 2. They possess a well-developed coelom (gonad and _pericar- dium), enteron, and haemocoel, quite distinct from one another. 3. The alimentary tract exhibits (or has lost) a radular sac in its anterior part. 4. The nervous system consists of a peri-oesophageal ring, whose supra-oesophageal (or dorsal) moiety is the cerebral com- missure, and the infra-oesophageal (or ventral) moiety is the labial commissure. The former gives off chiefly sensorial nerves, the latter nerves to the digestive tract. From their union two nervous cords arise on each side, a dorsal or pallial and a ventral or pedal ; from the former arise the visceral nerves, whose main trunks are frequently joined together under the digestive canal to form the infra-intestinal visceral commissure. 5. The general body-wall is differentiated into three regions: THE MOLLUSCA 33 (1) the antero-dorsal or cephalic, on which are borne most of the special sense-organs ; (2) the postero-dorsal or pallial, which forms a projecting fold around the body, and secretes on its external face a calcified cuticle or shell, and on its lower surface develops respiratory organs or ctenidia ; (3) the ventral or pedal, which is the organ of locomotion. 6. A so-called ‘“‘veliger” or free trochosphere larva is nearly always present in embryonic development ; its preoral ciliated ring grows out to form a natatory velum, and at its formative pole there is a “ preconchylian invagination ” or shell-gland. V. Bronomics AND DISTRIBUTION. Molluscs are essentially aquatic animals, but the most varied modes of existence may occur, even among members of the same class. The majority are inhabitants of the sea; a few live in fresh water ; a single order of Gastropods and a few isolated members of the same group are adapted to a terrestrial life. They are repre- sented in the three great groups of aquatic organisms, namely, in the Benthos, comprising creeping or fixed animals inhabiting the depth of the sea; the Necton, comprising animals that swim actively and can make headway against the currents ; the Plankton, comprising animals that float passively and cannot contend with the currents. The first group includes the littoral and abyssal Molluscs, among which the Necton is also represented. The two other groups include the pelagic Mollusca, the Cephalopods belonging exclusively to the Necton, while the free-swimming Gastropods, and those which inhabit pelagic Algae, some isolated Lamelli- branchs (Planktomya), and the larvae of various groups belong to the Plankton. The Mollusca are distributed over the whole surface of the earth and in all latitudes. Terrestrial forms are found on the highest mountains—some Stylommatophora at a height of 15,000 feet ; lacustrine forms (/imnaca) are found at a depth of 350 fathoms. The pelagic forms are not only distributed over the surface of the sea, but may descend to a depth of 2600 fathoms without reaching the bottom. Abyssal Molluscs are found in all oceans extending to a depth of 2800 fathoms from the surface. As a rule, Molluscs are free-living animals, and crawl, swim, or burrow, but some are sedentary in adult life. Only a few Gastropods and Lamellibranchs are fixed to their habitat. Their modes of alimentation are various. Some are commensal with Ascidians, ¢.g. Modiolaria; some with Echinoderms, as Montacuta, Lepton, and Scioberetia ; some with Crustacea, Lepton squamosum and Ephippodonta, or with Sponges (Vulsella), or Annelids (Cochliolepis). Others again are ectoparasitic on Echinoderms, such are Zhyca and 3 34 THE MOLLUSCA Stylifer (Fig. 20); or, like Hulima and Entovalva, are endoparasitic, also in Echinoderms. In the latter case the animal may become so degenerate in the adult state as to consist of little more than a sac containing the genital products, as for example Entosiphon (Fig. 21), Entocolax (Fig. 138), Entoconcha (Fig. 139), and Enteroxenos (Fig. 140). There are many cases of protective adaptation and mimicry in the various groups of Mollusca. The pelagic species are generally transparent and colourless or tinged with blue, but the most remarkable examples of mimicry are found among the forms un- protected by a shell (Nudibranchs, 3 Lamellaria, etc.), in which the a ow Fic. 20. Fic. 21. Stylifer celebensis, X 12. pr, pro- Entosiphon deimatis, x 2. 0, orifice boscis ; ps, pseudopallium ; sp, spire of the proboscis; ov, ova; pr, pro- of the shell not covered by the pseudo- boscis ; ps, pseudopallium ; s, fixative pallium. (After Kiikenthal.) siphon, (After Koehler and Vaney.) individual assumes the colour and aspect of its habitat, as for instance Hermaea dendritica on green algae, and Hermaea bifida on Griffithsia, a red alga, etc. The abyssal Molluscs are colourless, and are characterised by the thinness of the shell, the atrophy of the visual organs, and the development of tactile organs. Examples of convergence of form may also be noted, such as Marginella and Pseudomarginella among Gastropods, Pholas candida and Petricola pholadiformis among Lamellibranchs. The duration of life in individual Molluscs is ordinarily rather short. Marine Streptoneura may live for several years, and Lattorina littorea, when in captivity, has attained an age of nearly twenty years. Freshwater Molluscs may live for eight years (Paludina). THE MOLLUSCA 35 The Pulmonata are generally biannual, but Helix pomatia may attain an age of six years. The majority of Nudibranchs and Tecti- branchs appear to live for one year only. Many Lamellibranchs (Mytilus, Teredo) are adult at the end of one year; Avicula is adult at the end of two years; Ostraeca edulis is sexual at two years, becomes adult in five years, but may live for ten years in oyster- beds. The huge Z7idacna lives for about eight years, the Cyrenidae only two years, but the Anodontidae are remarkable for their longevity ; they do not become sexually mature till they are five years old, and they continue to grow to the age of twenty or thirty years. In the Cephalopoda it seems that Lossia does not live for more than a year, and Octopus not more than four years. Many Molluscs are able to fast for a long time. Cold affects them less than heat. Helix has been known to survive a tempera- ture of — 120°C., and small Gastropods live in thermal springs at a temperature of 42°C. Molluscan embryos and larvae generally perish, in temperate climates, at temperatures of + 31° C. and — 3° C. Descriptive zoologists have enumerated more than 28,000 species of living Molluscs, of which more than half are Gastropods. Fossil representatives of Molluscs are found in all deposits from the Palaeozoic onwards. 1. Distribution in Space. I. Marine Molluscs — A. Littoral Fauna.—The shores of con- tinents are divided into three provinces by great thermal variations. a. The North Polar province, with characteristic genera such as Cryptochiton, Molleria, Lacuna, Velutina, Onchidiopsis, Solariella, Machaeroplax, Volutharpa, Torellia, Cyprina, Mya, B. The South Polar province, with the characteristic genera Photinula, Struthiolaria, Cominella, Eatoniella, Cyamium, Lissarca, Philippiella, Modiolarca. y. The tropical province, or region of coral reefs, in which one may distinguish four sub-regions :—(1) The Indo-Pacific, the home of Nautilus and the chief forms of the Toxiglossa. The Mediterranean should be included in this sub-region, and the Australo-Zealandic division of it, just as is the case with the terrestrial fauna, presents special characters, as shown in Zvrigonia, Amphibola, etc. (2) The West African and (3) the East American sub-regions, which have several forms in common. (4) The West American, characterised by such genera as Jonoceros, Concholepas, etc. Occasionally species may be naturally or artificially acclimatised in various parts of these regions, but exchanges are only definitively effected between similar latitudes, as for example Littorina littorea between Europe and North America, and reciprocally Venus mercenaria and Petricola pholadiformis. B. The Abyssal Fauna, is not divisible into distinct provinces, and many of its species are universally distributed either in the . 36 THE MOLLOUSCA northern and southern parts of the same ocean or in several different oceans. Thus Limopsis aurita, Semele profundorum, Verticordia deshayesiana, Arca pteroessa are found in the Atlantic and Pacific; Hyalopecten pudicum and Silenia sarsii are common to the Atlantic and Indian oceans. Characteristic abyssal genera are Leptochiton, Scissurella, Margarita, Cyclostrema, Setia, Leda, Bathyarca, Limopsis, Hyalapecten, Dacrydium, Callocardia, and Septibranchs in general. C. The Pelagic Fauna.—a. The superficial forms are very widely distributed, but may nevertheless be described as belonging to polar and tropical provinces. The North and South Polar fauna are different: to the former belong Clione limacina, Limacina helicina ; to the latter Spongiobranchaca australis, Limacina antarcticu. B. The zonary or deep forms are probably more universally distributed, but are still imperfectly known; they include the luminous Cephalopoda. Il. Land and Freshwater Molluscs.—It is only a small number of groups that have quitted the sea to assume a freshwater or terrestrial existence, and among these no Amphineura nor Scapho- poda nor Cephalopoda are found. Among the Lamellibranchs only a few families are found in fresh water, viz. Cyrenidae, Dreissensiidue, Unionidae, Actheriidae (none of them primitive in organisation), and a few isolated types. Among the Gastropods we find very few Rhipidoglossa, Neritina, Hydrocaena, Titiscania ; chiefly Taenioglossa, e.g.the Valvatidae, Paludinidae, Ampullarudae, Hydrobudae, Melanidae ; some isolated types of Rachiglossa, and practically no Opistho- branchs. As for the terrestrial Mollusca, there are only a few families of streptoneurous Gastropods (Helicinidae, Cyclophoridae, etc.), and the whole order of Pulmonata. Of the last-named, one sub-order, the Basommatophora, has returned to an aquatic life, chiefly in fresh water, but retains for the most part a pulmonary respiration. It is mostly in warm regions, and particularly in those in which the sea is inclined to be brackish, that marine forms have penetrated into fresh waters. Certain inland seas also have become separated from the ocean, and have preserved a fauna which is partly of marine origin. Lakes Baikal and Tanganyika appear to belong to this category. The tropical regions in general are characterised by terrestrial forms, such as Vaginula, Helicina, Ampullaria, ete. Chilina and Bulimus belong to the Neotropical region. Clausilia is not found in North America, and, generally speaking, the Pulmonates with folded branchiae are absent from the New World. The Ethiopian province is the home of Achatina; the Australo-Zelandic of Janella, Rhytida, Vanganella, Latia; the Oriental region of Cyclophorus and the Rathouisiidae. The distribution of terrestrial and fluviatile THE MOLLUSCA 37 Molluses shows that the Asiatic and Australian regions are separated not by Wallace’s line, but by another line farther east. 2. Distribution in Time. The five classes of Molluses were already differentiated at a remote epoch of the Palaeozoic era. The Polyplacophora, the Cephalopoda, and Dentalium were represented in the Ordovician ; Diagrams of the five classes of Mollusca, from the left side. A, Amphineura; B, Scapho- poda; C, Gastropoda ; D, Lamellibranchia; 2, Cephalopoda. «a, anus; @.a, anterior adductor ; c.g, cerebral ganglion; f, foot; fu, funnel; g, ctenidium; h, heart in the pericardium ; h.a, posterior adductor; m, mouth; pa, pallium or mantle; p.g, pedal ganglion; pl.g, pleural ganglion ; ra, radula; st, stomach; st.g, stomato-gastric ganglion ; v.g, visceral ganglion. the Rhipidoglossa and the Palaeoconchs (Lamellibranchia allied to Solenomya), in the Cambrian. On the other hand, many ancient stocks have left no surviving descendants. But the appearance of existing genera or families supports the phylogenetic conclusions drawn from the study of comparative anatomy. Among the Cephalopoda it is the Tetra- branchs that appear in the Ordovician; the Ammonites appear 38 LITERATURE OF THE MOLLUSCA only in the Devonian, and the Dibranchs (Belemnites) at the beginning of the Secondary. But at the present day all the species of Tetrabranchs, some 7500 in number, are only represented by a few species of the single genus Nautilus; and as for the group of Belemnites, it has entirely disappeared since the end of the Cretaceous, its sole surviving and more or less distant represent- ative at the present day being the genus Spirula. Among the Gastropods the Aspidobranchs (Rhipidoglossa) are the first to appear; several families, such as the Capulidae and Pyramidellidae, date back to the Upper Silurian. On the other hand, there are but few Ctenobranchs in the Palaeozoic ; most of the families of this order make their appearance in the Secondary, and the same may be said of the Opisthobranchs, with the exception of the Actaeonidae, which are found, as also are the Pulmonata, in the Carboniferous. Of Lamellibranchs various Protobranchs and Filibranchs are found in the Silurian, but the other groups, as a rule, do not appear till the Secondary. The Palaeoconcha of the Primary, and the Rudistae, Diceratidae, Mono- pleuridae, and Caprinidae of the Secondary, have died out without leaving descendants. LITERATURE OF THE MOLLUSCA GENERALLY. I. Conchological. . Cooke. Molluses. The Cambridge Natural History, vol. ii. 1895. . Fischer. Manuel de Conchyliologie, 1887. Jeffreys. British Conchology, 1862-1869. . Simroth. Mollusca. Bronn’s Klassen und Ordnungen des Thierreichs, Bd. ii. 1895 till now. 5. Taylor. Monograph of the Land and Freshwater Mollusca of the British Isles, 1900 till now. 6. Tryon. Manual of Conchology, 1878 till now. 7. Woodward. A Manual of the Mollusca, 1880. oo Nh Il. Morphological. bis. Cuénot. L’excrétion chez les Mollusques. Arch. d. Biol. t. xvi. 1899. 7 8. Geddes. On the Mechanism of the Odontophore in certain Mollusca. Trans. Zool. Soe. London, vol. x. 1879. 9. Huxley. On the Morphology of the Cephaious Mollusca. Phil. Trans. 1853. 10. von Jhering. Vergleichende Anatomie des Nervensystemes und Phylogenie der Mollusken, Leipzig, 1877. Die Gehorwerkzeuge der Mollusken, Erlangen, 1876. 12; Zur Morphologie der Niere der sog. ‘‘ Mollusken.”’ Zeitschr. f. wiss. Zool. Bd. xxix. 1877. 13. Lankester. Mollusca. Encyclopaedia Britannica, 9th edit. vol. xvi. 1883. Contributions to the Developmental History of the Mollusca. Phil. Trans. 1875. 15. —— Note on the Coelom and Vascular System of Mollusca and Arthropoda. Quart. Journ. Micr. Sci. vol. xxxiv. 1893. LITERATURE OF THE MOLLUSCA 39 . Mitne-Edwards, Observations sur la circulation chez les Mollusques. Ann. d. Sci. Nat. Zool. sér. 3, t. viii. 1847. . Moynier de Villepotx. Recherches sur la formation et l’accroissement de la coquille des Mollusques. Journ. Anat. et Phys. 1892. . Pelseneer. Introduction & l’Etude des Mollusques, Bruxelles, 1894. Recherches morphologiques et phylogénétiques sur les Mollusques archaiques. Mém. Cour Acad. Belg. t. lvii. 1899. Hermaphroditism in Mollusca. Quart. Journ. Micr. Sci. vol. xxxvii. 1895. . Plate. Bemerkungen iiber die Phylogenie und die Kutstehung der Asym- metrie der Mollusken. Zool. Jahrb. (Anat. u. Ontog.), Bd. ix. 1895. . Schiemenz. Ueber die Wasseraufnahme bei Lamellibranchiaten und Gastro- poden. Mitth. Zool. Stat. Neapel, Bd. v. 1884, and vii. 1887. 23. Spengel. Die Geruchsorgane und das Nervensystem der Mollusken. Zeitschr. f. wiss. Zool. Bd. xxxv. 1881. . Thiele. Die Systematische Stellung der Solenogastren und die Phylogenie der Mollusken. Zeitschr. f. wiss. Zool. Bd. Ixxii. 1902. CHAPTER II THE AMPHINEURA CLASS I.—AMPHINEURA, von JHERING (1876) (=IsopLEuRA, Ray Lankester ; ACULIFERA, Hatschek). ) Order 1. Polyplacophora (Chitones). ) ~ Sub-Order 1. Eoplacophora. / Family 1. Lepidopleuridae. Sub-Order 2. Mesoplacophora. Family 2. Ischnochitonidae. 3. Mopaliidae. 4. Acanthochitonidae. 5. Cryptoplacidae. 2? 9 Sub-Order 3. Teleoplacophora. Family 6. Chitonidae. Order 2. Aplacophora. Sub-Order 1. Neomeniomorpha. Family 1. Lepidomeniidae. 2. Neomeniidae. 3. Proneomeniidae. 4. Parameniidae. 99 39 Sub-Order. 2. Chaetodermomorpha. Family 5. Chaetodermatidae. Historical.—The Chitones were formerly the only known forms of this group, and for a long time they were placed in the Gastropoda, near the genus Patella, the two forming the Order Cyclobranchia of Cuvier. When Chaetoderma and Neomenia were investigated from an anatomical point of view, von Jhering united them to the Chitones (1876), and placed the two in a division of ‘“ Worms,” which he called Amphineura. But the molluscan nature of these Amphineura is so clear, that they were reintroduced into the 40 THE AMPHINEURA 41 phylum Mollusca by Spengel, Hubrecht, Lankester, etc., and even von Jhering has since admitted this interpretation. Although Gegenbaur Sand Claus have again separated Chaetoderma and Neomenia from the Chitones, and placed the former in a distinct class (“Solenogastres ”), and the latter once more in the Gastro- poda, the unity of the Amphineura, as well as their molluscan nature, is now very generally accepted. Definition. —The Amphineura are a group of Mollusca characterised, firstly, by their more or less elongated and quite symmetrical body, with the mouth and the anus situated at its two ends; and secondly, by their mantle, which is always provided with numerous spicules embedded in a cuticle. General Description.—The mantle is very large, and always covers at least the dorsal surface and the sides of the body. The whole external symmetry reappears in the various internal organs. In the nervous system there are, on each side, two longitudinal cords (one pedal, one pallial) with ganglionic cells along their whole extent. They are united with one another in front, where there is a supra-oesophageal cerebral commissure. ‘The two pedal cords are also united by anastomoses, and in addition each of them also exhibits anastomoses with the corresponding pallial cord. The two pallial cords are united by a thick posterior com- missure on the dorsal’ side of the rectum. There are no otocysts. The buccal cavity is very generally provided with a radula (but mandibles are only present in a species of Chaetoderma). The anus and renal orifices are posterior. The heart is dorsally situated in the hind part of the body, and its ventricle is more or. less intimately united to the dorsal wall of the pericardium. All the Amphineura are marine in habit. They are found in all oceans and at nearly all depths. They existed in very ancient geological ages, for they are already present in the Ordovician (Lower Silurian). There are two very distinct Orders of Amphineura: (1) the Polyplacophora, (2) the Aplacophora. ORDER 1. Polyplacophora, Blainville. Definition.—Amphineura, whose chief characteristics are (1) the foot, occupies the whole ventral face of the body; (2) the mantle, bears eight transverse calcareous plates; (3) between mantle and foot there is on each side a more or less complete row of branchiae. -I. GENERAL DESCRIPTION AND EXTERNAL CHARACTERS The mantle covers the whole body on the dorsal side; its ventral extension is inversely proportional to that of the foot, and 42 THE AMPHINEURA all around the latter there is a pallial groove. The mantle secretes a shell consisting of eight plates or valves articulated with one another and arranged in longitudinal series. Each of these valves partially overlaps the following, except in some species of Cryptoplax ( = Chitonellus), in which the three hindermost are isolated. This articulation of the valves allows the animal to roll up. The two terminal (first and eighth) valves are semicircular, the six inter- mediate are quadrangular. They may be partially (Cryptoplax and some species of Acanthochiton) or even wholly (in adult Cryptochiton, but not in young ones) concealed by a redupli- cation of the mantle. Each valve is made up of two quite dis- similar calcareous layers: («@) the uppermost or tegmentum, which alone is visible externally ; (b) the deeper layer or articulamentum, which is porcellaneous, quite compact, and invisible in the living animal. In most of the lower Polyplacophora these layers are coextensive and have smooth edges, but in the higher forms the articulamentum projects beyond the -* outer layer into the substance of the mantle, Gray dorsal aspech shew. to which it is firmly attached. These pro- aoe ee tel eree uz jections of the outer or peripheral margins first. eyes on the second of the valves are termed ‘insertion plates”; shell- plate; ILI, third : shell-plate. they are generally slit or notched to form the so-called ‘“ teeth,” which may be either smooth and sharp along the edge or crenulated. The anterior margin of each valve, except the first, is invariably provided with two pro- jections called ‘ sutural laminae,” which underlie the hind margin of the valve next in front. The tegmentum has no representative in the shells of other Mollusca. It is formed by the fold of the mantle covering the edge of the articulamentum, and, as it grows in width, it extends over the latter. It is much reduced in Acanthochiton and aborted in the adult Cryptochiton. The stratified layers of the tegmentum are traversed by a system of numerous, nearly parallel, ramified canals through which special sense-organs pass to the surface (Fig. 24). Nearly the whole of the peripheral part of the mantle or ‘oirdle,” as it is called, is covered with chitinous or calcareous spicules of various shape, acicular or squamose. Lach spicule rests on an epidermic papilla and is formed by a single matrix cell. The head is more or less cylindrical, consisting of a short down- wardly curved snout with the mouth at its extremity. On either side of the mouth is a somewhat angular labial palp. A narrow furrow separates the head from the foot. The latter forms a ventral creeping surface, extending the whole length of the body Fic. 23. ‘ THE AMPHINEURA 43 from head to anus. The breadth of the foot is inversely’ pro- portional to the width of the lower edge of the mantle: it is broad in most of the Polyplacophora, but narrow in the Cryptoplacidae. Extending all round the foot, between it and the mantle on the ventral side, is the pallial groove, in which lie the gills. In the more primitive Chitons mucous thickenings extend into the groove, v ao 2 9°72. v Cy | ! fe Fic. 24. Transverse section of the lateral portion of the pallial teguments of Chiton. I, tegmentum ; II, articnlamentum ; III, pallial epithelium under the shell; IV, epithelium of the margin of the mantle; V, spicula; VI, cuticle of the mantle-margin; VlIa, periostracum; VII, megal- aesthetes ; VIII, micraesthetes. (After Blumrich.) fi reaching from the anus to its upper corner, or to the foot, or even to the inner wall of the mantle. II. ANATOMY. 1. The Alimentary Canal extends from one extremity of the body to the other. The mouth leads into the buccal cavity, on the ventral wall of which opens the radular caecum. The radula is long and reaches nearly as far back as the stomach. ach radular row includes seventeen teeth of various shape (Figs. 2, A; 74, E). The three central teeth are simple: on each side of them is a large 44 THE AMPHINEURA recurved thick and dark lateral tooth. Externally are six polygonal marginal teeth: of these the third differs from the rest, being more or less narrow, elongated, and curved, and sometimes its concave edge is ciliated (Zrachydermon). The fore part of the radula rests upon a cartilaginous mass, moved by a great many mus- cular bundles. Two pairs of glands open into the buccal cavity. The true salivary glands le at the sides, well forward, but behind the cerebral commissure ; they are slightly branched, but rather short, and have a very short duct. On the ventral wall, under the subradular organ, he two very small mucous glands close to one another and to the middle line. On either side, at Boreochiton cinereus, dorsal view of a female, the point where the pharynx without the shell-plates. I, first “intersegmen- passes into the short oesophagus, tum”; II, ovary; III, oviduct; IV, ventricle - : of heart; V, dorsal right muscle; VI, dorsal 18 the. opening of the sugar eho eel ese: VII, retractor muscle of gland a large glandular pouch with a papillose internal surface. The large and thin-walled stomach is surrounded by the liver mass. The two liver lobes are symmetrical in young Chitons, but become asymmetrical in the adult, the right lobe being the smaller and Fic. 26. Cryptoplax larvaeformis, left-side view, the posterior end partially opened. I, gonad; IT, genital duct; III, genital pore; IV, ventricle of heart; V, anus; VI, renal pore; VII, gills; VIII, foot ; IX, mantle ; 6, 7, 8, position of the sixth, seventh, and eighth shell-plates. anterior. They open into the stomach either by two distinct orifices (Chiton aculeatus), or by two orifices in a single duct (Lepidopleurus), or by a single aperture (Hanleya). The intestine is very long, as is usual in phytophagous animals, and is thrown into numerous THE AMPHINEURA 45 coils. The anus opens at the posterior extremity of the body, between the mantle and the foot (Fig. 28, a). 2. Circulation and Respiration.—The heart, enclosed in a large pericardium, occupies the postero-dorsal region of the body. It consists of a median elongated ventricle and two elongated symmetrical auricles. The openings of the auricles into the ventricle are subject to some variation. In the Lepidopleuridae, the Mopalidae, and Yonicella, Trachydermon, Boreochiton, etc., among the Ischnochitonidae, the auriculo-ventricular aperture on either side is single and anterior (Fig. 27); in the Acanthochitonidae, the Cryptoplacidae, and the Chitonidae generally there are two apertures on either side (Figs. 4 and 26); in Chiton squamosus there are three, and in Chiton goodalli four. The auricles are united to one another posteriorly, but there is never a posterior median auriculo-ventricular opening. The posterior auriculo-ventricular orifices are frequently asymmetrical. A single anterior aorta rises from the ventricle anteriorly and carries the blood to the various organs and inter- visceral blood-spaces. The venous blood from the different parts of the body is conducted back to a large sinus on either side near to the line of union of the mantle with the body. Closely connected with this same line of union on either side is a row of gills, situated between the foot and the mantle. The'number of pairs of gills varies from four in Lepidopleurus pagenstecheri to eighty in Acantho- pleura spiniger, but a careful comparison shows that the number of gills in the right hand row does not always correspond with that in the left. The gill-rows may be either of the holobranchial type, in which case they ex- tend over the whole length of the body, or of the mero- Migs fe branchial type, ip which they, Psst of Movie, dors! spect, 1, auricle are confined to a more or auricle; IV and V, afferent vessels ; VI, mantle ; 6, 7, ay ae 8, indicate the position of the sixth, seventh, and less limited space at the pos- eighth shell-plates. terior end of the body (Fig, 28). But these two types are connected by transitional forms, and they are not, generally speaking, characteristic of natural groups, nor are they determined by the greater or less size of the species. The genera with few gills are naturally merobranchial, and in the Lepido- pleuridae these organs are confined to the region covered by the two last shell-valves. The gills are inserted at the bottom of the pallial groove. The largest gill, which is also the last one in those forms in which no adanal gills are present, is always the first 46 THE AMPHINEURA behind the renal opening: it is the first to be formed and is the starting-point from which the rest of the gills are added either forwards or both forwards and backwards. Occasionally individual gills may be bifurcated or trifureated. ach gill has the typical ctenidial structure, consisting of an axis bearing an anterior and a posterior row of gill-lamellae or filaments. The blood from the above-mentioned longitudinal vessel is distributed to each gill by an afferent vessel running along the internal or pedal margin of the axis, and, after being oxygenated in the lamellae, is carried back by an efferent vessel running along the external or pallial edge of the axis to another longitudinal vessel which conducts it back to the corresponding auricle. 3. Excretory Organs.—There are two symmetrical kidneys, whose relations were first discovered by Sedgwick. Each of them con- Fie. 28. Ventral aspect of three species of Polyplacophora, showing the various sorts of gill-rows. A, Lepidoplewrus benthus ; B, Boreochiton cinereus; C, Schizochiton incisus. a, anus; f, foot; g, gills; m, mouth; pa, mantle; pa’, anal lobe of the mantle; p.s, pallial slit; te, pallial tentacles. sists of an elongated renal canal, situated on the lateral side of the visceral mass, and once folded on itself, so that its two ends are posterior. The internal or dorsal end opens into the pericardial cavity, through a ciliated aperture or funnel. The external or ventral end opens to the exterior, between two of the gills at the hinder part of the body. The renal canal is dilated immediately behind its external opening. It is excretory throughout its length, and the excretory surface is increased by numerous small much- branched caeca which lie close to the body-wall laterally and ventrally and open into the canal (Fig. 29). Various kinds of kidneys are to be found (Plate). They generally extend more or less forwards, and their extension is THE AMPHINEURA 47 generally correlated with that of the branchial row. The two branches of the renal canal may be fused together from before backwards until, as in Callistochiton and Nuttalochiton, the kidney has the form of a simple sac with more or less numerous arborescent appendages, and the pericardial and external apertures adjacent to one another at its hinder end. A similar form of specialisation may be seen in the kidneys of Lamellibranchs. The renal canal may be complicated by the addition of two accessory Fie. 29; Renal organs ot Boreochiton cinereus, dorsal aspect; on the right-hand side, the exterior ramifications of the antero-posterior renal part are alone drawn ; on the left-hand side, all the other ramifications are drawn. I, pedal cord ; Il, mantle; III, external ramifications of the antero-posterior (or terminal) renal part ; [V, reno-pericardial orifice ; V, posterior point of the urinary chamber; VI, external renal pore; VII, urinary chamber; VIII, postero-anterior (or initial) portion of the kidney ; IX, antero-posterior (or terminal) portion of the kidney; X, internal ramifications of the antero-posterior portion of the kidney ; XI, left outer limit of ITI ; XII, ramifications of the initial portion of the kidney ; 1-8, the eight ‘“‘segments” of the body. longitudinal branches, an anterior larger and a posterior smaller, which lie in the foot near the middle of the body. 4. Nervous System and Sense-organs.—There is no concentration of nerve-ganglion cells to form distinct ganglia, but the larger nerve- cords are ganglionic throughout their extent. There are two pairs of longitudinal nerve-cords, united in front of the buccal mass by a supra-oesophageal or cerebral commissure. Ganglionic enlargements on this commissure are found only in Callochiton doriae. 48 THE AMPAHINEVRA The two ventral or pedal cords are united beneath the digestive tract by numerous transverse anastomoses. The two lateral or Fic. 30. Diagrams of the excretory and reproductive organs of Amphineura. C, Proneomenia; D, Chiton. Br, etenidia; Cl, cloacal or pallial chamber of Proneomenia ; g, external aperture of the genital duct of Chiton; N, renal organ; O, gonad; P, pericardium ; 7, rectum; wu, external aperture of renal organ of Chiton. (From Lankester, after Hubrecht.) Fic. 30%, Ventral aspect of Acanthoplewra incana. I, mantle; II, mouth; III, foot; IV, gills; V, anus; VI, right renal pore; VII, right genital pore (these two pores are better seen on the left-hand side of the body). pallial cords are united posteriorly, dorsad of the anus, by a thick supra- rectal commissure (Fig. 31, Vill). The cerebral commissure inner- vates the palps, the lips, and the muscles of the buccal bulb. Below the buccal bulb it is prolonged into an anterior labial commissure, which in turn gives rise to a stomato-gastrie commissure: the last-named is to some extent ganglionic and has two branches, which unite with those of the opposite side on the upper and under side of the pharynx, and also with the infra-oesophageal subrad- ular commissure. The subradular commissure supplies a pair of ganglia which are in close connection with a peculiar sense-organ lying on the floor of the mouth, in front of the radula. The labial and sub- radular commissures, together with the subradular organ, correspond to the homonomous parts in the Scaphoda and Cephalopoda. THE AMPHINEURA 49 The two great ventral or pedal cords give rise to the pedal nerves. The two great lateral or pallial cords chiefly send nerves to the mantle and the gills, and thus correspond to the whole of the Vill Fic. 31. Nervous system of Fic. 75. Pteroceras, right-side view of the male, with the mantle laid open. a, anus; b.d, bile-duct; c.g, cerebral ganglion ; c7.s, crystalline style ; f.foot; g, gill; g.g, gonad ; g.o, genital orifice ; h, heart; hy.g, hypobranchial gland; i.g, infra-intestinal gland; im, intestine; k, kidney; m, mouth ; 02, oesophagus ; op, operculum ; p, penis ; pa, mantle; p.g, pedal ganglion ; pl.g, plural ganglion; ra, radula; 7.0, renal orifice ; 7.p, reno-pericardial orifice ; s.g, supra-intestinal gan- arin . . 2 y . : 7 glion ; si, siphon; s.gr, seminal groove; st, stomach; t, tentacle. (After F. M. Woodward.) the intestine. This structure is found in various Docoglossa, temporarily at least in Misswrella, in Trochus, in numerous Hydro- biidae such as Bithynia, Lithoglyphus, Spekeia, Tanganyicia (Fig. 78, cr.s), etc., in the Melaniidae and allied forms such as Paramelania, Nas- sopsis, Typhlobia, etc., and in Pteroceras (Fig. 75, cr.s) among the Strom- bidae. In many cases the stomach is furnished with a caecum, generally pyloric in position and contiguous to the openings of the hepatic ducts. This caecum is coiled in a spiral in many Rhipido- THE GASTROPODA 95 _ glossa, viz. in Plewrotomaria (Fig. 127, sp.c), Haliotis, the Turbinidae, etc., and in Nassopsis and Chytra (which, according to Moore, possess both the spiral caecum and the style-sac), but is simple and straight in Ampullaria, a large number of Opisthobranchia, the Limacinidae, the majority of the Cavoliniidae, Aplysia, several Doridomorpha (in which it is rugose internally, and has incorrectly been described as a “pancreas”), and finally in a number of Basommatophora, the Limnaeidae, and various Planorbidae. The liver or digestive gland constitutes the essential organ of digestion. It more or less completely surrounds the stomach, and is divided into lobes, the number and form of which vary in Fic. 76. Philine aperta, dorsal aspect; the body-wall is supposed to be transparent. a, anus; @.g, ab- dominal ganglion; c.g, cerebral ganglion; c.h, cephalie hood ; g, gill; g.o, genital (hermaphroditic) orifice; gz, gizzard; h, heart; in, intestine; k, Fic. 77 kidney; m, mouth; m.p, masticatory plate; os, osphradium; po, mantle; par, parapodia (lateral Alimentary canal of Zolis papil- lobe of foot); p.g, pedal ganglion; p./, inferior losa, dorsal view. an, anus; e, hind- pallial lobe; pl.g, pleural ganglion ; 7.m, retractor gut; h, hepatic appendages of the muscle of buccal mass; 7.0, renal opening; 7.p, mid-gut (all of which are not reno-pericardial opening ; s.g, seminal groove; sh, figured) ; m, mid-gut ; ph, pharynx. shell; s.i, supra-intestinal ganglion; st, stomach. (From Lankester, after Alder and (After Guiart.) Hancock.) different groups. Primitively there were two lobes, as in other Molluscs, and this number is, as a rule, retained in the Gastropods, but there are very few forms in which the lobes are equal and symmetrical, as in Neritina and Valrata. More frequently the topo- graphically left lobe is more deeply involved in the spire, and is larger from larval life onwards than the right lobe in dextral Gas- tropods (Figs. 61 and 116, B); the reverse is the case in sinistral forms. The right lobe may disappear, and the left lobe only persist 96 THE GASTROPODA in Paludina and Rissoa. But in Otina—a dextral form—it is the left lobe that is the smaller. The liver discharges its secretion into the stomach, but exceptionally it may discharge into the terminal part of the oesophagus or into the intestine (Philomycus bilineatus). As a rule there are two hepatic ducts whose openings into the stomach may sometimes be at some distance from one another (Natica), but may sometimes be fused as a result of specialisation, as in the majority of the Docoglossa, certain species of Murex, and some Euthyneura, viz. the Thecosomata (Fig. 60), Ancylus fluviatilis, Latia, etc. On the other hand, one of the orifices may be subdivided, so that three hepatic openings are formed, as in the Fissurellidae. In a few rare cases (Cyclostoma) isolated acini are found on the hepatic ducts, recalling the condition common in the Cephalopoda. Sometimes the liver lobes cover the whole stomach and open into it by multiple orifices ; this arrangement is found in various Opistho- branchs, such as Gastropteron and the Gymnosomata. ‘The extreme form of specialisation consists in the subdivision of the whole organ into tubes, which, like the gastric diverticula of Polyclads, extend through the greater part of the body, and even penetrate into external tegumentary appendages. ‘This peculiarity is found in many Nudibranchs, viz. the Eolidomorpha (Fig. 77) and the Elysiomorpha (excepting Cyerce and Lobiancoia), in which the rami- fications of the liver extend into the dorsal papillae, and in various Eolidomorpha communicate with cnidosaes, structures of ectodermic origin which in turn communicate with the exterior (p. 178). A similar arrangement occurs in the Polyclad Yungia. The digestive glands secrete a diastatic and peptic ferment, but in addition to their digestive properties they exercise, in the Euthyneura at least, an excretory function, and they also arrest the action of poisonous substances. Lastly, the digestive glands take a share in intestinal absorption. The intestine proper is a cylindrical tube, generally of uniform calibre throughout its course. It is sometimes separated from the stomach by a sort of valve. In nearly all cases it exhibits a well- marked longitudinal projection, the raphe or typhlosole, along a certain part of its course, and in some forms this projection is divided into two in such a manner as to form a groove bounded by two folds. In herbivorous Gastropods, such as Patella, the intes- tine is very long and thrown into coils; in carnivorous forms it is short and often straight as in Pteroceras (Fig. 75), Eolis (Fig. 77), Hemifusus (Fig. 99). The intestine traverses the ventricle of the heart in most Rhipi- doglossa (Fig. 55), the pericardium in Paludina, and the substance of the kidney in the Doliidae, Cassididae, Triton, and Fanella. In Murex, Purpura, and the Naticidae the rectal portion of the intestine is provided with a somewhat ramified gland, known as the anal THE GASTROPODA 97 gland, and in the Fissurellidae there is a longish glandular caecum in the same position, which opens near the anus and lies alongside the rectum as far as the point where the latter traverses the ven- tricle. Asa rule, the anus opens on the right side of the body (on the left side in sinistral forms) and more or less in front. But in those forms in which the coiling of the visceral sac is diminished or lost, this flexure of the digestive canal seems to be effaced and the anus lies at the posterior end of the body. This disposition is rare 1 a8 3 L : Ws AAC 4, Lg Fic. 78. Tanganyicia rufilosa, dorsal view, with the mantle laid open. a, anus; b.p, brood-pouch ; b.p.o, orifice of brood-pouch ; ce.g, cerebral ganglion ; c7.s, crystalline style; f, foot; g, gill; h, heart ; in, origin of the intestine or pyloric orifice of the stomach ; m, mouth ; od, oviduct; oe, termination of the oesophagus, or cardiac orifice of the stomach ; 0.0, oviducal orifice ; os, Osphradium ; pa, mantle; st, stomach ; s.i.g, supra-intestinal ganglion. (After Moore.) in the Streptoneura, but may be seen in Cypraea and Pterotrachea. It is, on the contrary, common in the Euthyneura, occurring in Doridium, Runcina, Aplysia (Fig. 154), the Doridomorpha (Fig. 79, VIII), Janus, Alderia, Limapontia, Testacella, the Oncidiidae (Fig. 59), and the Vaginulidae (Fig. 87). 2. The Circulatory System.—The blood is generally a colourless liquid containing amoebocytes. It is red in the genus Planorbis (with the exception of P. albus), in which haemoglobin is diffused in the plasma. The muscles of the buccal mass are impregnated 7 98 THE GASTROPODA by haemoglobin in a fairly large number of Streptoneura, ¢.9. Littorina, Buccinum, Natica, ete. In some few Gastropods the blood is of a bluish tint in consequence of the presence of an albuminoid containing copper called haemocyanin. In other cases the blood is coloured by pigments of extraneous origin absorbed by the amoe- bocytes ; this is the origin of the violet-red colour of the blood of Fusciolaria. In various Opisthobranchs, viz. Bullomorpha, Pleuro- branchidae, Doridomorpha (Fig. 79, XVII), there is a differentiated lymphatic gland, situated as a rule more or less anterior to the heart on the aorta. In a certain number of Streptoneura this organ consists of a sinus filled with cytogenous connective tissue and situated near the kidney ; in other cases it is diffused through the subcutaneous connective tissue. The heart is always dorsal and in the immediate neighbourhood of the respiratory apparatus (Figs. 79 and 82). It is only in the very archaic forms such as Pleurotomaria and the Fissurellidae, that it is still symmetrical and median as in the Cephalopods, Lamel- libranchs, and Amphineura, otherwise it is nearly always lateral, being situated on the left in dextral forms (Fig. 67). It is generally somewhat anterior in position (Figs. 82 and 88), but it may become posterior again as a result of secondary specialisation as in Pterotrachea (Fig. 143), Testacella, Oneidiwm, Peronia, and the Doridomorpha, and in the last named it resumes an apparent external symmetry (Fig. 79). The heart of Gastropods always includes an ovoid or piriform ventricle, and in the Rhipidoglossa (with the exception of the Helicinidae, Hydrocenidae, and Proserpinidae) two auricles, but the latter only retain their primitive symmetry in the Fis- surellidae, in which the ctenidia themselves retain their symmetry and the heart is median. In other Khipidoglossa, in which the heart is no longer median, the right auricle is the smaller (Fig. 55, VII), and it becomes more and more rudimentary. In all other Gastropods there is only one auricle, situated on the topographically left side (Fig. 82, aw): it is generally larger than the ventricle, but . its muscular fibres are fewer in number and its walls are thin, transparent, and extensible. The ventricle is traversed by the rectum in the Rhipidoglossa (except the Helicinidae), and in the more archaic forms is placed between the two-auricles, e.g. in Pleuro- tomaria (Fig. 127, h), Trochus (Fig. 55, VIII), ete. In the majority of the Streptoneura (Fig. 99, V), in the Pulmonates (Fig. 86, VII), and in some Bullomorpha—e.g. Actaeon, Limacina (Fig. 63), Clio virgula, and Clio acicula—this ventricle is posterior to the single auricle; in some Opisthobranchs (Phyllirhoé, Fig. 161) and Heteropods the auricle and ventricle are on the same transverse line, and in the majority of Opisthobranchs (Figs. 79, III, and 92, I), the Testacellidae, Oncidiidae, Pterotracheidae, and certain Calyptraeidae the ventricle is in front of the auricle. In adult THE GASTROPODA 99 individuals, during normal respiration, the ventricle beats not more than one hundred times nor less than thirty times in a minute. XVII XVI Vil Nin Fic. 79. Doris pilosa, opened dorsally. I, stomach ; II, liver; III, ventricle of heart ; IV, pericardium laid open; V, pallial vein; VI, gill; VII, branchial vein; VIII, anus; IX, renal pore; X, auricle ; XI, reno-pericardial orifice ; XII, posterior part of intestine (the anterior part is on the left); XIII, kidney; XIV, accessory genital glands; XV, tentacle; XVI, central nervous system ; XVII, hematic gland; XVIII, salivary gland; XIX, oesophagus. (After Hancock.) The mean frequency of the pulsations is sixty to the minute in forms most easily observed, such as Pulmonates, Nudibranchs, 100 THE GASTROPODA Bullomorpha, Thecosomata, and Heteropoda. During hibernation the heart of Gastropods does not beat more than twice a minute. The Gastropods in general have a well-developed arterial system, but the venous system is for the most part lacunar. A single artery takes its origin from the end of the ventricle opposite to the auricle—or from the posterior end of the ventricle in diotocardiate Rhipidoglossa—but in the Docoglossa (Fig. 82) one of its branches, namely, the genital artery, appears to have a distinct origin, as in the Cephalopoda. An intra- pericardial aortic bulb is found at the origin of the aorta in Putella (Fig. 80, V), various species of Fissurella, Ampullaria, Natica, and the Heteropoda, and a similar Fic. 80. but extra - pericardial bulb Heart of Patella vulgata, the auricle and ventricle in Stphonaria. In certain opened. I, ‘‘ branchial” vein ; [I, auriculo-ventricular valve; III, posterior aorta; IV, valve between the Heteropoda, ‘Thecosomata, ventricle and the aortic bulb; V, aortic bulb; VI, Tess : anterior aorta; VII, ventricle, with its internal and Nudibranchs there IS a muscule cola: VUTL aunels 1% pore laine valve at the origin of the cavity. (After Wegmann.) aorta. The ramifications of the aorta form an arterial system extending throughout the body, which is continued into a system of interorganic lacunae, without epithelial walls, into which the arterial trunks sometimes open suddenly by contractile orifices ; for instance, the cephalic artery of Patella and Haliotis, the pedal artery of Heteropods, the cephalic artery of ‘Thecosomata, ete. The venous blood is collected from the lacunar system into two large and important sinuses—an anterior or cephalo-pedal sinus and a posterior abdominal or visceral sinus. These two blood-spaces open into an anterior abdominal sinus lying beneath the pericardium. From the last named the blood is carried to the roof of the pallial cavity for oxygenation, on the right side by the rectal sinus (external to the rectum), on the left side by the more or less well- defined lateral sinus which runs along the anterior border of the mantle, and forms the “ pulmonary artery” in Pulmonata. Thus the venous section of the circulatory system ends in regular vessels, and in Aplysia the great abdominal sinus may be seen to open abruptly, by gaping orifices, into the afferent branchial vessel. The blood is carried from the rectal sinus to the respiratory apparatus by a transverse vessel or by a vascular network which generally forms an afferent branchial sinus running along the whole length of the branchia on the right side. But a very large part of the venous blood, larger in the archaic than in the more specialised THE GASTROPODA IOI forms, passes into the kidney by means of a portal system, and the efferent renal vein generally joins the rectal sinus or is carried direct to the afferent branchial sinus (Valvata). The venous blood of the kidney is therefore carried to the respiratory organs before it is returned to the heart; but in some Streptoneura (Vermetus, Littorina, Cyclostoma) and in certain Pulmonates the blood is carried direct to the auricle without passing through the respiratory apparatus. The respiration of Gastropods is primitively aquatic and remains so in the majority of forms. The organs of aquatic respiration consist of a pair of leafy expansions of the mantle, situated in the pallial cavity and called ctenidia. 