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A MONOGRAPH OF THE

LAND AND FRESHWATER MOLLUSCA

OF THE BRITISH ISLES

BIBLIOGRAPHY OF THIS VOLUME.

Part I., pp. 1-64, and pi. L, facing title, published October 26th, 1894.

Part 11. , pp. 65-128, and pi. 11. , facing p. 94, published August 24th, 1895.
Part III., pp. 129-192, published June 30th, 1896.

Part IV., pp. 193-256, published February 20th, 1897.

Part V., pp. 257-320, published November 13th, 1899.

Part VI. , pp. 321-384, published June 16th, 1900.

Part VII., pp. 385-454, and pi. III., facing p. 392, pi. IV., facing p. 396,
pi. V., facing p. 400, and pi. VL, facing p. 402, published December
31st, 1900.

A second title-page is supplied with Part VII., which may either be
substituted for the preliminary title given with Part L, or placed in front
of it.

’’ ''' ■ ' ^ . • . . y, '‘

Flo. 5. Fio.fi.

Fig I Hi'lix af’fji^isa vnr zonata Moq. Folkestone, collected bv Mrs Fitzgerald
Fio. 2. Helix aspersa viu: alho fasciala , Jeffreys, Garden, Tl-xford, Notts, collected
BY Mr.W a gain . Fio 3 Helix aspersn var fUimmea. Picard, Garden, Tlxford, Notts.
COLLECTED BY Mr.W A.Gain Fi g .+. /jccey/w voz: THOMPSON . Lou OH

Crincaum, Killahney, COLLECTED BY .M R. W F DE Vis M Es Kane Y\o.^ . Limox moxinius
vnr feruf^aarL, .Moq. (after Ferdssac.> Fio.O. Limnaa stagniHis var. appressa. Say,
Lake Michigan, U S A collected by Rev. E G.Bollks . Fio. 7. Helix pisana var. mxigna
Rossm. (AFTER Ross.MAS s LE R ) . V\G.B. HcHx iiemornlis var roneo- labiMa , Ix'iGOK.
Blagdon. .Somerset, collected by Miss F.M Helb. Fig. 3. Helix hprlensis var
lilacirin. Taylor, Chisi.ehurst, Kent, collected by Mr S.G Cockerell.

ITg 8.

MONOGEAPH

OF THE

LAND & FRESHWATER
MOLLUSC A

OF THE

BRITISH

BY

JOHN W. TAYLOR, F.L.S.

MEMBRE HONORAIRE DE LA SOCIETE MALACOLOGIQUE DE FRANCE,
EX-PRESIDENT OF THE CONCHOLOGICAL SOCIETY OF GREAT BRITAIN AND IRELAND,
LATE EDITOR OF THE “JOURNAL OF CONCHOLOGY ; ” ETC. ;

WITH THE ASSISTANCE OF

W. DENISON ROEBUCK, F.L.S., THE LATE CHARLES ASHFORD,

AND OTHER WELL-KNOWN CONCHOLOGISTS.

STRUCTURAL AND GENERAL VOLUME.

LEEDS :

TAYLOR BROTHERS, PUBLISHERS.

■

PREFACE.

The present work was undertaken with the object of placing in the
hands of those interested in the conchology of this country a treatise
dealing comprehensively and in detail with the many points of interest
presented by our native species of land and freshwater mollusca.

Hitherto, with few exceptions, the published works have viewed
this subject from very restricted standpoints, and have not attempted
to convey any detailed information of the intricate and marvellous
organization of the mollusca, nor to give any really comprehensive
survey of the subject or discuss the bearings their study could have
upon the larger problems that are yet far from solution by the scien-
tific world.

Very many years have been devoted to the study of the subject in
its various aspects and to the accumulation of information, in which
labours I had for some years the co-operation of my late dear friend,
Mr. Charles Ashford, to whom much of the anatomical detail given
in the work is due. Mr. W. Denison Roebuck, F.L.S., was also for a
lengthened period closely associated with me in its preparation and
still practically evinces in many helpful ways his deep interest in its
success, and it is in grateful recognition of the generous assistance I
have received that I associate their names with my own upon the
title-page.

The Council of the Conchological Society have practically demon-
strated their lively interest in my work by kindly permitting me to
retain in my own possession a considerable part of the society’s library,
a favour which has been of the greatest assistance to me ; while Mr.
W. E. Hoyle, M.A., of the Manchester Museum, has laid me under
heavy obligation by procuring me the opportunity of examining many
scarce books, which otherwise I should have had a difficulty in obtain-
ing. Prof. Paul Pelseneer, of Gand, has also given me valuable aid

VI.

PREFACE.

aud advice upon many critical points, and has at all times placed his
great knowledge and experience freely at my disposal, a favour I cannot
too cordially acknowledge.

Many other friends have likewise contributed valuable and valued
information and assistance, and most of these obligations liave been
acknowledged in their appropriate places in the text, but the willing
co-operation of many other well-wishers has been invaluable, and I
may especially mention Mr. R. D. Darbishire and Mr. Robert Welch,
to whom I am under so many and such varied obligations for their
unwavering interest in, and practical sympathy with, my labours, that
thanks are inadequate to express my appreciation of their help.

Although more than six years have been occupied in the production
of the present volume, the time cannot be considered excessive when
it is remembered that my time cannot be devoted exclusively to the
work and that the whole of the labour has devolved solely upon
myself, not only as regards the preparation of the text, but also in
producing the drawings and photograms from which the whole of the
737 figures or maps have been engraved or lithographed.

Financially, the work is not and cannot be a success, as no expense
has been spared to attain the very best results, so that even if the
whole of the small edition that has been prepared becomes exhausted,
the proceeds will not be nearly sufficient to repay even the pecuniary
outlay involved in its production.

The portion of the work devoted to genera and species will be com-
menced without unnecessary delay and, it is hoped, will be quickly
completed, but to attain this desirable result I must bespeak the
active aid of all those interested in the subject.

JOHN W. TAYLOR.

North Grange, Horsforth,

Leeds, Dec. 29th, 1900.

CONCHOLOGY

STRUCTURAL AND GENERAL.

A

MONOGRAPH

OF THE

LAND AND FRESHWATER MOLLUSCA

OF THE

BRITISH ISLES.

Definition of Conchology.

Concliology, tlie term by which the study of the mollusca is most
generally known, is a combination of the Greek words, Koyxi] (a shell-
fish), and Ar;yos(a discourse or treatise); and is usually understood to
embrace the study of the complete subject — not merely the shell,
hut also the animal which forms it. By some authors the term has been
restricted to the study of the shell only, and the word Malacology
used to designate the investigation of the animal or soft parts ;
although Tryon and some other scientists have proposed that Malaco-
logy shall be understood to embrace the complete subject, and super-
sede the older name.

The molluscan sub-kingdom embraces those organisms with soft
and fleshy bodies, enclosed or covered by a muscular sac which is
called the mantle, and which usually secretes a more or less regular
and .symmetrical shell, mainly composed of carbonate of lime, the
chief function of which would appear to be the protection of the
vital organs of the body. In some genera the shell is internal or
concealed beneath the mantle, it is then usually of a simple flattened
plate-like form or even reduced to a few granules.

The Mollusca are distinguished from the Articulata, by their bodies
not being segmented, and also by their nervous system consisting of

4

HISTORY AND CLASSIFICATION.

several pairs of irregularly di.sposed ganglia, which arrangement led
Professor Owen to apply the term Heterogangliata to them, in contra-
distinction to Homogangliata, by which term he designated the
iVrticulata on account of their ganglia being arranged in a paired
longitudinal series. Prom the Vertebrata, they are distinguished by
the absence of an internal bony skeleton.

History.

The extensive and important sub-kingdom Mollusca {mnllh,
soft), as now understood, embraces four Classes only. Cephalopoda,
(ta.stropoda, Scaphopoda, and Pelecypoda.

The PohjZDH, Bntchiopudd, and other groups, which were formerly
included, have been successively removed from the molliLscan sub-
kingdom and placed in other divisions.

I.innti originally separated the sub-kingdom Mollusca as now under-
stood, into two great divisions, placing the shell-bearing species
associated with other organisms in a groti]) he designated as Vermes
Tesfdced, and the nakeil, or internally-shelled s})ecie,s, he grouped
with many other very dilferent forms of life, and designated them
lVr;«p.s‘ Zoo'phiitd, a term which lie afterwards changed to Vermes
Mo! I used.

Paron Cuvier was the tirst to unite the Mollusca into one great
sub-kingdom, and though he e.xcluded many groujis of organisms
which were united with them by Linnb, he still retained several
wliich have been since excluded by more modern authors.

Our Briti.sh land and fre.shwater mollusca belong exclusively to tbe
two classes. Gastropoda and Pelecypoda, the remaining groups being
exclusively marine in babit.

Classification.

(Tissitication has for its object, not only the systematic arrange-
ment of the objects of study, but the combination in suitable groups
of those sjiecies having most affinity with each other, and jios.sessing
in common some recognizable determinate characters. When a number
of species possess this suitable similarity of organization they are
united in a group termed a genus; such of these groups or genera as
are distinguished by some common character are united in larger
grou])S, called families ; the.se larger groups or families are gathered
into still more numerous as.semblages, termed orders ; and finally

CLASSIFICATION.

O

combined into classes. All these divisions should possess in com-
mon, some peculiarity of greater or lesser importance, and all these
groups are or may be sub-divided into section.s, which with the prefix
of Sub-, indicate the pos.session of characters of lesser importance
than those distinguishing the chief groups.

The Animal Kingdom is divideil into several Sub-kingdoms, the
Vertebrata standing at the head, and by general concurrence among
scientists, the Mollusca occupy the second place, preceding the Arti-
cnlata and every other sub-kingdom.

The ^lollusca may be primarily divided into four Classes, based
upon the modifications of the foot or locomotive organ, and named
Cephalopoda, Gastropoda, Sca^hopoda, and Pelecypoda. The
Pteropoda, which formerly constituted a fifth class, are now con-
sidered to be Opisthobranchiate Gastropods. Two of these classes
are exclusively marine, leaving only the Gastropoda and Pelecypoda,
to which groups our British land and freshwater shells exclusively
belong. The names Gastropoda and Pelecypoda, refer to the
morphological peculiarities of the animals, the alternative terms
Univalve and Bivrdve, which are also in general use, respectively
expressing the character of the shells.

The Gastropoda are characterized by the development on the
ventral side of the body of a sole-like locomotive disc or foot, and by

Fig. 1. — An Anisopleurous Pulmonate Gastropod.

Helix aspersa v. zonata Moq.,

Folkestone, collected by Mrs. Fitzgerald.

its uudulatory or wave-like expansions and contractions the creature
moves. This class may be primarily divided into two groTips or
Sub-classes, Isopleura and Anisopleura, according as the chief
viscera have or have not been subjected to a toi’sion and a semi-
rotation, bringing the termination of the alimentary canal from its
presumed ancestrally posterior and medial position, towards an
anterior or lateral one, involving in this movement other organs and
their ducts ; this change of position is assumed to have been caused

6

CLASSIFICATION.

by and owing to the development of the shell as a protection and
covering to the vital organs of the body, and this shelly covering
not having retained its equilibrium has fallen over to one side and

Fig. 2. — Diagrams illustrating the progress and method of the assumed rotation of the
internal organs in the Anisopleura (after Lankester). The arrows indicate the direction of the
rotatory movement. A. nnrotated ancestral condition ; K. semi-rotation of the organs partly
accomplished; C. complete semi-rotation.— <2. anus; r.n. the primarily left and primarily

right nephridia or kidneys ; primarily left visceral ganglion, which after the torsion is

accomplished forms the sub-intestinal ganglion ; r.^-. primarily right visceral ganglion, which
subsequently becomes the supra intestinal ganglion.

to the i-eav, compressing and gradually displacing the termination of
the intestine and causing it to assume the position it now occupies.
The Isopleura, of which the C/tltoiis are examples, are practically
organized in a bilaterally symmetrical manner externally and
internally, the viscera not having been subjected to the torsion
alluded to. The Anisopleura to which all our land and freshwater
species belong, though presenting externally a bilaterally symmetrical
ai)pearauce of the head and foot, have been subjected to changes in
the position of the chief viscera by this semi-rotation of the visceral
sac ; they may be sub-divided into two Orders called Eutiiyneura
and Streptoneura, this separation being based upon the modi-
fication caused in the arrangement of the visceral nerve-loop,
by its being involved in, or escai)ing from, the twisting of the
viscera. In the Eutiiyneura, of which Limnau stagnalh is an
exanqile, the visceral nerve-loop is often comparatively short, and
on account of lying beneath the intestinal canal has escaped the
twisting to which the iqiper portion of the viscera has been sub-
jected. The Streptoneura differ from the Euthyneures owing to
the visceral nerve-loop lying above the intestines and being thus
involved in the twisting and rotation the organs have undergone.

CLASSIFICATION.

and consequently made to assume the form of the fig. 8 as in the
Viviparidw.

Fig. 3. — Nervous system of Limneea siagnalis^ as
typical of the short looped Euthyneurous condition
(modified after Lankester). r.b. and Lb. right and left
buccal ganglia ; r.c. and Lc. right and left cerebral
ganglia ; r.p. and l.p. right and left pedal ganglia,
with the otoc^’sts on their inferior face ; r.pL and l.pL
right and left pleural ganglia ; r.v. and l.v, right and
left visceral ganglia, the long nerve to the osphradium
or olfactory organ Oy is given off from the right visceral
ganglion ; ab. unpaired abdominal ganglion.

Fig. 4. — Nervous system
of Vivipara as a type of the
Streptoneurous condition(after
Ihering). r.b. and Lb. right
and left buccal ganglia ; r.c.
and Lc. right and left cerebral
ganglia ; r.p. and l.p. right and
left pedal ganglia with the
otocysts on short pedicels ;
r.pl. and Lpl. right and left
pleural ganglia ; s.b. and s.p.
the sub and supra-intestinal
ganglia ; ab. unpaired abdo-
minal ganglion.

In our British species of land and freshwater shells, the orders
Streptoneura and Euthyneura are exactly equivalent to the groups
Operculata and Inoperculata respectively, with perhaps the doubtful
exception of Nerithia. The Streptoneures are divided into two Sub-
orders, Zygobranchia and Azygobranchia, the first-named embracing
those Streptoneui’ous species in which although the semi-rotation of
the organs has taken place and the gills and other organs become

transposed in position, have yet re-
tained their bilateral symmetry, the
common Ormer or Ear-shell, Haliotis
tubercidata is an illustration.

The Azygobranchiata, of which
Vivipara and other Prosobranchs
are more or less typical, differ from
the preceding group, owing to the
compression and twisting of the vis-
cera having led to the loss of one of

Fig. 5. — A Streptoneurous Azygo-
branchiate Gastropod.

Valvata piscinalis Miill. X 3,
Sway, Hants., coll, by Mr. C. Ashford.
ct. ctenidium or exsertile branchial
plume ; r.ct. filiform appendage, prob-
ably^ the vestigial rudiment of the
primitively left branchial plume.

8

CLASSIFICATION.

6. — Gill or Ctenidlum of Viviparay a
Peclinil.jranchiate Gastropod (after Lankester).

/. intestine running parallel to axis of gill and end-
ing in the anus a, ; br. rows of elongate branchial
filaments.

the coinpuiieiit parts of several of tlie i)aire(l organs, tlius tlie
original left gill and other organs have become atrophieil, but the
right gill, etc., retained, though owing to the rotatory move-
ment the viscera have been subjected to, these originally de.xtrally
placed organs are now i)laced to the left of the rectum. The Azygo-
branchia may be separated into two sections : Pulmonata and
PuCTiNiiuiANCiiiATA, containing
the animals breathing air and
water respectively, the former
composed of those species which
have become modified and
adapted to a terrestrial life
and aerial respiration termed
Pneumonochlamyda by Lan-
kester, and Xenrobranchiata
by Macalister, of which Ci/clo-

xtomd ('/('(/((IIS is ail e.xample ; while the Pectiiiibranchiata embrace
all the operculate aquatic species.

The Euthyueurous Gastropods
comprise two Sub-orders, based up-
on the position and function of the
respiratory organs, viz. : Pulmonata
and Opistiiobranchiata ; of the
latter group the marine genus Build
is an e.xample, and the Eiitliyneiir-
ous Piilmonates comprise the bulk
of our native lanil and freshwater
molliisks. Though I have classed
together the Euthyueurous air-
breathers as simply Pulmonata, it
should be mentioned that some
Biologists do not regard the pul-
monary sac of the Helicidcc as
homologous with that of the Lim-
nd/kliv ; the respiratory cavity in
the former being said to be a modifi-
cation of the cloaca of the kidney,
hence the term Xepiiropneusta applied to them ; while that of the

- vx. . '

Fig. 7. — Diagram of the Lung of a
Pulmonate Gastropod, Ilelix aspcrsa L.

nephridium, with ureter crossing its sur-
face ; r. rectum ; a. auricle; z/. ventricle ;
b.b. canal bringing blood from hinder part of
Ijody ; c.r. canal communicating with body
cavitj-and also bringing blood to lung. The
darker veins carry the blood from these
canals to surface of lung ; the light veins re-
collect and convey to auricle after aeration.

CLASSIFICATION.

9

Fig. 8. — A Stylommato-
phorous Pul monate.

Succinca piitris f'L.),
Asliley Marsh nr. Bristol,
Collected by Miss Hele.

Limnieidw is considered to be identical with the
branchial chamber of the Pectinibranchs, the
term Branchiopneusta being used to express
this difference. Finally the Pnhnonates are
separated into two Sections
based npon the position of
the eyes : the Stylommatopiioha, whicli are
all terrestrial species and have the eyes placed
at or near the tips of the u])per tentacles as
in Helix, Succinea, etc. ; and the Basommato-
PHORA, which includes those species or genei’a in
which the eyes ai*e placed at or near the base of
the tentacles, as in Limnwa.

Fig. 9. — A Basomma-
tophorous Pulmonate.
Limtiaa peregi'a var.
ovata Drap.,

R. Tome, Doncaster.

Tlie class Pelecypoda an axe and 7roS-a foot, or axe-

footed), are exclusively aquatic and pre-eminently marine species.

Fig. 10. — An Equivalve Inequilateral Pelecypod.

Unio pictortim (L.), showing left valve,

Clumber Labe, Notts., collected ))y Mr. C. T. Mu.sson, F.L.S.
a.s. anal or e.xcurrent siphon ; br.s. branchial or incurrent siphon ; /. foot.

characterized by the possession of a somewhat linguifoim extensile
foot, usually more or less adapted for ploughing through or burrowing
in sand and mud, and are further distinguished by the development
of an external shell composed of two pieces, or valves, joined to-
gether by an elastic ligament at the dorsal or upper margin, and
often furnished in addition with interlocking teeth or denticles at the
hinge. The term Bivalve, by wbich they are widely and popularly
known, has reference to this universal presence of two valves to the
shell, while Lamellibranchiata which is also very generally used
refers to the lamellar or leaf-like character of their branchiae or

10

CLASSIFICATION.

gilLs. The class may be first divided into three Orders, according
to the nnmher and development of the Adductor muscles. This
mode of classification, though perliaps not perfectly satisfactory,
seems preferable to the various other methods of division that have

U.T

Fig. 11. — An Isoniyate, Integripalli.'ite Pelecypod.

Anodonta cygmea (L.), left valve,

Clumber Lake, Notts., collected by Mr. C. T. Musson, F.L.S.
a. ad. anterior adductor scar; p.ad. posterior adductor scar ; a.r. anterior pedal retractor scar ;
p.r. posterior pedal retractor scar ; u.r. umbonal or lesser retractor orretentor scars ; a.p. anterior
pedal protractor scar, the abdominal retentor scar of Clessin ; /./. palbal line.

at different times bee

a ad

Fig. 12. — A Heteromyate
Pelecypod.

D. polyniorpha (Pallas),
Gloucester Canal, Stroud,
Coll, by Mr. E. J. Elliott.
a. ad. ant. adductor scar ;
p.ad. post, adductor scar ;

post, pedal and byssal
retractor scar ; /./. pallial
line ; 1. ligamental pit.

n proposed : the Monomya, or one-muscled as
the Oyster ; Isomya, in which those muscles
are two in number, and appro.ximately e(iual
in size, as e.xemplified in the Unioitidw] and
IIeteromya, in which, although two muscles
are still developed, the anterior one is much
smaller than the postei’ior one, as in Dreis-
sensiu. Sub-orders are formed in the Isomya,
by the presence or absence of a conspicuous
sinus or indentation in the pallial line, in-
dicating when present the possession of
extremely long retractile siphons, and thence
called SiNUPALLiA, as expressing the indi-
cation the pallial line affords. The Inte-
GRiPALLiA, to which all our species belong,
have a non-sinuated pallial attachment.

The classification adopted is given also in tabular form, so that
the inter-relationship of the different groups can be understood at a
glance.

CLASSIFICATION.

11

Tabular View of the Sub-Divisions of the Mollusca, vrranged
TO shew their assumed Genetic Relationship.

The groups printed in italics arc those not represented amongst the
British Land and Freshicater Mollusca.

MOLLUSCA.

^

I I I I

Cephalopoda Gastropoda Scaphopoda Pelecypoda

Anisopleura Isopleura Heteromya Isomya Monoinya

^ I

1 I , I. . . I .

Euthyneura Streptoneura Integnpallia Sinupallia

I I ! I

Pulmonata Opistkobranckiata Zygobranchia Azygobranchia

Stylommatophora Basommatophora Pulmonata Pectinibranchiata

or Pneumonobranchiata

In all attempts at classification, it is necessary to carefully dis-
criminate between species showing similarity of form and habit but
not structurally conformable, and those in which the whole organism
is in harmony with the external aspect and mode of life. The first
show analogical relation only, but the latter are related homologically
and should therefore be classified together. If the resemblances
exist from a very early age, they are considered to be of the greatest
importance and to imply community of descent.

Almost every organ of the body has been proposed, at one time or
another, as a basis for the better arrangement of the Gastropoda,
the circulatory, nervous, reproductive, alimentary, and respiratory
organs, as well as the presence or absence of the operculum, the
arrangement and position of the eyes, etc., have all been or are now
used separately or together for the purposes of classification.

In the Pelecypoda, the muscular and respiratory systems have been
strongly relied upon for chief divisions ; the characters of the hinge,
with its interlocking teeth, and the development or absence of the
siphonal tubes, have also, always been considered to be important
features, but too much reliance should not be placed on any one
character for taxonomic purposes, and confirmation should always be
sought by other organs, as it will be readily conceded by everyone that
all organic characters are of varying importance according to circum-
stances, and this must of necessity be so in a natural classification
based upon the general organization and affinities of the animal and

12

CLASSIFICATION.

its shell, aiul not fouiuled upon any particular organ, or set of organs,
arbitrarily selected as in an artificial arrangement.

In former times, before the structure of the Mollusca was system-
atically e.Kamined, or its signibcance understood, they were arranged
according to the different shapes of the shells. Ijinmi was one of
the first to lay stress upon the structural details of the shell, noting
the character of the umhonal teeth, ligament, folds, sculpture, etc.,
and using them to separate various groups. He also attached great
importance to the form of the animal, and ranged all mollusks under
five heads, as Dorh, Limax, Tethys, Sepid, and Ascidid, which
division coincides in some measure with the classes accepted at
the present day.

Adanson introduced the system of classifying the bivalves in
accordance with the muscular impressions, and took note of the
operculum in Gastropods as an important character.

The use of Physiological characters was first suggested by Cuvier,
who established an arrangement based upon the pectdiarities of the
respiratory organs, and brought together all the })ulmonate species ;
he also proposed the still accepted terms, designating some of the
higher groups.

Lovfm and others have proposed the use of the lingual armature,
as suitable organs for establishing an improved arrangement of the
Gastropoda, and the figures that have been jniblished have often
confirmed the truth and value of the older genera, established solely
upon the morphology and character of the shell.

II. von Ihering advocates the use of the nervous system in preference
to the radula, respiratory organs, or other single character; and I
have followed Prof. Ray Lankester and adopted this system for
dividing two very important groups in the Gastropoda.

All classification, however, upon whatever basis it e.xists, which
places the objects in rotation, must be to a certain e.xtent arbitrary
and artificial, and of necessity violate the affinities of some of the
groups or species, because it may well be that those selected to pre-
cede or follow any particular species or group may be no closer allied
in general organization, than one or more others necessarily removed
further away. If this be so, then no hard and first line can truthfully
be drawn as to the proper secpience of many of the different groups
or species, and we can only place the species or groups, as the case

CLASSIFICATION AND NOMENCLATURE.

13

may be, in such order as appears to us to do the least violence to
their natural relationships, and cannot reasonably stigmatize as in-
correct or unscientific, as is so often done, a different arrangement, in
which other characters are allowed to have more weight than we
personally are disposed to give them.

LITERATURE.

Adams, H. & A. — The Genera of Recent Mollnsca, arranged according to
their Organization, 1853 — 8.

Chenn, J. C. — Manuel de Conchyliologie et de Paleontologie Conchylio-
logicpie, Paris, 1859 — 62.

Clessin, S.— Nomenclator Heliceorum Viventium, 1881.

Dali, W. H. — On the Hinge of Pelecypods, and its development, with an
attempt at a better subdivision of the group. — Amer. Journ. of Science,
Vol. xxxviii, pp. 445 — 462.

■ Fischer, P. — Manuel de Conchyliologie et de Paleontologie Conchylio-
logique, Paris, 1883 — 7.

Gegenbaur, C. — Comparative Anatomy, 1878, pp. 316 — 317.

Gill, Theodore. — Arrangement of the Families of Mollusca. — Smithsonian
Miscellaneous Collections, 1873.

Gioli, G. — I Lamellibranchi e la Sistematica in Paleontologia. — Bull. Soc.
Mai. Ital. xiv, pp. 101 — 143.

Grobben, C. — Das System d. Lamellibranchiaten. — Zoologischer Anzeiger,
vol. XV, pp. 171 — 375, 1892.

Ihering, H. von. — Versuch eines naturlichen Systemes der Mollusken. —
Jahrbucher d. Deutschen IMalakozoologischen Gesellschaft, Apl. 1876,
pp. 97 — 148.

Lankester, E. Ray. — Art. Mollusca. — Encyclopu'dia Britannica, ix. edit. ,
part 64, pp. 632 — 695, 1884.

Morch, 0. A. L. — On the Systematic Value of the Organs which have
been Employed as Fundamental Characters in the Classification of the
Mollusca. — ^Ann. and Mag. Nat. Hist., vol. xvi, pp. 385 — 396, 1865.

Morse, E. S. — Classification of the Mollusca based on the Principle of
Cephalization. — Boston, 1865.

Neumayr, M. — Z. Morphol. d. Bivalven-Schlosses. — Sitzgsber. d. Kais.
Acad. d. Wissenseh. in M'ien, 1883.

Pelseneer, P. — Introduction a I’Etude des Mollusques. — Mem. Soc. Royal
Malac. de Belgique, 1892.

Simrotli, Dr. H. — Dr. Bronn’s Klassen und Ordnungen des Thier-Reich.s,
Weichthiere, 1894 (still in progre.ss).

Troschel. F. H. — Das Gebiss der Sclinecken zur Begrundung einer natur-
liehen Classification, 1856 — 1879.

Tryon, G. Mk, jr. — Structural and Systematic Conehology, 1882.

M'ood-Mason, J. — Proe. Asiatic Society of Bengal, 1882, pp. 61 — 64.

' M'oodward, S. P. — Manual of tlie Mollusca, 1880.

N OMENCLATURE.

Tlie universal acceptance of the binomial system of nomenclature,
by the scientists of all countries, by which practice two names, a
generic and a specific one are applied to every distinct species — exactly
equivalent to the use among mankind of the Christian name and sur-
name— tlie generic name indicating the group to which the species

14

NOMENCLATURE.

belongs or is most closely related to, while the specific name deci-
sively separates it from all others in the genns, one name thus
showing the affinity of the organism and the other its divergence
Formerly the nse of a series of descriptive epithets was in vogue to
indicate species and must have proved in practice very cumbrous
and unwieldly, as the synonyms I shall presently give under the
specific heads will sufficiently show.

Linnd, though not the originator of the binomial system, was the
first to apply it to the whole of the animal and vegetable kingdoms,
and it has therefore been decided that recognized nomenclature shall
be considered to take its origin from him and date from 1758, the
year of publication of the 10th edition of the “ Systema Natune,”
in which work he first applied the binary system of nomenclature to
all organisms, which he had only partially done in the previous
editions. All names or epithets given to species prior to 1758 are
therefore not recognized in the nomenclature, except as synonyms,
but the earliest name published after that date if accompanied by a
recognizable description or figure is adopted and should not be altered,
except when mis-spelt by author or printer. The name of the person
who proposed the name, should in all cases follow that of the species
he has discriminated, but if the species is afterwards removed from
the genus in which it was placed by him, this is indicated by placing
the author’s name in parentheses, thus A vion ((ter (L.) was originally
described by Linne as Linm.v (iter, and the use of the parentheses
indicates the generic change; while Jleli.r nemordHs Linne retains its
original generic position, as is shown by their absence.

Some naturalists still consider that the author establishing the
genus should append his name to all the species embraced in it, and
this opinion has led to the alteration and division of many of the
genera. Scientists generally do not however agree with or accept this
doctrine, and little can be said in its fixvour.

The classical languages — Greek and Latin— are, by general consent,
chiefly used for the names of natural history objects ; tbe names of
Families and Sub-fiimilies being formed by the addition of idae and
inae respectively, to the genitive form of the name of the principal or
typical genus, this addition being made after the elision of the last
syllable, thus Helicidiv and Iletichuv respectively indicate the Family
and Sub-family of which the genus Helix is typical.

NOMENCLATURE.

15

Generic names, which are essentially substantives, are taken pre-
ferably from the Greek language, though they may also be taken from
the Latin or other tongue, but if the word be not Latin, it should be
treated as such and Latinized in the regular and orthodox way, and
should in wi’iting or printing always commence with a capital letter.
A generic name should consist of a single word, which may be either
simple or compound. In the compound or composite words the
attribute should always precede the chief term, as in Cyclostoma.
If the generic term is used in the adjective form, which is not
desirable, it should always take the feminine termination.

Generic names may be

Greek substantives, for which the rules of Latin transcription
must be followed, as in Ancylus, Physa, etc. These rules
require that at be rendered as ce ; a as i ; ov as u ; oi as 03;
V as y; 0 as th; 4> &sph; x as ck; k as c; yx as 7ich ; yy as ng ;
‘ as h ; os and ov if terminal are rendered as us and um
respectively.

Compound Greek words, the attribute being always placed
first, as in Stenogyirc, Cyclostoma, etc.

Latin substantives, as Auricula, etc.

Compound Latin words, as Semifusus, etc.

Derivatives from Greek or Latin words, expressing diminution,
comparison, re.semblance, etc., as HeUcella, Ilelicina, etc.

Mythological and Ancient words or names, as Venus, Cleopatra,
etc., the words or names taking the Latin termination if
not already possessing it.

Modern names ; these preserve their orthography and retain
any accents with which they may be surcharged, and if
terminated by a consonant add ius, ia, ium to the full and
complete name of the person to whom the dedication is
made, as Dreissensia, Mulleria, etc. Names ending in
e, i, o, y take the termination us, a, um, as Wiyvillea, etc.,
but if terminated by a or u add ia, but, in the latter case,
the letter t is interpolated for the sake of euphony, as
Payraudeautia, etc.

Names of Vessels ; according to their character these are
treated as mythological names, as Vega; or as modern
names, as Challengeria, etc.

IG

NOMENCLATURE.

Compound generic terms may be formed by a combination of
the names of two other genera, and when this practice serves
to express the position and affinities of the group it may
be adopted with advantage, as in ArloU incur, etc.

Names formed anagrammatically, as Mihuv.

The employment of generic names already in use in other depart-
ments of Zoology is not desirable, and wherever possible should he
avoided.

The Specific names should he formed of a single word, preferably
a Latin adjective or substantive, of a short and euphonious character,
though Latinized Greek words and undeclinable words of other lan-
guages may be admitted, and should be written or printed with a small
initial ; though upon this point there is some difference of opinion
amongst authors, some using an initial capital letter for personal and
geographical names and a small initial for all others. In certain
cases where the name of the object after which the organism is named
is formed of two words, the si)ecitic name may be double also, as
//. sancta’-heli'iuc ; or where a comparison is sought with another
object, as in ^1. cornu-arirfis, the two words may be legitimately
used, but should always be connected by a hyphen.

Specific names may be

Substantives or adjectives recalling some character or pecu-
liarity of the species, as J'ontiiudis, auricnldria, etc.

Names of persons to whom the species may be dedicated ;
these if in the genitive case are formed in masculine names
by tlie addition of a simple i to the full and exact name of
the person to whom the species is dedicated, as soirerbi/l,
or the name may be used in the adjective form taking
the termination anus, ana, or anum, in accordance with
the generic term, as In feminine names the

dil)th()ng ae is added to or combined with the name to
be Latinized as furtonw, rmnnc, etc. In those cases where
the name has been employed and declined in the Latin
tongue, it will follow the regular declension, as snn]ironii.

Geographical names if known to the Homans or Latinized
by the medimval writers, should also be in the genitive
or in the adjective form, as (intilhiriim, hurdi<i<(]riiAs,
(i'f/iipfi((cn.'!, etc. If the names have not been used in Latin

NOMENCLATURE.

17

the exact oitliograpliy of the radical is preserved, with any
accents with which it may be surcharged, tlie word Ijeing
used in the adjective form and receiving the snfhx ensis,
ius, icus, inus, itus, etc., if tlie genus be mascnline, as
in (dze)ien!^is, etc., the last syllable varying in

accordance with the gender of the generic term.

If the radicals of geographical or other names give rise to two or
more too closely similar derivatives, as ///spti/i/t.'! and ; or

Jlavtidi'!, -Ami JhiL'hitdh, these should not be emplo3md concnrrently
to distingnish different species in the same genns.

Greek prefixes or suffixes should onl}' be combined with words
derived from the same language ; but those of Latin origin are more
generally used, as scientific terms are essentially Latin in character.

The repetition of the same word for the generic, the specific, or
the varietal name of a species is undesirable and should whenever
possible be avoided.

Trinomiali.s.m is an extension of the Linnean method of nomen-
clature, by tbe addition of a third name, to indicate the more
important phases of specific variation, which name is preferably
derived from tbe Latin language, and in construction and modifica-
tion is subject to the same rules as the specific names ; if, howevei-,
the word Varietas in either its fidl or contracted form be interpo.sed
between the specific and varietal name, the varietal term if in the
adjective form, should ahvays take the feminine termination :
Example, Sphtcruim lacustre var. hracli^nuart, Bonrgt. If, however,
that word is not interposed, and it is not essential that it .Giould be,
then the varietal name must accord in gender with the generic
term ; Example, Spharium Idcustre brochontduam Bonrgt.

Mon.stro.sities when named, which is seldom desirable, take the
neuter termination, if the word Monstrum, or one of its contractions,
is interposed between the specific and monstral names, the latter
beingin the adjective form: Example, Lhnmm ptrepra \\\.)^hd^<trcrmm
Jeffr., but when the word Monstrum is omitted, tbe trinomial term
must agree with the generic name, as in the varieties : E.xample,
Limncm perecjra sinidrorsa Jeffr.

Though it is desirable that a name should recall or indicate some
character or peculiarity of the organism, it is not absolutely
essential that it shouhl do so, as a name is simply a name, mark, or

B

18

NOMENCLATURE AND SYNONA’MY.

s^Diibol set upon objects to distinguisli tlieni from otliers, ami is not
a defiiiitiou of their characters. Many scientists, however, owing to
the difficulty of finding appropriate and characteristic names which
express some quality pecnliar to the species, not slurred in a greater
or lesser degree by otliers in the same genus, decidedly prefer and
advocate names which are only arbitrarily connected with the
organism and denote or inqily no character or peculiarity of the
object. It is, however, very desirable that an uniform and conveir-
tional code of names should be used to indicate the same mode
of variation in the different species ; thus (lUxi could be used to
designate the pure white or albine shells, the term albhla being
reserved for the whitish forms, when it is considered necessary to
give them a special designation ; rufa could be employed for the
rufous specimens, luqnitica for the liver-coloured ones, roM-a for the
pink ones, etc., etc. Variations of form, sculpture, size, thickness,
markings, etc., could be similarly indicated by appropriate, ex-
pressive, and euphonious terms, the great aim being to ensure as far
as practicable the application of the same term to the same character
of variation, in every species.

LITERATURE.

Uei)ort of a Coininittee a])pointe(l “ to consider the rules hy wliicli the
Nomenclature of Zoology may he estahlished on a uniform and j)er-
uiaueut basis.” — IJejiort of the Twelfth Meeting of the IJritish Associa-
tion for the Advancement of Science, 1842, ))p. 105 — 121.

Report of a Committee “ appointed to report on the changes which they
may consider desirable to make, if any, in the Rules of Zoological
Nomenclature, drawn up by Mr. H. E. Stidckland, at the instance of
the Riitish Association, at their Meeting in Manchester in 1842.” —
Report of the Thirty-Fifth Meeting of the Rritish Association for the
Advancement of Science, 1865, pp. 25 — 42.

Dali, W. H. — Nomenclature in Zoology and Botany. —A Report to the
American Association for the Advancement of Science at the Nashville
Meeting, August 31, 1877. — Salem, Dec. 1877.

Tryon, G. W., jr. — Structural anil Systematic t'onchology, 1882.

Regies de la Nomenclature des ctres organises adoptees par le Congrcs
International de Zoologie. — Zoologischer Anzeiger, No. 3.31 ,Mch. 31 , 1890.

Regies de la Nomenclature adoptees jiar let'ongrcs Zoologiipie de Moscou.
— Zoologischer Anzeiger, No. 406, Nov. 28, 1892.

Synonymy.

From the wide distribution of many .species, tlie great number of
scientific publications in many languages, and tlie earnest pursuit of
scientific study by a constantly increasing number of students, it
almost necessarily follows that many species have names bestowed
upon them by more than one person, either from ignorance of each

SYNONYMY AND SHELL.

19

other’s labours, from a personal conviction of the unsuitability of
the name previously applied, or, from a misapprehension of specific
characters, which leads them to confuse one species with another, and
therefore apply theii- names incorrectly; thus Draparnaud mistook the
French form of Heliv aintkma for Helix cartuidana and thereui)on,
in the belief that the shell was new to science, described the true
cartusiana as Helix carthusianella ; the synonymy of the two species
ill reference to this illustrative incident is shown as follows : —

Helix eantimm Mont. j Helix cartusiana Miill.

Helix carthusiana \)Ya.\). ho» Miill. ! Helix carthusianella

The variability and wide dispersal of Limncea pereejra, and conse-
quently the protean forms assumed under different conditions of
e.xistence by this variable and mobile species, have led to its various
modifications being designated by very numerous names intended to
denote in the opinion of their authors either specific or varietal
differences. For this species alone over three hundred names have
been catalogued, all specifically synonymous, and the great bulk of
the names applied varietally must also be of the same character and
refer to modifications previously discriminated and named.

Probably these evils will never be entirely overcome, and it will
therefore be a continual task to investigate and place in the
synonymy of the approiiriate species the duplicate or incorrect
names bestowed or wrongly used from time to time. These
incorrectly applied and duplicate names are termed Synonyms.

Some of these names, though ajiplied to species already discrimi-
nated and named, may rejiresent strongly marked geographical or
zoological variations, and as indicating such are worthy of retention
in the varietal nomenclature.

Shell.

Tlie great majority of mollusks have an external covering or shell,
which is acknowledged to be so characteristic a feature in the group,
that the term Te.stacea (from testa a shell), has been very appro-
priately applied to them. One distinguished scientist. Prof. Ray
Lankester, has even imoposed the application of the term Conchifera,
or shell-bearing, to the whole of the Mollusca, a name previously
restricted to the Lamellibranchs. Although the internal oigans of
the animal often exhibit more important and permanent characters,
yet the close and intimate connection existing between the animal

20

STKUOTURE OF SHELL.

and its shell, which is also, as truly, an organ of the animal, confirms
and supports the importance attached to the shell in classification.

Shells are termed E.xternal, when they are capable of containing all
or part of the animal ; and Intern.\l, when enclo.sed or concealed within
the mantle, and serve not only as a support, but also as a iirotection
to the internal and vital organs, and may he considered to represent

Fir,. 11. — An Internnl Shell.
Li >11. IX »iaxi»ins L. X 2,
C'hrislcluirch, Hants.,
Collected hy Mr. C. Ashford.

Fig. 13. — An External Shell.
Helix noiioralis L.,
llltton, near Hath.
Collected hy Miss F. M. Helc.

the internal skeleton of tlie Vertebrates, giving similar evidence of
their natural affinities and relationship, the contour and structure of
the shell lieing always in harmony witli the organization of the aaiimal
and with their differences in form and composition, establish how ex-
ceedingly important is the study of the shell itself, and to geologists
esjiecially this importance is vastly increased, as their fossilized re-
mains are the only relics of the vast numbers of now totally extinct
sjiecies, and from these remains alone, we are able by induction and
comjiarison with onr recent forms, to infer with great jirobability the
organization, habits, and habitats of these long extinct organisms and
gain some clue to the physical conditions of these remote times.

Though differing considerably in appearance, structure and texture,
shells principally consist of an organic chitinous substance and car-
bonate of lime, with a chemical formnla of CaCO.-j. M. Delacroix
has stated that the shell of lleli.v jwmatln is composed of (idTb per
cent, of carbonate of lime, KJ'dO i)er cent, ot other mineral substances,
and 1S ()4 per cent, of organic matter, bnt a specimen of the same
species from Cheltenham, examined by Mr. Crowther, yielded
strikingly <lifferent results: the total weight of the shell was ()'2!)<S
grams, which analysis showed to be composed of (j'CiO.') grams of
inorganic substances and 'ITTb gram of organic matter, or 2’<S1S
per cent, of organic substances and DT'DSIG per cent, of caihonate
of lime and other earthy salts. An example of Jauukcu stiCfjnal/s,
weighing '081 gram, also examined by Mr. Crowther, yielded on
analysis ‘GGOd gram of mineral matter, chiefly carbonate of lime

STRUCTURE OF SHELL.

21

and '0207 gram of organic matter, or 9G'96 per cent, of inorganic
substances and .8 '04 per cent, of organic matter.

Tlie calcareous portion of the shell
has always an organic basis, which is
first secreted and then gradually
impregnated with the carbonate of
lime, which latter substance is some-
times deposited in layers of very
distinct character. The organic basis,
which is termed Conchyolin, main-
tains the life of the shell, for on the
death of the animal it soon disappears and the shell gradually becomes
almost pure carbonate of lime, and very brittle ; there are, however,
in some species traces of carbonate of magnesia, silicic acid, phosphate
of lime and minute quantities of other substances. The specific gravity
of shells generally is somewhat higher than that of Carrara marble,
and many are perceptibly harder than, and will scratch, calc-spar.

The inner layer of the shell, when duller than in nacreous shells, is
termed porcellanous, but it is often iridescent or pearly, this charming
appearance being caused by the peculiar disposition of the shelly matter
in thin overlapping la3mrs with minutely corrugated edges, which
diffract the light and thus causa the iiide.scent effect, the thinner and

more ti’ansparent the overlapping plates,
the more beautiful the lustre. This inner
layer is secreted by the whole surface of the
mantle and, according to Mr. Carrington,
owes its exquisite smoothness in Hell.r
jioiiKitid to a surface deposit of almost pure
silica. The free glandidar margin secretes
or forms the middle or prismatic layer,
consisting of prisms of carbonate of lime
arranged in a particular way.

The outer surface, epiconch, or periostracnm, perhaps better known
as the epidermis, is also a product of the collar of the mantle ; it is
of a chitinons nature with a complex chemical composition said to be
represented by the chemical formula CisHouNoOioi Rud varies
remarkably in its thickness and general character, appearing to be
analogous to the periosteum of the bones of the Vertebrates. It is

Fig. 16. — Surface of Nacre
or Pearl, highly magnified,
allowing tlie iinnute undula-
tions upon whici) the pearly
lustre depends (after Tryon).

Fig. lo.— Oblique section through the
shell of L'nio (magnified), showing the
three layers of which the shell is com-
posed (after Semper).
e. periostracum or epidermis, the ex-
ternal layer; prismaticor middle layer;
n. nacreous or inner layer.

22

STRUCTURE OF SHELL.

very persistent and almost indestructible and has been observed still
adherent to tertiary fossils ; its chief olhce -would appear to be to
protect the calcareous portion of the shell from the disintegrating
influence of external conditions, but on the death of the animal, if the
shell is left exposed to the weather, this epidermis is very quickly
deciduous, though practically persistent during the life of the animal.

This protective covering is strongly developed and remarkably
varied in freshwater shells, and in land species habitually fre-
quenting moist and shaded situations, it is also sometimes the seat
of the colouring matter with which shells are often ornamented,
but usually the pigment is resident in the calcareous portion of
the shell, the epidermis or i)eriostracum being generally of a trans-
parent or semi-transparent horny tint, through which the colouring
is seen more or less vividly. In some of the Philippine Bid'nni the
epiconch or epidermis is double, that is formed of two distinct layers,
and this peculiarity has been showii by i\Ir. 'I’ye to be shared by at
least one British species, the IlcJi.r (n-h/isfonim ; this duplication of
the periostracum is best seen in the variety .//i'Nywo/.s’, as the less
persistent external film is in that form darker in colour than the
inner layer, it however very quickly exfoliates, and is therefore
freciuently found only in more or less isolated and irregular i)atches,
chiefly upon the body whorl.

The varied sculpture and projecting processes which ornament
many species, and are sometimes especially indicative of maturity,
or of periodic cessation of growth, have often their internal support
and receive their character and form from the calcareous portion of
the shell, but the hairy or bristly appendages which distinguish many
species would appear to be solely epidermic in origin and character.

Giimbel has demonstrated by experiment the enduring character of
the outer or epidermic layer, and shown that carbonic acid gas dis-
solved the compact portions of shells more (juickly than those less
closely aggregated, agreeing thus with the observations of geologists,
which tend to show that the outer layer of shells is better preserved
than the nacreous, and this than the fibrillar layer.

If the carbonate of lime in a shell be removed by acid, the organic
residuum may still retain the shape of the shell, forming a sort of
membranous framework, as the chitinous epiconch is scarcely affected
by ordinary acids, though dissolved by caustic alkali. Mr. Crowther

THE SHELL IN UNIVALVES.

23

has demoustrated that a 10 per cent., or even a weaker, solution of
hydrochloric acid gives the most perfect and satisfactory results, a
stronger solution tending to injure or impair the exquisite delicacy
and beauty of this organic covering of the shell substance.

Shells are formed or secreted by the mantle, and are of infinitely
varied shapes, consistence and ornamentation, and though organi-
cally connected with the animal, are not vascular structures and have
therefore no inherent power to repair any injuries they may sustain,
but if the injuries are situated at or near the margin of the aperture
they are fully and completely repaired by the
collar of the mantle, with the pattern and
ornamentation perfectly reproduced, as in the
normal shell, so that the reproduced portion
is often only distinguished with difficulty ;
if, however, the injuries are remote from
the margin, the repairs are entirely made by
the visceral mantle and are thus deficient
of colour, ornamentation, or epidermis.

Fig. 17. — An Univalve Shell
showing injuries remote from
the aperture, as repaired by the
visceral mantle.

Helix nemoralis L.,

Peel, Isle of Man,
Collected by Mr. E. Collier.

The class Gastropoda, which includes all our Univalve shells, is
the most typical and numerous group of the Mollusca, exhibiting
in the highest degvee the characteristics of the sub-kingdom, and
showing least affinity in structure with other organisms.

The shell, with few exceptions, is composed of one single piece or
valve, hence the term Univalve, though Woodward considers this
single piece to he homologous with the two shells of a Bivalve united
above. The shell is usually of a conically tubular form, enrolled
more or less closely around a central axis, thus diminishing the

Fig. 18. — A Dextral Univalve.
Helix neiKoralis L.,
Piperstown, Co. Louth,
Collected by Miss S. Smith.

Fig. 19. — A Sinistral Univalve.
Helix nonoralis m. sinistrorsum F^r.
Sandhills, I’undoran, Co. Donegal,
From Miss F. M. Hele.

space occupied and securing a more portable and compact shell,
and is, with a few exceptions, coiled dextrally— that is, from left to
right. It is in most species (piite easy to distingui.sh a dextral
from a sinistral shell. A simple method is to hold the shell with its
apex upwards and its mouth directed towards you, when if the

■24

FORMS OF SHELL IN UNIVALVES.

aperture is on your right hand tlie shell is dextral, if on your left,
sinistrul, as shown in the foregoing figures.

The length of the tube, its shape, and its closer or more open
mode of convolution, gives rise to a great variety of forms amongst
the different .species, the principal of which are

Elongate, Terete, or Subulate, when the shell has
the spire greatly produced and pointed, as in
Ili'U.r acuta j^lulh, CwciUoide^ acicula, (Mull.),
lialca peri'evMi (L.), etc.

Fig. 2D. — Example : Helix acuta Miiller, Point Scarlet, near Castletown, Isle of Man,
collected by Mr. A. Taylor.

Turreteu, when the shell is elongate, but the upper
portion (jf the whorls are shouldered or angulated,
as in L'niuuva truncatula (Miilh).

Fig. 21. — Example : Limnwa truncatula var. turrita Clessin, ditch, Ilicriey, near
Bradford, Yorks.

CvLiNDurc.VL, when the shell is cylindrically elon-
gated, as ill Pupa muscorum (L.), Vertigo eden-
tula (Drap.), etc.

Fig. 22. — Example : Puf>a inuscoruiu var. clonc^ata Clessin x 3, rcjectamcmla of River
Stour, Sandwicli, Kent, collected by .\ir. S. C. Cockerell.

Fusiform, or Si’inole-.sii.vi'ED, when the shell is
swollen in the middle and tapering at each end,
as in Auxa trident (Fult.), C/ausi/ia lamiuata
(iMont.), etc.

Fig. 23— Example: Azcca tridcns yixx. noulctiana Dupuy X 3, Lewes, Sussex, collected
by Mr. T. S. Hillman.

Tufhun ATi'R), when the shell is of a conical shape,
with a. rounded base, as in Liiuihca sfa^f/udis
(Einiie), llpf/ini/a teutacuUda (L.), Viripara
rii'ijiara (L.), etc.

Fk;. L'L— E.xainpli; : Hytkinia ti iilaculata (I,.) X 2, River Lc-.v, C'lnniiroril, Essex, colleclvtl
b}' l)r. R. F. Scharfl', 15. Sc.

CoNTABULATE, ivlieii the shell is short, with
shouldered or angulated whorls, as in
Lnnna’a rfaguahr var. hodaiiiiea IMdler,
Plntra fiDitinal!^ v. iuttata Moij., etc.

Fiii. 2.3.— Example : Linuuca stai^nalis \:xx. bodainica Miller, Roden See, Swit/crland,
collected by Herr Schenk.

FORMS OF SHELL IN UNIVALVES. 2o

Patelliform, wlieu the shell is limpet-shaped or
conical, as in Ancylui^ Jiuvidtilis Mull.

Fig. 2o. — Example: Ancylus JIu7fiatilis Miill. X 2, Sv.'arraton, Hants., collected by
Rev. W. L. W. Eyre, M.A.

Globose, when the shell approaches a sphere
in .shape, as in Helix granulata Alder.

P'lG. 27. — Example : Helix granulata Alder X 2, Ashley Downs, near Bristol, collected
by Miss F. M. Hele.

Trochiform, or Conoid, when the shell is conical,
with a flattened base, as in Helix terrestris
Pennant, Hyalinid fulm (Miill.), etc.

Fig. 28. — Example ; Helix terrestris Pennant, Dover, collected by Rev. J. W. Horsley, M. A.

Lenticular, or Lens-shaped, when the shell is of
a depressed form, with a more or less acute
peripheral margin, as in Helix Idyicidd L.

Fig. 29. — E.vample: Helix lapicida L., St. Vincent Rocks, Clifton, near Bristol, collected
by Mr. J. \V. Cundall.

Depressed, when the spire is only slightly raised
above the body- whorl, as in Helix itdhi L.,

Hydlinid nitidiihi (Drap.), etc.

Fig, 30. — Example : Helix itala L., Tenby, S. Wales, collected by Air. W. H. Boland.

Dlscoidal, or (^uoit-shaped, when the shell
has the spire flattened or even sunk in
the centre, as in the Flduorbes, Vdlcdtd
cristdtd Miiller, etc.

Fig. 31. — Example : Planorbis corneus var. albina Moq., Mill pond, Lifi'ord, near King’s
Norton, Warwickshire, collected by Mr. J. Madison.

Gibbous, when the whorls are transversely
swollen, usually near the aperture, as
occasionally occurs in Limnad duriculdrid
(L.), Limnwd stdyndlis (L.), etc.

Fig. 32. — Example: Liiiintea auricularia var. ^ibbosa Taylor, pond, Moorlown, near
Leeds.

ScALARiFORM, wheu the whorls are almost separated from each
other, as occasionally observed in Helix porndtia L., Helix

2G

FORMS OF SHELL IN UNIVALVES.

aapcmi MiilL, Succiiteti putris (L.), Limmva peregra (Miill.),
and many other species.

Fk;. 33.— .\ Sc.M.iriform Helix-. Fig. 3L— -V Scalariforni Limn.xa.

I/c/i.v ncmoralis monst. scalnrc Fir., Limiura stagnalis m. scalari/ormc Ckll.,

Truro, Cornwall, Pond, Chislehurst, Kent,

Collected by Mr. J. H. James, A.R. l.C. Collected by Prof. T. D. A. Cockerell, F.Z.S.

Cer.vtoii), or SoALAUiT), wlieii the wliorls are
([uite detached and separate from eacli
other, often resembling a corkscrew, a. ram’s
horn or a cornncopia, as occasionally fonnd
in Ikilv mpcrsa Mhller, lldlv pomatia. L.,

Phdiorhis n/nh/'/icdtUK Miiller, /^((iiorhis
xj)in/rhit< Miiller, etc.

Kig. 35. — Example: as/crsa m, ( imeliu, garden

of IMavvnan Sanctuary, near Falmouth, collected by the
late Rev. W. Rogers, M.A.

A Whorl is one complete spiral coil
or volntion of the shell, and the one
completing the shell and ending at the
aperture is termed the Body-Whorl ;
this is nsnally, hut not invariably, the
most capacious as well as the last formed,
and in the diaicious species, as Cychstonni,
eleganx, is more tumid and volnminons
in female than in male individuals. The
whorls also vary in number in the diiferent .siiecies, some, as Vitr 'uKO,
'l\'xfnccll((; etc., having few and raiiidly-enlarging whorls, while others.

P'r'.. 3(5. — P'emale. Fra 37. — Male.
Cyclostoma eU'gans (Midi.),
Yarmouth, I. of Wight,
.showing the sexual difference in
the tumidity of the whorls.
Animals dissected and the sexes
verified by Mr. Clias. Ashford.

P'lG. 38. — A Paucispiral Univalve.

Viti'ina pelhicida v. dcprcssiuscida Jeffr. X 2,
Haldon, Exeter,

Collected by Mr. E. I). Manjuand.

as the various species of Ikaimrliix,

Fig. 39. — .V Mullispiral Univalve.
riauorbh coiitortus X 2,

River Colne, Watford,

Collected by Mr. J. Uojtkinson, F.I^.S.

etc., have nnmerons and more

closely-coiled volutions. The whorls also e.xhihit peculiar characters

SCULPTURE OF WHORLS IN UNIVALVES.

27

according to the specie.s, showing great diversity in sculpture, colour-
ing, and in the spinous, bristly or other appendages thereof. The
various characters of the whorls may be designated as

Striate, when the parallel scidpture is fine and close; termed
Spirally Striate when the stronger lines revolve with the
whorls, as \n Planoi'his albus (L.); and Transversely Striate
when they cross the wlioids and are more or less coincident
with the incremental lines of growth, as in the generality of
the testaceous mollusca. Tryon and other authors term the
spiral striation transverse or revolving, and regard the transverse
strise as longitudinal in character.

Fig. 40. — A Transversely
and Strongly-Striate Univalve.
Ifeli-v caf>crata Mont.,
Perth,

Collected by Mr. Henry Coates.

Fig. 41. — A Spirally Striate Univalve.
Planorbis allms (L.) X 3,

Scout Dam, Penistone,
Collected by Mr. L. E. Adams, R.A.

Hispid, or Pilose, when the whorls are more or

less densely covered with hairs, as in Helix
(jranulataKXAQx, H.kiitpiddl^lyxW., etc.; orthe
hirsute appendages may be of a more downy
character, as in the young of P. corneas (L.),
etc., which are then termed Pubescent.

Fig. 42. — Example: Helix gratmlaia Alder x 2, Ashley Downs, near Bristol, collected
by Miss F. M. Hele.

Coronate, when the spinous processes spirally
encircle the whorls in a coronate form, as in
Helix aculeata L.

Fjg. 43. — E.xample : Helix aculeata L. X 8, Bassenthwaite, Cumberland, collected by
Capt. W. J. Farrer.

Muricate, Echin.vte, or Spinose,' when the
granulations or ribs upon the whorls are
produced to a sharp point, as in Planorbis
nautileus var. crista (L.).

Fig, 44. — Example: Planorbis nautileus var. crista (L.)x8, pond, Roundhay, near Leeds.

Plicate, or Costate, when the whorls are strongly
ribbed or ridged transversely, as in Helix
palchella var. costata IMiill.

Fig. 45. — F^xample : Helix pulchclla var. costata Muller x 8, Pleshey Mount, near
Chelmsford, collected by Mr. R. Miller Christy, F.L.S.

■28

SCULPTURE OF WHORLS IN UNIVALVES.

SuLCATE, when the whorls are furrowed with
comparatively wide li'roovino's or channels,
as in Phtnorhis alhu^ var. sitlatfa Taylor,
and //e/i.v rottiiid((f<( AliUl.

Fig. 4(3. — Example: Helix rotundata Miilier X 2, Hessle, Vorksliire, collected by
Mr. J. D. Butterell.

Carinate, when the whorls are strongly and
acutely keeled, the carination is most usually
at the periphery, as in Helix lapicidd L., and
Helix terre!^fris Pennant.

Fig. 47. — Example: Helix lapicida L., St. Vincent Rocks, Clifton, near Bristol, collected
by Mr. J. W. Cundall.

Clnuulate, or Lirate, when the whorls are furnished
with spiral ribs or ridgings, as in Vijcloxtanid
eleijdii.'! (Mull. ).

Fig. 48. — Example: Cj'closlof/ia cle^’-iins (Midler), Preston Candover, Hants., collected
by Mr. H. P. Fit/gerald.

Decussate, Lacunose, Malleate, or Cancellate,
when the spiral and transverse stri;o or plicm of
the whorls form hy their intersection a series of
somewhat ([uad.rangular and slightly hollowed
areas; the intersecting lines form the style of
sculpture termed Ueticulate when they cimss each
other more or less ohlicpiely.

Fig. 49. — Example: Li)nna'a pulustris var. lacunosa I’aylor, stream, 1 .cvciithorpe
Pastures, near Leeds.

Varicose, when the thickening and som ‘times con-
sei|uent differeni colouring of the apmlnral
margin, occurring in some shells, during rest
periods in the process of growth, are not ah-
sorhed hy the animal when growth is resumed,
but remain crossing the whorls at regular or
irregular intervals, as in Limnaja stiujiddis (L.),
Helix lie mum /is L., etc.

Fig. 50. — Example: Linuuva stagjialis var. variesata Ha/ay, PefTer Burn, I.ufl'ness
Links, Haddingtonshire, collected by Rev. l)r, McMurtrie, F. R.S.E.

The Umbilicus is the central cavity at the base of the shell and
distinctly exists only when the columella is hollow, and is wide or
contracted in correlation with the loose or constricted manner of

THE UMBILICUS AND COLUMELLA IN UNIVALVES.

29

coiling ; when fairly developed so that one or more of the previous
whorls are visible, as in Ilellv the shell is said to be Umbili-

CATEi) ; if the orifice is small, as in Helix gninnldta, it is said to lie

Fig. 51. — A Widely Umliilicatcd Univalve.
llcU.v itala Linne,

Royston, Canibs.,

Collected by Mr. H. (b Fordham.

Fig. o2. — \ Perforate Univalve.
Helix _e^rnnulata .Alder X 2,
Moslyn, Flint,

Collected by Mr. W. 1). Roebuck, F.L.S.

Pervious or Perforate ; when very compressed, or a mere fissure,
it is termed Rimate, as in Viripara viripara (L.) ; but when the

Fig. 53. — A Rim.ate Univalve.
I’k'ipara Tivipara I..,
Canal, Marple,

Collected by Mr. William Moss.

Fig. 54. — An Imperforate Univalve.
Helix hortensis Midler,
Fordinj?bridge, Hants.,
Collected by Air. H. Richardson, M.A.

colnmella is solid the shell is then called Imuerforate ; some
species such as Helix hnytennix, Helix dxperxa, etc., are umbilicate
or perforate when young, but at maturity become imperforate by
the e.xtension of the lip over the umbilical cavity (fig. 56).

The Columella, or Pillar is the central portion or axis, real or
imaginary, around which the whorls of the shell
are coiled, but in very openly coiled or scalarid
specimeii.s the columella is only theoretically exist-
ent (p. 26, fig. 35). In the elongately spiral shells
the columella, though
always sinuous, may be
nearly straight as in
CUmsilid, but in other
cases, as in many Helicex,
it may be very tortuous
and strongly twisted.

Some species, as Neritina
fuvidtilix and Cdryeliium

niininuDu, absorb either wholly or in part not only

Fig. 55. — Section
through the shell of
Clansilia Inininata
(Mont). X 2, showing
the nearly straight
columella (from a sec-
tion cut by Mr. F.
Rhodes).

Fig. 56. — Section through shell
of Helix nenioialis L., showing
the somewhat twisted and hollow
columella and the method of closure
of the umbilicus at the maturity of
the shell (from a section cut by
Mr. F. Rhodes).

%

30

SPIRE, BASE, ETC., IN UNIVALVES.

the columella but also the shelly partitions separating the coils of
the body, so that in extreme cases the interior
of the .shell forms one simple cavity only, owing
to this absorption of its internal divisions.

Other species, as Cdrillolde.'^ acicnJa, I'extdci'lhi
sciitii/iim, etc., have the columella truncate
at its base ; this peculiarity has been held to Fio.oT—Univaivewiti.
indicate carnivorous propensities in the species

1 ‘i-'i* *1- liishopswood, Ross, Here-

6XlllOltlU;^ it. fordshire, collected by

Rev. R. W. J. Smart, M.A.

P'lG. 58. — Univalve F'lO. 59. — Univalve with

with Klongate Spire. Depre.ssed Spire.

L. f^lab a (Miiller), P. corncus albina Mo(j.,
Twenty Pits, Mill Pond, KifT«)rd,

near Manchester, near Ring’s Norton,

Coll, by Mr. J. R. Hardy. Warwickshire,

Coll, by Mr. J. Madison.

The Spire includes the
whole shell, with the excep-
tion of the last or body
whorl, and is very varied in
the character and disposi-
tion of its coiling. It may
be di.scoidal or Hat, as in
Phtnorhis, or greatly elon-
gated as in Limmrd (jidhrd.

The Apex or nucleus of the shell originates
in the ovum, and is the first and smallest
whorl, and in some genera has great signifi-
cance, being differently formed from the rest
of the shell. In the
JMk elongately coiled .species

%

Kit,. 00.

pi . , . , Univalve with Ape.x J’erfect.

llKG ij. the Li/una'a palustris Mull.,

. Maidenhead, Herks.,

tip IS lltlble to erosion ColI. by Mr. C. G. Harrelt.

and loss, the shell thus becoming decollate;
the discoidal freslnvater shells are not exempt
from this injury, the Plduorhes being found

Kig. G1.

A Decollate Univalve.

Limnwa pahistris Miiller

u\. (iecollatum JefTr., j. /*

Quarry, Christleton Rd.Che.ster, liot Ullire(|lieiltl V pGl lOnitcd tlirOU^(ll tllC CClltl’e
Coll, by Rev. H. Glanville . ®

liarnade, M.A. Oil aCCOUllt of tlllS 61*0-

sion and lo.ss of the earlier and smaller whorls.

The Base of the shell is the o])j)osite
extremity to the apex ; it is the anterior
end and is the last formed jiart of the .shell.

The Periphery is that portion of each
whorl which is the most outwardly produced

Pic;. G2.

Hasal aspect of an Univalve
(slightly enlarged).
Helix hortensis Muller,
Fordingbridge, Hants.,
Coll.byMr.H. Richardson M.A.

SUTURE, APERTURE, ETC., IN UNIVALVES.

31

and is usually medially placed between the
suture and the base, following the spiral course
of the volutions. In the carinate species, as
TTelix lapldda, the keel
decisively indicates its posi-

Fic. 63. — Univalve
with Carinate Periphery.

Ifelix lapicida L.,

St. Vincent Rocks, Clifton

near l>ristol, . . , , , ,

Coii.byMr.j.w.cunciaii. tioii, aiKi less sti'ongly SO

Fig. 64. —Univalve with
Sub-carinate Periphery.
Helix caper at a Mont.,
Perth,

Coll, by Mr. Hy. Coates.

Fig. 65. — Univalve
with Rounded Periphery.
Helix neJfiofalis L.,
Isle of Lisniore,

Coll, by Mr. A. Somerville,
B.Sc., F.L.S.

when the keel is only faintly developed, as
in Jlelir cdperaUi, when the .shells are termed
sub-carinate or angulated;
but in those species with regnlarly convex
whorls, as Helix nemoralis, its precise position
is more difficidt to define.

The Suture is the line of junction of one
whorl with another, and varies in character and
distinctness in accordance with the convex or
planate outlines of the whorls. It may even
be canaliculate or channelled, crenulated, or puckered, or simply
more or less deeply impressed.

The Aperture of the shell is the part last
formed and is the opening through which the
animal protrudes its body ; it may be almost
exactly round, semi lunar, or other .shape, and is
sometimes so greatly contracted with teeth or
folds as to form almost a matter of surprise how
the animal can insinuate its body through the
constricted space.

The Peristome or Peritreme is the margin of the apei'ture and
may be distinctly continuous and detached during
the whole life of the animal, as in Cydustoma
eIe(j<tnK, or only distinctly continuous and de-
tached at matur-
ity, as in Helix
hipicida and in
the Clmmlicv.

It may however
have the con-
tinuity of its outline tind character
broken by the penultimate whorl.

Fig. 66. — Univalve
with a Contracted
Aperture.

antiveriigo (Dp.)
X 20,

Hemsworth, Yorks.,
Coll, by Mr.C.Ashford.

Fig. 67. — Univalve
with Detached and Con-
tinuous Peristome.
Cyclos. elegans (Midi.),
Preston Candover,
Hants.,
Collected by
Mr. H. P. Fitzgerald.

Figs. 68 & 69. — Helix lapicida L.,
Wells, Somersetshire,

Showing the Continuous and Detached
Peristome of Adult shell, and the Interrupted
and Simple Peristome of the Immature stage.
Collected by Rev. S. Spencer Pearce, M.A.

8-2

APERTURES IN UNIVALVES.

and is then tenned “ intevnipted”; this separ-
ation is, however, only apparent, as the wliorl
is in all cases a complete tube, the pen-
nltiinate whorl not forming the inner wall of
the aperture, as has often been stated,
in^i^i^upt^^Peristome."'' but merely the foundation or support for the
^sV^uniTwrvorks.’, iiiiier portion of tlie last formed wliorl, thus
E.L.s. enabling' it to liave the tlunness and delicacy

which usually characterizes it and has caused its e.vistence to
lie overlooked or ignored. The left side which is so often closely
appressed and adherent to the preceding whorl, is called the
Inner or Oulumellar Lip, and also the Labium. Pfeiffer terms
the portion of the aperture supported hy tlie penultimate volution
tlie Parietal Wall.

The Palatal Lip, Outer Lip, or Labrum, is the right side of the
_ aiierture in de.xtral shells and is usually thin and

{ sharp in immature shells (p. 81 , f fiS); but in .some

^ y genera, as niialhiid, it remains so in full-grown

I'lc^. 71. — UnivMve .siieciineiis, but generally it is thickened, e.\-

willi Siln])lc Peristome. t ft i* t l i i

/«</</,! (I trap)., paiided, or develops tectli-like tolils, and other

Torquay. . ■ / t-

Coll, by .Mr. 11. s. DotUb proiiiiiieiices at maturity (j). 81, figs. Ol!, (i;)).

d'he Aperture has its length parallel with the
length of the shell, and its width transversely to
this ; its many moditications in form and character
may usually he ranged under one or other of the
following he-i Is, and is considereil to be

Longitudinal, when its length is iiarallel to or
coincident with the a.xis of the shell, as in
.'tfiujiKtlh (L.).

I' lc.. 7*2. — K.vainple : Lhnna'a sta^s^nalls (L.), Vartlley Chase, Northamptonshire, collected
by Mr. Lionel K. Adams, B.A.

Aurieorm, or Auriculate, when the aperture
has ajipro.ximately the shape or outline of
the human ear, as in many species of
Lhniuvhiw.

Fig. 73. — E.vample : Livinwa nuricularia var. nlhida Jeffr., near London, collected hy
the late Mr. J. Pickering.

APERTURES IN UNIVALVES.

33

Oblique, when it is produced more or less
obliquely to the axis or columella of the
shell, as iu Helix aspersci Midler, Helix
nemoralis L., etc.

Fig. 74. — Example: Helix nemoralis'L.y Bitton, near Bath, collected hy Miss F. M. Hele.

CoMPRBSSEU, when the aperture is diminished
or compressed at the entrance, as in Azeca
tridens (Pult.).

Fig. 75. — Example : Azeca tridens var. noidetiana Dupuy X 3, Lewes, Sussex, collected
by Mr. T. S. Hillman.

Circular, when almost perfectly round, as iu
Valvata 2^iscinaHs (Midi.).

Fig. 70. — Example: I'alsnita fiiscinalis X 3, Graiitstown, Tipperary, collected

by Mr. R. Rimmer, F.L.S.

Lunate, when semi-lunar or semi-circular, as in
Hi/(ilini(i lucidu (Drap.).

Fig. 77. — Example : Hyali7iia lucida (Drap.) slightly enlarged, Torquay, collected by
Mr. 13. Sturges Dodd.

Rounded, when not perfectly round, owing to
the interruption hy the penultimate whorl,
as in Helix pulchelhi Miill.

Fig. 78. — Example: Helix pulchella Miiller X 8, Kennington, Berkshire, collected by
Mr. W. Wiiitwell, F.L.S.

Transverse, when its greatest extension is at
right angles to the axis, as iu Helix
lapicida L.

Fig. 79. — Example: Helix lapicida L , St. Vincent Rocks, Clifton, near Bristol, collected
by Mr. J. W. Cundall.

Pyriform, when the aperture is pear-shaped iu
outline, the compressed portion formed hy
the posterior sinus and the swollen part
being at the anterior end, as in most species
of the genus Cldusilia.

Fig. 80. — Exatiiple : Claitsilia laitiinata (Mont.) X 2, Win-
chester, Hampshire, collected by Mr. J. R. Brockton
Tomlin, B.A.

C

34

APEIlTUllES IN UNIVALVES.

Patulous, when the aperture is openly ex-
panded, dilated or funnel-shaped, as in
IT(>li,r pulr/i('n<i Miill.

Fic. 81. — Example: Helix pulchclla IMiiller X 8, Kensington, Ilerk.shire, collected by
Mr. W. Whitwell, F.L.S.

Sinuous, when the outer margin is indented or
sinuate in one or more places, as in Vertigo
antivertigo (Drap.), Vertigo angustior Jeft’r.,
etc.

Fig. 82. — Example : I'ertig-o aniivertigo (Drap.) X 20, Hemsworth Dam, Yorkshire,
collected by Mr. C. Ashford.

Reflected, Retuse, or Revolute, when the
margin is folded or turned backwards, as in
Lininau peregra var. labiosa Jeffreys.

Fig. 83. — Example: Limna'a peregra var. labiosa Greenhcad Park, Huddersfield,

collected by Mr. J. Whitwham.

Inflected, or Involute, when the margin
is folded or turned inwards, as in Lininau
auricalaria var. gihhosa Taylor.

Fig. 81. — ICxample: Linimva aitricularia \Zi.T. gibbosa Taylor, pond, Moortown, near
Leeds.

Deflected, when the aperture is bent down-
wards from tlie spiral line of coiling on
the approach of maturity, as in Helix
itala L., Helix nemoralis L., etc.

Fig. 85. — Example : Helix itala L., Tenby, S. Wales, collected by Mr. W. H. Boland.

Dentate, when furnished with internal teeth
or projections, as in Pupa muscorum (L.),

Caryehium minimum Mull., etc.

Fig. 86. — Example : Carychimn Jiiinimuf/i Mnller X 16, Ceunant, near Welshpool,
collected by Mr. J. Bickerton Morgan.

MEASUREMENT, ETC., OF UNIVALVES.

35

Plicate, or Lamellate, wlien the internal
folds or teeth become rih-like in character,
as in Piipd ftecale Drap.

Fig. 87.— Example : Pit fa secale Drap. X 4, Mailing Hill, near Lewes, Sussex, collected
by Rev. S. S. Pearce, M.A.

Sept,4.te, when the interior of the whorls are
contracted by projecting shelly processes,
often leaving a tri-radiate opening for the
molhisk, as in Segmentina nitida (Miill.).

Fig.

8.— Example : Segmentina nitida (Muller) X 3, Deal, Kent, collected by Mrs.
Fitzgerald.

Labiate, or Marginate, when callously thickened externally or
internally at or near the margin, as in Helix nemomlis L.,
Helix hispida L., Pupa muacorum (L.), etc.

Fig. 89. — An Externally Marginate Univalve.
Pupa muscontm (L.) X 6,
Stivington, Northampton,

Collected by Mr. W. D. Crick, F.G.S.

Fig. 90. — An Internally Marginate Univalve.
Helix nemoralis L.,

Truro, Cornwall,

Collected by Mr. J. H. James, A.R.I.C.

The Length and Height of an ordinary spirally coiled LLiivalve
shell are considered to be coincident and to be the distance from
the base to the apex; some authors distinguish as simply the
Length, or Height, the distance between the apex and the base of
the umbilicus, and regard the distance from the lower part of the
aperture to the apex of the shell, as the Total Length ; the Breadth
is the distance through or across the most ventricose part of the shell,
parallel with the plane of the aperture, this being the maximum
diameter, the line through the whorls at right angles to tin’s, is
the minimum diameter. The Patelliform Ancyli are usually con-
sidered to have their Altitude or Height in the distance from the
base to the apex or summit ; their Length in the distance from the
anterior to the posterior margin of the aperture ; and Breadth in
the distance from side to side.

36

THE SHELL IN BIVALVES.

The Pelecypoda or Bivalves, also known as Lipocepiiala and
Lamellibranchiata, are exclusively aquatic mollusks, and differ
markedly from the Gastropoda, not only in their shell, but in many
points of their organization, and rank next that group in the number
and variety of its species and genera, though individually the
Pelecypods are relatively the most numerous.

The shells of Bivalves are typically composed of two distinct and
convex or datly conoid pieces or valves, which are ap})lied to the
right and left sides of the animal, and in the dimcions species, as in
the univalves, the shells of female individuals are said to be notice-
ably shorter and more ventricose than those of the males.

'I'he line along which the valves are joined together by the ligament
is called the hinge-line, and is placed on the dorsal region of the
animal, forming the Upper or Dorsal Marhin of the shell ; the
side op[)osite the hinge is the Ventral or Jjower Margin and is

always more or less thin and sharp ; the end upon which the liga-
ment is situated is the Posterior or Siphonal Margin, the orifices
of the hraiichial or iiicurrent and the anal or excnrrent sijihons being

STRUCTURE OF SHELL IN BIVALVES.

37

placed there; the opposite end forms the Anterior or Cephalic
Margin, and is the end where the month of the animal is placed.
The two valves are termed right or left, according as they are placed
on the right or the left side of the animal, and are easily identified
and discriminated ; one method is to place the shell in its natural
position as when the animal is crawling, with the ligament upwards
and towards the observer, and the opposite or anterior end pointing
forwards, in this position the right and left valves correspond to the
right and left hand of the person e-vamining it; or the separate valves
can be distinguished by placing or holding the valve before you, with
the inner surface upwards and the ventral margin toward yon, if when
in this position the ligament lies to the right, then the valve is the
right valve, if to the left, the left valve ; the functional ligament
always being more or le.ss posterior to the nmbones, never anterior
to them. Linn6 and many of the older naturalists described the
ventral or lower margin of the shell as the top, the hinge-line as the
base, and the left valve as the right, and vice versa. C. Pfeiffer and
others follow Draparnaud in regarding the siphonal end as the
anterior one, and as they consider the ventral margin to be the lower
one, the right and left valves of these authors necessarily correspond
with the left and right valves respectively of English conchologists.

The shells of the Uniovido', are like those of man}' Gastropods
composed of three distinct layers; the outer layer or epicouch covers
the external surface, and is reflected over the edge of the shell upon
the free margin of the mantle, with which it is said to be organically
connected. The middle or prismatic layer, according to Macalister,

is absent in the shell of ^ijhwrium,
it is however present in the genus
Anodonta, forming about half the
thickness of its valves, and is com-
posed of numerous polygonal prisms
set oblicpiely to the surface of the shell
and forming a very densely calcified
layer; the nacreous layer is usually
about the same thickness as the
prismatic layer, but it is in this re-
spect to a certain extent dependent upon and proportionate to the
age of the animal, it lines the whole internal surface of the shell.

Fig. 92. — Oblique section through
the shell of Unio (magnified), showing
the three layers of which the shell is
composed and the comparatively enor-
mous development of the nacreous layer
(after Semper).

Cy periostracum or epidermis, the ex-
ternal layer ; p. prismatic or middle
layer ; «. nacreous or inner layer.

38

STRUCTURE OF SHELL IN BIVALVES.

except the free inargiii of the valves, being secreted by the wliole
external epithelium of the mantle, and consisting of a number of
superimposed laminai laden with calcareous particles, as many as
twelve distinct laminai were clearly separated in a valve of an
apparently adult Anodoutu cnguea from Eurwell fish-pond, and we
have possibly in this feature another indication of the age of the
mollusk. In the genus Unto the prismatic layer is comparatively
thin, while the harder and more compact nacreous or inner layer is
very thick.

Though the shells of our Bivalves are approximately ecpial in
thickness thro\ighout their entire extent, yet at maturity there is in
most species a noticeable submarginal thickening developed around
the free edges of the valves, this thickening also occurs, though
less markedly, at the termination of each seasonal or periodic stage
of growth. ]Mo(piin-Tandon atlirms that the Bivalves are thickest
near the umbones, but although this may probably be the case in
most species, and even also in the Uiiloiies, when under the stimulus
of erosive action, they have ahuormally and enormously thickened
the umbonal region, l)y secreting additional layers of calcareous
matter, as a protection against the destructive action of acidulous
waters ; yet usually the thickest part in those shells is the area on
the anterior side near the ventral margin, and in position almost
coincident with the anterior part of the i)allial line and really forming
part of the Ventral Crest of Picard, this thickened part is chiefly com-
posed of the nacreous layer, the prismatic layer in the genus Unio
having its greatest thickness, both comparatively and actually, at
the posterior end of the shell.

The left valve of a specimen of A nodonta cugnea collected by Mr.
W. 1). Roebuck, F.L.S., in Burwell Fish-pond, near Louth, weighing
27 '506 grams, was analysed by Mr. Crowther by the wet process —
the same method as was adopted in the analysis of the shells of
Iltdiv jxinidtia and Limnau ><Uign(dh, the results of which were given
at p. 20 — and gave as a result 25’231 grams of inorganic, and 2'335
grams of organic substances, or 91 '53 per cent, of inorganic earthy
salts, and 8'47 per cent, of organic matter.

The right valve of another adult specimen from the same locality
weighed 36‘8G1 grams, and of this about one-third was analysed by
the dry method, and burned to Calcium oxide, CaO, when the loss of
moisture, organic matter, etc. was found to be 2U U08 per cent.

FORMS OF SHELL IN BIVALVES.

39

The much greater difficulty found in di.ssolving the calcareous
shell of Anodonta, than was experienced in dissolving those of Helix
pomatia and Limna’a stagitalis, suggests the probability that the
calcareous basis of the shell in Anodonta maybe more especially com-
posed of that form of carbonate of lime termed Aragonite.

Bivalves are mostly Equivalve, the right and left valves corres-
ponding with each other in form, size, etc., as in Anodonta cygnea
and other species. All our fresh-water Bivalves are, however, strictly
Equivalve shells, with the exception of Dreissensia polymorpJia which

is undoubtedly Inequivalve, the left
valve being somewhat larger than the
right, and to some extent overlapping
it near the acuminate umbones, and
in addition to this di.sparity in size
and shape, the byssal aperture or sinus
is usually placed exclusively upon the
right valve, though in some specimens
the byssal opening modifies more or less unequally the shape of both
valves and, in rare instances, that of the left valve only. Although
our .species are thus with one exception Equivalve, they are almost
invariably and universally Inequilateral or more or less unequal-

Fig. 93. — An Inequivalve Inequi-
lateral Bivalve.

Dreissensia polymorpha (Pallas),
Baker's Dock, Stourport,
Collected by Mr. J. W. Williams.

Fig. 94. — A Posteriori}* produced Inequilateral Bivalve.

Unio pictoriun (L.), right valve.

Hethersett Lake, near Norwich, collected by Mr. A. G. Stubbs.

sided, the umbo being placed towards one end, and the anterior side
being usually the .shortest, as in Unio pictorum, etc. ; but this is
reversed in Pisidium, as in many .species of that genus, the posterior
side is distinctly shorter than the anterior ; this interesting struc-
tural difference can very easily be verified by observing the position
of the ligament which in Unio will be found to be always at the

40

FORMS OF SHELL IN lUVALVES.

longer side and in Pi.i/diniii at the shorter end of the shell ; this
striking distinction was overlooked by Dr.
Jeffreys, who, in his “ British Conchology,”
erroneously described the posterior side of
the shell of Pis/Jiinii as that most produced.

AVhen the nnibo
is situate about tbe
centre of a syinnietri-
that the outline and
and posterior sides
correspond, the shell is called Eohilateral; fk-,. oo.— a Sub-equiia-

^ . ’ tenil liivalve.

some si)ecies of the genus SiiInci'/uiii have , ■'>■//,«■/■/«/« rAwoAr(Lcacii),

^ O J X 1.',.

almost e(inilatora.l shells. m

-* Lull, by Mr. W. D.CnckjI'.O.S.

I' u;. iK3. — An .\iUeriorly pro-
tluced Inequilateral lb\'alve.

I ''isid'nun a mnicimi ( M ill 1 . ),
right valve, X 2.

Canal, Ambergate,
Collected by Rev. H. Milne,'^.

cally formed shell, so
area of the anterior

Reniform shells are often caused by some injury to the mantle
margin, causing a deticieut secretion at the injured part, and if this
be along the ventral surface a more or less reniform or kidney-shaped
shell results, the amount of siituation depending upon the nature
and amount of the injury sustained hy the animal. The Phid'min
sbvtatam Bourg. is founded on a specimen of Phid'mm cinemun

Fk;. 97- — A Reniforni liivalve.

Unio inargariti/cr \ZiX. sinuata Lain., right valve,

Loch .\\ve, Argyleshire, collected by Mr. A. Somerville, II. Sc., F.L.S.

affected in this way. Lhdio nHirgaritif'r var. Pnmdta is an apparent
e.xample of this peculiarity of shape occurring normally, though Dr.
dray ascribes the form even in this case to the e.xcoriatiou of the
umbones. Mr. Madison has specimens of Anodontd c.yg)ie(i which,
owing to some injury, show this peculiarity in a very extreme form,
the valves being (piite cleft nearly to the umbones.

FORMS OF SHELL IN 15IVALVES.

41

Sympiiynote or Connate shells are those in which the valves are
united together along the dorsal margin, not oidy by the ligament
hut by continuous shell growth, thus forming a shell practically
composed of a single piece. This is a character found more especially

in Anodonta, bnt is confined to the
juvenile stages of growth, at least in
British specimens, the testaceous
connection of the valves sooner or
later becoming ruptured and broken
by the opening and closing of the
shell, and the connate peculiarity
thus lost. Mr. Lsaac Lea who so long
and thoroughly studied the Naiads
at one time attached great importance to this peculiarity and even
proposed to divide them into two chief groups, according as they
were or were not possessed of this character.

Fig. ^S. — A Symphynote or Connate
Ijivalve.

Anodonta cygnca (L.), young, pos-
terior end,

Grand Junction Canal, Brentford,
Collected by Mrs. Skilton,
Showing the testaceous junction of the
two valves on the posterior dorsal margin.

Alate or “winged” .shells are sometimes .seen in some of the
varieties of Anodonta ; the aim or “wings ” being formed by a com-
pressed upwai'd extension of the posterior dorsal borders, sometimes
exhibited in a very marked manner.

This peculiarity is like the symphy-
notic, a characteristic, more e.specially
affecting the juvenile life of species,
at least in British specimens,
gradually becoming less pronounced
and striking as the animal advances
in age and growth. The Symphynote
and Alate characters are often comhined together in the same
individual, but this is not ueces.sarily always the case.

When the two valves fit accurately together at the margins, and
appear to hermetically close the shell, as in
Sphwrium corneum and other species, the
shells are called Close. If, however, owing
to the margins of the .shell not exactly co-
inciding with each other in shape or outline,
the valves do not fit accurately together,
and more or less visibly open .spaces are left
between the margins of the two valves for the protrusion of the

Fig. 99. — An Alate Bivalve.
Anodonta anatina (L.), young, right valve,
Canal, Apperley Bridge, Yorks.,
Collected by Mr. J. A. Hargreaves.

Fig. 100. —A “Close” Bivalve.

Sphepriiim palliduju Gray,
posterior end, X 2,

River Foss, Blue Bridge, York,
Coll, by Rev. W. C. Hey, M. A.

42

THE UMBO IN BIVALVES.

siphons, etc., as is the case to a limited extent in the Naiads, the
shells are then called Gaping.

Fig. 101. — “Gaping" Bivalve.

Afiodonta anatina (L.),

Sandy bed of River Vare, Bramerton Wood-end, near Norwich,

Collected by Rev. S. Spencer Pearce, IM.A.

g. gape of shell on the posterior dorsal margin, for the protrusion of the siphons ; umbo or
nucleus of the shell ; L ligament.

The Umbo (see tig. 101) is the prominent part or apex of each
valve near the hinge, it is formed around
the embryonic shell, which is the nucleus
or apex of the nmbo in each valve. They
become wider apart with age and the
growth of the shell, and are sometimes
very different in character to the after-
growth, as in Pisidl/nii //('iis/oiroiiuin and
U/iio t/iui/diis, etc. In the different species
of Piilo the peculiar and remarkable in-
dnlation or sculpture of the iimbones is
becoming recognized and acknowledged as an important and reliable
character, not only for the purpose of accurate specific discrimination,
but also, for the arrangement of the species into natural groups, as
this peculiar feature of the genus is said to be remarkably constant
and less subject to modification than testaceous characters usually

Fig. 102. — Umboucs of I 'nio
iuvtidus Phil, x 2,

Evesham,

Collected by Mr. J. Madison,
Showing the nodules and
nodular ridges, charactcri/ing
the immature stage of giowlh.

I' IG. hcnslcnvnnum (Shepp.), Fig. lOl. — Pisidiuin hc>islo7vanutn (Shepp.),

young, magnified (after Jenyns). adult, posterior end, X 12,

Showing the position and character of Pond, Cockerion, Darlington,

the peculiar eave-like projection.s in the Collected by Mr. Charles Oldham,

young shell. Showing the greatly altered relative position

of the umbonal appendages at the maturity of
the shell.

are. The umbones are always turned towards the anterior end, and
in those foreign species with somewhat coiled umbones, the left valves

f CALICULATION, CRESTS, ETC., IN BIVALVES. 43

i

I bear great resemblance to the dextral shells of some gastropods, the

V right valve showing similar resemblance to sinistral forms.

Caliculation or Capping of the Um-
bones is apt to take place to a noticeable
extent only in those .species in which the
embryonal shell is of a comparatively large
size and .somewhat globular shape and the
succeeding shell-growth does not continue
on the same plane, as is occasionally .seen in
some species of Pisidhun and S2)ha’rium.
The Posterior and Anterior Cre.sts are most remarkably
developed and most noticeable in immature .shells, and mark olf the
posterior and anterior liuuts respectively, of the upper or dorsal
margin ; the posterior crest is sometimes distinctly and strikingly

Fig. 106. — A “Crested” Bivalve.

Anodonta anatina var. radiata Jeffr., right valve,

River Foss, Blue Bridge, near York, collected by Rev. W. C. Hey, M.A.

Showing the anterior and posterior crests of the dorsal margin.
ax, anterior crest ; px. posterior crest.

angulated in the adult shell of Anodonta, but in Unio the anterior
crest is often the most strongly marked.

The Rostrum or Beak is the produced posterior end of bivalve
sliells, and its extent is sometimes clearly defined on the posterior
margin by two bluntly angular ridges— the most ventral one being
the gonial ridge — which run towards the umbones. The term beaks
has often been applied to the umbones, but .should be discontinued
to avoid the po.ssibility of confusion. Dr. Brot who has esiiecially

Spiuerium /acustre (Miill.),
right valve, X 3,

Pond, Sandal, Yorks.,
Collected by Mr. J. Hebden.

44

IIOSTIU'M, Ll'NULK, KTC., IN BIVALVES.

stiuHed the Naiads, thinks the development of tlie rostniin is
induced by agitated or running waters, but tliis is evidently not

Ful. 107. — A Rosirate or Ileaked llnalve.

Anoiionta cygnva \‘:\.Xy^diniinuta Clessin, left valve,

Canal, Louth, Lincolnshire, collected hy Mr. H. Wallis Kew, F.L.S.
r. the produced posterior end or rostrum.

the only predisposing cause, as the shell now figured was taken
from the sluggish waters of the Louth canal, Lincolnshire.

The Lunule is the oval or heart-shaped depressed space in front
of, or anterior to, the nmbones, and opposite to.the ligament, and is
sometimes defined by a more or less noticeable line. In the separated
valves this space has been termed the Anterior Sinus, and
necessarily exists on both valves.

The Escutcheon or Corselet is the corresponding depressed space

sometimes e.xistingon the
posterior dorsal or liga-
mental margin. In the
separated valves it appears
as an elongate space on
each side of the ligament,
and has been called the
Posterior Sinus.
iMocpiin Tandon, the accomplished and accurate French con-
chologist, and many French and German authors, erroneously regard
the lunule as the space posterior to the umbones, and the corselet
or escutcheon as that anterior to them, a view diametrically opposed
to that adopted by English and American authors. Draparnaud, who
instituted the terms, clearly defines the position of the two areas, and
establishes the accuracy of the English opinion upon this point.

Fkl 108. — Anodonta nnatinn v. coniftlanaia Rossm.,
( Jumfrieston, near Tenby,

Collected by Mr. Fred. Walker.

Showing tlie position and aspect of the Lunule
and Ibscutcheon. In. lunule ; c. escutcheon.

ANGULAR RIDGES, HINGE, ETC., IN BIVALVES.

45

The Gonhim is the lower posterior angle and the junction of the
posterior and ventral margins; the Gonial Ridge is the elevated por-
tion resembling an indistinct and blunt keel, extending from the

Fig. 109. — Bivalve showing Gonial Ridge extending from the Umbo to the Gonium, where
the posterior and ventral margin.s join.

Unio pictorum (L.), right valve,

Hether.sett Lake, near Norwich, collected by Mr. A. G. Stubbs.

Gonium to the umbo, and marking off the gonial area ; it is some-
times very noticeable in Anndontd and Unio, and partly corresponds
to the Area of many authors.

The Podium is the lower anterior
angle, and indicates the point where
the anterior and ventral margins
merge ; the Podial Ridge is the
obsoletely angular line running from
the umbo to the podium, and cut-
ting off the podial area from the
sliell generally. It is strongly
developed in Dreissensia.

The Hinge uniting the two valves of the .shell is situate on the
dorsal margin and is formed by the chitinons liagment and a more
or less complicated series of denticles or teeth, which closely inter-
lock with each other and would appear to function as a fulcrum in
the opening and closing of the valves ; the locomotive bivalves
generally have the strongest and most powerful hinges, the .sedentary
and fixed forms usually having comparatively weak liinges and being
.sometimes (piite edentulous.

The Hinge Teeth or Denticle.s are more or le.s.s complex, shelly,
denticular processes or teeth, which with the ligament articulate the

Fig. 110. — Bivalve showing Podial
Ridge extending from Umbo to Podium at
junction of anterior and ventral margin.
Dreissensia poly7norpha (Pallas),
Baker's Dock, Stourporr,
Collected by Mr. J. W. Williams.

4G

THE HINGE TEETH IN BIVALVES.

sliells. Ill young sliells tliese processes or teetli are sharp and well
defined, but in aged ones they often become thickened and their
pecnliar characters even obliterated by the continned deposition of

shelly matter. These denticles are termed
Cardinal, or IIinc.e-tketii when placed
immediately beneath or between the
Umbones, and Antero-lateral or
PosTERO-LATERAL according as they are
situate on the anterior or posterior side
of the Umbones ; these lateral teeth are
generally distinctly lamellar in character,
and sometimes very distinctly and
strongly developed ; these projecting
shelly processes are generally arranged
.so as to fit between, and interlock with,
corresponding cavities in the opposite
valve. Occasionally the lateral teeth or
denticles are developed and not cardinal
ones, as in Unio, and shells with this type
of hinge-teeth have been called Priono-
desmacea by Dali, and Heterodonta by
Aeumayr; more freipiently, however, in Pelecypods generally, the
cardinal teeth alone are pre.sent. A formula has been devised for regis-
tering the different peculiarities of the hinge-denticles, the formula for
the right valve being jdaced above, and that indicating the dentition

Left Valine.

I

Eio. 112 — Hinge-Teetli of i’nio iuntidus Phil.

(lrol»y J^ool, Leice-ilersliire, collected l>y Mr. H. K. Quilter.
nj. antero-lateral lamcli.x; /./, posteru-lateral lamellai.

of the left valve beneath it, the cardinal denticles being first given,
followed by the laterals, thus Unit) ttmidns could he recorded as
Cardinal teeth ; Antero-lateral h ; Postero-lateral ^ ; which formula

I

Fio. Ill, — Diagram ofa transverse
section of the sheil of a Bivalve (after
Lankester), showing how the hinge
teeth act as a fulcrum in the opetting
and closing of the valves.
a. adductor muscles; /. ligament;
r.7f. and right and left valves
of the shell ; A. hinge or fulcrum ;
f.f. the short arms of the lever ;
ef.d. the long arms of the lever.

THE HINGE TEETH IN BIVALVES.

47

indicates that the cardinal denticles are deficient in both valves, and
that the right valve contains one antero-lateral and one postero-
lateral lamella, the left valve containing two on each side, ai-ranged
so as to interlock with the lamellar ridges in the other valve ; the
anterior laminm are always more or less cremate at their free margins
and the more prominent and central denticle of the left valve is often
distinctly bifurcate, as shown in the illustrative figure. Dr. Jeffreys
was in error in his account of the denticulation of the hinge of the
Uiiiones, ascribing the bidentate teeth to the right valve, which in
normal shells has only unidentate lamellse.

SijJiwrium rivicola may be considered to typify the shells possessing
cardinal and lateral hinge teeth, both of are somewhat variable,
in character. In well developed specimens the cardinal teeth

are often distinctly double in both
valves, the posterior cardinal tooth in
the right valve, and the anterior
cardinal tooth in the left valve, being
larger than the other, often with a
somewhat angular excavation and ap-
pearing as though formed by two
converging denticles, their ai)ices
pointing to the umbo. In the un-
usually developed specimen from Leicestershire (f. 113), the cardinal
denticles are more distinctly developed than is usual, and have a
great resemblance to three more or less sejiarate and converging
shelly processes ; the anterior lamellae of the right valve are two in
number, as in the normal shell, but in the left valve, a slightly
developed additional lamella is perceptible nearer to the umbo and
the outer .shell-margin. The posterior lamelhe of the right valve
have also developed an additional ridge also close to the outer margin
and near to the umbo, affording a groove for the interlocking of the
extra lamella appearing in the left valve ; this .specimen would
appropriately be indicated by the formula. Cardinal | ; Antero-
lateral f ; Postero-lateral |. In ordinary specimens the teeth may
he formulated as Cardinal#; Antero-lateral f; Postero-lateral
indicating that there are two cardinal teeth in each valve, and that
the right valve contains two antero-lateral and two postero-lateral
teeth, the left valve containing only one at each side interlocking

Fig.113 — Hinge-Teeth of Sphccrium
rivicola (Leach) X 4.

Canal, Blaby, Leicestershire,
Collected by Mr. H. E. Quilter.
c. cardinal denticles; aJ. antero-lateral
lamellcc; p.l. postero-lateral laniellje.

48

THE LIGAMENT IN BIVALVES.

with the bihd laterals of the right valve, and thus offering a marked
contrast to the denticles of the Unmtes, in which this arrangement
is reversed. Dr. Jeffreys, Reeve, and many other authors, have fallen
into error on this point.

It should perhaps be mentioned that many continental and American
conchologists regard the antero-lateral lamella) of the Unioiies as
cardinal denticles, considering the antero-lateral lamella) to be absent.

The Ligament is an nncalcified chitinons part of the .shell usually

Ku;. 114. — Hivalvt* with Kxtenial Ligament.

Anodontu amitina (L.),

Sandy Ited of River Vare, IJramerton Wood-end, near Norwich,

Collected by Rev. S. Spencer Pearce, M.A.

/. e.vternal ligament ; u. umbo ; g. gape.

attached to riilges along the dorsal margin, posterior to the nmhones,
and uniting the valves along the ni)i)er or dor.sal margin. It is narrow,
feeble and membranous, when existent anterior to the umbones, and is
only functionally elHcient and powerful posteriorly. It is large and
strong in A iKidoiifd, etc., but small in .some marine genera which
have a largo internal cartilage between the
v.ilves. It is strong, bi-ownish, convex, aaid
very flexible during the life of the animal,
but on its death becomes dry and brittle,
thongb regaining .some of its elasticity on
immersion in water. The ligament is usually
external, as in Anodanta, but is sometimes
internal and lodged in a ligamental pit in
each valve, as in Ihud !<sfdis/d polymorplm.
When the valves arc closed the elastic fibres
forming the external ligament are stretched,
but when the ligament is internal the fibres
are compres.sed, the effect in both cases
being the .same, causing the valves to oi)en
as .soon as the adductors are rela.xed. The
ligament is said to consist of two layers -
an outer one, corre.sponding to the epiconch of the shell, and an

I' lc. llo. — Hivalve with In-
ternal Ligament.

Dycissi’Hsia po/y/uor/>/ia ( Pallas),
( iloiicesler'Canal, Stroud,
Collected by Mr. K. J. ICIliott.

/. ligamental pit ; a. ad. ant.
adductor .scar; /.ad. post, ad-
ductor scar; p.r. post, pedal and
byssal retractor scar ; /./. pallial
line.

THE SURFACE IN BIVALVES.

49

inner portion, which combines two modes of striation, at right angles
to each other, and giving the laminate appearance of nacre with the
columnar appearance characteristic of the prismatic layer, and thus
apparently showing the morphological and developmental similarity
of the ligament and shell.

The External Surface of bivalve shells is generally more or less
smooth, but all are marked by the successive growth-lines, which
indicate the stages of increase in the size of the shell, as each of these
lines was at one time the actual margin of the valve. The growth
of a bivalve shell is not uniformly rapid in all directions, the rate of
increase being most rapid towards the ventral and posterior margins,
hence the umbo is always close to the dorsal margin and usually
nearer to the anterior than to the posterior end; the incremental lines
being more or less prominent according to the species. In some forms
as Pisidium amnicum the shell is deeply and widely sulcate concen-
trically, while in others, as the various species of Pisidium and
Sjdiwrium the periostraca may be clothed with short, stiff, and more
or less nnmerous microscopic hairs. Those on Sp/iwrium corneum are
.short, thick, and somewhat bent at the points, somewhat .sparingly
distributed, but most numerous and thickly set near the umbones,
and do not appear to be arranged in any set or geometrical order.

The Internal Surface of the valves is ordinarily whitisli, bril-
liant and often iridescent, but is sometimes delicately or richly
tinted with salmon, rose, azure or other colour, and occasionally in
some species is found of a deep livid blue or blui.sh-purple.

M. Picard has detected and recorded the presence of a broad ridge
or thickened part of the shell in the interior of the Uniones, arising
from the umbonal region and somewhat obliquely traversing the shell
towards the ventral margin, this elevated area he has named the
Ventral Crest, and the two divisions or chambers thus formed in
each valve he has termed the Anterior and Posterior Chambers
respectively, according as they occupy the antewor or posterior end
of the shell.

Colour is usually invested in the epidermis or periostracum, and
is generally somewhat uniform, though of a stronger and richer tint
towards the posterior end, the tinting being .said to be greatly in-
fluenced by the nature and composition of the inhabited water, and
to be more brilliant and elegant in still waters where there is a thick

I)

50

MARKINGS IN BIVALVES.

layer of soft mud ; in disturbed waters and on a different bottom the
shells are usually duller in colour and often eroded at the umbones.

Diversity of Markings is not a striking character of British
bivalves, the most remarkable ex-
ample being furnished by the angular
or zig-zag markings on the more
exposed surface of the shell of
Dreist^eiK^id puli/morj)/i((, the acutely
angulated podial ridge forming a
sharply defined boundary line, sepa-
rating the distinctly ornamented
posterior and general surface of the shell, from the plain and uniformly
coloured anterior or podial area, from which the angular markings
are (pute absent.

The Radiate markings, so noticeable at times on the Naiads, are
variable in colour, but are usually of some shade of yellow, brown, or
green. 'I’hey arise in the umbonal region, and are directed towards
the free margin, but generally those rays which occupy the posterior

Fk;. 1 17.--l*ivalve with Radiate Markings.

Anoilonta anaihia var. rad'iata JcfTr., riglil vaUc,

River Foss, Rliie J’ridgc, near York, collected hy Rev. W. C'. Hey, M.y\.

part of the shell, are more strongly coloured and more distinctly
defined than those on the anterior part, which in the genera Unln
and Anodoutd is often more or less deeiily imbedded in the sandy
or muddy bottom of the lake or stream. These radiate and zig-zag
markings are generally most vivid and distinct in immature shells,
usually becoming more or less indistinct and obliterated by age.

Fig. 116. — lUvalve with Zig-zag
Markings.

Dfi'issciisia po'yjnorpha (Pallas),
Baker’s Dock, Stourport,
Collected by Mr. J. W. Williams.

FORMS OF SHELL IN BIVALVES.

51

The Concentric Zones, occasionally occurring in some species,
sometimes offer a striking contrast of
colours, especially amongst the species
of the genus Sphierium. These compara-
tively broad and usually bright yellow
zonal markings mostly occur only at the
free margins of the valves, but at times
they alternate at regular intervals with
the normal greenish-brown groundcolour
of the shell, and have a pretty effect.
In Unio and Anodonta these concentric zonal markings are generally
darker in colour than the ground tint of the shell, in some cases
being quite black ; they represent according to Clessin the winter
growth of the shell, and therefore indicate the age of the animal.

In Form, Bivalves are Oblong, when their length, or distance
between the anterior and posterior margins, is gi-eater than the
width, or distance from the dorsal to the ventral margin, as in Unlo
pktorum, Splucrium pallidum, Plsidium milium, Qtc,.] and termed
Transverse, when the greatest length of the shell is in the opposite
direction as in Dreksensia. The ordinary differences of form amongst
onr bivalves are not numerous and may be broadly classed as

Oval when the shell is of an oval form, as
in Spka’rium rivicola (Leach), Pisidium
pusillum (Gmelin), etc.

Fig. 119. — Example: Sphcerium rhkola (Leach), left \’alve, X 1?, canal, Far Cotton,
Northampton, collected by Mr. W. D. Crick, F.G.S.

Rounded when the shell has a somewhat circular
outline, as in Pisidium nitidum Jenyns.

Fig. 120. — Example: Pisidium nitidum Jenyns, right valve, X 8, Hackfall, near Ripon,
Yorkshire, collected by Miss Emily K. Harrison.

Oblong when the shell has its greatest length
from the anterior to the posterior margins,
as in Unio pictorum (h.), Pisidium milium
Held., l^pluvrium jmllidum Gray, etc.

Fig. 121. — Example: Spharrium pallidum (»ray, right valve, X 2, canal, Accrington,
1862, collected by Mr. R. Wigglesworth,

Fig. 118. — Bivalve with Concen-
tric Markings.

Sphcerium corneu7n var. zniiata
Garn., right valve, X 2,

River Trent, Marnham, Notts.,
Collected by Mr. W. A. Gain.

FORMS OF SHELL IN BIVALVES.

Fig. 124. — Example: A>iodonta anatina var. co»t/>lnnata Rossm.,

Gumfrieston, near Tenby, collected by Mr. F. Walker.

Reniform when the shell is oblong, hut constricted near the centre
of the ventral margin, forming a kidney-shaped outline.

Triangul.vr when the shell has a
somewhat triangular outline, as
in Dreht^ensid jmhpnorphd
(Palla.s).

Fig. 122. — Example: Dreissensia />o/ymLy7-J>/ia Baker’s Dock, Stourport, collected

by Mr. J. W. Williams.

Trapezoidal or Surriiomboidal when the
shell is somewhat (piadrilateral in outline
and the opposite sides though somewhat
straight, are not parallel, as in ^plucrinm
Idcustre (Mull.).

Fig. 123. — E.vample: Spheerium (Mull, j, right valve, X 3, pond, Sandal, Yorks.,

collected by Mr. Joseph Hcbden.

Co.MPRESSED when the valves are ilattened or compressed, the
ventral margin forming a very acute angle, as in Anodontd
dndthid (L.), Spluvriuin lacnstre var. hrochouiaiid Bonrg., etc.

Fig. 12.5. — Example : Unio inari^ariti/er var. sinuata f.am., right valve.
Loch Awe, .\rgyleshire, collected by Mr. Alex. Somerville, B.Sc., F.L.S.

FORMS OF SHELL IN BIVALVES.

Tumid or Cordate when tlie valves are very con-
vex and swollen, often being somewhat heart-
shaped in section, as in SpJiivrium cnrneuin var.
nucleus (Stnder), Anodonta cjjgneci var. corduta
Rossm., etc.

Fig. 126. — E.vample: Sphceriuni corncuin var. (Stnder), anterior end, X 2, ditch,

laversham, Kent, collected by the late Miss Fairbrass.

F.vlcate when the shell though somewhat reniform in shape, has
the produced posterior end greatly liattened, and somewhat
curved.

Fig. 127. — Example: Um'o pkioi'^iiu \ax. platyrhitichoidca Dupiiy, right valve,
River Yare, Bramerton Wood-end, Norwich, collected by Rev. S. Spencer Pearce, M.A.

Truncate when the anterior or posterior
margin of the shell, as the case may
be, is not produced to a pointed
end, but more or less abruptly
terminated as in Pisldlum fontuudc
(Drap.), Unio i)kt(trum (L.), etc.

Fig. 128. — Exampleof a Pos-
teriorly Truncate Bivalve.

Pisidimn amnicum (Mull.), *
right valve, X 2,

Canal, Ambergate,
Collected by Rev. H. ^Iilncs, M.A.

Fig. 129. — E.vample of an Anteriorly Truncate Bivalve.
Unio picto'uvi (L.), right valve,

Helhersett Lake, near Norwich, collected by Mr. A. G. Stubbs.

54

mkasurkmk:st ov isivalves.

The Length of Bivalve shells, if the funnatioii and disposition of
the ar.imal and its organs be accepted as guides, is the distance from
the anterior to the posterior margins, not from the nmbo to the
front margin as proposed by Dr. Jeffreys, the oral extremity of the
animal being placed at the anterior end of the shell, and the
alimentary canal terminating near the i)Osterior margin ; the
Breadth, is the diameter transversely to this, that is from the
dorsal to the ventral margin — the length as proposed by Dr.
Jelfreys ; and the Thickness is considered to be at the greatest
external convexity of the valves.

IMuscular Impressions or Scars.

The more or less irregnlarly shaiied and depressed mnscular scars,
or impressions, especially noticeable on the internal snrhice of bivalve
shells, indicate the places where the muscles of the body are affixed
to the substance of the shell and the points where the animal and
shell are orgaidcally connected together.

In (tastropods, the columellar or retractor muscle, corresponding

to the posterior retractor of the
bivalves, leaves a double, or in some
spirally coiled species, a single but
not very conspicuous muscular scar
upon the columella, about the dis-
tance of a whorl from the aperture.
In Ilell.r j)nm((tla it is a fan-shaped
or triangular impression, extending
spirally round the columella for half
a volution, its further margin being
indicated by a slig
ridge, the acute angle of the cicatrix
being directed basally, and its upper
margin extending slightly upon the base of the preceding whorl.

In the Pelecypods, the principal muscular scars are the anterior
and posterior adductor impressions. In A iiodunta cj/rjiii'd the anterior
adductor scar is placed at the anterior end of the shell, the posterior
adductor scar at about the same distance from the posterior margin,
between the posterior end of ligament and the posterior margin of

htly perceptible

Fig. 130. — Helix pomatia L.,
Nieder K.nufungen, near Cnssel,
Collected liy .Mr. P. W. Munn.
Showing tlie character and position
of the scar (s), indicating the point of
attachment of the columella muscle (from
a section cut by -Mr. F. Rhodes).

MUSCULAR SCARS.

00

the shell. The cicatrix of the anterior pedal retractor is contiguous
to and joined with tire anterior adductor impression, at its upper
mai’gin. The impression of the anterior pedal protractor is much
smaller than that of the anterior adductor scar, and is placed pos-
teriorly and veutrally to it. The posterior adductor impression is
joined at its upper angle to that of the posterior pedal retractor.
In addition to these, the more distinct marks of muscular attachment,
there are a limited but variable number, of much smaller muscular
pits in the umbonal region, about e<pially distributed in size and
number upon the anterior and posterior sides of the umbones, and
not always exactly corre.sponding either in number or position in the
two valves, marking the points of attachment of several retractor or
retentor muscular fibres.

■UT

a. ad. anterior adductor scar; p.ad. posterior adductor scar; a.r. anterior pedal retractor scar;
posterior pedal retractor scar; ii.r, umbonal or lesser retractor or retentor scars; a.p.
anterior pedal protractor scar, the abdominal retentor scar of Clessin ; p.l. pallial line.

Moquin-Tandon asserts that the anterior adductor impressions are
always less-marked than those of the pofsterior adductors, this is
however incorrect, as the anterior adductor impression, especially in
JJnio, is usually much more deeply and distinctly impressed than
the posterior one, which, though somewhat larger in extent is not
nearly, so distinctly and strongly defined.

All these marks of muscular attachment become further apart and
more distant from the umbonal region as the growth of the shell pro-
ceeds, and in some cases it is possible to trace faint and gradually

50

SPECii';^.

narrowing impressions from the margins of the present scars, converg-
ing towards the nmbones, and showing the process of growth and
the successive shiftings of the muscles.

The Pallial-line, which in tlie Integripalliate species follows more
or less the outline of the ventral margin of the shell, is caused by the
impressions of the points of attachment of the muscular fibres of the
mantle, and indicates the line of attachment of the mantle to the
shell. The siphonal impression or pallial sinus only exists in those
shells with long and retractile siphons, its depth being an index of
their length; the small siphons of Sp/ucrium cause little or no inflec-
tion of the pallial-line.

Species.

Prior to the enunciation of the doctrine of evolution, the definition
of species was simple and clear, as they could be described as the
whole of the individuals descended from the pair originally created ;
the general organization and form of each species being considered
to be immutable and as fixed by the Creator. The universal accept-
ance of the principles of evolution compel us to regard species as
mobile and plastic, and although their characters may be modified by
the responsive reflex action of the organism adapting itself more or
less readily to the varying conditions of the environment, yet for
all practical i)urposes specific characters can be regarded as stable
and fixed, as any radical structural changes induced by the action
of the different agencies of the environment, re(pure lengthened
periods to modify a suflicient bulk of individuals to firmly establish
permanent and suflicient differences for specific distinction.

A species, therefore, may now be defined, as all the individuals
which bear such resemblance, not only to their parents and offspring,
but to each other, as to make it reasonably certain that they belong
to one common stock. This assemblage of individuals should also
be capable of inter-breeding amongst themselves, produce fertile off-
spring, and should not be too closely connected by intermediate
forms with other species or groups of individuals.

The general form of the shell, and the arrangement and peculi-
arities of the sculpture and colouring furnish the principal testaceous
characters of species in the Gastropoda ; in the Pelecypoda, the
difl'erent forms of the shell, the position of the umbones, the char-

SPECIES.

57

acter of the hinge, etc., are all important features in the discrimina-
tion of species; the anatomical criteria differ in different groups, but
ill the Gastropoda reliable features for the differentiation of species
are often found in the modifications of the different parts of the
reproductive system, etc.

Some species are remarkably constant and more persistent in the
retention of their characters than others; these inflexibly organized
forms do not readily accommodate themselves to, or vary in
response with the special nature of the environment, and are usually
restricted in their distiibutiou and difficult to acclimatize; according
to Dr. 0. Boettger, species of this character are ancient forms, which
have existed from tertiary times, and are found fossilized in the
deposits of that period, possibly these species have passed through
their period of variability or specific youth, and have entered upon
the period of decadence preceding their final e.xtinction.

Others species are remarkably variable, and readily and quickly
modify and adapt themselves to any change in their locality or sur-
roundings; species of this character are according to Dr. Boettger,
of comparatively modern origin, and are not found fossilized in the
deposits of tertiary age and have therefore been presumably evolved
from some pre-existing form since that period, the exuberant vari-
ations in form, size, colouring or texture they exhibit, are possibly
evidences of their recent evolution and the youth of their specific life.

The opinion has within recent years gained ground amongst
scientists in this country, that unless closely allied forms present
some internal organic difference, they cannot rank as species. This,
in my opinion, though an undoubtedly tiue and scientific test,
should yet be applied with judgment and discrimination and not
indiscriminately applied to every case, as the shell is just as truly
an oi’gan of the animal as the penis, spermatheca, dart, or
buccal armature, and this being so, the shell becomes a valid criterion
of difference, the only criterion if other sufficiently distinctive organic
modifications are absent. If this is not so, then to be consistent we
must unite under one specific name such forms as Helix hispida and
Helix rufescens, as the chief differences between these species are
testaceological rather than anatomical. Even Simroth with his vast
experience cannot really decide, whether in certain genera of slugs,
the external or internal characteristics possess the greater specific
value and constancy.

58

SPECIES AND VARIETIES.

Tlie elevation of variously modified forms, and also those of a
doubtful or transitional nature to specific rank, as is unfortunately
the practice with some of the most able and acute continental con-
chologists of the present day, is earnestly to be deprecated. The
treatment of these forms as varietal would sufficiently accentuate
any differences they might possess, and yet fully preserve the
necessary indication of their specific affinities ; this object our gifted
continental friends seek to attain by adopting a system of grouping,
which groups are, 1 believe, nearly if not (piite, co-ordinate with the
old Linnean and Lamarckian species, thus the group SUiguaViand
would in England be consideied to be iiractically synonymous with
the Linnean species JAmnwd sfdgiudis and tlie different forms coin-
jtosing that group, would he, to our English views, simple varieties of
that species. This unfortunate i)ractice of mnltiplying species upon
the slightest and most insufficient cliaracters, cannot fail sooner or
later to bring about a reaction, and thus cause more attention to be
directed to the common, rather than to the divergent characters of
species.

Varieties.

The tendency of olfsju-ing to resemble their parents is undeniable,
yet no two children or organisms are e.vactly like each other, or like
their parents in every particular, owing to being differently affected
individually by the pre-natal as well as the post-natal environment,
and diverging correspondingly from the likeness of their progenitors ;
these divergent forms are called

Varietie.s, and have been well defined as incipient species; marked
divergence has begun, which may under firvonrable circumstances
culminate in the evolution of distinct species. Varieties rank next in
imi)ortance to species, and in accordance with their greater or lesser
divergence from the typical form, have been subdivided and designated
by various subsidiary names, intended to convey the relative degree
of modification they have undergone.

Varieties may be individual, that is, occurring only in a more or
less isolated and sporadic way; or, they may be of a sexual character,
as in the diiecious species of both Univalves and Bivalves, in which
the shells of the female individuals are generally characterized by a
more obese and tumid form than those of the males. The peculiari-
ties distinguishing varieties may also be acquired during growth,

VARIETIES.

59

owing to the deferred development of .some of the organs of the
animal, or other causes, as in those specimens where banding or other
ornamentation, though not present in the early or youthful stages,
become gradually developed and intensified as growth proceeds ; or
the change from the parental characters may be the apparently direct
result of external causes, as has been demonstrated by Herr Hazay,
who has developed the short-spired globose form of Liiunwa peregnt
from the ova of the elongated typical form of the species, and vlce-
cersd, according as the ova were placed and reared in still pools, or
in “hard” running waters.

If the circumstances favouring certain variations be practically of
a permanent character, and affect the bulk of the individuals of a
species throughout a whole district, as may be the case where the
apparent determining causes are physical or climatic, or as they have
been termed Ectergogenetic, the modified form becomes hereditary
and is then termed a sub-species, geographical variety, or race.
These geographical varieties often have many of the characteristics
of good species, possibly as a conse(iuence of long isolation from the
typical form, and they cannot always with certainty be specifically
determined, even after an e.xamination of the structure of the animal;
thus according to Simroth the species of the genus Amalia are very
unstable, eacli country impressing its own local stamp upon the
species inhabiting it, and the majority of forms set up as distinct
species by viirious authors are only transition forms bridging o'ver
the interval between carinata and sowerbyi on the one hand and
carinata, and gagates on the other. Some species and genera are
however less subject to variation than others, and the.se groups or
species showing least adaptability to modified circumstances are
usually more or less restricted in their distribution.

The term Varieties when used in a restricted sense, refers to in-
dividuals which have developed or acquired very noticeable differ-
ences from the typical or parent form, but have not occupied any
special district to the virtual exclusion of the type, but coexist with
it, being more .sporadic and isolated in their occurrence, possibly
owing to the prediisposing causes being of a limited or evanescent
nature, or perhaps intrinsic to the individual, and not therefore of so
general and pervading a character as is the case where the mass of
the individuals inhabiting .some definite area are affected, as in the
geographical varieties.

GO

VARIETIES.

The mere number of individuals affected should not liowever lessen
tlie interest and scientific value of the differences exhibited, as there
must always of necessity be a full and sufficient predisposing cause
which it should be our aim to discover.

The internal organs of the animal are also ecpially subject to
modification, and it is cpiite conceivable that anatomical differences
might arise which would liave an important bearing on the origin of
specific differences, a modification of the sexual system might debar
or restrict intercourse with individuals of the species not similarly
affected, and thus pave the way to further and permanent modi-
fication. This aspect of the subject which has been termed Entergo-
genesis, has not received much attention up to the present time, so
that it is not at all certain, whether the internal change may not
often be the prior one, in the evolution of new and distinct species,
as Eimer from his observations on colouring considers that species
mainly originate from variation due to constitutional causes.

From whatever causes induced these modified and modifying forms
are of the highest interest and importance, as exhibiting in actual
progress the processes of differentiation which may ultimately lead
to the evolution of distinct species, it is therefore very desirable that
well-marked variations exemplifying the various lines of divergence
should be designated by a distinct and preferably conventional
varietal name. The adoption of this practice will undoubtedly
facilitate their study, though it is seldom desirable to attach special
and distinctive names to the intermediate forms connecting the
extreme varieties with each other or wdth the parent form. These
intermediate as well as the complex forms might where and when
desirable be distinguished by a judicious though temporary combina-
tion of names already applied, thus if it were wished to mention
from any cause a specimen exhibiting a colour-variation in combina-
tion with another peculiarity, its character could be concisely indicated
by combining the names of its chief modifications; a sinistral Lhmvva
iwmjra if also an albino would be alluded to as sinistrursnin-
at/idldam, and so on in other cases without however listing the names.

The term Sub-variety or Mutation is used when referring to the
slighter modifications either of the typical shell or of the varieties,
they are really the intermediate forms which connect and blend
together the well-marked varieties with each other and with the

SUB-VARIETIES.

61

typical form, and therefore possess a certain value and importance,
as enabling or as.sisting us to fix the varietal status, and refer to
their appropriate species, the doubtful and abnormal forms occasion-
ally met with ; but the relative importance of the varietal or sub-
varietal modifications cannot always be measured in accordance with
the more or less readily discernible nature of the differences exhibited.
The conspicuous differences in the variations of the banding of the
shells of Helix nemm'alis, Helix hortensis and other Pentateniate
.species, although palpable and unmistakeable to the most unpractised
eye, are relatively of very minor importance, in comparison with the
more subtle variations in form or character, which may often require
a trained eye and judgment to discern and appreciate; the variety
lutea of Helix hortensis stidctly speaking refers only to the bright
yellow shells, though generally understood to include all yellow forms,
and tliese can and have been sub-divided and named by different
authors, the greenish-yellow form has received the names of fiaro-
virens from Picard and flaco-viridis from Kickx, the greyish-yellow
forms have been styled griseo-lutea by Esmark, and all the innumer-
able band modifications whether of number, color, or arrangement
are sub-varieties or modifications of the more important varieties.

The Depressed and Conoid forms of species usually somewhat sub-
globose in shape, results from a more or le.ss rapid deflection of the
whorls ; if, in the process of growth, the whorls descend more quickly
than usual, we have as a result a more produced and elongated form
of shell with a smaller aperture, as in Helix nemoralis var. conica

Fig. 132. —A Conical variety of a Sub-
globose Univalve.

Helix nonoralis var. conica Pascal,
Seacroft, near Leeds.

Fig, 1.33. — A Depressed variety of a Sub-
globose Univalve.

Helix nemoralis var, planospira Picard,
Frutigen, S\vitzerland.

Pascal. Inversely, if the descending growth of the whorls be less
decisive than normal, then we have a depressed and more or less
planorbiform shell, as in Helix nemonilis var. planospira Picard, and
this form of modification usually results by correlation of growth in a
shell of greater diameter than ordinary with a more expanded aperture.

62

VARIATION IN FORM.

Land shells of elongate form, are often somewhat arboreal in habit
or at least more inclined to ascend to elevated positions, than the flat
spired forms, which woidd appear to he in many cases more geo-
philons, or ground-loving in habit; onr most depressed species. Helix
obvoluta is particularly noticeable for this peculiarity, naturally
there are exceptions to this rule, which however indicates in a general
way the tendencies of the various forms.

Fluviatile species tend to develop a lengthened shell under tlie
influence of a steady and rapid current, and short spired forms,

of otherwise elongate shells, more or
less characterize species inhabiting
lakes and other large bodies of water,
Liii/iKiu iK'vetjra var. bunietti and
Lliuinvd stagimlis var. bodamica may
he instanced as e.xemplifications of
this rule, and, as recorded at page 59,
Herr Ilazay has produced the long-
spired variety oi Li mncra 'peregm at
will from the ova of the globose form
by merely rearing them in a rapid current of water.

In the Pelecypods the shape may he modified by the greater or
lesser convexity of the valves, which may he considered analogous to
the conoid and depressed varieties in the Univalves. In those species

Tic. 13o. — L'nio iionidus IMiil.,

(Iroby Pool, Leicestershire, collected by Mr. H. Ik. (^iiilter.

Sliowing n regularly iiHlated burrowing llivalve, usually characteristic of still waters
(this specimen shows the pecidiarity of three tlistitjcl and successive margins to each valve).

which do not regularly imbed a portion of their shells in the bed of
the stream or pond, the tumidity or compression of the shell is some-
what uniform over the whole shell, hut in the species composing the
genera J and Unio, which usually live partly buried in the

Fic.. 131. — A Short spired variety
of an elongated Univalve.

Lininua stdi^tialis var. bodamJcii Miller,
Koden See,

Collected by Herr Schenk.

VARIATION IN FORM.

6.3

bed of the river or pond, the efifects of the special features of their
environineiit are shown more particularly at the posterior or siphonal
end of the shell, which is fully exposed to such modifying influences
as may exist. In still pools, lakes, or slowly flowing waters the shells
of these genera may be more or less equally inflated, resembling in
this respect those species which do not partially imbed their shells
in the muddy bottom of the water. In rapidly flowing streams and
rivers the shells are often specially characterized by a remarkable
compression and extension of the posterior end, as in Unio pictorum
var. platyrliinclioidea Dupuy — of which Dr. Jeffreys’ var. compress^a
is a sub-variety of somewhat broader form and slightly less sinuate
lower margin — this remarkable variety was originally discovered in

Fig. 136. — Unio pictonou var. platythinchoidea Dupuy,

Hethersett Lake, near Norwich, collected by Mr, A. G. Stubb.s.

Showing a compressed burrowing Biv'alv’e, usually characteristic of flowing waters.

this country by Mr. Bridgman in the River Wensum, near Norwich,
which is a slow and sluggish stream with a layer of soft mud over a
hard bottom ; the particular parts inhabited by this peculiar variety
are the places where the river bends sharply and forms what are
locally called “horse-shoe reaches,” the current rushing rather
sharply at the last bend to the opposite bank and forming an eddy
next the shore, the rush of the current removing all the loose
soft mud covering the hard bottom. These remarkable shells are
found burrowing in the hard ground just inside and at the edge
of the sharp current, next to the eddy, and are assumed with great
probability to be an effect of the ru.sh of the current and the con-
sequent washing away of the softer river bed, rendering it more
difficult for the mollusk to imbed its shell, this process being, how-
evei’, probably facilitated by the more blade-like character of the
shell generally, the broader valves when firmly imbedded preventing
the mollusk being washed from its position too easily, and as the
thin dorsal posterior edge of the shell is presented to the current,
there is less friction to overcome. It is, however, very remarkable

G4

VARIATION IN FORM.

Fig. 137. — Vnio tumidus var. (Mont.),

River Frome, Stapleton, Bri.stol,

Collected by Miss F. M. Hele.

Showing the compressed and somewhat curved pos-
terior margin, and the slightly unequal \'alves.

that the fine .specimen figured is from a lake near Noi’wich; possibly
there may be some .special features in the locality, or of its occurrence
there that would explain the seeming anomaly of its presence in still
waters. In the variety ovidh of Unio tumidus the same peculiar

compression of the pos-
terior margin is exhibited,
bnt the shell is somewhat
inequivalve, the left valve
being slightly concave on
the posterior end, while
the posterior end of the
right valve is convex in
even a greater degree.
These and other resnlts of environment tend to give a general local
likeness to allied species inhabiting the same river or lake — a fact
which has often been noted and commented on.

The (riimo.siTY which some species occasionally form by abruptly
enlarging and afterwards contracting the
diameter of the whorls, is very curions, and
the suggestion has been made that a
temporary accession of nourishing and
palatable food during the growth period,
would on account of the suddenly in-
creasing hulk of tlie animal necessitate
the unusual enlargement. Should this un-
usual food-sup2)ly become exhausted, or not
easily obtainable, the proportions of the
animal would become gradually reduced to the normal size and the
shell more or less quickly contracted in correlation with it.

Mr. R. R. C. Stenrns ascribes analogous bulgings in the American
PIdiiorIn'S merely to the periodicity of growth, owing to recurrent
periods of hibernation, the termination of each growth period being
marked by an expansion of the aperture, which may be consiilered
analogous to a varix, and the repetition of these variceal enlarge-
ments give the American species their special feature. The habit of
forming these enlargements would be continued for a period, even
though the species had migrated to districts where owing to more
e(|uable conditions hibernation was nnnece.ssary, though in time
they would revert to producing an even and regular growth.

Fig. 138. — A Gibbously In-
flated Univalve.

Limmra aurkuiaria var.
g-ihbosa Taylor,

Pond, Moortown, near Leeds.

VARIATION IN FORM.

65

Fig. 139. —An Univalve with
Gibbously Inflated body whorl.
Lifuncea stagnalis X}-..')^
Pond, Osmondthorpe, Leeds,
Collected by Mr. H.Crowther,
F.R.M.S.

Tin's transverse bulging of the wliorls during the course of growth
is occasionally observed in a pronounced form in many species,
especially in Limncva i^tacjiKilh, and would appear to he a very general
outward biological expression of a number
of abnormal conditions, as well as of a
period of superabundance of nourishing and
palatable food. In the autumn of 1894
all the specimens of Limncca stagnalis
found in a small pond at Osmondthorpe,
near Leeds, exhibited this remarkable in-
flation upon the body whorl, but those
gathered during 1895 in the same place did
not show the peculiarity, so that the cause
of the expansion, whatever may be its
nature, was evidently an evanescent one.
The pond has a rich and varied vegetation
and contains many forms of animal life, and it may be remarked that
leeches, which Ilerr J. Ilazay states are
sometimes the cause of whorl expansion,
were numerous in it. The very interesting
specimen of L. stagnalis var. hodamica,
which I owe to the kindness of Mr. Brockton
Tomlin, also shows this peculiarity in a very
striking manner.

Identical inflated growths are occasionally
developed by specimens in confinement,
and Mrs. Skilton has kindly furnished me
with a characteristic sketch of a specimen
of Limnwoj stagnalis reared in her aqua-
rium, which distinctly shows this remarkable whorl distension.

The Pelecypods, more especially Anodonta cygnea, are liable to a
similar inflation, though less markedly so than the Univalves ; this
gibbous swelling, when it does occur, is naturally of a concentric
character, in harmony with the lines of growth or increase.

The various Labiate or lipped forms have had several tlieories
advanced to account for their peculiarities. In some cases the sug-
gested explanation of the origin of the gibbous varieties may to some
extent apply to this deviation also, and if so the determining cirenm-

Fig. 140. — An Univalve with
Gibbously Inflated body whorl
(dorsal aspect).

L. stagnalisv, hodaviica Miller,
Boden See.

Collected by Herr Schenck.

E

r.o

A'ARIATION IN CHARACTER OF LIP.

stances would occur later than in the gibbons variety, and only just
prior to the final completion of the shell. Although the majority of
known specimens showing an expanded lip
are from tranquil waters, yet this peculiarity
has been assumed to be also the result of
the animal living in turbulent waters, com-
pelling it to cling closely to stones, etc., to
avoid being detached and washed away.
An analogous cause suggested hy several
observers is that it may be a conseiiuence of
the animal being compelled to reside mainly
upon and crawl over fiat and hard surfaces
during the growth period, as upon tank
sides in caidivity, or upon the hardened mud of ponds which have
become partially dried up.

Expanded or reflected lip growth has however often been observed
to occur during the autumn when the
reproductive season has terminated and
the cessation of this drain upon the
system enables the food consumed to
contribute solely to maintain and increase
the bulk of the animal and may thus
necessitate an expansion of the shell ; but
the enlargement may also occur at the
normal growth period, if suitable food
be abnormally plentiful and ethological
conditions fiivourable to such increase.

Fig. U2. — An Univalve with Ex-
pancleti lip.

Linnuca sta^^nnlis (L.),

Ash ton -under- Eyne,
Collected hy the late Mr. Lister
Peace.

Fig. in. — An Univalve with
Reflected lip.

L. f>eregrii v. lahlosa JefTr. X 2,
( ireenhc.'ul P.irk, Huddersfield,
Collectetl hy Mr. J. Whitwham.

'I’be Armature of the aperture or mouth of

Fig. 113. — Pupa scccilc Drap. X 1, Fig. 141. — Pupa sccaie

Mailing Hill, near Lewes, var. edentula Taylor X 4,

Collected hy Rev'. S. S. Pearce, M. A., Ingleton, Yorks.,

Showing the typical form and a perfectly edentulous variety of
a normally strongly dentate or plicate species.

other countries develop a varying number of

the shell is a feature
which is usually the
attribute of the per-
fectly ad\dt state.
Some species, as
Vertigo mlniitis-
simii, may exist in
our own country in
a perfectly edentu-
lous form, which in
denticles contracting

VARIATION IN ARMATURE OF APERTURE.

07

the aperture of the shell. Others, as densely deuticulate as Pupa
secale, vary in the number of teeth possessed by the mature shell,
and may even have a variety in which the whole of the denticles con-
tracting the aperture have become obsolete.

An interesting variety of Hijalln'm fulva, if the identification be
correct, is recorded from Cincinnati, U.S.A., in which the immature
shells develop within the interior of the last or body whorl, a number
of little denticles, radiating from the umbilicus like the spokes of a

wheel, appro.ximating in this respect to
the character of Gastrodonta, of which
genus several species are found in that
region. This peculiarity, which dis-
aiipears in the adnlt, is said to be a
probably defensive provision against a
small tender grub, which lives in beds
of leaves and preys upon small mollusks.
These structures are quite analogous
with the denticles and folds found in the post-embryonal Piqvi
cijlindracea and Pupa anglica, which also in a great measure disappear
at maturity, and are thus a character especially distinguishing the
juvenile stage of growth.

In Claiisilia the mouth is furnished with a nnmber of very
characteristic plaits or folds, which vary little in their relative
position, and are therefore of specific and ta.xonomic importance,
and e.xtensively relied upon by systematists as a basis upon winch
to form subgeneric divisions. A full, complete and precise nomen-
clature, and an accurate determination of tbe relative positions of
the various plaits and folds was thus very desirable, and Messrs.
E. A. Smith and B. B. Woodward, with the help of Dr. 0. Boettger,
have proposed a terminology which is probably the most thorough
and satisfactory yet published. These authors recommend the
restriction of the term PLiciE'to the plaits situated upon the palatal
or outer wall of the shell, and la.mell^e to those upon the columella
and the columellar-wall above. One of the chief plaits is the plica
lunata or lunella, a conspicuous and somewhat arcuate calcareous
thickening upon the palatal wall, which is often visible through the
shell, hut is however somewhat inconstant in form, being sometimes
replaced by, or separated into, a series of very short plicm, ranging
one above another in such a way as to suggest the strong probability

Figs. 14o & liG.—Pu/n anglica
CFer.) X 12,

Roundstone, Galway,
Collected by Mr. I’. Sturges Dodd.

