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A COURSE 


OF 


ELEMENTARY INSTRUCTION 


IN 


PRACTICAL BIOLOGY. 


/ V { 

tUt^ttf A COURSE OF 

ELEMENTARY INSTRUCTION 


IN 


PRACTICAL BIOLOGY 


BY 

T. H. HUXLEY, LL.D, F.R.S., 

ASSISTED BY 

H. N. MARTIN, M.A., M.D., D. Sc, F.R.S. 


REVISED EDITION' 
EXTENDED AND EDITED 

BY 

G. B. HOWES, 

ASSISTANT PROFESSOR OF ZOOLOGY, NORMAL SCHOOL OF SCIENCE 
AND ROYAL SCHOOL OF MINES, 

AND 

D. H. SCOTT, M.A., PH.D., 

ASSISTANT PROFESSOR OF BOTANY, NORMAL SCHOOL OF SCIENCE 
AND ROYAL SCHOOL OF MINES. 


WITH A PREFACE BY 
PROFESSOR HUXLEY, F.R.S. 

Honfcon : 
MACMILLAN AND CO. 

AND NEW YORK. 
1888 

[All Righfs resei-vtd.] 


First Printed 1875. Printed and Stereotyped 1876. 

Reprinted March- and Jtily 1877, February and December 1879, 1881, 
1882, 1883, 1885, March, September, December, 1886, 1887. 

Revised and extended edition, 1888. 


10 


CAMBRIDGE: PRINTED BY c. j. CLAY, M.A. AND SONS, AT THE UNIVERSITY PRESS. 


PREFACE TO THE REVISED EDITION. 


THE first edition of the Course of Practical Instruction in 
Elementary Biology appeared twelve years ago, and the 
motives which led to its publication are fully explained 
in the original preface, which is subjoined. The present 
edition has been carefully revised and, where necessary, 
enlarged by my colleagues Mr Howes and Dr Scott, assistant 
Professors in Zoology and Botany in the Normal School of 
Science and Royal School of Mines, and such additions 
and improvements are entirely their work. But besides 
these changes, the reader who compares the two editions 
will observe that the order in which the subjects are pre- 
sented is completely changed. In the first edition the 
lowest forms of life were first dealt with; the series of 
plants followed in ascending order ; and then the series of 
animals, from the Bell animalcule upwards to the Frog. 

No doubt there is much to be said for the principle of 
this arrangement, which leads the student from the study 
of simple to that of complex phenomena ; but the experience 
of the Lecture-room and the Laboratory taught me that 


vi PREFACE TO THE REVISED EDITION. 

philosophical as it might be in theory, it had defects in 
practice. 

All the simplest forms of life, which are easily accessible, 
are of very minute size and their study involves the use 
of high microscopic powers. The student who begins with 
them is therefore not merely introduced suddenly into a 
region in which everything is new and strange, but he has 
to familiarize himself with the use of unwonted means of 
exploration. By taking this road, the teacher (to whom the 
world of the microscope is so familiar that he is apt to 
forget its strangeness to students) sets himself against one 
of the soundest canons of instruction, which is to proceed 
from the known to the unknown, and from familiar methods 
of learning to those which are strange. 

After two or three years' trial of the road from the simple 
to the complex, I became so thoroughly convinced that the 
way from the known to the unknown was easier for students, 
that I reversed my course, and began with such animals as 
a Rabbit or a Frog, about which everybody knows something, 
while their anatomy and physiology is illustrated by in- 
numerable analogies with those of our own bodies. From 
this starting point we proceeded further and further into 
the unfamiliar regions of invertebrate organisation until we 
reached the border region between animals and plants, 
whence there was a natural and easy ascent to the most 
complicated vegetable organisms. 

This order is followed in the present edition ; which is 
greatly improved by the addition of the Earthworm and the 
Snail in the series of animal, and of Spirogyra in the series 
of vegetable, types. 


PREFACE TO THE REVISED EDITION. vii 

I have every reason to believe that our course of in- 
struction in Elementary Biology has been found useful by 
many learners and teachers. But whatever the value of 
our attempt to carry out a certain method of instruction, I 
am more than ever convinced that the method itself is one 
which will eventually be universally adopted, not only by 
teachers of the biological sciences as such, but by the 
teachers of so much of those sciences as constitute the 
foundation of medicine. 

No man can be competent to deal with the greater 
problems of biology as they are now presented to us, unless 
he has made a survey, at once comprehensive and thorough, 
of the whole field of biological investigation. The animal 
and the vegetable worlds are only two aspects of the same 
fundamental series of phenomena, and each is capable of 
throwing a flood of light upon the other. I know of no 
way by which such a broad, but not superficial, survey can 
be effected except the method adopted in this work. 

Again, while to my mind, nothing is more to be 
deprecated than the compulsory waste of the invaluable 
time of students of medicine, upon topics so remote from 
the serious business of their lives as are systematic Zoology 
and Botany, there is no preparatory discipline so well 
calculated to serve as a practical introduction to the study 
of Human Anatomy and Physiology, as that afforded by a 
proper laboratory course of Elementary Biology. 

Sundry experiments have left no doubt upon my mind 
that, by following such a course of three or four months' 
duration, the medical neophyte is enabled to enter upon 
his proper studies, provided with a practical knowledge of 


Vlll PREFACE TO THE REVISED EDITION. 

Anatomy, of Histology, and of the Elements of Embry- 
ology and of Physiology, such as under the present system 
is either not acquired at all, or is gained at the expense of 
time and labour which can be ill spared from practical 
subjects. 

T. H. HUXLEY. 

November, 1887. 


PREFACE TO THE FIRST EDITION. 


VERY soon after I began to teach Natural History, or what 
we now call Biology, at the Royal School of Mines, some 
twenty years ago, I arrived at the conviction that the study 
of living bodies is really one discipline, which is divided into 
Zoology and Botany simply as a matter of convenience ; and 
that the scientific Zoologist should no more be ignorant of 
the fundamental phenomena of vegetable life, than the 
scientific Botanist of those of animal existence. 

Moreover, it was obvious that the road to a sound and 
thorough knowledge of Zoology and Botany lay through 
Morphology and Physiology ; and that, as in the case of all 
other physical sciences, so in these, sound and thorough 
knowledge was only to be obtained by practical work in 
the laboratory. 

The thing to be done, therefore, was to organize a course 
of practical instruction in Elementary Biology, as a first 
step towards the special work of the Zoologist and Botanist. 
But this was forbidden, so far as I was concerned, by the 
limitations of space in the building in Jermyn Street, which 
possessed no room applicable to the purpose of a labora- 


X PREFACE TO THE FIRST EDITION. 

tory ; and I was obliged to content myself, for many years, 
with what seemed the next best thing, namely, as full an 
exposition as I could give of the characters of certain plants 
and animals, selected as types of vegetable and animal 
organization, by way of introduction to systematic Zoology 
and Palaeontology. 

In 1870, my friend Professor Rolleston, of Oxford, pub- 
lished his " Forms of Animal Life" It appears to me that 
this exact and thorough book, in conjunction with the 
splendid appliances of the University Museum, leaves the 
Oxford student of the fundamental facts of Zoology little to 
desire. But the Linacre Professor wrote for the student of 
Animal life only, and, naturally, with an especial eye to the 
conditions which obtain in his own University ; so that 
there was still room left for a Manual of wider scope, for 
the use of learners less happily situated. 

In 1872 I was, for the first time, enabled to carry my 
own notions on this subject into practice, in the excellent 
rooms provided for biological instruction in the New 
Buildings at South Kensington. In the short course of 
Lectures given to Science Teachers on this occasion, I had 
the great advantage of being aided by my friends Dr Foster, 
F.R.S., Prof. Rutherford, F.R.S., and Prof. Lankester, F.R.S., 
whose assistance in getting the laboratory work into prac- 
tical shape was invaluable. 

Since that time, the biological teaching of the Royal 
School of Mines having been transferred to South Kensing- 
ton, I have been enabled to model my ordinary course of 
instruction upon substantially the same plan. 

The object of the present book is to serve as a laboratory 


PREFACE TO THE FIRST EDITION. XI 

guide to those who are inclined to follow upon the same 
road. A number of common and readily obtainable plants 
and animals have been selected in such a manner as to 
exemplify the leading modifications of structure which are 
met with in the vegetable and animal worlds. A brief 
description of each is given; and the description is followed 
by such detailed instructions as, it is hoped, will enable the 
student to know, of his own knowledge, the chief facts 
mentioned in the account of the animal or plant. The 
terms used in Biology will thus be represented by clear and 
definite images of the things to which they apply ; a com- 
prehensive, and yet not vague, conception of the phenomena 
of Life will be obtained ; and a firm foundation upon which 
to build up special knowledge will be laid. 

The chief labour in drawing up these instructions has 
fallen upon Dr Martin. For the general plan used, and 
the descriptions of the several plants and animals, I am 
responsible ; but I am indebted for many valuable sugges- 
tions and criticisms from the botanical side to my friend 
Prof. Thiselton Dyer. 

T. H. H. 

LONDON, 

September, 1875. 


ADDENDUM. 

p. 24, 1. 12. After 'so-called ductless glands' 1 read 'other than the 
spleen already described (p. 16) '. 