2, Each ctenidium is the homologue of a 4 hy Ai single branchia of Chiton (Fig. 28, B, q), q \ () Ff of Nautilus (Fig. 276), or of Nucula . HV I\Z i . d WANG li (Fig. 206), but most usually only one, ‘ J Hl. namely, that of the topographically left | (G \ side, persists (Figs. 82 and 85). It is aa aN {] fy only in the more primitive Rhipido- 7%; ees glossa—viz. the Pleurotomaridae (Fig. > wa 127), the Fissurellidae (Fig. 81), and i Ce the Haliotidae—that a pair of ctenidia on ay persists. In the Fissurellidae these two : x fs organs are quite symmetrical and of 5 SSS ff equal importance, but in the Pleuro- a ie tomariidae and Haliotidae the topo- graphically right ctenidium is smaller than the left, and in all other Gastropods there is only a single ctenidium, that of the right side having completely dis- appeared. In all the Streptoneura, the Pleurobranchidae, Gastropteron, and the Dorsal view of a specimen of Fissurella from which the shell has been removed, and the anterior area of the mantle-skirt has been longi- tudinally slit and its sides reflected. a, cephalic tentacle; b, foot; d, left (archaic right) gill-plume; e, reflected mantle-flap ; ji, the fissure or hole in the mantle-flap traversed by the longitudinal incision; f, right (ar- chaic left) renal aperture; g, anus ; h, left (archaic right) renal aperture ; Lophocercidae each ctenidium is formed PR aiGAE EEL of flattened respiratory filaments which lie parallel to one another and are disposed perpendicularly along one or two faces of a branchial axis. Such a ctenidium is called “pectinate.” In the Opisthobranchs—the only Euthyneura that possess ctenidia—the ctenidium is a simple flat and projecting tegumentary lamina, transversely folded from its base to its ex- tremity in such a manner that the ridges of one face correspond to the furrows of the other face: such a branchia is called “ plicate.” Among the dibranchiate Aspidobranchs, Pleuwrotomaria, the Fissurellidae, and the Haliotidae have two rows of pectinations to each ctenidium, one on either face of the branchial axis (Fig. 81). Each ctendium is therefore formed like that of Chiton, Nautilus, or 102 THE GASTROPODA Nucula, and is similarly free to a greater or less extent at its distal extremity. But in Scisswrella (Fig. 54, IV) the right etenidium is already degenerate in so far that it has only a single row of filaments inserted directly on the wali of the pallial cavity. The other ctenidiate Aspidobranchs have only a single and equally bipectinate ctenidium, as has also Valvata (Fig. 132, gi). The two rows of respiratory filaments are equal in the dibranchiate Rhipidoglossa, in the Acmaeidae and Valvatidae, but in the mono- branchiate Rhipidoglossa the dorsal row—that is to say, the row between the mantle and’ the branchial axis—is already much reduced, and in the remainder of the Streptoneura this row of filaments has disappeared, as in the right ctenidium of Scissurella, and the single ctenidium is attached to the mantle for the whole of its length (Fig. 99, XVII). The individual branchial filaments are Fic. 82. Anterior part of the body of Acmaea, showing nervous and circulatory systems, dorsal aspect. «.g, abdominal ganglion; ao, aorta; au, auricle; b7.n, branchial (ctenidial) nerve ; br.v, branchial vein; ce.g, cerebral ganglion; gi, gill; 7.7.9, infra-intestinal ganglion; mu, columellar muscle ; 0s’, os’, left and right osphradia ; pa, mantle; pa.v, pallial vein ; pe.c, pedal cord ; pe.g, pedal ganglion ; pl.g, pleural ganglion ; s.i.g, supra-intestinal ganglion ; te, tentacle ; we, ventricle. usually simple, but sometimes their surfaces are folded, and again each filament may be in its turn leafy or beset with plications as in the Cephalopoda: this condition is found in Janthina. Each filament is a simple tegumentary projection without any internal endothelial lining. The wall of the blood-space contained in it is formed of connective tissue, thickened and compacted along the borders of the filament, where it forms a supporting structure, specially well developed on the ventral side. By these means the rigidity of the filaments, which are often very long as in Calyptraea, etc., is ensured. The cavities of the filaments are traversed by muscular trabeculae, by whose agency the whole filament may be contracted. In spite of the presence of ctenidial branchiae, there is a certain number of Gastropods in which the oxygenated blood returned to the auricle is not derived from these organs alone. A considerable quantity may come from various other parts of the mantle, or, in THE GASTROPODA 103 forms in which the mantle has disappeared as a shell-forming organ, from the dorsal envelope of the body, which in this case serves as an accessory respiratory organ. This phenomenon is to be seen in the Acmaeidae (Fig. 82, pa.v), the Heteropoda, the Pleuro- branchidae, and the Pneumo- dermatidae, these last-named families being naked. In the Pleurobranchidae, the Hetero- poda, and certain Acmaeidae the mantle is no longer fur- nished with accessory respira- tory structures, but in other Acmaeidae, such as Scwiria, ete., and certain Pneumoder- matidae (Fig. 84, VI, VII), a Fia. 84. Pneunonoderma, right-side view, with the head above. I, the expanded proboscis; II, anterior tentacle; III, posterior teutacle; IV, genital (herma- phroditic) opening; V, right fin; VI, Fig. 83. etenidium ; VII, posterior pallial gill; Tritonia lineata, dorsal view. VIII, posterior lobe of the foot; IX, I, rhinophore or _ posterior reno-anal cloaca; X, lateral margin of tentacle; II, dorsal appendage the foot; XI, penial orifice; XII, (pallial gill); III, right eye; sucker-bearing appendage; XIII, ven- IV, frontal veil; o, genital tral median papilla of the proboscis ; (hermaphroditic) orifice. (After XIV, seat of the mandibles; XV, ex- Hancock.) panded right hook-sack. ctenidium, or branchia properly so called, coexists with secondary respiratory organs or pallial branchiae: these lie below the mantle edge in Scurria and on the free surface of the posterior part of the body in the Pneumodermatidae. If the ctenidium is atrophied and disappears altogether, the mantle itself resumes the respiratory function which was previously localised in the ctenidium. This 104 THE GASTROPODA phenomenon may be found both in aquatic species and in forms adapted to terrestrial life, the different modifications of the mantle being as follows :— (1) There may be branchial structures varying in form and position, but not homologous to a ctenidium. In the Docoglossa these pallial branchiae are situated on the internal face of the mantle, as in Patella (Fig. 125, f). In various Gymnosomata (Clionopsis, Notobranchaea, ete.) they are situated on the posterior surface of the body as in the Pneumodermatidae. In the majority of the Nudibranchs they are on the dorsal surface of the body, sometimes localised round the anus as in the Doridomorpha (Fig. 79), sometimes concealed below a fold of the dorsal integu- ment as in Plewrophyllidia and certain porostomatous Doridomorpha, Phyllidia, and Corambe (Fig. 164, g). Or all kinds of accessory branchial formations may have disappeared, and the function of respiration is distributed over the whole free surface of the pallial integuments, as may be seen in various Docoglossa such as the Lepetidae and Bathysciadium ; in Firoloida among the Heteropoda ; in Dermatobranchus, Heterodoris, the Elysiomorpha (with the ex- ception of the Hermaeidae), and Phyllirhoé (Fig. 161) among the Nudibranchs ; in the Clionidae and Halopsychidae (Fig. 156) among the Gymnosomata. (2) An adaptation to a terrestrial life and the pulmonary respiration resulting therefrom is found in very different groups of Gastropods, but the different stages of evolution are best studied in the Streptoneura. In this group certain aquatic and littoral forms, though they possess ctenidia, have acquired the habit of living for a longer or shorter time beyond the reach of the water. This is the case with various species of Littorinu (L. rudis, L. neritoides, etc.), Cremnoconchus, Neritodryas, several Cerithiidae, etc. Consequently certain modifications of the internal surface of the mantle are induced, in the interior of the pallial or respiratory cavity. The filaments of the ctenidium— bipectinate in Neritodryas, but monopectinate in other forms—are often reduced in height and are prolonged more or less indefinitely on the right side “of the internal pallial surface to form vascular arborisations, as may be seen in the semi-aerial species of Lattorma (Fig. 85, x) and in Cremnoconchus. Finally, the ctenidium disappears altogether, and with it the hypobranchial gland and the efferent branchial sinus, and the venous blood of the rectal sinus is con- ducted to the afferent cardiac vein (corresponding to the efferent branchial vein) by the system of arborisations that extends over the whole roof of the pallial chamber. Such is the case in Cerithidea obtusa, which retains only the vestiges of the anterior extremity of the ctenidium. In many aerial Gastropods the ctenidium has totally disappeared and the roof of the pallial cavity THE GASTROPODA 105 is permeated by a rich vascular network (Fig. 86) in which the blood is oxygenated. In this manner the respiratory pallial chamber is transformed into a pulmonary cavity or lung, whose vascularised surface is irrigated by the blood derived from various parts of the body. The “lung” of Gastropods, then, is not a spongy organ, but a cavity strictly homologous to the pallial cavity. The pulmonate Gastropods exhibiting this structure are polyphyletic, that is to say, they belong to several different groups. Among the Strepto- neura we find three families of Via. 85. Littorina littorea, male, removed from its shell; dorsal aspect ; the mantle-skirt cut along its right line of attachment and thrown over to the left side of the animal so as to expose the Fia. 86. organs of its inner surface. «a, anus; br, : ctenidium ; c, heart; h, liver; i, intestine; m.c, Roof of the pallial cavity (lung) of columellar muscle (muscular process grasping Limax. Ventral aspect. I, cloacal (reno- the shell); p, penis; p.br, osphradium; 7, anal) orifice ; II, pneumostome ; III, reno- kidney ; 7’, aperture of the kidney ; ¢, testis; v, pericardial orifice; IV, rectum; V, renal stomach ; v.d, vas deferens ; v.d’, the groove-like duct; VI, kidney; VII, heart - ventricle ; part of latter; 7, vascular prolongations of the VIII, pericardium (cut open); TX, heart- ctenidial leaflets; y, hypobranchial gland. auricle ; X, ramifications of the pulmonary (From Lankester, after Souleyet.) vein. (After Leidy.) Rhipidoelossa, viz. the Helicinidae, Proserpinidae, and Hydrocenidae ; and three sub-groups of Taenioglossa without probosces, viz. the Cyclophoridae, Cyclostomatidae, and Aciculidae; and among the Euthyneura all the Pulmonates proper, including the aquatic as well as the terrestrial forms. In one family only of the Strepto- neura, the Ampullariidae, is the ctenidium preserved at the same time that a pulmonary cavity is present. In this family the pallial cavity is divided by an incomplete septum into a lung and a branchial cavity, the former being situated to the left of the ctenidium. The animal is therefore able to breathe by its gill in the water, and by its lung when out of the water, the air being 106 THE GASTROPODA admitted by a very extensible pallial siphon. In the pulmonate Streptoneura the pulmonary chamber retains the whole of the primitive opening of the pallial cavity ; in the Euthyneura, on the contrary, the opening of the lung or pneumostome is much reduced by the fusion of a large extent of the mantle border with the neck of the animal, a fusion that leaves only a minimal but extensible posterior aperture (Fig. 177, V) in the neighbourhood of the anus. This disposition allows of the blood, on its arrival at the lung, being carried round a more or less annular cireumpulmonary venous sinus. In the Oncidiidae the lung is somewhat rudimentary, being reduced to arborisations ramifying among the lobes of the kidney. In other Pulmonates such as Ancylus and the Vaginulidae (Fig. 87) the reduction of the lung is carried to the point of complete disappearance. Finally, there is a family of Pulmonates in which, instead of a vascularised lung, there is a pulmonary / | of ze leap abs Fic. 87. Vaginula occidentalis, right-side view, with the mantle partially removed on this side. an, anus; aur, auricle ; o.f, female orifice ; 0.7, renal opening in the rectum ; 0.7.p, reno-pericardial pore ; 0.7.u, orifice of the kidney in'the ureter ; p, foot ; pa, mantle ; pe, pericardium ; r, kidney ; ve, rectum (the dotted line shows the direction of the intestine); ten, tentacles; wr’, wr”, primary and secondary ureters ; ven, ventricle. chamber continued into numerous tubules which penetrate into the surrounding blood sinuses: these fracheate Pulmonates are the Janellidae (Fig. 90, tr). A large number of Pulmonate Gastro- pods, while preserving their aerial respiration, have returned to an aquatic life; such are the Basommatophora (Limnaeidae, ete.). Among these the marine genera Amphibola, Siphonaria, and Gadinia ; Limnaea abyssicola, an inhabitant of deep lakes; and Planorbis nautilus, have a pallial pulmonary cavity which, instead of being filled with air, may temporarily or continuously be filled with water, as in the larvae of aquatic Pulmonates. Here we see a return and readaptation to aquatic respiration, but for all that the ctenidium does not reappear, a fact which illustrates the irreversibility of evolution. But in these cases respiratory pallial outgrowths or secondary branchiae may be formed near the opening of the pulmonary cavity or even in its interior. Such is the contractile extrapulmonary tegumentary appendage at the base of which the anus opens in Planorbis (as this is a sinistral THE GASTROPODA 107 genus the appendage is to the left of the pallial aperture). In Planorbis corneus (Fig. 89, g) there is a single respiratory lobe, with a richly vascularised surface, and in Ancylus there is a similar | rd odin V Fic, 8s. Diagram of a sagittal section of Patella vulgata. br.a, branchial afferent vessel (artery) ; br.v, branchial efferent vessel (vein); b.v, blood-vessel ; ec, muscular substance forming the root of the foot ; cor, heart within the pericardium ; e, mantle-skirt ; f, papilla of the larger kidney ; g, anus ; 7, smaller kidney ; k, larger kidney ; 1, pericardium ; 7, liver; 0, mouth ; od.m, muscles and cartilage of the odontophore; p, snout; g, intestine in transverse section; 7, radular or lingual sac ; rd, radula; s, lamellated stomach ; ¢t, salivary gland; u, duct of same; 7, buecal cavity; w, gonad. (After Lankester.) structure, but the lung has disappeared. In Lulinus, including the sub-genera Jstdora, Pulmobranchia, etc., and in Miratesta there is a folded branchia. In Siphonarw the long plicated branchia which extends across the interior of the roof of the pulmonary Fic. 89. Planorbis corneus, removed from the shell; anterior view. «@, anus; f/f, foot; g, gill; k.o, renal aperture; m, mouth; os, osphradium; pu, mantle; pn, pneumostome; s/, pulmonary siphon. cavity, between the kidney and the rectum, is of the same character. This branchia is situated more posteriorly and to the right than the ctenidium of monobranchiate Gastropods (Fig. 174). The diverse characters of the respiratory apparatus of Gastropoda may be advantageously summed up in the following table :— THE GASTROPODA 108 ‘snjhoupy ‘pISaMIY ‘snuyng ‘snousoa siquoung js Adossadoe Arvuowyndetyxe \ , [ts Azosseooe Areuowynderzut f “DrLmUoydry ‘pynubn 4 ‘snaqzunnu sigLounjg “njoosshqn naw \ “UIT ‘nupyp ‘wuupyy ‘njoqrydwp J ‘piunjauloay ‘aepltnoly ‘oepryeuloys | -opok¢ ‘aeprtoydopaAg ‘ovpiurdaesoig = ‘aepruoooipAP ‘oeplurorpoyy ‘eyeuoung | ‘DIDYIUDLQOIONT \ . ‘sasdouoyg ‘eiourtqipun ‘eepryozeg f ‘ayoisdoynyyT ‘auoug ‘wprojoug \ “oylppiyg “eydiomorss{q ‘ovepryedary f “prsojyyndue ‘auprTRULlopououlneug pue oeproenloy ‘ARPIOVULOY IULOS pUv avpTITPOUBIGOINe,g “A[[RloMas VITPOURIGT}O9T, ‘AT[BIOUIS vIIpOURIqIUL}Oeg “esso[Hopldiyy, “2ynaA)n A “DJ ALNSSVO) ‘IEPTJOLULV]ET PUB M20 WOZOLNALT “OB PI[[OINSST Suny ojenbe yy Suny [ewe YyLM i s][to Atosseoor am | * td Arossooov ynoyyta | : : : : ; : ayeulqzoodouout f Lede, WoIywUtyoed [eiquea el ayeurqoadiq peqeurqood | ‘TeIpIU9}OOUOUL * — suotyeutqood yenbe Z yAIM * Joqyvals WMNIpIuezo 4yoT WAI * vrplueyo peotujouuds Z aE} eppreede aqumjoadiq % YyTM | Suny JHoy4IM pue [[Ls Arosseooe YALA . : ayeurood -OUOW WNIPIW9}0 JUST YT : rae ue pur Suny @ YAIA (Suny ou) Arequeunse4 SILYZVaIq [VTE Suny 8 Aq AToatsnjoxe 2 * otzenbe onay * Suny B yas | So vamar [ts Atosseo0e YUM i dca [[15 Atossaoon qnoygra | EeeTed ee bese 10) TIES yqta Suryyearq [erpra}) [erpruozorq THE GASTROPODA 109 3. Hxcretory Organs.—In the Gastropoda the kidneys are the essential organs of excretion, but the pericardial glands serve as accessory excretory organs, as also certain parts of the body in which the products of excretion are collected, forming veritable accumulative kidneys. (1) The kidneys are originally paired, as in all other Mollusca, and a single pair is found (Figs. 55, III, XIII; 81, f, h; 91, 127) in all the Aspidobranchia, except the Neritacea, including the Neritidae and allied families. These two kidneys open one on each side of the anus, but they do not retain their primitive symmetry in any Gastropod, and although they are independent of one another, the topographically left kidney is rudimentary, and that of the right side alone is functional in almost every case. See SENS ee «ott MANNS Reine Sh USA x RUDE es Wintly GAIN SNe ee ; ae Fic. 90. Transverse section of the lung of Janella. k, ureter; pa.c, pallial or pulmonary cavity ; po, pneumostome ; si, blood sinus ; tr, ‘‘ tracheae” or diverticula of the pulmonary cavity. (After Plate.) In the Neritacea (Neritidae, Titiscaniidae, Helicinidae, Hydro- cenidae, and Proserpinidae) and in all the Pectinibranchia and Euthyneura the topographically right kidney no longer exists. In Paludina the two kidneys coexist during development, but in the adult that of the topographical right side has disappeared. As regards the position of these organs, their primitive situation is wholly within the visceral mass (Docoglossa, Fig. 88, i), and their migration outside the visceral mass is a specialisation which begins to show itself in the Rhipidoglossa—at any rate, in the case of the left kidney (Fig. 127)—and is completely realised in the case of the single kidney in other Streptoneura and Tectibranchia, in which the excretory organ is more and more localised in the mantle (Figs. 75,k; 63,7). The kidney is always a dorsal organ, situated in the neighbourhood of the pericardium, with which it communicates by a ciliated aperture. In the detorted Aspidobranchs (Fissurellidae), however, the very rudimentary left kidney has lost this pericardial 110 THE GASTROPODA communication. lysiw is exceptional in that the kidney is placed below and partly surrounds the pericardium, and the reno-pericardial orifices are multiple, some ten being present (Fig. 92). Asa rule the external opening of the kidney is situated near the anus (Figs. 81 and 88), and sometimes the two open together into a sort of common cloaca, as may be seen in the Gymnosomata (Fig. 84, IX) and in certain Pulmonates, such as Limaz (Fig. 86, I), the Onci- diidae (Fig. 59), and Vaginula (Fig. 87), but not in V. willeyi. In rare cases, however, such as the Nudibranch Janus, the excretory aperture is distant from the anus. The external renal orifice is borne on a papilla in various Aspidobranchs with two kidneys (Fig. 88, 7), but is a simple slit, shaped like a button-hole, in the majority of Pectinibranchia (Fig. 99, IV) and Tectibranchia (Fig. 154, 0). Among the Pee- tinibranchs, however, Paludina hest Fic. 91. Diagram of the two renal organs of Patella, to show their relations to the rectum and to the pericardium. /, papilla of the larger kidney; g, anal papilla, with rectum leading from it; h, papilla of the smaller kidney, which is only represented by dotted outlines ; l, peri- cardium, indicated by a dotted outline (at its right side are seen the two reno- Fic. 92. pericardial pores) ; ff, the sub-anal tract of the large kidney given off near its papilla and seen through the unshaded smaller kidney ; ks.a, anterior superior lobe of the large kidney ; ks./, left lobe of same; ks.i, inferior sub-visceral lobe of same; ks.p, posterior lobe of the Elysia viridis, heart and kidney, dorsal aspect (somewhat schematic). I, ventricle of heart; II, external renal pore; III, auricle; IV, kidney; V, the various reno-pericardial pores on the left side (there are five such pores on the right-hand side); VI, the ventral right kidney. (After Lankester.) reno-pericardial pore ; VII, pericardium. and Valvata are exceptional in possessing an ureter which opens at the edge of the mantle. The same arrangement is found in many Pulmonata, especially in the Stylommatophora, in which an elongated ureter opens alongside of the anus at the margin of the pneumo- stome (Fig. 86, V). As regards its structure, the kidney in its simplest form is a sac lined by a secretory epithelium. By the infolding of its walls, the cavity of the sac is subdivided and the organ acquires an alveolar structure of spongy appearance, but in various pelagic forms it again becomes more or less tubular and transparent, e.g. in the Heteropoda (Fig. 141, q), in certain “ Pteropoda” (Fig. 60, ), THE GASTROPODA Til in Phyllirhoé (Fig. 161, 1). As a rule the kidney is a compact mass, without external projections, but it is divided into two lobes in Stenoglossa in general and also in some Taenioglossa, viz. Paludina and Cypraea. In a fairly large number of Nudibranchs (Dorido- morpha, Janus, etc.) the kidney is divided into ramifications which extend between the visceral organs of the greater part of the body (Fig. 79, XIII). In sundry Pectinibranchs—e.g. Littorina—there is a “nephric gland” which opens into the kidney, and consists of ciliated canals surrounded by conjunctive tissue. In addition to its excretory function the kidney may also serve for the conduction of the genital products. Thus in all Gastropoda with two kidneys, that is to say, in all the Aspidobranchia (Pleuwrotomaria, Trochus, Fig. 55, Fissurellidae, etc.) except the Neritacea, the gonad opens into the right kidney by a papilla situated near the external renal aperture. (2) The pericardial glands in the Aspidobranchs and Valvata are placed on the external walls of the auricles. In other forms they are localised on the internal wall of the pericardium, as in Littorina and Cyclostoma among the Pectinibranchs and in the Pleurobranchidae and Nudibranchia among the Opisthobranchs, or they are situated within the pericardium on the origin of the aorta, as in Aplysiidae. (3) Various excretory products may be accumulated in plasmatic cells (known as the “cells of Leydig”) in the conjunctive tissue of different parts of the body. This phenomenon is particularly common on the walls of arterial trunks, and may be seen in the caudal artery of Curinaria, and on the wall of the arterial trunks of certain Streptoneura and many terrestrial Pulmonates, in which caleareous concretions are found in the perivascular conjunctive tissue. The different forms of excretory apparatus and the special function of each can be revealed by the method of physiological injections. 4. Nervous System.—With the exception of the endoparasitic Entoconchidae, all Gastropods possess a well-developed nervous system in which the same cerebral, pedal, pleural, visceral, and stomato-gastric nerve-centres, and the same connectives and com- missures, are to be found as in other Molluscs. But the special character of the Gastropod nervous system is the asymmetry of the visceral centres and of the nerves arising from them, an asymmetry resulting from that of the visceral organs themselves. The most primitive form of nervous system is characterised, as in the Poly- placophora, by the absence of concentration in the ganglia. The cerebral centres in the Rhipidoglossa are situated at the sides of the oesophagus and are united by a long commissure which is itself ganglionated (Fig. 94). The pedal centres in Aspidobranchs (Fig. 94, pe.c), Paludina, and some other taenioglossate Pectinibranchs £12 THE GASTROPODA such as Cyclophorus and Cypraea, have the form of long ganglionated cords with multiple commissures or anastomoses. The pleural ganglia are but slightly differentiated in Pleurotomaria, in which genus they are placed on the dorsal pedal connective, at a nearly equal distance from the cerebral and pedal centres (Fig. 94, pl.c). In forms in which they are better developed, the pleural ganglia are still in intimate contact with the anterior part of the pedal centres, and there are two long connectives, the cerebro-pleural and the AVII Be Te Vin Fic. 93. Central nervous system of Patella vulgata, dorsalaspect. I, tentacular nerve ; II, left cerebral ganglion ; III, cerebro-pedal connective ; IV, cerebro-pleural connective ; V, left otocyst ; VI, left osphradium ; VII, pallial nerve ; VIII, anterior part of the pedal cord ; IX, supra-intestinal ganglion; X, pedal cords (their posterior endings are not drawn); XI, abdominal ganglion ; XII, pleural ganglion ; XIII, otocystic nerve; XIV, stomato-gastric ganglion ; XV, optic nerve ; XVI, labial commissure ; XVII, cerebral commissure. cerebro-pedal, on either side of the digestive tube, the pleuro-pedal connective being, on the contrary, very short. This arrangement is known as the ‘‘hypoathroid,” and is found in Aspidobranchia (Fig. 93) and several Taenioglossa, viz. Ampullaria, Cyclophorus, and Nassopsis. As a result of specialisation we get the ‘‘ dystenoid ” condition, in which the cerebral centres are approximated and the pleural ganglia are shifted nearer to the cerebrals, so that the pleuro-pedal connectives are elongated (Fig. 123, A). Finally, in the “ epiathroid ” condition, the pleural centres are either in contact or are fused with the cerebrals (Fig. 123, B), as is the case in the THE GASTROPODA 113 majority of the Pectinibranchia, including the Heteropoda, and in various Bullomorpha (¢.g. Actaeon, Fig. 57) and the thecosomatous “‘Pteropods” among the Opisthobranchia. At the same time the pedal ganglia are concentrated anteriorly to form more or less globular masses (Fig. 123, C, pe.q). Primitively the visceral commissure is somewhat extensive, and its ganglionic centres are tolerably far removed from one another, as may be seen in all the Streptoneura and the less specialised Euthyneura (Figs. 94, 57, etc.). These ganglionic centres are normally three in number: one is median, and is called the abdominal or the visceral ganglion proper (Fig. 93, XI); two are lateral, placed right and left on correspond- ing sides of the visceral commissure. The ganglion on the morphologically left side may be but slightly developed or may not be differentiated at all, as, for example, in monobranchiate Khipidoglossa. In con- sequence of the torsion of the visceral mass of Gastropoda, the visceral commissure is normally twisted into a figure of eight ; that is to say, the right moiety with the visceral ganglion is situated above the alimentary tract and is displaced to the left, the left moiety remains below the alimentary tract, but is inclined to the right (Fig. 57). Hence Fic. 94. the names supra-intestinal and infra-intestinal are respectively given to the two moieties and to the ganglia borne on them (Fig. 123), This disposition of the visceral com- missure is common to all the Streptoneura (as the name of the group signifies), in- cluding the Heteropoda and all the forms formerly called ‘“Orthoneura,” ic. forms in which the visceral loop was believed to have never been twisted ; it may also be clearly seen in the more archaic Euthyneura (which, Pleurotomaria, nervous system, dorsal aspect. br.g, branchial ganglion ; ¢.c, cerebral commissure; ¢.p.c, cerebro- pedal commissure; e.pl.c, cerebro - pleural commissure ; i.i, infra-intestinal portion of the visceral commissure ; la.c labial cominissure ; ot, otocyst ; pa.n, pallial nerve; pe.c, pedal cord ; pl.c, pleural centre ; pl.p.c, pleuro-pedal connec- tive; s.i, supra-intestinal part of the visceral commissure ; st.g, stomato-gastrie ganglion. (After F. M. Woodward.) as has been explained above, are detorted Gastropods), for instance, in various Bullomorpha (Actacon, Fig. 57, Scaphander, Bulla, ete.), and in Chilina. But in the three last-named genera the detorsion of the visceral commissure is already manifest, that is to say, its supra-intestinal moiety shows a tendency to return to the lower side of the alimentary tract, and its sub-intestinal moiety tends to return to the left side. This detorsion of the visceral commissure is complete in the rest of the Euthyneura, as may be 8 114 THE GASTROPODA seen in the Opisthobranchia (Figs. 95 and 159) and the Pulmonata (Figs. 96 and 97). Further, in all the Euthyneura but those which are the most primitive from this point of view, such as the Bullomorpha and Fig. 95. Nervous system of Aplysia (dorsal aspect), as a type of the long-looped Euthyneurous con- dition. The untwisted visceral loop is lightly shaded. ab.sp, visceral ganglion which repre- sents the abdominal + the supra- intestinal ganglia of Streptoneura, and gives off the nerve to the osphradium and another to an unlettered so-called “ genital ” ganglion; ce, cerebral ganglion ; o, osphradium ; pe, pedal ganglion and double pedal commissure ; pl, pleural ganglion (the stomato- gastric commissure and ganglia are omitted). (From Lankester, after Spengel.) Aplysia among the Opisthobranchs, the Auriculidae, Chilina, and Latia among the Pulmonata, there is a tendency to the approximation of the ganglionic centres and at the same time a shortening of the visceral commissure. This is carried so far that the ganglia come into contact and form a chain of several united nerve- centres between the pleural ganglia (Fig. 97). When it has reached this stage of evolution the whole nervous system is Fic. 96. Latia neritoides, central nervous system, dorsal view (the buccal mass is indicated by a dotted line). bu, buceal mass; co.vi, visceral commissure; 9.@, abdominal ganglion; g.bu, buccal ganglion; 4g.ce, cerebral ganglion; g.i.i, infra-intestinal ganglion ; g.pa, parietal ganglion; g.pe, pedal ganglion and double pedal commissure; g.p/, pleural ganglion ; g.s.i, supra-intestinal ganglion; 7.p.i, nerve of the inferior pallial lobe ; osp, osphradium ; rad, radula. concentrated in the cephalic region round the anterior part of the oesophagus, and finally all the ganglia—cerebral, pleural, pedal, and visceral are intimately united and localised on the dorsal surface of the oesophagus, a condition which may be seen in Plewrobranchus and THE GASTROPODA 115 the majority of the Nudibranchs (Fig. 159), and is pushed to an extreme in Zethys. In this case the pedal and visceral commissures are destitute of ganglia or nearly so on the ventral part of their course. It is only in the thecosomatous ‘ Pteropods” that the concentration of the ganglia takes place ventrad of the oesophagus, the dorsal part of the nervous system being formed only by a long cerebral commissure (Fig. 60, 1.8). In all Gastropoda there is an infra-oesophageal stomato-gastric commissure. In the more primitive forms (Aspidobranchia, Fig. 94) the stomatogastric system originates from a sub-oesophageal labial commissure, but in other Gastropods from the cerebral ganglia. Normally this stomato-gastric commissure bears a pair of e Hie. 97. Nervous system of Limnaea stagnalis (dorsal aspect), as a type of the short-looped Euthy- neurous condition. The short visceral loop, with its three ganglia, is lightly shaded. ab, abdominal ganglion (+infra-intestinal); ce, cerebral ganglion; 0, osphradium; pe, pedal ganglion ; pl, pleural ganglion ; sp, parietal ganglion or left visceral ganglion ; opposite to it ’ is the visceral ganglion of the right side, or supra-intestinal ganglion, which gives off the long nerve to the osphradium (in Planorbis, the osphradium and supra-intestinal ganglion are on the left side). (From Lankester, after Spengel.) ganglia situated below the radular caecum at the point of origin of the oesophagus from the buccal bulb (Fig. 146, g.bu). As regards the innervation of the different organs, the cerebral centres supply the head and buccal lips, the tentacles and other cephalic appendages, the eyes and the otocysts. The pedal ganglia send out nerves to the whole mass of the foot, including the epi- podium, and to a portion of the cervical region. The mantle and the organs connected with it are primitively—as in the Streptoneura —almost entirely innervated from the pleural centres, but they are also partially innervated by nerves which issue from the visceral commissure and the supra- and infra-intestinal ganglia, and pass to the ctenidia and osphradia. The last-named nerve-centres take a preponderant share in the innervation of the mantle in Euthyneura, 116 THE GASTROPODA especially in the Pulmonata, in which group the pleural ganglia scarcely ever give off any nerves. In all the Euthyneura except Actacon (Fig. 57), Chilina, and Lata (Fig. 96) the infra-intestinal ganglion is fused with the abdominal (Fig. 97, ab) in sach a manner that the latter appears to participate in the innervation of the mantle—for instance, in the innervation of the inferior pallial lobe and the pallial branchia of the Planorbidae—and the pallial nerves issuing from the left moiety of the visceral commissure originate from a special and newly-developed ganglion, viz. the parietal ganglion of the Pulmonata (Figs. 96, g.pa; 97, sp). As regards the viscera, the heart, the kidneys, and the gonad receive their essential nerve supply from the abdominal ganglion, the alimentary canal receives its nerves from the stomato-gastric centres, and these latter nerves sometimes exhibit accessory ganglia on specialised parts of the alimentary tract, such as the gizzard of Tectibranchia, ete. 5. Sense Organs.—In addition to sensory cells scattered over the whole surface of the body, Gastropods possess special sensory organs usually designated by the names rhinophore, osphradium, otocyst, and eye. While the whole surface of the integument is sensitive, tactile sensibility is more particularly localised in the anterior regions of the body: in the head, in the margin of the foot (in marine Streptoneura the whole ventral surface of the foot exhibits a fine nervous network), and in the regions of the body specialised to form tactile appendages of various shape and situa- tion. Such are the cephalic tentacles—especially the anterior pair in quadritentaculate Euthyneura; the labial palps (Fig. 117, te”), which bear a row of tubercles in some Pulmonates; the pedal tentacles of Vermetus (Fig. 45, p.t); the epipodial tentacles of the Rhipidoglossa (Fig. 130, XI), i which have ciliated sensory “fe Nea organs at their bases; and the pallial appendages, such as the dorsal papillae of the Nudibranchs. The Rhinophores, or olfac- tory organs, as they are called, Fic. 98. are likewise constituted by Bulla (Haminea) navieula, right-side view. c.h, the cephalic tentacles, especi- cephalic hood; e, eye; f, foot; k.o, hermaphrodite : Bac orifice; il, inferior pallial lobe; m, mouth; m.o, ally by the posterior pair in unmnal groove sh shell. (After Guiart) the quadritentaculate Euthy- neura. The whole surface of these tentacles is covered by little ciliated papillae, giving them a silky appearance, in many khipidoglossa, ¢.g. Scissurella, Haliotis, Trochus, Gena, Molleria, Cyclostrema, Neritina, in Caecum (Fig. 68, te), ete. The olfactory nerve divides into many ramifications which end on the surface of the tentacle in olfactory sensorial cells. In many THE GASTROPODA 117 forms, such as the terrestrial Pulmonata, the majority of the naked Opisthobranchia, Cyclostrema, Xenophorus, and all the Gastropods without an osphradium, these ramifications issue from a rhinophoric ganglion situated at the extremity of the olfactory nerve. The olfactory end-cells are frequently localised in a tract of higher epithelium at the extremity of the tentacle, or in a furrow ex- cavated in the surface of the tentacle (Pyramidellidae, Fig. 137, te, Solarium), and in many Opisthobranchia the sensitive surface of this olfactory prominence or cavity is increased by the development of numerous parallel pleats or foliations (Fig. 163, ¢). In terrestrial Pulmonates—e.g. Helirv—the sense of smell does not extend for a greater distance than half a metre, and then only in the case of exceptional odours ; the most usual distance at which odours are recognised is from one to three centimetres, but certain carnivorous marine Streptoneura—for example, Nassa—are able to recognise odours at a distance of more than two metres. The Osphradia are the sensory organs of the pallial or respiratory cavity, and exist in diverse forms. There is a pair of osphradia in all the bictenidiate Aspidobranchia and in the Docoglossa: in all other Gastropods the osphradium is unpaired. It disappears only in some terrestrial Streptoneura (Helicinidae and Cyclophoridae), in the Pleurobranchidae, the Nudibranchia, and all the Stylommato- phorous or terrestrial Pulmonates ; nevertheless in all the stylom- matophora (Limaz, Helix, ete.) the osphradium is present during development and during the first few days after hatching. To sum up, then, the osphradium is absent in aerial species or in aquatic forms devoid of a respiratory cavity, and when it is absent a rhino- phoric ganglion is present. An osphradium consists of a specialised and usually elevated and ciliated region of the epithelium, in which there is an accumulation of sensory cells. In the ctenidiate Gastro- pods the organ is situated on the outer side of the ctenidium (Fig. 99, XVI). The most simple form of osphradium is seen in the Strepto- neura, in which it is not differentiated into a definite organ, but is merely a localisation of neuro-epithelial cells on the course of the branchial nerve along the two supporting margins of the ctenidia, as in the Fissurellidae, or on an osphradial nerve running along the support and formed by a differentiation of the branchial nerve, as in other Rhipidoglossa, or again on a ganglion placed on the extremity of this special nerve at the base of the ctenidium. In other Gastropods the osphradium becomes a distinct terminal organ at the base or at the left (external) side of the single ctenidium, athwart the current of water which supplies the latter organ. The osphradium may persist in this place after the disappearance of the ctenidium, but only in aquatic forms such as the Patellidae, Gymnosomata, and basommatophorous Pulmonates. In the most archaic Taenio- glossa, viz. Paludina, Littorina (Fig. 85, p.br), Cyclostoma, Vermetus, 118 THE GASTROPODA the osphradium is a filiform epithelial ridge, overlying a nerve or ganglionated cord. Then, as a result of specialisation and multi- plication of its surface, the two sides of the ridge become garnished with pectinations, so that the organ acquires a deceptive resemblance to a branchia. This condition may be seen in the more specialised Taenioglossa, such as Natica, Cerithium, and the Strombidae, in which the pectinations themselves are arborescent ; in Cypraca, in which the Xt XI Fie. 99. A male Hemifusus tuba, removed from its shell and with the pallial cavity opened. I anus ; II, hypobranchial gland; III, spermiduet; IV, renal pore; V, lieart, in the opened pericardium ; VI, testis; VII, liver; VIII, oesophagus ; IX, columellar inuscle ; X, the spermi- duct cut through, with the mantle; XI, penis; XII, foot; XIII, proboscis; XIV, head; XV, pallial siphon ; XVI, osphradium ; XVII, ctenidium. (After Souleyet.) organ is trifid; and in the Rachiglossa (Fig. 99, XVI) and Toxiglossa. In the Euthyneura the osphradium is a simple epithelial projection of circular or elongated shape, lying above an osphradial ganglion, into which it is sometimes invaginated—viz. in certain basommatophorous Pulmonates—and the invagination is bifureated in Limnaca. In the last-named genus the osphradium is situated in the pallial cavity, to the left of the ctenidium ; in the Basommatophora it is close to the. pneumostome ; in S¢phonaria (in which the lung is filled with water) THE GASTROPODA 119 it is inside the pulmonary cavity (Fig. 174); m other forms with an aerial lung it is external (Fig. 89, 0s). Cyathiform bodies or gustatory bulbs, formed of taste-cells, are found on the lateral and ventral surfaces of the buccal cavity in sundry Rhipidoglossa, and at the sides of the buccal aperture in some Heteropoda. Analogous bodies have been found on the epipodial tentacles of Rhipidoglossa. The Otocysts, or statocysts, are hollow spherical vesicles, whose internal walls are lined by a ciliated epithelium containing sense- cells. These vesicles contain a liquid secreted by their epithelial walls, and in this liquid are calcareous auditory concretions of crystalline structure. There is a single large and spherical con- cretion or otolith in the more specialised Tectinibranchs and in a few adult Opisthobranchs (Loliger, the Elysiomorpha, Hedylidae, Pseudovermis, Fiona, and sundry Eolidomorpha), (viz. the Tergipedi- nidae, Cupellinia, Eolidiella, Eolis auwrantiaca and £. olivacea, Galvina picta and G. exigua). There are numerous and usually ovoid and elongated concretions, called Otoconia, in the Aspidobranchia (except Bathysciadium), in some of the less specialised Taenioglossa, such as Paludina, Ampullaria, Cyclophorus, Valvata, Nassopsis, and the majority of the Melaniidae, and in the Euthyneura in general, with the exception of the Opisthobranchs mentioned above. Oto- conia sometimes coexist with an otolith in certain Cerithiidae, Turritella, Doto, and Oncidium, but in all larvae there is only a single otolith (Fig. 116, A, III). Otocysts are absent in the adult Vermetus and in some Janthina. In creeping Gastropods the otoliths are situated in the foot, in the neighbourhood of the pedal ganglia (Fig. 93, V), and are often adherent to these nerve-centres. In swimming Gastropods, such as Heteropoda, Phyllirhoc, and Glaucus, they show a tendency to approach the cerebral centres, and the same tendency may be seen in the majority of Nudibranchs. In all cases the otocysts are innervated from the cerebral ganglion, as may be most clearly seen when they are at some distance from the pedal ganglia (Figs. 123, C, of; 142, wu; 146, of). The neuro-epithelial elements are concentrated in a macula acustica, placed opposite the expansion of the otocystic nerve, in the otocyst of Heteropoda. Cephalic eyes exist in almost all Gastropods, and there are, in addition, pallial eyes in certain Oncidiidae. The two cephalic eyes are situated on the tentacles, in the Euthyneura on the posterior pair of tentacles. In the Streptoneura these eyes are placed at the outer side of the base of each tentacle, and are borne on tubercles (Fig. 44, A, c) which may fuse with the tentacles, and thus, in a number of instances, give the eyes the appearance of being placed half-way up the tentacles, as may be seen in the Potamidae among the Ceri- thiidae, in Cypraea, many Rachiglossa, certain species of Conus (Fig. 144, V), and Plewrotoma: in the last named they are very near the 120 THE GASTROPODA extremities of the tentacles in the sub-genera Drillia and Clavatula. The ocular tubercle is better developed than the tentacle in the Strombidae (Fig. 75 #), and finally the tentacle may be aborted and the eye appear to be placed on its summit (Terebellum). It is really placed on its summit in Assiminea and in the adult ter- restrial Pulmonates or Stylom- matophora (Figs. 172, 177), but during the development of these forms it is some distance removed from it. In the basom- matophorous Pulmonates, and = in the Opisthobranchia the eye Rreeaae: is at the base of the tentacle, Axial section of the eye of Trochus wmbilicaris and in the latter group some- fyctustalie lens: AL, retina; 1H, eptle nerve; times at some distance from it and often buried beneath the integuments, especially in the Nudibranchia. As regards its struc- ture, the Gastropod eye typically consists of a retina or invagination of the tegumentary epithelium, in which sensory and pigment cells may be distinguished. The former are known as retinophora and are colourless ; their free extremities are much contracted, and their opposite extremities are continuous with prolongations of nerve- fibres. The latter, or retinulae, have expanded free extremities, and surround the retinophora. As these two kinds of cells arise by the differentiation of normal epithelial cells, they may not in all cases possess sharply defined characters, and may pass insensibly into one another: the colourless cells actually appear to be absent in the eyes of certain Opisthobranchia that are buried beneath the integuments. The visual organ is completed by accessory structures, of cuticular nature, secreted by the epithelium, and are more dis- tinct from one another in proportion as the eye is more highly specialised. These cuticular structures comprise the layer of rods and the refracting bodies properly so called. The layer of rods, or retinidia, caps the epithelial cells of the retina. These rods, little developed in the Aspidobranchia (Fig. 100, IV), attain their highest degree of specialisation in certain Rachiglossa (Strombidae) and in the Heteropoda (Fig. 101, B, VII). In the last named they are disposed in furrows perpendicular to the optic axis, an arrangement analogous to that found in another pelagic Gastropod, Gustropteron. ‘The refractive elements are the crystalline lens—a spheroidal body formed of concentric layers, which does not as a rule fill the cavity of the eye—and a less dense cuticular substance, known as the vitreous body, which surrounds the crystalline lens. In its most primitive condition the visual organ consists simply of an entirely THE GASTROPODA 20 retinal or pigmented invagination, still widely open to the exterior, whose epithelial cells are covered by a layer of rods, but the crystalline lens and vitreous body are altogether absent: this con- dition is realised in the Docoglossa. In a more advanced stage of specialisation the margins of the invagination become approximated, so that the ocular cavity, whose walls are pigmented throughout their extent, retains a small external aperture, through which water is admitted to bathe the crystalline lens: this condition may be seen in certain Rhipidoglossa, viz. Pleurotomaria, the Haliotidae, the Trochidae (Fig. 100), the Stomatellidae, and the Delphinulidae. Finally, the aperture of the ocular cavity is closed, and the crystal- line lens is covered in by two superimposed transparent epithelial layers, separated by a transparent layer of connective tissue. These two layers are (1) the internal cornea or “ pellucida,” a layer of small extent which is simply the anterior continuation of the retina, the two together forming the internal wall of the ocular sphere ; and (2) the cornea proper, which is external, and continu- ous with the tegumentary epithelium. This form of eye is found in all the Rhipidoglossa, with the exceptions mentioned above. In most other Gastropods the structure of the eye is practically the same as in the Rhipidoglossa with a closed cornea, with this differ- ence, that the pellucida is more and the pigmented retina propor- tionally less extensive. The retinal area becomes more and more restricted in proportion as the eye becomes more specialised—e.y. the Heteropoda—or ceases to be functional, c.g. Guivillea. There is often a blood space above the pellucida, as may be seen in Dolium, the Heteropoda, the Elysiomorpha, and the Basommato- phora. As regards the function of the eyes, it has been experiment- ally demonstrated that aquatic Gastropods are incapable of dis- tinguishing the form of objects, while the terrestrial species are able to distinguish them at a distance of one or two millimetres. The eye becomes rudimentary when it is buried in the integuments ; and further, it diminishes in size, though retaining its pigmenta- tion, in the following burrowing Gastropods: several Naticidae (Natica alderi, Amaura, etc.), various Bullidae (Scaphander, Philine, Doridium, Gastropteron, etc.), the Pleurobranchidae, many Nudi- branchs, and some Pulmonates, viz. Siphonaria, Auricula miduc, and A. judae. The eye may also become rudimentary through loss of its retinal pigment, while still retaining its superficial position : this is the case in species living in situations beyond the reach of the light, whether they be abyssal species (Guivillea) or inhabitants of subterranean waters (bithynia pellucida). Finally, regression may be carried so far that the eye, as a consequence of functional disuse, is wholly wanting in the adult state. This phenomenon may be seen in burrowing forms, such as various Naticidae, sundry species of Terebra, the Olividae (Olivella, Agaronia, Ancillaria), certain 122 THE GASTROPODA Marginellidae and Sullia; in subterranean Pulmonates, such as Caecilianella and Helix hauffeni; im abyssal Gastropods, such as Lepeta, Propilidium, Bathysciadium, Puncturella, Cocculina, a species of Eulima, Choristes, Oocorys, some species of Fossarus, Addisonia, a species of Chrysodomus, Plewrotoma nivalis, Bathydoris, and Gonieolis ; in internal parasites, such as the Entoconchidae and Ento- siphon ; among pelagic Gastropoda in Janthina and the “ Pteropoda.” Fic. 101. Eye of Pterotrachea. A, the whole left eye. I, retractor muscle; II, optic nerve; III, carina ; IV, the pellucida, or inner cornea, lacerated in order to show the lens; V, lens; VI, outline of the pellucida. B, sagittal section of the deeper part of the eye. I, lens; II, vitreous body ; III, limiting membrane; IV, retina; V, carina; VI, optic nerve; VII, retinal rods on their stands; VIII, retractor muscle ; IX, pigmented epithelium. (After Grenacher.) in addition to the cephalic eyes, certain species of Oncidiidae (Peronia) possess a large number of pallial eyes, situated on tubercles on the dorsal surface. Structurally these organs are character- ised by the fact that the retinal cells are reversed and their free ends are directed towards the interior of the body, the optic nerve traversing the retina, just as is the case in the vertebrate eye. The optic cavity is filled by a crystalline lens formed of a few large transparent cells. Another example of a pallial eye is found in Cerithidea obtusa ; in this case it is single, situated in the interior of THE GASTROPODA 12 Uo the respiratory cavity at the anterior extremity of the osphradium, and in it also the optic nerve traverses the retina. 6. Reproductive Organs—The Streptoneura are dioecious, with the exception of the genera Bathysciadium, Cocculina, Valvata, Mar- senina, Oncidiopsis, Odostomia, Entosiphon, Entoconcha, and Enteroxenos. All the Euthyneura are monoecious. In the dioecious Gastropoda sexual dimorphism is generally very slightly marked. The males are externally recognisable only by the penis, when this organ exists; their shape, however, is more elongate than that of the females, and their greatness is often smaller, as, for instance, in Rhipidoglossa, Paludinu, Littorina, various species of Crepidula, Pleurotoma, ete.: the most typical case in this respect is that of Lacuna pallidula (Fig. 7), in which the females are on the average ten times as heavy as the males. In addition, sexual differences are sometimes found in the aperture of the shell (Littorina obtusata), in the operculum (some species of Cerithium, Quoy and Gaimard), in the radular teeth (certain Buccinidae, Troschel), in the absence of the pedal sucker in the female Pterotrachea, of ten- tacles in the female of some /iroloida, and of the slit in the mantle in the male Vermetus. The gonad is always unpaired, even in the most archaic Aspido- branchia. It is generally placed on the dorsal side and at the summit of the visceral mass. It has the form of a racemose gland, made up of a great number of acini, and it may be compact or arborescent, with ramifications extending over and into the liver mass. In Aspidobranchia such as Plewrotomaria, the Trochidae, and Fissurellidae the gonad opens into the reno-pericardial duct, in the same manner as in some protobranchiate Lamellibranchs, viz. Solenomya. In all other Aspidobranchs, except the Neritacea, the gonad discharges into the kidney. In the Neritacea and Pectini- branchia the reproductive apparatus always possesses its own proper orifice, and there is a genital duct of greater or less length, which, however, is incompletely closed in various Melaniidae, Cerithiidae, Turritellidae, and Vermetidae. This duct opens into the pallial cavity to the right of the intestine in both sexes in the Ampul- lariidae, and in such forms as have not acquired a penis, that is to say, besides the four families mentioned above, in the Capulidae, Hipponycidae, and Solariidae. In all forms the male duct or spermiduct differs from the female duct or oviduct in the fact that it terminates in a copulatory organ (Fig. 99, XI). In its less special- ised form the spermiduct is continued into a seminal furrow or groove (Fig. 85, v.d’) which extends from the primitive genital orifice to the extremity of the penis, and is capable of being closed for part of its course, remaining open only in the neighbourhood of or on the penis. This condition is found in a large number of Taenio- glossa, viz. Ampullaria, the Littorinidae, Modulidae, Struthiolariidae, 124 THE GASTROPODA Chenopodidae, Cassididae, Doliidae, Trotonidae, Naticidae, Cyp- raeidae, Calyptraeidae, Xenophoridae, Strombidae (Fig. 75, s.gr) ; and in some Stenoglossa, viz. the Muricidae, Magilus, Voluta, Lyria, the Harpidae, Terebra, and in all the Heteropoda. In all other forms, that is to say, in a certain number of Taenioglossa and almost all the Stenoglossa, the spermiduct is closed in for the whole of its extent and the penis is hollow (Fig. 44, 1). Thus the male orifice is secondarily removed to the extremity of the penis, and consequently is at a considerable distance from the primitive position of the genital aperture, a position which is retained by the female aper- ture. A penis exists in the Neritacea among the Rhipidoglossa, and in all the Pectinibranchia, with the exception of those families of the Taenioglossa enumerated above. When it does not exist copulation cannot take place, and the ova are fertilised in the sea by contact with the spermatozoa emitted by the male. The penis exists only in a rudimentary form in sedentary species, but in all others it is a well-developed, non-invaginable excrescence, situated on the right side of the anterior part of the body, except in cases of situs inversus, when it is on the left. All the aerial Streptoneura are necessarily provided with a penis, since in them copulation is indispensable. But the penis is not homologous throughout the group; it is developed at different parts of the body, at the point where the spermiduct ends. Thus the Neritacea have a cephalic penis, as has also Paludina, whose penis is a part of the right tentacle. In the Ampullariidae and Cyclostomatidae the penis is developed from the mantle, but in all other forms it is exclusively of pedal origin. Sometimes it is provided with an external whip-like appendage or flagellum: such is the case in many Taenioglossa, viz. nearly all the Littorinidae except Cremnoconchus, in Dolium, and especially in Hydrobia, Bithynia, the Naticidae, the Lamellariidae, and the Heteropoda. The genital ducts are rarely provided with well-differentiated accessory organs in the dioecious Gastropoda. In certain cases there is a glandular tract in the oviduct, which is sometimes specialised to form an albuminiparous gland (Ampullaria, Paludina, » the Naticidae, Lamellariidae and Calyptraeidae, Triton and Cassidaria). There is a copulatory pouch or receptaculum seminis in the Neritacea, Paludinidae, Cyclostomatidae, and Heteropoda. In some Neritacea—viz. Neritina, Nerita, Navicella, ete.—the receptaculum has its own external opening distinct from the oviducal aperture ; this probably corresponds with the right kidney of other Rhipido- glossa, which in this case has been lost by the male sex (Thiele). In some freshwater Taenioglossa, e.g. Tanganyicia (Fig. 78) and Melania episcopalis (Fig. 109), the oviduct is continued into a ciliated groove which leads to an incubatory pouch situated in the head ; this pouch has been homologised with the penis by Moore. The THE GASTROPODA 12 ur males of Ampullaria and the Heteropoda also possess a vesicula seminalis, and the penis frequently is furnished with well-marked superficial glands (Littorinidae, Cassis, Terebra, and the Heteropoda). In some Taenioglossa, such as Paludina and Pteroceras, and in several Stenoglossa, such as Murex, Nassu, Purpura, ete., there are two kinds of spermatozoa, the one normal and filiform, the other vermiform ; the function of the latter kind is not yet explained. In Paludina, for example, these two kinds of spermatozoa exist in equal quantities, but the filiform kind, with a single cilium, originate from spermatids which have increased but little in size during the growth period, and contain the normal quantity of nuclear substance: these are the eupyrenic spermatozoa of Meves. The vermiform spermatozoa, on the other hand, have about six cilia apiece, originate from spermatids which have increased largely Follicles of the hermaphrodite gonads of Euthyneura. 