Side and liasal views of shell
showing the internal folds or plaits,
especially characterizing the j'outhful
post-embryonal stage of growth.

VARIATION IN ARMATURE OF APERTURE.

fiS

that tliis plait has arisen hy their coalescence; in the same way the
lainella-fnlcrans, which is placed npon the base of the pennltiinate
whorl, would seem to be a result of the thickening of part of the
lamella-spiralis, which blends with the similarly thickened lamella-
inserta, till they spread across to neighbonring folds, for when the
lamella-fulcrans is present, the lamella-spiralis and lamella-inserta are
quite absent or so greatly reduced as to be scarcely perceptible. The
superior lamella is sometimes joined to the lamella-spiralis, which
latter, with the subcolumellar lamella, arises from near the point of
attachment of the clansium to the columella.

Fig. 117. Fig. IIS. Fig. 11!). Fig. 150.

Meal iliayraiiunatie section.'^ of the shell of Cldusilia to show the position
and arran^feinent of the prineipal lainelhe and idieations (diaracteristie of the
G'einis (inodilied, after Smith and Woodward).

Fig. 1 17. — Dorsal view, with outer shell-wall removed to show the lamelhe.

Fig. 1 — Front view with portion of the shell-wall removed to show the position occupied by the
clansium and the sub-columellar lamella, and also showing the folds visible exteriorly.

Fig. 14!). — Front view with portion of shell-wall and columella removed to show the plica;.

Fig. 150. — I3asal view with shell-wall removed to show the lamella;.
a. Lamella superior. c. Lamella parallela. /. Plica; suturales.

/>. Lamella; interlamellares. Lamella fulcrans. k. Plica principalis.

c. Lamella inferior. Lamella spiralis. 1. Plicje palatales.

(i 1. amelia subcolumellaris. h. Lamella inserta. m. Plica lunala or Lunella.

b.s. Pasal or anterior sinus, cl. Clausium. c.f>. Callus palatalis. />.m. Plica; marginales.

Tlie formation of tliese apertnral lamelhic or plications wliicli wind
into tlie .shell are considered by Mr. W. II. Dali to be owing to the
gradual contraction or narrowing of the later whorls, which necessarily
throws into folds or wrinkles the conqjaratively volnminons mantle
margin by compressing it between the muscular foot and the shell-
wall. These ]»lications and lamelhe are formed by the semi-Hiiid
seci’etion from the general surface of the mantle, and are moulded
between tbe folds or wrinkles into which the mantle is thrown, the
elevated wrinklings of the mantle pressing against the shell-wall

VARIATION IN ARMATURE OF APERTURE.

69

FiTt. 151. — Lbnna'a stag7iaUs var. Fig. 152. — Helix 7te7no7‘aUs L.,
variegata Ha/ay, Bitton, near Bath,

Peffer Burn, Haddingtonshire, Collected by Miss F. M.'Hele,
Coll, by Rev. Dr. McMurtrie, F. R.S.E. ,

Showing in a fluviatile and in a terrestrial species the transverse
thickenings, marking rest periods and indicating the growth checks
sustained by the animal.

and allowing only the merest film of shell matter to be deposited
there, as they fit into and form the interstices between the apertural
ridges moulded by the spaces of the mantle folds. Those species with
the retractor muscle affixed high up the spire and which tlierefore
withdraw far within the shell, form the strongest apertural plaits
with the greatest prolongations into the interior of the shell.

The normal thickening of the shell towards the aperture, which in
some species culminates in the form of a raised internal ridge or rib

parallel to and
within the outer
or palatal mar-
gin of tlie shell,
is doubtless a
response to the
necessity for in-
creased strength
atthat partinthe
mature animal.
In the immature

stages of a mollusk, analogous transverse thickenings may occasionally
occur at regular or irregular intervals during growth, and some
species, as Limncca glahra and Limnwa stagnalis amongst aquatic
and Helix arhustoruin and Helix nemoralis amongst terrestrial
species, are especially addicted to this
habit, which is assumed to be an
outward indication of growth checks
sustained by the animal, owing to some
temporarily unfavourable conditions
of the environment.

In some of the aquatic species,
like Planorbis spirorhis, the inhibi-
tion of growth owing to exposure to
drought is also stated to determine the formation of this abnonnal
rib or thickening near the apertural margin, this peculiarity being-
shared by some of the Limnwcv ; a plenitude of calcareous matter
will naturally fircilitate the formation of this sub-marginal internal
rib, which is usually whitish or yellowish in tint, but in Ltmtuva
pdlustris and Limnwa, stagnalis frequently assumes a deep purple
or violet colour.

Fig. 153. — Lii/mcea peregi-a var.
jnajgiiiata Michaud X Iw,

A pond, Lewes, Sussex,
Collected by JMr. C. H. Morris,
Showing the internal sub-marginal rib,
indicative of exposure to drought or of
a plethora of calcic matter.

70

VARIATION IN SCULPTURE.

Ill some of the Ileltces, as Ilelir hurtcm^'is and many other species,
the regularly formed internal rib, which forms so conspicuous a feature

of the oral aperture in the adult, is
developed, according to Longe and
i\ler, only at the maturity of the shell,
owing to the atrophy of certain
glands of the margin of the collar,
which occupy a furrow or groove
parallel with the margin and within
which the projecting rib is moulded.

The Sculpture in Univalves and Bivalves is most usually trans-
verse or parallel with the lines of growth and the margin of the
aperture. It is at times very strongly developed and has perhaps
its most remarkable e.vample in Ih'lir
(tcnli'dfd, where the lamelho are produced
into a beautiful coronet of spines, a form of
ornamentation which is unhpie among
British species, but is more numerous
amongst tropical genera. The incremental
transverse striie are sometiniesconsiiicuously
developed in forms that arc generally smooth or have scarcely dis-
cernible growth lines, and occasionally specimens are met with in
which there is an apparent rhythm in the alternate series of tine and
coarse incremental lines, suggestive of positive transverse sculpture,
which may be sujiposed to be due to the more vigorous growth at

s variation in the prominence of the
growth lines is sometimes very regu-
lar in its recurrence and produces
the ribbed aiipearance seen in Ildix
pnlchcUd var. codata, Ilelix arhiis-
toriuti var. rudd, etc. Reeve has
stated that those mollusks developing
superficial sculpture are invariably
smaller than individuals of the same
species in which any kind of decora-
tive sculpture is avoided. This ob.served fact will account for the
di.sparity in size of Planorlih ]amt'dcm and its variety crista, a
characteristic so constant as to have led to the variety being con-

one time than another. T1

I k;. \ I cli.x arbitsicrrum var. rudis

Mulilf. (^lij'hlly enlarged),

Craig Farm, Monlro.se,
Collected by Mr. Win. Duncan,
Showing the regular development t)f
rihlets on an ordinarily .somewhat smooth
.shell.

Fig. 155. — //. aculcata Mull. X8,
I’as.senthwaite, Ciunljerland,
Collected by Capt. W. J. Farrer,
Showing the corona of .spines.

Fig. 151. — Helix horiensis Muller
(slightly enlarged),

Fordingbridge, Hants,,
Collected by I^Ir. H. Richardson, M.A.,
Showing the internal sub-marginal rib
indicative of maturity.

VARIATION IN SCULPTURE.

71

sideied a young stage of the typical form ; it is probably, however,
like Helix fuldielhi, one of our few dimorphic species. In Hyalinia
radlatula the sculpture is transversely incised, appearing to radiate
from the apex to the periphery, like the spokes of a wheel.

When this incremental sculpture is distinctly developed at some-
what regular intervals into more or less distant costulate ridges, and
the spiral sculpture is also elevated and widely separated, the in-
tersection of the elevated spiral and transverse lines causes a sunken
or flattened area to be perceptible,
forming the sculpture known as
decussate or malleate (so called on
account of presenting the appearance
of being caused by light blows of a
hammer or other instrument). These
malleations or facets are very often
(piite regular in their arrangement
and necessarily dependent on the
direction of the elevated striation to which they are owing. The
variety lacumsd of Lunmm palmtrh is a characteristic example.

Macgillivray ascribes the rough
and corrugately malleate sculpture
to e.xposure to drought, stating that
under such circumstances the shell
becomes wrinkled and “ marked with
long ridges or irregular sinkings like
the skull of a New Hollander.”

The shells of the Llnma uuv in-
habiting tropical and sub-tropical
countries are said to be usually
much more constant and uniform in sculpture, as well as in size and
shape, than their congeners from more
northern districts, and their texture is
also finer and smoother on the whole
than that of species living in the
colder regions.

Spiral or revolving sculpture is rare
in British shells, Cydustonm elecjam
being almost the only species which
clearly and strongly exhibits it,

FiC. 159. —External surface of body
whorl of Cyclostoiua elcgans Mull.,
showing the strong spiral ribs and less
prominent transverse striation (highly
magnified).

Fic. 158. — LiDDUPa pcrcgra Midi, x Iw,
Maidenhead, Berks.,

Collected by Mr. C. G. Barrett,
Showing the corrugately malleated
surface.

P’lG. 157. — Lrnnuea palusiris var.
lacunosa Taylor,

Stream, Leventhorpe Pastures, Leeds,
Showing a regularly decussate or mal-
leate surface.

72

VARIATION IN SCULPTURE.

though ill many other species the spiral sculpture or striation is
existent, but not often distinctly perceptible to the naked eye.

The spiral, like the transverse, striation is soinetiines incised and not
elevated, a character which is naturally not so noticeable and promi-
nent as the elevated sculpture, but is clearly and distinctly visible
with a lens upon the siirfiice of many species, oflering in Ifel/\v pisana
one of the many characters distinguishing it from Jleliv virgata.

In the Pelecypods the greater or lesser intensity and development
of the concentric strim, which are the representatives of the trans-
verse lines of accretion in the Univalves, are, broadly speaking, the
only moditication the sculpture undergoes.

The youthful stages of shell growth have also their special
characteristics, both in Gastropods and Bivalves; the nuclear or

apical whorls in Gastropods always
increasing more rapidly in size and
being often sculptured or adorned
in a different manner to the later
growth, have been mistaken for
and even described as different
species from the parent. Jleliv
(tcniedta has spirally sculptured
embryonal whorls, Pupti cplindracea an irregularly reticulate pattern
thereon, and other species possess more or less distinctive and special
characters. The umbones of some Bivalves also exhibit analogous
peculiarities, those of Vmo having a complex arrangement

of nodules and nodular ridges
(see p. 42, tig. 102), those of
rulo pieturum two rows of
radiately divergent tubercles
on each valve (see page Gd,
tig. IdG), and A]U)dii)it((, a
concentric series of ])romi-
nent angulated ridges and
obscure nodulations ; these
peculiarities being owing to
the permanent shell de-
veloping within the primitive
or glochidian shell of the embryo, the teeth of which prevent the
symmetrical and regular growth which characterizes the species

Fig. IGIK— /V/rr cylindracea Da Costa X ‘MK
Isle of I.isniore, Main Argyll,
Collected by iVIr. K. Staiulen,
Showing the tlellcaie reticulate sculpture
distinguishing the embryonal shell.

Fit.. Anodonia anaiina var. coiuplanata

Uossm. X 8,

(lunifrieslon, near Tenby,

Collected by Mr. F. Walker,

Showing the umbonal sculpture characteristic of
the species.

VARIATION IN SCULPTURE.

7.3

when the interference of the larval shell is removed. Other species
also possess peculiarities of a more or less striking and distinctive
character ; but all these youthful characteristics cease to be produced
after the youthful stage of growth is passed. There are likewise
developed in the youthful stage of Pisidiam kensloivanum peculiar
eave-like or wing-like projections, which are naturally formed at the
margins of the valves in the young shell, but as growth proceeds the
position they occupy is relatively and gradually altered thereby until
at maturity they are found at the umbones (see page 42, figs. 103, 104).

As previously remarked, spiral peculiarities in the Univalves, and
radiate ones in the Bivalves, arise from the effect of the continued
action during growth of those parts of the mantle forming the sculp-
ture, which is in fact moulded upon its surface; the transverse or
isolated sculpture being the outcome or result of seasonal or periodic
action of the secretory glands.

Abrasion has been held to sufficiently account for the smoothness of
shells usually distinctly sculptured, and although friction may account

for the smooth and
polished state in
marine shells, it is
not always the true
explanation. Speci-
mens or colonies of
Clausilia bidentata
are sometimes met
with ciuite smooth,
and this smoothness
is evidently not in-
variably caused by attrition as suggested by Dr. .Jeffreys, but is
owing to arrested development, the sculpture in them having never
existed, or at any rate not proceeded to completion, and indicating
non-possession and not loss. This partial exercise of qualities is seen
in many other ways amongst mollusks.

Fig. 162. — Clausilia bidentata
\2lX . la Turton X 2,

Birmingham,

Collected by Mr. J. Hopkins,
Showing the smooth surface
of the whorls arising from the
arrested development of the
regular sculpture.

IK;. 163. — C, bidentata var.
septentrionalis A. Schmidt x 2,
Gairloch, Ross-shire,
Collected by Mr. A. Somerville,
B.Sc., F.L.S.,

Showing the usual sculpturing
of the whorls characteristic of
the species.

Hairy processes of the periostraca, which may be differentiated
from spinous processes by being destitute of any interior calcareous
support or base and therefore entirely composed of chitinous
matter, are a characteristic of many species living in moist shady
places and hiding during the day beneath stones, under decaying

74

VARIATION IN PERIOSTRACAL APPENDAGES.

1 1 . J

* 4 M

./44^‘

Fig. IGF — Periostracum of Helix
rex^clata Midi, showing the arrange-
ment of the hairs upon its surface
(highly magnified).

leaves or logs, etc. ; the luollusks fre(iuentiiig such situations usually
possess shells of a dull and horny tint,
uithont the brightly-coloured markings
distinguishing species living a more e.\-
posed and prominent life. The epidermis
is also more than ordinarily thick and
perceptible, and is in some species pro-
duced or continued into delicate hairs
or bristles, the depressed or flat spired
species often possessing hairs of com-
paratively greater length than those
species whose whorls are more conically coiled. The hairs are usually
distributed over the surface of the shell in a more or less regular and
symmetrical manner, and being developed by processes of the mantle
margin and not produced at random, they
often have a perceptibly definite arrange-
ment in the different .species.

Accoi’diug to iMr. W. .Jeffery, these hairy
processes are formed as thick mucus on the
surface of the mantle parallel with the
plane of the whorls and are afterwards
elevated to their perpendicular position by
the succeeding calcareous layers.

Tye has observed that these hairy appendages in the terrestrial
snails are hygrostatic in character, and

- fr'A >

Fig. 1G). — A portion of one
of the spiral ridge.s of the ])eri-
oj'tracumof I'lanorlis alius var.
(lra/>arnau(li (Shepp.) showing
the hairs and their arrangement
upon the. ridge (after a highly
magnified original drawing by
Mr. G. SherrilT Tye).

become erect and cons})icuous during dami)

fe-.,;] • , 'll,!);

or moist weather, such as these mollusks
are most active in, the hairs then forming
a chei'ein'-de-frhe, probably very repellant
to most creatures disposed to prey upon
these mollusks, and thus may well be pro-
tective. The protective character of these
periostracal or epidermal ai)pendages is
sui)ported b}" the fact that many of our
larger freshwater as well as terrestrial si)ecies, like the Vivijxirw,
Plduorh 'ts conieus, llelir aintiaxa, etc., are in their young and more
helpless stage quite hispid, and thus reap such iwotection as this
defence may afford. The hispid surface of the young Fldiiurhis
Cornells is composed of twenty-five to thirty spiral rows of short

Fig. IGG. — Pla/toilis conieiis
(Iv.) 1") days old, X 12,

Showing ihc si)iral rows of
periostracal hairs characteristic
of the youthful stage,

(After an original drawing by
Mr. (T Sherrifi' Tye).

VARIATION IN PEIIIOSTRACAL APPENDAGES.

75

delicate hairs encircliug the whorls. In this state the shell is con-
sidered to be the Planorhis of Muller. Tlie Vlcipara

coiitcct(t in its embryonal and youthful stage of growth has three

principal rows of spirally disposed and
comparatively long hairs, of which the
two upper rows are the most strongly
developed. In addition to these there
are from twenty to forty intermediate
spiral ridges bearing much more minute
and delicate hairs, which rows are always
most numerous between the base and
the lowermost row of the stronger hairs,
and least numerous between the second
and the third rows. The number also
appears to increase wdth age, as the
penultimate whorl on one specimen whicli
was carefully examined had only five of these finely hispid ridges
between the suture and the first row of stronger liairs, wliile upon
the body whorl near the apertuie they had increased to twelve.

Tlie development of hairs is very variable amongst individuals of
the same species ; thus the v. Itispidosa of II. /t/.y)ida is a very good
example of liypertrichosis, being densely covered with stiff recurved
white hairs, while
Alder’s v. depilata of
the same species is
almost bald ; possibly
these differences are a
more or less direct re-
sult of the environ-
ment of the two forms.

These hairs are
generally caducous,
cylindrically subulate
and often borne upon
a little tubercle or swollen base, and are more especially a
characteristic of thin and dull coloured species, varying in their
character according to the species ; those of Helix revehita being
somewhat short and thick, and those of Helix granidata much longer
and more slender, with knotty prominences at irregular intervals,

Fig. 1G8. — Periostracal hairs
of Helix 7‘cvelata Michaud
(highly magnified),

Plymouth, Devon.

(After an original drawing
by Mr. G. Sherriff Tye).

Fig. 1G9. — Periostracal hair.s
Helix gramtlata Alder,
lighly magnified),

Halifa.v, Yorks.

(After an original drawing
^ Mr. G. Sherriff Tye).

Fig. 1G7. — Periostracal hairs or
processes upon embryonal Vhnpara
contecta Millet (highly magnified),
Manchester,

(.\fter an original drawing by Mr.
G. Sherriff Tye).

7G

VARIATION IN THICKNESS.

while those of Helix hhpida are usually more or less aiigulated or heiit,
with the tips directed forwards or towards the aperture of the shell.

These periostracal hairs are not coiihued to the Gastropods, hut are
equally possessed by the different species of Phldiiim, Spliarium,
etc. ; those upon the .shell of Sp/urriitm corneum are of microscopic
size, somewhat short, comparatively thick, bent at the tips and most
numerous in the umbonal region.

Substance, or thickness, is frequently the outcome of an ample ora
limited supply of calcareous matter, though the variation in this
character may also arise from an apparent physiological inability to
utilize the material presented, which action may be intensified or
diminished by chemical, meteorological, or other conditions. This
weight or thickness varies not only according to the species, some
having thin and almost purely chitinous shells while others are heavy
and dense ami almost entirely composed of calcareous matter, but
also according to age, young specimens being always more delicate
than adults living under the same conditions and containing propor-
tionately less calcic carbonate than the more aged shells, in which the
nacreous or inner layer may become abnormally thickened if the life
of the individual be from any cause greatly prolonged.

It has also been satisfactorily and conclusively shown that a tem-
perature above or below the optimum, which optimum varies for the
different specie.s, results in the minimising or even the ce.s.sation of
the shell-secreting function, and the growth, if any, is characterized by
greater delicacy as the temperature recedes from the optimum. Thus
the varieties ghichdh mxA thermcdis oi L'lminm jieregra which inhabits
glacial and thermal springs respectively, are ecpially distinguished for
the extreme delicacy and dwarf size of their shells. Specimens of
Llmnau perefjra found living in the warm
water of engine cisterns at Cheadle, Burn-
ley, and other places, are characterized
by the same extreme tenuity and
diminished size. This form is almost
ei|ually well-known by the two distinct
names, dlaphami and thenmdh, the first
descriptive of the character of the shell
and the second referring to its habitat.

The Burnley shells are, as I am informed by Mr, h'. G. Long, sub-
jected to a temperature of 84° Fahr., and are especially transparent

Fig. 170. — Linnuea peregra var.
ilu'7‘///aiis Foub^e X lA,

Mill cistern, (iannow, llurnley,
Collected by Mr. R. Wiggle.sworth,
Sliowing the effect upon tlte .shell
of too great a degree of warmth in
the iiihal>iled water.

VARIATION IN THICKNESS.

77

and also of diminished size ; the Cheadle specimens of the same
species, though smaller and thinner, are less transparent than the
Burnley shells, and are, according to the careful and connected
observations obligingly undertaken at my request by Mr. Masefield,
subjected to a temperature varying between 60° and 98° Fahr. ;
when the water rises towards the latter temperature these mollusks
crawl out from it and remain attached to the sides of the condensing
reservoir at some point above the water level until evening, when the
temperature owing to the stoppage of the engines, begins to fall again,
and on its decreasing to about 98° the mollusks have been observed
to re-enter the water, that temperature appearing to be the maximum
heat they are able or willing to endure.

Fluviatile species inhabiting great depths, much beyond those in
which they are normally found, also show marked attenuation of shell
substance, probably on account of the lower temperature to which
they are exposed hindering the free exercise of the shell-secreting
function. The Limnan stagiicclis dredged by Mr. Bryant Walker in
High Island Harbour, Lake Michigan, at a depth of 34 feet, is
remarkable for the delicacy of its shell, and this is also a very
striking character of the various abyssal forms of Limncva from the
depths of the Lake of Geneva.

In Helix aspersa v. tenuior found in Guernsey, where calcareous
strata are absent and the shell more largely composed of animal
matter, we have a very good example of the effect of a deficiency of
shell-forming material, the weight of a fairly characteristic specimen
of this variety, kindly given me by Rev. Dr. McMurtrie, being only
four grains, whereas the average weight of typical shells is about
32 grains. Helix nemondis shows similar, though less striking,
results, as specimens found by Mr. J. Ray Hardy upon the Volcanic
Slate, near the summit of the Macgillicuddy Reeks, co. Kerry, were
so excessively thin that many of the most fragile collapsed under
the necessary compression used in gathering or cleaning them, the
most delicate shell preserved intact weighing 3‘3 grains, or a little
more than one-quarter of the weight of ordinary individuals.

This deficiency of calcareous matter has also, according to Clessin,
often a marked effect upon the form of certain species, the .shells of
Clausilia being said to diminish in length and Helix lapicidu to
become rounded at the periphery.

78

VARIATION IN THICKNESS.

The opposite oi’ incrassate condition may be well illustrated by
TIf'U.v a.'^persa var. solidissitna Paulucci, a specimen of which, found
by the late j\Ir. C. Ashford on the rurbeck limestone at Swanage,
though of oidy normal size, weighed eighty - three grains; and
Mr. C. Jefferys has taken several specimens on the cliffs at Tenby
weighing over one hundred grains each, or more than three times
the weight of average individuals.

fh'li.r uemoralis normally weighs about 1 1 grains, yet a thick shelled
race, the variety crctkola of Miirch, which formerlj^ e.xisted in the West
of Ireland, and in a somewhat less pronounced form has been .shown
by i\fr. Collier to still e.xist there, attained a much greater weight.
A number of sub-fossil specimens of this variety, kindly sent me by
Prof. D’Arcy Thompson, had an average weight of 44 grains, the
heaviest weighing 78 grains and the lightest, a somewhat diminutive
shell, weighing la grains. This abnormal incrassation of the shell
substance is principally caused by the .secretion of additional and
thicker layers to the inner surface of the shell, and probably arises from
the mollusk living upon suitable geological strata, furnishing abundant
supplies of calcic matter, and also from the probable prolongation of
the life of the animal beyond the usual life-limit of the species, perhaps
owing to a succession of mild and equable seasons, the periodical de-
position of the shell matter by the visceral mantle occnrring regularly
at its proper season during the whole life of the animal. Post-mortem
deposits of calcic carbonate, by carbonate of lime entering the pores
in a fluid state, have been suggested as the cau.se of the unusual

thickness of the.se
shells, but a care-
fill e.xami nation of
sections throngh the
shell disprove this
suggestion, as they
clearly demonstrate
that this extreme
incrassation of the
.shell has taken place
ill a strictly normal manner, the inner laj^er upon the base of the
preceding whorls retaining its characteristic comparative teiinity,
being only modified by the delicate films of calcic matter, deposited
at the same time as the stronger layers which thicken the interior

Fir,. 171. — Section through
the shell of a normal 11. ni'i/io-
ralis r.., showintj the usual thick-
ness and other characters of the
species. Weight of section, 8
grains.

From a section cut liy Mr.
F. Rhodes.

Fk;. 172. — Section ihroiigli
the shell of a suh-fosi.il //. ucino-
ratis F.jfrom Dog’s Hay, Conne-
mara, e.\hibiting the remarkable
thickening of the shell-wall.
Weight of section, 43 grains.

From a section cut by Mr. J.
Ray Hardy.

VARIATION^ IN THICKNESS.

79

surface of what is or were the external shell-walls, and therefore
preserving the same relative thicknesses of the external and internal
shell-walls that distinguishes normal specimens.

Fluviatile species, though affected by the comparative abundance
or scarcity of calcic matter in relation to the thickness attained by
the shell, are also influenced greatly by other circumstances of their
environment, those individuals inhabiting rough or disturbed waters,
rapid and turbulent streams, etc., develop a thicker and stronger
shell than usual to better enable them to withstand the force of tlie
waves and currents to which they are exposed, and often show a
shorter spire and a more expanded and larger mouth, which necessarily
allows for greater clinging or adhesive power, and renders the mollusk
less liable to be detached and probably injured by wave violence.

In Anodons the light inflated form with thinly calcified valves
may, as in the Univalves, exhibit according to circumstances an
actual scarcity of shell-forming material or a idiysiological inability
to utilize it. Shallow waters with their greater variations of tempera-
ture and consequent checks to shell secretion, tend to produce thin
and lightly calcified shells, as do also the immense depths known to
exist in some lakes, perhaps in this case due to the constant low
temperature, much below the optimum for the species.

The effect of a plethora of calcareous matter or of functional
activity of the secretory organs is strongly exhibited in Anodonta
cygnea v. incrassata, and is shown not only by the greatly thickened
nacreous layer, but the plenitude of calcareous substance is often
strongly indicated by a heavy deposit of the limy matter in the form
of tufa, on the exposed posterior end of the shell.

A characteristic specimen of this variety from a brook at Tisbury,
Wiltshire, kindly given me by the late Mr. J. Pickering, w'eighs
2,227 grains or 5T2 ounces, while an example of the typical form of
equivalent size from Nagden, near Faversham, collected by the late
Miss E. B. Fairbrass, weighed only 322 grains, or about one-seventb
the weight of the variety incrassata. Rough and deep waters,
although not profound depths, are both said to tend to produce thicker
and stronger shells than those developed in shallow and more
tranquil waters.

Some species, as Unio margaritifer and Neritina fluviatiUs,
appear able to extract the necessary lime carbonate to form thick
and heavy shells even from the waters of gi’anitic districts, whilst

80

VARIATION IN SIZE.

other species, as Anculm fnriatUis, under similar conditions seem
unable to do so, their shells being unusually delicate and thin.

This dift’erence in the selective working of the tissues in different
species is true also in a lesser degree amongst the individuals com-
posing a species, which vary int(n- se in their power to utilize the
shell-forming material presented, although the thickness of the shell
would generally seem to be in inverse ratio to the hardiness of the
animal, the most hardy species or genera, or those which withstand the
most rigorous climates having only a thin external or internal shell,
as though the shell-forming energy of the creature was diverted to
strengthen more vital processes.

Size is not only influenced by the obvious causes of the abundance
or scarcity of suitable and nutritious food, the result of which would
be the proiluction of a larger or a more diminutive animal and shell
than would be developed under ordinary conditions, but is also in a
large degree dependent upon temperature and other circumstances.
The researches of Semper on the phenomena of growth, upon which
size is dependent, have shown that in Limuau stagnalis the size
attained by the shell is capable of correlation with the temperature
and amount of the inhabited water, as assimilation and growth
ecpuilly ceased if the degree of warmth exceeded 00° P. or fell below
53° P., the fullest vigour being enjoyed and the largest size attained
when the temperature ranged between 08° P. and 77° P.

The results of these researches are of great interest, and are more
or le.ss applicable to other specie.s, as demonstrating some of the con-
ditions governing growth — and therefore size — in mollusca generally,

and clearly establish that
the volume or amount of
water allowed to eachinollusk
is so decisive in its effect
upon growth that in the space
of six days the difference in
the size of the shells of those
in a large and those in a small
body of water becomes apparent ; the smaller the amount of water
per individual the smaller the shell and vice irrsft If the volume
of water be less than 5,000 cubic centimetres per individual, a
dwarfing influence is perceptible, the greatest differential effect being

P'lG. 173. — Volume-curve of Liuitura stagnalis^
showing the effects of various volumes of water upon
the size attained in a defmite period of G.3 days (after
Semper).

VARIATION IN SIZE.

81

shown between those sliells inhabiting 100 and 500 cubic centi-
metres respectively ; for, whereas
specimens reared in 100 cubic centi-
metres of water only acquired a length
of 6 mill, in 65 days, those in 250
centimetres reached 9 mill., those in
500 centimetres 12 mill., while the
individuals in 2000 cubic centimetres
grew to 18 mill, in the same space
of time. Ample food and healthy con-
ditions had been assured to each
mollnsk, and the experiment therefore
exhibits the dwarfing effect of too great an abundance of life in any
circumscribed area apart from scarcity of food. The rate of growth

Figs. 174, 175, 176, 177.

Four shells of Liinncea stagnalis^ each
65 days old and hatched from the same
mass of ova, but reared in different
volumes of water to demonstrate the effect
of the amount of water per individual
upon the size attained in a definite period
of time, and illustrating the Volume-curve
Fig. 173.

Fig. 174. reared in 100 cubic centimetres
of water ; Fig. 175, in 250 ; Fig. 176, in 500 ;
and Fig. 177, in 2,000 (after Semper).

20 I

o

15 ^
10 5'
5 §

rp

a

0

Age of mollusks in days.

Fig. 178. — Curve of time, showing the average rate of growth of Limncea stagnalis reared
in from 1,000 to 2,000 cubic centimetres of water (after Semper, modified).

is also far from uniform, as at first the young Lhnnwa grows at a
moderate rate, after which follows a period of quickened growth, until

Figs. 170,

Four figures of the shell of Limmea stagnalis to
show the amount and rate of increase in size and
\ to more strikingly demonstrate the period of most
rapid growth, averaged from specimens reared in
/ /\ from 1,000 to 2,000 cubic centimetres of water,

/ \ and illustrating the Growth and Time- Curve,

/ Fig. 178.

( J Fig. 179, 21 days old ; Fig. 180, 42 days old ;
^ ^ ^ Fig. 181, 60 days old ; and Fig. 182, 85 days old.

182.

at length, the older the animal the slower the growth. Maximum size
can only be attained by favourable conditions at these early and critical

periods, especially that of greatest increase, as that period once passed
cannot afterwards be fully compensated for by any subsequently
favourable conditions, the shell being then constructed on a more

F

VARIATION IN SIZE.

S2

diniinntive scale. A specimen that does not exceed 20 mill, in length
during the first season is necessarily undersized when adult.

Temperature exercises a very powerful influence upon the size
attained, as the young L'lnuKca only begins to assimilate food and

therefore grow, when the
waiter attains a temperature
of about 0,-5° Fahr., and
although a much lower tem-
perature does not seem to
be vitally injurious to the
mollusk, its effects are e.x-
hibited in the decreased
power of assimilation and
consequent checks to, or
inhibition of growth.
Semper has experimentally
demonstrated the effect of cohl in retarding the growth of specimens
in every other respect (juite as favourably circumstanced as those
attaining a much larger size.

The mean temperature of a dis-
trict may be apparently favourable
to a species, but this average may
be tbe result of two extremes, and
these extremes of temperature,
if occurring during the growth
periotl have a baneful influence
and unfavourably affect the size attained by the animal.

During tbe winter mouths, however, most of our land and fresh-
water mollusks are more or less complete hibernants, but on the
termination of this winter dormancy there quickly follow's in the
young a^ period of rapid assimilation and growth, and unfavourable
inlluences at tins season necessarily retard the growth and induce
dwarfed shells, as no after favourable circumstances can fully com-
pensate for retardation of growth in early life.

'I'hus we are enabled to understand and .appreciate the periodic
variations in size and the cbaracters in correlation with it, so often
notice<l to occur, more especially amongst the fre.shwater mollusks,
and to consiiler them with great probability to be the biological

Four fii^ures of the shell of L. stagnalis
show'iiis the retUiced sizeaitaiiied owin^ totlie
temperature of the inhabited water becoming
lowered to nearly oa Fahr., and illustrating
the Volume ami Growth Curve, Fig. 183.

Fig. 181, reared in 100 cubic centimetres ot
water ; Fig. ISa, in 2”)0 ; Fig. 180, in 500 ; and
Fig. 187, in 2,000 (compare Figs. 177 & 187).

Fi(',. 183. — Volume-curve of Linuutui stai:^naris,
totally altered by a sudden fall of temperature arresting
the growth. The various vessels containing the un-
eiiual bodies of water in which the Liinno<p lived,
stood by a window where the sun .shone for about two
hours in the afternoon, elevating the water in the
smaller ves.sels to a favourable temperature, but being
insulTicient to do so with the larger ones. Hence the
Lintmva in the largest vessel containing 2,00(1 cubic
centimetres of water, which should have been under
ordiiiarily favourable circumstances very much larger,
were actually smaller than those in many of the
smaller vessels (after Semper).

VARIATION IN SIZE.

S3

expression of the various climatic and other modifying circumstances
to which the mollusks have been subjected. A cold unfavourable
season would result in a smaller and more delicate shell, with pro-
bably more or less distinct transverse indications of the growth-checks
sustained, while another season of a milder and more favourable
character would result in larger and more uniformly grown specimens.

In Malham Tarn, a large body of water upon an elevated plateau,
1,250 feet above the sea, in the West York-
shire Highlands, Mr. W. Denison Roebuck
and Mr. .J. Darker Butterell, in Sept., 1883,
collected numerous specimens of Limncca
stagnali!^, which I found to clearly reflect
the low temperature and the thermometric
vicissitudes of the lake by a shell of great
comparative delicacy and small size, with the
many growth-checks strongly emphasized
by the whitish transverse thickenings
crossing the whorls and showing that part
of the shell-forming energy has evidently been here diverted to more
vital purposes. Other specimens obtained
during August, 1890, from the same place,
did not exhibit any striking diversity from
ordinary examples, and this was probably
owing to the active growth-periods being
during comparatively mild and favourable
weather.

An examination of the meteorological
statistics preserved by the Philosophical
Society at Leeds confirm and emphasize the
probable correctness of my conclusions.

The early spring of 1883 was characterized
by severe cold, frerpient snow storms, and
considerable fluctuations of temperature,
while that of 1890 was distinctly more
equable, and showed fewer and .slighter variations of temperature.

For every other species there are probably also certain conditions
of temperature, etc., exceptionally flxvourable to their growth and
development, which may be termed the optimum, subject to which
conditions progress and growth are most rapid and decisive, being

Showing the even regular
growth and larger size, as at-
tained under more favourable
circumstances.

Fig, 188. — Lij7in(pa stagnalis
var. fragilis-variegata Roe!).,
Malham Tarn, Vorks., Sept ,
1883,

Collected by Mr.W. D. Roebuck,
Showing its maturity by the
full number of whorls and the
inclement nature of the growth
periods by a small thin shell,
with many strong indications of
growth checks.

VARIATION IN SIZE.

,S4

either more vigorous while in progres.s, or the growth season longer
continued, the result in each case being the development of a larger
animal and shell. As this optimnm environment probably varies
for each .species, it follows that where these optimnm conditions are
most nearly approached, the species most favonrably affected will
develop the largest ami most vigorous mollu.sks, and divergence
from this optimum would result in a i)roportionately smaller animal
and shell.

Mqnahilifj'and suitability of temperatnre during tlie growth period,
which is essential to the development of the finest mollusks, is not
exclusively dependent ujion latitude, being largely intluenced by the
coidiguration of the land, the vicinity of the sea, and the prevailing
direction of winds and currents. Thus the British Isles, and more
especially Ireland, have -owing to their insular position and other
causes - an eipiahle and moist climate, and do not suffer from the
great heat in summer and the intense cold in winter that characterize
the great continental areas in the .same latitude, each of which
imiioses a check upon growth if occurring during the growth season.

])r. Jeffreys has asserted that
northern specimens generally
attain a larger size than the
same sjiecies in the south, and
(piotcs Draiiarnand’s remarks
.on the comi»arative size of the
shells of north and south France
in snp[)ort of his opinion; hut
this result can only occur with
such species as are most suitably
circumstanced in such districts,
and this is not merely a question
of a larger food supply being ohfainalde,
owing to the greater i)ancity of species
and individuals in northern districts, as
Dr. Jeffreys has supposed, but is depen-
dent, amongst other things, upon the
existence of a temperatnre at which
assimilation can he actively carried on.

(S})ecimens of IfeJix Kuprrxit from our
own country are far inferior in size to

Fig. 101. — Helix nspc7‘sa var.
minor Picard,

Cardiir,

Collected by Mr. F. \V. Wotlon,
Showin.-T the efTects of some un-
favourable conditions of the environ-
ment.

VARIATION IN SIZE.

H3

the gigantic exainple.s of the same species found in Algeria, and our
average Planorhis corneas are cpiite diminutive compared witli speci-
mens of the same species from southern Europe.

Inversely Balea perrersa would appear to find in North Britain and
in elevated situations its most congenial habitats, the Scottish speci-
mens being perhaps finer examples of the species than those from
more southern and warmer localities.

Granitic soils, peaty districts, or any foi’mation deficient of the
calcic carbonate of which shells are mainly composed, are character-
ized by shells not only of thin texture but dwarf size ; this diminu-
tion of size is also an effect of altitude, crowding of individuals, and,
according to iM. Locard, of darkness, or indeed of any other environ-
ment unfavourable to the fullest development of the species ; the
vicinity of the sea would also appear to have a dwarfing influence
ui)on terrestrial and fluviatile mollmsks unless counter-balanced by
other exceptionally favourable circumstances, and the same effect is
})roduced by very deep waters, such localities also exercising a
dwarfing effect upon the species inhabiting them.

A diminutive size in freshwater shells may also bo a result of
too great an abundance or overcrowding of individuals in the area
occupied, as demonstrated by Semper, who has enunciated as a
general princijde that huge bodies of water develop large shells, and
ponds or other bodies of water much restricted in area produce small
shells ; and this is asserted to be a general rule with fishes also, it
being well known that the further one advances up-stream and the
smaller the Trout become.

The Colouring of the mollusca seems largely dependent upon the
action of light, the more exposed surface of .spiral shells and the
posterior end of burrowing Bivalves being usually more richly
coloured or ornamented than the less exposed or buried portions, and
colouring generally is probably of great biological importance ; it is
also, as in other groups, most pronounced in brilliancy and variety
in the warmer regions of the globe, and becomes gradually reduced in
diversity and beauty as the poles are ai)proached. These known facts
led Dr. Fischer to propose for the mollusca three zones of colouration
corresponding with the thermal ones, viz. ; —

PoLYCiiROMic, for the brilliantly coloured shells chietly inhabiting
tropical countries. Examples : Licjuus virgineus (L.), West
Indies, pi. ii., fig. 8, and Helix plcta Born, Cuba, pi. ii., fig. 9.

VARIATION IN COLOUR.

8(;

Oligochromic, for the more soberly coloured and less varied shells
of the temperate latitudes. E-xamples : Helix pisana Muller,
iMeutone, pi. ii., tig. 10, and Helix nemomlis var. UbelUda
(llisso), Bath, pi. ii., tig. 11; and

Monochromic, for the simply coloured species characterizing the
colder regions. Examples: Vitrina pelliicida^&v. depressiuscida
Jetfr., Exeter, pi. ii., fig. 12, and Verticio (dpestris Alder,
Cottingley, pi. ii., fig. 13.

iMany exceptions naturally occur to these broad lines of distinction,
as these results are naturally more or less influenced and modified by
nature of soil, vegetation, altitude, and other circumstances, but
there can be no dispute that they express the leading features of
colour distribution upon the globe, though species with strong shells
are usually more vividly coloured than their congeners possessing
fragile and delicate ones.

Colouring in the mollusca may he due to the structural character
of the surface of the shell diffracting and dispersing the light rays,
but is more generally owing to the ahsori)tiou of certain of the
elements of light by the s})ecial substances in the shell termed pig-
ments, the i)articular colours produced varying according to the
chemical nature of the cou.stituents of the shell disi)laying the colour,
and being due to those rays or vibrations of light which are not
ahs(jrhed, hut reflected to the eye ; thus red is the result of the
absorption of all hut the red rays which are therefore reflected and
visible, while black is owing to the absori)tion of all the constituents
of light, and white to their complete reflection.

Structural (jr iridescent colouring is strikingly exhibited by the
inside of the valves of the Naiads, as well as occasionally by the

interior surface of some Univalves, and is
owing not to the varied absorptive power
of certain of the component parts of the
shell, but to a multitudinous series of
undulating parallel lines of exceeding
fineness which diffract the light and give
rise to a i)rismatic play of colour, varying
from red, through yellow, gveeu and blue
to violet, according as the point of view
becomes more and more obli(pie and the
lineation thereby more closely approximated, owing to the varying
angles at which the surface is seen.

Fig. 192. — Highly magnified sur-
face of a nacreous shell, showing the
minute parallel sculpture upon which
structural or prismatic colouring is
dependent (after Tryon).

VARIATION IN COLOUR.

S7

Tliat tlii« iirisniatic colouring is largely due to the light rays iiu-
piiiging on the iuuuinerahle tiiiely incised lines is demonstrated by the
fact that the iridescent eftect has been successfully imitated on steel
buttons by engraving u})on them similar fine and parallel lines. In
some species this beautiful effect is probably to some extent due to
the thin laminated structure of the naci’eous layer. All nacreous
shells, however, when polished become iridescent and form more or
less brilliant mother-of-pearl.

The colouration of the body of the animal, speaking generally,
would often appear to have little or no relation to that of the shell,
for Helix nemondis, which has the most brilliantly and variously
coloured shell of any of our native species, has an almost unifoimly
coloured animal, and uniformly horn-coloured shells are not always
borne, as might be e.xpected, upon uniformly coloured animals, Imt on
the contrary are sometimes, as in Limua-a, tenanted by animals with
the mantle strongly maculated and marbled with black and yellow.
The naked forms are also more brilliantly and variously coloured than
the animals of the testaceous species.

Shells which live most freely e.xposed to the light, if other circum-
stances be fiivourable, are the most brightly coloured, as Ileliv nemondlx
and Helix hurtensix, which sometimes almost rival tropical species in
the brilliancy and variety of their colours and banding, varying from
almost pure white, through yellow, pink, and chestnut, to deep
chocolate brown, while those species usually found secreted during the
day under stones, logs, etc., like the Hijaliniw, or which habitually live
on the ground or the trunks of trees, like the Bidiiniid, approximate
to these objects in aspect, their colouring being Procryptic or pro-
tective in character, the e.xceptions being the white or colourless
species, which however are usually of small size and very retiring in
habit.

Shells like those of Limax, which are developed within as well as
concealed by the mantle and thus e.xcluded from light, are always
white or colourless, and do not exhibit the diverse and varied tinting-
acquired by external shells.

In clear bright water the Aiiodmis and Unionea are often of a
bright green coloui’, sometimes beautifully rayed by a deeper tinge
of the same hue or by distinctly yellow or brown shades of colour ;
according to Herr .Jordan the radiate varieties are chiefly luit not
invariably found in flowing waters ; but the shells inhabiting the

VARIATION IN CULOl'K.

S8

iiioic turbid rivers and ponds, or any waters eoiitaminated with
sewage, etc., do not normally exldliit this bright and variegated
colouring, but are often of various shades of brown verging
occasionally upon black.

In our Gastropoda the colouring matter is generally speaking
resident in the calcareous part of the shell, and in the Pelecypoda
is found in the periostracuin or epidermis, but the colouring of some
Gastro])ods, as HeliJ' (icuhaUi, Chtus'dhi htmumtd, etc., is entirely or
chietly due to the periostracal investment, and not to the pigmenta-
tion of the calcareous part of the shell, such species resembling the
Pelecypoda in this re.spect. According to Krukenberg the red,
yellow and brown pigments, which are the most prevalent colours
amongst mollusks, belong to the Lipochromoids or Melanoids.

Prown of various shades is the most prevalent colour amongst both
our land and freshwater shells, although some freshwater species are
of a bright green, a colour not found among.st our land shells, the
nearest approach to it being by Ihll.r recehitu, ivhich in some
localities shows a strong though dull greenish shade. Camerano, who
has studied the Mollusca generally with the object of determining
the relative fre(piency of the various colours, finds that black is rare,
brown, grey, yellow, white and red all common, violet relatively com-
mon, while blue and green are more rarely met with.

The i)inks and violets are usually the most evane.scent colour.s, and
colouring generally amongst our land and fre.shwater mollmsks seems
to be more or less fugitive, if abnormal or unusual as to position,
thus the delicate purple .sometimes found on the lip of llcllx dxjierxd
soon fades and disappears. The normal dark spiral banding of the
fusco-labiate variety of Ihdlv hortenxh seems lU’actically permanent,
hut the abnormal colouring of the li[) is unstable, the pink element
first disappearing, followed more slowly by the brown.

Laud .shells may be modified or changed in colouring by adventi-
tious matter about their food, as Herr Ti.'^chbein has observed in
Gei'inany that IIl-Hc liorteiit<U when found in the neighbourhood of
tanneries a.ssumes a peculiar brownish hue. A(piatic shells are also
liable to be similarly affected by substances iutermi.xed with or dis-
solved in the water they inhabit, as Mr. Quilter has recorded that
specimens of Unto pictorum found in a certain part of Groby Pool,
Leicestershire, adjacent to a local out-crop of red triassic marl, had
the nacre tinged of a beautiful salmon colour by the oxide of iron

VARIATION IN COLOUR.

89

derived tlierefroni, the shells found in other portions of the pool
being (piite normal in this respect ; and Mr. Ileathcote noticed that
during the long drought in 1887, when the Ringley Canal was very
low and the surface covered by an iridescent scum from the aniline
dye-works, that all the Limnaa stagiudis in tliat locality were remark-
able for a noticeable metallic gloss and were much darker in colour,
and more strongly striated than normally ; but the specimens collected
in the same [ilace when the canal was high and clear were characterized
by the usual delicate pale horn colour and smooth texture of ordinary
individuals.

All aquatic shells whether univalve or bivalve are at times and in
certain localities entirely or partially covered externally with a reddish
tint; this is usually owing to living in ferruginous waters and is
caused by an extraneous deposit of oxide of iron. Analogous incrusta-
tions of tufa, carbonaceous or other mineral and confervoid matters,
give to the exterior of aquatic shells different tints, in accordance
with the nature of this superficial investment, and have given rise
to some unnecessary varietal names.

The peristome is sometimes identical in colour with the general
surfiice of the shell, but often, especially in those species with
thickened or distinctive lip structure, the colour is strikingly
different, as in the brown or horn-coloured shells which usually have
the peristome pure white, occasionally tinted with a delicate rose
colour. In other species, as HelU' iiemoralis, the colour of the lip
is very variable and its .special tint may overspread not only the
umbilical callosity, but the surface of the penultimate whorl, and
oven extend for some distance into the interior of the shell. This
lip colouring, especially if not an ordinary characteristic of the
species, is often very fugitive in character and soon fades after the
death of the animal. Draparnaud has observed that the peristome
of Helix insami may become of a bright rose colour if the animal be
kept without food for a length of time, and the same result is .said to
occur if the animal lives in warm and sunny places, this colouring
being .said to be deficient in those individuals living in less favoured
spots.

Albinism {nlbus, white) is generally owing to pathological causes
and is therefore strictly speaking a morbid condition of the animal,
consequent upon the impaired secretive power or abortion of the
colour glands, and their consequent physiological inability to secrete

90

VARIATION IN COLOUR.

the requi.site colouring matter, but perliaps iii some ca.ses from an
actual deticieiicy of pigment-forming material.

^Uhinisni may he a more or le.ss partial phenomeiiou, affecting only
a certain set or sets of organs, ami not modifying others, or may
embrace the whole animal, thus the shell of a mollusk may be destitute
of colouring or pigmentation and therefore an albino, without the
animal itself being necessarily albine. In fact, instances are number-
less in which a stronglyi)igmented animal has borne an albine or colour-
less shell, and the i)ossibility of this is easily appreciated when it is seen
that the albinism of the shell solely depends upon the selective working
of the glands of the mantle margin, which are extremely susceptible
to different intluences, as is shown by the fact that one can hardly
take up a .specimen of certain of our laud shells without noting the
variability in the intensity of the colouring of the ground tint at
different periods of growth, this being even more strongly e.xhibited
by the spiral banding, which is freipiently found to be totally destitute
of colouring matter at the commencement of a periodic growth, often
acquiring the normal depth of colouring by slow degrees only and as
the termination of the growth period is api)roached.

'I’rue albine .shells are (piite deficient of coloured pigment and may
have an opa(pie or a translucent character depending upon the disposi-
tion of the constituent particles forming the shell, as to whether they
reflect the light rays or allow their passage through the shell substance,
and must not, as is sometimes the case, be confused with bandle.ss
specimens of normally banded species wbicb may happen to possess
a whiti.sh ground colour, and are therefore merely ordinary individuals
in which the banding is suppressed; this difference is well illustrated
by the translucent-banded form of llelt.v virgdtd and the variety
(ilhicmis, the first being true albinos, while the latter are only ordinary
individuals in which the banding is deficient (.see pi. ii., figs. 4, 5).
Pai'allel cases are furnished by other species, Ilel'u' 2>isan(i,iox instance,
showing the two forms in the varieties alba and albtda re.spectively.

The occasionally different colouring of the nucleus of the .shells not
truly albine is sometimes relied upon as a means to readily distinguish
the true albinos, but this test is not an infivllible guide. An albine
shell, when borne by a i)igmented mollusk, is e.s.sentially similar to any
white-furred or white-feathered animal or bird, as tbe shell, like furor
feathers, is an e.ssentially cuticular structure (piite outside the animal,
and, though organically connected, it has been satisfactorily demon-

VARIATION IN COLOUR.

91

strated that a Helix can exist even when its organic connection with
tlie shell is completely severed.

It is quite certain that local circumstances do at times conduce to
the development of albine shells. One instance will suffice to sup-
port this view ; under stones in a dell on the cliffs near Hele Bay,
Ilfracombe, Mr. Brockton Tomlin, in March, 1887, found hundreds
of the white variety of Helix rotundata, and it is suggestive that
this state was practically universal and not confined to this particular
species, but was shared in by the associated species, Hyalinia celUiria
and Avion hovtensis. This variation, so plentiful within these narrowly
circumscribed limits, was not met with elsewhere in the neighbourhood,
clearly showing that the influence, whatever its nature, did not ex-
tend beyond the limits of this little valley.

Amongst Lepidoptera Mr. Poulton has satisfactorily shown that the
character of the larval food affects its colouring. He especially
instances Triphwna, pronuba fed in darkness upon the midribs of
cabbage leaves, which were ({uite unable to form the green and brown
colouration, although others fed under similar conditions upon more
normal food were typically coloured. Moquin-Tandon considered one
of the principal causes of albinism in mollusks to be the nature of the
soil and consequently the food, and as some corroboration of this
opinion it may be stated that M. Jules Colbeau long ago observed and
recoi'ded that about Dinant the translucently-banded Helix hovtensis
exhibited a noticeable partiality for gooseberry bushes, and Mr. A. E.
Boycott has recently remarked upon the predilection of this and
other albine forms for plants of the horse-radish, but although these
observers did not pursue the investigation further, yet it has been
actually demonstrated by Capt. W. J. Farrer that this albine modifica-
tion may sometimes be of a phytopliagic character as a change of diet
in connection with the different environment of captivity proved
to be sufficient to cause albine growth upon shells previously almost
melanic in colouring. A number of half-grown shells of Helix
hovtensis var. oUmcea and Helix avbiistovuni var. fasccc were
gathered at York and conveyed to Bassenthwaite, in Cumberland, and
there fed to maturity in captivity upon the leaves of turnip and
cabbage, the new growth in both species was of quite an albine
character and the junction of the contrasting colours sharply defined ;
but Mr. T. Scott has recorded an almost exactly opposite experience,
a young Helix m'bustovum ysx. Jlavescens fed upon cabbages, turnips.

VARIATION IN COLOUR.

‘J2

etc., Ibvnied tlie new growtli of a much darker colour than before,
although it is possible that in this case the different result may be
due to the additional articles of diet not enumerated.

According to iM. INlalard and other observers concealment by
isochromatic adaption to environment is very common amongst
crustaceans and other organisms, and we apparently see a striking
e.xample of this interesting phenomenon in the albine .specimens of
Papa cijlind raced found by Capt. Farrer upon a whitewashed wall at
Bassenthwaite, the white variety being contined exclusively to the
whitewashed portion, the type form existing only upon that part of
the wall left in its natural condition ; as collateral evidence of the
probable accuracy of the supposition that we have here a case of this
i.sochromatic adaptation to environment, without, however, defining
the [)rocess by which this adaptation has been brought about, wdiether
by the elimination of the normal form or other method, I may recall
the record given by Semper, on the authority of Dr. Braun, that white
rabbits are most certainly and easily reared in a white reflected light.

It is now well-known and acknowdedged that albinism is hereditary
and may be transmitted to offspring. This is not only practically
established by experience of the shells under natural conditions, but
has been fre(piently demonstrated with mollusks kept in captivity.

The increase in numbers of the .specimens of a white variety, to
the di.sadvantage of the ty[)ical form dwelling w'ith it, points only to
the persistence of some features of the environment favourable to
the variation or, according to (Jredler, indicates that the species has
reached the extreme limit of its horizontal or vertical distribution.

There appears to be a somewhat general consensus of opinion,
especially amongst Continental conchologists, that albinism in the
shell occurs most freely amongst tho.se mollusks inhabiting cold,
misty and sunle.ss localities, and the unusual numbers chronicled by
them during dull and sunless seasons and from subalpine districts,
which have something of this character, supports the theory, as also
does the assertion of Herr Dietz that e.xamples of IJelu' hertemh of an
albino character are most commonly found in wet years, and that those
with banded shells in normal seasons, have the growth of a wet season
deficient of the usual pigment.

Diametrically opposed to the preceding theory is the suggestion
that dry, warm and sunny seasons are favourable to shells assuming
the albine state, and there is some reason from analogy in believing

VARIATION IN COLOUR.

93

that such conditions will assist in the elimination of colouring
matter, and tend towards the dull white and bandless forms especially
characteristic of arid and desert districts.

Leucochroism (XevKoi white and colour) has been defined as
that state wherein the darker shades of the ground colouring or the
markings thereon are diminished in intensity, in extent, or both
combined, owing to the diffusion of a paler shade of colour, or to the
darker markings assuming a paler tint than is usual in typical in-
dividuals. This state may he considered as more or less intermediate
between the ordinary typical condition and the albine form, and the
illustrations of this variation are very numerous amongst mollusks,
the bandless varieties or the pale or thin banded forms of Ileli.r
nemoralh and the dull white bandless varieties of Helix virgatd may
be quoted as familiar instances (see pi. ii., fig. 4). One of the
causes of this state has been assumed to be exposure to dryness and
warmth, circumstances which M. Strobel has shown to induce this
state in Helix virgatd, and the accuracy of this opinion is confinned
by the knowledge that such forms are the prevalent ones in desert
regions, their colouring reflecting the heat to which they arc exposed,
and therefore preventing the drying-up of the natural moisture of the
animal. Mr. Dali thinks this leucochroic condition may be due to a
less fluent secretion of the animal products, which are the chief
components of the glistening epidermis of shells native to moister
regions. This and other variations may however also arise as a con-
sei^uence of the protection afforded by resemlilance to their sur-
roundings, as may to a certain extent be the case with the variety
dlbescens of Cyclostomd elegdns found by Mr. Brockton Tondin, upon
the white chalk cliffs at Lulworth.

Melanochroism (geX-ii-v black and colour) is the opposite

tendency to leucochroism, as it expresses the increase of darker shades,
either of the ground tint or markings, at the expense of the lighter
shades of colour, and is a tendency towards true melanism, being the
intermediate stage between the typical individual and the specimen
with black ground colour or markings. The term Phteism (f/)atos
dusky), which applies to dusky specimens, is not so precise in its
application and may refer to a case of leucochroism or melanochroism
according as the affected individual is more darkly or lightly pig-
mented than the typical form, without distingtiishing the mode by

94

VARIATION IN COLOUR.

which the colouring has been arrived at. A modified form of Ilelir
virgatd var. rufiila, with tlio bands present as in the t)"pical form, is
an interesting illustration of this phase of colouring (see pi. ii., fig. 3).

IMelanism (/xo\ur, black) is the opposite condition to albinism, and
is a consequence of the excessive action or hypertrophy of the colour
glands diffusing the colouring matter of the bands or other markings
over the snrfiice of the shell, and when this diffused pigment is black,
or approximately black in colour, the phenomenon is termed melanism.
'SI iss F. i\I. Ilele has observed that certain foods have an inflnence
upon the colouring of growing Ile/I.r (ispersa, as those specimens fed
upon lettuce leaves always ac(piired a darker colour, or the colouring
matter became more overspread than was usually the case, and Mr.
Standen has also recorded that the sinistra! Helix afipersa which he
fed to maturity upon “dainty food” lost its mottleil markings and
became almost uniformly black. The coalition of the black bands in
Helix nemnr(iH!f, etc., is a well known and common example of this
phenomenon ; a still more striking illustration being furnished by
the Helix circjdfd var. nigvet^cens (see jil. ii., fig. 2), which has been
observed by i\Ir. Ashford to be a very local form in tbe Isle of Wight
and to live chiefly upon Cdrclniis tenuifulius, but Mr. II. B. Ilewetson,
of Leeds, has foumi some very characteristic specimens of this variet}"
upon the Ragwort (Sedecio j((enlurd), on the sand-hills at Kilnsea,
near Spnrn, Yorkshire.

Eryturism (epvHpiH, red) and Erythrochroism are the terms ex-
pressing the development of the red pigment (see pi. ii., figs. G, 7, 9),
and would seem to be a biological exi)ression of a warm climate or
season, as we meet with this red form in Helix iiemornlis and Helix
l/(irteiisis much more i)lentifully and more richly coloured in the
southern counties of England than in the northern parts of the
country. This erythrous condition or colouring as existing in the
shell of Helix hortensi^ has been considered by Herr Weiidand,
under certain circumstances, to be protective in character, as for
instance, when the animal resides amongst fallen beech leaves, and he
has therefore distinguished and named this form the variety
owing to finding the shells in snch situations. Xanthous variation
(j)l. ii., fig. 1 l)when not pure would seem to be very closely associated
or connected with erythrism, and is often developed during gvowth as
a modification of the red colouring existing in early life or rice re?'sd.

Plate H-

Fig. 1.

Fig. 2.

fig.. 5.

Fig 'P.

fig 5- Fi/g. 7. FUj. 73.

Principal Phases of Colouring in. MoUiisca.Ftgs 1-7 ami 11.

Typical, hg. 1 . Heltx virgota. Da Costa x 2, Lewes, collected, hy MIT.S. Hillman .

Melanism. Fig. 2. H.virgatav.nigrescen.s Crat.x 2,AftonDowrisJ.ofWight.collected by.Mrc.Ashfurd..
Melanoc hroism. H.virgatay. raMo-^ortaia Taylor x 2. laugharne. collected bv Mr G.W. Mellons.

Leucochroism Fig F. H.virgatay. albicans Gratx 2, Newquay, collected by M.rX/i. James.
Albinism. Fig 5. Hvlrgatn.v. nlba Taylor x 2.Lewes. collected by MT C.H.Morris.

Erythrism. Fig. 6. Arion alyr v. izifat Lj. Minden.Germany, collected by HMichardson .
Erythrochroism Fig. 7. Helix nenwmlis v. rubella Pirard. KnoUingley. coTlecbed by .J.Cordnkes.
Xanthism. Fig. 11. Hnemamlis v. libellula (Hissoj.WinsUr collected by Rev.H.Milnes.

Type s of Colourinc! in. Thermal Zbrurs. Figs 8-IZ.

Polychromatism i Fig 8. Lirpms virgineiis (LjWcstIndie.s\

(orTropical coloxirtjiQ^ ftg.9. ITelix pictd. Born,. Cuba ^FirE.Cotliers collection.

OligoCHROmatism I Fig. 10. Helix pisana MillLMendme. collected by MVR.D.DarbUhire.
lorTmpemie .■cionrinrjF Fin. 11. Hnemamlis y. libellula (Risso)WinsUr' collected by Rev.H.Milnes.
Monochromatism l Fig.12. Vitnnapellaciitnv.depressiusciila .JefTcx S.colLhy MrKD.Marquand

ror Boreal cotounnqj J Fig. 15. Ytritgo dlpestris Aider x 8. Cottingley. YorLs

Fig. 6.

Fig 11.

Fig. 12.

Fig. 9.

Fig. 10.

J W. Taylor^ del.

Taylor Bros, Lut. Leeds,

>lr>

VARIATION IN BANDING.

95

The yellow or xanthous variety, Uhellula, of Helix nemoralls is often
noticed to pi’esent a strong rosy tint upon the earlier or apical whorls,
and this peculiarity is occasionally found so distinctly marked that a
special varietal name has been used to indicate it.

The Helix picta figured (pi. ii., fig. 9) also shows the intimate
relationship existing between erythrous and xanthous colouring, as
both colours are blended together upon the penultimate and preceding-
whorls. Indeed the shell, like other organs of the body, undergoes
in some species great mutations, in colour, as well as in markings
and other characters in the progress of its growth to maturity.

The real colour of the shell is sometimes greatly modified to the
eye by the colour of the chitinous periostracum, which may vaiy
from the pure white of the albine form, through the delicate i)rimrose
tint of the xanthochroic varieties, as seen in Helix arhustorum and
Helix aspersa (see pi. i., fig. 1), to the deep dark brown, as found
in Helix aculeata and other species, and according to its depth of tint
and thickness obscures and modifies the colour of the calcareous
surfirce beneath ; thus some of the yellowish brown and other varieties
of Helix iiemoraUs, etc., when denuded of their epidermis are found to
be of a more or less intense and livid violet colour, but other
Univalve species may chiefly or entirely owe their colouring to the
chitinous covering of the shell.

The Banding, or coloured markings, in our British Univalves have
usually a spiral character, the corresponding markings in the Bivalves
being those radiating from the umbones to the free margins of the
shell, thus differing diametrically from the general direction of the
sculpture, which is usually transverse or coincident with the lines of
accretion. These varied markings are formed by the glands of the
mantle margin, and their continuous exercise during growth produces
a connected and necessarily spiral band in the Gastropoda, and the
radiate markings in the Pelecypoda, their intermittent action giving
rise to transverse markings, spots, or blotches according to the ex-
tent of the development of the colour glands and the greater or lesser
intervals taking place between the periods of their secretory activity.

Mr. W. II. Dali has remarked that the tendency to striped markings
wonld probably aid in the concealment of the shells amongst the lights
and shadows of the grass and herbage, leading one to attribute these
markings to similar causes to those that may have also led to the
development of the striped markings of the Tiger.

96

VARIATION IN BANDING.

Fig. 193 — //. ca/>cf'ata Mont..
Perth,

Collected by Mr. H. Coates,
Probably largely destroyed )iy
sheep o\ving to its indefinite and
protective colouring.

Fig. 101. — Ili'Ux cnpcratn
var. ornata Picard,

Afton Downs, Isle of Wight,
Collected by Mr. Chas, Ashford,
Probably avoided by the sheep,
the distinct markings enabling
the shells to be easily perceived.

Rev. S. Spencer Pearce, on tlie contrary, attributes tlie development
of distinct banding, in species sncb as Ilellx'
caperata, to the greater visibility of the
shells so marked to those with mottled or
indistinct markings, as he found that the
strongly banded variety ornata pre-
ponderated in the places fed over by sheep,
which he therefore assumed perceived and avoided the striped form,
whose markings would thns appear to be
of a warning or aposematic character, while
probably destroying many of the less con-
spicuous, indistinctly banded specimens.

In the hedge-rows and other places not
l)rowsed over by the .sheep, the ordinary
mottled form prevailed and the distinctly striped variety was com-
paratively rare.

Some species have normally a definite nnmber of bands, the gronp
Pimtataiua, to which Ih'Vt.r ni'moraViif, /nirtrnsls, poinxxfta, and axxprrsxx
belong is characterized by possessing five bands in the typical form,
which are very constant in position, tliree being always above the
periphery and two below it, but they are snl)ject to great modification,
owing to the absence of one or more of the bands and to their
coalescence in many and varied combinations.

Simroth from his study of .slug colouration was led to regard the
second and fourth bands of the Pexitataoxia as the primitive and
original pair— corre.sponding to the ancestral mantle-bands of theslngs,
which are closely connected with the lateral blood .sinuses— wbich,
by the concentration of their lugment, have ac(piired a lighter border on
each side, throwing np the third band between them, and each develop-
ing an additional one outwardl}", the first and the fifth. This view is
scarcely borne out by tlie acknowledged fact, that the third band in
Heli.v nemoralh, when present at all, is the band wdiich first appears
upon the infant shell, and therefore implies for it an eaidier origin
than for the remainder.

A convenient method or formula was devised many years ago by
Herr Georg von Martens to facilitate the tabulation and record of
the band variations in the Pentatanua, for which pnrpo.ses the
character of the banding .sbonld always be taken from the last
whorl of the shell, as the markings .so often vary in character during

VARIATION IN BANDING.

97

the progress of gi’owth, the banding being usually isolated and
distinctly separate in youth anrl tending to become transversely
combined at the margin of the aperture on approaching maturity. By
this method a distinctive or special number
is applied to each of the five bands found
in the typical form of Tleli.r vemnrali>t, or
other species of the Pentatmniate grouj),
according to the position it occupies ou the
shell, the uppermost or one nearest the
suture being the first, and the lowermost
or one nearest the umbilicus the fifth, the type form, which has always
five distinct bands, being expres.sed by the formula 12345 (see f 1 95).

If a band is suppressed or absent, this is shown by the use of a
cypher 0 instead of its number; thus the
formula 12045 would signify that the
first, second, fourth, and fifth bands
were present, and the cypher in its
appropriate position would indicate the
absence of the third band (see f 19G) ;
if, however, the whole of the five bands

are absent and the shell be therefore
practically unicolourous from showing
only the ground tint, then this phase of
variation is expressed by the use of
five cyphers 00000 iu lieu of the appro-
priate numbers (see fig. 197).

The coalescence or fusion of the band-
ing is indicated by enclosing in paren-
theses, or by some other method which
will clearly show the peculiarity, the
numbers representing those bauds which
are united together, thus the formula
(12)3(45) would signify that the first
and second bands were united, and also
the fourth and fifth, the third only being free or isolated (see f. 1!)S).

When, however, the whole five bands are [iresent and united
together, presenting the appearance of one excessively broad baud
occupying nearly the entire surface of the whorl, and therefore only

Fk;. 19S. — IIcUx iicuioralis L.,
formula (12) 3 (lo),
Piperstown, co. Louth,
Collected by Kliss S. Smith.

Fig. 197- — IfcUxncmoralis L.,
formula 0001)9,

Isle of Lismore, Argyll,
Collected by Mr. A. Somerville,
P.Sc., F.L.S.

Fig 19f>. — Helix 7ti'i)iorali^ L.
formula 12015,
lUtton, near Path,
Collected by Miss F. M. Helc.

Fig. 195. — Helix ^leitwralis L.
type formula 12345,
Litton, near Path,
Collected by Miss F. .I\I. Hele.

OS

VARIATION IN BANDING.

Fig. 100. — IIcU.x newornlh L.,
formula

Truro, Cornwall,

Collected by Mr. J. 11. James, A.R.I.C

Fig. 200. — Helix nemoralis F.,
formula 12'U‘jIo.

allowing- the groninl tint to he visible along the sntnre and in the

ninhilical region (see fig. 100), this is
shown by enclosing the whole of the
five figures within the parentheses,
the formula being (12345).

Supernumerary or e.xtra hands may
also apparently he developed, so that
a specimen may seem to have si.\,
seven, or more hands, hnt these additions to the normal five, are
invariably owing not to a real increase in their number, but to the
separation or splitting np of one or more
of those normally existent, and con-
sequently these extra or sujiernumerary
hands are always finer and thinner than
the normal undivided hand would have
been. 'I'liis splitting up or sub-division of the hands can be indicated
in the formula by the use of a smaller figure placed in such a position

as to represent the situation actually oc-
cupied relatively to the regular banding
by the slender split-off handlet : thus,
if the third hand he .split about equally,
it .should be indicated by r2'3.'545 (see
iiG. /AA.r 200), or if the split-off handlet is

much n.arrower than the remaining portion of the hand from which it
has been separated and is placed beneath it, the formida .should be
I2.‘5"45 (see fig. 201), but if the handlet
he ])lacod above the haml it is derived
from, the smaller figure, by the position
it occupies, ecpially servos to indicate its
])o.sition and character, the formula being
12 15 (see fig. 202).

In those cases where, from their equi-distant position, it is difficult
or impossible to decide with certainty
from which of the normal bands the extra
'A liandlets have been dei'ived or .split off,

so that the appropriate numerals cannot
he used to indicate their ])osition and

Fig. 20.T — //i*//> iiciiroraiis L., • • n • i • j i

formula i2;{xi.), OFigiii, theii a small x is used instead

of a nnmher in the pro])er position to indicate their presence, thus

Fig. 202. — Helix ncuioyalis L.,
formula 12-!315,

VARIATION IN BANDING.

99

Fig. 20F — I/dix nenioraiis L.
formula

Spurn Point, Yorkshire,

a specimen as the one fi^urerl (fig. 20.S), wliicli possesses a slender
bandlet eipiidistant between tlie tliinl and fourth hands, would be
clearly indicated by the formula 12.9x b'5.

Indistinct, irregularly developed or spotted bands are indicated by
a colon in place of the numeral — an in-
distinct third band, provided the remain-
ing four bands are normally developed,
would be shown by the formula 12:4.5;
whereas if all the bands are indefinite
or irregular, the peculiarity would be

11,1 P.1 p 1 Collected bv Mr. W. E. Clarke.

expressed by the use oi tlie lormula f.l.s.

as in fig. 204. Some authors, however, consider that any of the
normal bands when indistinct or rudimentary are more suitably
indicated by the use of the small numeral, which I recommend
.should be restricted to represent the split-ofi’ bandlets.

A .specimen of HeU.r hortensis from Folkestone, kindly given me by
Mrs. Fitzgerald, appears to have eight .slender but distinct bands, on
account of their colouring matter being mainly concentrated at the

edges of each band, leaving the centre of
each band very little, and in some portions
not at all darker than the general ground
colour, this separation of the margin of
the bands gradually becoming more dis-
tinctly marked as growth proceeds, and
furnishing a very instructive illustration as to how the multiplication
of bands may come about, this specimen would be indicated by the
formula ] 2 m (fig. 20,5).

This division of, or breaking up of the banding is a modification
which has been ascribed to the effects of aridity or dryness, either of
season or locality, and that this cause probably induces band disin-
tegration, is shown by the fact that Mr. W. E. Clarke collected for
me, at Whitsuntide, 1<S82, several thousands of Thdix nemmiUh from
the .sand-hills at Spurn Point, Yorkshire, a locality which, according
to the meteorological reports, is one of the driest spots in the kingdom,
and it is remarkable that not a dozen of the immense number
gathered e.xhibited evenly developed and strongly marked banding,
the bands when present were all more or less broken up and discon-
nected (see fig. 204) and this circumstance furnishes modified
evidence of the evolution of bandless species in desert districts; this

Fig. 205. — Helix kortetisis Mull.,
formula 12.4.'i4455,
Folkestone, Kent,
Collected by Mrs. Fitzgerald.

100

VARIATION IN BANDING.

Fio. 200. — Helix ncufornlis L. x l.V,
Church Kenton, Voiks.,
Collected by Mr. W. I). Roebuck,
Showin.s; the tendency of the
bnnding to become conlluent at the
aperture of the shell.

susceptibility to climatic or meteorological influences has been
termed Ilormomorpliism.

The characterof the baudingsometimes
changes very markedly during growth in
.some individuals. In the early whorls
the bands may be quite separate and
distinct, and afterwards become gradually
united together as the termination of
growth or maturity is approached; tliis
change arising from the cxce,ssive
development or hypertrophy of the colour glands of the mantle.

This transverse coalition of all the bands may also take place
towards the completion of each little stage of growth, each recom-
nicnceinent exhibiting a practical atrophy of the colour glands or at

least a temporary failure of their func-
tion, and also a. rapid resumption of
t V \ ^ , Xwlfc excessive secretive power, 'i'his rhythm-

ical alternation of the hypertrophy and
practical atrophy of tlie colour glands
of the mantle margin results in the form
of IlrU.r iK'mwviIls which has heen called
the variety iiudiildtn by Gentiluomo.

'I'lie more or le.ss comi)lcte permanent atrophy of the glands forming
the banding may, however, occasionally
take place at the termination of one of the
jjerioils of growth, before the maturity of the
"hell, the growth afterwards made being
wholly or ])artially deficient of the banding,
ilistinctly present on the lu’eceding whorls.

In other cases, on the contrary, the
secretory power of the glands may be
undevelopo<l or dormant duilng
growth, and gTadually, or more rarely
suddenly develop in full strength as
maturity and the period of fullest
vigour is approached.

'i'he llammular or flame-like markings arc tho.se which are some-
what irregularly shaped and may be considered to fre([uently
originate from a disintegration of the jn-imitive spiral or longitudinal

2()7. — Helix fietfioralis var.
unditlaia lleiuiluonio X 1\,

I’lagctlon, near Bristol,
Collected i)y Miss K. M. Hele,
Sliowint; the alternation in the
secretive power of the colour glands
funning the banding.

Kig. 20<S. — H . hortensis Mull.,
Krutigen, Switzerland,
Showing the abrupt cessation
of the normal banding.

A

Kk

2(H). — Helix pisana'^\'\\\\. x 1',.
Tenby, South Wales,

Collected by Mr. J. R. II. Masefielil, M.A.,
Showing the abrupt commencemetu of
distinct banding.

VARIATION IN BANDING.

101

Fig. 210. — H. asj>ersa vzcc. Jla7inuca Pic. X K-,
Scarborough, Yorks.,

Collected by IMr. J. Ray Hardy,
Showing disintegrated or flammular banding.

unmistakable traces of

banding, both in shells and slugs, and transvei'se markings may
have often arisen from the re-
aggregation of these spots in the
direction more or less perpendi-
cnlar to that in which they were
primitively present, but it is not
unlikely that irregularly spotted
band-like markings indicate ir-
regularity of action, such as may
be looked for at the origin of
such glands, and thus occasionally represent nascent banding and not
invariably originate from primitively distinct and continuous markings.

Helix caiiti(um, Helix cartusinna, Helix rufescens, and a few other
specie.s, although normally uniformly coloured, occasionally exhibit

banding, which some assert are na.scent,
but are more probably the vestigial re-
mains of bands formerly existent; and
we are thus led to speculate upon the
probability of these species being at
one time distinctly banded forms, and
descended from primitively banded an-
cestors, without, however, implying that
the molluscan shell, as originally developed, was not unicolorous.
The evidences of this banding are rendered easily recognizable by the
pale peripheral zone, which is, according to my interpretation, the
intervening area between the upper and lower groups of bands.

The whitish transverse linear markings, which form the characteristic
feature of Limnwa jHilustris var. zebra,
are, I am inclined to believe, the result
of a certain amount of disintegration of
the shell substance, which apparently
takes place at somewhat regular inter-
vals, owing probably to some periodically
recurring deficiency in the secretion of
the protective epidermis. Analogous
markings from similar causes are some-
times noticed upon Bythinia tentaculata
and other species, but this feature is apparently more particularly a
characteristic of the Limnophysa inhabiting North America.

Fig. 211. — Helix cantiana var.
albocincta Ckll.,

Lund, near Osgodby, Yorks.,
Collected by Mr. Wm. Nelson,
Showing supposed atavistic evi-
dence of spiral banding.

Fig. 212. — Litiincea palust) is var.
zebra Tryon X 2,

“Swale,” Oakland Co., Mich., U.S.A.,
Collected by hlr. Bryant Walker,
Showing regular transver.se linear
markings, perhaps due to disintegra-
tion of shell substance or defective
periostraca.

102

VARIATION IN BANDING.

Fig. 213. — Limna-a pcrcgra (Mull.)
X U>

Scout Dam, Pcnlstone, Yorks.,
Collected by Mr. L. K. Adams, 1>. A.,
Showing the spiral linear mark-
ings, probably due to injury to
mantle-margin.

The Spiral White Lines so often noticed, especially in our fresh-
water shells, are not usnally what may be termed true colour bands,
as those of typical Lunnaa 2wre(jra var. are said to be, but are
probably the result of some injury to the
glandular mantle-margin, which inter-
feres with the secretion and deposition
of the usual epidermic covering to the
outer surface of the whorls, thus render-
ing the calcareous strata of the shell
more vividly perceptible. Mr. L. E.

Adams has freipiently noticed this pecu-
liarity amongst the Lhuntva jwrerjra
inhabiting Scout Lam, near Penistone, Yorkshire, where trout are
very numerous, and I consider these markings are })robably caused

indirectly by the fish, which have
injured or lacerated the mantle
with their teeth when attempting
to seize and feed upon the animal.
More severe injuries of this cha-
racter, from the same or other
causes, would probably result in
the entire thickness of the shell
substance being more or less
aflected, and in e.xtreme ea.ses the outer margin of the shell, where
the new growth takes place, might even become cleft.

In the Pelecypoda the same peculiarities are occasionally observable,
the radiating dull white linear markings, when present, corresponding
to the linear spiral markings of the Lunna klw, etc., and arc very
proliably attributal)le in origin to analogous causes.

.More severe injuries to the mantle, would, as in the Univalves,
result in the com]ilete severance of the substance of the valve, but
this severance is seldom so strikingly shown as in the specimen of
A iKiiloidft cinjiti 'i ligured, which has the left valve cleft almost to the
umbo, owing to the severe injury the corresponding mantle has sus-
tained in early life, but the right valve shows only a very marked
constriction to indicate the e.xtent of the injury done.

'I'hese malformed shells should more pro2)erly have been treated
upon in the succeeding cliaiher, but the desire to indicate the jn’o-
Ijable connection of such forms with those distinguished by the

Fig>. 211 21.5. — Lint/Ufa atirUtilaria L.),
J>avos I.akc, Swit/criaml,

CoIlccl^:tl by C'apt. W'. II. 'ruiTon, K.lh.,
Showing cleft ''licll >ubslancc probably tluc
to severe laceration of niaiule-maigin.

MONSTROSITIES.

103

development of spiral or radiate dull white lines, make it desirable
that these peculiarities should be treated of under this head.

Fig. 216. — Anodonta cygnca (L. ),

Sandwill Park, Staffordshire, collected by Mr. J. Madison,

Showing the effects of some severe laceration of the mantle, the result of which is seen in the
strongly separated parts of the left valve and in the deeply-furrowed right valve.

Monstrosities.

Monstrosities are generally considered to he those individuals
whose differences arise from pathological causes ; the name is like-
wise very aiipropriately applied to those malformations which may
be congenital and transmissible from one generation to another, as is
sometimes the case with the reversed monstrosities, although
M. Sanier, who endeavoured to perpetuate the reversed form of Ileliv
aspersa by accumulating several adult specimens and breeding from
them, found the few resultant progeny all dextral, and this experience
has been confirmed by others. The term monstrosity also indicates
specimens which have become deformed during growth, owing to some
intrinsic or extrinsic irritation or disturbance, perhaps causing

lot

MONSTROSITIES.

irregularity in tlie secretive power of the animal, and the correlation
which douhtless inseparaldy exists lietween the form and character of
the shell and the organs of the Ixjdy renders it very probable that
abnormality generally, indicates or is associated with, such functional
disturbances or ilifferences as are detrimental to the creature and
tend to its more easy destruction by its enemies, or by any unfavour-
able couditious to which it may be exposed. The researches of Mr.
K. ]'l. Call upon the relative abundance or rarity of the sinistral
monstrosity of Mi-Idiitho in the embryonal and the adult stages are
very signiticant, and show that the mortality amongst the sinistral
specimens is strikingly greater than amongst those normally coiled,
and would appear to corroborate the i)resuuied general physiological
weakue.ss of abnormal specimens. It is, however, sometimes difficult
to di.scrimiuate between a true variation and a monstrosity, but
malformations or monstrous growths seldom occur in the embryonal
stages, and an exaniination of the nucleus of the shell, whether
ruivalve or Ihvalve, generally offers a clue to distinguish these
accidentally malformed shells, as they frequently only develop the
abnormality after the commencement of a free life — in fact, monstrosi-
ties generally may be considered to l)e the more extreme examples of
accidental variation, and their study is n.sefnl as tending to elucidate
the range of specitic variability.

rnhealthy or unnatural conditions of life would appear to dis-
orgaiii/.e the animal functions, with the elfect that the resultant
growth is often irregular or abnormal in appearance and character.
A stream of water pumped I'rom a colliery at Leventhorpe Pastures,

I- H,. :;i7. Kk,. 2t,S. 21!), iMG. 220.

P/(inoH>is tayinalus Mull, (enlarged),

I’il stream. Leveiultorpe I’asUircs, Leeds, culleetcd by Mr. Jas. Heevers,

1 Jor.sal atid bide views <jf two individuals sliowinji the grotcsiiiie and irregular coiling assumed
to be the elleel of abnormal eondilions.

near Leeds, yielded a very large number of curiously twisted shells
of !*!(( nurhis fdr/idtfti.'t, of which a large proportion were sinistrally
coiled, and all of which were thickly encrusted with a dense black
carljonaceous deposit. So universally i)revalent were these remarkable
shells in this stream, that at one time it was a rarity to obtain a
normally coiled .specimen.

3I0NSTR0S1TIES.

105

f

A

Figs. 221, 1^1.— Linnuea stagnalis

Salt Marshes, Sea of Aral,

Collected by Mr. W. Bateson, M.A.,

Showing the result of living in periodically saline or
brackish waters.

Ill the saline marshes in the vicinity of the Sea of Aral, which
are, how'ever, for a cousiderahle period of each
year comparatively fresh, Mr. W. Bateson, M.A.,
found specimens of
Liinnau stagnalis, L.
aiiricnlaria, and L'lmnwa
peregra, some of which
appear to have undergone
a certain degree of modi-
fication, doubtless owing
to the exceptional cha-
racter of the environment;
through the kindness of
the Rev. A. II. Cooke,
M.A., I am enabled to
give several illustrations
of Limnwa stagnaUs and
Limnwa auriculnria, which will serve to illustrate the change in
form and character the peculiar features of the region has induced.
It is interesting to notice the comparatively slight effect the abnormal
conditions have produced in the Limnwa stagnalis, which are fine
and well-grown shells ; the unusual environment is, however, much
more strongly indicated by the Limnwa auricularia, which are
dwarfed and curiously mal-
formed towards the aperture,
thus confirming the results
of Beudant’s experiments,

Avhich showed Limnwa auri-
cularia to be more sensitive
than Limnwa stagnaUs to
the influence of saline w’ater.

Univalves generally, often become ribbed, keeled, or otherwise more
or less irregularly modified by the influence of an influx of brackish
or saline water. In the Miocene Tertiaries of Asia Minor, Prof.
Forbes found whole races of Neritina, Vivijiara, and Melanojisis
with the whorls ribbed or keeled, as if through the unhealthy
influence of an influx of this character.

The refuse of a chemical factory was prior to 1887 turned into the
lake in Drinkwater Park, near Prestwick, and the effects of this

Figs. 223, 224, 225. — Limnwa atiricularia (L.),
Salt Marshes, Sea of Aral,

Collected by Mr. W. Bateson, M.A.,

Showing the result of living in periodically saline or
brackish waters.

10()

MONSTROSITIES.

pollution of the water was lellected in the Limitud staijiuilis fonml
there, which exhibited somewhat swollen transverse growths near
the mature aperture and the growth lines
were altogether ruder and stronger in
character than in ordinary shells. The
^ following year, when the pollution of the

f ! water by this chemical refuse was stopi)ed,

‘ the succeeding generation of shells (puckly

indicated and reflected the greater purity
of the water by a reversion to the
regular outline and smooth even suri'ace
of mnanal shells.

Species usually inhabiting tran([uil or
gently ilowing waters tend to become de-
formed and dwarfed if subjected to the
inlluence of strong currents; this is strikingly exemidified in Uuio
finnidas found in the river Foss, near
York ; the si)ecimcns found close by
the overllow or bye-wash of the
Yearsley Locks, within the inlluence
of the current, being greatly dwarfed
and malformeil in their growth, differ-
ing very markedly from the sym-
metrically formed and fairly-sized
shells fre(inenting the sluggishly flowing river a short distance away;
'Ui h agitated waters are also usually correlated with an increase in

Kig. — L. sta^i^naiis (I..).

Lake, I )rink\valcr l*ark, near
I’rcsiwicli, Lancaslure,

Collected by Mr. W. fl. Heath-
cote, K.L.S.,

Showinjx by irregular growth
tlie baneLil innueucc of the
chemical refuse formerly cli^-
charged into the lake.

Fk.. 227. — L^nio iu/Kidus Phil.,
Yearsley T.ock, near York,
Cullecled by Rev. \V. C. Hey, M.A.,
Showing the dwarfing and distortion of
the siieil owing to proximity to the dam.

Kig. 228. — Cnio iiouidus Phil.,

Near \'car>Iey Lock, River Ko.ss, ^'ork, collected by Rev. \V. C. Hey, I\L.\.,

.Showing the ordinary form as found a Hiorl di.slance from the dam, in gently Ilowing waters.

the strength and devehipment of the hinge-teeth or denticles, which
are liable to become feeble and degenerate in ([uiet and unruflled
waters.

MONSTROSITIES

107

Figs. 229. 230, 231.— 2^. pengra (Mull.)xll,
A pool, near Geneva,

Collected by Dr. A. Brot,

Showing the deformation of the columella
and the base of shell, assumed to be caused
by Hydra viridis.

Dr. A. Brot has shown how some of the lowliest organisms may

influence even the form of the shell
in the mollusca, as he records that
during one season nine-tenths of
the specimens of Limncva peregra
living in a pool near Geneva, were
curiously malformed at the base of
the columella and anterior part of
the shell generally; this malforma-
tion, which was correlated with a certain dwarfing of the shell, was
concurrent with an extraordinary abun- ^

dance of Hydra viridis in the same pond.

The following year the Hydra had dis-
appeared, and this disappearance of the
Hydra was coincident with the disappear-
ance of the peculiarity in the shell, of
which the Hydra was apparently the ^ rTeiela,''^ ^

. 1 -j. Collecied by Dr. A. Brot,

plllUcliy CtlUSC, fliS tilG SnCCGGulll^ ^GllGlcl- Showing the normal form as found
, • !• r • *x 1 the pool with the malformed in-

tions of tlie Lunnoja were ij^uite normal, dividuais.

Herr Julius Hazay has also observed and recorded that the

“invasion” of the shell by the leech
may greatly influence the character of
the growth in Liiimau stagnalis, by
causing the animal to gibbously inflate
the outer margin of the aperture of
its shell on attaining maturity.

Dreissensia pulymorpha, like other
attached shells, is liable to malforma-
tion, owing to interferences during
growth, conseiiuent upon their situa-
tion in crevices and from contact with
hard substances. This species also
often causes distorted and irregular growth in Anodonta and other

Fig. 'I'Si. — Liinna'a stagnalis (L.),
Buda-Pesth,

(after Herr J, Ha^ay),

Showing the inflected lip, said to be
owing to the “invasion” of a leech.

their

valves together

with its

freshwater bivalves, by fastening
byssus.

It has been stated by Prof. Alplueus Hyatt that distortions of
Univalve freshwater shells have usually occurred in still, enclosed
waters with no outlet, and, although this is generally, it is far from
being universally true.

108

MONSTROlSITIEy— i^INISTRORSITY, ETC.

Tlie SiNiSTRORSiTY and Dextrorsity of the inolluscaii shell is a
very intricate and perplexing subject, which in some genera has given
rise to considerable discussion. The great majority of Gastropoda
have undoubtedly dextral shells, that is with the whorls turning spirally
from left to right, with the heart on the left side of the animal, and
the external apertures of the various oi’gans on the right. The
sinistra! or left-handed coiling is thus the exception or monstro-
sity, althongh some species and even genera are normally sinistral,
and possess an opposite arrangement of their internal organs to
dextral species, and the dextrally coiled shell becomes the exception
or monstrosity. Reversed monstrosities likewise conform to this
disposition of the vi.scera, a dextral monstrosity of a normally sinistral
■shell having its organs and orilices disposed as in those mollusks
which are normally dextral. This reversal of the direction of the
coiling, though liable to occur in all spiral shells, is of much greater
rarity in some species than in others — for, of Iltdiv nttniiJuta, our
commonest species of lldlv, only one recent sinistral specimen is
known, which was found by Rev. II. W. Lett, at Loughbrickland, in the
north of Ireland, and through his kindness is now in my collection.

All mollu.sks w’ith spiral shells are liable to this reversal in the
direction of their convolution, and bivalves and even slugs are affected
in an analogous way. In bivalves tlie right or left valves, as the case
may be, ac(piire the characters which normally distingui.sh the other,
but this reversal when it does occur is not very noticeable except
perhai)s in .some of the ineipiivalve .species. In the naked genera, the
occurrence of this state is outwardly shown by the transference of the
respiratory and other orifices to the side opposite to that on which
they are normally placed.

Locality would ajipear to have .some inllnence in inducing the
reversed coiling of shells, some hjcalities being well-known h^r the
regnlar recurrence of these monstrosities, while in other districts they
are scarcely known to occur. Cailliaud records the neighbourhocal of
Rochelle as noted for the fre(iuent occurrence of sinistral //c//.c«.sy^e/vs'((,
and l)r. Gwyn .leffreys states that he himself saw a colony of that
monstrosity in the garden of M. d’Orbigny in that city.

A sinistral race of llell.r /(cwo/'n/hs, almost analogous to that formerly
existent of Fiisns aiitiqiiiis, would appear to have at one time lived in
county Donegal, as the very numerous subfossil .shells picked out of
the immense sand-hills about Rundoran abundantly testify.

MONSTROSITIES — SINISTRORSITY, ETC. 109

The causes of this reversal of the normal arrangement are however
not at all known or understood. M. Bourguignat has hazarded the
suggestion that it may be caused by electrical conditions, the electric
current flowing in the opposite direction to the embryonal rotation,
the essential conditions being a metalliferous soil, moist weather to
influence the latent electricity of the metallic substances, and the
conjunction of the atmospheric and terrestrial electricity, as by
thunder at the period of the first manifestation of vitality l)y the
embryo. Prof Cams also considers that the direction of the coiling
of the shell and animal may possibly be determined by the direction
of the embryonal rotation.

Mr. 11. Ellsworth Call attributes sinistrorsity in Mehintho to the
crowding of the embryos in the oviduct in the early stages of their
existence ; his observations on that genus lead to the inference that
sinistral specimens are more delicately constituted than their
normally coiled brethren, as he found that sinistral exami)les con-
stituted li- per cent, of the total number of the embryos in the
oviduct of Mehmtho integra ; and 2h per cent, in Mehintho decha,
while judging from the numbers gathered in the adult stage, he
found only one-tenth per cent, survived.

In Limnwa Mr. II. E. Crampton, jun., has recorded that the ilirec-
tion of the cleavage during segmentation of the ovum, is of the
typically spii’al type, but in Physri the direction of this cleavage is
totally reversed. Dextrorsity and sinistrorsity are however (pialitios
inherent to the organization of the animal, and the particular arrange-
ment is usually correctly indicated by the position of the heart and the
external orifices of the reproductive and other organs of the bod^o

All embryonal Castropods are
primitively what are termed
Exogastric, and oidy become
Endogastric owing to the tor-
sion of 180° which is under-
gone by the visceral ,sac, which
twisting transfers the anus and
other organic orifices from the
rear to the anterif)r j)art of the
animal ; the incii)lent spire at
first enrolled towards the front or dorsally with reference to the
later whorls, becoming coiled towards the rear. According to Prof.

Fig. 234. Fig. 13,5.

Exogastric coiling. Endogastric coiling.

Diagrams showing the process hy which an
Exogastric mollusk becomes Endogastric by the
torsion of the visceral sac through an arc of 180 ,
a process determining the sinistrorsity or dextror-
sity of the shell (after Pelseneer). a. anus.

(The figures, for the sake of clearness and in-
telligibility, are drawn to represent a much later
stage of embryonal development than that at
which the torsion actually occurs.)

110

MONSTROSITIES — SINISTRORSITY, ETC.

Polseneor tliero arc no ;nlnlt (nistropod.^ winch are coiled oxoo-astri-
cally, hnt ainonii.^t the Cejdialopods the i\d<?/t(’7»sfnrni.shes an example
of this iirimitive arrangement. The original sinistrorsity or dextrorsity
of the coiling is determined by the method in which this torsion is
etfected : if twisted to the right the shell or coiling is dextral, if to the
left, sinistral, hnt the direction of the torsion is naturally correlated
with the arrangement nr disjiosition of the vital organs of the body.

If we are correct in ap])lying the same terms to the Pelecypoda,
and considering as the same jdienomenon the slight tendency to
coiling exhibited by onr freshwater Bivalves and more nnmistahably
by some marine forms as fm-urdia, etc., then we may regard all onr
British species as Ihxogasti'ic nr IhiosoOYR.XTE forms, as the apices of
their valves are directed anteriorly. None of onr freshwater species,
and oidy a limited number of marine forms, as Tr'Kjmhi, etc.,

are really Bmlogastric or OinsTiioc.vR.VTE, that is with the nmhones
directed towards the i)osterior margin of the shell.

liev. Leonard .Tenyns in his monumental and classical work, “A
Monograph on the Biitish 8])ecies of LV/c/a.s and has nn-

fortiinately erroneously hgnred all the Pi^idid therein as Oiastho-
gyrate or Lmlogastric, with the ajiices of the valves directed towards
the shorter or jiosterior margin, instead of to the longer or anterior
one, as they undoubtedly are ; this difference can he strikingly seen

Kig. 2‘M>. — I^isitiium hoislaivanuiii (Shepp.), F tr,. 21^7. — Pisidiupi henslo^vnnum (Shepp.),

adult, posterior end, X 12, yoiins, magnified (after Jenyns),

Poiul, Cockerton, Darlington, Showing, lliougli erroneously, an exogastric

Collected hy Mr. Charles Oldham, or o|)islh<\gyrate direction of the nmhones.

Showing the endogaslric or prosogyrate
direction of the um)>ones.

Iiy reference to, and comparison of my figure of Phidl urn hrnnhunmum
(tig. 2.‘h)), with tig. 2;)7, whicb is faithfully rc'produced from a. figure
in Mr. .Tenyns’ Monogra])b.

IIveERSTiiopiiv above; (rTp'x/jiy, turn). — Althongh sinistrally

or dextrally coiled shells arc usually iuhabited by animals sinistrally
or dextrally organized, as the case may he, yet exceptions are
known in which a sinistrally organized animal is the tenant of an
a])parently dextrally coiled .shell, and c/Vr ecr.s-d ; this curious feature
which is exhibited by the genus Phinorhlf:, has always been a fruitful
.source of di.scn.ssiou amongst conchologists, .some contending that

MONSTROSITIES — HYPERSTROPHY.

Ill

Planorhis is a dextral shell, others affirming it to be sinistral,
whilst a few, including the celebrated Lamarck and Deshayes, were
disposed to view the genus as amphidromic, some species in their
opinion being dextral and others sinistral in character. The
apparent anomaly is, however, ingeniously and satisfactorily ex^jlained
by the hypothesis of hyperstrophy, which makes clear the origin
and derivation of these puzzling shells, which are in ajipai’ent dis-
agreement with their in-
mates and architects, d'he
hyperstrophic theory may
be explained by imagining
a homocostrophic or orthos-
tro2)hic shell as Phi/iid,
which is .sinistrally coiled
and is inhabited by a siuis-
trally organized animal, to
have its s[)ire gradually
shortened until the shell
becomes discoid, owing to
the spire siidving to the
level of the body whorl, as
in Plannrhis, and if the process be farther continued the sjiire pro-
trudes at the opposite side, as in the genera Pompholy.r, Cdrlnifi'.r,
etc., all of which are sinistrally organized animals, but by the change
described now inhabit apparently dextral shells.

The terms Inversion or Hyperstrophy serve to indicate this change
by which the part originally forming the base of the shell in its normal
or primitive position becomes the nipper or spire fiice and vice rersd,
this process also apparently reversing the direction of the coiling of
the shell, although this reversal is arrived at in a totally different way
and does not affect the disposition of the organs of the animal, as
does a simple reversal of the coihng, which always involves the trans-
position of the various organs of the body, those organs normally
])laced on the right side of the animal being transferred to the left
side, and vice versa. Sinistrorsity or dextrorsity by inversion or
hyi)erstrophy is therefore essentially different from sinistrorsity or
dextrorsity arising from a .sim])le reversal in the direction of the
convolution of the shell. In the former case, although the mode of
coiling has been modified, the animal retains the usual arrangement

Fig. 238.

An orthostrophic sinistral
shell, as P/iysn, showing the
heart at base of whorl.

Fig. 239.

Intermediate, subdiscoidal,
sinistral form.

Fig. 240.

Discoid form, as Planoj'his.

Fig. 241.

Intermediate, subdiscoidal,
pseiido-dextral form.

Fig. 242.

A hyperstrophic pseudo-
dextral shell, as Povipholyx.
The heart is now seen to be
at spire side of body whorl.

Diagrammatic figures showing in a conventional and
simple way the change from an orthostrophic sinistral
shell to a hyperstrophic pseudo-dextral oiie.

112

MONSTROSITIES — nyPERSTROPHY.

(if its viscera, lint tlie basal part of flic sliell liecomes li}" transposition
of liy})erstroplnc orowtli the upper or spire face ; in tlie latter case,
it is tlie or^-ans of the animal that lieconie actually transposed in
jiosition, those niion the ri,nht side become idaced on the left, and
I'la- wrsd, but tlie shell is simply reversed in its direction of convolu-
tion, the basal and upper iiices of the shell retaining their positions
as in the normal individuals, and are not transposed as in hyjier-
strojihic specimens.

'I'lieoretically, there may thus be tour dittereut jdiases in the coiling
of Planorboid shells. Viewing the shell of Phiunrltis as being now
dextral, they may be simply sinistra! or simply de.xtral, or siinstral
or dextral by atavism, altbougli only three of these phases are actually
known, the simply dextral and simjily siinstral forms, and the
atavistically siuistral.

I )iaccrnmmaiic li)iurc'; showing the probably’ actual motlc by’ wliich the change from a sinislral
orihostrophic slicll to a hyperstrophic and psemlo-tlextral one lias taken place. The lieart is seen
to apjiarcnily move from the base to the upper part of the whorl.

In the series of figures preceding, 1 have endeavoured to dejiict
diugrammatically the gradual and actual mode by which the jiseudo-
de.xlral tor ultra-sinistral, as they are sometimes though less happily
t('rmed) shells of Pomphnlyx, PhinorhiK, etc., have jirobably arisen.
'I'be tig. 248 is assumed to represent an elongated Plnjtfa carrying
its shell with the apex directed to the rear as is normal ; the actual
and jiarticular mode of carrying the shell by the different sjiecies, is
doubtless always determined by the mechanical laws governing its
easiest portability in the medium in which they live. Fig. 244 is an
intermediate or trausitioiial form, which buds its original among some
of the foreign genera. Figs. 24;) — 247 may all be regarded as more
or less faithfully re}ireseutiug conit'/is, as the sjiire is still

slightly exserted on the. left side, and the shell carried nearly upright
as is usual. Figs. 24S and 24!), which show hyperstrophic develop-
ment a little further ailvanced, also demonstrate how uiion any
relaxation of muscular effort by the animal the shell falls naturally
into a more or less horizontal and truly dextral position. Figs. 2;)()
and 2;jl show the process advanced a stage further as in Plauorhis

MONSTROSITIES — HYPERSTROPHY.

113

contortii!^, the spire now showing on tlie riglit side, and leading to
Pomphnly.r (fig. 2n2), wliich represents one of the extreme psendo-
dextral or nltra-sinistral forms. In the series of figures illustrating
these marvellous changes, the heart can be seen in the orthostro-
phically sinistral Plnfsa to he towards the base of the whorl, and it is
instructive to note the change in its position in refei’ence to the shells
l)eing placed towards the upper or spire face of the whorl in the
hyperstrophic individual, ami this without any change in its position
amongst the viscera of the animal. The orifices of the reproductive
and other organs in all these forms continue upon the left side.

The shell of Pldiwrbis having become ])ractically dextral, or as it
may perhaps be more con-ectly termed pseudo-dextral, as indicating
its hjqjerstrophic origin from a shell primitivel)' sinistral, has naturally
assumed some of the modifications especi-
ally di.stinguishing the truly ph5dogenetically
dextral shells, the right or primitively basal
side of the aperture having by the inver-
sion of the shell become the upper side, has
ac([uired the characters suitable to its new
position and become more advanced in
growth, as the upper side usually is (see
page 2"), fig. 31). Fischer and Bou\'ier, who
assert that the anterior or basal part of
the aperture in Limiura and P/ii/m is the most advanced in growth
are incorrect in this and in the deductions
they derive therefrom.

The interesting specimen of Planorhis
s^pirorhis figured, is sinistrally coiled and
the elevated or snbdorsal position of the
keel testifies that if the normal shell be
considered as dextral or pseudo-dextral in
accordance with its position upon the animal,
we have here an actual instance of atavic
reversion to the original direction of con-
volution ; in fact, a reversal of the process
by which the pseudo-dextral shell of Planm'bis has beeu arrived at.
The rarity of what I venture to term the atavistically sinistral form
and the comparative frequency of the dextrally spiral monstrosity

F IG. 254. — Planorhis spirorlns
monst. priscuiu Taylor X 8,
Clay pond, Gorton, Manchester,
Collected by Mr. J. Ray Hardy,
Showing atavistic reversion to
the primitive sinistral direction
of coiling, the keel indicating
the sinistral organization of the
animal.

F IG. 253. — Planorhis war-
ginatus m. cochlea Krown X 3,
Risegate Eau, Gosherton,
Collected by Mr. H. Wallis
Kew, F.Z.S.,

Showing the pseudo-dextral
shell, with the keel sub-basal,
indicating a sinistral organiza-
tion of the animal.

114

MONSTROSITIES — ORGANIZATION OF.

would appear prima facie to clearly establish this latter direction as
having now become the normal one for the coiling of the shell.

The specimen of Plancrrhis carinafiis from Leventhorpe Pastures,
Leeds, is an e.xample of sinistrorsity arising from a simple reversal of
the now normal method of convolution, and nob from an atavistic
reversion to the primitive type, as in the Planorhis ftpirorhis (f. 254);
this is clearly attested by the position
of the keel, which is distinctly suh-basal
as in the pseudo-de.xtral typical form,
and shows that the animal forming it,
was dextrall}’ organized, as the keel
always corrosi)onds with and indicates the
side of the anus and other organic orifices.

'I'lie nervous S3'stem oft’ei’s confirmatory evidence of the sinistra!
character of the organization of the animal of Planorh/!^, l)j' the com-
]>arativel3' enormous development of the left visceral ganglion, which
disparit3’ in size, in comi)arisnn to the corresi)onding ganglion of the
right .side, is mainly owing to its innervating the special .sense organ —

Fkl 255. — Planoi'his carinatus
monst. sintstrorsuDi Taylor x li,
Leventhorpe Pastures, Leeds,
Showing a simple sinistral reversal
of the now normal pseiido-tlextral
coiling, tlie position of the keel in-
dicating the inmate to be de.xtrally
organized.

Kk;. — Nerve ring of a half-grown
Pltinorhis comeus (L.), with cerebral com-
missure cut and the cerebral ganglia thrown
back, showing the sinistral organi/ation of
l)>e animal by the comparatively verj* much
greater development of the left \ isccral gang-
lion (see also p. 7, lig. *5).

Fig. 257. — Nerve ring of Limncrn percf^rn
(Midi.), sltowing the dextral character of the
animal by the relatively greater development
of the right visceral ganglion (see also p. 7, f. ii).

tbo nsphradiiim — which is situate near the re.sjtiratory erifice on the
left side, but this organ is jilaced dextrally in the Liiniurlnw iu
(•(iiTolation with the opjai.site arrangement of the organs of the animal.

'I'lie character of tlie organization is further indicated by the
position of the heart, and the situation of the reproductive and other
orifices, the latter being always upon tbc right side of the body iu a
dextral animal ami upon the left side of a sinistral one. The heart,
wbicb is i)laced towards the periphery of the whorl in both dextral
ami sinistral shells, is on the contrary normally situate on the left
side of a dextral animal, ami on the right side of a sinistral one, but

MONSTROSITIES — HETEROSTROPHY.

115

does not invariably correctly indicate the organization, as it is always
in proximity to and in close association with the respiratory organs,
changing its position in correlation with the modifications which the
breathing organs are so liable to undergo. In Ancylus, which is a
hyperstrophic species, the respiratory cavity has been lost, and the
function of respiration assumed by the left margin of the mantle and
by a secondary pseudo-branchial appendage, which has been developed
on the same side, the heart having moved in correlation with this
development from its normally dextral position towards the left side,
so as to retain its proximity to the functional aerating organs, 'fhe
embryo of Planorhis corneiis has a spirally sinistral shell, with the
heart on the right side of the body, thus indicating a sinistral organiza-
tion of the animal, hut as growth proceeds the heart gradually moves
dorsally and nearer the left side, probably in correlation with the
development of an auxiliary hranchia upon the left side, and the shell
gradually becoming a discoidal and practically dextral species, and
therefore heterostrophic in character.

/

Figs. 258, 259. — Portion of spire of
Tiirhonilla y'ufa Phil., showing how the
change from hyperstrophically sinistral
to orthostrophicaily dextral coiling takes
place (after Fischer).

IlETEROSTROPnic (eVcpos, other [than usual way] ; a-rpocfn'i^ a turn)
shells are those which do not continue their growth in the same direc-
tion as they begun, Init at a certain
period of their existence gradually,
hut (piickly, change that direction, so
that a sinistrally organized species may
commence life as an orthostrophicaily
sinistral shell, and end as a hyper-
strophically dextral one ; or, on the
contrary, maybe at first hyperstrophic,
that is, a sinistrally organized animal
may have a dextrally coiled shell, which afterwards becomes sinistrally
convoluted or orthostrophic and in accord with the organization of
the mollusk, and vice versa ; yet the
enrolment of all these forms always
belongs to the same spiral, which
may, as pointed out, he at first nega-
tive and afterwards become positive,
or the reverse, the differently coiled
embiyonic portion being often left as though affixed to the side of the
apex of the spire. In addition to the Planorbes, we have an example
of these heterogyi-ate forms, as such shells are also called, in A ncylus

Fig. 2()0. — Apex of shell of Ancylus
yjuviatilis (Miill.), showing the onho-
sirophically sinistral coiling of early life,
which later becomes hyperstrophically
dextral in character (after Bourguignat).

Ilf)

MONSTROSITIES — SCALARIFORMITY.

wliich, according to M. Bonrgnignat, is in its early stages
sinistrally coiled, and only later tends to become a dextral shell, being
apparently somewhat analogons in this respect with Anastoma,
thongh coiled in the opi)osite direction.

A sinistral shell can he readily recognized by holding the shell with
the aperture towards the observer and its apex iiointed upwards, when,
it dextral, the ai)ertnre will he on the observer’s right, and, if sinistral,
on his left: hnt this simple and easy test does not enable ns to
detect or recognize those shells which have been subjected to hyper-
stro])hic develojnnent.

ScAE.AUiFORMiTY (.sYY^ a tlight of stah's ; and/w;;?^^, form) of the
shell is the separation or dislocation of the whorls and is a phenomenon
to which all s])irally coiled shells are liable, possibly owing to some
internal pecnliarity of, or injury to, the organization of the animal, or,

at least in some cases, to the adherence
of extraneous matter to the immature
shell or other cause interfering with
the close apposition of one whorl with
another, and in correlation with the
amonnt of ohstrnction the obstacle
offers to the normal growth, the degree
of scalarity in the shell is dependent,
as it nsnally follows for the rest of its
growth the direction tlins accidentally
given to it. If the interference he
comparatively slight and near the
sntnre, a canalicnlate sntnre may he formed, which may continne
([iiite to the aperture, or may only exist for a limited distance, the
growth becoming normal after passing beyond the ohstrnction.

Ilemarkahle examples of extreme scalarity are furnished by the
ceratoid specimens of //c//,r and

other species.

The flatly-coiled or discoid shells of
P/(niorl>lft are e([nally or even more liable
to become spirally elevated with more or
less regnlarity, as in Phtnorbls mdrffiuatm
monst. cochlea, which may in that state he
easily mistaken, at a casual glance, for
Valcaia 'phcinaUs, to wOiich species it hears a great resemblance.

Fig. 2()2. — Plnnorhis viar-
ginatus in. cochlea I’rown X 3,
Fisegale ICau, fiosiierlon,
Cijllecled I)y Mr. H. Wallis
Kew, F.Z.S.,

Showing a scalariform shell.

Fig. 2lil. — Heli.v asf>ei-sa monsl. cornu-
co/>ia (intclin,

iMnwnan Sanctuary, near Falmouth,
Collected by the late Rev. W. Rogers,
An c.vample of e.vtreme scalarity.

MONSTROSITIES — SCALARIFORMITY.

117

It was originally described in 1818 as a new species by Capt. Brown
under the name of Helix cochlea, and Dr. Tnrton the following year
described it as Helix terehra, but it was afterwards reduced from specific
rank and the shell allocated to its appropriate species when its affinities
were recognized. This dislocated spiral coiling seems to be more
especially the result of the peculiar and abnormal conditions arising
from living in waters modified by the warm water, and perhaps other
substances, emanating from steam engines. A reservoir at Swansea,
the water of which was kept at a high temperature by the influx of
condensed steam, etc., from steam engines, was inhabited by
Planorhis marginatus, and all the specimens tended to assume the
raised spiral form. The mill-pond at Roch-
dale, which has been so often recorded for
its plentifnl production of this monstrosity,
was subject to the same conditions as the
reservoir at Swansea. The whorls may also
become (piite detached and separate like
a Verrnetus or a corkscrew, although the
extreme openness of the spiral coiling is
seldom so pronounced and regular as in the paheogeuic specimen
of Planorhis spirorbis I have figured. Sometimes, but more rarely,
the whorls coil closely in a cylindrical
fashion, like those of Pupa ; I have only
seen this deviation in Planorhis mar-
ginatus and Planorhis vortex. Planorhis
marginatus seems especially liable to
produce these scalarid monstrosities, but
Planorhis spirorbis shows the most pro-
nounced and decided tendency to revert to the original sinistral
direction of coiling.

One of the causes inducing this scalarity in the Planorhes has
been conclusively demonstrated by Van den Broeck and others to be
the thick and occasionally matted growth of Lemna minor covering
the ponds inhabited by the Planoi'hes, and preventing the easy access
of the discoidal shells to the surface for respiration, the young and
the scalariform specimens being proved by experiment to penetrate
the dense vegetation with far greater ease and celerity.

In the Lake of Magnbe, in Belgium, where this deviation in
Planorhis marginatus was found in great abundance, and the normal

Fig. 264. — Planorhis vortex
monst. colu77iclla Taylor X 3,

Ditch, East Moors, Cardiff,
Collected by Mr. F. W. Wotton.

Fig. 'l^.-Pla7iorbis spirorbis
monst. priscu77i Taylor X 3,
Pond, Hayling Island, Hants.,
Collected by Mr. H. H. Haines.

ns

M(>NSTRO!?ITIES — SCALAIUFORMITY.

discoid form bvit rarely, tlie surface of tlie pond was tliickly covered
by a very dense growth of the Lcmna, but on the plant afterwards
dying away, the scalarid specimens ceased to be produced, and the
ordinary discoid shells only were to be found.

Herr Clessin records that the same deformities are produced in
various species by ponds filled with other water plants, or on the
shores of lakes among and between stones.

A further cause suggested is that, during the growth season, the
water in the ditches or ponds iidiabited by these species is often
nearly drietl up, and that the efforts of the creatures in forcing their
way through the thick mud in which they are sometimes left par-
tially imbedded, to again reach the Avater, may easily cause an
alteration in the direction of the new growth, if at the time in
proce.ss of formation.

H. Roliiaen endeavoured to produce scalariform specimens of
Helivcx, at will, by attaching plaster-of-Paris upon the penultimate
whorl, near the suture or line of attachment of one whorl with
another, but he was in a degree unsuccessful in the attempt, as the
mollusk.s, after surmounting the obstacle jdaced on their line of
growth, reverted to their normal manner of coiling, or produced only
irregularly grown and deformed shells, ([uite dilferent from the sym-
metrically and gracefully coiled scalariform shells naturally produced.
'I'he result of the e.xperiment led M. Roliiaen to believe that scalari-
formity in shells is owing to .some accidental modification in the
animal, such as the permanent contraction or relaxation of certain
muscles coidd produce.

!• !(.. '2V>'h — J/tii.f ncifiora/is inon^l. utihi/ i-
tornit: Taylor,

Uallyshaniion, l)onc*j;al,

(Mr. W. Swanslon’s collection),
showing a naturally grown scalariform shell.

Kkr 2GG. — Helix aspersa Miill.,
Reared by Mr. J. Madison,
Showing an artificially produced scalari-
fonn shell.

IMr. J. Madison has also endeavoured to [)roduce these scalariform
shells by similar means to those adopted by M. Rofliaen, and has been
to a similar extent successful in inducing the desired scalarity, but
hopes to have much more symmetrical, and finer results as he gains
more experience in their treatment.

MONSTROSITIES — POLYSTOMATISM.

119

Fig. 2G7. — Claitsilia bidcntata
(Strom) X 2,

Luton, Ijedfordshire,
Collected by Mr. J. Saunders,
Showing the two distinct
mouths of the shell.

PoLYSTOMATiSM (ttoAl's many, (TTOfia mouth) is a term denoting the
presence of more than one aperture to a shell, Rud is most liable to
occur amongst the individuals of those species with greatly contracted
apertures, especially those forming the genus Clausilia, which are,
under certain circumstances, liable to form an additional or second
aperture. These dual-mouthed shells might possibly be regarded by
novices as the joint production of two individuals united together,
but with the head and neighbouring parts distinct and separate — a
kind of Siamese twins — but this second aperture is probably formed
on account of some obstacle or hard particle
becoming fixed, temporarily or permanently,
in the normal one, thereby deranging or
obstructing the action of the clausium, and
preventing the egress of the animal, which
is therefore compelled to form a new outlet
or perish confined within its shell. This
new outlet is made by piercing the shell-
wall, usually about half-a-whorl distant from
the original one, and thus facing in the opposite direction, and is
formed e.xactly in the normal way. Mr. P. B. Ma.son mentions specimens
of Cldasilid with as many as four distinct mouths to the shell.

Although the wide-mouthed shells do not appear to be so liable
to this peculiarity as the ClaudVm, which have a very contracted
and dentate aperture, yet I have a very interesting distomate speci-
men of Limnwd auricularia, kindly given
me by Mr. H. Wallis Kew, and found by him
at High Bead), Epping Forest, in 1894. This
shell, from some inexplicable cause, has dis-
continued the use of the normal aperture,
and pierced the outer shell-wall or perhaps
availed itself of an accidental fracture of the
body-whorl, about a quarter of a volution
from the outer lip, and there constructed a
new and more contracted opening which,
despite its comparatively restricted size, appears to have been used as
the means of exit. This new growth, forming the protruded new out-
let, would appear to have been formed after the atrophy of the glands
of the collar, as it is deficient of epidermis, and is apparently formed
by the general surface of the mantle.

Fig. 268. — Lbunwa auricu-
laria (L.),

High Beach, Epping,
Collected by Mr. H. Wallis
Kew, F.Z.S.,

Showing two distinct and
separate apertures to the shell.

120

MONSTKOSITIES — POLYl’EHISTOMATISM.

PuLYPEHij'TOMATE (ttoAi's, iiiuiiy ; irtpi, aruuiul ; and o-ro/xa, mouth)
would perhaps be a more correct designation for certain shells, which
though differing somewhat from the tridy distoinate shells, are
yet eipially interesting, and of which the Limnau peregm
discovered by l\Ir. William Nelson in
the spring of 1883 in a small shallow
cattle pond at Allerton - Bywater, near
Leeds, are a remarkable illustration.

These shells, and all in the pond were
more or less affected, are somewhat
irregularly and often fantastically grown,
and in addition to thismalformed growth,
sometimes developed two or more complete peristomes or lips to
tlieir shells ; these lips, though more or less coiiHuent and grown
together at the imsterior margin of tlie shell, become (juite distinct
and separate at the anterior or basal portion, and the complete shells
have in some cases all the appearance of one or more distinct shells
enclosed within a larger e.xternal one.

Tlie I’elecypods also occasionally e.xhibit this duplication of the
apertural margin, and characteristic specimens i)resent, as in the

Fig. 2G0. — L. pcrc^ra (Miill.) X 2,
PoikI, Allerton-Pywaler, Vorks.,
Collected by Mr. W. Nelson,
Showing three diblincland separate
peristomes.

Fig. 270. — i'nio iionitius Phil.,

(irohy Pool, Leicestershire, collected by Mr. H. K. (Juilter,

Showing the formation of three distinct and successive peristomes.

I A mini <1 jn rrgra above mentioned, all the ai)pearance of several shells
enclosed within an outer larger one, and in an even more deceptive
manner.

These additional lips are usually of less anii)litude at their origin
than the one previously made, and have been noted to be often hjrnied
in spring, when the emaciation or reduction in bulk of the body which
may be assumed to take i)lace during hibernation has not heen fully
compensated for before the growth season has recommenced and this
diminisheil size of the body would necessitate a contraction in the

MONSTROSITIES — ABNORMAL GROWTHS.

121

size of the shell. Irregularity in food supply, due to the recurrence
of alternating periods of enforced abstinence, owing to food scarcity,
followed by terms during which ample supplies of nourishing and
palatable food are easily obtainable, may be supposed to conduce to
similar growths.

An Abnormal Continuation or prolongation of the regular growth
is occasionally made after the normal completion of the shell and
the formation of the lip, but in nearly all
these cases, owing to the glands of the
collar becoming' atrophied at the maturity
of the .shell, these extraordinary and abnor-
mal growths are exclusively secreted by
the visceral mantle, and are therefore quite
destitute of epidermis and of the middle
calcareous layer with which the coloring
matter is usually associated, having exactly
the same character and appearance as the
repairs made to damaged parts of the
shell, remote from the aperture and
beyond the reach of the collar ; snch
repairs are made solely by the visceral
mantle. These abnormal growths are
probably only another mode in which

■ 1 1. f , 1 1 1 T f r* 1 1 Showing abnormal continuation

tlie resiiit oi tlie prolonged lile oi tlie of growth,
animal may be manifested, and in all likelihood this assumed pro-
tracted life’s cycle of the mollusk is owing to unusual mildness of the
seasons. The locality where the specimens figured and others also
have been obtained is very suggestive, the neighbourhood being noted
for its genial and mild climate.

In some rare instances it may happen that the aperture is formed
prematurely, and normal growth be afterwards continued for a short
distance, and a new apertural margin formed, or it may be that in
some cases the atrophy of the glands of the collar may be delayed
longer than is usually the case.

Anomalous Combination Shells are those formed by the union of
two or more diverse shells, either owing to the circumstances producing
them occurring naturally, or through artificially bringing the desired
shells into the necessary close conjunction with each other, so that

Fig. 'I'lX.-Clausilia bidcntata
(Strom) X 2,

Cheltenham,

Collected by Mr. W. Nelson,
Showing abnormal continua-
tion of growth.

1-22

MONSTROSITIES — COMBINATION SHELLS.

the animal
its "rowtli.

may pennanently attach them together on continuing
M. Barthehny, director of tlie hlarseilles Miiseung once

found a Helix asperm which
had evidently become lodged
by some means within the
empty shell of a Linuava
st(((jn<ilh before attaiidng its
full growth, and which in
its progress to maturity,
attached its own shell by the
new growth to the shell of the
Limnaa.

Mr. Madison, of Birming-
ham, has been very successful
a number of

Figs. 273, 274. — Helix aspersa Miill.,
Collccled by M. I’arllicliny
(after S. Petit),

Showing the conjunction of two diverse shells.

had the oppor-

Fui. 273. — Helix asperaa Miill.,
Reared by Mr. J. Madison,
Showing a Darcelona nut iticor-
porated with its shell by the inollusk.

b

ill obtaining

these grotescpie sbells. Through his kiiuluess 1 have
tiinity of e.xaniining many of the results
of his patience and ingenuity. Some of
the Helix axpersa — with which species he
has mainly experimented — hehas induced
to incorporate with their shells, in the
process of their growth, full grown shells
of Helix c(ii/ti((iia and other species in
various odd positions; he has also con-
trived to join with the growing shell of
the inollusk more or less complete nut-shells and other objects. His
series of these curious monstrosities is interesting and remarkable.

In the Woodw'ardian Museum, Cambridge, there is a similar
monstrons specimen from ITverston, possibly naturally grown, in
wbich two shells of Helix aspersa have grown together in this way.

iM. Cailliaud lias described the method of producing the union of
these diverse .shells to be by breaking away the palatal or outer
margin of the shell of an Helix aspersd, or any other species that
may be selected for the operation, and then introducing the living
inollusk into the empty shell which it is desired should be incorporated
with or joined to its own, attaching the two together for a few days only
by the aid of thread or other suitable inean.s, the inollusk usually
ill that time has cemented the two shells together by the new growth
it has been stimulated to make by the removal of portions of its shell.

AUXILIARY ORGANS — OPERCULUM.

123

Auxiliary and Protective Organs.

Tliere are three ingenious, though dissimilar methods, hy which
Univalves close the apertures of their shells, for the double purpose
of protection against the intrusions of their enemies and to
prevent the desiccation or evaporation of the natural moisture of the
tissues of the body, during the mid-day periods of repose or the
more extended dormancy of mstivation and hibernation, and also to
guard against the extremes of cold, heat, and the injurious effects
of climatal fluctuations generally.

These anxiliaiy organs, known as the Operculum, the Clausium,
and the Epiphragm, are formed in an analogous way to the shell
itself, the secretion to form these different organs being ju'obably
poured out as a gelatinous substance holding calcareous matter in
solution, which hardens and crystallizes by exposure, the semi-Huid
chitinous matter, which constitutes the investing and permeating
organic framework, moulding itself around the growing crystals formed
by the calcareous matter present in the solution.

The Operculum {operio, to cover) is perhaps the most important
and universal of these contrivances for closing the mouth of the shell,
and is a special structure chiefly develoi)ed amongst the branchiferous
Gastropods, but has been retained in some genera which have pro-
bably become adapted to terrestrial life and aiirial respiration.

It originates upon the embryo in the ovum, above the foot, and at
the posterior end of the body, upon a restricted portion distinguished
by its denser texture, which has been termed the operculigerous lobe,
and presents, especially in genera foreign to our limits, very great
diversity of structure, but our native operculiferous species are very
few and do not exhibit the remarkable forms of many exotic species. It
may consist of chitinous layers, as in Vimpam contecta and other
species, but is sometimes strengthened by calcareous matter, as in
Neritum JluviatiUs, etc., the inner surface being always marked by a
muscular scar showing the point of attachment to the animal and shell.

The operculum is usually, but not invariably, the size of the aper-
ture it closes, and according to Mr. Kenneth McKean in Bpthinia
tentacuhita fits the mouth of the shell so accurately that if the
animal be killed with boiling water and allowed to dry up within the
shell, and it be afterwards held in the warm hand, the operculum will
by off with a considerable report owing to the expansion of the
confined air or gas.

1 24 AUXILIARY ORGANS — OPERCULUM.

'I'lie position of the operculum ui)oii the aniiiuil varies within cer-
tain limits in the ditl’erent species. In Xeritiua, when the animal is

crawling the opercnlum practically hinges
on the columella, hut in other genera it
may be at a comparatively considerable
distance from the aperture. The oi)er-
culum is brought over the mouth of the
shell to close the aperture when the
animal retires, by the contraction of the
retractor muscle to which it is attached ; the point of insertion usually
leaves a single scar upon the opercnlum, hut on that of Nerithui
j! iiciutiHs{\\Q\-Q aretwo scars, that formed by the hinder muscle being the
largest and forming a broad snhmarginal scar along the side adjacent to
the columella, while the scar at the anterior end is .smaller and is of a
somewhat ovate shape and situate at the ha.se of the opercular proce.ss,
termed the “p^'S. ” "hicli is, however, rudimentary in our Briti.sh
sjiecies, ami therefore usually (|uite (»verlooked by imjst conchologi.sts.
'I'lie muscles are attached to the shell at opposite ends of the pillar lip.

'I'lic operculnm varies even more than the shell in the relative
amounts of chitinous and calcareous matter contained in its composi-
tion. In some sjiecies, as Xeritiua j/iu'i(cfi/ir, the operculum has
comparatively less organic and more calcareous suhstances than the
.shell who.se mouth it closes, while that of \"irip(ira c/ivyiu/vt is purely
chitinous, the gravimetric te.sts made upon clean oiiercula by Mr.
Crowther showing no trace of lime, although the shell of that .species
contained 11 1 '2 I jier cent of earthy .salts.

'I’he compo.sitioii of the operculum of Xeritiua jlariatilis has been
termed “not .shelly ” by some authors, and imrely calcareous by others,
hut a careful analy.sis showed it to contain t)7';>2 percent of inorganic
matter and 2 (;7 jau' cent, of (organic .substances ; the .shell of the same
Species h(jwever contains more organic matter than its oj)erculum
having 4'4() per cent, of organic substances and only Pd'ot) i)er cent.
Ilf inorganic matter in its comj)osition. 'I’he organic skeleton of the
operculum of this .species is not destroyed even by mixed acids, the
chitiiunis framework preserving its form and elasticity uninii)aired
and making a jnetty object under a lens.

Ci/clartonia e/epaits, on the contrary, has le.ss chitinous matter in the
shell than in its operculum, the analy.sis showing the operculum to
contain ‘J2'7G iter cent, of inorganic matters and 7 "23 per cent, of

Fig. 270. — Section througli the
sliell o( //7c:uat///s, showing

the operculum /« ivV/J and the mode
in which the “rih" hinges upon the
columella, X 3 (section cut by Mr.
1'. Rhodes).

AUXILIARY ORGANS — OPERCULUM.

125

organic or chitinous substances, the shell having 98'94 per cent, of
inorganic and 1 '05 per cent, of organic matters.

These analyses of .shells and opercula made for me by IMr. Crowther,
still further demonstrate that the composition of the calcareous parts
of the shell and operculnm are not strictly identical in character, as
the calcareous matter of the shells rapidly dissolved and disappeared
upon immersion in h3'drochloric acid, while the calcic constituents of
the opercula were very difficult to dissolve, even in warm acid.

It has been suggested by Adanson, Gray, and others, that the shell
and its operculnm were together homologous with and represented the
two valves of the Bivalve, hut Huxley considered the operculum to
be the analogue, if not the homologue, of the byssus of the Bivalve,
and that it cannot represent the valve of the shell, which is a palllal
structure ; there is, however, a somewhat striking analogy between
them, as the operculum is attached to the shell itself tlirough the
body of the animal by a powerful muscle corresponding to the
posterior adductor of the Lamellibranchs, which it may be also con-
sidered to represent in function. Another remarkable peculiarity
possessed in common, is that when the month of the shell is closed
by a spii’ally coiled operculum the spiral always revolves in the oppo-
site direction to the spire of the shell, a dextral .shell having a
sinistral operculum and vice versa, exactly as is the case with the two
shells of a Bivalve, the right valve of which may be twisted or coiled
at the umbo to the right, in which case the left valve would he coiled
or turned to the left. In those species like Neritina fiivlatUis, the
similarity is still further marked by the development of complex
calcareous processes on the inner side of the operculum close tQ the
columella, which have been designated as the “rib” and “peg,” the
rib functioning similarly to the interlocking teeth in bivalves, and
even in species with a lamellate or concentric operculum, the nucleus
or representative of the umbo is always nearest to the columella, or
what would be the hinge line. The different forms of opercula are
characterized as

Spiral when .spirally formed; the coiling is sinistral in dextral
shells and dextral in those sinistrally coiled, and the increase
is derived from a portion only of the operculigerous lobe, exactly
as the increase in size of shells is due to the mantle margin.
Tlie spirally coiled opercula actually revolve or turn upon the
columellar muscle during the progue.ss of growth, as is slunvii

126

AUXILIARY ORGANS — OPERCULUM.

Fig. 27S.

Ciiliim X 3.

C}'ciosionin clc^aus (MiilL),
l»ox Hill, Surrey,

Collected Uy Mr. W.Whilwcll, F.L.S.

liy tlie fact that the termination of the .siiiral ivliere the enlaroe-
inent is exclusively made always ahnts against a certain definite
part of the aperture of the shell, and thus clearly establishes that
the oi)erculum must of necessity, in the course of growth,
actually revolve upon the end of the columellar muscle as many
times as there are whorls or coils indicated thei’eon. Tliese
s])iral opercula may he distinguished as
r.^ucLspiRAL, or few whorled,
the nucleus being placed
towards the basal or an-
terior end, as in Ci/chatooxi
c/cr/G/LS, Arinild I'mcdta ,Qt(\

'I'he o])orculum of Ci/rhi-
is chiefly and

very distinctly formed of two thin lamina', as its chan-
nelled edge clearly indicates ; or
Multispir.\l, or many whorled, the nucleus being situate
towards the centre of the
organ, as in ]’'((/raf(t
iitills, hut the number of
whorls iu tlie operculum
has no nocessary relation
to the number in the shell,
tlnnigh at times iu accord
with it. Dr. Jeffreys de-
scribes and figures the o])erculuni of Vdh'atd jusrliiiih'a
as formed of f(t to f 2 s]ural whorls, and Mo( pi in-Tan don
figures the same as containiug only t.l- volutions, though
descrihing it correctly in the text.

Concentric when the increase in size
tabes place from the whole surface
of the lobe, ami more or less eipially
aronnd the suh-central nucleus ;
such opercula do not alter their
])o.sition u])on the retractor muscle
to which they are atli.xed, hut ac-
commoilate themselves by simi>le
gTowth to tit the iucreaseil size <jf the aperture of the shell, as
ill Vminmi contectd, etc.

Fir.. 270. — A MuUispirally-coilecl
Operculum X 8.

l’n/7'atn piscinafis (Mull.),
River 'rarff, Kirkcutlbriglu,
Collecteil by Mr. F. K. Coles.

Fig. 277. — A Concentric Oper-
culum X 11.

i'k>ipara conh'cta Millet,
Southport,

Collected by Mr. CJ. \V. Chaster.

AUXILIARY ORGANS — CLAUSIUM.

127

Fig. 280. Fig. 281.

An Articulated and Sub-spiral Operculum X 4.

Ncritina /lu7naiitis (L.),

Canal, Northampton,

Collected by Mr. W. I). Crick, F.G.S.,

Fig. 280 showing the external face and the subspiral
formation of the operculum, with the projecting
“rib,” and Fig. 281 showing the interior face with
sub-marginal muscular scar, the “rib” and “peg,"
and anterior scar, at base of the apophyses.

r. rib or fulcrum ; /. rudimentary peg.

Articulated when furnished with more or less complex projections
or apophyses, which
appear to act like a
hinge, as in Nerit'ma
fluviatilis. The oper-
cnlnm of this species
has a broad flexible
margin, and is duplex
in character, being dis-
tinctly and marginally
snbspiral on the ex-
ternal face, but this feature is practically obscured on the
internal face by a later calcic deposit.

The different parts of the operculum may he distinguished accord-
ing to its position when applied to the month of the sliell, the Exterior
face lieing that facing outw'ardly and the Internal face that to which
the columellar muscle is attached; the part adjoining the base of the
aperture of the shell may likewise be termed the base or Anterior end
of the operculum, the opposite end being the upper or Posterior one,
the Palatal margin of the operculum is the one adjacent to tlie palatal
or outer lip of the shell, and the Columellar side the one adjoining
the columellar margin.

The Clausilium, or Clausium (claimim, an enclosure), as I prefer
to call it, is another ingenious contri-
vance, formed within the last whorls of
the shell in the genus Clam/l/a, also for
the purpose of closing the aperture
against outside enemies and preventing
desiccation. It is an elongate, some-
what oval, externally convex, and more
or less arcuate, nacreons-white plate or lamella, attaclied by a
somewhat cartilaginous, elastic and -

spirally twisted pedicle or footstalk to
the columella near the commencement
of the penultimate whorl, and has been
aptly compared to a door furnished
with an elastic spring. It also varies
greatly in its form and character in the
dift’erent species and in coiTelation with

"W

Fig. 282. —Clausium of Clausilia
Oidentata Strom X 8,

Stroud, Gloucestershire,
Collected by Mr. E. J. Elliott,
Showing the convex external face
of the clausium and its elastic pedicle
of attachment.

Fig. 28.3. — Clausium of Clansilia
cravcnensis Taylor x 8,

Starbolton, Yorks.,
Collected by Mr. W. I.). Roebuck,
Showing the convex external face
of the clausium anrl its elastic pedicle,
for comparison with that of Clausilia
bhicntata (hg. 282).

128

AUXILIARY ORGANS — CLAUSIUM.