ERRATA. 

p. 26, 1. 19, for ' Munro ' read ' Monro'. 
p. 384, foot-note, for 8576 read 8376. 


CONTENTS. 


I. 

FROG. 

General characters Development Specific characters of Rana tem- 
poraria and R. escuknta Splanchnic (pleuro-peritoneal) cavity and 
the organs of the viscera Neural cavity and the cerebro-spinal axis- 
Comparison of transverse sections across the head and trunk General 
comparison with Lobster and Crayfish Skeleton Digestive system- 
Lymph and blood vascular systems Heart Respiratory organs and 
respiration Urinogenital system Ductless glands Nervous system- 
Sense organs and integument Laboratory work . pp. i 172. 


II. 

FRESH-WATER CRAYFISH AND LOBSTER. 

Habitat General structure Exoskeleton and appendages Diges- 
tive system Circulatory system and heart Respiratory system Excre- 
tory organs Nervous system and sense organs Reproductive organs- 
Development^ Ecdysis Laboratory work. . pp. 173 239. 


III. 

EARTHWORM. 

Habitat General external characters Exoskeleton and setse Di- 
gestive system General structure of body wall and alimentary canal- 
Body cavity and mesenteries Excretory system Circulatory system 
Neurosensiferous system Reproductive organs Development Clitel- 
lum Laboratory work. ...... pp. 240 271. 


XIV CONTENTS. 

IV. 

COMMON SNAIL. 

Specific characters of Helix aspersa and PI. hortensis Habitat- 
General characters Shell or exoskeleton Digestive system Pulmo- 
nary sac and excretory organ Heart, compared with that of Crayfish- 
Circulatory system Nervous system and sense organs Reproductive 
system Development of Pond Snail (Lymncens stagnalis) Polar 
bodies Laboratory work. .... . pp. 272 304. 

V. 

FRESH-WATER MUSSEL. 

Habitat General characters Branchiae and alimentary canal, in 
relation to the branchial chambers and the exterior Circulatory system 
and heart Excretory organs Digestive gland and glycogenous tissues 
Nervous system and sense organs Reproductive organs Develop- 
ment Laboratory work. . ... pp. 305 341. 

VI. 

FRESH-WATER POLYPES. 

Habitat and movements Mode of feeding Reproduction and repro- 
ductive organs Histological structure Specific characters of Hydra 
fusca and H. viridis Comparison with green-plant and Amoeba 
Neurosensiferous apparatus Comparison with development of higher 
animals Laboratory work. ..... pp. 342 358. 

VII. 

BELL-ANIMALCULE. 

Infusoria, compared with other animals BELL-ANIMALCULE 
Habitat and movements Histological structure Physiology Green 
varieties and chlorophyll Reproduction Encystation Infusoria asso- 
ciated with Frog Laboratory work pp. 359 368. 


CONTENTS. XV 

VIII. 

PROTEUS ANIMALCULE. COLOURLESS BLOOD CORPUSCLES. 

AMCEBA. Habitat Movements Histological structure Physical 
constitution Physiology Chemical composition Effects of tempera- 
ture and electric shocks. COLOURLESS BLOOD CORPUSCLE. Facts 
which show Amoeba to be an animal Reproduction of Amceba 
Laboratory work. ....... pp. 369 376 

IX. 

YEAST. 

General characters Fermentation Appearance under the micro- 
scope Structure of cells Chemical composition Mode of multipli- 
cation Gemmation Spores Physiology Nutrition 7 Metabolism 
Laboratory work. ....... pp. 377 388. 

X. 

PROTOCOCCUS. 

Habitat Histological structure Physiology Chlorophyll Depen- 
dence on light Mode of multiplication Macrozoospores Microzoo- 
spores Laboratory work. ...... pp. 389 395. 

XI. 

SPIROGYRA. 

Habitat External characters Histological structure Cell-division 
Sexual reproduction by conjugation Zygospore Physiology Labo- 
ratory work. . . . , pp. 396 407. 

XII. 

BACTERIA. 

General characters Structure Movements Zooglcea stage- 
Spores Physiology Relation to putrefaction Life-history Labora- 
tory work. ......... pp. 408 414. 


xvi CONTENTS. 

XIII. 

MOULDS. 

Fungi Physiology Spores PENICILLIUM Habitat General 
characters Histological structure Asexual reproduction Conidia 
Development EUROTIUM Habitat General characters Reproduc- 
tion by ascospores MUCOR Habitat General characters Histologi- 
cal structure Asexual reproduction Development Conjugation- 
Germination of zygospore Laboratory work. . . pp. 415 429. 

XIV. 

STONEWORTS. 

Habitat External characters Histological structure Mode of 
growth Sexual reproduction Development Physiology Laboratory 
work Protoplasmic movements. ..... pp. 430 442. 

XV. 

BRACKEN FERN. 

External characters Histological structure Stem Leaf Root- 
Physiology Asexual reproduction Spores Germination Prothallus 
Sexual reproduction Embryo Alternation of generations Labora- 
tory work. . . pp. 443 459. 

XVI. 

BEAN-PLANT. 

External characters Reproductive organs Development Histo- 
logical structure Stem Leaf Root Homology of the reproductive 
organs with those of the Fern Physiology Laboratory work. 

pp. 460 481. 

APPENDIX. General On dissecting On injecting Microscope and 
Microscopic examination Preparation and use of reagents and culture 
solutions Sections and section cutting. . . . pp. 482 498. 

INDEX . .... pp. 499512. 


I. 

THE FROG (Rana temporaria and Rana esculentd). 

THE only species of Frog indigenous in Britain is that termed 
the 'common' or 'Grass Frog' (Rana temporaria]^ while, on 
the Continent, there is, in addition to this, another no less 
abundant species, the hind-limbs of which are considered a 
delicacy, whence it has received the name of the 'Edible 
Frog' (Rana esculenta\ Unless the contrary be expressly 
stated, the description here given applies to both species. 
The Edible Frog is usually larger than the other, and is 
therefore more convenient for most anatomical and physio- 
logical purposes. 

In the body of the Frog the head and trunk are readily 
distinguishable; but there is no tail and no neck; the con- 
tours of the head pass gradually into those of the body, the 
fore-limbs being situated immediately behind the former. 
There are two pairs of limbs, one anterior and one 
posterior. 

The whole body is invested by a smooth moist integument. 
The yellowish ground-colour of the skin is diversified by 
patches of a more or less intense black, brown, greenish, or 
reddish-yellow colour, and, in the Grass Frog, there is a 
large, -deep brown or black patch on each side of the head, 
behind the eyes, which is very characteristic of the species. 
The coloration of different frogs of the same species differs 
widely; and the same frog will be found to change its colour, 


2 ELEMENTARY BIOLOGY. [CHAP. 

becoming dark in a dark place, and light if exposed to the 
light. 

The body of the Frog presents only two median aper- 
tures, the wide mouth and the small cloacal aperture. The 
latter is situated at the posterior end of the body, but rather 
on its upper side than at its actual termination. It is com- 
monly termed the anus, but it must be recollected that it 
does not exactly correspond with the aperture so termed in 
the Mammalia. 

The two nostrils, or external nares, are seen at some dis- 
tance from one another upon the dorsal aspect of the head, 
between the eyes and its anterior contour. The eyes are 
large and projecting, with well-developed lids, which shut 
over them when they are retracted. Behind the eye, on 
each side of the head, there is a broad circular area of 
integument, somewhat different in colour and texture from 
that which surrounds it; this is the outer layer of the mem- 
brane of the tympanum, or drum of the ear. 

The fore-legs are very much shorter than the hind-legs. 
Each fore-limb is divided into a brachium, antebrachium and 
manus, which correspond with the arm, fore-arm and hand in 
Man. The manus possesses four visible digits which answer 
to the second, third, fourth, and fifth fingers in Man. There 
is no web between the digits of the manus. 

The hind-legs are similarly marked out into three divi- 
sions, femur, crus, and pes, of which the femur answers to 
the thigh, the crus to the leg, and the pes to the foot, in 
Man. The pes is remarkable not only for its great relative 
size as a whole, but for the elongation of the region which 
answers to the tarsus in Man. It will be observed, however, 
that there is no projecting heel. There are five long and 
slender digits, which correspond with the five toes in Man, 
and are united together by thin extensions of the integu- 


I.] THE FROG. 3 

ment constituting the web. The innermost and shortest 
answers to the hallux, or great toe, in Man. 

At the base of the hallux, the integument of the sole 
presents a small horny prominence, which overlies a bony 
calcar ; sometimes there is a similar but smaller elevation 
on the outer side of the foot: but there are no nails upon 
the ends of any of the digits of either the pes or the manus. 
Thickenings, or callosities, of the integument, however, occur 
beneath the joints of the digits, both in the pes and the 
manus. 

During the breeding season, the integument on the 
palmar surface of the innermost digit of the manus, in the 
male, becomes converted into a rough and swollen cushion. 
This, in the Grass Frog, acquires a dark-brown or black 
colour. 