4, of Helix; B, of Holis. a, ova; b, developing spermatozoa ; c, common efferent duct. (From Lankester, after Gegenbaur.) in size during the growth period, and contain only a small quantity of nuclear substance: they are known as oligopyrenic spermatozoa. In the monoecious Gastropods the gonad ordinarily occupies the same position and has the same relations as in the dioecious Streptoneura, but it may be much more subdivided, especially in certain Nudibranchs, viz. Phyllirhoé (Fig. 161, y) and Elysiomorpha. It has always a duct with its proper external orifice and a penis which is invaginable in most Euthyneura, but this latter organ is absent in hermaphrodite parasitic Streptoneura. The gonad differs from that of the dioecious Streptoneura in producing ova and spermatozoa in the same individual. In the most simple arrange- ment the two kinds of genital products are developed side by side, as may be seen in Valvata and in the majority of the Tectibranchia and Pulmonata (Fig. 102, A). In the more specialised condition there are male and female acini, the latter opening into the spermatogenous sacs in Oncidiopsis, the Pleurobranchidae, the majority of the Nudibranchia (Fig. 102, 5), with the exception of 126 THE GASTROPODA the Elysiomorpha. ntoconcha, Enteroxenos, and bathyscoadium are the only genera in which the male and female acini are quite distinct. In its most primitive condition the genital duct is hermaphrodite, that is to say, it is a spermoviduct throughout its length, and is therefore called monaulic. It generally is provided with an internal double longitudinal fold. The hermaphrodite aperture is situated on the right side, near the opening of the pallial cavity, and is connected by a ciliated seminal groove with the more anteriorly situated penis. This condition is found in the Bullomorpha (Fig. 98, s.7) in general, including the Thecosomata ; in the Aplysiomorpha (Fig. 154, 7), including the Gynmosomata (Fig. 84, IV, XI); and in the Pulmonata Pythia (Fig. 171). The edges of this seminal groove unite to form a complete tube in Cavolinia longr- rostris among the Bullomorpha, and among the Pulmonata in all the Auriculidae except Pytlia, and as a consequence the primitive genital aperture serves only for the emission of the female pro- ducts, the male products passing through a spermiduct closed throughout its extent. In subsequent stages of evolution of the genital duct the spermiduct takes its origin from the hermaphro- dite duct above the external opening: this latter duct, therefore, bifureates or becomes ‘‘diaulic,” the female branch of the duct opening by the primitive hermaphrodite orifice. | This condition is characteristic of Valvata and Oncidiopsis (Fig. 103), of Actaeon and Lobiger among the Bullomorpha, of the Pleurobranchidae and the Nudibranchia except the Doridomorpha and most of the Elysio- morpha, and of the Pulmonata. At the point of bifurcation the male and female sections of the duct are separated by a narrow slit, which only allows the spermatozoa to pass. In this case therefore, as in the dioecious Gastropoda, the female orifice remains in the same place as the primitive genital aperture, and the male orifice is carried far forward, to the extremity of the penis. The two external orifices, male and female, are thus at some distance from one another, as may be seen in Valvuta, Oncidiopsis (Fig. 103, f.0, pe), the Basommatophora in general, the Oncidiidae (Fig. 59, of, om), and Vaginula (Fig. 87, of). But the female aperture itself may be secondarily shifted from its original position, and come so near to the penial aperture as to be contiguous to it, a condition found in the Pleurobranchidae and the Nudibranchs in general; or the two apertures may reunite in a common cloaca, as in the Stylommatophora (Fig. 177, Il), Siphonaria, and Amphibola. In these various cases the female duct, like the hermaphrodite duct of the monaulic forms, bears a bursa copulatrix or receptaculum seminis, which in certain stylommatophorous Pulmonates, such as Helix aspersa, Clausilia, ete., is provided with an accessory branch (Fig. 104, Li.s). A third differentiation of the genital ducts is brought about ¢ THE GASTROPODA 127 when the female duct becomes bifurcated through the separation of the bursa copulatrix, the latter acquiring a separate external aperture but remaining in connection with the oviduct by its deeper extremity. In this manner two female orifices are formed; the one is the copulatory orifice, the other is the oviducal orifice serving for the passage of the ova. The genital duct is thus trifurcated or “ tri- aulic,” a condition which is not found in any Pulmonate, but is confined to certain Nudibranchs, viz. the Doridomorpha and the majority of the Elysiomorpha (Fig. 105). Fic. 104. Hermaphrodite reproductive appara- tus of Helix hortensis. d, digitate acces- sory glands on the female duct; E.d, dd Fic. 103. albuminiparous gland; jl, flagellum; p, penis; p.s, calciferous gland or dart-sae Oncidiopsis, hermaphrodite genital on the female duct; Z.s, receptaculum apparatus, dorsal view. a.g, albumini- seminis or spermatheca, opening into the parous gland; /.0, female orifice; g.g, female duct; uw, uterine dilatation of the hermaphrodite gonad; pe, penis; pr, hermaphroditic duct; v.d, spermiduct or prostate; 7.s, receptaculum seminis ; vas deferens ; v.e, hermaphroditie duct ; so, spermoviduct; sp, spermiduct; s.v, 2, ovo-testis. (From Ray Lankester, seminal vesicle. after Gegenbaur.) The penis is invaginable in all the Euthyneura with the exception of Actacon (Fig. 148, VI) and Umbrella. It is a pedal structure in nearly all Opisthobranchia, but in Umbrella it is cephalic. In the majority of Pulmonates the penial nerve arises from the cerebral ganglion, but the fibres of the nerve originate from the pedal and only traverse the cerebral ganglion. In monaulic species the penis often bears an appendage, and occasionally chitinous accessory structures: there is a_ single stylet in several species of Planorbis, in Glaucus, and many other 128 THE GASTROPODA Nudibranchs, the stylet being contained in a special pouch in certain species of Doris: in some other Nudibranchs there are multiple stylets. In addition to the bursa copulatrix, there are numerous and various accessory genital organs in the hermaphrodite Gastropoda. An albuminiparous and a mucous gland are found on monaulic ducts, generally near their distal end (Fig. 171, muc). In the diaulic Pulmonata there is a large albuminiparous gland on the hermaphrodite section of the duct (Fig. 104, #.d), and on the female part of the duct of Basgmmatophora there is an albumen gland corresponding to the uterine glands of Stylommatophora (Fig. 104, wv). The diaulic and triaulie Opis- thobranchs have also contiguous albumen and mucous glands on the oviducal part of the genital duct. The terminal portion of the oviduct of Stylommatophora is further provided with a glandular zone (Zonites), or with two multifid vesicles with a variable number of ramifications Limapontia, reproductive appara. (Eig. 104, d). Opening between the tus, dorsal aspect. a.d, albumini- two 1S a special pouch —seemingly a parous duct; a.g, albuminiparous O40 5 : . sland; h.d, hermaphroditic duct; Specialised multifid vesicle, which secretes Fe Oe as, mo; mucous Ovi 4 sharp calcareous dart (Fic..l04, gis) dueal gland; 0.0, oviducal orifice ; : : é ov, oviduct; p, penis; pr, pros- Before copulation the dart-sac is evagin- SaaS ee ores ened together with all the terminal part (vestibule) common to the repro- ductive organs, and the dart, which is caducous, pierces the skin of the conjugate. The spermiduct is sometimes furnished with amore or less elongate “prostate” gland, as in Valvata, Oneidiopsis (Fig. 103, pr), various Bullomorpha and Elysiomorpha (Fig. 105, pr). The penis of certain Stylommatophora is provided with a long hollow caecum, the “flagellum” (Fig. 104, #/), in the interior of which is secreted the spermatophore or capreolus. This is a thin-walled chitinous tube closed at one end and cleft at the other and filled with a quantity of sperm. When there is no flagellum the spermatophore is formed by the deeper portion of the penis. Sometimes the spermatophores are furnished with denticulations and even with arborisations (Fig. 106). The hermaphrodite gland (gonad) does not liberate ova and spermatozoa simultaneously, the discharge of the former occupying a very short time after copulation. Generally speaking, the hermaph- roditism is protandric, the spermatozoa being the first of the genital products to come to maturity. This hermaphroditism is THE GASTROPODA 129 not self-sufficient, and the union of two individuals is necessary for fertilisation. There are, however, instances of Pulmonates which have been insolated from the time of birth and have nevertheless laid eggs which have developed (Zonites cellarius, Limnaea). In all species possessing a penis, fertilisation is effected by copulation ; in species without a penis—e.g. Patella—artificial fertilisation is possible. During the venereal act the penis is thrust into the bursa copulatrix, when this latter structure is present, and discharges into it a quantity of sperm which subsequently fertilises the ova during their passage down the oviduct. Copulation and the act of oviposition that follows it take place at various seasons. In temperate regions they continue from early spring onwards, extending even into the winter, as is the case in Patella in the Fic. 107. Fic. 106. : +54 é Two Limnaea stagnalis in copulation, Spermatophore of Nanina the left one acting as male. I, tentacle wallacet, magnified. (After and eye ; II, penis; III, foot ; 1V, buccal Pfeffer.) veil. (After Stiebel.) Atlantic and Trochus striatus in the Mediterranean. In the stylommatophorous Pulmonates with a common genital orifice, the two copulating individuals mutually fertilise one another, each one acting as male and female, and the same is the case in the majority of Nudibranchs. In the hermaphrodites with distant genital apertures the same animal may act as male and female, but as a rule not simultaneously, unless, indeed, it unites with two or more individuals to form’ a chain, as may be seen in Limnaea, the Aplysiomorpha, ete. The copulation of two individuals is effected in the same manner as in the dioecious Gastropoda (Fig. 107). Ill. Empryovoey. The eggs may be laid or may develop within the maternal organism. In the oviparous species that do not copulate, the 9 130 THE GASTROPODA unfertilised ova are generally laid one by one and are not united by an accessory envelope (Patellidae, Haliotis, certain Trochidae of the sub-genera Gibbula and Trochocochlea), but in Fissurella and in Trochidae of the sub-genus Zizyphinus they are united by a gelatinous investment. In the species that copulate the ova are deposited within a few days after the act of copulation, the time varying from one day in sundry Nudibranchs to as many as fifteen days in some species of //eliz. The nidus may assume very various shapes. In aquatic species the shells surrounding the eggs may be embedded and united in a single gelatinous mass, which may be ribbon-shaped, more or less coriaceous, attached in littoral species, floating in pelagic species. This is more especially the case in the Euthyneura—viz. in the Basommatophora and Opisthobranchia, in which the ribbon is often coiled into a spiral—and also in many Taenioglossa (Littorinidae, Rissoidae, Hydrobiidae, etc.). In such cases each egg-shell contains a single ovum. Again, the egg-shells may be coriaceous (Rachiglossa), more or less independent, simply attached to one another (Luccinwn, Fusus, Pyrula), or fixed side by side on a common support (Purpura, Murex, Nassa, Fig. 108, Trophon, Voluta, etc.). In this case each shell contains a consider- able number of ova, but all of them do not complete their develop- ment. As special forms of nidus may be mentioned that of Natica, in which the eggs are united by agglutinated sand into a horny-looking ribbon coiled in a ring; that of Lamellaria, whose eggs are deposited in a sort of nest excavated in colonies of Synascidians. Finally, various forms of Streptoneura attach their eggs to various parts of their bodies, and vo thus appear to -be more or less incubatory, as, for instance, Hipponycidae and Capu- lidae (in Calyptraca the eggs are attached below the neck); or they may attach them to the external surface of the shell, e.g. Neritina, Hydrobia ulvae, and in excep- tional cases issoa; or to the internal face of the shell, e.g. Vermetus (Fig. 45, 00). In the oviparous Janthinae the eggs are attached to the float (Fig. 135, 0). The stylommatophorous or terrestrial Pulmonates generally lay in the earth Fic. 108. < : : isolated ova enclosed either in a gelatinous Egg-capsule of Nassa reticulata, a : : x 12. 0, aperture ; ov, eggs. envelope (Limaz, etc.) or in a calcified shell, ¢.g. certain species of Helix, Testacella, ete. In Bulimus these eggs may attain a length of three centi- metres, thus exceeding in size the eggs of many birds. The eggs of Ampullaria have also a calcified envelope; they are laid in the water and are agglomerated together. When Succinea lays its THE GASTROPODA 131 eggs in the water it surrounds them with a gelatinous mass, like the basommatophorous Pulmonates. In the ovoviviparous Gastropoda the progeny are born living after undergoing their development within the parent. They develop in the terminal portion of the oviduct in the following Streptoneura: Paludina, Typhobia; various species of Melania (Fig. 109), Littorina, Cymba, Janthina, Nassopsis, and the Entocon- chidae ; in the Opisthobranch Halopsyche ; and in numerous Pul- monates—viz. Glandina algira, Rhytida aequalis, Selenites voyanus, Helix rupestris, H. inversicolor, H. inaequalis, H. unidentata, H. erroned, H, studeriana, Patula cooperi, Acanthinula harpa, the genera Partula, Balea, Coeliaxis, Pupa muscorum, P. umbilicata, P. cylindracea, Clausilia ventricosa, C. similis, Achatina alabaster, and A. zebra, Stenogyra mamnillata (Fig. 8), S. octona, S. terebraster, S. domini- ciensis, S. decollata, S. lamellata, Ferussacia folliculus, F. lamellifera, Fia. 109. Melania episcopalis, out of its shell, showing the female genital SDATAUES, right-side view. @, anus; 0.0, brood-pouch opening ; b. Ps brood- -pouch ; f, foot ; 3 9-97, genital ciliated groove ; g.0, genital orifice ; m, mouth ; oc, eye; od, oviduct; op, operculum; ov, ovary. (After Moore.) F. procerula, F. debilis, Vaginula vivipara. The embryos develop in a special incubatory pouch excavated in the interior of the foot and connected with the extremity of the ciliated canal which passes from the female orifice to the head in Melania episcopalis (Fig. 109, b.p.) and Tanganyicia rufofilosa (Fig. 78, b.p). In viviparous Gastropods the ovum contains but little yolk, but in other forms the quantity of deutoplasm is greater, and is especially large in a number of Rachiglossa, such as Nassa, ete. The segmentation of the ovum is always total, and, except in cases in which the deutoplasm is scanty (Paludina), it soon becomes irregular. As a rule in Aspidobranchia, Taenioglossa, and Pul- monata, the two first cleavage planes are meridional, the first separating the right and left halves of the future animal. The third cleavage is equatorial and cuts off the micromeres at the animal pole from the macromeres at the opposite pole, so that, as a rule, there are four macromeres from the beginning (Fig. 9, A, B). These macromeres give rise to two more generations of micro- or 132 THE GASTROPODA ecto-meres, and the latter proliferate very rapidly. In such forms as Patella, Planorbis, and Limaz, the blastula formed in this manner shgl Fia. 110. Development of the river-snail (Paludina vivipara), in which the mouth and stomodaeum are formed independently of the blastopore, the latter persisting as the anus. ae, archenteron, or endodermic cavity ; an, anus; bl, blastopore ; d.c, directive or polar corpuscle ; d.v, velar area or cephalic dome; /, foot; m, mouth; mes, rudiments of the mesoderm; p.i, pedicle of invagination, the future rectum ; sh.gl, the shell-gland ; s.m, site of the as yet unformed mouth ; vr, velum. A, Gastrula phase (optical section). B, the Gastrula has become a Trochosphere by the development of the ciliated velar ring (optical section). C, side view of the Trochosphere with commencing formation of the foot. D, further advanced Trochosphere (optical section). E, the Trochosphere passing into the Veliger stage ; dorsal view showing the formation of the shell-gland. F, side view of the same, showing foot, shell-gland, velum, mouth, and anus. (After Lankester.) contains a large blastocoel between the micromeres and macromeres, but in other Gastropods this cavity is much reduced. In some THE GASTROPODA 133 types such as Paludina, Planorbis, etc., the endoderm formed by the macromeres is invaginated into the ectodermic layer formed by the micromeres, but in many cases, in consequence of the far more rapid multiplication of the micromeres and the much larger size of the macromeres, gastrulation is effected by epiboly, and the endoderm is invaginated at a later period; in this case the endodermic cavity or enteron is of small size. In most cases the blastopore closes, and the definitive mouth is formed by a new invagination at the point of closure: it is only in Paludina that a portion of the blasto- pore remains open and becomes the anus (Fig. 110, C, 01; F, an). The mesoderm is formed as two primary mesomeres from the more posterior of the two primitive macromeres (Fig. 11, mes). The mesodermic organs (definitive kidney, heart, etc.) do not arise until a late period, their place being taken, during the development, by provisional larval organs, such as superficial contractile sinuses and larval kidneys (Figs. 114, 118). The ciliated trochosphere larva is sometimes consti- tuted at a very early period, before the formation of the mesoderm —e.g. in Patella, Acmaea, and Trochus—and in such cases the embryo be- comes free at once. But in most cases the larva is not ve pgay ‘ ee Gs CTT [f= oh Fic. 112. fierce 2 Larva of Cavolinia tridentata, ventral aspect. Fia. 111. a@, anus; f, median portion of the foot; h, heart; 7, intestine; Kn, contractile sinus; Young veliger of Trochus, ven- m, mouth; mb, mantle-skirt ; me, subpallial tral aspect. f, foot; m, mouth ; chamber ; ot, otocyst; pn, lateral lobe of the pa, mantle; pa.c, pallial cavity ; foot (the future left fin); g, shell; 7, kidney; sh, shell; ve, velum. (After 8s, oesophagus; o, sac containing nutritive Robert.) yolk. (From Lankester, after Fol.) hatched out until a much later period, and a large part of the development is effected within the egg envelope. The larva—whose shell is often different from that of the adult—is characterised by its velum and by some other external or superficial larval organs. 134 THE GASTROPODA The velum is the locomotory ciliated ring, which arises antero- dorsally (Fig. 110, C, vr) and circumscribes the apical area. As in the Amphineura, it is only slightly prominent in the most archaic marine Aspidobranchia (Patella, Fig. 14, Acmaea, Trochus, Fig. 111, ve), but in other Gastropods it becomes more and more prominent, and eventually gives rise to a natatory velum formed of two lateral lobes with ciliated margins (Fig. 112). These lobes may in turn be subdivided into two (Fig. 121, ve) or three secondary lobes (for example, in Aflanta and in “ Ethella,” a larval form attributed to one of the Strombidae). In viviparous species, or in forms like Cenia and the Pulmonata, in which the young’ are Fig. 113. Trochosphere of Patella, in the 34th hour. I, flagellum in the apical area; IJ, left lip of the blastopore ; III, blastopore; IV, velum. (After Patten.) hatched in the adult condition, the velum becomes rudimentary or disappears altogether; in the Basommatophora (Fig. 119, A) it is developed to a slight degree, but only on the sides, and is not con- tinuous ; in the Auriculidae, Siphonariidae, and Oncidiidae, however, all of which are marine, a normal velum is present. The foot is always very short at first (Fig. 1, f), being repre- sented by a mere papilla, which in sundry instances is formed from two paired rudiments (Fig. 113, II) situated between the two ex- tremities of the primitive blastopore when this latter structure is elongated. The operculum is formed early, and exists in all testaceous larvae, even in cases in which the adult possesses neither shell nor foot: the only exceptions to this statement are the Pulmonata (excepting the Auriculidae, the Amphibolidae, and the THE GASTROPODA 135 eee Siphonariidae), the Cavoliniidae, and the Gymnosomata. The pedal glands are formed by ectodermic invaginations, and in some Species exist in the larva though they are absent in the adult (Purpura). The preconchylian invagination or shell-gland (Fig. 110, sh.gl) appears at the beginning of development in the centro-dorsal area behind the velum, on the side of the body opposite to the blastopore. It is surrounded by a ridge which gradually extends over the visceral sac and secretes the shell (Fig. 117, sh). In some Stylommatophora viz. Clausilia and Succinea, a pallial sac is formed which covers up the shell, but eventually opens again. The shell grows in thickness internally, fresh matter being added to it from the external surface of the mantle, but its increase in extent is dependent on the activity of the border of the mantle, where there are special glands which degenerate when the animal reaches the adult state. It is only at this period that the aperture of the shell acquires a lip, A Se JA VY Fig. 114. Embryo of Vermetus, ventral NSS LLG aspect. I, velum ; IT, contractile Larval shell of Nassa reticulata, sinus (“embryonic heart”); III, ventral aspect, x 30. h, hook of opening of the pallial cavity; IV, the dorsal edge of the aperture ; si, Shell ; V, foot; VI, left eye. (After future canal or shell-siphon; sp, Salensky.) spire. or 1s contracted in various ways to form, for example, the linear aperture of Cypraea, Cavolinia, etc. In Gastropoda that are naked in the adult state, the shell falls off soon after the reduction of the velum (Fig. 116), but in Cenia, Runcina, and Vaginula the shell- gland and shell are not developed, and the young animal, at the time of escaping from the egg, has already the naked form of the adult. The superficial contractile sinuses are portions of. the wall of the body, temporarily modified to ensure the circulation of the nutritive fluid in the system of cavities destined to become the circulatory apparatus of the adult. In the walls of these sinuses are muscular elements, whose fibres are sometimes disposed in regular meshes, as, for example, in the nuchal sinuses of the Rachiglossa. These organs are acquired in the course of ontogeny, and are developed in different regions: they are frequently found 136 THE GASTROPODA between the foot and anus, in front of the pallial cavity, ef Helix, Bithynia, Vermetus, the Rachiglossa, and nearly all the marine Gastropoda, including the “ Pteropoda,” Heteropoda, and Nudi- 3 ° O 03%0 oe PRP - A Fic. 116, Larvae of Eolis (Galvina) exiqgua. A, on the second day, left-side view. I, radula; II, foot; III, otocyst ; IV, operculum ; V, shell. 2B, on the third day, after the loss of the shell, dorsal aspect. I, eye; II, left liver lobe; III, foot; IV, anus; V, octocyst; V1, radula. (After Schultze.) B branchia. This sinus is displaced, together with the pallial aper- ture, along the right side towards the neck (Fig. 114, II), and finally is partly contained in the pallial cavity. In the Basom- matophora there is a velar dorsal sinus, and in the Stylommatophora, Helix aspersa, emoryo of the tenth day, right-side view. coq, shell; o.ca.c, external opening of the cerebral cavity ; p, foot; pa, mantle; po, contractile vesicle or podocyst; te’, the true tentacles ; te’”’, labial palp ; vit, vitellus. Arion, Limax, Clausilia, Helix, etc., but not in Succinea, there is a caudal vesicle, known as the pedal sinus or podocyst (Fig. 117, po). The larval kidneys are paired and generally symmetrical organs situated at the anterior end of the body, immediately behind the velum or apical area. In the marine Streptoneura they are caducous ectodermic projections, in which the products of excretion are THE GASTROPODA 137 accumulated. In the Opisthobranchs they are closed pouches ; in Paludina, bithynia, and the Pulmonates they are canals opening to the exterior. In the last-named group these organs consist of tubes of ectodermic origin, each of which bears an ampulla on the middle of its course, and its internal portion is formed of perforated cells and ends internally in a closed flame-cell. In the Basommatophora (Fig. 118, ve) these cells of the larval kidney are four in number, three being perforated and one a flame-cell. These organs are absent in Vaginula. The nerve-centres and organs of special sense originate from the ectoderm, almost always from an ectodermic thickening on the buccal side of the apical organ of the larva (Crepidula), but in Vermetus and the Cavoliniidae an ectodermic invagination has been described as taking part in the formation of each cerebral centre. Again, in the Rie. Ls; Embryo of Limnaea stagnalis, viewed from the right side. a, anus; c.g, cerebral ganglion; J, foot; in, intestine; m, mouth; 0.7, aperture of the embryonic kidney; pa, mantle; ra, radula ; re, embryonic kidney ; sh, shell; st, stomach ; vi, vitellus. (After Erlanger.) Pulmonates, even if the principal part of the cerebral centres is formed from an epithelial thickening, the posterior accessory lobe origin- ates from a subsequent ectodermic invagination (Fig. 117, 0.ca.c) —the “cerebral tube ”—the cavity of which generally disappears after the animal is hatched out, but persists in the adult Planorbis and Limnaea. The eyes arise in the velar field, near the cerebral centres, and are formed by invagination in the Aspidobranchia, Paludina, the Stylommatophora, etc., but from thickenings in Vermetus, and frequently after the veliger larva is hatched, as, for example, in many Nudibranchia, with the exception of the Tergi- pedinae (Fig. 61, ¢). The otocysts are always formed at an early stage, on the antero-lateral aspects of the foot, by invagination in the majority of marine Gastropods, but from ectodermic thickenings in many Pulmonata. At first they invariably contain a single otolith, even in the species which in the adult state possess multiple otoconia. In pelagic larvae the otocysts may often be seen to be asymmetrical, and sometimes the tentacles share this peculiarity 138 THE GASTROPODA As regards the formation of the internal organs of the adult, the stomach, the liver, and nearly the whole of the intestine arise from the endoderm. The liver lobes are formed before the absorption of the nutritive sacs borne on the posterior part of the larval stomach. The proctodaeal invagination, placing the intestine in communication with the exterior, is always of small importance, but, on the other hand, the buccal bulb and oesophagus, with their numerous accessory organs, are formed from an im- portant stomodaeal ectodermic invagination, which always corre- sponds in position with the extreme anterior end of the blastopore, whether the latter is closed or remains open. The remaining organs are formed in the same manner as in other Mollusca, as has been de- scribed in the first chapter, and the ontogeny of the Gastropoda does Fie. 119. Embryos and larvae of various Molluses, after the ventral flexure and before the torsion (for A), ventralaspect. 4A, Gastropod (Limnaea, after Fol) ; B, Dentaliwm (after Lacaze) ; C, Lamelli- branch (Dreissensia, after Meisenheimer); D, Cephalopod (Oigopsid, after Grenacher). «i, anus ; ar, arms ; e, eye; f, foot ; fu, funnel; g, gill; m, mouth ; ot, otocyst; pa, mantle ; pa.o, posterior pallial orifice ; pe.g, pedal ganglion ; sh, shell ; ve, velum ; vi, vitellus. not exhibit any special features other than certain post-larval meta- morphoses and the torsion produced during development (Fig. 51). Up to the trochosphere stage the larva is strictly symmetrical (Fig. 14, B), but afterwards the torsion sets in, as a result of which the asymmetry characteristic of adult Gastropoda is established. At first the aperture of the pallial cavity and the anus are always posterior (Fig. 118), as is the case in all symmetrical Molluscs (Fig. 22, A, B, D, E); then they are carried forward by a ventral flexure (Fig. 119) in the same manner as in the Cephalopoda, Scaphopoda, and many Lamellibranchia. But in the Gastropods a lateral torsion is superadded to this primitive flexure, causing the pallial aperture to pass from the postero-ventral surface (Fig. 51, A) over to the right side (Fig. 51, B), and thence to the antero-dorsal surface (Fig. 51, C). If the animal be supposed to have the mouth turned towards the observer, this torsion may be seen to follow the movements of the hands of a watch (Fig. 52). THE GASTROPODA 139 Post-larval metamorphoses occur in various cases. The velum, as seen above, disappears, being absorbed by a process of phago- cytosis. In various genera the operculum falls off, and so also does the shell in naked forms (Fig. 116, B) and in Lamellaria, in which a new shell is formed replacing the larval shell or Echinospira. It is only in rare cases that a second larval form exists after the disappearance of the velum and before the adult state is reached ; this is the case, however, in the gymnosomatous ‘ Pteropods,” in which three transverse and parallel ciliated rings are formed before the fins are completely developed (Fig. 120). The most anterior of these rings is made up of inter- rupted portions; the two others, & on the contrary, are continuous, and are situated respectively at the middle of the body and near the aboral extremity. These two continuous ciliated circles, and especially the more posterior, are preserved till a very late period, and sometimes persist in the adult, whose habits do not differ from those of the larva (Fig. 155). Sooner or later after their ex- pulsion from the oviduct, or after the nidus is laid, the eggs are hatched out: after a period of some twenty hours in 7rochus, after ten days in certain Nudibranchs (Ter- gipes), at the end of eighteen days in others (Cenia), after three or four weeks in Limnaea, after more than a month in Vualvata and certain ae species of Arion and Limaz. It is Larva of Spongiobranchaea «australis, x i ventral aspect. 0, mouth; e.c.¢, anterior only in exceptional cases that the ciliated ring; cc.m, middle ciliated ring; young are hatched out with the for a es Racy) eet ee characters of the adult, but this is the case m all the Pulmonates— with the exception of the Siphonariidae which have a marine veliger larva—in the Opisthobranchs Cenia and Runcina, and in sundry Streptoneura such as Littorina and Lacuna among the Taenioglossa, and Purpura and Buccinum among the Rachiglossa. In normal cases the young Gastropods are hatched out as free-swimming or pelagic veliger larvae (Fig. 61). This veliger has a very small foot and a more or less voluminous velum, the latter organ being smallest in the least specialised forms, such as 7vochus (Fig. 111), Patella, Fissurella, ete., and is the characteristic larval form in most opisthobranchiate 3) Trane aay 120. 140 THE GASTROPODA Euthyneura and in the majority of Streptoneura. Even in those Gastropods that are hatched out in the adult form, the veliger stage can generally be recognised, in a more or less reduced condition, within the egg membranes, e.g. in Buccinwm, Cenia, the basommato- phorous Pulmonates. In all Gastropods the velum is reduced in proportion as the foot develops; nevertheless, in a considerable number of pelagic larvae the veliger stage is preserved for a long time, and the velum persists, and often develops excessively long lobes even after the creeping foot is fully and normally developed : such is the case in “ Macgillivraya” (Fig. 121), “ Agadina,” “ Chele- tropis,” “ Sinusigera,” “Echinospira,” etc., all of which are special pelagic larval forms of Streptoneura which were long considered to Fig. 122. Shell of a young Fig. 121. Purpura —haemastoma, ““ Macgillivraya,” pelagic Jarva of a_siphonate enlarged, dorsal aspect. Streptoneurous Gastropod (Doliwm), ventral aspect, ca, canal of the adult ; x 12. f, foot; m, mouth; sh, shell; st, siphon ; fe, e.s, limit of the embry- tentacle and eye; ve, lobes of the velum. (After onic shell; sp, spire. MacDonald.) (After Dautzenberg.) be distinct genera. The velar lobes may even produce lobate expansions of the margin of the aperture of the shell, but these dis- appear when the velum is absorbed and the shell assumes the adult form (Fig. 122). IV. DEFINITION. The asymmetry of some of the principal organs of the body is the chief characteristic of the Gastropoda. The essential feature of this asymmetry is that the anus generally lies to one side of the median plane; that the ctenidium, the osphradium, the hypo- branchial gland, and the auricle of the heart are azygos, or at least are more developed on one side of the body than the other; and that there is only one genital orifice, which hes on the same side of the body as the anus. In other words, one-half—generally the morphologically left but topographically right half—of the anal complex is either atrophied or has disappeared altogether. This asymmetry, expressed by the transfer of the morphologically right THE GASTROPODA 141 organs to the left side, is the result of a torsional movement, which has carried the anus and pallial cavity from an originally posterior to an anterior position and at the same time has twisted the visceral commissure. V. BIroNoMIcs. The Gastropoda are essentially aquatic animals, and the more archaic species are marine. Some species are specially adapted to brackish waters. In fresh waters there are found sundry Strepto- neura, viz. certain Neritidae, the Ampullariidae, Paludinidae, Valva- tidae, Bithyniidae, Hydrobiidae, several Cerithiidae, the Melaniidae, Cremnoconchus, and Canidia; nearly the whole pulmonate group of Basommatophora ; and a single Opisthobranchiate, Ancylodoris. Finally, the stylommatophorous Pulmonates and Halicinidae, Cyclo- phoridae, Cyclostomatidae, and Aciculidae among the Streptoneura are terrestrial. In some forms that live in torrential streams, or are subject to being dried up periodically, the respiration is alternately aquatic and aerial, and the Amphibolidae, Siphonariidae, and Onci- diidae are examples of Pulmonates that have returned to a marine existence. The Gastropoda crawl at the bottom of the water, or on the land, or in a reversed position, on the film of mucus secreted on the surface of the water by the glands of the anterior groove of the foot (Basommatophora, Nudibranchia). The Strombidae are jumpers, and a considerable number of Gastropods are swimmers, e.g. the Heteropoda—which swim in a reversed position with the foot upwards—Janthina (Fig. 135), the “ Pteropoda,” Phyllirhoé, Acéra (Fig. 147), etc. Some families both of Streptoneura and Opistho- branchia burrow in mud or sand, e.g. the Naticidae, Bullidae, ete. Some genera are more or less sedentary, though able to move from place to place—such are Patella and Bathysciadiwm—but others are completely sedentary when adult, and may be fixed either by the substance of their shells—such are Vermetus and Magilus (the latter inhabits corals)—or by a calcareous plate secreted by the foot, as is the case in Hipponyx. The diet of Gastropoda varies according to the group under consideration. Generally speaking, the carnivorous habit is due to specialisation, often accompanied by the development of a_pro- boscis. Various forms of Gastropods live and feed on colonial invertebrates such as Synascidians, Hydrozoa, Anthozoa, and the like, and to a certaindegree mimic these forms. Thus Ovula lives on Gorgonia, Pedicularia on Corallium, Lamellaria on Leptoclinum, various Nudibranchs on sponges or Hydroids. Some Gastropoda are parasitic, generally in or upon Echinoderms, and belong either to the sub-group Capulidae, in which case they are ectoparasites, and had already acquired this habit in Palaeozoic times (Platyceras), or to the “ Aglossa,” that is to say, to the little group formed by mca! tae: 142 THE GASTROPODA the families Eulimidae (including Stylifer, parasitic on Asterids, Echinids, and Crinoids) and Entoconchidae, including Lutosiphon, Entocolax, Entoconcha, and Enteroxenos, all parasitic in Holothurids. Some thirty thousand species of Gastropoda have been enu- merated, of which twenty thousand belong to the present epoch and are distributed in every region of the globe. Of existing species more than twelve thousand are branchiate forms. Some marine species are found at a depth of over 2500 fathoms, and some Pulmonata live in the Himalayas at a height of nearly 17,000 feet above the level of the sea. Some freshwater Gastropoda (Hydro- biudae, Basommatophora) exist at a depth of 180 fathoms below the surface of certain lakes, e.g. Lake Baikal; others live in subterranean waters, and some Pulmonates are found in caverns into which the daylight does not penetrate. Palaeontology shows that these animals were already in existence in the Cambrian period, at the commencement of the Palaeozoic epoch. The size of Gastropods varies from a fraction of a millimetre to more than fifty centimetres. The largest forms are found not only among the testaceous species, such as Musus, Tritoniwm, Ancistromesus, Strombus, ete., but also among the naked forms: Tethys, for example, is more than thirty centimetres in length, and some species of Den- dionotus as much as twenty-five centimetres. VI. SystEMATIC REVIEW OF THE SUB-CLASSES, ORDERS, AND FAMILIES OF GASTROPODA. The class Gastropoda includes two well-defined sub-classes, Streptoneura and Euthyneura. Sus-Ciass I. STREPTONEURA, Spengel ( = Prosobranchia, Milne-Edwards = Cochlides, von Jhering). These are dioecious Gastropoda, with the exception of a few aberrant genera, and are characterised by the maximum torsion exhibited by the visceral mass and visceral commissure, the latter being always twisted into a figure of eight (Fig. 124, VII, IX). The right moiety of this commissure is situated above the digestive tube, and is known as the supra-intestinal ; the left moiety is situated below the digestive tube, and is known as the infra-intestinal. The pleural ganglia are often united to the opposite branch of the visceral nerve by an anastomosis of the pallial nerve, this condition constituting “dialyneury ” (Fig. 123, A, di’, di”): or there may bea direct connection by means of a longer or shorter connective pass- ing from the pleural ganglion to the ganglion borne on the visceral branch of the opposite side; this constitutes “zygoneury” (Fig. 125, B, C, 2, zy). Zygoneury is more frequently found on the Fia. 123. Nervous system of 3 Streptoneurous Gastropods, showing the dialyneury and zygoneury, dorsal aspect. A, Paludina (after Bouvier, somewhat modified); Bb, Triton (after Haller); C, Lamellaria (after Bouvier). ab.g, abdominal ganglion; br.n, branchial nerve; ce.g, cerebral ganglion ; c.pe, cerebro-pedal connective ; c.pl, cerebro-pleural connective; di’, di’, left and right dialyneury ; 7.7.9, infra-intestinal ganglion ; ot, otocyst; pa.n, pallial nerve; pe.g, pedal ganglion ; pl.g, pleural ganglion ; pl.pe, pleuro-pedal connective ; s.7.g, Supra-intestinal ganglion ; st.g, stomato-gastric ganglion ; vi.c, visceral commissure ; vi.c’, vi.c’’, Supra-intestinal and infra- intestinal part of the visceral commissure ; zy’, zy’, left and right zygoneury. 143 144 THE GASTROPODA right side; the connective passes from the right pleural to the infra-intestinal ganglion, and may have the effect of bringing Fic. 124. Trochus cinerarius, central nervous system, dorsal aspect, with the anterior part of the digestive tract. I, salivary gland; II, cerebral ganglion ;_ III, cerebro-pleural connective ; IV, pleural ganglion; V, right pallial nerve ; Wile pedal ganglion; VII, supra-intestinal part of the visceral commissure ; VIIT, posterior part of the glandular oeso- phagus; IX, infra-intestinal part of the visceral commissure ; X, abdominal ganglion; XI, oesophagus ; XI, radula ; XIII, supra-intestinal ganglion ;; XIV, osphradial ganglion and branchial nerve; XV, left pallial anastomosis or dialyneury ; XVI, glandular oesopha- gus; XVII, left pallial nerve ; XVIII, buccal mass; XIX, cerebro-pedal con- nective ; XX, stomato-gastric ganglion ; XXI, snout. the latter ganglion between the two pleural centres (Fig. 123, C, 2.7.9). The head of Streptoneura bears only a single pair of tentacles (Fig. 125, q). The radular teeth, when there is more than one on either side of the median tooth, are of several different kinds in each transverse row (Fig. 74, C, F). The heart is almost always posterior to the branchia. The sub-class in- cludes two orders, Aspidobranchia and Pectinibranchia. ORDER 1. Aspidobranchia. These are Streptoneura in which the nervous system is still but little concentrated (Fig. 124). The pedal centres have the form of long gan- glionated cords, to the anterior end of which the pleural centres are attached: the cerebral ganglia are widely separated from one another, and are united by a long commissure lying in front of the buccal mass and the salivary glands (Fig. 127, c.c). An infra-oesophageal or “ labial” cerebral commissure is present. The osphradium is but little specialised, and is situated on the branchial nerve. The otocyst contains numerous oto- conia. The eye is open (Fig. 100), or if closed has a very small pellucida. The central teeth of the radula are multiplied. | Ctenidia are almost always present; they are bipectinate and free at their distal ends (Fig. 81, d). Asa rule, the Aspidobranchs exhibit well-marked traces of the original bilateral symmetry, having two auricles to the heart and two kidneys (Fig. 127), the last named opening to the exterior at the end of short papillae (Fig. 88, fp The gonad has no accessory organs and discharges its products into THE GASTROPODA 145 the right kidney. In the Neritacea, however, there is only one kidney, namely, the left kidney, with a slit-shaped external aperture, and there is a distinct genital orifice, the oviduct being diaulic in the Neritidae. The order Aspidobranchia includes the most archaic Gastropods : it includes two sub-orders, the Docoglossa and Khipidoglossa. Sus-OrpER 1. Docoguossa. In these Aspidobranchs the nervous system (Fig. 93) is without dialy- neury, that is to say, there is no anastomosis between the pleural ganglia and the visceral nerve of the opposite side through the intermediary of the pallial nerve. The eyes are open and devoid of a crystalline lens. There are two osphradia, but neither hypobranchial glands nor operculum. The mandible is unpaired and dorsal. The radula generally has trabeculi- form teeth (Fig. 74, F), and there are at most three marginal teeth on either side. The heart has only a single auricle (Fig. 82, au), and neither it nor the pericardium are traversed by the rectum. The visceral mass is cone-shaped, without a spire. The sub-order includes about 1400 species. Faminy 1. AcMAEIDAE, Philippi. A single bipectinate ctenidium, free for the greater part of its extent, is present on the left side (Fig. 82). Genera—Acmaea, Eschsholtz ; without pallial branchiae ; Great Britain. Scurria, Gray; with pallial branchiae arranged in a circle beneath the mantle. Pectinodonta, Dall. Scenella, Billings ; from the Cambrian. Palaeacmagdy Hall; from the Silurian. Faminy 2. TRypirpimpag, Pilsbry. Muscle scar divided into numerous separate impressions. Genus—Tryblidiwm, Lindstrom ; Silurian. Faminy 3. PATELLIDAE, Guilding. No ctenidia, but only pallial branchiae disposed in a circle between the mantle and the foot (Fig. 125). Genera—Patella, Linnaeus ; the pallial branchiae forming a complete circle ; no epipodial tubercles; British seas, Ancistromesus, Dall; radula with an unpaired central tooth, which is wanting in Patella. Nacella, Schumacher; branchial circle complete ; epipodial tentacles present. Helcion, Montfort ; circlet of pallial branchiae interrupted anteriorly, beneath the head ; British seas. Helcioniscus, Dall. Faminy 4. Leperipasn, Gray. Dioecious, with otoconia; the head symmetrical, the foot elongated ; neither ctenidia nor pallial branchiae present ; a central tooth in the radula. Genera—Lepeta, Gray; without eyes. Lepetella, Verrill ; with eyes, Pilidiwm, Forbes. Propilidiwm, Forbes and Hanley. Faminy 5, BAtHyscIADIDAE, Dautzenberg and Fischer. Monoecious, with otoliths ; head provided with an appendage on the right side; radula without a central tooth. Genus—bathysciadium, Dautzenberg and Fischer ; abyssal (Fig. 126). Sup-OrpDrER 2. RHIPIDOGLOSSA. Aspidobranchia with a dialyneurous nerve-system, that is to say, with a pallio-visceral anastomosis (Fig. 124, XV); eyes with a crystalline lens (Fig. 100, I) ; a single osphradium, except in genera with two ctenidia ; one or two hypobranchial glands. Mandibles paired, lateral. Radula 10 146 THE GASTROPODA with very numerous marginal teeth, arranged like the sticks of a fan. Fic. 125, Patella vulgata, in its shell, seen from the pedal surface; 7, y, the median antero-posterior axis. «a, cephalic tentacle; b, plantar surtace of the foot; c, free edge of the shell; d, the branchial efferent vessel carrying aerated blood to the auricle, and here interrupting the circlet of gill lamellae; e, margin of the mantle-skirt ; f, gill Jamellae—special pallial outgrowths (uot ctenidia) ; g, the branchial efferent vessel ; h, factor of the branchial advehent vessel ; 7, inter- spaces between the muscular bundles of the root of the foot. (After Lankester.) Oesophagus with a frill, oesophageal glands (Fig. 124, XVI), and a stomachal caecum, often coiled in a spiral (Fig. 127, spc). Heart with two auricles ; ventricle traversed by the rectum (Fig.55) except in the Helicinidae, in which there is only a single auricle and the rectum only passes through the pericardium. An epipodial ridge on each side of the foot (Fig. 130, VIII), and cephalic expansions between the tentacles often present. FamMiLty 1. PLEUROTOMARIIDAE. Visceral mass and shell spiral; mantle and shell with an anterior fissure (Fig. 54, III) near the median line. ‘Two Bathysciadium, ventral aspect, magni- ctenidia ; a horny operculum. Genera— fied. ap, cephalic appendage; f, toot; Plewrotomaria, Defrance ; epipodium with- RS ese Te bac, pallial’ out tentacles; two bipectinate ctenidia (Fig. 127). Five living species from the Antilles, Japan, and the Moluccas. The first recent species (P. quoyana, Crosse and Fischer) was discovered in 1856; the animal was first Fic. 126. : . THE GASTROPODA 147 obtained in 1871, in a collection made off the Barbadoes by the ‘** Hassler” (A. Agassiz). The Moluccan species is nineteen centimetres in height. The genus includes several hundred extinct species, ranging from the Silurian to the Tertiary, but is rare in the last named. Scissurella, d’Orbigny ; epipodium with tentacles ; right ctenidium mono- pectinate (Fig. 128). Schismope, Jeffreys; the slit at the margin of the shell is closed in the adult and transformed into an orifice (Fig. 62). The following genera are exclusively fossil: Porcellia, Léveillé ; Devonian and Carboniferous. Kokenella, Kittl; Trias. Ditremaria, d’Orbigny ; Jurassic. Polytremaria, de Koninck; Carboniferous. Trochotoma, Deslongchamps; Trias and Jurassic. Cantantostoma, Sandberger ; cae é LE Ss GZ Cy RS an \ 26 San \ te it: ie NG \ ) t/ od Fie. 127. Pleurotomaria, with the pallial cavity laid open, right-side view. a, anus; aa, aorta; a.v, afferent branchial vessel; br.g, branchial ganglion; ¢c.c, cerebral commissure ; co, columellar muscle ; cr, crop ; ¢.v, efferent branchial vessel; /, foot; g, right or minor gill; g.d, genital duct; gg, gonad ; h, heart in the pericardium ; hy.g, hypobranchial gland; in, intestine; Li, liver ; /.k.0, opening of the left kidney; m, mouth; m.s, mantle slit; od, odontophore ; oe, oesophagus ; op, operculum ; os, osphradium ; pe.c, pedal cord ; 7, rectum ; 7.k, right kidney : r.k’, anterior part of ditto (dotted line) ; 7.k.0, opening of the right kidney ; 7.s, radular sac ; s.9, salivary gland ; sp.c, spiral caecum ; st, stomach. (After F. M. Woodward.) Devonian. Murchisonia, d’Archiac and Verneuil; Cambrian to Trias. Odontomaria, Roemer; Devonian. Famity 2. BELLEROPHONTIDAE, Mac- Coy. An exclusively fossil family, comprising more than 300 species extending from the Cambrian to the Trias. The shell is coiled in one plane and has an incision in the mid-dorsal margin of the aperture. Genera—Bellerophen, Montfort. Huphemus, MacCoy. Salpingo- stoma, Roemer. Trematonotus, Hall. Cyrtolites, Conrad. Faminy 3. EvompHaipAr, de Koninck. Also an extinct family, extending from the Cambrian to the Cretaceous. Spire slightly prominent ; umbilicus deep ; operculum calcareous. Genera—Huomphalus, Sowerby. Strapa- rollina, Billings. Ophileta, Vanuxem. Macluwrea, Lesueur. Platychisma, MacCoy. Straparollus, Montfort. Phanerotinus, Sowerby. Discoheliz, 148 THE GASTROPODA Dunker. Faminy 4. Hatioripan, Fleming. Spire of the visceral mass and shell much reduced; two bipectinate ctenidia, the right being Pas Fic. 128. Scissurella euglypta, removed from its shell, ventral aspect, magnified. br.d, right gill; br.s, left cill; m.vi, visceral mass ; oc, right eye ; op, operculum; p, foot; pa, mantle; ¢, snout ; te, left cephalic tentacle; te.ep, epipodial tentacles; te.pa, pallial tentacle; te.p.o, post-ocular tentacle. the smaller; no operculum. Genus—Halvotis, Linnaeus (Fig. 129), FamILy 5. VELAINIELLIDAE, Vasseur. An extinct family from the Jocene. Shell elongate, with numerous whorls ; columella and partitions Fie. 129. Haliotis tuberculata, right-side view. d, foot; i, tentacular process of the mantle, passing through the shell-foramina, (From Lankester, after Cuvier.) between the whorls absent ; internal cavity open from base to summit. Genus, Velainiella, Vasseur. Faminy 6. FIssurRELLIDAE, Risso. Visceral mass and shell conical; the anterior part of the mantle exhibits a slit or a hole in the median line; two symmetrical ctenidia ; no operculum. THE GASTROPODA 149 Genera — Emarginula, Lamarck; anterior border of the mantle and shell with a slit; British seas. Rimula, Defrance. Subemarginula, Blainville. Scutwm, Montfort ; mantle split anteriorly and_ partially reflected over the shell, which has no anterior slit. Zeidora, Adams. Puncturella, Lowe; mantle and shell with a foramen in front of the summit of the visceral cone; British. Fisswrella, Bruguitre ; mantle and shell perforated by a hole at the summit of the visceral cone, the hole leading into the branchial chamber; British. Glyphis, Carpenter. Fissurellidea, VOrbigny. Pupillia, Gray; mantle completely covering the shell. Lucapina, Gray. Megatebennus, Pilsbry. | Macrochisma, Swainson. Lucapinella, Pilsbry. Faminy 7. Coccuninipar, Dall. Shell conical, symmetrical, without slit or perforation; the summit inclined backwards. Genus — Cocculina, Dall; dioecious; abyssal. Famity 8. Trocaipar, d’Orbigny. Visceral mass and shell spirally eas pa XI Vu Fic. 130. Trochus (Gibbula) cinerarius, right-side view. I, shell; II, frontal lobes ; III, right eye and pedunele ; IV, right tentacle ; V, appendage of the right ocular peduncle ; VI, snout; VII, right epipodial lobe; VIII, epipodium ; LX, claviform appendage under the epipodial tentacle; X, posterior (operculigerous) part of the foot ; XI, epipodial tentacle. coiled ; a single ctenidium ; eyes open (Fig. 100); a horny operculum ; flattened lobes between the tentacles (Fig. 130, II). Genera—Tochus, Linnaeus ; no jaws; shell umbilicated ; spire pointed and prominent. Monodonta, Lamarck ; no jaws; spire not prominent; no umbilicus ; columella toothed. Olanculus, Montfort. Elenchus, Swainson. Photinula, Adams. Gaza, Watson. Gibbula, Risso; with jaws; three pairs of epipodial cirrhi without pigment spots at their bases (Fig. 130); British. Margarita, Leach ; from five to seven pairs of epipodial tentacles with a pigment spot at the base of each. Livona, Gray. Basilissa, Watson. FamiLy 9. STOMATELLIDAE, Gray. Spire of the visceral mass and shell much reduced; a single ctenidium. Genera — Stomatella, Lamarck ; foot truncated posteriorly ; an operculum present; no epipodial tentacles. Gena, Gray; foot elongated posteriorly; no operculum ; epipodial tentacles present. Stomatia, Helbling; foot not truncated ; operculum and epipodial tentacles absent. Faminy 10. DELPHINULIDAE, Fischer, Visceral mass and shell spirally coiled ; operculum horny ; in- 150 THE GASTROPODA tertentacular lobes absent. Genus—Delphinula, Lamarck ; with five pairs of epipodial tentacles. Famity 11. Liormpan, Gray. Shell globular ; margin of aperture thickened ; operculum horny, with a caleareous layer. Genus—Liotia, Gray. Faminty 12. CycLostREMATIDAE, Fischer. Shell flattened, umbilicated, not nacreous; foot truncated anteriorly and with the two angles prolonged into tentacles. Genera—Cyclostrema, Marryat (Fam. 50), Tetnostoma, Adams. Famity 13. TROCHONE- MATIDAE, Zittel. Exclusively fossil, from Cambrian to Cretaceous ; shell spiral and nacreous internally ; whorls without keels; aperture rounded. Genera—Tvrochonema, Salter ; from the Cambrian and Silurian. Hunema, Salter ; from the Ordovician to the Devonian. Amberleya, Morris and Lycett ; from the Trias to the Cretaceous. Oncospira, Zittel ; Jurassic. Famity 14. Turpintnan, Gray. Visceral mass and shell spirally coiled ; epipodial tentacles