/

Fig. 2St. — Clausium of C/ausiita
Inwiuata (Mont.) X S,

Cooper's Hill, Cheltenham,
Showini; the concave internal face
and the sinuate lower marj^in.

tlie jialatal plications tliat may be present in the sliell, exliibits a
coiTOspondinp; and apin’ojn'iate sinnation of its external outline, and

is an organ certainly deserving of mnch
more careful study than it has hitherto
received from British conchologists.

Uidike the opercnlum, which is at-
tached to the animal and present from
the earliest age, the clansium is attached
to the shell only, ami is not present in
the young, being only produced at the
a])proach of maturity, the pedicle being first formed and the lamella
gradually ailded to until completed.

When the animal emerges from the shell, the clansium is pushed by
the pressure of the body against the columella, into the groove between
the inferior and suhcolumellar lamelhu,
thus leaving the meansof exit free. On the
withdrawal oftheanimal intothe shell the
pressure of the body against the lamella
is removed and the elastic pedicle causes
the filament to spring into its normal
])osition, with its lower margin against
the exterior of the whorl, but when the
shell is thus closed there still exists a
small opening near the suture which is
conjectured to serve for res]iiration and
defecation. In the emi)ty shell from
which the animal inhahitant has been
removed and the lamella become rigid and dry, the elasticity can be
to some extent restored by immersion in water.

'riiough especially indicative of tbe
fill liquid’, there is found in Azera tridmiK
an imperfect, laidimentary and inflexible
lamella, which is attached along its whole
length to the columella, and has been
assumed to rejn-esent the more elastic
clansium. This rigid calcareous fold is
continued (piite to the aperture of the
shell, within which its rounded termina-
tion may ho seen ])arallel with the columellar margin.

Fig. 285. — Section through shell of
Clausilia hideutatn Strom, showing
tile dausium in sitr'i, X \ (section cut
liy Mr. F. Rhotle.n).

Fig. 280. — Azcca triiii-ns (Pult.) xfi.
Ronndh.'iy, near Feeds,
Sliowing the uifle.xihle calcareous
lamella, assumed to represent the
Clansium.

AUXILIARY ORGANS — EPIPHRAGM.

129

Daubenton was the first to notice tliis remarkable appendage, but
jMiiller gave the first full and accurate account of its function and
structure under the names of Ossicula and Scala. Draparnaud in LSOl
and Miller in 1822 independently discovered and described it, ap-
parently in ignorance of the work of their predecessors.

The Epiphragm (eVt, upon; c^pdy/xa, protection) or Ilybernaculum,
as it is sometimes called, is another means of protection to the
animal when enclosed in the shell, though differing essentially from
both the operculum and the clausium, as the former is permanently
attached to the animal and the latter permanently fixed to the shell,
while the epiphragm has no organic connection with either the shell
or animal. The epiphragm presents neither appendages nor incre-
mental marks, as in the clausium and operculum, and is only
temporarily adherent to the shell, from which it is cast off and
renewed as often as the animal’s necessities require.

According to Biuney, when the mollusk desires to form an
epiphragm, it withdraws within its shell, and brings the collar of the
mantle to near the level of the aperture, exuding therefrom a
quantity of mucus, more or less intermingled with calcareous particles,
sufficient to cover the exposed surface ; the mucous pellicle is then
detached from its adherence to the animal by a small quantity of air
emitted from the respiratory orifice, which projects the film into a
convex bubble-like form, the animal at the same moment shrinking
further within the shell, and the external air forcing the delicate
epiphragm to a fiat or even concave shape ; it then hardens and
becomes fixed to the inner margin of the aperture of the shell. All
these actions are almost instantaneously effected by the animal.

The epiphragm is composed of the mucoid secretions of the animal,
mingled with calcareous granules, some of which exhibit a concentric
structure ; it is permeable to air and
not softened by or soluble in water and
varies very greatly in character not only
according to the species, but even in the
same individual, according as to whether
it is secreted for protection during the
winter dormancy or merely to prevent
the drying of the tissues during diurnal
repose or enforced abstinence. The diurnal or summer epiphragm is.

Fig. 287. — Helix ne7noral{s L.

Castle Hill, Scarborough,
Showing in sitfi the thin, iritlescent
diurnal or summer epiphragm, with
the white calcareous thickening in
front of the respiratory orifice.

I

130

AlIXILIAR Y ORGANS — EPIPIIR AG JI.

ill tliis coiiiitiy, iiuicli more delicate and less iiiteniiiiigled with cal-
careous particles than that formed for winter protection, being often of
exceeding tenuity and transparency and heantifiilly iridescent. There
is an opaipie and usually very ajipareiit white calcareous spot opposite
the orifice of the respirator}- chamber, through which there often
passes an opening or slit in the film, which though not invariable in
its direction, is usually jiarallel with the outer margin of the shell.

The point where the animal was last in contact is often somewhat
puckered and irregular, and, like the circumscribed area ojiposite the
respiratory orifice, has a whiter ami more opaipie character, owing to a
greater density of the calcareous matter at that place. Additional
layers may be afterwards added which strengthen and thicken the film.

'I’lie winter or hihernal epiphragm
is always thicker and more solid
than the ordinary one. In llelir
pomatla it is very thick', strong, and
calcareous, with an outward con-
vexity, which seems to distinguish
those species with bulky bodies.
Animals with more meagre propor-
tions relatively to their .shell often
have the epiphragm deeply sunk
in the aperture. Species with a

Showing ,ho suongly calcareous winter j calcareOUS sliell aud tllOSe
epiphragm m situ.

destitute of a snhmarginal rib to the aiierture have very thin, delicate,
and often more or less imiierfect ones, and all intermediate stages e.xist.

If the weather becomes very severe the animal shrinks further
and further into the recesses of the shell, forming additional
epi[)hragms at short intervals from each other, these becoming more
and more delicate ami transparent and less and less mixed with
calcareous matter. I have myself counted as many as si.x of these
septa in a Yorkshire specimen of aspersa.

Some authors state that the eiiiphragm is only iiartially formed if
the aperture of the shell is already partly closed by adherence to the
shell of another mollusk or any other object, the epiphragm in that
case being said to be secreted merely to close uj) the space not
occupied by the oliject to which the mollusk is attached. I have,
however, frequently verified in //c/or ((.y)ersa that the ei)iphragm is
complete and extends over the whole aperture, and is not invariably
the partial production it has been asserted to be.

Fig. 288.— /rv//rz//(Z L.,
Faversham, Kent,

Collected by ibe late Mis.s K. lb 1‘airbrass,

AUXILIARY ORGANS — EPIPHRAGM.

131

According to ]\'I. Delacroix the epiiiliragm of Helix pomntla con-
tains nearly three times more animal or organic matter than the shell,
his analysis furnishing 57 '20 per cent, of organic matter, 28’()3 per
cent, of carbonate of lime, and 14'77 per cent, of other and undeter-
mined mineral substances. Mr. Growther, who has analysed an
epiphragm of the same species from Faversham, found it to contain
6‘83 per cent, of organic matter and 93'16 per cent, of inorganic
substances. This analy.sis though differing so markedly (quantitatively
from that of M. Delacroix agrees in showing the epiphragm of this
species to contain consideralily more organic matter than the shell.

Though the formation of an epiphragm is more especially a
characteristic of the inoperculate land shells, yet many freshwater
species in times of drought, when the streams and j)ools they inhabit
become dried up, not only bury themselves more or less deej)ly in
the mud, but some species of Flanorhis close the aqierture of the
shell by a strongiy-adherent, firm, whitish ei)iq)hragm. Fl'nwrbis
spirorbim is most addicted to the exercise of this power, and one of
its synonyms, Planorbis leuco^toma, probably indicates its habitual
indulgence in this habit, though other species have also been observed
in the same condition.

Those terrestrial species destitute of a sufficiently caqiacious externa l
shell, within which they can retire for protection during unusually
cold or dry weather, excavate for themselves a subten-anean chamber,
the walls of which are rendered smooth, coherent and firm by an
internal coating or lining of the mucous exudations of the animal.
This mucus-lined earth chamber, within which the creature lies snugly
ensconced in a contracted and tor})id state, may be considered as a
qieculiar and interesting modification of the apertural epiphragm of
the te.staceous sqiecies.

LITERATURE.

Adams, H. & A. — Tlie Genera of Recent ^lollusca, arranged according to
their Organization, 1853 — 8.

Andre, E. — Anat. et Pliys. Ancylns laeustris et Ancylus fluviatilis. — Rev.
Suisse Zool., i., qip. 427— 461, 1893.

Ashford, C. — Suggestions fora serial arrangement of the Variations of our
Bauded Land Shells. — Journ. of Conch., iii., qiq). 89 — 95, 1880.

Binney, W. G. — A Manual of American Land Shells. — Bull. U.S. Nat.
Mus. , No. 20, 1885.

Bourguignat, J. R. — Etude Synonymique sur les Mollusques des Alpes
IMaritimes, jurhlies par A. Risso en 1826, Paris, 1861.

De la Sinistrorsite des Espbces ; iu INIoitessier’s Hist. Malacol, du
d(3part. de 1’ Herault, 1868,

132

SHELL — LITERATURE.

Boycott, A. E. — Contributions towards a List of the Molliisca of Here-
fordshire.— Science Gossip, pp. 77 — 79, April, 1892.

Brido-man, John B. —A Variety Caused hy Locality (L^nio pictoruin var.
coinpressa). — (Quarterly Jonrn. of Conchology, vol. i., !>. 70, May, 187d.

Broeck, E. Van den. — (^Inelqnes mots s. lesBlanorhis coini)lanatu.s scalaires
deMagnee. — Bull. d. Soc. Mal.de Belgiipie, vol. vi.,pp. lxi.-l.\iii., 1871.

[Alode of artificially proilncing scalariforin .shells]. — Bull. d. Soc. !Mal.
BelgEine, vol. iii., pp. Ixxxii— iv., 1808.

Brot. Ang. — Etmle sur les Co(inilles de la Eamille des Nayades qui hahitent
le hassin dn Leman. — tleneva, 1807.

[.Anomalies observed in Swiss Mollusca. ]— Proe. A’erb. Soc. Mai. Belg. ,
vol. xii., p. xliii., 1877.

Cailliand. F. — Catalogue des Badiaires, cles .Annelides, des Cirrhipedes et
des Alollusques de la Loire Inferienre — Nantes, ISO.).

Call, B. Ellsworth. — Beversed Alelantliones. — Amer. Nat., vol. xix.,
p. 207, March, 1880.

Gn the (Quaternary and Becejit Alollnsca of the Great Basin, with
descrijitions of new forms. — Bull, of the U. S. Geol. Survey, No. 11,
pp. 807 — 410, ami 0 plates, 1884.

Chenn. J. Alannel de Conchyliologic et de Baleontologie Conchylio-
logiijne, Paris, 18.')9 — 02.

Cockerell, Sydney C. — Abnormal Spiral Banding in onr Land and Fresh-
water Mollusca. — .lournal of Conchology, vol. iv., ])p. 374 — o, Oct., 1885.

Cooke, Shipley and Beed. — AIolluscs and Brachiopods. — London, 1895.

Colbeau, Jules.— [T.aml Shells about Dinant.] — Bull. Soc. IMal. Belgicpie,
vol. i., p. Ixvi., 1804.

Cornisli, Vatighan, and Kendall, Percy F. — On the Alineral Constitution
of Calcareous Organisms. — Geol. Alag., F'eb., 1888, i)p. 00 — 73.

Dali, AV. 11. — On the Hinge of Pelecypods, and its development, with an
attempt at a better subdivision of the group. — Amer. Journ. of Science,
\ol. xxxviii. , ]!]). 445 — 4()2.

The Mechanical Cause of F’olds in the Aperture of the Shell of Gastro-
poda.— Amer. Nat., 1894, pj). 909 — 914.

Doild, B. Sturges. — Probable (’auses of .Vbnormal A'ariation in Limna'a. —
Journ. of Conch., vol. iv., p. 304, A]iril, 1885.

Doherty, AV. — Bemarks on a Dentate A’ariety of Conulus fulvus Drap. —
(Quart. Journ. of Conch., vol. i., ])p. 334 — 5, May, 1878.

Drai>arnaud, J. P. B. — Hist. Natnr. des Mollusipies terr. et lluv. de la
France. — Paris, 1805.

Dupny, I). — Hist. Nat. des Moll. terr. et d'eau douce (|ui vivent en 1’ ranee.
—Paris, 1847—52.

Esmark, B. — On the Land .and Freshwater Mollusc.a of Norw.ay. — Journ.
of Conch., vol. y., pp. DO — 131, 1880-7.

F'ischer, Di-. Paul. — Bemar(|nes snr la coloration generale des Coipiilles de
la Cote occidentale d'Ameriipie. — Journ. de Conch., vol. xxiii., pp. 105
— 112,1875.

Note s. la Sinistrorsite de la Coqnille des jennes Planorbes. — , Journ.
de Conch., )()1. x.xv. , pp. 198 — 200, 1877.

Manuel de Conchyliologie et de Paleontologie Conchyliologiiine, Paris,
1883 — 7.

Fdscher, P.anl, et Bonvier, FI. h. — Becherches et consider.ations sur
rasymmetrie des Alollusqnes Enivalves. — Journ. de Conchyl., April,
1892, pp. 117 — 207 and 3 plates.

Snr r enroulement des Alollnsqnes Enivalves. — Journ. de Conchyl.,
July, 1892, PI). 234 — 245.

Gr.ay, .1. Fi. — Afannal of the I.and and FTeshw.ater Shells of the British
Isl.ands, by AA'. Turton, new edition with .additions by .John Eilw.ard
Gray, London, 1840 and 1857.

SHELL — LITERATUBE.

133

Hey, W. C. — Freshwater Mussels in tlieOuse and Foss. — Junrn. of Concli.,
vol. iii. , pp. 268 — 273, Jannaiy, 1882.

Ihering, H. von. — Snr les relations naturelles des Cochlides et des
Ichnopodes. — Bull. Scient. de la France et de la Belg., T. .x.viii.,
pp. 180—1, 1891.

Jacqueinin, E. — L’ Histoire dn Developpeinent dn Flanorhis cornea. 1838.

Jeffery, W. — Nature and Development of the Hairs or Bristles on some
Land and Freshwater Shells, etc. — Jonrn. of Conch., v. , pp. 17-25, 1886.

Jeffreys, J. Gwyn. — British Conchology, London, 1862 — 0.

Jenyns, Rev. Leonard. — A Monograph on the British Species of Cyclas
and Pisidinm, Cambridge, 1832.

Johnston, George. — An Introduction to Conchology, London, 1850.

Jones, K. Hnrlstone. — IMollnscan Albinism and the tendency to the
phenomenon in 1893. — Jonrn. of Conch., vol. viii., pj). 3 — 11, Jan., 1895.

Lang, A. — Versnch einer Erklarnng der Asymnietrie der Gasteroi)oden,
Zurich, 1892.

Lankester, E. Ray. — Art. ^lollnsca. — Encyclopit'dia Britannica, ix. edit.,
part 64, pp. 632—695, 1884.

Macgillivray, AV. — A History of the Alollnscons Animals of the Counties
of Aberdeen, Kincardine, and Banff'. — London, 1843.

Martens, E. von. — Eigenthhmliche Filrbung von Helix hortensis. — Nachtr.
Deiitsch. Alai. Ges. , 1872, p. 44.

Alartens, G. von. — Ordn. d. Biinder a. d. Schalen v. Landschnecken. — 1832.

Alason, P. B. — Variation in the Shells of the Alollnsca. — Jonrn. of Conch.,
vol. vii., January, 1894.

McKean, Kenneth. — On the Mollnsca of the Club district. — Proe. and
Trans. Croydon Alicrosc. and Nat. Hist. Club, pp. 143 — 151, 1882 — 3.

AIoipiin-Tandon, A. — Histoire Natnrelle des Alollnsfpies terrestres et
ffnviatiles de France, 1855.

Pearce, S. Spencer. — On the Varieties of onr Bandeil Snails, especially
those of Helix caperata Alont. — Jonrn. of Conch., vi., pp. 123 — 135, 1889.

I’elseneer, P. — Introduction a I’Etnde des Mollnsr^nes. — Alem. Soc. Royal
Malac. de. Belgique, 1892.

Pfeiffer, Carl. — Naturgeschichte Dentscher Land nnd Sn.sswasser-AIollns-
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Pile, L. — Notice snr le Planorbis complanatns (forme scalaire). — Ann.
Soc. Mai. de Belgique, vol. vi. , pp. 23 — 27, 1871.

Ponlton, E. B. — The Colours of Animals, their meaning and use, especially
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Qnilter, H. E. — Land and Freshwater Mollnsca of Leicestershire. — Trans.
Leicester Lit. & Phil. Soc., April, 1888.

Reeve, Lovell. — The Land and Freshwater Mollnsca, indigenous to or
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Schwartz, E. H. L. — Shell Structure of Ammonoidea. — Geol. Alag., pp.
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Scott, T. — Conchological Notes — Helix arlnistorum. Shell growth. — Jonrn.
of Conch., vol. V., p. 230, October, 1887.

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Animal Life, London, 1881.

Simrotb, H. — Ueber einige Tagesfragen der Malacozoologie, hanptsiichlich
Convergenzerscheinnngen betreffend. — Zeits. Nat. Halle, T. Ixxii. , 1889.

Dr. Bronn’s Klassen nnd Ordnnngen des Thier-Reichs, Weichthiere,
1894 (still in progre.ss).

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AN IMAL- AiKNEU AL UKGAN IZATluN.

|;J4

Sykes, E. liuthven. — Note on Liiim:ea auricularia. — Journ. of Malac.,
vol. iii., |>p. 33 — 36, June, 1S!I4.

Tate, U. — A Plain aiul Easy Account of the Land and Eresli\vatei\M(dlusks
of ( treat Ihitain, Loudon, 1S6().

Tondin, J. 1!. P>.— Land Shells of Ilfracoinhe and neighhourhood.— Journ.
of Conch., \ol. V., itp. LSI— 1N3, Apiil, 1SS7.

Tryon, G. W.. jr. — Structural aiul Systematic Conchology, 188‘2.

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London, Oct., 18!)l, 8\'o, pp. 66.

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Journ. of Conch., v., !»[>. 221 — 5, 1887.

On the Periostracuin of Ileli.x arhustorum. — Conch., p. 53, Sept., 1892.

Woodward, S. P. — A Manual of the INIollusca, . . . London, 1875.

The Animal.

The iiiollu.sk.s or animals, forming the sliells described in the fore-
going iiages, liave soft, nnsegmented, and more or less bilaterally
symmetrical bodies, whose e.xternal morphological features have been
greatly changed by the e.xcessive development in size and moditica-
tion in form of particnlar organs, or by their diminution or even
total sipijiressimi and loss in mature life, 'i'he foot, the mantle, and
the ctenidia or hranchia' have perhaps undergone the most remarkable
changes, although the foot or podium has been comsidered to he the most
permanent and di.stinctive nmlluscan organ, and its moditications very
aiijiropriately used as the basis for forming the great divisions or
classes into which the mollusca have been primarily separated. This
enlargement or atrophy, as the ca.se may he, of the different organs of
the body has caused a remarkably diverse and varied asiiect in the
ditferent forms, hut these moditications are always correlated with
and dependent upon the changes in and elaboration of their various
and respective functions.

A'otwith.stauding the great divergence in external shape brought
about Ijy these moditications, the internal organization in the
ditferent genera }>resents a rather striking nniformity in many iioints,
and agree in po.s.sessing in common a number of .structural
characteristics not found in other groups of animals. Being without
an external or internal locomotory skeleton, the mollusca would seem
to he more especially adapted for an aipiatic life, the locomotion
of the terrestrial forms being limited and slow, although the different
genera may he adajited to live under almost every variety of terrestrial
and aipiatic conditions, and are capable of swimming, floating,
burrowing, crawling and even spinning mucous filaments to facilitate
locomotion when occasion reipiires their use. iSome species or groups

ANIMAL — EXTERNAL FEATURES.

135

Fig. 289. — Section through skin of Helix pomatia showing
epithelial and subepithelial structure, highly magnified (after
Vogt aud Yung), ep. epithelium; 1. small blood lacunze;
m. muscle-fibres ; 7n. gl. mucus glands.

are highly predacious, others purely phytophagous, hut the majority
of our forms are quite omnivorous and devour almost any substances
that come in their way.

E.xternally the whole surface of the animal is formed by a layer of
somewhat firm and elastic muscular tissue, overspread by cylindrical

epithelial cells, which
are often ciliated, more
especially in the a(|uatic
species, and in those
parts not habitually
concealed by the pro-
tecting shell ; the
ciliated areas in the
terrestrial forms being more restricted in extent. Scattered over
the whole external surface, but more densely aggiegated in certain
definite parts are a number of neuro-
epithelial cells forming the terminations
of the organs of general and special
sensibility in the mollusk. Intermingled
with them are the outlets of numerous
unicellular glands which secrete the more
or less viscous mucosity which renders the teguments supple and moist.

The body of the animal may be conveniently divided for study
into four chief areas or regions, viz. : — The Cephalic, the Pedal, the
Pallial, and the Visceral.

The Cephalic or Oral region is the anterior portion of the body,
and bears the mouth or oral aperture and most of the organs of
special sensibility, with appendages of various kinds.

The Pedal or Ventral region is typically a well developed abdominal
protuberance of variable shape, formed by a differentiation and
thickening of the cutaneous and muscular tissue of that region, and
constitutes the locomotor organ or foot. It varies in structure, size
and importance in correlation with the active or sedentary habits of
the animal.

The Pallial or Dorsal region is formed by a vascular expansion
or duplication of the integument, called the mantle or shield, which
partially or completely covers the more delicate parts or organs and
hangs down around the body, the intervening space or cavity between
the mantle and the body being kmown as the pallial chamber.

Fig. 290. — Neuro-epithelial cell of
Avion ater, highly magnified (after
Boll).

136 ANIMAL — INTERNAL ORGANIZATION.

and primitively ami usually contains the respiratory organs, and the
various organic apertures, its thickened glandular margin secreting
the calcareous and chitinous deposits forming the shell, although the
shell-secreting function is not confined to this part, as the M'hole
surface of the mantle is directly concerned in the formation of the
internal calcareous layers of the shell, the animal being attached
thereto hy powerful muscular hands, which are symmetrically paired
or unicpie according to the group : and finally

The Body or Visceral region, which is generally developed in a
more or less protuberant form and placed above the foot and partially
or comiiletely covered or enclosed hy the i)allium. It contains the
organs of reproduction, the heart or motive centre of the vascular sys-
tem, the alimentary canal, and various secretory and excretory organs.

Internally the general unity and agreement of the jdan of

organization, though it may have become more or less obscured hy

later develupments and modihcations, is much more evident.

Beneath the eiiithelium, the name given to tissue covering a free
.space, connective tissue of mesodermic origin is found, comjmsed

chiefly of vesicular and 2)lasm cells,
so closely interwoven with the
subcutaneous musculature as to
form a kind of dermo- muscular
tube, to which greater firmness and

rigidify is somefinies imparted by

numerous calcareous concretions,
produced hy, aud lodged within,
its ve.sicular cellules. This inter-
laced subcutaneous stratum, some-
times called the corium, at times
attains a great development, and
gives rise to outgrowths of various
kinds, which are liable to undergo
concrescence or fusion amongst themselves, or with other organs of
the body. The coelomic cavity contains the various organs of the
body ami a great develoi)ment of connective tissue, which is i)er-
meated in all directions hy numerous lueniatocades or hlood-siiaces,
the distension of which hy the circulatory fluid is the cause of the
turgescence or enlargement of the different organs. This tissue
originates in the form of polyhedral nucleated cells of homogeneous

Fig. 21H. -Typical Connective Tissue, rich in
plasm cells and shouin.;? interlacing fihrillar
bundles and small blood lacunai, from IJclix
nciuoralis^ highly magnified (after Brock).

ANIMAL — NERVOUS SYSTEM.

137

protoplasm, which with age acquire a fusiform, stellate or rounded
form, but vary in aspect in the different regions of the body, and
may become firmer, more compact
and rigid, and constitute skeletal
tissue, which suiTounds or is dis-
tributed amongst the muscular and
epithelial tissues, imparting con-
sistency and strength, and con-
stituting the supporting fi’amework
of the various organs.

The organs of the body may he
broadly classified according to their
function and structure under six chief heads or systems, viz. : — The
Xervous or Sensitive, the Alimentary or X'utritive, the Circulatory or
Vascular, the Secretory or Glandular, the IMuscular or ]\lotor, and
the Sexual or Reproductive systems.

The Xervous system, upon which all perceptive sensation depends,
is concentrated in paired ganglionic masses in correlation with the
bilateral aiTangement of many of the organs of the body, and may be
considered to be composed typically of four gvoups of more or less
distinctly paired neiwous masses or ganglia, viz. The Cerebral, the
Pedal, the Visceral or Parieto-splanchnic, and the Buccal or Stomato-
gastric. The Cerebral ganglia, which are placed above the oesophagus
and innervate the head and its organs, are chiefly sensory in function ;
the Pedal, which are suboesophageal in position and innervate the foot,
are more especially motor ; while the Parieto-splanchnic and the
Stomato-gastric centres, which are also situate or connected beneath
the alimentary canal, and innervate the viscera, are to a certain extent
analogous in function with the sympathetic system in mammals.

These various ganglia or nerve centres are constituted by a sui)er-
hcial or external layer of ganglion cells, which, according to Solbrig,
have no proper membrane and are chiefly unipolar, with long, branching
fibrillar extensions or processes, whose aggregation forms the central
part or nucleus of each ganglion, and also pass into the nervous cords
by which the various ganglia are connected together. Great varia-
tion exists in the degvee of approximation of the different ganglionic
masses ; sometimes by specialization they become fused together
and form a nerve-ring around the oesophagus, while in other groups
the constituent ganglia may he variously combined together or widely

Fig. 292.— Chitinous and 'connective tissue
framework of the outer ctenidium Anodonta
anatina, as e.vample of skeletal tissue, w.
transverse muscular fibres (after Vogt and
Vung).

ANIMAL — ALIMENTARY SYSTEM.

las

separated and distant. Tlie ner\'es arising from these various centres
innervate all parts of the body and take on detinite duties or functions ;

those proceeding to the muscles
are chietly efferent or motor, while
those terminating in sensory organs,
whether merely tactile or of a more
s])ecialized character, are termed
afferent or sensory.

The various organs of special
sense are nervous differentiations
ada})ted to the various forms of
percei)tion suitable to the environ-
ment and habits of the organism,
hut the whole surface of the body is more or less acutely sensible to
tactile and other imi)ressions, although perception is more especially
concentrated in the exposed and prominent i)ortions of the body.
The Auditory or Equilibrating organs are present in the active forms
and are alwaj's buried in the tissues of the foot, though innervated
by the cephalic ganglia, and consist of a pair of closed sacs, termed
otocysts, lined with ciliated sensorial ei)ithelium and enclo.sing cal-
careous concretions. The Cephalic E3'es are jiigmented invaginations
of the integument, usually closed by a layer of epithelium and con-
taining a ciystalline lens, and receiving their innervation from the
cephalic ganglia. The skin generally is howevei' dermatoptic and in
a measure sensible to the iiiHuence of light and shade. The Olfactory
organs are api)arently intlueneed in their i)Osition by the character of
the respiratory organs, as they may be located in the cephalic or in
the pallial region, or he recognizably present in both areas ; they are
formed by the development and local concentration of neuro-epithelial
cells, and according to their i»allial or cei)halic i)Osition may he in-
nervated by the visceral or h}" the sui)ra-oesophageal ganglia.

The Alimentary system by which nutrition is effected is a more
or less complicated and diversitied tube, composed chiefly of epithelial
tissue, and embraces an anterior apertiire or month, guarded by
external lobes or palps, which leads by the a’SOi)hagus into a stomach
or crop, into or near to which the usually voluminous liver or digestive
gland discharges its secretion Ijy suitalde ducts. Occasionally the
stomach has a c;ecal diverticulum, within which, or in the intestine
itself, there is a rod of gelatinous consistency, the Crystalline Style,

Fig. 293. Fig. 291. Fig. 295.

Ganglion cells of I'nio pktoruw^ highly
magnified (after Rawitz). Fig. 203 from
cerebral ganglion ; Fig. 204 from visceral
ganglion ; Fig. 205 from pedal ganglion.

ANIMAL — CIRCULATORY SYSTEM.

189

which is considered to be a secretion of the epithelinin of the intes-
tinal tract. The intestines are always considerably longer than the
body cavity containing them, and are therefore necessarily thrown
into a number of coils or convolutions, chietly amongst the lobules ot
the liver, the absorjitive surface being often greatly increased by a
longitudinal infolding of its surface, called the typhlosole.

The Circulatory system occupies the closed space or cavity

between the alimentary canal
and the external integument,
and is formed by definite vessels
in conjunction with a complex

Fig. 296. — A fragment of subfilamentar lacunar
or primitive mesohlastic tissue in Anodotita^
showing the trabeculcc and their nuclei (after
Holman Peck), cor. amceboid blood corpuscle,
ep. epithelium, nc. nucleus surrounded bygranular
protoplasm, tr. trabecula showing peripheral e.\-
pansion.

system of irregular spaces or
lacuna, which permeate among.st
the various organs and within
the interspaces excavated among
the viscera, the muscular and
connective tissue.

A dorsally placed heart or
central motor of circulation is always ju esent enclosed within a special
chamber or pericardium, and is always arterial or systemic, the
auricles receiving oxygenated
blood from the respiratory
organs and propelling it by
means of a muscular ventricle
through the body system.

The blood or Inemolymph,
which forms a large proportion
of the total weight of the body,
is usually a colourless or slightly
opalescent albuminous fluid,
containing numerous nucleated amoeboid corpuscles, which are shed
from the walls of the coelomic space.

By far the gTeater number of mollusca in general respire by means
of branchial or gills, and a few like Planorhis combine branchial and
pulmonary respiration, but species with solely aerial respiration are
confined to the Gastropoda. Respiration, however, is not confined to
special organs, but is participated in by the general integument and
more especially by the surface of the mantle, which is of a very
vascular character.

Fig. 297. — Ama;boid blood corpuscles of
Helix poinatia^ highly magnified (after Vogt
and Yung).

140

ANIMAL — GLANDULAII AND MUSCULAR SYSTEMS.

Fig. ‘298. — IClcmenis of liver or iligeslive gl;uid of Ifrii.v
poviatia^ showing its coniple.v structure, highly niagnificil
(after Vogt and ^'ung). ch. c. lime cells ; c. ft. cell
nuclei ; fat globules ; ,/<•/-. c. ferment cells ; granular
substance; iiz'.c. liver cells ; 7\ vacuolated ferment cells.

Tlie Glandular or Secretory system is a yeiy important one, not
only for preserving tlie external integnment in a moist and snpple
condition by a plentifnl secretion of nincns from tlie innnmerable
nnicellnlar goblet-sliaped glands scattered beneath and amongst the
epithelium, but for the elaboration of tbe various ferments and

secretions necessary for
digestion and for the
separation and elimina-
tion of noxious substances
from tbe body. 'J'he Liver
or Digestive Gland is one
of the largest and most
important organs of the
body, and has jirobably a
com})lex function, serving
not only as a store-
house for combustible fatty carbohydrates and a centre for secreting
digestive ferments, but also contains numerous lime-secreting cells,
whose jiroducts are said to be utilized iu the formation of the shell
and epijihragm. The Renal organs or Nejihridia, which are in close
association and connection with the iiericardium, are very glandular
in structure, and secrete or eliminate from the blood the waste jiro-
ducts of the body iu the form of urea or uric acid. The Pericardial
Gland is also an e.xcretory organ eliminating a still more acrid secretion,
and, like tbe renal organs, is richly irrigated by the blood system,
which circulates within tbe organ before entering the auricle.

Calcareous, Cbitinous, and Pigmentary subepithelial cells of con-
nective tissue are also })laced in different i)arts of the body, but are
more especially congregated at the tliickened edge of the mantle,
where they contribute to the formation and colouring of the shell.

The iMuscuLAR system is iuHnenced greatly in its character and
degree of develoiiment liy the presence or absence of an e.xternal
shell ; its tissue is generally formed by
smooth, cellular and unstriated band-like
iiljres, but those muscles callable of raiud
contraction afford indications of their
greater differentiation by displaying a
deceptive appearance of striation sometimes arising from transverse
rows of granules iierpendicnlar to the axis of the hbre. The muscular

Fig. 200. — Unstriated muscle-ribre
from foot of AU’ritina Jlni'iatiUsy
liighly magnified (after Boll).

ANIMAL — REPRODUCTIVE SYSTEM.

141

system is develoiied in two chief layers : the Somatic and the
Splanclinic, which are separated hy the coelomic or hlood space, and
are therefore practically independent muscnlar tubes, the somatic

layer forming the external tube
or body wall, and the splanchnic
the internal tube or alimentary
layer. The somatic, which is
subjacent to, or beneath the

Fig. 300. — Pseudo-striate muscle fibre from
buccal bulb of Neritina Jlu7'iatilis, highly
magnified (after Boll).

external epithelium and more or less interlaced noth the connective
tissue, is usualty the most developed, and, in addition to the
transverse or annular fibres, has more deeply seated longitudinal ones,
while radiate and oblitiue fibres are also present. The splanchnic layer
which chiefly surrounds the alimentary canal is more delicate, hut
exhibits the same arrangement of annular and longitudinal muscular
bundles as the somatic layer.

This muscular tissue may become of a firmer and denser texture
and show fibrous, membranous, or carfilaginous structure, and form
the powerful muscular bauds by which the animals are attached to
and withdrawn within their protecting shell.

Reproduction in mollusca is not accomplished by any of the
asexual methods which sometimes obtain in other lowly organized
animals, but is always the result of the complete activity of both the
male and female organs. The gonads or genital glands are usually
more or less imbedded within the liver or digestive gland, the sexual
elements, the spermatozoon and the ovum, being developed from the
epithelial walls of the constituent ca?ca.

The generative organs are developed in two chief tyjies — the
Dioecious or bisexual and the Monoecious or hermaphrodite type —
the dioecious type having the two sexes in different individuals and
often exhibiting a noticeable sexual dimorphism in shell and animal,
while in the monoecious or hermaphrodite type both sexes are
combined in the same animal by a superposition of the male upon the
female system. The prevalence of Proterandry or matiu’ation of
the male element before that of the female tends to prevent the
possibility of self-fertilization, which, however, has occasionally been
known to occur.

The reproductive system in mollusca is typically and primitively
dioecious, which is a simpler arrangement than the monoecious or
hermaphrodite condition, which usually exhibits several specialized

ANIJIAL — HYPOTHETICAL PRIMITIVE TYPE.

U2

accessoiT organs, and is a later and more complex development,
apparently intlnenced by the adoption of terrestrial or flnviatile life,
parasitism, tixed habits, etc.

The Hypothetical Primitive mollusk, from which all the varied
forms now existing have been derived, has been assumed, with great
probability, to have been a bilaterally symmetrical animal, which
possessed in addition to other general characters a well marked

locomotor foot or muscnlar creeping
disc and a more or less well-defined
head, bearing a ventral month and
])aired tactile processes or tentacles,
at the base of which were probably
pigmented eye spots. Dorsally the
animal was overspread by a fold of
the integument, called the mantle,
which hnng loose at the margins
around the body, forming a space or cavity between its free pendnlons
margin and the body-wall- the pallial cavity, within which were the
paired feather-like gills and the excretory outlets. This integnment
had the physiological jiower of secreting a more or less calcareous
shell, with a chitinons frameivork to which the retractor muscles of
the body were tirmly attacheil.

The nervons system exhibited the archaic character of long paired
nerve cords, with ganglionic enlargements on each side of the median
line, arising from the paired snpra-msoijhageal ganglia and connected
together beneath the alimentary canal or digestive tract, upon the
course of which various ferment glands are developed. The auditory
capsules or otocysts are i)laced in the anterior part of the foot, but
innervated by the cephalic ganglia. d'he olfactory organs are sensi-
ferous areas near the base of each branchia, which receive their nerve
su])ply from the ])allial ganglia. The gonads or genital glands are
])resent as dependencies of the iiericardial chamber, their i)roducts
reaching the exterior by the reno-pericardial orifices.

The circulatory organs were confined within the secondary cadomic
cavity or i)ericardium, the heart however being probably i)riniitively
doulde, as suggested by Dali for the Protopelecyjiod, with a ventricle
and an auricle on each side, the ventricles eventually fusing in the
meilian line and, in some groups, enclosing the rectum,

Fig. 301. — Hypothetical Primitive Mollusk,
showing e.xtenialiy the dorsal shell, paired
tentacles and over-hanging mantle margin
and internally the alimentary canal, heart,
branchia and genital glands, with longitudinal
untwisted nerve cords and ganglionic en-
largements (after Pel.seneer).

GASTROPODA — STREPTONEURA AND EUTHYNEDRA.

143

From this archetypal form our various species have been evolved in
the two well-marked divergent lines, Gastropoda and Pelecypoda,
characterized by and receiving their names from the modifications
the foot has undergone.

The Gastropoda, pursuing an active and more or less aggressive
mode of existence, have developed the most varied and numerous
forms and are the only group of mollusks containing species organized
for the respiration of free air ; they have also retained and variously
developed the sole-shaped locomotor foot and the distinct head of

Fig. 302.

Fig. 303.

Fig. 302. — Schematic figure showing the arrangement of the internal organs in Helix aspersa ns
typifying the Euthyneura. ^ Fig. 303. — Schematic figure showing the arrangement of the internal
organs in the Azygobranchiate Streptoneiira (after Lang).

a.g. abdominal ganglion ; b.g-. buccal ganglia ; c.£^. cerebral ganglia ; p.g-. pedal ganglia : pLg.
pleural ganglia ; p.v.g. pallio-visceral ganglia, representing the long twisted nerve cords and
ganglia of the Streptoncures ; sb.^. subintestinal ganglion ; sp.g. supraintestinal ganglion ; e. eye ;
os. osphradium ; a. anus ; oe, oesophagus ; k. kidney or nephridium ; r. rectum \g.o. genital orifice ;
p. male organ ; s.f. seminal furrow ; br. branchia ; pc. pericardium, enclosing the heart ; s. siphon ;
r.c. lung chamber, showing blood plexus \f. foot ; hyp.gl. hypobranchial gland ; op. operculum.

their assumed ancestor, and acquired or elaborated a very remark-
able prehensile and aggressive oral mechanism adapted for the seizure
and comminution of food, but owing to the une({ual pressure or strain
upon the body, caused by the development of an univalve shell, they
have lost the bilateral arrangement of many of their internal organs.

The various species have not however developed pari pasim, and
in accordance with the differences now exhibited are distinguished as
Streptoneiira and Euthyneura, the former characterized by the per-

144

HELIX — EXTERNAL FEATURES.

sistence of tlie tor.-iioii of the visceral commissures, and secondarily
by the less coniiilete degeneration in the group generall)" of the
primitively left organs of the pallia! complex ; and the Euthyneures,
which have untwisted nerve cords and a greater concentration of the
visceral nerve centres, with a more complete atrophy of the organs of
the originally left side, perhaps due to the partial detorsion which the
visceral sac has probably undergone.

Helix aspersa or //. pomut'Kt, which may he accepted as repre-
sentative of the Gastropoda, has a bilaterally symmetrical external
aspect, with a compact hut elongate body, covered with an external
cuticle composed of distinctly nucleated epithelial cells, distinctly
ciliated on certain portions of the body, and usually more or
less darkly pigmented and tuherculate, hut most strongly so in the
anterior and dorsal regions, the pigmentation and rugin becoming less
])ronounced and striking as the foot or the mantle are api)roached.

Fig. 301. — Helix nsf>ersa Mull.,

Kettering, Northamptonshire, collected by Mr. C. E. Wright,

Showing the arr.ingenient of the tentacles and labial lobes, the genital furrow, the foot margin,
the right and left lobes of the mantle separated by the partially expanded respiratory orifice, and
the approximate position of the termination of the alimentary canal.

Jldlr ((•<iier!<ii has a well develojR'd, distinct and hluntly roundeil head
])laced at the anterior end of a narrow, oblong body, and covered
with rounded and separate tubercles which show no trace of the
symmetrical surface canals or facial grooves ; there are four elongate,
retractile, divergent and finely granulated tentacles, the upper or
posterior ])air hearing the eyes at their summits, and being about four
times the length of the lower or anterior i)air. In other groups there
may, however, he two tentacles only, hearing the eyes either at the
ai)ex or at the base according to the genus. The elongate body is
covered externally by numerous tubercles or rugosities forming
about sixteen more or less ol)liipiely disposed longitudinal rows
at each side of the noticealdy ])aler and more elongate row of
mid-dorsal tuhei’cles which separate the two dorsal grooves or
furrows : the ill-defined lateral or genital groove extends on the

HELIX — EXTERNAL FEATURES.

145

right side from the genital orifice to the neighbourhood of the respira-
toiy opening, the corresponding gTOOve at the left side occupying a
similar position — these are erroneously termed the Facial Grooves by
Pilsbry. The colouring of the body is usually blackish grey on the upper
anterior surface, but becomes whitish with ill-defined tubercles as the
mantle is approached ; there is also a paler area below the lateral
groove, and the spreading sides of the foot or pleuropodia assume a
j^ellowish aspect from the abundance of minute lime cells covering
the tips of the tubercles in that region.

The ventral part, of the body is formed by the foot or locomotor plane,
a large and muscular expansion of an elongate shape, but roundetl
in front and terminating behind, in a bluntly pointed tail ; its upper
surface is somewhat spread out or flattened at the sides and defined
by a I’ather iiregular longitudinal groove, wliich is connected with
the grooves or furrows separating and forming the rugosities of tlie
body and from which about twenty-five chief fiuTOws descend more or
less perpendicularly to the sole at somewhat irregular intervals, the
interspaces being filled by flattish and irregularly shaped tul)ercles.

The mantle or pallium fits in a cap-like form upon the spirally coiled
and protuberant visceral sac, on the back of the animal ; it is of a dark
translucent grey colour, besprinkled with yellowish specks, probably
lime cells, and is formed by a
thin and transparent fold of the
integument, which becomes
thicker and more exclusively
glandular at the free margin or
collar, which contains the
principal shell - secreting cells
and exhibits, a colouring" corres-
ponding somewhat to the markings of the shell ; it is fused to the neck
of the animal and encloses anteriorly a spacious respiratory cavity,
the roof of which is covered with an intricate plexus of blood vessels
containing the blood undergoing oxygenation on its way to the auricle ;
a contraetile aperture for respiratory purposes, subjacent to a distinct
yellowish patch formed by thickly clustered lime cells, is situate on
the right side of the body and contains posteriorly within its margins
the outlets of the alimentary and renal organs, and also divides the
mantle into a left or anterior lobe and a right or posterior one. The

Fig. 305. “Schematic section of Flelix^ showing
position of respiratory cavity, etc. b.c. body or
visceral cavity ; c. collar of mantle ; >\c. respira-
tory cavity (after Binney).

K

HELIX — INTERNAL ORGANIZATION.

UG

hinder pallia! maro'in develops the cohuuellar lobule, a special jirocess
which forms the retlection coverini’' the umbilicus of the shell.

The Visceral or body region is developed dorsally to the foot and
abruptly protruded from its upper surface as a spirally twisted and
tapering sac, enclosed bj" the mantle and covered by a shell of similar
shape : it contains the hulk of the viscera of the animal and the repro-
ductive glands : the length or number of whorls of the sac in the
different species, corresponding to the obesity or slenderness of the
visceral mass.

Internally, although the primitively .symmetrical organization
has been more or less destroyed by the twisting or torsion the body
has undergone, j'et the organs may still be grouped under the
six heads proi)nsed for the classitication of the organs in mollusca
generally, viz. : Tlie Ner\'ons, the Alimentary, the Vascular, the
(Tlaudular, the [Muscular, aud the Reproductive systems. The

Fig. 30G. — Helix asf>ersa dissected from right side with liody wall and a portion of the genitalia
removed to show the relative po.sitions of some of the chief organs of the body. The kidney, the
ureter, and the pulmonary chamber opened and turned back (after Howes).

rt. auricle and v. ventricle of the heart; n.n. anterior aorta; alh.^l. albumen gland; a.7>.
afferent pulmonary veins; r..^. cerebral ganglia; cr. crop; c.r. columcllar retractor; f. foot;
h.ii. hermaphrodite duct; hermaphrodite gland; /•. kidney; cn'. ovispermatoduct ;

posterior aorta ; p.h. pharyngeal or buccal bulb ; pharyngeal retractor ; r. rectum ; s.g. salivary
glands ; sp. spermatheca ; u. ureter.

general and relative arrangement of the chief organs in our type does
not materially differ from that of onr other momecions monotremate
gastropods. The res])iratory organs are anteriorly ])laced, with the
external oritice at the right side of the body, the heart, within its
])ericaT’dial chamlier, being always in close connection with them and
normally situate towards the left side, the renal organ being in close

HELIX — NERVOUS SYSTEM.

147

proximity and actual connection with the pericardium by the ciliated
reno-pericardial funnel. The alimentary canal, with its enlarged food
receptacles, is convoluted chiefly amongst the lobes of the voluminous
liver, which occupies most of the upper whorls of the shell, and in

aa pg.

Fig. 307. — Slightly oblique transverse section in front of the columella of Helix aspct-sn, to
how the arrangement of the internal organs X 2 (after Howes).

a. a. anterior aorta ; alb.g. albumen gland ; cr. crop ; c.r. columellar retractor ; h.d. hermaphrodite
duct; h.g. hermaphrodite gland ; i. intestine; l.l. anterior lobe of liver; is, lateral pedal blood
sinus: ovispermatoducL ; pedal gland ; /.r. penis retractor ; p.v. pulmonary vessels;

r. rectum ; r,c. respiratory cavity; r.L posterior lobe of liver ; s.g. salivary glands ; sp.d. sperma-
theca duct ; st. stomach ; u. ureter ; v.s. visceral hlood sinus.

which are also imbedded the gonads or germinal glands ; the other
or accessory organs of the reproductive system are usually of a very
noticeable size and have the external aperture for their functional
exercise at the right side of the neck.

The Nervous system of Helix asperm is of a highly specialized
character, consisting of several more or less distinctly paired supra-
and sub-cesophageal ganglionic masses, which are concentrated around
the anterior end of the oesophagus and more or less completely fused
together to form the nerve collar, the component ganglia of which
are better studied in immature animals, as in adults they become more
welded together and less clearly distinguishable. The supra-oeso-
phageal mass is formed solely by the cerebral ganglia and the sul)-
msophageal by the buccal, the pedal, and the aggregated visceral
ganglia ; from these conjoined centres, which are all enclosed or
buried amidst a layer or sheath of connective tissue, nerves are
distributed to all pai'ts of the body.

The supra-fTeso])hageal or cerebral ganglia, the chief seat of the
sensory functions, are dorsally placed, a broad transverse commissural

HELIX — NERVOUS SYSTEM.

I ts

band connecting its coinponcnt parts above tbe a\sop]iagus anteriorly.
They give nerves to tlie liead and the neiglibonring organs, large nerves
arising from their perij)hery which proceed to the onnnatophores and
the lips, the lower tentacles being innervated chiefly by a branch from
the labial nerve ; the reproductive organs are also innervated by a
ner\'e emanating frnm the right side. From them also originate the

three pairs of connectives
which are the bonds of con-
nection between the various
groups of ganglia and form
the three more or less closely
approximate nerve collars
surrounding the msophagus,
the most anterior being formed
by the nnion of the cerebral
and buccal ganglia, the pos-
terior one by the cerebral
and the aggregated visc'eral
ganglia, ami the peilal and
cerebral centres uniting to
form the central collar. 'Phe
lesophagus, salivary ducts,
and i)haryngeal retractors
l)ass between the cerebral and
the visceral ganglia and the
anterior aorta between the
visceral and the i)edal centres.
The pedal ganglia are formed
by a itair of closely ai)posed
medullary masses united to-
gether by a broad commissure
and connected with the cerebral and aggregated visceral ganglia by
two i)airs of connectives. The i)edal ganglia are placed beneath the
(esophagus and above the foot, and constitute in part the sub-
(esophageal ganglionic mass, distriluiting nerve fibres ventrally to the
locomotor foot and pedal gland and laterally to the neighbouring
body wall.

The visceral or i)arieto-splanchnic ganglia are formed by five more
or less distinctly defined constituents, partially fused when young, but

Fig. 30S. — Helix aspersa dissected from above to
show the j^eneral arrangement of the nervous system
and cephalic retractors. 'I’he liody lias been opened
to right of the renal organ, the tenl.acles laid open,
and the crop, buccal retractor and genitalia mainly
removed, but cut ends shown (after Howes).

a. auricle and v. ventricle of the heart ; a. a. anterior
aorta ; buccal ganglia ; />.r. buccal retractor ; c.g.
cerebral ganglia ; c>\ crop ; c.r. columellar retractor ;

eye: k. kidney or nephridium ; )ii. mantle; o. om-
aiatophor ; pg, pedal ganglia ; p,o. pulmonary orifice ;
p.s. penis sheath ; r. rectum ; s.d. salivary duct ;
/. anterior tentacle; t.r. tentacular retractors;
u. ureter ; 7'. vagina; 7'.^’’. visceral ganglia.

HELIX — NERVOUS SYSTEM.

149

more completely so in adults ; the anterior pair, known as the pleural
ganglia, are joined by connectives with the cerebral ganglia, but are
in actual contact with the pedal centres and with each other ; the
pallial, known also as the visceral or intestinal ganglia, are placed
more posteriorly and intimately fused with each other and to the
more anterior pleural ganglia of their respective sides ; the termina-
tion of the visceral loop is formed by an abdominal ganglion, which
is closely adherent to and between
the right and left pallial ganglia. This
gTOup of ganglia innervates the body
wall, three sets of nerves being given off
fi-om the right and two from the left side
for this puiiiose, which enter the tissues
at the base of the visceral sac ; the re-
productive glands are innervated by a
strong nerve from the abdominal ganglion
which accompanies the posterior aorta
and sends a branch to the heart; many
fibres also enter and anastomose within
the glandular mantle margin and in-
nervate the mantle and its organs, and
the viscera generally receive their nerve
supply troni this centre, which fulbls the
role of a sympathetic system, regulating
the involuntary motions of the alimentaiy
and other organs.

The buccal or stomato-gastric ganglia
are small but distinct reniform nervous
masses which do not fuse together as do
the various other ganglia ; they are placed
at the sides of the buccal cavity, near
the outlets of the salivaiy ducts ; con-
nected by a delicate commissure passing beneath the oesophagus and
joined by pigmented connectives to the under surface of the cerebral
ganglia, they give off nerves to the mouth, the oesophagus and stomach.

The buccal mass has play backwards and forwards through the
cerebro-visceral nerve-ring, involving the buccal ganglia in its move-
ments, so that they may be in front or behind the cerebral ganglia,
according to the state of retraction or jirotrusion of the buccal bulb.

F'ig. 309. — Nerve centres from a
half-grown Helix asj>€rsa, to illus-
trate the relative positions of the
various ganglia and the origin and
distribution of the chief nerves,
highly magnified.

a. abdominal ganglion ; y.b. and
Lb. right and left buccal ganglia ;
r.c. and l.c. right and left cerebral
ganglia ; r,p. and l.p. right and left
pedal ganglia ; 7\pl. and LpL right and
left pleural ganglia ; r.v. and l.v. right
and left visceral or pallial ganglia;
c-b.c. cerebro • buccal connective;
c-p.c. cerebro - pedal connective ;
c-pl. c. cerebro-pleural connective ;
c.c. cerebral commissure ; a.p. an-
terior pedal nerve ; g. nerve to
ovotestis, with h. branch to heart ;
/. nerves to lips ; m. to anterior and
jn to posterior portion of mantle ;
o. to ommatophore ; cc. to cesophagus
and stomach ; /. to penis or male
organ ; ph. to pharynx ; p.p. to
posterior part of foot ; s.d. to salivary
ducts ; t. to lower tentacle and Ups.

l.jo HELIX — OLl-ACTORV AXl) Vli^l’AL ORGANS.

The general sensil)ility has its seat in the whole external integn-
nient, over which tine setitbrin nenru-ei)ithelial cells are profusely
distributed, whose irritability renders the surface excessively sensitive
to tactile inii)ressi(nis and i)robal)ly also to other intluences ; its
special develojunents are however more particularly localized in the
anterior region of the body and on its exsertile appendages.

The Olfactory sense is perhaps the most important faculty possessed
by the mollusca and is functionally operative and efficient at com-
paratively great distances ; it is exercised
by the olfactory organs or rhinophores,
situate at the distal extremity of the dorsal
or posterior tentacles, and innervated from
the cerebral ganglia, the nerve from which
ex])ands on its course within each tentacle
to foi’iu a large olfactory ganglion from
which arise the numerous nerve ramitica-
tions terminating in the layer of epithelial
olfactive cellules congregated together on
the somewhat more elevated epithelium
spread over the apical surface of the dorsal
tentacles. It is probable, however, that the
lower or anterior tentacles, which are well
and similarly innervated, aid in the exercise of the olfactory sense
in addition to their tactile function.

The Eves are two in number and ohli(|uely
placed at the tijts of the ilorsal tentacles,
hence called ommatoi>hores or eye-hearers ;
they are coiistituteil by a retina which arises
i’roin an invagination of the tegumentary
ei)ithelium and which contains .sensorial and
pigmented rods, arranged j)er])endicnlaily
to the optic axis of the eye ; the oval
crystalline lens is a cuticular formation
derived from the retinal epithelium and
does not entirely till the optic cavity, hut
is enclosed by a less dense cuticular sub-
stance, termed the vitreous body or humour.

The optic nerve springs from the cerebral
ganglion and reaches the oi)tic bulb in the rear, forming an enlarge-

opn.

Fk;. 311. — Eye nf Ucli.x
poniatiay highly magnified (after
Simroih).

r. inner cornea ; cii. cutis : cJ.
crystalline lens; <’/. epilhelium,
becoming thin and transparent
and forming the outer cornea ;
o.ju. outer membrane or sclera;
op.n. optic nerve ; ret. retina ;
t.n. tentacular nerve.

Fit;. 310. — Rhinophore of
fleli.v pomatia^ highly magni-
fied (after Flemming).

e. eye ; g.c. ganglion cells ;
g^.s. ganglionic layer ; ol.ep. olfac-
tory epithelial cellules ; ol.^.

olfactory ganglion; op.n. optic
nerve; pigment cells; r.

eye retractor ; i.r. tentacular
retractor.

HELIX — AUHITOliY AND GUSTATURY ORGANS. I o I

nieiit or ganglion before piercing the enclosing outer coat or sclera
and spreading out beneath the retina, not penetrating through and
overlaying the I’etinal rods, as in the vertebrates and in the pallial eyes
(jf the opisthobranchs.

The Auditory or E({uilibrating organs, known as the otocysts,
consist of a pair of convex and prominent vesicles, ivith a thin, colour-
less and transparent investment,
lined internally with sensorial and
ciliated epithelium, and containing,
suspended in the fluid contents,
numerous calcareous concretions or
otoconia of variable sizes, of which
1 20 have been counted in the upper
layers, within a single capsule,
though many were overlaid and
concealed and therefore uncounted.

The otoconia are oval and trans-
parent, with elongate nuclei, and
vary in number according to age,
being proportionately fewer in im-
mature animals ; they are always
in a state of inces.sant oscillation,
owing to the activity of the ciliated investment of the interior of the
sac, although they remain persistently aggregated towards its centre,
leaving a distinct space between the mass of otoconia and the walls
of the capsule. The otocysts are placed
upon the nnder-side of the pedal ganglia,
at or near the posterior outer corners, though
receiving their innervation from the cerebral
centre, the auditory nerve running from
the cerebral ganglia between the cerebro-
pedal and cerebro-visceral connectives to
the otocyst of their respective sides. The
otocysts, in addition to the auditory func-
tion they are assumed to possess, are
probably important aids in determining the
orientation of the body during locomotion.

The sense of Taste is considered by Simroth to be diffused over
the surface of the body, but to be specially localized in the terrestrial

Fig. 313. — Underside of sub-
oesophageal ganglia of Helix
aspersa, showing otocysts zfi
highly magnified.
a, abdominal ganglion : c-p.c.
cerebrO-pedal connective; c-pl.c.
cerebro-pleural connective ; <?/.
otocysts ; r.p. and l.p. right and
left pedal ganglia ; r.pl. and
l.pL right and left pleural gang-
lia ; r.zK and l.v. right and left
visceral ganglia.

nc,

F IG. 312. -Otocyst of Helix poniatia^ slightly
compressed, showing the internal ciliated
tract, etc., highly magnified (after Leydig).

azid. 71. auditory nerve ; c. cuticle ; cp. epi-
thelial layer ; muscular layer ; nc. epithelial
cells with large fusiform nuclei ; ot. otoconia.

152

HELIX — ALIMENTARY SYSTEM.

piilmonates in the aiiterioi- part of the buccal cavity, thong, h the oral
lobes at the sides ami aliove the mouth, which are furnished with
ganglia and innervated from the anterior tentacular nerve, have also
been assumed to be gnstatoiy in function.

The ^Vllment.iry system in fleliv dxpersn is formed by a muscular
buccal cavity or pharynx, opening externally by a mouth or oral aper-
ture, bounded by soft fleshy circular lips, and i)rovided with a hard,
dark brown, chitiiioiis n])per jaw, strongly convex anteriorly and
broadly crescentic in shape, with attenuate and rounded ends, and a

variable number of prominent vertical
ribs or folds strongly denticulating
both ujjper and lower 'margins, and
also sliowing perceptible longitudinal
striation or lines of increase. There
is also a i)eciiliar and somewhat pre-
hensile aj)paratus of an oblong shape, termed the odontophore or
radnla, which is attached like a tongue to the floor of the mouth, but
supi)ortcd and elevated in the centre by the gristly odontophoral
cartilage, and armed with innumerable and characteristically formed
lecurved denticles arranged iii regularly curved transverse and
straight longitudinal rows or series, the sjiecinieu figured having a
transver.se formula of -Ih-l- i;! at its widest part.

The central tooth is always symmetrically formed with elongate
basal attachment; the free upper margin is Irroadly reflected with a
stout median cutting i)oint or mesocoiie and a small lateral ectocone

Fui. i)ll. — Maiuliltlc or Jaw of an
llt'ii.v X 8, from Chrislchurch.

Hams.

Kk;. 315. — I lalf a transverse row of ilie lin.cual teeth of an atUili ifelix as/>crsa, cullectctl hy Dr.
h'cliarff near Dublin, showing the modifications in form from the symmetrical centre tooth to the
(juadricuspate marginals, from a higlily magnified photogruijh by Mr. 'J'. W. '1 liornton.

Showing the symmetrical median or central tooth, c. ; the first laterals to right and left of the
median tooth ; the 20ih and 23rd transverse rows iirustrating the transition teeth ; and the 31st,
3(>lh, list, and 13rd teeth of the marginal series.

at each side. 'I'he laterals are decidedly a, symmetrical, the inner
angle (jf basal attachment and the inner cutting 2»oint or endocone
gradually becoming deficient, but the outer cutting j)oint or ectocone
is gradually more largely develo2)ed, and eventually, as the marginals

HELIX — ALIMENTARY SYSTEM.

153

are approached, becomes veiy symmetrically bifid ; the mesocone also
gTadually becomes bifid, so that the denticles near the margins
present four strongly developed sub-equal denticulatious, ivitb a narrow
basal attachment; additional transverse rows are being constantly
added within the radular sac at the posterior end, to compensate for
the wearing away or loss of the functional portion anteriorly. The
movements of this important organ are controlled by numerous
extrinsic and intrinsic muscles.

The buccal cavity opens dorsally by a tbin-walled cesopbagus into
a large, fusiform and distensible crop, usually conspicuous by the yellow
colour of its contents and situate partly within the ultimate whorl of
the shell ; like the cesopbagus and other parts of the alimentary canal.

F IG. 316. — Alimentar>^ canal of Helix cispcrsa^ with appended glands, dissected out and seen from
right side. The generative, circulator^*, excretory*, and nervous systems removed and the buccal
cavity, stomach, bile ducts, intestinal canal, and pedal gland opened up (after Howes).

b.c. buccal cavity, showing radula, radular sac and jaw ; cr. crop ; f. foot ; h.g. hermaphrodite
gland or ovotestis ; l.l. anterior lobe of liver ; oesophagus ; p.g. pedal gland ; p.r, phar^'ngeal
or buccal retractor ; r. rectum ; r.i. posterior lobe of liver ; $.d. salivary duct ; s.g. salivary glands ;
st. stomach ; ty, typhlosole.

its lining membrane is tlu’own into a series of longitudinal folds
visible externally as longitudinal striatiou. ^Vdberent to its sides,
by fibres of connective tissue, are a pair of whitish lobulated organs,
the Salivaiy Glands, wbicb discharge their secretion, a soluble ferment
which converts starch into sugar, into each side of the buccal cavity
by means of two long and slender ducts. Beyond the crop the canal
again becomes nari’ow, but at the loop-like extremity of the first tract
(piickly expands to form the simple sacculated stomach, wbicb is
slightly constricted by a longitudinal fold, and its mucous membrane
also thrown into many longitudinal folds or ridges ; the cesopbagus
enters posteriorly near the external surface and between the right and

l.U HELIX — ALLMEXTAKV SYSTEM.

left lobes of the liver. The pyloric orifice lies beneath ami to the right
of the cardiac opening, the dncts of the liver or digestive gland
entering at different points.

The liver or digestive gland is the active organ of digestion and is
a. very large nnecj^nally bilobed gland of a reildish-brown colour,
composing a large part of the visceral hump and formed by a dense
aggregation of blind, branched tubules, lined by glandular epithelia.
The large anterior lobe is situate immediately behind' the mantle
cavity ami partially sub-divided into three subsidiary lobes whose
ducts unite before entering the stomach a little above the pylorus.
The small posterior lobe occupies the summit of the spire, opening
by a large duct near the top of the stomach almost ojiposite to the
entrance of the combined duct from the anterior lobe.

The organ is of very complicated function and structure (%ee p. 140,
f. 208), being formed of calcareous,
ferment, and hepatic or liver cells, with a
(luantity of fat globules interspersed; the
secretions of the ferment cells ai’e a
l)Owerful aid to the assimilation of the
ingested food, as they are not only
capable of digesting proteids but also
assist the salivary glands in the conver-
sion of starch to sugar. The calcareous
glands contain colourless granules of
carbonate or phosphate of lime, which are
assumed to be eventually utilized in the
formation of the shell or its ejiiphragm ;
the hepatic cells contain globules of a
spherical form, which excrete small
vesicles with yellowish contents.

After leaving the stomach, the intes
tinal canal keeps to the left side of the
body, and follows an S-shaped course,
imbedded within the tissues of the liver,
first in an upward and forward direction,
the second Hexure being held in position
anteriorly by the cephalic or anterior branch of tTie aorta; the third
flexure gradually approaches the right side of the body and occupies
a more dorsal position, skirting in its course the posterior margin of

Kig. 317. — Plan of the intestinal
convolutions in Helix aspersa^ also
showing how they are held in position
anteriorly by the anterior aorta, and
illustrating the relations of the heart
and nephridium.

a. auricle of the heart ; b. buccal
bulb ; k. kidney or nephridium ; p.v.
pulmonary vein ; r. rectum; sali-
vary glands and ducts overlying
crop ; st. stomach ; v. ventricle from
which arises the aorta.

HELIX — CIRCULATORY SYSTEM.

loo

the renal organ ; the hnal tract or rectum runs along the right margin
of the pulmonary cavity, beneath the ureter, and terminates at the
anus upon the posterior side of the respiratory orifice.

The Circulatory or Vascular system has for its centre and motor
the heart, which in Helix aspersa is, as in the Gastropoda generally,
divided into two chambers of approximately equal size, the auricle
and the ventricle ; the auricle has delicate walls and receives the
aerated blood by the pulmonary vein from the respiratory plexus and
passes it forward to the pyriform muscular ventricle, regurgitation
being prevented by a valvular arrangement at the junction of the
vessels. The heart is confined within a
thin-w'alled oval cavity or pericardium,
placed on the left posterior side of the roof
of the matitle chamber and in close and
actual connection with the renal organ by
the reno-pericardial funnel. The heart being
exclusively occupied in propelling the blood
through the system, is termed a systemic
heart. The ventricle transmits the oxy-
genated blood received from the auricle by
a single trunk or aorta, which bifurcates on entering the body cavity,
dividing into an anterior and a posterior trunk ; the anterior runs
parallel with the sacculated oviduct and along the right side of the
crop, passing beneath the intestinal tract and the spermatheca to the
right side of the body, giving branches to the salivary glands and the
anterior part of the foot ; it then passes through the nerve collar
between the pedal and aggregated visceral ganglia and is distributed
to the buccal mass and neighbouring parts.

The posterior aorta is at first associated with the intestinal tract
and maiidy supiilies the alimentary system and its dependent organs,
running (j^uite to the summit of the spire, contributing the blood
supply to both lobes of the liver, the gonads, etc., on its course.

These distinctly defined arterial vessels break up into more minute
vessels or empty themselves by funnel-shaped openings into irregular
blood spaces or lacunte amongst the connective tissue, which has hence
been termed lacunar tissue (see figs. 291 and 296). These smaller
blood spaces eventually unite with the large visceral sinus, which
runs from the top of the spire within the thickened upper edge of the
spirally-coiled visceral sac, or with one of the two large lateral sinuses

F(g. 318. — Heart of Helix
aspersay showing the connection
of auricle and venti4cle and in-
dication of walls of pericardium
(highly magnified).

a. auricle ; v, ventricle.

15G

HELIX — CIRCULATORY SYSTEM.

situate at the sides of the jieclal gland within the foot. The
lateral pedal sinuses are only indirectly, but the visceral sinus is
directly continnons with the great circular pulmonary sinus, which
surrounds the base of the pulmonary chamber, and adjoins the rectum,
Irom which it receives many small veins.

From the circular i)uhuonary sinus the blood is distributed upon
the sides and roof of the respiratory cavity, which is formed by a thin
fold of the mantle and bears within or on its surface, especially
anteriorly and along the right side, a very rich plexus of thin-walled
blood vessels, within which the blood becomes o.xygenated by exposure
to the air within the respiratory chamber.

Fig. 310. — Helix aspeesa from a dissection, after injection, to show the chief venous sinuses and
the respiratory and renal capillary systems. The pulmonary* sac is cut close along the rectum and
turned hack to show the whole pulmonary plexus at one view and the heart opened to show the
interior of the auricle and ventricle. The venous vessels are all darkly shaded (after Howes).

a.7'. aftereiu pulmonary' veins carrying the Mood for oxygenation to the pulmonary plexus from
the circular pallial sinus, c./.a*., which receives its supply chiefly from the visceral sinus, v.s.^ and
from the paired pedal sinuses, of which one is shown, ; ui. mantle margin; /.7a pulmonary
vein, whicli receives the arterialized blood from the re.spiratory plexus; r.p, renal capillary plexus.

Tlie alfcrent or iucuiiiing and the efferent or dei)artiug veins alter-
nate with great regularity and are in intimate connection by means of
a very comi)lex and intricate series of delicate vessels, the efferent
pulmonary vessels gradually uniting to form the great pulmonary vein,
a large venous trunk on the roof of the respiratory cavity, conveying
the arterialized blood direct to the auricle. A considerable volume
of the blood, however, has a portal circulation within the tissues of
the renal organ, during which the uric acid and other waste substances
are eliminated from it, the blood thus purified entering the pulmonary
vein by means of a large ami some small veins, without fully circulating
within the iiulmonary plexus.

HELIX — GLANDULAR SYSTEM.

157

Helix aspei'sa, like other mollusca, has little proper heat, and is
practically Poikilothermic or approximately of the same temperature
as the surrounding atmosphere, hecomiug colder or warmer internally
in accordance with, and in response to the variations of temperature
to which it is exposed. The contractions of the heart are more
numerous in the young than in the adult mollusk under similar con-
ditions, hut the number of pulsations has a wide diurnal range and in
our ordinary summer temperatures probably varies between twenty-
five and sixty-five per minute, even in the same animal, as the action
is intimately related to the external temperature, being accelerated
by increased warmth or active movement and diminished by cold,
under which latter circumstances the contractions become more feeble,
with however an occasional beat of full amplitude.

The Glandular or Secretory system, with which are included the
e.xcretory organs, are constituted of those organs or glands l)y which
substances differing in composition from the blood and necessary for
the proper exercise of the functions of the body are elaborated there-

from and utilized, or if hurtful expelled
from the system. It is composed not
only of the salivary and digestive glands,
which assist in the processes of digestion,
and the digitate, albumen, prostatic and
other glands, which are adjuncts to the
reproductive organs and are alluded to
under the systems with which they are
functionally connected, but the whole
surface of the body, foot and mantle is
more or less glandular and furnished with
unicellular glands, of which those con-
taining pigment give the surface of the
body or its various organs their charac-

Fig. 320. — Portion of Corium and
Cuticle of back of llelisc poinatia^
highly magnified (after Flemming),
to show its structure and glandular
nature.

C't.c. connective tissue cells, with
interspersed nuclei, n. ; ep.c. cylin-
drical epithelial cells ; h.c. hair cells ;
in. longitudinal and cross cut muscle
fibres ; /. pigment ; s.g^. slime or
mucous glands.

teristic colour. There are also numerous mucus cells scattered over
the whole surface, which maintain the exterior in a moist and pliant
condition. A very dense aggregation of such cells exists within the
Pedal gland, a medial supra-pedal invagination, which extends back-
ward within the foot and opens anteriorly by a cleft between the
mouth and foot; the contained glands secrete mucus abundantly,
which is expelled by the aperture in advance of the foot and serves
to lubricate the path to be taken by the mollusk.

HELIX — GLANDULAK AND MrSCULAR SYSTEMS.

1.5S

The Lymphatic glands are not strictly localized in onr type ; the
phagocytic or lyni])h cells being diffused amongst the connective
tissue in various parts of the body, although the function is most
actively carried on within the respiratory plexus in which the lym-
phatic cells thickly surround the larger pulmonary vessels.

The Xephridium kidney) or renal organ (see p. 146, f. 306),

an important secretoiy and the chief excretory organ, is of an ochreons-
yellow colour, and placed in the rear of the pallial cavity, between the
rectum and the pericardium. It communicates with the latter by a
ciliated canal, the reno-pericardial funnel, and with the exterior by a
thin-walled duct or ureter, which arises at the proximal end of the
kidney and runs along its right side to the distal end, returning along
the right side of the mantle cavity above the rectum to the pulmonary
orifice, the last tract forming the so-called secondary ureter.

'I’he organ is of a parenchymatous and vascular character, with
its internal walls thrown into a number of lamellar folds, projecting
within the lumen or cavity, and is permeated by an intricate j)lexus of
vessels through which venous lilood, somewhat intermingled with
arterial, circulates before reaching the auricle : its glandular secretory
ei)ithelium, which contains rounded granules or concretions, eliminates
from the blood the uric acid and other substances, which are expelled
from the system by the ureter.

The IMrscuLAR .system is very complicated, and its constituent parts
too numerous to be individually particularized. The principal, how-

FiCi. 321. — Disfiection showing the general muscular system of Helix aspersa and the arrange-
ment of the extrinsic muscles of the huccal bulb (after Howes).

i>J'. buccal bulb ; h.c. constrictor muscles of bficcal bulb ; c.i/i. columellar muscle ; eij/i. depressor
muscles of buccal bulb ; /. foot ; levator muscles of buccal bulb ; o. ommatophore ; o’, oeso-
phagus ; buccal protractor muscles; pharyngeal or buccal retractor ; r.s. radular sac ;

s.d. salivary ducts ; t. anterior tentacle.

ever, are the retractors of the foot, those of the huccal mass and
neighbouring organs, the penial retractor, the constrictor muscles of
the mantle margin and of the pulmonary aperture. Of a subsidiary

HELIX — MUSCULAR SYSTEM.

159

but interesting character, may be mentioned the extrinsic and
intrinsic muscles of the buccal bulb.

The muscles or cartilages here especially alluded to, are of a pearly
glistening white and very strong and ribbon-like in character.

The columellar muscle, by which the animal is organically attached
to the shell, is the largest and most important muscle of the body,
and is affixed at its distal end to the columella near the commence-
ment of the penultimate whorl (see p. 54, f 130) and passes beneath
the lung chamber, along the inner or right side of the spiral,
dividing to the right and left into numerous fibres which interlace
with the tissues of the foot.

Near its origin the columellar muscle gives rise to the paired
tentacular retractors, each of which, prior to entering the tentacles
and before re-bifurcation, gives off a broad tripartite muscle to the
anterior part of the foot ; the retractor of the dorsal tentacle expands
noticeably before reaching the apex, while that to the lower tentacle
again divides, sending a strong branch to the lip.

The pharyngeal or buccal retractor originates adjoining to and im-
mediately in advance of the paired tentacidar muscles and is formed
by a powerful ribbon-like muscle,
which divides before reaching the
buccal bulb, to which it is attached
ventrally and laterally by the ex-
panded ends.

The Penial retractor is a powerful
unpaired muscle attached to the distal
end of the penis sheath and to the
floor of the pulmonary chamber.

The extrinsic muscles of the buccal
bulb are formed by the pharyngeal
retractor and by a number of slender
muscular bands, which pass from its
exterior to the walls of the anterior region of the body, and in
accordance with their function are distinguished as depressor, levator
or protractor muscles.

The intrinsic muscles are formed chiefly by the protractor and
retractor fibres, attached to the radular cartilage anteriorly and
])osteriorly respectively, and communicating the motion to the
radular membrane.

F IG. 322. — Cephalic retractors of Helix
aspersa X 4.

c.m. columellar muscle; j. anterior
foot retractors ; pharyngeal or buccal
retractor ; /. tentacular retractors.

IGO

HELIX — REPRODtJCTIYE ORGAXi?.

The Reproductive organs of Helix aspersa, like those of the
Piihnonata generally, are of a hermaphrodite or monmcions character,
hut this hermaphroclitisin does not normally affect the necessity for
reciprocal union to ensure the fertilization of the ova.

The Ovotestis or Hermapihrodite Gland, the essential constituent
of the system, is lodged in the posterior lobe of the liver near the

Fig. 323. — Reproductive organs of Helix nspcrsn dissected out and isolated. Tlic penis sheath,
stylophore, uterus, atrium and vagina opened up— the penis sheath to show the inlromittent organ ;
the stylopliore, tlie contained dart ; and the uterus, its sacculate structure.

all\ gL allnimen gland ; d. dart in situ \ d.s. <lart sac or stylophore ; cp, epiphallus nagellum ;
h.d. hermaphrodite duct ; ni.gl. mucus glands ; ot. ovotestis or hermaphrodite gland ; /. penis ;
p.s. penis sheath ; pr. prostate or sperm duct ; p.r. retractor muscle of penis sheath ; sp. sperma-
iheca; sp.d. spermatheca duct with thick ca^cal diverticulum; 07<. uterine portion of ONiduct ;
v.d. vas deferens ; v.s. seminal vesicle or claw.

apex of the shell, and is constituted by an aggregation of converging
digitate -whitisb lobules, on whose internal walls the female and male
elements, distinguished as the Ova and the Spermatozoa originate,
the former as rounded and sei)arate cells, which continue their
development, adherent to the follicular walls ; while the spermatozoa
are filiform bodies with enlarged heads, usually aggregated in clusters.

HELIX — REPRODUCTIVE ORGANS.

161

which are dehisced at an earlier stage from the sides of the follicle,
their development proceeding within the follicular lumen. The
Hermaphrodite Duct, a sinuously convoluted tube, leads from the
ovotestis and conveys the ova and spermatozoa forward, but before
reaching the large, linguiform and yellowish Albumen Gland it bends
abruptly upon itself and forms a peculiar bent subclavate sac, known
as the Seminal Vesicle or claw. The duct then enters and traverses
the albumen gland, receiving therein its viscid secretion, by which the
ova become enveloped ; on the emergence of the duct therefrom,
the ova and spermatozoa are separated and flow within special
channels, the Sperm Duct and the Uterus, which, though united
exteriorly, are separated internally by two closely superposed
longitudinal septa. The uterus is of a clear bluish-white colour, with
strongly sacculate and voluminous glandular
folds, but the walls of the siierm duct are
formed by an aggregation of ochreous-white
prostatic follicles. As the conjoined ducts
approach the anterior end of the body, the
two channels separate or become diaulic, the
sacculated uterus becoming straight and
thick-walled and distinguished as the Ovi-
duct ; while the sperm duct becomes a
slender tube, termed the Vas Deferens, and
conveys the seminal fluid to the male organ,
passing beneath the right tentacular re-
tractor and becoming buried in the tissues
of the body wall for a short distance before
joining with the distal epiphallial prolonga-
tion of the penis sheath, which is still further extended by a long and
slender hollow filament, termed the Flagellum, within which the
Spermatophore, a peculiar
and characteristic filament
of agglutinated sperma-
tozoa is formed. The Penis
Sheath is a bluish-white
and somewhat muscular
tube, opening into the common vestibule or atrium close to the
external aperture, which is placed in the nuchal region, beneath the

I,

Fig. 325. — Spermatophore of Helix aspcrsa^ with more
highly enlarged sections, showing the structure of the
anterior and posterior portions (modified after Moquin-
Tandon).

Fig. 324. — Penis sheath, epi-
phalUis, and flagellum of Helix
aspersa x 3, showing the mode of
connection with the vas deferens.

eps. epiphallus ; fl. flagellum ;
g.o. common genital orifice ; p.s.
penis sheath ; r. penial retractor ;
V. vagina ; v.d. vas deferens.

162

HELIX — REPRODUCTIVE ORGANS.

iglit dorsal tentacle, wliose retractor muscle passes between and
separates the male and female organs ; a
powerful retractor muscle also arises from the
distal end of the penis sheath and is attached
medially to the door of the lung chamber.

The Spermatheca is a red-brown globular
vesicle, fixed by its neck to the distal end
of the ovispermatoduct and also complicated
by the attachment of a muscle from the
columellar retractor; it opens into the upper
jiart of the vagina, by means of a long
hollow stalk, which gives off about midway
a long and thick cmcal diverticulum, about
the same length as the flagellum, which is
fixed terminally at the base of the albumen
gland, and within which is lodged the spermatophore received during
])airiug from its i)artner in the sexual act.

d’he mucous glands or multibd vesicles, are paired tufts, each
c()mj)o.sed usually of
about 2.1 tassel -like
tubular glands, wliicli
open into the vagina
below the si)ermatheca ;

V . . Fig. 327. Fig. 328.

their secretion is rich Digitate Mucous Glands of Helix as^crsa X 2.

1 • 1 , Fig. 327. — An unusually ramose gland, bearing 16 branchlets.

HI CUlClC Sll n.StcHlCt'S, 323. — A very sparsely digitate one, with 14 branchlets only.

Fig. 326. — Portion of the Re-
productive organs of Helix
showing the separation
of the male and female organs
by the retractor muscle of the
right ocular tentacle X 3.

o. right ommatophore and its
retractor ; p.s. penis sheath ;
7’. vagina ; t. lower tentacle and
retractor ; g.o. common genital
orifice.

wliich have been assumed to assist in forming the outer egg envelope.

'I'he large, iiyriform, muscular dart sac or Stylophore is situate just
beneath the i)aired mucous glands and ojiens into the vagina slightly
above the vestibule or atrium, and serves for the inotection of the
dart, which it also secretes and protrudes. It is formed chiefly of
two layers ; a thick, translucent, greyish- white outer coat, compo.sed
of annular and longitudinal muscle fibres, and a thinner and more
vascular inner layer ; the less muscular distal end bears a small sub-
conical tubercle with some closely api)osed longitudinal rods at its
sides, which serves as the point of attachment for the base of the
Dart or spiculum amoris, whose point is thus directed towards the
aiierture. This curious weapon, which is soft and flexible when
removed from the sac, has a slightly curved, hollow, calcareous, and
])oiuted stem, somewhat expanded at the base, which fits upon and is

PELECYPODA.

163

sliglitly attached to the distal tubercle, and is strengthened by four
projecting and slightly twisted longitudinal blades, placed at right
angles to each other and slightly thickened and rounded at the

outer edges, which cause the dart
to revolve slightly during its pro-
trusion. The blades gTadually
diminish towards the point of the

Fig. 329 -Dart of Heiu aspersa X i, ^^^rt aiid inore abruptly basally,

Christchurch, Hants. conuected together at

intervals by crescentic and very thin calcareous films. The dart is
everted, and used by the animal as an excitant to its prospective
mate, during the amorous preludes which lead up to, and precede
sexual congress.

The Pelecypoda, on the other hand, differ widely from the Gastro-
poda, as they are exclusively aquatic animals which would appear to
liave adopted a more or less inactive and sedentary life, and retained
more completely than the Gastropoda the original bilateral symmetry
of their external and internal organs, but lost l)y degeneration or
atrophy such organs as were especially adapted to an active loco-
inotory existence, the probability of their former possession of sucli
organs being corroborated by brief traces of their existence during
larval life. The great development of vibratile cilia over the free
surface, more especially of the largely developed and paired ctenidia
or gills, render it probable that the continuous flow of food-laden
currents directed towards the mouth by their action, would also tend
by the easy nutrition thus secured to confirm the sedentary habits
of the animal and contribute to the degeneration of the cephalic
region by rendering it functionally unnecessary. The development of
the ample mantle lobes and their encompassing and protecting shells
becomes a necessary corollary of the adoption of inactive habits, as the
degeneration of the locomotory organs would naturally prevent active
escape from apprehended danger.

The Pelecypoda are broadly divided into three gTOups, viz. :
Isomya, Heteromya, and Monomya, characterized by the relative
degree of development of the adductor muscles of the shell, and which
like the, nerve cords in the Gastropoda equally indicate successive
stages of specialization.

164

ANODONTA — EXTERNAL FEATURES.

The Isomya are distinguished by tiie approximately eriual size of
the anterior and posterior adductors (see p. 10, f. 11); the Heteromya
by the reduction in size and importance of the anterior and the in-
creased size and importance of the posterior adductor (see p. 10,
f. T2) ; and the Monom}^, of wliich we have no representative in our
freshwater tanna, by the anterior adductor being atrophied in tlie
adult forms, and the posterior adductor only being developed.

The Isomya te Anodouta cijgnea or anatina, which we may regard
as tvpifying the Pelecyi)oda, has a more or less oval and laterally
compressed form, enclosed by amjile lateral mantle lobes which secrete
upon their external surface a corresi)onding pair of shelly valves,
united together dor.sally by a somewhat elastic chitinous ligament,
whose action tends to keep the valves apart ventrally, their closure
being effected by a pair of powerful adductor muscles passing through
the body and attached to the inner surface of the valves.

Fig. — Anodonta anatina^ showing the e.vtended mantle lobes, the anterior position of the
protrusible foot and the posterior and relative positions of the dorsal orifice, and the branchial and
anal siphons, as typical of the I^elecypoda.

a.s. anal or excurrent siphon ; hr.^, branchial or incurrent siphon ; d.o. dorsal orifice ; f. foot ;
w. mantle margin.

The External Features of Anodonta may, as in Tlelir, be
examined according as they belong to the Cephalic, the Pallial, the
I’edal, or the Visceral regions.

'Die (V])ha]ic region is degenerate and there are no cephalic eyes.
'I'lie oval mouth is without prehensile or masticatory organs, Imt is
surrounded by large and higbly vascular palps or li])S, richly supplied
with nerves and externally clothed by strong vibratile cilia, whose
action directs the food-laden currents to the mouth.

The Pallial region, in onr type, reaches a great develoj)ment, being
formed by two large, thin, trans})arent, and internally ciliated, leaf-like

ANODONTA — EXTERNAL FEATURES.

1G5

folds, which completely envelop the entire body of the animal to which
they are dorsally and laterally attached, but open ventrally, and en-
closing between them the pallial cavity, which, by the fusion of the
gill lamella!, is divided into an upper or supra-branchial and a lower
or infra-branchial chamber; in the latter are situate the foot, the gills,
the palps, the oral orifice, etc., while the rectum, the renal and the
genital organs open into the supra-branchial or exhalent chamber.
The mantle is formed of interlaced contractile muscidar fibres and
connective tissue, enclosing large and important blood spaces, which
seem to be in correlation with the largely develo2)ed foot.

The margins of the mantle were probably i)rimitively entirely open,
but in our type are fused together on the posterior margin, forming
the branchial and the anal orifices, and hence such species are ilis-

tinguished as biforate. This fusion
separates the pure in-coming infra-
branchial stream from the excurrent
supra-branchial one laden with
effete substances and excreta.

The branchial is the largest and
most ventral opening and is con-
tinuous with the general mantle
cleft, but may be functionally
limited by the close apposition of
the mantle margins.

The anal opening exhibits a sub-
sidiary fusion by which two out-
wardly distinct, but internally con-
nected apertures, are formed, the
one adjoining the branchial siphon and opposite the anus is the true
anal siphon ; the more dorsal opening is known as the renal and also
as the dorsal orifice, but the significance of its separation or the duty
it perforins is not as yet understood.

The local modification of the pallial margin, to form the branchial and
anal siphons with definitely localized sensitive processes is in a large
degree correlated with the activity of the animal, the circumscribed area
they occupy showing that a part of the body is usually concealed in the
mud ; while the greater development of the sensitive processes around
the inhalent opening enables the mollusk to detect the presence and
guard against the inhalation of injurious or distasteful substances.

Fig. 331.— Posterior aspect of Anodonta
cygnca to show the relative positions of the
external orifices and the mode' of closure of
the branchial siphon by the infolding of the
digitate filaments (after Howes).

a.s. anal siphon ; br.s, branchial siphon \ d.o.
dorsal orifice ; 1. ligament of shell ; m. mantle.

ANODONTA — INTERNAL ORGANIZATIOII.

The Pedal or foot region is anteriorly i)laced upon the ventral side
of the body, and is a large laterally compressed and strongly ciliated
muscular appendage or protuberance, acutely angulated below and
terminating in a pointed and sensitive tip, bearing on its posterior
margin three minute pit-like dei)ressions, which are the openings of
mucous glands, and of the degenerate byssal gland, but have been
assumed b}' some to be the external oritices of a water vascular
system. It is capable of protrusion greatly beyond the shell by
means of blood i)ressure, but is withdrawn by muscular contraction ;
and is esi)ecially adapted for forcing its way through mud and sand
by alternate expansion and contraction, being noticeably stronger in
those forms which habitually plough through or burrow within the
mud or sand.

'I’he Visceral sac or region is compressly oval, and (pdte concealed
by the overlapi)ing mantle lobes, but, as in the (}astroj)oda, it contains
the liver, the genital glands, the convolutions of the alimentary canal,
the circulatory organs, the renal organs, etc. ; along each side, above
the base of the foot, is a vascular longitudinal ridge, from each of
which depends a pair of long rellected branchial leaflets, which
originate behind the labial pal[)S and pass backwards ; and whose
moditicatioiis have been ably used liy Prof Pelseneer as a basis for
the cla.s.sitieation of the Pelecy})oda.

Fid. ‘^2. — Anodonta cyj^ncay with the right mantle lobe removed and pericardium opened to
show the general and relative arrangement of^ the organs of the body (modified after Howes).

a. auricle of the heart ; a. ad. anterior adductor; a.s. anal siphon ; br. branchix*, with posterior
suspensory ligament ; br.s. branchial siphon ; d.o. dorsal orifice, in connection with the anal siphon ;
/. foot, with the three pit-like depressions on the posterior margin indicated ; /. liver or digestive
gland ; nt. mouth ; vt.a. line of attachment of mantle to visceral mass ; />. palps ; p.ad. posterior
adductor ; pc. pericardium ; pc.gl. pericardial gland or Keber's organ ; r.o. renal organ or kidney ;
7’. ventricle of the heart.

The Internal ( Irganization of our ty[)e has retained the primitively
jtaired character that distinguished its hypothetical ancestor, such
organs as are not symmetrically paired being placed along the medial

ANODONTA — INTERNAL ORGANIZATION, ETC. 1G7

line. The nervous system is also of a paired character, but with tlie
different centres widely separated and developed correspondingly to
the morphological changes in the animal. The alimentary system is
convoluted more or less medially, the mouth being placed in the
middle line anteriorly beneath the anterior adductor, the termination

of the digestive system being at the
posterior end of the body. The
circulatory organs are dorsally
jdaced, the ventricle in the median
line, and enclosing the rectum, with
a symmeti'ically placed auricle at
each side, which receives the blood
from the branchiie adherent to
the same side of the body. The
glandular system, when localized
in definite organs, is also distinctly
paired, the liver being formed of
two lobes and the excretory neph-
ridial and pericardial glands have
their component parts placed to the
right and left of the me<lian line.
The muscnlar system partakes
strongly of the same bilateral uni-
formity, the various muscles or
retractors arising from one side of
the body having their counterparts
at the other. The reproductive
organs are also paired, genital
glands being present at both sides of the body, and each furnished
with a duct debouching into the cavity of the inner gill of their
respective sides.

All the organs of the body may be advantageously studied, as in
the Gastropoda, in connection with the particular system to which
they have the most intimate relations.

The Nervous system of Anodonta is of the simplest type, in which
well-marked ganglia exist, and is composed of three chief medullary
masses or ganglia, which are placed at considerable distances from
each other, but connected by long nervous cords, forming two very
long nerve rings or nerve loops, which, however, evidently confer a

a. auricle of the heart ; y. foot, showing
the cut sections of intestinal tract ; i.c. inner
ctenicliuni or gill, with supra-branchial cham-
ber open to and continuous with infra-
branchial chamber, ib.c. ; /. ligament of

shell ; in. mantle lobes, lining valves and
showing marginal pallial muscles ; o.c. outer
ctenidium; ^c. pericardium ; J>c.g. pericardial
gland or Keber’s organ : r. rectum, with
typhlosole ; r.o. renal organ or organ of
Bojanus, and showing the paired cerebro-
pleuro-visceral commissures ; sb.c. supra-
branchial chamber ; u. ureter ; z/. ventricle
of the heart ; v.c. vena-cava or great central
blood vessel.

ANODONTA — NERVOUS SYSTEM.

lOS

very efficient inter-coiiuiuuiication lietween the different ganglia, as
tlie least peripheral irritation leads to instant comhined action of
mantle edge, foot and shell.

The Cephalic or Cerebral gangiia, or more correctly Cerehro-pleural,
as the pleural ganglia are intimately fused with the cerebral in this
grou}), represent the supra-a.‘Sophageal ganglia of Ilel'hv, and are of
comparatively feeble development in correlation with the atrophy of
the head and the absence of the accompanying sensory organs. They
are placed just beneath the skin at the sides of the oral aperture and

Fi(.. — .Inodonta .slu»\vin.i; the disposition of llie ganglia and the general arrange-

ment and distrihnlion of the dependent nerves, as seen from the right side after retnoval of the
right matule loho. and the right cleniilia; the pericartlinm, the ventricle, and the right nephridiinn
opened up (motlilied after I)u\ernoy, Howes and others).

a. ad. anterior adductor; <1:.,?. anal siphon ; br. hranchia; br.n. branchial nerve ; b.a. branchial
>iphoti ; cerehro-pleural ganglia ; c-f*Lp.c. cerel)ro-pleuro-pedal connective ; cerebro-

pleuro-visccral commissure : d.o. dorsal orifice ; /; foot, with ramifying pedal nerves gastric nerve ;
t;.n. genital nerve ; /. liver or digestive gland ; ot. otocysl ; /. palps; />.ad posterior adductor ;

pe<lal ganglia ; />.n. pallial nervous ple.vns, showing numerous small ganglionic enlargements
anil the general anastomosis of the anterior anil posterior pallial nerves ; 7 . rectum ; ?*.?/. nerve to
rectum ; visceral or paricto-splanchnic ganglia ; v.n. visceral nerves from pedal centre.

immediately below and iu front of the pedal-protractor muscle, just
above the attachment of the mantle lobes, ami comiected together by
the cerebral commissure j)assiiig above the mouth ; they iiiiiervate
the palps, the anterior adductor, the region around the mouth and
the anterior jiart of the mantle.

The Pedal ganglia are also paired, although the constituents are
fused together; they are imbedded at the root of the foot, near the
junction of the muscular with the visceral part, hut rather distant
i'rom the cerehro-pleural centre, to which they are joined by straight
connectives, which are easily dissected out. The size of these ganglia
is always in direct comdation with the development and functional
importance of the foot.

ANODONTA — NERVOUS SYSTEM.

1G9

The Pleuro-pedal connectives, wliicli have been hitherto considered
to be a characteristic peculiar to the Gastropoda, are present in onr type,
but fused with the cerebro-pedal connective, forming the composite
or compound neiwous -cord, dis-
tinguished as the cerebro-pleuro-
pedal connective.

The Visceral, Osphradial, or
Parieto-splanchnic ganglia are the
largest in the whole system, and
are really composite ganglia formed
by the fusion of several ganglionic
masses, the more or less com])lete
conjunction of the constituent
ganglia being coi’related with the
greater or less degree of fusion
which the bilateral gills have under-
gone ; these ganglia are supeidicially
placed, and merely covered by
the tegumentary epithelium ; they
innervate the branchire, the siphons and the siphonal chamber, the
posterior adductor, the posterior part of the mantle, and the heart,
which is supplied by a nerve passing around the adductor. The nerve
trunks from the visceral ganglia innervating the posterior portion
of the mantle and those from the cerebro-pleural ganglia, which
innervate the anterior part, fuse or anastomose together and form
a marginal pallial nerve with an intricate plexus of ramifying nerve
fibrils and small ganglionic enlargements.

The Cerebro-pleural connective is lost owing to the intimate fusion
of the cerebral and pleural ganglia, and I therefore regard the long
nervous cords joining the cerebro-pleural and the visceral ganglia, as
commissures, and as really joining the pleural constituents of the cere-
bro-pleural ganglia with the visceral centre ; they run close together
between the anterior protractor and retractor muscles and the anterior
end of the pericardium, and traverse the inner surface of the renal
organs ; they then diverge, passing outside the posterior retractors, and
proceed to join the visceral ganglia. At the point of divarication of each
commissure there is a ganglionic enlargement, wdiich Moquin-Tandon
considered to be a genital and Huxley a subsidiary visceral ganglion.

Fig. 33.5. — Transverse section through
anterior region of A^iodonta cygnca to show
the relation of the mouth and labial palps and
the position and arrangement of the cerebro-
pleural and pedal ganglia (after Howes).

a. ad. anterior adductor ; c.c. cerebral com-
missure ; C’PLg. cerebro-pleural ganglia ;
C'Pl’p.c. cerebro-pleuro-pedal connective ; f.
foot ; l.p. labial palps ; in. mouth or oral aper-
ture ; p.g. pedal ganglia.

17(1

ANODONTA — SENSOR V ORGANS.

t

i \ f
\

Fk;. — *• I’rusli *' Sensory
CelN, highly magnified (after
Sochaezewer).

'i'he Stoiiiato-gasti'ic or buccal ganglia, which are so aj)i)areiit in the
(xastropoda, are not differentiated in Anodonta, hut in correlation
with the atrophy of the in-otrusihle head region have probably become
degenerate and intimately fused with the neighbouring cerebro-pleural
ganglia ; the visceral commissures now giving origin to some slender
nervous tibrils, which reach the alimentary canal, although splanchnic
nerves also arise from the chief centres.

'I'he iSENsoKY organs in our type are not of a highly specialized
character. 'I'he general surface is, however, richly supplied with a
mun])er of epithelial sensory cells of the .same character as those
found in the mollu.sca generally, and, in
addition, there are some larger cells bearing
tnfts of sensory hairs and known as “brush”
cells, which are j)articularly noticeable in
the Pelecypoda. 'Die perception of tactile
impressions is most keenly exercised by the
papilla' or tentacular })rocesses surrounding the branchial siphon,
but the percei)tion of touch is functionally active and etheient in other
exposed i)artsof the body. 'I’he labial palps, although enclosed within
the .shell, have probably a subsidiary tactile function, gnarding the
oral (iritice again.st the entrance of manifestly unlikely sub.stances.

'The Auditorv or Mipulibrating organs of Aimloiitd are formed, as
in lltdl.v, by a pair of small closed ve.sicles or otocy.sts, which in
Anoddufa are [jlaced near to but
not in contact with the pedal
ganglia, and connected by an audi-
tory nerve to the cerela'o-plenral
ganglia of their respective sides.

'I'he otocysts are imbedded in con-
nective tissue and e:ich surrounded
by an investing membrane. 'I’he
walls interiorly of the cysts are
formed of intermingled .sensory and
ciliated epithelial cells, which also
secrete the limpid thud which hlls
the sacs and within each of which
one large calcareous concretion or
otolith is suspended and ke})! in inces.sant motion by the action
of the vibratile ciliated investment. 'I’he otocysts are, however, not

Fig. 337. — Otocyst of Anodonta cj'^nca,
highly magnified (after Simroth).

and. n. auditory nerve ; c.t.c. connective
tissue cells ; cu. cuticle or enclosing mem-
brane ; t'p. ciliated and sensory epithelial
cells, supported upon cellular tissue ; ot.
otolith.

ANODONTA — ALIMENTARY SYSTEM.

171

always symmetrically developed, but when one otocyst only exists,
as occasionally happens, it is found to uniformly contain two otoliths.

The Olfactory sense is located more especially on the roof of the
branchial siphon at the base of the gills near the external orifice, but
is not exercised by distinctly differentiated or externally visible
organs, but by elongated epithelial sensory cells overlaying a portion
of the visceral ganglia, although innervated by a nerve from each of
the cerebro-pleuro-visceral commissures, which are said, however, to
really originate from the cerebral ganglia. The special function of
this organ has been considered to be to examine the inflowing current
of water which bathes the gills and brings nutriment to the mouth.

The Gustatory sense is probably not at all or very little exercised,
as no discrimination appears to be made in the selection of food
particles fi-om the general substances brought by the current, except
such supervision as is exercised by the labial palps.

Cephalic Visual organs are not present in the adult Anodonta,
but traces of such eyes are probably present during the early stages of
development, but these, if present, afterwards disappear, as when
covered by the shell they are useless and unnecessary ; the animals
are, however, acutely sensible to light and shade, the exposed surface
being able to discriminate and discern the distinction and respond to it.

The Alimentary system has its anterior ojjening in the transversely
oval mouth or oral aperture, which
is placed beneath the anterior
adductor muscle, and dor.sally to the
origin of the foot and surrounded
by an anterior or dorsal and a
posterior or ventral lip, which are
continuous with the lining mem-
brane of the month and gradually
expand on each side to form the
somewhat triangular palps, which
are transversely ribbed on their
inner faces and beset with vibratile
cilia, producing a current and con-
veying food particles along the
ciliated groove at their base, which leads towards and into the mouth,
the animal being totally dependent for sustenance upon the minute
organisms and food particles brought thereby. The mouth is

Kig. 33S.— Transverse section througli the
anterior region of Ajiodofiia cygnca^ to show
the relations of the stomach, the liver and its
ducts and the origin of the lyphlosole of the
first tract of the alimentary canal (after
Howes).

y". foot, with the first tract of alimentary
canal ; 1. liver, surrounding stomach and
showing the bile ducts on the left side ; p. labial
palps ; st. stomach, showing entrance of
oesophagus, etc. ; t. t^'phlosole.

172

ANODONTA — ALIME^JTARY SYSTEM.

(leticient of prehensile or masticatory organs and leads directly upwards
hy a short and distensible msophagns to the irregnlarly oval stomach,
which lies in front of the pericardinm and with the msophagus is im-
bedded within the digestive gland ; the stomach has thin walls with a
cadncons, cuticular lining, the Jhrhe trkuspide, which overlays and
protects the secretory cellnles : there is also a i)yloric cmcal diverticnlnm
opening on the right side which can be closed up, and contains a
gelatinous and transparent rod-like body, the Crystalline Style, a
freely projecting extension or prolongation of this cuticular stomachal
investment which is most distinctly developed in spring.

'I'he Digestive tract is convoluted within the visceral sac, especially
amongst the lobes of the enormous genital glands and in the tissues
above the foot; it originates from the ventral wall of the stomach,
passing slightly to the left side during its downward and somewhat
backward course, it then curves upwards somewhat parallel to the
l)osteri(n' margin, and cm ai)proaching the pericardium bends abruptly

I’ lO. 339. — Anodonta Q'ifWt’ri dissected to show the arrangement and convolutions of the alimen-
tary system; the right pallial lobe, branchitT; and palps have been removed and the alimentary
canal, ventricle of the heart and nephridium opened up to show their internal structure (after Howes).

rtr. auricle of the heart ; a. ad. anterior adductor ; a.s. anal siphon ; hr. branchiae ; hr.s. branchial
siphon ; d.o. dorsal orifice ; /. foot ; genital gland ; g.o. genital orifice ; ib.c. infra-branchial
chamber; /. fiver or digestive gland, with bile ducts opened up; ni. mouth; cc. oesophagus ;
p.ad. posterior adductor ; pc. pericardial chamber, showing the left reno-pericardial orifice near
the anterior end ; r. rectum ; r.o. renal organ or organ of liojanus st. stomach ; ty. typhlosole
of rectum ; w. ureter ; v. ventricle of heart,

backward upon itself, returning to the base of the foot on a course
parallel to Imt outside the first upw'ard tract, it again becomes ahrui)tly
bent u})wards, traversing the body in a backward direction and on the
right side of the body, gradually bending forward as the final tract
or rectum towards the antero-ventral region of the pericardium,
which it penetrates, passing through the ventricle and emerging
from the jjostero-dorsal surface of the pericardium, afterwards run-

ANODONTA — CIRCULATORY SYSTEM.

173

ning parallel to the postero-dorsal margin of the .shell above the
posterior adductor and terminating in the shallow cloacal cavity of
the snpra-branchial chamber.

The whole intestinal tract is lined by ciliated and glandular
columnar epithelium, the absorptive surface being greatly increased,
especially in the first and the terminal tracts, by the presence of the
typhlosole, an internal, thick, yellow, longitudinal ridge, formed by
a strong infolding of the ventral walls.

The digestive gland or liver is a somewhat symmetrical multilobed
and greenish-brown organ, composed of numerous brown branched

Fig. 340. — Tubule of Liver or digestive
gland of Anodonta anatina, highly magnified
(after Vogt and Yung).

cu. cuticle ; en. endothelium ; i.c. lime cells?
containing numerous refractive corpuscles?
some enclosing pigment granules.

Fig. 341. — Some elements of the liver of
Anodonta anatina, isolated and highly
magnified (after Vogt and Yung).

tubules, with hepatic, ferment and lime cells, as in Helix, and lined
with glandular cuboidal epithelial cells, with brown granular contents.
It opens into the stomach by two large and several smaller ducts.
As in Helix, the secretions probably change starch to sugar, i)roteids
to peptones, and emulsifies the fatty foods.

The Circulatory system is, as in Helix, composed of definite
arterial and venous vessels and of an inter-communicating system of
lacunar spaces. The heart, the pulsatile centre of the circulation, is
a yellowi.sh sac placed near the hinge of the shell, within the spacious
and elongate pericardium, and is formed of a median ventricle and
two symmetrical and laterally disposed auricles.

The auricles are paired, triangular, thin and somewhat transparent
sacs, with their apices attached to the opposite sides of the ventricle,
the broad basal ends receiving the blood aerated within the branchife
and pallial lobes of their respective sides, which they transmit to the

174

ANODONTA — CIRCULATORY SYSTEM.

ventricle by sinichrouous contractions, regurgitation being prevented
by the large pocket-shaped daps at the i)oint of junction, distinguished
as the anri-ventricnlar valves.

The ventricle, which receives the blood from the anricles, is a
medially placed vessel, of an elongate and pyriform shape, with the
thick and somewhat bilolied end directed posteriorly ; it has thick,
spongy and muscular walls formed of interlaced muscle dbres, and
gives origin to a large arterial trunk at each end, distingui.shed in
accordance with their re.spective positions as the anterior or the
posterior aorta, which transmit to the body the arterial blood expelled
from the ventricle by the strong and successive waves of contraction
which ]iass rhythmically from one end of the ve.ssel to the other.

Fig. 342. — Anodonta cygnca^ injecteil from the ventricle to show the arterial system. The right
pallial lobe, gills and mcsosoma partially removed and pericardium opened (after Howes).

a. auricle of heart : a. a. anterior aortic huUi ; a.s. anal siphon ; n.ad. anterior adductor ; a. pi. a
anterior pallial artery ; hr. ))ranchi;u or gills ; hr.s. branchial siphon ; d.o. dorsal orifice ; /. foot ;
/. liver or digestive gland; La. labial artery; l.p.a. left posterior artery; /. pedal artery:
p.a. origin of posterior aorta ; p.nd. posterior adductor ; p.p/.a. posterior pallial artery ; r.p.a. right
posterior artery ; v. ventricle of heart ; "'.a. visceral artery,

'I’he untcuiur aorta runs forward above the intestine, which it
])artially encloses, Iweaking up into various arteries, the two princij)al
being tbe visceral artery, which sup})lies the intestines, the digestive
and genital glands, and the pedal artery, which passes through the
cerebro-jdeunj-pedal nerve loop and sup})lies the foot, which is rendered
turgid and protrusible by blood pressure, the revulsion or reflux of the
contained Wood towards the ventricle, which takes place upon any
sudden contracti(jn or withdrawal of the foot being arrested by a
valvular arrangement in connection with the anterior aortic bulb ;
while the anterior pallial artery su})plies the oral lobes and spreads out
over the anterior part of the mantle and unites within the mantle
margin with the ])osterior pallial arteries.

ANODONTA — CIRCULATORY SYSTEM.

175

The posterior aorta is also furnished udth a valvular arrangement
preventing the reflux of the blood to the ventricle, and has a backward
course beneath the rectum, soon dividing into two large lateral
trunks, the right and left posterior pallia! arteries, whose principal

Fig. 3t3. — Transverse and somewhat dia-
grammatic section through the middle peri-
cardial region of Anodonta cy^nea, after
injection, to illustrate the circulation within
the branchiae, renal organ, pericardial gland,
and pallial lobes, and also showing the open
communication between the infra-branchial
chamber and the supra-branchial cavities of
the inner gills (after Howes). The vessels
containing venous blood are black, except the
efferent pedal veins, and the arrows indicate
the direction of the blood currents.

a, auricle of the heart ; a.v. afferent
branchial trunk ; c.7'. efferent branchial and
pallial trunk ; /. foot, showing the efiferent
pedal v'ein and its junction with the vena-cava;
ii'.c. lower or infra-branchial chamber ; i.c.
inner ctenidium or branchia ; ;//. mantle lobes,
showing pallial blood vessels, pb.v. ; o.c. outer
ctenidium or branchia ; pc. pericardium ;
pc.g» pericardial gland, showing capillary
plexus ; r. rectum, showing typhlosole ; r.pi.
renal capillary plexus ; sb.c. supra-branchial
chamber ; v. ventricle of the heart v.c,
vena-cava, or central venous blood sinus.

branches run along the free edge of the mantle, anastomosing therein
with the anterior pallial vessels, hut which early give off smaller
vessels, supplying the rectum, the pericardium, the posterior adductor,
the siidional retractors, and neighbouring tissues.

Fig. 344. — Anodonta cygnea, injected to show the larger vessels in connection with the venous
system, especially in relation to the plexus within the renal organs. The right mantle lobe
removed and the external gill lamina, pericardium and ventricle opened up (after Howes).

a. auricle of the heart ; a. ad. anterior adductor ; a.p. anterior protractor muscle ; af.br.v. afferent
branchial veins distributing blood within the gills ; ef.p.v. efferent pedal veins, continuous above
the nephridia with the vena-cava, the dotted line approximately indicating the position of
Kebers valvule ; /. foot ; p.ad. posterior adductor ; pc. pericardial chamber ; r. rectum, passing
through ventricle ; r.pl. renal capillary plexus ; v. ventricle of heart opened up to show the junction
of the auricle and the relations of the rectum.

After permeating the body, the blood eventually reaches the venous
sinuses, of which the principal are the pallial, the pedal and the great
longitudinal central blood vessel or Vena-cava, which represents the
circular jnilmonary sinus of JleU.v, and lies between the pericardium

17G

ANODONTA — CIRCULATORY SYSTEM.

and tlie foot, and to wliich many other vessels converge. It is
continnous witli, hnt separalile from, the pedal sinus by the powerful
sphincter muscle, known as Keber’s valvule, the action of which
renders possible the rapid turgescence of the foot. From the vena-
ca^'a the greater part of the Idood flow's through and irrigates the
renal organ and is then gathered up into the afferent branchial trunk
at the common base of the gills and from thence distributed by smaller
vessels to become arterialized by respiration wdthin the branchial

Fig. 31.). — Anodonia cygncn^ with the foot and the right mantle lobe removed, injected from
auricle, to further illustrate the circulatory system, and more especially the efferent pallial, branchial
and related vessels, and the capillary circulation within the pericardial gland. No note is taken of
the extensive series of pallial sinuses connected with the efferent branchial trunk (after Howes).

n. auricle of the heart ; a.ad. anterior adductor ; a.f>. anterior protractor muscle ; e/.hr.v. efferent
liranchial veins returning blood to auricle ; e/.hrj, efferent branchial trunk ; ef p,v. efferent pallial
veins; pc. pericardial chamber; //./. plexus within pericardial gland ; r. rectum traversing vent-
ricle ; V. ventricle of the heart opened to show the rectum and tlie auricular orifice.

I.imclliv, flowing as arterial l)lood into the efferent hrancliial arteries,
placed along the junction of the secondary limb of the inner gills
with the body wall, and also at the junction of the secondary limb of
the outer gills with the pallial lobes, where the blood combines with
that brought by the efferent pallial vessels from the mantle and pro-
ceeds thence to the auricle, either directly or by way of the pericardial
gland. Some venous blood, however, passes direct to the branchial
arteries or to the auricles without undergoing the })ortal circulation
through the kidneys, and a much larger (quantity, which has been
]iurifleil within the mantle lobes, does not enter either the renal organs
or the hranchia', hut, mixed with some from the outer gills, undergoes
a portal circulation within the i)ericardial gland before entering
the auricles.

Although the vascular mantle lobes largely assist in the oxygenation
of the blood, the respiratory organs are normally constituted by the
branchial lamellm or gills, which arise from a longitndinal vascular

ANODONTA — OIRCULATORY SYSTEM.

177

ridge on each side of the body, separated by the foot and known
as tlie right and left ctenidia or hrancliia", according to tlieir position.
They are each formed by a imir of trellised and vascnlar lanielhn,
united at the base and each composed of a descending adaxial or

jmmary lamella, which becomes

Fig. 346. — Transverse section through the
posterior region of A7iodonta cygnea^ im-
mediately behind the foot, to show the arrange-
ment of the organs and the coalition of the
supra-branchial chambers of the inner gills,
owing to the fusion of the secondary limbs
of the right and left inner gills (after Howes).

i.h. inner gill orbranchia; in. mantle lobes
with marginal pallial muscles; o.hr. outer
gill or branchia ; p.ad. posterior adductor
muscle; r, rectum, showing typhlosole; sh.
shell; sp.c. combined supra-branchial chamber
of the inner gills ; v.g. visceral or parieto-
splanchnic ganglia.

tilameiitar spaces and bridge over
of the cavity by interlamellar f

cutely reflected to form an ascending-
secondary limb, the distal margin
of each external gill being fused to
and vascularly continuous with
the mantle lol)e of its side ;
while the ascending or secondary
limbs of the inner gills are similarly
fused anteriorly with the visceral
body wall, hut posteriorly, the
secondary limbs of the right and left
inner gills fuse together and form
the partition or septum separating
the branchial and cloacal cavities.

The spaces or cavities between
the primary and the secondary
lamelhe of each gill are occupied
by exuberant suh-filamentar out-
gTowths, which obliterate the inter-
and bind together the opposite sides
ihrous or vascular junctions, which

arise at regular intervals, coincident in position with or forming the

larger vertical blood vessels.

The vertical filaments,
which were primitively the
respiratory organs, have in
Anodonta lost their original
blood-carrying function and
become comparatively firm
and solid rods supporting the
spong-y, lacunar and turges-
cihle blood permeated tissue,
within which definite blood
channels are excavated and

Fig. 347. — Fragment of the outer or primary limb
of the inner gill <A Anodonta., torn from the connected
inner or secondary lamella, to expose the constituent
filaments and the fenestras, highly magnilied (after
Holman Peck).

b.7'. large vertical blood vessels ; f. fenestr.x* or
water passages piercing the interlamellar lacunar out-
growth, i.s. ; p.f. primitive vertical filaments ; t.f.
transverse interfilamentar junctions.

respiratory processes carried on. The interlamellar junctions in the

M

178

ANODONTA — GLANDULAR SYSTEM.

outer gills are long vertical ridges of solid lacunar tissue placed at
intervals of about every seventh filament, and supporting a blood
vessel at each side. The interlamellar junctions of the inner gills are
hollow and vascular, and placed at intervals of about twenty filaments
apart, alternating in position on the primary and secondary limbs of
the gill.

The transverse filaments are wavy transverse rods crossing the
straight vertical filaments at regular intervals, and thus forming a
regularly trellised pattern and enclosing vertically oblong interfila-
mentary spaces, within which are the openings of undulatory rows
of minute, irregular and somewhat ohliipie fenestra' or water passages,
varying in size from to yoVc of an inch in diameter, which pass
through the suhfilamentar lacunar tissue of the gill cavity.

The (tLandular system in Anndontd is practically identical, in its
broad features, with that described in lleli.r, the mantle, and tissues
generally, presenting a very glandular structure, the glands being
formed of differentiated epithelial cells, with calcareous, pigmented
or mucous contents. Lime cells, capable of secreting nacreous or
shelly matter, are so plentifully distributed over almost every part of
the surface of the animal, that the stimulus or irritation of its delicate
tissues liy the accidental presence of any extraneous inorganic or
organic particles, immeiliately leads to the formation of pearls or
l)early concretions l)y the concentric deposition around the intruding
object, of calcareous substances similar in structure to the inner layer
of the shell itself, but varying somewhat in character according to the
j)osition in which the intruding i)articles may have become lodged.

The Nephridia, Renal organs, or organs of Bojanus are symmetrically
l)aired, tubular and sac-like, glandular or excretory organs, which are
each folded ipjon themselves at the posterior end, the ventral or
secretory limbs having their walls thrown into thick si)ongy brown
folds, clothed with blackish ciliated epithelium. Each dorsal limb, or
Ureter, is a thin-walled tube, very wide posteriorly, whose upper walls
are continuous with, and inseparable from, the floor of the pericardium,
while its floor is continuous with the roof of the glandular section
which it overlays.

The organs are placed side by side beneath the pericardium and in
front of the i)Osterior adductor, but, although separated by the Vena-
cava or groat central blood vessel, the excretory i)ortion or ureter of
each kidney is united by a wide inter-renal oval space near the anterior

ANODONTA — GLANDULAR SYSTEM.

179

end, and the two glandular parts are similarly, but more ventrally con-
nected. The secretory limbs are also joined anteriorly to the anterior
part of the pericardium by the reno-pericardial funnels, which open
mthin the pericardial cavity by a pair of somewhat crescentic slits.

Fig. 348. — Longitudinal section through the right Renal organ or Nephridium of Anodonta
cygnea^ illustrating its relation to the pericardium and also showing its structure and the intricate
series of connecting chambers between the glandular section and the ureter x 3 (after Rankin).

a. auricle of the heart ; br. left branchia ; br.n. branchial nerve ; f. foot ; k. kidney or renal
organ of right side laid open ; o.u. e.vternal orifice of right ureter ; f>.ad. posterior adductor ;
posterior retractor ; r.f. right reno-pericardial funnel, connecting the pericardium with the glandular
part of the kidney ; ti. ureter, showing the three complex chaml<ers intervening between the
glandular section ; zk ventricle of the heart ; v.g. visceral or parieto-splanchnic ganglia.

The venous blood on its way to the branchi;n from the vena-cava
circulates within an intricate renal plexus, the renal cellules during the
passage of the blood through the organ eliminating the nitrogenous
waste matters in the form of urea, uric acid, etc., which are ex2)elle<l
from the system by the right and left ureters, which terminate in a
' pair of small outwardly du’ected orifices with prominent whitish
margins, opening respectively into the right and left exhalent chambers
and always placed above the cei’ehro-pleuro-visceral commissure.

/

Fig. 349. — Dorsal view 'of Anodonta cygnea to show the position and aspect of the organ of
Keber or pericardial gland (after Grobben).

a.ad. anterior adductor ; a.r. anterior retractor \f. foot ; p.ad. posterior adductor ; p.r. posterior
retractor ; fc.gl. pericardial gland, the four anteriorly placed symmetrical scars are indications
of the anterior umbonal retentor muscles.

The Pericardial Glands or Keber’s organs are rusty-red, paired
glandular proliferations of the anterior epithelial walls of the peri-
cardium which have an excretory function analogous to that of the

180

ANODONTA — MXTSCULAR SYSTEM.

renal organs. Tliej" luive a rich sanguine irrigation mainly by the
arterial blood returning to the auricles from the mantle lobes and

outer gills, from -which the
glands eliminate a still more
acrid secretion than that of the
nephridia, which is probably
dischai’ged into the pericardium
and passes outwards by way of
the reno-pericardial orifice and
the ureter.

The Ijymphatic (Tlands are, as
in Hell.r, diffused amongst the
connective tissue in almost all
parts of the body, hut although
the function is more especially
concentrated within the gills,
it is not localized, and does not form a definite organ as in some of
the Oiusthohranclis.

The ]\Iuscui.AU system of Anodnnta, so far as relates to the larger
and more e.xtrinsic muscles, may l)e termed Pedal or Pallial, according
to the area witli which they are most closely identified ; there are,

U.T

Fid, 35(). — Longitudinal section through the
right accessory pericardial space of Anoiionta
cyf^nea to show tlie openings of the pericardial
gland and the reno-pericardial funnel and neigh-
bouring organs X 3 (after Orohhen).

right genital duct : X*. anterior end of kidney
in section, sliowing its glandular structure and the
more dorsally placed ureter ; t?. openings of peri-
cardial gland into the accessory space ; />.c. peri-
cardium ; A'-i'’/. pericardial gland ; r. rectum ;
7\/. reno-pericardial funnel.

Fig, 3.)1. — The left valve of an Anodonta cygnca from Clumber Lake, Notts., collected by
.Mr. C. T. Musson, F.L.S., showing the muscular scars, which indicate the places of attachment
of the extrinsic muscles.

a. ad. anterior adductor scar ; a./>. anterior pedal protractor scar, the abdominal retentor scar of
Clessin ; a.r. anterior pedal retractor scar ; /.ad. posterior adductor scar ; /./. pallial line ; /.r.
posterior pedal retractor scar ; n.r. umhonal retentor or pedal levator scars.

liowever, innumeralxle smaller, though intrinsic muscles beneath and
intimately connected with the general integument, while the walls of

ANODONTA — MUSCULAR SYSTEM.

181

the alimeiitaiy canal, the heart, the arteries and other organs are all
more or less closely invested with or composed of muscnlar fibres.

The i)laces of attachment of the extrinsic muscles to the internal
surface of the valves is indicated by distinct and permanent scars,
owing to the fibres composing the muscles being connected to the
epithelial cellules, whose calcified cuticle forms the nacreous lining
of the shell.

The Pallial muscles are chiefly developed towards the mantle
margin and are composed of variously directed and interlaced
muscular fibres, which, however, mainly run in three directions, viz. :
parallel to the mantle margin, at right angles to it, or perpendicnlarly
to the two first-named and joining the inner and outer pallial surfaces ;
those fibres running at right angles to the margin are the most strongly
and numerously developed, they are proximally attached to the

Fig. 352. — Muscular system of Anodonta JluviatiliSy illustrating the distribution and functional
area of the extrinsic muscles. The right mantle lobe and right branchiaj removed (after Simpson).

a. ad. anterior adductor; a./>. anterior protractor, showing the radiation of its muscular fibres
and their comparatively superficial position ; a.r. anterior retractor, showing its deeply seated
ramifications ; br. left branchiaj ; o.tn. orbicular muscles, showing their sub-marginal insertion in
the shell to form the pallial line, their posterior modification form the siphonal retractors ; p.ad.
posterior adductor ; pc. pericardium ; p.r. posterior retractor, the fibres of which are not so super-
ficially distributed generally, as those of the protractor, but less deeply imbedded than those of the
anterior retractor ; u.r. umbonal retentors or pedal levators, distributing their fibres over the
region of the stomach, pericardium, etc.

inner lining of the shell and form the retractor, s of the mantle margin,
being di.stinguished as the Orbicular muscles, their line of attachment
to the shell constituting the linear sub-marginal muscular scar, known
as the pallial line, which runs parallel with the ventral margin of the
shell and is also continuous with the external margin of the adductors.

At the posterior margin of the mantle, these complex and variously
divergent muscles become specialized to form the siphonal retractors,
the constituent muscular fibres taking a circular, longitudinal or
radial direction.

18l> ANODONTA — MUSCULAR SYSTEM.

The Adductor iiiuscles are also considered to be a great local
develoi)meiit of the pallial muscles, with which they are continuous ;
in Amxlunta the adductors are formed by two large, powerful and snh-
e([ual muscular masses, composed of numerous closely arranged
muscle tihres and jjlaced at opposite ends of the body, at about an
ecpial distance from the ligament ; they pass perpendicularly through
the body of the mollusk between the inner faces of the valves which
they unite together and close by their contractions, the anterior
adductor being anterior and dorsal to the mouth, while the posterior
lies beneath and anterior to the rectum, Imt they, in common with
the extrinsic muscles generally, gradually move with the growth of
the shell, diverging and becoming more distant from the hinge and
from each other, leaving traces of their former i)ositions by the
gradual narrowing and convergence towards the umhones of the
scars, which mark their })laces of ])rior attachment.

The Pedal mnscles are paired
.symmetrically, and formed by the
retractor, })rotractor, and levator
or I’etentor muscles, which are all
proximally attached to corres-
ponding jmsitions on the inner
surfaces of each valve, on which
they leave di.stinct impressions or
scars; distally they mainly ter-
minate amidst the intrinsic mus-
culature and tissues of the foot.

'I’he Anterior protractors are
111 u sc u lar masses formed by radiately
divergent muscle tihres, which assist
in the protrusion of the foot and
are spread over and suiierticially
attached to the surface of the foot
and lU'oximally in.serted on each
valve, a short distance from and
posterior to the anterior adductor.

'I'he Anterior letractors, at their origin, are often continuous
postero-dorsally with the neighbouring adductor, they iienetrate
deejily within the tissues of the foot, and for the most part are more
deejily imbedded than the fibres from the ])osterior retractors ; they

Kk;. — IVansvcrse section tlirougli

niuerior region Anoiionta anatina showing
tfie arrangement of the foot muscles anti ilie
tluplicature of mantle (after Vogt and Vung).

a. a. anterior aorta ; Iks. hlood sinus at base
of palps; c.nt. cross muscles seen ns cut
transversely ; c.t. connective tissue about
digestive gland ; l.ti. ducts of liver or diges-
tive gland ; l.ni. longitudinal pedal muscles ;
/./. lalnal palps ; nr. muscles between foot
and body ; p.a. pedal artery ; p.g. pedal
ganglia ; r. rectum ; st. stomach ; t.ni. trans-
verse pedal muscles.

ANODONTA — REPRODUCTIVE SYSTEM. 183

are more especially distributed along the anterior margin, some of
the fibres being also dorsally spread over the region of the liver.

The Po.sterior retractors are situate dorsally to, but contiguous with
the posterior adductor, and originate as firm muscular trunks ; the
fibres into which they are divided become more especially distributed
about the lower part of the body and along the free ventral edge of
the foot, and, though generally more deeply placed, are often closely
intermingled i\ith the more superficially placed protractor fibres.

The Umboiial reteiitor or Levator muscles are, in Anodonta, formed
by one or more gToups of more or less isolated fibres fixed near to or
within the umbonal area, their fibres spreading over the region of the
stomach and of the pericardium. Many of the fibres do not, how-
ever, reach the shell, their proximal extremities calcifying beneath
the mantle.

The Intrinsic Pedal muscles are very numerous and intricate and
formed by a complex arrangement of variously directed and inter-
lacing muscle fibres, the longitudinal ones being continuous with or
connected to the great retractors of the foot, while the transverse
muscle bundles and the more superficially placed layer of circular
fibres assist in its contraction and protrusion.

The Reproductive organs of Anodonta are normally of a dioecious
character, the two sexes being developed in different individuals,
although hermaplu’odite specimens are sometimes found.

Fig. 354. — Transverse section through the
anterior part of the pericardium of Anodonta
cygnca to show the position of the genital
and nephridial ducts and their relation to the
supra-branchial chambers of the inner gills
(after Howes).

c.pl'P.c. cerebro - pleuro - visceral commis-
sure, with the Vena cava beneath ; f. foot,
with contained genital glands and showing
cross sections of the intestinal tract and more
longitudinal ones of the subsidiary genital
ducts ; g.d. genital duct of left side opened
up to show outlet ; i.c. inner ctenidium, the
left showing the outlet of the genital and renal
ducts ; ibx. infra-branchial chamber ; 1. liga-
ment of shell ; mantle lobes lining shell
and showing marginal pallial muscles ; o.c.
outer ctenidium ; pc. pericardium ; pc.g. peri-
cardial gland or organ of Keber ; r. rectum
with typhlosole ; r.o. renal organ, glandular
portion, showing beneath the more dorsal
efferent renal chamber or ureter ; sb.c. supra-
branchial chamber ; u. the left ureter showing
the opening into the supra-branchial chamber
of the inner gill.

The geuital glands are very voluminous, symmetrically paired, and
placed at either side of the body, occupying the upper part of the

cpl.p

1S4

ANOltONTA — REPRODUCTIVE SYSTEM.

visceral mass, above tbe muscular part of the foot and investing the
convolutions of the intestinal tract : they are however of the simplest
ami most primitive character ami very similar in both sexes, although
the male gonad can often be recognised by its whitish colour, without
microscopic examination.

flach gland or gonad is formed by an immense aggregation of richly
brancbed and minute nicemose lobules, scarcely half-a-millimetre in
diameter, the ducts from which unite to
form a short common duct fi'om each gland,
which oi)ens by a minute aperture close by
the ureter into the cavity of the inner gill
within the sin)ra-branchial chamber of its
side.

'riiere are no accessory organs develoj)ed
in connection with the reproductive system,
and sexual congress is therefore im])ossible,
and necessitates the social aggregation of
these mollusks within limited areas to ensure the fertilization of tbe
ova, as tbe spermatozoa are simiily and freely discharged into the
surrounding water with tbe exbalent current by the male, and drawn
with tbe inlialeut water by the branchial siphon into the pallial cavity
of the female, probably fertilizing the ova while within the gill lamella'.

I' k;. 3.’)’). — A Loltulc of the
ticniial gland of Anodonta ana-
tina^ with its eflerent duct, and
^ho^ving the developing ova,
liii;hly magnified (after \’ugt and
Yung).

Altliougb, in tlie foregoing pages, 1 have briefly examined examples
of a typical (fastroi)od and Pelecypod, chiefly from a morphological
standj)oint, yet tbe various .species (jf our fauna, owing to the
specialization of habits or function they have undergone, exhibit such
modifications of their various organs that this phase of our study
would be incomplete without a fuller account of the organs individually,
detailing the differentiations in structure and function they each
undergo, and referihig to the i)bylogenetic and other points of intere.st
in connection therewith. For this pur2)0se I jR’opose to adhere to the
nietbod 1 have hitherto followed of first treating upon the external
featui-es and afterwards studying the internal oiganization.

THE PROSOMA OR CEPHALIC REGION.

185

The Morphology of the External Organs.

Fig. 35G. — Head and Tentacles of
a Ga.stropod, Helix aspersa X 2.

THE HEAD AND ITS ORGANS.

Tlie Cephalic region, which in both Gastropods and Pelecypods may
be distinguished as the Prosoina, is bilaterally symmetrical, and arises
in the emliryo from the upper surface of the Velar area, the size of
which, according to Gegenbaur, is correlated with the differentiation

of the head. In the adult this region
is indicated by the position of the oral
orifice, and in the Gastropoda is formed by
the distinct and usually well-developed,
somewhat cylindrical head and its appen-
dages, placed at the anterior end of the
body, and borne by a more or less
evident and intervening constriction or neck, on the right side of
which is placed the common genital orifice, or, as in the Streptoneures,
may bear the muscular and non-invaginable male organ. The whole
ceiihalic region is usually capable of being protruded beyond and
comiiletely withdrawn beneath the mantle for i)rotection.

In the Pelecypoda the distinct head of the assumed ancestor has
become atrophied and lost, and there is therefore no specialized or per-
ceptible head, its position being now only indicated outwardly by the
transversely oval mouth, with its encompassing lips and 2)alps.

The IMouth, or oral aperture with its labial aiipendages, is situated
on the ventral surface of the head, or may, as in Strei)toneures, be
placed at the extremity of a long and contractile rostrum. It
originates, during the development
of the embryo, as a simple invagina-
tion of the ectoderm, termed the
Stomodieum, which meets and joins
with the mesenteron or mid-gut.

In those cases where the blastopore
or orifice of primitive invagination remains permanently open to form
the mouth, a prominence or wall becomes developed which surrounds
or encompasses it.

In the mollusca, as in other Invertebrates, the mouth is only fitted
for the inception of food, the respiratory orifice, which in some of the
higher animals is in a measure confounded with the oral opening,
being quite removed from its proximity.

Fig. 357.^ — Mouth of Arion atcr X 10
(after Moquin-Tandon), showing also the jaw,
the upper and lower lips, and the lobulate
organs of Semper on the upper lip.

18G

MrZZLE AND FACIAL GROOVES.

Fig. 3oS. — Ventral aspect of
Limmca sta^nalis \?ix. Jragilis
showing the mouth and the at-
tenuate anterior margin of the
head, known as the Chaperon or
Hood.

The ]\IuzzLE or Prostoiiiium is the region anterior to the base of the
tentacles anti projecting in front of tlie month ; it is the essential
})art of the head, and intimately connected
with the power of forward locomotion in a
detinite direction and with the general
orientation or carriage of the body, and,
in the Gastropoda, is generally short, some-
what convex and angnlated at each side,
while its attenuate anterior margin was dis-
tinguished by Draparnand as the Chaperon
or Hood. This feature is very perceptible
in the species of the family Linuntidw.

The muzzle may, however, as in Cjcloxtoma , he produced into an
elongated and somewhat annulate pre-oral structure or Itostrnm, of a
more or less cylindrical shai)e, sometimes dilated or slightly cleft at its
distal extremity, which jiossesses lips and
other oral organs, and is snscei)tihle of a
considerable amount of elongation and con-
traction, Imt not being a retractile organ it
cannot he withdrawn within the l)ody cavity,
although its parts are so strongly contractile,
that when contraction takes i)lace, the mouth is so drawn in as to lie
at the bottom of a distinct depression.

None of our native si)ecios jtossess the introvertihle or truly retrac-
tile Prol)o.scis, which seems more particularly to characterize the
carnivorous Strei)tonenres.

In the Pelecyi>(Hla, the portion of the body anterior to the month,
which embraces the region of the anteri(jr adductor, may be regarded
as rei)re.senting the Prostoiniiim.

'I’lie I’ac'I al Grooves are an extension of the symmetrically arranged
yet intricate plexus of channels distributing the mncns over the body,
j and show upon the face or muzzle, in

some si)ecie8, as two little central and
parallel longitudinal channels, which are
prolongations of the dorsal grooves and
N'arionsly ramify over the anterior snr-

Auialia stnverhyi X 2. faCe of the lllllZzle.

In Amal'ui ><oirerhiii the two dor.sal channels clearly show upon the
forehead, and each usually throws off outwardly a delicate branch

Fig. 350. -Ventral aspect of the
contracted rostrum of Cyclostojna
clcgiX7is X -1 (after Simroth).

Fig. 3G0, — Facial Grooves of

CEPHALIC TENTACLES.

187

towards the base of the oiiiinatophore of its side, both main chaiiiiels
afterwards becoming rather regularly tritid before their final oblitera-
tion. In Limd.v maxlmus these light coloured grooves or mucus
channels are nincli simpler in character, each dorsal furrow merely
giving off one slender branch towards the ommatophore of its side.
All our Gastropoda do not, however, possess these distinctly detined
ramified channels, as I have been (luite unable to detect recognizable
indications of their presence in many species.

The Cephalic Tentacles, which arise during larval development
from the area encircled by the velum, are pre-eminently sensitive,
tactile and symmetrically paired processes of the body wall, and are
always innervated by the cephalic ganglia, and placed on the antero-
dorsal aspect of the animal. They are the most noticeable and prominent
appendages of the ce})halic region, being very mobile and possessing
a considerable variety and range of motion, and externally covered in
the terrestrial sj)ecies with fine granulations or annular ridges, and
in the acpiatic species with a veiy noticeable vibratile epithelium.

They may be divided, according to their structure, into two groups,
viz. : Retractile and Contractile. The retractile tentacles are hollow
and muscular cylindrical processes, each terminated by a bulbous en-
largement, and capable of being withdi’awn within the body of the
animal and are more especially a characteristic of the terrestrial
species. The contractile tentacles, for which Ehrenberg proposed the
term Vibracles to distinguish them from the retractile tentacles of the
Helices, are solid, homogeneous and projecting cephalic processes,
only capable of shrinkage or contraction, and are quite incapable of
being withdrawn within the body cavity like the retractile tentacles
of the Stylommatophores.

The Stylommatophores have usually two pairs of elongate, cylin-
drical and tapering hollow tentacles, which are filled with blood and
connected with the blood spaces of the head, and bear a well-develo])ed
bulbous distal extremity. The dorsal or posterior pair, in addition
to olfactory organs, bear the eyes at the bulbous end, being hence
termed Ommatophores or eye-bearers, and are usually three or four
times longer than the anterior jiair, which, however, are very similar
in general organization. The anterior tentacles, however, vary greatly
in their development ; in Buliminus and Biqxi they are very short,
and in Carychium quite rudimentaiy, while in Vertigo no external
trace of their existence can be detected.

