LIBRARY

UNIVERSITY OF
CALIFORNIA
SANTA CRUZ

A TREATISE ON ZOOLOGY

A

TREATISE ON ZOOLOGY

EDITED BY

E. BAY LANKESTER

M.A., LL.D., F.R.S.

HON. FELLOW OK EXETER COLLEGE, OXFORD; DIRECTOR OF THE NATURAL HISTORV
DEPARTMENT* OF THE BRITISH MUSEUM

PART V

MOLLUSCA

BY

PAUL PELSENEER, D.Sc.

Reprint A.ASHER & CO. Amsterdam 1964

TEEATISE ON ZOOLOGY

EDITED BY

EAY; ^ANKESTER

M.A., LL.D., F.R.S.

HON. FELLOW OF EXETER COLLEGE, OXFORD ; DIRECTOR OF THE NATURAL HISTORV
DEPARTMENTS OF THE BRITISH MUSEUM

PART V

MOLLUSCA

BY

PAUL PELSENEER, D.Sc.

LONDON

ADAM & CHARLES BLACK
1906

Exclusive Agents for U.S.A.
STECHERT-HAFNER SERVICE AGENCY, INC.

31 East 10th Street
New York, New York 10003

Sole agents for India:

Today & Tomorrow' s Book Agency,

22-B/5, Original Road, Karol Bagh,

New Delhi-5

PEEFACE

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.

E. KAY LANKESTEK.

December 1905.

CONTENTS

CHAPTER I

I'AGK

THE MOLLUSCA ... 1

CHAPTER II

THE AMPHINEUBA .-•'". . U-.. 40

t

CHAPTER III
THE GASTROPODA . . . . 66

CHAPTER IV

THE SCAPHOPODA . . . . , .197

CHAPTER V

THE LAMELLIBRANCHIA . . . . .205

CHAPTER VI

THE CEPHALOPODA . . . . . . 285

INDEX 347

CHAPTER I

THE MOLLUSCA

PHYLUM MOLLUSCA, CUVIER

PALLIATA, Latreille; MALACOZOA, de Blainville; HETERO-
GANGLIATA, Owen ; OiocARDiA, Haeckel ; SACCATA, Hyatt).

GRADE A. ISOPLEURA (Ray Lankester).
CLASS I. AMPHINEURA (von Jhering).
Order 1. Polyplacophora.

,, 2. Aplacophora.

GRADE B. PRORHIPIDOGLOSSOMOUPHA (Grobben).
CLASS I. GASTROPODA (Cuvier).
SUB-CLASS 1. STREPTONEURA.
Order 1. Aspidobranchia.
„ 2. Pectinibranchia.

SUB-CLASS 2. EUTHYNEURA.
Order 1. Opisthobranchia.

„ 2. Pulmonata.

CLASS II. SCAPHOPODA (Bronn).
(No Orders.)

CLASS III. LAMELLIBRANCHIA (de Blainville).
Order 1. Protobranchia.
„ 2. Filibranchia.
„ 3. Eulamellibranchia,
„ 4. Septibranchia.

GRADE C. SIEHONOPODA (Ray Lankester).
CLASS I. CEPHALOPODA (Cuvier).
SUB-CLASS 1. TETRABRANCHIA.

„ 2. DlBRANCHIA.

Order 1. Decapoda.
„ 2. Octopoda.

1 i

THE MOLLUSC A

I. 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 us are demonstnibly related to one another.

More recently H. von Jhcring propounded the view that this
assemblage of animals, believed to be closely related to one another,
was in fact unnatural, heterogeneous, and polyphylctic. 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

THE MOLLUSC A

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,

II. THE MORPHOLOGY AND LIFE-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 phlebcedesis (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. 56t*, g, i, 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 i&
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. Phyllirhoe 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

THE MOLLUSC A

mineral constituent is carbonate of lime, but from 1 to 2 per cent of
phosphate of lime is also present, and traces (less than \ 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

it

vt.

.£

Young embryo of Purjwra lapillus, from the left side, x 16. a, anus ; /, foot ; m, mouth ;
of, otocyst ; yi.a.c, post-unal 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 (Hipponyx)
or free (Argonauta).

The shell was for a long time the criterium of Molluscan
classification. But the progress of anatomical study showed that

THE MOLLUSC A

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, e'), 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 Pleurobranchus 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

THE MOLLUSC A

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 Digestive Trad. — 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 Entosiphon ; the alimentary tract is rudimentary in
the parasites Entocolax and Entoconcka ; it is absent altogether in
Enteroxenos.

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 Nautiliis.

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 MOLLUSC A

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
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
on either side of the central in almost
all Cephalopods (3.1.3). In the
Gastropods the number of teeth in
each row varies considerably in the
different sub-groups. The radular
ribbon issues from a pharyngeal
caecum, in which it is secreted, and
is applied to the surface of paired
cartilaginous pieces situated on the
floor of the buccal cavity. These
so-called cartilages have a charac-
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, etc.

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 Polyplacopho: » , but in other
forms they are generally differentiated into ferment cells and
excretory cells. From the physiological point of view this gland is

FIG. 2.

Transverse rows of the radula. A,
JioivochitoH ntber ; R, Natim dou&t; L\
I'ulselluin tf.tragonutn : D, Hossiii glau-
copis ; all much enlarged, c, central
tooth ; 7, lateral teeth ; m, marginal
teeth. (After G. (). Sars.)

THE MOLLUSC A

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 (Nassopsis) 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 Dentalium, 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 diret-, 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 MOLLUSC A

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

Fio. 3.

Diagram to show the relations of the heart in the Molluscs. A, part of the dorsal vascular
trunk and transverse trunks of a Chaetopod worm ; If, 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) ; a/, arteria abdominalis ; v, ventricle. Tho 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 Molluscs
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 M

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 sal ?8.i)ect. i, left anterior anricuio-

& ^ ventricular communication ; II, ven-

18 much reduced, Or may be aborted, tricle; III, right anterior afferent

as is the case in the majority of Gas- Sent vessels -, Vvnrieft ^urtcio'

trrmork /Fio- 3 TT\ VIII, left posterior auriculo- ventricu-

S ^lg. 6, &). lav communication.

Primitively a single, morphologically

anterior aorta is given off from the ventricle, and this condition
persists in the Amphineura and in the archaic Lamellibranchia.

FlO. 4.
Heart of Chiton pellis-serpentis, dor-

io THE MOLLUSC A

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 (Planoi'bis) or
may be localised in haematids (red blood corpuscles). These are
present in Pectunculus, Area, Ceratisolen [Lankester], Porvriiya, 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 MOLLUSC A

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,

FIG. 5.

Diagram* of transverse sections of the ctenidia of various Mollusca. I, Chiton ; II,
Pleurotvrnaria ; III, Trochus; lV,Nucula; V, Nautilus; VI, Chaetoderma ; VII, Haliotis; VIII,
Lacuna ; IX, Solenomya ; X, tiepia. a, afferent vessel ; e, efferent vessel ; pa, mantle.

as in Gastropods and Lamellibranchs. They are shorter in Nucula
than in Area; shorter in Area (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 ctenidium
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 MOLLUSC A

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
"lung."

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-pericardiul 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 Trochus, Solenomya, etc. (Fig. 5bis, g, i) • 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 Lk "lelli-
branchs and in the Scaphopods that the two distinct branches of
this duct become longer (Fig. 5 u\ j) ; then the common duct dis-
appears, and the gonad opens directly into the renal sac (Fig.
5** h, k).

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 ofily 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 Dentalium. 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).

THE MOLLUSC A

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

in

in

Fin. 5«">.

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 ; /, Prorhipidoglossum ; g, some Rhipido-

?loss& (KmcirqinHla, etc.); A, specialised Gastropod ; t, Protobranch Laniel li branch ; j, Pecten ;
, 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 Lainellibraiirhs.

THE MOLLUSC A 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 Cydostoma, 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."

1 6 THE MOLLUSC A

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 Molluscs 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 Molluscs
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 Molluscs :
(I) 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 MOLLUSC A 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
rgans, is. of great importance to the morphologist, and the more so
oecause 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, etc.) or at the
origin of important nerve trunks (Fig. 159, i). 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, etc.
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 Chitony
Fig. 24). These elements are particularly numerous in the most
exposed parts, such as the cephalic tentacles of Gastropods, the

18 THE MOLLUSC A

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 opcic nerve. The osphradia
(Ray Lankester) are situated near the entrance to the pallial cavity
(Figs. 58 and 89, 0s; 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 Jined 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 suoplying 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 otocrypts, 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 Molluscs
their equilibrium.

Tlie 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, Oncidiwn, 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 Nautilus (Fig. 6, A), or with a crystalline lens, as in Pleuroto-
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

Co.ep C

•^' •*••*** T-_

Int*

FIG. 6.

Diagrams of sections of the eyes of Mollusca. A, Nautilus ; B, Gastropod (Umax or Helix) 'r
C, Dibranchiate Cephalopod (Oigopsid). Co, external cornea ; Co.ep, internal cornea ; G.op,
optic ganglion ; Int, Infl, Intf, Infi, different parts of the integuments ; Ir, iris ; I, crystalline
lens ; i1, 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 Grenadier.)

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 dermatoptia
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 (Euthyneura), in some genera of Streptoneurar
in one order (Anatinacea), and in some isolated species of Lamelli-

20 THE MOLLUSC A

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, /). It has been shown that in the Cephalopods
hyperpolygyny is the rule, and in certain Atlantae 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. 5W*, d • 30, C) and the Cephalopoda (Fig.
56t'*, b). 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 (Trockus, Fig. 55 ; Solen&mya),
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 Khipidoglossa, 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
MMi puiuduia °* Polyplacophora, and of the Lamellibranch
The male in situ on Pseudokellya (Fig. 220) are invested by a continuous
the S&4I3& Sr cellular follicle. In hermaphrodite Molluscs the
fJniaieTwt'maiie2' f' 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

THE MOLLUSC A 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 (Vermetus, etc.), among freshwater Gastropods
(Melania, etc.), and even among the octopodous Cephalopods (Argo-
iiauta), but the number of truly
viviparous forms is very small.
Callistochiton among the Amphi-
neura and several genera of
aquatic and pulmonate Gastro-
pods are the only instances. Fia 8-

TliP rmmhpr nf PO-O-<S lairl i« vprv Stcnogjira mamillata, left side view, with four
t eggS laid IS Very embryos in the oviduct, em, embryo.

variable. It is always greater in

the case of those marine Molluscs 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 Ostraea 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 (Litliffo, 40,000), and pelagic Gastropods
(Cymbul-ia, 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 Vermetux, 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 MOLLUSC A

Limnaea, 20-100 eggs; Helix, 40-100; Ancylus, 5 or 6; Valvata,

1 7 ; Neritina, 50-60. Lastly, the number of eggs is small in

viviparous forms: in Pabulina there are about 15; in Subulina
{Fig. 8) there are 4.

III. EMBRYOLOGY.

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, etc.).
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 fche eridodermic cells,
called endomeres or macromeres. In the more primitive forms,
however, such as Patella (Fig. 9, A), and the Protobranchia, there is

FIG. 9.

Eggs of various Mnllusca, at the sain« stago, with 4 micromeres. A, I'att'Uu (Patten); /?,
Lacuna; C, Teredo (Uatschek) ; D, Sepia (Kolliker). ««i, 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 Paludma, 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 piimary
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, anH
Lamellibranchs (Teredo, Fig. 9, C, Cyclas, Unionidae), in which there

THE MOLLUSC A 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, Dreisscnsia,
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, W).

Formation of the Digestive Cavity ami 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 endoderrn.
But the formation of this double-walled sphere, the diblastula or

Fio. 10.

Two types of gastrulae. A, invaginate or einbolic (Chiton : after Kowalewsky) ; /,', epibolic
(Cifjndula : after Conklin). W, blastopore ; ec, ectoderm ; en, entoderni.

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, much as 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), Paludiiui, the Pulmonata, the
Nudibranchia, the Pteropoda, the Gymnosomata and Limacinidae,
the Scaphopoda, Nacula, Ostraea, 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 in vagina ted into the layer of micromeres. In
such case the micromeres as they multiply grow round the

24 THE MOLLUSC A

cndoderm and gradually surround it, leaving at the nutritive pole
an orifice, which is the blastopore. Examples of this mode of
formation are — Many streptoneurons Gastropoda (Trochus, Vermetus,
Crepidula, Fig. 11, Janthina), the majority of the Rachiglossa
(Columbella, Fusus, Nassa, Purpura, Urosalpinx), the Tectibranchs
(Acera, Pkiline, Aplysia, Thecosomata), and many Lamellibranchs
(Pecten, Modiolaria, Cardium, Teredo, etc.). 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, etc.,
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 : Nassa,
Purpiim, Fiung, etc. ; Tectibranchia : Accra, Aplysia, Carolinia, etc.),
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 Nasm 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 Molluscs the liver

THE MOLLUSC A 25

is formed from the wall of the enteron, generally as a pair of
diveVticula 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, III), Bithynia, various Opisthobranchs,
such as Aplysia and Nudibranchs, in basommatophorous Pulmonates,
Cydas, 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

Km. 11.

Eggs of Crepidula, showing tlin origin of the Hrst mesolermic cell. »»»«, macromeres ; »iesf
first niesodermic cell ; mi, inicroiueres. (After (Joiiklin.)

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,
Natica, Lamellaria, and Crcpidida ; Opisthobranchs : Aplysia,
various Pteropods and Nudibranchs ; Lamellibranchs : Cyrenidae,
Unionidae, Dreissemia, 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
VcrmetuS) Fusus, and Heteropods ; Pulmonata ; Dentalium ; Nucula ;
Ostraea.

26

THE MOLLUSC A

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, etc., are formed.
Thus the blastopore, if it
remains open, does not
become the mouth of the
adult. Paludina, however,

is an exception, in

that

Fio. 1-2.

Trochosphere of Patella,, sagittal section. W, blasto-
pore ; me, mesoderm ; sh.g, shell-gland ; the two dorsal,
ve, and the two ventral ciliated cells are the velar
cells. (After Patten.)

the whole of the blasto-
pore remains open and be-
comes the anus (Ray Lan-
kester), whilst the stomo-
daeum is formed at the
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 bhistoporic 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.

Ectodermic 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 properly

SO Called, SUCh as the foot,
,1 i ,1 ;j.

tne mantle, and the cteinclia,
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

FIQ. 13.

Trochosphere of Dreissensia, median sagittal section.
lil, blastopore; /!, flafpllnm ; in, intestine; p.a.c,
]>ost-anal cilia ; sh, shell ; «r, velum. (After Meiseu-

THE MOLLUSCA

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. U, 113), Dentalium

Fio. 14.

Three Trochospheres of Moll usca. A, /sc/t/ioe/uton, (Heath); B, Patella (Patten); C, Dreisscnsia
(Meisenheimer). a, anus ; /, foot ; fl, flagellum ; m, mouth ; p.a.c, post-anal cilia ; sh, shell;
of, 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 reucttt
for a greater or less distance

towards the posterior end Trochosphere of Dr»taZtK»i,sagittal median section,
nf thp Atnhrvn honnrrnno- w> blastopore ;fl, flagellum ; in, intestine ; /*<, mantle
emDryO, DeCOming Or shell-glaml ; w, velum. (Alter Kowalewsky.)

attached to it in such a

manner as to form a more or less extensive superficial investment

furnished with multiple ciliated rings, as in Dentalium (Figs. 15,

FIG. 15.

28 THE MOLLUSC A

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. il9, D; 257, 290,
291 ; Cyclas, Entovalva, etc.) or there is no free veliger, but a more
or le*ss 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 Pwpura (Fig. 1), among Gastropods, and Dreissensia

FIG. 1C.

Trochosphere of Yoldia, median sagittal section, a.a, anterior adductor muscle ; ap, apical
plate ; bl, blastopore ; c.0, cerebral ganglion ; fl, flagellum ; h.a, posterior adductor; in, intes-
tine ; li, liver ; ml, stomodaeum ; t, " test" or reflected velum, with 3 circlets of cilia. (After
Drew.)

(Figs. 1 3, 1 4, p.a.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 MOLLUSC A

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 imagination 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 secrete the shell.

The branchiae or denidia 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 N. //

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-

FIG. 17.

Trochosphere of Myzojnenia banyulensis.
A, after 36 hours ; B, after 100 hours, fl,
flagellum ; «?, velum. (After Pruvot.)

r.l

FIG. 18.

Veliger of Littorina, ventral view, x 80.
e, eye ; /, foot ; m, mouth ; ma, mantle ;
pa.e, pallial cavity ; r.l, right liver lobe ; s,
stomach ; t, 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, etc., 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. 1 1 9, D) ; in Gastropoda : in the
Aspidobranchs, Paludina, Bithynia, Calyptraea, Crepitlula, Nassa, the
Heteropoda, and the Pulmonata. The otocj'sts only are formed

30 THE MOLLUSC A

by invagination in some other Gastropods (Fusus), and in Dentalium
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 Aspidobranchg (Patella, Fig. 1 2, me; Trochus, Neritina\ the Pectini-
branchs (Paludina, Bithynia, Crepidida, Fulgur, etc., and seemingly the
Heteropoda), the Opisthobranchs (Philine, Umbrella., Aplysia, Clionc,
Chronwdoris, etc.), the basommatophorous and stylommatophor-
ous Pulmonates, the Scaphopods, the Lamellibranchs (Pisidium,
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 tne coelom does not originate by the invagination
of enterocoelic pouches (Tonniges 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 (Paludina, 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 MOLLUSC A 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, etc.

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 (JBithynia, Limax, Cyclas, 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 Molluscs 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 (Pulmouata, Cyclas,
Dreissensia, etc.), 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 Mollies 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 Trodms
among the Aspidobranchs ; fourteen hours in Yoldia among the

32 THE MOLLUSC A

Lamellibranchs ; twenty-four hours in PJtolasy etc. 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 )F 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, etc. 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.

Fio. 19.

Scheme of a primitive Mollusc, viewed from the left side, a, anus ; c.g, cerebral ganglion ;
/, foot ; g; gill, in the pallial cavity ; 0o, .gonad ; h, heart ; k, kidney; la.c, labial commissure ;
m, mouth ; pa, mantle ; pa.n, pallial nerve ; pe, pericardium ; p.g, pedal ganglion ; pl.g,
pleural ganglion ; ra, radula ; r.p.o, reno-pericardial orifice ; st, stomach ; st.gr, 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 MOLLUSC A 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 ext~-^al
face a calcined 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. BIONOMICS 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 (Limnaea) 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, e.g. Modiolaria ; some with Echinoderms, as Montacuta,
Lepton, and Scioberetia ; some with Crustacea, Lepton squamosum and
Ephippodonta, or with Sponges (Fulsella), or Annelids (Cochliolepis).
Others again are ectoparasitic on Echinoderms, such are Tliyca and

3

34

THE MOLLUSC A

Stylifer (Fig. 20) ; or, like Eulima 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 Mpllusca. 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,
Lamellarta, etc.), in which the

Fio. 20.

Stylifer celebensis, x 12. pr, pro-
boscis ; ps, pseudopallium ; sp, spire
of the shell not covered by the pseudo-
pallium. (After Kiikenthal.)

Fio. 21.

Entosiphon dnmatis, x 2. o, orifice
of the proboscis ; ov, ova ; pr, pro-
boscis ; ps, pseudopallium ; s, fixative
siphon. (After Koehler and Vaney.)

individual assumes the colour and aspect of its habitat, as for
instance Hermaea dendritica on green algae, and Hennaea 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
vnd Petricola pholadiformis among Lamellibranchs.

The duration of life in individual Molluscs is ordinarily rather
short. Marine Streptoneura may live for several years, and Littorina
littorea, when in captivity, has attained an age of nearly twenty
years. Freshwater Molluscs may live for eight years (Paludina).

THE MOLLUSC A

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; Ostraea edulis is sexual at two years,
becomes adult in five years, but may live for ten years in oyster-
beds. The huge Tridacna 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 Rossia 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, Felutina, Onchidiopsis, Solariella,
Machaeroplax, Volutliarpa, Toi'ellia, Cyprina, Mya. ft. The South
Polar province, with the characteristic genera PJwtinula, 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 Trigonia, 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 Monoceros, Condwlepas, 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 MOLLUSC A

northern and southern parts of the same ocean or in several
different oceans. Thus Limopsis aurila, Semele profundorum,
Ferticordia deshayesiana, Area 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, Hyalopecten, 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 Spongiobranchaea australis, Limacina antarctica. /3. The
zonary or deep forms are probably more universally distributed,
but are still imperfectly known; they include the luminous
Cephalopoda.

II. 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, Dreissensiidae,
Unionidae, Aetheriidae (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,Ampullariidae,Hydrobiidae, Melaniidae ;
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 F'aginula, Helicina, Ampullaria, etc. 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 MOLLUSC A

37

Molluscs 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 Molluscs 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 ; t', Gastropoda ; D, hamellibranchia ; E, Cephalopoda, a, anus ; a.a, anterior adductor ;
c.fif, cerebral ganglion ; /, foot ; /«, funnel ; </, 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 MOLLUSC A

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
Pyramid ellidae, 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.

1. Cooke. Molluscs. The Cambridge Natural History, vol. iii. 1895.

2. FiscJier. Manuel de Coiichyliologie, 1887.

3. Jeffreys. British Conchology, 1862-1869.

4. Simroth. Mollusca. Bronn's Klassen und Ordnungen des Thierreichs,

Bd. iii. 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.

II. Morphological.

7 bis. Cuenot. L'excre"tion chez les Mollusques. Arch. d. Biol. t. xvi. 1899.

8. Qeddes. On the Mechanism of the Odontophore in certain Mollusca. Trans.

Zool. Soc. London, vol. x. 1879.

9. Huxley. On the Morphology of the Cephalous Mollusca. Phil. Trans. 1853.

10. von Jhering. Vergleicheude Anatomie des Nervensystemes und Phylogenie

der Mollusken, Leipzig, 1877.

11. Die Gehbrwerkzeuge der Mollusken, Erlangen, 1876.

12. Zur Morphologic der Niere der sog. " Mollusten. " Zeitschr. f. wiss.

Zool. Bd. xxix. 1877.

13. Lankcster. Mollusca. Encyclopaedia Britannica, 9th edit. vol. xvi. 1883.

14. 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 MOLLUSC A 39

16. Milne- Edwards. Observations sur la circulation chez les Mollusques. Ann.

d. Sci. Nat. Zool. se>. 3, t. viii. 1847.

17. Maynier de Villepoix. Recherches sur la formation et I'accroissemeut de la

coquille des Mollusques. Journ. Anat. et Phys. 1892.

18. Pelseneer. Introduction a 1'Etude des Mollusques, Bruxelles, 1894.

19. — — Recherches morphologiques et phyloge'ne'tiques sur les Mollusques

archai'ques. Mem. Cour Acad. Belg. t. Ivii. 1899.

20. Hermaphroditism in Mollusca. Quart. Journ. Micr. Sci. vol. xxxvii.

1895.

21. Plate. Bemerkungen iiber die Phylogenie und die Eutstehung der Asym-

metric der Mollusken. Zool. Jahrb. (Anat. u. Ontog.), Bd. ix. 1895.

22. Schiemenz. Ueber die Wasseraufnahme bei Lamellibranchiaten und Gastro-

poden. Mitth. Zool. Stat. Neapel, Bd. v. 1884, and vii. 1887.

23. Spengel. Die Geruchsorgaue und das Nervensystem der Mollusken.

Zeitschr. f. wiss. Zool. Bd. xxxv. 1881.

24. Thiele. Die Systematische Stellung der Solenogastren und die Phylogenie

der Mollusken. Zeitschr. f. wiss. Zool. Bd. Ixxii. 1902.

CHAPTER II

THE AMPHINEURA

CLASS L— AMPHINEURA, VON JHERING (1876)
( = ISOPLEURA, Ray Lankester ; ACULIFERA, Hatschek).

Order 1. Polyplacophora (Chi tones).
Sub-Order 1. Eoplacophora.

Family 1. Lepidopleuridae.

Sub-Order 2. Mesoplacophora.

Family 2. Ischnochitonidae.
„ 3. Mopaliidae.
., 4. Acanthochitonidae.
„ 5. Cryptoplacidae.

Sub-Order 3. Teleoplacophora.
Family 6. Chitonidae.

Order 2. Aplacophora.

Sub-Order 1. Neomeniomorpha.
Family 1. Lepidomeniidae.
„ 2. Neomeniidae.

.. 3. Proneomeniidae.
,, 4. Parameniidae.

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 Chaetodernui 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 k-eintroduced into the

40

THE AMPHINEURA 41

phylum Mollusca by Spengel, Hubrecht, Lankester, etc., and even
von Jhering has since admitted this interpretation. Although
Gegenbaur and Glaus 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 Acanthochitori) or even wholly (in adult Cryptochiion,
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 : (a) 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
FIG. 23. outer layer into the substance of the mantle,

Young Toniciafastigiata, f wHinVi if - io firmlv ntfjipVipH ThpQP r»r<S
Gray, dorsal aspect, show- to WHlCn It IS nrmly attaCHCd.

ing the s first shell-eyes, i, jections of the outer or peripheral margins

first shell -plate; II, the J if,..

first eyes on the second of the valves are termed "insertion plates ;
!h2i-pfit?; 1H> thirl 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 Acantlwchiton 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
"girdle," as it is called, is covered with chitinous or calcareous
spicules of various shape, acicular or squamose. Each 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

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,

y|«tx

Fio. 24.

Transverse section of the lateral portion of the pallial teguments of Chiton. I, tegmentum :
II, articulainentum ; III, pallial epithelium under the shell ; IV, epithelium of the margin of
the mantle ; V, spicula ; VI, cuticle of the mantle-margin ; Via, periostracum ; VII, megal-
aesthetes ; VIII, micraesthetes. (After Blumrich.)

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. Each 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

VII

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 (Trachydermon).
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 lie 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, lie
two ver}' small mucous glands
close to one another and to the
middle line. On either side, at
the point where the pharynx
passes into the short oesophagus,
is the opening of the sugar
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

Fio. 25.

Jioreochiton cinereus, dorsal view of a female,
without the shell-plates. I, first " intersegmen-
tum " ; II, ovary; III, oviduct; IV, ventricle
of heart; V, dorsal right muscle; VI, dorsal
oblique shell-muscle; VII, retractor muscle of
the radula.

Fio. 26.

Cryptoplax larvae for mis, left-side view, the posterior end partially opened. I, gonad ; II,
genital duct; III, genital pore ; IV, ventricle of heart; V, anus; VI, renal ]>ore ; VII, gills;
VIII, foot; IX, mantle ; 0, 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 (Hatileyd). The intestine is very long, as
is usual in phytophagous animals, and is thrown into numerous

THE-AMPHJNEURA 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 Tonicella, 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 Acantlio-
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-

Vkranr-Viifll t\rr\p in wVnVVi thpv Heart of Mopalia, dorsal aspect. I, auricnlo-

Drancmal type, m wnicn tney ventricular communication ; II, ventricle; III, right

are Confined tO a more Or auricle ; IV and V, afferent vessels ; VI, mantle ; 6, 7,

, . . , 8, indicate the position of the sixth, seventh, and

less limited space at the pos- eighth sheii-piates.
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 AMPH1NEURA

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 trifurcated. Each 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-

Fio. 28.

Ventral aspect of three species of Polyplacophora, showing the various sorts of gill-rows.
A, Lepidopleurus bcnthus; B, Boreochiton cinerens ; C, Schizochiton incisus. a, anus; /, foot;
0, 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-
br,anched 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 Nuttakchiton, 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

FIG. 20.

Renal .organs of Boreovhiton cinereiis, 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 ; II, mantle ; III, external ramifications of the
antero-posterior (or terminal) renal part ; IV, 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 III ;
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 AMPH1NEURA

The two ventral or pedal cords are united beneath the digestive
tract by numerous transverse anastomoses. The two lateral or

V

Fio. 30.

Diagrams of the excretory and reproductive organs of Ainplmienra. C, Proneomenia; D,
Chiton. Br, ctenidia; Cl, cloacal or pallial chamber of 1'roneomenia ; g, external aperture of
the genital duct of Chiton ; N, renal organ ; 0, gonad ; P, pericardium ; r, rectum ; «, external
aperture of renal organ of Chiton. (From Lankester, after Hubrecht.)

pallial cords are united posteriorly,
dorsad of the anus, by a thick supra-
rectal commissure (Fig. 31, VIII).

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-gastric
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-

i, mantle; ii, mouth; ill, foot; iv, ular commissure. The subradular

gills ; V, anus ; VI, right renal pore ; VII, .. . ,.

right genital pore (these two pores are Commissure supplies a pair of ganglia
better 8een on the left-hand 8i5e of the which are jn dose 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.

VI

Fio.

Ventral aspect of Acanthoplet
i ; III,

THE AMPH1NEURA

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

pleural ganglia and the pallial
^^ nerves of the other Mollusca;

a great part of the viscera
(genital glands, kidneys, and
heart) also receives nerves from
these pallial cords.

The little differentiated
head region bears no special
sense-organ, except that the
outer edges of the snout taper
to form the labial palps. The
lower wall of the buccal cavity
is furnished with cyathiform

gustatory bodies, whose nerves
arise from the cerebral commis-

xn

XI

Fio. 81.

Nervous system of Acanthochiton dis-
crejxins, dorsal aspect. I, upper buccal
commissure ; II, upper buccal ganglion ;
III, stomato-gastric commissure ; IV, labial
commissure ; V, subradular ganglia and com-
missure ; VI, anterior (larger) pedal commis-
sure ; VII, peflal cord, with pallio - pedal
anastomoses ; VIII, supra-rectal pallial com-
missure ; IX, pallial cord; X, pedal anas-
tomosis; XI, stomato-gastric ganglia and
radular nerves; XII, oesophageal nerves;
XIII, cerebral commissure.

Placiph&rdla stimpsoni, ventral aspect ;
nearly natural size, a, anus ; ci, pallial
cirrhi ; g, gills (between the two rows of
gills is the oblong foot) ; w, mouth ; jm,
mantle ; te} tentacles of the interior edge
of the mantle. (After Plate.)

sure ; and, in front of the radula, there is the above-named " sub-
radular organ," an epithelial projection, with nervous endings, lying
on the two small subradular ganglia, and probably gustatory in
function (Fig. 31, V).

4

THE AMPHINEURA

One osphradium is generally present on each side of the internal
wall of the mantle, near the anus, more or less close to the last
gill. In the Lepidopleuridae there are branchial sense-organs,
related to accessory ganglia on the nerve of each gill (Burne). In
Pladphorella the lower free margin of the mantle bears, in its
anterior part, several long and thin appendages, which must be
considered as sensory tentacles (Fig. 32).

Shell-Eyes. — The tegmentum of the shell-valves is traversed "by
peculiar pallial sense-organs in the form of epithelial papillae,
containing nerve -endings covered with a cuticular hood. These
organs are innervated from the pallial 'cords. According to their
size, they are termed megalaesthetes or micraesthetes (Moseley).
In various species of Chitonidae (and specially in exotic littoral
forms of the sub -families Toniciinae and Liolophurinae), the
megalaesthetes are converted into eyes, in which retina and pig-
ment are always present. These eyes are frequently many
thousands in number, and are most numerous on the anterior
valve (Fig. 23, I). There are two kinds of such eyes: (1) Extra-
pigmental eyes, with pigment in the tegmentum only, generally

without a crystalline lens (except
Schizochiton incisus) ; (2) intra-
pigmental eyes, with pigment in
the body of the aesthete, and
always with a crystalline lens.
The eyes are arranged in rows
running diagonally from the
median anterior beak of the valve
to its external borders. There
may be only one such row on
either side, as in Schizochiton, or
many such rows, as in Tonicia ;
and in AcantJwpleura, in addition
to the several diagonal rows,
there are rows of eyes along the
posterior margin of the valve, but
these are not present in young
specimens. In Tonicia the first

Axial section of a,shell-eye of Acanthopleura Pair of e7e8 is developed, at the

tpinigtr. I, optic nerve with ganglionic cells ; close Of larval life, On the Second

II, pigmental capsule of the eye; III, teg- . ,. .

inentuiii of the shell; IV, rods of retina; shell-Valve. IheSC Organs are

sensitive to disturbances in the
water, and do not exist when
the mucous projections of the mantle, referred to above, are
present Even those species of Chitons that ;ire devoid of
eyes are affected by light and shade : some littoral species,
such as Boreochiton cinereus, do not move far from the light,

Flo. 33.

V, micraesthetes ; VI, calcareous cornea ;
VII, lens. (After Moseley.)

THE AMPHINEURA

while others, such as hchnochiton magdalenensis, are nocturnal in
habit.

5. Reproductive Organs. — All the Polyplacophora are unisexual.
The gonads are paired and symmetrical in Nuttalochiton hyadesi, but
in all other species the gonad is single and median. It lies on the
dorsal side of the body, between the aorta and intestine, and
extends from the anterior end to the pericardium (Fig. 25, II).
It is transversely wrinkled, and the ovary is frequently of a greenish,
the testis of a red colour (Chiton polii, Boreochiton cinereus, etc.). In
most species the ova are enclosed in a cellular follicle.

The paired genital ducts arise from near the posterior end of
the gonad on the dorsal surface. Each duct is twice bent on itself,,
being directed first forwards, then backwards, and finally transversely
toward the external opening. As a rule the gonaduct runs dorsad
of the pallial nerve-cord, and its external opening is external to the-
cord, but in Boreochiton ruber, B. marmoreus, and Katharina it runs
under the cord and opens internally to it. In the female the
oviduct has a thick glandular investment (Fig. 25, III). The genital
aperture is situated in front of the renal aperture, between two of
the posterior gills. There may be from one (Boreochiton, Lepido-
pleurus, etc.) to nine (Cryptoplax larraeformis : Fig. 26) gills between
the genital and the renal apertures.

III. EMBRYOLOGY.

The eggs may be laid separately, in which case they are invested
by a chitinous envelope fre-
quently provided with spinous
appendages ; or, as in hchnochiton
magdalenensis, they may be laid
in strings containing nearly
200,000 eggs (Fig. 34). These
strings are not attached, and
readily break into fragments.
In many cases the ova are re-
tained in the branchial furrow
of the mother and undergo their
development there (Chiton polii) :
in Hemiarthmm setulosum the
embryos are protected in this
manner until the eighth shell-
valve is formed. In Callistochiton I8chnochiton ^^^ female, iaying

viviparUS the OVa are developed eggs, l"nd part, ventral aspect. /, foot; g.

i . . . . , , ovary ; g.d, glandular oviduct ; o.g, gemtal

in the OVldUCt OI the mother, and orifice ; ov, ova ; pa, mantle. (After Heath.) £

there is no larval stage.

The segmentation is total and, in the early stages, regular.

FIG. 84.

52 THE AMPHINEURA

A gastrula is formed by invagination of the endodermic macromeres
(Fig. 10, A). The orifice of invagination or blastopore is placed
on the vegetative pole of the ovum, and does not close, but is
gradually shifted towards the anterior end of the embryo. By the
development of a ciliated ring or velum, in the centre of which
there is an apical tuft of cilia, the embryo becomes a trochosphere
larva (Fig. 14, A). The mesoderm arises from two endodermic
cells, originally situated at the hinder side of the blastopore : they
give origin to two bands of cells which extend right and left between
the enteron and the ectoderm. In each band a cavity appears
which becomes half of the coelom. The ectoderm around the
blastopore is invaginated to form the oesophagus, a diverticulum
of which becomes the radular caecum. At a late stage of develop-
ment the intestine is placed in communication with the exterior
by an anal invagination or proctodaeum. Anteriorly on the ventral
or pedal surface a second ectodermic invagination forms the great
pedal mucous gland, which is more or less atrophied at a later
period. The gills appear as papillae much later than the anal
invagination, the posterior one the first. The gonads originate by
proliferation of the anterior wall of the pericardium.

The four great nerve-cords originate as four longitudinal and
parallel ventral thickenings of the interior surface of the ectoderm,
the two thickenings on each side of the body being closely approxi-
mated to one another at the time of their first appearance. At
the extreme anterior end of each lateral or pallial cord and behind
the velum is an eye, containing a closed cavity, or forming a
simple epithelial ocellus. This eye disappears at a later stage, but
in some species persists for a considerable length of time.

The shell-valves are formed as transverse thickenings of the
dorsal cuticle behind the velum, the tegmentum being the first
part of each valve to be laid down. The eight valves generally
make their appearance simultaneously (Chiton olivaceus, Ischnochiton
magdalenensis), but sometimes the eighth valve is formed later than
the others (Chiton polii).

IV. BIONOMICS AND DISTRIBUTION.

The Polyplacophora are marine animals of sluggish habit,
creeping slowly and for no great distance. They are generally
herbivorous, and the majority of species live in the littoral zone, on
rocks or under stones, but some inhabit the deeper regions of the
sea, extending to a depth of more than 2100 fathoms (some
Lepidopleurus, etc.). They can easily be kept in aquaria. Poly-
placophora are distributed in all oceans and seas ; more than three
hundred living species have been recorded. They are fossil from
the Ordovician.

THE AMPHINEURA 53

V. SYSTEMATIC REVIEW OF THE SUB-ORDERS AND FAMILIES OF

THE POLYPLACOPHORA.
SUB-ORDER 1. EOPLACOPHORA, Pilsbry.

Tegmentum coextensive with articulamentum, or the latter projecting
in smooth, unslit plates.

FAMILY 1. LEPIDOPLEURIDAE, Pilsbry. Articulamentum without
insertion plates or with unslit plates ; terminal margins of end valve&
never elevated ; form oval or oblong. Genera — Lepidopleurus, Risso
( = Leptochiton, Gray) (Fig. 28, A). Without insertion plates, sutural
laminae small ; girdle minutely scaly or chaffy. L. cancellatus, Sow.
North Atlantic and Mediterranean ; various abyssal species. Hanleya, Gray.
The anterior valve with an unslit insertion plate. H. hanleyi, Bean. North
Atlantic. Hemiarthrum, Carpenter. Both anterior and posterior valves
with smooth, unslit insertion plates ; girdle downy. Microplax, Adams
and An gas.

To this group belongs the extinct family of GRYPTOCHITONIDAE,
Pilsbry, together with various narrow and elongated Palaeozoic genera,
whose one or two end valves have the terminal margins elevated.

SUB-ORDER 2. MESOPLACOPHORA, Pilsbry.

Insertion plates well developed and slit.

FAMILY 2. ISCHNOCHITONIDAE, Dall. All the valves with slits, and
the inner layer well covered by the outer. SUB-FAMILY 1. ISCHNO-
CHITONINAE. No shell-eyes ; sutural laminae separated ; the slits in the
valves 1 to 7 do not correspond with the ribs of the tegmentum.
Genera — Ischnochiton, Gray. Smooth girdle. Trachydermon, Carpenter
(with the sub-genera : Tonicella, Carpenter, and Boreochiton, Sars). Girdle,
with small squamous spicula. T. cinereus, Linnaeus (Fig. 28, B) ( = T.
marginatus, Pennant). North Atlantic. Chaetopleura, Shuttleworth.
Hairy girdle. Stenoplax, Carpenter. Stenoradsia, Carpenter. SUB-FAMILY 2.
CALLOCHITONINAE. With shell-eyes and united sutural laminae. Genus —
Callochiton, Gray. C. laevis, Pennant. North Atlantic and Mediterranean.
SUB- FAMILY 3. CALLISTOPLACINAE. No shell -eyes ; the slits in the
valves 1 to 7 corresponding with the ribs of the tegmentum. Genera —
Callistochiton, Carpenter (viviparous). Nuttalochiton, Plate.

FAMILY 3. MOPALIIDAE, Dall. Each intermediate valve with a
single slit ; girdle hairy. Genera — Mopalia, Gray. Placiphorella,
Carpenter (Fig. 32). Plaxiphora, Gray. Placophoropsis, Pilsbry.

FAMILY 4. ACANTHOCHITONIDAE, Pilsbry. Valves immersed in the
girdle, and with small tegmentum. Genera — Acanthochiton, Leach
( = Cryptoconchus, Guilding). Girdle with bundles of spicula. A. fasricu-
laris, L. North Atlantic and Mediterranean. Spongiochiton, Carpenter.
Katharina, Gray. Amicula, Gray. Cryptochiton, Middendorf. Valves
quite concealed ; no tegmentum. C. stelleri, Middendorf. Arctic.

FAMILY 5. CRYPTOPLACIDAE, Dall. Vermiform, with thick girdle
and small valves ; insertion and sutural plates strongly drawn forward,

54 THE AMPHINEURA

sharp and smooth. Genera — Cryptoplax, Blainville ( = Chtionellus, Lam.).
•Girdle without pores. C. larvaeformis, Blainville (Fig. 26). Eastern
Archipelago. Choneplax, Carpenter. Girdle, with hair bundles within
pores. C. strigatus, Sow.

SUB-ORDER 3. TELEOPLACOPHORA, Pilsbry.

All the valves, or at least the seven anterior, with insertion plates
cut into teeth by slits.

FAMILY 6. CHITONIDAE, Guilding. Characters of the Sub-Order.
SOB-FAMILY 1. CHITONINAE. No extra-pigmental eyes ; insertion plates
with pectinations between the fissures. Genera — Chiton, L. Squamous
girdle. Eudoxochiton, Shuttleworth. Shaggy girdle. Trachyodon, Dall.
Rcukia, Gray. SUB-FAMILY 2. TONICIINAE. Extra-piginentar shell eyes.
Genera — Tonicia, Gray. Girdle smooth or shaggy (Fig. 23). T. elegans,
Frembly. Acanthopleura, Gould. Enoplochiton, Gray. Squamous girdle.
E. niger, Barnes. Onithochiton, Gray. Schizochiton, Gray. Spinous girdle ;
posterior valve notched. S. incisus, Sow. (Fig. 28, C). Lorica, Adams.
Loricella, Pilsbry. Liolophura, Pilsbry.

ORDER 2. Aplacophora, von Jhering

( = Solenogastres, Gegenbaur = Telobranchia, Keren and Danielssen
= Scolecomwpha, Lankester).

Our knowledge of the Aplacophora begins with Loven, who in
1841 described the genus CJiaetoderma, and with Michael Sars, who
mentions Neomenia in 1868, under the name Soknopus, but without
description. Chaetoderma was for a long time believed to be a
Gephyrean worm ; and Neomenia was at first included among the
Opisthobranchiate Gastropoda in a new Order, Telobranchia, by
Koren and Danielssen.

Von Jhering was the first to point out the affinities of these
two remarkable organisms with the Chitones, and to unite them in
the new phylum Amphineura (1876); but he classed this phylum
with the Vermes. Gegenbaur also classed the two genera CJiaeto-
derma and Neomenia as worms under the name Solenogastres. But
Hubrecht demonstrated the molluscan nature of the new genus Pro-
neomenia, and its relationship to the Chitones. Lankester supported
this view, and was followed by nearly all contemporary zoologists.
It is generally believed that the Aplacophora are degenerate forms
of Amphineura, derived from a chitonoid ancestor.

Definition. — The chief characteristics differentiating the Apla-
cophora from the Polyplacophora are the following : ( 1 ) they are
worm-like in shape ; (2) the body is completely invested by the
mantle ; (3) the mantle is devoid of a shell, but bears numerous
calcified spicula over its whole surface ; (4) the digestive tract is
straight.

THE AMPHINEURA

55

General Description. — The mantle covers the whole body,
and is clothed by a rather thick cuticle, in which are implanted
spicula (Fig. 35) developed from the tegumentary epithelium. The
foot is nearly aborted or wanting. The nervous system consists of
four great longitudinal trunks, with pedal and pedo-pallial anasto-
moses. The digestive tract is straight, the Aplacophora being carni-
vorous. The blood is red. The gonads are in open continuity with
the fore part of the pericardium. The coelomo-clucts, corresponding
to the renal sacs of the Polyplacophora, are gonaducts, and open
externally into a posterior cloacal chamber, which serves as a
rudimentary branchial cavity. There are two groups of Aplaco-
phora : the Neomeniomorpha and the Chaetodermomorpha.

Fio. 35.

Spicules of various Aplacophora. A, Neomenia (Wiren); B, Dondcrsia (Hubrecht) ; C,
Paramenia (Pruvot} ; D, Proneomenia ; E, Stylomenia (Pruvot) ; F, .Myzomcnia (Pruvot) ; G,
Chaetoderma (Wiren). i.c, internal cavity.

SUB-ORDER 1. NEOMENIOMORPHA.

Aplacophora with a distinct longitudinal ventral groove ; bi-
sexual, with paired genital glands and without differentiated liver.

I. EXTERNAL CHARACTERS.

The mantle extends over the sides of the body so as to cover
the greater part ot tne ventral surface, leaving only a narrow
median longitudinal furrow uncovered. The pallial cuticle, which
is very thick in some species, contains a number of long, hollow,
calcified, acicular, or flattened spicules (Fig. 35) borne on epithelial
papillae. In some cases, when it is very thick, the cuticle also
includes sensory papillae. A small longitudinal projection in the
ventral furrow is the vestige of the foot. The antero-ventral region
of the body is occupied by a large mucous gland, whose secretion is
poured into a ciliated pit in the anterior part of the ventral furrow,
the whole structure corresponding to the embryonic pedal gland of
some Chitones. Smaller mucous glands are also found along the
pedal projection. Posteriorly there is a terminal cloacal or branchial
cavity, into which opens a thick mucous gland, situated between
the foot and anus.

THE AMPHINEURA

II. ANATOMY.

Digestive Trad. — The mouth is anterior and ventral, and is
frequently surrounded by papillae, probably sensory in function.
It opens into a muscular and sometimes protractile pharynx lined
by a thick cuticle. The salivary glands and radular sac open into
the pharynx. The radula (Fig. 36), when present, comprises several
rows of teeth, and may be (1) polystichous, with a continuous line
of teeth in each row (Proneomenia and Macellomenia), in which case
a basal membrane may be present, forming a true continuous
polyserial radula (Proneomenia acuminata, P. sluiteri, P. gerlachei\ or
absent, forming a discontinuous polyserial radula (P. vagans) ; (2)
distichous, with two separate teeth (Pammenia, Pararhopalia, Ismenia,

B

M

L^-\>

A

Fio. 36.

Radula (transverse rows) of various Neo-
meniomorpha. A, Proneomenia (Hubrecht) ;

CB, Lepidonunia (Kowalewsky and Marion);
fJJiMh C, Macellomenia (Pruvot); D, Amphimenia

(<— — J (Thiele) ; E, Stylomcnia (Pruvot).

Lepidomenia, Dinomenia) ; (3) monostichous, with a single tooth
(Stylomenia, Dondersia, Amphimenia, Proparamenia). The radula is
entirely absent in the Neomeniidae, in Rhopalomenia, Pruvotia,
Strophomenia, and Notomenia.

The salivary glands form a symmetrical pair, lying on the
ventral side, and opening on a subradular prominence ; their ducts
sometimes unite before opening into the pharynx. They correspond
to the subradular glands of the Polyplacophora and the posterior
salivary glands of the Cephalopoda. In some forms there is a
second pair of salivary glands, dorsal or dorso-lateral in position,
opening by a single duct into the mid-pharynx (Paramenia, some
species of Proneomenia: Fig. 37, gl.s.d). Several genera, among
them Neomenia, are devoid of salivary glands. The oesophagus is
generally short, and leads into a cylindrical and rectilinear stomach,
which frequently sends forward a caecum dorsad of the oesophagus,
and is provided with symmetrical lateral caeca, giving to the organ
the appearance of regular segmentation. The whole surface of the

THE AMPHINEURA

57

stomach is lined by a secretory, or so-called hepatic epithelium,
and its dorsal wall is ciliated. The intestine is straight and short,
with thin walls lined by a ciliated epithelium. The anus opens
into the branchial or cloacal chamber, together with the kidneys
and sometimes the anal mucous gland (Fig. 38).

Circulatory System. — There are no true blood-vessels with
definite walls, but there are two well-marked blood -spaces — a
ventral sinus between the foot and digestive tract, and a dorsal
tubular sinus or aorta whose hinder part forms a contractile heart.
The heart is enclosed in the pericardium and is fastened to its
dorsal wall, except in Neomeniat where it is free. The blood is red
owing to the presence of haemoglobin in the rounded or ovate
blood-corpuscles.

In the Neomeniidae and most of the Parameniidae there is a

Proneomenia gerlachei, right half of the anterior part of the body ; left-side view, b, mouth ;
cae, pharyngeal caecum ; com.p, pedal commissure ; cu, cuticula ; fo.ti, ciliated fossa ; g.c,
cerebral ganglion ; gl.g, gonad ; gl.s, salivary gland ; gl.s.d, dorsal salivary gland ; p, foot ; pap,
buccal papillae ; pha, pharynx ; ro, radula ; sin, ventral sinus ; st, stomach.

more or less extensive circlet of gills on the inner walls of the
cloacal chamber. These gills are epithelial folds or laminae, whose
cavities communicate freely with the haemocoele and the above-
mentioned sinuses. In the species in which no gills are present
the venous blood of the ventral sinus is oxygenated through the
epithelium of the inner wall of the cloacal chamber and the surface
of the foot. Where gills are present the blood passes into them
and is returned to the heart by two auricular ducts in .Neomema.

Excretory Organs. — — The pericardium occupies the posterior
region of the body dorsad of the rectum. The dorsal and lateral
parts of its inner wall are ciliated, and its cavity communicates
with the exterior by means of a pair of renal ducts, which open
into the cloacal chamber below the anus. In Strophomenia the renal
orifices are adjacent, but separate from one another as in Chaetoderma,
but in all other Neomeniomorpha the renal ducts open into the
cloaca by a common aperture (Fig. 30, C). As in the Polyplaco-

THE AMPHINEURA

phora, the renal tubes are first directed forwards and then turn
sharply backwards to run parallel to their former course. But the
kidneys of Neomeniomorpha are very different both in structure and
conformation from those of the Polyplacophora ; they serve also as
efferent ducts for the genital products, and their inner walls —
particularly the conjoined terminal pouch — are very glandular, and
fopn an organ* which secretes the egg-shell. Moreover (except in
Lepidomenia, in which they are very simple) they bear one or two
pairs of caecal appendages on the proximal part of their course,
the caeca nearer to the pericardium serving as sperm reservoirs.

Nervous System. — On the dorsal side, and in front of the buccal
bulb, there is a large supra-oesophageal nerve-mass, formed b^ two
conjoined ganglia, and often provided with accessory lobes. Two
ganglionated nerve -trunks are given off from each side of this

Pio.

Proneomenia gerlachei, right half of the posterior part of the body, left-side view, ca.g.co,
common median cavity of the two shell-glands ; d, cloaca ; com.l, supra-rectal pallial com-
missure ; com.p, the most posterior pedal commissure ; cu, cut icula ; du.g, opening of the gonad
in the pericardium ; gl.co, shell-gland of the left kidney ; gl.g, left gonad ; in, intestine ; o.d,
dorsal sense-organ ; o.g, common opening of the two reno-genital ducts ; p, foot ; per, peri-
cardium ; r, left kidney ; re, rectum ; ven, ventricle of heart ; ve.s, seminal vesicle : * anterior
limit of the junction of the two shell-glands.

cerebral ganglion ; that on the dorsal side being the pleural, that
on the ventral side the pedal cord. The two cords may originate
separately from the cerebral ganglion, or may be fused at their
origin and diverge after entering a pleural ganglion (Neomenia).
They correspond to the homonomous cords in the Polyplacophora.
The pedal cords enlarge to form a pair of .pedal ganglia, united by
a thick pedal commissure, and are continued posteriorly as two
regularly varicose trunks united by transverse anastomoses. The
two pallial cords are joined together posteriorly by a supra-rectal
commissure, which is double in Proneomenia sluiteri, but absent in
Dinomenia verrucosa and Rhopalomenia indica. An ovoid ganglion is
generally borne on the supra-rectal commissure. The pallial cord
of either side is united to the corresponding pedal cord by more or
less numerous anastomoses. In some forms, e.g. Paramenia, the
pedal cords are united to the pallial some way in front of the supra-
rectal commissure. A small anterior infra-oesophageal or stomato-

THE AMPH1NEURA 59

gastric commissure is given off from the cerebral mass, and enters
a pair of small ganglia situated in the median line between the
oesophagus and the radular sac ; moreover, the two same upper
buccal and subradular commissures as in the Chitones are present,
at least in Proneomenia and Rhopalomenia (Heath).

The only organs of special sense are the club-shaped epithelial
papillae in the thickened cuticule of the Proneomeniidae, Neommia,
and the following Parameniidae, Dinomeniff,, Proparamenia, and
Para-menia. There is also a median invaginable sensory papilla
situated on the dorsal posterior surface, above the rectum. It is
not covered by the cuticle, and may be multiple, as in Dondwsia,
or absent, as in Hemimenia and perhaps Stroplwmenia.

"Generative Organs. — The Neomeniomorpha are hermaphrodite.
The gonads are paired tubular structures, separately opening
posteriorly into the pericardium (Fig. 30, C) and extending forward
close under the dorsal sinus to near the front end of the body. The
ova are developed on the median, the spermatozoa on the outer
wall of each gonad. The sexual products pass into the pericardium,
whence they are driven by the pericardial cilia into the kidneys,
which, as has been explained above, serve as gonaducts and are
provided with receptacula seminis and shell-glands. In several
species paired excitatory organs, in the form of protrusible cal-
careous spicules, are situated in the cloacal chamber on either
side of the uro-genital orifice.

III. EMBRYOLOGY.

Little is known of the development of the group. The ova are
laid separately. In Myzomenia bani/ulensis (Pruvot)
the segmentation is regular, and an invaginate
gastrula with an originally posterior blastopore is1
formed. An anterior ciliated ring or velum is
formed, having in its middle a tuft of cilia, which
is eventually transformed into a single terminal
flagellum (Fig. 17). The external surface of the
trochophore larva thus formed is made up of a
number of ciliated test -cells, which — as in the
Lamellibranchiate Yoldia — eventually are cast off Fjo 30

and the mantle is formed beneath. The post- An advanced larva
velar region of the embryo elongates, and its of Myzomenia banyu-
ectoderm cells develop spicules. Finally, the Sy^kfter6 the^teSt
velum disappears, and seven imbricated calcar- pjjjjjjj11 off- (After
eous plates, made up of more or less flattened,
closely - apposed spicules, are formed on the dorsal surface
(Fig. 39).

6o

THE AMPHINEURA

IV. BIONOMICS.

The Neomeniomorpha are marine animals, living in depths of
from 15 to 800 fathoms, but are most abundant in 50 fathoms.
They inhabit oozy bottoms, and are found crawling on corals and
hydroid zoophytes, on which they feed. They have been found
in nearly all seas except the S.E. and N.W. Pacific and the
S. Atlantic. The British genera are Neomenia, RJwpalomenia, and
Myzomenia. About forty species, included in twenty genera, have
been recorded up to the present time.

V. SYSTEMATIC REVIEW OF THE NEOMENIOMORPHA.

FAMILY 1. LEPIDOMENIIDAE, Pruvot. Slender, tapering behind,
with subventral cloacal orifice ; thin cuticle without papillae ; flattened
spicules ; no gills. Genera — Lepidomenia, Kowalewsky and Marion.

FIG. 40.
Proneomenia gerlachei, left-side view. 6, mouth ; d, cloaca ; *i, foot-groove ; t, head.

Ismenia, Pruvot. Ichthyodes, Pruvot Stylomenia, Pruvot. Dondersia,
Hubrecht. Nematomenia, Siinroth. Myzomenia, Simroth. M. banyulensis,
Pruvot. Mediterranean and Plymouth.

FAMILY 2. NEOMENIIDAE, von Jhering. Short, trun-
cated in front and behind ; cloacal orifice transverse ;
gills present ; rather thin cuticle ; no radula. Genera —
Neomenia, Tullberg. N. carinata, Tullberg. North
Atlantic, N. and N.W. Scotland. Hemimenia, Nierstrasz.
FAMILY 3. PRONEOMENIIDAE, Pruvot, Elongated,
cylindrical, rounded at both ends ; thick cuticle with
acicular spicules ; radula polystichous or wanting.
Genera — Proneomenia, Hubrecht (Fig. 40). Amphi-
menia, Thiele. Echinomenia, Siinroth. Rhopalomenia,
Simroth. It. aglaopheniae. Mediterranean and Ply-
mouth. Notomenia, Thiele. Pruvotia, Thiele. Stropho-

men^ Pravot-

FAMILY 4. PARAMENIIDAE, PrUVOt. Short, and

' **' truncated in front ; thick cuticle (often without papillae) ;
gills and radula present Genera — Paramenia, Pruvot
(Fig. 41). Macellomenia, Simroth. Pararhopalia, Simroth. Dino-
menia, Nierstraez. Cyclomenia, Nierstrasz. Proparamenia, Nierstrasz,
Uncimenia, Nierstrasz. Kruppomenia, Nierstrasz.

Fio. 41.

cryo-
phUa, ventral as-

THE AMPHINEURA 61

SUB-ORDER 2. CHAETODERMOKORPHA.

Aplacophora without distinct longitudinal ventral (or pedal)
groove, with unpaired unisexual gonad, with differentiated liver,
and with posterior cloacal chamber provided with two bipectinate
gills.

Anatomy. — The mantle covers the whole surface of the body,
which is therefore cylindrical and vermiform in appearance. The
hinder half of the body is a little stouter than the anterior ; the
posterior extremity swollen and bell-shaped, forming the widely
cloacal chamber. The whole body has a uniform covering of short,
compressed, calcareous spicules implanted in the cuticula.

The mouth is anterior, terminal, and crescentic, owirig to the
presence of a rounded ventral shield. Chaetoderma radulifera alone
is provided with mandibles. The buccal cavity, whose anterior part
is partially protrusible, bears on its floor a very peculiar radula,
which may consist of (a) a single large tooth (Fig. 43, C), upon which
two small teeth are placed (C. nitidulum and C. productum) ; (b) a
single large tooth, upon which
is a row of teeth (C. guttu-
rosum; (c) no large tooth,
several rows of three teeth one
behind the other (C. raduli- FlG 42

fera); (d) Several distichous CHMtodema rUHdul^, Loven. The cephalic

TOWS of tWO teeth each (C. enlargement is to the left, the cloacal or pallial

, „ .\ m • t \- chamber (containing the concealed pair of ctenidia)

Challengen). 1 WO pairs OI Sail- to the right. (From Lankester, after Graff.)

vary glands, similar to those

in the Neomeniomorpha, open into the buccal cavity. The diges-
tive tract is quite straight, and narrows towards the middle jof
its course to form the intestine. Just before it narrows it receives
the duct of a more or less extensive hepatic caecum, which extends
backwards on the ventral side of the intestine. The hepatic caecum,
large in most species, is feebly developed in C. challengeri. The
anus opens in the median line in the cloacal chamber (Fig. 43, B).

The heart is posterior and dorsal, and lies nearly free in the
pericardial cavity. It is traversed by the retractor muscles of the
gills. In its main features the circulatory system resembles that
of the Neomeniomorpha. The posterior extremity of the body is
hollowed to form a bell-shaped cloacal cavity, which has a con-
tractile aperture and contains a pair of large branchiae placed
symmetrically right and left of the anus. Each branchia bears a
double row of branchial plates, as is the case in the Polyplacophora
(Fig 43, B).

The two renal ducts are more evidently true excretory organs
than in the Neomeniomorpha. They originate from the posterior

62

THE AMPHINEURA

corners of the pericardial cavity, run forward under the floor of
the pericardium, and then turn 'outwards and backwards to run
back to their respective apertures right and left of the anus.
Their thin walls are lined by a ciliated epithelium, and there are
no accessory generative organs.

In the nervous system there are two intimately fused cerebral

r

FlO. 43.

Chaetoderma nitidnlum. A, median sagittal section ; B, sagittal section of the posterior
extremity ; C, sagittal section of the anterior extremity, a, anus ; br, retractor muscle of the
branchiae ; c.g, cerebral ganglion ; d.t, digestive tract ; g, gill ; go, gonad ; h, heart ; t, intestine ;
k, kidney ; I, liver ; m, mouth ; me, " mesothorax " ; p.c, pallial suprarectal commissure ; p.d,
pericardial duct ; pe, pericardium ; pe.c, pedal commissures ; pr, " prothorax " ; r, radula ; «.c,
Hublingual commissure. (After Wiren.). «

ganglia bearing accessory lobes. Each ganglion gives rise to two
longitudinal nerve -cords, the ventral or pedal cord being more
slender than the dorsal or pallial cord. In the anterior part of
their course the pedal and pallial cords of either side run parallel
and adjacent to one another, but in the posterior region of the
body they are fused together, as in Paramenia, and the two pallio-
pedal cords thus formed are united dorsad of -the rectum by a

LITERATURE OF THE AMPHINEURA 63

ganglionic swelling. A small perirectal commissure originates
from this swelling. The pedal cords are united with one another
and with the pallial cords of the same side by anastomoses in the
anterior region of the body. A small stomato-gastric commissure,
bearing two small stomato-gastric ganglia on the middle of its
course, arises from the cerebral ganglia and surrounds the
oesophagus. There are no organs of special sense except a dorsal
posterior and mediae -pit, corresponding to the precloacal fossa of
the Neomeniomorpha.

The sexes are separate. The azygos gonad occupies the same
position as the paired gonads of the Neomeniomorpha, and com-
municates by a median aperture with the pericardial cavity. The
generative products are conducted from the periqardium to the
exterior by the renal ducts. The embryology of the group is quite
unknown.

The Chaetodermomorpha are marine animals feeding on lowly-
organised forms of life, such as Protozoa, etc. They are found in
oozy bottoms from a depth of 15 fathoms to abyssal regions.
The nine recorded species of the single genus Chaetoderma, come
from the North Atlantic, North Pacific, and Arctic Oceans, the Sea
of Marmora, the Eastern Archipelago, and the Philippine Islands.

Family CHAETODERMATIDAE, von Jhering. Genus — Chaetoderma,
Loven. The characters are those of the sub-order. Limifossor, Heath
(Alaska).

PHYLOGENY OF THE AMPHINEURA.

The Polyplacophora present the most archaic characters among
the Amphineura. The Aplacophora, on the other hand, are
specialised in the following respects : (1) in the great reduction of
the foot ; (2) the disappearance of the shell (Cryptoplax, among the
Polyplacophora, shows how these two reductions may take place
simultaneously) ; (3) the absence of the radula in several forms.
The Chaetodermomorpha seem to be more specialised in these
points than the Neomeniomorpha.

LITERATURE OF THE AMPHINEURA.
I. Polyplacophora.

1. van Bemmelen. Zur Anatomie der Chitonen. Zool. Anzeiger, 1883, p. 340.

2. Blumrich. Das Integument der Chitonen. Zcitschr. f. wiss. Zool. lii.

1891, p. 404.

3. Bimic. Notes on the Anatomy of Hanleya Hanleyi, M. Sars. Proc.

Malacol. Soc. ii. 1896, p. 4.

4. Oarnault. Sur la structure et le developpement de I'oauf et de son follicule

chez les Chitonides. Arch. Zool. Exper. (2), vi. 1888.

5. Haddon. On the Generative and Urinary Ducts in Chitons. Proc. R.

Dublin Soc. new sen iv. 1885.

64 LITERATURE OF THE AMPHINEURA

Q. Haddon. Report on the Polyplacophora. Challenger Reports, Zoology, Part
xliii. 1886.

7. Haller. Die Organisation der Chitonen der Adria. Arb. Zool. Inst. Wien,

iv. v. 1882, 1883.

8. Beitrage zur Kenntniss der Placophoren. Morph. Jahrb. xxi. 1894.

9. Heath. The Development of Ischnochiton. Zool. Jahrb. Anat. u. Ontog.

xii. 1899.

10. von Jhering. Beitrage zur Kenntniss der Anatomic von Chiton. Morph.

Jahrb. iv. 1878.

11. Kowalewsky. Embryogenie du Chiton Polii. Ann. Mus. Marseille, Zool. i.

1883.

12. Lawn. Ueber die Entwickelung von Chiton. Arch. f. Naturgesch, 1856.

13. Mctcalf. Contributions to the Embryology of Chiton. Stud. Biol. Labor.

Johns Hopkins Univ. v. 1893.

14. Middendorf. Beitrage zur einer Malacozoologia Rossica — I. Beschreibung und

Anatomic neuer Chitonen. Mem. Acad. Petersbourg (6), vi. 1849.

15. Moseley. On the Presence of Eyes in the Shells of certain Chitonidae, and

on the Structure of these Organs. Quart. Journ. Micr. Sci. new ser. XXT.
1885.

16. Pelseneer. Recherches morphologiques et phylogene'tiques surles Mollusques

archaiques. Mem. cour. Acad. Belg. Ivii. 1899.

17. Plate. Die Anatomie und Phylogenie der Chitonen. Zool. Jahrb. Suppl.

iv. v. 1897, 1899, 1901.

18. Reiiicke. Beitrage zur Bildungsgeschichte der Stacheln im Mantelrande der

Chitonen. Zeitschr. wiss. Zool. xviii. 1868.

19. Sampson. The Musculature of Chiton. Journ. of Morphol. xi. 1895.

20. Schiff. Beitriige zur Anatomie von Chiton piceus. Zeitschr. wiss. Zool. ix.

1858.

21. Scdgwick. On certain Points in the Anatomy of Chiton. Proc. R. Soc.

London xxxiii. 1881.

216/*. Wcttstein. Zur Anatomie von Cryptoplax larvaeformis Burrow. Jenaische
Zeitschr. xxxviii. 1903.

II. Aplacoplwra.

22. von Graff. Anatomie des Chaetoderma nitidulum. Zeitschr. wiss. Zool.

xxvi. 1875.

23. Hansen. Auatomiske Beskrivelse af Chaetoderma nitidulum. Nyt.

Magaz. Naturvid. xxii. 1877.

23W*. Heath. The Nervous System and Subradular Organ in two genera of
Solenogastres. Zool. Jahrb. (Anat. und Ontog.) xx. 1904.

24. Heuscher. Zur Anatomie und Histologie der Proneomenia Sluiteri. Jenaische

Zeitschr. Naturw. xxvii. 1893.

25. ffubrecht. Proneornenia Sluiteri. Nied. Arch. f. Zool. Suppl. i. 1881.

26. Dondersia festiva gen. et spec. uov. Donders Feestbundel. Nederl.

Tijdschr. van Geueesk. 1888.

27. Kowalewsky et Marion. Contribution a 1'histoire des Solenogastres ou

Aplacophores. Ann. Mus. Marseille, Zool. iii. 1887.

28. Kowalewsky. Sur le genre Chaetoderma. Arch. Zool. Exper. (3), ix.

1901.

29. 2iicratrasz. The Soleuogastres of the " Siboga " Expedition. Resul tats des

Explorations ... a bord du Siboga, xlviL 1902.

LITERATURE OF THE AMPHINEURA 65

30. Pruvot. Sur 1'Organisation de quelques Ne'omeniens des Cotes de France.

Arch. Zool. Expe"r. (2), ix. 1891.

31. Sur deux Ne'omeniens nouveaux de la Me'diterranee. Arch. Zool.

Exper. (3) vii. 1901.

32. Sur le developpement d'un Soldnogastre. Comptes rendus Acad. Sci.

Paris, cxi. 1890.

33. Thiele. Beitrage zur vergleichenden Anatomie der Amphineuren. Zeitschr.

f. wiss. Zool. Iviii. 1894.

34. Tullberg. Neomenia, a new Genus of Invertebrate Animals. Bihang K.

Svensk. Vet. Akad. Handl. iii. 1875.

35. JViren. Studien liber die Solenogastres. K. Svensk. Vet. Akad. Handl.

xxiii. and xxiv. 1892, 1893.

CHAPTER III

THE GASTROPODA

CLASS II.— GASTROPODA, CUVIER
( = PARACEPHALOPHORA, Blainville ; ANISOPLEURA, Lankester).

SUB-CLASS I. STREPTONEURA.
Order 1. Aspidobranchia.

Sub-Order 1. Docoglossa.
„ 2. Bhipidoglossa.

Order 2. Pectinibranchia.