present; eyes closed; operculum calcareous and thick. Genera— Turbo, Linnaeus; shell globular, thick, with short spire. Astralium, Link. Mélleria, Jeffreys; shell thin, umbilicated, with very short spire. Cyclonema, Hall. Famity 15. PHASIANELLIDAE, Troschel. Shell not nacreous, without umbilicus, with prominent spire and polished surface. Genus— Phasianellu, Lamarck. Faminy 16. UmpontiIDAb, Adams. Shell flattened, not umbilicated, generally smooth, without a nacreous layer ; operculum horny. Genera—Umbonium, Link. Isanda, Adams. Faminty 17. NeriropsiDAg, Fischer. Shell semiglobular, with short spire ; operculum calcareous, not spiral. Genera—Neritopsis, Grateloup. Naticopsis, MacCoy ; from the Devonian to the Trias. Faminy 18. Macturitipan, Fischer. Shell discoid, deeply umbilicated, with few whorls ; operculum spiral, thick. Genus—Maclurites, Lesueur ; from Cambrian and Silurian. Famity 19. NERITIDAE, Lamarck. Shell with very low spire; without um- bilicus and without a nacreous layer ; internal partitions frequently absorbed ; operculum calcareous, provided with an apophysis; epipodium slightly developed, without tentacles; a single ctenidium; a cephalic penis present. Genera— Nerita, Adanson ; marine. Neritina, Lamarck ; freshwater ; British. Nerztodomus, Morris and Lycett; Jurassic. Detanira, Stoliczka ; Cretaceous. Septaria, Férussac ; shell boat - shaped, with a large aperture and symmetrical muscular im- pressions. Pzleolus, Sowerby ; from the Jurassic and Cretaceous. Faminy 20. TiTiscANIIDAE, Bergh. With- out shell and operculum, but with a pallial cavity and a ctenidium. Genus—Titiscania, Bergh (Fig. 131) ; these uinabina: from the Pacific Ocean. Famity 21. HELIcINIDAR, dorsalaspect. I,eye; Pfeiffer. No ctenidium, but a pulmonary cavity He aos allied present; epipodium without tentacles; heart with a Pacey gill. single auricle, and not traversed by the rectum; no inandible ; operculum without apophyses. Genera— Helicina, Lamarck. FEutrochatella, Fischer. Stoastoma, Adams. Bourcteria, Pfeiffer, Faminy 22. Hyprocentpar, Fischer. No ctenidium, but a pulmonary cavity present; foot obtuse ; operculum calcareous, with an Fig. 131. THE GASTROPODA 151 apophysis. .Genus—Hydrocena, Parreys; from Dalmatia. Faminy 23. PROSERPINIDAE, Fischer. Differs from the two last families in not having an operculum. Genus—Proserpina, Gray ; from Central America. ORDER 2. Pectinibranchia. These are Streptoneura with a somewhat concentrated nervous system ; without a labial commissure, except in Paludina and Ampul- laria. The nerve-collar is situated behind the buccal bulb, except in Ampullaria. ‘There is a single well-differentiated, independent, and often pectinated osphradium. The eye is always closed, and the internal cornea (pellucida) is extensive. Each otocyst contains a single otolith, except in some forms of 'Taenioglossa devoid of a pro- boscis, e.g. Paludina, Valvata, Ampullaria, Cyclophorus, Typhobia, Bythoceras, Nassopsis, certain Cerithiidae, etc. The central tooth of the radula is single or absent. There is no longer any trace of bilateral symmetry in the circulatory, respiratory, and excretory organs, the topographically right half of the pallial complex having completely disappeared. The heart has only a single auricle—that of the morphologically right side—and is not traversed by the rec- tum. The ctenidium is monopectinate and attached to the mantle throughout its length, except in Adeorbis and Valvata, the latter genus being the only Pectinibranch with a bipectinate ctenidium. The single kidney usually opens directly by a slit-shaped aperture (but exceptionally by a ureter in Paludina, Cyclophorus, and Valvata), and never serves for the passage of the sexual products. The gonad always has a separate orifice of its own. The male gencrally has a penis (Fig. 44, A, A). The Pectinibranchia are divided into two sub-orders—Taenio- glossa and Stenoglossa. Sup-OrpDER 1. TAENIOGLOSSA. In these Pectinibranchs the radula has normally three teeth on each side of the median tooth, viz. one lateral and two marginals (Fig. 2, B; 74, B). The stomatogastric ganglia are situated behind the buccal mass, and are united to the cerebral centres by long connectives which are in part recurrent and deeply situated. The salivary ducts, when sufficiently long, traverse the nerve-collar. The oesophagus is nearly always devoid of an unpaired gland. Usually there is neither a proboscis nor a siphon. The sub-order includes two distinct groups or tribes, which are respectively creeping and swimming forms, namely, the Platypoda and Heteropoda. TRIBE 1. PLATYPODA. Normal Taenioglossa, but slightly modified, and of creeping habit. The foot is flattened ventrally, at all events in its anterior part (Strom- bidae). The otocysts are situated close to the pedal nerve-centres. Acces- 152 THE GASTROPODA sory organs are rarely found on the genital ducts, but are present in Palu- dina, Cyclostoma, the Naticidae, Calyptraeidae, etc. Mandibles are usually present. The intestine is long. The Platypoda form the largest group of the Mollusca, comprising nearly sixty families of unequal value, some of which are not thoroughly well known from an anatomical point of view. FamiLy 1. PALUDINIDAE, d’Orbigny, Ctenidium monopectinate ; pedal centres in the form of ganglionated cords; the kidney is provided with a ureter; viviparous ;_ fluviatile. Genera—Paludina, Lamarck. Neo- thawma, Smith ; from Lake Tanganyika. Tylopoma, Brusina; from the Tertiary. Famriity 2. CychopHoripak, Gray. Pallial cavity devoid of a ctenidium and transformed into a lung; pedal centres in the form of ganglionated cords ; otocysts with otoconia; aperture of the shell and the operculum circular ; terrestrial. Genera—Pomatias, Hartmann ; shell turriculated. Diplommatina, Benson. Hybocystis, Benson. Cyclophorus, Montfort ; shell umbilicated, with a short spire and horny operculum. Cyclosurus, Morelet ; shell uncoiled. - Dermatocera, Adams; foot provided with a horn-shaped protuberance at its posterior end. Spiraculum, Pear- son ; aperture provided with a sutural tube at its superior angle. FAMILY 3. AMPULLARIIDAE, Gray. A monopectinate ctenidium present, and to the left of it a pulmonary sac, separated from the ctenidium by an incom- plete septum ; oesophageal nerve-collar in front of the buccal bulb ; penis pallial; amphibious. Genera — Ampullaria, Lamarck ; visceral sac and shell coiled dextrally. Lanistes, Montfort ; shell sinistral ; spire short or obsolete. Meladomus, Swainson; shell elongated, sinistral. Faminy 4, Lirrortnipar, Gray. Ctenidium monopectinate ; oesophageal pouches present ; pedal nerve-centres concentrated ; a pedal penis near the right tentacle. Genera—Littorina, Férussac ; shell not umbilicated ; foot devoid of appendages ; marine forms of semi-aerial habit (Fig. 85). Lacuna, Turton ; foot with two posterior appendages ; marine forms of exclusively.aquatic habit (Fig. 7). Cremnoconchus, Blandford ; shell umbili- cated ; of exclusively aerial habit; Indian. Risella, Gray. Tectarius, Valen- ciennes, Faminy 5. FossaripAg, Fischer. Shell turbinated and umbili- cated ; head with two cephalic lobes, as in some Rhipidoglossa. Genus Fossarus, Philippi. Famriry 6. PuRPURINIDAR, Zittel. An exclusively fossil family ; shell thick, with prominent spire, angular whorls, and oval aperture. Genera— Purpurina, VOrbigny; Jurassic. Brachytrema, Morris and Lycett ; Jurassic. Sculites, Conrad ; Ordovician. FAmILy 7. PLANAXIDAE, Adams. Shell not umbilicated, with pointed spire; the external border of the shell sharp; a short pallial siphon. Genus — Planaxis, Lamarck. Faminy 8. CycLosroMaTIpAB, Pfeiffer. Pallial cavity transformed into a lung; pedal centres concentrated ; otocysts with otoliths ; no mandibles; a deep longitudinal pedal groove present ; terrestrial. Genera—Cyclostoma, Draparnaud ; shell turbinated ; opercu- lum calcareous; British. Omphalotropis, Pfeiffer; shell turriculated ; operculum horny. Faminy 9. AcicuLIDAE, Gray. Shell narrow and elongated ; operculum horny; pallial cavity a pulmonary chamber ; otocysts with otoconia. Genus— Acicula, Hartmann. Famiry 10. VALVATIDAE, Gray. Ctenidium bipectinate, free throughout its length ; a pallial filament on the right side; hermaphrodite ; fluviatile. Genus— THE GASTROPODA 153 Valvata, Miiller (Fig. 132); British, Famity 11. Rissorpar, Gray. A - monopectinate ctenidium ; epipodial filaments present ; one or two pallial tentacles; snout elongated. Genera — Rissoaw, Fréminville ; operculum simple. Rassoina, d’Orbigny ; operculum with an apophysis. Stiva, Hedley. Famity 12. Lrrroprpan, Fischer. Foot with an epipodium bearing three pairs of tentacles and an operculigerous lobe with two appendages ; in- habitants of the Sargasso weed. Genus—Litiopa, Rang. Faminy 13. ADEORBIIDAE, Fischer. Mantle with two posterior appendages ; ctenidium large and capable of being protruded’ from the pallial cavity ; shell depressed and umbilicated. Genus—Adeorbis, Wood ; British (Fig. 133). Faminy 14. JEFFREYSIIDAE, Fischer. Head with two long labial palps ; shell ovoid, umbilicated ; operculum horny, semicircular, concentric, and earinated. Genus—Jeffreysia, Alder. Faminy 15. HomanoGyriDag, Sars. Shell flattened ; operculum horny, circular ; no cephalic tentacles. Fic. 132. Valvata pisecinalis, dorsal aspect, Fic. 138. magnified. jf, foot; gi, gill; m, Adeorbis subcarinatus, ventral aspect. f, mouth ; op, operculum ; pa.t, pallial foot; g, gill; m, mouth; op, operculum ; tentacle ; sh, shell; te, cephalic pu.c, pallial cavity ; pa.t, pallial tentacle ; sh, tentacle. (After Bernard.) shell; t, tentacle. (After F. M. Woodward.) » Genera—Homalogyra, Jeffreys ; British. Ammoniceras, Vayssicre. FAMILY 16. SKENEIDAE, Fischer. Shell depressed and umbilicated, with a rounded aperture ; cephalic tentacles long. Genus—Shkenea, Fleming ; British. Famriy 17. CHoristipak, Fischer. Shell spiral ; four cephalic tentacles; eyes absent; two pedal appendages behind the operculum. Genus—Choristes, Verrill. Faminy 18. ASsIMINEIDAE, Fischer. Shell conical, with a short spire; operculum horny, spiral; eyes situated at the free extremities of the tentacles. Genus—Assiminea, Leach ; estuarine ; British. Faminty 19.. TRUNCATELLIDAE, Gray. Ctenidium mono- pectinate ; snout very long, bilobed ; foot very short; spire elongated and truncated ; marine and littoral. Genus—TZruncatella, Risso. FAMILY 20. Hyprosipasr, Fischer. Shell with prominent spire; ctenidium monopectinate ; sexes separate ; penis distant from the right tentacle and generally appendiculated ; otocysts with otoliths ; brackish water or fluviatile. Genera—Hydrobia, Hartmann; shell conical, smooth with scarcely convex whorls; operculum horny; brackish water; British. Baikalia, von Martens; from Lake Baikal. Pomatiopsis, Tryon ; foot 154 THE GASTROPODA divided into two sections by a transverse furrow; penis without an appendage. ithynella, Moquin-Tandon. Lithoglyphus, Miihlfeldt ; shell globular with short spire. Spekia, Crosse ; viviparous; from Lake Tanganyika. ‘anganyicia, Crosse (Fig. 78). Limnotrochus, Smith ; from Lake Tanganyika. Chytra, Moore. Littorinida, Eydoux and Souleyet. Bithynia, Gray ; shell conical with an oval aperture; oper- culum calcareous, concentric ; habitat fluviatile; British. Stenothyra, Benson ; aperture rounded and contracted ; operculum calcareous, spiral. Famity 21. Mrevanupak, Gray. Shell spiral, the spire somewhat elon- gated ; operculum horny ; foot and snout short ; mantle border fringed ; viviparous (Fig. 109); fluviatile. Genera—Melania, Lamarck ; shell turri- culated ; aperture rounded and enlarged anteriorly. Haunus, Montfort ; spire very long; aperture of shell notched anteriorly. Paludomus, Swainson; shell short, thick, with rounded aperture. Melanopsis, Férussac. Nassopsis, Smith. Bythoceras, Moore ; from Lake Tanganyika. Faminy 22, TypHostipA£, Moore. Foot wide; tentacles elongate ; shell turriculated, with carinated whorls, the carinae tuberculated or spiny. Genera—Typhobia, Smith. Bathanalia, Moore; from Lake Tanganyika. Famity 23. PLEUROCERIDAE, Fischer. Like the Melaniidae, but the border of the mantle is not fringed and the reproduction is oviparous. Genera—Pleurocera, Rafinesque ; shell elongated ; the aperture canaliculated anteriorly. Anculotus, Say ; shell short, globular ; the aperture rounded anteriorly. Faminy 24. PSEUDOMELANIIDAE, Fischer. An exclusively fossil family ; shell turriculated, with prominent spire and elongated oval aperture. Genera—Pseudomelania, Pictet and Campiche ; Secondary and Tertiary. Loxvonema, Phillips; Palaeozoic. Macrochilus, Phillips ; Devonian to Trias. Faminy 25. SuBuLitmasg, Fischer. An exclusively fossil family ; shell turriculated with a narrow aperture, elongated and canaliculated anteriorly. Genera—Subulites, Conrad ; Cambrian to Car- boniferous. Fusispira, Hall; Ordovician. Huchrysalis, Laube ; Trias. FamILy 26. NERINEIDAE, Zittel. An exclusively fossil family ; shell with numerous whorls, with multiple folds in the lumen of the whorls. Genera— Nerinea, Defrance ; Jurassic and Cretaceous, Aptyxiella, Fischer ; Trias and Jurassic. Ptygmatis, Sharpe ; Jurassic and Cretaceous. FAMILY 27. CERITHIIDAE, Fleming. Shell with elongated spire and numerous tuberculated whorls; aperture canaliculated anteriorly; snout long ; pallial siphon short. Genera—Cerithiwm, Adanson ; aperture oval ; operculum oval, with submarginal nucleus. Bittiwm, Gray ; operculum circular, with central nucleus; siphon rudimentary. Potamides, Brong- niart ; eyes situated above the bases of the tentacles; ctenidium rudi- mentary ; brackish water. | T'riforis, Deshayes ; shell sinistral. Laeocochlis, Dunker and Metzger. Cerithiopsis, Forbes and Hanley. Famity 28, Mopvipa®, Fischer. This family differs from the Cerithiidae in having a shell with a short spire, without a siphon ; the eyes are placed midway up the tentacles. Genus—Modulus, Gray. Famity 29. VERMETIDAE, @VOrbigny. The animal is fixed by the shell, the last whorls of which are not in contact with one another ; foot small, discoidal, with two anterior pedal tentacles, one on each side of the supra-pedal gland, Genera—Vermetus, Adanson ; shell without a notch on the exterior border of the aperture ; THE GASTROPODA 155 mantle slit in the female only (Fig. 45); pedal tentacles elongate. Siliquaria, Bruguitre ; mantle and shell slit in both sexes for the whole length of the branchial cavity ; pedal tentacles rudimentary. Faminy 30. CArcrIDAr, Gray. Shell almost completely uncoiled in one plane, and furnished with internal septa; aperture circular. Genus—Caecum, Fleming (Fig. 68) ; British. Famity 31, Turrirecnipar, Clark. Shell very long with numerous whorls ; head large and prominent ; mantle border fringed ; no siphon; foot broad and truncated. Genera—Turritella, Lamarck ; British. MJesalia, Gray. Mathilda, Semper; the summit of the shell hyperstrophic. Famity 32. SrRuTHIOLARIIDAE, Fischer. Spire of shell conical; aperture pointed and subcanaliculated anteriorly ; foot oval, rather small; head elongate with short tentacles ; siphon very slightly developed. Genus—Struthiolaria, Lamarck. FAMILY 33. CHENOPODIDAE, Fischer. Spire of shell elongated ; margin of aperture expanded ; foot elongated and narrow ; snout short ; tentacles long ; siphon very short. Genera — Chenopus, Philippi; British. Alaria, Morris and Lycett ; Jurassic and Cretaceous. Spinigera, d’Orbigny ; Jurassic. Diartema, Piette ; Jurassic. Famity 34. SrrompBrpa®, Gray. Foot narrow, arcuate, compressed laterally, without ventral sole (Fig. 75, f) ; snout long ; ocular peduncles longer and stouter than the tentacles. Genera—Strombus, Lin- naeus ; shell ovoid, with elongated aperture ; mantle border and aperture of shell not digitate. Pteroceras, Linnaeus ; mantle border and aperture of shell digitate. Rostellaria, Lamarck ; spire of shell elongate ; aperture prolonged anteriorly into a canal and laterally into an aliform expansion (Fig. 46). Terebellum, Klein ; shell elongated with a short spire ; tentacles aborted. Famity 35. XENOPHORIDAR, Philippi. Snout elongated ; foot divided transversely into two parts, the posterior part bearing the oper- culum ; shell conical, carinated. Genera—Xenophorus, Fischer (Fig. 134) ; with foreign substances agglutinated on the shell. Hotrochus, Whitfield ; from the Silurian. Fairy 36. Capuntpan, Fleming. Visceral sac and shell conical, but slightly incurved posteriorly ; a tongue-shaped projection between snout and foot ; columellar muscle horseshoe-shaped. | Genera— Capulus, Montfort. Thyca, Adams ; parasitic on Asterids; without a radula ; foot rudimentary. Platyceras, Conrad; from the Silurian onwards. Famity 37. Hirronycrpar, Fischer. Visceral mass and shell conical ; foot feebly muscular, capable of secreting a ventral calcareous plate ; animal fixed. Genera—Hipponyx, Defrance. Mitrularia, Schumacher ; the shell with an internal appendage shaped like a half-horn. Faminy 38. CALYPTRAEIDAR, Broderip. Visceral mass spiral; shell flattened, with a short spire; lateral cervical lobes present ; foot short and circular ; accessory genital glands present. Genera—Culyptraca, Lamarck ; shell spiral, with central summit and circular aperture ; British. Crepidula, Lamarck ; shell oval, with nearly obsolete spire and marginal summit, furnished with an internal horizontal posterior septum. Crucibulum, Schumacher ; shell conical, with an internal corniform appendage (Fig. 69). Fairy 39. Naricipar, Recluz. Foot divided into two, the posterior half bearing the operculum ; a wide epipodial velum ; tentacles flattened ; snout elongate; shell turbinated. Genus—Narica, Recluz. Faminy 40. Naticipan, Swainson. Foot highly developed and provided 156 THE GASTROPODA with an aquiferous system; propodium reflected over the head; eyes deeply seated or absent ; operculum spiral ; burrowing animals. Genera —WNuatica, Adanson; shell globular, thick and polished, umbilicated, with a semi-lunar aperture (Fig. 47); British. Amaura, Moller ; shell not umbilicated, thin, with an oblong aperture. Szgaretus, Lamarck ; shell auriform, with a very short spire and large aperture ; operculum small and rostrate. Faminy 41. LAMELLARIIDAE, d’Orbigny. Shell thin,. more or less covered by the mantle, and with a small spire ; no operculum or propodium ; mandibles fused dorsally. Genera—Velutina, Fleming ; shell only partially covered by mantle; British. Lamellaria, Montagu ; shell internal, spiral, transparent ; British. Marsenina, Gray ; shell not completely covered by the mantle ; hermaphrodite. Oneidiopsis, Beck ; Fig. 134. Xenophorus ecutus, animal and shell, left-side view. a, snout; b, cephalic tentacles ; c, left eye; d, anterior part of the foot (to the right of this is seen the posterior lobe of the foot bear- ing the sculptured operculum f). (From Lankester, after Owen.) shell internal, membranous, without spiral; hermaphrodite. FamiLy 42. TRICHOTROPIDAE, Gray. Shell with short spire, umbilicated, carinate and pointed. Genus—Tvrichotropis, Broderip and Sowerby. Faminy 43. SEGVENZUDAE, Verrill. Shell trochiform, with canaliculated aperture and twisted columella ; operculum spiral. Genus—Seguenzia, Jettreys abyssal. Faminy 44. JANTHINIDAE. Shell thin; operculum absent tentacles bifid ; eyes absent ; foot short, provided with an epipodium and secretes a float ; radula with similar pointed teeth (Fig. 74, D); pelagic. Genera—Janthina, Lamarck ; shell blue, with a short spire ; ctenidium with long pointed filaments, capable of being protruded from the pallial cavity (Fig. 135). Recluzia, Petit; shell white with elongated spire. Faminy 45. CyprarIDAE, Fleming. Shell inrolled, solid, polished, the spire nearly hidden, the aperture very narrow in the adult; pallial aperture provided with a short anterior siphon ; a short proboscis ; anus posterior ; foot broad; osphradium with three lobes; mantle reflected . ? . ? ali THE GASTROPODA 157 over the shell (Fig. 70). Genera—Cypraea, Linnaeus ; shell ventricose with a crenelated columella, Pustularia, Swainson ; differs from Cypraea in having an internal shell. Ovula, Bruguitre ; columella smooth, both ends of the aperture canaliculated (Fig. 136). Pedicularia, Swainson ; attached to corals; foot small ; shell irregular with an expanded aperture. Erato, Risso; shell piriform, with a prominent spire. Faminy 46. -Trironipar, Adams. Shell turriculated and siphonated, thick, each Fic, 135. Female Janthina, with egg-float (a) attached to the foot. b, egg-capsules ; c, ctenidium; d, cephalic tentacles. (From Lankester, after Owen.) whorl of the spire provided with varices; foot broad and truncated anteriorly ; pallial siphon well developed ; a proboscis. _Genera—T'iton, Montfort ; varices not continuous from one whorl to another ; eyes at the bases of the tentacles (Fig. 44, A). Persona, Montfort ; whorls irregular ; eyes half-way up the tentacles. Ramnella, Lamarck ; varices continuous from one whorl to another. Faminy 47. COLUMBELLINIDAR, Fischer. An exclusively fossil family ; shell with prominent spire, narrow aperture, and callous columella. Genera—Columbellina, VOrbigny ; cretaceous. Colwm- bellaria, Rolle; Jurassic. Zittelia, Gemellaro; Jurassic. Petersia,Gemellaro ; Jurassic. Faminy 48. Cassrpipar, Adams. Shell ventricose, with elongated aperture and short spire; foot broad and rounded anteriorly ; proboscis and siphon long ; oper- culum with marginal nucleus. Genera—Cuassis, Lamarck ; shell varicose, with narrow aperture. Cassidaria, Lamarck ; shell with- out varices, aperture oval and canalicnlated. Onzscia, Sowerby ; shell oval, with a linear aperture. Famity 49. OocORYTHIDAER, Fischer. Shell globular and Bie eae ventricose ; aperture oval and BeuNEN CRE tee 5 a fants Ae ee sige canaliculated : operculum spiral. is naturally carried in a reflected condition so as ; : to cover in the sides of the shell. (From Lan- Genus—Oocorys, Fischer ; abyssal. ester, after Owen.) Famity 50. Donipaxr, Adams. Shell ventricose, with short spire and wide aperture; no varices and no operculum ; foot very broad with projecting anterior angles ; siphon long. Genera—Dolium, Lamarck; shell with a short canal; ocular tubercles distinct from the tentacles; mantle’ not reflected over the shell. Pyrula, Lamarck ; canal long ; spire very short ; mantle reflected over the shell; eyes sessile (Fig. 71). Famity 51. Soarimpag, 158 : THE GASTROPODA Chenu. Shell spiral, conical, with flattened spire, umbilicated ; head short; tentacles split throughout their length; foot short. Genera— Solarium, Lamarck. Torinia, Gray. Fluxina, Dall. Faminy 52. ScaLARIIDAE, Broderip. Shell turriculated with numerous whorls and an elongated spire; head short, with a short proboscis; foot small, truncated anteriorly ; siphon rudimentary. Genera—sScalaria, Lamarck ; shell elongate with a circular aperture, whorls very convex, ornamented with longitudinal projecting lamellae ; British. Eglisia, Gray. Crossea, Adams. Aclis, Loven. The three following families of Taenioglossa Platypoda have neither radula nor jaws, and are therefore called Aglossa. ‘They are suctorial animals with a well-developed proboscis, and are often commensal or parasitic on Echinoderms; some are abyssal. The series affords a remarkable example of the regressive evolution of various organs as a result of parasitism. Faminy 53. PyRAMIDELLIDAE, Gray, Summit of spire heterostrophic (Fig. 65, B); tentacles deeply grooved externally or split at their extremities; foot truncated anteriorly ; a projection, the “mentum,” between the head and foot; an operculum present. Fic. 137. Turbonilla scalaris, right-side view. f, foot; m, mouth; me, mentum; op, operculum ; pa, mantle; sh, shell; te, tentacle. (After Loven.) Genera—Pyramidella, Lamarck ; ‘columella folded, tentacles corniform. Turbonilla, Leach; columella not folded (Fig. 137). Odostomia, Fleming ; columella provided with a tooth; hermaphrodite ; British. Myxa, Hedley. Faminry 54. Evunimipar, Adams. Visceral mass. still coiled spirally ; shell thin and shining, generally with a pointed summit ; tentacles without a groove. Genera—Eulima, Risso; foot well developed, and with an operculum ; animal usually free, but some live in the digestiye canal of Holothuriae in the Fiji Islands, in the Philippines, and in Europe, e.g. Eulima distorta in Holothuria intestinalis. Niso, Risso. Scalenostoma, Deshayes. Hoplopteron, Fischer. Mucronalia, Adams (=Stylina, Fleming); foot reduced, but still operculate ; eyes present ; animal fixed by its very long proboscis, which is deeply buried in the tissues of an Echinoderm ; no pseudopallium. Stylzfer, Broderip ; the operculum is lost, but a rudiment of the foot remains ; tentacles very small or absent ; eyes, otocysts, and a branchia present ; animal fixed by a large proboscis forming a pseudopallium which surrounds the whole of the shell except the more or less projecting extremity of the spire (Fig. 20); sexes separate; parasitic on all groups of Echinoderms in different seas. | Hntosiphon, Koehler and Vaney ; visceral mass still coiled ; shell much reduced; proboscis very long, forming a pseudo- THE GASTROPODA 159 pallinm, which covers the whole body and projects beyond in the form of a siphon, and serves to put the animal in communica- tion with the external world and for the passage of the ova (Fig. 21); a foot is retained, and also a nervous system and oto- cysts ; neither eyes, branchia, anus, nor rectum; the stomach is a sac with ramifying caeca ; hermaphrodite ; parasitic in the Holothurian Deima blakei, in the Indian Ocean. ntosiphon forms the transition to the next family. Famity 55. Enro- CONCHIDAE, Fischer (= Cochlo- syringia, Voigt). Neither shell nor spirally coiled visceral mass ; no sensory organs, nervous system, branchia, or anus ; body reduced to a more or less tubular sac ; endoparasitic in Holo- thurians ; probably all herma- phrodite, with separate male and female gonads ; incubatory (“viviparous”); with conchi- ferous and operculiferous veliger larvae, without a retractor veli muscle. Genera — Entocolaz, Voigt ; visceral mass essentially genital and forming a swelling surrounded by the — pseudo- pallium ; digestive orifice or proboscis at the free extremity ; orifice of the pseudopallium at the opposite extremity by which the animal is fixed; a second accessory aperture of the pseudo- pallium serves for the passage of the genital products. Two species parasitic in Holothurians in the Pacific: EH. ludwigi, in Myriotrochus vrinkit from the Behring Sea (Fig. 138); and £. schiemenzt in Chirodota pisanti from Chili. Entoconcha, J. Miiller MW Tu TT LUT TT Li 9) IV: Fig. 138. Entocolux ludwigi, in situ, x 30. I, fixative apparatus ; II, ovary; III, uterus; IV, buccal orifice; V, oviduct; VI, genital orifice ; VII, ova separated from the ovary, by dehiscence; VIII, cavity around the ovary, formed by the pseudo- pallium ; IX, orifice of this cavity ; X, integument of the Holothuria. (After Voigt.) (Fig. 139) ; body elongated and tubular ; the aperture of the digestive tract rudimentary and situated at the fixed extremity of the body ; protandric 160 THE GASTROPODA hermophrodite with separate male and female gonads ; parasitic in the testis of Holothurians, causing their abortion. Three species are known: one in Synapta digitata (Mediterranean), one in Holothuria edulis (Philippines), and one in a Holothuria from Puget Sound in the North-East Pacific. Hnteroxenos, Bonnevie ; no pseudopallium and no alimentary tract; male and female gonads separate, with a single common genital orifice; larvae operculiferous. . ostergreni (Fig. 140); parasitic in the intestine of Stichopus (Norway). Fic. 139. Entoconcha mirabilis, in situ, mag- nified. I, oral extremity ; IL, remains of the digestive tract ; III, testis; IV, oe t : 3 : Fic, 140. ovary; V, antimesenteric vessel of ; f the Synapta in which ELntoconcha is Enteroxenos ostergreni, Bonnevie. parasite. (After J. Miiller.) ov, eggs. (After Bonnevie.) TRIBE 2. HETEROPODA. These are free-swimming Taenioglossa, with the foot flattened laterally and the otocysts situated near the cerebral ganglia. There are no mandibles and the intestine is short. All the Heteropoda are pelagic, and are much modified in adaptation to this mode of existence. The foot is very large, and has the form of a fin compressed bilaterally ; it bears, in the male at least, a sucker on its ventral aspect (Fig. 142, d’). The visceral sac or “nucleus” and mantle form a progressively smaller and smaller part of the mass of the body (compare Figs. 142 and 143), but the head always remains large and forms a cylindrical snout. The cerebral nerve-centres are in juxtaposition; the pleural ganglia, still visible in the Atlantidae and Pterotracheidae, are attached to them, and there are thus two pedal connectives on either side, namely, the cerebro- pedal and the pleuro-pedal ; these are separate proximally in Atlanta, but is THE GASTROPODA 161 fused together for their whole length in other forms. The pedal centres are situated at the base of the fin (Fig. 142, v). The visceral commissure is fairly long, is crossed, and bears several ganglia, but there is neither dialyneury nor zygoneury. In the Carinariidae, however, there are secondary uncrossed viscero-pedal anastomoses, and in the Pterotracheidae the pedal connectives are fused with the anterior part of the visceral commissure, and behind the pedal ganglia the two branches of this com- missure are fused together for the greater part of their length. The osphradium is a more or less elongated ciliated organ, situated in the pallial cavity to the left of the branchia. The otocysts are situated near Fic. 141. Oxygyrus keraudreni, male, right-side view. A, head; a, mouth and odontophore ; B, anterior part of the foot; b, cephalic tentacles ; c, eye; d, natatory foot and its sucker ; e, posterior lobe of the foot ; 7, operculum ; i, mantle and pallial cavity ; i, ctenidium ; /:, retractor muscle of the foot (columellar muscle) ; 7, optic tubercle ; m, oesophagus ; 7, salivary gland ; 0, rectum and anus ; p, liver; g, kidney; s, ventricle ; w, the otocyst attached to the cerebro-pleural ganglion ; w, testis; x, auricle of the heart; y, vesicula seminalis; z, penis. (From Lankester, after Souleyet.) the cerebral ganglia (Fig. 141, wu). The eyes are very large and highly differentiated in structure ; they are placed at the sides of the cerebral ganglia and at the bases of the tentacles (Fig. 141, c) when the latter organs exist (Pterotrachea and the female in some Firoloida are devoid of tentacles). The alimentary canal is furnished with a protractile pharynx containing a characteristic Taenioglossate radula with very powerful lateral and marginal teeth. The oesophagus is very long and slightly dilated in the middle of its length. The stomach and liver are situated posteriorly (Fig. 142, m) , the intestine is always very short, and in the Pterotracheidae it is no longer bent forward (Fig. 143). /The heart is situated near the stomach, and in the less specialised Heteropoda (Atlantidae, Carinariidae) is clearly disposed in the same manner as in other Streptoneura, but in the Pterotracheidae, which have undergone detorsion, it has clearly become an opisthobranch ia 162 THE GASTROPODA heart. In the Atlantidae there is an aortic bulb; the arterial vessels always end abruptly in sinuses. The ctenidium is monopectinate and completely enclosed in the pallial cavity in Atlanta (Fig. 141, 2), but it pro- jects in Carinaria (Fig. 142, 7), is no longer covered by the mantle in Ptero- trachea (Fig. 143, br), and finally has completely disappeared in F%roloida. The kidney is a transparent and sometimes contractile sac, which has the same relations as in other Taenioglossa and opens not far from the anus (Fig. 141, q). The gonad is situated beside the liver (Fig. 141, w). The genital duct is always rather short, and opens alongside of the anus; in the male it exhibits a dilatation, the vesicula seminalis (Figs. 141 and 142, y), and its aperture communicates with the penis by means ofa seminal groove. The penis is situated at the base of the foot, and is provided with a glandular Fia. 142. Carinaria mediterranea, male, right-side view. A, the animal; B, the shell removed; C, D, two views of the shell of Cardiopoda. a, mouth and odontophore ; 0, cephalic tentacles ; ¢, eye ; d, the fin-like anterior lobe of the foot ; ’, its sucker ; e, posterior part of the foot; f, salivary glands ; h, margin of the mantle ; 7, ctenidium ; m, oesophagus ; 7, stomach ; 0, anus; p, liver ; t, aorta, springing from the ventricle ; w, cerebro-pleural ganglion ; ¥, pedal ganglion ; w, testis ; 2, visceral ganglion ; y, vesicula seminalis ; z, penis. (From Lankester, after Souleyet.) appendage or flagellum. In the female the genital duct is furnished with a copulatory bursa and an albuminiparous gland. The Heteropoda lay floating eggs imbedded in a gelatinous matrix ; the larvae are charac- terised by the velum, which is divided into four or six lobes. All the Heteropoda are pelagic and transparent, and are generally found in dense bands in warm and temperate zones, swimming slowly in a reversed position, that is to say, with the foot uppermost. They are all car- nivorous. The tribe includes three families which afford a good example of regressive evolution accompanying a process of detorsion and a return to bilateral symmetry, as in the Opisthobranchs. The specialisation of the group is marked by a progressive reduction, and finally by the disappearance first of the operculum, afterwards of the mantle, and finally of the ctenidium and tentacles. The genus Atlanta is still provided with a well-developed coiled shell and an operculum, and is THE GASTROPODA 163. characteristically prosobranchiate. In Carinaria the shell is uncoiled and rudimentary, and there is no operculum. Pterotrachea has neither shell nor tentacles and is opisthobranchiate. Finally, Firoloida has lost the ctenidium. Faminy 1. ATLANTIDAE, Rang. Visceral sac and shell spirally coiled in one plane ; foot divided transversely into two parts, the posterior part bearing an operculum with a sinistral coil (Fig. 48), while the anterior part forms a fin provided with a sucker. Genera—Orygyrus, Benson ; shell capable of containing the entire animal, carinated only on the last whorl and near the aperture. Atlanta, Lesueur; shell capable of con- taining the whole animal, carinated throughout ; aperture with fissures (Fig. 141). Faminy 2. CartNarripag, Grasset. Visceral sac and shell conical and small in proportion to the rest of the body, which cannot be withdrawn into the shell ; foot elongated, fin-shaped, with a sucker but without an operculum. Genera—Carinaria, Lamarck (Fig. 142). Cardio- ae 7 ee i J eC —— —— Fig. 148. Pterotrachea mutica, seen from the right side. a, pouch for the reception of the snout when retracted ; br, ctenidiuin; c, pericardium ; g, cerebral ganglion ; g’, pedal ganglion ; i, intestine ; mt, posterior part of the foot ; n, so-called visceral nucleus ; oc, cephalic eye ; ph, pharynx; pr, fin-like anterior part of the foot ; v, oesophagus ; w, osphradium ; z, caudal appendage. (From Lankester, after Keferstein.) poda, @Orbigny (Fig. 142, C, D). Faminy 3. PreRorTRACHEIDAE, Gray. Visceral sac very much reduced, without shell and mantle ; anus on the posterior part of the body ; foot provided with a sucker in the male only. Genera—Pterotrachea, Forskal ; no tentacles ; actenidium present ; a filiform appendage at the posterior extremity of the foot (Fig. 143). Firoloida, Lesueur ; tentacles present, but no ctenidium and no posterior appendage to the foot. Pterosoma, Lesson. Sus-ORDER 2. STENOGLOSSA. Pectinibranchs in which the nervous system is much concentrated and always zygoneurous. The perioesophageal nerve-collar is always posterior to and is not traversed by the salivary glands. The stomato- gastric ganglia are situated close to the cerebral nerve-centres and far behind the buccal mass, the last-named organ being greatly reduced. A well-developed proboscis, an unpaired oesophageal gland (the gland of Leiblein or poison-gland), a pallial siphon, and a penis are always present. The osphradium is bipectinate, The radula is narrow, and in the majority of genera (Rachiglossa) has a single lateral on each side of the median or rachidian tooth: in the remainder of the group (Toxiglossa) there is no median tooth, and the radular formula is therefore 1.0.1. The sub-order is accordingly divided into two tribes. 164 THE GASTROPODA TRIBE 1. RACHIGLOSSA. These are Stenoglossa with a highly-developed proboscis, a pallial siphon, and rudimentary jaws: the radular formula is 1.1.1 (Fig. 74, H). Famity 1. TURBINELLIDAE, Sowerby. Shell solid, piriform, with a thick folded columella ; foot broad; proboscis long; tentacles conver- gent; lateral teeth of the radula bicuspidate. Genera—Turbinella, Lamarck ; shell with short spire and long canal. Cynodonta, Schumacher ; spire and canal short; shell tuberculated. Fulgur, Montfort; shell piriform ; tentacles short. Hemifusus, Swainson; shell fusiform with carinated whorls ; tentacles short (Fig. 99). Tudicla, Link. Strepsidura, Swainson. Faminy 2. Fascronarimpan, Adams. Shell elongated, with a long siphon ; head small and narrow, with short tenacles ; foot rather broad and short; lateral teeth of the radula multicuspidate. Genera Fasciolaria, Lamarck. Fusus, Lamarck. Clavella, Swainson. Laturus, Montfort. Faminty 3. Mirrrpar, Adams. Shell fusiform and _ solid, the spire pointed, the aperture elongated and the columella folded ; no operculum ; tentacles elongated, bearing the eyes at their sides; foot narrow ; proboscis very long; siphon moderately long. Genera—WMitra, Lamarck. Turricula, Klein. Cylindromitra, Fischer. Imbricaria, Schumacher. Faminy 4. Buccrnipar, Fleming. Foot large and broad ; eyes at the bases of the tenacles; shell ovoid, with oval aperture; a horny operculum. Genera—Chrysodomus, Swainson; shell fusiform, solid, with an unguiculate operculum; British. Liomesus, Stimpson ; shell ovoid, with a very short canal ; tentacles short ; lateral teeth of the radula unicuspidate. Buccinwm, Linnaeus ; shell ventricose with a wide aperture ; operculum oval with sub-central nucleus ; tentacles moderately long ; lateral teeth with three or four cusps; British. Comnella, Gray ; shell fusiform ; the operculum oval to piriform, with an apical nucleus. Tritonidea, Swainson ; shell ventricose ; operculum like that of Cominella. Pisania, Bivona; shell with a short canal; operculum unguiculate ; lateral teeth tricuspidate. Huthria, Gray ; shell fusiform, with elongate spire and canal. Phos, Montfort ; foot broad with two lateral projections anteriorly and a slender posterior filament. Dipsacus, Klein; foot elongated ; tentacles long ; shell ovoid, solid, with a short canal; lateral teeth bicuspidate. Faminy 5. Nasstpan, Swainson. Foot broad, with two slender posterior appendages ; siphon long; shell ovoid, with a short canal; operculum unguiculate. Genera— Nassa, Lamarck ; external border of the aperture of the shell thickened ; marine ; British. Canzdia, Adams; exterior border of the aperture simple; fluviatile. Bulla, Gray ; shell polished; tentacles without eyes; foot very broad; a burrowing form. Famiry 6. Muricipan, Fleming. Foot truncated anteriorly ; tentacles elongated, bearing the eyes on their sides, more or less high up; shell with moderately long spire and canal, ornamented with ribs, often spiny. Genera—Murex, Linnaeus ; eyes half-way up the tentacles ; canal almost closed ; British. Trophon, Montfort ; eyes at the bases of the tentacles; shell lamellar; canal open; British. Typhis, Montfort ; sheli with closed canal and tubular spines. Urosalpina, Stimpson. Lachesis, Risso. Famity 7. PurpurRIDAE, Broderip. Foot PHE GASTROPODA 165 short, obtuse posteriorly ; shell thick with a short spire, the last whorl large and the canal short ; aperture wide ; columella flattened ; operculum horny. Genera—Purpura, Bruguiére; shell not umbilicated, aperture smooth ; British. Rapana, Schumacher ; shell ventricose, umbilicated. Monoceros, Lamarck ; shell like that of Purpura, but the aperture shifted backward and bearing a conical tooth on its external border. Sistrwm, Montfort ; shell thick, spiny, the aperture contracted by the thickening of the margins of the aperture. Concholepas, Lamarck ; shell ovoid, the spire short and the aperture widely dilated. Faminy 8, Hatiipag, Fischer. Foot large and thick ; without an operculum ; tentacles thick and flattened ; shell ventricose, thin, and smooth, with a wide aperture. Genus—Halia, Risso; from Cadiz and Morocco, Faminy 9. CANCEL- LARIIDAE, Adams. Snout short; tentacles long, with the eyes at their bases and external; foot small; no operculum; siphon short; shell ovoid with short spire and folded columella. Genus — Caneellaria, Lamarck. Famity 10. CoLtumBEeLLtipAr, Adams. Foot large, tentacles long and convergent; spire of shell prominent, aperture narrow, the canal very short and the columella crenelated, Genus — Columbella, Lamarck. Faminy 11. CORALLIOPHILIDAE, Chenu. Foot short ; ten- tacles slender and convergent ; siphon short ; radula absent; shell irregular; sedentary animals living in corals. Genera— Corallio- phila, Adams; shell deformed, with a wide aperture and a short canal ; operculum present. Rhizochilus, Steenstrup; no operculum; the aperture of the shell irregular, with the canal prolonged into a tube. Leptoconchus, Riippel ; no operculum ; the shell globular with a wide aperture. Magilus, Montfort ; an operculum present ; the last whorl of the shell uncoiled and very thick. Rapa, Klein; an operculum present ; shell globular and umbilicated, the aperture provided with a canal. Faminy 12. VoLuTiIpar, Gray. Head very flattened, and transversally widened, with the eyes on the Conus lineatus, ventral aspect. sides 5 snout short ; foot broad ; siphon with Tore Pecan internal appendages. Genera— Voluta, Lin- cavity; U1, operculum; LV, an- naeus; head with eyes; Australian seas. ue pee rateae VE Guivillea, Watson ; no eyes; abyssal. Cymba, siphon; VII, mouth. (After Broderip and Sowerby ; viviparous. FamIny aa 13. Onivipak, d’Orbigny. Eyes, when present, on the middle of the tentacles; fore part of the foot with a transverse groove; a posterior pallial tentacle ; generally burrowing. Genera— Oliva, Bruguicre ; eyes ; no operculum. Olivella, Swainson; tentacles without eyes ; an operculum. Ancillaria, Lamarck. atic caecum. : (After Vayssiére.) 4 the visceral mass marked off from the posterior part of the foot; dorsal tegumentary append- ages absent or reduced to a single pair; spicules developed in the integument. Genus— Hedyle, Bergh (Fig. 168); from the Black Sea, Sea of Marmora, Mytilene, Flores. Fammy 4. PSEUDOVERMIDAE, Pelseneer. Head devoid of tentacles; body elongated ; the anus on the right side. Genus— Pseudovermis, Periaslavzeff (Fig. 169); from the Black Sea and Mytilene. Famity 5. Procronotmar, Alder and Hancock. Anus situated posteriorly in the median line of the back ; anterior tentacles atrophied; foot broad. Genera — Janus, Vérany ; a median crest between the rhinophores ; British. Proctonotus, Alder and Hancock ; no intertantacular crest ; British. Famtty 6. Doronrpak, Adams. Bases of the rhinophores surrounded by a sheath; dorsal papillae club-shaped and more or less tuberculated, arranged in a single row on either side of the dorsum ; no enidosacs. Genera—Doto, Oken ; a frontal veil; British. Gellina, Gray ; no frontal veil. Heromorpha, 180 THE GASTROPODA Bergh. Fanny 7. Fronipax, Alder and Hancock. Dorsal tegumentary papillae provided with a membranous expansion ; liver in the form of two longitudinal canals into which the caeca of the dorsal papillae open ; male and female orifices at some distance from one another ; pelagic. Fic. 167. Pleurophyllidia lineata. A, dorsal view; B, ventral view. 0b, the mouth; 7, lamelliform pallial gills (the posterior part of the foot bears a median glandular tract). (From Lankester, after Souleyet.) Fic. 169. Pseudovermis paradoxus, dorsal aspect. a, anus ; cd, cnidosac ; e, eye ; k, kidney ; 1, liver; m, mouth (on the 7 ventral side, seen through Fie. 168. the transparent head) ; ns, Hedyle glandulifera, dorsal aspect. e, nervous system ; of, oto- eye ; f, foot (posterior part) ; ”.s, nervous cyst; ph, pharynx; st, system; ph, pharynx ; sp, spicula ; v.m, stomach. (After Kowalew- visceral mass. (After Kowalewsky.) sky.) Genus— Fiona, Hancock and Embleton. Famity 8. PLEUROPHYLLIDIDAE, Adams. Anterior tentacles in the form of a digging shield; mantle naked ; tegumentary papillae or “branchie” situated along the sides of the foot, beneath the mantle border. Genus— Pleurophyllidia, Meckel (Fig. 167). Famity 9, DerMATOBRANCHIDAE, Fischer. Like Plewro- THE GASTROPODA 181 phyllidia, but wholly devoid of “branchiae.”’ Genus—Dermatobranchus, van Hasselt. TRIBE 4. ELYSIOMORPHA. Nudibranchia in which the liver ramifies in the integuments and extends into the dorsal papillae. The genital duct is always triaulic, and the male and female orifices are distant (Fig. 105). The gonad is divided into spheroidal hermaphrodite lobules. There are no mandibles, and the radula is uniserial. There is never more than one pair of tentacles, and these are wanting in Alderia and some species of Limapontia. The otocysts contain each a single otolith. Famity 1. Hermarrpar, Adams. Foot narrow; dorsal papillae without nematocysts, linear or fusiform, and disposed in several series. Genera—Hermaea, Loven ; rhinophores split throughout their length ; dorsal papillae linear ; anus antero-dorsal ; British. Stiliger, Ehrenberg ; rhinophores simple ; dorsal papillae fusiform or ovoid ; anus antero-dorsal. Alderia, Allman; anus median and posterior; no tentacles; dorsal papillae linear; inhabitants of brackish waters; British. Faminy 2. PHYLLOBRANCHIDAE, Bergh. Foot broad; dorsal papillae without TTR Sigg oo Fic. 170. Cenia cockst, left-side view, magnified a, anus. (After Hancock.) nematocysts, flattened and foliaceous. Genera—Phyllobranchus, Alder and Hancock ; foot simple ; anus latero-dorsal. Cyerce, Bergh; ventral part of the foot divided transversely ; anus median. FAminy 3. PLaKo- BRANCHIDAE, d’Orbigny. Body depressed, without dorsal papillae, but with two very large lateral expansions with dorsal plications ; head flattened ; eyes approximated. Genus—Plakobranchus, van Hasselt. Faminy 4. EtysiipAk, Adams. Body elongated, with lateral expansions; head rounded and eyes separated ; tentacles large; foot narrow. Genera Elysia, Risso ; British (Fig. 160, D, E). Tridachia, Deshayes. Famtty 5. LIMAPONTIIDAE, Adams. No lateral expansions of the body and no dorsal papillae ; body planariform ; anus dorsal, median, and posterior. Genera —Limapontia, Johnston ; no tentacles ; head and body devoid of crests ; British. Actaeonia, Quatrefages; head carinated laterally; British. Cenia, Alder and Hancock ; head with two long tentacles (Fig. 170). ORDER 2. Pulmonata, Cuvier. Euthyneura with a pallial cavity but no ctenidium. The pallial aperture is diminished by the fusion of the mantle border with the neck, and reduced to a comparatively small contractile orifice at its posterior extremity (Fig. 177, V). The pallial cavity and shell are 182 THE GASTROPODA often reduced ; the latter may be partially covered over, or internal, or even absent. There is never an operculum in the adult, except in Amphibola, and an operculum is only found during development in the Auriculidae, Siphonariidae, and Oncidiidae, all of which are marine forms. In the pallial cavity the interior wall of the mantle is traversed by vascular arborisations (Fig. 86, X), and thus con- stitutes a pulmonary organ adapted for breathing air. In the Janellidae the pulmonary cavity is prolonged into fine respiratory canaliculi (Fig. 90, fr), and thus becomes a tracheal lung. It is much reduced in the Oncidiidae, and in Ancylus and the Vaginulidae it disappears as a consequence of the complete abortion of the pallial cavity. In some rare cases the pulmonary cavity may be filled with water, and then its wall may give rise to a secondary branchia which is not the equivalent of a ctenidium (Siphonaria, Fig. 174, III). In other cases the inferior pallial lobe, situated beneath the pulmonary orifice of the Basommatophora, may be transformed into a branchia (Planorbidae, Figs. 89, g, and 175, br). The auricle of the heart is usually anterior (Fig. 86), as is the case in the most archaic. Opisthobranchs, and it is only in the excessively detorted forms such as Testacella and the Oncidiidae that the ventricle lies in front of the auricle. The kidney usually has a more or less elongated duct or “ureter ” (Stylommatophora, Fig. 86, V). In the nervous system, as a rule, all the ganglia are concentrated round the oesophagus and are closely apposed to one another (Fig. 146), but this is not the case in some archaic 3asommatophora such as Chalina, Auricula, Latia (Fig. 96). In the Auriculid Pythia, the spermiduct re- tains the character of an open ciliated groove leading from the hermaphro- dite aperture to the penial orifice Fic. 171. (Fig. 171, ci): in other Auriculidae Reproductive apparatus of Pythia. this groove is simply closed to form Seen ania ea te a canal extending from the herma- Hest ar gg, ONO tees eo PUOOILe tO the male orifice. In all phrodite orifice ; 7.0, male orifice ; ‘ muc, mucous gland; pe, penis; ret, ree Other Pulmonates there is no longer tractor muscle of penis ; 7.s, recepta- : : Pi culum seminis; sp, spermiduct; spo, & Common genital orifice, but the Drove; Uh seminal vesicle hermaphrodite duct bifureates to form a distinct oviduct of greater or less length, and the primitive hermaphrodite aperture becomes the female orifice. As a result of secondary changes, the orifices THE GASTROPODA 183 ee | of the oviduct and penis may be approximated, a condition found in the majority of the Stylommatophora (Fig. 104). The Pulmonates never have a free larval form; if a veliger is developed it is always contained in the egg membranes. The majority of Stylommatophora do not pass through a veliger stage, and in other forms the velum is almost always ill developed (Fig. A series of Stylommatophorous Pulmonata, showing the reduction of the shell. A, Helix pomatia ; B, Daudebardia brevipes ; C, Testacella, haliotidea; D, Arion ater. a, external shell in ‘A, B, C; shell-sac (closed) in D; b, orifice of the pallial or pulmonary cavity. - (From Lankester, after Ferussac, Pfeitfer, and Reeve.) 