188

CEPHALIC TENTACLES.

Both pairs are exceedingly Ilexible and can, at the will of the
animal, be withdrawn for safet)" within the body cavity by the con-
traction of the special retractor ninscle, hxed to the apex of each
tentacle, a mode of retraction termed .Vcrendiolic by Prof. Ray
Lankester; their eversion and also elongation being accomplished by
blood pressure and the successive or wave-like contraction of the
annular or transverse muscular hbres of the organ, the apex or bulbous
end being the last part i)rotruded ; this method of eversion or unfolding
by the sides has been distinguisheil by the term Pleurecbolic, in con-

Fig. 3G2. Fig. 3(>3.

Fig. 3(U.

Rctraciile tentaclc.'% of a Styloiniuatophore, showin;? llie retractor muscle and illustrating the
various stages of the mode of retraction and eversion, termed Acrembolism and Pleurecbolism.
'The figures viewed from left to right show the tentacle in process of retraction and from right to
left .as undergoing extension or protrusion.

Fig. 3(>1 .shows the tentacle completely extended ; Fig. 301 completely invaginated ; Figs. 302
and 303 illustrating tlie intermediate stages.

tradistinction to the terms Acrecholic and Pleurenibolic, which
distinguish the i)rocesses by which the introvertiltle or retractile pro-
bosces of some ^Streptoneures are ])rotruded and retracted.

The Streptoneura of our fauna have only two rvell-developed
tentacles, wliicli may be comparatively thick and rounded at the e.x-
tremity, as in Cijclodoma elegdns;, or extremely long and delicately
tajiering to a tine point, as in Buthhihi tentafiddt((, which receives
its specific name fnmi the length and delicacy of its tentacles, but

l)oth forms are contractile only,
and cannot be retracted or drawn
within the body cavity for protec-
tion, as can the hollow retractile
tentacles of the Stylommatophora.
Although, in the terrestrial species
of Strei)toneura, an organ of olfac-
tiem may be located near the apex of each tentacle, as in the Stylom-
matophora, yet the eyes are placed on sluu't i)edicels behind, which
are more (jr less intimately fused or combined with the more develoi)ed
tactile tentacles.

The right tentacle of the male in some gnmps, as in the Vhlpdrw,
is noticeably stouter than the left, this sexual dimorphism being due

Fig. 3lV). — Dor.'tal a.'^pect of the cephalic
region of Cyclostonia elcgans^ showing the con-
tractile tentacles x 1 (after Motiuin-Tandon).

CEPHALIC TENTACLES AND LABIAL PALPS.

189

to its containing the male organ of reproduction, tlie tentacle being-
perforate at the apex for its protrusion, but when not located within
the tentacle, this organ may be placed as a non-invaginable projecting

Fig. 366. — Head of Vhnpara vivipara d
to show the malformed right tentacle, due to
containing the male organ of reproduction
(after Simroth).

Fig. 367.— Valvata piscinalis showing the
large non-invaginahle male organ on the right
side of the neck (after Moquin-Tandon).

process of the body wall, behind it, upon the right side of the neck
and there simulate a third tentacle, as in the Yalmtidw.

The two tentacles of the Basommatophora are also contractile only
and are elongately subulate or flatly triangular processes, according to

the genus, the right tentacle being
often distinctly broader basally
than the left ; the whole surface is
covered with fine, transparent and
very sensitive vibratile cilia, which
have a very vigorous rhythmical
movement, producing perceptiljle
currents in the surrounding water,
as is evidenced by the attraction or
repulsion of small floating particles,
according as they have become
involved in the apiiroaching or departing current. This action is
always most striking when the animal is in
motion with its tentacles extended, becoming-
weak and languid if the tentacles are con-
tracted or the animal he injured or sickly.

In Ancyliis fluviat'dis cilia of the ten-
tacle continue in motion for nearly a hour
after the excision of the tentacle from the

head, the g-yrations it performs recalling the rotation of the emhry
which is also caused by cilial action.

The Labial Palps or lobes in (Gastropods are, when distinctly
developed, exceedingly mobile processes around the mouth, capable
of a considerable amount of extension and contraction, and delicately
sensitive to tactile impressions, receiving- their innervation from the
cerebral ganglia, and ])reserved in a moist and sensitive condition by

Fig. 368. — Head of Planorhis juarghiatiis^
showing the contractile and slender subulate
tentacles, X 10.

Fig. 360. — Head of Liimura
stagnalis^ showing the character-
istic thin, triangular and contrac-
tile tentacles.

0,

190

LABIAL PALPS.

M i

Fui. 370. — Mouth of
as/>t'rsa X {. shoNving the lateral
lobes or Ups and upper jaw (after
Howes).

tlie special mucous secretions from the unicellular glands of the organ
of Semper; they represent the largely developed bilobed velum of
larval life and are retaineil in the Limmvida’ in full proportions by
the adult, hut have lost the marginal fringe of relatively very long
cilia and also the locomotor function.

Some authors distinguish three circum-oral lobes in the Gastropods,
an upper lip which is somewhat rounded
and often hears a number of pai)ill;e, and
two lateral ones, which however are usually
regarded as representing a cleft lower lip.

'I'liese processes are not retractile like
the ommatophores and are chiefly found in
the predacious si)ecies,l)nt are also largely developed in the Llmna’ida\
furniing a considerahle circum-oral e.xpansion or enlargement, but in
a less pronounceil form these labial lobes are jn’esent in other
])ulmonates. In Liiixt.r, virion, etc., the upper li]) bears a number of
distinct and rounded tubercles or ])a])illa‘, into winch the glands of
Semper’s organ debouch (see j). liSo, f .'i.'iT), and which are innervated
bv a liranch from each of the

anterior tentacular nerves, which
gives off to each ]iapilla of its side
a nervous branch upon whii'b a
small ganglion is developed.

The laliial palj)s are, however,
a more es])ecial feature of the
I’elecypods. 'I'hey consist of two
])airs of triangnlarly-oval, thin and
biglily vascular processes, inner-
vated by tlie cerebro-])leural ganglia
and covered with richly ciliated o])itheliuni. 'fhey are formed by the
excessive prolongation and out-growth of the anterior and ])Osterior

margins of the oral ai)erture and hang
down within the mantle cavity, enclosing
between them a ciliateil groove conducting
directly to the mouth the particles of food
brought within the influence of the
currents which the action of the cilia
perpetually excite, and are therefore more especially alimentary and
respiratoiy in function rather than of a tactile oi’ sensory character,

Kui. 371. — .\nterior region of Anodonia
cygnca, showing the position of the mouth
and the relative disposition of the labial lobes
and foot (after Moiiuin-Tandon).

a.p. right anterior palp ; f. foot ; /./. right
posterior jtalp ; ni. mouth.

Fig. 372. — Anterior and posterior
labial palps from the right side of
Anodonia cygnca, isolated, X 3
(after Moquin-Tandon).

LABIAL PALPS.

191

Though a very constant characteristic of the Pelecypoda, they
are apparently quite absent in some few marine genera, but in

others are so greatly developed as
to be even larger than the branchipe;
they have been termed the lesser
and the accessory branchife by
Swammerdam and other authors,
as their gveat vascularity and posi-
tion, each in connection with a large
pallial sinus, suggests some connec-
tion with the respiratory function, their ctenidiform appearance being
materially increased by the jiresence of numerous transverse folds or
ridges, which are most pronounced to-
wards the distal margin, becoming less
distinct or even deficient as the base of
attachment is approached. These trans-
verse ridges also vary considerably in
number and relative size, according to
the species, those of Unio being propor-
tionately larger than those of Anodonta,
and much more so than Dreissensia, in which there are thirty-five of
these ridges on each palp, six times finer than the branchial filaments
In Anodonta there are sixty-five ridges on each palp, while in
Spluvrium corneum var. nucleus there are only twelve.

The bases of the palps are practically almost joined to and continuous
with the lines of attachment of the gill-lamelhe, the anterior palps
being apparently continuous or coterminous with the outer gill-

Fig. 375. — Anodo7ita cygnca, with, the palps
and gill-lamellae removed to show the apparent
continuity of the labial palps and the gills (after
Lankester).

a. anus ; a. ad. anterior adductor ; a.p. line of
attachment of anterior palp, practically continuous
with line of attachment of outer gill ; f. foot ;
g.o. left ureter ; l.c. axis of the left ctenidium or
gill, showing lines of attachment of inner and outer
gills; m. mouth ; n.o. orifice of left reproductive
gland ; p.ad. posterior adductor ; p.p. line of
attachment of posterior palp, practically con-
tinuous with line of attachment of inner gill.

laminm and the posterior palps being similarly continuous with the
line of attachment of the inner branchim, leading Prof. Lankester to
suggest that the branchim and labial palps may be modifications of a
double horse-shoe shaped area of ciliated filamentous processes which
existed in the more primitive mollusk.

Fig. 374. — Four ridges of the
labial palps of Afiodonta cygnca
highly magnified (after Moquin-
Tandon).

Fig. 373. — Three ridges of the labial palps
of Afiodonta cygnea, to show the arterial
vessels, highly magnified (after Keferstein).

192

FOOT AND PERIPODIAL GROOVE.

THE PEDAL OR VENTRAL REGION.

'I'he Podium or foot, vliich arises daring development as a promi-
nence between tlie month ami the anus, is the most per.sistent and
characteristic mollnscan organ, and is formed by an excessive develop-
ment and specialization of the cellular and nnstriated somatic muscula-
ture of the ventral surface of tlie body, in adaptation to a creeping-
mode of life, receiving its innervation from special nervous enlargements
called the jiedal ganglia. The -whole surface contains iunumerahle
unicellular mucous glands, and, in addition, there are important and
extensive aggregations of similar cells situate in certain definite parts,
M'hich render i)rohable a mori)holog-ical connection between the glands
of the Pelecypoda and those of the (histroi)oda.

In (lastroi)ods the foot, though- varying greatly in size and shape,

usually ])resents a long and broad
])lantar surface or sole, which
occupies the whole ventral surface
of the body, but tho.se species with
narro-w plantar area are ai)parently
endowed with more rai)id loco-
motive j)owers than those -with a
more exi)anded surface. In the
aquatic species the surface of the
foot is richly covered -^vith vibra-
tile cilia, but in those of terrestrial
hal)it the ciliated area is compara-
tively restricted.

'I'he Peripodial (Jroove or pedal
fuiTow is a more or less distinctly
marked groove, separating the body
region from the sole and is more especially found in the nude species ;
it runs parallel with the edge of the sole of the foot along its whole
length round the body, and is occupied by a more or less con.spicuons
row of narrow, oblong, horizontal
tubercles, upon which the tuhercles
of the .sides of the body rest un-
comforniably. 'I'he groove in some
genera rises slightly towards the
tail, where there is often a Caudal
mucous gland containing a greater development and concentratifui of

Fig. 376. — Ventral aspect of the fool of
Helix asf>cysa^ showing its character and
general form, as seen crawling up a slip of
glass (from an instantaneous photograph).

Fig. 377. — Peripodial Groove and Foot
Fringe of Arion ater x 2.

fr. foot fringe ; p.f. peripodial groove or
pedal furrow.

FOOT FRINGE AND PODIAL LOBES.

193

mucous cells. The super-families, Aulacopoda and Holopoda, are
based upon the presence or absence respectively of the pedal grooves,
which, when present, are ventrally circumscribed by the Foot Fringe,
a feature distinctly present in some forms and constituting the lateral
border of the foot. In Avion it is often very brightly and vividly
coloured, and variegated at regular intervals by numerous dusky and
black, alternately placed, vertical lineoles, which in strongly coloured
individuals may be continued across the side areas of the sole. As
the tail is approached these lineoles become placed nearer together
and more obliquely directed.

The foot, in some groups, gives off various lobes or processes,
which when arising from the Epipodium, a thickened ridge along

Mthe upper margin of the sole, ai'e known
as Epipodia; the Operculigerons lobe of
the Streptoneures, which secretes the
operculum, is a dependence of the hinder
portion of this e])ipodial ridge, while the
Fig. 378.— Prosoma of vivipara. Ceplialic lobes of Vivipdva are a develop-

vivipara $ (after Moquin-Tandon),

to show the epipodial Cephalic lobes, meiit of the anterior part, such processes
being distinguished from cephalic tentacles by receiving their innerva-
tion from the pedal or pleural and not from the cerebral ganglia.

Analogous processes, termed Parapodia, may, however, originate
along the basal edge of the sole ; such outgrowths, though highly
developed in many Opisthobranchs, are not noticeably present in our

Fig. 379.

Fig. 380.

Diagrammatic sections through the body of a Streptoneurous and of a Tectibranchiate Gastropod,
showing the relative positions of the Epipodial and Parapodial lobes (after Lang).

Fig. 379. — A Streptoneure ; f. foot, with epipodial lobes ; sh. shell; v.s. visceral or body cavity.
Fig. 380. — ATectibranch ; f. foot, with parapodial lobes ; sh. shell ; v.s. visceral sac with ctenidium.

land and freshwater species, although the spreading sides of the foot
of Helix pomatia may be regarded as incipient parapodia.

In certain extra-British species, the primitively sole-shaiied foot
has, by adaptation to special modes of life, lost its original form and
by transverse constrictions, become formed into three regions, termed
the Propodium, the Mesopodium, and the Metapodinm, which respec-

N

r

DIVISIONS OF THE I'OOT.

1 ;» I

lively indicate its anterior, middle, and posterior regions, yet in onr
native species, with the exception of Acicuhi, which, according to
Dr. (fray, has a transversely divided sole like TruncateUa, these parts
are so intimately blended together that we are only able to dis-
tinguish the metapodinm owing to its being indicated by the oper-
cnlum on its ni)per surface.

'rhongh not divided transversely, the sole may have well marked
longitudinal divisions, and this feature is carried to the greatest ex-
tent in Ci/clostoiixc elegants, in which
species the foot is medially cleft
and separated along its whole
length, each part being advanced
alternately during locomotion. In
V(tlv(tf(( pisciiialiti and D. criatxtd
this cleavage is confined to the
prolonged anterior part of the foot, where the divided parts become
widely separated and divergent, simnlating a pair of jiodial tentacles.
In onr native species of Vlviparx,
although the anterior portion of the foot
is similarly prolonged beyond the muzzle,
it is not medially cleft, so that the crea-
ture is said to be prevented from feeding
except when at rest.

In Lima,)’, A)-io)), etc., the sole is more or less distinctly
longitudinally tripartite, the side areas being nsnally more darkly and
distinctly pigmented than the locomotory mid area, owing to the
thickening of the epithelial and snb-epithelial mnscnlature which

Fir,. 3Sl. — Cyclostoma elegans, showing
the longiiutlinally cleft foot, with the right
segment in use, the left being contracted and
raised, X 2 (after Simroth).

Fig. 382. — I’alvaia J>lscifiallsy
showing the cleft and divergent
anterior ends of the foot, X 2.

Fig. 383. — Sole of Lhna.v cine>ro-uiy:e>% showing the trifasciate foot and the muscular waves of
the mid area, vi.sible during movement (after Simroth).

prevents its free pigmentation, d'he side and mid areas in Llma.r,
though not in Ai'hin, are also separated by more or less distinct longi-
tudinal furrows, which, though often imperceptible during life, become
visible after the immersion of the animal in boiling water or alcohol ;
but in the testaceous Enthyneures the entire sole is more or less

REPTARY AND SUBREPTATORY FOOT.

195

locomotory and muscular, being apparently homogeneous in structure
altliough the mode of pigmentation is not uniform, even in closely
allied species. In Helix aspersa trifasciation is perceptible owing to
the greater pigmentation of the side areas, but in Helix pomatia the
mid area is the most darkly coloured, the sides being usually (piite
unpigmented and very distinctly defined thereby.

In the Pelecypods the foot arises ventrally from the body, and in
Nucula and otlier archaic s})ecies forms a
fiat sole or creeping disc, by the expansion
of the deep longitudinal cleft therein; such
forms are distinguished as Reptary, and
present a curious similarity to Helix pomatia
and certain other species, in which the foot
is longitudinally folded up in the same
manner when the animal is retiring wdthin its shell.

j\Iost of our species are, however, Subreptatory, possessing a laterally
compressed, very extensile and fiexible linguiform or axe-shaped
organ, with annular muscular bands to assist in its extension and
longitudinal muscles for its retraction, being, however, still expansible
as a fiattened crawling disc, although the longitudinal groove charac-
terizing the primitive Reptary foot has become lost. The degTee of

Fig. 386. — Drcissetisia polyiuorpha (Pall),
Fig. 385. — Sphcerium rhncola (Leach), Canal, Northampton,

showing the Subreptatory burrowing or Collected by Mr. L. E. Adams, B.A.,

crawling foot. Showing the digiiiform and vestigial foot.

development is in correlation with the habits and locomotory powers
of the mollusk, as it may be modified to form an efficient burrowing
organ and tend to assume a more anterior position or become somewhat
digitiform and vestigial, as in Dreissensia. The tip is often more
deeply coloured and of a reddish tint, owung to the presence of
Tetronerythrine, a substance which corresponds with the hfemoglobin
of Planm-his and the higher animals and serves for cutaneous respira-
tion by its great affinity for oxygen.

The tissue of the protruded foot becomes rapidly firm and rigid by
blood pressure or, as some believe, by inception of the surrounding

Fig. nuc/cus (h.)

(after H. A. Adams), showing
the longitudinally grooved or
primitiv’e Reptary foot.

106

PEDAL GLANDS.

water within a system of vessels wliieh may or may not communicate
with the circulatory hlood system ; the orihces supposed to he aquiferous
are, however, merely the outlets of aggregatetl mucous glands or the
vestigial opening of the hyssogenous gland which are all placed on the
posterior side of the foot. In Xaticd josephimi, a marine Gastropod,
it has, however, been fully establi.shed that, ([uite independently of the
l ilood system, the foot does contain a very comple.x and extensive water
vascular system, hy means of which the foot can he very rapidly
expanded and extended for locomotion.

'fhe surface of the foot is richly ciliated and furnished with a great
number of unicellular mucous glands, but there are also distinct
invaginations of the ectoderm or integument, known as Pedal glands,
where mucous cells are aggregated together and distinctly localized.

An Anterior Pedal Gland is i)ossossed by the active a(|mdic Strep-
tonenres, which opens at the anterior end of the foot by a transverse

groove and secretes mucus for
the lulirication of the foot and
to aid in the process of crawling.
This gland is represented in the
Puhnonates and in terrestrial
Streptoneures by the Snpra-
I’edal gland, known also as the
sinus of Kleehurg, a long e])ithelial tube with ciliated ventral snrfiice,
jilaced between the muzzle and the foot, which was formerly thought
to he an oltactory organ, Imt
which serves as a reservoir and
duct for the mucus which its
inve.sting cells abundantly
secrete. In C^clostfinid this
gland becomes bihd posteriorly
in harmony with the longitu-
dinally divided foot.

'I’he Ventral Pedal tSinus is
found in Cydmfnmd and many
Streptoneures, being comparable
with the byssal cavity of the
Pelecypods. It opens on the
anterior portion of the foot-sole,
torming the apertiu'e of the sole gland, whose glandular epithelial

Fua 387. — Prosoma of Helix x 2, r'howing ihe
position of the Supra-Peclal Gland,

Fig. 388. — Supra-Pedal Gland of Cyclosto7)ia
elegans{2i{\.^x Siniroth), highly magnified, showing
the bifid posterior prolongations.

PEDAL GLANDS.

197

walls project into the lumen of the body, as a multitude of rauiifyiug
tubules and follicles.

The Caudal gdaiids are often found in terrestrial Gastropods at the

upper surface of the posterior end of
the body, and form a sinus or cavity,
such as is present in Hyalinhi
and very conspicuous in Arion.
In the foreign genera the gland
is sometimes distinguished by the
development of a more or less
striking pr-otnberance. Its secre-
tions, which are very abundant and
much denser than those from the
skin, accumulate in the more or
less triangular caudal cavity.

The Pelecypods sometimes possess on the posterior median line
an orifice which is homologous with the Ventral pedal sinus of the
Gastropods, and communicates with a byssal cavity in which are
gathered the secretions of the foot glands, which have permeated
the epithelial cellules lining the byssal cavity, and harden on ex2)osure
in elastic adhesive filaments, whose aggregation forms the byssus and
serves to attach the animal, as in Dreissensla. The byssal gland
varies greatly in development in different genera and is often present
in the young stage when absent in the adult. The calcareous plug of
Anomia is a modified byssus.

In addition, there are in some species two other glandular orifices,
one anterior and the other posterior to the position occupied by the
vestigial byssal aperture, which it is possible may represent the
anterior and posterior mucous glands of the Gastropoda.

Although mucus is emitted from all parts of the body, that secreted
by the Supra-Pedal gland is of the greatest consistency, and in the
nude species especially, is exuded so plentifully as to leave an
iridescent silvery or tinted mucous trail which marks the course the
animal has travelled. This mucus hardens very quickly on exposure
to air or water, becoming very tenacious and firm, and is utilized by
some species as a means of locomotion and for descent from or ascent
to an elevated position.

Fig. 389. — The posterior dorsal aspect of
Hyalinia. cellaria.^ contracted after scalding,
to show the Caudal INIucus cavity, and in-
cidentally the rugosities of the body, the
fringe and the peripodial groove, X 16.

fr. fringe ; vi.gl. caudal mucous gland ;
p.f. peripodial furrow.

19S

1>ALLIAL FUSION.

The Pallial Region.

'File ]\Iantle, or Palliiiiii, is a tliiii and vascular fold of the iiitegu-
iiieiit, which is fused to and covers the dorsum of the body and arises
during development around the primitive shell gland, its thickened
and glandular margins, which are the active formative organs of the
shell, enclosing, in conjunction with the body wall, a pallial cavity
communicating more or less freely with the external medium and pro-
tecting the resiiiratory organs, which may exist as gills or ctenidia
for the respiration of water or, in the terrestrial species, may take
the form of a lung constituted by an intricate network of blood vessels
distributed upon the roof of the pallial cavity. In the Streptoneures
and the more i)riniitive Pelecypods large I I}qiobranchial mucous
glands are developed within the pallial cavity between the rectum and
the branchiic.

The Fusion of the pallial margins to each other and to the body
wall to form an enclosed resi)iratory cavity, has not been carried to a
great extent amongst the Streptoneures of our fauna, the cavity being
more or less freely open anteriorly to the inhabited medium.

In the Euthynenres this process has, however, become further
advanced, and the jiallial margins have fused with the body wall,
leaving only a .small contractile lateral oribce for respiratory and
excretory purposes, which ilivides the mantle more or less distinctly
into an anterior and a posterior lobe (.see p. 144, f. 304).

In the Pelecyiioda the mantle is e(|ually developed laterally, en-
closing a symmetrical iiallial cavity. In the more archaic forms, as

Di.-iSr.nms illu.'itratmg the position anti mode of fusion of the mantle lohes of the Pelecypoda
(after Lang). The arrow.s indicate the direction of the currents. right mantle iobe \f. foot.

Fig. Illustrating the primitively open mantle with unseparated respiratory currents.

Fig. HOI.— liiforate Pelecypod, showing a single point of fusion of the right and left mantle
lobes, and separating the inhalent and exhalent currents.

Fig 392.— A Triforate Pelecypod, showing two points of fusion, which form the e.'ihalent and
inhalent orifices and a large pedal aperture.

Nucula or Trujonia, the pallial margins are quite free ventrally, no
provi,sion being made, except sucb as is provided by cilial action,
tor the separation ot the pure incoming and the impure out-flowing
currents. Specialization is evidenced by a vascular fusion of the
mantle margins, primarily to ensure the separation of the in-Howing

PALLIAL FUSION AND PROLONGATIONS.

199

and out-flowing streams, as this fusion almost invariably takes place
near the middle of the posterior margin and cuts off fi’om the great
ventral cleft a small exhalent postero-dorsal orifice, directly opposite
to the anus ; the species with this single point of fusion, which thus
divides the gTeat mantle opening into two apertures, a large antero-
veutral pedo-hranchial cleft and a smaller dorso-posterior anal opening,
are termed Biforate. The Naiads illustrate this stage of specialization,
although the anal cleft is divided by a central subsidiary fusion into
two distinct though coiiiiected orifices.

The succeeding stage is characterized by a second point of fusion
of the mantle margin, which invariably takes place at a point more
ventral than the first and near the junction of the ventral and posterior
margins, separating the great pedo-hranchial cleft into a branchial and
a pedal opening, the anterior one serving for the protrusion of the
foot, and the posterior one, which adjoins the anal pallial opening,
forming the branchial or inhalent aperture ; there are thus three
openings, which subserve three distinct functions ; such forms are
kuowm as Triforate.

This process of fusion is carried to a still further extent in species
not within the scope of our studies, both by more points of con-
crescence and by their gTeater extent.

The Prolongation of the respiratory apertures to form retractile
siphons is a further and extreme specialization of the fusion of the
mantle margins, and appears to be a characteristic of an aquatic
existence, being strikingly developed among the carnivorous marine
Streptoneures. Amongst our species this feature is not noticealily
developed, although in Vivipara the i-ight cephalic lobe, which is an
outgrowth of the foot, becomes folded and forms a siphon which con-
ducts the respiratory water to the branchial cavity.

Fig. 393. — Limtuea stagnalis V7\.x. fragilis
(L.), Chislehurst, Kent, collected by Mr. S. C.
Cockerell, showing the respiratory aperture
contracted.

Fig. 394. — Li))i>upa pcregc>'(^ (Miill.), Christ-
church, Hants., showing the prolongation of
the pulmonary aperture as a respiratory tube.

Amongst the Basommatophora the Limnwcc especially are capable

PALLIAL prolongations.

•200

of foniiiiiK the pallial margin of the respiratory orifice into a long,
conical and extensile tube, the delicately sensitive apical orifice of
which is kept closed until it reaches the surface of the water, when
it is opened to the air for respiratory purposes.

In the Pelecypoda the develoiinient of the branchial and anal
orifices to form elongate siphons is ai)parently one of the modifica-
tions more esi)ecially fitting the mollusk for flnviatile or estuarine life
hut is more palpably correlated with the habit of burrowing deejily
in the muddy or sandy bed of the water they inhabit, and where this
lieculiar habit of concealment is carried out to the greatest extent
the longest siidions are developed, and the constant and regular
stream of water necessary for respiratory and alimentary purposes is
only able to enter and leave the pallial cavity by means of the
elongate si])hons, whose protractile orifices i)roject into the water above
tlie place of concealment of the animal ; while in those species which

Fig. 395. — Pisuiiunt amnicttin (Miill.) Fig. 396. — Spha'rium corneum (L.) X 2,

X 2, illustraling the development of a single illustrating the development of two distinct

siphon. siphonal tubes.

Kettering, collected by Mr. C. E. Wright. Kettering, collected by Mr. C. E. Wright.

live or move freely in the water, the mantle is usually completely open
with res})iratory apertures very slightly or not at all prolonged and the
papillcC, tentacles and other protuberances more or less sensory in
character are distributed indiscriminately along all the free mantle
margin. In tlie burrowing forms these accessory sensoiy organs are
more or less concentrated at the posterior margin, around the siphonal
ai)ertures, but more especially at the branchial or inhalent opening.

These prolonged muscular tubes or siphons, which are mostly
protruded by blood pressure and withdrawn by the contraction of the
modified orbicular muscles, are often separated and form two out-
wardly distinct channels, as in Sphwnum, but are very variable in
their relative length; in Dreissensia and S}}hwrium the branchial
siphon is longer than the anal one ; but in Pisidimi the reverse is very
strikingly shown, as although the anal siphon is greatly prolonged,
the branchial aperture remains unseparated and undifferentiated from
the great mantle cleft.

PALLIAL OUTGROWTHS.

201

Fig. 397. — Planorbis corneus {L,.), showing
the exsertile Auriform Lobe (after Pelseneer).
rJ. respiratory or auriform lobe.

Tlie Extension or outgrowth of the mantle margins may, as in the
Euthynenra, form the Auriform Lobe, known as the respiratory
and also as the fecal lobe, a tegumentary appendage near the respira-

toiy orifice, which may bear the
anus or termination of the rectum.
In Planorhis this lobe is largely
develoi)ed and exsertile with a rich
vascularization, and a similar but
much smaller and slightly twisted
prominence has been observed to
exist in certain species of the Helicida'. The “balancier” of Vitr'ma
is a somewhat spatulate outgrowth above the respiratory orifice,
kept in almost incessant motion by the animal. The Columellar
Lobule, a somewhat triangular pallial process of the hinder margin,
is also developed in some species and is especially noticeable in those
forms in which the umbilicus is closed by a shelly deposit.

In the Streptoneura of our fauna the instances of pallial outgTOwths
are few and insignificant. In Yimpara, the right mantle margin
bears a number of slender but hollow processes of various sizes,
which give rise to the spiral rows of minute hairs which encircle the
young .shell, and Valvata possesses a well developed pallial tentacle
on the right side which has been thought to be the vestigial
representative of the vanished, but primitively left ctenidium.

In the Pelecypoda similar processes evidently exi,st on the mantle
of Sphcurium corneum, whose shell when young bears numerous
small and projecting hair-like processes.

The Enclosure of the shell within the mantle, owing to the exten-
sion and fusion of the pallial margins, is known to exist in exotic
species belonging to each of the groups of mollusca represented in our
fauna, yet it is only in the Euthyneures that we have species which
enable us, though disconnectedly, to show some of the stages in this
particular line of pallial specialization, which leads us from the typical
Helix, with the mantle margins extending to or slightly overlapping
the aperture of the shell, to Avion, with the shell covered in and
practically lost by the overfolding of the mantle.

That Avion and other naked species are derived from forms with
distinctly developed shells is shown not only by their retention of the
vestiges of a shell, but by passing through a stage of development in
which a distinct spiral shell, containing the intestinal sac, is present.

2(»2

PALLIAL OUTGROWTHS.

and the asynniietry of their internal organs and external orifices can
only he satisfactorily explained as having been inherited from ancestors
with spirally twisted intestinal sacs and shells.

In Vitrina we have the first distinct stage in this process of the
degeneration of the shell hy its enclosure within the pallial folds,
which project anteriorly in the form of an incipient limacoid shield
and laterally as a si)atnliform lobe, both partially overspreading the
external surface of the shell, which is evidently reduced in size as well
as in substance, as the body of the animal is now only capable of
being wholly contained within the shell during dry weather.

P//>/s(> fontinaliK, though not a Stylommatophore, will serve to show
a further advance in the develo})ment of the mantle lobes, as although
they still have a very digitate character, especially ou the left side,
they have almost oversjiread the shell. The comparatively large size
of the foot is due to the diminution in size of the shell.

Pig. 398. Fig. 399. Fig. 4(10.

Illustrating the stages of the proce.ss leading to the degeneration and loss of the shell owing to
its enclosure within the pallial lobes.

Fig. 398. — I'itrina fcUucida (Midi.) X 1.4, Horsforth, near Leeds, showing the first stages of
pallial e.\pansion. Fig. 'i'Xi.—Physn fimthialis {J..) X 2, River Tome, Doncaster, illustrating a
further advance of the process. _ Fig. 400. — Atuphipff'lca glutinosa (Midi.), Skidby Drain, Hull,
collected by Mr. F. W. Fierke, in which the shell is almost entirely enveloped by the m.antle.

Amphqn'pkd glutinosa, another Basommatophore, idthough able
to entirely cover the shell by its extended p;dlial lobes, does not
usually do so, a small rhomboidal dorsal space being generally left
uncovered, enabling the maculate body of the .uiimal to be seen
through the transparent shell. The foot does not exhibit any disiiro-
portionate size in comparison with the size of the shell, owing to the
degeneration the shell is undergoing having more especially affected
its substance and not its magnitude. In :dl these cases it is instruc-
tive to observe the noticeable paucity in the number of whorls of the
shell and the exceeding delicacy and tenuity of its substance, both
characters induced by the overwrapping of the mantle lobes.

The genus Avion illustrates the disappearance of a definite shell,
the anterior mantle or shield, as it is called, having assumed a very
tough and leathery consistency, its margins comi)letely overlapping
and fusing together to f(.)rm a sac enclosing the calcareous granula-
tions which rejiresent the vestigial shell.

pallial outgrowths and degeneration.

‘20;^.

When thiLS developed, the interior surface of the mantle having-
become permanently external, assumes special sculpture and markings
in harmony with those of the body. In the Limaces it becomes
more or less regularly concentrically fniTowed, hut in Avion these
concentric wrinkles are not perceptible, the whole surfiice being some-
what uniformly granular,
although during strong

Fig. 101. — Arion horteiisis F^r., Horsforth, near COlltractlOn ail appcaraiice
Leeds, illustrating the complete infolding of the shell n . • .j. • j •

by the mantle and its consequent atrophy and loss. Oi COllCGlltriC StriRtlOll IS

apparent at the anterior end. In Amalia the mantle, though simply
rugose, displays a smooth, somewhat rhomboidal furrow, which is
deepest on the right side ; it is sub-angulate in fi-oiit, rounded on the
left side and distinctly angulate on the right, the point joining the anal
furrow anterior to the respiratory orihce ; its use may possibly be to
drain some secretion into the mantle cleft.

In the Pelecypoda of our fauna we have no examples of such high
pallial specialization as we find in the Arionidw and Limacidw,
although such a form is actually known ; the genus Chlamydoconcha
having the mantle lobes so greatly developed that they have com-
pletely enclosed the shell, the valves of which have lost their con-
necting ligament and adductors and are now separately imbedded
within the pallial lobes.

The Reduction in Size of the mantle and shell may be in correlation
with the detorsion of the visceral sac or from adaptation to special or

Fig. 402. — Tcstacella haliotidea Drap., Oxford, collected by Prof. E. B. Poulton,

Illustrating the reduction of the mantle and shell resulting from the detorsion of the body and
adaptation to a special mode of life, and incidentally showing the strongly marked lateral grooves.

peculiar habits of life, and we have a striking exemplification of this
feature in the genus Testacella, a group of mollusks especially adapted
to a subterranean existence, in which the visceral sac has become
untwisted and the respiratory organs returned to the rear of the
animal, the mantle being reduced to the smallest dimensions and
placed at the extreme hinder end of the body, its shell forming a shield
or protection at the rear while the creature is traversing the worm-
burrows in search of the worms upon which it feeds.

204

BODY SCULPTURE.

With the atrophy or redaction of the shell and its predominant
intlnence as a modifying factor lost, the foot, the body, and the
mantle are free to develop sncli protective moditications in form,
colour, textnre or function as may he best adapted to compensate for
its loss, snch compensation may be by the development of a thicker
and tougher integument, of a more abundant mncosity, or of colonring
or markings harmonizing more closely with the nsnal snrronndings of
the animal ; in marine species, stinging cells, antotomy or voluntary
amputations of portions of the body, and a great capacity for regenera-
tion of injured parts may be instanced as some of the compensatory
attributes that have been accpured.

The Visceral or Body Region.

'I'he Body is usually more or less covered by the mantle, and consists
in the testaceous species of the dorsally projecting, visceral sac and
the connected cavity above the muscular foot. It varies in shape
according to the genus and in the xirionidw and Lbnacidw the spirally
coiled dor.sal region, which characterizes the testaceous Gastropods,

Diagrammatic sections showing the arrangement of the visceral sac, etc., in the coiled HcUcidte
and the secondarily symmetrical Lintacid<e (after Hinney).

Fig. 403. — L'lDia.x. Fig. 404. — Jlciix. b.c. body or visceral cavity ; c. collar of mantle ; r.c.
respiratory chamber ; sh. shell.

has become depressed and battened out, so that all external trace of
its former coiled condition is lost and a secondary external symmetry
acquired ; the mantle and shell being also reduced iu size, the body
region is consecpiently permanently exposed and its integument has
therefore accpiired a thicker and more coriaceous character.

The surface of the body, though generally thin, soft and flexible, is
covered, in the terrestrial si)ecies, by more or less closely disi)Osed and
prominent rugosities, which vary in number and character according
to the species, the interstices between them serving to distribute over
the surface of the body the mucus poured forth by the glandular
integument, but in addition to the local diffusion of the mucus thus
secured, there are deep and longitudinally disposed grooves, which
extend from the pallial region to the anterior part of the body, and
give off during their course many subsidiary and ramifying branches.

BODY SCULPTURE.

205

Fig. 405. — Sticcinea piitris (L.)
X 3, Christchurch, Hams., showing
the dorsal grooves.

The Dorsal Grooves form the principal longitudinal gTooves or
furrows ; they are a pair of parallel and
deeply marked channels, separated by
a row of elongate tubercles, and extend
from between the tentacles, along the
centre of the back, and may be con-
tinued anteriorly upon the muzzle as the
facial gTooves.

Tlie Lateral Grooves are distinctly developed only in the testaceous
forms, the right lateral groove arising near the pneumostome and
reaching to the base of the tentacle near the genital opening, the
left gToove when present having a similar course ; and the tubercles
or rugosities of the body being usually noticeably larger and more
oblong above the grooves than beneath, this difference in character
being sometimes very sharply marked. These grooves, though now
only serving to assist in the dissemination of the fluid mucus over
the body, probably indicate the position of the ciliated conduit,
which formerly conveyed the seminal fluid from the genital glands to
the male organ ; they are
especially developed in Teata-
cella, arising together be-
neath the anterior margin of
the mantle, and traversing
the sides of the body, giving
off during their course a number of anteriorly directed furrows, whose
ramifications are gradually obliterated in the general roughness of
the integument.

In the Pelecypoda the usually oval body, being entirely enclosed by
the mantle lobes, is soft, smooth and somewhat strongly ciliated, hut
the viscera have also become deeply sunk within the foot.

In the Anisopleurous Gastropods, the dorsally protruding body has
been subjected to a very remarkable and combined antero-ventral and
lateral twisting or torsion, which renders it more compact and brings
together the opposite ends of the alimentary canal. Such torsion is,
however, not confined to Gastropods, or even to mollusca, as analogous
processes have been observed to take place in Crustacea, Biyozoa,
Echinoderms and other forms of life.

The ontogenetic history shows this twisting in the Gastropods to
occur before anything else which alters the primitive form, as the

Fig. 406. — HyaUniahelvetica'^\\xm x 2, Horsforth,
near Leeds, showing the lateral grooves.

20G

TORSK^N OF THE liODY.

animal is strictly symmetrical np to the Troclios})liere stage, the pallial
cavity being then in the rear, as in the hypothetical primitive mollusk,
bnt is brought to the front above the neck by the cessation on the
right side of the embryo of the growth, which is uninterruptedly con-
tinued on the left. This torsion, eft'ected during development in the
Streptoneures, is also manifest in the Euthyneures at the commence-
ment of embryonic life, Imt becomes indefinite and in great part lost
at a later stage by a movement or twisting in the opposite direction.

The Antero-ventral torsion to which the primitive exogastric
inclination of the liody is due, i)robably arose on account of the
increasing size of the foot seimrating more and more widely the
anterior and posterior openings of the alimentary canal. The lateral
twist of the body, with which the antero-ventral torsion is practically
combined, is owing to the continually increasing protrusion of the
hernia-like visceral dome and the development upon it of a long,
heavy shell, giving protection to and a means of concealment for the
entire animal, which was gradually becoming more actively rci)tant.

Fig. 109.

Fig. 110.

Diagrams illustrating the various positions which it is possible for the hypothetical, unwieldy
elongated shell to assume (after Lang). columellar muscle ; c. clenidia or gills ; a. anus.

Fig. 4(17 shows the shell in its hypothetical primitively upright position.

Fig. 4(1S shows the shell forwardly inclined, the most unfavourable position for locomotion, but
the most favourable imaginable for the exercise of the functions of the posterior pallial organs.

1' ig. 4(11) shows the shell inclined to the rear, the most favourable position for locomotion, but the
most unfavourable for the exercise of the functions of the organs confined within the compressed
mantle cavity.

P'ig. 410 shows the shell inclined to the left side, the position it would most probably assume as
combining least interference with locomotion and with the exercise of the functions of the posteriorly
placed pallial organs.

As seen by the illustrative tigures, wlien the shell became so
unwieldy from its increasingly elongate form and necessarily unstable
e(iuilibrlum that it could no longer lie conveniently canded in an
upright position, it would probably gradually lean over to one side,
which, all things considered, would be the most favourable position
it could occui)y, Imt during locomotion, it woidd naturally tend to

become more posteriorly directed.

In this position the compression due to the recumbent shell would
bear heavily upon the organs 2)laced at the left side of the body, if
the shell leaned over to that side, and the compressed organs would

TORSION OF THE BODY.

■207

gradually become displaced and move towards the right side of the
body, which would be favourably influenced for their reception by
the strain of the shell upon the opposite side, and the shell would
become more and more posteriorly placed according as the organs
beneath moved round towards the right, to attain the most favourable
position for the free exercise of their functions, which would be the
side of the body opposite to that upon which the shell was recumbent,
until owing to the constant tendency of the shell to take up a position
in the rear as that most favourable to locomotion, and the equally
constant and con-elated movement of the organs to attain a position
opposite to it as offering least interference with their functions, the
l»allial organs eventually occupy the anterior part of the body

opposite the shell, which has at length
deflnitely assumed the posterior position
most favourable to locomotion, and also
to the free action of the now anteriorly
placed respiratoi-y and excretory organs.

But when the shell became long and
unwieldy and tended to fall over to the
side of the animal, the body and shell
could no longer retain their simple conical
shape, as owing to the lateral inclination
of the shell the base of the visceral dome
would be uncovered at the right side if
the inclination of the shell was to the left,
and the gTOwth necessary to protect the part thus uncovered would
necessitate a quicker increase there, which would consequently be the
point of maximum growth and hecome convex, while the opposite or
underside would be the point of minimum gTowth and become concave.
If the shell retained the same position during growth a discoid shell
would be produced, but if the growing shell on account of its shape,
increasing weight, or other cause becomes altered in position towards
the right the point of maximum growth would be changed and the
spirally coiled dextral shell and visceral sac would result, which
the now asymmetrical pallial cavity has assisted to perpetuate.

The long continuance of the unfavourable conditions to which the
primitively left organs of the pallial complex were subjected by the
compression due to the heavy external shell, eventually brought about
their more or less complete degeneration and loss, thus leaving vacant

Fig. 411. — Diagram illustrating
the graduation of the compression or
strain to which the visceral dome is
subject if the shell be inclined to the
left (after Lang). The thickest lines
indicate the point of greatest com-
pression and the thinnest lines the
point of least compression. The
arrows indicate the direction in which
the twisting takes place, owing to the
position of the shell on the left side.

TORSION OF THE BODY.

208

tlie space at the anterior right side of the pallia! cavity which the
atrophied organs wonld normally have occupied ; the organs of the
left side of the cavity have, however, moved backwards towards the
right and filled the vacant space ; hy this nnwinding movement or
l)raetical partial detorsion the aims, which was placed near the median
line aliove the neck, eventually came to occupy a position at the
extreme right of the mantle cavit}".

In the Streptonenres this torsion of the body is gTeater than in the
other gTonps, but the asymmetry of the internal organs is not always so
complete as in the less distinctly twisted Euthynenres, some genera
still retaining the primitively paired gills, nephridia, and other organs,
hnt the i)allial opening is placed at the front, over the neck of the
animal, and the pleuro-ahdominal commissures are crossed, both cir-
cnmstances owing to the twisting undergone hy the body.

In the Euthynenres, although the twisting of the body is less, as
shown liy the lateral opening of the pallial cavity and the relative
positions of the pallial organs, yet the asymmetry of the internal
organs is greater, as all traces of the originally left half of the primi-
tively j)aired organs have disappeared and renders reasonable the
sn})position of Prof. Pelseneer that the Euthynenres are to he regarded
as derived from and as in a more advanced stage of specialization than
the Streiitoneures, which are our most primitive forms and that the
less amount of body twist and greater internal asymmetry they exhibit
is owing to a process of partial detorsion which the Euthynenres have
j)rohahly undergone ; all those animals whose visceral dome has under-
gone com[ilete detorsion, as shown Ijy the return of the respiratory
and other organs to their primitive position at the rear of the animal,
are liable to the disappearance or partial atrophy of the mantle and
shell, as strikingly shown in the Oinsthohranchs and in the terrestrial
genus TcstaceUa, which is distinctly opisthopneumonic, the respira-
tory organs being now posterior to the heart.

Although our Pelecypods show little sign of having undergone any
noticeable torsion of the body, except such coiling as the Prosogyrate
umhones indicate, yet the group is not exempt from it, as the animals
of the genus Trlducna clearly show that their body in its relation to
the shell has been snbjected to an anterior rotation or twist of
nearly 180°, which has brought the posterior adductor muscle to
near the ventral margin of the shell and the mouth or oral aperture
close to the umhones.

NERVOUS SYSTEM.

209

The Internal Organization.

The internal organization of the mollusca is characterized by a
certain degree of uniformity due to the common origin of the phylum,
but this general ancestral likeness has been partially obliterated by
the development of adaptive characters, more especially correlative
with the special habits of the animals.

NERVOUS SYSTEM.

The nervous system, upon which sensation and muscular motion
depend, resembles in some respects that of Vermes ; it is of para-
mount importance in the animal organization, while being the last to
be influenced by the morphological modifications undergone hy the
animal, its peculiarities acquire very great phylogenetic significance,

and have been used by Scbimkewitsch
as the basis for the classification of all
Bilateralia, the mollusca being termed
Tetraneura, and characterized by the
possession of cephalic ganglia, with paired
ventral and lateral nervous cords. It is
also more generally used in a restricted
way to separate two great groups of
Gastropods, according as the pleuro-
abdoniinal commissures are straight or
still twisted by the torsion which the
body of the animal has undergone.

The nervous system consists essentially
of nucleated ganglion cells and nerve
fibres, forming Ganglia, Connectives,
Commissures, and Nerve Fibrils, which
are invested by the Neurilemma, a some-
what fibrous and more or less deeply
pigmented sheath of connective tissue.
Although primitively characterized by
the absence of any local concentration
of its various parts, which were probably
constituted by ganglionic nerve cords, such as still represent the
pedal

Fig. 412. — Diagram of the nervous
system of a mollusk, showing the
bilateral arrangement of its consti-
tuent parts and their relation to the
median line of the body.

g. ganglia, or paired aggregations
of nervous tissue ; con. connectives,
the longitudinal nerve cords joining
dissimilar ganglia and never crossing
the median line of the body ; co7n,
commissures or transverse nerve
cords, connecting the moities of the
same ganglionic centre and therefore
always crossing the median line of
the body ; n.f. nerve fibrils.

ganglia of Vivipara, yet usually the nervous tissue has now

15/11/9G,

0

210

NERVOUS SYSTEM — GANGLIA.

become decicledly concentrated and forms enlargements or ganglia
in various i)arts of the hotly, which are connected together by nervous
cords and give rise to innumerable delicate nerve fibrils, whose
ramifications extend to all parts of the animal.

Tiie Ganglia are the most important part of the nervous system,
anil are constituted by concentrated masses of whitish, or somewhat
pigmented, nerve tissue, which arise during embryonal development
by the thickening and subse<tueut invagination of the epiblast or

integument. They are composed of ganglion cells of variable size,
each of which may be furnished with some minutely delicate processes
called Dendrites, and one or more strong fibrillar prolongations, the
cells being known as Unipolar, Bipolar or Multipolar, in accordance
with the number of these important nerve fibres emanating from them ;

I'Tg. 41G. Fig. 417.

Fig. IK). — Axis cylinder of the visceral ganglion cellsof Unio pic torn ni {V,.) X 500(after Rawilz).
Fig. U7. — Axis cylinder of the cerebral ganglion c^\\so( A noi{o?it a anatina (L.)x500(after Rawitz).

these various prolongations are furnished with a central core or axis
cylinder, and serve to connect the constituent cells of the ganglia with
each other and with other parts of the nervous system.

The ganglion cells, however, differ in their arrangement fi'om that
olitaining in the Vertebrates, as they are di.sposed radially around
the central portion or nucleus, which is constituted by the aggregation
of their filirillar prolongations, and also gives origin to the more
homogeneous nerve fibrils. Small spherical cells exist only in the
nioi'e anterior lobes of the cei’ebral ganglia or its connections and
are assumed to be the seat of the more specialized sensory faculties.
Dui’ing rest the ganglion cells store nj) nei’vous energy and also
chromatophilous substances which become used up during their

NERVOUS SYSTEM — CONNECTIVES AND COMMISSURES.

211

activity. Exercise or the transmission x>f nervous stimuli is always
accompanied by enlargement of the nerve cells and their nuclei, and
exhaustion is shown by their shrivelling and the presence of diffuse
chromatin therein.

Ganglia may be of a primary, secondarj% or accessory character.
The primary ganglia are the large compact and paired nerve masses,
which have their moities placed at opposite sides of the body, but
connected together by commissures, which always cross the median
longitudinal line : they comprise the cerebral or supra-oesophageal
ganglia and the ganglia directly connected therewith by paired
connectives ; the secondary or commissural ganglia are the lesser
nerve masses which are more or less closely associated together to
form the compound visceral ganglia ; and the accessory nerve masses
are the small additional ganglia developed on the courses of the
various nerves to subserve some special function.

The Connectives are important nerve trunks richly furnished with
ganglion cells along their whole course ; they are always longitudinally
directed and do not cross the median line, but connect together the

ganglia at the same side of the body.
The three connectives which primitively
originate from the right cerebral ganglion
are the cerebro-pedal, which connects
the right cerebral and the right pedal
ganglia ; the cerebro - pleural, which
joins the right cerebral and the right

Fig. 418. — Section through cerebro-
pleuro - pedal connective of Unio
pictortivt showing the ganglion
celjs interspersed amongst the nerve
substance, X 175 (after Rawitz).

pleural ganglia ; and the cerebro-buccal, which unites the right cerebral
with the right buccal or stomato-gastric ganglion, when the latter are
recognizably present ; the left cerebral ganglion is similarly joined to
the left moities of the other ganglia, and in addition the right and left
pedal ganglia are also united with the right and left pleural ganglia
by the pleuro-pedal connectives.

The Commissures are transverse nerve cords, usually with few
ganglion cells, which cross the median line of the body more or less
directly and connect together the moities of the same ganglionic
centre placed at opposite sides of the median line ; thus the cerebral
commissure joins the right and left moities of the cerebral ganglia
above the oesophagus, while the remaining ganglia, the pedal, the
visceral, and the buccal or stomato-gastric, are similarly connected
beneath it.

212

NERVOUS SYSTEM — NERVE FIBRILS.

The Nerve Fibrils are the delicate whitish nerve threads, composed
nearly exclusively of parallel longitudinal filaments arising directly
from the ganglia or from the various nerve cords, and whose minute
ramifications extend to every part of the body; they act as con-
ductors or conveyors of nerve force or stimuli, to and from the
various ganglia and the different organs without affecting the inter-
vening tissues through which they necessarily pass ; they may be
divided, according to their function, into Afferent or Sensoiy and
Efferent or Motor nerves.

The Afferent nerves terminate on the surface of the body or within
the sensory organs, in the form of suitably modified neuro-epithelial
cells, and convey tactile or more distinctly specialized acts of per-
ception to the cerebral or other ganglia, and also connect together the

Fig. 419. — Afferent nerve fibre, connecting the integumental neuro-epithelial cell with the sensory
ganglion cell, within which is the nuclear network and the nucleolus, X 600 (after Hernard).

sensory cells therein. At the surface of the body they form slender
and fusiform, or externally expanded cells, sometimes bearing tufts of
sensory hairs, but the ends may also become divided and di.stributed
within the integument.

The Efferent nerves unite together the motor cells of the ganglia,
and convey neivous impulses or impressions from the ganglia to the
various organs of the body. The efferent nerves may be of a Motor,
Sympathetic or luhihitory character. The Motor nerves are those
which terminate within and excite contractions of the muscles of the
body, or if distributed amongst the glands, excite a more abundant

aJ w

Fig. 420. — Efferent nerve fibre, with the motor ganglion cell, from which it arises, and showing
its connection to a muscle cell, X 6UU (modified after Boa.s).

flow of their secretions ; the Sympathetic nerves regulate the involun-
tary and more or less rhythmical motions of the internal organs, while
the Inhibitory nerves, which chiefly or solely arise from the cerebral
ganglia, affect the action of all other nerve centres, moderating or
annulling their influence. The afferent and efferent nerves traverse
the organs together, but are quite distinct and equally cease to act
when their connection with the centre is interrupted or destroyed.

NERVOUS SYSTEM — GASTROPODA.

213

In the Mollusca there are generally four chief nerve masses or
ganglia, which may be broadly classified as Supra-oesophageal and
Sub-oesophageal, according to their position above or beneath the
alimentary canal. The supra-oesophageal neiwe mass is composed
solely of the Cerebral or Sensory ganglia, while the compound sub-
oesophageal group is formed by the Pedal or Motor ganglia, and the
Visceral and the Buccal or Stomato-gastric centres, which to a certain
extent are comparable to a sympathetic system. The cerebral and
pedal ganglia are essentially nerve centres for the ectodermic organs,
the buccal ganglia for those of the endoderm and the combined
visceral centre for those of mesodermic origin. All these centres
are each more or less distinctly paired in correlation with the bilateral
arrangement of many of the organs of the body, but they are all

Fig. 421. — Diagrammatic obliquely dorsal view of the nervous system of a Gastropod, showing
the four nerve centres and their commissures enclosed separately within dotted lines.

b.g. paired buccal ganglia (the curved line and arrow indicate the change in position they undergo
in some species by the retraction of the buccal bulb) ; c.g. paired cerebral ganglia ; p.g, paired pedal
ganglia ; the compound visceral centre is also enclosed by a dotted line and is formed by the
pleural ganglia, pa.^. pallial ganglia, and ab.g, abdominal ganglion.

liable to vary in size and importance and in the amount or mode
of fusion with each other or with neighbouring ganglia in accordance
with the specialization the animal or its organs have undergone.

The Gastropoda, in their nervous system, exhibit throughout our
British species the four normal paired nerve centres, which form three
more or less confluent nerve loops encircling the alimentary canal,
all of which arise from the supra-oesophageal ganglia, and, according
as they do or do not exhibit a twist or crossing of the posterior
nerve cords, have been distinguished as Streptoneura and Euthyneura
respectively.

The Streptoneura or Chiastoneura constitute a group practically
co-exteusive with the older gvoups Prosobranchiata and Operculata,
and is composed of the most primitive and archaic of our species, the
nervous system being still characterized by the innervation of the male
organ of reproduction from the pedal ganglia, by the widely separated
visceral centres, and more especially by the remarkable crossing of
the pleuro-abdominal commissures arising from the semi-rotation of
the visceral sac.

•214

NERVOUS SYSTEM — STllEPTONEURA AND EUTHYNEURA.

In the Euthyneura the male organ is innervated froiiit he cerebral
and not from the pedal ganglia, and the pleuro-abdominal commis-
sures do not exhibit the crossing that so markedly characterizes the
Streptonenres, bnt Prof. Pelseneer lias demonstrated the probability
of the former existence of a similar torsion which is shown not only by
the retention of a partial streptoneury by some of the more arcliaic
})nlmonate genera, bnt by the right pallia! ganglion still occupying a
more elevated iiositiou than the left, perhaps due to its previous
su})ra-intestinal position.

Fig. 423. — Diagram of the nervous system of an Euthyneure, Lijnntea pcrcgra (Milll.), showing
the concentration of the visceral ganglia and the dextral position of the morphologically right
osphradium (modified after Spengel).

abdominal ganglion ; buccal commissure; h.g. buccal ganglia; cJkc* cerebro-buccal
connectives ; c,g, cerebral ganglia ; c.p.c, cerebro-pedal connectives ; l.d. left dialyneurous nerve ;
t?/. otocyst ; osphradium ; p.g. pedal ganglia ; pci^g- pallial ganglia ; pleural ganglia ;

pl.p.c. pleuro-pedal connectives; p/.pa.c. pleuro-pallial commissures \p.a.c. pleuro-abdominal com-
missures ; r.d. right dialyneurous nerve ; sb.g» subintestinal ganglion ; sp.g. supra-intestinal ganglion.

Ill the Stylommatophora the greatest aniount of specialization
is exhibited, the various ganglia having become more or less
closely aggregated around the jdiarynx, behind the buccal bulb, by
the shortening of the conneetives and commissures, the buccal bulb
being capable of withdrawal or protrusion through the cerebro-
visceral nerve loop, as in Ilelix asj^ersa and other species, but in some
genera, as Sacciuea, the cerebro-iileiiral connectives have by specializa-
tion become so short and the cerebro-visceral opening so contracted
thereliy that the buccal bulb cannot be withdrawn through the nerve-
ring, and is therefore practically immoveable.

NERVOUS SYSTEM — PELECYPODA.

215

The Basommatophora do not exhibit so marked a concentration of
the ganglia as is shown by the Stylommatophora, bnt Flanorhh
displays the same constriction of the cerebro-visceral nerve ring

Fig. 4*24. — Semi-schematic view of the prosoma of LbnaXy
showing the arrangement of the ganglia, nerves and other
organs and their relation to the protrusible and retractile
buccal bulb, X 3 (after Pelseneer).

a. abdominal ganglion ; c. cerebral ganglia, with the in-
fero-posterior buccal ganglia and also showing nerve pro-
longations to the eyes, rhinophores, labial lobes, Semper’s
lobes, etc. ; (e. oesophagus ; pedal ganglia ; p.gl. pedal
gland ; pL pleural ganglia ; S.l. Semper’s lobes ; u. anterior
aorta : v. visceral or pallial ganglia.

around the oesophagus as exists in Succinea,

Fig. 425. — The buccal bulb of
Succinea pittr.'s(X“)i showing the
close constriction of the cerebro-
^'isceral nerve ring around the
oesophagus, cephalic retractors and
saliv'ary ducts, owing to the
shortening of the cerebro-pleural
connectives, which totally prevents
the retraction of the buccal bulb
through the nerve ring, X 8.

which eciually prevents the

withdrawal of the buccal bulb.

In the Pelecypoda the nervous system is c^uite symmetrical and
apparently simpler in character than in the Gastropods, but this
chiefly arises from the fusion and combination of ganglia which are

Diagrammatic dorsally oblique views of the
nervous system, to show the mode by which the
apparently simpler nervous organization of the
Pelecypoda has arisen from the more complicated
arrangement of their assumed ancestor.

Fig. 426. — Nervous system of a primitive
mollusk, showing the posteriorly directed buccal
ganglia, the distinct pleural and pallial centres,
and the paired abdominal ganglia.

Fig. 427. — An intermediate stage, showing the
approximation of the pallial and abdominal and of
the cerebral and pleural ganglia, which eventually
fuse and form the visceral or parieto-splanchnic
and the cerebro-pleural ganglia respectively of the
Pelecypoda, the cerebro-pedal and the pleuro-
pedal connectives also combining in a part of their
course owing to the increasing approximation of
the pleural to the cerebral ganglia ; the buccal
ganglia also tend to combine with the cerebro-
abdominal nerve cords.

Fig. 428. — Nervous system of a Pelecj’pod,
showing the completion of the fusion of the cere-
bral and pleural ganglia, and of the pallial and
abdominal ganglia to form the cerebro-pleural and
visceral ganglia respectively. The buccal ganglia
and connectives are completely fused with the
commissures from the cerebro-pleural ganglia, and
the cerebro-pedal and cerebro-pleural connectives
have also become intimately joined together.

ai.g^. abdominal ganglia ; b.g". buccal ganglia ; c.c. cerebral commissure ; c.g. cerebral ganglia ;
c.p.c. cerebro-pedal connective ; c.pLp.c. cerebro-pleuro-pedal connective ; c.pl.u.c. cerebro-pleuro-
visceral commissures ; c.pl.c. cerebro-pleural connective ; c,pl.g. cerebro-pleural ganglia ; pa.a.c.
pallio-abdominal commissures ; Pa.g. pallial ganglia ; p.g, pedal ganglia ; pLg. pleural ganglia ;
pLpa.c. pleuro-pallial commissures ; pl.p.c. pleuro-pedal connective ; v.g. visceral ganglia.

often distinctly separated in Gastropods. Usually there are only
three distinct but widely separated nervous masses, known as the

•JIG NERVOUS SYSTEM — PELECYPODA.

cerobro-pleural, the pedal and the visceral or parieto-splaiichuic centres,
which are joined together by connectives and connnissnres forming two

nerve loops encircling the alimentary
canal, the long and important cerebro-
plenro-visceral commissures, which ex-
tend almost the whole length of the
body, containing many ganglion cells.

The efi'erent nerves, which give rise
to the contraction of the adductor
muscles, always arise from the ganglia
in their immediate proximity, but the
inhibitory nerve tibres, which produce
their relaxation and alloAV the shell to
gape owing to the elasticity of the liga-
ment, are stated to arise exclusively
from the cerebral ganglia.

The buccal or stomato-gastric and
the j)leural ganglia and the pleuro-
pedal connective, wddch were formerly
considered as peculiarly characteri.stic
of the (xastropoda, are also really
ju'esent in Pelecypods, but are usually
so intimately fused with the neigh-
bouring parts of the nervous system
that their combination can only be
satisfactorily demonstrated by the
microscoi)ical examinations of suitable sections.

The Cerebral or Sensory ganglia, sometimes also termed the
liuccal, sui)ra-cesophageal or post-oesophageal ganglia, originate as a
paired epihlastic thickening within the velar area and are sometimes
fused together, but when separate the constituent parts are joined by
commissures above the oesophagus, by the siile of which these ganglia
are placed. In adolition to innervating the head and its sensory
organs, they give off branches to the anterior body wall ami to the
otocysts, and are the chief point of convergence of the afferent nerves,
lint vary in development in correlation with the functional importance
of the organs innervated, and are joined by connectives with the
sub-oesophageal centres forming nerve loops which surround the
alimentary canal.

of a Pelecypod, Anodonta cygnea (L.).

a. ad. anterior adductor nerves; a.itt.
anterior mantle nerves; h.n. branchial
nerves ; c.c. cerel)ral commissure ; c.pl.g.
cerebro-pleural ganglia ; c.pl.p.c. cere-
bro-pleuro-pednl connectives ; c.p/.7>.c.
cercbro-pleuro-visceral commissure ; /.«.
rectal and cardiac nerves ; m.n. median
mantle nerves ; of. otocyst ; p, posterior
mantle nerves ; p.n. pedal nerves ; r.ti.
renal nerves ; s.n. nerves to siphonal
tentacles ; x>.g. visceral ganglion ; v.p.n.
nerves along kidney to hinder part of foot.

NERVOUS SYSTEM — CEREBRAL GANGLIA.

217

In the most primitive Streptoueures the cerebral ganglia are joined
in front of the buccal mass, but behind it in the more specialized
forms; in Vivipam and J^eritina there is an additional but
sub-cesophageal cerebral commissure, distinguished as the labial
commissure, which passes beneath the cesophagns, and forms a fourth
nerve collar around the alimentary canal.

In the Stylommatophora the cerebral ganglia are closely approxi-
mated dorsally, and distinct regions, from which special groups of
nerves originate, are distinguishable therein, which have therefore

been differentiated as the
Protocerebrou, Mesocerebron,
and Metacerebron. In the
anterior protocerebral region,
as well as in the terminal
ganglia of the upper and
lower tentacles and labial
lobes, small .spherical sensory
ganglion cells of uniform size
are congregated, and in
Helix pomatia especially the
ganglion cells of the cerebral
ganglia are more differentiated in size and polarity than those of the
Basommatophora.

Electrical or mechanical stimulation of the cerebral ganglia of
Helix produces little or no perceptible effect, and the animal can
survive their removal for four or five weeks, although remaining
perfectly motionless.

In the Pelecypoda the snpra-oesophageal or cerebro-pleural ganglia
are generally small in correlation with the diminished importance of
the cephalic region. They are placed near the pedal protractor and
innervate the anterior adductor, the labial lobes, and the oral region
generally, besides giving off the anterior pallial nerves, which ramify
within the pallial margin and unite with the posterior pallial nerves
arising from the visceral ganglia. They also furnish the nerves to
the otocysts and, according to Pelseneer, to the osphradia also, and
are composed of the cerebral ganglia united with the pleural
ganglia of the visceral centre. This combination of the ganglia is
clearly shown in the archaic genus Niicuki, in which the pleural
ganglia, though in close proximity, have not yet fused with the cere-

Fic. 430. — Cerebral ganglion cells, with their
nerve prolongations, from Anodonta anatina (L.),
X 500 (after Rawitz).

'218

NERVOUS SYSTEM — PEDAL GANGLIA.

bral centre, and conse(iuently the pleuro-pedal connectives are still
distinct from the cerebro-pedal connectives, with which, in most
si)ecies, they are intimately fused to form the compound cerebro-
pleuro-pedal connective.

The Pedal ganglia, also called the antero-inferior or suboesophageal
ganglia, are placed beneath the msophagus and within or near the foot

and are more especially
motor ; they are earlier
in development and
more constant in their
character than the
viscei'al centres, and
innervate the foot and
its dependencies, being
correlated in size with
its development ; they
are joined with the
cerebral and visceral

Fig. 431. — Pedal ganglion cells, with their nerve prolonga- ^ .1* 1 * 1

tions, from L/nio pictoru/n X oOO (after Rawitz). Uy pclllPtl COU-

nectives and are usually in intimate association with the otocysts.

In many Streptoneures the pedal ganglia still I'etain the archaic
character of long ganglionic nerve cords, traversing the foot longi-
tudinally and united at intervals
by numerous slender commissural
fibrils, in addition to the chief pedal
commissure at the anterior end of
the foot, near the junction of the
cerebral and visceral connectives.

Tbe regular repetition of these
slender commissures recalls the
ladder-like ai’rangement of the
pedal nerves in the Isopleura. The
male organ of repr(jduction is of
l)edal nature and usually innervated
by the pedal ganglia.

In the Euthyneura the pedal
ganglia have generally become intimately fused and approximated to
the ventral side of the oesophagus, and usually bear the otocysts
adherent to or actually imbedded in their umler surface.

F'ig. 432.~Sole of yivipara vivipara (L.)
to show the pedal nerve cords, which represent
the pedal ganglia and also showing the central
pedal blood sinus, X 3 (after Siniroth).

NERVOUS SYSTEM — BUCCAL AND VISCERAL GANGLIA.

219

Electrical or mechanical stimulation of the suboesophageal ganglia
of Helix causes vigorous muscular agitation, but the animal only
suiTives their removal about twenty-four hours.

Some Opisthobranchs possess in addition to the usual commissural
connection between the pedal ganglia, a second, or as it is termed,
a parapedal commissure.

In the Pelecypoda the pedal ganglia are usually placed at the root
of the foot near the junction of the visceral and muscular parts, and
usually partially or closely fused together, with the otocysts in close
proximity, although the otocystic nerves arise from the cerebral centre.

The Buccal or Stomato-gastric ganglia are usually placed near the
outlet of the salivary ducts, and vary greatly in their position in
relation to the cerebral ganglia, according to the amount of protrusion
of the buccal bulb ; they are connected together beneath the origin of
the oesophagus, and, unlike other centres, are connected solely with
the cerebral ganglia, and have only indirect communication with the
pedal or visceral ganglia ; they innervate the stomach, oesophagus,
salivary glands, anterior aorta, the pharyngeal muscles, etc., and are
to some extent sympathetic in function.

In the Streptoneura they were primitively permanently posterior to
the cerebral ganglia, which were fixed in advance of the buccal bulb,
but in many of the Euthyneures and more highly developed Strep-
toneures, the buccal bulb is capable of protrusion beyond or retraction
behind the cerebro-visceral nerve ring ; and as the buccal ganglia are
fixed beneath the origin of the oesophagus, they participate in its
movements and may therefore be in front of or behind the cerebral
ganglia according to the state of protrusion or retraction of the
buccal mass.

In the Pelecypoda the buccal or stomato-gastric ganglia, which in
the primitive mollusk innervated the anterior portion of the alimen-
tary canal, are not apparent, but in correlation with the diminished
importance of the head region, have degenerated and probably fused
with the cerebro-pleuro-visceral commissures, which now supply the
nerves to the early course of the alimentary tract.

The Visceral ganglia, variously named the parieto- splanchnic,
viscero-pleural, postero-superior, median or inferior, may be regarded
as the characteristic nerve centre of the mollusca, and chiefly
innervate the mesodermic organs; they are usually unsymmetrical

220 NERVOUS SYSTEM — VISCERAL GANGLIA.

and composed of several distinct, secondary gangdionic enlargements,
known as the pleural, the pallial or visceral, and the abdominal
ganglia, which are developed upon the conrse of the commissure,

which connects together the moities of
the pleural ganglia and would a})pear to
correspond with the pleuro-visceral cords
of the Isopleura, they innervate the
circulatory, the reproductive and the
excretory organs.

The Pleural constituents of the visceral
centre are the most anteriorly placed, and
it is naturally with them that the cerebral
and pedal connectives are joined. They
are exceedingly unstable in position, not
only in reference to their degree of
approximation with the associated ganglia

Fig. 433.— Visceral ganglion cells •

with their nerve prolongations, from ot tlieir SpeCUll gTOUp, but tO Otliei’ CeiltreS,
Unio piciortim (L.), X 500 (after i n •

Rawitz). as they may fuse into one mass with

their own centre, or become intimately fused with the cerebral or
with the pedal ganglia, and widely separated from their true position
and associations; they chieHy innervate the mantle, the coluniellar
muscle, and the body wall behind the head.

The Pallial, parietal, intestinal or visceral ganglia, as they are
variously termed, have been supposed to represent, in a concentrated
form, the many nerves supplying the gill leaflets in the Isopleura ;
they innervate the respiratory organs, the osphradia and the mantle
generally, and are developed upon the pleuro-abdominal commissures,
and when distinct from the abdominal centre divide them each into
an anterior Pleuro-pallial commissure, uniting the pleural and pallial
ganglia, and a posterior Pallio-ahdominal commissure connecting the
pallial with the Abdominal ganglion, the latter ganglion terminates
the nerve loop and more especially innervates the genital gland and
viscera, and although now usually apparently single, has probably
arisen by fusion from a primitively paired condition.

In the Streptoneura the visceral ganglia are often much scattered
and a considerable distance apart, and owing to the rotation of the
visceral dome, described at page 206 et seq., tlie organs originally
occupying the right side of the mantle cavity at the rear of the animal
have become transferred to the left siile above the neck, and the

NERVOUS SYSTEM — VISCERAL GANGLIA AND STREPTONEURY. 221

originally left posterior organs become placed on the right side of the
now anterior mantle cavity, and as the pallial ganglia have been in-
volved in this movement, the originally right pallial ganglion has
passed to the left side of the body above the intestine, and has therefore
been distinguished as the Supra-intestinal ganglion, and innervates the
primitively right ctenidium and osphradium, which the torsion of the
body has also transferred to the left side of the anterior pallial cavity,
while the primitively left pallial ganglion has passed beneath the

Fig. 134.

Fig. 435.

Fig. 436.

Fig. 437.

Diagrams illustrating the process by which the crossing of the visceral nerves or Streptoneury is
accomplished (after Lang). Fig. 434 shows the primitive untwisted condition of the nerves.
Fig. 435 and Fig. 436 show the process partially accomplished, and Fig. 437 shows the crossing of
the commissures completed, the semi-rotation of the visceral sac being accomplished. The arrows
indicate the direction of the movement.

a. anus ; /. foot; //. heart ; Lc. left ctenidium, with osphradium at base; l.v, left visceral or
pallial ganglion ; i?. oesophagus ; p.Lc. primitively left ctenidium and osphradium, now however
placed on the actual right of the body owing to the rotation of the visceral sac; p.l.v. primitively
left, but now the actually right visceral or pallial ganglion ; p.rx. primitively right, but now the
actually left ctenidium and osphradium ; p.r.v. primitively right, but now actually left visceral or
pallial ganglion ; r.c. right ctenidium and osphradium ; r.v. right visceral or pallial ganglion.

intestine to the right side of the body and is now known as the
Sub-intestinal ganglion; the commissures connecting these ganglia
to the pleural and abdominal ganglia, which were straight and un-
twisted in the hypothetical primitive mollusk, are by this movement
crossed and form a figure of 8, this feature constituting Streptoneury.

In the Euthyneura the aggregation of the various constituents of
the visceral ganglia is earned out to the greatest extent, the whole
of the ganglia having usually become more or less concentrated and
fused together around the pharynx, owing to which and to the partial
detorsion the visceral sac has undergone, the pleuro-abdominal
commissures are not crossed and the osphradium, when retained, is
placed at the side of the body to which it morphologically belongs,
while the increased importance of the cephalic region, and the reduc-
tion and displacement of the mantle posteriorly has resulted in the
innervation of the mantle devolving upon the pallial ganglia.

In the Pelecypoda the visceral or parieto-splanchnic ganglia are
widely distant from the cerebro-pleural centre, and as the pleural

NERVOUS SYSTEM — DIALYNEURY.

0-)->

constituents of tliis centre have by specialization become quite
separateil and fused with the cerebral ganglia, are probably formed
by the fusion of the pallial and abdominal centres of the primitive
mollnsk, the moities of this centre being however still separate in the
])rimitive genus Xaculii. The visceral ganglia are usually in contact
with and ventral to the posterior adductor muscle and innervate the
gills, the posterior adductor, and the viscera generally. They also
give origin to the posterior pallial plexus, which innervates the
respiratoiy oribces and the mantle margins and fuses midway therein
with the pallial nerve from the cerebro-pleural ganglia.

'fbe term (Irtboneuroid was formerly applied to the nervous system
of Xeritiud and Ilvlkhui, the supra - inte.stinal commissure and
ganglion being stated to be debcient in those groups, and the
crossing of the pleuro-abdominal commissures, characteristic of the
Strei>tonenra, being consecpiently denied to exist. This belief is,
however, erroneous, as no truly ortboneuroid mollnsks are known.

Dialyneury exists only in the Streptoneura and consists in the
establishment of a direct nerve connection between the constituent
ganglia of the visceral centre, morphologically belonging to 0})posite
sides of the body ; this connection arising on the left side by the

Fig. 438. — Nervous system of Cyclostoma
elcgans (Mull.), illustrating Dialyneury (after
Lacaze-Duthiers).

Ld. nerve from the left pleural ganglion fused
with the pallial branchial nerve, arising from the
supra-intestinal ganglion and forming left Dialy-
neury ; r.d. nerve from the right pleuro-pedal
connective anastomosing with the pallial nerve
from the subintestinal ganglion and constituting
right Dialyneury.

ah.g. abdominal ganglion ; b.c. buccal commis-
sure ; h.g. buccal ganglia ; c.b.c. cerebro-buccal
connective; cerebral ganglia; c.p.c. cerebro-
pedal connective ; ot. otocyst ; osp, osphradium ;
p.g. pedal ganglia;//.^, pleural ganglia ; //./.r.
pleuro-pedal connective ; p/.pa.c. pleuro-pallial
commissure ; />.a.c. pallio-abdominal commissures ;
sb.g. subintestinal ganglion ; sp.g. supra-intestinal
ganglion.

mantle nerve from tlie left pleural ganglion fusing with the branchial
nerve emanating from the supra-intestinal or primitively right pallial
ganglion, thus forming a nerve loop above the alimentary canal ;
and by a similar junction having been effected beneath it on the right
side of the body between the pallial nerve arising from the right
pleuro-i)edal connective, but whose bbres probably originate in the right

NERVOUS SYSTEM — ZYGONEURY AND SENSORY ORGANS.

223

pleural ganglion and the pallial nerve from the primitively left pallial
or sub-intestinal ganglion, the crossing of the pleuro-abdominal com-
missures having brought these ganglia into close proximity, although
prior to it occupying opposite sides of the body.

Zygoneury is an exaggerated development of Dialyneury, in which
a much closer api)roximation or even a fusion takes place on one side
of the body only, of the pleural and pallial ganglia, morphologically
belonging to opposite sides of the median line, owing to the shortening
of the pleuro-pallial commissure aud of the anastomosed nerves, whose
connection constituted Dialyneury ; usually it is the primitively

Fig. •139. — The nervous system of
Bucchium undatujn (L.), illustrating
Zygoneury to the right, and incidentally
Dialyneury to the left (after Pelseneer).

sb,g. subintestinal ganglion fused to the
right pleural ganglion and constituting
Zygoneury to the right ; supra-

intestinal ganglion ; l.d. nerve joining
the pallial nerve from the left pleural
ganglion to the branchial nerve emanating
from the supra-intestinal ganglion and
constituting Dialyneury to the left.

ab.s^. abdominal ganglion branchial
nerves ; c.g. cerebral ganglia ; p.g. pedal
ganglia ; p.n. pallial nerve; pLg. pleural
ganglia; pLp.c. pleuro-pedal connective ;
pa.a.c, pallio - abdominal commissures.

left pallial or sub-intestinal ganglion which becomes closely associated

with or actually fused to the right pleural ganglion, and constitutes

Zygoneury to the right ; more rarely the primitively right pallial or

supra-intestinal ganglion is similarly connected to the left pleural
ganglion, and is distinguished as Zygoneury to the left.

THE sensory organs.

Interspersed among the glandular, ciliated, and simple epithelial
cells, which cover the external surface of the mollusk, are a number
of elongate or superficially expanded neuro-epithelial cells, known
also as Flemming’s cells, which often bear one or more sensory hairs
at the free end, and vary in number in the various areas, but may be
congTegated together in certain definite parts of the body, each
cell being continued at the base into a nerve fibre, which is
connected with the central nervous system. These cells have not

224

OLFACTORY ORGANS — OSPHRADIUM.

primitively a definite and precise function, and may respond to
difi’erent stimuli, but when densely aggregated together in restricted

areas of the body they form the sensory
organs which, by the development of
specialized parts adapted to collect and
transmit particular forms of stimulation,
convey to the mollusk more or less
definite impressions of the character of
external objects ; thus, the optic nerves
are only sensitive to rays of light, and
the olfactory nerve to the i>resence of
odours, whereas the less specialized sensi-
bility to tactile impressions is distri-
buted over the entire surface of the body, which is extremely sensitive
to the slightest contact.

Fig. i40. — Sensory and epithelial
cells, showing their arrangement,
highly magnified (after Garnault).

ep,c. epithelial cells ; s.c, neuro-
epithelial or sensory cells.

The Olfactive faculty is undoubtedly possessed by the mollusca,
and almost every part of the animal has been suggested, at one time
or another, as the seat of this function, l)ut modern investigation
favours the view that although the tentacles and the sensory area near
the resi)iratory orifice are the chief seats of this sense, yet the oral
cavity in llellr, L'nnncca, and some other genera has also some olfac-
tory power, while the whole soft skin of the animal, which somewhat
resembles a pituitary memlwane, is probably also more or less sensible
to the perception of odours.

In the different genera this sense is more especially concentrated
in, and exercised by morphologically distinct regions of the body,
which according to their position are termed Osphradia or Rhinophores,
the former being more esi)ecially adapted to a(piatic and the latter
to aerial respiration : where both are present, their different degree
of functional development is probably in inverse proportion to each
other, one being probably in process of develo})ment and the other
undergoing degeneration.

The OsPHRADiUM (ocrc^paSior, from ocrc^pafro/rat, to smell) Or pallial
olfactory organ, known as the organ of Lacaze and also as Spengel’s
organ, is a primitively paired sensory structure, formed by tracts of
suitably modified ciliated epithelium, usually innervated from the
visceral or pallial ganglia and placed at the outer base of each ctenidium,
functioning as an examiner and co-ordinator of the sensations received
from the stream of inhalent w'ater which bathes the gills.

OLFACTORY ORGANS — OSPHRADIUM.

225

The originally paired cdiaracter of the ospliradiuiu is still retained
by the Pelecypods and the more archaic Streptonenra, bnt in the
Gastropoda of onr fauna the torsion undergone by the body has,

in dextral species and individuals,
resulted in the atrophy and loss of
the osphradinin and other organs of
the primitively left side and of those
of the primitively right side in such
forms as are sinistrally coiled.

The osphradium seems to be more
particularly correlated with an
acpiatic habit of life and the i)re-
sence of a luanchial cavity, as it is
j)ractically absent in terrestrial
genera, and in those aquatic forms
deficientof a pallia! chamber, though
still persisting in some species
that have comparatively recently
relimprished an aquatic life and
branchial respiration, but when thus present it always corresi)onds
more or less closely in position with that of the vanished ctenidium,
with which it was primitively associated. In its simplest form the

Fig. 441. — Osphradium or palHal olfactory
organ of Planorbis cornens (L.), highly
magnified (after Felix Bernard).

bi.s. blood sinus ; c. olfactory pit ; c.t. con-
nectiv'e tissue : ^.c. olfactory' ganglion cells;
s.cp. olfactive epithelium.

Figs. 442. 443. 414. 445. 446. 147.

Various forms of cells from the osphradium or olfactory pit of Liuincra stag'nai/s {h.). highly
magnified (after Simroth).

Fig. 442. — Goblet cell. Fig. 443. — Ciliated cell. Fig. 444. — Group of cells, one united to a nerve
cell by a nerve thread. Fig. 445.~Group of cells with yellow pigmented nuclei and ner\e pro-
longations. Fig. 446. — Olfactory bipolar and Fig. 447. multipolar ganglion cells.

osphradium is merely a., localization of suitable epithelial sensory
cells, connected with the integument and placed within or near the
entrance to the respiratoiy cavity, upon the course of the branchial
nerve, or upon a .special o.sphradial nerve or ganglionic enlargement

2/1,97.

p

OLFACTOKY ORGANS — RlIINOPHORES.

•22()

derived from it. In some marine Strei)tonenra the osphradial ridge
1)}^ specialization acqnires bilateral pectinations and, from its resem-
blance to the gills, was formerly known as the Parabrancbia, being-
supposed to represent the atrophied primitively left ctenidium, bnt
in other groups it may be a simple or bifurcate vibratile pit or
invagination, with its special ganglion placed at the bifurcation or at
the blind end.

The Riitnophores (fn^, fnyos, nose; (f>e:po),to bear) are the olfactory
organs of the head, and in the Stylommatojdiora are i)laced in the
more elevated ei)ithelium at the apex of the tentacles, a situation
which seems to be more es])ecially a characteristic of the terreskial
snails. An olfactory ganglion is jdaced near the distal end of each

Fig. 448. — Rhinophore or cephalic olfactory
orjjan of Cyclostoina clcgans (Miill.) x 30
(after Garnault).

cii. cuticle ; olf, c/>. olfactory epithelium ;
olfactory nerve with terminal hranchlets;
;//. t. muscular and connective tissue with
blood sinuses.

Fig. 440. — Isolated olfactory sensory cells
from the rhinophore or cephalic olfactory
organ of Cyclostoma clcgans (Miill.), highly
magnified (after Garnault).

tentacle and gives origin to numerous fine nervous ramifications,
which reach the delicate external epithelium and terminate in
numerous sui)erficial olfactory cellules. The olfactory ganglia are
connected to special lobes of the cerebral ganglia, and associated with
the optic and acoustic nerves which arise from the same lobes.

The Supra-pedal gland has been, and by some authorities is still,
regarded as the chief seat of the olfactory sense, owing to its rich
innervation and the presence of a number of sensory cells in the lumen
of the gland.

The Streptoneura, which are essentially a(piatic mollusks, possess
the osphradium, usually in the form of a filiform, and often pectinate,
ridge, placed within or near the entrance to the resinratory cavity,
upon a nervous cord or a small ganglionic enlargement, arising from

OLFACTORY ORGANS — GASTROPODA.

227

the supra-iiitestinal ganglion, which is the hoinologue of the right
pallia] or visceral ganglion of the Euthynenres.

In CijcJostoma and other species, which have comparatively recently
become adapted to a terrestrial life and aerial respiration, the rhino-
phores have become developed and acquired functional efficiency and
an organization quite similar to those of the Stylommatophora or
typical land snails, although the osphradium associated with their
primitively aquatic mode of life is also recognizably present, but
probably undergoing degeneration.

In some of the more primitive Streptoneura, other sensiferous areas,
formed by congregations of sensory cells and bearing sensory setin
are found near the bases of the epipodial tentacles, receiving their
innervation from the pedal ganglia.

In the Stylommatoi^hora, although the anterior tentacles possess
some degree of olfactory power, this sense is more especially concen-
trated in the dorsal pair, the bulb-like terminations of which are
especially rich in fine club-shaped sense cells, with rods placed
amongst specially modified epithelial cells, the somewhat clavate
olfactoiy ganglion in each rhinophore being placed close to the bulbous
distal end, and giving rise to several short, thick and divergent
nervous branches, wdiose numerous ramifications form a beautiful and
delicate tuft of nervous fibrils, distributed upon a delicate gTanular
membrane beneath the moist integument at the apex of the tentacle.
The ganglion vardes in volume in correspondence with the keenness
or feebleness of the olfactory sense and in some Hijalhi'm is scarcely
noticeable, while in Helix piscina it has four times the thickness of
the olfactory nerve.

The osphradium, being an organ more especially adapted to aquatic
life, is generally absent in the Stylommatophora ; it is, however, still
retained in a feebly-developed state at the lower posterior corner of
the lung cavity in Testacella and by some Helices. It has also been
detected to be present during development in Limax.

In the Basommatophora, the tentacles were considered to be the
seat of this faculty by Lespes and Moquin-Tandon, the nerves are
however not so decidedly concentrated as in the Stylommatophora,
but more equally distributed over their whole extent, the superficial
surface of the tentacles being increased by elongation in Planorbis
and by attenuation and dilatation in Limnwu, although there is stated
to be an olfactory ganglion near the tip, quite removed from the eye.

•2-28 OLFACTORY ORGANS — BASOMMATOPHORA AND PELECYPODA.

with which the oltactory sense is so closely associated in the Helices,
etc. Lacaze-Duthiers considers the external Imsal enlargement of the
tentacles to also i)Ossess olfactory power.

In the L'nnna'idu’ the osphradinm has persisted after the loss of
the gill with which it was primitively associated, and now exists in
the form of a ronnded ei)ithelial ridge, placed npon or as a vihratile
])it, invaginated within a small olfactory ganglion, this olfactory sinus
lieing simple in the sinistra! genera P/anorbis, etc., hnt

hifnrcate in the dextral genns LImita’ii, and, as might he expected,
P/iinorhIs has retained the osphradinm of the originally left side, and

the innervation hythe left visceral
ganglion, while L/iniufti has re-
tained that of the original right
si<le and receives its nerve supply
from the right visceral ganglion
Init being an aipiatic sensory organ,
whose role is to guard the entrance
to the pallial cavity, it has (piitted
its ])rimitive position inside the
mantle chamber and l)ecome ex-
terior to it, partly due to the
contraction of the iiallial opening in the ancestors of the Pnlmonates,
hnt mainly because water does not now normally enter the pallial
cavity of the Lhantriilv. In bdpli(ni(iri(i,i\ marine Ba.sommatophore,
in which the water now enters the lung, the o.s])hradinm is i)artially
within the cavity.

iSimroth at one time considered the os])hradinm to he the medinm
by whicdi these pnlmonate apnatic snails became atapiainted with
their arrival at the surface of the water for the pnri)Ose of respiration.

In the I’elecypoda, S})engel has demonstrated in Anodontd and
other siiecies a i)aired osjdiradial structure richly supiilied with nerves,
situate upon the roof of the inhalent siphon, near the origin of the
branchial nerves, and close to the posterior addnctor, analogous
in position and structure with the osidiradia of the axpiatic ({astroijods.
It is a specially moditied crest of epithelium, consisting of a thin layer
of elongated sensory cells, })laeed near to and innervated from the
visceral ganglia, hnt according to Pelseneer tlie nervous connection is
really with the cerehro-pleural ganglia, by means of the cerehi’o-
plenro-visceral commissures.

Fig. 150. — Litumca percg^'a (Mull ) ex-
tracted froni its shell and the mantle flap turned
back to show the position of the osphradinm
in relation to the pulmonary orifice, etc., X 3.

/. foot : f.o. female aperuire ; w, mantle
flap : m.o. male aperture ; os. osphradinm ;
pulmonary orifice ; sp. spire.

OLFACTORY ORGANS — EXERCISE ANl) POWER.

221)

111 addition to the true osphradia, there have been detected in
certain species not within oiir scope, other sensory organs of probably
analogous function, which may exist in the Asiphonated species as a
pair of epithelial papillated sensory areas, iuneiwated from the
posterior pallial nerve and placed at each side of the anus.

In the Siphouated forms these organs may exist upon the siphonal
retractors or at the base of the branchial siiihon in the form of papilhe,
tentacles, or lamellai, and receive their innervation from a special
siphonal ganglion.

Odours of various kinds are undoubtedly attractive to snails and
slugs, which, in all probability, discriminate their food by the aid of the
olfactory sense, this faculty in A vion and other genera being effectually
functional at comparatively gveat distances, even for isolated objects
of restricted size. IMoij^uin-Tandon has recorded that in the Jardiii des
Plantes, Toulouse, he observed one rainy day two Liman- maximm
crawling from different points towards a decaying apple ; he raised the
fruit and moved it to the right and afterwards to the left of the
animals, but the Limaces unerringly changed their direction in ac-
cordance with the altered position of the fruit, never moving in a
wrong direction. When the fi’uit was held above them the tentacles
and body were directed towards it and efforts apparently made to
find some means of reaching the food.

It has also been well established that snails (quickly emerge from
their shells when food they like is placed beside them, the odour in
these cases being the only available indication of its presence, visual
assistance being impossible.

Helix aspevsa, as is knovm, will fiequently traverse with much labour
broad dusty roads and climb rough walls to reach some favourite food,
this being another evidence of the keenness of the olfactory faculty.

In the Pelecypoda the evidences of the exercise of this function are
few. Mr. King has, however, recorded the attraction by putrefying
flesh of large numbers of Pisidium pusillum, which, in a few days’
time, were found clustered upon the skull of a fox placed in a small
ditch to soak, doubtless feeding upon the minute floating particles of
flesh and the organisms developed thereon.

The Exhalation of strong and special odours by the animals of
certain genera is probably connected with their season of reproduc-
tion and may possibly be of a signalling character, and though, in
some cases, doubtless of a protective nature, would seem to imply in

280

OLFACTORY AND VISUAL ORGANS.

the animals themselves the i)owei’ to iierceive them. Our British
/Ii/aHiiice, especially when irritated or itlnnged in hot water, emit a
strong and i)nngent smell of garlic, more or less intense according to
the species and to the accidental circnmstances inllnencing it, the power
cnlminating in Hiidltnid dUldrid. All Ilj/alinitv do not however
secrete this nnpleasant odour, as at least one foreign species emits a
fragrant musky perfume, and has been styled Ilydluud frdgrdns
on this account. Certain species of CldHsiUa and Fupd have been
observed to give ont a perceptible spermatic odour, as also does
Aple.rd Inipnorum when the animal is crushed. Fleliv pomdtid is
said to smell strongly of hemlock in the beginning of June, a smell
which does not proceed from browsing on the plant, but from an
exhalation peculiar to thesea.son of reju-oduction, while Fuio pictorum
and allied s])ecies at the same season have been stated to strongly
exhale a caprine or goat-like odour.

The sense of Sight is possessed by the bulk of our native species,
either in the larval or adult stage, but it is probable that all our
species are, in addition, more or less acutely sensible to the iierception
of light and shade, owing to the sensitiveness of the neuro-epithelial
cellules of their external integument.

It was formerly thought that the mollusca were (piite blind, the
eye-specks being regarded as merely ornamental si)ots without any
useful function, but their com})lex structure would a])pear to indicate
greater visual power than they have as yet been actually shown to
possess, and in the least S2)ecialized forms will at least enable the
creatures to discriminate night from day and thus warn them to seek
places of safety from their more numerous diurnal enemies.

The visual organs in the various gvoups are known as Cei)halic,
Dorsal or Pallial eyes, according as they are develoi)ed upon the head
region or upon the more ex})Oseil portions of the body or mantle,
their origin being probably due to the local moditication of the
external integument through the attraction and accumulation of
pigment gi’anules at those i)arts of the body most exposed to the
action of light.

The Cephalic Eyes originate behind the velum and in their primi-
tive form are merely simjjle cup shaped invaginations of the external
epithelium lined with pigmented and retinal cells and rods, such as
are still possessed by Pdtelld and other archaic species. They were
probably originally possessed by all mollusks, and are retained in

CEPHALIC EYES — POSITION AND STRUCTURE.

231

various degrees of specialization by almost eveiy Gastropod, and still
])erceptible during develojuueiit in the Pelecypods. They difier from
the Vertebrate and also from the pallial molluscan eye in the optic
nerve being distributed posterior to the retinal rods, which are
directed towards the crystalline lens. In the Gastropoda the cephalic
eyes are always two in number, usually black or blackish in colour and

Fig. 451. Fig. 452. Fig. 453.

Heads of examples of the three chief groups of Gastropods, to show the position of the cephalic eyes.

Fig. 451, — Vh'ipara vivipay-a (L.), showing the eyes on short pedicels exterior to the tentacles,
a position especially characterizing the Streptoneurous species (after Moquin-Tandon).

Fig. 452. — Lim?i(Fa sia^nalis (h.). River Tome, Yorks., showing the eyes at the inner base of
the tentacles, as illustrative of the Basommatophora.

Fig. ibZ.— Succhica put?'is Christchurch, Hants., X 3, showing the eyes at the tips of the
tentacles, as an example of the Stylommatophora.

placed upon or at the base of the tentacles at the anterior part of the
body. They are usually more or less spherical, though inclining to
an elongate shape in the ai^uatic species, but their size bears no
relation to that of the mollusk, being almost rudimentary in Testacella
and veiy large in Carijchlum, bnt as usual are })roportionately larger
in the enibiyo than in the adult.

The Cephalic eyes of any of onr species are not appreciably inferior
to the highly organized eye of Helix, which has a very complicated
structure, the Optic nerve which arises from an anterior lobe of the

cerebral ganglion being joined with
the tentacular nerve, from which it
separates at a variable distance fi’om
the eye. In Agriolimax agrestis and
T'estdcelki haUotidea this separation
takes place quite at the base of the
tentacle, but in Helix aspersa quite
within it. The nerve usually contains ganglion cells and expands into
an optic ganglion before reaching and spreading over the rear of the
Retina, the part actually sensitive to the impact of light, which occupies
the rear of the optic chamber, and is a cuticular formation, originating
from the epithelial cells of the base of the invagination and constituted
by Retinophores and Retinules,. both of which arise from differentia-
tions of normal cells and blend together insensibly in character.

Fig. 454. — Section through partially
retracted ommatophore of Helix aspersa
Mull., X 8, with the retractor removed
to show the position of the eye during
retraction and the junction within the
tentacle of the delicate optic with the
larger olfactory nerve

(.'EPUALIC EYES — STllUCTriiE.

'The Retinmilinres aro elongate colourless seusory cells with very cou-
tractecl free eiuls, and with their bases joined to and continuous with

tlie nerve pr(.)long'ations : while the Retniules

Fig. 4.V).

Fig. 456.

are pigmented cells with

Fig. 457.

Tlnee assumed stages in the evolution from the simple to the more highly organized cephalic
eyes of Gastropods, showing the retinal rods directed towards the lens and the distribution behind
them of the optic nerve, and also exhibiting ditTerent degrees of specialization at which further
development has been arrested in certain species.

P'ig. 455. — Simple epithelial invagination forming the primitive cephalic eye of Patella^ highly
magnified (after Hilger). <’/. epithelium ; optic nerve ; y. retina, with superposed retinal

rods and a mucoid accumulation, which is assumed to represent the origin of the refractive body.

Fig. 456. — Cephalic eye of Trochus^ highly magnified (after Hilger), showing the arrestment of
development before the formation of the cornea, etc. t'p. epithelium ; 1. crystalline lens ; op.n.
optic nerve ; r. retina, with retinal rods.

Fig. 457. — Cephalic eye of Ifeii.v pofiiatia L., highly magnified (after Simroth), as exemplifying
the degree of organization attained by the eye of the llritish e.vtra-marine mollusks. c. inner
cornea ; cu. cutis ; cJ. crystalline lens ; <■/. epithelium, becoming thin and transparent and forming
the outer cornea ; o.m. outer membrane or sclera ; op.n. optic nerve ; ret. retina ; t.n. tentacular nerve.

their free extremities very wide, so that they encompass or surround

the retinopliores, and constitute the i)igmented layer, formerly
descrihed as the Choroid, hut which does not correspond to the pig-
mented vascular layer knuwn hy that name in the Vertehrate eye; in

t [i/cliisfo/i/a eler/xns the ]»igniented retinules are hlled hy black granules,

Fig. 45S. Fig. 450.

Fig. 4.)8. — Relinophores or sensory cells and Retinules or pigmented cells from the retina of
Cyclostonia f Mull.), highly magnified, to show their arrangement (after Garnault). 7'ct.

retinophore ; rs. rctinule.

Fig. 450. — Diverse forms of the Retinophores or sensory cells from the retina of Cydostoina
(Mull.), highly magnified (after Garnault).

which, when freed from the cells, have active In-owidan movements.
'I’he Crystalline lens, with the develoi)nient of which the 02)tic vesicle
Ijeconies a true eye and capable of forming a more or less definite
image on the retina, is a transparent splueroidal body of concentric

PALLIAL AND DORSAL EYES.

233

structure and somewhat gelatinous consistency, secreted by the
retinal epithelium and surrounded partially or entirely by a more
fluid cuticular substance, the Vitreous body, these refractive parts of
the eye being probably primitively represented by a mere accumulation
of mucus within the integumental invagination. The transparent
outer Cornea is formed by an extension of the outer integument over

the optic vesicle and varies in convexity
and jn’ominence, while the inner Cornea
or pellucida is immediately beneath and
formed by the colourless internal wall
of the ocular bulb. The Sclerotic is the
bard structureless membrane often
difficult to separate fr’om the cornea
which surrounds and gives to the eye its
distinctive form.

By disuse, owing to the adoption of
special or peculiar habits of life, the eyes
may, as in Carilioides, become diminished in volume and buried in
the integument, or may retain their superficial position and degenera-
tion arise from the loss of the pigmentation.

The Pallial and Dorsal Eyes or Ocelli are secondarily-acquired
visual organs, difl’ering totally in many respects from the more primitive
cephalic eyes, and conforming in important features to the structure
of the eyes in Vertebrates. They are especially developed in the
Pelecypoda on the more exposed parts of the mantle margins, owing to
the primitive cephalic eyes, temporarily present during development
and during the free-swimming larval stage, becoming atrophied and
lost, as when overgrown and enclosed by the mantle and shell they
are useless. In Ouchidium, a genus of marine pulmonates, dorsal eyes
are developed, in addition to the cephalic eyes, in the forms in-
habiting certain districts which are coincident with the range of the
Feriophthalinus, a leaping shore fish, which preys upon them.

In the Pelecypods the pallial eyes have originated upon the nerves
arising from the innumerable small ganglia of the marginal pallial
plexus, and may be little more than pigmented spots, acutely sensible
to light, scattered upon the more exposed parts of the mantle, and,
as in Area, may, by their combination in groups, form composite eyes
resembling in structure certain simple Arthropodan eyes, each con-
stituent eye or ommatidium being formed of a conical visual cell,

Fig. 4G0. — Optic bulb of Helix
poviaiia L., after maceration, x 25
(after Simroth), showing the arrange-
ment of the pigmented cells.

234

PALLIAL AND DORSAL EYES — STRUCTURE AND ORIGIN.

enclosed by six cylindrical pigment cells and a cuticnlar cornea, with
bliform interstitial cells interposed between the oniinatidia; or, as
in Pecten, the pallial eyes by specialization may become of very com-
plicated and elaborate strnctnre, a subepithelial cellular lens which
originates fi-om the emlnyonic ectoderm covering the eye and the optic
nerve spreading out around and above the retina, or as in the dorsal
eyes of Onclihlium, piercing the retina posteriorly, the iioint of entry
of the retinal rods forming the “ blind spot,” as in the Vertebrate

Fig. 401. Fig. 4G2. Fig, 403.

Sections through the Pallial and Dor.sal eyes of Area, Pveten and Onchidium, to illustrate
their differences in organization from that of the cephalic eyes.

Fig. 401. — The composite eye of Area harbata, higlily magnified (adapted from Rawilz),
showing its complex structure. i,c. interstitial cells ; p.c. pigmented cells ; r.c. retinal cells, with
rod-like bodies ; r.r, retinal rods.

Fig. 462. — The pallial eye of Peeten, highly magnified (after Patten), showing the diffusion of the
nerve fibres above the retina, e. cornea ; ep. pigmented epithelium ; g.e, ganglion cells ; 1. lens ;
m.t. muscular and connective tissue with blood spaces; op.n. optic nerve ; r. retina ; r.r. retinal
rods; se. tapetum, pigmented epithelium and sclerotica.

Fig. 463. — The dorsal Onchidium vemiculatmn, highly magnified (after Semper), showing

the piercing of the retina by the optic nerve and the consequent formation of the “blind spot”
and the distribution of the nerve fibres above the retina, c. cornea ; 1. lens ; op.n. optic nerve ;
*>. pigment layer ; r. retina.

eye, the resemblance tn which ami the divergence from the molluscan
cephalic eye being, in both forms, further emidiasized by the visual
rods being turned towards the body away from the light, and the
retina generally being reversed in its arrangement to that obtaining
in the cephalic eye.

Pallial eyes, with few exceptions, a2)pear to be especially develo})ed
amongst littoral species, and the more recent relimpiishment by
I ) reh^nnsla , in comparison with the Naiads and other more ancient
tluviatile forms, of a littoral for a Huviatile life has been held to
account for the more perceptible presence of the pigmented visual
cells with highly refractive cuticle, which are concentrated on the
siphonal margin of that species.

In addition to and independent of the more or less definite iconoptic
vision by the more specialized eyes of the mollusk, the integument
of many species also possesses a certain degree of Permatoptic

UERMATOPTIC VISION.

235

power, the various species, according to their habits, exhibiting a
more or less striking response to sudden illumination or shading, the
reaction being more or less apparent in accordance with the intensity
of the light or depth of the shadow, this perceptive power being due
to the sensibility of the peripheral neuro-epithelial cells; the Rev.
J. E. Tenison-Woods, how'ever, affirms the presence in the mollusca
generally of a multiplicity of minute eyes, corresponding to the
Aesthetes of the Isopleura, these organs being said to exist, not only
on the mantle-lobes of the animal, but even upon the opercula and
the outer surface of the shell itself, while in addition there are large
isolated eyes within the shell substance.

Such species as markedly react to light are distinguished as
Phot-optic, those which are strikingly afi'ected by shade as Skioptic,
while the species which perceptibly respond to both light and shade
are known as Photoskioptic.

According to Nagel, Helix pomatia and Helix hortensis, if left for
a time undisturbed, are acutely skioptic, but Helix arhustorum is
less markedly affected, especially if the animal be a darkly pigmented
one, while the slugs generally are said to be only slightly responsive,
although Mr. E. J. Lowe, who had charge of the “Himalaya
Eclipse Expedition” of 1860, stationed near Santander in Spain, has
recorded his observation there of the intense skioptic sensibility of
Avion uter and also of Helix pisana, as shown by their almost
immediate response to the advent of the gloom at 3 p.m., due to the
obscuration of the sun’s disc, both .species being observed to be actively
moving about as at dusk, even before the eclipse became total.

Unio pictorum, Unio margaritifer , and other species are photo-
skioptic, for, in addition to a perception of a sudden accession of
light, they are also keenly responsive to sudden .shading, as is evidenced
by the rapid withdrawal of the mantle and closure of the shell, the
latter species immediately closing its shell if the sun becomes over-
cast, the water muddied or even if a boat passes above at a scarcely
perceptible speed.

In the Streptoneures the eyes are elevated upon slightly contractile
special eye stalks or ommatophores, external to and more or less
closely fused with the tentacle, and not invaginahle. In some of the
more archaic marine Rhipidoglossa the eye is not always closed by
the cornea, but is merely a simple tegumentary invagination, lined
with sensory and pigmented epithelium.

23G

VISUAL ORGANS — EXERCISE AND POWER.

Ill the Styloiiiiiiatophora the eyes tlioiigh in tlie adult bume
obliciuely at the extremity of tlie iipjier or dorsal tentacles, are lateral
during developnient, only act|iiiring the apical position at a later
perioil, a situation wliich enables them to he readily protruded or
invaginated within the tentacle for iirotection, hut they are only
functional when the tentacle is fully protruded. In this invagina-
tion or retraction the relative position of the crystalline lens and
the ocular bulb are reversed, the retractor muscle causing the lens to
descend the tentacular tube in advance of the body of the eye. The
genus VertKjo, in which, though bitentaciilate, the eyes are borne at
the tip of the tentacles, is also Stylommatophorous.

In the Basonmiatoi)hora the eyes are sessile and placed at the
internal base of the tentacles, and often contain a blood s])ace between
the outer cornea and inner cornea or pellucida. They have generally
veiy feeble ocular powers, for although Stiebel considers Lhnnwn,
.'(fiKjiiiili.'! to be better endowed in this respect than the Helices, Lespes
has shown that the allied genus Pl'()i(>rl>is only perceive objects when
in very close proximity to their visual organs.

In the Pelecypoda, although the cei)halic eyes are absent in the
adult stage, they are retained by throughout the free-

swimming larval stage, and are transitorily present in other species at
an early stage of their development. In comi)ensation for the suh-
sei|uent loss of these cephalic visual organs, })rimarily due to their
enclosure within the valves of the .shell, numerous pallial eyes are in
l)rocess of development along the mantle mai'gius, which are more or
less acutely sensible to light and shade.

All our land and freshwater mollusca are umpiestionahly myoitic :
they do not perceive the ultra violet rays, but are especially adapted
fur vision in dim creimscular light, as exposure to bright sunlight
ai)pears to have a dazzling or l)linding effect upon them. Must
(tastrojiods .shun the full noon-day glare, and seldom voluntarily
leave their retreats except during twilight or total darkness. The
a(puitic Pulmonates have very feeble ocular powers and cannot dis-
criminate the form of objects even in immediate ];)roximity to their
eyes, but the terrestrial species have a much keener perception, experi-
ment demonstrating that in a dim light Helices perceive large and
bulky objects at a distance of six centimetres, but in a bright light
their power of vision is much impaired, and this distance is so greatly
reduced that it may not even exceed four millimetres. Vk'ipdra

AUDITORY OR EQUILIBRATING ORGANS.

‘237

contecta is comparatively long sighted, perceiving objects at a distance
of thirty centimetres from the eye, or if the mollusk be crawling in
the gloom the sudden advent of a bright light at a greater distance
will cause it to at once retire within its shell. Cyclo^toma elegans
can also distinguish the hand of the observer when within eight
inches or twenty centimetres, and abruptly contracts within and
closes the shell on its nearer approach.

The Auditory or Equilibrating organs were quite unknown in the
mollusca prior to their discovery in the Cephalopoda by the celebrated
anatomist, John Hunter. In 1838 Siebold detected the same organ
in Anndonta, Unio, and other Pelecypods, and afterwards in many
(lastropods, and its resemblance, in some species, to the auditory
organs of certain tish-emhiyos strengthens the generalization that
the fully developed organs of the lower animals may often represent
those of the higher forms of life in an early stage of their development.

The sense of hearing in mollusks cannot, however, be very acute, as
the so-called auditory organs, when jiresent, are reduced to their
simplest expression, two small closed sacs, termed otocysts, filled

Fig. 464. — Section of the otocyst
of Neritina Jfuviaiilis (L.), highly
magnified (after Boll).

aud.il. otocystic or auditory nerve ;
ep. epithelium ; ot. otoconia ; vi.
muscular layer with connective tisr.ue.

'"fFiG. 465. — Otocyst of Anodonta cygnea
(L.), showing the cellular walls, the en-
closed otolith, and more especially the
exterior distribution of ihe otocystic
nerve, highly magnified (after Simroth).

with a limpid fluid, and each holding in suspension one or many
crystalline and sometimes coloured calcareous concretions, which vary
in size, form and chemical constitution in the different species. The
epithelial walls which secrete the endolymph or humour filling the
sac, consist of ciliated and sensory cells, the latter with fine rod-like
processes connected directly with the auditory nerves, whose fibres
are distributed over the walls of the vesicle ; while the ciliated
cells by their action create the incessant quivering and oscillation of
the otoliths or otoconia, their concussion or contact with the longer

■238

AUDITORY OR EQUILIBRATING ORGANS — EUNCTION.

seiisoiT hairs u])on the walls of the sac indiiciHg or leading to the
suitable reflex actions of the animal.

Although termed auditory organs, they are prohabl)'’ only sensitive
in a very limited degree to sound audible to human ears, but have a

Fig. — Porlion of ilie otocyst

of Sphariufu comeimt (I,.), highly
magnified (after Siniroth), showing
the otolith, o/., in contact with the
sensory hairs.

Fig. 4G7. — Terminal nerve cells
from the walls of the otocyst of
Cyciostofiia i'h'gnns (Mull.), highly
magnified (after Garnault).

much keener perception of any disturbance of the inhabited medium

or of the surface to which the foot may be applied, d'heir chief function
is undoubtedly to regulate the orientation and preserve the equilibrium

of the body by aiding in the percei)tion of the horizontal position
during locomotion, probably by reflex muscular action, induced by
the varying movements of the otoliths upon the sensory nerve-endings.
'I'his function is the more likely to be the predominant one, as this

organ becomes atrophied in the adult stage of the flxed forms, such as
Di ■eissensid, though present in the free swimming early stages of growth.

The otocysts are most highly developed in the active forms, and in

the reptant .siieciesare usually found near to or actually in contact with

Fig. 408. — Diagram of the
nervous system of IVjtcu/a^
showing the open canal of
invagination from the otocysts
to the exterior, and incidentally
the still separate cerebral and
pleural ganglia and their con-
nectives (after Pelseneer).

ot. otocyst; ot.d. otocystic
duct ; ab.g^. combined pallial
and abdominal ganglia ; c.g.
cerebral ganglia ; c./ c. cerebro-
pedal connectives ;
cerebro - pleuro • pedal connec-
tive ; osp. osphradium ;
pedal ganglia ; pleural

ganglia; pl.p.c. pleuro- pedal
connective ; pl.v.c. pleuro-
visceral commissures.

the pedal or locomotory
ganglia, Imt in the natant
forms they tend to approach
the cerebral ganglia, fiom
which centre they receive
their innervation. In our
Oastropods they vary in the
position they occupy, being
com])aratively remote from
the pedal ganglia in Cydo-
stomd ; actually placed upon
or imbedded within their

posterior outer surface, as in the Stylommatophora ; or, as in Nerltina,

may be close to, yet quite distinct from, the ganglionic mass.

Al’DITORY ORGANS — OTOLITHS AND OTOCONIA.

‘239

The otocysts originate in the embryo as simple paired invagina-
tions of the outer epithelium of the foot, the canal of invagination
or Kblliker’s canal, as it is termed in the Cephalopods, persisting only
in the adult Nucain and other primitive Pelecypods, and opening
externally at the anterior end of the foot, the otoconia being-
composed of grains of sand or other extraneous particles.

The calcareous concretions or “hearing stones” contained within
the sacs are, like the calcareous basis of the external shell, usually
composed of that form of carbonate of lime termed Aragonite, and
dii’ectly originate from the cells of the sac.

They may be classified for the purposes of study as (Otoliths and
Otoconia, according to the number and character of the concretions
contained in the cysts.

The Otoliths (o?s, ear; Xi0os, stone) are comparatively large, often

solid, and more or less spherical con-
cretions, usually distinguishalde from
the calcareous spherical granules found
in other parts of the body or mantle
by their concentric structure and radial
striation ; they always exist singly within the cysts, and do not increase
in number with the age of the animal.

Fig. 469.— Otolith from the otocyst
of SphcFriuin cornezan (L.), higlily
magnified (after Simrotb).

The Otoconia (ocs, ear ; /coi-ta, dust) are smaller, more numerous,
and more variable in shape than the otoliths, and may be of a simple
or compound form; the simple form embraces all otoconia with a
regular and simple outline, as those characterizing llijalbua and other
genera ; the compound forms are distinguished by distinct and usually
symmetrical divi.sions or segments, each .showing a minute central
area, the demarcation into two or four divisions predominating.

Figs. 170. 171. 172. 173. 171. 175. 176. 177. 178. 17!). 180. 181.

Simple and compound otoconia from the otocysts of various species of British Euthyneurous
mollusca to show some of the differences in form, highly magnified (after Schmidt).

Figs. 170—172 represent the prevailing forms in the Stylommatophora generallj-. Fig. 173 more’
particularly belongs to the Basommatophora. Fig. 171 is more especially found in Hyalinia.‘
Figs. 175, 176 are from Helix pomatia, but these peculiar forms are only occasionally found
and are also not confined to that species. Figs. 177- 180 are similarly from Helix hortensis,
Fig. 180 being an end view of Fig. 179, and Fig. 181 is from Limax cinereo-niger.

while the partition into three, five or six segments is less frequent.
The number in each cyst also increases with the age of the animal,
in an embryo of Limnwa atagnalk Siebold counted only fifteen of

240

AUDITORY ORGANS — STREPTONEURA AND EUTHYNEURA.

these concretions, in one still younger Wagner observed only nine or
ten, and Ponchet found in another example but seven, though the
adult animal nsnally possesses more than a hnndred. The cysts also
do not always contain an e(iual number of otoconia, nor are they
exactly uniform in size and shape, even in the same sac.

The otolith, which is the primitive form in which these concretions
first arise during the embryonal develo})ment of all onr mollusks, is
still retained by and more particularly characterizes those genera and
species of Streptoneura and Pelecypoda, which in many other resi)ects
are amongst onr most highly sjtecialized forms, whereas the more
archaic genera of these groui)s and the Euthyneura lose the otolith
jiresent during their embryonal life and ac([nire otoconia.

'The otocysts are always more easilv examined in the immature
than in the adult animal, even in the smaller species, as the whole
body can be pressed between the glass slii)s and the action and
movements of the otoconia studieil for tifteen minutes or more l)efore
they tinally cease. In the Naiads this organ is much more diflieult
of e.xamination and study.

In the kStreptoneuro.s, the otocysts are not usually so intimately
connected with the i)edal ganglia as in the Euthyneiires, and, as in
the highly specialize I Cjjdo^tonut ekr/iiuft, may retain the primitive
arrangement of a single large spherical otolith in each cyst, which

almo.st blls the whole, vesicle, and in which
the concentric lines of accretion or junction
])redominate, although radial striation is
also present, as when crushed it invariably
breaks into live i)ieces. t'onie si)ecies which
are, however, otherwise less highly specialized
have an exceedingly large number of oto-
conia, as Xf'rlfind iiri<(fiJi.-i ; those of

Kig. 4S2. — Otolith from the
otocyst of Cyclostoma elegans
(Mull.), highly magnified (after
Garnault), showing its spherical
form, distinct concentric struc-
ture and radiate striation.

Vdh'dtd are quite like tho'C of the Helices, being oval and some-
times angulated at the end, with a yellow central area and a darker
nucleus, while certain forms halhtually ])ossess an otolith and
otoconia in each cyst.

In the Euthyneiires the otocysts are usually placed upon or
actually imbedded in the pedal ganglia, the free side being usually
more convex than the one attached to the ganglia. They contain
numerous otoconia, which though generally more or less oval in shape,
with minute central area, yet often show considerable variety of out-

AUDITORY ORGAN'S — EUTHYNEURA AND PELECYPODA.

241

line, the otoconia of the Styloinmatophora being usually of a broadly
oval form, while those of the Basonnnatophora are more lenticular

Figs. 484. 485.

Fig. 483. — Underside of the pedal ganglia of Hyaluiia alliaria (Miller), highly magnified,
from Redcar, collected by Mr. Baker Hudson, showing the position of the otocysts upon them.
ot. otocj^st ; c.c. cerebrO'pedal connective.

Fig. 484 side view and Fig. 485 front view of otoconia from otocyst of Helix pomatia L., showing
the central nucleus and radiate striation, highly magnified (after Leydig).

in character. The otocystic nerve to each sac is a delicate fibril

Ijdng between the cerebro-pedal and the cerebro-pleural connectives
of their respective sides and arising from the cerebral ganglia.

In Pelecypods, although the more archaic genera still retain the
canal of invagination communicating with the exterior, yet in the
adults of our forms the otocysts have become closed and contain only
a single otolith in each sac, that of Sphwriim
being a flattened sphere, with radial stria-
tion, much smaller in size than the cyst
contaiinng it, though other species not
members of our fauna may possess a number
of otoconia in each sac, or an otolith may
be found with otoconia. In the fixed forms,
as Dre/sseiisia, the otocysts are wanting in
the adult stage, though present during development.

The auditory nerves are closely joined with the cerebro-pleuro-pedal
connectives, although their fibres arise from the cerebral centre.

Fig. 486. — Otolith from the
otocyst of Spha‘rium corncuvi
(L.), highly magnified (after
Simroth), showing its oval form,
strong radial striation and
peculiar nuclear space.

Fig. 487. — Otocyst of left side of Anodonia^ showing its close connection with the pedal ganglia
and the innervation from the cerebro-pleural ganglion, enlarged (after Simroth).

aud.H. otocystic or auditor>* nerve ; c.p.g. cerebro-pleural ganglion ; c.pl.p.c. cerebro-pleuro-pedal
connective ; ot. left otocyst, with otolith ; p.g. pedal ganglia.

Uenerally speaking the auditory organs of the Unionida?- and the
Ilelicida' form the ends of a series which the other groups unite by inter-
mediate gradations. Some Streptoneures show by their otoliths more
atfinity to the Pelecypods, while others approach the Styloinmatophora.

1/2/97.

242

SONANT AND GUSTATORY ORGANS.

Sound is said to be produced or eiuitted by certain foreign niollnsks,
and Ileli.r apertd, a reputed Briti.s]i species, is stated to emit a distinctly
audible cry wbeii disturbed, but our native species are not known
to emit any sound whatever, except perhaps the audible snap or click
which may be beard when an aipiatic i)ulmonate, as Limnaa, opens
its pnlmonary aperture fjr respiration upon reaching the surface of
the water ; pnlmonate mollusks generally when suddenly alarmed
may however b)" the spasmodic contraction of their bodies and the
conseipient forcible expulsion of the air from the mantle cavity,
ju-oduce a perceptible noise, varying somewhat in character according
to the force of the contraction and the (piantity of mncus accumulated
arouud the respiratory oritice.

What has been called the “IMusicof Snails” is created by the
crawling of the animal on a pane of glass or other suitable substance,
bnt the sound thus produced is a purely mechanical effect and in no
sense the voice of the animal — it may be easily imitated by drawing a
moist huger along the edge of a wine glass, 'rids sound, which
resemliles that of an .3i](dian hai'i), is usually only lieard at du.sk or
during the night; and the source of the mysterious sound being
fre([uently nnsu.sj)ected it has often caused a feeling of su})erstitions
dread and forms the basis of an interesting story l)y ^Irs. Bowdich.

'I'be (tUSTATOry sense is doubtless i)osse.ssed l)y the (hustropoda, as
is evidenced by the predilection of different species for special foods,
'rids faculty i)robably has its locaticm within or al)out the Imccal
cavity, as the tongue being closely beset with bard chitinous denticles,
neces.sary for the rasping and comminution of fooil does not ap])ear
to be a suitable organ for the development of this special sense.

'I'lie multilobular dor.sal and lateral li})S, wbich constitute the
organ of >Senii)er, are probably the seat of the gustatory sense, each
lobe l)eing furnished with a small ganglion ])laced beneath a deep
ej)itbelium with a thick cuticle and connected with a branch from the
anterior tentacular nerve.

In the Streptonenra the organs of Semper are not developed, but

Garnault has detected within the buccal
cavity of Cyddutomd elepans a number
of nerve cells beneath a thick cuticle,
some terminated by a delicate blament.

Fig. 488. — Gustatory cellule from
the wall of the buccal cavity of
Cyclostoma clegans ('Miill.), highly
magnified (after Garnault).

which, although somewhat similar in general character to tactile cells,
he considers may have a gustatory function.

GtrSTATORY ORGANS — ORGANS OF SEMPER.

243

In the Euthyneura the organs of Semper, although especially
developed in the Arionidcv and Limacldw, are also present in the
Stylonnnatophora generally, the lateral lobes receiving their innerva-
tion from the cerebral ganglia, and the dorsal lobes, according to
Hanitsch, receiving two small nerves from the bnccal ganglia ; each
lobe possesses a small ganglion composed of small spherical ganglion
cells, such as are found in the more specialized sensory regions of the

Fig. 489. — Side view of buccal mass of
Limax cinereo-ft2\^e7' Wolf, X 2, showing
Semper’s organ (after Sochaczewer).

Ij.b. buccal bulb ; c.g. cerebral ganglia ;
y. jaw; i,n, labial nerve; i.t. lower tentacles ;
O', oesophagus ; p.n. nerve piercing beneath
side muscles of pharynx; s,d. salivary ducts
s.gl. Semper’s organ ; t. tentacle.

Fig. 490. — Longitudinal section through
head of AgrioUynax agrestis (L.), X 20,
showing Semper’s glands, gland cells and
muscles (after Hanitsch).

ep. epithelium ; g.c. gland cells; j. jaw ;
m. muscle bundles ; s.^. glands of the organ
of Semper, showing their unicellular character
and independent ducts.

cerebral ganglia. The epithelium of these special regions is excep-
tionally thick, as in other sensory areas, and each lobe is moistened by
a very fluid secretion from the cluster of somewhat pyriform cells they
contain, each cell being furnished with a delicate duct with outlet upon
special papilla) placed above the lateral lips at each side of the month.

The Basommatophora, although possessing labial ganglia of homo-
logous nature to those of the Stylonnnatophora, have not the
distinctly lobulated lips characteristic of Semper’s organ.

The presence of the unicellular glands, whose secretions impart the
moistness to the gustatory tissues, has induced some observers to regard
Semper’s organ as a buccal salivary gland, homologous with the anterior
salivary glands found in certain other grou})S of mollusks.

Simroth is of opinion that the sense of taste is concentrated in the
front of the buccal cavity in land shells, but he has not detected this
specialized region in aquatic forms, and concludes the sense is in
them more diffused over the whole outer surface of the body.

In the Pelecypoda the faculty is hardly developed, but may be
exercised by the internal surface of the labial tentacles, which are
richly innervated and act as guards to the month, though little dis-
crimination ai)pears to he exercised in selecting food, almost anything
small enough to enter the mouth being swallowed,

244

TACTILE ORGANS.

Tlie Tactile .sense is well developed in the inollnsca, being resident
in all parts of the external skin, which is very soft and moist and
acutely sensitive to the slightest contact. This faculty is e.specially

exercised by externally expanded
nenro-epithelial cells bearing tufts of
sensoiy hairs and by long and fusiform
nucleated cells, which may he pro-
longed externally into one or more
hue setiform sensitive processes, and
internally are directly continuous with
the nerve tihrils, these cells being
most strongly and numerously
developed on the most prominent or
exposed jiarts of the body naturally functioning as tactile organs.

In the (histro])oda this sense, though diffused generally over the
surface of the body, is most actively exercised by the anterior tentacles
and labial lobes, which are jiossessed of the most delicate susceptibility
to contact with external objects.

F'ig. 401. — Section through the anterior
tentacle of flelix pontaiia L., to show
the peripheral tactile cells and general
structure, highly inagnilied (after Flem-
ming).

s.c. sensory cells ; cp. epithelium ; /.r.
pigment ; n.c. large nucleated cells ;
c. transverse section through muscles.

Fig. 402.

Fig. 103.

Fig. 402. — AtTerent nerve and connected afferent ganglion cell, showing its tactile terminations
within the external epithelium, X GOO (modified after I’uas).

Fig. 403. — Terminal nerve cells and Fig. 401 Epithelial ciliated cells from the tentacle of
/ 'h'ipiira 7'ivipaya (L.), highly magnified (after Simroth).

In the l’elecy])oda tlie tactile sense cells are distributed over the

surface of tlie body and niiintle. The tip of the foot seems e.specially

f

Fig. 495. — Tentacles of
the branchial siphon of
,-i uoiionfa cx^nt'a {\j.\ X 10
(after Moquin-Tandon).

sensitive and is probably the most effective
organ of touch. 'I'lie papillary processes of the
sijihons and the mantle margins generally are
exquisitely sensitive to tactile impressions, as
are the labial tentacles, but the latter are

perhaps scarcely organs of touch in the sense intended here,

ALIMENTARY AND NUTRITIVE SYSTEM.

ti45

ALIMENTARY SYSTEM.

The Alimentary or digestive system is well developed in the mollusca,
and may be described as a long tube of variable width, convoluted
within, but attached by strands of connective tissue to the walls of
the primary body cavity or coelom, and which, in the last or rectal
tract of its course, may, in certain groups, traverse the pericardium
or secondary body cavity, and sometimes even pass through the
ventricle of the heart also, performing different functions in the
various portions of its tract or course, all of which have for their
objects the extraction of nourishment from the ingested food and its
assimilation by the animal for the growth or reparation of its various
organs or tissues and the subsei|uent excretion from the body of
w'aste or hurtful substances..

The whole enteric tract may be conveniently divided into three
regions, an anterior, a median and a terminal portion, according to
the position and chief function of its various parts.

Fig. 496.— Alimentary canal of Helix (Miill.), showing the proposed regional division

of its tracts (modified after Howes).

f.g. fore-gut or anterior region of the alimentary tract ; m.g. mid-gut or stomachal region and
hind-gut or intestinal region.

b.c. buccal cavity, showing radula, radula sac and jaw ; cr. crop ; f. foot ; h.g. hermaphrodite
gland or ovoteslis ; LI. anterior lobe of liver ; cc. oesophagus ; p.g. pedal gland ; p.r. pharyngeal
or buccal retractor ; r. rectum ; r.L posterior lobe of liver ; ^.^/.salivary duct; s.g. salivary glands ;
st. stomach ; ty. typhlosole.

The Anterior region of the alimentary canal or fore-gut is of
ectodermic origin and has an ingestive and comminatory function.
It comprises the buccal bulb, with its specialized developments, and
the oesophagus or gullet.

The Median or digestive portion of the tract is of endodermic
origin and constituted chiefly by the stomach, a dilatation or enlarge-
ment of the mid-gut, which in some species contains a chitinous or
cartilaginous rod and, with a considerable part of the hind-gut, is

24G

ALlMKM’i’AUY SYSTEM- -HIND-GUT OK INTESTINE.

closely siiiTOunded by or imbedded M itbiii the large and miiltilobed
liver or digestive gland, which yields a digestive ferment. Sometimes
there are several noticeable dilatations in this region, the most
anterior of which may function as a crop and others as grinding-
gizzards for the more etfective trituration of the food before arriving
at the true stomach or digestive sac.

The Terminal and post-median part or hind-gnt comprises the
intestinal tract beyond the stomach, which, though much longer
than the body containing it, is not, as might be rashly supposed by
the uninitiated, indiscriminately coiled within the cavity without
any particular or definite arrangement of its often long and numerous
tracts, for each species, and more especially those of ])hyto})hagou,s
or omnivorous habit, e.xhibits the most intricate, yet marvellously
regular convolutions, the peculiarities of which are so markedly
special to each species that many forms can be identified by this

Fi(j. li)7- Fig. 498.

Fig. 197. - Alimentary tract of Arion hortensis F(fr., X 1, Horsforth, near Leeds, showing the
conjj)le.\ intestinal convolutions of an omnivorous species.

Fig. 198. — .\liinenlary tract of Tvstacclla lialiotidea Drap,, X 2, Horsham, Susse.x, collected by
Mr. T. 8. Hillman, and showing the simple intestinal coiling of'a predacious species.

feature alone. The intestinal canal of the strictly predaceous species
has always a much simpler and shorter course, Imt is ecpially adapted
to file nature of the food upon which the creature naturally subsists.

This portion of the alimentary tract lias pi’incipally an absorjitive
and excretory function, although intestinal digestion is also carried
on along the greater part of its course. It terminates at tlie
anus, which is of ectodennic origin and primitively placed at flic
posterior end of the body, but in the Anisopleurous Gastropods
the torsion of tlie visceral sac, due to the development of a heavy
univalve shell, has, generally speaking, transferred the orifice towards
the front, with the re.siiii-atory and other apertures with which it is
usually associated.

ALIMENTARY SYSTEM — BUCCAL BULB.

247

The Stomodeum (o-rojaa, month ; oSatos, belonging to a way) or
anterior region of the alimentary tract, which comprises the month
with its related parts and also the oesophagus, is always placed at the
anterior end of the body, and in some forms originates as a simple
epiblastic invagination of the body-wall of the embryo, which meets
with and opens into the mesenteron or median part of the alimentary
canal ; sometimes, however, it is formed by the persistence of the
blastopore, or orifice of embryonal invagination formed during the
gastrula stage of development.

In the Gastropoda the oral aperture is surrounded by variously
shaped lips which open into the buccal cavity or pharynx, whose walls,
especially ventrally and laterally, are formed by thick longitudinal
and annular muscular layers constituting the buccal bulb, which in
the more primitive inollusk was placed behind the cerebro-pedal nerve
collar, but in the more specialized forms is now in front of it.

The buccal bulb is protruded or retracted by means of special
muscles, which, according to their function, are distinguished as
Protractors or Retractors respectively.

In the Streptoueura, Garnault has studied their an’angement in
Cyclostoma elegans, and has described the protrusion of the buccal

mass as mainly due to the contraction
of the powerful lateral protractors,
which arise from the smaller segments
of the mandibles and are attached
to the external integument near the
oral aperture : these are supplemented
by longitudinal muscles within the
walls of the buccal bulb.

The retraction is chiefly effected
by two long paired muscles affixed to
the larger jaws, which pass somewhat
divergently backwards through the oesophageal ring, and mingle with
and become lost amongst the pedal strands of the columellar muscle.

In the Euthyneura the protractors of the buccal mass are several
small muscular bands attached to the buccal bulb and to the anterior
walls of the head region. The retraction is chiefly performed by a
branch or branches usually arising from the columellar muscle, which
are attached to the ventral and lateral surfaces of the bulb and exhibit
much interesting variation in the different species.

Fig. i99. — Buccal bulb of Cyclostoma
elegans fMull.), X 10, showing its chief
retractor and protractor muscles (after
Garnault).

a.p. anterior protractors; b.b. buccal
bulb ; l.p. lateral protractor muscles ;
£P. oesophagus ; p.r, pharyngeal or
buccal retractors ; 7’.s. radula sac.

248

ALIMENTARY SYSTEM — BUCCAL CAVITY.

I'lie entrance to the buccal cavity is furnislied with certain hard
cuticular formations, known as the jaws and odonto[)hore, wliich are
distinctly connected together hy a ])artially chitinous membrane, the
presence of wliicli can be clearly demonstrated when the caustic
solution used in the preparatory })rocess is not too strong.

'Fhe mandibles or jaws consist of one or more variously arranged
hard chitinous structures, more or less encompassing the oral aperture,
while the radiila, or odontophore, is a linguiform cartilaginous cushion,

which occupies the floor
of the mouth cavity, and
is beset with numerous
hard recurved denticles,
serving conjointly with
the mandibles for the pre-
hension and comminution
of food, thus facilitating
the effective action of the
digestive fluids of the
stomach and also of the
secretions from the sali-
vaiy glands, whose ducts open into the buccal cavity.

The interior of the buccal cavity generally is lined hy cylindrical
ei>ithelial cells, overlaid hy a thick cuticle, but the roof is covered
with a thin Imt strong and partially chitinous membrane or palatal
plate, connected anteriorly with the cutting edge of the monognathous
jaw, and overlaying a thick stratum of comjilexly arranged muscle
fibres, having a longitudinal, transverse and dorso-ventral direction,
which would appear t(j confer ui)on the upper jaw great freedom of
motion in various directions.

In the Pelecypoda generally there is practically no iiharyngeal
siiecialization, on account of their mode of life not necessitating the
active search for food, which consists of minute particles or organisms,
not needing mastication, brought in hy the ijihalent current which
their ciliary apparatus i)crpetually e.xcites ; they do not, therefore,
possess the accessory and i)rehensile organs which characterize the
(Jastropoda, as the oral aperture o])ens directly into the msophagus,
although some (jf the more archaic Pelecy])ods still retain a buccal
cavity with two small and laterally symmetrical glandular sacs,
which jjerhaps represent the salivary glands of the Gastro])ods.

Fig. oOO. — Longitudinal section through the imecal
hull) of a Streptoncure (after Lankester) .showing the
disposition of the teeth and jaws and the organs of the
head generally.

/».r. buccal cavity; h.c. head cavity; j. lateral mandible
or jaw ; Lc. lingual cartilage ; w. mouth ; a\ esophagus;
p.iu. lingual protractors, posteriorly to them are the
retractors ; r, radula or odontophore ; 7\s. radula sac ;

sinus behind the radular sheath ; v.vi. ventral retractor
muscles of the buccal mass.

ALIMENTARY SYSTEM — MANDIBLES.

249

Tlie jMandibles or Jaws are solid cuticular chitinoiis tliickeuiiigs,
with acute or deiitated edges, placed at the anterior part of the
buccal cavity ; they are almost universally present in the Gastropoda,
serving chiefly as prehensile organs for the purpose of seizing or biting
off particles of food, and the modiflcations to which they are subject are
most readily appreciated if, as suggested by Lang, they are considered
as originating from a circlet of jaws surrounding the entrance to the
oral cavity; such as are still possessed by Umbrella, Tylodina and
other Opisthobranchs, and of which special parts have been retained
by the various genera, specialization being evidenced by an increasing
siini)licity and by the reduction in number of the primitively numerous
separate parts, owing to the atrophy and loss of certain of the
segments and the more or less complete and differing modes of fusion
of the parts retained.

The muscular arrangements for the efficient action of the mandibles
in the pleurognathoiis species have been studied, in Cydortoma, by
Garnault, who flnds that, although the mandibular muscles are to
some extent complicated with those actuating the radula and buccal

bulb generally, yet there are several
distinct muscles directly concerned in
their movements, the principal being
a powerful transverse muscular baud,
attached by each end to the external
sides of, and connecting together the
larger jaws, which by its contraction
are brought into close apposition above
the radula, the succeeding and
alternating separation or re-opening
of the jaivs being due to tlie relaxa-
tion of the transverse convergent
or approximating muscle and the simultaneous contraction of the
lateral divaricators.