The Frog, when at rest, habitually assumes a sitting pos- 
ture much like that of a dog or cat. Under these circum- 
stances the back appears humped, the posterior half being 
inclined at a sharp angle with the anterior half. The ver- 
tebral column, however, will be found to be straight, and the 
apparent hump-back arises, not from any bend in the verte- 
bral column, but from the manner in which the bones 
of the hip-girdle are set on to the sacrum. 

The walk of the Frog is slow and awkward, but it leaps 
with great force, by the sudden extension of the hind-limbs, 
and it is an admirable swimmer. 

In a living Frog, the nostrils will be seen to be alter- 
nately opened and shut, while the integument covering the 
under side of the throat is swollen out and flattened. The 
sucking in and circulation of the air needed for the Frog's 
respiration is connected with these movements. 

The upper eyelid of the Frog is large and covered with 
ordinary pigmented integument, and it has very little 


4 ELEMENTARY BIOLOGY. [CHAP. 

mobility. That which performs the function of the lower 
eyelid in Man, is a fold of the integument little pigmented 
and, for the most part, semi-transparent, resembling the 
nictitating membrane of a bird rather than an ordinary 
lower lid. If the surface of the cornea be touched, the 
eyeball is drawn inwards under the upper lid, which de- 
scends a little, at the same time as the lower lid 
ascends over the ball, to meet the upper lid and close 
the eye. 

As is well known, Frogs emit a peculiar croaking sound, 
their vocal powers being more especially manifested in the 
breeding season, when they collect together at the surface of 
ponds, pools and sluggish streams, in great numbers. At 
this season, which commences in the early spring for the 
Grass Frog, but much later on in the year for the Edible 
Frog, the male seeks the female and, clasping her body 
tightly with his fore-limbs, remains in this position for days 
or even weeks, until her ova are discharged, when he 
fecundates them by a simultaneous out-pouring of the 
seminal fluid. Shortly after the eggs pass into the water, 
the thin layer of mucus secreted by the oviduct, with 
which each egg is surrounded, swells up by imbibition and, 
with that which surrounds the others, it gives rise to a 
swollen mass, in which the eggs remain imbedded during the 
early stages of their development. 

The process of fecundation above alluded to, usually 
results in the fusion between each egg and one of the sper- 
matozoa contained in the seminal fluid, and it is only 
when this has been effected that the egg, which is then said 
to be fertilized, is competent to reproduce the species. It 
follows that the fertilized ovum is a compound of the egg of 
the female and a spermatozooid of the male; and it has been 
accordingly termed the oosperm, by way of distinction from 


I.] THE FROG. 5 

the unfertilized egg (ovarian ovum) as it leaves the body 
of the female. 

The development of the eggs is closely dependent upon 
temperature, being greatly accelerated by warmth and re- 
tarded by cold. The process of yelk-division, or segmen- 
tation which commences within a few hours of impreg- 
nation, can be readily observed when the eggs are examined 
as opaque objects under a lower power of the microscope. 
It is ushered in by the appearance, on the surface of the 
egg, of a furrow which passes completely round the same, 
and, gradually deepening, constricts it into two equal 
halves. Each of these again becomes subdivided, and, the 
process being repeated, there results a mulberry-like mass 
of embryo-cells, from which the formative tissues of the 
body are ultimately derived. Segmentation such as this, 
in which the first furrow completely cleaves the whole egg 
into two, each successive one similarly subdividing that cell 
with which it is related, is termed complete or holoblastic. 

While still within the mucus investment the embryo 
assumes the form of a minute fish, devoid of limbs and with 
only rudiments of gills, but provided with two adhesive 
discs on the ventral side of the head behind the mouth. 

After leaving the egg, the larva acquires three pairs of 
external brancliitz having the form of branched filaments, at- 
tached to the sides of the hinder part of the head. Narrow 
clefts in the skin at the roots of the branchiae lead into the 
back of the throat or pharynx. Water taken in at the 
mouth passes out by these branchial clefts. The animal 
crops the aquatic plants on which it lives, by means of the 
horny plates with which its jaws are provided. 

In the Tadpole, as the larval Frog is called, the intestine, 
which is relatively longer than in the adult, is coiled up like 
a watch-spring in the body cavity. A membranous lip, 


6 ELEMENTARY BIOLOGY. [CHAP. 

the surface of which is beset with numerous horny papillae, 
surrounds the mouth, and the muscular tail acquires a large 
relative size. The eyes, the nasal and auditory organs 
become distinct, but no limbs are at first visible. 

A fold of the integument in the hyoidean region, called 
the opercular membrane, now grows back over the external 
gills and unites with the integument covering the trunk, 
leaving only a small aperture on the left side, through which 
the ends of the external gills of that side may, for some time, 
be seen to protrude. The external gills atrophy, and are 
succeeded functionally by short processes developed from 
the opposing faces of the branchial clefts the internal 
branchm. The rudiments of the limbs appear, rapidly elon- 
gate and take on their characteristic shape, the hind pair 
only being at first visible on account of the anterior pair 
being hidden under the opercular membrane. The lungs 
are developed and, for a time, the tadpole breathes both by 
them and by its internal gills. 

As the legs grow the tail shortens and, at last, is re- 
presented merely by the pointed end of the body ; the gape 
elongates until the angle of the mouth lies behind the eye, 
instead of a long way in front of it, as in the tadpole ; the 
labial membrane and the horny armature of the mouth 
disappear, while teeth are developed in the upper jaw and 
on the roof of the mouth ; the intestine becomes less and 
less coiled as, not growing at the same rate as the body, 
it becomes relatively shorter; and the animal gradually 
changes its diet from vegetable to animal matters the 
perfect Frog being insectivorous. 

The two species, Rana temporaria and Rana esculenta, 
are distinguishable by the following external characters. In 
Rana temporaria, the interspace between the eyes is flat or 
slightly convex, and its breadth is usually greater than, or 


I] THE FROG. 7 

at least equal to, that of one of the upper eyelids. The 
diameter of the tympanic membrane is less than that of the 
eye, often much less. The horny elevation on the outer side 
of the pes is small or absent, and that on the inner is 
flattened and has a rounded margin. A patch of dark 
colour extends from the eye backwards over the tympanic 
membrane. The males have the cushion on the radial side 
of the manus black, and they are devoid of vocal sacs. 

In Rana esculenta, on the other hand, the interspace be- 
tween the eyes is usually concave and narrower than the 
breadth of one of the eyelids. The diameter of the tym- 
panic membrane is as great as that of the eye. The horny 
elevation on the inner side of the pes is elongated, com- 
pressed and brought to a blunt edge, so as almost to resem- 
ble a spur, and a small outer elevation is constantly present. 
There is no patch of colour at the sides of the head, such 
as exists in Rana temporaries, and the cushion of the inner 
digit in the male is not black. The males have a large 
pouch on each side of the head, behind the angle of the 
jaw, communicating with the cavity of the mouth, and, when 
they croak, these pouches, becoming dilated, assume the 
form of spherical sacs. 

Having thus become acquainted with the general cha- 
racters and life-history of the Frog, and with those features 
of its organization which are visible to the naked eye and 
without dissection, its structure may next be studied in 
detail. 

If the trunk be laid open, it will be found to enclose 
a cavity in which some of the most important viscera the 
stomach and intestine, the liver, the pancreas, the spleen, 
the lungs, the kidneys and urinary bladder, and the repro- 
ductive organs are contained. As this cavity answers to 


8 ELEMENTARY BIOLOGY. [CHAP. 

those of the pleurae and of the peritoneum in the higher 
animals, it is termed ti\e pleuroperitoneal cavity ; and the soft 
smooth membrane which lines it and covers the contained 
viscera is \^& pleuroperitoneal membrane. 

The vertebral column traverses the middle of the roof of 
this cavity, and the layer of pleuroperitoneal membrane 
which lines each lateral wall of the cavity, passes downwards 
on each side of the vertebral column and joins its fellow in 
the middle line to form a thin sheet, the mesentery, which 
suspends the alimentary canal. In the triangular interval 
left between these two layers before they unite, a wide 
canal (subvertebral lymph sinus), the dorsal aorta and the 
chain of sympathetic ganglia, are situated. 

The antero-dorsal moiety of the pleuroperitoneal cavity 
is occupied by the gullet, which places the mouth in com- 
munication with the stomach. Beneath the gullet the 
pleuroperitoneal cavity is separated only by a thin partition 
from a chamber, the pericardium, which contains the heart. 
The posterior face of the partition is constituted by the 
pleuroperitoneum, its anterior face by a membrane of 
similar character, the pericardial membrane, which lines the 
pericardium and is reflected on to the heart, in the same 
way as the pleuroperitoneum lines the pleuroperitoneal 
cavity and is reflected on to the intestine. The exposed 
surfaces of both the pericardial and pleuroperitoneal mem- 
branes are kept permanently moist by a fluid (serous fluid] 
which more or less completely fills the cavities which they 
enclose; hence they are termed serous membranes. 

A layer of the muscular fibres which enter into the body- 
wall is continued inwards at the anterior boundary of the 
pleuroperitoneal cavity and is attached to the sides of the 
oesophagus and to those of the pericardium, thus consti- 
tuting a so-called diaphragm; which, it will be observed, is 


I.] THE FROG. 9 

situated in front of the lungs, and not behind them, as in 
the higher animals. 