119, A, ve). The Pulmonates are for the most part aerial, but some live in fresh water, and others, but they are exceptional cases, are marine. The Pulmonates are distributed over the whole world, and include some seven thousand species, of which more than half belong to the genus Helix. Most of them enter into a resting stage during some part of the year; in the summer in hot climates, in the winter in cold climates. In our country the hibernation lasts for rather more than a third of the year. 184 THE GASTROPODA The Pulmonata are divided into two sub-orders, Basommatophora and Stylommatophora ; the former are generally aquatic, the latter terrestrial. Sus-ORDER 1. BASOMMATOPHORA. Testaceous Pulmonata with an external shell. The head bears a single pair of well-developed contractile but not invaginable tentacles, at the bases of which are the eyes (Fig. 107, 1). The stomach, or at least a part of it, is very muscular. The penis is at some distance from the female aperture, except in Amphibola and Stphonaria. All have an osphradium (except the Auriculidae, which are terrestrial), which is situated outside the pallial cavity in those forms in which water is not admitted into the lung (Limnaea, Planorbis, Fig. 89, etc.). There is a veliger stage in the development, but the velum is reduced. Famity 1. Auricunmag, Blainville. Terrestrial and usually mari- time animals ; the genital duct monaulic, the penis being connected with the hermaphrodite opening by an open or closed groove (Fig. 171); shell with a prominent spire, the internal partitions often absorbed and the aper- ture denticulated. Genera—Auricula, Lamarck ; foot not divided ; tentacles swollen at their extremities; shell thick, oval, with an elongated aper- ture, and two folds on the columellar border. Cassidula, Férussac ; foot Fic. 173. not divided transversely, but bifid Otina otis, left-side view. cog, shell; oc, posteriorly 5 tentacles tapering ; shell eye; p, foot. solid, umbilicated, with a short spire. Alexia, Leach ; tentacles swollen and pigmented at their extremities; shell thin with a pointed spire, the exterior border of the aperture slightly thickened; British (Fig. 67). Melampus, Montfort ; foot divided transversely and bifid behind ; shell solid, with a short spire and a narrow aperture. Carychiwm, Miiller ; tentacles thick and short, with the eyes on the inside ; shell small and short ; the aperture oval with a denticulated internal border ; terrestrial ; British. Scarabus, Montfort ; foot not divided ; tentacles tapering ; shell oval with a pointed spire, and a very constricted aperture, the margins bearing alternate teeth. Leuconia, Gray ; foot divided ; tentacles short and compressed ; shell thin, oval, with a conical spire ; aperture oval, the columellar border with a single fold; British. Blawneria, Shuttle- worth ; shell sinistral; aperture elongated, with a single columellar fold. Pedipes, Adanson ; foot divided transversely ; shell globular ; the two borders of the aperture dentate ; partitions not absorbed. Famrty 2. Ormnipak, Chenu. Shell with a short spire and a wide oval aperture ; tentacles short. Genera—Otina, Gray ; shell auriform ; marine ; British (Fig. 173). Camptonyxz, Benson; shell conical with a spiral summit ; terrestrial. F Amity 3. AMPHIBOLIDAE, Adams. Visceral mass and shell spirally coiled ; head broad, without prominent tentacles; foot short, operculated. Marine. Genus—Amphibola, Schumacher; from New Zealand, Famity 4. SIPHONARIIDAE, Adams. Visceral mass and shell THE GASTROPODA 185 conical ; tentacles atrophied ; head expanded ; genital orifices contiguous ; marine animals, with an aquatic pallial cavity containing secondary branchial laminae. Genera—Siphonaria, Sowerby (Fig. 174). Hercynella, Kayser; from the Devonian. Faminy 5. Gaprytpan, Gray. Visceral mass and shell conical; head flattened ; pulmonary cavity aquatic, but without a branchia ; genital orifices separated. Genus—Gadinia, Gray. Famity 6. CHILINIDAE, Dall. Shell ovoid with a short spire, wide aperture, and folded columella ; tentacles broad and flattened ; inferior pallial lobe thick ; visceral commissure still twisted. Genus— Chilina, Gray ; rivers of Patagonia. Famity 7. Limnartpan, Broderip. Shell thin, dextral, with prominent spire and oval aperture ; tentacles angular and flat; no inferior pallial lobe. Genera—Limnaea, Linnaeus (Fig. 107); shell wholly external, with a pointed spire; British. Amphi- Fria. 174. Siphonaria algesirae, removed from its shell. I, heart in the pericardium ; II, kidney ; III, pallial intrapulmonary gill; IV, mantle; V, columellar muscle; VI, anus ; VII, pneumostome, to the left of which (in the pulmonary cavity) is the osphradial papilla; VIII, inferior pallial lobe ; IX, renal pore. peplea, Nillson ; shell in great measure covered by the mantle, globular, with a very short spire; British. Faminy 8. PompHotyaipDaxn, Dall. Shell hyperstrophic (ultra-sinistral, that is to say, with an apparently dextral coil) with an obtuse spire; the animal sinistral. |. Genera—Pom- pholyx, Lea; tentacles dilated at their extremities ; shell depressed, the last whorl ventricose ; from California. Choanomphalus, Gerstteldt ; shell umbilicated, with convex whorls; tentacles slender; Lake Baikal and California. Faminty 9. PLranorpipaE, Adams. Visceral mass and shell sinistrally coiled ; inferior pallial lobe very prominent and transformed into a branchia; tentacles tapering. Genera— Planorbis, Guettard ; shell discoid; branchia not folded (Fig. 89); British. Bulinus, Adanson ; shell ovoid with prominent spire ; branchia folded (Fig. 175). Miratesta, Sarasin. Famity 10. ANcyLIpAE, Menke. Shell conical, not spirally coiled; tentacles short and compressed ; inferior pallial lobe 186 THE GASTROPODA transformed into a branchia. Genera—Ancylus, Geoffroy ; no pulmonary cavity ; animal dextral or sinistral ; visceral commissure shortened ; shell without internal septum ; British (Fig. 176). Latia, Gray ; a pulmonary cavity ; visceral commissure long ; shell with a posterior internal septum ; from New Zealand. Gundlachia, Pfeiffer. Famity 11. Paystpas, Dall. Visceral mass and shell sinistrally coiled ; shell thin, with a narrow aperture ; tentacles cylindrical ; no inferior pallial lobe. Genera— Physa, Draparnaud; shell oval, partly covered by the edges of the mantle, which are divided into angular tags; British. Apleza, Fleming ; shell with a pointed spire; edges of the mantle not divided and very slightly re- flected over the shell ; British. Fic. 176. Bre. Ancylus fluviatilis, dorsal Bulinus tabulatus, ventral aspect. view. To the left, the head br, pallial extrapulmonary gill; co, with the two cephalic ten- heart ; 0, mouth; p, foot; pa, mantle ; tacles. (From Lankester, after pns, pneumostome ; te, tentacle. Reeve.) Sup-ORDER 2. STYLOMMATOPHORA. Pulmonata with two pairs of tentacles (except the Janellidae and Vertigo, which have only a single pair); these tentacles are invaginable, and the eyes are borne on the summits of the posterior pair. The male and female genital orifices open into a common vestibule except in the Ditremata (Vaginulidae and Oncidiidae). A suprapedal gland is present in nearly all the groups. With the exception of Uncidiwm, there is no longer a veliger stage in the development ; the embryo is often furnished with a contractile pedal vesicle (Fig. 117). The Stylommatophora may be divided into four tribes : the Holognatha, Agnatha, Elasmognatha, and Ditremata. TRIBE 1. HoLOGNATHA. Jaw simple, without a superior appendage. Famity 1. SeLeniripar, Fischer. Radula with elongated and pointed teeth, like those of the Agnatha; a jaw present. Genera— Selenites, Fischer ; shell external, depressed, widely umbilicated. Plutonia, Stabile ; animal limaciform, with flattened internal shell and a posterior pulmonary aperture. Trigonochlainys, Bottger; no shell. Famimy 2. ZONITIDAR, Pilsbry. Shell external, smooth, heliciform or flattened ; radula with pointed marginal teeth. Genera— Zonites, Montfort ; shell depressed, wholly external; British. Artophanta, Desmoulins ; THE GASTROPODA 187 mantle produced anteriorly into a cervical lobe ; foot with a posterior dorsal mucous pore. Orpiella, Gray; differs from Ariophanta in having a horn-shaped protuberance at the hinder extremity of the foot. Vitrina, Draparnaud ; the mantle projects in front and on the right side, and partially overlaps the thin and depressed shell ; foot elongated, without a posterior mucous pore ; British. Helicarion, Férussac ; differs from Vitrina in having the foot truncated anteriorly, with a posterior mucous pore. Faminy 3. Limactpak, Gray. Shell almost completely covered by the mantle, or internal. Parmacella, Cuvier ; shell unguiform with a spiral summit ; the mantle occupies the centre of the body and completely covers the shell except for a very small orifice above the spire. Limav, Linnaeus ; shell wholly internal, without a spiral summit ; mantle reduced, and situated on the anterior part of the body ; pulmonary aperture towards the hind end of the pallial border ; British. Urocyclus, Gray ; shell oval, without a spire, internal except for a small median orifice in the hinder part of the mantle; pulmonary aperture in the middle of the pallial border; African. Parmarion, Fischer. Amalia, Heynemann. Agriolimaz, Mirch. Mesolimar, Pollonera. Mono- chroma, Simroth. Paralimax, Bottger. Metalimax, Simroth. Famity 4. PHItomycipAk, Fischer. No shell; the mantle covers the whole surface of the body ; radula with squarish teeth. Genus—Philomycus, Férussac ; foot broad; genital orifice near the right tentacle. Famity 5. OsTRACOLETHIDAE, Simroth. Shell largely chitinous, not spiral, its calcareous summit projecting through a small hole in the mantle which elsewhere covers it. Genus—Ostracolethe, Simroth. Faminy 6. ARIONIDAE, Gray. Shell internal or- absent; animal limaciform ; mantle restricted to the anterior and middle part of the body; radula with squarish teeth. Genera—Arion, Férussac ; respiratory orifice at the anterior end of the pallial border ; genital orifice close to the respiratory orifice ; shell reduced to simple isolated calcareous granules; British (Fig. 172, D). Geomalacus, Allinann ; shell internal, oval; Ireland. Aviolimax, Mérch. Anadenus, Moreh. Faminy 7. HELIcIpAE, Gray. Shell with medium spire, external or par- tially covered by the mantle ; mandible folded ; radula with square teeth ; genital orifice below the right posterior tentacle ; geni- tal apparatus generally provided with a dart-sac and multifid vesicles. Genera — Helix, Lin- Fic. 177. naeus ; shell globular, conical or Helix, nemoralis, right-side view. I, anus; II, depressed, with a rounded or ex- ute! (ermaphrodite) pore; IID anterior ten: panded aperture (Figs. Ws A pneumostome in its maximum distension. and 177); British. (A large number of sub-genera has been established, which includes more than 4000 species: Polygyra, Say. Sagda, Beck. Plewrodonta, Fischer von Waldheim. Helicodonta, Férussac. Helicophanta, Beck. Acavus, Mont- fort. Sitala, Adams. Chlorites, Beck. Hapalus, Albers, etc.) Bulimus, 188 THE GASTROPODA Scopoli ; shell ovoid, with oval or elongated aperture and a thickened border. Hemphillia, Binney and Bland; shell unguiform, its edges covered by the mantle; North America. Berendtia, Crosse and Fischer. Cochlostyla, Férussac. thodea, Adams. Famity 8. ENDODONTIDAE, Pilsbry. Shell spiral, external, generally ornamented with ribs ; borders of the aperture thin and not reflected ; radula with square teeth ; genital ducts without accessory organs. Genera—Endodonta, Albers, Punctum, Morse. Sphyradiwm, Charpentier. Laoma, Gray. Pyramidula, Fitzinger. FamiLy 9. ORTHALICIDAE, Fischer. Shell external, ovoid, the last whorl swollen, the aperture oval, with a simple border ; radular teeth in oblique rows. Genus—Orthalicus, Beck ; American. FAMILY 10. BULIMULIDAE. Fischer ; jaw formed of folds imbricated externally and meeting at an acute angle near the base. Genera—Bulimulus, Leach ; shell elongated, oval, external. Peltella, Webb and van Beneden; shell auriform, in- ternal. Amphibulimus, Montfort. Faminry 11. CyLINDRELLIDAE, Fischer, Shell turriculated, with numerous whorls, the last whorl more or less detached. Genus—Cylindrella, Pfeiffer ; aperture circular, with reflected peristome ; summit commonly truncated ; America. Famity 12. PUPIDAE, Fleming. Shell external, with elongated spire and numerous whorls ; aperture generally narrow ; male genital duct without multifid vesicles. Genera— Pupa, Lamarck ; shell cylindrical, dextral with obtuse summit ; aperture parallel to the axis, small and contracted ; British. Hucalodiwm, Crosse and Fischer ; shell turriculated, the summit truncated, the aperture ~ oval. Vertigo, Miller ; shell small, ovoid, the summit obtuse, the aperture small and contracted by numerous teeth ; dextrally or sinistrally coiled ; a single pair of tentacles; British. Buliminus, Ehrenberg; shell umbilicated, ovoid, with elongated aperture and a simple columella ; British. Clausilia, Draparnaud ; shell turriculated, sinistral ; aperture oval; the columella with corrugations and a movable piece, the clausilium, by means of which the mouth of the shell can be closed ; British. Balea, Prideaux ; shell sinistral, differs from Clausilia in the absence of columellar corrugations and clausilium. Zospewm, Bourguignat ; no eyes, shell short and dextral. Megaspira, Lea. Strophia, Albers. Anostoma, Fischer. FaAmiIty 13. SrTENOGYRIDAE, Fischer. Shell elongated, with a more or less obtuse summit ; aperture oval with a simple border. Genera—Achatina, Lamarck ; shell ovoid, the spire conical, the last whorl ventricose ; the columella twisted. | Stenogyra, Shuttleworth ; shell turriculated ; the whorls numerous, increasing slowly (Fig. 8). Ferussacia, Risso; shell small, thin, and brilliant ; aperture elongate, oval ; British. Caecilianella, Férussac ; shell cylindrical, the spire elongated, the columella truncated ; eyes absent; subterranean in habit; British. Cionella, Jeffreys. Azeca, Leach. Opeas, Albers. Ehodea, Adams. Faminy 14. HELIcreRIDAR, Fischer. Shell bulimoid, dextral or sinistral; radular teeth narrow at their bases, expanded at their extremities and multicuspidate. Genera—Helicter, Férussac. Tornatellina, Beck. TRIBE 2. AGNATHA. No jaws; the radular teeth narrow and pointed ; carnivorous. This group is possibly polyphyletic. THE GASTROPODA 189 FamiLy 1. Oxneactntpar, Adams. Shell oval, elongated, with a narrow aperture ; neck very long; labial palps prominent. Genera— Oleacina, Bolton (= Glandina) ; aperture truncated anteriorly ; columella smooth. Streptostyla, Shuttleworth ; columella with a fold; aperture elongate, not truncated anteriorly. Faminy 2. TEsTacELLIDAE, Gray. Shell globular or auriform, external or partly covered by the mantle. Genera—Streptaxis, Gray ; shell external, heliciform, the last whorls generally set obliquely to those first formed. Gbbulina, Beck; shell cylindrical, umbilicated. Aerope, Albers ; shell external, globular, with a small umbilicus ; radular sac enormous; from South Africa. Rhytida, Albers ; shell depressed, with a very wide umbilicus ; from New Zealand. Daudebardia, Hartmann ; shell coiled, only occupying the posterior part of the body ; animal limaciform ; the genital orifice situated between the right tentacle and the shell (Fig. 172, B). Testacella, Cuvier (Fig. 172, C) ; shell small, auriform, situated at the posterior extremity of the limaciform body ; genital orifice near the right tentacle. Chlamydophorus, Binney ; shell plate-shaped and nearly completely covered by the mantle. Schizo- glossa, Hedley. Famity 3. Rarnourstpar, Heude. Animal naked, devoid of a shell, with a carinated mantle covering the whole body ; male and female orifices distant ; the female orifice near the anus. Genera— Rathouisia, Heude. Atopos, Simroth, TRIBE 3. ELASMOGNATHA. The jaw with a well-developed dorsal appendage. Faminty 1. SuccinEmpDArE, Chenu. Anterior tentacles much reduced ; male and female orifices contiguous but distinct ; shell thin, spiral, with a short spire. Genera—Succinea, Draparnaud ; shell external, oblong, with a large aperture; British. Homalonyx, d’Orbigny ; shell auriform, the spire scarcely projecting ; the edges of the shell covered by the Fic. 178. Aneitea macdonaldi, Gray, left-side view. pa.c, pallial cavity; ps, pneumostome ; is tentacle. (After MacDonald.) mantle ; animal limaciform ; American. Hyalimax, Adams; shell oval, wholly internal. Neohyalimax, Simroth. Faminy 2. JANELLIDAR, Gray. Limaciform animals, with an internal rounded shell; the mantle very small and triangular ; the pulmonary chamber with tracheae ; no anterior tentacles. Genera—Janella, Gray. Aneitella, Cockerell. Aneitea, Gray (Fig. 178). Triboniophorus, Humbert. All from the Australo-Zelandic region. TRIBE 4. DITREMATA. Male and female genital orifices distant (Fig. 59, 0,f, 0.m). Famity 1. VERONICELLIDAE, Gray. Terrestrial, naked, limaciform 190 LITERATURE OF THE GASTROPODA animals, without a shell ; the female orifice on the right in the middle of the body ; the anus posterior. Genus—Vaginula, Férussac (Fig. 179), Famrity 2. OncripDAE, Philippi. Limaciform naked marine animals, without a Fig. 179. Vaginula luzonica. A, dorsal aspect; b, ventral aspect. I, posterior tentacle ; II, anterior tentacle ; III, mouth; IV, mantle; V, female orifice; VI, foot; VII, anus. (After Souleyet.) shell ; female orifice near the anus, at the posterior end of the body ; reduced pulmonary cavity with a distinct pneumostome (Fig. 59, pus). Genera—Oncidium, Buchanan ; body elongated and narrow; penis with Fic. 180. - Oncidiwm tonganum, left-side view. (From Lankester, after Quoy and Gaimard.) accessory apparatus; from the Indian Ocean. Oncidiella, Gray ; body oval; mantle thick, with an emarginated border ; penis without accessory apparatus ; British (Fig. 59). Peronia, Blainville ; body oval ; the mantle covered with ramified appendages and oculiferous tubercles. LITERATURE OF THE GASTROPODA. A. Gastropoda generally. 1. Amaudrut. La partie antérieure du tube digestif et la torsion chez les Mollusques Gastéropodes. Ann. des Sci. Nat. Zool. (8), vii. 1898. 2. Backer. Die Auge einiger Gastropoden. Arb. Zool. Instit. Wien, xiv. 1902. 3. Baudelot. Necherches sur l'appareil générateur des Mollusques Gastéropodes. Ann. des Sci. Nat. Zool. (4), xix. 1863. 4. Boutan. La cause principale de l’asymétrie des Mollusques Gastéropodes. Arch, de Zool. Expér. (3), vil. 1899. “I LITERATURE OF THE GASTROPODA I9I - Biischii. Bemerkungen iiber die wahrscheinliche Herleitung der Asym- metrie der Gastropoden, spec. der Asymmetrie im Nervensystem der Prosobranchiaten. Morph. Jahrb. xii. 1887. . Fischer, H. Recherches sur la Morphologie du foie des Gastéropodes. Bull. Scientif. France et Belgique, xxiv. 1892. . Fischer and Bouvier. Recherches et considérations sur l’asymétrie des Mollusques Univalves. Journ. de Conchyl. (3), xxii. 1892. - Gilchrist. On the Torsion of the Molluscan Body. Proce. Roy. Soe. Edinburgh, xx. 1895. . Grobben. Die Pericardialdriise der Gastropoden. Arbeiten Zool. Inst. Wien, ix. 1890. —— KEinige Betrachtungen tber die phylogenetische Entstehung der Drehung und der asymmetrische Aufrollung bei den Gastropoden. Arb. Zool. Inst. Wien, xii. 1899. . Hilger, Beitriige sur Kenntniss des Gastropoden Auges. Morph. Jahrb. x. 1885. . Houssay. Recherches sur l’opercule et les glandes du pied des Gastéropodes. Arch. de Zool. Expér. (2), ii. 1884. . Jehring, H. von. Sur les relations naturelles des Cochlides et des Ichnopodes. Bull. Scientif. France et Belgique, xxiii. 1891. . Lacaze-Duthiers. Otocystes ou capsules auditives des Mollusques (Gastéro- podes). Arch. de Zool. Expér. (1), i. 1872. . Lang. Versuch einer Erklarung der Asymmetrie der Gastropoden. Viertel- jahrschr. naturforsch. Gesellsch. Zurich, 36, 1892. . MacDonald. On the Natural Classification of Gasteropoda. Journ. Linn, Soc. London (Zool.), xv. 1881. - Pelseneer, Sur l’ceil de quelques Mollusques Gast¢ropodes. Ann. Soc. Belge de Microse. xvi. 1891. Prosobranches aérieus et Pulmonés branchiféres. Arch. de Biol. xiv. 1895. . Souleyet. Voyage de la “ Bonite.” Zoologie, t. ii. 1852. . Willem. Observations sur la vision et les organes visuels de quelques Mollus- ques Prosobranches et Opisthobranches. Arch. de Biol. xii. 1892. B. Streptoneura. . Bergh. Die Titiscanien. Morphol. Jahrb, xvi. 1890. . Bernard. Recherches sur les organes palléaux des Gastéropodes Proso- branches. Ann. des Sci. Nat. Zool. (7), ix. 1890. Recherches sur Valvata piscinalis. Bull. Scientif. France et Belgique, Xxli, 1890. . Blochmann. Ueber die Entwickelung der Neritina fluviatilis. Zeitschr. f. wiss. Zool. xxxvi. . Bobretzky. Studien tiber die embryonale Entwickelung der Gastropoden. Arch. f. mikr. Anat. xiii. 1877. . Bonnevie. Enteroxenos Ostergreni ein neuer, in Holothurien schmarotzen- der Gastropode. Zool. Jahrb. (Anat. u. Ontog.), xv. 1902. . Bouvier. Systeme nerveux, morphologie générale et classification des Gastéropodes Prosobranches. Ann. des Sci. Nat. (Zool.) (7), iii. 1887. Etude sur Vorganisations des Ampullaires. Mém. Soc. Philomath. Paris (centenaire), 1888. 192 LITERATURE OF THE GASTROPODA 29. Bouvier and Fischer. L’organisation et les aftinités des Gastéropodes primitifs d’apres l'étude anatomique du Pleurotomaria Beyrichi. Journ. de Conchyl. 1902. 30. Boutan. Recherches sur l’anatomie et le développement de la Fissurelle. Arch. de Zool. Expér. (2), iii. bis, 1886. Mémoire sur le systeme nerveux de la Nerita polita et de la Navicella pareellana. Arch. de Zool. Expér. (3), i. 1893. 32. Carpenter. On the development of the Embryo of Purpura lapillus. Trans. Mier. Soe. ili. 1855. 33. Carriére. Die Fussdriisen der Prosobranchier und das Wassergefiiss-System der Lamellibranchier und Gastropoden. Arch. f. mikr. Anat. xi. 1882. 34. Claparede. Anatomie und Entwicklungsgeschichte der Neritina fluviatilis. Arch. f Anat. u. Phys. 1857. 35. Conklin. The Embryology of Crepidula. Journ. of Morphol. xiii. 1897. 36. Drummond. Notes on the Development of Paludina vivipara, with special reference to the Urogenital Organs and Theories of Gastropod Torsion. Quart. Journ. Mier. Sci. xlvi. 1902. 37. Erlanger, von. Zur Entwicklung von Paludina vivipara. Morphol. Jahrb. xvii. 1891. dl. 38. Zur Entwickelung von Bithynia tentaculata. Mitth. Zool. Stat. Neapel. x. 1892. 39. On the paired Nephridia of Prosobranchs, the Homologies of the only remaining Nephridium of most Prosobranchs, and the Relations of the Nephridia to the Gonad and Genital Duct. Quart. Journ. Mier. Sci. xxxiii. 1892. 39 bis. Fisher. The Anatomy of Lottia gigantea, Gray. Zool. Jahrb. (Anat. und Ontog.), xx. 1904. 40. Fol. Sur le développement embryonnaire et larvaire des Hétéropodes, Arch. de Zool. Expér. (1), v. 1876. 41. Garnault. Recherches anatomiques et histologiques sur le Cyclostoma elegans. Actes Soc. Linn. Bordeaux, 1887. 42. Gegenbaur. Untersuchungen itiber Pteropoden und Heteropoden. Leipzig, 1855. 43. Gibson. Anatomy and Physiology of Patella vulgata. Trans. Roy. Soe. Edinburgh, xxxii. 1885. 44, Haller. Untersuchungen iiber marine Rhipidoglossen. Morph. Jahrb. ix. 1883. 45. Die Morphologie der Prosobranchier gesammelt durch die ‘‘ Vettor Pisani.” Morph. Jahrb. xiv. xvi. xvilil. xix. 1888-1893. 46. Studien iiber docoglosse und rhipidoglosse Prosobranchier nebst Bemerkungen tiber die phyletischen Beziehungen der Mollusken unterei- nander. Leipzig, 1894. 47. Koehler and Vaney. Entosiphon Deimatis, nouveau Mollusque parasite d'une Holothurie abyssale. Revue Suisse de Zool. xi. 1903. 48. Koren and Danielssen. Bidrag tie Pectinibranchiernes Udviklingshistorie. Bergen, 1851, 1852. 49, Kiikenthal. Parasitische Schnecken. Abhandl. Senckenb. naturf. gesellsch. xxiv. 1897. 50. Lacaze-Duthiers. Mémoire sur l’anatomie et l’embryogénie des Vermets. Ann. des Sci. Nat. (Zool.) (4), xiii. 1860. LITERATORE OF THE GASTROPODA 193 51. Lankester, E. Ray. On the originally Bilateral Character of the Renal Organs of Prosobranchia and on the Homologies of the Yolk-Sac of Cephalopoda. Ann. Mag. Nat. Hist. (5), vii. 1881. . Lensen. Systeme digestif et systeme génital de la Néritina fluviatilis. La Cellule, xvi. xx. 1899 et 1903. . MacDonald. On the Anatomy and Classification of the Heteropoda. Trans. Roy. Soc. Edinburgh, xxiii. 1862. . MacMurrich. A Contribution to the Embryology of the Prosobranch Gasteropods. Stud. Biol. Labor. Johns Hopkins Univ. iii. 1886. . Moore. The Molluses of the Great African Lakes. Quart. Journ. Micr. Sci. xli. xlii. 1898, 1899. . Miller, J. Ueber Synapta digitata und iiber die Erzeugung von Schnecken in Holothurien. Berlin, 1852. . Oswald. Der Riisselapparat der Prosobranchier. Jen. Zeitschr. xxviii. 1893. . Patten. The Embryology of Patella. Arb. Zool. Instit. Wien, vi. 1885. . Perrier. Recherches sur Vanatomie et Vhistologie du rein des Gastéro- podes Prosobranches. Ann. des Sci. Nat. (Zool.) (7), vill. 1889. 59 bis. Randless. Some Observations on the Anatomy and Affinities of the 60. Trochidae. Quart. Journ. Micr. Sci. xlviii. 1904. Robert. Recherches sur le développement des Troques. Arch. de Zool. Expér. (3), x. 1903. 1. Salensky. Etudes sur le développement du Vermet. Arch. de Biol. vi. 1887. . Sarasin, P. Entwickelungsgeschichte der Bithynia tentaculata. Arb. Zool. Zoot. Instit. Wiirzburg, vi. 1882. . Sarasin, P. and F. Ueber zwei parasitische Schnecken. Ergebn. Forsch. Ceylon, i. 1887. . Tobler. Zur Anatomie von Parmophorus intermedius Reeve. Jen. Zeitschr. xxxv. 1902. . Ténniges. Die Bildung des Mesoderms bei Paludina vivipara. Zeitschr. f. wiss. Zool. Ixi. 1896. . Vayssiére. Etude sur l’organisation de |’ Homalogyra. Ann. des Sci. Nat. (Zool.) (7), xix. 1895. . Voigt. Entocolax Ludwigii, ein neuer seltsamer Parasit aus einer Holothurie. Zeitschr. f. wiss. Zool. xlvii. 1888. Wegmann. Contributions & Vhistoire naturelle des Haliotides. Arch. de Zool. Expér. (2), ii. 1884. Notes sur l’organisation de la Patella vulgata. Rec. Zool. Suisse, iv. 1886. Willcox. Zur Anatomie von Acmaea fragilis Chemnitz. Jen. Zeitschr. XXxli. 1898. Woodward, M. F. Anatomy of Pterocera. Proc. Malacol. Soc. i. 1894. The Anatomy of Pleurotomaria Beyrichii, Hilg. Quart. Journ. Mier. Sci. xliv. 1901. C. Opisthobranchia. . Alder and Hancock. A Monograph of the British Nudibranchiate Mollusca. Ray Society, 1845, 1855. . Bergh. System der Nudibranchiaten Gastropoden. (Semper. Reisen im Archipel der Philippinen, ii. 1892.) 5. Boas. Spolia Atlantica. Bidrag tie Pteropodernes Morfologi og Systematik samt tie Kundskaben om deres geografiske Udleredelse. Dansk. Vid. Selsk. Skr. (6), iv. 1886. 13 194 LITERATURE OF THE GASTHOVOUA . Davenport. On the Development of the Ceratain Aeolis. Bull. Mus. Comp. Zool. Cambridge, xxiv. 1893. . Fischer. Recherches anatomiques sur un Mollusque nudibranche appartenant au genre Corambe. Bull. Sci. France et Belgique, xxiii. 1891. Fol. Sur le développement des Ptéropodes. Arch. de Zool. Expér. (1), iv. 1875. . Gilchrist. Beitriige zur Kenntniss der Anordnung, Correlation und Function der Mantelorganen der Tectibranchiata. Jen. Zeitschr. xxviii. 1894. . Guiart. Contribution & l’étude des Gastéropodes Opisthobranches et en particulier des Céphalaspides. Mém. Soc. Zool. France, xiv. 1901. . Hancock. On the Structure and Homologies of the Renal Organ in the Nudi- branchiate Mollusca. Trans. Linn. Soc. London, xxiv. 1864. Anatomy of Doridopsis. Trans. Linn. Soc. London, xxv. 1865. 83. Hecht. Contribution a l'étude des Nudibranches. Mém. Soc. Zool. France, vili. 1896. . Herdman. On the Structure and Functions of the Cerata or Dorsal Papillae in some Nudibranchiate Mollusca. Quart. Journ. Micr. Sci. xxxiii. 1892. . Heymons. Zur Entwickelungsgeschichte von Umbrella mediterranea. Zeitschr. f. wiss. Zool. lvi. 1893. bis. Kowalewsky. Etudes anatomiques sur le genre Pseudovermis. Mém. Acad.-Pétersbourg (8), Phys. Math. xii. 1901. 85 ter. Les Hédylidés, étude anatomique. Mém. Acad. Pétersbourg (8), Phys. Math. xii. 1901. 86. Kwietniewski. Contribuzioni alla conoscenza Anatomo-zoologica degli Pteropodi Gimnosomi del mare Mediterraneo. Ric. Lab. Roma ed Altri. Lab. Biol. ix. 1903. . Lacaze-Duthiers. Anatomie et physiologie du Pleurobranche orange. Ann. des Sci. Nat. (Zool.) (4), xi. 1859. . Mazzarelli. Monografia delle Aplysiidae del Golfo di Napoli. Mem. Soe. Ital. Scienze (3), ix. 1893. 89. Contributo allo conoscenza delle :Tylodinidae, nuova famiglia del gruppo dei Molluschi Tectibranchi. Zool. Jahrb. (System), x. 1897. 90. Moquin-Tandon. Recherches anatomiques sur l’ombrelle de la Méditerranée. Ann, des Sci. Nat. (Zool.) (5), xiv. 1870. . Peck. On the Anatomy and Histology of Cymbuliopsis calceola. Stud. Biol. Labor. Johns Hopkins Univ. iy. 1890. . Pelseneer. Report on the Pteropoda. Zool. ‘‘ Challenger ”’ Expedit. parts lviii. Ixy. Ixvi. 1887, 1888. 93. Recherches sur divers Opisthobranches. Mém. Cour. Acad. Belg. liii. 1894. 94. —— Sur la condensation embryogénique chez un Nudibranche. Trav. Stat. Zool. Wimereux, vil. 1899. . Trinchese. Aeolididae e famiglie Affine. Atti. R. Accad. Lincei (8), xi. 1882. . Vayssiére. Recherches anatomiques sur la famille des Bullidés. Ann. des Sci. Nat. (Zool.) (6), ix. 1880. 97. Recherches zoologiques et anatomiques sur les Mollusques opisto- branches du golfe de Marseille. Ann. Musée Marseille (Zool.), ii. ili. vi. 1885, 1888, 1901. 98. Viguier. Contribution a l’étude du développement de la Tethys fimbriata. Arch. Zool. Expér. (3), vi. 1898. 99: 100. 101. 102. 103. 104. LITERATURE OF THE GASTROPODA 195 D. Pulmonata. André. Contributions a l’anatomie et 4 la physiologie des Ancylus lacustris et fluviatilis. Revue Suisse de Zool. i. 1893, Recherches sur la glande pédieuse des Pulmonés. Revue Suisse de Zool. ii. 1894. Babor. Ueber die wahre Bedeutung des sogenannten Semper’schen Organs der Stylommatophoren Sitzungsber. K. Bohm Ges. Wiss. (Math. Nat. Cl.), 1895. Beddard. On some Points in the Anatomy of the Nervous System of the Pond-Snails. Proce. Roy. Soc. Edinburgh, xi. 1882. Behme. Beitrige zur Anatomie und Entwickelungsgeschichte des Hern- apparates der Lungenschnecken. Arch. f. Naturgesch, ly. 1889. Beutler. Die Anatomie von Paryphanta Hochstetteri. Pfr. Zool. Jahrb. (Anat. und Ontog.), xiv. 1901. 104 bis. Bohmig. Beitrige zur Kenntniss der Centralnervensystems einiger Pulmo- 109. naten Gasteropoden: Helix pomatia und Limnaea stagnalis. Leipzig, 1883. . Bouvier. Sur Vorganisation des Amphiboles. Bull. Soc. Philom. Paris (8), iv. 1892. - Brock. Die Entwickelung des Geschlechtsapparates der Stylommatophoren Pulmonaten nebst Bemerkungen iiber die Anatomie und Entwickelung einiger anderer Organsysteme. Zeitschr. f. wiss. Zool. xliv. 1886. - Collinge. On the Anatomy of certain Agnathous Pulmonates. Ann. Mag. Nat. Hist. 1901. . Coutagne. Recherches sur le polymorphisme des Mollusques de France. Lyon, 1895. Cuénot. Ktudes physiologiques sur les Gastéropodes Pulmonés. Arch. de Biol. xii. 1892. . Deschamps. Recherches d’ Anatomie comparée sur les Gastérepodes Pulmonés. Ann. Soe. Sci. Bruxelles, 1898. . Erlanger. tudes sur le développement des Gastéropodes Pulmonés. Arch. de Biol. xiv. 1895. . Fol. Sur le développement des Gastéropodes Pulmonés. Arch. de Zool. Expér. (1), viii. 1880. . Hanitsch. Contributions to the Anatomy and Histology of Limax agrestis. Proc. Biol. Soe. Liverpool, ii. 1888. . Henchman. The Origin and Development of the Central Nervous System in Limax maximus. Bull. Mus. Comp. Zool. Cambridge, xx. 1890. . Hutton. Notes on the Structure and Development of Siphonaria australis, Quoy and Gaimard. Ann. Mag. Nat. Hist. (5), ix. 1882. . Jhering, H. von. Ueber den uropneustischen Apparat der Heliceen. Zeitschr. f. wiss. Zool. xli. 1884. Morphologie und Systematik des Genitalapparates von Helix. Zeitschr. f. wiss. Zool. liv. 1892. . Joyevx-Laffuie. Organisation et Développement de l’Oncidie (Oncidium celticum, Cuv.). Arch. de Zool. Expér. (1), x. 1882. ‘eller, Anatomie von Vaginula Grayi. Zool. Jahrb. v. Suppl. . Kofoid. On the Early Development of Limax. Bull. Mus. Comp. Zool. Cambridge, xxvii. 1895. . Kohler. Beitrage zur Anatomie der Gattung Siphonaria. Zool. Jahrb. (Anat. und Ontog.), vii. 1893. LITERATURE OF THE GASTROPODA 122. Lacaze-Duthiers, H. de. Du systéme nerveux des Mollusques-Gastéropodes pulmonés aquatiques. Arch. de Zool. Expér. (1), J.; 1872. 123. —— Histoire de la Testacelle. Arch. de Zool. Expér. (2), v. 1888. 124. —— Anatomie du Gadinia garnoti. Comptes Rendus Acad. Sci. Paris, C, 1885. 125. Des organes de la reproduction de l’Ancylus fluviatilis. Arch. de Zool. Expér. (3), vil. 1899. 126. Lankester, E. Ray. Observations on the Development of the Pond-Snail (Lymnaeus stagnalis), and on the Early Stages of other Mollusca. Quart. Journ. Mier. Sci. xiv. 1874. . Leidy. Special Anatomy of the Terrestrial Gasteropoda of the United States (in Binney: The Terrestrial Air-breathing Mollusks of the United States, I). Boston, 1851. 128. Meisenheimer. Entwickelungsgeschichte von Limax maximus. Zeitschr. f. wiss. Zool. lxii. Ixili. 1896, 1898. 129. —— Zur Morphologie der Urniere der Pulmonaten. Zeitschr. f. wiss. Zool. Ixv. 1899. 130. Nabias, de. Recherches histologiques et organologiques sur les centres nerveux des Gastéropodes. Actes Soc. Linn. Bordeaux, xlvii. 1894. 131. Recherches sur le systeme nerveux des Gastéropodes Pulmonés aquatiques. Trav. Labor. Soc. Scient. Arcachon, 1899. 132. Nalepa. Beitrige sur Anatomie der Stylommatophoren. Sitzungsber. Akad. wiss. Wien, lxxxvii. 1883. 133. Pelseneer. Etudes sur des Gastéropodes Pulmonés. Mém. Acad. Belg. liv. 1901. 134. Pérez. Recherches sur la génération des Mollusques Gastéropodes. Mem. Soc. Sci. Phys. et Natur. Bordeaux, 1873. 135. Plate. Studien iiber Opisthopneumone Lungenschnecken. Zool. Jahrb. (Anat. und Ontog.), iv. vil. 1891, 1893. 136. Beitriige sur Anatomie und systematik der Janelliden (Janella Schauinslandi, n. sp., und Aneitea berghi, n. sp.). Zool. Jahrb. (Anat. und Ontog.), xi. 1898. 137. Poirier. Observations anatomiques sur le genre Urocyclus. Bull. Soc. Malacol. France, iv. 1887. . Rabl. Ueber die Entwickelung der Tellerschnecke. Morph. Jahrb. v. 1879. . Rowzaud. Recherches sur le développement des organes génitaux de quelques Gastéropodes hermaphrodites. Montpellier, 1885. . Sarasin, P. and Ff. Aus der Entwickelungsgeschichte der Helix Waltoni. Ergebn. nat. Forsch. Ceylon, i. 1888. Die Siisswassermollusken von Celebes, Wiesbaden, 1898.— Die Landmollusken von Celebes, Wiesbaden, 1899. . Schmidt. F. Beitriige sur Kenntniss der Entwickelungsgeschichte der Stylommatophoren. Zool. Jahrb. (Anat. und Ontog.), viii. 1895. 3. Sharp. Beitriige sur Anatomie von Ancylus fluviatilis (O. F. Miller) und Ancylus lacustris (Geoffroy). Wiirzburg, 1883. . Sicard. Recherches anatomiques et histologiques sur le Zonites Algirus. Ann. des Sci. Nat. (Zool.) (6), i. 1874. . Simroth. Ueber die Niere der Pulmonaten. (Semper. Reisen im Archipel der Philippinen, iii. 1894.) . Yung. Recherches sur le sens olfactif de l’Escargot. Arch. de Psychol. ili. 1903. CHAPTER IV THE SCAPHOPODA CLASS III.—SCAPHOPODA, Bronn (= SoLENoconcHA, de Lacaze-Duthiers). Definition.—Marine bilaterally symmetrical Prorhipidoglosso- morpha ; the body and shell elongated along the antero-posterior axis and nearly cylindrical. The right and left margins of the mantle are united ventrally and thus form a complete tube sur- rounding the body, but with an anterior and a posterior aperture. The head is somewhat rudimentary and devoid of eyes, but bears two dorsal appendages furnished with numerous long filaments (Fig. 183, I). The foot is cylindrical and adapted to digging. A radula is present, but there is no ctenidium. The sexes are separate. fistorical.—These animals were formerly mistaken for tubicolous Annelids, and afterwards were classed among the Gastropoda, near Fissurella, Blainville, in 1819, was the first to rank them as a distinct order of Gastropoda under the name “ Cirrhobranchia.” In 1857 de Lacaze-Duthiers, as the result of a careful anatomical investigation, created the division Solenoconcha to receive Dental ium, making his new division equivalent to Lamellibranchia, and includ- ing the two groups, together with the Brachiopoda, in a class Acephala. Since de Lacaze-Duthiers’ memoir, the Solenoconcha have been universally recognised as a division equivalent to the Lamellibranchia and Gastropoda, but the name Scaphopoda, proposed by Bronn in 1862, has been more generally used for the sake of uniformity. More recent investigations, however, have shown that the Scaphopoda are more nearly akin to the Gastropoda than to the Lamellibranchia. I. GENERAL DESCRIPTION AND EXTERNAL CHARACTERS. The shell (Figs. 181, D, E and 186) has the form of a very elongated cone, slightly curved, the concavity of the curve being dorsal: it is capable of containing the entire animal. The larger 197 198 THE SCAPHOPODA orifice of the shell and subjacent mantle is morphologically the anterior or cephalo-pedal aperture. Near the smaller posterior aperture the shell, being older, is also thicker. The anterior aperture of the mantle has a conspicuously thick border. The posterior aperture is emarginated by a ventral sinus and is furnished interiorly with a dorsal and a ventral valve, which are capable of being applied to one another. ‘The animal lives buried obliquely in the sand, only the posterior extremity projecting into the water, and therefore it is the posterior aperture that is at once inhalant and exhalant and serves for the expulsion of the excrements and (Cé(((\\\ “WX! Fic. 181. Dentaliwm vulgare. A, ventral view of the animal removed from its shell ; B, dorsal view of the same; C, right-side view of the same; D, the shell in section; E, right-side view of the animal in its shell, with cephalic appendages (captacula) exserted as in life. a, mantle; a, longitudinal retractor muscle; @’, fringe surrounding the anterior opening of the mantle- chamber ; a’, the posterior appendix of the mantle ; b, anterior circular muscle of the mantle ; bo’, posterior circular muscle of the mantle; c, ce’, longitudinal retractor muscle; e, liver; J, gonad ; k, buccal mass (seen through the mantle) ; q, left kidney ; s’, anterior extremity of the foot ; w, w’, longitudinal blood-sinus of the mantle. (From Lankester, after Lacaze-Duthiers. ) the genital products. In the extended state of the animal the foot and cephalic tentacular filaments project from the anterior opening. The pallial cavity extends continuously from one aperture to the other. In the middle and posterior regions of the body the liver, the gonads, and even the kidneys, extend into the mantle and may increase its thickness to such an extent that the pallial cavity is reduced to a rather narrow canal (Siphonopodidae). The head is situated at the anterior end of the body on the concave or dorsal side. In shape it is a sort of cylindrical projection or proboscis, and is contractile but not invaginable. In the Dentaliidae its anterior aperture is surrounded by eight palps or lobes with scalloped margins, but in the Siphonopodidae it is THE SCAPHOPODA 199 flattened and devoid of palps (Fig. 183, VI). Laterally and pos- teriorly it is provided with two pouches, and quite at its posterior end, on either side of its dorsal surface, are two broad, symmetrical, and flattened tentacular lobes (Fig. 183, IV) which appear to be homologous with the cephalic lobes of Rhipidoglossa (Fig. 130, II). The cephalic filaments or “captacula” (Fig. 181, E) are inserted on the margins of these lobes, and when extended, radiate in all directions from them (Figs. 182, ca; 183, I). These captacula are of unequal length, autotomous, and capable of regeneration: they are ciliated, highly contractile, and their extremities are swollen and club-shaped, with a small lateral con- cavity in each. These organs are in the first instance tactile, but also prehensile. The difference in their length is the result of their regeneration after being lost. The foot has the form of an elongated cylinder, is very extensible, and when forcibly projected beyond the aperture of the / a a) : ; Ife / 4 fae ta vr ee g Fic. 182. Diagram of the organisation of Dentaliwm, left-side view. a, anus; ca, captacula; ¢.g, cerebral ganglion ; f, foot; go, gonad ; in, intestine; k, left kidney ; /a.c, labial commissure ; li, liver; m, mouth; 0, orifice leading into the perianal sinus; 0c, oesophagus ; pa, mantle ; p-g, pedal ganglion, with otocyst ; pl.g, pleural ganglion ; po, posterior orifice of the mantle ; ra, radular sac ; st.g, stomato-gastric ganglion. shell, serves as a digging organ. In the Dentaliidae it is pointed in front, but has an oblique wing-shaped fold or pleat on either side of its free extremity: these two folds are contiguous on the ventral but interrupted on the dorsal side. In the Siphonopodidae the foot ends in a retractile dise with papillated margins (Fig. 183, VII), and in Pulsellum there is a filiform tentacle in the middle of the disc. The powerful retractor muscles of the foot form two symmetrical bundles inserted far back on the dorsal side of the shell (Fig. 181, ¢) II. ANATOMY. 1. Alimentary Canal.—The non-invaginable proboscis (Fig. 183, V, VI) leads directly into a true buccal cavity situated in the trunk at the base of the foot (Fig. 182, f). In the interior of this buccal cavity there is an azygos dorsal mandible and a ventral radula. The radular sac is short, but its muscles and cartilages are powerful and form a buccal mass of Jarge size. The radula is short and arcuate, with five teeth in each transverse row, the formula being 200 THE SCAPHOPODA 1.1.1.1.1 (Fig. 2, C). The central tooth is simple and subquad- rangular; the laterals stout and subtrigonal, tricuspidate, with wide bases and reflected borders ; the marginals have the form of subquadrangular non-denticulate transverse plates. The oesophagus is rather short and is provided with two large lateral symmetrical pouches, directed ventralwards; these correspond to the oesophageal pouches of the Polyplacophora and Aspidobranchia. The stomach is nothing more than the most posterior bend of the digestive canal (Fig. 182). It presents a small posterior ciliated pyloric caecum, and receives the ducts of the liver. The last-named organ is situated behind the stomach and the rest of the alimen- tary canal. It is made up of radiating caeca (Fig. 182, li), gathered into two lobes which extend into the sides of the mantle, and open right and left into the so-called stomach or posterior bend of the alimentary canal. if Though the two liver lobes are symmetrical in Siphonodentalium, an- 35 ; terior end of body, dorsal the Dentaliidae, they are no longer so in vevile: Il eadulae mass, Siphonodentalium. In this genus the principal DR iat ade mass of the liver lies in front of the gonad buccal pouch; VI, mouth; and is continued posteriorly into two long lotic? VY? *™™l yarallel caeca extending to the extremity of the body ; the organ has no longer an apparent symmetry, but all its radiating caeca are directed to the left side and open into the “stomach” by a single orifice. The intestine bends forward (Fig. 182, im) and forms several loops, all of which lie in the anterior part of the body, near the buccal mass, and finally opens in the mid-ventral line behind the visceral commissure. In the Dentaliidae there is an anal gland on the right side of the rectum (Fig. 182, a). 2. Circulatory Apparatus.—The structure of the circulatory system is exceedingly simple. There are no differentiated vessels, not even a ventricle with well-developed muscular walls. At the most there is a more contractile portion of the blood-system in the neighbour- hood of the anus, but it has no afferent or efferent vessels, and is continuous with the rest of the blood-spaces. These latter are sinuses, without an endothelial lining, distributed between the organs in the different parts of the body. The principal sinuses are: the perianal, the pedal, the visceral, and the pallial. It is in the last- named that the anterior dorsal and ventral portions are more clearly defined and have something of the appearance of vessels. Two buttonhole-shaped orifices, situated near the renal apertures, place the perianal sinus in communication with the external medium and Fic. 183. THE SCAPHOPODA 201 admit of the expulsion of blood during violent contractions of the body (Fig. 182, 0). There is no specialised respiratory apparatus. Respiration is effected by the internal surface of the mantle, particularly by the anterior ventral region. 3. Hacretory Organs.—The Scaphopoda have two symmetrical kidneys, situated in front of the gonad on the ventral side of the middle of the body (Figs. 181, g, and 182, %). They have the form of two short but fairly wide sacs with pleated walls, lying between the intestinal mass and the stomach. They have no communica- tion with one another and have no reno-pericardial duct. They open to the exterior on either side of the anus. 4. Nervous System and Sense Organs.—The nervous system of the Scaphopoda comprises the same four pairs of principal nerve ganglia as are found in the Gastropoda and Lamellibranchia, in addition to the stomato-gastric system. The cerebral ganglia are joined to one another and are situated on the dorsal side of the oesophagus: they innervate the proboscis with its palps and the tentacular lobes and captacula. Each cerebral ganglion is in close juxtaposition to the corresponding pleural ganglion (Fig. 182, ¢.g, pl.g), which innervates the mantle. The cerebral and pleural ganglia are united to the pedal ganglion of the same side by a long connective which is apparently single in the distal part of its course, but bifurcates just before it reaches the cerebral and pleural ganglia, sending a branch to each. The two pedal ganglia are situated in the foot (Fig. 182, p.g) and are attached to one another. The visceral commissure takes its origin from the pleural ganglia. It is rather long, and bears on the posterior part of its course two symmetrical visceral centres (Fig. 182, v.g) in the form of simple and ill-defined ganglionic swellings, lying on either side of the anus close beneath the tegumentary epithelium, and thus resembling the visceral ganglia of the Lamellibranchia. These two centres are united by a commissure passing in front of the rectum. From the cerebral ganglia there arises—as in many other Molluscs—an infra-oesophageal labial commissure (Fig. 182, /a.c), bearing a ganglion on either side, from which a branch of the stomato- gastric commissure properly so called (Fig. 182, sf.) is given off, as is the case in the Polyplacophora, Aspidobranchia, and Cephalopoda. The stomato-gastric commissure passes to the ventral side of the oesophagus, between it and the buccal bulb, and bears two or four symmetrical ganglia on the middle of its course. The labial com- missure also gives off a nerve on each side, which passes to the subradular organ and terminates below it in a ganglion. The Scaphopoda have only three differentiated sensory organs : the captacula or tentacular filaments, the subradular organ, and the otocysts. The tentacles, which are seemingly tactile and olfactory organs, are dorsal in position and have the form of flattened lobes 202 THE SCAPHOPODA (Fig. 183, IV), on which the numerous filiform appendages or captacula are inserted. The extremity of each captaculum is swollen and club-shaped with a small lateral pit, and contains a terminal ganglion and a system of ganglion cells whose prolongations are continued into neuro-epithelial elements situated in the lateral pit. The subradular organ is a ciliated ridge on the ventral side of the buccal cavity opposite to the mandible. The epithelium of this ridge contains nerve end-cells, and beneath it are two small nerves derived from the labial commissure, each ending in a small ganglion. The otocysts are situated in the foot (Fig. 182) on the posterior face of the pedal ganglia. They are innervated from the cerebral ganglia and each contains numerous otoconia. 5. Reproductive Organs.—The sexes are always separate. The gonad is unpaired and median, and is extremely long, occupying the whole of the postero-dorsal region of the body, below the retractor muscles (Figs. 181, f and 182, go). It is divided into symmetrical transverse lobes, and its anterior extremity is contracted to form a duct, which diverges to the right and opens into the right kidney, as in the Aspidobranchia. Ill. EMBRYOLOGY. The ova are laid singly, and undergo irregular segmentation immediately after fertilisation. The ectodermic cells multiply much more rapidly than the large endodermic cell or entomere, which remains for some time unsegmented (Fig. 184, ma). Finally, the entomere segments in its turn, and the endodermic cells derived from it are invaginated to form a gastrula with a large blastopore, situated at the posterior extremity. The embryo elongates and acquires an anterior apical tuft of cilia (Fig. 15, //), behind which at first two and afterwards three, or sometimes four, parallel ciliated rings are formed. These ciliated rings constitute the locomotory velum, and their number diminishes in proportion as the velum, which is more or less reflected backwards over the body, becomes more prominent (Fig. 185, III). The blastopore remains open, and gradually travels along the ventral side towards the anterior extremity of the larva. A shallow shell-gland is formed on the dorsal side and extends right and left over the whole dorsal surface, forming two lateral, parallel, and sym- metrical pallial lobes which extend ventrally and finally unite together (Fig. 185, II). In this manner the tubular mantle is formed round the body. The shell secreted by the mantle is at first cupuli- form, but subsequently, like the mantle itself, becomes tubuliform as the result of the fusion of its lateral margins (Fig. 119, B). The expanded embryonic shell may still be seen at the initial extremity in some specimens of Siphonodentalium. THE SCAPHOPODA 203 The pedal prominence arises on the ventral surface and grows forward ; after the disappearance of the larval velum the foot is used for creeping. The cerebral ganglia arise as two deep symmetrical ectodermic invaginations in the velar area. The otocysts are formed as invaginations of the surface of the foot, and the pedal ganglia originate after the otocysts from thickenings of the ectoderm. The endodermic cavity gives rise to the stomach and _ intes- tine. The liver is developed in connection with the wall of the stomach. The anal opening is not formed till a very late period. At the end of five or six days the velum atrophies, the young animal ceases to swim and begins to crawl along the sea bottom. % Fic. 184. Fic. 185. Embryo of Dentalium, with six Larva of Dentalium, aged one micromeres or ectodermic cells and a half day; ventral aspect. and a single macromere or endo- I, foot; Il, mantle; III, velum dermic cell. ma, macromere ; mi, forming a sort of test. (After micromere. (After Kowalewsky.) Kowalewsky.) ‘ IV. BIoNoMIcS AND DISTRIBUTION. The Scaphopoda are marine burrowing molluscs, and as a rule only allow the posterior extremity to project from the sand in which they hide themselves. They feed on the lowest organisms, Diatomacea, Protozoa, ete. There are 150 living and nearly 275 fossil species of Scaphopoda. The living forms are distributed throughout all seas from the littoral to a depth of 2500 fathoms. The fossil species extend back to the middle Silurian, but are most abundant from the Cretaceous onwards. V. REVIEW OF THE FAMILIES OF SCAPHOPODA. There are two different types in this homogeneous group, but the differences between them are not of more than family value. Famity 1. Dentanimar, Gray. Foot conical with a laterally ex- panded and dorsally interrupted encircling sheath. Shell tubular, curved, with the greatest diameter at the anterior aperture, and tapering evenly to 204 LITERATURE OF THE SCAPHOPODA the posterior aperture. Genera—Dentalium, Linnaeus ; posterior orifice of the shell truncated, entire, without an incision or accessory tube. Antalis, Adams ; posterior orifice with a short incision. issidentalvwm, Fischer ; posterior extremity with a long fissure on the ventral side ; abyssal. Fustiaria, Stoliczka. Schizodentaliwm, Simroth ; ventral border of the posterior aperture with a series of small a f/f’ _ holes arranged in a straight line. Heterochisma, ; Sunroth. Fia. 186. Faminy 2. SIPHONOPODIDAE, Simroth. Cadulus gracilis, Jeffreys, shell, Foot expanded distally into a symmetrical disc, bee raat ys Bee ee ; with a crenate continuous edge (Fig. 183) or son.) simple and vermiform without well-developed lateral processes ; shell often contracted towards the anterior aperture. Genera—Siphonodentalium, Sars; foot ending in a median disc without a median appendage. Cadulus, Philippi (Fig. 186). Dischides, Jeffreys. Pulsellum, Sars ; terminal dise of the foot with a median appendage. Hntalina, Monterosato. LITERATURE OF THE SCAPHOPODA. 1. Boissevain. Beitrage zur Anatomie und Histologie von Dentalium. Jenaische Zeitschr. xxxvili. 1904. 2. Clark, W. On the Animal of Dentalium tarentinum. Ann. and Mag. of Nat. Hist. (2), vii. 1851. 3. Deshayes, G. P. Anatomie et monographie du Genre Dentale. Mém. Soe. Hist. Nat. Paris, ii. 1825. 4. Fol, H. Sur Vanatomie microscopique du Dentale. Arch. Zool. Expér. et Gén. (2), vii. 1889. . Kowalewsky, A. Etude sur l’embryogénie du Dentale. Ann. Musée d’Hist. Natur. Marseille, Zool. i. 1883. 6. Lacaze-Duthiers, F. J. H. Histoire de Vorganisation et du développement du Dentale. Ann. des Sci. Nat. Zool. (4), vi. vii. 1856-1857. 7. Léon. Zur Histologie des Dentalium Mantels. Jen. Zeitschr. f. Naturw. Bd. xxix. 8. Nassonow. Zur Morphologie der Scaphopoden. Biol. Centralbl. x. 1890. 9. Plate, Z. Ueber den Bau und die Verwandtschaftsbeziehungen der Soleno- conchen. Zool. Jahrb., Abth. f. Anat. u. Ont. v. 1892. 10. Sars, M. Om Siphonodentalium vitreum, en ny Slaegt og Art af Dentali- dernes Familie. Universitets programm. Cluistiania, 1861. Malakologiske Jagttagelser—II. Nye Arten af Slaegten Siphonoden- talium. Forh. Vidensk. Selsk. Christiania, 1865. or ial CHAPTER V THE LAMELLIBRANCHIA CLASS IV.—THE LAMELLIBRANCHIA, BuaINnvILLE (= ACEPHALA TESTACEA, Cuvier ; CONCHIFERA, Lamarck ; PELEcypopA, Goldfuss ; LIPOCEPHALA, Ray Lankester). Order 1. Protobranchia. Sub-Order 1. Solenomyacea. #3 2. Nuculacea. Order 2. Filibranchia., Sub-Order 1. Arcacea. 2. Trigoniacea. ee 3. Mytilacea. 