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APRS 1929

ZOOLOGY OF THE INVERTEBRATA

LOOLOGY
OF THE INVERTEBRATA

A TEXT-BOOK FOR STUDENTS

BY

ARIHUR HE. SHIPLEY, MA,

FELLOW AND ASSISTANT TUTOR OF CHRIST'S COLLEGE AND DEMONSTRATOR OF
COMPARATIVE ANATOMY IN THE UNIVERSITY OF CAMBRIDGE

LONDON
ADAM AND CHARLES BLACK
1893

C—

YRERETS
(CLOJOOXS C609 ey,
’ CAN BAGIKEITL 6

PREFACE

In this book I have tried to give such an account of the
Invertebrata as might be useful to students in the upper
forms of Schools and at the Universities, who are already
acquainted with the elementary facts of Animal Biology. The
volume is in no sense a work for advanced students, and hence
no references to original sources have been given, and the
names of the various investigators who have promoted our
knowledge have been mentioned as sparingly as possible.

In order to keep the book within reasonable limits, I have
not described fully certain types which are dealt with in the
admirable elementary text-books of Huxley and Martin, and
Marshall and Hurst; but, with this reservation, I have en-
deavoured to describe some one example of each of the larger
groups, and then to give a short account of the most interesting
modifications presented by other members of the group.

The last few years have witnessed a great extension in
our knowledge of the structure and relationship of the Inver-
tebrata. The earth has been ransacked for new forms, and
improvements in microscopes and in technique have facilitated
a more minute and thorough examination of these forms in
the laboratory. This increase in our knowledge has neces-
sarily been accompanied by a rearrangement of material ;
many intermediate forms have been discovered, and unexpected
relationships have been revealed, and these have entailed a
revised classification.

vi ZOOLOGY

These facts have led me to treat the subject largely
from a morphological standpoint, touching but lightly on the
Histology, Embryology, and Natural History of the forms
described. More space has been, as a rule, devoted to those
animals which are regarded as intermediate between the larger
groups than to the more specialised members of the groups.

Any system of classification is to some extent a matter of
personal judgment. I do not suppose that adopted here has
any finality, but I hope the tables given will be of use to the
student as expressing the results of the most recent research.

In preparing the volume I have been much helped by
numerous friends, to whom my best thanks are due. Dr.
D. Sharp, Dr. Hickson, Mr. Beddard, Mr. J. J. Lister, Mr.
F. G. Sinclair, Mr. C. Warburton, and Mr. MacBride, have all
given me the most generous assistance, and, above all, I am
most deeply indebted to my friend Mr. 8. F. Harmer, who has
in the most kind way read through the proof-sheets, and whose
careful revision has saved me from many errors.

To the Delegates of the Clarendon Press I owe thanks
for permission to use Fig. 133, taken from Rolleston and
Jackson’s Forms of Animal Life. Uerr Fischer of Cassel has
kindly given me leave to use some reductions from the admir-
able diagrams of Professor Leuckart; these occur in the
groups Echinodermata and Arthropoda, and are acknowledged
under each eut; similarly the firm of Wieweg and Son have been
good enough to allow me to use four figures taken from Vogt
and Yune’s Lehrbuch der Praktischen Vergleichenden Anatomie.
I am also indebted to Messrs. Macmillan and Co. for their
kindness in allowing me to use Figs. 37, 89, and 90, all of
them taken from Professor Parker’s Hlementary Biology.

ARTHUR E. SHIPLEY.

Curist’s CoLLEGr, CAMBRIDGE,
March 1893.

CONTENTS

CHAPTER I
INTRODUCTION .
CHAPTER II
PROTOZOA
CHAPTER: Il

MertAzoOA—PORIFERA

CHAPTER IV

CoELENTERATA
CHAP BER Vi

CoELOMATA

CHAPTER, Wi
PLATYHELMINTHES

CHAP PERF Wil
NEMERTEA

CHAPTER Vill
NEMATODA

CHAPTER IX

HIRUDINEA

PAGE

36

115

131

viii ZOOLOGY

CHAPTER xX

CHAETOPODA

CHAPTER XI
GEPHYREA

CHAPTER XII

BRACHIOPODA

CHAPTER XIII

POLYZOA

CHAPTER XIV

Mo.uusca

CHAPTER XV

ECHINODERMATA

CHAPTER XVI

ARTHROPODA—-CRUSTACEA

CHAPTER XVII

PROTOTRACHEATA

CHAPTER XVIII

MYRIAPODA

CHAPTER XIX

INSECTA

CHAPTER XX

ARACHNIDA

CHAPTER XxXI

CHORDATA

PAGE

138

W779

189

224

253

300

310

321

388

423

CHAPTER I
INTRODUCTION

PROTOPLASM is the name given to that colloidal, jelly-like
substance which forms the basis of all life on this globe.
Every living organism consists of protoplasm and the products
of protoplasm. Whilst life lasts it is continually renewed
from food which passes into the organism, and which, by
the action of the protoplasm already there, is built up into
new protoplasm. At the same time other portions of the
protoplasmic body of the organism are being broken down,
and the products thus formed are either thrown out from the
body as excreta, or remain in the body, either stored away as
useless, or in most cases performing some useful function, such
as that of protecting the organism by forming a cyst or shell
or internal skeleton.

The protoplasm of living beings is arranged in a series of
units or elements, termed cel/s, and with very few exceptions
each cell contains one or more specialised portions of proto-
plasm which take up staining material more readily than the
body of the cell, and which are termed nuclez. An organism
may consist of but one cell with its nucleus or nuclei, but
more commonly it is composed of an enormous number of
cells, connected together, and each dominated by a single
nucleus. In either case, whether the organism is unicellular
or multicellular, the cell is capable of an extraordinary degree
of differentiation, and may assume the most diverse forms.
In the multicellular beings similar cells are massed together
into aggregates which form the various tissues composing the
body of the higher organisms. In unicellular forms the cells

1

2 ZOOLOGY

composing the body sometimes remain in connection with one
another, but they never form definite tissues, and the cells of
such an aggregate are physiologically distinct and independent
of one another, the whole forming a colony of unicellular
beings.

The organic world has developed in two diverging direc-
tions, one corresponding to the animal the other to the
vegetable kingdom, and though there is no difficulty in
distinguishing the higher forms of these two kingdoms, it is
often by no means an easy matter to determine whether some
of the lower forms should be grouped with the plants or with
the animals; hence any scheme of classification is largely
dependent on individual opinion. There are a number of
characters which if met with in an organism would justify us
in claiming it as an animal, but in many cases one or more of
these animal features are absent, and again other features may
be present which, as a rule, are only found in plants, so that it
becomes at once evident that the line between animals and
plants, at any rate in their lowest forms, represents no scientific
frontier, but is an arbitrary boundary which is apt to be shifted,
now forward now backward, according to the opinion of the
various investigators.

The most important morphological difference between plants
and animals is perhaps the presence of a cellulose coat which
encloses, at any rate during some part of its life, the vegetable
cell. Cellulose is a substance which has a definite chemical
composition, and which, though practically universal in plants,
is very rarely met with in animals. Another constituent
found in all green plants, but rare in animals, is chlorophyll;
the presence of this enables the plant in sunlight to take
in carbon dioxide, which serves as part of its food; chlorophyll
is, however, not found in all plants, the Fungi, an important
section of the vegetable kingdom, being devoid of it.

The physiological differences between plants and animals
are more striking than the morphological. Plants can live
upon much simpler compounds than animals; they can absorb
their nitrogen in the form of nitrates or simple compounds
of ammonia, and their carbon in the form of carbonic acid, or some
othersoluble compound; thus they can live on liquid inorganic food

INTRODUCTION 3

which may enter the organism at any point, and consequently
plants require no mouth or digestive cavity, or organs for the pre-
hension of food. Animals, on the other hand, require more com-
plex compounds; their nitrogen, with scarcely an exception, must
be supplied in the form of proteids, and their carbon in the form of
starch, sugar, or fat. Some of these compounds are not soluble,
and hence an animal must ingest its food in a more or less solid
state; and to that end it is usually provided with a mouth and
digestive tract, with organs for the prehension of food, and with
locomotor organs so that it may find its food. Since the food
of animals does not exist in nature except as the products of
living beings, it is obvious that animals are ultimately depend-
ent on the plant world for their means of subsistence.

The broken-down products of the protoplasm are
usually excreted by special organs set apart for this purpose
in animals, but in plants the waste products are either diffused
from the surface of the organism, or are stored away in the
plant. There are no special excretory organs.

In both plants and animals the most lowly organised beings
consist of one cell, and the unicellular organisms are termed
the Protophyta and Protozoa respectively. The Metaphyta and
Metazoa, or the multicellular plants and animals, consist of a
number of cells arranged in more or less definite tissues, but
even these multicellular beings pass through a unicellular stage,
that of the ovum, whose repeated divisions after fertilisation
give rise to the cells composing the body of the animal or
plant.

The Protozoa are therefore the simplest and most primitive
animals, and it is natural to place them at the bottom of the
animal kingdom.

Animal Kingdom

SCHEME OF CLASSIFICATION OF THE
ANIMAL KINGDOM

( ( Proteomyxa . Protomyxa, Vampyrella.
Myxomycetes . Chondrioderma, Fuligo.
Tehes Nuda—A moeba, Pelomyxa.

* | Testacea—Arcella, Difflugia.
Labyrinthulidea
GYMNOMYXA Perforata — Rotalia, Globi-
gerina.
* | Imperforata—Gromia, Orbi-
tolites.
Heliozoa.. . Actinophrys, Actinosphaerium.
Radiolaria . . Acanthometra, Collozowm.

Reticularia

Lissoflagellata —Zuglena.
PROTOZOA Flagellata . : { Ghosts as Codosiga,
Proterospongia.
Dinoflagellata
Rhynchoflagellata — Noctiluca.

CoRTICATA .< Ciliata Heterotricha—Stentor.

Peritricha—Tvrichodina, Vor-
ticella.
* | Holotricha — Paramoecium,
Opalina.
i ; Hypotricha—Luplotes.
Acinetaria . Acineta, Dendrocometes.
[ Monocystidae
hic Monocystis.
| Sporozoa _ | Gregarinidea Polyeystidae
Wee Clepsidrina.
orifera. Coecidiidea— Coccidiwm.
ACOELOMATA eset
Platyhelminthes.
Nemertea.
Nematoda.
Hirudinea.
METAZOA Chaetopoda.
Gephyrea.
Concerts Brachiopoda.
Polyzoa.
Mollusca.
Echinodermata.
Arthropoda.
\ Chordata.

Note.—In the tables of classification those groups which are not described in

the text are printed in italics. After the title of the minor sub-divisions of
the group, the name of one or more typical genera belonging to that sub-division

is added in italics.

CHAPTER II
PROTOZOA

CHARACTERISTICS.— Unicellular, or uf composed of more than
one cell, such elements not arranged in tissues. Food ingested
by a special mouth or by any part of the cell substance.
Reproduction never takes place by ova and spermatozoa. Some
forms are colonial.

Group A. GYMNOMYXA.

The Protozoa have been divided into two groups, the
Gymnomyxa, corresponding with the old group Rhizopoda ;
and the Corticata, which comprise the Infusoria and Gregarin-
idea. The former group includes all those forms which, like
Amoeba, have, during the dominant phase of their life-history,
no limiting membrane. Their protoplasm is consequently
exposed, at any rate at one portion of their surface, and tends
to run into processes or pseudopodia, which vary in appearance
in the different species. Food may generally be ingested at
any point of the naked protoplasm.

Although the amoeboid condition is the one in which
these organisms most frequently occur, they may pass through
other phases, such as rounded spores enclosed in a membrane
(chlamydospore), naked spores with a lash-shaped pseudopodium
(flagellula), etc. Not infrequently two or more individuals
fuse together, and this fusion may be the precursor of repro-
duction. When the bodies of numerous amoebiform indi-
viduals run together to form a large mass of protoplasm, the
result is known as a Plasmodium.

6 ZOOLOGY

The classification here adopted is taken from Lankester’s
article on Protozoa.

Ciass I. Proteomyxa.

The simplest forms of Gymnomyxa are grouped together
in the class Proteomyxa. As an example of this class the life-
history of Protomyxa aurantiaca, a minute organism found in
1867 by Professor Haeckel, living on the coiled shells of the
Molluse Spirula, in the Canary Isles, may be described. Many
of these shells were found bearing on their white surface a
minute globular mass of an orange-brown colour. Each
globule or cyst consisted of a central mass of protoplasm,
surrounded by a structureless membrane; in the older cysts
the central protoplasm appeared to be segmented into a num-
ber of parts, each of which, on the bursting of the membrane,
escaped in the form of a flagellula or pear-shaped swarm-spore.
These moved actively about by the lashing of their whip-like
pseudopodium, and soon underwent a change in form; instead
of one pseudopodium which acted as a flagellum, they devel-
oped several, and then moved about like so many amoebae.
After creeping about for some time, these amoeboid organisms
fused together and formed a plasmodium, which in some cases
attained such a size as to be visible to the naked eye. The
plasmodium gave rise to many branching ragged pseudopodia,
by whose aid it ingested great numbers of diatoms and other
food particles. It was much vacuolated, although none of the
vacuoles were contractile. After crawling over the Spirula
shell for a time the plasmodium retracted its pseudopodia and
became spherical; it then surrounded itself with a cell wall, and
the contents of the cyst thus formed broke up into flagellulae
in the way indicated above. No nucleus has yet been observed
in any phase of the life-history of this organism.

Other genera have been described which live parasitically
upon Spirogyra (Vampyrella spirogyraec) or Diatoms (Archerina
Boltoni, described by Lankester). In the latter chlorophyll
corpuscles are present, and seem to dominate the cell body
in a manner suggestive of a nucleus, which is otherwise
absent.

PROTOZOA 7

Cuass II. Myxomycetes.

The Myxonycetes differ from the Proteomyxa in their
spores being always coated (chlamydospores), and in the fact
chat these are formed in definite cysts (Fig. 1, B), sometimes
supported on columns, or in naked groups called sori. They

Gale

A. Plasmodium of Didymium leucopus (after Cienkowski). x 350.
B. Spore cyst of Arcyria incarnata (after De. Bary).

differ from all other Protozoa in being rarely aquatic; they
usually live in the air, in damp places. Their plasmodia may
attain a great size, several square inches in area, and form the
largest masses of undifferentiated protoplasm to be met with.
They live on organic particles; they are often of brilliant
colour.

The life-history of most of the Myxomycetes is a repeti-
tion of that of Protomyxa: in some the flagellula phase is
omitted, the chlamydospore giving rise directly to an amoeboid

8 ZOOLOGY

organism, provided however witha nucleus. These amoebulae
may multiply by fusion, but ultimately they run together and
form the plasmodia (Fig. 1, A), which form the dominant and
characteristic phase in the life-history of the Myxomycetes.

Fia, 2.

A, A portion of the plasmodium of Bad- E. Amoebulae formed by meta-
hamia, x 3%, showing a pseudo- morphosis of flagellulae.
podium (1) commencing to enclose F. Two amoebulae fusing to
a piece of mushroom stem. After form F”’,

Lister. G and G’. Stages in the formation of a

B. Spore of Chondrioderma. three-celled plasmodium.

C. Spore of Chondrioderma dehiscing. H. A small plasmodium.

D. Flagellulae which have emerged from (B-H., after Cienkowski.)

the spores,

Chondrioderma difforme, the species illustrated in Fig. 2,
has a small plasmodium, easily visible to the naked eye. This
species occurs commonly on old bean-stalks. The plasmodia

PROTOZOA 9

may be easily obtained by soaking some dried bean-stalks in
water for twenty-four hours, and then keeping them in a moist
chamber for ten days or so; at the end of this time plasmodia
may be observed crawling over the stems, etc.

The sulphur-coloured Fuligo (Aethalium) is a genus which is
met with in considerable masses creeping over the tan in tan-
yards ; others occur in rotten wood, decaying bean-stalks, and
dung. The spore cysts may or may not be stalked, and the pro-
toplasm enclosed within them does not all become spores, but
the remnant forms a meshwork of fibres differing in details in
the various genera. This network, termed a capillitiwm,
serves to support the spores, and possibly helps in their escape
when the surrounding wall gives way. The walls of the
cysts may be strengthened by the deposition of calcium
carbonate. The coating of the spores is of a cellulose nature:
a substance usually associated with the vegetable kingdom, but
not unknown among animals, especially amongst the Protozoa.
At times the plasmodia contract and surround themselves by
a cyst, and pass through a quiescent period. This condition is
known as the sclerotiwm.

Myxomycetes are capable of retaining their vitality for long
periods of time in a dried-up condition; they resume their
active life again when supplied with moisture. About 300
species of Myxomycetes have been described, chiefly by
botanists, who regard these organisms as being allied to the
Fungi.

CLass III. Lobosa.

The individuals of this group are those Protozoa in whose
life-history the amoeboid phase predominates. The pseudo-
podia are lobose, thick, blunt processes of protoplasm, which
are never filamentous and never anastomose. One or more
contractile vacuoles are found, and it is stated that urates have
recently been demonstrated in connection with these vacuoles
in some Amoebae. The amoeboid individuals may conjugate
from time to time, but do not form plasmodia. They some-
times encyst, and the cyst is a resting one (hypnocyst) and
not a reproductive one (sporocyst). The usual form of repro-
duction is fission, which may pass into gemmation. The dis-

fe) ZOOLOGY

tinction between the endoplasm and ectoplasm found in these
and other Gymnomyxa is more apparent than real, and depends
only on the presence or absence of food and other granules,
the actual protoplasm of the organism being of one consistency.

Some of the Lobosa have acquired the power of forming shells,
and this affords a convenient character by which we can divide
the class into two orders: (1) the Nuda, and (2) the Testacea.

Order 1. Nuda—The most familiar example of the
former order is the Amoeba, of which there are many species
quite distinct from the amoeboid spores of the Myxomycetes,
which are often taken for Amoebae. The various species differ
one from another in the nature of their pseudopodia and in the
character of their nuclei. In some species the former are little
more than low eminences, standing out from the general
surface, in others they are long finger-shaped processes which
stream rapidly hither and thither. Some members of this
order, as the Amoeba princeps and Pelomyxa, have numerous
nuclei scattered through the body: in the first-mentioned form
these arise by the gradual “fragmentation” of the original
nucleus. Such a multinucleated condition is constant in some
species. In some cases the soft protoplasmic body has been
observed to contract away from, and to lie within, a very thin
cuticular membrane, which maintains the outline that the
Amoeba possessed the moment before contracting; this cuticle
is not usually visible, except in Lithamoeba, when it exists it
must be very attenuated and elastic.

Pelomyxa is one of the largest of the Lobosa, the species P.
palustris having a diameter of more than 2 mm. The external
protoplasm is clear and produced into pseudopodia (Fig. 3).
The inner mass is crowded with vacuoles, and contains in addi-
tion to the numerous nuclei (5, Fig. 3) a number of refringent
bodies of unknown function (6, Fig. 5),and many food particles.
It has been observed to set free minute amoeboid spores, which
probably grow into new Pelomyxas.

Order 2. Testacea.—The shell which encloses the proto-
plasmic body of these Lobosa may be soft and cuticular, and
may then be strengthened by grains of sand adhering to it, or
it may be hard. In either case the protoplasm can be extruded
from an aperture in the shell. Arcella (Fig. 4) is a common

PROTOZOA II

genus found in the soft debris at the bottom of clean ponds
and ditches, and on the surface of aquatic plants. The shell is
chitinoid, and arched on the upper surface, flat on the lower, so

Fic. 3.—Portion of a Pelomyzxa, highly
magnified.

1. Clear external layer of protoplasm,
ectoplasm.

bo

. Central protoplasm, crowded with
granules, etc.—endoplasm.

. Pseudopodia.
. Refractive bodies.

. Nuclei.

a Oo — WwW

. Cylindrical crystals scattered through
the protoplasm.

that it is somewhat dome-shaped or hemispherical in form.
In the centre of the flat surface is a circular opening through

Fie. 4.—Arcella vulgaris, Ehr.

Shell.

. Protoplasm within the shell.

. Protoplasm without the shell—pseudo-
podia.

. Nucleus ; there is more than one.

. Contractile vacuole.

. Aperture of shell.

. Space where the protoplasm has with-
drawn from shell.

. Gas vacuoles.

oo bh)

STD OE

ioe)

which the protoplasm protrudes in the form of blunt pseudopodia.
The protoplasm within the shell encloses more than one
nucleus, several contractile vacuoles, arranged round the circular

I2 ZOOLOGY

border, and numerous food vacuoles. In addition we find one
or more contractile vacuoles which enclose no liquid, but a
gas, possibly CO, This gas vacuole serves as a hydrostatic
balance ; when it disappears the Arcella sinks. Two individuals
are sometimes found lying with their flat surfaces applied to
one another in the process of conjugating. This has been in
some cases observed to precede reproduction, which takes place
by the constriction of small portions of protoplasm, either from

Fic.

5.—Arenaceous Moraminifera.
a. Exterior of Saccammina. b. The same laid open.
c. A portion of the test more highly magnified. d. Pilulina.

e. Portion of test more highly magnified.

the protruding pseudopodia or from the protoplasm enclosed in
the shell. In the latter case the abstricted portions escape
through the shell mouth and grow up into new Arcellae.

Difflugia is a genus with a soft shell strengthened by the
presence of sand particles and diatoms ; the various species have
various shapes, some being flask or urn shaped, and one is
slightly coiled.

Ciass IV. Reticularia (Foraminifera).

In these Protozoa, the pseudopodia are filiform, and anas-
tomose into a fine reticulum, along the strands of which gran-

PROTOZOA 13

ules may be seen streaming, evidence of the active movement
of the protoplasm. They are never entirely naked, but are
enclosed in a shell, which may be chitinous, calcareous, or com-
posed of agglutinated sand grains (Fig. 5). There may be one
or many nuclei, and a contractile vacuole has not been observed
in most cases. Their method of reproduction is not very well
known; it may take place by fission, or by the formation of
buds. There are both marine and freshwater representatives, of
this class. The enormous variety of forms under which the
shells of the Reticularia present themselves, and their importance
in building up large masses of chalk, limestone, ete., have always
attracted the attention of naturalists. The class was formerly
divided into two groups: the Perforata, those whose shell is
pierced by numerous fine pores all over its surface, through
which the filiform pseudopodia find exit ; and the Imperforata,

Fic. 6.—Globigerina, as cap-
tured in the tow-net near the

surface.

without the minute pores, but with one or more larger openings,
for the exit of the protoplasm. This division is, however, tending
to be obliterated. Many of the shells consist of one chamber
only (monothalamia, Fig. 5), others, as they grow in size, accom-
modate their increased bulk by the addition of more chambers
(polythalamia, Fig. 7), and it is chiefly the marvellous variety
of ways by which the new chambers are added which

14 ZOOLOGY

produces the great divergency of forms. In some cases the
protruding pseudopodia deposit a secondary shell, which
obliterates the outline of the primary shell, and usually masks

Fic. 7.—Globigerina bulloides, as seen in three positions.

its form. The mud at the bottom of the Atlantic and other
seas is composed to such an extent of the calcareous shells
of Globigerina bulloides (Fig. 7), which, when the protozoan dies,
sink to the bottom, that it 1s usually known as Globigerina ooze.

Oy SERA) eee

Fic. 8.—Globigerina ooze from 1900 fathoms.

The living Globigerina (Fig. 6) floats at the surface of the sea, the
protoplasm extending round the shell and forming a much vacuo-
lated envelope to it. Some slight idea of the enormous number
of these organisms which must have lived to build up the foram-
iniferous rocks which extend from the Palaeozoic times onward
may be formed from the fact that D’Orbigny estimated there
were 160,000 shells in a gramme of sand from the West Indies,
and Schultze gives 1,500,000 in 15 grammes of sand from

PROTOZOA 15

the coast of Sicily. The nummulitic limestone of the Medi-
terranean basin is composed of the calcareous shells of

eo

Fic. 9.

1. A piece of Nummulitic limestone from 2. Vertical section of Nummulites.
the Pyrenees, showing Nummulites 38. Orbitoides.
laid open by fractures through the
median plane.

Nummulites, 1 Foraminiferan, which sometimes acquired the
diameter of a shilling. Other species, such as Fusulina and

Fic. 10.—Rotalia with pseudopodia extended through the pores of the shell.

Rotalia (Fig. 10), also took a large share in building up the
imestones of the Old World.

16 ZOOLOGY

Gromia is a form found in both fresh and salt water ; it has a
membranous shell of the imperforate type, with an opening at

“I

Fic. 11.—Gromia oviformis,

Duj.

. The shell.

. Protoplasm inside the

shell.

. Protoplasm outside the

shell.

. Numerous nuclei.

. A Diatom surrounded by

pseudopodia.

. Pseudopodia anastomos-

ing.

. Ingested diatoms.

one or both ends, from these the protoplasm passes out and forms
a layer round the outside of the shell, from which the fine
reticulating pseudopodia arise. The shell is thus completely
imbedded in protoplasm, both inside and outside. In Lieber-

PROTOZOA 17

kiihnia (Fig. 12), an allied form, the pseudopodia anastomose
to a great extent and form a close reticulum.

Fic. 12.—Lieberkiihnia, with
reticulate pseudopodia,

CLass V. Heliozoa.

Mostly spherical in form, sometimes supported by a siliceous
skeleton, and with radiating stiff pseudopodia. The protoplasm
of the body is very. vacuolated, and contains one or more nuclei.
Near the surface of the body one or more contractile vacuoles
may be observed. With few exceptions, they inhabit fresh
water.

Actinophrys sol, the sun animaleule (Fig. 13), is one of the
common microscopic objects found in still fresh water. It may
be met with floating amongst the leaves of submerged plants,
and presents a globular body which undergoes slight changes of
outline, and is usually very vacuolated. The single nucleus
occupies a central position, the contractile vacuole is on the
surface, and food vacuoles containing portions of algae, infusoria,
etc., may be seen throughout the body. The pseudopodia are
stiff and hair-like, and are supported by an axial fibre; they
can be withdrawn into the body. When they come in con-
tact with a particle of food they bend slowly over it, and bring
it near to the surface of the protoplasmic body, when it is

swallowed with the surrounding drop of water, and thus a food
2

18 ZOOLOGY

vacuole is formed. Encystment rarely takes place. Actinophrys
and another genus, Lhaphidiophrys, have been observed to form

Fic. 13.—Actinophrys sol, Ehrb. From Bronn.

1. Nucleus in centre of body. 4. A mass of food in a food vacuole.
2. Axis of pseudopodium extending into 5. Superficial vacuolated protoplasm.
cell as far as nucleus. 6. Deep, finely granular protoplasm.

3. Contractile vacuole.

colonies by incomplete fission. Reproduction commonly takes
place by fission, but in some cases spores have been observed ;
those of Actinosphaertum being provided with a siliceous shell.

This last-named genus (Fig. 14) is much larger than Actino-
phrys; it contains numerous nuclei, situated in the deeper
protoplasm. The pseudopodia are supported by an axial ray.
Rhaphidiophrys is usually found in colonies ; it has a skeleton of
siliceous spicules, matted together round the body, each spicule
lying tangentially to the surface. Acanthocystis has siliceous
rays arranged radially ; they are of two kinds: short ones, which
are forked at their outer end, and long stout ones. They are
attached to the body by a small disk. Finally, leading on to
the condition found in the Radiolaria, Clathrulina (Fig. 15),

PROTOZOA 19

a stalked genus, has a spherical siliceous shell perforated by
numerous openings.

Fra. 14.—A portion of A ctino-
sphaerium Kichhornii,
Ehrb., highly magnified,
seen in optical section.
From Bronn.

1. Nuclei.

2. Ectoplasm.
3. Endoplasm.
4

. Pseudopodia with axis.

5. Food mass in food vacuole.

Fic. 15.—Clathrulina elegans, Cienk.
x 150-200. From Bronn.

1. Stalk.
2. Shell.

3. Pseudopodia protruding through apertures
in shell.

20 ZOOLOGY

Criass VI. Radiolaria.

Organisms which are either spherical or with one principal
axis whose body is divided into a central mass containing
one or more nuclei and a peripheral portion, by the presence
of a membrane known as the “central capsule.” This is
perforated so that the intracapsular protoplasm is continuous
with the extracapsular protoplasm. A well-developed skeleton,
in most cases siliceous, is present. This consists either of
loose siliceous spicules or of a continuous skeleton which
may take the form of lattice-work spheres, arranged con-
centrically, and united to one
another by radial spicules,
which project beyond the sur-
face of the body. The skele-
tons of Radiolarians occur in
vast numbers on the floor
of some seas, forming a layer
of siliceous ooze (Fig. 16).
The skeleton may be wholly
outside the central capsule,
or it may be partially within
it. Numerous fine pseudo-
podia radiate around — the

Fic. 16.—Radiolarian ooze from 4475 body ; these unite to some
fathomieini@antral Pacific: extent, nodes of protoplasm
being found at the point of
union. <A streaming of the protoplasm along the pseudopodia,
as in Heliozoa and Reticularia, takes place, and granules have
been seen to circulate between the intra- and extra-capsular
protoplasm. No contractile vacuole has ever been observed.
The protoplasm is much vacuolated: a condition commonly
met with in those Protozoa which, like the Radiolaria, swim
near the surface of the sea.

Some very remarkable bodies, known as yellow cells, are
found widely distributed amongst the Radiolaria. These are
small oval yellow bodies, only found in the extracapsular pro-
toplasm. They were formerly regarded as part of the body of

PROTOZOA 21

the Radiolarian ; more recent research has, however, shown that
they continue to live after the death of the animal, that they
multiply in more than one way, occasionally forming mobile
swarm-spores, that similar cells occur in the tissues of many
Coelenterates, and that they contain chlorophyll, although this
colouring matter is masked by a yellow pigment. A nucleus
and a cellulose cell-way are also present. These features have
caused these yellow cells to be regarded as unicellular algae,
living in a state of commensalism with the Radiolarian, and
they have received the name of Zooxanthella nutricola. They
are not found in all species, and are usually absent in
Acanthometra, and in the other species with a horny skeleton.

The protoplasm contains, in addition to the yellow cells,
numerous oil or fat globules, and crystals and concretions of
unknown use.

No conjugation has ever been observed in this class; repro-
duction is sometimes by simple fission, which commences first In
the central capsules. Spore formation in the central capsules
also takes place, and results in the formation of mobile spores ;
but the details are complex, and the exact sequence of events
not thoroughly understood.

Many form colonies by the fusion of their extracapsular
protoplasm. That of Collozowm, the individuals forming which
are devoid of skeleton, may be an inch or more long. The
various members of the colony are held together by a gelatin-
ous matrix.

Group B. CorTIcaTa.

The animals which are grouped together in this second
division of the Protozoa have as a common feature a differen-
tiation of the protoplasm into a more fluid central portion and
a firmer cortical layer usually associated with a limiting mem-
brane, which surrounds their body and gives it a definite shape.
As a consequence of the presence of this cortical layer, these forms
which take solid food have acquired one or more channels through
which the nutriment is ingested, and usually a definite area
whence the undigested remnants are extruded. The parasitic
forms, which live in the nutritive fluids of their hosts, are
usually devoid of any such cell mouth or anus. The presence

22 ZOOLOGY

of the cortical layer has also rendered locomotion by pseudo-
podia rare, and those Corticata which move about actively
do so as a rule by means of rows of cilia or by a single or
paired flagellum.

Cuass I. Flagellata.

The bodies of the members of this class are usually very
minute, and always contain a nucleus; they are moved by the
lashing of one, sometimes by two or three flagella, A mouth

Fia. 17.—I. Typical form of Huglena viridis, Ehrb., after Sav. Kent.

1. Contractile vacuole. 3. Gullet and origin of flagellum,
2. Pigment spot. 4. Nucleus.
Il. Il. IV. V. Four views of Huglena viridis, showing the change of shape
consequent upon the euglenoid movement.

may be present, but in those forms which live in nutritive
fluids the nourishment is usually imbibed by the whole surface
of the body. One or more contractile vacuoles occur, and
sometimes a pigment spot is situated at one end of the body.
Conjugation sometimes occurs, and is followed by the breaking
up of the body into spores, reproduction also takes place by

PROTOZOA 23

simple fission. Many Flagellata form colonies, the individuals
of which are imbedded in a gelatinous matrix.

Luglena viridis (Fig. 17) is a minute oval Flagellate found in
puddles by the wayside, or on roofs, ete. It has a thin cuticle,
and undergoes curious rhythmical changes of outline. The elon-
gated spindle-shaped body shortens, and becomes correspond-
ingly thicker. The thickening appears then to travel to the
posterior end of the body and die out. The animal has at this
moment its elongated spindle-shaped form; it then shortens
again, and the whole movement is repeated. At the anterior
end is a single long flagellum, which by its lashing drags
the body swiftly through the water. Lankester has dwelt
on the difference between the action of such a flagellum
(tractellum) and of one that propels an organism in front
of it, as the tail of a spermatozoa or the flagellum of Bacteria
(pulsellum).

tound the base of the flagellum is a depression, the mouth,
which leads into the central protoplasm; and close to this, and
apparently opening into it, is a reservoir communicating with a
contractile vacuole. A pigment spot also is found in the same
region, but the reticulate nucleus occupies the centre of the
body. The whole body is coloured green, by chlorophyll
granules. Grains of paramylum, a body with the same com-
position as starch, are also found in the protoplasm.

Hypnocysts, or resting encysted forms, are frequently formed
amongst the Flagellata, when they find themselves in un-
favourable circumstances. The encysted Huglena may emerge
after a certain period of rest from the Hypnocyst, or it may
whilst in the cyst divide into 2 or 4 spores each of which
emerges as a young Euglena. Reproduction by multiple fission
has also been described in this species, a vast number of spores
being formed, each of which grows into a new individual. Con-
Jugation also takes place in the Flagellata, and is usually
followed by encystment and the division of the contents of the
cyst (sporocyst). At other times fission may occur in the free
state. Sometimes macrogonidia and microgonidia are produced,
and the latter fuse with one another or with adult individuals
(Protococcus).

The Flagellata are divided into two groups: the JLzsso-

ZOOLOGY

flagellata, with no collar round the base of the flagellum; and

Fic. 18.—A branch of Codo-

siya cymosd, Sav. Kent.

1. The stalk.

2. Protoplasmic cell body,
showing nucleus and
granular protoplasm.

3. Collar.

4, Single flagellum.

J

Most Flagellata live in fresh water ; some are marine, and
some parasitic, living in the alimentary canal or blood of

the Choanoflagellata, in
which the protoplasm is
produced into a collar which
surrounds the anterior end,
from the middle of this the
single large flagellum takes
its origin. Codosiga (Fig. 18)
isa colonial form of this kind,
composed of long branching
stalks, the end of each branch
bearing an ___ individual.
These collared flagellates
have a striking resemblance
to the collar cells lining
the flagellate chambers in a
sponge; and a genus, Pro-
terospongia (Fig. 19), dis-
covered by Saville Kent, in
which the individuals of
the colony are sunk in a
jelly, lends some support
to the view that Sponges
may have originated from
colonies of Choanoflagel-
lata. In this genus the
individuals near the sur-
face are of the typical
form; but certain wander-
ing amoeboid cells have
sunk into the central jelly,
and some of these have
become spherical, and then
divided up into micro-
gonidia, in a manner recall-
ing the formation of sper-
matozoa in a Sponge.

PROTOZOA 25

Vertebrates and Arthropods. Huglena viridis often exists in
such numbers as to turn the water green, and a species of
Haematococcus is responsible for the red snow of the Arctic
regions. Many of them, such as Polytoma, thrive in putrid

Fie. 19.—Proterospongia Haeckeli, Sav. Kent. x 800.

1. Nucleus. 6. Other individuals undergoing
2. Contractile vacuole. fission.

3. Collar. 7. Individual with collar contracted.
4. Flagellum. 8. Individual divided up into number
5, Amoeboid individual sunk in sup- of spores (microgonidia).

We}

porting jelly. . Jelly-like supporting matrix.

liquids, such as the water of macerating tubs, and these forms
are mostly saprophytic.

Some of the lower forms are apt to withdraw their flagellum
and become amoeboid (Cilzophrys) ; in others (Cercomonas), the
posterior end of the body is very apt to throw out pseudopodia,
and the young of many species exhibit amoeboid movements.
These facts support the view that the Flagellata are derived
from the Gymnomyxa; and indeed there are certain forms
which might equally well find a place in the class Proteo-
myxa,

Ciass II. Rhynchoflagellata.

This class contains but one or two genera. One of them,
Noctiluca, attains a large size: y!; of an inch in diameter. It is

26 ZOOLOGY

of a spherical form, and grooved on one side like a peach. From
the bottom of this groove a very large transversely-striated
flagellum takes its origin. Near the base of the flagellum is
the mouth, opening into a sort of pharynx; a second smaller
flagellum has its origin in the latter. The protoplasm of the
globular body is very reticulate. No contractile vacuole has
been observed. At times octiluca withdraws its flagella
and passes into a resting condition, but it does not form a cyst.
This animal is interesting, as it is phosphorescent, and gives rise
to a large part of the phosphorescence of temperate seas. The
seat of the lght is said to be the superficial protoplasm.
teproduction is by fission, but motile swarm-spores are also
formed in large numbers. Conjugation has been observed.

Cuiass III. Giliata.

This class is characterised by the possession of cilia as
locomotor organs, arranged either in a perioral ring, or forming
a more or less complete covermg. A nucleus is always present ;
this may be single, and is then accompanied by a paranucleus,
or it may be distributed in small fragments throughout the
body. One or more contractile vacuoles are present. The
shape of the body is very various. Some Ciliata are united
into colonies, and some form gelatinous tubes in which they
live; the majority, however, are free-swimming. Conjugation is
common, but usually does not end in permanent fusion. Fission,
usually simple, but sometimes multiple, is the usual method of
reproduction.

This class has been divided into four Orders, characterised
by the arrangement and nature of the cilia.

Order I. Peritricha.—Cilia arranged in an anterior ring
or spiral, to which a posterior ring may be added. The rest of the
body wnerliated.

Torquatella has its cilia fused to one another, and so a
vibratile membrane is formed which surrounds the anterior end.
Trichodina is very common, crawling on the tentacles and body-
wall of Hydra; it is pyramidal in shape, and has two circlets
of cilia. On its sucker-like base a curious horny toothed ring
is situated.

PROTOZOA 27

Vorticella is attached by a stalk to submerged water-weeds,

etc. Up the centre of this stalk runs a muscle fibre, a differ-
entiation of the protoplasm, attached at intervals to the
cuticular sheath of the stalk. The differentiation of cortical
and medullary protoplasm is well marked. The nucleus is a
coiled loop. The animal sometimes encysts, but this is prob-

Fic. 20.—Trichodina pediculus, Ehrb. x 300.
I. View of the base.

1. Mouth.

bo

. Contractile vacuole.

3. Corneous collar.

commas | Il. View from the side.
rl.

i

1. Corneous collar,

a4) 2 and 3. Ciliated rings.

eS 4. Nucleus.

ably only the formation of a hypnocyst, and has no repro-
ductive significance. Binary longitudinal fission is the com-
monest form of reproduction, one half remaining on the stalk,
the other (macrozooid) acquiring a ring of cilia and swimming
away to settle elsewhere. At other times the Vorticella
divides into eight microzooids, which conjugate permanently
with the sessile individuals. These also occasionally produce
microzooids by budding, and the colonies are also increased by
the formation of buds.

Order II. Heterotricha— The body is covered uniformly
with short cilia, and a cirelet or spiral of long cilia is developed
in relation to the mouth.

Stentor has a moniliform or beaded nucleus, and a consider-
able number of paranuclei. In some cases these latter
correspond in number with the beads of the nucleus. S.
polymorphus is one of the largest Ciliata, reaching a length of
35 in. In this genus conjugation takes place by the oral face,

28 ZOOLOGY

as in Paramoecium, and fission is oblique. Recent observation
on this and other forms shows that as long as the products of
artificial division contain part of the nucleus with its chromatin,
they are capable of regenerating the lost parts; those portions
of the body which are without any portions of the nucleus die.

Lalantidium is a genus which lives parasitically in the
human colon, and with Jyctotherus, is found in the rectum
of Anura, ete. The latter is interesting, since it 1s provided
with a permanent anus with a cuticular lining. In most Cihata
the situation of the cell anus is constant, but there is nothing
to indicate its position, except when waste matter is being
expelled.

Order III. Holotricha.—Jn this order the body is uni-
formly clothed with short cilia, arranged in regular rows. Some-
times those on the adoral surface are slightly longer than the
others.

Paramoecium is one of the commonest genera of this
order. Close underneath its cuticle in the ectosarc, is a layer
of oval bodies, the Zvrichoeysts; these, when the animal is
irritated, discharge threads, which have probably the same
functions as the stinging threads in the nematocysts of
Coelenterata.

Maupas has recently described the conjugation of Para-
moecium aurelia, which takes place as follows. As soon as two
individuals come together, the paranuclei, of which there are
two (Fig. 21, 1), separate themselves from the nucleus, increase
in size (Fig. 22, A), become spindle-shaped, and ultimately divide
into two (2 and B). The two halves of each divide again (C), so
that a stage is found with eight similar portions of the original
paranucleus: in each individual (3 and 4). Of these eight
corpuscles, seven are absorbed and disappear (5); the eighth
alone, and this is always that one which lies nearest to the
mouth, undergoes further change. This corpuscle increases
in size and divides into two (6 and D), thus giving rise to the
male and the female pronucleus. The former of these passes out
of each conjugating individual into the other, and there fuses
with the female pronucleus (7 and E). The conjugating animals
now separate. The “ fertilised” paranucleus now divides into

PROTOZOA 29

Fic, 21.—Paramoecium aurelia in process of conjugating. Maupas.

1. The two paranuclei in each individual becoming spindle-shaped and com-
mencing to divide.

2. Stage with four paranuclei in each individual.

3. The four paranuclei again divide. The division is almost complete in the left
Paramoecium.

4. Stage with eight paranuclei.

5, Seven paranuclei being absorbed, and the one nearest the mouth remaining and
dividing in two, the male and female pronuclei.

6. Exchange of male pronuclei.
7. The male has fused with the female pronucleus to form the fertilised paranucleus.

8. The fertilised paranucleus divides.

9. The resulting halves divide again.

10. The two halves at the posterior end form the new paranucleus ; the two at the

anterior end, the new nucleus.

The disintegration and dissolution of the nucleus are shown in the same series of figures.

30 ZOOLOGY

two (8 and 9, and F), and each half divides again (G), so that
each individual contains four fragments of paranucleus: two at
one end of the body and two at the other (9). The two at

Fic. 22.—Diagram of changes undergone by
paranuclei of Paramoecium aurelia during WP ---
conjugation. Maupas.

A. Increase in size of paranuclei.

B,. 1st division of paranuclei. Gee.

C. 2nd division of paranuclei, and disappearance
of seven-eighths. aoe

D. Division of remaining portion into male and ‘
female pronuclei. | eee

E. Fusion of male and female pronuclei.

F. Division of fertilised paranucleus into two D -----
halves.

G. Division of these halves. Cc

H. Of the four quarters shown inG, one forms B
the new nucleus of young Paramoecium which is
formed by fission, the other divides into two and
forms two paranuclei, one in each of the new indi-
viduals.

the posterior end undergo no change, and form the paranuclei
of the new individuals which result from the subsequent
fission ; the two at the anterior end increase, and are destined
to form the nuclei of the new individuals (10). Before this
is completed, however, the two paranuclei have again divided

Fic. 23.—Opalina ranarum, Ehrb. From Broun.

1. Nuclei.

2. Ectoplasm.

(H), so that after fission each new individual contains one
nucleus and two paranuclei.

Whilst the paranucleus of the original Paramoecium has
been undergoing these changes, the nucleus has first become

PROTOZOA 31

mammullated and then band-like, and ultimately undergoes
fragmentation. The fragments persist some time, and in other
species, P. caudatum, possibly take part in forming the new
nucleus. In P. aurelia they ultimately disappear, the majority
of them being in all probability extruded.

Opalina ranarum (Fig. 23) lives in the rectum of a Frog.
As it grows, its nucleus divides, until a great number of nuclei
are found. The animal then slowly segments, until each
portion contains only one or two nuclei; these form a cyst,
and in this condition leave the body of the frog. When eaten
by a Tadpole, they emerge, grow, and the nucleus again begins
to divide. In Opalinopsis this division of the nucleus has
been carried further, and it exists in the form of a fine powder
scattered through the endoplasm, the particles of which at
times coalesce and form a single nucleus again.

Order IV. Hypotricha.— These Ciliata have a flat ventral
surface, completely ciliated, or provided with enlarged muscular
cilia. The dorsal surface is conver, wneiliated, but sometimes
bears vretractile setae. Both mouth and anus are well
developed.

In this group the cuticle is sometimes strongly developed,
and forms a protective plate of some thickness; in the Euplo-

Fic. 24.—ELuplotes patella. After Btitschli.
. Mouth.

2. Hypotrichous processes.

1
2,
3. Nucleus.
4, Cilia of oral groove.
5

. Contractile vacuole.

tidae this exists on the dorsal surface only. The distinction
between endoplasm and ectoplasm is almost lost. | Encyst-
ment is not uncommon, and one species (Gastrostyla vorax)
has been kept alive in a hypnocyst for the space of two
years.

to

Oo

ZOOLOGY

Cuass IV. Acinetaria.

No cilia or flagella present, but a number of tentacular
processes, which may be adhesive or may be tubular and
suctorial. The Acinetaria are usually fixed, and most com-
monly stalked (Fig. 26). The nucleus is single, and often
branched. One or more contractile vacuoles occur. Repro-
duction takes place by binary fission and gemmation ; the latter
is often internal.

The Acinetaria are either marine or freshwater, and they
are all carnivorous, living chiefly on the soft parts of Infusoria.

Fic. 25.—Sphaerophrya magna, Maupas. x 300.

1. Individuals of Colpoda parvifrons, a ciliated Infus-
ra) orian whose soft parts are being sucked up by the
Sphaerophrya.

2. The nucleus,

\ 3. One of the hollow tentacles ending in a knob.
: r=5--3
i i)

The cuticle may be thin, but in some cases a definite mem-
branous capsule is formed. Two kinds of tentacles may be
found: one long and adhesive, whose function is to catch and
hold the prey; the other is shorter, tubular, and ends in a
sucker,—these latter are sometimes provided with a spiral
thickening. The soft protoplasm of Infusoria, on which they
prey, 1s sucked up through these hollow tentacles (Fig. 25).
Dendrocometes has a round body, from which four to six many-
branched stout arms project. Each branch ends in a point,
which is said to be hollow, and by means of which food is
sucked into the body. In this genus, and in one or two others,
the contractile vacuole has an excretory duct.

Acineta (Fig. 26) is a stalked form with a membranous
cup; the tentacles are arranged in two clusters at each side of
the body.

teproduction may be by fission, or by external gemmation,
or by internal gemmation, in which case a brood - pouch is
formed, which may be open, but is more commonly closed.

PROTOZOA 33

The bud, or buds, are formed in the floor of this cavity.

When they leave the
parent they are ciliated ;
a fact which lends support
to the view that the Acine-
taria are descended from
the Cihata.
lead a wandering life, but
after a time settle down,
lose their cilia, and acquire
tentacles.

Chass V. Sporozoa.

The members of this
class are all parasitic; and
correlated with this condi-
tion of life is the absence
of locomotor organs, the
absence of any mouth,—
the nutriment being ab-
sorbed all over the body,—
and a reproductive process
which results in the forma-
tion of a very large number
of young. The nucleus is
always single even when the
cell is divided into two
chambers. No contractile
vacuole is present. The
cortical layer of protoplasm
may show traces of fibrilla-
tion.

Of the four sub-classes
which compose this class,
that of the Gregarinidea
is the most important. The
true Gregarines, with very

They at first

. Knobbed tentacles.
. Membranous shell.
. Nucleus.

Fic. 26.—Acineta grandis, Sav. Kent.

Stalk. 5. An example of
Acineta lemnarum,
showing relative size
of the two species.

few exceptions, pass their early life as cell parasites, afterwards

3

34 ZOOLOGY

emerging and living parasitically in the various cavities of
their host. The Coccidiidea pass their whole life as cell
parasites. The true Gregarimes are divided into the Mono-
cystidae, whose body is not divided into two chambers, and
which inhabit Annelids, Gephyrea, Platyhelminthes, and Tuni-
cata; and the Polycystidae, in which a transverse partition
divides the cell into an anterior and posterior chamber, the
latter invariably containing the nucleus. An anterior outgrowth,
the epimerite, which serves to attach the Gregarine to the tissues
of its host, is often present, but this is shed sooner or later.
The Polyeystidae have hitherto only been found in the
alimentary canal of Arthropods.

Monocystis magna (Fig. 27) is frequently to be found with its
anterior end embedded in one of the epithelial cells of the en-

AS)
YS)

Fic. 27.—Five individuals of Monocystis magna (Schmidt), with their anterior
ends embedded in the cells of the rosette-shaped inner end of the vas deferens of
Lumbricus terrestris.

1. Part of the vas deferens of JZ. 3. The nucleus.
terrestris. 4. The ectoplasm.
2. The endoplasm of the Gregarine. 5. The cuticle.

larged inner rosette-shaped openings of the vas deferens of the
common earthworm. It is visible to the naked eye, and
sometimes attains a length of 5 mm. The body is limited by

PROTOZOA 35

a thin cuticle; within this lies the cortical protoplasm, which,
though full of granules, is transparent. The medullary proto-
plasm is dark brown and opaque. Biitschli has shown that
some of the granules are composed of a starch-like material.
The body exhibits movements of a euglenoid character; waves
of contraction passing down the elongated cell. The flowing
about of the protoplasm is rendered visible by the granules.
The nucleus is clear and vesicular, with few granules, and it
lies in the centre of the cell.

At times two individuals come together and surround them-
selves by a spherical capsule; apparently no true fusion takes
place, but the bodies of the Gregarines commence to form spores.
This spore formation proceeds from without imwards in each
cell, but the whole protoplasm is not always used up for this
purpose. The spores are shuttle-shaped, they acquire a capsule
(chlamydospores), and are often spoken of as pseudonavicellae.
The pseudonavicellae escape from the cyst by its bursting, or in
Clepsidrina, a Polyeystid, by special sporoducts. Their contents
divides into eight elongated bodies, known from their shape as
falciform bodies ; these leave the pseudonavicella, and probably
grow up directly into the adult form. A recent observer has,
however, stated that the contents of the pseudonavicella does
not break up into falciform bodies, but the protoplasm becomes
grooved, and thus the appearance of segmentation is produced.
According to him, the whole contents of the pseudonavicella
escapes and grows in a new Gregarine,

Many of the Polycystidae are more highly differentiated
than the species described above; their cuticle may be ridged
or tuberculated, and is frequently produced into hooks in the
epimerite, and the cortical layer of protoplasm may show traces
of fibrillation. When these septate forms conjugate, they
usually lie side by side. Gregarina gigantea, which inhabits
the alimentary canal of lobsters, attains the astonishing length
of # of an inch,

Coceidiidea are minute spherical cells which infest the
epithelium of the intestine, the liver cells, etc., of Vertebrates,
Mollusea, and Insects. Whilst still in their cell host, they
give rise to chlamydospores and falciform young.

CHAPTER III
METAZOA

CHARACTERISTICS.— Multicellular animals, which pass through
a unicellular stage, the ovum or egg. This multiplies by
division, and the cells thus formed, instead of remaining
equivalent to one another, become differentiated and are
arranged in tissues. Reproduction takes place by means of
ova and spermatozoa.

ACOELOMATA.

Metazoa in which a two-layered condition is the predomi-
nant one. . The ectoderm and the endoderm may constitute
the whole animal, but in many cases an intermediate layer (the
mesoderm or mesogloea) lies between them. This middle layer
may be homogeneous, but is more usually invaded by cells from
one of the two layers, or from both. The cavities of the
Acoelomata, except certain ectodermal pits, are in all cases con-
tinuations of the primary central cavity lined by endoderm,
and no cavities exist lned by mesoderm comparable to a
coelom. Radial symmetry about an axis passing through the
mouth is a primitive and common feature of this subdivision.
The animals which constitute it are exclusively aquatic, and
almost entirely marine.

Homocoela—Ascetta.
Heterocoela—Grantia, Leucandra.
if Hyalospongiae—Hyalonema, Euplectella.
Non-CALCAREA~ Spiculispongiae—Halisarca, Oscarella, Geodia.
| Cornacuspongiae—Luspongia, Velinea, Spongilla.

CALCAREA
rortrEra

METAZOA 37

PorrFERA (the Sponges).

CHARACTERISTICS.— Animals of very varied size and shape.

Numerous minute pores allow the passage of water into the
interior of the sponge, and the water is discharged through
larger openings known as Oscula. The current of water 1s
maintained by certain flagellate cells, which are usually
aggregated in what are known as flagellate chambers. The
mesoderm is well developed, and usually gives rise to a skeleton
of calcareous, siliceous, or horny material ; it also gives origin
to the reproductive cells. Sponges may be unisexual or
hermaphrodite. They are aquatic, and, with the exception of
the Spongillidae, they are marine. They are devoid of
tentacles and of nematocysts.

The simplest type of Sponge is that of Ascetta primordtalis,

described by Haeckel. It is a hollow vase-like structure borne

on a stalk with its free end open. This
opening is the osculwm. The walls are per-
forated by a series of small circular apertures,
the “pores,” and its cavity is lined by a layer
of flagellate collared cells, whose activity
keeps a current of water entering the pores
and finding an exit through the osculum.
The flagellate cells are endodermal. The
outside of the vase-like body is covered with
ectoderm, and between these two layers is a
mesodermic tissue which produces triradiate
calcareous spicules. The flagellate endoderm
cells are said to possess contractile vacuoles.
In the more highly organised Sponges the
endodermic lining of the central cavity has
lost its flagellate character and become a
flat epithelium.

Grantia compressa 18 a sponge with a
calcareous skeleton, which is frequently met
with attached to rocks and stones round
our coast. It is of a whitish colour, seldom

Fig. 28.—Ascetta pri-
mordialis, Haeckel.
After Haeckel.

more than an inch long, and rather variable in outline; a

38 ZOOLOGY

Fic. 29.—Part of a section through
Grantia labyrinthica, vertical to
the margin and to the two surfaces
of the wall of the cup. After
Dendy.

. Inhalent pore.

Exhalent canal.

Inhalent canal.

Cavity of flagellate chamber.
. Pore area.

. Gastral skeleton,

. Dermal skeleton.

. Tubar skeleton.

. Embryos.

CONTR OV CO ND

common form is somewhat flask
shaped. At its free end are
situated one or more slit-like
openings, the oscula. The body
is compressed from side to side,
and its wall is pierced by
numerous minute inhalent pores,
which lead by a_ system of
branching tubes into the central
cavity.

The substance of the sponge
is composed of three layers
the ectoderm, the endoderm, and
between them the mesoderm.
The ectoderm consists of flat-
tened cells covering the outside
of the sponge, and lining certain
pits or depressions which are
pushed into the substance of
the sponge, and are termed in-
tercanal spaces. The openings
from the exterior into the inter-
canal spaces are termed “pores”
(1, Fig. 29). Several pores
are usually grouped together,and
form the pore area. The inter-
canal spaces open on their inside
by numerous apertures, called
by Sollas “ prosopyles,” into the
flagellate chambers (4, Fig. 29).
These flagellate chambers are
the most characteristic feature
of the Sponges. They are lined
by collared flagellate cells similar
to those of the Choanoflagel-
lata. Their flagella keep up
a constant current of water,
which passes in at the pores

through the intercanal spaces and _ flagellate chambers,

METAZOA — 39

and into the central cavity, thence it leaves through the
oscula.

Embryological research shows that we must regard the collar
cells of the flagellate chambers, the cells lining the tubes which
lead from them to the central cavity, and the cells lning
the latter cavity, as endoderm. The mesoderm is a gelatinous
tissue in which certain cells are found embedded; some of
these form ova or break up into spermatozoa, whilst others give
rise to the skeleton of calcareous spicules.

In sections of Grantia the intercanal spaces (3, Fig. 29)
may be seen lying between the flagellate chambers, but quite
distinct from these. They are lined by flat epithelial cells,
and they ultimately open by a more or less wide mouth on to
the exterior on the one hand, and by a series of circular pores,
the prosopyles, into the flagellate chambers. These intercanal
spaces are formed by the pushing in of the outer coating of the
sponge, and are lined by ectodermal cells similar to those
covering the outside of the sponge. In some sponges they
reach a great degree of complexity.

The ectoderm of sponges is, as a rule, composed of flat cells

j} ]
f flabelliformis. Diagram
of a portion of a flagel-
late chamber, showing
the various parts of the
collared cells and their
relation to Sollas’s
membrane, which con-
nects together the mar-
gins of the collars.
After Dendy.

( Fic. 30. — Stelospongus

1. Body of flagellate cell.
2, Its nucleus.

3. Its collar fusing at its
edges to form 5,

4, The flagellum.
5. Sollas’s membrane,

in a single layer; rarely these cells become columnar, and bear
flagella (Oscarella lobularis). The endoderm consists, in all
but the Homocoela, of two kinds of cells: (i.) flat pavement

40 ZOOLOGY

cells, which line the central cavity and the ducts opening into
it ; and (ii.) collared cells, which line the flagellate chambers, and
in the Homocoela the general cavity. In Grantia the flagellate
chambers do not open directly into the central cavity, but into
a short exhalent canal (2, Fig. 29), the entrance to which is
guarded by a sphincter diaphragm. The endoderm lines the
whole canal system from the prosopyles to the osculum. In
several genera distributed among several orders the collars
which surround the base of the flagella are at their outer ends
fused to form a membrane, which was first described and
figured by Sollas (Fig. 30, 5). Bidder has shown that if a
Leucandra be placed in water with carmine suspended in it,
the water which comes from the oscula is always free from
carmine granules, thus showing the presence of a very efficient
filter, presumably the fused collars of the flagellate cells. It
is still an open question whether
the space within this membrane,
between the body of the flagellate
cells, is empty, or occupied by a
transparent gelatinous substance.
The mesoderm is a gelatinous
layer, with branched or stellate
cells scattered through it. _Amoe-
boid cells (Fig. 51) wander through
its substance, and convey nutriment
from one part to another, and when
occasion arises assist in removing
irritant foreign matter from the
body of the sponge ( phagocytes).
The branching mesoderm cells have
been traced into direct. proto-
Fic. 31.—Branching connective plasmic continuity with both
cuore’ See gee ectoderm and endoderm. The
Sollas. reproductive cells are also meso-
dermal, and the fertilised ovum
develops in a space in the gelatinous mesoderm (9, Fig. 29),
which is lined by a layer of flat endothelial cells, also meso-
dermal in origin.
Certain mesodermal cells in the neighbourhood of the

ee

pee tee a ee NR TE NET rp NENT
aa = Sere ees

= A Se

eae tre ree eee?

Fic, 32.—Spicules
originating in
single cells.
After Sollas.

I. From Stelletta.

adult Craniella cranium.

METAZOA 41

diaphragms in the exhalent canals of the flagel-
late chambers are believed to be muscular, and
a nervous nature has been attributed to others
situated near the inhalent pores.

The skeleton of Grantia consists of cal-
careous spicules, most of which are of a
triradiate shape (6, 7, and 8, Fig. 29). Each
spicule commences to appear in one of the
mesodermal cells, but as it increases in size it
may protrude from this. The spicules are said
to gradually work towards the exterior of the
sponge, and to be discharged as waste matter.

The character of the skeleton is made use
of in classification. Only a very few sponges—
Halisarca, Oscarella, and Chondrosia—are devoid
of any kind of supporting structure. Those
which possess calcareous spicules have been
grouped together as the Calcarea, and opposed
to all the other sponges, or Non-calcarea. The
skeletons of this latter group may consist of
siliceous spicules, or of a fibrous substance—
spongin. The siliceous, lke the calcareous
spicules, originate in a single mesodermic cell
(Fig. 32); both assume a great variety of size and
shape, and the former may be articulated or
fused to one another. The organic skeleton,
found in the Order Cornacuspongiae, consists of
spongin, a substance chemically allied to silk.
It is secreted by a number of mesodermic cells
termed spongoblasts, which form a layer all
round the fibre, and a multicellular cap covering
the ends (Fig. 34). The fibrous skeleton of Hu-
spongia, devoid of spicules, and characterised
by the regular arrangement of the network and
the smallness of the meshes, forms the bath
sponge of commerce.

In Grantia some of the amoeboid mesodermic

Ill. The same from
IV. A four-rayed spicule from Theonella Swinhoei.

II, From embryo of Craniella cranium.

42 ZOOLOGY

cells may be noticed withdrawing their pseudopodia, and passing
into a spherical resting condition. These form the ova. Others

Fig. 33.—Various forms of Sponge spicules.

divide up into an immense number of spermatozoa (Fig. 35), each
with a head and long vibratile tail. In Grantia labyrinthica

AG

\\

Fic. 34.—Sections through horny fibre of Dendvilla. A, Longitudinal section ;
layers of spongin, surrounded by a layer and surmounted by a cap of spongo-
blasts; «@, fibrous sheath. B, The same in transverse section. After Von
Lendenfeld. ;

Dendy has described the ripe ova making their way through the
mesoderm to the epithelium of the inhalent canals, and passing

METAZOA 43

through the epithelial lining of these ducts. They then hang
freely, supported by a short peduncle, into the lumen of the
canal (Fig. 56), and are doubtless fertilised in this position by

Fic. 35.—1-7, Development of. spermatozoa in Sycandra raphanus; 8, mature
spermatozoa, after Polejaeff (x 792); 9, a sperm morula in Oscarella lobularis
(x 500); 19, an isolated mature spermatozoon, after Schulze ( x 500).

spermatozoa carried in by the inhalent current from another
sponge. After fertilisation they must return back into the
mesoderm, where the larva develops. <A similar migration
of ova has been described by Weismann in many Hydroids.

Fic. 36.

1. Ovum (Grantia labyrinthica)
hanging in lumen of inhalent canal.

2. Epithelium lining inhalent canal.
After Dendy.

The early stages of development take place whilst the ovum
is in the mesoderm; and in the Non-calearea a special invest-
ment of epithelial cells lines the cavity in which the embryo lies.
Many sponges are hermaphrodite, and then the spermatozoa
usually mature before the ova; others are unisexual. Repro-
duction by gemmation occurs in some species, buds being
formed which, as a rule, include portions of all the three
layers; these separate from the parent form, and grow into
new sponges. In Spongillidae, the only freshwater family,
resting buds or gemmules are produced, and their production
involves the death of the sponge. The gemmules consist. of
certain yolk-bearing cells enclosed in a complicated capsule,
which serves to protect the cells until the external circum-
stances permit them to emerge and grow up into a new sponge.

44 ZOOLOGY

Artificial fission has been successfully adopted in the cultiva-
tion of sponges for commercial purposes.

All sponges are marine, with the exception of the family
Spongillidae, the commonest species of which is Spongilla
fluviatilis, an incrusting mass with crater-like oscula, commonly
found on the woodwork of locks, weirs, etc., in our rivers. It
may be coloured green by the presence of chlorophyll. Many
other sponges are brightly coloured, and they may assume a
very great variety of shapes. Some emit a powerful and un-
pleasant odour, which may, like the presence of the spicules,
tend to prevent their being devoured.

The classification of the Porifera cannot be regarded as
settled. That at the head of this chapter is suggested by
Vosmaer.

A. The CALCAREA ‘wncludes those forms which possess a
skeleton of calcareous spicules, generally triradiate in shape. The
collar cells are large.

This class comprises two orders :

G.) Homocoela, in which the endoderm consists wholly of
collared cells, which line the central cavity. Ex. Leuco-
solenia.

This group includes all those forms which were formerly
known as Ascones.

(i.) Heterocoela, in which the endoderm is differentiated into
(a) flat epithelial cells, lining the central cavity and
excurrent canals, and (b) collar cells, confined to the
flagellate chambers. Ex. Grantia, Sycon, Leucandra.

B. The NON-CALCAREA possesses a skeleton of siliceous spicules
or spongin ; very rarely none at all. The spicules may be isolated,
articulated, or fused. The collar cells are markedly smaller than
those of the Calcarea.

The group includes three classes: (.) Hyalospongiae
(Hexactinellidae), (ii.) Spiculispongiae, and (iii.) Cornacu-
spongiae. The first of these three classes is much more clearly
defined than the other two; indeed the latter tend to run into
one another.

METAZOA 45

(i.) Hyalospongiae——~Skeleton of siliceous spicules, which are
usually sexradiate, isolated, or fused into a trellis-work.
Usually deep-sea forms. Many fossils. Ex. Hyalonema,
whose spicules may reach a length of two feet ; Euplec-
tella, or Venus’s flower-basket.

(i1.) Spiculispongiae.—sSkeleton absent in a few forms; im
the great majority consisting of siliceous spicules,
usually independent, but sometimes articulated together,
or united by organic material. One of the sub-orders,
the Myxospongiae, is devoid of skeleton. Ex. Hali-
sarca, Oscarella. In the Tetractinellidae, one of the
largest subdivisions, the spicules are to a great extent
four-rayed. Ex. Geodia, Tetilla.

(iii.) Cornacuspongiae.—sSkeleton of wniaxile spicules united
by spongin, or of spongin. Inhabit the sea, brackish or
Jresh water, Ex. Euspongia, the sponge of commerce ;
Velinea, Spongilla (the freshwater sponge), ete.

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10 VINILOV.LOO

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CHAPTER IV
COELENTERATA

CHARACTERISTICS.— Acoclomata with a definite shape. The body
is usually radially symmetrical about an axis which passes
through the mouth. The ectoderm is separated from the en-
doderm by a middle layer—the mesogloea—which may be
structureless and devoid of cells, or may contain numerous
cells. The tissues are not pierced by a series of pores, and
there are no collar cells. Protective organs known as nematocysts
are characteristic of the group, with the exception of almost
all the CTENoPHORA. Alternation of generations is common,
and also the formation of colonies by budding. All the
members of the group are aquatic, and most of them marine.
This group is divided into four classes :

A. HYDROMEDUSAE
. SCYPHOMEDUSAE

B
C. ACTINOZOA.
D. CTENOPHORA.

; = Hydrozoa.

Crass A. HYDROMEDUSAE.

CHARACTERISTICS.— The Hydroid form may be free or sessile, single
or colonial. It is rarely without tentacles, which are nearly
always solid. A horny perisare or a calcareous skeleton may
be developed. Asexual reproduction by gemmation usually
takes place, the hydroid form budding off a medusiform sexual
individual. The Medusa has a velum, and a double nerve
ring. The sensory organs are ocelli and otocysts or modified
tentacles. The Hydromedusae are bisexual, and the sexual
cells are typically ectodermic, sometimes endodermic. No
gastral filaments are present. The medusa may arise directly
JSrom the egg, but this is rare.

48

A. Vertical sec
18

2
3
4
5.
6
tf
8.

ZOOLOGY

tion of Hydra.
Ectoderm.
Endoderm.

Mesogloea.
. Mouth.

Coelenteron.

. Hypostome or oral cone.
. Pseudopodia of endoderm

cells.
Flagella of endoderm cells,

9 and 9’,

. Two buds

Large and small nemato-
cysts.

in different

stages of development.

. Ovary.

. Single ovum.

. Testis.

B. Portion of transverse section through

body wall of Hydra, more highly
magnified.

COLLENTERATA 49

The simplest form of Hydromedusa is represented by Hydra,
which exists only in the hydroid form. Its reproductive organs
show no trace of a medusoid nature; and although the medusae
can be traced in other and more specialised species through
stages of degeneration till they become little more than pro-
tuberances on the body-wall full of sexual cells, still there is
nothing in the ovary and testis of Hydra to warrant the view
that they are not simply sexual organs.

In some Hydromedusae a distinct alternation of generations
is present; that is, the hydroid person produces asexually, by
budding, a medusoid person which produces sexually, by means
of ova and spermatozoa, the hydroid person again. Thus asexual
and sexual modes of reproduction alternate in the life-history
of these animals, and each mode is associated with a distinct
kind of animal: the asexual with the hydroid, usually a fixed
form; the sexual with the medusoid, a free-swimming form.
This kind of alternation of generation—budding alternating with
the sexual method—has been termed metagenesis; it occurs in
many of the lower animals.

Although the fixed hydroid differs a good deal in appear-
ance from the free-swimming medusa, they can both be reduced
to a common type. In both forms of person very considerable
complexity of form is often combined with great simplicity of
ultimate structure. Many forms are colonial, and the in-
dividuals composing the colonies are commonly modified to
subserve various functions, and thus may become degraded to
the level of organs. ;

1. Ectoderm. 12. Flagella.
2. Endoderm. 13. Vacuole.
3. Mesogloea. C. Two ectoderm cells.
4, Layer of muscular processes of 1. Nucleus.
ectoderm cells cut across just 2. Muscular tails.
outside mesogloea. D. An endoderm cell of H. viridis.
5. Interstitial cells. 1. Nucleus.
6. Cnidoblast containing nemato- 2. Chromatophores.
cysts. 3. Ingested nematocyst.
7. Nematocyst. E. A large nematocyst with extended
8. Cnidocil. barb.
9. Nucleus of endoderm cell. F. A small nematocyst.
10. Ingested diatom. G. A spermatozoon.

11. Pseudopodium.
A, B, and CG, after Jeffery Parker; D, after Lankester; F and G, after Howes.
4

50 ZOOLOGY

Tubularia indivise is a marine colonial Hydromedusan
borne on a branching anastomosing stolon attached to sub-

Fia. 38.—A colony of Tubularia
indivisa. After Allman
(natural size).

. Cireumoral tentacles,

. Aboral row of tentacles.

. Mouth.

. Blastostyle.

. Hydrocaulus.

Oo oO fF CO ND HE

. Hydrorhiza.

merged objects. At intervals the stolon sends up straight
unbranched stems, each of which terminates in a hydroid person,
generally termed a hydranth. The branching stolon may be:

COELENTERATA 51

termed the hydrorhiza, and the single stem the hydrocaulus.
Both the hydrorhiza and the hydrocaulus are protected by
a thin chitinoid investment, the pervsare. This tubular
covering, however, stops short at the base of each hydranth.
The living tissue within the perisarc is known as the coenosarc ;
it consists externally of a single layer of ectoderm, which
secretes the perisarc, and internally cf an axis of endoderm
traversed by ciliated canals; these serve to place the cavities
of the various hydranths in communication with one
another.

Each hydranth is a somewhat flask - shaped structure
bearing two rings of tentacles; one composed of short tentacles
situated round the mouth, the other, of much larger tentacles,
arises from the middle of the body, where the diameter is
greatest. The bases of the circumoral tentacles are visible as
slight projections on the body-wall for some little distance below
their point of emergence. Their ectoderm is crowded with
nematocysts, and contains muscle cells, glandular cells, ganglion
cells, usually bipolar, and four kinds of nematocysts. Their
endoderm consists of several rows of cartilaginoid cells, which
serve as a stiffening skeleton.

The digestive cavity of the hydranth is spacious, it is lined
by endoderm cells, which in many species digest intracellularly.
There is a thickened layer of endoderm forming a ring for the
support of the larger tentacles. The middle layer or mesogloea
is structureless and thin.

The relationship of the hydroid to the medusoid person is
best explained by means of diagrams (Fig. 39). The oral axis
of the hydroid is shortened, and the circumference of the middle
part of the body is correspondingly increased. The ring of large
tentacles is thus carried out to the edge of what is known as
the umbrella ; the oral cone, with its ring of tentacles, remaining
in the position of the umbrella handle. This change of external
shape is accompanied by the obliteration of certain parts of the
coelenteron or central cavity. Along certain areas in the
umbrella the endoderm cells come in contact and fuse, forming
the endodermal lamella (Fig. 39, II. 12). This fusion takes
place in such a way as to leave certain tracts open, the most
important of which are the circular vessel running round the

tN

ZOOLOGY

ur

edge of the umbrella, and the radial canals, which communicate
with the cavity of the oral cone on the one hand and the
circular canal on the other. On the aboral surface of the
endodermal lamella the middle layer usually becomes much

Ws

WY

Fic. 39. a

thickened, its gelatinous substance may remain structureless,
or cells may invade it.

Tubularia is one of those Hydromedusae which do not
give rise to free medusae. The medusa is produced, but does
not break away, it remains connected with the hydranth by
the aboral pole. Ina mature individual a racemose extension
of the body-wall is formed between the two rows of tentacles.

COELENTERATA 53

This is the blastostyle (Fig. 38, 4), and it bears a series of buds
called gonophores. These buds increase in maturity as they
approach the end of the blastostyle, so that a single blastostyle
may illustrate the various stages in the development of the
buds. The gonophores or rudimentary medusoid persons arise
as elevations of the ectoderm, into which the endoderm pro-
jects. At the free end of the bud the ectoderm then thickens,

EOS

nee,
nana
rer,

Fic. 39.—Diagrams to show the relations of (I.) a Hydroid polype to (II.) a Hydro-
medusa and to (III.) a Seyphomedusa.

1. Ectoderm, shaded. 9. Tentacle into which the endoderm
2. Endoderm, dotted. extends.
3. Structureless lamella, black line. 10. Generative organs. In II. they occupy
4. Coelenteron. Anthomedusan position.
5. Extension of coelenteron into tentacles 11. In II., Generative organs in Lepto-
in I., and forming radial canals in medusan position.
II. and III. In IIL., Sub-genital pit.
6. In J., Mouth. 12. In II., Endodermal lamella.
In IIL., Velum. InIII., Foldofumbrella over tentacle.
7. Gelatinous tissue, cross-hatched. 13. The gastric filaments, remains of the
8. Circular canal. taeniolae.

and in this thickened portion a split appears in such a way as to
separate a central portion, the manubrium, from a circular por-
tion which surrounds the former and forms the umbrella. The
space thus constituted, which is lined everywhere by ectoderm,
is the sub-umbrella cavity (Fig. 40). The endoderm projects both
into the manubrium and the umbrella; in those forms which
break off as free medusae, the manubrium acquires a mouth, which
leads into a cavity—the coelenteron—lined by endoderm. The
endoderm of the umbrella in Tubularia is a flat plate of tissue
enclosing no cavity except round the rim, where slight remnants
of a circular canal can be found, and from this rudiments of
radial vessels lead to the cavity of the manubrium. Rudi-

54 ZOOLOGY

mentary tentacles may occur on the gonophore. As stated
above, the medusoid persons in Zubularia do not break away
or develop further. The gener-
ative organs are found on the
walls of the manubrium (Fig. 39,
II.), the medusoid persons bearing
either male or female cells, but
Fic. 40.—Diagrams of the forma- not both.

tion of Medusae by budding. In those species in which

2 hihater | er peace teen the medusoid person is completed,

as in Fig. 89. The Coelenteron other structures develop; ten-
is black. After Korschelt and

Heider tacles and sense organs arise
I.—Commencement of bud. round the edge of the umbrella,

a muscular fold, the velum, is
formed inside the rim of the um-
brella (Fig. 40, IV.) and functions
as a swimming organ, and the
medusa breaks away and swims
freely through the water. The
existence of these two phases in
II,.—Thickening of ectoderm and the life-history of one organism

cupping of endoderm. has rendered necessary a double
classification. The order to which
Tubularia belongs is the Gymno-
blastea-Anthomedusae : the first
word referrmg to the nature of
the hydroid form, the second to
that of the medusoid.

Order 1.
Gymnoblastea-Anthomedusae.

IIJ.—Formation of sub-umbrella cav-
ity in the ectoderm.

CHARACTERISTICS.— These HHydro-

zou have probably always a
hydroid stage, which is very various in appearance, sometimes
non-colonial, but more usually the hydroids are united into
colonies. The ectoderm may form a _ perisare, but this
is never continued into a cewp or hydrotheca surrounding

COELENTERATA 55

the hydranth, nor are there capsules surrounding the gono-
phores.

The medusae may be well developed and free, or they may be
permanently attached to the hydranth (gonophore), or they may
not develope beyond rudimentary
buds (sporosacs), and finally,
in Hydra they are not formed
at all. When free, they may
be provided with ocelli at the
base of their marginal tentacles,
usually on their outer surface.
The sexual cells are arranged
round the manubrium, either
uniformly or in bands. Most
Anthomedusae are small.

The tentacles of the hy- Tee LOr
droid are nearly always solid, IV.—Sub-umbrella cavity opened,
Hydra, however, is an exception erp mete Ceara ca
I g
to this rule; they are usually Ectoderm.
arranged in one circle as in Hydra,

Endoderm.
Structureless lamella.

or in two as in TZubularia; in Manubrium.
: 6 Radial canal.
the family Clavidae, however, Vole

Gelatinous tissue.

they are irregularly scattered over
Sub-umbrella cavity.

the surface of the hydranth.

There is no special aggregation of nerve cells in the
hydroid stage, but in the medusa a nerve ring is present round
the edge of the umbrella; it is split into an upper and lower
nerve ring by the insertion of the velum. ‘The ocelli consist
of a collection of pigment spots, and a cuticular lens is present
in Jizzia. The sexes as a rule are separate, the genus Hydra
again forming an exception. Reproduction by fission is rare,
but sexual reproduction by budding is common in both the
hydroid and the medusoid stage. When it takes place in the
latter, a medusa is invariably the result.

ee ENTED CNG fo) ed

Order 2. Calyptoblastea-Leptomedusae.

CHARACTERISTICS.— The hydroid forms of this genus never have
more than one row of tentacles round the mouth. The

56 ZOOLOGY

tentacles are solid. The ectoderm secretes a perisare which

is continued into a cup, the Hydrotheca, surrounding the

Hydranth. The groups of medusiform buds are similarly

enclosed in a capsule, the Gonotheca.

The medusae of this group are all Leptomedusae, and are
characterised by having four, eight, or more radial canals,
on which the generative glands are always situated. The
tentacles on the rim may be few or very numerous. Ocelli
are found in two families ; more commonly the sense organs
take the form of hollow vesicles, the otocysts, in which the
otolith cells are formed from the ectoderm.

The hydroids belonging to this order are colonial, the
colonies being arranged in branching filaments, which have a
superficial resemblance to some of the branching colonies of
Polyzoa. Certain families are distinguished by the way in
which the hydranths are placed on the branch. In the CAm-
PANULARIDAE each hydranth is stalked; 11 the PLUMULARIDAE
the hydrothecae are sessile on one side of the branch only; in the
SERTULARIDAE they are sessile, and on both sides of the branch.

Certain tentaculoid structures, termed nematophores, occur
in relation to the hydrothecae of the PLUMULARIDAE. They are
solid, with an endodermic axis, and knobbed at the end, and
the knob contains nematocysts and sense cells. Their ectoderm
has been seen to ingest carmine granules, and they have been
observed to bend into the hydrotheca and eat up the remains
of dead hydranths of the same colony.

The medusae are often rudimentary, and remain attached
to the blastostyle, as the hydroid individual which gives rise
to them is called. The free medusae arise from the Cam-
panularian hydroids; the gonophores of the Plumularians and
Sertularians do not become detached.

Order 3. Hydrocorallinae.

This is a very well-marked order, in which the hydroid
stage only has hitherto been found.!’ The hydrorhiza in these
animals deposits a copious secretion of carbonate of lime instead
of a chitinoid perisare. By this means considerable masses

1 A very primitive form of medusa bearing male organs only (spermospores)
has been recently described in Millepora Murray.

COELENTERATA 57

of lime are built up, simulating some of the true corals.
Certain tubular spaces are left for the accommodation of the
hydranths, which can be withdrawn into them. The hydranths
are colonial, and of two kinds : gastrozoids, provided with mouths,
which are the nutritive persons of the colony ; and dactylozoids,
elongated mouthless persons well armed with nematocysts.

The order is divided into two familes: (i.) the MILLE-
PORIDAE and (11.) the STYLASTERIDAE.

(i.) THE MILLeporIpAE.— This family may have an arborescent
or branching skeleton, consisting of an outer living part
which surrounds an inner and older dead part. The
younger parts of the pores, in which the living hydranths
are found, are separated from the older ones, wherein
their predecessors lived, by horizontal partitions known as
tabulae. The colonies are hermaphrodite.

(il.) THE STYLASTERIDAE.— These are always arborescent, never
encrusting, and their colonies are unisexual.

The hydranths may be scattered irregularly, but more
usually the gastrozoids are surrounded by a regular circle of

Fic. 41.—Longitudinal median section
through a Stylasterid. After Hickson.

1. Gastrozoid.
2. Dactylozoid.
3. Style.

4. Coenosarcal canals.

Or

Coenosare, calcareous,
6. Mouth.

Tentacle.

“I

dactylozoids. The gastrozoid (Fig. 41) is usually provided
with tentacles, but in some of the STYLASTERIDAE these are
wanting. The dactylozoids are long tentacular structures with

58 ZOOLOGY

no mouth, they bear short knobbed branches, or tentacles, in
the Milleporidae.

The generative cells of Jillepora, which is hermaphrodite,
arise in the ectoderm of the coenosarcal tubes, which connect
the gastrozoids and the dactylozoids. The spermospores or cells
which are destined to break up into spermatozoa, migrate
through the mesogloea into the endoderm, and then travel along
the tubular coenosare to a hydranth, usually a dactylozoid.
They pass into the cavity of the hydranth, and then re-enter
the endoderm, and push out the mesogloea into a diverticulum
between the tentacles. The number of the diverticula or
sporosacs on each dactylozoid varies from one to five. The
spermatozoa mature in the sporosacs. The ova make their way
in a similar manner through the mesogloea into the endoderm ;
here they attach themselves by a stalk to the inside of the
mesogloea and grow considerably. The ovum may wander
about to seek a more favourable position for fertilisation, which
probably takes place in the lumen of the canals. Similar
wanderings of the sexual cells take place among the Hydro-
medusae,

Order 4. Siphonophora.

CHARACTERISTICS.— These are HYDROMEDUSAE which live together
in colonies floating at or near the surface of the sea (PELAGIC).
The members of the colones are hydriform individuals alone
(VELELLA),o7 hydriform and medusiform, they have undergone
great modifications, so that in each colony a great number of
persons are present performing various functions, and exhibit-
ing a great diversity of form.

The chief modifications are as follows: (.) the Gastrozoid,
whose function is to absorb nutriment. It has a mouth, and
communicates at its aboral end with the tubular coenosare
connecting the various persons. (i1.) Hydrophyllia: these are
protective covering-pieces, which have a central endodermic
canal, and are usually borne on the coenosare. (1.) Tentacles :
these may be short and tubular, or may attain the length of
many feet (Physalia). They are usually branched, and each
branch is provided with a battery of nematocysts. (iv.) Dac-
tylozoids: hydroid structures without a mouth, and usually

COELENTERATA 59

well armed with nematocysts. (v.) Vectocalyces: swimming
bells. They consist of the umbrella of a medusoid, with four
radial canals, but without a manubrium or mouth. (vi.) Pneu-
matophores: these form floats, and the air secreted within
them serves to keep the whole colony in a vertical position.
(vii.) The sexual persons: these may become free medusae of
the craspedote type—that is, provided with a velum; or they
may remain undeveloped as sporosacs. The medusae have their
generative organs on the radial canals (Velel/a), or on the
manubrium (Physalia). The colonies are usually herma-
phrodite.

The seven modifications described above are not all to be
met with in every Siphonophoran, but usually four or five of
them coexist in each colony, thus giving rise to a form of
extreme complexity ; various combinations of these persons also
permit great variety amongst the different species. Many of
them are brilliantly coloured in parts, and are amongst the
most beautiful marine objects which float along the surface of
the sea. They are common in the Mediterranean and open
seas, Velella and Diphyes bemg occasionally found on our
shores.

The two remaining orders of the HypromMEDUSAE—the
TRACHOMEDUSAE and the NARCOMEDUSAE—have no hydroid
stage, but the ova in most cases give rise immediately to the
medusae. They are characterised by the possession of sense
organs formed by modifications of the tentacles on the rim of
the umbrella. They are termed tentaculocysts, and into them
alone of the sense organs of the Hydromedusae does the endo-
derm enter. One or more otoliths formed from the endoderm
cells, which correspond with the axis of the ordinary tentacle,
contain crystalline concretions, and form the auditory organ.

Order 5. Trachomedusae.

CHARACTERISTICS.— The Trachomedusae have their tentaculocysts
Sree or enclosed in capsules, Coecal radial canals may be
present, which open into the circular canal, but never reach
the central stomach.

60 ZOOLOGY

The generative glands are on the sub-umbrella surface of
the radial canals. Limnocodium, the only freshwater medusa
with whose anatomy we are acquainted, is placed by Lankester
in this order. It forms an exception to the rule of the absence
of a hydroid form. A small hydranth has been described
as budding off the medusae, which are found at intervals in
tanks of the Victoria regia in the Botanical Society’s Garden,
vegent’s Park.

Order 6. Narcomedusae.

CHARACTERISTICS.—T7he Narcomedusae always have their ten-
taculocysts free. The tentacles arise some way wp the aboral
Jace of the umbrella, not from its edge. Their bases are con-
nected with the edge of the umbrella by stiffening rods of tissue
termed Peronia. These may also be found in the Tracho-
medusae.

The generative organs arise from the sub-umbrella surface
of the stomach, not on the radial canals.

Ciass B. SCYPHOMEDUSAE,

CHARACTERISTICS.—The hydroid stage of this sub-class is a
polype, which may give rise to the medusa, not by budding
but by transverse fission. It is termed the Scyphistoma. The
mouth of the Scyphistoma is squarish, and the coelenteron is
sub-divided by four ridges, termed taeniolae, which project
Jrom the sides into its lumen.

The medusa has also a square mouth, whose angles may be
produced into four oral processes. The edge of the wmbrella
is lobed. The sense organs are modified tentacles, into the
base of which the coelenteron is produced. No continuous
nerve ring exists, but scattered nerve centres are found round
the margin, and no true velum is present. CHARYBDAEA
Jorms, however, an exception to this statement. The generative
cells are endodermic in origin, and the medusae are unisexual.
In the Scyphomedusae a primary series of four tentacles

corresponding to the four angles of the mouth are the first to

be formed. This affords a convenient method for mapping
out the regions of the body. The radii on which they are

COELENTERATA 61

formed are termed perradii, the next four are situated half-
way between the perradii, and are known as interradial
tentacles; and eight more may be added, one between each
perradius and interradius, and these are called adradial. The
same convention is made use of in describing the position of
the various organs in medusae of other classes.

The most striking features in the Scyphistoma are the
taeniolae, which project into the enteric cavity and divide its
outer portion into four chambers (Fig. 39, 13). The taeniolae
are four in number, and are inter-
radial in position. They are
comparable with the mesenteries
in the Actinozoa.

Towards the end of spring the
Scyphistoma passes into the Stro-
bila stage, it then becomes con-
stricted on the aboral side of its
tentacles, and thus a disk is partly
cut off, behind this a series of
furrows arise, cutting the Scyphi-
stoma into a series of segments
(Fig. 42). These separate off and
form the immature medusae or the
Ephyrae. Eight bitid lobes have
grown out, which give to the
Ephyrae their characteristic eight-
rayed appearance. ach lobe
encloses in its notch either a
perradial or interradial tentacle
destined to become a tentaculocyst.
The gastric cavity extends into
each lobe, and the taeniolae be-
come detached from the aboral F!- 42:—Strobila of Aurelia aurita.

: : z : After Haeckel.

side of the disk and give rise to
gastric filaments. The same pro-
cesses of growth go on in each of
the segments of the Scyphistoma.

The Ephyra becomes a medusae chiefly by the filling out of
the adradial spaces, and it thus acquires a circular outline.

1. Base of Strobila.

2. Sense organ.

3. Marginal tentacle.

4, Lappet on side of sense organ.

62 ZOOLOGY

The position of the tentaculocysts, however, always marks the

position of the eight original lobes.

Aurelia is a Seyphomedusan very commonly met with round
If the adult

our coasts swimming at the surface of the sea.
medusa be examined, it will be seen that the original four-lobed

chamber of its Scyphistoma has given off a number of branch-
ing enteric canals which ultimately open into a circular vessel.
Between these canals the aboral and oral endoderm has given

aye

L

\

i

Vina

iy

AD | |

yy ay Nj sary ay

ni)

Fic. 43.—Aurelia aurita.
5. An adradial canal.

1. Mouth.

2, Cireumoral perradial processes. 8. The circular canal.

3. Tentacles on the edge of the umbrella. 9. Marginal lappets hiding tentaculo-
cysts.

4, One of the branching perradial canals.
There are four of these, and four 11. Gastral filaments.

similar interradial canals.
rise by conecrescence to the endodermal lamella (Fig. 39).
Hight adradial canals are given off from the central chamber
between these branching canals, and these pass directly to the

circular canal without giving off any branches.
The mouth of Awrelia is surrounded by four perradial

COZLENTERATA 63

processes, and the manubrium is short. The coelenteron is
ciliated. In Rhizostoma the four oral processes are divided into
eight, and have fused together in such a way as to occlude the
mouth. This is compensated for by the presence of fine canals
which open at one end into the gastric cavity, and at the other
on the frilled edges of these processes. The food is absorbed
through these canals.

The gelatinous layer of the mesogloea in Awelia is
traversed in all directions by fibrous cells and by wandering
amoeboid cells. The muscles are in some cases formed of
transversely-striated processes of epithelial cells; in the oral
processes of some medusae, however, distinct nucleated muscle
cells occur.

The sense organs of Aurelia are modified tentacles, which
bear endodermal otocysts and ectodermal pigment spots or
eyes. An aboral and an oral pit, both lined by specialised
epithelium on the surface of the disk, are regarded as olfactory.
The coelenteron is prolonged into the modified tentacles.