Sub-Order 1. Taenioglossa.
„ 2. Stenoglossa.

SUB-CLASS II. EUTHYNEURA.
Order 1. Opisthobranchia.

Sub-Order 1. Tectibranchia.
„ 2. Nudibranchia.

Order 2. Pulmonata.

Sub-Order 1. Basommatophora.

„ 2. Stylommatophora.

Definition. — The Gastropoda, together with the Scaphopoda and
the Lamellibranchia, form the branch Prorhipidoglossomorpha of
the Mollusca, that is to say, a group in which the gonads are no
longer in direct communication with the pericardium, the foot is
wholly posterior to the head, and a visceral commissure is present.
The Gastropods are a class of the Prorhipidoglossomorpha specially
characterised, firstly, by their asymmetrical organisation ; secondly,
by their well-developed head ; and thirdly, by their shell, which is
formed of one piece and coiled in a spiral, at least in the larval
stage.

THE GASTROPODA 67

I. GENERAL DESCRIPTION AND EXTERNAL CHARACTERS.

The three external divisions of the body, head, foot, and mantle
are well defined. The head is well developed, and forms a more or
less cylindrical mass, but is sometimes flattened. At its anterior
extremity is the mouth, and dorsally it bears one or two pairs of
tentacles. There is one pair of tentacles in the Streptoneura
(Fig. 44), the " Thecosomata " (Fig. 63), in PhyllirJwe (Fig. 161),
Tkecue&Oj the Proctonotidae, the Elysiidae (Fig. 170), the basom-
matophorous Pulmonates, and Janella (Fig. 178). There are two
pairs in the majority of Opisthobranchs (Fig. 154) and in the
stylommatophorous Pulmonates (Fig. 172). The tentacles either
are or bear sensory organs ; they are contractile, and in the Stylom-
matophora invaginable. The right tentacle of both sexes bears an
appendage in Bathysdadium (Fig. 126), certain Trochidae (Fig. 130),.
and Calyptraea. The form of the tentacles varies greatly in different
groups. Sometimes they are atrophied, and they may even dis-
appear without leaving a trace, as in OliveUa, Homalogym, certain
species of Terebra, Pterotrachea (Fig. 143), Limapontia, and Pseudo-
vermis (Fig. 169). In the majority of the Bullidae the two pairs
of tentacles are enlarged and transformed into a quadrangular shield
(Fig. 148), the four corners of which correspond to the tips of the
four tentacles. The single pair, much reduced in certain Basom-
matophora (Amphibolidae, Otinidae, Fig. 173, Siphonariidae),
similarly gives rise to the appearance of a flattened disc on the top
of the head. The anterior pair of tentacles in the Pleurobranchidae
(Fig. 157) and in various Nudibranchs (Tritoniidae, Fig. 83, Den-
dronotidae, Tethyidae, etc.) is transformed into a more or less
well -developed frontal veil. Finally, the tentacles are flattened
(Narica); split (Pyramidellidae, Fig. 137, Solarium, the posterior
pair in many Opisthobranchs) ; bifurcate (Janthina, certain Elysio-
morpha) ; or multifid (the posterior pair in many Nudibranchs,
Dendronotus, Ancula, Fig. 163). In some species, on either side of
the buccal orifice, there is another pair of appendages of greater or
less length, known as the labial palps. These are found in Trochus
infundibulum, Ampullaria, Jeffreysia, CJwristes, among the Strepto-
neura ; and among the Euthyneura in sundry Pulmonates (Glandina,
Limnaea, in which they form a sort ot buccal veil, Fig. 107), and
in Tectibranchs. In addition to the above-mentioned cephalic
appendages of the adult, the following structures should be noted :
the cephalic or frontal lobes, situated between the two tentacles
and consisting of projections of various shape, in many Rhipido-
glossa and in Fossarus ; the dorsal median crest in Olivella and
Janus; and finally, the pseudopallium, an expansion of the
cephalic integument surrounding the whole shell, with the excep-

68

THE GASTROPODA

tion of the summit of the spire, in Stylifer and allied parasitic
forms (Fig. 20).

1. The Foot. — This is primitively and normally formed by a
powerful mass of ventral muscles with a more or less elongated

FlQ. 44.

A, Triton vanegatum, animal and shell, seen from the right side, a, siphonal notch of the
shell occupied by the siphonal fold of the mantle-skirt ; b, edge of the mantle-skirt resting on
the shell ; c, cephalic eye ; d, cephalic tentacle ; e, proboscis or buccal introvert in a state of
eversion ; /, foot ; g, operculum ; h, penis ; i, under-surface of the mantle-skirt, forming the
roof of the sub-pallial chamber. (From Lankester, after Poli.) V, sole of the foot of Hemifusus
tuba, to show, a, the pore of a pedal gland ; h, median line of the foot. (From Lankester, after
Souleyet.)

ventral creeping surface (Fig. 44, B). But this primitive condition
may be modified in relation to different conditions of existence.
Thus, among sedentary Gastropods the foot is reduced to a simple
discoidal prominence in such fixed forms as Vermetus (Fig. 45) and

FlO. 45.

Vermetus triqueter, with broken shell ; left-side view, co, columellar muscle ; /, foot ; m,
mouth ; o, aperture of the shell ; op, operculum ; or, eggs ; pa.s, mantle slit ; p.t, pedal tentacles ;
*A, shell. (After Lacaze-Duthiers.)

Magilus. In Bathysciadium (Fig. 126) the ventral surface of the
foot assumes the form of a sucker, the central portion of which is
covered by a thick cuticle, and the circumference is ciliated. In
the parasitic forms Stylifer and Thyca the foot is atrophied and is

THE GASTROPODA 69

represented only by a small ventral appendage. Among the free-
swimming Gastropods we find that in the Heteropods the foot is
laterally compressed to form a vertical natatory lobe held upper-
most in swimming (Fig. 142), but in Phyllirhoe it no longer exists as
a differentiated organ (Fig. 161). In leaping Gastropods, such as
Rostellaria among the Strombidae (Fig. 46), the foot is also laterally
compressed, and its ventral surface, if not displaced anteriorly, is
not flat. In Harpa the posterior part of the foot may be cast off by
a process of autotomy.

The creeping sole is often divided by a median longitudinal
furrow ; this may be seen in sundry Rhipidoglossa, e.g. Trochus,
Stomatella, Phasianella ; and in Taenioglossa such as Littorina and
Cydostoma : in the last-named genus the two halves of the foot
contract alternately during progression. A transverse furrow,
crossing the anterior half of the foot, is found in the Olividae,
Pomatiopsis, many Auriculidae, Otina, and Cyerce.

Certain parts of the foot may exhibit special differentiations.
(1) Its two anterior angles are prolonged into tentacles in Cyclostrema,
Valvata (Fig. 132), CJwmtes, Olivella, Eolis, etc. (2) The anterior
margin of the foot may be furnished with a number of small tactile
papillae as in Trochus, etc., or there may be a small fleshy projection,
called the mentum, between it and the mouth, below the aperture
of the supra-pedal gland, as in the Pyramidellidae (Fig. 137),
Siliquaria, Aclis, Vermeius. In Capulus there is a^ little projecting
tongue-shaped structure above the anterior margin of the foot and
below the snout, and in Vermetus two symmetrical tentacles are
present in the same position, on either side of the aperture of the
supra-pedal gland. (3) In various fossorial Gastropods the whole
anterior region of the foot is somewhat elevated above the head,
to form the propodium. This region is distinctly separated from
the rest of the foot by a constriction in the Harpidaefand by a
transverse furrow in the Olividae. The propodium is particularly
well developed in the Naticidae, in which it is reflected over the
whole cephalic region to form a powerful digging organ (Fig. 47).
(4) The lateral margins of the foot are expanded to form fins or
parapodia in certain Olividae, and particularly in a number of
Opisthobranchs, as, for example, in Gastropleron, Acera, etc. ; among
the Bullidae, the Pteropods, Aplysia, etc. In Notarchus these two
lobes are united above the body in such a manner as to form a
muscular sac open in front, but closed behind and at the sides. By
forcibly expelling water through the anterior aperture, the animal
makes use of the sac as an organ of locomotion. (5) The posterior
region of the foot is often separated off as a distinct operculigerous
lobe, as may be seen in the Strombidae (Fig. 46), Xenophorus
(Fig. 134), and the Atlantidae (Fig. 141). In some Marginellidae
there is a posterior dorsal discoid lobe. In Nassa and in allied

70 THE GASTROPODA

forms the posterior extremity of the foot bears a pair of tentacles
which are sometimes bifurcated, and in Phos there is a single filament
in this position. In Pterotrachea the foot terminates posteriorly in
a long filiform contractile appendage, bearing several annular vari-
cosities. In Cymbulia the posterior lobe of the foot also ends in a
long whip-like appendage. (6) On the sides of the foot, at about
the middle of its height, there is often a ridge, the epipodium,
extending from the head to the posterior end of the foot. This
ridge is specially well developed in various Rhipidoglossa (Fig. 1 30,
VIII), and may bear appendages of greater or less length, sensory
organs, and pigment spots, the last-named, however, showing no
trace of the structure of eyes. The anterior part of the epipodium

Fio. 46.

Rostellaria rectirostris, animal and shell, right-side view, a, snout or rostrum ; 1>, cephalic
tentacle ; c, eye ; d, anterior part of the foot ; e, posterior (operculigerous) part of the foot ; /,
operculum ; h', anterior canal of the shell, occupied by the pallial siphon. (From Lankester,
after Adams.)

generally forms a cervical lobe, which exhibits a characteristic
asymmetry in certain Trochidae. The epipodium is found also
in Litiopa, the Rissoidae, Naricay Janthina, etc., and a portion of
it is represented by the cervical lobes in Paludim, Ampullaria,
and Calyptraea.

The surface of the foot is normally furnished with a large number
of unicellular mucous glands, and very often these cells are specially
accumulated in invaginations of the integument, distinguished as
pedal glands. The most important of these invaginations are — (1)
The anterior groove of the foot (Fig. 144, IV), into which open the
so-called labial glands : it is often continued into a fairly long canal.
This anterior pedal gland is very generally present in the aquatic
creeping species of Streptoneura and Opisthobranchs ; it secretes
the mucus which lubricates the surface of the foot, and is auxiliary
to creeping whether it be on the bottom ot the sea or on the

THE GASTROPODA 71

surface in a reversed position. (2) The supra-pedal gland opens in
the middle line between the snout and the anterior border of the
foot. It is most commonly found in sessile Streptoneura ( Fermetus,
Hipponyx) and in terrestrial forms such as Cydostoma and the
Pulmonata. It is often very deep, and extends for nearly the
whole length of the foot : its walls are thrown into folds and are
ciliated ventrally in the majority of the Pulmonates. (3) The
ventral pedal pore, situated in the middle line in the anterior
moiety of the foot, is the aperture of a more or less extensive and
often ramified cavity into which the glands of the sole or the pedal
glands properly so called pour their secretion (Figs. 44, B; 144, I).
This organ is comparable with the byssogenous gland of Lamelli-
branchs (Fig. 197), and is found in the following genera: in
Cydostoma, in which it is composed of multiple tubules ; in Cypraeu,
Hemifusus (Fig. 44), Cassis, and a large number of Rachiglossa and
Toxiglossa, viz. in the Fasciolariidae, Turbinellidae, Nassa, Murex, the
Olividae, Marginellidae, and Conidae (Fig. 144). Its opening was
formerly mistaken for an aquiferous pore. (4) The posterior mucous
glands may be either dorsal or ventral in position. The former are
characteristic of terrestrial Gastropods, such as the Pulmonates and
certain Cyclostomatidae, in which they are often surmounted by a
simple or multiple horn-shaped protuberance (Orpitlla, Plertrophorus,
Dermatocera). The ventral posterior glands are simple localisations
of the dermic glands, and occur in various Opisthobranchs ; they are
not sensibly invaginated in the Pleurobranchidae and Pleuro-
phyllidae, but are invaginated and form a long canal in Gastropteron.
The product of secretion of the pedal glands in many cases solidifies
on contact with the air of water and serves for the suspension of
the animal. In some species of Limax, Litiopa, Cerithidea, etc., it
assumes a filamentous form ; and in both sexes of Janthina, whether
viviparous or not, it is filled with air-bubbles and forms a float,
covering the ventral surface of the foot, beneath which the animal
is suspended (Fig. 135).

The ventral border of the flattened and fin-like mesopodium of
the Heteropoda exhibits, in the male at any rate, an invagination in
the form of a sucker (Figs. 141, 142, d'). A similar sucker exists
on the ventral or pedal area of some species of Phyllirhoe, but in no
Gastropod does the foot exhibit an aquiferous pore, in the sense
formerly attached to this term. In some forms, however, and at
all events in the Naticidae, there is a system of aquiferous spaces in
the foot ; these spaces are completely separated from the circulatory
apparatus and serve to distend the foot (Fig. 47, VIII) in the action
of burrowing in the sand or mud.

The foot often bears on its posterior dorsal aspect a solid
sclerite, known as the operculum, which, on the retraction of the
animal, serves to close the aperture of the shell. The operculum

72

THE GASTROPODA

is sometimes borne on a differentiated portion of the foot as in
Xenophorus (Fig. 134), Pteroceras (Fig. 75), Atlanta (Fig. 141), or on
a distinct expansion, which in Natica is reflected over a portion of
the shell. An operculum is present in almost all adult Streptoneura,
the exceptions being the Docoglossa, the Fissurellidae, the Haliotidae,

FIG. 47.

BP

Natica josephina, fully expanded ; right-side view. I, exhalant orifice ; II,
•t of propodium reflected on the shell ; IV, tentacles ; V, shell ; VI, poste
lected on the shell ; VIII, hind-part of the foot. (After Schiemenz.)

propodium ; III,
rior part of foot

Gena, Stomatia, the Proserpinidae, Calyptraeidae, Capulidae, Hip-
ponycidae, Cypraeidae, Doliidae, Marginellidae, Harpidae, the
majority of the Mitridae, many Cancellariidae and Conidae, Oliva,
the Janthinidae, etc. But in all these cases, with the exception of
the larva of Stylifer, an operculum is present during development,

•n.

Operculum of Oxygyrus, x 30y external aspect, a.s, attachment surface ; n, nucleus of the
opercular spire.

as may be seen, for example, in the Patellidae, Fissurella, Calyptraea,
Janthina, Carinaria, etc. The naked Streptoneura, Entoconcha,
Enteroxenos, Pterotrachea, Firoloida also have an operculated shell
in the larval stage of development. Among the Euthyneura, on
the other hand, only Actaeon and Limacina among the Opistho-
branchs, and Amphibola among the Pulmonates, possess an oper-
culum in the adult stage, but the great majority, even of the naked

THE GASTROPODA

73

forms such as the Nudibranchs, the Cymbuliidae, and Pleurobranchus,
are provided with an operculated shell during their development,
the only exceptions being some highly specialised forms, e.g. the
Pulmonates (excepting the Auriculidae, Siphonariidae, and On-
cidiidae, which have an operculum during development), Buncina,
Cenia, and of the " Pteropods," the Cavoliniidae and Gymnosomata.
An operculum may be present or absent in the adults of the
same genus, as may be seen in Stomatella, Vermetus, Valuta, Mitra,
Pleurotoma, and Conus. It may be absent in certain individuals of
the same species as in Volutharpa ampullacea, or it may be normally
caducous in aged individuals
as in Limacina antarctica and
L. kelicina. The composition
of the operculum varies very
much in the different groups
of Gastropoda. It is com- j^^^^^^&m ,Ofl

\

Ofl

Fio. 49.

Lirnacina antarctica, young
specimen with the operculum
in situ, f.sp, false spire ; op,
operculum.

FIG. 50.

Cyclostrcma decussatum.
culuui (op).

Shell and oper-

monly horny, or it may consist of a horny plate covered by a thin
calcareous layer, as in Liotia among the Delphinulidae and Cistula
among the Cyclostomatidae ; or, finally, it may be completely calcified,
as in the Turbinidae, Phasianellidae, Neritidae, etc. Its conformation
is originally spiral, and in this case the spire is always inverse to
that of the shell, even in the Atlantidae (Fig. 48), except in certain
cases of hyperstrophy described below. It may, however, be con-
centric, imbricated, or scaly (Strombidae, Fig. 75, op), and it maybe
furnished with lateral apophyses as in Neritina, Eissoina, and Stiva.
Some non-operculate testaceous Gastropods, as, for instance, many
stylommatophorous Pulmonates and some species of Planorbis,
secrete glutinous or calcareous epiphragm which closes the mouth
of the shell during hibernation or aestivation. In Hipponyx the
foot secretes a calcareous plate by means of which the animal
fixes itself to the substratum.

2. Visceral Sac, Mantle, and Shell. — The mantle normally covers
the whole of the visceral sac and projects all round it, leaving only
the head and foot projecting on the ventral side. On the anterior
or on the lateral aspect, or exceptionally on the posterior aspect, as

74

THE GASTROPODA

in the Cavoliniidae and Cymbuliidae, there is a space left between
the mantle and the body, constituting the pallid cavity. This
pallial cavity has a situation opposite to that which it occupies in
other Molluscs (Fig. 22), due to the torsion which the Gastropxl
body undergoes towards the end of its development.

FIG. 51.

Three larvae (veligers) of TrocJius, during the process of torsion, viewed from the right side
of the shell. A, nearly symmetrical larva ; ]}, a stage 1£ hour later than A ; C, a stage 3} hours
later than B. /, foot ; op, operculum ; pa.c, pallial cavity ; ve, velum. (After Robert.)

The process by which this torsion is brought about may be
referred, on ultimate analysis, to a morphological phenomenon
common to the Cephalopods (Fig. 119, D), Scaphopods (Fig. 119, B),
and Lamellibranchs (Fig. 119, C), as well as to the Gastropods.
This phenomenon is the ventral flexure which takes place in an
antero-posterior sagittal plane, about a transverse axis situated at

•n&c,

Ct.

Fio. 52.

Diagram of the torsion of the visceral commissure in the Streptoneura seen from the buccal
side. A, before the torsion, whose direction is indicated by the arrow ; B, after the torsion,
a, anus ; ab, abdominal ganglion ; ce, cerebral ganglion ; i.i, infra-intestinal ganglion ; m,
mouth ; pa.c, pallial cavity ; s.i, supra-intestinal ganglion.

right angles to the main antero-posterior axis of the animal, and results
in the approximation of the two ends of the digestive canal. As
a consequence of this flexure, the visceral mass and shell, which were
originally saucer- shaped, become thimble-shaped, or are produced
into a more or less pointed cone, and during the flexure there is a
simultaneous coiling of the visceral sac and the shell covering it in
a dorsal or anterior direction, so that an exogastric coil is produced,

THE GASTROPODA

75

as may be seen in the Patellidae, Fissurellidae, and Trochidae
(Fig. 51, A). This disposition of the shell is the same as that which
obtains in other Molluscs with coiled shells (Nautilidae, Fig. 270),
but without lateral torsion. But in Gastropods, during the com-
pletion of the metamorphosis, there is a lateral torsion subsequent
to the primitive ventral flexure, as a result of which the originally
dorsal or exogastric shell becomes ventral or endogastric (Fig. 51, C).
This lateral torsion is causally connected with the growth of the
ventral creeping surface, which primitively was very short, but
eventually increases in length, and in so doing tends again to
remove the pallia! opening, and with it the anal and renal orifices
and the respiratory organs, away from the head. The approxima-
tion of these organs to the head is therefore necessarily effected by
a lateral torsion in a plane perpendicular to the primitive ventral
flexure ; that is to say, about a dorso-ventral axis situated in the
same median sagittal plane as the antero-posterior axis. It is this

second lateral torsion, then, in-
volving all the organs contained
in the shell — the cephalo- pedal

Fid. 53.

Four stages of the development of a Gastropod,
showing the process of the body -torsion. A,
embryo without flexure ; />, embryo with ventral
flexure of the intestine ; C, embryo with ventral
flexure and an exogastric shell ; D, embryo with
lateral torsion and an endogastric shell (the
arrows indicate the direction of the torsion),
a, anus ; /, foot ; m, mouth ; pa, mantle ; pa.c,
}>allial cavity ; ve, velum. (After Robert.)

Fio. 54.

Scisturdla lytteltonensis, but of its
shell, dorsal aspect I, snotit ; II, right
tentacle; III, pallial slit; IV, right
gill; V, rectum; VI, gonad ; VII, left
kidney ; VIII, left half of the columellar
muscle ; IX, left gill ; X, left eye.

mass being supposed to be fixed or vice versa — which brings the
pallial aperture and the anus from a posterior to an anterior position
(Fig. 53).

During this lateral torsion the following changes are necessarily
produced in the original organisation of Gastropods : — (1) The
anus being carried forward along one side of the animal, the
organs situated on either side of this orifice change their relative
positions ; those which were morphologically on the right become

THE GASTROPODA

topographically on the left side, and vice versa. (2) The visceral
commissure, while maintaining its position in respect to the
digestive canal, becomes twisted (Fig. 52) in such a manner that
its right moiety with its ganglion passes over to the dorsal side of
oesophagus (Fig. 57), and is therefore called supra-intestinal, while
the left moiety passes under the oesophagus towards the right side,
which explains the name infra-intestinal given to this portion of
the commissure and the nerve-centre borne on it. (3) The
original symmetry of the organisation disappears. The anus
does not remain in the centre of the pallial cavity, but is dis-
placed towards the right side. The organs situated on the topo-
graphically right — but morphologically and originally left — side
atrophy (Pleurotomaria, Scissurella, etc.), and eventually disappear.
An essential feature of the asymmetry of Gastropods is the atrophy
or disappearance of the topographically right (morphologically left)

Fio. 55.

Trochus cinerarius, heart and
kidneys, dorsal aspect (some-
what schematic). I, left renal
pore; II, right renal pore ; III,
right kidney; IV, papilla with
the common opening of the peri-
cardium and of the gonad into
the right kidney ; V, right reno-
pericardial duct ; VI, anterior
part of the gonad ; VII, right
auricle; VIII, ventricle; IX,
pericardium ; X, left auricle ;

XI, left i-eno-perirardial orifice;

XII, branchial efferent vessel ;

XIII, left kidney ; XIV, rectum ;
XV, gill.

half of the circumanal complex, involving the '•tenidium, auricle,
osphradium, hypobranchial gland, and kidney. In forms with
situs inversus, or, as they are generally called, sinistral forms, the
phenomenon is reversed : the organs of the left side are preserved,
those of the right side atrophy or disappear. In dextral Gastropods
the only structure found on the topographically right side of the
rectum is the genital orifice. But this is not an original organ.
It is wanting in forms which, like Pleurotomaria, Haliotis, etc., have
preserved the maximum of symmetry. Moreover, in the most
primitive stage of organisation, the gonads opened into the kidneys.
As soon as the asymmetry makes its appearance, even while there
are yet two kidneys, the genital products are conducted only into
the right kidney (Patellidae, Trochidae, Fig. 55, Fissurellidae).
Consequently the right kidney cannot disappear altogether, but
persists in part as the gonaduct. The latter structure, therefore,
is the remains of the topographically right kidney, a view which

THE GASTROPODA

77

has been confirmed by the study of the embryology of Paludina.
(4) The coil of the visceral sac and shell becomes endogastric.
Originally these structures were coiled dorsally or, in other words,
were exogastric (Fig. 53, C), but as a result of a rotation through
an angle of 180°, the coil necessarily becomes ventral or endo-
gastric (Fig. 53, D). Most usually, however, the coils of the
visceral sac and shell do not remain in the same plane, but the
summit of the spire gradually comes to project on the side which
was originally left, but which at the end of development is finally
and topographically right (Fig. 44). Thus a spiral coil is formed
which has the advantage of giving a more compact form to the
shell and its contents, and of diminishing its diameter. In those
forms in which the torsion and asymmetry is dextral, the coil of
the spire is conformable since it also is dextral ; that is to say, it
follows the direction of the hands of a watch if the shell is viewed
from the summit of the spire (Figs. 47 and 132, etc.). Nevertheless,
the coil of the shell is by no
means the cause of the torsion ;
both are foreshadowed in the
segmentation of the ovum, in
which there is a complete reversal
of the direction of the cleavage
planes in sinistral as compared
with dextral Gastropods. The
apparent direction of the coil,
however, may be changed by a pro-
cess of liyperstrophy (see below,
p. 82), and finally the coil of the

Fio. 57.

Nervous system of Actaeon torna-
tilis, in situ, dorsal aspect. I, buccal
gland ; II, buccal mass ; III, cerebral
ganglion; IV, infra -intestinal part
of the visceral commissure, with a
small pallial ganglion ; V, infra-
intestinal ganglion ; VI, right sali-
vary gland ; VII, abdominal ganglion
and genital nerve ; VIII, oesophagus ;
IX, supra - intestinal part of the
visceral commissure ; . X, supra-
intestinal ganglion.

FIG. 50.

Shell of a very young Patella
vulgata, viewed from the right
side, x 25. sp, apical spire.

visceral mass and spire may disappear in the aduL, ieaving the in-
ternal torsion and asymmetry unaltered, but producing a secondary
external symmetry, as in the Patellidae (Fig. 56), Fissurellidae, etc.
(5) By de torsion, or movement in a contrary direction, the anus
and circumanal complex (with the exception of the male or herma-
phrodite genital aperture) may be carried back to a posterior posi-

THE GASTROPODA

tion. This tendency to detorsion may be observed in exceptional
cases among the Streptoneura (Pterotrachea, Fig. 143), but it is
specially characteristic of the whole group of the Euthyneura, lead-
ing to the untwisting of the visceral commissure, which, in this
group, is obviously twisted only in Adaeon (Fig. 57). When detorsion
is carried to its extreme limit as in Pterotrachea, it is accompanied
by a reduction or disappearance of the mantle and visceral sac and
opisthobranchialism. In the least specialised Opisthobranchs and
Pulmonates the detorison is not complete, and the pallial aperture is
carried only to the right side (Figs. 148, 67); but in the most specialised

Phillne aperta, ventral aspect, a, anus ;
/, foot; g, gill ; glj, glandular fossa; g.o,
genital orifice (seen through the foot) ; k.o,
renal pore ; os, osphradium ; pa, inferior
pallial lobe. (After Quiart.)

Oncidiclla patelloideg, ventral aspect, an,
anus ; gl, tentacular gland ; o, mouth ; o./,
female orifice ; o.m, male orifice ; p, foot ; pa.
mantle ; pns, pulmonary orifice ; ti.p, lateral
groove ; te, tentacle.

forms the anus and the pallial cavity (if the latter is retained) arc
moved back to the posterior extremity of the body, as in Philine
(Fig. 58), Aplysia (Fig. 1 54), Doridomorpha (Fig. 79), and many other
Nudibranchs, such as Janus, Alderia, Limapontia, and Cenia ; and
among Pulmonates in Testacella, Vaginula (Fig. 179), and Oncidium
(Fig. 59). In this manner a secondary external symmetry is re-
established. The detorsion of the organism is complete in the
Tectibranch Cavoliniidae (" straight Thecosomatous Pteropods "), in
which one may recognise a torsion of 180° in a direction opposite
and equal to that of the original torsion, the result of which is that
the genital duct is twisted round tiie alimentary canal and the
pallial cavity is shifted to the ventral surface (Fig. 60). It should

THE GASTROPODA

79

be noted that in those Euthyneura which are detorted in the adult
condition, the primitive torsion is manifest in the course of develop-
ment, and in the larvae the pallial cavity is anterior and dorsal, the

anus anterior, just as is the
case in an adult Streptoneura
(Fig. 61).

The pallial cavity normally
contains the apertures of the
anus and the renal ducts ; and,
as it also contains the ctenidial
branchiae, together with their
sensory organ, the osphradium,
it constitutes the respiratory
cavity. There is, in addition,
between each branchia and the
rectum a more or less dif-
ferentiated glandular region
known as the hypobranchial
gland or pallial mucous gland
(Figs. 75 and 85), which is
characteristic of aquatic species.
Two such glands are found,

•m

FIG. GO.

Clio striata, removed from its shell, with
the head above, right-side view, a, anus ;
a. g.g, accessory genital glands ; /, foot (pos-
terior lobe); fi, left fln (the right one is
cut away) ; gg, gonad ; h, heart ; h.o, her-
maphrodite orifice ; k, kidney ; li, liver ; m,
mouth ; m.o, male orifice ; m.p, mastica-
tory stomachal plate ; n.s, central nervous
system ; oe, oesophagus ; pa.c, pallial cavity ;
pa.g, pallial gland ; pe, penis ; spo, sperm-
oviduct ; st, stomach and bile-duct ; (, right
tentacle.

Fio. 61.

Veliger of Eolis (Galvina) picta,
ventral view, a, anus ; e, right
eye ; /, foot ; in, intestine ; k,
kidney; l.li, left liver lobe; m,
mouth ; op, operculum ; ot, right
otocyst ; pa.c, pallial cavity ; r.li,
right liver lobe ; r.mu, retractor
muscle ; st, stomach ; ve, velum.

one on either side of the rectum, in various Rhipidoglossa, such as
Pleurotomaria (Fig. 127), Haliotis, Turbo, etc., but only one, namely,
that of the left side, in the majority of aquatic Gastropods with a
well -developed mantle. . This glandular organ becomes median
and nearly symmetrical in the Cavoliniidae (Fig. 60) and the
Cymbuliidae.

8o

THE GASTROPODA

The pallial cavity is largely open in the Streptoneura ; its orifice
is narrower in the Tectibranchs (Fig. 148, IV), and is much reduced
in the Pulmonates (Figs. 67 and 177), as the result of the almost
complete fusion of the mantle border with the neck.

The mantle border projects somewhat beyond the shell that
covers it, and may be furnished with little tentacles, with glands
and pigment spots. The border is not continuous in the most
archaic forms, but presents in the median line, or at a neighbouring
point morphologically equivalent to the median line, a more or less
deep longitudinal slit, as may be seen in the Pleurotomariidae (Figs.
54, 127, and 128), in Emarginula, and Scutum. This slit corresponds
in position with the extremity of the rectum, and admits of a more
rapid expulsion of the excrements and the respiratory fluid. The
edges of the slit may fuse together at one or more points, leaving
one or more orifices in the mantle and in the shell on the dorsal
side of the pallial cavity (Fig. 62), as in Fissurella, Puncturella, and
Haliotis. An analogous slit is also present in Siliquaria and Pleuro-
toma. In the female Vermetus
there is a median slit in the
border of the mantle (Fig.
45), but no corresponding
fissure in the shell ; in this

Fio. 62.

Schismope lacuniformis, seen
from the umbilicus, a, aperture
of the shell ; /, foramen ; u,
umbilicus. (After Watson.)

Fio. 63.

Limacina antarctica, removed from its
shell, dorsal aspect, an, auricle ; gl.pa,
pallial gland ; go.se, seminal groove ; na,
right fin ; pa, mantle ; r, kidney ; te.d, right
tentacle; te.g, left tentacle; ve, ventricle
of heart.

case the mantle slit admits of the fixation of the eggs to the
internal wall of the shell, to which they remain attached up to the
time of hatching.

At the left or anterior corner of the pallial aperture the mantle
edge is often produced into a tube with a ventral slit (Fig. 99, XV) ;
this tube or siphon serves to admit water into the pallial cavity.
A siphon exists only in specialised Streptoneura ; it is but slightly
developed in the Cerithiidae, is rather larger in the Strombidae
(Fig. 75, si), and attains its greatest dimensions in the Cassididae and
Doliidae and in all the Rachiglossa and Toxiglossa. In the Volu-
tidae the siphon is furnished with an internal appendage. Ampul-
laria also possesses a long siphon, which may serve either for

THE GASTROPODA 81

pulmonary or for branchial respiration. On the right side of the
pallial opening the mantle border sometimes bears a tentacle, as in
Valvata (Fig. 132), Oliva, Strombus, Acer a, and Gastrupteron. In
Adeorbis there are two such tentacles (Fig. 133). In many Tecti-
branchs the mantle edge at the right side of the pallial opening
bears a large inferior pallial lobe (Fig. 148, I), which forms the
"balancer" in the Thecosomata. This lobe is also found in the
basommatophorous or aquatic Pulmonates, and in some species of
this group it is converted into a pallial branchia (Figs. 89 and 175).

The dorsal surface of the mantle secretes a shell, formed of a
single piece, which necessarily reproduces the form of the mantle,
or rather of the visceral sac contained in the mantle. As the
visceral sac is always coiled (even in forms with conical shells like
the Patellidae and Fissurellidae and in the various Gastropods which
are naked when adult the visceral sac is coiled during develop-
ment), it follows that the shell is also coiled. The curvature of the
coil, or conchospiral, is, generally speaking, a logarithmic spiral.
The spire, that is to say, the totality of the whorls, with the excep-
tion of the last formed, may be excessively prominent, as, for
example, Terebra, Turritella, Turbonilla, certain Cerithiidae, etc., or
may exhibit every possible disposition, until the prominence dis-
appears and the shell becomes discoid al as in PlanorUs, Atlanta
(Fig. 141), etc.

The various whorls of the spire are normally contiguous, but
it occasionally happens that, after a certain number of turns, the
visceral mass and the shell appear to unroll more or less completely,
and to continue their course either in a much looser spiral or in a
slightly curved line, or even in a nearly straight line (Vermetus,
Fig. 45, Magilus, Cydosurus, Caecum, Fig. 68). The extremity of
the last whorl may also form a certain angle with the direction of
the preceding whorls, as, for example, in certain helicomorphous
Pulmonates (Anostoma).

The coil, commencing from the initial point of formation or
summit, is dextral when the shell, held with the summit towards
the observer, has the mouth or aperture below and to the right.
It is sinistral when, under the same conditions,, the aperture is to
the left. Dextral shells are much more common than sinistral.

This direction of the coil, when it is not obscured by " hyper-
strophy," is conformable with that of the asymmetry of the organ-
isation ; that is to say, a sinistral coil correspords completely to the
situs inversus viscerum of a dextral Gastropod. This situs inversus
may be seen in the genera Trifwis, Laeocochlis, Actaeonia, Blauneria,
Clausilia, Physa ; in certain species of the genera Fulgur, Neptunea,
Bulimulus, Helicter, Vertigo, Ariophanta (Nanina), Ancylus, Diplom-
matina ; and in some teratological individuals of Buccinum undatum,
Littorina littorea, Neptunea antiqua, Limnea stagnalis (in which the

6

82

THE GASTRO DA

monstrosity has been sometimes fixed by heredity), Helix, Arion, and
various other Pulmonates. There are, however, forms in which the
coil is hyperstrophic : in this case the whorls which form the spire
are very slightly prominent ; the spire becomes flatter and flatter,
and finally becomes concave and is transformed into a false umbilicus.
At the same time the part corresponding to the umbilicus (the
cavity opposite to the spire) of normally coiled forms becomes
prominent and constitutes a false spire. The coil then appears to
be sinistral, although the asymmetry of the organisation remains
dextral, as, for example, in Lanistes and the coiled thecosomatous
Pteropods, in which the opercular spiral follows the same direction
as the apparent spire of the shell (Fig. 49) ; or reciprocally in
PlanorUSy especially in individuals which are scalariform or terato-
logically unrolled, such as Choanomphalus and Pompholyx (Fig. 64).
Finally, it may sometimes be observed that the spiral in which the
coil is formed insensibly changes its nature or its apparent direction
after the first larval whorls are completed. This is the pheno-

Fio. 64.

Passage from a sinistral orthostrophic form (a) to a pseudo-dextral hyperstrophic one (ft) ;
the heart is indicated in black, in order to show the constancy of the sinistral organisation.
(After J. W. Taylor.)

menon of heterostrophy, in which the spiral from being negative
eventually becomes positive ; that is to say, the coil that was at
first hyperstrophic becomes finally orthostrophic. Examples of
this phenomenon are Solarium (the larval shell of which has been
called Ayadina), Mathilda, the Pyramidellidae (Fig. 65), Melampus,
and various Bullidae.

The line along which two successive whorls of the shells cease
to be in contact with one another is the " suture." The portion of
the shell separating the successive whorls of the visceral spire may
be resorbed in certain cases (many Auriculidae, some Neritidae,
Cypraea, Olivella, etc.), resulting in the concrescence of the whorls
of the visceral sac, or even in the suppression of, its coils, as may
be seen in several species of the genus Auricula (Fig. 67). On
the other hand, the animal may desert the first whorls of the coiled
shell, and cut itself from them by the formation of a transverse
partition or septum : this operation may, in certain cases, be
repeated several times, e.g. Vermetus, Turritella, Caecum (Fig. 68),
Truncatella, Triton (Fig. 66), Cuvierina, etc. In the families
Cylindrellidae, Stenogyridae (Rumina decollata), and Pupidae, and

THE GASTROPODA

in the genera Truncatella, Cerithidea, Caecum, and Cuvierina, the

portion of the shell beyond the septum may be truncated and lost,

or the first whorls may be filled up by a calcareous deposit as in

Magilus. In the conical shell of various Capulidae (Taenioglossa),

Zeidvra, and Septaria (Rhipido-

glossa) and Latia (Basommato- B A

phora)' there is an incomplete

internal septum, corresponding

to the interior margin of the

aperture, which has become

Odostomia dipsycha. A, the entire shell,

seen from the aperture side ; B, the hetero-

strophic apex, more magnified. (After
Watson.)

Fio. 66.

Section of the shell of Triton, a, apex ;
a.c, anterior canal (or siphon) of the aperture
of the shell (a.c to p.c, aperture of the shell) ;
p.c, posterior canal of the aperture; s,
sutures of the whorls ; w, whorls of the
shell ; occupying the axis, and exposed by
the section, is seen the "columella" or
spiral pillar. The upper whorls of the
shells are seen to be divided into separate
chambers by the formation of successively
formed "septa." (From Lankester, after
Owen.)

/to

t/n,

•Win,

Fio. 67.

Auricula (Alexia) bidentata, removed
from its shell, ventral aspect. /, foot ; in,
intestine ; k, kidney ; l.p, labial palp ; tn,
mouth ; m.gl, pallial gland opening into the
pallial cavity; pa, mantle; p.o, pneumo-
stome or pulmonary orifice ; te, posterior
tentacle ; te', rudimentary anterior tentacle ;
vi.m, visceral mass, whose different whorls
are fused together.

prominent. In certain genera this septum is folded into the shape
of a trumpet, the cavity of which affords a lodgment for a pro-
jection of the posterior part of the foot (Crucibulum, Fig. 69). In
the last whorl of the shell of Clausilia there is an accessory piece,
the clausilium, attached to the columellar axis by an elastic
support : this piece closes the mouth of the shell when the animal

THE GASTROPODA

is retracted, but is pushed back against the axis when the animal
is extended.

The Gastropods are attached to their shells by the columellar
muscle (Fig. 45, co\ and withdraw themselves into their shells by its

Fio. 68.

Caecum. A, entire shell, left-side view, o, aperture ; .<*, septa ; sp, spire. (After de Folin.)
B, animal with truncated shell, e, eye ; /, foot ; m, mouth ; op, operculum ; sp, septum ; te,
tentacle. (Alter Plate.)

contraction. This muscle is symmetrical .and horseshoe-shaped in
species with conical shells (Patella, Septaria, Capulus, etc.), but in
other species it is asymmetrical. It is oval in Haliotis, and its
insertion on the columella is nearly linear in coiled forms. The

Fio. 69.

Shell of Crucibulum, seen from below, showing
the inner whorl 6, concealed by the cap-like outer
whorl, a. (From Lankester.)

Fio. 70.

Cypraea europaea, dorsal
view, x 8. /, foot ; ma,
mantle ; sh, shell ; n,
pallial siphon ; t, tentacle.

power of this muscle is often considerable : in Patella vulgata it can
resist a traction of fifteen kilograms. The columellar muscle is
naturally absent in forms without shells (Nudibranchs, Oncidium,
Vaginula), but is present in Testacella.

3. Origin of Naked Forms. — In many cases the oorders of the

THE GASTROPODA

mantle are reflected over the shell and cover a greater or less part
of its external surface. This condition is found in various Fissurel-
lidae (Fissurellidea), in Marsenina, in many Cypraeidae (Fig. 70) and
Marginellidae, in Pyrula(Fig. 71), Aplysia (Fig. 15 4), many Bullidae,
and various Pulmonates, such as Vitrina, Parmarion, Hemphilia,
Homalonyx, Amphipeplea, etc. The portion of the internal surface of
the mantle that has thus become external may bear more or less well-
developed and ramified appendages (Cypraea), and the other surface
of the reflected mantle may sometimes secrete an external coating
of enamel over the portion of the shell to which it is applied. The
borders of the mantle, extending more and more over the shell,
may finally meet, unite, and thus form a closed sac containing the

FIG. 71.

Animal and shell of Pi/rula laeviyata, seen from above, a, siphon ; ft, head-tentacles ; ("',
head ; d, foot, expanded as in crawling ; h, the mantle-skirt reflected over the sides of the
shell. (From Lankester, after Owen.)

shell, which, together with the visceral sac contained in it, suffers
a diminution, or even an almost complete disappearance, of its
spiral form, so that the animal appears to be quite naked. This
condition may be seen in Pupilia among the Fissurellidae, in the
majority of the Lamellariidae, in Pustularia among the Cypraeidae,
in many Tectibranchs, such as Notarchus, Doridium, Gastropteron,
Philine, Pleurobranchus, and in sundry limaciform Pulmonates. In
some cases the shell-sac remains in communication with the exterior
by means of a fine ciliated canal, situated at the posterior end of
the body (Philim, Doridium). In the Tectibranchs the internal
shell is often very slightly calcified, and at the same time the
pallial cavity becomes more and more reduced. Finally, the shell
and the shell-cavity disappear, leaving the mantle absolutely naked

86 THE GASTROPODA

and without a spiral coil At the same time there is a return to a
secondary external symmetry. This phenomenon may be seen in
the Titiscaniidae, Pterotrachea (Fig. 143), Euncina, Phyllaplysia, the
gymnosomatous " Pteropods" (Fig. 84), the Cymbuliidae (Fig. 151),
Pleurobranchaea (Fig. 157), the Nudibranchs (Figs. 160, 161, etc.),
the Philomycidae, the Oncidiidae (Fig. 59), and the Vaginulidae
(Fig. 179). In these cases, excepting Cenia and ftuncina, the shell
exists only during development, and falls off at the close of larval
life. As a rule, the pallial cavity is reduced at the same time
(Pterotrachea, Pleurobranchaea, Gastropterori), or it may disappear
together with the ctenidium, and the external surface of the dorsal
visceral envelope may give rise to various appendages such as the
cerata or dorsal "branchial " papillae of Nudibranchs (Fig. 160, A, c)
and the terminal branchia of the Gymnosomata (Fig. 84, VII). In
one instance in which the larval shell is caducous a second per-
sistent shell is formed, covered by the mantle : such is the case in
Lamellaria, whose primary shell is covered with spines, and was for-
merly believed to belong to another animal to which the name of
Echinospira was given.

In parasitic Gastropods the naked condition of the adult is the
result of an essentially similar process, but the shell is covered over
by a cephalic expansion known as the " pseudopallium " (Fig. 20, ps).
Finally, the nudity of certain "Heteropods" (Pterbtracheidae) is
due to the progressive reduction of the visceral sac and the dis-
appearance of the mantle. In many Gastropods that are naked in
the adult condition calcareous spicules of some size are developed
in the sub-epithelial conjunctive tissue of the mantle, e.g. in the
Pleurobranchidae and in Doridomorpha, the Hedylidae among the
Nudibranchs. In the Cymbuliidae (Fig. 151, II) the sub-epithelial
connective tissue gives rise to a pseudo-conch.

II. ANATOMY.

1. The Alimentary Canal. — This comprises, in the various forms
of Gastropods, a buccal cavity connected by the oesophagus with a
stomachal cavity, and an intestine properly so-called, the last-named
being tolerably long and coiled. The buccal cavity and the
oesophagus are of ectodermic origin, and taken together form
the fore gut. The buccal cavity normally opens at the extremity
of the head, which generally has the form of a cylindrical snout
slightly inflected towards the ventral surface (Fig. 130, VI). In
many cases, however, the opening of the buccal cavity is carried
backward by the development of an invagination of the pre-oral
integuments, and thus an apparent mouth is formed which is not
morphologically equivalent to the true mouth, the latter being
carried to the anterior extremity only by an evagination of the

THE GASTROPODA

tegumentary ingrowth, which in this manner gives rise to a
proboscis. When this extensible proboscis is evaginated the
oesophagus forms its interior lining ; when it is invaginated the
oesophagus forms its posterior continuation. Such is the pleurec-

L

^

f\

fll

\

al-

Fio. 72.

Diagrams explanatory of the nature of so-called proboscides or "introverts." A, simple
introvert completely introverted. B, the same, partially everted by eversion of the sides, as in
the Nemertine proboscis and Gastropod eye-tentacle = pleurecbolic. C, the same, fully everted.
D, E, a similar simple introvert in course of eversion by the forward movement, not of its sides,
but of its apex, as in the proboscidean Rhabdocoels = acrecbolic. F, acrecbolic ( = pleurembolic)
introvert, formed by the snout of the proboscidiferous Gastropod, al, alimentary canal ; d,
the true mouth. The introvert is not a simple one with complete range both in eversion and
introversion, but is arrested in introversion by the fibrous bands at c, and similarly in eversion
by the fibrous bands at I). G, the acrecbolic snout of a proboscidiferous Gastropod, arrested
short of complete eversion by the fibrous band &. H, the acrembolic ( = pleurecbolic) pharynx
of a Chaetopod fully introverted, al, alimentary canal ; at d, the jaws ; at a, the mouth ;
therefore a to d is stomodaeum, whereas in the Gastropod (F) a to d is inverted body surface.
I, partial eversion of //. K, complete eversion of H. (After Lankester.)

bolic proboscis of Ray Lankester (Fig. 72) found in the Cypraeidae,
Naticidae, Lamellariidae, Scalariidae, Vermetus, the Capulidae,
Calyptraeidae, Strombidae, and Chenopodidae among the Strep-
toneura, and in some Opisthobranchs, viz. Doridium, the Pleuro-
branchidae, Aplysia, the Gymnosomata, and the Doridopsidae: In
other cases the proboscis cannot be wholly retracted, and then the

88 THE GASTROPODA

wall of the digestive tube is folded twice on itself during invagina-
tion. This is the pleurembolic proboscis of Ray Lankester (Fig. 72)
found in the Rachiglossa (Fig. 99, XIII), in certain Toxiglossa, and in
the Doliidae, Cassididae, and Tritonidae among the proboscidiferous
Taenioglossa. In the Naticidae there is a glandular disc on the
ventral face of the proboscis which serves to perforate the shells
of the Lamellibranchs on which they feed, and in the Pneumo-
dermatidae there are suckers in the same position situated on two
retractile lobes and either isolated or united to one another.

The mouth leads into the buccal or pharyngeal cavity, which is
the first of the principal dilatations of the digestive tract. The
salivary glands open into it, and the chitinous masticatory sclerites
are attached to its walls. The whole, together with the muscular
masses which actuate the masticatory apparatus, forms the buccal
bulb or pharynx (Fig. 74, A), situated behind the oesophageal nerve-
collar in the more archaic species, but in front of it in the more
specialised Gastropoda (Fig. 146). In some carnivorous forms,
such as Glandina and Testacella, the pharynx may be more or less
completely evaginated, forming a false pleurecbolic proboscis. The
chitinous buccal sclerites are of two kinds, mandibular and radular.
(1) The mandibles are solid cuticular thickenings situated at the
anterior end of the buccal cavity. In the majority of Streptoneura
and Opisthobranchs they are paired, the members of the pair being
lateral and symmetrical (Fig. 73, A) ; they are smooth or scaly,
generally with trenchant, but sometimes with denticulated margins.
These paired mandibles are usually quite separate from one another,
but in the Naticidae they are in contact dorsally, and in Lamelkiria
they are clearly fused together on the dorsal side to form a single
piece. Similarly there is only a single median mandible formed by
the fusion of two symmetrical pieces in the Patellidae, in Aegirus

(Doridomorpha, Fig. 73, B), and in
all the Pulmonates. This median
mandible is dorsal, its lower or free
border is trenchant, nearly horizontal,
and frequently provided with a median
projection. Two lateral and sym-
metrical accessory cuticular thicken-
FIO. 73. ings are found in the majority of

Mandibles of Gastropoda. A, paired the baSOmmatOphorOUS PulmonatCS
lateral mandibles of Janui ; B, dorsal /7"Vw«/T«/7 Plnnnrhie ofp \ Tn rt*r
mandible of AegirM. (After Hancock.) (******, flanOTtoS, CtC.).

tain Aplysiomorpha in which the

mandibles are ventral there is a patch of horny spines on the
roof of the buccal cavity (Notarchus\ and in certain cases these are
divided into two symmetrical groups enclosed in diverticula, which
have the form of evaginable sacs (Gymnosomata). In the Rachi-
glossa the mandibles are rudimentary, and they are absent in many

THE GASTROPODA 89

Trochidae, in Neritina, in the Helicinidae, in Cydostoma, in Thyca, in
the Pyramidellidae, Eulimidae, Entoconchidae, and Coralliophilidae,
in all the Toxiglossa, in the Heteropods, in Actaeon, Tornatina,
Scaphander, Doridium, the Lophocercidae, Cymbuliopsis, Gleba, Clionc,
Umbrella, Dwis, the porostomatous Doridomorpha, Tethys, the
Elysiae, Gadinia, Amphibola, the Testacellidae, etc.

(2) The radula is a sort of ribbon of greater or less width, formed
of distinct and separate chitinous teeth, borne on a single supporting
membrane. It is secreted in a ventral caecum (Fig. 74, A, n), in which
it is almost wholly contained, but its anterior extremity stretches
out on the floor of the buccal cavity, Avhere it forms a median
projection (Fig. 74, A, p). The radular ribbon is supported by a
system of paired cartilaginous pieces furnished with protractor and
retractor muscles (Fig. 74, A, I, m), the action of which causes the
radula to move to and fro and work like a rasp on the prey seized by
the animal. The teeth are secreted at the bottom of the caecum or
sheath of the radula, by a small number of matrix cells ; in front of
these is -a transverse row of cells which secrete the basal membrane.
The teeth are disposed in transverse rows, and in each row there is
a median tooth called the " central " or rachidian tooth, on either
side of which the remaining teeth of the row are symmetrically
disposed. In the Euthyneura all the lateral teeth are generally
similar to one another (Fig. 145), but in the Streptoneura, when
there is more than one tooth on either side, they are divided into two
clearly defined groups. The teeth nearest to the central are the
"laterals," properly so-called, and differ from the more elongated
external teeth, which are known as the " marginals " or uncini (Fig.
2, m). The number of teeth in any given transverse row is
constant in any given species ; it may, however, increase slightly
with age, at any rate in various Aplysiidae and in the terrestrial
Pulmonates. On the other hand, the number of teeth is variable
from group to group, and generally is more considerable in the less
specialised than in the more specialised groups. Thus, in the
Streptoneura the Rhipidoglossa have numerous lateral teeth on
either side of the central ; the Taenioglossa have only three lateral
teeth on either side, the Rachiglossa only one. Among the
Opisthobranchs many teeth are included in each transverse row
in Actaeon and the Pleurobranchidae, but there are only three in
the thecosomatous " Pteropods " and only one in the Elysiae. The
number of successive transverse rows also varies from species to
species, and consequently the total number of teeth in the radula
is very different in different forms. There are sixteen (one tooth
in each row) in certain Eolidae and Elysiae ; about two hundred and
fifty in Buccinum undatum-, 1920 in Patella vulgata; 3500 in
Littmina littorea ; 6000 in Doris tuber culata ; 8343 in Limnaea
stagnalis ; 15,000 in Helix aspersa ; 26,800 in Limax maximus;

Fio 74

Radulae of varipus glossophorpus Mollusca. A, diagram showing mouth, oesophagus, and
lingual apparatus of a Gastropod in median sagittal section, a.l, lower lip ; a.u, upper lip ; b,
jaw of the left side ; c, outer surface of the snout ; d, oesophagus ; e, fold in the wall of the
oesophagus behind the radular sac (71) ; /, anterior termination of the radula and its bed, the
point at which it wears away ; g, base of the radular sac or recess of the pharynx ; h, cartila-
ginous piece developed in the floor of the pharynx beneath the radula, and serving for the
attachment of numerous muscles, and for the support of the radula; i, anterior muscles ; fc,
posterior muscles attached to the cartilage ; I, muscle acting as a retractor of the buccal mass ;
m, muscle attached to the lower lip ; n, posterior extremity of the radular sacj o, the bed of
the radula or layer of cells by which its lower surface is formed ; p, the raflula or lingual
ribbon ; q, opening of the radular sac into the pharynx or buccal cavity ; r, cells at the extreme
end of the inner surface of the radular sac which produce, as a cuticular secretion, the rows of
teeth of the upper surface of the radula.

B, radula or lingual ribbon of Paiudina vivipara, stripped from its bed.

C, a single row of teeth from the radula of Trochu* dnerarius (Rhipidoglossate) ; formula :
00.5.1.6.00.

D, a single row of teeth from the radula of lanthina fragilis (Stenoglossate) ; formula :
oo.O.oo.

E, a single row of teeth from the radula of Trachydtrmon cinereum (Amphineura) ; formula :
3.1.2.1.1.1.1.1.2.1.3.

Ft a single row of teeth from the radula of Patella vulgata (Docoglossate) ; formula :

G, a single row of teeth from the radula of Cypraea helvola (Taenioglossate) ; formula :

' H, a 'single row of teeth from the radula of Nassa annulata (Rachiglossate) ; formula :
1.1.1. The common Whelk is similar to this.

90

THE GASTROPODA 91

36,000 in Tritonia hombergi-, 40,000 in Helix ghiesbrechti ; 75,000
in Susania tuberculata ; and as many as 750,000 in Umbrdla. It
follows that the length of the radular ribbon varies very much ; it
is considerable in Cydostoma and Patella (Fig. 88, r\ in which it
exceeds the length of the body, and in the Littorinidae, in which
it is coiled into a spiral so as to occupy less room ; in one species,
Tectarius, it attains to seven times the length of the body.

The form of the teeth is also constant in a given species, but
varies from group to group, and is therefore, when taken in
conjunction with their number, of considerable assistance in
characterising the divisions of the Gastropoda, especially of the
Streptoneura ; hence the importance of the radula in systematic
works. But occasionally the radula may vary in the individuals of
the same species, as, for example, in the Buccinidae ; and, on the
other hand, groups tolerably far apart from one another may
exhibit analogous features in the radular teeth. Further, it has
been shown that the number of teeth in a transverse row varies in
all the groups founded upon this character. Among the Taenio-
glossa, in which the radular formula is -2.1.1.1.2, the two marginals
are absent in Lamellaria and Jeffreysia ; and contrariwise, there are
more than two marginal teeth in certain species of Turrtietta, in
Struthiolaria, and Triforis. A still larger number of teeth, but no
median tooth, is found in Solarium, Scalaria, and Janthina. In the
Rachiglossa, characterised by the formula 1.1.1, the central tooth
is reduced in Columbella, and the laterals absent in the Marginellidae
and in certain Volutidae and Mitridae, and in the young Harpa, the
adult in the last-named genus being devoid of a radula. Finally,
although the radular formula of the Toxiglossa is given as 1.0.1,
there is a central tooth, and more than one lateral in sundry Pleuro-
tomatidae (Spirotropis : 1.1.1.1.1). The radula is absent in a few
genera only, and those are generally parasitic or suctorial forms,
such as Thyca, the Eulimidae, Pyramided idae, Coralliophyllidae, and
certain Terebra among the Streptoneura, and in the Tornatinidao,
Cymbuliopsis, Gleba, the Doridiidae (in which a vestige of the radular
caecum is still retained), the porostomatous Doridomorpha (Dori-
dopsis, Coranibe, Fig. 164, Phyllidea), and the Tethyidae.

The buccal opening of Gastropods is furnished with glands,
often in considerable quantity (Bullidae, Nudibranchs), and in many
stylommatophorous or terrestrial Pulmonates these glands are
so highly developed as to form lobulated masses known as the
" organs of Semper." But in all Gastropods, with very rare excep-
tions, the salivary glands proper open into the interior of the buccal
cavity on either side of the radula. These organs are generally
simple mucous glands, without any digestive action, but in certain
forms — Dolium galea is an instance — their secretion contains as
much as 4 per cent of sulphuric acid, which serves to dissolve the

92 THE GASTROPODA

calcareous spicules of the animals taken as food. In the aspido-
branchiate Streptoneura and in many other Gastropods the salivary
glands are racemose in structure, but in more specialised genera
they have the form of more or less elongated tubes (Janthina) or of
sacs (Dolium). In the Aspidobranchs, Ampullaria, and the Actaeo-
nidae (Fig. 57) the salivary ducts are very short and open behind
the perioesophageal nerve-collar, but the glands traverse the nerve-
collar, and their ducts are long and open in front of it in the
majority of Gastropods. This is the case in all the Euthyneura —
the salivary glands being situated very far back in the Pleuro-
brancheae — and in the Taenioglossa, with the exception of Natica,
certain species of Calyptraea, etc., in which the ducts are too short
to traverse the nerve-collar. Finally, in the Stenoglossa and
Heteropoda the salivary glands open in front of, but do not
traverse the perioesophageal nerve-collar, their ducts, if they are
sufficiently long to reach it, passing outside the structure. In
certain forms, e.g. Fulgur, Conus, many Terebra, Umbrella, several
Pulmonates, etc., the two salivary glands appear to be fused, but
retain their individuality. In some siphonate probosciferous
Taenioglossa, such as Dolium, Cassis, Triton, Voluta, and also in
- Pleurobranchaea, the salivary ducts bear a dilatation near their
extremities. The two glands exhibit a certain degree of asymmetry
in Stromhus, Xenophorus, and some species of Atlanta. In several
cases there is more than one pair of salivary glands ; the Docoglossa
possess two pairs, with distinct and separate ducts. In Janthina
and Scalaria there are two pairs of glands, lying close together and
appearing to be formed by the bifurcation of a single pair. There
are also two separate pairs — the second pair being ventral and
anterior to the normal pair — in various Rachiglossa, Purpura,
Trophon, Valuta, Cancellariidae, and Haliidae ; with the exception
of the Muricidae this second pair is anterior to the perioesophageal
nerve-collar, and its ducts are often fused in the median line.
Many probosciferous Opisthobranchs also have more than two
salivary glands : in the porostomatous Doridomorpha (Dcnidopsis,
Phyllidiidae) the second pair is ventral and anterior, with a single
duct ; in PleurobrancJiaea and Pleurobranchus there is a third dorsal
and median gland.

The buccal cavity is followed by an oesophagus, with plicated
walls. This oesophagus is generally long, and often presents dila-
tations on its course, which may be described under one or any
other of the following headings: — (1) A sort of simple pouch with
thin walls,. as in the Heteropods (Figs. 141 and 142, m) and certain
Opisthobranchs and Pulmonates, or sometimes a muscular swelling,
as in Murex, Amphibola, Doris, etc. (2) In the majority of the
Aspidobranchs there are, as in the Chitonidae, paired anterior
glandular oesophageal pouches, with papillated internal walls.

THE GASTROPODA 93

These organs also recur in Littwina. (3) An unpaired folded
dilatation near the middle of the oesophagus is found in various
carnivorous Taenioglossa, e.g. the Naticidae, Lamellariidae, and
Cypraeidae; in the last named it is well developed and has
a lamellate internal wall. In the same position in the Cassididae
there is a pouch separated from the oesophagus and opening into
it by a slit. (4) In all the Taenioglossa, with the exception of
Cancellaria, the Harpidae, and some species of Terebra, an important
oesophageal gland, known as the " gland of Leiblein," opens into
the middle of the oesophagus. Slightly developed in the Olividae
and Fasciolariidae, this organ appears under diverse forms : it is
a thick glandular mass in Murex, a long caecum with thin walls
in Buccinum, and in Toxiglossa it forms the so-called "poison
gland," whose duct traverses the perioesophageal nerve -collar,
as in Valuta, and opens into the buccal cavity, giving the whole
structure the appearance of a third salivary gland. In Haifa
and Marginella this organ forms a siphon opening into the oeso-
phagus by its two extremities. (5) In Nerita there is also an
unpaired oesophageal gland, and among the Opisthobranchs one
finds an azygous dorsal pouch in some Bullomorpha, an oesophageal
caecum in the Elysiomorpha, and a long glandular appendage in
the Lophocercidae.

Tbf terminal part of the oesophagus sometimes presents modifi-
cations which produce an apparent modification of the configuration
of the stomach following immediately after. This terminal portion
is differentiated to form a gizzard with thick muscular walls and
furnished internally with masticatory teeth or plates. The last
named are variable in number, and may be simply chitinous
and pointed or calcified and flattened. This arrangement is found
in a large number of Opisthobranchs, viz. in the majority of Bullo-
morpha (Fig. 76, m.p), including the "Pteropoda Thecosomata"
(Fig. 60, m.p), in various Aplysiomorpha, and in certain Nudi-
branchia Tritonomorpha (Marionia, Scyllaea, Melibe). The muscular
girdle of this gizzard is also recognisable in a certain number of
basommatophorous Pulmonates, viz. Amphibola, Auricula, and in
Limnaea it is differentiated to form two globular and symmetrical
muscular projections. In consequence of the proximity of the
specialised portions of the terminal part of the oesophagus to the
stomach, the latter appears, in certain cases, to be divided into
several successive portions separated by constrictions, notably in
Aplysia, and also in Amphibola and Limnaea, in which the oesophagus
exhibits an ampulliform dilatation in front of the gizzard.

The stomach proper consists of a simple enlargement of the
digestive canal, and its walls are normally and fairly consistently
thin, especially in the Streptoneura. The internal wall of the
stomach, however, may frequently be lined by a more or less thick

94

THE GASTROPODA

and extensive cuticle, which is generally more fully developed near
the origin of the intestine, and may extend into it, as in Paludina,
Cydostoma, and certain Pulmonates. Sometimes this lining presents
a specialisation in the form of a longer or shorter cuticular projec-
tion known as the crystalline style, which may be lodged in a thick-
walled caecum or may project as a rod into the proximal part of

Pio. 75.

Pteroceras, right-side view of the male, with the mantle laid open, a, anus ; b.d, bile-duct ;
c.g, cerebral ganglion ; cr.s, crystalline style ; /, foot ; g, gill ; g.fi, gonad ; g.o, genital orifice ; h,
heart ; hy.g, hypobrancliial gland ; i.g, infra-intestinal gland ; in, intestine ; k, kidney ; m,
mouth ; oe, oesophagus ; op, operculuin ; p, penis ; pa, mantle ; p.g, pedal ganglion ; pl.g, plural
ganglion ; ra, radula ; r.o, renal orifice ; r.p, reno-pericardial orifice ; s.g, supra-intestinal gan-
glion ; *i, 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 Fissurella, 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 thp St.rom-
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 Pleurotomaria (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

ancl *orm of wnicl1 varv in

Fia. 76.

Philine aperta, dorsal aspect ; the body-wall is
supposed to be transparent, a, anus; a.g, ab-
dominal ganglion ; c.g, cerebral ganglion ; c.h,
cephalic hood ; y, gill ; g.o, genital (hermaphroditic)
orifice ; gz, gizzard ; h, heart ; in, intestine ; k,
kidney ; m, mouth ; m.p, masticatory plate ; os,
osphradinm ; pa, mantle ; par, parapodia (lateral
lobe of foot) ; p.g, pedal ganglion ; p.l, inferior
pallial lobe ; pl.g, pleural ganglion ; r.m, retractor
muscle of buccal mass ; r.o, renal opening ; r.p,
reno-pericardial opening ; s.g, seminal groove ; sh,
shell ; s.i, supra-intestinal ganglion ; st, stomach.
(After Guiart.)

Alimentary canal of Eolis papil-
losa, dorsal view, an, anus ; e, hind-
gut ; h, hepatic appendages of the
mid -gut (all of which are not
figured) ; m, mid-gut ; ph, pharynx.
(From Lankester, after Alder and
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 Fakata. 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 (Phikmycus 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), Ancylm 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 (Cydostonw,) 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 cnidosacs, 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 Ranella. 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. As a 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

.0

Fio. 78.

Tanganyicia ruJUosa, dorsal view, with the mantle laid open, a, anus ; b.p, brood-pouch ;
b.p.o, orifice of brood-pouch ; ce.g, cerebral ganglion ; cr.s, crystalline style ; /, foot ; g, gill ; h,
heart ; in, origin of the intestine or pyloric orifice of the stomach ; m, mouth ; od, oviduct ; Of,
termination of the oesophagus, or cardiac oriiice of the stomach ; o.o, oviducal orifice ; os,
osphradium ; pa, mantle ; st, stomach ; s.i.g, supra-intestinal ganglion. (After Moore.)

in the Streptoneura, but may be seen in CypmcAi 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, e.g.
Littorim, Buccinum, Natica, etc. In some few Gastropods the blood
is of a bluish tint in consequence of the presence of an albuminoid
containing copper called Juiemocyanin. 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
Fasciolaria. 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, Oncidium, 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 Rhipidoglossa, 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, au) : 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), etc. In the majority
of the Streptoneura (Fig. 99, V), in the Pulmonates (Fig. 86,
VII), and in some Bullomorpha — e.g. Adaeon, Limacina (Fig. 63),
Clio virgula, and Clio acicula — this ventricle is posterior to the
single auricle; in some Opisthobranchs (Phyllirhoe, 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

x«v

XII

XI

IV

VI

IX

VIII

Fio. 79.

DoritpUosa, 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, Nudibranehs,

ioo 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 -de. /eloped 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 Patella (Fig. 80, V),
various species of Fissurella,
Ampullaria, Natica, and the
Heteropoda, and a similar
but extra - pericardial bulb

Heart of Patdlti vulgata, the auricle and ventricle in Swhonaria. In Certain

opened. I, "branchial" vein; II, auriculo- ventricular TT j mi

valve; III, posterior aorta; IV, valve between the Heteropoda, IhCCOSOmata,
ventricle and the nortic bulb ; V, aortic bulb ; VI, i XT A -v. u *u

anterior aorta ; VII, ventricle, with its internal and Nudlbranchs there IS a

muscular columns ; VIII, auricle ; IX, pores leading valvp at trip oricn'n nf flip

into the auricle the blood of the roof of the pallia! VaiVG ai tne

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, etc.
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

101

primitively aquatic and
The organs of aquatic

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, Cydostoma) and in certain Pulmonates the blood is carried
direct to the auricle without passing through the respiratory
apparatus.

The respiration of Gastropods is
remains so in the majority of forms,
respiration consist of a pair of leafy
expansions of the mantle, situated in
the pallial cavity and called ctenidia.
Each ctenidiurn is the homologue of a
single branchia of Chiton (Fig. 28, B, g\
of Nautilus (Fig. 276), or of Nucula
(Fig. 206), but most usually only one,
namely, that of the topographically left f.
side, persists (Figs. 82 and 85). It is 9
only in the more primitive Ehipido-
glossa — viz. the Pleurotomariidae (Fig.
127), the Fissurellidae (Fig. 81), and
the Haliotidae — that a pair of ctenidia
persists. In the Fissurellidae these two
organs are quite symmetrical and of
equal importance, but in the Pleuro-
tomariidae and Haliotidae the topo-

d.

81.

. . ,, . . ... . ,-. Dorsal view of a specimen of

graphically right CtenidlUm IS Smaller Fissurella from which the shell has

than the left, and in all other Gastropods
there is only a single ctenidium, that of

the right side having completely dis- (archaic right) gill-plume ; «, reflected

j T ii ,1 cu J.T- mantle-flap ; fi, the fissure or hole in

appeared. In all the Streptoneura, the the mantle -flap traversed by the

Pleurobranchidae, Gastropteron, and the ^^Sa^^^S^'i

Lophocercidae each Ctenidium is formed h> left (archaic ri«ht)renal aperture;
- *o . £1 , . , P, snout. (After Lankester.)