Though not an invariable rule, it is usual amongst our species for a
ilefinite type of jaw to be associated with an odontophore of a certain
character, thus the oxygnath jaw of HyaUnki is usually correlated
with aculeate marginal teeth, which imply a carnivorous tendency ;
while the strongly ribbed odontognathoiis jaw is generally found vflth
(quadrate and minutely cusped marginals, which are usually held to
indicate a preference for vegetable foods.

Fig. 501. — Mandibles of Cyclostojjict
clegans (Miill.), x 10, showing their
principal actuating muscles (modified
after Garnault).

c.m. approximating or convergent
muscle; d.Jit. lateral divaricator muscles;
l.p. lateral protractor muscles.

ALIMEN T All Y S Y STEM — POLY PL ACOGN AT HA.

2j0

Out Gastropoda maybe eonveuieutly grouped for study as Agiiatlui
and Giiathopliora, according as they do or do not possess this buccal
armature.

The Agnatiia (<«, Mithout; yi’ddo'j, jaw) embrace those species
entirely destitute of definite or distinct jaws, and are limited in
this country to the species of the genus TedacelUi, although, even
in that group, the upper or dorsal mandible is represented by an
indistinct chitinous thickening.

The Gnathophor.i (ycddo?, jaw; to bear), or jaw bearei's,

exhibit great diversity in the character and disposition of their
mandibular ai)paratus and, in accordance with the number of their
constituent parts, may be conveniently divided into five principal
groups or sections, distinguished as Polyi)lacognatha, Tetragnatha,
Dignatha, Trignatha, and iMonognatha, although the peculiarities
characterizing these divisions, like those separating all other groui)s,
are not .Aiarply marked, but are more or less insensibly blended
together by intermediate forms and thus really indicate successive
and divergent or, iirobably in some cases, convergent stages in their
jirogTess of specialization.

The ruLYPL.YCOGNATiiA (ttoXis, many ; a j)late or piece :

yi'udo5, jaw) embrace the groups Sphi/ntdium and Panctaui, the
former instituted for the reception of W'liujo cdentala and the latter
for Ileliv minuthsi Did of Jjca, a form
apparently synonymous with our
Hidir pygmifd, all of which agree in
possessing the remarkable peculiarity
of segmented or comj)Osite and nearly
circunioral mandibles, composed of a
number nf somewhat ([uadrate plates,
each formed by long chitinous fibres
extending as a fringe lieyond tlieir
sharp free edges. The plates, though overlapping each other laterally,
are distinctly separated medially, all however being slightly con-
nected together by a delicate membrane.

At the present time Jlelir pipjDut'it and Vertigo edentula are the
only species in this country actually known to posssess this remark-
able type of jaw, llell.r nipestris, which, on strictly testaceological
gnjunds, is apparently so closely allied to Ilellr piigmird, being a
decidedly monognathous sjjecies.

Fig. o02. — Segmented or primitive
Polyplacognathoiis mandibles from Helix
pygniwa I)rap., Jiighly magnified (after
Schacko).

ALIMENTARY SYSTEM TETRAGNATIIA.

251

The polyplacognathoiis or composite jaw is an excessively ancient
and primitive type, jirobably especially characteristic of a once almost
nniversally dispersed and more uniform molluscan fauna than any
existing at the i)recent day.

This type of jaw is, however, still retained by a limited number of
holarctic species and by Laomu, a helicoid genus inhabiting the
Southern Hemisphere, these few species at the present time probably
solely constituting the now widely scattered and isolated remnants
of this ancient fauna, in whose surviving members the specialization
of the buccal armature has become arrested and has therefore lagged
more or less behind that of the other organs of the body.

The Pleurognatiious species embrace the (iuadrimaxillate and
biniaxillate forms and practically includes all our Streptoneures ; the
paired lateral chitinous jaws, though usually distinctly separated, are
in Ldinellarki and other marine species manifestly fused together
dorsally, forming a single piece. They are thickest at the free inner
edge, more gradually blending with the muscles at the outer margin,
with smooth or characteristically sculptured surfaces, the peculiarities
of which may differ greatly in the vai’ious species. They are placed
somewhat horizontally at each side of the buccal cavity, but working
against each other; they are probably, however, functionally feeble
and serve more especially as points of attachment to the various
muscles actuating the radula and buccal bulb generall3L

Tbe Tetr.ygnatiia (rerpa-, four ; yvaSo^, the jaw) or (^[uadrimaxillate
species are exem})liffed by Cydostoina
elegans, in which the paired lateral
jaw's are placed on each side of the
radula, each lateral pair being com-
l)Osed of a small and somewhat cunei-
form posterior segment more or less
intimately adherent by its contiguous
margin to the anterior and larger
one, which is of an irregularly oval
form, with sinuate inner margin and
a somewhat hexagonally papillate
surface, the papillre being arranged
in soniewbat regular series, maiidy
tending to converge towards the sinus on the inner margin, to which
side this peculiar sculpture is more particularly restricted.

Fig. 503. — Pleurognathous Qiiadri-
maxillate mandibles of Cyclostoma
elegans (Miill.), from Box Hill, Surrey,
collected by l\Ir. W. Whitwell, X 12,
showing the peculiar sinuation of the
inner margins and the irregularly hexa-
gonal sculpture of the larger segments
(photographed by Mr. T. W. Thornton
from a careful preparation by Mr. J. W.
Neville).

ALIMENTARY SYSTEM — DIGNATIIA AND TRIGNATIIA.

Fig. 50L — Pleurognatlious Inmaxillate
maiulil)les of Bythinia tcntaculata
X from canal, near Noltingham,

collected by Mr. A. CL Stubbs, showing
the peculiar inytiliform shape and smooth
unsculplured surface (photographed by
Mr. T. \V. 'J'hornton from a careful pre-
paration by Mr. J. W. Neville).

Tlie Dignatii.v two : ■ynWo^, jaw) are by far tlie most numerous
iStreptoneurous group, embracing- all the bimaxillate species, of which
IhitJiin'm tcntdcnldtn may be taken as typical. Jjike Cijclostonut ,
the Ihithinlw are often stateil to be
entirely destitute of jaws, but they
really })ossess two, one at each side
of the buccal cavity, both of which
are of a somewhat inytiliform sliaiie,
almost jierfectly transparent and
totally without noticealde surface
sculpture. The smaller segments of
the (piadrinia-xillate jaws liave in the
Dignatba become lost or perliajis fused
with the larger anterior segments,
which are now alone jiresent.

Certain extra-British tmlmonate siiecies are, according to Lang,
dignathous, althongh not pleurognatlious, the jaws being })laced on
the roof and Hoorof the entrance to the buccal cavity.

In Vdlntfd, however, which in many features is of very luhnitive
organization, there is a vestigial indication of an upper jaw, and it
thus links together the tri-niaxillate hermaphrodite forms with the
hi-maxillate dimeious ones, forming another curious feature in its
.'^omewliat anomalous organization.

The TuKiN.vrii.v [rpl-, three; yr«dos', jaw) or trimaxillate species
are, in this country, practically confined to the Limna hhc, and are
characterizeil h}^ the iiossession of a
well-develoiied transverse upper jaw,
with sometimes a ju-omiiience upon the
free edge and a pair of lateral jaws which
are generally much smaller and slighter,
and sometimes alnio.st vestigial, hut in
some of the species of P/anorhis and
A/ici/his the dorsal and lateral limbs
have ajiparently become more or less fused together and thus form a
single horse-shoe sha]»ed buccal plate.

Ill Linuum pryet/nt, which may he regarded as a typical representa-
tive of this groiif), the well-developed, convex and somewhat
lenticular upper or dorsal jaw is of a reddish horn-colour, hut
blackish along the free cutting edge, which, although exhibiting an

4

i

Fig. 505. — 'I'rignalhous clorso-
j)leural mandibles from Linnnea
peregra (Mvill.), X 20, Cliristchurcb,
Hants.

ALIMENTARY SYSTEM — MONOGNATHA.

253

irregular contour in immature animals, in the adults presents a
distinct median notch, with usually a broad flat projection at each
side and a more prominent angle towards the outer margins, the
projecting angles indicating the marginal terminations of four slight
and indefinite rib-like thickenings which can in some lights be
occasionally detected. The acute ends of the dorsal jaw are firmly
attached to the pointed extremities of the almost linearly crescentic
lateral jaws, which are placed at right angles to the upper jaw and
have their concavity outwardly directed.

In action the dorsal and lateral jaws do not move simultaneous!}',
but the upper jaw is first brought down and the side jaws close up
laterally.

The i\IoNOGNATHA (/xduos, single ; yrctdos, jaw), or mollusks with a
single mandible, usually possess a more or less semilunar or crescentic
jaw of a hard and chitinous nature, placed dorsally at the entrance to
the oral cavity and varying in consistency from a very thick to quite
a delicate substance, and from a deep opaque brown to a translucent
amber, the colour being always deepest along the free cutting edge ;
but in some groups, as Pupa, the entire jaw has the appearance and

colour of cartilage.

Fig. 506. — Oxygnathous jaw of L'nnax
inaximiis L., in process of development,
showing its bilateral origin, magnified
(after Wiegmann).

Fig. 507. -Mandible of Helix ptdchclla
Miill., X 40, Seamer, near Scarborough,
collected by Mr. J. A. Hargreaves,
showing the posterior palatal extension.
(Photographed by Mr. T. \V. Thornton
from a preparation by Mr. J. W. Neville.)

The Monognathous jaw really originates, according to Wiegmann,
as two separate lateral parts, which afterwards unite in the median
line, thus furnishing further corroborative evidence of the derivation
of the monognathous jaw from a more ancient ty])e, composed of a
greater number of parts.

From the posterior lower margin of the jaw there arises a partially
chitinous plate or membrane, which extends taperingly backwards
upon the roof of the buccal cavity, gradually blending with it, and
doubtless strengthening the jaw and its cutting edge ; this feature
attains its maximum development in the distinctly defined palatal
plate of the Elasmognatha. Mr. W. G, Binney however, as I think

254

ALIMENTARY SYSTEM — MONOGNATHA.

erroneously, evidently regards the palatal plate of the Elasniognatha
as not honiologons with the mandibular palatal extension found in
other monognathous groups.

In the monognathou.s species the mandihle is opposed by the divided
lower lip, which acts the part of a lower mandible in grasping the
substance to be devoured and enabling the odontoiihore to rasp off
particles of food, which are carried to the oesophagus by its action.

d'he Monognatha may be ranged under five chief groups, viz. : —
Pycnognatha, Odontognatha, Leioguatha, Oxygnatha, and Blasnio-
gnatha, which are re.spectively characterized by the absence or presence
of several more or less vertical thickenings or ribs, more especially
upon the anterior surface of the jaw, by the development of a median
projecting beak or by the possession of a large (piadrangular accessory
palatal plate.

'I’he Pycnognatha (tti'ki'os', crowded ; yi'd^^o?, jaw) often possess
a somewhat convexly arcuate jaw, rvithout the median beak or projec-
tion. It is e.specially characterized by the numerous tine and delicate
vertical rilis, sometimes covering the
whole anterior surface of the jaw,
though occasionally only i)erceptil)le

towards the cutting edge, which thus
, /• 1 14 Ku'.. ’>08. -A Striated or Pycno.^natlious

necoines niiely crenulato. Anion^'st mandible, x j/c/lv /u/c/u'/Za urn.,

‘ from vSeamer, near Scarloroii?li, collected

our inono^natlious fetyloinniatojmora, UyNIr. J.A. Hargreaves. (Photographed
‘ , by Mr. 'I'. W. Thornton from a prepara-

this type of mandihle is probably the 'w Mr- J- w. Neville.)
tirst .stage in the .siiocialization of the julmitive comim.site jaivs ivhich
still characterizes our and other siiecies, this moditica-

tion arising from the fusion of the originally sepiirated plates, the
over-la])iiing lines of junction giving rise to the characteristic vertical
stria', although, as suggested by Pilshry, this condition may also he
reached through the odontoguathous stage by the degeneration of the
ribs. 'I’he Ihdim'nti and some Helices are e.xamples of this group.

'I'he Odontognatha (oSoih-, tooth ; yrd^o?, jaw) is rvell illus-
trated by the Arionhlir and many IJ('Hcl(hv and embrace those
species whose jaws hear, esj)ecially ujion their anterior surface,
more or less numerous and prominent ])arallel or slightly convergent
ribs, which ])roject beyond and denticulate the free margin, and
sometimes the upi)er margin also. 'I’hese ribs and their denticula-
tions are usually more distinctly develo])ed where their number is
limited and less .strongly marked when more numerously pre.sent,

ALIMENTARY SYSTEM — MONOGNATHA.

255

but young shells have fewer and less prominent ribs and denticles
than older specimens, the median ribs first appearing and development
following on towards the extremities of the jaw, thus being analogous
to the growth of the teeth in man,
whose incisors or cutting teeth first
appear, these being followed by the
molars, etc., and lastly by the wisdom
teeth. In addition to these well-
marked ribs, there are numerous fine
vertical strim and also incremental
strim or lines of growth, which are parallel with the cutting edge.

Mr. Crowther has shown that the strength of the jaw and the
number of the ribs may be modified by the environment, a soft,
succulent herbage developing few ribs on a comparatively delicate jaw,
while the same species living on coarser fare by dusty road-sides have a
harder jaw with stronger and more numerous denticles, but the
immature animals always possess a more delicate jaw, with fewer and
slighter ribs, than their mature companions in the same locality.

The Leiognatha (Acto?, smooth; yvido^, jaw) typically possess
a smooth mandible or jaw, from which
all the striation has become obliterated
and Avhich show no trace of the
median rostrum or beak, which is so
striking a feature in the oxygnath jaw
and may be viewed as the antithesis
of the odontognatha ; in Leiognatha
the jaw has lost all trace of ribs or stria}
and is ai)parently of homogeneous composition, while in the odonto-
gnatha the ribs and denticulations have assumed great prominence.

The Oxygnatha (o^ih, sharp ; yvaOos, jaw) are exemplified by
the Lhnacidw and Vitriuidce, which possess a jaw strongly arcuate
from front to back, but smooth on
the surface, owing probably to the
disappearance of the delicate rihlets,
characteristic of the pycnognatha ;
they are, however, more especially fig. 511.- a Rostrate or o.\ygnathous

. . -Ill 1 • • 11 mandible, Limax flavus L., X 10,

distinguished by being vertically Christchurch, Hants.

carinate in the centre, the keel terminating in a median beak or

projection on the cutting margin.

Fig. 510. — An Unstriated or Leio-
gnathous mandible, Pupa cylindracea
(Da Costa), x 40, Bev’erley, collected and
prepared by Mr. J. D. Butterell.

Fig. 509.-A Ribbed or Odontognathous
mandible, Helix poinatm L., x 10, from
Preston Candover, Hants., collected by
the Rev. H. P. Fitzgerald.

ALIMENTARY SYSTEM — ODONTOPIIORE.

256

'I’he Elasmognatiia (eXan-fm, a metal ])late; yi'a^o?, jaw) or
Ai)pentlicnlate jaw is a tyiie whose great peculiarity consists in the
development of a very large, somewhat sipiare accessoiy palatal plate,
which extends j)osteriorly backwards upon the roof of the mouth ; it
is of similar material and consistency and about two-thirds the width
of the jaw itself, with which
it exhihitscontinuity of struc-
ture. 'I'he upper portion of
the jaw is imbedded in the
tissues, ami the free portion
is characteristically horse-
shoe shaped with a strong and
jHiinted median projection.

'I'he Elasmognath jaw is
restricted in this country to
the genus Sikt'uk'j, although
our s])ecies vary somewhat in the character of the jaw itself, S/icriii&d
r/('(/iiiis possessing a practically oxygiiath jaw uj)on which the
])osteriorly projecting palatal a])i)endage is developed, while Hiicc.'nmi
pntritt, in addition to the well marked median beak or rostrum,
which is the characteristic of the oxygiiatha, also displays strong
and distinct transverse radiate ridges, simulating those of the true
odontognathous sjiecies.

'I'he OnoNToi’iioRE ((VSoik', tooth ; </>e/><n, to hear), Radula, or lingual
ribbon, is a tongue-like cartilaginous process iirojecting upon the
door of the huccai cavity, and forming a somewhat ju'chensile
apparatus, with its fi-ee surface covered with an immense number of
minute, hackwardly directed teeth, arranged in regular longitudinal
and transverse rows, and of strikingly different forms in the different
genera and species, the whole resting upon the suh-radular membrane,
which is continuous with the lining of the huccai cavity, and i)laced
111)011 tlie two somewhat confluent odontophoral cartilages, which are
clo.sely iiniteil in the median line by fibrous and muscular tissue.
'I'he very general possession of this organ, in a very largo section of
the mollusca, has led to the term (do.sso])hora., or tongue-hearing,
l>eiug applied to the groups possessing it.

'I'he Radula Sac, from which the radula is developed as a some-
what tubular outgrowth, is an eiiithelial invagination of variable
length in the median line of the iloor of the mouth or huccai cavity,

Fig. 512 front view and Fig. 513 side view of tlie
Appendiculate or F'dasmognatlioiis maiulible of
SiH'ci/iea />Ntris (F.)> X --5, from Chrisicliurch,
FlaiUs., showing tlie convexity of the jaw generally
and llie strongly tlevelojied accessory palatal plate.

ALIMENTARY SYSTEM — DEYELOPMENT OF ODONTOPIIORE. 257

often posteriorly extended beyond the buccal bulb. It is filled with
connective tissue and its distal ventral walls bear the Odontoblasts
(oSois, tooth ; /SXacTTo^, a bud) or tooth-forming cells, a few cells
with large nuclei and clear protoplasm, as
in the Pulmonates, or a greater number of
smaller cells, only distinguishable from
ordinary epithelial cells by their greater
length, but whose arrangement always coin-
cides with that of the teeth they secrete ;
these, however, after their formation by the
odontoblasts, become hardened for use by a
superficial deposit of “enamel” from epithelial cells above the radula,
and are then of an amber colour, an appearance which is soon lost and
the teeth blunted, broken and worn
away when they come into active
use ; this wearing away and loss of
the anterior functional part of the
radula is compensated for by the
progressive growth fi’om the radula
sac of newly-formed teeth and their
supporting membrane, exactly like a
finger nail on its bed, in which the
wearing away of the anterior free
margin is compensated for by its own
forward growth. According to Dr. Sterki, Liiwix campestris, which is
closely allied to, if not actually identical with, our AgrioUmax Icevis,
forms in this way not less than 800 transverse rows of teeth during
its ordinary life-term, and this implies at least eight entire changes of
denticles ; some Helices he affirms produce 2,000 or more transverse
rows, indicating 16 — 18 total changes of teeth by the animal.

The Development of the radular teeth in the embryo begins in
the form of mere chitinous nodules, which, in the succeeding trans-
verse rows, acquire many long and sharply pointed cusps or processes
before eventually attaining the adult or permanent form ; this
transitory phase in their development has been termed the Echinate
(eyftos, a hedgehog) stage. At first there are also fewer longitudinal
rows of teeth than are afterwards present, the additional rows being
added at the outer margins and not intei’polated between the rows

R

Fig. 515, — Diagrammaiic longitudinal
section through the posterior end of the
radula sac of a Pulmonate, showing
the teeth and basal membrane in process
of formation (after Rossler).

d.m. basal membrane of the radula;
c. formative cells of the basal membrane ;
od. odontoblasts or formative cells of the
radular teeth ; /. radular teeth.

Fig. 514. — Epithelial cells
from pharynx of Helix pomatia
L., highly magnified (after Vogt
and Vung).

ALIMENTARY SYSTEM — ODONTOPIIORAL MUSCLES.

•2 .38

already present ; these also originate in the nodular form, pass through
the echinate stage and in the succeeding transverse rows gradually

acciuire the characters of true
marginals ; the laterals also,
in the same way, increase
somewhat correspondingly in
number hy the gradual
change of what were the
marginals of the embryonal
mollnsks into the laterals of
more mature animals, the
character of the teeth in the
longitudinal series and their
relative position on the mem-
hrane hecoming modified
thereby. These changes are
j)eculiar to the embryonal
>tage and due to modifications of the odontoblasts, as the same
grou]) of cells forms all the teeth in the same longitudinal row, this
fact elucidating the can.se of the unvarying recurrence of deficient,
deformed or abnormal teeth the whole length of the radula, which has
l)een so often observed.

The IMuscular DEVELurMENT of the buccal mass is exceedingly
comjilieated and varies in arrangement in the different groups, as
many as twenty distinct extrinsic and intrinsic muscles having been
distinguished as concerned in the efficient use of the radula alone.

Fig. 517. -Dissection showing the Extrinsic buccal muscles of Helix asfiersa Mull, (after Howes).
h.b. buccal bulb ; b.c. constrictor muscles of buccal bulb ; c.ni. columellar muscle ; ^/.w. depressor
muscles \ /. foot ; l.)u. levator muscles ; o. ommatophore ; ic. uesophagus ; buccal protractors ;

p.r. pharyngeal retractor ; r.s. radular sac ; s.d. salivary ducts ; t. anterior tentacle.

their alternating contractions and relaxations causing the radula to
travel backwards and forwards and thus rasp against any object to
which it may he apjdied, the ju'esence in their substance of

‘.rs /'A

Fig. 510. — Radula of an embryo of Limax cam-
/•estris shewing the nodular character of the teeth on
first development and thechangesundergone in passing
through the Echinate intermediate stage before attain-
ing the adult form, highly magnified (after .Slerki).

The lowermost series is that of an adult.

The perpendicular row of numerals indicates the
number of transverse rows that have existed on the
radula, reckoning from their first development.

The horizontal numerals give the position of the
individual teeth in the transverse rows reckoning from
the central tooth.

ALIMENTARY SYSTEM — ODONTOPHORAL MUSCLES.

259

liaimogiobiii testifying to the increased respiratory activity neces-
sitated by their vigorous movements.

The Extrinsic muscles pass from the odontophore, chiefly to the
outer walls of the prosoma, and actuate the entire organ ; they are
known as Retractor.s, Protractors, Levators, or Depressors, according to
the function they perform. The Protractors
pass forwards and downwards from the
buccal bulb to the cephalic integument
and protrude the radula; the Levators are
above the Protractors and affixed to the
cephalic wall near the anterior tentacles ;
the Depressors underlie the Protractors and
pass obliquely backwards, and, with the
Levators, assist to determine the special
licking motion of the protruded radula,
which is then bent over the supporting-
cartilage in front of the oral aperture ; the
Retractor is a powei-ful muscle or series of muscles with a bifid or
multifid attachment to the buccal bulb, and distally affixed to the
columella of the shell or to the integument itself in the nude species.

The Intrinsic muscles also consist chiefly of Retractors and Pro-
tractors which arise from the walls
of the huccal bulb and are affixed to
the posterior and anterior parts re-
spectively of the radula, chiefly con-
trolling its lesser movements and
also spreading out the radula during
its protrusion, thereby divaricating
and erecting the individual teeth
for effective use ; the sides again
converging during retraction and
forming a somewhat prehensile
apparatus. All species, however,
do not use their odontophores in
precisely the same way, as, ac-
cording to Dr. Sterki, Planoj-hes
move the radula from behind,
forward ; PJiys(t the sides towards the centre, while in Llmna a the
radular motion is a combination of the two methods ; the vai’ious

Fig. 519. — Median longitudinal section
through the prosoma of an Euthyneure
(modified after Howes), X 3, showing the
disposition of the Intrinsic radular muscles,
and incidentally the arrangement of the jaw
and the organs of the prosoma generally.

b.c. buccal cavity; f. foot ; /./. inner lip;
j. jaw or mandible; Lc. lingual cartilage;
l.L lower lip; l.p. lingual protractors;
l.y\ lingual retractors ; o. ommatophore ;
ce. cesophagus ; o.s. orifice of left salivary
gland ; p.g, pedal gland ; p.r. pharyngeal
retractors ; r. radula ; r.s. radula sac ;
s.d. right salivary duct ; t. anterior tentacle.

Fig. 518. — Muzzle retractor of
Cyclostoina elt’gaiis iPsVxxW.')^ X 3
(after Siniroth).

r.n?. retractor muscles ; l.in.
muscles, whose action gives the
licking motion to the odonto-
phore.

ALIMENTARY SYSTEM — ODONTOPIIORAL TEETH.

•280

Fig. 520. — Track of Helix aspersa
formed by feeding on the paste and
lime shading upon a greenhouse roof,
Christchurch, Hants, June, 1883.

modes of using the odoiitopliore when feeding are also grai)hically
sliown wlieu snails have fed upon the paste and whiting mixture so

frequently ap])lied as a summer shading
to greenhouse roofs ; tlie serpentine or
meandering series of more or less pyri-
form tignres impressed upon the com-
pound by the licking action of the
tongue are seen to differ in their
arrangement according to the species,
showing that each kind of snail when
feeding moves its head from side to side
in a more or less characteristic manner
as the animal advances, hut generally
speaking, the method of using the
odontopl\ore resembles that of the
tongue of a cat when licking, this action rasping particles from the
food to which the radnla is applied.

The Radular or Basal Membrane, to which the teeth are attached
and which together with the teeth form the radnla, is also formed
within the radular sac, by the transverse range of secretory cells
anterior to the odontoblasts siilitting at the ends into fibres, which
are placed side by side, the whole being supported upon the paired
lingual cartilages, wherein are numerous hranched cartilage cells
imbedded within a clear matrix, and to Avhich some of the muscles
actuating the radnla may be attached. At the base of the cartilages
and anterior to the free end of the radnla, there is usually a sac-like
deitression in the door of the buccal cavity, the signidcance of which
is not as yet understood.

The Surface of the Radular Membrane may be divided longi-
tudinally into dve areas, grouped as the Central, the Admedian and
the Marginal, one or more of which may be dedcient in special
groups or genera.

The Central or Rachidian area is the narrow longitudinal mid-
region or Rachis, and bears the median teeth ; the Admedian areas
or Pleune are paired and placed at each side of, and adjoining the
median one ; they bear the asymmetrical lateral teeth, while the two
Marginal areas are occupied by the marginal teeth or uncini, the
particular features of each type of tooth being correlated with its
position upon the I’adular membrane.

ALIMENTARY SYSTEM — ODONTOPHORAL TEETH.

261

The Radular Teeth or denticles, according to their position and
character, may also he classified as Central, Admedian or Lateral, and
iMarginal, and are all reflected posteriorly, the reflected points or
cusps being known as Mesocones, Ectocones or Endocones, according
to the relative position they occupy on the individual teeth.

The Central teeth, which occu^iy the rachis or longitudinal mid-line
of the radula, are symmetrically formed, but do not originate by the
coalescence of two adjoining laterals, except perhaps among the
Limnanda', in which the central teeth may, as in Planorbis, show no
central cu.sp, but two eijually developed lateral cusps. The convex
anterior margin of each tooth often overlaps the base of the pre-
ceding tooth, and is usually trifidly reflected posteriorly, the median
reflection or cusp being known as the Mesocone and the smaller side
cusps as the Ectocones.

Fig. 521.— Central or Median Tooth of Helix aspcrsa JMiill., highly magnified.

b. basal plate ; r. reflected portion ; in. mesocone or middle cusp, with c. cusp or cutting point ;
cc. ectocone or outer cusp with cutting point.

Figs. 522, 523. — Admedian or lateral teeth of Helix aspcrsa Miill., from right and left sides of
and adjacent to the median row.

b. basal plate ; r. reflected portion ; in. mesocone or middle cusp, with c. its cusp or cutting
point; cn, endocone or inner cusp ; cc. ectocone or outer cusp.

Fig. 524. — Intermediate or Transition tooth of Helix asj>crsa Miill.

in. mesocone, showing endoconic bifurcation ; cc. ectocone or outer cusp.

Fig. 525. — Marginal tooth or Uncinus of Helix aspersa !Mull.
bifid mesocone ; ec. bifid ectocone.

The Admedian or Lateral teeth occupy the Pleura; or longitudinal
areas, adjoining the central one, and are usually asymmetrical modi-
fications of the median teeth, becoming more and more primitive, or
unlike the symmetrical central teeth the further they recede from
them. Tlie anterior margin is strongly reflected posteriorly, the term
Mesocone being retained for the reflection, representing the middle
projection of the rachidian series ; the term Ectocone designating the
cusp nearest the outer margin, while the cirsp on the inner side of
the tooth, nearest the centre of the radula, is called the Endocone.

The Marginal teeth or LLicini occupy the longitudinal outer
areas of the radular membrane, and in many species show a wider
base and more numerous denticulations ; they also tend to approach

ALI31ENTA11Y .SYSTEM — OlniXTuriloKAL NOTATION.

tlie median line at a more acute angle than the lateral teeth usually
do, aud viewed l»y the light of their development, are the most primi-
tive form of tooth e.xistent on the odontophore.

The change in character from the symmetrical median tooth to the
asymmetrical laterals and marginals is usually decisive and may be
marked, amongst other things liy the partial or entire loss of the
endocone or inner ensj) and a corresponding enlargement of the
mesocone or midille cus]), which with the ectoeone or outer cusp
may become deejily cleft, this divergence of character becoming more
and more marked as the outer fringe of the radula is approached,
aud lieing also more or less closely correlated with the direction or
curvature of the transverse rows, which is greatly varied in the

Fic.

Kici. .c'G. I'll,. 326. Fiti. rV2'J.

I )iagrammalic figure:* Nliow'mg ihc varied dire'ctions of llie transverse rows of teeth in dilTereiit
species.

Fk;. r>2(». — Tcstacclla haliotidca Urap. I Fig. ,>28. — ! f elix lapicuia 1,.

Fit;. ,)27. — I 'cllctia lacustris \ Fig. 521). — Physa/ontinalis

different si)ecies, an abrupt change in their direction being always
accompanied by an e(pially marked change in the character of the
teeth, while if the rows are straight or the change of direction very
gradual, this change is correspondingly slow, and between the well
marked laterals and typical marginals several transitional teeth may
he interposed.

A Aot.vtion or Formula has been devi.seil to e.xpress, hy means
of signs ami nundjcrs, the general arrangement and some of the
more salient characters of the radula of many of our species. 'J'he
possiliility of doing this is .simplitied by the trail, svorse rows of teeth
being bilaterally alike, while the longitudinal rows are each .straight
and contain similar teeth along their whole length.

The writing of the formula is accomjili.shed by iilaciug a numeral
to reiire.seiit the central tooth, the particular numeral u.sed according
with the number of central teeth iire.seiit in a transver.se row; the
.same cour.se is pursued with the laterals and marginals when these
are homogeneous in shape and character, the numerals representing
which, separated hy the sign + , are jilaced at each side of the central
figure in .similar positions to those actually occuiiied hy the teeth

ALIMENTARY SYSTEM — ODONTOPHORAL NUTATION.

•268

themselves ; thus the formula 20 4- 4 + 1 + 4 + 20, would indicate that
ill each transverse roiv there was one central tooth Hanked by four
lateral and twenty marginal teeth, each series of a practically
homogeneous character. Sometimes the marginals are so minute and
comiiact or so numerically variable that it is difticnlt or impossible to
state their exact number ; in such cases the sign of infinity ( oo) may
appropriately be used to indicate them. When, however, the teeth
composing a series are markedly heterogeneous in form and general
character, the numerals representing them may he used individually
or in suitable combinations, so that their dissimilarity may be
emphasized, thus cc + 1.1.1.1. + 1 + 1. 1,1.1. + x would signify that
there was one central tooth, with four dis.similar laterals, and
an indefinite number of homogeneous marginals at each side.

The number of trainsverse rows should also be added to the formula,
preceded by the sign x , which will often enable the total number of
teeth on the radula to be readily ascertained if desired, as although
their number is approximately constant in full-grown individuals of
the same species, it varies very considerably in different groups and
even in different species, and is not at all dependent on the size of
the animal, for Ihjallnia luctda has only about 945 denticles, whereas
Helii' ohvoluta, a species of about the same dimensions, has 15,300.

Increased precision in notation may be attained by the use of
larger or smaller figures to indicate the relative sizes of the teeth and
also by placing beneath the numeral rei)resenting the number of teeth
in each group, a second series to denote the number of reflections or
cusps upon the individual teeth ; if these consist of a variable number
of minute and numerous pectinations, they may he indicated by the
sign of infinity oo , as already suggested for the representation of
marginal teeth when numerously present; where, however, the number
of teeth or pectinations do not exceed 20, and the amount of variation
is not accurately known, it will be more satisfactory to give the ascer-
tained number as near as may be with the marks of increase or decrease
as most appropriate, thus 14 < would convey the information that 14
or more teeth or pectinations were present ; 1 4 that the variation

was towards a lesser number, while cfd^ would indicate that the
(piantity present ranged above and behjw the number indicated, thus :
+ § + -«■ + §+ l-i- X 38 = 950,

the full dental formula for Hyfdlnia alUarki, shows that species, in
the particular preparation examined, to possess 950 teeth, contained

RIIIPIDOGLOSSATE TEETH.

2CA

ill 38 transverse rows, each with a trifidly reflected median tooth,
flanked on either side by two lateral teeth with three cusps, and by
ten or more aculeate marginal teeth, the innermost having two cutting
points and being transitional in character.

The Cl.\ssification of the odontophores of our native species is a
task of considerable difficulty, but their study at once suggests the
desirability of separately considering and grouping the Streptoneurous
and Euthyneurous forms.

The Streptoneura have long been known to possess such very
persistent and characteristically varied types of teeth that their
peculiarities have, by almost universal consent, been utilized as a
basis for forming natural groupings of this section of the mollusca.
Our Streptoneurous species may all be placed under the two well-
known groups, Ilhipidoglossa and Tsenioglossa.

The Rhipidoglossa {piirk, fan ; yA.wcrcra, tongue) are especially
characterized by the extraordinary number and marlved uniformity
of the uncini or marginal teeth, which are usually very compactly
arranged in a somewhat curvilinear or fan-like manner, diminishing
gradually in size as they approach the outer margins of the radula.

Fig. 531 Transverse row of teeth from the odontophore of Ncritina Jhiviatilis (L.), highly

magnified. River Nene, Northampton, collected by Mr. L. E, Adams, B.A., and prepared by
Mr. J. W. Neville.

In Neritina fluv'mfiUs, our only representative of this group, the
central teeth are obscurely trifid, the laterals of very dissimilar size
and shape, with the flrst and the outermost of the scries exceptionally

T.ENIOGLOSSATE TEETH.

■2H.}

large and broad ; the former may be known as tlie IMajor lateral, to
mark its superior size, while the latter is distingnished as the Caijitnli-
form tooth, on account of its fancied resemblanae to the capital of a
column ; the marginals are very numerous and compact with two
or more cusps. The formula may be expressed as

^ + 3 + ^

The affinity of the terrestrial air-breathing genera, Helkina and
Proserpina, to our branchiate Neritina fluviatilis is demonstrated by
the similarity in character of their dentition.

The T.ENIOGLOSSA (rati'ia, ribboii ; yAwcro-a, tougue) to which prac-
tically all our Streptoneurous species belong, are chiefly remarkable for
the extraordinary length and narrowness of the radula. They are
usually characterized by bearing seven longitudinal rows of teeth,
composed of a central tooth, with one or sometimes two somewhat

Fig. 532. — Transverse row of teeth from the odontophore of r/v/^ara vivipara (L.), highly
niagnifiedj Northampton, collected by Mr. L. E. Adams, 13. A., and prepared by Mr. J. \V. Neville.

ample admedian or lateral ones, and one or more, but usually two,
more slender marginals at each side, all closely serrate or dentate
at the upper or cutting edge and the outer series often outwardly
directed.

This type of dentition is shown by Vivipara vivipara, whose chief
peculiarities may be expressed by the formula

To^ + yiro + T + + 10^12 >"90 = 630,

signifying that there are 630 teeth upon the membrane aiTanged in
90 transverse rows, each containing a central tooth, flanked on
either side by two lateral teeth and a single marginal, all strongly
pectinated upon their cutting edges, the chief feature of which is
the large (juadrangular central cusp, present upon all the teeth
except the marginals or uncini.

A similar general arrangement is found amongst the Nucleo-
branchs, in which, however, the lateral teeth are more strictly
aculeate, corresponding to their more carnivorous habits of life.

•JGli STEN0I)0>JT01’110H.VTK TEETH.

Tlie Euthyneur.v or pulinonate species, the most highly si)ecialize(l
of the Gastroi)oda, were all formerly relegated to the Cteiioglossa,
a grou]) to which Clio, Actaum, Ihlichut, Limmco, Hdi.v and other
terrestrial, Hnviatile and marine genera were also referred.

^Vfter carefnl stndy and examination of many types, I have tenta-
tively placed our Euthynenrons sjjecies in two chief divisions,
Stenodontophora and Eurydontophora, based upon the more or less
broad and (piadrate t>r narrow and sole-shaped form of the basal i)lates
l)y which the teeth are attached to the lingual membrane.

The Stexodontopiior.v ((rreros', narrow ; oSoih', tooth ; </)€/>w, to bear)
are those species or genera with teeth (jf an
aculeate character affixed to the radnlar
membrane by a narrow and somewhat sole-
shai)ed base of attachment, from the whole
surtace of which there arises a strongly
recurved spine-like tooth.

'I'he surface of the radnla usually pre-
sents a median and two marginal areas, and
typically the teeth are uniform in character
in each series, the nie<lian row, when i)resent, being sometimes formed
by tritidly retlected teeth, and the
marginals varying only in the size they
attain, the largest and most powerful
being placed near the outer margins,
corresponding to tlie prominences of the
lingual cartilage and the greater func-
tional imi)ortance thus conferred by that
l)0.sition in the seizure of i)rey, while those
nearest the median line and the extreme
marginals are the smallest, a gradual
increase of size taking place from the
median line and a much more rapid and decisive enlargement from
the outer marginal series.

It is the tyj)e of radnlar teeth for carnivorous mollu.sks and is
characterized by comparatively limited series of long, narrow,
loosely ranked spinous teeth, which apiu'oach the median line from
the lateral margins at a posteriorly directed acute angle, as in
TestaceUd ; hut in Plnjsa fontindlis the angle formed, although equally
acute, points in the ojiposite direction.

F' \c,. 531. — Section across the heail
of Tcstncclla hnlloiidia Drap. ,
showing the form of the lingual car-
tilage anti the disposition of the
radnla, etc. (after Lacaze-Duthiers).

7)1. matrix ; i.7)i. intrinsic muscles;
7-.C. radnlar cartilage with superim-
])oscd radnla.

Fit;. 533. — Typical .\culeaie
or Acanthoglossate tooth showing
the sole-shaped base of attach-
ment, highly magnified.

ACANTHOGLOSSATE AND BELOGLOSSATE TEETH.

267

The Steiiodoiitoplioroiis species, according to the character of the
apices of the teeth or the modification they have undergone, may be
divided into three chief groups, viz. : Acanthoglossa, Beloglossa
and Echinoglossa.

The Acanthoglossa (aKavda, a prickle ; yAwcra-a, tongue) possess
spine-like or sickle-shaped teeth (as fig. o.Sd), a form which would
seem more especially to characterize the carnivorous genera, but no
species under our especial survey possesses a radula exclusively formed
of this type of tooth, although Rhytidu and other tropical genera
show characteristic examples ; this group is, however, enumerated
here as some of our genera possess Acanthoglossate teeth in conjunc-
tion with those of the Pycnoglossate type, and in such cases the
Acanthic teeth always form the marginal series and generally tend
to approach the median line at a more acute angle than the (quadrate
teeth usually do.

The teeth may be simply thorn-like or, by cleavage of the apex,
form bispinose or trisi)inose teeth, the accentuation of this feature
becoming more and more marked as the margin of the radula is
approached.

Proctonotlda’ amongst the Opisthobranchs and Bhjtlda zmowg
the Pulmonates show characteri.stic exam})les of this type, almost
identical in form and arrangement.

The Beloglossa (fitXos, an arrow ; yAwcru-i/., tongue) or species
with barbed teeth are confined in this country to the predatory genus

Testacella, and would appear to be a special modification of the
Acanthoglossate type, adapted to more securely retaining their hold
upon the earthwonns upon which the Testacellw chiefly prey.

2GS

ECHIXOGLOSSATE TEETH.

The uduiitophore of Tcstacelht haliotidea may be formulated as
"¥^ + {} + S + |} + -r‘=xd8 = l,dG8,

showing that there are 1,8G8 teeth arranged in 38 transverse rows,
all of whicdi are dehcient of the middle and lateral series, but possess
1 8 marginal teeth at each side, all of which are strongly barbed on
one side of the apex like a fish-hook and may also he furnished with
a sharp blade-like cutting edge on the convex side of the apex. The
base of attachment ac(|uiros knobbed extremities, owing to the enlarge-
ment of each end, for firmer attachment to the radnlar membrane.

Typically the Beloglossate radnhn are deficient of a median row of
teeth, although a minute mid-tooth may occasionally be met with in
some part of the membrane.

The Echinogloss.v (eyu'os', a hedgehog ; yAwo-o-a, tongue) may be
an aberrant form of the Acanthoglossate teeth, with more numerous
s])inons terminations and a more pronounced curve of the reflected
liortion or more probably it may have ari.^en from a different stock, as
the radical difference in the mode of convergence of the lateral trans-
verse rows would seem to point to a different derivation.

Fig. 5.‘^G. — Median portion of a transverse row of llie teeth of Physa fontinalis (L.) liighly
magnified, from Cambridge, collected and prepared by Kev. Prof. Gwatkin, M.A.

The Echinoglossa are not oidy remarkable for the large accessory
oval plate or knob attached to and projecting anteriorly beyond the
teeth, but also for the acute convergence of the transverse rows
from the lateral margins towards the anterior portion of the membrane,
instead of towards the posterior end as in mollusks generally.

The individual teeth are very closely and compactly arranged, ex-
cept near the median line, where the smaller size of the teeth leaves a
perceptible space between the transverse rows ; the mid-tooth shows
long and jnoniinent lateral margins, which in Phyi^a fontnialis are
partially overwrai)iied Ijy or fused with the adjacent teeth. The
marginals are very nnmerons and practically uniform throughout,
varying only in the number of cutting i)oints they disi)lay.

EURYDONTOPIIOROUS TEETH.

269

Tliis type of tootli is possessed by Phjjsa faiitinali.^, and its
characters may be broailly expressed by the formula

X 57=19,893.

The genus Chilina, a primitive group of fluviatile snails inhabiting
South America, has teeth of the same general character, bearing a
similar knobbed enlargement of the anterior end of the base of
attachment and the transverse rows of teeth having the same anteriorly
directed arrangement.

The Eurydontophor.v bi’oad ; oSois, tooth ; to bear)

are those species with teeth characterized by a somewhat square base

of attachment to the radular membrane,
and distinguished from the Aculeate
type of teeth by their gradual diminution
in size, in proportion as they recede
from the centre of the membrane, their
greatest development being near the
centre — perhaps in correlation with the
median longitudinal ridge upon the
lingual cartilage, which probably endows
the teeth thereon with increased func-
tional importance, and leads to their
acquiring greater strength than those
less favourably placed for the efficient
exercise of their powers.

The teeth are usually divisible into three series, distributed upon a
central, two lateral, and two mar-
ginal areas ; the lateral and marginal
areas, however, often blend so in-
sensibly together that no distinct
line of separation can be made out
between them ; this doubtful space
bears teeth of a similar undecided
character, as they partake of the
characters of both series and are known as transitional teeth.

The Eurydontophora have usually numerous transverse rows of
closely-set cuspidate teeth, a form especially adapted for the reduc-
tion of vegetable food, and, according to the character of the individual
teeth, may be tentatively arranged in four groups, viz., Pycnoglossa,
Zeugoglossa, Myriaglossa and Dichogiossa.

Fig. 537. — Transverse section
through the buccal bulb of A^io-
livtax a^restis (L.), x30, showing the
form of disposition of the radula and
radular cartilages (after Hanitsch).

b.c. buccal cavity ; in, ventral
muscles of buccal bulb; r.c. radular
cartilages with superimposed radula;
s,d. salivary ducts.

Fig. 538.

Fig. 539.

Fig. 538. — Typical Quadrate or Eurydontate
tooth as seen from above, highly magnified.

Fig. 539. — Side view showing the reflection
and cutting points, highly magnified.

270

PYCXOGLOSSATE AND ZEUGOGLOSSATE TEETH.

The PrCNOGLOSSA (ttvkvo^, crowded ; y/\wcro-a, tongue) may he con-
sidered as the typical dentition of the Puhnouates generally and of the
Helices in particular. It is characterized by the enormous number and
close arrangement of the individual teeth, which resemble mosaic work
in their compact methodical arrangement. The mid-tooth is usually
tritidly retlected with the mesocone much the longest, while the
laterals and marginals are more or less asymmetrical moditications of
the type of the central tooth, each tooth becoming more numerously
denticulate and with wider base as the margin is approached. The
transverse rows are usually gently curved, ai)proaching the median
line at almost right angles. Tliis gradual change in direction gives
rise to intermediate or transitional teeth, connecting impercei)tibly the

Fid. 540. — Representative teeth of hnlf a transverse row of teetli o Helix nsf>ersa Mull., hii^lily
niagnil'ied, collected by Dr. ScharlT near Dublin.

The numerals appended to the figures of ihe teeth indicate their position in the tran.sverse row.

lateral and marginal series, ilellv aspersa is a typical example of
this group, and its i)eculiarities can he exinessed l)y the formula :

4- 1 + x Uo=12,(; 1 5,

showing that species to possess 12,01.7 teeth, contained in 1-1.7 trans-
verse rows, each containing a central tooth, bearing 3 cusps, 20
laterals at each siile with 2 cusps, and 33 marginals and transitional
teeth, with 3 — 4 cusps each.

The Zel’Goglossa paired; y/Vdio-cra, tongue), of which

J^hinorbh corneus may be taken as an example, are distinguished by
the paired or hitid cusps to the teeth composing the median longi-

Fii;. .m. — Representative teetli from a transverse row of the oilontophore of Planorhh
roivn-Ki (1..), hii^hly magniriei.1, collected at Northampton by .Mr. L. E. .\dams, 11. A., prepared by
.Mr. J. W. Neville.

The mimerals aiipended to the figures of the teeth indicate their position in the transverse row.

tudinal row ; the laterals being also hicuspidate and the marginals
e.xhihiting the comh-like teeth of the Acanthoglo.s.sate tyjie. The
formula of Pldnorbh corneus may be written as :

_|. s + i + s + X 200=1 3,400.

MYRIAGLOSSATE AND DICflOGLOSSATE TEETH.

271

This peculiar dentition is in this country restricted to the
PUmorhes, but has been shorvn to be also possessed by their possible
progenitors, the so-called Pki/sa’ of Australia, the representatives of
which, although now restricted to the Southern Hemisphere, had

1) robably in former times a much more extended range.

The IMyriaglo.ssa (/Lirptov, numberless ; yAwo-o-a, tongue) have more
simply shaped and uniform teeth than many of the other Eurydonto-

2) horous groups, and are characterized by the possession of a well-
defined, though slender, mid-tooth, with a trifid reflection flanked by

' ■ '

Fig. 542. — Transv'erse row of teeth from the odontophore of Helix pyginepa Drap. (highly
magnified), Cambridge, prepared by Prof. Gwatkin.

numerous closely set bicuspidate and obscurel}" tricu.spidate teeth of
a practically uniform and usually simple hooked character ; the
formula for JMlr pygmoca, a representative of this group, may be
expressed .is :

The Dichoglossa double ; yAwo-o-a, tongue) are represented

by the genera IlyaUnla, Llnmx, etc., and are distingui.shed by
possessing tricuspid median teeth, with variously cu.sped quadrate
teeth on the central and pleural areas of the radula, the marginal series
l)eing formed by teeth of the Acanthoglossate or Echinoglossate type.

:->5

Fig. 543. — Transverse row of teeth from the odontophore of Hyalinia nitidula (Drap.), highly
magnified, prepared by Mr. J. W. Neville.

The numerals appended to the figures of the teeth indicate their position in the transverse row.

HydUma nitidula may be taken as typical for this section, and the
peculiarities exhibited by its odontophore may be formulated as
+ 4 + ^ + V + 35—2,485.

This group may be looked upon as a link between the Aculeate and
Quadrate teeth, as it combines Ijoth forms on the same membrane,
and would thus seem to markedly indicate the omnivorous character
of the species or groups possessing it. In this group certain genera
will fall which further investigation may probably demonstrate to
lie more suitably classified under other heads.

272 PREPARING THE OBONTOPHORES AND MANDIBLES FOR STUDY.

'riie Preparation of the buccal armature is of such importance,
not merely on account of the intrinsic interest of tlie organs them-
selves, hut because their study sheds so much light upon other aspects
of the science, that a brief account of the methods adopted for this
purpose by Pi’of. (irwatkin, Mr. W. AIoss, Mr. J. W. Neville and
other prominent microscopists will he useful.

The mollnsk is killed by immersion in boiling water and, if a species
of moderate size, extracted from its shell, and the head cai’efully
opened from above, when the buccal bulb containing the jaw and
odontophore will he disclosed ; if, however, the species be too small
for convenient dissection in this way, the shell with the contained
animal may he crushed between two glass slips.

The buccal bulb of the larger species or the crushed mass of the
more minute ones are i)laced in a watch-glass or test tube containing
a solution of Caustic Potash, and allowed to remain therein for a day
or two to dissolve the muscular investment.

When greater expedition is desirable, the buccal bulb of the larger
animals may he boiled in the i)Ota.sh solution in a test tube or watch-
glass and the minute species upon the slide upon which they have been
crushed, taking care in each case that the solution is not too strong.

When the desired organs are freed from extraneous matter, wash
well in clean water and if necessary place in a weaker potash solution
fur a few hours; then give a final thorough washing, u.sing, if thought
advisable, a very tine camel’s-hair brush to assist the cleansing
process, more especially at the hinder end of the radula, but to secure
the perfect removal of the potash, the radula may again be placed in
imre water for some hours.

When thoroughly clean, the jaw and odontophore are transferred
to and immersed in a small drop of glycerine with which the prepara-
tion will be thoroughly permeated in about half-an-hour, when they
may he hnally transferred to a clean slip, upon which a droplet of
glycerine has lieen placed, and the jaw and odontophore arranged in
the desired positions under the microscope. If the odontophore does
not spread out flat this may he due to a constricting upper
membrane, which, with a lower non-constricting one, needs careful
removal. If the radula is unavoidably somewhat torn in the process,
it will be no disadvantage, as it will enable the teeth to be examined
in various aspects, and in fact it is desirable to purposely make a
tear ([uite across the odontophore to achieve this result.

PREPARATION AND STAINING OF ODONTOPHORES.

273

AVheii satisfactorily arranged, breathe upon a clean cover-glass and
place it upon the object -without enclosing air-bubbles, and then, while
carefully avoiding moving the glass cover, wipe off the superfluous
glycerine with a soft rag, and with a tine brush dipped in quick-
drying gold size run a connecting line round the glass cover and slide
and lay aside for a day or two to dry, before finishing off with cement.

If Glycerine Jelly be preferred as the mounting medium, the bottle
containing the jelly should be placed iu a cup of hot water until
li(iuefied, and when the radula and jaw are satisfactorily arranged on
the slide, place a cover-glass over them, and secure it by a clip, before
running the now fluid jelly beneath the cover, under which it will
(juickly penetrate by capillary attraction ; when thoroughly permeated,
boil for a moment to get rid of vacuoles or vapour bubbles, and i)lace
the slide aside in a cool place for two or three weeks; the superfluous
jelly can then be removed and the mount completed with a ring of
brown cement and a finishing coat of gold size. The objection to the
use of glycerine is its h3^gi-oscopic nature, and in some districts the
injurious effects resulting from this (quality can scarcely be securely
guarded against by the most careful ringing.

Canada Balsam is also used as a mounting medium when it is
intended to stain the radula or where it is desired to use the polari-
scope in the examination of the prepai’ations, and though the Balsam,
in course of time, renders the teeth very transparent, that is no real
obstacle to the successful use of the polai'izing apparatus.

Staining, in the opinion of many microscopists, greatly facilitates
the study of the more minute odontophores, a well-stained preparation
showing the teeth as though formed of coloured glass or crystal.
Although many stains are used bj' microscopists, the Eosin-Haima-
to.xylin })rocess, as practised by Mr. E. W. W. Bowell, being practically
permanent and so excellent in many ways, may be selected as a
representative one.

In this process, the ladula, after the final washing previously
described, is wanned in water slightly acidulated with acetic acid to
neutralize any trace of alkali left in the preparation ; it is then dehyd-
rated with absolute alcohol, placed upon a clean excavated slide, and
Ehrlich’s undiluted Hpematoxylin applied for two or three minutes ;
should the blue stain, after its development by washing in tap water,
prove to be too strong, the fault is (quickly corrected by a momentary
sojourn in alcohol or water faintly acidulated by Hydrochloric Acid.

s

274

ALIMENTARY SYSTEM — THE (ESOPHAGUS.

SfSJ/

Fig. oil. — ^’ariolls cells from
the lesophaijus of I/cli.v ^ofnatia
L.. highly magnilied (after Vogt
and Vung).

I’lie IIaHnatox34iii stain acts by outlining the basal plates and
staining the edges of the structures generally, and is strengthened and
assisted in emphasizing important details and more especially the
cones, by the use of a saturated aqueous solution of Eosin, which
should l)e used for five or ton minutes, after which deliydrate with
absolute alcohol through cigarette paper and clear with oil of cedar,
then arrange the object on the slide, diy off the clearing agent with
cigarette paper, and put a drop of Canada balsam, preferably in Xylol,
on the object, and then place the cover glass in its i)ositiou and com-
plete by cementing.

The (Esophagus 1 shall cany ; (/)ayai', to eat) or tlullet, is a

ciliated tube of variable length, thickness, colour, and markings in
the different s})ecies, and which, though
sometimes tle.xuous and in Neritina even
sinuous in character, usually has au almost
direct course extending in the Castropoda
from the i)harynx to the stomach, but iu the
Pelecypoda originating at the oral orifice owing to the absence of
jiharyngeal si)ecialization. Its limits are ill detined, due to the im-
perceiitible change in its structure and
cai)acity, the walls being very di.sten.sible
owing to the longitudinal folds into which
they are thrown. Interiorly it is lined
with cylimlrical and j)artially glandular
epithelium, and exteriorly by muscular
layers, whose successive contractions im-
pel the food onwards towards the stomach,
before reaching which the tube may ex-
pand to form one or more distinct enlarge-
ments, separated by imjre or less definite
constrictions, corre.sponding to and in-
dicating division of function.

The Crop, the most anterior of the
(esophageal enlargements, acts as a kind
of reservoir or i)reliminary receptacle for
the ingested food, and is a large and fusiform thin-walled sac, often
conspicuous by tbe colour of its contents, occupying the front of the
visceral hump in the testaceous .species and tilling a considerable part
of the bodj" cavity. The lining membrane resembles the msophagus

Fig. 545. — Alimentary canal of
Limmca ^^crcgi’a Mull., X 4, showing
the relative positions of the crop,
paired giz/ards, stomach, etc.

b.h. buccal hulh ; c. crop ; g. paired
gizzards ; st. stomach ; /. plecton ;

rectum ; ic. oesophagus ; s.g. sali-
vary glands.

ALIMENTARY SYSTEM — SALIVARY GLANDS.

275

iu being thrown into a series of distensible longitndinal folds, visible
through the thin walls and giving the organ a striated appearance.
In Testacella and probably other species, the crop may acquire
stronger and more muscular walls and assume the functions of the
true stomach by canying on the processes of active digestion therein.

The Gizzards or organs for the mechanical gi’inding of food are
present in some species and placed on the foregnt between and
partially beneath the crop and the stomach. In Limncva they con-
sist of two globular and laterally paired piirple-brown muscnlar
pouches formed by an excessive local development of the nmsciilar
investment of the oesophageal tube, and ai’e usually partially filled
with sand or gravel to assist in the crushing and trituration of the
food before undergoing the process of digestion within the true
stomach, as it is only posterior to such muscular enlargements that
the true digestive ferments are encountered.

The four cavities, the crop, the paired gizzards and the stomach,
thus concerned in the storage, tritui’ation and digestion of food really
form only a single chamber with four recesses, and bears a general
external resemblance to the Quatrefoil of Gothic architecture or may
be likened to the nave and transept of a cathedral, the lateral gizzards
representing the transepts and the crop and stomach the nave of
the building.

The Salivary Glands (saliva, spittle), whose presence in the mol-
Insca is apparently correlated with the
development of a pharynx, and which do
not therefore exist in the Pelecypoda, except
perhaps in such archaic genera as Nuciila,
etc., in which there are paired glandular
pouches opening into a vestigial buccal
cavity, which may represent the early form
of these organs, that of a pair of simple
tubules, with the secretory part located at
the distal end, as in Acta’on and other
archaic Gastropods. The organs of Semper,
which I have regarded as more especially
gustatory in function, are considered by
many to be homologous with and to repre-
sent the Buccal or Anterior Salivary Glands present in the Cephalo-
poda, Amphineura and other gxoups.

Fig. 546.— Salivary glands of
Ileli.x hortciisis Mull., x 3,
showing the character and mode
of apposition to oesophagus.

b.b. buccal bulb ; ce, oeso-
phagus ; s.g. salivary glands
with their ducts, s.d.

276

ALIiMENTAUV SYSTEM — SALIVARY GLANDS.

In tlie Gastropoda, tlie salivary glands arise as simple outgrowths
of the alimentary canal, and are i)aired foliaceons lohnlate organs,
often fused together dorsally, composed of hranched hlind tubules

lined with glandular epithelium and
attached by connective tissue to the
sides of the msophagus or to the walls
of the foregut or crop, and though
there is a general resemblance in this
organ among the different species,
yet there are some divergent forms,
the most striking example being
Ci/closfonia elegaua, whose
glands in their natural position are
curiously coiled up, hut when un-
folded resemble the handles of church-hell ropes.

'I'he secretory cells are large and somewhat oval, with large oval
nuclei, which can he rendered visible by reagents ; they are invested
by connective tissue, containing free nuclei. The secretions escape
from the individual cells by the rupture of
their investing ti.ssue, and are gathered
eventually into the usually darkly i>ig-
mented common ducts of each gland,
which are placed at each side of, and
acconqianying the (esoi)hagus through the
nerve ring, and convey the fluid into
the in)i)er part of the Imccal cavity, where
it is discharged by enlarged outlets.

The constituents of the salivary secre-
tions differ in the different groups, some
marine genera even .secreting sulphuric
or hydrochloric acid, hut the Gastroiioda of our country usually
secrete a ferment which, in addition to mixing with and moistening
the food and thus assisting its passage along the digestive canal, also
converts the starch of the food into glucose or sugar. In our
branchiate .species these .secretions have been a.scertalned to con-
tain Calcium, Mucin, Sulphocyanate and Calcium-pho.sphate, and
l)ossihly a trace of Chlorine, while in the Pulmonates, Calcium and
Chlorine are the chief constituents, l^uliihocyanate and Calcium-
pho.sjdiate being doubtfully pre.sent.

Fit,. — Transverse section

through Salivary gland to show the
arrangement of the cells, highly
magnified (after Vogt and Viing).

sl.c. nucleated salivary cells ; c.c.
scattered connective tissue cells; <L
lumen of duct of gland, showing
some of the more minute duct end-
ings; c/>. epithelium.

(I

Fig. 547. Fig. 548.

Fig. 547. — Anterior part of cesophagus
of Cychstoina t7ci.’n!//A OInll X X 3, show-
ing the disposition of the Salivary glands.

r.^. cerebral ganglia; s.i^. sali\ary
glands ; a\ cesophagus.

Fig. 5IS.-Salivary gland of Cyclosioma
cU'gans (.Midi.) opened out.

ALIMENTARY SYSTEM — STOMACH.

277

Tlie Stomach or miil-iutestinal sac is a specialized enlargement of
the digestive tube, in or near to which the chief digestive processes
are performed and whose walls are often thickened and strengthened
by constrictor muscles, and although, in
many species, the stomach seems blended
morphologically and functionally with the
crop, the two organs are often perceptibly
distinct. It is usually of an elongate or
ovoid form, but, being placed at and forming
the termination of the first alimentary tract,
it is often so bent and curved as to seem a lateral outgTOwth of the
alimentary tube, the cardiac or oesophageal and the pyloric or intestinal
apertures becoming more closely approximated in proportion to the
abruptness of the angle formed by the returning tract.

Fig. 550. — Epithelial cells
from stomach of Helix pom atia
L., highly magnified (after V ogt
and Yung).

Fig. 551. — Interior of stomach of
CyclosioDia ele^^ans (Mull.), x 4, showing
its complicated and sacculate walls (after
Garnault).

ce. oesophagus ; i. intestine ; d.g. diges-
tive glands and ducts.

Fig. 552. — Section through the walls of the
stomach of Helix pomatia L., highly magnified
(after Vogt and Yung).

cti, cuticle ; e.c. cylindrical nucleated epithelial
cells with interposed lacunas ; 7ti. muscular layer
with nucleated connective tissue.

Interiorly the walls of the stomach are beset with glands secreting a
digestive fluid and thrown into longitudinal folds continuous with
those of the oesophagus and often
crossed by more indistinctly trans-
verse ones, giving the stomach a
somewhat sacculate aspect. There
is often a coecum or accessory sac
on the right side in the pyloric
region, the Stylotheca (cttuXos, a
rod ; 9i]K7], a receptacle), which may
extend between the convolutions of the intestines, and contains the

Fig. 553. — Alimentary tract of Dreissensia
polymorpha (Pall.), more especially to illus-
trate the position and character of the Stylo-
theca (after Moquin-Tandon).

in. mouth ; st. stomach : p. plecton ; r.
rectum piercing the heart, h. ; s.c. pyloric
coecum or stylotheca.

278

ALIMENTARY SYSTEM — CRYSTALLINE STYLE.

crystalline style. In some species, this sac can be shut off from the
stomach by a valve, or, as in Utiionidw and other groups, may become
fused with the initial part of the intestine, communicating therewith
by a narrow slit.

The Fl^che-tricuspide or three-pointed body is a firm and gelatinous
cuticular investment of tlie internal walls of the stomach, especially

developed towards its pyloric
end and even continued with-
in the intestine itself. This
stomachal coating, which is
continuous with the crystal-
line style, especially charac-
terizes the Pelecypoda, but is
present in many Gastropods,
and is secreted by the epithe-
lium of the stomach, chiefly
for the protection of its deli-
cate walls and the secretory
cellules therein, but in certain
marine genera this structure
may become differentiated to form variously shaped masticatory plates.

Tlie Grystalline Style, formerly supposed to be correlated with the
absence of mandililes, is a semi-transparent variously shaped rodlet of
concentric structure, continuous with and of similar consistency to the
Fleche-tricuspide, of which it is a specialized outgrowth, usually
projecting freely into the cavity of the stomach from the pyloric coecal
sac, secreting and containing it. It bears some general resemblance
to a })estle and mortar, and probably assists
to more intimately intermi.x the food in
the stomach with the gastric ferments,
which are usually poured directly into the f,,.. 555.-Crys..-iiiine style of
stomach from the digestive gland in those eIuaigTd%ft^^fMoquiii-Ta®n^^^^^^^
species possessing the crystalline style, but where the pyloric sac is
not developed the digestive fluid may be emptied into the plectou,
whose restricted diameter allows a thorough iiitermi.xture to readily
take jtlace. The stylet and its extensions being exposed to the action
of the digestive fluids become softened and partially dissolved,
furnishing the material for surrounding with a soft glutinous film any
sharp, angular parficles accidentally swallowed with the food, thus

f'ui. 5ot. — Median section through Stomach and
Stylotheca of Donax, showing the Crystalline Style
in situ and the arrangement of the Fleche-lricuspide
on the stomach walls, greatly magnified (after Harrois).

st. stom.ach, with the Fleche-tricuspide f.t. ; a\
cesophagus ; i. intestine ; sc. Stylotheca, with the con-
tained and projecting Crystalline Style c.s.

ALIMENTARY SYSTEM — DIGESTIVE GLAND.

279

preventing the laceration of the walls of the stomach and intestines,
and facilitating the ])assage from the body of the irritant objects.

These protective developments are, however, not persistent organs,
but disappear and are renewed periodically, probably forming during
times of plentiful food supply, and disappearing when a prolonged
scarcity of food has led to their ab.sorption by the animal, in a similar
way to that in which other animals absorb superabnndant tissues
during periods of famine.

The Digestive Gland, perhaps better known as the liver, is the
active organ of digestion and is a large brownish or greenish organ,
partially or entirely enveloping the stomach and adjacent organs,
more especially in the Peleeypoda, in which it is more developed than
in the Gastropoda, an increased size of the digestive glands being often
correlated with a reduction in the extent of the gut.

The organ is usually formed by two chief, but unequal, lobes, the
left lobe being larger than the right, this asymmetry being apparent

from the first development or rapidly
becoming so, except in Neritlna and
Valmta, in which they are e(|ual and
symmetrical during development. It
consists of innumerable acini, cleft
into digitiform processes or cceca,
which are aggregated into lobules of
varied size and complexity, bound to-
gether and surrounded by connective
tissue and usually encompassed by a
plexus of delicate blood vessels, which
in Avion ater and other species are
opaque milk-white showing strikingly
against the dark background, while
externally the whole gland is sur-
rounded by a blond sinus. There is
an outer structureless membrane, and
internally the organ is chietly com-
posed of three kinds of cells, viz., fer-
ment cells, liver cells and lime cells.
The ferment and liver cells enclose
grannies of fat, albumen and pigment and differ chiefly physiologically.
The lime cells, which contain phosphate or carbonate of lime, are

Fig. .550. — Digestive tract of Lwimca
stagnatisiX'^^’, X 2, showing the digestive
gland and its ducts.

b.b. buccal bulb ; s.g, salivary glands ;
O’, oe.sophagus ; c, crop ; g. gizzards ;
st. stomach : d.gl, digestive gland and
its ducts ; anus.

ALIiMENTAKV SYSTEM— -DIGESTIVE GLAND.

■2 SO

plentiful in many groups, Imt greatly reduced in number in the
Limua'ida' and scarcely })resent in Snccined ; they probably represent
a store of calcareous matter to be utilized in the growth of the shell
or the formation of the epiphragm.

The ferment is a rather thin dark yellowish fluid, decolorized and
dissolved by Nitric Acid, and is probably a derivative of ha?matoidin.
It is conveyed by the tiny lobular ducts which gradually unite together
and linally enter the stomach anterior to the pyloric ciiecum, when
present, but otherwise, usually behind the stomach and into the initial
l)art of the intestine, by one or more, but usually by two chief
ducts ; ill some cases, as in Ci/c/ostoiiKi, the ducts may bear isolated
acini, wliich have been considered as pancreatic cocca, although such
developments in the Cephaloiioda have been shown to correspond in
function with the salivary glands of the higher Vertebrates.

'I'he digestive gland functions chiefly as a pancreas, but there are
reasons for regarding it as also possessing hepatic functions. The
peptic ferment is stated to be identical with Krukenberg’s llelico-
pepsin, while the diastatic ferment, which disappears during
hibernation, is stated to be capable of dissolving raw starch, but has
no action on cellulose. The fat emulsifying power also disapiiears
in winter.

In the Pelecypoda generally the dige.stive gland has been ascer-
tained to contain Diastatic ferments, I’ancreatin, Peptones and
doulitfully (ilycogen, while in (lastropoda tlie contents are similar
with the addition of Sodium. Put the preci.se constitution of the
(iastrojiod liver, as e.xemplifieil in /It'li.v ponmtht, is, according to
Dr. Levy, by alcoholic extract, Enterochlorophyll, Lecithin, Oleic
and fatty Acids, and as ash. Chlorine, Pho.siihoric and Suljdiuric
acid. The a(pieous extract yielded Sugar, Glycogen, Sinistrin,
Globulin coagulating at Gbc, Ilypoxanthin and other bases precipitable
by iihototungstic acid, and as a.sh. Potassium, Sodium, Calcium,
Magnesium, ^langanese, Cblorine, Phosphoric and Sulphuric acids,
with traces of iron. In winter .silica was also found as an ash
constituent. The ethereal extract yielded onl)^ a trace of fat.

Glycogen (C,iIIioOs) or, as it is sometimes called, Liver-sugar,
is a white amorphous amyloid substance, insoluble in alcohol or ether,
and when dissolved in water exhibits a strong dextro-rotatory in-
tluenee on polarized light, and is distinguished by its power to change
to sugar or glucose in the presence of animal ferments. It is found

ALIMENTAKY SYSTEM — INTESTINE.

281

ill most of the tissues of many mollusks, but is more especially fouml
ill the digestive gland, making its aiiiiearance therein about 17
hours after feeding and disappearing entirely after one to three days’
festing. It forms I'To per cent of the digestive gland in Heliv
pninati((, decreasing during liibernation to 0'429 per cent. It would
appear to be formed more especially from starchy food and is probably
a respiratory fuel substance, as it disappears from the blood after its
oxygenation in the respiratory organs, and is present in the muscles
ill a ratio inverse to their activity.

The Intestine, or gut, which arises at the stomach and terminates
at the anus, has its inner epithelial layer overlaid by a him of closely

adherent connective tissue, with
numerous glandules together con-
stituting the mucous membrane.
Exterior to this comhined layer is
the muscular stratum, whose con-
tractions serve to impel the food on
its course through the digestive
canal. The intestine is greatly varied in its length and mode of
convolution in the different groups and even in the different species,
but there is no distinct division into large and small intestinal tracts
as in the vertebrates, although the relative size of the parts may be
reversed in many species, the pyloric end being often the largest.

Fig. 557. — Ciliated and other cells from
the lining membrane of the intestinal canal
of Helix aspe7-sa Midi., highly magnified
(after Howes).

The two largest were actively secretory.

Fig. 558.

Fig. 559.

Fig. 560.

Fig. 561.

Figs. 558-561. — Diagrammatic figures showing the mode in which the chief intestinal flexure
has originated (after Butschli). st. stomach ; a. anus; r.g. right gill ; l.g. left gill ; //. heart.

The spiral twisting undergone by the visceral sac of most Gastro-
pods during the progress of body torsion, has necessarily involved
in its movement the intestinal canal and other organs contained
therein, and it is remarkable that in some of our nude forms, as
the genera Amalia and Avion, the whole of the intenial organs

ALIMKNTAR Y SYSTEM — PLECTON.

2 8 "2

Ijeliiiul the shield still retain a YCiy considerable twist, equal to
about one and a half s[)iral turns and recalling the similar twisting

exhibited by the internal organs of
/iitlimiiiHS, and yet, excei)t the lateral
position of the organic orifices, there
are no external evidences of their
spirally coiled viscera, and it forms

removed, showing the spirally twisted . ^ i ,• r ,i

digestive gland and intestinal tract, X 2. Un6*Xp0Ct0l.l COlTObOrtltlOU 01 tllO

former i)Ossession of a spiral shell by these groups.

The Intestinal canal may he conveniently divided into two sections,
an anterior section, the Plecton, which is usually more or less com-
plexly convoluted, and a straighter terminal one, the Rectum.

The Plecton (-AeKToc, twisted or twined) originates upon the
ventral side of the stomach, fnmi which it is sometimes separated by
a sort of valve, and in the herbivorous
and omnivorous species is often very
long and complexly convoluted, a feature
which has arisen chietly by the elonga-
tion of the ])rimitively straight and
simple canal; the coiling exhibited is,
however, never continuous in one direc-
tion, like a watch-spring, hut is reversed
from time to time, so that the tracts
cimsidered as convex are ])ractically
e([ualled by others bent in an oi)posite
direction and forming what is known as a
“reversed spiral,” an arrangement which
always takes })lace when a lengthening
hod)' with fixed ends is confineil within
a limited .sj)ace.

'I'he Plecton, though continuing the
digestive processes set up by the stomach and also receiving the
secretions of the digestive gland in those species not i)ossessing the
crystalline style, is chiefly absorptive in function, this jn'oeess being
facilitated by the development on the ventral side of the intestinal
tube, es])ecially in the earlier i)art of its course, of a strong inhdding
(jf its walls, which greatly increases the al)sorptive surface and forms
what is known as the T)q)hlosole. This absorption of the nutritive
products of digestion from the alimentary tract is not accomplished

P'lG. 503. — Alimentary tract of Sue-
cinco. dedans Kisso, x 5, Exminster
Marshes, Devon, collected by Mrs.
Smith, showing the character of the
plectonic and rectal tracts.

h.b. buccal bulb; cp. oesophagus;
c. crop, blending with stomach st. ;
p. plecton or coiled intestine ; r.
rectum.

ALIMENTARY SYSTEM — RECTUM.

28.3

Fig. 564. — Portion of intestinal
canal of T esiacella halioiitiea Drap.,
showing the plexus of blood vessels
upon its surface, highly magnified
after Lacaze-Duthiers).

by special organs, as in Vertebrates, but is effected by endosmosis
through the intestinal walls into the blood contained within a plexus

of blood vessels distributed over the
whole surface of the alimentary canal
and is thence carried by the blood to
every part of tlie body, the functions of
digestion, absorption and circulation
being thus closely united.

The Rectum {rectum, straight) is the
straight terminal section of the intestine, and often differs in colour
and character from the preceding convolute portion, being sometimes
more muscular and palpably thicker and sacculate, as in Plunoi’bis
corneas, or may be more slender, as in the Limaces. In our Pelecy-
pods, in Neritina and other of the more primitive Streptoneura, the
rectal tube in its course towards the exterior is embraced by the
ventricle of the heart, but in Vivipara the pericardium only is pierced
and in other groups every gradation is found leading to the final
freedom of the rectum from all contact with the heart.

The rectum bears upon its outer side a band of longitudinal
muscular fibres which retract the collar, thus shortening the rectal
tube and expelling the contents in various forms, according to the
species and to some extent according in colour with the nature of
the food. Ordinarily the excrementitious matters are e.xpelled in a
vermicular or twisted shape or they may, as in Cyclostoma, assume a
spherical form. The anus or excretory orifice is closed by a kind of
sphincter muscle, and being always in
association with the respiratory cavity,
if one be present varies its position with
the breathing organ, but its termination
always lies in the path of the excurrent
stream, if a special one is present. In the Pelecypods it is placed at
the hinder end of the body above the posterior adductor, Imt in most
Gastropods it opens more or less anteriorl)", in dextral specimens
upon the right side of the body and in sinistral individuals on the
left, and is sometimes placed upon the fmcal lobe, a small and
slightly twisted outgrowth, which in Planorbis has a rich vasculariza-
tion. In Testacelbt, whose visceral coil has become untwisted by the
detorsion of the body, tbe anus has reverted to its primitive
posterior position.

Fig. 565. — Respiratory orifice of
Agriolimax agrestis (L.), showing
the anterior anal cleft, x 3.

ALIMENTAR Y SYSTEM— TRIODROMA.

'J84

'I’he Re^tatheca (rccfd, straiglit ; t/iecu, a sheath), a reiiiarkal)le
hliud (Hvertieuluiu, arises about inidway in tlie course of the rectum
and extends backwards above tlie stomach in certain of our nude
species, but its signiticance or function is unknown, altliough in Birds
analogous structures have been correlated with the function of

digesting chitin and cellulose, and it
is probable that this is also its
function in slugs, as fungi, which are
mainly composed of cellulose, are a
favourite food with the species pos-
sessing the cmcuni. A7'io)i ate/' is
also stated by Simroth to possess a
cylindrical ca'cum, situate behind the
hepatic ducts, which he regards as
probably possessing special digestive
power, and thus may be analogous in
function to the Rectatheca.

Our British species may be pro-
visionally sei)arated into three groups,
viz. : — Dichodroma, Triodroma and
Rentadroma, which are based upon the
number of tracts the intestinal canal
exhibits, although the tracts in all the
groups vary greatly, not only in their
length, but in the number and direction of their subsidiary flexures.

The 'I'riodrom.v (rpt-, three; ^/)o/ro«, a tract), which is the prevailing
type of intestinal convolution in our British .species, po.s.sesses only
three chief intestinal tracts beyond the stomach, the first loop being

4*

Fio. 507. — Alimentary tract of Kclix lapicida L., X 4, as exemplifying the section Triodroma.

always ventral to the stomach and having a forward course, which
is considerably varied in detail in the different s^iecies, but usually
ascending above the oesophageal tract where the first anterior loop is
formed, which in the Euthyneura is held in position by the ceiihalic
branch of the aorta, afterwards passing more or less diagonally back-
wards and there bending forward to the rectum.

Fir.. 500. — Alimentary tract of Lintax
/Ia7'us L., showing the large intestinal
cceciim or Rectatheca, x 2.

buccal bulb ; c.^. cerebral ganglia ;
cr. crop, blendifig with the stomach st. ;
a. anus; c.ui. intestinal c«x:cum or
Rectatheca.

ALIMENTARY SYSTEM — FOOD.

285

Tlie Dichodroma double ; Spo/xos, a tract or course) com-

prise those species in which the intestinal tracts have become reduced
to one forward and one backwardly directed section ; the detorsion the
viscera has been subjected to having merged together the rectum and

9

Fig. 568. — Alimentary tract of Testacella haliotidca Drap., enlarged, exemplifying the section
Dichodroma.

the posteriorly directed plectonic tract, this process also uncoiling the
cephalic artery from its sustaining position around the anterior
intestinal loop.

Tlie Pentadroma (Trh'xe, five ; Spopos, a tract) show five tracts or
courses beyond the stomach and, as in the Triodromous species,
have the first anterior intestinal loop encircled by the cephalic artery ;

Fig. 569. — Alimentary tract of Limax iiiaximus L., exemplifying the .section Pentadroma.

the two additional tracts in Limax maximus and its immediate
congeners have the additional anterior loop passed around the
])haryngeal retractor, which being affi.xed to tbe dorsal integument
holds this loop in its proper position, tlie final backwardly directed
tract bending in the rear to join the final tract or rectum.

Fig. 571.

Fig. 570. — Anterior folds of the intestinal tract of Limax maxltnus L., showing how the coils
are held in their anterior position.

/. plecton; r. rectum; a. aorta dividing into v.a. visceral artery and c.a. cephalic artery, the
latter encircling the first anterior coil ; p.r. pharyngeal retractor, holding the second coil in place.

Fig. 571. — Side view showing the pharyngeal retractor encircled by the second anterior intestinal
coil and its attachment to the dorsal integument.

/. the second anterior coil of the plecton ; p,r, pharyngeal retractor fixed to dorsal integument b.

The Food of the Pelecy})oda consists chiefly of Infusoria and the
various floating microscopic organisms brought to them by the cur-
rents produced by the ciliary investment of the branchim and other

DEFENCES UF PLANTS AGAINST SNAILS.

280

organs, although this method only allows a purely passive selection
of the nutrient particles to be made. The more active Gastropoda,
however, often exercise great discrimination in the selection of their
food, althongh their tastes are not identical wiih onr own, except
perhaps in their fondness fur saccharines, most .species being partial
tu the sweet parts of j)la.nts. In other respects our tastes are different;
C7ntroj>/ii//lnm temidum, though relished by many snails, produces
unpleasant sen.sations on the human tongue, while many papilionaceous
or pea-like i)lants, pleasant or merely insipid to ourselves, are carefully
avoided by snails or only nibbled under stress of hunger. Although
many Gastropods are more or less omnivorous, yet some species retain
or have ac([uired a special power of feeding upon certain plants, which
are adeiiuately defended against others not similarly modified.

Plants, being the staple food of mollusks, would be much more
■severely ravaged by them if their constant attacks during countless
ages had not contributed to develop a variety of i>rotective devices,
liruhahly most formidable in those plants which formerly suffered
must severely from their depredations. These acipiired defences are
now su universally })resent that Stahl has not found a single phanero-
gam unfurnished with some means of pnffection, rendering such
plants more or less unpalatable or difiicnlt of access, so that only
dire necessity compels the omnivorants to feed sparingly upon the
least protected parts of the less perfectly defended species, and
although Arum atrr and AgrioUma.v agrestis are so pre-eminently
omnivorous and greedy that few i)lants are altogether safe from their
attacks, yet even their ravages are infinitely reduced in extent by the
varicil ohstacles to he overcome before the desired food is obtainable.

'I'liese harriers are indeed often so insuperable that certain sensi-
tively organized species feed by preference upon dead or decaying leaves,
jirohahly thus exhibiting their keen sn.sceptibility to the chemical pro-
teciion so many j)lants enjoy, a jn'otection which, being dissipated on
the fall of the leaf, enables them to he then partaken of without injury.

Cultivated i)lants alone are not adeipiately armed, having pro-
bably lost l>y .selective culture the re])ellant substances or structures
to whicb they owed their i)reservation in a wild state, so that they are
now greedily devoured l)y snails and slugs, and owe their continued
existence in their present form solely to man’s protection.

The Defensive Devices of i)lants operative against .snails may be
mechanical or chemical, and although it is difficult to recognize a close

STRUCTURAL DEFENCES OF PLANTS AGAINST SNAILS.

287

comiectioii between a definite group of animals and tlie protective
arrangements of certain plants, yet such reflex contrivances un-
doubtedly exist, although the same protective devices may be
operative against very diverse animals. Certain groups of plants are,
however, distinguished liy the predominance of a certain mode of
protection, although few liave the same protection in all their parts,
dowers having usually different defensive devices to the vegetative
portions, and the internal protection when present differs in character
from that of the exterior.

The Structural Defences embrace a prickly or hairy investment,
and the hardening of the stems and foliage by the silicidcation or
calcidcation of the more exposed tissues, and such plants are probably
still acceptable to molluscan palates when their external defences can
be overcome.

The Silicidcation of tlie exterior of many of our gxasses. Horsetails
(E(|uisetacem) and Cyperacem not only gives rigidity and dimness to
the plants, but is a real protection against snails, heliciue teeth
being practically helj)less against the defence it od’ers; its efdciency is
shown in some tropical grasses, in which this silicidcation is so pro-
nounced as to render them totally undt even for feeding cattle.

Mosses are also protected by their highly silicided tissues, shown
in the stid' pointed hairs, serrate margins and rough capsule stems,
features particulai'ly noticeable in Fiinaria hygrometrica.

Calcidcation of the tissues is the defence of many plants, and this
protection may be internal and due to the deposition of carbonate of
lime within the cells. Erysimum cheiranthoides being rendered so
hard from this cause that it is avoided by even Agriolimax agrestis,
whereas Chara and other aquatic groups are calcided externally,
assuming an e(|ually protective incrustation of the same substance.

Oxalate of lime is abundant in the outer tissues of Orchids,
Amarjdlids, Narcissi, Tyylm latifoUa, Arum maculatum and other
plants, and generally exists in the form of Raphides a needle),

minute, needle-like crystals, 2Uo 'jf “icli in length, which

are always most plentiful near the surface and confer comparative
immunity against attacks by snails and many other animals, as they
wound the palate and cau.se a .strong burning sen.sation within the
mouth of any creature attempting to feed upon the plants containing
them ; they have also been known to give rise by contact to a
form of eczema, even in human subjects.

288

ClIEMirAL DEFENCES OF PLANTS AGAINST SNAILS.

Tlie Chemical Defences are constituted by more or less nauseous
secretions, most abundant in the parts most liable to attack and due
to bitter principles, tannin, acrid juices or exudations, essential and
volatile oils, alkaloid, mucoid, or gelatinous secretions and by other
obnoxious substances as yet undetermined.

Tannin or 'rannic .Vcid exists in the epidermal cells and hairs of
ferns, ro.ses, geraniums, ericas, pajnlionaceous and leguminous plants,
and is a very powerful protective ; many compositie are also excep-
tionally rich in this substance, to which they owe their disagreeable
smell, while to V((Hsneri((, H jidrocharh, PotdmiHjcton and other
a([uatic plants it gives j)artial protection, supplemented in many cases
by the dei)Osit of nnmerons rai)bide.s ; while in the freshwater alg:e
belonging to the genera Vaucherhi, >Sj>iro(ji/r((, and in Conferva), etc.,
it exists in such ([uantities that a good ink can be jwepared from the
alcoholic solution of their chloroi)byll.

.Vcrid juices are repugnant to snails and therefore the sap of Iiunu'.r,
O.i’dl/.'i, etc., ethciently })rotects these plants from many snails.
Essential oils also safeguard the plants containing them, the gallic oil
of the Allium tribe, the essential oils of Jtufd and the Lahiata- con-
ferring an immunity from attack by most .sj)ecies. The Willow-herbs
receive a certain amount of protection from the acrid volatile oil
.secreted by the glandular hairs, while the Alkaloids pre.sent in the
Solanataao and the bitter principle characterizing the Centians perform
the same duties to the plants secreting them.

jMucoid and gelatinous secretions or excretions, when well developed,
are also an elticient barrier against snails. Xitelld si/iicdrpd secretes
a gelatinous investment which acts as a strong deterrent to Limniva
sfd(jii((/ts and jirobably other sj)ecies, while (dlh'md (jranuxiim, a
gelatinous lichen, is left untouched by both land and iluviatile snails.

These various defences remb'r it jirobable that the mollusca though,
api)arently, living in the midst of ])lenty are often in reality only able
with diftlculty to eke out a lU'ccarious existence. This is confirmed
by the exhaustive exi)eriments upon various snails carried out by
JMr. (Jain, which demonstrateil, for e.xample, that out of 192 varieties
of food — cbielly the commoner plants of the vicinity of Newark,
Notts. — offered to a. colony of Helix hortenai^, no less than 139 were
ai>parently so elliciently protected that they were i[uite untouched and
17 others only slightly nibbled, even after iletinite periods of starva-
tion. Of the .3(1 remaining foods more or less freely partaken of, 21

CIRf'ULATORY SYSTEM — PERICARDIUM AND HEART.

280

M'ere cultivated plants and 4 were fungi, and only the residuary 1 1
M'ere M’ild phanerogamic plants, but 6 of these were not very freely
eaten and not one was devoured with that avidity which characterizes
snails when really pleasant food is offered, for at such times they con-
sume enormous quantities, eating the night through without inter-
mission, AgrioUmax agrestis having been known to devour one-third
its own weight within twenty-four hours, and when we see the destruc-
tion \vi-ought amongst plants defended in such various ways, we must
conclude that many would soon be entirely extirpated if the barriers
to their fi’ee consumption were removed.

The Circulatory or Vascular system, known also as the Ilreinocad
(af/xa, blood ; KotA-os, liollow), is greatly developed in the mollusca,
and consists of blood vessels and .sinuses, shut off from the general
digestive cavity, of v’lich it may, however, be regarded as an adjunct,
as it is the medium by which nutriment is absorbed from the alimentary
canal and carried to all parts of the body.

A portal circulation is constituted by that portion of the .systemic
circulation of the blood which flows to and circulates within the
kidney or renal organ prior to entering the auricle.

The Pericardium (vre/u', around ; KapSia, heart) is a thin-walled
.sac, often thick and glandular in front, which contains or encloses
the heart, and is partially embraced by the renal organ. It is con-
stituted by an isolated jiart of the secondary body cavity or coelom,
who.se epithelial lining also extends over and covers the exterior of
the heart. The pericardial cavity receives the acrid secretion of the
pericardial gland which is passed from the system by way of the
reno-pericardial funnels.

The Heart is the central and chief blood vessel, and is a dorsally
placed contractile organ, symmetrical and median only in Pelecypods

and in the most archaic Gastropods.
In those Gastropods whose viscera
have been most modified in position
by the torsion and subsequent
partial detorsion the body has

Fig. 572. — Heart of Helix 7>irgata i ,11 , • i . n

Da Costa within the opened pericardium and linClGrg'OllG, tllG llGtirt, lU tlGXtralJy
also showing the close apposition of the renal •! i • t • i

organ or kidney. C011G(1 llUllVldlUXls pOSSGSSlllg' a FG-

a. auricle; 7C ventricle; k. kidney or • , ♦, ♦.tip

renal organ. spiratory cavity, OCCUplG.S tllG iGit

anterior side of the body, but is placed at the right side in sinistral
specimens, and it is only when detorsiou is complete that the heart

25,10,99.

T

riUCl'LATOKY SYSTEM — VENTllIl'LE.

‘21K)

again occupies it^ more pviuiitivc i)ositiou at the rear of the aniiiial ;
aJways, iioweYev, inaintainiug a close proxiiiiity to tlie respiratoiy

organs, tliough not placed, as
in iishes, between the veins of
the l)ody and the branchia!,
but Ijetween the arteries and
the respiratory organs, receiv-
ing therefrom the vitalized
blood, which it propels
through the system, and
hence is called an arterial or
systemic heart. Interiorly the
heart is variously chambered,
Imt its walls are destitute of
any endothelial covering, so
that the mn.scle fibres are in
direct contact with the blood.

'I’lie heart is constituted by
two or more connected cham-
hors, known according to the
function they discharge, as Ventricles and Auricles.

The Ventkicle {ventricuhi^, diminutive of venter, the stomach;
the old anat(nnists were in the habit of terming any small cavity or
dilatation furnisheil with an inlet and outlet a “Ventricle,” i.e., a
little stomach) is tyjiically a median longitudinal ves.sel, usually
innervated by the abdominal
ganglia, which by its
powertid wave-like contrac-
tions forces through the body
the blood received from the
auricles. It is often ohconic
in shape, with the cavity
enclo.sed by thick, opa(pie
and mu.scnlar walls, formed
of granulated unstriped muscle-tihre thickly felted together and
supported internally by a number of muscular i)illars or coJamnw
cnrnic, and is imjhahly derived from a much more ancient arrange-
ment, in which there was a pair of longitudinal blood vessels, one
at each side of the centro-dorsally placed rectum, which gradually

Fig. 573. Fu.. 574. Fk;. 575.

Diagrams illiistratins stages in the development of
the pericardium and heart in S/'ha-rium conicuni
( i (after Ziegler).

Fig. 573.— E.arly stage of development, showing the
paired pericardial vesicles and nascent auricles.

r. rectum, entirely free from the pericardial vesicles ;
/./. paired pericardial vesicles at each side of, hut
distinct from the rectum ; a. a. inv.aginations of
lateral walls of itericardial vesicles forming the rudi-
ments of the auricles.

Fig. 574.— Intermediate '‘tage, showing the forma-
tio.i of the ventricle as two separated chamhers.

r. rectum, now enclosed by the ventricles ; a,a.
auricles : 7’. 7’. paired rudimentary ventricles, separated
by a median septum, and not yet forming a single
vessel ; p.p. pericardial cas’ilies.

Fig. 575.— Heart showing the fusion of the paired
pericardial anti ventricular cavities, owing to the
absorption or loss of their dividing septa.

r. rectum, now surrounded by ventricle ; n.a.
auricles ; 7'.7'. ventricle, now constituted liy a single
ca\ ily ; /./. pericardium.

Fu;. 571). — Ycnlr'icltt: oC . I fwtfonfa X 2

(after Rankin), laid open, showing the internal valvular
arrangements and the enclosing pericardium.

an. auricle ; a.7'. anterior ventricular valve ; /.7'.
posterior ventricular valve ; r. rectum.

CIRCULATORY SYSTEM — AURICLE.

291

united in tlie median line to form a common propulsive vessel, en-
closing the rectum between their walls.

The Auricles {nuricul't, diminutive of aiiris, the ear ; the auricles

in man being said to resemble
the external ears of some (quad-
rupeds) are generally pyriform,
thin and transparent, with few
muscle-fibres, usually innervated
by the pallial ganglia, and often
smaller than the Ventricle,
especially in the Pulmonata ;
they receive the blood direct
from the respiratory organs
and discharge it into the vent-
ricle by a slender neck, its
reflux being prevented by the
auri-ventricular valves at the junction. Valvular contrivances may
also be qiresent in various other qiarts of the system, more esjiecially
in coimection with the dittereiit turgescible organs, as the foot,
tentacles, siqilioiis, etc. The number of auricles varies in correlation
with the number of respiratory organs, the Pelecypoda always
qiossessing two symmetrical auri-
cles, corresqionding to their qiaired
brauchiie, but in our Gastropoda
they are reduced to one only, owing
to the loss of the primitively left
branchia. The contractions and
dilations of the auricles, when
paii’ed, ai’e always simultaneous,
and in every case alternate with those of the ventricle.

The number of auricular chambers to the heart has formed a
basis for the grouping of the mollusca in two sections, Diotocardia
and Monotocardia, which, like other structural details, are also of
value as showing phylogenetic relationship.

The Diotocaruiate (Siw, two ; (oTa, auricles ; KapSia, heart) heart
is characteristic of the Pelecypoda and Zygobranchiate Streptoneura,
and is composed of a pair of symmetrically disposed lateral auricles
and a single ventricle, which is often pierced by the rectum, and
though the most complex is the more qu’imitive form.

Fig. 578. — Transverse section through the
heart of Anodonta cygnea (L ), X 2 (after
Rankin), showing the structure of the walls
of the ventricle, the arrangement of the auri-
cular valves and the position of the rectum.
an, auricles ; r. rectum ; ty. typhlosole.

Fig. 577. — Heart of Patella with the ventricle
laid open, to show the muscular pillars or
colummp cariKF and the valvular opening.'^ to the
auricle and to the arterial system, greatly en-
larged (after Wegmann).

V, interior of ventricle with the vertical
cohtmme carno’ and showing the valve of the
auricle to the left and the aortic valve towards the
base ; b.iK branchial vein, also showing the
openings through which the blood from roof of
pallial cav’ity enters the auricle ; auricle ; a. a.
anterior aorta ; p,a. posterior aorta ; a.h. aortic
bulb.

•202

cniCUr-ATiiRY SYSTEM -AORTA.

The jMonotocardi.vte (/ioro9, single ; wrn, auricles ; KupSiu, heart)
heart more esi)ecially characterizes the Piilmoiiata, iii M'hich the organ
is larger than in the Azygobranchiate Streptuneura, M’hich also possess
it; although the most simple form, it is a simplicity derived from the
more complicated Diotucardiate organ, and consists of a single

Fig. 579. Fig. 580. Fig. 581. Fig. 582.

Diagrams showing ihe character of the heart in various groups of moliusca and its structural
relationship to the more primitive organization of the Anneliils (after Gegenbaur).

Fig. 579.— Fart of the dorsal propulsory vessel of ventricle of a worm with some of the lateral
contributory vessels or auricles.

Fig. OvSO. — Heart and paired auricles of jY<j7(ti7u$ showing the reduction to two pairs of auricles,
corresponding to the four branchiaj.

Fk;. 581. — I )iotocardiate heart of a Felecypod, showing the further reduction of the lateral
auricles to a single pair in correlation with the paired branchta;.

Fu;. 582. — Monotocardiale heart of a Gastropod, showing the single auricle, its fellow having
disappeared in conformity with the loss of the primitively left branchia.
a. auricle ; f. ventricle ; a. a. anterior aorta ; /.a. posterior aorta.

ventricle :ind a single auricle, the anrimdar reduction being correlated
with the loss of the left branchia' and also with the presence of the
single pulmonary chamber.

'I'he Circulatory vessels are usually divided into an arterial and
a venous system. The Arterial system, in addition to the heart, is
constituted by the aorta*, tlie arteries, the arterial lacumT, and the
capillaries, all conveying the blood centrifugally, or from the heart to
the various organs of the body. The Venous .system is composed of
tubular ve.s.sels and a limited number of spacious cavities or venous
siuu.ses, the encloseil venous blood moving centripetally or from the
organs and e.xterior of the l)ody towards the heart, becoming accumu-
lated within the venous sinuses Ijefore entering the respiratory organs.

'I'he Aorta (do/iTedg a. lengthened form of dei/)(o, to raise or hang
u}), so called because it was sipiposed to hang up and keep in position
the vertebrate heart, as indeed to some extent it does) is the main
trunk of the arterial system in the mollu.sca and is usually short,
originating at the ventricle and directly receiving the blood from it
for distribution through the body. In the Pelecypoda there is usually
an anterior and a posterior aorta, which arise from opposite ends of
the longitudinally placed ventricle, Imt in (Uir Gastropods the repre-

CIRCULATORY SYSTEM — ARTERIES, ETC.

298

seutatives of the anterior and po.sterior aortie of the Pelecypoda
combine before reaching tlie ventricle, to form a single aortic vessel,
their approximation and basal fusion being probalily due to the body
torsion the Gastropoda have undergone.

The Arteries (ai/p, air ; T>/p«o, to keep ; the ancients believing
these vessels naturally contained air) originate by the furcation of the
aortic and are of smaller calibre. In the Gastropoda one branch,
dividing and redividing, traverses the body and supplies the intestinal
tract, the digestive gland, the genital gland, etc., and is known as the
Visceral artery, while the other, known as the Cephalic artery, bends
round and supplies the head and its organs, encircling the hrst

Fig. .583. — Tcstacella halhtidca Drap. laid open dorsally and the viscera partially removed to
show the arterial blood vessels, x 2 (after Lacaze-Duthiers).

st. stomach ; r.s. radular sac ; a. auricle of the heart ; ventricle, from which originate the
anterior and posterior aortae and the subsidiary arterial vessels.

anterior intestinal coil and sending a strung branch to the foot. In
some species, and especially in ^-1 riun (iter, the walls of the arteries
and arterioles are greatly thickened by a siUTOuuding sheath of con-
nective tissue, containing numerous calcareous and fatty particles,
which gives the vessels an opm^ue, milk-white appearance, beautifully
contrasting with the dark tissues upon which their complex ramihca-
tions are traced.

The arterial vessels may terminate and be joined to the venous
system by finer and more delicate vessels or may 0})en by wide
funnel-shaped and sometimes contractile orifices into laciime.

The L.\cun.e (Jiicuna, a pool), Ihema-
tocades or arterial blood sinuses, are
the intervening spaces which permeate
between the various organs of the body ;
they vary greatly in size and capacity,
and are destitute of proper endothelial
covering.

The Capill.vries (ccipUki, a hair) are the minute, thin-walled blood
vessels which, in some forms, constitute the terminations of the

Fig. 58i.— Connective ti>.sue cel s
of virion ntcr (L ), showing the
origin of lacunre, highly magnified
(after Brock).

294

CIRCULATORY SYSTEM — VEINS, ETC.

sinaller arteries and tlie hegiimiiig of the smaller veins ; these inter-
mediary vessels which cunneet together the arterial and the venous
sy.stems are distinctly developed in TestaceUd and other species.

The Veins {vena, blood vessel) are the blood channels which convey
the blood back to the heart, whether by way of the respiratory organs
or direct ; they are continuous with and receive the blood from the
capillaries, hut gradually unite to form larger vessels, which
eventually empty into the large venous sinuses iireparatory to
diffusion in the respiratory organs.

Tlie Venous Sinuses, or blood reservoirs, are large cavities within
which the blood, exhausted of its oxygen and loaded with the waste

I'Ki. oSx— I )iagrain of the circuialory .'^ysicin of especially illustrating the venous sinuses

(after GritVilijs).

7'..^. venous sinus ; r.7'..Y. circular jmlmonary sinus ; a. aurie'e, receiving the liloocl after aeration
in the pulmonary ple.xus ; 7-. \ eniricle, giving olT the anterior and posterior aorlat.

matters from the oxidation of the tissues, is accumulated after its
circuit of the body, prior to entering the renal and resi)iratory organs
for purification.

In the (lastropoda the chief venous sinuses are in the pedal and
]iallio-visceral regions, while in the I’elecypoda the chief venous
sinus is known as the Vena-cava, and is a spacious cavity lying
longitudinally beneath the iiericardium.

'I'he Blook or Iheniolymph blood ; Jifinpha, water) is the

circulatory fluid, and is a slightly viscous semi-transparent albuminoid
tlnid, remarkable for the (piantity of calcic carbonate it contains, as
shown by its effcrve.scence wlien treated with acids. It supplies the
vaihnis glands with the material from which they elaborate their
various secretions and also receives the iirodiicts of the oxidisation of
the various tissues, conveying them to the excretory organs for

CIRCULATORY SYSTEM — BLOOD AND ITS CONSTITUENTS. 295

elimination from the body. Analysis shows Carbonate and Phosphate
of Lime, Carbonate and Chlorhydrate of Soda, O.xide of Iron, and
a trace of O.xide of Manganese to be some of the constitnents of
mollnscau blood.

The blood may form fnlly half the total weight of the body in the
Pelecypoda and about one-sixth in the Pnhnonates, this relatively
large volume enabling a portion to be utilized to protrude or stiffen
different parts or organs of the body, as strikingly seen in the pro-
trusion and e.xtension of the
tentacles in the Gastropoda and
in the tnrgescence of the foot in
the Pelecypoda, this being ac-
complished by permitting the
inrush of blood to the j)articnlar
organs to continue and retaining
it therein by the action of suit-
ably dis})Osed sphincter muscles,
the most important being known
as “ Keber’s Valvule,” whose
action permits the free ingress
of blood to the foot, but by the
closure of the gveat afferent
renal vein prevents its esca})e therefrom, thus retaining all the blood
within the foot and enabling it to (piickly become firm and rigid for
locomotory purposes.

H.emocyanin (atp.a, hlood ; Kvaveos, dark bine), a proteid in
combination with copper, with a chemical composition of Cgr, 7,
Hi 30 3 ^22:5 CnS.i 0.5 8, is also usually present in mollnscan blood
and functions in a similar, but feebler, way to luemoglobin, by
absorbing oxygen from the air or water and carrying it to the more
remote tissues of the body, the bluish or violet colour, characterizing
it when rich in oxygen, being gradually lost as that substance becomes
abstracted by the tissues with which it comes in contact.

H.EMOGLOBIN (af/xtt, blood ; ghhus, a sphere), is an albuminoid in
association with iron, which during respiration enters freely into an un-
stable combination with oxygen, from which it is again separated by
the tissues as the blood circulates through the body. It is present in
the buccal muscles of many species, whose energetic action calls
for more active o.xygeuation than hremocyanin can accomplish. The

Fig. 5S6. — Keber’s valvule in Anodonta cy^nca
var. celU'usis C. Pfr., greatly enlarged (after
Fleischniann).

k.v, sphincter of Keber’s valvule ; r.c. renal
cavities ; pc. pericardium ; r.p.f, reno-pericardial
funnel.

21)6

CIRCrLATORY SYSTEM — AMCEBOCYTES.

Ki(,. .Vn7- — lUooil

orpiiscics or anuubocytcs i)f
Helix foniitia L., fixed wiili osniic acid, liigldy
iiuignifictl (after N’ogi and Wing).

same active respiratory substance is found abundantly in the blood
of adult rianorbes, but not confined within special corpuscles, as in
man or in the molluscan genera Sokii, etc., hut diffused through the
circulatory iluid, to whicli it gives a bright pink appearance; this
s])ecial abundance of haunoglobin in PI((iiorbis may be considered to
be in direct correlation with the transitional character of their respira-
tory .system and the feebly oxygenated state of the stagnant pools in
which they so often live.

The Amcebocytes ((tpeZ/^io, to change ; kvtos, a cell) or white blood
corpuscles, known also as Phagocytes, are minute, indistinctly

nucleated, unicellular organisms
of variable size, resembling
those of man in structure and
exhibiting the same ama'boid
movements. They possess vari-
ous assimilating and nutrient
functions and contain more
oi- less abundant refractive
albumonogenousgTanule.s,'\vho.se
])rotoplasm is believed to serve
as a sturehduse for the accumulation of fat and albuminoids and to
form tbe means ready for the re])air of wounded tissue.

The Ammbocytes seem from their origin to he connective tissue
cells e.s])ecially adapted to live in an albnminous medium and are
numerously pre.sent in the blood ; they originate on the walls of the
lymphatic glands and arc reproduced hy direct divi.sion, ami possess
a smooth diaiihauous outer membrane and a nodally thickened reticu-
lated framework, with a more unstahle material iu the meshes.

Tbe Pulsations {pulxo, I beat) or rhythmical contractions of the
Ventricle of the heart furnish by their number a reliable index to the
activity of the circulation, and in certain species of Gastropods are
visible througb tbe base of tbe last whorl of the shell, and in some
delicately shelled Pelecypods perceptible near the umhones.

'I’he alternate contractions and relaxations of the heart are so
persistent that they have been observed to continue for some time
after its removal from the l)ody of the animal and when completely
drained of blood ; according to Lister, the pulsations will recommence
even twelve hours after excision if the (jrgan be moistened with blood.

The activity of the circulation is, however, intluenced by many

CIRCULATORY SYSTEM — PULSATIONS OF THE HEART.

297

conditions ; age, exercise and temperature, each contributing to con-
trol its actions, while other less direct intlnences exert a subsidiary
modifying effect.

Injuries to the shell or to the animal have also a disturbing effect
upon the activity of the heart, whose pulsations are greatly accelerated
even by the careful removal of a piece of the shell, so that any
attempt to ascertain the pulse rate in the thick-shelled species, by
removing, however carefully, the shell covering the cardiac region,
would only yield misleading results.

Age, as in other animals, has a great influence on the rapidity of
the heart’s pulsations. In man, according to Carpenter, the pulse
decreases in rapidity from about 135 at birth to <S5 in youth and 72
in adult life, and in the mollnsca there is the same change from the
rapidly pulsating heart of the embryo to the comparatively deliberate
contractions of the mature animal ; this being confirmed by Stiebel,
who has recorded that in the embryo of Linuuva there are from 50 to
70 pulsations per minute, which decrease to 30 as the animal advances
in growth and eventually sink to 20 at maturity. The retarding
influence of age is readily verified by comparing the rate of pulsations
in immature and adult specimens of the same species under similar
conditions ; thus an immature IlelLv cantiana showed 56 pulsations
per minute, and a mature specimen of the same species 44 only ;
a young Helu' kortensis showed 74 per minute, while a full-gTown
individual was only 5.S per minute.

Exercise has also, as in man and other animals, a most striking
effect on the heart, varying according to the amount of exertion and
other circumstances, the mere act of emerging from the shell almost
instantly accelerating the pulse rate. A Iljjalinia cellaria, whose heart
in repose beat 40 times per minute, immediately increased to 64 on
the emergence of the animal from its shell ; Helix hortensis under
similar circumstances showed a similar rapid augmentation from 58
to 80, the acceleration in all cases being more abrupt at the muscular
effort to commence movement than at the effort iieceG.sary to con-
tinue it, thus the pulsations of a quiescent Helix fjrannhittt rose
abruptly at the earliest movement from 46 to 54 per minute, after-
wards gradually increasing to 58, 60 and 64 as the animal extended
itself.

Temperature is of pre-eminent importance in influenciug the
action of the heart, although its effects have been overlooked by

CIRCULATORY SYSTEM — PULSATIONS OF THE HEART.

'29S

must ivriters on malacological subjects, who have been usually
content to cite the bare numerical result of a single observation,
without noting the comlitions affecting the rajjidity of the pulsations.

jMoqniu-Tamlon, in his admirable work on the Mollusca of France,
records that the heart of Vitrlnn ])j/reinuc<( beats 44 times per minute
and states that kSt. 8imon had noted So pulsations in ffeli.r fnsca,
leading to the erroneous conclusion that the circulation of JfclLv is
normally twice as active as that of IMr. Alder has also

recorded that he counted 120 pulsations per minute in I'itriiM
pel/iicidd, and this observation also conveys a wrong impression, as to
obiserve so feverish a rate IMr. Alder iirobably held the shell between
his lingers during examination, which also may have taken place in
the sun or in a very warm room, as the heart of that species when
resting in its usual haunts seldom exceeds 50 pulsations per minute,
its oi)timum rate being probably between 50 and 40.

Mo(|uin-Tandun has also recorded that the range of pulsations in
(iastropods varies from 25 to S5 per minute, leading his readers to the
wrong conclusion that the pulse never rises above the latter number
nor falls below the lesser one.

The striking effect of warmth in stimulating the heart’s action is
readily seen by observing the pulsations of a suitalde species in its
cool natural retreat and again after it has laid a minute upon the

The vcriical lines connect llic corresponding points of temperature and pulse rate.

'I'he vertical lines connect the corresponding points of temperature and pulse rate.

Fi<;. .588. — T)iagram of the pulsations of the heart of Helix hoj-tensisy espcciallj’ illustrating the
close correlation of its activity wiili the changes of tcmpcr.aiure and show ing the stimulating action
of warmth and the inhibitory character of a decreasing temperature.

palm of the hand, when the rajud change from a deliberate to a
(piickly beating imlse will be plainly visible to the eye. Vitrina
2Klluckl(i, under such circumstances, may increase its heart’s pulsa-

CIRCULATORY SYSTEM — PULSATIONS OF THE HEART.

299

tioiis from 50 to 98 beats per minute, and a young Helix a.'fpersa from
70 to 110. wliile if the warmth be increased the heart’s action seems
to degenerate to a rapid and tremulous agitation, after which heat
rigour probably soon supervenes.

Reductions of the temperature will similarly lower the pulse with
equal rapidity, the pulsations becoming less and less numerous
until, at a few degrees below freezing point, they may be reduced to
3 or 4 feeble contractions per minute. A HyaLinia cellar ia, whose
pulse whilst on the palm of the hand beat at the rate of 74 per minute,
was exposed to the cool draught at a slightly open window and the
pulse within two minutes fell to 26.

The heart, being so responsive to variations of temperature,
quickening under the influence of noon-day warmth, and being re-
tarded by the colder air at night, produces, in the rate of pulsations,
a well-marked diurnal range, which more or less closely corresponds
to the daily variations exhibited by the thermometer.

This susceptibility is indeed so delicate that even the play of the
observer’s warm breath during a short examination is sufficient to
appreciably accelerate its rate of contraction ; we should, therefore.

l^iimher of he.'irt pulsations per minute.

0 5 10 15 20 25 30 35 40 45 50 55

Fig. 589. — Thermal-pulsatoiy curves of Helix mfcscois^ Helix ^i^ranulala and Hyalinia
cellaria, illustraiing the efl’ects of fluctuations of temperature as variously aflecting the rapidity of
the heart’s pulsations in different species.

naturally expect to find an extremely rapid pulse in summer when
the thermometer registers 80° or more, but, with few exceptions, our
species do not voluntarily expose themselves to such heat, but retire

300

RESPIRATION.

to cooler (Quarters aiuoiig damp moss or herbage, etc., where, owing
to evaporation, the temperature may he as mucli as 20° below that
indicated l>y a neighbouring thermometer.

Every species ami every individual, however, naturally seeks those
conditions most agreeable to its own welfare, and it is probable that
in correlation with this habit there is for every species a special
o[)timiim external temj)eraturc and also an oj)timmn pulse-rate,
especially suited to the action of its organs and to the re(piiremeiits
of its economy. Some species, like Hcliv pisuna and Helix eartmlana,
habitually exi)o.se themselves to the full glare of a burning sun and
have prohalily a high optimum pulse-rate; others, which secrete them-
selves during the heat of the day in moderately dry and sheltered
spots, attacheil to stems or undersides of leaves in hedgerows, have a
l)ulse-rate varying between 3') and GO; while species which habitually
hide themselves in wet moss or at the roots of damp herbage range
between 2') and 43 per minute.

The .\(^uiEERors or water-vascular system in the mollusca is most
develojted in the marine Pelecypods, some species possessing a coni-
plete network of ramifying canals within the foot, which, by the
ince])tion of water from ivithout, render the foot turgid and linn,
supplementary to the tiirgescence due to the retention of the blood
therein.

Absorbent or minute i)ore canals opening to the e.xterior have also
been allirmed to exist in our Eritish Unionidmand S]i)luerii(he and are
stateil to have been observed even in Helix jKiniatid and other
terrestrial sj)ecies, the Limaces being specially noticeable for the rapid
absorption of moisture by their integument.

Respiration is a jimcess vital to aiiinial existence, and in the lower
forms of life may he accomplished simply by an interchange between
the surface of the body and the surrounding medium, hut in the more
highly organized animals this interchange between the gases of the
blood and tissues is chielly iierformed by specialized and suitably
lilaced organs, whose res[)irations or breathings, like the pulsations of
the heart, vary in nundier in different sjiecies and also differ accord! ng
to temperature, and the age, amount of exertion, etc., of the
individual, but are always much more slowly and irregularly per-
formed, the energy and activity of the organism being in proportion
to the amount of oxygen absorbed.

RESPIRATOR V ORGANS — CTENIDIA.

801

Tlie fiuictioii of respiration is to sujiply oxygen to the blood and
tissues and to eliminate the gaseous products of decay, and essentially
consists in the exposure of the impure venous blood to the vivifying
influence of air, or water containing air, so that oxygen is absorbed
and carbonic acid eliminated.

This result in the mollusca is accomplished chiefly by brauchitie in
the ai^uatic species and by a lung cavity in the terrestrial forms.
Auxiliaiy to the respiration carried on in these specialized organs,
there is cutaneous respiration and tissue or internal respiration.

Branchle (^pdi'yia, the gills of a fish) or Gills, the specialized
organs for the respiration of water, are differentiations of the integu-
ment, and are in strict correlation with an a(jnatic life, and therefore
of gi’eater extent and complexity than the lung of the Pulmonates,
to compensate for respiring a medium containing so little oxygen.

The Ctenidia (Krei-tStoi', a little comb) or primitive molluscan gills
are typically symmetrical and paired free plume-like structures,
although it is only in some of the Pelecypods and Zygobranchiate
Gastropods that their original character and arraugemeut are preserved.

They are assumed to have arisen
as simple ridges at each side of
the body, along a line extending
from the mouth to the anus, known
as the Lophophoral (Xd(/)os, a
plume ; c^dpcoj, to carry) line on
account of its relation to the oral
disk or lophojihore of the Polyzoa,
etc. These ridges, by elongation,
each give rise to a row of hollow,
^ciliated respiratory processes,
usually stiffened by chitinous rods,
along one edge, each filament con-
taining afferent and efferent axial vessels, and bearing at each side
numerous delicate and perpendicular vascular proces.ses, lined in-
teriorly with connective tissue and supported ly muscular trabeculai,
which under nervous influence, relax and contract, as.sisting to
alternately receive and expel the blood. In the ancestors of most
of the active Gastropoda the lateral gill-processes and the area
occupied by them, from various causes, become more restricted and
tend also to be relegated towards the rear of the animal.

Fig. 590. — Anodonta cygnea (L.) with
mantle, gills and labial palps removed to
show the Lophophoral line (after Lankester).

a. a. line of attachment of the anterior
palp and /./. of the posterior palp, con-
tinuous with l.c. the line of attachment of
the left ctenidium or gill, jointly forming the
Lophophoral line ; a. ad. anterior adductor;
p.ad. posterior adductor; iii. mouth foot;
n.o. nephridial opening ; g.o, reproductive
orifice.

302

RESPIRATION IN PEEECYPODA.

In oiir Pelecypotla the liraiioliial iilanieuts have coiitiiiuecl to
elongate, and to secure t'reedoin of growtli have bent back upon
themselves, sn that the paired tilanients on each side suspended from
their i)oint of support, which i)reviously formed an inverted V, are, by
the retlected growth, converted into a tigure resembling the letter W.

'file separate tilanients may, however, combine together and form a
j)late-like, although iierforate, gill, this fusion and vascular continuity
of the constituent tilanients being preceded by the close interlocking

of the cilia clothing their surface
and followed by a more or less in-
timate interlainellar concrescence.
The primitive tilamentous condition
may, however, arise secondarily
bj" the splitting nji of previousl}^
e.xistent lamellate gills, as is stated
by Korschelt to be the case with
Sph(trium.

The posterior mantle margin, in
the burrowing sjiecies, is often
produced into one or a pair of
tubular processes or siphons for
the purpose of conveying the water to and from the gills ; the lower-
most, known as the branchial or afferent sijihon, is encircled by a
number of long sensitive tilanients or tentaciila; the other, known as
the anal or efferent aperture or siphon, carries away the respired water
after it has passed over the branchim, and is usually shorter and
more dorsally placed, with occasionally a tilamentous termination.

In the marine Imrrowing species, the respiratory siphons are very
long and very extensile, Imt usually corresiiond to the de])th of the
burrow occupied by the mollusk, although species like Anod(»ita
rjiguea, which possess comparatively rudimentary siphons, sometimes
live buried beneath ten inches or more of soft mud and yet preserve
free communication with the water above by means of vertical perfora-
tions through the soil, formed and kept open by tbe siphonal currents.

'I'be Pelecypoda have been classihed by Pelseneer into five groups,
based ui»on tbe amount of siiecialization the gills have undergone,
the simplest being known as Protobranchiata and the most .sjiecialized
as Septibranchiata, these being connected by tbe groups Filibranchiata,
Eulamellibranchiata and P.seudolamellibranchiata ; all our British

RESPIRATION IN PELEOYPODA AND GASTROPODA.

species, however, are Eulainelliliranchs, in wliich the filanieiitary
processes have become fused together and form more or less complexly
perforated and folded gill plates, lying in a branchial chamber ; the
interlamellar cavities, in some species, serving as marsupial or in-
cubatory pouches for the protection of the eggs or young.

The delicate branchial tissue is easily detached in minute Hakes by
compression or friction, the detached fragments moving about like
living Infusoria liy the action of the cilia clothing their surface.
Miiller actually described these motile particles as species of his
Infusorian genera, Trichodd and lAUicophra.

In Gastropods the gills, though simpler in character, are constructed
on the same iilan as those of the Pelecypods and occupy a similar,
though more restricted, position, hut, owing to body torsion, the

primitively left gill has become
atrophied in all our species, al-
though still present in a more
or less primitive form in the

Fig. 592.— Ctenidium or gill of a Monoto- r/ ^ i • , rm

cardiate Gastropod showing its pinnate character /iyC'ObrailCllUlUl. lllG 2'llls cU'C

(niter mng). °

cl. ctenidium or gill with efferent Mood ves.sel USUally HOW Ot a Seinipilinate
le.nding to the auricle, rr.; f'. ventricle terminating t , -.I j.1, • c i

in rt <1. anterior aorta and /.«. posterior aorta. CliaraCter Wltll the aXlS tUSCd tO

the roof of the mantle chamber, the respiratory processes being
arranged parallel to each other, lilce the teeth of a comb, and freely
projecting into the respired -water.

In the branchiate species resjiiration is [irobalily more or less
continuous when in process, more especially in the Pelecypoda, in
which the alimentary function is so intimately combined with that

Fig. 593. — Vnio pictoy-nni (L.) with right valve and mantle removed to show the courses of the
water currents during respiration (after 6lt).

The arrows indicate the courses traversed by the inspired water.

of respiration. The currents produced by the dense ciliary invest-
ment enter by the inhalent aperture, and are aftirmed to How in a
steady and continuous stream along more or less definite and precise

HKSPIRATION — PULMONARY f'lIAMBKR.

;!(it

trucks or courses, ])ussiiig through or over tlie gills and leaving the
body by the exhaleiit aperture.

Secondary Branch i.e are developed amongst our native species
only in the Liminvahv, a group which have relinij[uished terrestrial
life to resume an atpiatic one, and which are even now undergoing
the process of re-adaptation to the respiration of water, this being

shown by the diminution or loss
of the pulmonary cavity and the
increasing vascularity of the ex-
sertile, tegumentary appendage
bearing the anus and known as
the Auriform lobe ; this new
organ (jf resj)i ration is now
aetively functional in Phtuorbh
Cornells and other species. In
the marine genera Patelld, etc.,
this re-adaptation has taken
the form of vascular outgrowths
within the respiratory cavity,
but the same result may he attained in other groups by different
methods.

Fto Auriform lolteor secondary bram liia

of I'/anorl>is corncus (li-)i X 12, showing its
liiglily vascular cliaracter (after Pclscncer).

alimentary canal, but that of the I’ulmonates is really only a modi-
fication of the branchial cavity of the a([uatic species, in which the

'I’lie Pulmonary Chamber of the Pulmonata is not morihologically
a true luug, as in the Vertebrates, although i)hysiologically performing
similar functions. The vertebrate lung is a diverticulum of the

Fifb oOo. — Roof of pulmonary cavity of
Liniax (L.)» seen from l>elow X 3

(after Leidy), showing the relationship of
the lieart and the blood vessels of the lungs.

a. auricle of the heart receiving the oxy-
genated blood from the lung plexus; 7'.
ventricle of the heart ; /r. kidney or renal
organ ; u. ureter ; r. rectum ; c.o. excretory
orifice ; r.o. respiratory orifice.

Fig. oOG. — Longitudinal section through
mantle of Cyclostoma elcgans (Midi.), highly
magnified, showing the folds of the vestigial
branchia (after Oarnaidt).

RESPIRATION IN PULMONATA.

cteiiidium or primitive gill has become atrophied and lost, and the
anterior margin of the cavity has become fused with the dorsal
integument, except at one point which constitutes the pulmonaiy
aperture, where air is admitted and expelled for respiratory purposes,
or, as in the aijuatic Pulmonata, for hydrostatic purposes also. Upon
the walls and more especially upon the roof of the respiratory cavity,
a complex network of delicate blood vessels has been developed, a

change necessitated by the adop-
tion of terrestrial life and aerial
respiration by the ancestors of
the Pulmonata ; although the Pul-
monates are not a homogeneous
group, but of polyphyletic origin,
several distinct families having
branched off in this direction. The
pulmonary chamber has been aptl}'
compared to a single air cell of
the mammalian lung, as in both there is a cavity lined by a delicate
vascular membrane supplied with impure venous blood, with air in
contact with the free surface.

In terrestrial and Huviatile Pulmonates, although the breathing or
opening and closing of the single pulmonary orifice is more actively
rhythmical than in the branchiferous species, yet there is not the same
methodical and regular isochronous succession of respiratory move-
ments as previously described in the movements of the heart.

Si^/are of water ^^Sec ^^Sec

ScAi-E : — 30 mill. = one hour.

Fig. 503. — Diagram illustrating the respiratory action at 66 F. of a specimen of Planorbis
corneiis from Wansford, near Bev’erley.

The time.s mentioned on the diagram repre.sent the number of seconds the respiratory orifice
remained open to the air at each inspiration, their duration being too brief to allow of indication
according to scale. The horizontal line below the level of the surface of the water is to scale and
represents the time the animal remained beneath the surface between the respiratory acts.

The renewal of the air within the pulmonary cavity takes place when
fhe respiratory aperture is opened, and is chiefly accomplished by
diffusion ; exactly as when a door is opened to ventilate a room, the
incoming purer air being stated to follow a certain well-defined course
within the lung-cavity, and to gradually replace that which has become
effete by respiration ; the process being, however, assisted by the con-
tractions and relaxations of the muscular walls of the cavity.

21 10/9D.

Fig. 597. — Blood sinus of lung wall of
Helix pojiiatia L., highly magnified (after
Vogt and Vung).

b.s. blood sinus; ep. epithelium ; m. mus-
cular layer beneath a stratum of connective
tissue bearing pigment cells ; c.t. connective
tissue cells.

U

ClTTANE(nTS RESriRATION^.

;!()('>

Thermal comlitions also variously affect or intluonce tlie activity ot
tlie res}»iratory function in ilifforent species, some species being more
susceptible ami responsive to the tluctuations of temperature tlnin

Fir,. .5nn. — Liin.'i.v ninximus L., with shield removed, to show the course traversed hy the
respiratory air current (after Dr. T. Williams).

The arrows show the general direction alTirmed to he followed hy the pure air at each inspiration.

others. 'I’lie tluvi:itile Pulmonates do not, however, exclusively

respire air, l)ut may at times he observed to regularly open and
close their resi)iratory orifice when beneath the surface, more especially
when the inhabited water de])arts from a medium temperature.

Kumher of seconds per hour occupied in respiration.

0 111 20 30 10 jO GO 70 80 00 100 110

Fiii. (5)0. — Thermal-respiratory curves of Liinnaui L'nnnu’a auricularia and Pinn-

ot his corncus, illustrating tlie varying degree in which changes of temperature ail'ect the rapidity
of respiration in dilTereiit species.

Nr)Ti’:. — 'File results indicated in tlie above diagram of the action of the respiratory organs show
the average results of a large numher of ohservaiions upon individuals kejJt in conllnement, and
it is jjossihle lli.it a more extended study under less arlificinl conditions will modify to some extent
the results attained, as it may eliminate any elTects due to abnormality in the mollusks themselves
or their surroundings.

CrTANEOi's Resiuration i.s actively carried on through the general
integument, e.specially hy the .slugs and other genera, and though
usually subsidiary to that of the gills or lungs, yet, in some forms,
as Auodoitfu, etc., the surface of the mantle may i)erform the func-
tion of re.spiration even more effectually than the gills.

Cutaneous re.siiiratinii in the Pulmonatc .species may, under certain
c()nditions, he the chief mode of respiration, and i)ractically constitute

TISSUE RESPIRATION.

307

the wliole respiratory function, as in tlie cold abyssal depths of the
Lake of (leneva, where several minute species of Liinncm permanently
dwell, their ^lulmonary sacs filled with water, and aipiatic respiration
taking place by the lung cavity and by the integument, a prolonga-
tion of the acpieous respiration of the embryo and newly-hatched
young of the aij[uatic Pulmonates.

During winter, when the pools are frozen and access to the air cut
off, various species of Liminvtdw may often be observed beneath the ice
crawling actively about and probably mainly respiring by their skin.

Respiration by the skin is assisted by the presence therein of
superficially placed coloring matters with an affinity for oxygen, as
e.xem])lified in the orange-coloured foot of many Pelecypods, this
colouring being usuallj' due to Tetronerythrin, a substance comliining
readily with oxygen. The integument of Limax etc., has

also yielded pigments which, in addition to other duties, are also
functionally respiratory.

Tissue Respiration is greatly developed in mollusca and is chiefl}"
performed by means of the varied pigments so plentiful in the
molluscan organism, and although their chief function is doubtless
respiratory, as they combine with and retain oxygen within the
system, yet they have also other functions, as in perfecting protective
resemblances or acting as screens to underlying cells.

These pigments, known as Enterochloro})hylls and Enterohaunatins,
were first discovered by Dr. Sorby, and apparently contribute to replace
hmmoglobiu in the Invertebrate system.

The Enterociilorophylls (evrepov, gut ; green ;

a leaf) found in the digestive gland are identical with the hepato-
chroniates, and occur dissolved in oil globules and in the pi'otoplasm
of the secreting cells, though also found in a granular form. The}’
are probably formed by the action of the digestive fluids upon the
chlorophyll of the food, and eventually become lodged within the
digestive gland and other organs.

The Enteroh.ematins (Lwepor, gut ; atfia, blood) also occur chiefly
in the digestive gland, though present in various other parts of the
body. Myoh.ematin (pis, muscle ; afpu, Idood) is the true intrinsic
coloring matter of invertebrate muscle, while IIistoirematin (urTos,
tissue ; aipa, blood) is characteristic of organs and tissues, but both
may be reinforced or replaced by hannoglobin where extra activity
of internal respiration is reipiired.

TEMl’KRATrUK AND .ESTrVATIl )N.

:!os

rn)b;il)ly all those substances are fornieil on the same basis, as
b!eniato]:)ori)b_yrin is yielded on decomposition by all of them.

The 'rE.Mi’EiiATDRE of wavm-blooded animals is maintained at a
nearly uniform standard under all changes of external temperature
by combustive proces.ses within the body, but in the mollusca and
other cold-blooded animals, owing to their sluggish respiration, the
oxygenation is so feeble that very little heat is generated and the
bodil}' temperature fluctuates with that of the inhabited medium.

Repeated observations have establi.shcil that the temperature of
land snails practically accords with that of the atmosphere if it be
moist, but in dry weather the heat of the animals may be reduced
below th.it of the air, prob.ibly by the increased evaporation from the
body of its natural moisture.

Although a single Hi'H.v or Lhna.v confined within a limited space
causes no perceptible thermometric change, yet if .several be enclo.sed
together the temperature has been noted by different observers to
ri.se from D'21° to

'I'he Relecy])oda likewise maintain a temperature similarly in accord
with that of tbe water they inhabit, varying in the Anodontw,
according to different observers, from 1 '0° colder to warmer than
the respired water.

d'lsTiVATioN {(isfirfi, to })a.ss the summer) is the period of torpidity
undergoue during the prevalence of dry, hot, summery weather, and
though, in this country, this state is essentially transient and short,
yet in warmer regions this tor])or persists for lengthened periods,
embracing the entire dry .season, the land mollu.sks con.structiug a
more or less tilmy and delicate epiphragm (see p. 12!)) and burying
tbem.s(‘lves more or less deejily in the ground or attaching them.selves
by a viscous .secretion in some -suitable position. Many freshwater
.'jiecies also bury themselves deeply in tbe .soft mud when the waters
they inhabit are becoming dried up.

Hot dry weather is especially fatal to slugs, which therefore burrow
into tbe earth and enclo.se tbem.selves within a coating of mucus,
which on drying ]>revents further evaiioration. 'flic tigurative and
beautifully e.xpressive simile of the fate of the ungodly given in our
I’rayer Books, “ Consume away like a snail,” aptly illustrates their
inability to withstand heat or dryness.

The forms most subject to seasonal torpidity are naturally tho.se
most remarkable for their tenacity of life, some species being known

HIBERJSTATIOlSr.

809

to survive after more tliau five years’ abstinence from food ; even
our Hdiv neniundis has been recorded as having endured more
than tliree years’ starvation, and many other striking examples of
this faculty are known.

Hibernation (Jdherno, to spend the winter), or winter torpor, is
induced in the mollusca and other organisms by the advent of cold,
and is obviously related to sleep, of which it seems but an intensifica-
tion, enabling the mollusk to successfully resist the extreme reduction
of temperature and the absence of accustomed food.

At the approach of winter and in the more sensitive species often
as early as October, the mollusks, being then plumper and better
nourished than at other times, gTadually become less voracious and
more sluggish and lethai'gic, the terrestrial species retiring to their
accustomed or temporary places of shelter, frecpiently clustering
together in the crevices of walls, rocks, and trees, or ensconcing
themselves deeply amongst dead leaves or in the earth, in which latter
case the mouth of the shell is invariably directed upwards and often
level with the surface of the soil, the epiphragm or cover to the
mouth of the shell (see p. 1.80) being then secreted, to protect the
animal from the weather and other dangers and to prevent the
evaporation of its natural moisture, the activity of their respiration
also diminishing as the temperature becomes lower and lower, until
the animals fall into a hibernal sleep or die.

This comatose state may be partial or complete according to the age
of the animal, the hardihood of the species and the character of the
winter, whether it lie continuously severe or present comparatively
mild intervals ; as during such intervals, if sufficiently mild, the
winter sleep, especially of the more immature individuals, may be
broken and the mollusk wander about in search of food.

In a hard winter the animal contracts more and more closely
within the spire of the shell, forming any additional epiphragms
necessitated by the smaller compass into which the mollusk has com-
pressed itself ; the young individuals are, however, less susceptible
to cold than mature animals, retiring later into winter (quarters and
re-appearing earlier and perhaps only becoming reall)' torpid during
the continuance of actual frost, this superior hardihood of the
younger animals being possibly due to their more active circulation.

Many of the fluviatile species during severe weather bury them-
selves in the mud of the })0uds or rivers they inhabit, and even

IIIBEKNACULA.

?)10

/)n;/sseu!ii<( easts oil’ its l)yssus aiiil also retires beueatli the bottom
mud, as its temperature is always higher than that of the super-
imi)osed water.

'J'he amount of cold mollusks can endure is, however, not unlimited,
as iMopuiu-Tandou records that Helices, though capable of enduring
1()° Fahr., freeze at 14° Fahr., and the endurance of this great cold
implies the ])ossession of internal heat sufficient to counteract the
reduction of temperature, perhai)s i)artially due to the excess of
respiratory ])igments present in the tissues in winter.

IIiiimiNACULA {lill>eni((culnm, a winter abode) or winter shelters may
lie more or less adventitious or may be places of more regular resort
utilized liy the mollusks, not only during their seasons of protracted
torpidity, w hether arising from cold or dryness, hut as places of safety
during their diurnal siesta.

In certain districts the carhoniferous limestone rocks are almost
honeycomhed hy tubular e.xcavations, which, though iirohably made
and (diietly tenanted by //c//,r ((.'tjH'/ya, are occasionally occupied by
other species, not only to pa.ss through the periods of hihernation
and a'stivation, but as regidar resorts for rest and shelter.

d’hese galleries, which almost invariably take an upward direction,
perpendicular to the bedding of the strata, rarely occur on rocks
apjiroacbing grit or on rock-taces exposed to the prevailing winds, hut
are usually clu.stered heneath iirojecting rock-ledges or pierced in
the face oftho.se clilfs facing ea.st or north-east, heing thus protected
from the wet west and south-west winds. When placed uiion the
i'ace of a vertical cliff the buiTows may originate as a slight channel
and sink gradually into the rock ; frepuently, however, tliey originate
beneath a slight prominence, as though the snails had fjrmerly
sheltered there and gradually worked their way into the stone.

These rock tunnels are generally about (jiie inch in diameter and
sometimes three inches or more in deiith, smooth and regularly
slnqied inside, but often containing subsidiary depressions upon their
walls, due to a persistent n.se of those iiarticular sjiots as resting jilaces
by many .snails ; they must not, however, he confused with the oval
or circular cavities due to weathering nor with the Ihtter.spar con-
cavities so common in the magnesian limestone, whose w'alls are often
encrusted with crystals of lime, as such natural cavities freipiently are.

These tunnels were formerly surmised to be the work of the Pholades
or other marine boring mollusks, during the period the rocks were

HIBEIiNACULA.

?,11

submerged iu the ocean, and that upon their upheaval the ({astropods
now occu})ying these burrows merely appropriated them as convenient
places of shelter, hut that the snails have themselves formed these
rock-tunnels may, however, he almost couhdently assumed, not only
because Helices, especially Helix ai^persa, are generally ahundant
near the burrows and that living specimens are always found iu the

Fig. 601. — Hibernncula or Rock-burrows formed by llelLx: aspcrsa Mull., discovered in the
Great Ormes Head, North Wales, by Mr. R. D. Darbishire, H.A. (modified after Prof. Bonneyj.

The vertical cliff had a north aspert ; the small detached fragment at base, though from a south
aspect formed the roof of a horizontal fissure.

freshest and least weathered tunnels, hut also from their characteristic
(im'nding direction with the opening below, which clearly distinguishes
these Ilelicidiau cavities from those of the marine boring mollusks,
which usually follow a descending direction with the mouth of the
tunnel opening ah(jve.