No regular nerve ring exists in Scyphomedusae, with the
exception of one genus, Charybdaea ; but nerve fibres occur in the
region of the sense organs, and are connected with scattered
ganglion cells.

The ova and spermatozoa arise from endodermal cells, and
escape through the mouth. Four large pits may be excavated
in the sub-umbrella ectoderm, and these form sub-genital
pouches, the skin of which is thin, and forms only a slight mem-
brane between the sea-water and the genital cells (Fig. 39, IIL.).
This arrangement may promote the respiration of these parts.

In some Scyphomedusae, eg. Pelagia, the medusa rises
directly from the ovum without the intervention of a Scyphi-
stoma.

Cuiass C. ACTINOZOA.

CHARACTERISTICS.—Single or colonial Coelenterata. The mouth
leads into an ectodermic invagination, the stomodaeum or oeso-
phagus ; this is attached to the walls of the body by a series of
radial mesenteries, so that the coelenteron is divided into a
central portion and a series of radiating intermesenteric
chambers. The generative cells are endodermic, and le im

64 ZOOLOGY

the mesentery. There are no special sense organs. Nemato-

cysts occur, and are more complicated than those usually

found in the Hydrozoa.

The most fundamental distinction between the Actinozoa
and the Hydrozoa lies in the presence of the mesenteries and
the consequent division of the coelenteron into a central
chamber and several radiating lateral chambers, which all open
below into the central chamber. In the Hexactinia these
chambers are put into direct communication with each other
by one or two pores, which pierce the mesenteries near their
upper end. The existence of these mesenteries is to some extent
foreshadowed by the taeniolae of the Scyphomedusae. In two
forms recently described by Danielssen, Fenja and Aegir, the
oesophagus is continued to the aboral disk, where it opens to
the exterior by an anus; thus a body cavity is shut off from
the digestive cavity. In Aegir, however, these two cavities
communicate by a series of pores which lead from the inter-
mesenteric chambers into the alimentary canal near the anus.
In Fenja each intermesenteric chamber opens to the exterior
by a pore close to the anus. Thus a ring of genital pores is
formed. In both genera the various intermesenteric cavities
communicate with one another by pores at the oral end of the
mesentery.

The Actinozoa have an apparent radial symmetry which
does not hold true for all parts; but a genuine bilateral
symmetry exists.

The Actinozoa are sub-divided into two orders: (i.) the
HEXACTINIA (ZOANTHARIA) and (ii.) the OcTacTiINIA (ALCY-
ONARIA).

Order 1. HEXACTINIA.

CHARACTERISTICS.— Tentacles simple; they and the mesenteries
are very generally some multiple of six. Single or colonial ;
when colonial a continuous organic or calcareous skeleton is
usually deposited by the ectoderm.

Actinia mesembryanthemum is a beautiful red sea-anemone
common in rock pools round our coasts. When in the
expanded condition it may be seen that the animal is in the
form of a short cylinder, with one end firmly attached to a stone

COELENTERATA 65

or the rocks, the other end free. The mouth is an elongated
slit in the middle of the peristome or free end, it is surrounded
by several rows of tentacles (Fig. 44). At the ends of the
elongated mouth are special grooves which are continued down
the oesophagus and are lined with especially long cilia (Fig. 46).

Fia. 44.—Colony of sea-anemones (Sagartia parasitica) on shell of hermit crab.

When the mouth is closed the central parts are in apposition,
but the grooves, called Siphonoglyphs, remain always open, and
through them a current of water may be kept circulating in
and out of the animal even when it is in its most contracted
condition. Cerianthus has only one siphonoglyph. The oeso-
phagus ends with a free edge, and never reaches the base of
the sea-anemone.

The mesenteries are vertical radial partitions which extend
from the peristome to the base. The outer edge is continuous
with the inner side of the body-wall. The inner edge in the
primary mesenteries is divided into two parts (Fig. 45). The
part nearest the peristome is continuous with the outside of the
oesophagus, but below the lower edge of the oesophagus the inner

5

66 ZOOLOGY
ee eee eee

edge of the mesentery is free. The secondary mesenteries have
not reached the oesophagus in Fig. 46, so that the whole
extent of their inner edge is free. The mesenteries are grouped
in pairs, and the members of each pair are separated by an

Fic. 45.—A mesentery of Tealia
crassicornis. After the Hertwigs.

. Edge of mouth.

2. External and internal pores in the
mesentery.

. Mesenterial filament.

. Testis follicles,

5. Cireular muscle.

. Radial muscle fibres.

. Longitudinal muscle fibres.

. Parietal longitudinal muscle fibres.
. Lower edge of the stomodaeum.

intramesenterie space, while the various pairs have an inter-septal
chamber between them. The secondary mesenteries always occur
between two primary ones. Each mesentery is pierced by a
round hole, and in some species by two, so that the various
intermesenteric chambers open into one another above, as well
as all communicating with the central chamber below.

Along one side of each mesentery runs a longitudinal
bundle of muscle fibres from the peristome to the base. These
assist the sea-anemone to contract. They are as a rule facing
one another in each pair. But on each side of each siphono-
glyph is a mesentery known as the directive mesentery (Fig. 46),
and on these the longitudinal muscles turn away from each
other. Transverse muscle fibres are found on the mesenteries
on the side where the longitudinal muscles do not exist. There
are also sphincter muscles running round the peristome, and
parietal muscles running obliquely from the walls to the base

COELENTERATA 67

of the body. The nervous system consists of scattered ganglion
cells, chiefly in the peristome and tentacles.

The free edge of the mesentery below the level of the
oesophagus is divided into three lobes; the middle one is
crowded with nematocysts and glandular cells, the outer lobes

Fig. 46.—Transverse sec-
tion through the body
of <Adamsia dia-
phana, in the region
of the stomodaeum.
After the Hertwigs.

1. The directive mesen-
teries.

2. Longitudinal muscle
fibres in the mesen-
teries, cut across.

3. The siphonoglyphs.

A. Primary mesenteries,
12.

B. Secondary mesenteries,

12

C. Tertiary mesenteries,
24.

D. Quaternary mesenter-
ies, 48.

are ciliated. When a piece of solid food is swallowed, the
edges of several of the mesenteries come together and surround
it, and the secretion of the glandular cells helps to digest it.

The sexes are usually separate, the generative cells arising
from the endoderm of the mesenteries (Fig. 45); the young
escape through the mouth, A. mesembryanthemum being vivi-
parous.

In some species the free edges of the mesenteries are pro-
duced into long whip-like processes, called acontia, armed with
nematocysts. These are protruded through the mouth or
through special pores in the body-wall called cinclides. They
are found in Sugartia. Occasionally there is a central pore in
the base of the body, and as a rule the tentacles are perforated
at their ends; and in some of the deep-sea forms the tentacular
pores are large, in others the tentacles are reduced, the pores
only remaining as a circlet of holes surrounding the mouth.

68 ZOOLOGY

The Hexactinia are divided into three groups :

G1.) Zhe ACTINIARIA, which are devoid of any kind of skeleton,
are usually single, and are mostly adherent to some
foreign body ; occasionally they live half embedded in
mud or sand. Cerianthus, Actinia.

(ii.) Zhe ANTIPATHARIA : they possess a horny axial skeleton
secreted from their ectoderm ; they are colonial, and form
large branching structures. Antipathes.

(iu.) Zhe MADREPORARIA are solitary or colonial ; their most
remarkable characteristic 1s their power of secreting a
calcareous skeleton. The skeleton is often very massive,
and recent research has shown that it is entirely formed
Jrom the ectoderm. Oculina, <Astraea, Madrepora,
Fungia, Caryophyllia.

The MADREPORARIA are of the greatest importance in the
history of the earth. They are the true corals, and their
skeletons form by far the greater part of the coral rock which
has built up a considerable portion of the earth’s crust. eef-
forming corals do not as a rule grow below the forty-fathom
line, and are not usually found north or south of a belt ex-
tending 30° each side of the equator.

As the coral grows, large masses of the coenenchyma or
common skeleton become covered over by the younger forma-
tions. This skeleton may be quite solid and dead, or it may
be pierced by canals which shelter coenosarcal tubes of living
matter, connecting one individual with another. This enables
us to divide the Madreporaria into two divisions: (1.) Perforata,
with the skeleton perforated by the cavities which lodge the coeno-
sarcal tubes, and (ii.) the Aporosa, in which no such perforations
exist.

The form and shape of the skeleton is extremely varied,
and often complicated by the colonial habits of the actinozoan.
But whatever its shape, and however deeply it may have pene-
trated into the body of the soft gelatinous-looking animal, it is
always formed by ectoderm, and is consequently always outside
the animal, whose tissues are, as it were, moulded over it.

COELENTERATA 69

The skeleton commences to appear by the ectoderm of the
base secreting a flat plate between it and the substance on which
the young actinozoan is fixed. From this plate a number of
radially-arranged vertical ridges grow up (Fig. 47, 2). These are,

Fic. 47.—Diagram to illustrate anatomy of Galaxea espert. After Hickson.

1. The theca. 7. Mesentery.

2. The septa. 8. Lower edge of stomodaeum.

3. The basal plate. 9. Free edges of mesenteries beneath
4. Flesh covering the theca. the stomodaeum.

5. Tentacles. 10. The mesenteric filaments.

6. Mouth.

like the rest of the skeleton, secreted by ectoderm ; and as they
grow they push the ectoderm and the skin of the base up into
the coelenteron. These vertical plates are termed septa.
Partly by the fusion of the external edges of the septa, and
partly by the upgrowth of a circular rim from the basal plate,
a circular ridge is formed. This ridge forms the wall of
the cup or theca, and like the septa it projects into the
eoelenteron, pushing the body-wall before it; occasionally a
second circular rim, external to but concentric with and close to
the first, is formed, the epitheca, and this forms a ridge round

7° ZOOLOGY

and outside the base of the animal. Some of the septa may
coalesce in the centre of the body, and thus the columella is

Fic. 48.—Caryophyllia borealis, Fleming, a simple coral, twice the natural size.
After Sir Wyville Thomson.

produced ; this is usually continued as a little pillar pointing
towards the mouth. The outer wall of the theca frequently

Fia. 49.—Astraea pallida, Dana, a compound coral in its living condition.
After Dana,

bears ridges, the costae, which do not necessarily correspond
with the septa; the latter may be connected with their neigh-
bours by horizontal shelves, termed dissepiments.

COELENTERATA 7

Neither the septa nor the costae correspond with the
mesenteries, but are situated in intermesenteric spaces. Like
the mesenteries, they may increase in number, secondary
septa arising between the primary. Most of the corals which
form massive skeletons increase the number of individuals in
the colony by budding; in some the theca of each member of
the colony remains distinet (Madrepora, Oculina, Astraea)
(Fig. 49), in others complications arise by the fusion and
obliteration of the walls of the theca, ete. (Meandrina).

Order 2. OCTACTINIA.

CHARACTERISTICS.—Colonial Actinozoa with eight pinnate ten-
tacles and eight mesenteries, which bear the longitudinal
muscles on their ventral surface, that is, on the face which
looks towards the single siphonoglyph.

The well-known skeleton of the organ-pipe coral, Zubipora,
consists of a stolon or encrusting lamina which attaches the
colonies to some foreign body, and of a series of tubes in which
the polyps live, termed corallites, which arise from the stolon.
The corallites are externally connected together by horizontal
plates, forming the platforms or exothecal tabulae (Fig. 50); and
within each corallite is a series of fabulae, the top one of which

Fie. 50.—A portion of the corallum of Tubipora
musica of the natural size, showing the tubular
corallites and the exothecal tabulae or plat-

forms.

cuts off the polyp from the dead skeleton below. New coral-
lites constantly arise from the platforms, so that the whole coral
increases in circumference as well as in height as it gets older.

The platforms are formed by outgrowths of the lips of the
living coral, and are at first very thin; they are traversed
by many branching canals.

ZOOLOGY

“NI
iS)

Within, the cavity of the corallites is divided into a series
of chambers by the presence of partitions termed tabulae ;
these may be simple flat plates, but more often they are cup-
shaped, and in some cases are drawn down in the centre into
funnel-shaped structures. The tabulae often give off tubes,
which run out into the platforms.

The whole skeleton is so compact that it appears to be
formed of a continuous homogeneous deposit of calcium car-
bonate. In reality, however, it consists of a number of spicules,
each with minute serrations which fit ito other serrations on
the neighbouring spicules.

The polyp wall is built up of the ectoderm, mesogloea, and
endoderm. The mesogloea contains a few scattered cells and
fibres, as well as the skeletal spicules, which, however, in those
cases where the embryology is known, originate in certain ecto-
dermal cells which wander afterwards into the mesogloea.

The tentacles, eight in number, have about fifteen pinnae
on each side in a single series. They are hollow, their cavities

Fic. 51.—Transverse section of
a polypof Tubipora purpurea.
After Hickson.

. Stomodaeum.

. Cilia of siphonoglyph.

. Ectoderm of stomodaeum and
of outer surface of body-
wall.

4, Endoderm lining mesenteric
chambers.

5. Longitudinal muscle fibres in
mesentery, cut across.

6, Calcareous spicules,

7. Parasitic diatoms on the
ectoderm,

. Mesogloea.

Co bh Fe

Go

D. Dorsal surface.
V. Ventral surface.

opening into the intermesenteric chambers, over which they
are placed. Their ectoderm is ciliated. The whole body of
the polyp, including the tentacles, can be withdrawn into the
corallite. The stomodaeum is ciliated throughout, and on one

COELENTERATA 73

side, the ventral, there is a special groove (Fig. 51) lined with
long cilia, the siphonoglyph.

The stomodaeum is supported by eight mesenteries ; on the
ventral side of each of these are placed the powerful retractor
muscles, which draw the polyp swiftly into the corallite at the
approach of danger. The two dorsal mesenteries alone are
continued far below the lower edge of the stomodaeum in the
form of mesenteric filaments, their edge being much thickened,
bilobed, and covered with cilia. The endodermal cells are
probably some of them amoeboid, and digestion may be intra-
cellular.

The ova are found attached to the dorsal and dorsolateral
mesenteries, immediately below the stomodaeum.

The tabulae are formed by the mesogloea splitting into
two layers: the outer remains attached to the ectoderm, the
inner layer with the endoderm; the latter shrinks away from
the outer layer, and then in this contracted condition begins to
secrete a fresh layer of spicules, which ultimately stretches
across the corallite. Hence the space below each tabula is
morphologically a space in the mesogloea. :

The polyps of the Zubipora remain free and distinct one
from another ; in other groups of the OcractTINIA, however, they
may be sunk in a well-developed coenosarc, as in Alcyonium,
commonly known as “dead men’s fingers,’ or they may be
arranged side by side, their lateral surfaces fusing in the form of
a leaf-like plate, as in the Pennatulidae (Fig. 52). In Aleyoniuwm
the skeleton is not continuous, but consists of spicules scattered
loosely through the coenosare. The leaf-like plates of Penna-
tula are borne on each side of a rachis, this is continued into a
stalk free of polyps. Both stalk and rachis are traversed and
supported by a long calcified horny rod, secreted by an
epithelium whose origin is uncertain.

Among the Alcyonidae and Pennatulidae the individual
zooids are often of two kinds. In Pennatula, for instance, the
leaf-like expansions are composed of a single layer of polyps
(autozoids) fused side by side, whilst the zooids (siphonozords)
cover that surface of the rachis on to which the bases of
the leaves do not extend, and pass up between the leaves.
The zooids differ from the polyps, having no tentacles or

74 ZOOLOGY

retractor muscles, only two of their mesenteries are continued
below the level of the oesophagus and bear mesenteric fila-

Fic.

Ou

co @D

10.

52.—A longitudinal section through a
polyp of Pennatula phosphorea. After
Marshall.

Mouth.

Walls of stomodaeum.

Free edges of mesenteries below the level of
the stomodaeum, showing short mesen-
terial filaments.

Long mesenterial filaments.
Feathered tentacles.
Calyx.

Spicules in body-wall.
Spermatospheres.

Mesentery showing protractor and retractor

muscle fibres.

Coenenchyme.

ments, they have a well-developed siphonoglyph, but no repro-

ductive system.

The cavities of all the individuals are put into communi-
cation by means of a number of ramifying coenosarcal tubes

lined by endoderm.

The Pennatulidae are phosphorescent, and emit a bright
glowing light when disturbed, this is said to originate from

COELENTERATA 75

eight cords of fatty cells attached to the oesophagus in both
kinds of polyps.
Ciass C. CTENOPHORA.

CHARACTERISTICS.— Pelagic Coelenterata, usually spheroidal, more
rarely band-shaped in form. Hight meridional rows of
vibrating plates composed of fused cilia form the locomotor
apparatus. A large parr of retractile tentacles are usually
present, which can be withdrawn «into pouches. At the
aboral pole is a special sense organ. They are all herma-
phrodite, and pelagic.

This group of animals possesses considerable importance

from a phylogenetic point of view. Haeckel has described a

Fic, 55.—Hormiphora plumosa. After
Chun. Side view.

1. Mouth leading into stomach.

2. Aboral pole with sense organ.

3. Funnel.

4. Recurrent canals running back to-
wards oral pole.

5. One of the eight bands of fused cilia.

6. One of the eight canals running to-
wards 5.

. A tentacular pouch.

Ty

. A tentacle.

co OO

. Gelatinous tissue.

remarkable Anthomedusan named Ctenaria ctenophora which
has many of the characteristic features of a Ctenophor; whilst

76 ZOOLOGY

on the other hand two curious organisms, the Coeloplana of
Kowalevsky and the Ctenoplana of Korotneff, have lately been
discovered which unite some characters of the Ctenophora
with others of the Turbellaria.

In a typical Ctenophor, one of the Cydippidae, such as
Hormiphora, the mouth leads into a flattened stomach lined
with ectoderm, which in its turn opens into the funnel, lined
with endoderm (Fig. 53). The funnel gives off two gastric canals,
which pass out towards the base of the long tentacles. These
two primary canals give off a secondary canal on each side,
which forks, and forms tertiary canals (Fig. 54), of which there-
fore there are eight. Each of these eight canals opens into
one of eight meridional canals which lie under the rows of
vibratile plates, and which end blindly both at the oral and
aboral pole.

The two long tentacles can be completely retracted into their
pouches ; they bear peculiar adhesive cells.

The characteristic vibratile plates are formed by a number
of very large cilia fused together side by side; an arrangement
also met with in some of the Hypotricha.

The central nervous system consists of an area of ciliated

Fic. 54.—Hormiphora plumosa.
After Chun. Aboral view.

2. Aboral pole with sense organ.

5. One of the eight bands of
fused cilia.

6. One of the eight canals running
towards 5.

8. A tentacle.
9. Gelatinous tissue.

SS. sagittal plane.

cells at the aboral pole. This area is sunk into a depression
which contains certain otoliths, and from which nerve cells
pass to the meridional rows of paddles. This specialised sensory

COELENTERATA 77

apparatus possibly serves as a balancing organ, and helps to
keep the floating animal the right way up.

The reproductive organs are arranged along the meridional
canals, the male cells on one side and the female cells on the
other of each canal. The ova and spermatozoa escape through
the canals, and eventually leave the body through the mouth.

The main features of the anatomy of the Ctenophora have
been indicated in order to render intelligible their possible
relationship on the one hand to the Anthomedusae and on the
other to the Turbellarians. There is a mass of interesting
detail with reference to these animals which cannot be referred
to here.

The Anthomedusan Ctenaria has the mouth of its umbrella
very much contracted, and the edges have grown round and
over the manubrium, which is small. The opening into this
sub-umbrella cavity corresponds with the opening into the
stomach of the Ctenophor ; and the lumen of the latter, lined as
it is with ectoderm, corresponds with the sub-umbrella cavity
of Ctenaria. The shape of the medusa is very like that of
Cydippe, and its surface is provided with eight rows of modified
ectodermal cells, which correspond in position with the
eight rows of vibratile plates in Ctenophors. The arrange-
ments of the enteric canals also approaches that of Cydippe,
and the resemblance between the two animals is further in-
creased by the presence in both of two long fringed tentacles
which project from pouches as in the Ctenophora.

The Cestus veneris, or Venus’s girdle, is a Ctenophor in which
the spherical form has been replaced by a flattened band-like
shape. It is found swimming at the surface of warm seas, and
moves through the water by a series of graceful undulations.
Beroe, in which the stomach attains a very great size, has no
tentacles.

The group is a carnivorous one, the chief food being pelagic
organisms. Many of them are phosphorescent.

CHAPTER V
COELOMATA

In the Acoelomata there is a common cavity, the Coelenteron,
which is lined by endoderm cells, and which pervades various
parts of the body. Whatever cavities exist in these animals,
with the exception of certain ectodermic pits, are all diverticula
of this one primitive cavity, and remain in connection with it.

The Coelomata, on the other hand, start with an Arch-
enteron, probably the equivalent of the Coelenteron; but this
is replaced by two distinct and separate cavities—that of
the alimentary canal, and that of the body. The latter is
termed the Coelom, and is entirely shut off from the cavity of
the digestive system. The cavity of the alimentary canal is
lined by endoderm ; between the endoderm and ectoderm a
new layer of cells has appeared, the mesoderm, and it is in this
layer, and lined by it, that the coelom appears.

The Coelomata have typically a bilaterally symmetrical
form, which is however in many cases lost. In front of the
mouth there is a prostomiwm, or preoral lobe. The mouth
and anus, when present, are lined by invaginations of the ecto-
derm, termed the stomodaeum and proctodaeum respectively.

The very important cavity, the coelom, which distinguishes
the Coelomates from the lower animals, is characterised by the
following peculiarities. (1) It develops as one or more
diverticula from the primitive archenteron (enterocoel), or it
arises as a space or spaces in the mesoblast (schizocoel), or it is a
remnant of the segmentation cavity, into which a lining of meso-
blast grows (archicoel) ; it is consequently always lined by meso-
blast. (ii.) Its walls give rise to the reproductive cells, which
are set free into a portion of the coelom, and leave the body

COELOMATA 79

either through the nephridia or by special ducts or apertures.
Qu.) It communicates with the exterior through the nephridia,
or the organs which excrete waste nitrogenous matter.

It is probable that the body-cavities or coeloms which
originate in different manners may not be homologous through-
out the Coelomata; on the other hand they all possess the
characteristics enumerated above.

There are other cavities which arise in the mesoblast to
which the above characteristics do not apply. These are the
vascular and lymphatic systems; they contain blood and
lymph. In some Coelomata these systems are composed of
vessels with certain muscular differentiations to propel the
contained fluid ; in others, they form large spaces which simulate
the appearance of the body-cavity of other animals. Such
spaces are termed pseudocoels or haemocoels; they occur in
Arthropods and Molluscs, and when they are present the true
coelom is very much reduced. It is not impossible that the
vascular system is but a part of the general coelom; in many
cases the two systems are distinct, but in others—as the Leeches,
where they communicate through the botryoidal tissue, and
in Vertebrates through the thoracic duct—there is an indirect
connection, whilst in Nemertines the coelom and vascular
system appear to be one,

The mesoderm, which is such an important feature in the
Coelomata, occupies the same position between the ectoderm
and endoderm as the mesogloea of the Coelenterata; it is not,
however, always regarded as homologous with the mesogloea,
partly because the latter appears originally as a clear gelatinous
layer which is devoid of cells, and may remain so throughout
life ; but also because cells, when they do wander into the meso-
gloea, do not arrange themselves in definite tissues.

CHAPTER VI

PLATYHELMINTHES

{ Acoela—Convoluta, Proporus.
Rhabdoceclida Rhabdocoela—Mesostoma, Mi-
crostoma, Vortex.

TNE \ Alloiocoela—Plagiostoma.

PLATY HEL- Tricladida—Planaria, Gunda.
MINTHES Dendrocoelida ~ Polycladida—Thysanozoon,
Yungia.

CrstopA—Taenia, Bothriocephalus.

Monogenea—Aspidogaster, Polystomum.

LE DA : . ; ; }
TREMATO Digenea—Distoma, Fasciola, Bilharzia.

®

The three classes included under this heading—the TURBEL-
LARIA, the TREMATODA, and the CestopA—incelude those animals
which stand in the nearest relationship to the Coelenterata.

CHARACTERISTICS.—They are not very typical members of the
sub-grade Coelomata, because, although they possess a distinct
mesoderm, the coelom itself is reduced to mere splits and
regular cavities between the mesodermic cells. The absence
of any well-developed coelom may, however, be due to de-
generation. The PLATYHELMINTHES ave further characterised
by the absence of a distinct vascular system, and the alr-
mentary canal has no anus. The nervous system consists
of a plexus of nerves, mostly on the ventral side of the
animal. As we ascend in the group the nerves become
more concentrated. A central nerve ganglion, the brain,
is found which in the higher forms gives off two longitudinal
cords which may be connected by transverse commuissures.
An excretory system, consisting of fine branches, often intra-
cellular, which at their inner end terminate in flame cells,
at their outer end open to the exterior, is very characteristic
of the group.

PLATYHELMINTHES 81

The PLATYHELMINTHES are hermaphrodite ; in the female
organs a vitellarium is often found. Reproduction may be
asexual at times, and then an alternation of generations
takes place.

Cuass I. TURBELLARIA.

CHARACTERISTICS. — Free - living Platyhelminthes, whose ovat,
usually flattened body is covered with cilia. A mouth, a
muscular pharynx, and an alimentary canal exist, but no
anus. No special respiratory system or vascular system, or
hooks, are present. Nervous system, a paired cerebral
ganglion and two lateral nerve cords. With few exceptions
hermaphrodite.

The Turbellaria are mostly aquatic, inhabiting the sea
and fresh water, but a few live on the earth amongst damp

Fic. 55.—Various forms of Turbellaria,
all natural size, and viewed from the
dorsal surface. After Von Graff.

4. Convoluta paradoxa, Oe.

Vortex viridis, M. Sch.

. Monotus fuscus, Gff.

d. Thysanozoon brocchii, Gr., with ele-
vated anterior extremity (after
Joh. Schmidt).

Rhyncodemus terrestris, O. F. Miiller
(after Kennel).

Jf. Bipalium ceres, Mos. (after Moseley).

oS 8

is)

SS

. Polycelis cornuta, O. Sch., attached
by the pharynx (ph) to a dead
worm (after Johnson).

Ss

surroundings (Fig. 55); a very few are parasitic, and then

occur in Mollusca or Holothurians. Several are common in

ditches and standing water in England; Planaria lactea, a

Dendrocoel, especially so. One of the Rhabdocoela, which
6

82 ZOOLOGY

are simpler in their organisation, Mesostoma, is, however, not
infrequently found in ponds and streams, and the transparency
of its body permits a more thorough examination of its internal
organs than is the case with most of the members of the group.

Mesostoma Ehrenbergii is a flat leaf-shaped Rhabdocoel,
its dorsal surface being but very slightly vaulted. Its length
does not exceed 15 mm., and its greatest breadth 5 mm.
Another member of this genus has a square cross-section,
with the angles somewhat produced. The body is very trans-
parent, and sometimes nothing of it can be seen but the brown
stomach and occasionally the red eggs.

The epidermis is composed of flat cells, with irregular out-
lines and conspicuous nuclei. The whole surface of the body
is covered with fine cilia, somewhat longer on the ventral side
than on the dorsal. Within the layer of ectoderm cells, but
separated from it by a basement membrane, is a thin sheet of

Fig. 56.—Integument of
Mesostoma lingua, O. Sch.
After Von Graff.

1. Epidermis with perfora-
tions (2) through which
the rhabdites (3) project.
Beneath is the basement
membrane (4), and _ be-
neath this again the
muscular layers consist-
ing of circular (5), longi-
tudinal (6), and diagonal
(7) fibres.

circular muscle fibres, and within this a layer of longitudinal
fibres, crossing the outer layer at right angles, and a few
oblique fibres (Fig. 56). These tissues form the integument,
and surround a mass of tissue, the parenchyma, in which the
various organs of the body are embedded. The coelom is
broken up into irregular spaces or splits by the presence of
numerous dorso-ventral muscle fibres and connective tissue
strands. The lacunae left between these branching fibres

PIEEADNIROLMINE THLE S, 83

contain a fluid in which certain cells float. Some of these
cells contain the yellow pigment which gives the animal its
yellowish colour. Unicellular slime - glands, with longer or
shorter ducts, which open into the surface of the integument,
are comparatively numerous, and connective tissue cells are
also to be met with in the parenchyma.

The rhabdites are homogeneous refractive little rods
which occur in most Turbellaria, and are usually found in
great numbers either embedded in, or protruding from, the
epidermis. They escape from the body, and often occur in
ereat numbers in a slimy deposit the animal leaves on its
track ; when they are expelled they leave a round hole in the
ectoderm cells. In some species they are secreted in the
ectoderm cells, in others, as in Mesostoma, from special cells
beneath the integument (Fig. 57); these cells, however, arise
from the ectoderm and remain connected with it by fine pro-
cesses along which the rhabdites travel.

The connective tissue cells and the rhabdite-forming cells,

Fic. 57.—Transverse section through the pharynx of Mesostoma Hhrenbergii,
O. Sch. After Von Graff.

1. Mouth. 6. Yolk glands.
2. Pharynx walls crowded with glandular 7. Testes.
cells. 8. Nerve cord.
3. Walls of alimentary canal. 9. Integument beneath cuticle.
4, Salivary glands. 10. Pigment cell.
5. Rhabdite-forming cells. 11. Dorso-ventral muscle fibres.

with some strands of muscle fibres, constitute the paren-
chyma. In Mesostoma this tissue is not so well developed as
in most Turbellaria, and the spaces containing fluid are corre-

84 ZOOLOGY

spondingly large, in other forms the parenchyma occupies,
with the exception of a few small lacunae full of fluid, the
whole space within the integument; the digestive, nervous,
excretory, and reproductive systems are embedded in it.

The mouth opens on the ventral surface a little in front
of the middle of the body. It leads into a pharynx whose
wall, just within the mouth, is drawn out into two pharyngeal
pouches. The next portion of the pharynx has a very thick
muscular wall, and internal to this are two more pharyngeal
pouches. The pharynx leads directly into the stomach, the
demarcation between them being shown by the change in the
lining epithelium, and by the presence of
the salivary glands (Fig. 57). These
consist of numerous pear-shaped gland-
ular cells, with ducts which open at the
junction of the pharynx and stomach.
The stomach of Mesostoma is a simple
sac, of uniform diameter. Owing to the
position of the mouth near the middle of
the body, the stomach may be divided
into a short preoral and a longer postoral
region. The stomach is lined by a single
layer of cells, which vary much in shape,
and appear to exhibit amoeboid move-
ments similar to those of the endoderm
in Hydra, and they ingest nutritious
food-particles in the same intracellular
way. No anus is present, and undigested
matter is ejected through the mouth.

The excretory system consists of (1.)
Main trunks of Main trunks which open to the exterior,

Fic. 58.

the excretory system of (jj.) secondary branches given off from
Mesostoma Ehrenbergii,

0. Sch. After VonGraff. these, and (iii.) the excretory cells.

They open on to the ex-

In Mesostoma the main ducts open one
terior close to the mouth.

on each side close to the external pharyngeal
pouches in the mouth (Fig. 58). From
each opening a transverse duct runs dorsalward on each side of
the pharynx and intestine; when it reaches the dorsal side of
the alimentary canal it divides into two, one branch running

1, Pharynx.

PLATVHELMINTHES 85

forward and one running backward on each side of the body.
These branches give off the very numerous secondary ducts
which ramify all over the body. The secondary branches give
off numerous minute side branches, each of which ends in
a flame cell. The flame cells are pear-shaped cells, the stalk
being formed by a flagellum which projects into the lumen of
the minute duct. The body of the cell is often branched ; it
contains a large nucleus, and a vacuole which is continuous
with the lumen of the duct. The fluid contained in the
excretory system is clear and free from corpuscles, it is kept
in motion by the flagella of the flame cells.

The nervous system consists of a central organ, the brain,
and certain nerves running from it. The brain is somewhat

Fic. 59.—Plan of a Rhabdocoelous
Turbellarian. Von Graff.

. Bursa copulatrix.

hor oe

. Brain.

Hye.

. Germarium.

. Intestine.

. Longitudinal nerve trunk.
. Mouth.

. Pharynx.

oOo onrr nr OP OO

. Receptaculum seminis.

—
So

. Salivary glands.

11. Testis.

12. Uterus, containing an egg.
13. Yolk gland.

14. Vesicula seminis.

g. Chitinous copulatory organs.
6%. Common sexual aperture.

oblong in shape, and separated into two halves by a slight fur-
row. It is situated between the pharynx and the anterior end
of the animal, and is embedded in the parenchyma. From each
corner a strong nerve is given off. The anterior nerves run to

86 ZOOLOGY

the anterior end of the body, and break up into a number of
fine branches. The nerves arising from the posterior angles
run backwards on each side of the pharynx and stomach,
rather ventral to the latter. Von Graff figures a transverse
commissure connecting these two posterior nerves just behind
the pharynx.

A pair of eyes are situated directly upon the dorsal side
of the brain, they are composed of two triangular aggregations
of pigmented cells.

Turbellaria are, with few exceptions, hermaphrodite, and

. 60.—The reproductive organs of
Mesostoma Ehrenbergit. After R.
Leuckart, slightly altered.

. Pharynx.

2. Common male and female genital
opening.

. Ovary.

. Yolk gland,

. Shell gland.

. Receptaculum seminis.
7. Uterus with eggs.

. Testis.

. Vas deferens.

. Vesicula seminis.

. Penis.

. Outline of alimentary canal.

their female reproductive organs are complicated by the egg
being formed from two sets of glands. The ovum, with its

LACA DN LENIN TES. 87

nucleus, arises in the germariwm, but the yolk or food-material
which serves to nourish the developing embryo has its origin
in another gland, the vitellarvum.

In Mesostoma the male organs comprise a testis running
along each side of the body near the surface; it is of a clear
white colour, and follicular nature (Fig. 59). The testis com-
municates with a vas deferens, arising by one or two branches
from the middle of the gland. The vasa deferentia of each
side unite just behind the pharynx, and form a short ductus
seminalis which traverses a coiled penis. At the base of the
latter is a vesicula seminalis. The penis les in a genital
recess, into which the female organs also open; the opening
of this recess hes behind the pharynx.

The ovary consists of a number of oval follicles, grouped
together on each side of the stomach. The ovary of each side
opens separately into the uterus near the opening of the latter
into the atrium genitale. The yolk glands (Fig. 60) he one
on each side of the body, and their ducts unite into a common
channel, which opens into the genital recess. The two uteri
lie between the testes and the ovary, one on each side of the
body ; they are a pair of tubes which open right and left in
the genital recess, and when they are full of eggs they are
very conspicuous objects. Other unpaired glands open into
the genital recess, one of these is the bursa copulatrix, another
forms the receptaculum seminis, and the third is the shell
gland.

Mesostoma produces two kinds of eggs: summer eggs, with a
thin, transparent shell, and winter eggs, with thick, brown,
horny shells. The developement of the summer eggs takes
place whilst in the uterus. The winter eggs are laid in the
autumn, and can withstand a considerable amount of desicca-
tion. Copulation is said to be reciprocal, and fertilisation
always takes place in the atrium genitale.

As a rule, Mesostoma Ehrenbergu is found living in still
or slowly-flowing clear water, especially where rushes and
sedge grow, and where the bottom is of clay. It swims quietly
through the water by means of the undulations of its body, or
glides with its cilia along the stems of water-weeds. It feeds
on the minute freshwater crustacea, small worms, and insect

88 ZOOLOGY

larvae. When it has caught a Daphnia, for instance, it will
wrap its body round it and attack it with its proboscis; very
frequently it makes prisoners of its prey by ensnaring them
with threads of mucus. In the autumn these animals become
of an opaque white colour, lose their power of movement, and
sink to the ground. The survival of the species through the
cold of winter is ensured by the existence of the well-
protected winter eggs, a device frequently met with amongst
fresh-water creatures.

Mesostoma is not a large Turbellarian; the marine forms
often measure more than an inch in length, and are usually
flattened and leaf-like (Fig. 55); the land Planarians, on the

Fra. 61.—Plan of an Acoelous Turbellarian.
After Von Graff.

. Eye.

Mouth.

Otolith.

Ovary.

Digestive parenchyma.

Testicular follicles.

Vesicula seminalis.

. Male copulatory organ.

, Common sexual aperture.

+0 OF 1m OT BP Oo DD OH

Oy

other hand, are elongated and linear: one of this has been
described which attains a length of nine inches. The marine
forms are often brilliantly coloured, and their dorsal surface
beset with papillae.

PLATVHELMINTHES 89

The position of the mouth in the different species of Tur-
BELLARIA varies greatly ; in some it is anterior, in others it is
ventral and median, and it may be nearly at the posterior end

of the body. True nematocysts,
such as are found in the COELEN-
TERATA, exist in the ectoderm of
a few genera, amongst others in
Microstoma. Some of the ecto-
dermic cells are also modified, and
form adhesive or glutinous areas
which make up for the want of
suckers.

The pigment may be in the
ectodermal cells, or, as in
Mesostoma, in the parenchyma ;
Vortex viridis and Convoluta
Schultzii_ contain cells coloured
with chlorophyll and with starch
in them. These are probably
symbiotic algae.

The arrangement of the
muscle fibres in Jesostoma is
very simple; the diagonal layer
exists Im many genera, and in
some of the Dendrocoels there
may be as many as six separate
layers.

The disposition of the phar-
ynx and stomach in Turbellarians
is very various, and has served as
a basis for the classification of
the class. The muscular part of
the pharynx may be very much
enlarged, and capable of being
protruded through the mouth,
and acting as a powerful sucker.

4

13

LA

(I
4

ie

ae

cs

ay

aa
sea
ize

11

Fic. 62.—Plan of a Triclad Turbel-
larian. After Von Graff.

1. Anterior.
1’,1”. Posterior branches of alimentary
canal.

5. Oviduct.
9. Tentacle.
10. Vas deferens.
2, 3, 4, 6, 7, 8, 11, 12, 13, as in Fig. 59.
Q. Female copulatory organs.
é 9. Common sexual aperture.

In one division of the Rhabdocoelida, the Acoela (Fig. 61),
the pharynx ends in the solid parenchyma, into which the food
passes, and is there digested ; in the Rhabdocoela the alimentary

90 ZOOLOGY

canal is a straight and unbranched cavity, such as exists in
Mesostoma. The other great division of the class, the Den-
drocoela, have a branched stomach, the main division of which in
the Polycladida is ciliated, the branches only being lined with
an amoeboid epithelium, which digests intracellularly. The
branches may anastomose, and in rare instances, Yungia and
Cycloporus, they open on to the exterior.

The excretory system is absent in Acoela; in Rhabdo-
coela the main trunk may be single and open posteriorly,
or double, and then the two ducts may, as in Jfesostoma, open
separately and near the mouth, or together at the posterior end.
In the Dendrocoels the main trunks open by paired apertures
situated on the dorsal surface. The main trunks may be
ciliated, the finer branches are probably always intracellular,
piercing the cells and not lying between them.

The two main nerve cords are rarely connected by trans-
verse commissures in the Rhabdocoels, but in the Triclads this
is the usual arrangement. In the Polyclads there are many,
usually eight, nerve cords which diverge from the central cere-
bral ganglion (Fig. 63). Sensory cells provided with tactile
hairs oecur in the ectoderm. The eyes are usually two or four
in number, but they may be more numerous, and in the Poly-
clads they increase by division. Auditory vesicles also occur,
though they are rare in the Dendrocoels; they are often single,
and consist of a vesicle full of fluid in which a calcareous
otolith floats. The anterior end of the body is remarkably
sensitive, and in some genera forms a tactile proboscis which can
be retracted into a sheath; this, together with a pair of lateral
ciliated grooves which lie one on each side of the brain in many
Rhabdocoels, affords matter for a comparison with the members
of the class Nemertea.

Turbellarians, with the exception of two genera, Miero-
stoma and Stenostoma, are hermaphrodite, but many of them
are protandrous—that is to say, their male reproductive cells
mature before the female. Most Rhabdocoels and all Tri-
clads have a common genital opening for both male and female
duets ; others have separate apertures, and then the male is
usually anterior to the female. Self-fertilisation is said to
occur in the summer eggs of some Rhabdocoels.

PLATVHELMINTHES QI

co CONTI OD

Ovum Ww bore

Fic. 63.—Plan of a Polyclad.

. Brain.

. Intestinal branches.

. Anterior unpaired branch.
. Longitudinal nerve cord.

Mouth.

. Oviduct.

. Ovarian follicle.

. Pharynx.

. Pharyngeal pouch.

10.
Male
12.
13.

é.

9.

After Von Graff.

Stomach.

Testicular follicle.

Uterus.

Vas deferens,

Male copulatory organ, with the
male aperture behind.

Female copulatory organ, with the
female aperture before it.

The eyes are omitted.

g2 ZOOLOGY

The family Mierostomida is unique in the group in possess-
ing the property of asexual reproduction, which takes place by
transverse fission. The posterior third of the
body becomes cut off by a septum, and grows
until it equals in size the anterior half.
Then each portion again cuts off its posterior
third, and these again grow (Fig. 64). By
this process of segmentation and equalisa-
tion chains of 4, then 8, then 16, and some-
times even 32 individuals are formed. Each
forms a mouth, and for some time the chain
persists, but the individuals ultimately
become sexually mature and then separate.
They lay eggs during the autumn, which
persist through the winter, and these give
rise in the spring to the budding individuals.

Two curious animals, the Coeloplana and
the Ctenoplana, have recently been described
by Kowalevsky and Korotneff respectively,
which are intermediate in structure between
the CTENOPHORA and the TURBELLARIA.
Coeloplana is minute, its flattened body
covered with cilia, creeps along the surface
on its ventral face. In the middle of its
back is a sensory vesicle enclosing an otolith.
Fic. 64.—Microstoma On each side of its body, at right angles to

lineare, Oe.» under the plane of the stomach, is a long feathered

going division. There

are 16 ecu enn 8 tentacle which can be withdrawn into a
ith mouthapertures, ; A
Aaa the-pade o¢ pouch. The mouth in the middle of the

the first (m), second ventral surface opens into a stomach which

(m’), third (m”), and. , : 1

fourth (m’”) genera- gives off numerous anastomosing canals, two

tion, The fifth gen- of which pass dorsally, one in front and one

eration has not yet : ;

acquired a mouth behind the otocyst, and there end blindly.

ee patee Von Ctenoplana has much the same shape as

£ be Y 7 ajo . .

eG aiateade coves: Coeloplana. In addition to the uniform

2. Eye spots. covering of cilia, there are on the dorsal sur-

3. Intestine. 5 c

face eight bands of etenophoral plates corre-

sponding to those of the Ctenophors. The alimentary canal

resembles that of Coeloplana. The sense organ, situated in the

PLATVHELMINTHES 93

middle of the dorsal surface, 1s a structure resembling the aboral
sense organ of Ctenophors ; on each side of the body is a tentacle
with short side branches. In the neighbourhood of the ten-
tacles is the opening of a branching system of canals, which
have been compared with the excretory system of Turbellarians.
Beneath the ectoderm is a basal membrane which encloses an
outer layer of longitudinal muscles and an inner of transverse
muscle fibres; there are also dorso-ventral muscles.

From this short description it will be seen that these two
animals resemble Ctenophors in (1.) their aboral sense organ ;
(ii.) the presence of ctenophoral plates (Ctenoplana) ; (iii.) the
pair of solid, retractile, feathered tentacles; (iv.) the general
arrangement of their body. On the other hand they resemble
the Polyclads in (i) their flat shape, uniform ciliation, and
creeping motion ; (i.) their basal membrane (Ctenoplana) and
disposition of muscle fibres; (i1.) the branched stomach with
ventral mouth; (iv.) the possession of an excretory system
(Ctenoplana ?).

These two animals serve to show that there may have
been a connection between the Ctenophora and the Polyclads ;
and the resemblance is emphasised by the fact that both
groups are hermaphrodite. On the other hand, it is not easy
to homologise the nervous system of the two groups. The
Ctenophors have nothing corresponding with the excretory
system of Turbellarians, and the mesogloea of the former does
not necessarily represent the mesoderm of the latter. Further,
if the view that there is a connection between the CTENOPHORA
and the TURBELLARIA be accepted as sound, it must be through
the Polyclads, in many respects the most complicated tribe,
and in this case the other members of the group must be
regarded as degenerate.

The Turbellaria are classified as follows :

A, RHABDOCOELIDA.—Of small size, body cylindrical or de-
pressed, with or without an intestine ; when it is present
iw is simple and unbranched. Female genital glands
compact, not follicular. Genital orifice single or double.

Tribe 1. Acoela.— No intestine ; digestion takes place in
general parenchyma, No nervous system or excretory

94 ZOOLOGY

system. Hermaphrodite ; follicular testis and paired
ovaries. Marine. Frequently with brown or green
parasitic algae. Convoluta, Proporus.

Tribe 2. Rhabdocoela.—Stomach distinct from parenchyma,
and simple. Pharynx complicated. Compact testes and
ovary, the latter divided into a germarium and vitel-
larium. Otocysts rare. Marine, freshwater, and land
forms.

Prorhynchus inhabits damp earth. The MEso-
STOMIDA and VoRTICIDA are the chief freshwater familes ;
the latter includes two parasitic genera—Grafilla found
in Gastropods, and Anoplodium in Holothurians.

Fic. 65.—Plan of an Alloiocoelous Turbellarian.
After Von Graff.

. Bursa copulatrix.

. Brain.

Eye.

. Germarium.

. Intestine.

. Longitudinal nerve trunk.
. Mouth.

. Pharynx.

. Testis.

. Yolk gland.

. Vesicula seminis.

. Oviduct.

. Chitinous copulatory organs.
. Common sexual aperture.

Hee
SNH ODOANAMNPEWNHH

Bg
+0

Tribe 3. Alloiocoela—Stomach lobed or irregular, pharynx
present, testes follicular. Otocysts occur in the Jamily
Monotida.

All marine, except Plagiostoma Lemani, which in-
habits the deep water of certain Alpine lakes.

PEATVRELMINTHES 95

B. DENDROCOELIDA. — Forms with flattened body and
branched “intestine. Testes and ovaries follicular.
Otocysts very rare.

Tribe 1. Tricladida.— Body elongated. Intestine in three
main branches, which diverge from a cylindrical retractile
proboseis, Testes and vitellarium follicular. Germa-
rium compact. Genital aperture single.

Planaria and Dendrocoelum live in fresh water.
Ganda, which shows traces of metameric structure, and
Bdelloura, which is an ectoparasite of Limulus, are
marine. The leech-like land planarians are chiefly

tropical. Rhynchodemus terrestris and Geodesmus
bilineatus are European. The former is found in
England amongst damp bark, etc., in gardens and
woods.

Tribe 2. Polycladida.— Body thin and broad. Numerous
branched intestinal caeca open into the stomach. Testes
and ovaries follicular. Genital apertures separate, the
male anterior to the female. A ventral sucker some-
times present. Marine. Thysanozoon, Yungia.

Crass II. CESTODA.

CHARACTERISTICS. — Hndoparasitic Platyhelminthes, devoid of
mouth and alimentary canal. Organs of adhesion, in the
shape of chitinoid hooks or suckers, enable the parasite to
attach itself to its host. The nervous system is composed of
a cerebral ganglion and two lateral nerve cords. The coelom
is represented by irregular splits in the mesodermie paren-
chyma. The exeretory system ws of the Platyhelminthine
type, opening to the exterior by one or more pores, which are
sometimes furnished with a pulsating vesicle. The Cestoda
are hermaphrodite, the generative organs being usually
repeated many times.

One of the commonest Tapeworms found in man is Zaenia
saginata (mediocanellata) (Fig. 66), and it will be a convenient
form to describe.

The worm in question may attain a length of five or six
yards, and may be composed of many hundred segments, often

ZOOLOGY

Cry

2100, 90 0 oF

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25.0 %0$

66.—Anatomy of Taenia (from Leuc

kart).

9. Vagina.
10. Ovaries

FI
Portion of Taenia saginata.

11. Shell glands.
12. Yolk glands.

51
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x
ame. x 8.
Head of Taenia solium, showing the

Head of the s

A.
B.
C.

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PLATYVYHELMINTHES 97

termed proglottides, which increase in size as they recede from
the head. The body of a tapeworm may be divided into three
regions: (i.) the head, (11.) the neck, and (iii.) the segmented
trunk.

The head of 7. saginata (Fig. 66) is spherical in shape, and
bears on its sides four well-developed suckers. Other species,
as 7. soliwm, in addition to the suckers, are provided with a
double cirelet of chitinoid hooks, which assist the suckers to
attach the worm to the inner surface of the alimentary canal
(Fig. 66, C) of its host. The head is mobile, and can shift its
point of attachment with ease.

The neck is the region immediately succeeding the head ;
its most anterior half is not segmented. The first trace of
division into segments is the appearance of shallow grooves
which separate the various proglottides one from another.
As they grow backward the proglottides increase in size, and
those situated a foot or more behind the head are sexually
mature.

The surface of the body is covered by a thin clear struc-
tureless cuticle, the layer of cells beneath this, corresponding
with the ectoderm of other animals, is composed of long-tailed
cells, the tails running down into the parenchyma. The body
of the tapeworm is practically solid, the coelom being repre-
sented by poorly-developed splits in the parenchyma.

The muscle fibres are arranged in longitudinal trans-
verse and dorso-ventral bundles. The outermost layer, the
longitudinal, is not a very definite layer, but consists of a
number of unstriated fibres scattered through the parenchyma.
The transverse muscles lie immediately within the longitudinal ;
they serve to divide the parenchyma into a central and a
cortical portion. The dorso-ventral fibres run from one sur-
face to the other, and are very irregularly arranged. The
muscle fibres are non-striated, and often branched at their
ends. The animal has very considerable powers of extension
and contraction.

The parenchyma is composed of ill-defined connective
tissue cells, amongst which are scattered, especially in the
cortex, a number of ovoid calcareous corpuscles (Fig. 67),
about whose function little is known. They have been vari-

7

98 ZOOLOGY

ously regarded as excretory in nature, and as material for
counteracting the acidity of the digestive fluids of their host.
The excretory system consists of an annular ring in the
head, from which four ducts corresponding in position with
the suckers pass backward. Two of these soon disappear, and
the other two pass down one on each side of the proglottides,
just inside the longitudinal muscle layer (Fie. 67). These

10 get) (22 abies
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Fic. 67.—Transverse section through a mature proglottis of Taenia.

1. Cuticle. 6. Ovary.
2. Tailed cells of ectoderm. 7. Follicle of testes with sperm morulae.
3. Longitudinal muscle fibres cut across. 8. Longitudinal excretory canal.
4. Layer of circular muscles. 9. Longitudinal nerve cord.
5. Split in the parenchyma which lodges 10. Uterus.
a calcareous corpuscle. 11. Oviduct.

two lateral ducts coalesce at the posterior end of the last
proglottis, and open there by a common vesicle. A transverse
vessel at the posterior end of each proglottis serves to place the
two longitudinal ducts in communication. The main ducts are
provided with valves, which only permit the flow of fluid
towards the external opening. <A series of secondary ducts
arise from these main ones and ramify all over the body. The
secondary ducts give off still finer tubules, each of which ends
in a flame cell. The cilium of this cell hangs down into the
lumen of the tubule, which is here slightly enlarged and
funnel-shaped. Some observers maintain that this funnel-
shaped end of the tubule opens by a pore into the splits in the
parenchyma which represent the coelom, but this is a disputed
point.

There is a central nervous system in the head. This gives

PLATVHELMINTHES 99

rise to some nerves which pass forward and supply the suckers,
and to two stout nerve cords which pass back along each side
of the proglottides, lying just outside the longitudinal ducts of
the excretory system (Fig. 67).

Both male and female reproductive organs are repeated in
each proglottis (Fig. 66). The testis is composed of very
numerous vesicles in which spermatozoa arise, and which are
each attached to one of the branches of the ramifying vas
deferens. Thus the testis is dispersed all over the proglottis.
The branches of the vas deferens unite and form a common
tube, which is slightly coiled, and which runs from the centre
of the proglottis to the common genital pore situated in the
middle of one side (Fig. 66). The portion of this common vas
deferens lying next the orifice has very muscular walls, and
can be extruded. It functions as a penis.

Self-fertilisation takes place, and is probably the usual
method, there is no evidence to show that one proglottis
fertilises another.

The vagina opens into the genital pore a little behind the
penis, it then passes backward to a small swelling, the
receptaculum seminis. In this the spermatozoa are stored
until the ova are ripe for fertilisation. The ovaries are two in
number, and are composed of numerous tubules on a branch-
ing duct. Each ovary gives off an oviduct, and the two
unite, and then receive a small duct which comes from the
receptaculum seminis and conveys the spermatozoa ; it is there-
fore called the fertilising canal (Fig. 66). The oviduct then
receives a duct from the yolk gland, which lies between and
behind the ovaries, and passing through a small spherical
shell gland, which deposits the shell, enters the uterus.

The uterus is at first an inconspicuous simple sac, whose
only opening is that from the oviduct. As it becomes full of
eggs it increases greatly in size, and becomes much branched ;
eventually it occupies almost the whole of the interior of the
proglottis, the reproductive organs of both sexes having atro-
phied (Fig. 66, F). A proglottis which is ripe for separation
consists of little more than a sac—the uterus—crowded with
minute spherical eggs, which eventually escape by the rupture
of its walls.

100 ZOOLOGY

The terminal proglottis breaks off from the rest of the
Tapeworm owing to the contraction of its muscles, its rupture
affects the transverse excretory duct of the segment in front,
which is put into communication with the outer world, and thus
forms the new terminal vesicle, which opens to the exterior.

The ripe proglottis passes out of the alimentary canal of
its host, and the eggs with which it is crowded escape by the
rupture of its walls. In some species the free proglottides,

|
|
|

Fic. 68.—Development of Zaenia. From Leuckart.

A, Cysticercus bovis, from beef. Natural D. Stages in the development of the

size. brood capsules in Hehinococcus,

B. Invaginated head of Cysticercus before «a. The thickening in the parenchyma of
the formation of the suckers. the bladder.
x 20. 6. Subsequent formation of a cavity in it.

C. Invaginated head of Cysticercus cellu- c. Development of the suckers.
losae, showing the bent head. x30. ad. A capsule with one head invaginated.
e. A capsule with two heads. x 90.

after they have left their host, retain a considerable power of
movement, and crawl over blades of grass, ete. In this way
their ova are disseminated, and stand a better chance of
being eaten by their second host, in whose body alone they
can develop. Some of them succeed in making their way,
either by means of the food or water, into the stomach or

PLATVHELMINTHAES Iol

intestine of an ox. Here the egg shell is dissolved by the
action of the digestive juices, and a small embryo, the proscolex,
emerges (Fig. 66, G). The proscolex is a minute spherical
embryo provided with three pairs of hooks, by the aid of which
it burrows its way through the wall of the alimentary canal,
and eventually passes into some blood-vessel, or into the body-
cavity. If the former is the case, it is carried either to the
liver, brain, lungs, muscles, connective tissue, or eye (Fig. 68).
Its presence causes a cyst to be formed round it, pathological
changes being induced in the surrounding tissues of the host.

The embryo soon loses its hooks and begins to grow.
Some of the cells in its interior liquefy, and a vesicle full of
fluid results. These vesicles attain a length of 4 to 8 mm., and
when found between the muscle fibres of beef or pork, the meat
is technically termed measly. At one side of the vesicle the
head commences to be formed; it arises inside out as a projec-
tion into the lumen of the vesicle (Fig. 68). This projection
is hollow, and on its walls, facing its own lumen, the suckers
and rudimentary ring of hooks arise, whilst in the substance
of its walls the excretory system is being formed. The head
then turns inside out, and the result is a Cysticercus or bladder
worm. The Cysticercus consists then of the head and short
neck, termed the scolev, and of the bladder or vesicle. That
formed by the embryos of TZaenia saginata is known as
Cysticercus bovis, from the host it inhabits (Fig. 68). As
long as it remains in the body of the ox, the Cysticercus is
incapable of further developement ; if, however, it is swallowed
by a man, the vesicle is digested, whilst the head fixes itself to
the walls of the intestine, and commences to divide into pro-
elottides.

LirE-HistoRY OF TAENIA SAGINATA.

NCOLERe seer eten: in man gives rise by strobilisation to the
Proglottides......... these leave their host carrying with them the

(ON ieoneenepanccnor which, when found on grass or in water, contain the
Six-hooked S aenneee embryo or proscolex. This passes into alimentary canal of an

ox, aud working its way into the tissues of this intermediate
host, becomes the

Cysticercus..........or bladder-worm. When this is eaten by man it develops
into the

Scolex.

102 ZOOLOGNX

The question whether the proglottides which are cast off
one by one by the tapeworm should be regarded as individuals,
is one which has given rise to much difference of opinion.
The comparison which has been instituted between a single
proglottis and the body of a Trematode gives some support to
the view that the scolex produces by strobilisation a number
of individuals (the proglottides), which in their turn reproduce
sexually. If this view be retained, the Taeniidae exhibit a
well-marked alternation of generations.

On the other hand, the nervous, excretory, and to some
extent the muscular systems are common to all, and the
detached proglottides are not capable of individual life or

Fic. 69.—Various forms of 'Tape- Worms.
A. Tuenia echinococcus. x 12. From Leuckart.
B. Archigetes Sieboldii. x 60. From Leuckart.
C. Echinobothrium typus. * 10. From Van Beneden,
D. Caryophyllaeus mutabilis. x about 5. From Carus.

maintenance. It is true that they are stated to increase in
size when separated, but this may be due to imbibition of
fluids, and it is doubtful how far it corresponds with growth.

PLATVAELVMINTHES

103

Further, the separation of parts of the body containing repro-
ductive cells occurs in the hectocotylsation of the Cephalo-
pods, and this is no longer regarded as an instance of

alternation of generations.

It is an interesting fact that, with the exception of Archigetes,
which inhabits the Oligochaet Tubifex rivulorum, the sexual form

of the Cestoda are entirely confined to Vertebrate hosts.

The

Cysticercus form, although usually found in Vertebrata, has also
been observed in the bodies of Molluses, Arthropods, and Worms.
Some interesting divergences from the arrangements of the

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Fra. 70.—Bothriocephalidae.

A. A segment of Bothriocephalus latus,
showing the generative organs from
the ventral surface.

Excretory vessels.

Cirrus.

Cirrus pouch.

Vas deferens.

Vaginal opening.

Vagina.

Shell gland.

Oviduct.

Ovary.

COICO CTU ACO; ROE

10. Yolk glands.

11. Their duct.

12. Uterus.

13. Uterine opening. The testes are not
visible from this side. x 23.
From Sommer and Landois.

B and C. Marginal and lateral view of B.
cordatus, showing the cephalic
grooves. x 5. From Leuckart.

D. Ciliated larva of B. latus. x 60.
From Leuckart.

organs in Taenia are met with in Bothriocephalus latus, the
largest Cestode which inhabits the human intestine; it may

104 ZOOLOGY

attain a length of nearly ten yards. ‘The head is flattened,
and bears two lateral slits; the genital pores are not on the
side, but on one surface of each segment. The male orifice is
distinct, and in front of the female, and the uterus has an
aperture for the exit of the ova, behind the female orifice
through which the spermatozoa are introduced. The asexual
stage has been found in certain freshwater fish. This parasite
is chiefly met with in Russia and Central Europe.

Certain genera, as Amphilina, found in the body-cavity of
the Sturgeon, and Amphiptyches in the stomach of the Chimaera,
have flat bodies with one anterior sucker. Their embryos are
ciliated, and their female reproductive organs closely resemble

Fic. 71,—Tetrarhynchus.

A. General view of the worm. x 4.

B. Head, showing the suckers, proboscides, and excretory canals. x 25,

C. Portion of a proboscis showing the two forms of hooks, highly magnified.
All after Pintner.

those of Trematodes. They are therefore looked upon as con-
necting the latter class with the Cestoda. Ligula is another
genus in which the segmentation into proglottides does not occur.

Although, if the proglottides be not regarded as distinct
individuals, there is no alternation of generations in Taenia
saginata, i some other species this phenomenon is brought

PLATVHEEMINTHES 105

about by the formation of many scolices from one proscolex.
Thus, in Zaenia coenurus, the bladder-worm which gives rise
to the “staggers” in sheep produces several heads, and thus
several scolices are produced asexually, which in their turn,
if they attain their right host, reproduce sexually.

The Zaenia solium, which is common in man, has its
bladder-worm, Cysticercus cellulosae, in the pig; it 1s, however,
also found in man, and is the cause of considerable disturb-
ance, often ending in the death of the host. Zaenia echinococeus,
which is found in the sexual form in dogs, exists in the Cysti-
cercus condition in man.

The genus 7etrarhynchus is curiously modified, it appears
to be flattened in a plane at right angles to that of other
Cestoda. The head bears four long hooked proboscides, which
can be protruded from two disks; each of the latter seems to
be homologous with two of the suckers of Taenia.

The Cestoda are divided into seven families :

Family I. Amphilinidae—Amphilina, found in Sturgeon.
5. II. Caryophylaeidae—Caryophyllacus, found in intestine of Cyprinoid

fishes,

+ III. Pseudophyllidae—Bothriocephalus, Liqula, Archigetes, found in
fishes.

0 IV. Diphyllidae—Zchinobothriwm, found in Selachians.

3 V. Tetrarhynchidae—Tetrarhynchus.

55 VI. Tetraphyllidae—Anthobothrium, Calliobothrium, found in Sela-
chians.

» VII. Taeniidae—Zacnia.

Cuass II]. TREMATODA.

CHARACTERISTICS.—Platyhelminthes with a cylindrical or flat
leaf-like body, devoid of segmentation. Their adhesive organs
are tn the form of suckers. Hooks are rarely present. The
excretory system ends internally in flame cells, and opens to
the exterior by a contractile vesicle, or by two pores. They
are parasite and hermaphrodite ; both reciprocal and self-
fertilisation occur. The embryo may develop directly, or it
may pass through a series of stages, in some of which asexual
reproduction takes place.

Fasciola (Distoma) hepatica, commonly known as_ the
liver fluke, is found in the liver of diseased sheep. It is
about # of an inch long, and has a flattened leaf-like shape.

106

ZOOLOGY

A. Fasciola hepatica, from the ventral
surface (x 2), the alimentary and
nervous systems only shown on the
left side of the figure, the excretory

1. Right main branch of the intestine.

Bren /2.

only on the right.

A diverticulum.
Lateral ganglion.
Lateral nerve.
Mouth.
Pharynx.
Ventral sucker.
Cirrus sac.

Left anterior dorsal excretory vessel.
. Main vessel.
. Left anterior ventral trunk.

Excretory pore.

B. Anterior portion, more highly magni-

eR
eee Sh LS) Ee

fied,
Cirrus sac.
Ductus ejaculatorius.
Female aperture.
Ovary.
Oviduct.
Penis.
Shell gland,
Anterior testes.
Uterus.
Vasa deferentia.
Vesicula seminalis.

. Yolk gland.
. Its duct (from Marshall and Hurst,

after Sommer).

C. Genital sinus and neighbouring parts.

ie
2.

Ventral sucker.
Cirrus sac.

PLATVHELMINTHES 107

The cuticle which covers its body is inflected at the mouth,
and at the genital and excretory pores. The nature of the
cuticle, like that of Cestodes, is a matter of dispute, some
authorities looking upon it as a basement membrane, whilst
others hold the view that it is a metamorphosed layer of cells.
It is perforated by numerous fine pores, and is produced into
many backwardly-directed spines.

The intestine, which consists of two main branches giving
off numerous secondary ones, is hned by a layer of amoeboid
cells, and the digestion of the solid food, such as blood cor-
puscles, is intracellular.

The reproductive organs are similar to those met with in
the Cestodes, with the addition of a channel known as the
Laurer-Stieda canal, whose function, although the subject of
much debate, still remains uncertain. The canal is given off
from the common duct of the yolk gland, just before it enters
the substance of the shell gland to unite with the oviduct.
The canal opens dorsally upon the surface of the animal. Two
views have been held as to its use: it is regarded by some
as the duct through which the spermatozoa enter the female
organs, and in Polystoma (Fig. 74, B) this has actually been
observed ; on the other hand it has been urged that in some
species, notably in Fasciola, it is too minute for this purpose,
and the second view has been propounded, that it acts as a
valve, and permits the escape of an excess of the secretion
of the yolk glands, or of spermatozoa.

The method of fertilisation in the liver fluke is not very
definitely settled, probably self-impregnation takes place.

The life-history of the Fasciola hepatica may be briefly
summarised as follows. The sexual form lives in the liver
and bile ducts of sheep and other domesticated animals. Its
fertilised eggs develop to some extent in the uterus, and

o

3. Genital pore. D. A ciliated internal end from the ex-
4. Evaginated cirrus sac (? penis). cretory apparatus.

5 ral aA . Is

a nae 2 ee 1. Orifice of the flame cell (highly
6. Vasa deferentia. ae ;

= same aie magnified).

7. Vesicula seminalis.

8. Ductus ejaculatorius. E. Egg of Fasciola hepatica, x 330 (from
9. Accessory gland (from Sommer). Thomas).

108

ZOOLOGY

Fic. 73.—Five stages in the life-history of Lwsciola hepatica, all highly magnified.

D.
E.

A. The free-swimming embryo.
B.
C. The young redia, the digestive tract

The sporocyst containing young rediae.

shaded.
An adult redia, a daughter redia, two
cercariae, and germs.
The free cercaria. The figures have
the same significance throughout.
Nearly ripe cercariae.

Cystogenous cells.

Daughter rediae.

Limbs of the digestive tract.

Head papilla.

Eye-spots.

Same degenerating.

Germinal cells.

Cells of the anterior row.

OO NI OUR we tO

10.

11.
12.
13.
14.
15.
16.
Ze
18.

19:
20.
21.
22.

9°

“v0.

Embryo in optical section, gastrula
stage.

Pharynx of redia.

Digestive sac.

Oesophagus.

Lips of redia.

Collar.

Processes serving asrudimentary feet.

Embryos.

Trabeculae crossing body-cavity of
redia,

Birth opening.

Morulae.

Oral sucker.

Ventral sucker.

Pharynx. All from Marshall and

Hurst, after Thomas.

PLAT VHELMINTHES 109

are cast out from the body into the bile duct in such quanti-
ties that it has been computed that each fluke produces half a
million eggs.

The further development of the embryo only takes place
outside the body, and at a low temperature. If these condi-
tions be present, at the end of two to three weeks the ege
gives birth to a free-swimming ciliated embryo. This is a
conical larva, provided with a double eye-spot, and rudiments of
an excretory system in the form of ciliated funnels (Fig. 73, A).
If this embryo is fortunate enough to be born in a pond or
ditch, it swims about looking for a certain species of water snail,
Limnaca truncatula. If it fails in its quest, it dies in eight
or ten hours; on the other hand, if it succeeds, it immediately
sets to work to bore into the soft tissues of the snail. This it
effects by elongating its head papilla into a pointed structure,
and revolving on its axis by means of its cilia. When once
it has forced an entrance into the tissues of the snail, it loses
its cilia and becomes a Sporocyst.. This is an oval sac of cells,
whose wall is covered with a cuticle and contains circular and
longitudinal muscle fibres, and is lined by an epithelium (Fie.
73, B). The Sporocyst may multiply by transverse division.
Within its body certain germinal cells arise, and these ultimately
form a Ledia, which bores through the walls of the Sporocyst,
and makes its way to the liver of the snail (Fig. 73, C and D).
The walls of the Sporocyst close up, and the process is repeated ;
but if too many Rediae are produced they may cause the death
of the Snail. The Redia is a cylindrical larva with a terminal
mouth, which leads through a pharynx into a blind stomach
lined with a single layer of cells. A little way behind the
mouth the surface of the body is raised into a circular ring,
and posteriorly there are two projections which assist the larva
in its movements. The excretory system is well developed, and
the cells lining the body-wall give rise to the germinal cells.
These latter may produce fresh Rediae, but as a rule they give
rise to Cercaviae: organisms which differ from their parent by
the possession of a forked alimentary canal, two suckers, a
tail, and certain cystogenous cells. The Cercariae escape from
the Rediae through an opening just behind the collar; they are
at first active, and make their way out of the body of the snail

110 ZOOLOGY

into the water (Fig. 73, E). They then swim about for a time,
and ultimately settle on some water-plant, or during a flood
on the grass, and by means of the cystogenous cells envelop
themselves in a cyst. If they are then swallowed by the
grazing sheep, they make their way to the bile duct, and there
develop into the sexual Fasciola hepatica. It is thus evident
that in the life-history of this Trematode there is an alterna-
tion of generations, during which there are several occurrences
of asexual reproduction.

LIFE-HISTORY OF FASCIOLA HEPATICA.
Sexual Adult (Sheep).
|
Ciliated Embryo (Water and Snail).

Sporocyst (Snail).

Sporocyst (by division). Redia (Snail).
= a |
tedia (by gemmation). Cercaria (encysted on grass).

Sexual Adult (Sheep).

The disastrous effects which this internal parasite pro-
duces on its host are evidenced by the fact that it is caleu-
lated that one million sheep are annually lost in the United
Kingdom from what the farmers call “liver rot” alone.

The TreMAToDA are divided into the Monogenea and the
Digenea.

A. The Monogenea develop directly, without the intervention
of asexual forms. They inhabit therefore one host only,
and are with few exceptions ectoparasitre.

Amongst the exceptions to the last statement, is the species
Aspidogaster conchicola, which inhabits the pericardial cavity
and the nephridia of the freshwater mussel (Anodon) (Fig. 74).

A very curious Trematode inhabits the gills of the
minnow. Its embryo is ciliated and free-swimming, and is
termed a Diporpa; it, however, soon loses its cilia and settles
down on the gills of its host. At first it lives singly, but
after a time two individuals come in contact, and one seizes
the dorsal papilla of the other by its ventral sucker; they
then twist round so that the ventral sucker of the second is

PEATYVHELMINTHES To

able to attach itself to the dorsal papilla of the first, and in
this condition there is an actual fusion of the tissues of the

Dj) =
MHavpose®

C

Fic. 74.

A. Diplozoon paradozum, two united individuals.

B. Polystoma intergerrimum. x about 100. After Zeller.

C. Microcotyle mormyri. x 7.

E. Two views of the chitinous framework of a sucker of Aine belones, highly
magnified. After Lorenz.

F. Aspidogaster conchicola. x about 25. After Aubert.

G. Gyrodactylus elegans. x about 80. After Wagner.

suckers and papillae. This double organism is known as the
Diplozoon paradoxum (Fig. 74).

Polystoma intergerrimum, another of the Monogenea, is
common in the bladder of the frog (Fig. 74). It lays its eggs
in the spring, and by protruding its body from the anus of the
frog, manages to deposit them in the water. The young larvae

112 ZOOLOGY

after a short free life attach themselves to the gills of a tad-
pole. When the gills atrophy, the larvae proceed down the
alimentary canal and eventually reach the bladder of the
young frog. Here they take five or six years to reach
maturity. This Trematode has at its hinder end a disc, round
which are grouped numerous hooks and suckers.

Gyrodactylus elegans has a similarly-situated triangular
plate which bears two large hooks in the centre, and sixteen
smaller ones round the edge, by means of which it attaches
itself to the fins of sticklebacks and other freshwater fish
(Fig. 74). Its most remarkable feature is that it is viviparous,
and its embryos before they leave the body of their mother
have already developed their embryos inside them; and the
latter may contain their embryos, so that four generations may
be included under the cuticle of the sexually mature animal.

B. The Digenea have always one, and usually several asexual

intermediate generations intercalated between the sexual,
and their life-history usually involves residence in two
distinct hosts.

The asexual generations usually inhabit some Mollusc, more
rarely they attack fish. The sexual forms are found in all
classes of the Vertebrata. The genus Distoma includes
more than three hundred species, eight of which infest the
human race.

One of the most dangerous human parasites is Bilharzia
haematobia; it is remarkable amongst Trematodes for its sexes
being separate. The mature worms are found in couples, the
female partly enclosed in a gynaecophoric canal or groove on
the under side of the thicker male. They inhabit the blood-
vessels of the bladder and give rise to considerable disturbance
in the system. Their eggs escape with the urine, but their
future fate is not known.

Leucochloridium paradoxum is parasitic in the body of a
snail, Suceinea putris; it develops two sacs which grow into
the tentacles of its host, which may ultimately be ruptured
by the increase of these structures.

Both the Cesropa and the TREMATODA have been consider-
ably modified by leading an endoparasitic life. They have
lost their locomotor organs, and are dependent on cilia or on

PLATYHELMINTHES 113

the boring hooks of their larvae for a change of host; as some
compensation they are amply endowed with organs of adhesion
in the form of either hooks or suckers. They have further

Fie. 75.—a, Bilharzia haematobia, the thin female in the gynoecophoric canal of the
stouter male, x 15 (after Leuckart). 6, Distoma macrostomum, showing the
digestive, and the greater part of the genital apparatus, with the cirrus pro-
truded, x 30. c, Snail (Succinea), the tentacles deformed by Leucochloridium,
nat. size. d, Leucochloridium removed from the tentacle, nat. size (after Zeller).
e, Bucephalus polymorphus, highly magnified (after Ziegler). .f, Portion of a
sporocyst containing Bucephali in process of developement, x about 50 (after
Lacaze Duthiers).

acquired the power of producing an enormous number of eggs,

a necessary provision when the remoteness of their chance of

hitting on the right host is taken into account; this power of

propagation is further increased in many cases by the asexual
8

114 ZOOLOGY

budding of the embryos. In the Cestopa, the group in which
parasitism has left the deepest mark, the whole alimentary system
has disappeared leaving no trace, and the food is absorbed
through the skin. In both groups the sense organs, for which
they can have but little use, are very poorly or not at all
developed.

There can be little doubt that the Cestopa and TREMA-
TODA are connected, or that the former have become more
modified and departed farther from their common ancestor,
than the latter. Lang’s researches lead him to look for the
ancestors of the TREMATODA amongst the TURBELLARIA, and
especially amongst the Triclades, which group contains some
species not easily distinguished from the ectoparasitic Trema-
todes, but for their ciliation.

CHAPTER VII
NEMERTEA

Palaeonemertea—Carinella, Polia.
NEMERTEA~ Schizonemertea—Lineus, Cerebratulus.
Hoplonemertea— Tetrastemma, Geonemertes, Malacobdella,

CHARACTERISTICS. — This class is characterised by a ciliated
ectoderm, which at the anterior end of the body is sunk in,
and forms a pair of ciliated grooves or pits. There is a
protrusible introvert, which may be armed with hooks and
spines, opening above the mouth. A nerve comnvissure sur-
rounds it. The nervous system consists of two cerebral
ganglia, gwing off two lateral nerves which extend through-
out the body, and may unite above the anus. The alimentary
canal is not branched, but may bear lateral caeca ; it ter-
minates in an anus. The generative organs are simple
and paired ; the sexes are usually distinct. With few excep-
tions, the Nemertea are marine.

The Nemertines are mostly found amongst seaweed and
coral rock, and they are frequently of the most brilliant colour.
Pelagonemertes is, however, pelagic, and like most pelagic
organisms is transparent, and JMJalacobdella is parasitic, living
in certain Lamellibranchs. A few inhabit fresh water, such
as Tetrastemma aquarum dulcium from North America, and
an unknown species of the same genus recently found in
England. Two species of TZetrastemma and two species of
Geonemertes are terrestrial.

Probably the members of no class vary so much in size as
do the Nemertines; many of them are quite small, whilst
others attain the length of many feet, and Professor M‘Intosh
records finding a Lineus marinus which measured thirty yards,
and even then was only half uncoiled. They possess extreme

116 ZOOLOGY

powers of contractility, but are very easily broken into frag-
ments.

Tetrastemma flavida, which may serve as a type of the
class, is a pinkish Nemertine an inch or more in length, which
is found under stones or in fissures of the rock when the tide
is down. It occurs in all European waters from Scotland to
the Red Sea; it is extremely delicate, and the slightest touch
may serve to break it.

The ectoderm of this animal is columnar and ciliated.
Beneath the ectoderm, and separated from it by a basement
membrane, is the thin layer of circular muscles, and this layer
in its turn surrounds a thickish layer of longitudinal muscles

Fig. 76.—Diagrammatic section to
show disposition of parts in a
Hoplonemertean (such as Tetra-
stemma). After Hubrecht.

Cellular portion of integument.
Basement membrane.
Circular muscular layer.
Longitudinal muscular layer.
Lateral nerve.

Cavity of proboscis sheath,
Proboscis.

Intestine.

Lateral blood-vessels.

Dorsal blood-vessel.
Connective tissue.

SS) SE) ESTED SES oS) I

a

(Fig. 76). From the latter, fibres arise and pass in various
directions through the body, certain of these are especially
conspicuous, running in a dorso-ventral direction between the
diverticula of the alimentary canal, and these give the body
the appearance of being segmented, but the bundles of muscles
are not very regular, nor are they always opposite each other.
A layer of diagonal muscle-fibres usually occurs within the
longitudinal.

The integument of Nemertines encloses a more or less
solid mass of parenchyma, in which the various organs of the
body are embedded. In this there are two kinds of spaces.
Firstly, there is the space into which the proboscis is with-
drawn, and the blood-vessels. These contain a fluid in which
corpuscles float, and they represent that kind of coelom known
as an archicoel. And then there are the spaces in which the

NEMERTEA 117

generative cells arise, and certain spaces found in one or two
species between the diverticula of the alimentary canal. The
morphological value of these spaces is still under discussion.
They do not contain a corpusculated fluid.

The mouth is situated on the ventral side, and is sur-

Fic. 77.—Diagram of the organs of a Nemertine. I. from below.

II. from above.
After Hubrecht.

1. Mouth. 6. Brain lobes.

2. Intestinal diverticula. 7. Longitudinal nerves.
3. Anus. 8. Proboscis.

4. Ovaries. 9, Proboscis sheath,

5. Nephridia. 10.

Proboscis pore.

rounded by swollen lips, it leads into a muscular oesophagus
which soon opens into a spacious stomach. The stomach has
a wide lumen, and it occupies a large part of the animal; it

118 ZOOLOGY

is produced into a certain number of lateral diverticula, but
these do not seem to be very definite in number or size
(Fig. 77). The stomach is lined by a layer of cells which
are capable of assuming very
different outlines at different
times; they often break away
from the wall and are seen
floating in the lumen of the
digestive canal. There is no
special muscular coat, but some
of the muscle-fibres running
through the parenchyma are
attached to the walls of the
stomach. In most Nemertines
the alimentary canal is ciliated.

The anus is terminal.
Fic. 78.—Introvert of a Hoplonemertine, ;

with stylet, ‘‘reserve” sacs, and The most characteristic

muscular bulb, After Hubrecht. organ in the Nemertines is the
A. Retracted, Cet ; ‘ : :
Bo Werte introvert or proboscis, which

consists of the hollow eversible
anterior end of the animal. In its retracted condition this is
invaginated into a cavity, the lumen of the proboscis sheath,
just as the finger of a glove may be inverted into the glove.
The cavity of the proboscis sheath is a closed one, and full of
a corpusculated fluid; the walls of this cavity, ae. the pro-
boscis sheath, are extremely muscular, when they contract
the pressure of the fluid drives the introvert forward and it is
everted. In many Nemertines the proboscis sheath extends
the whole length of the animal, and only ends just above the
anus. The method of the eversion of this proboscis is interest-
ing; when it begins to protrude, it is the walls of the organ
which first grow forward, and the extreme end of the proboscis
—often armed with a spine—is the last part to appear, and
is therefore only to be seen when the proboscis is fully ex-
tended. It is retracted by a special muscle inserted into the
tip of the proboscis behind the spine, and arising from the
base of the proboscis sheath; when this contracts, the first
portion to disappear is the tip. The aperture through which
the proboscis appears is either terminal or ventral, but almost

NEMERTEA 119

invariably in front of the mouth; more rarely it opens with it
(Malacobdella).

Tetrastemma has a well-developed spine at the end of its
proboscis, and on each side a couple of small secondary ones.
Certain glandular structures open by a duct near the base of
the spine, and possibly secrete a poison. In those Nemertines
in which the introvert is constantly in use, the walls of the
proboscis sheath are extremely muscular; and this defensive
organ can be shot out with the greatest velocity, and at times
with such force as to break off. When this is the case, it
retains its vitality for some time, and crawls about independ-
ently. This may be accounted for by the enormous develope-
ment of nervous tissue found in its walls. The animal is
capable of reproducing its lost introvert.

A closed system of blood-vessels lined with an epithelium is
present (Figs. 76 and 80). It comprises a median dorsal vessel

5

Fia. 79,—Anterior portion of the body of a Nemertine.
After Hubrecht.

= Bram.

. Lateral nerves.

. Proboscis sheath,
. Proboscis.

ore wd

. External aperture through which the intro-
vert is everted. The mouth and oesophagus
are indicated by dotted lines.

which runs along the body just below the proboscis sheath, at
the posterior end this divides into two branches above the
anus, and the branches run forward as two lateral trunks
situated in the longitudinal muscle layer. At the anterior
end the three trunks again unite, and from their point of
union give off a loop which in many species encircles the
proboscis sheath. The dorsal and lateral trunks in most forms
communicate by transverse vessels which le between the
diverticula of the alimentary canal. The blood is colourless in
Tetrastemma, but in some other species it contains haemoglobin.

120 ZOOLOGY

It is stated to flow forwards in the lateral, and backwards in
the dorsal vessel.

The nephridia of Nemertines are paired and situated
anteriorly (Fig. 77). Their ducts open to the exterior by one
or more openings on each side of the body, and they always
lie above the nerve trunk. These ducts are lined by a single
layer of ciliated epithelial cells, and are sometimes much
branched ; their inner ends vary a good deal in different genera,
and there is considerable discrepancy in the accounts of
different observers. In the freshwater TZetrastemma the ends
of the branched ducts are said to terminate in flame cells, and

Fic. 80.— Diagrammatic sections to
show disposition of internal organs
in (I.) Carinella, a Palaeonemertine,
and (II.) a Schizonemertine.

1. Cellular portion of integument.
2. Basement membrane.
3. Circular muscular layer.
4, Longitudinal muscular layer.
5. Second circular muscular layer in I.
6

. Second longitudinal muscular layer
in IT.

7. Nervous layer.

8. Lateral nerves.

9. Cavity of proboscis sheath.
10, Proboscis or introvert.

11. Intestine.

12. Lateral blood-vessels.

13. Dorsal blood-vessel.

14. Connective tissue.

the whole system is compared to that of Turbellarians. The
system is embedded in the parenchyma. In Carinella a portion
of the wall of the lateral blood-vessel is modified to form the
internal end of the nephridium. This forms a spongy gland
which is continuous with the duct, the latter is also stated to
open at two points into the blood-vessel.

The central nervous system consists of two pairs of ganglia
in the head united by two commissures. One of these, the

NEMERTEA 121

smaller, lies dorsal to the proboscis sheath, the other between
the proboscis sheath and the oesophagus. It will thus be
seen that the proboscis is surrounded by a nerve ring, a re-
lationship to the nervous system which is usually confined to
the alimentary canal of Invertebrates.

The dorsal and ventral ganglion are separated by a deep
eroove. The dorsal half gives off nerves to the eyes and
fore part of the head. The ventral half is continuous with
the main lateral nerve trunks. These two trunks run back on
each side of the body, embedded in the layer of longitudinal
muscle fibres. In Schizonemertea there is a third lobe borne
on the dorsal aspect of the brain; and in Hoplonemertea this
lobe may be distinct and connected with the brain only by
a nerve. In some species it is hollow, and its walls ciliated.
In the last-named subdivision the longitudinal nerves give
off numerous segmentally-arranged nerves, but in the Palaeo-
and Schizo-nemertines these are replaced by a delicate plexus
which lies between the external longitudinal and the circular
muscles (Fig. 80). The main trunks may unite above the
anus in the Hoplonemertines, as in Peripatus and Chaeto-
derma. A median nerve runs back from the supra-proboscidian
commissure and supplies the proboscis sheath and proboscis.

The sense organs in Tetrastemma consist of four eyes
which seem to be little more than pigment spots devoid of
lens or other accessories.

A ciliated groove exists on each side of the head; each of
these leads into an oval sac which comes into close relationship
with the cerebral ganglia. These are the lateral organs, and
their nature is the cause of much discussion. They appear to
arise in the Schizo- and Hoplo-nemertines partly from the
epiblast of the skin and partly from the oesophagus. In the
Schizo-nemertines, where the nervous system is coloured red
with haemoglobin, they have been regarded as_ respiratory
organs; but this does not explain their use in the other two
subdivisions, and they have been variously regarded as sense
pits and as excretory organs. The arrangement of their ex-
ternal ciliated openings affords a useful basis for classification.

Tetrastemma, like most members of the class NEMERTEA, 1S
dioecious. The ovaries and testes are arranged along each

122 ZOOLOGY

side of the body, alternating with the diverticula of the ali-
mentary canal (Fig. 77). They consist of sacs which arise in
the dorso-ventral muscles (dissepiments), and are at first
closed. The ova and mother-cells of the spermatozoa are prob-
ably derived from the cells lining the walls of these sacs.
When the reproductive cells are ripe, each sac opens to the
exterior by a dorsally-placed pore. The eggs are often de-
posited in mucous tubes secreted by the skin. Geonemertes
palaensis, Tetrastemma hermaphroditica, and T. Kefersteinit, are
hermaphrodite ; and Prosorhochmus Claparedit and Monopora
vivipara bring forth their young alive.

Among the ciliated ectodermal cells of many Nemertines,
a number of unicellular glands occur; their secretion forms a
copious mucus, which usually takes the form of a tube, in
which the animal lives for a time, and which may be
strengthened by grains of sand, ete.

The opening of the mouth is beneath or behind the
cerebral ganglia, and in Akrostoma, Malacobdella, and some
others, the proboscis opens into the dorsal side of the mouth.
The proboscis may be armed with rhabdites, and some observers
have described nematocysts in Cerebratulus, etc.; these obser-
vations, however, have not been confirmed. The morpho-
logical nature of the proboscis and its sheath affords matter
for much divergence of opinion. It is usually regarded as a
developement of the anterior protrusible and retractile part of
the body which occurs in the Turbellarian Proboscidea,
Hubrecht, who has advocated a relationship between the
NEMERTINES and the CHorDATA, regards the hypophysis cerebri
of the latter as representing the proboscis, whilst the notochord
represents its sheath. The latest writer on the subject,
Biirger, lays stress upon the fact that the opening of the pro-
boscis is never quite terminal, and on the relationship it holds
to the mouth. He is inclined to regard the organ as a great
developement of the Turbellarian pharynx, which has ceased to
open into the alimentary canal, and has acquired a hollow
sheath into which it can be withdrawn.

In the Palaeo- and Schizo-nemertines the blood-vessels
break up into a series of lacunar cavities in the head. In
Drepanophorus the corpuscles are red with haemoglobin.

NEMERTEA 123

In Langia the lateral cords approach each other dorsally :
an arrangement which, according to Hubrecht, might result in
the formation of a dorsal cord such as is found in the Chordata.

The group as a whole is carnivorous, the larger species
feeding on the tubicolous Chaetopods. They have the power
of breaking up into pieces when irritated, and it is said the
Schizonemertines can reproduce a head in connection with the
various fragments.

The NEMERTEA are classified as follows :

(i.) Palaeonemertea.—WNo deep lateral slit on the side of the
head. No stylet in the proboscis. Mouth behind the
level of the cerebral ganglia. Carinella, Polia.

(ii.) Schizonemertea.— A deep longitudinal slit on the
side of the head, which leads to a ciliated duct which
passes down to the cerebral ganglion, Lateral nerve
trunks between the longitudinal and inner circular
muscle layer. Haemoglobin in the nervous system.
Mouth behind the level of cerebral ganglia. Lineus,
Cerebratulus, Langia.

(iii.) Hoplonemertea.—One or more stylets in the proboscis.
Mouth generally in front of cerebral ganglia. Lateral
nerves internal to the muscular layers. No deep longi-
tudinal slits on the side of the head. Akrostoma,
Drepanophorus, Tetrastemma, Geonemertes, Malacob-
della.

The older classifications divided the group into two sub-
divisions : the Anopla and the Enopla. The former corresponded
with the Palaeo- and Schizo-nemertines, the latter with the
Hoplonemertines.

CHAPTER VIII
NEMATODA

CHARACTERISTICS.— Animals with an elongated unsegmented body,
tapering at each end. A well-developed cuticle is secreted by
the epudermis. A digestive system is present, und the excretory
system takes the form of lateral ducts which open antervorly
by a median ventral pore. As a rule, they are dioecious,
and many are endoparasitic ; among the parasitic forms an
alternation of hermaphrodite and bisexwal generations may
occur. A ciliated epithelium is universally absent.

The Nematoda are colloquially known as thread-worms.
The order contains a great number of species, many of them
parasitic ; in fact, there are said to be as many species of para-
sitic Nematodes as all the other endoparasites together.
About twenty different species attack man, and they occur in
almost every organ of the body, often inducing sufficient trouble
to cause death. The free species are usually small, often
microscopic. The parasitic forms are as a rule larger, the Guinea
worm, Milaria medinensis, which lives in the subcutaneous
tissues of men and horses in the tropics, attains a length of
6 feet, and the female Hustrongylus gigas, which lives in the
kidneys of mammals, may be 3 feet or more long.