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, Pleurotomaria, 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 Scissurella (Fig. 54, IV) the right ctenidium
is already degenerate in so far that it has only a single row of
filaments inserted directly on the wall of the pallial cavity. The
other ctenidiate Aspidobranchs have only a single and equally
bipectinate ctenidium, as has also Valmta (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

Fio. 82.

Anterior part of the body of Acvuiea, showing nervous and circulatory systems, dorsa
Aspect, a.g, abdominal ganglion ; ao, aorta ; an, auricle ; ftr.n, branchial (ctenidial) nerve
br.v, branchial vain; ee.g, cerebral ganglion; gi, gill; i.i.g, infra-intestinal ganglion; mi/,
coluinellar muscle ; os', ot"t left and right osphradia ; pa, mantle ; pa.v, pallial vein ; pe.c, pedal
cord ; pe.gr, pedal ganglion ; pl.g, pleural ganglion ; s.i.g, supra-intestinal ganglion ; te, tentacle
ve, 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 Scurria,
etc., and certain Pneumoder-
matidae (Fig. 84, VI, VII), a

FIG. 84.

FIG. 83.

Tritonia lineata, dorsal view.
I, rhinophore or posterior
tentacle ; II, dorsal appendage
(pallial gill); III, right eye",
IV, frontal veil; o, genital
(hermaphroditic) orifice. (After
Hancock.)

VII

right - side view,
with the head above. 1, the expanded
proboscis ; II, anterior tentacle ; III,
posterior tentacle ; IV, genital (herma-
phroditic) opening : V, right tin ; VI,
ctenidium ; VII, posterior pallial gill ;
VIII, posterior lobe of the foot; IX,
reno-anal cloaca ; X, lateral margin of
the foot ; XI, penial orifice ; XII,
sucker-bearing appendage ; XIII, ven-
tral median papilla of the proboscis ;
XIV, seat of the mandibles ; XV, ex-
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 pal Hal branchiae are situated on the internal face of
the mantle, as in Patella (Fig. 125, /). In various Gymnosomata
(Clionopsis, Notobranchaea, etc.) they are situated on the posterior
surface tf 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 Pleurophyllidia 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 Phyllirhoe (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 Littorina (L. 'nidis,
L. neritoides, etc.), Cremnoconchw, 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 Littorina
(Fig. 85, x) and in Crcmnoconchus. 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

IX

Fio. 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
organs of its inner surface, n, anus ; br,
ctenidium ; c, heart ; h, liver ; i, intestine ; m.c,
columellar muscle (muscular process grasping
the shell) ; p, penis ; p.br, osphradium ; r,
kidney ; r1, aperture of the kidney ; t, testis ; v,
stomach ; v.d, vas deferens ; v.d', the groove-like
part of latter; x, vascular prolongations of the
ctenidial leaflets ; y, hypobraucliial gland.
(From Lankester, after Souleyet.)

Fio. SO.

Roof of the pallial cavity (lung) of
Umax. Ventral aspect. I, cloacal (reno-
anal) orifice ; II, pneumostome ; III, reno-
pericardial orifice ; IV, rectum ; V, renal
duct; VI, kidney; VII, heart - ventricle ;
VIII, pericardium (cut open); IX, heart-
auricle ; X, ramifications of the pulmonary
vein. (After Leidy.)

Rhipidoglossa, 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

io6

THE GASTROPODA

admitted by a very extensible pallial siphon. In the puhnonate
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 circumpulmonary
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

HTM, Van

Fro. 87.

I'ayinula occidentalis, right-side view, with the mantle partially removed on this side, an,
anus ; aw, auricle ; o.f, female orifice ; o.r, renal opening in the rectum ; o.r.p, reno-pericardial
pore ; o.r.u, orifice of the kidney in the ureter ; p, foot ; pa, mantle ; pe, pericardium ; r, kidney ;
re, rectum (the dotted line shows the direction of the intestine) ; ten, tentacles ; ur", ur",
primary and secondary ureters ; ren, ventricle.

chamber continued into numerous tubules which penetrate into
the surrounding blood sinuses : these tracheate 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, etc.).
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
Planwbis wrneus (Fig. 89, g) there is a single respiratory lobe, with
a richly vascularised surface, and in Ancylus there is a similar

FIG. 88.

Diagram of a sagittal section of Patella vulgata. br.a, branchial afferent vessel (artery) ;
br.v, branchial efferent vessel (vein) ; b.r, blood-vessel ; c, muscular substance forming the root
of the foot ; cor, heart within the ]>ericardium ; e, mantle-skirt ; /, papilla of the larger kidney ;
g, anus ; i, smaller kidney ; k, larger kidney ; I, pericardium ; n, liver ; o, mouth ; od.m, muscles
and cartilage of the odontophore ; j>, snout ; q, intestine in transverse section ; r, radular or
lingual sac ; rd, radula ; s, lamellated stomach ; t, salivary gland ; v, duct of same ; r, buccal
cavity ; w, gonad. (After Lankester.)

structure, but the lung has disappeared. In Bulinus, including
the sub-genera Isidom, Pulmobranchia, etc., and in Miratesta there
is a folded branchia. In Siphonaria the long plicated branchia
which extends across the interior of the roof of the pulmonary

Planorbis corneus, removed from the shell ; anterior view, o, anus ; /, foot ; g, #11 ; fc.o,
renal aperture ; m, mouth ; as, osphradium ; pa, mantle ; pn, pneumostome ; si, 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 : —

io8

THE GASTROPODA

l! ..!.'•

'W

11 ll

® ^

~ a . 3 * • • 'S> «

^ ^

11 l! ft

y

^ . ^^

2 a &< £»
II 1g S§

•5

« n c
-£> o o

fee • g^S * 8

«.S <N£ | 3

•55 .££ .... 5-5

e6

i

.JJ .

•re •£•£ 12 *

+*

I "II '

^ r • i '

. . .

•a | o g
5 B • "s ^s • • • •

« S 5 «

^2 .2 -g §•

«8 T3 • S § • ' ' '

c *S o< o

.- -I

il.^i. --. -

OH -M -S ns

fUla

-

M

°* *1 . J- 3 • • r

.4 .4 r 9 e ^

*J -M PH o •!-;

'5 '£ IJ *sb_ .
gB

I

ea

? 1

- § 3

§ ^ bC

'aS S ^> . .

>>

•=• S >>

^3^_ S g to .2
1 |J ||| 1

Jo
>»

s

i^ri

c ,3 g

1 §'1 IgS

1

§ « «

§ ^3 rfi
5) -M -M

:s s ^ J*^ •&

9

£ > >

^

If

15^3

THE GASTROPODA

109

3. Excretory 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, /, 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.

Fio. 90.

Transverse section of the lung of Janetta, 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, k), 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, r). 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

no

THE GASTROPODA

communication. Elysia 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). As a 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 Lirnax (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, /), but is a simple slit,
shaped like a button -hole, in
the majority of Pectinibranchia
(Fig. 99, IV) and Tectibranchia
(Fig. 154, o). Among the Pec-
tinibranchs, however, Paludina

Fio. 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 ; <j, anal papilla,
with rectum leading from it; h, papilla
of the smaller kidney, which is only
represented by dotted outliiu-s ; I, peri-
cardium, indicated by a dotted outline
(at its right side are seen the two reno-
pericardial pores) ; /, 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.l, left lobe
of same ; ks.i, inferior sub-visceral lobe
of same; ks.p, posterior lobe of the
right kidney. (After Lankester.)

Fio. 92.

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 tive such pores on
the right-hand side); VI, the ventral
reuo- pericardia! 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, fc),

THE GASTROPODA m

in Phyllirlioe (Fig. 161, I). 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 (Pleurotomaria, 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 Valvaia,
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 Cydostoma 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 Carinaria, and on the wall of the arterial trunks of
certain Streptoneura -and many terrestrial Pulmonates, in which
calcareous 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

112

THE GASTROPODA

such as Cyclophoru$ and Cypi'aea, 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,^?/.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

Fia. 93.

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, CydopJwrus, 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 vFig. 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

U'n-t

majority of the Pectinibranchia, including the Heteropoda, and in
various Bullomorpha (e.g. Actaean, 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.g).

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
the names supra-intestinal and infra-intestinal

.. •, ,, ... J'lenrotomaria,

are respectively given to the two moieties system, dorsal
and to the ganglia borne on them (Fig. 123).
This disposition of the visceral com-

Fn:. 04.

coium insure ; c.pl.<,
cerebro • pleural commissure :
miSSUre IS Common to all the StreptOlieUra i.i, infra-intestinal portion of

(as the name of the group signifies), in-
cluding the Heteropoda and all the forms
formerly called "Orthoneura," i.e. forms in pi-p-c, piem-o"- pedal

, . , X • 11 IT lit tive» s-i» supra-intestinal part

Which the Visceral loop Was believed to have of the visceral commissure ;

never been twisted ; it may also be clearly (After^M^woS^
seen in the more archaic Euthyneura (which,

as has been explained above, are detorted Gastropods), for instance,
in various Bullomorpha (Actaem, Fig. 57, Scaphander, JBulla,
CLC.), 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
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

<tb.

Fio. 05.

Nervous system of Aylysiu
(dorsal aspect), as a type of tin-
long -looped Euthyneurous con-
dition. The untwisted visceral
loop is lightly shaded. ab.pi>,
visceral ganglion which repre-
sents the abdominal + the supra-
intestinal ganglia of Streptoneuru,
and gives off the nerve to the
osphradinm and another to an
unlettered so - called " genital "
ganglion ; ce, cerebral ganglion ;
o, osphradium ; pt, pedal ganglion
and double pedal commissure ;
i>t, pleural ganglion (the stomato-
gastric commissure and ganglia
are omitted). (From Lankester,
after Spengel.)

Fie. 06.

iMia neritoide*, central nervous system, dorsal
view (the buccal mass is indicated by a dotted line),
bit, buccal mass ; co.vi, visceral commissure ; y.a,
abdominal ganglion ; <j.bii, buccal ganglion ; y.ce,
cerebral ganglion; g.i.i, infra - intestinal ganglion;
f/.jw, parietal ganglion ; g.pe, pedal ganglion and
double pedal commissure ; g.rf, pleural ganglion ;
g.s.i, supra-intestinal ganglion ; n.p.i, nerve of the
inferior pallia! lobe; osp, osphradima ; nul, 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 Pleurdbranchus and

THE GASTROPODA

the majority of the Nudibranchs (Fig. 159), and is pushed to an
extreme in Tethys. 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, n.s).

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

t?

FIG. 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, aft,
abdominal ganglion (+infra-intestinal) ; ce, cerebral ganglion ; o, osphradium ; pe, pedal
ganglion ; pi, 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 buccaj, 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,

n6

THE GASTROPODA

especially in the Pulmonata, in which group the pleural ganglia
scarcely ever give off any nerves. In all the Euthyneura except
Adaeon (Fig. 57), Chilina, and Latia (Fig. 96) the infra-intestinal
ganglion is fused with the abdominal (Fig. 97, ab) in such 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, etc.

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 Vermctii-s (Fig. 45, p.t) ; the epipodial tentacles of the

Rhipidoglossa (Fig. 130, XI),
which have ciliated sensory
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,
are likewise constituted by

Bulla (//fimtnea) navicula, ri^ht-side view, c.h, the Cephalic tentacles, CSpeci-
cephalic hood; «, eye; /, foot; h.o, hermaphrodite ,, , r Al . .r .

oritice; i.1, inferior pallial lobe; m, mouth; m.o, ally by the posterior pair 111

male orifice ; r/i, rhinophore (Hancock's organ); s.g, .1 miadritpntannlutp Fiithv

seminal groove ; sh, shell. (After Guiart.) tne quaanteniaCUldl/e J!Altny-

neura. The whole surface of

these tentacles is covered by little ciliated papillae, giving them a
silky appearance, in many Rhipidoglossa, e.g. Scissurella, Haliotis,
Trodius, Gena, Molleria, Cyclostrema, Neritina, in Caecum (Fig. 68, te),
etc. The olfactory nerve divides into many ramifications which end
on the surface of the tentacle in olfactory sensorial cells. In many

Fid. !)8.

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, t). In terrestrial
Pulmonates — e.g. Helix — 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 (Limax, Helix, etc.) 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 \T 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), Cydostoma, Vermetus,

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 Cypwea, in which the

FIG. 99.

A male Hemifiuua tuba, removed from its shell and with the pallial cavity opened. I
ns ; II, hypobranchial gland ; III, spermiduct ; IV, renal pore ; V, heart, in the opened
pericardium ; VI, testis ; VII, liver ; VIII, oesophagus ; IX, columellar muscle ; X, the spermi-

-I, penis ; XII, foot ; XIII, probe
I, ctenidium. (After Souleyet.)

pericardium ; VI, testis ; VII, liver; VIII, oesophnKua , m., wiumcmti nn.ovio , .«., uuo o^cmn-
duct cut through, with the mantle ; XI, penis ; XII, foot ; XIII. proboscis ; XIV, head ; XV,
pallial siphon ; XVI, osphradium ; XVII, ctenidii

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 in vagi nation is bifurcated in Limnaea. 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 Siphonaria (in which the lung is filled with water)

THE GASTROPODA 119

it is inside the pulmonary cavity (Fig. 174) ; in other forms with an
aerial lung it is external (Fig. 89, os).

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 (Lobiger, the Elysiomorpha, Hedylidae,
Pseudovermis, Fiona, and sundry Eolidomorpha), (viz. the Tergipedi-
nidae, Capellinia, Eolidiella,, Eolis aurantiaca and E. 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, Cydophorus, 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 Fermetus
and in some Janlhina. 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, Phyllirhoe, 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, ot; 142, u; 146, oi). 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 Pleurotoma : in the last named they are very near the

120 THE GASTROPODA

extremities of the tentacles in the sub-genera Drillia and Clavaiula.
The ocular tubercle is better developed than the tentacle in the
Strombidae (Fig. 75 t), 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
Flo 100 is at the base of the tentacle,

Axial section of the eye of Trochu* wnbilicaris and in the latter group SOmC-
I, crystalline lens; II, retina; III, optic nerve; ti^pa of cnmp rli«stflnp0 frnm it

IV, retini.lian layer or rods.

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 pigmont 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, Gastropteron. 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 12

retinal or pigmented imagination, 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.g.
the Heteropoda — or ceases to be functional, e.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 (Scaphandei*, Philine,
Doridium, Gastropteron, etc.), the Pleurobranchidae, many Nudi-
branchs, and some Pulmonates, viz. Siphonaria, Auricula midae,
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, Andllaria\ certain

122

THE GASTROPODA

Marginellidae and Bullia; in subterranean Pulmonates, such as
Caecilianella and Helix hauffeni ; in abyssal Gastropods, such as
Lepeta, Propilidium, Bathysciadium, Puncturella, Cocculina, a species of
Eulima, Choristes, Oocwys, some species of Fossarus, Addisonia, a
species of Chrysodomus, Pleurotoma nivalis, Bathydoris, and Gonieolis ;
in internal parasites, such as the Entoconchidae and Ento-
siphon -, among pelagic Gastropoda in Janthina and the " Pteropoda."

Fio. 101.

Eye of PUrotrachea. 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. 11, 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 .Grenadier.)

In addition to the cephalic eyes, certain species of Oncidiidae
(Peronui) 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 123

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, Falvata, Mar-
senina, Oncidiopsis, Odostomia, Entosiphon, EntoconcJia, 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, Paludinti, Littorina, various species
of Crepidula, Pleurotoma, etc. : 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 Cerithiuni, Quoy and
Gaimard), in the radular teeth (certain Buccinidae, Troschel), in
the absence of the pedal sucker in the female PterotracJiea, of ten-
tacles in the female of some Firoloida, 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 Pleurotomaria, 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, Magtius, 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, h). 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 Hydrobitt, ftithynin, 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, Pahidina, the
Naticidae, Lamellariidae and Calyptraeidae, Triton and Castidaria).
There is a copulatory pouch or receptaculum seminis in the
Neritacea, Paludinidae, Cyclostomatidae, and Heteropoda. In some
Neritacea — viz. Neritim, Nerita, Naviwlla, etc. — 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. Tanganyika (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

125

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 Pahidina and Pteroceras, and in
several Stenoglossa, such as Murex, Nassa, Purpura, etc., 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

FIG. 102.

Follicles of the hermaphrodite gonads of Euthyneura. A, of Helix; I), of Eolis. 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. Phyllirhoe (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 Valmta and in the majority of the Tectibranchia
and Pulmoriata (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, B), with the exception of

126 THE GASTROPODA

the Elysiomorpha. Entoconcha, finteroxenos, and Bathysciadium 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.g) in general, including the Thecosomata ; in
the Aplysiomorpha (Fig. 154, i), 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 longi-
rostris among the Bullomorpha, and among the Pulmonata in all the
Auriculidae except Pythia, 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,
bifurcates or becomes "diaulic," the female branch of the duct
opening by the primitive hermaphrodite orifice. This condition is
characteristic of Valvata and Oncidiqms (Fig. 103), of Adaeon 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 Valvata, Oncidiopsis
(Fig. 103,/.r), pe), the Basommatophora in general, the Oncidiidae
(Fig. 59, o.f, o.m), and Vaginula (Fig. 87, o.f). 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, II), 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, Claitsilia, etc., is provided with an accessory branch
(Fig. 104, Ji.8).

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 trif urcated 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).

FIG. 103.

Oncidiopsis, hermaphrodite genital
apparatus, dorsal view, a.g, albumini-
parous gland ; /.o, female orifice ; y.g,
hermaphrodite gonad ; pe, penis ; pr,
prostate ; r.s, receptaculum seminis ;
so, spermoyiduct ; sp, spermiduct ; s.v,
seminal vesicle.

FIG. 104.

Hermaphrodite reproductive appara-
tus of Helix hortensis. d, digitate acces-
sory glands on the female duct ; E.d,
albuminiparous gland ; fl, flagellum ; p,
penis ; p.s, calciferous gland or dart-sac
on the female duct; li.s, receptaculum
seminis or spermatheca, opening into the
female duct; n, uterine dilatation of the
hermaphroditic duct ; v.d, spermiduct or
vas deferens ; v.e, hermaphroditic duct ;
z, ovo-testis. (From Ray Lankester,
after Gegenbaur.)

The penis is invaginable in all the Euthyneura with the
exception of Actaeon (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

00

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,
mm). In the diaulic Pulmonata there
is a large albuminiparous gland on the
hermaphrodite section of the duct (Fig.
104, E.d), and on the female part of the
duct of Basommatophora there is an
albumen gland corresponding to the
uterine glands of Stylommatophora (Fig.
104, u). The diaulic and triaulic 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
(Fig, 104, d). Opening between the

\ O * / i O

tus, dorsal aspect, n.d, aibumini- two is a special pouch — seemingly a

parous duct; a.g, albuminiparous ... -, ,. .« , . , , . .

Kland; h.rf, hermaphroditic duct ; Specialised multifid VCSlcle, which Secretes

dua?v«ian?r»io,^^ a snarP calcareous dart (Fig. 104, p.s).

no, oviduct;' ji, ' penis ; pr, pros- Before copulation the dart-sac is evagin-

tate ; r..«, recepteculuni somims ; xp, . "

spermidiu-.t ; vo, vulva. ated 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 a more or less elongate " prostate " gland, as in Falvata,
Onddiopsis (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 herm.iph-
roditism is protandric, the spermatozoa being the first of the
genital products to come to maturity. This hermaphroditism is

Fia. 105.

i, reproductive appara-

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 cellaring, 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

Fio. 107.

Two Limnaea stagnalis in copulation,

Spennatophore of Nanina the left one acting as male. I, tentacle

wattacei, magnified. (After and eye ; II, penis ; III, foot ; IV, 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, etc. The copulation of two
individuals is effected in the same manner as in the dioecious
Gastropoda (Fig. 107).

III. EMBRYOLOGY.

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 Helix. 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 (Buccinum, Fusus, Py?-w/a), 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
thus appear to be more or less incubatory,
as, for instance, Hipponycidae and Capu-
lidae (in Calyptraea the eggs are attached
below the neck) ; or they may attach them
to the external surface of the shell, e.g.
Neritina, Hydrolia ulvae, and in excep-
tional cases Eissoa ; or to the internal face
of the shell, e.g. Vermetus (Fig. 45, ov).
In the oviparous Janthinae the eggs are
attached to the float (Fig. 135, b).

The stylommatophorous or terrestrial
Pulmoriates generally lay in the earth
isolated ova enclosed either in a gelatinous

Egg-capsule of Nassa reticulata, , , T . \ . , . ~ ,

x 12. o, aperture ; ov, eggs. envelope (Limax, etc.) or in a calcified
shell, e.g. certain species of Helix, Testacella,

etc. 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. Glandira algira, Rhytida aequalis, Selenites voyanus,
Helix rupestris, H. inversicolor, II. inaequalis, H. unidentata, H.
erronea, 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 mammillata (Fig. 8), S. octona, S. terebr aster, S. domini-
ciensis, S. decollata, S. lamellata, Ferussacia folliculus, F. lamelliferaf

Fio. 109.

Melania episcopalis, out of its shell, showing the female genital apparatus, right-side view,
a, anus ; 6.0, brood-pouch opening ; b.p, brood-pouch ; /, foot ; g.gr, genital ciliated groove ;
g.o, genital orifice ; m, mouth ; oc, eye ; od, oviduct ; op, operculum ; ov, ovary. (After Moore.)-

F. procerula, F. debilis, F'aginula 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, etc.
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 Limax, the blastula formed in this manner

Fio. 110.

Development of the river-snail (I'aludiiui vivijnrd), in which the
5 formed independently of the blastopore, the latter persisting as tin

mouth and stomodaeum

are formed independently of the blastopore, the latter persisting as the anus, ae, archenteron,
or endodermic cavity; an, anus; II, blastopore ; d.c, directive or polar corpuscle; d.v, velar
area or cephalic dome ; /, foot ; in, mouth ; meg, rudiments of the mesoderin ; 71.?, pedicle of
invagination, the future rectum ; sk.gl, the shell-gland ; s.m, site of the as yet unformed mouth ;
IT, velum. A, Qastrula phase (optical section). IS, 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 1), further advanced Trochosphere (optical section).
K, 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 aims.
( After Lankeater.)

contains a large blastocoel between the nricromereu 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, bl ; 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 mc~

ot

Kn

Pio. 111.

Young veliger of Troclius, ven-
tral aspect. /, foot ; m, mouth ;
]M, mantle ; pa.c, pallial cavity ;
*h, shell ; ve, velum. (After
Robert.)

FIG. 112.

Larva of Cavolinia triilentata, ventral aspect.
a, anus; /, median portion of the foot; h,
heart ; i, intestine ; K u, contractile sinus ;
TO, mouth ; mb, mantle-skirt ; me, subpallial
chamber; ot, otocyst; pn, lateral lobe of the
foot (the future left fin) ; q, shell ; r, kidney ;
s, oesophagus; <r, sac containing nutritive
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.

«34

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. Ill,
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 Atlanta 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

Fio. 113.

Trochosphere of J'atelht, in the 34th hour. I, Hagellum in the apical area ; II, 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. I,/), 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
«hell nor foot : the only exceptions to this statement are the
Pulmonata (excepting the Auriculidae, the Amphibolidae, and the

THE GASTROPODA

135

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
(Purpurd).

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,

in

KIG. 114.

Embryo of Vermctus, ventral
aspect. I, velum ; II, contractile
sinus ("embryonic heart"); III,
opening of the pallial cavity ; IV,
shell ; V, foot ; VI, left eye. (After
Salensky.)

FIG. 115.

Larval shell of Nasso. rrticiilata,
ventral aspect, x 30. h, hook of
the dorsal edge of the aperture ; si,
future canal or shell-siphon • ftp,
spire.

or is 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, Ituncina, 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, e.g.
Helix, Bithynia, Fermetus, the Rachiglossa, and nearly all the marine
Gastropoda, including the " Pteropoda," Heteropoda, and Nudi-

Fio. 116.

Larvae of Rolls (Galvina) exigna. . A, on the second
day, left-side view. I, radula ; II, foot ; III, otocyst :
IV, operculum ; V, shell. 7?, on the third day, after
th« loss of the shell, dorsal aspect. I, eye ; IF, left
liver lobe; III, foot; IV, amis; V, ootocyst ; VI,
radula. (After Schultxe.)

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,

•Vit

Helix asptrsa, embryo of the tentli day, right-side view, coq, shell ; o.co.c, external opening
of the cerebral cavity ; p, foot; pa, mantle; po, contractile vesicle or podocyst; te", the true
tentacles ; /«'", 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, JSithynia, 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, re) these cells of the larval kidney are four in number,
three being perforated and one a flame-cell. These organs are
absent in Vagi-nuki.

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

FIG. 118.

Embryo otLimnma stagnates, viewed from the right side, a, anus ; c.g, cerebral ganglion ;
/, foot ; in, intestine ; m, month ; o. r, aperture of the embryonic kidney ; pa, mantle ; ra,
radula ; re, embryonic kidney ; sh, shell ; st, stomach ; vi, vitellus. (After E danger.)

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, o.ca.c)
— the " cerebral tube " — the cavity of which generally disappears
after the animal is hatched out, but persists in the adult Planorlis
and Limnaea. The eyes arise in the velar field, near the cerebral
centres, and are formed by invagination in the Aspidobranchia,
Paludinu, the Stylommatophora, etc., but from thickenings in
Fermetus, and frequently after the veliger larva is hatched, as, for
example, in many Nudibranchia, with the exception of the Tergi-
pedinae (Fig. 6 1, e). 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

Kio. 11'.).

Embryos and larvae jot various Molluscs, after the ventral flexure anil before the torsion (for
A), ventral aspect,
branch

anus ; or, anus ; e, eye ; /, toot ; fit, tunnel ; g, gill ; in, mouth ; ot, otocyst ; JKI, mantle ; JKI.O,
posterior pallia! orifice ; pc.g, petlul ganglion ; ah, shell ; vi; velum ; vi, vitellus.

inoryos ana larvae 01 various MOIIUSC.S, arter tne ventral nexure ana oetore me torsion (tor
eutral aspect. A, Gastropod (Limnaea, after Fol) ; B, Dcntalium (after Lacaze) ; C, Lamelli-
ch (Drcissensia, after Meisenheimer); J), Ophaloixxl (Oigopsid, after Grenadier), aw,
; ar, anus ; e, eye ; /, foot ; fit, funnel ; g, gill ; in, mouth ; ot, otocyst ; JKI, mantle ; JKI.O,

not exhibit any special features other than certain post-larval meta-
morphoses and the torsion produced during development (Fig. 51).
Up to the trochospheie stage the larva is strictly symmetrical
(Fig. 1 4, 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. 1 20). 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 Trochus, 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 Vahata and certain
species of Anon and Limax. It is ventral aspect 6 mouth- cca anterior

Only in exceptional Cases that the ciliated ring ; c.c.m, middle ciliated ring ;
, , -i j • ,1 >•! c.c.p, posterior ciliated ring ; na, fin ; pt

young are hatched out with the f00t. (After Racovitza.)
characters of the adult, but this

is the case in 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 Trochus (Fig. Ill), Patella, Fissurella, etc.,
and is the characteristic larval form in most opisthobranchiate

Fl°- 12°-

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 Bucdnum, 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 " M acgillivraya " (Fig. 121), " Agadina" " Clwle-
tropis," "Sinusigera" " Echinospira" etc., all of which are special
pelagic larval forms of Streptoneura which were long considered to

Fin. 121.

" Mwgillivraya," pelagic larva of a siphonato
Strcptoneurous Gastropod (Doli-tim), ventral asi>ect,
x 1*2. /, foot ; w, month ; sh, shell ; si, siphon : tf,
tentaclo and eye ; re, lobes of the velum. (After
MacDonald.)

Fio. 122.

Shell of a young
Purjmra haemastoma,
enlarged, dorsal aspect.
c«, canal of the adult ;
e.s, limit of the embry-
onic shell ; sp, spire.
(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 lies 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. BIONOMICS.

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," Phyllirhoe, Accra
(Fig. 147), etc. Some families both of Streptoneura and Opistho-
branchia burrow in mud or sand, e.g. the Naticidae, Bullidae, etc.
Some genera are more or less sedentary, though able to move from
place to place — such are Patella and Bathyscicidium — 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 certain degree mimic these forms. Thus Ovula lives
on Gorgonia, Pedicularia on Corallium, Lamellaria on Leptodinum,
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

142 THE GASTROPODA

the families Eulim.Iae (including Stylifer, parasitic on Asterids,
Echinids, and Crinoids) and Entoconchidae, including Entosiphwi,
Entocolax, Entoconc/ia, 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-
biidae, 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 Fusus, Tritonium, Ancistromesus,
Strombus, etc., but also among the naked forms : Tethys, for example,
is more than thirty centimetres in length, and some species of Den-
dronotus 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.

SUB-CLASS 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 be a
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.
123, B, C, zy, zy"). Zygoneury is more frequently found on the

Fio. 123.

Nervous system of 3 Streptoneurous Gastropods, showing the dialyneury and zygoneury.
dorsal aspect. A, Paludina (after Bouvier, somewhat modified); B, Triton (after Haller) ; C,
Lamellaria (after Bouvier). a6.gr, 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; i.i.g, infra-intestinal ganglion ; ot, otocyst; pa.n, pallial nerve; pe.g, pedal
ganglion ; pl.g, pleural ganglion ; pl.pe, pleuro-pedal connective ; s.i.g, supra-intestinal ganglion ;
st.g, stoniato-gastric ganglion ; ri.c, visceral commissure ; vi.cf, vi.c", supra-intestinal and infra-
intestinal part of the visceral commissure ; zy', zy", left and right zygoneury.

143

144

THE GASTROPODA

xxi

right side ; the connective passes from the right pleural to the
infra -intestinal ganglion, and may have the effect of bringing

the latter ganglion between the two
pleural centres (Fig. 123, C, i.i.g).
The head of Streptoneura bears only
a single pair of tentacles (Fig. 125, a).
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.

xx

XIX
XVIII

FlO. 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 ; VI,
pedal ganglion; VII, supra -intestinal
part of the visceral commissure ; VIII,
posterior part of the glandular oeso-
phagus; IX, infra - intestinal part of
the visceral commissure ; X, abdominal
ganglion ; XI, oesophagus ; XII, radula ;
XIII, supra-intestinal ganglion ;, XIV,
osphradial ganglion and branchial
nerve ; XV, left pallial anastomosis or
dialynmiry ; XVI, glandular oesopha-
gus ; XVII, left pallial nerve; XVI II,
buccal mass ; XIX, cerebro-pedal con-
nective ; XX, stomato-gastric ganglion ;
XXI, snout.

opening to the exterior at
The gonad has no accessory

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). As a 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

the end of short papillae (Fig. 88, /).

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 Rhipidoglossa.

SUB-ORDER 1. DOCOGLOSSA.

In these Aspidobranclis 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, cm), 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.

FAMILY 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.
Xcurria, Gray; with pallial branchiae arranged in a circle beneath the mantle.
Pectinodonta, Dall. Scenella, Billings ; from the Cambrian. Palaeacma,
Hall ; from the Silurian. FAMILY 2. TRYBLIDIIDAE, Pilsbry. Muscle
scar divided into numerous separate impressions. Genus — Tryllidium,
Lindstrom ; Silurian. FAMILY 3. PATELLIDAE, Guilding. No ctenidia, but
only pallial branchiae disposed in a circle between the mantle and the
foot (Fig. 1 25). 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. FAMILY 4.
LEPETIDAE, 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. Lepdella,
Verrill ; with eyes. Pilidium, Forbes. Propilidium, Forbes and Hanley.
FAMILY 5. BATHYSCIADIDAE, Dautzenberg and Fischer. Monoecious, with
otoliths ; head provided with an appendage on the right side ; radula
without a central tooth. Genus — tiathysciadium, Dautzenberg and
Fischer; abyssal (Fig. 126).

SUB-ORDER 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

THE GASTROPODA

with very numerous marginal teeth, arranged like the sticks of a fan.

d
c

x <,

TUZ..C,

FIG. 125.

Patella vulgato, in its shell, seen from the pedal surface ; x, y, the median antero-posterior
axis, a, cephalic tentacle ; b, plantar .surface 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 ; c, margin of the mantle-skirt ; /, gill lamellae— special pallial outgrowths (not
ctenidia) ; g, the branchial efferent vessel ; h, factor of the branchial advehent vessel ; i, 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, sp.c). 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.

FAMILY 1. PLEDROTOMARIIDAE.
Visceral mass and shell spiral ; mantle
and shell with an anterior fissure (Fig.
54, III) near the median line. Two
ctenidia ; a horny operculum. Genera —
Pleurotomaria. Defrance ; epipodium with-
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

/ux,

Fio. 126.

Btithysciaduim, ventral aspect, magui
fled, aj), cephalic appendage ; /, foot

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.
Xdssurella, 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, LeVeiHe" ; Devonian
and Carboniferous. Kokenella, Kittl ; Trias. Ditremaria, d'Orbigny ;
Jurassic. Polytremaria, de Koninck ; Carboniferous. Trochotoma,
Deslongchamps ; Trias and Jurassic. Cantantostoma, Sandberger ;

FIG. 127.

Flcitrotomaria, with the pallial cavity laid open, right-side view, o, anus ; CM, aorta ; a.v,
afferent branchial vessel ; br.g, branchial ganglion ; c.c, cerebral commissure ; co, columellar
muscle ; tr, crop ; e.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; l.k.o, opening of the left kidney; m, mouth; m.s, mantle slit; od, odontophore ; oc,
oesophagus ; op, operculum ; os. osph radium ; pe.c, pedal cord ; r, rectum ; r.k, right kidney ;
r. A', anterior part of ditto (dotted line); r.k.o, opening of the right kidney ; r.,«, radularsac; s.g,
salivary gland ; sp.c, spiral caecum ; st, stomach. (After F. M. Woodward.)

Devonian. Muirhisonia, d'Archiac and Verneuil ; Cambrian to Trias.
Odontomaria, Roemer ; Devonian. FAMILY 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 — Bellerophcn, Montfort. Euphemus, MacCoy. Salpingo-
stoma, Roemer. Trematonotus, Hall. Cyrtolites, Conrad. FAMILY 3.
EUOMPHALIDAE, de Koninck. Also an extinct family, extending from
the Cambrian to the Cretaceous. Spire slightly prominent ; umbilicus
deep ; operculum calcareous. Genera — Euomphalus, Sowerby. Strapa-
rollina, Billings. Ophileta, Vanuxem. Maclurea, Lesueur. Platychisma,
MacCoy. Straparollus, Montfort. Phanerotinus, Sowerby. Discohelix,

I48

THE GASTROPODA

Dunker. FAMILY 4. HALIOTIDAE, Fleming. Spire of the visceral mass
and shell much reduced ; two bipectinate ctenidia, the right being

oc

Fio. 128.

Scisfitrclla cugli/pta, removed from its shell, ventral aspect, magnified, br.d, right gill ; 1>r.s,
left gill ; m.vi, visceral mass ; oc, right eye ; op, operculum ; p, foot ; pa, mantle ; t, snout ; tr,
left cephalic tentacle ; te.ep, epipodial tentacles ; te.pa, pallial tentacle ; te.p.o, post-ocular
tentacle.

the smaller ; no operculum. Genus — Haliotis, Linnaeus (Fig. 129).
FAMILY 5. VELAINIELLIDAE, Vasseur. An extinct family from the
Eocene. Shell elongate, with numerous whorls ; columella and partitions

Fio. 129.

llaliotis tuberculata, right-side view, d, foot ; t, 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, Vclainiella, Vasseur. FAMILY 6. FISSURELLIDAE, 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. Simula, Defrance. Subemarginula,
Blainville. Scutum, 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. Fissurella, Bruguiere ; 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, d'Orbigny. Pupillia, Gray ; mantle completely covering
the shell. Lucapina, Gray. Megatebennus, Pilsbry. Macrochisma,
Swainson. Lucapinella, Pilsbry. FAMILY 7. COCCULINIDAE, Dall.
Shell conical, symmetrical, without slit or perforation ; the summit
inclined backwards. Genus — Cocculina, Dall ; dioecious ; abyssal.
FAMILY 8. TROCHIDAE, d'Orbigny. Visceral mass and shell spirally

XI

FIG. 130.

Trodius (Gibbula) cinerarius, right-side view. I, shell ; II, frontal lobes ; III, right eye and
peduncle ; IV, right tentacle ; V, appendage of the right ocular peduncle ; VI, snout ; VII, right
epipodial lobe ; VIII, epipodium ; IX, 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 — Trochus,
Linnaeus ; no jaws ; shell umbilicated ; spire pointed and prominent.
Monodonta, Lamarck ; no jaws ; spire not prominent ; no umbilicus ;
columella toothed. Clanculus, Montfort. Elenchus, Swainson. Photinula,
Adams. Gaza, Watson. Gibbula, Kisso ; 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. FAMILY 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. FAMILY 11. LIOTIIDAE, Gray. Shell globular;
margin of aperture thickened ; operculum horny, with a calcareous
layer. Genus — Liotia, Gray. FAMILY 12. CYCLOSTREMATIDAE, Fischer.
Shell flattened, umbilicated, not nacreous ; foot truncated anteriorly
and with the two angles prolonged into tentacles. Genera — Cydostrema,
Marryat (Fam. 50). Teinostoma, Adams. FAMILY 13. TROCHONE-
MATIDAE, Zittel. Exclusively fossil, from Cambrian to Cretaceous ; shell
spiral and nacreous internally ; whorls without keels ; aperture rounded.
Genera — Trochonema, Salter ; from the Cambrian and Silurian. Eunema,
Salter ; from the Ordovician to the Devonian. Amberleya, Morris and
Lycett ; from the Trias to the Cretaceous. Oncospira, Zittel ; Jurassic.
FAMILY 14. TURBINIDAE, 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. Molleria, Jeffreys ; shell thin, umbilicated,
with very short spire. Cyclonema, Hall. FAMILY 15. PHASIANELLIDAE,
Troschel. Shell not nacreous, without umbilicus, with prominent spire
and polished surface. Genus — Pliasianelki, Lamarck. FAMILY 16.
UMBONIIDAE, Adams. Shell flattened, not umbilicated, generally smooth,
without a nacreous layer ; operculum horny. Genera — Umbonium, Link.
Isanda, Adams. FAMILY 17. NERITOPSIDAE, Fischer. Shell semiglobular,
with short spire ; operculum calcareous, not spiral. Genera — Nerilopsis,
Grateloup. Naticopsis, MacCoy ; from the Devonian to the Trias. FAMILY
18. MACLURITIDAE, Fischer. Shell discoid, deeply umbilicated, with
few whorls ; operculum spiral, thick. Genus — Maclurites, Lesueur ; from
Cambrian and Silurian. FAMILY 19. NEUITIDAE,
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. Neritodomns,
Morris and Lycett ; Jurassic. Deianira, Stoliczka ;
Cretaceous. Septaria, Fcrussac ; shell boat - shaped,
with a large aperture and symmetrical muscular im-
pressions. Pileolus, Sowerby ; from the Jurassic and
Cretaceous. FAMILY 20. TITISCANIIDAE, Bergh. With-
out shell and operculum, but with a pallial cavity and
a ctenidium. Genus — Titiscania, Bergh (Fig. 131) ;
from the Pacific Ocean. FAMILY 21. HELICINIDAE,
Pfeiffer. No ctenidium, but a pulmonary cavity
present ; epipodium without tentacles ; heart with a
cavity ; iv, gill, single auricle, and not traversed by the rectum ; i>o
mandible ; operculum without apophyses. Genera —
Helicina, Lamarck. Eutrochatella, Fischer. Stoastoma, Adams. Bourcieriu,
Pfeiffer. FAMILY 22. HYDROCENIDAE, Fischer. No ctenidium, but a
pulmonary cavity present ; foot obtuse ; operculum calcareous, with an

Fio. 131.

Tititcanw limacina,
<loreal aspect. I, eye ;
II, tentacle ; III,
opening of the pallial

THE GASTROPODA 151

apophysis. Genus — Hydrocena, Parreys ; from Dalmatia. FAMILY 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, Cydophorus, Typhobia,
Bythoceras, Nassopsis, certain Cerithiidae, etc. The central tootli 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 Falvatu, 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, Cyclopliorus, and Falvata),
and never serves for the passage of the sexual products. The
gonad always has a separate orifice of its own. The male generally
has a penis (Fig. 44, A, h).

The Pectinibranchia are divided into two sub-orders — Taenio-
glossa and Stenoglossa.

SUB-ORDER 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-
thauma, Smith ; from Lake Tanganyika. Tylopoma, Brusina ; from the
Tertiary. FAMILY 2. CYCLOPHORIDAE, 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. Dermatoc&ra, 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, sinistml.
FAMILY 4. LITTORINIDAE, Gray. Ctenidium monopectinate ; oesophageal
pouches present ; pedal nerve- centres concentrated; a pedal penis near
the right tentacle. Genera — Littorina, Fe"russac ; 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. FAMILY 5. FOSSARIDAE, Fischer. Shell turbinated and umbili-
cated ; head with two cephalic lobes, as in some Rhipidoglossa. Genus —
Fossarus, Philippi. FAMILY 6. PURPURINIDAE, Zittel. An exclusively
fossil family ; shell thick, with prominent spire, angular whorls, and oval
aperture. Genera — Purpurina, d'Orbigny ; Jurassic. Brachytrema,
Morris and Lycett ; Jurassic. Scalites, 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. FAMILY 8. CYCLOSTOMATIDAE, 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. FAMILY 9. ACICULIDAE, Gray. Shell narrow and
elongated ; operculum horny ; pallial cavity a pulmonary chamber ;
otocysts with otoconia. Genus — Acicula, Hartmann. FAMILY 10.
VALVATIDAE, Gray. Ctenidium bipectinate, free throughout its length ; a
pallial filament on the right side ; hermaphrodite ; fluviatile. Genus —

THE GASTROPODA

'53

Valvata, Miiller (Fig. 132); British. FAMILY 11. RISSOIDAE, Gray. A
monopectinate ctenidium ; epipodial filaments present ; one or two pallial
tentacles ; snout elongated. Genera — Rissoa, Fre"minville ; operculum
simple. Rissoina, d'Orbigny ; operculum with an apophysis. Stiva, Hedley.
FAMILY 12. LITIOPIDAE, 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. FAMILY 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).
FAMILY 14. JEFFREYSIIDAE, Fischer. Head with two long labial palps ;
shell ovoid, umbilicated ; operculum horny, semicircular, concentric, and
carinated. Gemis— Jejfreysia, Alder. FAMILY 15. HOMALOGYRIDAE,
Sars. Shell flattened ; operculum horny, circular ; no cephalic tentacles.

Fio. 132.

Valvata piscinalis, dorsal aspect,
magnified. /, foot ; gi, gill ; m,
mouth ; op, operculum ; pa.t, pallial
tentacle ; sh, shell ; te, cephalic
tentacle. (Alter Bernard.)

Flo. 133.

Adeorbis siHmirinatus, ventral aspect. /,
foot ; <7, gill ; m, mouth ; op, operculum ;
pa.c, pallial cavity ; pa.t, pallial tentacle ; sh,
shell ; t, tentacle. (After F. M. Woodward.)

Genera — Homalogyra, Jeffreys ; British. Ammoniceras, Vayssiere. FAMILY
16. SKENEIDAE, Fischer. Shell depressed and umbilicated, with a
rounded aperture ; cephalic tentacles long. Genus — Skenea, Fleming ;
British. FAMILY 17. CHORISTIDAE, Fischer. Shell spiral ; four cephalic
tentacles ; eyes absent ; two pedal appendages behind the operculum.
Genus — Clwristes, Verrill. FAMILY 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. FAMILY 19. TRUNCATELLIDAE, Gray. Ctenidium mono-
pectinate ; snout very long, bilobed ; foot very short ; spire elongated
and truncated ; marine and littoral. Genus — Truncatella, Risso. FAMILY
20. HYDROBIIDAE, 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, Hartmaun ; 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. Bithynella, Moquin - Tandon. Lithoglyphus, Miihlfeldt ;
shell globular with short spire. Spekia, Crosse ; viviparous ; from Lake
Tanganyika. Tanganyicia, Crosse (Fig. 78). Limnotrochus, Smith ;
from Lake Tanganyika. Chytra, Moore. Littorinida, Eydoux and
Souleyet Bithynia, Gray ; shell conical with an oval aperture ; oper-
culuni calcareous, concentric ; habitat fluviatile ; British. Stenothyra,
Benson ; aperture rounded and contracted ; operculum calcareous, spiral.
FAMILY 21. MELANIIDAE, 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. Faunus, Montfort ;
spire very long ; aperture of shell notched anteriorly. Paludomus,
Swainson ; shell short, thick, with rounded aperture. Melanopsis,
Fe'russac. Nastopsis, Smith. Bythoceras, Moore ; from Lake Tanganyika.
FAMILY 22. TYPHOBIIDAE, Moore. Foot wide ; tentacles elongate ; shell
turriculated, with carinated whorls, the carinae tul>erculated or spiny.
Genera — Ty phobia, Smith. Bathanalia, Moore ; from Lake Tanganyika.
FAMILY 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. FAMILY 24. PSEUDOMELANIIDAE, Fischer. An exclusively
fossil family ; shell turriculated, with prominent spire and elongated oval
aperture. Genera — Pseudomelania, Pictet and Campiche ; Secondary and
Tertiary. Loxonema, Phillips ; Palaeozoic. Macrochilus, Phillips ;
Devonian to Trias. FAMILY 25. SUBULITIDAE, 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. Euchrysalis, 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 — Cerithium, Adanson ; aperture oval ;
operculum oval, with submarginal nucleus. Bittium, Gray ; operculum
circular, with central nucleus ; siphon rudimentary. Potamiiles, Brong-
niart ; eyes situated above the bases of the tentacles ; ctenidium rudi-
mentary ; brackish water. Triforis, Deshayes ; shell sinistral. Laeocochlis,
Dunker and Metzger. Cerithinpsis, Forbes and Hanley. FAMILY 28.
MODULIDAE, 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. FAMILY 29. VERMETIDAE,
d'Orbigny. 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) ; peclal tentacles elongate. Sitiquaria,
Bruguiere ; mantle and shell «lit in both sexes for the whole length of
the branchial cavity ; pedal tentacles rudimentary. FAMILY 30. CAECIDAE,
Gray. Shell almost completely uncoiled in one plane, and furnished with
internal septa ; aperture circular. Genus — Caecum, Fleming (Fig. 68) ;
British. FAMILY 31. TURRITELLIDAE, Clark. Shell very long with
numerous whorls ; head large and prominent ; mantle border fringed ;
no siphon ; foot broad and truncated. Genera — Turritella, Lamarck ;
British. Mesalia,, Gray. Mathilda, Semper ; the summit of the shell
hyperstrophic. FAMILY 32. STRDTHIOLARIIDAE, 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 — CJienopus, Philippi ; British. Alaria, Morris and Lycett ;
Jurassic and Cretaceous. Spinigera, d'Orbigny ; Jurassic. Diartema,
Piette ; Jurassic. FAMILY 34. STKOMBIDAE, Gray. Foot narrow, arcuate,
compressed laterally, without ventral sole (Fig. 75, /) ; 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. FAMILY 35. XENOPHORIDAE, 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. Eotrochus, Whitfield ;
from the Silurian. FAMILY 36. CAPULIDAE, Fleming. Visceral sac and
shell conical, but slightly incurved posteriorly; a tongue-shaped projection
between snout and foot ; columellar muscle horseshoe-shaped. Genera —
CapuluSj Montfort. Thyca, Adams ; parasitic on Asterids ; without a radula ;
foot rudimentary. Platyceras, Conrad; from the Silurian onwards.
FAMILY 37. HIPPONYCIDAE, 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. FAMILY 38.
CALYPTRAEIDAE, Broderip. Visceral mass spiral ; shell flattened, with
a short spire ; lateral cervical lobes present ; foot short and circular ;
accessory genital glands present. Genera — Calyptraea, 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). FAMILY 39. NARICIDAE, Recluz. Foot divided into two, the
posterior half bearing the operculum ; a wide epipodial velum ; tentacles
flattened ; snout elongate ; she'll turbinated. Genus — Narica, Recluz.
FAMILY 40. NATICIDAE, 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
— Natica, Adanson ; shell globular, thick and polished, umbilicated,
with a semi-lunar aperture (Fig. 47) ; British. Amaura, Holier ; shell
not umbilicated, thin, with an oblong aperture. Siyaretus, Lamarck ;
shell auriform, with a very short spire and large aperture ; operculum
small and rostrate. FAMILY 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 — Veluti?ia, Fleming;
shell only partially covered by mantle ; British. Lamellarw, Montagu ;
shell internal, spiral, transparent ; British. Marseniua, Gray ; shell not
completely covered by the mantle ; hermaphrodite. Oticidiop*Mt Beck ;

FIG. 134.

Xenophonis exutus, animal and shell, left-side view, a, snout ; bt cephalic tentacles ; c, left
eye ; d, anterior part of the foot (to the ri^ht of this is seen the posterior lobe of the foot bear-
ing the sculptured operculum/). (From Uinkester, after Owen.)

shell internal, membranous, without spiral ; hermaphrodite. FAMILY
42. TRICHOTROPIDAE, Gray. Shell with short spire, umbilicated, carinate
and pointed. Genus — Trichotropis, Broderip and Sowerby. FAMILY 43.
SEGVENZIIDAE, Verrill. Shell trochiform, with canaliculated aperture
and twisted columella ; operculum spiral. Genus — Seguenzia, Jeffreys ;
abyssal. FAMILY 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.
FAMILY 45. CYPRAEIDAE, 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 ; osph radium with three lobes ; mantle reflected

THE GASTROPODA

'57

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, Bruguiere ; 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. FAMILY 46.
TRITONIDAE, Adams. Shell tnrriculated and siphonated, thick, each

FIG. 135.

Female Jatithina, with egg-flout (ri) attached to the foot, b, egg-capsules ; c, ctenidium ; <7,
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 — Triton,
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. Ranella, Lamarck ; varices continuous
from one whorl to another. FAMILY 47. COLUMBELLINIDAE, Fischer. An
exclusively fossil family ; shell with prominent spire, narrow aperture, and
callous columella. Genera — Columbellina, d'Orbigny ; cretaceous. Colum-
bellaria, Rolle ; Jurassic. Zittelia, Gemellaro ; Jurassic. Peter sia, Gemellaro ;
Jurassic. FAMILY 48. CASSIDIDAE, Adams. Shell ventricose, with
elongated aperture and short spire; foot broad and rounded anteriorly;
proboscis and siphon long ; oper-
culum with marginal nucleus.
Genera — Cassis, Lamarck ; shell
varicose, with narrow aperture.
Cassidaria, Lamarck ; shell with-
out varices, aperture oval and
canaliculated. Oniscia, Sowerby ;
shell oval, with a linear aperture.
FAMILY 49. OOCORYTHIDAE,
Fischer. Shell globular and
ventricose ; aperture oval and

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, kester, after Owen.)
FAMILY 50. DOLIIDAE, 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). FAMILY 51. SOLARIIDAE,

FIG. 136.

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. FAMILY 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 — Scalaria, Lamarck ;
shell elongate with a circular aperture, whorls very convex, ornamented
with longitudinal projecting lamellae ; British. Eglisia, Gray. Crossed,
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. FAMILY 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.

TurbonUla scalaris, ri^ht-side view. /, foot; w, mouth ; me, mentum ; cj>, operculum ; j>o,
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. FAMILY 54. EULIMIDAE, 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 digestive canal of Holothuriae in the Fiji Islands, in the
Philippines, and in Europe, e.g. Eulima distorta in Holothuria intestinalis.
Niso, Risso. tfcalenostoma, Deshayes. Hoplopteron, Fischer. Mucronalia,
Adams ( = Stylina, Fleming) ; foot reduced, but still operculate ; eyes
present ; animal fixed by its very long probosci?, which is deeply buried
in the tissues of an Echinoderm ; no pseudopallium. Stylifer, 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. Entosiphon, Koehler and Vaney ; visceral mass still
coiled ; shell much reduced ; proboscis very long, forming a pseudo-

THE GASTROPODA

159

pallium, 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. Entosiphon
forms the transition to the next
family. FAMILY 55. ENTO-
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 — Entocolax,
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

• ,1 V, •/> Entocolux ludwigi, in situ, x 30. I, fixative

in the Pacific : E. ludwigi, m apparatus ; II, ovary ; III, uterus ; IV, buccal

Miiri'ntrnrlti/9 rinbi'i' fi-nm fhp orifice; V, oviduct; VI, genital orifice; VII, ova

Mynotroclius nnlai Horn tne separated from the <£* by dehiscence; VIII,

Behrin<* Sea (Fig. 138) ; and E. cavity around the ovary, formed by the pseudo-
7 . ••/«.• j 1 • • • pallium ; IX, orifice of this cavity ; X, integument

schiemenzi m Chirodota pisanii Jfthe Holothuria. (After Voigt.)

tv

FIG. 188.

from Chili. Entoconcha, J. Miiller

(Fig. 1 39) ; body elongated and tubular ; the aperture of the digestive tract

rudimentary and situated at the fixed extremity of the body ; protandric

i6o

THE GASTROPODA

liermophrodite 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. Enteroxenos, Bonnevie ; no pseudopallium and no
alimentary tract ; male and female gonads separate, with a single
common genital orifice ; larvae operculiferous. E. ostergreni (Fig.

140); parasitic in the intestine of
Stichopus (Norway).

Fio. 139.

mirubilix, in situ, maj,'-
nilied. I, oral extremity ; 11, remains
of the digestive tract ; III, testis ; IV,
ovary ; V, nntiinesenteric vessel of
tho Syrutiita in which Kntuconcha is
parasite. (After J. Mailer.)

Fio. 140.

Enteroxeiios oxtergreiii, Bonnevie.
ov, eggs. (After lionnovie.)

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

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 bronchia. The otocysts are situated near

FIG. 141.

Oxygyrus kcraudrnni, male, right-side view. A, head ; «, mouth and odontophore ; B, anterior
part of the foot ; h, cephalic tentacles ; c, eye ; </, natatory foot and its sucker ; c, posterior lobe
of the foot ; /, operculum ; h, mantle and pallial cavity ; i, ctenidium ; A;, retractor muscle .of
the foot (columellar muscle) ; /, optic tubercle ; m, oesophagus ; «., salivary gland ; o, rectum and
anus ; p, liver ; «/, kidney ; s, ventricle ; n, the otocyst attached to the cerebro-pleural ganglion ;
w, testis ; x, auricle of the heart ; y, vesicula scminalis ; z, penis. (From Lankester, after
Souleyet.)

the cerebral ganglia (Fig. 141, u). 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 orgai*
exist (Pterotrachea and the female in some Firoloida are devoid of tentacles).
The alimentary canal is furnished with a protractile pharyn* 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, w) ,
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

ii

162

THE GASTROPODA

heart. In the Atlantidae there is an aortic bulb ; the arterial vessels
always end abruptly in sinuses. The ctenidium is inonopectinate and
completely enclosed in the pallial cavity in Atlanta (Fig. 141, i), but it pro-
jects in Carinaria (Fig. 142, i\ is no longer covered by the mantle in Ptero-
trachea (Fig. 143, In-}, and finally has completely disappeared in Firoloida.
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, 7). The gonad is situated beside the liver (Fig. 141, ?c). 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 of a seminal groove. The
penis is situated at the base of the foot, and is provided with a glandular

FIG. 142.

I'arinaria wcditerraneii, male, right-side view. A, the animal ; Ji, the shell removed ; C, /),
two views of the shell of ilimiiopotltt. a, mouth and odoiitophora ; b, cephalic tentacles ; c, eye ;
</, the tin-like anterior lobe of the foot ; d\ its sucker ; «, posterior part of the foot ; /, salivary
glands ; h, margin of -the mantle ; i, ctenidium ; ?», oesophagus ; n, stomach ; o, anus ; j>, liver ;
t, aorta, springing from the ventricle ; n, cerebro-pleural ganglion ; r, pedal ganglion ; w, testis ;
x, visceral ganglion ; y, vesicula seminalis ; z, penis. (From Lankester, alter 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 165

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.

FAMILY 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 — Oxygyrus, Benson -r
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). FAMILY 2. CARINARIIDAE, 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-

FIG. 143.

Pterotrachea. mutica, seen from the right side, a, pouch for the reception of the snout when
retracted ; br, ctenidium ; 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, d'Orbigny (Fig. 142, C, D). FAMILY 3. PTEROTRACHEIDAE, 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 ; a ctenidium 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.

SUB-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 pallia! 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.

1 64 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).
FAMILY 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. FAMILY 2. FASCIOLARIIDAE, 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. Latirus,
Montfort FAMILY 3. MITRIDAE, 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 — Mitra,
Lamarck. Turricula, Klein. Cylindromitra, Fischer. Imbricaria,
Schumacher. FAMILY 4. BUCCINIDAE, 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. Buccinum, Linnaeus ; shell ventricose with a wide
aperture ; operculum oval with sub-central nucleus ; tentacles moderately
long ; lateral teeth with three or four cusps ; British. Cominella, 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. Euthrio. 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. FAMILY 5. NASSIDAE, 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. Canidia,
Adams ; exterior border of the aperture simple ; fluviatile. Bullia,
Gray ; shell polished ; tentacles without eyes ; foot very broad ; a
burrowing form. FAMILY 6. MURICIDAE, 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. Typl^is,
Montfort ; shell with closed canal and tubular spines. Urosalpinx,
Stimpson. Lachesis, Risso. FAMILY 7. PURPURIDAE, Broderip. Foot

THE 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, Bruguiere ; shell not umbilicated, aperture
smooth ; British. Bapana, 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. Sistrum,
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. FAMILY 8. HALIIDAE,
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. FAMILY 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 — Cancellaria,
Lamarck. FAMILY 10. COLUMBELLIDAE, Adams. Foot large, tentacles
long and convergent ; spire of shell prominent, aperture narrow, the
canal very short and the columella crenelated.
Genus — Columbella, Lamarck. FAMILY 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 find umbilicated, the
aperture provided with a canal. FAMILY 12.
VOLUTIDAE, Gray. Head very flattened, and FIO 144

transversally widened, with the eyes on the conus lineatus, ventral aspect,
sides ; snout short ; foot broad ; siphon with T> orj.Hce °,f the pedal gland ; n,

, _ *• _ . mantle and opening of the palhal

internal appendages. Genera — V oluta, Lin- cavity ; in, operculum ; iv, an-
na PUS • liPfld with PVM • Australian RPJI<? terior glandular groove of the
naeus , ieaa wun eyes, Australian seas. foot. v^ eye and tentacle; VI,

Guivillea, Watson ; no eyes ; abyssal. Cyniba, siphon ; vn, mouth. (After
Broderip and Sowerby ; viviparous. FAMILY &

13. OLIVIDAE, 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, Bruguiere ; eyes ;
no operculum. Olivella, Swainson ; tentacles without eyes ; an operculum.
Ancillaria, Lamarck. Agaronia, Gray. FAMILY 14. MARGINELLIDAE,
Adams. Foot very large ; mantle reflected over the shell. Genera —
Marginella, Lamarck ; foot without operculum ; a central gland-pore.
Pseudomarginella, Carriere ; foot with an operculum and an anterior gland-

166 THE GASTROPODA

pore. FAMILY 1 5. HARPIDAE, Chenu. Foot very great ; without oper-
culum ; shell with a short spire and longitudinal ribs ; siphon long.
Genus — Harpa, Lamarck.

TRIBE 2. TOXIGLOSSA.

Stenoglossa without jaws, and with a radular formula of 1.0.1 ; a
*l poison gland " present, whose duct traverses the nerve-collar.

FAMILY 1. PLEUROTOMATIDAE, Loven. Shell fusiform with an elongated
spire ; the margin of the shell and mantle notched ; siphon rather long ;
eyes situated on the sides of the tentacles. Genera — Clavatula, Lamarck ;
operculum piriform with a lateral nucleus ; eyes near the extremities of
the tentacles. Pleurotoma, Lamarck ; operculum oval with nucleus near
the summit ; eyes near the bases of the tentacles. Mangilia, Risso ; no
operculum; eyes half-way up the tentacles. Beta, Gray. Pusionella,
Gray. Pontiotliauma, Smith. FAMILY 2. TEREBRIDAE, Adams. Shell
turriculated, with numerous whorls ; aperture and operculum oval ; foot
small ; eyes at the summits of the tentacles ; siphon long. Genus —
Terebra, Adanson. FAMILY 3. CONIDAE, Gray. Shell conical, with a
very short spire and a narrow aperture with parallel borders ; eyes
borne near the middle of the external sides of the tentacles ; an ungui-
form operculum. Genus — Conns, Linnaeus (Fig. 144).

SUB-CLASS II. EUTHYNEURA, Spengel
( = Platymalakia, von Jhering = Androgyna, Morch).

These are hermaphrodite Gastropoda, whose radula is generally
composed of uniform teeth on each side of the median tooth
(Fig. 1 45). The head in most cases bears two pairs of tentacles ;

it is only in Lophocercus,
the Elysiomorpha,
Hedyle milaschewitchi,
and the Janellidae that
there is a single pair.
The Euthyneura are
Fl°- 145- specially characterised

Acera bullata, a single row of teetli of the radula; fonmila : v fi rlpf^rcinn nf tliPi'r
«.!.«. (From Lankester, after Loven.) Dy tj

organisation when adult;

this detorsion is particularly well manifested in the visceral com-
missure, which is no longer twisted, except in some archaic forms
of Tectibranchs (Actaeon, Fig. 57) and Pulmonates (Chilina), and
shows a tendency to the concentration of all its elements round
the oesophagus (Fig. 146). To such a degree is this concentration
carried that, with the exception of the majority of the Bullomorpha
and of dplysia (Fig. 95), the whole central nervous system is
aggregated in the cephalic region (Fig. 97), sometimes on the dorsal
side, as in the Pleurobranchidae and Nudibranchia (Fig. 159),
sometimes on the ventral side as in the Thecosomata (Fig. 60, n.s).
The pedal centres are frequently united by a second " parapedal "

THE GASTROPODA 167

(Figs. 95, pe, and 96, g.pe) commissure. The sub-class includes the
two orders, Opisthobranchia and Pulmonata.

ORDER 1. Opisthobranchia, Milne-Edwards.

Marine Euthyneura with aquatic respiration ; the ventricle of
the heart is generally anterior, and the pallial cavity, when present,
is widely open. There is a marked tendency to a reduction of the
shell, which may become internal or disappear. In the naked
forms spicules are sometimes developed (Pleurobranchidae, Dorido-
morpha, Hedylidae, Fig. 168, sp.). The order comprises two sub-
orders, Tectibranchia and Nudibranchia.

iv te

r

FIG. 146.

Central nervous system of Limnaen ftagnalis, right-side view. Itu, buccal mass ; g.a, ab-
dominal ganglion ; g.lii, buccal or stomato-gastric ganglion ; fi.ce, cerebral ganglion ; g.p, pedal
ganglion ; g.pl, pleural ganglion ; g.s.i, supra-intestinal ganglion ; lo.d, dorsal lobe of cerebral
ganglion ; lo.l, lateral lobe of cerebral ganglion ; n.co, columellar nerve ; n.la, labial nerve ; u.o.
optic nerve ; n.pa, riglit pallial nerve ; n.par, parietal nerves ; u.pe, penial nerve ; n.te,
tentacular nerve ; oe, oesophagus ; ot, otocyst and nerve.

SUB-ORDER 1. TECTIBRANCHIA, Cuvie'r.

Opisthobranchs provided in the adult state with a mantle and a shell,
with the exceptions Runcina, Pleurobranchaea, the Cymbuliidae, and some
Aplysiomorpha. There is a ctenidium, except in some " Thecosomata "
and " Gymnosomata," and an osphradimn. The sub -order includes three
tribes, the Bullomorpha, the Aplysiomorplia,and the Pleurobranchomorpha.

TRIBE 1. BULLOMORPHA.

In these Tectibranchs the shell is usually well developed (it is want-
ing in Runcina and the Cymbuliidae), and may be external or internal.
There is no operculum except in the Actaeonidae and Limacinidae (Fig.
49, op). The pallial cavity is always well developed, and contains the
ctenidium, in part at least : this ctenidium, except in the Lophocercidae,
is of the " folded " type. With the exception of the Aplustridae, Lopho-
cercidae, and Thecosomata, the head is devoid of apparent tentacles, and
its dorsal surface forms a digging disc or shield usually separate from the
neck, and with more or less scolloped margins. The edges of the foot
(parapodia) are continuous with the ventral face of that organ (Fig. 147,/),
and are often transformed into highly -developed fins (Fig. 151, VI).

168

THE GASTROPODA

Posteriorly the mantle forms a large " pallial lobe " under the pallial
aperture (Figs. 98, i.l ; 148, I). The stomach is generally provided with
chitinous, or even calcined, masticatory plates (Fig. 76, m.p). The visceral
commissure is fairly long, except in such specialised forms as Runcina,
Lobiger, and the Thecosomata (Fig. 60, n.s). The hermaphrodite genital
aperture is connected with the penis by a ciliated groove, except in Actaeon
(Fig. 148), Lobiger, and Cavolinia longirostris, in which the spermiduct is a
closed tube. The Bullomorpha are swimmers or burrowers.

FAMILY 1. ACTAEONIDAE, Adams. Cephalic shield bifid posteriorly;
the margins of the foot slightly developed ; the genital ducts diaulic ; the
visceral commissure streptoneurous ; the shell thick, with a prominent
spire and elongated aperture ; columella generally folded ; a corneous
paucispiral operculum. Genera — Actaeon, Montfort ; British (Fig. 148).
Solidula, Fischer von Waldheim. Tornatellcea, Conrad ; extinct Triplaca,
Tate ; from the Eocene. Adelactaeon, Cossmann. Actaeonina, d'Orbigny ;
Carboniferous to recent. Bullina, Ferussac. Bullinula, Beck. Actaeo-

Acera bullata, swimming,
left-side view. /, flu (foot) ;
m, mouth ; sh, shell. (After
Guiart.)

Fa:. 148.

Actaeon tnrnatilis, removed from its shell, right-side view.
I, inferior lobe of tho mantle; II, glandular hollow pallial
appendage (extending to the first whorls) ; III, pallial (hyi>o-
branchial) gland ; IV, opening of the pallial cavity ; V, eye and
cephalic hood ; VI, penis.

nella, d'Orbigny ; • from
the Cretaceous. Vol-
i-aria, Lamarck ; Eocene.
Odostomiopsis, Thiele.
FAMILY 2. RINQICU-
LIDAE, Fischer. Cephalic disc enlarged anteriorly and forming an open tube
posteriorly ; shell external, thick, with a prominent spire ; no operculum.
Genera — Ringicula, Deshayes. Pugnus, Hedley. Cinulia, Gray ; from the
Cretaceous. Avellana, d'Orbigny ; from the Cretaceous. Fortisia, Bayan ;
from the Eocene. FAMILY 3. TORNATINIDAE, Fischer. Margins of the
foot not prominent ; no radula ; shell external with inconspicuous spire ;
no operculum. Genera — Tornatina, Adams ; British. Retusa, Brown.
Volvula, Adams. FAMILY 4. SCAPHANDIUDAE, Fischer. Cephalic shield
short, truncated posteriorly ; eyes deeply imbedded ; three calcareous
stomachal plates, two broad and paired, one narrow and azygos ; shell
external, with reduced spire. Genera — Scaphander, Montfort ; British.
Sabatia, Bellardi ; Eocene. Atys, Montfort. Smaragdinella, Adams.
Cylichna, Loven ; British. Amphisphyra, Loven ; British. FAMILY 5.
BULLIDAE, d'Orbigny. Margins of the foot well developed ; eyes super-
ficial ; three chitinous stomachal plates ; shell external, with reduced

THE GASTROPODA

169

spire. Genera — Bulla, Linnaeus; British. Haminea, Leach; British
(Fig. 98). FAMILY 6. ACERATIDAE, Pilsbry. Cephalic shield continuous
with the neck ; twelve to fourteen chitinous stomachal plates ; a posterior
pallial filament passing through a notch in the shell. Genera — Acera, O. F.
Miiller; British (Fig. 147). Cylindrobulla, Fischer. Volvatella, Pease.
FAMILY 7. APLUSTRIDAE, Chenu. Foot very broad ; cephalic shield with

Fio. 140.