Thus, in the trunk, on the ventral side of the vertebral 
column, the body presents two cavities, a large posterior 
pleuroperitoneal cavity, and a small anterior pericardial 
cavity; while neither of these communicates directly with 
the exterior, there is in the female an indirect communica- 
tion by the oviducts. 

On the ventral side of the head, the very wide mouth 
opens into a spacious buccal cavity, the roof of which is hard 
and firm, while the floor is soft and flexible, except so far as 
the middle of it is occupied by a broad, flat, for the most 
part gristly plate, the body of the hyoid bone. Within the 
lips the upper jaw is beset with numerous sharp small teeth, 
and two clusters of similar teeth are to be seen in the fore 
part of the roof of the mouth ; the latter, being attached to 
the bones termed the vomers, are the vomerine teeth, while 
the former, attached to the premaxillcz and maxilla, are 
maxillary teeth. The lower jaw or mandible is edentulous. 

At the sides of the clusters of vomerine teeth are the 
apertures teamed. posterior nares, by which the nasal chambers 
communicate with the mouth. At the sides of the back part 
of the throat two wide passages, the Eustachian recesses, lead 
into the tympanic cavities, which are closed externally by the 
tympanic membranes. In the male Rana esculenta the small 
apertures of the vocal sacs are seen on the inner side of each 
ramus of the jaw, close to the angle of the gape below and in 
front of the Eustachian recesses. In the middle of the back 
of the throat is the opening of the oesophagus, closed by the 
approximation of its sides except during deglutition, while in 
the median line of the hinder part of its floor lies a longitu- 
dinal slit, the glottis. A fleshy tongue, bifurcated and free 
at its posterior end, is attached anteriorly to the middle part 


10 ELEMENTARY BIOLOGY. [CHAP. 

of the lower jaw. In a state of rest, therefore, it lies on the 
floor of the mouth with its free end turned backwards, and 
one point on each side of the glottis. 

The gullet, after traversing the so-called diaphragm, 
passes into the elongated stomach. At its posterior end this 
narrows and joins the slender small intestine. Though short, 
this is too long relatively to the length of the pleuroperi- 
toneal cavity to lie straight in it. It is, therefore, thrown 
into sundry folds which are suspended to the dorsal wall of 
that cavity in the manner before described. Finally, the 
small intestine enters the dilated short large intestine, and 
this opens -into a chamber with muscular walls, the cloaca, 
the external aperture of which has been already mentioned. 

Thus the alimentary canal is a tube which traverses the 
body from the oral to the anal apertures ; and the heart, en- 
closed in the pericardium, is situated in the middle line on 
the ventral side of the same. 

Separated from the pleuroperitoneal and buccal cavities by 
the bodies of the vertebras and the hard roof of the buccal 
chamber which continues the direction of these forwards, is 
an elongated cavity, widest in the head but becoming very 
narrow posteriorly, which is closed on all sides by the bony 
and other elements of the head and spinal column. This is 
the neural cavity and contains the brain and spinal cord, 
which together constitute the cerebro-spinal nervous axis. The 
neural cavity is lined by a serous membrane resembling the 
peritoneum and the pericardium, and this arachnoid mem- 
brane is reflected on to and covers the contained cerebro- 
spinal axis, so that the latter is related to it as the heart is to 
the pericardial membrane. 

The cerebro-spinal nerves which are given off from the 
brain and spinal cord pass to their destination through the 
boundary walls of the neural cavity. 


I.] THE FROG. II 

A transverse section of the head in the region of the eyes 
will shew, in the middle line, a dorsal cavity in which the 
anterior part of the cerebro-spinal axis, the brain, is con- 
tained, separated by the solid floor of the skull from a 
ventral cavity, the mouth. 

A transverse section of the trunk will shew a dorsal 
cavity containing the posterior part of the cerebro-spinal 
axis, the spinal cord, separated by the solid floor of the 
vertebral column from a ventral cavity enclosed by the 
alimentary canal and continuous with that of the mouth. 
But the backward continuation of the alimentary canal lies 
within the large pleuroperitoneal chamber, of which there is 
no indication in the head. 

If a transverse section of the trunk of the Frog be com- 
pared with one across the middle of the body of the Crayfish 
or Lobster (Chapter n.) it will be seen that while the chief 
nervous centre is on one side of the alimentary canal and 
the heart on the opposite side in both cases, the face of the 
body on which the nervous centre lies is that on which the 
Crayfish or Lobster naturally rests, while in the Frog it is 
the reverse. The limbs are turned towards the neural side 
in the Crayfish and away from it in the Frog, and the like 
difference obtains between all Arthropoda and all Vertebrata. 

Using the term skeleton, in its broadest sense, for the 
framework which protects, supports and connects the various 
parts of the organism, it consists in the Frog of four kinds of 
tissue ; the Horny, the Osseous, the Cartilaginous and the 
Connective. Moreover, the hard parts are either developed 
in the integument, constituting an exoskeleton, or they are 
deeper seated and belong to the endoskeleton. 

Leaving aside a question that may arise as to the nature 
of some of the cranial bones, the exoskeleton in the Frog is 


12 ELEMENTARY BIOLOGY. [CHAP. 

almost absent, being represented only by the horny coating 
of the calcar. 

The endoskeleton, on the contrary, is well developed and, 
as in all the higher Vertebrata, may be resolved into an 
axial and an appendicular portion. 

The adult axial endoskeleton is represented by the spinal 
column and the skull. 

The appendicular endoskeleton consists of the limbs and 
the pectoral and pelvic arches to which they are attached. 

In the order of development, the endoskeleton is at first 
represented by a membranous rod or notochord alone ; 
secondly, nascent connective tissue and cartilage are super- 
added to the notochord ; thirdly, these acquire their special 
characters ; fourthly, they become replaced by bone, wholly 
or in part. 

The process of conversion or replacement indicated under 
the last head is very incomplete, even in the adult Frog, 
in which remains of the notochord are to be found in the 
centres of the vertebrae (intra-vertebral bodies] ; while the 
cartilage, of which the greater part of the skeleton at one 
period of larval existence was composed, to a great extent 
persists. 

Such cartilage is found forming the free surfaces of the 
bodies of the vertebrae, the extremities of the caudal style 
(iirostyle) and the ends of the transverse processes ; and it 
enters largely into the girdles. In the skull, nearly all the 
bony elements may be removed, leaving behind the primi- 
tive cartilaginous skull, or Chondro-cranium^ altered only so 
far as parts of it have been replaced by bone. 

It furnishes a floor, side walls and roof to the brain-case, 
interrupted only by three spaces (fontamlles) in its roof 
covered in by membrane, and by the foramina for exit 
of the cranial nerves. In front it is continued forward 


I.] THE FROG. 13 

between the two nasal sacs, as a cartilaginous partition 
(septum nartum), from which are given off, dorsally and 
ventrally, transverse alas of cartilage which furnish a roof 
and a floor, respectively, to the nasal chambers. These 
pass into one another where the chondro-cranium ends an- 
teriorly and give rise to a truncated terminal face, the lateral 
angles of which are produced outwards and forwards into 
two flattened pra-nasal processes ; these widen externally 
and support the adjacent portions of the premaxillae and 
maxillae. From the ventral face, just behind the truncated 
anterior end of the chondro-cranium, spring two slender 
cartilages, the rhinal processes. Each of these inclines to- 
wards the middle line and ends against the middle of the 
posterior face of the ascending process of the premaxilla 
by a vertically elongated extremity. An oval nodule of 
cartilage is attached to the posterior face of the above- 
named process, and serves to connect it with the 
rhinal process. On the dorsal face of the chondro-cranium, 
just above the point of attachment of the rhinal processes, 
the external nasal apertures are situated, and the outer and 
posterior margins of each of these apertures are surrounded 
and supported by a curious curved process of the cartilagi- 
nous ala the alinasal process. Where the sphenoidal and 
the ethmoidal portions of the sphenethmoid meet, a stout, 
transverse, partly osseous and partly cartilaginous bar is 
given off, which is perforated at its origin by the canal for 
the orbito-nasal nerve. It then narrows, but becoming 
flattened from above downwards, rapidly widens again, and 
its axe-head-like extremity abuts against the inner face of 
the maxilla. The anterior angle of the axe-head is free; 
the posterior angle is continued back into a slender carti- 
laginous pterygoid rod which bifurcates posteriorly ; this (the 
siispensoriuui] furnishes the articulation for Meckefs carti- 


14 ELEMENTARY BIOLOGY. [CHAP. 

lage which forms the core of the ramus of the lower-jaw or 
mandible. 

The floor of the mouth is supported by a plate of carti- 
lage (the hyoid\ this is attached to the skull by a slender 
cartilaginous band or cornu which is connected with the 
auditory capsule. 

The pectoral and pelvic arches (see Laboratory work) 
are, in the young state, paired undivided cartilages, and the 
development of bone in and upon them does not really 
destroy this continuity, the cartilage persisting at the ends 
of the bones, and between them in the cavities for articu- 
lation of the limb bones. 