Ascaris lumbricoides inhabits the human intestine and
stomach, and is not uncommon in children. It is a white
cylindrical animal pointed at each end. The female measures
from 9 to 14 inches in leneth. The male is about half as
long; it is rarer than the female, and may be distinguished by
its curved hinder end, and the presence of two bristles in the
neighbourhood of the anus.

The mouth is terminal and surrounded by three lips, a

NEMATODA I2

ur

median dorsal one bearing two tactile papillae, and two lateral.
The anus is a transverse opening close to the hinder end. The
excretory opening is minute ; it is situated on the ventral surface,
a little way behind the anterior end of the
body. The female generative pore is also in
the middle ventral line, about a third of the
total length of the body from the head. The
male generative organs open with the anus.

The integument consists of a _ well-
developed cuticle, which is turned in at the
various openings. The hypodermis which
lies under this cuticle is a granular layer of
protoplasm, with scattered nuclei, Within
this layer are the longitudinally-arranged
muscle - fibres (Fig. 82). These are very
peculiar cells, that part of them next the
hypodermis is transversely striated, and con-
tractile; the inner half, however, which is
turned towards the coelom, is granular, and
contains the nucleus of the cell. This mus-
cular layer is broken up into quadrants by
the presence of a dorsal, a ventral, and two
lateral areas. The coelom, which is bounded
by the granular portion of the muscle-cells,
contains a fluid, but it is doubtful if this is
corpusculated. There appears to be no
splanchnic mesoderm surrounding the ali-
mentary canal, and the coelom is probably
not homologous with that of a Chaetopod,
for instance.

The alimentary canal runs straight from
the mouth to the anus. The mouth leads
Fic. 81.—A lateral into an oesophagus lined by an infolding of

vee Siegen ee chitin, whose walls are very thick and
yuris, to show

the disposition of muscular, and its lumen is triradiate in

the various organs. : ae
Revor Caleb. transverse section. The oesophagus is

1. Mouth. 2. Oesophagus. 3. Enlargement of the oesophagus armed with
chitinous teeth. 4. Intestine. 5. Opening of the segmental tubes (placed by
mistake on the dorsal instead of the ventral surface). 6. Testes. 7. Vas
deferens. 8. Cloaca. 9. Papillae.

126 ZOOLOGY

separated from the intestine by a slight constriction.
The latter is often flattened dorso-ventrally, it possesses no
intrinsic muscles, and is lined by a layer of columnar cells
(Fig. 82). On both the outside and the inside of the canal is
a thin cuticle, apparently secreted by the columnar cells, and
the internal cuticle is perforated by a number of minute pores.
The rectum is of smaller diameter than the intestine, its walls
contain muscle-fibres ; in the male the vas deferens opens into
it, and its posterior end thus forms a cloaca (Fig. 81).

There is no vascular system in Nematodes. The excretory
system consists of two tubes, which run along the lateral line

Fic, 82.—Transverse section through about the middle of the body of Ascaris.
Slightly diagrammatic.

1. Dorsal median nerve. 7. Accumulation of granular protoplasm
2. Ventral median nerve. round—

3. Cuticle. 8. Lateral excretory canals.

4, Hypodermis, a granular layer. 9. Intestine.

5. Muscle-cells, the striated outer border. 10. Uterus with eggs.

6. Muscle-cells, the granular nucleated 11. Ovarian tubules.

inner part.

of the animal, separating the longitudinal muscles of each side
into a dorsal and a ventral portion (Fig. 82). Almost a third
of the body-length from the anterior end these two canals give

NEMATODA 127

off transverse branches, which unite, and open by a minute
pore in the ventral middle line. The canals end blindly, their
walls consist of a granular protoplasm containing nuclei con-
tinuous with the subcuticular protoplasmic layer, and of an
internal refractive layer. They contain a fluid.

The granular layer of protoplasm which hes between the
cuticle and the longitudinal muscles is also heaped up in the
middle dorsal and ventral lines, thus forming a ridge sur-
rounding the dorsal and ventral nerves. This separates the
dorsal and ventral longitudinal muscles into two lateral halves.

The nervous system consists of a ring surrounding the
oesophagus, which may be swollen into an inconspicuous
ganglion on the ventral side. The ring gives off anteriorly six
short nerves which run towards the head; of these two are
lateral and run in the lateral line, and the other four are
arranged symmetrically, one each side of the dorsal, and one
each side of the ventral middle line. ‘The ring gives off
posteriorly a dorsal and ventral median nerve, the chief
nerves in the body. The ventral nerve stops in front of the
anus, where it bears a ganglion. The dorsal and ventral
nerves are connected at intervals by lateral commissures,
which usually arise alternately. Probably four smaller nerves
also pass backward from the oesophageal ring, lying in the
same lines as the four small nerves which run to the head.
The nerves all lie in the granular protoplasm surrounded by
the longitudinal muscles.

The sexes are separate. The male reproductive organs lie in
the hinder third of the body (Fig. 81). The testis is single, and
consists of a long tube which winds about in the body-cavity,
and at its lower end opens into the long vesicula seminalis.
The testis is lined with a layer of nucleated protoplasm. The
mother cells of the spermatozoa arise from a central rachis ;
when they break off from this they divide into two and then
into four, each quarter then becomes a spermatozoon. Whilst
in the body of the male, the spermatozoa have a rounded out-
line, but when introduced into the female they exhibit
amoeboid movements. This peculiarity, together with the
absence of any tail to the spermatozoa, is characteristic of the
group of Nematodes.

128 ZOOLOGY

The testis opens into a vesicula seminalis of a much
greater diameter than the testis tube, its lining epithelium
throws out processes into the lumen which resemble pseudo-
podia. These possibly perform the same function as the cilia
which usually occur in the vesicula seminalis of other animals,
cilia being entirely unknown in Nematodes.

The vesicula seminalis opens into a ductus ejaculatorius,
with muscular walls. This ductus opens on the dorsal side
of the rectum. On each side of it is a sac containing a
chitinous spicule which is protrusible, and is doubtless used
in copulation.

The female organs are double, and consist of ovaries,
oviducts, uteri, and a vagina, the latter opening on the
ventral middle line. The ovary consists of a tube in which
the egg cells are formed in enormous numbers as stalked
structures borne on a rachis. The oviduct differs from the
ovary only in containing free ova, it leads on each side into a
uterus in which numerous spermatozoa are found, and where
the fertilisation of the ovum takes place. The two uteri
unite, and open by means of a short vagina to the exterior.

The eggs are laid in millions, each surrounded by a smooth
shell. The embryos develope in water or in damp earth, and
are probably introduced into their human host by the drinking
of dirty water.

The majority of Nematodes are parasitic, at any rate during
a portion of their life, but a good many lead a free existence in
damp earth, moss, and decaying matter, or in salt or fresh
water. These are mostly minute forms, and are capable of
withstanding a considerable amount of desiccation. The free-
living forms, with certain others that inhabit plants, are
included in the family Anguillulidae.

Tylenchus tritici does great damage to corn crops, its
presence leads to the grains of corn being replaced by a dark
brown gall. Inside this gall a small cluster of these minute
worms are found. When one of the galls is sown with the
seed, and rain follows, the parasites leave the gall and infest
the young plants. The parasites pair within the gall on the
corn ear, and eggs are laid within the gall.

Amongst the Nematodes which are parasitic in animals,

NEMATODA 129

Ascaris nigrovenosa has a curious history. It is a common
parasite in the lungs of frogs and toads, and in these hosts the
parasites are hermaphrodite. Their eggs pass into the ali-
mentary canal of the Amphibian, and eave the body, the
embryo then developes into a bisexual form known as the Rhab-
ditis generation; in this form the ova develope in the uteri,
and the young embryos, making their way through its walls,
devour the whole interior of their mother until only the
cuticle remains, they then emerge and live in mud or water
until swallowed by a frog, when they resume the first form.

Oxyuris vermicularis inhabits the human intestine, and
is particularly common in the caecum; its ova when laid con-
tain embryos already mature, hence it spreads with great
rapidity. The ova are swallowed, and the solvent action of
the gastric juice sets free the young embryos in the stomach,
whence they pass into the intestine.

Filaria sanguinis hominis passes its larval life in the body
of mosquitos, but the sexual female inhabits the lymphatic
glands of man in Australia, India, China, and Egypt, giving rise
to elephantiasis, ete. The embryos circulate in the blood and
give rise to further disease; they are readily sucked up by a
biting mosquito, and in this way the parasites are doubtless
disseminated.

Trichina spiralis (Fig. 83) is a very minute Nematode which
encysts in or between the muscle fibres. The adult worm lives

Fic. 83.— Trichina encysted

. ioe - amongst muscular fibres.
: ita tas SS FATT ((((((((( © 2
mc la cin aA After Leuckart.

i cc (( ([e«« (as

((
CUCM Ce

in the alimentary canal of man and of other carnivorous mam-
mals; it is viviparous. The young bore their way through the
wall of the intestine of their host and encyst in the muscles.
They do not become sexually mature unless eaten by some
animal,—often a rat, and sometimes a pig,—in which case its
flesh is liable to become “ trichinised,’ and may carry the
disease Trichinosis to man.

130 ZOOLOGY

Nematodes are usually arranged in several families, as the
Ascaridae, the Filariidae, the Anguillulidae, the Strongylidae.
The grouping of these families into larger subdivisions is a
matter of considerable difficulty, and no system which has as
yet been proposed has met with general acceptance.

CHAPTER IX

HIRUDINEA

Rhynchobdellidae—Pontobdella, Clepsine.

Hirudinea Gnathobdellidae—Hirudo, Nephelis,

CHARACTERISTICS.— Animals with a ringed integument, a certain
number of the annuli or rings corresponding with each
true segment. A posterior ventral sucker formed by the
Jusion of some of the posterior somites is present. The
coclom is much reduced by the ingrowth of connective tissue ;
it communicates with the vascular system, and contains the
same fluid. The mouth is anterior, and usually surrounded
by a sucker; the anus ws dorsal to the posterior sucker.
Hermaphrodite, with genital openings ventral and median,
the male in front of the female. Mostly aquatie and blood
sucking.

Amongst the Triclade Turbellarians a certain segmentation
begins to appear, and reaches its highest point in Gunda seg-
mentata, where the alimentary canal has 25 lateral divert-
icula, there are 25 testes and 24 pairs of vitellaria, and
the dorso-ventral muscles are arranged segmentally. In
the Nemertines we also find every stage from entirely un-
segmented animals to those in which the alimentary canal,
the generative organs, the blood-vessels, the muscles, and
even the proboscis sheath, present a certain repetition of parts
which is called segmentation. It is usual, but by no means
universal, for the segmentation of the various organs to agree,
so that one segment of the body contains a segment or repre-
sentative of each system of organs. Very often, however,
some segments of one organ may be suppressed, or fail to
develope ; and again many segments of one system of organs, as,

to

ZOOLOGY

for example, the segmentally-arranged nerve ganglia, may fuse
together, and thus the segmentation becomes irregular,

The Hirudinea are the first group in which segmentation
forms a distinctive feature. The integument is ringed, and in
the medicinal leech, Hirudo medicinalis, five annuli correspond
with a segment, in Pontobdella four, and in Lranchellion three.
The limits of each true segment are, however, marked out by
the arrangement of the colour bands.

A cuticle corresponding with the mucous tubes of Nemer-
tines is formed from the secretion of unicellular glands; it is
constantly being worn off and replaced.

The body-cavity is much reduced by the great developement
of muscles and connective tissue, and in the medicinal leech
its chief remains form the dorsal and ventral sinuses, it is,
however, more conspicuous in the Rhynchobdellidae.

The bodies of those forms, such as Clepsine and Nephelis,
where the muscles are strongly developed and the connective
tissue is sparse, are peculiarly firm and rigid, but forms lke
Aulostoma, and to a less extent Hirudo, where the connective
tissue predominates, are extremely limp and flabby. The cells
of this connective tissue are embedded in a gelatinous matrix,
and they may assume the following characters : (1.) fat cells, or
cells crowded with fat globules, common in Clepsine; (ii.)
elongated branched cells crowded with globules which are not
fat, these pass into fibres at times; (ill.) pigment cells; (iv.)
vaso-fibrous and botryoidal cells, forming a tissue which
is composed of certain rounded cells crowded with brown pig-
ment and arranged in rows; by a change in their interior,
channels arise which pierce the cells, and these ultimately open
on the one side into the closed system of blood-vessels, and on
the other into the coelomic sinuses. The botryoidal tissue
appears to pass into the vaso-fibrous tissue by the cells
dividing and becoming small, and the walls becoming very
thin, and the nuclei of the cells dropping out. Many of the
minute capillaries thus formed run between the columnar
epithelial cells of the ectoderm, and here the oxygenation of
the blood takes place.

In Nemertines the vascular system is one with the
coelomic. The space which contained the corpusculated fluid

HIRUDINEA 133

was the space in which the inner ends of the nephridia lay,
and was archicoelic in its origin. In Hirudinea this space is
divided into two: a series of spaces lined with an endothelium,
the true vascular system ; and a series of sinuses with no special

Fic. 84.—Diagrams of transverse
sections: I., through Clepsine ;
II., through Hirudo. A. G.
Bourne.

a

Alimentary canal.
Dorsal sinus.
Nerve cord.
Ventral sinus.
Lateral sinus.

6. Ovary.

7. Dorsal blood-vessel.

8. Inner end of nephridium,
9. Testis.
0
1

)

oUe cot

.

. Lateral blood-vessel.
. Nephridium.
12. Vesicle of nephridium.

cellular lining, and enclosing various organs of the body, the
coelom. These two series of spaces open into one another
directly in the Rhynchobdellidae, and through the botryoidal
tissue in the Gnathobdellidae. In Clepsine (Fig. 84, I.) and
Pontobdella the dorsal sinus contains a dorsal vessel, the ventral
sinus contains the nervous system, a ventral vessel, the ovaries,
and in Clepsine the inner ends of the nephridia. There are
also two lateral sinuses in which in Pontobdella a lateral vessel is
found. In Hirudo (Fig. 84, IL.) there are a dorsal and ventral
sinus, and two lateral vessels. The ventral sinus encloses the
nervous system. The ovaries and testes lie in special sinuses.
The internal end of the nephridium is placed in the testis sinus
in those segments in which both occur.

The alimentary canal of Leeches falls into five sections:
G.) the muscular pharynx, which may possess two or more
commonly three jaws, and numerous glands whose secretion in
Hirudo serves to prevent the blood upon which the animal
lives from coagulating; (ii.) the oesophagus and proventri-

134 ZOOLOGY

culus, which in Hirudo is enormous, and produced into eleven
pairs of lateral caeca—it serves as a storehouse for the blood ;
(ii.) the digestive stomach, usually very small; (iv.) the intes-
tine ; and (v.) the rectum. Sections (i.) and (v.) are formed by
epiblastic invaginations. The alimentary canal of Aulostoma
is ciliated ; an interesting peculiarity, since this leech does not
live on blood, but on small water-worms, etc. The Rhyn-
chobdellidae have a protrusible proboscis.

The nephridium in Pontobdella (Fig. 85, I.) is a continuous

Fie, 85.—Diagrams of the ne-
phridia in (I.) Pontobdella and
(II.) Hirudo. A. G. Bourne.

if;
1. Funnels.

2. Branched network.

3, Caecal tubules,

4. External opening.
ne

. Funnel.

. Ducts in testis lobe.

. Ducts in main lobe.

Pon

Ducts in caecal end of main
lobe.

Ducts in apical lobe,

OK

. Unbranched tube passing to
exterior,

. Vesicle.

~I

8. External opening.

network of fine tubules, which is spread through the greater
part of the body. This network opens at intervals into a blood
sinus by 10 pairs of internal funnels occurring in the segments
9-18. The lumen of the funnel is usually occluded, a condition

HIRUDINEA 135

which is even more pronounced in Hirudo, The tubules con-
sist of simple or branched cells with an intracellular lumen,
they unite at intervals, increase in size, and open by an inter-
cellular duct at 10 external pores, Sranchellion and Piscicola
probably possess a similar nephridial network.

Clepsine and Hirudo have paired nephridia distinct from
one another. The funnel in Hirudo lies in the same blood
sinus as the testis (Figs. 84, IL, and 86); it consists of lobed
ciliated cells, and its lumen is always occluded. The ducts
leading from the funnel are much branched and intracellular,
they at length unite and open into a vesicle which leads to the
exterior (Fig. 85, II.). In Mephelis and Trocheta the funnel
lies in a hollow of the botryoidal tissue. It has recently been
maintained that the structures, usually ciliated and often oc-
cluded, which are found at the inner ends of the nephridia have
nothing to do with those organs, but may take some part in
maintaining the circulation of the blood.

The nervous system consists of two cerebral ganglia
and a ventral chain, which in Hirudo contains 23 gangha
(Fig. 86). The cerebral ganglia give off nerves to three
minute ganglia which supply the jaws, and also nerves to the
eyes and goblet-shaped sense organs. A number of simple
eyes are found in the head in most forms ; in Piscicola they are
also found in the posterior sucker. The ventral nerve-chain
lies in the ventral blood-sinus (Fig. 84, IT.).

Leeches are hermaphrodite; the genital openings are ven-
tral, median, and unpaired, the male being in front of the
female. In Hirudo there are nine pairs of testes, arranged in
segments 8 to 16; in Nephelis the testes are numerous, and
seattered irregularly. They open into short transverse ducts,
which unite into a longitudinal vas deferens. Each of the latter
becomes coiled at its anterior end, forming an epididymis, and
the two unite to form a single short duct. This opens to the
exterior by a muscular protrusible penis, at the base of which
prostatic glands are usually found (Fig. 86).

The true ovaries are filamentous bodies contained in
capsules. These capsules, usually called the ovaries, occur in
Hirudo in the seventh segment, one on each side of the nerve
cord. The internal openings of the oviducts perforate the walls

136 ZOOLOGY

of the capsule, and lie in its lumen. The cavity of the capsule
also contains certain amoeboid corpuscles, and probably repre-

is
7h ie
eee

oa.

Fig. 86.—Hirudo medicinalis, opened along the
median dorsal line, slightly diagrammatic. A. G.
Bourne.

1. Cerebral ganglion.

2. Oesophagus.

3. Ist postoral ganglion.
4, Penis.

5. Epididymis.

. Ovisacs.

. Vas deferens.

6
7. Glandular enlargement of the oviducts.
8
9

. 2nd pair of testes.

10. Lateral vessel.
11. 9th pair of nephridia.
12, Vesicle near external opening of nephridium.

13. 23rd ganglion.
14. Posterior sucker.

sents part of the coelom. The oviducts unite and pass into
a muscular vagina, their walls are glandular, and secrete an
albuminous fluid in which the eggs float in the cocoon.

The segments on which the reproductive organs open form
the clitellum, which consists of certain segments with glandular
walls, the secretion of which hardens and forms in most forms
a cocoon in which the fertilised eggs mature. In Clepsine the
eggs are attached to some foreign substance, and the female
sits over them till they hatch, and then they attach them-

HIRUDINEA 137

selves to her body. Nephelis deposits its cocoons on water-
plants, Aulostoma and Hirudo in damp earth.

Leeches are usually inhabitants of fresh water; sometimes
they live in salt water, and more rarely on land. They
usually move in loops by the aid of their anterior and posterior
suckers, but they can swim well. The land forms are most
common in Asia south of the Himalayas, and in the East
Indies and Australia. A gigantic form, Macrobdella Valdi-
viana, lives underground in Chili, and is said to reach the
length of 24 feet. They are, with few exceptions, parasitic,
living on the blood of Vertebrates.

The HrirupINEA are divided into two groups:

(i.) Rhynchobdellidae.— Cylindrical or flat, elongated body
with both suckers well marked, fore part of the body
retractile, forming a proboscis. The vascular and the
coelomic spaces are in direct continuity; the blood
does not contain haemoglobin. Pontobdella, Clepsine,
Piscicola.

(ii.) Gnathobdellidae.—Mouth sucker-like, pharynx armed
with three jaws. No proboscis. The vascular and the
coelomic spaces are in indirect continuity. The blood
contains haemoglobin. Hirudo, Aulostoma, Nephelis.

CHAPTER X
CHAETOPODA

Archiannelida,
Naidomorpha—JNais, Chaetogaster.
ongocasta{ becoming — Lumbricus, Megascolides,
Eudrilus, Perichaeta.
Errantia—WNereis, Aphrodite, Eunice, Tomopteris.
Sedentaria—Arenicola, Sabella, Capitella.

Chaetopoda
Polychaeta

CHARACTERISTICS.—Segmented animals, with a more or less pro-
minent prostomium or region in front of the mouth. Loco-
motion effected by cilia, or by setae implanted in the body
wall or borne by lateral processes of the body termed para-
podia. Hach seta ts the product of a single cell. The
segments are divided externally by grooves, internally by septa.
A pair of nephridia are typically found in each segment.
The Chaetopoda are divided into three sub-classes: the

ARCHIANNELIDA, the OLIGOCHAETA, and the POLYCHAETA.

ARCHIANNELIDA.

CHARACTERISTICS.— Marine worms with small prostomium. The
segmentation of the body is externally marked by rings of
ciliated cells, and by slight grooves. There are no setae or
parapodia or branchiae, but the head bears one or more pairs
of tentacles. The longitudinal muscles are in four bands.
The nervous system retains its connection with the hypodermis
throughout life. The head bears a pair of ciliated grooves.
The Archiannelida comprise a group of minute marine

animals, which are to some extent intermediate between the

Turbellarians and the Chaetopoda. The group includes four

genera: Polygordius, Protodrilus, Histriodrilus, formerly known

as Iistriobdella and classified with the leeches, and Dinophilus.

CHAETOPODA 139

Protodrilus Leuckartit is a small worm-like animal found
in the sand at Pantano, an inland arm of the sea in the neigh-

bourhood of Messina (Fig. 87).
It creeps about in a Nemertine-
like manner by means of the
cilia which clothe the body.
The segmentation is shown
externally by two rows of cilia
on each segment, and by slight
grooves which separate neigh-
bouring segments from one
another. The number of the
segments increases with the
age of the animal. The head
bears a pair of hollow ciliated
tentacles, into which a section of
the coelom extends (Fig. 87).
The ectoderm consists of
cubical epithelial cells, amongst
which the ducts of many uni-
cellular glands open. The cells
lining a shallow groove which
runs all along the ventral aspect
of the worm bear specially long
cilia. There is a double row
of cilia on the head in front of
the mouth, and an anterior and
a posterior circlet upon each
segment. Protodrilus, like Poly-
gordius, has no circular muscles ;

the longitudinal fibres are yg, 87.—View of Protodrilus Leuckartti.

arranged in four bands, two
dorso-lateral and two ventro-
lateral. An oblique longitudinal
muscular septum running from
each side of the body to near
the ventral median line divides the
and two lateral portions (Fig. 90).
The alimentary canal consists

oe eh

After Hatschek.

Tentacle.

Ciliated pit.

Oral cavity.

Muscular appendage of oral cavity.
Alimentary canal.

body-cavity into a median

of a ciliated oesophagus

140 ZOOLOGY

and an intestine. On the ventral wall of the oesophagus a
U-shaped tube opens; one limb of this tube is enormously en-
larged, and is very muscular. A somewhat
similar stomodaeal musculature occurs in
the pharynx of most Chaetopods, and would
seem to be comparable to the odontophore
of Molluses, and with the ventral part
of the muscular pharynx in Turbellarians.
The intestine is moniliform, there being a
constriction between each segment. It is
supported by the transverse septa and by
median dorsal and ventral mesenteries (Fig.
90). Its lumen is ciliated. The anus is
terminal.

The vascular system consists of a
median dorsal vessel, which sends a
branch along each tentacle. Other
branches bring the colourless blood back
from the tentacles, and these then fuse to
form the median ventral vessel. Certain
lacunae between the epithelial cells of the
intestine and its musculature appear to

Fic. 88.—View of a ne- Supply the dorsal vessel with the fluid it
phridium of Protodrilus eontains.

Leuckartii. After Hat- 6710 : :
schek. The nephridia consist of an internal

1. Internal opening funnel (Fig. 88), from the edge of which a
3 i ee large cilium depends into the lumen of the
3. Cilia of anterior ring tube which is ciliated ; this passes through
of the segment. . a0 5
4. Cilia of posterior &® Septum, as in ZLumbricus, and finally
ring of the seg- opens to the exterior on the lateral line.
5. Basin The nervous system remains in the
skin (Fig. 90); it consists of a cerebral
mass, with circum-oesophageal commissures, which pass into
two ventral cords. The latter are separated from one
another by the ventral groove, but are connected by trans-
verse commissures.
Protodrilus is hermaphrodite, Polygordius dioecious; the
ovaries lie in the first seven segments. The ova are derived
from some of the cells lining the coelom in the neighbourhood

CHAETOPODA I4I

of the ventral middle line (Fig. 90). The testes are similarly
built up from peritoneal cells, situated on both sides of the
oblique septa, in the segments which succeed the seventh.

pig)

wy

Ht
Hat

Fic. 89.—Polygordius neapolitanus. (After Fraipont.)

A. The living animal. x about 5. D. Portion of body, showing
B. Anterior end of the worm seen from the 1. Segments separated by grooves.
right side, more highly magnified. 2. Grooves.
1. Prostomium. E. Ventral view of posterior end, show-
2. Peristomium. ing the last three segments.
3. Tentacle. 1. Segment.
4, Setae on tentacle, 2. Groove.
5. Ciliated pit. 3. Anal segment,
C. Ventral view of the same. Numbers 4, Anus,
as in B. 5. Ring of papillae.
6. Mouth.

Histriodrilus, which lives parasitically upon lobsters’ eggs,
is somewhat more highly organised than Protodrilus. The
body is differentiated into regions, the nervous system has

142 ZOOLOGY

distinct ganglia in each somite, the stomodaeal muscular bulb is
armed with three teeth, and the sexes are separate.

ZN Rei
LAK
A

10 002C ony
Tel BIT:
ney

SS 7

Pe {
Tider
———

is}
12
12S

Fic. 90.—Polygordius neapolitanus.
A. Transverse section of a male Poly- 9. Oblique muscular septum covered
gordius, with coelomic epithelium.
1. Cuticle. 10. The testes.
2. Ectodermic epithelium. 11. Ventral nerve cord, continuous
3. Muscle plates. with 2.
4. Parietal coelomic epithelium. B. A spermatozoon. :
5. Visceral coelomic epithelium. C. Horizontal section of a mature female
6. Ciliated endodermal epithelium. Polygordius.
7. Dorsal blood-vessel in dorsal mesen- 1, 2, 3, and 6as in A.
tery. 12. The septa.
8. Ventral blood-vessel in ventral 13. Ova.

mesentery.

The body-wall has undergone partial histological degeneration, and is ruptured in
two places to allow the escape of the ova (13) which crowd the coelomic space.

Polygordius is the largest of the Archiannelids. PP.
lacteus is 40 mm. long (Fig. 89). The longitudinal ventral

CHAETOPODA 143

groove of Protodrilus has in this genus closed in, and forms a
canal within the nerve cord. ed blood occurs in this genus,
and the dorsal vessel gives off lateral branches, which, however,
end caecally. The sexes are distinct, and the ovaries or testes
arise in the posterior segments (Fig. 90).

The last member of the group, Dinophilus, is a minute
marine animal. ‘Two species, J). gigas and D, taeniatus, have
recently been described by Weldon and Harmer from the coast
of Devonshire and Cornwall. The body consists of a head or
prostomium, which bears two eye-spots, and whose cilia are
uniform or arranged in two preoral circlets. The mouth opens
on the second segment or peristomium, and then follow five
or six segments, and finally a postanal unsegmented tail. In
both the above-mentioned specimens the entire ventral surface
of the animal is uniformly ciliated, and each segment has one
or two bands of cilia. WD. vorticoides is uniformly ciliated all
over. The nervous system is in contact with the skin. The
coelom is traversed by strands of connective tissue in D. gigas ;
and in D. taeniatus there are more definite spaces connected
with the inner ends of the nephridia. In D. gigas an excretory
system of the Platyhelminthine type, with flame cells, has
been described, but in D. taeniatus and D. gyrociliatus, 5 pairs
of nephridia are found, each with a triangular appendage
hanging into the lumen of their ciliated duct. The sexes are
separate, and in the male YD. taeniatus the fifth pair of
nephridia appear to have become modified and form vesiculae
seminales. A penis is present, and seems to be inserted
indifferently into any part of the skin of the female.

There is little doubt that Dinophilus should be classified
with the other members of the group Archiannelids; on the
other hand, its median genital pore, the presence in some
species of the Platyhelminthine excretory system, and the
method of fertilisation adopted by PD. taeniatus which is
paralleled in the Polycladida, support the view of the Platy-
helminthine origin of these worms.

THE OLIGOCHAETA.

CHARACTERISTICS.— The Oligochaeta are characterised by the ab-
sence of antennae, parapodia, branchiae, and cirrhi. Their

144 ZOOLOGY

pharynx is devoid of armature. They are hermaphrodite,

and their reproductive organs are confined to a few segments.

Their ova are laid in cocoons. Their developement is direct.

The Oligochaeta were at one time divided into two
groups: the Terricolae, which live chiefly on land, and the
Limicolae, which are mostly aquatic. Recent research has,
however, broken down the structural barriers which were
believed to exist between the members of these two groups.
The oligochaet worms are now arranged by Benham in a
number of families, which allow themselves to be grouped in
two divisions: (i.) the Naidomorpha, in which asexual repro-
duction takes place; and (ii.) the Lumbricomorpha, in which it
does not. The earthworm is the most familiar example of the
latter subdivision.

One of the most curious features found in many of the
Oligochaets is the dorsal pore. In Lumbricus this pierces the
skin on each segment in the middle dorsal line, and places the
coelom directly in communication with the exterior. The pores
occur in this genus on all the segments except the first six or
seven. They are closed by a sphincter muscle, and opened by
an anterior and posterior longitudinal band of muscles. They
are found in several species of the Oligochaets,—Lumbricus, etc.,
—but do not occur in Polychaets. Megascolides, a gigantic
Australian worm, measuring from 4 to 6 feet in length, ejects
through its dorsal pores the milky coelomic fluid with which
it coats the walls of its burrows.

The function of the modified skin of certain segments
which constitutes the clitellum is to form the cocoons in
which the eggs are deposited. It may completely enclose the
body, and is then known as a cingulum, or it may be incom-
plete. In the aquatic forms it only includes one segment :
that on which the vas deferens opens. The capsulogenous
glands also found in the skin give rise to the albuminous fluid
found in the cocoon in which the ova and spermatozoa are
deposited. This secretion serves to nourish the developing
embryos.

The septa which divide the body internally into segments
are almost absent in Acolosoma; only one, dividing the head
from the body, is present.

CHAETOPODA 145

The setae vary a good deal in number and shape in differ-
ent species (Fig. 91), but each is the product of a single cell
which les at the base of the sac from which the seta protrudes.

The alimentary canal of many of the lower Oligochaets is
ciliated; in Lumbricus the lining epithelium from the mouth
to the gizzard secretes a cuticle, but the intestine is lined by

Fic, 91.

a. Penial seta of Perichaeta ceylonica.

6. Extremity of penial seta of Acan-

AA
‘s A x thodrilus. After Horst.

A ,
A c. Seta of Urochaeta. After Perrier.
ARK A
USK d. Seta of Lumbricus.

A\
ee e. Seta of Criodrilus.
KA f
Aah

modified retractile cilia. Criodrilus, which inhabits the mud,
and Pontodrilus, which lives on the sea-shore, have no gizzard ;
both these genera are also without nephridia in the anterior
10 or 15 segments. The typhlosole which is so characteristic
in the intestine of Lumbricus (Fig. 92) is also absent in the
latter genera as well as in Megascolides. In Rhinodrilus it
forms a spiral fold running round the intestine.

The blood is contained in a series of closed vessels. The
plasma of the blood is usually coloured red by haemoglobin
which is dissolved in it, and not confined to the corpuscles.
Numerous flattened corpuscles float in it. The coelomic fluid
found in the body-cavity contains colourless amoeboid corpuscles.

The nephridial system of leeches shows how a single pair
of nephridia in each somite, distinct from all the others, may
arise from a scattered network. In Oligochaets a similar series
of stages in the developement of a single pair of nephridia in

10

146 ZOOLOGY

each segment is found, and has been described by Beddard,
Spencer, and others. Perichaeta aspergillum has a nephridial
network of fine tubules which permeates the body. It is
doubtful if any internal funnels opening into the coelom exist
in the anterior segments, but they do in the posterior half of
the body, and here they are very numerous. On the other

SS
Sepa,
SON] \,

AB AY \} WN ly A
VZRAAAZY AD
NAS NGNAINIS BE

1

Fic, 92.—Diagrammatic transverse section through one of the posterior segments
of Lumbricus. Partly after Marshall and Hurst.

1. Nephridium. 8. Typhlosole.

2. Funnel of nephridium. 9. Dorsal blood-vessel connected by a
3. Nerve cord. vertical branch with typhlosole,
4, Epidermis, and by branches with intestinal
5. Circular muscles. blood plexus.

6. Longitudinal muscles. 10. Supraneural vessel.

7. Dorsal and ventral pairs of setae, 11. Infraneural vessel.

On the left side are indicated the chief vessels given off from the main trunk to
the body-wall and nephridium. After Beddard.

hand there are numerous openings to the exterior, both an-
teriorly and posteriorly. This network is continuous, and
shows no trace of segmentation. In P. armata there is a
similar network of fine tubules, but in addition there is in each
segment a pair of large nephridia which pierce the septum in

CHAETOPODA 147

front and open into the preceding segment by a well-developed
funnel. In Megascolides there are a great number of minute
nephridial tubules, consisting of a short straight tube and a
longer coiled tube, scattered all over the inner surface of the
skin. These small nephridia have an intracellular duct, and
are well supplied with blood-vessels. They open to the
exterior, but no internal opening has been found. In addition
to these smaller nephridia, the posterior half of the body has
in each segment a pair of large nephridia, with an internal
funnel-shaped opening. When: these large nephridia are
traced forward through the region of the middle of the body,
it is seen that they first lose their internal funnel, and then
gradually decrease in size, and ultimately merge into the
smaller nephridia. Thus the specialisation of the nephridia
appears to commence posteriorly. The small and large ne-
phridia are connected by a longitudinal duct.

The next stage towards the condition found in Lumbricus
is when the network becomes discontinuous at the septa,
and does not spread from segment to segment. This stage
is almost reached by Deinodrilus, and quite by Acanthodrilus
and Dichogaster. Then, as is shown in the case of P. armata
and Megascolides, certain of the tubules of the network enlarge,
and form large nephridia, and the network gradually ceases to
be formed. Two pairs of such large nephridia exist in each
segment in Brachydrilus; one pair then disappears, and the
condition of Lumbricus (Fig. 92) is attained.

The aquatic Oligochaets have one pair of nephridia in
each somite; the funnel is absent in Chaetogaster.

In certain land worms the nephridia of the anterior seg-
ments become modified, and undergo a very remarkable
change of function. In Acanthodrilus dissimilis, in Dicho-
gaster, and in Digaster, all three possessing a_nephridial
network, some of the tubules on each side of the pharynx
become connected with a duct which opens into the buccal
cavity. In Megascolides we have a similar change of function.
The walls of the pharynx are pierced by a number of tubules,
with an intracellular lumen, which opens into the cavity of
the alimentary canal, and whose secretions pass into the
pharynx. In every respect these tubules resemble the tubules

148 ZOOLOGY,

of the nephridial network. This extraordinary change of a
nephridium into a salivary gland is paralleled in the Arthro-
pod Peripatus, in which developement shows that the salivary
glands are modified nephridia.

Three giant fibres, consisting of a sheath with a clear con-
tents, occur dorsal to the ventral nerve cord in nearly all
Oligochaets. Connections have been recently traced between
them and the nerve fibres. Their function was formerly
thought to be solely for the purpose of support; hence they
have been termed the newrochord, and have been compared
with the notochord of the Chordata in their physiological
action.

The Oligochaets are hermaphrodite: in the CHAETOGASTRIDAE
the spermatozoa develope in the coelom, in Lumbricus the

Fig. 93.—Genital segments of
Iumbricus (slightly altered
from Howes’ Biological Atlas).
The left side represents the
immature, the right, the
mature condition, so far as the
male reproductive organs are
concerned. After Beddard.

1. Anterior pair of testes; the
second pair are in the
next segment.

. Seminal vesicles.

. Spermathecae.

Vas deferens.
Ovary.

Oviduct.
Receptacula ovorum.
Nephridia.

Nerve cord.

IO OP oD

Ser fe)

testes become enclosed in special vesiculae seminales which
are outgrowths from three of the septa (Fig. 93). In these
vesiculae the spermatozoa mature.

In the aquatic Oligochaets the ova ripen in the coelom
or in an egg sac similar to the vesiculae seminales of Lum-
bricus.

The testes are usually four in number, but there may be
only one pair, as in Geoscoler. There is a single pair of ovaries,

CHAETOPODA 149

which are very constant in position, being with hardly an ex-
ception in the 13th segment. In Hudrilus (Fig. 94) the ovary
is enclosed in a muscular sheath. The ciliated oviduct passes
through the sheath, and ends in a funnel-shaped mouth in the
ovary. The muscular sheaths of the oviduct and ovary are

Fie. 94.—Female reproductive apparatus of Eu-
drilus. On the right side the spermatheca has
been cut away to show the contorted oviduct, 4.

1. Ovary. 2. Spermatheca.

3. Gland opening into conjoined duct of sper-
matheca and oviduct. After Beddard.

4. Oviduct.

continuous. The oviduct is convoluted, and opens to the ex-
terior on the 14th segment, together with a spermatheca and
a small glandular body. The opening of the oviduct in Peri-

Fic. 95. —Diagrams of various earth-
worms to illustrate external char-
acters. A, B, C, anterior segments
from the ventral surface. D,
hinder end of body of Urochaeta.

A. Lumbricus; 9 and 10, segments
contain spermathecae, the ori-
fices of which are indicated ;
14, segment bears oviducal
pores ; 15, segment bears male
pores; 32, 37, first and last
segments of the clitellum.

B. Acanthodrilus ; 1, orifice of sper-
mathecae ; ? , oviducal pores ;
3, male pores,

C, Perichaeta; the spermathecal pores
are between segments 6 and 7,
7 and 8, and 8 and 9, the ovi-
ducal pore on the 14th, the male
pores on the 18th segment.

In all the figures the nephridial
pores are indicated by dots, the setae
by strokes.

chaeta 1s single and median. The various positions of the
genital apertures, and their relations to the nephridia and setae
in various genera, are shown in Fig. 95. In the aquatic
Oligochaets the nephridia are not found in those segments
which lodge the reproductive organs and their ducts; in
the terrestrial forms they coexist. Some of the setae in the

150 ZOOLOGY

neighbourhood of the reproductive segments are modified and
assist In copulation (Fig. 91).

Certain of the aquatic Oligochaets multiply asexually by
fission. In Aeolosoma, in many respects the most primitive of
the Oligochaets, one of the segments enlarges, forms a pro-
stomium, and then breaks off from the anterior half. In the
NAIDIDAE and the CHAETOGASTRIDAE, a “zone of fission ” is formed
between two segments when the worm has reached a certain
size. This zone divides into two halves; the posterior of these
forms a head for the posterior set of segments, the anterior
gives rise to a series of new segments forming the tail of the
anterior animal. In this way chains of zooids are formed.
These at length are set free, and differ from the mature
worm only in the absence of the reproductive organs, clitellum,
and genital setae, which they acquire later.

No asexual reproduction is known amongst the Lumbrico-
morpha, but they possess a considerable power of reproducing
lost parts.

THE POLYCHAETA.

CHARACTERISTICS.—Marine worms, with numerous setae in bundles
borne on parapodia. The head is distinct, and usually bears
tentacles and palps ; the somites of the trunk carry cirrhi and
sometimes branchiae. As a rule the Polychaeta are dioecious
and have an indirect metamorphosis.

The Polychaeta are divided in (i.) the Errantia and (ii.)
the Sedentaria or Tubicola ; these subdivisions are characterised
as follows :

(i.) The Errantia are free and carnivorous, with a large pro-
stomium, which usually bears tentacles and eyes. The body is
rarely divided into regions ; the parapodia are large ; the pharynx
is protrusible and provided with ehitinous jaws or with papillae.

APHRODITIDAE, EUNICIDAE, NEREIDAE, SYLLIDAE, ALCIOPIDAE,
TOMOPTERIDAE.

(ii.) The Sedentaria are tube-building worms, whose. tube may
be fired. Body often divided into regions. Prostomium and para-
podia small ; pharynx never armed with teeth ; vegetable feeders,

CHAETOPODA I5I

ARENICOLIDAE, CAPITELLIDAE, CHAETOPTERIDAE, TERE-
BELLIDAE, SERPULIDAE.

The Polychaeta include a vast variety of worms, which
either swim about freely in the sea or inhabit tubes, from the
open mouth of which they often protrude the anterior end of
their bodies. They are very generally brightly coloured, and
many of them, especially the fixed forms, with their feathery
tentacles and branchiae, are objects of great beauty. With
three exceptions, they are exclusively marine; a few are pelagic,
and, as is usual with such a habit of life, their body is trans-
parent. One or two only are parasitic, one
living in the coelom of the Gephyrean Bonellia,
another in the branchial cavity of a barnacle,
Lepas.

Arenicola piscatorum, the common lugworm,
is a member of the sub-division Sedentaria,
which tunnels out tubular passages in the
sand, boring down into it with its head, and
then turning the anterior end of the body
up again, thus assuming the shape of a U. It
can be dug up in considerable quantities in
sandy places round our coasts when the tide
is low; its presence being indicated by numer-
ous little heaps of cylindrical sand castings, the
undigestible remnants of its food.

The worm may attain the length of ten or
more inches, and is of a blackish-brown colour
with a tinge of green.

The body of the animal is divisible into
three regions (Fig. 96): an anterior or neck of
6 segments, a middle or gill-bearing region of
13 segments, and a tail region of variable

- c Fic. 96. — Areni-
length, in which the segments are not well gota piscatorwm.
marked.

The chief characteristic which separates Polychaetous
from Oligochaetous worms is the presence of parapodia.
These, when typically developed, are lateral outgrowths of
the body-wall of each segment, into which the coelom is con-
tinued. The parapodium is usually divided into a dorsal and a

152 ZOOLOGY

ventral half; the notopodiwm and the newropodium respectively.
Each of these may bear (i.) a bundle of bristles, the setae ;
(i1.) in the midst of the setae, a single large bristle, the
aciculum; (iii.) solid fleshy prolongations of the body-wall,
containing a nerve, and probably tactile in function, the cirrhi;
(iv.) respiratory organs, processes of the body-wall well sup-
plied with blood-vessels, and sometimes containing a prolonga-
tion of the body-cavity, the branchiae. These last are borne
as a rule only by the notopodium.

The parapodia are not well developed in Avenicola. The
first nineteen segments bear each a small notopodium in
which a bundle of setae spring, and on the ventral surface a
small neuropodium, which bears a row of hooked bristles.

The gills borne on the 7th to the 19th segments are
feathery branched structures, through whose thin walls the red
blood is visible. The tail bears no parapodia.

Each of the segments of the body is divided into five small
rings: an unusual feature in Chaetopods, recalling the annula-
tion of the HIRUDINEA.

The integument consists of the same elements as are
found in Lumbricus: (1.) a cuticle, (i1.) an epidermis of columnar
cells crowded with pigment cells, (i11.) a continuous sheath of
circular muscles, (iv.) a layer of longitudinal muscles, much
broken up by the presence of the bundles of setae, etc., and
(v.) a lining of peritoneal epithelium.

The coelom is very spacious; at the anterior end of the
body it is traversed by three septa, which mark the limits of
the first three segments. There are no other septa in the first
nineteen segments, but the tail is divided into as many
chambers as there are rings by vertical septa. The body is
further partially divided into three divisions by two longi-
tudinal incomplete mesenteries, which run obliquely from the
side of the body to near the middle ventral line. The central
division lodges the alimentary canal, the lateral contain the
nephridia. This dividing up of the body-cavity recalls the
arrangement in the Archiannelids. The coelom is full of a
corpusculated fluid, in which, during the breeding season, the
ova and spermatozoa are found in great quantities.

The alimentary canal runs in a straight line from the

CHAETOPODA 153

mouth to the terminal anus. The pharynx can be protruded,
and is then seen to be covered with papillae. The mouth opens
into the oesophagus, which bears at its hinder end a pair of
long glandular bodies, possibly homologous with the calciferous

Fic. 97.—Anterior end of Avrenicola piscatorum laid open
by a median dorsal incision to show the internal
organs. After Vogt and Yung.

. Proboscis beset with papillae.

aan

i2759 90)
moo tb et

. Oesophagus.
. Muscles which retract the oesophagus.

ES

DABLST ae.

. Diverticula which open into the hinder end of the
oesophagus,

5. Stomach.

6. Intestine.

71 and 71°, 1st and 13th, or last, branchia.
. Masses of chloragogenous cells.

. Heart.

10. Dorsal blood-vessel.

. Vessels to and from the branchiae.

at
=
ral
|
2
ws |
|

an
om
om
a
=
re
1

Ain
ASUAY AMEE,

Na
|
si

7
i!
to

. Nephridia.

glands of Lumbricus (Fig. 97). The intestine, which traverses
the gill-bearing region, is coloured yellow by the presence of
yellow chloragogen cells in its walls, resembling the similar cells
on the walls of the intestine in Lumbricus. These cells con-
tain concretions, which seem to be set free in the coelomic fluid,
and are possibly excreted by the nephridia. The walls of the
intestine are somewhat wrinkled, and are rather thin. The

154 ZOOLOGY

lumen of the alimentary canal is usually distended with sand,
which is eaten in large quantities by the worm for the sake
of the small amount of vegetable debris which may be mixed
with it. At the commencement of the tail the intestine passes
into the rectum, which is supported by the numerous septa of
this region, and ends in the terminal anus.

The blood-vessels consist of (i.) a dorsal vessel (Fig. 97),
which at the anterior end anastomoses with the ventral vessel
—the blood flows forward in this; (ii.) a ventral vessel under-
neath the alimentary canal, in which the blood flows backward ;
(ii1.) a subintestinal vessel which les in the wall of the
intestine parallel and dorsal to (i1.). In the first six of the
gill-bearing segments this vessel receives the efferent vessels
from the gills. There are also a pair of small lateral vessels
which end anteriorly in the heart.

The heart consists of a pair of enlarged, muscular, con-
tractile transverse vessels, which le in the sixth segment.
They receive blood from the dorsal, subintestinal, and lateral
vessels, and by their contraction force it into the ventral
vessel. There are numerous capillaries given off from the
chief vessels to supply the various organs of the body; the
blood is red.

The blood in the ventral vessel is mainly venous, in each
of the thirteen segments which carry gills this vessel gives off
a pair of afferent branchial vessels, one of which passes to
each gill. The gill consists of a number of branching fila-
ments, into each of which the body-cavity is prolonged. Up
one side of the filament runs the afferent vessel; down the
other side courses the efferent vessel to open in the seventh to
the twelfth segments into the subintestinal vessel, and in the
thirteenth to the nineteenth segments into the dorsal vessel.

The nephridia are twelve in number, a pair being found
in each of the last four segments of the neck and the first two of
the gill-bearing region. They consist of the usual funnel-shaped
opening into the body-cavity, of a large vesicle which opens to
the exterior, and of a glandular swelling which opens into the
vesicle, and is probably the secreting portion of the apparatus.
In the breeding season the whole organ is crowded with ova
or spermatozoa.

CHAETOPODA 155

The nervous system consists of two small cerebral ganglia,
which are connected by circum-oesophageal commissures with
a ventral cord which is embedded amongst the longitudinal
muscles. This gives off a number of lateral nerves, and is
supported by two giant fibres, but does not exhibit any divi-
sion into ganglia and inter-ganglionic connectives.

Arenicola has no eyes, but it possesses what are not com-
mon in Chaetopods, namely otocysts. On each of the cerebral
ganglia a small hollow vesicle is found. The walls of this
consist of connective tissue with a lining of very columnar
cells, probably ciliated. The vesicle contains a fluid in which a
number of concretions—otoliths—float ; a special nerve passes
to its walls. The whole structure is strikingly like the otocyst
of many Lamellibranchs.

Arenicola is dioecious, and the ovaries and testes occupy
similar positions in the male and
female. The ova and spermatozoa are
formed from certain of the peritoneal
epithelial cells, which become in the
breeding season heaped up round the
bases of the nephridia. They break off
and float in the coelomic fluid, and jy4 98, ova originating from

leave the body through the nephridia. the lining epithelium of a
1 1 ee : parapodium of Tomopteris.
The head of Avenicola is not After Gegenbaur.

provided with any special appendage,
but in those worms which lve permanently in fixed
tubes, the anterior end of the body often bears the
branchiae, and is usually provided with tentacles. TZerebella
is provided with numerous tentacles, into which the coelom is
prolonged ; they are exceedingly extensile, and stretch out in the
form of a network all round the worm. Behind the tentacles
are situated the branchiae. The appendages of the prostomium
are sometimes distinguished by the name antennae from those
of the peristomium, on which the mouth opens, which are
termed the tentacles. Ventrally-situated palps, probably tactile
organs, are also common on the head. In some of the Serpu-
lidae a modified tentacle on the head forms an operculum, which
closes the tube when the worm is retracted.

The division into different regions, which is well marked

156 ZOOLOGY

in Arenicola, is even more conspicuous in some worms, @g.
Chaetopterus ; but it is not a general feature of the group.

Aphrodite, the sea-mouse, is a Polychaet of oval outline,
its notopodia bear a number of hairs, some iridescent, and
others which are matted together into a feltwork covering
the whole animal. This worm is further protected by a number
of plate-like elytra, also borne by the notopodia, but situated
beneath the feltwork ; they may be modified cirrhi, but the two
structures exist in some of the seg-
ments. Elytra are also found on
Polynoe.

The nature of the tubes of the
Sedentaria is very various. It may
be soft, or of a parchment-like con-
sistency, and it may be strengthened
by a deposit of grains of sand or shell,
or it may consist entirely of the latter,
very skilfully agglutinated together.

The SABELLIDAE (Fig. 99) and
SERPULIDAE, which live in fixed tubes
closed at the lower end, have a ventral
ciliated band, which is grooved in the
former family, whose function is to
carry up the undigested matter ex-
truded from the alimentary canal, and
pass it out of the tube.

In both subdivisions of the Poly-
chaeta the pharynx is often protrusible ;
Bea Savelin vacteolouat and in many Errantia it is armed

Mont. After Montagu. | With stout teeth, which in some species
of SYLLIDAE are said to be traversed
by the duct of a poison gland.

In the HestonrpaE (Fig. 100) and a few others a pair of
diverticula from the oesophagus,resembling in position the gland-
ular appendages of Arenicola, contain air, probably secreted
from the blood. The resemblance of these structures to lungs
has been noticed by many observers. Those families provided
with such structures have as a rule no branchiae. Another
family of worms, the CAPITELLIDAE, are provided with a

CHAETOPODA 157

“siphon,” that is, a tube which opens at both ends into the
alimentary canal. The siphon never contains food, and its
function is probably respiratory. A similar
structure runs from one part of the alimen-
tary canal to another in the Echiuridae,
and in Echinoids. The CAPITELLIDAE and
some other families are without any blood
system. In other worms the principal vessels
are similar to those deseribed in Avenicola ;
the red blood of some forms is due to
haemoglobin dissolved in the plasma, in
others the blood is green or almost colourless.

The typical arrangement of the nephridia,
one pair in each segment, is often interfered
with. They usually fail in the anterior
segments when there is a large pharynx, and
in the tubicolous forms their number is
usually much reduced: eg. eight pairs in Pe eee ae
Terebella and six pairs in Arenicola. The hae ce
genus Capitella are remarkable for having
several pairs of nephridia in each segment, the number increas-
ing in the posterior end up to six or seven pairs in this genus.
The nephridia are themselves subject to much variation ;
one nephridium may have several funnels, and may be con-
nected by a tube with another, and sometimes the organ
breaks up into small tubules. The whole arrangement recalls
the excretory system of some of the earthworms described
above.

The ventral nerve cord of some of the tubicolous Poly-
chaeta has its right and left half divaricated, and connected
by numerous transverse commissures. ‘This is well shown in
Serpula, and in a less degree in Sabella. Eyes are very generally
present, and are usually confined to the prostomium. Poly-
ophthalmus, however, has a number of lateral eyes, a pair to
each somite; whilst Branchiomma bears them on its branchial
filaments. Otocysts, such as those of Avenicola, are rare.

The Polychaets, with some exceptions, are dioecious. The
generative organs are usually developed in relation to a blood-
vessel, which no doubt serves to nourish them; in the Seden-

158 ZOOLOGY

taria they often correspond in number with the nephridia.
Their products ripen in the coelomic fluid (Fig. 98), and usually

escape through the nephridia,
| they may however escape by
Vea rupturing the body-wall, Im-
ah pregnation takes place exter-
nally. The eggs are sometimes
laid in small masses of jelly ;

REE

4
a

ie sometimes they remain under
\ps the care of the parent, under the
f ie } elytra in Polynoe, in a cavity in
1s the operculum in some SER-

: oe

PULINAE, and attached to the
tube amongst the TEREBELLIDAE.
Asexual reproduction is not
common ; it occurs, however, in
the SERPULIDAE and SYLLIDAE.
In the former family a head
is formed by one of the seg-
ments in the middle of the
Fic. 101.—Parent body, and the animal then
stock of Autoly- divides just in front of this.
tus cornutus.
After A. Agassiz. In some of the SYLLIDAE,
Autolytus, for example, one of
the posterior segments, usually the last, gives
rise to a new individual; this may be repeated,
and chains of zooids are formed (Fig. 101).
These zooids break off, develope generative
organs, and reproduce sexually. As the original
worm was without sexual organs, this genus
exhibits an alternation of generations; a very
uncommon phenomenon in Chaetopods. It is
further complicated by sexual dimorphism, the

i

sur

an Db
ae
.& \\
Wl

ps

‘

ia

a

h
Ary

y,
y

\

Ca
ee ey,
=.
. Css
BE
Beas

Fic. 102.—Wereis
pelagica, L.
After Oersted.

male worm being in many respects different in appearance from
the female. A somewhat similar phenomenon occurs in Nereis
(Fig. 102), one form being known as Heteronereis: this genus
is polymorphic, for in addition to the male and female forms,

hermaphrodite individuals also occur.

CHAPTER, Xi

GEPHYREA

{ Achaeta—Phymosoma, Sipuneulus, Phascolion.
| Chaetifera—Bonellia, Echiurus, Thalassema.

Gephyrea

CHARACTERISTICS.—Subeylindrical marine animals, with very
slight indications of segmentation. The anterior part of the
body is either retractile, forming an Introvert, or it bears an
extensile Prostomium. Setae or chitinoid hooks usually
present. The nervous system consists of a circum-oesophageal
ring and a ventral non-ganglionated cord. No special re-
spiratory or locomotor organs exist. A closed vascular system
is present, and the coelom is spacious. Nephridia are present,
and serve as a rule as ducts for the exit of the reproductive
cells, as well as functioning as excretory organs.

The Gephyrea are divided into two sub-classes :

I. The Achaeta, characterised by the anterior end of the
body being retractile. The introvert is withdrawn
into the body by special retractor muscles in the same
way as the proboscis of a Nemertine. No setae are
found, but the introvert is usually armed by rows of
chitinoid hooks. The mouth is anterior and terminal.

II. The Chaetifera have a segmented larva, but the segmenta-
tion is lost in the adult. There is a long extensile
prostomium which is easily broken off. A pair of
ventral setae are found. Anus terminal; special
branching organs open on the one hand into the coelom,
and on the other into the rectum, they possibly function
as nephridia. One to eight anterior nephridia serve
as genital ducts.

160 ZOOLOGY

The Gephyrea Achaeta include ten genera; of these Phas-
colion and Phascolosoma occur in our seas, the former usually
making its home in the shells of dead molluses, the latter
living at the bottom of the sea half buried in sand.

The largest genus of the class is Phymosoma; it

Fic. 103.—Semi-diagrammatic view of the right half of the head of Phymosoma varians,
seen from the inner surface.

1. Mouth. 8. Brain.
2. Lower ventral lip. 9. Circular nerves at base of ridges
3. Oesophagus. bearing hooks.
4, Portions of the coelom, seen in three 10. Sense organ at base of ridges bearing
places. hooks.
5. Blood sinus in lower lip corresponding 11. Rings of hooks.
with 4 in Fig. 105. 12. Retractor muscle.
5’, Blood sinus surrounding brain, and 138. Extensile collar.
opening into 5”, the dorsal vessel. 14. Pit leading to brain.
6. Skeletal tissue surrounding mouth. 15. Lophophore.
7. Ventral nerve cord. 16. Eye-spot.

contains twenty-eight species, which, with very few exceptions,
are confined to the tropics, in many respects it resembles
Phascolosoma, and, as its structure has been lately worked out,
it will form the most convenient type for description.

GEPHYREA 161

Phymosoma varians is a West Indian species found em-
bedded in the soft coral rock, in which it bores tubular
passages, probably dissolving the soft rock by some chemical
excretion. Its colour is brownish-yellow. In its extended
condition it is about 5 cm. long and about $ em. broad,
tapering at each end. ‘The anterior half of the body, the
introvert, can be withdrawn into the posterior half, just as
the finger of a glove can be invaginated into the hand.

The mouth is terminal, and is at the end of the introvert.
Dorsal to the mouth is a crown of eighteen or twenty short
tentacles arranged in a horse-shoe, the lophophore (Figs. 103 and
105). The dorsal ends of this horse-shoe are continuous with
the dorsal ends of a thickened lower lip, between which and
the crown of tentacles or lophophore the mouth opens. The
mouth has therefore the form of a crescentiform slit. In
the hollow of the horseshoe-shaped lophophore the skin is
wrinkled and pigmented; close beneath it, and in direct con-
tinuity with it, les the bilobed supra-oesophageal ganglion.
About 2 mm. behind the mouth, a very extensile fold of tissue
forms a ring-like collar round the base of the head. ‘This
collar can be produced so as to cover in the whole head.

The introvert is distinguished from the rest of the body
by the presence of numerous rows of minute chitinoid hooks
(Fig. 103), which alternate irregularly with certain papillae
to be described below.

The integument consists of the following layers: (i.) the
ectoderm, (i1.) circular muscles, (i1.) longitudinal muscles, and
(iv.) peritoneal epithelium. The ectoderm is a single layer of
cubical cells. Those covering the lower lip, and that side of
the tentacles turned towards the mouth, bear cilia. The
ectoderm of the concave side of the lophophore and its hollow
is crowded with black pigment, and at two places it is con-
tinuous with the substance of the brain. Over the rest of the
body the ectoderm secretes a thick cuticle, which is only
broken by the presence of the skin papillae.

These papillae are very characteristic of the Gephyrea ;
they are formed by the ectoderm becoming folded into the
shape of a double narrow-mouthed conical cup. The outer
layer of cells resembles the ordinary ectoderm ; the inner, how-

abil

162 ZOOLOGY

ever, are enlarged wedge-shaped cells which almost fill up
the cavity of the cup. They form a secretion which passes
out through the narrow opening. The mouth of this is
protected by special horny plates, modifications of the
cuticle. The papillae are scattered all over the body, and
as they stand out from the surface, they give the animal a
rough appearance.

Within the ectoderm is a layer of circularly-arranged
muscle fibres broken up into circular bands in the introvert,

Fia.104.—The body of Phymosoma
varians laid open by an incision
a little to the left of the median
dorsal line, so as to show the
internal organs. The introvert
is retracted,

et

Opening of introvert.

Position of brain, the two eye-
spots are shown. This marks
the level of the head.

Dorsal vessel.

iS)

Left dorsal retractor muscle.
Left ventral retractor muscle.
Generative ridge.

Ventral nerve cord.
Nephridia.

Coiled intestine.

Rectum.

Spindle muscle.

NS SUR go

se So

—
C=)

and forming a continuous sheath in the trunk; internal to
this are the longitudinal muscles, continuous in the introvert,
but arranged in about twenty anastomosing bundles in the
trunk. Within this layer, the coelom is lined by flat epithelial

GEPHVREA 163

cells. From the longitudinal bundles four stout muscles arise,
two dorsal and two ventral. These pass to form a muscular
ring ensheathing the oesophagus, just behind the head. They
are termed the four vetractors, and their function is to draw
in the introvert.

The alimentary canal consists of a straight oesophagus,
into which the mouth passes without any armature, and
which in its turn passes into a coiled intestine. Both these
parts are ciliated, the cilia of the oesophagus being continuous
with those of the lower hp and tentacles. The intestine is
coiled round a special “spindle” muscle, which arises from the
extreme posterior end of the body, passes up the axis of the
coil, and joins the longitudinal muscles of the body-wall near
the anus (Fig. 104). A short rectum passes to the anus
which terminates the alimentary canal, the anus pierces the
body-wall just behind the line of division between the introvert
and the trunk.

The vascular system is closed and is confined to the anterior
end of the animal. Its most conspicuous part is a vessel which
lies on the dorsal side of the oesophagus between the retractor
muscles. The vessel is closed behind, and gives off no capillaries.
At the anterior end it opens into a large sinus into which the
brain protrudes; from this sinus a circular vessel is given off
which runs round the lower lip, and when full of blood, it
serves to distend the latter. Another part of the vessel runs
along the base of the lophophore, giving off branches into each
tentacle. It is possible that the blood may become oxygenated
in the tentacles, but the chief function of the whole system is
to distend the tentacular crown and lower lip. The fluid in
this system is corpusculated.

The coelom is very spacious, and contains a corpusculated
fluid which bathes all the internal organs. The corpuscles
are larger than those of the vascular system. The contraction
of the circular muscles of the skin forces this fluid forward,
and in this way the introvert is everted.

The nephridia, or excretory organs, of the Gephyrea are
often termed “ brown tubes.” In Phymosoma they are two in
number, one on each side of the ventral nerve cord (Fig. 104).
They have the form of elongated sacs, which hang down

164 ZOOLOGY

into the body-cavity. At their upper ends the sacs are attached
to the body-wall, and open to the exterior a little in front of
the level of the anus. Each sac consists of two portions: a
posterior glandular part lined by large glandular cells, which

give off vesicles containing their excretion, and a muscular
non-glandular anterior half, which opens both on to the

Fie. 105.—Diagram showing
relation of nervous system, vas-
cular system, and oesophagus in
Phymosoma varians. Partly
after Selenka.

1. The brain, represented rela-
tively too small.
2. Nerves to skin of preoral lobe.

3. Lophophore ; each tentacle is
represented by its blood

sinuses and its nerve.

4, Blood sinuses of lower lip.

Or

Oesophagus.

Dorsal blood-vessel.

Su ge

Ventral nerve cord.

exterior and into the coelom. The opening into the latter
space is situated close to the external opening, and is guarded
by a frilled, funnel-shaped lip, thickly ciliated. The wall of
the organ contains many muscle fibres, and it is capable of
considerable change of form.

The nervous system consists of a bilobed brain in con-
tinuity with the epidermis of the concavity of the lophophore
(Fig. 105). It gives off a pair of lophophoral nerves, which
run along the base of the tentacles, sending off a nerve into

GEPHYREA 165

each. Laterally the two lobes are continued into stout
nerves which embrace the oesophagus, and fuse to form a
ventral cord. On each side the ventral cord is supported by
two longitudinal muscles, and the whole is loosely attached to
the ventral surface of the body-wall by muscular strands.
The cord shows but slight traces of double origin, it bears no
ganglia, but ganglion cells are uniformly distributed on its
ventral surface. It gives off a series of lateral nerves, which
form complete rings round the body, situated in the skin
(Figs. 103 and 105).

Two pits of large ectodermal cells, crowded with dense
black pigment, have sunk on each side into the brain. They
are hollow, and contain a coagulum in dead specimens. They
are usually spoken of as eyes.

Phymosoma is dioecious. Both the ovary and testis are
formed of a ridge of the peritoneal epithelium which runs
across the body at the base of the ventral retractor muscles.
Certain of the cells of this ridge break off and float in the
coelomic fluid. In the female they become ova, in the male
they are the mother cells of the spermatozoa. The ova grow
a good deal whilst in the body-cavity, and secrete a thick egg
shell; ultimately they leave the body through the nephridia.
The spermatozoa derived from one mother cell always remain
connected as long as they are in the body-cavity, and in this
condition are taken up by the funnel-shaped internal openings
of the nephridia. The ova are fertilised externally in the
water.

Certain of the Gephyrea achaeta differ in many points
from Phymosoma. Sipunculus has no lophophore, and the
mouth is surrounded by a frayed fringe, which, like the
tentacles of other forms, is well supplied with nerves and
blood-vessels.

Many species are without the hooks on the introvert.
A layer of oblique muscles les very commonly be-
tween the circular and longitudinal fibres. The capacity
of the dorsal vessel, which acts as a reservoir for receiving
the blood when the tentacles and head are retracted, is in-
creased in some species of Phymosoma by a number of lateral
diverticula, and in some Sipunculids by the addition of a

166 ZOOLOGY,

ventral vessel. Stpunculus and Phascolosoma have remarkable
bodies known as “urns” floating in their coelomic fluid. They
are bell-shaped structures, with a ring of cilia round the mouth,
anda nucleus. These remarkable corpuscles are formed by the
division of certain large cells on the wall of the dorsal blood-
vessel, they were formerly thought to be parasitic Infusoria.

The Achaeta have no special organs of locomotion, and
probably do not move about much. Sipunculus and Phas-
colosoma usually live half embedded in the sand, which they
swallow in large quantities. Phascolion lives in empty worms’
tubes or in molluse shells, and its body is often permanently
twisted, accommodating its shape to that of its home. Phymo-
soma lives in holes or passages in coral rock, or in holes
between stones. Asa rule the members of this subdivision
occur only in comparatively shallow water.

The Gephyrea chaetifera are provided with a_ pro-
stomium, which may acquire enormous proportions. In bonellia
it may, when fully extended, attain a length of 2 or 3 feet,
whilst the body is only 14 to 2 inches long. In this genus it
is bifid at the end. In Hehiurus, Bonellia, and Thalassema
there are a pair of large chitinoid hooks placed anteriorly on
the ventral side of the body, and in some species of Echiwrus
there is one, sometimes two, posterior circlets of setae, each
seta originating from a single cell, like those of the Chaetopods.

Bonellia viridis is coloured a bright green by a pigment
termed “bonellein,’ which is not identical with chlorophyll.
The mouth in the Chaetifera lies at the base of the pro-
stomium, which is ciliated and grooved, and is doubtless used
to catch minute organisms for food; the intestine is looped
and the anus terminal. In Bonellia, Echiwrus, and Thalassena
a “siphon” or collateral intestine, such as is found in the
CAPITELLIDAE and ECHINIDS, is present.

Branched organs open into the rectum in most of the
Chaetifera. At the end of each branch is a small funnel-
shaped ciliated opening leading into the coelom. The cells
lining the tubes of these branches have been seen crowded
with excretory granules, and they may possibly function as
nephridia as well as serve to regulate the amount of fluid in
the coelom.

GEPHYREA 167

The vascular system is more complex in the Chaetifera
than in the Achaeta. The dorsal vessel in Hehiwrus opens
behind into a circular blood-vessel which surrounds the oeso-
phagus. At its anterior end it enters the prostomium and runs
to the tip of this organ, here it splits, and the two branches
return, one down each side of the prostomium, till they have
passed the mouth, when they unite to form a median supra-
neural blood-vessel. This is connected with the peri-
oesophageal circular ring by a transverse vessel. Haemo-
globin has been detected in the coelomic corpuscles of
Thalassema.,

The last-named genus may have from one to four pairs of
nephridia, according to the species, Zchiwrus has usually two
pairs.

The nervous system, like the vascular system, is continued
into the prostomium, running all round the edge, and finally
uniting below the oesophagus, thus forming a circum-oeso-
phageal ring, which gives off the ventral cord. In no place is
the nerve ring or cord thickened to form anything like a
ganglion.

In #ehivrus and the female Bonellia the coloemic epi-
thelial cells which surround the ventral vessel enlarge and
form the reproductive cells, which are thus favourably situated
for receiving nourishment.

There is a very remarkable dimorphism in the genus
Bonellia. The female is a fair-sized animal, with a body 2
inches long, but the male is a microscopic planarian-lke
organism which lives in a recess of the nephridium of the
female. It is from 1 to 5 mm. long, and is ciliated all over.
Its intestine is not functional, and it ends blindly both in front
and behind. The spermatozoa arise from the coelomic epi-
thelium, and escape by a modified nephridium. A nervous
system; but no vascular system, is present.

The male larva is said to cling to the prostomium of ‘the
female, and thence to pass into the mouth, where it undergoes
its final changes, then it creeps out from the mouth and into
the nephridium, where it spends the rest of its life. Another
genus, Hamingia, has a similarly degenerate male, which also
lives in the nephridia of the female.

168 ZOOLOGY:

Those members of the armed Gephyrea whose developement
has been investigated show unmistakable affinities to the
Chaetopods. Their larvae exhibit a metameric segmentation,
but the somites disappear early. Traces of segmentation are
retained in the adult in a few cases, such as the four pairs of
nephridia in one species of Zhalassema, the double ring of
setae in Eehiurus Pallasii, and possibly in the rings of hooks
and circular nerves of many forms. A connecting link between
the Gephyrea armata and the Chaetopoda may exist in the
curious worm Sternaspis. This animal, usually classed with
the Chaetopoda, retains a well-marked segmentation ; and its
blood - vessels, whilst resembling in their disposition the
more important vessels of the Gephyrea, open into a well-
developed system of capillaries. On the other hand the looped
intestine, one pair of brown tubes, retractile anterior end of its
body, and—in Sternaspis spinosa—a long bifid prostomium, de-
scribed by Sluiter, are all features shared in common with the
Gephyrea.

The unarmed Gephyrea have an abbreviated developement
which shows no traces of metameric segmentation, but this
hardly seems a sufticiently important difference to warrant the
breaking up of the group.

CHAPTER XII

BRACHIOPODA

Ecardines—Lingula, Crania, Discina.

EE EERUSEOES Testicardines—Argiope, Terebratula, Waldheimia.

CHARACTERISTICS.—Coclomata devoid of organs of locomotion, and

usually fixed in the sand on to some foreign body, by a
peduncle. A bivalved shell encloses the body. The valves
are dorsal and ventral, and in one subdivision are hinged to
one another. They are lined by dorsal and ventral extensions
of the body-wall, termed the mantles ; these often bear chitin-
oid setae round their edges. A lophophore surrounds the
mouth, bearing ciliated tentacles. The alimentary canal is
ciliated, and receives the secretion of two branched glands, the
liver ; it is in one sub-division aproctous. One, rarely two,
pair of nephridia exist. Exclusively marine.

The existing Brachiopoda are interesting as the survival of

what in early geological time was a
very widely distributed and very numer-
ous group of animals. The two genera
Lingula and Discina extend from the
Cambrian, the oldest group of the
Silurian rocks, to the present day; and,
judging by their shells, they appear to
have undergone but little change during
the vast period of time which must
have elapsed since they lived. They are
found in great numbers, both of indi-
viduals and of species, in these older

Fic. 106.— Waldheimia
cranium.

A. Ventral,
B. Dorsal valve.

Paleozoic formations; but the group seems to have been most
flourishing in the Devonian seas, for upwards of 60 genera and

170 ZOOLOGY

1100 species have been described from Devonian rocks, Since
this epoch they have dwindled, and at the present day not
more than about 100 species exist.

Argiope (Cistella) neapolitana is a small Brachiopod found
attached by a peduncle to pieces of rock at a depth of about 70
metres in the Mediterranean. The dorsal and ventral shells
entirely cover the body except the peduncle, which projects
through a “beak” formed by the ventral or larger shell. The

Fic. 107.—A longitudinal vertical median
section through Argiope neapolitand.
Ventral shell.

Canal containing blood-vessel.

Sub-oesophageal nerve ganglion.

Pow Por

Mouth.

OO

Stomach.

2

Peduncele.

“I

Plexus of blood-vessels.

Median crest on dorsal shell.

i

Organic membrane which has separated
from shell during the process of de-

calcification.

dorsal shell is rather the smaller; both are of a brownish hue
with small white spots. The body of the Avgiope lies almost
entirely in the dorsal shell (Fig. 107), and is supported by
certain ridges which this shell bears on its inner surface. The

BRACHIOPODA 171

whole animal is about 2°5 mm. long, and about the same
in breadth.

The shells are secreted by the body-wall or by the
mantle. Since the body les chiefly in the dorsal shell, the
larger part of the latter is secreted by the body-wall, and the
dorsal mantle is of small extent; on the other hand, the
greater part of the ventral shell is lined by a fold of integu-
ment, the ventral mantle.

The substance of the shell is composed of minute calcare-
ous spicules kept together by a network of organic fibrils
(Fig. 107). The shell is pierced by numerous canals, whose
outer ends are somewhat enlarged and covered with a cuticle.

Since the mantle is formed of a duplicature of the body-
wall, it is necessarily double, and the body-cavity extends into
it, in some places this space lodges the reproductive organs.
The mantle sends a prolongation into each of the canals in the
shell, which is continuous with some of its blood-vessels. These
prolongations contain blood-
corpuscles, and doubtless
serve to nourish the organic
fibrils which keep together
the calcareous spicules of
the shell. The lophophore
occupies a considerable part
of the dorsal shell, and forms
a large part of the body-
wall. Its shape is oval, its
border running parallel to
the edge of the shell, except
at the anterior median line, ; a
where a narrow deep in- Last

Fic. 108.—Waldheimia flavescens. Interior

dentation almost divides it of dorsal valve, to show the position of the
into two, and thus gives lophophore. A portion of the fringe of
: cirrhi has been removed to show the
it a somewhat horse-shoe brachial membrane, and a portion of the
shape. The indentation is spiral extremities of the arms.

3 F : A. Position of mouth.
occupied by a median ridge

in the dorsal shell (Fig. 107). The lophophore carries
round its edge, on the dorsal side of the mouth, from
70 to 100 tentacles; at the base of the tentacles is a ciliated

172 ZOOLOGY

groove, whose other side is formed by a lip which also runs
round the edge of the lophophore (Fig. 109). The tentacles are
partially ciliated as well as grooved, and any particles of
food they come in contact with are carried down the
groove to the mouth, which opens in its posterior median line.
In other genera the lophophore stands out from. the surface of
the body and becomes curiously coiled and rolled up, as in
Waldheimia (Fig. 111), in which animal it is supported by a
calcareous loop.

The mouth is a transverse slit leading into a_ short
oesophagus; this is attached by mesenteric strands to the

Fic. 109.—Transverse section through the middle of Avrgiope neapolitana. The
section includes the posterior limit of the lophophore, but is anterior to the
brood pouches.

1. Stomach. 7. Ventral shell.

2. Gastroparietal bands. 8. Vascular canal in shell.

3. Ovary in dorsal shell. 9. Canal at base of lophophore, which
3’, Ovary in ventral shell. sends a branch into each tentacle.
4, Dorsal adjustor muscle. 10. Lip forming with the tentacles a
5. Occlusor muscle. groove.

6. Left mesentery; posteriorly this 11. Dorsal shell.

fuses with the right to form a
single mesentery.

end of the median projection of the dorsal shell, and it opens
directly into the globular stomach. On each side of the aliment-
ary canal is the liver, composed of six or seven thick tubules,
which unite and open into the stomach by a broad mouth.
The lumen of the liver is often full of secretion, it is lined by
vacuolated cells. The stomach opens behind into a short intes-
tine which has no anus, and which, like the rest of the aliment-

BRACHIOPODA 173

ary canal, is ciliated. The alimentary canal is supported by
a median sheet of connective tissue, the mesentery, which
passes from it to the ventral shell’ (Fig. 109), and by two lateral
sheets, termed the gastroparietal bands, which pass out from
the stomach to the sides of the body-wall.

Owing to the peculiar relations of the animal to its shell,
the body-cavity becomes very complicated, it is partly pro-
duced into the mantles which line the shells, and here the
reproductive organs partially lie. At the posterior and lateral
regions the body-wall is pushed in, in such a way as to form
two lateral brood pouches, which lie behind the level of the
lophophore, and are enclosed by the shell. The embryos
undergo the early stages of their developement in these pouches.

The coelom is traversed by four bundles of muscle fibres, two
of which open and close the shell, the other two move the shell

Fic. 110.—Waldheimia flavescens. Diagram showing the muscular system.
After Hancock,

1. Ventral valve. 7. Divaricators.

2. Dorsal valve. 8. Accessory divaricators.
3. Calcareous loop. 9. Ventral adjustors.

4. Mouth. 10. Peduncular muscles.
5. Extremity of intestine 11. Dorsal adjustors.

6. Adductor. 12. Peduncle.

on its peduncle. ‘The latter are termed adjustors, and a pair
arise from each valve of the shell and are inserted into the
peduncle. By their contraction they raise or depress the shell,
and by contracting alternately they may also serve to rotate it.
The occlusor muscles have a double origin from the dorsal shell,

174 ZOOLOGY

but the two parts unite to form a single tendon, which is in-
serted into the ventral shell. The divaricators are very small.
They arise from the ventral shell, and are inserted into the
dorsal valve in such a relation to the hinge as to cause the
shell to open when they contract. Additional muscles are found
in other members of the group, those of Waldheimia and Lin-
gula are shown in Figs. 110 and 113.

tunning round the edge of the lophophore, at the base of
the tentacles, is a canal which is probably continuous with the
general body-cavity. It gives off a branch into each tentacle,
and the latter are probably extended by the entrance of the
coelomic fluid into them (Fig. 109).

There is a closed vascular system containing a corpus-

=

<a) \

<a

SSS |

yy)

Frc. 111.—View of the inner side of the right half of Waldhetmia australis.
From a dissection by J. J. Lister.

1. Mouth. 9. Internal funnel-shaped opening of
2. Lophophore. nephridium.

3. Stomach. 10. Peduncle.

4. Liver tubules. 11. Body-wall.

5. Median ridge on dorsal shell. 12. Tentacles.

6. Heart. 13. Coil of lip.

7. Intestine ending blindly. 14, Terminal tentacles,

8. Peduncular muscle.

culated fluid. The vessels composing it are irregularly
scattered through the tissue of the body. They are especially

BRACHIOPODA 175

developed in the mantle and in those parts of the body-wall
next to the shell, and send off numerous caecal processes into
the canals permeating the substance of the latter. The blood is
probably aerated as it comes through the vessels of the mantle.
The presence of a central heart in Argiope is a matter of dis-
pute if it exists, it is a contractile vesicle situated dorsal to
the stomach; a spherical vesicle is found in this position in
Waldheimia, but its relation to the blood-vessels is not very
definitely known.

The nephridia, which also function as genital ducts, open
internally, with large funnel-shaped mouths, which are directed
towards the posterior end of the dorsal shell. These openings
lead to short tubes which run in that part of the body-wall
which is pushed in to form the brood pouch; into this they

Fre, 112.—The posterior quarter of a Waldheimia australis has been removed, in
order to show the relations of alimentary canal, nephridia, etc. The coelom is
represented black. From a dissection by J. J. Lister.

1. Dorsal shell. 7. Intestine.

2. Ventral shell. 8. Tendons of adductor muscles.

3. Stomach. 9. Ovary.

4, Liver. 10, Internal funnel-shaped opening of
5. Gastroparietal bands. nephridia with three ova drop-
6. Heart. ping in.

eventually open. The walls of the tube consist of a connect-
ive tissue basement membrane lined by glandular cells
crowded with brown concretions. Some of these cells are
also ciliated.

176 ZOOLOGY

The ova are modifications of the cells lining the coelom.
There are four ovaries, one on each side in the dorsal and
in the ventral shell. The cells are borne on an axis, and all
stages from the ripe ovum to the unmodified peritoneal cell
may be seen on the same axis. The ripe ova fall into the
coelom and leave the body through the nephridia. They
undergo the early stages of their developement in the brood
pouches. No testes have been described, and it is uncertain
whether this species is hermaphrodite or not.

The nervous system consists of a circum-oesophageal nerve
ring, which is enlarged into a well-marked sub-oesophageal
ganglion lying in the epidermis. ‘This hes in that part of the
body-wall which overhangs the mouth, just behind the base of
the tentacles. The nerve ring swells into a small supra-
oesophageal ganglion, which is not so large or so well marked
as the sub-oesophageal. The latter gives off a nerve which
runs round the edge of the lophophore, and nerves to the
dorsal and ventral mantles.

The Brachiopoda are divided into two orders :

(1.) The Eecardines, whose shell is chitinous and but slightly
strengthened by a deposit of calcareous spicules. The shell has no
hinge and no internal skeleton to support the arms. The ali-
mentary canal terminates in an anus, median and ventral in
Crania and lateral in Lingula.

Lingula, Glottidia, Crania, and Discina.

(ii) The Testicardines have shells composed of calcareous
spicules, the valves are hinged together, and there is usually an
internal skeleton supporting the arms of the lophophore. There
1S NO ANUS.

Argiope, Terebratula, Terebratulina, Rhynchonella, Theci-
dium, Waldheimia.

In the Lingulidae the dorsal and ventral valves are about
the same size; in all other Brachiopods the ventral is much
the larger, and except in Crania always les uppermost.

In some genera, as Argiope and Lingula, the body
occupies most of the space enclosed by the valves of the shell ;
in Zerebratula and some others the body takes up but a small
portion of this space, the remainder being occupied by the arms
of the lophophore, which stand out from the surface of the

BRACHIOPODA 177

body, and may be coiled in a very complicated manner. In

Rhynchonella the lophophore is
protrusible, but this is excep-
tional.

The edges of the mantle
usually carry a row of setae,
which arise from ectodermal pits,
as in Chaetopods.

The intestine in Lingula is of
some length, it takes one or two
twists, and terminates in an anus
which opens at the right side into
the mantle cavity between the
shells. In Discina also the anus
is lateral, but in Crania it opens
in the median line into a cavity
which lies between the posterior
ends of the valves where the
peduncle would normally be
found.

The food of Brachiopods con-
sists chiefly of Diatoms and
minute unicellular Algze, which
are brought to the mouth by the
action of the cilia on the lopho-
phore.

The only case of serial repeti-
tion of parts presented by the
Brachiopoda is the two pairs of
nephridia found in the genus
Rhynchonella.

The sexes are separate in
Crania, but Lingula, and probably
some others, are hermaphrodite.

The recent Brachiopods are
found in all seas, usually at
moderate depths, within 100
fathoms. Lingula and Gilottidia

ODMH OR oot

oie’
Ho

tH
3)

=

. 113.—Lingula anatina. Dia- .

gram showing the muscular
system: after Hancock.

. Dorsal valve.
. Ventral valve.

Peduncele.

Heart.
Alimentary canal.
Anal aperture.
Umbonal muscle.
Central muscle.

. Transmedial muscle or sliding

muscle.

. Anterior muscle.
. Middle muscle.
. Adjustors, enabling valves to

move forward and backward on
each other.

sometimes live between tide marks, but may extend to a

12

178 ZOOLOGY

depth of 70 metres. They anchor themselves in the mud, and
their long, hollow peduncle forms a sand-tube around itself.
Some Testicardines have been found at great depths; they
usually attach themselves to the rocks, and, when they are
found at all, occur in considerable numbers.

CHAPTER XITi
POLYZOA

Phylactolaemata—Plumatella, Cristatella, Lophopus.

Cyclostomata—Crisia, Hornera.

Ctenostomata—Paludicella, Alcyonidium.

Cheilostomata—Bugula, Membranipora,
Flustra.

Entoprocta—Loxosoma, Pedicellina.

Ectoprocta |

Polyzoa Gymnolaemata

CHARACTERISTICS.—Small coelomate animals, invariably possess-
ing the faculty of budding. The colonies nearly always fixed.
The ectoderm secretes,as a rule, a cuticle, which may be horny
or calcareous. The intestine is bent in the form of a U, the
anus and mouth being approximated ; between them is situated
the nerve ganglion. The mouth is surrounded by a series of
ciliated tentacles. The individuals of the colonies may be
hermaphrodite, but the generative cells may ripen at different
tumes.

The Polyzoa comprise a very great number of species, which
can be grouped into two main subdivisions :

G.) The Eetoprocta, in which the anus lies outside the circlet
of tentacles which surrounds the mouth.

(ii.) Zhe Entoprocta, or those forms in which the cirelet of
tentacles or lophophore embraces both ends of the alimentary canal,
the anus as well as the mouth.

The latter subdivision contains very few forms, but the
former includes a great number of species, mostly marine; a
few, however, inhabit fresh water.

Plumatella fungosa is a fairly common representative of the
freshwater Ectoprocta. It occurs all over Europe, on pieces
of submerged trees, etc., living by preference in stagnant
or slowly-flowing water. Each individual of the colony lives

180 ZOOLOGY

in a thin chitinous tube, from the mouth of which the animal
protrudes under favourable circumstances, and into which it
withdraws in time of danger.
The size of the colony varies a
good deal, it may, however,
attain a diameter of some inches,
and may weigh a pound or more.

The chitinous tube is a modi-
fication of the cuticle, and is
secreted by the epidermis of
the body-wall. The cuticle is
usually spoken of as the ectocyst,
the body-wall underlying it
being called the endocyst. The
anterior portion of the body is
capable of being extended beyond
the mouth of the tube, and
bears a _ series of tentacles

Fic. 114.—A portion of Plumatella
Sungosa seen in vertical section. arranged 1a: horseshoe - shaped

ea ae lophophore. This portion can
. Mouth of tubes. : :
2 Cavitytoe tubes: also be retracted, and in this
3. Statoblasts. condition the space in which
4. Piece of wood in which the Ae
Coleaearsieremine: the tentacles le is termed the

tentacle-sheath.

The body-wall, with its cuticle, is horny in Plumatella,
gelatinous in Lophopus, and calcareous in most marine Polyzoa.
It is often known as the zooeciwm, whilst the extrusible part of
the organism, with the tentacular crown and the alimentary
canal, etc., is distinguished as the polypide.

The body-wall of Plumatella contains a layer of external
circular, and of internal longitudinal muscles, and is lined by
a ciliated epithelium; at its lower end it becomes free from
the ectocyst, and by the contraction of the muscle fibres in
this unattached region the coelomic fluid is forced forward, and
serves to extrude the polypide. Certain muscle fibres stretch
from the endocyst to the wall of the extrusible portion of the
body. These have been termed the parieto-vaginal muscles,
and serve to prevent the full extrusion of the polypide. The
zooecia at their basal ends open into one another, and the

POLEVZOA 181

body-cavities of the various members of the colony are in free
communication.

The lophophore is in the form of a double horse-shoe, it
bears from forty to fifty ciliated tentacles, which, by the current
they set up, assist in bringing minute algae, etc., as food to the
mouth. The bases of the tentacles are connected together by
a fine membrane or web, sometimes called the calyx. On the
side of the horse-shoe nearest the mouth is situated a ciliated
extension of the body-wall. This lobe, which more or less
overhangs the mouth, is the epistome.

The alimentary canal is U-shaped, the mouth opens into
an oesophagus, which is ciliated in some species. This leads
into a stomach. From the stomach a rectum turns forward
again and opens to the exterior outside the ring of tentacles,
but not very far from their base. The walls of the intestine
contain muscle fibres; the single layer of cells lining the
stomach enclose brown granules, which apparently increase
in number with the age of the polypide. These are probably
excreta, which for some reason or another do not find their
way out of the body.

A strand of tissue of considerable importance in the life-
history of the animal passes from the posterior end of the
stomach, and is attached to the body-wall of the animal, near
the posterior end. It is termed the fwniculus, and doubtless
serves to prevent the polypide from being extruded too far.
The coelom is spacious, and contains a corpusculated fluid which
is kept in motion by the ciliated cells lining the body-wall.
It is continued into the lophophore, and into each tentacle, but
is partly divided into two by an incomplete septum which
stretches across the body below the level of the base of the
lophophore.

The nervous system consists of a bilobed ganglion lying on
the oesophagus, between it and the anus. It is situated just
in front of the imperfect septum which stretches across the
animal in this region. At the sides the two lobes extend
round the oesophagus, forming a complete circum-oesophageal
nerve ring, each lobe also gives off a nerve which runs along
the base of the lophophore, and which furnishes a small nerve
to each tentacle.

182 ZOOLOGY

No nephridium has been described in Plumatella; in an
allied form, Cristatella, a pair of ciliated tubes are, however,
said to lead from the body-cavity and to open by a common
pore between the anus and brain. The interpretation of these

Fic. 115.—View of right half of Pluwma-
tella fungosa, slightly diagrammatic.
After Allman and Nitsche.

. Lophophore.

. Mouth.

. Epistome.

Anus.

. Nerve ganglion.

. Oesophagus.

NIaoa rp wn Fe

. Stomach.

. Rectum.

. Edge of fold of body-wall.
. Wall of tube. Ectocyst.
. Parieto-vaginal muscles.

co 0

a
So

—VOO Oo

jt ft
SS) ie

. Funiculus.

—
co

. Body-wall. Endocyst.

. Testis.

. Testis, more mature.

16. Statoblast.

17. Ovary.

18. Spermatozoa free in body-cavity.
19, Calyx.

20. Retractor muscle.

et
oe

ducts is a subject of uncertainty. The functions of a renal
apparatus may possibly be delegated to those large cells in the
stomach in which brown granules accumulate during the life
of the polypide.

Plumatella is hermaphrodite. The ova develope from the
cells which line the body-wall, near the anterior end. The
testes are formed from cells covering the upper end of the
funiculus; these cells multiply, and become spermatozoa.

The cells of the funiculus at its lower end give rise

POLVZOA 183

to some very remarkable structures known as_ statoblasts
These have the morphological significance of buds; they con-
sist of a little heap of cells which secrete around them a
chitinous shell.