Hydatina vexillum, as seen crawling, a', anterior part of the foot ; 1>, b', cephalic tentacles ;
i, shell. (From Lankester, after Adams.)

four tentacles ; shell external, thin, without prominent spire. Genera —
Hydatina, Schumacher (Fig. 149). Aplustrum, Schumacher. Micromelo,
Pilsbry. FAMILY 8. PHILINIDAE, Adams. Cephalic shield broad, thick,
and simple ; shell wholly internal, thin, the spiral much reduced and the
aperture very large. Genera — Pkiline, Ascanius (Fig. 68) ; gizzard with
three similar calcareous masticatory plates ; British. Cryptophthalmus,
Ehrenberg. Chelinodnra, Adams. }'haneropkthalmus, Adams. Colpo-
daspis, Sars ; British. Colobocephalns, Sars.
FAMILY 9. DORIDIIDAE, Fischer. Cephalic
shield ending posteriorly in a median point ;
mantle well developed ; shell internal,
largely membranous ; digestive canal with-
out radula and without masticatory plates.
Genera — Doridium, Meckel. Navarclius,
Cooper. FAMILY 10. GASTROPTERIDAE,
^Fischer. Cephalic shield pointed behind ;
shell internal, chiefly membranous with a
calcined nucleus, nautiloid ; parapodia well
developed, forming fins. Gastropteron, Kosse.
FAMILY 11. RUNCINIDAE, Adams. Cephalic
shield continuous with the dorsal integu-
ments of the body ; no shell ; ctenidium
projecting from the mantle cavity; four
stomachal plates. Genus — Runcina, Forbes ;
British. FAMILY 12. LOPHOCERCIDAE,
Adams. Shell globular or ovoid, external ;
foot elongated, the parapodia separate from
the ventral surface of the foot ; genital duct diaulic ; visceral commissure
short. Genera — Lobiger, Krohn ; parapodia divided into two fins on each

?io. 150.

Luphocercus sieboldi. A, dorsal
aspect ; /», ventral aspect ; C, the
shell. /, foot ; /', parapodia or
anterior lateral lobe of foot, re-
flected on the shell ; m, mouth ;
ah, shell ; t, tentacle. (After
Souleyet.)

THE GASTROPODA

side ; two pairs of tentacles; Mediterranean. Lophocercus, Krohn ; parapodia
undivided and applied to the shell ; a single pair of tentacles ; Mediter-
ranean (Fig. 150). FAMILY 13. LIMACINIDAE, Gray. Dextral animals
with visceral mass and shell coiled "pseudo-sinistrally" (ultra-dextrally) ;
operculum with sinistral spiral ; pallial cavity dorsal. Genera — Peraclis,
Forbes ; head proboscidiform, with symmetrical tentacles ; a ctenidium.
Limacina, Cuvier ; head much reduced ; the right tentacle larger than the
left (Fig. 63); British. FAMILY 14. CYMBULIIDAE, Cantraine. Adult
without shell ; a sub-epithelial pseudoconch formed by the connective
tissue ; pallial aperture ventral. Genera — Cymhulia, PeVon and Lesueur ;
pseudoconch thick; foot with a median ventral filament (Fig. 151).
Cymtiuliopsis, Pelseneer ; pseudoconch thin, with a large cavity. Gleba,

Cymbulia peroni, swimming, left-side view. I, position of the mouth, seen through the tin ;
1 1, the sub-epithelial pseudoconch ; III, visceral mass ; IV, pallial cavity ; V, posterior flagellum
of the foot ; VI, left tin. (After Delle Chiaje.)

Forskal ; pseudoconch thin, with scarcely any cavity. Desmopterus, Chun ;
each fin with a posterior filament. FAMILY 1 5. CAVOLINIIDAE, d'Orbigny.
Visceral mass and shell not coiled, symmetrical ; pallial aperture ventral.
Genera — Cavolinia, Abildgaard ; visceral mass and shell more or less
flattened dorso-ventrally (Fig. 153) ; pallial appendages present which pass
through lateral fissures in the shell. Clio, Browne ; mantle without
projecting appendages ; shell not septate ; universally distributed (Fig. 152).
Cuvierina, Boas ; shell with a posterior septum ; circular in section. The
three last families form the group formerly known as " Thecosomatous
Pteropods." These animals are characterised, in contrast to other allied
Mollusca, by the foot, which is entirely transformed into two anterior
symmetrical fins ; by the existence of a mantle and mantle-cavity ; by the
absence of eyes in the adult ; by the absence of a ctenidium, except in

THE GASTROPODA

171

certain species of Peraclis and Cavolinia ; and by the position of the nerve-
centres at the sides and on the ventral side of the oesophagus. All three
families are pelagic.

FIG. 153.

Shell of Cavolinia tridentata, seen
from the right side. /, postero - dorsal
surface ; g, antero-ventral surface ; h,
median dorsal spine ; i, mouth of the
shell. (From Lankester, after Souleyet.)

TRIBE 2. APLYSIOMORPHA.

In these Tectibranchs the shell
is always much reduced and more
or less internal, or it may be alto-
gether lost in the adult, e.g. in
Phylkiplysia and the Gymnoso-
mata. The head bears two pairs
of tentacles. The margins of the
foot, or parapodia, are separate
from the ventral surface and are
generally transformed into natatory
lobes (Fig. 155, fi). The visceral
commissure, except in Aplysia, is
very much shortened. The genital
duct is monaulic ; the hermaphro-
dite duct is connected with the
penis by a ciliated groove (Fig.
154). The animals comprised in
this tribe are crawling or swim-
ming forms.

FAMILY 1. APLYSIIDAE,
d'Orbigny. The shell partly
covered in, or internal (absent in
Aplysiella) ; the foot long, with
well - developed ventral surface.
Genera — Aplysia, Linnaeus ; shell
incompletely covered ; parapodia
broad ; visceral commissure long ;
British (Fig. 154). Dolabella,
Lamarck. Dolabrifer, Gray. Aplysiella, Fischer; shell only slightly
covered in ; parapodia slightly developed ; visceral commissure short.
Phyllaplysia, Fischer ; parapodia slightly developed ; no shell. Notarchus,
Cuvier ; shell internal, much reduced ; parapodia fused together dorsally
to form a contractile sac surrounding but not attached to the visceral sac.

FIG. 152.

Clio acicula, ventral aspect. C,
wing-like lateral lobe of the foot ; d,
median posterior lobe of the foot ; c,
genital opening ; h, pointed extremity
of the shell ; i, anterior margin of the
shell ; n, stomach ; o, liver ; p, heart ;
u, hermaphrodite gland. (From Lan-
kester, after Bouleyet.)

Kiu. Io4.

Aplysia lejwrina (dorsal aspect), with the parapodia and mantle reflected from the mid-line,
a, anterior cephalic tentacle ; />, posterior tentacle (between a and b, the eyes) ; c, right para-
podia ; (I, left parapodia ; e, hinder part of visceral hump ; /.o, anterior part of the foot, under-
lying the head ; f.p, posterior extremity of the foot ; ft, ctenidium ; ft, the mantle-skirt tightly
npread over the horny shell and pushed with it towards the left side ; i, the spermatic groove ;
k, the common genital pore ; /, orifice of the grape-shaped gland ; ?», osphradium ; n, outline
of part of the, renal sac below the surface ; o, external aj>ertuiv of the kidney ; p, anus. (After
Lankester.)

-fin,

Fio. 155.

Dexiohmnduua pauciilens, Unas,
ventral aspect, V- f-r, l»osterior
ciliated ring ; /, anterior jwvrt of the
foot; /', posterior part of the foot;
ft, fins or parapodia ; g, gill ; pr, pro-
boscis ; .«n, suckers ; <, tentacle.
(After Hoas.)

Fin.

IIfitn)v*yrhe (juitdirhntuli, ventral aspect,
the body-wall removed, the head to the right-
hand side, o, the month; r, the lin-like
lateral lobes of the foot ; »/, the anterior
median part of the foot ; '•, cephalic tentacles ;
/, the posterior median part of the foot;
!>', retractor muscles; /, appendages of the
cephalic tentacles ; «>', anus ; o, pt liver ;
», '", w, genitalia ; v, genital pore. (From
r, after Souleyet.)

172

THE GASTROPODA

173

FAMILY 2. PNEUMONODERMATIDAE, Gray. Shell and mantle absent ; foot
shorter than the visceral mass, and with a much-reduped ventral surface ;
parapodia highly developed and fin- shaped ; pharynx evaginable, with
suckers. Genera — Dexiobranchaea, Boas ; suckers independent ; no terminal
posterior branchia. Pmumonoderma, Cuvier ; suckers united on two lobes ;
a quadriradiate terminal branchia. Sponyiobranchaea, d'Orbigny ; a
simple annuliform terminal branchia. Schizobracliium, Meisenheimer ;
acetabuliferous appendages ramified. FAMILY 3. CLIONOPSIDAE, Costa.
No buccal appendages or suckers ; a very long evaginable proboscis ; a
quadriradiate terminal branchia. Genus — Clionopn^ Troschel. FAMILY 4.
NOTOBRANCHAEIDAE, Pelseneer. Posterior branchia triradiate. Genus —
Notobranckaea, Pelseneer. FAMILY 5. THLIPTODONTIDAE, Kwietniewski.
Head very large, not marked off from the body ; neither branchia nor
suckers ; fins situated near the middle of the body. Genus — Thliptodon,
Boas. FAMILY 6. CLIONIDAE, Gray. No branchia of any kind ; a
short evaginable pharynx, bearing paired conical buccal appendages or
" cephalocones." Genera — Clione, Pallas. Paraclione, Tesch. FowUrina,
Pelseneer. FAMILY 7. HAI.OPSYCHIDAE, Pelseneer. No branchia ; two long
and branched buccal appendages. Genus — Halo-psyche, Boas (Fig. 156).

The last six families form the group formerly known as the " Gymno-
somatous Pteropoda," characterised by the absence of the mantle and shell,
the reduction of the ventral surface of 1X

the foot, and the fin-shaped parapodia
placed at the anterior end of the body.
They are all pelagic.

TRIBE 3. PLEUROBRANCHOMORPHA.

In these Tectibranchs there are
two pairs of tentacles. The foot is
devoid of parapodia. There is no
pallial cavity, but there is always a
single ctenidium situated on the right
side and occupying the space between
the mantle and the foot. The genital
duct is diaulic, without an open
seminal groove ; the male and female
apertures are contiguous. The vis-
ceral commissure is short, and re-
sembles that of the Nudibranchs in
showing a tendency to the fusion of
the supra-intestinal and sub-intestinal
with the pleural ganglia, and the
concentration of all the ganglia on
the dorsal side of the oesophagus.

FAMILY 1. TYLODINIDAE, Mazza-
relli. Shell external and conical ; the
anterior tentacles form a frontal veil ; the ctenidium extending only over
the right side ; a distinct osphradium. Genus — Tylodina, Kafinesque ;

Fio. 157.

Pleuroltranckaea meckeli, dorsal aspect. I,
posterior tentacle or rhinophore ; 1 1, mantle ;

prebranchial gland ; VII, genital (herma-
phrodite) orifice ; VIII, the fused anterior
tentacles ; IX, expanded proboscis.

174 THE GASTROPODA

Mediterranean. FAMILY 2. UMBRELLIDAE, Gray. Shell external, conical,
and much flattened ; anterior tentacles very small and situated together
with the mouth in a notch in the foot below the head ; ctenidium very
large, extending above the neck. Genus — Umbrella, Lamarck (Fig. 158).
FAMILY 3. PLEUROBRANCHIDAE, Gray. Shell covered by the mantle or
absent ; the interior tentacles form a frontal veil ; spicules are formed in
the mantle ; foot flattened. Genera — Pleurobranchus, Cuvier ; mantle
long and broad ; shell internal, with a short spire. Bertkella, Blainville.
Haliotinella, Souverbie. Osca?iius, Leach ; British. Oscaniella, Bergh.
Oscaniopsis, Bergh. Pleurobranchaea, Meckel ; mantle .short and narrow ;
no shell (Fig. 157).

I'lO. 158.

Umbrella metliterrmua, right side view, a, mouth; b, cephalic tentacle ; A, ctenidium. The
free edge of the mantle is seen just below the margin of the shell. (From Lankester, after
Owen.)

SUB-ORDER 2. NODIBRANCHIA, Cuvier.

Naked Opisthobranchs without a shell in the adult state ; without
ctenidium and osphradium. These animals are generally slug-like and
exhibit an external symmetry. The visceral mass, except in the Hedylidae,
is no longer a sac marked off from the foot, and the dorsal integuments
frequently give rise to appendages which are subservient to respiration.
The nervous system is much concentrated ; the ganglia are generally
united on the dorsal side of the oesophagus ; the supra-intestinal and
infra-intestinal ganglia are fused with the pleurals (Fig. 159, a) ; the fusion
of the centres is sometimes carried to a great extent (Tethys), but the
several infra-oesophageal commissures (pedal, visceral, and stomato-gastric)
always remain distinct. The visceral commissure is always reduced, and
is generally without a ganglion. Accessory stomato-gastric or "gastro-
oesophageal " ganglia are present. The gonad is subdivided into male
and female acini (Fig. 102, B) except in the Elysiomorpha. The Nudi-
branchia are marine, generally carnivorous, and brightly coloured,
affording many instances of mimicry. There is no osphradium, but its
absence is compensated by the increased development of the olfactory organ
or rhinophore. In ontogeny the free veliger stage of Nudibranchs (Fig. 61)
is followed by a planariform creeping stage, during which the shell is
rapidly lost (Fig. 116, B) ; and finally the dorsal appendages are acquired,
notably the dorsal papillae of the Eolids, of which the most anterior are
the first to be developed. Cenia is the only form that leaves the egg in
the adult condition ; it has no embryonic shell, and the embryonic velum

THE GASTROPODA 175

is extremely reduced. The pliylogenetic relationships between the Nudi-
branchs and Tectibranchs are clearly exhibited by the organisation of the
Pleurobranchomorpha, in which there is neither a pallial cavity nor an
osphradium, and the respiration is largely pallial. The shell is altogether
absent in Pleurobranchaea ; the nervous system is concentrated on the
dorsal side of the oesophagus ; spictiles and cnidocysts are found in the
dorsal integuments. The mantle of the Doridomorpha is completely
homologous with that of the Pleurobranchidae, and is in no wise to be
regarded as an epipodium reflected over the dorsal surface of the body.

Nervous system of Gonwdoris, dorsal view, a, cerebro-pleural ganglion, with eye and oto-
cyst ; l>, pedal ganglion ; c, sub-cerebral commissure ; d, visceral commissure ; e, visceral nerve ;
/, genital nerve ; g, penial nerve ; h, pallial nerve ; i, tentacular nerve and ganglion ; j, stomato-
gastric ganglion.

TRIBE 1. TRITONIOMORPHA.

Nudibranchia in which the liver is wholly or partially contained in
the visceral mass. The anus is lateral, on the right side. There are
generally two rows of ramified dorsal appendages (Fig. 83, II). The genital
duct is diaulic ; the male and female orifices contiguous. FAMILY 1.
TRITONIIDAE, Adams. The anterior tentacles form a frontal veil ; the
foot rather broad. Genera — Tritotiia, Cuvier ; stomach without horny
plates ; British (Fig. 83). Marionia, Vayssiere ; stomach with horny plates.
FAMILY 2. SCYLLAEIDAE, Alder and Hancock. No anterior tentacles ;
dorsal appendages broad and foliaceous ; foot very narrow ; stomach with
horny plates. Genus — Scyllaea, Linnaeus ; pelagic. FAMILY 3. PHYLLIR-
HOIDAE, Adams. No anterior tentacles and no dorsal appendages ; body
laterally compressed ; transparent natatory forms. Genus — Phyllirhoe,
Peron and Lesueur (Fig. 161). FAMILY 4. TETHYIDAE, Alder and
Hancock. Head broad, surrounded by a funnel-shaped velum or hood ;
no radula ; dorsal appendages foliaceous. Genera — Tetliys, Linnaeus ;
foot broad; no mandibles (Fig. 160, B). Melibe, Rang; foot narrow;
mandibles present. FAMILY 5. DENDRONOTIDAE, Alder and Hancock.
Anterior tentacles forming a scolloped frontal veil ; dorsal appendages and
tentacles similarly ramified. Genera — Dendronotus, Alder and Hancock ;

THE GASTROPODA

British. • Campaspe, Bergh. FAMILY 6. BORNELLIDAE, Fischer. The
dorsum garnished on either side with papillae at the bases of which are

Fio. 160.

A, Eolis papillosa, dorsal view: a, posterior cephalic tentacle (rhinophore) ; b, anterior
cephalic tentacle ; c, the dorsal papillae. B, Tethys leporitm, dorsal view ; a, the cephalic hood ;
b, cephalic tentacle ; e, neck ; d, genital pore ; e, anus ; /, large dorsal papillae ; {/, smaller
dorsal papillae ; h, margin of the foot. C, Doris tuber<mlata, seen from the pedal surface ; b,
margin of the head ; /, sole of the foot; m, mouth ; sp, the mantle. D, K, dorsal and lateral
view of Elysia viridis ; 6, tentacle ; cp, lateral outgrowths. (From Lankester, after Hancock,
Cuvier, and Allmann.)

Fio. 161.

Phyllirhoe hucephalum, right-side view ;
the internal organs are shown as seen by
transmitted light, a, mouth ; b, radular
sue ; c, oesophagus ; (/, intestine ; d,
stomach ; /, the genital pore ; f, anus ;
<i, tl', 0", </"', the four lobes of the liver ;
h, the heart (auricle and ventricle) ; I, the
renal sac ; I', the ciliated reno-perirardial
duct ; 7d, the external opening of the
renal sac ; n, the cerebral ganglion ; o,
the cephalic tentacles ; w, the parasitic
medusa Alnestru, usually found attached
in this position ; »/, the ovo-testes. (From
Laukester, after Keferstein.)

ramified appendages. Genus — Bornella, Gray. FAMILY 7. LOMANOTIDAE,
Bergh. Body flattened ; the two dorsal borders prominent and foliaceous
Genus — Lomanotus, Verany ; British.

THE GASTROPODA

177

TRIBE 2. DORIDOMORPHA.

Nudibranchia with external symmetry, in consequence of the median
position of the anus, which is posterior and generally dorsal, and sur-
rounded by ramified pallial appendages constituting a secondary branchia
(Fig. 162, g}. The liver is not ramified in the integuments. The genital
duct triaulic. Spicules present in the mantle.

FAMILY 1. POLYCERATIDAE, Abraham. A more or less prominent
frontal veil ; branchiae non-retractile. Genera — Euplocamus, Philippi
(Fig. 162); ramified dorsal appendages on the border of the mantle.

Fio. 162.

FAiplocamus crocrxs, dorsal aspect,
o, anus ; /, foot ; fr.a, frontal append-
ages ; g, gill ; j>a.«, pallial appendages ;
r/i, rhinophore. (After Vavssiere.)

FIG. 103.

Ancula cristate, dorsal view, a,
anus ; br, pallial gill encircling the
anus (external to these respiratory
appendages are seen ten other club-
like pallial appendages); t, posterior
(branched) cephalic tentacle or rhino-
phore. (From Lankester, after Alder
and Hancock.)

Polycera, Cuvier ; the mantle border bears on each side a single posterior
pointed appendage ; British. Thecacera, Johnston ; the mantle border
with club-shaped appendages ; the branchia formed of three lobes directed
forwards ; British. Aegirus, Loven ; body tuberculate ; rhinophores not
lamellar ; a dorsal mandible ; British. Plocamopherus, Leuckart. Palio,
Gray. Crimora, Alder and Hancock. Triopa, Johnston, British. Trio-
pella, Sars. FAMILY 2. GONIODORIDIDAE, Adams. Mantle border pro-
jecting ; frontal veil reduced and often covered by the anterior border of
the mantle. Genera — Goniodoris, Forbes ; frontal veil not continuous
with the mantle ; mantle quadrangular and incised posteriorly ; British.
Acanthodoris, Gray ; mantle oval, papillate ; rhinophores retractile ; British.
Idalia, Leuckart ; mantle reduced and fringed with long appendages ;

12

178 THE GASTROPODA

rhinophores very long, non-retractile ; British. Ancula, Loven ; mantle
border scarcely distinguishable, without appendages ; rhinophores branched ;
British (Fig. 163). Doridunculus, Sars. Lamellodoris, Alder and Han-
cock. Ancylodoris, Dybowsky, the only freshwater Nudibrunch, from Lake
Baikal, probably belongs to this family. FAMILY 3. HETERODORIDIDAE,
Fischer. No branchia. Genus — Heterodoris, Verrill and Emerton.
FAMILY 4. DORIDIDAE, Gray. Mantle oval, covering the head and the
greater part of the body ; anterior tentacles ill developed ; branchiae
generally retractile. Genera — Hexabranchus, Ehrenberg ; branchiae made
up of separate fascicles, retractile within distinct
cavities. Doris, Linnaeus ; mantle elliptical,
covering the whole body ; branchiae tri- or
quadri-pennatifid ; British (Fig. 160, C). (Sub-
genera — Archidoris, Bergh. Rostanya, Bergh.
Aldisa, Bergh. Cadlina, Bergh. Jbrumio, Bergh.
Platydoris, Bergh). Chromodoris, Alder and
Hancock ; body long and narrow ; foot longer
than the mantle ; branchial plumes simply
pinnate. FAMILY 5. DORIDOPSIDAE, Alder.
Pharynx suctorial ; no radula ; peri -branchial
rosette on the dorsal surface, above the mantle
border. Genus — Doridopn*, Alder and Hancock.
FAMILY 6. CORAMBIDAE, Bergh. Anus and
branchia posterior below the mantle border.

Genus-6'orro»fc, Bergh (Fig. 164). FAMILY 7.
g, paiiial gills : m, mouth ; ]>a, PnYLLiDiiDAE, Alder and Hancock. Pharynx
H.'Fischer!/' to * suctorial ; branchiae surrounding the body and

placed between the mantle and the foot. Genera

— Pkyllidea, Cuvier ; anus dorsal. Fryeria, Gray ; anus posterior between
the mantle and the foot.

The three last families constitute the sub -tribe " Porostomata,"
characterised by the reduction of the buccal bulb, which is transformed
into a suctorial apparatus.

TRIBE 3. EOLIDOMORPHA ( = Cladohepatica).

Nudibranchs in which the whole of the liver is contained in the
integuments and the tegumentary papillae (Fig. 77). The genital duct
is diaulic, and the male and female orifices are contiguous. A pair of
laterally placed mandibles is present (Fig. 73, A). The anus is antero-
lateral, except in the Proctonotidae, in which it is median. The tegu-
mentary papillae are not ramified : they frequently contain terminal sacs
(cnidosacs), which communicate on the one hand with the exterior, on the
other hand with the digestive canal (Fig. 165). The cnidosacs contain
neinatocysts, which according to Wright and to Grosvenor are derived
from the various species of Hydroids on which the animals feed. The
nematocysts are invaginated while they are in the cnidosacs, but when
expelled from them they are evaginated (Fig. 166). In some species of
Hedyle and Pseudovermis, in which there are no tegumentary papillae,

THE GASTROPODA

179

cnidosacs are found in the integuments ; e.g. Pseudovermis paradoxes
(Fig. 169).

FAMILY 1. EOLIDIDAE, d'Orbigny. Dorsal papillae spindle-shaped or
club-shaped, each ending in an open sac of endodermic origin which
communicates with a hepatic caecum and contains nematocysts. Genera
— Eolis, Cuvier ; the anterior angles of the foot prominent ; rhinophores
smooth ; dorsal papillae compressed ; British {

(Fig. 160, A). Facelina, Alder and Hancock ;
rhinophores foliated; radula
triserial ; British. Tergipes,
Cuvier ; rhinophores simple ;
radula uniserial ; dorsal pa-
pillae in a single row on
either side ; otocyst with an
otolith ; British. Gonieolis,
Bergh ; no eyes. Cuthona,
Alder and Hancock. EmUe-
tonia, Alder and Hancock.
Galvina, Alder and Hancock.
Calma, Alder and Hancock.
Hero, Loven ; a frontal
velum ; rhinophores simple ;
dorsal appendages in umbel-
liform clusters. FAMILY 2.
GLAUCIDAE, Gray. The
body furnished with three
pairs of lateral lobes bearing
the tegumentary papillae ; FIG. 165.

free_ Sagittal section of a
„ dorsal papilla of Kol is. c.s,

forma, cnidocystic sac ; d, duct

Fio. 160.

Evaginated cnidocyst
from Kol is jnim-tnta, x 500.
(After Vayssii-rft.)

foot very narrow

swimming pelagic

Genus -Glow, Forster. JNjjj*

FAMILY 3. H E D Y L I D A E, cnidocystic sac ; ep, exter-

Bergh. Body elongated ;
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. FAMILY 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. FAMILY 5. PROCTONOTIDAE, Alder and
Hancock. Anus situated posteriorly in the median line of the back ;
anterior tentacles atrophied ; foot broad. Genera — Janus, Verany ;
a median crest between the rhinophores ; British. Proctonotus, Alder
and Hancock ; no intertantacular crest ; British. FAMILY 6. DOTONIUAE,
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 cnidosacs. Genera — Doto, Oken ;
a frontal veil ; British. Gellina, Gray ; no frontal veil. Heronwrpha,

i8o

THE GASTROPODA

Bergh. FAMILY 7. FIONIDAE, 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.

PliitrophiillitUa lixeittu. A, dorsal view ; li,
ventral view. 6, the mouth ; 7, lamelliforni
pallial gills (the posterior part of the foot bears
a median glandular tract). (From
after Souleyet.)

Fio. 168.

lleilyle glandul(fera, dorsal aspect, e,
eye ; /, foot (posterior part) ; -M..S, nervous
system ; ph, pharynx ; sp, spicula ; r.m,
visceral mass. (After Kowalewsky.)

Fio. 160.

rmis parailoxits,
dorsal aspect. a, aims; nl,
cnidosac ; e, eye ; /, , kidney ;
/, liver; m, mouth (on the
ventral side, seen through
the transparent head) ; ».s,
nervous system ; ot, oto-
cyst ; ph, pharynx ; st,
stomach. (After Kowalew-
sky.)

Genus— Fiona, Hancock and Embleton. FAMILY 8. PLEUROPHYLLIDIDAE,
Adams. Anterior tentacles in the form of a digging shield ; mantle
naked ; tegumentary papillae or " branch i« " situated along the sides of
the foot, beneath the mantle border. Genus — Pleurophyllidia, Meckel
(Fig. 167). FAMILY 9. DERMATOBRANCHIDAE, Fischer. Like Pleuro-

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.

FAMILY 1. HERMAEIDAE, 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. FAMILY 2.
PHYLLOBRANCHIDAE, Bergh. Foot broad ; dorsal papillae without

Fio. 170.
Cenia cocksi, 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. FAMILY 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. FAMILY 4.
ELYSIIDAE, 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. FAMILY 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 interral,
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 tine respiratory
canaliculi (Fig. 90, tr), 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^-Jln 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, <-/, and 1 75, br). \ The auricle
of the heart is usually anterior (Fig. 86), as is the ck§te 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
Basommatophora such as Ckilina,
Auricula, Latia (Fig. 96). In the
Auriculid Pythui, the spermiduct re-
tains the character of an open ciliated
groove leading from the hermaphro-
dite aperture to the penial orifice
(Fig. 171, ci) : in other Auriculidae

Reproductive apparatus of Pythia. this grOOVC is Simply closed to form

a canal extending from the herma-

mnc, mucous gland ; pe, penis ; ret, re- other PulmonatCS there IS 110 longer
tractor muscle of penis ; r.s, recepta- ., •, • /» i .1

culm., aemiuia; *;>; spermiduct ; MM, a common genital orifice, but the
(TrtTpiaS ; ve'3' 8eminal vesicle' hermaphrodite duct bifurcates 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

of the oviduct arid 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.

Fia. 172.

A series of Stylonmiatophorous Pulmonata, showing the reduction of the shell. A, Helix
pomatia ; B, Damivltanlia brevipes ; C, Textacella haliotidea ; D, Arion ater. a, external shell in
A. I>, C ; shell-sac (closed) in D ; ft, orifice of the pallial or pulmonary cavity. - (From Lankester,
after Ferussac, Pfeitt'er, and Reeve.)

11(J, 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.

1 84 THE GASTROPODA

The Pulmonata are divided into two sub-orders, Basommatophora
and Stylommatophora ; the former are generally aquatic, the latter
terrestrial.

SUB-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, I). 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 Siphonaria. 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.

FAMILY 1. AURICULIDAE, 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, Ferussac ; foot

FIG. 173. ^ not divided transversely, but bifid

otina otis, left-side view. coq, shell ; oc, posteriorly ; tentacles tapering ; shell
eye ; p, foot. solid, umbilical ed, 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 bind behind ; shell
solid, with a short spire and a narrow aperture. Carychium, 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. Blauneria, Shuttle-
worth ; shell sinistral ; aperture elongated, with a single columellar
fold. Pedipes, Adanson ; foot divided transversely ; shell globular ; th(
two borders of the aperture dentate ; partitions not absorbed. FAMILY 2.
OTINIDAE, Chenu. Shell with a short spire and a wide oval aperture ;
tentacles short. Genera — Otina, Gray ; shell auriform ; marine ; British
(Fig. 173). Camptonyx, Benson; shell conical with a spiral summit;
terrestrial. FAMILY 3. AMPHIBOLIDAE, Adams. Visceral mass and shell
spirally coiled ; head broad, without prominent tentacles ; foot short,
operculated. Marine. Genus — Am.phibola, Schumacher; from New
Zealand. FAMILY 4. SIPHONARIIDAE, Adams. Visceral mass and shell

THE GASTROPODA

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. FAMILY 5. GADINIIDAE, Gray. Visceral
mass and shell conical ; head flattened ; pulmonary cavity aquatic, but
without a branchia ; genital orifices separated. Genus — Gadinia, Gray.
FAMILY 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. FAMILY 7. LIMNAEIDAE, 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-

iti

IV

Fia. 174.

Siphmtaria algesirae, removed from its shell. I, heart in the pericardium ; II, kidney ; III,
pallial intrapulmonary gill ; IV, mantle ; V, columellar muscle ; VI, anus ; VII, pneumostoine,
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. FAMILY 8. POMPHOLYGIDAE, 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, Gerstfeldt ; shell
umbilicated, with convex whorls ; tentacles slender ; Lake Baikal and
California. FAMILY 9. PLANORBIDAE, 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. FAMILY 10. ANCYLIDAE, Menke. Shell conical, not
spirally coiled ; tentacles short and compressed ; inferior pallial lobe

1 86

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 witli a posterior internal septum ;
from New Zealand. Gundlachia, Pfeiffer. FAMILY 11. PHYSIDAE, 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. Aplexa,
Fleming ; shell with a pointed
spire ; edges of the mantle not

•n/rvi

divided and very slightly re-
flected over the shell ; British.

FIG. 175.

Lillians talmlatus, ventral aspect.
lir, pallial extrapuliiionary jjill ' co,
heart; o, mouth; p, loot; j*t, mantl** ;
pns, pnemnostoine ; \#t tentacle.

Fio. 17f>.

A nnihts flurintilis, dorsal
view. To the left, the head
with the two cephalic ten-
tacles. (From Lankester, after
Reeve.)

SUB-ORDER 2. STYLOMMATOPHORA.

Pulmonata with two pairs of tentacles (except the Janellidae and I'crtigo,
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 Uncidium, there is no
longer a veliger stage in the development ; the embryo is often furnished
with a contractile pedal vesicle (Fig. 117).

The Sty lorn matophora may be divided into four tribes : the Holognatha,
Agnatha, Elasmognatha, and Ditremata.

TRIBE 1. HOLOGNATHA.

Jaw simple, without a superior appendage.

FAMILY 1. SELENITIDAE, 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. Triyonochlamys, Bottger ; no shell. FAMILY 2.
ZONITLDAE, Pilsbry. Shell external, smooth, heliciform or flattened ;
radula with pointed marginal teeth. Genera — Zonites, Montfort ;
shell depressed, wholly external; British. Ariophanta, Desmoulins ;

THE GASTROPODA 187

mantle produced anteriorly into a cervical lobe ; foot with a posterior
dorsil 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, Ferussac ; differs
from Vitrina in having the foot truncated anteriorly, with a posterior
mucous pore. FAMILY 3. LIMACIDAE, Gray. Shell almost completely
covered by the mantle, or internal. Parmacella, Cuvier ; shell unguifonn
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.
Limax, 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. Parniarion, Fischer.
Amalia, Heynemann. Ayriolimax, Morch. Mesolimax, Pollonera. Mono-
chroma, Simroth. Paralimax, Bottger. Metalimax, Simroth. FAMILY 4.
PHILOMYCIDAE, Fischer. No shell ; the mantle covers the whole surface
of the body ; radula with squarish teeth. Genus — Philomycus, Ferussac;
foot broad ; genital orifice near the right tentacle. FAMILY 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. FAMILY 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, Ferussac ; 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).
Geomalacux, Allmaiin ; shell internal, oval ; Ireland. Ariolimax, Morch.
Anadenus, Murch. FAMILY 7.
HELICIDAE, 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- FIG. 177.

IiaeilS ; shell globular, conical or Helix nemoralis, right-side view. I, anus; II,

depressed, with a rounded or ex- £»£! ^ff^JlS^- SS&^.

panded aperture (Figs. 172, A imeumostome in its maximum distension.

and 177) ; British. (A large

number of sub-genera has been established, which includes more than
4000 species : Polyyyra, Say. Sagda, Beck. Pleurodonta, Fischer von
Waldheim. Helicodonta, Ferussac. Helicophanta, Beck. Acamis, Mont-
fort. Sitala, Adams. Chlorites, Beck. Hapalns, Albeis, etc.) Bulimus,

1 88 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. Kerendtia, Crosse and Fischer.
Cochlostyla, Ferussac. Rhodea, Adams. FAMILY 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. Sphyradium, 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. FAMILY 1 1. 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. FAMILY 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. Eucalodiuni,
Crosse and Fischer ; shell turriculated, the summit truncated, the aperture
oval. Vertigo, Midler ; shell small, ovoid, the summit obtuse, the aperture
small and contracted by numerous teeth ; dextrally or sinistrally coiled ;
a single pair of tentacles ; British. Jhdiminus, 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. Zvspeum, Bourguignat ;
no eyes, shell short and dextral. Megaspira, Lea. Strophia, Albers.
Anostoma, Fischer. FAMILY 13. STENOGYRIDAK, 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. Stmoyyra, Shuttleworth ; shell
turriculated ; the whorls numerous, increasing slowly (Fig. 8). Fcrussacia,
Risso ; shell small, thin, and brilliant ; aperture elongate, oval ; British.
Caecilianella, Ferussac ; shell cylindrical, the spire elongated, the columella
truncated ; eyes absent ; subterranean in habit ; British. Cianclla,
Jeffreys. Azeca, Leach. Opeas, Albers. RJuxlea, Adams. FAMILY 14.
HELICTERIDAE, Fischer. Shell bulimoid, dextral or sinistral ; radular teeth
narrow at their bases, expanded at their extremities and multicuspidate.
Genera — Helicter, Ferussac. Tornatellina, Beck.

TRIBE 2. AGNATHA.

No jaws ; the radular teeth narrow and pointed ; carnivorous. This
group is possibly polyphyletic.

THE GASTROPODA 189

FAMILY 1. OLEACINIDAE, Adams. Shell oval, elongated, with a
narrow aperture ; neck very long ; labial palps prominent. Genera —
Oleacina, Bolton ( = Glandina) ; aperture truncated anteriorly ; colnmella
smooth. Streptostyla, Shuttle worth ; columella with a fold ; aperture
elongate, not truncated anteriorly. FAMILY 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. Gibbulina, Beck ; shell
cylindrical, umbilicated. Aerope, Albers ; shell external, globular, with a
small umbilicus ; radular sac enormous ; from South Africa. Rkytida,
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-
ylossa, Hedley. FAMILY 3. RATHOUISIIDAE, 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.

FAMILY 1. SUCCINEIDAE, Chenu. Anterior tentacles much reduced ;
male and female orifices contiguous but distinct ; shell thin, spiral, with
a short spire. Genera — tiuccinea, 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

Fio. 178.

Antitea macdonaldi, Gray, left-side view, pct.f, pallial cavity; ps, pneumostome ; t,
tentacle. (After Mac Donald.)

mantle ; animal limaciform ; American. Hyalimax, Adams ; shell oval,
wholly internal". Neohyalimax, Simroth. FAMILY 2. JANELLIDAE, 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, o.f, o.m).

FAMILY 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, Ferussac (Fig. 179). FAMILY
2. ONCIDIIDAE, Philippi. Limaciform naked marine animals, without a

Kin. 179.

Vayinulii hizonicn. .1, dorsal aspect; 11, ventral asj)e(jt. I, posterior tentacle; II, anterior
tentacle; III, mouth ; IV, mantle ; V, female oriiice ; VI, foot ; VII, anus. (After Souteyet.)

shell ; female orifice near the anus, at the posterior end of the body ; a
reduced pulmonary cavity with a distinct pneumostome (Fig. 59, pns}.
Genera — Oncidium, Buchanan ; body elongated and narrow ; penis with

Fio. 180.
Onculiuni tongaiium, left-side view. (From l^ankester, after Quoy and Gaimaul.)

accessory apparatus ; from the Indian Ocean. OncMiella, 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. Aniaudrnt. La partie anterieure du ti^e digestif ct la torsion chcx les

Mollnsqiies Gasteropodes. Ann. des Sci. Nat. Zool. (8), vii. 1898.

2. Hacker. Die Auge einiger Gastropoden. Arh. Xool. Instit. Wien, xiv. 1902.

3. Baiidelot. Hecherches sur 1'appareil geudrateur dcs Mollusques Gasteropodes.

Ann. des Sci. Nat. Zool. (4), xix. 1863.

1. Bontan. La cause principale de 1'asyme'trie des Mollusques Gasteropodes
Arch, dc Zool. Expe'r. (3), vii. 1899.

LITERATURE OF THE GASTROPODA 191

5. Butschli. Bemerkungen liber die wahrscheinliche Herleitung der Asym-

metric der Gastropoden, spec, der Asymmetrie im Nervensystem der
Prosobranchiaten. Morph. Jahrb. xii. 1887.

6. Fischer, H. Recherches sur la Morphologie du foie des Gaste*ropodes.

Bull. Scientif. France et Belgique, xxiv. 1892.

7. Fischer and Bouvier. Recherches et considerations BUT 1'asymetrie des

Mollusques Univalves. Journ. de Conchyl. (3), xxii. 1892.

8. Gilchrist. On the Torsion of the Molluscan Body. Proc. Roy. Soc.

Edinburgh, xx. 1895.

9. Grobben. Die Pericardia! druse der Gastropoden. Arbeiten Zool. Inst.

Wien, ix..!890.

10. Einige Betrachtungen iiber die phylogenetische Entstehung der

Drehung und der asymmetrische Aufrollung bei den Gastropoden. Arb.
Zool. Inst. Wien, xii. 1899.

11. Hilgcr. Beitrage sur Kenntniss des Gastropoden Auges. Morph. Jahrb.

x. 1885.

12. Houssay. Recherches sur 1'opercule et les glandes du pied des Gaste"ropodes.

Arch, de Zool. Exper. (2), ii. 1884.

1 3. Jehring, H. von. Sur les relations naturelles des Cochlides et des Ichnopodes.

Bull. Scientif. France et Belgique, xxiii. 1891.

14. Lacaze-Duthiers. Otocystes ou capsules auditives des Mollusques (Gaste'ro-

podes). Arch, de Zool. Exper. (1), i. 1872.

15. Lany. Versuch einer Erklarung der Asymmetrie der Gastropoden. Viertel-

jahrschr. naturforsch. Gesellsch. Zurich, 36, 1892.

16. MacDonald. On the Natural Classification of Gasteropoda. Journ. Linn.

Soc. London (Zool.;, xv. 18bl.

17. Pelseneer. Sur 1'oeil de quelques Mollusques Gasteropodes. Ann. Soc. Beige

de Microsc. xvi. 1891.

18. Prosobranches aeriens et Pulinonos branchiferes. Arch, de Biol.

xiv. 1895.

19. Souleyct. Voyage de la "Bonite." Zoologie, t. ii. 1852.

20. Willem. Observations sur la vision et les organes visuels de quelques Mollus-

ques Prosobranches et Opisthobranches. Arch, de Biol. xii. 1892.

B. Streptoneura.

21. Bergh. Die Titiscanien. Morphol. Jahrb. xvi. 1890.

22. Bernard. Recherches sur les organes palleaux des Gasteropodes Proso-

branches. Ann. des Sci. Nat. Zool. (7), ix. 1890.

23. Recherches sur Valvata piscinalis. Bull. Scientif. France et Belgique,

xxii. 1890.

24. Blochmann. Ue,ber die Entwickeluug der Neritina fluviatilis. Zeitschr. f.

wiss. Zool. xxxvi.

25. Bobrctzky. Studien iiber die embryonale Entwickelung der Gastropoden.

Arch. f. mikr. Anat. xiii. 1877.

26. Bonncvie. Enteroxenos Ostergreni ein neuer, in Holothurien schmarotzen-

der Gastropode. Zool. Jahrb. (Anat. u. Ontog.), xv. 1902.

27. Bouvier. Systeme nerveux, morphologic geneVale et classification des

Gasteropodes Prosobranches. Ann. des Sci. Nat. (Zool.) (7), iii.
1887^

28. Etude sur Porganisations des Ampullaires. Mem. Soc. Philomath.

Paris (centenaire), 1888.

192 LITERATURE OF THE GASTROPODA

29. Bouvier and Fischer. L'organisation ct les affinites des Gasteropodes primitifs

d'apres 1'etude anatomique du Pleurotomaria Beyrichi. Journ. de Conchyl.
1902.

30. Bontan. Recherches sur 1'anatomie et le developpement de la Fissurelle.

Arch, de Zool. Exper. (2), iii. bis, 1886.

31. Memoire sur le systeme nerveux de la Nerita polita et de la Navicella

parcellana. Arch, de Zool. Exper. (3), i. 1893.

32. Carpenter. On the development of the Embryo of Purpura lapilltis. Trans.

Micr. Soc. iii. 1855.

33. Carrttre. Die Fussdriisen der Prosobranchier und das Wassergefuss-System

der Lamellibranchier und Gastropoden. Arch. f. mikr. Anat. xi.
1882.

34. Claparede. Anatomie und Entwicklungsgeschichte der Neritiua 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. Micr. Sci. xlvi. 1902. A

37. Erlanger, von. Zur Entwicklung von Paludina vivipara. Morphol. Jahrb.

xvii. 1891.

38. Zur Eutwickelung 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. Micr. Sci. xxxiii.
1892.

39 bis. Fisher. The Anatomy of Lottia gigantea, Gray. Zool. Jahrb. (Anat.
und Ontog.), xx. 1904.

40. Fol. Snr le diiveloppement embryonnaire ct larvaire des Hcteropodes.

Arch, de Zool. Exper. (1), v. 1876.

41. Gamault. Recherches anatomiques et histologiques sur le Cyclostoma

elegans. Actes Soc. Linn. Bordeaux, 1887.

42. Gegenbaur. Untersuchungen iiber Pteropoden und Heteropoden. Leipzig,

1855.

43. Gibson. Anatomy and Physiology of Patella vulgata. Trans. Roy. Soc.

Edinburgh, xxxii. 1885.

44. Holler. Untersuchungen iiber marine Rhipidoglossen. Morph. Jahrb. ix.

1883.

45. Die Morphologic der Prosobranchier gesammelt (lurch die " Vettoi

Pisani." Morph. Jahrb. xiv. xvi. xviii. xix. 1888-1893.

46. Studien iiber docoglosse und rhipidoglosse Prosobranchier nebst

Bemerkungen iiber die phyletischen Beziehungen der Mollusken tmterei-
nander. Leipzig, 1894.

47. Koehler and Vancy. Entosiphon Deimatis, nouveau Mollusque parasite

d'une Holothurie abyssale. Revue Suisse de Zool. xi. 1903.

48. Karen and Daniclssen. Bidrag tie Pectinibranchiernes Udviklingshistorie.

Bergen, 1851, 1852.

49. Kilkenthal. Parasitische Schnecken. Abhandl. Senckenb. naturf. gesellsch.

xxiv. 1897.

50. Lacazc-Duthicrs. Memoire sur 1'anatomie et I'embryogenic des Vermets

Ann. des Sci. Nat. (Zool.) (4), xiii. 1860.

LITERATURE 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.

52. Lensen. Systeme digestif et systeme genital de la Neritina fluviatilis. La

Cellule, xvi. xx. 1899 et 1903.

53. MacDonald. On the Anatomy and Classification of the Heteropoda. Trans.

Roy. Soc. Edinburgh, xxiii. 1862.

54. MacMurrich. A Contribution to the Embryology of the Prosobranch

Gasteropoda. Stud. Biol. Labor. Johns Hopkins Univ. iii. 1886.

55. Moore. The Molluscs of the Great African Lakes. Quart. Journ. Micr.

Sei. xli. xlii. 1898, 1899.

56. Mutter, J. Ueber Synapta digitata und liber die Erzeugung von Schnecken

in Holotlmrien. Berlin, 1852.

57. Oswald. Der Riisselapparat der Prosobranchier. Jen. Zeitschr. xxviii. 1893.

58. Patten. The Embryology of Patella. Arb. Zool. Instit. Wieu, vi. 1885.

59. Pcrrier. Recherches sur 1'anatoinie et 1'histologie du rein des Gastero-

podes Prosob ranches. Ann. des Sci. Nat. (Zool.) (7), viii. 1889.
59 bis. landless. Some Observations on the Anatomy and Affinities of the
Trochidae. Quart. Journ. Micr. Sci. xlviii. 1904.

60. Robert. Recherches sur le developpement des Troques. Arch, de Zool.

Expe'r. (3), x. 1903.

61. Salcnsky. Etudes sur le developpement du Vermet. Arch, de Biol. vi. 1887.

62. Sarasin, P. Entwickelungsgeschichte der Bithynia tentaculata. Arb.

Zool. Zoot. Instit. Wiirzburg, vi. 1882.

63. Sarasin, P. and F. Ueber zwei parasitische Schnecken. Ergebn. Forsch.

Ceylon, i. 1887.

64. Tobler. Zur Anatomic von Parmophorus intermedius Reeve. Jen. Zeitschr.

xxxv. 1902.

65. Tbnniges. Die Bildung des Mesoderms bei Paludina vivipara. Zeitschr. f.

wiss. Zool. Ixi. 1896.

66. Vayssiere. Etude sur I'organisation de 1'Homalogyra. Ann. des Sci. Nat.

(Zool.) (7), xix. 1895.

67. Vvigt. Entocolax Ludwigii, em neuer seltsamer Parasit aus einer Holothurie.

Zeitschr. f. wiss. Zool. xlvii. 1888.

68. Wegmann. Contributions a 1'histoire naturelle des Haliotides. Arch, de

Zool. Exper. (2), ii. 1884.

69. Notes sur 1'orgauisation de la Patella vulgata. Rec. Zool. Suisse, iv.

1886.

70. Willcox. Zur Anatomic von Acmaea fragilis Chemnitz. Jen. Zeitschr.

xxxii. 1898.

71. Woodward, M. F. Anatomy of Pterocera. Proc. Malacol. Soc. i. 1894.

72. The Anatomy of Pleurotomaria Beyrichii, Hilg. Quart. Journ. Micr.

Sci. xliv. 1901.

C. Opisthobranchia.

73. Alder and Hancock. A Monograph of the British Nudibranchiate Mollusca.

Ray Society, 1845, 1855.

74. Bergh. System der Nudibranchiaten Gastropoden. (Semper. Reisen im

Archipel der Philippinen, ii. 1892.)

75. Boas. Spolia Atlantica. Bidrag tie Pteropodernes Morfologi og Systematik

samt tie Kundskaben om deres geogratiske Udleredelse. Dansk. Vid.
Selsk. Skr. (6), iv. 1886.

13

194 LITERATURE OF THE GASTROPODA

76. Davenport. On the Development of the Cerata in Aeolis. Bull. Mus. Comp.

Zool. Cambridge, xxiv. 1893.

77. FiscJwr. Recherches anatomiques sur un Mollusque nudibranche appartenant

au genre Corambe. Bull. Sci. France et Belgique, xxiii. 1891.

78. Fol. Sur le ddveloppement des Pteropodes. Arch, de Zool. Expe>. (1), iv.

1875.

79. Gilchrist. Beitriige zur Kenntniss der Anordnung, Correlation und Function

der Mantelorganen der Tectibranchiata. Jen. Zeitschr. xxviii. 189.4.

80. Guiart. Contribution a 1'^tude des Gasteiopodes Opisthobranches et en

particulier des Cephalaspides. Mem. Soc. Zool. France, xiv. 1901.

81. Hancock. On the Structure and Homologies of the Renal Organ in the Nudi-

branchiate Mollusca. Trans. Linn. Soc. London, xxiv. 1864.

82. Anatomy of Doridopsis. Trans. Linn. Soc. London, xxv. 1865.

83. Hecht. Contribution a I'e'tude des Nudibrauch.es. Mem. Soc. Zool. France,

viii. 1896.

84. Herdman. On the Structure and Functions of the Cerata or Dorsal Papillae

in some Nudibranchiate Mollusca. Quart. Journ. Micr. Sci. xxxiii. 1892.

85. Hcymons. Zur Entwickelungsgeschichte von Umbrella mediterranea.

Zeitschr. f. wiss. Zool. Ivi. 1893.
85 bis. Kowalewsky. Etudes anatomiques sur le genre Pseudoverniis. Me"m.

Acad. Petersbourg (8), Phys. Math. xii. 1901.
85 tcr. Les Hedylides, utude anatomique. Mem. Acad. Petersbourg (8),

Phys. Math. xii. 1901.

86. Kwietnitwski. Contribuzioni alia conoscenza Anato. - zoologica degli

Pteropodi Gimnosomi del mare Meditervaneo. Uic. Lab. Roma ed Altri.
Lab. Biol. ix. 1903.

87. Lacaze-Duthiers. Anatomie et physiologic du Pleurobranche orange. Ann.

des Sci. Nat. (Zool.) (4), xi, 1859.

88. Mazsarelli. Monogratia delle Aplysiidae del Golfo di Napoli. Mem. Soc.

Ital. Scienzo (3), ix. 1893.

89. Contribute allo conoscenza delle Tylodinidae, nuova famiglia del

gruppo dei Molluschi Tectibranchi. Zool. Jahrb. (System), x. 1897.

90. Moquin-Tandon. Recherches anatomiques sur 1'ombrelle de la Me'diterranee.

Ann. des Sci. Nat. (Zool.) (5), xiv. 1870.

91. Peck. On the Anatomy and Histology of Cymbuliopsis calceola. Stud.

Biol. Labor. Johns Hopkins Univ. iv. 1890.

92. Pelseiieer. Report on the Pteropoda. Zool. "Challenger" Expedit. parts

Iviii. Ixv. Ixvi. 1887, 1888.

93. Recherches sur divers Opisthobranches. Mem. Cour. Acad. Belg.

liii. 1894.

94. Sur la condensation embryog^nique chez un Nudibranche. Trav.

Stat. Zool. Wimereux, vii. 1899.

95. Trinchese. Aeolididae e famiglie Affine. Atti. R. Accad. Lincei (3), xi.

1882.

96. Vaysstere. Recherches anatomiques sur la famille des Bullides. Ann. des

Sci. Nat. (Zool.) (6), ix. 1880.

97. Recherches zoologiques et anatomiques sur les Mollusques opisto-

branches du golfe de Marseille. Ann. Musee Marseille (Zool. ), ii. iii. vi.
1885, 1888, 1901.

98. Viguier. Contribution a 1'etude du d^veloppement de la Tethys fimbriata.

Arch. Zool. Exper. (3), vi. 1898.

LITERATURE OF THE GASTROPODA 195.

D. Pulmonata.

99. Andrt. Contributions & 1'anatomie et a la physiologic des Ancylus lacustris
et fluviatilis. Revue Suisse de Zool. i. 1893.

100. Recherches sur la glande pedieuse des Pulmones. Revue Suisse

de Zool. ii. 1894.

101. Babor. Ueber die wall re Bedeutung des sogenannten Semper'schen Organs

der Stylommatophoren Sitzungsber. K. Bbhin Ges. Wiss. (Math. Nat.
CL), 1895.

102. Beddard. On some Points in the Anatomy of the Nervous System of the

Pond-Snails. Proc. Roy. Soc. Edinburgh, xi. 1882.

103. Behme. Beitriige zur Anatomie und Entwickelungsgeschichte des Hern-

apparates der Lungenschnecken. Arch. f. Naturgesch, Iv. 1889.

104. Beutler. Die Anatomie von Paryphanta Hochstetteri. Pfr. Zool. Jahrb.

(Anat. und Ontog.), xiv. 1901.

104 bis. Bohmig. Beitriige zur Kenntniss der Centralnervensystems einiger Pulmo-
naten Gasteropoden : Helix pomatia und Limnaea stagnalis. Leipzig, 1883.

105. Bouvier. Sur 1'organisation des Amphiboles. Bull. Soc. Philom. Paris

(8), iv. 1892.

106. Brock. Die Entwickelung des Geschlechtsapparates der Stylommatophoren

Pulmonaten nebst Bemerkungen iiber die Anatomie und Entwickelung
einiger anderer Organsysteme. Zeitschr. f. wiss. Zool. xliv. 1886.

107. Collinyc. On the Anatomy of certain Agnathous Pulmonates. Ann. Mag.

Nat. Hist. 1901.

108. Coutagne. Recherches sur le polymorphisme des Mollusques de France.

Lyon, 1895.

109. Cit6not. Etudes physiologiques sur les Gaste"ropodes Pulmones. Arch, de

Biol. xii. 1892.

110. Deschamps. Recherches d' Anatomie comparee sur les Gasteropodes Pulmone's.

Ann. Soc. Sci. Bruxelles, 1898.

111. Erlanger. Etudes sur le deVeloppement des Gasteropodes Pulmones. Arch.

de Biol. xiv. 1895.

112. Fol. Sur le ddveloppement des Gasteropodes Pulmones. Arch, de Zool.

Exper. (1), viii. 1880.

113. Hanitsch. Contributions to the Anatomy and Histology of Limax agrestis.

Proc. Biol. Soc. Liverpool, ii. 1888.

114. Henchman. The Origin and Development of the Central Nervous System

in Limax maximus. Bull. Mus. Comp. Zool. Cambridge, xx. 1890.

115. Button. Notes on the Structure and Development of Siphonaria australis,

Quoy and Gaimard. Ann. Mag. Nat. Hist. (5), ix. 1882.

116. Jhering, H. von. Ueber den uropneustischen Apparat der Heliceen.

Zeitschr. f. wiss. Zool. xli. 1884.

117. Morphologie und Systematik des Genitalapparates von Helix.

Zeitschr. f. wiss. Zool. liv. 1892.

118. Joycux-Lqffuie. Organisation et Developpement de 1'Oncidie (Oncidium

celticum, Cuv.). Arch, de Zool. Exper. (1), x. 1882.

119. Keller. Anatomie von Vaginula Grayi. Zool. Jahrb. v. $uppl.

120. Kofoid. On the Early Development of Limax. Bull. Mus. Comp. Zool.

Cambridge, xxvii. 1895.

121. Kohler. Beitrage zur Anatomie der Gattung Siphonaria. Zool. Jahrb.

(Anat. und Ontog.), vii. 1893.

196 LITERATURE OF THE GASTROPODA

122. Lacaze-Duthiers, H. de. Du systeme nerveux des Mollusques Gasteropodes

pulmon^s aquatiques. Arch, de Zool. ExpeV. (1), J. ; 1872.

123. Histoire de la Testacelle. Arch, de Zool. Expe"r. (2), v. 1888.

124. Anatomie du Gadinia garnoti. Comptes Rendus Acad. Sci. Paris,

C, 1885.

125. Des organes de la reproduction de 1'Ancylus fluviatilis. Arch, de

Zool. Exper. (3), vii. 1899.

126. Lankester, E. liay. Observations on the Development of the Pond-Snail

(Lymnaeus stagnalis), and on the Early Stages of other Mollusca. Quart.
Journ. Micr. Sci. xiv. 1874.

127. 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. Entwickclungsgeschichte von Limax maximus. Zeitschr.

f. wiss. Zool. Ixii. Ixiii. 1896, 1898.

129. Zur Morphologic der Urniere der Pulmonaten. Zeitschr. f. wiss.

Zool. Ixv. 1899.

130. Nabias, de. Recherches histologiqnes et organ ologiques sur les centres

nerveux des Gast6ropodes. Actes Soc. Linn. Bordeaux, xlvii. 1894.

131. Recherches sur le systeme nerveux des Gasteropodes Pulmone's

aquatiques. Trav. Labor. Soc. Scient. Arcachon, 1899.

132. Nalcpa. Beitrage sur Anatomie der Stylommatophoren. Sitzungsber.

Akad. wiss. Wien, Ixxxvii. 1883.

133. Pelscnecr. Etudes sur des Gasteropodes Pulmone's. Mem. Acad. Belg. liv.

1901.

134. Perez. Recherches sur la generation des Mollusques Gasteropodes. Mem.

Soc. Sci. Phys. et Natur. Bordeaux, 1873.

135. Plate. Studien iiber Opisthopneumone Lungenschnecken. Zool. Jahrb.

(Anat. und Ontog.), iv. vii. 1891, 1893.

136. Beitrage 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.

138. Rail. Ueber die EntwickehmgderTellerschnecke. Morph. Jahrb. v. 1879.

139. Itouzaud. Recherches sur le deVcloppement des organes genitaux de

quelques Gasteropodes hermaphrodites. Montpellier, 1885.

140. Sarasin, P. and F. Aus der Entwickelungsgeschichte der Helix Waltoni.

Ergebn. nat. Forsch. Ceylon, i. 1888.

141. Die Siisswassermollusken von Celebes, Wiesbaden, 1898. — Die

Landmollusken von Celebes, Wiesbaden, 1899.

142. Schmidt. F. Beitrage sur Keniitniss der Entwickelungsgeschichte der

Stylommatophoren. Zool. Jahrb. (Anat. und Ontog.), viii. 1895.

143. Sharp. Beitrage sur Anatomie von Ancylus fluviatilis (0. F. Miiller) und

Ancylus lacustris (Geoffrey). Wiirzburg, 1883.

144. Sicard. Recherches anatomiques et histologiques sur le Zonites Algirus.

Ann. des Sci. Nat. (Zool.) (6), i. 1874.

145. Simroth. Ueber die Niere der Pulmonaten. (Semper. Reisen ini Archipei

der Philippinen, iii. 1894.)

146. Yung. Recherches sur le sens olfactif de 1'Escargot. Arch, de Psychol.

iii. 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 ante ro- 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.

Historical. — These animals were formerly mistaken for tubicoious
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 Dentalium,
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

i98

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

A or

Fin. 181.

Dentalium vnh/are. A, ventral view of the animal removed from its sholl ; R, 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. «, mantle ; a',
longitudinal retractor muscle ; a", fringe surrounding the anterior opening of the mantle-
chamber ; a'", the posterior appendix of the mantle ; ?>, anterior circular muscle of the mantle ;
V, posterior circular muscle of the mantle ; c, c', longitudinal retractor muscle ; c, liver ; /,
gonad ; k, buccal mass (seen through the mantle) ; <i, left kidney ; s', anterior extremity of the
foot ; w, w1, longitudinal blood-sinus of the mantle. (From Lankester, after Ijacaze-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

Fio. 182.

Diagram of the organisation of Dentdliitm, left -side view, a, anus; ca, captacula; c.g,
cerebral ganglion ; /, foot ; go, gonad ; in, intestine ; k, left kidney ; ?ct.c, labial commissure ;
li, liver ; m, mouth ; o, oritice leading into the perianal sinus ; or, oesophagus ; jta, mantle ;
p.g, pedal ganglion, with otocyst ; fl.g, pleural ganglion ; po, posterior orifice of the mantle ;
ra, radular sac ; st.y, 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 disc with papillated margins (Fig. 183, VIII), 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, c)

II. ANATOMY.

1. Alimentary Canal. — The non - in vaginable proboscis (Fig. 183,
V, VI) leads directly into a true buccal cavity situated in the trunk
at the base of the foot (Fig. 182, /). 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 large size. The radula is short and
arcuate, with five teeth ir 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.
Thoucrh the two liver lobes are symmetrical in

Sivhonode.ntalinm. an- , -f\ ,, T- i ^i i

terior end of body, dorsal the Dentaliidae, they are no longer so in
SSfle/hlTSS^iai1'; Siphonodentaliwn. In this genus the principal
iv, right tentacular lobe, mass Of the liver lies in front of the gonad

without the captacula ; V, , . . , . . . ,

buccai pouch ; vi, mouth ; and is continued posteriorly into two long
£&<«•?' VIIIf tenninal parallel 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, in) and forms several
loops, all of which lie in the anterior part of the body, near the
buccai 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

THE SCAPHOPODA 201

admit of the expulsion of blood during violent contractions of the
body (Fig. 182, o). There is no specialised respiratory apparatus.
Respiration is effected by the internal surface of the mantle,
particularly by the anterior ventral region.

3. Excretory 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, q, and 182, k). 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, c.g, pig), 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 cither side of the anus close
beneath the tegumeritary 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, la.c),
bearing a ganglion on either side, from which a branch of the stomato-
gastric commissure properly so called (Fig. 182, st.g) 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. Repi'odudive 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. 18 1,/ 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.

III. 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. 1 85, 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 se«i at the initial extremity
in some specimens of Siplwnodentalium.

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.

FIG. 184.

Embryo of Dentalium, with six
micromeres or ectodermic cells
and a single macronwre or endo-
dermic cell, ma, inacromere ; mi,
micromere. (After Kowalewsky.)

FIG. 185.

Larva of Dentalium, aged one
and a half day ; ventral aspect.
I, foot; II, mantle; III, velum
forming a sort of test. (After
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, etc.

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.

FAMILY 1. DENTALIIDAE, 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. Fissidentalium,
Fischer ; posterior extremity with a long fissure on the ventral side ;
F-ustiaria, Stoliczka. Schizodentalium, Simroth ; ventral border
of the posterior aperture with a series of small
holes arranged in a straight line. Heterochisma,
Simroth.

FIG. 186. FAMILY 2. SIPHONOPODIDAE, Simroth.

Cadulus gracttis, Jeffreys, shell, Foot expanded distally into a symmetrical disc,

left view, a anterior orifice; wjth a crenate continuous edge (Fig. 183) or

p, posterior orifice. (After Wat- . _ 6 « j i i

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 disc of the foot
with a median appendage. Entalina, Monterosato.

LITERATURE OF THE SCAPHOPODA.

1. Boissevain. Beitriige zur Anatomie und Histologie von Dentalium. Jenaische

Zeitschr. xxxviii. 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 monographic du Genre Dentale. Mem. Soc.

Hist. Nat. Paris, ii. 1825.

4. Fol, H. Sur 1'anatomie microscopique du Dentale. Arch. Zool. Expe'r. et

Ge"n. (2), vii. 1889.

5. Kowalewsky, A. Etude sur 1'embryoge'me du Dentale. Ann. Muse'e d'Hist.

Natur. Marseille, Zool. i. 1883.

6. Lacaze-Duthiers, F. J. H. Histoire de I'organisation et du de"veloppernent

du Dentale. Ann. des Sci. Nat. Zool. (4), vi. vii. 1856-1857.

7. Lton. Zur Histologie des Dentalium Mantels. Jen. Zeitschr. f. Naturw.

Bd. xxix.

8. Nassonow. Zur Morphologic der Scaphopoden. Biol. Centralbl. x. 1890.

9. Plate, L. 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. Christiania, 1861.

11. Malakologiske Jagttagelser — II. Nye Arten af Slaegten Siphonoden-
talium. Forh. Vidensk. Selsk. Christiania, 1865.

CHAPTER V

•

THE LAMELLIBRANCHIA

CLASS IV.— THE LAMELLIBRANCHIA, BLAINVILLE

( = ACEPHALA TESTACEA, Cuvier ; CoNCHiFERA, Lamarck ;
PELECYPODA, Goldfuss ; LIPOCEPHALA, Ray Lankester).

Order 1. Protobranchia.
Sub-Order 1. Solenomyacea.
„ 2. Nuculacea.

Order 2. Filibranchia.
Sub-Order 1. Arcacea.
„ 2. Trigoniacea.

3. Mytilacea.
„ 4. Pectinacea.
„ 5. Dimyacea.

Order 3. Eulamellibranchia.
Sub-Order 1. Ostraeacea.
„ 2. Submytilacea.
„ 3. Tellinacea.
„ 4. Veneracea.
,, 5. Cardiacea.
„ 6. Chamacea.

7. Myacea.
„ 8. Adesmacea.
„ 9. Anatinacea.

Order 4. Septibranchia.
Sub-Order. Poromyacea,

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 LAMELL1BRANCHIA

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
the Protobranchia : they are situated pos-
teriorly beyond the gills. The margins
of the mantle normally present redupli-
cations, generally three in number
(Fig. 187, pa, pa\ pa"), and in the
Pectinidae the most internal of the three
is turned inwards to form the " velum "
(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
is?. the oxygen of the surrounding medium,

Kenya, «d»rWeu/arfa, Montagu, and is most conspicuous at those points
where the respiratory fluid enters the

pallial Cavity.

*• ^

The edges of the two pallial lobes
may remain free throughout their
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

cud.

orifice ; o", pedal orifice ; o'", ex-
halant orilice ; pa', external duplica-
ture of the pallial edge ; pa", internal
ditto ; pa"', median ditto ; *u', fu",
first and second sutures of the pallial
edges. (After Denhayes.)

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, Entovaha, 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

CLOU

rrt

f

CL

FIG. 188.

Area lactea, Linnaeus, ventral aspect. o.a, anterior adductor ; a.?, anterior lip ; a.p, anterior
labial palp ; 1>, byssus ; /, foot ; </', internal gill-plate ; g", external gill-plate ; g.a, gill-axis ; h.a,
posterior adductor ; m, mouth ; pa, mantle ; p.l, posterior lip ; re, rectum ; v.c, visceral com-
missure ; v.g, visceral ganglion. (Alter Deshayes.)

other words, in a 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

2o8 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, o.p) : hence the name " Trifora " given to Lamellibranchia
which exhibit this arrangement. The second orifice is called the

JMTlttO

cf^ lunuh

Fio. 189.
Left valve of Mvretrix, 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, o.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 Kelly a, 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, o"). 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 Asper-
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 Lutraria,
T/iracia, etc.

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 either — (1) inde-
pendent of one another throughout their length, as, for example, in
the Tellinidae (Figs. 190, Ir.s, a.s ; 245, g, g), Donacidae, Thracia,
etc. ; or (2) partially fused together, as may be seen in Tapes,
Solenocurtus (Fig. 194), Saxicava (Fig. 246); or (3) completely
united to one another, as in Mactra, Dosinia, Mya. Liitntria, Pholas,
Teredo (Fig. 195), etc. The branchial siphon is usually the longer
of the two, and in Scrobiculuria is more than four times as long as
the body. Sometimes the siphons may attain to a still greater

Fio. 190.

Tellina planata, left-si<le view, a..-?, anal siphon ; ?<r..<, branchial siphon ; /, 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, etc.

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 (Mytilus,
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

Fio. 191.