In like manner, the bones of the limbs consist originally 
of cartilaginous models of the perfect bone ; but, as deve- 
lopment proceeds, the middle of the cartilaginous model 
commonly becomes invested by a sheath of true bone, while 
calcareous deposits take place in the cartilage close to its 
growing extremities. As the bone grows, the superadded 
sheath invades the middle of the cartilage and more or less 
replaces it ; while the terminal portions of cartilage continue 
to grow and enlarge, and the calcareous deposit within them 
increases, without however reaching their surfaces. Thus 
one of the larger adult limb bones (say the femur) consists 
of a median portion or shaft^ and of two terminal caps of 
cartilage containing calcined epiphyses overlying, and more 
or less enclosed within, the hollow ends of the shaft. 

Seeing that the bony elements of the adult skeleton arise 
by superaddition to and replacement of a cartilaginous pre- 
decessor, it follows that those portions of it which remain 
permanently cartilaginous are persistent representatives of 
latter or embryonic endoskeleton. 

The general disposition of the parts which are seen in 
the mouth has already been described. 


L] THE FROG. 15 

Teeth are present only in the upper jaw and roof of the 
mouth. They are small, with recurved and pointed crowns. 
New teeth are constantly being developed in the gum to 
replace those which are worn out or broken away, and as 
they attain their full size these teeth become ankylosed to 
processes of the subjacent bone. Their distribution and 
characters are such as to render mastication an impossibility; 
they are prehensile and utilized as hooks by means of which 
the animal as it were gets outside its prey. The eversible 
tongue is utilized as a means of capture of smaller creatures, 
chiefly insects. 

The gullet passes without change of diameter into the 
stomach, which lies on the left side of the pleuroperitoneal 
cavity and is nearly as long as it. The stomach narrows 
posteriorly and the almost tubular terminal portion bends 
round sharply and passes into the small intestine. A slight 
constriction (pylorus] marks their point of junction. The 
small intestine runs forwards parallel with the stomach, so 
that with the latter it forms a sort of loop; it is continued 
on coiled up into a sort of packet which lies to the right 
side of the pleuroperitoneal cavity, being held in its place 
by a mesenteric fold of the peritoneum. Thence the small 
intestine proceeds backwards in the middle line and opens 
into the anterior end of the dilated large intestine. 

The inner wall of the stomach is raised up into a number 
of strong longitudinal folds which project into its cavity 
and give it a stellate appearance in transverse section. 
Similar but more delicate folds are met with in the small 
intestine, the lining-membrane of which is produced into 
parallel series of semi-lunar folds whose free edges project 
backwards. 

The opening of the ileum into the large intestine is val- 
vular, its edges projecting backwards into the cavity of the 


1 6 ELEMENTARY BIOLOGY. [CHAP. 

latter. On the dorsal aspect the large intestine presents a 
slight forward dilatation, which may be regarded as a rudi- 
ment of a caecum. 

The liver is very large, and incompletely divided into 
two lobes, the left of which is further subdivided into two. 
The gall bladder is attached to the posterior face of 
the right lobe. The bile duct opens into the duo- 
denum, at some distance behind the pylorus, running 
through the pancreas and receiving the duct of that organ 
on its way. 

The rounded spleen lies in the mesentery, projecting 
more to the left than to the right side, near the point at 
which the small intestine first becomes coiled. 

The apparatus of circulation in the Frog consists of the 
blood and lymph vessels and their contents. 

The lymph is a colourless fluid containing colourless 
nucleated corpuscles which exhibit amoeboid movements: 
it is contained partly in large spaces immediately beneath 
the integument; in the pleuroperitoneal cavity and pro- 
bably in the other serous cavities; and, partly, in capillaries 
and larger trunks which are interlaced with and accompany 
the blood-vessels. The largest of the trunks is the great 
sub-vertebral lymph-sinus, which lies between the layers of 
the root of the mesentery and communicates by small pores 
with the pleuroperitoneal cavity. 

The blood consists of a colourless plasma which contains 
colourless corpuscles, similar to those of the lymph, and in 
addition a great number of oval nucleated red corpuscles. 
It is contained in the blood-vessels, which consist of capil- 
laries, arteries and veins, the two latter being connected on 
the one side by the capillaries and, on the other, by the 
heart into which they open. The lymphatics and the 
blood-vessels are brought into connexion with one another 


I.] THE FROG. I/ 

at opposite ends of the body, through the agency of two 
pairs of contractile muscular sacs (lymph-hearts), which pump 
the lymph contained in the wide lymphatic vessels and in 
the. pleuroperitoneal cavity into the great veins in their 
neighbourhood. 

The blood and lymph systems may thus be regarded as 
subdivisions of a common circulatory system. 

The heart is connected with the walls of the pericardium, 
by the vessels which enter and leave it, and by a slender 
band which passes from the dorsal face of the base of the 
ventricle to the posterior dorsal wall of the pericardial 
chamber. 

The heart consists of four readily distinguishable seg- 
ments, (i) the sinus venosus^ (2) the atrium, (3) the ven- 
tricle^ and (4) the tnmciis arteriosus, disposed in such a 
manner that the sinus venosus, which is the hindermost 
division, lies in the middle line on the dorsal aspect 
of the heart : the atrium is also median and on the 
dorsal side but is in front of the sinus venosus ; the 
ventricle is median, ventral and posterior; and the truncus 
passes obliquely forwards from the right side of the 
ventricle and is ventral and anterior. The heart there- 
fore may be compared to a tube divided by constriction 
into four portions and bent somewhat into the shape of 
an S. 

The sinus venosus receives on each side, in front, a large 
vein, the vena cava superior; while behind the, usually sin- 
gle, vena cava inferior opens into it. It opens by a valvu- 
lar aperture into the atrium. The latter shews no signs of 
division externally, but internally, it is divided by a deli- 
cate partition, the septum of the auricles, into a smaller left 
auricle and a larger right auricle. The sinus venosus opens 
into the atrium, to the right of the septum and therefore 

M. 2 


1 8 ELEMENTARY BIOLOGY. [CHAP. 

into the right auricle. Into the left auricle, the common 
pulmonary vein, formed by the junction of the veins from 
the right and left lungs, opens. 

At its posterior end the atrium opens by the auriculo- 
ventricular aperture into the ventricle. 

A small valve, prevented from flapping back by fine ten- 
dinous cords, exists on each side of this aperture, and the 
septum of the auricles is continued back upon the faces of 
these valves and ends by a free edge between them, thus 
dividing the auriculo-ventricular aperture itself into two 
openings. 

The walls of the sinus and of the atrium are very thin. 
Those of the ventricle, on the other hand, are thick and 
spongy, only a comparatively small, transversely elongated, 
cavity being left at its anterior end or base. At the 
right-hand extremity of this is the aperture which leads 
into the truncus arteriosus. Three semilunar valves, which 
open from the ventricle into the truncus, surround this 
opening. 

The walls of the truncus arteriosus are thick and mus- 
cular, though not nearly so thick as those of the ventricle. 
At its anterior end it appears to divide into two trunks, 
which diverge and immediately leave the pericardium to 
pass on to the sides of the gullet. The elongated undi- 
vided part is the pylangium, the terminal part common to 
the divergent trunks is the synangium. The former is 
divided throughout its length by a sort of fold which is 
attached to the dorsal wall while its opposite edge is free. 
Three semilunar valves separate the pylangium from the 
synangium, in which are the openings, posteriorly, of the 
pulmonary arteries, anteriorly of the carotid trunks ; while, 
at the sides, the cavity of the synangium opens into those 
of the right and left aortic arches. The apparently simple 


I.] THE FROG. 19 

branches into which the truncus arteriosus divides, are, in 
fact, each made up of three separate trunks, the pulmo- 
cutaneons trunk behind, the aortic arch in the middle and 
the carotid trunk in front. 

When the heart is in action, the sinus venosus, the atrium, 
the ventricle and the truncus arteriosus contract in the 
order in which they have just been named. Each contracts 
as a whole, so that the two auricles are emptied simulta- 
neously. The blood from each is forced into the correspond- 
ing half of the spongy cavity of the ventricle, so that the 
right half of the ventricle contains venous blood and the 
left arterial blood. When the systole of the ventricle takes 
place, the blood which is first driven into the truncus arte- 
riosus (the opening of which is, as has been seen, at the 
right end of the cavity) is therefore venous. It fills the 
conus arteriosus and, finding least resistance in the short 
and wide pulmonary vessels, passes along the left side of the 
median valve into them. But as they become distended 
the next portion of blood, consisting of the venous and 
arterial blood which have become mixed in the middle of 
the ventricle, passes on the right side of the longitudinal 
valve into the aortic arches. And, as the truncus becomes 
more and more distended, the longitudinal valve, flapping 
over, tends more and more completely to shut off the 
openings of the pulmonary arteries and to prevent any 
blood from flowing into them. 

Finally, the last portion of blood from the ventricle, 
representing the completely arterialized blood of the left 
auricle which is the last to arrive at the opening of the 
truncus, passes into the carotid trunks and is distributed to 
the head. 

The principal vessels of the Frog are disposed as fol- 
lows : 


20 ELEMENTARY BIOLOGY. [CHAP. 

A. Arteries. Efferent in relation to the heart, breaking up 
into lesser branches. 

1. The system of the anterior aortic arch (carotid 
trunks), distributing blood to the parts of the head 
generally and to the brain. 