HOMING.

The ability of tlie Helices, in course of ages, to excavate these
tunnels can scarcely be (inestioned, as, in addition to their demons-
trated power to abrade limestone and chalk with their odontoidiores,
]\I. Bonchard-Chantereux has aftirnied from actual experiment that
their mucoitl secretions exhibited a distinctly atdd reaction, testified
by the reddening of litmus paper, and would, therefore, tend to dis-
solve the rock and thus facilitate the process of the excavation.
I’robably, however, the movements of the snails within the cavities
have been a chief cause of their excavation, the wearing power of
the friction of the foot being clearly demonstrated by the worn margins
of the cavities, and by the sunken tracks leading thereto, worn away
in the rocks by the })assage to and fro of the countless generations of
snails which have for untold ages sought their shelter.

These rock galleries or other permanent shelters, regularly resorted
to hy snails as resting places after their crepuscular or nocturnal
rambles, imply the })osses,sion of a sense of direction, or what may be
termed orientation, in those si)ecies possessing regular abodes; this
perce|ition or recognition of hjcality may be due to the delicacy of
their olfactory .sense, and has been distingui.shed as the faculty of
homing.

This Homing jiower has been e.specially observed in Helix axpersd,
though several other of our terrestrial species have been undeniably
demonstrated to also ikjs.scss settled places of abode or homes to which
they regularly return, yet there are doubtless many others which
have no settled habitation, but conceal tbcmselves alone or in com-
pany beneath any suitable .shelter which may liappen to ho convenient
to their fooil.

The inter-tidal peregrinations of the marine limpet ami its unfailing
return to the precise spot ni)on which it is in the habit of resting,
tirst altracted attention to this subject, and it has been demonstrated
that their track when carefully Ibllowed almost invariably describes a
double looi) winch may he likeneil to a variably proportioned figure of
8, and though this peculiarity is not shared by every .s^jecies, yet the
jiath, followed by .some of our terrestrial homing .snails, during their
foraging ox])cditinn.s, have been ob.served to exhibit or de.scrihe the
same remarkaltle lignre.

Helix ((njirrsd is particularly noticeable tor its love of home and
for the exertions it will make to regain its shelter, having been
oljserved to traverse with great lahonr broad dusty roads or climb

GLANDULAR SYSTEM.

813

rough walls to reach some favourite food, and when satiated not
retiring at daybreak to the shelter of any convenient crevice, as might
be supposed, Imt almost invariably retracing its often toilsome and
arduous way to reach its favourite shelter, a peculiarity that has been
verified by many observers on numerous occasions.

I’he complex tracks formed by the nocturnal foraging expeditions
of Lhnax maximns, L.^ffavus, and jorobably other species, which are
sometimes so readily traced by the mucous trails they leave behind,
also very frecpiently describe tlie double-loo}) or figure of 8 already
mentioned, as distinguishing the track of Patella vulgata.

Fig. 602. — Mucous track of Limax Jlai’us L., 19 feet in length, as observed by Mr. H. Wallis
Kew, F.Z.S., on a flagged garden path at Louth, Lincolnshire.

Mr. Lionel E. Adams at my re(piest kindly made many careful
diagrams of limacidian tracks at Ashbourne, Derbyshire, and these
almost invariably formed the same peculiar figure. The animals on
setting out are probably guided by the olfactory sense as to the course
pursued, but make a wide sweep upon the return home, and usually,
though not invariably, cross the outward track at some point before
again reaching the desired haven.

The Glandular .system is a well-developed and specially charac-
teristic feature of the molluscan organism.

A gland is constituted by a collection or aggregation of simple
secretory cellules which separate or elaborate frtjm tlie blood certain
products, which may be utilized in physiological processes or, if
noxious, can be speedily expelled from the body.

314 GLANDULAR SYSTEM— -DERMAL CELLS AND SUPRA-PEDAL GLAND.

Tlie glands discliargiiig e.\teriially are cliietly imicons, byssal, pig-
nient and calcic glands, while the internal glands yield various products
essential in the processes of digestion, reproduction and other })hases
of animal economy.

The chief mncons glands are the Ventral and Snpra-pedal glands,
the Candal gland and the nyi)o-hrancliial gland, hnt, in addition to
these more important organs, there are

The Dermal Cells which are scattered plentifully over all the
external surface of the body not covered by the shell, and ahundantly
secrete a tluid mncus, which is clear and transparent in many si)ecies,
hut tinged in others with pigment or may he obscured and rendered

Kj(;. G()3. — Section ilirough a rugose glandular area of llie back of Helix poniatia L., showing
tile scattered mucous and other cells, highly magnified (after Vogt and Vung).

ch.c. lime cells filled with granular substance ; cp. epithelium ; in.^L mucous cells, some showing
nuclei ; /. lacuna; ; nt. muscular fibres to skin.

somewhat oj)a([ue by lime, which jireserves the integument in a cool,
moist and supjjle condition, a state vitally essential to their very
existence, desiccation of the skin being (piickly fatal. This dermal
mucous secretion, especially of slugs, is also in some degree lu’o-
tective, evidenced by the manifest distaste of its adhesive character
shown by some of their enemies.

The Anterior or .Supra-Pedal ({land, known also as the Sinus
of Kleehurg and formerly considered as having an olfactory function,
is a very important organ in the (lastntiiods, as it su])i)lies the luhri-

Fig. G04. — 'I'estacella haliotidea Drap., X 2, laid open, the lingual diealh, with its powerful
retractor muscles, turned outwards and the remaining viscera removed lo .show the position and
general character of the Supra-Pedal Gland.

l.s. lingual sheath : t.r. tentacular retractor of right side ; sp.g. supra-pedal gland.

cant mucus for smoothing the path to he traversed by the animal and
also assists t(j ensure the necessary adhesion to the objects upon or
over which it may crawl.

GLANDULAR SYSTEM — VENTRAL GLAND.

315

The gland is composed of large and oval nucleated secretory cells,
with pale finely grannlar contents, which lie in the snrroniiding tissue
and open on its walls, and is usually a vertically compressed and

conspicuously folded canal
strongly ciliated on its
ventral surface and often
(piite as long as the foot
itself, occupying the median
line of the b(jdy above the
sole, and partially embedded
amongst the i)edal muscles,
but sometimes lying ([iiite free within the body cavity, it serves as a
reservoir and duct for the mucus issuing from the innumerable
intercellular passages leading to it.

The e.xternal aperture of the gland is between the mouth and the
anterior end of the foot, the mucus being driven out by the action of
the cilia, by muscular comiu’essiou
of the cavity, by the undulatory
action of the foot during loc(jm(j-
tion, and by the general movements
of the whole body, and forming the
glistening iridescent tracks which
so distinctly mark the path tra-
velled by the mollusk (see p. 313,
f. G()‘2, and which are not (jnly
percei)tible on land, l)ut in the stiller pools these slime-tracks are left
on the surface of the water by the larger Lhnna'cv, and may at times
be observed of considerable length.

The numerous mucous tracks of Llmnajn dagnalis observed by Mr.
Henry Crowther upon the surface of Tag Lijck, near Elland, Yorkshire,
on a warm still day in August, 1393, were several yards in length,
crossing and recrossing each other many times.

Slime-tracks do not, however, actually possess the gias.sy smoothness
of surface they apparently present to a cursory observer, but are really
composed of a multitude of transverse wavy ridges, about a millimetre
apart with intervening depressions, this appearance being evidently a
retlecti(ni and effect of the undulatory movements of the foot-sole.

The Ventral Gland present in Cgclostoma and other Streptoneura,
as well as in the Limnwkhv, is a ramified cavity within the foot,

Fig. GDC. — Portion of pedal gland of
Testae t'lla hnliotidca Drap. , highly magnified
(after Lacaze-Duthiers), showing its convo-
luted character and the investing tissue.

s c

Fig. 605. — Transverse section through the pedal
gland of Liniax maxiiuus L., highly magnified.

hi. lumen or cavity of gland ; s.c, nerve cells ; g.c.
ganglion cells ; /. lacunae.

316

GLANDULAR yY.STEiM — MUCOUS FILAMENTS.

witliiii which is accuiuiikted tlie viscid mucus secreted tlie folli-

cular tissue l)y which it is densely invested. The gland opens upon
the lower snrhice of the foot towards its anterior end and corresi)onds

to or is probably homologous with

the byssal gland of the Pelecypoda,
secreting a viscid and very tena-
cious mucus by means of which
tirm adhesion can be secured to
their resting jilace, or a strong
tdament can be formed for siuspen-
sion or descent from an elevated
position.

I’he l\Iucous Filaments formed
by the attenuation of the viscid and
tenacious .slime emitted from the
foot glands, which, by its property
of hardening when in contact with
air or water, supplies the mollusca
with a ready means of locomotion or

(>07. — Mucous ir.'ick on smTacc of suspeusion fioiu Suitable clevatcd

added greatl}' to our knowledge of this subject.

The Ib'itish Isles, owing to their cool and dami) climate, are
es[)ecially favourable countries for the oliservation of this curious and
interesting habit amongst our land mollu.sca, the .slugs pos.se.s.sing this
]'(jwer in tlie most marked degree, L'nmi.r inarfjinatm IMull. olim
JJnui.r (trlxinnii Bouch.-(’h. jierforming these actions with e.special
ease and celerity, though other .sjiecies under similar circumstances
form the.'<e su.spensory filaments with great facility, lowering them-
selves from a liranch or other elevated object to a lower level
hy attaching the viscid mucus accumulated at the tail to the branch
or other object upon which the animal may happen to be and then
by launching into the air, attenuating and lengthening out into a
slender thread-like filament the accumulated mucus, a fresh supply
for its increasing length being afforded by its continued free exuda-
tion from the foot-gland.s, which is carried towards the tail by the
active undulatory motion of the sole or locomotory disc, the sides
of the foot being brought nearer together and forming a guide or

GLANDULAR SYSTEM — MUCOUS FILAMENTS.

‘Ml

groove leading to tlie origin of the snspensoiy filament, and altliongli
the mucus may become too thin to safely sustain the weight of the
creature when gorged to repletion, yet when in need of food tlie
mucus is more tenacious and becomes available as a ready means of
transportation from one level to another.

Fig. 608. Fig. 609.

Fig. GOS. —Ar/on hoi'tensis F^r. descending by the aid of a slime thread.

Fig. ()0n. — Arion suhfusctirS Drap., young, re-ascending by means of a slime thread, which it
had previously descended.

(Modified from original sketches by Mr. H. Wallis Kew, F.Z.S.)

It is, however, principally by the immature animals that this
method of locomotion is indulged in, as when full size and weight is
attained this method of progression is not so essential and becomes
more precarious and uncertain.

The same mucous filament can also be made use of, if necessary, to
re-ascend to the point of suspension, this being accomplished by bring-

GLANDULAR SYSTEM — MUCOUS FILAMENTS.

31 S

ing tlie extremities of tlie body together and transferring the point of
attaclnnent of the snsjjonsory tilainent from the tail to tlie head, the
tilanient re-traversed in ascending being accumulated as an irregular
mucous mass near the tail. The mucous tilanient has been ascertained
by iMr. T. lloy to he produced by Ltmud' filaiis, a variety of Agrioliiii'tx
agn'sfls, at the rate of one-third of an inch per minute, while in regard
to its possible length iMr. II. Growtlier, in August, 1S90, at Truro,
observed a specimen of the .same sjiecies in the act of descending from
the branch of an elm tree twelve feet from the ground, the slug when
ohserveil having already descended seven feet of this distance.

Some Limaces have also been observed to use this power of pi’O-
ducing mucous threads during .sexual congre.ss, spirally coiling around
each other’s bodies and su.sjiending themselves heads downwards
during that function by means of a jointly produced mucus cable.

The tluviatile mollusks, owing to the greater density of ivater, are,
however, the greatest adejits at this mode of travelling, the Pliysinai,

and especially Aplecta hyp-
noram, making free use of
this interesting mode of pro-
gres.sion, and readily forming
upwardly or downwardly
directed mucous threads of
considerable length, athxing
them between ditferent points
where they may remain in
liosition fur a length of time
and become thickened and
strengthened each time of
ii.sage by the adhc.uon of the
him of iiincns left behind h)'
each .snail using the hlament.

These hlaments,when hxed,
offer a convenient and direct
means of access to the surface
for respiratory imrposes or ])ermit an ea.sy descent into the depths
when the Inng cavity is inflated with air and the animal and its .shell
thus rendered lighter than the n-ater, into nhich it can only enter by
expelling a portion of the uir contained in the Inng-sac or by crawling
down a hxed hlament, the stem of a plant or other suitable object.

Fid. GIO.— Suspensory mucous filament alTi.ved to
water surface aiul formed by Liuuuea auyicitlaria
(L.) in the aquarium.

GLANDULAR SYSTEM — CAUDAL AND IIYPOBRANCIIIAL GLANDS. 319

Upward tlireads can only be formed by the aqnatic Pulmonates,
as beino- attached to some submerged object and always directed
towards the surface of the water, they can only be formed by
individuals using their air-intlated lung-sac as a hydrostatic organ
enabling them to rise to the surface of the water, as they are then of
less specific gravity than the water they inhabit.

Downward threads may be attached to the surface film of the water
or to any object elevated above the surface of the mud, in the former
case the exposed expanded hice of the mucous filament being slightly
depressed or hollow acts like a boat and siqqmrts the thread
depending from it. The branchiate Streptoneura, especially when
yonng, can form the downward threads, Bythinla tentacuhita being-
observed to be particularly addicted to suspending itself from the
surface of the water by this means. These filaments can also be
formed by Pulmonates, which have expelled some of the air from the
respiratory chamber and thus become heavier than the water they
inhabit and tend to fall to the bottom.

The formation of mucous cords is not, however, confined to the
Gastropods, as they are also made use of by certain of the Pelecypoda,
especially when young, Sphccrium lamstre being especially noted for
indulging in this habit of suspending itself, sometimes for hours, from
the vegetation or ihe surface of the water, by one or more mucous
threads ; the rate of production of these filaments being recorded as
three hours for the formation of a filament half-an-inch in length.

The Caudal Gland is usually constituted by an actively secretory
area, and a more or less triangular receptacle or cavity upon the upper
surface of the extremity of the tail, and is present in a variously
developed form in many diverse genera, but is especially conspicuous
in the members of the genus Arion.

In Avion the glandular portion is formed by an aggregation of
minute brownish, semi-transparent and rounded secretory cellules,
which combine to form long, irregularly sinuate lobes, separable by
maceration, the gland secretes considerable (piantities of rather clear
and tenacious mucus with great rapidity, especially during the
pairing season, when large and conspicuous globules of glutinous
mucus frequently accumuhite within the caudal cavity or receptacle.

The IIypobranchial Gland is a localized and variously shaped
mucous gland, intersected by nerves and blood vessels, and serving
for the lulndcation of the respiratory cavity and the oi’gans thei’ein.

OLANDULAK SVSTEAI — UVSSAL GLAND.

20

III tho liniiiL-liiato species it is tpimd as a more or less (listiuctly
localized origan, with projectiii”- folds or leaflets augmenting its

secretory surface, and is
placed between the rectum
and the brauchia on the
roof of the respiratory
cavity, the gland being
capable, on occasion, of
pouring out an enormous
ipiantity of mncns which
escapes through the re-
spiratory orifice.

Fu.. (ill. — I)isseclion of / Vrv/ztrrt vk'ipara (L,) (after T 4-1 F) 1 x . j.1

lleriiariJ), greatly enlargetl, sliowiiig the position of the tllG 1 UllllOllcXlGS tllG

Ilypobranchial gland within the respiratory cavity, ami i t • x l* x* xl

incidentally the arrangement of other pallial organs and IS llOt (llStlllCtly

the innervation of the osphradinm. , i* i i i • i

hr. hranchia, with leallets partially removed; ^^.d. ioCilllZCd illUl tllG GpltllG-

gcnilal iliict ; hypohrancliial gland ; c;. osphradiuin ; i- i i i i n i

r. rectum. Iml ^iaiKUilar ecllnlGS arc

distributed over the walls of the respiratory cavity.

'I'lie celebrated Imiierial or Tyrian imrple of the ancients was a
jiroduct of the hjqiohranchial gland of species of Mnre.r, heaps cf
whose broken shells may still be
seen upon the Tyrian .shores.

The secretion, though colonr-
lo.ss when discharged from the
gland, becomes more or less
brilliantly coloured in correla-
tion with the intensit}'’ of the
light to which it is subjected,
pa.ssing through an intermediate
and definite .series of colour changes and emitting an nnplea.sant
odour during the iiroce.ss.

The Byssal (Jland, though the homologne of the ventral gland of
the (iastroi)oda, is yet a characteristic peculiarity of the more
sedentary Ikdecypods, enabling them to securely maintain jiosses.sion
of any suitable station they ma)" have .selected as a permanent abode.

'I’he byssal gland opens niion the median line of the hinder surface
of the foot and consists of a byssal cavity with longitudinally jdaited
walls and numerous divergent ramifying channels, from which emanate
the chitinous fluid which is secreted jiartially by their epithial walls
and partly by the glandular cells imbedded in the tissues, whose

Fjg. 012. — Transverse highly magnified section
through the Hypobranchial gland or mucous rib of
/ "n'iparn vhdpnra (L.) (aflei ilernard), showing
its character and close relationship to the hranchia
and the subjacent blood sinus.

hr. branchial filament in section, showing venous
connection with h.s, blood sinus; hypo-

branchial gland or mucous rib.

BYSSAL SECRETl()?rS.

321

Fig. 613. — Transverse section of a furrow
of the byssogenous cavity of Modiolaria
discors^ X 250 (after Cattie), showing the
byssal filament and the formative secretion
passing from the byssogenous cells between
the epithelial cells to the byssal furrow,
h. byssal filament ; h.c. byssogenous cells,
their secretion flowing between the epithelial
cellules, e.z.

secretions permeate between the epitlielial cellules and accuinnlate
within the byssal cavity, flowing therefrom by a duct into a semilunar

groove or furrow invested by large
mncus cells which runs along the
ventral edge of the foot and is
capable of being converted into a
closed canal, wherein the chitinous
secretion is moulded into threads
or filaments, which harden quickly
on exposure, their adherent puncti-
form distal extremities being
formed within a cup-like depression
at the anterior end of the byssal
furrow, within which is secreted
the adhesive substance by the aid
of which attachment is made.

The byssus is composed of a bundle of tough chitinous fibres,
resembling horn in some of its physical characteristics, but adhesive
when first formed and therefore available as a means of anchorage
to foreign objects. It can, however, if necessary be thrown bodily off
and replaced by a new one when the animal desires to change its
position, or the mollusk can
ascend any smooth vertical sur-
face by alternately fixing and
rejecting a series of successively
secreted byssal attachments,
the rejected byssal tufts of
Dreissensia being regarded by
Dr. Mbrch as constituting the
Tiihnlaria cas^pia of Pallas.

This gland when highly developed, as in Dreiasensia, exercises a
prejudicial influence upon the development of the foot itself, which
may cease to be functional as an efficient locomotory organ, and
diminish in size in inverse ratio to the development of the byssus, for
which it comes eventually to serve merely as a support, the posterior
pedal retractor muscles even becoming fixed to the gland and
functioning as byssal I’etractors.

In the UnUmklce, Sphwriidw, etc., the organ is more or less vestigial
in the adult, though present and functional in the young. In

Fig. 614. — J\Iytihis cduh's with e.xtended foot
in process of attaching a byssal filament (after
Meyer and Mdbius),

13/1/1900.

V

322

SHELL SECRETION.

Anodonta, the lal■^’al bj’ssal organ is a prominent and transparent tube,
arisinir from the left side of the visceral mass and coiled aronnd the

adductor muscle, but opening on the
median line of the body and emitting
one or two long filaments, which, besides
serving to anchor the embryos within
the brood pouch, also tend to keep the
glochidia together by their entanglement.

The byssal threads of Pinna, an exotic
marine genus, are so long and delicate,
and possess such a beautiful silky lustre
that, according to Ogilvie, they are
woven by the Italians into a valuable fabric, a manufacture known
also to the ancients ; Modiola utilizes its byssal filaments to form a
nest or retreat, strengthening the walls by attaching extraneous
matters thereto ; while the shelly plug of Anomia, by which it is fixed
to the ground, must also he regarded as a modified byssal attachment.

Some exotic marine species, as Trigonia, which, when adult,
possess neither byssus nor byssal gland, have retained the byssal
cavity, the duct and even the retractors ; the abortion of the byssus
is generally correlated with an increase in the size of the foot and
with increased activity in the animal.

The CoNCiiAL or Shell Gland originates during the Trochosphere
stage of larval life, as an invagination of the thickened centro-dorsal
area of the body of the embryo ;
it secretes a viscid chitinous
sulistance which hardens on
exposure and is assumed to
vestigially represent a shell
formerly possessed by the mol-
lusca, but which has become lost
and is replaced by the secondary
shell they now possess. We
may thus speak of a Primary,
a Secondary and even, in some
cases, a Tertiary shell in the
mollusca, recognizing that each
fleeting embryonal phase is necessarily incomplete and often discon-
tinuous owing to a su])pression in the embryo of their full development.

Fig. G16. — Embryo of LijiiniPa stag;naii's {L.,),
approaching the Veliger stage, highly magnified,
to illustrate the position and a.spect of the conchal
or shell gland (after Lankester).

shell gland ; m. mouth ; r. rectum ;
developing digestive gland ; /«. pronephros
or larval kidney ; /. foot ; 7'. velum ; e.gi. cerebral
ganglion.

Fig. 015.— Larva or Glochidium
of Anodonta cys^nea (L.), greatly
enlarged (modified after Balfour).

sh. shell, showing porous structure ;
ad. adductor; hys. byssus; s.s.
sensory sct.-c ; ;//. retractor muscle of
apex of shell.

CALCIC GLANDS.

323

111 some genera this transitorily developed primitive shell soon
disappears and the shell-sac becomes everted, the thickened margins
forming the collar of the mantle and with the enclosed area secreting
the permanent shell.

Other groups, as Linicur, Clausilia, Vivipara, Neritina, etc., how-
ever retain this embryonal vestige or Protoconch upon the apex of
the permanent shell of later life. In the Limaces the invaginate
gland closes up and the chitinoiis particle forms the nucleus of the
permanent shell, which is secreted by the enclosing walls. In the
Clausilia the minute vestigial shell is also enclosed and completely
invested by the epithelium, which, however, is soon ruptured and the
protoconch becomes partially external, the permanent shell being
formed in continuity with it.

In the Pelecypoda a primitive shell, the Protostracum, is also
developed early in embryonal life, and is followed by a Prodissoconch
stage, the vestiges of which are frequently observed upon the umbones
of immature shells. The conchal gland appears opposite the blasto-
pore or orifice of embryonal invagination, as a saddle-shaped group of
epithelial cells, secreting a uniform saddle-shaped film, which later
becomes calcified laterally to form the paired valves, the uncalcified
median part of the pellicle uniting the valves is placed over the median
groove and becomes the ligament.

The Calcic Glands (calx, lime) are numerously distributed over
the whole mantle-surface, but most richly developed along the mantle-
margin in the shell-bearing species, and contributing to form the
shell. Lime cells are also numerous in the digestive gland, their pro-
duct being affirmed to be eventually largely utilized by the Gastropods
in the production of the calcareous epiphragm ; they are also
distributed over the whole external surface of the body, especially in
tho.se species destitute of definite shells, calcareous granules or spicula
being deposited in the skin, and probably contributing to the future
development of a new shelly covering or protection for the body, to
replace that now practically lost by degeneration, and constituting a
renewal of the cycle of development of an external shell, such as has
taken place more than once in the past, as evidenced by the transitory
vestiges present temporarily in the early larval stages of many species
and therefore preceding the shell they now possess.

Lime cells are also freely distributed throughout the general
tissues of the body, their action under suitable conditions producing

PE.VULS-- -THEIR FHRMATICIN.

:v2i

separate m- attaclied calcareous cencretioiis, which are especially
characteristic of the Pelecypods, and being formed by the same or
similar glands to those secreting the shell resemble it in character ;
the concretions of ^[rc<( are nsnally violet, of Phnid rose coloured,
and in other groups they likewise appertain in colour and structure
to the interior of the particular shell to which they belong, the
species with porcellanons shells producing concretions resembling
marble, while those from nacreous shells display a more or less
brilliant opalescent lustre and are distinguished as Pearls.

Pearls are perhaps the most valuable production of the mollusca,
and, hehu'C the systematic and successful prosecution of the Oriental
pearl-tisheries, were very largely derived from the Unin nuu'garitifer,
a species which e.xists not only in the British Isles, hut throughout
the northern circumpolar regions, the production of pearls being
formerly so especially identitied with the Unionida', that the name
Cnio, signifying a pearl, was ap])lied to the tyiiical genus.

Pearls, as well as the kindred but less beautiful porcellanons or
tibrous concretions, consist of successive and alternating la3mrs of
calcareous ami chitinous matters, deposited around any irritating ex-
traneous particle or particles which may have gained entiy amongst
the delicate glandular tissues. In some localities the eggs or bodies
of Atd.r, lhirtg)lidliis, or other of the minute internal parasites may
he the predisposing cause, in others a grain of sand or other foreign
irritant substance may furnish the nucleus and necessary stimulus
for secretory activity, the intrusive atom becoming enclosed by succes-
sive accretions until it may eventually attain such a size as to preclude
the closure of the valves and cause the death of the animal.

But from whatever causes they may originate, these deposits of
])oarly matter are iiroduced at the expense of the shell, and it is,
therefore, not surprising to find that the shells of pearl-hearing
individuals are often deformed, and can usualty be recognized by the
asymmetry of their valves, the constriction of the lower margin of the
shell, or the presence of railiatiug grooves or ridges, as it is seldom
that a regularly formed shell contains a pearl.

Peai’ls may he formed in almost any part of the tissues, in the sub-
stance of the mantle, between the body and the gills, between the
gills and the mantle, or between the mantle and the shell; sometimes
they are found singly, at others several occur together, either free
or adherent to the interior of the shell or t() each other.

PEARLS — THEIR CHARACTER AND USES.

325

The shape too is veiy variable and may be spherical, ovoid, pyriform
or iiTegular, perhaps dependent upon the character and shape of the
nucleus around which the pearl is formed, although perfectly spherical
pearls are affirmed to always originate by the enclosure of the irritating
particle within an ampulla or cyst filled with an organic fluid, which
undergoes lamellar condensation around the intrusive atom, the
interstices of the chitinous layer becoming filled with a calcareous
deposit. The delicate wall of the cyst afterwards becomes ruptured
and the incipient pearl or concretion is freed, so that the periodic
deposition of pearly substance can continue to be uniforndy and
evenly applied.

If a pearl lying loose in the tissues becomes lodged between the
mantle and the shell it may become attached to the inner surface of
the shell by the successive accretions of pearly matter, and thereby
lo.se its spherical form and the lustrous iridescence characterizing
free pearls.

The most valuable and esteemed pearls are of a lustrous white,
delicately tinged with azure or .salmon, or those of an ex(|uisite
rose color. The iridescence, which gives to pearls their greatest

charm, is due to the diffraction of the
light by the partially transparent and
minutely corrugated layers forming the
exterior of the gem ; the thinner and
more transparent these layers the more
beautiful the lustre, the superiority of
the Oriental pearls in this re.spect being
the reason of their gTeater beauty and
value compared with British pearls.
Besides the corrugated furrowing, there are a number of fine dark
lines T?Vo ii^ch apart, which run in different directions or

from pole to pole, and may add to the lirstrous effect.

l.'nlike precious stones, pearls, being animal products, tj^uickly fade
and decay and only great care keeps them in good condition for any
length of time; they will tarnish when worn next the .skin or even
when enclosed in a jewel box. AVdien dim and lustreless, their bril-
liancy can, however, be restored by “peeling,” a process skilfully
practised by the Chinese, who use for this purpose a keen knife, files,
pearl powder and a scrap of leather, the final polishing being given by
the leaf of a particular plant.

Fig. 617. — Surface of Pearl,
highly magnified, showing the mi-
nute undulations upon which the
pearly lustre depends (after Tryon).

PEARLS AND PEARL-FISHERIES.

82(;

Pathological causes may also beget an irritation which is liable to
iuilnce, in the substance of the adductor innscles, the formation of
small and irregularly-shaped concretions, which are called Sand or
Seed pearls and used for enriching embroidery, etc.

British pearls have been celebrated from the earliest times for their
size and brilliancy, the crowns uf the ancient British kings being-
encircled with pearls, as shown by their coinages, and Suetonius
records that the hinie of their loveliness was the chief inducement
that led Julius Cicsar to undertake the comiuest of this country to
obtain them. Pliny and Tacitus concur in stating that he dedicated
and hung in the Tenii)le of Venus (Jenetrix, a buckler made of
British pearls, and though Pliny remarks that the pearls used
were small ami poor, yet, on the other hand, the Venerable Bede
comments especially upon the orient lustre and brightness of the
native pearls, while in modern times Dr. Leach has stated that pearls
from our Unio margaritifer yiQxa often sent to India and re-imported
to this countiy as Oriental pearls.

In North .Vmerica the prehistoric Indians carried on the Uniu pearl
fishery upon an extensive scale, especially in the Scioto and Miami
valleys. The robes of their great chiefs were enriched by a lavish
display of e.xcpiisite pearls, which were always pierced by means of
red-hot copper wire to ensure secure attachment. These treasures
were always buried with their owners, and hundreds of thousands of
what had been large and magniticent pearls have been obtained from
the burial mounds of Ohio, (leorgia and other jdaces; these are,
however, now worthless, except as curiosities, being blackened and
spoilt by lire, perhaps from being thrown into the flames of the altars,
or have become rotted and cemented into masses by water filtering
to them through the soil during their long burial.

The Chinese who, in the thirteenth century, discovered the mode
of liroducing pearls, also obtain pearl-covered images or other objects
by introilucing into the .shell of the living mollusk small models of the
figure or shape required, which become in due time covered by a pearly
layer or deposit.

European attem})ts to produce pearls have not been financially
successful, although the celebrated Linnc owed his elevation to the
noltility i)artly through his efforts to ju'oduce pearls artificially, by, it
is sui)po.sed, luerciug small holes through the .shell and introducing
thereliy grains of sand to form the nuclei of the desired pearls.

PIGMENT CELLS.

327

The Unio peaii-fi.slieries are still somewhat desultorily carried on
ill various parts of the British Isles, North America, Germany and a
few other countries, but were formerly of much greater importance
and extent.

Even at the present day the fisheries still existent in various Irish
and Scotch rivers occasionally yield valuable pearls, but during the
eighteenth century the Tay fishery was very productive, the value of
the pearls found therein from 1761 — 1764 being about £10,000.

The Welsh pearls were also noted for their lustrous beauty, the
Conway being said to have furnished a pearl of especial purity which
Sir Richard AVynne presented to Queen Catharine, and which,
according to Reeve, is now set in the crown of Queen Victoria,
although the Keeper of the Regalia .states there is no mention of
such a gem in the description of the Crown jewels.

The Pigment Cells {pigmenfum, paint or colour) are distributed
throughout the body, but are perhaps most plentiful in the connective
tissue subjacent to the external epithelium, and in the testaceous
species are chiefly congTegated at the mantle-margin, passing in-
sensibly into calcic and mucous cells, the three mutually intergradiiig
as is shown in Arion rufiis, Limax flavus and other .species, in which
pigment is associated with and stains the dermal mucus and assists
to give the body its distinctive tint ; similar effects are exhibited
in Agriolimax agrestis, in which the functional relationship of the
mucous and lime cells is exemplified by the limey mucus they so
plentifully exude.

This expulsion of colouring and other matters from the body may
be regarded as a true excretory function, quite analogous to that seen
in the periodic moulting of the feathers in birds and the .shedding of
hair in animals, as Uric acid and other colouring matters are waste
products of the organism, which have probably been seized upon by
the phagocytic cells and carried to the external surface of the body ;
the exhaustion of the supply of colouring matters at the surface by its
long continued or too copious exudation with the slime, when the
animal has been closely confined for a length of time or greatly
irritated, probably accounts for the instability of colouring in adult
slugs. Under such circumstances Limax fldvm is said to pass rapidly
from light yellow to dull olive-gTeen, and Avion atev has been recently
observed by Air. Gain to pass in a very short space of time from
orange-yellow, through chocolate-brown to grey, tinged and spotted

INFLUENCE OF AGE ON PIGMENTATION.

328

with orange, with grey lateral handings, before again eventually
reverting to the orange-yellow colour which distingui.shed it when
tirst found.

riginent may be a natural product of the organism, or an inherent
characteristic of the substances composing the body, as exemplified by
the dee[) dull red colo\ir of hamiatin, the base of luemoglobin, and
therefore not dependent on the action of light, which is not really
essential to its i)roduction, as is demonstrated by the varied coloura-
tion of the internal organs and l)y the brilliant tints of many deep sea
animals which permanently dwell in cimmerian darkness. Its distri-
bution and arrangement is, however, largely intinenced by selective
and other forces, and also dependent on the character of the tissues
and the nature of the genend environment, being modified by age, the
amount of heat or cold, moisture or drought, food, light or darkness
or, in fact, by anything which affects the i)hy.sical constitution of the
body and may by retarding or accelerating chemical changes or com-
binations produce changes of colour.

Age has great inflnence on colouring, Linuu' fhcvtis and other
s[)ecies becoming darker with advancing age, and this chrumological
change assists ns to a better understanding of a i)robably more primi-
tive colouring, as the accepted law of coloration in animals is for the
young of allied species or genera to bear more resemblance to each
other and to their common ancestor than the adults do, the succes-
sive changes undergone during growth probably hinting at the series of
adaptations necessitated by environment during their .specific life.

In Arl<iii nuniiitns, one of fhe most primitive species of that genus,
a greeni.di tint is indicated by its early develoi)ment, as jn-obably an
ancient colouring of that sjjecies, this colour changing from time to
time during growth, through yellow with slate coloured dorsal and
lateral lines, to nearly uniform yellowi.^h-white before finally becoming
grey on the hack, with greyish-yellow sides and yellower caudal region,
the mantle assuming a somewhat uniform dull greyi.sh-orange colour.

Arldii <(tcr has also been noted to undergo even more remarkable
and varied colour changes during growth, both probably imlicating
adaptations to stations succe.ssively occupieil during the extension of
their range, the observed scale of changes undergone in dermal
cobnation by the Arions and other gToui)s thus suggesting the i)robable
route of their evolution to the attainment of their ju’esent tints, and
although the genetic .sequence of colours in the mollusca has not yet

imflue:nce of food and temperature on pigmentation. 329

been satisfactorily worked out, it has probably diverged and varied in
response to environment from a comparatively simple and more or
less uniform tint of animal and shell towards the more striking and
distinct colours they now so fre({uently exhibit, the more fugitive and
advanced colours being the result of greater chemical activity and
change amongst the constituents of the body, and are probably those
most recently ac(piired and which have not yet become an integral
and permanent part of the organization.

Food has been undeniably demonstrated to modify the colours of
certain insects and birds, and it is probable that a particular diet will
to some extent modify and iiiHuence the intensity and character of
the pigmentation in the mollusca. Mr. Hawkins, in “The Ncituralist”
for February, 1899, has i)ublished some practical observations on the
apparent inlluence of food upon the colours of the shells of Helices,
which it would be of the greatest interest to confirm or refute.

Cold has been demonstrated to inhibit the formation of the red
pigment, but to be favourable to the development of the black, which
is generally due to Melanin, a substance which is practically identical
with the colouring matter of the cephalopod ink and is usually found
in minute particles in the dermal epithelial cells as well as in those
of the other parts of the body, its greater abundance being correlated
with superior physical vigour, as it is in relation to and in a great
measure dependent upon the mass of blood in the organs from which
it is secreted and deposited in the external integument in response to
external influence, the effect of cold being demonstrated by Simroth
to induce darkne.ss of colouration in the slugs, especially if they are
subjected to its influence during spring, at the period of their most
active gTOwth and development.

A further confirmation of this law of colouring is afforded by the
observation of the Rev. Dr. Xornian of the darkening A griollmax
agrestis under the diminishing temperature of autumn and by the
known fact that Limax cinereo-nigtr, the northern race of Liniax maxi-
intis, is often totally black, while in warm Italian regions the species
develops a series of brilliantly colmired and strikingly marked forms.

Limax marginatm^ (Mull.) offers still more striking confirmatory
evidence of the effect of cold and moisture in inducing melanism.
In the north and north-western parts of this country and on
mountain sides this species becomes darker in colour and loses the
glaucous and translucent aspect which is its usual characteristic on

330

PROTECTIVE RESEMBLANCE.

wanner and drier grouiul. (’)ii the Italian inonntains the transition
fnnn the ordinary translncent glancous specimens found in the valleys
to the intensely dark oi)a(pie siieciinens inhabiting the cold and
cloudy nionntain regions can be clearly traced, and although these
sombre forms may not be limited geographically to particularly humid
regions or cold northern latitudes, yet their appearance is always in-
dicative of the local or transient })eculiarities of their environment.

Heat principally affects and increases the formation of the red
pigment and under artificial conditions has been experimentally
demonstrated by Simroth to inhibit the dermal disposition of the
black pigment in Arion ater and Limax maxhnu!^ and also to favour
the development of albinoes, the individuals, however, only remaining
albine under a continuance of the warmth, while other specimens
from the .same batclies of eggs reared under more natural conditions
acipiired the colourings characteristic of the species.

The re<l colouring matter, which has been shown to be to some ex-
tent dependent u])on warmth for its production, has been .shown by
Simroth to be probably a warning colour in xiriun, as many creatures
to whom he offered xirion rufus as food either totally rejected it or
ate only the viscera, and as the red i)igment is jirobably a waste
product of the tissues, discharged by the dermal glands, this effect is
not imi)robable.

The pigmentation of the animals of our land and Huviatile mollusca
does not generally e.xhibit any remarkable differences in the distribu-
tion of the colouring, the variations being chiefly confined to
dilferences in the intensity of the general colouring ; the greatest
variety is shown by the naked species, which being fully e.xposed to
the full effects of external inHueiices, are more cpiickly affected by
and resi)onsive to changes in their environment and therefore exhibit
greater diversity in the external pigmentation of the body.

The Protective Resemblance of the animal or shell of various
species to some natural oliject of the environment is due in a great
measure to external coloration, the specially imitative mode of its
distribution or arrangement being probably gradually acipiired by the
preservation and perpetuation of those individuals most closely simu-
lating the particular object. A strikingly coloured animal or shell,
strongly contrasting with the surroundings amongst which the
creature exists, must, unless it is otherwise protected, inevitably be
more easily detected by its enemies, thus tending to the elimination

PROTECTIVE RESEMBLANCES AND DEVICES.

331

and destruction of the more conspicuous specimens, and the pre-
servation of those variations wliich harmonize most closely with the
environment, while heredity will assist in the perpetuation of those
individuals, which either by colouring, form, or habit are most
difficult to distinguish amidst the surroundings amongst which they
habitually live.

Amongst exotic species many striking instances exist of the pro-
tection afforded by resemblances to other objects, and although in
our own more prosaic country we can scarcely hope to have examples
of so striking and beautiful a character, they are yet of the highest
interest and probably of vital importance to the welfare of the
different species.

Amongst the slugs, Mr. G. Sherriff Tye has recorded the similitude
oi A vion hortensis and AgrioUmax agrestis to the fallen bloom sheaths
of the Black Poplar (Fopulus nigra L.). This resemblance is affirmed
to be sometimes so perfect that the keel, pallial line, and even the
corrugated surface are so strikingly simulated as to render the
deception quite complete, and Dr. Scharff and others have recorded the
striking similarity between the animal of Geomalucm maculosus
and the foliage of Frullania dilatata and other liverworts and lichens,
amongst which it lives and finds its food, while other .species have
been .shown to closely resemble other familiar and inedible objects.

Amongst laud shells, Buliminus obscnrus has long been noted for
an analogous habit to that of the burrowing bivalves, and its adven-
titious protective covering does undoubtedly vary according to the
situation inhabited. In woods where the trees are clad with lichens,
this little shell is similarly clad and then resembles little moss-covered
knots or excrescences upon the bark of the trees ; or, if found on dry
hedgebanks or on roadside trees or walls it often bears a most natural
resemblance to a misshapen piece of mud or stone.

Protection is probably also secured by Helix fusca through its
wonderful resemblance to the decaying capsule or seed-case of the
Red Campion ( Lychnis diurna). This resemblance is, according to
Mr. Masefield, so faithful as often to require a close scrutiny to
determine whether the doubtful object be a snail or a seed pod, as
this .species is the exact colour of the capsule when wet — a trans-
imrent horn colour, and the bottom of the seed-case being light-
yelloAv exactly reproduces the appearance of part of the viscera of
the mollusk as seen through the shell.

KESAL ORGANS OK NEPHllIDIA.

O O

ooJ

Mr. L. E. A<1 aiiis has roL-eutly observed that, on tlie sandliills at
Sandwich, //e//j- airtusidua is cliieliy found upon the Hound’s
Tongue (Cijnogloi^sum officiiDde), clinging to the witliered steins and
so closely simulating the clusters of burr-like seeds that it is difficult
to distinguish the shells in the sunlight.

Limiiau’ when crawling on the bed of a stream or pond assimilate
in a remarkable way to their surroundings, and the darkly mottled
mantle which often shows dimly through the shell does not render
them more perceptible, but rather tends to their closer approximation
with tbe appearance of their surroundings.

The \"lvlj)ar/a(f are often found so thickly coated with mud that
no portion of the actual shell can be seen, and the resemblance to,
and assimilation with, tlie bed of the canal or river is complete. This
incrustation olten contains fragments of plant tissues and may also
be rich in Alg(t', chietly represented by numerous species of Diatoms.
OscUlatur'uc are sometimes eipially plentiful in the deposit and
impiently, in the living condition, imparting a greenish tint thereto.

Amongst bivalves tbe tufacoous or muddy deposit upon the pro-
truding posterior part of the valves is well known to all conchologists,
who readily acknowledge the i>erfection of the disguise, which is only
penetrated by the opening of the valves and the protrusion of the
siidions. Often this incrustation becomes the seat of growth for
Ahjic or other water plants, and the difficulty of detection is corres-
pondingly increased.

'I'he A'epiikidia kidney), Kenal organs or Kidneys, known

in Oastroi)ods also as the Precordial gland, are typically paired and
dor.sally placed excretory organs, always .symmetrical in .symmetrically
organized animals with paired gills, and metameric in Ndiitilus,
in which the respiratory organs have a serial character, but single in
most Gastropods in correlation with the loss of the moities of many
other of their primitively paired organs.

These organs in the mollusca assume a variety of forms in exotic
genera or the constituent parts may jiermeate amongst the various
organs of the body; usually, however, they consi.st of a pair of tubules,
each of which is closely folded upon itself, forming a looj), connected
proximally by the ciliated reno-pericardial funnel with the base of
the pericardial cavity or secajndary ccjclom, with which they are always
in intimate relation. The proximal tract or limb is enlarged and
sacculate with rich vascularization and constituted by browni.sh or

RENAL ORGANS.

883

Fig. 618.— Kidney cells of Helix
arbustofum L. , highly magnified,
showing the contained Uric acid
concretions (after Boll).

yellowish tissue, containing nninerons ca'ca and projecting glandnlar
lamellre or trabecnloe, overspread by a densely ciliate la3"er of secretor}'
cells, wbicb fill np the lumen of the organ and contain a yellowish or

greenish Hnid with concentrically formed
concretions, similar to those in the renal
organs of other animals, the rupture of
the cell-walls allowing their escape.

The deoxidized and impure blood re-
turning from its circuit of the body,
laden with the waste products of the
oxidation of the tissues, joins with some arterial blood from the lung
and circulates within the kidnej'S before reaching the respiratory
organs, thus constituting a portal circulation which partially purifies
the blood by eliminating therefrom the nitrogenous waste matters, in
the form of Urea, Uric Acid, Galcium-phosphate and other substances,
amongst which Ammonia, Creatinin, Tyrosin, Leucosin, (fuauin, etc.,
have been recorded.

The excretory substances vary somewhat in character in the different
groups, the Pelecypoda chiefly expelling Urea, which is formed by
the more or less complete oxidation of the anatomical elements of
muscular tissue and is produced most plentifully during periods of
abstinence or food scarcity ; while manj' Streptoneures excrete Uric
acid, which results from an
incomplete oxidation, due to
the blood being surcharged
with pe[)tones which the
tissues are unable to assimi-
late, a state consequent upon
a plethora of food.

In the Pelecypoda the
kidneys are known as the
Organ of Bojanus, the
simplest form being found
in Nucula and other Proto-
branchiates, in which they
consist simply of a pair of
folded and separate cylindrical sacs, placed beneath the pericardium
and in front of the posterior adductor, each sac possessing a .spacious
lumen and similar secretoiy walls throughout its extent, the pericardial

Fig. 619. — Diagram formed from several combined
transverse sections through Anodonfa, showing the
relative positions of the kidneys or renal organs and
their ducts (after Griesbach).

n. nephridia, with r./. reno-pericardial funnels and
7i. ureters ; pc. pericardium ; n. auricle ; v. ventricle ;
s. vena-cava or blood-sinus ; r. rectum ; g. genital
ducts.

34

RENAL ORGANS.

and excretory oritices of each gland being placed anteriorly, the
excretory opening being confluent with or near the genital aperture
and the excreta, especially in the more archaic genera, being expelled
in a Huid form.

In the more advanced genera, as in the Unionidiv, etc., the secretory
walls become more complicated and the glandular surface augmented
in the proximal or ventral limb, to which it becomes chiefly restricted,

Fig. 620. Fig. 621.

Figs. 620 and 621. — Transverse sections through two regions of the renal organs of Anodonta
cys^nea (L.), highly magnified (after Rankin).

k. secretory section of kidneys ; u. ureter ; h.s. blood sinus ; /, foot ; c.pl.v.c. section of cerebro-
pleuro-visceral commissure.

the distal or superior limb forming the duct to convey the secretions
to the exterior and opening into the mantle cavity, always above the
cerebro-pleuro-visceral commissure ; but sometimes, as in Sphevrium,
etc., within a common urogenital cloaca; in most groups, however, the
renal and genital apertures are distinct, although the kidneys them-
selves, as well as their ureters, communicate freely with each other,
especially in the more specialized forms.

In the Streptoneura the primitively paired character of the kidneys
still persists in a more or less distinct form in the Diotocardia, yet
the right kidney, though still connected with the pericardium and
mantle-chamber, has entirely lost its renal function and has become

utilized as a channel for the conveyance
to the exterior of tlie genital products ;
the left kidney, however, .still retaining
its exclusively renal and secretory
character.

In other Streptoneures the left kidney
is alone present in adults iu correlation
with the retention of the moieties of
other paired organs, and is situate to
the left of the rectum, though actually
traversed b)' that organ in some genera. The right kidney has, how-
ever, also been detected to be transitorily present in Vivipara, etc.,
during embryonal development, its ureter, however, persisting in the
adult, but acting solely as a genital duct.

Fig. 622. — Sttcctnea putris (L.).
X 3, showing position of kidney or
renal organ.

r. renal organ or kidney ; h. pul-
monary plexus ; i. intestine; 4. heart.

RENAL ORGANS AND THE URETER.

335

In the Euthyiieures there is also but a single kidney, the representa-
tive of the right kidney of the hypothetical primitive mollusca and

of the Pelecypod ; it is placed upon the
roof and in the rear of the pulmonary
chamber, between the pericardium and
the rectum and is of the parenchymatous
type, the complex folds and lamellse of
the walls projecting into the cavitj" and
often quite filling up the lumen of the organ.

The Ureter is the ciliated thin- walled excretory dnct of the kidneys;
it is paired in the Pelecypoda in correspondence with the paired
glandular sections whose products they discharge, their apertures
being usually placed above the base of the foot and opening into the
supra-branchial or cloacal chambers, in close vicinity to or in con-
junction with the reproductorj" orifice.

The duct of each kidney is folded back upon the secretory section
and are separated by the Vena-cava, but they usually communicate
by means of the oval inter-renal space near their outlets ; they
represent the Primary Ureter of the Gastropoda.

In those species which retain their primitive organization the genital
glands having no special ducts discharge their products into the
nephridia, which are transmitted to the exterior by the ureter.

In our Streptoneura the kidney is placed at the rear of the mantle
cavity, the slit-like excretory aperture, which characterizes many of
the groups, opening directly into the pallial cavity, although in
Vivipara and Valvata the orifice becomes a tubular and elongated
duct, which is distinguished as the Primary Ureter, a name applied to
the first direct excretory tract originating at the kidney, and dis-
charging the waste matters towards the exterior.

In the Euthyneures the urinary duct has a more complex develop-
ment and the various stages are to be observed leading from a simple
aperture, opening directly into the pallial chamber, to a long and
almost sinuous duct, conveying the renal secretions quite to the
exterior of the body.

The Primary Ureter or renal efferent duct is represented by a
simple orifice in certain species of Planorhis, but is well developed
and prolonged towards the pulmonary orifice in most other Basom-
matophora, in Cionella, Pupa, BuUminus and some of the more
primitive Helices, or, instead of extending directly towards the

Fig. 623. — Longitudinal section
through the kidney of A^'iolimax
a^^restis L., X 50, showing its com-
plicated structure (after Hanitsch).

33(5

SErCtNDARY UreTER AND PRONEPHROS.

aporturo, it may assume a liackwavd directioii, fusing witli tlie wall
of the secretory sac ami opening at the extreme rear of the mantle-
chamher, as in TcstdccUit, etc., while an intermediate stage leading
to the highest development ot the ureter is seen in the formation in
some Helices ot a more or less open channel, leading from the aperture
of the backwardly directed primary ureter in the rear of the mantle-
chamher to the pulmonaiy orifice ; this channel eventually becomes

Kig. G’2t. Fig. 02.). Fig. 020. Fig. 027. Fig. 028.

Diagrams illustrating the development of the Ureter in the Gastropoda (after Lang).

r. kidney or renal organ ; /.«. primary ureter ; s.u. secondary ureter ; r. rectum ; f>.o, respira-
tory orifice ; /i. heart, within its pericardium.

Fig. 02 L — Portion of respiratory chamber with the e.vcretory renal orifice existing as a simple
papillar opening, as in certain Planorbes, etc.

Fig. 62.5. — Shows the elongation of the simple exxretory orifice into a long and definite duct,
the Primary Ureter as in the Hasommatophora and certain Sireploneures, etc.

Fig. 626. — The Primary Ureter is directed backwards and adherent to the kidney, opening at
the back of the respiratory cavity, as in Tcstacciia, etc.

Fig. 027. — Shows the formation of an open channel leading to the exterior from the renal
opening in the rear of the chamber, as in certain Helices.

Fig. 02S. — Shows the formation of the open channel into a definite duct, the .Secondary Ureter
and its junction with the rectum, as in our most highly organized Helices, etc.

clo.sed and forms a detiiiite duct, di.stingui.shod as the Secondary
Ureter, the name applied to the differently directed tract in con-
tinuation of the hackwardly directed primary ureter of the Testacelhv,
hut following a different direction, parallel with and opening into or
near the rectum, a-^ in Ariou, AmaUd, Umax, Yitr'ina, ITyalinia and

the more highly developed Helices.
The Pronephros (-/.o, hefore ;

Fig. 620. — Embryo of Plnnorbis cornctis
(L.), seen from the left side, X IHO (after Fob),
showing the Pronephros or primitive kidney.

/;/. pronephros or primitive kidney ; c.o. its
external orifice ; in. mouth ; r. rectum ; n.
nephridium or permanent kidney, also showing
external orifice ; d.gl. digestive gland ; in. in.
mantle margin ; e.gi. cerebral ganglion ;
/>.gi. pedal gland.

i'€</)/)r)s, kidney), Wolffian bodies or
provisional renal organs, known also
as Stiebel’s canals, are possessed
by many embryonic mollusca and
are es])ccially characteristic of the
Trochospherc stage of larval life,
as they atrophy and disappear
before the close of the Veliger
])hase of develoiunent.

They arise by ectodermic in-
vaginations in the anterior region
of the body, behind the velnm, but

considerably in advance of the later and permanent kidneys of adult

PERICARDIAL GLAND.

337

life, they are alway.s paired and are best developed in the a([uatiG
puhnonates, consisting of anteriorly directed V-shaped tubes, opening
into the body cavity ; the cephalic or longer limbs are richly ciliated
and directed towai-ds the Velar area, the shorter or pedal limbs being
nnciliated and directed towards the foot; the cellular dorsally-placed
apical sacs contain concretions and open exteriorly at the sides of
the neck.

In the Streptoneures these organs are formed by a mass of excretory
cells, with numerous vacuoles containing concretions placed at each
side of the body. At a later stage the vacuoles unite to form a
cavity filled with a brown gTannlar mass.

The larval kidneys have been observed in many Pelecypoda, each
being constituted by a deeply situate ciliated canal and a more super-
ficial part, with an external opening at the postero-ventral side of the
cephalic region, and an internal one within the body cavity.

The Pericardial Gland (jepl, around ; KapSia, heart) or Keber’s
organ has an apparently important excretory function in many
mollusks, and is a thick and spongy glandular differentiation of tlie
pericardial epithelium covering the walls of the amides and closely
connected with the vascular system, but always constituted by flat-
tened cells, destitute of the concretions characterizing the renal cells.

In the Pelecypoda it arises as a pericardial investment of the
auricle or at the anterior angle of the pericardium, which would appear
to be its most primitive position, and though often found as a prolifera-
tion of the anterior pericardial walls, is not always developed at the
same place or in exactly the same way. It is an organ quite analogous
to the kidneys, having a rich sanguine irrigation, mainly by the
arterial blood returning to the auricle, extracting therefrom a more
acrid secretion than that eliminated by the kidneys, which, in
Cardium and other marine genera, has been determined to be Hippuric
acid; this is discharged into the pericardium and flows through the
reno-pericardial funnels into the kidneys and thence to tlie exterior
by the ureters.

Except in Nucida and other archaic genera, the pericardial glands
are almost universally present in the Pelecypoda in the form of paired
reddish glands, upon the auricular walls witliin the pericardial cavity,
or as an agglomeration of glandular tubules protruding from the
anterior corner of the pericardium into the mantle lobes, both these
forms being found among the species of our fluviatile genera.

3,2, 1900.

w

CONCRETIONARY GLAND.

.S3.S

Among the Streptoneuves tlie gland in the Diotocardia maintains
its jirimitive position upon or near to tlie walls of the anrieles, the
pericardial cavity being contracted by its proliferations, hut in the
Monotocardia it is found upon the internal pericardial walls.

The Concretionary Gland is characteristic of Cydostoma, although
organs of somewhat similar aspect and probably analogous functions
exist in Blthynia tentaculata and doubtless other species. The gland
is to be regarded as a secretory organ and store-house for Uric acid
and probably other waste substances, and was surmised by Garnault
to have been acquired by the ancestors of the Cyclostomldcc when

they relimpiished a(|uatic for terres-
trial life, the more frequent periods
of rest necessitated by the gveater
ductuations of temperature, hindering
the action of the kidneys, and the
Uric acid accnmulating within the
concretionary gland, to be afterwards
re-absorbed and passed away from
the system by the ureter when active
life was resinned, as the concretionary
gland has no excretory duct nor does
it communicate either with the pallial
'I'he gland is a greyish or brilliant
white organ, occiqiying a dorsal position beneath the kidney and
composed nf dense tufts of simple or branched follicles, some of
which may he two millimetres in length, disposed among the intes-
tinal convolutions, all being bmind together by loose connective
tissue and encompassed by a rich vascular plexus.

'J'his organ is variously developed, individually and seasonally, being
more pronounced in autumn than in spring, the follicles at the former
time being filled by multitudes of solid
splimroidal concretions formed by concen-
tric lamelhe, disposed around one or more
nuclei. The colour of the gland is entirely
dependent upon the number of concretions
liresent in the follicles, the organ show-
ing the characteristic brilliant white colour
when they are numerous and being
greyish when the contained concretions are less plentiful

I’jG. — Follicle of Gland of Con-
cretion of C^clostoma clegaiis (Mull.),
highly magnified (after Garnault).

cavity or the digestive tube.

Fk;. G31. — Concretion from
Concretionary Gland of Cyclo-
sto/>in cU’gans (Mull.), highly
magnified (after (xarnault),
showing the concentric lamellar
structure.

LYMPHATIC GLAND.

339

The concretions are translucent in Cydostoma costulatum, but
only occasionally so in Cydostoma elegans, they may, however, be
rendered transparent and their complex structure demonstrated by
immersion in weak alkaline solutions. Ammonia, Potass or Soda
water. They dissolve instantly without effervescence in Sulphuric
acid, and the various reactions show the concretions to be almost
entirely composed of Uric acid.

The interspaces between the concretions are filled with a grey mass
of immobile Bacilli, three to four g long, which however exhibit

Brownian movements. They are variable
in size and shape and often united
together in pairs, and their constant
presence in this closed cavity contain-
ing so much alternately deposited and
re-absorbed Uric acid, would seem to
indicate symbiotic action, the bacilli having probably some impor-
tant function either in connection with the deposition or the
re-absorption of the Uric acid concretions.

The Lymphatic Gland {lympha, water) or spleen, the formative
organ of the ammbocytes or white blood corpuscles, thougli present
in our land and fluviatile species, is not so distinctly localized as in
the Opisthobranchs, the lymphatic cells being more generally difi’used
throughout the connective tissue, though usually most numerous and
active in or near the respiratory organs, especially along the course of
the afferent cardiac vessels and upon or near the auricle, and hence
it has been termed the “ Gland of Auricle” by some observers.

Although the grouping of the lymphatic cells is so variable in
character, their aggregations are always constituted by a layer or
stratum of connective tissue, crowded with nuclei, which become
invested by protoplasm containing refractive ferment granules, the
amoebocytes eventually passing through the meshes or interstices of
the connective tissue and falling into the blood stream.

In Dreissensia this sanguineous or blood-making gland, as it has
been termed, is in the gill itself, close to the afferent vessels, but in
the Gastropoda it varies greatly in position. In Limax and Helix the
gland occurs as a thick stroma surrounding all the efferent pulmonary
vessels ; but in the Lhnncddw the gland is not distinctly separable
from the pulmonary vessels. In our Streptoneures the lymphatic organ
may have a dual develojiment, being not only represented along the

>

Fig. 632. — Bacilli of Gland of
Concretion of Cydostoma elegans
(Mull.), highly magnified (after
Garnault).

340

MUSCULAR SYSTEM.

basal portion of the gill and opening into the branchial vein, but
a specialized area of connective cytogenons tissue, the Nephridial
gland, invests the renal vascular plexus, and encloses lacunar spaces,
which communicate with the auricle, the ammbocytes passing into
the blood within its cavity.

The amoebocytes and the large vesicular wandering cells, known
as the “cells of Leydig,” take up and absorb sickly and degenerating
tissue and foreign bodies wdiich have gained entrance into the system,
indigestible or insoluble particles becoming encapsuled and removed
from the circulation, a process of excretion which occurs in many
animals; many of the mucus, pigment and other cells so numerously
present in the external tissues are wandering cells, probably con-
veying their contents towards the surface of the body, they also act
as storehouses for the accumulation of a reserve store of nutriment
in the form of glycogen.

i\Iany of onr .species, owing to the energetic phagocytary action of
their ammbocytes, can withstand, without apparent injury, the
introduction into the body of many poisonous substances or large
(quantities of bacterial disease germs. Our IleUx pomnt'ia\\&^ been
demonstrated to successfully resist the deleterious presence of such
organisms or substances within the body, the bacteria soon becoming
collected together in the most delicate qmrts of the lung, which are
essentially qdiagocytic in function.

The Muscular System embraces the organs by which the move-
ments of the body are accomplished, under the stimulus of the
efferent nerves from the various ganglionic centres.

This power of motion or movement is possessed by every animate
creature, but in the lowliest organisms where there is little differentia-
tion of i)arts, the whole body is mobile and contractile, constantly
changing in shape by the inces,sant retraction or protrusion of different
jiarts of the body substance in the form of Pseudopodia (\pevSys,
false ; ~o8- foot) a qnimary form of movement exhibited by the
ama'bocytes or white blood corpuscles, present in the blood of the
mollusca and other animals.

Cilia (ciliiim, an eye-lash) and Flagella (Jf<igelliun, a whip-lash)
are finer and more delicate ju’olongations or extensions of the body
std)stance, but imire i)ermanent in character; they form more advanced
organs of loconnjtion, particularly cbaracteristic of the Infusoria and
of the Wdiger and Trochosphere stages of the molluscan embryo.

MUSCLES — INVOLUNTARY AND VOLUNTARY.

841

As we ascend the scale in the animal king<loin or arrive at a later
stage in the development of the mollusca, true locomotor and other
muscles become more distinctly differentiated and it hecomes due to
their alternate contraction and extension that movements are effected.

Muscles in most animals are what are popularly known as flesh, and
are constituted by bundles of fibres collectively enclosed by a strong
membrane, each constituent fibre being surrounded by a thin sheath
of connective tissue and arranged with its length parallel with the
direction or pull of the muscle, and also connected with a nerve cell,
whose stimulation causes the contraction of the filament and draws
together tlie parts to which the opposite ends of the muscle are affixed.

Muscles may be Voluntary or Involuntary, according as they are
or are not under the control of the animal, although it is probable
that many apparently voluntary muscular movements are merely
reflex actions in response to external stimuli.

Involuntary or Unstriated Muscles are predominant in the

molluscan organism, but are more es-
pecially characteristic of the splanchnic
muscular layer, and are composed of
greatly elongated, smooth and unstriped
muscle-fibres, which generally contract
slowly and rhythmically, as exemplified in the regular and periodic
movements of many of the internal organs.

The Voluntary or Pseudo-stri.ate Muscles in the mollusca are
chiefly retractors, but also embrace the integumental muscles, tlie
protractors, the levators and the extensors, but the protractor and
other muscles are in their action usually subsidiary to concentrated
blood pressure in causing the
protrusion of the extensible or-
gans of the body.

In the mollusca, the Voluntary
muscles show transverse granu-
lation or are entwined by spiral fibrillm which give to the muscular
filaments a striated aspect. This incipient transverse striation is
especially characteristic of molluscan voluntary muscle, being pre-
sent in the buccal mass of many Gastropods, and in the adductors of
the Pelecypoda. It is the biological expression and mechanical
result of their increased function and of the numerous waves of
contraction of the muscle substance, as the striation is incomplete

Fig. 633. — Unstriated muscle fibre
from foot of Neritina Jiuviatilis
(L.), highly magnified (after Boll).

Fig. 634. — Pseudo-striate muscle fibre from
buccal bulb of N'l’f'itina /Juviatilis highly
magnified (after Boll).

COLUMELLAR MUSCLE.

342

or wanting in .slnggisli mollnsks, and most prononnced in tlie
more active forms.

Tlie general cliaracter of tlie muscnlatnro of tlie molliisca is, in a
great measure, dependent upon the development of a protecting shell,
which furnishes a firm attachment to the great retractor muscle.s of
the body, hy whose action the animal is withdrawn within its .shelter,
the columellar muscle of the Gastropods apparently representing the
more nnmerons retractors of the Pelecypoda.

The Columellar i\luscLE in the testaceons Gastropods is the
principal retractor of the body, its presence being typically correlated
with the possession of an external shell into which the body may be
wholly or jjartially withdrawn for protection ; it also constitntes the
sole connection between the animal ami its shell, the muscle being
organically tixeil to tbe .shell-axis or columella and running forward
beneath the resi)iratory cavity, the constituent glistening Avhite fibres
dividing and becoming distally distributed among and interlacing with
the mnscnlatnre of the foot, chiefly in the longitudinal median region ;
it also gives off from its npi)er surface subsidiary yet powerful
anteriorly-directed muscular strands which are known as the cephalic
retractors.

d'he Cei’iialio Retractors (K£</jaA/;, the head) form a very impor-
tant part of the musculature of the body, the constituent parts being

distinguished as Pharyngeal orTentacnlar
retractors, according tn the function they
discharge.

'riie Pharyngeal or Buccal retractors
are always median and may be formed of
paired and slightly divergent muscular
slips or of a more powerful single
muscle, but they always pass through
the nerve ring to become fixed to the
buccal bulb by divided or by simply
expanded extremities.

The Tentacular retractors are always
l)aired, corresponding muscles being pre-
sent for the right and the left sides of
the body, which may be united posteriorly with the great colnmellar
muscle or, as in certain of the nude species, may arise inde^ien-
dently from the integument. They also exhibit special minor

Fig. G35. — Cephalic retractors of
.-i ma/ia (l)rap.) X 2, showing
the airangement of the pharyngeal
and tentacular retractor muscles.

/. pharyngeal retractors ; /. tenta-
cular retractors.

CEPHALIC RETRACTORS — DICHORHIZA AND MONORHIZA. 343

features which are more or less specifically or generically charac-
teristic, the retractor of the right ommatoi)hore, in many species,
passing between and separating the penis and the vagina, while the
retractor of the right lower tentacle passes beneath the penis, which
is thus confined within the loop the retractors form.

Although the cephalic retractors are less specialized in the Strep-
tonenra than in the Stylommatophora, yet the coluniellar retractor
in the former group exhibits a special modification, due to the pre-
sence of the operculum upon the dorsal surface of the foot, the latter,
however, in coiTelation with the acquirement of paired invaginable
tentacula, exhibit greater complexity anteriorly, the tentacular
muscles functioning for the independent or collective withdrawal of
these organs within the body; more delicate muscular strands may
also be given ofi’ to other organs to facilitate their retraction.

The cephalic muscles vary in complexity and may for the purposes
of .study be divided into three groups : Dichorhiza, Monorhiza, and
Trichorhiza, based upon the number of their points of attachment to
the columellar muscle or to tlie integument in the nude .species.

The Dichorhiza fii i)arts ; a root) or two-muscled

species exhibit the simplest form of cephalic musculature posse.ssed
by our Gastropoda, and would appear
to be especially characteristic of the
Streptoneura and the Basommatophora,
being quite deficient of any trace of
tentacular retractors in correlation with
their possession of n on-retractile ten-
tacles; the pharyngeal retractors, which
alone are present, are two distinctly
separated muscular strands, arising from
the great columellar muscle and affixed
to the buccal bulb. In the Basommato-
phora the penial retractors may also
emanate from the columellar muscle
near the same spot.

The Monorhiza (/xdi'o?, single ; p'i(a, a root) are those forms in
which the muscles for the retraction of the head, tentacles and
adjacent organs are combined together medially to form a common
stem at their point of origin from the columellar muscle. This group
embraces tlie Helices, certain Ihjalinkv, and the genera Amalia,

Fig. 636. — Cephalic retractors of
Liptincca (MiiU.), X 3, illus-

trating the section Dichorhiza, and
incidentally .'showing the origin and
character of the penial retractors.

c.m. columellar muscle ; p.r.
pharyngeal retractors ; r. penial re-
tractor; p.s. penis sheath ; v.d, vas
deferens.

844

CEPHALIC RETRACTORS — TRICHORHIZA.

Advioliimur, Lhud.v, Siicciiiea, etc., and in respect to this portion of
tlieir organization these genera are less highly specialized than Ar/oii,
Tc:<f<a-eUn, etc, which ai)pertain to the groiq) 'I’richorhiza.

The tentacular retractors are uppermost
and originate mo.st posteriorly upon the
eohunellar innsele, and in some species
midway in their course give off mnscular
strands to the anterior region of the foot.

Before reaching the base of the tentacles
each muscle divides, the larger branch enter-
ing the ni)per tentacles or ommatophores,
while the smaller one enters the lower or
anterior tentacles, dividing again in most
species before doing so and sending a branch
to the labial lobe. In Sncc/um the labial
retractors are absent, but the lower tenta-
cnlar retractor at the right side gives off a
short stout muscle, which is attached to
and acts as a sid)sidiary retractor to the penis-sheath.

The pharyngeal or hnccal retractor is the median muscle and passes
through the nerve-ring, becoming attached at one or more points to
the buccal bulb; it may, as in Sacclnea, be cleft to its base or, as is
more usual, form a single strand which divides or merely dilates at its
attachment to the buccal bulb.

The Trichorhiza (rptx'), in three parts ; a root) or species
with three distinct pro.ximal muscular
attachments embrace Testace/ht, Arlon,
and certain The muscle

strands in tho.se .s})ecies pos.sessing well
developed shells, as Ilijd/lnld, arise from
the great eohunellar retractor, the
}»haryngeal muscle always having the
mo.st posterior origin upon it, differing
in this respect from the group Monorhiza,
in which it usually has a more anterior
origin. In the Arionidw, etc., the
proximal terminations of the pharyngeal
and tentacular retractors are affixed separately to the integument
in the rear of the resi)iratory cavity, the pharyngeal retractor is

Fig. 638. — Cephalic retractors of
Arion suh/uscus Drap. X 3, illustrat-
ing the section Trichorhiza.

/. pharyngeal retractor ; t. tenta-
cular retractors.

I ■

! ^

j -

' A

Fig. 637. — Cephalic retractors
of Limax maxbnus L., X 2,
showing their common origin
from the vestigial columellar
muscle, and illustrating the
section Monorhiza.

/. pharyngeal retractor ; i,
tentacular retractors.

ADDUCTORS.

345

deeply cleft and arises to the right of the median line but posterior
to the origin of the tentacular retractors.

Many differences in detail chai'actei’ize the muscular arrangements
of each group, Testacella in certain of its species developing a paired
series of lateral muscles to the lingual sheath, which augment the
contractile power of the terminal pharyngeal retractor, whose attach-
ment has been transferred to the lingual sheath in correlation with
its great development.

In the Pelecypoda the muscular system is strikingly symmetrical
in accordance with their general organization, and consists chiefly of
Adductors and Retractors, with other less important muscles having
protractor or other functions.

The Adductors {ad, to; duco, I lead) are the very thick and power-
ful muscular pillars which connect together and close the valves of
the shell of the Pelecypoda ; they are considered to originate as modifi-
cations of the pallial musculature, and each muscle has its opposite
ends attached to con-esponding areas of the concave internal surfaces
of the right and left valves, their places of attachment being shown
by the more or less perceptible scars or impressions left thereon,
which vary in size and distinctness according to the age of the animal.

The adductors have long been utilized for facilitating the classifica-
tion of the Pelecypoda, and although their employment for this
purpose is not now so fashionable as that of certain other organs of
the body, yet if reasonable allowance be made for aberrant or
specialized forms, and probably less allowance than required by other
modes of arrangement, they remain as valuable and reliable for the
purpose as any, furnishing also data for the phylogenetic history of
the group and marshalling together the most nearly allied species.

According to the number and relative development of the adductors
the Pelecypoda are divided into three groups : the Isomya or Dimya,
the Heteromya, and Monomya.

The Isomya (hVos, equal ; pi’s, muscle) is represented by Anodonta
and other of our species, and possesses paired adductors aiqn'oxi-
mately equal in size; the Heteromya (erepos, different; pi's, muscle) to
which gToup our Dreissensia belongs has two unequal muscles, the
anterior one being in process of degeneration and often conspicu-
ously smaller than the more centrally placed posterior one and
tending to occupy a more and more anterior and less functionally
important position in proportion to the enlargement and centraliza-

346

KETRAPTORS IN PELECYPODA.

tion of the posterior adductor ; while iii the IMonomya (/xoros, one ;
/ii's, niuscde) of which tlie (t3'ster is an example, the anterior adductor
has become completely atrophie<l and lost, the enlarged posterior
adductor assuming a more central position in the shell.

The adductors are distinguished as Anterior and Posterior, terms
expressive of their relative positions in reference to that of the
animal inhabitant.

The Anterior adductor is most dor, sal in position and placed in
front of and in constant association with the mouth, and is the first

developed in the embryo, the more
ventrally placed Posterior adductor
being ventral to the rectum with which
it is always in close relation ajipear-
iiig later, but their ])oints of fixation
to the shell gradually become more
and more ventral in correlation with
the growth of the shell, their hulk
also correspondingly increasing, the

Kig. 630. — Em})ryo of Anodonta seen
from the left side, enlarijed (after Gutte),
showing the early origin of the anterior
adductor.

a. a. anterior adductor ; hi. blastopore ;
c. ciliated area ; sh, shell.

newly-formed portion being generally distingui.shable by its lighter
colour.

The adductors act by closing the valves of the shell, a poidion of
their substance lieing composed of involuntary or smooth muscle
fibres, and the residue may he the pseudo-striate fibres characteristic
of molluscan voluntary muscle ; the valves, owing to the antagonistic
action of the ligament, tend to remain slightly oj)en when the
muscles relax, this position being their state of rest or equilibrium.

The strength of the adductors is very great and, in certain cases,
tliej' have been known to resist a force many thou, sand times greater
than the weight of the animal it,self.

The liETRACToRS of the Pelecypoda are symmetrically arranged
and paired muscles, strongly attached to corresponding areas of the
concave inner surface of each valve of the shell, on which they leave
l)ermanent traces of their i)re,sence in the form of scars, the constituent
fibres being distribiued within the foot or other organs to which they
may belong. In the archaic genus Nucula, the retractors emanate
as usual from each valve and form an almost continuous series of
muscular bundles between the adductors, but in more .specialized
forms thej" become concentrated, each muscle occupying a definitely
circumscribed area of the shell surface.

LOCOMOTION IN GASTROPODS.

847

In our Lsomyate species tlie pedal retractors, which serve for the
withdrawal of the foot, consist of two pairs of powerful muscles,
aftixed to the right and left valves at opposite ends of the shell, near
to or continuous with the adductors, and distinguished as the Anterior
or Posterior pedal retractors, according to the position they occupy.
In some exotic Monomyate species, as Pecten, the right and left pedal

Fig. 640. — Left valve Aiiodonta cygnea (L.), showing the position and character of the pedal
musculature and the arrangement of the adductors characteristic of the Isomya.

a.a. anterior adductor ; p.a. posterior adductor ; a.r. anterior retractor of the foot ; /.r. posterior
retractor ; ti,r. umbonal retractors or pedal levators; a.p. anterior protractors ; /. foot.

retractors are both affixed to the left valve and not eiiually distributed
to both as is usual, or as in the byssiferous species the posterior
retractors may, owing to the degeneracy of the foot, become trans-
formed into the byssal retractors.

In Dreissensia, our only representative of Heteromya, the anterior
pedal retractors are greatly attenuated and distally fixed to the

umbonal region of the shell,
the constituent fibres being
distributed to the anterior
base of the foot. The
posterior retractors are
correspondingly enlarged,
attaining a comparatively
enormous size, their posi-
tion being indicated by an indistinct oblong scar of attachment near
the superior margin of the valves and anterior to the scar of the
posterior adductor; they have, however, become partially transformed
into byssal retractors.

The Locomotion or progi-ession of terrestrial testaceous Gastropods
is more tedious and laborious than that of the a(iuatic forms, owing

Fig. 641. — Left valve of Drc’issfns/a polymorpha
(Pallas), showing the muscular system characteristic of
a byssiferous Heteromyan.

a.a. anterior adductor : p.a. posterior adductor ; a.7‘.
anterior pedal retractor; p.r. posterior pedal retractor,
also functioning as retractor of the byssus.

34S

LOCOMOTION — RATE OF PROGRESSION.

Fig. G12. Fig. 013.

Schematic figures, showing the arrangement of the extensile
locomotory muscles and of the varioiiNly distributed contractile
fibres of the Helt.x foot (after Simrolh).

Fig. 042. — Plan of the distribution of the muscular fibres as
seen from above.

Fig. 043. — Diagrant of the arrangement of the locomotory
muscles as viewed laterally.

to the weiglit of the lioily and shell being greater in air tlian in
water.

(xastropods generally move with a true gliding motion, the foot-sole
being continually adherent to the .surface upon which they are crawling
and not alternately loosened and re-applied thereto.

The locomotory muscles consists of longitudinal, transverse and
ohliipie fibres, closely interlaced with the somatic pedal musculature.
The obliipie contractile fibres shorten the foot and cause the lateral
bending, the longitudinal fibres being extensile and constituting

the true locomotory
muscles ; they are
stimulated into ac-
tivity by the action
of the pedal ganglia
and nerves, the intri-
cate plexus of sympa-
thetic pedal nerves
which rhythmically
continue the locomotory muscular action, creating a series of suc-
cessive and distinctly perceptible waves of contraction and e.xtension,
flowing over the foot-sole from behind, forwards ; and although the
continuance of locomotory effort is governed by the rhythmical
action of the sympathetic system, yet the rate of motion is mani-
festly shown to be under the control of the animal by their varying
rates of progress and by the differing numbers of locomotory waves
passing over the ventral surface of the foot. During the course of
a brief summer evening’s study of this feature, in a .specimen of
Helix nemoraUs, at a temperature of 63° Fahr., I noted 50, 42, and
36 ofthe.se undulatory muscular waves per minute.

The rate of progression in Gastropods varies in accord with the
environment, with the size of the animal and in corre.spondence with
the shape and area of the locomotory disc, those species with long
and narrow locomotory areas having greater powers of progression
than tho.se possessing a broad and short foot, and smaller species
being relatively more active than those of larger size.

The Limaces, in which the locomotory muscular fibres are restricted
to the median longitudinal third of the foot-sole, are the most active
forms, travelling 13 to 14 centimetres per minute or at the rate of a
mile in about eight days.

LOCOMOTION — RATE OF PROGRESSION.

.849

In the Helices and other terrestrial genera the locoinotory disc
presents a greater and more varied proportional area, and the rate
of progress varies considerably in the different species, the smaller
forms being relatively or even actually more nimble than the larger
ones. Helix cantiaim travelling 75 millimetres or more per minute
upon a horizontal surface or at the rate of a mile in about 14 days
16 hours, a rate which is not exceeded by even Helix aspersa.

Cyclostoma elegans, to avoid or overcome the frictional resistance of
close contact with the soil, while crawling, alternately raises from the
ground and extends forward each lateral half of its longitudinally
divided foot, seeking also to aid its progress by the accessory fixation
of the snout, which is moistened by the secretion of special mucus
glands, and yet it scarcely progresses 25 millimetres per minute, or
at the rate of a mile m 44 days.

The aquatic branchiate species crawl upon the bed of the waters
they inhabit or over and upon submerged objects, and although the
greater density of water renders the weight of their shell less burthen-
some than it would be upon land, their average progress is but about
25 millimetres per minute or a mile in 44 days.

The Basommatophora, in addition to peregTinatious upon the bed
of the stream or pond, can by virtue of their greater buoyancy, due
to the air within the respiratory cavity, float upon the surface and
crawl with inverted shell upon the under side of the water-film by
the successive undulations of the foot-sole as in the terrestrial species,
these undulations being recorded by the transversely ridged mucous
track left behind upon the surface of the water (fig. 607, p. 316);
their progress is, however, aided by the strong vibratile cilia clothing
the tentacles and the margins of the head and body and is stated to
average 50 millimetres per minute or a mile in 22 days, although
Ancyliis Jluviatilis has been recorded to travel only a little more
than one millimetre per minute, or a mile in 2 years and 10 months.

Special observation at a temperature of 66° Fahr. showed that a
moderate sized Limncca peregra could crawl 75 millimetres per
minute or a mile in 14 days 16 hours, while a half-grown Planorbis
corneus, under similar conditions, accomplished 88 millimetres in
the same space of time or a mile in 1 2 days 1 1 hours.

The Pelecypoda are very sluggish in their movements, the hatchet-
shaped foot being more especially adapted for ploughing through sand
and mud, and pi’obably thereby disturbing the minute organisms

350

REPRODUCTIVE SYSTEM.

upon which they feed. In other cases the foot may be sjn’ead out
laterally and form a disc.

iMessrs. Bo3’cott and Bowell have, however, recorded that the Unto
m((rg((rit'ifer progresses 15 feet i)er day, or about 3 millimetres per
minute, and a mile in 352 daj'S.

The most sluggish of onr species is the adult Dreissensia, which
becomes tixed bv its byssns to some suitable spot for considerable
periods, this inactive adult life is compensated for by the activity of
the young, which are free swimmers in their larval stage.

Within certain limits, snails can carry considerable weights without
l)erceptibly imi)eding their rate of progress, showing that ordinarily
they do not make full use of the strength they possess, certain Helices
having been demonstrated to be able to travel on a horizontal surface
with a weight tifty times their own, or ascend vertically, burthened
with a weight nine times that of the weight of animal and shell com-
hined. iNlr. 11. Crowther has also experimentally demonstrated that
Heliv aspersa can, even when loaded with a weight of 50 grammes
(gi’amme= 15 '432 grains) ascend a vertical glass plate at a speed of
seven millimetres per minute, but when the weight was increased
to G8'9 grammes, the animal though able to raise the load, could
not progress ; while Jleli.v (irhusturum, whose foot area is barely
eight inches, has, under the same conditions, ascended at a similar
speed with a weight of <sj- grammes, hut a weight of 8| grammes was
heyond its strength, as the animal was (pdte unable to raise the
hnrthen and slijjped off the glass.

The Reproductive or Sexual System in the mollusca is very varied
in the character and complexity of its component jiarts, the simpler
the organizatimi the fewer the sexual characters exhibited, while
sexual differentiation is naturally most iwoiiounced in the most highly
organized types, and although all organisms tend to vary in an
intinite variety of ways, the different organs are not e(iually affected
nor do they undergo modifications in a similar way nor in an e(|ual
degree.

The sexual organs at ordinary times are only normally of moderate
bulk, but at the approach of the pairing season they become turgid
and increase vastly in size, often occnjiying the greater jiart of the
body cavity. This iiairing season is not the same for all .species, but
si)ring is perhaps the most favoured season, the reproductive organs
at that period being pre-eminently noteworthy for the great abun-

REPRODUCTIVE SYSTEM — DIOiCIA.

351

(Umce of large glycogen-bearing plasma shells by which they are so
densely enveloped, this feature being most strikingly displayed by
their accumulation among and around the constituent follicles of the
germ glands ; their presence being clearly concerned in the provi-
sioning and maturation of the ova and spermatozoa, as the store
around the germ glands and sexual organs generally becomes
exhausted during the reproductive season.

Although reproductive power is usually associated with the attain-
ment of full gTOwth, it is well established that sexual maturity, with
power to perpetuate their kind, is often fully acquired by individuals
whose shells are far from being completely grown and therefore quite
destitute of the usual adult characters.

The male organs fiequently mature somewhat in advance of those
of the female, constituting Proter.yndry (tt/dwtos, first ; arqp, male)
or more rarely, as in AgrioUmdx kvvis, may exhibit Proterogyny
-po>ro<;, first ; yvyT), female), the female organs first accpiring func-
tional perfection. In many of the Stylommatophora, however. Prof.
Babor has verified that the genital organs almost invariably undergo
a series of successive metamorphoses, in which the animals are first
functionally unisexual and only subsequently become hermaphrodite ;
this condition, however, is not always the termination of their sexual
development, as the same animal may again become unisexual, by
the atrophy of the sexual organs first developed and the retention of
those acquired later.

In accordance with their sexual characteristics, the mollusca fall
naturally into two great groups, Dioecia and Monmcia.

The Dkecia (Si'w, two ; otKo?, house) or rnisexual species comprise
the great majority of the mollusca, and include all the Chitons and
Cephalopods, and nearly all Pelecypods and Streptoneura.

This group is especially composed of the simply organized or
primitive species and of certain of the more active and highly
specialized groups, the sexual organs being often so simple and
undifferentiated, and so similar in the two sexes as to be undis-
tinguishable except by microscopic examination, often consisting
merely of a genital gland or glands, composed of ramified aggregations
of cceca of simple structure, and a duct or ducts leading therefrom
and opening within the exhalent chamber in the Pelecypoda or
directly to the exterior immediately behind and near to the anus
in the Aphalliate Gastropoda.

DICECIA — APHALLIA AND EXOPHALLIA.

So2

Tliese genital ducts may be special, or the nepliridial ducts may be
utilized, the genital products falling into the kidneys direct or by
way of the pericardium and thence conveyed to the exterior.

The Dicecia for convenience of study may be classified as Ajdiallia,
Exophallia, and Cryptophallia.

The Apiiallia (a, not ; (/xiXAos, penis) are characterized by the
absence of any organ by which copulation can be accomplished, the
reproductive organs simply consisting of a paired ovary or testis, and
the ducts leading therefrom to the exterior, no accessory organs are
developed, the Si)ermatozoa being simply shed by the male into the
circumambient water and some making their way to the ova or to the
oviducal tract of the female ; this organization is possessed by all
the Dioecious Pelecypoda, the Ghitonidar, and many of the more
archaic Diotocardiate Gastropods. There is little sexual dimorphism
displayed, but the female of Unio tumidus is said to develop a broader
.shell than that of the male.

The Exophallia (e^o, external; (fiuXXo'i, penis) embrace those
dioecious species in which the
males have acquired an ex-
ternal copulatory organ, pro-
jecting freely from the right side
of the neck and arising as a
muscular outgrowth from the
body-wall ; it may be as a
dependence of the head as in
I'ir/jHtnt, etc., of the mantle as
in .1 mpullarhi, or of the foot as
in the generality of species.

It is strongly erectile and
extensile by concentrated blood
l)ressure, and though not
eversible and retractile as in
the Gryptoi)hallia, it can often
be bent in a sigmoid form and
hidden beneath the mantle
folds, the spermatozoa being conveyed thereto, in the more primi-
tive forms, in which the male organ is a solid and thick appendage,
liy an open ciliated duct ; in more highly organize<l forms this duct
becomes closed and included within the body, and constitutes the

Fig. GI4. Fig. 645.

Fig. 644. — Male reproductive organs of Cycle-
stoina clegans x .3, illustrating the

organization of the Diccciate E.xophallia.

p. penis ; v.d. vas deferens ; t. testis ; pr,
prostate.

Fig. C45. — Female reproductive organs of
Cyclostoma elegans (Mull.), X 3 (the indistinct
and only partially separated spermatheca is not
shown).

ov. ovary ; 7ti. sacculated or glandular oviduct ;
V. vagina ; <?. female orifice.

DKECIA — CRYPTOPIIALLIA.

353

vas deferens, which may widen into a seminal glandular vesicle or
prostate in some part of its course.

The female organs develop) an albumen gland, a glandular sacculate
oviduct and a more or less definite spermatheca or vesicle to receive
the fertilizing spermatozoa. All our dioecious Streptoneures, except
Neritina and Vivipara, are exophalliate, Cydostoma, Bithynia, etc.,
being examples. There is also sometimes a certain degree of external
sexual dimorphism, the male possessing a slenderer form and a per-
manently projecting male organ, and the female being larger and
relatively more turgid. In some genera this dimorphism is variously
displayed, by Littorina at the mouth of the shell, by Cerithium in the
operculum, by Nassa in the radula, etc.

The Cryptophallia (k^wtos, hidden; c^aXAos, penis) are in the
Dicecia restricted in this country to Neritina Jluviatilis, in which
the male copulatory organ is stated to be retractile within a penis
sheath capable of withdrawal
into the body cavity, as in the
Pulmonata, although Vivipara
may also be regarded as
belonging to this group, as the
contractile male organ is con-
cealed within the right teirtacle,
which is sensibly deformed
thereby.

The general character of the
organization of the dioecious
Cryptophalliate Gastropods is
not, however, sensibly diver-
gent from the usual dioecious
type, and only differs from the
Exophallia by the retractibility
of the male organ, although the
vas deferens is of an enormous
length, the prostatic portion of
its course being combined into
a large compact mass upon the
penis sheath, a similar concen-
tration of the prostate, however, exists in Vivipara, Cydostoma, and
even in Siicdnea.

Fig. 6i6. Fig. 647.

Fig. 616. — Male reproductive organs of Ncri-
ti7ia Jluviatilis X 4 (after Moquin-Tandon),
illustrating the Diosciate Cryptophallia.

t, testis; v.cl. vas deferens or sperm duct with
enlarged sperm vesicle or epididymis efi. ; pr.
prostate ; p.s. penis sheath ; 7n.o, male orifice.

Fig. 617. — Female reproductive organs of Neri-
tina Jluviatilis {hj, X 4 (after Moquin-Tandon).

0. ovary ; ov. oviduct ; alb. gl. albumen gland ;
sp. spermatheca ; zU. uterus or matrix ; v. vagina ;
f.o. temale orifice.

20/3/1900

X

354

MON(ECIA — APHALLIA AND EXOPHALLIA.

The Moncecia (fiovos, one ; olkos, house) in which group both sexes
are combined in the same individual, is in its lowest forms, except in
this respect, very little different from the Dioecia ; still in addition to
the combination of both sets of organs, the group generally shows
greater specialization and a remarkable development of accessory
sexual organs. Hermaphroditism, according to Pelseneer, appears to
be due to the grafting or superposition of the male system npon that
of the female, and to have been apparently inflnenced in this direction
by the adoption of terrestrial or fluviatile habits or parasitism.

The increased bulk and complexity of the sexual organization, owing
to the combination of the male and female organs within the body of
each individual and the number of highly differentiated accessories
that have been developed, is so marked that the greater part of the
body cavity is occupied by them, especially during the pairing season,
wlien they appear to dominate the whole organism.

Yet, although both sexes are thus combined in each individual, the
hermaphroditism is not complete, as conjugation with a second indi-
vidual is normally always essential to ensure the fertilization of the
ova and the development of the offspring.

For the purposes of study, the Monoccia,like the Dioccia,may be sepa-
rated into three chief groups : Aphallia, Exophallia, and Cryptophallia.

The Aphallia (<i, not ; c/jaAAos, penis) are restricted to the Pelecy-
poda in general, and include a few genera more especially fluviatile
in habit, as Sp/ucriam, Pisidium, and certain species of Unionidw ;
they, however, differ little from the Aphalliate Dimcia, e.xcepting that
both tlie sexual elements are developed within the same individual,
though the male and female gonads may occupy, as in the Spliceriidw ,
separate regions of the body, but as the ova and sperm are not
usually developed simultaneously, the difficulty of appreciating their
l)eculiarities is considerably increased especially when but one excre-
tory duct is present.

The Exophallia (f^o, external ; </)aAAo?, penis) are also closely
similar to their Exo})halliate Dioecious kindred, except for the com-
bination of male and female sexual organs within the body cavity of
each individual, and tlie increase in number and complication of
the su])plenientary organs. The Monocciate Exophallia are few
in number, our only representatives being the species of the genus
Valmta, in which group a primitive simplicity of general organization
persists in spite of the acciuirement of the hermaphrodite sexual

MOXCECIA — CRYPTOPHALLIA.

355

combination, shown by the reten-
tion of the permanently projecting
male copulatory organ, distinguish-
ing other Streptoneures, Valmta
not having acquired the retractile
penis characteristic of most herma-
phrodite species.

The Cryptophalli A (kpvttto^,
hidden ; ^aAAos, penis) are charac-
terized by the possession of a
male conjugatory organ, which is
suiTounded or enclosed by a pro-
tecting sheath completely retractile
within the body cavity, and also
exhibiting a great accession and
complexity of accessory organs.

The Ciyptophallia in accordance
with the separation or comhination of the apertures of the male and
female system of organs, may be subdivided into two groups :
Ditremata and Monotremata.

Fig. 6i8. — Reproductive organs of yaivata
x4(after Bernard), illustra-
ting the Monoeciate Exophallia.

ot. ovotestis ; k.d. hermaphrodite duct ; /r.
prostate ; v.d. vas deferens ; p. penis ; a7>. o\'i
duct ; c.p. copulatory pouch or sperinatheca
the uterus of Pelseneer ; a.g. albumen gland
the spermatheca of Pelseneer; ac.gl. acces
sory shell gland, the albumen gland of Pel
seneer \/.o, female orifice.

The Ditremata (Si'oj, two ; Tpqp-a.,
cavity) comprise the Limnceidcc
and Carychiidce and are charac-
terized by the marked separation
of the male and female orifices ;
the male aperture is placed beneath
the tentacle upon the right side of
the neck in the dextral species,
and on the left side in those sinis-
trally coiled ; the female aperture
being situated beneath the mantle-
flap in the pallial region on the
same side of the body but com-
paratively remote from the male
aperture.

This position of the female
genital aperture is a survival of
the archaic arrangement found in
some of the Diotocardia in which

Fig. 649. — Reproductive organs of Zzwwtf'a
stagnalis (L.), x2, illustrating the Monceciate
Ditremata.

ovt. ovotestis ; pr. prostate ; v.d. vas
deferens ; p. penis ; ret. penis retractors ;
p.s, penis sheath with its protractors ; >n.a.
male aperture ; alb.gl. albumen gland ; n.gl.
nidamental gland ; ut. uterus ; ero. oviduct ;
sp. spermatheca ; vag. vagina ; f.o. female
orifice.

MONCECIA — MONOTREMATA.

3oG

the sexual products of botli sexes are expelled by ducts opening from
the pallial region, a position still retained by the female aperture in
this group. There is also a gi’eater complexity and differentiation
of the albuminous glandular part of the female system, probably in
correlation with the albuminous mass within which the eggs of the
Limnccldiv are deposited.

The Monotremata (judros, single ; ’rp"]p-n, cavity) embrace those
bermapbrodite species in wbicb both male and female organs open
exteriorly by a common o,perture ; they exhibit the highest organiza-
tion attained by the sexual organs in the species within the sphere
of our studies aciiuiring a greater complexity and wealth of acces-
sory organs. The external aperture, though common to both series
of organs, yet during extrusion exhibits a terminal female opening
and a masculine lateral one.

For convenience of study the Monotremata may be separated into
three groups ; Haplogama, Gynogama, and Belogama.

The Haplogama (d7rA.oi's', simple; ydpo^;, marriage) are the most
simply organized of the j\Ionotremata, establishing them as regards
their genitalia to be the most ancient
type ; their organization comprising on
the male side the ovotestis, the her-
maphrodite duct which ends in a
coecum at the base of the ample albu-
men gland, the prostatic tract which is
adherent to the glandular oviduct,
but later becomes free as the vas
deferens, and joining the penis which
is enclosed by a sheath, to which a
retractor muscle is affixed. The
female organs embrace the ovotestis,
the oviduct, and the vagina, where
the .spermatlieca usually opens.

Except for the presence of an
appendix as an adjunct to the penis
in certain species, and which may
possibly be a relic of a primitive flagellum, such as is still per-
sistent in liit/iyiiid and other groups, and of a so-called appendicula
on the female side, there are no accessory organs such as those
developed in the Stylogama.

F IG. 650. — Reproductive organs of Zua
Itibrica (Miill.), X 12 (after Ihering), illus-
trating the Cryptophalliate Haplogama.

s.d. sperm duct; ZKd, vas deferens;
p.s. penis sheath; r. retractor muscle;
ap. appendix ; a.^. albumen gland ;

OIK glandular oviduct ; sp. spermatheca ;
V. vestibule ; v.gL vaginal gland.

MONCECIA— GYNOGAMA AND STYLOGAMA.

357

Fig.

of

651. — Reproductive organs
Arion horiensis F^r., X 2, illustrating
the Cryptophalliate Gynogama.

<?/.ovotestis ; h.d. hermaphrodite duct ;
pr. prostate ; v.d. vas deferens ; ep.
epiphallus ; a.g. albumen gland ; ov,
sacculated or glandular oviduct ; sp,
spermatheca ; z>ag. vagina ; at, atrium ;
v.g. vestibular gland ; r.;;?. retractor

muscles attached to spermatheca and
vagina.

The Gynogama (yw-i], female ; ya/j-os, marriage) are confined in
this country to the Ar'ionidw, and are particularly charactei’ized by
the atrophy and loss of the male
intromittent organ, and the transfer
of its function and retractor muscles
to the vagina and spermatheca which
usurp its function and are everted
during copulation, the male portion
being merely the amplified sperm
duct or epiphallus which moulds the
spermatozoa in the form of a sperma-
tophore for transference to the
copulatory pouch of its mate. The
atrium or vestibule which opens be-
neath the pulmonary orifice on the
right side of the body is enveloped by
a dense glandular pad which may
represent the digitate glands of the
Stylogama.

The Stylogama (srfAos, a rod; ydfj-o^, marriage) are the most
complexly organized of the ]\Iono-
tremata, often developing a number
of highly differentiated organs in
connection with the reproductive
function.

The female organs possess highly
specialized vaginal prostates or
vesiculm multifidse in the form of
ramified digitate glands, which are
usually paired and placed at each
side of the vagina, into which they
open ; the number of these glan-
dular digitations varies greatly in
the diflferent species, or even in the
same species ; there may be few or,
as in Helix pomatia, they may,
though vaiying greatly individually
reach thirty or forty digitations to
each gland.

Fig. 652. — Reproductive organs of Helix
lapicida L., X 2, illustrating the Crypto-
phalliate Stylogama.

ot. ovotestis ; h.d. hermaphrodite duct ;
p7\ prostate ; v.d. vas deferens ; Jl. flagellum;
ep. epiphallus; p.s. penis sheath; r. penial
retractor ; cn>. sacculate oviduct ; sp. sperma-
theca ; d. its diverticulum ; vi.g. digitate
mucus glands ; d.s. dart sac ; vag. vagina.

358

REPRODUCTIVE ORGANS— GONADS.

Near to the vaginal apertures of the digitate glands is the opening
of the Stylo]diore, or dart sac, which commonly consists of an ovoid
muscular sac within which is secreted a pointed calcareous spiculum
used in the preludes leading up to sexual conjugation.

The spermatheca or copulatory pouch often develops an additional
and more capacious diverticulum, which may attain a considerable
length, and usually receives the sperniatophore transferred during
copulation.

The male organs are chietly augmented by the development of
the dagellum, a blind glandular diverticulum at the distal end of the
l)enis sheath, within which or in an intermediate epiphallial tract
the sperniatophore is moulded; these spermatophoral tracts may be
separated from the penis sheath by a strong and outwardly visible
s})hincter muscle, or the separation may be less distinct.

The Reproductive System of the Dioeciate species have fewer con-
stituent parts than the gastropodous Monoecia, in which a variety of
auxiliary organs have been developed, sujiplementing or more perfectly
discharging the neces.sary functions in connection with reproduction.

The CfoNADS (yoi'os, seed) or germinal glands, the essential organs
of the sexual system, are paired and symmetrical in the Pelecypoda
but single in the Gastropoda. These organs possess a structureless
outer wall, the internal germinal epithelium being composed of
rounded cells, and derived from the walls of the cadomic or secondary
body cavity of which they form a more or less definite part.

In the Dimciate Gastropods and Pelecypods there are male gonads
or testes, producing only spermatozoa or zoosperms, and female
gonads or ovaries, producing eggs only, but in the ovotestis of the
Monoeciate or hermaphrodite species both eggs and spermatozoa may

Fig. G.).1. Fig. G54.

Fig. (U),!.— Ovotestis of Limnaa peregra (Miill.), X .1, showing its lobiilated arrangement.

Fig. (DI. — Ovotestis of Helix aspersa Miill., X 3, showing its sometimes tufted character.

be itroduced by the same gland, although in the hermaphrodite
Pelecypods Spharium, Pisidium, etc., the male and female gonads
are separated in two regions, an anterior male region and a female
more posterior one, with, however, a common efferent duct.

In the Gastropoda, the richly lobed and convergent diverticula
forming the gland vary greatly in their compactness and general

KEPRODUCTIVE SYSTEM — HERMAPHRODITE DUCT, ETC.

359

aspect and arrangement, and usually lie within the body cavity,
between the lobes of the digestive gland, with which its parts may be
intimately intermingled. In the Pelecypoda the paired gonads are
usually richly branched tubular or lobate masses, often occupying the
base of the visceral mass and permeating amongst the intestinal coils.

The Hermaphrodite Duct (‘iS'pp]?, Mercury ; A<Ppo8lti], Venus)
the conjoint canal of the ova and semen, is only found in the monoe-
cious species, originating at the ovotestis or hermaphrodite gland,
and terminating in the seminal vesicle at the base of the albumen
gland ; its swollen part is the epididymis of continental authors, but
the duct is very variable in its character and extent, it may be
voluminous, sinuously convoluted and deeply pigmented as in Suc-
cinea, simple and nearly straight as in Hyalinia, or beset with
numerous glandules along the greater part of its course as in many
of the Limnceidce.

The Seminal Vesicle {semen, seed; veskula,A\m. of m’/ca, a bladder)
or Claw, known also as the Epididymic coecum, is a variously formed

coecal diverticulum, situate at the base
of the concave side of the albumen
gland, to which it is closely apposed ;
it is sometimes constituted by a mere
swollen convolute termination of the
hermaphrodite duct, or, as in Succinea,
may be paired, and open with the albu-
men gland into a fertilizing cavity, but
in some species beneath the point
where the swollen portion is imbedded
in the albumen gland there is a lateral
tube bearing several blind ramifying
tubules lined with ciliate uugranulated
epithelium, which is lodged between
the ascending and the swollen de-
scending part of the efferent canal and in the adult contain living
spermatozoa which fertilize the ova before passing within the saccu-
lated and glandular oviduct.

The Albumen Gland {album, white) is an adjunct of the female
system, and is a light-coloured linguiform organ, convex behind
and concave in front, where the hermaphrodite duct terminates
in the seminal vesicle. The gland is very slightly adherent to the

Fig. 655, — Succinea elegans Risso, x 6,
showing the character and relationship of
the pigmented hermaphrodite duct, the
paired seminal vesicles, the albumen
gland, and the ovotestis.

a.g, albumen gland ; k.d. hermaphro-
dite duct ; ot. ovotestis ; v.s, seminal
vesicles.

3G0 REPRODUCTIVE ORGANS — SPERM DUCT AND VAS DEFERENS.

first part of the ovispermatoduct which may he hollowed for its
reception and with which it comninnicates. It varies in size, not
only according to the species but periodically, being very voluminous
at the pairing season, when it plentifully secretes a viscid albuminous
fluid containing globules and granular matter with which the descend-
ing ova become surrounded.

The Sperm Duct (a-kpiLa, seed) in the dioecious species originates at
the testis or male gonad, it is often of considerable length and may
follow a tortuous course, usually becoming differentiated as a pros-
tatic glandular enlargement in some part of
its course before reaching the male organ.

In the monoecious species there is a
combined conduit or hermaphrodite duct
which conveys both ova and sperm, the two
becoming separated at the seminal vesicle,
the ova following the oviduct, and receiv-
ing their store of albumen, etc., and the
zoosperms passing down the conjoint sperm
duct which is attached to the concave side
of the oviduct and beset with glandular follicles, forming a prostate,
which becomes greatly swollen at pairing times ; the separation between
the oviduct and sperm duct may be incomplete, as in Avion, in which
the two channels communicate along their whole combined course.

The Vas Deferens {vas, a vessel; defero, to carry away) is the
sperm conduit when freed from adherence to the oviduct and before
its arrival at the male organ ; on its course it may develop a seminal
sac, as in Limnau, or become enlarged near its termination, and
secrete the si)ermatophore, as in Hyalinia. In
some of the primitive Exophalliate Gastropods
the .sperm duct terminates externally in the
pallial region as in the Aphalliate species, but
in correlation with the development of an
external copulatory organ, an open ciliated
conduit became established, leading along the
side of the body from the pallial termination
of the sperm duct to the apex of the intro-
mittent male organ; this open duct hecame gradually enclosed within
the body, and now constitutes the vas deferens, a certain section of its
course even yet, however, retaining an intermuscular course beneath

Fig. 657. — Open ciliated
external sperm-duct of Peiia
coronata (highly magnified),
(after Pelseneer).

s.f. seminal furrow ; 7n.
mantle ; f. fool.

Fig. 60S. — Section through the
prosialic portion of sperm duct
Limmva /^w^r/I(^iull.), X 10,
showing its glandular character.

REPRODUCTIVE ORGANS — FLAGELLUM, ETC.

361

the integument. The primitive external spermatic groove present in
the ancestors of the Pulmonates, and still persisting in some Opistho-
hranchs, has left indication of its former presence and external position
in the lateral or genital groove connecting the pallial opening with the
reproductive orifice which is still found in so many species.

The Flagellum {flagellum, a whip-lash) is the blind diverticulum
often found in highly organized Gastropods as a prolongation of the
epiphallus or of the distal end of the penis-sheath, wherein is secreted

Fig. 658. — Male reproductive system of
Bithynia tentaculata (L.), X 6, showing the
semi-independent flagellum.

t. testis ; v.d. vas deferens terminating at
the apex of penis \fl. flagellum, opening in a
separate but subsidiary prominence thereon.

a sheath or case for the safer transfer of the seminal element to the
partner. It is very variously shaped, externally and internally, and
the spermatophore moulded within it is an exact reproduction or cast
of the shape and denticulations of the interior of the coecum.

In Bithynia and certain species of Streptoneura, as well as in
Ancyliis, the flagellum opens to the exterior more or less indepen-
dently of the penial orifice of the sperm duct, the orifice of the
flagellum in Bithynia being upon a subsidiary but distinct bilobation
of the penis ; an intermediate but interesting modification of this
form of flagellum is found in Buli-
miniis and Pupa, in which the flagel-
lum does not form a continuation of
the distal end of the penis-sheath as in
Helix, etc., but opens into the common
vestibule or into the lower part of the
penis sheath, and it would appear not
improbable that the appendix to the
penis-sheath of certain Gastropods is
homologous with this organ.

The Epiphallus (stti, upon ; <^aAAos,
penis) or Patronenstrecke, is merely an
enlargement of the anterior end of the
vas deferens, and includes the tract
between the outlet of the vas deferens
and penis, and has not usually a retractor muscle, nor is it evertible

Fig. 659. — Reproductive organs of
Bulimmus 7iiontanus (Drap.), X 3,
showing the epiphallus and also the
flagellum subsidiary to but proximally
connected with the penis.

albumen gland ; ot, ovotestis
h.d. hermaphrodite duct; ov, oviduct;
v, vagina ; JJ. flagellum ; v.d. vas defe-
rens ; ep. epiphallus ; p.s. penis sheath ;
r. retractor; sp. spermathecaand branch.

362

REPRODUCTIVE ORGANS — PENIS.

Its function in common with the flagellum is merely to accumu-
late and agglutinate the spermatozoa together or enclose them within
a Arm chitinous sheath or spermatophore which varies in its shape
according to the species.

The Penis (penis, a tail) is the masculine intromittent organ, and is
only developed in our fauna amongst the Gastropoda, always occupy-
ing the right side of the anterior part of the body in dextrally
organized individuals.

In the Streptoneura it is a permanently external outgrowth from
the boily-wall, and may he a dorsal development as in Cyclostoma,
with innervation by the sub-intestinal ganglion, a cephalic organ as
in Vivipara, a pedal organ as in Valvata, or a pallial organ as in
the exotic Ampullaria, their character being indicated by their
inneiTation.

The penis sheath to which the vas deferens conducts the spermatic
fluid encloses the male intromittent organ, which occupies the distal
end of the sac, and may he separated from the flagellum or epiphallial
tract by a constricting muscular annulus. The sheath is usually a
large somewhat fusiform or clavate sac, but assumes a gi’eat variety

m. m.

Fig. 6G0. Fig. G61. Fig 6G2

Fig. G60. — I’ak'ata (Miill.), X 2, showing the permanently projecting male organ.

Fig. G61.— Penis sheath of Helix ru/escciis Penn., opened to show the male intromittent
organ, X 12.

Fig. GG2. — Penis .sheath of Limneca /a/wi/Wi (Midi.), X 10, opened after pairing before com-
plete retraction, showing how the sac becomes the intromittent organ by eversion.

p. penis ; f.s. penis sheath ; v.d. vas deferens ; r. retractor muscle ; m.m. longitudinal muscular
pillars, possibly protractors and guides.

of shapes, and furnishes important characters utilized in classiflcation
and in the differentiation of species, affording in the Succinece a
ready means of separation between the doubtful intermediate speci-
mens connecting Siicclnea putris and S. elegans.

REPRODUCTIVE ORGANS — APPENDIX AND UTERUS.

363

From the naked and permanently external organ of the Strep to-
neures, many lines of variation have arisen, leading to the form
concealed within an ample sheath or sac and capable of retraction or
protrusion through the genital orifice, a form especially characteristic
of the Euthyneura ; or the typical intromittent organ may itself
become atrophied and its function be performed by the inversion of
the penis sheath as in many Limnww, while in the Arionidw the
sheath also becomes lost, the epiphallus opening directly into the
genital vestibule, and the intromittent function being relegated to
the vagina and spermatheca duct.

In Helix acuta the penis sheath contains a perforate calcareous
body to which the epiphallus and retractor are fixed. Our Zoni-
toides present a similar feature formed, however, by the apposition of
two calcareous but somewhat dissimilar hollowed or channeled plates.

Fig. 663. — Proximal portion of sexual
organs of Zonitoides excavata (Bean), X 10,
(from a photograph by Mr. W. Moss),
showing the position and character of the
calcareous penial plates and the organization
generally.

st. stylophore or dart sac, showing natural
position of dart and character and position
of the coronal gland, c.gl. ; p.s. penis sheath
with calcareous channeled plates; vag, vagina;
sp. bifid spermatheca duct.

a.g.

Fig. 664. — Reproductive organs of
Helix acuta Miill., X 2, more especially
to show the position and character of the
appendix.

a.g. albumen gland ; ot. ovotestis ;
h.d. hermaphrodite duct; ov. oviduct;
V. vagina ; s.d. sperm duct ; v.d. vas
deferens ; ep. epiphallus ; p.s. penis
sheath with retractor ; sp. spermatheca.

The Appendix is an external adjunct to the reproductive system,
opening into or near to the penis sheath ; its function is uncertain,
but I do not regard it as improbable that its affinities are with the
semi-independent flagellum found in Bithjnia, Buliminus, etc., and
other groups which have a similar position in relation to the penis.

The Uterus or Glandular Oviduct is the convolute and spacious
duct with sacculate glandular walls through which the ova pass after
fertilization, becoming well developed and surrounded by the secre-
tion of its walls. In the hermaphrodite species it is more or less
intimately united with the prostate or glandular sperm duct, from

364

REPRODUCTIVE ORGANS — VAGINA AND EGERSIDIA.

which it separates as the vagina, the sperm duct becoming the vas
deferens.

The Vagina (ir(g(na, a slieath) is the oviduct wlien freed from its
adherence to the glandular sperm duct; it then becomes more
muscular and contracted, and several auxiliary organs open into it,
the uppermost being the vaginal glands ; these may exist as a dense
investment surrounding the vagina, or in the more advanced forms
take the shape of a variable number of digitate or finger-shaped
tubes, which are usually paired and placed at either side of the
vaginal tube.

Tig. GGo. — Proximal portion of reproduc-
tive organs of llyalinia ai/iaria (Sillier),
X 6, showing the position and character of
the vaginal glands.

Fig. GG6. — Proximal portion of reproduc-
tive organs of Helix y-^i/escens Penn,, X 6,
showing the character and arrangement of
the paired digitate vaginal glands.

cn>, oviduct; 7'.gL vaginal glands; s.d.
sperm duct ; XKd, vas deferens ; p.s. penis
sheath ; sp. spermaiheca.

v.gL vaginal glands ; v, vagina with dart
sacs ; p s, penis sheath.

The vaginal glands discharge directly into the vaginal tract, or in
the case of the digitate glands may retain their secretions and dis-
charge the secreted contents as recpiired.

The Appendicula is an outgrowth of the female system, whose
particular function is as yet unknown, but it has been assumed to act
as a receptacle for spermatophores.

The Egersidia (eyepo-ts, an exciting, an awakening) are possessed
in various forms by widely different groups of mollusks and are
special organs whose function is to stimulate or excite sexual passion
or desire and thus include not only the fieshy “reizkorper” of the
Lhnacidw and the fully calcareous or chitinous love-darts of the
Helices and other genera, but any organ by whose actions amorous
feelings are encouraged.

Although so different in aspect and structure, the calcareous love-
dart and tlie flesliy rei/.kiirper are eiiually and simply excitatory
organs, and numerous intermediate forms exist linking them together,
all subserving the same purpose of producing or increasing the amo-
rous desire leading up to sexual congress, as the egersidia in their

REPRODUCTIVE ORGANS— SARCOBELUM.

365

typical form take no part in the true coupling, serving only as their
name implies to provoke that act.

Excitatory functions are not, however, a trait restricted to either
sex, as stimulatory adj uucts to both the male and female organs have
been demonstrated to exist, and it is probable that most mollusks
are provided with special stimulatory organs or possess some other
means of allurement or attraction to sexual union.

According to their character the excitatory organs may be grouped
under the two heads, Sarcobela and Gypsobela.

The Sarcobelum (a-apyo, flesh; /5eA.os, an arrow) or e.xcitatory organ,
the “reizkorper” of the Germans, “organ
excitateur” of the French, is usually a
soft and fleshy ling inform eversible pro-
cess, erectile by blood pressure, and
occasionally furnished with a harder cal-
careous point with which each animal
strokes, pats, and caresses its prospec-
tive partner during their amorous pre-
ludes. This organ is usually located
within the genital passage, near the
outlet, and may be cleft at the base for the passage of the copula-
tory organs.

Unlike the Gypsobelum, which is more particularly an adjunct to
the female system, the Sarcobelum is more especially, though not ex-
clusively, a masculine excitatory organ, and is usually present in the
form of an erectile muscular
appendage within the penis
sheath, as exemplified in
Agi-iolimax agrestis and
other species, but similar
alluring developments exist within the atrium of other species, occu-
pying an intermediate position between the two groups of organs in
the hermaphrodite species and not strictly supplementary to the
organs of either sex, or these stimulating appliances may, as in
Amalia, be slightly within the vagina or other feminine duct, and
really appertain to the female system.

In the Dioecious Viviparidw we find a probable prototype of the
Egersidium in the erectile fleshy appendage upon the inner walls of
the vaginal tube, which may be regarded as a primitive Clitoris or

Fig. 667. — Spermatheca duct of
Zua lubrzca{lsl\i\\.\ X 30, laid open
to show position and character of the
sarcobelum or excitatory organ (after
Ihering).

Fig. 668. — Ag^olzmax agrestis with its sarco-
belous excitatory organ protruding.

366

REPRODUCTIVE ORGANS — GYPSOBELUM.

feminine excitatory organ, perhaps derived from some earlier form
from which originated tlie diversely constituted egersidia of the

Stimulatory functions are, however, not
strictly confined to special egersidia, as the male
organ may itself hear at its apex a vibratile
appendage whose function is probably of an
excitatoiy character.

The Gypsobelum (yv'pov, lime; fieXos, an
arrow), love-dart, or Spiculum amoris, is essen-
tially a feminine stimulatory organ, and is a
slightly riexible, straight, curved, or even slightly twisted glistening-
white weapon, formed principally of carbonate of lime, and becoming
fragile and brittle when dry ; its free end terminates in a fine point,
and the enlarged base fits upon a conical tubercle at the bottom of
the ilart-sac.

The dart is formed very rapidly, the process usually occupying less
than a week; the shaft first a])poars as a slender spicule attached to
the apex of the tubercle, increasing simultaneously in length and
breadth, the blades which are moulded by the
walls of the sac being next formed, the conical
base and annulus being the last to be finished,
these are sometimes composed of numerous
longitudinal calcareous rods, resembling a
cricketer’s leg-guard, and crenulate at top and
bottom, the tubercle having corresponding
sulci, and projecting into the expanded base
of the dart.

The mode of usage of the dart does not yet seem to be universally
known; the old writers considered it to be a missile hurled by one

snail at another, and this mode
is still spoken of by some modern
writers, as though the dart was
launched through the air and
buried in the tissues of the com-
panion snail. The dart is fitted
upon the tubercle, attachment
being assisted by a viscid secretion which extends within the hollow
shaft of the dart itself, the dart being exserted for use by the eversion

Fig. 071.— Partial dissection of //c/i.r aspersa
Miill., showing portions of love-darts of previous
partners which have become lodged in the viscera.

Fig. 670. — Annulus of
dart of lli’li.v aspersa
Mull., X 3, with adherent
viscous secretion as left
after the loss of the dart.

various genera.

i

Fig. 060, — Terminal part
of male organ of Planorbis
fi7r//^/^,y(L.),greatly enlarged
(after Moquin • Tandon ),
showing the vibratile stimu-
latory appendage.

REPRODUCTn’E ORGANS — GYPS OBELTJM.

367

of the dart-sac, its exposed point being pressed against and slightly-
piercing the body of the companion snail.

Owing to the slight attachment to the tubercle the dart may he
lost during use, and fall to the ground, or become adherent to the
exserted organs, and be afterwards withdrawn with them into the body,
working its way amongst the organs, and eventually becoming lodged
in the viscera, as many as three darts have been found thus lodged
in the interior of the body of a single animal.

Great variation in form of the love-darts exists amongst even the
few teliferous Briti.sh species, and a scale or series of forms from
simple to complex may easily he constructed, showing the gradual
modifications leading from one type of dart to another, but a start-

© -0“

Fig. 672. Fig. 673.

Magnified diagrammatic sections of darts of certain species of British teliferous Gastro-
pods, showing the gradation from a simple to a complex structure.

Fig. 672. Helix hispida L. Fig. 673. Helix itala L.

Fig. 671. Helix aspersa Mull. Fig. 675. Helix pisana Mull.

lingly close affinity in the shape and general character of the dart is
exhibited by species distinctly different in general aspect, thus Helix
lapicida and Helix arhustorum have practically identical darts, those
of Helix aspersa and Helix nemoralis possess the same peculiarities,
and there are other remarkable approximations in the aspect of the
darts the animals of which, judged by their shells alone, are not very
intimately related.

Equally striking is the remarkably different darts sometimes
possessed by closely allied species, those of Helix nemoralis and
Helix hortensis being so remarkably distinct that doubtful inter-
mediate forms of these species can only be settled with absolute
certainty by their aid.

Schmidt affirms a correlation between the character of the dart and
the number of bands present upon the shell, those species with a
pyramidal subulate dart and mucous glands of more than eight coeca
have normally not more than five bands ; those species, like Helix
arhustorum, with a lanceolate dart and two simple or bifid mucous
glands, have never more than four, while two subulate curved darts
are associated with numerous spirally arranged linear markings upon
the shell.

Fig. 674. Fig. 675.

368 REPRODUCTIVE ORGANS — IIAPLOSTVLA, ETC.

Darts may be found within the dart-sac at all times of the year,
but some species are much more liable than others to lose them, and
if lost just prior to hibernation, it is probable that their renewal will
be delayed until spring, but in Trlckutoxon, an exotic genus of slugs,
the darts are permanent and are even furnished with chitinous sheaths.

The tfypsobela or love-darts, according to the greater or lesser
modifications they display, may for purposes of study be conveni-
ently grouped in four sections, based upon the degree of complexity
attained by the supporting lateral blades, viz., Haplostyla, Dispatho-
styla, Tetraspathostyla, and Heterospathostyla.

The Haplostyla (dvrA-ois, simple; smAos, pillar)
embrace those species which possess a round and
simply subulate dart, without any strengthening
accessory blades or buttresses or any distinct apical
developments or definite basal rod-like ornament-
ation or enlargement ; these simply formed or
primitive darts are often paired, the stylophores
or dart-sacs occupying coiTespouding positions at
opposite sides of the vagina.

The Dispathostyla (dvo, two ; cnrddi), a blade ; ?ti>Aos, a pillar)
possess darts of the simply subulate Haplostylous type, with
the addition of a pair of sti'engthening blades or buttresses placed
at opposite sides of the weapon ;
these Idades may be restricted to
the free end which therefore be-
comes more or less enlarged, and
forming in its extreme develop-
ment a tlattened lanceolate head,
as seen in Helix lapicida.

In its more primitive form it
illustrates the origination of a pair
of lateral blades or buttresses near
the apex ; these, however, often do
not ac(iuire great prominence, but
sometimes extend the length of the
dart ; the most rudimentary form
of the dart is exhibited by Helix
aipemta, but Helix virgata shows
the lateral apical blades as distinct formations.

Fig. 677. Fig. 678,

Fig. 677. — Gypsobelum or love-dart of
Helix virgata Da Costa, X 8, with section
showing the paired lateral blades, and illus-
trating the Dispathostyla.

Fig. 678. — Gypsobelum or love-dart of
Helix lapicida L., X 8, with section of
head, showing the exaggerated develop-
ment of the paired lateral blades and their
assumption of the lanceolate form.

Fig. 670. — Gypsobe-
lum or love -dart of
Helix p^ilchclla Mull.,
X20, showing the primi-
tive simplicity of the
weapon, and illustrating
the Haplostyla.

REPRODUCTIVE ORGANS — STYLOPHORE.

369

Fig. 670. — Gypsobelum or
love-dart of Helix pomatia L.,
X 6, with an oblique section
showing the quadruple blades
characteristic of the Tetraspa-
thostyla.

The TeTRASPATHOSTYLA (rer/Das, four; (TiraOri, a blade; 5ruXos, a
pillar) or four-bladed darts, show a great advance in complexity upon
the dispathous form, chiefly by the forma-
tion of two other blades at right angles to
those already present; the four blades are
not always e(|ually salient, as the pair repre-
senting the blades of the Dispathostyles may
be fully formed before the more recently
acquired pair are beyond the rudimentary
stage, the base is usually encircled by a
series of regularly arranged rodlets, encirc-
ling the basal tubercle, and the spaces
between the blades may in certain species
become connected together by a number of
regularly disposed crescentic Aims. A
tendency to the character of the Heteros-
pathostyla is shown by the channeling of
the outer margin of the blades, and thus forming a link with them.

The Heterospathostyla (erepos, different; cnraOrj, a blade; stvXos,
pillar) or variously edged dart-bearers, show the highest specializa-
tion attained by the dart, the four-bladed
weapon of the Tetraspathes losing their
simple edges, each blade splitting longi-
tudinally and being reflected outwardly,
forming double flanges to each blade, or
eight edges to each dart, but occasionally
towards the free end the four primary
blades may project beyond the point of
reflection of the flanges, each blade thus
showing three edges, so that a dart witli
eight edges near the base will exhibit twelve
towards its apex.

These reflected flanges are the last parts
formed, as is shown by the fact that an
otherwise perfect dart may occasionally be
found in which the reflected parts are still quite membranous.

The Stylopiiore (o-tuXos, a rod ; to bear) or dart sac is an

appendage to the female genital system, which secretes, protects, and
protrudes the dart. It is usually a short claviform pouch opening
11/6/1900 Y

Fig. 680. — Gypsobelum or
love-dart of Helix hortetisis
Miill., X 8, with oblique section
showing the complex structure
of the blades distinctive of the
Heterospathostyla.

370

REPRODUCTIVE ORGANS — STYLOPHORE.

into the vagina below the aperture of the digitate glands, and
is composed of a thick outer layer of transverse and longitudinal
ninscle tihres, which are thinnest at the summit of the sac, and facili-

Fig. 681.

Fig. 632.

Fig. 633.

Fig. 684.

Dart sacs of different species of Helices, with the vaginal digitate glands, showing the evolution
from the multiple to the simpler single sac.

Fig. 681. — Bifid laterally paired sacs of Helix ntfcsccns Penn., X 3.

Fig. 682. — Bilaterally paired sacs of Helix itala L., X 3.

Fig. 683.— Unilaterally paired sacs of Helix fusca Mont., X 3.

Fig. 684. — Dart sac or stylophore of Helix pomatia L.

tate its eversion; the more delicate and glandular inner layer is
adherent to the outer envelope, it is often deeply pigmented and
secretes a viscous lubricating fluid.

For convenience the dart sac of the British species may be sepa-
rated into two groups, in which the teliferons sacs are single or
paired; both, however, may he more or less completely divided, giving
an e.xternal appearance of double and (j^nadrnple sacs, but only the
outer sacs develop darts, the subsidiary additional sacs which always
lie nearest the vaginal passage showing no indication of ever having
done so, and it is not improbable that these auxiliary sacs may be
a modified form of the coronal glands present in Zonitoides.

In Zonitoides the lubricant
glands are concentrated in the form
of an oval pouch protruding
externally near the apex of the
dart sac and opening therein ;
this peculiar glandular outgrowth
represents a remarkable feature
strikingly developed in the exotic
genus Ariophmtd, in which it
takes the form of a circlet of
similar outgrowths around the sub-
terminal portion of the sac ; such
apical glandular developments have been distinguished by Pilsbry
as coronal glands.

Fig. 685. — Reproductive organs of Zoni-
toides excavata (Bean), X 10, showing I he
glandular outgrowth or coronal gland of the
dart-sac (after photo, by W. Moss).

st. stylophore or dart sac, showing natural
position of dart and character and position
of the coronal gland, c.gl. ; p.s. penis sheath
with calcareous channeled plates; vag. vagina;
sp. bifid spermatheca duct.

REPRODUCTIVE ORGANS — SPERMATHECA AND ATRIUM.

371

The Spermatheca (o-n-epfxa, seed ; Oeya-, a sheath) i.s a stalked vesicle,
developed in the Euthyneures and some of the Streptoneures as an
addition to the female organs to receive the Spermatophore or seminal
fluid from the male organs of its partner.

Usually it takes the form of a vaginal or vestibular diverticulum,
■with a terminal sac-like enlargement ; in Pupa, Clausilia, and certain
groups of Helices the stem develops an auxiliary diverticulum, known
as the copulatory branch (see fig. 323, page 160), which, when w'ell
developed, flir exceeds the length of the primary duct, and sometimes
acquires a sac-like termination.

A most remarkable variation from the typical spermatheca, shared
by the North American Gastrodoutse, is found in Zonitoides, in which
the stem becomes divided or cleft, the chief or most capacious duct
opening into the penis sheath and the other in the normal position
upon the vagina; a similar feature is said to be exhibited by Clausilia
and Balea and appears to culminate in the African Trochommpha, in
which Pfeifer could find no external opening for the male organ, the
cleft spermatheca duct being therefore assumed to be a contrivance
to ensure self fertilization.

Fig. 686. — Reproductive organs of Zoni-
toides excavata (Bean), X 3, showing the
bifid spermatheca duct.

ot. ovotestis ; h,d. hermaphrodite duct ;
a.g. albumen gland ; s.d. sperm duct ; p s.
penis sheath; oz>. oviduct; v. vagina, with
vaginal gland ; sp. spermatheca with divided
duct ; st. siylophore or dart sac.

Fig. 687. — Reproductive organs of
Arion circuinscriphis X 2, show-

ing the vestibular gland.

of. ovotestis ; a.g. albumen gland ; s.d.
sperm duct ; v.d. vas deferens ; ep. epi-
phallus ; cn’. oviduct ; sp. spermatheca,
with its retractor ; v.p. vestibular gland.

The Atrium {atrium, an entrance-hall) or Vestibule, is the thick-
walled and often longitudinally ridged spacious cavity opening to the
exterior and wdthiu which the various organs of the reproductive sys-
tem converge ; it may also contain the Sarcobelum, or excitatory organ,
and is enveloped exteriorly in A riun by a compact and dense glandular
pad, whose secretions are discharged directly into the vestibule.

372

REPRODUCTION AND PAIRING.

Reproduction in tlie inollusca is invariably sexual and entirely
dependent upon the complete activity of the generative organs, as
although the ovum without fertilization undergoes segmentation up
to a certain stage, yet the stimulus of the male element is essential to
successful and regnlar develoj)ment.

Some of onr species are extremelj' prolific, as many as two million
eggs lieing estimated by one observer as the annual production of a
large Auodonfa cygnea, and although all our species by no means
approach this enormous rate of increase, yet a sufficient number
generally survive to enable the different species to maintain their
gruiind, their multiidication being effectively counteracted by number-
less enemies and dangers, otherwise we should in a short time be
literally overwhelmed by the vast numbers annually developed.

Pairing does not take place in the Pelecypoda or in the more
archaic (Jastropods, which are unjirovided with the necessary organs
for the purpose, but all jjhalliate species exercise this power, although
in remarkably diverse ways.

Fig. ()S8. — l.ove-m or co’inin?' of a slnistrai and dextral IIclix aspcrsfi Midi, modified

from a nature sketcli by \V. H. Hcalhcote, K.L.S.

The preludes to tlie sexual act vary in the different species, certain
of the sings marching round and round in a slowly contracting circle
and also mntmilly patting, caressing and fondling each other with their
tentacles, labial lobes and egersidia, and devouring the mncus from
each others boilies ; the Arions also coiij^ume the accumulated mucus
upon the caudal gland of the prospective partner, which has probably
some excitatory effect upon the animals and possibly hastens the
desired conjugation.

Some Helices during their preliminary manoeuvres not only make
nse of their love darts, but mutually touch and caress with their

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BEPRODUCTION — PAIRING AND ITS PRELUDES.

373

tentacles, which are curiously drooping at the tips during this period,
possibly from the partial withdrawal of the blood to other organs ;
they also frequently simultaneously elevate the anterior portion of
their bodies, bringing the raised part into
close, but temporary, apposition, touching
p and rubbing against each other and probably

increasing the mutual excitement by the
use of their love darts.

In the Dioeciate species and certain of the
Monceciate Ditreinata, the conjugation is
simple, one individual being male or acting
as male only, the partner being female or
fulfilling feminine duties exclusively, the
necessary conjunction being effected usually
after probably some preliminary co(iueting.

In the Monoecia, the conjugation is
generally more complex, as fertilization is
reciprocal in many species, each individual
simultaneously fulfilling the role of both
male and female with another individual.
The amorous caresses of the Monoecia, which
precede their conjugation, are also striking
and long continued, and may, in some
species, be continued for the space of ten
hours, certain highly specialized and remark-
able organs, the Egersidia, being developed
for excitatoiy purposes.

In Limax maxhnus and certain other
species, the prospective pair after their
voluptuous preludes and circular promenade, suspend themselves
heads downward from some suitable spot by a conjoined strand of
mucus mutually intertwining their bodies and
the essential organs being exserted and also
externally intertwined in a very complicated
manner during the act.

In the Ditremate Limmva although the
effect of the pairing of two individuals is that
one only is fertilized, as in the Dioecia, yet on account of the widely
separated apertures other individuals may join the original pair and

Fig. 689. — Pairing of Limax
maximus L., slightly modified
from a nature sketch by L. E.
Adams, B.A.

Fig. 690. — Pairing of
Limmca pcregra (Mull.).

374

REPRODUCTION — SPERMATOZOON.

one perform the part of male to the individual already acting as the
male, while another specimen may perform the female part to the one
of the original pair acting as female, which acts as male to the new-
comer ; even then the number of animals taking part may still be
similarly added to and a chain of animals formed, of which all except
the terminal individuals will be reciprocally fertilized.

Some observers have expressed the opinion that some species, as
Helix aspersa, pair but once, as although
isolated after a single pairing, they have
been observed to continue to deposit
fertile eggs for four successive seasons;
this phenomenon may, however, arise
from the retention and continued vitality
of the spermatozoa or from autofecunda-
tion, but it is certain that many species
may 2)air fre(|uently at short intervals,
as is occasionally shown to be probable
by the fragments of several love-darts
amongst the viscera (f. 671, p. 366), or
more undeniably by the presence of two or more spermatophores
within or near the spermatheca.

Pairing has also been found to occasionally occur not only between
closely allied sjjecies, as Helix nemomlis and 11. hortensis, but also
between species usually considered perfectly distinct or even between
ditfereut genera, as between Pupa and Buliminus. The union of
Steiiogym decollata and Helix pimiia has been chronicled by Gassies,
the resultant hybrid progeny, though often scalariform and bizarre,
usually resembling their mother.

The Spermatozoon (o-Trep/xa, seed; ^oov, animal) or Zoosperm, the
essential male element, is a minute highly specialized motile cell,
resembling an active protozoan or flagellate infusorian and is usually
a filiform body witli small cephalic enlargement, almost wholly com-
posed of nuclein or chromatin, and a filiform contractile tail which
may have a dilated extremity ; it possesses great vitality, enduring
great extremes of temperature, and may retain its fertilizing powers
for lengthened periods ; it is paralysed by acids and stimulated by
alkaline substances.

In the hermaphrodite species the spermatozoa and ova are developed
within the ovotestis ; ripening more or less alternately, the spermatozoa

P'lG. GOl, — Rival Spermatophores
within the spermatheca of Amalia
sinueybyi (F^r.). X G. showing the
result ofa second pairing; the second
spermatophore finding the appropri-
ate quarters already occupied, bursts
through the walls of the sac.

/

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REPRODUCTION — SPERMATOZOON.

375

are usually first developed aud are arranged with their heads to the
walls of the gonad in intimate connection with the nutritive cells, and
are shed from the germinal epithelium in the form of mother cells or

Fig. 692. Fig. 693. Fig. 694. Fig. 695. Fig. 696.

Development of the Spermatozoa of Cyclostoma elega7ts (Mull.), highly magnified (after Garnault).
Figs. 692, 693.— Groups of Spermatogonies. Fig 69A. — Group of Spermatocytes.

Fig. 695. — Cluster of immature Sper'natozoa. Fig. 696. — Maturing and mature Spermatozoa.

Fig. 697. — Dimorphic sperma-
tozoa of Vivipa7‘a vivipara (L. ),
greatly magnified (after Recluz).

spermatocytes, which mature and separate into their constituent
spermatozoa whilst free within the lumen of the lobule, the ova
retaining their position upon the epithelial walls until mature.

In certain dioecious species two forms of .spermatozoa may be found
— an elongate one with a caudal filament
and spirally twisted head, the other long,
cylindrical, and slender, without any
cephalic enlargement, but with a terminal
tuft of extremely fine filaments; these are
affirmed to be formed by an agglomeration
of miniature spermatozoa and were at one
time regarded as parasitic organisms,

Ehrenberg applying the name of Phacelura paludinw to the form
peculiar to the Paludinidw.

The spermatozoon has a vermicular or axial rotatory motion, and
when in contact with the egg has been noted in some forms of life to

move around the ovum in regular circles
of varying orbit, so that it eventually
meets the micropyle or minute aperture
leading to the interior of the egg, fusing
with the protoplasm projecting therefrom
and losing its enveloping membrane,
which fuses with the egg membrane
and closes the micropyle against other
spermatozoa. If polyspermy results owing
to cold or weakness of the ovum it may give rise to abnormal offspring.