Right-side view of a Mactra, the right valve
of the shell and right mantle-flap removed, and
the siphons retracted, br, W, outer and inner
gill-plates ; c, umbo of the shell ; m.a, anterior
adductor muscle ; m.p, posterior adductor
muscle ; m.s, pallial retractor muscle of the
siphons; p, foot; t, labial palp; to, 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

Three stages in the development of Ostraea, right-side view. A, protomonomyarian stage of
0. edulis (after Woodward) ; B, dimyarian stage ; and C, deutomonomy arian stage of 0. virginiana
(after Jackson), a, anus ; u.a, anterior adductor ; c.g, cerebral ganglion ; /, foot ; g, gill ; in,
intestine ; l.l, left liver; l.p, labial palp; m, month ; oe, oesophagus ; p.a, posterior adductor ;
p.e, pallial edge ; p.g, pedul ganglion ; pr, prodissoconch ; r.l, 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, Modiolaiia, Pecten, Ostraea (Fig. 192, A), Dreissensia
(Fig. 224, rt.«), Unionidae (Fig. 227, z), Pisidium, Montacuta, Lasaea,
Entovalva, Cardium, Pseudokellya, etc.), but diminishes in importance

THE LAMELLIBRANCHIA

211

in adult Mytilidae, and disappears altogether in Mytilus latm (Fig.
193, E) and M. mtridionalis. 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 posterior adductor muscle is ventral and anterior to the
anus (Figs. 188, h.a ; 192, C, p.a). 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-

Ilight valve of six various Lamellibranchs, showing the various stages of the morphological
development of the adductor muscles. A, Pectunmlun ; B, Myrina ; C, Modiolaria ; D,
Modiola ; E, Mytilus latus ; F, Pecten. a, anterior adductor ; a.r, anterior foot retractor ; b,
shell beak; li, ligament; />, posterior adductor; p.i, pallial impression; p.r, p.r', 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. A single family may contain
examples of Isomyaria, Anisomyaria, and Monomyaria (Fig. 193,
C, D, E), and all, in the course of their development, pass through
three different stages with regard to the arrangement of the adductor
muscles. In the first stage, called the protomonomyarian stage, the
anterior adductor, being the first to be formed, is alone present.
In the second stage the two adductors coexist ; this is the dimyarian

212

THE LAMELLIBRANCHIA

£

stage (Fig. 192, B). In the third or deutomonomyarian stage, the
anterior adductor has disappeared (Fig. 192, C).

The two adductors, by their contraction, bring together the
valves and close the shell. They are diminished in size when the
valves lose their mobility, as, for example, in Galeomma, Ephippod&nta,
and Scioberetia, and they actually disappear in Aspergillum and
Chlamydoconcha. These muscles are generally perpendicular to the
surfaces of the valves, but in some Lamellibranchia that are fixed
by one side, they may be very oblique, e.g. Anomia, Pecten, the

Rudistae. The fibres of the adductors
are attached to epithelial cells of the
mantle which produce the hypostracum
or substance of the muscular impres-
sions. In many cases the fibres of
each adductor may be divided into
two distinct parts of different appear-
ance (Pecten, Ostraea, etc.), of which
the principal part in the monomyarian
Lamellibranchs is formed of apparently
striated fibres (see p. 5), this appar-
ent striation being particularly well
defined in the muscles of the swim-
ming Lamellibranchs, Pectinidae, and
Limidae, which are capable of very
rapid contraction. The absolute force
exerted by the adductor muscles is
analogous to that of vertebrate
muscles : in some cases they can resist
the traction of a weight equal to
several thousand times the weight of
the animal deprived of its shell.

In the siphonate Lamellibranchia
the pallial fusions separating the
branchial and pedal orifices are often
furnished with crossed muscular
bundles, called cruciform muscles,
passing from the edge of one valve
to that of the other, and thus forming
accessory adductor strands : these may
be seen in Tellina, Syndosmya, and

0.4

Fio. 194.

soknocurtus strigiiiatu*, ventral as- J)0jiax among the Tcllinacca, and in

pert, a.*, anal siphon ; br.s, branchial "®L

siphon;/, foot; mu, cruciform pallial boienOCUrtUS (-tig. 194, mU). In SpCClCS

called "closed," in which the mantle
fusions are very extensive, these muscles
are continuous along the whole ventral border of the valves, between
the pedal and branchial orifices (Saxicava, Fig. 246, pa).

THE LAMELLIBRANCHIA 213

The shell of Lamellibranchs is formed of two valves, each
corresponding to a lobe of the mantle. The internal layer of the
shell is secreted by the whole external surface of the mantle, but
the external layer is secreted only by the thickened mantle edges.
The internal layer is often nacreous, and may exhibit pathological
products called "pearls," which are formed by the secretion of
nacreous substance by the mantle round foreign bodies. These
are generally of parasitic origin : the scolex of a Cestode forms the
nucleus of a pearl in the genus Meleagrina of Ceylon and the Gambier
islands; the larvae of Trematodes form similar nuclei in various
European Lamellibranchs.

Though they are primitively symmetrical and commonly remain
so, the valves become very asymmetrical in some species of Area,
in the Anomiidae, Pecten, Ostraea, C&rbula, Chama, Pandora, Myocliama,
the Rudistae (Fig. 244), etc. In certain somewhat modified forms
in which the foot, though more or less large, is feebly retractile,
the valves do not meet and fit perfectly together along the ventral
edge and are "gaping," as may be seen in the Pholadidae, Gastro-
chaenidae, etc. But with the exception of Cklami/doconcha and
Sdoberetia, in which the shell is internal, the valves fit together
perfectly along the dorsal border, and are articulated with one
another by a system of teeth and sockets which collectively form
the hinge (Fig. 189), and only tend to be atrophied in forms whose
valves have little mobility, especially in boring species. The valves
are additionally united (except in the Pholadidae and Teredinidae,
hence named Adesmacea, and a few other forms) by a ligament of
a chitinous nature. This ligament is primitively continuous with
the shell, and is, in fact, the uncalcified portion of the pallial cuticle,
that is to say, of the originally single shell. The ligament finally
becomes external (Fig. 189) or internal; in the latter case it is a
" resilium." Its action is antagonistic to the adductor muscles, and
consequently it causes the valves of the shell to gape.

In the youngest stages of the Protobranchia, Filibranchia, and
various Eulamellibranchia, a series of little transverse denticulations,
constituting a primitive hinge or provinculum (Bernard), is developed
on each side of the ligament, or at any rate behind it in forms
devoid of an anterior adductor muscle. The permanent hinge teeth
are only formed at a later period, by the growth of distinct laminae
on the surface of the hinge. Thus, in the typical Eulamellibranchia,
the first lamellae originate at the extremities of the hinge surface,
below the provinculum, and grow towards the centre of the hinge
area ; the internal ends of the anterior lamellae become hook-
shaped, and their hooks become separated from their external ends ;
the latter form the anterior lateral teeth, while the hooks become
the cardinal teeth, and the posterior lamellae give rise to the
posterior lateral teeth.

214 THE LAMELLIBRANCHIA

Sundry methods have been proposed for representing the hinges
of Lamellibranchs by formulae. The most logical is that of Munier-
Chalmas and Bernard, which takes the origin of each element into
account. In this system the primitive lamellae are indicated by
Roman numerals, even numbers being used for the left valve, odd
numbers for the right valve, preceded by the letter A if they are
anterior to the ligament, by the letter P if they are posterior to it.
Each definitive tooth is indicated by an Arabic numeral corresponding
to the number of the primitive lamella from which it is derived
(A2 in the case of All, etc.), and is preceded by the letter C if it
is a cardinal, or L if it is a lateral tooth, and is further followed by
the letters a, b, etc., if it corresponds to the first, second, or other
segment formed by the folds of the lamella. Thus CA26 stands
for the left cardinal tooth originating from the posterior segment of
the anterior lamella II.

In some exceptional cases the two valves of the shell are fused

Fio. 195.

Sagittal median section of Teredo, a, anus ; a.a, anterior adductor muscle ; a.s, anal siphon ;
br.s, branchial siphon; c.g, cerebral ganglion; g, gill; h, heart; m, month; p.a, posterior
adductor ; p.g, pedal ganglion ; r.o, renal opening ; r.p, reno-pericardial orifice ; v.g, visceral
ganglion. (Partly after Qrobben and Beuck.)

together dorsally ; such shells are called symphinote, and examples
may be found in the adults of some species of Pinna, Unio, Anodonta,
and Hyria. But even when the borders of the mantle are almost
completely fused together on the ventral side, the two valves are
never fused ventrally to form a single tube like the shell of the
Scaphopoda. Nevertheless, when the shell gapes and the mantle
borders are largely fused together and provided with long conjoint
siphons, the portions of the mantle that project beyond the valves
may secrete a long calcareous tube (Teredo, Fistulana), which may
be fused to the shell, as in Aspergillum, or the two valves themselves
may be fused together dorsally as in the four genera mentioned
above. In some other siphonate Lamellibranchs with gaping shells
the portions of the mantle that project from the shell may secrete
accessory protective sclerites, which may be independent of the
valves, as, e.g., the dorsal sclerites of Pholas and the sclerites of
certain species of Thracia, or may be united to the shell as is the
siphonal tube of Pholadidea. In Teredo two movable calcareous
plates, actuated by special muscles, are formed symmetrically right

THE LAMELLIBRANCHIA

215

and left of the free extremity of the siphonal mass. These " pallets,"
as they are called (Fig. 247, II), probably serve to protect the free
extremities of the siphons.

The valves generally bear on their internal surfaces distinct
impressions of the insertions of the pallial, orbicular, siphonal
adductor and retractor muscles of the foot, and therefore it is
possible to infer something of the organisation of the animal in the
case of fossil species. In general, the anterior side of the shell of
the Lamellibranchia is the shorter, and the " umbones " or summits
of the two valves are directed anteriorly, but in some forms, called
for this reason " opisthogyrous," the posterior side is the shorter :
such are Nucula, Donax, Montacuta, Entovalva, and Cyrtodaria.

The larval portion of the shell, or " prodissoconch," like that of
the Gastropoda, is often distinct from the following portion, and
may even be separated from it by a crest
or ridge (Fig. 196, p) : this feature is
especially well marked in incubatory
forms with large embryos. Also, in the
same manner as has been described for
Gastropods, the external cliiplicature of
the mantle border may be reflected over
the outer surface of; and cover a more
or less considerable extent of, the shell
in the Galeommidae and in the endo-
parasite Entovalva ( = Synapticola). By an
exaggeration of this process the mantle
may even come to form a closed sac
around each valve, a feature which may FlG- 19ti>

, . , , , , n i • j t Pliilolinja sublaevis, right valve,

be seen in the three genera Lpliippodonta, outer aspect, p, prodissoconch.

Chlamydoconcha, and Sciobcrdia, and also

in a species commensal with a Synapta in the Philippines (Semper).

As in the other classes of the Mollusca, the foot is a muscular
projection from the ventral surface ; its size and form are very
variable, according to the habit of life adopted by the animal.
The mass of the foot is frequently invaded by a portion of the
viscera, at least by a part of the digestive canal, the liver, and the
gonads, the last-named being superficial. In species in which the
foot is very mobile, its two lateral faces are united by transverse
muscular bundles.

In its most primitive form the foot is a cylinder, more or less
flattened from side to side, and terminated by a ventral plantar
surface (Protobranchia, Figs. 230, 231 ; Pccfunculus, Modiolarca, Fig.
241). But more usually the foot is still further flattened, and
terminates below in a more or less elongated keel, which may end
in two points, an anterior and a posterior as in Trigonia, or in a
single point, which is always anterior. This latter arrangement is

216 THE LAMELLIBRANCH1A

the most common, and is found, for example, in the Unionidae
(Fig. 242), Tellino, (Fig. 190, /), and Cardium (Fig. 243). The
anterior pointed end may be so much elongated, for example, in
Poromya, as to give the foot the appearance of a cylindrical tentacle,
sometimes slightly swollen at its free extremity (many Lucinidae,
Fig. 238, III), or of a long cylinder directed forward and sometimes
ending in a swelling of constant shape (Solen, Mycetopus). In some
cases the foot may secondarily acquire an enlarged free extremity
with a creeping surface, e.g. in Galeomma, Lepton, and certain species
of Erycina. In Spondylus it ends in a pedunculated globular
appendage. Some Anatinacea, such as Pholadomya and Halicardia,
have an accessory foot-like organ, the so-called opisthopodium, on
the posterior extremity of the visceral mass. In MytUus, also, a
distinct posterior carinated projection may be seen behind the
extensible pedal cylinder ; this has been called the " Punch's
hump." There is, on the other hand, an anterior and dorsal
tongue-shaped projection on the foot of Tapes decussatus.

Finally, the foot may become rudimentary through disuse in
genera with restricted or no locomotory powers. This is especially
the case in boring Lamellibranchs with extensive fusion of the
mantle edges, such as PJiolas and Teredo (Fig. 247, VI), and in such
forms as are fixed by a byssus or by the substance of the shell,
such as Peden (Fig. 235, /), Ostraea, Aetheria, etc.

The foot, then, is the locomotory organ, as it is in other
Mollusca. Its special function is to grope in the shifting soil and
to slowly drag along the animal by its successive contractions and
extensions, its anterior extremity being supported or fixed. These
movements of the foot are due to turgescence, produced by the
afflux of blood into the pedal sinuses, and its subsequent contrac-
tion by means of the retractor muscles.

The foot is never provided with an aquiferous pore through
which, as was for a long time believed, water can penetrate into
the circulatory system. But it very frequently presents a more or
less posterior orifice in the middle line corresponding to the ventral
pedal pore of Gastropoda (Fig. 144, I) and leading into a cavity
known as the byssogenous cavity (Fig. 197, I), into which certain
unicellular glands situated in the foot discharge their secretion.
This secretion, passing between the epithelial cells of the byssogenous
cavity, hardens on contact with the water and forms threads of
conchiolin, which unite to form the trunk of the byssus (Fig. 197,
IV). This structure serves to attach the animal, but the fixation is
not necessarily permanent ; the old byssus may be abandoned and
a new one formed (Area, Mytilus, Avicula, Dreissensia, etc.). The
byssogenous organ is poorly developed in the Protobrahchia, in
which group the byssogenous cavity is situated far back (Fig. 204,
VIII), and a functional byssus is absent. When it attains to its

THE LAMELLIBRANCHIA

217

maximum of specialisation the byssogenous cavity presents a number
of internal folds or plates (Fig. 197) which increase the secreting
surface ; the trunk of the byssus is thick (Fig. 199, IV), is formed

Fio. 197.

Transversal section of the foot of Lyonsia,
through the byssus -orifice. I, byssogen-
ous glands; II, byssus-cavity ; III, byssus-
orifice of the foot ; IV, byssus ; V, roots of
the byssus.

Fio. 198.

Transversal section of a groove of the
byssogenous cavity of Mndiolaria discors.
I, byssogenous glands; II, epithelium of
the byssogenous cavity; III, roots of the
byssus ; 1 V, secretion of the byssogenous
glands passing between the epithelial cells.
(After Cattie.)

more or less deep in the mass of the foot, and becomes engaged in
a semi-cylindrical groove hollowed out along the ventral keel of the
foot in front of the orifice of the byssogenous cavity (Fig. 236, b.gr).
The walls of this groove contain a considerable number of large
unicellular mucous glands. The byssus is particularly well

FIG. 199.

Arm lactfd, Linnaeus, left-side view (the left half of the _ man tie removed).

I, anterior

, , -

adductor ; II, labial palps ; III, foot ; IV, byssus ; V, ventral edge of the internal left gill-plate ;
VI, right gill ; VII, anus; VIII, mantle ; IX, posterior adductor ; X, branchial axis ; XI, direct
lamina of the external gill-plate; XII, reflected lamina of the external gill-plate. (After
Deshayes.)

developed in Anomia, Area (Figs. 188, 199), Mytilus, Pinna, Avicula
(Fig. 236), Pecten, various Myacea (Saxicava, etc.), Anatinacea
(Lyonsia), Cardiacea (Tridacna), Ureissenshi, etc. In the genus
Anomia the byssus is of peculiar form, being partly calcified and of a

218 THE LAMELLIHRANCHIA

stony consistence, whence it is called the " ossiculum " ; it projects
on the right side through a hole in the flattened valve of that side.

In Modiolarca the byssogenous cavity is preceded by a second
glandular cavity (Fig. 241, gl.p\ but the latter takes no part in the
secretion of the byssus. In some cases the whole of the byssogen-
ous cavity degenerates in the adult, as may be seen in certain
species of Unio, or it is closed as in Cydas, in which genus it and
the byssus are highly developed during embryonic life. In the
endoparasite Entovalw the byssogenous apparatus appears to be
modified to form a so-called "organ of adhesion" (Fig. 240, f.ffl).

The foot, with the viscera contained in it, is attached to the shell
by retractor muscles, of which there are normally four pairs. Two
pairs, the retractors and protractors, are anterior and situated near
the anterior adductor muscle ; one pair, the elevators, is median ; and
one pair of retractors is posterior and close to the posterior adductor
muscle. These various muscles are inserted symmetrically near the
dorsal border of the valves and between the two adductors. In the
more primitive Lamellibranchs these muscles are greatly extended in
a longitudinal direction (Fig. 231, f.e\ and in certain Protobranchia
they may form an almost continuous series ; but otherwise it is only
the four retractors at the extremities of the foot that are well
developed, the remainder being rudimentary or atrophied (Fig. 202,
a.f.r, p.f.r). In general, the so-called Monomyaria, or forms with a
single and that the posterior adductor, have only retained the
posterior retractors of the foot, and these muscles only exist on one
side in various forms that are fixed by one valve : thus in Pecten
only the left retractor is present, and even this is aborted in P.
magellanicus. When the foot becomes reduced as an organ of
locomotion, and, in compensation, the byssogenous apparatus assumes
a large size, the retractor muscles, especially the posterior pair, take
their origin from the latter structure, and thus become the retractor
muscles of the byssus.

II. ANATOMY.

1. The Alimentary Canal. — The mouth is situated at the anterior
end of the body, dorsal of the base of the foot (Fig. 188, m). In
Solenomya (Fig. 231, m) it lies behind the anterior adductor muscle,
but it is on the ventral side of this muscle in all other Lamellibranchia
with two adductors. Except in Anomia, in which it is asymmetrical,
it is asymmetrical transverse aperture compressed between two lips,
of which one is dorsal and anterior, the other is ventral and posterior.
These lips have simple borders as a rule, but in the Pectinidae they
are scolloped and even ramified (Fig. 235, I) ; they are generally
continued on either side into two lobate prolongations, called the
labial palps, of which the external is the prolongation of the anterior
lip. In the genus Area (Fig. 188) the lips pass insensibly into the

THE LAMELL1BRANCHIA

219

palps, but usually the palps become suddenly much broader than
the lips. The palps are formed from part of the velar area of the
larva and assume various forms, but are most commonly triangular.
Their inner surfaces are transversely folded arid ciliated in such a
manner as to conduct all particles coming within their reach into
the buccal orifice. They are poorly developed or absent in various
Lucinidae, such as Axinus (Fig. 238) and Corbis, and in Limopsis and
some species of Cuspidaria. On the other hand, they are very large
in the Tellinidae, surpassing the gills in size in this family, and the
anterior pair is very large in Poromya (Fig. 249, a.p). In the

st

Fio. 200.

An adult specimen of Yoldia livwtula, as it appears while feeding — partially immerged in
mud. e.s, exhalant siphon ; i.s, inhalant siphon ; p.ap, palp appendages ; s.t, siphonal tentacle.
(After Drew.)

Nuculidae and Ledidae the posterior angles of each pair of palps
are produced to form a common tentaculiform appendage bearing a
groove along the whole of its ventral surface ; these appendages can
be thrust out beyond the shell and assist in obtaining food (Fig.
200, p.ap). In Solenomya the two palps are rudimentary, but the
tentacular prolongation persists in the form common to the other
Protobranchia, with its ventral groove forming a continuation of the
interlabial space (Fig. 231, p.l.).

In the family Nuculidae among the Protobranchia there is still
an anterior dilatation of the alimentary canal representing the buccal
cavity and provided with two lateral and symmetrical glandular

220 THE LAMELLIBRANCHIA

pouches ; but in all other Lamellibranchia the mouth leads directly
into the stomach through a short oesophagus (Fig. 201, oe\ which
is rarely muscular (Poroniya) and is sometimes nearly aborted. The
stomach is a large and generally laterally compressed ovoid or
piriform sac, more or less deeply buried in the viscero-pedal mass
(Figs. 207, st ; 231 and 234, st). Its walls are thin and not muscular
except in some carnivorous forms such as the Septibranchia.
The stomachal epithelium is lined with a thick but caducous cuti-
cular coat, visible even in the larval stage (Ostraea, Fig. 192, A) :
this cuticle serves to protect the secretory cells of the stomach.

The stomach is very commonly provided with a pyloric caecum,
lined by a richly ciliated columnar epithelium. The caecum may be
long, especially in Domx, Mactra, Solen, Plwlas, and Teredo, and
sometimes extends into the ventral part of the foot, or into the
mantle, penetrating into the right lobe in Anomia, the left lobe in
Mytilus latus. It is, however, short in some forms, e.g. in Trigonia.
It corresponds to the caecum of the crystalline style in certain
Gastropoda (Pteroceras, Fig. 75), and like it contains a cylindrical
product, the crystalline style (Fig. 201, cr.s), which is more or less
continuous with the cuticular lining of the stomach. In the
following forms the caecum is fused with the initial part of the
intestine, and communicates with it by a narrow longitudinal slit :
Area, Mytilus edulis, Ostraea, Pecten, the Lucinidae (Montacuta), the
Tellinidae and Psammobiidae, Cardium, the Unionidae, Mya,
Solenocurtus, and the Septibranchia. The extremity of the crystalline
style projects into the stomach and is gradually eroded by the
action of the digestive secretions ; the product of its solution forms
a sort of cement which encrusts any hard substances that may have
been ingested and thus protects the delicate walls of the intestine
from injury. Sometimes the stomach is furnished with a second
ventral caecum, which may be anterior, as in Mytilus, or posterior, as
in the Pholadidae and Teredinidae (Fig. 195).

The liver consists of a pair of voluminous, more or less sym-
metrical acinous glands which occupy the whole space surrounding
the stomach, and may extend into the foot (Figs. 207, 222, hep).
Posteriorly and dorsally the liver is generally covered over by the
gonads. In the adult Nuculidae and Ledidae the left lobe is the
larger, and the coils of the intestine are situated on the right side.
It should be noted that, in developmental stages, the left liver lobe
of Lamellibranchia, like that of the Gastropoda, is larger than the
right (Fig. 192, l.l, r.l). The hepatic orifices leading into the
alimentary canal are often multiple, even in some Protobranchia,
but in development and in many adult forms (Solenomya, Adacnarca,
Modiolaria,, various Erycinidae, Pseudokellya, etc.) there are only two
more or less symmetrical orifices. As a result of specialisation
these larval apertures may multiply, and various numbers are found

THE LAMELLIBRANCHIA

221

in adult forms, viz. three in certain Nuculidae, in Chama, and
Spondylus ; four in Area ; five in Pectunculus, Philobrya, and Pecten ;
and as many as twelve in Mytilus. The lumen of the hepatic
glands may be of considerable size, and form part of the digestive
and absorptive cavity. In certain Lucinidae (Montacuta, Axinus,
Fig. 238) the hepatic glands, together with the overlying gonads,
project into the pallial cavity in the form of arborescent tufts.

The intestine almost always arises from the ventral side of the
stomach, and is sometimes provided with a valve at its origin
(Pinna). It is short and rectilinear or scarcely coiled in Solenomya,
in sundry Filibranchia such as Area, Pectunculus, Limopsis, Philobrya
(Fig. 234), Anomia, and in the Septibranchia (Fig. 251, in) ; but

cu,

cot

FIG. 201.

Median sagittal section of the anterior part of tho digestive tract of Donax. a.l, anterior
lip ; cae, caecum ; cr.s, crystalline style ; ctt, stomachal cuticle ; in, intestine ; m, mouth ;
oe, oesophagus ; p.l, posterior lip ; st, stomach. (After Uarrois.)

more usually, as the Lammellibranchs are nearly all herbivorous, it
describes a certain number of convolutions in the viscero-pedal mass
(Fig. 242, al). These may vary from one to a dozen in number,
and sometimes they are confined to one side of the body ; in the
Nuculidae and Ledidae, for example, they are on the right side.
The intestine is ciliated throughout its whole length, and its rectal
portion is generally provided with an internal longitudinal ridge.
In Nucula (Fig. 204, XIV), Area, and Anomia the rectum passes
ventrad of the ventricle of the heart, as it does in Amphineura ;
but it traverses the ventricle, in rhipidoglossate fashion, in the
majority of Lammellibranchia. But in Malletia, Avicula, most
species of Ostraea, Miilleria, and Teredo (Fig. 195) it is dorsad
of the heart. Finally, the rectum always passes over the dorsal
side of the posterior adductor muscle, and ends behind it in

222

THE LAMELLIRRANCHIA

CLCU

the middle line, except in a few fixed forms, such as Pecten (in
which the anus is to the left of the middle line, Fig. 234, a), Ostraea,
etc. In some species of Pecten and Lima the rectum is recurrent,
and nearly completely surrounds the posterior adductor muscle.
In some special cases, viz. in various Aviculidae, and especially in
Pinna, the free extremity of the rectum bears an erectile appendage.
2. Circulatory Apparatus. — The vascular system of Lamelli-
branchs, like that of all other Molluscs, is completely closed, and
water cannot possibly enter into the circulation. The system is
composed of more or less dilated and spacious, but none the less
true vessels, and of sinuses with connective tissue walls, but without
an endothelium. Not only is the vascular system completely cut
off from the surrounding medium, but it is also cut off from the
pericardial cavity, as may clearly be seen in red-blooded forms,
whose pericardial fluid is colourless and, like that of other Lamelli-
branchs, totally devoid of blood corpuscles.

The blood always forms an important part of the mass of the
body, often constituting a half of its weight. It contains nucleated

amoeboid corpuscles (amoebocytes), and
in some cases, particularly in arenicol-
ous or limicolous species, non-amoeboid
corpuscles containing haemoglobin.
Such is the case in various species of
Area (A. trapezia, A.pexata, A. tetragona,
etc.), in* Pectunculus violacescens, Tellina
planata (and around the nerve-centres
in T. fabula), Poi'omya granulata, and
some Solenidae such as Ceratisolen
legumen. While red in these latter
forms, the blood in certain Veneridae,
Cardiidae, Dreissensiidae, etc., is of a
bluish tint owing, to the presence of
haemocyanin. Tn addition to its normal
function, the blood plays an important
part in causing turgescence of tegumen-
tary expansions, the mantle and siphons
and the foot.

As in all other Mollusca, the central
organ of the circulation is on the dorsal
terior giii-piate ; /La,>>8terior adduc- side (Fig. 202, ve), near the hinge of

tor; /it, hinge- lobe of mantle; k, ., i,f , '. '' , . , . 5

kidney ; l.p, labial palp ; yxi, mantle ; the shell, and IS contained 111 a peri-

pe.g, pericardial gland ; p.f.r, posterior rarflinm Tn aHnlt AnnmiiHap Vmw

foot retractor ; «, rectum ; «i, siphon ; c uae> l

ve, ventricle. ever, it projects freely into the pallial

cavity, behind the adductor muscle.

The heart always consists of a median ventricle and two generally
symmetrical auricles : it is only in such forms as Anomia that the

ou,

ft

n^au

Fia. 202.

,

Tapes pullaster, without its shell,
dorsal aspect, with several organs seen
through the mantle. a.a, anterior
adductor muscle ; o.ft, aortic bulb ;

THE LAMELLIBRANCHIA

223

auricles are altogether asymmetrical. The ventricle lies com-
pletely free in the pericardial cavity ; it is, however, fused to the
dorsal wall of the pericardium throughout its length in Pliodon,
and for a part of its length in Pandora. The walls of the
ventricle are always very muscular, and contain free and inter-
laced bundles or muscle fibres. The situation of the ventricle
varies very much, even in tolerably closely related species : it
is dorsad of the rectum in Nucula (Fig. 204), the Anomiidae,
and Area ; traversed by the rectum in the great majority of
Lamellibranchia (Fig. 231, v) ; and finally ventrad of the rectum
in Malletia, Ostraea (except 0. cochlear), Mulleria, and Teredo
(Fig. 195). The ventral position of the ventricle, in species
remotely allied to one another, is a phenomenon of convergence
due to the shifting of the base of the gill away from the primitive
position of the heart. It should be observed that the transi-
tion to the ventral position is to be seen in Pinna, Perna, and
Avicula : in the first-named the ventricle still forms a very slender
ring above the intestine, but in the two last genera it is simply
attached for its whole length to the ventral side of the intestine.
In Nucula and Area the ventricle appears to be formed of two
symmetrical halves : it is really elongated transversely, and con-
tracted in the middle of its length. In adult Lamellibranchs the
ventricle may beat rather slowly — e.g. twenty
times per minute in the oyster, six times per
minute in Anodonta — but in the young of
Ostraea the pulsations may be as many as one
hundred per minute.

The auricles communicate with the ventricle
by a narrow slit on each side, the apertures
being provided with muscular valves which
prevent the reflux of blood from the ventricle.
The auricles are thick and muscular only in
the Nuculidae, Solenomyidae, Anomiidae, and
in a lesser degree in Pectvnculus. In these
diverse but relatively primitive forms (and also
in Pecten and some other types), the auricle of
either side is connected only with the anterior }[1' vfl»V™le '> 1V> aortu-

• ••••• M i i • i VAIter * Oll.^

or basal extremity of the efferent branchial
vessel, a disposition which is common to other groups of Mollusca and
indicates the primitively posterior situation of the ctenidia. In this
case the auricles are elongated (Fig. 204, XII) and their maximum
diameter is close to the ventricle. In all other cases their walls
are thin and moderately muscular, they enter into relation with
the gills along a considerable extent of the efferent branchial vessel,
and they are triangular in form (Fig. 234, aur\ with the maximum
diameter nearest the gill. When the ventricle contracts the

FIO. 203.
Heart of Ostraea

224

THE LAMELLIBRANCHIA

auricles dilate, so that the three together always fill the pericardial
cavity. The walls of the auricles are frequently invested with a
brownish-coloured glandular epithelium, constituting the pericardial
glands (see below, p. 233). Sometimes the two auricles com-
municate with one another inside the pericardium. In the
Pectinacea (Pectinidae, Aviculidae) and Ostraeacea (Fig. 203), and

also in Pectuiicidus, Pkilobrya,
and the Mytilidae, this com-
munication lies behind and
to the ventral side of the
ventricle and its aorta ; in
Isocardia it is anterior and
dorsad of the aorta. The
same tendency to the union
of paired symmetrical organs
may be seen in the kidneys
and gonads.

When the circumanal com-
plex— that is to say, the
posterior adductor muscle, the
mantle borders, and especially
the siphons — are only slightly
developed, the ventricle only
gives off a single anterior
aortic trunk, just as it does
in the Amphineura and Gas-
tropoda. This is the case in
the Anomiidae and Mytilidae.
Or the posterior aorta may
be very small or indistinctly
marked off from the anterior
aorta, as in Pedunculus and
some species of Nucula-, but
' in all other Lamellibranchs,

u

liver; X, afferent sinus ; XI, retractor muscle of forms, there are ftlwaVS tWO
the labial palps ; XII, auricle ; XIII, ovary ; XIV,

rectum ; xv, ventricle. aortae, an anterior and a pos-

terior, clearly separated from

one another and of more or less equal importance. The anterior
aorta is dorsad and the posterior ventrad of the intestine, except,
of course, in Nucula and other forms in which the heart is
dorsal. The pedal branch of the anterior aorta passes between
the cerebral and pedal ganglion - pairs. In Ostraea, Fulsella,
Tridacna, and Teredo the two aortae are secondarily fused to form
one ; again an instance of convergence in unrelated species, due to
the shortening of the antero-posterior axis of the body.

THE LAMELLIBRANCHIA

225

The foot, the mantle, and the siphons derived from the latter
are gorged with blood when their muscles are relaxed, and their
sudden contraction often produces a reflux of arterial blood towards
the heart. In Lamellibranchs with a well -developed foot and
siphons, the return of blood into the ventricle is prevented by
valves situated at the origins of the aortae, and a sphincter is also
often to be found at the root of the posterior aorta, and sometimes
a valve in the siphonal artery. In addition, highly developed
aortic bulbs, separated from the ventricle by one of the above-
mentioned valves, are frequently present, generally on the posterior
aorta, where a large bulb may be seen, within the pericardium, in
many Siphonates, particularly in the Veneridae (Tapes, Fig. 202, a.b\
Petricolidae, Tridacnidae, Mactridae, etc. A bulb or aortic dilata-
tion also occurs on the anterior aorta, inside the pericardium in
Pecten and the Mytilidae, outside the pericardium in Anodonta.
The arterial blood forced back towards the heart by the contraction
of the foot or mantle or siphons enters and fills these various bulbs.

The blood carried to the different parts of the organism by the
ultimate ramifications of the arterial trunks finally enters the
venous sinuses, of which the most
important are the pallial sinuses,
the pedal sinus, and the great
median ventral sinus. The last {
named is situated between the
pericardium and the foot, and is
separated from the pedal sinus by "'
the valve of Keber, which prevents
the foot from emptying itself of ™
blood when in movement. It is
from this great unpaired median
sinus that the greater part of the
blood is derived that passes through
the kidneys and thence goes on to
the gills. But a certain quantity
of blood is carried to the auricles
without having passed through the
gills : this blood is brought from Vla- m-

.-,£ ^ ' T> t Transverse section through an Anodonta,

the mantle, lOr example, in reCten. about the mid-region of the foot, a, auricle;

T>IP P««Piitiil rp<sr»iratnrv nrcnn '"'• Ollter gill-plate ; b'r', inner gill-plate

ine essential respiratory organ (each colllposed of two lamenae); ft f00t;

of the Lamellibranchs is a pair of *, intestine; m, mantle-flap; p, p't peri.
. , . -r. i • T - • caniial cavity. (From Lankester, after

ctemdia. Each ctenidium is a Gegenbaur.)
lateral pallial offset, occupying a

longer or shorter space between the mantle and the posterior part
of the visceral mass. It may extend as far forward as the labial
palps (Fig. 241, br\ but in the most archaic forms the gills still
occupy a relatively posterior position (Figs. 230, 231, g\ while in

15

226 THE LAMELLIBRANCHIA

specialised forms they reach to the anterior extremity of the body
(Fig. 221). Each ctenidium consists of a hollow vascular axis
bearing on each face a row of more or less flattened hollow filaments,
which are nothing more than simple expansions of the axis. In the
Protobranchia the filaments are broad, simple, and free (Fig. 230, g),
and the two rows are situated on opposite sides of the axis (Fig.
206, A, B). In all other Lamellibranchia the filaments are more or
narrow, and the two rows are normally parallel to one another

Fio. 20C.

Diagrammatic sections taken transversely to the axes of the gills of various Lamellibranchs.
A, Nucula ; B, Solenomya ; C, Dimya ; D, the majority of the Lamellibranchs ; E, Donax faba ;
F, Donax variahilis, Tapes, Venus; G, iMsaea; H, Tellina; J, Lyonsia; K, Litcinu, Montacuta.
a, axis ; 6, direct (usually descending) lamella of the outer gill-plate ; r, reflected (usually
ascending) lamella of the outer gill-plate ; d, direct or descending lamella of the inner gill-plate ;
e, reflected or ascending lamella of the inner gill-plate ; /, leaflets of the outer gill-plait- ; g,
leaflets of the inner gill-plate. (After Hide wood.)

and directed towards the ventral surface (Fig. 206, C-K). The distal
moieties of the filaments are, however, reflected ectaxially and
dorsalwards, in such a manner that each row forms a double
lamina, that is to say, consists of two leaves or lamellae (Fig. 205,
brt hr*) between which there is an interlamellar space or cavity,
serving, in some species, for the incubation of the ova.

In the Filibranchia the successive filaments of each ctenidial
row are locked together by ciliary junctions, sometimes specialised
to form ciliated discs whose cilia interdigitate closely with one
another (Fig. 210, A, cj). The direct and reflected limbs of each

THE LAMELLIBRANCHIA

22?

individual filament — and consequently the two lamellae of each gill-
plate — are joined together by bridges or interlamellar junctions,
which are formed of connective tissue only in the Pectinidae, but
are vascular in the Aviculidae. Finally, the different elements of
the branchial apparatus are much more intimately connected in the
various groups of Eulamellibranchs, in which there are always
vascular interfilamentar and interlamellar junctions (Fig. 237).
Thus the blood brought to the gill by the afferent vessel is conducted
by vessels which run between the lamellae and communicate with

Fio. 207.

Adac.narca nitens, Pels., transverse section, br, right internal gill-plate; br1, left internal
Bill-plate (without reflected lamina) : br", external gill-plates (with reflected lamina) ; ca.b,
byssus cavity ; com.v, visceral commissure ; hep, liver ; in, intestine ; pa, mantle ; per, peri-
cardium ; r, kidney ; st, stomach ; tcs, testis.

the filaments on either hand, forming in this manner the inter-
lamellar junctions.

Each gill -plate may be thrown into a very regular series of
transverse folds, each fold involving a fixed number of filaments ;
this is the case in the Pectinacea, the Ostraeacea, and the more
specialised forms of Eulamellibranchia. In the last-named the
folding is still but slightly marked in the Veneridae, but becomes
much more so in the Cardiacea (in Tridacna a single fold may
contain as many as seventy filaments), the Myacea, etc. In the
Pectinacea and Ostraeacea the filament forming the junction between
two successive folds becomes thicker and more important than the

228

THE LAMELLIBRANCHIA

others, constituting a principal filament lying at the bottom of the
furrow between two successive folds. Not all the Lamellibranchia
possess complete gills consisting of two gill -plates each formed
of two reflected lamellae ; in Anomia aculeata and Dimya none of the
gill - plates have reflected lamellae ; in Adacnarca the reflected
lamella is absent from the inner plate (Fig. 207, brf) ; in Lasaea
and all the Anatinacea there is no reflected lamella in the outer
plate, and finally, the external plate is aborted in certain Lucinidae
(Lucina, Corbis, Muntacuta, Cryptodori), in Scioberetui, and the Tere-
dinidae (Fig. 206, K). The external gill-plate, whether complete
or not, instead of being directed ventrally with its lower border
parallel to that of the inner plate, may be directed dorsally, and
in such case may be without the reflected lamina, as in Solenomya
(Fig. 231, g), or may possess it, and be either smooth, e.g. Tellina
(Fig. 206, H), or folded, e.g. the Anatinacea.

The posterior, that is to say, the distal ends of the branchial
axes are primitively free, as in the aspidobranch Gastropoda (Figs.

82, 127), and in such case the gills
show no concrescence inter se, nor
do the free extremities of the re-
flected lamellae unite with the
mantle. This primitive condition
is found in the Protobranchia (Fig.
231), the Arcidae (Fig. 208, d), the
Trigoniidae, the Mytilidae, and the
Pectinidae (Fig. 235, y) ; and among
the Filibranchia it is only in the
Anomiidae that the gills are united
by the dorsal edges of the internal
lamellae of the inner plates. But
in all other Lamellibranchs the
gills, in addition to this union, are
joined to the mantle by the upper
edges of the external lamellae of
the outer gill -plate, and anteriorly,

View of the ventral (nedal) aspect of the where the visceral mass illterpOSCS

animal of Area noac, the mantle-flap and f nrpvpnf fhp union nf tho rpflortprl

gill-ftlaments having been cut away, a, to prevent Lf

mouth ; b, anus ; c, free curved extremity lamellae of the inner gill-plates,

of the gill-axis of the ri'^ht side ; ((, do. of °

the left side; e, /, anterior part of these these latter are attached to the

^ilT^r'irS"Srt111u»c,eb;0dJ; viscero - pedal mass (Fig. 209,

rttoWlTS'iif SttVSj B' c- D>- These vf io«s Ullions °f

m, sole of tho foot ; n, byssus cavity. (After the extremities of the reflected

lamellae, whether with one another

or with the mantle or with the viscero-pedal mass, may be effected
by simple ciliary junctions — e.g. in Avicula, Pinna, Anomia, Solen,
the Anatinacea — or by a true concrescence.

J

Fio. 208.

THE LAMELLIBRANCHIA

229

The result of these multiple unions is that the gills form a
partition, extending as far as the division between the two posterior,
anal and branchial, pallial orifices (Fig. 209, D), and dividing the
pallial cavity into two chambers, called respectively the supra-
branchial or cloacal and the infra-branchial chamber (Fig. 209, i, i).
The respiratory water generally enters the pallial cavity by the
postero- ventral side (by the branchial orifice or by the branchial
siphon, if the latter is differentiated) ; thence it passes, as through

Fio. 209.

Diagrams of transverse sections of a LamHlibranch to show the adhesion, by concrescence,
of the gill-lanx-Mae to * he mantle-flaps, to the foot, and to one another. A shows two conditions
with fiv* gill-;ixis ; 11, condition at foremost region in AnoJonta; C, hind region of foot in
An-rulonta; D. region altogether posterior to the foot in Anoaonta. a, visceral mass; b, foot;
c, mantle-flap ; </, axis of gill or ctenidium ; e, adaxial lamella of outer gill-plate; er, reflected
lamella of outer gill-plate ; /, adaxial lamella of inner gill-plate ; fr, reflected lamella of inner
gill-plate ; ;;, line of concrescence of the reflected lamellae of the two inner gill-plates ; h,
rectum ; i, supra-branchial space of the nib-pallia! chamber. (After Lankester.)

a filter, through the trellis-work of the branchial filaments con-
stituting the partition in question, and is expelled from the supra-
branchial chamber by the anal orifice of the mantle or by the anal
siphon.

In one whole group, the Septibranchia, this branchial partition
loses its normal structure in consequence of a predominant develop-
ment of its contractile elements, by which it is converted into a
muscular septum perforated by apertures leading ventro-dorsally
(Fig. 211). The water passes through these apertures from the
infra-branchial into the supra-branchial or cloacal chamber. Kespira-

230

THE LAMELLIBRANCHJA

tion is effected in the latter chamber by the internal surface of
the mantle, which is bathed by a strong current of water passed
through by the contractions of the muscular septum.

As regards the structure of the gills, it has been known since
1877 (Peck) that in all the Lamellibranchia each constituent fila-
ment of the gill is clothed externally by an epithelial layer con-
tinuous with the epithelium of the general surface of the body.

o

ep-

B

lac.

Fid. 210.

Ctenidial filaments of Mytilus edulis. A, part of four filaments seen from the outer face in
•order to show the ciliated junctions c.j. I!, diagram of the posterior face of a single complete
filament with descending (direct) ram us and ascending (reflected) ram us ending in a hook-like
process ; ep, the ciliated junctions ; i.l.j, iuter-lamellar junction. C, transverse section of a
filament taken so as to cut neither a ciliated junction nor an inter- lamellar junction ; b.c, blood
corpuscle ; ch, chitinous tubular lining of the filament ; f.e, frontal epithelium ; l.f.t', ciliated
edge-cells ; J./.e", lateral cells with long cilia ; lac, blood lacuna traversed by a few processes of
connective tissue cells. (From Lankester, after Holman Peck.)

At certain points this epithelium is modified and bears powerful
cilia, particularly on the two ventral edges of each filament, where
the so-called "corner cells" (Fig. 210, Lf.e), by the action of their
cilia, keep up a brisk current of water over the surface of the gills.
There are also "lateral" ciliated cells on the two faces of each
filament, which ensure the ciliary union between successive fila-
ments. Internally each filament presents a supporting structure,
formed by paired longitudinal thickenings of the sub-epithelial

THE LAMELLIBRANCHIA

231

connective tissue. This thickening is specially well developed on
the internal sides of the lamellae in the Anomiidae, Arcidae, and
Trigoniidae (Filibranchia, in which the filaments are very loosely
held together), while in the rest of the Lamellibranchia the thicken-
ing is most developed on the external or ventral side.

The cavity of the branchial filaments is divided lengthwise by a
connective tissue septum in the Anomiidae, Arcidae, and in Pecten.
The afferent branchial vessel runs in the dorsal half of the axis in
the Protobranchia, and consequently the blood enters each filament
on the dorsal side and passes to the ventral side to enter the efferent
branchial vessel leading to the auricle. Thus in each filament
there are two currents running in opposite directions, but continuous

Fio. 211.

Transverse section of Cuftpidaria, taken through the heart. I, branchial septum ; II,
branchial nerve ; III, sphincter of branchial orifice ; IV, mantle ; V, septal orifice ; VI, posterior
retractor of the foot; VII, testis ; VIII, intestine; IX, .accessory genital gland; X, visceral
commissure; XI, ventricle; XII, pericardium ; XIII, auricle; XIV, kidney.

with one another. The same thing may be seen in the narrow and
still independent filaments of the Anomiidae and Arcidae, but when
the cavities of successive filaments are put into communication with
one another along the free borders of the reflected lamellae, there is
but one current in each filament running from the afferent vessel
(whose position is variable) to the efferent vessel common to the
two gill-plates.

In addition to their respiratory function, the gills are accessory
to the function of alimentation. The action of their cilia produces
a constant current from behind forwards, which carries particles
suspended in the water towards the labial palps, and consequently
towards the mouth. In some rare cases — for example, in Mytilus —
an accessory respiratory apparatus is developed in addition to and

232

THE LAMELLIBRANCHIA

outside the ctenidial branchiae, in the form of little secondary pallial
outgrowths, constituting the folded organs called " frills."

3. Excretory Organs. — The principal excretory organs are the
kidneys, which are symmetrical organs situated below the peri-
cardium in the postero-dorsal region of the body : they generally
extend back to the posterior adductor muscle, but not so far in
the Protobranchia (Fig. 231, k). They have the form of two sacs,
with glandular walls, irrigated by the venous blood passing to the
gills and opening on the one hand into the pallial cavity by
orifices situated at their anterior ends and external to the visceral
commissure, and on the other hand into the pericardium. This
latter organ is a median dorsal pouch, situated in the posterior
part of the visceral mass and enclosing the heart (Fig. 204, I ;
205,^?). In the Anomidae alone of all the Lamellibranchia the
pericardium is greatly reduced, does not contain the heart, and con-
sists of two small ramified spaces. The
pericardium communicates with the kidneys
by two symmetrical ventral reno-pericardial
or internal renal orifices (Fig. 212, i'i>\ and
in Anoinia the kidneys communicate with
the two small ramified spaces mentioned
above. The tubes of the gland of Keber,
which ramify in the mantle, also open into
the pericardium. The pericardium is always
completely shut off from the circulatory
system, a fact which can readily be demon-
strated in Lamellibranchs with red blood.

The structure of the kidneys is simplest
in the Protobranchia. In this group each
kidney has the form of a more or less

Fio. 21'J.

dorsal aspect, a.a, anterior cylindrical sac folded on itself in such a

adductor; an, auricle; </, right , A .r • j- i i i

genital gland; g.o, genital manner that the pcncardial and external

."^iiS" orifices are both anterior. The lumen of

cardinm ; ;v.f7, pericardia} the sac is large, its wall is glandular and

gland; re, rectum; r.o, ronal ., .

opening; rp, renopericardiul Uniform throughout its extent, and the

oriflee; K, stomach; *, ven- two _ fctfneys jo not communicate with
one another (Solenomya, Fig. 213). This

essential character of a tube folded into a U-shape, so that
one branch is antero- posterior and the other postero- anterior,
is preserved throughout the Lamellibranchia, but as a result
of specialisation the interior surfaces of the renal sacs are more
and more increased by the formation of multiple folds, giving
a spongy appearance to the organs. Sometimes, also, the
terminal part or postero -anterior branch loses its excretory
character and is modified to form a simple duct, which more
or less surrounds the other branch (Unionidae, Fig. 242 (C), an, or).

THE LAMELLIBRANCHIA

233

In other cases the differentiation into two branches folded one over
the other disappears through the reduction of the antero-posterior
branch ; the kidney is then a simple sac into which the reno-
pericardial duct opens. This may be seen in some Filibranchia.

The two kidneys do not communicate with one another in
Solenomya and in many Filibranchia, but a communication between
their anterior ends is already present in Yoldia and Leda, and
a communication, often of considerable extent, between their
posterior ends is found in the majority of the more specialised
forms, e.g. Modiolarca, Lasaea, Donax, Tapes, Fseudokellya, and
especially in the Myacea, Pholadidae, and Anati
nacea. The renal organs are excessively ramified
and extend over the whole surface of the visceral
mass in Ostraea, and both in this genus i.nd in
Pholas they surround the posterior adductor
muscle. The kidneys similarly extend veiy tar
forward in Mytilus and in the majority of the
Anatinacea, penetrating into the mantle itself \\\

in Lyonsiella. Finally, in the Septibranchia the FIG. 213.

kidneys are almost wholly immersed in the Left kidney or .sw«n»-

Tvillial ainiie n?i<Y 911 YTV\ wi/a WKV/i/emr (if «, ventral

pailiai SinUS ^rlg. Jll, AlV;. aspect. I, posterior part

In the most archaic Lamellibranchia the StSSif' ww-'ll!1 mS
renal secretion is passed out of the body in pericardial orifice; iv,

I- -j r r L • .LI A-I t c duct of the gonad.

a liquid form, but in others in the form of

solid concretions, exhibiting concentric layers of growth, and in

normal conditions containing only urea.

The excretory function is carried out by the pericardial glands
as well as by the kidneys. These glands are differentiations of
the epithelial wall of the pericardium, and may be localised on
and impart a brownish tint to the auricles, as in many Filibranchia
(Arcidae, Mytilidae, Pectinidae) and the Ostraeacea, or they may
be near the auricles as in the Aviculidae. In this condition
they are less well developed in the more specialised groups, but
they reappear in Pholas and Sa.ncava. The glands frequently
exist in the form of a glandular lining of the anterior part of
the pericardium or of the glandular diverticula which pass from the
pericardium into the mantle (Fig. 212, pe.ff). This arrangement
may be seen in the Unionidae — the diverticula constituting the
" organ of Keber " — in certain Lucinidae, Veneridae (Fig. 202, pe.g),
Tellinidae, Solen, Pliolas, and . •Ispergillum. In the last-named
genus these diverticula used to be called pericardial veins at a
time when the pericardium was thought to be a blood sinus. The
pericardial glands excrete hippuric acid, which is poured into the
pericardium, and from thence passes into the kidneys.

4. Ncrroitx System and Sense-Organs. — The different pairs of nerve-
centres are always placed at some distance from one another in the

234 THE LAMELLIBRANCHIA

Lamellibranchia. In the Protobranchia alone are there four dis-
tinct pairs of ganglia, cerebral, pleural, pedal, and visceral, in the
adult (Fig. 214). In this group there is a pleural ganglion attached
to the cerebral ganglion on either side, as is the case in the
Scaphopoda and the "epiathroid" Gastropoda (Figs. 182 ; 123, B).
There are therefore two pedal connectives on each side (Solenomya
and Nucula), namely, the cerebro-pedal and the pleuro-pedal con-
nectives, which are free in the initial part of their course (Fig.
214, c.p.c, pl.p.c), but are fused together half-way towards the
pedal centres in Nucula, and for nearly the whole of their length
in Solenomya, as is the case in Dentalium (Fig. 182) and the
Atlantidae. In all other Lamellibranchia the pleural centres are
intimately fused with the cerebral, and there is only a single pedal

cm

Fio. 214.

Nervous system of Nucula nudnis, viewed from the left side, and a little ventrally. ce.g, cere-
bral ganglion ; c.n, cerebral nerve ; c.p.c, cerebro-pedal connective ; o.n, otocystic nerve ; o.o,
otocystic orilice ; os, oaphradium ; ot, otocyst ; pa.n, pallia! nerve ; p.g, pedal ganglion ; pl.g,
pleural ganglion ; pl.p.c, pleuro-pedal connective ; vi.c, visceral commissure ; vl.g, visceral
ganglion.

connective on each side (Fig. 215, B). Nevertheless, in all the
Lamellibranchs belonging to different groups that have been studied
from this point of view, a pleural ganglion distinct from the cerebral
has been recognised in the course of development (Modiolarca,
Dreissensui, Lasam, Teredo).

In all the Lamellibranchia the cerebral, or rather the
cerebro-pleural, centres are connected with the pedal and visceral
centres: thus there are two distinct commissures, the pedal
and the visceral. In Mytilus, however, the visceral commis-
sure is fused for a certain distance with the pedal connectives.
The visceral commissure is always long, and issues from the pleural
ganglia in Nucula and Solenomya, from the cerebro-pleural ganglia
in other Lamellibranchia. It runs somewhat superficially right
round the viscero-pedal mass, inside the renal orifices (Fig. 231, r.o),
and bears on the posterior part of its course a large pair of ganglia

THE LAMELLIBRANCHIA

235

(Fig. 215, c), and in exceptional cases a little ganglion at about the
middle of its length on either side, at the point of origin of
the branchial, pallial, or visceral nerves. These additional ganglia
occur in Dreissensia and in some other genera of Eulamellibranchia,
viz. the Unionidae, Cardium, Lutraria, Mya, and Solen. Each of
the three chief pairs of ganglia presents the same general
characters in the entire class, and special characters in certain
forms.

The cerebro-pleural ganglia are supraoesophageal and are
situated above the buccal orifice ; generally on the posterior face
of the anterior adductor muscle when this exists (Figs. 230, 251, c.g).
In the Solenomyidae alone do they occupy a more posterior position
(Fig. 231, c.g). In the Protobranchia, and in Mactra cwallina and
Venus, the cerebro-pleural ganglia are attached to one another, but
in all other forms they stand
apart. They innervate the labial
palps, the anterior adductor
muscle, and the anterior part of
the mantle, and send fibres to the
osphradia and otocysts.

The pedal ganglia are situated
in the mass of the foot at a
greater or less distance from the
cerebral centres ; they are always
attached to one another (Figs.
214, p.g- 215, 1>). When the
foot is atrophied they become
more and more reduced — e.g. in
Teredo (Fig. 195, p.g), Ostraea,
Pecten (Fig. 215, C)— and the
pedal connectives become very
short.

The visceral ganglia are situ-
ated some distance behind the

Tw-kcfpri™' arMnpfr»r YniiQflp in all

posterior adductor muscle m an

the Protobranchia (Fig. 231, V.g\ ganglion - pair ; b, pedal ganglion - pair ; o,
, . . T 11\. c i • i visceral ganglion - pair. (From Lankester,

but in other Lamellibranchia they after Gegwibmr.)
are to be found on the ventral

face of this muscle (Figs. 188, 218, 219, etc., r.g\ except in Tlirada,
in which they are in front of it, and in some highly specialised
forms in which they are again behind it, as, for example, in Pholas,
and particularly in Teredo, in which the posterior adductor is
shifted forward (Fig. 195, v.g). The visceral ganglia are generally
superficial, and barely covered by the tegumentary epithelium
(Figs. 188, 236), but in Lima they are somewhat deeply embedded
in the visceral mass. The two ganglia are primitively distant

Fio. 215.

Central nervous system. A, of Teredo;
of Anodonta; C, of Pecteit. a, cerebral

236 THE LAMELLIBRANCHIA

from one another, and remain so in most Protobranchia (Fig.
214, vi.g), in the Anomiidae, most species of Area (Fig. 188, v.g),
in Adacnarca and Philobrya, the majority of the Mytilidae, Avicula
(Fig. 236), Ostraea, and certain Lucinidae (Montacuta). On
the other hand, they are in juxtaposition in Yoldia, Pedunculus,
Limopsis, certain species of Area, the Trigoniidae, Modiolaria, the
Pectinidae, most Eulamellibranchia, and the Septibranchia. The
visceral centres innervate the gills, the heart (by recurrent nerves
passing round the posterior adductor muscle), the posterior part of
the mantle, and the siphons. The anterior pallial nerves issuing
from the cerebro-pleural centres and running along the borders of
the mantle anastomose with nerves issuing from the visceral ganulia
to form a complete pallial circle on either side. In some Eulamelli-
branchia (Dreissensia, Pholadidae, and Teredinidae) there is a small
but distinct ganglion mass in front of the visceral ganglia, and
united to the two branches of the visceral commissure. In
Dreissensia this accessory ganglion gives off several nerves, chiefly
to the viscera.

The Lamellibranchia have no differentiated stomato-gastric
system ; the median faces of the two branches of the visceral
commissure give rise to nervous strands which pass to the
alimentary canal.

Tactile sensibility is specially localised in the most exposed
parts of the body, that is to say, in the borders of the mantle along
which run the circumpallial nerves formed by the anastomosis of the
anterior pallial nerves from the cerebro-pleural ganglia with nervous
trunks issuing from the visceral centre. The mantle borders very
often bear sensory papillae, or more or less well developed tentacles
throughout their extent, e.g. in Solenomya (Fig. 231, pa), Lepton, Pedcn
(Fig. 235, pa), and above all Lima : in this last genus the tentacles are
long, contractile, and disposed in several rows. When the borders
of the mantle are fused together at various points, these sensory
papillae are localised at the posterior ends, at the place of entrance
of the respiratory fluid, or at the margins of the siphons (Figs. 219,
221), or round the two siphons to form a sort of tentacular crown,
as may be seen, for example, in Cardinal (Fig. 243, «...«, br.s), Tapes,
Corbula, Poromya (Fig. 249, p.t). In some cases there are highly
developed tentacles ; thus in Lepfnn and Galeomma there is a median
azygos tentacle at the anterior end at the point of union of the two
mantle lobes, and two symmetrical tentacles in the same situation
in Solen. There are two symmetrical tentacles at the posterior end in
Solenomya, and a single lateral tentacle on the right or left side in
the Ledidae (Yoldia, Fig. 230, *./, Leda, and MaUetia). The labial
palps are not highly specialised tactile organs, and serve as acces-
sory alimentary rather than sensory organs.

At the origin of each great branchial nerve, close to the visceral

THE LAMELL1BRANCHIA 237

ganglion — and consequently on the posterior adductor muscle in
most cases — there is an accessory ganglion (Fig. 214, os\ above which
the tegumentary epithelium is modified to form a sensory organ,
and is often pigmented, as for example in Area. This organ cor-
responds to the osphmdium of the Gastropoda, and its situation at
the point of attachment of the gill renders it probable that it serves
to test the respiratory fluid. The osphradial ganglion receives
nerve-fibres not from the visceral ganglion, but from the cerebral
ganglion by way of the visceral commissure.

Another organ of an analogous nature, lying on the posterior
adductor muscle on either side of the anus (and consequently
behind the osphradia), is found in many asiphoriate forms, for
example, in the Arcidae, the Trigoniidae, the Pectinidae, and
the Aviculidae. It forms a little papilla or epithelial elevation
at the end of a nerve strand given off from the posterior pallial
nerve, which in turn is given off from the visceral ganglion. In
these Lamellibranchs the two little organs in question often show
a tendency to asymmetry, that of the right side being better
developed than that of the left. In the siphonate Lamelli-
branchia, in which the gills are united together posteriorly
and conceal the posterior adductor muscle, the sensory organ in
question is displaced along the course of the posterior pallial nerve,
and lies at the internal end of the inhalent or branchial siphon,
often lying over a "siphonal" ganglion developed at this place.
In such case the organ may be an epithelial projection in the form
of a glandular and sensory plate (Leda, Donax, and Pholax), or a
projecting lamina (Mactra, Scrobicularia, etc.), or even a tuft composed
of many papillae (Tellinu). Lastly, an adoral
sense-organ, provided with an accessory ganglion,
exists in the neighbourhood of the palps in Nucula
and Poromya.

The otocysts or statocysts, as is the case in
the majority of the Mollusca, are situated in the
pedal mass in proximity to the pedal ganglia pio 216

(Figs. 230, ot; 242, ay), and they may even be otoc^°t of'.
deeply embedded in these centres, for instance, c> capsule; e, ciliated

£ < , ,, T • i / r 77- T/ \ cells li'iiiitf the otocys-

in Galeomma, and the Leptomdae (Lasaea, Kellya). tic capsule ; <>, otoiith.
In the majority of the Protobranchia (Nucula, ^ijf******' ***
Leda, Solenomya), in Area, and in some Mytilidae
(Mf/tilus, Lithodomus) these organs are simply deep invaginations
(otocrypts) of the superficial epithelium of the foot, and com-
municate with the exterior by a fine canal which opens on the
side of and in the dorsal region of the foot (Fig. 214, ot, o.o) :
this canal is closed in the adult Yoldia. In the adult Solenomya
the otocysts have disappeared. In Leda they each contain an
otoiith, but in Nucula, Area, and the Mytilidae they contain

238 THE LAMELLIBRANCHIA

numerous irregularly-shaped auditory particles. In the rest of the
Lamellibranchia the otocysts are completely closed spherical cavities,
containing a number of auditory particles (otoconia) in the Fili-
branchia, but a single large otolith in the Eulamellibranchia and
Septibranchia, with the exception of Saxicava and the Anatinacea, in
which both otoconia and an otolith coexist in each otocyst. In
Ostraea both otoliths and otoconia appear to be absent.

The cavity of the otocyst is generally lined with ciliated cells
(Fig. 216, e\ but cilia may be absent in forms which have otoliths.
The nerves supplying the otocysts do not originate from the pedal
ganglia, but are branches of the cerebro-pedal connectives (Fig. 214,
o.n), and their fibres can be traced back to the cerebral ganglia. As
regards the physiology of the otocysts, it has been shown that
Lamellibranchs — e.g. Anomia — are able to appreciate sounds trans-
mitted through the water.

Cephalic eyes in the adult state are found only in certain Fili-
branchia ; viz. in the Mytilidae and Avicula (Fig. 236, e). They are
situated at the bases of the first direct filaments of the inner gill-
plates, and each consists of a simple pigmented epithelial fossa which
contains a cuticular crystalline lens, but they do not seem to confer
any great sensibility on the species that possess them. Some other
Lamellibranchia have cephalic eyes during larval life : they are situ-
ated outside the velum, like the eyes of the larvae of Polyplacophora.
One may suppose that the mantle and the shell, which cover up the
whole of the body, render cephalic eyes of little use. Further, by
way of organic counterpoise one finds that the absence of cephalic
eyes is compensated by the development of analogous organs on the
only parts of the body that can be projected from the shell, that is
to say, on the edges of the mantle and the siphons. The most simple
arrangement consists in the presence of pigmented cells at the
extremities of the siphons or around the posterior pallial apertures,
the existence of such cells coinciding with an increased photodermatic
sensibility whether for both a sudden illumination and a sudden
obscuration as in Pholas, Litliodomus, Mactra helvacea, and Tellina
complanata ; or for a sudden obscuration only, as in Ostraea and
certain species of Cardium and Venus • or for an increase of illumina-
tion, as in Lima and Psammobia vespertina. As the result of
specialisation, pigment spots of this kind are transformed into
veritable eyes, situated on the projecting edges of the mantle and
siphons.

Pallial eyes arising in this manner are <?f several different kinds,
of which the principal are those occurring in the Arcidae, Lima,
and the Pectinidae, Spvndylus, and some species of Cardium.

In the greater number of Arcidae, namely, in the genus Area,
except A. diluvii, and in Pedunculun, the pallial eyes are but little
differentiated in structure, but, are collected in groups ; that is to say,

THE LAMELLIBRANCHIA

239

they are compound or faceted eyes, each element of which is a
pigmented cell or ommatidium with a cuticular cornea. In Lima
excavata (L. hians and L. loscombii have no eyes) there are from
eighteen to twenty-three eyes on the border of each mantle flap,
consisting of very deep pigmented fossae, at the bottom of each of
which there is a layer of rods and a refractive body.

In Pecten (with the exception of abyssal species) and Spondylus
the eyes have a more complicated structure : they are isolated and
always in larger number on the left or superior than on the right

o rv

FIG. 217.

Sagittal section of the pallial eye of Pccten pusio. c.u, complementary optic nerve; co,
cornea ; I, crystalline lens ; o.n, optic nerve ; o.p, optic peduncle ; p.e, pigmented epithelium ;
p.1, pigmented layer ; re, retina ; r.n, retinal nerve ; ro, rods ; o, septum ; to, tapetum. (After
Bawitz.)

or inferior mantle lobe, and they are of different sizes and irregularly
arranged. Each eye is borne on a short tentacle projecting from
the internal duplicature of the mantle border (Fig. 235, e) and its
essential structure is that of a sub-epithelial ocular globe. The more
superficial moiety of the ocular wall forms the retina in such fashion
that the transparent retinal elements have their free extremities
turned towards the interior of the globe (Fig. 217, re), and each is
capped by a cuticular rod. The deeper moiety of the ocular wall,
as well as the part of the tentacle surrounding it, is pigmented. In
the interior of the ocular cavity there is a refringent layer — the

240 THE LAMELLIBRANCHIA

tapetum — of cuticular or secretory origin, which gives the eyes of
Pecten and Spondylus their brilliant lustre. The optic nerve arises
from the circumpallial nerve and subdivides : one of its branches
passes round the ocular globe to reach the retina. Between the eye
and the external corneal epithelium or pellucida there is a cellular
lens or conjunctiva, which is extra-ocular and consequently sub-
epithelial. In some cases the corneal epithelium itself is thickened
above the eye (Fig. 217, co).

In some species of Cardium — in C. rusticum, for example — the
siphons are the only parts of the animal which project from the
bottom when the animal is buried, and the tentacles surrounding
them are provided with eyes whose structure is analogous to that of
the eyes of Pecten and Spondylus, with this difference, that in the
former the pigment is situated in the connective tissue surrounding
the ocular globe.

5. Generative Organs. — The sexes are separate in the Lamelli-
branchia in general, but the whole order of Anatinacea is herma-
phrodite, and also some small isolated groups, viz. the Cyrenidae, the
genera Poromya, Tridacna, Kellya, Lasaea, Entovaha, and Scioberetia
(the two last named being parasitic), and certain species of Pecten,
Ostraea and Cardium, and Anodonta imbecilis. Sexual dimorphism is
recognisable only in certain species of Unio ( U. batavus and U. tumidus)
and in Lampsilis, in which the female is rather broader than the male,
and in Astarte, in which the border of the shell is smooth in the male
but crenelated in the female. In the genus Teredo there is hyper-
polygyny, the males being only in the proportion of 1 : 500 to the
females. There is never a copulatory organ, nor yet an accessory
gland, unless perhaps in the male Cuspidaria. The gonads are
paired and symmetrical, superficially placed, and generally occupy
the most dorsal and posterior part of the visceral mass, often extend-
ing thence into the foot. They are united and communicate with
one another in Donax, Lasaea, Adacnarca, .Chlamydoconcha, Cuspidaria,
etc. In exceptional cases they extend into the mantle, either into
both lobes, as in all the Mytilidae except Dacrydium and some
species of Chama, or into one lobe only as in the Anomiidae. In
some genera of Lucinidae, e.g. Muntacuta and Axinus, the gonads,
together with parts of the liver iobes, project into the pallial cavity
in the form of arborescences. Each gonad is an acinous structure
and its caeca may be much ramified, for instance, in Ostraea.