2. The system of the middle aortic arch (aortic trunk), 
distributing blood to the body and limbs, together 
with the organs of the viscera other than the lungs. 

3. The system of the posterior aortic arch (pul mo- 
cutaneous trunks), distributing blood to the lungs 
and skin. 

B. Veins. Afferent in relation to the heart, formed by the 
union of lesser factors (they break up only in the case 
of the portal veins). 

T. The system of the superior cava, formed on each 
side by the union of the veins bringing back the 
blood from the head, fore-limbs, and parts adjacent. 
Special veins (great cutaneous] are concerned in the 
return of the blood from the skin. 

2. The system of the inferior cava, formed by the union 
of the efferent-renal, genital and hepatic veins. 

3. The system of the anterior abdominal and renal-portal 
veins ; formed by the bifurcation of the veins coming 
in from the hind-limbs. The former receives blood 
from the urinary bladder and the body-wall, and 
at its anterior end divides into two branches 
which go to the corresponding lobes of the liver. 
The latter gives off branches (afferent renal veins) 
which break up in the substance of the kidney. 

4. The system of the vena portcz (hepatic-portal vein) 
formed by the union of the veins which bring back 


1.] THE FROG. 21 

the blood from the alimentary-canal and its appended 
glands, with the spleen. This vessel enters the liver 
on the left side, breaking up within that organ; before 
doing so, it enters into a direct anastomosis with the 
anterior abdominal vein. 

5. The system of the pulmonary rein, formed by the 
union of the veins of the right and left lungs. 

The slit-like glottis of the Frog is formed by the appo- 
sition of two longitudinal folds of the mucous membrane 
of the mouth, each of which contains a cartilage of similar 
form. These cartilages are the arytenoid cartilages. They 
are articulated with an annular cartilage (laryngo-tracheal} 
which supports the wall of the very short chamber which 
represents the larynx and trachea. When the two folds of 
the glottis are divaricated, there are seen between them two 
membranous pouches, the free edges of which meet in the 
middle line, while anteriorly and posteriorly they pass into 
the mucous membrane which lines the faces of the longitu- 
dinal folds. These are the vocal ligaments, and the slit 
between them is what answers to the glottis in Man. 
It is by their vibration that the croak of the Frog Is pro- 
duced. 

Laterally the laryngo-tracheal chamber opens into the 
lung of each side. The lung is a transparent oval sac, 
somewhat pointed posteriorly, which lies at the side of the 
oesophagus in the anterior region of the pleuroperitoneal 
cavity. It is covered by a layer of the pleuroperitoneal 
membrane which represents the visceral layer of the pleura 
in the higher animals. The wall of the pulmonary sac is 
produced inwards so as to give rise to a network, which is 
much more prominent in the anterior than in the posterior 
part of the lung and divides the periphery of the cavity 


22 ELEMENTARY BIOLOGY. [CHAP. 

into numerous air-cells, on the walls of which the ramifi- 
cations of the pulmonary vessels are distributed. 

The lungs are elastic, the distended lung collapsing sud- 
denly when it is pricked, and they contain abundant mus- 
cular fibres. 

It is essential to respiration that the mouth should be 
shut, and it is said that frogs may be asphyxiated by keeping 
their mouths open. 

Inspiration is effected by a buccal force-pump. The 
mouth being shut and the external nostrils open, the floor 
of the mouth is depressed, and the buccal cavity fills with 
air. The muscles of the flank next come into play, exer- 
cising a pressure upon the surrounding viscera which suffices 
to expel the air (expiration). 

The nostrils being then shut, the hyoid, and with it the 
floor of the mouth, is raised, and, the aperture of the gullet 
being at the same time closed, air is forced through the 
glottis, distending the lungs. 

Expiration is doubtless aided by the contraction of the 
intrinsic muscular fibres of the lungs ; and it may be that 
those fibres which form the so-called diaphragm also tend 
to diminish the capacity of the lungs. 

In addition to its principal pulmonary apparatus of re- 
spiration, the Frog has a secondary respiratory apparatus in 
its moist and delicate skin. A considerable amount of venous 
blood is, in fact, constantly supplied to this organ by the 
large cutaneous branch of the pulmo-cutaneous artery. It 
has been experimentally ascertained that frogs in which the 
lungs have been extirpated will continue to live and respire 
for a considerable time, especially at a low temperature, by 
means of the skin. 

The kidneys are elongated and flattened from side to side, 
and are kept in position by the continuation of the peri- 


I.] THE FROG. 23 

toneum over their ventral faces. The ducts of the kidneys 
pass along their outer edges and, approaching as they pass 
backwards, open by two slit-like apertures in the posterior 
wall of the cloaca. 

The urinary bladder (itrocysf] is a large bilobed sac, 
opening posteriorly, by a wide median aperture, into the 
antero-ventral end of the cloaca. 

The testes are ovoidal yellowish bodies situated in front 
of the kidneys and enveloped in peritoneum, a fold of which, 
forming a sort of testicular mesentery or mesorchium, is de- 
rived from that which covers the ventral face of the kidney. 
The delicate vasa efferentia of the testes may be seen travers- 
ing this fold to enter the substance of the kidney. They 
communicate with the urinary tubules, and thus the duct of 
the kidney serves not only as the duct of the urinary se- 
cretion but as the vas deferens. 

The spermatozoa of the Frog are filiform bodies with 
cylindrical, more or less linear, nucleus bearing heads. 

The ovaries are broad lamellar organs, very large and 
much folded and plaited in the breeding season. In- 
numerable ovisacs, or follicles, containing dark-coloured 
ova, are scattered through the substance of the ovary and 
give rise to projections on its surface as they become 
fully developed. The ova are finally thrown off by 
dehiscence. 

The oviducts are long convoluted tubes situated on each 
side of the dorsal wall of the abdominal cavity, to which they 
are connected by peritoneal folds; each curves over the 
outer face of the root of the lung. Their anterior ends are 
very slender, and terminate by open mouths at the sides of 
the pericardium, between the attachment of the so-called 
diaphragm and the lobe of the liver. For the greater part 
of their length their walls are thick and glandular, and 


24 ELEMENTARY BIOLOGY. [CHAP. 

swell up when placed in water. Posteriorly, the oviducts 
dilate into capacious thin-walled chambers and end, close 
together, by openings which are situated in the dorsal 
wall of the cloaca immediately in front of the apertures 
of the ureters. Remnants of the oviducts are usually pre- 
sent in the male. 

Each ovum, when ripe, consists of a protoplasmic yolk- 
laden mass or vitellus, enclosed in a structureless vitelline 
membrane, and containing a germinal vesicle, within which 
are several 'germinal spots.' One half of the vitellus is 
deeply coloured, the other pale. 

The so-called ductless glands are three in number. The 
Thymiis; a small rounded body situated immediately behind 
the suspensorium, in a position corresponding to the dorsal 
ends of the obliterated branchial arches. The Thyroid ; 
represented by two or more oval bodies, which are found 
attached to the bases of the aortic arches. The Adrenals; 
yellow bodies imbedded in the ventral face of the kidney. 

The actions of the different parts of the organism of the 
Frog are coordinated with one another and brought into 
relation with the external world by means of the muscular 
and nervous systems and the organs of sense. 

The muscles consist partly of striped and partly of un- 
striped fibres, the former being confined to the muscles of 
the head, trunk and limbs and the heart, while the latter 
are found in the viscera and vessels. The former are usuallv 

j 

arranged in sets, the actions of which may be antagonistic 
and simple or coordinated and complex. An account of 
the disposition of the muscles in the hind-limb will be 
found in the Laboratory work. 

The nervous system is conveniently divisible into two 
parts, the cercbro-spinal and the sympathetic. The cerebro- 
spinal nervous system again consists of the brain, or encepha- 


I.] THE FROG. 25 

Ion, with its nerves, and the spinal cord, or myelon, with its 
nerves. 

The encephalbn lies in the cranial cavity, which it nearly 
fills, and is divisible into the hind-brain, the mid-brain and 
the fore-brain, which last again comprises three divisions; 
the median thalamencephalon, and the paired cerebral 
hemispheres and olfactory lobes. 

The greater part of the hind-brain is formed by the 
medulla oblongata, which is the continuation of the myelon 
forwards and presents, when laid open from its dorsal 
aspect, a triangular cavity, the apex of which is directed 
backwards. The cavity is the fourth ventricle ; it com- 
municates behind with the central canal of the myelon, 
while, in front, it narrows into a passage which connects the 
fourth ventricle with the brain cavities anterior to it. The 
thick lateral ridges of nervous substance at the sides of the 
fourth ventricle, which represent the restiform bodies, pass, 
in front, into the outer extremities of a short broad tongue- 
shaped plate, convex ventrally and concave dorsally, which 
overhangs the anterior part of the fourth ventricle, and 
is the cerebellum. 

In front of this, the dorsal moiety of the mid-brain is 
formed by two oval bodies, the optic lobes. When laid open, 
each is seen to contain a cavity or ventricl-e which com- 
municates with the iler a tertio ad quartuin ventriculum, 
as the ventricle of the mid-brain is termed. The floor 
of this canal is formed by the thick principal mass of 
the cerebro-spinal axis. It exhibits a median longitudinal 
depression or raphe, and in this region represents the erura 
cerebri. 