The freshwater Polyzoa usually die down at the approach
of winter, and the continuance of the race is provided for by
the persistence of the statoblasts. These structures are usually
formed during the autumn, and escape after the decay of the
parent organism. Their chitinous shell in most cases is a
complicated structure ; part of it contains air vesicles, the air
being secreted from the protoplasm of the cells which have
formed the shell. Thus the latter forms a float; in some
cases, however, the statoblasts are attached to submerged
stones, and the floating ring is then rudimentary or absent.
The formation of these structures, capable of resisting the
winter frosts, in freshwater Polyzoa acquires an additional
interest when they are compared with similar contrivances
found in other members of the freshwater fauna. Spon-
gula fluviatilis, the freshwater sponge, also dies down at the
approach of winter; it also forms remarkable bodies, termed
gemmules, which consist of a collection of cells protected
by curious spicules termed amphidiscs, and from which a new
sponge arises in the spring. In the same connection the
ephippian eggs of Daphnia, which are also supported by an air
float, and in other respects have a striking resemblance to some
statoblasts, and the winter eggs of Rotifers and Planarians, may
be mentioned. The low temperature of winter, which affects
the comparatively small bulk of fresh water much more than
the ocean, where beyond a depth of a few fathoms the cold
hardly affects the temperature of the water, has apparently
called forth these modifications.

A. ECTOPROCTA.

The Polyzoa are divided into two groups,—(a) the EnrTo-
procTa and (0) the Ecroprocra,—according as to whether the
anus is included or not in the circlet of tentacles which sur-
rounds the mouth. The Ectoprocta are further characterised
by the possession of a well-developed coelom. This group

184 ZOOLOGY

includes an immense number of species, and has been divided
into two subdivisions: (i.) the PHYLACTOLAEMATA, which
inhabit fresh water; and (1i.) the GYMNOLAEMATA, which are
almost invariably marine.

The Phylactolaemata are further distinguished from the
Gymunolaemata by the presence of an epistome and the shape
of their lophophore, which is that of a horse-shoe, and by the
formation of statoblasts. The structure of a member of this
subdivision has been illustrated by the description of Pluwmatella ;
in this genus the body-cavities of the various polypides are in
communication, though some of the polypides are partially
separated by an imperfect septum. In Lophopus and Cristatella
the coelom in each polypide is in free and open communication
with that of all the others. The last-mentioned genus forms
colonies, which may attain the length of over two inches. The |
colony is oval in outline, and the polypides project from its
upper convex surface; the lower surface is flat, and on this the
whole colony creeps slowly along on submerged stems or stones.
This mode of progression of the colony is one of the very few
instances of any co-ordination of function which exists between
the various individuals which compose a Polyzoan colony.
The Phylactolaemata are all hermaphrodite.

The Gymnolaemata have a circular lophophore, and are
devoid of an epistome. With the exception of a few genera,
they are marine. In Paludicella the funicular tissue of the
various individuals communicates by means of certain perfor-
ations known as rosette plates, but in the marine forms the
zoeecia are more independent. The ectocyst may be calcareous,
horny, or gelatinous, and the various zooecia may be aggregated
together in an almost infinite variety of ways. From time to
time the polypide dies down, the tentacular crown and aliment-
ary canal degenerating and forming what is known as the
“brown body,” which is coloured by the concretions which
have accumulated within the wall of the stomach. This
brown body lies in the zooecium until the endocyst produces
a bud, and then it may become included in the alimentary canal
of the bud or young polypide; here the nutritive matter which
it may contain is doubtless absorbed, and the undigestible
matter passes out of the intestine of the young polypide.

POLYZOA 185

In some of the Gymnolaemata there is a pore by means of
which the sea-water can be admitted into the coelom when it is
desirable to expand the polypide. This pore may be guarded
by a circlet of bristles, which tend to prevent the entrance of
grains of sand or other foreign bodies. In certain individuals
of some species of Aleyonidiwm, etc., there is a ciliated canal
which leads from the coelom to the exterior; this is known as
the “inter-tentacular organ,” it probably serves as an exit for
the generative cells, at any rate spermatozoa have been observed
to leave the body by this channel. In most species, however,
the generative products escape only by the dying down of the
polypide.

The Gymnolaemata are divided into three classes, according
to the character of their zooecia and the nature of their cell
mouths when the polypides are retracted.

(i.) The CycLostomata.— These have tubular zooecia, always
calcareous. The cell mouth is circular, and with no
apparatus for closing it. Many of them are found
fossilised, probably because their calcareous skeleton ws
easily preserved. Crisia, Hornera, etc.

(ii.) The Crenostomata.—The zooecia are soft, and their
apertures guarded by a folded frill. Bowerbankia, one
of this sub-order, has a muscular gizzard armed with
teeth, situated between the oesophagus and _ the
digestive stomach. Paludicella, one of the few
freshwater members of the Gymnolaemata, belongs
here, and Alcyonidium. There is some reason to
suppose that the Phylactolaemata are derived from
this group of the Gymnolaemata.

(iii.) The CHEILOSTOMATA.—This is the largest subdivision,
and its members are clearly characterised by the posses-
sion of a lid or operculum, which closes the mouth of
the zooecium when the polypide is retracted. The
zooecia are calcareous.

This subdivision exhibits a considerable degree of poly-
morphism. Some of the individuals of the colonies are modified
to form structures known as avicularia, resembling in shape a

186 ZOOLOGY

parrot’s beak. The two halves are constantly opening and
closing, and by their action in catching small worms, etc., they
probably serve as defensive organs, as well as assist in keeping
the colony clean. The smaller beak is believed to be a modified
operculum, whilst the larger corresponds with a much modified
zooecium. These structures exist in very various degrees of
perfection, those of the genus Bugula being amongst the most
specialised.

The vibracula are long stiff processes which move up and
down, and are possibly tactile in function, they are believed
to be homologous with the lower beak of an avicularium. In
one genus they move in unison, and thus the colony exhibits
some degree of co-ordination.

B. ENTOPROCTA.

This group contains but few genera. The mouth and the
anus are both surrounded by the lophophore, which is circular.
The tentacles can be bent over the mouth, but the anterior end
of the body cannot be retracted into the posterior half. The
coelom is almost completely obliterated. A pair of nephridia
are present.

This group is chiefly founded on the structure of two com-
paratively well-known marine genera, Loxosoma and Pedicellina.
Loxosoma is unique amongst Polyzoa, inasmuch as it is not
colonial; like most Polyzoa, it increases by budding, but the
buds separate from the parent organism. Both the genera are
stalked, in Pedicellina the stalk arises from a creeping stolon,
and the calyces or the bodies of the individuals often drop off,
and are replaced by the regeneration of new ones at the end of
the stalks, a process apparently analogous to the formation of
brown bodies in ectoproctous forms. In ZLoxosoma the stalk,
which carries the calyx, is at least in the young condition pro-
vided at its lower end with a foot-gland, by means of which it is
usually attached to some marine animal. The paired nephridia
of Loxosoma consist of ciliated intra-cellular ducts piercing
a few large cells, and probably each beginning with a flame
cell. The ducts open to the exterior between the ganglion
and the oesophagus.

POLYZOA 187

Most species of the Entoprocta are dioecious, and the
generative organs have special ducts. Besides the sexual
reproduction, they multiply also by the formation of buds.
This process amongst the Polyzoa is remarkable, inasmuch
as the endoderm is not represented in the tissues of the bud ;
in most other animals which reproduce by budding, all the
three embryonic layers occur in the bud.

The affinities of the Polyzoa are somewhat obscure. The
developement of the Entoprocta and their adult structures
point to the origin of the group from some ancestor which
is represented in the ontogeny of the Mollusca, Chaetopoda,
and armed Gephyrea by the Trochosphere larva. On the
other hand, the Phylactolaemata have a certain marked resem-
blance to the unarmed Gephyrea, and if this resemblance
be not homoplastic, we must regard the Gymnolaemata, and
still more the Entoprocta, as degenerate forms.

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CHAPTER XIV
MOLLUSCA

CHARACTERISTICS.— Unsegmented Coelomata, with a primitive
bilateral symmetry. Their body is soft, and is dorsally
produced into a fold, the mantle, which usually secretes a
shell. The ventral part of the body forms, as a rule, a
muscular process, the foot, which may be modified in various
ways, but whose function is usually to assist in locomotion.
Respiration is typically carrved on by a pair of vascular
processes, which project from the body-wall, and are termed
the ctenidia. Near the base of these organs is a modified
patch of epithelium, whose function is olfactory, and this has
been termed the osphradium. The portion of the body-cavity
in which the heart lies, the pericardium, communicates directly
with the exterior by means of the nephridia. The heart is
systemic, and the circulation partly lacunar. The nervous
system typically consists of a pair of cerebral ganglia in the
head, a pair of pedal ganglia in the foot, and a pair of
pleural ganglia in the body. The last pair are wnited by a
long commissure, the visceral nerve cord, which may become
twisted. The sense organs comprise the osphradia, otocysts
in connection with the pedal ganglia, tactile tentacles on
the head, and in many cases eyes. The developement
includes a characteristie larva, the Veliger.

The phylum Mollusca includes a large number of animals
which exhibit the greatest variety of structure and habit. The
majority of them are marine, some inhabit fresh water, and
many are terrestrial. The group includes the class Cephalopoda,
the members of which are the largest, and at the same time
the most ferocious of invertebrates. Some members of the

190 ZOOLOGY

phylum are pelagic, and consist of the most transparent and
delicate tissues, others are sessile, being fixed either by cords
secreted by a gland in the foot (Mytilus) or by the surface of
the shell (Ostvea), whilst, again, others bore long funnel-shaped
passages in the rocks or in submerged pieces of wood, ete.

The very various animals which compose this phylum
may be separated into two main divisions, according as to
whether they retain a well-marked prostomium or not.
Those which have lost a definite cephalic region have probably
done so in correlation with a sessile, inactive hfe. They form
the division Lipocephala. The other division comprises those
Mollusea which possess a well-developed head, associated with
a toothed lingual ribbon, capable of a biting or rasping action,
borne on a cushion and moved by certain muscles, the whole
apparatus constituting the odontophore. This organ has given
a name to the division, the Glossophora.

Division I. LIPOCEPHALA.

CHARACTERISTICS.—Mollusca with rudimentary prostomium,
no odontophore, and no eyes. Hither sessile, or with very
feeble powers of locomotion.

This division contains but one class, the Lamellibranchiata.

CuLass Lamellibranchiata.

Lipocephala which have retained the primitive molluscan
bilateral symmetry. The body is laterally compressed, and
the mantle is bilobed, each lobe secreting one valve of the
bivalved shell. The two valves, right and left, are united by
a dorsal elastic ligament. The ctenidia or gills are largely de-
veloped, and by the currents their cilia create, assist in bringing
food to the mouth. The foot is usually plough-shaped, and
contains part of the viscera. It may be used for boring in
sand or rock, more rarely for crawling. ‘The pericardium, part
of the coelom, is in communication with the exterior by means
of a pair of nephridia. The generative glands are simple, and
have no accessory organs connected with them.

In the common freshwater mussel, Anodonta cygnea, the
shells are equivalve. Each valve is composed of three layers:

MOLLUSCA 191

(i.) the periostracum, or outermost layer—this is thin and
horny, and not calcified, and is formed by the thickened free
edge of the mantle; (i1.) the prismatic or middle layer, con-
sisting of closely-packed calcareous polygonal prisms—this is
also deposited by the edge of the mantle; (iii.) the nacreous
or mother-of-pearl layer, which lines the inside of the shell—
it is composed of laminae of calcareous matter, and is de-
posited by the whole of the surface of the mantle and body
in contact with the shell. It is this last layer which, when
deposited in concentric layers round foreign particles, such
as grains of sand, etc., produces pearls.

The shells of some Lamellibranchs are not equivalve, e.g.
the oyster, Ostrea, which is attached to rocks by means of
its larger valve. In Pholas there are additional calcareous
plates inserted dorsally between the two valves; and in
Teredo, the mollusc which does so much damage by boring
into wood, the valves fail to completely cover the body,
which secretes a calcareous lining to the tube in which it
lives.

The valves of the shell are kept in apposition by adductor

Fria. 116.—Section through Anodonta, to show mechanism of
opening and of closing the valves. After Lankester—
Zoological Articles reprinted from the Encyclopedia
Britannica.

1. Right valve of shell.
2. Left valve of shell.

. Hinge.

em ch

. Elastic ligament.

Or

. Adductor muscles.

muscles. These may be two in number, an anterior and a
posterior, or the posterior may alone persist (Monomyaria).
The edge of the mantle is thickened, and in some genera
it bears tentacles and eyes. Posteriorly it is notched in such
a way as to form two apertures, which remain open when the

192 ZOOLOGY

edges of the remainder of the mantle are in contact. These
openings form the dorsal and ventral siphons. In some
Lamellibranchs, eg. Mactra, Cyclas, etc., these notches, by the
fusion of their edges, are converted into tubes, which in some
genera attain a length of several inches. The ventral siphon
serves to admit fresh water, bringing with it oxygen and food,
and the dorsal siphon gives exit to a stream of water which
carries away the waste products and generative cells.

The foot is not developed in the OSTREIDAE, and is
small in Mytilus, the marine mussel. In the cockle, Cardiwm,
and in 7rigonia, it can be suddenly bent, and by this means
the animal jumps along. In Solen the foot is suddenly
retracted, and in this way water is violently forced out of
the siphons, and the animal is propelled forwards. Pecten
flies through the water, with its dorsal surface downward,
by the flapping of the valves of its shell. The foot often
bears a special gland, which secretes a number of horny filaments
known as the byssus, which serve to anchor the animal
to the ground. This structure is well seen in Arca and
in Mytilus.

The mouth, which is median, and ventral to the anterior
adductor muscle when the latter is present, lies in a
groove formed by the anterior and posterior labial palps.
These are ciliated structures, which resemble to some extent
the gills, and doubtless serve to convey minute organisms
to the mouth as food. The alimentary canal is ciliated.
The stomach gives off a caecum, which in many
genera lodges a crystalline style. The function of the style
is obscure, but it appears to consist of an albuminoid
material. The intestine is coiled, and leads to a straight
rectum, around which the ventricle of the heart is often
folded. A fold of the intestine, or typhlosole, increases
its surface. A paired gland, the so-called liver, pours its
secretion into the stomach.

Two auricles return the arterialised blood to the ventricle,
which in Arca is double; the ventricle gives off an anterior
and posterior aorta, which distributes the blood all over the
body. The blood from the mantle is in Anodonta returned
directly to the auricles; the rest of the blood is collected into

MOLLUSCA 193

a vena cava in the floor of the pericardium, and is thence sent
through the nephridia to the gills and returned to the
auricles. The circulation is partly lacunar, the blood being
contained in irregular splits in the tissues and not in distinct
vessels. The blood contains amoeboid corpuscles, and is usually
colourless ; two species, however, Solen legumen and Arca Noe,
contain haemoglobin in their corpuscles.

The gills consist primitively of an axis, which is fused to
the body for the greater part of its course; this contains an
efferent and an afferent blood-vessel. The axis gives off two
series of filaments, which hang down parallel to one another,
thus forming two lamellae. The filaments of both series may
be bent up, forming V-shaped structures, those of the outer
series having their free ends external and next to the mantle,
whilst those of the inner series have their free ends internal
and next to the foot, so that each series forms a gill with an
outer and an inner lamella. In Mytilus and some others the
outer and inner limbs of each filament are connected by
certain pieces of tissue termed interlamellar concrescences.
Neighbouring filaments are kept parallel to one another by an
arrangement unique in the animal kinedom. Each filament
bears certain patches of ciliated cells, and the cilia of two opposite
patches are interlocked, in the same way as a couple of brushes
when put together. In more complex genera these ciliary
junctions are replaced by interfilamentous concrescences, and
in Anodonta the interlamellar and interfilamentous concres-
cences are developed to such an extent as to leave but narrow
passages through which the water circulates. The free ends
of the filaments of the outer lamella of the external gill, and
of the inner lamella of the internal gill, very frequently fuse
with the contiguous organs, the mantle, or the foot.

Between the lamellae of each gill a certain space is de-
veloped which is more or less continuous with that of the
other gills. This epibranchial space often serves to lodge the
developing ova, it communicates with the dorsal siphon,
through which the waste products leave the animal.

Each gill filament contains a blood-vessel, and it is often
stiffened by two rods of a chitinous material. Its outer
epithelium bears cilia, which serve to create a current of

13

194 ZOOLOGY

water, which enters the pallial chamber by the ventral
siphon.

The nephridia of Lamellibranchs are usually known as
the Organs of Bojanus. There is a single pair, and each con-
sists of a glandular or secretory portion which has an opening

' t ' ‘\
4116 46) 11 19

Fic. 117.—Diagrams of a Schematic Mollusc. After Lankester—Zoological Articles
reprinted from the Encyclopedia Britannica.

A. Dorsal view, showing the heart, 9. Internal opening of nephridium.
pericardium, generative organs, 10. External opening of nephridium.
and nephridia. 11. Opening of genital gland.

B. Ventral view, showing the nervous 12. Cerebral ganglion.
system. 13. Pleural ganglion.

C. Lateral view. 14. Pedal ganglion.

1. Mouth. 15. Visceral ganglion.

2. Nerve ring. 16. Foot.

3. Oesophagus. 17. Anterior aorta.

4. Liver. 18. Gill.

5. Anus. 19. Tentacle.

6. Pericardium. 20. Auditory vesicle.

7. Heart. Ventricle. 21. Olfactory ganglion,
8 in A. Auricle. 22. Abdominal ganglion developed on
8 in C. Wall of pericardium. the visceral loop.

into the pericardium, and of a ureter which opens to the exterior
in the neighbourhood of the orifice of the generative glands. In
the oyster the kidney is much less compact, and its secretory
part is scattered through the body, even reaching the mantle.

MOLLUSCA 195

The nerve ganglia are usually rendered conspicuous by
their bright orange colour. The cerebral ganglia, which lie
one on each side of the mouth, probably represent the cerebral
and pleural ganglia of other molluscs; they are united
both with the pedal ganglia in the foot and with the olfactory
(parieto-splanchnic) situated on the ventral face of the posterior
adductor muscle. A pair of auditory vesicles, lined with
ciliated cells and containing a single otolith, are usually
present close to the pedal ganglia, and are innervated by a nerve
from the cerebro-pedal commissure, which probably comes from
the cerebral ganglia. Tactile papillae or tentacles are common
round the edge of the mantle. In some cases the tentacles
have been modified and form eyes, which attain a great degree
of complexity. In Pecten, Spondylus, etc., these eyes have a
remarkable resemblance to the vertebrate type of eye, inasmuch
as the optic nerve passes in front of the retina, and the retinal
elements are thus turned away from the light. The epithelium
in the neighbourhood of the olfactory ganglion is modified to
form an organ of smell, by means of which the quality of the
water flowing in through the ventral siphon may be tested.

The Lamellibranchs with few exceptions are dioecious.
The generative organs are branched glands usually situated in
the foot, though in Mytilus they occur in the mantle. The
generative cells are formed in the caecal processes of the gland,
and they leave the body by a right and left simple duct which
is continuous with the walls of the gland, and in some cases
opens into the duct of the kidney (Spondylus, Lima, and
Pecten).

Division II]. GLOSSOPHORA.

CHARACTERISTICS.—WMollusca with a prostomium more or less
developed and a buccal cavity armed with a rasping tongue,
the radula, which together with its accessory parts constitutes
the odontophore.

The Glossophora comprise three classes :

(i.) Gasteropoda.
(ii.) Scaphopoda.
(iii.) Cephalopoda.

196 ZOOLOGY

CLASS Gasteropoda.

CHARACTERISTICS.— The GASTEROPODA have a foot which is in
the main a crawling organ, it is simple, median, and has a
broad flat surface. The foot is often divisible into three
divisions, termed the pro-, meso-, and meta-podium.

The Gasteropoda are divided into two sub-classes :

i. Gasteropoda Isopleura.

CHARACTERISTICS.— The Gasteropoda Isopleura retain the primi-
tive bilateral symmetry of the group. The body is elongated,
the mouth anterior and the anus posterior. The viscera
generally are paired and bilaterally symmetrical.

This subclass includes six genera, which are distributed
amongst three orders. The best-known genus is Chiton, in
which the shell is metamerically divided into eight parts. The
gills or ctenidia are also metamerically repeated to the number
of sixteen or more, and at the base of each is a patch of
olfactory epithelium, the osphradium. Chiton, like Chaetoderma,
another member of the subclass, is dioecious, in the former the
generative cells escape by special ducts. In Meomenia and
Chaetoderma, however, they leave the body by means of the
nephridia.

The nerve ganglia are not very markedly developed, but
ganglion cells are scattered all along the well-defined nerve-
trunks. In some Chitons, eyes furnished with a lens, retina,
cornea, etc., have been described as existing on the shell
plates.

ii. Gasteropoda Anisopleura.

CHARACTERISTICS.—Jn the members of this subdivision the head
and the foot have retained a bilateral symmetry, but the
visceral hump with its included organs has undergone a twist
which has resulted in rotating the anus and posterior part of
the viscera to the right. The angle through which the anus
has been twisted varies in different groups ; tt may be as much
as 180°, and in this case the anus lies above the middle line
of the neck. One of the ctenidia is usually atrophied, and
one of the nephridia specialised as a generative duct. The

MOLLUSCA 197

mantle developes a shell, which often increases the asymmetry

of the animal by being spirally coiled. This shell is often

capacious enough to shelter the whole animal, thus forming a

kind of house into which the animal can withdraw. The

foot is usually provided with a mucous gland.

The Gasteropoda Anisopleura are subdivided into two
branches: Streptoneura (Prosobranchiata) and Euthyneura.

Branch A. STREPTONEURA.

CHARACTERISTICS.— The first branch comprises those Molluses in
which the torsion has proceeded to such an extent that the
anus has become anterior, and the right gill and osphradium
have crossed anteriorly to the left, whilst the left gill and
osphradium have come round posteriorly to the right. As a
consequence one limb of the visceral nerve loop is pulled over
the other and a figure of & is produced.

This branch includes two orders: Zygobranchiata and

Azygobranchiata.

Order 1. ZYGOBRANCHIATA.

CHARACTERISTICS.— The first order includes all those forms in
which, although the torsion is complete, so as to bring the anus
near to the anterior median line, the atrophy of the cten-
udium of one side has not usually taken lace, and the
generative cells leave the body through one of the nephridia
which still retains its renal function. No accessory generative
organs occur, and the visceral hump is coextensive with the
Soot.

This group includes three families. The best-known genera
are Haliotis, known as the Ormer in the Channel Islands, where
it forms an article of diet, Fisswrella, and Patella or the
limpet.

Patella vulgata, the common limpet, is protected by a
conical dome-shaped shell, whose average length is about two
inches. The edges of the shell are not quite smooth, and their
inequalities generally correspond closely with those of the
rock upon which the animal is situated. Limpets are usually
found between the tide-marks, and if they wander away from
the spot on which they usually occur when covered by the

198 ZOOLOGY

tide, they are stated always to return to it before the water
has again receded.

The visceral hump is covered by the conical shell. The
body-wall at its edge is produced into a fold, the mantle. The
ventral surface of the animal consists of the muscular oval

Fic. 118. Diagram of a vertical median section of a Limpet, Patella vulgata. After

Lankester—Zoological Articles reprinted from the Hncyclopedia Britannica.
1. Mouth. 10. Heart in pericardium.
2. Odontophore. 11. Nephridium.
3. Radula. 12. Opening of larger nephridium.
4, Radula sac. 13. Branchial efferent vessel (vein).
5. Buccal cavity. 14. Branchial afferent vessel (artery).
6. Laminated stomach. 15. Salivary gland.
7. Intestine cut across. 16. Generative gland.
8. Liver. 17. Edge of the mantle.
9. Anus.

foot, between which and the mantle a groove exists which
lodges the gills. The foot is attached to the shell by a
circular muscle which is incomplete anteriorly.

A distinct head exists, and this carries a pair of tentacles
with a pair of eyes which appear as black specks near the base
of the tentacles. Above the head the groove between the foot
and the mantle deepens into a large pallial cavity. Into this, not
in the median line, but slightly to the left of it, the anus opens,
and on each side of the anus lie the openings of the renal
organs (Fig. 119). On the neck are also situated two small
bodies representing the ctenidia, which are fully developed in
the allied forms Haliotis and Fisswrella; in connection with
these a patch of olfactory epithelium, the osphradium, has also
been discovered. The function of these ctenidia, the original
breathing organs, has been assumed by certain folds of the
mantle forming the actual gills.

MOLLUSCA

199

The mouth leads into the cavity of the buccal mass, this
is partially obliterated by the developement of a large ventral

5).
6.
Uc
cS

1. Head. 8.

2. Tentacle.
3. Mantle skirt. 9.
4. Muscles forming root of foot, and 10.
adherent to the shell. ale

Fic. 119.—Side view of anterior end of Limpet,
Patella vulgata. Part of the mantle is cut
away to show the contents of the pallial cham-
ber. After Lankester—Zoological Articles re-

printed from the Encyclopedia Britannica.

Small nephridium.

Large nephridium.

External opening of small] ne-
phridium.

External opening of large ne-
phridium.

Anus.

Rudimentary ctenidium.

Pericardium.

mass, over which the tooth-ribbon or radula works. The
ventral mass contains certain cartilaginous nodules, and is very

i}
'
’
!

9

Fia. 120.—Vertical section through the neck of Patella vulgata.
After R. J. Harvey Gibson.

Mouth.

Buccal cavity.
Palatal tooth.
Radula.
Odontophore.

OUR oo No

Anterior cartilage.
Oesophagus.
Radula sac.

Foot.

Ose ice

muscular. The radula, which runs over it, is continued into a
sac, from the blind end of which it grows (Fig. 120). The radula

200 ZOOLOGY

and its sac attain an extraordinary length in the limpet, often
twice the length of the animal; they lie between the viscera
and the muscular foot. Two pairs of yellowish salivary glands
pour their secretion into the buccal cavity by two ducts on
each side, and many mucous glands also open into it.

The oesophagus leads from the buccal mass into the stomach.
The walls of this organ are much folded, it receives by
numerous ducts the secretion of the liver. The latter is a
large organ occupying the greater portion of the space in the
visceral hump, and enveloping a considerable proportion of the

Fig. 121.—Semi-diagrammatic view of
intestinal coils of Patella vulgata. After
R. J. Harvey Gibson.
1. Buccal mass.

. Rectum.

Crop.

. Stomach,

oO FP cw ND

. Coils of intestine.

alimentary tract. The intestine which passes from the true
stomach makes a loop and then again enlarges into a second
stomach, which is bent upon itself; after this the intestine coils
in a most complicated way and ultimately ends in a rectum,
which opens to the exterior on the anal papilla in the anterior
pallial chamber (Fig. 119). The whole alimentary canal is lined
throughout by ciliated cells; the extent of its convolutions are
shown by the fact that it may attain a length of over fourteen
inches, in an animal a little more than an inch long.

The heart consists of a single auricle and ventricle, in
the allied forms Haliotis and Fisswrella two auricles exist. It
is enclosed in a pericardium situated in the posterior angle of
the anterior pallial chamber. A large vessel, the branchial
vein, runs on each side round the edge of the mantle at the base
of the gills; anteriorly the two vessels unite and empty into the
auricle. A muscular valve separates the auricle from the ven-
tricle. The cavity of the latter is much broken up by strands

MOLLUSCA. 201

of muscle fibres; it opens into the left and right aortae, the
former supplying the circular muscle. Both aortae soon termi-
nate in lacunar spaces, from whence the blood presumably
passes to the gills. The blood is colourless, and contains
amoeboid corpuscles.

The nephridia are paired, but the right is much larger
than the left. They open to the exterior by small renal
papillae, situated one on each side of the anal prominence, and
also, according to some observers, internally by two minute
pores into the pericardium. ‘The existence of the reno-peri-
cardial openings has recently been denied, both in Patella and
in Fissurella. Haliotis and Trochus possess a left reno-peri-
cardial duct only. The left kidney lies between the rectum
and the pericardial chamber. The right kidney, which is
aborted in other Anisopleura, occupies a large space in the
visceral hump. In part of its course it is closely applied to
the generative organs, and when the ova and spermatozoa are
ripe they are stated to burst into the lumen of the kidney, and
so to leave the body through the renal papilla on the right of
the anus. The lumen of the kidney is much broken up by
ridges which project into it from its walls. The ridges are
covered with glandular epithelium, which is partly ciliated ; in
the substance of the ridges numerous blood-vessels ramify.

The nervous system is very complex, it comprises several
pairs of ganglia, the most important of which are the cerebral,
the pedal, and the pleural. The cerebral ganglia are situated
at the base of the tentacles, they give off nerves to the eyes
and to the tentacles. The two ganglia are united by a com-
missure above the pharynx ; they also give off a commissure on
each side which passes to an anterior superior buccal ganglion.
From each buccal ganglion two commissures arise, one uniting
it with the similar ganglion of the other side, the other pass-
ing posteriorly to a posterior superior buccal ganglion, which is
in its turn united with the similar one on the other side. Thus
the buccal nervous apparatus consists of a square of commis-
sures with a ganglion at each angle. ‘The cerebral ganglia are
connected with one another by a commissure which runs
underneath the buccal mass ; this bears two small ganglia—the
inferior buccal ganglia.

202 ZOOLOGY

From the posterior end of each cerebral ganglion two com-
missures pass backward, the outer one passing into the pleural
ganglion, the inner to the pedal. Each pleural ganglion is
connected with the pedal of its own side, and the two pedals
are united by a pedal commissure. The pleural gives off two
stout nerves. The outer of these soon splits, one branch going
to the gills and mantle, the other to the circular muscle which
attaches the animal to its shell. The second nerve given
off from the pleural forms the origin of the visceral loop. This
is a nervous loop, which, starting at each end from the pleural
ganglion, forms a figure of 8 twist. In its course it gives off
a nerve to an olfactory ganglion lying at the base of each of
the rudimentary ctenidia. The olfactory nerve going to the left
ctenidium arises from the loop near to the right pleural gan-
clion, that to the right ctenidium arises near the left ganglion.
This twisting of the visceral loop is characteristic of the
Streptoneura,

The pedal ganglia give off each two large nerves, which
supply the muscles of the foot.

The tentacles have a tactile function; at their base the
eyes are situated—they consist of a pair of pits sunk in the
surrounding tissue. The epidermal cells lining these pits
become modified and deeply pigmented, and are connected by
an optic nerve with the cerebral ganglia. A similar simple
eye, consisting of an open pit lined with pigmented cells, is
found in Nautilus.

Limpets are dioecious ; the position of the generative glands
is similar in the two sexes (Fig. 118) between the muscular
foot and the digestive organs, rather near the posterior end.
Like other members of the Zygobranchiata, the generative glands
possess no ducts, and their contents leave the body through the
right nephridium.

Order 2. AZYGOBRANCHIATA.

CHARACTERISTICS.— The <Azygobranchiata, which constitute the
other order of the Streptoneura, have lost their original left
ctenidium and osphradium. The right nephridium does not
exist as such, but is most probably represented by the generative

MOLLUSCA 203

duct. The left nephridium, which was in Patella smaller

than the right, and the left ctenidium and osphradium, are

retained. The anus lies on the right of the neck of the
animal. The Azygobranchiata are dioecious, and the males
are often furnished with a large penis.

The great majority of Azygobranchiata are adapted for
creeping at the bottom of the sea (Reptantia), and for this
purpose have a large muscular foot with a flat sole. They
are often spoken of as sea-snails ; the shell which encloses and
protects the visceral hump is usually coiled. A large gland
is not unfrequently found lying alongside the rectum ; in the
genera Murex and Purpura its secretion turns purple when
exposed to the light, and it was in ancient times used as a
dye. The posterior surface of the foot in some species bears
a calcareous or horny plate, the operculum, which serves to
close the mouth of the shell when the animal is retracted.
The foot itself shows a tendency to break up into three
portions: anteriorly the propodium, in the middle the meso-
podium, and posteriorly the metapodium, which bears the
operculum,

This group includes, amongst many others, Buccinum, the
whelk, and Zittorina, the periwinkle. Paludina, the river-snail,
and Valvata are freshwater members of the group, and so is
the terrestrial Cyclostoma, which has no gill, the mantle
chamber having become a respiratory organ. It lives in
damp places. ntoconcha mirabilis lives parasitically in the
body of Synapta digitata; this is exceptional, as parasitism is
very rare amongst the Mollusca.

A few Azygobranchiata have become modified in con-
nection with a pelagic mode of life. These form the section
Natantia, also known as the Heteropoda. As in other
pelagic organisms, their tissues have become wonderfully
transparent, and of a gelatinous consistency. The foot has
become a swimming organ. Its division into pro-, meso-, and
meta-podium is well marked. Atlanta has a coiled transparent
shell, into which the body and foot may be withdrawn, and
the metapodium carries an operculum. In Carinaria the
foot is by far the largest part of the animal, and the relatively
small visceral hump is covered by a small hyaline shell. In

204 ZOOLOGY

Pterotrachea the visceral hump is still more reduced, and is
devoid of a shell.

The sense organs and nervous system are unusually well
developed in this subdivision, the otocysts being usually
closely attached to the cerebral ganglia. The lingual ribbon
has moveable lateral teeth, which divaricate when the tongue

Fia. 122.—Diagrams of a series of
Molluses to show the form of
the foot and its regions and the
relations of the-visceral hump
to the antero-posterior and
dorso-ventral axes. After
Lankester—Zoological Articles
reprinted from the Hncyclo-
pedia Britannica,

I, A Lamellibranch.
II, An Anisopleurous Gasteropod.
III. A Cephalopod.
A. Anterior surface.
P. Posterior surface.
D. Dorsal surface.
V. Ventral surface.
. Mouth.
Anus.
Mantle cavity.
Foot.

Lo a LSI

is protruded, but come together when that organ is withdrawn,
by means of these the Natantia, which are carnivorous, catch
other pelagic organisms to feed upon.

Von Erlanger has shown in the developement of Paludina
that the glandular portion of the nephridium arises as an
evagination of the pericardium, and the mouth of the evagin-
ation remains as the reno-pericardial pore, when such an orifice
exists. The genital gland arises as a proliferation from the
pericardial wall at a spot where a rudimentary evagination has
been formed which represents the missing nephridium. ‘The
duct of the nephridium and the duct of the gonad are sym-
metrically situated and homologous involutions of the epiblast.

MOLLUSCA 205

Thus, in this animal at least, and probably in all Molluscs,
the cavity of the generative organs and of the glandular part
of the kidney is part of the coelom, and the generative cells
are formed from coelomic epithelial cells.

Branch B. EUTHYNEURA.

CHARACTERISTICS.—The second great branch into which the
Gasteropoda Anisopleura is divided differs from the Strepto-
neura in the fact that the torsion of the visceral hump has
proceeded to a less extent, and that consequently the peri-
cardium 1s placed obliquely in front of the mantle cavity and
gul. For the same reason also the one side of the visceral loop
has not become pulled over the other by the forward rotation
of the gill and osphradium, and the loop is untwisted. The
condition of the gill and kidneys is as in Azygobranchiata.
The right auricle is wanting. With one exception, no
operculum is found. All Euthyneura are hermaphrodite, a
sharp distinction from the Streptoneura. The shell is often
but slightly caleified, and it and the mantle tend to disappear.
The Euthyneura comprise two orders: (i.) the Opistho-

branchiata and (i1.) the Pulmonata.

The Opisthobranchiata are characterised, as their name
implies, by the position of the ctenidium behind the heart.
The branchial vein opens into the auricle, which is situated
behind the ventricle. The shell is often absent, and when it is
developed it is frequently covered by a fold of the mantle.
Both the mantle and the ctenidium may, like the shell, be
wanting, the function of the ctenidium may be carried on by
processes of the body-wall.

In some Opisthobranchs the margin of the foot is produced
into two broad flaps, which may stand out at right angles to
the axis of the foot, or may in some cases be folded up against
the sides of the body.

One of the most characteristic features of this order is the
presence of processes of the body-wall termed cerata or dorsal
papillae. The cerata vary very much in size, number, and
arrangement. Processes of the liver are proloneed into some
of them, these have been termed hepatocerata to distingusih

206 ZOOLOGY

them from those which are simply diverticula of the body-wall.
These cerata often coexist with well-developed gills, and their
minute structure does not point to any very definite respiratory
function ; it seems not improbable that their varied shape and
colour may be in some cases protective and in others con-
spicuous and warning. In those Opisthobranchs which possess
hepatocerata, such as Doto and £olis, the liver is not a compact
gland, but consists of a number of diverticula given off from
the alimentary canal, each diverticulum passing into one of the
cerata, and being large enough for food particles to pass into
it and be there digested. In Zolzs the liver diverticula do not
end blindly, but are stated to open into an invagination of the
ectoderm termed the cnidophorous sac. This opening is guarded
by a minute sphincter muscle. The cnidophorous sac, which in
its turn opens to the exterior, is hned by a number of large cells,
cnidoblasts, which are crowded with nematocysts or thread-cells ;
these recall the stinging organs of the Coelenterata. The
everted threads of these nematocysts are armed with both
large and small spines.

In Aplysia, Bulla, and Pleurobranchus the original cten-
idium has been retained, but is situated behind the heart, in Doris
and its allies the ctenidium appears in a modified form as a
circlet of feathered processes which surround the median dorsal
anus; in Lolis, Tethys, etc., it has completely disappeared. In
Aplysia there is a large gland, whose secretion is said to be
poisonous, which opens just below the osphradium near the
anterior end of the ctenidium; and numerous small cutaneous
glands open on the under surface of the mantle, in Aplysia
these produce a purple secretion.

The Opisthobranchs are, like the Pulmonata, hermaphrodite ;
and the generative organs consist of a hermaphrodite gland or
ovo-testis. Some of the cells of this gland form ova, whilst
others divide up and become spermatozoa. From the ovo-
testis a hermaphrodite duct leads to an albuminiparous gland,
in the substance of which the cuct coils. Just where the
duct leaves the gland it gives off a small diverticulum, the
vesicula seminalis. The duct then passes on to the external
opening, but just before it reaches that it receives the duct of
a spherical spermatheca. When eggs leave the body by means

MOLLUSCA 207

of this external opening situated in front of the ctenidium,
they are enveloped in a gelatinous coating deposited by the
albuminiparous gland, and are impregnated by the spermatozoa
of another individual, which has been stored up in the sperma-
theca. The spermatozoa when they pass out of the genital
pore pass along the spermatic groove, which runs along the
right side of the head and terminates in a muscular penis, by
the aid of which the spermatic fluid is introduced into the
genital pore of another individual and finds its way to the
spermatheca.

The Opisthobranchiata show a considerable tendency to
lose some of their organs; this process of degeneration is
carried farthest in one of the sub-orders, the Haplomorpha, in
which neither mantle-fold, ctenidia, nor cerata are found.
Phyllirhoe has little but its odontophore to show its relationship
with the Mollusca. It is a flattened, Planarian-like, transparent
pelagic organism, about half an inch long. Its skin contains
numerous unicellular glands, which are said to secrete a
phosphorescent slime. The ovo-testis in this animal is double.
A small Hydromedusa, Mnestra, is frequently found attached
by the aboral surface of its body to these animals. In
Rhodope the degeneration has gone still farther, and the
odontophore has disappeared.

Recent research has shown that the group of animals
which formerly ranked as a class, the Pteropoda, are really
allied to the Opisthobranch Gasteropoda. The Pteropoda
are subdivided into two orders, the Thecosomata and the
Gymnosomata. The former consists of three recent families,
and is allied to the Bulloidea; the latter contains five
families, and is allied to the Aplysioidea, members of the
Opisthobranchiata. The failure to recognise the correct
affinities of these animals was to some extent due to their
external symmetry, but this is a secondary feature which
does not affect their internal organs. The animals com-
posing this class are all carnivorous and pelagic. In
correspondence with their mode of life, they are delicate
organisms with transparent tissues, those amongst them pro-
vided with a shell—the Thecosomata—having a hyaline one.
In both orders the margin of the foot is prolonged and

208 ZOOLOGY

modified into fins, which in the Thecosomata embrace the
head. The anterior portion of the digestive tract is evaginable
in Clio, and bears a number of unicellular glands opening upon
cones. The secretion of these glands is adhesive, and they
serve as organs for the capture of prey. Pnewmodermon has
a pair of appendages which bear suckers similar in structure to
those found in the Cephalopoda.

Order 2. PULMONATA.

CHARACTERISTICS.— This second order of the Euthyneura has
possibly become modified from a palliate Opisthobranch
ancestor, in correspondence with the altered conditions of life
involved in the change from an aquatic to a terrestrial
habitat. The etenidium has atrophied, and the edge of
the mantle has fused with the body-wall, leaving only one
small opening which leads from the pallial chamber to the
exterior—this is the resprratory pore. The walls of the pallial
chamber are very vascular, and they function as lungs.
An operculum is never present.

This order includes the land-snails and slugs. As a rule,
its members live on land, and they all breathe air when adult,
even those like the pond-snail Zimnaea, which lives in water,
but whose mantle chamber contains air. The mantle cavity of
the young freshwater Pulmonates is stated at first to contain
water, this is afterwards replaced by air. The great extent to
which the blood-vessels and capillaries are developed in the
Pulmonata is possibly connected with this habit.

No true operculum is found in any Pulmonate, but many
secrete a temporary lid to their shell when they withdraw into
it for the winter. This temporary operculum is called a
hibernaculum. In the slugs the shell may be small and even
quite atrophied.

Onchidium and Peronia are members of a family which
inhabit the sea-shore and brackish marshes. Onchidiwm is
remarkable for possessing, in addition to the normal pair of
cephalic eyes, a number of dorsal eyes scattered over the
integument. These latter, like the eyes in the mantle of
Pecien and Spondylus, are not constructed on the usual

MOLLUSCA 209

invertebrate type, but, as in the eyes of vertebrates, the
nerve pierces the layer of sensory cells, and is distributed
to that side of them which is nearest the lens. In Onchidium,
as in Pecten, etc., the eyes are probably modifications of certain
simple tentacles which are borne on the mantle.

CLass Scaphopoda.

CHARACTERISTICS.—Llongated cylindrical Gllossophora. The
mantle has extended onto the ventral surface,and has fused in
the middle ventral line. It has secreted around it a eylindri-
cal shell. The foot can be protruded through the anterior
opening of the shell. No heart is present. The visceral loop
of the nervous system is unturisted. Duoecious, the generative
products escape through the right nephridium.

This class includes but three genera, of which the best-
known is Dentalium. The cylindrical shape of its body
may be correlated with a burrowing habit of life, and it is
interesting to note that a similar shape is found amongst

BES sox (8 sj Fic. 123.—Diagram of the ana-
RR tomy of Dentaliwm. Lateral
view of organs, showing as
though by transparency. After
Lankester—Zoological Articles
atoms = 8 reprinted from the Hncyclo-

i ‘ / ' ‘ . . .
ot / p ' cedia Britannica.
TE 15 10 G10: 7 a

1. Mouth surrounded by pinnate ten- 10. Peri-oral part of mantle cavity.
tacles. 11. Foot.

2. Oral process. 12. Cerebral ganglion.

3. The ctenidial filaments. 13. Pleural ganglion.

4, Odontophore. 14. Olfactory ganglion placed on visceral

5. Oesophagus. loop as in the Lamellibranchiata,

6. Left lobe of liver. according to Spengel.

7. Anus. 15. Pedal ganglion.

8. Peri-anal part of mantle cavity. 16. Left nephridium.

9. Appendix of mantle skirt separated

by a valve from 8.

the sand-boring Lamellibranchiata, such as Solen. The
mantle is ensheathed by a shell, which is at first incom-
plete ventrally. The shell resembles a truncated elephant’s
tusk, it is open at both ends, the larger opening is the
anterior one, and the concave surface is dorsal.
The foot is protrusible through the anterior opening of
14

210 ZOOLOGY

the shell, it terminates in a trifid lobe. Dorsal to it is
the oral cone or head, at the end of which the mouth opens,
surrounded by short pinnate tentacles (Fig. 123). A buccal
mass and a radula are present; two liver lobes symmetrically
placed open into the stomach, from which the intestine passes
to open by the anus in the ventral middle line.

A right and left nephridium are present, and open to the
exterior on either side of the anus. There is no heart, but
the coelom contains a colourless blood. At the base of the
oral cone a number of ctenidial filaments have their origin.
These are capable of very considerable extension. The nervous
system consists of a pair of cerebral ganglia, close to which he
the pleural ganglia. Long commissures connect the cerebral
with the pedal ganglia, The visceral commissure is also long,
and bears the olfactory ganglia, situated in front of the anus, in
the same position as in Lamellibranchs. The generative gland is
alike in both sexes; it is situated dorsally, and its products
make their exit through the right nephridium.

CLASS Cephalopoda.

CHARACTERISTICS.—Bilaterally symmetrical Glossophora. The
visceral hump is elongated, not twisted ; the sub-pallial chamber
is chiefly developed posteriorly, and contains the gills, anus,
and excretory pores. The shell may be external or internal,
in a few cases it 1s absent. The foot has grown round the
head, and is broken wp into the characteristic arms of the
Cephalopoda, provided with suckers. Part of the foot forms
a funnel-like siphon, which guides the water as it is expelled
from the pallial cavity. The vascular system is well
developed, in addition to the central heart consisting of a
ventricle and two auricles, an accessory branchial heart exists
at the base of each gill in all but Nautilus. Powerful beak-
like horny or calcareous jaws guard the mouth, and the
radula is well developed. Chromatophores are present in the
integument. The Cephalopoda are dioecious.

The Cephalopoda are divided into two orders: (i.) The

TETRABRANCHIATA or the TENTACULIFERA and (1i.) the DI-

BRANCHIATA or the ACETABULIFERA.

MOLLUSCA PAID

(1.) CHARACTERISTICS.— The Tetrabranchiata are characterised as
follows. The siphon is not complete ; the edges overlap one
another, but are not fused ; the lobes of the circumoral foot
carry tentacles, not suckers. There are two pairs of ctenidia
and two pairs of nephridia. The coelom opens straight on
to the exterior, and not into the nephridia. There are two
oviducts and two vasa deferentia, but the left is in both cases
rudimentary. The shell is large, external, and chambered.
No ink sac, salivary glands, or branchial hearts exist.

This order contains very many extinct forms, but only
one living genus—Nautilus.

(i.) CHARACTERISTICS.—The Dibranchiata have but one pair of
ctenidia and one pair of nephridia. The edges of the siphon
have fused so as to form a complete funnel. The arms or
processes of the foot which surround the head bear cwp-like
suckers. Branchial hearts exist at the base of the gills. The
coclom communicates with the exterior through the nephridia,
and not directly ; the oviducts may be paired or single ; the
vas deferens, with one exception, is single. An ink sac and
salivary glands exist. The sense organs are highly developed.
The Dibranchiata comprise two sub-orders: the Decapoda

and the Octopoda.

a. CHARACTERISTICS.— The Decapoda have ten arnvs, two of which
are very long, and differ in appearance from the others. The
suckers are stalked, and provided with a horny ring. The
body is elongated, and bears lateral fins. The shell is enclosed
by an upgrowth of the mantle, and is therefore internal.

B. CHARACTERISTICS.—The Octopoda have eight similar arms,
bearing sessile suckers, which are not strengthened by a horny
ring. The body ws short and globular. The oviducts are
paired. There is no shell in or on the visceral hump.

The Cuttle-fish or Sepia officinalis is common in most seas,
and in the spring, when it approaches the shore to deposit its
egos amongst the rocks, it is easily caught. In considering the
anatomy of this form, it is important to orientate the animal
correctly ; with this view it should be placed mouth down-
wards, then its foot will be ventral, its visceral hump dorsal,
and its mantle cavity posterior. For the sake of convenience

it is, however, better to twist the animal through a right

212 ZQOELO GM

angle, and describe it as it swims, with its foot and mouth
anterior, the visceral hump posterior, the mantle cavity ventral,

Fic. 124,

A. Loligo vulgaris. B. Pen of the same, reduced in size. *f
a. Arms. D. View of the head from in front, show-
t. Tentacles. ing the arms (a), the tentacles (¢), the
C. Side view of one of the suckers, show- mouth (m), and the funnel (/).
ing the horny hooks surrounding the

margin,
and the shell or cuttle-bone, which may be felt through the
skin, dorsal. The most dorsally-placed pair of arms, really the
most anterior, are termed the first pair.

Sepia, being a Decapod, has five pairs of arms, of these,
the fourth pair are unlike the others, They are much longer,

MOLLUSCA 213

and can be withdrawn into pouches at their base; they do not
bear their suckers scattered uniformly over their inner surface,
but the suckers are all aggregated in a swollen pad at the free
end of the arm (Fig. 126). The suckers are very remarkable
organs, they are cup-like structures whose rim is strengthened
by a toothed horny ring. A retractor muscle can deepen the
cavity of the cup, so that when the edge of the cup is applied
to any object and the muscle contracts, the sucker adheres to
the object by the pressure of the surrounding medium. In

Fic. 125.

a. Internal skeleton of Sepia ornata. Rang.

6. Internal skeleton of Histioteuthis Bonelliana. D’Orb.
c. Internal skeleton of Spirula fragilis. Lamarck.

d, Animal of Spirula Peroniti.

Sepia, as in other Decapods, the suckers are stalked. In the
male; the fifth arm on the left side has lost some of its
suckers, and this is termed the hectocotylised arm, vide p. 222.

That portion of the foot which is modified to form the
sucker-bearing arms is homologous with the fore-foot or pro-
podium of other Mollusca (Fig. 122) The mid-foot or

mesopodium has become converted into the siphon, a funnel-

214 ZOOLOGY

like structure open at both ends. The posterior aperture
communicates with the mantle cavity. When the edges of
the mantle are in close apposition to the body-wall, to aid
which a pair of cartilaginous nodules exist on the mantle
edge, which fit into corresponding depressions on the outside
of the funnel, and the muscles of the mantle contract, the
water in the mantle cavity is forced violently through the
siphon. The result of this is, the Sepia darts backwards. In
the lumen of the siphon is a small valve which only allows
the water to pass one way; this possibly represents the hind-
foot or metapodium.

The cuttle-bone or shell of Sepia is entirely internal. It
lies along the dorsal surface in a sac formed by the concres-
cence of certain folds of the mantle in this region (Fig. 126).
It consists of a posterior horny portion, which is continued
forward by a series of calcareous plates deposited by the
inner wall of the sac; between these plates air is found. This
air must be secreted by the surrounding tissues, it probably
assists the Sepia to balance itself.

If the mantle be divided and the mantle chamber exposed,
the anus will be seen situated in the middle line near the
posterior end of the siphon. Close to it the duct of the ink
sac opens. A little way behind the anus, and on each side of
it, is situated a nephridial opening, and at about the same
level on the left side is the aperture of the genital duct.
The large ctenidia lie one on either side, and in the female
Sepia a pair of large nidamental glands are to be seen through
the body-wall.

The mouth is surrounded by a circular lip and guarded by
two strong horny beaks resembling those of a parrot, except
for the fact that the under beak is the larger and more pro-
minent (Fig. 126). The buccal mass is large and muscular, it
contains a well-developed radula. The rows of teeth consist
of five central conical teeth and one hook -shaped tooth on
each side. The oesophagus, a narrow tube, passes from the
buccal mass straight to the posterior end of the body, and
opens into a thick-walled stomach. At this point the intes-
tine bends forward ventrally, and gives off a curved caecum of
considerable size. From this the rectum passes along the

MOLLUSCA 21

wal

ventral body-wall to the anus. A pair of small salivary
glands le on either side of the oesophagus just behind the
cartilaginous skeleton of the head; their two ducts unite into
a single channel, which opens into the buccal mass in the
neighbourhood of the radula.

The liver is of considerable size; it is bilobed, and the
anterior end of each half reaches as far forward as the salivary
glands; the duct of each lobe arises about its middle, and
runs back parallel with the oesophagus, to open into that part

Fic. 126.—Diagram representing a vertical, approximately median antero-posterior
section of Sepia officinalis. From a drawing by A. G. Bourne. After
Lankester—Zoological Articles reprinted from Encyclopedia Britannica.

1. Mouth. 11. Lumen of siphon.

2. Upper beak. 12. Branchial heart.

3. Lower beak. 13. Appendage of branchial heart.
4. Odontophore. 14. Viscero-pericardial aperture.
5, Nerve ring. 15. Renal glandular mass.

6. Oesophagus. 16. Left ctenidium.

7. Crop. 17. Subpallial chamber.

8. Gizzard. 18. Valve in siphon.

9. Anus. 19. Afferent branchial vessel.
10. Cuttle bone enclosed by a growth of

the mantle.

of the intestine just behind the stomach which gives oft the
eaecum. The bile ducts are enwrapped by the unpaired
diverticulum of the nephridia, and this, where in contact with
them, developes spongy excretory tissue, the so-called pan-
creatic caeca. The ink bag lies to the right of the stomach, its
duct runs parallel to the rectum, and opens to the exterior.
Its secretion forms a pigment named after the animal, and
by the expulsion of this the surrounding water is made inky,
and thus serves as a screen to cover the escape of the squid.
The coelom of Sepia contains the stomach, the heart with

216 ZOOLOGY

its chief vessels, the branchial hearts, and in its posterior half
the genital gland. It is partially divided into two by an in-

Fia. 127. — Central
organs of the cir-
culation, gills, and
renalorgans of Sepia
officinalis. After
John Hunter.

vv’. Visceral veins.
a, Aorta.

v, Vena cava.

c. Ventricle.

d. Auricles.

e. Branchial hearts.
b. Branchiae.

r. Renal organs.

complete septum. It opens into the nephridia by a minute
pore on each side.

The heart consists of a ventricle with two auricles opening
into it. The ventricle is continued in front into an anterior
aorta, which gives off vessels to the mantle and liver and runs
forward to the head and arms, and behind into the posterior
aorta, which supplies the generative organs and the fins, ete.
The blood passes largely by capillaries but partly by lacunar
spaces, into the veins. Of these, the largest is the anterior
vena cava, which has a ventral position and splits into two
branchial veins. These latter are beset with diverticula of the
nephridia, and they receive numerous veins which bring back
the blood from the generative organs, the ink sac, etc. Just
before they enter the branchial hearts they are joined by veins
from the mantle and posterior end of the visceral hump. The
branchial hearts are pulsating muscular enlargements at the
base of the ctenidia, whose contractions force the blood through
the gill. A mass of excretory tissue—the pericardial gland—

MOLLUSCA 2G

is developed on the wall of the coelom, beneath each branchial
heart. The blood, after passing through the ctenidia, is
returned to the auricles.

The blood contains colourless corpuscles: in the oxidised
condition it is nearly colourless, but when venous it is bluish.
The colour is due to haemocyanin, a substance containing
copper, which is diffused through the serum.

The. ctenidia are organs of considerable size. In the
normal state their long axis is parallel with the longitudinal
axis of the body, and they are attached throughout their whole
length to the body-wall. The axis bears a double row of plate-
like lamellae, which decrease towards the anterior end, thus
giving a pyramidal shape to the organ. An afferent vein from
the branchial heart traverses the axis and gives off branches to
the lamellae; here the blood is aerated, and is then returned
by an efferent vein which runs parallel and close to the former,
this leads to the auricle.

The nephridia are paired, right and left, but they are con-
nected by two transverse portions, an anterior and a posterior.
The former of these transverse communications gives off a
diverticulum which stretches, as the unpaired nephridial sac,
back as far as the genital gland. The ventral wall of the
nephridia is smooth, but the dorsal wall, which is wrapped round
the branchial veins, and into which numerous veinlets run, is
spongy and glandular. At the anterior end of each kidney is
a short ureter which opens to the exterior at the side of the
anus. Near the inner end of the ureter there is a rosette-
shaped opening covered with ciliated epithelium, which leads
into the coelom.

Cephalopods, which are the largest and most ferocious of all
the invertebrates, have developed an internal cartilaginous
skeleton, a very unusual arrangement outside the phylum
Vertebrata. The cartilage consists of a structureless matrix,
through which numerous cells are scattered; the cells give off
branching processes which permeate the substance in all direc-
tions. Nodules of this cartilage exist in processes of the
mantle edge, and fit into corresponding depressions on the edge
of the siphon when the mantle is closed, and also along the
base of the lateral fins, but the most considerable developement

218 ZOOLOGY

of cartilage is in the head. Here there is a cephalic cartilage
of complicated form, which is pierced by the oesophagus. It
ensheaths the chief nerve ganglia, the ear is embedded in
it, and it forms two recesses which lodge the eyes. Another
portion affords some support to the bases of the arms, and there
is also a flat piece situated in the neck known as the nuchal
plate.

The chief nerve ganglia are aggregated round the oeso-
phagus, close behind the buccal mass, and are embedded in the

Fic. 128.—Lateral view of the nervous centres
and nerves of the right side of Octopus vul-
garis. From a drawing by A. G. Bourne.
After Lankester — Zoological Articles re-
printed from the Hncyclopedia Britannica.

Cerebral ganglion,

The optic nerve.

Pedal ganglion giving nerves to arms.

Pleuro-visceral ganglion.

Right visceral nerve.

Right stellate ganglion of the mantle, con-
nected by a nerve to the pleural portion
of 4.

Branchial branch of 5,

8. Olfactory branch of 5.
9. Buecal ganglion.
10. Buccal mass.

SNS Co a

>

cartilaginous skeleton. The cerebral ganglion on the dorsal
side of the oesophagus gives off a pair of nerves which end in
the superior buccal ganglion, from which a pair pass to
the inferior buccal ganglion, both lying on the surface of the
buccal mass. In connection with these ganglia there is a well-
developed stomatogastric system. lLaterally each cerebral
ganglion is continued into two very stout optic nerves ;
these expand into the optic ganglia, situated at the back
of the eye.

The cerebral ganglion gives off two circum-oesophageal com-
missures, which pass down to the nervous mass on the ventral
surface of the oesophagus. This mass is composed of three
ganglia very much fused together. Anteriorly le the pedal

MOLLUSCA 219

ganglia, which give off ten large nerves, one to each arm; they
also supply the siphon. The auditory nerves also arise from
the pedal ganglia, although their fibres may be traced to the
cerebral. The pedal ganglia are partially marked off from the
fused pleural and visceral by the presence of a small foramen
through which a blood-vessel passes. From the pleural por-
tion of this compound nerve centre a stout nerve passes to the
stellate ganglion, situated at the angle between the mantle and
the head. It can be seen shining through the integument
when the mantle cavity is exposed. From this ganglion nerves
radiate to the muscles of the mantle. The visceral half of the
fused ganglion gives off a pair of stout visceral nerves, which
unite to form a loop. These visceral nerves supply the gener-
ative organs, the kidneys, and other viscera, and each sends a
stout branch to a ctenidium.

The eyes of Sepia are of great complexity. They have a
striking but superficial resemblance to the Vertebrate eye, and
fundamental differences exist between these two types of visual
organs. Anteriorly the eye is covered by a transparent cornea,
which in Sepia is closed. The cornea is protected by certain
folds of skin, which can cover it in by the contraction of a
sphincter muscle, and there is also a horizontal lower eyelid.
Within the cornea is the anterior chamber of the eye, into
which the folds of the iris project; they partially cover the
lens, which consists of an outer and an inner part separated by
a membrane. The lens is supported by the ciliary body, which
with the lens occupies the anterior half of the retinal chamber.
The retina, which completes the wall of this chamber, is two-
layered, and the nerves which pass to it from the optic ganglion
enter the retina posteriorly.

The auditory apparatus consists of two otocysts sunk in
the cephalic cartilage. Their cavities have an irregular shape,
and are lined by an epithelium, which is ciliated in places,
they contain an endolymph, in which a single spherical otolith
floats.

An olfactory function is attributed to two small invagina-
tions of the skin, situated one just behind each eye. The sacs
open to the exterior by a small sht-like aperture; they are
lined by a ciliated columnar epithelium, amongst which are

220 ZOOLOGY

certain special sense cells, each provided with a single sense
hair. This organ is supplied by a nerve which arises from a
special ganglion situated near the base of the optic ganglion.
No osphradia corresponding with those of other Molluscs have
yet been described in Sepia.

Certain large cells crowded with pigment, situated in the
subepidermal connective tissue, play an important part in the
life of a Cephalopod. Attached to these cells, which are called
chromatophores, are a number of radiating muscle fibres; when
these contract, the cavity of the cell enlarges, and the contained
colour becomes diffuse; the chromatophores contract by their
own elasticity, and when contracted the colour is concentrated.
The whole system is under nervous control, and the colour of
the animal may change with startling rapidity In the Sepia
and other members of the group this faculty is used as a pro-
tection, the colour of the animal tending to assimilate itself to
that of the surrounding rocks or sand. In addition to the
chromatophores, the subepidermal tissues contain other modified
connective tissue cells known as iridocysts; these cells are so
modified as to produce iridescent colours by the diffraction
of light.

Sepia is a dioecious animal which lays eggs. The male is
usually somewhat smaller than the female, and its arms are
relatively longer; the fifth arm on the left side is hecto-
cotylised, that is, it is modified in connection with the process
of depositing the spermatozoa. It is thickened at its base,
and almost devoid of suckers. The testis lies at the extreme
end of the visceral hump, in a capsule—part of the coelom—
into which opens a more or less coiled vas deferens, the
walls of which are much folded, and provided with numerous
glandular diverticula. Whilst passing down this vas deferens
the spermatozoa are divided up into packets, and_ the
glandular walls secrete around each packet a_ cuticular
spermatophore. Finally, the sperm duct opens into a large
receptacle known as Needham’s sac, in which the spermatophores
are stored up; they pass to the exterior by the genital pore
situated to the left of the anus, and they are deposited in the
hectocotylised arm, and are possibly introduced by it into the
mantle cavity of the female at the time of oviposition.

MOLLUSCA 2

i)
—

The spermatophores are complex structures about 2 cm.
long, they have a receptacle in which the minute spermatozoa
are stored up, and a long tightly-coiled spiral, thread, the ex-
pansion of which explodes the capsule, and the spermatozoa
rush out.

In the female the ovary occupies the same position as the
testis in the male; the cavity of both these generative glands
communicates with the pericardial portion of the coelom,
though partly shut off from it by a septum. A cushion
projects into the lumen of the ovary, which bears ova in various
stages of developement ; from the ovary the oviduct, which is
ciliated, passes to its external opening to the left of the anus.
Accessory glands are present ; of these the most important are
a large pair of nidamental glands, which deposit the substance
of the egg capsules; in Sepia there is a second smaller pair of

i
fi pie ery

a Vi ‘i am sil
jet

NG Wye

Fic. 129.—a, Male of Argonauta argo, with the hectocotylised arm still contained

in its enveloping cyst, four times enlarged (after H. Miller). 6, Hectocotylus of
Tremoctopus violaceus (after Kolliker),

nidamental glands, as well as the large ones. The egg capsule
is prolonged into a stalk, by means of which the eggs are kept
together, and the collection of eggs somewhat nespid tiles a cluster
at grapes.

In Sepia one of the arms in the male is slightly modified,
and probably assists in the deposition of the spermatozoa, but in

tv
to
to

ZOOLOGY

certain Octopods this modification is carried much further. In
Argonauta argo the third arm on the left, and in Ocythoe tuber-
culata the same arm on the right, becomes detached from the
male, and is placed in the mantle cavity of the female. It carries
a small sac charged with spermatophores, and was at one time
looked upon as a parasite, and the name /Zectocotylus was given
it. The male, after losing
its arm, always reproduces
it again. In the female
Argonauta the eggs are
earried about in the shell;
this is the only member of
the Octopoda which has a
shell, and it does not cor-
respond with the shell of
other Cephalopods, but is
formed from the expanded
ends of the two dorsal
arms.

In other Dibranchiata
the shell varies from the
external coiled chambered
shell of Spirula to the
horny pen of Loligo. Even
in Spirula (Fig. 125) the
Fic. 130.—Argonauta argo, the Paper shell is partially sur-

Nautilus, female. The animal is repre-

sented in its shell, but the webbed dorsal rounded by folds of the

arms are separated from the shell which mantle, and in other forms

they ordinarily embrace. ie aitalciceshade riser fae
gether so that the shell comes to le in a closed sac. In the
Tetrabranchiata, Nautilus and the extinct Ammonitidae, the
shell is external, and chambered. The animal lies in the
last-formed chamber, and closely fits it. The chambers are
separated from one another by septa, and the whole is traversed
by a membranous tube, the siphunele, which is a continuation
of the integument of the animal. The chambers are full of
a gas probably secreted by the dorsal integument, and they
doubtless serve as a float.

In Nautilus the fore-foot is broken up into certain flattened

MOLLUSCA

N
N

wo

lobes, which differ in their arrangement in the two sexes. The
lobes bear at their edges cylindrical tentacles, which can be
retracted into muscular sheaths. Probably the tentacles cor-
respond to the suckers in the Dibranchiata. In some species
of cuttle-fish the suckers are replaced by hooks, or both may
coexist ; the arms in the Octopoda are usually connected by a
fold of skin forming a web, which is no doubt of use in swim-
ming. The arms of Architeuthis, a gigantic form, sometimes
attain the length of 40 feet, and the total length of the body
and arms may measure 60 feet.

The beak which guards the mouth is calcareous in Nautilus,
and horny in other Cephalopods. The possession by Nautilus
of two pairs of auricles which open into the single ventricle
is correlated with the two pairs of ctenidia. There are in
this same animal two pairs of nephridia; this repetition of
parts is almost unknown in Mollusca, the only other case
being the gills and shells of Chiton, and it is therefore par-
ticularly interesting.

The chief nerve ganglia in Nautilus are band-like, and
hardly to be distinguished from the commissures which con-
nect them. The nerves to the mantle are numerous, and are
not aggregated into one stout cord as in the Dibranchiata. The
same animal is provided with a pair of osphradia, situated at
the base of the anterior ctenidia; these organs have not yet been
discovered in other Cephalopods. The eye of Nautilus is one
of the most remarkable organs found in the order. It has the
shape of a kettledrum.; the tense membrane, which is external,
being pierced at its centre by a minute hole, which leads into
a dark chamber lined by the retina. The latter is bathed by
sea water, which enters through the minute pore. The mechan-
ism by which images must be formed on the retina resembles
that of a pin-hole camera.

CHAPTER XV

ECHINODERMATA

Asteroidea—Asterias, Solaster, Brisinga.
Ophiuroidea— Astrophyton, Ophiopholis.
Crinoidea—Comatula, Pentacrinus.
Regulares—Zchinus, Toxopneustes.
Clypeastroidea—Clypeaster, Rotula.
Spatangoidea—Spatangus, Brissus.
( Actinopoda—Holothuria, Cucumaria, Deima.
( Paractinopoda—Synapta, Ohirodota.

Echinodermata Bebencides

Holothuroidea

CHARACTERISTICS.— Animals with a primitive bilateral symmetry,
which is in the adult replaced by a more or less regular radial
symmetry, usually pentamerous. The skin 1s hardened by
calcareous deposits, which may take the form of scattered
spicules or of plates which build up an almost complete shell,
but in all cases they are mesodermic structures, A well-
developed coelom is present, and part of it becomes cut off
Jrom the rest to form the water-vascular system, which ws
both locomotor and respiratory in function. The five radial
vessels of this system correspond with five areas, the “ambu-
lacra” ; the angles between them form the “ interambulacra.”
The alimentary canal usually opens to the exterior at both
ends, but an anus may be absent. The sexes are usually
distinct, and developement is nearly always associated with a
metamorphosis. They are excluswely marine.

The Echinodermata are divided into five classes :

I. ASTEROIDEA.
II. OPHIUROIDEA.
III. CriInompEA.
IV. EcHINOIDEA.
V. HOLOTHUROIDEA.

ECHINODERMATA

tN
i)
wt

Ciass I. ASTEROIDEA (Starfishes).

CHARACTERISTICS.—Lehinodermata whose body is flattened dorso-
ventrally, and is produced into arms or rays, which are usually
jive or more ir number. These arms are longitudinally
grooved on the ventral surface, and the tube-feet lie in this
groove. The madreporie plate is dorsal and interradial in
position. The alimentary canal sends caecal diverticula into
the arms. The generative organs are interradial in position
at the base of the arms. Pedicellariae usually present.
Asterias rubens is one of the commonest of starfishes, and is

constantly left stranded on our shores by the retreating tide.

Its body consists of a central disk, from which five arms or

radii project. The surface on which it habitually rests or

moves, and on which the mouth opens, may be termed the
ventral, the upper and more convex, where the anus is situated,
may be called the dorsal.

From the mouth five grooves radiate along the arms, these
are the ambulacral grooves, and they lodge the tube-feet; between
each two grooves, and consequently interradial in position, are
five sets of oral spines, which project over the mouth and perhaps
assist in feeding. If the tube-feet be removed from each ray,
it will be seen that the ambulacral groove is formed of two rows
of ambulacral plates, situated right and left of the middle line of
the radius (Fig. 131). Each right plate is so placed as to form
an angle, open ventrally, with the corresponding left plate, and
between the adjacent plates of each side certain pores exist
which give exit to the tube-feet. The groove is covered in by
the integument, and lodges two radial canals, of these the most
ventral is divided by a vertical septum, and is called, for
reasons mentioned below, the “ peri-heemal” space. The dorsal
canal is the radial trunk of the water-vascular system. At the
outer end of the ambulacral plate a series of adambulacral
ossicles are situated, and these support three rows of moveable
spines. Those spines which are nearest to the centre of the
disk form the oral spines mentioned above ; these are borne by
the first adambulacral ossicles, one set on each side of an inter-
radius.

At the distal end of each arm the ambulacral plates end in

15

226 AOQOROGN4

a single ossicle, which supports a terminal tentacle bearing a
number of pits of pigmented cells, called collectively the eye-
spot. Between this single ossicle and the other ambulacral

Fic. 181.—Diagram of a transverse section of the arm of a Starfish.

1, Epidermis. 12. Adambulacral ossicle.
2. Mesoderm. 13, Radial trunk of water - vascular
3. Perihaemal space in the skin. system.
4, Peritoneal lining of body-cavity. 14. Radial trunk of blood vascular
5. A branchia. system of Ludwig.
6. Paired caeca from intestine. 15. Radial nerve connected with plexus
7. Mesentery supporting caeca. under epidermis.
8. Spine. 16. Ampulla of tube-foot.
9. Ossicle in skin. 17. Tube-foot.

10. Pedicellaria. 18. Perihaemal space.

11. Ambulacral ossicle. 19. Coelom.

plates all the new plates appear. The tentacle at the tip of the
arm, together with the eye-spot, is surrounded by a circlet of
spines.

On the dorsal surface of both disk and arms numerous
spines are scattered, and amongst them many pedicellariae
(Fig. 131). These must be regarded as modified spines; they
consist of a basilar plate and of two blades which snap against
one another like the two limbs of a pair of forceps—in some of
them the blades cross one another as they do in a pair of
scissors. The function of these pedicellariae seems to be to
catch hold of foreign bodies, and so keep parasites from settling

ECHINODERMATA 227

on the skin or penetrating through the branchiae into the
coelom.

On the dorsal surface of the disk, situated interradially, lies
the madreporic plate, through which the water-vascular system
communicates with the exterior. The two arms which lie right
and left of this plate are termed the “ bivium,” and contrasted
with the other three or “ trivium”; in mapping out the various
organs of the body these will be found to be convenient terms.
The anus lies near the centre of the dorsal surface of the
disk.

The skin is formed of (i.) an outer cylindrical epithelium
with nerve fibrils at the base, (i1.) an intermediate connective
tissue layer with some muscle fibres,—this is the matrix for the
spines and plates,—and (111.) an inner coelomic epithelium, which
is ciliated; this last lines the true coelom or enterocoel, a
spacious cavity containing the alimentary canal, the generative
organs, ete. The coelom contains a fluid in which amoeboid
corpuscles float.

The angle which the two series of ambulacral plates in each
arm make with one another is floored in by the outer layer of
the integument, the nerve plexus of which is thickened and
forms the radial nerve (Fig. 151). The cavity thus formed is
the radial perihaemal vessel or blood-vessel of French authors ;
it is divided into a right and a left portion by the presence of
a median mesentery. This mesentery in this species, but not
in others, has a certain amount of glandular tissue in it, which
Ludwig describes as a blood-vessel.

On the dorsal surface of the starfish numerous delicate
processes of the skin may be seen projecting above the general
level of the body-wall. These thin-walled extensions of the
integument are known as dermal branchiae; the coelomic fluid
passes freely into them, and they doubtless serve as respiratory
organs (Fig. 151). It has been recently shown that some of the
amoeboid cells of the coelomic fluid (phagocytes), when they
have eaten any particles which it is desirable should be ejected
from the body, make their way to the walls of these dermal
branchiae, and force a passage through them to the exterior,
whence they are washed away.

Besides the enterocoelic ciliated body-cavity, there are a

228 ZOOLOGY

number of vessels. They constitute the blood system according
to French authors. The radial one has already been mentioned ;
the five radials unite with a circum-oesophageal ring, which is
stated to open into the body-cavity by five interradial pores.
Inside this is another ring-shaped vessel, into which a large
sinus surrounding the stone canal—the axial sinus—opens.
Besides this there is an aboral pentagon which sends off inter-
radially pairs of vessels which dilate and surround the genital
organs.

The mouth is situated centrally on the ventral surface,
surrounded by a ring of nervous matter. The mouth leads by
a short oesophagus into a large stomach, the walls of which are
folded in many saccul. When the starfish attempts to devour
young molluses or shellfish which are too large to be taken in
at the mouth, these sacculi are protruded and enclose the prey.
They are retracted by special muscles. The walls of both the
oesophagus and the stomach are ciliated, and the eversible
portions contain many glands, the secretions of which possibly
exercise a paralysing effect on the prey. The stomach is
followed by a pentagonal pyloric portion with its angles
situated radially. From each angle a short duct passes to
the base of each arm, and here opens into two large hepatic
caeca, which occupy a large portion of the space in each arm
and extend to its tip. Each caecum is supported by two dorsal
mesenteries. From the pyloric portion a short rectum passes
to the anus, which is in the next interradius to that bearing
the madreporic plate, and is almost central. The rectum gives
off two short caeca, which lie in two neighbouring interradii
—that between the left and central arm of the trivium, and
between the left arm of the trivium and bivium.

The water-vascular system consists of a circumoral ring
which gives off five radial vessels, one running along each arm,
and a single interradial stone canal, which passes from the
circumoral ring, and opens to the exterior at the madreporic
plate, which is calcified.

The madreporic plate is marked externally by a number
of radial grooves; at the bottom of each of these is situated a
row of pores; these open into a series of tubules, which collect
into an ampulla, and this in its turn opens into the lumen of the

ECHINODERMATA 229

stone canal. The stone canal is lined by a ciliated epithelium,
surrounded by calcified connective tissue, a ridge projects into
its interior, and the free edge of the ridge may bifurcate, each
half then folding back upon itself. The circumoral ring bears
nine glandular bodies, composed of branching tubules lined
with cubical cells, and opening into the ring. ‘These bodies
are known as Tiedemann’s bodies. The stone canal opens in
the position where the tenth of these bodies should be. It is
possible that the corpuscles which float in the fluid of the
water-vascular system are formed in these bodies.

The radial vessels which pass along the arms lie ventral
to the ambulacral plates, between them and a transverse muscle
which runs between each pair (Fig. 131). Opposite each
tube-foot the radial vessel gives off a transverse branch. Each
branch passes between the ambulacral ossicles, and opens into
a vesicular expansion, the ampulla, situated in the coelom.
From this another vessel passes to the tube-foot. The con-
traction of the ampulla forces fluid into the tube-foot, and so
extends it. At the tip of the arm the radial tube ends in an
unpaired terminal tentacle, at the base of which is a thicken-
ing beset with eyes. The tentacle has a very well-developed
nervous layer.

The blood system described by German authors is founded
on misinterpretation. They describe a radial vessel, an oral
ring, and an aboral ring, and a connecting heart lying inside
the corresponding organs described above. The radial and oral
vessels are nothing but the thickened septa of the true vessels,
the heart is a solid glandular organ, and the aboral vessel is
the genital rhachis, partly degenerate. The rhachis is in
connection with the so-called heart.

The nervous system is diffused all over the body, but
better developed in some parts than in others. The epidermis
contains numerous sense cells, prolonged at their bases into
nerve fibrils; these are not very abundant on the dorsal
surface, but along the ridge which lies between the tube-feet,
and in a ring which surrounds the mouth, both sense cells and
nerve fibres exist in great quantities. The triangular ridges
which occupy the ventral surface of the arms unite in a ring
round the mouth, and constitute the central nervous system

230 ZOOLOGY

(Fig. 152). The outer cells of this ridge are mainly sense
cells, and ganglion cells and nerve fibres occur at their bases.
The nerve layer is also well developed on the tube-feet.

Fra. 132.— View of blood-vascular system
of a Starfish as described by German
writers. Modified from Ludwig.

1. Cireumoral ring.

2. Radial vessel with branches to am-
pulla.

3. Heart.

4, Circumoral ring.

5. Dorsal end of heart passing into the
skin.

6. Vessels to intestine.

7. Paired vessels passing to generative
glands,

Asterias rubens is dioecious. The generative organs con-
sist of five interradial pairs of glands, which are alike in both
sexes, and when mature each extends into two neighbouring
arms (Fig. 133). Except during the breeding season, the size
of the glands is inconsiderable. Each gland opens to the
exterior by a single duct, which terminates in a_ perforated
plate situated dorsally and interradially. The various glands
are connected together by a genital rhachis, and they are
supplied by the above-mentioned genital vessels, which dilate
to form a sinus round the glands. Fertilisation takes place
externally.

The Asteroidea are mainly inhabitants of shallow water,
though a considerable number of species from great depths have
been described. The arms are usually five in number; one
species of Solaster has, however, thirteen, and Lrisinga has nine
to twelve arms, which are more sharply marked off from the disk
than is the case with other Asteroidea. The same genus is
devoid of dermal branchiae, of eye-spots, and of ampullae at the
base of the tube-feet.

The family ASTROPECTINIDAE is, with one exception, charac-
terised by the anus being absent, and by the tube-feet being

ECHINODERMATA

to

Fic. 133.—The common Starfish (A sterias rubens), dissected to show motor, digestive,
and reproductive systems. After Rolleston and Jackson.

1. Central radius of trivium. 9. Ampullae of tube-feet.
2. Right arm of trivium. 10. Ambulacral plates, inner surface.
3. Left arm of trivium. 11. Pyloric portion of stomach.
4. Left arm of bivium. 12. Duct leading from stomach to paired
5. Right arm of bivium. caeca,
6. Madreporic plate and canal. 13. Cardiac division of stomach bulging
7. Arborescent ‘hepatic’? caeca, two in into arm.
each arm. 14. Anus.
8. Generative glands.

to
to

ZOOLOGY

arranged in two rows on the ventral surface of each arm,
and not in four, as appears to be the case in Asterias.
Their tube-feet have pointed extremities, and not a sucking-
disk.

Besides the ampullae on the radial vessels, additional

Fic. 184.—Solaster papposus (upper surface).

reservoirs for the water-vascular fluid usually occur on the
circumoral ring; these are termed /Polian vesicles, and are
usually five or ten in number. It is doubtful whether the
vesicles which occur near the right position in Asterias rubens
are really Polian vesicles, that is, opening into the ring, or
whether they are the first pair of ampullae of each radial
vessel. In one species, Cribella oculata, some of the openings
in the madreporic plate lead into that section of the body-
cavity which surrounds the heart and stone canal, instead of
into the latter canal.

The Asteroidea have great powers of regenerating lost
parts. Arms broken off grow out again from the disk, and
even the whole disk may be regenerated from a single
separated arm.

ECHINODERMATA

to
1os)
Oo

Crass II. OPHIUROIDEA (Brittle Stars),

CHARACTERISTICS.—Lchinodermata with a central disk bearing
long slender arms, into the cavity of which no part of the
alimentary canal is prolonged. There is no anus. The
madreporic plate is ventral, and usually is an oral plate.
There is no ambulacral groove, and the tube-feet are lateral in
position.

This class is allied to the Asteroidea, and is sometimes
included with the latter in a single class. The Ophiuroids,
however, differ from the
Asteroids in the sharp dis- ie
tinction between disk and germany
arms,a condition approached ‘% %
by Brisinga, m the absence
of any digestive diverticula
in the arms, in the ventral
position of the madreporic

‘
e WU AAda gant, MN aes
plate, and in the almost khnantiiiee

universal absence of pedi-
cellariae. In the adult also
the ectoderm is absent ex-
cept on the tube-feet. FS

The arms are long and
slender, in most cases they
are protected by four rows
of plates, a ventral, a dorsal, and two lateral, the tube-feet
protrude between the ventral and lateral; they have no
ampullae. The nervous system has sunk under the skin,
and is protected by the ventral plates. Dorsal to it is the
radial blood-vessel, and dorsal to that the water-vascular
vessel. In a transverse section of the arm, the greater part
of the space 1s occupied by the ambulacral ossicles. Originally
paired, these have fused and become single; they are grooved
dorsally and ventrally. The dorsal groove lodges part of the
coelom, the ventral the above-mentioned vessels and nerve
cord.

The mouth is armed with certain modified ossicles; it is
central in position, and leads into a spacious stomach, which

Fic. 135.—Ophiopholis bellis (upper surface).

234 ZOOLOGY

is produced into five radial and five short interradial caeca.
The walls of the stomach are lined by a ciliated epithelium,

Fic. 136.—Diagram of a transverse
section of an Ophiuroid.

1. Radial nerve, with lateral
branches.

bo

So-called radial blood-vessel.
Radial water-vascular trunk.
Tube-foot.

Ventral plate.

oo

oO

Lateral plate.
Ambulacral ossicles.

Dorsal plate.

Cs) CONT OD

Dorsal portion of coelom.

~_
<=

Muscles.

pao
=

. Lateral nerve.

12. Origin of lateral nerve.

and are supported by connective tissue strands, which traverse
the coelom to the body-wall. There is no anus.

The water-vascular system consists of a circumoral ring,
which bears four Polian vesicles; in the fifth interradius it
gives off the ciliated stone canal, which is simple and un-
calcified, this passes to the madreporic plate on the ventral
surface. In Astrophyton there are five madreporic plates, one
in each interradius, and five stone canals. The radial vessels
which arise from the ring bear no ampullae, but give off
branches which pass directly to the conical tube-feet. Cor-
puscles tinged with haemoglobin occur in the water-vascular
fluid of one species.

The true vascular system resembles that of Asterids. The
aboral ring has, however, an undulatory curve, being ventral
in the interradii. MacBride has recently proved that both the
axial sinus and the aboral ring are involutions of the coelom.
The so-called heart is nothing but a genital stolon, whence the
genital rhachis grows out. The genital stolon in the earliest

ECHINODERMATA 235

stage is a mere thickened ridge of peritoneum, so that here, as
in other Coelomata, the generative cells are derived from the
lining of the coelom.

The circumoral nerve ring, like the radial nerves, has lost
its connection with the epidermis, and has sunk into the body.

1

en rT TTF ATEN TNT ATTN RTT TNTCATTIAMMATHAEEKTTANAT a SSS —o ,

Ls . unin i> 7 :

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ENS

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Ve4

/} so a AN .

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141 10" 6

Fic. 137.—A diagrammatic vertical section of an Ophiuroid, after Ludwig. The
circumoral systems of organs are seen to the left, cut across, their radial pro-
longations cut longitudinally, to the right.

1. Body-wall. 101. External interradial muscle.

2. Mouth. 10?. Internal interradial muscle. (The line

3. Body-cavity. should point to the dotted tissue. )

31, Body-cavity of the arm. 11. Water-vascular system: to the left

4, Oral ossicles. the circumoral ring, to the right the

5. Torus angularis. radial vessel.

6. Oral plate. 12. Polian vesicle.

71. 1st ambulacral ossicle. 13. Nerve ring and radial nerve.

7°, 7°, 74. 2nd to 4th ambulacral ossicle. 14. So-called blood-vessel.

81, 8°, 8°. 1st to 3rd ventral plate. 14 (to the right). Genital rhachis enclosed
9. 1st oral foot. in aboral sinus.

10. Transverse muscle of the 2nd joint. 15. Radial perihaemal canal.

The radial nerves in the arms are frequently segmented, a
ganglionated swelling occurring corresponding with each ossicle.

The generative organs consist of numerous caeca which
open into a genital bursa. The bursae are ten in number, and
le one on each side of each arm; they open ventrally by a slit-
like aperture at the base of each arm. A genital rhachis con-
nects the generative organs, which are surrounded by a
blood-sinus, as in Asterids. Amphiura squamata is hermaph-
rodite, and it is stated that when certain internal parasites,
Orthonectidae, infest the coelom, it ceases to produce eggs, but
produces a greater number of spermatozoa.

Some of the Ophiuroids give off a phosphorescent light from
the back of their arms.

Ophiopholis bellis (Fig. 155) exists in great numbers in the

236

ZOOLOGY

northern European seas. Like many other members of the
class, it is brilliantly coloured. The different specimens of the
same species exhibit a surprising amount of variation both in
their colour and markings.

Crass III. CRINOIDEA (Sea Lilies).

CHARACTERISTICS.— The dorsal or aboral surface usually prolonged

FI

x
Ie

into a jointed stalk, by which the animal is fixed. The calyz,
consisting of the disk and arms, in some species breaks off from
the stalk and leads a detached existence. The jointed arms
bear lateral pinnules. The tube-feet take the form of ten-
tacles arranged in groups on the disk, arms, and pinnules.
No madreporic plates exist, but certain holes lead from the
water-vascular system into a ramifying system of vessels,
whence others open to the exterior.
The skeleton of the Crinoids is composed of a number of
ossicles with a very definite
arrangement. The topmost seg-
ment of the jointed stalk is
termed the centro-dorsal plate ;
in the Comatulidae, which lose
their stalk when adult, this
persists as the central aboral
plate, and bears several whorls
of cirrhi which have a root-like
appearance. The stalked forms,
such as Pentacrinus caput Med-
usae, also have numerous cirrhi,
arranged in whorls on their stalks.
From the centro-dorsal piece five
radial plates radiate; these are
continued by second and third
radial ossicles, and the last of
these bears two brachials (Fig.
138.—Pentacrinoid larval forms 141). These brachials form the
of Comarda. Natural size and first of a series which form the
axis of each of the ten arms.

The growing point of the arm forks at short intervals, and one

ECHINODERMATA 237

branch of the fork alternately, right and left, remains small
and constitutes a pinnule, a method of branching which occurs
in plants, and is termed
by botanists scorpioid
dichotomy.

The arms and _ their
pinnules have a grooved
ciliated ventral surface,
at the disk the grooves of
the two arms: of a pair
unite, and the five grooves
thus formed run to the Wy
mouth. The arms are "
flexible, and the free Crin-

CoO
te =f

oids swim through the sea 2, Ce SY &F pay
by the graceful undula- ; aS Be
: \s S on DS
tions of these processes. eet iG
. Hd, say OOS
In atransverse section 4 ME EH
hy

+
ROR Seas

aN

Zon

L
qaqaacacs<

co oa
ase

of the arm the following
parts may be distin-
guished: dorsally a large
brachial ossicle which is

D>
=;
CAI

traversed by an axial Ei g
. se
nerve, the contiguous We S|
5 - : oh g
ossicles being united and sh g
: Sid 9
moved bya pair of muscles HY EY &
= DY 4 4
(Fig. 140). Ventral to HH EE &
. . O +4
the ossicle is the body- Q ENS: g
: . 7 FO
cavity broken up _ into “ee
four ; SPACES: which com- Fic, 139.—Pentacrinus caput Medusae.
municate atintervals. One After Guttard,

of these is dorsal, one ven-
tral, and two lateral, the ventral portion is traversed by the sterile

generative rhachis. Below these coelomic spaces lies the radial
water-vascular vessel which gives off alternating branches to
the nonsuctorial tube-feet. At the side of the ambulacral
groove some spherical bodies of unknown function are situated,
these are termed sacculi, and consist of a membrane enclosing a

large group of spherules.

238 ZOOLOGY

The pinnules resemble the arms, with the exception that
the generative rhachis has become functional, producing either
ova or spermatozoa. The rhachis, both in the arms and in the

10 1

Fia. 140.—Transverse section of a Cri-
noid arm (partly diagrammatic). After
Milnes Marshall.

Ambulacral groove.
Ambulacral nerve.
Ambulacral water-vessel.
Tube-feet.

Pinnule.

Coeliac (dorsal) canal.

Subtentacular (lateral) canal.

cot oO OP ON EF

Ventral canal: contains genital rhachis.
Muscles connecting the joints of arm.
Axial cord.

H
aS

Its branches.

12. Branch to pinnule.

pinnules, is surrounded by a blood-plexus, and the whole is
enclosed by the ventral division of the body-cavity, which is
relatively much larger in the pinnules, corresponding with the
enlargement of the rhachis. The generative cells escape through
a series of special pores. At the tips of both arms and pinnules
all the sections of the body-cavity communicate with each
other.

The mouth is central, and the anus is interradial in
position and on the oral surface of the disk; the alimentary
canal is coiled, and lined by a ciliated epithelium. The coelom
in the disk is much broken up by strands of connective tissue
which support the viscera. The mouth is surrounded by
vascular, water-vascular, and nervous rings, which each give off
extensions into the arms (Fig. 141). The water-vascular ring
gives off numerous ciliated canals which open into a series of
vessels which communicate with the exterior by a series of

ECHINODERMATA 239

ciliated pores which traverse the integument. This system
represents the stone canal of Asterids. In one species of

Hm cob

Fy

v0.