Fig. 698. — Fertilizing receptacle of
Succinea puiris (L.), X 20 (after
Ihering), showing its connection with
the seminal %esicles, etc.

7>.s. seminal vesicles ; h.d. herma-
phrodite duct ; ov. oviduct ; v.d,
vas deferens.

REPRODUCTION — SPERMATOPHORE AND OVUM.

37 G

The Spermatopiiore (cnrepixa, seed; to bear) or Capreolus, is
a variously shaped elongate body, composed of the hardened secre-
tions of the walls of the tlagelliiin, the epiphallns or the widened part
of the vas deferens. It is usually a Hexible but firm husk, which
becomes brittle on exposure, usually closed at one end and open at the
other, and containing zoosperms. The Spermatophore owes the

I k;. 099. ITg. 700. Fig. 701.

Fig. — Spermalophore of Helix virgata Da Costa, X 4.

Fig. 700. — Spcrmalopliore of .-1 tnalia Sinverbyi (F<1t.), X G, in situ, as secreted by the epiphallus.

Fig. 701.— Spermatophore Autalia senverbyi (Fcr.), x G, in situ, after transference to sperma-
theca of partner.

remarkable shaiies and complicated denticulations it assumes in the
different species to the character of the cavity in which it is formed or
moulded. Its function is to more perfectly ensure the transfer of the
sjiermatozoa from one individual to the spermatheca of another during
the process of pairing.

The Ovum {ovain, an egg) may be regarded as a modified epithelial
cell, corresponding not with the spermatozoon but with the mother
s])erm-cell, the division of the nucleus of the ovum and the expulsion
of the p(dar globules being paralleled by the repeated division under-
gone by the sperm cells. The ovum encloses within the vitelline
mendirane a clear nuclear fluid or nucleoplasm with minute nucleoli
and a complex system of filiform coils or loops which contain the germ
plasma of AVeissmann ; it is externally enveloped by an albuminous
layer and surrounded by an excessively thin, shining and transparent
membrane or chorion, which may ac(iuire opacity and hardness from
the gradual deposition npoii its inner surface of large rhomboidal
crystals of carbonate of lime, forming an exipiisite microscopic object ;
the lime deposit may, however, be confusedly granular, wdiile, in cer-
tain terrestrial S2)ecies, the external envelope may be calcareous or, as
in the Lhnnwidtu and Succiiiew, the egg membrane may be soft and

REPRODUCTION — OVUM.

377

transparent and the eggs aggregated and enclosed within a mass of
albuminous matter.

The egg originates upon the walls of the lobules composing the
gonad, and in its early stages resembles an amoeboid cell, but becomes
rounded and encysted by the reception and storage of nutritive matter,
through the micropyle, an opening in or prolongation of the vitelline

Fig. 702. — Ovarian ovum
of Helix aspersa Miill.,
greatly enlarged (after Hux-
ley and Martin), showing
micropyle.

Fig. 703. — Lobule of the ovotestis of
Helix hortensis Mull., highly magnified,
showing the maturation of spermatozoa
within the lumen of the lobule and of ova
upon its walls (after Gegenbaur).

membrane, by which the ovum is fixed to the ovarian walls during
development, and through which the spermatozoon usually enters for
fertilization ; this aperture in ova not perfectly mature may be
stopped by a peculiar lenticular body, known as Keber’s- corpuscle.

The eggs of the terrestrial species are usually deposited, a few days
after pairing, in moist and shady places, the animals often forming an
oblique excavation in the earth for the purpose, in which they partially
bury themselves during the process, the tentacles being contracted,
and an interval of four, five or more minutes elapsing between the
deposition of each egg, the duration of the process occupying from
twenty to forty hours.

After deposition the eggs increase rapidly in size, for the mass
deposited may, owing to this property, in twenty-four to thirty hours
exceed the total bulk of the animal.

The eggs of aquatic Gastropods are generally affixed to plants,
stones or other submerged objects, and Neritina attaches them some-
times also to the shell itself and that so securely
that a part of the egg shell may remain per-
manently fixed to the shell or other surface
to which it may be applied.

The ova of some species are placed in
variously shaped capsules or ovisacs secreted by
the walls of the oviduct, each capsule containing
a number of ova, arranged in special modes, peculiar to the different
‘species ; although in Neritina JlmiatiUs only one egg in a capsule
becomes developed, the rest discontinuing development at or before the

Fig. 704. — Egg capsules of
Valvata cristata (Miiller),
greatly enlarged (after
Moquin-Tandon).

378

REPRODUCTION — ONTOGENY.

Fig. 70.5.— Fgg of Limtura stagnnlh
(L.), showing iis first segmentation and
the expulsion of the polar globules,
highly magnified (after Ray l.ankester).

tiv.st proce.sses of cell division, the embryo devouring the rest of the ova
in the capsule, which thus supply it with nutriment.

The Ontogeny (orro, being; yh'os, race) or development of the in-
tlividual from the ovum, known also as Embryology, during which the
embryo passes through a series of larval stages or phases of development
before acquiring adult form, which are a condensed and modified but
evanescent repetition or recapitulation by the individual mollusk of
the various forms and characters possessed by the whole chain of its
ancestors, and is, therefore, an epitome of the Phylogeny or develop-
ment of the race.

Upon the maturation of the egg, and before its fertilization, it
separates from the ovarian wall, the clear ])rotoplasm accumulating

at the animal or formative pole, and
the darker food yolk forming the
opposite and larger segment distin-
guished as the vegetative or nutritive
})ole. The nucleus approaches the
walls of the vitellus at the formative
pole and divides mitotically, one half
the nucleus being exi)elled as the first polar globule or directive
corpuscle, the remaining moiety of the nucleus again undergoing
division, and half the remaining nuclear matter is extruded as the
second polar globule, thus leaving the germinal vesicle with only one-
fimrth of the nuclear matter originally present, which is then known
as the female pronucleus.

Ui)on fertilization the head of the
■Spermatozoon fu.ses longitudinally with
the female pronucleus, and transverse
segmentation or cell division of the
combined nucleus takes place at the
limit of its growth, the direction of
the cleavage furrows being eiiuatorial or meridional, according as

they coincide with or are perpendicular
to the chief axis.

The segmentation of the nucleus may
he direct or indirect.

Amitotis (d, without ; piros, thread)
or direct division only takes place as a
rough and ready means of division of the larger cells and rarely occurs.

Fig. 706.— Early embryo of PisidiKvi
pnsilluin (Gmelin), highly magnified,
showing the meridional and equatorial
cleavage grooves (after Ray Lankester).

Zz

> f '

Fig. 707. — Direct or Amitotic cell
division, showing the nucleus in pro-
cess of separating to form two
daughter nuclei (after Carnoy).

REPRODUCTION— MITOSIS.

379

It is accomplished by the elongation of the nucleus, which becomes
dumb-bell shaped ; the neck becoming further constricted and
eventually dividing, forming two cells, the whole process being very
rapidly accomplished.

Mitosis (furos, thread) or indirect segmentation is the prevalent
mode of nuclear division and ensures a more perfect dividing of its
chromatin elements ; the process is characterized by the enlargement
of the nucleus and the appearance of beautiful spiral stars. It is always
preceded by the resting condition, the chromatin or stainable part
having then the aspect of a complexly coiled thread, which gradually
becomes more distinct, and breaks up into a number of sections or
loops, the nuclear membrane and nucleoli disappearing, and the
centrosomes becoming apparent at opposite poles ; these constitute
the foci of a characteristic arrangement of protoplasmic fibres forming
the spindle figure, the chromatic loops become arranged around it
at the equatorial plane and contribute to form the Monaster or

Fig. 708. Fig. 709. Fig. 710. Fig. 711. Fig. 712. Fig. 713.

Diagrammatic figures representing various stages in the Mitotic or indirect segmentation of the
nucleus (modified after Waldeyer).

Fig. 708. — Resting nucleus, showing the encircling nuclear membrane, nucleolus and chromatin
network.

Fig. 709. — Polar view of “ Loose Skein ” stage, with centrally and excentrically disposed loops.

Fig. 710. — Monaster stage, as seen from pole. c. cytaster or polar star ; ch. cleft chromosomes,
radially disposed.

Fig. 711. — Monaster stage, viewed laterally, c. cytaster ; ch. cleft chromosomes radially arranged
around s.^ spindle figure.

Fig. 712. — Dyaster or Twin-star stage, viewed laterally, c. cytaster, ch. cleft chromosomes
separated and travelling along the spindle figure towards the poles to form the daughter nuclei.

Fig. 713. — Separated nuclei, hut cell protoplasm not yet divided. remains of spindle figure in
hilus of chromatic figure ; h. hilus or pole ; d. line of impending separation of the protoplasm of
the two cells.

equatorial plate, the angles of the loops being towards the centre of
the spindle figure and the limbs projecting peripherally; the loops
afterwards split longitudinally, the divided halves separating and
travelling along the spindle threads to opposite poles to form twin
daughter stars and constituting the Dyaster stage. These processes
are accompanied by a constriction of the cell, transversely to the axis
of the spindle, which continues until it is divided into two separate
cells, the spindle, centrosomes, etc., disappear, and the chromatin of
the now separate nuclei each acquire a new nuclear membrane and
assume the resting condition prior to a repetition of the process.

380

REPRODUCTION — MORULA AND GASTRULA.

'Die eggs of our British species contain comparatively little stored-
up food-yolk and the segmentation is therefore complete or Holohlastic
(o/\os, whole; BXaa-Tij, bud) and only exceptionally incomplete or
j\Ieroblastic part ; /SXaa-Ti], bud) as in the Cephalopoda, in which

a large part of the egg is formed of nutritive substances and takes no
part in the division, which is always most active and complete at the
animal or formative pole.

The segmentation cellules, however, vary in size and are distinguished
as Micromeres and Macromeres, the cleavage process being known as
E(pial Segmentation when the cellules are approximately ecpial in size,
and Uiieiiual Segmentation when they are markedly different.

The Micromeres or segmentation cellules of the animal pole are
small and poor in nutritive yolk, they originate at the point of expul-
sion of the polar bodies, and give rise to
the ectoderm, the mantle, the embiyonal
and adult organs of locomotion, the nervous
and sensorial .systems.

The jMacromeres, or nutritive cellules, are
larger than the Micromeres, and richer in
yolk, they divide more slowly and occupy
the opposite pole, and constitute the Eiidoderm, retaining the primi-
tive functions of receiving and digesting food.

The iMoRULA (dim. of morum, a mulberry). Polyblast or Blastula,
constitutes the first .stage of develop-
ment, the segmentation having been
continued until the vitellus has ex-
ternally the aspect of a uniform
mulberry-like mass of nucleate cells,

the interior forming the segmentation f IG. 715. — Morula stage of Pisidiuin

. . pusilliDH (Gmelin), highly magnified

cavity 01' Jilastococl. (after Ray Lankester).

The Gastrula (dim. of yaa-ryp, the stomach) forms the second
phase of development, and has the form of a sac, its ectoderm or outer
layer being formed by the micromeres, and the inner layer hy the
macromeres or endoderm cells, the gastrula arising in those eggs with
little food yolk by the emboly or invagination of the macromeres or
vegetative cells within the more rapidly multiplying micromeres or
formative cells, but where more food-yolk is present the gastrula is
formed by epiboly or overgrowth of the macromeres by the micro-
meres, as in Blpkarium, etc.; the invagination is known as the

F IG. 711. — Egg of lUthynia at
formative pole, showing the un-
equal segmentalionof the vitellus
into macromtres and micromeres
(after Pelseneer).

REPRODUCTION — TROCHOSPHERE.

381

Fig. 716. — Median section of Gastriila
stage of Vivipara, seen from left side,
greatly enlarged (after Erlanger).

bl. blastopore; bl.g. blastoporic groove ;
a. archenteron or primitive digestive
cavity ; b. blastoccel or segmentation
cavity ; ec. ectoderm ; en. endoderm ; w.
mesoderm ; c, coelom ; v. velum.

Archenteron, or primitive digestive cavity, and its opening at the
nutritive pole is the Blastopore (/3Aao-To?, a bud ; Tropos, a passage) or

elongated primitive mouth of the
Gastrula; it usually becomes gradually
closed, the middle part forming the
foot, an invagination in its anterior
part constituting the stomodmum or
oesophagus, and the proctodmum or
anus arising in its posterior part, both
communicating with the Archenteron
or digestive cavity.

The ectodermic outer envelope of the gastrula, and its invaginated
endoderm, enclose between them a cavity, the blastoccel, which
eventually becomes the blood space or Hmmocoel (af/xa, blood ; koiAos,
cavity), and acqirires chiefly from the endoderm a cellular tissue,
the Mesoderm (/xeo-o?, middle; Sep/m, skin), which becomes split up
into numerous sinuses and separates into a somatic or exterior and a
splanchnic or internal layer, originating the reproductive and ex-
cretory organs, the muscular system, the heart, and circulatory
system generally.

Contractile sinuses arise in the
cephalic region and in the walls of
the body, a large posterior sinus or
caudal vesicle may also be developed,
which contracts alternately with the
somatic or cephalic vesicles, and tem-
porarily serves to circulate the fluid
through the body before the developing
heart becomes functional.

The Trochosphere (rpoyds, a hoop ; (r<^aipa, ball) stage still retains

a bilateral symmetiy of the organs, the
torsion of the body and the approxima-
tion of the two ends of the alimentary
canal not having yet been accom-
plished. It is remarkable for the
barrel shape of the embrjm and the
possession of a cilial investment which
is most distinctly developed as a
preoral girdle or ridge, which forms a characteristic feature of

Fig. 717. — Embryo of Agrioliiuax
agrcstis (L.), greatly enlarged (after Van
Beneden and Windischmann) showing the
well developed pulsatory caudal vesicle.

/./. labial lobes ; c.v caudal vesicle ;
in. mantle ; oni. ommatophores ; f. foot ;
a.t. anterior tentacles.

The arrow indicates the direction of
the rotation of the embryo within the egg.

Fig. 718. — Trochosphere of Vivipara
(enlarged after Biitschli).

in. mouth ; 7a velum ; st. stomach ;
a. anus ; f. foot ; in. mantle and shell.

382

REPRODUCTION — VELIGER.

Fig. 719. — Early embr^’O of Limncea
fcregra (Mull.), highly magnified (modi'
fied after Dumortier), showing the
general character of the embryonal
rotation.

The arrow indicates the direction of
the motion.

tlie Ti’ochosphere stage ; their action sets the albuminous contents of
the egg in motion, and facilitates the inception through the egg
membrane not only of oxygen, but of the nutritive matter from the
enveloping albuminous mass within which some eggs are enveloped ; it
also establishes a kind of vortex in which the embryo itself is gradually

involved, so that it begins an oblique
rotatory movement upon its own axis,
with the anterior part of the animal in
front, varying in raj)idity according to
temperature and age, and eventually
also revolving around the internal
walls of the egg cavity; this complex
motion has been happily likened in a general sense to that of the diurnal
and annual rotation of the planetary bodies around the sun, and con-
tinues up to the time the embryo can perform voluntary movements.

The Veliger {velum, a sail ; gei-o, 1 bear) stage is distinguished
from the Trochosphere by the more distinct development of molluscan
attributes, by the torsion of the visceral sac, characteristic of adult
Gastropods, and especially by the enlargement of the anterior region,
to form the Velum, which may be i)r(donged into lobes or processes
fringed with powerful cilia, and constitute the organs of locomotion
persisting in the adult of Limnmi as the subtentacular lobes.

In the terrestrial and tiuviatile genera the animal hatches out in
the adult form, the various larval
stages being very transient or even
suppressed and passed through within
the egg. The Velum is not therefore
needed as a locomotory organ and is
reduced to one or more rings of cilia,
l)ut in most marine spepies and in
Drelsseusia the embryo is hatched
early as a free swimming Veligerous
larva, the highly contractile and well-
developed pre-oral ciliated velar lobes not oidy acting as organs of
locomotion, but probably also assisting in respiration and circulation.

Certain groui)s, probably owing to special dangers to their offspring,
have acquired the habit of retaining the ova within the body until the
hatching has actually taken place, as in Vivljxtra, Anndonta, and
certain species of Papa, Cl(tnPdl<(, Tlelir, etc., the young being

Fig. 720. — Veliger stage of Drehsensla
polyifiorpha{ Palla.s), with velum extended,
greatly enlarged (after Korschelt).

7'. velum fully extended and showing
pigmented median area ; sh. shell ; p.
pigmentation beneath oral aperture.

REPRODUCTION OF LOST PARTS.

383

nourished by the secretions of the brood pouch, within which they
may remain, as in the Sphceriidcv, until they are fully one-third the
size of the parent shell.

In the although the earlier phases of their development

are passed through within the gill-cavities of the parent, the larvte
upon exclusion adopt a parasitic life, fixing
themselves upon the fins or gills of fishes
and becoming encysted thereon by a patho-
logical development of the tissues of the
host, but are so different from the adult
animal that they were formerly described
as independent parasitic organisms under
the name of Gloclildium parasiticimi, and it is only after a secondary
metamorphosis, undergone during encystment, that they assume the
adult form.

Experiments have demonstrated the power of mollusks to reproduce
or renew the mantle, the foot, the tentacles, or even the head when
these have become injured or separated by accident or design, but it
is essential that the cerebral ganglia should not have sustained serious
injury. Certain extra-British species are known to spontaneously and
voluntarily cast off the hinder part of the foot when in danger, taking
advantage of the circumstance to escape.

LITERATURE.

(Additional to the works enumerated on page 131 et seq.)-

Adams, L. E. — Observations on tlie Pairing of Liniax maximus L. — Jonrn.
of Conch., July, 1898.

Ashford, C. — On the Action of tlie Heart in the Helicidie during Hiberna-
tion.— Journ. of Conch., April, 1882.

The Darts of British Helicidm. — Journ. of Conch., 188.3-1884.

Balfour, F. M. — A Treatise on Comparative Embryology. — London, 1880.

Bell, F. Jeffrey. — Comparative Anatomy and Pliysiology. — London, 1885.

Bernard, Felix. — Rechercbes sur les Organes Palle;iu.x des Gasteropodes
Prosobranches. — An. d. Sci. Nat., 1890, pp. 89—401, and 10 plates.

Binney, W. G. — On the .Jaw and Lingual Membrane of North American
Terrestrial Pulmonata. — Proc. Ac. Nat. Sci., Philad., 1875.

The Terrestrial Air-breathing Mollusks of the United States and the
adjacent territories of North America. — Cambridge, July, 1878.

Boas, J. E. V. — Text Book of Zoology, translated by J. W. Kirkaldy and
E. C. Pollard, London, 1896.

Bonney, T. G. — On tlie Supposed Occurrence of Pliolas burrows in the
upper part of the Great Orme’s Head. — Geol. Mag., 1869, pp. 483 — 9,
and pi. xvii.

Bouchard-Chantereaux — Catalogue des Mollusques terrestres et Iluviatiles
* * dans le departenient due Pas-de Calais. — Boulogne, 1838.

Bowell, E. W.W. — The Odontophores of Mollusca. — Sci. Goss., June, 1897.

Fig. 721. — Embryos of Unio,
encysted upon the gills of a
Perch, greatly enlarged (after
Pelseneer).

384

ANIMAL — LITERATURE.

Claus, C. — Eleiuentaiy Text-Book of Zoology. — Translated and edited by
A. Sedgwick with assistance of F. G. Heathcote, 1885.

Creighton, C. — Glycogen of Snails and Slugs, 1899.

Crowther, H. — Alolluscan Jaws : their Variation in II. nemoralis, H. hor-
tcnsis, and var. hybrida. — Science Gossip, Jan., 1883.

Dali, W. II. — Pearls and Pearl Fisheries. — Anier. Nat., June, 1883.

Davis, J. U. Ainsworth. — A Text-Book of Biology. — London, 1888.

Gain, W. E. — Some remarks on the Colour-changes in Arion intermedins
Normand. — Conchologist, Sept., 1892.

Garnault, P. — liech. Anat. et llistol. sur le Cyclostoma elegans. — Actes
d. 1. Soc. Linn, de Bordeaux, 1887.

Gassies, J. B. — Ohs. de M. Gassies sur mie Note de INI. Lecoq, rel. aux
accoupl. adulttb'ins ch. (juelq. iSIoll. terr. — Journ. de Conch., 1852.
Gassies et Fischer. — Monographic du genre Testacelle, — Actes Lin. Soc.,
Bordeaux, 1856.

Gegenbaur, C. — Elements of Comparative Anatomy, revised by E. Kay
Lankester. — London, 1878.

tlilchrist, J. D. F. — On the Torsion of the Molluscan Body — Pioc. Royal
Soc., Edinburgh, 1895.

Grilliths, A. B. — 'I’he Physiology of the Invertebrata, 1892.

Iluxlej', T. 11. — A Manual of the Anatomy of Invertebrated Animals. —
London, 1877.

Kew, II.AVallis.— Tlie Faculty of Homing in Gastropods. — Nat., Oct., 1890.
Korschelt. E. — On the development of D. polymorpha. — Ann and Mag.
Nat. Hist., Feb., 1892.

Lacaze-Duthiers, 11. — Hist. d. 1. Testacelle. — Arch. Zool. Exp. et Gen., 1887.
Lang, -Vrnold. — Text-Book of Comparative Anatomy. — London, 1896.
Lankester, E. Ka}-.— On the Development of the Pond Snail.— Quartl.
Joiir. Micros. Soc., 1874.

Maselield, J. K. B. — Life in the Hot-water Reservoir at the Tape Mill,
Cheadle, Staffordshire. —Trans. North Staff. Nat. Field Club and Archl.
Soc., 1896

Moss, 4V. — The Value of the Radiila as an aid to Cla.ssification. — Trans.
Manch. Micros. Soc., 1894.

Pilsbry, H. A. — Guide to the Study of Helices. — Manual of Conchology,
Helicidii', vol. ix., Philada., 1894.

Rolleston, G. — Forms of Ajiimal Life, 1870.

Scharff, R. F. — On the Organs of Sense in the British Land and Fresh-
water iMollusca. — Journ. of Conch., Ai)ril, 1885.

Schmidt, A. — Ceber d. Gehiirorgan d. Mollusken. — 1857.

Semper, K. — The Natural Conditions of Existence as they affect Animal
Life, London, 1881.

Simrotli, H. — A’ersuch. Naturges. Deutsch. Nacktschn. Eur. Verwandten
Zeitscli. Wissen. Zool., Aug., 1885.

Ueber d. Sinneswerkzeuge uns. einheimischen Weichthiere. — Zeitsch.
AVissen. Zool., 1876.

Die Tliatigkeit der AVillkurlichen Alusculatur unserer Landschnecken.
— Zeitsch. Wissen. Zool., 1878.

Stahl, E. — Ptlanzen und Schnecken, Jena, 1888.

Sterki, V. — Growth Changes of the Radula in Land-Mollusks. — Proc. Ac.
Nat. Sci., Philad., part iii., 1893.

Taylor, J. W. — Life Histories of British Helices — H. arbustornm, Journ.
of Conch., October, 1881.

Life History of Helix aspersa. — Journ. of Conch., July, 1883.

Tye, G. Slierriff. — Molluscan Threads. — t^uart. Jour, of Conch., Nov., 1878.
AValdeyer, AV. — Karyokinesis and its relation to tlie process of Fertiliza-
tioti. — (Quartl. Jour. Alicros. Soc., 1899.

GEOGRAPHICAL DISTRIBUTION.

385

The Geographical Distribution of the terrestrial mollusca over
the surface of the earth is a subject fraught with many abstruse but
interesting problems, bearing not only upon the origin of the various
species and groups hut upon that of the entire animal and vegetable
kingdom.

Although the more simply organized and primitive forms are now
so widely diffused, it is owing chietly to their vast antiquity that this
has been accomplished, as the dispersal of the terrestrial species is but
slow, and almost invariably across more or less intimately connected
tracts of country, their range in time enabling them to take advantage
of the probably nnmerons geographical changes and varied land con-
nections to overspread the globe.

The simpler and more primitive the species or group and the more
ancient its origin, the wider but more discontinuous is its range in
space, while the more complex and recent forms have a comparatively
restricted yet more compact distribution.

Distribution or dispersal has, however, doubtless been influenced
by the climatal changes the globe has undergone, these fluctuations
having been such that at no distant date a colder climate extended
over a large part of the northern hemisphere, and although the
severity of this epoch would appear to have been greatly exaggerated,
jmt it was undoubtedly accompanied by the formation of extensive
glaciers. These frigid conditions were preceded by a warmer miocene
period, during which deciduous trees and evergreens flourished within
ten degrees of the pole, but these changes of climate were so exces-
sively slow, that if any power of adaptability be conceded to organized
life, we are compelled to allow that most of the less severe changes
would have been guarded against by snitable modifications of the
organisms in response to the gradually changing conditions to which
they were subjected.

The changes of habitat by most species are, however, not due merely
to climate, but to the evolution of more advanced races, whose migra-
tions are the chief cause of the restriction of the less adaptable and
more ancient forms of life to remote, inclement or isolated regions,
where they are temporarily comparatively free from the competition
of more advanced forms; arctic animals and plants are not following
the colder conditions from preference, but because they are com-
pelled by the stronger forms to fall back and adapt themselves to
cold or barren stations not occupied by the stronger races.

10/8/1900

z

BIRTH-PLACE OF LIFE-TYPES.

.S86

The pliysioal obstacles to uniform dispersal are mountain chains,
deserts, marshes, rivers, arms of the sea, or any natural features dis-
similar to those to which the particular .species is more especially
adapted. Some of these barriers to dispersion have apparently been
permanent through vast geological periods, hut iu other cases effective
barriers have been formetl after considerable diffusion of the earlier
types of life has taken j)lace.

Islands, especially in the warm and tropical zones, are often exceed-
ingly rich iu mollusca, and sometimes exhibit faume which are
remarkably distinct, owing to the survival and external modification
therein of archaic forms of life which were formerly much more
uuifurmly dispensed over the globe, hut which have long ago been
exterminated or driven off from the neighbonring continental lands in
which comi)etition is more active: the British Isles, however, do not
possess a special and pecnliar fauna, their isolation being too recent to
show any but the slightest ditfereutiatiou from the coutiuental forms.

The classical researches of Pilshry, Semper ami others into the
organization of the Ilelicidm, in connection with information derived
from other .sources, enable us to iudicate the probably true place of
origin of the chief types of .structure, not only of Helicidic but of
other more imjxutaut groups, ami to sketch out a i)rol)able route by
which the earth has become ])opulated, for although evolution in a
lesser degree is a characteristic of every region, the theatre of the
evolution of the great groups of all forms of life appears to have been
much more restricted, and a consideration of the circumstances in-
clines one to the belief in a cbief evolutionary area, in which have arisen
the more important types of structure at present inhabiting the globe.

'I'lie Place of Origin of the chief types of terrestrial organized life
is the Eurasian tract, which is the largest land mass u])on the globe,
embraiug all the cool and temi)erate parts of the old world and having
hut few absolutely insuperable barriers, there is a freedom of commu-
nicati(m with a conse(pient rivalry and struggle for existence and
supremacy of such intensity that those forms of life able to maintain
themselves upon tliis extensive continental region exhibit a superiority
of adaptability and organization with an ability to i)rosper and increase
under adverse conditions, which enables them easily to overcome the
more archaic species inhabiting restricted or insular areas with which
they come in competition and also to dominate the life of all other
l)arts of the globe.

I’AUNISTIC SIGNIFICANCE OF EURASIAN TRACT.

387

The organisms of Europe, especially of Xortli Central Europe, being
the most advanced in development, show this superiority in the most
marked degree, and as may be e.xpected from their stronger yet more
adai)table character and conseiiuent greater power of successfnl
dispersal there are few peculiar species, and these consist chiefly
of archaic and weaker types, which have not yet been eliminated,
but are being gradually isolated or otherwise driven to the confines of
the region before becoming finally extinct.

This pre-eminence of its organic life may be partially consequent
upon the diversity of its surfiice and the genial, yet bracing, climate
it enjoys, free from the great extremes of heat and cold characterizing
Siberia, Central Asia and even Eastern Europe, characters due to its
permeation by the sea, and to the prevalence of genial westerl}" winds
bringing moisture and warmth from an ocean whose temperature is
modified by the gulf stream.

The invigorating climate and variety of terrestrial conditions, com-
bined with the complex nature of the organic environment, tends to
confer a marked degree of adaptability on the species living therein,
while the greater bionomic uniformity characterizing other divisions
of the globe leads to a more exact adaptation with the special
environment and favours high specialization, with consequent decrease
or loss of adaptability to conditions other than those with which
their variation is correlated, so that without prejudging the position
of the chief centre of active evolution during former arrangements of
land and water, we are led by these and other considerations and
under present conditions to regard the Xorth Central European region
as the birth-place of the chief types of life at present occupying the
terrestrial portions of the globe; and, as progress is dependent not
merely upon the nature of the physical but more essentially upon
that of the organic environment, it is only by association with and
competition amongst the strongest and most advanced races that the
highest excellence or development can arise, so that we must still look
to the Xorth Central European region for the continued evolution of
the most adaptable and dominating forms of life, which the excessive
severity of the life struggle will inevitably evolve.

As although tropical climes conduce to the development of species
of large size, brilliant colouration and a wondrous variety of ornamenta-
tion, yet, probably partially owing to the weakness of their organic
environment, they chiefly differentiate externally or specifically, by

3S8

DISPERSAL OF DOMINANT RACES.

external adaptation to modified liabits or environment without tlie
marked structural advance that wouhl probably ensue were the asso-
ciated and competitive organisms themselves more highly developed;
this is demonstrated by the fact that in Australia and other I’emote
regions of the globe occupied by the lowlier forms of life and which
have not yet been invaded by the most advanced races, although a
rich variety of species are developed, there has been little or no material
advance in structure.

Tlie place of origin of the mollusca and other terrestrial organisms
has, however, by most writers been located in the remote, inaccessible
and comparatively nnknown regions of Central Asia, a belief based
mainly upon a mathematical calculation fixing a central point in the
range of species, the presence there of a maximum number of species
of certain genera belonging to more generalized forms of life than
tliose of Eurojie, the discovery of more numerous fossil remains or
in earlier strata than the beds of Europe containing similar relics
and the ab.sence of any evidence that the forms now confined to Asia
have ever inhabited the extreme North or South of Europe.

I'nless, however, a group be a dominant one, its original home is
not necessarily indicated by the aggregation at the present day of
its constituent species, as the true evolutionary area of a group when
no longer dominant may not retain even a single representative of the
genus or family, its species having been expelled or overcome by the
stronger forms which have arisen and suj)planted them, while the
geological record is confessedly too incomplete and fragmentary to
overthrow conclusions based upon the solid facts of structure and
geographical distribution by the merely negative evidence it may
otter, evidence also peculiarly liable to continual correction and
alteration by the results of future research and discovery; therefore,
so far from agreeing with the theory of the eastern origin of the
various forms of life or the reasoning by which it is supported, I
regard the Central Asiatic i)lateau and Asia generally in a lesser degree
as an asylum where those weaker or less adaptable forms of life still
exist, which have migrated or been expelled from the regions more
immediately adjacent to the active evolutionary centre by the intense
Itressure and competition of the highly organised and more adaptable
forms, which will inevitably in process of time invade their present
refuge, only in turn to be disp(jssessed by the still more advanced
forms which will assuredly follow.

DISPERSAL OF DOMINANT RACES.

389

Tliese improved races as evolved become the dominant ones and
rapidly increase in numbers, so that dispersal becomes a necessity, and
they will therefore gradually spread and drive before them to the
mountains, the deserts, or to more remote or inhospitable districts
those of the preceding occupants with which they enter into the
closest competition, and this, not necessarily by means of active

Fig. 722. — Map illustrating the geographical continuity of distribution and the occupation of the
primary evolutionary area by the dominant Pentatpeniate Helicidas poviatia, etc.).

Fig. 723. — Map broadly illustrative of the distribution of the less advanced yet comparatively
highly organized genera Helicella (of which Helix virgata may be considered as a type), Helico-
(ionta{\\fh\c\\ embraces Helix oln>oliita)2.r\di Helicigona (of which Helix arbustoitivi is representa-
tive), and shewing the progress of their expulsion from the primary evolutionary area and the
initiation of discontinuity of distribution.

VERTICAL DISTRIliUTION.

;]0(i

eoliriict or perceptible struggle, but because the invading organisms
are more adaptable to the cliinatal or other vicissitudes of the environ-
ment and will under comparatively unfavourable conditions prosper
and increase in numbers. The range of a dominant species is tlius
geogra])hica]ly continuous, while that of a dispossessed or weaker
species becomes disconnected or discontinuous, owing to their isolation
in various more or less undesirable districts, where, how'ever, for a
period they will be dominant species, disjmssessing in turn the
relatively still weaker previous occupants, and becoming specialized
by adajjtation to the more e.xtreme conditions to which they are sub-
jected and jirobably thus obliterating hereditary ancestral features
and originating new racial or specific characteristics.

The Diei-tsion of an imju-oved race, or one tilling some previousl}"
inade([uately occupieil s})here, whether of man or of more lowly organ-
isms, from this a.ssumed centre of dis])ersion, is governed by the same
great laws and ]>riucii)les, the occupation by the stronger races of the
more desirable regions adjacent to those already inhabited, and the
eventual more or less comj)lete e.xpulsioii therefrom of the more primi-
tive and (•omi)etitive species, the dispersal varying in rapidity and
direction not only according to the vigour of the species already
occupying the region, which may more or less succes.sfully retard effec-
tive dis]iersal in certain directions, but also by the nature of the
]ihysical obstacles to be overcome ; the.se may consist merely of districts
undesirable to occupy, or may be desert lands, arms of the sea, hroad
e.xpanses of water, rivers, or mountain ranges, all of which inter-
pose obstacles to disper.sal wbich can only be overcome by ages of
time, the more feeble .s])ecies being eventually compelled by the
])re.ssure of the imiu'oveil races to ad()j)t new habits of life less actively
(•om])etitive or adapt themselves to the more inhospitable districts,
rliaracterized by extremes (jf physical or cliinatal condition to which
they are driven, or be gradually exterminated, and we thus in
temjierate climes acipiire a mountain, desert, or other i'aiina, which
is representative of forms of life which may be allied to but is of
earlier and more generalizi'd ty]ie than those occupying the more
desirable regions of the plains.

The Vertical or llypsometrical and Bathymetrical di.stribution of
the mollusca and other organisms is subject to the same general laws
as those already described as governing horizontal dispersal. The
phenomena have been locally studieil by many authors and zones

PERIODICITY OF ABUNDANCE AND SCARCITY.

391

defined, distinguished by the association of certain mollusks, with a
preponderance of particular trees and other vegetation. The weakest
terrestrial forms, are, however, always restricted to the more extreme
localities, while the more advanced species occupy the more desirable
areas of lesser altitude ; the stronger aquatic species similarly inhabit
the shallower waters, driving the weaker species or individuals into
those of greater depth.

Periodicity, or cycles of abnormal abundance or rarity in the life of
a species or group, also influences the increase and diffusion of all
organisms. A group, species or variety may more or less rapidly attain
a maximum of abundance and therefore dispersive power from no
apparent assignable cause, though probably owing to circumstances
being exceptionally favourable to the mode of life or constitution of
the particular species affected ; this period of abnormal abundance and
consequent enforced dispersion may continue for a variable period,
but sooner or later a decline sets in and the species, if not a dominant
one, is gradually reduced in numbers until it may ultimatel}' become
quite rare or even extinct.

This phenomenon in a local and restricted wa}" is known to most
field-naturalists ; a pond near Binningham formerly swarmed with
Velletia lacustris var. compressd, but this abnormal abundance after a
time began to wane, until the species became quite rare or had arrived
at its minimum in that place. Amphlpeplea rjlntinom, has been
especially noticed to be affected by this periodicity, and it may well be
that Dreissensid polpmorph i owes its rapid diffusion in Europe to
the advent of a great maximum period of abundance, paralleled in
an evanescent wvay by the irruptions of the immense flocks of Pallas’s
sand grouse into Europe, or the migrations of the hordes of Lem-
mings, and if so we .shall doubtless observe in due course in
our Dreisspnsia a diminution of its excessive numbers as its period
of prosperity wanes, as the invasions or irruptions of a weaker species
within a region occupied by a stronger race, filling approximately the
same sphere of life, can only be of a temporary character, as the
stronger species will eventually reassert its superiority and dispossess
the feebler form, which will more or less (quickly di.sappear. Possibly
the fossil remains of Dreissensid in Europe may point to a former
period of prosperity and extended diffusion, or may be merely indica-
tions of its continuous existence in the European region within which
it probably originally emanated.

302

ROUTES OF MIGRATION.

The Routes by wliicli dispersal has probably been chiefly accom-
plished from the assumed evolutionary centre in North Central
Europe, in which the highest forms of life are found and to which
area the British Isles are immediately adjacent, is shown by the
accomi)anying map, which indicates that the chief route for the
occupation of Asia and America was by the narrow and comparatively
fertile region lying to the north of the Central Asian desert and
mountain plateau ; on reaching the Pacific shores a furcation has
taken place, one branch crossing by an Aleutian bridge to North
America and spreading southward to the west of the great mountain
chain, and eventually occupying the entire continent, while the second
contingent travelled southwards, occuj)ylng China and passing into the
IMalayan Archipelago and Australasia or to the west towards India.

An important stream of colonists has also left North Central
Europe, occupying France and the British Isles and ])assing across or
around the mountain chains limiting the North Central European
region to the south, and have occupied the Iberian, Italian and Balkan
peninsulas and Asia Minor, crossing by the ancient land bridges to
Africa and eventually finding their way by the Nile valley to the
south of the vast Saharan barrier and opening up to the immigrants
the entire African continent, while the Caucasian migrants more
especially press towards the east by way of Persia and Afghanistan,
more slowly overrunning the arid and elevated country to the north
of Persia and to the east of the Caspian Sea.

The inclement northern region, the more inhospitable parts, of the
great Central Asian plateau and other similar districts become more
slowly overrun by the comparatively weaker races, forced aside by the
tide of stronger immigrants, and in these more inhospitable districts
the relatively weaker races comjielled in turn to be their occupants are
successively dominant and by adaptation or specialization become
more suited b.) the harder conditions of life to which they are e.xpo.sed
or become e.xtinct.

That the routes described probably broadly represent the jiaths
traversed in turn by the various improved races, as they became
developed within the limits of the chief evolutionary area, is strikingly
indicated by the distribution of the Helicidre, whose characteristic
assemblages serially representing the different stages of i)rogress
towards the most perfected type of Helicidian organization, are distri-
buted over the globe in strict accordance with the relative perfection or

APPROXIMATE ROUTES TRAVERSED BY THE HELICIDA^ AND OTHER ORGANISMS

FROM THE I-KOBAIiLE EVOLUTIONARY CENTRE, WHICH HAVE LED TO THE UNIVERSAL DISPERSAL OF LiFE OVER THE GlOBE.

Plate III.

. ^he stronger U’aves Represent the hfiain courses of the tnigratoty stream \ the closer rippling indicates the relative slowness of the advance.

ROUTES OF MIGRATION, ETC.

393

.simplicity of their various parts and contiguity to the evolutionary
area, the most simply organized being the furthest removed from the
evolutionary centre and leaving fewest traces of their former presence
therein, while in accord with increasing complexity and closer affinity
to the dominant race are the occupied districts more and more closely
adjacent thereto.

Although the general direction of this migration of .species is
nndeniable, yet the most closely allied forms, from the similarity of
their foods and modes of life, being naturally the most keenly
competitive, tend to disperse in diverse directions, where less severe
opposition than that of their closest allies is encountered, and we
have in this also the explanation of the different local areas often
occupied by closely related forms and the eventual restriction of their
general range; thus Helix hortensis tends to be more northern than
Helix nemomlis, and Helix aspersa more western than Helix pomatia,
and although these species are undoubtedly sometimes found as-
sociated, this association is not a permanent one, as the weaker .species
must in the end eventually succumb.

There has been little mutual interchange of faunas, as has been
so often affirmed, the observed intermingling being essentially due
to the invasion of weaker areas by the stronger forms of life, and
not to the occupation by the weaker of districts already tenanted by
vigorous species, although a few primitive forms, owing to their small
sfze, the adoption of special foods, or modes of life le.ss actively com-
petitive with the dominant races, may obtain or have retained a footing-
in districts from which most of their congeners have long been expelled.

M. Bourguignat’s affirmation that mollusks can only be succe.ssfully
acclimatized from North to South or from East to West had doubtless
reference to his own observations in France, and in this case exactly
expresses the direction in which the introduced mollnsk would be
placed amongst weaker races, and tlms have more likelihood of pros-
pering, at least so far as competition with indigenous forms was
concerned ; this principle is clearly demonstrated by the rapid dif-
fusion of a relatively strong .species when placed amongst a much
weaker fauna, as evidenced by the sparrow and other forms of life in
North America, the rabbit, etc., in Australia and New Zealand, the
successful establishment of Helix aspersa at so many points of the
globe, and by many other instances of the rapid increase of stronger
races when jilaced in the midst of a palpably weaker fauna.

3‘U

RANGE OF HELICID.E: BELOGONA.

Fig. 724. — Reproductive or-
gans representative of the
Relogon.a Siphonadenia, Helix
{ rachca) hortensis MiilL, York.

Tlie Belogona Sipliouadeuia an arrow ; yoi'o?, seed ; a-iffiov,

tube ; dSijr, a gland) of Pilsbry, tire most bigldy developed Helices
ui)oii the globe, are tyi)ically distinguished by a well-developed dart
apparatus and digitiform vaginal mucus
glands, characters which culminate in the
subsidiary group Pentatmnia (irevTiL, five ;

TuivLu, a fillet or band), of which our ffeli.r
nemor(iIl.<, lleli.v etc., are examples.

This group is especially characteristic of
the European region, where the most highly
organized of the group are found, the more
ancient and morphologicall}' less perfect of
the .siphonadeniate fitrms, as Frnticicoht,

IF/iomitix'n, etc., which being early evolved
are more widely .spread, constituting the
advance guard of the new group, and have
already spread over the Mediterranean
sub-region and i)artially acro.ss Asia, intermingling with the rear of
the retreating Euadeniate race, whom the}' have supjdanteil and
driven otf from the North Central European area, in which the
Euadenia were formerly ])redominant.

'I'he Ihdogona Euadenia (/ieA.o?, an arrow ; yoi'os', seed ; ey well ;
a gland) are a less highly organized grou}), ])os.sessing a simpler
dart apparatus and sacculate mucus glands upon the dart sac. Tins
group attains its greatest and most
characteristic deveinpment in Eastern
Asia, the genus llr/icoxfpla, with its
primitive dart apparatus, constituting its
advanced guard in the old w(jrld, having
])enetrated to the tropical islands of the
Indo-Malayan region ; this group, how-
ever, still exists in the ^lediterranean
region and in Central Asia, mingling
with, but retiring before, the advancing
kSiphonadeniate forms, the Euadeniate
.sj)ecies being now expelled from the
chief evolutionary area, except for the
degenerate He/ i, r /niftnim, which still lingers on Central European
soil, the solitary repre.sentative there of this formerly dominant race.

representative of the Belogona Kua-
(lenia, Helix {^Epi f>hragiiiopho^n'S
tyaski var. caya/nacensis Hemphill
(after Pilsbry).

RANGE OF HELICID^: EPIPHALLOGONA, ETC.

395

Though this group is uow a waning oue in the Old World, it is the
most advanced and dominant one on American soil, having crossed
by the Aleutian bridge and invaded North America, but being pre-
vented by the intervening arid and mountain regions from effective
eastward extension, spreads southwards along the Pacific shores,
eventually penetrating to South America and the West Indian Islands,
probably reaching the latter area by way of Yucatan, as the Euadenia
have not yet invaded the Lesser Antilles.

The Epiphallogona (errl, upon ; (fxiXXos, penis ; yoros, seed), of
which Pilsbry’s West Indian Teleophallogona seems an earlier form,
the more characteristic species of which retain an additional flagellate
appendix to the male organ, is remarkable for the development of
an epiphallus and flagellum upon the penis and by the total lack of
the dart apparatus.

This somewhat primitive group has probably
originated in the same area and travelled by the
path that the much later developed Euadeniate
forms afterwards followed, and have been driven
still further from the evolutionary centre by the
Euadeniate migrants, whose advance guard over-
laps the districts they occupy. Though still found
in South Eastern Asia, from Japan to India, they
now chiefly occupy the ef|uatorial and tropical
islands of the Indo-Malayan region and the adja-
cent Australian continent, 'fliey preceded the of ^ thf "ErTphXgona!
Euadeniate race in America, by whom they have eCnsoMafer sf^
been driven towards the south, occupying at the
present time Central America, the whole of the West Indian Islands
and Northern South America, often associated with the competitive
Euadenia, but extending beyond them on all sides, except along the
route by which the newer and stronger race are advancing.

The Proto gona (TrpwTos, first ; yoi-os', seed), as the still simpler
forms are denominated, possess the simplest genitalia, without any
accessory organs, as dart sac or mucus glands on the vagina and
without epiphallus or flagellum on the penis.

This group, which formerly overspread almost the entire globe, is
of still more ancient origin, and having been driven entirely from
tbe northern hemisphere in the old world by the series of more
advanced forms which successively followed them they now exist

396

RANGE OF HELICID.E: HAPLOGONA.

only in the most remote regions, often separated by the ocean,
mountain ranges or desert lands from species of more complex
organization and greater vigour, their chief
asylums being the regions furthest removed and
most difficult of access from the evolutionary
centre, as the extreme southern extremities of
Africa, South America, Australia, Tasmania,
and the more remote equatorial islands of
the Indo-i\Ialayan region, but their rear is
closely pressed upon and overlapped by their
epiphallophorous successors.

Eastern North America is also stocked by
numerous species of this very primitive group
which are there the dominant race, being shielded by the Rocky Moun-
tain ranges from the intrusion and conq)etition of the more highly
organized Euadeniate species inhabiting the Pacific slope.

The Haplogona (utt/Vois, simple; yoi'O'?, seed) are the most lowly of
the Ilelicidian groups and from the simplicity of their general
organiz.jxtion are considered to stand near to tlie common progenitor of
the Ilelicidie and their close allies, and this is
further emphasized by the exceedingly wide
distribution their great anti(puty has enabled
them to attain, as representatives are found
even in the Arctic regions, but throughout the
Southern hemisphere the family is met with
more abundanily, especially in New Zealand,

Tasmania, the extreme south of South America,

Southern Australia and South Africa, and is also
the predominating Helicoid in the oceanic
islands of Polynesia and elsewhere.

Ppon continental lands, probably from occu-
])ying different stations and their habits not
directly confiicting with the dominant and higher Ilelicidian fauna,
a few s])ecies of small .size, like onv flelt\r rotundafa, Ilell.r rupei^trts,
etc., still exist in areas occupied by the most advanced races ; but in
North America we find the Hajdogona represented by a number of
fine species occupying the elevated and desert Rocky Mountain region,
which so effectively divides the invading Euadenia from the much
weaker, but inedominating, fauna of the eastern states.

Fig. 728. — Reproductive
organs representative of the
Haplogona X 3, Helix
( Pyramidula ) rotundata
Miill., Roundhay, Leeds.

Fig. 727. — Reproductive
organs representative of the
Protogona, Helix ( Poly-
Sdy>‘ei) injlecta Say (after
Pilshry).

Plate IV.

.

ZOO-GEOGRAPHICAL REGIONS.

397

The variable areas occupied by different species, which rightly
understood are also an index to their relative antiquity, have led to
the division of the earth’s surface into a number of regions or districts
to express the differences shown by one area in comparison with
another. These divisions, if correct, should be broadly applicable to
other forms of life and confirm the unity of the plan of development,
not only emphasizing the differences in character and structure of the
inhabitants, but also indicating the relative ages of the groups
characterizing the divisions, and as the areas represent marked periods
in migration from the evolutionary centre, the organisms inhabiting and
characterizing them will change with the progress of time, and in the
future, as in the past, will support groups of animals and plants different
from those constituting their predominant features at the present day.

The Geographical Regions into which the globe may thus be
broadly separated are known as the Arctic, Palsearctic, Nearctic,
Ethiopian, Palseotropical, Neotropical, and Australasian, and these
divisions, all of which may be still further sub-divided, often accord
more or less closely with striking physical features either of the
present day or of comparatively recent geological epochs, the more
ancient and pronounced the barriers to dispersal the more striking
the differences of the faunas of the districts they separate.

To illustrate the special characteristics of the different geographical
regions, I have again selected as most suitable the members of the
family Helicidte, not only on account of their world-wide distribution,
but because the general organization of the group has received such
careful and thorough study at the hands of a number of competent
observers, and their philosophical division by Pilsbry, according to
the general character of their internal organization, assists ns to see
how beautifully their gradations of structural complexity coincide
with the broad features of their distribution, so that we are often
able merely from a study of the relative remoteness or contiguity of
their habitat to the evolutionary area to predicate with considerable
confidence the degree of structural perfection to which they have
attained, as the most highly organized groups occupy the actual
evolutionary area, while the most simply constituted are furthest
removed therefrom, showing that the various steps leading to this
greater perfection of organization have all originated within the district
occupied by the latest developed and morphologically higher groups,
from whence they have each in turn spread over the globe, overcoming

39S

ZOO-GEOGRAPHICAL REGIONS.

or driving- liefore tlieiii tlieir relatively weaker predecessors or isolating
them within the limits of undesirable districts.

Although, therefore, the conclusions arrived at are based chieHy
upon the material afforded by this important grou]), yet they will be
found to be borne out Ity more extended and deeper study and will
also be broadly applicable to other organisms.

The Ai’STRAlasian region embraces Australia, the large eipiatorial
islands adjacent thereto, Xew Zealand and the islands of Polynesia,
and is the most primitive zoological region, possessing only the
simj)lest and weakest organisms, whether of maidvind or other
creatures. It is characterized hy the })resence of Endodonta and
other of the most lowly constituted forms of life, the morphologicall}"
higher groujis not yet having spread so far.

The Neotropical region, which embraces South America and the
West Indian Islands, is almost ecpially primitive and weak, possessing
only ancient and .simple forms of life. It pos.se.sses, towards its southern
extremity, the haijlogonous group Ampliido.rit, and the protogonous
genus Pidipjiivut'm, which attest the ancient character of its mollusks,
the simiiler forms of the more modern dart-bearers having only
penetrated as far as its northern parts and to the islunds of the
(Jreater Antilles.

The region e.xhihits its relationship with South Africa and
Australasia hy retaining a preponderance of the simjjly organized
groups which at one perind overspread the whole surface of the globe,
but appear to bave only differentiated e.xternally in the size, shai)e
and general character of the shell in response to the varying character
of the environment they encountered in the course of their great
migrations, the internal organization lueserving in the main its original
or primitive simplicity.

The AVest Indian islands exhibit all tbe peculiarities of pronounced
insidarity, displaying a remarkable individuality in the preservation of
a marvellous development of Operculates and of a primitive section of
Ilpiphallogonous Helices, reproducing in an analogous way the same
characteristic association of those groups as is found in the Indo-
Alalayan region, and although the Helices are morphologically low,
they are yet in advance of the rrotogonous species characterizing the
Atlantic and (lulf States of North America.

The Oriental region includes India, Further India and the
islands adjacent to the e(piator ; it is bounded on the north by the

ZOO-GEOGRAPHICAL REGIONS.

399

Himalayas and liy the southern waterslied of the Yang-tse-Kiang,
meeting with the Pacific near Shanghai ; the west boundary is formed
hy the desert lands of North-West India and South Central Asia.

This region is distinguished malacologically hy the great develop-
ment of Operculates and the predominance of the Epiphallogonous
gToup of Helices, peculiarities shared with the West Indian Islands.

The Ethiopian region includes Southern Arabia, all Africa south of
the Sahara, and the Malagasian sub-region. Its fauna is of a very
lowly stamp, especially in its extreme southern part and in the sub-
sidiaiy island of Madagascar, the charactei’istic mollusks showing a
remarkable affinity with those of Australia and other primitive regions.

Tlie Arctic region is circumpolar and extends from the Arctic
ocean on the north to the limits of the Nearctic and Palmarctic
regions respectively, and although possessing so limited a fauna, it
cannot well be treated otherwise than as a distinct region, as the
Pahnarctic and Nearctic regions have each a Helicidian fauna of a
radically different stamp, the Euadenia being dominant in the latter
region, while in the former they are decidedly a waning race.

Although the fauna of this region is restricted chiefly to freshwater
races and to Helices and other genera of small size, capable of resisting
a rigorous climate, possibly diffused throughout the Canadian region of
North America by migration from Northern Europe, over the assumed
ancient Pliocene connection by way of Greenland ; the fauna is yet in
a measure comparable with the Mongolian fauna, as the region is
occupied in great part by the weaker terrestrial species thrust aside
hy the tide of stronger forms advancing from the European sub-region
across Central Asia along the more fertile tract of country north of
the desert region.

The freshwater .species, however, inhabiting the extensive and con-
nected lake region of boreal North America, will, from the keener
competition they necessarily contend against, tend naturally to
become more dominant than individuals, even of the same species,
confined to more restricted and less competitive areas.

The Nearctic region embraces the continent of North America,
south of the Arctic region, and may be divided into three sub-regions :
Californian, Central and Alleghanian, but owing to the insuperable
obstacle to the ready migration of the stronger races presented by the
mountain ranges which bisect the continent from north to south there
is a great inequality in the vigour of the occupants of the different

400

PAL.EARCTIC REGION AND SUB-REGIONS.

regions, for while in the Californian snh-region we meet with a pre-
ponderance of comparatively highly organized belogonons species,
comparable with those of Japan and China, the more remote eastern
slope, or Alleghanian snh-region, chiefly displays fine and nnmerons
representatives of primitive protogonous types, comparable to those
of South Africa, South America or Australia, while the arid Central
sub-region is chai’acterized by the possession of large examples of the
even more archaic Haplogonous Ilelicoids.

The Pal.earctic region, as restricted, is the largest of the zoological
divisions, and extends from the sonthern limit of the Arctic zone on
the north to the Himalayas and the Sahara in the south, and em-
braces the whole extent of the Eastern Hemisphere from the Atlantic
to the Pacific.

To express the difl’erences in the character of the fauna, this enormous
tract of country has been divided into three sub-regions : Mongolian,
^lediterranean, and European.

The IMongolian sub-region embraces the bleak and barren wastes
of Tartary and the elevated mountain regions of Central Asia,
including the district around Lake Baikal, which retains so many
archaic forms of molluscan life. The more arid parts of the snh-region
are occn])ied chiefly by the weaker Xerophiloid forms, characterized
by whitish coloration and distinct sculpture, while the more fertile
country further to the north is occupied by Fruticiculoid forms, allied
to those of Europe, the whole fauna being more nearly related to the
North American fauna or to the European post-tertiary deposits,
rather than to the existing fauna of middle Europe.

The Mediterranean sub-region includes the countries encircling
the ^lediterranean Sea and extends eastwardly to Persia and Afgha-
nistan, and is separated from the stronger North Central European
region by the interposition of great monntain chains, which are a
powerful obstacle to the rapid diffusion of improved races ; this sub-
region is characterized by the development of the relatively simjile
species of the genera Cumpijlivd, Ilelia'lla, etc., which show a wealth
of species within this area, and also retains within its limits many
more species less advanced in development than are found within the
area of the more vigorous North Central sub-region.

The European sub-region is bounded on the south by the mountain
chains which separate it from the Mediterranean region, on the north
by the southern boundary of the arctic region, on the west by the

ZOO-GEOGRAPHICAL, REGIONS OF THE GLOBE

{jHodified after Wanace).

Plate V.

1 Papuan, 2 Australian, 3 Polynesian, 4 Maorian.

MOLLUSCAN FAUNA OF THE BRITISH ISLES.

401

Atlantic, and on the east by the Ural Mountains and the Caucasus.
The characteristic Helicine inhabitants are undoubtedly the Penta-
trenia, a group embracing our familiar species Helix aspersa, Helix
nemoralis, etc., which are the most highly organized Helices upon the
globe, and possess a pre-eminent power of adaptability to novel con-
ditions and an ability to prosper under comparatively unfavourable
conditions. Although it is probable that the tertiary molluscan remains
are usually correctly referable to the groups still inhabiting their
respective districts, yet in this sub-region the strata of more ancient
periods would, if preserved, probably display relics of more generalized
t3^es from which the widely distributed and more primitive groups
have been derived.

The British Isles belong to the European sub-region, and their
molluscan fauna has been derived therefrom prior to the formation
of the English Channel, when there was an actual connection at one
or more points, the early isolation of this country doubtless contri-
buting in some degree to the paucity of our fauna in comparison with
that of the continent, although had the connection still e.xisted we
must still have looked for diminished numbers of species and indi-
viduals as we approach the north and become more remote from the
centre of dispersion.

The total number of terrestrial mollusca inhabiting these islands is
127, of which 82 are land shells and 45 freshwater ; of this number
Ireland possesses 105 species, of which 69 are land and 36 freshwater
shells. Its early separation from Great Britain has prevented the
influx of a few other species which exist in the north-western counties
of England. Scotland, though continuous with England, has not
favourable geological or physical features, and its geographical ex-
tension northwards also acts prejudicially upon the development and
exten.sion of many forms of molluscan life, so that we find only 102
species resident therein, of which 68 are land and 34 freshwater, and
these are mostly restricted to its more southern parts.

The present fauna of these isles consists of a number of more or
less archaic or simpler forms and a series of improved or stronger
races or species, these becoming evolved by the competition and
struggles for existence continually taking place, more especially in
the extensive, densely inhabited and therefore more competitive areas,
and with the more highly developed organisms— the stronger races
which arise being more exactly adapted to the environment and also

B 2

6/12/1900

402

■WESTERN OR CELTIC BRITAIN.

more adaptable to its modifications than their weaker predecessors,
gradually overcome or dispossess them of the more favourable regions,
starving out and driving the previous possessors to remote areas or com-
pelling them to take refuge in the less desirable districts to which their
range becomes more and more restricted and conseiipiently isolated.

Viewed in regard to its mollusca, the British Isles may be divided
into a Western or Celtic ami an Eastern or Teutonic province ; and
although these districts cannot be rigorously defined, as some species
have advanced beyond their fellows, while others, owing to later
advent or greater susceptibility to changes of environment have not
advanced so far, yet they undoubtedly express the salient feature of
our molluscan fauna and its connection with the general scheme of
distribution.

The Western or Celtic province comprises the whole of Ireland
and the western portions of England, Scotland and AVales as delimited,
its characteristic feature consisting of the presence of a number of
weaker species, whose originally conterminous areas of occupation
have been cleft in twain by their more or less complete expulsion from
the South-Eastern and Midland districts of England by the advancing
general body of improved .s2)ecies, as although the later developed
Pentatreniate species have outstripped their less highly organized
brethren and overspread the whole of the British Isles, this is due to
their marked superiority to the bulk of our fauna in organization and
adaptability.

Probably the oldest, as it is also geographically the most remote
section of this AVestern fauna, comprises the peculiar forms of life
occupying the extreme south-west of Ireland, many of whose component
si)ecies are also found inhabiting the west of the Iberian peninsula ;
these forms, representeil among the mollusca by Geomalncus macnlosm^,
are not imi)robably on the verge of extinction, being now reduced to
and confined within these restricted districts by the pressure of the
more highly organized forms of life which have already driven them
from the more easterly tracts which they probably formerly inhabited,
and are now gradually invading and dispossessing them of the terri-
tory upon which they still linger.

The older notion, which regards as the original home of a primitive
.species the districts wherein it now exists, is in my view manifestl}^
inaccurate, and we must regard the regions now occupied by weaker
groups as one of the various stages of their retreat before the advance

Plate VI.

EASTERN OR TEUTONIC BRITAIN.

403

of the improved and improving races, which invade this country
in such a way as tends to divide its previous occupants into a northern
and a soutliern section, as exemplified by the distribution of (Jnio
margaritifer, Pupa anglka and other species ; the northern section
being driven towards tlie nortli, and not spreading or having spread
soutliward as is the prevalent belief.

This waning western fauna is exemplified by Heli.v fnsca, Helix
lamellata, Papa angliai, Saccinea oblonga, Pnio margaritifer, etc.

The Eastern or Teutonic province, which embraces the whole
eastern districts of Britain, consists chiefly of the more highly
organized and later immigrant species, which have invaded our South-
Eastern shores and advanced mainly in a westerly and north-westerly
direction, driving liefore them the feebler western si)ecies and
gradually isolating them or restricting the area they inhabit to Ireland
and to the southern or northern extremities of Britain. In Ireland
there is a less severe competition, owing to the later advent and limited
number of the more vigorous eastern types, so that many weaker
species are still flourishing, although the feeble remnant of the
Iberian molluscan fauna, now restricted to narrow limits in the more
remote south-western district, is on the point of e.xtinction.

Among these more dominant eastern species may be enumerated •
Helix nemoralis, H. aspersa, H. pomatia. Pupa secale, Planorhis
corneas, Limncea peregra, Unio pictorum, etc.

The Geological history or distribution in time of the mollusca,
forcibly displays the operation of the same laws as govern their
distribution in space, furnishing evidence by their fossil remains, not
only of the successive evolution of new forms, but also of the eventual
extinction or gradual expulsion from the vicinity of the evolutionary
area by the more vigorous and later developed species of the weaker
and more primitive previous inhabitants.

Many of these weaker forms, however, still survive, their survival
being probably due to the adoption of dissimilar habits or foods to those
of the more dominant species among which they live, others though
locally extinct, still exist in other regions, finding a respite from their
inevitable and impending extinction by continual retreat to more and
more distant regions before the advancing hosts of improved forms.

Many of the older rocks have lost all traces of the fossils they un-
doubtedly originally contained and this obliteration of the precious
relics of a byegone life, leaves us, so far as direct evidence is con-

404

FOSSILS.

cerued, in a state of helpless uncertainty as to the character of the
more i)rimitive life forms. Most strata also are of marine origin, and
fossilized land and freshwater .species are naturally seldom met with.

Fossil, though meaning anything dug out of the ground, is re-
stricted to the relics of organized life entombed in the rocks ; the term
Subfossil being usually applied to them when found in beds at present
in course of deposition. Conchologically a fossil may be the actual
shell itself not noticeably altered, or the shell substance may have
peri.shed, owing to the percolating water having dissolved and carried
away in .solution the carbonate of lime of which it is composed, and
which as dissolved may be replaced by a deposit of silica or other
substance, sometimes preserving not only the external form and
appearance, but even in great part the internal structure, or the cast
or impression only, may be left, which, however, may exhibit every
peculiarity or detail of the original shell with minute accuracy.

All rocks containing fossils are stratified and, except those of cal-
careous composition, are mainly formed by at|ueou.sly deposited layers
of mud, sand, or other material derived from the waste of the land,
and although the first or earliest stratified deposits were neces-
sarily formed from the disintegration of the igneous rocks, yet
sub.se(pient beds are formed in great part fi'om the waste of previou.sly
formed strata which have become elevated above the water level, and
in this way the same material has been worn away by atmospheric
forces and redeposited elsewhere, and as this may have occurred again
and again the destruction and loss of their fossil contents is almost
assured, for as soon as dry land is formed it is immediately acted upon
by rain, frost and other atmospheric agents, and the consequent
erosion and denudation provides the sediment for the formation of the
new rocks, which are deposited in layers or strata, a succession of which
more or less similar in character is called a Formation.

The formations are grouped together in three great divisions, known
as the Primary, the Secondary and the Tertiary periods or Systems.

The P vL.EOZOIC (TrdXaids', old ; life) or Primary system embraces
the Archtean, Cambrian, Silurian, Devonian, and Carboniferous .series
of rocks, and is remarkable for the marvellous development of the
Trilobites, an extinct group of Crustacea, restricted to the Palaeozoic
era, which attained its maximum about the close of the Cambrian
period. It is also characterized by the presence of holostomatous
Castropods, although the Pelecypods preponderate in numbers.

PALEOZOIC FOSSILS.

405

Tlie Cambrian rocks in this country are enormously developed,
probably being not less than five miles in thickness ; they rest uncon-
formably on the still more ancient Archrean rocks, which have lost all
traces of the organisms that in all probability lived during the period
of their deposition, so that the relics of the organized life of the
Cambrian period are the earliest of which we have cognizance in this
country, but we find therein well organized representatives of all the
classes of mollusca, and we must, therefore, look immeasurable ages
further back for the ancestral form from which they originally
diverged, all traces of which have been obliterated by the excessive
denudation and changes which the earlier strata have undergone.

No representatives of land and freshwater genera are recognized in
Cambrian strata, but, as those groups are directly derived from
marine species, it is probable that the earlier forms would retain for
a time a marine facies and not be readily separated from the truly
marine species from which they originated.

The Devonian rocks are well distributed over the British Isles, and,
with the exception of strata found in Devon and Cornwall, are probably
mainly of fresh-water origin and known as the Old Red Sandstone,
the colouring of the strata being due to iron oxides. This formation is
remarkable for the discovery at St. John’s, New Brunswick, of the
earliest known Pulmonate, Pupa primcvva, and in this country for
the appearance of

Archanodon jukesi Baily,

a species scarcely distinguishable externally from the ordinary Ano-
donta of our own day, and the first undoubted representative of our
fresh-water fauna, which has been found near Cork, at Kiltorkan
and Tallow Bridge in county Waterford; near Caerleon in Monmouth,
and in Northumberland.

The Carboniferous system is so called because it contains the chief
coal deposits, known as the Coal measures, which are as much as
10,000 feet thick in South Wales. Conchologically, this deposit is
remarkable for the discoveiy in the South .Joggins Coal-field, Nova
Scotia, of a number of terrestrial Pulmonate species referable to
various genera, and in this country for the appearance of a wealth of
species of primitive Unionidie and Mytilidse, classified as Carbonicola,
Anthracomya, and Naiadites.

The Carbonicola awA Anthracomya are Unioniform genera, differing
from the modern Unioiies in the dorsal and posterior position of the

CARBONIFEROUS FOSSILS.

40r)

acce.ssory anterior pedal scars. The A uthmromija differ from Carboni-
colu by i)Ossessing a broadly e.xpanded and truncate posterior region
and a well-defined gonial ridge.

The X((l)idifes iwe ineiinivalve Mytiloid forms, characterized by the
anteriorly directed and subterminal umbones, and externally resem-
bling l)reis.‘<eiisia in shape and ornamentation as well as in the
distinct presence of the byssal notch.

The fossils of this formation are -

I’XIOXID.K.

Carhu))ir(il(i riciifd (.1. Sow.),

— V. vhnml)oidaUs Hind,
rnifjiildfn ( Ityi'kliolt),
toitirjiKi Hinil,
aqiiiliiKi (J. deC. Sow.),
cuHcifonnis Hind,
dcgans (Kirkby),
gibbuxfi Hind,
iniriilaris Hind,
obtiisd Hind,
ora/ix (Martin),
jiol ntoiifrnxix { l?ro w n ),
robiix/ii (J. de ('. Sow.),

}-iii/iixii (Hrown),
xiini/ix (Hrown),
xiibcijiixtricfd (J. Sow.),
xubrofini(bi ( Hrown),
tiirgii/d (Hrown).

I'inti { KirkLy),

A)if/irdrt)iii>/d dddjiixi Salter,

— V. c.r/idiixd Hind.
cdlciferd Hind,

(hiinbrdtd (.1. de ('. Sow.),

Idun'oldtd Hind,

td vix V. xcoficd Ktlieridge jr.,

Anthraroini/a ininimn (Ludwig),

— V. cdrinatd Hind, i

mndioldfix (,I. de C. Sow.),

— V. cKvtdtn (Hrown),
oboratn Hind,
phillipsi (Williamson),
pnlchra Hind,
pumild Salter,
scncx Salter,
xubccnfndix Sal ter,
xiibpdrdllcld ( Portloek),
ivdcncinixix Hind,
uvirdi Etheridge,
willidiiixniii (Hrown),

— V. dbtdxd (Ludwig).

MVTILID.i;.

Xaidditcx Cdrinata (J. de C. Sow.),
— V. tiiiiiidd Itind,
cvdxxd (Fleming),

— \'. iiiodioli/uniiix (Hrown),
cloiigdtd Hind,
nuKjua Hind,

'inodiol((]'ix (J. de C. Sow.),
obcxn (Fitheridge jr. ),
quudrata (J. de C. Sow.),
tridnguldrix (J. de ('. Sow.).

'I’be i\lEStizoic {peao'i, middle ; ^w//, life) or Secondary strata include
the Trias, the Jurassic and the Cretaceous formations, and are charac-
terized by the predominating development of the Pelecypoda and also
contain fossil remains of genera long extinct in this country, but still
fiourisbing in lands more distant from the evolutionary centre.

'I'be Mehoiiddu', which now characterize the iMalayan peninsula,
the African t.^)ntinent, and are tilso numerous in Eastern North
America tuid other primitive regions, were formerly abundant in this
country, as testified by their remains in the Oolite, the Cretaceous
and succeeding strata. Corblcnla and rnlo were also numerous in
the secondary rocks, l)ut the former is no longer found in this country,
but restricted to distant areas, and the latter have noiv but three
representatives, although in Eastern North America they abound at
the present day. Neritina, Vivipura, and Valvata, are all archaic

LIASSIC FOSSILS.

407

forms represented in oolitic strata, and are now restricted in this
country to very few representatives.

The Triassic system is not so well displayed in this country as in
Germany, where the deposits are readily divisible into three sections,
from whence arose the distinguishing name. It is mainly a marine
formation, and characterized by the advent of siphonated Streptoneura,
but otherwise resembling the Palneozoic era, as we know of no
undoubted fossils of terrestrial mollusks therefrom in England. In
its faunal aspect this formation has been compared to New Zealand
and Madagascar at a comparatively recent period.

The Jurassic system receives its name from the Jura mountains,
where it is well displayed ; it shows a prevalence of the siphonated
gastropods and also the advent of the Opisthobranchiate forms.
It embraces the Lias and the Oolitic formations and has been con-
sidered by Phillips to represent the organic aspect of Australia at
the present day.

The Lias, apparently a quarryman’s corruption of layers, is remark-
able for the appearance of the Ammonites, which quickly attain a
most remarkable development, and in this country for the advent of
certain well differentiated genera of pulmoniferous Gastropods, not
previously recognized in British strata. The known species recoi’ded
from liassic strata are :

V.\LV.\Tin.E.

HELICID.E.

Helix dawsoni ^loore.

rui’iD.E.

Vertigo murchisoncc Moore.

LniN.EID.E.

Planorhis viendipensis Moore.

P.VLUDESTRlNin.E.

Pcdudestrina solkbda (Danker).

Valvcda anomala ^loore,
pxjgmea Moore.

nESP<ENID.E.
Dcsjxena Igelli (Moore).

NERITID.E.

Neritinn arenacca Terq. ,
canal is Terq.,
hcttangiensis Terq.

The Oolites (wov, egg ; At^^os, stone), so named on account of con-
sisting of a mass of small rounded egg-like particles, are according to
the classification adopted in England, divided into three sections :
the Lower Oolites, the Aliddle Oolites, and the h pper Oolites, and are
remarkable as containing in the Bavarian deposits the remains of the
oldest-known bird, the Archwopteryx macrura.

The Lower Oolites embrace the Inferior Oolite, the Great Oolite,
and Cornbrash. The Stonefield Slate occurs at the base of the Great
Oolite ; its fossil remains show that the life of the period greatly
resembled that of Australia at the present daj’', where marsupials,
sharks cycads, and pines still fiouri.sh.

408

OOLITIC FOSSILS.

Tlie Lower Oolites display the advent of the genera Melania
and Corhicuht, unknown in earlier formations in England, comprising
rei)resentatives as ennmerated :

MEL.VXIIU.E.

Melania incrmis Tate,

Lejito.ris troc/i ifortnis Tate.

PALUDESTRIXID.K.

Paluelcfitrina calcdonica (Tate),
jn-artirsor (Saiidberger).

V1VIP.\RI1).E.

Vivipara lanfjtonensi^ (Hudlestoii),
scoika (Tate).

VALV.vnn.E.

Valrafa comes Hndleston,
priecnrsor Tate.

NERITID/E.

Aki'itina arata Tate,
staffinensis Forbes.

UNIONID.E.

Unio distortiis Bean,
staffincnsis Forbes.

CORBICULID.E.

Corbicida arata (Forbes),
brj/cci (Tate),
cucidlafa (Tate),
vunninghami (Forbes), ,
jamesoni (Forl)es),
maceullochi (Forbes).

'I'he Middle Oolites embrace the Kelloway Rock, O.xford Clay, and

Coral Rag, and exhibit no terrestrial or fluviatile fossil remains.

The Upper Oolites include the Kimmeridge Clay, Portland Lime-
stone, and the Piirbeck beds; the latter strata display a prevalence of

freshwater conditions, the grey freshwater limestones so characteristic
of this formation known as Purbeck marble, which was so largely used

by mediccval architects for the interior ornamental parts of ecclesias-
tical edifices, being almost entirely made np of fossilized Vivipara, the
Vivipitra elungata being the predominant si)ecies. The deposits also
show an increase in the Melaniidcv, while Physa makes its appear-

ance.

The land and freshwater fossils of this epoch embrace the following-
species : —

LIMN.Ein.E.

Liinna fi ji/ii/suidcs Fibber,

I'hi/sa bristovi Lyell,

U'caldiana t'oqnaiid,

Planorbis Jishcri Forbes.

MKLANIID.E.

Mclani(( jnipici (,J. de C. Sow.),
Melanopsi.s at/cnnafa J. de C. Sow.,
liarpaformis Dunker,
popei J. de C. Sow.,
riajosa Dunker,
trkarinata J. de C. Sow.

VAI.VATin.E.

Valcata hclkoidcs Forbc.s.

VIVIPARIDAS.

Vivipara curinifcra (J. de C. Sow.).
clongata (J. de C. Sow.),
sussexicnsis (Maiitell).

UNIONIDyE.

Unio comprcssus J. de C. Sow.,
valdcnsis Mantell,

A nodonta giurbcckensis Morris.

CORBICULID.E.

Corbicnln angulata (J. de C. Sow.),
clongata (J. de C. Sow.),
gibbosa (,J. de C. Sow.),
media (.J. de C. Sow.),
mcmbranacca (,J. de C. Sow.).

The Cret.vceous (creta, chalk) system, which terminates the
Mesozoic period, is named from the chalk which constitute its most
characteristic strata, the freshwater deposits of the lower division
are known as the Wealden, from their best development being in the
Weald, the formation is considered to be probably derived from the
accumulations, either in a lake or in an estuary of the detritus of a

WEALDEN FOSSILS.

409

great river flowing from the north-east. The Weald clay is of a pale
grey and is near 1,000 feet thick and contains hands of shelly lime-
stone, known as Petworth marble, which are thickly studded with
fossils of Vivipara, chiefly Vivipara fluviorum Sowerby. The fossils
are distinctly freshwater species and embrace Vivipara, TJnio, Mela-
nopsis, Corbicula, etc.

In North America, where more favourable conditions existed at this
period for the preservation of fossil remains, many subgeneric groups
flourishing at the present day are found to have lived as early as the
close of the cretaceous epoch. Acella, LimnojViysa, Gyraulus, Bathy-
omphalus, Aplecta, Physa, and other subgenera of Limnceidw are
distinctly represented in the Laramie and other strata. The Helicidce
were almost as diversified as at the present day, forms apparently
referable to Aglaia, Epiphragmophora, Strobila, Pyramidula, Trio-
dopsis, etc., being found, while the Unionidw showed also a remarkable
differentiation, as subordinate types largely identical with many still
Mississippian, even then existed, though many living tj^pes had appa-
rently no living representatives at that period.

The known British fossils of this era are :

MELAXIID.E.

Melania popei (J. de C. Sow.),

Melanopsis attenuata J. de C. Sow.,
popei J. de C. Sow.,
tricarinata J. de C. Sow.

VIVIPAEID.E.

Viripara carinifera (J. de C. Sow.),
elonqata (J. de C. Sow.),
fluviorum (J. de C. Sow.),
sussexiensis (Mantell).

NERITIU.E.

Neritina flttoni Mantell.

UNIOXID.E.

Unio adtoicus J. de C. Sow.,
antiquus J. de C. Sow.,
comqjressus J. de C. Sow.,

UNIONID.E.

Unio cordiformis J. de C. Sow.,
gualtieri J. de C. Sow.,
mantcUi J. de C. Sow.,
martini J. de C. Sow.,
porrectus J. de C. Sow.,
snbfruncafus J. de C. Sow.,
valdensis Mantell.

CORBICULID.^:.

Corhicida nngxdata (J. de C. Sow.),
elongata (J. de C. Sow.),
gibhosa fJ. de C. Sow.),
major (J. de C. Sow.),
media (J. de C. Sow.),
membranacea (.1. de C. Sow.),
subquadrata (J. de C. Sow.).

The Tertiary period opens with the elevation of the gi’eater part
of the British Isles above the sea, which were therefore subjected to

the unavoidable denudation and waste of surface that would furnish

the material for the formation of rocks elsewhere, instead of being
more or less submerged and receiving deposits from the waste of
other lands ; an interval thus exists between the lower tertiary beds
and the cretaceous strata, and the lapse of time this gap represents
mu.st have been enormous, as with perhaps one or two exceptions all
the cretaceous species have disappeared, before the deposition of the
lowest tertiary beds, and this is the more remarkable as the number

410

EOCENE FOSSILS.

of known species has in the interval hecome nearly double in number.
On the Continent, however, this great break in the succession of
strata is not nearly so marked, and in North America the series
connecting the two formations is fiiirly represented by the Laramie
formation.

This period in this country embraces three groups of strata, the
Eocene, the Oligocene, and the Pliocene formations, the predominating
development of the Gastropoda being the most remarkable feature of
the period, but also showing a much more decided approximation to
the present inhabitants of our country generally, the proportion of
living to extinct species increasing from perhaps 5% in the Eocene to
7.")% or more in the later deposits.

Few remains of our present species are found earlier than the Eocene
beds of the d'ertiary period, and in this country many strata, which
would probably have yielded large numbers of fossils, have been swept
away by the extensive denudations extending over vast ages of time,
so that not even fragmentary relics are now available for study.

The Eocene (h'js-, dawn; Kiunk, recent) is the oldest of the tertiary
group, its deposits chielly occuj)ying two great depressions in the
chalk, known as tlie London and Hampshire basins, and being con-
sidered to sIkjw the origin or dawn of the lU’csent fauna of the earth,
as its beds contain remains of genera which although now extermi-
nated in this country, still exist in closely-related forms in the more
remote regions of the globe, showing that a different geographical
distribution of organisms from the present existed in former times.
Many genera of mollusca whicli were in Eocene times inhabitants of
this country are now restricted to other and distant climes, as A mphi-
(Iromns which is nf)W found chiefly in the Indo-Mala5"an region,
Camptocenoi now ccmtined to India, etc.

The following are the known s})ecies from this formation : —

imi.IMUI.IO.E.

Amphidroiinia ri/li/riisis (Hoissy),
fouiixfi'iiitiis (Sow. ).

I’UIMD.E.

Megaspim ri/lindricK Newt. & Harris.

LIMN.Ein.E.

Liinnari ri/liiidrir(( Newton ik' Harris,

Pitluircllii rirliiiiiiii Edwards,

P/tiuftrlds ciioiiijdi(di(ti •). Sow.,
licin'istunia .1. Sow..
invcrtna Newton ik Harris,

Id riijdt ns Desli.,

Ci( iiipfarcrds /irisfii in ( iod win-.\nsten,
— V. ohtnsa (iodwin-Austen,

AURICULID.E.

Pcdipcs gldhcr Edward.s.

MELANtlO.E.

Mddnin hegscdna Pliilippi,

Mcldnopsis dncdldrioidrs Desliayes,
hurcinoiden Eer.,
huirinidnm Desliayes,
cdrindtu .1. de ('. Sow.,
inin-ostiinid Edwards MS.,
2iseiulo-siiljuldtd Newton,
solid/ is Desli.,

Meld ndtrid ignotn Edwards MS.,
inipiindtd ( Defrance),
vidciinica (Sehlotli).

EOCENE FOSSILS.

411

MELANIin.E.
Coidustjjlus gloho.sus Edwards ]MS.

PALUUESTRINID.E.
Faludcstrinri ambigua Edwds. MS.,
si(hpulchra Edwards MS.,
Tomickia microstoma (Desliayes),
teres Edwards MS.,
tuba (Desliaj'es),

Pyrgula indchra (Kaincourt),
Bithynella toebstcri (Moms),
Stenothyra parkinsoni (Morris).

VIVIPARID.E.

Vivipara aspersa (Michaud),
lenta (Solander).

NERITID^.

Neritina consobrina Fer. ,
globulus (Fer.),
passyana Desh.,
vicina Melleville,

— V. jaspidea De.sli.

U.VIONID.E.

Unio edwardsi S.V.M’ood,
michntidi Desh.

ENIOXID.E.

Unio subparedlcla S. V.M'ood.

CORBICULin.E.

Corbicida adunca (Edwards MS.),
ultirupestris (Edwards MS.),
cmccjis (S.V. Wood),
britannica (Desh.),
charpentieri (Potiez & Michaud),
cordata (Morris),
erassa (Desliayes),
cuneiformis (3 . Sow.),
deperdita (Lamarck),

/ (fie A /e « s ( R ick 111 an ) ,
forbesi (Desliayes),
intermedia (Melleville),
obovata (.J. Sow. ),
pullastra (S. V.AVood),
sororculn (Edwards MS.),
strigosa (S.V.M'ood),
subdepressu (Edwards ^IS.),
tellinella (Fer.),
trigona (Desh.),
tumida (S.V. Wood).

The Oligocene (oA.tyos, few ; Katvos, recent) the fluvio-marine serie.s
of Forbes, is considered to be the representative of the early stages of
the Miocene period in the Britisli Isles; it shows a still closer approxi-
mation to the pre.sent fauna than that of the preceding strata, its
remains possessing so great an interest and beauty that a .short sum-
mary of the situation and character of the different beds is given.
Its deposits consist of marls, sands, clays, and limestones, and are
confined to the Isle of Wight and to Hampshire, the estuarine and
freshwater conditions under which the strata were mainly deposited
being shown by the abundance of Cerithium, Potamomya, Corbicida,
Limncea, etc.

The Oligocene deposits are subdivided into four chief beds, desig-
nated by the names of the localities where they are well displayed :
the Headon, the Osborne, the Bembridge, and the Hempstead beds.

The Headon series are exhibited at Totlands and Colwell Bays and
Headon Hill, Planorhis euomphalus Sow’, being the characteristic
fossil of the series. The beds may be subdivided into an upper, a
middle, and a lower series. The middle Headon is mainly marine or
brackish. The lower series is composed of clays and marls with
intercalated beds of freshwater limestone, and is also displayed at
Hordwell Cliffs in Hampshire. The upper Headon is freshwater, and
shows characteristic Limmean limestones, shales, and marls.

The Osborne series is visible at St. Helens, Osborne, Headon Hill,

Colwell, Totlands, and Gurnet Bays.

412

OLIGOCENE FOSSILS.

The Bembridge series, of which PliDwrbis discus Edwards is per-
haps the most characteristic fossil, is exhibited in the cliffs of Whitecliff
Bay, along the shore and low cliffs under Hempstead Hill, at Sconce,
at the crest of Headon, and at a few inland limestone quarries.

The series of freshwater marls are separated by a marine bed from
the limestone band which contains teri’estrial puhuonate remains as
well as fossilized Vivipara-, Plcmorhes, and Limnwoo.

The Hempstead beds are the uppermost of the series and have been
almost obliterated by the enormous amount of denudation to which
they have been subjected, the only remnants of this series being at
Hempstead Hill, near Yarmouth, Isle of Wight. They are constituted
by clay and shaly marls, and were deposited under alternating marine
and tluviatile conditions.

The fossil remains from the Oligocene beds are very numerous and
comprise :

Tr:STACKLIJD.E.

GlaniUna brevis Edwards MS.,
couvcj’u (S. V. Wood),
cosfcl/afd (J. Sow.),

— V. ((bbrcvirifa (Edwards).

helicid.e.

Ilyalinia cVin’bani (Edwards),

Icia (Newton & Harris),
scoiieietisis (Newton & Harris),

Helix etheridgei Edwards ^IS.,
headuuen sis Ed wards,
morrisi S. V. Wood,
oeelusa Edwards,
omphdlits Edwards,
pseiido-globosa ()rl)i<,my,
pscudn-labgrintlncd Sandberger,

.9 ubldbgrin thicd { Eil wards),
tropifevd Edwards,
vecticiisis E( 1 wards.

liULlMUI.ID.E.

Amphidronws clliptiens (.J. Sow.),
lavolongns (Hoiibec),

PUriD.E.

Pupa orgza Edwards,

iiudti.spii-dta Newton & Harris,
perdentdtd Edwards,
vecticiisis Edwards MS.,

Vertigo dubid (Newton & Harris),

Cldusilid stridtdld Edwards,

Megaspira Newt. & Harris,

STKNOGYKID.E.

Aelddind eglindrivd Edwards MS.,

Alia headonensis (Newton Harris),

SUCCIXEimE.

Sueeincd edircirdsi Eorbes,
im persp icua E d w ard s ,
gjcrsjiicda S. V. M ood,
s2Xirndcensis Desliayes,

LIMNiElD^.

Lininwd diigiista Edwards,
arenidarin Desli.,
cauddtd Edwards,

— V. dbbrcvidta Edwards,
eincta Edwards,
columclldris J. de C. Sow.,
eonvexd Edwards,
eostellata Edwards,
fdbnld Hrongniart,
f usiforinis . Sow.,

— V. deformis Edwards,
gibbosula Edwards,
headonensis Newton & Harris,
^ SCO B ron gn i ar t ,

— V. distorta Edwards,

— V. clongatn de Serres,
minima J. Sow.,
mixta Edwards,
ovum Brongniart,
pgramided is Brongniart,
recta Edwards,
snblatd Edwards,
siibquadrata Edwards,
snleata Edwards,
tenuis Edwards,
tumida Edwards,

Segment ina obtusa (J. Sow.),
Planorbis biungulatus Edw'ards,
discus Eilwards,
elcgans Edwards,
euomphed'us J. Sow.,
goniobasis (Sandberger),
hemistomai. Sow.,
lens Brongniart,
oligyratus Edw’ards,
plaiystoma Edwards,
soivcrbyi Bronn,
tropis Edwards,

OLIGOCENE FOSSILS.

413

LIMN.Ein.E.

Ancylus (?) lotus Edwards,

Velletia elcgans (J. de C. Sow.),

MEL.\N1ID.E.
Melania acuta (J. Sow.),

— V. excavata Morris,

— V. tumescens Edwds. MS.,
contabulata Edwds. MS.,
nysti Nyst,

3Ielanoj)sis carinata J. de C. Sow..
fusiforniis a . Sow.,
pscudo-siibulata Newton,
subcarinata Morris,
subnlata J. Sow. ,

Coptostylus brevis (J. de C. Sow.),
PALUDESTEINin.E.
Paludestrina anceps Edwards MS.,
dubuissoni (Boiiillet),
injlata (St. Fond),
peracuta Edwards MS.,
subangidata Edwards MS.,
Tomichia duchasteli (Ny.st),
polita (Edwards),

Pyrgida ditropis Edwards MS.,
pxdchra (Raincourt),

— V. denticulata Edwds. MS.
Bithyiiella pidchra (Desli.),
Stenothxjra lubricclla (Braun),
meaiana (Desliayes),
parvida (Morri.s),
pupa (Nyst),

RISSOID.E.

Potamaclis forbcsi (Morris),
peracuminata (Morris),
turritissima (Forbes),
tcoodi Edwards MS. ,

VIVIPARID.E.

Vivipara angulosa (J. Sow.),

— V. orbicularis (Morris),
distinguenda (Desliayes),
globxdoides (Forbes),
lenta (Solander),
vestita Edwards MS.,

CYCLOPHORID.E.
Dissostoma mumia (Lamarck),
Cyclotus cinctus Edwards,

7mdus Edwards,

CYCLOPIIORID.E.

Craspedopoma elizabcthm Edwards,

Pomatias hctei-ostoiiia (Edwards),
minuta Edwards MS.,
rotundata, Edwards MS.,

Callianella Uevis (Sandberger),

DESPCENID.R.

Despania woodwardi Edwards MS.,
NERITID.E.

Nei'itina aperta, (J. de C. Sow.),

— V. zonula S. V. 4Vood,
concava J. Sow.,
forbcsi S. V. AVood,
fuhninifera Sandberger,
pUmxdata Sandberger,
tx-istis Forbes,

UNIONID.E.

V nio gibbsi Morris,

— V. headonensis S. V. Wood,
solandi'i J. de C. Sow.,
tuincscrns S. V. Wood,
vcctensis S.V. Wood,

CORBICULID.E.

Sphccriurn bristovii (Morris),
tumidida (S. V. Wood).
headonense Edwards MS.,
mox-risi Edwards MS.,

Corbicida cestuarinn (Edwards MS.),
ai-exxaria (S. V. Wood),
cyclad iforin is (Desliayes),
depcrdita (Lamarck),
gibbosxda (Morris),
mactx'ceformis (Edwards MS.),
obliqua (Desliayes),
obovata (J. Sow.),
obtusa (Morris),
pisuxn (Desliayes),
pxdchx'a (J. de C. Sow.),

— V. wrighti (Morris),
scmistrkda (Desliayes),

— v.foi'tis (Edwards MS.),
sxtbregxdaris (Edwards MS.),
tcnera (S. V. Wood),
tx'unsvcrsa, (Morris).

DREIS.SENSIID.R.

Dx-cisscxxsia bx'ardi (Brongniart).

The Pliocene [-n-Xeiov, more; uaivos, recent) strata succeed the
Oligocene in this country, as during the whole of the intervening
Miocene period these islands were elevated above the sea, and prob-
ably united with the continent, but at the beginning of the Pliocene
era the south-eastern districts were again submerged, and those vari-
ous sand-banks and shell deposits were accumulated which constitute
the ‘Crag.’

The Yalvata antiqua of Sowerby and related forms are now removed
from the list of extinct Pliocene and Pleistocene .species, as they are
still found in this country in a living state.

414

PLIOCENE FOSSILS.

The Coralline or White Crag, tlie most ancient of the Ea.st Anglian
deposits, is composed of shelly sand and marls, the term coralline
being due to the inimen.se (piantity of coral-like polyzoa it contains,
mail}'' of which still retain the iiosition they occupied when living.

The Red Crag is formed by local beds of dark-red or brown ferru-
ginous sand, tlieir colour being derived from iron oxides; they re.st
nnconformably against and upon the White Crag. One of the most
interesting shells of this formation is Fasitf: contrarius, a form closely
allied to which still exists near Vigo Bay.

The Norwich or Mammalian Crag consist also of shelly sand and
gravel, attaining in places a thickness of from loO feet to 180 feet.
The name is derived from one of the localities where the beds are
well exi)osed, and the descriptive name is in allusion to the presence
of bones of the iMastodon and other mammalia which are found in

places at the base of the deposit.

The Pliocene fossils of species now extinct in the British Isles are :

IIKLICID.E.

lldix fr II Hr 1(1)1 ^Nliiller,

/eiix Fer. .
lartrrf .Miiller,
iiiaininfii Miiller,
riiliii/iiinxa A. Seluiiiilt,
ri/xfi S. V. Wood,
siittoiiciixix S. \'. Wood,

I’UI’ID.E.

Cldiisiliti plioceud S. y. Wood,

P.VLUDE.STRINID.E.

PaliKlcstrinii ohtiixii v. rccn’l K.&W. ,
jiciidiiln S. V. Wood,
h'reliclldtd (Nyst),

vivii’.Mtin.n.

Vii’i/idi'd i/ldcidlis (S. V. Wood),
iiu'dia (S. Woodward),

COUBICULID.E.

t'urbicida flitminalis (Miiller).

'I’lie PostTertiary strata maybe considered as inaugurating afourth
or (|naternary epoch, and as linking the life of the Pliocene iieriod
with tliat of tlie ju’esent day; its beds are composed of various super-
ficial deposits in which all or nearly all the mollusca are recent species.

Tlie geological history of our British species is in its origin still
wrapped in obscurity, as tlie pleistocene remains though showing certain
.species now extinct in this country, exhibit also many of our present
species, apparently as far as the shell enables us to judge, quite as
sharply differentiated as at the present day, so that we must look
far into the jiast before we can hope to meet with relics of the pro-
genitors of the present molluscan fauna of our country, as we have
no distinct traces left behind even of the various stages, as shown by
the embryonic whorls, through which the iiresent specialization and
perfection of their shell structure has been acquired.

These, post tertiary beds may be separated into two groups, which
are distinguished as Pleistocene and Holocene.

POST-TERTIARY FOSSILS.

415

The Pleistocene (wXeuTTos, most; Kau-ds, recent) Post Pliocene,
Glacial, or Diluvial beds, as they are variously called, are rather few
and fragmentary in this country, consisting only of such remnants as
have escaped destruction by the enormous denudation to which its
deposits have been subjected.

The pleistocene beds would appear to have been deposited during
a gradual refrigeration of the climate, until what is known as the
“Ice Age” prevailed, the condition of a great part of the British Isles
being compared at this period to that of Greenland at the present day.

These deposits, also known as the Palieolithic age, are the first con-
taining undoubted evidence of the existence of man, his presence at
this period being attested by the discovery of the roughly chipped
flint arrow-heads and other weapons and implements associated with
remains of the mammoth, hippopotamus, rhinoceros, lions, bears, and
other animals characteristic of the period in this country.

The Holocene (oXws, entirely ; /catvos, recent) or Post Glacial period,
is composed of recent superficial deposits, river alluvia, peat moors,
sand dunes, lacustrine deposits, etc., which contain no fossilized
remains of species now extinct, the differences shown by the mollusca,
compared with those existing at the present day in the same region,
being now confined to variations, which although they may not now live
in the British Isles, yet are still found in neighbouring countries.
It is also known as the Xeolithic age, the stone implements of the
savage races of mankind living at this period being more highly
finished than the ruder ones of the preglacial peoples.

The Post-Tertiary fossils now extinct in this country are :

LIMACID.E.

Limax modioliformis Sandberger,
HELICID.E.

Helix friificinn Miiller,

nemoralis v. creticola Alorch,
rudcrata Studer,
iimbrom Paitscli,

PUPID.E.

Vertigo concinna Seott,

Claiisilia piimila v. sejunctn Scliiiiidt,
LIMX.EIU.E.

Lirnmea pedustris aff. diluviana And.

VIVIPARID.E.

Vivipara clactonensis (S.V. Wood)

PALUDESTRINID.E.
Paludestrina marginata (Alicliaud),
Bithgnella sfeeni (E. von Marten.s),
Bithgnia ovatida Sandberger,
Neinatiirclla runtoniuna Sandberger,
UXIO.MD.E.

Unio Uttorcdis Lamarck.
pictorum V. limosa Nils.

copancuLiD.E.

Spluerium corneinn v. vicenamim Koh.
Corbicida flumimdis (Miiller),
Pisidium amnicuni v. astartoides

(Sandberger).

The faunal changes which have taken place on the earth is shown
by the preceding varying lists of the species obtained from the different
geological formations. These changes in the molluscan fauna have
their analogies or counterparts in the succession of life observed in all

4ir) ENEMIES OF MOLLUSC A — MAMMALIA.

otlier classes of the aiiiiiial and vegetable kingdoms, displaying the
unity of the plan for the diffusion of organic life over the globe and
emphasizing the reality and truth of the extinction of the weaker and
more primitive races or their expulsion from those countries adjacent
to the evolutionary area by the later developed and more adaptable
races as already described under geographical distribution.

The earlier deposits contain fossilized remains of species or genera
wholly extinct at the present day or now living only in inclement
regions or in countries far distant from the regions in which they
formerly existed. In the later rocks the number of such forms steadily
diminish, and the area of their present distribution becomes less and
less distant from the creative centre, the species gradually approxi-
mating to, and eventually becoming absolutely identical with, the
present inhabitants of the district where the fossilized remains are
found.

The Enemies of the mollusca are very numerous, as they constitute
a favourite and nourishing food for many animals, their defenceless
condition and sluggish movements rendering them an easy prey to
many creatures besides man, their only i)rotection being the di.staste-
fulness of certain species, or their power of concealment, as their shell
only affords protection against their weaker or less astute enemies.

The Mammalia are very destructive to the molluscan life, more
especially during the oft-recurring periods of scarcity of their accus-
tomed food.

The Hats in this country destroy and devour large numbers of
Ilelir IT. neinoraUs, etc., this being evidenced by the large

number of their broken shells strewn about their holes ; in winter,
they laboriously dig up from their concealment in the ground the
hybernating or aestivating mollusks, whose whereabouts they have
detected, and have even been observed to ascend hollyhocks and other
plants and bring down to their holes for food the IleUx aspersa
infesting them, the broken shells, the relics of the feast, being left
strewn about their retreats.

In Australia the Bush Rat {Mas arboricola Mad.) shows the same
predilection, and destroys large numbers of the Helix aspersa which
live in the Botanic Gardens at Sydney, always accompli, shing this
purpose by breaking in at the apex of the .shell.

The Voles generally, prey upon the mollu.sca, the Bank Vole evinc-
ing a predilection for Helix fusca, though also destroying other species.

ENEMIES OF MOLLUSCA — BIRDS.

417

Fielfl-]Mice also consume large quantities of inollusea, breaking into
the shell by gnawing away tbe side of the whorl, and from the ascer-
tained extent of their depredations and those of their congeners, the
devastations of the mice must he a decided check upon molluscau
increase. Included amongst the list of species preyed uj)on by these
animals ai’e Heli.r cantiana, H. <irhustorum, H. asperm, II. ruft'Scenif,
H. hispida, H. nemoral/s, H. hortensh, IlyaVmhi celhiria, etc.

Mr. C. E. Wright detected a run of these creatures, about ten yards
long, beneath the thick grass
and nettles in a quarry near
Lincoln, along the whole length
of which broken shells were so
thickly strewn that in the space
of twelve inches he counted dis-
tinct remains of ninety-six shells
of Helix nemoralis and II. hor-
temb, besides those of a number
of smaller species, which would give a total of about three thousand
shells in this restricted area. So eager and acute are mice in the
pursuit of their prey that during winter they have been known to
burrow into the thick snow to gain access to the hybernating IIeUce.<
of whose presence beneath they were apparently aware ; while the
Water Shrew dives beneath the surface to secure Lunnmi auricular ia
and Planorhis corneus for food.

Otters and rats have also been recorded as preying upon freshwater
mollusks, breaking away the ventral margin of the valves of the
Anodonta-, etc., with their teeth to gain ready access to the animal
inhabitant.

The Hedgehog has been deemed by many observers to be one of the
most persistent enemies of land shells, while the Fox is accused of
regaling himself in winter upon them when more substantial food is
difficult to obtain. Rabbits are also accused of occasionally devour-
ing Helix aspersa and other of the larger species, and justly so, judging
by the number of gnawed empty shells strewn about their burrows
and the absence of traces of any other animal likely to cause the
destruction amongst them.

Birds are especially destructive to molluscau life, the insectivorous
species making mollusks a staple article of their diet during the winter
months. The Tlinrsh tribe at all times, but especially in winter, feed

Fig. 729. Fig. 730.

Fig. 729, Helix aspersa Miill., and Fig. 730,
Helix fienioralis L., illustrating the manner in
which they are destroyed by Field-Mice.

Collected by Mr. C. E. Wright in an ironstone
quarry at Lincoln.

15/12/1900

C2

418

ENEMIES OF MOLLUSOA — BIRDS AND BATRACHIANS.

largely upon Helix nemoralis, H. Iwrtensis, and other species, seizing
the shell by the outer lip, and striking it repeatedly against a stone
until broken, or fixing the shell in some suitable crevice and pecking at
it until fractured, a particular stone being often selected to which the
shells are carried for the purpose of
being broken thereon. These sacri-
ficial stones, known as “ Thrushes’
altars,” are usually in open posi-
tions and easily recognized, not only „ ,

° ■' Figs. 731 and 732, W/jT L.,

by their slimy surface and the shell- illustrating the manner in which these

shells are broken by Thrushes, etc.

fragments adherent thereto, but by Kmerlng'"^

the little heaps of broken shells which are strewn around them.

Starlings, Fieldfares, Redwings, and many other birds devour great
(piantities of the smaller species during the winter months, Zua
luhrica being a fiivourite food of the Starling, while the Fieldfare and
Redwing search for Helix virgata and other species. In times of stress
the (foldcrest resorts to the same food, seeking out from their hiding-
places Hdlea, Cldusilia hidentata, Pupa mnsconim, etc. The Bearded
Titmouse and Reed Bunting devour great quantities of the Succinecv]
the 'I’itlark searches for Helix capemta to vary or make up for the
deficiencies of its more fiivourite coleopterous diet, and the Grey
Wagtail preys upon Ancyluff fluxiatiUs and Sphcerium corneum in
our streams and ponds.

The Heron feeds upon Limnaea stagnalis and other species and also
upon the Anodonti, with which it will fly up into the trees, breaking
the shell against the branches; the Hooded and Carrion Crows, which
also feed upon the same species, have been observed to carry them to
a considerable height and to drop them to the ground to break the
shell, so that they can more readily get at the animal.

The Dipper haunts the rocky streams, and the Water-Rail the
])Ools, preying upon the mollusks and other aquatic creatures therein,
while the Land-Rail is said to become quite fat in the summer months
by feeding upon the various snails.

'I'he Batraciiians are also very partial to mollu.sks. Frogs and Toads
more especially devouring considerable quantities on occasions, and
this is so well known that the garden attached to the laboratory of
Agricultural Chemistry at Rouen by the introduction thereto of 100
toads and 90 frogs was in a month completely cleared of the slugs and
snails which had previously so infested it that the growth of any useful

ENEMIES OF MOLLUSCA — FISHES AND INSECTS. 419

plant had been quite impossible. The Frogs and Newts also eat the
different .species of Limnwa and Planoi'bis of our ponds and streams.

Fish in general are very partial to the mollusca, feeding greedily
upon them, and the havoc thus caused amongst the marine species by
the enormous numbers they consume has been frequently chronicled,
but the destruction amongst the freshwater species has not attracted
so much attention.

The beneficial effect of water-snails as nourishing food, especially
for trout, is shown by the rapid growth of fish placed in streams or
ponds in which mollmsks abound. The ravages of fish amongst mol-
lusks are not, however, confined to such species as di.sport themselves
more or less actively at the surface or amongst the vegetation, but is
also carried on amongst the minute mud-loving Pisidia, which in
America have been shown to be an important food of the Whitefish.

The Gillaroo Trout, which lives in the Irish loughs, and other famous
breeds also, subsist chiefly upon mollusks which give them the
exquisite flavour which has rendered them so famous and prized by
epicures. Specimens of the Gillaroo Trout have been caught gorged
to repletion with Blthynki tentaciilata and other fre.shwater species,
and the remarkable and peculiar thickening of the stomach-walls of
this trout has been attributed to the fact of shelled snails forming so
large a part of its diet.

The Eel is another rapacious devourer of the mollusca, as many as
350 shells of Valvata piscinalis, in addition to those of other species,
having been obtained from the stomach of a single eel.

The Barbel has been noted as having a special predilection for
Vdlvata i)iscin(dis and also for Sphivrium corneum, and many fi.sh,
and more e.specially gold carp, regard Physa fontmalis as a choice and
delicate morsel, while the Boach is recorded to feed even upon the
eggs of the various species.

The CoLEOPTERA prey freely upon the mollusca, the Dytisciis
marginalis being particularly destructive to the Limufeidfe generally,
but apparently preferring Limnceci stagnalis to other species, although
accumulations of the shells of Planorbis corneus with the sides of the
whorls bitten aw'ay, to allow of easy access to the animal, have been
recorded as the work of this species.

The Silphidte also destroy the smaller land .species, the Rev. A. H.
Cooke stating that they fracture the shells by striking them against
their own prothorax.

4-20

ENEMIES OE MOLLUSCA — INSECTS, ETC.

Drilus, a coleopteron allied to the glow-worm, and also its larva,
attacks and devours nemond'm, H. hortensis, and H. aspersa, the

larva taking np its abode within the shell of its victim, exchanging
its domicile when necessary by attacking a larger individual, and
appropriating the shell, enclosing itself within it by a fibrous web
before undergoing its metamorphoses. The beetle emerges as an
imago in October, when the molluscs again begin to be torpid.

The species of the genera Cychrin^, Carahus, and the families
Sfop/zyliitlchr and Ilydropliilida’ all prey more or less eagerly upon
snails, the attenuate head and prothorax of the Cychri enabling them
to readily insinuate themselves within the shell of their victims ;
the larva; of all these gi-oups are also verj" voracious, while the larva
of the Olow-worm, which feeds almost exclusively on small mollusks,
is believed by Fowler to derive its phosphorescent powers from this
source.

Ants have been observed by IMr. E. J. Lowe to ferociously attack
and destroy snails as large as Helix aspeesii when they have ventured
too near the nests. In one case more than a hundred empty shells
of that species found near a large ant’s nest were considered to be
remains of mollusks destroyed by the ants.

Although the enemies of the mollusca are almost legion, and include
members from almost every class of the animal kingdom and so des-
tructive that it is marvellous that any individuals escape their numer-
ous foes and live to perpetuate the race, yet, in addition to them,
there are also enemies even amongst their own ranks which are scarcely
less destructive than their more legitimate foes.

In the British Isles although many species intermittently display
malacovorous or cannibalistic propensities, such habits are not normal,
but often induceil by hunger, or other e.xcitant, Ifycdinia lucida being
perhaps the most readily addicted to gratifying its cannibalistic
tastes.

]\Iany foreign genera are, however, strictly and exclusively malaco-
vorous, feeding chiefly upon the jiliytophagous species of snails. In
South Africa the great Aerope caffra eagerly pursues and greedily
devours the Helix cn^persa which has accidentally or purposely been
introduced into that country, while in North America, at Charlestown,
South Carolina, the introduced Rumina decollata is said to be exter-
minating the Helix nemoi-alis, which was also a flourishing colony in
that city.

PARASITES.

421

111 addition to the destruction due to active effort, the Unionidw
are sometimes killed mechanically by the agglomeration of Dreissensia
poli/morpha upon their valves, preventing them opening for respiratory
and other purposes.

Parasites are organisms which at any period of their lives are depen-
dent for food, shelter, or protection, upon some other animal or animals,
with whose welfare they are, therefore, vitally concerned, and con-
sequently they do not at any time destroy their host, although some
forms are known to be the cause of castration in Heliv aspersa and
other species.

They are not, as formerly believed, present within or upon the body
only as a result of the diseased or vitiated condition of the blood or
tissues of the host, and therefore necessarily indicative of an un-
healthy condition of the body, nor is there a special class or race of
parasites, corresponding to that of bii’ds, reptiles, or other groups, as
all tlie classes of the animal kingdom have given off from their inferior
ranks some branches in this direction, probably consisting of those
weaker forms which being unable to successfully compete with the
newer and stronger races which have successively been evolved have,
in order to avoid extermination, been compelled to adopt a parasitic
life, their form becoming modified and degenerating by the atrophy of
the organs unsuited to their adopted life. From the severity of the
life competition, parasites have become so numerous that there are
few or probably no animals which do not entertain a more or less
numerous party.

The parasitic organisms dependent upon the mollusca are, with a
few exceptions, little known, and the cycles of life which many undergo
have only been thoroughly worked out in one or two species, but it is
certain that many of our native species harbour one or more of these
creatures and thus provide them with fooil and shelter, while several
of our mollusks are knowm to be liable to be infested by eight or ten
quite distinct species, which either affix themselves upon the exterior
of the body or live amongst the viscera, and may even be found in
the pericardial cavity. One species at least, though not in this
country, is infested by a species of fish which makes use of mollusks
as a nidus for its ova, the embryos being hatched and developed
amongst the branchial filaments. The young mollusks of the same
family are, however, themselves parasitic upon fishes, affixing them-
selves to and deriving nourishment from their hosts.

4-22

ENDO-PARASITES.

'L'rue parasites are entirely (lependeiit upon, and unable to exist
apart from, their hosts, as their alimentary canal has become degener-
ate and their nourishment is derived solely from the fluids of their
host, which are constantly being absorbed through the general inte-
gument and assimilated by the animal independent of its will.
Mutualists, commensals, or messmates, however, only avail themselves
of the shelter and protection that close proximity affords, feeding
independently of or in company with their entertainer.

Parasites, according to their habits and modes of life, may, for our
purpose, be divided into three sections, Ecto-parasites, Endo-parasites,
and Commensals.

The Enuo-Parasites of the mollusca are chiefly drawn from the
Trematodes, a large number of whose species pass through one or more
of the intermediate stages of their life’s cycle within the bodies of
various mollu.sks, many attaining their perfect or sexual development
within the body of some vertebrate ; each species is, however, more

Fig. 7:i3.

Fig. 73i.

Fig. 73.5.

Fig. 736.

Fig. 737.

Fasciola hc/>atica^ an endodermic parasite, showing the successive stages through which this
species passes before attaining sexual maturity (highly magnified, after Marshall and Van Beneden).

Fig. 733. — Free ciliated embryo.

Fig. 734.— Sporocyst, as living usually in lung cavity of Livinoca truncatula.

Fig. 735.— Redia, as living amongst the viscera and especially within the digestive gland of the
mollusk into which it has migrated from the lung cavity.

Fig. 736. — Cercarian stage which has escaped from the mollusk and again become free, eventually
encysting upon the grass and being eaten by sheep.

Fig. 737. — The mature sexual Distonia^ as developed from the cercarian stage within the bile
ducts of sheep.

or less restricted not only to particular species, but to special or
determinate parts or organs thereof.

These flat or soft worms usually begin existence by following a free
aquatic life, travelling by the aid of a ciliated investment and eventu-
ally effecting a lodgment within the body of the first suitable animal

ECTO-PARASITES AND COMMENSALS.

423

tli6y BiicouiitGr, wliicli is usually a luollusk, bGCOiiiuig scolicGs ov vgsi-
cular worms amongst tliG couuGctivG tissuG, musclos, etc., but at a
latGi- stagG occupying tliG digestive or respiratory passages which are
in free communication with the exterior.

The Ecto-Parasites are not nearly so numerous, the best known
examples being the Aca?y, found so commonly upon the bodies of the
terrestrial species, and the species of Aia.z^, which infest the Unionidee.

The Conchophthirus lives within and probably subsists upon the
body mucilage of various mollusks, both univalve and bivalve, while
ChcctogastcT, Mutzui, and other forms live within the respiratory or
mantle cavity of different species.

Amongst the Ecto-Parasites must also be placed the Micrococcus
conchivorus, a protophyte upon the shells and destroying its outer
layers, a process in which the species of Batrachospermum, Chwto-
phora, and other cryptogams assist.

Fig. 738. — An Ectodermic Para-
site from Hyalinia ccllaria (Miill.),
Philodromus Ihnacmn Jenyns X 30.

Fig. 739. — A Commen.sal, Mess-
mate, or Mulualist, Epistylis coarc-
iata Clap, and Lach.,a colony stock
(highly magnified after Saville Kent).

The Commensals or Mutualists are also often derived from the
lower ranks of the animal world, and simply make use of the shell or
body of the mollusk as an abode or place of fixation, and in such
positions we may frequently find forests of Vorticella and other Infu-
soria. That these colonies are not always harmless has been
demonstrated by Mr. R. Standen, who has established the proba-
bility that suitably-placed colonies of Epistylis or other urticating
genera are often responsible for the scalarid and other monstrosi-
ties of Planorbis spirorbis and doubtless other species.

The Uses of the land and fresh- water mollusca in this country for
food, ornament, medicine, or in the Arts are neither numerous nor
important. Probably, however, the principal value of the mollusca
to the human race generally is that they provide us directly and in-
directly with abundance of food, and although the terrestrial mollusca

424

USES — AS FOOD.

are not generally n.sed in this country as aliment, yet in some districts
they are freely consumed either for nonrishment or medicinally ; in
other and Wc\rmer countries, however, their use as food is much more
general and comparatively small species are utilized for this purpose.

As Food, the snail was one of the creeping things denounced in
Scripture (Leviticus, cap. xi.) as unclean, and its use for that pur-
pose forbidden, yet the larger kinds of testaceous land snails have been
held in repute in all ages, even by the Chinese and Hebrews for their
alimentary or curative properties, and the masses of Heliv shells
found in the caverns inhabited by the primitive men of the Stone
Age, i)robably indicate the indulgence of similar tastes by these
savage races, while kjokkenmikldings or heaps of kitchen refuse,
formed by countless generations of extinct pre-historic peoples, are
found in the United States, Brazil, Australia, New Zealand, Denmark,
Scotland, Ireland, England, etc. These immense mounds are some-
times hundreds of yards in length, and largely composed of the .shells
of edible mollnsks, bones of mammals, birds and fish, broken pottery
and primitive implements of bone or other material, and occadonally
contain terrestrial mollnsca, as in Denmark, in which Helix nemo-
/•((lis is found, while IIc'Ux (i^perxii has been recorded from a neolithic
kitchen-midden at Hastings, and from depo.sits resembling kitchen-
middens about a mile from the present banks of the Merse}', while
those of Florida have been noted to contain freshwater species.

'I'he predilection of the Homans for this food is widely known,
although this is stated to have been due, not to any special reli.sh for
such an insipid article of diet, but to a belief in its aphrodisiacal
virtues. The prevalence of Helicophagy among the Homans was,
however, so universal that they not only collected snails and imported
the more delicate and esteemed kinds from Illyria, Africa and other
places, but bred and fattened them for the table in specially arranged
farms or Cochlearia, a plan originated by Fulvinus Hirpinus, at
Tar([ninium, about .'>() B.C. d'hese Cochlearia were preferably some-
what shaded areas, encompassed by water, where in addition to the
growing vegetation, the snails were fed upon sodden wine dregs, bran,
Hour and vai'ious aromatic herbs, and under this generous diet they
ac([uircd a refined tiavonr and grew to a good size. This taste is also
evidenced by the use amongst them of an utensil, made from bone,
silver or other material, termed a Cochleare, especially adapted for
this purpose. This little implement had one end fashioned like an

USES — AS FOOD.

425

ordinary egg-spooii, while the other end was pointed for the purpose

of hooking the snail from its shell. That its name Cochleare was

derived from its usage may be inferred from the epigram by Martial :

“ Sum cochleis lialjilis, seil nec minus utilis ovis,

Namquid scis potius cur Cochleare vocer,”

which Sir W. W. Gull has freely rendered as

“ I am clever at Winkles, for eggs not less fit,

Then why Tm called Cochleare question your wit.”

IS^SP

Fig. 740.— Cochleare, or Roman silver spoon, found at Little Horwood, Buckinghamshire, reduced
to about half size of original (from Sir John Evans' collection).

Fig. 741. — Cochleare, or Roman silver spoon, found near Woodchester, Gloucestershire, reduced
to about half size of original (from Sir John Evans' collection).

if

Fig. 742. — Cochleare, or Roman silver spoon, found in the Thames, reduced to about half size of
original (from Sir John Evans’ collection).

In medifcval times snails were especially reserved in Denmark as a
privileged article of food for the nobility and gentry.

At the present day snails are largely used for human food in the
warmer countries of Europe and elsewhere, more especially during the
Lenten season, as the Roman Church permit their use as food during
that jferiod. They are stated to contain 1 7 % of nitrogenous matter
and to equal the oyster in nutritive propeities.

Snails are to this day cultivated for food in various parts of Europe
in special Snail-farms or Escargotih’es. One at Chalet St. Denis, near
Fribourg, described bj'- Mr. R. D. Darbishire, which fattens sixty to
eighty thousand Helix pomatia annually, consists of a large meadow
fenced in by boards about a foot high. The snails annually needed to
restock the farm are gathered every spring in the vicinity of the farm
by the farm labourers and at once placed on one-half the meadow
and left there until .Tuly, when they are transferred to the other half
of the field, which is divided by hoardings, about a foot high, into
numerous square spaces which are filled with moss, the snails being
fed therein upon cabbage until they become very fat and of a greenish-

42G

USES — AS POOD.

white colour. Towimls Sei)teinber the snails burrow into and hide
among, st the moss with the aperture upward and closed by the cal-
careous winter epiphragm. In this condition they can be exported
and are worth 17 francs per 1,000 ; some, however, do not form
epiphragms and, as they must be used more quickly, only realise 10
francs per 1,000. Paris alone is said to consume fifty tons daily
when in season, the most esteemed kinds coming chiefiy from Dau-
phin4 and Burgundy.

Snail eating is also very prevalent in Spain, where snails are
recognized articles of commerce, the women who deal in them, known
as Caracoles (from Caracole, a snail) congregate in the Snail market
with their baskets of snails before them, crying their wares and
occasionally cracking a .shell with their teeth to convince buyers of
the (juality.

In more remote countries many species belonging to genera not
generally considered edible in Europe, are consumed as articles of
food, Xeritina by the inhabitants of Mauritius and Guadeloupe,
and Ciiiuiies and XerltiiKc by the natives of the Solomon Isles,
Vivipanc by those of Cambodia, Balimi by the New Caledonians,
while Anodonta edtdis is regularly reared for food by the Chinese in
the ditches of Song-Kiang-Fou.

In this country, although several species of marine mollusca are
universally used and more or less highly valued as dainty or appe-
tising food, the non-marine species are not nearly so generally utilized
for the purpose, probably on account of the greater insipidity of their
tlesh. In some parts of the British Isles, more especially in the
western districts, Ileli.v aspcrsa is, however, held in good repute as an
excellent article of diet. The glass-blowers and others about Bristol,
Knottingley, in Yorkshire, and other places, not only use Helix aspersa
for food but consider it a cure for consumption, and so great is the
demand that in Bristol it furnishes a somewhat regular occupation
to gather them, as in summer, when considered unfit for human food,
they are used as food for ducks. Dr. Gray records that the glass-
workers of Newcastle formerly held an annual snail-feast, collecting
the snails them.selves the Sunday before the feast, and the working-
men of Lancashire had the reputation of indulging in a similar
custom.

The Unionidoc generally are considered edible in some districts and
are eagerly consumed in the i)oorer districts of Southern Europe,

USES — MEDICINAL.

427

when roasted and dipjied in oil or scattered over with bread crumbs
and scalloped. TJnio marcjaritifer was formerly considered as one of
the daintiest of foods, and the Anodontiv are considered edible in
many places abroad and are also eaten by the peasantry around
Lough Schur, Leitrim.

As Medicine, the Ancients considered the slugs and certain snails
to possess extraordinary virtues and attributed sovereign powers to
them in the treatment of various disorders. According to the then
current belief there was scarcely an ailment to which men or domestic
animals were liable which could not be cured by the proper use of
preparations of these animals. This exaggerated estimate of the
efficacy of these objects has been transmitted through many centuries,
and in some secluded and unsophisticated districts the belief in the
manifold virtues of these or similar remedies still exist.

The testaceous species, however, never appear to have attained the
celebrity in medicine acquired by the naked mollusks, but were more
used as articles of food, although in common with them, they have had,
even in comparatively modern times, a widely extended use, and were
considered a cure for Ague, Scrofula, Dropsy, Pleurisy, Fevers,
Asthma, Consumption and Pulmonary complaints generally, either
consumed living or prepared in a variety of ways, which were thought
to best conserve their efficacy.

Avion ater, Limax maximiis, L.flavus, Helix aspersa, H.nemoralis,
H. hortensis and H. arbustorum all at one time occupied places in the
Materia Medica or were the base of pharmaceutical preparations, and
even pearls long maintained a great medicinal reputation, a celebrity
due to the testimony of the Arabian physicians.

The Limacelle or internal shell of the Slug was held in high repute
as an exceptionally powerful remedial agent for toothache, the pains
being said to instantly cease when the little calcareous grains formed
in Avion are placed in the hollow tooth.

For dysentery, it was recommended that five slugs (preferably
African ones) be burned and mixed with the weight of a demi-denier
of Acacia, and two-spoonsful of this mixture to be taken in Myrtle
or other thick wine, with an equal quantity of warm-water, or in
severe cases to be administered as a clyster.

For healing ulcers, the ashes of Dormice, Wild Rats, Earthworms
and Slugs mixed with oil was considered very efficacious. The ashes
of burnt slugs were also believed to be especially powerful in healing

428

USES — MEDICINAL.

all ulcers of the foot, aiul Marcellas Empiricus recomuieiuled the same
as a remedy for hydrocephalus in children, while Kiraiiides prescribed
the application of a slug pounded, with incense, to arrest bleeding at
the nose.

Snails prepared in various ways used to be highly esteemed as a
cure for various injuries and diseases, ancient physicians regarding
snails pounded up with their shells as a remedy endowed with discu-
tient and resolvent properties, and the shell alone, when powdered,
as a diuretic.

Pliny, the elder, recommended snails for a cough or for pains in
the stomach, but it was considered essential that an uneven number
should be taken.

It is, however, in the treatment of pulmonary complaints that the
greatest cclehrity has been attained and in consumption the use of
preparations of Ueli.r and Ilelir pomat'm are said on good

evidence to be strikingly effectual. Lovell Reeve, in his “British
Land and Freshwater Shells,” published in 1862, says: “Mr. Barlow,
of the firm of John Dickinson and Co., paper-makers, informs me
that he has a brother who was in the last stage of consumption,
when their father resolved to try the experiment of a diet of Apple
Snails. The expressed mucilaginous juice of the snail was admin-
istered to the patient, without his knowledge, in every conceivable
form. It was taken in jellies and conserves, in gi-avies and with
entremets of meats. In the course of a twelvemonth the invalid was
entirely cured ami went to the Crimea, ami is living at this moment
a strong hearty man.”

Slugs have com})aratively recently been recommended in cases of
consumption by medical men. A relative (jf my own, who in his youth
was considered to have consumptive tendencies, by advice made
Ayrldlima.r a regular article of diet for some time, and in his

later years certainly showed no evidence of consumptive taint.

In this country when medicinally used for jndmonary complaints
or consumption they may be boiled in milk or made into a muci-
laginous broth, but may also be eaten alive or, if a shelled species,
the shell pricked through with a large pin to enable the patient to
suck the oozing liciuor.

Snail syrup, ])repared by i)assiug a stout thread through the shell
and body of a number of snails, and suspending them over a dish
of coarse brown sugar, upon which their mucilaginous exudations are

VARIOUS MINOR USES.

429

allowed to drop, is recommended by the village dames of Sussex as
a specific for coughs and colds.

Figuier has extracted from Helices an odorous and sulphurous
animal oil, which he has named Helicine, by means of which Dr.
Lemare is stated to have radically cured cases of consumption.

In Martin Lister’s time snails, and particularly Helir pomatia, had
long been considered as restorative in hectic fever cases.

In modem times preparations from snails have been employed by
qualified medical men for the treatment of many disorders, Mr. W. G.
Binney recording that in 1863 the Syrup of Snails was prescribed to
ailing members of his family by two regular French physicians in Paris.

A liniment of great local repute, for the relief or cure of Lumbago,
Rheumatism, Bruises, Sprains, etc., etc., was formerly prepared by the
late Mr. John Crowther, of Pontefi’act, by placing a number of Helix
nspei’sa within a large tin vessel, upon a warm boiler, the dark-brown
oily matter derived from their desiccation when mixed with ammonia
being ready for use.

In Veterinary medicine, Puton records that the husbandmen of the
Vosges used the calcined and powdered shells of Helices to destroy
the films that form on the eyes of domestic animals.

The Minor Uses of the mollusca are very various and often very
localized, the shells of mollusks are said to have been used as

Drinking Vessels by the Ancient Britons, and to have been the only
ones generally possessed by them ; the Highlanders, in the more
secluded districts, are said even yet to use them for the same purpose.

As Cream Skimmers, the thin-edged valves of A and Unio
have frequently been used in many country districts, and those of
Unio margaritifer are, or were recently, used in the Isle of ]\Ian as
scoops and as porridge spoons; while the shells of Helix pomatia
are used in France among Peach and Apple trees as traps for ear-
wigs, etc.

As Colour receptacles, the valves of Unio pictorum were formerly
employed by Flemish painters and, though they are now quite obsolete
for this purpose, they may still be occasionally obtained containing a
preparation of gold and silver for illuminating, though even for this
purpose the shells of Mytilus edulis seem now more in vogue.

For Button-making and other purposes, the nacreous or mother-o’-
pearl lining of the Lhiiones has been used commercially, and when
finely pulverized it makes a very excellent polishing powder for hard

430

VARIOUS GENERAL USES.

materials, while the aborigines of Port Curtis, Queensland, polish
their spears, boomerangs and waddies with the sharp edges of broken
shells of Heliv ciuminghami.

Colour of a somewhat brilliant violet, used by the mural painters of
the sixteenth century, is stated by Dumas and Persoz to have been
yielded by finely pulverized shells of Neritina flumatilis.

As Manure, Dreissensia polymorpha, which often exists in such
incredible numbers within a very limited area, has been used with
excellent effect in Lancashire for enriching the land.

Fertilization of Flowers may probably be sometimes accomplished
by mollusks crawling over them during cold or damp weather when
insects are not abroad. Magnus has recorded and especially noticed
the actuality of this process with AgrioUmax Iwvis and Chrysan-
themum vulgare.

Cement was made in Lister’s time by pricking the body of Helix
aspersa and collecting the fluid exuding therefrom, which when mixed
with an equal quantity of albumen and quicklime and well pounded,
form a durable and excellent cement for marble or stone, hardening
almost immediately.

Pounded snails were used at Montpellier to moisten the wooden
moulds, to prevent the adherence thereto of the wax figures and
allowing them to come easily away with a fine surface, and are said
also to have been formerly successfully utilized in the manufacture or
adulteration of cream.

As Food for Sheep, Helix virgata especially has long been credited
with contributing materially to the nourishment of sheep and as
being re.sponsible for the superior flavour of the South Down and
Dartmoor mutton, as it is quite impossible for the sheep to pasture
on the downs without devouring immense numbers of these snails.

This excessive abundance of Helix virgata, in some favoured locali-
ties, is so remarkable as to have originated the sensational reports of
“ showers of snails,” when these animals have appeared suddenly
from their hiding places in vast numbers after rain, following upon a
period of dry weather.

As Food for Fishes, the mollusks are very important and it is a very
prevalent belief that in rivers where Unio margaritifer exists the
trout fishing is markedly improved ; while in America the smaller
Pisidia have been shown to form one of the most important articles
of food of the Whitefish. According to Mr. Sturges Dodd, thq

USES — MONETARY AND DECORATIVE.

431

Barbel, Roach, Rudd, Chub, Grayling, Gudgeon, Bream, Perch, and
Burbot all feed upon aquatic mollusks.

As Bait, Anodon, TJnio and Vivipara are much used by fishermen,
Unio margaritifer especially being so employed, many boat loads
being said to be taken from the mouth of the Ythen, near Aberdeen,
and employed in the Cod and Ling fishery ; the use of Dreissensia,
as bait for Perch, by an angler led to the discovery of its existence in
this country ; while the larger Limncece are successfully used for bait
by the Leicestershire anglers.

As Money, certain shells, either in their natural state or worked into
particular shapes and strung together, forming Wampum, have been
almost universally used as money or as a medium for barter by all
savage and barbarous races, and although marine species are almost
invariably used for the purpose, yet Wampum was formerly made
from the shells of the Unlonidte by the Indians of New Brunswick,
Canada, and Achatina monetaria is similarly used by the natives
of Benguela.

For Decorative purposes or for personal ornamentation the Pearl
is “par excellence” the most prized object furnished by the mollusca,
yet the shells themselves, wholly or in part of many marine species,

Fig. 7A3. — Heliciclian necklace, made by the peasantry of Donegal, and composed solely of H elix
nemoratis^ reduced to one-fourth natural size (Mr. R. Welch's collection).

are much used by savage tribes for the same purpose, their brilliancy
and attractiveness being so superior to that of the non-marine forms,
which are, however, occasionally used for personal decoration, as in
South America, where the aborigines use the shells of Ampullaria,
Orthaliciis, Lahyrinthus BuUmidiis for ornamenting the elaborate

432

SUPERSTITIONS.

cloaks worn by women of rank, while the large Biil/ml are worn as
breast ornaments ami for other purposes. In the Island of Iona, Helix
itala and Helix (icuta are strung together to form necklaces, and at
Bundoran, in Donegal, and elsewhere. Helix neinomUs is similarly
employed, a practice regarded by Mr. Welch as a survival of a
prehistoric custom. The primitive men of the stone age probably
also adorned themselves with similar ornaments, as is testified by the
pierced shells of various species found in the caverns they frequented
in South-Western France, among which numei’ous shells of Viviparu
lentil are found, probably procured from the Isle of Wight, where they
are now so abundant in a fossil state.

From the earliest times preparations have been made from snails,
which were believed to be beneficial to the complexion, and compara-
tively recently the licpiid procured from them by distillation was used
by ladies to give whiteness and freshness to the complexion.

Superstitious reverence, in one form or another, has been accorded
to the mollusca by the more ignorant and credulous people of every
age, due to the emblematic exaltation of certain forms as symbolic of
the vital phase of religious faith, or to the imaginery popular belief
ill their efficacy as charms or amulets to ward off or protect the wearer
from injury or di.sease.

In ancient times the Egyptians venerated the Scarabieus or Sacred
Beetle as typifying in its life-history the resurrection, and in like
manner the (Jauls and Ancient Britons reverenced the Snail, as a visible
emblem or symbol of our resurrection and immortality, the image of
a shell .so often found .sculptured within the ancient Gallic tombs,
being emblematically expressive of the belief of these primitive people
in man’s resurrection and immortal life, and jiossibly the presence of
Helix shells in ancient Briti.sh burrows and tumuli may have some
similar significance.

The Romans habitually ate snails at their funeral repasts around
the tombs of those dear to them or at those of persons whose memory
they wished to honour, the evidence of the prevalence of this custom
is found in the masses of shells strewn about the cemeteries of
Pompeii. This incorporation of the snail among their funeral cere-
monies being probably a relic of the still older belief in the existence
of some mysterious link between the grave, silent snail and the spirit
of their ancestors, a superstition probably originating from the circum-
stance of finding snails living within the vaults of their forefathers,

SHELLS AS CHARMS OR AMULETS.

433

and the gradual attribution to them of a sympathetic attraction and
affection for the places of sepulchre where repose the dead.

The Romans, who derived many of their superstitions from the
Greeks, especially reverenced the internal shells of the slugs, believing
them to be powerfully curative in cases of tertian, quartan and inter-
mittent fevers when worn around the neck of the patient and falling
towards the heart, and that diseases of the head or headaches were
cured by carrying the shell upon the person or rubbing the forehead
with the minced or pounded animal; while the granular substance
representing the shell in Avion, if suspended from the necks of
infants, was firmly believed to facilitate teething.

Warts are believed by many rural folk to be easily removable if a
living slug be rubbed over the affected part and the animal then im-
paled upon a thorn, in some secluded place, and left to die. As the
snail dies and gradually shrivels up, the wart, being impregnated
with its matter, will shortly do the same and gradually disappear.

Worn firagments of shells or Snail-stones were formerly esteemed
in the Scottish Highlands and in Guernsey as a remedy for affections
of the eyes, but the Snail-stone of Scotland, to which many mysterious
virtues were long ascribed, was merely a piece of blue glass.

In some barbarous countries many species, especially if sinistrally
coiled, are reverenced as sacred, or as charms protecting the owner
from evil spirits or disease.

The Kabyles of Algeria perforate the ends of the valves of Unio
pict(yvum, which they call thimah’riu, and suspend them around the
necks of their children as Amulets, believing them to be a powerful
protection against evil influences.

The negroes of Prince’s Islands formerly were in the habit of
suspending a string of Helix bicarinata above the doors of their
cabins, as an act pleasing to the gods and calculated to secure their
protection ; while Achatina perdix was formerly forbidden to be ex-
ported from the East Indies, probably from some ancient superstition
regarding it.

Reversed varieties of the Turbonilla or Chauk Shell are held sacred
in the far East. In India the God Vishnu is represented holding this
shell in his hand, while in China they are kept in the Tem2)les, and
used only for anointing the Emperor on his coronation, for the
administration of medicine on important occasions, and for bestowal
by the Emperor upon high officials, whose duties oblige them to cross

C2

22,12/1900

434

EXORCISM AGAINST AND AUGURY BY SNAILS.

tlie sea, as the sacred shell when blown is believed to have power to
still the W8,ves and thus ensure safe voyages.

Snails have, however, at times fallen under the ban of the Church,
and a prayer of the holy martyr, Trypho of Lampsacus, who lived
about the tenth century A.D., contains the following quaint exorcism
directed against them.

“0 ye Caterpillers, Worms, Beetles, Locusts, Grasshoppers,
Woolly-Bears, Wireworms, Longlegs, Ants, Lice, Bugs, Skippers,
Cankerworms, Palmerwornis, Snails, Earwigs, and all other crea-
tures that cling to and wither the fruit of the Grape and all other
herbs, I charge you by the many-eyed Cherubim and by the six-
winged Seraphim, whicli fly around the Throne, and the holy Angels,
and all the Powers, etc., etc., hurt not the Vines nor the land nor

the fruit of the trees nor the vegetables of , the servant of

the Lord, but depart into the wild mountains, into the unfruitful
woods, in which God hath given j'ou your daily food.”

Augury or Soothsaying, to foretell the result of any impending-
conflict, is practised in Japan and other places by means of Vivipara
japonica, specimens of which are ])laced at opposite corners of a tray
to represent the belligerents and those advancing reveal the con-
quering party.

The Sea Dyaks of Sarawak similarly establish the guilt or innocence
of accused persons, by the accuser and accused each selecting a land
shell, upon which lemon juice is squeezed, the one moving first shows
the guilt or innocence of its owner, according as rest or motion has
been agreed upon to prove the case.

Divination, even at this day, is said to be practised by the rustic
English and Irish maidens who believe that, if on May-day morning,
the small white slug (Agriolimax agrestisT) be placed upon the
hearth or other smooth surface lightly sprinkled with flour or fine
dust, it will by its track describe thereon and thus reveal the initial
of their unknown lover’s name.