In front of the mid-brain comes the hinder division of 
the fore-brain, or thalamencephalon, which is very distinct in 
the Frog and contains a median cavity, the third ventricle. 


26 ELEMENTARY BIOLOGY. [CHAP. 

On each side, the cavity of the third ventricle is bounded 
by a thick mass of nervous matter into which the crura 
cerebri pass. These are the optic thalami. The roof of 
the third ventricle is very thin and easily torn through ; its 
fore part is prolonged up to form a delicate process in con- 
nexion with an ovate body, which is lodged between the 
posterior parts of the cerebral hemispheres and represents 
a portion of \hz pineal gland. The front part of the floor of 
the ventricle, on the other hand, is produced into a back- 
wardly directed process, the infundibulum. This is con- 
nected below with a highly vascular mass, the pituitary 
body. 

The hemispheres are elongated bodies, broader behind 
than in front, where they are marked off only by a slight 
constriction from the olfactory lobes. 

Anteriorly, the wall of the third ventricle is thickened 
to form the lamina terminalis ; on each side, between this 
and the peduncle of the pineal gland, is a small aperture, 
the foramen of Munro, which places the median third- 
ventricle in communication with the paired lateral ventricle 
of the cerebral hemisphere. 

The lateral ventricle is continued on either side into the 
base of the olfactory lobe to form the olfactory ventricle. In 
front these lobes become nerve-like cords, which leave 
the skull and spread out on the posterior faces of the 
olfactory sacs. 

The inner faces of the olfactory lobes are confluent with 
each other, and there pass between corresponding parts 
of opposite halves of the brain bands of fibres or com- 
missures (see Laboratory work) the most important of which 
runs through the substance of the lamina terminalis and 
represents the corpus callosum. 

The entire cerebro-spinal axis is invested in a highly 


I.] THE FROG. 27 

vascular membrane or pia mater. This becomes immensely 
thickened, above the hind-brain and on the inner faces 
of the hemispheres, to constitute the choroid plexuses. The 
former of these is median and overlies the greater part 
of the fourth ventricle. The latter is paired ; in its growth 
each half forces its way into the lateral ventricle, pushing the 
thin inner wall of the same in front of it ; while therefore 
it lies, in a sense, within that cavity, it is in reality 
outside it. 

There are ten pairs of cranial nerves ordinarily so-called, 
the first two of which are proved, by their development, to 
be lobes of the brain. 

1 . If actor ii. 

The olfactory lobes. Their nerves are distributed 
exclusively to the olfactory sacs. 

2. Opt ici. 

These diverge from the base of the brain in front of 
the infundibulum. They are originally outgrowths 
of the thalamencephalon which secondarily become 
connected with the optic lobes. They are distributed 
exclusively to the retina of the eye. 

Of the remaining cranial nerves five pairs leave the skull 
in front of the auditory capsules, while one pair enters those 
capsules and two pairs pass out behind the same. 

The Pr&auditory nerves are the following. 

3. Mo tores oculorum 

arise from the front part of the floor of the mid-brain 
and are distributed to all the muscles of the eye 
except the external rectus, the superior oblique and 
the retractor bulbi. 


28 ELEMENTARY BIOLOGY. [CHAP. 

4 . Pathetici 

arise from the floor of the mid-brain and pass out, 
on the dorsal aspect of the brain, between the cere- 
bellum and the optic lobes. They are distributed 
to the superior oblique muscles of the eye. 

5. Trigemini 

take their origin in the front part of the floor of the 
hind-brain and, passing out at its sides, each dilates 
into a yellow enlargement the Gasserian ganglion- 
which lies in front of the auditory capsule, in the 
foramen by which the nerve, after leaving the ganglion, 
passes out of the skull. 

This ganglion is connected with the trunk of the sixth 
and seventh nerves and with the anterior end of the sym- 
pathetic (some of the branches which appear to be given 
off from it really belong to the sixth and the seventh nerves, 
see infra). Beyond the ganglion, the nerve divides into 
two main branches, the orbito-nasal, and the maxillo-mandi- 
bular. 

i. The orbito nasal (usually termed the first division of 
the fifth nerve); passing through the antorbital pro- 
cess of the skull, it is finally distributed to the nasal 
mucous membrane and to the integument of the nose. 
It anastomoses with the fourth nerve, and sends a 
branch to the Harderian gland. 

ii. The maxillo-mandibular ; forks over the mouth-cavity 
into two trunks, usually termed the second and third 
divisions of the fifth nerve. 

a. Preoral or Maxillary, passes outside the eye and 
is distributed to the integument of the upper jaw. 


I.] THE FROG. 29 

b. Postoral or Mandt&ular, passes between the 
temporal and pterygoid muscles, over the articu- 
lation of the mandible and along the inner face 
of the latter, to the symphysis, giving off branches 
to the integument, muscles, teeth and tongue* 

6. Abducentes 

arise from the floor of the hind-brain and leave the 
ventral surface of the medulla oblongata close to the 
middle line. Each then unites so closely with the 
Gasserian ganglion and with the orbito-nasal division 
of the fifth as to appear to be only a subdivision 
of the latter. Its fibres are distributed to the external 
rectus and retractor bulbi muscles of the eye. 

7. The Fad ales 

take their origin from the floor of the hind-brain, 
behind the fifth and in common with the eighth; 
and, leaving the hind-brain, enter into close con- 
nexion with the Gasserian ganglion. Each then 
divides into two branches, an anterior and a pos- 
terior. 

i. The anterior or palatine nerve ; distributed to the 
roof of the mouth and palate. 

This nerve is in anastomosis with the maxillary 
branch of the fifth. 

ii. The posterior branch. It forks over the tympanic 
cavity into two trunks; a smaller pretympanic which 
may represent the chorda tympani and a larger post 
tympanic or hyoid nerve^ which supplies the muscles 
of the hyoid and floor of the mouth. 

8. The And it or ii 

arise in common with the foresroinef. Each divides 

O O 


3O ELEMENTARY BIOLOGY. [CHAP. 

into two branches which enter the auditory capsule to 
reach the organ of hearing. 

The Post-auditory nerves are : 

9. The Glossopharyngei. 

These nerves arise, side by side with the next, from 
the medulla oblongata ; and the roots of both leave 
the skull by an aperture behind the auditory capsule 
on each side, and form a common ganglion. Each 
passes downwards and forwards to the root of the 
tongue, which organ it finally supplies. Moreover, it 
gives off muscular branches and forms an anastomo- 
sis with the seventh. 

10. The Pneumogastrici or Vagi. 

Immediately after leaving the ganglia these nerves 
separate from the glossopharyngeal and each gives 
off a cutaneous branch to the dorsal integument of 
the head and trunk : it then divides into two 
branches, one of which is distributed to the larynx, 
the other to the heart, lungs, and stomach. (Sym- 
pathetic fibres are in part bound up with these.) 

The my clou or spinal cord is continued back from the 
hind-brain as a subcylindrical cord, which lessens somewhat 
rapidly towards its apparent end at the level of the seventh 
vertebra. It does not really end here, however, but is con- 
tinued back as a slender filament, \\\.filum terminate, to the 
commencement of the canal of the urostyle. The diameter 
of the cord is somewhat enlarged opposite the origin of the 
nerves for the limbs. In transverse sections, the cord is 
seen to be not truly cylindrical but to be indented by 
two longitudinal grooves, one dorsal and one ventral, which 
leave but a small connecting bridge between its two halves. 


I.] THE FROG. 31 

In the centre of this is a canal, the canalis centralis, the 
cavity of which is continued forwards into the fourth ven- 
tricle. 

Ten symmetrically disposed pairs of nerves come off 
from the sides of the cord, each nerve having two roots, one 
from the dorsal surface of the lateral half of the cord and 
one from the ventral surface. The dorsal root presents a 
small ganglionic enlargement, beyond which it is bound up 
in a common sheath with the ventral root to form the com- 
mon trunk of the spinal nerve. The roots of the hinder 
spinal nerves are very long and lie, side by side, in the 
spinal canal. 

The first spinal nerve leaves the neural canal by the 
interspace between the arches of the first and second 
vertebrae, so that there is no nerve in the Frog answering to 
the suboccipital. It gives a branch to the muscles which 
move the head upon the backbone, but the main trunk of it 
descends behind the mandible, along with the glosso- 
pharyngeal nerve, and is distributed to the muscles of the 
tongue. Its distribution therefore answers to that of the 
hypoglossal nerve in the higher Vertebrata. 

The second and third spinal nerves unite to form a 
l brachial plexus] and are distributed chiefly to the fore- 
limb. 

The fourth, fifth and sixth spinal nerves go to the middle 
parietes of the body. 

The seventh, eighth and ninth, are large nerves which 
unite to form the lumbosacral plexus, whence nerves are 
given off to the posterior parietes of the body, and to the 
hind-limb. 

The tenth spinal nerve leaves the neural canal by the 
coccygeal foramen, and is distributed to the adjacent 
parts. 


32 ELEMENTARY BIOLOGY. [CHAP. 

Sympathetic. 