Fig. 141.—A longitudinal section through the plane of the mouth and anus of
Pentacrinus decorus, Wyv. Th. After Carpenter.

Mouth. 6,, 62, 63. First, second, and third radial
Alimentary canal. plates.
Anus. 7,;, 7g. First and second distichal
On the left, the axial cord of the (brachial) plates.
ray; on the right, extensions of 8. The more or less calcified connective
nerves from the axial cord into tissue in the body-cavity.
the plated perisome of the ventral 9. Central vascular axis of stem.

side. 4;, ambulacral nerve. The 10. A cirrhus.

central nervous mass is shown at 11. Genital rhachis.

4, near the basal plate. 12. Ligament between the ray joints.
Basal plate. 13. Radial water-vessel.

The black plexus of blood-vessels in the centre of the figure is the plexiform gland,
containing the genital stolon.

Rhizocrinus there is one canal and one pore in each interradius,
but the number is much increased in other Crinoids.

The five genital strands are continuous with a central

genital stolon, which here, as in Asterids, has been mistaken for
a heart by German authors. Around this stolon are numerous
vessels, which in the central capsule of the dorsal nervous

240 ZOOLOGY

system dilate into chambers which give off vessels to the cirrhi.
Above they communicate with a plexus of vessels around the
oesophagus, this plexus communicates with the distal portion
of some of the stone canals.

The chief nervous system is situated dorsally ; it consists of
a mass of nervous matter lying within the circle of basal
ossicles, and giving off a large nerve to the stalk, which
supplies branches to all the cirrhi, and five radial nerves, each
of which divides into two, and the resulting nerves supply
each arm and govern their movements. This system is con-
tinued into the pinnules; it is probably connected here and
there with the ambulacral system of nerves, whose function
seems to be mainly sensory. This dorsal or anti-ambulacral
system may be derived from concentrations of a subepidermal
nervous system, such as exists in Asterids, which have sunk
into the body.

Crinoids are attacked by an order of highly-modified
Chaetopods, termed Myzostomidae. These occur only on the
Crinoidea, and live parasitically either on the disk or arms ;
their presence often causes local abnormalities of growth, pro-
ducing swellings sometimes termed galls. The order includes
two genera, Myzostoma and Stelechopus. Extinct Crinoids seem
to have suffered from the same parasite.

Crass IV. ECHINOIDEA (Sea Urchins).

CHARACTERISTICS.—Spheroidal o7 heart-shaped Echinodermata,
sometimes flattened dorso-ventrally. The calcareous ossicles
take the form of definitely-arranged plates usually immovably
united by their edges, and of moveable spines. The number
of radii always five in recent forms. Mouth and anus present.
A ciliated ectoderm covers the body of the Echinoids,

beneath this is a nerve plexus. The calcareous plates which

constitute the shell of the animal are developed in the con-
nective tissue of the integument. The apical series of plates
consists of a dorso-central piece surrounded by ten plates ; five
of them, the radials or ocular plates, bear sense organs, the
alternating five, interradial in position, are pierced by the genital
pores. The ambulacral plates abut against the radials, and it is

ECHINODERMATA 241

between the most dorsal ambulacral and the radial plates that
new ambulacral pieces are intercalated. One of the ambulacra

Fic. 142.—A portion of the shell of
Echinus gracilis. After Agassiz.

a. Ambulacral plates.
b. Poriferous zone.

c. Interambulacral plates.

is regarded as anterior, and an interradius is posterior ; in those
forms in which the anus is not central, it lies in this posterior
interradius. Adopting this orientation, the madreporic pores
are usually found on the right anterior genital plate.

Both the ambulacral or radial and the interambulacral or
interradial areas are composed of a double row of pentagonal
plates, firmly united with all the contiguous plates. Each of
the ambulacral plates is formed by the fusion of several small
plates, the pore-plates ; these latter are pierced by two holes,

Fic, 143.—Spine of an Echinid. After Leuckart.

1. Spine.
2. Basal knob.

3. Circular muscle of spine.

rs

. Ligament.

through which two processes from the water-vascular system

pass and fuse to form one tube-foot. Both the radial and

interradial plates bear calcareous knobs, upon which long

spines are articulated; these are moved by certain muscles

attached to their base, and form important locomotor organs.

Pedicellariae, with usually three jaws, are also present. Some
16

242 ZOOLOGY

of these are provided with glands which open to the exterior
near the tip of the jaws; the glands are said to secrete a sticky
fluid by means of which the Echinoid attaches to itself pieces
of seaweed, etc., which screen it from observation. The smaller

Fic. 144.—Pedicellariae of Kchinus saxatilis.

After Gegenbaur.

a. Open. 6, Closed,

pedicellariae serve chiefly to clean the surface of the body, and
some of them serve as locomotor organs, and to catch passing
worms, etc. They are well supplied with nerves, and some of
them have in addition a special tactile organ.

The peristomial area immediately surrounding the mouth

Fic. 145.—View of Sea Urchin, with part of the shell removed to show the course
of the alimentary canal (from Leuckart). After Cuvier. 4

1. Mouth, surrounded by five teeth (dis- 5. The siphon.
placed). 6. Oral vascular ring.

. Lantern of Aristotle. 7. Aboral sinus.

. Oesophagus, coiled intestine, and 8. Blood-vessel accompanying intestine.
rectum. 9, Ampullae at base of tube-feet.

4, Ovaries with oviducts.

ww bo

ECHINODERMATA 243

is soft and membranous, with scattered ossicles. The mouth
opens into an oesophagus, surrounded in the Regulares and
Clypeastroids by a complicated masticatory apparatus known
as Aristotle’s Lantern. The oesophagus extends into the inter-
radius of the madreporic plate, and opens into an intestine
which takes a spiral course, finally opening by the anus, which
may be nearly central in position or quite eccentric. The
intestine is accompanied by a second tube, the siphon, which
may have been pinched off from the intestine, into which it
opens at each end. The whole is held in position by numerous
strands of connective tissue.

The body-cavity is spacious and is filled with a fluid in
which amoeboid corpuscles float, similar to those found in the
water-vascular system.

The circumoral water-vascular ring lies at the dorsal end
of Aristotle’s Lantern. The ring gives off in each inter-
radius a diverticulum or Polian vesicle, and in each radius a
radial vessel which runs along the inner surface of the ambu-
lacral plates ; it bears a number of ampullae, which open, as a
rule, by two ducts into the tube-feet, these vary much in
structure; when suctorial the sucker contains calcifications.
In the interradius of the madreporic plate a stone canal, which
may be membranous or calcified, passes to an ampulla which
opens by the madreporic plate.

The blood system of Echinoids is still involved in obscurity.
There is a circumoral ring adjacent to the water-vascular ring,
giving off two vessels which run one on each side of the
intestine, and there are probably radial vessels, and one or
more vessels accompanying the stone canal. Glandular tissue
representing the so-called heart of other forms is developed in
the wall of this structure.

In the Regulares ten buccal gills are usually found pro-
jecting from the peristomial area around the mouth; these are
hollow arborescent diverticula of the coelom, resembling in
essential structure the dermal branchiae of the Asteroids.

There is a circumoral nervous ring situated in the angle
between the base of Aristotle’s Lantern and the peristome ;
this gives off five radial nerves, each of which ends in a sensory
prominence of the epidermis, which traverses the ocular plate.

244 ZOOLOGY

The radial nerves send branches to the tube-feet, from the base
of which a nerve passes to the sub-epidermal plexus of nerve

LLL

Ze

Fic. 146.—Diagrammatic vertical section of a Sea Urchin (from Leuckart),
After Hamann.

1. Mouth. 10. Aboral sinus containing so-called
2. Intestine cut short. blood-vessel.

5. Siphon. 11. Circumoral water-vascular ring.

4. Rectum. 12. Oral nerve ring.

5. Anus. 3. Tube-foot with ampulla.

6. Ventral vessel on intestine. 14. Radial nerve.

7. Dorsal vessel on intestine. 15. Radial water-vascular vessel.

8. Stone canal. 16. Polian vesicle.

9. Madreporic plate. 17. Muscles.

18. Ocular plate.

fibrils, which ramify all over the body just outside the calci-
fications, and govern the movement of the pedicellariae and
spines. :

The generative organs typically consist of five arborescent
glands, though the number is often reduced, lying interradially,
and opening on the genital plates. In the young they are all
connected by a circular genital rhachis; they become very
conspicuous in the breeding season.

The pore plates of the paired ambulacral areas are in the
female Hemiaster philippii extended and depressed so as to
form four deep oval cups. In these the eggs are deposited

ECHINODERMATA 245

and the young develope, being kept in position by some of the
spines bending over them.

SSS S
= — —— —S-= SSS SS
SSSSSSS ONS \
—————S = Sf es
— —S== ge
<< SS Z

Fic. 147.—Spatangus purpureus.

The Echinoidea are divided into three subdivisions :

Gi.) Regulares.—Sphacroidal or flattened circular bodies.
Ambulacral and interambulacral areas equal in
length. Central mouth and subcentral anus. Complex
masticatory apparatus—Aristotles Lantern — present.
Echinus, Toxopneustes.

(1.) Clypeastroidea.—Shield-shaped, often flattened bodies.
Central mouth, with Aristotles Lantern. Very broad
ambulacra, with their dorsal ends forming a peta-
lod rosette round the apical plate; small tube - feet.
Anus excentric. Clypeaster, Rotula.

Gu.) Spatangoidea.—/rreqular heart-shaped bodies. Mouth
and anus excentric. No Lantern of Aristotle. Ambu-
lacra petalord, and the anterior one unlike the others.
Spatangus, Brissus.

Ciass V. THE HOLOTHUROIDEA (Sea Cucumbers).

CHARACTERISTICS.— Lehinodermata with elongated bodies, usually
pentagonal in cross section. The integument is leathery,

246 ZOOLOGY

and contains small scattered calcareous ossicles. The mouth

is surrounded by a circlet of retractile tentacles, into which the

water-vascular ring sends extensions. The madreporie plate
usually opens into the body-cavity. The anus is usually
terminal.

The body of the Holothurians is elongated along an oral-
apical axis. The ambulacra are five in number; they may be
equally developed, or three of them,
the trivium, may be flattened and
form a creeping sole upon which the
animal rests; the bivium is then con-
vex. This occurs in Psolus and in all
the Elasipoda. When this specialisa-
tion of radii takes place, the tube-feet
are modified on the trivium. In other
cases the tube-feet are scattered all
over the body, and in others—the
Synaptae—they are entirely wanting.
The skin is covered by an ectoderm
with an external cuticle; within this
is a layer of connective tissue, in which
cells laden with pigment and cal-
eareous ossicles are scattered. This
layer also includes a nervous plexus.
The connective tissue sheath surrounds
a muscular layer whose fibres run in
a circular direction, and more inter-
nally are five radial bands of longi-
tudinal muscles, one running along each
ambulacrum, and lying beneath the water-vascular vessel and
nerve ; anteriorly these bands are attached to the pharyngeal
ossicles, which are radial and interradial in position. The
ossicles in the integument are always small in size; they may
be simple spicules, or may assume a number of very elegant
forms in the different genera. In the Elasipoda they exist
in the mesenteries and in the walls of the alimentary canal,
as well as in the integument.

The coelom is large, and is lined with ciliated cells; a
special section of it surrounds the pharynx, and in the outer

Fic. 148.—Holothuria
papulosa.

ECHINODERMATA 247

walls of this the pharyngeal ossicles are formed; these are
notched for the passage of the radial nerve and water-vascular

vessel.
In some of the Synaptae the alimentary canal runs nearly

Fria. 149.—Spicules of Holothuroidea.
After Semper.

q fea a and. Anchor and anchor plate of
OWE Synapta indivisa. Semper.
4) =I c. Spicule of Chirodota rigida.
J Semper.
d. Wheel spicule of Chirodota
vitiensis. Griffe.
e. Spicule of TZhyone chilensis.
Semper.
Jt, g, th. Anchor and anchor plate of
Synapta godefroyii. Semper.
i. Spicule of Rhopalodina lageni-
formis. Gray.

straight from the mouth to the anus, but as a rule it forms a
coil with three limbs. The mouth is situated in the centre of

Fic. 150.— Diagram of
a transverse section
through the body of

a Holothurian. From

Leuckart.
5

11" 12m 9 diac
1. Dorsal surface, dorsal interradius. 11’, 11”, 11”. The mesenteries of the
2. Ventral surface. three limbs of the intestine.
3. Left dorsal radius. 12’, 12”, 12”. The three limbs of the
4. Right dorsal radius. intestine.
5. Right ventral radius. 13. Respiratory trees, the left surrounded
6. Left ventral radius. by a rete mirabile of blood-vessels.
7. Radial nerve. 14. Two tubules of the generative organs
8. So-called radial blood-vessel. lie to the right of the genital duct.
9. Water-vascular vessel. 15. Ventral blood-vessels.

10. Radial muscles.

a peristomial area, and is in the Elasipoda directed ventrally.
The mesentery of the first descending limb of the alimentary
canal is situated in the interradius, in the middle dorsal line,

ZOOLOGY

sane SUUREEEUIIRIT OS™

-_=-

ae
r- | 94
je=ea di

=

Fia. 151.—View of the internal organs of a Holothurian which has been cut open

ie

to

a ew)

along the middle dorsal line.

6.

Radial ossicle of the calcareous ring,
into which the longitudinal muscle
is inserted.

Interradial ossicle of the calcareous
ring.

Radial water-vascular vessels.

Circumoral ambulacral ring.

Polian vesicle.

ice) Coy

From Leuckart.

Two stone canals ending in Madre-
poric plates; the upper one is
attacaed to the dorsal mesentery,
the lower one hangs freely.

Circumoral blood-vessel.

Ventral blood-vessel.

Dorsal blood-vessel.

Anastomosing branch between dif-
ferent parts of the ventral blood-
vessel.

ECHINODERMATA 249

that of the second or ascending limb in the left dorsal inter-
radius, and that of the third or second descending limb in the
right ventral interradius. The pharynx is followed by a
stomach with muscular walls; the intestine forms the longest
portion of the alimentary canal ; the posterior end of the rectum,
or the cloaca, is rhythmically contractile, and takes in and sends
out sea water; special muscles run between it and the body-
wall.

Certain appendages known as respiratory trees open into the
cloaca. These are sometimes regarded as homologous with the
two interradial caeca which open into the rectum of Asterids.
They are branched structures, usually two in number; each
terminal ramification opens by a fine tube into the coelom, and
they doubtless serve to introduce sea water into that space.
Their function is probably in part respiratory, and they re-
semble in structure the similar organs in the armed Gephyrea.

In some species some of the basal ramifications of the
respiratory trees are modified into the so-called Cuvierian
organs. In these the peritoneal covering becomes glandular,
and when the animals are irritated they are discharged into
the water through holes torn at their base in the cloacal wall,
and swell up into long tenacious elastic threads, which serve
the purpose of entangling their enemies. At times, when much
disturbed, the Holothuroidea will throw out their whole intes-
tine through the anus; but it is probably regenerated.

The water-vascular system consists of an oral ring, which
gives off five radial vessels, these run at first upwards and out-
wards, and give off branches to the oral tentacles; the tentacles
may increase in number with age. The tentacles assist in the pro-
cess of feeding, either shovelling in mud or sand—in which case

11. Anterior part of alimentary canal. 19. Generative organs.

12’, 12”, 12”. The three limbs of aliment- 20. Opening of generative duct.
ary canal, 21. Circular muscles in body-wall.

13. Cloaca. 22. Right dorsal muscle.

14. Cloacal opening with five teeth. 23. Right ventral muscle.

15. Radiating muscles of cloaca. 24. Median ventral muscle.

16. Organs of Cuvier. 25. Left ventral muscle.

17’, 17”. Respiratory trees. 26. Left dorsal muscle.

18. Dorsal mesentery with free posterior
margin.

The tentacular ampullae are omitted ; the mouth is in the centre of the divided
tentacles.

ZOOLOGY

to
un
°

the intestine, like that of the Gephyrea, is full of sand—or en-
tangling food particles; and in the latter case the tentacles are
then thrust into the mouth, which removes any nutritive particles.
The radial vessels pass through notches in the radial ossicles of
the pharyngeal calcareous ring, and run along the ambulacra
giving off tube-feet outside the bundles of muscle fibres. They
are absent in one group, and devoid of tube-feet in others. The
ampullae of the tube-feet are embedded in the circular muscle
layer in the Elasipoda, and in many of this group the stone
canal opens on the dorsal surface, and in others it lies in the
tissue of the integument; in other subdivisions it is supported
by the mesentery, and the madreporic plate opens freely into
the coelom. It may or may not have calcareous walls; the
fluid in this system contains numerous corpuscles.

The vascular system consists of spaces in the connective
tissue not lined by an epithelium. There is a circular space
round the pharynx, just behind the water-vascular ring. This

Fie. 152.—Sea Cucumber Cucumaria crocea (Falkland Islands) bearing its young.
After Sir Wyville Thomson and Murray, ‘‘ Challenger’”’ Narrative.

communicates with a dorsal and a ventral intestinal vessel, and
these two are connected by numerous anastomoses round the
walls of the alimentary canal. ‘The dorsal vessel is in connec-
tion with a plexus which surrounds the left respiratory tree.
There are no radial vessels.

The circumoral nerve ring gives off five radial nerves, and
nerves to the tentacles. There is a nerve plexus in the skin

ECHINODERMATA 251

and the tube-feet. In Synapta ten auditory vesicles contain-
ing numerous otoliths have been described at the base of the
radial nerves.

The generative organs are either a single gland situated at
the left of the dorsal mesentery, or a double gland, one on each
side of it; the glands are continuous with a single duct, which
opens in the dorsal middle line close to the base of the ten-
tacles. With one or two exceptions, the Holothuroidea are
dioecious.

The young of one species, Cucumaria crocea, found near
the Falkland Isles, are attached in rows on each side of the
dorsal ambulacrum. The early stages of developement ap-
parently take place rapidly, and the embryos are arranged in
position by the tube-feet of the ambulacrum.

In the East Indies some species form an article of com-
merce under the name of Béche-de-mer. They are dried and
sold to the Chinese, who use them in the preparation of soup.

The Holothuroidea are classified as follows :

I. Actrnopopa.—Ladial canals present in the water-vascular

system.

a. Aspidochirotae—7he tentacles are peltate in form,
respiratory trees are present. Holothuria, Miulleria.

b. Elasipoda.— Tentacles as above. The dorsal tube-feet
produced often into very long stiff processes. Respira-
tory trees rudimentary or absent. Stone canal sometimes
opens to the exterior. Deima, Elpidia.

ce. Dendrochirotae.— The tentacles have a dendriform shape.
Cucumaria, Thyone.

d. Molpadiidae.— The tentacles are simple or pinnate. The
radial canals bear tentacles, but no other tube-feet.
Molpadia, Caudina.

II. Paractinopopa.— The tentacles are pinnate. No radial
canals, no tube-feet, no respiratory trees. Synapta, Chirodota.

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ARTHROPODA

CHARACTERISTICS. — Bilaterally symmetrical Coelomata, with
a chitinous exoskeleton. Their body is segmented hetero-
nomously. The segments usually bear a pair of jointed
appendages, those in the neighbourhood of the mouth are
modified im connection with the prehension and mastication
of the food. The nervous system consists of a brain or.
supra-oesophageal ganglion, a ring round the oesophagus, and
a ventral, usually segmented, nerve cord. A heart is
typically present dorsal to the alimentary canal, blood enters
it through a series of lateral ostia ; the coelom is reduced, and
to some extent replaced by a haemocoel. The sexes are typi-
cally distinct, and the pared genital glands usually open by
paired ducts. Cilia are universally absent from the group,
with the single exception of Peripatus.

The Arthropoda may be divided into two large groups,
according to the nature of the breathing organs: (i.) the
BRANCHIATA, which breathe by gills and are typically aquatic ;
and (ii.) the TracnEaTa, which breathe by tracheae or lune
books, and are typically terrestrial.

The Branchiata include but one class, the Crustacea.
The Tracheata include four: (i.) the Prototracheata, (ii.) the
Myriapoda, (iii.) the Insecta or Hexapoda, and (iv.) the
Arachnida. The first three classes may be grouped together
as the Antennata, and opposed to the last class, the
Arachnida.

254 ZOOLOGY

I. BRANCHIATA.

Ciass CRUSTACEA.

CHARACTERISTICS.— Aquatic Arthropods, which breathe either
through the general surface of their skin or through
specialised extensions of the same, the branchiae or gills.
Two pairs of antennae are found, and the appendages are
as a rule biramous. A limb-bearing thorax is either free or
united with the head. The usually segmented abdomen may
or may not bear appendages. Some of the limbs are modified
to form jaws. The gills ave usually extensions of the basal
joint of some of the appendages. The whole group, both in
its internal and external features, 1s, with few exceptions,
rigidly bilaterally symmetrical.

The Crustacea are divisible into two series: (A) the

Entomostraca and (B) the Malacostraca.

A. ENTOMOSTRACA.

A. The Entomostraca inelude many comparatively small
and simply-organised Crustacea, the number of whose segments
varies within wide limits. A large carapace, which may enclose
the whole body, is often present. The demarcation between
thorax and abdomen is often shown by the opening of the
generative organs. Paired compound eyes and an unpaired
simple eye often coexist. There is no masticating stomach. The
developement almost always includes a Nawplius stage.

The ENTOMOSTRACA consists of four orders :

1. PHYLLOPODA.

2. OSTRACODA.
3. COPEPODA.
4, CIRRHIPEDIA.

Orper 1. PHYLLOPODA.

CHARACTERISTICS.—Crustacea, with usually elongated and well-
seymented body, partially covered by a shield-like carapace,
which may be laterally prolonged to form a bwalved shell.
The number of segments and appendages varies greatly, but
there are never less than four leaf-like lobed swimmang-feet.

ARTHROPODA 255

The Phyllopods are divided into two sub-orders: (a) the
Cladocera and (0) the Branchiopoda.

a. Cladocera.—The Cladocera or water-fleas are all small.
Their body is laterally compressed, and their carapace takes the
form of a bivalved shell, within which the larger part of the
body lies concealed. A pair of large biramous antennae are used
as swimming organs.

The Cladocera include many species common in freshwater
streams and inland lakes. Daphnia pulex and Daphnia longispina
occur frequently in ditches and ponds in England, and although
they are of minute size, 4 or 5 mm. in length, they form a
convenient type of this sub-order. The sexes differ both in
size and structure, and it will be convenient to describe the
female first, and afterwards to mention those points of differ-
ence which the male presents.

As is usual in Crustacea, the body of Daphnia is divisible
into three regions: the head, the thorax, and the abdomen.
The large bivalve shell which encloses the body like the
valves of a Lamellibranch, is an extension of the dorsal surface
of the cephalic segments. The head is provided with a pair
of antennules, uniramous, very small, and bearing olfactory
hairs ; a pair of antennae which are biramous and very long
and are used for swimming; a pair of mandibles; and one
pair of maxillae. The larva has two pairs of maxillae,
but the second pair disappear before the adult stage is
reached. The thorax consists of five segments, which are free
from the shell. Each segment bears a pair of lamelliform
swimming-feet. The abdomen is three-jointed, and carries no
appendages ; it is curved forwards ventrally, and terminates
in an unsegmented post-abdomen or telson. The abdomen
bears dorsally several processes which assist in enclosing the
brood pouch, a space left between the dorsal side of the thorax
and abdomen and the shell. The post-abdomen on which the
anus opens bears two long dorsal tactile setae, and ends in
two hooks or styles.

Appendages of Daphnia.

1. Antennules, uniramous and small. 6. 1st thoracic swimming-feet,
2. Antennae, biramous. 7. 2nd $3 5
3. Mandibles. 4, Ist maxillae. 8. 3rd 3 a
5. 2nd maxillae, disappear during 9. 4th 55 Fy
larval life. 10. 5th By ts

256 ZOOLOGY

The head bears a large median compound eye, which is
formed by the fusion of two originally lateral eyes, and behind
this lies a single simple eye.

\

oe
| MI

As A2

Fic. 153.—Side view of female of Daphnia similis. After Claus.

1. Antennules. 9. Heart.

2. Antennae. 10. Brood pouch.

3. 1st pair of legs. 11. Shell gland.

4, 2nd pair of legs. Th. 3 and Th. 5. 8rd and 5th thoracic
5. 3rd pair of legs. segments.

6. 4th pair of legs. A.1, A.2, A.3. Ist to 38rd abdominal
7. 5th pair of legs. segments.

8. Hepatic diverticulum.

An upper lip guards the entrance to the alimentary canal,
and the mouth lies between the two-toothed mandibles; the

ARTHROPODA 257

digestive tube passes straight through the body, with hardly
any change of diameter, to terminate in the anus in the post-
abdomen. The only structures which open into it are a pair
of small curved caecal processes which are given off near the
anterior end, and which are usually regarded as liver diver-
ticula.

The heart, which is much shorter than is usual with Crust-
acea, is correlated with the small size of the animal. It con-
sists of an oval sac, the muscular nature of whose walls is very
evident. The sac is suspended in a pericardium which con-
tains blood; this blood enters the heart through a single ostium
on each side, and is forced out by the rhythmic contractions of
the organ through an anterior opening. Although there are
no blood-vessels with distinct walls, the blood follows a definite
course, flowing in channels through the various parts of the
body and shell. The blood contains amoeboid corpuscles.

A coiled gland, which ends blindly at its inner end, opens
to the exterior in the region of the second maxillae (Fig. 153).
This is termed the shell- or maxillary gland, and it is the
characteristic nitrogenous excretory organ of the Entomostraca,
as opposed to the antennary gland of the Malacostraca. In
Estheria the gland terminates in a vesicle, the walls of which
are lined by flat epithelial cells, and it has been suggested
that this may represent a portion of the primitive coelom, just
as does the vesicle at the inner end of the nephridium in
Peripatus. The larvae of some Phyllopods possess an anten-
nary gland as well as a shell gland, but this disappears before
the adult stage is reached.

Many species of Daphnidae, e.g. Sida, have also a neck gland ;
these animals swim on their backs, and the neck glands secrete
a sticky substance which enables them to attach themselves to
foreign bodies.

The brain in Daphnia gives off two stout nerves, which
pass forward and almost immediately fuse to form a large optic
ganglion, which supples the compound eye; it also gives off
nerves to the simple eye, to a curious sense organ composed of
an aggregation of ganglion cells in the neck, and to the first or
olfactory antennae. <A pair of circum-oesophageal commissures
surround the oesophagus, and the large swimming antennae

if

258 ZOOLOGY

are supplied by the first sub-oesophageal gangha. The right
and left strands of the ventral cord remain distinct and separate
from one another throughout their course, being united by
commissures at the various gangha. Of these one pair supplies
the muscles which move the mandibles and maxillae, and there
is a pair for each pair of legs. The last pair of ganglia give
off posteriorly a fine nerve, which supplies the sensory spines
of the abdomen.

The ovaries le one on each side of the alimentary canal ;
they are tubular, and reach as far forwards as the heart, and
their walls are continuous with those of the oviducts which
open into the brood-pouch between the abdomen and the shell.
The ovary is broken up into a series of segments, each of which
contains four cells. One of these becomes an ovum and in-
creases in size by absorbing the other three. In the case of
the large winter eggs, the contents of two or more segments are
absorbed by the cell destined to become the ovum.

The male is but little more than half the length of the
female; the first pair of antennae, which are minute in the

Fig. 154.—Side view of male Daphnia
similis, magnified to the same extent as
Fig. 153. After Claus.

1. Antennules.

2. Antennae.

3. Testis.

4. Ductus ejaculatorius.

5. Rectum,

8. Hepatic diverticulum.

9. Heart.

11. Shell gland.

female, are here of considerable size, though not so large as the
second. They are provided with numerous olfactory hairs.
The first pair of swimming legs are provided with a claw and
a spine which project between the two valves of the shell.
The space between the abdomen and the shell is a narrow

ARTHROPODA 259

split, and is not hollowed out to form a brood-pouch, as is the
case in the female.

The testes occupy relatively the same position in the body
as the ovaries, lying one upon each side of the alimentary canal.
They are continuous with the vas deferens, which opens by
means of a muscular ductus ejaculatorius upon the post-
abdomen.

The small males are much rarer than the females; they are
usually to be found in the autumn, but sometimes occur at
other times of the year, when the conditions of life become un-
favourable. During the summer the female produces a number
of summer eggs, which hatch out in the brood-pouch. The
enormous fertility of the water-fleas is shown by the fact that
in nineteen days a female D. pulex produced five broods, the
total number of young being 209; and it has been calculated
that the descendants of a single individual, which becomes
mature in ten days, and then produces broods of fifteen young
every three days, would amount to over twelve million in less
than two months. The rapidity of developement is rendered
possible by the nutriment stored up in the summer eggs, and
this is in some species augmented by the secretion of additional
food material into the brood-pouch.

Like many other river animals, such as freshwater Polyzoa
and Sponges, the Daphnia have developed a means of ensuring
the existence of the species through the frosts, etc., of winter.
This is effected by means of the winter eggs. These eggs
are larger than the summer ones, and contain more
yolk, a correspondingly large amount of the contents of the
ovary being absorbed during their maturation. They are in-
capable of developing without fertilisation. The winter eggs
pass into the brood-pouch, and a part of the carapace of the
mother becomes in this region modified to form a capsule for
the eggs, this is called the ephippiuwm. At the next ecdysis
the ephippium, which usually contains two eggs, is thrown off
and floats away. It is a bivalved structure and has a very
striking resemblance to the statoblasts of some Polyzoa. The
ephippium may be redeveloped by the female even when
fertilisation does not occur, but in this case no eggs are laid;
it may also be replaced by the ordinary brood-pouch.

260 ZOOLOGY

The characteristic larval stage of the Entomostraca, the
Nauplius, is not present in the Cladocera, except in the genus
Leptodora, and there it is confined to the winter-egg genera-
tion.

The Cladocera are as a rule freshwater inhabitants, living
in enormous numbers in lakes, ponds, and springs; only a few
species flourish in brackish water or in the sea.

b. Branchiopoda.—The branchiopoda are Phyllopods of
considerable size, with clearly segmented bodies often partially
covered by a shield-shaped or laterally compressed shell. They
possess from ten to sixty pairs of foliaceous swimming append-
ages, which bear well-developed gulls.

The Branchiopoda differ from the Cladocera in the fact
that they are larger, consist of more segments, and are generally
more complicated in their structure. They present considerable
differences in the various species. Lstheria and Limnadia bear
large bivalved shells which completely enclose the body, Apus
has a shield-shaped dorsal shell which covers the head and
body, but leaves the tail free, whilst Branchipus is devoid of
any shell.

The flattened leaf-like appendages of Apus have been
looked upon as a primitive type from which the appendages of
other Crustacea may be derived. This type of appendage is
almost completely retained in the foliaceous maxillae of Astacus.
The abdominal appendages, that is, those which are situated
behind the genital openings, are the least specialised, and these
present an unjointed axis which bears on its inner edge six
processes termed endites, which bear numerous setae. The
axis ends in a sub-apical lobe, and carries on its outer sides
two exites; of these the distal is large, and has been termed
the flabellum, the proximal is devoid of setae, and forms the
branchia.

In the female the appendage of the 11th thoracic segment,
which bears the opening of the oviduct, is modified; the 6th
endite and the sub-apical lobe are enlarged to form a hollow
cup, over which the flabellum closes like a lid, this forms a
receptacle for the ova, and the appendage is known as the
oostegopod.

ARTHROPODA 261

Appendages of Apus cancriformis.

1. 1st pair of antennae (antennules). 5. 2nd maxilla.

7, Pratl a ‘A 6-16. The 11 pairs of thoracic limbs.
3. Mandible. 17-68. The 52 pairs of abdominal limbs.
4. 1st maxilla.

The annulations of the abdomen are much fewer than the
number of appendages; the nerve ganglia, however, correspond
with the limbs. The last two or three segments carry no
appendages. The two nerve cords are separated by a consider-
able interval, being connected by transverse commissures at the
ganglia. The heart is elongated, and extends through the
eleven thoracic segments, with a pair of ostia in each. In
Branchipus the heart extends throughout the whole body.

The Branchiopoda are frequently parthenogenetic, and the
males are much rarer than the females; one species of Apus
has recently been shown to be hermaphrodite, the posterior end
of the generative gland producing spermatozoa. They inhabit
freshwater lakes and pools, and one genus, Artemia, lives
in brine pools, in which the salt may be so concentrated as to
be fatal to all other forms of life. Their eggs are capable of
surviving long periods of drought, embedded in the dried-up
mud: a property they share with those of the Cladocera,
the Cyclopidae, and the Rotifera, ete.

OrpER 2. OSTRACODA.

CHARACTERISTICS.—Small, usually laterally compressed Entomo-
straca, with an unsegmented body bearing seven pairs of
appendages ; the abdomen is rudimentary. The whole body
is enclosed in a bivalved shell.

The group Ostracoda includes a great number of genera
and species, but it is nevertheless a very homogeneous assembly,
the various species differing but little from one another. The
bivalved shell which encloses the animal has a striking re-
semblance to that of some Lamellibranchs; the valves are
divaricated by means of an elastic ligament which occupies
about the middle of the dorsal surface, and are occluded by an
adductor muscle.

The body is not segmented, but head, thorax, and a rudi-
mentary abdomen can be distinguished. The appendages are
as follows :

to
On
iS)

ZOOLOGY

Appendages of Cypris.

1. Ist pair of antennae (antennules). 5. 2nd pair of maxillae.

Aa ends 55 “ 6. Ist ,, thoracic limbs.
3. Mandibles. Us Pail 35 ».

4, Ist pair of maxillae.

The antennae are usually adapted for walking or swim-
ming, and in some of the marine forms the shell is notched, so

Fic. 155.—Lateral view of Cypris can-
dida. After Zenker.

. Antennules.

Antennae.

. Mandibles.

. Ist maxillae.

2nd maxillae.

1st pair of legs.

. 2nd pair of legs.

Tail.

Eye.

SOND oO-F CoN er

that the antennae can be protruded even when the shell is
closed. In Cypridina the anterior pair bear olfactory hairs,
and in Cypris the second pair end in hooked bristles, by means
of which the animal can anchor itself.

The mandibles are strong and toothed; they bear a palp,
which is usually elongated and leg-like. The second maxilla
functions sometimes as a maxilla, sometimes as a leg; there
are usually two, rarely three, thoracic legs; the abdomen is
devoid of appendages, and is rudimentary; it may end in a
caudal fork, as in Cypris, or in a plate beset with setae.

The oesophagus expands into a crop, which lies in front of
the true stomach. The last-named region of the alimentary
canal gives off a hepatic diverticulum on each side, which is
prolonged into the cavity of the shell. The anus opens at the
base of the abdomen. These animals are entirely carnivorous.
A heart is often absent; when it exists, as in Cypridina, it lies
on the dorsal surface, in the region where the body and shell
are in continuity. There are as a rule no special respiratory
organs, respiration probably taking place through the general
surface of the body. A shell gland is present, and opens in
the region of the second maxilla.

There is a cerebral ganglion and a short ventral chain of
ganglia, which, however, often fuse together to form a com-
plex ventral nervous mass. The single eye of the Nauplius

ARTHROPODA 263

larva is usually retained, but some forms have in addition a
compound eye.

The Ostracoda are dioecious, and the males are easily dis-
tinguishable from the females; the former usually possess some
organs for holding the latter; in Cypridina this is found on
the second antennae, in Cypris on the second maxillae, and they

Fic. 156.—Transverse section through the body
and shell of Cypris candida. After Zenker.

. Shell.

. Inner fold of mantle lining shell.

. Ligament between the two halves of the
shell.

. Adductor muscle.

Body.

. Intestine.

. Liver tubes extending into the shell.

. Testes sending prolongations into the shell.

a pe

rn or

“TI

[o.)

are also provided with more highly developed sense organs.
The ovaries and the testes may, like the liver diverticula,
extend into the lining of the shell (Fig. 156). The accessory
male organs are very complicated, and the spermatozoa attain
a great size, being in some cases longer than the body. Cypris
attaches its ova to water-plants, but Cypridina carries them
about within the shell of the female until they hatch out.

OrpDER 3. COPEPODA.

CHARACTERISTICS.—Lntomostraca with an elongated segmented
body, without a dorsal shell. The thorax bears four or five
biramous swimming feet ; the abdomen, which consists of four
segments, 1s devoid of limbs. Some species are parasitic, and
are then more or less degenerate.

An enormous number of very variously modified Crustacea
are included in the group Copepoda. The free-swimming
forms are distinguished by the constant number, and by the per-
sistence, of their paired appendages. The parasitic forms, which
are very numerous, undergo every stage of degeneration, and in
the extreme cases lose all trace of their Entomostracan affinities
in the adult condition. The systematic position of these forms
is, however, clearly shown by the history of their developement.

264 ZOOBO.GNG

The Copepoda are divided into two sub-orders: (i.) the
Branchiura, which includes the two genera Argulus and Gyro-
peltis; and (i1.) the Eucopepoda, which embraces the mass of
the Copepods, both free-swimming and parasitic.

(i.) The Branchiura are known as Carp-lice, Argulus
being parasitic upon Carp and Sticklebacks. These animals
differ considerably from the members of the Eucopepoda. In

Fia. 157.—Argulus foliaceus, female,
seen from the ventral side. After Jurine.
1. Pointed rostrum.
2. Antennules.
3. Antennae.
4, Hye.
5. Sucker on anterior ramus of 2nd
maxilla,
Liver.

Ovary.

oN SD

Eggs leaving the body.

oe)

. Posterior ramus of 2nd maxilla.

Argulus the mouth is prolonged into a suctorial tube, within
which lie concealed the serrated mandibles and_ styliform
first maxillae: a modification of the mouth parts which is
common amongst certain orders of Insects. In front of the
mouth is a styliform weapon, which also lies in a sheath. The
second pair of maxillae, the so-called maxillipedes, are modified
to form organs of adhesion, the anterior ramus taking the form
of a sucking disk, the posterior being hooked. Behind these
are found four pairs of swimming legs, all of them, except the
last, concealed by the body. The abdomen terminates in
two caudal plates; the whole body is flattened dorso-ventrally.
The male is more active than the female, and possesses copu-
latory appendages on the last thoracic limbs; the eggs are not
carried about in the usual Copepod fashion, but are deposited
upon surrounding objects.

ARTHROPODA 265

(ii.) The Eucopepoda are further subdivided into: (a) the
Gnathostomata or free-swimming forms with masticating mouth
appendages; and (b) the Parasitica, in which the mouth parts
are modified for sucking or piercing, and whose body ws imeom-
pletely segmented.

(a) GNATHOSTOMATA.—The genus Cyclops, which includes
many species living in fresh or brackish water in Great Britain,
is fairly typical of this subdivision. In shape its body has been
compared to that of a split pear with its flat side ventral,
tapering posteriorly. The head bears five pairs of appendages,
viz. (i.) antennules, (ii.) antennae, (iii.) mandibles, (iv.) Ist
maxillae, (v.) 2nd maxillae. Dorsally its terga form a con-
tinuous carapace, and are fused with the first thoracic tergum.
The thorax consists of six segments, the five posterior being
free dorsally as well as ventrally, except in the female, where
the last thoracic segment is fused with the first abdominal.
The abdomen consists of four cylindrical segments devoid of
appendages, the last bears the furcal caudal processes so
characteristic of the Entomostraca.

Appendages of Cyclops.

1. Antennules. 5. 2nd maxillae (maxillipedes).
2, Antennae. 6-9. Four pairs of thoracic limbs.
3. Mandibles. 10. 5th pair sp rr

4, Ist maxillae. (rudimentary).

The antennule is a well-developed appendage, which acts
as a strong oar, in the male it also acts as a clasper, and
is correspondingly modified; the antennae are short and
four-jointed ; the mandibles guard the mouth, one on each
side; they and the 1st maxillae have rudimentary palps.
The 2nd maxillae are biramous, the split extending to their
base; the shell gland or excretory organ opens upon the
first joint of the outer ramus. The first four thoracic limbs
are flattened from before backward; they are biramous, and
their bases are united by a median plate, which extends across
the middle ventral line. The fifth thoracic segment bears a
pair of rudimentary feet at the sides of the ventral surface.
The next segment has a rounded cross section like those of the
abdomen, with which it is generally grouped; but as it bears
the openings of the genital ducts, it is better to regard it as

266 ZOOLOGY

the sixth and last thoracic. It bears a pair of appendages
which are reduced to a small valve-like structure overlying
the sexual aperture. In the female this last thoracic segment
is fused with the first abdominal. . The four abdominal seg-

Fic. 158.—Dorsal view of male Cyclops. The
reproductive organs are diagrammatic.
After Hartog.

1. Antennae.
2. Carapace.

. Testis.

3

4, Vas deferens.

5. Vesicula seminalis.
6

. Kye.

ments are cylindrical! in shape, and are entirely devoid of
appendages ; the last, however, bears the caudal fork.

The mouth leads into a narrow gullet which ends in the
anterior end of the stomach, an oval sac extending back to
about the second thoracic segment. The chitinous cuticle

ARTHROPODA 267

which covers the body of the animal is invaginated at the
mouth, and lines the gullet and the anterior third of the
stomach. The rest of this organ is lined by large columnar

Fic. 159.—Longitudinal vertical median section through Cyclops, partly
diagrammatic. After Hartog.

1. Cerebral ganglion. 7. Proctodaeum.
2, Ventral nerve cord, ganglion omitted. 8. Ovary.

3. Mouth. 9. Uterus.

4. Stomodaeum. 10. Spermatheca.
5. Cells lining posterior part of stomach. 11. Eye.

6. Intestine.

cells, some of which contain fat globules, and others granules
which pass into the intestine, and so out of the body. These
granules have been regarded by some authorities as urinary.
The intestine stretches from the stomach to the hind end of
the second abdominal segment, and then passes into a rectum,
which is lined with a chitinous cuticle continuous at the
anus with the general chitinous covering of the body. No
liver diverticula open into the alimentary canal of Cyclops,
although these structures are found in some other Gnatho-
stomata, but there are a pair of salivary glands which open
by a common duct into the oral face of the labrum, a process
which overhangs the mouth anteriorly.

No heart exists in Cyclops, but the space in which the
alimentary canal les contains a colourless fluid, in which
colourless corpuscles float. The space which contains this
fluid is much broken up by connective tissue trabeculae and
strands of muscle, which support the alimentary canal and
generative organs. The various muscles are striated, and their
contraction causes the stomach and intestine to move rhythmic-

268 LOO LOGY

ally backwards and forwards in such a way as to move the
corpusculated fluid forward in the dorsal part of the body and
backward in the ventral. At the same time certain dilator
muscles attached to the rectum cause this tube to expand and
take in through the anus a certain amount of water, which is
subsequently ejected again. This rhythmical taking in and
ejecting of water has probably a respiratory significance, and the
process has been termed anal respiration. It has been observed
in numerous Crustacea amongst various classes, e.g. in Argulus
and Caligus amongst the Copepoda; in Daphnia, Moina, and
the larvae of Apus amongst the Phyllopoda ; in Gammarus and
Asellus amongst the Arthrostraca; and in the Zoaea-larvae of
Macrura and Brachyura. The interchange of gases between
the circulating medium and the surrounding water may, in the
case of Cyclops, where the integument is thin, take place all
over the body, but in those animals whose cuticle is thick it
may reasonably be supposed to take place more readily through
the thinly-lined rectum.

The kidney consists of the typical Entomostracan shell- or
maxillary gland ; it is a simple tube ending blindly at one end,
and opening to the exterior on the second ramus of the second
maxilla at the other. The functions of the kidney are believed
to be partly taken over by the walls of the intestine, which
excrete granules supposed to be urinary. The larva of Cyclops
is said to possess an antennary gland.

The nervous system consists of a supra-oesophageal mass
which gives off nerves to the eyes and to the antennules; of
two circum-oesophageal cords from which the nerves to the
antennae arise; and of a single ventral cord which extends to
the fifth thoracic segment, where it bifurcates, and continues
through the abdomen as two cords, which ultimately end in
the furcal processes. The ventral cord presents no marked
distinction into ganglionic and interganglionic regions.

Besides the numerous sensory hairs, each supplied with
nerve fibres, the median frontal eye, divided into three parts, is
the sole sense organ.

The Copepoda are dioecious; in Cyclops the ovary is a
median gland situated beneath the first thoracic tergum. The
oviduct, which is continuous with the ovary, gives off a series

ARTHROPODA 269

of uterine processes in which the ova accumulate, and finally
opens on the posterior thoracic segment, which in the female is
fused with the first abdominal. Just at the point of opening
the oviducts receive the ducts of the spermatheca; this is a
sac lying within the fused segments, and having a special
pore through which the spermatozoa make their entrance
(Fig. 159).

The testis resembles the ovary in form and position; the
vasa deferentia are rather coiled, and may be divided into
different sections, they open into two vesiculae seminales, one
on each side of the sixth thoracic segment, and these open to
the exterior upon the same segment (Fig. 158).

One fertilisation suffices for many broods of ova; the eggs
as they leave the oviduct are surrounded by a cement-substance
which forms an investment for each egg and keeps them
together in an oval mass, which the female carries one on each
side of her abdomen. One of the ovisacs may contain from
seventy to ninety ova.

The Calanidae differ from the Cyclopidae in the possession
of a well-developed heart, which in Calanella is produced into
a cephalic artery; and in the fact that their antennae are
biramous. The Notodelphidae which inhabit the branchial
chamber of Ascidians have their antennae modified for attach-
ment, and the posterior thoracic segments of the female are
fused together and form a brood-pouch in which the eggs
develope.

(b) ParasirticA.—The parasitic or semi-parasitic Copepods
have their mouth parts adapted for piercing and sucking ; their
body is usually incompletely segmented, and the abdomen is
reduced. The males are often smaller than the females to whom
they adhere.

Most of the Parasitica live on fish, hence their common
name, fish-lice; they may inhabit the gill-chamber, or the
pharynx, or they may live on the skin, in which the female
buries half her body, and in some instances, e.g. Penella, they
even bore into the body and live partly embedded in the tissues.

Chondracanthus gibbosus, which inhabits in considerable
numbers the gill-chamber of the Lophius, or fishing-frog, exhibits
many of the peculiarities of these remarkable epizoa. The

270 ZOOLOGY

female may be half an inch long; the body is flattened, and
has lost most signs of segmentation, it is produced laterally
into two folds, which have a crimped or frilled appearance ; pos-

Fie. 160.—Chondracanthus gibbosus.
A, Female from under surface.
. Antennae, hook-like,
. Ist pair of legs.

i
2
3, 2nd pair of legs.
4, Males adherent to female.
5

. Egg bags.
B. Male, more highly magnified.
1, Antennules.
. Antennae.
. Mouth parts.
. Ist pair of legs.
. 2nd pair of legs.
. Testis.

. Vas deferens.

aoanr om oO BP WO. ND

. Spermatophore.

teriorly it is produced into two long white filaments, the ovisacs.
The head forms a kind of hood which bears antennules and
antennae, the latter modified into strong hooks, by means of
which the animal attaches itself to its host. The labrum
which overhangs the mouth does not form a tube enclosing
the mandibles, as is often the case in this group. The

.

ARTHROPODA 271

mandibles and both pairs of maxillae form claws. Behind
these are two pairs of bifid lobes representing the first two
pairs of feet. The abdomen is represented by a small papilla ;
just in front of this the oviducts open. The male is much
smaller than the female, and retains a much more definite
segmentation ; it is found clinging on to the female by means
of its antennary hooks in the neighbourhood of the opening of
the oviduct. It possesses an eye, and its caudal extremity
ends in two processes. Both male and female, like so
many other parasites, have very largely developed generative
organs.

Many of the parasitic Copepods have departed still farther
from the Crustacean type than Chondracanthus. The Lernaeidae
are vermiform, with their mouth parts forming a piercing
and sucking tube. J. branchialis is found on the Cod. The
Lernaeopodidae have their maxillipedes enlarged, and in the
females united to form an organ of attachment to their host.
In this family the swimming-feet have entirely disappeared.
Some species are parasitic on Sharks and on the Salmon.

OrpEeR 4. CIRRHIPEDIA.

CHARACTERISTICS.—/ixed Crustacea whose body is enclosed in a
fold of the skin, which is generally strengthened by calcareous
valves. The body is indistinctly segmented. There are usually
six pairs of thoracic feet, and the abdomen is rudimentary.
Hermaphrodite, with mobile spermatozoa. Hxclusively marine.
The class Cirrhipedia may be divided into five orders :

1. Thoracica.

. Ascothoracica.
. Abdominalia.

Apoda.

. Rhizocephala.

Ot H Oo bo

The last four of these orders are composed of parasitic
species, whose habits have involved considerable modifications
in their structure.

The Thoracica include the common forms Zepas and Balanus
and many other genera, which have retained more of their

272 ZOOLOGY

Crustacean characters than their parasitic congeners, but owing
to their fixed habit of life they have undergone numerous
modifications. Both the parasitic and sessile forms pass through
a freely mobile larval stage, and it is not until they reach
the last of numerous larval stages that they either attach
themselves to some host or settle down upon some foreign
body. Whilst this is taking place, the larva, which is now in
what is termed the Cypris stage, takes no food, but lives upon
the nutrient material stored up in a well-developed fat-body, a
condition of quiescence which recalls the pupa stage of many
insects.

Like so many other sessile animals, the Thoracica fix them-
selves by their head; the anterior end of this in the Lepadidae

Fig. 161.—Side view of Lepas anatifera.
After Leuckart.

. Stalk.
Carina.

. Tergum.

~ OF SS

. Scutum,

grows out into a long stalk which projects beyond the shell,
and serves to lodge some of the internal organs of the body.
The body is enclosed in a reduplication of the skin, which is

ARTHROPODA 27

1S5)

continuous with the body only in the region of the head. This
mantle is strengthened by five calcareous plates, the carina
median and dorsal, two scwta near the stalk, and two terga at
the free end. Owing to the disposition of these plates, the
mantle can only be opened along the ventral surface; when
opened the biramous thoracic legs can be protruded, and their
movement sets up currents in the water which bring food to
the mouth. In Pollicipes and Scalpellum, genera in which the
stalk is smaller than in Lepas, there are a number of triangular
secondary calcareous plates which arise round the top of the
stalk and form a kind of collar round the body of the animal.
Some of these secondary plates are still further developed in

Fic. 162.—View of Bal-
anus tintinnabulum
after removal of the
right shell. From
Leuckart and Nitsche.
After Darwin.

Tergum.

Scutum.

Outer shell in section.
Antennae,

Ovary.

Oviduct.

Opening of oviduct.
Labrum.

Adductor muscle.

Depressor muscle of
tergum.

11. Depressor muscle of
scutum.

12. Mantle cavity.

Bw OM ES So hort

& §2 ge

Balanus, which is without a stalk, and here they form a
calcareous tube consisting of six pieces, the median dorsal one
being regarded as equivalent to the carina (Fig. 162). Within
this tube the body of the animal lies protected by four plates,
the two scuta and two terga.

The head is not marked off from the thorax, except by the
position of the appendages, and the abdomen is reduced to a
short stump, at the end of which the anus is situated.

Appendages of Lepas.

1. Antennules. 4. 1st mavxillae.
2. Antennae (lost in larval life). 5. 2nd 4
3. Mandible. 6-11. 6 pairs of thoracic limbs.

18

274 ZOOLOGY

The head bears one pair of antennae, the first. Its second
joint bears a disk on which the duct of the cement gland opens.
In Lepas and Balanus this appendage is minute, and situated
at the base of attachment. The cement gland lies in the stalk
of the stalked forms, its secretion hardens into a cement which
serves to attach the animal to some foreign body.

The second pair of antennae, although present in the larva,
are thrown off at the last moult, and are therefore not found in
the adult. Above the mouth is an upper lip or labrum, and
on each side of it is a mandible; between the mandible and
the labrum is a structure called the palp, which, however, is
not the homologue of the ordinary Crustacean palp. There
are two pairs of maxillae, the posterior pair being fused together
to form a kind of labium.

The thorax bears six pairs of appendages, the biramous
nature of which recalls the limbs of the Copepods (Fig. 163).
The rudimentary abdcmen has no appendages, it terminates in
a long penis, which is usually bent forward between the thoracic
legs.

The mouth leads by a short oesophagus into a globular
stomach provided with certain hepatic diverticula ; the intestine
passes off from the stomach and ends in a short rectum. The
anus is situated dorsally at the base of the penis.

In addition to the hepatic diverticula certain glands have
been described lying near the stomach, with which they com-
municate by a duct on each side. These glands secrete a fluid
which has probably some digestive action, they have been
termed pancreatic glands, formerly they were described as
ovaries.

The Cirrhipedia seem to be devoid of any special circulatory
apparatus. The space between the internal organs-of the body
is largely filled up with connective tissue, but certain cavities
occur which seem to be lined by an endothelium, and which
have been regarded as truly coelomic. Into these spaces a pair
of ducts open by means of funnel-shaped orifices. These
ducts have been traced in one or two genera, and have been
found to open on to the exterior at the base of the second maxilla,
the appendage which bears the aperture of the Entomostracan
excretory organ, the shell gland. These tubes are believed to

ARTHROPODA 27

ut

have an excretory function, and if their inner end opens into
a genuine coelomic cavity, they would satisfy the conditions of
a nephridium and form an interesting transition between these
widely distributed excretory organs and the shell gland of
other Entomostraca.

The existence of special respiratory organs is a matter of
some uncertainty, certain processes at the base of the thoracic
legs in Lepas, and on the inner surface of the mantle in Balanus,
have been regarded as branchiae by some authorities, but their
precise function seems doubtful.

The nervous system of Lepas is composed of a supra-oeso-
phageal ganglion, connected by commissures of considerable
length with a ventral chain. This usually comprises five
ganglia, the fifth is larger than the others and gives off two
pairs of nerves, hence it probably represents the fusion of two
primitively distinct ganglia. In the Balanidae the whole
ventral nerve cord has fused into a common nerve mass. The
supra-oesophageal ganglion gives off nerves to the stalk, to the
mantle, and to the eyes; the mouth appendages and the first
pair of thoracic limbs are supplied from the infra-oesophageal
ganglion, The only sense organs which are definitely known
are a pair of rudimentary eyes, which have fused together in
Lepas, but are distinct in Balanus.

The Cirrhipedia are peculiar amongst Crustacea, in that
with few exceptions they are, as is frequently the case with
sessile animals, hermaphrodite (Fig. 163). The testes form a
branched gland upon each side of the alimentary canal; the
numerous caeca of this gland unite into a vas deferens which
dilates into a vesicula seminalis on each side of the body, the
two vasa deferentia unite into a single ductus ejaculatorius
which traverses the penis. The spermatozoa are motile, a
condition not otherwise met with in the Crustacea except
amongst the Ostracoda, and then only when they have entered
the female ducts.

The ovaries are very racemose glands, situated in the
Lepadidae in the upper end of the stalk, in the Balanidae
between the membranous or calcareous base of attachment
and the mantle (Fig. 162). The oviducts, one on each side of
the body, pass up towards the first thoracic limbs and open

276 ZOOLOGY

into a sac; this in turn opens by a duct lined with chitin at
the base of the first thoracic appendages. The walls of this
sac appear to secrete the cement by means of which the ova

Fic. 163.—A view of Lepas
anatifera, cut open longi-
tudinally to show the dis-
position of the organs.
From Leuckart and
Nitsche, partly after Claus.

1. Stalk.

2. Carina.

3. Tergum.

4. Scutum.

5. Antennae.

6. Mandible with “ palp ” in
front.

7. 1st maxilla.

8. 2nd maxilla.

9. The six pairs of biramous
thoracic limbs.

10. Labrum.

11. Mouth.

12. Oesophagus.

13. Liver.

14. Intestine.

15. Anus.

16. Ovary.

17. Oviduct.

18. Testes.

19. Vas deferens.

20. Penis.

21. Cement gland and duct.

22. Adductor scutorum
muscle, which closes
the shell.

23. Mantle cavity.

are bound together. It will be noticed that the opening of
the oviduct is situated much farther forward than in other
Crustacea. It les in the segment which succeeds that
upon which the excretory organs open, and it has been sug-
gested that the sac and its duct may possibly represent an
original segmental organ.

The ova when laid are cemented together, and form in the
Lepadidae flattened masses which are attached to a fold of the
mantle, and form very obvious structures easily seen when the
shell is opened.

In spite of the fact that, with few exceptions, the Cirrhi-

ARTHROPODA 277

pedia are hermaphrodite, there are certain genera, e.g. Zb/a and
Scalpellum, in which males have been described. These are
dwarfed forms, often very degenerate, which live usually two or
three at a time within the mantle of the normal hermaphro-
dite or female, and are known as complemental males.
Their degree of degeneracy varies within wide limits, and it
seems as a rule to increase with the depth of the water in
which they live. Three species of Scalpellum which inhabit
shallow water, S. peronii, S. rostratum, and S. villoswm, are pro-
vided with males which have retained the division of the body
into a capitulum and a peduncle; in eight other species, which
extend to a depth of 700 fathoms, the males have lost this
division of the body, but still retain rudiments of shell
valves; in thirteen other species, which were almost all taken
from depths of upwards of 1000 fathoms, even these have dis-
appeared. The male of Scalpellum regiwm, one of the most
degenerate, is a minute animal about 2 mm. long, attached to the
inner surface of the scutum of the female by means of minute
antennae which are provided with cement glands. No other
appendages are visible. The body is oval, rounded at each
end, and covered with a chitinous cuticle, which is produced
into short spines. The alimentary canal is rudimentary and
functionless, the mouth does not open, and the mouth append-
ages are gone. There are a supra-oesophageal ganglion, con-
necting cords, and one infra-oesophageal ganglion ; the eyes
have disappeared. The generative apparatus alone is well
developed, but the female organs have completely disappeared,
the testis and vesicula seminalis are single.

The remarkable genus Scalpellum presents yet a further
complication in its sexual arrangements. Its species may be
arranged in three groups:

A. Those which are truly hermaphrodite, and in which no
complemental males exist. Ex. Scalpellum balanoides.

B. Those which are hermaphrodite and yet possess comple-
mental males. Ex. Scalpellum villosum, peronu, vulgare,
rostratum, etc.

C. Those which are unisexual, the females large and normal, the
males minute and living parasitically in the mantle of
the female. Ex. Scalpellum ornatum, regium, vitrewm, ete.

278 ZOOLOGY

The genus /d/a presents only the latter two of these degrees
of sexual differentiation.

The remaining groups of Cirrhipedes are parasitic, and
have undergone considerable degeneration.

(ii.) The Ascothoracica consist of three species: Laura
gerardiae, Synagoga mira, and Petrarca bathyactidis. These are
parasitic or semiparasitic in the Actinozoa. They possess a
large lateral carapace, into which the digestive and repro-
ductive organs extend, a condition of things characteristic of
Ostracods; in other essential respects they resemble the
Cirrhipedes.

(iii.) The Abdominalia include the two genera Alcippe and
Cryptophialus. They are unisexual, and in the former the
male is dwarfed. They live parasitically, boring into the
caleareous shells of Molluses and Cirrhipedes.

(iv.) The Apoda are composed of only one genus, Pro-
teolepas. It has a maggot-like body consisting of eleven
segments, and has no thoracic or abdominal limbs. ‘The
mouth is a sucking one, and its appendages are present; the
alimentary canal is rudimentary. It lives within the mantle
of other Cirrhipedes, and seems to be truly parasitic, living on
the juices of its host. It is hermaphrodite.

(v.) The Rhizocephala comprise a few genera which are
parasitic chiefly on Crustacea. They have reached an
extreme stage of degeneration, their body being rounded,
and without any trace either of segmentation or of appendages.
No alimentary canal exists in Sacculina, which is frequently
to be found on the abdomen of Carcinus moenas or other crabs;
the alimentary canal is not present even in the Nauplius
larva. This genus, like so many other parasitic Cirrhipedes,
attaches itself to its host in the Cypris stage, fixing itself on
the carapace or legs just at the origin of a hair where the skin
is soft. It usually chooses some young individual in which
the integument has not yet completely hardened. The Cypris
fixes itself at first by means of its first pair of antennae, it
then moults and throws off its skin, and the cellular body of
the Sacculina now migrates through the cavity of its antenna
into the body of the crab. It then makes its way to the
intestine and comes to rest in that region of the body where

ARTHROPODA 279

it will ultimately appear at the outside. In addition to the
globular body, which is eventually pushed outside the skin of
the crab’s abdomen, the parasite has a short peduncle which
passes through into the body of the host and gives off an im-
mense network of roots which ramify through all the tissues
of the crab, and extend even into its limbs. It is by means
of these processes that the parasite absorbs its nutriment.
This drain upon the resources of the crab does not seem to
affect its health, but its growth is arrested, and as a conse-
quence it does not cast its skin, an operation which would
naturally be fatal to the Sacculina. Fortunately the latter
appears to live only three years, and when it dies the crab
resumes its growth.

B. MALACOSTRACA.

CHARACTERISTICS.— The Malacostraca include the more conspicu-
ous and more highly differentiated Crustacea. The number of
segments and pairs of appendages is constant. With one
exception, there are nineteen segments, each bearing a parr of
appendages. The head consists of five, the thorax of eight
segments. The abdomen has six segments, and ends in
an wnsegmented telson. The excretory organ usually opens
on the second antenna, and is called the antennary gland, as
opposed to the Entomostracan maxillary or shell gland. The
Nauplius larva, so characteristic of the Entomostraca, is rare
in the Malacostraca. Some of them hatch out from the egg
in the adult condition ; the majority, however, pass through a
complicated metamorphosis, the larva leaving the egg in the
form of a Zoaea, which is characterised by the presence of the
seven or eight anterior pairs of appendages, a swimming tail,
and two lateral compound stalked eyes, as well as a median
Nauplius eye. The proctodaeum and stomodaeum form a
larger part of the alimentary canal of the adult than is the
case in the Entomostraca.

The MALACOSTRACA include three orders :

1. LEPTOSTRACA.
2. THORACOSTRACA.
3. ARTHROSTRACA.

280 ZOOLOGY

OrpeR 1. LEPTOSTRACA.

CHARACTERISTICS.— This order includes but three recent genera:
Nebalia, Paranebalia, and Nebaliopsis; they have bivalved
shells, eight free thoracic segments with limbs of the Phyllopod
type, and eight abdominal segments, with two caudal pro-
CESSES.

Nebalia forms an interesting transitional form between the
primitive Phyllopoda on the one hand, and the Malacostraca
on the other. It is of small size, with a laterally compressed
body, partially enclosed in a bivalved cephalothorax which
springs from the head. This cephalothorax extends over all
the thoracic and four of the abdominal segments; it is closed
by a special transverse muscle like that of the Ostracoda.

The appendages are:

1. Antennules. 5, 2nd pair of maxillae.

2. Antennae. 6-13. 8 pairs of thoracic limbs.
3. Mandibles. 14-19. 6 pairs of abdominal limbs.
4, 1st pair of maxillae.

The second antennae in the male, which is a smaller
animal than the female, are produced into processes as long as
the body. The mandibles bear a three-jointed palp, a structure
not found in Phyllopods. The eight thoracic segments are
very short from behind forwards; they each bear a pair of
foliaceous appendages, which closely resemble the typical
Phyllopod limb. Amongst these the female carries her eggs.
The eight abdominal segments are considerably longer than
the thoracic ; the first four bear large swimming-legs, consist-
ing of a broad protopodite and an exopodite and endopodite ;
the next two segments bear similar but much smaller append-
ages, whilst the last two are limbless, so that the number of
appendages is the typical Malacostracan nineteen, though there
are twenty-one segments. The last segment bears two anal
furcae, again an Entomostracan feature.

Another primitive arrangement presented by Nebalia is
the fact that the ventral nerve cord is to some extent con-
tinuous with the hypodermis. In the abdomen the two cords
run apart from one another, and are connected by transverse
commissures. The eyes are stalked.

The characteristic Malacostracan excretory gland is found

ARTHROPODA 281

opening on the second antennae. The Entomostracan shell
gland, however, is found in the larva, and rudiments of it per-
sist in the adult.

The Leptostraca are exclusively marine; they appear to
be the survivors of what was once, judging from the numerous
allied fossil forms, a large order. They possess great tenacity
of life, and are able to live in water which is so full of the
products of decomposition as to be fatal to most other animals.
The order includes three genera,—WNebalia, Paranebalia, and
Nebaliopsis,—and it is probably cosmopolitan.

OrpEeR 2. THORACOSTRACA.

CHARACTERISTICS.—Malacostraca in which all the thoracic or the
anterior thoracic segments are fused with the head to form «
cephalothorax, which is enclosed by a dorsal shield or carapace.
The eyes are compound, and, with few exceptions, are borne
on moveable stalks.

This order contains four sub-orders, the members of which
have attained very different degrees of developement. Whilst
some of them in their adult condition have a marked resem-
blance to the larvae of the more highly developed groups, others,
as for instance the Decapods, are the largest and in some
respects the most highly differentiated of the Crustacea.

The sub-orders which compose the order Thoracostraca

are :
1. CUMACEA.
2. STOMATOPODA.
3. SCHIZOPODA.
4, DECAPODA.

Sub-order 1. CUMACEA.

CHARACTERISTICS.— The carapace is small, and four or five of the
thoracie segments are free. There are two pairs of maxilli-
pedes, and six pairs of other thoracic legs; of the latter the
two antervor at least are biramous or Schizopod-like. The
abdomen in the female is devoid of appendages, except the sixth
segment, which bears a pair of caudal styles ; the male has a
varying number, 2,3, or 5 pairs of abdominal swimming-
Jeet in addition.

282 ZOOLOGY

This is not a large group, and its relation to the other
Thoracostraca is the subject of much difference of opinion.
The best-known genera are Diastylis (= Cuma) and Leucon.
Among the points of interest presented by these animals are
the following :—the second antennae, rudimentary in the
female, are in the male as long as the body, a sexual dis-
tinction which exists also in Nebalia. The mandible is with-
out a palp, as in the Phyllopoda. There are only one pair of
gills, which are of large size, and are borne by the second pair
of maxillipedes. The two eyes lie close together, or have fused
into a single mass, which, contrary to the usual rule in the
Thoracostraca, is sessile. The brood-pouch, in which the eggs
undergo their developement, is formed from processes, probably
epipodites, of the fourth, fifth, and sixth thoracic legs, an
arrangement which is also met with in the Schizopoda and
the Arthrostraca.

Little is known about the habits of these animals; they
live together, usually on a sandy bottom, at considerable depths,
they rest during the day and come to the surface and move
about at night.

Sub-order 2. STOMATOPODA.

CHARACTERISTICS.— The carapace is short, and leaves a variable
number of thoracic segments free. Portions of the head bear-
ing the eyes and antennae are also free and moveable. There
are five pairs of maxillipedes, and three pairs of biramous
thoracic feet. The abdomen is large, and the abdominal
appendages carry the gills.

The Stomatopoda are animals of considerable size, the
larger species of Squilla attaining a length of 7 or 8 inches or
more. The carapace is short, and does not cover the three
thoracic segments which bear legs; the five segments in front
of these, which carry the five pairs of maxillipedes, are
much shortened. The portion of the head bearing the eyes,
and that carrying the antennae, are free and moveable, and the
ventral portions of the segments covered by the carapace are
also capable of a certain amount of movement upon one another.
The six abdominal segments are large, and end in a broad telson.
The first antenna consists of a basal shaft bearing three long

ARTHROPODA 28

Oo

multiarticulate flagella ; the second antenna has a large squama
or scale.

The mandibles bear a palp, and the two pairs of maxillae
are small and weak. The maxillipedes are the most charac-

Wi ae
LIRR
\

Po) > C -4
Th SS as 4 |
2 Iv A eS, om Sy V/
y Ss ‘Y [ Wk

: Wan. - ===
’ J 3 any 6 Ny m
\ ih
aN ae “|
4

Fic. 164.—Squilla mantis, seen from the left side. After Leuckart and Nitsche.
1. 1st antenna. 8-10. Ist to 3rd biramous swimming-
2. 2nd antenna. legs.
21. Scale, exopodite, of 2nd antenna. 11-16. Ist to 6th abdominal _ legs,
3. 1st maxillipede. the anterior five pairs bearing
4, 2nd maxillipede. branchiae.
5, 3rd maxillipede. 17. Branchiae.
6. 4th maxillipede. 18. Penis.
7. 5th maxillipede. 19. Eyes.

teristic appendages of this order; there are five pairs of them,
turned forward towards the mouth (Fig. 164). The anterior
pair are thin and feeble, but terminate in a small pair of sub-
chelae which help to hold the prey; the second pair are the
largest appendages of the body. Their terminal joints are
strong and toothed, and shut down upon the penultimate like
the blade of a knife into its handle; this arrangement has been
termed subchelate, and it exists in all the maxillipedes of this
group. The three succeeding maxillipedes are smaller, and
terminate in small rounded subchelate joints. The three free
thoracic segments carry biramous swimming-feet. The six
abdominal segments also bear each a pair of swimming-feet,
which are remarkable for carrying the gills on the external
ramus. ‘The first pair are modified in the male in connection
with reproduction.

The elongated condition of the heart, which stretches from
the thorax through the abdomen, is doubtless correlated with

284 ZOOLOGY:

this position of the branchiae; in each segment it gives off a
pair of lateral arteries, and in front it ends in ophthalmic and
antennary arteries (Fig. 165).

The liver extends into the abdomen, and is divided into
ten pairs of caeca. <A pair of glandular diverticula open into
the rectum near the anus; they are regarded as excretory.

Fic. 165.—A Squilla mantis, with the
shell removed from a portion of the
dorsal surface to show the internal or-
ganisation. After Leuckart and Nitsche.
1. Ist pair of antennae.

2, 2nd pair of antennae.
21, Scale, exopodite, of 2nd antenna.

3. 2nd maxillipede.

4, Heart, with thirteen pairs of ostia, and
numerous paired vessels supplying
the limbs.

5. Median unpaired vessel supplying the
eyes and antennae,

6. Ovary.

7. Oviduct opening at base of (8) in Fig.
164.

8. Stomach,

9, Liver diverticula from the intestine,
these lie under the ovary.

10. 6th abdominal appendage.

The generative organs also lie in the abdomen, the oviducts,
however, reaching into the three free thoracic segments, being
situated between the alimentary canal and the heart. The
vas deferens opens on the last pair of thoracic appendages, the
oviduct on the last but two. An antennary gland does not
appear to be present.

Unlike most Crustacea, the Stomatopoda do not carry their
eges about with them, but deposit them in the burrows in

ARTHROPODA 285

which they live. The eggs require for their developement a
current of water, which is produced by the action of the
abdominal swimming-feet of the parent. The group is ex-
clusively marine; the members of it inhabit shallow water,
and either live in crevices in coral rock, or burrow in the sand.
They often rest in the mouths of their burrows with nothing
but their eyes exposed above the sand; in this way they lie
in wait for their prey, which they seize with astonishing
rapidity by means of their powerful subchelate maxillipedes.
They are extremely active in their movements, and difficult to
catch, retiring to the inner end of their burrows at the slightest
alarm.

Sub-order 3. SCHIZOPODA.

CHARACTERISTICS.—Small Thoracostraca ; the carapace is large
and soft, the eight thoracic limbs are biramous. . Those modi-
fied to form maxillipedes do not differ markedly from the
others. The eyes are stalked.

The Schizopoda retain throughout their life a condition
which resembles that of the last of the series of larval forms
which take part in the metamorphosis of some macrurous
Decapods. This larva is known as the Mysis stage, and is
called after the opossum-shrimp, one of the best-known
Schizopods.

The members of this sub-order differ markedly from the
Stomatopoda, in which group the maxillipedes attain the greatest
importance, for in the Schizopods each of the eight pairs of
thoracic appendages are biramous legs, none of them being
modified to form maxillipedes, although the two anterior pairs
may tend in a shght degree to resemble the mouth appendages.
The first antennae are biramous, and in the male are provided
with a curious comb-like structure covered with olfactory hairs.
The second antennae, a pair of mandibles, and two pairs of
maxillae complete the appendages of the head.

The carapace is large, and attached to the body only by a
narrow area of fusion in the dorsal middle line; in some forms,
as Siriella, it leaves most of the thoracic segments uncovered.

The abdomen consists of six segments and a telson; the
first five abdominal appendages in the female are usually small,

286 ZOOLOGY

but are better developed in the male; the sixth is flattened and
lamelliform, and assists the telson in forming the swimming
caudal fin. In J/ysis an auditory sac is situated in the base of
the endopodite of this last abdominal pair of limbs. In the
family Euphausiidae there is a remarkable series of luminous
organs, situated, as a rule, a pair on the peduncles of the eye,
another on the basal joint of the second and seventh pairs of
thoracic legs, and one in the middle ventral line on the first four
abdominal segments. These organs emit at times a beautiful
phosphorescent light, and they seem to be quite under the
control of the animal. Their use is unknown. Huphausia is
further remarkable amongst the Malacostraca for having a
Nauplius stage in its ontogeny.

Sub-order 4. DECAPODA.

CHARACTERISTICS.— Malacostraca with usually stalked eyes. The
thoracic segments are fused with the cephalic, and with rare
exceptions they are entirely covered by the carapace. The
posterior five pairs of thoracic limbs are uniramous and seven-
jointed, and some of them are chelate.

The Decapoda include a great number of species which
superficially exhibit considerable differences of form and habit,
but in essential features the group is very homogeneous. It
may be split up into two divisions.

Group 1. MACRURA.

CHARACTERISTICS.—Abdomen long, four or five pairs of abdo-
minal limbs, and a well-developed caudal fin.

This includes the Carididae (shrimps and prawns), Astacidae
(cray-fish and lobsters), Paguridae (hermit-crabs), ete.

Group 2. BRACHYURA.

CHARACTERISTICS.— Abdomen short and reduced, and bent up
and applied to the ventral surface of the thorax. In the
male the abdomen is narrow, and rarely bears more than two
pairs of feet; in the female it is broader, and has four pairs
of appendages.

ARTHROPODA 287

This group includes the crabs, which are classified in a
great number of families.

In Decapods the region of the head is usually marked off
from the thoracic portion by a fold in the carapace, the cervical
groove ; and in the larger forms the cephalothoracic shield is
frequently divided up into areas corresponding to the position
of various internal organs. The last thoracic segment occasion-
ally remains moveable on the others.

The sides of the carapace enclose the branchial chamber,
and are known as branchiostegites; the number of gills

Fic. 166.—Gecarcinus ruricola (land-crab of Monserral, West Indies).

varies. The water-supply enters through the slit-like opening
between the edge of the branchiostegite and the body in the
Macrura, but in the Brachyura there is a special narrow opening
situated in front of the first pair of walking-legs. The current
is maintained by a specialised portion of the second maxilla,
the scaphognathite, which flaps to and fro. This process either
represents the epipodite, or the epipodite and exopodite fused.
The two pairs of maxillae to some extent retain the foliaceous
character of the primitive Phyllopod appendage, but all the
other appendages depart widely from this type.

A few Decapods, as Birgus latro, allied to the hermit-

288 ZOOLOGY

crabs, and Gecarcinus amongst the Brachyura, have forsaken
their natural element, and have come to live on land. They
retain their gills, and the gill cavity contains both air and
water. In Aivgus—a curious animal which is said to climb
palm-trees at night—there is, however, a distinct modification
of structure. The lower part of the gill space contains the
numerous but small gills; this is shut off from the upper part
by the infolded edge of the branchiostegite, and the cavity
thus formed is a true lung, since it is full of air, and its
walls are produced into numerous vascular folds, which receive
impure blood from the body and return it oxygenated to the
heart. Such a change, from water-breathing animals to
terrestrial air-breathing animals, is paralleled in the Pul-
monata, amongst which an intermediate form exists in the
tropical water-snail Ampullaria, which has both a_ well-
developed branchial cavity with gills and a well-developed
pulmonary chamber, and uses them alternately to breathe
water or air.

The obscure question as to the nature of the body-cavity
and the homology of the antennary or green gland in
Crustacea has recently had some light thrown upon it by
Weldon’s researches on Palaemon serratus and other Decapods.
If the carapace of a Palaemon be removed a delicate sac will
be found occupying the dorsal part of the cephalothorax, and
extending from the anterior end of the head to the generative
gland, to which it is closely attached. This cavity, termed
the nephro-peritoneal sac, is lmed by epithelial cells, and
exhibits many of the relations of a coelomic body-cavity.
At its anterior end the sac gives off on each side a duct,
which passes down and opens into the urinary bladder, thus
putting the nephro-peritoneal sac in communication with the
exterior through the excretory organ. The duct is lined by
elandular cells, and gives off numerous caecal processes, which
branch and ramify in the neighbouring tissues; in addition to
these there is also a structure known as the “ end-sac,’ the
cavity of which also opens into the urinary bladder. The
walls of this end-sac are produced inwards into its lumen,
dividing it up into a number of chambers lined with glandular
cells; these walls are well supplied with blood-vessels, and

ARTHROPODA 289

the septa contain numerous capillaries, so that the whole
organ has been compared with the glomerulus of the Vertebrate
kidney, and doubtless subserves the same functions. It is
by no means certain that the above-mentioned sac is coelomic
in nature, and in his last paper Weldon is inclined rather to
regard it as an enlarged portion of a nephridial system, such as
exists in M/ysis, and not as a remnant of a primitive coelom.

The history of the developement of Palaemonetes varians,
recently described by Allen, throws some leght upon the
nature of the body-cavity in this group. The body-cavity of
this animal consists of four regions: (i.) a dorsal sac in which
the cephalic aorta lies, (ii.) a central cavity containing the
liver, intestine, and nerve cord, (iii.) two lateral cavities con-
taining the proximal ends of the shell glands, and (iv.) the
cavities of the limbs containing the distal ends of the same
glands. Of these, the first, or dorsal sac, is truly coelomic, its
cavity being homologous with that of the dorsal portions of the
mesoblastic somites of Peripatus (vide p. 308). The central
and lateral cavities, and those of the legs, represent a pseudocoel.
The nephro-peritoneal sac described by Weldon arises in this
genus from an enlargement of the tube of the green gland.

In the long-tailed Decapods it is usual to find six pairs
of abdominal ganglia, but in Pagurus, the hermit-crab, there
is only one large one. In these animals the abdomen is soft and
distorted into the shape of the interior of the Mollusce’s shell
which affords it shelter; the abdominal limbs are usually
rudimentary, but the chelae or first pair of thoracic limbs are
large, and can be closed down over the mouth of the shell,
acting as a kind of operculum.

In the Brachyura a great concentration of the nervous
system has taken place, and the ventral ganglia have all fused
together into a common oval mass. The Decapods, in addition
to the main chain of ganglia, possess a very extensive and
complex system of visceral nerves.

Besides the olfactory hairs on the first pair of antennae,
and the compound stalked eyes, it is characteristic of the
Decapods to possess auditory organs, situated at the base of
the antennules. These take the form of hollow sacs open to
the exterior; their walls support auditory hairs connected

19

290 ZOOLOGY

with the auditory nerve. In the watery contents of the sac
certain particles of sand are suspended, and act as otoliths.
In connection with this it is interesting to note that certain
genera can produce stridulating noises either, as in Alpheus,
by clapping together the two claws on the larger leg, or, as
in Palinurus, the rock-lobster, by rubbing the second joint of
the antennae against a portion of the carapace.

OrpER 38. ARTHROSTRACA.

CHARACTERISTICS.— Malacostraca with sessile eyes. No cephalo-
thoracic shield; seven, rarely fewer, free thoracic segments,
and as many pairs of legs. Heart elongated.

The appendages of the Arthrostraca are arranged as
follows: two pairs of antennae, one pair of mandibles, two pairs
of maxillae, and one pair of maxillipedes, seven pairs of free
thoracic legs, and six pairs of abdominal legs. The free thoracic
segments are six in number in Zanais, five in Anceus, the
anterior having in these genera fused with the head. The
abdomen may be reduced to a mere process, but usually it
is fully developed, and ends in an unsegmented telson.

The antennary gland is usually present, and opens on the
base of the antenna. The compound facetted eyes are always
sessile. The ova are usually carried about in brood-pouches
formed by processes borne on the thoracic legs (oostegites).
The young do not as a rule pass through a larval stage.

The <Arthrostraca are divided into two sub-orders, char-
acterised as follows :

Sub-order 1. AMPHIPODA.

CHARACTERISTICS. — Arthrostraca with laterally compressed
bodies ; the thoracie appendages carry the gills ; abdomen
elongated ; it bears three anterior pairs of swimming-
feet, and three posterior pairs of backwardly directed feet
adapted for jumping.

As a rule, the Amphipods are small, but a few, some of them
living in Arctic seas or at great depths in the ocean, attain
several inches in length. They inhabit both salt and fresh
water, and progress by swimming or jumping. The males

ARTHROPODA

291

may usually be distinguished by the developement of their
olfactory hairs on the first antennae, by the absence of

Se =

Fic. 167.—Gammarus neglectus.

I.-VI. Cephalothorax.
VIL-XIII. Free thoracic segments.
XIV.-XIX. The six abdominal segments,
Anterior antennae.
Posterior antennae.
. Mandibles.
Ist maxillae.
2nd maxillae.
. Maxillipede.
. Thoracic limbs.
. Three anterior abdominal limbs
for swimming.

MWA oF Cobh

_

mn
San

a

oostegites, and by the presence of
the anterior thoracic feet.

Female bearing eggs seen in profile.
From Leuckart and Nitsche, after G. O. Sars.

17-19. Three posterior abdominal limbs

for jumping.

20. Heart with six pairs of ostia.

. Ovary.

2. Hepatic diverticula.

23. Posterior diverticula of the ali-

mentary canal.

. Median dorsal diverticulum.

25. Alimentary canal.

26, Nervous system.

27. Ova in egg pouch, formed from
lamellae on the coxae of the
three anterior thoracic limbs.

strong prehensile hooks on

Appendages of Amphipods.

1. Antennules. 6.
2. Antennae.

3. Mandibles.

4. 1st maxillae. 17-19.
ys PAL oe

Maxillipedes (fused).

7-13. Thoracic legs.
14-16. Abdominal legs (turned forward).

» », (turned backward).

292 ZOOLOGY

The mandible carries a three-jointed palp, and the maxilli-
pedes fuse in the middle line to form an under lp. The bases
of the thoracic limbs of the females bear on their inner surface
a process, probably the epipodite, which projects towards the
middle line, and with its neighbours forms the brood-pouch.

VY,
\ 2

Fic. 168.—The mouth appendages of Gammarus neglectus.
From Leuckart and Nitsche, after G. O. Sars.

. The mandible.

1

2. Its palp.

3. 1st maxilla.
4, 2nd maxilla.

5. Maxillipede of each side together forming an under lip.

A little distal to this, but on the same surface, is a vascular
process, the gill. The heart stretches through the thorax, and
has usually a pair of valves in the second, third, and fourth
thoracic segments. A well-developed “ fat-body” is often
present, lying amidst the viscera.

Certain Amphipods, as Gammarus, Orchestia, Talitrus,
Caprella, etc., have two caeca which open into the alimentary
canal at the junction of the mid and hind gut. These caeca,
which stretch either backwards or forwards, contain numerous
concretions in their walls. They have been compared to the
Malpighian tubules of the Tracheata, but there is no certain
evidence to show that they excrete nitrogenous waste matter

ARTHROPODA 293

from the system, and although they open close to its end, they
belong to the mid gut and not to the proctodaeum.

The abdomen is reduced to a limbless process in the
LAEMODIPODA, a group which includes Cyamus ceti parasitic on

Fig. 169.—Gammarus neglectus. Section through the
third thoracic segment. From Leuckart and Nitsche,
after G. O. Sars.

—

. The heart. ®& :

ae he alimentar?” canal.

. The ovary.

. The hepatic diverticula.
The nervous system.
The epimeron.

“STO OP OO LO

. The thoracic appendage bearing—
. The lamina forming the brood-pouch (oostegite), and
. The branchiae.

co CO

the skin of whales, and in the family CAPRELLIDAE which
comprises curious elongated thin animals of a very grotesque
appearance, mostly found living amonest Polyzoa and Hydroids.
The family PHRONIMIDAE includes some forms which have an
enlarged head; the female Phronimea is a good deal larger than
the male, and is usually found swimming about in a barrel-
shaped investment formed by the transparent. colonies of the
compound Ascidian Pyrosoma; other allied forms live in
jelly-fish.

Sub-order 2. ISOPODA.

CHARACTERISTICS. — Arthrostraca with usually a dorso-ventrally
depressed body ; thorax of six or seven free segments ; abdomen
often reduced, it bears lamelliform appendages, the endo-
podites of some of which function as gills.

A very typical example of an Isopod is presented by the
little brownish-gray animal <Asel/us aquaticus, which inhabits
lakes, large ponds, and marshes. Its body is flattened, and
composed of three regions—the head, the thorax, and the abdo-
men; of these the thorax is far the largest, and consists of
seven free segments and one fused with the head. The abdom-
inal segments have all fused together with the exception of
the first, which is very small, and bears rudimentary appendages.

294 ZOOLOGY

Appendages of Asellus.

1. Antennules. 6. Maxillipedes } thoracic

2. Antennae. 7-13. Walking legs ae

3. Mandibles. 14-19. Abdominal legs

4. 1st maxillae. (only five in the female).
5. 2nd A

The appendages are nearly the same as in Amphipods ; there
are two pairs of antennae, the second being much the larger; both
are uniramous. The mandibles carry a palp. There are two
pairs of maxillae and a pair of mavyillipedes, and seven pairs of
walking thoracic limbs, of which the anterior are directed forward,
the posterior backward. The most anterior of all are prehensile
organs, and lie forward against the maxillipedes; they are en-
larged in the male, and take no part in locomotion. There are
six pairs of abdominal appendages in the male, and five in the

vixii =.
¥ 2 1 wi20 aap Rie Ae ee: Bw
- ~—fnge S N

Fic. 170.—Asellus aquaticus. Side view of female. From Leuckart and Nitsche,
after G. O. Sars.

I.-VI. The six anterior segments 7-13. The thoracic limbs.
forming the cephalothorax. 14. Ist abdominal appendages,
VII.-XIII. The seven free thoracic seg- 16. 3rd abdominal appendages.
ments. 17. 4th abdominal appendages.
XIV.-XIX. The six abdominal segments, 18. 5th abdominal appendages.
partly fused. 19. Last abdominal appendage.
1. The anterior antennae. 20. Eyes.
2. The posterior antennae. 21. Heart, with three pairs of stigmata.
3. The mandible (palp). 22. Ovary and oviduct opening on
4. The Ist maxilla. base of 5th thoracic limbs.
5. The 2nd maxilla. 23. Brood-pouch.
6. The maxillipede.

female ; im the former the second pair are modified in connection
with the opening of the genital duct, this pair are absent in the
female. The three following pairs act as branchiae; the exo-
podite and endopodite are both squarish, lamelliform structures,
the former lying over and protecting the latter, which has very

ARTHROPODA 29

ut

thin walls, and acts as the branchia. The last pair of append-
ages project backward like caudal processes.

The mouth is situated far forward, and the short oesophagus
lined with chitin has a nearly horizontal course. The stomach
is small, and les almost entirely in the cephalothorax ; it is
also lined with chitin, which is thickened at parts, and it con-
tains a number of hairs and teeth, which may act as strainers.
The intestine is a wide tube running quite straight to the
anus, which lies on the ventral surface of the posterior end of
the body. The liver consists of two pairs of lateral caeca,
which extend back as far as the intestine. They open by a
common duct on each side, at the junction of the stomach with
the intestine.

There is a cerebral ganglion connected by commissures
with two fused pairs of sub-oesophageal ganglia, then come seven
pairs of gangha corresponding with the seven free thoracic seg-
ments, and finally a complex ganglion formed of three or four
gangha fused together, which supplies the abdomen. The com-
missures which connect the various ganglia are separate and
distinct.

The elements which form the eyes are arranged on each
side of the head in four patches (Fig. 172); there do not
seem to be any auditory organs. Olfactory hairs exist on the
small anterior antennae.

The heart is an elongated vessel situated in the dorsal
middle line; it appears to be closed behind, but anteriorly it

Fic. 171.—Asellus aquaticus. Section through
third thoracic segment. From Leuckart and
Nitsche, after G. O. Sars.

Anterior end of heart (aorta).

Ovary.

Alimentary canal,

Hepatic diverticula.

Nervous system.

Base of thoracic limbs with inward projections
(oostegites) which form the floor of the brood-
pouch.

SR go ho

is prolonged into an aorta. Three pairs of ostia situated in
the last three thoracic segments open into the heart. The
widest part of the heart is situated in the abdomen; the aorta

296 ZOOLOGY

gives off a vessel which supplies the head and its appendages ;
both the aorta and the heart also give off lateral branches,
which supply each segment. No antennary gland is present.
Asellus, like the majority of Isopods, is dioecious. The
ovaries consist of two sacs, entirely independent of one another,
which occupy the thorax, and extend into the abdomen, A little
behind their middle point, in the fifth free thoracic segment, a

Fic. 172.—Asellus aquaticus.
Male viewed from above.
From Leuckart and
Nitsche, after G. O. Sars.

1. Anterior antennae.

(ih A

2. Posterior antennae.

pairs

LY

ae To
ore Thoracic limbs. \s! y/| S
10. The last pair of abdom- ZAR PS ke

inal limbs.

, h

G4

ha —~

11. Testes with their efferent
canals,

\
NY
y

The nervous system is shown
black.

short oviduct descends from the ovary, and opens on the sternum
of that segment; this oviduct seems also to function as a recep-
taculum ovorum; at their exit the ova pass into the brood-
pouch formed by oval lamelliform processes (oostegites) borne
by each of the four pairs of anterior walking limbs.