4. Pectinacea. et 5. Dimyacea. Order 3. Eulamellibranchia. Sub-Order 1. Ostraeacea, Submytilacea. Tellinacea. Veneracea. Cardiacea. Chamacea. Myacea. Adesmacea. Anatinacea. Order 4. Septibranchia. Sub-Order. Poromyacea, DID OP 9 Lo Definition—The Lamellibranchia are Molluscs with an internal and external symmetry. The cephalic region is rudimentary, and the mantle, divided into a right and a left lobe, secretes a bivalve shell which covers and encloses the whole body. The cephalic region 205 206 THE LAMELLIBRANCHIA is only furnished with a pair of labial palps on each side. The foot is ventral, generally adapted to burrowing and without a plantar surface. The two pallial lobes are united by one or two transverse muscles which close the two valves of the shell. There are two lateral and symmetrical ctenidial branchiae under the mantle ; their distal extremities are directed posteriorly and their filaments may exhibit an extreme degree of concrescence, either among themselves or with the mantle or with the visceral mass. I. GENERAL DESCRIPTION AND EXTERNAL CHARACTERS. The mantle consists of two thin tegumentary lobes attached to the trunk dorsally, and extending over the sides to the ventral surface so far that they can be brought together below the foot. Thus the whole of the animal’s body may be covered by the mantle. In structure, the mantle is normally rather thin, and there is only some connective tissue and a few muscular fibres between the internal and external layers of epithelium. In some few cases the gonads may extend into the mantle: into both lobes in the Mytilidae, into the right lobe only in the Anomiidae. The internal surface may present glandular modifications, of which the most important are the hypobranchial glands characteristic of 0 the Protobranchia: they are situated pos- teriorly beyond the gills. The margins fra. LY A) su” of the mantle normally present redupli- oe cations, generally three in number _ (Fig. 187, pa’, pa", pa’), and in the 2 Pectinidae the most internal of the three is turned inwards to form the ‘‘ velum ” pa (Fig. 235). The margins of the mantle of Lamellibranchs are frequently fur- nished with glands, pigment spots, and various sensory organs in the form of tentacles, and even of eyes. The pig- mentation of the pallial border is due to the combined action of the light and Fic. 187. the oxygen of the surrounding medium, Kellya suborbicularis, Montagu, 2nd is most conspicuous at those points eee see cone itiant Where the respiratory fluid enters the orifice; 0”, pedal orifice; o”, ex- pallial cavity. Racat aa ie eye aa The edges of the two pallial lobes te eset Feel may remain free throughout their edges. (After Deshayes.) extent; this is the case in Nucula, the Anomiidae, the Arcidae (Fig. 188) the Trigoniidae, and the Pectinidae (Fig. 235). In all other Lamellibranchia the pallial lobes are partially united by the ad \: fo) mt THE LAMELLIBRANCHIA 207 concrescence of the internal reduplicature of their margins; this union may be localised in one, two, or even three more or less extensive regions. Thus, there is only one line of union in the Solenomyidae (in which it is long, Fig. 231), the Aviculidae, the Ostraeidae, Hntovalva, Scioberetia, the Mytilidae, the Carditidae, the Astartidae, the Crassatellidae, the majority of the Lucinidae, the Unionidae (Fig. 242), and in certain species of Cyrenidae ; in Fic. 188. Arca lactea, Linnaeus, ventral aspect. a.a, anterior adductor ; a.l, anterior lip ; a.p, anterior labial palp ; }, byssus ; /, foot ; g’, internal gill-plate ; g’’, external gill-plate ; g.a, gill-axis ; h.a, posterior adductor; m, mouth; pa, mantle; p./, posterior lip; re, rectum; v.c, visceral com- missure ; v.g, visceral ganglion. (After Deshayes.) other words, ina very large number of Submytilacea. This single line of union is always posterior, and is the prime factor in the formation of an aperture opposite to the anus (Fig. 231, a.or) known as the exhalant pallial or ‘‘anal” orifice. It serves for the evacua- tion of the excrements, of the water which has been used for respira- tion, etc., and is, in the manner indicated, entirely cut off from the rest of the pallial aperture through which the respiratory and food- bearing currents of water find an entrance, and through which the foot is thrust out. Lamellibranchs with this disposition of the pallial border have received the name of ‘ Bifora.” It should be noted that 208 THE LAMELLIBRANCHIA in many Unionidae the anal orifice is itself divided into two, the more anterior aperture being dorsal and the more posterior—considered topographically—being the anal opening proper. In addition to the first fusion, there is a second in the Ledidae among the Protobranchia, in the Dreissensiidae and the Mutelidae among the Submytilacea, and in all other Eulamellibranchia and the Septibranchia (Fig. 249). In Castalia, a member of the Mutelidae, it has been observed that the second fusion may be present or absent in different individuals. This second fusion of the pallial borders is always pretty close to the first (Fig. 241), and forms the boundary of an orifice almost in juxta- position to the anal aperture, leaving in front a third orifice (Fig. 241, 0): hence the name “ Trifora” given to Lamellibranchia which exhibit this arrangement. The second orifice is called the Yl host “ \iumpres 2 Fic. 189. Left valve of Meretriz, from the inner face. (From Lankester, after Owen.) branchial or inhalant, and the third the pedal orifice. The last-named is generally very large (Figs. 194, 221, 0.p, etc.), but its extent is always in inverse ratio to the extent of the second fusion and in direct ratio to the size of the foot protruded through it (Figs. 219, 246). In the genus Kellya,- however, it is not the third or anterior aperture that serves for the passage of the foot, but the second or ventral aperture (Fig. 187, 0”). Finally, when the second fusion extends for a long distance, that is to say, when the foot is very anterior, rudimentary, or cylindrical, a fourth pallial aperture may be formed between the pedal and branchial apertures, and therefore within the region of the second fusion. This disposition may be seen in some Solenidae, in Lutraria and Glycimeris, and in sundry Anati- nacea, such as Myochama, Chamostraea, Thracia, Pholadomya, and A sper- gillum, which are sometimes called, on this account, ‘‘ Quadrifora.” This fourth orifice probably arises as a subdivision of the pedal orifice ; it is placed far forward in Solen, and is both inhalant and THE LAMELLIBRANCHIA 209 exhalant in this genus ; but is posterior and only exhalant in Lutravia, Thracia, ete. Frequently the two posterior pallial orifices, anal and branchial, or at least the anal, as in some Lucinidae, are more or less pro- longed in the form of muscular tubes which may be extended for a greater or less distance beyond the shell (Fig. 190); this feature is found in the majority of burrowing and boring Lamellibranchs. These tubes are known as siphons, and may be eitler—(1) inde- pendent of one another throughout their length, as, for example, in the Tellinidae (Figs. 190, b7.s, a.s; 245, g, g’), Donacidae, Thracia, ete.; or (2) partially fused together, as may be seen in J apes, Solenocurtus (Fig. 194), Saxicava (Fig. 246); or (3) completely united to one another, as in Mactra, Dosinia, Mya. Lutraria, Pholas, Teredo (Fig. 195), ete. The branchial siphon is usually the longer of the two, and in Scrobicularia is more than four times as long as the body. Sometimes the siphons may attain to a still greater => Wy, “ee Fic. 190. Tellina planata, left-side view. a.s, anal siphon; br.s, branchial siphon; jf, foot; pa, tentaculiferous border of the mantle; sh, shell. (After Poli.) degree of development, and may form an important part of the body-mass, or even surpass it in size. The extreme limit of evolu- tion in this direction is exhibited by Teredo, in which these organs, while receiving the same nerve supply as in other Lamellibranchia, constitute the greater part of the mass of the animal; the anal siphon extends right forward and the branchial siphon contains the gills, as is also the case in Solenocurtus, Fistulana, Saxicava, ete. There are two opposite currents in the pallial cavity. The first is postero-anterior in direction, and is set up by the action of the cilia clothing the surface of the branchiae ; the second runs in the reverse direction on the ventral side near the edges of the mantle, and wards off foreign substances from the pallial cavity (Jytilus, Cardium, etc.). In Pinna and Solen this second current is created by a large longitudinal ciliated ridge on each side. The two lobes of the mantle are furnished with several distinct pallial muscles which are inserted on the shell and are divisible into the following distinct groups :—(1) The orbicular muscle, extending right round the periphery of each lobe, and serving to attach it to 14 210 THE LAMELLIBRANCHIA the shell and as a retractor of the pallial border. (2) At the posterior end a specialised part of the orbicular muscle originates from and serves as the retractor of the siphons (Fig. 191, m.s); its development is proportional to that of the siphons, and it interrupts the evenly curved line formed by the orbicular muscle. The Fic. 191. Right-side view of a Mactra, the right valve of the shell and right mantle-flap removed, and the siphons retracted. br, b7’, outer and inner gill-plates ; ec, umbo of the shell; m.a, anterior adductor muscle; m.p, posterior adductor muscle; m.s, pallial retractor muscle of the siphons; p, foot; ¢, labial palp; ta, anal siphon; tr, branchial siphon. (From Lan- kester, after Gegenbaur.) muscles leave an ‘impression ” on the inner surface of each valve of the shell, and the impression of the orbicular muscle or “ pallial impression” (Fig. 189) is indented by a “sinus” formed by the siphonal muscles. This ‘‘sinus” is scarcely ever absent in siphonate forms except in the Lucinidae and in Cuspidaria, in which the siphons are not retractile, and in the latter genus are protected by prolongations of the posterior part of the shell. (3) The adductor muscles of the shell are transverse pallial muscles uniting the two lobes of the mantle and the two shell-valves secreted by them. There are at the most two adductors; the anterior is dorsal and in Fig. 192. Three stages in the development of Ostraea, right-side view. A, protomonomyarian stage of O. edulis (atter Woodward) ; B, dimyarian stage ; and C, deutomonomyarian stage of O. virginiana (after Jackson). a, anus; a.@, anterior adductor ; ¢.g, cerebral ganglion; f, foot; g, gill; in, intestine ; /./, left liver; /.p, labial palp; m, mouth ; oe, oesophagus ; p.a, posterior adductor ; p.e, pallial edge; p.g, pedal ganglion; pr, prodissoconch ; 7./, right-liver lobe; sh, shell ; st, stomach ; ve, velum; v.g, visceral ganglion. front of the buccal aperture (Figs. 188, a.a; 191, m.a), but extends considerably towards the ventral side in Modiolaria and Chama. The anterior adductor muscle is the first to appear in development (Nucula, Mytilus, Modiolaria, Pecten, Ostraea (Fig. 192, A), Dreissensia (Fig. 224, a.a), Unionidae (Fig. 227, 2), Pisidiwm, Montacuta, Lasaea, Entovalva, Cardiwm, Pseudokellya, etc.), but diminishes in importance THE LAMELLIBRANCHIA ote in adult Mytilidae, and disappears altogether in J/ytilus latus (Fig. 193, E) and MW. meridionalis. It is very small or more usually absent in the Anomiidae, the Pectinacea, and the Ostraeacea, much reduced in Teredo, and absent in the adults of Philobrya, Miilleria, and Tridacna. The Lines adductor muscle is ventral and anterior to the anus (Figs. 188, h.a; 192, C, pa). When the anterior adductor is diminished in size or ’ disappears in the adult, the posterior adductor necessarily becomes more central in order that its mechanical efficiency may be increased. This may be seen in the forms known as Monomyaria, and is accompanied by a shortening of the antero- he Fig. 193. Right valve of six various Lamellibranchs, showing the various stages of the morphological development of the adductor muscles. A, Pectuneulus; B, Myrina; C, Modiolaria; D, Modiolu; E, Mytilus latus; F, Pecten. a, anterior adductor; a.r, anterior foot retractor; 0b, shell beak; li, ligament; p, posterior adductor; p.i, pallial impression ; p.r, p.7", posterior retractors of foot and byssus ; t, hinge-tooth. posterior axis and a proportional increase of the dorso-ventral axis of the body, a phenomenon particularly well marked in the Tridacnidae. It should be observed that the species with a single adductor muscle belong to very various groups and are generally sessile forms: the Monomyaria, therefore, are polyphyletic and do not constitute a natural group. 6 fee Ss Anatinacea, but the female aper- B 4 5 : : = ture is outside the visceral commis- = sure, and therefore in the normal 2) oe “,e . 3 and original position of the Lamelli- > . . Q branch genital orifice, whereas the male aperture is within the visceral Ss commissure. In Poromya the male fot a and female ducts of each side open into a common orifice, external to 2 the visceral commissure. In all » . Ky these hermaphrodites the male So Va products are the first to ripen. Pseudokellya cardijormis, section of a part Accidental cases of hermaphro- of the ovary. ce.f, follicular cells ; fol, ovular ditism have been met with in follicle ; ov, ovarian egg. A : : , dioecious Lamellibranchs (Mytilus, Unionidae), and a unisexual individual of the normally hermaphro- dite species Pecten gluber has also been described. THE ELAMELLIBRANCAIA 24 LoS) The testis of a male or hermaphrodite is always readily recog- nisable by its brilliant white colour; on the other hand, the ovary is often red (Mactra, Donaz, etc.). The ovum is derived from a cell of the ovarian epithelium, but in most cases the neighbouring cells contribute to the formation of its vitellus (Cyclas, ete.). The ovum is surrounded by a vitelline membrane, which is often fairly thick (Unionidae, Anatinacea, etc.), and is only interrupted at the micro- pyle, or point of attachment to the ovarian wall. It is at this point that the spermatozoon effects an entrance. The vitelline membrane disappears after the first stages of segmentation, except in incubatory forms. \ \V/ c al. Ife pea Fic. 235. Pecten jacobaeus, ventral aspect. a, anus; eé, pallial eyes; f, foot; g, gill; h.a, posterior adductor; 7, intestine; /, lips; l.p, labial palps; m, mouth; ov, ovary ; pa, mantle (reflected edge) ; p.c, pallial cavity ; sh, shell; ¢, testis. (After Poli.) Faminy 1. VULSELLIDAE, Adams. Mantle open ; foot without byssus ; the shell high and the hinge without teeth. Genus—Vudlsella, Lamarck. Faminy 2. AVICULIDAE, Swainson. Foot provided with a very stout byssus (Fig. 236). The gills fused to the mantle ; shell very inequilateral ; the cardinal border straight, provided with two auriculae, of which the posterior is the longer. Genera—Avicula, Bruguitre ; the auriculae of the shell very prominent; heart attached to the ventral face of the rectum ; British ; fossil from the Devonian to the present day. Meleagrina, Lamarck; shell sub-quadrangular, the auriculae not very prominent. A species of this genus, Meleagrina margaritifera, from the Indian Ocean, Persian Gulf, etc, forms precious pearls. Malleus, Lamarck ; shell irregular, high and narrow, with broad subequal The following genera are exclusively fossil :—Limopteria, auriculae. THE LAMELLIBRANCHIA 261 Hall ; Devonian and Carboniferous. Pseudomonotis, Beyrick ; Devonian and Cretaceous. Cuassianella, Beyrich ; Trias. Monotis, Bronn; Trias. Daonella, Mojsisovies; Trias. Posidonomya, Broun ; Silurian to Jurassic. FamILy 3. PRrastnipan, Stoliczka. Shell inequilateral with anterior umbones, and a prominent anterior auricula ; the dorsal border arched ; the hinge with a single fossa and a single tubercule on each valve. Genus—Prasina, Deshayes. Famity 4. PrertnerpAn, Goldfuss. Shell thick, very inequilateral ; the cardinal border straight, with two auriculae and a notch for the byssus under the right anterior auricula ; an extinct family from the Palaeozoic. |Genera— Pterinea, Goldfuss ; Silurian to Carboniferous. Rhombopteria, Jackson; Silurian. Actinodesma, Sand- ULM g Se aes CARTES A aes Sea = 2 Fie 236. Avitula tarentina, Lamarck, from below. a, anus; ad, adductor muscle ; b.gr, byssal groove of the foot ; by, byssus; ¢, eye; f, foot; g, gill; l.p, labial palp; m, mouth; pa, mantle ; sh, shell ; vi.c, visceral commissure ; vi.g, visceral ganglion. (After Poli.) berger ; Devonian. FAmIty 5. LUNULICARDIIDAE, Fischer. Shell thin, triangular, very inequilateral, the anterior end truncated ; the umbones terminal ; the cardinal border straight ; without hinge teeth. An extinct family from the Silurian and Devonian. Genera—Lunuli- cardium, Minster; Silurian and Devonian. Patrocardiwm, Fischer ; Silurian. Babinka, Barrande; Silurian. Famiiy 6. CoNnocarprpag, Neumayr. Shell thick, subtriangular, the anterior side truncated and gaping ; cardinal border straight and prolonged into two auriculae of which the anterior is very long and narrow ; hinge with a lateral tooth and a reduced cardinal tooth. Dimyarian. An extinct family from the Palaeozoic. Genus—Oonocardiwm, Bronn ; Silurian to Carboniferous. Famity 7. AMBONYCHIIDAE, Miller. Shell inequilateral, without an anterior auricula, the umbones anterior and terminal ;, hinge with two 262 THE LAMELLIBRANCHIA cardinal teeth and two posterior oblique lateral teeth. Dimyarian, the anterior adductor being very small. An extinct family from the Silurian and Devonian. Genera—Ambonychia, Hall; Silurian. Byssonychia, Ulrich ; Silurian. Gosseletia, Barrois ; Devonian. Clionychia, Ulrich ; Silurian. Famity 8. Myauinipag, Frech. Shell very inequilateral, the posterior part greatly enlarged ; the umbones anterior or terminal ; the hinge straight, without teeth ; adductors subequal. An extinct family from the Silurian to the Cretaceous. Genera—Myalina, de Koninck ; Silurian and Devonian. Hoplonvtilus, Sandberger ; Devonian. Ptycho- desma, Hall; Devonian. Anthracoptera, Salter; Carboniferous. Per- gamidea, Bittner; Trias. Mysidea, Bittner; Trias. Aucella, Kyser ; Jurassic and Cretaceous. Famity 9. AmussIIDAE, Ridewood. Gills with- out interlamellar junctions. Shell orbicular, smooth externally, with radiating costae internally. Genus—Amussiwm, Klein. Faminy 10. SPONDYLIDAE, Fleming. Shell very inequivalve, fixed by the right valve, which is larger than the left. The ligament elongated in a transverse direction. No byssus. Genera—Spondylus, Linnaeus ; shell with spiny ribs, and adherent by the spines. Plicatula, Lamarck ; shell folded, adherent by the umbo of the right valve. Faminy 11. PECTINIDAE, Lamarck. Shell ornamented with radiating ribs; the dorsal border provided with two auriculae. Foot byssiferous. Mantle borders pro- vided with eyes (Fig. 235). Genera—Pecten, Lamarck ; shell orbicular, with equal auriculae ; without a byssal sinus; British. Chlamys, Bolten ; shell higher than it is long; the anterior auricula the larger, and pro- vided with a byssal sinus; British. Pedwm, Bruguicre. Hinnites, Defrance. Pseudamussium, Adams. Camptonectes, Agassiz. Hyalopecten, Verrill ; abyssal. Sus-OrDER 5. DIMYACEA. Dimyarian Lamellibranchia with an orbicular and almost equilateral shell; adherent ; the hinge without teeth and the lgament internal. Gills with free non-reflected filaments. Family Driuyipar, Dall; with the characters of the sub-order. Genus—Dimya, Ronault ; recent, in abyssal depths, and fossil since the Jurassic. ORDER 3. Hulamellibranchia. Lamellibranchia in which the edges of the mantle are generally united by one or two sutures (Figs. 221, 241, etc.). Two adductor muscles are usually present (Figs. 238, 241, 242, etc.). In the gills the branchial filaments are united at regular intervals by vascular junctions which transform the linear interfilamentar spaces into a series of fenestrae (Fig. 237). Similarly the lamellae of each gill- plate have vascular junctions which form afferent vessels in the interior of the plates. The gonads always have their own proper external orifices. The order comprises the following nine sub-orders : —Ostraeacea, Submytilacea, Tellinacea, Veneracea, Cardiacea, Chamacea, Myacea, Adesmacea, Anatinacea, THE LAMELLIBRANCHIA 263 Sus-ORDER 1. OSTRAEACEA. Monomyarian Eulamellibranchia, or with a very small anterior adductor muscle. The mantle is open; the foot rather small; the branchiae folded ; the shell inequivalve. Famity 1. Lian, D’Orbigny. Foot digitiform, with a bysso- genous apparatus. Borders of the mantle provided with long and numerous tentacles. Gills not united with the mantle. Shell pro- vided with auriculae. Genera—Lima, Bruguitre ; the individuals of this genus form a sort of nest by means of the byssus, or swim by Fic. 237. A portion of the gill of Venus. e.b.v, efferent branchial vessel ; g.f, gill filaments ; g.v, afferent branchial vessels. (After Bonnet.) clapping the valves of the shell together. Limaea, Broun. Faminy 2. OstREIDAE, Gray. Foot much reduced and devoid of a byssus, Heart generally on the ventral side of the rectum. The gills fused to the mantle. Shell irregular, fixed by the left and larger valve. Genera Ostraea, Linnaeus ; foot absent in the adult ; eatable and cultivated for commerce ; some species, such as the British 0. edulis, are hermaphrodite. Faminy 3. Exntemipas, Gill. Shell thick, inequilateral, the anterior side being the shorter. Monomyarian, with the muscular impression on a prominent myophorous apophysis. Genus—EKligmus, Deslongchamps ; an extinct genus from the Jurassic. Faminy 4. Prynmaz, Meek. Shell elongated. Dimyarian, with a very small anterior adductor 264 THE LAMELLIBRANCHIA muscle. Shell truncated and gaping posteriorly. Foot byssiferous. Genera—Pinna, Linnaeus ; heart traversed by the intestine; anus pro- jecting and appendiculated. Cyrtopinna, Morch. Aviculopinna, Meek ; fossil from the Carboniferous and Permian. Pinnigena, de Saussure ; fossil from the Jurassic and Cretaceous. Atrina, Gray ; from the Car- boniferous to the present day. Sus-OrpER 2. SUBMYTILACEA. Eulamellibranchia in which the mantle is only slightly closed ; generally there is only a single suture. Siphons absent or very short. Gills smooth. Nearly always dimyarian. Shell equivalve, with an external ligament. Famity 1. DREISSENSIIDAE, Gray. Two pallial sutures and two short siphons ; pedal orifice short. Foot cylindrical with a stout byssus. Shell elongated ; the hinge without teeth ; the summits of the valves with an internal septum. Genus—VDreissensia, van Beneden ; an in- habitant of fresh water, but originated from the Caspian Sea ; acclimatised in England about 1824. Faminry 2. MopIoLARcIDAE, Gray. Mantle with two sutures. The foot byssiferous, with a plantar surface and a glandular cavity in front of the byssogenous cavity. The two branchial plates serve as incubatory pouches. Genus—Modiolarca, Gray ; sub- antarctic (Fig. 241). Famity 3. ASTARTIDAE, d’Orbigny. A single pallial suture. Foot elongate, without a byssus. Shell concentrically striated; the ligament external. Genera—Astarte. Sowerby ; British. Woodia, Deshayes. Opis, Defrance; fossil from the Secondary. Pro- socoelus, Keferstein ; fossil from the Devonian. Faminy 4. CRASSATELLIDAE, Gray. Mantle with a single suture; foot short. Shell thick with concentric striae ; the ligament external. Genera—Orassatella, Lamarck. Cuna, Hedley. Faminy 5. CarpiTipa®, Férussac. Mantle with a single pallial suture ; foot carinated, often byssiferous; palps short. Shell thick with radiating costae; the ligament external. Genera—Cardita, Bruguiere. Thecalia, Adams. Milneria, Dall; incubatory, California. Venericardia, Lamarck. Faminty 6. CONDYLOCARDIIDAEK, Bernard. Dis- tinguished from the family Carditidae by the presence of an external ligament. Genera—Condylocardia, Bernard. Carditella, Smith. Cardi- topsis, Smith. Faminy 7. Cyprinipag, @Orbigny. Mantle open in front, and with two pallial sutures, The branchial and anal orifices papillose, the latter projecting. External gill-plates smaller than the internal. Genera—Cyprina, Lamarck; British. Cypricardia, Lamarck. Coralliophaga, de Blainville. Plewrophorus, King; fossil from the Devonian to the Trias. Anisocardia, Munier-Chalmas; fossil from the Jurassic to the Tertiary. Veniella, Stoliczka; fossil from the Cre- taceous to the Tertiary. Famity 8. IsocarpmIpDAE, Gray. Mantle largely closed, the pedal orifice generally small; the anal and branchial orifices sessile ; gill-plates of equal size ; foot short. Shell globular with prominent and coiled umbones. Genus—lIsocardia, Lamarck ; British. Faminy 9. CaLLocARDUDAE, Dall. The anal and branchial orifices of the mantle provided with siphons. The external gill-plate smaller than the internal. Shell ventricose, but elongated ; the umbones not promi- THE LAMELLIBRANCHIA 265 nent. Genus—Callocurdia, Adams; abyssal, Faminy 10. Lucrytipan, VOrbigny. The anal orifice of the mantle sometimes produced into a siphon. Anterior adductor muscle within the pallial line. Labial palps very small. Gills without an external plate. Shell rather thin. Genera —Luceina, Bruguicre ; mantle with two sutures; visceral mass smooth ; foot vermiform ; British. Montacuta, Turton ; shell with a single suture, foot short, byssiferous; visceral mass with arborescent projections ; British. Oryptodon, Turton ; mantle with a single aperture ; foot short ; visceral mass smooth. Famrty 1]. Corprpas, Dall. Shell thick with denticulated borders. The anal orifice provided with a valve, but not with a siphon. Foot elongated and pointed. Genera — Corbis, Cuvier. Gonodon, Schafhautl ; fossil from the Trias and Juras- sic. Muttella, Stoliczka ; fossil from the superior Cretaceous. FamMILy 12. UNGULINIDAE, Adams. Mantle without siphons ; the pedal orifice long. Foot greatly elongated, vermiform, ending in a glandular enlarge- ment (Fig. 238, III). Anterior adductor muscle in contact with the pallial line. Gills with two plates ; labial palps small. Marine. Genera — Ungulina, — Daudin ; Fic. 238. mantle with a single suture ; vis- Axinus flecwosus, Montagu, viewed from the left eceral mass smooth. Diplodonta, side. I, anterior adductor muscle ; II, glandular ; portion of the mantle ; III, foot; IV, gonad pro- Bronn 3 mantle with two sutures ; Jecting into the pallial cavity ; V, internal plate British, Azinus, Sowerby; mantle ofthe ttl VIL posterior adnctod muscle V1 with a single suture ; visceral mass anterior retractor of the foot. with arborescent excrescences (Fig. 238); British, Famity 13. CyRENELLIDAE, Fischer. Mantle provided with two elongated, united, non-retractile siphons. Two gill-plates to each gill; labial palps elongated. Inhabitants of fresh water. Genera— Cyrenella, Deshayes. Joanisiella, Dall. Famity 14. TANCREDIIDAE, Fischer. Shell elongate, sub-triangular ; the ligament external. Hinge with two cardinal teeth on the right and one or two on the left valve. Posterior lateral teeth stout. An extinct family ranging from the Trias to the Cretaceous. |Genera—Tancredia, Lycett; ‘Trias to Cretaceous. Meekia, Gabb ; Cretaceous. Faminty 15. UNtIcarpDIIDAR, Fischer. Shell sub-orbicular, more or less ventricose, nearly equilateral, with concentric striae ; pallial line simple; hinge with a single cardinal tooth on each valve. An extinct family ranging from the Carboniferous to the Cre- taceous. Genera—Unicardium, d’Orbigny ; Trias to Cretaceous. Scaldia, de Ryckholt ; Carboniferous. Psewdedmondia, Fischer ; Carboniferous. Famity 16. Lepronipan, Gray. Shell thin, not covered by the mantle and not gaping. Mantle without siphons; gills with two gill-plates ; foot long and byssiferous. Marine, hermaphrodite and incubatory animals. 266 THE LAMELLIBRANCHIA Genera—Kellya, Turton ; mantle with two sutures and three orifices, the pedal orifice being the middle and not the anterior of the three (Fig. 187) ; foot linguiform ; the external gill-plate with a reflected lamella; British. Lepton, Turton; mantle with a single suture ; the mantle edges provided with tentacles ; foot with a plantar ventral surface ; commensal ; British. Lasaea, Leach ; a single pallial suture ; the foot linguiform and elongated ; the external gill-plate not reflected (Fig. 206, G); British. Hrycina, Lamarck; fossil from the Tertiary. Pythina, Hinds. Scacchia, Philippi. Sportella, Deshayes. Cyamiwm, Philippi. Famity 17. Gayz_oMMIDAE, Gray. Mantle more or less completely reflected over the shell. Foot well developed, generally byssiferous. Shell thin, gaping; the adductor muscles much reduced. Genera—Galeomma, Turton ; shell incompletely covered by the mantle; a single pallial suture ; a large azygos anterior pallial tentacle, and a short anal siphon present. A byssal groove in the foot; British. Scintilla, Deshayes. Hindsiella, Stoliczka. Ephippo- donta, Tate ; shell internal; a single pallial suture; gills with two gill- plates; commensal with the shrimp Aaius; Australian. The three following genera with an internal shell probably Dall; two gill-plates; a pallial suture ; an anterior orifice leading into a caecum ; no adductor muscles; sexes separate ; from California (Fig. 239). Scioberetia, a single pallial suture ; foot large, elon- gated, with a byssal groove ; hermaphro- dite and commensal with a Spatangid, Triphylus ; from Cape Horn. Entovalva, Voeltzkow (Fig. 240); mantle fairly open, with a single suture; foot large, with a posterior pore; hermaphrodite and ineubatory ; endoparasitic in Synapta (=Synapticola, Malard), Madagascar and Atlantic. Faminy 18. KErLLYELLIDAE, Fischer. Mantle with a single pallial suture ; anal orifice with a very short Fic. 239. siphon ; foot elongated ; gills with two Chlomydoconcha oreutti, Dall. A, dor- Unequal plates. Shell ovoid ; the liga- sal aspect ; B, left-side view. @.0, anal ment external ; the anterior lateral eave Pe aoeaeane UO: hinge tooth below the cardinal tooth. Genera — Kellyella, Sars. Turtonia, Forbes and Hanley ; British. Allopagus, Stoliczka ; fossil from the Eocene. Lutetia, Deshayes ; fossil from the Eocene. Faminry 19. CyRENIDAE, Gray. Mantle with two siphons, which are more or less intimately united together and have papillose orifices. The sexes separate. Shell with external ligament; the pallial line usually with a sinus, Freshwater forms. Genera—Cyrena, Lamarck. Corbicula, Megerle. Batissa, Gray. Velorita, Gray. Galatea, Bruguiere. Fischeria, Bernardi. Faminy 20. belong to this family :-—Chlamydoconcha, * Bernard ; gills with a single gill-plate ; | THE LAMELLIBRANCHIA 267 CycLADIDAE, Clark. Mantle with one siphon or with two free siphons, which have simple orifices. _Hermaphrodite ; the embryos incubated in the external gill-plate. Shell with a simple pallial line. Freshwater. Genera—Cyclas, Bruguitre (= Sphaerium) ; two siphons ; British (Fig. 218). Pisidium, Pfeiffer ; asingle analsiphon ; British. FAmILy 21. RANGIIDAE. Mantle with two short siphons united at their bases, and with papillose orifices. Foot linguiform. Shell with prominent umbones and an internal ligament. Genus—Rangia, Desmoulins; from brackish water in Florida. Faminy 22. Carpinupa®, Zittel. Shell elongated, inequi- lateral, the posterior side being the longer; the ligament external ; the pallial line simple; dimyarian. An extinct family, ranging from the oc aie Fic, 240, Entovalva, left-side view. a, anus; c.g, cerebral ganglion ; f.g/, foot-gland; g.gl, gonad ; i.c, incubatory chamber; in, intestine; J, liver; m, mouth; pa, mantle; sh, shell. (After Voeltzkow.) Devonian to the Cretaceous. Genera—Cardinia, Agassiz; Trias and Jurassic. Anthracosia, King ; Carboniferousand Permian. Anoplophora, Sandberger ; Trias. Pachycardia, Hauer; Trias. Famity 23. MrEGA- LODONTIDAE, Zittel. Shell inequilateral, thick, dimyarian, with pro- minent umbones; the posterior adductor impression borne on a myo- phorous apophysis. An extinct family, ranging from the Devonian to the Cretaceous. Genera—Megalodon, Sowerby ; from the Devonian to the Jurassic. Pachyrisma, Morris and Lycett; Trias and Jurassic. Durga, Bohm ; Jurassic. Dicerocardivm, Stoppani; Jurassic. Faminy 24. Unronipakz, Fleming. Mantle with a single pallial suture and no siphons. Shell equilateral, with lateral hinge teeth or no hinge teeth. Inhabitants of fresh water. Development through a glochidium 268 THE LAMELLIBRANCHIA stage (Fig. 242). Genera—Unio, Retzius ; shell thick, the hinge toothed. This genus includes more than a thousand species, the majority from the northern hemisphere. Anodonta, Lamarck; shell thin; the hinge without teeth ; British. Psewdodon, Gould. Quadrula, Rafinesque. Arconaia, Conrad. Monocondylaea, VOrbigny. Solenaia, Conrad. Mycetopus, d’Orbigny ; foot cylindrical, with a terminal swelling ; South America, Famity 25. Mvure.rpAk, Gray. This family differs from the Unionidae in having two pallial sutures and a distinct branchial orifice; the shell is never fur- nished with lateral hinge teeth. Freshwater. Genera—Mutela, Scopoli. Pliodon, Conrad. Spatha, Lea. Jridina, Lamarck. Hyria, Lamarck. Castalia, Lamarck. Aplodon, Spix. Plagiodon, Spix. Famity 26. AETHERIDAE, Adams. Shell irregular, generally fixed in the adult state. Mantle with a single suture; foot absent; anterior adductor muscle Fic. 241. Modiolaria trapezina, Lamarck, viewed from the left side ; the left mantle lobe is removed. ad’, ad’, anterior and posterior adductor muscles; br’, br’, internal and external gill-plates ; gl.p, foot gland ; 0.a, 0.b, anal and branchial orifices of the mantle ; 0.by, byssal orifice of the foot ; 0.p, pedal orifice of the mantle ; p, foot; pal, labial palp ; re.p, posterior retractor muscle of the foot. sometimes reduced or absent; from fresh water. Genera— Aetheria, Lamarck ; anterior adductor well developed ; African. Miilleria, Férussac ; no anterior adductor; American. artlettia, Adams. Susp-ORDER 3. TELLINACEA. Eulamellibranchia in which the mantle is not extensively closed, with two pallial sutures and two well-developed siphons; the gills smooth. The foot is compressed and elongated. The labial palps very large. Dimyarian; the pallial line has a deep sinus. Famity 1. Trnnirpar, Deshayes. The external branchial plate directed upwards (Fig. 206, H). The siphons separate and elongated. Foot with a byssogenous apparatus. Palps very large. Ligament of shell external. Genera—VTellina, Linnaeus; slightly inequivalve ; foot large ; British (Fig. 190). Gastrana, Schumacher ; equivalve ; the foot slightly developed ; British. Capsa, Bruguitre. Macoma, Leach, Faminy 2. ScROBICULARIIDAE, Adams. External gill-plate directed upwards. Siphons separate and excessively long. Foot without a byssus. The ligament partly internal, lodged in a concavity in the hinge. Genera— ’ THE LAMELLIBRANCAIA 269 S ah ay, ay Ul a “Pag am b 4 ‘1 au Fic. 242. Diagrams of the external form and anatomy of Anodonta cygnaea (2), ventral view, all ,the other figures seen from the left side. (1) animal removed from its shell; a probe g passed into the infra-branchial chamber through the excurrent siphonal notch. (2) view from the ventral surface of Anodonta, with its foot expanded and issuing from between the gaping valves. (3) the left mautle-flap reflected upwards so as to expose the sides of the body. (4) diagrammatic sagittal section of Anodonta to show the course of the alimentary canal. (5) the two gill-plates of the left side reflected upwards, so as to expose the fissure between foot and gill where the probe g passes. (6) diagram to show the positions of the nerve ganglia, heart, and kidney. a, centro-dorsal area ; b, margin of the left mantle-flap ; c, margin of the right mantle-flap ; d, ex- current (anal) siphonal notch of the mantle-margin ; e, incurrent (branchial) siphonal notch ; Jf, foot ; g, probe passed into the superior division of the sub-pallial chamber through the anal siphonal notch, and issuing by the side of the foot into the infra-branchial chamber ; h, anterior adductor muscle ; i, anterior retractor muscle of the foot ; k, protractor muscle of the foot; J, posterior adductor muscle; m, posterior retractor muscle of the foot ; n, anterior labial palp ; 0, posterior labial palp ; p, base-line of origin of the reflected mantle-flap from the side of the body ; q, left external gill-plate ; 7, left internal gill-plate ; rr, inner lamella of the right inner gill-plate ; 7.9, right outer gill-plate ; s, line of concrescence of the outer lamella of the left outer gill-plate with the left mantle-flap ; t, pallial tentacles ; wv, the thickened muscular pallial margin which adheres to the shell and forms the pallial line of the left side; v, that of the left side; w, the mouth; 2, aperture of the left kidney, exposed by cutting the attachment of the inner lamella of the inner gill-plate ; y, aperture of the genital duct; 2, fissure between the free edge of the inner lamella of the inner gill-plate and the side of the foot, through which the probe g passes into the supra-branchial chamber ; aa, line of concrescence of the inner lamella of the right inner gill-plate with the inner lamella of the left inner gill-plate ; ab, ac, ad, three pit-like glandular depressions in the median line of the foot; ae, left shell-valve ; af, space occupied by the liver ; ag, space occupied by the gonad ; ah, muscular substance of the foot ; ai, opening of bile-duct into the stomach ; ak, stomach; al, rectum traversing the ventricle of the heart ; am, pericardium ; an, glandular portion of the left kidney ; ap, ventricle of the heart ; aq, auriculo- ventricular orifice ; a7, non-glandular portion of the left kidney ; as, anus ; at, reno-pericardial orifice ; au, pore joining the two parts of the kidney ; av, internal pore of the kidney leading to the external pore x; aw, left cerebral ganglion ; az, left pedal ganglion; ay, left otocyst; az, left visceral ganglion; bb, floor of the pericardium, separating that space from the kidney. (After Lankester.) 270 THE LAMELLIBRANCHIA Scrobicularia, Schumacher; estuarine; British. Syndosmya, Recluz ; British. Cumingia, Sowerby. Famity 3. Donacipar, Fleming. Ex- ternal gill- plate directed ventrally. Siphons separate, of moderate length, the anal siphon being the longer. Foot large and compressed. Shell inequilateral, the anterior side being the longer; the ligament external. Genera—Donaz, Linnaeus; British. _ [phigeneia, Schumacher. Fammy 4. Mesopesmatipar, Deshayes. External branchial plate directed ventrally. Siphons separate and equal. Shell inequilateral, the anterior side being the longer ; ligament internal. Genera—Meso- desma, Deshayes. Ervilia, Turton; British. Faminy 5. CARDILIIDAE, Dall. Shell very high and short, ventricose, dimyarian, the posterior adductor impression borne on a prominent myophorous apophysis. Ligament partly internal. Genus—Curdilia, Deshayes ; from the Pacific Ocean. Famrty 6. Macrripar, Gray. External branchial plate directed ventrally. Siphons united, more or less invested by a chitinous sheath. Foot long, stout, bent at an angle and without a byssus. Shell sub- triangular and nearly equilateral ; the ligament partly internal. Genera —Mactra, Linnaeus ; British (Fig. 191). Mulinia,Gray. Harvella, Gray. Raeta, Gray. Eastonia, Gray. Heterocardia, Deshayes. Vanganella, Gray. Sup-OrDER 4. VENERACBA. Eulamellibranchia with two pallial sutures; the siphons generally somewhat elongated and partially or wholly united. Gills slightly folded. A bulb on the posterior aorta. Ligament external. Famity 1. VENERIDAE, Gray. Foot well developed. Adductor muscles subequal. Pallial sinus shallow or absent. Genera—Venus, Linnaeus; siphons rather short, their distal extremities free ; foot without byssus ; British. Dosinia, Scopoli; siphons long and fused together throughout their length; foot truncated without a byssus; British Tapes, Megerle; siphons rather” long and incompletely fused ; foot byssiferous ; British (Fig. 202). Cyclina, Deshayes. Lucinopsis, Forbes and Hanley ; British. Meretriz, Lamarck (Fig. 189). Circe, Schumacher ; British. Venerwpis, Lamarck. Famity 2.~ Perriconipar, d’Orbigny. Boring Lamellibranchs with a reduced foot. The shell more or less elongated, with a deep pallial sinus. Genera—Petricola, Lamarck ; the British species P. pholadiformis, originally an inhabitant of the United States, has been acclimatised for some years in the North Sea: it has boring habits as and mimics Pholas candida. FamiIny 3, GLAUCOMYIDAB, Chenu. Siphons very long and united. Foot small. Shell elongated, thin, with a deep pallial sinus. Inhabitants of fresh or brackish water, Genera—Glaucomya, Woodward ; from 8.E. Asia. Tanystphon, Benson ; from India. Sus-OrDER 5. CARDIACEA. Eulamellibranchia with two pallial sutures. Generally with short siphons. The foot cylindrical, more or less elongated, furnished with a byssogenous apparatus. The gills much folded. Shell equivalve, with radiating costae and an external ligament. THE LAMELLIBRANCHIA 27 Faminy 1. Carprpar, Gray. The mantle slightly closed ; siphons very short and surrounded by a single circle of papillae which are often oculiferous (Fig. 243, 0.t). Foot very long, geniculated. Pallial line of the shell without a sinus; two adductor muscles. Genera—Cardium, Linnaeus ; adductor muscles subequal ; British (Fig. 243). Psewdokellya, Pelseneer (Fig. 221). Both Byssocardiwm, Munier-Chalmas, and Litho- cardium, Woodward, fossils from the Eocene, have a much reduced anterior adductor muscle. Famriy 2. LimnocarpiDA®, Stoliczka. Siphons very long, united throughout their extent. Shell gaping; two adductor muscles. Inhabitants of brackish waters. Genera—Adacna, Eichwald ; from the Caspian Sea. Limnocardium, Stoliczka ; from the Caspian Sea and fossil from the Tertiary. Arcicardium, Fischer; fossil from the Tertiary. Faminy 3. Trrpacnipak, Broderip. Mantle closed to a con- siderable extent, the orifices distant from one another ; no siphons. The foot short, with a more or less well developed byssus, TP, aspect. e, pedunculated eye; fi, fin; m, P ‘ eas Rs x mouth ; ¢, tentaculararm. (After Hoyle.) embrace it. Certain Oigopsida, however, e.g. Taonius suhmii, Ray Lankester (Fig. 253), and the embryos of an allied form known as Grenacher’s embryo (Fig. 119, D) and of Loligo peali, have very prominent pedunculated eyes. On the other hand, Nautilus, whose eyes are also somewhat prominent, has in addition two ciliated tentacles on either side of the head, one in front of and the other behind the eye (Figs. 255, 1,4; 293, a.o.t, p.o.t). The foot forms a crown of appendages surrounding the mouth: the edges of this crown are not deeply divided in Nautilus, but are much more so in the Dibranchia. In Nwutilus the circumoral pedal crown is divided into lobes each of which bears a group of tentacles, the total number of tentacles being about ninety in the THE CEPHALOPODA 287 SS female, but only sixty in the male. These tentacles have laminated but not ciliated surfaces; they are adhesive and prehensile, and are retractile within special tentacular sheaths. When the animal is extended they radiate outwards from the mouth. In the female there are three tentaculiferous lobes in immediate contact with the buccal aperture (Fig. 255, c, @): these are the right and left and the ventral interior lobes. The last named (which is absent in the male) bears a laminated organ, supposed to be olfactory in function and known as Owen’s organ, in the middle of its free border (Fig. 255, n), and fourteen tentacles on each moiety of the lobe. The {/ Fic. 254, Tremoctopus velifer, Verany, viewed from the dorsal side, showing the four dorsal arms joined together by a membrane. (After Verany.) right and left interior lobes bear twelve tentacles apiece. The muscular mass of the foot forms a broad ring round the three interior lobes, and is particularly thick and strong in the dorsal region (Fig. 255, g), where it is modified to form a hood which protects the whole animal when it is retracted within its shell. On the external face of the hood is a concavity in which the spire of the shell is lodged. The tentacles borne on this ring are called “digital,” and are larger than the “labial” tentacles borne on the three interior lobes. The digital tentacles are nineteen in number on each side in the female, and are disposed more or less regularly in three unequal rows. It is only the dorsal pair of tentacles that belongs to that part of the muscular ring which forms the hood, the last-named 288 LHE CEPHALOPODA structure being largely composed of an extension of the sheaths of the tentacles in question. On the ventral side an extensive part of the internal surface of the muscular ring is laminated, Fia. 255. Male (upper) and female (lower) specimens of Nautilus pompilius, as seen in the expanded condition ; oral view, showing the disposition of the tentaculiferous lobes and the differences between the two sexes. a, the shell; b, the outer ring-like expansion or annular lobe of the cireumoral mass of the foot, dorsally forming the hood ; ¢, the right and left inner lobes of the foot, each carrying twelve tentacles in the female, in the male divided into p, the ‘‘ spadix ” (hectocotylus) on the left side, and q, the ‘‘anti-spadix,” a group of four tentacles, on the right side ; d, the inner inferior lobe of the foot (reduced in the male to a paired group of lamellae) ; e, the buccal cone, fringing the jaws with a series of minute papillae; f, the tentacles of the outer lobe, projecting from their sheaths ; g, the two most posterior tentacles, belonging to the hood ; i, superior ophthalmic tentacle; k, inferior ophthalmic tentacle; l, eye; m, paired laminated organ on each side of the base of the inner inferior lobe of the female; m, olfactory lamellae upon the inner inferior lobe, in the female; 0, the funnel; p, the spadix (in the male) or hectocotylised portion of the left inner lobe of the foot, representing four modified tentacles ; q, the antispadix (in the male), being four of the twelve tentacles of the right inner lobe, isolated from the remaining eight. (After Lankester.) THE CEPHALOPODA 289 forming the so-called “organ of Valenciennes,” peculiar to the female and serving for the attachment of the spermatophores (Fig. 255, m). In the Dibranchia the pedal appendages have the form of four or five pairs of symmetrical and generally elongate arms. In the Octopoda there are eight similar arms, and the whole length of the ventral surface of each is covered by suckers which are often very numerous and highly specialised in structure (Fig. 256). It seems probable that it is the suckers and not the arms that are com- parable with the tentacles and tentacle-sheaths of Nautilus. In the Decapoda, in addition to the eight arms corresponding to those of the Octopoda, there are two additional “tentacular” arms, of which one is situated between the third and fourth sessile arms on either side of the posterior part of the head. These two tentacular arms are longer and more slender than the others (Fig. 298, A), and the suckers are generally confined to their free extremities, which are enlarged and club-shaped ; in some forms, however, they bear suckers along their whole length (Fig. 297, I1). The tentacular arms are further distinguished from the sessile arms by the fact that they are more or less retractile within special pouches: they are com- pletely retractile in Sepia, Sepiola, and Fossia, incompletely retractile in Loligo, very slightly retractile in the majority of the Oigopsida, and finally they are united to form a beak-like appendage in Fhynchoteuthis. In some Oigopsida, such as Leachia, Chawnoteuthis, some species of Cheiroteuthis, and Grimalditeuthis (Fig. 258), the tentacular arms are reduced to mere stumps: in the adult Veranya they are similarly reduced, but the young still retain small tentacular arms. Similarly a notable reduction of the ordinary or sessile arms, particularly on the dorsal side, may be observed in some Cheiroteuthidae and Cranchiidae. Some or all of the eight sessile arms may be united by a more or less complete inter- brachial membrane: the four dorsal arms are united in this manner in 7'remoctopus (Fig. 254), the six dorsal arms in /Zistioteuthis, and all eight arms in some species of Hledone, in Alloposus, and in the adult Cirrhoteuthidae and Amphitretidae, the membrane ex- tending in the two last-named families to the tips of the arms, but in the young of Cirrhoteuthis (Fig. 260) the membrane is not fully developed. In the female Argonauta the two dorsal arms are enlarged to form a veil (Fig. 301, IV), which is applied to the mantle and secretes a protective calcareous shell. Finally, in most cases a single arm of the male, or a portion of the circumoral pedal crown in Nautilus, is modified to form a copulatory organ, which is some- times detachable. This is the hectocotylus, or spadix in Nautilus, which will be described in detail under the head of reproductive apparatus. 19 290 THE CEPHALOPODA The suckers are pedunculated in the Decapoda, the peduncles being axial or lateral, but they are sessile in the Octopoda (Fig. 256), They generally form a double series along the internal, that is to say, the ventral or buccal faces of the arms, but there is a single series in Hledone and Cirrhoteuthis (Fig. 260). In some cases, however, there are more than two rows, eg. Spirula (Fig. 268, ar), Gonatus, Dosidicus, Tritaxeopus, Ctenopteryx (on the three dorsal pairs of arms), and Sepia (Fig. 299, c). In point of structure, each sucker consists of a globular or cylindrical projection, comprising an annular surface of application with a central cavity whose capacity can be augmented by the retraction of its floor. The floor is provided with perpendicular muscular fibres (Fig. 256, I), whose contraction causes the sucker to adhere to the prey or to the substratum. The surface of application of the sucker is Fic. 256. Axial section of a sucker of Argonauta. I, muscular fibres retracting the bottom of the sucker ; II, radiating muscular fibres ; III, annular muscular fibres ; IV, floor of the cavity of the sucker ; V, sphincter muscle ; VI, tooth on the margin of the sucker. (After Niemiec.) augmented by the action of radiating muscular fibres (Fig. 256, I), and its adherence is further assured by the cuticular rugosities of this surface. These cuticular structures are simply small projections in the Octopoda, but in the Decapoda there is a complete chitinous ring with denticulated edges which are often very prominent, and in some cases a single denticulation may become very large and preponderant and thus transform the sucker into a hook-bearing organ. In Onychoteuthis true functional suckers coexist with the hooks, but in the adult Veranya the suckers are nothing more than the bases of the hooks. In various species of Chevroteuthis the tentacular arms bear suckers in which the muscular system is feebly developed and there is neither a central piston nor a horny ring, but the bottom of the cupule is covered by a great number of anastomosed epithelial filaments which constitute an organ for fishing. In Cirrhoteuthis, in addition to the row of suckers, there are tentacular filaments on each arm alternating with the suckers. THE CEPHALOPODA 291 In addition to the foot proper, whose edges constitute the circum- oral appendages, the Cephalopoda possess an epipodium which is well developed, but highly specialised to form a funnel. The epipodial nature of the funnel may be specially well seen in young embryos (Figs. 257, fu; 119, D, fw), in which this organ is situated laterally and posteriorly, between the mantle and the foot. Primitively the funnel has the form of two symmetrical lateral lobes, which simply incline towards one another and overlap in Nautilus (Fig. 276). In the Dibranchia, however, these two lobes become fused together during development (Fig. 290, (9) g) and form a complete tube projecting beyond the pallial cavity (Figs. 253 and 258, etc., fu). Through this tube the excrements, the secretion of the ink-sac, and the generative products are ejected. The interior of the funnel is generally provided with a larger or smaller valve, attached to its anterior or dorsal face; as, for instance, in the Nautilidae (Fig. 276, b) and the majority of the Decapoda (Fig. 259, fu); but this structure is absent in Leachia among the Oigopsida and in the Octopoda. In addition, the in- Fira. 257. Young embryo of Sepia officinalis, viewed from the dorsal side. a, anus ; Fic. 258. e, eye; fu. funnel; gi, gill; m, mouth ; Grimalditeuthis richardi, ventral as- ot, otocyst ; pa, mantle and shell; 2, pect. a, arms; ¢, left eye; fi’, anterior vitellus; 1, 2, 3, 4, 5, arms. (After fin ; ji’, posterior fin ; fu, funnel. (After Kolliker. ) Joubin.) ternal wall of the funnel is furnished with an epithelial outgrowth of variable form, constituting a mucous gland called Miiller’s organ. Powerful muscular bundles, originating from the cephalopedal mass and from the sides of the funnel, unite together and are inserted symmetrically on the sides of the shell (Fig. 272, m). In Nautilus they are inserted on the interior of the shell, in the Dibranchia on its external surface, in Spirwla on the margins of the last chamber. 