In the most primitive arrangement there is no proper generative
aperture ; each gonad discharges its products into the reno-peri-
cardial duct, as may be seen in the Protobranchia (Solenomya, etc.) ;
but a secondary union between the reno-pericardial duct and the
external extremity of the postero-anterior branch of the kidney
allows the generative products to pass direct to the external renal
orifice (Fig. 213, IV, II). In many other forms the gonad still opens

THE LAMELLIBRANCHIA 241

into the kidney of the same side, not near the pericardial orifice,
but nearer to the external aperture, e.g. in the Anomiidae and
Pectinidae, or close to the external orifice, as in Area.. In other
cases the gonad and the kidney open together into a common slit or
cloaca (Ostraea, Cyclas, Fig. 218, g.o, and certain Lucinidae). Finally,
in those cases in which there is a separate generative aperture, it
may either be situated on a papilla common to it and to the renal
orifice (Mytilus edulis), or, as is most frequently the case, it may be
in the immediate neighbourhood of the renal orifice, and like it,
situated to the outside of the visceral commissure (Fig. 242, (6) ?/).
When normal hermaphroditism occurs in the Lamellibranchia,
it may exist in one of the following different forms. In the first
each gonad is entirely hermaphrodite throughout its extent ; that

Cyclas, left-side view, after removal of the left pallial lobe, gill, and auricle. a.o, anterior
adductor ; a.o, auricula-ventricular orifice ; a.r, anterior foot retractor ; a.s/anal siphon ; br.s,
branchial siphon ; /, foot ; g, tight gill ; g.o, genital orifice ; in, intestine ; k, left kidney ; I,
liver ; ov, ovary ; p.a, posterior adductor ; p.r, posterior foot retractor ; t, testis ; v, heart-
ventricle ; v.g, visceral ganglion and commissure (posterior part).

is to say, uniformly composed of acini capable of producing ova and
spermatozoa simultaneously or successively. This condition is
found in Ostraea edulis, 0. angasi, 0. plicata, 0. lurida (other species
of Ostraea, viz. 0. virginica, 0. glomerata, and 0. angulata are
dioecious), Kellya, and Lasaea, In the second form there are male
and female acini lying side by side throughout the whole extent of
the gonad, e.g. Tridacna, Cardium oblongum, and C. norvegicum. In
the third form the gonads are differentiated into regions of different
sex, the anterior region being male and the posterior female (Fig.
235, t, ov\ but these are not separate from one another, and have a
common duct and a single orifice : this is the case in Peden herma-
phroditus, P. maximus, P. jacobaeus, P. opercularis, P. glaber, P. irra-
dians, and P. flexuosus (P. inflexus and P. varius are dioecious). The
same arrangement is found in the Cyrenidae (Cyclas, etc.), in which,

16

242

THE LAMELLIBRANCHIA

however, the male and female portions of the gonad are not actually
contiguous, but are united by a short canal (Fig. 218, t, w\ so that the
spermatozoa have to pass through the ovarian cavity before they are

Lyonsia nm-^egica, left-side view after removal of left pallial lobe and left gill, o, anus ; a.a,
anterior adductor ; a.s, anal siphon ; l.o, bysaal orifice ; hr.n, branchial nerve; br.s, branchial
siphon; /.o, female orifice; g, gill (direct inte..ial lamina); g', reflected internal lamina of
the right gill ; g", outer plate of the gill ; /.]>, labial palp.; m.o, male orifice ; o, ovary ; p.a,
posterior adductor ; p.o, pedal orifice of the mantle ; t, testis ; -e.g, visceral ganglion.

eliminated. Finally, in the fourth mode, an ovary and a testis com-
pletely separated from one another exist on either side of the body,
each having its own proper duct anu external orifice. This is the
case in all the genera forming the order Anatinacea and in P&romya
among the Septibranchia. In these forms the ovary is dorsal and

posterior, the testis more anterior
and ventral (Fig. 219, t.o). The
male and female genital orifices of
the same side are contiguous ; they
open on a common papilla in the
Anatinacea, but the female aper-
ture is outside the visceral commis-
sure, and therefore in the normal
and original position of the Lamelli-
branch genital orifice, whereas the
male aperture is within the visceral
commissure. In Poromya the male
and female ducts of each side open
into a common orifice, external to
the visceral commissure. In all
these hermaphrodites the male
products are the first to ripen.

Pteudokellya cardiformis, section of a part Accidental CaSCS of hermaphro-
of the ovary, c^follicular cells ; ^, ovular difcism haye been met wifch jn
loilicie , oi», ovarian egg. t

dioecious Lamelhbranchs (Mytilus,

Unionidae), and a unisexual individual of the normally hermaphro-
dite species Pecten gkiber has also been described.

Fio. 220.

THE LAMELLIBRANCH1A 243

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, Donax, 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, etc.). 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. A true ovarian follicle, formed of a continuous and regular
envelope of epithelial cells, has been described only in Pseudokellya,
(Fig. 220, fol).

an,

m ^

Fio. 221.

Pseudokellya cardiformis, Smith, left-side view (the left pallial lobe removed), ad', ad"T
anterior and posterior adductor muscles; br, br1, internal and external 'gill -plates ; em,
embryos in the internal gill-plate ; o.a, anal orifice of the mantle ; 0.6, branchial orifice of the-
mantle ; o.p, limits of the pedal orifice of the mantle ; p, foot ; pal, labial palp ; rep, rep',
anterior and posterior foot-retractor.

III. EMBRYOLOGY.

Viviparous Lamellibranchs are unknown, but some few appear
to be viviparous because they are incubatory. This is the case in
some Filibranchia (Area, vivipara and Philobrya) and in many Eula-
mellibranchia, principally in the Submytilacea (certain species of
Ostraea, Condylocardia, Lasaea, Bornia, Scioberetia, Entovalva, Thecalia,
Unionidae, Cyrenidae, Pseudokellya, Teredo, etc.). The ova then
are hatched after their escape from the genital organs, but in the
greater number of incubatory forms they are retained for a
certain time, in some cases up to the time of hatching, in the inter-
lamellar branchial spaces. In certain Unionidae (Castalina, Arconaia,
Pseudodon, etc.) and in Lasaea (Fig. 222) and Pseudokellya (Fig.
221, em) they are retained in the internal interlamellar space, as

244

THE LAMELLIBRANCHIA

also in the Cyrenidae (Cyclas, etc.), in which special pouches are
developed to contain the ova, the maturer ova being the more
anterior. In the Unionidae of the Old World and of North
America they are retained in the external interlamellar spaces, and
in other Unionidae (Qitadrula, Sckistodesma, Gibbosula, Cuneopsis) and
in Modiolaria in both the external and internal interlamellar spaces.
In some other Lamellibranchia, e.g. Ostraea edulis and other herma-
phrodite species of Ostraea such as 0. angasi and 0. lurida, and

cud"

tl*

PlO. 222.

ntbra, a transverse section through the posterior part of the body, showing embryos
in the gills, ad', ad", anterior and posterior adductor muscles ; br, gill ; cat, caecum ; g.c,
cerebral ganglion ; g.vi, visceral ganglion ; hep, liver ; in, intestine ; ot, otocyst ; p, foot ; pa,
mantle ; pal, labial palp ; st, stomach ; vi, vitellus.

in Entovalva, the earlier stages of development are passed through
in the pallial cavity, outside the gills. In all other Lamellibranchia
the eggs are laid one by one, generally in the spring or summer
in temperate climates. In Nucula delphinodonta they are collected
together in a mucous sac fixed to the posterior part of the shell,
and are there incubated.

Fertilisation may be effected externally to the maternal parent,
as, for instance, in Pecten, the dioecious speciea of Ostraea, Modio-
Jaria, Dreissensia, Mactra, Pholas, etc., and in all these forms artificial
fertilisation is possible ; or it may be effected in the pallial cavity,

THE LAMELLIBRANCHIA

245

in the cloacal or suprabranchial chamber, as in Cardium and several
other incubatory forms, or in the oviduct itself in Ostraea edulis.

The formative pole of the ovum is opposite to the micropylar
end. The segmentation is unequal from the first cleavage onwards.
The macromere formed at the first cleavage is loaded with yolk
granules and remains single for a long time, but gives rise to the
three first groups of micromeres, which partly cover it as with a
cap (Fig. 9, C). Finally, the macromere divides to form the endo-
derm cells. The gastrula is rarely formed by invagination (Pisidium,
Kay Lankester), but in nearly all cases by epiboly, or sometimes
by a process midway between the two, in which there is at first
an epiboly resulting from the multiplication of the small ectodermic
cells surrounding the single macromere, and finally an invagination
after division of the macromere. This process is found in Ostraea,
Cyclas, and the Unionidae, and in the two last-named the segmenta-
tion cavity is very large and the enteron small (Fig. 227). The
blastopore remains open in some cases, e.g. in Ostraea, but closes in
Cyclas, Pisidium, the Unionidae, Dreissensia, Teredo, etc. But the
mouth and oesophagus are soon formed by a secondary ectodermic
invagination at the point of closure of the blastopore. The' yolk
remains in connection with the dorsal surface of the enteron and is
slowly absorbed. The endoderm gives rise to the stomach and the
two liver lobes and to the intestine ; the liver lobes often display
a marked asymmetry, the left lobe being larger than the right in
Mytilus, Dreissensia, and Yoldia. The anal ectodermic invagination
placing the intestine in communication with the exterior is gener-
ally at the extreme posterior end of the embryo, is very short, and
very late in appearance. The mesoderm originates, at an early
period, from the most posterior of the four primary endoderm
cells ; the resulting mesomeres take up a position between the
ectoderm and endoderm in the form of two symmetrical mesoderm
bands.

In its general characters the development of the Lamelli-
branchia conforms to the type observed in the other classes of
the Mollusca, but a certain number of special features must be
noted. (1) The shell- gland makes its appearance at an early
period in the normal position ; that is to say, at the formative
pole, nearly opposite to the blastopore (Fig. 223, sk). It is single,
like the shell-gland of all other Molluscs. During its extension it
gives rise to a saddle -shaped cuticular pellicle, which becomes
calcified at two symmetrical points, right and left of the middle
line. These two centres of calcification eventually form the two
valves of the shell, but, except in the Unionidae, they do not
develop as fast as the subjacent lobes of the mantle. The two
valves remain united by the median and dorsal part of the primitively
single shell, and the ligament is formed at this line of union.

246

THE LAMELLIBRANCHIA

This condition is reached during the veliger stage ; the shell,
which is at first too small to contain the whole animal, is called
the prodissoconch, and is characterised by its two symmetrical
valves with a simple linear hinge. After this stage a sudden

FlO. 223.

Development of 0$tr<iea tdvlis. A, blastula stage, with commencing invagination at bl, the
blastopore. B, optical section of a somewhat later stage, in which the invagination of the shell-
gland, sk, has commenced ; bl, blastopore ; ec, ectoderm ; en, endoderm. C, similar optical
section of a little later stage. The invagination connected with the blastopore is now more
contracted, d\ and cells, me, forming the mesoderm, are separated. 1), similar section of a
latter stage (trochoaphere) with closed blastopore bl ; m, the mouth ; s, shell, on the surface of
the shell-gland sk. E, surface view of an embryo at a period a little more advanced than D.
F, the same embryo seen as a transparent object, a, anus ; e, intestine ; ft, foot ; m, mouth ;
tk, shell-gland ; st, stomach ; tp, velar area of the prostomium. The extent of the shell and com-
mencing upgrowth of the mantle-skirt is indicated by a line forming a curve from a to F. On
the dorsal side of the stomach is the anterior adductor muscle. (From Lankester, after Horst.)

change is effected in the secretory activity of the mantle, and
the embryonic shell or prodissoconch is often separated from the
rest of the shell by a more or less projecting ridge, indicating
this modification during growth (Fig. 196,^). (2) The velum, which
serves as the larval swimming organ, is a circular outgrowth with

THE LAMELL1BRANCHIA

247

a ciliated border, lying in front of the blastopore. It is never
lobed, and is often provided with a single central flagellum, e.g.
in Yoldia (Fig. 225, a.c), the Mytilidae, Dreissensia (Fig. 224, /),
Cardium, Montacuta, Entovalva, Mactra, and Teredo, but there is no
flagellum in Pecten, Ostraea, Avicula, Pholas, Nucula, and the
Unionidae ; it is very much reduced in the incubatory species and
quite nul in Pisidium. As will be explained further on, the velum
may be turned back in such a manner as to cover and adhere to
the whole body of the larva, thus giving rise to the "testaceous"
larvae peculiar to the Nuculidae. (3) In almost all Lamellibranchs
an important invagination is formed near the posterior extremity
of the foot: this is the byssogenous cavity (Fig. 224, by), which is

Fio. 224.

Veliger of Dreissensia polymorpha, left-side view, n, anus ; a.a, anterior adductor ; by,
byssus gland ; cr, caecum of the crystalline style ; /, foot ; /, flagellum ; h, heart ; t, intestine ;
I, liver ; m, mouth ; mu, retractor muscles ; ot, otocyst and pedal ganglion ; p.a.c, post-anal
cilia ; re, embryonic kidney ; .s£, stomach ; v, velum ; v.g, visceral ganglion. (After
Meisenheimer.)

formed even in species devoid of a byssus in the adult state. In
Cyclas, for instance, there is a larval bycsus by which the embryo
attaches itself to the incubatory branchial cavity. (4) In the middle
of the velar area there is an apical plate formed by an ectodermic
thickening, from which the paired cerebral ganglia originate. In
Yoldia each cerebral ganglion is formed from a deep tubular
invagination, and similarly in Dreissensia an apical fossa grows in
from the apical plate, and the cerebral centres are formed from
its deeper part. The pedal centres arise from ectodermic
thickenings between the larval mouth and anus (Fig. 224, ot). The
pleural ganglia are distinct from the cerebral during larval life, in
Dreissensia, Modiolaria, Lasaea, and Teredo, at any rate. Two larval
eyes with cuticular lenses occur in many forms, on either side the

248 THE LAMELLIBRANCHIA

velum, at the base of the first internal branchial filament, but their
persistence has not been demonstrated except in the Mytilidae and
Avicula (Fig. 236, e). On either side of the pedal centres an
ectodermic invagination gives rise to an otocyst; the invagina-
tions close up in most cases, but remain open in Nucula and
Mytilus. The apical portion of the velar area gives rise to the
labial palps. (5) In all groups of the Lamellibranchia (Nuculidae,
Mytilidae, Avicula, Ostraea,Yig. 192, g, Dreissensia, Entovalva,Pisidwm,
Anadonla, Fig. 228, br, etc.), the branchiae originate in the form of
filaments, which develop one by one from behind forwards, at the
posterior part of the body, on the right and left sides, between the
mantle and the visceral mass. The filaments of the internal gill-
plate are the first to be formed, afterwards those of the external
gill-plate : it is only at a late period that the filaments are reflected
and unite with one another. (6) Two larval kidneys have been
found in several groups (Dreissensia, Cyclas, Teredo), in the form of
small organs of ectodermic origin, situated on either side of the
anterior end of the larva, behind the velum, and opening to the
exterior by their hinder ends (Fig. 224, re). Each organ consists
of two cells (Dreissensia), of which one is deep and ciliated, the othei
is tubular, with an intra-cellular canal leading from the flagellum of
the deeper cell to the external orifice. (7) In the trochosphere or
veliger larva provided with a bivalve shell, the anterior adductor
muscle is the first to be developed, as may be seen in Nucula, the
Mytilidae, Ostraea, Pecten, Lasaea, Entovalva, Dreissensia, Pisidium,
the Unionidae, Cardium, etc. In considering the evolution of the
larva one must distinguish between two quite different modes
of development, one of which may be called the normal mode,
while the other is characterised by the parasitism of the larva
and subsequent metamorphoses (Unionidae). In the first mode
one may further distinguish a development through a veliger
larva, which occurs in most Lamellibranchs, and a development
through testaceous larvae, characteristic of the Nuculidae. In the
development with a veliger stage, the larva may be free, as is
the case in many marine forms and in the freshwater Dreissensia,
or it may be retained and incubated in the gills, as in Cyclas,
Kellya, Teredo, etc. When the larva leads a free existence its velum
is always rather prominent (Fig. 224, v), but when it is retained
and incubated by the parent the velum is reduced or sometimes
disappears altogether (Cyclas, Unionidae, Entovalva). When the
velum is absorbed the foot becomes highly developed, even in
such forms as become sedentary and fixed in after life, such as
Pecten, Avicula, etc., unless indeed they attach themselves at a
very early period.

In the Nuculidae, which have test-larvae, we find that in
Yoldia and Nucula proxima the ova are set free in the water

THE LAMELLIBRANCHIA 249

and the larva is free-swimming. But in Nucula delphinodonta the
female constructs a thin-walled mucoid egg-case, attached to the
posterior portion of the shell and in communication with the
pallial chamber : into this case the ova are passed as soon as they
are laid, and undergo their development. In Yoldia and Nucula
proxiina a gastrula is formed by epiboly and then the greater
part of the ectoderm gives rise to a " test," which is really a
ciliated velum formed in a normal position at the apical pole,
but reflected in such a manner as to completely cover the former
ectodermic surface of the body — viz. the shell-gland, etc. — leaving
only a small opening opposite to the apical plate, in which the
stomodaeum and eventually the proctodaeum are formed (Fig. 16).
The test consists of five rows of flattened cells, the three median
rows bearing circlets of long cilia (Fig. 225). A long ciliated
flagellum, like that of many Lamellibranch larvae, is borne in the

Fio. 225.

Surface view of a forty-five hour embryo of Yoldia limatula. a.c, apical cilia ; U, blastopore ;
x, depression where the cells that form the cerebral ganglia come to the surface. (After Drew.

centre of the apical plate. When the larval development is com-
pleted, the test, with its stalk and apical plate, is stripped off and
cast away within the space of a few minutes (Fig. 226) ; the apical
cilia shrivelling up and the test cells breaking apart and frequently
falling to pieces at once. In the larva of Nucula delphinodonta the
test is covered with short diffuse cilia, there is no flagellum, and
the disruption and casting off of the test occupies several hours,
the parts near the apical plate being the last to disappear. The
testaceous larvae of the Nuculidae should be compared with the
larvae of Dentalium (Fig. 15) and of Myzomenia (Fig. 17).

A development with secondary metamorphosis, acquired in the
course of ontogeny, is peculiar to the Unionidae. In this family
the eggs are laid in spring or summer, and on leaving the genital
orifice pass into the interlamellar space of the internal gill-plate ;
thence into the interlamellar space of the outer gill-plate by way
of the posterior extremity of the gill, where the two spaces com-

250

THE LAMELLIBRANCHIA

municate with one another behind the branchial axis. In the
European Unionidae the eggs are incubated and pass through the
earlier stages of Jieir development in the outer gill-plate (see above,

FIG. 226.

Reconstruction of an embryo of Yoldla limaMa at a stage during "casting," represented as
seen from the right side, with the right shell-valve and mantle lobe removed, a.a, anterior
adductor muscle ; c.g, cerebral ganglion ; /, foot ; g, rudiment of gill ; int, intestine ; ot, oto-
cyst ; p.a, posterior adductor muscle ; p.g, pedal ganglion ; r, pouch that leads to the cerebral
ganglia ; r.l, right lobe of the digestive gland ; std, stomodaeum ; t, adhering test cells of
velum ; v.g, visceral ganglion. (After Drew.)

p. 226, for an account of the segmentation and endodermic invagi-
nation, Fig. 227, II). In Castalia, Arconaia, Pseudodon, etc., the eggs
are incubated in the internal gill-plate, and in Quadrula, Schisto-
desma, Gibbosula, and Cuneopsis both gill -plates are used for
incubation. The shell-gland, as soon as it is formed, produces a
shell which grows as fast as the mantle, and
is provided with a large anterior adductor
muscle (Fig. 227, I). A ciliated disc, corre-
sponding to the ciliated post-anal surface of
Dreissensia (Fig. 224, p.a.c), is formed behind
the blastopore and causes the embryo to
rotate in the egg-shell (Fig. 227). These
first phases of development take about two
Embyro of Anodonta, left- months for their accomplishment, and in
to^e0; European Unionidae the embryos hibernate
^hieid I jn the interlamellar space without undergoing
any appreciable structural modification In
the following spring they are hatched out, and escape through
the dorsal or anal pallial aperture in the form of a peculiar larva

tteo

THE LAMELLIBRANCHIA

251

called a " glochidium " (Fig. 228). This larva is characterised by
the possession of hooks in the middle of the lateral borders of its
valves and by its larval byssus — which is not homologous with that
of other Lamellibranchs. This byssus appears to issue from, but
in reality winds round, the adductor muscle, and originates from a
single glandular epithelial cell, deeply embedded in the tissues on

-JJ.Ctd

dr-

FIG. 228.

Two stages in the development of Anoilouta ; both figures represent the " glochidium " stage.
A, when free swimming, shows the two dentigerous valves widely open. B, a later stage, after
fixation to the fin of a fish, a.atl and ad, anterior adductor muscle ; al, alimentary canal ; au.v,
otocyst ; br, branchial filaments ; by, byssus ; /, foot ; mt, mantle-flap ; p.ad, posterior adductor ;
*, teeth of the shell ; sh, shell. (From Lankester, after Balfour.)

the dorsal and anterior side of the muscle. The glochidia swim

actively by clapping together the valves of the shell, and eventually

attach themselves to the gills or fins of a fish, and become encysted

in consequence of a pathological development of the epithelium of

their host. This parasitic existence lasts for a period varying from

two to six weeks, during which the glochidia are nourished by the

epidermic elements of their host, absorbing them by means of the

ectodermic cells of the embryonic mantle. During this time most of

the definite organs of the adult, the

foot, otocysts, gills, etc., which were

not required in larval life, are de-

veloped, largely as the result of the

proliferation of the cells of two sym-

metrical cavities situated behind the

adductor muscle. In a general way

the development of the organs follows

the normal course, but some — the

borders of the mantle, for instance —

are formed anew. The glochidium

i 11 . ty.-, . ,-, -, Parasitic larva of Anodonta on the

Shell IS not Cast On OUt persists, tnOUgn eighth day of parasitic life ; ventral view.

ot

FIG. 229.

if nnrlpro-npc Q pmicirlAraKIp n\M*r\crei /I foot ; 0, gill-filaments ; pa, new mantle ;

it undergoes a considerable cnange 0<>ot0cyst. (After scinerhoitz.)
of shape. The posterior ciliated shield

and the byssus disappear. During the early part of the parasitic
life the mouth acquires an opening into the previously closed
endodermic cavity or archenteron, but the anus is not formed till

252 THE LAMELLIBRANCHIA

the close of parasitic life, and its formation is not accompanied
by a sensible ectodermic invagination. When the young Unio quits
its host its evolution is not complete. The gills continue to grow
slowly, their external plates not being developed until the third
year, and sexual maturity is not attained until the fifth year, but
growth continues for some time after.

IV. BIONOMICS AND DISTRIBUTION.

All the Lamellibranchia are aquatic. The great majority are
marine, but some few families have penetrated into fresh waters.
All the members of the class feed upon microscopic organisms,
chiefly Diatomaceae and other low forms of plant life. Only the
Septibranchia and some other abyssal forms are truly carnivorous.

In general, the Lamellibranchs are burrowing forms, living
half -buried in muddy or sandy bottoms, and in this case their
plane of symmetry is vertical. But many forms are completely
sedentary and are fixed by the byssus, or in a more definitive
manner, by the shell itself, as is the case in Spondylus, Ostraea,
Aetheria, Myochama, etc. In these genera the plane of symmetry
becomes horizontal, and the animal usually lies on the right side,
e.g. Pinna, Hinnites, Spondylus, Plicatula, Anemia, and the Rudistae ;
more rarely on the left side as in Ostraea, Eequienia, and Cliama
generally. Some Lamellibranchs live in holes which they excavate
either in wood, as in the case of Teredo, or in stone, as Lithodomus,
Saxicava, Pholas, Clavagella, etc., or even in the shells of other
Molluscs. Lithodomus is only found in calcareous rocks, and bores
its hole by the aid of the acid secretion of glands situated in the
antero-dorsal and postero-dorsal regions of the mantle.

Some Lamellibranchs, such as Lima, are nidamentous, and
construct a nest by means of the byssus. Lima Mans builds its
nest in the space of three weeks, and may afterwards return and
reconstruct another from it. Modiolaria marmorata and Entodesma
cuneatum pass their existence deeply buried in the tests of
Ascidians, and Vulsella lives in a similar manner in sponges ; but
the few commensalistic or parasitic forms generally live on or in
Echinoderms : thus Montacuta lives on Spatangids, Scioberetia in
the incubatory pouch of an Asterid, Entovalva in the oesophagus of
a Synapta. On the other hand, Ephippodonta is commensal with a
prawn, and certain species of Lepton with Gebia.

Only a few species are very active : Tellina, Yoldia, etc., execute
leaping movements by forcibly contracting the foot ; Lasaea, Cyclas,
etc., crawl on immersed bodies or on the surface of the water ;
other forms, notably the Pectinidae and Limidae, swim by rapidly
opening and closing the valves of the shell; and some elongated
forms in which the mantle edges are fused for a considerable

THE LAMELLIBRANCHIA 253

extent swim by forcibly expelling water from the posterior aperture
of the mantle (Solen, Solenomya).

In point of size the Lamellibranchs vary from a length of a few
millimetres to more than seventy centimetres (Pinna and Tridacna,
some specimens of the latter genus weighing as much as 310 Ibs.).
The fossil Hippurites attained to the length of a metre.

There are more than 5000 living species of Lamellibranchia, of
which 1000 are Unionidae. They are distributed all over the
world, and some marine forms extend to a depth of 2700 fathoms.
Fossil forms appear in the Cambrian, and become very numerous
in species from the Silurian onwards. Some large groups, such as
the Palaeoconcha of the primary and the Rudistae of the secondary
deposits, are quite extinct.

V. REVIEW OF THE ORDERS AND FAMILIES OF LAMELLIBRANCHIA.

The classification of this homogeneous group has long presented
great difficulties, for the different organs or apparatus, such as shell,
muscles, siphons, etc., that have successively been employed as
bases of classification, have not given satisfactory results.

Ray Lankester was the first to suggest (in 1884) that the
structure of the gills might furnish characters of classificatory
value, and the present writer has constructed on this basis a
phylogenetic classification in which the class is divided into five
groups. This classification has put various families, such as the
Anomiidae, Trigoniidae, Dreissensiidae, etc., into their proper
places, and has been largely adopted. Objections to it have,
however, been raised, notably by Dall, who has urged that the
genera Eudroa (Anatinacea) and Callocardia (or Vesicomya,
Cyprinidae) have protobranchiate gills, and that the system of
classification according to branchial characters is consequently
without foundation. But the recent investigations of Ride wood,
undertaken at the instance of Ray Lankester, have shown that
it was the objections of Dall that had no foundation : Eudroa and
Callocardia have typical eulamellibranchiate gills.

As the result of the advancement of our knowledge, the
classification of the Lamellibranchia founded on the structure of
the gills has been ameliorated by the suppression of the order
" Pseudolamellibranchia," and the two diphyletic sub-orders which
it included, the Pectinacea and the Ostraeacea, may be respectively
located in the Filibranchia and the Eulamellibranchia, thus making
these two old-established orders correspond to the new orders
proposed by Ridewood under the names Eleutherorhabda and
Synaptorhabda.

On the other hand, the shell (and particularly its hinge) is the
only other organ that has been retained as a basis of the general

254 THE LAMELL1DRANCH1A

classification of the Lamellibranchia, especially by palaeontologists,
and the subdivisions adopted in this system correspond more or
less with those based on the structure of the respiratory organs.
Thus the following are very nearly synonymous terms : —

Prionodesmacea = Protobranchia + Filibranchia.
Teleodesmacea = Eulamellibranchia - Anatinacea.
Anomalodesmacea = Septibranchia + Anatinacea.

As regards the value of the last order, Septibranchia, in it the
characteristic organs that have given the name to the whole class
Lamellibranchia are so profoundly modified, that they differ much
more from all the other different kinds of gills than the latter differ
from one another, and therefore, even if the Septibranchia should
not be placed in contrast to all other Lamellibranchia, they at
least constitute a group equivalent to the three other groups,
Protobranchia, Filibranchia, and Eulamellibranchia.

Thus the Lamellibranchs are divisible into these four orders.
It will be remarked that the numerous studies on the organisation
of Lamellibranchia made since 1891, have shown that there has
been a progressive evolution in each of these four orders, and that
consequently such important organs as the heart, kidneys, and
otocysts may exhibit marked differences in relatively nearly related
types, and that no strictly pure primitive types have been retained.

From the point of view of phylogeny the most archaic
Lamellibranchia are those in which the foot has a " plantar " ventral
surface like that of Gastropoda and Pulsellum among the Scaphopoda.
These archaic forms constitute the Protobranchia (Solenomya, Fig.
230, Yoldia, Fig. 231, etc.), in which the gonads still retain openings
into the initial or pericardial portion of the kidneys, and the
branchial filaments are free and not reflected. From these Proto-
branchia are derived the Filibranchia, whose branchial filaments
are reflected, but are still devoid of vascular junctions : these in
turn have given rise to the Eulamellibranchia, which are more
specialised in respect of the complication of the ctenidia. Finally,
eulamellibranchiate forms analogous to the Anatinacea represent
the source from which the Septibranchia have been derived.

ORDER 1. Protobranchia.

These are Lamellibranchia whose distinctive character is the
possession of gills with flat and non-reflected filaments disposed in
two rows on opposite sides of the branchial axis (Fig. 206, A, B).
The mantle is provided with a hypobranchial gland lying on the
outer side of each gill. The foot has a plantar ventral surface (Fig.
230, /) and the byssogenous apparatus is but slightly developed.
The nervous system generally presents a distinct pair of pleural

THE LAMELLIBRANCHIA 255

ganglia, and the otocysts are generally open. The gut may be pro-
vided with a relic of the pharyngeal cavity, which in some cases is
furnished with two lateral glandular sacs. The auricles of the
heart are muscular ; the kidneys are rather simple in structure and
glandular throughout their extent. The sexes are separate : the
gonads have retained their primitive communications with the initial
or internal extremities of the kidneys, but as the two branches of
each kidney have acquired a secondary communication at their
anterior ends, the genital products pass direct to the external
orifice of the kidney by this passage (Fig. 213).

sto

Fio. '230.

Adult specimen of Yoldia Hmatula, represented as seen from the right side, and showing the
internal organs, a.a, anterior adductor muscle ; a.f.m, anterior foot muscle ; b.g, byssal gland ;
c.g, cerebral ganglion ; e.s, exhalant siphon ; /, foot ; g, gill ; h, heart ; int, intestine ; i.s, in-
halant siphon ; l.p, labial palp ; ot, otocyst ; p.a, posterior adductor muscle ; pap, palp
appendage ; p.e, posterior expansion of the margin of the mantle ; p.f.m, posterior foot muscle ;
p.g, pedal ganglion ; s.(, siphonal tentacle ; sto, stomach ; v.g, visceral ganglion. (After Drew.)

FAMILY 1. SOLENOMYIDAE, Gray. In the gills one row of branchial
filaments is directed dorsally and the other ventrally (Fig. 231, g). The
mantle has a long postero-ventral suture, and a single posterior orifice.
The labial palps of each side are fused together. The shell is elongate ;
the hinge has no teeth ; the periostracum is thick. Genus — Solenomya,
Lamarck. FAMILY 2. NUCULIDAE, Gray. The labial palps free, very
broad and provided with a posterior appendage ; all the branchial
filaments are oriented transversely ; the shell has an angular dorsal
border and the hinge is pliodont ; the mantle is open throughout its
extent. Genera — Nucula, Lamarck ; the heart situated on the dorsal
side of the rectum. Acila^ Adams (Cretaceous, Tertiary, and Recen").
Promicula, Hedley. FAMILY 3. LEDIDAE, Adams. The same characters
as the Nuculidae, but the mantle has two posterior sutures and two
united siphons ; the heart traversed by the rectum. Genera — Leda,
Schumacher; the mantle borders produced posteriorly into two lobes
which simulate a third siphon. Yoldia, Moller ; siphons elongate ;

256

THE LAMELLIBRANCHIA

ligament internal (Figs. 200, 230). Malletia, Des Moulins ; the ligament
external. Nvtulina, d'Orbigny. FAMILY 4. CTENODONTIDAK, Wohr-
mann. An extinct family from the Silurian ; the shell is nuculiform
and the hinge presents an uninterrupted arcuate row of teeth. Genera —
Ctenodonta, Salter. Cuculella, Fischer. Cardiolaria, Meunier-Chalmas.

The fossil group Palaeoconcha, Neumayr, is connected with the
Protobranchia through the Solenomyidae. It contains the following
families, all of which are extinct : — FAMILY 1. PRAECARDIIDAE, Neumayr
Shell equivalve, with the hinge dentition of Area. Genus — Praecardium,
Barrande ; from the Silurian and Devonian. FAMILY 2. ANTIPLEURIDAE,
Neumayr. Shell inequivalve ; the hinge with an obscure resemblance to
that of Area. Genus — Antipleura, Barrande; from the Silurian.
FAMILY 3. CARDIOLIDAB, Neumayr. Shell equivalve and ventricose ; the
hinge without teeth. Genus — Cardiola, Broderip ; from the Silurian and
Devonian. FAMILY 4. GRAMMYSIIDAE, Fischer. Shell thin, equivalve,

a. en.

FIG. 231.

Solenomya togata, Poli, left-side view (the left pallial lobe and gill cut away), a, anus ; ad',
ad", anterior and posterior adductor ; ao, aorta ; a. or, anal orifice of the mantle ; an, heart-
auricle ; c.g, cerebral ganglion ; /, foot ; f.e, foot elevator ; f.p, foot protractor ; /r', fr", anterior
and posterior foot retractor ; g, right gill ; hy.g, hypobranchial gland ; k, Kidney ; ra, mouth ;
pa, mantle ; pc, pericardium ; p.g, pedal ganglion ; p.l, palp appendage ; pl.g, pleural ganglion ;
r.o, renal opening ; st, stomach ; v, heart-ventricle ; vi.c, visceral commissure ; vi.g, visceral
ganglion.

oval, or elongate, the cardinal border thickened but without teeth.
Genera — Grammysia, Verneuil ; from the Silurian and Devonian.
Protomyay Hall, from the Devonian. Cardiomorplia, de Koninck ; from
the Silurian to the Carboniferous. FAMILY 5. VLASTIDAE, Neumayr.
Shell thin, very inequivalve, the hinge without teeth. Genus — F7osta,
Barrande ; from the Silurian. FAMILY 6. SOLENOPSIDAE, Neumayr. Shell
equivalve, thin, greatly elongated, the urnbones very far forward.
Genus — Solenopsis, MacCoy, from the Devonian to the Trias.

ORDER 2. Filibranchia.

These are Lamellibranchs whose main character is the possession
of gills formed of parallel, ventrally directed, and reflected filaments.
The successive filaments are joined together by cilia disposed in
"ciliated discs" (Figs. 210, A; 232, i.f.j). The foot is generally

THE LAMELLIBRANCHIA

257

provided with a highly developed byssogenous apparatus. The
order comprises five sub-orders — the Anomiacea, Arcacea, Mytilacea,
Pectinacea, Dimyacea.

SUB-ORDER 1. ANOMIACEA.

Very asymmetrical animals with a single large posterior adductor
muscle. The heart is not contained in the pericardium, lies dorsad of the

Fio. 232.

A portion of the gill of Mytilus, showing the filaments : the median part is cut out. a.b.r,
afferent branchial vessel ; e.b.v, efferent branchial vessel : i.f.j, interfilatnentar ciliated junction ;
i.l.j, interlamellar connective tissue junction. (After Bonnet.)

rectum, projects into the pallial cavity, and gives off a single and anterior
aorta. The reflected borders of the inner gill-plates of either side are
fused together in the middle line. The gonads open into the kidneys,
and the right gonad extends into the mantle. The shell is thin and the
animal fixed.

Family ANOMIIDAE, Adams. Foot small. The inferior (right) valve
of the adult is perforated to admit of the passage of the byssus. Genera
— Anomia, Linnaeus ; byssus large and calcined ; British. Placuna,
Bruguiere ; byssus atrophied in the adult Hypotrema, d'Orbigny.
Carolia, Cantraine. Ephippium, Bolten. Placunanomia, Broderip.

17

258 THE LAMELLIBRANCHIA

SUB-ORDER 2. ARCACEA.

Symmetrical animals, with the mantle open throughout its extent,
and with generally well -developed anterior and posterior adductor
muscles. The heart lies in the pericardium and gives off two aortae.
The gills are free and without interlamellar junctions. The renal and
genital orifices are separate.

FAMILY 1. ARCIDAE, Gray. The borders of the mantle bear com-
pound pallial eyes. The labial palps are direct continuations of the lips
(Fig. 199). The hinge is "pliodont," that is to say, it has numerous
teeth on either side of the umbones, and the teeth are perpendicular to
the edge. Genera — Area, Linnaeus ; foot byssiferous ; heart above the
rectum ; hinge straight (Figs. 188, 199) ; British. Pectunculus, Lamarck ;
foot without byssus, but with a plantar surface ; the heart traversed by
the rectum ; the hinge curved ; British (Fig. 193, A). Scaphula, Benson ;
from fresh water ; India. Argina, Gray. Bathyarca, Kobelt. Barbatia,
Gray. Senilia, Gray. Anadara, Gray. Adacnarca, Pelseneer. FAMILY 2.
PARALLELODONTIDAE, Ball. The shell of Arca» but with the posterior
hinge teeth elongated and parallel to the cardinal border. Genera —
Cucullaea, Lamarck ; recent and fossil from the Jurassic. All the other
genera are fossil, e.g. Parallelodon, Meek and Worthen ; from the Devonian
to the Tertiary, Carbonaria, Meek and Worthen ; from the Carboniferous,
etc. FAMILY 3. LIMOPSIDAE, Dall. Shell sub-orbicular, the hinge curved,

the ligament simple with the trans-
verse axis longer than the longitudinal ;
foot elongate, pointed anteriorly and

i i ^^jgffri^' N posteriorly. Genera — Limopsis, Sassi ;

shell covered with a hairy epidermis ;
the anterior adductor frequently much
reduced (Fig. 233). Trinacria, Mayer ;
from the Tertiary. FAMILY 4. PHILO-
BRYIDAE, Bernard. The animal, like
that of LimopsiSj without an anterior
adductor muscle ; the shell thin, very
inequilateral, the anterior part atro-
phied, the umbones projecting and
FIO. 233. formed by the prodissoconch. Genera

Umo1»i,longitilosa,p*}*., interior aspect —Philobrya, Carpenter (Figs. 196,
of the right valve1. a.o, anterior adductor 234). FAMILY 5. CYRTODONTIDAE,
impression; I, hgamentar fossa; p.a, pos- _-.*/ . „ ., ...

terior adductor imprewion ; t, hinge-tooth. Wohrmann. An extinct family With

an equivalve short, convex and

inequilateral shell, the anterior side of which is short; the hinge teeth
oblique or horizontal. Genera — Cyrtodonta, Billings ; Silurian and
Devonian. Cypricarditcs, Conrad ; Silurian. Vanuxemia, Billings ;
Silurian. FAMILY 6. TRIGONIIDAE, Fleming. Foot elongated, pointed
in front and behind, the ventral border sharp. The byssogenoue
apparatus atrophied and devoid of a byssus. The labial palps distinct
from the lips. Shell thick. Hinge with striated teeth. Genera —
Trigonia, Bruguiere ; shell sub-triangular, the umbones directed back-

THE LAMELLIBRANCHIA 259

wards. This genus was very abundant in the Secondary epoch, particularly

in Jurassic seas. There are six living species, all of which live in

Australian seas. The animal of Trigonia was first found by Quoy and

Gaimard in 1827. Schizodus,

King ; from the Permian. Myo-

phoria, Bronn ; from the Trias.

FAMILY 7. LYRODEBMIDAE,

Ulrich. Shell inequilateral, the

posterior side being the shorter.

The hinge short, bearing teeth

disposed in the shape of a fan.

An extinct family, from the

Silurian. Genus — Lyrodesma,

SUB-ORDER 3. MYTILACEA.

Symmetrical Lamellibranchia

in which the anterior adductor 284'

Tnnc/-1a ia alwaxralpQa rlpvplrvnprl Philobrya sublaevis, Pels., viewed from the left

muscle is always less developed side . the left vMM lobe removed> ^ posterior

than the posterior (the " aniso- adductor muscle ; an, anus ; au, auricle of the

„ j . . t . i , lieart : br, gill ; br.s, branchial axis ; by, byssus :

myarian" condition) or IS absent ^.ge, gonad; n.pa, pallial nerve; p, foot; pa,

"R f1 D "R^ Thp mantle ; pal, labial palp ; re.p, re, p', anterior and
15, U, JJ, ft> 111 1X)sterioVJ retractor muscles of the foot; st,
heart gives off a Single vessel stomach ; ven, ventricle of the heart.
only, the anterior aorta. The

gills are smooth, the gill -filaments all alike and provided with inter-
lamellar junctions. The gonads generally extend into the mantle and
open at the sides of the kidneys. The foot is linguiform and byssiferous.
FAMILY 1. MYTILIDAE, d'Orbigny. Shell inequilateral, the anterior
side being short ; the hinge without teeth ; the ligament external. The
mantle has a posterior suture. Cephalic eyes present. Genera — Mytilus,
Linnaeus ; the shell with terminal umbones ; British. Modiola, Lamarck ;
the umbones behind the anterior extremity ; British. Lithodmnus, Cuvier ;
the shell sub-cylindrical, adapted to boring. Modiolaria, Loven ; posterior
pallial orifice provided with an elongated siphon; anterior adductor
fairly high; British. Crenella, Brown. Stavelia, Gray. Dacrydium,
Torell. Myrina, Adams. Idas, Jeffreys. Septifer, Recluz. FAMILY 2.
MODIOLOPSIDAE, Fischer. Shell elongate, thin, inequilateral, enlarged
posteriorly ; the ligament external ; the adductor muscles subequal. An
extinct family from the Silurian to the Cretaceous. Genera — Modiolopsis,
Hall ; from the Silurian. Modiomorpha, Hall ; from the Devonian.
Myoconcha, Sowerby ; from the Carboniferous to the Cretaceous. FAMILY
3. PERNIDAE, Fleming. Mantle open throughout No anterior adductor
muscle. Shell very inequilateral ; the ligament multiple and lodged in a
series of vertical fossae. Genera — Perna, Bruguiere. Shell sub-quad-
rangular, the right valve notched for the passage of the byssus ; gills free
posteriorly. Crenatula, Lamarck ; shell thin, flattened, irregular, without
a byssal notch ; inhabits sponges. fiakewellia, King ; fossil from the
Permian. Gervilleia, Defrance ; fossil from the Trias to the Eocene.

260

THE LAMELL1BRANCHIA

Odontoperna, Freeh ; fossil from the Trias,
from the Jurassic to the Cretaceous.

Inoccramus, Sowerby ; fossil

SUB-ORDER 4. PECTINACEA.

Lamellibranchia with an open mantle and devoid of an anterior
adductor muscle. The gills are folded, and the filaments at the summits
aud bottoms of the folds are different from the others. The gonads are
contained in the visceral mass and generally open into the kidneys.
Foot usually rudimentary.

Pecten jacobatus, ventral aspect o, anus ; e, pallial eyes ; /, foot ; g, gill ; h.a,
adductor ; i, intestine ; I, lips ; l.p, labial palps ; m, mouth
edge) ; p.e, pallial cavity ; sh, shell ; t, testis. (After Poli.)

TAMILY 1. VULSELLIDAE, Adams. Mantle open ; foot without byssus ;
the shell high and the hinge without teeth. Genus — Vulsella, Lamarck.
FAMILY 2. AVICDLIDAE, 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, Bruguiere ; 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
auriculae. The following genera are exclusively fossil : — Limopteria,

THE LAMELLIBRANCHIA

261

Hall ; Devonian and Carboniferous. Pseudomonotis, Bey rick ; Devonian
and Cretaceous. Cassianella, Beyrich ; Trias. Monotis, Bronn ; Trias.
Daonella, Mojsisovics ; Trias. Posidonomya, Bronn ; Silurian to Jurassic.
FAMILY 3. PRASINIDAE, 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. FAMILY 4. PTERINEIDAE, 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. Actinodesmay Sand-

-vtc

Fio 236.

. Avicula tarentina, Lamarck, from below, a, anus ; ad, adductor muscle ; b.gr, byssal groove
of the foot ; by, byssus ; e, eye ; /, foot ; g, gill ; Lp, labial palp ; m, mouth ; pa, mantle ; sh,
shell ; vi.c, visceral commissure ; vi.g, visceral ganglion. (After Poli.)

berger ; Devonian. ' | FAMILY 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, Miinster ; Silurian and Devonian. Patrocardium, Fischer ;
Silurian. Babinka, Barrande; Silurian. FAMILY 6. CONOCARDIIDAE,
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 — Conocardium, Bronn ; Silurian to Carboniferous.
FAMILY 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. Gosseldia, Barrois ; Devonian. Clionychia, Ulrich ;
Silurian. FAMILY 8. MYALINIDAE, Freeh. 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 — Myalinat de Koninck ;
Silurian and Devonian. Hoplomytilus, Sandberger ; Devonian. Ptycho-
desma, Hall ; Devonian. Anthracopterctj Salter ; Carboniferous. Per-
gamidea, Bittner ; Trias. Mysidea, Bittner ; Trias. Aucella, Kyser ;
Jurassic and Cretaceous. FAMILY 9. AMUSSHDAE, Ridewood. Gills with-
out interlamellar junctions. Shell orbicular, smooth externally, with
radiating costae internally. Genus — Amusvium, Klein. FAMILY 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. FAMILY 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. Pedum, Bruguiere. Hinnites,
Defrance. Pseudamustium, Adams. Camptonectes, Agassiz. Hyalopecten,
Verrill ; abyssal.

SUB-ORDER 5. DIMYACEA.

Dimyarian Lamellibranchia with an orbicular and almost equilateral
shell ; adherent ; the hinge without teeth and the ligament internal.
Gills with free non-reflected filaments.

Family DIMYIDAE, Dall ; with the characcers of the sub-order.
Genus — Dimya, Renault ; recent, in abyssal depths, and fossil since the
Jurassic.

ORDER 3. Eulamellibranchia.

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 gonacls 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 LAMELL1BRANCHIA

263

SUB-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.

FAMILY 1. LIMIDAE, 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, Bruguiere ; the individuals of
this genus form a sort of nest by means of the byssus, or swim by

FlO. 237.

A portion of the gill of Venus, e.b.v, efferent branchial vessel ; g.f,
afferent branchial vessels. (After Bonnet.)

filaments ; g.r,

clapping the valves of the shell together. Limaea, Bronn. FAMILY 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.
FAMILY 3. ELIGMIDAE, Gill. Shell thick, inequilateral, the anterior side
being the shorter. Monomyarian, with the muscular impression on a
prominent myophorous apophysis. Genus — Eligmus, Deslongchamps ;
an extinct genus from the Jiirassic. FAMILY 4. PINNIDAE, 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.

SUB-ORDER 2. SDBMYTILACEA.

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.

FAMILY 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 — JJreissensia, van Beneden ; an in-
habitant of fresh water, but originated from the Caspian Sea ; acclimatised
in England about 1824. FAMILY 2. MODIOLARCIDAE, 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). FAMILY 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. FAMILY 4. CRASSATELLIDAE,
Gray. Mantle with a single suture ; foot short. Shell thick with
concentric striae ; the ligament external. Genera — Crassatella, Lamarck.
Cuna, Hedley. FAMILY 5. CARDITIDAE, Fe'russac. 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. FAMILY 6. COXDYLOCARDIIDAE, Bernard. Dis-
tinguished from the family Carditidae by the presence of an external
ligament. Genera — Condylocardia, Bernard. Carditella, Smith. Cardi-
topsis, Smith. FAMILY 7. CYPRINIDAE, d'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. Pleurophorus, King ; fossil from the
Devonian to the Trias. Anisocardia, Munier-Chalmas ; fossil from
the Jurassic to the Tertiary. Venidla, Stoliczka ; fossil from the Cre-
taceous to the Tertiary. FAMILY 8. ISOCARDIIDAE, 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 — Isocardia, Lamarck ; British.
FAMILY 9. CALLOCARDIIDAE, 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 — Callocardia, Adams ; abyssal. FAMILY 10. LUCINIDAE,
d'Orbigny. 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
— Lucina, Bruguiere ; 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. Cryptodon, Turton ; mantle with a single aperture ; foot short ;
visceral mass smooth. FAMILY 1 1 . CORBIDAE, 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. Mutiella, Stoliczka ; fossil
from the superior Cretaceous.
FAMILY 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 — Unyulina, Daudin ;
mantle with a single suture ; vis-

V:,

FIG. -238.
Axlriut Jlexnaxux, Montagu, viewed from the left

ceral mass smooth. Diplodonta. side. I, anterior adductor muscle; 1 1, glandular

T> i -,i , portion of the mantle; III, foot; IV, gouad pro-

Bronn ; mantle with two sutures ; jecting illto the pallial cavity; v, internal ulate

British. Axinus, Sowerby ; mantle °f <*« «m ; vi i, posterior adductor muscle ; viii,

. J ' rectum; IX, posterior retractor af the foot; X,

With a Single suture ; Visceral mass anterior retractor of the foot.

with arborescent excrescences (Fig.

238); British. FAMILY 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. FAMILY 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.
Meelcia, Gabb ; Cretaceous. FAMILY 15. UNICARDIIDAE, 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. Pxeudedmondia, Fischer ; Carboniferous.
FAMILY 16. LEPTONIDAE, 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

c.o

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. Erycina,
Lamarck ; fossil from the Tertiary. Pythina, Hinds. Scacchia, Philippi.
Sportella, Deshayes. Cyamium, Philippi. FAMILY 17. GALEOMMIDAE,
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
A Axius; Australian. The three following

•*^ • genera with an internal shell probably

belong to this family : — Chlamydoconcha,
Dall ; two gill-plates ; a pallial suture ;
an anterior orifice leading into a caecum ;
no adductor muscles ; sexes separate ;
from California (Fig. 239). Scioberetia,
Bernard ; gills with a single gill-plate ;
a single pallial suture ; foot large, elon-
gated, with a byssal groove ; hermaphro-
dite and commensal with a Spatangid,
Triphylua; from Cape Horn. Entovalva,
Voeltzkow (Fig. 240); mantle fairly
open, with a single suture; foot large,
with a posterior pore ; hermaphrodite
and incubatory ; endoparasitic in Synapta
( = Syiiapticola, Malard), Madagascar and
Atlantic. FAMILY 18. KELLYELLIDAE,
Fischer. Mantle with a single pallial
suture ; anal orifice with a very short
siphon ; foot elongated ; gills with two
unequal plates. Shell ovoid ; the liga-
ment external ; the anterior lateral
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. FAMILY 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. FAMILY 20.

Fio. 230.

CMamydoconcha orcutti, Dall. A, dor-
nal aspect ; B, left-side view, a.o, anal
orifice ; c.o, caecal orifice ; /, foot ; pa,
mantle. (After Bernard.)

THE LAMELLIBRANCHIA

267

CYCLADIDAE, Clark. Mantle with one siphon or with two free siphons,
which have simple orifices. Hermaphrodite ; the embryos incuhated in
the external gill-plate. Shell with a simple pallial line. Freshwater.
Genera — Cyclas, Bruguiere ( = Sphaerium) ; two siphons ; British (Fig. 218).
Pisidium, Pfeiffer ; a single anal siphon ; 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. Genusp— Rangia, Desmoulins ; from brackish water
in Florida. FAMILY 22. CARDINIIDAE, 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

Fio. 240.

Entowdva, left-side view, a, anus ; c.g, cerebral ganglion ; f.gl, foot-gland ; g.gl, gonad ; i.c,
incubatory chamber ; in, intestine ; I, liver ; in, mouth ; pa, mantle ; sh, shell. (After
Voeltzkow.)

Devonian to the Cretaceous. Genera — Cardinia, Agassiz ; Trias and
Jurassic. Anthracosia, King ; Carboniferous and Permian. Anoplophora,
Sandberger ; Trias. Pachycardia, Hauer; Trias. FAMILY 23. MEGA-
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. Dicerocardium, Stoppani ; Jurassic. FAMILY 24.
UNIONIDAE, 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 LAMELL1BRANCHIA

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. A nodonta, Lamarck ; shell thin; the hinge without
teeth ; British. Pseudodon, Gould. Quadrula, Rafi nesque. Arconaia, Conrad.
Motwcondylaea, d'Orbigny. Solenaia, Conrad. Mycetopus, d'Orbigny ;
foot cylindrical, with a terminal swelling ; South America. FAMILY 25.
MUTELIDAE, 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. Iridina, Lamarck. Hyria, Lamarck.
Castalia, Lamarck. Aplodon, Spix. Plagiodon, Spix. FAMILY 26.
AETHERIIDAE, Adams. Shell irregular, generally fixed in the adult state.
Mantle with a single suture ; foot absent ; anterior adductor muscle

FlQ. 241.

Modiolaria trapezina, Lamarck, viewed from the left side ; the left mantle lobe is removed.
ad', ad", anterior and posterior adductor muscles ; br1, br", internal and external gill-plates ;
gl.p, foot gland ; o.a, o.b, anal and branchial orifices of the mantle ; o.by, byssal orifice of the
foot ; o.p, pedal orifice of the mantle ; p, foot ; jxil, 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. Mulleria, F^russac ;
no anterior adductor ; American. Bartlettia, Adams.

SUB-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. Diinyarian ; the pallial line has a deep sinus.

FAMILY 1. TELLINIDAE, 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 — Tellina, Linnaeus ; slightly inequivalve ; foot large ;
British (Fig. 190). Gastrana, Schumacher ; equivalve ; the foot slightly
developed ; British. Capsa, Bruguiere. Macoma, Leach. FAMILY 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 LAMELL1BRANCHIA

269

(U

Fia. 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 mantle-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 ; 6, 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 ; /,
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 ; I,
posterior adductor muscle ; m, posterior retractor muscle of the foot ; n, anterior labial palp ;
o, posterior labial palp ; ft, base-line of origin of the reflected mantle-flap from the side of the
body ; q, left external gill-plate ; r, left internal gill-plate ; rr, inner lamella of the right inner
gill-plate ; r.g, 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 ; u, 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 ; x, 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 ; *, 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 ; a/, space occupied by
the liver ; ag, space occupied by the gonad ; oA, muscular substance of the foot ; ai, opening of
bile-duct into the stomach ; afc, 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; ar, non-glandular portion of the left kidney ; as, anus ; at, reno-pericardial
orifice ; aw, pore joining the two parts of the kidney ; av, internal pore of the kidney leading to
the external pore x ; aw, left cerebral ganglion ; ax, left pedal ganglion ; ay, left otocyst ; az,
left visceral ganglion ; 66, floor of the pericardium, separating that space from the kidney.
(After Lankester.)

270 THE LAMELLIBRANCHIA

Scrobicularia, Schumacher ; estuarine ; British. Syndosmya, Recluz ;
British. Cumingia, Sowerby. FAMILY 3. DONACIDAE, 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 — Donax, Linnaeus ; British. Iphigeneia, Schumacher.
FAMILY 4. MBSODESMATIDAE, 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. FAMILY 5. CARDILIIDAE,
Dall. Shell very high and short, ventricose, dimyarian, the posterior
adductor impression borne on a prominent myophorous apophysis.
Ligament partly internal. Genus — Cardilia, Deshayes ; from the Pacific
Ocean. FAMILY 6. MACTRIDAE, 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.

SUB-ORDER 4. VENIRACEA.

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.

FAMILY 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). Cycling Deshayes. Lucinopsis, Forbes
and Hanley ; British. Meretrix, Lamarck (Fig. 189). Circe, Schumacher ;
British. Venerupist Lamarck. FAMILY 2. PETRICOLIDAE, 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. pholadiformia, 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. FAMILY 3. GLAUCOMYIDAE,
Chenu. Siphons very long and united. Foot small. Shell elongated,
thin, with a deep pallial sinus. Inhabitants of fresh or brackish watei
Genera — Glaucomya, Woodward ; from S.K Asia, Tanysiphon, Benson ;
from India.

SUB-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 equi valve, with
radiating costae and an external ligament.

THE LAMELLIBRANCHIA

271

FAMILY 1. CARDIIDAE, Gray, The mantle slightly closed ; siphons
very short and surrounded by a single circle of papillae which are often
oculiferous (Fig. 243, o.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). Psevdokellya,
Pelseneer (Fig. 221). Both Byssocardium, Munier-Chalmas, and Litho-
cardium, Woodward, fossils from the Eocene, have a much reduced anterior
adductor muscle. FAMILY 2. LIMNOCARDIIDAE, 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. FAMILY 3. TRIDACNIDAE, 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. A single adductor

Fio. 243.

Cardium etlule, left-side view. «..<?, anal siphon ; br.s, branchial siphon ; ;, foot ; li, ligamen
of the shell ; o.t, eye-spots on the tentacles ; .sfc, shell. (Alter Deshayes.)

muscle. The gills narrow. The shell thick. Genera — Tridacna,
Bruguiere ; byssus stout ; shell gaping anteriorly ; from the Indian
and Pacific Oceans. Hippopus, Lamarck ; byssus reduced ; shell not
gaping.

SUB-ORDER 6. CHAMACEA.

Asymmetrical, inequivalve, fixed Eulamellibranchia, with extensive
pallial sutures and distant pallial orifices ; no siphons. Two adductor
muscles present. The foot reduced and without a byssus. Shell thick,
without a pallial sinus.

FAMILY 1. CH AMID AE, Gray. Shell with subequal valves and promi-
nent umbones more or less spirally coiled ; ligament external. Genera
— Chama, Bruguiere ; the free valve only slightly ventricose ; shell
lamellated or spiny. JHceras, Lamarck; shell smooth, the umbones
largely divergent and coiled ; the adductor muscles (at least the anterior)
attached to myophorous apophyses ; fossil from the Jurassic (Fig. 244, A).
Requienia, Matheron ; the fixed valve spirally coiled ; the free valve

272

THE LAMELL1BRANCHIA

operculiform ; fossil from the Cretaceous (Fig. 244, B). Matheronia,
Munier-Chalmas ; fossil from the Cretaceous. FAMILY 2. CAPRINIDAE,
d'Orbigny. Shell inequivalve ; the fixed valve spiral or conical ; the
free valve not operculiform but coiled or spiral ; ligament internal ; sub-
stance of the shell generally
pierced with large parallel canals.
An exclusively fossil family,
from the Cretaceous. Genera
— Caprina, d'Orbigny ; the free
valve larger than the fixed and
coiled (Fig. 244, C). Caprinula,
d'Orbigny ; fixed valve elongated
and conical, free valve small and
coiled (Fig. 244, D). Caprotina,
d'Orbigny. Ichthyosarcolites, Des-
marets. Playioptychns, Matheron.
Polyconitex, Roulland. FAMILY 3.
MONOPLEURIDAE, Munier-
Chalmas. Shell very inequi-
valve ; the fixed valve conical or
spiral, the free valve operculiform
and slightly or not at all spiral ;
ligament external. No canals in
the substance of the shell. An
exclusively fossil family, from
the Cretaceous. Genera — Mono-
pleura, Matheron (Fig. 244, E).
Valletta, Munier-Chalmas.
Baylea, Munier-Chalmas. The
two following families, desig-
nated by the common name of
Rudistae, are closely allied to the
preceding : they also comprise
some extinct marine forms from Secondary deposits. These animals, of
littoral and often gregarious habit, were fixed by the conical and more or
less elongated right valve ; the adductor muscles were not inserted perpen-
dicularly to the surface of separation of the two valves ; the free left
valve has a sub-central umbo, is not spiral, and is furnished with promi-
nent myophorous apophyses to whose external faces the muscles were
attached ; this valve was only movable in 'a vertical direction. FAMILY 4.
RADIOLITIDAE, Gray. Shell conical or biconvex, without canals in the
external layer. Genera — Radiolites, Lamarck ; valves ornamented with
longitudinal costae ; a ligament present ; from the Cretaceous (Fig. 244, F).
Biradiolites, d'Orbigny ; no ligament ; Cretaceous. FAMILY 5. HIP-
PUBITIDAE, Gray. Fixed valve long, cylindro- conical, with three
longitudinal furrows, corresponding internally to two pillars which serve
to support the siphons. Anterior adductor muscle with two separate
insertions on the fixed valve. Genera — Hippurites, Lamarck ; Cretaceous.
Arnaudidy Bayle ; Cretaceous. The family Diceratidae, the most ancient

FIG. 244.

Some genera of fossil Chaiuacea and Rudistae.
A, DiAxras arietinum; £, Requieuia ammonia; C,
Caprina adversa; D, Caprinnla Baylei; E, Mono-
pleura imbricate ; F, Radiolites angeioiles. (Chiefly
after d'Orbigny.)

THE LAMELLIBRANCHIA 273

of the Chamacea, and possibly derived from the Megalodontidae of the
Palaeozoic and the Trias, has given rise to a branch that has survived to
the present epoch (Chamidae) and to various others that became extinct
at the close of the Secondary period. In all cases, the forms in which
the umbo of the free valve is coiled have preceded the forms with an
operculiform free valve — Requienia being derived from Diceras and
Chama from Matheronia ; in the same way among the Rudistae liadiolites
appears to be derived from Caprina. The Hippuritidae, by the depth of
the fixed valve, the reduction of the cavity, and the absence of the
ligament, indicate the last stage of the evolutionary series.

SUB-ORDER 7. MYACEA.

Eularnellibranchia in which the mantle is closed to a considerable
extent ; the siphons are well developed, the gills much folded and
frequently prolonged into the branchial siphon. The foot is compressed
and generally byssit'erous. The shell gaping, with a pallial sinus.

FAMILY 1. PSAMMOBIIDAK, Gray. Siphons very long and quite
separate. Foot large, flattened from side to side and pointed. Shell

Psammobifi floricla, right side, showing expanded foot (c)
and g, branchial, and <j', anal siphons. (From Lankester,
after Garner. X

oval, elongated, with a deep pallial sinus and an external ligament.
Genera — Psammobia, Lamarck ; the posterior end of the shell sub-
truncated ; British (Fig. 245). Sanguinolaria, Lamarck. Asaphis,
Modeer. Elizia, Gray. Solenotellina, de Blainville. FAMILY 2.
MYIDAE, Gray. Mantle largely closed ; siphons united for the greater
part of their length and surrounded, near their extremities, by a circlet
of tentacles. Foot reduced. Shell gaping, with an internal ligament ;
the left valve provided with a spoon-shaped projection for the ligament.
Genera — Mya, Linnaeus ; siphons elongated, covered by a chitinous
sheath, and incompletely retractile ; foot small ; palps elongated ; British.
Sphenia, Turton ; British. Tuyonia, Gray. Platyodon, Conrad. Crypto-
mya, Conrad. FAMILY 3. CORBULIDAE, Fleming. Shell sub-trigonal,
inequivalve, the left valve less convex than the right ; the pallial sinus
shallow ; the ligament partly external. Siphons short, united, com-
pletely retractile. Foot large, pointed, often byssiferous. Palps reduced.
Genera — Corbula, Bruguiere ; siphons surrounded by a common circlet of
tentacles ; shell short ; British. Corbidomya, Nyst ; shell elongated ;
branchial siphon with a special tentacular crown. Paramyct, Conrad.
Erodona, Daudin, and Hinielln, Adams, are lluviatile forms from South
America. FAMILY 4. LUTRARHDAK, Adams. Mantle extensively

18

274

THE LAMELLIBRANCHIA

closed ; siphons long and united throughout their length ; a fourth
opisthopodial pallial aperture. Foot rather large, compressed. Shell
elongated, with a deep pallial sinus and a spoon-shaped projection for the
ligament on each valve. Genera — Lutraria, Lamarck ; British. Tresus,
Gray. Standella, Gray. FAMILY 5. SOLENIDAE, Leach. Elongated,
burrowing animals. The foot more or less cylindrical and powerful,
without a byssus. Gills narrow. Shell long, truncated, and gaping at
each end ; the ligament external. Genera — Solenocurtus, de Blainville ;
siphons large, partially united, incompletely retractile ; pallial sinus deep ;
foot very large and linguiform (Fig. 194); British. Tayelus, Gray;
posterior extremity short ; pallial sinus very deep ; estuarine. Ceratisolen,
Forbes and Hanley ; siphons long, separate ; gills rather short and not
folded ; British. Cultelhis, Schumacher ; siphons rather short ; extremity
of foot dilated ; British. Siliqua, Megerle ; siphons of medium length ;
foot dilated ; shell compressed. Solen, Linnaeus ; siphons short ; foot
elongated ; shell rectilinear, cylindrical ; the umbones anterior and
terminal ; British. Ensis, Schumacher ; siphons very
short ; a fourth pallial orifice ; shell arcuate, the um-
bones anterior and sub-terminal ; British. FAMILY 6.
SAXICAVIDAE, Gray. Mantle extensively closed ; with
a small pedal orifice (Fig. 246, /); siphons elongate,
covered by a chitinous sheath and wholly or largely
united; gills prolonged into the branchial siphon.
Foot small. Shell gaping, with an external ligament.
Genera — Saxicava, Fleuriau ; bores holes in rocks ;
siphons free at their extremities ; foot byssiferous ;
British (Fig. 246). Glycimeris, Lamarck; siphons
very long and completely united ; a burrowing form.
Cyrtodaria, Daudin ; shell inequilateral ; the anterior
side the longer ; siphons united, incompletely retractile.
FAMILY 7. GASTROCHAENIDAE, Gray. Shell thin,
Saxicava arctica, ven- without teeth, gaping widely at the anterior end.
Son? 6°™, branchial Anterior adductor much reduced. Foot small and
siphon; 'by, byssai without a byssus. Gills narrow. Mantle extensively
mantle; 4, s'helV **** closed ; with long united siphons. Genera — Gastro-
chaena, Spengler ; a boring form, with a cylindrical
foot ; the shell regular and rarely enclosed in an adventitious tube ;
British. Fistulana, Bruguiere ; a burrowing form with a very small
compressed foot ; shell with a denticulate border, always enclosed in a
regular, non-adherent, fragile, club-shaped adventitious tube.

FIG. 246.

SUB-ORDER 8. ADESMACEA.

Eulamellibranchia with very long united siphons and a largely
closed mantle. The foot short, truncated, discoid, and without a
byssus. The gills prolonged into the branchial siphon. The shell gaping
and devoid of a ligament, but with .-> styloid apophysis in the umbonal
cavities.

FAMILY 1. PHOLADIDAE, Adams. Shell capable of containing all

THE LAMELLIBRANCHIA

275

the organs ; the heart traversed by the rectum ; two aortae. The shell

with a pallial sinus ; the dorsal region protected by accessory calcareous

pieces. Genera — Photos, Linnaeus ; foot cylindrical ; siphons free near

their extremities ; British. In Pholas there are four accessory plates ; in

Zirphaea, Leach, two; in Barnea, Leach, one.. Pholadidea, Goodall ;

foot rudimentary ; siphons completely united and their extremity

surrounded by a fringed disc ; shells elongated, in the adult prolonged

posteriorly by a short calcareous tube, which surrounds the siphons -r

British. Jouannetia, des Moulins ; foot rudimentary ;

siphons completely united ; shell globular, and the right

valve prolonged posteriorly by a rostriform appendage.

Xylophaga, Turton ; siphons separate at their extremities ;

foot narrow ; shell globular with two accessory dorsal

plates ; British. Martesia, Leach ; siphons long, united ;

foot absent in the adult ; shell ovoid with a ventral plate

in addition to the dorsal plates. FAMILY 2. TERE-

DINIDAE, Fleming. Shell globular, covering a small

portion only of the vermiform body. Heart on the

ventral side of the rectum (Fig. 195, h) ; a single aorta ;

siphons long, united to a large extent and furnished with

two posterior calcareous "pallets" (Fig. 247, II). Genera

— Teredo, Linnaeus ; a borer in wood ; secretes an

adventitious non - adherent tube ; British. Xylotrya,

Leach ; the pallets articulated.

SUB-ORDER 9. ANATINACEA.

Hermaphrodite Eulamellibranchia, in which the
ovaries and testes are distinct and have separate orifices
(Fig. 219, o, $). The foot generally rather small. The
mantle frequently presents a fourth orifice. The ex-
ternal gill-plate directed dorsally and devoid of a reflected
lamella. Hinge of shell without teeth.

FAMILY 1. THRACIIDAE, Dall. Mantle with a fourth
pallial orifice ; the pedal orifice elongated ; siphons branchial siphon •
rather long, quite separate, and completely retractile vi, foot?™
and invertible. Shell with a deep pallial sinus.
Genera — Thracia, de Blainville ; shell with a large spoon-shaped tooth -T
British. Astlienothaerus, Carpenter ; shell without spoon-shaped teeth,
FAMILY 2. PERIPLOMIDAE, Dall. Siphons separate, naked, completely
retractile, but not invertible. Pallial sinus shallow ; no ligament.
Genera — Cochlodesma, Couthouy. Periploma, Schumacher. Tyleria,
Adams. FAMILY 3. ANATINIDAE, Gray. Siphons long, united, covered
by a chitinous sheath, and not completely retractile. Foot slender.
Pallial sinus well marked. Genera — Anatina, Lamarck. Shell thin and
gaping, with spoon-shaped teeth. Plectomya, de Loriol ; fossil from the
Jurassic and Cretaceous. FAMILY 4. PHOLADOMYIDAE, Gray. Mantle
extensively closed, with a fourth orifice. Siphons very long, completely
united, naked, and incompletely retractile. Foot small, with a posterior
appendage. Shell thin, with an external ligament and a well-marked

Pio. 247.