LITERATURE

(Additional to the works enumerated on page 383 et seq.)-

Beneden, P. J. van. — Animal Parasites and Messmates. — 1876.

Bell, K. G.— Land Shells of the Bed Crag. — Geol. Mag., 1884, pp. 262—4.
Carpenter, G. H. — Tlie Problems of the British Fauna. — Nat. Sci., Dec.,
1897.

Cobbold, T. S. — Entozoa, an Introduction to the Studj' of Helminthology.
1884.

Cossmann, M. — Catalogue d. Coquilles Fossiles de I’Eocene de Environs
de Paris.— Bruxelles, 1886-1889.

Edwards, F. E. — A Monograph of the Eocene Mollusca. — Pak-eont. Soc.,
1852.

Gardner, J. Starkie. — On the Land Mollusca of the Eocene. — Geol. Mag.,
June, 1885.

LITERATURE. 435

Heilprin, A.— The Geographical and Geological Distribution of Animals.
— London, 1887.

Hind, Wheelton.— A Monograph of Carbonicola, Anthracomya, and Naia-
dites. — Palaeont. Soc. , 1894-6.

On Three New Species of Laiuellibranchs from the Carboniferous
Rocks of Great Britain. — Quart. Journ. Geol. Soc., 1899, p. 365.

Hudleston, W. H. — A Monograph of the British Jurassic Gattropoda. —
Paheont. Soc., 1896.

Hughes, Mrs. McKenny. — On the Mollusca of the Pleistocene Gravels in
the Neighbourhood of Cambridge. — Geol. Mag., 1888.

Kennard, A. S. — Notes on the Alollusca from a Kainwjish at Darcnth.
Kent. — Proc. Mai. Soc., Oct., 1896.

Kennard and Woodward. — The Mollusca of the English Cave-Deposits. —
Proc. Mai. Soc., Nov., 1897.

The Pleistocene Non-Marine Mollusca of Ilford. — Proc. Mai. Soc.,
Feb., 1900.

A Revision of the Pliocene Non-Marine Mollusca of England. — Proc.
Mai. Soc., March, 1899.

Kennard, Woodward, and Webb. — Tlie Post- Pliocene Non-Marine Mol-
lusca of Essex. — Essex Nat , 1897, pp. 87-109.

Kent, W. Saville. — A Manual of the Infusoria. — 1880-1.

Moore, C. — Abnormal Conditions of Secondary Deposits when connected
with the Somersetshire and South Wales Goal-Basin. — Quart. Journ.
Geol. Soc., 1867.

Laver, H. — Periodicity in Organic Life. — Essex Nat., 1893, pp. 51-64.

Newton, R. Bullen. — Systematic List of the Frederick E. Edwards Collec-
tion of British Oligocene and Eocene Mollusca. —1891.

On Archanodon jukesi. — Geol. Mag., June, 1899.

Newton and Harris. — Description of some New or Little-Known Shells of
Pulmonate Mollusca from the Oligocene and Eocene Formations of
England. — Proc. Mai. Soc., March, 1894.

Prestwich, J. — Observations on the Eocene Strata of England, Belgium,
and the North of France. — Quart. Journ. Geol. Soc., 1888.

Reynes, J. — L’Escargot, Sa Rehabilitation. — Paris, 1874.

ScharfF, R. F. — ^The History of the European Fauna. — 1899.

Scott, Thos. — Preliminary Notes on a Post-Tertiary Freshwater Deposit
at Kirkland, Leven, and at Elie, Fifeshire. — Proc. Roy. Physic. Soc.
Edinb., 1890-1, p. 335.

Wallace, A. Russel. — The Geographical Distribution of Animals. — 1876.

Wood, Searles V. — A Monograph of the Crag Mollusca, 1848-50, and
Supplement, 1872. — Palsont. Soc.

A Monograph of the Eocene Mollmsca. — Palceont. Soc., 1877.

Woodward, B. B. — Note on the Pleistocene Land and Freshwater Mol-
lusca from the Barnwell Gravels. — Proc. Geol. Ass., vol. x., no. 7.

On the Pleistocene (Non-Marine) Mollusca of the London District. —
Proc. Geol. Ass., vol. xi. , no. 8, 1890.

LIST OF SUBSCRIBERS.

Ailains, Lionel E., B.A., 68, Wolverhampton Road, Stafford.

Aldridge, Rev. .J. M., M.A.. Maisey Hampton Reetory, Fairford.

Adkin, R., F.E.S., WelKield. 4, Lingards Road, Lewisham, S.E.

Atkinson, F. E., M.R.C.S., L.R.C.l’., etc. , Whitefriars, Settle.

Archihald, C. F., M.B.O.U., 9, Cardigan Road, Leeds, and Rusland Hall,
Ulverston.

Arnold, Bernard, F.L.S., Milton Lodge, near Gravesend.

Babor, J. F., vii., 748, Prague, Bohemia.

Backhouse, J., F.L.S., F.Z.S., M.B.O.U., Daleside, Harrogate.

Baillie, W., Brora, N.B.

Barnacle, Rev. H. Glanville, IM.A., F.R.A.S., St. John’s College, Grimsargh.
Banks, W. H., Hergest Croft, Kington, Herefordshire.

Barker, R. H. , (trosvenor Bank, Scarborough.

Barnsley Naturalists’ Society.

Beeston, H. Hawkestone, Havant, Hants.

Birchall, E. , 18, Moorland Road, Leeds.

Blackburn, Rev. E. P., Belmont, Hoyland, near Barnsley.

Blackmore, J. C., F.G.S., Falkirk, Whatley Road, Clifton.

Blackshaw, J. C., 158, Penn Road, M'olverham2rton.

Bliss, J., Smyrma.

Bloomer, H. Howard, 35, Paradise Street, Birmingham.

Bostock, E. D. , F.L.S., F.R.M.S., Tixall Lodge, Stafford.

Bowell, Rev. E. W. W., The Cockpit, Parkgate, Cheshire.

Boycott. A. E., The Grange, Hereford.

Bradford Naturalists’ Society.

Bradford Public Library.

Branson, F. W. , F. I.C., Wynneholme, Headingley, Leeds.

Breeden, Guy, 38, Station Road, King’s Norton.

Brierley, Mrs. H. G. , Glen View, Gledholt, Huddersfield.

Bristol Naturalists’ Society.

Bristol IMu.seum and Reference Library, Queen’s Road, Bristol.

Brode, Rev. T. Ainsworth, B.A., 3, Penley’s Grove Street, York.

Buckell, E. , 'Wykeham House, Romsey.

Bullen, Rev. R. A.shington, M.A., F.L.S., F.G.S., Axeland, Horley, Surrey.
Rumpus, J. & E., Ltd., Holborn Bars, E.C.

Burton, F.ISL, F.L.S., F.G.S., Highfield, Gainsbrough.

Butterell, J. Darker, Manor House, Wansford, Beverley.

Cash, W., F.G.S., F.R.M.S., Commercial Street, Halifax.

Cairns, R., 159, (^ueen Street, Hurst, Ashton-under-Lyne.

Chaini), H., c/o S. & J. "Watts & Co., Manchester.

Chaytor, R. C., Scrafton Lodge, Middleham.

Christy, R. Miller, F.L.S., Pryors, Broomfield, near Chelm.sford.

Clapham, S. C., F.Z.S., Fryern House, Court Road, Eltham.

Clapp, G. 11. , 116, "Water Street, Pittsburgh, LLS. A.

Coates, H., F. R.S.E., Pitcullen House, Pertli.

Cockerell, Prof. T. D. A., F'.Z.S., Las Cruces, New Mexico, U.S.A.

Cockerill, J., 6, Park Lane, Holgate, York.

Coles, C. S., The Pheasantries, Hambledon, Cosham, Hants.

Collier, E., Carlton House, Whalley Range, Manchester.

LIST OF SUBSCRIBERS.

437

Collinge, W. E., F.Z.S. , The University, Birmingham.

Conchological Society of Great Britain and Ireland, Owens College, Manchester.
Cornish, J. E., 16, St. Ann’s Square, Manchester.

Crick, W. D., F.G.S., Nine Springs, Cliftonville, Northampton.

Crook, Rev. G. W., M.A., St. Andrew’s House, Ilournemouth.

Crowther, H., F.R.M.S., The Museum, Leeds.

Crowther, J. E., Portland Street, Elland.

Dacie, J. C. , 14, Montserrat Road, Putney, S.W.

Daniel, A. T., M.A., Richmond Terrace, Shelton, Stoke-on-Trent.

Darbishire, R. D., B.A., Victoria Park, Manchester (two copies).
Darnborough, F., Croft Villa, Eaglescliffe, Yarm.

Denny, Prof. A., F.L.S., Firth College, Sheffield.

Dillon, Hon. R. E. , D.L., Clonbrock, Ahascragh, Galway.

Dixon, J. Bassett, Ribblesdale House, Preston.

Dodd, B. Sturges, Vine Villa, 62, Noel St., Gregory Boulevard, Nottingham.
Drake, R. Ingalton, Eton College, Windsor.

Dulau & Co., 37, Soho Square, W, (three copies).

Eccles, J. C., 20, Winckley Stieet, Preston, and 3, Dudley Terrace, Ventnor.
Edwards, T. , Cliftonville, Equity Road, Leicester.

Edward Pease Public Library, Crown Street, Darlington.

Essex Field Club, Buckhurst Hill, Essex.

Evans, W., F.R.S.E., M.B.O.U., 18a, Morningside Park, Edinburgh.

Evans, Mrs. A., Brimscombe Court, Tlirupp, near Stroud.

Eyre, Rev. W. L. W., M.A., Swarraton Rectory, Alresford.

Falloon, Mrs., Christchurch Vicarage, Dover.

Farrah, J., F.L.S., F.R.Met.Soc., Jefferies Coate, Harrogate.

Farrer, Cant. W. J., Chapel House, Bassenthwaite.

Fierke, F. vV., 73, Redbourne Street, Hull.

Fitzgerald, Rev. H. P., M.A., F.L.S., Wellington College, Berks.

Fox, W. A., Cleckheaton.

Franklin, W. E., 42, Mosley Street, Newcastle.

Friedlander & Sohn, Carlstrasse, 11, Berlin (three copies).

Garforth, W. E., J.P., etc., Halesfield, Normanton.

Garnett, Roland, 175, Lee Street, Oldham.

Glasgow Natural History Society.

Godlee, Theo., Whips Cross, Walthamstow.

Godwin-Austen, Lt.-Col. H. H., F.R.S., etc., Nore, Godaiming.

Gould, Edith, 9, Culford Gardens, Chelsea.

Goulding & Son, 20, Mercer Row, Louth.

Grevel & Co., 33, King Street, Covent Garden, W.C. (two copies).

Gude, G. K., F.Z.S., 114, Adelaide Road, Hampstead, N.W.

Gyngell, W., 13, Gladstone Road, Scarborough.

Hargreaves, J. A., 3, Ramshill Road, Scarborough.

Harmer, F. W., F.G.S., Oakland House, Cringleford, near Norwich.

Harrison, Albert, F.C. S. , F. L. S. , F. R.M. S. , 72, Windsor Rd., Forest Gate, E.
Harrison, G. Maredydd, Nightingale House, Manchester Road, Southport.
Hawell, Rev. J., M.A., F.G.S., Ingleby Greenhow Vicarage, Middlesbrough.
Heathcote, W. H., F.L.S., 47, Frenchwood Street, Preston.

Heginbothani, C. D., 3, Estcourt Street, Devizes.

Hibbert, C. R. C., Riccardo’s Down, Abbotsham, Bideford.

Hillman, T. Stanton, F.E.S., Eastgate Street, Lewes.

Holmes, Wb J. O., F.L.S. , Strumpshaw Hall, Norwich.

Hopkinson, J., F.L.S., F.G.S., F.R.Met.Soc., Weetwood, Watford.

Horsley, Rev. J. W., M.A , St. Peter’s Rectory, Walworth.

Jackson, E. H., 5, Lower Derby Road, Watford.

James, J. H., A.R.I.Cornw., 3‘, Truro Vean Terrace, Truro.

Jenner, J. H. A., F.E.S., 4, East Street, Lewes.

Jones, K. Hurlstone, M.B., R.N., F.L.S., H.M.S. Repulse.

438

LIST OF SUBSCRIBEES.

Kane, W. F. de Visiues, D.L., M.A., M.K.I.A. , F.E.S., Drunireaske House,
Monaghan.

Kegan, Paul & Co., Charing Cross Road, London (two copies).

Keogh, J. W. H., Inca, Parkwood Road, Boscombe.

Kew, H. Wallis, F.Z.S., 157, Ferine Park Road, Hornsey, N.

Knight, Rev. G. A. Frank, M.A., F.C. Manse, Auchterarder, N.B.

Lawson, P., F.R.M.S., 11, The Broadway, Walham Green, S.W.

Leeds Industrial Co-operative Society (Educational Department).

Leeds Public Library.

Leicester, A., The IMount, Aston-Clinton, Bucks.

Linen Hall Library, Donegal 1 Square North, Belfast.

Linton, John, 25, Wordsworth Road, Smallheath, Birmingham.

Loydell, A., 36, Milton Road, Acton, W.

Lucas, B. R. , 3, Dyar Street, Winnington, Northwich.

Madison, J., 167, Bradford Street, Birmingham.

Mallalieu, Harold, Shady Grove, Delph viA Oldham.

IManchestcr Conchological Society, Owens College, Manchester (two copies).
Mansel-Pleydell, J.C., D.L., F.G.S., F.L.S., Wnatcombe, Blandford.
MaseHehl, J. R. B., M.A., Rosehill, Cheadle, Staff.

Mason, P. B., J.P., F L.S., F.Z.S., etc., Trent House, Burton on-Trent.
.Mayfield, A., 88. Stafford Street, Norwich, and Mendlesham, Stowmarket.
McAndrew, J. J., F.L.S., Lukesland, Ivybridge, South Devon.

McKean, Kennetli, F.L.S., 1, Lewin Road, Streatham,S. W.

McMurlrie, Rev. Dr. J., M.A., 5, Inverleith Road, Edinburgh.

Melvill, J. Cosmo, M.A., F.L.S. , Brook House, Prestwich.

IMills, F. W., F.R.M.S., Thornlcigh, Huddersfield.

IMilnes, Rev. H. , The Friary, Priory Street, Cheltenham.

Montgomery, A. M., 32, The Grove, Ealing.

Morris, C. H., School Hill, Lewes.

Mo.ss, W., F.C. A., 13, Milton Place, Ashton-under-Lyne.

Museum of Science and Art, Dublin.

National Library of Ireland, Dublin.

Nelson, W., Prospect View', Crossgates, near Leeds.

Newstead, il. H. L., B.A., Rose Villa, Prospect Road, Woodford Green.
Newton, R. Biillen, F.G.S., 7, jMelrose Gardens, West Kensington Park, W.
Northampton Natural History Society and Field Club.

North Kent Entomological and Natural History Society.

Norton, Rev. Tlios., Wychling Rectory, near Sittingbourne.

Oldham, Clias., Ahlerley Edge, Cheshire.

Orr, Hugh Lamont, tlarfield Street, Belfast.

Pannell, Ch., jr. , East Street, Haslemere.

Parke, Geo. H., F.L.S., F.G.S., St. John’s, Wakefield.

Parry, Lt.-Col. G. S., 18, Hyde Gardens, Easthourne.

Pawson, A. H., J.P., F.L.S., F.G.S., Farnley, near Leeds.

Pearce, Rev. S. Sjiencer, M.A., Long Combe Vicarage, Woodstock.

Petch, Tom, B. A., Hedon, Hull.

I’reston Scientific Society.

Petty, S. Lister, Queen Street, Ulverston.

Ransom, E. , 16, Friars Street, Sudbury.

Raven, Eustace, La Couture, St. Peter’s Port, Guernsey.

Rhodes, J., F.E.S., Municipal Technical Schools, Accrington.

Roebuck, W. Denison, F.L.S., 259, Hyde Park Road, Leeds.

Rose, James, M.A., 1, Raw'linson Road, Oxford.

Rowntree, Allan, Broom Lodge, Scarborough.

Salford Borough Royal Museum and Library.

Scharfi', R. F., Ph.D., B.Sc., M.R. I.A., Museum of Science and Art, Dublin.
Shillito, J. G., 20, Elmore Road, Sheffield.

LIST OF SUBSCRIBERS.

439

Sich, Alfred, F.E.S., Brentwood, Barrowgate Street, Chiswick.

Simpkin, Marshall & Co. , 4, Stationers’ Hall Court, E. C.

Smith, W. J. , 41, North Street, Brighton.

Sorhy, H. Clifton, LL.D., F.R.S., F.L.S., F.G.S., etc., Broomfield, Sheffield.
Sotheran, H. & Co., 140, Strand, W.C.

Stalley, H. J., 68, Little Britain, E.C.

Stanford, E., 26, Cockspur Street, Charing Cross, S.W.

Stedman, R. B., 33, High Street, Godaiming.

Stevens, B. F., & Brown, 4, Trafalgar Square, W.C.

Stonestreet, Rev. W. T., 307, Great Clowes Street, Higher Broughton,
Manchester.

Stubbs, A. G., Staincliffe, Granville Road, Eastbourne.

Stump, E. C., 16, Herbert Street, Moss Side, Manchester.

Sykes, E. Ruthven, B.A., F.Z.S., 3, Gray’s Inn Place, AV.C.

Sykes, R., Lochiel, Cumbernauld.

Syms, Richard, F.R.Hist.Soc., Bidngton, 429, Barking Road, E.C.

Thacker & Co., 2, Creed Lane, E.C.

Thin, Jas., 54, South Bridge, Edinburgh.

Thompson, Beeby, F.C.S., F.G. S., 55, Victoria Road, Northampton.

Tomlin, J. R. Brockton, B. A., F.E.S., Stancliffe Hall, Matlock.

Tomlin, W., 24, Trinity Street, Cambridge.

Treacher & Co., Brighton.

Turner, E. C. , Coggeshall, Essex.

Turner, E. H. , A.C.A., 21, Bairstow Street, Preston.

University College, Aberyst^vyth.

University College, Nottingham.

Vaughan, J. Williams, Velinne\vydd, Talgarth, Brecon, R.S.O.

Varty-Sraith, J. C., Nandana, Penrith.

Waddell, Rev. C. H., B.D., The Vicai’age, Saintfield, Co. Down.

Wager, Harold, F.L.S., Arnold House, St. Barnabas, Derby.

Wakefield, H. R. , 7. Montpellier Terrace, Swansea.

Walker, Bryant, Moffat Buildings, Detroit, U.S.A.

Warrington Museum.

Ward, F. H. J., M.R.C.S., 8, Lyndhurst Villas, The Park, Ealing, W.
Watkins & Doncaster, 36, Strand, W.C.

Watson, Rev. R. Boog, LL.D., F.R.S.E., F.L.S., F.G.S., U.F.C. Manse,
Cardross, N.B.

Watson, Hugh, Lauder Grange, Corbridge-on-Tyne.

Webb, J. Stenson, Winscombe House, Far Headiugley.

Webb, Wilfred M., F.L.S., “Odstock,” 7, Campbell Road, Han well, W.
Welch, R., 49, Lonsdale Street, Belfast.

Weston Park Public Museum, Sheffield.

Wheldon J. & Co. , 58, Great Queen Street, W. C. (two copies).

Whitwell, W., F.L.S., 4, Thurleigh Road, Balham, S.W.

Williams, J.W., M.R.C.S. ,F.L.S., etc., 128, Mansfield Rd. , Gospel Oak, N. W.
Wilson, J. C., 124a, Stamford Street, Ashton- under-Lyne.
Woodruffe-Peacock, Rev. E. Adrian, L.Th., F.L.S., F.G.S., CadneyVicarage,
Brigg.

Woolston, T., 22, Wilson Street, Middlesbrough.

Wotton, T. W., “Marguerite,” Richmond Wood Road, Boui'nemouth.
Wright, C. E., Woodside, Kettering.

Yorkshire Philosophical Society, The Museum, York.

Yorkshire Naturalists’ Union, Leeds.

INDEX.

Jicfcroiccs io jiijiircs and cxphotatory text arc giuen in Eomaii numerals,
llcfcrcnccs to the text only are in Italic numerals.

Al)(loniinal gaii<;lion page?, 149, 230.

Abnormal growth 121, cause of 131.

Abrasion 73.

Absorbent canals 300.

Absorption of columella 30.

Abyssal depths, effects 77, 70, So.

Acantlioglossa 266, 267.

Acrecbolic protrusion 1S8.

Acrembolic retraction 188.

Aculeate teeth 266.

.Vdductor muscles, 1S3, 345, anterior
IS.', 346. 347, in .1 nndonta 1S3, classi-
lication by 10, 345, ]>osterior 1S3,
346, 347, structure 346.

Admedian radular area 360.

.\dmedian teeth (see lateral teeth).

-Estivation 30S.

-Vlferent, nerves 212, ]mlnionary veins
l.")6, tactile nerves 244.

Age, inlluence on colour 32S, on heart
])ulsation 207.

-Vgnatlia 350.

Agrinlhnax agrr.stis, buccal section
269, embryo 381, nepbridial section
33.7, respiratory and anal orilices 283,
sarcobclum exserted 36.), semper’s
organ 243, vor.acity 3 SO.

Ayrioliinax Iwri.',’, proterogyny 351.

-Mate bivalves 41.

-\lbinism SO, pi. ii., f. 5, c.auses.W.

-\lbumen gland ,3.')9, Helix ((sjicrsr( 160,
161.

-Miment.ary system 13S, 24.5, of arche-
type 143, Anodonta ryynca 171, 172,
Arion hortensis 246, Dreissensia
/lolyinorpha 277, lIcH.c aspersa 153,
1.53, 154, 245, lleli.v la/iicida 284,
Umax /fariis '2H4, I., maxim ns2Si7i,
Limniva perryra 274, L. staynrdis
279, Suceinca clegans 282, Tcstaeclla
halintidea 246, 28.5.

Altitude, elfect of <9.J.

Amalia carinata 50.

A mid id gagates, cephalic retractors 342.

Amalia soteerhyi, body torsion 282,
facial grooves 186, rival spermato-
pbores 374, spermatopboie in epi-
[iballus 376, sperinatophore in sper-
matheca 376.

Amitosis 378.

Ama'bocyte.sof //effx ponmtia 139,296,
340.

Amorous preludes in g.astropods ,372.

Amphipeplca glutinosa 202, pallial
extension 201, 202, periodicity 59/.

Amulets 433.

Ancylus fluviatilis, form 25, apex of
shell 115, speed 5.^.9.

Animal, external features 134,
Helix 144, of pelecypoda 163, 164,
185, literature 3S3.

Anisopleura 5, torsion 5, 6, 109, 205,
206.

Anodonta, ad<luctors 1S3, 345, calcic
cells 178, cephalic region I64, cepha-
lic eyes 171, clear water, effects on
colouring 87, embryo .346, gill struc-
ture 177, glandular system 178,
lacunar tissue 1,39, levators 183,
mu.scular system ISO, 181, nephri-
dial section 33.3, orbicular muscles

181, otocyst and nerve 241, pallial

line 181, pallial region I64, pedal
region 164, 166, posterior pedal

muscles 183.

Anodonta anatina ■12, abate 41, axis of
cerebral ganglion cells 210, cerebral
ganglion cells 210, 217, chitinous
frame of ctenidium 137, embryonal
sculpture 72, external features 164,
genital lobule 184, ligament 48,
liver lobule 173, liver elements 173,

* section showing peilal muscles, etc.,

182, visceral ganglion cells 210,
young 41.

v. complanata 44, 52, 72, v.

radiata 43, 50.

Anodonta cygnea, .36, alimentary tract

172, arrangement of organs 166, and
section 177, arterial system 174,
.arteries of p.alps 191, cephalic eyes
171, cerebral ganglia 168, chemical
structure of shell 38, cireulatory
.system, section 175, circulation 176,
continuity of palps and gills 191,
crystalline style 173, 278, effect of
l)lethora of lime 70, lliiche tricuspi<le

173, genital ducts, section showing
18.3, gill cavities 177, gill structure
177, glochidial byssus 322, gusta-
tory organs 171, heart 173, section of
291, injuries, effect of 103, keber’s
valvule 176, 295, labial palps 171,
190, liver 173, lophophoral line 301,

INDEX.

441

Anodonta ci/(jnca (contd. ).
mouth 190, muscular system 181,
347, muscle-scars 10, 55, 180, neph-
ridial section 179, 334, nervous sys-
tem 167, 168, 216, olfactory m'gans
171, orbicular muscles 181, otocysts
170, 237, otolith 170, pedal ganglia
168, pericardial gland 179, 180, pro-
ductiveness 372, ridges of palps 191,
section, showing nerve-centres 169,
stomach 172, stomach, section of 171,
symphynote 41, tactile siphonal ten-
tacles 244, typhlosole 171, 172, 173,
venous system 175, ventricle 290,
visceral ganglia 169, young 41.

V. cordata 53, v. diminuta 44,

V. incrassata 79.

Anodonta Jluviatilis, muscular sys-
tem 181.

Annulus of dart. Helix aspersa 366.

Anterior adductor 182, 343, 347, de-
velopment of 346.

Anterior, chamber of bivalves .^.9, crest
43, gland 314, gut 2^5, margin 37,
pedal gland 196, 314, pedal re-
tractors 182, 347, protractors 182,
salivary glands 275, sinus 44.

Anteriorly-produced bivalves 40.

Anteriorly-truncate bivalves 53.

Antero-lateral hinge-teeth 46.

Antero-ventral torsion 206.

Aorta 292, anterior, of Helix 155, of
Anodonta 174, posterior, of Helix
155, of Anodonta 175.

Aperture 31, 32, auriculate 32, com-
pressed 33, contracted 31, circular
33, deflected 34, dentate 34, in-
flected 34, longitudin.al 32, lunate
33, marginate 35, oblique 33, patu-
lous 34, plicate 35, pyriform 33,
reflected 34, rounded 33, sej)tate 35,
sinuous 34, transverse 33.

Apex, defined 30.

Aphallia, dioecia 352, monoccia 354.

Aplexa hypnoruni, odour from 230.

Appendages, umbonal 42.

Appendicula 364.

Appendiculate jaw 256.

Appendix 356, 363.

Aquiferous system 196, 300.

Area barhata, pallial eyes 234.

Archetypal mollusk, organization 142.

Archenteron 381.

Arctic region 397, 399, pi. v.

Area of bivalv'es 45.

Arion, caudal gland 197, 319, semper’s
organ 190, 243.

A rion ater, arteries 293, colour changes
during growth 327, connective tis-
sue-cells 293, foot fringe 192, mouth
185, organs of Semper 185, neuro-
epithelialcell 135, peripodial groove
192, vision 235.

v. rufa pi. ii., f. 6.

Arion cireinnseriptus,fiex\\oX organs 371.

Arion hortensis 203, alimentary tract
246, mucous (ilament 317, pallial
out-growth 203, sexual organs 357.

Arion suhfuscus, cephalic retractors
344, mucous filament 317.

Armature of aperture 66, in young 67,
Clausilia 68, dentate 34, plicate 35,
marginate 35, septate 33.

Arteries 293, Anodonta cygnea 174,
Arion ater and Testacdla lialio-
tideu 293.

Articulate operculum 127.

Atavism 113.

Atrium 371.

Auditory organs 138, 237, of arche-
type 142, of Anodonta 170, of Helix
151, canal of 2.38.

Augury by snails 434-

Aulacopoda 193.

Auricle, gland of (see Lymphatic gland)

Auricles .2.97, Helix aspersa 155, Ano-
donta 173, 174.

Auriculate apertui-e 32.

Auriform a))erture (see Auriculate).

Auriform lobe, Flanorbis corneus 201,
304.

Auri-ventricular valves 174-

Australasian region 397, 398, pi. v.

Auxiliary organs 123.

Azcca tridens, columella lamella 128.

V. nouletkum 33, aperture 33.

Azygobranchia, defined 7.

Bacilli of concretionary gland 339,
function 339, movements 339.

Bait 431.

Balea. perversa, form 24, habitat 85.

Banding 95, abrupt development 100,
causes of 96, development 98, disin-
tegration 99, foi'niulm 96, fusion
100, rhythmic development 100,
vestigial 101.

Basal membrane 260.

Basal plate 266, 269.

Base of univalves 30.

Basommatophora, defined 9, locomo-
tion 349, nervous system 214, 215,
otoconia 239, speed 349, ureter 336,
retractors 343.

Bathymetrical distribution 390.

Batrachian enemies 4I8.

Beak of bivalves 43, 44.

Beloglossa 267, formula 268.

Belogonaeuadenia, sexual organs 394,
distribution pi. iv.

Belogona siphonadenia, sexual organs
394, distribution pi. iv.

Bembridge deposits 412.

Bibliography 13, 18, 131, 383, 405.

Biforate pelecypod 165, 198.

Bilateralia 209.

Bipolar ganglion cells 210.

Birds as enemies 417.

442

INDEX.

Bithynia tcntaculatu, foriii 24, jaws
2o2, male organs 361, operculum
123, segmentation of ovum 380.

Bivalve (see Pelecypoila).

Blastoco'l 3S1.

Blastopore 245, 381.

Blastula (see Morula).

Blood 139, 294-

Blood-sinus of lung 30o.

Body, region 136, of Anodonta 166, of
Helix 146, 204, whorl 26.

Branchim 301.

British Isles, fauna of 401, pi. vi.

“Brush” sensory cells 170.

Branchiopneusta, defined 9.

Branchia' 301.

Buccal armature, preparation of 272,
staining 273.

Buccal bull)247, co-ordination of arma-
ture 249, gastropods 342, euthyneura
‘25d,Ar/riolima.c arjrcstis, section 269,
Tcatacclla haliotidea, section 266,
Linutx cinereo -niijer 243, Cyclo-
stoma clcgans 247, Helix as/icrsa
152, streptoneura, section 248, pro-
tractors 247, 259, retractors 159, 247,
259, 342,344, levators depressors
259, 342, extrinsic muscles 153, 158,
159, 258, intrinsic muscles 153, 159,
259.

Buccal ganglia 137, gastropoda 149,
213, 219, pelecypoda 170, 216, 219.

Buccal salivary glands 275.

Buccin urn und((tum,ner\ons system223

Bidim in us monta n us, sex u al organs 36 1 .

Button making 4-9.

Byssal gland 197, 316, 320, byssal fur-
row, section 321.

Byssus 321, attachmentof 321, glochi-
dial 322.

Cwcilioides acicula, form 24, trunca-
tion of columella 30.

Calcai'eous cells 140, 17S.

(’alcic glands 323.

Caliculation 43.

Cambrian strata 405.

Cancellate sculpture 28.

Capillaries 293.

Capping (see Caliculation).

Cai)reolus (.see Spermatoj)hore).
Carboniferous, fossils 4O6, strata 405.
Cardinal teeth 46, 47.

Carinate, univalve 28, periphery 31.
Canjchiuni minimum, absorption of
columella 29, aperture 34.

Caudal, gland 192, 197, 314, 319, vesicle
.381.

Celtic province of British Isles 402,pL vi.
Cement 430.

Central, radular area 260, teeth 152, 261.
Cephalic, region 135, of Helix aspersec
185, 188, eyes 138, in Anodonta 171,

in gastropods 230, 231, lobes 193,
margin 37, tentacles 187, 188, 189.

Cephalic retractors, 342, Amalia ga-
gates 342, Avion suhfuscus 344,
Limax maximus 344, Limncca pere-
gra 343, Helix aspersa 159.

Cephalic ganglia (see Cerebral ganglia)

Ceratoid univalve 26.

Cerebral ganglia 137, 213, 216, axis of
cells of 210, cells of, in Anodonta
anatina 217, Anodonta cygnea 168,
Helix aspersa I47, 148, styiommato-
phora 217, pelecypoda 217.

Cerebro-pleural, connectives 76’9, gang-
lia 168.

Chambers, anterior and posterior of
bivalves 40.

Chaperon 186.

Chemical structure of univalve shells
20, of pelecypod shells 38.

Chemical defences of plants 288.

Chiastoneura (see Streptoneura).

Chitin cells I40.

Circulatory system 139, in Anodonta
173, 174-177, in Helix aspersa 155,
156, 289.

Cingulate univalve 28.

Circular aperture 33.

Classification 4, literature 13, alimen-
tary canal 284, egersidia 365, mus-
cular system 10, 20, 342, teeth 264,
sexual organs 351, table of 11.

Clau.nl ia, clausium 127, causes of folds
68, lime scarcity, effect on form 77,
nomenclature of oral folds 67, 68,
odour from 230.

Clausilia hidentata, abnormal growth
121, clausium 126, distomate and
cause of distomatism 119, section of
shell 128.

v.jmrvida 73, v. sep)tentrionalis 73

Clausilia ei'avencnsis, clausium of 127.

Clausilia laminata, form of shell 24,
form of aperture 33, clausium 128,
section of shell 29.

Clausium or Clausilium 127, 128.

Claw of Helix 160, 161, 359.

Clear water, effect on colouring 87.

Climate, effect of 84.

Clitoris 365.

Close bivalve 41.

Cochleare or Roman spoons 425.

Cochlearia 434-

Cold, intliience on colour 329, on size
82, on growth 82, on thickness 83.

Colouring 49, adaptive 92, adventitious

88, distribution on shell 40, 50, in
gastropods 88, procyptic 87, struc-
tural or prismatic 86, of peristome

89, zones of 85, effect of age on 328,
of clear water 87, of cold 329, of food
91, of heat 330, of light 85, 87, of
turbid ■water 88.

Colour receptacles 439.

INDEX.

443

Columella 29, absorption of ^9, lip 3£,
truncation 30.

Columellar lobule £01.

Coluinellar muscle, in gastropod 34£,
in Helix 159, scar of 54.

Colmnnce cariue 291.

Combination shells 121, 122.

Compressed, bivalves 52, causes of 63,
aperture 33.

Commissures 209, 211.

Concentric, markings in bivalves 51,
operculum 126.

Conchal gland (see Shell gland).

Conchifera, defined 19.

Conchology, defined 3.

Conchyolin 21.

Concretionary gland 338, concretion of
338, function 338, bacilli of 339.

Connate bivalves 41.

Connectives 148, cerebro-pleural and
pleuro-pedal 160, 209, section of 21 1.

Connective tissue 136.

Conoid univalves 25, 61.

Constrictor muscles, pallial 158, pneu-
mostome 158.

Contabulate univalve 24.

Continuous peristome 31.

Contracted aperture 31.

Coralline crag 414-

Coronal glands 370.

Coronate univalve 27.

Corselet 44.

Cordate bivalves 53.

Costate sculpture 27.

Crests of bivalve shell, anterior and
posterior 43, ventral 38, 49.

Cretaceous, fossils 409, strata 4O8.

Crop 153, 274

Crowding, effects of 85.

Crystalline style 755, 245, 282, of A )io-
donta 172, 278, of Donnx 278.

Ciyptophallia 352, 353, gynogaina 357,
haplogama 356, stylogama 357.

Ctenidium 301, chitinous framework
of 137, of Viviimra 8, diotocardiate
pelecypod 302, monotocardiate
gastropod 302.

Cutaneous, respiration 306, cells 135.

Cylostoma elegans, auditory hair cells
238, buccal retractors 247, cleft foot
194, cephalic region 188, concre-
tionary gland 338, concretion 338,
dialyneury 222, gustatory cells 242,
locomotion 349, mandibular mus-
cles 249, mandibles 251, muzzle
retractors 259, nervous system 214,
222, olfactory cells 226, operculum
126, optic cellules 232, otolith 240,
pallial section 304, peristome 31,
retractors 259, rhinophore 226, ros-
trum 186, salivary glands 276, sculp-
ture of shell 28, 71, sexual organs
352, sexual dimorpliism 26, speed
349, spermatozoa, and development

of 375, stomach, interior of 277,
supra-pedal gland 196, ventral, 315.

v. albescens 03.

Cylindrical univalves 24.

Dart (see Gypsobelum).

Dart sac (see Stylophore).

Darkness, effect of 85.

Decollation 30.

Decorative shells 431.

Decussate sculpture 28.

Defensive devices of j)lants 286.

Deflected aperture 34.

Dentate apertui e 34.

Depressed univalves 25, 30, 61, 62.

Depressor muscles 250.

Dermal cells. Helix immatia 314.

Dermatoptic vision 138, 171, 234.

Detached peristome 31.

Development, heart 290, 292, radula 258

Devonian strata and fossils 405.

Dextral univalves 23.

Dextrorsity 108.

Dialyneury 222.

Dichodroma 285.

Dichoglossa 271, formula 271.

Dichoriza 343.

Dicecia 25, 141, 351, cryptophallia 353,
exophallia 352.

Diffusion 390.

Digestive gland 138, I40, 245, 279,
Anodonta 173, elements of 140, 173,
ferment of 280, function 154, 173,
280, Helix aspersa 154, lobule of
173, Limnwa stagnalis 279, struc-
ture 154, 173.

Dignatha 250, 2-52.

Digitate glands in Helix aspersa 162.

Dimorphism 26, 71, 353.

Dimya (see Isomya).

Diotocardia 291.

Diotocardiate pelecypod 302.

Discoidal univalves 25.

Dispathostyla 368.

Distomatism 119.

Distribution, bathymetrical 390, geo-
graphical 385, geological 403, hypso-
metrical 390, of pentatienia 389, sub-
dominant helicidre 389, vertical 390.

Ditremata 355.

Diurnal range, heart pulsation 157, 200.

Divination by snails 434-

Donax, lleche tricuspide 278.

Dorsal (see Pallial region), cuticle 157,
eyes 230, 233, 234, grooves 205, mar-
gin of bivalves 36.

Dreissensia piolijmorpha, alimentary
tract 277, form 39, 51, 52, labial palps
101, ligamental pit 48, markings of
shell 50, muscle scars 10, muscular
system 347, otocysts 24I, periodicity
301, podium 45, veligerous stage
382, vestigial foot 195, vision 236.

Dyaster or twin stars 379.

444

INDEX.

Eastern province, British Isles 4Wj’,phvi.

Echinate sculpture 27.

Eclhnoglossa 268, formula J60.

Ectocones loJ, 2(31.

Efferent, nerves 212, 316, pulmonary
veins 156.

Egersidia 364-

Egg, capsule 377, cleavage grooves
378, expulsion of polar bodies 378.

Elasmognatlia 254, -56.

Elongate univalve 24, 30, causes of 62.

Embryo, rotation of 382, shell sculp-
ture of 72, cause of 72.

Endocones 152, 261.

Endoderm 3S0.

Endogastric coiling 109.

Enemies 41(^> batrachians 4iS, birds
417, fish 41^1 insects 476, malaco-
vorous gastropods 42(1, mammalia^iS

Enterochloro]>hylls 307.

Entergogenesis 60.

Enterolnematin 307.

Eocene, fo.s.sils 410, 4II1 strata 4I6.

Epiconch 21, chemical structure of 21,
duplex 22, function 22.

Epidermis 21.

Eiddidymic co'cum 359.

Ei)iphragm, cliemica.l structure 131,
formation of 129, function 130, Helix
ncmoralis 129, Helix ponmtia 130,
7Yrt»or6w7Ji,snmmer 129, winter 13().

Epiphallus .361.

EpiphallogonaJOo, distribution pi. iv.,
sexual organs 395.

Epipodium 193.

Epithelial cells224,of Helix ponmtici 135

E([uilateral bivalves 40.

Equilibrating organs 133, 151.

Equivalve bivalves 9, 36, 39.

Erytlirism 94, ph ii. , f. 9.

Erythrochroism 94, pi. ii., f. 7.

Escutcheon 44.

H/n.ffi/lis coarctrifa 423.

Escargotieres 425.

Ethiopian region 399, j)!. v.

Eulamellibranchiata 302.

Euroi)ean subregion 490, jil. v.

Eurydontophora 269.

Eurydontate teetli 269.

Euthyneura 6, buccal musculature .247,
2.59, derivation of 203, nepliridium
335, nervous system 214, organiza-
tion 143, otocysts 249, pulmonata 8,
teeth chassilication 266.

Exercise, inlluence on pulsation 297.

Exogastric coiling 109.

Exoi)hallia, dicccia 352, moiuecia 354,
355.

Exorcism against snails 424.

Expanded lip 66.

External, ligament 48, surface of bi-
valves 49, shell 20.

Extrinsic buccal muscles 153, 258, 259,
of Helix 158, 159.

Eyes, cephalic, 133, 230, Anodonta
eygnea 171, dorsal 233, 234, evolu-
tion of 232, Helix pomatia\5(i, pallial
234, strueture 231.

Facial groo^■es I45, 186.

Falcate bivalves 53.

Fasciola hepatica 422.

heeding track. Helix aspersa 260.

Ferment of digestive gland 230.

Fertilizing vesicle 375.

Filibranchia 302.

Flagellum 358, 361, of Helix 160, 161.

Flammular markings 101.

Fleche tricuspide 172, of Donax 278.

Flemming’s cells 223.

Flowing water, effects on colour 37.

Food 285, influence on colour 91, 329,
of pelecypods 285.

Foot, cleft 194, fringe 192, trifascia-
tion of 194, reptary 195, subreptatory
195, vestigial 195.

Foregut 245.

Forms of bivalves 51, compressed 52,
cordate 53, falcate 53, oblong 51,
oval 51 , reniform 52, rounded 51, sub-
rhomboidal 52, transverse 51, trape-
zoidal 52, triangular 52, truncate 53,
tumid 53.

Formula for hinge-teeth 46, Jfl.

Formulre for pentatreniate banding
96, 97, 98, 99.

Fossils 494i carboniferous 4O6, dev-
onian 405, eocene 410, 4II1 liassic
407, oolitic 498, oligocene 412, 413,
pliocene 414, post-tertiary 415, weal-
den 499.

Fusiform univalve 24.

Ganglion cells 138, 209, 210, structure
1.37, 138, axis cylinder of 210.

Gaping bivalves 42.

Gastropoda 5, locomotion of 34S, mus-
cular .scars 54, nervous .system 213,
organization 143, ureter 335, 336.

Gastrula stage of development 380, 381.

Generic names, formation of 15.

Genetic table 11.

Genital glands (see Gonads).

Geograpliical, distribution 385, regions
397, pi. V., variety 59.

Geological, history 403, literature 435.

Gibbous univalve 25, 65, causes of 64.

Gills 597, cavities of 177, structure 177.

Gizzards 246, 275.

Gland 313, albumen 160. 161, 359, of
auricle 339, byssal 320, calcic 323,
caudal 192, 197, 314, 319, concretion-
ary 338, coronal 370, digestive 138,
140, 245, 279, digitate 162, hypo-
branchial 198, 314, 319, lymphatic
339, mucous 162, 364, .37(), nephri-
dial 540, pericardial 74f^j 337, salivary

INDEX.

445

276, .supra-peclal 157, 196, 226, 314,
vaginal 364, ventral 196, 314, vesti-
bular 357.

Glandular system I40, Anodonta 178,
313, Helix 157.

Globose univalve 25.

Glochidmm parasitimm 322, 383.

Glossopliora 256.

Glycogen 280.

Gnatliopliora 250.

Gonads 358, of archetype I4I, in
Anodonta 184, of gastropods 358.

Gonial ridge 45.

Goniuni 45.

Growth and time curve in Limnwa
stagnalis 81.

Gullet (see (Esophagus).

Gustatory organs 151, 242, 272, Ano-
donta cygnea 171, Cyclostoma elcgans
242, Helix 151.

Gut 281, anterior 245, median 245,
terminal 246.

Gynogama 357.

Gypsobelum, of Helix aspersti 163, H.
hortensis 369, H. lapicida 368, H.
pomatia 369, H. pulchella 368, H.
virgata 368, annulus of 366, lodged
in viscera 366, diagrammatic sections
of gypsobela. Helix aspersa 367, H.
hispida 367, H. itala 367, H. 2nsana
367 ; in sitft Helix aspersa 160, Zoni-
toides excavata 363, 370.

Habits, influence on shell 62, 76.

Hairy processes of periostraca 73, for-
mation and uses of 74.

Haplogama 356.

Haplogona 396, distribution 396, pi. iv.
sexual organs 396.

Haplostyla 368.

Hpematin 328.

Hmmatoporphyrin 308.

Hsematocoeles 293.

Hfemocoel 289, 381.

Haemocyanin 295.

Hsemoglobin 295, 328.

Hfemolymph (see Blood).

Headon beds 411-

Heat, influence on colour 330, on shell
substance 76.

Heart 139, Anodonta cygnea section of
291, development 290, 292, Helix as-
persa 155, primitive arrangement of
142, pulsation of 157, 296.

Helix, arrangement of locomotory
muscles 348, diagram showing body
cavity 204, diagram showing pul-
monary cavity 145, external fea-
tures 144, glandular system 178,
supra-pedal gland 196, tactile sense
150, ureter 336, venous sinuses 294.

Helix aculeata, embryonal sculpture
72, 73, sculpture 27, 70.

Helix acuta, form 24, sexual organs 363.

Helixarhustorum, duplex periostracum
22, nephridial cells 333, strength
350, varicosity of shell 69, vision 235.

V. jlavescens 22, 91, v. fusca 91,

V. rudis 70.

//c/far asy)ers«, alimentary canal 153,154
245, amorous preludes 372, artifici-
ally scalarid 118, buccal retractors
159, cephalic region 185, cephalic
retractor 159, columellar retractor
159, combination shells 122, dart 163,
dart, section 367, dart, annulus of
366, darts in viscera 366, digestive
gland, structnre and function 154,
eaten by mice 417, external features
144, extrinsic buccal muscles 158,
159, 258, eye retractor 231, feeding
track 260, form of shell 33, formula
of odontophore 152, 270, heart 155,
hibernacula 310, 311, homing 312,
imperforate shell 29, intestinal cells
281, labial lobes and mouth 190, lip
colouring 88, locomotory waves in
foot 192, lung 8, mandible 152,
medicinal uses of 427, muscular sys-
tem 1-58, nerve ring 149, nervous
.system 148, odontophore 152, 261,
270, oesophageal cells 274, olfaction
229, organization 143, otocysts in
situ 151, ovarian ovum 377, ovotestis
358, penial retractor 159, pharynx
cells 257, pulsations of heart 1.57,
sexual organs 160, 162, speed 349,
strength 50, tentacular retractoi’s
159.

v. albo-fasciata pi. i., f. 2, v.

flammea 101, pi. i., f. 3, v. major M,
V. minor 84, v. solidissima 78, v.
tenuior 77, v. zonata pi. i., f. 15,
95, m. cornucopia 26, 116, ni. sinis-
trorsuni 108.

Helix cantiana, speed 349, young 74,
vestigial banding 101.

V. albocincta 101.

Helix caperata 96,sculpture27,keel 31.

V. ornata, procryptic colouring

of 96.

Helix fusca, stylophore 370.

Helix granulata, form 25, periostracal
hairs 27, 75, umbilicate 29.

Helix hispida, affinities 57, dart, sec-
tion 367.

V. depilata 75, v. hispidosa 75.

Helix hortensis, base of shell 30, band
multiplication 99, apertural rib 70,
band cessation 100, dart 369, in)per-
forate shell 29, light, effect upon
colour 87, maturation of ova and
spermatozoa 377, otoconia 239,
thermo-pulsatory curve 298, vision
236.

V. fagorum 94, v.flavo-virens 61,

V. flavo-viridis 61, v. griseo-lutea 61,

446

INDEX.

Helix hortensis (contd.).

V. lilacinn, jil. i., f. 9, v. Intea 61, v.
olivacea 91.

Helix itala, apevtuve 34, dart, section
367, form 25, stylopliore 370, uinbili-
cate 29.

Helix lapicida, alimentary tract 284,
,ai)ertnre 33, arrangement of teetli-
rows 262, dart 368, form 25, keel 28,
31, lime deliciency, effect on shell 77,
peristome 31, sexnal organs 357.

//f/(.r«fj«om^fA’20,23,abnormalgro\vth
121, aperture 33, aiiertural rib 35,
banding, irregular development of
100, band variation 97, connective
tissue 136, disintegration of banding
99, eaten by birds 41d, by mice .^77,
fusion of bands 100, summer epi-
pbragm 129, light, effect on colour-
ing A’7, necklace of 431, periphery 31,
peristome 32, section of shell 29, 78,
varicose thickening 69.

V. conica 61, v. crcticola, section

78, V. dktphnna 77, v. lihellnla 86,
95, pi. ii., f. 11, V. roscohtbiata pi. i. ,
f. 8, V. jdnnospira 61, m. sealavc 26,
m. scednrifoniic 118, m. sinisirorsmn
23, 108.

Helix obvoluta, geojjliilous habits of 62.

Helix pietri 85, pi. ii., f. 9.

Helix pisann,\t\. ii., f. 10, dart, section

367, scul|)ture 72, vision 235.

V. fdbn 90, v. edhida 90,v. magna

pi. i., f. 7.

130, auditory organs 151,
cutaneous cells of 135, dart 369, der-
mal cells 314, dorsal cuticle 157, eye
150, 232, winter epipbragm, 1.30,
elements of liver 140, mandible 255,
nacreo\is layer of sliell 21, odours
from 2.30, (esophageal cells 274, ojitic
bulb 233, otoconia 151, 239, 241,
otocysts 151, pharyngeal cells 257,
rhinophore 150, section of stomach
walls 277, stylopliore 370, tactile
cells 244, vision 235.

Helix pulchell((, aperture 33, 34, dart

368, mandible 254, palatal mandi-
bular extension 25.3.

Helix pggnia'o, mandible 250, odonto-
phore 271, oilontophoral formula 271

Helix revclata, jieriostracal hairs 75,
arrangement of 74.

Helix rotundfdo, sculpture 28.

V. alba 91, m. .•siiiistrorsum 108.

Helix rufescens, affinities 57, digitate
glands .364, penis 362, stylopliore
370, vestigial banding 101.

Helix virgata, pi. ii., f. 1, dart 368,
heart 289, leucochroism and causes
of 93, spermatoiihore 376.

V. alba, pi. ii. , f. 5, v. albicans

pi. ii., f. 4, V. nigrcsccns 94, pi. ii.,
f. 2, V. rnfula 94, pi. ii.j f. 3.

Hempstead beds 412.

Hermaphrodite (see Monoecia).

Hermaphrodite duct 359, of Helix 160,
161.

Heterodonta 4d-

Heterogangliata 4-

Heterogyrate 115.

Heteromya 10, I64, 345, .347.

Heterospathostyla 369.

Heterostrophy 11.5.

Hibernacula '310, Helix aspersa 311.

Hibernation 82, 309.

Hinge denticles 46, 47, formula of
46, 47.

Hinge of biv.alves 45, 46.

Hispid univalves 27.

Histoluematin 307.

History 4, geological 403.

Holoblastic segmentation 380.

Holocene deposits 415.

Holopoda 193.

Homing 312, Limax favus ,313.

Homogangliata 4-

Hood 186.

Hora'omorphism 100.

Hyalinia, haliits 87, procryptic colour-
ing of 87, odours from 230, otoconia
2.39.

Hgalima alliavia, odontophore 264,
odontophoral formula 263, odour
from 230, otocysts 241, vaginal
glands 364.

Hgalinia ce/7nrm, caudal gland 197.

V. alba 91.

Hgalinia f Vagrans, odour from 230.

Hyalinia ftdva, armature of .aperture
in young 67.

Hyalinia helvetica, lateral grooves 205.

Hyalinia, Incida, cannib.alistic 420,
form of aperture .33, peristome 32.

Hyalinia nitidula, odontophore 271,
odontoplior<al formula 271.

Hgalinia radiatula, sculpture 71.

Hyperstrophy 110, 111, 112.

Hypobranchi<al gland 198, 314, 319, in
Viwipara vivipara and section 320.

Hypsometrical distribution 390.

Imperforate univalve 29.

Incrustation of shell 332.

Inequilateral shell 9, 36, 39.
Inequivalve shell .39.

Inflated bivalve 62.

Inflected aperture 34.

Ingestive tract 244-
Inhibitory nerves 212, 216.

Injuries, effects of, on shell 102, 103,
on heart pulsation 297.

Inner layer of shell 21, secretion of 21.
Inner lip 32.

Inoperculata 7.

Integripallia 10.

Intermediate teeth 261.

INDEX.

447

Internal, ligament 48. o’-ganization
136, organization of Helix cispersn
146, 147, rib 35, 70, shell 20, surface
of bivalves Jfi.

Interrupted peristome 31, 32.

Intestinal ganglia (seeVisceral ganglia).

Intestine, 2Ifi, 282, in Helix aspersa
154, cells of 281, torsion 281, 282.

Intrin.sic, buccal muscles. Helix 150,
259, pedal in Anodonta 183.

Inversion 111, 112.

Involuntary muscles 341.

Involute aperture 34.

Isomya 10, 164, 345, 347.

Isopleura 5.

Jaw (see Mandible).

Jurassic strata 407-

Keber’s, organ 179,557, valvule77i?,295.

Kidney (see Nephridium).

Kiokkenmoddings 4~4-

Kleeburg’s sinus 196, 314.

Kolliker’s canal 239.

Labiate univalves 34, 35, 65, 66, causes
of labiation 66.

Labial lobes, in iZefc 759, 190, arrange-
ment of 191, in Anodonta 171, 190,
blood system of 191, structure of 191.

Labial palps (see Labial lobes).

Labium 32.

Labrum 32.

Lacaze’s organ (see Ospliradium).

Lacunm 293.

Lacunar tissue 139.

Lacunose sculpture 28.

Lamellm of aperture in Clausilia 67, 68.

Lamellate aperture 35.

Lamellibranchiata 9.

Lateral teeth 152, 261.

Lateral grooves in Helix 1 44, 205.

Leiognatha 254, 255.

Leucochroism 95, pi. ii., f. 4.

Lenticular univalves 25.

Levator muscles 258, 559, Anodonta 183.

Leydig’s cells 34O.

Liassic strata and fossils 407.

Ligament 48.

Light, influence on colour 87.

Liguus virgineus, 85, pi. ii., f. 8.

Limax, diagram showing body caruty
204, nervous system 215, semper’s
organ 190.

Limax campestris, teeth development
258.

Limax cinereo-niger, otoconia 239,
trifasciate foot-sole 194, semper’s
organ 243.

Limax flavm, alimentary tract 284,

I colour changes during growth 327,
homing 313, lung 304, mucous track
313, jaw 255.

Limax maximus, alimentary tract and
its supports 285, cephalic retractors
344, jaw, immature 253, olfaction
229, shell 20, supra-pedal gland,
section of 315, pairing 373.

V. fenissaci pi. i., f. 5.

Lime cells (see Calcic cells).

Lime, effects of deficiency 77, 85, of a
plethora 78.

Limnceidce, abyssal variation of 77,
labial lobes 100, ventral gland 315.

Limncea auricularia, form 25, disto-
mate 119, injuries to 102, malformed
105, mucous filament 318, mucous
track 316.

V. alba 32, v. gibbosa 25, 34, 64.

Limncea glabra 30, varicosity 69.

Limncea glutinosa, pallial outgrowth
202, periodicity 391.

Limncea peregra 107, alimentary canal
274, cephalic retractors .343, environ-
ment effects 62, jaws 252, malleate
71, malformed by T/yr/m 107, nerve
ring 114, nervous system 214, ospli-
radium 228, ovotestis 358, pairing
373, plasticity of form 62, prostatic
section 360, polyperistomate 120,
respiratory siphon 199, rotating
embryo 382, speed 349.

V. burnetti 62, v. cliapliana 76,

v. glacicdis 76, v. involnta pi. i., fig. 4,
v. labiosa 34, 66, v. marginata 69,
v.ovccta 9, y.pictcc 102, v. thermcdis 76

Limncea pcdustris 30, marginal rib 69,
penis of 362.

V. lacnnosa 28, 71, v. zebra 101,

m. decollatum 30.

Limncea stagncdis, alimentary canal
279, chaperon 186, chemical structure
of shell 20, egg, showing expulsion of
polar bodies 378, eye 231, expanded
lip 66, form 32, gibbously inflated
65, growth 81, 82, lip 66, marginal
rib 69, meteorological influence,
effects of 83, mucous tracks 315,
nervous system 6, osphradial cells
210, 225, saline influence, effects of
105, sexual organs .355, sliell gland
322, tentacles 189, variation, causes
of 83, varicosity 69.

— — V. appressa, pi. i. , f. 6, v. bocla-
mica 24, 62, 65, v. fragilis 186, 199,
V. fragilis-variegata 83, v. varie-
gata, 28, 69, m. smlariforme 26.

Limncea trnncatida 24, parasite of 422.

V. turrita 24.

Lingual ribbon (see Odontophore).

Lip, columellar 32, inner 32, outer 32.

Lipocephala 36.

Lipochromoids 88.

Lirate sculpture 28.

Literature, of classification 13, nomen-
clature 18, shell 131, animal 383,
geological, etc. 435.

448

INDEX.

List of siibscvibers 436-9.

Lis’er (see Digestive gland).

Locomotion 313, 316, 317, 318, 340,347,
rates of 34S.

Longitudinal aperture 32.

Lower margin of bivalves 30.

Lophophoral line, Anodonta 301.

Love-dart 366, Helix nspcrsn 163, II.
hnvtensis'i&i, H. Ir/picida 368, H. po-
vintia 369, H. 2^>dclH'l/n 368, II.
virrjatn 368, diagrammatic sections
of Helix a.'ipcrsn, H. hi-yiidn, H. itala
and H. pi.'iana 367, in sitft Helix as-
persa 160, Zonituidcs cxcavatn 363,
370.

Lunate aperture 33.

Lung, Helix aspcrsn 8, Limax flavus
304, blood sinus in lung of Helix
jmmatia 305.

Lunule 44.

Lvmi)liatic gland 330, Anodonta ISO,
'Helix 158.

Macromeres 380.

Malacology 3.

Malleate, seuli)tnre 28, 71, cause of 71,
Limna’n pcregm 71.

^lammalian enemies 4IO.

Mandibles, 248, 24IK Bithynia tcntacn-
lata, 252, Cyelostoma clegans 249,
251, development 240, muscles of
249, Helix a.ytcr.vt 152, H. pulchella
253, 254, H. pygniwu 250, Lijna.v
inaxiniK.^ 253, Liinna-a peeegra 252,
Pupa rylindracca 255.

Mantle 145.

Margin, anterior or cephalic 37, dor-
sal, lower, posterior, siplional, upper
and ventral 36.

Marginate aperture 35, 69, causes 60,
Planorbifs spirorhis 60.

ISI.arginal, teetli 261, area ."FCd.

Marine intluence, ell'ect of 85.

Markings of bivalves 50, 51.

Measurement of bivalves 54, uni-
\-alves 35.

Median, area 60, gut ^5, teeth 261.

Medicinal uses 437.

Mediterranean, subregion 400, pi. v.

Melanin 329.

Melanism 94, pi- ii-, f. 2.

Mel.anochroi.sm 93, pi. ii., f. 3.

Melanoids 88.

Meroblastic segmentation 380.

Mesocerebron 217.

Mesocones 152, 261.

Mesoderm 381.

Mesopodiuni 103.

Mesozoic strata 400.

Met.acerebron 217.

Metapodium 193.

Meteorological inlluences, effects on
shell 83.

Micromeres 380.

Micropyle 377.

Migration, routes of 392, pi. iii.

Mitosis 378.

Modiolaria discors, section of byssal
furrow 321.

Mollusca, as food 434'< fts medicine 437,
as ornaments 48I, as objects of
superstition 242, 432.

Monaster 379.

Mongolian subregion 400, pi. v.

Monochromic colouring 86, pi. ii.,
f. 12, 13.

Mono^cia 141, 354, cryptophallia 355,
ditreniata 355, exophalha 354, 355.

Monognatha 250, 253, origin 253.

Monomya 10, IG4, 346.

Monorhiza 343, 344.

Monotocardia 291.

jMonotocardiate gastropod, ctenidium
of 302.

Monotremata 356, gynogama357, hap-
logama 356, stylogama 357.

Monstrosities 103, causes of I04,
chemical refuse 106, Hydra viridis
107, interference by Drcissensia 107,
leeches 107, nomenclature 17, frit-
water 104, polluted waters I04,
.saline waters 104, stagnant waters
107, water-current 106.

Morula stage of segmentation 380.

Motor, ganglia 213, nerves 212.

IMouth 138, 152, 170, 185, 190.

Mucous, cells 157, filaments 316, 317,
glands of Helix aspersa 162, H.
fiisea, H. iteda, H. poniatia 370, H.
rnfescens 364, 370, and Hyalinia
aliiaria 364, tracks 313, 315, 316,
use of 576, 317, 318.

Multifid vesicles (see Mucous glands).

Multipolar ganglion cells 210.

Multisfural, univalves 26, operculum
126.

Muricate sculpture 27.

Muscular scars 54, Anodonta cygnea
55, 180, bivalves 54, Drcissensia 10,
Helix pomatia 54.

Muscular system I40, 34O, Anodonta
181, 346, 347, Drcissensia 347, Helix
158, somatic I4I, splanchnic I4I.

Muscle, pseudo-striate 141, unstriated
140.

“Music” of snails 242.

Mutation 60.

Muzzle 186,reti-actorsof Cyclostoma25Q

Myoh.'cmatin 307.

Myriogiossa 271, formula .^77.

Mytilus edulis, attaching byssus 321.

Nearctic region 399, pi. v.
Necklace of Helix nenioralis 431.
Neotropical region 398, pi. v.
Nepbropneusta 8.

Nephridial gland 34O,

INDEX.

449

Nephridia. and functions 1^0, Ano-
doHtu 17S, 179, -iJ-', 333, A.cy(jnea,
section 179, 334, A/jrioliinnx agrcs-
tU, section 335, Helix loS, Succinca
jintris, position 334, Helix arbus-
forum, cellular .structure of 3.33.

Xeritina fluviatiliji, incra.ssatioii 79,
odontophore 264, odontophoral for-
mula J'b’J, operculum 127, operculum
in situ 124, otocyst 237, pseudo-
striate muscle-fibre 141, sexual or-
gans 353, unstriate muscle fibre 140.

Nervous system, 137, 209, afferent 212,
Anoclonta cygnea 216, of archetype
142, basommatopbora 215, efferent
212, eiithyneura 214, fibrils of 209,
212, gastropoda 213, Helix aspersa
147, 148, inhibitory 212, Limax 215,
Limmm stagnalis 7, motor 212,
nerve ring of Helix aspersa 149,
pelecypoda 107, 168, 215, strepto-
neura 213, stylommatophora 214,
Succinca putris 215, sympathetic
212, torsion of 221, Vivipara 7.

Neurobranchiata S.

Neuro-epithelial cell oi Arion ater 135.

Nomenclature, principles of IS, oral
folds in Clausilia 67, literature IS,
of monstrosities 17.

Norwich crag deposits 474-

Nucleus of univalves .30, sculpture 72.

Nucula, auditory canal 238.

Nucula nuchus, reptaiy foot 195.

Oblique aperture 33.

Oblong bivalves 51.

Ocelli (see Dorsal eyes).

Odontoblasts 257.

Odontognatha 234, 2-55.

Odontophore 248, 250, 261, develoji-
ment 2.57 . 258, function 248, growth
153, Helix aspjersa 152, 261, 270, H.
pygnuca 271, Hyalinia alliaria 264,
H. nitidula 271. Ncritina Jluviatilis
264, Physa fontinalis 268, Planorbis
corncus 270, Testacclla halioticlea
267, Vivipara vivqxira 265, notation
of 262, transverse arrangement of
’’ teeth upon 262.

Odours, exhalation, perception of 229.

Oisophagus 138, 172, 274, cells of 274,
Helix aspersa 153.

Olfactoiy organs 138, of archetype I42,
224, sensory cells of 225, 226, Plan-
orbis Cornells 225, in A nodonta 171,
function and position 224, of Helix
pomatia 130.

Oligochromic colouring SO, pi. ii. ,
f. 10, 11.

Oligocene, fossils 412, 413, strata 477.

Ommatophores 187.

Onchidium verruculatum, dorsal eyes
234.

(Jntogeuy 205, 378.

22/12 1900

Oolites, fossils of 498, strata 407.

Operculata 7.

Operculigerous lobe 193.

Operculum 123, articulate 127, chemi-
cal structure 124, concentric 126,
Cydostoma clcgans 126, multispiral
126, Xeritina Jluviatilis 127, peg .and
rib of 124, 127, paucispiral 126, spiral
725, subspiral 127, Vo.lvata piscinalis
126, Vivipara contccta. 126.

Opistliogyrate llo.

Opisthobranchiata 8.

Optic, bulb 233, sensory cellules 232.

Oral, region 135, folds 08.

Orbicular muscles of Anodonta 181.

Organization, literature of 383.

Organs of Bojamis (see Nephridia).

tfriental region 398, pi. v.

Ornamentation of bivalves 50.

Orthostrophy 111.

Orthoneuroid 222.

Osborne beds 477.

Osphradial (see Visceral ganglia).

Osphradium 224, section in Planorbis
Cornells 225, po.sition in Liinnaa
peregra 228, cells of 210, 225.

Otoconia 2.39, of enthyneura 239,
Helix pomatia 151, 241.

Otocysts 237, Anodonta. cygnca 170,
Helix a.s])er.sa\5\, H. pomatia 151.

Otoliths 239, Anodonta cygnca 170,
Cyclo.stoma clcgans 240, Spkccriuvi
corncuni 239, 241.

Outer lip 32.

Oval bivalves 51.

Over-crowding, effects of 85.

Oviduct of Helix 160, 101.

Ovotestis, Helix aspersa 160, 358. If.
hortensis, maturation of ova and
spermatozoa in 377, L. peregra. 358.

O VO viviparity 382.

Ovum 141, 100, 370, ovarian ovum 377,
maturation of 377.

Oxygnatha 255.

Pairing 372, 373, 374.

Palatal, lip .32, plate 24S, 253, 256.

Palwarctic region 400, pi. v.

Palieozoic, fossils 405, 400, strata 404.

Pallial, atrophy 203, extension 149,
199, 202, eyes 2.30, 2.33, 2.34, fusion
198, ganglia 220, line 50, 180, 181,
muscles of Anodonta ISO, 181, re-
gion 1.35.

Pallium 145, 198.

Parabranchia 220.

I’arapodia 19.3.

Parietal, ganglia I48, ^vall 32.

Parieto-splanchnic (seeViscer.al ganglia)

Parasites 4-77, commensals 423, ecto-
parasites 423. endo-parasites 422.

Parasitism of Un io 383.

Patella, heart 291, eye 232.

Patelliform univalve 25.

D 2

INDEX.

4,i0

Patronenstrecke 361.

Patulous aperture 34.

Paueisjiiral, univalve ‘26, operculum 126

Pearls fislierie.s o.Jd, formation 3.24,
medicinal rei)utation 4-2^ structure
86, 325.

rcctcn, pallial eyes 234.

Pectinibranchiata S.

Pedal, ganglia 137, 143, J13, ganglion
cells of Unio picturinn 218, of Aiw-
(h)uta 168, of Helix I4S, gland 157,
3.27, mu.scles of Anodonta ISO, 182,
133, nerves of Vivipara 218, region
135, 192, retractors in Helix 153,
lielecyi)oda 347.

Pelccypoda 9, 36, adductors 345, buccal
cavity .243, buccal ganglia .210, byssal
gland 316, mucous lilaments 319,
pericardial glaml 337, pronephros
337, retractors 34i>, salivary glands
34s, structure of shell 37, growth 4'3,
ne])hridia 333, nervous .system 167,
215, 217, osphr.adium 3.23, j)allial
eyes .2.{3, sculpture .^9, torsion 7203,
visceral ganglia 331.

Pe/lrr eoroiinto, sperm duct 360.

Penial plates 363.

Penis 362, in basommato]ihora 343,
Helix finpcr.'ia 161, 162, Jl. ni fencoi.^
362, Liiiinwei pedustris 362, Planor-
hi.'i curnciis 366, Snerinen 344-, Vfd-
ciilti jiitieinali.'s 189, 362, Vieipara
riri/iiird 189, retractor in 759.

Pentadroma 285.

Pentatamia, development and arrange-
ment of banding 96, formuhe 96,
geographical distribution 389.

Peripodial groove 192.

Perforate univalve 29.

Pericardial gland l.'/0, 337, Anodunta

179, function I40.

Pericardium, Anodoiifacipjiica section

180.

Pei'iostrjicum 21.

Periostracal appendages 73, 74, 75,
formation of 74, use of 74-

I’eriphery 59, carinate 31, rounded 31,
snbearinate 31.

Peristome 31, 32, continuous 31, de-
tached 31, interrupted 32, simple
32.

Peritremc (see Peristome).

I’ervious univalve 29.

Periodicity 391.

Phadsm 93, pi. ii., f. 3.

Phagocytes 396.

Pharyngeal, retractor 342, in Amalia
ipajates 342, in Avion suhfuscus 344,
in Helix a.'ipersa 159, in Lima.v maxi-
mas 344, Limmca percejra 343.

Pharynx cells 257.

Philodromus limacam 423.

Photoskioptic vision 235.

I’hylogeny 11, 373,

Phijsa foniinalis 202, arrangement of
teeth-rows 262, odontopliore 268,
odontophoral formula 369, pallial
outgrowth 202.

V. inflata .24.

Pigment cells I40, 173, 337, excretory
function of 3.27.

Pillar of shell 29.

Pilose shell 27.

Pisidium amnicam, form 40, 53, si-
phonal tube 200.

Pisidium fontinalc, form 53.

Pisidium hensloiranum, prosogyratc
umbones 110, umbonal appendages
42, 73.

Pisidium milium, form 51.

Pisidium nitidum, form 51.

Pisidium pusillum, cleavage in egg
segmentation 378, form 51, morula
stage 380.

Pisidium sinuatwm 40.

Place of origin 336.

Planorbis, ureter 336.

Planorbis nlbus, spiral striation of 27.

V. draparnaudi, hairy ridges of

shell 74, V. sulcata 23.

Planorbis carinatus, monstrosities
from |iit water 104.

• m. sinisfrorsum 114.

Planorbis eontortus 26.

Planorbis corneus, auriform lobe 201,
304, form 25, male organ 366, nerve
ring 114, odontopliore 270, odonto-
phoral formula, 279, osphradium 225,
periostracal hairs on young 27, 74,
pronephros 336, respiration 305,
speed 349, spire 30, variation in
size 35.

V. albinn 25, 30.

Planorbis niarfjinatus, tentacles 189.

m. roehlca 113, 116.

Planorbis nauf ileus, dimorphic 70.

V. crista 27.

Planorbis siinilis 75.

Planorbis spirorbis, apertural rib 69,
epiphragm 131, scalarid 26.

m. jiriscum 113, 117.

Planorbis umhilicatus see inarginatus.

Planorbis vortex m. columella Wl.

Plants, chemical defences of 233, de-
fensive devices of 286, structural
defences of 287.

Plecton 280, 282.

Pleistocene deposits 415.

Pleune 260, 201.

Pleural ganglia I40, 230.

Pleurecbolic protru.sion 188.

Pleurembolic retraction 188.

Pleurognatha 248, 249, 251.

Pleuro-pedal connectives 169.

Plicic of aperture in Claus ilia 67, 68.

Plicate, aiierture 35, sculpture 27.

Pliocene, fo.ssils 414> strata 473.

Pneumonochlamyda 8.

INDEX.

4.51

Podial ridge 45.

Podium 45, 192.

Poikilothermic 157.

Polar globules 378.

Polyblast (see Morula).

Pol3'chromic colouring 85, pi. ii. , f. 8, 9.

Polyperistomatism 120, causes of 130,
in Limna-a peregra and Unio tinnid-
us 120.

Polyplacognatha 2.30, character 251.

Polystomatism 119, causes of 119.

Portal circulation 156, 289.

Post-tertiai-y, fossils IfH, strata Ifllf.

Posterior, adductor 346, chamber in
bivalves 4'>-, crest 43, margin in
bivalves 36, pedal retractor in pele-
cypod 183, 347, sinus 44.

Postero-lateral teeth 46.

Posteriorly' produced bivalve 39.

Posteriorly' truncate bivalve 40, 53.

Precordial gland (see Nephridia).

Premature atrophy of banding 100.

Preparation of buccal armature 272.

Primary, period 404, shell 323, ureter
335.

Primitive banding of Helices 101.

Prionodesmacea 46.

Prismatic shell layer and secretion of 21

Prociyptic colouring 87.

Prodissoconch 333.

Pronephros 336, in pelecypods 337, in
streptoneura 337.

Propodium 193.

Prosoma 135, 185.

Prosogy'i-ate shells 110.

Prostate, section 360.

Prostomium 186.

Protective, organs 123, 124, 126, 127,
resemblance 330.

Proterandiy I4I, 351.

Proterogyny 351.

Protocerebron 217.

Protoconch 333.

Protogona 395, distribution pi. iv.,
sexual organs 406.

Protopelecypod, circulatory' sy'stem

Protostracum 333.

Protractors 359, anterior in Anodonta
182, lateral buccal protractors in
Cyclostoma 247.

Pseudo-dextral coiling 113.

Pseudo-lamellibranchia 302.

Pseudopodia 34O.

Pseudo-striate muscle-fibre 341.

Pubescent shells 27.

Pulmonary cavity, diagi'am showing
position of 145, Helix aspersa 8,
Umax jlavus 304.

Pulmonata, azygobranchia <?, euthy'-
neura 8, radular sac, section 257.

Pulsations of heart 296, diurnal range
1.57, 299, influence of age 297, of
exei-cise 297, of shell injury' 297, of
temperature 157, 297.

Pupa, odours from 230.

Pupa cmglica, apertural armature in
young 67.

Pupa cylindracea, embryonal sculp-
tm-e 72, mandible 255.

Pupa muscorum, aperture 34, labiate 35

V. elongata 24.

— secede 66, aperture 35.

V. edcntula 66.

Pycnoglossa 270, formula of 270.

Pycnognatha 25.3, 254.

Pyriform aperture 33.

Quadrate teeth 269.

Quadrimaxillate (see Tetragnatha).

Race, defined .59.

Kachidian area 260.

Rachis 260.

Radiate markings in bivalves .30.

Radula (see Odontophore).

Radula, sac 2.56, section 2.37.

Radular membrane 260.

Rectatheca 284.

Rectum 283.

Reflected aperture 34, cause of 66.

Red crag 414-

Reizkorper 364, 365.

Renal organs (see Nephridia).

Reniform bivalves 40, 52.

Repairs of shell 23.

Reproduction I4I, 372.

Reproductive system I4I, 350, oi arche-
ty'pe 143, Auodonta 183, Helix 160.

Reptary foot 195.

Respiration 139, 300, function of 301,
Umax maximus 306, Limneea auri-
cularia 306, L. peregra 199, 306,
Planorbis corneus 305, 306, Unio
pictorum 303.

Respiratory, cavity, position in Helix
145, 204, in Umax 204, structure in
Helixas persa 8, Umax Jlavus 304.

Respiratory, currents in Umax maxi-
mus 306, Unio pictorum 303, orifice
283, siphon 199, 200.

Reticulate sculpture 28.

Retinophores 232.

Retinules 232.

Retractile tentacles 187.

Retractors 259, anterior pedal of Ano-
dontal82, 347, buccal45<9, 159,byssal
347, cephalic 342, columellar 158,
1.59, gastropods 342, pelecypoda 346,
347, orbicular 181, penial 1.58, 343,
344, posterior pedal in Anodonta
182, 183, 347, .siphonal 181, tenta-
cular 342.

Retuse 34.

“Reversed spiral,” intestinal canal 282

Revolute 34.

Rhinophore 226, Cyclostoma elegans
226, Helix pomatia 150.

INDEX.

4o->

Rliipidoglos.^a 264, formula 2G^.
Kibl)e(l jaw (see Odontognatha).
liimate univalve 29.

Rostrate jaw (see O.xygnatlia).
Rostrum 42, d4, 186.

Rotation of embryo 382.

Rough waters, ettects of 79.

Rounded, aperture 33, bivalve ul,
l)eripbery 31.

Routes of migration 392, pi. iii.

Salivary glands, section 276, Cyclo-
stonia clegans 276, Helix ti.spersr/ 153,
H. horteusin 275.

Sarcobelum 365, Aijrioliinax agrestis
365, Ziiri liibrica 365.

Scalarid univalve 26.

Scalariform univalve 25, 26.

Scahariformity 116, 117, causes of 117,
artilicially produced 118.

Sculpture 70, significance of 22, 27,
inliuence on size 70, of Ci/rlonfoiiKi
elrf/avs 71, embryonal shell 72.

Secondary, period 4')G, shell 5, ureter
336.

Secretory (.see (Jlandular system).

Segmented jaw (see I’olyplacognatha).

Segmentiua nitida, aperture 35.

Seminal vesicle 101, 3.59.

Semper's organ 185, 190, 243, 275, in
Agridlitnax agrrsti.s 243, Liinax
cinerco-niger 243.

Sensory, ganglia (see Cerebral ganglia)
nerves (see Afferent nerves), organs
223, cells 170, 224.

Sei)tate ai)erture 35.

Se.xual, dimorphism 26, 30, .353, sys-
tem 350.

Shallow water, efl'ects of 79.

Shell gland 322.

Shell, literature 131, short-spired uni-
valve and cause of 62, significance
of 19.

Shells as money 431.

“ Showers of snails ” 430.

Sight 230.

Simple peristome 31, 32.

Sinistra! univalve 23.

Sinistrorsity 2'4,10S, cause of lo9.

Sinupallia 10.

Sinuous aperture .34.

Sinus, anterior 44, posterior 44.

Sii>honal, margin 30, retraetois, Atw-
donfa 181, tubes 199, 200.

Size, correlation with temper.ature 80,
effect of altitude on 85, crowding
of darkness 85, of environment 8o,
marine influence 85, water volume
80, 82.

Skiojitic vision 235.

Somatic muscles I4I.

Sonant organs 242.

Specific names, formation of 10.

Species, defined 50.

Sj)eed, of gastropods 348, Cyclodoma
349, basommatophor.a 349, AnegJua
fl a eiatilis 349, Dreissensia 350, Helix
aspeesa 34.9, H. cetntiona 349, Limax
34s, Limneva peregra 349, Felecy-
poda 349, Planorbi.'i corncus 349,
Uirio viorgaritifce 350.

Spengel’s organ (see Osphradium).

Sperm duct 360, of Helix 160, 101.

Spermatheca e>iH. n.-iper.sa \^Q,102,35S.

Spermatophore, of Helix aspersa 161,
of H. virgafa 376, of Amalia soirer-
bgi in epiphallus as secreted 376, in
spermatheca as transferred in pair-
ing 376, rival sperniatophores in
spermatheca 374.

Spermatozoa I4I, of Heli.r 100, 374,
development 375, dimorphic 375.

Splavrium eorneiim 4I, development
290, hinge teeth 47, 53, periostracal
hairs 49, 70, 201, otolitli 241, otolith
and sensory hairs 238, siphonal tubes
200.

V. 7nicleii.'i 53, 191, v. vittata 51.

Sp/urriiim lacu.stre, caliculation 43,
form 52.

Spha-i'iiim pallidiem 41, form 51.

Sjdta’i'ium, I'ieicola form 40, 51, hinge
teeth 47, sub-reptatory foot 195.

Spiculum amoris 366.

Spinose sculpture 27.

Spiral ojierculum 1.25, 126.

Spiral white lineation 102, causes of 102

Spiral striation 27.

S|)ire, defined 30.

Splanchnic muscles I4I.

Spleen (see Lymi)hatic gland).

Spoons, Roman 424.

Staining of buccal armature 273.

Stenodontophora 266.

Stiebel’s canals (see Pronephros).

Stomodicum 185, 247.

Stomato-gastric gangli.a 1.37.

Stomach, 245, 277, Anodemta 171, 172,
Cgclo.stoma elegaiis 277, Helix as-
pci-.m 153, cells of, in H. pomatia
277, section of w.alls of, in Helix
pomatia 277.

Strength of snails 3.50.

Streptoneura, 0, anterior pedal gland
190, huccal bulb section 248, buccal
muscles 247, epipodial lobes 193,
nephridia 334, 536, nervous system
213, odontophoi al classification 204,
operculigerous lobe 193, organiza-
tion of 143, perie.ardial gland 338,
pronephros 337, retractors 343, teeth
of 264, 265, tor.sion of nerves 220, 22 1 .

Striated jaw (see Pycnognatha).

Striation 27, spiral 27, transverse 27.

Structural defences of plants 287.

Structure of shells ,2i, bivalve 21, 37,
univalve 20.

INDEX.

4.53

Stylogania 357.

Stylonimatophora 9, cerebral ganglia
217, nervous system 214, otoconia
239, retractors 3JS, tentacles 188.

Stylopliore 358, 369, development 370,
Helix aspersa 160, 162, H.ftisca, H.
ifala, H. pomatio, and H. rufesccns
370.

Stylotheca 138, 172, Dreiasens'ia pohj-
morpha 277, Donax 278.

Sub-oesphageal ganglia 147, of gastro-
poda 213.

SuD-carinate periplieiy 31.

Sub-equilateral bivalve 40.

Sub-reptatory foot 195.

Sub-rbomboidal bivalves 52.

Subscribers, list of 436-9.

Sub-species, defined 59, 60.

Sub-spiral operculum 127.

Substance of sliell 76, causes of varia-
tion in 76.

Subulate univalve 24.

Sub-variety, defined 60.

Succinea, penial retractor 344-

Succinea degam, alimentaiy tract 282,
sexual system 359.

Succinea putris 9, dorsal grooves 205,
eyes 231, fertilizing vesicle 375, jaw
256, nervous sj’stem 215, position
of nepliridium 334, scalariform 26.

Sulcate sculpture 28.

Superstitions 432.

Supra-oesopliageal (see Cerebral gang-
lia).

Supra-pedal gland 226, functions 197,
Helix 157, 196, 314, Limaxmaximm
section Z\o,Testacella haliotidca 314.

Surface, external and internal of bi-
valves 41^-

Suture 31.

Sympathetic nerves 212.

Symphynote bivalves 41.

Synonymy IS.

Tactile, sense 244, afferent and efferent
nerves 244, mAnodonta 170, inHelix
1.50.

Tactile siphonal tentacles 244.

Taste (see Gustatory sense).

Tienioglossa 265, formula 265.

Tectibrancli, parapodia of 193.

Teeth, 152, development of 257,central
1.52, lateral 152, mai’ginal 1.52, tran-
sitional 152, 261.

Temperature .jOc?, effect upon shells 76,
82, 83, upon pigmentation 329.

Tentacles, contractile 187, 188, 189,
Cgclostoma 188, Limneva stognalis
189, Planorhis marginatus 189,
para vimpara 189.

Tentacles, retractile 187, 188, 189, re-
tractors 159, 342.

Terete univalve 24.

Terminal gut 246.

Tertiary, period 409, shell, 322.

Testacea 19.

Testacella, ureter 336, musculature 344.

Testacdlu scutulum, columella trun-
cation 30.

Testacella haliotidca 203, alimentary
canal 246, 285, arrangement of teeth
262, arterial system 293, buccal sec-
tion 266, odontopliore 267, odon-
tophoral formula 268, intestinal
venous plexus 283, supra-pedal
gland 314, 315.

Tetragnatha 250.

Tetraneura 209.

Tetraspatliostyla 369.

Tetronerythrine 195, 307.

Teutonic province 402, pi. vi.

Thermo-pulsatory curves of Helix
granulata, H. rtifesccns, and Hya-
linia cellaria 299, H. hortensis 298.

Thermo-respiratory curves of Liiniura
auvicularia, L. p>cregra, Planorhis
eorneus 306.

Time and growth-rate curve of Lim-
neva stagnalis 81.

Time and water-volume curve of
Limna’a stagnalis 80.

Temperature and water-volume cur\e
of Limna;ci stagnalis 82, correlation
with size 80.

Tissue respiration 307.

Torsion. 205, anisopleura 5, 6, 109,
206, of internal organs 6, of intes-
tinal canal 281, in pelecypoda 110,
208, visceral nerves 221.

Transition teeth 261.

Transverse, aperture .33, bivalves 51,
striation 27.

Trapezoidal bivalve 52.

Triassic strata 407.

Trichorhiza 344.

Trifoi'ate bivalve 198.

Trignatha 250, 252.

Triodroma 284.

Trinomialism 17.

Triangular bivalves 52.

Trochosphere 34O, 381.

Troclius, eyes of 2.32.

Trochiform univalve (see Conoid).

Truncate, columella 53, significance
of 30, bivalve 5.3, anteriorly and pos-
teriorly 53.

Turbid waters, effect on colour 88.

Turbinated univalves 24.

Turhonilla rufa, heterostrophie spire
115.

Tumid bivalves 53, causes of tumidity 62

Turreted univalves 24.

Typhlosole 139, in Anodonta 171, 172.

'173, 282.

Umbilicus 28.

Umbonal retentor muscles, Anodonta
183.

454

INDEX.

Unibonal sculpture, Anodonta anct-
tina 72, Helix arulcata 72, Pujm
ct/lindmcca 72, U»io piefonnn 72,
fmnidus 42, 72.

Umbones 42, appendages of, in Pisi-
diuni liOfilournttim 42, 73, 110.

Unciiii 261.

Unionidtv as food 4.26.

Unio, section of shell 21, 37, embryos
par.asitic on gills of perch 38.3.

Unio margaritifer, locomotion 350,
vision 2.17.

V. sinuata, form 40, 52.

U nio jnctoruni 9, axis cylinder of vis-
ceral ganglion cells 210, cerebral
ganglion cells 1.38, form 39, 53,
gonial ridge 45, odonr from 230,
jiedal ganglion cells 138,218, respira-
tory currents 303, visceral ganglion
cells 138, 220, vision 235.

V. eoin/nrssa 63, v. pUdtjvhyn-

choidca 53, 63.

Unio tnmidus 106, form 62, hinge teeth
46, malformed 106, polyi)eristomate
120, umbonal sculpture 42, 72.

V. ova/i.'i 64.

Unipolar ganglion cells 210.

Univalve 23.

Unstriated, jaw 255, muscles 341.

Upper margin of bivalves 36.

Urea I40, 179, 333.

Ureter, Anodonta 178, 179, 335, deve-
lo))ment 3.36, primary 335, 336,
secondary 336.

Uiic acid 140, 1.58, 170, 3.27, 333, 338.

Uses, in augury 434^ fis bait 331, in
button-making 429, .as cement ^30,
colour-receptacles 4-29, cream-skim-
mers 423, drinking vessels 429, in
fertilization of flowers 430, as food
for fish 430, as food for sheej) 430,
manure 430, as medicine 427, as
money 431, for i)ersonal decoration
431, ks pigment 430, as polishing
powder 429, as jjorridge spoons 420.

Uterus .363, of Helix 160, 161.

Vagina 364, glands of 364.

Valvata eristetta 25, egg capsules 377.

Valmda jnscinalis 7, aperture 3.3,
cephalic region 189, cleft foot 194,
operculum 126, penis 189,362, sexual
organs 355.

Variation, of banding 96, in shell .sub-
stance 76, causes 76.

Varicose sculpture 28, causes 69.

Varico.sity, causes of 28, 69, Helix
arbrntoriim 69, Helix nemoredis 69,
Linimca glabra 69, L. stagnalu 28,
69, V. fragilh-variegata 83, v. vetrie-
gata 28, 69, Planorbis spiirorbis 69.

Varieties, defined 5<?, nomenclature 60.

Vas deferens 360, of Helix 160, 161.

Vascular system (see Circulatory).

V eins 294-

Veliger stage of development 382.

Velletia laeustris, arrangement of
teeth-rows 262, peiiodicity 391.

Velum 382.

Vena-cava 175, 178, 294, 335.

Venous, intestin.al plexus 28.3, sinus
Helix 294, .system in H. aspersa 156.

Ventral, crest 38, 49, gland 196, SI4,
315, margin 36, region (see Pedal).

Ventricle, Anodonta cygnea 174, 290,
Patella 291.

Vertigo alpestris 86, pi. ii. , f. 1.3.

Vertigo antivertigo, aperture 31, 34.

Vertigo angustior 34-

Vertigo edentula v. elongata 24.

Vertigo mimdissima, dentate 66.

Vestigial foot 195.

^'ibracles 187.

Visceral, g.anglia 757, 148, 169, 212, 219,
220, axis of cells 210, cells of 1.38,
210, nerve-cord, torsion of 221, re-
gion (see ]3ody region).

Vitrinct pellnrida, pallial growth 202.

V. dcpressinscida 26, pi. ii. ,f. 12.

Vivipara, ctenidium 8, development of
381, nervous system 7, penostracal
hairs 74, trochosphere of 381.

Vivipara contecta, operculum 126,

' periostracal hairs 75, vision of 237.

Vivipara vivipara, cephalic eyes 2.31,
ceph.alic lobes 193, cephalic region
and tentacles 189, form 24, hypo-
branchial gland .320, odontopliore
265, odontophoral formula 265, ri-
mate 29, section of hypobranchial
gland 320, dimorphic spermatozoa
375, eyes 231, gastrula 381, pedal
nerves 218, tactile cells 244.

Volume of water and temperature
curve of Limneea stngnalis 82.

Volume of water and size curve of
Limneea stagnalis 80, 81.

Voluntary muscles 341.

West province, British Isles 403, pi. vi.

Weahlen, fossils 409, strata 409.

Whorls, of shell 26, striation of 27.

Widely umbilicate univalve 29.

Wolflian bodies (see Pronephros).

Xanthism 94, pi. ii., fi^. 11.

Xanthochroism 95, pi. i., f. 1.

Zonal markings in bivalves 51.

Zygobranchiata, defined 7.

Zeugoglossa 270, formula 270.

Zonitoides excavata, coronal glands
370, gypsobelum in situ .363, 370,
penis 363, sexual organs 363, 370, 371.

Zig-zag markings in bivalves 50.

Zua hibrica, sarcobelum 365, .sexual
organs 356.

Zygoneury 223.

PART I. (Issued Oct. 2Sth, 1894).

If/ ''

A

)4^0N0GEAPI^

OF THE

N

LAND & FRESHWATER

\

X MOLLUSC A i

OF THE

y BRITISHXISLES.

BY

t JOHN W. TAYLOR, F.L.S., X

MEMBEE HOXORAIRE DE LA SOCIETE MALACOLOGIQUE DE FRANCE,
PRESIDENT OF THE CONCHOLOGIC.VL SOCIETY OF GRE.VT BRITAIN AND IRELAND,
EDITOR OF THE “JOURNAL OF CONCHOLOGY ; ”

&C., &C., &C. ;

WITH THE A.SSISTANCE OF
W. D. ROEBUCK, F.L.S., THE LATE CHAS. ASHFORD,

AND OTHER WELL-KNOWN CONCHOLOGISTS.

LEEDS :

TAYLOR BROTHERS, PUBLISHERS, SOVEREIGN STREET.

1894.

PRICE SIX SHILLINGS.

PRELIMINARY

XjZST oz- STJBS0Z^IBZ]K.S,

ARRANGED IN THE ORDER AS RECEIVED.

Darbishire, R. P., B.A., F.G.S., Victoria Park, Manchester.

Mason, P. B., J.P., M.R.C.S., F.L.S., F.Z.S., Horninglow St., Burton-on-Trent
Adams, Lionel Ernest, B.A., 77, St. Giles Street, Northampton.

Crick, Walter D., F.G.S., 7, Alfred Street, Northampton.

ScharfF, R. F., Ph.D., B.Sc., M.R^L^, Curator of the Natural History Museum,
Dublin ; 22, Leeson Park, DWlin.

Whitwell, Wm., F.L.S., 4, Thurleigh Road, Balham, London, S.W.

Moss, William, F.C.A., 13, Milton Place, Ashton-under-Lyne.

Hodges, Figgis & Co., 104, Grafton Street, Dublin.

Eyre, Rev. W. L. W., M.A., Swarraton Rectory, Alresford, Hants. ’ '
Gude, G. K., 5, Giesbach Road, Upper Holloway, London, N.

Gain, W. A., Tuxford, Newark, Notts.

James, J. H., A.R.I. Cornwall, 3, Truro Vean Terrace, Truro, Cornwall.'

Kew, H. Wallis, F.Z.S., 20, Toi-bay Road, Broudesbury, N.W.

Morris, C. H., Lewes, Sussex.

Collier, Edwd., 1, Heather Bank, Moss Lane East, Oxford Road, Manchester.
Milnes, Rev. H., M.A., Winster Vicarage, near Derby.

Barnacle, Rev. H. Glanville, M.A., F.R.A.S., The Vicarage, Holmes Chapel,
Crewe, R.S.O.

Clapham, Sidney C., Hurst Lodge, Gravel Hill, Bexley Heath.

Parry, Lieut. -Col. G. S., 18, Hyde Gardens, Eastboixrne, Sussex.

Dulau & Co., 37, Soho Square, W. (2 copies).

Chaytor, R. C., Scrafton Lodge, Middleham, Bedale, Yorkshire.

Coates, Henry, F.R.S.E., Pitcullen House, Perth.

MacAndrew, J. J., Lukesland, Ivy Bridge, Devonshire.

Oldham, Charles, Sale, Cheshire.

Cairns, Robert, 159, Queen Street, Hurst, Ashton-under-Lyne.

Leicester, Alfred, 1, Priory Gardeirs, Weld Road, Birkdale, Southport.

Roberts, Rev. E. Dale, M.A., 175, L(^lls Road, Handsworth, Birmingham.
Holmes, W. J. 0., F.L.S., Strumpshaw Hall, Norwich.

Hadow, G. K, 66, Warwick Road, South Kensington, S.W.

Madison, James, 167, Bradford Street, Binuingham.

McMurtrie, Rev. Dr., M.A., 5, Inverleitji Place, Edinburgh.

Stanford, E., 26, Cockspur Street, Charing Cross, S.W.

Borrer, W., M.A., Cowfold, Horsham.

Richardson, Hugh, M.A., The Gables, Elswick Road, Newcastle.

Lawson, P., 11, The Broadway, Walham Green, S.W.

[to be continued.]

PART II. (Issued Aug. 24th, 1895),

A

MONOGEAPH

OF THE

LAND & FRESHWATER
MOLLUSCA

OF THE

BRITISH ISLES.

BY

JOHN W. TAYLOR, F.L.S.,

MEMBRE HONOR^\.IEE DE LA SOCIETE MALACOLOGIQUE DE FRANCE,
PRESIDENT OF THE CONCHOLOGICAL SOCIETY OF GREAT BRITAIN AND IRELAND,
EDITOR OF THE “JOURNAL OF CONCHOLOGY ; ”

&C., &C., &C. ;

WITH THE ASSISTANCE OF
W. D. ROEBUCK, F.L.S., THE LATE CHAS. ASHFORD,

AND OTHER WELL-KNOWN CONCHOLOGISTS.

LEEDS :

TAYLOR BROTHERS, PUBLISHERS, SOVEREIGN STREET.
1895.

PRICE SIX SHILLINGS.

PRELIMINARY

XjIST 0:P STJBSOE/IBEE.S,

ARRANGED IN THE ORDER AS RECEIVED

(continued from part I.).

Cockerell, Prof. T. D. A., P.Z.S., Las Cruces, New Mexico, U.S.A.

Hopkinson, Jno., F.L.S., The Grange, St. Alban’s.

Dixon, J. Bassett, Frenchwood Tannery, Preston.

Newton, R. B., F.G.S., 7, Melrose Gardens, Kensington Park, W.

Wilson, J. C., 7, Warrington Street, Ashton-under-Lyne.

Horsley, Rev. J. W., M.A., St. Peter’s Rectory, Walworth.

Arnold, Bernard, F.L.S., Milton Lodge, Milton, next Gravesend.

Walker, Bryant, 18, Moffat Buildings, Detroit, U.S.A.

Stump, E. C., 16, Herbert Street, Moss Side, Manchester.

Watson, Rev. R. Boog, LL.D., etc.. Free Church Manse, Cardross.

Christy, R. M., Pryors, Broomfield, near Chelmsford.

Butterell, J. D., Imperial Chambers, Bowlalley Lane, Hull.

Webb, W. M., F.L.S., Duke Street, Chelmsford.

Mallalieu, Harold, New Delph, via Oldham.

New.stead, A. H. L., Roseacre, Epping.

Norton, Rev. Thomas, Wychling Rectory, near Sittingbourne, Kent.

Stubbs, A. G., 9, Park View, Gloucester.

Wheldon, J., & Co., 58, Great Queen Street, London, W.C. (.S copies).

CoUinge, W. E., F.Z.S., Mason’s College, Birmingham.

Petch, Tom, B.A., 27, Wisbech Road, King’s Lynn.

Wright, Charles East, Orchard View, Kettering.

Fitzgerald, Rev. H. P., M.A., Wellington College, Berks.

Mayfield, A., 88, Stafford Street, Norwich.

Farrer, Capt. W. J., Chapel House, Bassenthwaite, Keswick.

Nelson, Wm., Gandy Row, Crossgates.

Hillman, T. S., Eastgate Street, Lewes.

Sykes, E. R., B.A., 13, Doughty Street, London, W.C.

Treacher, H., & Co., Brighton.

Jones, K. Hurlstone, St. Bride’s Rectory, Old Trafford, Manchester.

Bullen, Rev. R. Ashington, B.A., F.G.S., Shoreham Vicarage, Sevenoaks.
Pearce, Rev. S. Spencer, M.A., Coombe Vicarage, Woodstock, Oxon.

Jones & Evans, 77, Queen Street, Cheapside, London, E.C.

Conchological Society, The Museum, Leeds.

Keogh, J. W. D., 3, Victoria Terrace, Mount Radford, Exeter.

Museum of Science and Art, Kildare Street, Dublin (per Hodges, Figgis & Co.
( Continued on third page of cover.)

LIST OF SUBSCRIBERS.—

Simpkin, Marshall, Hamilton, Kent & Co., 4, Stationers’ Hall Court, E.C.

Clapp, Geo. H., 116, Water Street, Pittsburgh, Pa., U.S.A.

Wohlleben, Th., 45, Great Russell Street, London, W.C.

Edwards, T., Waterloo House, Coventry Street, Leicester.

Daniel, A. T., M.A., Richmond Terrace, Shelton, Stoke-on-Trent.

Conchological Society, Owens College, Manchester (2 copies).

Rose, Jas., M.A., 1, Rawlinson Road, Oxford.

Crowther, H., F.R.M.S.. The Museum, Leeds.

Broadley, A., 2, May Street, Keighley.

National Library of Ireland, Dublin (per Hodges, Figgis & Co.).

Babor, Prof. J. F., Prague, Bohemia.

Branson, F. W., F.I.C., F.C.S., Wynneholme, Headingley, Leeds.

Brierley, Mrs. H. G., Glen View, Gledholt, Huddersfield.

Darbishire, R. D., B.A., etc., Victoria Park, Manchester (second copy).
Montgomery, A. M., 32, The Grove, Ealing.

Sich, Alfred, F.E.S., Villa Amalinda, Burlington Lane, Chiswick.

Museum of Science and Art, Edinburgh (per Jas. Tliin).

Drake, R. Ingalton, Eton College, Windsor.

Boycott, A. E., The Grange, Hereford.

Fox, W. A., 14, Commercial Street, Leeds.

Essex Field Club (per W. Cole).

North Kent Entomological and Natirral History Society (per H. J. Webb).
University College, Aberystwyth (per J. H. Salter, B.Sc.).

Welch, R., 49, Lonsdale Street, Belfast.

Godlee, Theo., Whip Cross, Walthamstow.

Bardsley, D. W., 43, Yorkshire Street, Oldham.

Ranson, Ed., 16, Friars Street, Sudbury.

Evans, Wm., F.R.S.E., Morningside Villa, Mount Pleasant Road, Rothesay (per
Bell & Bradfute).

Melvill, J. C., M.A., F.L.S., Brook House, Prestwich.

Bristol Naturalists’ Society (per C. King Rudge).

Jenner, J. H. A., F.E.S., 4, East Street, Lewes.

Fierke, Fred. W., 52, Francis Street West, Hull.

Reynolds, Richard, F.I.C., F.C.S., Cliff Lodge, Headingley.

Baillie, W., Brora, Sutherlandshire, N.B.

Grevel, H., & Co., 33, King Street, London, W.C.

Denny, Prof. Alfred, Firth College, Sheffield.

Combridge & Co., 18, Grafton Street, Dublin.

Parke, Geo. H., F.L.S., St. John’s, Wakefield.

Shillito, J. G., 20, Elmore Road, Sheffield.

( Continued on fomth page of caoer).

LIST OF SUBSCRIBERS. — Continued.

Tomlin, Brockton, B.A., The Green, Llandaff.

Eccles, J. C., 3, Dudley Terrace, Ventnor, Isle of Wight.

Evans, Mrs. A., Briinscoinbe Court, Thrupp, Stroud.

AVarrington Museum (per C. Madeley).

Public Museum, AVestoii Park, Sheffield (per E. Howarth).

Gould, Edith, 8, Ashburu Place, London, S.W.

Cash, AVm., F.G.S., F.R.M.S., 35, Commercial Street, Halifax.

Northamptonshire Natural History Society (perH. N. Dixon).

Linen Hall Library, Douegall Square, North, Belfast.

Clark, Dr. Jas., Ph.D., M.A., A.R.C.S., Laurel Bank, Headingley, Leeds.
Archibald, Chas. F., Ruslaud Hall, Ulverston.

Hibbert, C. R. C., F.Z.S., F.E.S., Sefton Park, Slough (per H. Sotheran & Co.).
Webb, .1. Stensou, AVinscombe House, Far Headingley, Leeds.

Godwin-Austen, Lt.-Col. H. H., F.R.S., Shalford Park, Guildford.

Atkinson, F. K, Whitefriars, Settle.

Stock, Elliot, 62, Paternoster Row, London, E.C.

Bradford Naturalist and Microscopic Society (per F. Rhodes).

Masefield, J. R. B., M.A., Rosehill, Cheadle, Staffordshire.

Bradford Free Library (per Butler AVood).

Smith, J. Charles, Nandana, Penrith.

Tye, G. Sherri ff, 10, Richmond Road, Handsworth, Birmingham.

AV^otton, F. AV., Mount Stuart, Rothe.say, Bute.

Dowsett, A., Castle Hill House, Reading.

McKean, Kenneth, F.L.S., 1, Lewin Road, Streatham, London, S.W.

Beeston, Henry, Gordon Villa, Rothwell, Northamptonshire.

Hewetson, H. Bendelack, F.L.S., F.Z.S., M.R.C.S., etc. (Eye and Ear Department,
Leeds Infirmary), Hanover Square, Leeds.

Yorkshire Naturalists’ Union (per AV. Denison Roebuck, F.L.S.).

Lewis, H. K., 136, Gower Street, London, W.C.

Glasgow Natural History Society (per A. Somerville, B.Sc., F.L.S.).

Farrah, John, f’.R.Met.Soc., Crescent Road, Harrogate.

Knight, Rev. G. A. Frank, M.A., 11, Southpark Terrace, Hillhead, Glasgow.
Pawson, A. H., Farnley, Leeds.

Bumpus, J. & E., Ltd., Holborn Bars, London, E.C.

Barrett, H. L., St. Andrews, Watford.

Crook, Rev. G. Walter, 54, Buxton Road, Stratford, London, E.

Garforth, AV. E., J.P., C.E., F.G.S., Halesfield, Normanton.

Lewis, H. K., 136, Gower Street, London, W.C. (second copy).

Rogers, Robt., 58, Bridge Street, Northampton.

Barnsley Naturalist and Scientific Society (per H. Wade).

(To he continued).

PART III. (Issued June 30th, 1896).

[.\LI, EIGHTS KESEEVlCn.]

A

MONOGEAPH

OF THE

LAND & FRESHWATER
MOLLUSCA

OF THE

BRITISH ISLES.

]$Y

JOHN W. TAYLOR, F.L.S.,

MEMBEE IIOXOEAIEE DE I.A SOCTETE MALACOLOGIQUE 1)E FEANCE,
EX-PEESfDEXT OF THE COXCHOLOGICAE SOCIETY OF GEEAT BEITAIX AXI) lEELAXD,
LATE EDITOE OF THE “JOUEXAL OF COXCHOLOGA' ; ”

, t'cC., i!cc. ;

WITH THE .\SSISTAXCE OF
AV. I). EOEBUCK, F.L..S., THE LATE CHA.S. ASHFOEI),

AXO OTHEE AVELL-KXOWX COXCHOLOGI.STS.

PRICE SIX SHILLINGS.

PRELIMINARY

XjZST

ARRANGED IN THE ORDER AS RECEIVED

(t'ONTINUKU FROM PART It.).

llawell, llcv. J., ]M.A., Iiiglelty (xreenliow Vicinage, Midillesbro’.

Fallooii, Mrs., Cliristchurcli Vicamge, Dover.

Petty, S. Lister, Queen Street, Ulverston.

Public Library, Jjeeds (per J. Yates).

Manson, R. Taylor, Dernebohn, Darlington.

Leeds Industrial Co-ojierative Society, Educational Dept, (per J. Sbepperd).

AVard, Frederick II. J., AI.R.C.S. Eng., F.R.AI.S., S, Lyndhurst Villas, Tlie Park,
Ealing, \V.

Prime, Henry, Lock-Box II lo, (Jarden City, Long island. New York, U.S.A.
Raven, Eustace, Cberiy Cot, Kew, SuiTey.

Vaughan, J. AVilliains, Telinnewydd, 'ralgartli R.S.O., Breconshire.

Rowntrec, .Mien, Broom liodge, Scarborough.

Dacic, .1. C., lOo, Fiiper Richmond Road, Putney, S.AV.

Eilward Pease Public Libraiy, Crown Street, Darlington (per B. R. Hill).

Barker, R. li, (Jrosvenor Bank, Scarborough.

Bowell, E. AV. \V., Huntsham, Brampton, North Devon.

AA'ager, Harold, F.L.S., Bank Anew, Stainbeck Lane, Chapeltown, Leeds.

(Wnish, J. E., 1(1, St. Ann’s Stpiare, Alanchester.

Blackshaw, J. C., loH, Penn Road, AA’^olverbampton.

Rhodes, John, F.E.S., Alunicipal Technical School, Accrington.

'riiomjison, Beeby, ;>o, A’^ictoria Road, Northampton.

Dodd, B. Sturges, (17, Beech Avenue, New Basford, Nottingham.

Johnston, J., 82, Linthoiiie Road, Aliddlesbrougb.

Friedliinder Solin, Carlstrasse 1 1, Berlin, N.AVi

(I'o hf contiiiited.)

THE COLLECTOR’S MANUAL

OF

British Land and Freshwater Shells,

BY LIONEL E. ADAMS, B.A.,

HON. TREASUREK CONCHOI.OCICAL SOCIETV.

Illustrated by Collotype <5^ Engraved Figures of the species prom Original Drawings,

By A. SICH, G. W. ADAMS, and the AUTHOR.
SECODSriD EIDITIOIT

Containing a full enumeration and description of all the recognized varieties,
with diagnostic tables of the more difficult genera, framed for the purpose of facili-
tating the easy identification of the more critical species.

A full and detailed Census of the known Distribution of every Species,
including the results of the latest researches, will be added.

PRICE, s;- PLAIN and 10,6 COLOURED, NETT.

A few rojnes irifh diiplirntc plates ( eoloured ami plain ) at Idl- per eopnj, nett.

TAYLOR BROTHERS, Publishers, LEEDS.

OPINIONS OF THE PRESS ON THE FIRST EDITION.

“SciKNCK Gossii’,” May, 1885.

“ A beautifully got-up little manual, with exquisitely engraved figures of every
British species. Perhaps no department of natural history has come more to the
front lately than that of land and freshwater mollusca. Mr. .\l)AMS is well known
as a conchologi.st, and he therefore knows what he is writing about. Moreover, he
also knows how to present his knowledge in a useful form. The present work,
besides describing every species, its habits, localities. Sec., gives an account of all the
varieties, hints on arranging and preserving shells, 8;c.”

“ .\ i iiEN.EUM,” May 9th, 1885.

“ Young conchologists are likely to find this little manual, which is the w'ork of
an experienced collector, of much service in determining and classifying their
treasures. About one hundred and thirty species of land and fre.shwater shells occur
in our own country, and by the aid of Mr. Adams' clear descriptions any intelligent
student ought to have but little difficulty in identifying these species, and even in re-
cognizing their chief varieties. The descriptions are supplemented by a series of
excellent figures, mostly executed by Mr. Gerald W. Adams, the author’s brother. .\
glossary of technical terms, carefully accentuated, finds a place at the end of the book. ”

THE

OF CONCHOLOGY

rVULlSHED UNDER THE DIRECTION OK

^bc d'oiuuU of tbc C^oncbological .§'0tictn
of 6rcut Britain anb Jlrclanb.

The Journal contains Original Papers on Recent and
Fossil MoUusca, both British and Foreign, and the
Proceedings of the Society and its Branches,
as well as Notices of all Books and
Memoirs added to the Library.

IT IS PUBLISHED QUARTERLY, AND IS SENT POST FREE FOR

61- per Annum.

Tlic Annual Su1>scrii>tion to tlie Society is 5,-, and the .Journal is
sent rcfiularly to all Meinhers who are not in arrcar.

All Communications may be addressed to
THE SECRETARY of the CONCHOLOGICAL SOCIETY,
THE OWENS COLLEGE, MANCHESTER.

PART IV. (Issued Feb. 20th, 1897).

[ALL RIGHTS RESERVED.]

A

MONOGRAPH

OF THE

LAND & FRESHWATER
MOLLUSCA

OF THE

BRITISH ISLES.

BY

JOHN W. TAYLOR, F.L.S.,

MEMBRE HONORAIRE DE LA SOCIETE MALACOLOGIQUE DE FRANCE,
EX-PRESIDENT OF THE CONCHOLOGICAL SOCIETY OF GREAT BRITAIN AND IRELAND,
LATE EDITOR OF THE “JOURNAL OF CONCHOLOGY ; ”

&C., &C., &C. ;

WITH THE ASSISTANCE OF
W. D. ROEBUCK, F.L.S., THE LATE CHAS. ASHFORD,

AND OTHER WELL-KNOWN CONCUOLOGISTS.

LEEDS :

TAYLOR BROTHERS, PUBLISHERS.

1897.

PRICE SIX SHILLINGS,

PRELIMINARY

LIST OF STJBSOI^IBFE/S,

ARRANGED IN THE ORDER AS RECEIVED

(continued from part III.).

Garnett, Roland, 175, Lee Street, Oldham.

Hargreaves, J. A., 3, Rainshill Road, Scarbi’O.

Stediuan, R. B., 33, High Street, Godahning.

Burton, F. M., F.L.S., F.G.S., Hightield, Gainsborough.

Symes, Richard, F.R.Hist.S., Melbourne House, 87, Barking Road, E.

Tomlin, W., 24, Trinity Street, Cambridge.

Loydell, A., 19, Chaucer Street, Acton, W.

Backhouse, J., F.L.S., F.Z.S., M.B.O.U., Daleside, Harrogate.

Thacker, W., & Co., 2, Creed Lane, E.C.

Sorby, H. C., LL.D., F.R.S., F.L.S., F.G.S., F.R.M.S., Broomfield, Sheffield.
Linton, John, 157, Muntz Street, Smallheath, Birmingham.

Stonestreet, Rev. W. T., 12, Wellington Street, E., Higher Broughton.

Crowther, J. E., Portland Street, Elland.

Yorkshire Philosophical Soc., York (per H. M. Platnauer, B.Sc., F.G.S.).
Blackmore, Jas. C., F.G.S., Falkirk, Whatley Road, Clifton.

Stalley, H. J., 68, Little Britain, E.C.

Bliss, J., Smyrna.

Smith, W. J., 41-43, North Street, Brighton.

Gyngell, W., 5, Murchison Street, Scarborough.

Birchall, Edward, 18, Moorland Road, Leeds.

Salford Borough Royal Museum and Library, Peel Park, Salford, Lancashire
(per Ben H. Mullen, M.A.).

Friedlander & Sohn, Carlstras.se 11, Berlin, N.W. (2 additional copie.s).

(To be continued.)

WILD BIRD PROTECTION

AND

NESTING

By JOHN R. B. MASEFIELD. M.A.,

Vice-President of the North Staffoi'dshire
Naturalists'’ Field Club,

With Illustrations in the text of various designs of Boxes, Brackets,
etc., that have actually been used by Wild Birds for
Nidification, and

NINE COIiEOXYPE PEACES,

And a Full List of the Orders made under the “ Wild Birds
Protection Acts,” on the application of County Councils,
with the Names of the Species protected.

PRICE FIVE SHILLINGS.

LEEDS: TAYLOR BROS., PUBLISHERS, SOVEREIGN STREET.

THE COLLECTOR’S MANUAL

OF

British Land and Freshwater Shells,

BY LIONEL E. ADAMS. B.A.,

HON. TREASUREK CONCHOLOGICAL SOCIETY.

Illustrated by Collotype dr* Engraved Figures of the species from Original Drawings,

By A. SICH, G. W. ADAMS, and the AUTHOR.

o

SE3C03Nri3 EIDITIOnST

Containing a full enumeration and description of all the recognized varieties,
with diagnostic tables of the more difficult genera, framed for the purpose of facili-
tating the easy identification of the more critical species.

A full and detailed Census of the known Distribution of every Species,
including the results of the latest researches, will be added.

PRICE O/- PLAIN, and 10/6 COLOURED, NETT.

A few copies leith duplicate plates ( coloured and plain) at 15 j- per copy, nett.
Post Free 5c1. per Copy Extra.

TAYLOR BROTHERS, Publishers, LEEDS.

Now Ready, compute, 8vo., cloth, with Coloured Map, price £1 Is.,

THE FLORA OF WEST YORKSHIRE,

By FREDERIC ARNOLD LEES, M.R.C.S., etc.

This work is perhaps the most complete work of the kind ever issued for any district,
including detailed and full records of 1,044 Phanerogams and Vascular Cryptogams, 11 Characese,
348 Mosses, 108 Hepatics, 258 Lichens, i,oog Fungi, and 382 Freshwater AIgm, making a total of
3,160 species.

LEEDS : TAYLOR BROTHERS, Publishers, Sovereign Street.

THE

CHOLOGy

PUBLISHED UNDER THE DIRECTION OF

Counctl of tlje Concijo logical Socbtg
of (great Britain aiib Irdanb.

The Journal contains Original Papers on Recent and
Fossil Mollusca, both British and Foreign, and the
Proceedings of the Society and its Branches,
as well as Notices of all Books and
Memoirs added to the Library.

IT /S PUBLISHED QUARTERLY, AND IS SENT POST FREE FOR

6/- per Annum.

The Annual Subscription to the Society is 5/-, and the Journal is
sent regularly to all Members who are not in arrear.

All Communications may be addressed to
THE SECRETARY of the CONCHOLOGICAL SOCIETY,
THE OWENS COLLEGE, MANCHESTER.

PART V. (Issued Nov. 13th. 1899).

[ALL RIGHTS RESERVKD.]

A

MONOGRAPH

OF THE

LAND & FRESHWATEll
MOLLUSCA

OF THE

BRITISH ISLES.

BY

JOHN W. TAYLOR, F.L.S.,

ME.MliUE IIOXORAIRE HE L.V SOCTETE M.VLACOLOGKiUE DE FRANCE,

EX- PRESIDENT OF THE CONCHOLOGIC.VL SOCIETY OF ORE.VT RRITAIN AND IRELAND,
LATE F:DIT0K OF THE “JOURNAL OF CONCHOLOGY ; ”

&C., ;

WITH THE ASSISTANCE OF
W. D. ROEBUCK, F.L.S., THE LATE CHAS. ASHFORD,

-vnd other well-known CONCHOLOGISTS.

LEEDS :

TAYLOR BROTHERS, PUBLISHERS.
1899.

PRICE SIX SHILLINGS.

PRELIMINARY

LIST OF SUBSCI^IBLI^S,

ARRANGED IN ORDER AS RECEIVED

(CONTINUKD FROM PART IV.).

Brusilia, Profes.sor Spiridon, Zagreb, Agraiu, Croatia.

Cockerill, J., G, Park Lane, Holgate, York.

Blackburn, Rev. K. Pcrc}', IIo)dan(l, near Barnsley.

Aldridge, Rev. J. M., iMaisey Hampton Rectory, Fairford, Gloucester.

Dulau & Co., 37, Soho S([uare, London, W.

Kegan, Paul, Trench & Co., Paternoster House, Charing Cross Road (2 copies).
University College, Nottingham, per Professor Carr, F.L.S.

Manscll-Pleydell, J. C., 1).L., J.P., Whatcombe, Blandford.

Turner, E. E., Post t)lhce, Coggeshall, Esse.x.

Harrison, G. Maredydd, Nightingale House, Manchester Road, Southport.
Bloomer, H. Howard, .35, Paradise Street, Birmingham.

Champ, H., c/o S. & .T. Watts dt Co., Manchester.

Heginbothom, Chas. 1)., 3. Estcourt Street, Devizes, Wilts.

Wheldon, J., & Co., 58, Great QueeiiiStreet, Lincoln’s Inn Fields, W.C.

JiUcas, B. R., 3, Dyar Terrace, Wilmington, Northwich.

Preston Scientific Society (per W. H. Heathcote, F.L.S.).

Sykes, Robert, Lochiel, Cumbernauld, Lanarkshire.

Williauhs, J. W., M.R.C.S. (Eng.), L.R.C.P. (Loud.), 128, Mansfield Road,
Gospel Oak, N.W.

Wakefield, H. R., 7, Montpellier TeiTace, Swansea.

Evans, C. W., Kington, Herefordshire.

Watkins & Doncaster, 36, Strand, W.C.

Waddell, Rev. C. H., The Vicarage, Saintfield, co. Down.

Mills, F. W., Thornleigh, Hudder.sfield.

Educational Supply, 42a, Holborn Viaduct, E.C.

Coles, C. S., Hoe Moor House, Hambledon, Cosham, Hants.

Orr, Hugh Lamont, Garfield Street, Belfast.

(To he continued.)

Now Ready, complete, 8vo., cloth, with Coloured Map, price £1 Is.,

THE FLORA OF WEST YORKSHIRE,

By FREDERIC ARNOLD LEES, M.R.C.S., etc.

This work is perhap.s the most complete work of the kind ever issued for ruiy district,
including detailed and full records of 1,044 Phanerogams and Vascular Cryptogams, 11 CharaceJu,
348 Mosses, 108 Hepatics, 258 Lichens, 1,009 ^^tingi, and 382 Freshwater Algae, making a total of
3,t6o species.

LEEDS : TAYLOR BROTHERS, Publishers, Sovereign Street.

THE

J

LOF

1

j

OLOGy

I’UBLISHEU UNDER THE DIRECTION OF

Cmutdl of tljc 'Condjobgical ^ocictn
of 6rcat Britain anti Jlvclanb.

The Journal contains Original Papers on Recent and
Fossil Mollusca, both British and Foreign, and the
Proceedings of the Society and its Branches,
as well as Notices of all Books and
Memoirs added to the Library.

/T /S PUBLISHED QUARTERLY, AND IS SENT POST FREE FOR

6/- per Annum.

Tlie Annual Subscription to the Society is 5/-, and the Journal is
sent regularly to all Members ^^'llo are not in arrear.

All Communications may be addressed to
THE SECRETARY of the CONCHOLOGICAL SOCIETY,
THE OWENS COLLEGE, MANCHESTER.

WILD BIRD PROTECTION

By JOHN R. B. MASEFIELD, M.A.,

Vicf-Prrshhut of the North Staffordshire
Naturtdists’ Field Clvh,

With IlIiistnitiiMis in the text of vavioiis dosiffiis of Boxes, Bmikets,
ete., that have aetnally been used by Wild Birds for
Niditication, and

NXNS COXilL.O'rYPE: PX^AXSS,

Alul a Full Jjist of the Orders made under the “ Wild Birds’
Frotectiun Acts,” on the application of Comity Councils,
with the Names of the Species protected.

PRICE FIVE SHILLINGS.

LEEDS: TAYLOR BROS., Publishers, SOVEREIGN STREET.

THE COLLECTOR’S MANUAL

British Land and Freshwater Shells,

BY LIONEL E. ADAMS, B.A.,

HON. THEASUKER CONCIIOLOCICAL SOCIETY.

Iltustraled hy Collotype iSs Engraved Fignres of the species from Original Drawings,

By A. SICH, G. W. ADAMS and the AUTHOR.

SEOonsrzD ezditioit.

(‘ontiiiiiiii}' a full enumeration ami description of all the recognized varieties,
with diagnostic tables of the more difficult genei'a, foamed for the purpo.se of
facilitating the easy identification of the more critical species.

A full and detailed Census of the known Distribution of every Sjiccies,
including the results of the latest researches, will be added.

PRICE S - PLAIN, and lO'G COLOURED, NETT. #

A few copies with duplicate plates ( coloured and plain) at_ IS j- per copy, nett.
Po.sT Fukk 5d. I’ER Corv Extra.

LEEDS: TAYLOR BROS., Publishers, SOVEREIGN STREET.

PART VI. (Issued June l6th, IdOO).

[all rights reserved.]

A

MONOGRAPH

OF THE

LAND & FRESHWATER
MOLLUSC A

OF THE

BRITISH ISLES.

BY

JOHN W. TAYLOR, F.L.S.,

MEMBRE HONORAIRE DE L.V SOCIETE M.VLACOLOGIQUE DE FRANCE,
EX-PRESIDENT OF THE CONCHOLOGICAL SOCIETY OF GREAT BRITAIN AND IRELAND,
LATE EDITOR OF THE “JOURNAL OF CONCHOLOGY ; ”

&C., i&C., &C. ;

WITH THE ASSISTANCE OF
W. D. ROEBUCK, F.L.S., THE LATE CHAS. ASHFORD,

AND OTHER WELL-KNOWN CONCIIOLOGISTS.

LEEDS :

TAYLOR BROTHERS, PUBLISHERS.

1900.

PRICE SIX SHILLINGS.

TO OUR SUBSCRIBERS.

ri'^HE present part concludes the consideration of the Animal and its
Shell, and I propose to complete the Volume during the present
year by the issue of a concluding part, dealing succinctly with the
Geographical Distribution, Geological History, Parasites, Uses, etc., with
Index and Glossary.

The Specific Volume will then be at once proceeded with, and I would
bespeak the co-operation and help of all interested in the thorough and
detailed working out of the subject.

SOME RECENT OPINIONS OF OUR SUBSCRIBERS.

ZaGREB-AgRAM, CROAtlA.

“ I have just received your publication ‘ A Monograph of the Land and Fresh-
water Mollu.sca of the British Isles,’ and wish to e.xpress to yon luy admiration of
your splendid and beautifully arranged work, and beg you to enrol me amongst
your subscribers.” — With all re.spect, [I’rof.] Spiridon Brusina.

Nov. 21st, 1899.

“ Much j)leased with last number of ‘ Monograph.’ ” — Yours truly, R. Welch.

15th Nov., 1899.

“Your new part has all the completeness and all the beauty of get-up of its
predecessors. Don’t let the mirage of biological completeness detain you [from
early completion]. Wishing you health and strength to complete the work as
thoroughly as it has been begun.” — Yours very truly, Wm. Whitwell.

Nov. 26th, 1899.

“ I hope we shall not have to wait so long for the issue of the next part of your
admirable work.” — Yours faithfully, H. P. Fitzgerald.

17th Nov., 1899.

“ I was very pleased to receive Part v. * * * and to note that your high
ideal of finish is so well sustained in it.” — Yours very truly, KoBT. CAIRNS.

18th Nov., 1899.

“ Liist number of your book to hand, I was glad to see it. It is very good.” —
With regards, yours faithfully, G. Sherriff Tye.

21st Nov., 1899.

“ I beg to tlnank you for your extremely interesting Part V. just received *

— Yours very truly, H. Wallis Kew.

July 28th, 1899.

“ I have ordered your work from a local bookseller, who says Part V. is not yet
l)ublished. If this be so, I am quite satisfied, as such a magnificent work is well
worth waiting for.” — Yours faithfully, F. H. Jackson.

Nov. 17th, 1899.

“ I was very pleased to see another part of your ‘ Monograph,’ and hope we may
welcome moie parts before very long.”— Yours very truly, W. L. W. Eyre.

Nov. 15th, 1899.

“ I have received Part V. and I am amazed at the learning in this work of
yours.” — Yours truly, K. D. Darbishire.

PRELIMINARY

XjIST OIF STJBSOE.IBEK;S,

ARRANGED IN ORDER AS RECEIVED

(continued from part V.).

Erode, Rev. T. Ainsworth, 3, Penley’s Grove Street, York.

Darnborough, F., Croft Villa, Eaglescliff, Yarm.

Breeden, Gny, 304, St. Vincent Street, Ladywood, Birmingham.

Bostock, E. D., Tixall Lodge, StalFord.

Woodrulfe-Peacock, Rev. E. Adrian, L.Th., F.L.S., etc., Cadney Vicarage, Brigg.
Franklin, W. E., 42, Mosley Street, Newcastle-on-Tyne.

Sotheran, H., & Co., 140, Strand, W.C.

Watson, Hugh, Lauder Grange, Corbridge-on-Tyne.

Bristol Museum and Reference Library, Queen’s Road, Bristol (per E. Acland
Taylor).

Kane, W. F. de Vismes, M.A., M.R.LA., F.E.S., Clonbrock, Ahascragh, Galway.

•m E

OF

OL

PUBLISHED UNDER THE DIRECTION OF

Clje Council of tlje Concljological Socicf^
of ^rcat gritain anil JrclaniJ.

The Journal contains Origrinal Papers on Recent and
Fossil Mollusca, both British and Foreign, and the
Proceedings of the Society and its Branches,
as well as Notices of all Books and
Menaoirs added to the Library.

IT IS PUBLISHED QUARTERLY, AND IS SENT POST FREE FOR

61- per Annum.

The Annual Subscription to the Society is 5/-, and the Journal is
sent regularly to all Members who are not in arrear.

All Communications may be addressed to
THE SECRETARY of the CCNCHCLCGICAL SCCIETY,
THE GWENS CCLLEGE, MANCHESTER.

WILD BIRD PROTECTION

AND

NESTING BOXES,

By JOHN R. B. MASEFIELD, M.A.,

Vice-President of the North Staffordshire
Naturalists’ Field Chib,

With Illustrations in the text of various designs of Boxes, Brackets,
etc., that have actually been used by Wild Birds for
Nidification, and

NINE COI^EOrrYPE PEAfTES,

And a Full List of the Orders made under the “ Wild Birds’
Protection Acts,” on the application of County Councils,
with the Names of the Species protected.

PRICE FIVE SHILLINGS.

. LEEDS: TAYLOR BROS., Publishers, SOVEREIGN STREET.

THE COLLECTOR’S MANUAL

OF

British Land and Freshwater Shells,

BY LIONEL E. ADAMS, B.A.,

HON. TREASURER CONCHOLOGICAL SOCIETY.

lllust rated by Collotype Engraved Figures of the species fi-om Original Drawings,

By A. SICH, G. W. ADAMS and the AUTHOR.

SEOOnSTID EIDZTIOlsr.

Coiitaininjfa full enunier.ition and de.scription of all the recognized varieties,
with diagnostic tables of the more difficult genera, framed for the purpose of
facilitating the easy identification of the more critical species.

A full and detailed Census of the known Distribution of every Species,
including the results of the latest researches, will be added.

PRICE S - PLAIN, and 10/6 COLOURED, NETT.

A few copies loith duplicate plates (coloured and plain) at tSj- per copy, nett.
Post Free 5d. per Copy Extra.

LEEDS: TAYLOR BROS., Publishers, SOVEREIGN STREET.

PART VII. (Issued Dec. 31st, 1900).

[ALL EIGHTS KESEEVED].

A

MONOGRAPH

OF THE

LAND & FRESHWATER
MOLLUSCA

OF THE

BRITISH ISLES.

BY

JOHN w: TAYLOR, F.L.S.,

MEMBEE HONOEAIRE DE LA SOCIETE MALACOLOGIQUE DE FEANCE,
EX-PEESIDENT OF THE CONCHOLOGICAL SOCIETY OF GEEAT BEITAIN AND lEELAND,
LATE EDITOR OF THE “ JOURNAL OF CONCHOLOGY ; ”

&C., &C., &C. ;

WITH THE ASSISTANCE OF

W. DENISON ROEBUCK, F.L.S., THE LATE CHAS. ASHFORD,

AND OTHER WELL-KNOWN CONCHOLOGISTS.

LEEDS :

TAYLOR BROTHERS, PUBLISHERS.

1900.

PRICE SIX SHILLINGS.

TO OUR SUBSCRIBERS.

T N the present part, Lists of the Fossils of the various Land and Fresh-
water Genera are given, arranged under the different formations in
which they have been found.

Criticism of these lists is cordially invited with a view to securing
greater correctness and the more rigorous elimination of all species ex-
clusively of estuarine or brackish-water habitat.

Accurate and complete lists are especially desired in view of the
intention to illustrate in succeeding parts every fossil species of our Land
and Freshwater Shells.

JOHN W. TAYLOR,

Noeth Grange, Horseorth, Leeds.

SOME RECENT OPINIONS OF SUBSCRIBERS.

11, Stratuearn Place, Edinburgh, June 29tli, 1900.

“ I enclose a postal order — with thanks for Part VI. of your ‘ Monograph.’ It
is .a really remarkable work of quite e.xceptional ability.” — I am, yours faithfully,
Robert Roog Watson, LL.D.

Museum of Science and Art, Dublin, June 22iul, 1900.

“ The arrival of another part of your beautiful ‘ Monograph ’ reminds me that it
is years ago since I heard from you. There is a good deal in these parts that was
new to me, and they must have cost you an immemse amount of labour. — Yours
sincerely, R. E. Scharff.

Nore, Godalming, 19th June, 1900.

“ Your Part VI. of the ‘ Monograph of the Land and Freshwater Mollusca of
the British Isles reached me yesterdiiy, and I must express mj' admiration of the
way in which you are bringing it out. The illustrations are beautifully done, and
exemplify the diflerent parts of the animal .so truthfully it cannot fail to stimulate
a little more interest in the beauty of the organization of the mollusca than exists
at present among collectors.” — With best wishes, believe me, yours very truly,
H. H. Godwin-Austen.

114, Adelaide Road, Hampstead, N.W., June 21st, 1900.

“With G. K. Gude’s compliments and congratulations on the continued success
of your sj)lendid work, which bids fair to eclipse every other work of its kind
hitherto published.”

PRELIMINARY

LIST STJLSGE.IBI]I^S,

ARRANGED IN ORDER AS RECEIVED

(continued from part VI.).

Dillon, Hon. R. E., D.L., Clonbrock, Ahascragli, Galway.
Pannel, Ch., jr., East Street, Hasleinere.

Goulding & Son, 20, Mercer Street, Louth.

Grevel & Co., 33, King Street, Coveut Garden, W.C.

Adkin, R., F.E.S., Wellfield, 4, Lingards Road, Lewisham, S.E.
Ilariner, F. W., F.G.S., Oakland House, Cringleford, Norwich.
B. F. Stevens & Brown, 4, Trafalgar Si^uare, W.C.

0

THE

OF CONCHOLOOy

PUBLISHED UNDER THE DIRECTION OF

Council of lljc Concijo logical Sucictg
of Crcat gritain anb Jfrclani).

The Journal contains Original Papers on Recent and
Fossil Mollusca, both British and Foreign, and the
Proceedings of the Society and its Branches,
as well as Notices of all Books and
Memoirs added to the Library.

IT IS PUBLISHED QUARTERLY, AND IS SENT POST FREE FOR

61- per Annum.

The Annual Subscription to the Society is .5/-, and the Journal is
sent regularly to all Member.? who are not in arrear.

All Communications may be addressed to
THE SECRETARY of the CCNCHCLCGICAL SCCIETY,
THE GWENS CCLLEGE, MANCHESTER.

THE NATURALIST:

A Klot\thly Journal of [Natural History for tl^e florth of England.
Edited by WM. DENISON ROEBUCK, F.L.S.,

With the assistance in Special Departments of

J. GILBERT BAKER, F.R.S., CHAS. P. HOBKIRK, F.L.S. ,

W. EAGLE CLARKE, F.L.S., GEORGE T. PORRITT, F.L.S.,

ALFRED MARKER, JVt.A., F.G.S.. JOHN W. TAYLOR, F.L.S.,

and W. BARWELL TURNER. F.C.S., F.R.M.S.

8vo., Monthly, price 6d.

Annual Subscription, payable in advance, 6/6 post-free ; 6/- accepted in case of Subscriptions
paid direct to the Leeds office on or before the 31st March in each year.

V

WILD BIRD PROTECTION

AND

NESTING BOXES,

By JOHN R. B. MASEFIELD, M.A.,

Vice-President of the North Staffordshire
Naturalists' Field Club,

With Illustrations in the text of various designs of Boxes, Brackets,
etc., that have actually been used by Wild Birds for
Nidification, and

Nivrs coXiUorrYPE peates.

And a Full List of the Orders made under the “ Wild Birds’
Protection Acts,” on the application of County Councils,
with the Names of the Species protected.

PRICE FIVE SHILLINGS.

LEEDS: TAYLOR BROS., Publishers, SOVEREIGN STREET.

THE COLLECTOR’S MANUAL

OF

British Land and Freshwater Shells,

BY LIONEL E. ADAMS, B.A.,

ON. TREASURER CONCHOLOGICAL SOCIETY.

Illusirated oy Collotype Engraved Figures of the species from Original Drawings,

By A. SICH, G. W. ADAMS and the AUTHOR.

SEOOITID EZDZTIOIT.

Containinj^a full enumeration and description of all the recognized varieties,
with diagnostic tables of the more diiticult genera, framed for the purpose of
facilitating the easy identification of the more critical species.

A full and detailed Census of the known Distribution of every Species,
including the results of the latest researches, will be added.

PRICE S/- PLAIN, and 10/6 COLOURED, NETT.

A few eopies with duplieate plates ( coloured and plain ) at 15 j- per copy, nett.
Post Free od. per Copy Extra.

LEEDS: TAYLOR BROS., Publishers, SOVEREIGN STREET.