ARTHROPODA 297

The testes lie in the five posterior thoracic segments. They
are independent of one another, and consist of three sacs, which
open one after another into a narrow vas deferens, the latter
ends in an elongated opening on the last thoracic segment
(Fig. 172).

The Isopoda are carnivorous ; many of them are parasitic,
but seldom completely endoparasitic, living chiefly on the skin
or in the mouth of fishes, or in the branchial chamber of
Decapods. The group Anisopoda, which includes the genus
Tanais, approaches most nearly the Amphipods. TZanais has
a small carapace, which includes the first of the thoracic
segments which bear walking legs; its body is not much
depressed, and generally it has an Amphipod appearance. ‘The
abdominal legs are adapted for swimming, and do not function
as gills. The heart also lies in the thorax.

Two different forms of male are described in Tanais dubius :
one provided with a great developement of olfactory hairs on
the first antennae, the other with large clasping append-
ages.

The other group of the Isopoda, the Euisopoda, have a
relatively small abdomen, which carries branchial feet. The
eroup contains several families, some of which are parasitic,
and some of which are terrestrial in their habits.

The CYMOTHOIDAE are partly parasitic on fish, partly free-
living; their mouth parts are adapted either for biting or
sucking. They are remarkable amongst Malacostraca for being
hermaphrodite and protandrous, the young animals producing
spermatozoa, the older animals ova.

The SPHAEROMIDAE, which live in salt and_ brackish
water, are interesting from their habit of rolling themselves up
in a ball like the Oniscidae or wood-lice. The IDOTEIDAE have
their last abdominal appendages modified to form an operculum,
which protects the preceding branchial hmbs; the same pair
of appendages in the ASELLIDAE are styliform, and project back-
ward; many of the last-mentioned family are freshwater
inhabitants ; one species bores holes in wood submerged in
the sea.

The BopyrIDAE are a very remarkable family of Isopods,
which live parasitically in the branchial chamber of prawns.

298 ZOOLOGY

They are dioecious and markedly dimorphic, the dwarf male
living attached to the body of the female. The female is
somewhat disk-shaped, asymmetrical, and with but slight
traces of segmentation, and no eyes. The male is elongated,
segmented, and provided with eyes. The mouth parts are
rudimentary ; in the female the seven thoracic legs bear
oostegites, which form a brood-pouch. In those species with
a piercing mouth the upper and lower lps form a suctorial
tube, within which the mouth parts are enclosed in the form
of piercing stylets. A very remarkable fact connected with
the parasitism of the Bopyridae is that the presence of certain
species of this group has the effect of materially altering the
reproductive organs of its male host. For instance, a male
Pagurus infested by Phryxus paguri has its abdominal append-
ages of the female type, and its testis is degenerate and the
spermatozoa imperfect. The same is true for many other
species,

In the family ENTonIscipAE the more complete parasitism
has involved a greater departure from the ordinary Isopod
type. Their body is a limbless sack, which lives in an in-
vagination pushed into the bodies of Cirrhipedes, Paguridae, and
Crabs. The invagination retains its opening to the exterior.
The sexual forms of Portunion are very remarkable; the
large deformed parasite is a protandrous hermaphrodite,
functioning in its adult stage as a female; besides this form
there are small males which remain in a larval stage, and also
degraded complemental males. It seems that out of the
numerous larvae, those which obtain the most advantageous
position in the host will become the hermaphrodites and will
ultimately produce eggs; those which occupy the next best
position become the males, which retain their larval features,
whilst the most disadvantageously situated larvae degenerate
and form the complemental males. The genus Cryptoniscus is
commonly parasitic on the Rhizocephala, which are themselves
parasitic on other Crustacea; it is stated that if the Rhizo-
cephala die the Isopods still continue to receive nutriment
through the root-like processes of their dead hosts, as if they
were parts of its own body.

The family ONIScIDAE, the wood-lice, have become terres-

ARTHROPODA

trial in their habits, living on the land, usually in damp places;

in several respects their structure approaches
that of the Insects; the mandible has no
palp, and the exopodites of two or more of the
abdominal limbs are sometimes provided with
tubular air passages, which are respiratory ;
they show, however, no detailed resemblance
to the tracheae of the higher Arthropods.
The first antennae are in many species quite
rudimentary. Many of them, like the SpHAE-
ROMIDAE, possess the power of rolling themselves
up in a ball when disturbed.

Fic. 173.—Oniscus
asellus, the com-
mon Wood-louse.

CHAPTER XVII
TRACHEATA

Ciass I, PROTOTRACHEATA
OnycHoPHoRA (PERIPATIDEA), Peripatus

CHARACTERISTICS.— Animals with soft caterpillar-like bodies,
with a pair of antennae, a pair of jaws, a pair of oral
papillae, and numerous pairs of walking legs, each bearing
claws. Respiration by means of tracheae, the stigmata of
which are numerous and scattered. Nephridia present.

The Prototracheata include a single genus, Peripatus, which
is morphologically one of the most interesting animals known ;
its developement, made known to us chiefly by the researches
of Sedewick, is also of the highest morphologicai import,
and our recently-acquired knowledge of it has solved many
problems of Arthropod structure. Its distribution is also
interesting; it has been found in New Zealand, Australia, the
Cape of Good Hope, South America, the West Indies, and
possibly in Sumatra.

Peripatus capensis is a very beautiful-looking animal, of a
velvety green colour dorsally, shading off into an orange-brown
on the under surface. The female is larger than the male, and
when adult may measure 65 mm., the male being about three-
quarters as long. The skin is thrown into numerous ridges,
which are beset with a number of papillae, each bearing a spine.

Appendages of Peripatus capensis.
1. Antennae.
2. Jaws in buccal cavity, armed with two cutting blades.
3. Oral papillae, with orifice of slime glands.
0. Seventeen pairs of clawed walking-feet.
1. Anal papillae.

TRACHEATA 301

A pair of large antennae are borne on the head; these are
composed of a series of annuli, each ring consisting of a number
of fused papillae, and consequently beset with rows of short

mannnnnininsil

zoel

Fic. 174.—Large adult example of Peripatus capensis of natural size. From Moseley.

bristles. At the base of each antenna, on the dorso-lateral
part of the head, an eye is situated. At each side of the head
is placed an “ oral papilla,” at the free end of which the slime
glands open. Within the buccal cavity lie a pair of jaws,
each armed with a pair of sickle-shaped toothed cutting blades,
which are cuticular in origin.

The remaining appendages are seventeen pairs of walking-
legs, which, with the exception of the fourth and fifth pairs in
both sexes and the last pair in the male, resemble one another
closely. Each leg is of a truncated conical shape, and bears
rings of papillae; it terminates in a foot provided with two
cuticular claws. On the inner surface of each leg, near its
base, is the slit-like opening of a nephridium. The anus is
terminal, and guarded on each side by the last pair of append-
ages, the anal papillae. The genital opening is sub-terminal
and ventral.

The skin consists of a layer of hypodermal cells which
secrete the cuticle; within this is a double stratum of circular
muscle fibres crossing one another slightly obliquely, and sur-
rounding a layer of longitudinal fibres. The latter are arranged
in bundles: two dorsal, two lateral, and three ventral. A sheet
of dorso-ventral muscle fibres runs from the space between the
dorsal and lateral bands to the outer side of the median ventral
band, dividing the body-cavity into three longitudinal spaces :
a median which contains the alimentary canal the slime
glands and the generative organs, and two lateral which lodge
the nephridia, the salivary glands, and the nervous system.
The lateral space is continuous with the cavities of the
feet. There are special muscles which move the limbs, and
others in the walls of the alimentary canal; throughout the

302 ZOOLOGY

body the muscle fibre is unstriated, except in the case of the
muscles attached to the jaws, where the fibres are distinctly

striated.

The buecal cavity, which contains the two .jaws, opens

behind into a muscular pharynx, but

it is continued ventrally

somewhat behind this opening, and the recess so formed receives
the united duct of the two salivary glands. These are glands of
considerable size, and they extend a long way down the body,
lying in the lateral portion of the body-cavity ; they have a

So OF me

Fia

. 175.—Peripatus capensis, male,

dissected to show the internal
organs. x 2. After Balfour.

. Antennae showing antennary

nerve.

. Oral papilla.

31, 3! 1st, 2nd, and 10th leg of
right side.

. Brain and eyes.
. Circum-oesophageal cord.

. Ventral nerve cord of right side,

showing the transverse com-
missures,

. Pharynx.

. Stomach.

. Anus.

. Male generative opening.

. Salivary glands.

. Slime glands and reservoir.

. Enlarged crural gland of the

17th leg.

144, 141°. 4th and 10th nephridia of

right side,

remarkable origin, since the history of their developement shows
that they are modified nephridia, a condition of things which

TRACHEATA 303

recalls the modified segmental organs which open into the oeso-
phagus in some of the Oligochaets. The pharynx is very
muscular, and has a triradiate lumen ; it is strikingly unlike the
same region of the digestive tube in any other Arthropod, but
shows considerable resemblance to the pharynx of many of the
Chaetopods. It communicates by a short oesophagus with a
large stomach, which extends from the level of the second pair
of legs to nearly the posterior end of the body. The stomach
lies quite freely unsupported by any mesentery; it ends in a
short muscular rectum, which passes to the anus. The
pharynx, oesophagus, and rectum are all lined with chitin con-
tinuous with that covering the body.

The vascular system consists of a tubular heart, which lies
between the two dorsal muscle bundles along the whole length
of the body. Paired ostia situated two in each segment, on
the dorsal surface of the heart, put the cavity of this organ in
communication with the surrounding pericardial space. The
pericardial membrane which limits this space is attached on
each side to the body-wall; it forms a kind of meshwork with
numerous holes, by means of which the central division of the
body-cavity communicates with the pericardium.

The space spoken of above as the body-cavity in which
the chief: organs of the body lie, is not a true coelom. That
is, it does not communicate with the exterior by means of
nephridia, the lining of its walls does not give rise to the
generative cells, and it does not arise as a definite split in the
primitive mesoblastic somites. A true coelom is found in Peri-
patus, but it has a different fate, and the space mentioned
above as the body-cavity has nothing to do with it. The
latter space originates either as a split between the endoderm
and ectoderm, or as a hollowing out of spaces which appear
in the thickened somatic walls of the somites. Speaking
broadly, the central compartment and the heart arise in the
former manner, the lateral spaces, with the cavities in the
appendages and the pericardium, arise in the latter. These
various cavities all communicate with one another. Thus the
heart and the various portions of the body-cavities form a series
of spaces which have been termed haemocoelic. They have
nothing to do with the coelom, but are “a series of enormously

304 ZOOLOGY

dilated vascular trunks, of which the heart is the narrowest,
and alone possesses the property of rhythmically con-
tracting.”

The heart is suspended in the pericardium by a number of
strands of tissue, and around these a curious collection of cells,
which has been compared to the “ fat-body ” of insects, is aggre-
gated. This tissue, from its distribution, has probably some
action on the blood, and it is possible that it represents
functionally the lymphatics of Vertebrates and the botryoidal
tissue of Leeches.

The respiratory system is tracheal. Each trachea consists
of a simple opening to the exterior,—the stigma,—a short tube
which dilates at its inner end, and a number of very minute
tracheal tubules which arise from the dilated inner end of the
tube, and which are distributed to the tissues of the body.
The tracheal tubules are very fine, and for the most part un-
branched ; they exhibit slight traces of spiral striation. The
stigmata are more or less evenly scattered over the whole
surface of the animal, opening between the papillae; there are,
however, a double dorsal and a double ventral row, and some
on the anterior and posterior face of each leg; there is also a
large median ventral stigma just in front of the mouth; this
supplies part of the nervous system.

A nephridium occurs in the lateral section of the body-
cavity at the base of each foot (Fig. 175). Each nephridium
consists of the following parts: (1.) the external opening which
lies near the base of each leg; this leads by a short duct into
(ii.) an expanded vesicle or collecting portion lined with large
flat cells; from this a coiled tube (iii.) passes, which is lined
in various regions with four different kinds of epithelial
cells. This tube ends in a funnel-shaped internal opening,
the lips of which are continuous with the walls of a vesicle.
The study of the developement has shown that the lumen of
this vesicle, like the nephridium itself, is part of the original
coelom, which has become separated off from the rest (Fig.
16): The first two somites, those of the antennae and
claws, do not develope nephridia; the nephridia of the third,
the oral papillae, are converted into the salivary glands; the
next three segments have small, and the fourth and fifth pairs

TRACHEATA 305

of legs, enlarged nephridia; the remaining twelve are normal,
and resemble one another.

The nervous system consists of a pair of supra-oesophageal
ganglia, united by circum-oesophageal commissures with two
ventral cords. Anteriorly each supra-oesophageal ganglion is
prolonged into a nerve, which runs to an antenna (Fig. 175).
Several nerves run to the skin, and laterally the optic nerves
arise, and supply the eyes. A pair of sympathetic nerves
emerge posteriorly from the brain; they run back in the wall
of the pharynx, and unite on the oesophagus; both in their
origin and distribution they closely resemble the sympathetic
nerves of Chaetopods.

Posteriorly the supra-oesophageal ganglia are continuous
with the circum-oesophageal commissures, which in their turn
pass into the ventral nerve cords. These latter lie in the
lateral division of the body-cavity, and are consequently
separated by a wide interval, but, like the pedal nerves of the
Isopleurous Gasteropods, they are connected by a number of
transverse commissures, nine or ten in each segment, the first
of these lying immediately behind the mouth. ‘There are
seventeen ganglionic enlargements on the ventral cords, cor-
responding with the seventeen pairs of legs, and the circum-
oesophageal commissures bear two ganglionic swellings, which
supply nerves to the jaws and oral papillae. The ganglion cells
are not confined to the swellings, but are distributed all along
the cord. ach ventral ganglion gives off two large nerves,
which pass into the legs, and a number of smaller nerves, which
pass to the body-wall, etc.

One of the most interesting features of the nervous system
of Peripatus is that the ventral nerve cords pass dorsally at
the posterior end of the body, and fuse together above the
anus (Fig. 175), like the united visceral and pedal commissures
in Chaetoderma.

The eyes lie at the base of the antennae; beneath them is
an optic ganglion; in their minute structure they resemble
the eyes of Chaetopods or Gasteropods rather than those of
Arthropods.

The female is larger than the male, but the only external
structural difference is the existence of a small white papilla

20

306 ZOOLOGY

on the ventral surface of each of the two seventeenth legs
in the male; the enlarged crural gland of this segment opens
at the apex of this. The genital organs are all included in
the central division of the haemocoel. The unpaired external
opening is ventral, and a little in front of the anus; on each
side of it is a genital papilla, which represents the appendage
of the twenty-first somite, and shows its homology with the
legs by sometimes bearing claws. The male organs consist on
each side of a testis, a prostate gland, and a vas deferens.
The two vasa deferentia unite into a single duct which opens
at the genital pore; at the same spot two glandular tubes,
accessory glands, also open. The crural glands of the seven-
teenth pair of legs are very much enlarged in the male, but
their exact function is not known. The spermatozoa are
filiform, and are united into bundles or spermatophores ; these
are deposited by the male on any portion of the body of the
female. It is unknown how the spermatozoa reach the ova, but
they are always to be found in the cavity of the ovary.

The ovary is unpaired, but is divided by a septum into two
tubular halves; it is provided with two oviducts, which dilate
into uteri. The ovary lies between the fifteenth and sixteenth
pairs of legs; a receptaculum seminis is present, and cilia have
been detected on its walls. The occurrence of cilia is remark-
able, as they are not found elsewhere in the Arthropoda.
Peripatus capensis is viviparous ; the fertilised eggs pass into the
uteri in April, but are not hatched till the May of the follow-
ing year; the period of gestation is thus thirteen months, and
for the first month the ova of one generation, and the nearly
mature embryos of the previous generation, co-exist in the uterus.

The ducts of the generative glands are formed from the
same portion of the twenty-first mesoblastic somite which
gives rise to the nephridia in other segments; they may there-
fore be regarded as modified nephridia, or, in other words, the
generative ducts are nephrodinic. The generative glands
themselves, the ovary and testes, are formed from parts of
the true coelom of the sixteenth to the twentieth somite,
and thus, as in so many other animals, the generative cells
arise from the lining of the coelom, and pass to the exterior
through modified nephridia.

TRACHEATA 307

Certain glandular structures, known as crural glands, occur
in every pair of legs except the first; they consist of a vesicle
placed in the lateral portion of the body-cavity, and lined with
columnar cells; this communicates with the exterior by a short
tube. The crural gland of the seventeenth pair of legs is in the
male enormously enlarged, and reaches forward as a tubular
diverticulum as far as the ninth pair of legs; its exact function
is unknown.

A pair of slime glands lie in the central division of the body-
cavity ; each communicates with a reservoir which opens by a
duct on one of the oral papillae. They excrete a sticky slime,
which is ejected with some force when the animal is irritated.

In Peripatus Edwardsii, a South American species, the
crural glands are absent in the female, and only occur in the
male in two segments; the genital opening is between the last
par of legs, and there are no genital papillae; the ovary
is double, and the spermatophores are 13 inch long. The
stigmata are irregularly scattered. In Peripatus Novae Zea-
landiae the tracheae are said to be branched.

The importance of Peripatus is twofold: in its structure
it combines features of two or three different phyla, and the
history of its developement has done much to explain the more
peculiar characteristics of Arthropod structure, and to bring
these animals in line with what is known of other groups.

Both its distribution and its structure point to its being
a very archaic form. The arrangement of its nervous system,
the sympathetic nerves, the muscular pharynx, the structure
of the eyes, the serially repeated nephridia, the com-
paratively short stomodaeum and proctodaeum, the thinness
of the cuticle, and the hollow nature of the appendages, are
all features which are naturally associated with the Chaeto-
poda; some of these features are also met with in the more
primitive Mollusca. On the other hand, the segmented
appendages, the modification of some of the appendages as
mouth organs, the presence of antennae, the tracheal nature
of the respiratory organs, the structure of the heart and of
the generative organs, are all features shared in common by
the Tracheata and many by the Arthropoda in general. Thus
Peripatus combines some of the more important characteristics

308 ZOOLOGY

of two, if not three, of the most important phyla of the animal
kingdom. Its developement is no less interesting; it would
be beyond the scope of this book to dwell upon the early
stages of the embryology, but some of the later stages
have cleared up so many difficulties in the structure of
adult Arthropods that a short reference to them must be
made.

The morphological nature of the body-cavity, and of the
heart, which opens freely into it in all Arthropods, has always

(SOMME,

—
a
=
S
S

S
Z mom»

Frc. 176.—Diagram of the arrangement of the coelomic and haemocoelic cavities of
Peripatus, at the time of its birth. After Sedgwick.

1. Enteron, alimentary canal.

31, Haemocoelic cavity of heart.
)

Coelomic cavity of generative gland. 4. Nervous system.
21, Coelomic cavity of nephridia. 5. Slime glands.
3. Haemocoelic cavity, general ‘‘ body-
cavity.”

The true coelom is everywhere surrounded by a thick black line.

been a difficulty ; the developement of Peripatus shows us that,
in this genus at all events, it has no connection with the true
coelom, but is a haemocoel, and arises partly by a hollowing
out in the tissue of the mesoblastic somites and partly from
the persistence of a split between the ectoderm and endoderm.
The continuity of the walls of the generative organs with the
genital ducts is explained by the fact that the generative

TRACHEATA 309

gland is a persistent portion of the original coelom, and the
ducts are in all probability modified nephridia, which open
into this portion of the coelom. The ova and spermatozoa
are formed from cells lining the coelom, as is so commonly the
case in the Coelomata. A small portion of the coelom also
persists as a vesicle or swollen termination to the nephridia,
which therefore correspond in their relations with the nephridia
of other animals, and are tubes opening from the coelom to
the exterior. Nephridia have not yet been described in many
of the Arthropods, so that, although their presence in Pevi-
patus is extremely interesting, the details of their relationship
are not so important for the elucidation of Arthropod structure
as are the origin of the body-cavity, heart, and generative
organs ; and if we may assume that these latter organs arise
in other Arthropods in essentially the same way as they do
in Peripatus, we shall have an explanation of some of the most
difficult problems of Arthropod morphology.

Specimens of Peripatus capensis are found beneath stones and
bark, especially amongst rotten wood, on the slopes of Table
Mountain. They are animals which avoid the light, and
require moist surroundings. They move slowly, testing the
ground with their antennae, which are very sensitive; the
body is borne above the ground by the numerous legs. When
irritated, they can expel their slime, which is very sticky, to
a distance of almost a foot. They are carnivorous, their food
consisting of small insects, etc. The female will produce from
thirty to forty young, which are born in the spring, and may
be seen at this time of year crawling over the body of their
mother.

CHAPTER XVIII
TRACHEATA

Cuass II]. MYRIAPODA

Chilopoda—Lithobius, Scolopendra, Scutigera.

MrEraropa Diplopoda (Chilognatha)—Julus, Polyxenus, Pawropus.

CHARACTERISTICS.—Tvracheate Arthropoda with a distinct head
and a number of similar somites ; no distinction of thorax
and abdomen. A pair of antennae, mandibles, and maxillae,
and numerous six- or seven-jointed clawed legs present.

Of all the Tracheata, with the exception of Peripatus, the
Myriapoda exhibit least signs of specialisation in their external
structure. The segments posterior to the head, which in the
GEOPHILIDAE may amount to some hundreds, are all very
similar, and they are not externally grouped together into any
regions such as thorax or abdomen.

The Myriapoda are divided into two orders : (i.) the Chilo-
poda and (ii.) the Diplopoda or the Chilognatha.

Order 1. CHILOPODA.

CHARACTERISTICS. — Myriapoda with dorso-ventrally compressed
body. Antennae long, with many segments. The second parr
of postoral limbs form the poison claws. One sternum and
one pair of legs to each segment. Genital orifice posterior.
Stigmata lateral, tracheae branching and anastomosing.
Lithobius forficatus is the commonest English centipede ; it

is found all over Europe, in the summer living under stones,

leaves, etc., and in the winter hiding itself in the earth. It is
about one to one and a half inch long, and of a chestnut-

TRACHEATA

311

brown colour. In external appearance it is very like its larger

subtropical congener Scolopendra.

The head bears the multiarticulate antennae,
with about forty segments, and just behind their
insertion, the eyes, which are composed of
twenty-five to forty single eyes grouped together.
Immediately behind the head, and articulated
with it, is the very narrow segment which bears
ventrally the poison claws. Behind this are
fifteen similar segments, nine of which are
larger than the others, and somewhat irregularly
arranged ; each segment is covered dorsally by
a squarish tergum ; the difference in size of the
segments is not apparent on the ventral surface,
the sterna being all of the same size. The terga
and sterna are connected laterally by a soft
flexible skin which bears the stigmata.

Appendages of Lithobius forficatus.

1. Antennae. 4. Limb-like appendages.
2. Mandibles, 5. Poison claws.
3. Maxillae. 6-20. Fifteen walking-legs.

The appendages are: (i.) the antennae; (ii.)
a pair of mandibles with a toothed cutting edge,
they are jointed, but, like those of Insects, are
devoid of a palp (Fig. 178); (ai.) a pair of
maxillae, consisting of a palp and a fused median
portion; (iv.) a pair of limb-like appendages
turned forward, with their bases in contact.
Behind this are (v.) the poison claws, a pair of
stout large claws which contain in their last
two joints the poison gland; the duct of this
opens on the convex side of the apex. In
Scolopendra a large basilar segment succeeds the
head; this consists of four embryonic segments

Fie. 177. — Scolo-
pendra morsi-
tans. After
Buffon.

a. Cephalic tergite.
6. Basilar tergite.
c. First postceph-
alic appendage
(=third postoral),
d. Third postceph-
alic appendage.
e. Antenna,
J. Second — postce-
phalic appendage
(=poison claw).
g. Last pair of ap-
pendages enlarged
and turned back-
wards,

fused, and bears iv. and v., and sometimes a pair of walking
legs, but the latter are frequently lost in the adult (Fig. 177).

They do not occur in Lithobius.
The remaining fifteen segments bear each a

pair of seven-

jointed legs, arising on the lateral margin of the ventral sur-

ty

ZOOLOGY

face, and terminating in a claw. The fifteenth pair are often
directed backwards. The anus is terminal, and the genital
pore in both sexes is just in front of it, on the ventral surface.

Fie. 178.—Mouth parts of Scolo-
pendra morsitans. After Buffon,

1. The poison claws or 4th postoral
appendages,

s. Median cutting processes
formed by the anterior edge of
the basilar sterna.

2. One of the mandibles with its
cutting edge to the left.

3. The maxillae and 8rd _postoral
appendages,

a, Limb-like appendages.

c, Palp-like maxillae.

6. Small process formed by
their fused bases.

4, Ventral view of head with jaws
removed.

@. Hye. e. Labrum.

i The alimentary canal runs straight through the body with-
out any loops. It consists of a short stomodaeum, which
receives near the mouth the secretion of a pair of salivary
elands, of a wide mesenteron, and of a rectum, which opens by
the terminal anus. Two long white tubes—the Malpighian
tubules—open into the posterior end of the mesenteron ; they
are longer than the body, and are consequently somewhat
coiled. The Malpighian tubules secrete uric acids and urates,
and thus function as organs for the excretion of nitrogenous
waste matter.

The Chilopoda are carnivorous, Zithobius living upon flies,
insect larvae, and earthworms, which are quickly killed by the
poison from the poison claws; these also assist by holding the
prey whilst the jaws tear it in pieces.

The alimentary canal occupies a considerable portion of the
body-cavity ; this space is to some extent occluded by the “ fat-
body ” which in Myriapods and Insects forms large masses of
tissue abundantly supplied with tracheae. The body-cavity is
full of blood, which is kept in circulation by the contractile
heart. The latter organ stretches all along the dorsal surface,
lying immediately beneath the integument. It consists of
fifteen chambers, one in each segment: the first of these, which

TRACHEATA 313

les just behind the cephalic shield, gives off a median and two
lateral vessels ; the former supplies the head and mouth parts,
the latter form a ring round the oesophagus and unite to form
a ventral vessel which lies above the nerve cord. These vessels
open into lacunae, which ultimately communicate with the
body-cavity, and from this the blood returns to the heart
through paired valvular openings in each chamber. The heart
is supported by a pericardium, to which are attached certain
muscles, the alae cordis; these arise from the body-wall. The
blood is colourless, and contains numerous white corpuscles.

A pair of stigmata are found on the third, fifth, eighth,
tenth, twelfth, and fourteenth leg-bearing segments, situated on
the soft tissue between tergum and sternum, immediately
behind the base of each leg. Each stigma opens into a swollen
sac, which gives off two main tracheae and a number of smaller
ones, which supply the neighbouring parts. The arrangement
of the larger branches varies in the anterior and posterior ends
of the animal, but two main branches are usually present, one
running dorsally, the other ventrally ; they divide into smaller
and smaller branches, and ultimately form a network which
ramifies through every organ of the body. ‘The tracheae are
kept open by a spiral thickening of their chitinous lining.

The ventral nerve cord bears sixteen ganglia, each of which
gives off three nerves on each side to the legs and adjacent
muscles. The first of these supplies the poison claws; the
cord is connected by circum-oesophageal commissures ending in
the bilobed cerebral ganglion which gives nerves to the eyes,
antennae, and mouth organs. When a basilar segment is pre-
sent, the corresponding ganglia are fused together. In some
Chilopoda the first few ganglia of the ventral nerve cord are
more or less completely fused; some writers have held that
this indicates a division of the segments of the body into
thorax and abdomen. Besides the eyes, sensory hairs are found
on the antennae, and in Scwtigera there is a peculiar sense organ
on the ventral part of the head consisting of a pouch lined with
sensory hairs, each of which is connected with a nerve fibril.

Lithobius is dioecious, and the generative organs usually
attain their full size during the spring. The testis consists of
a blind tube, the lining cells of which give rise to the sperma-

314 ZOOLOGY

tozoa. The tube is narrow anteriorly, then somewhat wider,
and finally it narrows posteriorly into a duct, and opens by it

Fie. 179.

A. Scutigera rubro lineata. After Buffon.
B. Tergum and part of a second tergum of the same, enlarged to show the
position of the stigmata, 0,0. p, Hinder margin of tergum.

into a circular canal which surrounds the rectum, and receives
the opening of two tubular vesiculae seminales.

Ventrally this canal enlarges into a chamber which receives
the ducts of two pairs of accessory glands of considerable size ;
it opens to the exterior, on the ventral surface of the last
segment, immediately in front of the anus. The spermatozoa
are filiform.

The ovary is a single tube, dorsal to the alimentary canal,
and reaching as far forward as the head, it is continuous with
the oviduct; this divides into two branches, one of which
passes on each side of the rectum, and the two unite again in
a chamber which, like the corresponding structure in the male,
receives the secretion of two pairs of accessory glands. <A pair
of hollow vesicles, the receptacula seminis, also open into this
median chamber. The latter opens to the exterior just in
front of the anus, the opening being provided with a pair of
minute jointed claws.

The exotic species of Scolopendra may attain the length of
six inches, and their bite is extremely painful,and even dangerous.
Cryptops and Geophilus have no eyes: the latter possess a great

TRACHEATA 315

number of segments. Some members of the family GEOPHILIDAE
are phosphorescent, and secrete from certain glands on the
ventral surface a luminous slime; since this is produced by
both male and female, and neither of them has eyes, the
secretion is regarded as a means of frightening or warning off
enemies. The male Geophilus spins a web, and drops a sperma-
tophore in the middle of it, and the female comes and fertilises
herself. Geophilus longicornis is common in Britain; the
female coils herself up and sits on her eggs, and is stated not
to leave them until they are hatched. Cryptops hortensis, with
twenty-one pairs of legs, is also British.

Scutigera has very long antennae and legs, the latter in-
creasing in length at the posterior end (Fig. 179). This genus
has facetted compound eyes, and its tracheal system is peculiar ;
the stigmata are median and dorsal, one for each segment,
opening in a notch at the posterior edge of each tergum.
Certain species produce a rattling noise by rubbing their legs
together.

Order 2, DIPLOPODA (Chilognatha).

CHARACTERISTICS.— The members of the second sub-order of the
Myriapoda are characterised by their bodies being cylindrical
or subcylindrical, and their antennae short, of seven segments
only. Except at the anterior end, the segments bear two parrs
of legs, and the bases of the legs are near together ; there are
also two pairs of stigmata on every segment. The generative
aperture is at the base of the second or third pair of legs.

A

Fra. 180.—Ventral view of Polyxenus lagurus (after Bode) much enlarged, actual
length a little over ;4;th of an inch.

a. Position of genital openings.

The Diplopoda are all vegetable feeders, and have no
poison claws. The genus Polyxenus is somewhat intermediate

316 ZOOLOGY

between the two main subdivisions of the Myriapoda, for
although it is a vegetarian, and its generative organs open
anteriorly, it resembles the Chilopods in the bases of the legs

h m

Fra. 181.—Inner view of the sterna of a single segment of Judws londonensis, much en-
larged to show the structure and arrangement of the tracheal organs. After Voges.
The two pairs of tracheae are seen 7 sifu, the posterior pair overlapping the anterior,

h. The posterior margin of the body ring st. Tubular chamber of tracheae.

(tergum). t, Fine tracheae given off from it.
7. Anterior border; between thetwolie ms. Respiratory muscle attached to
the two terga. tracheal sac.

m, Wentral body muscle,

beimg somewhat apart, and in the character of its filiform
spermatozoa, which are contained in spermatophores, as is
usually the case in the last-named order. Its body, which
is about 54, inch long, is covered with tufts of hairy scales,
probably defensive.

The commonest genus of Diplopoda is ulus; a good
many species of this genus occur in Britain, the most frequent
being Julus terrestris, which is sometimes an inch or more
long, and is often to be found curled up under bark or ‘stones.
In this animal the tergum forms an almost complete ring,
interrupted in the ventral line only by two sternal plates,
one in front of the other. In all the segments after the
fourth post-oral each of these plates bears a pair of legs, so
that each segment with its single tergum corresponds with
two pairs of legs, and has also two pairs of stigmata, one in
front of the base of each leg, two nerve ganglia, and two cardiac

TRACHEATA 317

chambers ; these facts, together with others derived from em-
bryology, show that each tergum corresponds with two primitive
somites. The legs have five joints and a terminal claw.

Segments and Appendages of Julus.

1. Antennae. 5. One pair of legs.
2. Mandibles. ‘ : 6. This segment bears no legs.
3. Maxillae, fused across ae Cra 7. One pair of legs.
middle line. 8. The succeeding segments bear two
4, Leg-like appendages, modified in male. pairs of legs.

The cephalic appendages comprise a pair of antennae, a pair
of mandibles with broad crushing surfaces, and a pair of
maxillae which have fused across the middle line and which
form a bilobed plate. The appendages are borne on the head ;
the first post-cephalic segment has a broad tergum, and bears
ventrally a pair of leg-like appendages, which are turned
forward, and probably assist in the act of feeding; the same
appendage is in some species modified in the male, and forms
a blunt hook-like process. The second post-cephalic segment
bears a normal pair of legs, the third has none, and the
fourth one pair, the succeeding segments have two. The
generative orifice in both sexes is on the third segmerit, just
behind the bases of the second pair of legs. In the male
the seventh post-oral segment bears only one pair of legs
and a complex copulatory apparatus not connected with the
internal organs. This apparatus is of great systematic value.
The female Julus, like that of Geophilus, watches over its
eggs.

Some genera of the Polyzonidae, e.g. Siphonophora (Fig.
182), have the anterior part of the head and the mouth-
parts prolonged into a sucking or piercing snout. Most of
the Diplopoda possess a series of glands which open to the
exterior by a row of lateral foramina repugnatoria, one on
each segment; these emit an offensive fluid; in one species,
Fontaria, this fluid breaks up into prussic acid and _ benzal-
dehyde (oil of bitter almonds).

Except in Glomeris, where the tracheae are branched as
in the Chilopods, the respiratory organs resemble those of
Peripatus. The stigma opens into a tracheal sac, from which
a number of short unbranched tracheae arise. There are four
of these on each segment. The GLOMERIDAE have shortened,

318 ZOOLOGY

broad bodies, and curl themselves up like wood-lice, and in this
condition are very often mistaken for the latter.

Fie. 182.

1. Head and anterior somites of Siphon-
ophora portoricensis. After Koch.

2. Diagram of the arrangement of the
anterior somites and appendages of

d, 3rd or generative somite, devoid
of appendages and sterna, but bearing
the generative apertures.

e. Single appendage of 4th somite.

a female Zulus londonensis. After
Moseley.
a. Modified tergum of the 1st post-
oral somite (dorsal plate or collum),
6. A short single appendage of the
same somite, of four joints and a

J, g. Dual appendages of succeed-
ing somites.

3. Hook-like postcephalic appendage of

male of same attached to its plate of
support (=one half of modified
sternum ?)

claw only, turned towards the mouth. 4. Mandible of same.

c. Single appendage of the 2nd 5, The four-lobed plate formed by the
somite, of five joints and a claw like fused single pair of maxillae.
the remaining appendages.

Pauropus and Scolopendrella are genera which are sometimes
placed in two different sub-orders, the Pauropidae and the

£2
a eo (

WW
: AL

Fic, 183.—Enlarged view of Pawropus huxleyi. After Lubbock.

Symphyla, which rank with the Chilopoda and Diplopoda.
Pauropus is very small; it has ten segments, and Lupauropus

TRACHEATA 319

but five, each of which in the last-named genus bears two
pairs of legs. The last segment of the antenna of Pauwropus
bifurcates and bears three flagella (Fig. 183).

Scolopendrella, the genus which constitutes the sub-order
Symphyla, has obvious resemblances to certain members of
the most primitive sub-order of the Insecta, the Thysanura,
and in spite of the fact that no clear division of thorax and

Fia. 184.—Scolopendrella immaculata,
highly magnified. Slightly altered
from Packard.

a. Caudal stylets.
b, 6. First postcephalic appendages.
c. Antennae.

2. One of the functional legs further
enlarged (from Wood Mason),
showing the five joints and
terminal pair of claws,

6, Inner rudimentary leg of same
somite.

abdomen exists, and that practically all the segments bear
legs, and there are only two pairs of mouth appendages, it
has been proposed to class this animal with the Thysanura.
Scolopendrella is but 5 or 6 mm. long; behind the head there
are fifteen terga, but only thirteen sterna exist, and twelve
pairs of legs; the latter are five-jointed and terminate in two
claws (Fig. 184), as in Campodea, the genus of Thysanura it
most closely resembles. At their base is a small process
which gives the limb almost a biramous character, <A pair
of caudal styles bear the apertures of certain silk glands.

Insecta

(

A.

CoLLEMBOLA—Podura, Sminthurus.
APTERA . . THysaANurA—Lepisma, Machilis.

DERMAPTERA—Forficula ¢ Cursoria—Blatta, Periplaneta.
Gressoria—Mantis, Phasma.
Acridiidae—Acridium.
Locustidae—Locusta.
Gryllidae—Gryllus,
Gryllotalpa.

ORTHOPTERA . { ORTHOPTERA GENUINA

Saltatoria

NEUROPTERA. Termes, Aeschna, Ephemera, Phryganea.

MICROLEPIDOPTERA— Tinea, Tortrix.
Geometrina—Cheimatobia, Fidonia.
LEPIDOPTERA Noctuina—Plusia, Agrotis.
MACROLEPIDOPTERA< Bombycina—Bombyx, Cossus.
Sphingina—Sphinz, Acherontia.
Rhopalocera—Papilio, Vanessa.

‘PENTAMERA—Dytiscus, Carabus.
HETEROMERA—WMeloe, Lytta.

COLEOPTERA . PSEUDOTETRAMERA—Cuwrculio, Scolytus, Cerambyzx.
PsEUDOTRIMERA—Coccinella.

HETEROPTERA—WNotonecta, Reduvius, Acanthia.
HEMIPTERA . 4 HomorprEra—Cicada, Aphis, Coccus.
| ParasiticA—Pediculus.

APHANIPTERA—Pulex.
DIPTERA . DIPTERA GENUINA—Musca, Tipula, Cecidomyia.

PHYTOPHAGA—Sirex, Lophyrus.
EntomopHAGA—Ichnewmon, Cynips, Pteromalus.
7. T 3 >
HYMENOPTERA Formicariae—Formica, Oecodoma.
AcULEATA 4 Vespiariae—Vespa, Polistes, Hwmenes.
Apiareae—Apis, Bombus.

CHAPTER XIX
TRACHEATA

Cuass III. INSECTA

CHARACTERISTICS.— Tracheata whose body is divided into three dis-
tinct regions: head, thorax, and abdomen. The head carries
the antennae and three pairs of mouth appendages. The
thorax is conyposed of three segments, each with a pair of legs,
and usually the posterior two segments bear each a pair of
wings. The abdomen ws devoid of limbs, and consists of a
varying number of segments; ten may be made out in some
species, but the number is often less.

The class Insecta includes an enormous number of species,
probably far more than the whole of the rest of the animal
kingdom put together. The single order of beetles—Coleoptera
—contains more than 120,000 described species, and there is
reason to believe that the flies—Diptera—are as numerous
or even more so. At the present date, the total number of
named species of insects must be very nearly a quarter of a
million.

The principles on which this enormous amount of material
has been classified and brought into order rest upon (i.) the
structure and arrangement of the mouth parts, (i1.) the charac-
ters of the wings, (ili.) the relation of the first thoracic segment
—the prothorax—to the rest of the thorax, and (iv.) the
degree of metamorphosis.

The arrangement of the mouth organs is intimately con-
nected with the food of the insect; by the modification or
suppression of some of the three pairs of oral appendages or
parts of them, a very great diversity of structure is produced,

21

22 ZOOLOGY

Lo)

which is of the utmost value in any system of classification.
The character of the wings, and the relation of the prothorax
to the rest of the thorax, are connected with the powers of flight.
In some sub-orders wings are entirely absent, and in others,
although they are fully developed, they may be thrown off, as
in the ants, and in the workers amongst the white ants or
Termites. The degree of metamorphosis which an insect under-
goes in passing from the egg to the adult, though possibly a
good criterion for phyletic relationship, is of less use for
practical purposes of classification, inasmuch as it assumes the
life-history of the insect to be known, and this is by no means
always the case.
The Insecta are divided into eight orders—

1. APTERA.
ORTHOPTERA.
NEUROPTERA.
LEPIDOPTERA.
HEMIPTERA.
COLEOPTERA.
DIPTERA.
HYMENOPTERA.

bo

OS

Can a ale a se

Before considering the subdivisions and characteristics of
these orders, it will be advisable to obtain an insight into the
structure and anatomy of some fairly typical insect form, and
the common cockchafer, J/elolontha vulgaris, one of the Coleop-
tera, both on account of its size and its frequency, will form a
convenient type.

The cockchafer is about # to 1 inch long, and the chief
divisions of an insect body into head, thorax, and abdomen
are easily recognised. The head bears a pair of antennae, and
three pairs of mouth appendages. The antennae differ in the
two sexes; they consist of ten segments, the first of which is
known as the scape. In the male the last seven joints, and in
the female the last six joints, are flattened out into a series of
plate-like processes, which have given the name Lamellicornia
to the subdivision of the Coleoptera to which the cockchafer
belongs. They are much longer and larger in the male than
in the female, and in both, each lamella bears an enormous

TRACHEATA

Lo)
Go

number (some thousands) of shallow pits lined by specialised
sense cells connected with nerves, which apparently function
as olfactory organs.

Immediately behind the base of the antennae lie the com-

pound eyes.
Appendages of Melolontha,

1. Antennae. 5. Ist pair of legs, prothoracic.
2. Mandibles, without a palp. 6. 2nd 5 mesothoracic.
3. 1st maxillae. 7. 8rd 53 metathoracic.
45/2nd 5; = Labium.

The oral appendages comprise the typical insect mouth
parts, a pair of mandibles, and two pairs of maxillae. The
anterior part of the head forms the clypeus, and this is con-
tinued into a hinged portion, the /abrwm, which overhangs the
mouth. On each side of this orifice les a mandible, a_biting-
jaw of pyramidal shape, whose opposed edges bear a number
of teeth. The first pair of maxillae are behind the mandibles ;

Fic. 185.—View of the posterior surface of the head of
Melolontha vulgaris. After Strauss-Durckheim.

1. Eyes.

Opening into head for oesophagus, nerve cord, ete., to
pass through.

Base of the cut-off antennae.

Ist maxillae.

Maxillary palp.

Labrum.

Labium (=fused second maxillae),

Labial palp.

bo

WS OUR go

each consists of a basal piece which articulates with the head,
the cardo, this bears another joint, the stipes, and the stipes
terminates in an inner piece with one tooth, the dacinia, and
an outer piece, the galea, with a row of teeth. A maxillary
palp is inserted into the distal end of the stipes. The second
pair of maxillae have fused together and formed a plate-like
lower lip, the labiwm. ‘This consists of a mentum and sub-
mentum, and it carries a pair of labial palps. The function of
both pairs of palps is sensory.

The thorax is made up of three segments, called respect-
ively the pro-, meso-, and meta-thorax; each of them carries on
its ventral surface a pair of legs. The anterior pair are
directed forward and the two posterior backward. Each lee
consists of the following segments, a cova, a trochanter, a femur,

324 ZOOLOGY

a tibia, and the five-jointed tarsus, the distal joint of which
carries two claws.

The dorsal part of the prothorax forms a broad shield, the
pronotum. The mesothorax bears dorsally the anterior pair of
wings, which are horny and hard, and are termed e/ytra; they
afford a protective covering to the membranous posterior wings,
and to the abdomen as far as the eighth segment. The meta-
thoracic wings are membranous, they stretch out at right angles
to the body and are used for flight, at other times they are
folded under the elytra. The superficies of these wings is
divided into a number of small areas or cells by the presence
of chitinous tubules, in which tracheae and nerves ramify ; these
“cells” are of great importance in Insect classification.

The third division of the body, the abdomen, is by far the
bulkiest ; it comprises eight segments, each composed of a

B Fic. 186.—A male Melolontha
@ vulgaris, seen from above,
slightly enlarged. After
Vogt and Yung.

Head, stretched forward.

Prothorax.

Mesothorax, scutellum.

. Metathorax.

. Abdomen.

. Anterior wing (elytron) of
right side, turned for-
ward.

7. Posterior wing of right side,
expanded.

8. Maxillary palps.

9. Femur of third right leg.

10. Tibia of third right leg.

11. Tarsus of third right leg.

a oP wre

dorsal plate, the tergum or notum,and a ventral plate, the sternum,
the soft integument which connects the sides of these successive
plates is pierced by the apertures of the six pairs of abdominal
stigmata. The eighth tergum is prolonged into a long bluntly
pointed process, which overhangs the openings of the alimentary
canal and generative organs (Fig. 186).

The alimentary canal of the cockchafer is about six times
as long as the body, and is therefore necessarily thrown into
loops more or less coiled (Fig. 187). This is unusual amongst
Arthropods (though common in Insects), in which the digestive
tract is as a rule a straight tube, running directly between

TRACHEATA

Oo
wn

mouth and anus. The mouth is overhung by the labrum, and
has the mandibles and first maxillae on either side; behind
it is bounded by the labium or fused second maxillae; the
mandibles cut and crush the food, which is held in position
by the maxillae. The passage of the food into the mouth is
assisted by a hairy prominence on the anterior surface of the
labium.

The mouth leads into an oesophagus which pierces the
nerve mass, and then swells into an inconspicuous crop; this

Fic. 187.—View of male Melolontha vulgaris,
from which the dorsal integument and heart
have been removed to show the internal

organs. After Vogt and Yung.

1. Cerebral ganglion. 10. Malpighian tubules, brown portion,
2, 1st thoracic ganglion. with caeca.

3. 2nd and 3rd thoracic ganglion. 11. Malpighian tubules, distal end.

4. Fused abdominal ganglia. 12. Tracheae with vesicles.

5. Oesophagus. 3. Testes, opening into coiled vasa
6. Mid-gut. deferentia.

7. Small intestine. 14. Penis.

8. Colon. 15. Single vas deferens.

9. Rectum.

opens into a brown mid-gut, in which the processes of diges-
tion are mainly carried on. The mid-gut passes into a finer
tube, the small intestine, which receives the Malpighian tubules,
and this in its turn passes into the colon, which has on its
inner side six longitudinal muscular ridges; this opens through
the rectum to the exterior. With the exception of the mid-
gut, the alimentary canal is lined with a thin layer of chitin,
continuous at the mouth and anus with the exoskeleton, and
this is cast at the ecdysis of the exoskeleton. In Melolontha
neither salivary glands nor hepatic diverticula are described.
The Malpighian tubules are four in number; they are very

326 ZOOLOGY

long, and are closely applied to the outside of the alimentary
canal (Fig. 187). Each of them consists of a free end, which is
usually white, and of a brown portion which bears numerous
small side diverticula, giving the tubule a feathered appear-
ance; they open into the small intestine. The cells lining
the tubule contain crystals of uric acid, which are excreted
through the rectum.

The tracheal system, which carries air to every part
of the body, communicates with the exterior by eight pairs
of stigmata. The first two of these are situated close behind
the base of the first and second legs, between the pro- and
meso-, and meso- and meta-thorax respectively. The remain-
ing six are found on the soft integument which unites the
terga and sterna of the seven anterior abdominal segments.
Each stigma is surrounded by an oval ring of chitin, and the
opening can be closed by the action of certain muscles. It
leads into a large trachea, which in the first thoracic stigma
swells into a considerable vesicle ; from this two branches pass
off and enter the head. The most dorsal of these unites with
its fellow of the opposite side, and the single trunk gives
branches both to the eyes and to the brain; the other branch
also unites with its fellow, and supplies the antennae and
mouth appendages. A third branch arises from the same
enlargement and runs to the anterior pair of legs, and several
smaller branches supply muscles. Besides these, a stout branch
runs backward and opens into the main trachea of the second
stigma; this bears in its course many oval tracheal vesicles
(Fig. 187), and gives off branches to the elytra; two or three
other branches with vesicles also pass backwards, and one of
them supplies the second pair of legs. The main trachea from
the second stigma gives branches to the membranous wings,
the third pair of legs, and longitudinal branches which open
into those of the adjacent stigmata.

The abdominal tracheae are very regularly arranged; the
six stigmata on each side open into a trachea, which immedi-
ately divides into a dorsal and a ventral branch; these arch
round, pass backward, and meet together again in the main
trachea of the next segment. The dorsal and ventral arches
of the last stigma unite to form a ring, and at the point of

TRACHEATA 327

union give off a trachea to the generative organs. Each of the
dorsal loops of the system thus formed breaks up into six or
eight smaller tracheae, which pass dorsally, giving off fine
branches to the various viscera, and frequently terminating in
vesicles ; the ventral loops also give off smaller branches, and
each of the last six gives rise to a long trachea, which passes
backward and opens into a large swelling in the fifth abdom-
inal segment; similar branches come from both sides of the
body, thus the right and left tracheal system is in communi-
eation within the body.

Each trachea consists of a tube of very thin transparent
chitin, which is strengthened and kept expanded by a spiral
thickening of the chitin; this gives the trachea its character-
istic spiral appearance. The chitin is secreted by a layer of
polygonal cells, with conspicuous nuclei, which surround the
tracheae. The vesicles are simply oval swellings on the
tracheae. The finest branches ramify between the cells which
compose the various tissues, and thus in a tracheate animal
the cells are directly supplied with air, and are not dependent
upon the blood for their supply of oxygen. Owing to the
complete intercommunication of the various tracheae the whole
system could be filled with air from any one stigma, so that
if anything rendered the supply from some of them inefficient,
it could be made right by the others. The vesicles when
charged with air doubtless serve to render the body of the
beetle lighter during flight.

The heart of the cockchafer les in the median line immedi-
ately beneath the dorsal integument; it consists of a tube
closed behind but open in front, with contractile muscular
walls. In the abdominal section of this tube there are eight
pairs of ostia, with valvular lips; through these the blood enters
the heart, and by its contractions is propelled forwards. The
ostia mark the hmits of the eight chambers into which the
heart is sometimes said to be divided ; anteriorly it is continued
into a vessel, the so-called aorta, which passes as far forward
as the head and then suddenly ends with an open mouth.
The heart is lodged in a space, the pericardium, whose dorsal
wall is formed by the terga of the various seements, and the
ventral by a pericardium or pericardial membrane. The alary

328 ZOOLOGY

muscles, which correspond in number with the cardiac cham-
bers, and have a wedge-shaped outline, are attached at one
end to the integument, and at their broader extremity to the
pericardial membrane; when they contract the latter is de-
pressed. This membrane consists of connective tissue, pierced
by numerous oval apertures; when it is depressed the blood in
the body-cavity passes through it, and at the same time the
diastole of the heart taking place, the blood enters through the
eight pairs of ostia, and at the systole is forced forward and so
out of the open mouth into the body-cavity again. In this
way the blood, which is a colourless fluid with amoeboid
corpuscles, is kept in circulation.

The body-cavity of Insects is to a great extent occluded by
the various viscera, but in addition to the alimentary canal,
generative organs, etc., there is a considerable amount of a
tissue, known as the fat-body, which is formed primitively
from mesoblast cells lining the integument. This fat-body is
especially abundant in the larvae, where to some extent it acts
as a storehouse for reserve material, particularly in those
Insects which pass through a protracted pupa stage; it is also
found in mature Insects, and is usually present to a greater or
less extent on the pericardial membrane. In the Tracheata,
where the air is directly conveyed to the cells of all the tissues,
the blood has to a great extent lost its respiratory function ; it
is still, however, of the utmost importance. It bathes all the
internal organs, and these, as is usually the case when organs
are surrounded by nutrient media, do not form solid compact
masses, but are branched and subdivided as much as _ possible.
The food which has been digested in the alimentary canal is
thus distributed by the blood into which it passes, the fats are
stored up by the fat-body, and the nitrogenous excreta, the
urates or uric acids, are either conveyed straight to the Mal-
pighian tubules, or are stored up in the cells of the fat-body.
From time to time these cells break down, and then the stored-
up urates are taken by the blood to the Malpighian tubules,
and from them pass out of the body. The body-cavity in
Insects, as is probably the case in all Arthropods, is a haemo-
coel, and the true coelom is probably confined to the lumen of
the generative organs. The developement of a tracheal system

TRACHEATA 329

of breathing, and the consequent absence of a respiratory
function of the blood, has taken place concurrently with the
formation of a new method of ridding the body of its waste
nitrogenous matter. In most other Coelomata this is effected
either by means of tubules ultimately ending in flame cells, or
by nephridia, and these two methods are connected by inter-
mediate forms; but in the true Tracheata the nitrogenous
matter leaves the body by caecal diverticula of the alimentary
canal, formed usually from the proctodaeum, but sometimes
from the mesenteron. These Malpighian tubules receive the
matter they are to excrete either at first hand from the blood,
or the urates, etc., have been stored for a time in the cells of a
mesoblastic tissue, the fat-bodies, and, when these disintegrate,
the nitrogenous matter is carried by the blood to the tubules,
and thence passes through the rectum to the exterior.

The nervous system of Jelolontha is very concentrated,
instead of the double nerve cord enlarging into a ganglionic

wes Ge ws
soup ----8 Fre. 188.—View of nervous system of Melolontha

| vulgaris. After Vogt and Yung.

. Cerebral ganglion.
2. Sub-oesophageal ganglion.

. Ist thoracic ganglion.

\
=
SS
== »
——
'
\ v
'
'
'
H
Oo
oO fF WwW WY He

ae — . 2nd thoracic ganglion.
| 1
Aili | Ke ak . ord thoracic ganglion.
Zi ih ee ; :
2 || Mi aN 6. Fused abdominal ganglia.
Ui —— FH | — { N =
Hi = | 7. Nerves to antennae.
—7) |) WW NW
=e] = | 8. Optic nerves.
5 | ee See - ;
= f Ss --10 9. Origin of sympathetic nerves.

. Abdominal nerves, a pair to each segment,
; which split into an anterior and posterior
y | branch.

UM
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oe

mass in each segment, the ganglia are to a great extent fused
into a central mass, from which the nerves radiate.

The supra-oesophageal ganglion occupies a considerable part
of the head; it consists of two well-marked lobes separated by

330 ZOOLOGY

a slight groove. Each lobe is continued laterally into a stout
optic nerve, which supplies the compound eyes; besides this it
gives off a nerve to the antenna of its own side, which branches
abundantly in the lamelliform segments, and a third nerve to
the labrum or upper lip. Two short commissures encircle the
oesophagus, and unite in the sub-oesophageal ganglion, which
also lies in the head; this ganglion supplies nerves to each of
the mouth appendages, the mandibles, and first and second
maxillae. From the sub-oesophageal ganglion two commissures
pass backward, and enter the first or prothoracic ganglion,
which gives off nerves to the thoracic muscles and first pair of
legs. Close behind this is a large ganglionic mass, formed by
the fusion of the meso- and meta-thoracic ganglia, its double
origin being shown by a transverse groove (Fig. 188). This
compound ganglion supplies nerves to both pairs of wings, and
to the posterior two pairs of legs.

The abdominal ganglia are all fused into one mass, which
is withdrawn into the thorax, and lies in the metathorax
immediately behind the ganglion of that segment; indeed, it
seems as if part of the abdominal nervous system is absorbed
into the last-named ganglion, which is said to supply nerves to
the first abdominal segment ; the remaining seven pairs of nerves
arise from the abdominal mass, and pass backwards to their
respective segments, where they split into an anterior and a
posterior branch.

In addition to the central nervous system, there is a
small sympathetic system, which consists of the following
parts. A pair of fine nerves arise from the supra-oesophageal
ganglion and fuse in the middle line, and so form a minute
triangular ganglion lying in the head (Fig. 188); from this
a median unpaired nerve passes back and forks over the crop,
and the branches unite into a small ganglion again. There are
also two pairs of minute ganglia which innervate the heart
and tracheal system, these are situated just behind the supra-
oesophageal ganglion.

Like all other Insects the cockchafer is dioecious, and the
female may be distinguished from the male by having six
lamelliform segments in its antennae, whereas the male has
seven.

TRACHEATA 331

The testes lie in the fourth and fifth abdominal segments ;
they consist on each side of six small flattened bodies, each of
which has a short duct. The six ducts unite into a single
vas deferens, which is much coiled; just before the vasa
deferentia of the two sides unite they are rather swollen,
and form vesiculae seminales, they then receive the secretion
of two coiled accessory glands. The united vasa deferentia
open into an extremely large and complicated ejaculatory
apparatus, which can be protruded just below and in front
of the rectum.

The ovaries consist of six tubes upon each side; their inner
tapering ends are united into a strand of tissue which is attached
to the tergum of the first abdominal segment; the ova arise
from the endothelal cells which line these tubes. The cells are
undifferentiated at the inner end of the tube, but as they approach
the oviduct they assume more and more the character of the ripe
ova; between each two eggs is a mass of cells whose function
is to afford nourishment to the ova, which attain a considerable
size. The six tubules on each side unite into an oviduct, and
the two oviducts fuse and form the vagina, which opens just
in front of the rectum. A small accessory gland and a sper-
matheca are present, and, in addition to these, a large bursa or
sac, into which the penis is introduced during fertilisation.

The adult cockchafers may be seen flying about in the
dusk during the months of May and June; they live upon the
leaves of deciduous trees, and at times do a good deal of damage
by denuding the branches of their foliage. The female deposits
her ova, in clumps of about thirty, several inches below the
surface of the ground. Each ege gives rise to a larva with a
brownish, hard, chitinous head, and a white body of twelve
segments, the last two of which are swollen into a “sack.”
The three segments immediately succeeding the head are each
provided with a pair of four-jointed legs. The larva creeps
through the earth, and lives on roots, in this way often causing
considerable loss to the agriculturist. The larva lives three
years, and in this time grows to a considerable size; at the
end of the third summer it burrows to a depth of about two feet
in the ground, and there forms a spherical cell; in this it turns
into a brown chrysalis. The pupa thus formed is a pupa

bo

ZOOLOGY

Os
Os

libera, that is, its appendages are free, and not hidden under a
covering, as is the case with the Lepidoptera. The pupal stage
lasts till the following spring, and in the interval the individual
has undergone great changes; its nervous system, with a gan-
glion in each segment, has become concentrated, its wings have
developed, and its appendages have assumed their adult form.
The perfect insect or imago emerges from the pupa some little
time before it appears on the surface, but during the month of
May in its fourth year the mature cockchafer makes its way
above ground, and is found hanging underneath the leaves of
the trees which serve it as food.

The life-history of Melolontha affords a good example of a
complete metamorphosis, with its larval, pupal, and imaginal
stages. The egg gives rise to a larva which has little or no
resemblance to the adult insect, and the change from the
vermiform larva to the winged insect is effected during the
period of quiescence which constitutes the pupal stage. Many
insects undergo a similar metamorphosis, whilst the young of
others are but miniatures of their parents. Intermediate con-
ditions between these two extremes are not uncommon, and
the variations which the life-history of the various orders of
insects present are of use in the classification of this class.

Orper 1. APTERA.

CHARACTERISTICS.— Wingless insects whose body is covered with
scales or hairs. The segments of the thorax are not fused
together. The mode of progression is either running, or
springing with the aid of an apparatus borne on the ventral
side of the abdomen. There is no metamorphosis.

The Aptera form the most primitive order of insects. This
order consists of a few genera, which are grouped in two sub-
orders, (i.) the Collembola and (i1.) the Thysanura, differing
considerably from one another.

Sub-order 1. Collembola.

The members of this group are widely distributed, but
very inconspicuous. Specimens of them may be found under

TRACHEATA 333
stones or dried leaves, on roofs, ete., and some of them live on
the surface of the water, upon which they move actively.

The head bears a pair of antennae with few joints (4-8).
The prothorax is usually compressed; there is no trace of
wings, and no evidence that the group ever possessed them.
Each of the three thoracic segments bears a pair of legs with
four or five joints.

The abdomen is short; the Sminthurinae have apparently
only two or three segments, the Podurinae six. On the ventral
side of the first abdominal segment is a structure known as
the “ventral tube”; this in Podura and Lipura is a simple
tubercle, but in other genera it takes the form of a tube, which
in Sminthurus is divided into two halves at its end, from each
half a long delicate tube can be protruded at the will of the
animal. The ventral tube is essentially a protrusible part of
the integument, it may be compared with somewhat similar
structures in the Thysanura. Its function is possibly an ad-
hesive one. The springing apparatus consists of a forked
process borne on the fifth, or, as is stated in Podwra, on the
fourth segment; this process is directed forwards, and in those
species which jump the best, it is retained in position by
two chitinous hooks which form the “catch”; these hooks in
Tomocerus are borne on the third abdominal segment. The
spring acts by the process pressing violently against the
ground, and the insect is thus propelled into the air; the
process is then folded under the abdomen again, and retained
in position by the catch. This saltatorial apparatus is absent
in some species, as Lipura, Anura, ete.

The nervous system consists of the usual chain of ganglia,
but the number in the abdomen is reduced. In Sminthurus
and others there is only one abdominal ganglion. Eyes may
be absent or present, in the latter case they consist of two
little groups of at most eight simple eyes.

The mouth appendages are, as is usual in insects, a pair
of mandibles and two pairs of maxillae; the first pair are
provided with palps, and the second are partially fused into
an under lip. All the mouth appendages can be withdrawn
into a cavity, and in this respect the Collembola resemble
the Myriapod Scolopendrella. The alimentary canal is a

334 ZOOLOGY

straight tube stretching between the mouth and anus. It
is at present unsettled whether any salivary glands or Mal-
pighian tubules exist.

The heart, which les in the middle dorsal line in Macro-
stoma, is said to have five pairs of valves. The blood is
yellowish and corpusculated. It seems doubtful if a tracheal
system exists in many of the Collembola, but in the larger
Sminthurinae a pair of stigmata open on the under side of
the head, a very unusual position; from these bundles of
tracheae radiate.

Like all other Insects, the Collembola are dioecious; there
is very little external difference between the sexes. The
developement is direct.

Sub-order 2. Thysanura.

The Thysanura are of larger size than the Collembola, and
have to a much greater extent the appearance of insects.
One of the most familiar genera is Lepisma, often termed the
“ silver-fish,’ a quickly-running, silvery-gray insect, which
infests old chests of drawers and disused cupboards. It is a
nocturnal insect, and hides away during the winter. The
genus Machilis is found in woods, etc., or on rocky sea-coasts,
where it lives between stones or in clefts of the rock, but it
loves to run on warm sunny places. Campodea is found under
fallen leaves or stones in shady places and in loose earth. Japyx
also shuns the light; it is found widely distributed in Europe,
but not in cold places.

The number of abdominal segments is always ten, and the
abdomen ends in three long many-jointed processes or cerci.
The three thoracic segments each bear a pair of legs; in
Machilis the coxae of the two posterior pairs of legs bear pecu-
liar processes, which externally resemble certain paired processes
found on the ventral surface of the abdomen in different
species of Thysanura. These processes, however, are regarded
by some authorities as the representatives of abdominal limbs ;
in Machilis they are found on the second to the ninth seg-
ments, in Japyzx on the first to the seventh, in Lepisma only
on the eighth and ninth—in the last-mentioned insect the

TRACHEATA 335

coxal processes are wanting. Similar processes occur internal
to the base of each of the twenty-two pairs of legs in Scolo-
pendrella.

Some very remarkable spherical protuberances of the
integument near the middle line are found in JMMachilis and
Campodea, projecting between the abdominal appendages.
They are twenty-two in number in the former genus, a pair pro-
jecting behind the sterna of the first, sixth, and seventh segments,
and two pairs behind those of the second, third, fourth, and
fifth. These protuberances appear to be extended by the
forcing into them of some of the blood. They have special
muscles which retract them, and as a rule they are found in
the retracted condition. They probably serve as respiratory
organs. They are absent in Lepisma and Japyx.

The number of ganglia in the abdomen is eight, except in
Campodea, where only seven have been described. In the
last-named genus the nervous system is in intimate connection
with the hypodermis. Machilis has a pair of large compound
eyes. The Thysanura are all provided with salivary glands
and Malpighian tubules, and the heart has nine pairs of ostia.
The tracheal system is fairly well developed; in Machilis a
pair of stigmata are found on the meso- and meta-thorax, and
on each of the abdominal segments from the second to the
ninth ; the tracheae do not anastomose.

The primitive position of the Aptera is shown (i.) by the
absolute absence of wings, (ii.) by the direct developement,—this
is, however, shared by several other orders of insects,—(iii.) by
the presence of abdominal appendages, (iv.) by the very slight
developement of the cuticle, and (v.) by the general resemblance
of some of the genera to the larvae of higher forms. This is
recognised by the application of the term campodiform to the
larvae of most insects with direct developement, and to some
of those, e.g. certain families of beetles, with indirect.

OrpER 2, ORTHOPTERA,

CHARACTERISTICS.—Lnsects with direct developement. Prothorax
Sree. Lbiting mouth parts. Wings usually unequal, the
anterior pair small and hard, the posterior membranous.

336 ZOOLOGY

The insects grouped together in the order Orthoptera are
all of a fair size, and compared with the beetles and flies are
comparatively few in number. They may be classified in
two groups: (i.) the Dermaptera, comprising the earwigs, and
(ii.) the Orthoptera genuina, which include the cockroaches,
grasshoppers, locusts, crickets, etc.

1. Dermaptera.

FORFICULIDAE. — This family consists of the earwigs,
the most familiar of which in our country is the genus
Forficula. The body is elongated, the head flattened, with
filiform antennae, round eyes, and no ocelli. The prothorax
is free, the anterior wings short and horny; the posterior,
which are folded longitudinally and transversely beneath them,
are membranous. ‘The abdomen has nine segments, and termi-
nates in a pair of forcep-like processes which have been homo-
logised with the cerci anales of other forms. These insects
are nocturnal in their habits, concealing themselves in flowers
and fruit during the day. The female watches over her
young.

The remaining groups of the Orthoptera—the Cursoria,
the Gressoria, and the Saltatoria—are usually grouped together
as the Orthoptera genuina.

2. Orthoptera Genuina.

I. Cursor1a.—This sub-order comprises the various species
of cockroach which are found all over the world. The body
of these insects is flat and oval, the pronotum is large, the
antennae long, the legs are adapted for running, and the
tarsus is five-jointed; a pair of ringed cerci anales are
present.

There are about 800 species of cockroaches: some, as
for example Polyzosteria, are wingless ; others, as Heterogamia,
have the females wingless; whilst Blatta (Phyllodromia) and
Periplaneta, the species found in Europe, bear wings in both
sexes, except P. orientalis, the female of which is wingless.
Cockroaches avoid the light, and are nocturnal in their habits

TRACHEATA 337

and fond of heat. The eggs are laid in a capsule or ootheca,
which is variously shaped in the different species; it is often
carried about by the female protruding between the terminal
segments of the abdomen for some days before it is deposited.

II. GRESSORIA include two very remarkable families of
Insects, the Mantidae and the Phasmidae. Their legs are
adapted for walking.

The Mantidae have their anterior pair of legs modified to
form predatory organs. The toothed tibia can be folded down
against the femur, as the blade of a pocket-knife into the
handle. This subchelate appendage is used in capturing
other insects or spiders for food. The prothorax, which bears
these enlarged appendages, is very much elongated. The
abdomen is elongated and oval. The commonest colour of these
Insects is green. The eggs are laid in regular clumps on
sticks or stones. Mantis religiosa is found in South Europe ;
the devotional attitude in which it sits, with the anterior legs
raised, has obtained for it the name of the praying insect ;
many legends and superstitions centre around it.

The Phasmidae are mostly tropical insects of large size which’
feed on leaves. ‘They are slow in their movements, and escape
observation by their very extraordinary resemblance to various
natural objects amongst which they live. The genus Phylliwm
of the East Indies mimics various forms of leaves, the veins on
the wings resembling the venation of the leaf, and in some
cases the legs bear flattened leaf-like expansions which in-
crease the resemblance; others have holes in their wings and
a dried appearance which simulates that of a tattered, withered
leaf. The genus Phasma includes many species of an elongated
shape which closely resemble dried twigs; one species attains
the length of 12 inches. Ceroxylus laceratus is covered
with tufts of processes which give it the appearance of a mossy
twig. The whole family affords a very striking example of
protective resemblance.

III. SaLratortaA.—This division includes all those forms
which have the legs modified for jumping, such as the grass-
hopper, locusts, and crickets. It may be divided into three
families :

1. Acridiidae or Grasshoppers.—The body is compressed,

22

338 ZOOLOGY

with a large vertical head. The antennae are short, and the
hind legs are enlarged for jumping ; the tarsus has three joints ;

o

Sa
ware ttatrE

Fic. 189.—Pachytylus migratorius. Natural size.

they produce a chirping noise by rubbing their tibia against a
vein on the anterior wing, and their auditory organ is situated
on the first abdominal segment. The female has no projecting
ovipositor. The eggs are laid in cocoons in packets of 50 to
100 at a time.

Some of the grasshoppers are very voracious, and as they
move in immense swarms, they occasion very considerable

PRACHEATA 339

damage. One species, Acridiwm migratorium, which is found
all over Europe and Asia, moves as a locust swarm, and devours
every green thing which it comes across.

Fria. 190.—Acridium peregrinum. Natural size.

Some species attain a large size, measuring four or six
inches in length.

2. Locustidae.—The Locusts are usually of a green or
brown colour; they have long filiform antennae, and their
wings lie vertically along the side of the body. The auditory
organ is situated upon the tibiae of the anterior pair of legs ;
the tarsus is four-jointed. The female bears a pair of long,
sabre-like processes which form the ovipositor; this bores into
the ground, and the eggs are deposited by it. The stridulating
noise of the male is caused by drawing the rough vein of the
left anterior wing over a file-like structure situated on a vibrat-
ing membrane at the base of the right.

340 ZOOLOGY

Locusta viridissima is one of the commonest European
forms.

3. Gryllidae.— The crickets have a shorter and more

Fic. 191.—Mole cricket
(Gryllotalpa vulgaris).

1. Eggs.

bo

Young just hatched.

3. Larva after first
moult.

4. Adult, nat. size.

cylindrical body than those of the two preceding families.
Their antennae are long and filiform. The male produces an

f aS >

eae NY NY
Sy wae Win SSy wwe |

Fig. 192.—Rocky Mountain Locust (Caloptenus spretus).
a. Females in various positions ovi- d,e. The earth partially removed to il-

positing. lustrate an egg mass already in
b. Egg pod extracted from the ground place and one being placed.
with the end broken open. J. Shows where such a mass has been

c. A few eggs lying loose on the ground. covered up.

TRACHEATA 341

irritating noise by rubbing the short anterior wings against the
posterior. As in the preceding family, the auditory organ is
on the proximal end of the anterior tibia. The tarsus is three-
jointed. The females are usually provided with a straight
ovipositor, and the males attach a spermatophore containing
semen to the genital orifice of the female.

Gryllus campestris is the field cricket, and G. domesticus the
house cricket. Gryllotalpa vulgaris, the mole cricket, leads
mainly a subterranean life; it is of a brown colour, and has its
two anterior legs short and thick, and adapted for digging.
The female lays from 200 to 300 eggs in a nest the size of a
hen’s egg, situated some inches below the surface of the ground.

The Orthoptera genuina, from their habit of moving in
immense swarms and devouring all the green parts of plants

dock lad =

SRP PTE

IIo r$ Fee =

Fic. 193.—Caloptenus italicus. Natural size.

which come in their way, are Insects of great economic 1m-
portance. The females usually lay their eggs in waste and
inaccessible places termed in America “ mauvaises terres” ; the
young larvae when hatched make their way to more cultivated
districts. As an example of the enormous number of these
insects, it may be mentioned that in the spring of 1882 over
1300 tons of locusts’ eggs were destroyed in the island of

342 ZOOLOGY

Cyprus, and over 12,000 tons of locusts. Various species
compose the locust swarms in different parts of the world.

Acridium peregrinum does. much harm in India and
Algeria. Swarms of Caloptenus spretus, another of the Acri-
diidae, have been known to clear off every green thing over 300
square miles in Colorado in less than six weeks. In Minne-
sota 300 ege capsules, each containing thirty eggs of this
species, were found on an average in every square foot. These
figures give some idea of the astounding numbers of these
locust swarms. :

OrpeER 8. NEUROPTERA.

CHARACTERISTICS.—Insects with membranous wings, both parrs
alike, with the veins forming a more or less close network.
The mouth parts are, as a rule, of the biting type. Meta-
morphosis complete or inconrplete.

The Neuroptera form a rather heterogeneous collection of
Insects, which, however, resemble each other in the character
of their wings. Many of the subdivisions of this order have
but little in common, and it is difficult to group them into
sub-orders ; it will therefore be advisable to consider a few
of the more important forms under the designation of their
families.

Family 1. Termitipar.—The white ants flourish most
abundantly within the tropics; certain genera, however, as
Calotermes, and some species of Termes, occur in subtropical
and temperate climates.

The antennae are short; the abdomen of nine segments is
oval and flattened, unlike the linear abdomen of most of the
Neuroptera. The wings when at rest are unfolded, and le
flat upon the back (Fig. 194).

The TERMITIDAE, like the more highly organised ants and
bees, live in communities, and the individuals have undergone
considerable modifications, correlated with their particular
functions in society. The sexual forms are winged; the
apterous members of the community are either larvae, which,
unlike the larvae of the Hymenoptera, take an active share in
the work of the nest, or are neuters, 7.e. individuals with
sexual glands, which, however, do not reach maturity, and

TRACHEATA 343

which are apparently functionless. The neuters may be
workers with small rounded heads, or soldiers with greatly
enlarged heads and most formidable mandibles.

Fic. 194.—White Ant (Termes bellicosus).
A. Winged male, B. Soldier, C. Queen.

The communities live as a rule underground ; some species
construct nests of such size and strength as to serve as watch-
towers for the big game of South Africa. These nests are 12
to 15 feet in height. Others live on tree-trunks, etc., and
cover the branches with little tunnels built of pellicles of clay
which they bring up from below, and line with excrement.
They invariably work in the dark, building the tunnels from
the inside; if anything breaks down part of their work, the
workers disappear, and the powerful “soldiers” take their place
and defend their home.

Those of the larvae which are not destined to become
workers or soldiers acquire wings, and a few weeks afterwards
they leave the nest, and pair whilst flying in the air. They
then fall to the ground and lose their wings; in this condition
a number of them perish, but some of them, guided by a few

344 ZOOLOGY

neuters, will succeed in founding a new nest. In this a special
chamber is set apart for the queen, whose body swells enor-
mously. It may attain a length of more than 3 inches, and is
distended by an enormous ovary. The queen lays eggs at the
rate of 80,000 to 90,000 a day, and these are carried away
and cared for by the workers.

In Termes lucifugus, found in South Africa, the larvae
which mature in the spring become kings and queens, those
which mature in the summer become complementary kings
and queens, and replace the functional ones if occasion arises.
The king dies in the autumn, but, although the queen ceases
to lay eggs during the winter, she survives, and resumes the
ego-laying in the spring.

The nests of Calotermes are the most incomplete; there is
no special chamber for the queen, and their home consists of
passages tunnelled in trees.

Family 2. TurrpsmpaAzE.—A family of very small, usually
black insects with fringed wings. Their body is long and

Fic. 195.—Corn thrips (Zhrips cere-
alium), female. Magnified.

narrow, their antennae long and slender, and their mouth parts
suctorial. Thrips cerealium does a good deal of harm to wheat
crops, others injure flowers, etc. They are sometimes regarded
as a separate order of Insects, and called the Thysanoptera ;
other authorities place them with the Hemiptera.

Family 3. EPHEMERIDAE—The Ephemeridae or May-flies
spend but a short part of their life in the imago condition, at
most only a few hours. They are delicate insects with a long
body and a ten-jointed cylindrical abdomen which ends in two
or three very long anal filaments. The imago takes no food,
its mouth parts are rudimentary, and the oral cavity is
stated not to open into the alimentary canal. The ducts of
the reproductive organs do not unite in either sex, but open
independently, one on each side of the ninth abdominal seg-
ment in the male, and between the seventh and eighth in the
female.

TRACHEATA 345

The larvae are aquatic, and feed on other insects, etc.; they
have well-developed mouth parts. The tracheal system is
closed, and the larvae breathe by means of plate-like gills,
which are borne to the number of six or seven pairs on the
anterior abdominal segments. The tracheae ramify in these
eills, which are moved about in the water, and possibly serve
to some extent as locomotor organs. These gills have been
regarded by some authorities as structures from which the
wings of Insects in general may have originated.

The larvae moult very frequently, in one species more than
twenty times, and live two or three years. They pass into a
pupa stage, and from this a winged insect emerges, this is the
subimago, it takes a short flight, and then casts its skin, and
gives exit to the imago. The male fertilises the female on the
surface of the water, and shortly afterwards the latter drops
her eggs into the stream or pond, and then dies.

Family 4. LrpenLuLipAE—The dragon- flies are large

Fic. 196.
A, The anterior portion of the body of Aeschna cyanea freed from the puparium.
B. The tail being extricated.

346 ZOOLOGY:

insects with a thin cylindrical abdomen, but an enormous
head and thorax. Many of them are strikingly beautiful.
The generative organs of the male open on the ninth abdominal
segment, but there is a kind of vesicula seminalis on the second

Fic. 196.

C. The whole body extricated.

D. The perfect Insect (Aeschna cyanea), the wings having acquired their full
dimensions, resting to dry itself, preparatory to the wings being horizontally ex-
tended.

segment of the abdomen, into which the semen is transferred,
and is thence introduced into the females. In some species
the female then flies over the water, touching it at intervals

TRACHEATA 347

with the end of her abdomen, and depositing an egg at each
dip, or in other species she deposits the eggs on submerged
water-plants.

The larvae are very voracious, and feed upon other insects,
their lower lip or labium is peculiarly modified into a structure
known as the “ mask,” this can be suddenly shot out, and serves
to capture food. The larva of Agrion has at the end of its
abdomen three leaf-like gills, but other species breathe by their
rectum, the walls of which are richly supplied with tracheae.
The entrance and exit of the water is controlled by three valves,
which can be opened or closed at will; in some species the
sudden expulsion of water serves to propel the larva through
the water. This anal respiration recalls a similar change of
function of the posterior part of the alimentary canal in some
Crustacea (see p. 268). The pupa stage, which precedes the
- Imago, is in the Libellulidae an active stage, and is sometimes
termed the “nymph” (Fig, 196).

Family 5. MyRMELEONTIDAE.—The ant-lion, Myrmeleo, in
the imago condition has clubbed antennae, a small prothorax,
a large mesothorax,
and wings of equal
size. The larvae live
at the bottom of
little conical sandy
pits, which they ex-
cavate ; they lie par-
tially embedded in
the sand at the bot-
tom of the pit, and
seize with their powerful mandibles any insect, ete., which
happens to stray over the edge. The mouth is closed,
and the food is sucked in through perforations in the
mandibles. It is stated that the proctodaeum of the larva
does not open into the alimentary canal, but is modified to
form a silk gland, which serves for the spinning of the cocoon
in which the pupa envelops itself.

Family 6. In the Family Hemeropupae the larvae of
Chrysopa and Hemerobius, which are known as Aphis lions, feed
on Aphides. They also have the proctodaeum modified to form

Fic. 197.—Ant-lion, Myrmeleon formicarius.

348 ZOOLOGY

a silk gland. The larvae of another genus, Mantispa, are para-
sitic ; they pass their life in the ovisacs of spiders, into which
they burrow to devour the ova.

Family 6. PHRYGANIDAE.—This family is sometimes placed
in a distinct sub-order, the Trichoptera; it comprises the
insects popularly known as caddis-flies. The head bears
long filiform antennae, and a pair of hemispherical projecting
eyes. The prothorax is small; the wings have few veins, and
are longer than the body; the posterior pair can be folded.
The wings are covered, as in the Lepidoptera, with microscopic
hairs or scales. The mouth parts are rudimentary, more
especially the mandibles, and the first maxillae and labium are
modified. The resemblance of this family to the Lepidoptera
is further marked by the general appearance of the imago,
which approximates to that of some members of the Micro-
lepidoptera, and of the cylindrical larva and quiescent pupa ;
the latter resembles that of a moth, but has free limbs and
wings.

The larvae known as caddis-worms live in tubular cases,
which they build up of particles of sand, shells, or bits of
erass or other plants, the material varying in different species.
At times they are wholly retracted within these cases; at
other times their head and thorax project, and they walk
about carrying the case retained round their abdomen by two
recurved hooks. Like the EPHEMERIDAE and LIBELLULIDAE,
some of the larvae have their tracheal system closed, and
carry tracheal gills. They are either carnivorous, and then
very voracious, or purely herbivorous. The case is closed at
both ends at the end of larval life, and serves as a cocoon for
the pupa, which developes into the imago out of the water.
The female deposits her eggs in gelatinous clumps on sticks
or stones in the water.

Orper 4. LEPIDOPTERA.

CHARACTERISTICS.—Lnsects with suctorial mouth parts, which take
the form of a spirally rolled proboscis. The four wings are
similar, and are covered with minute scales. The prothorax
is fused with the mesothorax. The metamorphosis is complete.

TRACHEATA 349

The Lepidoptera are a very homogeneous group, contain-
ing a large number of species. They are familiar to every
one as moths and butterflies.

The head is large, and covered with hairs; it bears com-
pound eyes, and sometimes ocelli are also present. The
antennae are straight, but
vary a great deal in their
details. The mouth parts have
undergone very remarkable
modifications; the labrum
and mandibles are aborted ;
the first maxillae are each
elongated into a very long,
grooved, closely-jointed struc-
ture, and when this is opposed
to its fellow the whole forms
a closed tube, which, when
at rest, is coiled under the
head lke a watch-spring; in
many species the two halves
of this proboscis are held to-
gether by a number of minute
hooks. The maxillary palps
are rudimentary, except in Fic. 198.—Silk-worm moth, Bombyx mori.
the Tineidae, where they are A. Female. B. Male.
well developed.

The second maxillae or Jabium form the spinnerets in the
larva or caterpillar, but they disappear in the imago; their
palps, however, persist, and are large and hairy.

The thoracic segments are all fused together, the wings are
large, and the © rior and posterior of each side are occasion-
ally hooked together.. In some of the Geometridae the wings
are aborted in the females. The scales which give the beautiful
colour to the wings are morphologically hairs, which are flattened
out, and variously marked. The legs are weak, the tarsus five-
jointed. The abdomen has ten segments, some of them con-
cealed, it is covered with hairs.

The internal organs show the following modifications. There
are only two thoracic ganglia. The two anterior abdominal

350 ZOOLOGY

ganglia of the caterpillar abort, and the next four or five per-
sist. There are eight stigmata, the anterior between the pro-
and meso-thorax, the remaining seven in the abdomen; the
tracheae which arise from the latter bear air vesicles.

The length of the proboscis varies, and is said to correspond
with the position of the nectaries in the various flowers upon
which the Lepidoptera feed. The nectar is sucked up the
hollow tube formed by the maxillae by the action of a suctorial
stomach which communicates by a short stalk with the oesoph-
agus. There are as a rule six Malpighian tubules.

The sexes are usually distinct, the male being in many
cases the more beautiful. A few Lepidoptera are partheno-
genetic. This phenomenon occurs sometimes in the silk-worm
moth Bombyx mori, and in some of the Psychidae. The eggs

Fic, 199.—Larva of Bombyx mori.

are usually laid on such plants as the larvae, when hatched, feed
upon. The larvae are commonly known as caterpillars; these
bear three pairs of five-jointed thoracic feet, and, in addition,

Fic, 200.—Head, pro-leg, and leg of Bombyx mort, larva.

two to five pairs of unjointed pro-legs, which may occur on the
third to the sixth abdominal segments, and on the last. These

TRACHEATA 351

pro-legs as a rule terminate in a ring or semicircle of chitinous
hooks. The larval life may endure from a couple of weeks to
three years; it is followed by the quiescent
pupa stage.

The pupa may be suspended by the hind-
most pro-legs, and this position may be rendered
the more secure by a rope of silk round the
thorax, as in Pieris, or the pupa may be
enclosed in a silken cocoon, as in the silk-
worm, or simply buried in the earth, as in the
Sphingidae. The pupa has the hmbs of the
insect enclosed in a common covering, and is
hence known as a pupa obtecta, as opposed pyc, 201.—Cocoon
to the pupa Libera of the Coleoptera, in which of Bombyx mori.
the limbs stand out freely from the body.

The Lepidoptera may be divided into two sub-orders :

Sub-order 1. Microlepidoptera.

CHARACTERISTICS.— These are usually very small and delicate
moths, with, as a rule, long setiform antennae. The cater-
pillar has eight pairs of legs, terminating in a circlet of hooks
—“ pedes coronatt.”

They are as a rule secluded during daylight. Many of
their larvae burrow in the mesophyll of leaves or buds, or form
tubular cases by rolling the leaves together.

The following families may be mentioned :

Family 1, PTERoPHORIDAE.—Small moths with a long
slender abdomen and long legs. Their wings are hairy, the
anterior pair are usually more or less cleft, and the posterior
pair are divided almost to their base into three (Pterophorus), or
into six (Alucita), separate lobes. They form no cocoons, but
the larva attaches itself by its tail to some leaf or twig, sheds
its skin, and becomes a pupa.

Family 2. TinerpAr.—tThis is a very numerous family.
The Tineids have bristle-like antennae. Both the maxillary
and labial palps are well developed. The narrow wings are
frmged with hairs. Many of the larvae burrow in leaves,
others live together in nests, and they usually spin slight

ZOOLOGY

Los)
unr
ie)

silken cocoons. Many of them are destructive: 7’inea sarcitella
is the clothes moth, 7. tapezella the fur moth, 7. granella lays
its egg in grains of corn and the caterpillars devour the grain.
The genus Solenobia is parthenogenetic.

Family 3. Torrricipar—tThe leaf-rollers have short palps
and oblong anterior wings. They are as a rule larger than the
Tineids. The moths fly at night, and lay their eggs on the
buds of the trees, which are attacked by their larvae. The
caterpillars roll the leaves into cylinders, and in these turn into
brown pupae in silken cocoons. Tortrix viridana is common
on oak-trees. Retinia buoliana attacks pine-trees.

Family 4. Pyratmar.—The members of this family bear
long slender palps. They are as a rule gregarious, and fly in
the twilight. The larvae have a glassy appearance, and bear
but few hairs. The female of one species, Aphomia colonella,
creeps into bee-hives and deposits her eggs there; the larvae,
which are found in great numbers, devour the honey, to the
ereat detriment of the hives.

Sub-order 2. Macrolepidoptera.

CHARACTERISTICS.— Lepidoptera of large size, with a complicated
system of nervures on the wings. The feet are generally,
though by no means always, provided with a semicircle of
hooks—* pedes sub-coronatt.”

I, GEOMETRINA.

Slender moths, whose large thin wings lie horizontally
when at rest. The antennae are bristle-like, and in the male
sometimes toothed. The caterpillars have a varying number
of pro-legs, usually two pairs, and their manner of moving has
given them the name of loopers. When at rest they fix
themselves by the hindmost legs and raise the anterior half
of the body; in this position they may remain for hours, when
frightened they drop, but remain attached to their base by a
small thread of silk. They either spin cocoons under leaves,
or form brown chrysalids under the earth.

Many are injurious to fruit trees, as Cheimatobia brumata,

TRACHEATA 353

the female of which has rudimentary wings. Midonia piniaria
attacks Conifers.

II. NOCTUINA.

The group includes the forms popularly known as owlets ;
it is the largest group of the Lepidoptera, containing over 2500
species. Most nocturnal moths of fair size belong to it. The
antennae are long, sometimes pectinate in the male. The fore-
wings are small, and the larger posterior wings are folded under
them when at rest. They are usually of a dull colour, and
there is almost always a round spot and a kidney-shaped patch
in the middle of the anterior wing. There is little variation
between the sexes, or between the different species in the moth,
but the caterpillars differ considerably. The latter are striped
and barred, naked, or more rarely hairy ; they usually have five
pairs of pro-legs, but some have four. The pupae are usually
underground, enclosed in earthen cocoons. The eggs are laid
singly, and the larvae are not gregarious.

The Noctuina include numerous families, amongst whom
the Plusiidae, the Agrotidae, and the Ophiusidae may be
mentioned.

III. BOMBYCINA.

The members of this group are often termed spinners.
They are large unwieldy moths, often very beautiful and
strange in form. ‘Their body is usually very hairy (Fig. 198),
the head is small and sunken, and the mouth parts are reduced
and sometimes obsolete. The antennae are setiform, in the
male pectinate; the last-named sex are as a rule more
brilliantly coloured and more active than the sluggish female.
The wings of the female Orgyia are reduced, and are absent
altogether in Psyche. The eggs are laid in groups, and are
covered with a woolly substance; the caterpillars have sixteen
legs, and are usually hairy. The cocoons are made above
ground, the naked larvae forming theirs of silk, the more hairy
kinds mixing their hairs with a slighter amount of silk. The
sexes are usually very distinct, and the females attract the
males from great distances. Parthenogenesis occurs in the
family Psychidae.

23

354 ZOOLOGY

This group contains a number of well-known moths, such
as Lasiocampa quercus, the oak egger; Bombyx mori, the silk-
worm ; Cnethocampa processionea, the processional moth ; Cossus
ligniperda, the goat moth, etc.