Teredo navalis,
Linnaeus, ventral
aspect. I, shell ;
II, pallets ; III,
anal siphon ; IV,

276

THE LAMELLIBRANCHIA

pallial sinus. Genera — Pholadomya, Sowerby ; some species living and
abyssal ; numerous fossil species from the Trias onwards, the maximum
in the Jurassic. FAMILY 5. ARCOMYIDAE, Fischer. Shell finely granular,
equivalve, thin ; the hinge without teeth ; the ligament external ; pallial
sinus. An exclusively fossil family, from the Secondary and Tertiary.
Genera — Arcomya, Agassiz ; from the Trias to the Eocene. Goniomya,
Agassiz ; Jurassic and Cretaceous. FAMILY 6. PHOLADELLIDAE, Miller.
Shell oval, the posterior extremity attenuated and gaping ; cardinal
border thin and devoid of teeth ; ligament external ; posterior adductor
muscle large. An exclusively fossil family, from Primary
deposits. Genera — Pholadella, Hall ; Devonian. ljhytimya,
Ulrich ; Silurian. Allorisma, King ; Carboniferous and
Permian. FAMILY 7. PLEUKOMYIDAE, Zittel. Shell inequi-
lateral, thin ; the pallial line deeply sinuous ; the cardinal
border of one valve covering that of the other and hiding
the ligament, which is therefore sub -internal. An ex-
clusively fossil family from Secondary formations. Genera
— Pleuromya, Agassiz ; from the Trias and inferior
Cretaceous. Gresslya, Agassiz ; Jurassic. Ceromya, Agassiz ;
Jurassic. FAMILY 8. PANDORIDAE, Gray. Shell thin,
inequivalve, free ; the ligament internal ; no pallial sinus.
Siphons very short; foot elongate. Genera — Pandora,
Bruguicre ; British. Coelodon, Carpenter. Clidiophora,

Carpenter. FAMILY 9. MYO-
CHAMIDAE, Dall. Shell very
inequivalve, solid, with a
pallial sinus. Siphons short ;
a fourth pallial orifice
present ; foot small. Genera
— Myochama, Stutchbury ;
shell irregular ; fixed to
other shells by the right
valve ; Australian. Myodora,
Gray ; shell free, trigonal ;
the left valve flattened.
FAMILY 10. CHAMOSTREI-
DAE, Fischer. Mantle
largely closed. A fourth
pallial orifice present ; pedal
orifice small. Siphons very
short and separate. Shell

Atpergittum vaginiferum ; to the left side, the whole fiYP(l 11V fhp T\a]\t valvp irrp-
shell, dorsal view/the anterior part below ; to the right nxed DV.tJ ve> ir

side, the anterior part, magnified, to show the original gular, Without a pallial Sinus ;
valves a, now embedded in a continuous calcification of ,. „__._,. .'-.^-....i nan*,0
tubular form. (From Lankester, after Owen.) ligament internal. Uenus —

Chamostrea, de Roissy ;

Australian. FAMILY 11. CLAVAQELLIDAE, d'Orbigny. Mantle largely
closed ; pedal orifice extremely small ; a fourth pallial orifice present ;
siphons fairly long, united ; foot very rudimentary and without a byssus.
The ligament external ; the valves continued backwards into a calcareous

Fio. 248.

THE LAMELLIBRANCHIA

277

tube secreted by the siphons ; pallial line sinuous. Genera — Clavagella,
Lamarck ; left valve fused to the tube ; adductor muscles well developed ;
a boring form. Brechites, Guettard ( = Aspergillum, Lamarck) ; the two
valves fused to the tube and external (Fig. 248) ; no posterior adductor
muscle ; the anterior adductor much reduced ; the anterior extremity
bearing numerous tubular projections serving for adhesion ; Indian and
Pacific Oceans. FAMILY 12. LYONSIIDAE, Fischer. Mantle largely
closed, with a fourth pallial orifice ; siphons short, invertible ; foot
byssiferous. Shell thin, granular externally ; the pallial sinus feeble ;
the ligament internal. Genera — Lyonsia, Turton ; shell regular and
elongated; British (Fig. 219). Entodesma, Philippi ; shell irregular,
truncated behind ; a boring form, sometimes found in the tests of
Ascidians. Mytilimeria, Conrad ; shell regular, ventricose, gaping behind.
FAMILY 13. VERTICORDIIDAE, Wood. Siphons short ; the gills papillose ;

CLCL

pet,

FIG. 249.

Poromya tornata, left-side view, a.a, anterior adductor; a.p, anterior labial palp; a.s,
anal siphon ;/, foot; g.l, gill lamellae on the septum; ft^ heart; ha, posterior adductor; in,
intestine; li, liver; pa, pallial suture; p.p, posterior labial palp; p.t, pallial tentacles; r.p,
retractor posterior pedis ; r.s, retractor of the septum ; s, septum ; vj, valvular fold of the
branchial aperture.

foot small ; palps well developed. Shell globular, very slightly gaping,
without a pallial sinus. Many species abyssal. Genera — Verticordia,
Wood ; mantle largely closed ; the pedal orifice small. Euciroa, Dall ;
heart situated above the rectum. Lyonsiella, Sara ; foot byssiferous.
Halicardia, Dall.

ORDER 4. Septibranchia.

The Septibranchia are dimyarian Lamellibranchs in which the
mantle remains fairly open and has two sutures and two siphons.
The foot is long and slender ; the byssus rudimentary or absent.
The pallial line is simple or very slightly sinuous. The essential
character of the group is the disappearance of the gills as respiratory
organs, a character which is not found in any other Lamellibranch.
The gills are transformed into a muscular septum (Fig. 249, s)

278

THE LAMELLIBRANCHIA

which extends from the anterior adductor muscle to the point
•of separation of the two siphons, and surrounds and is continuous
with the foot. This septum, therefore, has exactly the situation
and the relations of the branchial septum of the majority of the
Lamellibranchia, which divides the pallial cavity into two chambers.
The group is derivable, more or less directly, from the Anatinacea,
through the series Lyonsiti, Lyonsiella, Poromya, CetoconcJia, Cuspidaria,
in which one may observe a gradual increase in the amount of
muscular fibre in the gill filaments or in their reduced equivalents,
so that any objection to the branchial origin of the septum, because
of its muscularity, cannot hold good. The muscular septum is
inserted on the shell, especially in the neighbourhood of the two
adductor muscles. The origin of the anterior and posterior exten-
sions of the septum and of its muscular attachments to the two
extremities of the shell is to be found in the physiological contrac-
tions necessary to create a current of water on the respiratory
surface of tl^e supra-septal chamber. The septum is, in fact, always
pierced by paired orifices, which admit of the passage of water.

The Septibranchia are all marine,
inhabit considerable depths of the
sea, and are carnivorous. The order
only comprises one sub-order, the
Poromvacea.

CLO

FAMILY 1. POROMYIDAE, Ball.
Siphons short and separate ; the bran-
chial siphon provided with a large
valve. Foot pointed and not byssi-
ferous. The branchial septum bears two
groups of transversely elongate orifices
on either side ; these are formed by
a few branchial filaments, with or with-
out junctions. The palps are large.
All the members of the family are her-
maphrodite. Genera — Poromya, Forbes ;
no pallial sinus ; British (Fig. 249).
Dermatomya, Dall ; a pallial sinus
present LiopistJia, Meek ; fossil from
the Cretaceous. FAMILY 2. CETOCON-
CHIDAE, Ridewood. Branchial septum
bearing three groups of orifices on each
side ; these orifices are separated by
rudimentary branchial filaments. Palps
large ; siphons short, separate, the branchial siphon with a valve. Genus
— Cetoconcha, Dall ( = Silenia, Smith); abyssal (Fig. 250). FAMILY 3.
CUSPIDABIIDAE, Fischer. Siphons long and united, their extremities
surrounded by tentacles. Foot narrow, with a rudimentary byssus.
Palps greatly reduced or absent. Branchial septum pierced by four or

m o

FIG. 250.

A ventral view of Cetoconcha, removed
from its shell, a.o, anterior septal
orifices ; a.p, anterior palp ; /, foot ; m,
mouth ; m.o, median septal orifices ; pa,
mantle ; p.o, posterior septal orifices ;
p.p, posterior palp ; se, branchial sep-
tum ; si, retractile branchial siphon.
(After Ridewood.)

LITERATURE OF THE LAMELLIBRANCHIA 279

five pairs of very narrow symmetrical orifices. The sexes separate.
Genus — Cuspidaria, Nardo ; British (Fig. 251).

aa

FIG. 251.

Cuspularia cuspidata (Olivi), left-side view, after removal of left half of the mantle. «, anus ;
a.a, anterior adductor ; a.f.r, anterior foot retractor ; a.p, anterior labial palp ; a.s, anal siphon ;
br.n, branchial nerve ; br.s, branchial siphon; ft.r, branchial valve; c.g, cerebral ganglion;/,
foot; g.g, genital gland; g.o, genital orifice ; h, heart; in, intestine; A;, kidney; k.o, kidney
opening; m, mouth; p.a, posterior adductor; p.f.r, posterior foot-retractor; p.g, pedal gan-
glion; p.l.p, posterior labial palps; s, septum; s.o, septal oritice ; s.r, septal retractor; st,
stomach ; vi.g, visceral ganglion.

LITERATURE OF THE LAMELLIBUANCHIA.
A. General.

1. Ahting. Untersuchungen iiber die Eiitwickeluiig des Bojanus'schen Organ

und des Herzens der Lamellibranchier. Jenaische Zeitschr. xxxvi. 1901.

2. Barrois, Th. Les glandes du pied et les pores aquiieres chez les Lamelli-

branches. Lille, 1885.

3. Le stylet cristallin des Laniellibrauches. Revue biol. Nord France, i.

1890.

4. Bernard, F. Premiere, deuxieme, troisieme, quatrieme et derniere note sur le

deVeloppement et la morphologic de la coquille chez les Lamellibranches.
Bull. Soc. Geol. France (3), xxiii., xxiv., xxv. 1895, 1896, and 1897.

5. Recherchcs ontogeniques ct morphologiques sur la coquille des Lamelli-
branches. Ann. des Sci. nat. Zool. (8), viii. 1898.

6. Blanchard, E. Observations sur le systeme nervcux des Mollusques

Acephales- Testaces on Lamellibranches. Ibid. (3), iii. 1845.

7. I'Organisation du Regne Animal : Mollusques Acephales. Paris, 1851.

8. Bonnet, R. Der Ban und die Circulationsverhiiltnisse der Acephalentkieme.

Morph. Jahrb. iii. 1877.

9. Boutan, L. Recherches sur le byssus des Lamellibranches. Arch, de Zool.

Exper. (3), iii. 1895.

10. Biitschli. Notiz zur Morphologic des Auges der Muscheln. Festschr. 500

jahr. Bestand Ruperto-Carola nat.-med. Ver. Heidelberg, 1886.

11. Carazzi, D. Contribute all' istologia e alia fisiologia dei Lamellibranchi.

Mittheil d. Zool. Stat. Neapel, xii. 1896 ; Internat. Monatsschr. f. Anat.
u. Phys. xiv. and xx. 1897 and 1902.

12. Carrtere. Die Driisen im Fusse der Lamellibranchiaten. Arbeiten Zool.

Zoot. Instit Wiirzburg, v. 1879.

280 L1TERA TURE OF THE LAMELLIBRANCHIA

13. Caltie. Les Laraellibranches recueillis dans les courses du "Willem Barents.

Bydr. tot do Dierk., 1884.

14. Coutance. De 1'energie et de la structure musculaire chez les Mollusques

Acephales. Paris, 1878.

15. Dall. Tertiary Mollusks of Florida. Part III. A new Classification of the

Pelecypoda. Trans. Wagner Free Instit. of Science, iii. 1895.

16. Deshaycs. Histoire naturelle des Mollusques (Exploration scientifique de

1'Algerie). Paris, 1844-1848.

17. Duvcrnoy. Memoires sur le systeme nerveux des Mollusques Acephales.

Mem. Acad. Sci. Paris, xxiv. 1853.

18. Ehrenbaum. Untersuclmngen tlber die Structur und Bildung der Schale

der in der Kieler Bucht haiifig vorkommenden Muscheln. Zeitschr. f.
wiss. Zool. xli. 1884.

19. Fleischmann. Die Bewegung des Fusses der Lamellibranchiaten. Zeitschr.

f. wiss. Zool. xlii. 1885.

20. Flemming. Ueber Bindesubstanz und Gefasswandung im Schwellgewebe der

Muscheln. Arch. f. mikr. Anat. xiii. 1877.

21. Georgimtch. Recherches sur les glandes du pied des Lamellibranches.

Geneve, 1895.

22. Grobben. Die Pericardialriise der Lamellibranchiaten. Arb. Zool. Inst.

Wien, vii. 1888.

23. Ueber den Bulbus arteriosus und die Aortenklappen der Lamelli-
branchiaten. Ibid. ix. 1891.

24. Hancock. On the boring of the Mollusca into rocks. Ann. Mag. Nat. Hist.

(2), ii. 1848.

25. Horst. 1st der Byssus ein Cuticularbildung ? Tijdschr. Ned. Dierk. Vereen.

(2), ii. 1889.

26. Kellog. A Contribution to our Knowledge of the Morphology of Lamelli-

branchia. Bull. U.S. Fish Comm. x. 1890.

27. Jameson. On the Origin of Pearls. Proc. Zool. Soc. London, 1902.

28. Janssens. Les branchies des Acephales. La Cellule, ix. 1893.

29. Lacaze-Duthiers. Recherches sur les organes genitaux des Acephales Lamelli-

branches. Ann. des Sci. nat. Zool. (4), ii. 1854.

30. Memoire snr 1'Organe de Bojanus des Acephales Laniellibranches.

Ann. des Sci. nat. Zool. (4), iv. 1855.

31. Memoire sur le developpement des branchies des Mollusques Acephales

Lamellibranches. Ibid. (4), v. 1856.

32. Letellier. Etude sur la fonction urinaire chez les Mollusques Acephales.

Arch, de Zool. Exper. (2), v. bis, 1887.

33. Loven. Bidrag till Kiinnedomen om Utvecklingen af Mollusca Acephala

Lamellibranchia. K. Vet. Akad. Handl. 1848.

34. Menegaux. Recherches sur la circulation chez les Lamellibranches marins.

Besanfon, 1890.

35. Mitra. The cristalline style of Lamellibranchia. Quart. Journ. Micr. Sci.

xliv. 1901.

36. Mitsukuri. On the structure and significance of some aberrant forms of

Lamellibranchiate Gills. Quart. Journ. Micr. Sci. xxi. 1881.

37. Neumayr. Beitrage zur einer morphologischen Eintheilung der Bivalven.

Denkschr. k. Akad. d. wiss. Wien, math.-naturw. Cl. Iviii. 1891.

38. Patten. Eyes of Molluscs and Arthropods. Mitth. Zool. Stat. Neapel, vi.

1886.

LITERATURE OF THE LAMELL1BRANCHIA 281

39. Peck, E. H. The minute structure of the gills of Lamellibranch Mollusca.

Quart. Journ. Micr. Sci. xvii. 1877.

40. Pelseneer. Contribution a I'e'tude des Lamellibranches. Arch, de Biol. xi.

1891.

41. Les yeux cephaliques chez les Lamellibranches. Ibid. xvi. 1899.

42. Rawitz. Der Mantelrand der Acephalen. Jenaische Zeitschr. xxii., xxiv.,

xxvii. 1888, 1890, 1892.

43. Rice. Die systematische Verwerthbarkeit der Kiemen bei den Lamelli-

branchiaten. Jenaische Zeitschr. xxxi. 1897.

44. Ridewood, W. G. On the structure of the Gills of the Lamellibranchia.

Phil. Trans. B. cxcv. 1903.

45. Roule, L. Recherches histologiques sur les Mollnsques Lamellibranches.

Journ. Anat. et Physiol. 1887.

46. Schrciner. Die Augen bei Pecten und Lima. Bergens Mus. Aarbog, 1896.

47. Sharp, B. On the Visual Organs in Lamellibranchiata. Mitth. Zool. Stat.

Neapel, v. 1884.

48. Soubeiran. Essai sur les ganglions medians ou latero-superieurs des Mol-

lusques Ace"phales. Paris, 1858.

49. Stenta, M. Zur Kenntniss der Stromungen im Mantelraume der Lamelli-

branchiaten. Arb. Zool. Inst. WieiT, xiv. 1902.

50. Thiele, J. Die Mundlappen der Lamellibranchiaten. Zeitschr. wiss. Zool.

xliv. 1886.

51. Die Abdominal Sinnesorgane der Lamellibranchier. Ibid, xlviii. 1889.

52. Yung, E. De 1'innervation du ca-ur et de Faction des poisons chez les Mol-

lusques Lamellibranches. Arch, de Zool. Expor. (1), ix. 1881.

B. Special.

53. Alder and Hancock. On the branchial currents in Pholas and Mya. Ann.

Mag. Nat. Hist. (2), viii. 1851.

536". Anthony. InHuence de la fixation pleurothetique sur la morphologic des
Mollusques Acephales Dimyaires. Ann. des Sci. nat. Zool. (9), i. 1905.

54. Babor. Ueber das Centralnervensystem von Dreissenia polymorpha. Pall.

Sitzungsber. Bohm. gesellsch. Wiss. math.-natur. Cl. 1895.

55. Barrois, Th. Sur la structure de YAnomia ephippium. Bull. Sci. Dep. Nord

(2), ii. 1879.

56. Note sur I'embryogenie de la Moule commune, Mytilus edulis. Ibid.

(2), ii. 1879.

57. Bernard, F. Scioberetia anstralis, type nouveau de Lamellibranche. Bull.

Sci. France et Belgique, xxvii. 1896.

58. Condylocardia, type nouveau de Lamellibranches. Journ. de Couchyl.

1896.

59. Les genres Philobrya et Hochstetteria. Ibid. 1897.

60. Anatomic de Chlamydoconcha Orcutti, Lamellibranche a coquille in-
terne. Ann. des Sci. nat. Zool. (8), iv. 1897.

61. Beuk. Zur Kenntniss des Baues der Niere und der Morphologic von Teredo.

Arb. Zool. Inst. Wien, xi. 1899.

62. Bloomer. The Anatomy of the British Species of the Genus Solen. Journ. of

Malacol. viii., ix. 1901, 1902.

63. The Anatomy of certain species of Ceratisolen and Solecurtus. Ibid. x.

1903.

282 LITERATURE OF THE LAMELLIBRANCHIA

64. Brooks, W. K. The development of the Oyster. Studies Biol. Labor.

Johns Hopkins Univ. i. 1880.

65. Deshayes. Memoire anatomique sur 1'Iridine du Nil. Mem. Soc. Hist.

Nat. Paris, iii. 1897.

66. Dou-oilU, H. Etudes sur les Rudistes. Mem. Soc. Geol. France, Paleon-

tologie, i., iii. 1890, 1893.

67. Drew. Some observations on the Habits, Anatomy, and Embryology of

Members of the Protobranchia. Anat. An/eiger, xv. 1899.

68. Yoldia limatula. Mem. Biol. Labor. Johns Hopkins Univ. iv. 1899.

69. The Life-History of Nucula delphinodonta. Quart. Joum. Micr. Sci.

xliv. 1901.

70. Drost. Ueber das Nervensystem une die Sinnesepithelien der Herzrauschel

(Cardium cdule). Morpii. Jahrb. xii. 1886.

71. Dubois. Auatomie et Physiologic comparee de la Pholade dactylc : Structure.

locomotion, tact, olfaction, gustation, vision dermatoptique, photogenic.
Ann. Univ. Lyon, ii. 1892.

72. Egger. Jouannetia Cumingii, Sow. Arb. Zool. Zoot. Inst. Wiirzburg, viii.

1887.

73. Faussek. Ueber die Ablagerung des Pigments bei Mytilus. Zeitschr. wiss.

Zool. Ixv. 1898.

74. Fullarton. On the development of the Common Scallop (Pecten opercularis).

Eighth Ann. Rep. Fish. Board Scot. iii. 1890.

75. Gottc. Bemerkungen iiber die Embryonalentwickelung der Anodonta

piscinalw. Zeitschr. wiss. Zool. xli.

76. Grobben. Beitrage sur Kenntniss des Baues von Cuspidaria cuspidata.

Arb. Zool. Inst. Wien, x. 1892.

77. Beitrage sur Morphologie und Anatomie der Tridacniden. Denkschr.

math.-naturw. 01. K. Akad. wiss. Wien, Ixv. 1898.

78. Zur Kenntuiss der Morphologie und Anatomie von Meleagrina aowie

der Aviculiden im Allgerneinen. Ibid. Ixix. 1900.

79. Hancock. On the Animal of Chamostrea albida. Ann. Mag. Nat Hist. (2),

ii. 1853.

80. On the Animal of MyocJiama anomoides. Ibid. (2), ii. 1853.

81. Hatschek. Ueber Entwicklungsgeschichte von Teredo. Arb. Zool. Inst

Wien, iii. 1880.

82. Hoeck. Les organes de la generation de /huitre. Tydschr. Ned. Dierk.

Vereen. Suppl. Deel i. 1884.

83. Horst. On the development of the European Oyster (Ostrea edulis). Quart.

Journ. Micr. Sci. xxii. 1882.

84. Huxley. Description of the Animal of Trigonia. Proc. Zool. Soc. London.

1849.

85. Jackson. The development of the Oyster, with Remarks on allied genera.

Proc. Bost. Soc. Nat. Hist xxiii. 1888.

86. Jhering, H. von. Phylogeny of the Pelecypoda ; the Aviculidae and their

Allies. Mem. Boston Soc. Nat. Hist. iv. 1890.

87. Die Gehbrwerkzeuge der Mollusken in ihrer Bedeutung fur das

Naturliche System derselben. Erlangen, 1876.

88. Johnstone. Cardium. Liverpool Mar. Biol. Com. Mem. ii. 189».

89. Keer. Bydrage tot de Kennis van den Paaiworm. Leiden, 1903.

90. Kishinouye. Note on the eyes of dnrdium midicum, Reeve. Journ. Coll.

Sci. Tokyo, vi. 1894.

LITERATURE OF THE LAMELLIBRANCHIA 283

91. Korschelt. Ueber die Entwickelung vonDreissenapolymorjma. Sitzungsber.

Ges. naturforsch. Fr. Berlin, 1891.

92. Lacaze-Duthiers, F. J. H. Memoire sur 1'organisation de 1'Anomie (Anomia

ephippium). Ann. des Sci. nat. Zool. (4), ii. 1854.

93. Lacaze-Duthiers, H. de. Morphologic des Acephales. ler Memoire. Anatomie

de 1'Arrosoir (Aspergillum dichotomum). Arch, de Zool. Exper. (2), i.
1883.

94. Morphologie de Tridacna elongata etde Hippopus. Ibid. (3), x. 1903.

95. Langer. Ueber das Gefasssystem der Teichmuschel. Denkschr. k. Akad.

wiss. Wien math.-naturw. Cl. viii., xii. 1855, 1856.

96. Lankcstcr, E. Ray. On Green Oysters. Quart. Jour. Micr. Sci. xxvi. 1886.

97. Lilie. The Embryology of the Unionidae. Jour, of Morphol. x. 1895.

98. List. Die Mytiliden. Fauna uiid Flora Neapel, xxvii. 1902.

99. Mayoux. L'existence d'un rudiment cephalique, d'un systeme nerveux

stomato-gastrique et quelques autres particularity's morphologiques de la
Pintadine. Bull. Soc. Philom. Paris (7), x. 1886.

100. Meisenheimer. Entwickelungsgeschichte von Dreissensia polymorpha.

Zeitschr. wiss. Zool. Ixix. 1900.

101. Morse. Remarks on the relations of Anomia. Proc. Bost. Soc. Nat. Hist.

xiv. 1871.

102. Fieri. Recherches physiologiques sur Tapes decussata et quelques Tapidees,

Laval, 1895.

103. Purdie. The Anatomy of the Common Mussels (Mytilus lotus, edulis, and

magellanicus). Studies in Biology, No. 3, published by the Colonial Mus.
and Gcol. Survey Dept. New Zealand, 1887.

104. Rankin. Uber das Bojanus'sche Organ der Teichmuschel (Anodonta cygnea,

Lam.). Jenaische Zeitschr. xxiv. 1890.

105. Ruder. The Metamorphosis and Post-larval Stages of Development of the

Oyster. Rep. U.S. Fish Comm. for 1882, 1884.

106. Sabatier. Anatomie de la Moule commune. Ann. des Sci. nat. Zool. (6), v.

1877.

107. Sassi. Zur Anatomie von Anomia ephippium. Arb. Zool. Inst. Wien, xv.

1903.

108. Schierholz. Ueber Entwickelung der Unioniden. Denkschr. k. Akad. wiss.

Wien math.-naturw. Cl. Iv. 1889.

109. Schmidt, F. Beitrag sur Kenntniss der postembryonalen Entwickelung der

Najaden. Arch. f. Naturgesch. li. 1885.

110. Sigerfoos. Note on the Organisation of the Larva, and the Post-larval

Development of Shipworms. Johns Hopkins Univ. Circul. xv. 1896.

111. Stempell. Beitrage zur Keuntniss der Nuculiden. Zool. Jahrb. Suppl. iv.

1898.

112. Zur Anatomie von Solenomya togata. Ibid. (Anat. u. Ontog.),

xiii. 1900.

113. Stauffachcr. Eibildung und Furchung bei Cyclas cornea. Jenaische

Zeitschr. xxviii. 1893.

114. Toureng. Sur le systeme nerveux du Dreissensia polymorpha. Comptes

rendus Acad. Paris, 118, 1894.

115. Tullberg. Ueber die Byssus des Mytilus edulis. Nova Acta Reg. Soc.

Scient. Upsala, 1877.

116. Vaillant. Recherches sur la famille des Tridacnides. Ann. Sci. nat Zool.

(5), iv. 1865.

284 LITERATURE OF THE LAMELLIBRANCHIA

117. Vaillant. Anatomic de deux Mollusques de la famille des Mall6ac£es. Ibid.

(5), ix. 1868.

118. Voeltzkow. Entovalva mirabilis. Zool. Jahrb. (Auat. u. Ontog.) v. 1891.

119. Willcm &ndMinne. Recherches experimentales sur la circulation sanguine

chez 1'Anodonte. Mem. Cour. Acad. Belg. Ivii. 1899.

120. Wilson. On the development of the Common Mussel (Mytiliis edulis).

Fifth Ann. Rep. Fish. Board Scot. 1887.

121. Woodward, F. M. On the Anatomy of Ephippodonta MacDougalli, Tate.

Proo. Malacol. Soc. i. 1893.

122. Note on the Anatomy of the larva of the European Oyster,

(Ostrea edulis, Linn.). Proc. Malacol Soc. i. 1895.

123. Anatomy of Millleria Dalyi, Smith. Proc. Malacol. Soc. iii.

1898.

124. Ziegler. Die Entwickelung von Cyclas cornea Zeitschr. wiss. Zool. xli.

1885.

CHAPTER VI

THE CEPHALOPODA

CLASS V.— THE CEPHALOPODA, CUVIER.

Order 1. Tetrabranchia.
Sub-Order 1. Nautiloidea.

„ 2. Ammonitoidea.
Order 2. Dibranchia.
Sub-Order 1. Decapoda.
Tribe 1. Oigopsida.
„ 2. Myopsida.
Sub-Order 2. Octopoda.
Tribe 1. Leioglossa.
„ 2. Trachyglossa.

Definition. — The Cephalopoda are perfectly symmetrical Mollusca,
in which the edges of the foot are transformed into circumoral
appendages completely surrounding the head, and the epipodium
is modified to form an exhalant muscular tube or funnel consisting
of two free or united lobes, situated behind the head at the opening
of the pallial cavity, and serving as a conduit for the water from
this cavity. In the nervous system all the typical ganglion-pairs
are concentrated in the head, and are applied to or contained in
the interior of a cartilaginous skeletal piece. The renal organs are
constituted by the glandular covering of the afferent branchial
vessels. The coelom communicates with the exterior either directly
or by the intermediary of the paired kidneys, and by a second pair
of ducts serving as gonaducts. The gonad is situated in the coelom
and is not continuous with the gonaducts. A portion of the
circumoral pedal crown is " hectocotylised," that is to say, modified
to form a copulatory organ in the male. The development is
characterised by the incomplete segmentation of the ovum.

I. GENERAL DESCRIPTION AND EXTERNAL CHARACTERS.

In comparing the Cephalopoda with other Mollusca, one finds
that the ventral surface is much abbreviated and the length of the

285

286

THE CEPHALOPODA

body reduced (Fig. 22, E). This is the result of the displacement of
the foot, whose lateral borders surround the head and are joined
together in front of the mouth. In consequence of this shortening
of the antero-posterior axis, the two extremities of the digestive

canal are closely approximated,
and the pallial cavity opens im-
mediately behind the head (Fig.
252, w, a).

The head is highly developed,

f1

but has hardly any other ap-
pendages than those formed by
the edges of the foot which

17V

OA,

Fio. 252.

Diagram of the structure of a Cephalopod,
as seen from the left side in its proper mor-
phological position, a, anus ; or, arms ; ce,
central nervous system, with eye ; coe,
coeloin ; /», funnel ; g, gill ; go, gonad ; h,
heart ; A;, kidney ; I, liver ; m, mouth ;
pa, mantle ; r.o, renal orifice ; r.p, reno-
pericardial orifice ; st, stomach.

Pio. 253.

Taoniiis suhmii, Lankester, ventral
aspect, e, pedunculated eye ; Ji, fin ; m,
mouth ; t, tentacular arm. (After Hoyle.)

embrace it. Certain Oigopsida, however, e.g. Taonius suhmii, Ray
Lankester (Fig. 253), and the embryos of an allied form known
as Grenadier's embryo (Fig. 119, D) and of Loligo pcili, 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, i, k; 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 Nautilus 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

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, d) : 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

FlO. 254.

Tremoctopus vdifer, 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

THE 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,

Fio. 255.

Male (upper) and female (lower) specimens of Nautilus pompiltus, as seen in the expanded
condition ; oral view, showing the disposition of the tentaculifcrous lobes and the differences
between the two sexes, a. the shell ; b, the outer ring-like expansion or annular lobe of the
circumoral mass of the foot, dorsally forming the hood ; c, the right ami 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) ;
«, the buccal cone, fringing the jaws with a series of minute papillae ; /, the tentacles of the
outer lobe, projecting from their sheaths ; g, the two most posterior tentacles, belonging to the
hood ; t, superior ophthalmic tentacle ; k, inferior ophthalmic tentacle ; I, eye ; w, paired
laminated organ on each side of the base of the inner inferior lobe of the female ; n, olfactory
lamellae upon the inner inferior lobe, in the female ; o, the funnel ; p, the sjuidix (in the male)
or hectocotylised portion of the left inner lobe of the foot, representing four modified tentacles :
g, theantispadix (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. 250). 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, II). 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 Hossia, 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
PihyiiclwteutUis. In some Oigopsida, such as Leachia, Channoteulhis,
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 Tremodopus (Fig. 254), the six dorsal arms in Histioteuthis,
and all eight arms in some species of Eledone, 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 Eledone and Cirrhoteuthis (Fig. 260). In some
cases, however, there are more than two rows, e.g. 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, 1),
whose contraction causes the sucker to adhere to the prey or to
the substratum. The surface of application of the sucker is

PIG. 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 Nieniiec.)

augmented by the action of radiating muscular fibres (Fig. 256, II),
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 Cheiroteuthis 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.

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 ; 1 19, D, fu), 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) q) 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-

Fro. 257.

Young embryo of Sepia offidnoiis,
viewed from the dorsal side, a, anus ;
e> eye ; /«, funnel ; gi, gill ; m, mouth ;
of, otocyst ; pa, mantle and shell ; vi,
vitellus ; 1, 2, 3, 4, 5, arms. (After
Kolliker.)

fi"

FIG. 258.

Grimalditeuthis richardi, ventral as-
pect, a, aims ; c, left eye ; fi', anterior
lin ; fi", posterior tin ; fu, funnel. (After
Joubin.)

ternal wall of the funnel is furnished with an epithelial outgrowth
of variable form, constituting a mucous gland called Muller'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 Spirula 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), etc., 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, 1) extends back to the initial chamber
of the shell, and ife enclosed in a calcareous tube or shell siphuncle
which perforates all the septa (Fig. 268, si). 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, e.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, i.s). In some
Nautiloidea, e.g. the dextral or sinistral Trochoceras, and in sundry
Ammonoidea, e.g. the sinistral Turrilites 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 Lituites, 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 faculties, 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. 2G8 and 270), and it is largely internal. In certain fossil
Dibranchia the nmltilocular 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
calcareous 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 OmmafostrepJies 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 Idiosepius 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 Cirrhoteuihis.

294

THE CEPHALOPODA

It follows that in all living Cephalopoda 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

PlO. 259.

L'Unopleryx cyprinoidcs, ventral as|>oct.
«, anus ; e, eye ; fl, tins ; /«•, funnel with
valve ; ol, olfactory organ or rliinophore ;
no, socket of the funnel ; te, tentacular
arms. (After Jonbin.)

Fiu. 200.

Cirrhotfuthi.i mcongensis, Hoyle (young speci-
men), ventral aspect. /, fin ; /it, funnel ; m,
mouth. (After Hoylfi.)

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, c; 259, .s0), the whole constituting the so-
called " resisting apparatus " of foreign authors. In certain Oigopsida
of the family Cranchiidae (CrancJtia, Lcachia) 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 Arnphitretus 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 Grimcdditeuthis and Symplecto-

THE CEPHALOPODA

295

teuthis 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, Ji). These organs always originate at the aboral

A

FIG. 261.

Two fossil Nautilitls, left-side view. A, OplihVioceras simplex, Barrande ; A', mouth of the
shell ; 11, J'tenocwas alatum, Barrande. f.s, foot (arms) sinus ; i.s, infundibular sinus. (After
Barrande.)

extremity of the mantle (Fig. 290, (4) ft) — 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 Taonius (Fig. 253) and OmmatostrepJies (Fig. 297), and they
may be duplicated, the two fins on each side lying close together,
as in Grimalditeuthis (Fig. 258,/,/') 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 Thysanoteuthis, 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. 2">9, 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
or even near the anterior end, as in Cirrko-
teuthis (Fig. 260).

Except in Nautilus (Fig. 270, /) 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, r, g). In some

FIG. 262.

Internal shells of Cephalopoda. A, shell of
Belemnotvuthis dupiniana (Neocoiuian). /?, shell
of Sepvt Orbignyana. C, shell of Spirulirostra
Bellardii (Miocene) ; the specimen is cut so as to
show in section the chambered shell and the
laminated " guard " deposited upon its surface ;
A shell of Spinila laevis. (After Lankester.)

Fio. 203.

The chitinous internal
shell, orgladius.of Loligo,
the anterior ]»rt upper-
most. (From 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 CEPHALOPODA 297

the Dibranchia, chromatopliores 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 mesddermic 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 cliiefly 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, Hisliopsis, Pteri/fjioteuthis, etc.,
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 Pterygioteuthix.

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.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 CEPHALOPODA

Loligo, Sepia, etc., 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 "

Fio. 264.

Cartilaginous skeleton of Cephalopoda. A , capito-pedal cartilage of Nautilus, ventral aspect.
«, ridge which supports the pedal portion* of the nerve-centre. M, 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 officimtlis. (From Lankester, after
Keferstein.)

mentioned above is formed by sub-epithelial cartilaginous projections
and depressions.

It has been shown that Lepitloteuthis, 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 arbore-scens
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 Ocythoe, 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. The 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, ft).

The buccal aperture, situated in the middle of the pedal
appendages (Fig. 260, w), is surrounded by a circular lip garnished

with papillae. Further-
more, in the decapodous
Dibranchia there is a
buccal membrane which
may be very extensive

Fio. '265.

Minute structure of the cartilage of Loligo.
a, simple, and b, dividing cells ; c, canaliculi ; d,
an empty cartilage capsule, with its pores ; e,
canaliculi in section. (From Lankester, after
Ftirbringer.)

Fio. 266.

Mandibles of Nautilus,
in situ, dorsal aspect.
l.m, lower or ventral
mandible ; u.m, upper or
dorsal mandible. (After
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, ?>m, dm). These mandibles have recurved insertion-plate*,
to which the large muscles forming the greater part of the mass of the
buccal bulb are nttached. In Nautilus the trenchant borders of the
mandibles are covered by a calcareous deposit (Fig. 266), and the
fossils known by the name of Rhynclwliths are nothing else than
the beaks of Tetrabranchia ; for instance, Rhyncholitlies hirundo is the
beak of Temnocheilas 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); Gonatits, 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

PIG. 267.

lladula of Cephalopoda. A, a single row of lingual teeth of Nautilus pompilius ; B, two rows
of lingual teeth of Sepia officincUis ; C, lingual teeth of Elcdone cirrhosa. (From Lankest»r
after Kefcrstein, 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
buccal 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, s.g) : 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 (Spirilla, Ommatostrephidae, Fig.
282, II, Onychoteuthis, Veranya, Gonatus, etc.). 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 theDibranchia 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, oe). 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, Eossia, 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 Spirula (in which genus

fun.

Fio. 268.

Spirula, a nearly median sagittal section, seen from the left side, a, anus ; or, arms ; o.f,
aboral fossa ; b.d, bile-duct ; c.c, cephalic cartilage ; c.g, cerebral ganglion ; d.m, dorsal man-
dible ; /.c, funnel collar ; fi, fin ; /it, funnel ; i.b, ink-bag ; li, lip ; liv, liver ; ma, mantle ; ma',
shell secreting part of the mantle ; oe, oesophagus ; o.g, optic ganglion ; ot, otocyst ; m.c,
pallial cavity; p.g, pedal (brachial) ganglion ; pn, "pancreas"; p.s, pyloric sac; ra, radula ;
s.g, salivary gland ; sh, shell ; si, shell siphuncle ; sji, last septum of the shell ; st, stomach ;
t, tentacular arm ; t.<l, pallial terminal disc; to, tongue ; v.m, ventral mandible; r.?i, visceral
nerve ; w.b, white body. (Alter Huxley and Pelseneer.)

the liver is partly contained in the last chamber 01 tne .shell, Fig.
268, liv), in Onychoteuthis, Ommatostrephes, Loligo, and the Octopoda,
with the exception of Argonaufo 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 Oc'topoda 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, pri). In the Octopoda these
follicles are situated only on the initial part of the hepatic 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
0. 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
up of a deeper part, or gland proper, the cavity
of which is septate, and a reservoir, into which
the glandular part opens by a very small «, ink-bag ; 6, its opening

•a i.i • • ii iiJ i J i1^0 the rectum ; c, com-

ormce : the reservoir specially well developed mencement of the caecum ;
in the Decapoda. This ink-sac occupies a some- ^Jj™} £^pSU£
what superficial position to the side of the v» the ' stomach opened

T r . , ~ . 7 ., . longitudinally ; x, probe

visceral mass. In some species of Sepiola it is passed through the pyio-
trilobed, two lateral accessory organs being SfciffiS) Lankester'
joined to it. It extends to the posterior ex-
tremity of the body in Sepia (Figs. 271, i.s -, 272, t\ and is buried
in the superficial part of the liver in all the Octopoda except
Argonauta. 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.
2. Circulatwy Apparatus. — The Cephalopoda, or at any rate the

Fia. 269.
Alimentary canal of

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

a b.v.

Fio. 270.

Diagram representing an approximately median sagittal section of a female Xnittilus
jtnmpiliu*. The parts which are quite black are the cut muscular surfaces of the foot and buccal
mass, o, the shell ; an, anus ; «.?>. t>, afferent branchial vessel ; b, the nuchal plate ; c, the integu-
ment covering the visceral hump; «•/•, crop; </, 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 ; /, the
pjillial chamber with two of the four gills ; g, the vertically cut median portion of the funnel ;
yizz, gizzard ; h. the capito-pedal cartilage ; t, the valve of the funnel ; int, intestine ; I, tlie
siphuncular pedicle (cut short) ; m, the hood or dorsal enlargement of the outer lobe of the foot ;
?i, tentacles of the outer lobe; n.e, nerve-collar; nept, aperture of the kidney ; ni, nidamental
gland ; oe, oesophagus ; p, tentacles of the inner inferior lobe ; tj, buccal membrane ; r, 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 I^ankester.)

contractile expansions of the efferent branchial vessels (Fig. 277, au).
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 Loligi, 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,

(fVZT.

FIG. 271.

Diagram representing an approximately median sagittal section of Sepia officimlis ; 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 ; 6, nuchal cartilage ; br.b,
branchial heart ; c, the integument covering the visceral hump ; cr, 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 ; /, the pallial chamber ; g,
the vertically cut median portion of the funnel ; gizz, the gizzard ; i, the valve of the funnel ;
i.s, ink-bag ; m, the two upper lobes (arms) of the foot ; n, the long prehensile arms ; n.c, the
nerve-collar; n.n.a, aperture of the left kidney; o, the fifth or lowermost lobe (arm) of the
foot ; p, the third arm ; q, buccal membrane ; re, renal glandular mass ; s, the lower jaw ; t, the
radula ; v, theupper.jaw ; vent, ventricle of the heart ; triac.jKT.ojwr*, viscero-pericardialai>erture;
x, the viscero-peri cardial 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.

306

THE CEPHALOPODA

277, v.c, p.v, ab.v). 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,
a.r\ 277, s.b) which forms the "spongy body" or essential part of
kidney (see below). Except in Nautilus, each afferent vessel is

v.lr

FIG. 272.

Ventral view of a male Sepia, obtained by cutting longitudinally the firm mantle-skirt, and
drawing the divided halves apart, a, aims ; Hr, the single pair of ctenidia ; c, cartilaginous
socket in the funnel, to receive c', the cartilaginous knob of the mantle-skirt, — the two con
stituting the " pallial hinge apparatus " ; C, the head ; gt the azygos genital papilla anu
aperture ; i, the valve of the funnel ; J, the funnel, which has been cut open ; m, retractor
muscle of the head and funnel ; 1\ the tins ; r, renal papillae ; R, the glandular tissue of the
left kidney, which has been cut open ; t, ink-bag ; r.br, branchial efferent vessel ; v.br', bulbous-
enlargements (auricles) of the branchial vessels. (From I^ankester, 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, c.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 (oxy haemocyanin). 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

Tip

a.r

ex

c.v

Fro. 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 ; c.b, branchial heart ; c.v, capsule of the branchial heart ; np, external aperture of
the right renal sac ; r.d.v.c, right descending branch of the vena cava ; r.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.b) 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

THE CEPHALOPODA

Tetrabranchia, has two pairs of branchiae (Fig. 276). All other
Cephalopoda 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, Er\ but in some Dibranchia
the two sides of the organ are somewhat unequal in size. A
branchia is composed of lamellae whose number varies in different
forms, being least in the Octopoda, in which the axial branchial cavity,
separating the two rows of lamellae, is excessively developed.
Each branchial lamella is thrown into transverse folds, which are
in turn folded, so that the respiratory surface is largely increased.

FIG. 274.

Diagram showing the relations of the four nephridial sacs, the viscero-pericardial sac, and
the heart and large vessels in Nautilus ; ventral view. a.b.v, advehent branchial vessel ; 0.0,
cephalic aorta ; e.v.b, efferent branchial vessel ; neph, the two left renal sacs, each with its
independent aperture; r.e, glandular enlarged walls of the advehent branchial vessels (two
small bodies in each renal sac ; and one large body on each of the four vessels, in the viscerp-
pericardial sac) ; v.c, vena cava ; vent, ventricle of the heart ; visc.per.apert, arrow introduced in
the left aperture of the viscero-pericardial sac ; x, viscero-pericardial sac (the dotted line indi-
cates its backward extension, vide Fig. 270, x). (After Lankester.)

The branchiae are not ciliated, as they are in other Mollusca, the
contractions of the muscular mantle sufficing to produce a current of
water sufficient for respiration. The rate of the respiratory move-
ments of the mantle is variable, and is generally quicker in the
Decapoda than in the Octopoda.

In Nautilus (Fig. 276) the branchiae are free throughout their
extent, but in the Dibranchia they are attached dorsally to the
mantle by their afferent borders (Fig. 272). A special glandular
organ, whose function is not exactly known, is situated along the
line of attachment : it receives the blood which, having circulated
through the nutrient vessels of the gill, has to pass through the
kidney along with the venous blood from the mantle, to be returned

THE CEPHALOPODA 309

thence into the respiratory vessels of the branchia for oxygenation
before it is finally carried to the heart.

3. Excretory Apparatus. — The coelom of the Cephalopoda is very
extensive. It comprises the gonocoele and the pericardial coelom ;
these cavities communicate freely with one another (Fig. 252, coe)
and are only separated by an incomplete septum, which is atrophied
in Sepia. In Nautilus this coelom extends into the aboral region of
the body and its genital division — which communicates with the
pericardial division by three orifices in the septum — passes into the
dorsal region and extends nearly as far forward as the middle of the

Fio. 275.

View of the ventral surface of a male Nautilus, the mantle-skirt being completely reflected
so as to show the inner wall of the sub-pallial Chamber and the four ctenidia and the foot cut
short, a, muscular band, passing from the funnel to the integument ; an, anus ; c, mantle-
skirt ; l.sp, aperture of the rudimentary left spermiduct ; neph.a, aperture of the left anterior
kidney ; neph.p, aperture of the right posterior kidney ; olf, protective papilla of the osphra-
dinm ; pe, penis ; visc.per, left aperture of the viscero-pericardial sac ; x, post-anal papilla.
(After Lankester.)

oesophagus (Fig. 270, x). But the pericardial coelom is a flattened
ventral cavity situated immediately beneath the body- wall : it contains
the heart with its four auricles (Fig. 274) and the pericardial glands
or portions of the follicular glandular appendages of the branchial
vessels. In the Dibranchia, the coelom of the Decapoda contains
the heart, the gonad, and the branchial hearts with their glandular
appendages (pericardial glands, Fig. 273, c.b, x), but it is so much
reduced in the Octopoda that it contains only the gonads and the
appendages of the branchial hearts, its anterior part having dis-
appeared (Fig. 278).

In the Decapoda the coelorn forms a vast pouch, with a
constriction between the posterior or genital division and the
anterior pericardial division, and it is produced into lateral annexes

THE CEPHALOPODA

for the lodgment of the branchial hearts (Fig. 273, c.v). In the
Octopoda the anterior division no longer exists ; the genital capsule
is connected with the capsules of the appendages of the branchial
hearts by long canals (Fig. 278, a.d), and even these are suppressed
in Philonexis and Argonauta.

In all Cephalopods each of the two divisions of the coelom is in
open communication with the exterior. In the Dibranchia this com-

C-""

an---'

Fio. 276.

View of the ventral surface of a female Nautilus, the mantle-skirt being completely reflected
«o as to show the inner wall of the sub-pallial chamber (compare with Sejriti, Fig. 'J72). «,
muscular band passing from the funnel to the integument; an, anus; b, valve of the funnel ;
c, the mantle-skirt retroverted ; g.n, nidamental gland ; lov, aperture of the rudimentary left
oviduct; neph.a, aperture of the left anterior kidney; neph.p, aperture of the left posterior
kidney; olf, protective papilla of the left osphradium ; r.ov, aperture of the right oviduct ;
visc.per, left aperture of the viscero-pericardial sac ; x, post-anal papilla. (After Lankester.)

munication is effected through the kidneys : there is a reno-peri-
cardial canal on either side which opens into the cavity of the kidney,
more or less close to its external orifice (Figs. 273, y ; 277,-r./)). But
in Nautilus the pericardium opens directly to the exterior by means
of two symmetrical orifices situated close to the posterior renal
apertures (Fig. 276, visc.per} ; these must be regarded as the orifices
of the reno-pericardial ducts which have migrated to the surface.
In the Octopoda, in which the pericardial division of the coelom

THE CEPHALOPODA 311

has disappeared, the anterior extremities of the capsules of the
branchial hearts communicate with the kidneys (Fig. 278, r.p).

The renal capsules are thin-walled and somewhat voluminous
sacs in all the Cephalopoda. In Nautilus they are four in number, are
ventral and superficial, and have no communication with one another
or, as has been explained, with the pericardium. Each of the four
capsules has its own simple slit- like orifice (Figs. 275 and 276,
neph.a, neph.p), and each contains a small portion of the glandular
appendages of the afferent branchial vessels, the appendages being
formed by ramifications of these same vessels, covered by an
excretory renal epithelium. The appendages situated on the other

v.n

A

ev

Heart, kidneys, and gills of Spirilla, ventral aspect. a.n, anterior aorta; ab.v, abdominal
vein; a.p, branchial heart-appendage; o.r, afferent branchial vessel; ou, heart-auricle; b.h,
branchial heart ; b.n, branchial nerve ; e.v, efferent branchial vessel ; g, gill ; g.a, genital artery ;
7, junction of the visceral nerves ; 7,-, kidneys : fc.o, kidneys opening ; p.a, pallial arteries ; p.v,
pallial vein ; r.p, reno-pericardial opening ; s.b, spongy renal glandular bodies ; v.c, vena cava ;
ven, heart- ventricle : v.n, visceral nerve. (After Huxley and Pelseneer.)

side of these vessels, in the pericardial coelom, are also excretory
organs, and constitute the pericardial glands.

In the Dibranchia there are two renal capsules, also ventral and
superficial ; these two kidneys are attached to one another in the
median line in the Octopoda, and they communicate to a greater or
less extent with one another in the Decapoda, with the exception of
Spirula (Fig. 277, k). In the majority of the Decapoda the renal sacs
extend as far as the lower surface of the shell, on the anterior or
physiologically dorsal side, and are traversed in this region by the
hepatic ducts. Each contains one of the two divisions of the vena
cava (Fig. 273, r.s.v.c, r.d.v.c) as well as the terminal part of the
abdominal vein. All these vascular trunks are covered by spongy
glandular appendages (Fig. 273, «.?•), whose structure is similar to
that of the corresponding parts of the renal organs of Nautilus; these
appendages constitute the secretory portion of the kidneys. The
external orifices of the renal sacs of the Dibranchia are situated

312 THE CEPHALOPODA

at their cephalic extremities ; they are symmetrically disposed on
either side of the rectum (Fig. 272, ?•), on the somatic wall of the
pallial cavity, and are more or less close to the pallial aperture,
being further from the aperture in Ommatostrephes (Oigopsida) than
in Sepia (Myopsida). In the Decapoda Myopsida the renal orifices
are situated on prominent papillae.

The excretory products of the Cephalopoda consist, in part at
least, of solid concretions, and do not contain uric acid, but chiefly
guanin.

The appendages of the branchial hearts of the Dibranchia (Fig.
273, x) correspond morphologically with the pericardial glands of
other Mollusca. The glandular investment of the branchial hearts

is also excretory, experi-
ment having shown that it
plays the same physiological
part as a pericardial gland.
4. Nervous System. — In
all the Cephalopoda the
essential parts of the
nervous system are cen-
tralised in the head, round
Pia 27g the initial part of the oeso-

, ' ' ' _. phagus (Fig. 271, n.c). In

Diagram of the coelom of a female Octopod, a.s seen *r ,., ,* /

from the ventral side. a.d, the so-called aquiferous AtautllVS the concentration

duct; a.p, appendage of the branchial heart; b.h, r fL nprVA /,pnfrpc io IPCC

branchial heart; ca, capsule of branchial heart; g.c, c ' «erve-

genital coelom (gonocoele); o, ovary; o.d, oviduct ; than in the Dibranchia, each
o.flr, oviducal gland ; o.o, oviducal orifice ; r.p, reno-

pericardial orince. (After Brock.) pair Of Centres With its COm-

rnissure being represented

by a ganglionic half-hoop. Of the three half-hoops forming the
central nervous system, one, the cerebral, is dorsal, and the two others
are continuous with it and ventral. The more anterior ventral half-
hoop is the pedal centre, the more posterior the visceral. The pedal
centre innervates the funnel and the circumoral appendages, the pedal
origin of these organs being demonstrated by this innervation in
the adult. In the female each of the two large nerves passing to
the interior ventral series of tentacles bears a large ganglion at the
point where it breaks up into branches to supply the supposed
olfactory or lamellar organ (Fig. 280, x, y). The visceral centre
gives off nerves to the mantle, the branchiae, and the viscera, the dis-
tribution of these nerves being analogous to that of the Dibranchia
described below. Finally, the dorsal or cerebral centre gives off nerves
to the eyes, the otocysts, the lips, etc. A labial commissure is also
present, arising by a double root (Fig. 279, VIII) from the cerebral
centre and passing below the sub-radular organ ; and as is the
case in the Polyplacophora, the Aspidobranchia, and the Scaphopoda,
the stomato-gastric commissure arises from the labial commissure in

THE CEPHALOPODA

313

all Cephalopods. In Nautilus the stomato-gastric commissure passes
under the pharynx immediately behind the radula and bears a
buccal ganglion (Fig. 279, VII) on either side.

In the Dibranchia the nerve-centres are much more completely
enclosed in the cartilaginous cephalic capsule than in Nautilus, and
consequently many nerves — notably the pallial nerve — traverse the
cephalic cartilage at their origin. The cerebral centres themselves
appear externally to be unpaired, and in the Decapoda they are
divided transversely into a small anterior (Fig. 282, III) and a
large posterior lobe, the latter being separated by some considerable
distance from the former in various Oigopsida, such as Ommato-
strephes (Fig. 282, IV), Spirula, etc., but the distance is less in Sepiola

II!

IV

VI
v/i i
VHI

Fio. 270.

Nautilus, central nervous system, left-side view. I, radula ; II, stomato-gastric commissure ;
III, cerebral ganglion, with the optic nerve in section ; IV, visceral ganglion ; V, oesophagus ;
VI, pedal ganglion; VII, stomato-gastric ganglion; VIII, root of the labial commissure; IX,
labial commissure ; X, " tongue " ; o, otocyst.

and Loligo, and is very small in Sepia. These two lobes are united
by a pair of slender connectives, which are sometimes fused together
for a certain distance. In the Octopoda, on the other hand, the
cerebral mass is apparently single, the two lobes above mentioned
being intimately fused together, and their limits are barely indicated
by a transverse furrow, behind which is the posterior lobe with six
longitudinal furrows on its surface. The cerebral centres of all the
Dibranchia give off a large optic nerve on either side, each nerve
expanding to form a very large ganglion, whose size is greater than
that of the whole mass of the cerebral centres. As in Nautilus, a
labial commissure is given off from the anterior part of the cerebral
centres (Fig. 279, IX), and the stomato-gastric commissure originates
from the labial commissure. Finally, the cerebro- pedal pair of
connectives issues from the anterior part of the cerebral mass ;
these connectives are simple in the Octopoda (Fig. 281), but in the

THE CEPHALOPODA

Decapoda there are two on each side, namely, the cerebro-pedal and
the cerebro-brachial. The ventral or sub-oesophageal nervous mass
is formed by the visceral and pedal centres : these are fairly closely
united together (as they are, for instance, in Helix), and are only
separated in the middle line to admit of the passage of an aortic
vessel which runs dorsad of the visceral and ventrad of the pedal
centres ; a similar arrangement occurs in sundry Gastropods.

The pedal ganglia are divided transversely into two distinct pairs,
the anterior or brachial and the posterior or pedal ganglia proper

olf.p.p

Fio. 280.

Diagram of the nervous system of a female Nautilus pompilius, ventral aspect, cer, cerebral
ganglion ; m, nerves to the mantle ; n.iiif.br, posterior branchial nerve ; n.olf, olfactory nerve
terminating under the olfactory papilla ; n.sup.br, anterior branchial nerve ; n.visc, genito-
branchial nerve, or chief visceral nerve ; n.x, nerve accompanying the vena cava, which lies
between this and the similar nerve of the right side ; olf.p.p, the right olfactory papilla; oj>t,
optic ganglion ; ov, the oviduct ; ped, pedal ganglion ; pi, pallial part of the visceral ganglionic
commissure ; x and y, ganglion-like enlargements on pedal nerves to the median lobe of the
inner circlet of the circumoral tentacular lobes. (After Ray Lankester and Bourne.)

(Fig. 282, XII, XIV). This division is most marked in the Oigopsida
(Ommatostrephes, Spirula, Fig. 268, p.g, etc.), but is less marked in
Sepia. In all the Decapoda the brachial centres are divided anteriorly
into ten large nerves which pass into the arms, and anastomose with
one another at their bases. These centres also have connectives
joining them to the anterior and the posterior cerebral lobes (Fig.
282). In the Octopoda the brachial and pedal centres are much
more closely approximated (Fig. 281), and the former naturally give
off only eight nerves to the eight arms. The brachial nerve-centres
extend, together with the arms which they innervate, round either
side of the oesophagus, >nd in the Octopoda they meet dorsally and

THE CEPHALOPODA

315

are united by a thin supra -oesophageal commissure in the adult.
The pedal centres proper supply nerves chiefly to the funnel, and
thus correspond to the dorsal moieties of the pedal cords of
Rhipidoglossa which innervate the epipodium ; but they also send
fibres to the brachial nerves, and therefore, in conjunction with
the brachial ganglia, control the locomotory functions.

The pleural centres lie on the sides of the posterior part of
the sub-oesophageal mass ; they are but little differentiated and
scarcely visible externally, and they give off the two great pallial
nerves (Fig. 281, pi). The visceral
centres are situated on the ventral
side of the mass, and give off the
large visceral nerves, which arise
separately in Spirula and the
Octopoda, but are more or less
fused at their origin in Ommato-
strephes, Sepia, etc. The pallial
or "stellate" ganglia (Fig. 281,
gang.stdl) are secondary centres
on the course of the pallial nerves,
and are situated on the internal
wall of the mantle near its an-
terior or dorsal border. These
ganglia are connected by a trans-
verse supra-oesophageal commis-
sure, which is slender and is
formed by the union of the two
nerves of the pallial siphon in
Spirula, is larger in sundry other
Oigopsida (Ommatostrephes, Ony-
choteuthis, Enoploteutliis, Gonatus,
Veranya, Thysanoteuthis), is re-
duced in Loliyo, and is absent in
the adult Sepiola. This commis-
sure, together with the two fused

G ... . Lateral view of the nervous centres and

nerves OI the pallial Siphon Ol nerves of the right side of Octopus vulgaris.

Spirula, represents the two primi-
tive pallial nerves, and is the

homologue Of the pallial COrds, nerve ; ped, pedal ganglion ; pi, pleural
., j i r -, , ganglion ; t'tsc, visceral ganglion. (After Lan-

united by a commissure dorsad kester.)

of the intestine, of Amphineura ;

whereas the large pallial nerves of the Dibranchia are neogenetic

structures, evoked by the great development of the mantle

borders, which are reflected over and finally enclose the shell,

and give rise to the fins, etc. In some cases the visceral nerves

are also united by a commissure in the form of a transverse

FIG. 281.

316 THE CEPHALOPODA

bend lying near the bifurcation of the vena cava on the dorsal side
of the rectum : this commissure may be seen in Spirula (Fig. 277,;),
Sepia, and Eledme, and in Ommatostrephes it bears a large ganglion,
known as the ganglion of the vena cava. In Ommatostrephes,
Eledone, etc., there is yet another secondary nerve -centre at the
origin of the brachial nerve.

The stomato-gastric system of the Dibranchia consists of a pair
of conjoined ganglia situated below the oesophagus and immediately
behind the buccal bulb (Fig. 282, XIII) ; these ganglia are united to
the cerebrals (the anterior lobe in the Decapoda) by the intermediary
of the labial commissure, as has been described above. They give
off nerves to the alimentary canal, these nerves extending as far
as the stomach, where they enter a large ganglion, an offshoot from
which anastomoses with the visceral nerve.

The structure of the nerve-centres of the Cephalopoda resembles
that of other Molluscs ; they consist of a thick and continuous
superficial layer of nerve ganglion cells beneath which is a fibrillar
reticulum formed by the terminations of the centripetal nerve fibres
and the prolongations of the superficial ganglion cells. These
fibrillar centres are united by fibrillar connectives — namely, the
cerebro-brachial, the cerebro-pleural, the pleuro-pedal, the pleuro-
visceral, and the pleuro-brachial — many of which are short and
covered over by the continuous layer of superficial ganglion cells.

The Cephalopoda are well provided with sensory organs, possess-
ing, in addition to the tactile structures, rhinophores, statocysts,
and well-developed eyes. The sense of touch is more particularly
localised in the arms of the Dibranchia and the tentacles of the
Tetrabranchia.

In all the Cephalopoda there is an olfactory organ situated near
and below the eye on each side of the head. In sundry Oigopsida,
such as Cheiroteuthis, Ctenopteryx (Fig. 259, ol\ it is a projection, some-
times pedunculated as in Cheiroteuthis and Doratopsis-, in Nautilus
it is a cavity hollowed out in a tubercle ; more generally it is a
simple fossa of greater or less depth, as is the case in Sepia and
the majority of the Dibranchia. The epithelium of this organ
contains numerous sensory cells, and the nerve supplying it arises
from the superior frontal lobe of the cerebral ganglion. This nerve
is at first bound up with and appears to branch off from the optic
nerve near a little tubercle situated on the latter, but it receives no
fibres from it.

In Nautilus the ciliated and lamellar pre-ocular and post-ocular
tentacles are apparently accessory olfactory organs ; the ciliated
interbranchial papilla of each side is placed on a sensorial area
innervated by the fibres of the two branchiae (Fig. 280, n.oif\
The post-anal papilla (Figs. 275, 276, x) is also ciliated, but is not
supplied by any special nerve. In the Dibranchia the branchial

THE CEPHALOPODA

317

ganglion of Eledone and Oiamatostrephes occupies a situation analo-
gous to that of the osphradial ganglion of Gastropoda and Lamelli-
branchia, but the epithelium overlying it is not sensory. It seems
probable that an osphradium is not required in the Dibranchia, in
consequence of the proximity of the olfactory fossa to the opening
of the pallial cavity.

The statocysts or otocysts are two in number, and are always
closed vesicles in adult Cephalopoda ; they are essentially organs of
equilibration. In Nautilus they are situated at the sides of the
pedal centres (Fig. 279, o), and are closely applied to the cephalic
cartilage. In the Dibranchia they are placed ventrally between
the pedal and visceral centres (Fig. 282, X), and are wholly embedded
in the cranial cartilage, being separated from one another only by
a thin partition. The cavity of each otocyst is continued, in the

FIG. 282.

Central nervous system and anterior part of the digestive tract of Ommatostreplics, left-side
vitiw. I, radula ; II, "anterior" salivary gland ; III, anterior buccal ganglia and commissure;
IV, cerebral ganglion ; V, section of the optic nerve; VI, oesophagus; VII, left pallial nerve;
VIII, "posterior" salivary gland; IX, visceral ganglion and nerve; X, seat of the otocysts ;
XI, infundibular nerve ; XII, pedal ganglion ; XIII, stomato-gastrie ganglion ; XIV, brachial
ganglion and beginning of the live left brachial nerves ; XV, labial commissure ; XVI,
"tongue" ; XVII, mouth.

Dibranchia, into a small canal which is buried in the cartilage in
the Decapoda but not in the Octopoda. This canal, known as
"Kolliker's canal," ends blindly, and is the remnant of the em-
bryonic connection of the otocyst with the exterior (Fig. 1 1 9, D, ot).
The internal wall of the otocysts of the Dibranchia is not simple,
but is raised into several well-marked ridges separated by furrows.
The sensory epithelium is localised at the anterior end of the organ,
and forms a macula acustica, and the essential part of the otocystic
nerve terminates in this macula and in a lateral ridge. The nerve
originates from the cerebral ganglion and traverses the pedal centre
obliquely. In Nautilus each otocyst contains numerous otoconia,
but in the Dibranchia there is a single otolith balanced on the
principal macula acustica : this otolith consists of an organic and a
calcareous moiety, except in Eledone, in which genus it is wholly
organic.

The eyes in all Cephalopoda are situated on the sides of the

3i8

THE CEPHALOPODA

head and are generally sessile. They are, however, pedunculated
in many embryos (Fig. 290, (8), (9)) and in the adult Ta&nius (Fig.
253, e) and other Cranchiidae, and also in some Amphitretus (Octopod).
The eye of Nautilus (Fig. 293, e) is an open vesicle with a minute
aperture (Fig. 6, A) : it is devoid of any kind of refractive apparatus,
and its internal retinal wall is pigmented throughout. In the
Dibranchia the cavity of the eye is closed, as it is in the majority
of Gastropoda, and the ocular globe consists of the same essential

J3C

Fio. 283.

Horizontal section of the eye of Septa, at, argentine integument ; C, external cornea ; ci,
ciliary body ; g.o, optic ganglion ; ik, cartilage of the " iris " ; k; Jf, capeular cartilage ; KK,
cephalic cartilage ; L, lens ; o, optic nerve ; 1', retinal pigment ; Re, l:i, external and infernal
layer of the retina ; IT, white body. (From Lankester, after Hensen.)

parts, viz. retina, cornea, and crystalline lens, with various accessory
parts added, making it a very complex and perfect organ of vision.
The ocular globe is applied to the cephal'c cartilage, is sometimes
contained in a more or less incomplete orbit formed by a wing-
shaped expansion of the cartilage (Sepia), and is provided with a very
large optic ganglion (Fig. 283, g.o). In the Dibranchia the retina
occupies the inner part of the ocular cavity, and the rods are turned
towards the light. The cornea is situated between the two segments
of the cuticular body forming the crystalline lens (Fig. 283, L) :
above the more superficial and smaller segment of the lens a fold of
the integument forms a contractile iris, with a circular (Oigopsida)

:i.

.: -:-

320 THE CEPHALOPODA

aperture of the shell are wider in the male than in the female.
The maximum of sexual dimorphism is found in Argonauta, in
which genus the males are much smaller than the females : the
latter may attain to fifteen times the length of the other sex, and
they have an external shell and the characteristic enlargement of
the dorsal arms (Fig. 301, IV), both of which features are absent in
the males. Generally speaking, the males are also distinguished by
the phenomenon of hectocotylisation, which consists in a curious
modification for copulatory purposes of a part of the pedal circum-
oral crown (see p. 323).

It has been shown that the majority of the Cephalopoda are
liyperpolygynous, that is to say, the males are less numerous than
the females : thus in some species of Loligo the males are to the
females as 15 : 100, in Octopus as 25 : 100, and in the six specimens
of Spirula hitherto examined only one was a male. Nautilus pom-
pilius, on the other hand, is hyperpolyandrous, but in N. macrompfialus
more females have been found than males. Again, in those Octopoda
in which the hectocotylus is autotomous, the males appear to be
more numerous, for as many as four hectocotyli have been found
in the pallial cavity of a single female.

The ovary or testis of the Cephalopoda is single and median ;
it is situated near the aboral extremity of the body in the coelom,
and is, in fact, nothing more than a projection from the wall of the
latter cavity (Fig. 252, gg). The gonaducts open into the coelomic
cavity, without being directly continuous with the gonad (Figs. 278,
o.d, and 286, V, II) ; they bear accessory glands on their course
(Figs. 284 and 286, I, VI, VII), and their external apertures are
on the somatic wall of the pallial cavity (Figs. 275, pe, l.sp; 276,
T.WJ l.ov). The male duct has no copulatory organs at its extremity,
but in the Dibranchia a single arm (or two arms in Spirula and
Idiosepion) and in Nautilus a part of the circumoral crown is modified
for the purpose of fertilisation : this modification is temporary and
periodic in the Dibranchia, permanent in Nautilus.