292 THE CEPHALOPODA Other differentiated muscular bundles may be recognised ; they are mostly due to the specialisation of the funnel. In the Tetrabranchia (Nautilus) the mantle is covered by an external shell, which is partly overlapped by a small dorsal pallial lobe (Fig. 270, d): the retractor muscles of the head and foot are | inserted symmetrically on either side on the internal surface of this shell. The female Argonauta also bears an external shell which covers the mantle, but has no muscular attachments and is not homologous with the shells of other Cephalopods: it does not originate from a pre-conchylian invagination or shell-gland, but is of pedal origin, and is only formed some ten or twelve days after birth by the palmate extremities of the two dorsal arms. The animal is not attached to this shell. In all other Cephalopoda the shell is covered over by the mantle, or at least is partly covered in Spirula (Fig. 295). The shell therefore is internal, and often is rudimentary, as in the majority of Decapoda, or it may be nearly obsolete, as in the Octopoda. The shell of living and fossil Nautiloidea, of Ammonoidea, Spirula (Fig. 268, sp), and of various fossil Dibranchia, such as the Belemnitidae, Spirulirostra (Fig. 262, C), ete.,is provided with internal septa, disposed perpendicularly to the axis of the coil. It is only the last of the chambers thus formed that is occupied by the body of the animal, but a prolongation of the pallial integument known as the pallial siphuncle (Fig. 270, /) extends back to the initial chamber of the shell, and is enclosed in a calcareous tube or shell siphuncle which perforates all the septa (Fig. 268, sz). This pallial siphuncle does not communicate with the coelomic cavity: in Nautilus and Spirula it is a simple vascular vermiform process of the mantle, whose cavity consists of a venous sinus and whose wall contains a ramification of the pallial artery. It apparently plays a part in the hydrostatic function. At the point where the shell siphuncle traverses each septum it is generally surrounded by a small reduplication of the latter, forming the so-called siphuncular neck. The chambers traversed by the siphuncle do not communicate with one another nor with the shell siphuncle: they are filled with a nitrogenous gas and form a hydrostatic apparatus. The external multilocular shell is straight in some palaeozoic Nautiloidea (Orthoceras), but in the majority of Tetrabranchia it is arcuate or more or less completely coiled in such a manner as to form a discoidal shell whose whorls are all in the same plane. In the majority of Tetrabranchia (Nautilus, Fig. 270) the coil is exo- gastric, that is to say, it is turned towards the dorsal aspect, but in some forms, ¢.g. Phragmoceras, Cyrtoceras, Ptenoceras (Fig. 261, B), it is turned towards the ventral side and is therefore endogastric ; the direction of the coil cannot be determined by the position of the siphuncle, which traverses the septa at various points, but by THE CEPHALOPODA 293 the form of the aperture and the position of the ‘ hyponomous ” sinus, which corresponds to the funnel (Fig. 261, zs). In some Nautiloidea, ¢.7. the dextral or sinistral 77ochoceras, and in sundry Ammonoidea, ¢.g. the sinistral Zwrrilites and Cochloceras and the dextral Bostrychoceras, the coil may be produced into a _helicoidal or turriculated spire. And in other cases again the last whorls of shell, whether it be discoidal or helicoidal, may be partly un- coiled, as may be seen, for example, in Litwites, which is largely uncoiled, or in Ophidioceras, in which only a small extent of the shell is uncoiled. Finally, the shell may become secondarily rectilinear in the adult, as in Baculites, among the Ammonoidea. In Spirula the shell is coiled in one plane, but it is endogastric, that is to say, coiled in the opposite direction to that of Nautilus (Figs. 268 and 270), and it is largely internal. In certain fossil Dibranchia the multilocular shell, whether it be straight or partially coiled, has become internal (Belemnitidae, Spirulirostra) and forms the phragmocone (Fig. 262, C). In such cases it is surrounded by a caleareous secretion of the reflected portion of the mantle, which is not homologous with the shell of other Molluscs, and forms the pointed rostrum or guard at the end opposite to the head (Fig. 262) and the cephalic plate or pro-ostracum at the anterior or dorsal end. Thus there is, in the shells of these Cephalopoda, an element which is not represented in the shells of other Mollusca. In the living Dibranchia, with the exception of Spirula, the phragmocone and the rostrum of this internal shell have become very rudimentary. In Sepia, for example, the shell is composed of parallel layers united together by short pillars of calcareous sub- stance, and has a stratified and alveolar structure: at its posterior end a little hollow marks the position of the phragmocone, and a short pointed external projection represents the rostrum, the bulk of the shell being formed by the anterior pro-ostracum, on which the retractor muscles of the cephalopedal mass are inserted. In the Oigopsida the guard is no longer calcified, and the shell has the form of a chitinous plume or gladius, but in Ommuatostrephes there is a small posterior conical cavity representing the remains of the phragmocone. In the Loliginidae and Sepiolidae the shell is similarly repre- sented by a chitinous gladius (Fig. 263), but in these families it is so much reduced that it only occupies the anterior portion of the body. In Jdiosepius this shell is nearly obsolete, and it is absent altogether in certain Sepiolidae and some allied forms such as Stoloteuthis, Inioteuthis, Sepioloidea, and Sepiadarium. Finally, in the Octopoda there is no longer a true shell, but only some simple chitinous rudiments, on which the retractor muscles of the head and funnel are inserted ; these may be paired, as in the case of the lateral stylets of Octopus ; or unpaired, as in the case of Cirrhoteuthis. 204 THE CEPHALOPODA It follows that in all living Cephalopods except Nautilus the shell is localised on the anterior or physiologically dorsal side of the body, and is enclosed by the mantle, which therefore appears to be a naked, bell-shaped sac (Figs. 252, 254, 287, etc.). The whole circumference of the mantle border is free in the Decapoda (Fig. 259), with the exception of Sepiola, in which it is fused to the head anteriorly in the middle line. Similarly, in the Octopoda, the border of the mantle is fused to the head anteriorly and laterally, whereby the pallial aperture is much reduced, especially in Cirrho- teuthis (Fig. 260) and Opisthoteu- this (Fig. 300). In the Decapoda a more secure union between the mantle and the funnel, during the expulsion of the water used in respiration Fic. 259. Ctenopteryx cyprinoides, ventral aspect. Fic. 260. a, arms; e, eye; fi, fins; fw, funnel with valve; ol, olfactory organ or rhinophore ; Cirrhoteuthis meangensis, Hoyle (young speci- so, socket of the funnel; te, tentacular men), ventral aspect. ji, fin; fu, funnel; m, arms. (After Joubin.) mouth. (After Hoyle.) through the latter structure, is ensured by the following mechanism : the free borders of the mantle bear on each side a cartilaginous pro- jection (Fig. 272, c’) which fits into a corresponding depression in the funnel (Figs. 272, ¢; 259, so), the whole constituting the so- called ‘resisting apparatus ” of foreign authors. In certain Oigopsida of the family Cranchiidae (Cranchia, Leachia) and in the Octopoda this apparatus is but feebly developed, and in Cirrhoteuthis, where it would be useless, it has disappeared. Otherwise the funnel is quite independent of the mantle: it is only in Amphitretus among the Cirrhoteuthidae that the mantle border is united to the funnel by a ventral suture, leaving an opening into the pallial cavity on either side. Similarly, in Grimalditeuthis and Symplecto- THE CEPHALOPODA 295 feuthis among the Oigopsida, there are two infundibulo-pallial sutures, In the Dibranchia the mantle is a very muscular organ, which, by its contractions, serves two purposes. By alternately and rhythmically drawing in and forcing out the water that enters the pallial cavity between the funnel and the border of the mantle, it acts as an accessory respiratory organ, and by violently expelling water through the funnel it acts as an efficacious locomotory organ, causing the animal to execute sudden retrograde movements. In the majority of Cephalopods with internal shells (Decapoda) and in the Cirrhoteuthidae, the mantle is produced into lateral symmetrical expansions or fins of various form and position (Figs. 253, 260, and 268, fi). ‘These organs always originate at the aboral Fic. 261. Two fossil Nautilids, left-side view. A, Ophidioceras simpler, Barrande; A’, mouth of the shell; B, Ptenoceras alatwm, Barrande. /f.s, foot (arms) sinus ; i.s, infundibular sinus. (After Barrande.) extremity of the mantle (Fig. 290, (4) @)—even in Octopus, in which genus they eventually disappear—as two triangular or rounded out- growths. ‘They remain localised at the aboral extremity in Spirula, in which genus they are situated close together at the point where the two halves of the mantle reunite behind the shell (Fig. 295). In most other Oigopsida they are still terminal and close together, but they tend to shift further forward on the anterior or dorsal surface, as in ZYaonius (Fig. 253) and Ommatostrephes (Fig. 297), and they may be duplicated, the two fins on each side lying close together, as in Grimalditeuthis (Fig. 258, fi’, fi’) and Vampyroteuthis. But in all other cases they diverge to take up positions opposite one another on the right and left sides of the body, and show an increasing tendency to occupy the whole length of the body, as in 7hysanoteuthis, where they are triangular (Fig. 298, B), and in Sepioteuthis, where they are rounded. In Sepia the fins extend the whole length of the mantle, 296 THE CEPHALOPODA but are reduced so as to be of the same width throughout (Fig. 272, P). The fins of Ctenopteryx are similar, but are pectinated, that is to say, they consist of a thin membrane supported by muscular fibres (Fig. 259, ji). On the other hand, in species with a short and globular mantle the fins are shifted away from the aboral extremity, and are situated either in the middle of the body, as in Sepiola, or even near the anterior end, as in Cirrho- teuthis (Fig. 260). Except in Nautilus (Fig. 270, f) and Spirula (Fig. 268, pa.c), where it is shallower, the pallial cavity extends from its opening behind the head to the aboral extremity or summit of the body. It contains the branchiae and the anal, renal, and genital orifices (Fig. 272, Br, a, 7, g). In some Fic. 262. Internal shells of Cephalopoda. 4, shell of Belemnoteuthis dupiniana (Neocomian). B, shell Fig. 263. of Sepia Orbignyana. OC, shell of Spirulirostra The chitinous internal Bellardii (Miocene) ; the specimen is cut so as to shell, or gladius, of Loligo, show in section the chambered shell and the the anterior part upper- laminated ‘‘ guard” deposited upon its surface ; most. (From Lankester, D, shell of Spirula lwevis. (After Lankester.) after Owen.) forms it is divided longitudinally by a muscular junction between the mantle and the visceral mass, starting from either side of the anus: such is the case in the essentially littoral forms with a short pallial sac, such as Sepiola and the Octopodidae. In Opisthoteuthis the pallial cavity is particularly narrow and shallow, and the pallial sac scarcely projects ; in consequence of the diminu- tion of the ventral flexure the animal is flattened and discoid (Fig. 300), and the anus has returned to the posterior position which it occupies in primitive Mollusca. Beneath the epithelium the integument contains, at least in THE CEPAALOPODA 297 the Dibranchia, chromatophores or extensible pigment cells, whose activity produces the remarkable colour changes characteristic of these animals. The chromatophores are cells originally of ecto- dermic origin, which sink below the epithelium and become connected with contractile radiating mesodermic fibres. The pigment cells are simple but multinuclear, since they contain secondary nuclei situated at the bases of the muscular fibres. Different cells contain different coloured pigment: yellow, brown, red, or blue in the Decapoda. Each cell exhibits a constant though feeble tremulous movement, and may suddenly be extended, by a reflex action, under the influence of emotion or excitation, or as a more direct result of volition the chromatophores of the same colour may assume a definite condition of contraction or expansion, which gives the body a tint analogous to that of surrounding objects. In the latter case the action of the chromatophores is under the direct influence of the cerebral centres of the nervous system, and section of one of the optic nerves puts an end to voluntary changes of colour on the same side of the body. The chromatophores are chiefly dis- tributed over the anterior surface (or upper surface when the animal is in its natural position) of the mantle, the head, and the external sides of the arms. In the Decapoda there is, in addition to the chromatophores, a layer of reflecting cells which give these animals their iridescent hues. In certain Oigopsida belonging to the zonary or deep plankton, for example, Histioteuthis, Calliteuthis, Histiopsis, Pterygioteuthis, ete., the surface of the body bears luminous organs, all of which are oriented towards the anterior extremity. The essential structure of these organs consists of a deeper photogenous layer and of super- ficial refracting elements. They may even extend into the interior of the pallial cavity, as, for example, in Pterygioteuthis. In the deeper parts of the integument the connective tissue is often concentrated to form cartilage of analogous structure to that of the Vertebrates, but characterised by the existence of processes of the cartilage cells which ramify in the matrix and anastomose with one another (Fig. 265). This cartilage is specially well de- veloped in the head. In Nautilus there is a capito-pedal cartilage, shaped like a letter H (Fig. 264, A), which only supports the ventral part of, the nerve-centres, two of its branches extending into the base of the funnel. In the Dibranchia the cephalic cartilage completely encloses the central nervous system and the otocysts and is traversed by the oesophagus (Fig. 268, ¢.c). In some cases the cephalic car- tilage is produced into anterior expansions ; such are the pre-orbital cartilages surrounding the eyes of Sepia (Fig. 264, C). Various muscles, notably the retractor muscles of the head, take their origin from this “cranial” cartilage. There are also cartilaginous skeletal elements in other parts of the body of various Cephalopoda. In 298 THE: CEPRALOPEDA Loligo, Sepia, ete., there are elongated cartilaginous lamellae at the bases of the fins. There is a nuchal cartilage at the base of the neck of all the Dibranchia in which the mantle is not fused to the head; consequently this cartilage is absent in Sepiola and the Octopoda (Fig. 264, D). It serves for the insertion of the lateral muscles of the funnel. Cartilaginous pieces also occur at the internal extremities of the retractor muscles of the head and funnel, and even in the two branchial laminae (Sepia). In the Decapoda there is sometimes a T-shaped basi-brachial cartilage at the bases of the arms on the anterior (dorsal) side of the head (Sepia, Fig. 264, C); it is united to the cranial cartilage and serves for the insertion of the brachial muscles. Finally, the ‘resisting apparatus ” Fig. 264. Cartilaginous skeleton of Cephalopoda. A, capito-pedal cartilage of Nautilus, ventral aspect. a, ridge which supports the pedal portion of the nerve-centre. , right-side view of the same ; the large anterior processes are sunk in the muscular substance of the funnel. C, cephalic cartilages of Sepia officinalis. D, nuchal cartilage of Sepia officinalis. (From Lankester, after Keferstein.) mentioned above is formed by sub-epithelial cartilaginous projections and depressions. It has been shown that Lepidoteuthis, a form not yet sufficiently well known, but apparently a member of the Oigopsida, is ex- ceptional in that the superficial portion of the integument gives rise to a layer of hard, projecting, regularly disposed, imbricated scales, lying above the chromatophores. In Octopus arborescens there are ramified and contractile tegumentary papillae. In several Dibranchia the integument contains certain so-called “aquiferous ” cavities, which open to the exterior by special pores, but have no communication with the circulatory system. In addition to the pockets of the tentacular arms of Decapoda, there are cephalic pores on the back of the head and at the base of the funnel in Ocythoé, and buccal pouches on the ventral side of the THE CEPHALOPODA 299 inner base of the crown of arms: one such buccal pouch occurs in Loligo and two in Sepia, and they may play an accessory part in fecundation. In some exotic species of Sepia there are pouches in the mantle. II. ANATOMY. 1. Lhe Alimentary Canal.—The digestive tube of Cephalopoda comprises a buccal mass with two mandibles and a radula, a long oesophagus, a muscular stomach with a pyloric caecum, and a short intestine which turns forward and opens in the middle line below the funnel (Fig. 252, a). The buccal aperture, situated in the middle of the pedal appendages et 260, oa is surrounded by a circular lip garnished with papillae. °F urther- more, in the decapodous Dibranchia there is a buccal membrane which may be very extensive Fic. 266. 7 YBA ee Eze Mandibles of Nautilus, Minute structure of the cartilage of Loligo. in situ, dorsal aspect. a, simple, and b, dividing cells; ¢, canaliculi; d, im, lower or ventral an empty cartilage capsule, with its pores; e, mandible ; w.m, upper or caualiculi in section. (From Lankester, after dorsal mandible. (After Furbringer.) Owen.) and be divided into lobes alternating with the arms,'and the lobes may even be furnished with small suckers, as may be seen in some species of Loligo. The buccal cavity or pharynx has very thick muscular walls. Internally it is provided with two powerful mandibles, one ventral and the other dorsal (Fig. 266); the tip of the ventral mandible overhangs that of the dorsal, forming a beak like that of a parrot (Fig. 268, vm, dm). These mandibles have recurved insertion-plates, to which the large muscles forming the greater part of the mass of the buccal bulb are attached. In Nautilus the trenchant borders of the mandibles are covered by a calcareous deposit (Fig. 266), and the fossils known by the name of /t/yncholiths are nothing else than the beaks of Tetrabranchia ; for instance, Rhyncholithes hirundo is the beak of Temnocheilus bidorsatus, of the Trias. 300 THE CEPHALOPODA As in the Amphineura, the Gastropoda, and the Scaphopoda, the floor of the buccal cavity is occupied by the anterior part of the radula, which issues from a pharyngeal caecum. Each transverse series of this radula is formed by a median tooth, with three symmetrically disposed teeth on either side; the only exceptions to this rule being—Nautilus, which has four teeth on either side (Fig. 267, A); Gonatus, which has only two teeth on either side ; the Cirrhoteuthidae, which have no radula and have therefore been named Leioglossa. In front of the radular prominence is the so-called “tongue,” a fleshy projection (Fig. 268, to) covered by a Fic. 267. Radula of Cephalopoda. A, asingle row of lingual teeth of Nautilus pompilius ; B, two rows of lingual teeth of Sepia officinalis; C, lingual teeth of Eledone cirrhosa. (From Lankester, after Keferstein, Troschel, and Loven.) somewhat thick papillated cuticle: it corresponds to the sub-radular organ of other Molluscs. The salivary glands, of which two pairs are present in many Cephalopoda, pour their secretion into the buccal cavity. In Nautilus there are no posterior salivary glands, but on each side of the buccal cavity there is the orifice of a gland situated in the buecal wall and corresponding to the anterior salivary glands of the majority of the Dibranchia. In the latter order all the Decapoda have posterior salivary glands, situated fairly far forward opposite the cephalic cartilage (Fig. 268, sg): they are compact, acinous, almond-shaped structures composed of convoluted and bifurcated tubes; their ducts unite immediately they leave the glands to form a single median duct, which runs alongside of the oesophagus and opens, like the duct of one of the pairs of glands in the Aplacophora, at the summit of the sub-radular organ. The anterior THE CEPHALOPODA 301 pair of salivary glands is relatively slightly developed, and is conspicuous only in the Oigopsida (Spirula, Ommatostrephidae, Fig. 282, II, Onychoteuthis, Veranya, Gonatus, ete.). In the Myopsida, however, there is an unpaired intra-bulbar glandular mass, lying behind the radula at the entrance of the oesophagus, and this corresponds to the embryonic condition of the anterior salivary glands of the Oigopsida and Octopoda. The last-named have also two pairs of well-developed salivary glands. The anterior pair consists of two flattened acinous glands attached to the posterior surface of the buccal bulb, their short ducts opening on either side into the postero-lateral part of the pharynx. The topographically posterior or abdominal glands are absent in Cirrhoteuthis, but in other Octopoda they are present, and are relatively larger than the similar pair in the Decapoda, but have the same structure and relations, save for the fact that they are situated farther back near the oesophageal proventriculus. The secretion of the posterior salivary glands of the Octopoda contains a proteolytic ferment and is poisonous ; the secretion of the corresponding glands of Sepia contains, in addition, a diastatic ferment. In addition to the salivary glands proper, all the Dibranchia possess a sub-lingual gland in front of the sub-radular organ. It is of small size and is formed by the infolding of the epithelium of this region. The oesophagus is long in all the Cephalopoda, and it may be enlarged to form a crop or proventriculus: this enlargement is gradual in Nautilus (Fig. 270, oe, cr), abrupt in the Octopoda, with the exception of Cirrhoteuthis, but in the Decapoda the oesophagus is of the same diameter throughout (Fig. 268, oc). The true stomach is a more or less globular or elongated pouch, with fairly thick muscular walls, and is situated at the summit of the visceral mass (Fig. 271, gizz): its two orifices, the cardiac and the pyloric, are anterior. At the initial part of the intestine, close to the stomach, is a thin-walled caecal diverticulum of various shape. It is spherical in Nautilus, Rossia, and Leachia, elongated and much larger than the stomach in Loligo, but it is more frequently coiled in a spiral, like the spiral caecum of sundry rhipidoglossate and other Gastro- poda; such is the case, for example, in Spirula (Fig. 268, p.s), Ommatostrephes (Fig. 269, e), Sepia, and the Octopoda. The hepatic ducts open into the stomachal caecum. The liver is formed by two symmetrical glands, which are separate from one another during development (Sepia), but are generally partially fused together in the adult. This organ exhibits its minimum state of concentration in Nautilus, consisting of four lobes, each with its proper duct. In the Dibranchia the liver is more compact and consists of two lateral lobes, which are only united to a small extent near the middle of their length in 302 THE CEPHALOPODA Rossia and Sepia, but are much more intimately united in Sepiola, and are almost entirely fused together in Spzrula (in which genus OTe ‘ \\ - 1 Li at Fic. 268. Spirula, a nearly median sagittal section, seen from the left side. a, anus; ar, arms; @.f, aboral fossa; b.d, bile-duct ; ¢.c, cephalic cartilage; c.g, cerebral ganglion; d.m, dorsal man- dible ; fc, funnel collar ; fi, fin; fu, funnel ; 7.b, ink-bag ; i, lip; liv, liver; ma, mantle; ma’, shell secreting part of the mantle; oe, oesophagus; 0.g, optic ganglion; ot, otocyst; pa.c, pallial cavity ; p.g, pedal (brachial) ganglion; pn, ‘“‘pancreas”; p.s, pyloric sac; 7a, radula ; s.g, salivary gland; sh, shell; si, shell siphuncle; sp, last septum of the shell; st, stomach ; t, tentacular arm ; t.d, pallial terminal disc; to, tongue; v.m, ventral mandible; v.n, visceral nerve; w.b, white body. (After Huxley and Pelseneer.) the liver is partly contained in the last chamber of the shell, Fig. 268, liv), in Onychoteuthis, Ommatostrephes, Loligo, and the Octopoda, with the exception of Argonauta. In these last cases the liver THE CEPHALOPODA 303 appears to be an undivided ovoid or globular mass, but it is traversed by the oesophagus, and its double origin is further demon- strated by the hepatic ducts, which are two in number, in all the Dibranchia. In the Decapoda the hepatic ducts are long (Fig. 268, b.d) and traverse the kidneys ; in the Octopoda they are short. In the former sub-order the ducts are covered by the so-called “pancreatic” glandular follicles, whose structure is a little different from that of the liver (Fig. 268, pn). In the Octopoda these follicles are situated only on the initial part of the hepatie ducts and are nearly buried in the mass of the true liver. Digestion is wholly effected in the muscular stomach by the action of the trypsin secreted by the liver and by the diastatic ferment secreted both by the liver and the ‘pancreatic ” follicles. The intestine is relatively short and of uniform diameter. In Nautilus and the Octo- poda it is slightly sinuous, but in the Decapoda it is straight. The anus is situated in the middle line towards the anterior part of the pallial cavity (Fig. 272, a), and is often fur- nished with lateral valves. With the exception of Nautilus, Cirrhoteuthis, Octopus arcticus, and O. piscatorum, all the Cephalopoda, including the fossil Belemnites, have an ink-sac, consisting of a highly-developed rectal caecum developed early in embryonic life from the dorsal wall of the intestine and opening into the extreme terminal part of the rectum. This sac is made epee up of a deeper part, or gland proper, the cavity —iimentary canal of of which is septate, and a reservoir, into which Ommutostrephes sagittatus ; the buccal inass is omitted. the glandular part opens by a very small 4, ink-bag; 5, its opening ¥e , ie : . ll : ll d ] 1 into the rectum; ¢, com- orince : t e€ reservoir specia iV we eve Opec mencement of the caecum ; in the Decapoda. This ink-sac occupies a some- % SPi@l portion of the 2 ne ‘ caecum; oe, oesophagus ; what superficial position to the side of the %, the stomach opened : f : vane: -, - longitudinally; 2, probe visceral mass. In some species of Sepiola it is passed through the pylo- oI ne aie ; -_., lus. (From lLankester, trilobed, two lateral accessory organs being after Home.) : joined to it. It extends to the posterior ex- tremity of the body in Sepia (Figs. 271, i.s; 272, ¢), and is buried in the superficial part of the liver in all the Octopoda except Argonawuta. The Cephalopoda are able, at will, to expel the secretion contained in the reservoir of this anal gland through the funnel, and thus conceal themselves by producing a dense cloud in the water. An oxydising diastase, called tyrosinase, is concerned in the production of the secretion, the latter being known as melanin. ? f=) 2. Circulatory Apparatus.—The Cephalopoda, or at any rate the 304 THE CEPHALOPODA Dibranchia, have a more complete and perfect circulatory system than other Mollusca, the blood being nearly entirely contained in true vessels. The heart is situated somewhat superficially near the middle of the posterior or physiologically ventral surface (Fig. 252, h). It lies in a pericardial cavity (Fig. 252, coe), except in the Octopoda, in which sub-order this cavity is much reduced (Fig. 278, ca). The essential part of the heart is the median ventricle (Fig. 277, ven), the lateral and symmetrical auricles being nothing more than simple Fic. 270. Diagram representing an approximately median sagittal section of a female Nautilus pompilius. The parts which are quite black are the cut muscular surfaces of the foot and buccal mass. «, the shell; an,anus ; a.b.v, afferent branchial vessel ; b, the nuchal plate ; c, the integu- ment covering the visceral hump; cr, crop; d, the mantle flap or skirt in the dorsal region, where it rests against the coil of the shell; e, the inferior margin of the mantle-skirt resting on the lip of the shell represented by the dotted line; e.b.v, efferent branchial vessel; f, the pallial chamber with two of the four gills ; g, the vertically cut median portion of the funnel ; gizz, gizzard ; h, the capito-pedal cartilage ; i, the valve of the funnel ; int, intestine; 7, the siphuncular pedicle (cut short); m, the hood or dorsal enlargement of the outer lobe of the foot ; n, tentacles of the outer lobe; x.c, nerve-collar ; nept, aperture of the kidney ; nz, nidamental gland ; oe, oesophagus ; p, tentacles of the inner inferior lobe; g, buccal membrane ; 7, upper jaw ; r.e, renal glandular masses on the walls of the afferent branchial veins ; s, lower jaw; t, radula; vt, ventricle of the heart ; x, the viscero-pericardial sac. (After Lankester.) contractile expansions of the efferent branchial vessels (Fig. 277, aw). In Nautilus there are four such auricles, returning blood from the four branchiae, but in the Dibranchia there are only two. In general the ventricle is slightly asymmetrical, except in Nautilus (Fig. 274, vent), in which it is transversely elongated, and in Loligo, in which it is elongated antero-posteriorly. The entrances of the auricles into the ventricle and origins of the aortae from it are guarded by valves. The aortic vessels consist of —(1) a cephalic or principal aorta, which runs forward (Fig. 277, a.a) and supplies the whole of the anterior part of the body with blood ; (2) a posterior or abdominal aorta, which is smaller, especially in the Octopoda, and carries blood to the THE CEPHALOPODA 305 posterior part of the mantle, including the siphonal prolongation of Nautilus and Spirula and the fins of the various Dibranchia ; (3) a small genital artery, which may originate from the abdominal aorta (Fig. 277, g.a), or separately from the ventricle: it may even be triple, as in Nautilus, where there-is one artery for the gonad, one for its duct, and one for the homologue of the duct, the pyriform appendage. In Nautilus the circulation is partly lacunar, except in the integuments, but in the Dibranchia the vascular apparatus is remarkably perfect, and sinuses are, as a rule, absent, the blood passing from the arteries into the veins through the intermediary of capillary vessels provided with an endothelium. Nevertheless, 7 ck : aby TMG Vise per: aperc. Fie. 271. Diagram representing an approximately median sagittal section of Sepia officinalis; this drawing is intended to be compared with the foregoing one. a, internal shell; a.b.v, afferent branchial vessel ; an, anus ; app, appendage of the branchial heart ; b, nuchal cartilage ; br.b, branchial heart ; c, the integument covering the visceral hump ; er, crop ; ct, the left ctenidium ; d, the reflected portion of the mantle-skirt forming the sac which encloses the shell; e, the inferior margin of the mantle-skirt ; e.b.v, efferent branchial vessel; f, the pallial chamber ; g, the vertically cut median portion of the funnel ; gizz, the gizzard; 7, the valve of the funnel ; i.s, ink-bag ; m, the two upper lobes (arms) of the foot; n, the long prehensile arms; 7.c, the nerve-collar ; ”.7.a, aperture of the left kidney; 0, the fifth or lowermost lobe (arm) of the foot ; p, the third arm; g, buccal membrane ; re, renal glandular mass ; s, the lower jaw; ¢, the radula; v, the upper jaw ; vent, ventricle of the heart ; visc.per.apert, viscero-pericardial aperture ; x, the viscero-pericardial sac. (After Lankester.) in the Octopoda there is a large venous sinus on the course of the blood returning to the gills: this sinus surrounds the oesophagus and salivary glands, the hepatic ducts, the anterior aorta, etc., and communicates by a large venous trunk with the great vena cava which carries to the gills the greater part of the blood coming from the body. In Nautilus the whole visceral cavity is a vast blood- sinus communicating with the vena cava by a number of perforations in the walls of the latter vessel, in the same manner as, in Aplysia, the abdominal sinus communicates with the afferent branchial vein. The vena cava of Cephalopods consists of a principal trunk directed antero-posteriorly : this trunk in Nautilus (Fig. 274, v.c) is divided into four, and in the Dibranchia into two afferent branchial veins, each of which is joined by a pallial and an abdominal vein (Fig. 20 306 THE CEPHALOPODA 277, v.c, p.v, abv). Each afferent branchial vessel and the terminal portion of each abdominal vein is enclosed in the cavity of a kidney and is covered externally by an excretory glandular coat (Figs. 273, ar; 277, s.b) which forms the “spongy body” or essential part of kidney (see below). Except in Nautilus, each afferent vessel is Hie. 272. Ventral view of a male Sepia, obtained by cutting longitudinally the firm mantle-skirt, and drawing the divided halves apart. a, anus; Br, the single pair of ctenidia; c, cartilaginous socket in the funnel, to receive ¢’, the cartilaginous knob of the mantle-skirt,—the two con- stituting the ‘“‘pallial hinge apparatus”; C, the head; g, the azygos genital papilla and aperture ; i, the valve of the funnel; J, the funnel, which has been cut open; m, retractor muscle of the head and funnel; P, the fins; 7, renal papillae; &, the glandular tissue of the left kidney, which has been cut open ; ¢, ink-bag ; v.br, branchial efferent vessel ; v.br’, bulbous: enlargements (auricles) of the branchial vessels. (From Lankester, after Gegenbaur.) expanded at the base of the gill into a contractile glandular swelling known as the “branchial heart,” which is also provided with a gland- ular appendage, the homologue of the pericardial gland of other Mollusca (Fig. 277, b.h, a.p). Both branchial heart and appendage are contained in the coelom (Fig. 273, ¢.v) in the Decapoda, but in the Octopoda only the appendage of the branchial heart is sur- rounded by the pericardial cavity (Fig. 278, ca). In addition to the THE CEPHALOPODA 307 branchial hearts, a large part of the venous system is contractile, and this is notably the case with the vena cava and its two afferent branches. ' The venous blood is blue through the presence of haemocyanin, which becomes colourless on oxidation (oxyhaemocyanin), The pressure of the blood in the arteries of the Cephalopoda is very considerable and exceeds that of some Vertebrates: in Octopus it amounts to eight centimetres of mercury. In the head of the MND NONGOO ee a a= Fia. 273. Diagram of the renal sacs, and the veins which run through them, in Sepia officinalis ; ventral view, the upper walls of these sacs are supposed to have been removed. a.r, glandular renal outgrowths ; ¢.b, branchial heart ; ¢c.v, capsule of the branchial heart ; mp, external aperture of the right renal sac ; r.d.v.c, right descending branch of the vena cava; 7.s.v.c, left descending branch of the vena cava ; v.a.d, right abdominal vein ; v.a.s, left abdominal vein ; v.b.a, vein from the ink-bag ; v.c, vena cava; v.g, genital vein; v.m, mesenteric vein; v.p.d, right pallial vein ; v.p.s, left pallial vein ; w.k, viscero-pericardial sac (dotted outline); x, appendage of the branchial heart; y, y’, the left and right reno-pericardial orifices. (From Lankester, after Vigelius.) Dibranchia there is a lymphatic gland near each eye: this gland is. known as the ‘‘ white body” (Fig. 268, w.d) and is the remains of a degenerate portion of the central nervous system of the embryo. The branchiae or ctenidia are situated in the pallial cavity on either side of the visceral mass. They originate posteriorly in the embryo, between the mantle and the foot (Fig. 257, gi), and after- wards sink in towards the bottom of the pallial cavity where their axes are inserted (Figs. 272, Br; 276), their free ends pointing towards the head. Nautilus, the only living representative of the 308 LHE CEPHALOPODA Tetrabranchia, has two pairs of branchiae (Fig. 276). All other Cephalopods have a single pair of branchiae, and thus constitute the order Dibranchia, much richer in living species than the Tetrabranchia. The branchiae are bipectinate (Fig. 272, br), but in some Dibranchia the two sides of the organ are somewhat unequal in size. 5 11, ¢2, #3, t4, the tirst, second, third, tomous. This peculiarity is found in of ie hectoontzice 9 ate mien the Philonexidae and Argonautidae. In ae He ONSTE pte Geen Ocythoé and Tremoctopus the third right Lankester, after Gegenbaur.) arm is modified (Fig. 287, h), in Argonauta the third left; but in all these genera the modified arm constitutes a veritable hectocotylus, that is to say, a caducous organ. This hectocotylus originates, and apparently also is regenerated, in a capsule or cyst in which it lies coiled up on itself: being shielded from the light, it is Fic. 287. THE CEPHALOPODA 325 devoid of chromatophores. Eventually the membrane of the cyst bursts and remains attached to the dorsal surface of the arm, forming the spermatophore sac. The uncoiled arm is pedunculated, that is to say, is attenuated towards its base, and it bears at its extremity a little pouch (Fig. 287, «) containing a long filament, which is extended prior to the act of fertilisation (Fig. 287, y). The spermatophore sac communicates with a canal in the interior of the arm, and this canal is continued into the terminal filament and opens by an orifice at its free extremity. The hectocotylus when detached is able to live and move about for a considerable time, until finally it penetrates into the pallial cavity of a female and fixes itself in the neighbourhood of the genital aperture. In those Dibranchia in which the hectocotylus is not autotomous the hectocotylised arm (or arms) is inserted into the pallial cavity of the female (Fig. 288, 3) in such wise as to deposit the spermato- phores in the terminal portion of the oviduct in Octopus, or to fix Fig. 288. Copulationiof Octopus. A, the female; B, the male. fw, funnel of the female ; 3, third right hectocotylised arm of the male. (After Racovitza.) them in the neighbourhood of the oviducal orifice in Fossia and Sepiola. In Sepia and Loligo the spermatophores are simply deposited on the ventral lobes of the buccal membrane, and in Nautilus they are deposited on the folded lamellae on the ventral side of the buccal orifice (Fig. 255, m). The eggs are laid shortly after copulation. In Nautilus they are laid singly, each egg being about four centimetres long and surrounded by two thick shells, the outermost of which is partly open (Willey). In the Dibranchia the eggs are aggregated together, but in the Octopoda and in Sepia, Sepiola, and Rossia each egg has a separate envelope, whereas they are united to form longer or shorter gela- tinous strings, which are joined together and fixed by one extremity in Loligo, but are single and floating in the pelagic Oigopsida. In Eledone only about sixty eggs are laid at one time, in Octopus more than a hundred, and some species of Loligo lay more than 40,000 eggs. Some Octopods are incubatory: the female Argonauta, for example, protects the eggs in the shell peculiar to her sex. THE CEPHALOPODA Oo No On Ill. Empryouocy. Our knowledge of the embryology of Cephalopoda is confined to the Dibranchia, the development of Nautilus being unfortunately still unknown. The ovum is remarkable, even in the cases of Nautilus and the ovarian ovum of Spirula (Fig. 285), for the enormous quantity of yolk contained in it. In contrast to all other Mollusca, the segmentation is incomplete: at no period does the ectoderm completely cover in the vitelline mass, so that there is no proper blastopore, or rather the blastopore is enormous and is represented by that part of the vitellus that is not covered by ectoderm (Fig. 290, (2), (3), e). This peculiarity in the development of Dibranchia, however, is only an exaggeration of the phenomena observable in the epibolic ova, pr ovided - with an abundant yolk, of certain Gastropoda (Fig. 10, B), and it has been shown that in the archaic Dibranchia (the Oigopsid Cephalopod of Grenacher, Fig. 119, D, vz) the quantity of yolk is less than bE : in the other members of the order, and that “0 the ectoderm extends much farther over it. As the formative protoplasm is localised at the narrower end of the egg, the segment- ation is restricted to this end (Fig. 289, bi), and results in the formation of a germinal disc or embryonic area. In the course of subsequent development the embryo is like- wise restricted to this end, and never covers the whole surface of the vitelline mass, on Fic, 289. which it appears to be seated (Fig. 291). Egg of Loligo in the first Lhe extent of the embryonic area and of Segmentation stage. i, the the free surface of the yolk are in inverse vitellus. (After Watase.) ratio to one another: the external vitelline mass is smaller in Loligo than in Sepia, smaller still in Argonauta, and reduced to a minimum in the Oigopsida (Fig. 119, D). The embryonic area forms the ectoderm: the so-called peri- vitelline or yolk membrane is formed as a proliferation of cells from a limited part of the periphery of the ectoderm, the region of proliferation marking the anal side. The cells thus formed migrate over the whole surface of the yolk and form a layer of scattered nuclei investing it (Fig. 290, (7), h). At a later period the same anal edge of the periphery of the embryonic area gives rise to a second cellular layer, the endoderm : it is at first crescentic in shape, but subsequently becomes ring-shaped, and eventually forms a continuous circular sheet below the ectoderm (Teichmann). At a still later period the ectoderm gives rise to cells constituting the genital rudiment and other mesodermic elements: these cells WL THE CEPHALOPODA 327 also originate at the anal side of the blastoderm, behind the place where the shell gland is formed externally, and extend in the form of a crescent, right and left, between the ectoderm and endoderm, toward the anterior part of the blastoderm. After the mesoderm has been established in this manner, a thickened specialised portion of the endoderm constitutes the rudiment of the mesenteron and forms a little vesicle lying close upon and widely open to the yolk, and situated in the middle line, below the posterior part of the mantle, between the rudiments of the two branchiae (Fig. 290, (6), 7). This vesicle is the rudiment of the alimentary tract : it ultimately gives rise to the stomach, the two lobes of the liver (which are separate from the first), and the intestine (Fig. 290, 1). The oesophagus and its annexes, viz. the radula, the salivary glands, etc. (Fig. 290, (7), J, s), are formed by a precocious stomodaeal invagination, and the anus is formed later, by an excessively short proctodaeal invagination. Thus the mouth arises relatively near to the nutritive or vegetative pole, as it does in other Mollusca, and the less abundant the yolk, the nearer it is to the vegetative pole, as in the Cephalopod of Grenacher (Fig. 119, D). The mantle arises in the middle of the embryonic area (Fig. 257, pa), and in its centre is the shell gland, but the borders of the latter structure are reflected inwards and approach one another to form the shell sac. In certain highly differentiated Octopoda (Argonauta, Ray Lankester) the shell sac disappears before it is closed up, but in the Decapoda, with the exception of Spirula, it is completely closed, and it grows pari passu with the mantle (Fig. 290, ¢), while the shell develops within it. Posteriorly to the mantle, between it and the epipodium, appear the bud-like rudiments of the branchiae (Fig. 290, (6), m), and the folds that form the branchial lamellae gradually make their appearance and become in their turn folded. As development advances the pallial cavity becomes deeper, and the branchiae are gradually covered by the mantle. Throughout the earlier part of embryonic life the cephalic mass is excessively large (Fig. 290, (8), (9)), but its preponderance insensibly diminishes in subsequent stages. This cephalic mass is formed by the antero-lateral regions of the embryonic area, and it bears the rudiment of an eye at each posterior corner (Fig. 290, (9), d). During these earlier phases of embryonic development the mouth is not in any sense surrounded by the circumoral append- ages. The foot, in fact, is at first formed by the lateral and posterior borders (Fig. 257, 1, 2, 3, 4, 5) of the embryonic area, and these borders are rapidly divided into ten projections in the Decapoda, or eight projections in the Octopoda and the Cephalopod of Grenacher (Fig. 119, D). But in the course of development these lobes, while they grow in length, also advance gradually THE CEPHALOPODA 8 Fic. 290. \ ‘ THE CEPHALOPODA 329 along the sides until the most anterior of them reach the mouth (Fig. 291), and becoming united in front of it, eventually surround it completely. : A paired epipodial outgrowth, the origin of the funnel, is formed early in development: its two posterior lobes become prominent and bend inwards toward one another (Fig. 290, ¢), thus establishing the condition which is permanent in the adult Nautilus (Fig. 276), but finally, in the Dibranchia, they fuse together completely and form a perfect tube. All the nervous centres—the cerebral, optic, visceral, and pedal —are formed separately as proliferations of the ectoderm. The pedal centres give rise, by subdivision, to the ganglia of the arms. The eyes (Fig. 292, A, B) and otocysts originate as invaginations of the ectoderm, which eventually close up. The otocysts arise Fia. 290. Development of Loligo. (1) view of the cleavage of the egg during the first formation of embryonic cells. (2) lateral view of the egg at a little later stage ; a, limit to which the layer of cleavage-cells has spread over the egg; b, portion of the egg as yet uncovered by cleavage- cells ; wp, yolk membrane cells; kp, cleavage-pole where first cells were formed. (3) later stage, the limit a now extended so as to leave but little of the egg-surface (6) unenclosed ; d, eyes; e, mouth; u, mantle sac. (4) later stage, anterior surface, the embryo is becoming nipped off from the yolk sac (g). (5) view of an embryo similar to (3) from the cleavage-pole or centro-dorsal area. (6) later stage, posterior surface. (7) section in a median sagittal plane of an embryo of the same age as (4). (8) viewof the anterior face of an olderembryo. (9) view of the posterior face of an embryo of the same age as (8). Letters in (3) to (9) :—a, lateral fins ; b, mantle-skirt ; c, supra-ocular invagination to form the ‘‘ white body”; d, the eye; e, the mouth ; ep, outer layer of the embryo; f1, f2, f*, f4, f°, the five paired processes (arms) of the foot ; g, rhythmically contractile area of the yolk sac; h, dotted line showing internal area occupied by yolk; k, first rudiment of the funnel; /, sac of the radula; m, stomach ; mes, mesoderm ; n, rudiments of the gills; 0, the otocysts; p, optic ganglion; q, distal portion of the ridges which form the funnel; 7, vesicle-like rudiment of the intestine formed independ- ently of the parts connected with the mouth; s, rudiment of the salivary gland ; ¢, the closed shell sac ; uv, the open shell sac, formed by an uprising ring-like growth of the central dorsal area; w, the mantle-skirt commencing to be raised up around the area of the shell sac. (After Lankester.) laterally on the sides of the foot outside the epipodium (Fig. 290, (6), 0); they close up at a relatively late period, often retaining a rudiment of the original external canal, and then approach one another till they come in contact in the median line. When the ocular cavity is closed, the external part of the crystalline lens is formed separately from the internal segment. At the sides of the optic ganglia a pair of cellular masses, formed by ectodermic invaginations, becomes the white bodies of the adult (Fig. 290, ¢) ; they are the relics of a pair of embryonic ganglia (lateral cerebral lobes). The coelomic cavity is hollowed out in the mesoderm as two symmetrical spaces, right and left of the intestine ; it gives rise to the kidneys and the pericardium. The two kidneys are formed independently of one another in their definitive positions. The heart is also formed from the pericardial wall as two paired ‘rudiments. Finally, a portion of the coelomic wall gives rise to the gonad. \ 330 THE CEPHALOPODA The vitelline mass diminishes insensibly during the growth of the embryo, and is for the most part absorbed at the time of hatching. The yolk sac is independent of the stomach, and is only in contact with it over a small area in the middle line. save i202 Fic. 291. Embryo of Sepia officinalis, on its vitellus, left-side view. an, anus; br, gill; 7.Jo./, invagina- tion of the lateral cerebral lobe; na, fin; pa, mantle; vit, vitellus. I, II, III, IV, V, the five left arms. IV. BIoNomMIcS AND DISTRIBUTION. All the Cephalopoda are marine, and very active animals. They swim rapidly by expelling the water from the pallial cavity through the funnel, sometimes with so much violence that they can spring for some distance out of the water (Ommatostrephes). The fins of the Dibranchia are organs of balance rather than of locomotion. All the Cephalopods are in the highest degree carnivorous: many Fig. 292. Diagrams of sections showing the early stage of development of the eye of Loligo, when it is, like the permanent eye of Nautilus, an open sac. A, first appearance of the eye as a ring- like upgrowth; B, ingrowth of the ring-like wall so as to form a sac, the primitive optic vesicle. (After Lankester.) of them destroy a large number of edible fish and Crustacea, but, on the other hand, many of the pelagic forms fall a prey to the toothed whales. Some Cephalopods attain to a very considerable size: the body of some species of Architeuthis, without the head, may measure two and a half metres in length, and when the head and extended 5 rns ia Naa 1 THE CEPHALOPODA 331 tentacular arms are taken into account, they may be from twelve to eighteen metres long. Hence these Mollusca have given rise to various fabulous tales, and they have been known by man from the remotest periods of antiquity, as is evidenced by their representa- tions on some of the most ancient monuments from Mycenae, Egypt, and Greece. In the present day some four hundred species of Cephalopoda are distributed throughout all the seas of the world. Some species, especially those with a short and rounded pallial sac, such as the Octopodidae and Sepiola, are strictly littoral—indeed Sepiola and also Rossia are fossorial in habit. Other species are inhabitants of the open sea, and among these various forms of Oigopsida dwell in great depths: Spirula is found down to 1000 fathoms; Cranchia and Bathyteuthis down to 1700 fathoms; Histiopsis at a depth of nearly 2000 fathoms; Calliteuthis at 2200; and Cheiroteuthis down to 2600 fathoms. Many of these deep-sea Oigopsida are luminous. The history of the Cephalopoda extends back to the remotest geological times. Orthoceras and other forms allied to Nautilus, but as yet uncoiled, are abundant in the most primitive Palaeozoic formations. The subdivision of the Ammonitoidea, related to the Tetrabranchia, is distributed from the Devonian to the end of the Secondary period. The Dibranchia do not appear till the end of the Secondary epoch, during which they were characteristically represented by the Belemnitidae, a group which, like the Ammoni- toidea, became nearly completely extinct at the end of this period. V. REVIEW OF THE ORDERS, SUB-ORDERS, AND FAMILIES OF THE CEPHALOPODA. The class Cephalopoda comprises two orders, the Tetrabranchia and the Dibranchia. Palaeontology, as well as morphology, shows that the Tetrabranchia (Nautilus, etc.), that is to say, the Cephalopods with multiple branchiae, auricles, and kidneys, and with an external chambered shell, are the most archaic. The Dibranchia are more specialised, inasmuch as they have lost the anterior branchiae, auricles, and kidneys, and their shell has become rudimentary. The earliest Dibranchia were descended from rectilinear forms with a multilocular external shell devoid of a rostrum, and they gave rise in turn to Spirula, the Belemnitidae, and the allied Oigopsida. From the last named were derived, as the result of a yet more profound specialisation, on the one hand the Myopsida, on the other hand the Octopoda, by the loss of the tentacular arms (already so much reduced as to be almost lost in some Oigopsida), and by the more and more complete atrophy of the shell. 