IV. SPHINGINA.

The hawk-moths or humming - bird moths are large
Lepidoptera with short bodies and long powerful wings. Their
flight is swift and sustained, and they fly usually at twilight.
The antennae are short and taper to a point. The proboscis is
very long, and can suck up honey from the depths of a flower
without the insect alighting. The sexes are as a rule alike.
The caterpillars have sixteen legs, and the last segment bears
an anal horn or tubercle. They elevate the anterior portion
of their body like a Sphinx, and remain for hours in this posi-
tion; as a rule they are brightly coloured, and their skin is
smooth. The pupae form rough cocoons of earth underground,
and the proboscis is usually free. About 400 species are
known, many of which are tropical.

Sesia apiformis, the clearwing, has transparent wings and
a bee-like appearance; Acherontia atropos is the death’s-head
moth ; Sphinx ligustri the privet moth.

V. RHOPALOCERA.

The butterflies are mostly brightly coloured, and are diurnal
in their habits, loving the sun. The majority are easily dis-
tinguished from the moths by their clubbed or knobbed
antennae. Their body is small, and the abdomen is, relatively
to the rest of the body, considerably smaller than in the moths.
The legs are slender and often reduced, rendering walking a
matter of some difficulty. The wings are held erect when the
insect is at rest, and the anterior is never linked to the
posterior by a bristle and socket, as is often the case with
moths. The caterpillars have sixteen feet, and are naked or
hairy, with varying markings and tubercles. They do not
form cocoons, but turn into chrysalids with an angular contour;
as a rule these are suspended to a twig or stalk by a silken

TRACHEATA 355

band which cuts into the thorax; they are sometimes orna-
mented with bright metallic spots or patches.

A few species, as Vanessa, hibernate, but most butterflies
pass the winter in the larval or pupal state. The cycle of
their developement does not extend over a year, but there may
be two generations in a twelvemonth.

The genus Papilio contains over 300 species; P. machaon
is the swallow-tail. The family PrertDAE contains the numerous
“whites.” Vanessa cardui is the “ painted lady,” and V. io the
“peacock,” Apatura iris the “ purple emperor,” ete.

OrpDER 5. COLEOPTERA.

CHARACTERISTICS.—Jnsects with masticating mouth parts. The
anterior wings are horny, and in some cases fused together.
They do not overlap, but meet together in the middle line,
forming a straight suture. The prothorax is moveable. The
metamorphosis 1s complete.

The order Coleoptera has received more attention at the
hands of entomologists than any other order of Insects, and the
number of species of beetles named and described far out-
numbers that of any other group. The beetles form a fairly
homogeneous assemblage ; and although they vary considerably
in size and shape, they do so to a much less degree than the
Orthoptera or Hemiptera. It is a comparatively easy matter
to recognise a beetle. As a rule they are sombre in hue, but
some of them show very beautiful metallic colours, especially
after rain. ‘Their outline is usually oval, but it may be linear
or almost round.

The head is well developed, and may be free or partially
hidden under the projecting prothorax; it bears antennae, which
are usually two-jointed and of very various shapes. The antennae
are in many cases different in the two sexes. With the excep-
tion of a few blind species which inhabit dark caves, beetles
usually have a pair of compound eyes; in the GYRINIDAE or
whirligigs, which swim half immersed in the water, the eye is
divided into two halves, one for seeing in the air and one for
the water. Ocelli are as a rule absent. In the weevils and
some allied families the head is elongated, and the mouth and

356 ZOOLOGY

oral appendages are at the end of a long snout. The mouth
appendages are of the type described in Melolontha; as a rule
the maxilliary palp is four-jointed, the labial palp three-
jointed.

The prothorax is well developed, the mesothorax small,
and the metathorax of fair size. The legs are usually adapted
for running, but in some cases they are flattened for swimming
or strengthened for digging. The number of joints in the
tarsus is usually four or five, but it may be smaller, and this
variation forms the basis for grouping the various families into
sub-orders.

The anterior wings or elytra, when at rest, meet in a
straight line which terminates anteriorly at a small triangular
area of the mesothorax termed the scutellum, often invisible
except when the wings are opened or the prothorax extended.
In some families, as the STAPHYLINIDAE, the wings only extend
over the anterior abdominal segments, leaving the larger part
of the abdomen exposed. In rare cases they and the hind
wings are absent, as in the female Lampyris.

The elytra are in some species fused together, and the
posterior wings are then feebly if at all developed; flight is
therefore impossible. In the more normal forms the beetle,
when flying, extends the elytra at right angles to the body, and
keeps them in this position motionless (Fig. 204).

The ventral surface of the abdomen is more strongly pro-
tected by chitin than the dorsal, which is covered in by the
thick elytra. The hinder segments are often invaginated, and
form a recess connected with the openings of the generative
organs.

One or two genera of the ELATERIDAE, and almost all the
LAMPYRIDAE, are provided with phosphorescent organs, usually
in both sexes. In the males of the latter order, the light-
giving structures shine through the ventral surface of the two
posterior abdominal segments; in the former they are placed
in the prothorax, and on the suture between the thorax and
abdomen; in both cases they consist of numerous fatty cells,
with a very rich supply of tracheae and nerves.

Beetles usually lay their eggs in the neighbourhood of the
food which will afford support to their larvae. The latter are

TRACHEATA 357

either free-living, somewhat Myriapod-like grubs, with three
pairs of well-developed legs, or are soft, white, almost legless
larvae, which live in the earth or burrow in timber, ete.

The pupae have their limbs and wing-cases projecting—
pupa libera. They may be free, or enclosed in rough cocoons
of earth or wood-chips.

The very numerous families of the Coleoptera may be
arranged in four groups, corresponding with the number of
joints in the tarsus. These divisions have but a slight scien-
tific value, but are useful in dealing with such an enormous
number of species as are found in the Coleoptera :

(i.) The PENTAMERA, with five joints in the tarsus.

(ii.) The HETEROMERA, with jive tarsal joints on the two
anterior pairs of legs, and four on the posterior.

(iii.) The PSEUDOTETRAMERA, with one joint of the five-
jointed tarsus very small and ineonspicuous.

(iv.) The PSEUDOTRIMERA, with one joint of the four-jointed
tarsus very small and inconspicuous.

Under each of these subdivisions a few families may be
mentioned.

Sub-order 1. Pentamera.

Family CrcINDELIDAE—Tiger-beetles; these have very
large heads, broader than the thorax, with prominent eyes,
long curved mandibles, and slender legs. They are usually of
a brown or green colour with a metallic sheen, and are often
ornamented with spots or patches. They frequent sunny
places, such as the sandy margins of streams, and their larvae
are found in tubular passages in the soil. These larvae are
provided with two tubercles ending in hooks, which are
outgrowths of the ninth segment, and which serve to hold
them to their tubular dwellings; the anterior portion of their
body projects from the surface of the ground, in order to seize
any prey which comes within their reach.

Family CARABIDAE.—A very large family, whose limits are
difficult to define. They are predaceous insects, with running
legs, and their hind wings are not infrequently absent. They are

358 ZOOLOGY

found amongst grass, or under stones or bark, and as a rule
roam about at night. Their larvae are found in the same situa-
tions as the beetles; they are rather broad, and their terminal
segment is usually provided with two processes.

Family DyriscipAE.—Water-beetles, sometimes known as
“ water-tigers.” Some are large oval beetles, others are quite
minute, their hind limbs are flattened, covered with hairs, and
adapted for swimming. Their antennae are devoid of any
sensitive pubescence. ‘The first three joints of the tarsus are
in the males of the larger forms modified to form a plate-like
organ. The larvae are very voracious; the mouth is closed,
but the large pincer-like mandibles are perforated, as in
Myrmeleo, and the juices of the fish, tadpoles, or other
aquatic animals which fall into their clutches are sucked up
through these. The genus Dytiscus is furnished with nine
pairs of dorsal stigmata, and the beetles breathe by coming to
the surface of the stagnant water in which they live, expiring
the used air through the last large pair of stigmata, and tak-
ing in a new supply under their elytra.

Family STaPHYLINIDAE.— This group includes the rove-
beetles and devil’s coach-horses. They have long linear
bodies, with very short elytra, which leave the five or six
posterior abdominal segments exposed. They inhabit damp.
places under stones, manure-heaps, etc., and are often found
amongst moss or leaves, or amongst fungi. Many of them
live in ants’ nests. Some tropical species of this family are
viviparous.

Family SCARABEIDAE or LAMELLICORNIA.— This family
contains 700 genera and over 10,000 species of beetles. The
antennae end in lamelliform plates, such as have been de-
scribed in Melolontha vulgaris. The body is as a rule thick
and squarish, the legs often short and fossorial. Many of them
attain a gigantic size. The larvae are thick fleshy grubs with
a horny head and the posterior segments swollen out, baggy,
and incurved.

Family ELATERIDAE.—Skip-jack beetles with serrated an-
tennae, and an elongated body rather flatly arched. There is
an articulation between the pro- and meso-thorax, and when
the prosternal spine is suddenly brought down into the

TRACHEATA 359

mesosternal cavity, it causes the beetle, if lying on its back,
to be projected into the air, whence it usually falls on its feet.
The larvae are known as “ wire-worms,” and are very destruc-

op Fie. 202.—Elater lineatus, the “ skip-jack ”
beetle, with its larva the ‘‘ wire-worm.”
One of the larvae is enlarged to show the
markings on the terminal segment.

tive, feeding on the roots of grasses and other plants. They
are long cylindrical grubs generally of a reddish-brown hue,
and are extremely tough and tenacious of life. later lineatus
is the common skip-jack beetle.

Sub-order 2. Heteromera.

Family TENEBRIONIDAE.—An ill-defined family, with many
mimetic forms. The elytra are rounded at their ends and cover
the abdomen, the hind wings are frequently wanting. The
larvae are linear, flattened, and horny, and resemble wire-
worms. Many of these beetles shun the light and are sombre
in colour, some have an unpleasant smell, and others are covered
with a powdery secretion. The larva of Yenebrio molitor is
known as the meal-worm.

Family Metomart.—The head is bent forward, the legs
are long, and the bodies are elongated and soft. The beetles
are frequently found on flowers. The larvae are parasitic.
The larvae of Meloe attach themselves to the bodies of various
species of bee; they are thus conveyed into the hives, where
they feed upon the food provided for the larvae of the bees.
The larvae pass through a metamorphosis which is more com-
plicated than is usual in insects, this is termed hypermeta-
morphosis. Lytta vesicatoria, the Spanish fly, is used as a
vesicant.

360 ZOOLOGY

Sub-order 3. Pseudotetramera.

Family CURCULIONIDAE.—The weevils are easily recognised
by the prolongation of their head into a snout; the antennae

Fic. 203.

. Balaninus glandium, magnified.
. The same, natural size.

. The larva, magnified.

™ oF bh -

. The same, natural size.

5. Head and snout of the female
magnified to show the arrange-
ment of the antennae.

6. The same parts of the male.

are usually bent, and lie partly in a groove at the side of the
snout (Fig. 203). The mouth with its appendages is situ-
ated at the extremity of this prolongation. Their bodies are
often minute and hard; they feign death when disturbed.
Their larvae are white, fleshy, footless grubs, with thick jaws ;
before transformation they spin silken cocoons. The number
of species is very great, about 10,000. Salaninus glandium
lays its eggs in hazel-nuts and acorns; its larva feeds upon the
substance of the nut.

Family ScoLtytipAr.—This family was formerly sometimes
called the Bostrychidae ; it includes beetles of small and incon-
spicuous size, whose rounded head is sunk beneath the pro-
thorax, which is large, and forms almost half the body. The
larvae resemble those of the preceding family; they have no
legs, but their skin is ridged, and bears short hairs. These
beetles and their larvae live in societies, boring passages in the
wood of trees, on which they feed. In this way incalculable
damage is done to forest trees, etc., especially to Conifers. The
female lays her eggs in recesses of the passage she has made,

TRACHEATA 361

and each larva as it hatches out continues the recess into a
long tunnel; in this way very peculiar markings are produced,
which are characteristic of the various species. Bostrychus
typographicus.

Family CERAMBYCIDAE.—Often termed Longicorns, they are
large showy beetles with oblong cylindrical bodies and long,
usually eleven-jointed, recurved antennae. Their eggs are laid
in crevices of the bark, and their larvae often bore passages in
the wood; they may live one to three years, and then form
a cocoon of chips near the mouth of their tunnel. Cerambyzx
heros, Saperda carcharias.

Family CHRYSOMELIDAE.—The leaf-beetles are oval in shape
and convex dorsally; they are as a rule
small, and of bright colours. The larvae
have always three pairs of legs; many of
them burrow in the soft mesophyll of
leaves; they fix themselves by their hinder
end to leaves before pupating. Chrysomela
decemlineata is the Colorado beetle. Haltica Fic.204.—Haltica nem-
nemorum, the turnip-fly, and H. oleracea, fly). (he aps
which attacks cabbages, also belong to
this family.

Sub-order 4. Pseudotrimera.

Family CoccrnELLipAE.—The lady-birds are hemispherical
in shape, usually of a red or yellow colour, with a varying
number of black spots. They lay long yellow eggs, usually in
the proximity of plant-lice, which are eagerly devoured by the
larvae when they hatch out. The larvae are soft-bodied grubs
beset with tubercles; they attach themselves by their pointed
tail to leaves, and cast their skin; this they do not throw off,
but remain in it during the pupa stage (coarctate pupa). The
beetles pass the winter under bark, etc.

OrpER 6. HEMIPTERA.

CHARACTERISTICS.—Jnsects with mouth parts adapted for pierec-
ing and sucking, in the form of a jointed rostrum. Two
pairs of wings, which may be alike or may be different.
Metamorphosis incomplete.

LoS)
ON
to

ZOOLOGY

This order comprises numerous insects familiarly known
as bugs or lice. They present very great variety of form,
some of them having short soft bodies with almost every trace
of segmentation lost, whilst others are large and hard.

The mouth parts are adapted for taking up fluid. The
labium is modified into a joimted sheath which guards the
other appendages; at its upper end the hollow structure is
closed by the labrum. Within the tube thus formed lie four
rigid stylets, which represent the two mandibles with sharp-
ened tips, and the two anterior maxillae of unequal length
with serrated edges. The maxillary palps are absent and the
labial palps are very small.

The antennae are short and three-jointed, or long and
multiarticulate. The eyes are usually small; sometimes two
ocelli are present. In the larger species the body is very
often flat and angular in outline. There are usually four
wings, rarely only two, and sometimes they are entirely want-
ing. In the former case the anterior wings have their basal
half horny and their distal half membranous, whilst the pos-
terior wings are membranous (Heteroptera), or both pairs are
membranous (Homoptera).

The legs are usually of the walking type, the tarsus is
two- or three-jointed. The lateral margin of the abdomen is
greatly developed in some species. The stigmata are usually
conspicuous ; in the aquatic species there are a pair at the end
of the abdomen, often borne at the tip of long processes.

The Hemiptera in most cases emit a fluid with a very dis-
agreeable smell. This is secreted from a pair of pores on the
under surface of the thorax, near the coxae of the middle pair
of legs. This objectionable fluid is defensive in function.
Other members of the group produce considerable quantities
of wax, which is secreted by unicellular cutaneous glands.

The young resemble the adults, but are without wings.
The males of the CocciDAE alone form pupae within a cocoon,
and thus undergo a complete metamorphosis.

The Hemiptera are divided into three sub-orders :

1. HETEROPTERA.
2. HOMOPTERA.
3. PARASITICA.

TRACHEATA 363

Sub-order 1. Heteroptera.

CHARACTERISTICS.— Zhe Heteroptera have the proximal half of
their anterior wings horny, the distal half membranous ;
they lie flat, overlapping one another. Many are apterous.
The prothorax is large and free. The proboscis arises from
the front part of the head, and when at rest lies against the
thorax.

A few families may be mentioned :

Family NoroNECTIDAE (water-boatmen).—These insects
always swim on their back, which is convex, like the bottom
of a boat, whilst the ventral surface is flattened. The legs
are long, especially the posterior pair, which are flattened for
swimming. They fly well, but can scarcely walk; when dis-
turbed they dive beneath the surface, carrying a supply of air
for respiration beneath their wings. They remain for some
time under water, holding on to aquatic plants, ete.

Family NEPIDAE (water-scorpions).—The members of this
family are provided with a pair of long tracheal tubes at the
end of their abdomen. Their body is flat and oval (Vepa), or
elongated and linear (Ranatra); their fore limbs are raptorial,
their hind limbs adapted for swimming. They are carnivorous,
living chiefly on the larvae of aquatic insects and young fish.
Their eggs are laid in the water, on stems of plants or under
stones.

Family HyproBaTIDAE.—Aquatic insects of oval or elon-
gated form, which run rapidly on the water’s surface, and are
usually found in colonies. The antennae are four-jointed and
unusually long. There are often two adult forms found at
the same time—one kind being winged, the other wingless.
This family includes the Halobates, a marine insect found
swimming on the surface of the sea in the tropics. It feeds
on dead animals which float on the surface, and is said to
attach its eggs to the Sargassum sea-weed.

Family Repuvupar.—A very large and diverse family,
including many insects of brilliant colour and some of con-
siderable size. The proboscis is short and three-jointed. They
are predaceous, and live for the most part on the blood of

364 LOOLOGY

other insects, though they occasionally attack other animals.
Several species, as Opsicoetus (Reduvius) personatus, attack the
bed-bug.

Family TinciTmDaE.—The members of this family are for
the most part small; they are found in considerable numbers
on leaves and shrubs; their appearance is very characteristic.
The anterior wings have the appearance of a network, and
processes resembling them project from the sides of the thorax.
The proboscis and antennae each have four joints.

Family ACANTHIIDAE.— The family includes Acanthia
lectularia, the bed-bug, a flat oval insect devoid of wings. The
proboscis has three joints, the antennae four. It is very ten-
acious of life. Many species of the same genus live upon
birds.

Family CapsipAE—A very numerous family, whose mem-
bers are active both in running and flying. They are mostly
of a medium size, oval in outline, and convex. Their body is
usually soft. Many of them are frequently found in fruit.

Family PENTATOMIDAE.—In this family the scutellum is
very large, often equalling in size the area of the abdomen.
It is a large family, the members of which are brightly coloured.
They are often found on shrubs, and live on caterpillars or
leaves.

Sub-order 2. Homoptera.

CHARACTERISTICS.— Both pairs of wings alike ; when at rest they
lie flat, unfolded, overlapping one another. The wings are
often absent. The head is usually continuous with the pro-
thorax, so that there is no neck.

This group contains a number of species very diverse in
their structure, and often with extremely complicated - life-
histories, in which parthenogenesis and “alternation of genera-
tions” play a great part.

Family CrcapIpAk (Cicadas).—These insects are well known
from the chirping noise they keep up. They are usually of
large size, with an extraordinarily broad head fused on to the
prothorax, with two large eyes at the angles, and three ocelli.
The anterior wings are larger than the posterior. The male is
provided with a kind of drum on the under side of the base of

TRACHEATA 365
the abdomen. These drums are furnished with a curiously
ribbed surface, and the characteristic noise of the Cicadas is
said to be produced by the vibrations of the ribs set in
motion by air forced against them. The females have stout
ovipositors ; in Cicada septemdecem the females lay their eggs
in slits which they cut in young twigs, the larva hatches out
in six weeks, drops to the earth, and buries itself. It remains
underground till the seventeenth year, when it emerges, be-
comes adult, pairs, and as soon as the eggs are deposited
disappears.

Family FuLGorIpAE—The antennae are bristle-like and
three-jointed. The insects are very diverse in structure, many
of them have the most extraordinary outgrowths of the upper
part of the head. These protuberances may equal in size the
rest of the insect’s body. Fulgora candelaria and F. lanternaria
are stated to be phosphorescent, but this appears doubtful.
Some species excrete wax from their abdomen in such quan-
tities that they have a commercial value in China.

Family CERCOPIDAE (Frog-hoppers).—The anterior wings
of these insects are opaque. Their three-jointed antennae end
in a bristle. The head is triangular, with two ocelli. <Aphro-
phora spumaria, the cuckoo-spit, is an insect about + inch
in length. It can take very extended leaps. Its larva sur-
rounds itself by a white frothy fluid which it excretes from its
intestine. It is common in England on leaves of plants, ete.,
in fields. The eggs are deposited in punctures in the leaves.

Family APHIDIDAE (Plant-lice)—Small insects with oval
or pear-shaped bodies. The wings, when present, are trans-

Fie. 205.—Siphonophora
JTanariva.

. Winged aphis.

. Natural size of same.

3. Wingless form.

. Natural size of same,

parent, and with few nervures; the anterior and posterior wing
of each side are fastened together by a hook. Proboscis two-

366 ZOOLOGY

jointed. Antennae three- to seven-jointed. The sixth ab-
dominal segment often bears a pair of tubes through which a
sweet fluid, the honey dew, is excreted. Some excrete also
a powdery bloom.

Plant-lice are usually brown or greenish in colour; they
live upon cell sap, inserting their proboscis into the tissues of
the leaf, stem, or root, and in this way often produce galls.
Their life-history is very complex ; as a rule males and females
coexist in the autumn. The females lay fertilised ova, the
winter eggs, from which in the spring incomplete females, with
no receptacula seminis, emerge. These give rise to innumer-
able parthenogenetic generations, but after a certain number of
these, males again make their appearance. In many species,
however, the male is not yet known.

The genus Aphis is very common on plants, and causes
great trouble to gardeners. Certain of them are tended and
protected by some species of ants, who feed upon the honey
dew secreted from their “ honey-tubes.”

The Phylloxera vastatrix, which infests vines, affords a
good example of the complicated life-
history presented by the Aphididae. The
wingless root-dwelling forms—vradicola—
are found with their proboscis firmly
fixed in the tissues of the young roots.
They do not move about, but lay little
clumps of thirty to forty parthenogenetic
egos, which give rise in six to twelve days,
according to the temperature, to young
larvae. These moult once or twice, creep
about a little, and then fix themselves by
their proboscis and lay parthenogenetic
eggs, like their mother. In this way

Fic. 206.—Root-inhabit-
ing form (radicola) of many agamic generations succeed one

Phylloxera vastatriz : :
with proboscisinserted another, and the rate of increase is so

into tissue of root of creat that it has been calculated that
vine. After Girard. © : ; ;

the descendants of a single insect which

laid its eggs in March would number twenty-five millions by

October.
As autumn comes on some of the eggs give rise to larvae

TRACHEATA 367

=)

which are provided with the rudiments of wings ; before their
last change of skin they creep above ground, and then at the

Fic. 207.—Phylloxera vastatriz, winged female
which lives on leaves and buds of vine, and
lays, parthenogenetically, eggs of two kinds,
one developing into a wingless female, the
other into a male. After Girard.

final moult a winged female emerges and flies away. This
form serves to spread the vine disease from one district to

Fia. 208.

a. Phylloxera vastatriz, male
produced from small egg
(c) laid by winged female
(Fig. 207).

b. Large egg.
c. Small egg.

d. Wingless female from large
egg (6) laid by winged
female.

After Girard.

another. It is also parthenogenetic, but lays two kinds of
egos. From the larger of these a complete female hatches out,
whilst the smaller produces in eight to ten days a male. This

368 ZOOLOGY

is the first and only appearance of this sex in the life-history
of the Phylloxera. The male is devoid of mouth and aliment-
ary canal; it fertilises the female, which soon after lays a
single fertilised egg, the so-called “winter ege.” This is
deposited in some crevice or crack in the bark of the vine ; in
the spring a “stock-mother” hatches out of this egg and makes
her way to the young buds of the vine, and inserts her pro-
boscis into the upper surface of a leaf. The irritation thus set
up causes the formation of a hollow gall on the under surface
of the leaf, which opens to the exterior on the upper surface.
The stock-mother lays eggs, and her offspring—gallicola—give
rise to new galls, but ultimately some of them descend to the
eround, burrow beneath it, and attach themselves to the roots,
and thus become radicola.

The complicated life-history of this form may be expressed
by the following table:

Root-infesting form § (radicola)
Root-infesting aay 2nd generation

Root-infesting form, 3rd generation, etc.

Winged form 2

a egg Small egg
Wingless female Male

“A
Winter egg

Stock-mother
Gall-producing form @ (gallicola)
Gall-producing form 2, 2nd generation, ete.

Root-infesting form 9 (radicola)

Family CoccipDAk (Scale Insects, Bark Lice, Mealy Bugs).—
The members of this group differ a good deal both in their life-
history and in their structure, and very frequently the two sexes
of the same species are markedly different in appearance and
habits. The antennae are usually long, eight to eleven joints, and
filiform ; the tarsus is two-jointed. The males alone amongst

TRACHEATA 369

Hemiptera have a complete metamorphosis ; the adult male has
one pair of wings, the anterior, the posterior being replaced by
a pair of bristle-like processes, the ha/teres,as in the Diptera.
No mouth is present.

The female, after the first ecdysis, becomes almost stationary,
she retains her proboscis, which is embedded in the tissues
of the plant on which she lives, as a rule she loses her
limbs, and almost all trace of segmentation; the successive
skins that she casts either remain over her body forming a
scale, or she secretes a waxy or woolly covering. The eggs
are laid under the body of the mother, which ultimately dies,
but remains as a covering for her offspring; under this the
young may remain some little time before seeking a convenient
place on their plant host to insert their own proboscis.

Some of the Coccidae are of commercial value, Coccus cacti
furnishes the pigment cochineal, and another species produces
shellac. Most of the scale insects, however, are injurious to
the plants upon which they live, and cause great loss to
horticulturists and fruit-growers. Aspidiotus conchiformis is
the well-known mussel scale on apple trees, etc., and A. aurantii
attacks orange groves.

Sub-order 3. Parasitica.

CHARACTERISTICS. — These are wingless Hemiptera, commonly
known as lie; they live as ectoparasites on the skin of
mammals, sucking their blood.

The proboscis is fleshy and unjointed, with, as a rule, a circle
of recurved hooks round its base. There are two small simple
eyes; the antennae have five joints. The legs arise from the
edge of the prothorax; they terminate in a hooked claw, which
works against a projection of the tibia; this forms an admir-
able apparatus for clinging on to the hairs of their hosts. The
young do not undergo any metamorphosis.

Pediculus capitis is the head louse, and P. vestiimenti infests
the body of all races of man. It is said that peculiar varieties
infest the different races; thus those that live on negroes are
nearly black, whilst the Chinese have a yellowish, and the
natives of South Africa an orange variety. The genus which

24

370 ZOOLOGY

infests cattle, squirrels, and other animals is Haematopinus, of
this there are several species.

OrvER 7. DIPTERA (Flies).

CHARACTERISTICS.—Jnsects with piercing and sucking mouth
parts, The anterior wings are membranous ; the posterior
are replaced by knobbed processes—the halteres. The pro-
thorax is fused with the rest of the thorax. The meta-
morphosis 7s conyplete.

The Diptera form one of the largest orders of insects, and
when completely worked out it will probably be found to
include at least as many species as the Coleoptera. The mem-
bers of the order are of moderate size, with freely moveable
spherical heads. The compound eyes are large, and in the male
they sometimes fuse together across the dorsal middle line.
There are three ocelli. The antennae are either short and end
in a tactile hair—the arista,—as in Musca, or are long and fili-
form as in Zipula, where they have thirty-six joints.

The mouth parts consist of a soft sucking proboscis known
as the haustellum, ending in two swollen lobes. This is partly
formed by the labium, which is devoid of palps. In front of
this lies the elongated labrum, and between the labrum and
labium an unpaired stylet, the epipharynx. The mandibles
and first maxillae also form stylets, and the latter are provided
with palps. Both the mandibles and maxillae may be rudi-
mentary.

The mesothorax forms the largest part of the thorax.
The wings are transparent, with few nervures, and with micro-
scopic hairs and scales. The inner margin of the wing is
usually notched, dividing it into two lobes, the alula and
squama. They vibrate with great rapidity, 350 times per
second in the fly. In a few cases they are absent.

The posterior wings are replaced by halteres (Fig. 209),
which are short processes usually ending in a knob, Their
function is not definitely determined, but to some extent they
appear to act as balancers, and when removed the fly cannot
control its flight.

The legs are slender and often long; the tarsus is five-

TRACHEATA 371

jointed, and terminates in two claws; between these is the
pulvillus, a fleshy vesicle with tubular hairs, which secrete a
sticky fluid.

The abdomen may be short and conical, or long and
cylindrical. There is no true ovipositor, but the terminal
segments are retracted into the preceding, and can be pro-
truded telescopically.

The nervous system is very concentrated ; in some families,
as the Muscipas&, the Hrppoposcrpak, and the OESTRIDAE, there
is, besides the brain, only one large ganglion; this is situated
in the thorax, and gives off nerves to the abdomen.

The alimentary canal has a stalked sucking stomach, which
opens into the oesophagus.

The sexes do not show much external differentiation; as a
rule the eyes in the male are larger, they are sometimes fused
together. The eggs are smooth, oval, and slightly curved ;
they are often provided with a micropyle. In the TIPULIDAE,
the daddy-long-legs (Fig. 209), they are mature when the
pupal skin is cast, and are laid immediately by the imago.

The larvae are white, fleshy, cylindrical maggots. They
may have a distinct head, as in the TIPULIDAE, or a head may
be absent, as in the Muscipar. In the first case they have
biting mouth parts and are often parasitic, in the second they
suck up liquid nutriment. The ova are usually deposited upon
the food, either animal or vegetable, in which the larvae
burrow and on which they feed. Many of the larvae are
aquatic. They change into pupae within the last larval skin,
—pupa coarctata,—or cast this skin and become moving pupae
which swim in water—pupa obtecta.

Sub-order 1. Aphaniptera.

The PuLiciIpAE.—This is an aberrant order of Diptera;
it comprises the fleas. These insects have no wings, though
there are small flat appendages on the meso- and meta-thorax.
Their legs are large, and are adapted for leaping. The body is
compressed. There is no labrum; the labium is small, with
long palps; the mandibles form serrated stylets, and the
maxillae have palps. The female lays eight to ten eggs, which

72 ZOOLOGY

Go

are deposited amongst the dust in cracks or crevices; the
small larvae have distinct head and jaws.

Pulex irritans is the common flea. Sarcopsylla penetrans 1s
the chigoe or jigger of South America; the female burrows
into the foot of man or other mammals, and deposits her eggs
there. If not removed the larvae hatch out and give rise
to ulcers.

Sub-order 2. Diptera genuina.

Family CULICIDAE (gnats and mosquitoes)—_The members
of this family are provided with very long and slender mouth
parts. They are very widely distributed, extending from the
arctic circle to the equator; the females lay their eggs on the
surface of the water, on which they float in a boat-shaped mass.
The larvae live at the bottom of ponds or swamps, eating
decaying vegetable matter, and occasionally rising to the sur-
face for air, which they take in through a special respiratory
tube. The pupae are curiously curved and somewhat club-_
shaped; they swim actively about. The males do not leave
the neighbourhood of the swamps where they are bred, but the
females infest houses, etc. Culex pipiens is the common species
of gnat in Britain.

Fic. 209.—Tipula oleracea (the daddy-
long-legs).

Larva.

bop

Pupa case.

Imago.

co

e

Eggs, natural size.

Family Trputmpaz (daddy-long-legs or crane-flies), — The
familiar daddy-long-legs has long filiform antennae and very

TRACHEATA 373

long slender legs. The mesonotum bears a V-shaped mark,
and the abdomen is long and cylindrical. Their larvae burrow
underground, and do considerable damage to crops by gnawing
roots, etc. They are known as leather-jackets, and are of a
whitish-brown colour and grub-like appearance. Z%pula oleracea,
T. maculosa, and T. paludosa are all common English species.
Family CECIDOMYIIDAE (gall - flies)—This is a family of
small Diptera, which give rise to galls in plants. Their wings
have few nervures, usually three longitudinal ones; they are
rounded at their free ends; the point of attachment is, how-
ever, very narrow. The antennae have numerous joints, and
are moniliform. The proboscis is short and the legs long. The
females have a well-developed ovipositor, by means of which they
puncture some plant and deposit their egg therein. This in
some cases gives rise to a gall, in which the larvae develope.
The pupa stage may also be undergone in the gall, or it may

Fic. 210.—Cecidomyia destructor
(the Hessian-fly).

1. Insect.
2. Larva,
3. Pupa or ‘flax seed.”

All magnified.

be free. The larvae of some of the Cecidomyias produce
parthenogenetic ova, from which young are born, a phenomenon
known as paedogenesis. Cecidomyia destructor is the well-
known Hessian-fly. (. salicis produces galls on willows.

Family TABANIDAE (horse-flies).— Tabanus is the horse-fly,
a large Dipterous insect. The male does not bite, but lives on
the nectar of flowers. The bite of the female, however, is
very painful and poisonous. Cases have been recorded of horses
on the prairies being worried to death by these insects. The
larvae of Zabanus are said to live upon snails, those of allied
genera live in water.

Family BompyLipar.—Very hairy flies, swift in flight,

374 ZOOLOGY

and often to be found in sunny paths, etc. They lay their
egos in bees’ hives, and the fleshy smooth maggots devour the
larvae of the bees.

Family SyrpHipAE—This is a family of brilliant yellow
and black flies somewhat resembling wasps. They have a
large head, and the eyes, which are very large, meet across
the middle line in the male. They are found in sunny places,
hovering motionless in the air, and then making a sudden dart
at some flower upon whose nectar they feed. The genus
Syrphus lays its eggs singly upon flowers, and the larvae feed
upon Aphides, which are seized by the mouth parts situated
at the end of the first segment ; this segment is then retracted
into the second, and the second into the third. The larvae
of other species are found in water or in bees’ nests; the
rat-tailed larva of Hristalis is a well-known object in fresh
water. Its body is prolonged posteriorly into a long respira-
tory tube.

Family Conoripar.—The members of this family also re-
semble wasps, a resemblance which is probably partly protective,
and which furthermore enables many of them to lay their eggs
in or on the bodies of the insects they mimic. The Conopidae
have a pedunculated abdomen, and their proboscis is unusually
long, The eggs of Conops are probably laid on the soft tissue
between the segments of some Hymenopterous insect, the larval
and pupal stages are found within the body of the host, and
the fly emerges between two of the abdominal segments, often
breaking the abdomen of its host in two.

Family OESTRIDAE (bot-flies)—The bot-flies have short,
stout, hairy bodies, with minute antennae and rudimentary
mouth parts. The eggs are laid on some place whence the
parasitic larvae can easily effect a lodgment in its host. The
larvae are thick, fleshy, apodal maggots, with eleven segments,
which are usually provided with spines or hooks, by means of
which they can move about within their host. Those which
live in the alimentary canal of mammals have hooks, and attach
themselves by these to the walls of the stomach. The stig-
mata are borne on a horny plate at the posterior end of the
animal, the end which is generally turned to the external
world. The pupal stage is passed through on the ground.

TRACHEAT A

Lo)
NI
ur

Gastrophilus equi, the horse-bot, lays its eggs on the hairs
of the hips and legs, the horse licks these off, and the larvae
hatch out in its stomach; the larvae are found from May to
October hanging in clusters on the wall of the rectum. Hypo-
derma bovis, the ox-bot, deposits its egg beneath the skin of
cattle ; the larvae hatch out, and cause large hollow cysts to
form around them; they he in these cysts with their stigmatic
plate directed to the opening. estrus ovis, the sheep-bot, is
said to be viviparous; the female deposits larvae alive in the
nostril of the sheep, whence they make their way to the frontal
sinuses.

Family Muscipar.—This family, which is very extensive,
includes the common house-fly and blue-bottle fly, etc. The
antennae are three-jointed, and end in a bristle. The proboscis
terminates in a fleshy bilobed process. The
wings have four simple longitudinal veins.
The abdomen has only five segments visible
externally, but others are invaginated. The
larvae are white, cylindrical, apodal maggots,
with a posterior pair of spiracles, and some-
times a prothoracic pair as well.

Musca domestica and MM. vomitoria are the
house and blue-bottle flies. The tsetse fly,
which is so poisonous to cattle in South Fic. 211.—Glossinia
Africa, is Glossinia morsitans. The Tachin- eo Chen Tee
idae lay their eggs in caterpillars, within
whose body their larvae are parasitic. Several species are
stated to be viviparous.

Orpver 8 HYMENOPTERA.

CHARACTERISTICS.—Insects with biting and licking mouth ap-
pendages. The prothorax is fused with the mesothorax.
The four wings are membranous, with few nervures, the
hind wing on each side bears a row of hooks, by means of
which it is hooked to the anterior wing, and the two move
together. The metamorphosis is complete.

The Hymenoptera include the ants, bees, and wasps,
insects which, with regard to their social habits and instincts,

376 ZOOLOGY

stand not only at the head of their own phylum, but in front
of all other animals, man alone excepted. It is not a very
large order, only about 25,000 species are described. All of
these are terrestrial, and most of them inhabit the warmer and
more temperate parts of the globe.

The head is freely moveable, the eyes large and prominent,
and, as is often the case in insects, they are larger in the male
than in the female. ‘There are three ocellii The antennae
are often crooked, and then consist of a basal joint or shaft,
and ten to twelve shorter joints; they may be straight.

The mouth is adapted for biting or licking; there is a
small labrum, and the mandibles are large and stout. The
maxillae and Jabium are elongated, palps being present in
each case. The nectar upon which bees feed is licked up by
the ligula, and deposited upon a sheath formed of the labial
palps and maxillae, and in the sheath thus formed the food
passes up to the mouth. The ligula is the front edge of the
labium. In bees it is enormously developed, and divided
into three lobes, the two outer of these are termed paraglossae.

On the mesothorax are two small scales known as the
tegulae, covering the base of the wings.

The legs have a five-jointed tarsus, and in bees the tibia
and tarsus, especially those of the posterior pair of legs, are
covered with short hairs, these help to collect and convey
home the pollen grains the bees have gathered during their
frequent visits to flowers.

The abdomen is as a rule pedunculated, the two anterior
segments forming the peduncle. In the female the abdomen
ends in an ovipositor, which in the Aculeata is modified and
forms a sting. This complicated apparatus developes from
six protuberances on the embryo, four on the last but one, and
two on the last segment. These protuberances elongate and
form a grooved process with two stylets and a pair of lateral
sheaths, besides these there are certain supporting plates.
The poison consists of formic acid with some fatty sub-
stances ; it is secreted in a special gland, which communicates
with a reservoir, this opens at the base of the grooved
process.

The nervous system consists of an unusually large and.

TRACHEATA 377

complex brain, two thoracic ganglia, and five or six abdominal.
The alimentary canal is long, with large salivary glands, and a
suctorial stomach, or, in the ants, a gizzard. The number of
Malpighian tubules is great, 20 to 150.

With few exceptions, the larvae are apodal white grubs,
living either parasitically in the bodies of other insects, or in
plant galls, or in special cells prepared for their reception. In
two families, however, they resemble in appearance and_ habits
the caterpillars of the Lepidoptera. As a rule, the larvae
have a retractile head, with short mandibles, maxillae, and
labium. The pupae are mostly surrounded by a silken cocoon.

The wax-secreting apparatus consists of numerous glands,
mostly unicellular, which open to the exterior by fine chitinous
tubes. The wax of bees is secreted in fine transparent plates
on the under surface of the abdomen.

The order may be divided into three sub-orders :

1. PHYTOPHAGA.
2. ENTOMOPHAGA (Parasitica).
3. ACULEATA.

Sub-order 1. Phytophaga.

CHARACTERISTICS. — Hymenoptera with a well-developed ovipositor
which sometimes functions as a borer. The abdomen 1s
sessile. The larvae feed on plants, and resemble cater-
pulars.

Family UrocertpaE (Wood-wasps).—The insects are large
for Hymenoptera, with elongated bodies. The abdomen of the
female terminates in a long ovipositor, with which she bores
holes into wood to deposit her eggs there. The larvae are
white grubs, with three pairs of very small legs and strong
mandibles; they eat out passages in the wood, and form
silken cocoons mixed with sawdust, in which the pupal stage
is passed. The complete insect emerges in these galleries,
and eats her way through the bark to the outside world.

Sirex gigas, one of the largest of these insects, attacks in
this way the wood of Conifers. Sirex juvencus is a smaller
species,

Family TENTHREDINIDAE (Saw-flies)—This is a numerous

378 ZOOLOGY

family of Hymenoptera with short bodies ; the abdomen is sessile.
The antennae vary a good deal, but are never elbowed; their

Fic, 212.—<Athalia spin-
arum (Turnip Saw-
fly). After Curtis.

1. Saw- fly, magnified,
with lines to left show-
ing natural size.

2. Eggs in incision in
leaf.

3. Egg, natural size.

4,5, 6. Caterpillars feed-
ing on turnip leaf.

7. Pupa case.

8. Pupa.

variations afford a basis of classification. The tibia of the fore-
leg is provided with two spines. The ovipositor is short, and
retracted when not in use; it consists of two saw-like processes
protected by two valves.

The females deposit their ova in punctures in the epidermis
of plants; one egg is usually laid in each slit. At the same
time a drop of fluid is secreted, which is said to cause a flow
of sap to the injured part, and this sap is stated to be absorbed
by the egg, which increases in size. Only one genus—WNematus
—forms galls, and these are found in the leaves of the willow
tree. Nematus resembles the bees and wasps in the fact that
its unfertilised parthenogenetic eggs give rise to males. As a
rule in the animal kingdom parthenogenetic eggs give rise to
females.

The larvae are very like caterpillars. Usually they are
found in colonies, and are of a brown or greenish colour. They
may be distinguished from the young of Lepidoptera, which
never have more than five pairs of pro-legs, by possessing six,
seven, or eight pairs. Their heads are also more globular, and
the eyes more distinct. When at rest they usually curl round
the posterior end of their body (Fig. 212) in the form of a note
of interrogation. They are frequently to be found on the leaves
of willows, limes, poplars, and conifers. They are said to
emit an acid fluid from lateral pores on their body when
irritated.

TRACHEATA 379

The pupae he in a cocoon which is found in the neighbour-
hood of their food plant, often on the ground. <Athalia spinarum
is the turnip saw-fly; and Lophyrus pini causes much damage
to young Scotch firs.

Sub-order 2. Entomophaga.

CHARACTERISTICS.— The abdomen is pedunculated. A well de-
veloped ovipositor is present in the female. The larvae are
usually parasitic in the larvae of other insects, sometimes in
plants ; they are apodal and aproctous.

Family CynipiparE (Gall-flies)—Small Hymenoptera with
a much-compressed abdomen, the first and second segments of
which are large, the others very short. There is a long coiled
ovipositor which arises near the base of the abdomen, and is
only fully extended when in use. ‘The ova are large, and are
said to increase in size during developement. The larvae are
short white fleshy apodal grubs, which feed on the galls in
which they live. The pupae may be in the gall or under
eround. Some are parasitic in Diptera and Aphides.

The oak-apple is formed by a member of this family,
Andricus terminalis; the common spherical woody galls in
the oak, by Cynips kollari; and the “spangle galls” in the
leaves of the same tree by Newroterus lenticularis. Rhodites
vosae, another member of this family, gives rise to the beauti-
ful moss or bedeguar galls on rose-trees.

Family IcHNEUMONIDAE (Ichneumons).—Insects with long

Fic. 213.
Aphideus avenae, to the
left.
si Ephedrus plagiator, to the
right.

slender bodies, with an exserted, often very long ovipositor.
The abdomen has seven segments. The antennae are

380 ZOOLOGY

slender and many-jointed; they are seldom elbowed. The
ova are deposited on or in the bodies of caterpillars
or the larvae of other Hymenoptera. The larvae are white,
fleshy, footless grubs which feed on the organs of their
hosts, commencing with the fat-bodies and other indifferent
tissues. Rhyssaw persuasoria, which has an ovipositor three
inches long, is said to bore through a considerable thickness
of wood to deposit its eggs in the body of the larvae of Sirem.
Ichnewmon laminatorius lays its eggs in the larvae of Sphinx
pinastri, Aphideus avenae and Ephedrus plagiator in the bodies
of Aphis.

Family CHancipipAE.—This family includes numerous
species of small size and of metallic hue. Their antennae are
usually elbowed, and their wings devoid of veins. The differ-
ences between the sexes are as a rule very marked. They lay
their eggs in the eggs or larvae of almost every kind of insect.
Some are parasitic in the parasitic Zchnewmons, others in the
Hessian-fly and in Musca, whilst other species, as Preromalus,
lay their eggs in the larvae of Bostrychus and Hylesinus, ete.
A few species give rise to galls.

Sub-order 3. Aculeata.

CHARACTERISTICS.—TZhe female is, with few exceptions, provided
with a stinging apparatus, or modified ovipositor, at the end
of the abdomen, which is only protruded when in use. The
abdomen is stalked. The male has, as a rule, thirteen joints
in its antennae, the female twelve. Usually cells are con-
structed in which the apodal and aproctous larvae are
reared by the females.

Group 1. FORMICARIAE (Ants).

Ants have usually a small thorax, and, compared with the
thorax or abdomen, a very large head. The first, or first and
second abdominal segments form the peduncle. The antennae
are elbowed, and have one more joint in the males than in
the females. The wings, when present, extend beyond the
abdomen, and they have few nervures.

TRACHEATA 381

As a rule, the males are smaller than the females. They
live in communities, which comprise, besides the winged males
and females, a number of wingless workers or neuters, These

Fia, 214.—Formica rufa (Wood-ant).

1. Female. 2. Male. 3. Neuter.

are in reality aborted females, and, like the functional indi-
viduals of that sex, are provided with poison glands. The
poison consists of formic acid, and is ejected into wounds made
either by the sting or the biting mandibles. Some of the
workers, as is the case in the Termites, are specialised as
“soldiers” with very formidable jaws and large heads. These
defend the ant-hills when they are attacked.

The workers or neuters survive the whole year, hibernating
during the winter months. Some of the females also may
hibernate, but the greater number of both males and females
live for a short time only, during the summer. No food is
stored up in the ant nest or formicarium for winter consump-
tion, as those individuals which persist through the cold
weather become torpid and cease to feed. With the return of
spring the females which have persisted lay eggs, and these, or
in some species the eggs and larvae of the preceding autumn
which have lasted through the winter, develope into a new
brood, producing males, females, and workers, The larvae are
most carefully tended by the workers, which feed them with
semi-digested food from their own stomachs. The sexes pair
whilst flying in the air; the males then die, the females cast
their wings and either start off to form a new colony or are
led back by the workers to the old. The ova are very small.
The structures which are commonly called the eges of the
ants are the white oval cocoons.

The nests are usually excavated in the ground or in a

382 ZOOLOGY

rotten tree, or are built up of clay. The ants live upon both
animal and vegetable substances, and are very fond of sweet
things. Some of them keep Aphides, and by gently stroking them
with their antennae they induce them to secrete some of their
honey-dew, which the ants greedily lick up. Certain species
of beetles are also always found living with ants, though the
relationship between them and their hosts is not understood.
Certain species, as Polyerqus rufescens, and in some countries
Formica sanguinea, make slaves of other and smaller species.
The slaves are carried off either as ova or pupae, and are reared
by the masters, who become so dependent upon their slaves
that if these be removed the colonies of P. rwfescens perish.
The leaf-cutting ant Oecodoma cuts small circular pieces
out of leaves, which are carried home often by another indi-

Fria. 215.—Leat-cutting and foraging ants.

1. Ocecodoma cephalus. 2. Eciton drepanophora. 3. Eciton erratica.

vidual, and it is believed that a fungus is grown upon these
leaves, which the ants eat. The nests of this genus are very
large, and are built of clay. The leaf-cutting ant does very
considerable damage to vegetation, and it is difficult to keep
them away from any spot. They have been known to tunnel
under a river to reach a wood.

Group 2. VESPIARIAE (Wasps).
} i

Wasps have slender, almost naked bodies, of a usually
yellow and black colour; the antennae are usually elbowed ;
the wings are long and narrow, and longitudinally folded when
the insect is at rest.

There are three families: the VESPIDAE, or social wasps, and
two families of solitary wasps—the EUMENIDAE and MASARIDAE.

Family VESPIDAE.—Social wasps, whose colonies contain

TRACHEATA 38

Go

males, females, and workers; the last-named are females which
sometimes produce parthenogenetic eggs. These colonies are

Fic, 216.—Nest of Vespa sylvestris.

annual, existing for the summer only. In the autumn all die,
with the exception of a few fertilised females, which creep into
crevices of trees or under stones,
and hibernate through the winter.
In the spring the female emerges
and commences to build a nest;
this is constructed of fragments of
wood gnawed up and mixed with
saliva, the whole making a papery
substance. As soon as two or
three cells are finished the female Bias ole Vesparuja.
lays an egg in each, and when the
white apodal grubs hatch out they have to be fed, whilst at
the same time the mother is widening and deepening their
cells and adding others.

The larval stage lasts about two weeks, and then the grubs

384 ZOOLOGY

cease to eat and turn to pupae in their cells. The imago
emerges in ten days, and sets to work to enlarge the nest. As
soon as the perfect insect vacates its cell, it is cleaned out and
another egg is deposited in it.

During the first half of the summer, only workers appear,
but later males and females make their appearance, the former
from the parthenogenetic eggs of the later broods of workers ;
all these kinds are winged, but the workers are smaller than
the males and females. The sexes pair whilst flying, and
soon afterwards the males die.

There are seven species of Vespa found in Great Britain ;
of these the hornet, Vespa crabro, is the largest. This does
not extend north of the Midlands; its nest is larger than the
common wasp V. vulgaris, but its colonies contain fewer indi-
viduals. V. rufa has a reddish tinge on its legs; it, like
V. vulgaris and germanica, builds its nest in the ground, whilst
V. sylvestris, arborea, and norvegica are tree-wasps, building
their nests in trees.

The other European genus of this family, Polistes, occurs
round the Mediterranean. Its nest consists of a single layer

Fic. 218.—Polistes tepidus and nest.

of cells, forming a comb which is vertically or obliquely placed,
and is not covered in by an outer case, like the nests of the
various species of Vespa.

Family EUMENIDAE.— Lumenes coarctata is the only British

TRACHEATA 385

species of this family; it makes small rounded cells of mud,
which it attaches to some plant, very generally
to heath. In each cell it lays one egg, and
stores up some provision of honey to serve as
food for the larva; the cell is then closed.
Some species of this genus are carnivorous,
and when this is the case the mother stings
some caterpillar or other insect larva in the yy. 919, gwmenes
ventral nerve cord in such a way as to render smithit.

it motionless without killing it; the imert

larva is then deposited in the cell to serve as food for the

erub of the wasp.
Family MAsSArtDAE—No members of this family occur in

Fic. 220.—Masaris vespiformis.

Britain, and the number of genera is small. They construct
nests in banks of earth, with passages leading down to them.

Group 3. Fossoria.

These are sometimes termed digging wasps; they have no
bend in their antennae, and their legs are elongated. The
females construct passages in sand or earth, or sometimes in
wood, and lay their eggs at the end of these tubes. They live
upon honey and pollen, and either convey fresh food to their
larvae every day or store up in the tube a sufficient number
of insects or larvae, paralysed by a sting in the nervous

aE

o

386 ZOOLOGY

system, to suffice for the larva till it pupates. Each species
always attacks a particular kind of insect and carries it home
as food for its larvae; thus Cerceris bupresticida always
attacks the larvae of the beetle Buprestis, Sphex flavipennis
attacks Gryllus, and S. albisecta various species of Oedipoda.
Another allied family, the Chrysididae, often lay their eggs
in the nests of the Fossoria and other Hymenoptera. They
are green or black, and their sting is devoid of a poison-bag.

Group 4. APIARIAE (Bees).

In the bees the body is thick and short, and as a rule
hairy. In the workers the tibia and tarsus, especially of the
posterior legs, are broadened and covered with hairs lke a
brush; these serve to gather and carry home the pollen
grains. The labium and maxillae are often very long, and can
reach to the nectaries at the base of some of the longest
flowers. Whilst obtaining food in this way bees very frequently
effect the cross fertilisation of the flowers they visit. The
anterior wings do not fold. Both the females and workers
have stings, which in many cases are provided with recurved
spines, so that if inserted into a foreign body they cannot be
retracted.

The division of labour which plays such a prominent part
in the economy of the higher Hymenoptera reaches the highest
pitch amongst the bees. The queen-bee alone in Apis mellifica
—the honey bee — lays fertilised eggs, sometimes at the

Worker-bee. Drone. Queen-bee.
Fic. 221.—Apis mellifica.

rate of 3000 a day; she and the workers live through the
winter, but the drones all perish in the autumn. The drones
are the males of the community; they arise from unfertilised

TRACHEATA 387

egos laid by the queen, who can lay at will either fertilised
or unfertilised ova.

During the winter the queen-bee and the workers live upon
the food stored up in the hive; when spring returns she
deposits eggs, first in the cells of the workers and then of the
drones. After a time certain large royal cells are constructed,
and in each of these she lays a fertilised eg¢; the larvae which
proceed from these eggs receive a richer nourishment and
become queens. The drones take twenty-four days to de-
velope, the workers twenty, and the queens sixteen. Before
the eldest of the royal pupae gives rise to a queen in the
imaginal state, the queen mother with a number of the workers
leave the hive and swarm. ‘Thus a new colony arises. The
young queens fight until all but one are killed, or the others
swarm ; the victorious one remains as queen of the hive. Soon
after the metamorphosis is complete the queen is fertilised by a
drone whilst flying in the air. The drone immediately dies,
and the queen, which has only been fertilised once, can con-
tinue to lay fertilised ova for several years.

A hive may number as many as twenty to thirty thousand
individuals, of which the drones do not form more than one
per cent.

Bombus, the humble-bee, makes underground nests which
contain from fifty to two hundred individuals. This genus
does not make cells, but lays its eggs in a mass of pollen
accumulated in the centre of the nest; the larvae eat their
way through this, and ultimately turn into pupae. A single
fertilised female survives the winter, and inaugurates a new
colony in the following year.

CHAPTER XxX
TRACHEATA
ARACHNIDA

BRANCHIATE

Forms Trilobita—Olenus.

Eurypterina—Lurypterus, Pterygotus.
Niphosura—Limulus.

( Scorpionida—Scorpio, Buthus.
| Pseudoscorpionida—Chelifer, Obisiwi.
Pedipalpi—Phrynus, Lhelyphonus.

Solifuga—Galeodes.
J Tetrapneumones— ygale,
Forms * Atypus.
Araneida fy ; .
Dipneumones—Lpeira,
Lycosa.

| Phalangida—Phalangium, Gonyleptus.

( Acarina—Jvodes, Sarcoptes.
inguatulida.

Ae A es atulida

Forms Tardigrada.
aan eo! | Pyenogonida.

|

| ate
ARACHNIDA 4 TRACHEATE

|

|

L

CHARACTERISTICS.— Arthropoda with a cephalothorax (prosoma)
marked off from the rest of the body by the presence of a carapace
and bythe character of its limbs. The abdomen may be segnented
or unseginented, and is sometimes divided into two regions,
the mesosoma and the metasoma, the latter may bear a posterior
spine. Four pairs of walking-legs are usually present. The
breathing apparatus may take the form of branchiae adapted
for aquatic respiration, or of lung-books, or tracheae for
breathing air. An internal skeleton in the form of a plate,
termed the endosternite, is present in many forms. The
genital orifice is usually on one of the anterior segments of the
abdomen. They are, with the exception of one order, bisexual.
The Arachnida fall into three groups—those that breathe

water, those that breathe air, and certain aberrant forms,—

and the members of groups differ to a very considerable extent.

TRACHEATA 389

The Branchiate group includes three classes :

J. EuryprertNa (Merostomata). II. TRILOBITA.
III. XipHosura (Poecilopoda).

Of these the first two are extinct, whilst the third is
represented by a single recent genus, Limulus, the king-crab.
This, like its fossil congeners, is marine.

The tracheate division of the Arachnida comprises seven
classes :

T. SCORPIONIDA. V. ARANEIDA.
II. PSEUDOSCORPIONIDA. VI, PHALANGIDA.
II]. PEDIPALPI. VII. ACARINA.

TV. SOLIFUGA.

The aberrant forms are—
I. LINGUATULIDA. II. TARDIGRADA.
III. Pycnoconipa (Pantopoda).

Of these the first class is parasitic and the third is marine.
The Arachnida form a’most heterogeneous assemblage; the
group affords shelter to a number of forms whose affinities are
by no means clear, and whose structure is in some cases so
modified as to possess few or no Arachnid characteristics.

A, THE BRANCHIATE GROUP.

CLass III. Xiphosura.

The very remarkable creature which is popularly known
as the king-crab, and scientifically as Limulus, is an inhabitant
of the warmer waters of the east coast of America, the East
Indian Archipelago, and the western shores of the Pacific. It
is found in from two to six fathoms of water, moving about in
the mud or sand, and living chiefly upon certain worms, It
may attain a length of several feet.

The body of Zimulus is enclosed in a thick chitinous
cuticle, the dorsal surface of which forms a large shield or
carapace. This is produced laterally into two backwardly
directed processes, and it covers in the prosoma, the anterior
region of the body, which bears six pairs of appendages.
Anteriorly near the middle line are a pair of simple eyes,
and behind and nearer the sides are a pair of compound eyes.

39° ZOOLOGY

Behind the prosoma, the body is covered in by an abdominal
carapace, the anterior part of which shows dorsally faint traces
of being composed of seven segments. This region corresponds
with the mesosoma of other forms; behind it the metasoma pre-

A
SSS
SS
KY
‘i
bh S
c

Fic. 222.—Under side of Limulus polyphemus, Latr., @ .

C. Carapace. 3a’. Detached pedipalps of 6.
Th. Abdomen(=meso- and meta-soma). 4-7. Thoracic walking-legs.
T. Telson or spine. 8. Lamellae with genital openings,
2. Chelicerae. 9-13. Branchiferous lamellae.
3.

Pedipalps. m. Mouth.

sents a smooth unsegmented surface. The anus is situated at the
end of the metasoma, and a long pointed spine extends behind it.

Appendages of Limulus.

1. Chelicerae. 7. Plates with genital pores.
2. Leg-like appendages (pedipalpi). 8. 5, », branchiae.

3. 39 99 Q Ee) 99 2?

4, 9? 29 10 39 29 99

5. 9 39 1 1. 9 32 be)

6. > bel 12. 2) ”? 9?

The appendages which are found on the ventral surface of
the body commence with a small three-jointed pair of chelicerae,
placed one on each side of the upper lip, which overhangs the
mouth. The next five pairs of appendages are leg-like, and
are arranged round the mouth; they consist of six joints—the
proximal one or coxa is enlarged, and its anterior border is

TRACHEATA 301

produced into a process which helps to surround the mouth
and form a biting organ. In the female of L. polyphemus, the
first five of these appendages are chelate, but in the male the
first is enlarged but is not chelate; in both sexes the sixth
appendage terminates in a number of elongated flattened
plates, and this limb is used in the burrowing or digging
operations in which the animal delights. All these append-
ages are borne on the prosoma; the seventh appendage, or the
first mesosomatic, consists of a semicircular plate-like structure
hinged on to the body and bearing on its posterior face the
two genital pores. ‘This genital plate or operculum folds over
and almost covers the five succeeding appendages, which are also
plate-like, but, hke the former, exhibit traces of a double origin.
Each of these, from the eighth to the twelfth, carries a pair of
respiratory organs, in the form of branchiae composed of a great
number of thin plates like the leaves of a book. Behind the
twelfth is the unsegmented metasoma, which bearsno appendages.

An internal skeleton or endosternite, in the form of a plate
of fibro-cartilage, lies between the alimentary canal and the
elongated nerve collar. It is not connected in any way with
the exoskeleton, but gives origin to a number of muscles. <A
somewhat similar structure is found in Apus and in some
other Crustacea.

The alimentary canal, as is usual with the Arthropoda,
excepting the Insects, runs in a median line from mouth to
anus without convolutions. The mouth is situated some dis-
tance behind the anterior end of the body; it leads into a
suctorial pharynx, which is lined by chitinous ridges. The
pharynx runs forward and widens into a stomach, which turns
back, curves posteriorly, and is separated by a valve from the
mid-gut ; the latter is the absorbent part of the alimentary tract.
It extends through the body, and terminates in a short procto-
daeum with folded walls. The only gland which opens into the
alimentary canal is a large yellow organ, the so-called liver,
which communicates with the mid-gut by two pairs of ducts.

The vascular system is very complete, and, unlike many
Arthropods, the arteries do not end in irregular lacunar spaces,
but are connected with the veins by a definite capillary system.
The heart consists of an elongated tube, partially divided into

392 ZOOLOGY

eight chambers, into the anterior end of each of which a pair
of ostia open (Fig. 223). The heart ends blindly behind, but
in front is continued into a truncus arteriosus; from the base
of the latter an artery arises on each side, which passes, to-
gether with a vessel from each of the anterior chambers of
the heart, into a large collateral artery which runs outside the
heart, but parallel toit. The collateral vessels unite behind, and
are continued backwards as a single supra-anal vessel. Still

Fic. 223.—Limulus polyphemus. Diagrammatic view of left half of body seen from
the inside. From Leuckart, partly after Packard.

1-5. The 5 pairs of thoracic limbs. 19. Bile ducts; the openings of two
6. The operculun. into the intestine are seen.
7-11. The gill-bearing mesosomatic limbs. 20. Liver.
12. Mouth. 21. Heart, with eight venous ostia.
13. Anus, 22. Efferent branchial veins leading into
14. Spine or Telson. pericardium.
15. Chilaria. 23. Frontal artery dividing at
16. Oesophagus. 24. Into two marginal arteries.
17. Muscular proventriculus, 25, Left aortic arch.
18. Intestine. 26. Supra-anal artery; the sub-anal

artery is shown ventral to this.

The solid black structure beneath the alimentary canal, lying in a blood space,
is the nervous system.

farther forward the truncus gives off two cerebral arteries, which
pass into a vascular ring which surrounds the oesophagus, and
encloses the nerve collar. From this rmg a number of vessels
arise Which supply the appendages, and it is continued backward
into a supraspinal vessel in which the ventral nerve cord lies.

The capillaries in which the arteries terminate open into
certain reservoirs; passing from these the blood traverses the
gills, and is then returned by a system of branchiocardiac

TRACHEATA : 303

canals to the pericardium, and so by the ostia into the con-
tractile heart. The blood has a bluish tinge, due to the pre-
sence of haemocyanin, and contains numerous oval corpuscles.

Fic. 224.—Diagram of cir-

culatory system of Limulus

polyphemus. From Leuck-

art, after Milne-Edwards.

\ \Weezz<-------9
(a 2 10

—

SS
\
ee 8
/ 13
1. Oesophagus. 10. Ventral artery surrounding ventral
2. Heart with 8 pairs of ostia. nerve cord and giving off branches
3. Aortic arch, the two branches of to mesosomatic limbs and gills.
which unite into a ring surround- 11. Longitudinal lateral vein giving
ing the oesophagus and mouth. branches to gills, the blood is re-
4. Frontal artery. turned from gills to pericardium by
5. Marginal artery. the vessels marked (22) in previous
6. Collateral artery, running parallel figure.
with heart, and supplied by 7 12. Cutaneous nerves which have no
vessels from the heart. arterial sheath.
Supra-anal artery. 13. Ventral nerve cord in ventral artery.

Sub-anal artery.
One of the 5 pairs of vessels going to
the 5 thoracic limbs.

am

. Lateral eye.

The gills, which are borne upon the posterior face of the
five posterior pairs of appendages, consist of a number (150) of
very delicate plates, each composed of two thin membranes, in

the space between which the blood circulates.

The plates lie

parallel to one another like the leaves of a book, and the water

circulates between them.

A large gland, in its natural state of a brick-red colour, is

situated at the base of the leg-like appendages.

Tt consists of

a longitudinal portion, from which four lobes are given off,

394 , ZOOLOG V

corresponding with the second, third, fourth, and fifth prosomatic
limbs. In the adult this structure, which has been termed the
coxal gland, appears to have no duct, but in the young, both an
internal and an external opening have been described. The
former opens into a space in the connective tissue which lies
between the gland and the ventral blood sinus; the external
opening is situated on the dorsal surface of the coxa of the fifth
appendage. The chitinous covering of the animal is continued
a short distance into the duct. The gland thus appears to
have the relationship of a nephridium, and it is worthy of note
that it opens upon the same appendage in numerical sequence
as does the shell-gland of the Entomostraca, the latter having
its orifice on the second maxillae, or fifth appendage.

The nervous system of Limulus consists of a supra-oeso-
phageal nerve mass which gives off five nerves, supplying the
ocelli, the compound eyes, and the integument in the region of
the head (Fig. 223). From the sides of this mass pass a pair
of oesophageal commissures, which come together some dis-
tance behind the oesophagus; the commissures are, however,
united together by a number of transverse connectives situated
behind the oesophagus. This elongated oval collar supphes
nerves to all the limb-like appendages, and to the operculum
which bears the genital orifices. After the fusion of the two
circum-oesophageal commissures, the nervous system is prolonged
backward as a ventral nerve cord, which during the first half
of its course gives off no nerves, but its posterior half supplies
five pairs of nerves, which pass to the last five appendages and
the surrounding parts.

Both the oesophageal collar and the ventral nerve cord, and
many of the more important nerves, are ensheathed in blood-
vessels.

Limulus is dioecious, and the male can be distinguished
from the female by the thicker and non-chelate character of the
second pair of appendages. Both the ovary and the testis are
retiform, the network of tubules which compose these glands
extending through the pro-, meso-,and meta-soma. The tubules
of the testes are in communication with a number of spherical
sperm vesicles, which contain immature spermatozoa ; the latter,
when ripe, are provided with a motile tail. Both the ovaries

TRACHEATA 395

and the testes communicate with the exterior by means of two
ducts, which open independently on the posterior face of the
operculum or seventh segment. Fertilisation is external.

The propriety of placing Limulus amongst the Arachnida
has not been universally accepted, but its resemblance to
Scorpio, even in points of detail, is striking, and the relation-
ship thus indicated is strengthened by the structure of the
fossil EuRYPTERINA, which are to some extent intermediate
between these two orders. They have six pairs of thoracic
limbs, and the region between the genital plate and the anus
is divided into a number of segments gradually diminishing
in size.

B. THE TRACHEATE GROUP.

Cuass I. Scorpionida.

CHARACTERISTICS.— Arachnida with six pairs of appendages on
the prosoma, of which the first and second pairs are chelate,
the latter being enlarged. There is a mesosoma of seven
segments, and a metasoma of five, terminating in a curved
spine armed with a poison gland. There are four pairs of
lung-books.

Scorpions inhabit warm and tropical countries, hiding for
the most part under stones, etc., during the day, but running
about after dusk. They usually carry their metasoma turned
back over the back (Fig. 227). There are several genera:
Scorpio, Buthus, Androctonus, etc.

Their body is covered by a cuticle, which in some places
is thickened and forms stout plates. Six of these have
coalesced on the dorsal surface of the prosoma and form a
carapace which bears from three to six pairs of simple eyes.
Two of these are close together near the median line, the rest
are arranged along the anterolateral edge. Behind the
carapace are seven short broad terga belonging to the meso-
soma. Each of these is connected with its corresponding
sterna by soft skin; but the last has to some extent fused
with the seventh sternum, forming a complete chitinous ring.
The five segments of the metasoma are completely encased in
chitin, and so is the postanal poison sting.

396 ZOOLOGY

Appendages of Scorpio.

1. Chelicerae. 7. Plates with genital pores.
2. Pedipalpi. 8. Pectines.

3. Walking-legs. 9. Lung-books.

4, 1 10. 5p

5 “ 11. %

6. 4 12. %

The first pair of appendages, or chelicerae, are short, three-
jointed, and chelate. They are directed forward. The second
pair, or pedipalpi, are very much enlarged, and six-jointed ;
they end in a swollen powerful pair of nippers; the coxae or
basal joints of this pair of limbs have a biting process which
euards the entrance to the alimentary canal. The remaining
prosomatic limbs are walking-legs; they are seven-jointed, and

Fic. 225.—Ventral view of pro- and
meso-soma of Buthus afer. From
Leuckart, after Cuvier.

H

. Chelicerae.
. Pedipalpi.

oe
© OMA bw

. Ist to 4th pair of ambulatory legs.
. Genital operculum.
. Pectines.

. 4 pairs of stigmata on the 3rd-6th
mesosomatic region,

10. 1st metasomatic segment.

not chelate. The first and second of these ambulatory ap-
pendages have their coxal joint enlarged and turned forward,
and the processes thus formed play some part in the ingestion
of food. The coxae of the last two pairs of walking-legs are
fused together, but those of the left side are separated from
those of the right by a small sternum.

The seventh pair of appendages, or first mesosomatic pair,

TRACHEATA 39

N

are probably represented by a small rounded plate with a
notch in the middle of its border. This bears on its posterior
aspect the genital pores. The eighth pair of appendages are
termed the pectines; they take the form of an axis, which
carries a single row of short processes set like the teeth of a
comb; these are probably tactile in function. The remaining
segments in the adult scorpion are devoid of appendages,
though there are six more pairs of limbs in the embryo; but
these do not develope, and are lost.

The third, fourth, fifth, and sixth mesosomatic sterna have
each a pair of slit-like openings leading into the lung-books
or respiratory organs. These correspond numerically with the
last four pairs of branchiae in Limulus.

The endosternite is a free skeletal plate giving attach-
ment to muscles. It les in the prosoma above the nervous
system, and is pierced by a blood-vessel.

The mouth is extremely minute; it leads into a small
pharyngeal sac with elastic chitimous walls. Certain muscles

Fic. 226.—Dorsal view of Buthus occitanus, the
dorsal integument has been removed to show
the digestive organs. From Leuckart, after
Blanchard.

1, Chelicerae.

2. Oesophagus.

3. Salivary glands.
4. Intestine.

5. Liver.

6. Ducts of liver.

i

Malpighian tubules.

ao

Intestine.

act as divaricators of this sac, and thus it functions as a
suction-pump, and by its means the scorpion can suck in the
juices of its prey, usually spiders or insects. A narrow

308 ZOOLOGY

oesophagus leads from this sac to a second enlargement, which
receives the ducts of a pair of salivary glands, structures
which are usually associated with a terrestrial mode of life.
The succeeding digestive portion of the alimentary canal re-
mains narrow; it receives four or five ducts which convey the
secretion from a corresponding number of lobes of the liver.
The latter is a considerable gland which takes up a good deal
of space in the wide mesosoma, and even extends into the
narrow metasomatic segments. One or two pairs of delicate
Malpighian tubes are present, and these have been recently
shown in one species to be developementally outgrowths from
the mesenteron ; a pair of these tubes are branched. A procto-
daeum is present, and ends in an anus situated ventrally at
the end of the metasoma.

The heart in Scorpio, as in Limulus, consists of a median
tube of eight chambers ; it is continued backward in the scorpion
as a posterior aorta which traverses the metasoma. A pair of
valvular ostia open into the anterior end of each chamber,
and a pair of lateral arteries take their origin from the pos-
terior end of each division, The eight chambers lie in the
seventh to the thirteenth segments, the last containing two
chambers. From the anterior end of the heart a truncus
arteriosus leads forward; this vessel gives off two lateral
branches, which embrace the oesophagus and then unite into a
median artery which runs backward above the nerve cord.
In front of this ring the anterior aorta divides into two lateral
vessels and a median one, these supply the appendages of the
prosoma, the brain, and other organs. After passing through
the body, the blood collects in a ventral reservoir and passes
thence to the lung-books. Here it is oxygenated, and is then
conveyed by special veins back to the pericardium, and so
into the heart. The blood in Androctonus is, when oxygenated,
of a deep indigo blue, coloured by haemocyanin ; its corpuscles
are oval, and are remarkably large.

The four pairs of oval stigmata, which are obliquely placed
on the sterna of the ninth, tenth, eleventh, and twelfth seg-
ments, lead into sacs, into the lumen of which project numerous
lamellae. These lamellae, of which there may be as many as
130, arise from a definite axis, which is for the most part

TRACHEATA 399

adherent to the wall of the sac, only a short portion being free.
Between the thin walls which constitute each lamella, the blood
flows, whilst the air circulates between the lamellae.

Z ENG fp E . | Less
(On USES & re BPI :

=
19 :
i 9 13" 8 ae caer 6 7 5

Fic. 227.— View of internal anatomy of Buthus, showing digestive, circulatory,
respiratory, and nervous systems. From Leuckart, after Newport and Blanchard.

1. Chelicerae. 12. Anus.

2. Pedipalpi. 131-13'%, Lung sacs.
3-6. Ambulatory limbs. 14. Heart.

7. Pectines. 15. Posterior aorta.

8. Mesenteron. 16. Anterior aorta.
9. Lobules of liver, with ducts 17. Brain.

entering mesenteron. 18. Median eyes.

10. Malpighian tubules, portions of. 19. Lateral eyes.
11. Proctodaeum. 20. Poison gland.

A pair of coxal glands occupy a position in the prosoma
near the base of the fifth and sixth appendages; they appear
to be actively secretory, but apparently in the adult have no
outlet. In the embryo, however, according to Laurie, this
gland originates as a tube which opens to the exterior at the
base of the fifth appendages, and internally into a coelomic
space. The coxal gland of Scorpio, like that of Limulus, thus
seems to be of the nature of a nephridium, but the part
which it plays in the excretion of nitrogenous waste matter,
and whether it shares this function with the Malpighian
tubules, is a subject still requiring investigation.

The nervous system of Scorpio comprises a supra-oesopha-
geal ganglion which sends nerves to the central and marginal

400 ZOOLOGY

eyes, and a circum-oesophageal collar, which gives off the
ventral nerve cord (Fig. 227). The nerves to the first six pairs
of appendages, as well as to the genital plate, the pectines,
and the two following segments, arise from the collar or the
sub-oesophageal ganglion. The ventral cord for some distance
bears no ganglion, the first being situated in the eleventh seg-
ment and supplying the third pair of lung-books. Behind
this there are six pairs of ganglia, one in each segment, the

Fic. 228.—Transverse section through the body of Huscorpius italicus in the
region of the endosternite. After Lankester.

1. Alimentary canal. 6. Right ventral nerve cord.
2. Caeca of gastric gland (liver). 7. Supraneural blood-vessel.
3. Anterior aorta. 8. Chitinous tergum.
4. Endosternite. a: 46 sternum.
5. Supraneural plate of endosternite. 10. Right coxal gland.

The dotted areas represent sections of various muscles.

last being in the fourth metasomatic segment. The sense
organs are the simple eyes ‘borne on the carapace, one pair
near the middle line, and a small group on each side near the
edge, and the pectines, which may be tactile in function.

The poison glands are two in number, both situated in
the postanal spine. They are provided with a muscular tunic,
the contractions of which serve to express the poisonous
secretion. Each gland has a duct, and the ducts open by
separate orifices close to the apex of the spine. The poison
is fatal to most small animals, such as spiders and insects ;

TRACHEATA 401

and owing to the way the metasoma is usually carried, over
the head, it can readily be injected into any prey which has
been caught and held by the pedipalpi.

The generative glands, like those of Limulus, consist of a
network of tubules; these are hollow, and the cells lining
their lumen give rise to the reproductive cells. The testes
consist of two pairs of longitudinal tubules united by cross
branches, on each side of the body; the efferent duct leads to
the external opening on the first mesosomatic somite ; its distal
end is modified to form an intromittent organ, and it bears
accessory glands.

The ovary is single, and consists of three longitudinal
tubules united by transverse ducts; it les ventral to the
liver, and is to some extent embedded in that organ. The
ovary is situated in the mesosoma, and the oviducts run
forward, one on each side, to open upon the genital operculum.
The ova are formed by the growth of cells lining the tubules,
and they project from the surface in the form of follicles.
They are fertilised in situ, at any rate, in one species. After
going through the early stages of segmentation, they pass into
the oviduct, and there complete their developement. The young
are born in a condition resembling their parents, the scorpion
being viviparous.

Ciass II. Pseudoscorpionida.

CHARACTERISTICS.— The abdomen is not divided into meso-
and meta-soma, but is broad and flat, and consists of ten or
eleven somites ; the animals are all minute; they breathe by
tracheae ; the pedipalpr are chelate.

In many respects the Pseudoscorpions resemble minute
scorpions, but their abdomen is not produced into a tail, nor
does it terminate in a poison gland. They breathe by
tracheae, which open externally by two pairs of stigmata
situated in the third and fourth abdominal somites. Like
spiders, they are provided with spinning glands, which lie
partly above the liver in the prosoma, and which open at
the tip of the moveable joint of the chelicerae.

26

402 ZOOLOGY:

Appendages of Chelifer.

1. Chelicerae. 4, 2nd walking-legs.
2. Pedipalpi, very large. 5. 38rd + 3
3. Ist walking-legs. 6. 4th * -

Coxal glands are present in the form of closed tubes,
which may be bent once; these lie in the region of the last

Fic. 229.—Chelifer sesamoides,
Savigny.

a. Thorax (prosoma),

b, Abdomen.

c. Chelicerae.

d. EKyes.

e. Hinder segment of thorax.

J. Front segment of thorax.

h. Pedipalpi.

three pairs of legs, and at present no opening to the exterior
has been described.

The ventral ganglia have fused into a circular mass, from
which nerves radiate to the various organs.

The intestine is folded in a single loop, a very rare thing
in Arachnids. The rectum has a diverticulum in which, as
is the case with spiders, the excrement accumulates.

The genital opening is between the second and third
abdominal sterna. The females carry the eggs about attached
to the abdomen, and the young live for some time in a small
web formed from the secretion of the spinning glands.

There are several genera of Pseudoscorpions: Chelifer,
Obisium, Chthonius, and Chernes, all have a wide distribution.
Chelifer cancroides is known as the book-scorpion, as it is
found among old books and papers. Other species live under
bark, or in moss in damp places; they feed mostly on mites
and small insects. They can run rapidly, sideways or back-

TRACHEATA 403

ward, and are often transported long distances by clinging
with their pedipalpi to flying beetles, ete.

Crass III. Pedipalpi (Scorpion-spiders).

CHARACTERISTICS.— Zhe pedipalpi are clawed or chelate, and the
anterior pair of legs are prolonged into long antenniform

processes. Abdomen of eleven or twelve segments, distvict
from thorax ; there are two pairs of lung sacs.

y
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Stale ee Rea Dee a ees Weekes
Fic. 230.—Phrynus medius, Koch.
a. Moveable fangs or claws on fourth d. Chelicerae.
joint of pedipalpi (%), forming e. Abdomen.
with claws (c) on third joint jf. Button at end of abdomen.
a modified didactyle claw.

h. Eyes.
6. Thorax,

7. Long antenniform legs.

404 ZOOLOGY

This group includes the two genera Phrynus and Thely-
phonus; they are confined to the tropical and subtropical
regions of both the Old and the New World. ‘They are of
considerable size.

The abdomen is distinctly marked off from the thorax ;
it consists, in Phrynus, of eleven segments, and does not

\e
Z

v 1 2 Ne 3
Soqlela meine | ee ee notes

Fic. 231.—Thelyphonus giganteus, Koch.

@. Pedipalpi. g. Tail.

b. Moveable fang or claw forming with h. Chelicerae,

c. Claw on 4th joint, a didactyle claw. m. Hyes.

d. Claw on 8rd joint. o. First palpal joint, with characteristic
jf. Segmental elongation of abdomen denticulations,

supporting tail.

exhibit any distinction of meso- and meta-soma; in Thely-
phonus, however, the tenth, eleventh, and twelfth segments
are small, and the twelfth bears a long-jointed filament
representing the telson.

TRACHEATA 405

Appendages of Pedipalpi.

1. Chelicerae. 4, 2nd pair of legs.
2. Pedipalpi. by eitel xr
3. Ist pair of legs, antenniform. 6. 4th ,, 3s

The chelicerae are clawed, and probably contain poison
glands; the pedipalpi are clawed in Phrynus, and chelate
in Thelyphonus. The elongated anterior legs function as
antennae, which they resemble in structure. The other legs
are seven-jointed. A pair of closed coxal glands lying be-
tween the second and fourth pairs of legs have recently been
described.

The genital orifice is ventral, at the anterior end of the
abdomen, and the respiratory sacs open, one pair on the

Fig. 232.—Thelyphonus, portion of under side.

a. Moveable claw on pedipalp.
b. Fixed claw on pedipalp,
ce, Claw on third palpal joint.
d, Coxal joint of pedipalp.

e, f. Sternal plates,
g. Orifice of sexual organs.
h, Place of labium,

o, Orifices of respiratory organs,

posterior edge of both the second and the third abdominal
segments. Phrynus, like the scorpions, produces its young
alive. There are eight eyes: two large ones near the centre
of the cephalothorax, and six small ones round its
margin.

Thelyphonus seems to be nocturnal in its habits, and passes
the day under pieces of bark, ete. When irritated, it is said
to carry its tail erect like the scorpions, and the chief interest
of the group lies in their forming an intermediate link
between the Scorpionida and the Araneida.

406 ZOOLOGY

Crass IV. Solifuga.

CHARACTERISTICS.—The head and abdomen are distinct from
the thorax, which consists of three segments; the chelicerae
are chelate, and the pedipalpr leg-like. The abdomen con-
sists of nine segments. Respiration is carried on by
tracheae.

The best-known species of this group is Galeodes, which is
chiefly found in warm places in the Old World. It is an
animal of considerable size; the body of an Indian species is
described as being the size of a thrush’s egg. CGaleodes

Fic. 233.—Galeodes araneoides,
Pallas.

@. Chelicerae.

b. Eyes.

c. Head.

d. Thorax.

Jj. Abdomen.

g. Pedipalpi.

h. Palpiform legs.

k. Digital joint (capsule).

o. Shear-like points of falx (end
joint of chelicera).

7. Anus.

araneoides has a body two inches long, and with the legs may
extend over ten inches.

In the division of its body into head, thorax, and abdomen,
and in its method of breathing, Galeodes approaches the In-
secta. The body and limbs are both well covered with
thick-set hairs.

Appendages of Galeodes.

1. Chelicerae, very strong. 4, 2nd pair of walking-legs.
2. Pedipalpi, limb-like. 5. 3rd
3. Ist pair of walking-legs. 6. 4th

” 93

” 92

TRACHEATA 407

The chelicerae are very strong, and project in front of the

head ; the lower limb is moveable, and works vertically against
the fixed upper half. The pedipalpi are limb-like. The
anterior pair of legs belong to the head; their basal joint
serves as a cutting (maxillary) process, at the side of the
mouth, an arrangement similar to that found in Limulus
and Scorpio. Like the pedipalpi, they are directed forward,
and like them may serve as tactile organs.

The three posterior legs, which are borne by the three
free thoracic segments, are clawed. Another point in which
these Arachnids resemble Insects is the presence of a well-
formed tarsus. The abdomen is composed of nine or ten
segments.

The basal joint of the fourth pair of legs bears five curious

Fic. 234.—Under side of Galeodes arane-
oides, with legs and palpi truncated.

a. Coxa.

e. Basal leg-joints.

eX. 1st joint of 1st pair of legs.

J. Labium.

h. Racket-shaped appendages.

7. External orifice of genital organs.

k. Tongue.

m. Pedipalpi.

o. Openings of respiratory organs at base
of 2nd pair of legs.

p. Ovifices leading to tracheae at fore margin
of 2nd and 3rd segments of abdomen.

7. Anus.

¢. Fixed upper fangs or claws of chelicerae.

. u. Moveable lower fangs or claws of cheli-

P P cerae.

=a)

racket-shaped processes, pointing backwards, of unknown
function.

The tracheae open to the surface by three pairs of
stigmata; the anterior pair are on the thorax, the other two
open behind the second and third abdominal segments.

The stomach is provided with lateral caeca; the anus is
posterior, and the genital orifice opens on the first segment of
the abdomen. Paired coxal glands are found in the thorax ;
they are much coiled, but apparently have no opening to the
exterior.

408 ZOOLOGY

A pair of poison glands are found in the thorax, closely
applied to the walls of the stomach. The ducts are coiled, and
open near the bases of the chelicerae ; muscle fibres are described
near the orifice, and the contraction of these is believed to eject
the poison into the wounds caused by the chelicerae.

Two simple eyes occur in the head. The animals are
nocturnal, and spend the day under stones or rubbish, or in
holes in the ground. They are extremely voracious, and live
on large insects, such as beetles and grasshoppers; they will
even attack scorpions, and small vertebrates such as lizards
and mice. The female lays about fifty eggs at a time, and the
young are hatched in an immature condition.

Ciass V. Araneida (Spiders).

CHARACTERISTICS.—Abdomen unsegmented, soft, and stalked ;
chelicerae with poison glands, pedipalpi leg-like, two or four
lung sacs, and four or six spinnerets.

Epeiva diademata is one of the largest species of British
spider, and at the same time is a very common one, being
found in its wheel-shaped web in most gardens and woods ; it
therefore serves as a convenient type of the order.

The head is united with the thorax, but the abdomen is
constricted at its base, and being swollen and unsegmented,
gives a very characteristic appearance to the members of this

group.
Appendages of Hpeira.

1. Chelicerae. 4, 2nd pair of walking-legs.
2. Pedipalpi. 5. ord 50 Rs
3. 1st pair of walking-legs. 6. 4th A n¢

The chelicerae are two-jointed, the terminal joint being
curved and pointed, and capable of folding down in a sub-
chelate fashion; at the base of these appendages lie a pair of
poison glands, and these pour their secretion through a duct
which opens to the exterior near the tip of the terminal joint.
This poison is capable of killing insects and seriously affecting
larger animals.

The pedipalpi have a cutting blade-like basal joint which
takes part in mastication, as is the case in Limulus, Scorpio,

TRACHEATA 409

and Galeodes. They are usually six-jointed, and are frequently
clawed, but never chelate. In the male as it grows older the
terminal joint of the pedipalps grows larger, and after the
final moult it appears as the palpal organ, whose presence may
modify the shape of the adjacent joints. The palpal organ
varies in different species,
but it consists essentially
of a hollow sac which com-
municates with the exterior
by a duct, opening at the
tip of the segment. The
use of these organs is to
deposit the spermatozoa in
the receptaculum seminis
of the female.

The four legs are seven-
jointed, the terminal joint
bearing two or three claws,
and in some species a num-
ber of short hairs, which
aid them in walking up
walls and on ceilings.

The abdomen is sepa-
rated from the thorax by
a constriction, it is unseg-
mented and soft, and is
larger in the female than
in the male. Near its base

on the ventral surface is Thee

oe 5 _ Fie, 235.—A Spider (Cambridgea fasciata
the unpaired genital open Koch) Adult male ,
ing, and on each side of 1-7. Seven joits of leg.

this lies the opening of a
pulmonary sac; in some species there are two pairs of
these openings, the posterior pair leading in some species
(Mygale) into a second pair of pulmonary sacs, in others
(Argyroneta) into a tracheal system.

Near the posterior end of the abdomen are found the
spinnerets, these are four or six in number, according to the
species. In Epeira diademata, one of our largest spiders, there

410 ZOOLOGY

are four conical two-jointed spinnerets, whose apices meet
together when at rest; if these be separated, two smaller
single-jointed spinnerets are disclosed. Each of these projec-
tions is very mobile, and they can be separated and approximated
with ease. They are perforated at their apices by a number
of minute pores, amounting to about 600 in all, through which
the “silk” leaves the body. This silk is secreted by an enor-
mous number of glands which lie in the abdomen ; these in the
species in question are of five distinct kinds. Each kind of
gland has not only a definite relation to the spinnerets, some
supplying two pairs and others only one, but the threads
secreted from the various kinds of glands differ in quality, and
are used for different purposes. Thus the lines in the con-
centric threads of the well-known wheel-like webs differ from
the radial lines in being sticky, and so serving to hold the
captured flies, etc., and these again differ from the threads
which form the cocoon, or from those used to bind up captured
prey; and each of these various kinds of thread is the product
of one definite set of glands.

Between and a little behind the posterior spinnerets the
anus is situated.

In Lpeira the two stigmata leading to the pulmonary sacs
are on a level with the genital orifice. The cavities of the two
pulmonary chambers are in communication with one another
across the median line. Lach cavity is to a great extent
occluded by a number (about sixty) of horizontally placed
lamellae, which are attached as a rule to the wall of their
sac by their anterior and lateral edges, but present a free
edge posteriorly. These lamellae have very thin chitinous
walls, which are prevented from collapsing by the presence of
a number of little cellular pillars. Between the dorsal and
ventral wall of each lamella the blood circulates, whilst the
air passes in the slit-like spaces between the neighbouring
lamellae.

In addition to the pulmonary sacs, Hpeiva also has a
tracheal system. A single stigma opens just in front of the
anterior spinnerets, and leads into a median sac; from this
four tracheae emerge. These are chiefly distributed to those
organs which lie behind the pulmonary sacs. In other species,

TRACHEATA 4It

as in Argyroneta, the tracheal stigmata are situated just behind
the pulmonary, in the same position as the second pair of lung
sacs in the Tetrapneumones.

The heart in Zpeira is separated from the dorsal integu-
ment as well as from the intestine by some of the lobes of the
liver; it lies in a pericardium, and is confined to the abdomen.
The heart is described as giving off an anterior and a posterior
aorta, and four pairs of lateral vessels. Three pairs of lateral
ostia admit the blood which has collected in the pericardium
into the heart ; this contracts, and forces it through the blood-
vessels. The anterior aorta splits in the thorax, and each half
bends backwards and downwards to supply the legs and
neighbouring parts. From the summit of each bend a cephalic
artery runs forward to supply the organs in the head. The
course of the lateral vessels in the abdomen cannot be easily
followed, as the vessels have very thin walls, and soon lose
themselves in the tubules of the liver, ete. The blood is
ultimately collected in various sinuses, one of which is con-
tinuous with the spaces in the lamellae of the lungs. From
these organs it is returned to the pericardium, and thence to
the heart.

The blood is colourless, and contains relatively few large
round corpuscles, but many amoeboid ones.