The females of nearly all the Oigopsida (Thysanoteuthidae,
Ommatostrephidae, Onychoteuthidae, Gonatidae, etc.), and of the
Octopoda with the exception of the Cirrhoteuthidae, are the only
members of the Cephalopoda that preserve the primitive number
of two functional and symmetrical gonaducts. In them the two
oviducts originate near the same point in the genital capsule of
the coelom (Fig. 278), and their external orifices are more deeply
(aborally) situated in the pallial cavity in those forms in whicli
the hectocotylus of the male is caducous. In Nautilus there ia
only a single functional gonaduct, situated on the right side, but
its left homologue is always present in the form of a rudimentary
duct known as the " pyriform appendage " (Lankester and Bourne),
which is provided with an external orifice (Fig. 284, Pyr) but has

THE CEPHALOPODA 321

no internal communication with the coelom. The artery of the
pyriform sac forms a symmetrical pair with that of the right
gonaduct, so that there can be no doubt as to the homology of the
former organ. On the other hand, all the male Dibranchia and
the females of Spirula, the Myopsida and the Cirrhoteuthidae, have
a single gonaduct, and this always on the left side (Fig. 272, g).

The ovaries and testes, as well as their ducts, are strictly com-
parable with one another from a morphological point of view, but
they differ somewhat in structural details. The ovary is simply
a portion of the wall of the coelom from which the ova originate.

-R.G.O

R.G.O

Fid. 284.

Diagrams of the male and female generative organs of the pearly Nautihis, to show the
relation of the rudimentary duct of the left side to the testis and ovary respectively, and of the
cardiac ventricle to the organs of both sides. Ventral aspect. Ac, accessory gland of the male
apparatus ; Alb, albuminiparous gland of the female apparatus ; Fo, foramen in the membrane
which attaches the pyriform appendage to the ventricle and to the testis or ovary (this foramen
places two portions of the viscero-pericardial sac in free communication with one another) ;
L.G.O, left genital orifice; N, Needham's sac in the male, in which' the spermatophores are
formed ; 0, ovary ; P, penis ; Pyr, Owen's pyriform appendage, attached by a membrane to the
ventricle of the heart, and also to the testis or ovary ; R.G.O, right genital orifice ; T, testis ;
V, cardiac ventricle, with its four branchial veins. (After Ray Lankester and Bourne.)

This region generally forms a conspicuous projection, into which the
coelomic epithelium is deeply invaginated in such a manner as to
constitute an ovarian cavity communicating with the genital coelom
by a narrow aperture. The ova that originate from the wall of
this ovarian cavity are no longer superficial cells of the wall itself,
but have emigrated below the ovarian epithelium, have grown in
size, and have come to project into the cavity of the ovary, carry-
ing the epithelium before them, in the same manner as the ova of
many Amphineura and of Pseudokellya. The ova which thus lie
beneath the true coelomic epithelium also become surrounded by
an interior follicle formed at the expense of the cells in their

21

322 THE CEPHALOPODA

neighbourhood. This follicle is nourished by an important vascular
supply, and its surface of contact with the ovum is increased by the
formation of equatorial and meridional folds (Fig. 285, fo) which
penetrate into the substance of the ovum and secrete the vitellus.
This vitellus forms an increasingly large part of the mass of the
ovum and pushes the formative protoplasm and
the nucleus up to its narrower pole opposite to
the peduncle of attachment.

When mature the ovum acquires a chorion
with a micropyle, escapes by dehiscence of its
external envelope into the coelomic cavity or
genital capsule (Figs. 252, coe; 278, g.c\ and
passes into the genital duct. In its passage
through the oviduct the egg traverses a more
FIG. 285. Qr jesg voluminous glandular enlargement of the

duct, situated on the wall of the genital capsule

HLSyVMd11pei'- itself in Nautilus> at the middle °f the duct in
aeneer.) a the Octopoda, near the free extremity of the duct

in the Decapoda. This glandular enlargement is
formed of two distinct portions in the Octopoda (Fig. 278, o.g) and is
feebly developed in Argonauta, whose eggs are protected by the
external shell. In addition to the true oviducal glands there are
other accessory glands, unrelated to the genital ducts, in female
Cephalopods. These are differentiations of the wall of the pallial
cavity, and occur 'on the pallial wall in Nautilus (Fig. 270, n), but
on the somatic wall in the Dibranchia. In the latter order they
form two distinct masses, one on either side of the rectum, whereas
in Nautilus they form a continuous mass (Fig. 276, g.n). In certain
Oigopsida (Enoploteuthis, Cranchia, Leachia) and in the Octopoda
these organs are absent. In the Dibranchia these " nidamentary "
glands open near the genital orifice, and are generally accompanied
by a second pair, as, for example, in Sepia: they produce the
external envelopes of the eggs, formed by an elastic substance which
hardens rapidly on contact with the water.

In the male, the testis is the specialised portion of the coelomic
wall from which the spermatozoa are developed (Fig. 286, III) : its
structure is comparable with that of the ovary. The spermatozoa,
when mature, pass through an orifice into the genital capsule
properly so called, and thence into the spermiduct which originates
from the wall of this capsule and opens externally into the pallial
cavity, on the right side in Nautilus (Fig. 275, pe), on the left side
in the Dibranchia (Fig. 286, VIII). Certain glandular pouches and
a terminal reservoir are found on the course of the spermiduct.
Nautilus has only one glandular pouch, but in the Dibranchia
there are, as a result of specialisation, two pouches: (1) the
ves^ula semiralis, which is a simple enlargement; (2) the prostate.

THE CEPHALOPODA

323

The terminal reservoir is knoAvn as Needham's sac or the spermato-
phore sac (Fig. 286, VII). Between the vesicula seminalis and the
prostate the spermiduct may exhibit a small tubule which opens
into the coelom (Sepia), and in exceptional -cases (Philonexis) the
deeper part of the spermiduct may be divided into two canals,
both of which open into the portion of the coelom containing the
testis.

The sperm lies free in the initial part of the spermiduct, but
when it reaches the first glandular pouch it begins to be surrounded
by a tube-shaped envelope or spermato-
phore. In the Dibranchia these tubes
are completed in the interior of the
prostate, and are then arranged parallel
to one another in the reservoir or
spermatophore sac. When mature they
are passed directly from the genital
duct into the funnel, the terminal
papilla of the spermiduct being ex-
tended for this purpose, and thus they
enter the hectocotylised arm. Each
spermatophore consists of an elastic
tube invaginated into itself ; the deeper
part of the invagination constitutes the
spermatic reservoir, and the more ex-
ternal part, forming the connective, is
greatly contracted and often coiled into
a spiral. When the ripe spermato-
phore is expelled the connective is
extended and evaginated, carrying in
its interior the reservoir which causes
it to burst: the reservoir in its turn
splits open and allows the spermatozoa
contained in it to escape. These struc-
tures, which are comparable to the

Fio. 286.

Male genital organs of Loligo, ven-
tral aspect. I, seminal vesicle ; 11,
spermiduct; III, testis; IV, genital
coelomic capsule ; V, origin of the
. spermiduct in the coelomic genital

Of Certain pulmonate capsule ;VI, spermatophore sac ; VII,
/7 11 „!! prostate ; VIII, genital orih'ce. (After

Gastropods, are generally rather small ; f,uvenioy.)
but they attain a length of eight centi-
metres in Ekdone, and in the Octopoda with an autotomous hecto-
cotylus, they are as much as fifty centimetres long when unrolled.
In Nautilus their structure is simpler : they have the form of coiled
tubes and are little more than thirty centimetres long.

The organ of copulation in Nautilus is the spadix, in the
Dibranchia the hectocotylised arm. The spadix of Nautilus is a
modified region — comparable with the hectocotylus — of the interior
ventral lateral lobe. The modification is persistent and involves
four tentacles, which are united to form a projection contained in a

324

THE CEPHALOPODA

common sheath and provided with a circular glandular area : the
eight remaining tentacles of the lobe are unaltered. The modifica-
tion usually affects the left side (Fig. 255, p), but it has also been
observed on the right. On the side opposite to the spadix the four
corresponding tentacles are isolated from the other eight and
constitute the so - called antispadix. In the Dibranchia the
hectocotylised arm of the Decapoda generally belongs to the las
pair, counting from the anterior or dorsal face, that is to say, the
fourth pair of true arms, but to the third pair in the Octopoda.
In the majority of the Oigopsida it is
the left fourth arm that is hectocotylised
(Onychoteuthidae, Ommatostrephidae), as
is the case in Loligo and Sepia ; in Rossia
and Sepiola the fourth left arm is hecto-
cotylised and the fourth right partially
so ; in Idiosepion and Spirula both arms
of the fourth pair are hectocotylised, and
in the last named they are contained in
a common envelope. In the Octopoda
the third left arm of Scaeurgus, the third
right arm of Octopus and Eledone, and
the second of the right side of Cirrhoteuthis
are hectocotylised. In Enoploteuthis,
Eledone, and Octopus the extremity of
the hectocotylised arm is modified and
assumes the shape of a spoon ; in Sepia
the base of the arm is affected, the
modification consisting in the disappear-
ance of the suckers ; in Idiosepion and
Rossia and Loliolus the suckers disappear
over nearly the whole length of the arm,
and in the two first named a longitudinal
membrane is developed along its exterior
aspect and abundant mucous glands along
its internal surface. In some Octopoda
the hectocotylised arm is still more pro-
view, h, the third arm of the right foundly modified, inasmuch as it is auto-
side, or hectocotylus ; i, funnel ; . mi • i • r i •

ft, ft, fl, t*, the tirst, second, third, tomous. Ihis peculiarity is found m
ofth^hectoco^ius^y'^heKnent ^ne Philonexidao and Argonautidae. In
!£3^tfi&r<E5 0cy*M and Tr^ctop^ the third right
Lankester, after G*genbaur.) 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

Fio. 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, a) 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

Fio.

Copulation.of Octopus. A, the female ; B, the male, fu, funnel of the female ; 3, third right
hectocotylised arm of the male. (After Racovitza.)

them in the neighbourhood of the oviducal orifice in Rossia 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.

326 THE CEPHALOPODA

III. EMBRYOLOGY.

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 Spimla (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, provided with an abundant yolk, of
certain Gastropoda (Fig. 10, B), and it has been shown that in the
archaic Dibranchia (the Oigopsid Cephalopod of Greriacher, Fig.
119, D, in) the quantity of yolk is less than
in the other members of the order, and that
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, &/),
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
Flo. 289. which it appears to be seated (Fig. 291).

Egg of Loiigo in the first The extent of the embryonic area and of
segmentation stage, w, the the free surface of the yolk are in inverse

four first blastomeres ; in, ,* i • n«

vitellus. (After Watase.) ratio to one another : the external vitelline
mass is smaller in Loiigo 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

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), r). 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, r).

The oesophagus and its annexes, viz. the radula, the salivary
glands, etc. (Fig. 290, (7), /, 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 (Argomuta,
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 paripassu with the mantle (Fig. 290, t\ 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), n), 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

328

THE CEPHALOPODA

(1)

(7)

FIG. 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, q\ 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

FIG. 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 ; ap, 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,

nbryo is

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) view of the anterior face of an older embryo. (9) view
of the posterior face of an embryo of the same age as (8). Letters in (3) to (9) :-- a, lateral fins ;

mouth ; ep, outer layer of the embryo ; /i, A /3, /*, /G, 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 ; I, sac of the radula ; m, stomach ; IMS,
mesoderm ; n, rudiments of the gills ; o, the otocysts ; p, optic ganglion ; q, distal portion of
the ridges which form the funnel ; r, vesicle-like rudiment of the intestine formed independ-
ently of the parts connected with the mouth ; *, rudiment of the salivary gland ; t, the closed
shell sac ; u, 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), o) ; .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, c) ;
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.

Fio. 261.

Km

tion of
left arms.

bryo of Sepia offlcinalit, on its vitellus, left-side view, an, anus ; br, gill ; i.lo.l, invagina-
' the lateral cerebral lobe ; na, fin ; pa, mantle ; vit, vitellus. I, II, III, IV, V, the five

IV. BIONOMICS 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

Fio. 292.

Diagrams of sections showing the early stage of development of the eye of Ldigo, 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

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
liossia 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. KEVIEW 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.

SUB-ORDER 1. MAUTILOIDEA.

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 emergiDg 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 Gomplwceras, Phraymoceras, 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 circumoral crown. The shell may attain to a length of two
metres (Endoceras).

FAMILY 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. FAMILY 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. Discosorus, Hall; Silurian. Huronia,
Stokes ; Silurian. Loxoceras, MacCoy ; from the Silurian to the Carbon-
iferous. FAMILY 3. ENDOCERATIDAE. 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. FAMILY 4. GOMPHOCERATIDAE. Shell globular, straight or
arcuate, the aperture contracted to the shape of a T. Genera — Gompho-
cera*, Sowerby ; Silurian. Phraymoceras, Sowerby ; Silurian. FAMILY 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. FAMILY 6. POTERIOCERATIDAE. 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. FAMILY 7. CYRTOCERATIDAE. Shell slightly curved ; the
aperture simple ; the siphuncle wide and the septa approximated. Genus
— Cyrtoceras, Goldfuss ; Devonian.
FAMILY 8. LITUITIDAE. Shell
coiled in one plane with the ter-
minal part uncoiled ; the aperture
contracted. Genera — Lituites, Bar-
rande ; Silurian. Ophidioceras,
Barrande ; Silurian (Fig. 261, A).
FAMILY 9. TROCHOCERATIDAE.
Shell helicoidally coiled; dextral
or sinistral ; the last whorl gener-
ally uncoiled. Genera — Trocho-
ceras, Barrande; Devonian.
Adelphoceras, Barrande ; Devonian.
FAMILY 10. NAUTILIDAE. Shell
coiled in one plane ; the aperture
wide and simple ; the siphuncle
central. Genera — Nautilus, Lin-

TUX,

FIG. 293.

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. Gyroceras, de
Koninck ; from the Silurian to

thp ParhrniifpT-mia HW/VMMVIA Nautilus macromphalus creeping on a horizon-

OaroomteroUS. Jlercoceras, tal surface, anterior view. a.o.t, anterior ophthal-

Barrande ; Silurian. Ptenoceras. mic tentacle ; e, eye ; ho, hood ; in, infuudibulum ;

TT T^ . /T,. -.„, -r^v pa, nuchal part of the mantle; p.o.t, posterior

Hyatt; Devonian (Fig. 261, B). ophthalmic tentacle ; sh, shell. (After Willey.)

Discites, MacCoy ; Carboniferous.

FAMILY 11. BACTRITIDAE. 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.

SUB-ORDER 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 THE CEPHALOPODA

the aperture, instead ot 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 Ainmonitoidea have a globular initial chamber which is
absent in Nautiloidea (though it may possibly be present but caducous or
not calcined 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, Stoliczkaia, 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 ol
the septa form simple undulations, those which point backwards being
known as "lobes," and those which point forward towards the aperture
as "saddles."

FAMILY 1. GONIATITIDAE. Shell nautiloid with simple sutures and a
ventral siphuncle. Genera — Goniatites, de Haan ; De/onian and Carbon-
iferous. Anarcestes, Mojsisovics ; Devonian. FAMILY 2. CLYMENIIDAE.
Shell nautiloid ; sutures simple ; the siphuncle dorsal, that is to say,
internal Genus — Clymenia, Minister ; from the Upper Devonian.

THE CEPHALOPODA 335

TRIBE 2. PROSIPHONATA.

The siphuncular necks project in front of the septa. The septa!
sutures present deeply indented lobes and saddles.

FAMILY 1. ARCESTIDAE. 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. Cydoldbus, Waagen ;
Permian. Arcestes, Mojsisovics ; Trias. Lobites, Mojsisovics; Trias.
FAMILY 2. TROPITIDAE. The shells globular, but differing from those of
the Arcestidae in having radiating and tuberculated costae. Genera —
Thalassoceras, Gemmellaro ; Permian. Tropites, Mojsisovics ; Trias.
Sibirites, Mojsisovics ; Trias. FAMILY 3. CERATITIDAE. Shells coiled,
with a large umbilicus ; the terminal chamber short ; sutures with
simple saddles. Genera — Trachyceras, Laube ; Upper Trias. Ceratites,
de Haan ; Trias. Dinarites, Mojsisovics ; Trias. Some genera with
helicoidal shells are related to these coiled forms, viz. Cochloceras,
Hauer ; Trias : also some straight forms, e.g. Wiabdoceras, Hauer ; Trias :
they have been placed in distinct families by some authors. FAMILY 4.
PINACOCERATIDAE. Shell compressed, smooth ; the terminal chamber
short ; the suture very complicated, convex. Genus — Pinacocerasy
Mojsisovics ; Trias. FAMILY 5. PHYLLOCERATIDAE. Shells coiled, the
whorls overlapping one another ; the suture formed of numerous lobes
and saddles. Genera — Phylloceras, Suess ; Jurassic. Bhacophyllites,
Zittel. FAMILY 6. LYTOCERATIDAE. 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. Turrilites, Lamarck ; coiled in a sinistral helicoidal spire ;
Cretaceous. Baculites, Lamarck; the adult straight and elliptic in
section ; Cretaceous. FAMILY 7. AMMONITIDAE. Shell coiled, with
narrow whorls which do not embrace one
another ; aperture simple ; a horny anapty-
chus present. Genera — Ammonites, Lamarck ;
Jurassic. Arietites, Waagen ; Jurassic. Aego-
ceras, Waagen, Lias. FAMILY 8. HARPOCERA-
TIDAE. Shell discoid and flattened, with a
carinated border ; the aperture provided with
lateral projections ; a calcareous aptychus,
formed of two pieces. Genera — Harpoceras, pIO> 294.

Waagen ; Jurassic. Oppelia, Waagen ; Jurassic. Morphoceraspseudoaruxps,right-
Lissoceras, Bayle ; Jurassic and Cretaceous, ^j^o^gtor.™.;
FAMILY 9. AMALTHEIDAE. Shell flattened, buccal orifice. (After Douviiie.)
with a prominent carina continued anteriorly

into a rostrum. Genera — Amaltheus, Montfort; Lias. Cardioceras,
Neumayr ; Jurassic. Schloenbachia, Neumayr ; Cretaceous. FAMILY 10.
STEPHANOCERATIDAE. Shell not carinated, but with radiating oostae,
which are often bifurcated ; aperture often provided with lateral pro-

336 THE CEPHALOPODA

jections which contract it ; aptychus formed of two pieces. Genera —
Stcphanoceras, Waagen ; Jurassic. Morphocerast Douvill^ ; 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, d'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, te). 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.

SUB-ORDER 1. DECAPODA.

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 eacli side of the head. These
tentacular arms are moio 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 Bactrites. In the living genera, with the
exception of Spirula, the shell is a chitinous gladius.

FAMILY 1. BELKMNOTEUTHIDAE, 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, Mqjsisovics ; Trias.
BelemnoteuthiSj Pearce ; Jurassic and Cretaceous (Fig. 262, A). Acantho-
teuthis, Wagner and Minister ; Jurassic. FAMILY 2. ADLACOCERATIDAE,
Fischer. An extinct family in which the shell is formed of a phragmocone

Fio. 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. Xiphoteuthis, Huxley ;
Lias. FAMILY 3. BELEMNITIDAE, 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 — Bekmnites, Lister ; 350 species
from the Jurassic and Cretaceous. Diploconus, Zittel ; Upper Jurassic.
FAMILY 4. BELOPTERIDAE. 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). FAMILY 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. FAMILY 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,
d'Orbigny ; fins aboral, simple, and rhom-

Fio. 296.

Doratopsis vermicularis (Riippel),
dorsal aspect. «, cerebral ganglia;
e, eye ; Jl, fin ; nu.c, nuchal cartilage ;
t, tentacular arm; 1, 2, 3, 4, pair of
arms. (After Weiss.)

Fio. 297.

Ommatostrephes gagittatus, Lamarck, dorsal
aspect. I, mantle ; II, tentacular arm ; III, fin ;
IV, eye ; V, arma. (After Verauy.)

boidal (Fig. 297) ; British. Ctenopteryx, Appellof ; fins pectinate, as long
as the body (Fig. 259). Hathyteuthis, Hoyle ; fins terminal, rudimentary ;
tentacular arms filiform ; abyssal. Rhynchoteuthis, Chun ; tentacular arms
united to form a beak-shaped appendage. Symplectoteuthis, Pfeiffer. Trachelo-
teuthis, Steenstrup. Dosidicus, Steenstrup. Architeuthis, Steenstrup ; this is
the giant genus among the Cephalopoda. FAMILY 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. FAMILY 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. Enoplo-
teuthis, d'Orbigny ; tentacular arms well developed ; hook-bearing suckers

Fio. 298.

Decapod Cephalopoda. A, Cheiroteuthis Veranyi, dorsal aspect; B, Thysanote-uthis rhombus,
dorsal aspect ; C, Leachia q/clura, ventral aspect. (From Lankester, after Verany, Troschel,
Ferussac, 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. Lepidoteiithis, Joubin. FAMILY 9. GONA-
TIDAE, Hoyle. Body elongated ; fins terminal. Radula with only two
lateral teeth. Genus — Gonatus, Gray. FAMILY 10. CHEIROTEUTHIDAE,
Gray. Tentacular arms long and not retractile. Body elongated ; fins
large and rounded. Resisting apparatus well developed. Genera —

340 THE CEPHALOPODA

Cheiroteuthist d'Orbigny ; with suckers along the whole length of the
peduncle of the tentacular arms (Fig. 298, A). Doratopsis, Rochebrune ;
body much elongated, ending in a 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.
HistiopsiSj 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). FAMILY 11. CRANCHIIDAE, 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, Lesuenr ; 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. MYOPSIDA.

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 phraginocone, and
is calcified (Sepiidae) or simply chitinous. The Myopsida are more
littoral in habit than the Oigopsida.

Fio. 298"*.

Sepia officinalis, swimming, light -side view, a, arms; ft,, fins; /«, funnel. (After
Merculiano.)

FAMILY 1. SEPIIDAE, d'Orbigny. Body wide and flattened ; fins
narrow and extending the whole length of the body (Fig. 298*"*). Shell
calcareous 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. FAMILY 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 — Sepiola, Leach ; head
united to the mantle in the anterior (dorsal) region ; a fossorml British
genus. Rossia, Gray ; head not united to the mantle ; British.

THE CEPHALOPODA

34i

Stoloteuthis, Verrill, and Inioteuthis, Verrill, have no internal shell.
Heteroteuthis, Gray. Euprymna, Steenstrup. FAMILY 3. IDIOSEPIIDAE.
Steenstrup. Body elongated, with rudimentary terminal fins. Internal
shell almost lost. Genus — Idiosepius, Steenstrup. ; this tiny Cephalopod
is only Ij centimetre long, and has a mucous pore at the aboral

Fio. 299.

Sepia riffldnalis, dorsal view of a dead specimen, with the short arms spread out and the long
arms pulled out of their sacs, o, neck ; 6, lateral tins ; c, 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. FAMILY 4.
SEPIADARIIDAE, Steenstrup. Body short ; the mantle fused to the head
anteriorly (dorsally). No shell. Genera — Sepiadarium, Steenstrup ; tins
short, situated at the aboral extremity of the body ; from the Pacific Ocean.
Sepioloidea, d'Orbigny ; fins nearly as long as the body ; Australian. FAMILY
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 Hay den, from the Cretaceous,
are distinguished by their broader gladius. Plesioteuthis, Wagner, from
the Jurassic and Cretaceous, has a long and narrow gladius.

FIG. 800.

Opisthoteuthis deprcssa, Ijima and Ikeda, dorsal aspect. art arms ; e. eye ; fi. fin ; /u, funnel.
(After Ijima and Ikeda.)

SUB-ORDER 2. OCTOPODA.

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 CIRRHOTEUTHIDAE, Keferstein. Arms united by a mem-
brane, and bearing tentacular filaments on either side of the suckers
(Fig. 260). Genera — Cirrhoteuthis, Eschricht ; the pallial sac prominent
and the fins large ; a pelagic form. Opisthoteuthis, Verrill ; body
flattened, with small fins ; a deep-sea form (Fig. 300). Vampyroteuthist
Chun ; four fins. Some fossil Octopoda bearing fins are known ; e.g.
Woodward, from the Cretaceous.

THE CEPHALOPODA 343

TRIBE 2. TRACHYGLOSSA.

These are Octopoda with a radula and without true fins.

FAMILY 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. FAMILY 2. ALLOPOSIDAE, 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.
OCTOPODIDAE, d'Orbigny. Arms long and equal, without a true inter-
brachial membrane. The hectocotylus is not caducous. No cephalic

Fio. 301.

Argonauio. 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. Scaeurgus, Troschel. Pinnoctopus, d'Orbigny. Cistopus,
Gray. Japetella, Hoyle. FAMILY 4. PHILONEXIDAE, d'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 — TremoctopVA, Delle Chiaje ; the two
dorsal pair of arms are united by a membrane. Ocythoe, Rafinesque ;
without an interbrachial membrane (Fig. 287). FAMILY 5. ARQO-
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 LITERATURE OF THE CEPHALOPODA

LITERATURE OF THE CEPHALOPODA.

A . Tetrdbranchia .
(a) Living.

1. Dean. Notes on Living Nautilus. Amer. Natur. xxxv. 1901.

2. Griffin. The Anatomy of Nautilus pompilius. Mem. Nat. Acad. Sci.

Washington, viii. 1900.

3. Haller. Beitrage zur Kenntniss der Morphologic von Nautilus pompilius.

Denkschr. Med. Nat. Gesellsch. Jena, viii. 1895.

4. Huxley. On some Points in the Anatomy of Nautilus pompilius. Journ.

Linn. Soc. London, iii. 1858.

5. Joubin. Recherches sur 1'appareil respiratoire des Nautiles. Revue Biol.

Nord. ii. 1890.

6. Keferstein. Beitrage zur Anatomie des Nautilus pompilius. Gotting.

Nachrichten, 1865.

7. Kerr. On some Points in the Anatomy of Nautilus pompilius. Proc. Zool.

Soc. London, 1895.

8. Lankester and Bourne. On the Existence of Spengel's Olfactory Organ and

of Paired Genital Ducts in the Pearly Nautilus. Quart. Journ. Micr. Sci.
xziii. 1883.

9. MacDonald. On the Anatomy of Nautilus umbilicatus, compared with that

of Nautilus pompilius. Phil. Trans. 1855.

10. Owen. Memoir on the Pearly Nautilus (Nautilus pompilius), with illustra-

tions of its external form and internal structure. London, 1832.

11. Valenciennes. Nouvelles recherches sur le Nautile llamb£. Archives du

Museum, Paris, ii. 1841.

12. Van der Hoeven. Contributions to the Knowledge of the Animal of Nautilus

pompilius. Trans. Zool. Soc. London, iv. 1850.

13. Bydraagen tot de ontleedkundige Kennis aangaande Nautilus pom-
pilius. Verhandel. k. Akad. Amsterdam, iii. 1856 (translated in Ann.
Mag. Nat. Hist. (2), xix. 1857).

14. Vayssiere. Etude sur 1'organisation du Nautile. Ann. d. Sci. Nat. Zool.

(8), ii. 1896.

15. Vrolik. Lettre sur quelques points de 1'organisation de 1'animal du Nautile

flambi'. Mem. Soc. Linn. Normandie, x. 1855.

16. Willey. Contribution to the Natural History of the Pearly Nautilus. A.

Willey's Zoological Results, part vi. 1902.

(b) Fossil.

17. Branco. Beitrage zur Entwicklungsgeschichte der fossiler Cephalopoden.

Palaeontographica, 1879, 1880.

18. Foord. Catalogue of Fossil Cephalopoda in the British Museum, Part I.

1888 ; Part II. 1892 ; Part III. 1897 (by Foord and Crick).

19. Hyatt. The Fossil Cephalopods of the Museum of Comparative Zoology.

Bull! Mus. Comp. Zool. Cambridge, i. 1868.

20. Genera of Fossil Cephalopods. Proc. Boston Soc. Nat. Hist. xxii. 1884.

LITERATURE OF THE CEPHALOPODA 345

B. Dibranchia.

1. Appellof. Die Schale von Sepia, Spirula und Nautilus. K. Svensk. Vet.-

Akad. Handl. xxv. 1894.

2. Bert. Memoire sur la physiologic de la Seiche. Mem. Soc. Sci. Phys. et

Nat. Bordeaux, v. 1867.

3. Bobretzky. Observations sur le developpement des Cephalopodes (in Russian

language). Bull. Soc. imp. Amis. d. Sci. nat. et Ethnogr. Moscow, 1877.

4. Bourquelot. Recherches sur les phenomenes de la digestion chez les

Mollusques Cephalopodes. Arch, de Zool. Expe>. (2), iii. 1884.

5. Brock. Versuch einer Phylogenie der Dibranchiaten Cephalopoden.

Morph. Jahrb. vi. 1880.

6. Ueber die Geschlechtsapparat der Cephalopoden. Zeitschr. f. wiss.

Zool. xxxii. and xxxvi. 1879, 1882.

7. Brooks. The Development of the Squid (Loligo Pealii, Lesueur). Annivers.

Mem. Boston Soc. Nat. Hist. 1880.

8. Chtron. Recherches pour servir a 1'histoire du systeme nerveux des

Cephalopodes Dibranches. Ann. d. Sci. nat. Zool. (5), v. 1866.

9. Delage. Sur une fonction nouvelle des otocystes comme organes d'orienta-

tion locomotrice. Arch, de Zool. Exper. (2), vi. 1887.

10. d'Orbigny and Ftrussac. Histoire naturelle, ge"nerale et particuliere, des

Cephalopodes acetabuliferes, vivants et fossiles. Paris, 1835-1848.

11. Faussck. Untersuchungen iiber die Entwicklung der Cephalopoden. Mitth.

Zool. Stat. Neapel, xiv. 1900.

12. Frtdtricq. Sur 1'organisation et la physiologic du Poulpe. Bull. Acad.

Belg. (2), xlvi. 1878.

13. Oirod. Recherches sur la poche du noir des Cephalopodes. Arch de Zool.

Exper. (1), x. 1882.

14. Goodrich. Report on a Collection of Cephalopoda from the Calcutta Museum.

Trans. Linn. Soc. (2), vii. 1896.

15. Grenacher. Zur Entwickelung der Cephalopoden. Zeitschr. f. wiss. Zool.

xxiv. 1874.

16. Grobben. Morphologische Studien iiber den Harn und Geschlechtsapparat

sowie die Leibeshb'hle der Cephalopoden. Arb. Zool. Inst. Wien, v.
1882.

17. Hancock. On certain Points in the Anatomy and Physiology of the

Dibranchiate Cephalopoda. Nat. Hist. Review, 1861.

18. On the Nervous System of Ommatostrephes todarus. Ann. Mag. Nat.

Hist. (2), x. 1852.

19. Harris. Die Statocysten der Cephalopoden. Zool. Jahrb. (Anat. und

Ontog.) xviii. 1903.

20. Hoyle. Report on the Cephalopoda collected by H.M.S. "Challenger"

during the years 1873-76. Zool. Chall. Exped. part xliv. 1886.

21. Huxley. On the structure of the Belemnitidae. Mem. Geol. Surv. Unit.

Kingd. Monogr. ii. 1864.

22. Huxley and Pclseneer. Report on the Specimen of the Genus Spirula. Zool.

Chall. Exped. part Ixxxiii. 1895.

23. Ijima and Ikeda. Description of Opisthoteuthis depressa, n. sp. Journ. Coll.

of Sci. Tokyo, viii. 1895.

24. Jatta. I Cefalopodi viventi nel golfo di Napoli. Fauna und Flora des

golfes von Neapel, xxiii. 1896.

346 LITERATURE OF THE CEPHALOPODA

25. JouUn. Structure et developpement de la branchie de quelques Cephalopodes

dcs Cotes de France. Arch, de Zool. Exper. (2), iii. 1885.

26. Recherches sur la coloration du tegument chez les Cephalopodes. Ibid.

(2), x. 1892.

27. Recherches sur 1'appareil lumineux d'un Cephalopode (Histioteuthis

nuppellii). Bull. Soc. Sci. et Med. Quest. Rennes, ii. and iii. 1893, 1894.

28. Contribution a 1'etude des Cephalopodes de 1'Atlantique Nord ; and

Cephalopodes provenant des campagnes de la Princesse- Alice. Re"sultats
Camp. Sci. Albert lcr de Monaco, ix. (1895), xvii. (1900).

29. Kblliker. Entwickelungsgeschichte der Cephalopoden. Zurich, 1844.

30. Korschdt. lieitrage zur Entwickelungsgeschichte der Cephalopoden.

Festschr. fur R. Leuckart, 1892.

31. Milne-Edwards and Valenciennes. Observations sur la circulation chez les

Mollusques. Mem. Acad. Sci. Paris, xx. 1840.

32. Pclsenecr. Sur la valeur morphologique des bras et la composition du

systeme nerveux des Cephalopodes. Arch, de Biol. viii. 1888.

33. Phisalix. Recherches physiologiques sur les Chromatophores des Cephalopodes,

etc. Arch. Phys. Paris (5), iv. vi. 1892, 1894.

34. Racovitza. Mceurs et reproduction de la Ilossia macrosoma. Arch, de Zool.

Expe>. (3), ii. 1894.

35. Risso. Les Cephalopodes du parage mediterraneen du Comte" de Nice.

Nice, 1854.

36. Solger. Zur Kenntniss der Chromatophoren der Cephalopoden und ihre

Adnexa. Arch. f. Mikr. Anat. liii. 1898.

37. Uexkiill, von. Physiologische Untersuchungen iiber Eledone moscJiata.

Zeitschr. f. Biol. xxviii. xxx. xxxi. 1892-95.

38. Verany. Cephalopodes mediterraneens. Genes, 1851.

39. Verany and Vogt. Memoire sur les hectocotyles et les males de quelques

Cephalopodes. Ann. des Sci. nat. Zool. (3), xvii. 1852.

40. Verrill. The Cephalopods of the North-East Coast of America, I. and II.

Trans. Connect. Acad. v. 1880-81.

41. Vialleton. Recherches sur les premieres phases du developpement de la

Seiche. Ann. des Sci. nat. Zool. (7), vi. 1888.

42. Vigelius. Ueber das Excretionssystem der Cephalopoden. Nied. Arch. f.

Zool. v. 1880.

43. IVatasc. Observations on the Development of Cephalopods. Stud. Biol.

Lab. Johns Hopkins Univ. iv. 1888.

44. 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

Allopagus, 266

Anoploplwra, 267

Abralia, 339

Alloposus, 343

^Mostoma, 188

Acanlhoceras, 336

AUorisma, 276

Antalis, 204

A canthochiton, 53

A media, 187

Anthracoptera, 262

Acanthodoris, 177

Amaltheus, 335

Anthracosia, 267

Acanthopleura, 54

vl?n.a?tra, 156

Antipleura, 256

Acantlwteuthis, 337

Amberleya, 150

Antispadix, 324

Acavus, 187

Amboni/c/n'a, 262

Aplacophora, 51

Acephala, 205

A mien la, 53

J/>fem, 186

Accra, 169

J mmon iceras, 153

Aplodon, 268

Achatina, 188

Ammonites, 335

Aplustrum, 169

Acicula, 152

Ammonitoidea, 333

Aplysia, 171

Acila, 255

Amphibola, 184

Aplysiella, 171

Aclis, 158

Ampkibulimuj, 188

Aplysiomorpha, 171

ylcmaeo, 145

Amphimenia, 60

Aptychus, 334

Actaeon, 168

Amphineura, 40

Aptyxiella, 154

Actaeondla, 168

Amphipeplea, 185

/Irca, 258

/Ictoeofita, 181

Amphisphyra, 168

Arcacea, 258

Actaeonina, 168

Arnphitretus, 343

Arcestes, 335

Actinoceras, 332

Ampullaria, 152

Archidoris, 178

Actinodesina, 261

Amussium, 262

Architeuthis, 338

Aculifera, 40

Anadara, 258

Arcicardium, 271

yirfacno, 271

Anadenus, 187

Arcomya, 276

-4fforwarca, 258

Anal glands, 8, 96, 200

Arconaia, 268

Addisonia, 122

Anarcestes, 334

Argina, 258

Adductores, 210

Anatina, 275

Argonauta, 343

Adelactaeon, 168

Anatinacea, 275

Arietites, 335

Adelphoceras, 333

Ancillaria, 165

Ariolimox, 187

Adeorbis, 153

A ncistromesus, 145

yJrioTt, 187

Adesmacea, 274

Ancistroteuthis, 339

Ariophanta, 186

Aegirus, 177

Ancula, 178

Arm, 289

Aegoceras, 335

Anculotus, 154

Arnatidia, 272

./lerope, 189

Ancylodoris, 178

Articulamentum, 42

Aesthetes, 50

Ancylus, 186

Asaphis, 273

Aetheria, 268

Androgyna, 166

Ascoceras, 333

Agadina, 140

Aneitea, 189

A tipergillum, 277

Agaronia, 121, 165

Aneitella, 189

Aspidobrauchia, 144

Aglossa, 158

Anisocardia, 264

Assiminea, 153

Agnatlia, 188

Anisorayaria, 211

Astarte, 264

Agrinlimax, 187

Anisopleura, 66

Asthenothaerus, 275

-1/ario, 155

Anodonta, 268

Astralium, 150

Alderia, 181

Anomalodesrnacea, 254

Asymmetry, 76, 111

<4Wwrt, 178

Anomia, 257

Atlanta, 163

^fearfo, 184

Anomiacea, 257

.Ifopos, 189

347

348

INDEX

AtractUcs, 337

Bullina, 168

Ceromya, 276

Atrina, 264

Bidlinulo, 168

Cetoconcha, 278

Atys, 168

Bullomorpha, 167

Chaetodertna, 63

Aucella, 262

Byssocardium, 271

Chaetodermomorpha, 61

Aulacoctras, 337

Byssonychia, 262

Chaetopleura, 53

Awicula, 184

Byssus, 216

C/w7na, 271

Arellano, 168

Bythoceras, 154

Chamacea, 271

Avicula, 260

Chamostrea, 276

Xt»tCM&>ptntta, 264

Owttino, 178

Chaunoteuthis, 339

^Ixintw, 265

CO^M/IW, 204

Cheiroteuthis, 340

^zeca, 188

Caecilianella, 188

Chdinodura, 169

Caecum, 155

Chenopiis, 155

Babinka, 261

CallistochUon, 53

Chilina, 185

Bactrites, 333

CaUiteuthis, 340

CTuYcm, 54

Baculites, 335

CaUocardia, 265

Chitonellus, 54

Baikalia, 153

Callochtton, 53

ChlamydoconcJta, 266

Bakewellia, 259

CO/TTUI, 179

Chlamydophorus, 189

JSa/ea, 188

Calyptraea, 155

CMamys, 262

Baltoceras, 332

Campaspe, 176

Chlorites, 187

Barbatia, 258

Camptonectes, 262

Choanowphalus, 185

Barnea, 275

Camptonyx, 184

Choneplax, 54

BartUtia, 268

Cancellaria, 165

Choristes, 153

Basilissa, 149

Canidia, 164

Chroniatophora, 297

Basommatophora, 184

Cantantostoma, 147

Chromodoris, 178

Bathanalia, 154

Caprina, 272

Chrysodomiis, 164

Bathyarca, 258

Caprinula, 272

C%<ra, 154

Bathydvris, 122

Caprotina, 272

Ciliated discs, 226

Bothy sciadium, 145

(%>*», 268

Cinulia, 168

Bathyteuthis, 338

Captacula, 199

Cionella, 188

Batissa, 266

Capulus, 155

Circe, 270

Bayanoteuthis, 337

Carbonaria, 258

Chrhobranchia,'197

.Bayka, 272

Cardiacea, 270

Cirrhoteuthis, 342

Jte/a, 166

Cardtiia, .270

Cistopus, 343

Belemnites, 337

Cardinal teeth, 213, 214

Cladohepatica, 178

Belemnoteuthis, £37

Cardinia, 267

Clanculus, 149

Bcllcrophon, 147

Cardioceras, 335

Clausilia, 188

Bdoptera, 337

Cardiola, 256

Clavagdla, 277

Belosepia, 340

Cardiolaria, 256

Clavatula, 166

Beloteuthis, 342

Cardiomorpha, 256

Clavella, 164

Berendtia, 188

Cardiopoda, 163

Clidiophora, 276

Berthella, 174

Cardita, 264

C7io, 170

Bifora, 207

Cardtidla, 264

CTwme, 173

Biradiolitcs, 272

Carditopsis, 264

Clionopsis, 173

Bithynella, 154

Cardium, 271

Clionychia, 262

Bithynia, 154

Carinaria, 163

Cloacal chamber, 229

Bittium, 154

Carolia, 257

Clymenia, 334

Bivalvia, 213

Carydiium, 184

Cnidosacs, 96

Blauneria, 184

Cassianella, 261

Cocculina, 149

Boreochiton, 53

Cassidaria, 157

Cochlides, 42

B&rnella, 176

CassidijUa, 184

Cochlidepis, 33

Bourcicria, 150

Ca*««, 157

Cochloceras, 335

Brachytreina, 152

Castalia, 268

Cochlodesma, 275

Branchial hearts, 306

Cavolinia, 170

Cochlostyla, 188

Brtchites, 277

Cfewia, 181

Coelodon, 276

Buccinum, 164

Cephalopoda, 284

Coelomoduct, 13

Buliminu*, 188

Cerata, 86

Coelomopore, 13

Bulimulus, 188

Ceratisolen, 274

Colobocephalus, 169

Bulimus, 187

Ceratites, 335

Colpodaspis, 169

Bulimis, 185

Centhidea, 104

Columbtlla, 165

^»t//a, 169

Cerithiopsis, 154

Columbellaria, 157

jBuHia, 164

Cerithium. IRA

Columbellina, 157

INDEX

349

Columellar, 84

Cfym&a, 165

Dom, 178

Cominella, 164

Cymbulia, 170

Dosidicus, 338

Commissure, 16

Cymbuliopsis, 170

Dosinia, 270

Conchifera, 205

Cynodonta, 164

Z)o<o, 179

Concholepas, 165

Oypraea, 157

Dreissensia, 264

Conchyoline, 3

Cypricardia, 264

Z)rtftta, 120

Condyloc&rdia, 264

Cypricardites, 258

Z>ttrya, 267

Connective, 16

Cyprina, 264

Conocardium, 261

CYyrena, 266

Conus, 166

Cyrendla, 265

Eastonia, 270

Coralliophaga, 264

Oyrtoceras, 333

Echinomenia, 60

Coralliophila, 165

Cyrtodaria, 274

^grZma, 158

Corambe, 178

Cyrtodonta, 258

Elasmognatha, 189

Corbicula, 266

Cyrtolites, 147

Eledone, 343

Corits, 265

Cyrtopinna, 264

Elenchus, 149

Corftwta, 273

Eleutherorhabda, 253

Corbulomya, 273

Dacrydium, 259

Eligmus, 263

Cosmoceras, 336

Daondla, 261

AYma, 273

Cranchia, 340

Daudebardia, 189

y^ysta, 181

Crassatella, 264

Decapoda, 336

Elysiomorpha, 181

Cremnoconchus, 152

Dejanira, 150

EmarginiUa, 149

Crenatula, 259

Ddphinula, 150

Embletonia, 179

Crendla, 259

Dendronotus, 175

Endoceras, 332

Crepidula, 155

Dentalium, 204

Endodonta, 188

Crimora, 177

Dennatobranchus, 181

Eudogastric, 77

Crioceras, 336

Dermatocera, 152

Enoplochiton, 54

Crossed, 158

Dermatomya, 278

Enoploteuthis, 339

Crucibulum, 155

Desmopterits, 170

A'rww, 274

Oryptochiton, 53

Detorsion, 77

EntcUina, 204

Cryptoconchus, 53

Dexiobranchaea, 173

Enteroxenos, 160

Cryptodon, 265

Dialineury, 142

Entocdax, 159

Cryptomya, 273

Diartema, 155

Entoconclut, 159

Oryptophthalmus, 169

Diauly, 126

Entodesma, 277

Cryptoplax, 54

Dibranchia, 336

Entosiphon, 158

Crystalline style, 94, 220

Diceras, 271

Entomlva, 266

Ctenidium, 11

J)icerocardium, 267

Eolidomorpha, 178

Ctenodonta, 256

Dimya, 262

AJ^ts, 179

Ctenopteryx, 338

Dimyacea, 262

Eoplacophora, 53

Cucullaea, 258

Dinarites, 335

Eotrochus, 155

Oucidella, 256

Dinomenia, 60

Ephippium, 257

Oultellus, 274

Diploconus, 337

Ephippodonta, 266

Cumingia, 270

Diplodonta, 265

Epiphragm, 73

Cwno, 264

Diplommatina, 152

Epipodium, 70

Cuspidaria, 278

Dipsacus, 164

£rato, 157

Cuthona, 179

Dischides, 204

Erodona, 273

Cuvierina, 170

Discites, 333

^rw^ia, 270

Cyamium, 266

Discohelix, 147

Erycina, 265

tyrfa«t 267

Discosorus, 332

EtheUa, 134

Gydina, 270

Ditremaria, 147

Euccdodium^ 188

Cydolobus, 335

Ditremata, 189

Euchrysalis, 154

Cyclomenia, 60

Docoglossa, 145

Euciroa, 277

Cydonema, 150

Dolabdla, 171

Eudoxochiton, 54

Cyclophorus, 152

Dolabrifer, 171

Eulamellibranchia, 262

Oyclostoma, 152

Dolium, 157

JSulima, 158

Cydostrema, 150

Donax, 270

Eunona, 150

Cydosurus, 152

J)ondersia, 60

Euomphalus, 147

Coerce, 181

Doratopsis, 340

Euphemus, 147

Cylichna, 168

Doridium, 169

Euplocamus, 177

Cylindrdla, 188

Doridomorpha, 177

Euprymna, 340

Cylindrobulla, 169

Doridopsis, 178

Euthria, 164

Cylindromitra, 164

Doridunculus, 178

Euthyneura, 166

350

INDEX

£utrochatella, 150

Gonodon, 265

Histioteuthis, 340

Exogastric, 74

Gosseletia, 262

Holobranch, 45

Grammysia, 256

Holognatha, 186

Facelina, 179

Gresslya, 276

Uomalogyra, 153

Fasciolaria, 164

Grimalditeuthis, 340

ffomalonyx, 189

Faunus, 154

Gryptochitonidae, 53

Jloplites, 336

Ferussacia, 188

Guivillea, 165

Hoplomytilus, 262

Filibranchia, 256

Gundlachia, 186

Iloplopteron, 158

Fiona, 180

Gymnosomata, 173

Huronia, 332

Firoloida, 163

Gyroceras, 333

Hyalimaoc, 189

Fischeria, 266

Hyalopecten, 262

Fissidentalium, 204

Haemocyaniiie, 10

Hybocystis, 152

Fissurella, 149

#afta, 165

ffydatina, 169

Fissurellidea, 149

ffalicardia, 277

Hydrobia, 153

Fistulana, 274

Haliotinella, 174

Hydrocena, 151

Fluxina, 158

Haliotis, 148

Hyperstrophic, 82

Foot, 68, 199, 215, 286

Halopsyche, 173

Hypobranchial gland, 79

Foot gland, 70

Jlaminea, 169

Hypostracum, 4

Fvrtisia, 168

Hamites, 335

Hypotrema, 257

Fossarus, 152

Hancock's organ, 116

tfyna, 268

Fowlerina, 173

Jfanleya, 53

Fryer ia, 178

Hapalus, 187

Ichthyodes, 60

Fulgur, 164

ffarpa, 166

Ichthyosarcolites, 272

Funnel, 291

ffarpoceras, 335

7<fa^o, 177

Fusispira, 154

Harvella, 270

/rfa*, 259

Fustiaria, 204

Hectocotylus, 324

Idiosepiiis, 341

.FIWMS, 164

/fofyfc, 179

Imbricaria, 164

/Trfcum, 145

Inioteuthis, 340

Gadinia, 185

Heldoniscus, 145

Inoceramus, 260

Galatea, 266

Helicarion, 187

Insertion plates, 42

Galeomma, 266

Helicina, 150

Jphigenia, 270

Galvina, 179

ffelicodonta, 187

Iridina, 268

Gastrana, 268

Helicophanta, 187

/sando, 150

Gastrochaena, 274

Helicter, 188

Ischnochiton, 53

Gastropoda, 66

tfe/ix, 187

Isidora, 107

Gastropteron, 169

Hemiarthrum, 53

Jsmenia, 60

tfoso, 149

Hemifusus, 164

Isocardia, 264

tfetfina, 179

Hemimenia, 60

/sodonta,

tfena, 149

HemphUlia, 188

Isomyaria, 211

Geomalacus, 187

Hercoceras, 333

Isopleura, 1, 40

Geoteuthis, 342

Hercynella, 185

Gervilleia, 259

Hermaea, 181

Janella, 189

Gibbula, 149

Herniaphroditisni, 19

Janthina, 156

Gibbulina, 189

^ero, 179

Janus, 179

Gladius, 293

Heroiiiorpha, 179

Japetella, 343

Glandina, 189

Heterocardia, 270

Je/reysia, 153

Glaucomya, 270

Heterochisma, 204

Joanisiella, 265

Glaucus, 179

Heterodoris, 178

Jorunna, 178

Gtfe&o, 170

Heterogangliata, 1

Jouannetia, 275

Glochidium, 251

Heteropoda, 160

GloMocera.1, 333

Heterostrophic, 82

Katharina, 53

Glycimeris, 274

Heteroteuthis, 340

Keber's organ, 233

GfypAw, 149

ffexabranchiis, 178

/Te%o, 266

Goinphoceras, 332

Himella, 273

Kellyella, 266

Gonad, 20

Hindsiella, 266

KokeneUa, 147

Gonaduct, 20

Hinge, 213

Kntppvmenia, 60

Gonatus, 339

Hinnites, 262

Goniatites, 334

Hipponyx, 155

Labial commissure, 16

Gonieolis, 179

Hippopu3t 271

Labial palp, 218

Goniodoris, 177

Hippurites, 272

Lachesis, 164

Goniomya, 276

Histiopsis, 340 Zxwuno, 152

INDEX

Laeocochlis, 154

Lorica, 54

Miratesta, 185

Lamdlaria, 156

Loricella, 54

J/ftro, 164

Lamellibranchia, 205

Loxoceras, 332

Mitrularia, 155

Lamellidoris, 178

Loxonema, 154

Modiola, 259

Lanistes, 152

Lucapina, 149

Modiolarca, 264

Laoma, 188

Lucapinella, 149

Modiolaria, 259

Lasaea, 266

Lucina, 265

Modiolopsis, 259

Xaiia, 186

Lucinopsis, 270

Modiomorpha, 259

Latirus, 164

Lunulicardiuin, 261

Modulus, 154

Leachia, 340

Lutelia, 266

Molleria, 150

Zerfa, 255

Lutraria, 274

Monoceros, 165

Leibleiu's gland 93

Lyonsia, 277

Monochrcnna, 187

Leioglossa, 342

Lyonsiella, 277

Monocondylaea, 268

Zgpeta, 145

Lyrodesma, 259

Monodonta, 149

Lepetella, 145

Lytoceras, 335

Monomyaria, 211

Lepidomenia, 60

Monopleura, 272

Lepidopleurus, 53

Macellomenia, 60

Monotis, 261

Lepidoteuthis, 339

Macgillivraya, 140

Montacuta, 265

Leptochityn, 53

Maclurea, 147

Mopalia, 53

Leptocoiichus, 165

Madurites, 150

Morphoceras, 336

Lepton, 266

Macoma, 268

Mucronalia, 158

Leuconia, 184

MacrochUus, 154

Mulinia, 270

Ligament, 213

Macrochisma, 149

Mulleria, 268

Ziwu/, 263

Macroscapkites, 335

Muller's organ, 291

Limacina, 170

Mactra, 270

Murchisonia, 147

Limaea, 263

Magilus, 165

J/wrez, 164

Liniapontia, 181

Malacozoa, 1

3/w<e/a, 268

Limax, 187

Malletia, 256

Mutidla, 265

Limifossor, 63

Malleus, 260

J/ya, 273

Limnaea, 185

Mandibles, 6, 88, 299

Myacea, 273

Limnocardium, 271

Mangilia, 166

Myalina, 262

Limnotrochus, 154

Margarita, 149

Mycctopus, 268

Limopsis, 258

Marginella,

Myochama, 276

Limopteria, 260

Marionia, 175

Myoconcha, 259

Liolophura, 54

Marsenina, 156

Myod&ra, 276

Liomesus, 164

Martesia, 275

Myoph&ria, 259

Liopistha, 278

Matheronia, 272

Myopsida, 340

Zto^ia, 150

Mathilda, 155

Myrina, 259

Lipocephala, 205

Meekia, 265

Mysidea, 262

L'Lssoceras, 335

Megalaesthetes, 50

Mytilacea, 259

Lithocardium, 271

A/egalodon, 267

Mytilimeria, 277

Lithodomus, 259

Megaspira, 188

Mytilus, 259

Lithoglyphus, 154

Megatebennus, 149

3/yaw, 158

LUiopa, 153

Mdadomus, 152

Myzonienia, 60

Littorina, 152

Melampus, 184

Littorinida, 154

Melania, 154

Nacella, 145

Lituites, 333

Mdanopsis, 154

JVani'na, 81

Liver, 7, 44, 95, 200, 220,

Meleagrina, 260

Narica, 155

301

Jtfeiifte, 175

^asm, 164

Livona, 149

Mentum, 158

Nassopsis, 154

Lobes (accessory cerebral),

Meretrix, 270

AWica, 156

137

Merobranch, 45

Naticopsis, 150

Lobiancoia, 96

J/esafta, 155

Nautiloidea, 332

Lobiger, 169

Mesodesma, 270

Nautilus, 333

Lobites, 335

Mesoliniax, 187

Navarchus, 169

Zo%o, 342

Mesoplacophora, 53

Needhani's sac, 323

Loligopsis, 340

Metalimax, 187

JVematomenia, 60

Loliguncula, 342

Micraesthetes, 50

Neohyalimax, 189

Loliolus, 342

Micromelo, 169

Neomenia, 60

Lomanotus, 176

Microplax, 53

Neomeniomorpha, 55

Lophocercus, 170

Mti.n«na, 264

Neothauma, 152

352

INDEX

Nephric gland, 111

Otoliths, 18, 119

Photinula, 149

Nerinea, 154

Ow£», 157

Phragmoceras, 332

Nerita, 150

Oxygyrus, 163

Phragmoteuthis, 337

Neritina, 150

Pkyllaplysia, 171

Neritodomus, 150

Pachycardia, 267

Phyllidia, 178

Neritopsis, 150

Pachyrisma, 267

PhyUirJwe; 175

Niso, 158

Palaeacma, 145

Phyllobranchus, 181

Notarchus, 171

Palaeoconcha, 256

PhyUoceras, 335

Notobranchaea, 173

Palaeoctopus, 342

Phyltoteuthis, 342

Notomenia, 60

Pafto, 177

PAysa, 186

Nuchal plate, 264

Palliata, 1

Phythimya, 276

Nucula, 255

Paludiita, 152

Pileolus, 150

Nuculina, 256

Paludomus, 154

Pilidium, 145

Nudibranchia, 174

Pandora, 276

Pinacoceras, 335

Nuttalochiton, 53

Paracephalophora, 66

Pinna, 264

Paraclione, 173

Pinnigena, 264

Octopoda, 342

Paralldodon, 258

Pinnoctopus, 343

Octopus, 343

Paramenia, 60

Pisania, 164

Ocythof, 343

Paramya, 273

Pisidium, 267

Odontoniaria, 147

Parapodia, 69

Placiphordla, 53

Odontopcrna, 260

Pararhopalia, 60

Placophoropsis, 53

Odostomia, 158

Parmacella, 187

Placuna, 257 '

Odostomiopsis, 168

Parmarion, 187

Placunanomia, 257

Oigopsida, 336

Pate/to, 145

Plagiodon, 268

Oleacina, 189

Patrocardium, 261

Plagioptychus, 272

OJiw, 165

Pearls, 213

Plakobranchus, 181

Otaxjtfo, 165

Pecfew, 262

Planaxis, 152

Ommatostrephes, 338

Pectinacea, 260

Planktomya, 33

OmphaLotropis, 152

Pectinibranchia, 151

Planorbis, 185

Ontidietta, 190

Pcctinodonta, 145

Platyceras, 155

Oncidiopsis, 156

Pectunculus, 258

Platydiisma, 147

Oncidium, 190

Pedicularia, 157

Platydoris, 178

Oncospira, 150

Pedipes, 184

Platymalakia, 66

Oniscia, 157

Perfu»/i, 262

Platyodon, 273

O/iitochiton, 54

Pelecypoda, 205

Platypoda, 157

Oiiychoteuthis, 339

/^e/to, 188

Plaxiphora, 53

Oocorys, 157

Pdtoceras, 336

Pledomya, 275

Opecw, 188

Peradis, 170

Pledropliorus, 71

Operculum, 71

Pergamidea, 262

Plesioteuthis, 342

Ophidioceras, 333

Pericardic glands, 13

Pleural gan ;lion, 112, 201,

Ophileta, 147

Pericardium, 12

234

Opw, 264

Periostracum, 4

Pleurobranchaea, 174

Opisthobranchia, 167

Periploma, 275

Pleurobranchomorpha, 173

Opisthopodium, 216

Perisphinctes, 336

Pleurobrandius, 174

Opisthoteuthis, 342

Pe/-?wi, 259

Pleurocera, 154

Oppdia, 335

Peronia, 190

Pleurodonta, 187

Orpidla, 187

Persona, 157

Pleuromya, 276

Orthalicus, 188

Petersia, 157

Pleurophorus, 264

Orthoceras, 332

Petricola, 270

Pleurophyllidia, 180

Orthoneura, 114

Phan&rophthalmus, 169

Pleurotoma, 166

Oscanidla, 174

Phanerotitius 147

Pleurotomaria, 146

Oscaniopsis, 174

Plw.sia.ndla, 150

Plicatula, 262

Oscanius, 174

PhUitie, 169

Pliodon, 268

Ostrucolethe, 187

PhUobrya, 258

Plocavwp/tcrus, 177

Osiraea, 263

Philomycus, 187

Plutonia, 186

Ostraeacea, 263

PhlelxBilesis, 8

Pneuvwnodernia, 173

CWwio, 184

Pholaddla, 276

Podocyst, 136

Otocardia, 1

Pholadidea, 275

Polycera, 177

Otoconia, 119

Pholadomya, 276

Polyconites, 272

Otocrypt, 18

7^/to^, 275

Poli/gyra, 187

Otocyst, 18

P/W5, 164

Polyplacophora, 41

INDEX

353

J'olytremaria, 147

Purpurina, 152

Scalenostoma, 158

Pomatias, 152

Pusionella, 166

Scalites, 152

Pomatiopsis, 153

Pustularia, 157

Scaphander, 168

PompJwlyx, 185

Pyramiddla, 158

Scaphites, 336

J'untiothauma, 166

Pyramidula, 188

Scaphopoda, 197

Popanoceras, 335

Pyrula, 157

Scaphula, 258

Porcellia, 147

Pythina, 265

Scarabus, 184

Poromya, 278

Scendla, 145

Porostomata, 178
Posidonomya, 261
Potamides, 154

Quadrifora, 208
Quadrula, 268

Schismope, 147
Schizobrachium, 173
Schizochiton, 54

Poterioceras, 333

Schizodentalium, 204

Praecardium, 256

Rachiglossa, 164

Schizodus, 259

Prasina, 261

Radiolites, 272

Schizoglossa, 189

Prionodesma, 254

Radsia, 54

Schloenbachia, 335

Proctonotus, 179

Radula, 6

Scintilla, 266

Prodissoconch, 246

Raeta, 270

Scioberetia, 266

Proneomenia, 60

Randla, 157

Scissurella, 147

Pronucula, 255

Rangia, 267

Scolecomorpha, 54

J'roparamenia, 60

Rapa, 165

Scrobicidaria, 270

Propilidium, 145

Rapana, 165

Scurria, 145

Prorhipidoglossa, 12

Rathouisia, 189

Scutum, 149

Prorhipidoglossomorpha, 1

Recluzia, 156

Scyllaea, 175

Proserpina, 151

Requienia, 271

Seguenzia, 156

Prosiphonata, 335

Resilium, 213

Selenites, 186

Prosobranchia, 142

Retractor muscle, 5

Semper's organ, 91

Prosocodus, 264

Retrosiphonata, 334

Senilia, 258

Protobrancbia, 254

Retusa, 168

-Sepia, 340

J'roto»iya, 256
Provinculum, 213

Rhabdoceras, 335
Rhacophyllites, 335

Sepiadaritim, 340
Sepidla, 340

Pruvotia, 60

Rhinophore, 18

Sepiola, 340

Psammobia, 273

Rhipidoglossa, 145

Xepioloidta, 340

J'xctulamussiiim, 262

Rhizochilus, 165

^epioteuthis, 342

I'HCudedmondifi, 265

R/iodea, 188

Septa, 82, 292

Pseudodon, 268

Rhombopteria, 261

Septaria, 150

Pscudokellya, 271

Rhopalomenia, 60

Septibranchia, 277

Pseudolamellibrauchia, 253
Pxeudomarginella, 34, 165

Rhyncholithes, 299
Rhynclwteuthis, 338

Septifcr, 259
Shell-eyes, 50

Pseudomelania, 154

Rhytida, 189

Sibirites, 335

Pscudowonot;i, 261

Riniula, 149

Sigaretns, 156

Psuuilopalliuir , 67

Rinrjicula, 168

Silenia, 278

J'seudovermis, 179

Risella, 152

Siliqua, 274

Ptenoceras, 333

Rissoa, 153

Siliqicaria, 155

Pterinea, 261

Rissoina, 153

Siphon, 209

Pteroceras, 155

Rossia, 340

Siphonaria, 185

Pteropoda, 170, 173

Rostanga, 178

Siphonodentalium, 204

Pterosoma, 163

Rostdlaria, 155

Siphonopoila, 1

Pterotrachea, 163

Rudistae, 272

Sistrum, 165

Pterygioteuthis, 339

Rumina, 82

Si tola, 187

Ptychoceras, 335

Runcina, 169

^fifceneo, 153

Ptychodesma, 262

Smaragdinella, 168

Ptygmatis, 154

Sabatia, 168

Solarium, 158

Pugnus, 168

Saccata, 1

SoZew, 274

J'ulmobranchia, 107

Sagda, 187

Solenaia, 268

Pulmonata, 181

Salpingostoma, 147

Solenochlamys,

Pulsellum, 204

Sangninolaria, 273

Solenoconcha, 197

Punctum, 188

Saxicava, 274

Solenocurtus, 274

Puncturdla, 149

Scacchia, 266

Solenogastres, 54

y^joa, 188

Scaeurgus, 343

Solenomya, 255

PupUlia, 149

Scalaria, 158

Solenopsis, 256

Purpura 165

Scaldia, 265

Solenopus, 54

23

354

INDEX

Solenotdlina, 273

raenioglossa, 151

Trigonia, 258

Solidula, 168

Tff^tw, 274

Trigonochlamys, 186

Spadix, 323

Tancredia, 265

Trinacria, 258

Spatha, 268

Tanganyicia, 154

2-7-ioprt, 177

Spekia, 154

Tanysiplion, 270

Triopella, 177

Spermatophore, 128, 323

TVKWUMS, 340

Triplaca, 168

Sphaenia, 273

ra/>e5, 270

Triton, 157

Sphaerium, 267

Tectariiis, 152

Tritonia, 175

Sphyradium, 188

Tectibranchia, 167

Tritonidea, 164

Spicula, 42

Tegmentum, 42

Tritoniomorpha, 175

Spinigera, 155

Teinostoma, 150

Trochoceras, 333

Spira, 81

Tttleodesmacea, 254

Trochdithes, 333

Spiraculum, 152

Teleoplacophora, 54

Trochonema, 150

Spirotropis, 91

Teleoteuthis, 339

Trochosphere, 27

Spirilla, 338

TeWma, 268

Trochotoma, 147

Spintlirostra, 337

Tellinacea, 268

Trochus, 149

Spondyliis, 262

Telobranchia, 54

Trophon, 164

Spongiobranchaea, ] 73

Tentacles, 67

Tropites, 335

Spongiochiton, 53

Terebdlum, 15i>

Truncatella, 153

Sportella, 266

Terebra, 166

TryUidium, 145

Standella, 274

rmHfo, 275

rwrficto, 164

Stavdia, 259

Tergipes, 179

Tugonia, 273

Stenoglossa, 163

Test, 28, 240

Turbinella, 164

Stenogyra, 188

Testacdla, 189

rwrJo, 150

Stenoplax, 53

r^Ay*, 175

Turbonilla, 158

Stenoradsia, 53

Tetrabranchia, 332

Turricula, 164

Stenothyra, 154

Teutlwpsis, 342

Turrilites, 335

Stephanoceras, 336

Thalassoceras, 335

Turritdla, 155

.SK^er, 181

Thecacera, 177

Turtonia, 266

£<iw, 153

Thecalia, 264

Tyena, 275

Stoastoma, 150

Thecosomata, 170

Tylodina, 173

Stoloteuthis, 342

Thermoscopic eyes, 319

Tylopoma, 152

Stomatdla, 149

TWptodwi, 173

Ty^pAw, 164

Stvmatia, 149

Thracia, 275

Typhobia, 154

Straparollina, 147

2%ca, 155

Straparollus, 147

Thysanoteuthis, 339

Umbilicus, 80

Strepsidura, 164

Titiscania, 150

Umbo, 215

Streptaxis, 189

Tonicella, 53

Umbonium, 150

Streptoceras, 333

Tonicia, 54

Umbrdla, 174

Streptoneura, 142

Torinia, 158

Uncimenia, 60

Streptostyla, 189

Toniatdlaea, 168

Uncini, 89

Strombus, 155

Tornatellina, 188

Ungulina, 265

Strophia, 188

Tornatina, 168

Unicardium, 265

Strophomenia, 60

Torsion (body's), 74

tfnto, 268

Struthiolaria, 155

Toxiglossa, 165

Uretery, 182

5^t/«r, 158

Tracheal lung, 106, 189

Urocoel, 15

Styliger, 15

Trachdotenthix, 338

Urocydus, 187

StyZtna, 158

Trachyceras, 335

Urosalpinx, 164

Stylomenia, 60

Trachydermon, 53

Stylommatophora, 186

Trachyglossa, 343

Vagimda, 190

Subemarginula, 149

TracJiyodon, 54

Fo^^ia, 272

Submytilacea, 264

Trematonotiui, 147

ra/rato, 152

Sutnilites, 154

Trenwctopus, 343

Vampyroteuthis, 342

Sitccinea, 189

7Ves7«, 274

Vanganftta, 270

Supra -intestinal ganglion,

Triauly, 127

Vanvxemia, 258

113

Tribonioph&rus, 189

Velainidla, 148

Sutural lamina, 42

Trichotropis, 156

Veliger, 27

Symplectoteuthit, 338

Tridachia, 181

Velarita, 266

Synapticola, 266

Tridacna, 271

Velum, 27

Synaptorhabda, 253

Trifora, 208

Vdutina, 156

Syndosmya, 270

Trtforis, 154

Veneracea, 270

INDEX

355

Venericardia, 264

I7a«to, 256

Xylophaga, 275

Vejterupis, 270

Trw^*te, 165

Xylotrya, 275

Veniella, 264

Volnthuiya, 73

Venus, 270

Volvaria, 168

Vemnya, 339

Volvatella, 169

roW»a, 255

VermetHs, 154

Volvida, 168

Verticordia, 277

Vulsella, 260

Zeidora, 149

Vertigo, 188

Zirpliaea, 275

Vesicomi/a, 253

iromfta, 264

Zittdia, 157

Visceral commissure, 16

Zonites, 186

Vitrina, 187

XeHophoriis, 155

Zospeum, 188

Viviparity, 21, 131

Xiphoteuthis, 337

Zygoneury, 142

THE END

THE UNIVERSITY LIBRARY

UNIVERSITY OF CALIFORNIA, SANTA CRUZ

SCIENCE LIBRARY

This book is due on the last DATE stamped below,

JUN2 1971

JUN 2

WAR 15 1972

REC'D MAR 7

•G9(J7948s8)2477

STARCH AT iinr