332 THE CEPHALOPODA ORDER 1. Tetrabranchia, Owen. In these Cephalopoda the whole of the visceral mass is protected by an external, multilocular, siphunculated shell, which may or may not be coiled; only the last compartment of the shell is occupied by the body of the animal. The head bears numerous appendages in the form of pedal tentacles, which are retractile within sheaths (Fig. 293, te). The funnel is formed of two separate moieties. There are four branchiae, and four kidneys without reno-pericardial orifices. The pericardium opens directly to the exterior. The cephalic cartilage is wholly situated on the ventral side of the oesophagus (Fig. 270, h) and only supports the ventral part of the nervous centres. The eyes are open and have no crystalline lens (Fig. 6, A). The Tetrabranchia comprise two sub-orders, the Nautiloidea and the Ammonitoidea. Sus-ORDER 1. NAUTILOIDEA. This group is distinguished from the Ammonitoidea by the initial chamber, which is in the form of an obtuse cone bearing on its summit a “ cicatrix,” elongated dorso-ventrally and situated opposite the extremity of the blind end of the siphuncle: it is probable that the siphuncle passed through this cicatrix on emerging from a true initial chamber or proto- conch, which may have been uncalcified or caducous. The sub-order comprises nearly 2500 fossil species, but only a few living species of the genus Nautilus, In certain fossil forms the aperture of the shell may be contracted to such an extent that the animal was probably able to protrude only the appendages of the circumoral crown, but not its head. These contracted apertures are said to be “composite” when they have lobes of different form, as in Gomphoceras, Phragmoceras, etc. In these apertures the ventral part, corresponding to the funnel, is separated from the rest by a constriction, and constitutes the “ hyponomous sinus” ; the remainder of the aperture is more or less lobate and corresponds to the external parts of the cireumoral crown, The shell may attain to a length of two metres (Hndoceras). Famity 1. ORTHOCERATIDAE. Shell straight or slightly curved, with a simple aperture, a large terminal chamber, and a cylindrical siphuncle. Genera—Orthoceras, Breyn ; from the Silurian to the Trias. Baltoceras, Holm; Silurian. Faminy 2. AcTINoceRATIDAE. Shell straight or slightly curved, with a wide siphuncle contracted at the level of the septa by rings or swellings. Genera—Actinoceras, Bronn; from the Silurian to the Carboniferous. D¢scosorus, Hall; Silurian. Huwronia, Stokes ; Silurian. Lozoceras, MacCoy ; from the Silurian to the Carbon- iferous. Famity 3. EnpoceRATIDAE. Shell straight, with a wide marginal siphuncle, the siphuncular necks produced into tubes which fit into one another. Genera—Endoceras, Hall ; shell straight ; from the Silurian. Faminy 4. GoMPHOCERATIDAE. Shell globular, straight or arcuate, the aperture contracted to the shape of a T. Genera—Gompho- ceras, Sowerby ; Silurian. Phragmoceras, Sowerby ; Silurian, Famity 5. THE CEPHALOPODA 333 ASCOCERATIDAE. Shell straight, ampulliform; the summit truncated ; the terminal chamber occupies nearly the whole length of the shell on the ventral side. Genera—Ascoceras, Barrande ; Silurian. — Glossoceras, Barrande; Silurian. Famrty 6. PorertoceraTipAr. Shell straight or curved, fusiform, contracted at the two extremities ; the aperture simple ; the siphuncle contracted at the levels of the septa. Genera— Poterioceras, MacCoy ; from the Silurian to the Carboniferous. Streptoceras, Billings ; Silurian. Faminy 7. Cyrtoceratipar. Shell slightly curved; the aperture simple ; the siphuncle wide and the septa approximated. Genus —Cyrtoceras, Goldfuss ; Devonian. Famity 8. Lirvrripar. Shell eoiled in one plane with the ter- minal part uncoiled ; the aperture contracted. Genera—JLitwites, Bar- rande ; Silurian. Ophidioceras, Barrande ; Silurian (Fig. 261, A). Famity 9. TROCHOCERATIDAE. Shell helicoidally coiled; dextral or sinistral ; the last whorl gener- ally uncoiled. Genera — Trocho- ceras, Barrande; Devonian. Adelphoceras, Barrande ; Devonian. Famity 10. Navutimipar. Shell coiled in one plane ; the aperture wide and simple; the siphuncle central. Genera—Nautilus, Lin- naeus (Figs. 270 and 293); four living species are known from the Indian and Pacific Oceans: they are gregarious, nocturnal animals, living at some depth. Trocholites, Conrad; Silurian. (Gtyroceras, de Koninck ; from the Silurian to f the Carboniferous, Hercocoras, 4, Nautilus mecronplalus creeping on a horizon Barrande ; Silurian. Ptenoceras, mic touteelss e eye a fe hod ae n, aan ; a . . pa, nuchal part 0 ne mantle; p.o.t, posterlor Hyatt ; Devonian (Fig. 261, B). ophthalmic tentacle; sh, shell. (After Willey.) Discites, MacCoy ; Carboniferous. Faminy 11. Bacrritrpar. Shell straight, conical; the siphuncle narrow and marginal, and the siphuncular necks long and infundibuliform ; septa united to the shell by an undulating line. Genus—Bactrites, Sandberger ; Silurian and Devonian. Fie. 293. Sus-OrpDER 2. AMMONITOIDEA. The Ammonitoidea are distinguished from the Nautiloidea by their initial chamber, which is spheroidal like that of the Belemnitidae and Spirulidae ; by their siphuncle, which is narrow and simple, whereas that of the Nautiloidea is wide, but often reduced in diameter by internal deposits ; by their septa, which are generally convex on the side nearer 334 LHE CEPHALOPODA the aperture, instead of being concave as in the Nautiloidea; finally, by the sutures (intersections of the septa with the shell), which form a more or less complex sinuous line, instead of being simple as in the Nautiloidea. Although the Ammonitoidea have a globular initial chamber which is absent in Nautiloidea (though it may possibly be present but caducous or not calcified in the latter group), their shell has the same structure as that of Nautilus, and was indisputably external. The chamber containing the body of the animal is very deep, more so than in Nautilus. Like the Nautiloidea, the Ammonitoidea did not possess an ink-sac. A consider- able number of Ammonitoidea resemble such Nautiloid forms as Gomphoceras, Phragmoceras, etc., in having a contracted aperture, indicat- ing an analogous structure of the cephalopedal organs: such contracted apertures may be seen in Arcestes, Lobites, Stolicekaia, and especially in Stephanoceras, but this contraction is carried to an extreme in Morphoceras pseudoanceps (Fig. 294). In this genus the aperture is almost completely closed by the lobes which form its borders and circumscribe five small orifices ; there is a central oblong orifice which probably corresponded to the mouth ; two circular lateral orifices, one on either side of the central, may perhaps have served as windows for the eyes; and the two remaining orifices, which are partly limited by the preceding whorl, probably served for the passage of the pedal appendages, and do not correspond to any part of the contracted apertures of Nautiloidea. A calcified structure, consisting of a single piece (Anaptychus) or of two symmetrical moieties (Aptychus) is sometimes found in the terminal chamber of Ammonitoidea : its constant position shows that it could not have been an operculum, and it is supposed to have been a calcified cartilage situated at the base of the funnel. The Ammonitoidea are, geologically speaking, younger than the rest of the Tetrabranchia. They appeared in the Devonian and became com- pletely extinct at the end of the Secondary period. They were littoral in habit, and lived in troops like Nautilus. Some of the coiled forms are as much as seventy centimetres in diameter. More than 5000 species have been described, and it has been found necessary to divide the originally single genus Ammonites first into genera, then into families, and even into tribes. TRIBE 1. RETROSIPHONATA. The siphuncular necks project behind the septa as in the Nautiloidea, These are the most ancient Ammonitoidea, belonging exclusively to the superior Palaeozoic strata, from the Devonian upwards. The sutures of the septa form simple undulations, those which point backwards being known as “lobes,” and those which point forward towards the aperture as “saddles.” Famity 1. Gontatiripar. Shell nautiloid with simple sutures and a ventral siphuncle. Genera—Goniatites, de Haan ; Devonian and Carbon- iferous. Anwrcestes, Mojsisovics; Devonian. Faminty 2. CLYMENIIDAE. Shell nautiloid; sutures simple; the siphuncle dorsal, that is to say, internal. Genus—Clymenia, Minster ; from the Upper Devonian. THE CEPHALOPODA 1S) Go wm TRIBE 2. PROSIPHONATA. The siphuncular necks project in front of the septa. The septal sutures present deeply indented lobes and saddles. Faminty 1. Arcestrpar. Globular and smooth or nearly smooth forms, with a reduced umbilicus; the terminal chamber very deep, occupying nearly a whole whorl of the spire; an aptychus present. Genera — Popanoceras, Gemmellaro; Permian. Cyclolobus, Waagen ; Permian. Arcestes, Mojsisovics; Trias. Lobites, Mojsisovics; Trias. Faminy 2. Tropitrpar. The shells globular, but differing from those of the Arcestidae in having radiating and tubereulated costae. Genera— Thalassoceras, Gemmellaro; Permian. Tropites, Mojsisovics; Trias. Sibirites, Mojsisovics ; Trias.. Faminy 3. CeRaAtiTiIpAr. Shells coiled, with a large umbilicus; the terminal chamber short; sutures with simple saddles. Genera—Trachyceras, Laube; Upper Trias. Ceratites, de Haan; Trias. Dvinarites, Mojsisovics; Trias. Some genera with helicoidal shells are related to these coiled forms, viz. Cochloceras, Hauer; Trias: also some straight forms, e.g. Rhabdoceras, Hauer; Trias: they have been placed in distinct families by some authors. Famrty 4. PINACOCERATIDAE. Shell compressed, smooth ; the terminal chamber short; the suture very complicated, convex. Genus — Pinacoceras, Mojsisovics; Trias. Faminy 5. PHyLLOCERATIDAE. Shells coiled, the whorls overlapping one another ; the suture formed of numerous lobes and saddles. Genera — Phylloceras, Suess; Jurassic. Rhacophyllites, Zittel. Famity 6. Lyroceratmar. Shell discoid, the whorls loosely united or uncoiled ; the sutures deeply indented but with only three saddles and lobes. Genera—-Lytoceras, Suess; Jurassic and Cretaceous. Macroscaphites, Meek; uncoiled and recurved; Cretaceous. Hamites, Parkinson ; flexed three times; Cretaceous. Ptychoceras, d’Orbigny ; Cretaceous. T'wrrilites, Lamarck ; coiled in a sinistral helicoidal spire ; Cretaceous. aculites, Lamarck; the adult straight and elliptic in section; Cretaceous. Faminy 7. Ammonitipar. Shell coiled, with narrow whorls which do not embrace one another ; aperture simple; a horny anapty- chus present. Genera—Ammonites, Lamarck ; Jurassic. Arvetites, Waagen ; Jurassic. Aego- ceras, Waagen, Lias. Faminy 8. HaRrpocera- TIDAE, Shell discoid and flattened, with a carinated border ; the aperture provided with lateral projections; a calcareous aptychus, formed of two pieces. Genera—Huarpoceras, Fic. 294. Waagen ; Jurassic. Oppelia, Waagen ; Jurassic. Morphoceras pseudoanceps, right- Lissoceras, Bayle ; Jurassic and Cretaceous, side view. 4.0, orifice for arms ; e.0, eye-orifice ; s.b.0, infundibulo- Faminy 9. AMALTHEIDAE. Shell flattened, buccal orifice.’ (After Douvillé.) with a prominent carina continued anteriorly into a rostrum. Genera—Amaltheus, Montfort; Lias. Cardioceras, Neumayr ; Jurassic. Schloenbachia, Neumayr ; Cretaceous. Faminy 10. STEPHANOCERATIDAE, Shell not carinated, but with radiating costae, which are often bifurcated ; aperture often provided with lateral pro- 336 THE CEPHALOPODA jections which contract it; aptychus formed of two pieces. Genera— Stephanoceras, Waagen ; Jurassic. Morphoceras, Douvillé ; Jurassic (Fig. 294). Perisphinctes, Waagen ; Jurassic. Peltoceras, Waagen ; Jurassic. Hoplites, Neumayr; Cretaceous. Acanthoceras, Neumayr ; Cretaceous. Cosmoceras, Waagen ; Jurassic. Various more or less com- pletely uncoiled forms are related to this family, viz. Scaphites, Parkinson ; Cretaceous. Crioceras, @Orbigny ; Cretaceous. ORDER 2. Dibranchia, Owen. In these Cephalopoda the external surface of the visceral mass is naked and is only protected by a more or less rudimentary shell, which is situated on the aboral surface and covered by the integuments of this region. The female Argonauta is the only member of the group that has a wholly external shell, but this is not adherent and is secreted by the dorsal arms. ‘The head of the Dibranchia bears eight acetabuliferous arms, and there is frequently a fifth pair of more or less retractile arms, situated between the third and fourth pair (Fig. 295, ée). The funnel is always a com- pletely closed tube (Figs. 287, 301, etc.). There are two branchiae and two kidneys, each of the latter having a pericardial orifice (Fig. 273, y). The cephalic cartilage is traversed by the oesophagus and encloses all the principal nervous centres. The ocular cavities are closed and the eyes have a crystalline lens (Fig. 283). Chromato- phores are present in the integument and an ink-sac is generally present. The Dibranchia include two sub-orders, the Decapoda and the Octopoda. Sus-OrpDER 1. Decapopa. In this sub-order, in addition to the eight pairs of normal arms, there is a more or less well developed ‘“‘tentacular” arm situated between the third and fourth normal arms, on each side of the head. These tentacular arms are more or less retractile within special pouches, and as a rule they only bear suckers at their free extremities. The suckers are pedunculated and provided with horny rings. The eight normal arms are shorter than the body. ‘There is generally a fairly well developed internal shell, and there are usually lateral fins of various width (Figs. 295, 296, etc., fi). The heart lies in a coelomic cavity. Nidamentary glands are usually present. The Decapoda comprise two tribes, the Oigopsida and the Myopsida. TRIBE 1. OIGOPSIDA. The members of this tribe are characterised by the presence of a wide orifice, occupying the optic axis, in the external false cornea of the eye. As a rule two oviducts are present. In the fossil genera the shell has a multilocular phragmocone with a siphuncle ; the initial chamber of this shell is globular and larger than the second chamber. The most ancient forms are characterised by the small size of the rostrum, the THE CEPHALOPODA 337 slight development of the pro-ostracum, and the large size of the phragmocone. The group is probably derived from the straight Tetrabranchia, such as JBactrites. In the living genera, with the exception of Spirula, the shell is a chitinous gladius. FamIty 1. BELEMNOTEUTHIDAE, Zittel. An extinct family in which the shell has a well-developed phragmocone and the rostrum is reduced to a calcareous envelope surrounding it; the siphuncular necks are directed backwards, as in the Nautiloidea ; there were ten equal arms provided with hooks. |Genera— Phragmoteuthis, Mojsisovics ; Trias. Belemnoteuthis, Pearce ; Jurassic and Cretaceous (Fig. 262, A). Acantho- teuthis, Wagner and Miinster; Jurassic. Faminy 2, AULACOCERATIDAE, Fischer. An extinct family in which the shell is formed of a phragmmocone ae * Frye. 295. Spirula. A, dorsal aspect; B, ventral aspect. a, arms, e, eyes; fi, fins; fu, funnel; pa, mantle; po, posterior fossa; sh, shell; te, tentacular arms; t.d, terminal pallial disc. (After Chun.) with widely distant septa ; the siphuncular necks are directed anteriorly ; the rostrum is well developed and claviform. Genera—Aulacoceras, Hauer ; Trias. Atractites, Giimbel; Trias and Jurassic. Xviphoteuthis, Huxley ; Lias. Faminy 3. BrLemNiTIpAr, de Blainville. An extinct family with a short phragmocone provided with a ventral siphuncle and prolonged dorsally into a long pro-ostracum; the rostrum highly developed and cylindrical. Genera— Belemnites, Lister ; 350 species from the Jurassic and Cretaceous. Diploconus, Zittel ; Upper Jurassic. Famity 4. Betoprertpar. Rostrum and phragmocone well developed ; the phragmocone often curved ; the initial chamber small. Genera— Beloptera, de Blainville; Eocene. Bayanoteuthis, Munier-Chalmas ; Eocene. Spirulirostra, d’Orbigny ; Miocene (Fig. 262, C). Faminy 5. SPIRULIDAE, d’Orbigny. The two dorsal and ventral sides of the aboral 22 338 THE CEPHALOPODA extremity of the shell are left uncovered by the mantle (Fig. 295). The shell is calcareous, coiled endogastrically, multilocular and siphunculated (Fig. 268, sh). The fins are posterior. Genus—Spirula, Lamarck ; three living species are known ; they live at great depths, and only a few entire individuals have been obtained: live speci- mens are very rarely seen. Famity 6. OMMATOSTREPHIDAE, Gill. The shell is in- ternal and chitinous, ending aborally in a little hollow cone. The tentacular arms are rather short and thick. The suckers have denticulate rings. Genera—Ommatostrephes, dOrbigny ; fins aboral, simple, and rhom- Fic. 296. Doratopsis vermicularis (Riippel), Fic. 297. dorsal aspect. ce, cerebral ganglia ; : e, eye; fi, fin; nz.c, nuchal cartilage ; Ommatostrephes sagittatus, Lamarck, dorsal t, tentacular arm; 1, 2, 3, 4, pair of aspect. I, mantle; Il, tentacular arm; III, fin; arms. (After Weiss.) IV,eye ; V, arms. (After Verany.) boidal (Fig. 297); British. Otenopteryx, Appellof ; fins pectinate, as long as the body (Fig. 259). Bathyteuthis, Hoyle ; fins terminal, rudimentary ; tentacular arms filiform ; abyssal. Rhynchoteuthis, Chun ; tentacular arms united to form a beak-shaped appendage. Symplectoteuthis, Pfeiffer. T'rachelo- teuthis, Steenstrup. Dosidicus, Steenstrup. Architeuthis, Steenstrup ; this is the giant genus among the Cephalopoda. Famity 7. THYSANOTEUTHIDAE, THE €CEPHALOPODA 339 Keferstein. Arms enlarged, bearing two rows of suckers and filaments. Fins triangular, extending along the whole length of the body. Genus— Thysanoteuthis, Troschel (Fig. 298, B) ; Mediterranean. Famity 8. ONycHO- TEUTHIDAE, Gray. Fins terminal. Tentacular arms long; the suckers provided with hooks, Genera—Onychoteuthis, Lichtenstein; the hook- bearing suckers exist only on the well-developed tentacular arms. Hnoplo- teuthis, VOrbigny ; tentacular arms well developed ; hook-bearing suckers Fic. 298. Decapod Cephalopoda. A, Cheiroteuthis Veranyi, dorsal aspect; B, Thysanoteuthis rhombus, dorsal aspect ; C, Leachia cyclura, ventral aspect. (From Lankester, after Verany, Troschel, Feérussac and d’Orbigny.) on all the arms. Veranya, Krohn; body very short; fins obtuse ; tentacular arms atrophied in the adult; Mediterranean. Chaunoteuthis, Appellof; body elongated; fins prominent and pointed; tentacular arms atrophied. Pterygioteuthis, Fischer. Ancistroteuthis, Gray. Abralia, Gray. Teleoteuthis, Verrill. Lepidoteuthis, Joubin. Famity 9, Gona- TIDAE, Hoyle. Body elongated; fins terminal. Radula with only two lateral teeth. Genus—Gonatus, Gray. FaAminy 10. CHEIROTEUTHIDAE, Gray. Tentacular arms long and not retractile. Body elongated ; fins large and rounded. Resisting apparatus well developed. Genera— 340 THE CEPHALOPODA Cheiroteuthis, @Orbigny ; with suckers along the whole length of the peduncle of the tentacular arms (Fig. 298, A). Doratopsis, Rochebrune ; body much elongated, ending ina spine ; dorsal arms very short (Fig. 296) ; Atlantic and Mediterranean. Histioteuthis, d’Orbigny ; the six dorsal arms are united by a membrane ; the body covered with photogenous organs. Histiopsis, Hoyle ; the membrane of the dorsal arms only reaches half- way up the arms; luminous organs present. Calliteuthis, Verrill; no brachial membrane ; luminous organs present. Grimalditeuthis, Joubin ; the fin of each side is divided into two separate lobes: no tentacular arms (Fig. 258). Famitry 11. Cranconimpas, Gray. The eight normal arms are very short. The eyes prominent. The fins small and terminal. Genera— Cranchia, Leach ; body bursiform; sessile arms short; fins entirely aboral. Loligopsis, Lamarck; body elongated, conical; tentacular arms slender. Leachia, Lesueur ; tentacular arms aborted; the funnel without a valve (Fig. 298,C). Taonius, Steenstrup; body elongate ; sessile arms rather short; eyes pedunculated (Fig. 253). TRIBE 2. MyYopsIDA. The members of this tribe are characterised by having a closed external cornea, and by having only a single oviduct, viz. that of the left side. The internal shell has no longer a distinct phragmocone, and is calcified (Sepiidae) or simply chitinous. The Myopsida are more littoral in habit than the Oigopsida. Fic. 298bis, Sepia officinalis, swimming, right-side view. o, arms; ji, fins; fu, funnel. (After Merculiano.) Famity 1. Sepipar, d’Orbigny. Body wide and flattened; fins narrow and extending the whole length of the body (Fig. 298%). Shell caleareous and laminated, forming the “sepion.” Genera— Belosepia, Voltz; a rudiment of the rostrum and phragmocone present; Eocene. Sepia, Linnaeus ; shell with a rostrum (Figs. 262, B, and 299); British, Sepiella, Steenstrup ; shell without a rostrum. Faminy 2. SEPIOLIDAE, Leach. Body short, rounded at the aboral end; fins rounded, inserted on the middle of the length of the body. Shell chitinous, narrow and shorter than the body, or absent. Genera—WSepiola, Leach ; head united to the mantle in the anterior (dorsal) region ; a fossorial British genus. Rossia, Gray; head not united to the mantle; British. THE CEPHALOPODA 341 - Stoloteuthis, Verrill, and Inioteuthis, Verrill, have no internal shell. Heteroteuthis, Gray. Huprymna, Steenstrup. Famity 3. IDIOSEPIIDAE. Steenstrup. Body elongated, with rudimentary terminal fins. Internal shell almost lost. Genus—Jdiosepius, Steenstrup ; this tiny Cephalopod is only 14 centimetre long, and has a mucous pore at the aboral Fig. 299. Sepia officinalis, dorsal view of a dead specimen, with the short arms spread out and the long arms pulled out of their sacs. a, neck; b, lateral fins ; ¢, the eight shorter arms; d, the two long tentacular arms; e, the eyes. (From Lankester, after Owen.) extremity of the body; it inhabits the Indian Ocean. Famtty 4. SEPIADARIIDAE, Steenstrup. Body short; the mantle fused to the head anteriorly (dorsally). No shell. Genera—sSepiadariwm, Steenstrup ; fins short, situated at the aboral extremity of the body ; from the Pacific Ocean. Sepioloidea, d’Orbigny ; fins nearly as long as the body; Australian. Famity 5, LoLIGINIDAE, Leach. Body elongated and conical ; fins triangular or 342 THE CEPHALOPODA rounded, and extending farther forward than the aboral half of the body. Tentacular arms partly retractile. The shell is a well-developed chitinous gladius (Fig. 263). Genera—Loligo, Lamarck ; fins triangular, confined to the aboral half of the body; British. Sepioteuthis, de Blainville ; fins prominent but rounded, extending over the whole length of the body. Loliolus, Steenstrup. Loliguncula, Steenstrup. The following fossil genera, known by their gladius and ink-sac, have been placed near Loligo :—Teuthopsis, Deslongchamps. Beloteuthis, Miinster, and Geoteuthis, from the Lias, and Phylloteuthis, Meek and Hayden, from the Cretaceous, are distinguished by their broader gladius. Plesioteuthis, Wagner, from the Jurassic and Cretaceous, has a long and narrow gladius. Fic. 300. Opisthoteuthis depressa, Ijima and Ikeda, dorsal aspect. «7, arms; e, eye; fi, fin; fu, funnel. (After Ijima and Ikeda.) SuB-ORDER 2. OcToOPoDaA. These Dibranchia have only eight arms, which are all similar and are longer than the body. The body is short and rounded aborally. The suckers are sessile. The heart is not contained in the coelom. There are no nidamentary glands. The Octopoda comprise two tribes, the Leioglossa and Trachyglossa. TRIBE 1. LEIOGLOSSA. The members of this tribe have no radula. All the arms are united together by a complete membrane. Fins are developed on the sides of the body. Family CrRRHOTEUTHIDAE, Keferstein. Arms united by a mem- brane, and bearing tentacular filaments on either side of the suckers (Fig. 260). Genera—Ctrrhoteuthis, Eschricht ; the pallial sac prominent and the fins large; a pelagic form. Opzisthoteuthis, Verrill; body flattened, with small fins ; a deep-sea form (Fig. 300). Vampyroteuthis, Chun; four fins. Some fossil Octopoda bearing fins are known; e.g. Palaeoctopus, Woodward, from the Cretaceous. THE CEPHALOPODA 343 TRIBE 2. TRACHYGLOSSA. These are Octopoda with a radula and without true fins. Famity 1. AMPHITRETIDAE, Hoyle. The funnel is attached to the middle line of the mantle, dividing the pallial aperture into two. The eight arms are united by a membrane. Genus—Amphitretus, Hoyle ; pelagic. Famity 2. Attoposrpas, Verrill. All the arms united by a membrane. The mantle is joined to the head by a dorsal band and two lateral commissures. Genus—Alloposus, Verrill ; pelagic. FAMILY 3. Ocropopipak, @’Orbigny. Arms long and equal, without a true inter- brachial membrane. The hectocotylus is not caducous. No cephalic Fia. 301. Argonauta argo, Linnaeus, left side of the female. I, funnel; II, mantle; III, eye; IV, dorsal webbed arm. (After Verany.) aquiferous pores. Genera—Octopus, Lamarck ; the suckers in two rows on each arm; British. Eledone, Leach; a single row of suckers on each arm ; British. Scaewrgus, Troschel. _Pinnoctopus, d@Orbigny. Cistopus, Gray. Japetella, Hoyle. Famity 4, Pattonexipan, @Orbigny. Males and females naked. The hectocotylus is autotomous. The arms are un- equal in size but similar in the two sexes. Aquiferous pores are present on the head and funnel. Genera—Tremoctopus, Delle Chiaje ; the two dorsal pair of arms are united by a membrane. Ocytho?, Rafinesque ; without an interbrachial membrane (Fig. 287). Faminy 5. ARGo- NAUTIDAE, Cantraine. The hectocotylised arm autotomous. The ex- tremities of the dorsal arms are enlarged in the female (Fig. 301), and secrete a shell in which the body is contained. The males are very small and naked. Genus—-Argonauta, Linnaeus. 344 On Wife 18. ill), 20. LITERATURE OF THE CEPHALOPODA LITERATURE OF THE CEPHALOPODA. A. Tetrabranchia. (a) Living. . Dean. Notes on Living Nautilus. Amer. Natur. xxxv. 1901. . Grifin. The Anatomy of Nautilus pompilius. Mem. Nat. Acad. Sci. Washington, viii. 1900. . Haller. Beitraige zur Kenntniss der Morphologie von Nautilus pompilius. Denkschr. Med. Nat. Gesellsch. Jena, viii. 1895. . Huxley. On some Points in the Anatomy of Nautilus pompilius. Journ. Linn. Soe. London, iii. 1858. . Joubin. Recherches sur l'appareil respiratoire des Nautiles. Revue Biol. Nord. ii. 1890. . Keferstein. Beitrage zur Anatomie des Nautilus pompilius. Gotting. Nachrichten, 1865. . Kerr. On some Points in the Anatomy of Nautilus pompilius, Proce. Zool. Soe. London, 1895. . Lankester and Bourne. On the Existence of Spengel’s Olfactory Organ and of Paired Genital Ducts in,the Pearly Nautilus. Quart. Journ. Micr. Sci. Xxlil. 1883. . MacDonald. On the Anatomy of Nautilus umbilicatus, compared with that of Nautilus pompilius. Phil. Trans. 1855. . Owen. Memoir on the Pearly Nautilus (Wautilus pompilius), with illustra- tions of its external form and internal structure. London, 1832. Valenciennes. Nouvelles recherches sur le Nautile flambé. Archives du Muséum, Paris, ii. 1841. . Vander Hoeven. Contributions to the Knowledge of the Animal of Nautilus pompilius. Trans. Zool. Soc. London, iv. 1850. Bydraagen tot de ontleedkundige Kennis aangaande Nautilus pom- pilius. Verhandel. k. Akad. Amsterdam, iii. 1856 (translated in Ann. Mag. Nat. Hist. (2), xix. 1857). . Vayssiere. Etude sur Vorganisation du Nautile. Ann. d. Sci. Nat. Zool. (8), li. 1896. . Vrolik. Lettre sur quelques points de l’organisation de l’animal du Nautile flambé. Mém. Soc. Linn. Normandie, x. 1855. Willey. Contribution to the Natural History of the Pearly Nautilus. A. Willey’s Zoological Results, part vi. 1902. (b) Fossil. Branco. Beitriige zur Entwicklungsgeschichte der fossiler Cephalopoden. Palaeontographica, 1879, 1880. Foord. Catalogue of Fossil Cephalopoda in the British Museum, Part I. 1888 ; Part II. 1892 ; Part III. 1897 (by Foord and Crick). Hyatt. The Fossil Cephalopods of the Museum of Comparative Zoology. Bull. Mus. Comp. Zool. Cambridge, i. 1868. —— Genera of Fossil Cephalopods. Proc. Boston Soc. Nat. Hist. xxii. 1884. LITERATURE OF THE CEPHALOPODA 345 B. Dibranchia. . Appelléf. Die Schale von Sepia, Spirula und Nautilus. K. Svensk. Vet.- Akad. Handl. xxv. 1894. . Bert. Mémoire sur la physiologie de la Seiche. Mém. Soc. Sci. Phys. et Nat. Bordeaux, v. 1867. . Bobretzky. Observations sur le développement des Céphalopodes (in Russian language). Bull. Soc. imp. Amis. d. Sci. nat. et Ethnogr. Moscow, 1877. . Bourquelot. Recherches sur les phénomenes de la digestion chez les Mollusques Céphalopodes. Arch. de Zool. Expér. (2), iii. 1884. . Brock. Versuch einer Phylogenie der Dibranchiaten Cephalopoden. Morph. Jahrb. vi. 1880. . ——— Ueber die Geschlechtsapparat der Cephalopoden. Zeitschr. f. wiss. Zool. xxxii. and xxxvi. 1879, 1882. . Brooks. The Development of the Squid (Zoligo Pealii, Lesueur). Annivers. Mem. Boston Soc. Nat. Hist. 1880. . Chéron. Recherches pour servir & Vhistoire du systtme nerveux des Céphalopodes Dibranches. Ann. d. Sci. nat. Zool. (5), v. 1866. . Delage. Sur une fonction nouvelle des otocystes comme organes d’orienta- tion locomotrice. Arch. de Zool. Expér. (2), vi. 1887. . @Orbigny and Férussac. Histoire naturelle, o¢énérale et particuliére, des g g ) Céphalopodes acétabuliferes, vivants et fossiles. Paris, 1835-1848. . Faussek, Untersuchungen iiber die Entwicklung der Cephalopoden. Mitth. Zool. Stat. Neapel, xiv. 1900. . Frédéricg. Sur Vorganisation et la physiologie du Poulpe. “Bull. Acad. Belg. (2), xlvi. 1878. . Girod. Recherches sur la poche du noir des Céphalopodes. Arch de Zool. Exper. (1), x. 1882. . Goodrich. Report on a Collection of Cephalopoda from the Calcutta Museum. Trans. Linn. Soe. (2), vii. 1896. . Grenacher. Zur Entwickelung der Cephalopoden. Zeitschr. f. wiss. Zool. Xxiv. 1874. . Grobben. Morphologische Studien iiber den Harn und Geschlechtsapparat sowie die Leibeshohle der Cephalopoden. Arb. Zool. Inst. Wien, v. 1882. 7. Hancock. On certain Points in the Anatomy and Physiology of the Dibranchiate Cephalopoda. Nat. Hist. Review, 1861. . — On the Nervous System of Ommatostrephes todarus. Ann. Mag. Nat. sty (2) xe 852: . Harris. Die Statocysten der Cephalopoden. Zool. Jahrb. (Anat. und Ontog.) xviii. 1908. . Hoyle. Report on the Cephalopoda collected by H.M.S. ‘‘ Challenger” during the years 1878-76. Zool. Chall. Exped. part xliv. 1886. . Huxley. On the structure of the Belemnitidae. Mem. Geol. Sury. Unit. Kingd. Monogr. ii. 1864. ‘ 2. Huxley and Pelseneer. Report on the Specimen of the Genus Spirula. Zool. Chall. Exped. part Ixxxiii. 1895. . Tima and Ikeda. Description of Opisthoteuthis depressa, n. sp. Journ. Coll. of Sci. Tokyo, viii. 1895. . Jatta. I Cefalopodi viventi nel golfo di Napoli. Fauna und Flora des golfes von Neapel, xxiii, 1896. LITERATURE OF THE CEPHALOPODA 43. 44, . Joubin. Structure et développement de la branchie de quelques Céphalopodes des Cotes de France. Arch. de Zool. Expér. (2), iii. 1885. — Recherches sur la coloration du tégument chez les Céphalopodes. Jbid. (2), x. 1892. . —— Recherches sur l’appareil Jumineux d’un Céphalopode (Histioteuthis Riippellit). Bull. Soe. Sci. et Méd. Ouest. Rennes, ii. and iii. 1893, 1894. — Contribution a l'étude des Céphalopodes de l’ Atlantique Nord ; and Céphalopodes provenant des campagnes de la Princesse-Alice. Résultats Camp. Sci. Albert 1 de Monaco, ix. (1895), xvii. (1900). . Kolliker. Entwickelungsgeschichte der Cephalopoden. Zurich, 1844. . Korschelt. Beitrage zur Entwickelungsgeschichte der Cephalopoden. Festschr. fiir R. Leuckart, 1892. . Milne-Edwards and Valenciennes. Observations sur la circulation chez les Mollusques. Mém. Acad. Sci. Paris, xx. 1840. 2. Pelseneer. Sur la valeur morphologique des bras et la composition du systeme nerveux des Céphalopodes. Arch. de Biol. viii. 1888. . Phisalix. Recherches physiologiques sur les Chromatophores des Céphalopodes, etc. Arch. Phys. Paris (5), iv. vi. 1892, 1894. . Racovitza. Mceurs et reproduction de la Rossia macrosoma, Arch, de Zool. Expér. (3), ii. 1894. . Risso. es Céphalopodes du parage méditerranéen du Comté de Nice. Nice, 1854. . Solger. Zur Kenntniss der Chromatophoren der Cephalopoden und ihre Adnexa. Arch. f. Mikr. Anat. liii. 1898. . Uerkiill, von. Physiologische Untersuchungen iiber Zledone moschata. Zeitschr. f. Biol. xxvili. xxx. xxxi. 1892-95. . Verany. Céphalopodes méditerranéens. Génes, 1851. . Verany and Vogt. Mémoire sur les hectocotyles et les males de quelques Céphalopodes. Ann. des Sci. nat. Zool. (3), xvii. 1852. . Verrill, The Cephalopods of the North-East Coast of America, I. and II. Trans. Connect. Acad. v. 1880-81. . Vialleton. Recherches sur les premieres phases du développement de la Seiche. Ann. des Sci. nat. Zool. (7), vi. 1888. . Vigelius. Ueber das Excretionssystem der Cephalopoden. Nied. Arch. f. Zool. v. 1880. Watase. Observations on the Development of Cephalopods. Stud. Biol. Lab. Johns Hopkins Univ. iv. 1888. Weiss. On some Oigopsid Cuttle-fishes. Quart. Journ. Micr. Sci. xxix. 1888. INDEX To names of Classes, Orders, Sub-Orders, and Genera; and to technical terms. Abdominal ganglion, 113 Abralia, 339 Acanthoceras, 336 Acanthochiton, 53 Acanthodoris, 177 Acanthopleura, 54 Acanthoteuthis, 337 Acavus, 187 Acephala, 205 Acera, 169 Achatina, 188 Acicula, 152 Acila, 255 Aclis, 158 Acmaea, 145 Actaeon, 168 Actaeonella, 168 Actaeonia, 181 Actaeonina, 168 Actinoceras, 332 Actinodesma, 261 Aculifera, 40 Adacna, 271 Adacnarca, 258 Addisonia, 122 Adductores, 210 Adelactaeon, 168 Adelphoceras, 333 Adeorbis, 153 Adesmacea, 274 Aegirus, 177 Aegoceras, 335 Aerope, 189 Aesthetes, 50 Aetheria, 268 Agadina, 140 Agaronia, 121, 165 Aglossa, 158 Agnatha, 188 Agriolimax, 187 Alaria, 155 Alderia, 181 Aldisa, 178 Alexia, 184 Allopagus, 266 Alloposus, 343 Allorisma, 276 Amalia, 187 Amaltheus, 335 Amaura, 156 Amberleya, 150 Ambonychia, 262 Amicula, 53 Ammoniceras, 153 Anmonites, 335 Ammonitoidea, 333 Amphibola, 184 Amphibulimus, 188 Amphimenia, 60 Amphineura, 40 Amphipeplea, 185 Amphisphyra, 168 Amplhitretus, 343 Ampullaria, 152 Amussium, 262 Anadara, 258 Anadenus, 187 Anal glands, 8, 96, 200 Anarcestes, 334 Anatina, 275 Anatinacea, 275 Ancillaria, 165 Ancistromesus, 145 Ancistroteuthis, 339 Ancula, 178 Anculotus, 154 Ancylodoris, 178 Ancylus, 186 Androgyna, 166 Aneitea, 189 Aneitella, 189 Anisocardia, 264 Anisomyaria, 211 Anisopleura, 66 Anodonta, 268 Anomalodesmacea, 254 Anomia, 257 Anomiacea, 257 347 Anoplophora, 267 Anostoma, 188 Antalis, 204 Anthracoptera, 262 Anthracosia, 267 Antipleura, 256 Antispadix, 324 Aplacophora, 51 Aplexa, 186 A plodon, 268 Aplustrum, 169 Aplysia, 171 Aplysiella, 171 Aplysiomorpha, 171 Aptychus, 334 Aptyxiella, 154 Arca, 258 Arcacea, 258 Arcestes, 335 Archidoris, 178 Architeuthis, 338 Arcicardium, 271 Arcomya, 276 Arconaia, 268 Argina, 258 Argonauta, 343 Arietites, 335 Ariolimax, 187 Arion, 187 Ariophanta, 186 Arm, 289 Arnaudia, 272 Articulamentum, 42 Asaplis, 273 A scoceras, 333 Aspergillum, 277 Aspidobranchia, 144 Assiminea, 153 A starte, 264 Asthenothaerus, 275 Astralium, 150 Asymmetry, 76, 111 Atlanta, 163 A topos, 189 348 INDEX Atractites, 337 Atrina, 264 Atys, 168 Aucella, 262 Aulacoceras, 337 Auricula, 184 aAvellana, 168 Avicula, 260 Aviculopinna, 264 Axinus, 265 Azeca, 188 Babinka, 261 Bactrites, 333 Baculites, 335 Baikalia, 153 Bakewellia, 259 Balea, 188 Baltoceras, 332 Barbatia, 258 Barnea, 275 Bartletia, 268 Basilissa, 149 Basommatophora, 184 Bathanalia, 154 Bathyarca, 258 Bathydoris, 122 Bathysciadium, 145 Bathyteuthis, 338 Batissa, 266 Bayanoteuthis, 337 Baylea, 272 Bela, 166 Belemnites, 337 Belemnoteuthis, 337 Bellerophon, 147 Beloptera, 337 Belosepia, 340 Beloteuthis, 342 Berendtia, 188 Berthella, 174 Bifora, 207 Biradiolites, 272 Bithynella, 154 Bithynia, 154 Bittiwm, 154 Bivalvia, 213 Blauneria, 184 Boreochiton, 53 Bornella, 176 Bourcieria, 150 Brachytrema, 152 Branchial hearts, 306 Brechites, 277 Buccinum, 164 Buliminus, 188 Bulimulus, 188 Bulimus, 187 Bulinus, 185 Bulla, 169 Bullia, 164 Bullina, 168 Bullinula, 168 Bullomorpha, 167 Byssocardium, 271 Byssonychia, 262 Byssus, 216 Bythoceras, 154 Cadlina, 178 Cadulus, 204 Caecilianella, 188 Caecum, 155 Callistochiton, 53 Calliteuthis, 340 Callocardia, 265 Callochiton, 53 Calma, 179 Calyptraea, 155 Campaspe, 176 Camptonectes, 262 Camptonyx, 184 Cancellaria, 165 Canidia, 164 Cantantostoma, 147 Caprina, 272 Caprinula, 272 Caprotina, 272 Capsa, 268 Captacula, 199 Capulus, 155 Carbonaria, 258 Cardiacea, 270 Cardilia, 270 Cardinal teeth, 213, 214 Cardinia, 267 Cardioceras, 335 Cardiola, 256 Cardiolaria, 256 Cardiomorpha, 256 Cardiopoda, 163 Cardita, 264 Carditella, 264 Carditopsis, 264 Cardium, 271 Carinaria, 163 Carolia, 257 Carychium, 184 Cassianella, 261 Cassidaria, 157 Cassidula, 184 Cassis, 157 Oastalia, 268 Cavolinia, 170 Cenia, 181 Cephalopoda, 284 Cerata, 86 Ceratisolen, 274 Ceratites, 335 Cerithidea, 104 Cerithiopsis, 154 Cerithium, 154 Ceromya, 276 Cetoconcha, 278 Chaetoderma, 63 Chaetodermomorpha, 61 Chaetopleura, 53 Chama, 271 Chamacea, 271 Chamostrea, 276 Chaunoteuthis, 339 Cheiroteuthis, 340 Chelinodura, 169 Chenopus, 155 Chilina, 185 Chiton, 54 Chitonellus, 54 Chlamydoconcha, 266 Chlamydophorus, 189 Chlamys, 262 Chlorites, 187 Choanomphalus, 185 Choneplax, 54 Choristes, 153 Chromatophora, 297 Chromodoris, 178 Chrysodomus, 164 Chytra, 154 Ciliated dises, 226 Cinulia, 168 Cionella, 188 Circe, 270 Cirrhobranchia, 197 Cirrhoteuthis, 342 Cistopus, 343 Cladohepatica, 178 Clanculus, 149 Clausilia, 188 Clavagella, 277 Clavatula, 166 Clavella, 164 Clidiophora, 276 Clio, 170 Clione, 173 Clionopsis, 173 Clionychia, 262 Cloacal chamber, 229 Clymenia, 334 Cnidosaes, 96 Cocculina, 149 Cochlides, 42 Cochliolepis, 33 Cochloceras, 335 Cochlodesina, 275 Cochlostyla, 188 Coelodon, 276 Coelomoduet, 13 Coelomopore, 15 Colobocephalus, 169 Colpodaspis, 169 Columbella, 165 Columbellaria, 157 Columbellina, 157 INDEX Columellar, 84 Cominella, 164 Commissure, 16 Conchifera, 205 Concholepas, 165 Conchyoline, 3 Condylocardia, 264 Connective, 16 Conocardium, 261 Conus, 166 Coralliophaga, 264 Coralliophila, 165 Corambe, 178 Corbicula, 266 Corbis, 265 Corbula, 273 Corbulomya, 273 Cosmoceras, 336 Cranchia, 340 Crassatella, 264 Cremnoconchus, 152 Crenatula, 259 Crenella, 259 ‘vrepidula, 155 Crimora, 177 Crioceras, 336 Crossea, 158 Crucibulum, 155 Cryptochiton, 53 Cryptoconchus, 53 Cryptodon, 265 Cryptomya, 273 Cryptophthalmus, 169 Cryptoplax, 54 Crystalline style, 94, 220 Ctenidium, 11 Ctenodonta, 256 Ctenopteryx, 338 Cucullaea, 258 Cuculella, 256 Cultellus, 274 Cumningia, 270 Cuna, 264 Cuspidaria, 278 Cuthona, 179 Cuvierina, 170 Cyamium, 266 Cyclas, 267 Cyclina, 270 Cyclolobus, 335 Cyclomenia, 60 Cyclonema, 150 Cyclophorus, 152 Cyclostoma, 152 Cyclostrema, 150 Cyclosurus, 152 Cyerce, 181 Cylichna, 168 Cylindrella, 188 Cylindrobulla, 169 Cylindromitra, 164 Cymba, 165 Cymbulia, 170 Cymbuliopsis, 170 Cynodonta, 164 Oypraea, 157 Cypricardia, 264 Cypricardites, 258 Cyprina, 264 Cyrena, 266 Cyrenella, 265 Cyrtoceras, 333 Cyrtodaria, 274 Cyrtodonta, 258 Cyrtolites, 147 Cyrtopinna, 264 Dacrydium, 259 Daonella, 261 Daudebardia, 189 Decapoda, 336 Dejanira, 150 Delphinula, 150 Dendronotus, 175 Dentalium, 204 Dermatobranchus, 181 Derinatocera, 152 Dermatomya, 278 Desmopterus, 170 Detorsion, 77 Dexiobranchaea, 173 Dialineury, 142 Diartema, 155 Diauly, 126 Dibranchia, 336 Diceras, 271 Dicerocardium, 267 Dimya, 262 Dimyacea, 262 Dinarites, 335 Dinomenia, 60 Diploconus, 337 Diplodonta, 265 Diplommatina, 152 Dipsacus, 164 Dischides, 204 Discites, 333 Discohelix, 147 Discosorus, 332 Ditremaria, 147 Ditremata, 189 Docoglossa, 145 Dolabella, 171 Dolabrifer, 171 Dolium, 157 Donax, 270 Dondersia, 60 Doratopsis, 340 Doridium, 169 Doridomorpha, 177 Doridopsis, 178 Doridunculus, 178 Doris, 178 Dosidicus, 338 Dosinia, 270 Doto, 179 Dreissensia, 264 Drillia, 120 Durga, 267 Eastonia, 270 Echinomenia, 60 Hglisia, 158 Elasmognatha, 189 Eledone, 343 Hlenchus, 149 Eleutherorhabda, 253 Hligmus, 268 Llizia, 273 Elysia, 181 Elysiomorpha, 181 EKmarginula, 149 Embletonia, 179 Endoceras, 332 Endodonta, 188 Endogastric, 77 Linoplochiton, 54 Lnoploteuthis, 339 Ensis, 274 Entalina, 204 _ Enteroxenos, 160 Entocolax, 159 Entoconcha, 159 Entodesina, 277 Entosiphon, 158 Entovalva, 266 Kolidomorpha, 178 Eolis, 179 Eoplacophora, 53 Kotrochus, 155 Ephippium, 257 Ephippodonta, 266 Epiphragm, 73 Epipodium, 70 Erato, 157 Erodona, 273 Ervilia, 270 Erycina, 265 Ethella, 1384 Hucalodium, 188. Huchrysalis, 154 Euciroa, 277 Eudoxochiton, 54 Eulamellibranchia,: 262 Hulima, 158 Hunema, 150 Euomphalus, 147 Euphemus, 147 Euplocamus, 177 Huprymna, 340 Huthria, 164 Euthyneura, 166 350 INDEX Eutrochatella, 150 Exogastric, 74 Facelina, 179 Fasciolaria, 164 Faunus, 154 Ferussacia, 188 Filibranchia, 256 Fiona, 180 Firoloida, 163 Fischeria, 266 Fissidentalium, 204 Fissurella, 149 Fissurellidea, 149 Fistulana, 274 Fluzina, 158 Foot, 68, 199, 215, 286 Foot gland, 70 Fortisia, 168 Fossarus, 152 Fowlerina, 173 Fyryeria, 178 Fulgur, 164 Funnel, 291 Fusispira, 154 Fustiaria, 204 Fusus, 164 Gadinia, 185 Galatea, 266 Galeomma, 266 Galvina, 179 Gastrana, 268 Gastrochaena, 274 Gastropoda, 66 Gastropteron, 169 Gaza, 149 Gellina, 179 Gena, 149 Geomalacus, 187 Geoteuthis, 342 Gervilleia, 259 Gibbula, 149 Gibbulina, 189 Gladius, 293 Glandina, 189 Glaucomya, 270 Glaucus, 179 Gleba, 170 Glochidium, 251 Glossoceras, 338 Glycimeris, 274 Glyphis, 149 Gomphoceras, 332 Gonad, 20 Gonaduct, 20 Gonatus, 339 Goniatites, 334 Gonieolis, 179 Goniodoris, 177 Goniomya, 276 Gonodon, 265 Gosseletia, 262 Grammysia, 256 Gresslya, 276 Grimalditeuthis, 340 Gryptochitonidae, 53 Guivillea, 165 Gundlachia, 186 Gymnosomata, 173 Gyrocerds, 333 Haemocyanine, 10 Halia, 165 Halicardia, 277 Haliotinella, 174 Hatliotis, 148 Halopsyche, 175 Haminea, 169 Hamites, 335 Hancock’s organ, 116 Hanleya, 53 Hapalus, 187 Harpa, 166 Harpoceras, 335 Harvella, 270 Hectocotylus, 324 Hedyle, 179 Helcion, 145 Helcioniscus, 145 Helicarion, 187 Helicina, 150 Helicodonta, 187 Helicophanta, 187 Helicter, 188 Helix, 187 Hemiarthrum, 53 Hemifusus, 164 Henvimenia, 60 Hemphillia, 188 Hercoceras, 333 Hercynella, 185 Hermaea, 181 Hermaphroditism, 19 Hero, 179 Heromorpha, 179 Heterocardia, 270 Heterochisma, 204 Heterodoris, 178 Heterogangliata, 1 Heteropoda, 160 Heterostrophic, 82 Heteroteuthis, 340 Hexabranchus, 178 Himella, 273 Hindsiella, 266 Hinge, 213 Hinnites, 262 Hipponyx, 155 Hippopus, 271 Hippurites, 272 Histiopsis, 340 Histioteuthis, 340 Holobranch, 45 Holognatha, 186 Homalogyra, 153 Homalonyx, 189 Hoplites, 336 Hoplomytilus, 262 Hoplopteron, 158 Huronia, 332 Hyalimax, 189 Hyalopecten, 262 Hybocystis, 152 Hydatina, 169 Hydrobia, 153 Hydrocena, 151 Hyperstrophic, 82 Hypobranchial gland, 79 Hypostracum, 4 Hypotrema, 257 Hyria, 268 Ichthyodes, 60 Ichthyosarcolites, 272 Idalia, 177 Idas, 259 Idiosepius, 341 Imbricaria, 164 Inioteuthis, 340 | Tnoceramus, 260 Insertion plates, 42 Iphigenia, 270 Tridina, 268 Tsanda, 150 Ischnochiton, 53 Tsidora, 107 Ismenia, 60 Tsocardia, 264 Isodonta, Isomyaria, 211 Isopleura, 1, 40 Janella, 189 Janthina, 156 Janus, 179 Japetella, 343 Jeffreysia, 153 Joanisiella, 265 Jorunna, 178 Jouannetia, 275 Katharina, 53 Keber’s organ, 233 Kellya, 266 Kellyella, 266 Kokenella, 147 Kruppomenia, 60 Labial commissure, 16 Labial palp, 218 Lachesis, 164 Lacuna, 152 Laeocochlis, 154 Lamellaria, 156 Lamellibranchia, 205 Lamellidoris, 178 Lanistes, 152 Laoma, 188 Lasaea, 266 Latia, 186 Latirus, 164 Leachia, 340 Leda, 255 Leiblein’s gland 93 Leioglossa, 342 Lepeta, 145 Lepetella, 145 Lepidomenia, 60 Lepidopleurus, 53 Lepidoteuthis, 339 Leptochiton, 53 Leptoconchus, 165 Lepton, 266 Leuconia, 184 Ligament, 213 Tima, 263 Limacina, 170 Limaea, 263 Limapontia, 181 Limazx, 187 Limifossor, 63 Limnaea, 185 Limnocardium, 271 Limnotrochus, 154 Limopsis, 258 Limopteria, 260 Liolophura, 54 Liiomesus, 164 Liopistha, 278 LTiotia, 150 Lipocephala, 205 Lissoceras, 335 Lithocardium, 271 Lithodomus, 259 Lithoglyphus, 154 Litiopa, 153 Littorina, 152 LTittorinida, 154 Litwites, 333 Liver, 7, 44, 95, 200, 220, 301 Tivona, 149 Lobes (accessory cerebral), 137 Lobiancoia, 96 Lobiger, 169 Lobites, 335 Loligo, 342 Loligopsis, 340 Loliguncula, 342 Loliolus, 342 Lomanotus, 176 Lophocercus, 170 INDEX Lorica, 54 Loricella, 54 Loxoceras, 332 Loxonema, 154 Lucapina, 149 Lucapinella, 149 Lucina, 265 Lucinopsis, 270 Tunulicardium, 261 Lutetia, 266 Lutraria, 274 Lyonsia, 277 Lyonsiella, 277 Lyrodesma, 259 Lytoceras, 335 Macellomenia, 60 Macgillivraya, 140 Maclurea, 147 Maclurites, 150 Macoma, 268 Macrochilus, 154 Macrochisma, 149 Macroscaphites, 335 Mactra, 270 Magilus, 165 Malacozoa, 1 Malletia, 256 Malleus, 260 Mandibles, 6, 88, 299 Mangilia, 166 Margarita, 149 Marginella, Marionia, 175 Marsenina, 156 Martesia, 275 Matheronia, 272 Mathilda, 155 Meekia, 265 Megalaesthetes, 50 Megalodon, 267 Megaspira, 188 Megatebennus, 149 Meladomus, 152 Melampus, 184 Melania, 154 Melanopsis, 154 Meleagrina, 260 Melibe, 175 Mentum, 158 Meretrix, 270 Merobranch, 45 Mesalia, 155 Mesodesma, 270 Mesolimax, 187 Mesoplacophora, 53 Metalimaz, 187 Micraesthetes, 50 Micromelo, 169 Microplax, 53 Milneria, 264 Miratesta, 185 Mitra, 164 Mitrularia, 155 Modiola, 259 Modiolarca, 264 Modiolaria, 259 Modiolopsis, 259 Modiomorpha, 259 Modulus, 154 Molleria, 150 Monoceros, 165 Monochroma, 187 Monocondylaea, 268 Monodonta, 149 Monomyaria, 211 Monopleura, 272 Monotis, 261 Montacuia, 265 Mopatia, 53 Morphoceras, 336 Mucronalia, 158 Mulinia, 270 Miilleria, 268 Miiller’s organ, 291 Murchisonia, 147 Murex, 164 Mutela, 268 Mutiella, 265 Mya, 273 Myacea, 273 Myalina, 262 Mycetopus, 268 | Myochama, 276 Myoconcha, 259 Myodora, 276 Myophoria, 259 Myopsida, 340 Myrina, 259 Mysidea, 262 Mytilacea, 259 Mytilimeria, 277 Mytilus, 259 Myza, 158 Myzomenia, 60 Nacella, 145 Nanina, 81 Narica, 155 Nassa, 164 Nassopsis, 154 Natica, 156 Naticopsis, 150 Nautiloidea, 332 Nautilus, 333 Navarchus, 169 Needham’s sac, 3238 Nematomenia, 60 Neohyalimax, 189 Neomenia, 60 Neomeniomorpha, 55 Neothauma, 152 Nephrie gland, 111 Nerinea, 154 Nerita, 150 Neritina, 150 Neritodomus, 150 Neritopsis, 150 Niso, 158 Notarchus, 171 Notobranchaea, 178 Notomenia, 60 Nuchal plate, 264 Nucula, 255 Nuculina, 256 Nudibranchia, 174 Nuttalochiton, 53 Octopoda, 342 Octopus, 348 Ocythoé, 343 Odontomaria, 147 Odontoperna, 260 Odostomia, 158 Odostomiopsis, 168 Oigopsida, 336 Oleacina, 189 Oliva, 165 Olivella, 165 Ommatostrephes, 388 Omphalotropis, 152 Oncidiella, 190 Oncidiopsis, 156 Oncidium, 190 Oncospira, 150 Oniscia, 157 Onitochiton, 54 Onychoteuthis, 339 Oocorys, 157 Opeas, 188 Operculum, 71 Ophidioceras, 333 Ophileta, 147 Opis, 264 Opisthobranchia, 167 Opisthopodium, 216 Opisthoteuthis, 342 Oppelta, 335 Orpiella, 187 Orthalicus, 188 Orthoceras, 3832 Orthoneura, 114 Oscaniella, 174 Oscantopsis, 174 Oscanius, 174 Ostracolethe, 187 Ostraea, 263 Ostraeacea, 263 Otina, 184 Otocardia, 1 Otoconia, 119 Otocrypt, 18 Otocyst, 18 INDEX Otoliths, 18, 119 Ovula, 157 Oxygyrus, 163 Pachycardia, 267 Pachyrisina, 267 Palaeacma, 145 Palaeoconcha, 256 Palaeoctopus, 342 Palio, 177 Palliata, 1 Paludina, 152 Paludomus, 154 Pandora, 276 Paracephalophora, 66 Puraclione, 173 Parallelodon, 258 Paramenia, 60 Paramya, 273 Parapodia, 69 Pararhopalia, 60 Parmacella, 187 Parmarion, 187 Patella, 145 Patrocardiwmn, 261 Pearls, 213 Pecten, 262 Pectinacea, 260 Pectinibranchia, 151 Pectinodonta, 145 Pectunculus, 258 Pedicularia, 157 Pedipes, 184 Pedum, 262 Pelecypoda, 205 Peltella, 188 Peltoceras, 336 Peraclis, 170 Pergamidea, 262 Pericardie glands, 18 Pericardium, 12 Periostracum, 4 Periploma, 275 Perisphinctes, 336 Perna, 259 Peronia, 190 Persona, 157 Petersia, 157 Petricola, 270 Phanerophthalmus, 169 Phanerotinus, 147 Phasianella, 150 Philine, 169 Philobrya, 258 Philomycus, 187 Phlebcedesis, 8 Pholadella, 276 Pholadidea, 275 Pholadomya, 276 Pholas, 275 Phos, 164 Photinula, 149 Phragmoceras, 332 Phragmoteuthis, 337 Phyllaplysia, 171 Phyllidia, 178 Phyllirhoé, 175 Phyllobranchus, 181 Phylloceras, 385 Phylloteuthis, 342 Physa, 186 Phythimya, 276 Pileolus, 150 Pilidium, 145 Pinacoceras, 335 Pinna, 264 Pinnigena, 264 Pinnoctopus, 348 Pisania, 164 Pisidium, 267 Placiphorella, 58 Placophoropsis, 58 Placuna, 257 Placunanomia, 257 Plagiodon, 268 Plagioptychus, 272 Plakobranchus, 181 Planaxis, 152 Planktomya, 33 Planorbis, 185 Platyceras, 155 Platychisma, 147 Platydoris, 178 Platymalakia, 66 Platyodon, 273 Platypoda, 157 Plaxtiphora, 53 Plectomya, 275 Plectrophorus, 71 Plesioteuthis, 342 Pleural ganglion, 112, 201, 234 Pleurobranchaea, 174 Pleurobranchomorpha, 173 Pleurobranchus, 174 Pleurocera, 154 Pleurodonta, 187 Pleuromya, 276 Pleurophorus, 264 Plewrophyllidia, 180 Pleurotoma, 166 Pleurotomaria, 146 Plicatula, 262 Pliodon, 268 Plocamopherus, 177 Plutonia, 186 Pneumonoderma, 173 Podocyst, 136 Polycera, 177 Polyconites, 272 Polygyra, 187 Polyplacophora, 41 Polytremaria, 147 Pomatias, 152 Pomatiopsis, 153 Pompholyx, 185 Pontiothauma, 166 Popanoceras, 335 Porcellia, 147 Poromya, 278 Porostomata, 178 Posidonomya, 261 Potamides, 154 Poterioceras, 333 Praecardium, 256 Prasina, 261 Prionodesma, 254 Proctonotus, 179 Prodissoconch, 246 Proneomenia, 60 Pronucula, 255 Proparamenia, 60 Propilidium, 145 Prorhipidoglossa, 12 Prorhipidoglossomorpha, 1 Proserpina, 151 Prosiphonata, 335 Prosobranchia, 142 Prosocoelus, 264 Protobranchia, 254 Protomya, 256 Provineulum, 213 Pruvotia, 60 Psammobia, 273 Pseudamussium, 262 Pseudedmondia, 265 Pseudodon, 268 Pseudokellya, 271 Pseudolamellibranchia, 253 Pseudomarginella, 34, 165 Pseudomelania, 154 Pseudomonotis, 261 Pseudopallium, 67 Pseudovermis, 179 Ptenoceras, 333 Pterinea, 261 Pteroceras, 155 Pteropoda, 170, 173 Pterosoma, 163 Pterotrachea, 163 Pterygioteuthis, 339 Ptychoceras, 335 Ptychodesma, 262 Ptygmatis, 154 Pugnus, 168 Pulmobranchia, 107 Pulmonata, 181 Pulsellum, 204 Punctum, 188 Puncturella, 149 Pupa, 188 Pupillia, 149 Purpura 165 INDEX Purpurina, 152 Pusionella, 166 Pustularia, 157 Pyramidella, 158 Pyramidula, 188 Pyrula, 157 Pythina, 265 Quadrifora, 208 Quadrula, 268 Rachiglossa, 164 Radiolites, 272 Radsia, 54 Radula, 6 Raeta, 270 Ranella, 157 Rangia, 267 Rapa, 165 Rapana, 165 Rathouisia, 189 Recluzia, 156 * Requienia, 271 Resilium, 213 Retractor muscle, 5 Retrosiphonata, 334 Retusa, 168 Rhabdoceras, 335 Rhacophyllites, 335 Rhinophore, 18 Rhipidoglossa, 145 Rhizochilus, 165 Rhodea, 188 Rhombopteria, 261 Rhopalomenia, 60 Rhyncholithes, 299 Rhynchoteuthis, 338 Rhytida, 189 Rimula, 149 Ringicula, 168 Risella, 152 Rissoa, 153 Rissoina, 153 Rossia, 340 Rostanga, 178 Rostellaria, 155 Rudistae, 272 Rumina, 82 Runcina, 169 Sabatia, 168 Saccata, 1 Sagda, 187 Salpingostoma, 147 Sanguinolaria, 273 Saxtcava, 274 Scacchia, 266 Scaeurgus, 343 Scalaria, 158 Scaldia, 265 Oo Scalenostoma, 158 Scalites, 152 Scaphander, 168 Scaphites, 336 Scaphopoda, 197 Scaphula, 258 Scarabus, 184 Scenella, 145 Schismope, 147 Schizobrachium, 173 Schizochiton, 54 Schizodentalium, 204 Schizodus, 259 Schizoglossa, 189 Schloenbuchia, 335 Scintilla, 266 Scioberetia, 266 Scissurella, 147 Scolecomorpha, 54 Scrobicularia, 270 Scurria, 145 Scutum, 149 Scyllaea, 175 Sequenzia, 156 Selenites, 186 Semper’s organ, 91 Senilia, 258 Sepia, 340 Sepiadarium, 340 Sepiella, 340 Sepiola, 340 Sepioloidea, 340 Sepioteuthis, 342 Septa, 82, 292 Septaria, 150 Septibranchia, 277 Septifer, 259 Shell-eyes, 50 Stbirites, 335 Sigaretus, 156 Stlenia, 278 Siliqua, 274 — Siliquaria, 155 Siphon, 209 Siphonaria, 185 Siphonodentalium, 204 Siphonopoda, 1 Sistrum, 165 Sitala, 187 Skenea, 153 Smaragdinella, 168 Solarium, 158 Solen, 274 Solenaia, 268 Solenochlamys, Solenoconcha, 197 Solenocurtus, 274 Solenogastres, 54 Solenomya, 255 Solenopsis, 256 Solenopus, 54 23 354 $$$ Solenotellina, 273 Solidula, 168 Spadix, 323 Spatha, 268 Spekia, 154 Spermatophore, 128, 323 Sphaenia, 273 Sphaerium, 267 Sphyradiun, 188 Spicula, 42 Spinigera, 155 Spira, 81 Spiraculum, 152 Spirotropis, 91 Spirula, 338 Spirulirostra, 337 Spondylus, 262 Spongiobranchaed, 173 Spongiochiton, 53 Sportella, 266 Standella, 274 Stavelia, 259 Stenoglossa, 163 Stenogyra, 188 Stenoplax, 58 Stenoradsia, 53 Stenothyra, 154 Stephanoceras, 336 Stiliger, 181 Stiva, 153 Stoastoma, 150 Stoloteuthis, 342 Stomatella, 149 Stomatia, 149 Straparollina, 147 Straparollus, 147 Strepsidura, 164 Streptaxis, 189 Streptoceras, 333 Streptoneura, 142 Streptostyla, 189 Strombus, 155 Strophia, 188 Strophomenia, 60 Struthiolaria, 155 Stylifer, 158 Styliger, 15 Stylina, 158 Stylomenia, 60 Stylommatophora, 186 Subemarginula, 149 Submytilacea, 264 Subulites, 154 Succinea, 189 Supra-intestinal ganglion, 113 Sutural lamina, 42 Symplectoteuthis, 338 Synapticola, 266 Synaptorhabda, 253 Syndosmya, 270 INDEX Taenioglossa, 151 Tagelus, 274 Tancredia, 265 Tanganyicia, 154 Tanysiphon, 270 Taonius, 340 Tapes, 270 Tectarius, 152 Tectibranchia, 167 Tegmentum, 42 Teinostoma, 150 Teleodesmacea, 254 Teleoplacophora, 54 Teleoteuthis, 339 Tellina, 268 Tellinacea, 268 Telobranchia, 54 Tentacles, 67 Terebellum, 155 Terebra, 166 Teredo, 275 Tergipes, 179 Test, 28, 240 Testacella, 189 Tethys, 175 Tetrabranchia, 332 Teuthopsis, 342 Thalassoceras, 335 Thecacera, 177 Thecalia, 264 Thecosomata, 170 Thermoscopic eyes, 319 Thliptodon, 173 Thracia, 275 Thyca, 155 Thysanoteuthis, 339 Titiscania, 150 Tonicella, 53 Tonicia, 54 Torinia, 158 Tornatellaea, 168 Tornatellina, 188 Tornatina, 168 Torsion (body’s), 74 Toxiglossa, 165 Tracheal lung, 106, 189 Tracheloteuthis, 338 Trachyceras, 335 Trachydermon, 53 Trachyglossa, 343 Trachyodon, 54 Trematonotus, 147 Tremoctopus, 343 Tresus, 274 Triauly, 127 Triboniophorus, 189 Trichotropis, 156 Tridachia, 181 Tridacna, 271 Trifora, 208 Triforis, 154 Trigonia, 258 Trigonochlamys, 186 Trinacria, 258 Triopa, 177 Triopella, 177 Triplaca, 168 Triton, 157 Tritonia, 175 Tritonidea, 164 Tritoniomorpha, 175 Trochoceras, 333 Trocholithes, 333 Trochonema, 150 Trochosphere, 27 Trochotoma, 147 Trochus, 149 Trophon, 164 Tropites, 335 Truncatella, 153 Tryblidium, 145 Tudicla, 164 Tugonia, 273 Turbinella, 164 Turbo, 150 Turbonilla, 158 Turricula, 164 Turrilites, 335 | Turritella, 155 Turtonia, 266 Tyleria, 275 Tylodina, 173 Tylopoma, 152 Typhis, 164 Typhobia, 154 Umbilicus, 80 Umbo, 215 Umbonium, 150 Umbrella, 174 Uncimenia, 60 Uncini, 89 Ungulina, 265 Unicardium, 265 Unio, 268 Uretery, 182 Urocoel, 15 Urocyclus, 187 Urosalpinxz, 164 Vaginua, 190 Valletia, 272 Valvata, 152 Vampyroteuthis, 342 Vanganella, 270 Vanuxemia, 258 Velainiella, 148 Veliger, 27 Velorita, 266 Velum, 27 Velutina, 156 Veneracea, 270 INDEX 355 5 I a EN Venericardia, 264 Viasta, 256 Xylophaga, 275 Venerupis, 270 Voluta, 165 Xylotrya, 275 Veniella, 264 Volutharpa, 73 Venus, 270 Volvaria, 168 F Veranya, 339 Volvatella, 169 Yoldia, 255 Vermetus, 154 Volvula, 168 Verticordia, 277 Vulsella, 260 Zeidora, 149 Vertigo, 188 Zirphaea, 275 Vesicomya, 253 Woodia, 264 Zittelia, 157 Visceral commissure, 16 Zonites, 186 Vitrina, 187 Xenophorus, 155 Zospeum, 188 Viviparity, 21, 131 Xiphoteuthis, 337 Zygoneury, 142 THE END > Printed by R. & R. 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