The mouth is guarded on each side by the maxillary process
of the pedipalpus, and in front and behind by an upper and
lower lip; it is a transverse slit and leads into the pharynx,
a narrow tube lined with chitin which passes perpendicularly
upwards and forms a right angle with the next section of the
alimentary canal, the oesophagus. This tube is also lined with
chitin, it is encircled by the nerve ring and opens into an ex-
pansion known as the sucking-stomach. The lumen of the
latter is triangular in cross section, and its walls are strengthened
by chitinous plates; strong muscles unite the dorsal wall of
this organ with the chitinous integument of the tergum, and
similar muscles pass between its ventro-lateral walls and the
endosternite ; the contraction of these muscles enlarges the
lumen of the organ, and the juices of the prey are thus sucked
into the digestive canal of the spider.

The sucking-stomach communicates with the very small

412 ZOOLOGY

true stomach, this gives off a remarkable series of caeca, two of
which pass forward and end blindly near the poison glands.
In some species, as Zegenaria domestica and Agelena labyrinthica,
these two caeca fuse together and form a ring above the

Fic, 236.—Semi-diagrammatic view of a Spider (petra diademata), to show internal
organisation. After Warburton.

1. Mouth. 11. Dorsal vessel or heart, with lateral
2. Suctorial stomach. ostia.
3. Liver ducts. 12. Lung-sac.
4. Malpighian tube. 13. Ovary.
5. Stercoral pocket. 14. Acinate and pyriform silk-glands.
6. Anus. 15. Tubuliform silk-gland.
7. Dorsal muscle of stomach. 16. Ampulliform silk-gland.
8. Lower portion of stomach. 17. Aggregate or dendriform silk-gland.
9. Cerebral ganglion, giving off nerves 18. Spinnerets or mammillae.
to the eyes. 19. Falx (distal joint of chelicera),
10. Thoracie ganglion, giving off nerves 20. Poison gland.
to the legs. 21. Hye.

cerebral ganglion. The stomach gives off four pairs of lateral
caeca, each of these passes into the base of a leg and then turns
back again and ends blindly between the ventral nerve mass
and the ventral integument. These caeca in Lpeira diademata
end blindly, but in some species they fuse together and form a
common cavity. Thus the stomach and its caeca may in the
Araneida form a very complex system of anastomosing loops,
some of which project a short way into the legs.

From the stomach the intestine passes backward; it tra-
verses the constricted stalk between the cephalothorax and
abdomen, and then takes a curved course lying beneath the
heart, and finally opens into a large rectum. The intestine
gives off numerous tubules which bifurcate into a large number
of small ducts which ultimately end blindly; these constitute

TRACHEATA 413

the “liver,” a very extensive glandular organ which occupies a
large part of the cavity of the abdomen. The secretion which
it pours into the intestine is chiefly of use in digesting proteids.

The cloaca or “stercoral pocket” is an extensive chamber
which occupies about one-sixth of the abdominal space; the
faeces seem to accumulate in this in considerable masses.
It opens by the anus, which hes behind the posterior spin-
nerets.

The Malpighian tubules, the excretory organs of the
spiders, are four long fine white ducts, closed at their free
end and opening at the other into the intestine just where the
latter passes into the cloaca. Their secretion contains guanine
or some allied body.

A pair of coxal glands are present in Lpeira, but in a very
degenerated state ; in Tegenaria they are larger, and show some
trace of a duct, and in the young, just-hatched spiders, a duct
can be traced which opens to the exterior on the coxal joint of
the first pair of legs; the position of this opening is thus farther
forward in the Dipneumones than is usually the case in
Arachnids, but in a specimen of another genus, Dysdera rubicunda,
a second opening has been described on the third pair of legs,
the usual position.

Two poison glands of a pyriform shape are found just
under the integument in the anterior end of the cephalothorax,
their ducts traverse the chelicerae and open at the tip of these
appendages. In Amaurobius the poison is said to be secreted
and stored up through the winter, consequently this genus is
especially venomous during the spring.

The nervous system in “petra lies chiefly in the posterior
half of the cephalothorax ; compared with some other Arachnids
it exhibits great concentration (Fig. 236). The supra-oeso-
phageal ganglion is large, and supplies nerves to the eyes and to
the chelicerae, it is connected by lateral commissures with the
sub-oesophageal nervous system. The ventral chain of ganglia,
which are distinct in many Arachnids, in the Araneida are fused
into one large ganglion situated in the cephalothorax. In
Epeira this lies under the sucking-stomach and upon the ends of
the gastric caeca, it is star-shaped, with numerous rays, of which
the four middle ones on each side are stouter than the anterior

414 ZOGEOGY

and posterior. The rays are each continued into nerves; of
these the first pair is continuous with the circum-oesophageal
commissures, the second supplies the pedipalpi; the next four
stout rays supply the four legs, and the posterior pair is con-
tinued back into the abdomen, the two nerves lying so close
together as to be often mistaken for one.

The sense organs of spiders are limited to eyes which are
always simple, and to taste organs. The number and arrange-
ment of the eyes are of great use in classification, the various
families having a different and definite arrangement of these
organs. In Epeira the visual organs are situated on the
anterior part of the cephalothorax; there are four large eyes
arranged quadrilaterally, and on each side of the square are two
smaller eyes, the members of each pair being connected by a
ridge of chitin.

The male, as is usually the case in spiders, is smaller than
the female, and whilst the latter usually sits in the centre of
the circular web, the male is to be found hidden under the leaves
of a neighbouring bush. .

The ovary is situated in the abdomen; it lies ventrally,
and is surrounded by the caeca of the liver and spinning-glands.
It consists of two hollow tubes which unite posteriorly, and
are continued backward as a thread; anteriorly each ovary is
continuous with an oviduct; during the breeding season the
ovaries are much swollen, and the ova form projections on the
walls of the organ (Fig. 236). The oviducts open into a uterus,
and this opens into a recess on the ventral wall of the
abdomen. ‘The external genital armature of the female is
called the epigynium; it is often of a very complex character,
and its nature is of considerable use in determining the species
of a spider. In addition to the opening of the oviducts, it
also receives the external ducts of the two spermathecae ; these
ducts may be short and wide, or long and coiled. There are
also a pair of internal ducts which lead from the spermathecae
to the oviduct, and along which the spermatozoa pass to
fertilise the ova before they are laid. The epigynium is
rendered more complex by the presence of numerous structures
which serve to guide the palpal organs of the male into the
external openings of the spermathecae; it only exists in its

TRACHEATA 415

complete form in the mature female, and appears after the
ninth or last moult.

The testis in the male consists of two caeca, placed ven-
trally in the anterior part of the abdomen ; each passes into a vas
deferens, and the two vasa deferentia unite together in a small
vesicle which opens to the exterior just behind the level of the
pulmonary sacs. In Zegenaria guyoniw the semen is deposited
on a web constructed for the purpose, and taken up by the
palpal organs and by them introduced into the spermatheca of
the female, an operation not unattended by danger, as the
female, when hungry, has been known to seize and devour
the small male. The number of eggs laid varies from
above one thousand (Argiope cophinaria) to two (Oonops
pulcher) ; they are generally deposited in cocoons. The Lyco-
sidae carry their cocoons attached to the abdomen of the
mother, and when the young are hatched they are borne on
her back till the first moult. Zheridion carries the cocoon
between the base of the legs, and if it be lost searches about
diligently till it is found.

The Araneida are divided into two sub-orders:

1. TETRAPNEUMONES, with four lung sacs, and as a rule

four spinnerets.

2. DIPNEUMONES, with two lung sacs and six spinnerets.

Sub-order 1. TETRAPNEUMONES.

These are large hairy spiders which do not weave webs,
but burrow in the earth, lining their tubular tunnels with a
thick web. They sit at the entrance of these holes waiting for
their prey, which, in the case of the gigantic South American
Mygale avicularia, often takes the form of small birds. Other
members of this sub-order are Cteniza and Nemesia, the trap-
door spiders, found in Southern Europe; these genera close
the entrance of their tubular home with a lid or trap-door.
Both these genera have two pairs of spinnerets, of which the
posterior pair are very long and bend up over the abdomen.
Atypus, the only genus of Tetrapneumones found in Britain,
has six spinnerets.

The endosternite, which was well developed in Zimulus and

416 ZOOLOGY

Scorpio, is also found in Mygale. Coxal glands are also pre-
sent, in Mygale they seem to be closed, but in Atypus they
open on both the first and third pairs of legs.

Sub-order 2. DIPNEUMONES.

This sub-order contains the majority of spiders, which are
classified in very numerous families. petra diademata belongs
to the EPEIRIDAE, a family the members of which make the well-
known circular webs with radiating lines. Another family,
the LycosmpAk, or wolf-spiders, includes the Lycosa tarantula of
Italy and Spain. The THOMISIDAE, or crab-spiders, have a flat
round abdomen and rather short legs; they frequently run side-
ways, and build no webs. The AGELENIDAE make horizontal
webs, prolonged at one point into a tunnel, in which the
spider sits until some prey becomes entangled in the web,
when it rushes out, kills it, and binds it up. This family
includes the Agelena labyrinthica and Tegenaria derhamiu, the
commonest household spider. Argyroneta aquatica, which also
belongs to this family, makes a bell-shaped, water-tight nest,
attached to some submerged water-plant. This it fills with
air, carrying it down from the surface in bubbles which it has
entangled between its spinnerets and the posterior pair of legs.

Ciass VI. Phalangida.

CHARACTERISTICS. — Arachnida with their abdomen not con-
stricted off from the cephalothorax ; four pairs of very long
and slender legs; they breathe by tracheae only ; chelicerae
chelate.

The Phalangida, sometimes called the Opilionina, and
popularly known as harvestmen, resemble spiders in appear-
ance, but have no constriction between the abdomen and thorax,
and are almost always of a sombre gray, brown, or blackish

hue.
Appendages of Phalangium.
1. Chelicerae. 4, 2nd pair of walking-legs.
2. Pedipalpi. 5. 3rd 5 3
3. 1st pair of walking-legs. 6. 4th ep p

TRACHEATA 417

The chelicerae are chelate, and the pedipalpi are not modi-

Fic. 237.—Phalangium copticum, Savigny.
e. Pedipalpi.
j. Junctional line of thorax and ab-

. Chelicerae.
domen.

c. Hyes.
. (to right) Thorax.

d. Abdomen,

fied for purposes of fertilisation, but are short and limb-like.

The four pairs of legs are very long and thin, and very easily

Fig, 238.—Chelicerae and pedipalpi of Phalangium
copticum, seen from in front.

break in two; the proximal joint of the first two pairs of legs

is produced into a process, the coxa or maxilla, which assists
27

418 ZOOLOGY

in eating, and the third leg also sends in a process towards the
mouth, recalling the condition of things in Scorpio.

The abdomen consists of six to ten segments; its sterna
project forward, and, as the anterior one bears the genital pore,
this orifice is situated at the level of the third pair of legs.
Just behind this are the two stigmata which open into the
tracheae. These are at first wide, but they soon narrow and
subdivide into small branches ; the whole system is strengthened
by a spiral thickening of chitin.

The oesophagus is wider than in spiders, and the Phalangids
eat solid food; the stomach is provided with a number of
caeca, and there are a pair of Malpighian tubules; the anus is
terminal. The coxal glands are well developed; they consist
of a coiled tube, which it is suggested has been mistaken for
the Malpighian tubules; this opens at one end into a ventrally
placed sac, and at the other to the exterior at the base of the
third pair of legs.

The heart is a long dorsal vessel with three chambers and
three pairs of ostia. The nervous system consists of a bilobed
supra-oesophageal ganglion and a concentrated ventral mass.
There are no spinning-glands.

The Phalangids have no external indications of sex. Both

Fic. 239.—Phalangium cornutwm, Linn. (Harvestman). Profile, with legs and
palpi truncated.

a. Eye eminence. d. Sheath of penis protruded.
6, Chelicerae. e. Penis.
c. Portion of mouth apparatus. J. Glans.

TRACHEATA 419

ovary and testis are in the form of ring-shaped glands; the
ova are said to be fertilised in the ovary. The testes some-
times produce ova as well as spermatozoa. The female is
provided with a large ovipositor, and the male with a large
penis ; both of these structures are usually retracted within
a sac.

The females lay their eggs under stones or in crevices in
the ground during the autumn; the adults of both sexes then
die, so that until the eggs hatch out in the following spring no
Phalangid is to be seen. They are largely nocturnal in their
habits, and feed on small insects, spiders, etc., but at times
they are cannibal. Their long thin legs enable them to run
over grass and hay, and to steal with a “gliding spring” upon
their prey. There are about twenty-four species found in
Britain.

Cuass VII. Acarina (Mites).

CHARACTERISTICS.—Abdomen unsegmented and fused with thorax.
The oral appendages are adapted for piercing, sucking, or
biting. Tracheae usually present.

The mites comprise an immense number of species, which
vary greatly both in appearance and in habits; as a rule they
are minute in size with stout roundish bodies. Many of them
are parasitic on either plants or animals, others live on cheese,
etc., and some are predaceous.

Appendages of Acarina.

1, Chelicerae. 4, 2nd pair of walking-legs,
2. Pedipalpi. 5. 3rd a ss
3. Ist pair of walking-legs. 6. 4th 56 a

The chelicerae are clawed or chelate, or they may form
piercing stylets, in which case they are protected by a sheath
formed by the base of the pedipalpi. The rest of the pedi-
palpus projects as a tactile palp, or may be clawed. The four
pairs of legs vary in different species, they usually end in a
pair of claws, but these may be replaced by a sucking-disk.
The claws are often wonderfully adapted to fit round the
hairs of animals upon which the mites may be living as ecto-
parasites,

ZOOLOGY

The alimentary canal is often provided with salivary
glands ; the stomach may give off numerous caeca, which in

iL € A /,

Fic. 240.—Cheyletus jlabellifer

(Book Mite, quite unconnected
with books).

some cases are forked. The stig-
mata are two in number, situated
near the hind pair of legs, the
tracheae may be long and fine, in-
terlacing with the viscera, but in
some species (Nothrus) they are
short and thick, and in Hoplophora
they are still shorter and end in
swollen vesicles.

As a rule a circulatory system is
absent, but the GAMASIDAEB, or beetle
mites, are described as having a two-
chambered heart with two pairs of
ostia.

A coxal gland has been de-

scribed, but no opening to the exterior has yet been found.
The nervous system is very concentrated, one or two pairs of
eyes may be present or these organs may be entirely absent.
The male and female generative glands are very much alike ;
as in Phalangids, they form a ring. Their external opening is
on the anterior end of the abdomen or between the last pair of
legs. The Acarina are oviparous, the young are hatched with

three pairs of legs and undergo a num-
ber of ecdyses. Sphaerogyna ventricosa
is said to give birth to mature mites
which are fertilised as soon as. born.

The Acarina are divided into many
families, some of which may be men-
tioned. The DERMATOPHILI comprise
one genus, Demodex, which is found
living in hair follicles both in domesti-
cated animals and in man. It has a
suctorial rostrum, four pairs of rudi-
mentary legs, and a long annulated
abdomen.

Fic. 241.—Demodex folli-

culorum, Simon.

Under side.

a, Rudimentary legs.

b.

Abdomen.

The SARCOPTIDAE are microscopic mites which live parasitic-
ally in the skins of mammals, and give rise to diseases known

TRACHEATA 421

as the mange or the itch. The female Swrcoptes scabei makes a
tunnel in the skin and sits at the inner end, pushing the eggs

towards the exterior as they are
laid.

The PHYTOPTIDAE are gall mites,
and make amongst others the curious
conical excrescences which are so
common on the leaves of lime trees,
maples, etc. In many of them the
posterior pair of legs are replaced by
bristles.

The HyYDRACHNIDAE or water-
mites are usually brightly coloured.
They often hang on to water-insects,
and may be frequently found attached
by their rostrum to Dytiscus, Nepa,
etc. One species, Atax bonzi, is
common in the mantle-cavity of Unio.

Fic. 242.—Sarcoptes scabei (the
Itch Mite), female. After
Meguin.

The TROMBIDIIDAE are brightly-coloured mites, whose larvae

Fig. 243.—Izodes aegyptius, Savigny.

a. Chelicerae. d. Thorax.
6, Pedipalpi. jf. Abdomen.
c. Head.

often live parasitically on spiders or insects. Some of them,
as Tetrarhyncus teleariuvs, commonly known as the red spider

422 ZOOLOGY

spin webs under leaves, in which whole colonies of the mites
dwell.

The Ixoprmpak or ticks are blood-sucking mites which live
on undergrowth in forests; the females crawl upon man,

! Fic. 243.—The same (Jzodes aegyptius) ; under side.

a. Chelicerae. e, f. Maxillae and labium soldered
6, Pedipalpi. together.

c. Genital aperture. g. Sternum.

d, Anal aperture. 1-7, Joints of leg.

cattle, or even snakes, and attach themselves by their strong
rostrum. They suck blood to such an extent that their bodies
sometimes swell to the size of a small walnut.

The TYROGLYPHIDAE include Tyroglyphus siro, the cheese
or flour mite, and several other species which feed on vegetable
substances.

CHAPTER XXI

CHORDATA

Enteropneusta—Balanoglossus.
HeMICHORDATA 4 Cephalodiscida—Cephalodiscus.
Rhabdopleurida—Rhabdopleura.

Larvacea—A ppendicularia.

. Thaliacea—Doliolum, Salpa.
CHORDATA < Urocuorbara (Tunicata) Wacidinecs =! Olona, ‘Botr#llue, Pyro:
soma.

CEPHALOCHORDATA—A mphioxus.

VERTEBRATA.

I. Hemicuorpata (Enteropneusta, etc.)
II. Urocuorpata (Ascidians or Tunicata).
III. CEPHALOCHORDATA.
IV. VERTEBRATA.

CHARACTERISTICS.— The phylum Chordata consists of coclomate
animals characterised by (i.) the possession of gill-slits or
apertures leading from the pharynx to the exterior, these
may persist through life, or they may be but temporary
openings existing only in the embryo; (ii.) by the presence
of a skeletal rod, the notochord, which is formed in the dorsal
middle line by cells budded off from the hypoblast of the
embryo ; (iii.) by a dorsal nervous system, which, with a few
exceptions, is tubular and does not form a nervous ring
round the alimentary canal; (iv.) by the segmentation of
the mesoblast, which, although often obscured in later life,
is always found in the earliest stages.

From some points of view the Chordata is the most im-
portant of the various phyla which make up the animal
kingdom. The first three groups are either degenerate or

424 ZOOLOGY

contain but few species; the fourth group, however—the
Vertebrata—has, from the size of its numerous members and
the great variety of form they present, and above all from the
fact that it culminates in the genus Homo, acquired a great
importance, and it was formerly customary to oppose this
eroup of Vertebrata to the remainder of the animal kingdom,
which were classed together under the general heading Inverte-
brata. This division of the animal world was to a great extent
supported by the fact that much more was known about the
anatomy and developement of the comparatively conspicuous
Vertebrata than about the much less accessible and often
minute Invertebrata, but in late years our knowledge has been
much increased in the latter direction, and it is now recognised
that the group Vertebrata is, from a strictly morphological
standpoint, of no greater interest than any of the other large
eroups which compose the animal kingdom,

Ciass I. Hemichordata.

CHARACTERISTICS.— The anterior end of the body forms an elon-
gated proboscis, at the base of which the mouth opens. The
region surrounding and immediately behind the mouth ws
termed the “collar,” and this is succeeded by a trunk con-
taining the generative organs. A series of pores or gill-
slits are generally present. A diverticulum of the pharyna
projects forward into the proboscis-stalk and forms the noto-
chord, The sexes are separate.

The Hemichordata are a group recently constituted by
Bateson to contain the genus Balanoglossus. Harmer’s investi-
gations on the structure of Cephalodiscus have shown that that
genus must be assigned a place near balanoglossus, and still
more recently Fowler’s researches have shown that Rhabdo-
pleura rnust also be included in the group. The two last-
named forms were previously placed in the neighbourhood of
the Polyzoa; at present we know nothing of their embryology.
The group now comprises the three sub-classes (1.) Entero-
pneusta, (ii.) Cephalodiscida, (111.) Rhabdopleurida, each repre-
sented by a single genus.

CHORDATA 425

Sub-class I. ENTEROPNEUSTA.

CHARACTERISTICS.—Soft worm-like animals with ciliated ectoderm.
The trunk, succeeding the collar, is long and somewhat
flattened. The alimentary canal is straight, and the anus
opens at the end of the trunk. There are numerous gill-
slits, which inerease in number during life.

There are several species of alanoglossus described.

Fic. 244,—View of an adult male Balanoglossus Kowalevskit. Magnified one and a
half times. After Bateson.

1. Proboscis. 6. Mouth.

2. Collar, 7. Gill-slits.

3. Trunk. 8. Lateral edge of the body where it
4. Region of Testes. becomes flattened.

5. Tail. 9. Anus.

B. clavigerus and minutus are found in the Bay of Naples,
B. salmoneus and robinii off the coast of Brittany. The

426 ZOOLOGY

species which is in the main described below is B. kowalevski,
which, together with B. brooksii, is found on the east coast of
the United States.

Balanoglossus differs from other members of the phylum
with which it is grouped in the fact that its body is covered
externally with cilia, and in this respect it resembles a Nemer-
tine. The ciliated epidermis contains a considerable number
of unicellular mucous glands, which secrete a very copious
mucus. This secretion serves to line the tubes in the sand
and mud in which the animal lives. In one species the
mucus hardens into a definite tube, in the walls of which
grains of sand are embedded. The body of Balanoglossus has
usually a very characteristic odour.

The body-cavity or coelom consists of a single unpaired
portion occupying the proboscis, a paired portion in the collar,
and a paired portion in the trunk. These are derived from
five coelomic pouches of the archenteron of the embryo. The
original cavities of these are, however, much obliterated by the
growth of stellate connective tissue cells (Fig. 245). The spaces

: Fia. 245.—Section, partly diagrammatic, through
$+ 7-3 the respiratory part of the trunk of Balano-
Zz NS glossus. The whole course of a gill-slit
a 8 could not be seen in a transverse section, as
the slits run obliquely.

en
atta

Dane ur Ya

"io
1. Dorsal portion of alimentary canal. 7. Nerve plexus at the base of the skin.
2. Ventral portion of alimentary canal. 8. Longitudinal muscle fibres.
3. Dorsal nerve cord, in the skin. 9. Connective tissue cells filling up the
4, Dorsal blood-vessel. coelom.
5. Ovary. 10. Ventral blood-vessel.
6. Gill-slit. 11. Ventral nerve in the skin.

between the cells communicate with the exterior in the pro-
boscis by a ciliated proboscis pore,—in one species this is
paired,—and the right and left collar cavities open to the
exterior by a right and left ciliated collar pore. These latter

CHORDATA 427

have been compared to the “brown tubes” of Amphioxus.
Underlying the epidermis is a well-marked layer of longitudinal
muscle fibres. The muscles of the trunk show no trace of
metameric repetition.

The mouth opens ventrally between the base of the proboscis
and the anterior rim of the collar. It leads into a straight
alimentary canal. The anterior half of the digestive tube is
partially divided into a dorsal and ventral half by two lateral
horizontal folds. The gill-slits open into the dorsal half.
Behind the region of the gill-slits the intestine is characterised
by a ciliated dorsal and ventral groove. In some species
paired hepatic caeca open at intervals into this region, and in
at least one species these diverticula are described as opening
on to the exterior. A median dorsal and ventral mesentery
support the intestine.

In the region of the collar the alimentary canal gives off
a diverticulum, which grows forward and supports the pro-
boscis. The cells of this diverticulum become vacuolated, and
assume an appearance which is common in the notochordal
tissue of higher animals. The lumen of the diverticulum
disappears, except at its base, and the whole structure, which
extends through but a short region of the body, has been
regarded as a notochord. This interpretation is supported
both by its mode of origin and its structure. On the other
hand, the chief blood-vessel is dorsal to it, instead of being
ventral to it, as in the higher Chordata.

The paired gill-slits are visible externally as small pores
situated in the dorso-lateral grooves of the anterior portion of
the trunk. Each gill-slit opens internally into the dorsal
thick-walled section of the alimentary canal. They increase
in number throughout life, new slits arising behind those
already existing. When they first appear they are circular in
outline, but, as is the case in Amphioxus, a tongue-like process
grows down from the dorsal surface and reduces the opening
to a U-shaped aperture. Between neighbouring gill-slits and
in the tongue-shaped process there is a skeletal rod, the whole
forming a branchial skeleton comparable with that of Amphi-
oxus. The gill bars receive a supply of blood from the dorsal
blood-vessel, and water passes through the gill-slits from the

428 ZOOLOGY

alimentary canal to the exterior. The slits are arranged
obliquely, so that in a single transverse section it is impossible
to see the whole course of any one. In the section (Fig. 245)
the gill-slit has been drawn diagrammatically.

The posterior edge of the collar projects backward over a
few of the anterior gill-slits, the number varying in different
species. This fold is termed the opercular fold, and the recess
covered in by it has been regarded as a rudimentary atrial
cavity.

The vascular system comprises a dorsal vessel which
extends from the tail to the heart. The latter is a thin-

Fic. 246.—Diagrammatic longitudinal vertical
section through the anterior end of Balano-
glossus minutus. Slightly altered, after
Bateson.

1. Dorsal nerve cord.

iw)

Central nervous system (7.e. in the coliar
region).

Cord running from the central nervous system
to the skin.

. Ring of nervous tissue round the collar.

Ventral nerve cord.

. Dorsal blood-vessel.

. Heart.

. Ventral blood-vessel.

co ST Os OU >

. Proboscis gland.

. Notochord.

. Cavity of proboscis.
. Cavity of collar.
Mouth.

Gill-slits.

. Oesophagus.

eS Se eS eR ee
oO rF OF De CO CO

walled pulsating vesicle lying in the base of the proboscis, just
dorsal to the anterior end of the notochord. The heart is

CHORDATA 429

connected with a plexus of capillaries ramifying in a glandular
structure, which forms a cap to the anterior end of the noto-
chord. This is termed the proboscis gland. From the
posterior end of the collar a well-developed ventral vessel
passes backward, supported like the dorsal vessel in a median
mesentery. These chief vessels are placed in communication
with one another by plexuses of capillaries in the skin and in
the walls of the alimentary canal, and the skin plexus is
specialised into a more or less definite circular vessel connect-
ing the dorsal and ventral vessel in the opercular fold or the
posterior edge of the collar. The blood is said to be free from
corpuscles, but the fluid which occupies the remnants of the
coelom contains amoeboid corpuscles. The course of the
blood is forward in the dorsal, and backward in the ventral
vessel.

The nervous system consists of a dorsal and ventral cord,
which lie in the skin, and extend from the anus to the posterior
edge of the collar; at this level the ventral cord divides into
two strands, which pass round the alimentary canal and join
the dorsal cord (Fig. 246). The dorsal cord in the region of
the collar has lost its connection with the epidermis, and by a
process of delamination, aided by invagination at its ends, has
come to form a partially tubular cord. This is the portion of
the nervous system in which the cellular elements are to a great
extent aggregated. Its posterior end receives the dorsal nerve
and the two branches of the ventral nerve. In some species
three nerves arise from this central nervous system and pass
towards the dorsal skin, these three nerves have been compared
to the dorsal roots of spinal nerves in Vertebrates. Anteriorly
this central nervous system is continuous with a well-marked
sub-epidermic plexus of nerve fibrils which exists in the pro-
boscis (Figs. 246 and 247); a similar network lies in the skin
of the trunk, and is continuous with the dorsal and ventral
nerves.

The various species of Balanoglossus are all dioecious.
Both ovaries and testes consist of sacs which open directly on
to the epidermis, from which they are probably derived. These
sacs occur in the region of the gill-slits, and open externally to
the latter; they are also found serially repeated along that

430 ZOOLOGY

part of the trunk which succeeds the branchial region. The
ova do not escape singly through the external orifice, but the
whole follicle breaks away and then disintegrates.

The systematic position of Balanoglossus has given rise
to much divergence of opinion amongst zoologists. Bateson’s

Fie. 247.—Section through Balanoglossus behind the region of the gill-slits.

2. Alimentary canal supported byadorsal 7. Nerve plexus at the base of the

and ventral mesentery and showing epidermis.
the dorsal and ventral grooves lined 8&8. Longitudinal muscle fibres.
by long cilia. 9. Connective tissue cells filling up the
3. Dorsal nerve cord in the skin. coelom.
4. Dorsal blood-vessel. 10. Ventral blood-vessel.
5. Ovarian follicles, opening to the 11. Ventral nerve cord in the skin.
exterior.

recent researches on the embryology of this form, however,
justify us in placing it amongst the Chordata, but it has
affinities in at least two other directions. Certain species,
in the course of their developement, pass through a larval
stage termed the Yornaria, which shows the closest resem-
blance to the characteristic Bipinnaria larva of the Echino-
dermata. The presence of this larva in the ontogeny of
these two groups seems to point to some connection between
their remote ancestry, and this to some extent is emphasised
by the fact that the Echinodermata, like Balanoglossus, are
ciliated externally. Again, the structure of the body-wall, its
external ciliation, the form of the body, the absence of seg-
mentation in the muscles, the structure of the generative
organs, and perhaps the proboscis, are all features which recall
the similar parts in the Nemertines.

CHORDATA 431

Sub-class I]. CEPHALODISCIDA.

CHARACTERISTICS.— The pharynx is pierced by one pair of gill-
slits. The alimentary canal has a neural flexure, so that
the mouth and anus are approximated. The collar bears
twelve tentacular plumes, which are hollow ; their cavities are
continuations of the collar cavity.

This sub-class contains one species, Cephalodiscus dode-
calophus, which, owing to Harmer’s researches, has been

AG

4 i \ ; i:

i

Fic. 248.—Ventral view of Cephalodiscus dodecalophus. After M‘Intosh,

1. Tentacular plumes.
2. Bud at the end of pedicle, two others are also shown.
3. Proboscis.

associated with Balanoglossus, and placed in the group Hemi-
chordata. Cephalodiscus is an organism which reproduces by.
budding, and it has a certain superficial resemblance to some
Polyzoa, but it shows closer affinities to Balanoglossus in its
internal anatomy. It resembles the last-named genus in the

432 ZOOLOGY

division of its body into three regions,—the proboscis, collar,
and trunk,—and in the arrangement of its coelomic cavities and
the possession of proboscis- and collar-pores. Moreover, it is
provided with gill-slits, with a diverticulum of the alimentary

Fie, 249.—Longitudinal section of an
adult Cephalodiscus, supposed to
be taken sufficiently on one side
of the middle line to allow of the
representation of one of the ovaries,
and of one of the proboscis pores.
After Harmer.

. Proboscis.

i 7. Ovary.
21, Body-cavity of proboscis. 8. Anus.
2°. Body-cavity of collar. 9. Pigmented oviduct.
28, Body-cavity of trunk. 10. Central nervous system.
3. Notochord (really visible only ina 11. One of the proboscis pores.
median section). 12. Mouth.
4. Operculum. 13. Pharynx or branchial region of gut.
5. Pedicle or stalk cut through. 14. Oesophagus.
6. Intestine. 15. Stomach.

canal (notochord) growing into the proboscis stalk, and with
a nervous system which closely resembles that of Balanoglossus.

Cephalodiscus has only been found once. It was dredged
in the Straits of Magellan by the “Challenger” from a depth
of 245 fathoms. The various “ polypides,” with their budding
pedicles, live inside a coenoecium or tubular case secreted around
them, in much the same way as Appendicularia secretes its
“house.”

Sub-class III. RHABDOPLEURIDA.

CHARACTERISTICS.—Gill-slits and proboscis pore absent. The
intestine has a neural flexure. There are two tentacular
plumes having the same relation as in the Cephalodiscida.

CHORDATA 433

Lhabdopleura normani has been dredged in the Hardanger
Fjord, off the Shetlands, and off one of the islands of the
Tristan d’Acunha group. It consists of an irregularly branch-
ing colony attached to foreign bodies. The zooids are very
minute; they are connected by a stem, and the whole is
ensheathed in a tubular investment, probably secreted by the
proboscis (epistome). A pair of processes bearing tentacles,
into which the cavity of the collar space is continued, exist,

Fic. 250.—Side view of Rhabdopleura normani. Partly diagrammatic. After
Lankester and Fowler.

TID OU Oo DO Ht

. Proboscis (epistome). 8. Notochord.
. Mouth. 9. Dotted line indicating the division
. Stomach. between the regions of the body
. Intestine. and of the collar.
Anus. 10. Dotted line indicating the division
Stalk. between the regions of the collar
. Right tentacular arm, only one row and of the proboscis,

of tentacles is shown on each arm.

The animal is represented as transparent to show the alimentary canal and notochord.

and closely resemble the similar structures in Cephalodiscus.

The zooids creep up the tube in which they are enclosed by

means of the proboscis, and are retracted by means of muscle
28

434 ZOOLOGY

cells. The relations of the notochord, a solid diverticulum
of the pharynx, correspond with those of Balanoglossus and
Cephalodiscus.

Cuiass Il. Urochordata (Tunicates or Ascidians).

CHARACTERISTICS.— Hermaphrodite Chordata, with free-swimming
larvae, which usually become sessile and degenerate adults.
These are either solitary or form colonies. In the adult the
nervous system is, with few exceptions, reduced to a single
ganglion, the elongated nervous system and the notochord
being confined to the larval stages. A metamorphosis usually

OCCUPS,

Fig. 251.—<Ascidia mentula, from the right side.
After Herdman.

br. Branchial aperture.

at. Atrial aperture.
Pomnests

The simple Ascidians—Ascidiae simplices—have a more
direct life-history, and to some extent a less modified structure

CHORDATA 435

than many of the other members of Urochordata. Ciona
intestinalis, which may serve as a type of this group, is
abundant in the Mediterranean, and is found widely distributed
in temperate seas. It is a hyaline transparent creature, when
young presenting the appearance of opalescent glass, but as it
grows old it is apt to become overgrown with foreign organ-
isms, etc., and presents an opaque appearance. It attains a
length of 5 or 6 inches.

At one end the Ciona is attached to a rock or some other
foreign substance, at the other end the mouth is situated,
surrounded by eight lobed processes, this may be regarded
as the anterior end of the animal. About an inch behind
the mouth, and on that side of the animal which may be
regarded as the dorsal, another aperture surrounded by six

Fic. 252. — Diagrammatic

section of part of mantle

and test of an Ascidian,

showing the formation of
a vessel and the structure
of the test. After Herd-

man,

m. Mantle. s, s’. Blood sinus in mantle being drawn
e. Ectoderm. out into test.

tc. Test cell. mc. Mantle cells.

tm. Matrix. y. Septum of vessel.

ble. Bladder cell.

lobes is found; this is the atrial pore, and through this the
water which has passed through the perforated pharynx and
purified the blood, the waste matter from the intestine, and the
generative cells are all discharged.

The whole animal is enveloped in a hyaline ¢wnic or test,
which is a cuticular excretion of the ectoderm, and into which
ectodermal cells and blood-vessels wander. The test is turned
in for a short distance at both the oral and atrial openings; at

436 ZOOLOGY

the posterior end it is produced into various processes and
lobes which fit into crevices of the rock, ete., and serve to fix
the animal; the true skin or dermis is continued into these
processes. The gelatinous substance which composes the test
of Ciona contains numerous cells split off from the ectoderm ;
in the genus in question many of these cells soon die, but in
others they live for some time, forming fusiform or stellate
cells, often pigmented, or they develope a large vacuole (Fig.
252), or in some genera they secrete calcareous spicules. The
test is undoubtedly a cuticle secreted by the ectoderm, but it
is kept alive to a certain extent by the cells which wander
into it, and by the blood-vessels which make short incursions
into it. The test contains in many instances a chemical
substance identical or closely allied to cellulose, a substance
rarely met with in animals, but almost universal in plants.
Kowalevsky has recently shown that in some species the cells
which wander into the test arise from the mesoderm, and pass
through the ectoderm on the way to their final resting-place
in the test.

The ectoderm, which secretes the test, forms a single layer
of cubical cells; beneath this is a layer of muscles arranged
in large longitudinal bands, with few anastomoses, and
numerous small transverse bands, which anastomose freely.
Nerves and blood sinuses also ramify in the skin.

The general disposition of the organs of the body in a
simple Ascidian is as follows: the mouth leads into a large
branchial sac, which extends throughout four-fifths of the
body; this is pierced by very numerous slits, which, instead
of opening directly to the exterior, communicate with a large
chamber, the atrial cavity, which completely surrounds the
branchial sac, except along the middle ventral line, and which
opens to the outside world through the atrial pore. The
atrial cavity is produced originally by an invagination from
the exterior, and is consequently lined throughout by ectoderm.
Behind the branchial sac, occupying the posterior fifth of the
animal, is a closed space, in which the stomach, heart, and
generative organs are enclosed; the intestine and ducts of the
reproductive glands run up the dorsal surface of the branchial
sac, and open into the atrial chamber, the latter near its pore.

CHORDATA 437

A constant current of water, maintained by the action of
the cilia lining the pharynx, enters the mouth and passes out
through the slits in the branchial sac into the atrial cavity,
and out at the atrial pore, carrying with it the waste matter

Fic. 253.—Diagrammatic dissection
of Ascidia mentula to show the
anatomy of a simple Ascidian.
After Herdman.

at. Atrial aperture.
br. Branchial aperture.
a. Anus.
brs. Branchial sac.
dl. Dorsal lamina.
dt. Dorsal tubercle.
end. Endostyle.
h. Heart.
z. Intestine.
m. Mantle.
ng. Nerve ganglion.
c. Oesophagus.
@.a. Oesophageal aperture.
ov. Ovary.
por. Peribranchial cavity.
7. Rectum.
st. Stomach.
(i UNG
tn. Tentacles.
vd. Vas deferens.
ngl. Subneural gland.

from the alimentary canal and also the generative products
when ripe.

A little distance within the oral opening is situated a ring
of tentacles, which project across the mouth and _ possibly
function as a filter; the area between this ring of tentacles
and the branchial sac is termed the prebranchial zone. The
branchial sac is a large space with perforated walls; it is
attached to the mantle or body-wall along the median ventral
line, and the large ventral blood-vessel, which communicates
behind directly with the heart, is situated along this line of
attachment. The rest of the branchial sac is separated from
the mantle by the peribranchial or atrial chamber, which
opens to the exterior by the atrial pore. The rectum and

ZOOLOGY

438

Saath

atiinaegtanecstatemseearitt

ras

Both the branchial and

the atrial cavities have been opened by a longitudinal incision to display the in-

ternal organs.

g on its right side.

View of Ciona intestinalis lyin

Fia. 254.

branchial sac to the stomach, rather

6. Oesophageal opening leading from the
diagrammatic.

5, Endostyle.

3)

3

mM

i

3

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qi

SE

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Base

m ec

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= =
Ss co

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CHORDATA 439

the genital ducts run for some distance along the dorsal
middle line, and with these runs the dorsal blood-vessel.
The walls of the branchial sac are also connected with the
mantle at irregular intervals by blood-vessels, which pass from
the bars to supply the substance of the mantle. The branchial
bars run at right angles to one another, and leave between
them small ciliated slits or stigmata, through which the water
taken in at the mouth escapes into the peribranchial chamber,
the current being maintained by the cilia. The transverse
bars contain blood-vessels communicating with the dorsal
and ventral blood-vessels. Connecting two adjacent transverse
bars are a number of small longitudinal bars, which divide the
space up into the stigmata. There are two kinds of transverse
bars, the primary and the secondary, the latter being the
smaller. In addition to the small longitudinal bars, there are
also some large ones situated in a different plane from the
others, farther inside the branchial sac; these are connected
by a short vessel with the transverse bars at their points of
intersection (Fig. 256), and at the same spot they give off
little finger-shaped processes, which hang into the lumen of
the sac.

A ciliated groove, known as the hypopharyngeal groove or
endostyle, runs along the ventral line of the branchial sac
(Fig. 254). The lips of the groove project into the cavity
of the sac, and it is lined by cells which are partly glandular
and partly ciliated. At the posterior end it is continued into
a cul-de-sac, which has a slight spiral twist ; anteriorly its lips
are continuous with the peripharyngeal bands, two ciliated
ridges which encircle the anterior end of the branchial sac

7. Stomach. 16. Heart.
8. Intestine showing typhlosole, part 17. Ovary.
of it removed to show subjacent 18. Pore of vas deferens. The openings
structures. of the oviduct and the vas deferens
9. Rectum. are shown enlarged to the right.
10. Anus. 19. Testicular follicles on intestine; the
11. Atrial aperture. greater part of them have been
12. Inner surface of mantle, showing removed with the intestine.
longitudinal and transverse muscle 20. Oviduct.
fibres. 21. Septum shutting off that part of
13. Dorsal tubercle. the body-cavity which contains
14. Subneural gland and brain. the heart, stomach, and generative

15. Cut edge of branchial sac. organs.

440 ZOOLOGY

and form the posterior limit of the prebranchial zone (Fig.

. 255.—Transverse section through
© the branchial region of a Ciona intes-
tinalis. After Roule.

1. Atrial chamber. 8. Rectum.
2. Branchial chamber. 9. Oviduct.
3. Test. 10. Vas deferens.
4, Mantle. 11. Ciliated endostyle.
5. Vessel passing from a branchial bar 12. Branchial slit, stigma.
into the mantle. 13. Branchial bar connected with mantle.
6. Ventral blood-vessel at base of endo- 14. Muscle fibres.
style. 15. Dorsal lamina.
7. Dorsal blood-vessel at base of dorsal
lamina,

254). The anterior of these two ridges is the most pro-
minent; it forms a simple circle; the posterior is, however,

-Tr
Fig. 256.
A. Part of branchial sac of
Ascidia from inside.
B. Transverse section of same, “sg
drawn to different scale. ons \V, a VEVAVAVAY:
tr. Transverse vessel. O hei rn iia
d. Connecting duct. aay fasta a

hm. Horizontal membrane.

° . . hm Crest
il. Internal longitudinal bar, \ Ae

lv. Fine longitudinal vessels.

p, p'. Papillae.

sg. Stigmata.

continuous with the dorsal lamina, a structure which runs

CHORDATA 441

along the dorsal middle line of the branchial sac. In Ciona
the dorsal lamina is divided up into a number of langquets,
or tongue-like processes, which hang into the lumen of the
sac (Fig. 254). One of these is given off at the level of each
transverse vessel, and in this and some other respects they
resemble the finger-like processes borne on the longitudinal
bars. The dorsal lamina extends to the end of the branchial
sac, and terminates close to the mouth of the oesophagus.

Ciona lives upon minute organisms, etc., which float into
the branchial sac with the water which is continually stream-
ing through the body. These small particles become entangled
in strands of mucus, and are directed to the dorsal lamina by
the action of the cilia borne by the peripharyngeal groove
and the endostyle or hypopharyngeal groove; the languets of
the dorsal lamina, or epipharyngeal band, guide the food into
the entrance of the oesophagus. The mucus which serves to
entangle the food particles is probably partly secreted by the
glandular cells of the hypopharyngeal groove, but probably
also to a great extent by a gland which is situated under the
central nerve ganglion.

This glandular structure, usually known as the subnewral
gland, is a compact body with few ramifications; its duct
opens by a flattened mouth, which sometimes is folded in the
most complicated fashion, but in Ciona is curved into a simple
horse-shoe, situated dorsally near the posterior margin of the
prebranchial zone. This gland has been regarded by some
writers as homologous with the hypophysis cerebri of the
Vertebrate brain. Some authorities have regarded this gland
as a renal organ, but its function is more probably to secrete
the mucus in which the food particles become entangled.

The mouth of the oesophagus is an oval slit situated at
the dorsal side of the branchial sac close to the end of the
dorsal lamina, it leads into a short transparent tube, the oeso-
phagus, which soon expands into the spherical stomach. There
are no muscle fibres in the wall of the oesophagus, nor indeed
in the whole length of the alimentary canal, except in the
rectum; the food is propelled onward by means of the cilia
which line the digestive tract. The stomach is large, and its
posterior half is covered by the follicles of the testis; it leads

442 ZOOLOGY

into the intestine, the first part of which is also covered by
the same structures (Fig. 254). The intestine makes a shght
twist round the ovary, and is then continued into the rectum,
which runs straight along the dorsal wall of the branchial sac

Fic. 257.—Mouth of the subneural gland and neighbouring parts in Ascidia
mentula. After Herdman.

egr. Epibranchial groove. dl. Dorsal lamina.

pp. Peribranchial groove. sgd. Duct of subneural gland.
tn. Tentacles, il. Internal longitudinal bars.
sg. Stigmata, z Peribranchial zone.

dt. Opening of duct of subneural gland.

and opens into the atrial cavity. The internal surface of the
first part of the intestine is much increased by the existence of
a typhlosole which projects into its lumen.

The heart is contained in a pericardium situated ventral
to the oesophagus in the angle between the posterior limit of
the branchial sac and the stomach (Fig. 254). The peri-
cardium contains a corpusculated fluid, its cavity is derived
from the original coelom of the larva. The heart is a cylin-
drical tube bent into the shape of a V, the angle pointing
dorsalwards. One arm of the V is continuous with a ventral
or branchio-cardiac vessel or sinus which runs along the line

CHORDATA 443

of attachment of the hypopharyngeal groove; the other arm
is continued into a cardio-visceral vessel, which breaks up into
many splits or sinuses amongst the viscera. From these splits
in the tissues of the various organs the blood passes into a

Fic, 258.—Diagram of
circulation in a simple
Ascidian. Herdman.

br. Mouth. z. Intestine.
at. Atrial aperture. bc. Branchiocardiac or ventral vessel.
a. Anus. cv. Cardiovisceral vessel.
brs. Branchial sac. vb. Viscerobranchial or dorsal vessel.
oe. Oesophagus. vt. Vessels to test.
h. Heart.

viscero-branchial vessel situated at the base of the dorsal
lamina. From this the blood passes into the vessels in the
lateral bars of the branchial sac which carry the blood down
to the ventral vessel, and it thus returns to the heart. A
peculiarity of the circulation in Ascidians is that its course
is from time to time reversed, after contracting for a certain
number of times in one direction the heart stops and then
recommences in the other, thus reversing the course of the
circulation.

The vessels arising from each end of the heart give off
branches into the test; these subdivide, and their smaller
branches usually end in spherical cavities (Fig. 252). They
probably serve to nourish the test and keep it alive, and in
some species they may possibly play some part in respiration.
The blood contains amoeboid and spherical corpuscles.

The cavity of the heart and of the blood sinuses con-
nected with it is directly derived from the blastocoel or
segmentation cavity of the embryo; this is an interesting fact,
taken in conjunction with the similar origin of the space of
the heart in the lamprey, and possibly in other Vertebrates.
The nature of the space in which the stomach, ovary, and
pericardium lie, is at present a matter of some uncertainty ;
it contains a corpusculated fluid.

444 ZOOLOGY:

The free-swimming larvae of the Tunicata are provided
with a tubular nervous system derived from the epiblast.
This has an enlarged anterior end into which ‘two unpaired
sense organs—a dorsal eye and a ventral auditory sac—project.
The rest of the nervous system is traversed by a canal, and in
its course along the tail of the larva it gives off paired nerves
to the segmentally arranged muscles. In the larva a noto-
chord also is present underlying the nervous system. When

Fic. 259.—Diagrammatie section through the an-
terior dorsal part of Ascidia mentula, showing
the relations of the nerve ganglion, subneural
gland, ete. After Herdman.

ti. Tentacle.

t. Test.

m. Mantle.

dt. Opening of subneural gland.
pp. Peribranchial band,

t’. Test turned in at mouth.
dl. Dorsal lamina.
sgd. Duct of subneural gland.
sgl. Subneural gland,

ng. Brain,

n. Anterior nerve.

n’. Posterior nerve.

brs. Branchial sac.

the larva fixes itself, the notochord and the greater part of the
nervous system atrophy. In Ciona the latter is reduced to an
oblong ganglion, situated just below the ectoderm and above
the subneural gland, in the angle between the oral and atrial
cones. The ganglion is solid, and gives off numerous nerves,
chiefly from its angles; these exhibit a rather marked asym-
metry, the nerves of the left side dividing close to their origin,
whilst those of the right remain for some distance un-
branched. The specialised sense organs of the larva have
atrophied.

Ascidians have no nephridia, and their nitrogenous waste

CHORDATA 445

matter is not as a rule expelled from the body, but is stored
up in certain cells in which the renal products continue to ac-
cumulate throughout life. In Ciona the renal cells are found
close under the epidermis, in the neighbourhood of the opening
of the vas deferens; they are of an orange colour, and con-
tain granules which give micro-chemical reactions character-
istic of uric acids and urates. It is the accumulation of these
cells which forms the orange-red ring around the external
opening of the vas deferens. The cells have no ducts, but
since they are separated from the surrounding water by but a
thin layer of epithelium, it has been thought that their excreta
may diffuse out. In other genera of simple Ascidians, the
renal cells are arranged around a vesicle into which they pour
their secretions; the cavities of these vesicles are closed, and
the nitrogenous waste matter does not leave the body. Like
the lumen of the genital glands and of the pericardium, the
cavities of these vesicles are possibly derived from the coelom.
The vesicles are usually of a brown colour, and are found in
the loop of the intestine, extending along its wall.

The Ascidians are hermaphrodite. In Ciona the testes con-
sist of numerous follicles branching over the stomach and
intestine ; these are whitish in colour, and their presence gives
this part of the alimentary canal a peculiar appearance; the
larger of the follicles gradually unite to form a narrow duct,
the vas deferens, whose wall is continuous with that of the
testis. The vas deferens runs along by the side of the rectum,
and ultimately opens into the atrial cavity about an inch in
front of the anus. The cells lining the cavity of the follicles
of the testis give rise to the spermatozoa. The latter are
minute, with small heads and long tails; they apparently
ripen and are discharged from the body at the same time as
the ova.

The ovary is a comparatively compact gland situated in
the general perivisceral space, in a loop of the intestine; the
ova are modified cells lining the walls of its cavity. The
walls of the ovary are continuous with the oviduct, which
runs alongside the vas deferens and opens into the atrial
cavity close behind the pore of the male duct. The oviduct
may be distinguished from the vas deferens by its large size,

446 ZOOLOGY

and often by the presence of ova in it; the vas deferens is
a very narrow duct of an opaque white colour.

The structure of an adult Ascidian, such as Ciona, shows
but slight resemblance to that of the more typical Chordata,
but if the life-history of one of these creatures be followed out,
it is seen that the larval stages are much more highly differ-
entiated than the adult, and that in all essentials they conform
to the type of the Chordata. The free-swimming tadpole

Fic. 260.—Stages in the embryology of a simple Ascidian. After Kowalevsky.
A. Embryo showing body and tail and ep. Epiblast.

completely formed neural canal. hy. Hypoblast.
B. Larva just hatched: the tail is cut ne. Neural canal.
off. oc. Ocular organ of larva.
C. Transverse section of tail of larva. m. Muscle cells of tail.
adp. Adhering papillae of larva. mes. Mesenteron.
at. Epiblastic atrial involution. mc. Mesoderm cell,
au. Auditory organ of larva. nv. Cerebral vesicle at anterior end of
ch. Notochord, neural canal.

larva of the simple Ascidians is provided with a tail, in which
is a Skeletal rod of supporting tissue, the notochord. Unlike
the same structure in other Chordata, this rod is confined to
the tail. Above this hes the tubular nervous system, which
gives off several pairs of nerves to the muscles of the tail; these
latter show some traces of metameric repetition. Anteriorly
the nervous system is enlarged, and a median eye and auditory
sac are connected with it. The origin of the various organs
in the larva closely resembles that of the other Chordata.
The gill-slits in the larva do not exceed a few pairs in
number, and it has been maintained that the numerous
stigmata opening through the walls of the branchial sacs

CHORDATA 447

do not correspond with so many gill-slits, but are rather sub-
divisions of a single original pair.

The Urochordata are divided into three orders: (i.) Larv-
ACEA, (ii.) THALIACEA, and (i11.) ASCIDIACEA.

Order 1. LARVACEA.

The Larvacea include but four genera, the best-known of
which is the genus Appendicularia. The members of the
group are of extreme interest, since they have undergone no
degeneration, but retain those features of the active larval
condition which are lost in the other members of the group.

Appendicularia, like the other Larvacea, is a minute free-

Fic. 261.—Semi-diagrammatic view of Appendicularia from the right.
After Herdman.

a, Anus. ot. Otocyst.
at, One of the atrial apertures. ov, Ovary.
app. Tail. pp. Peripharyngeal band.
brs. Branchial sac. ng. Cerebral ganglion.
br. Branchial aperture. ng’. Caudal ganglion.
dt, Dorsal tubercle. ng’. Enlargement of nerve cord in tail.
end, Endostyle. so. Sense organ (tactile) on lower lip.
h. Heart. sg. Ciliated aperture in pharynx.
i. Intestine. st. Stomach.
m. Muscle band in tail. tes. Testes.
n. Nerve cord in body. u. Notochord.
n'. Nerve cord in tail. uw’. Its cut end.
oe. Oesophagus.

swimming organism, found near the
parts of the ocean. Its body is divided into a short trunk and

surface of the water in all

448 ZOOLOGY

a long tail which is attached ventrally to the body and is bent
forward. The mouth leads straight into the branchial sac,
which opens directly to the exterior by two ciliated apertures ;
there is no atrial chamber. The hypopharyngeal groove is
short, and there is no dorsal lamina. There is an oesophagus
stomach and intestine which ends in the anus situated just in
front of the ciliated pores. The main nervous ganglion is in
connection with an otocyst and a pigment spot or eye, it gives
off posteriorly a nerve cord, which passes by the side of the
alimentary canal into the tail and then runs along the left
side of the notochord. In the tail the nervous axis enlarges
into several ganglia, which give off nerves to the surrounding
parts. The notochord is confined to the tail, and the muscles
in the same region are broken up into segmentally repeated
bands. The heart is said to be composed of two cells. The
testes and ovaries are at the posterior end of the body, and
open directly to the exterior.

Appendicularia, like the other members of the order, pos-
sesses the power of secreting with extraordinary rapidity a
temporary gelatinous covering or test, which corresponds with
the test of Ciona. This test is, however, soon cast aside, but
another one may be formed shortly afterwards.

The Larvacea do not reproduce by budding, and their
developement is direct.

Order 2. THALIACEA.

This order contains certain free-swimming forms, which in
the adult state are not provided with a tail with notochord,
etc. Some members of this order, as Doliolum, are single
animals with a complicated alternation of generations in their
life-history. The sexual form is hermaphrodite, and the ovum
gives rise to tailed larvae which grow into asexual forms dif-
fering slightly from the sexual generation. These asexual
forms reproduce by budding. The buds develope into the
sexual generation, which is complicated by being polymorphic ;
there being three forms, of which only one has functional
generative organs.

Other members of this group present still greater com-

CHORDATA

plexities, since the sexual generations form colonies.
Salpidae are the most striking example of this.

is

449

The
The solitary

Fic. 262.—Doliolum denticulatum, sexual generation from the left side.
After Herdman.

. Muscle bands.

.. Nerve ganglion.

. Stigmata.

. Subneural gland.

. Peribranchial cavity.
. Atrial lobes.

. Sense organs,

. Branchial lobes.

. Dorsal tubercle.

. Nerves.

form
chain or stolon of embryos.

or smaller groups, and
sexual organs.

Fia.

gem.

. Atrial aperture.

.. Ovary.

z. Intestine.

. Stolon of buds.

. Heart.

Testis.

Branchial sac.
Endostyle.
Peripharyngeal band.

pp.
br. Branchial aperture, mouth.

of this family gives rise by a process of budding to a
These become detached in larger

263.—Posterior part of the solitary form
of Salpa democratica-mucronata, showing
a chain of embryos nearly ready to be set
free. After Herdman.

Young aggregated Salpae forming the

chain,

. Stolon.

. Muscle band.
mest:

. Visceral mass.

each of them when mature produces
Their ova when fertilised give rise to the
29

450 ZOOLOGY

solitary forms. The sexual forms are always protogynous, the
ovum reaching maturity before the spermatozoon ; thus self-im-
pregnation is prevented.

All the members of this order are pelagic, and, as is usual
with those animals which live at the surface of the sea, they
are very transparent, or of a bluish hue.

Order 3. ASCIDIACEA.

This order includes some forms, such as Ciona, which are
fixed, and rarely reproduce by budding; but it also includes
certain free-swimming pelagic colonies of Ascidians, and certain
fixed colonies the individuals of which have no separate tests,
but are embedded in a common mass, which increases by gem-
mation. In the free-swimming forms the individuals are
arranged in a cylinder with their mouths on the outer side
and their atrial openings abutting on the hollow of the cylinder.
There is but one genus of these pelagic forms, Pyrosoma, which
includes, however, many species.

INDEX

The names of Genera are printed in Italics.

ABDOMINALIA, 278
Acanthia, 364
Acanthiidae, 364
Acanthocystis, 18
Acanthodrilus, 145, 147,
149
Acanthometra, 21
Acarina, 419
Acetabulifera, 210
Achaeta, 159
Acherontia, 354
Acineta, 32, 33
Acinetaria, 32
Acoela, 88, 89, 93
Acoelomata, 36, 47
Acontia, 67
Acridiidae, 337
Acridium, 339, 342
Actinia, 64, 67, 68
Actiniaria, 68
Actinophrys, 17, 18
Actinopoda, 251
Actinosphaerium, 18, 19
Actinozoa, 47, 61, 63,
278
Aculeata, 380
Adamsia, 67
Adradii, 61
Aegir, 64
Aeolosoma, 144, 150
Aethalium, 9
Agelena, 412, 416
Agelenidae, 416
Agrion, 347
Agrotidae, 353
Akrostoma, 122
Alcippe, 278
Alcyionidae, 73
Alcyonaria, 64, 71
Alcyonidium, 185
Alcyonium, 73
Alloiocoela, 94
Alpheus, 290
Alphidius, 380

Alternation of generations,
47, 81, 102, 104, 158,
364, 448

Alucita, 351

Alula, 370

Amaurobius, 413

Ambulacra, 225, 241, 246

Ammonitidae, 222

Amoeba, 5, 9, 10

Amoebula, 8

Amphilina, 104, 105

Amphipoda, 290

Amphiptyches, 104

Amphiura, 235

Ampullaria, 288

Anal respiration, 268, 347

Anceus, 290

Andricus, 379

Androctonus, 395, 398

Anguillulidae, 128

Animal kingdom, 2

Anisopleura, 196

Anisopoda, 297

Annelids, 34

Anobothrium, 105

Anodonta, 110, 190, 192,
193

Anopla, 123

Anoplodium, 94

Antennary gland,
279, 280, 288

Antennata, 253

Anthomedusae, 56, 77

Antipatharia, 68

Antipathes, 68

Anura, 28, 333

Apatura, 355

Aphaniptera, 371

Aphididae, 365

Aphis, 366, 380

Aphomia, 352

Aphrodite, 156

Aphrophora, 365

Apiariae, 386

29*

257,

| Apis, 386

Aplysia, 206
Aplysoidea, 207
Apoda, 278
Aporosa, 68
Appendicularia, 447

Aptera, 332
| Apus, 260, 261, 268, 391
| Araneida, 408
| Arca, 192, 193
| Arcella, 10, 11, 12

Archerina, 6

Archiannelida, 138

Archicoel, 78

Archigetes, 102, 103, 105

Architeuthis, 223

Arcyria, 7

Arenicola, 150, 153, 157

Argiope (a Brachiopod),
170

Argiope (a Spider), 415

Argonauta, 221

Argulus, 264, 268

Argyroneta, 409, 411, 416

Arista, 370

Aristotle’s Lantern, 243

Artemia, 261

Arthropoda, 25, 34, 79,
103, 253

Arthrostraca, 282, 290

Ascaris, 124, 126, 129

Ascella, 37

Ascidia, 442

Ascidiacea, 450

Ascidians, 434

Ascones, 44

Ascothoracica, 278

Asellidae, 297

Asellus, 268, 293

Aspidiotus, 369

Aspidochirotae, 251

Aspidogaster, 108, 111

Astacidae, 286

Astacus, 260

452

Asterias, 225, 231
Asteroidea, 224, 225, 230
Astraea, 68, 70
Astropectinidae, 230
Astrophyton, 234
Atalanta, 203

Atax, 421

Athalia, 379

Atrial chamber, 436
Atypus, 415
Aulostoma, 132, 137
Aurelia, 61, 62
Autolytus, 158
Autozoids, 73
Avicularia, 185
Azine, 111
Azygobranchiata, 203

BADHAMLIA, 8
Balaninus, 360
Balanoglossus, 425
Balantidium, 28
Balanus, 271, 273
Bdelloura, 95
Béche-de-mer, 251
Beroe, 77

Bilharzia, 112, 113
Bipalium, 81
Bipinnaria, 430
Birgus, 287

Bivium, 227, 246
Blastostyle, 53
Blatta, 336

Bojanus, organs of, 194
Bombus, 387
Bombycina, 353
Bombyliidae, 373
Bombyx, 350, 354
Bonellein, 166
Bonellia, 151, 166, 167
Bopyridae, 297
Bostrichidae, 360
Bostrychus, 361, 380
Bothriocephalus, 103, 105
Botryoidal tissue, 132
Bowerbankia, 185
Brachiopoda, 169
Brachydrilus, 147
Brachyura, 268, 286, 289
Branchellion, 132
Branchial hearts, 210
Branchiata, 253, 254
Branchiomma, 157
Branchiopoda, 260
Branchiostegites, 287
Branchipus, 230, 233
Branchiura, 264
Brisinga, 230, 233
Buccinum, 204
Bucephalus, 113

ZOOLOGY

Bugula, 186
Bulla, 206
Bulloidea, 207
Buthus, 395
Byssus, 192

CALANELLA, 269

Calanidae, 269

Calearea, 36, 41

Caligus, 268

Calliobothrium, 105

Caloptenus, 342

Calotermes, 342

Calyptoblastea - Leptome-
dusae, 55

Campanularidae, 56

Campodea, 334

Capillitium, 9

Capitellidae, 156

Caprella, 292

Caprellidae, 293

Capsidae, 364

Carabidae, 357

Carcinus, 278

Cardium, 192

Cardo, 322

Carididae, 286

Carina, 273

Carinaria, 204

Carinella, 120, 123

Caryophyllaeus, 102, 105

Caryophyllia, 68, 70

Cecidomyia, 373

Cecidomyiidae, 373

Cell, 1

Cellulose, 2, 436

Central capsule, 20

Cephalodiscida, 431

Cephalodiscus, 424, 431

Cephalopoda, 102, 189,
210

Cerambycidae, 361

Cerambyz, 361

Cerata, 205

Cercaria, 107

Cerceris, 386

Cercomonas, 25

Cercopidae, 365

Cerebratulus, 122

Cerianthus, 65, 68

Ceroxylus, 337

Cestoda, 80, 95, 112

Cestus, 77

Chaetifera, 159

Chaetoderma,
305

Chaetogaster, 147

Chaetogastridae, 148, 150

Chaetopoda, 123, 138, 140,
168, 177, 187

121, 196,

Chaleididae, 380
Charybdaea, 60, 63
Cheimatobia, 352
Chelifer, 402
Chernes, 402
Cheyletus, 420
Chilognatha, 310, 315
Chilopoda, 310
Chimaera, 104
Chiton, 196, 223
Chlamydospore, 5, 7, 35
Chloragogen cells, 153
Chlorophyll, 2, 6, 44
Choanoflagellata, 24, 38
Chondracanthus, 269
Chondrioderma, 8
Chondrosia, 41
Chordata, 122, 423
Chromatophores, 210, 220
Chrysididae, 386
Chrysomela, 361
Chrysomelidae, 361
Chrysopa, 347
Chthonius, 402
Cicada, 365
Cicadidae, 364
Cicindelidae, 357
Ciliata, 26, 33
Ciliophrys, 25
Cinclides, 67
Cingulum, 136, 144
Ciona, 435
Cirrhipedia, 271, 298
Cistella, 170
Cladocera, 255, 261
Clathrulina, 18, 19
Clavidae, 55
Clepsidrina, 35
Clepsine, 132
Clio, 208
Clitellum, 144
Clypeastroidea, 248, 245
Clypeus, 323
Cnethocampa, 354
Coccidae, 362, 368
Coccidiidea, 34, 35
Coccinellidae, 361
Coccus, 369
Codosiga, 24
Coelenterata, 28, 47, 89,
79
Coelenterates, 21
Coelenteron, 51, 63, 78
Coelom, 78,\118, 132, 152,
181, 205, 215, 234, 246,
288, 303, 328
Coelomata, 78, 235
Coeloplana, 76, 92
Coenenchyma, 68
Coenosarc, 51, 68, 74

Coleoptera, 321, 355
Collembola, 332
Collozoum, 21
Colpoda, 32
Columella, 70
Comatula, 236
Comatulidae, 236
Commensalism, 21
Conopidae, 374
Conops, 374
Convoluta, 81, 89, 94
Copepoda, 263, 268
Coral, 68
Corallites, 72
Cornacuspongiae, 41, 44,
45
Corticata, 5, 21
Cossus, 354
Costae, 70
Coxa, 323
Coxal gland, 394, 399,
402, 405, 407, 413, 416,
418, 420
Crania, 176, 177
Craniella, 41
Craspedote, 59
Cribella, 232 .
Crinoidea, 224, 236, 240
Criodrilus, 145
Crisia, 185
Cristatella, 182, 184
Crustacea, 254
Cryptoniscus, 298
Cryptophialus, 278
Cryptops, 314, 315
Ctenaria, 75, 77
Ctenidia, 189, 190, 193
Cteniza, 415
Ctenophora, 47, 76, 92
Ctenoplana, 76, 92
Cucumaria, 251
Culex, 372
Culicidae, 372
Cuma, 282
Cumacea, 281
Curculionidae, 360
Cursoria, 336
Cuttle-fish, 211
Cuvierian organs, 249
Cyamus, 293
Cyclas, 192
Cyclopidae, 261, 269
Cyclops, 265
Cyclostoma, 204
Cydippe, 77
Cydippidae, 76
Cymothoidae, 297
Cynipidae, 379
Cynips, 379
Cypris, 262

INDEX

Cypris larva, 272, 278
Cysticercus, 101

DactyLozorps, 57, 58
Daphnia, 88, 183, 255,
268

Decapoda, 211, 286
Deinodrilus, 147
Demodex, 420
Dendrilla, 42
Dendrochirotae, 251
Dendrocoela, 81, 89, 95
Dendrocoelum, 95
Dendrocometes, 32
Dentalium, 209
Dermaptera, 336
Dermatophili, 420
Diastylis, 282
Diatoms, 6
Dibranchiata, 211, 228
Dichogaster, 147
Didymium, 7
Difflugia, 12
Digaster, 147
Digenea, 110, 112
Dimorphism, 158,
298
Dinophilus, 138, 143
Diphyes, 59
Diplopoda, 310, 315
Diplozoon, 111
Dipneumones, 415, 416
Diporpa, 110
Diptera, 321, 370
Directive, 66
Discina, 169, 176, 177
Dissepiments, 70
Distoma, see Fasciola
Doliolum, 448
Dolo, 206
Doris, 206
Drepanophorus, 122
Dysdera, 413
Dytiscidae, 338
Dytiscus, 338, 421

167,

EcARDINES, 176
Echinobothrium, 102, 105
Echinodermata, 224
Echinoidea, 157, 224, 240
Echinus, 241

Echiurids, 157

Echiurus, 166, 167
Ectocyst, 180

Ectoprocta, 179, 183
Elasipoda, 246, 251
Elater, 359

Elateridae, 356, 358
Elytra, 156, 324, 356

Endites, 260
Endocyst, 180
Endodermal lamella; 51,
62
Endosternite,
416
Endostyle, 439
Enopla, 123
Enterocoel, 78
Enteropneusta, 425
Entoconcha, 204
Entomophaga, 379
Entomostraca, 254, 257,
265
Entoniscidae, 298
Entoprocta, 179
Kolis, 206
Epeira, 408
Epeiridae, 416
Ephedrus, 380
Ephemeridae, 344
Ephippium, 259
Ephyrae, 61
Epibranchial space, 193
Epigynium, 414
Epitheca, 69
Eristalis, 374
Errantia, 150
Estheria, 257, 260
Eucopepoda, 264, 265
Eudrilus, 149
Euglena, 22, 23, 25
Euisopoda, 297
Eumenes, 384
Eumenidae, 384
Eupauropus, 318
Euphausiidae, 286
EHuplectella, 45
Euplotes, 31
Eurypterina, 395
Euspongia, 41, 45
Eustrongylus, 124
Euthyneura, 197, 205
Exites, 260
Exothecal tabulae, 71

391, 397,

F'ASCIOLA, 105, 106

Fat-body, 304, 312, 328

Femur, 323

Fenja, 64

Filaria, 124, 129

Fissurella, 197, 198, 200,
201

Flabellum, 260

Flagellula, 5, 7, 8, 22,
24

Fontaria, 317
Foraminifera, 12
Forficula, 336
Forficulidae, 336

454

Formica, 382
Formicariae, 380
Fossoria, 385

Frog, 31, 111
Fulgora, 365
Fulgoridae, 365
Fuligo, 9

Fungia, 68
Funiculus, 181, 184
Fusulina, 15

GALAXEA, 69
Galea, 323
Galeodes, 406
Gallicola, 368
Gamasidae, 420
Gammarus, 268, 292
Gasteropoda, 94, 196
Gastrophilus, 375
Gastrostyla, 31
Gastrozoids, 57, 58
Gecarcinus, 288
Gemmules, 43
Geodesmus, 95
Geometrina, 352
Geonemertes, 115, 122
Geophilidae, 310, 315
Geophilus, 314
Geoscolex, 148
Gephyrea, 34, 159, 187,
249
Germarium, 87
Globigerina, 13, 14
Glomeris, 317
Glossinia, 375
Glossophora, 190, 195
Glottidia, 176, 177
Gnathobdellidae, 133, 137
Gnathostomata, 265
Gonophore, 53
Gonotheeca, 56
Graffla, 94
Grantia, 37, 38, 39, 42,
43
Gregarinidea, 5, 33, 34
Gressoria, 337
Gromia, 16
Gryllidae, 340
Gryllotalpa, 341
Gryllus, 341, 386
Guinea-worm, 124
Gunda, 95, 131
Gymnoblastea - Anthome-
dusae, 50, 54
Gymnolaemata, 184, 185
Gymnomyxa, 5, 10, 25
Gymnosomata, 207
Gyrinidae, 355
Gyrodactylus, 111, 112
Gyropeltis, 204

ZOOLOGY

| HAEMATOCOCCUS, 25

Haematopinus, 370
Haemocoel, 79, 303, 308,
328
Haliotis, 197, 198, 200,
201
Halisarca, 41, 45
Halobates, 363
Halteres, 369, 370
Haltica, 361
Hamingia, 167
Haplomorpha, 207
Haustellum, 370
Hectocotylisation,
213, 220, 222
Heliozoa, 17, 20
Hemerobiidae, 347
Hemerobius, 347
Hemiaster, 244
Hemichordata, 424
Hemiptera, 361
Hepatocerata, 206
Hesione, 157
Hesionidae, 156
Heterocoela, 44
Heterogamia, 336
Heteromera, 357, 359
Heteronereis, 158
Heteropoda, 204
Heteroptera, 363
Heterotricha, 27
Hexactinellidae, 44
Hexactiniae, 64
Hibernaculum, 208
Hippoboscidae, 371
Hirudinea, 131, 152
Hirudo, 132, 134, 137
Histioteuthis, 213
Histriobdella, 138
Histriodrilus, 138, 141
Holothurians, 81, 94
Holothuroidea, 224, 245
Holotricha, 28
Homocoela, 40, 44
Homoptera, 364
Hoplonemertine, 116, 118
Hoplophora, 420
Hormiphora, 75, 76
Hornera, 185
Hyalonema, 45
Hyalospongiae, 44
Hydra, 26, 48, 49
Hydrachnidae, 421
Hydranth, 51, 56
Hydrobatidae, 363
Hydrocaulus, 51
Hydrocorallina, 56
Hydroids, 43, 293
Hydromedusae, 47, 52,58
Hydrorhiza, 51, 56

102,

Hydrophyllia, 58
Hydrotheca, 56
Hydrozoa, 47, 64, 84
Hymenoptera, 375
Hypnocyst, 9, 23, 31
Hypoderma, 375
Hypopharyngeal
439
Hypotricha, 31, 76

groove,

IBLA, 277

Ichneumon, 380

Ichneumonidae, 379

Idoteidae, 297

Imperforata, 13

Infusoria, 5

Insecta, 321

Insects, 35

Intermesenteric space, 66

Interradii, 61

Interseptal chamber, 66

Inter-tentacular organ.
185

Tridocysts, 220

Tsopleura, 196, 305

Isopoda, 293, 297

Tulus, 316

Ixodes, 421

Ixodidae, 422

JAPYX, 334

LABIUM, 323

Labrum, 323

Lacinia, 323
Laemodipoda, 293
Lamellibranchiata, 190
Lamellicornia, 322, 358
Lampyridae, 356
Lampyris, 356

Langia, 123

Languets, 441

Larvacea, 447

Laura, 278
Laurer-Stieda canal, 107
Leeches, 79

Lepadidae, 272

Lepas, 151, 271, 273, 275
Lepidoptera, 348
Lepisma, 334
Leptodora, 260
Leptomedusae, 55
Leptostraca, 280
Lernaeidae, 271]
Lernaeopodidae, 271
Lernaeus, 271
Leucandra, 40, 44
Leucochloridium, 112, 113
Leucon, 282
Leucosolenia, 44

Libellulidae, 345
Lieberkiihnia, 16
Ligula, 104, 105, 376
Lima, 195
Limicolae, 144
Limnadia, 260
Limnaea, 109, 208
Limnocodium, 60
Limpet, 197
Limulus, 95, 389
Lineus, 115, 123
Lingula, 169, 174, 177
Lingulidae, 176
Lipocephala, 190
Lipura, 333
Lissoflagellata, 23
Lithamoeba, 10
Lithobius, 310
Littorina, 203
Dizzia, 55
Lobosa, 9
Locusta, 340
Locustidae, 339
Loligo, 212, 222
Longicorns, 361
Lophopus, 180, 184
Lophyrus, 379
Loxosoma, 186
Lumbricomorpha, 144,
150
Lumbricus, 34, 140, 144,
149
Lung-books, 398
Lycosa, 416
Lycosidae, 415, 416
Lytta, 359

MACHILIS, 334
Macrobdella, 137
Macrogonidia, 23
Macrolepidoptera, 352
Macrostoma, 334
Macrura, 268, 286
Mactra, 192
Madrepora, 68, 71
Madreporic plate, 227, 228
233
Malacobdella,
122
Malacostraca, 254,
279
Malpighian tubules, 292,
312, 325, 328,
350, 377, 398,
418
Mantidae, 337
Mantis, 337
Mantispa, 348
Manubrium, 53
Masaridae, 384

115,

INDEX

455

Maxillary gland, 257, 262,
265, 268
Meandrina, 71

Medusa, 47
Megascolides,
147
Meloe, 359
Meloidae, 359
Melolontha, 322, 358
Mentum, 323
Mesoderm, 36, 40
Mesogloea, 36, 47, 58, 63,
72, 79, 93
Mesosoma, 390
Mesostoma, 82, 94
Metagenesis, 49
Metamorphosis, 332
Metaphyta, 3
Metasoma, 390
Metazoa, 3, 36
Microcotyle, 111
Microgonidia, 23
Microlepidoptera, 351
Microstoma, 89, 90, 92
Millepora, 58
Milleporidae, 57
Mimicry, 337, 359, 374
Mnestra, 207
Moina, 268
Mollusca, 35, 79, 81,
103, 140, 187, 189,
278
Molpadiidae, 251
Monoceystidae, 34
Monocystis, 34
Monogenea, 108
Monomyaria, 191
Monopora, 122
Monothalnia, 13
Monotus, 81
Murex, 203
Musca, 370, 375, 380
Muscidae, 371, 375
Mygale, 409, 415
Myriapoda, 310
Myrmeleo, 347, 358
Myrmeleonidae, 347
Mysis, 285, 286, 289
Mytilus, 190, 192, 193,
195
Myxomycetes, 7, 9
Myxospongiae, 45
Myzostomidae, 240

144, 145,

NAIDIDAE, 149

Naidomorpha, 144

Narcomedusae, 59, 60

Natantia, 204

Nauplius, 254, 260, 278,
279, 286

Nautilus, 210, 222
Vebalia, 280, 282
Vebaliopsis, 280

Nectocalyces, 59

Nematocysts, 28, 47, 57,

59, 89, 122, 206

Nematoda, 124, 126

Nematophores, 56

Nematus, 378

Nemertines, 79, 90, 115,

131, 430

Nemesia, 415

Neomenia, 196

Nepa, 363, 421

Nephelis, 132, 134, 137

Nepidae, 363

Nereis, 158

Neurochord, 148

Neuroptera, 342

Neurotus, 379

Noctiluca, 25

Noctuina, 353

Non-calcarea, 36, 41, 43,

44

Nothrus, 420

Notodelphidae, 269

Notonectidae, 363

Nucleus, 1, 10

Nuda, 10

Nummudlites, 15

Nyctotherus, 28

Nymph, 347

OBISIUM, 402
Octactiniae, 64, 71, 73
Octopoda, 211, 223
Oculina, 68, 71
Ocythoe, 222
Odontophore, 140, 190
Oecodoma, 382
Oestridae, 371, 374
Oestrus, 375
Oligochaeta,
143, 303
Onchidium, 208
Oniscidae, 297, 298
Onychophora, 300
Oonops, 415
Oostegopod, 260
Opalina, 30
Opalinopsis, 31
Opereculum, 155
Ophiopholis, 135, 233
Ophiuroidea, 224, 233
Ophiusidae, 353
Opilionina, 416
Opisthobranchiata, 205
Opsicoetus, 364
Orbitoides, 15
Orchestia, 292

103, 138,

456

Orgyia, 353

Orthonectidae, 1385

Orthoptera, 335

Orthoptera genuina, 336

Oscarella, 39, 41, 48, 45

Osphradium, 189, 196,
220

Ostracoda, 261, 275, 278,
280

Ostrea, 190

Ostreidae, 192

Oxyuris, 125, 129

PAEDOGENESIS, 373
Paguridae, 286, 289, 298
Palaemon, 288
Palaemonetes, 289
Palaeonemertine, 120
Palinurus, 290
Paludicella, 184
Paludina, 204
Papilio, 355
Paractinopoda, 251
Paraglossae, 376
Paramoecium, 28, 29
Paramylum, 23
Paranebalia, 280
Paranucleus, 28
Parapodia, 151
Parasitica (Hemiptera),
369
Parasitica, 265, 269
Parasitism, 33, 112, 115,

194. S128 37 eles
204, 235, 240, 271,
298

Patella, 197

Pauropus, 318

Pecten, 192, 195, 208

Pectines, 397

Pedicellaria, 226, 241

Pedicellina, 186

Pediculus, 369

Pedipalpi, 403

Pelagia, 63

Pelagic, 58, 115

Pelagonemertes, 115

Pelomyzxa, 10

Penella, 269

Pennatula, 73, 74

Pennatulidae, 73

Pentacrinus, 236, 237,239

Pentamera, 357

Pentatomidae, 364

Perforata, 13, 68

Perichaeta, 145, 146, 149

Peripatus, 121, 148, 257,
289, 300

Peripharyngeal bands, 439

Periplaneta, 336

ZOOLOGY

Perisare, 47, 51
Peritricha, 26
Peronia, 60
Peronia, 208
Perradii, 61
Petrarca, 278
Phagocytes, 40
Phalangida, 416
Phalangium, 417
Phascolion, 160, 166
Phascolosoma, 160, 166
Phasma, 337
Phasmidae, 337
Pholas, 191
Phosphorescence, 26, 74,
77, 235
Phronimidae, 293
Phryganidae, 349
Phrynus, 404
Phryzus, 298
Phyllactolaemata, 184
Phyllirhoe, 207
Phyllium, 337
Phyllodrania, 336
Phyllopoda (Cirrhipedia),
254, 268, 280, 282
Phylloxera, 366
Phymosoma, 160, 161
Physalia, 58, 59
Phytophaga, 378
Phytoptidae, 421
Pieridae, 355
Pieris, 351
Pilulina, 12
Plagiostoma, 94
Planaria, 81, 95, 183
Plasmodium, 5, 6, 7
Platyhelminthes, 34, 80
Pleurobranchus, 206
Plumatella, 179, 182
Plumularidae, 56
Plusiidae, 353
Pneumatophores, 59
Pneumodermon, 208
Podura, 333
Podurinae, 333
Polia, 123
Polian vesicles, 232, 234,
243
Polistes, 384
Pollicipes, 273
Polycelis, 81
Polycladida, 90, 91, 143
Polychaeta, 138, 150
Polyeystidae, 34
Polyergus, 382
Polygordius, 138
Polymorphism, 158, 448
Polynoe, 156, 158
Polyophthalmus, 157

Polypide, 180
Polystoma, 107, 111
Polythalmia, 13
Polytoma, 25
Polyxenus, 315
Polyzoa, 56, 179, 259, 293
Polyzosteria, 336
Pontobdella, 132, 1384
Pontodrilus, 145
Porifera, 36

Portunion, 298
Proboscidea, 122
Proctodaeum, 78, 279
Proglottis, 97, 100
Pronotum, 324
Proporus, 94

Proscolex, 101, 105
Prosobranchiata, 197
Prosoma, 389
Prosopyles, 38
Prosorhochmus, 122
Prostomium, 78
Proteolepas, 278
Proteomyxa, 6
Proterospongia, 24
Protococeus, 23
Protodrilus, 138, 139
Protomyxa, 6, 25
Protophyta, 3
Protoplasm, 1
Prototracheata, 300
Protozoa, 3, 5
Pseudocoel, 79
Pseudonavicellae, 35
Pseudopodia, 5, 6, 9
Pseudoscorpionida, 401
Pseudotetramera, 357, 360
Pseudotrimera, 357, 361
Psolus, 246

Psyche, 353

Psychidae, 350, 353
Pteromalus, 380
Pterophoridae, 351
Pterophorus, 351
Pteropoda, 207
Pterotrachea, 204
Pulex, 371

Pulicidae, 371
Pulmonata, 205, 208, 288
Pulsellum, 23

Pulvillus, 371

Pupa coarctata, 361, 371
Pupa libera, 331, 351, 357
Pupa obtecta, 351, 371
Purpura, 203
Pyralidae, 352
Pyrosoma, 293, 450

RapDicoia, 366
Radiolaria, 18, 20

Ranatra, 363
Redia, 109
Reduviidae, 363
Reduvius, 364
Regulares, 243, 245
Reptantia, 203
Reticularia, 12, 13, 20
Retinia, 352
Rhabdites, 82, 83
Rhabditis, 129
Rhabdocoela, 81, 83, 89, 94
Rhabdopleura, 424, 433
Rhabdopleurida, 432
Rhaphidiophrys, 18
Rhinodrilus, 145
Rhizocephala, 278, 298
Rhizocrinus, 239
Rhizopoda, 5
Rhizostoma, 63
Rhodites, 379
Rhodope, 207
Rhopalocera, 354
Rhynchoflagellata, 25
Rhynchonella, 176, 177
Rhyncobdellidae, 132, 187
Rhyncodemus, 81, 95
Rhyssa, 380
Rotalia, 15
Rotifera, 183

SSABELLA, 156
Sabellidae, 156
Saccammina, 12
Saceuli, 237
Sacculina, 278
Sagartia, 65, 67
Salpidae, 449
Saltatoria, 337
Saperda, 361
Sarcopsylla, 372
Sarcoptes, 421
Sarcoptidae, 420
Scape, 322
Scapellum, 273, 277
Scaphognathite, 287
Scaphopoda, 209
Scarabeidae, 358
Schizocoel, 78
Schizonemertine, 120
Schizopoda, 282, 285
Sclerotium, 9
Scolex, 101, 105
Scolopendra, 311, 314
Scolopendrella, 318, 333,
335
Seolytidae, 360
Scorpio, 395
Scorpionida, 395
Scuta, 273
Scutellum, 356

INDEX

457

Seutigera, 313, 315

Scyphistoma, 60, 61, 63

Scyphomedusae, 47, 60, 63

Sedentaria, 150, 156, 157

Sepia, 211

Septa, 69

Serpula, 157

Serpulidae, 155, 156, 157

Sertularidae, 56

Sesia, 354

Shell gland, 257, 262, 265,
268, 274, 281

Sida, 257

Siphonoglyph, 65,71,73,74

Siphonophora (a Myria-
pod), 317

Siphonophora, 58

Siphonozoids, 73

Siphuncle, 222

Sipunculus, 165

Sirex, 377, 380

Siriella, 285

Sminthurinae, 333, 334

Sminthurus, 333

Solaster, 230, 232

Solen, 192, 193

Solenobia, 352

Solifuga, 406

Sori, 7

Spatangoidea, 245

Spermospores, 56, 58

Sphaerogyna, 420

Sphaeromidae, 297

Sphaerophrya, 32

Sphex, 386

Sphingidae, 351

Sphingina, 354

Sphinx, 354, 380

Spiculispongiae, 44

Spirogyra, 6

Spirula, 6, 213, 222

Spondylus, 195, 208

Sponges, 24, 37, 259

Spongilla, 44, 45, 183

Spongillidae, 37, 43

Spongin, 41

Sporocyst, 9, 23, 109

Sporosaes, 59

Sporozoa, 33

Squama, 370

Squilla, 282

Staphylinidae, 356, 358

Statoblasts, 183, 259

Stelechopus, 240

Stelleta, 41

Stelospongus, 39

Stenostoma, 90

Stentor, 27

Sternaspis, 168

Stipes, 323

Stomatopoda, 282
Stomodaeum, 63, 72, 78,
279
Streptoneura, 197
Strobila, 61
Strobilisation, 101
Sturgeon, 104, 105
Stylasteridae, 57
Subimago, 345
Submentum, 323
Subneural gland, 441
Succined, 112, 113
Sycandra, 43
Sycon, 44
Syllidae, 156, 158
Symphyla, 318
Synagoga, 278
Synapta, 204, 246, 251
Syrphidae, 374
Syrphus, 374

TABANIDAE, 373
Tabanus, 373
Tabulae, 72
Tachinidae, 375
Tuenia, 95, 96, 98, 105
Taeniolae, 60, 61, 64
Talitrus, 292
Tanais, 290, 297
Tarsus, 324
Tealia, 66
Tegenaria, 412, 413, 415,
416
Tegulae, 376
Tenebrio, 359
Tenebrionidae, 359
Tentaculifera, 210
Tentaculocysts, 59
Tenthredinidae, 377
Terebella, 155, 157
Terebellidae, 158
Terebratula, 176
Teredo, 191
Terga, 273
Termes, 342
Termitidae, 342
Terricolae, 144
Testacea, 10
Testicardines, 176, 178
Tethys, 206
Tetilla, 45
Tetrabranchiata, 211
Tetractinellidae, 45
Tetranyneus, 421
Tetrapneumones, 415
Tetrarhyncus, 105
Tetrastemma, 115, 122
Thalassema, 166, 167, 168
Thaliacea, 448
Theca, 69

458

ZOOLOGY

Thecidium, 176
Thecosomata, 207
Thelyphonus, 404
Thenea, 40
Theonella, 41
Theridion, 415
Thomisidae, 416
Thoracica, 271
Thoracostraca, 281
Threadworms, 124
Thrips, 344
Thripsidae, 344
Thysanoptera, 344
Thysanozoon, 81, 95
Thysanura, 319, 334
Tibia, 324
Tiedemann’s bodies, 229
Tinea, 352
Tineidae, 349, 351
Tingitidae, 364
Tipula, 370, 373
Tipulidae, 371, 372
Tomocerus, 333
Tornaria, 430
Torquatella, 26
Tortricidae, 352
Tortriz, 352
Trachea, 327
Tracheata, 253, 300, 321
Trachomedusae, 59
Tractellum, 25
Trematoda, 80, 102, 104,
112

Tremoctopus, 221
Trichina, 129
Trichinosis, 129
Trichocysts, 28
Trichodina, 26, 27
Trichoptera, 348
Tricladida, 90, 95, 114
Trigonia, 192
Trivium, 227, 246
Trochanter, 323
Trocheta, 134
Trochosphere, 187
Trochus, 201
Trombidiidae, 421
Tubicola, 150
Tubifex, 103
Tubipora, 71, 72
Tubularia, 50, 52, 53
Tunicata, 34, 435
Turbellarians, 77, 80, 89,
114, 122; 131, 138,
140
Tylenchus, 128
Tyroglyphidae, 422
Tyroglyphus, 422

Unio, 421
Uroceridae, 377
Urochaeta, 145, 149
Urochordata, 434

VALVATA, 203
Vampyrella, 6

THE END

Vanessa, 355
Vegetable kingdom, 2
Velella, 58, 59
Veliger, 189
Velinea, 45
Velum, 47, 60
Vertebrata, 25, 35, 79,
103
Vespa, 384
Vespariae, 382
Vespidae, 382
Vibracula, 186
Vitellarium, 81, 87
Vortex, 81, 89, 94
Vorticella, 27

WALDHEIMIA, 169, 172
Winter eggs, 259
** Worms,” 103

XIPHOSURA, 389

YELLOW CELLS, 20
Yungia, 95

ZoAEA Larva, 268, 279
Zoantharia, 64
Zooecium, 180

Zooids, 73
Zooxanthella, 21
Zygobranchiata, 197

Printed by R. & R. CLark, Edinburgh

o. WINDNANNII

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