The sympathetic system consists of ganglia, usually ten 
in number on each side, connected by longitudinal com- 
missures, and situated on the ventral face of the vertebral 
column ; in the region of the dorsal aorta they come into 
close relation with it. Each sympathetic ganglion is joined 
by a communicating filament or ramus with one of the 
spinal nerves, and the most anterior ganglia are connected, 
in the same way, with the ganglia of the ninth and tenth 
cerebral nerves. Thence a delicate cord passes into the 
cranial cavity on the inner side of the periotic capsule, and 
unites with the Gasserian ganglion. 

The branches of the sympathetic accompany the vessels, 
and large branches are given to the viscera. 

The sheath of the ganglion of each spinal nerve encloses 
a milk-white body (perigatiglionic gland] whose function is 
unknown. Each consists of a tubular gland, lined by a 
single-layered epithelium and containing calcareous matter 
in a finely crystalline state. When fully formed these glands 
force their way through the inter-vertebral foramina, appearing 
as a series of concretionary masses lying around the spinal 
nerves at their points of exit from the column, and alternating 
with the bases of the transverse processes of the vertebras. 

The Olfactory organs occupy all the space between the 
mesethmoid cartilage, the antorbital processes, and the 
premaxillae and maxillae, and open in front and externally 
by the external nares, behind and internally, into the mouth- 
cavity, by the posterior nares. Each consists of an essential 
part or olfactory sac, the inner face of which is lined by a 
peculiar epithelium, which receives the olfactory branches 
of the trigeminal nerves, and an accessory part consisting of 
a partly cartilaginous, partly bony, capsule. 


I.] THE FROG. 33 

The Eyeball is lodged in the orbit and protected by the 
eyelids, described above. It has four recti muscles which 
proceed from the inner wall of the orbit, and are attached 
to the circumference of the globe; within these is a retractor 
muscle with similar attachments, ensheathing the optic 
nerve, while two oblique muscles proceed from the anterior 
and inner wall of the orbit and are attached to the dorsal 
and ventral faces of the bulb. In addition, a fine tendon 
passes from the outer end of the lower eyelid, or nictitating 
membrane, and is attached to the fibres of the retractor 
bulbi the effect of which is that when the bulb is retracted 
the nictitating membrane is raised over the eye. The upper 
lid has no muscles. A secretory organ, termed the Harde- 
rian gland, is situated in the anterior part of the orbit 
beneath the superior oblique muscle. 

The essential part of the eye is the inner lining or retina, 
which receives the fibres of the optic nerve ; to this there 
are superadded a vascular pigmented choroid and a car- 
tilaginous sclerotic, which together constitute an accessory 
capsule. The lens is nearly spherical. 

The Ear consists of an essential part the membranous 
labyrinth receiving the fibres of the auditory nerve, lodged 
in an accessory partly osseous, partly cartilaginous, periotic- 
capsule; to the latter are superadded the columella auris, 
the tympanic membrane and the tympanum. 

The labyrinth consists of three semicircular canals which 
open into a vestibule divided into utriculus and sacculus. 
The latter, especially, contains a great quantity of white 
crystalline calcareous otoliths. 

On the outer side of the vestibule is a small dilatation 
which is possibly a rudimentary cochlea. 

The membranous labyrinth is filled with a fluid (endolymph], 

M. 


34 ELEMENTARY BIOLOGY. [CHAP. 

and contained, as has been stated, in the periotic capsule 
into which it fits but loosely; the interval between the two 
being filled with a fluid, the perilymph. In the outer face 
of the periotic capsule is an opening, t\\Q fenestra ovalis, into 
which the end of the colnmella auris fits. This columella is 
shaped like a pestle, the end of the handle of which is fitted 
with a cross-piece. The rounded inner end of the pestle, 
which is fixed by fibrous tissue into the fenestra ovalis, is 
cartilaginous. The middle of the handle is ensheathed in 
bone, while the outer part is cartilaginous. The cross-piece 
is fixed into the inner face of the membrana tympani, which 
is covered externally by the integument, and lined internally 
by the mucous membrane of the tympanic cavity, which is 
continuous with that of the mouth through the Eustachian 
recess, and wraps round the ventral face of the columella. 
A sound wave, impinging upon the drum of the ear, is trans- 
mitted through the agency of the columella to the perilymph 
and endolymph, auditory epithelium and nerve, to the brain. 

The Tongue. This organ, as has been seen, is fixed only 
in front to the mandible, and by the anterior half of its ven- 
tral aspect to the floor of the mouth; the posterior half 
being free and bifid at the extremity. Narrow-ended and 
broad-ended papillae (papilla filiformes and fungiformes) are 
scattered over the whole dorsal aspect of the tongue and are 
largest in front ; small glands lie between these papillae. 

The fungiform papillae contain the ultimate ramifications 
of the glossopharyngeal nerve, and the epithelium covering 
their summits is peculiarly modified. 

The Integument. No special organs of touch have been 
observed, but the integument is remarkable for the immense 
number of close-set simple glandular caeca (cutaneous glands) 
which open upon its surface. In the swollen integument 


I.] THE FROG. 35 

which covers the base of the inner digit in the males, large 
papillce with interposed glands are developed. 

A singular spheroidal sac-like body known as the browspot 
or inter-ocular gland, occurs in the integument of the fronto- 
parietal region of the head. In the young animal it is in 
connection with the pineal gland, and represents the rudi- 
ment of the median or pineal eye a structure which is 
more fully developed in some Lizards. 

Cells containing pigment abound in the integument and 
undergo remarkable changes of form, the pigment being 
sometimes drawn together into a spheroidal mass at other 
times distributed in a radiating fashion. 

LABORATORY WORK. 

Frogs may best be killed with chloroform. Place the 
animal under an inverted tumbler together with a square 
inch of cotton-wool saturated with chloroform ; cover with 
a cloth and leave for 10 15 m, 

A. General external characters. 

1. Its division into head, trunk, two pairs of limbs or 
appendages. 

2. Its anterior or head end; pointed and bearing the 
mouth, eyes, and other organs of the higher senses. 
Its posterior or tail end. Its dorsal or back region ; 
clad in a darkly coloured integument. Its ventral 
or belly region; clad in a whitish integument. Its 
lateral or side area -, bearing the two pairs of limbs. 
(Work over the specific characters given on pp. 6, 7.) 

a. The head. 

Somewhat triangular, with the blunted apex 
turned forwards and passing, without any neck- 
constriction, into the trunk. 


36 ELEMENTARY BIOLOGY. [CHAP. 

a. The prominent eyes with their eyelids. 

/?. The membrana tympani^ a thin part of the in- 
tegument stretched over a hard ring, on each 
side, behind and somewhat below the eyes. 

y. The anterior nares ; two small apertures near 
the middle line at the end of the snout. 

S. The month-opening; note its boundaries and 
extent. 

e. The browspot ; lying in the mid dorsal integu- 
ment of the head on a level with the front of the 
eyes. Clearly visible under a hand lens. 

. Open the mouth widely; the fleshy tongue will 
be seen, with its bifurcated free end turned 
backwards ; teeth are present only in the upper 
jaw and on the roof of the mouth. 

b. The trunk. 

Tapering towards the hinder end, and allowing 
the hard parts of the skeleton to be felt beneath 
the soft integument on the dorsal side, and in 
the anterior half of the ventral aspect. Note the 
doacal aperture near the dorsal surface of its 
posterior end. 

c. The limbs. 

a. The anterior pair; their three subdivisions, 
brachtum, antebrachium, and manus ; the four 
digits. 

fi. The posterior pair ; their length as compared 

with that of the anterior; their subdivision into 

femur, crus, and pes: the five long digits ; the 

well-developed web; the horny prominence on 

the inner side. 


I.] THE FROG. 37 

B. Preliminary, and general disposition of the viscera. 

i. Place the animal on its back and pin down high and 
dry, inserting the pins through the limbs and point of 
snout. Raise the ventral integument with forceps and 
slit it up with scissors along the middle line from the 
lower jaw to the origin of the hind limbs; pin back 
the two flaps and note : 

a. The skin; it is but loosely connected with the sub- 
jacent muscular wall of the trunk, the two being 
separated by spacious chambers (lymph cavities, cf. 
Sect. I. a). 

b. A large vein (great-cutaneous) on the under-surface 
of each flap of skin. 

c. Some of the muscles of the body wall ; covered by 
a thin sheath or aponeurosis, through which they 
can be seen- 

a. The rectus abdominis; running from pelvis to 
sternum along the middle line, and divided into 
a number of segments by transverse tendinous 
intersections. 

A large vein (anterior-abdominal} will be seen, 
running along the ventral middle line, immediately 
under cover of this. 

J3. The pectoralis ; an immense tract of tissue arising 
from the ventral wall of the trunk externally, and 
in front ventrally, to a. It is subdivided into a 
series of lesser muscles which converge towards 
the base of the fore-limb. (Note that it is 
confluent posteriorly with a, and, in front, sub- 
divided up by tendinous intersections.) 

y. The mylohyoid or sub-maxillaris ; a sheet of 
muscle, tendinous in the middle line, whose 


38 ELEMENTARY BIOLOGY. [CHAP. 

fibres pass transversely across the floor of the 
mouth. It is subdivided into a larger fasciculus 
which supports the floor of the mouth, and a 
smaller ribbon-shaped one which passes back on 
either side to the angle of the lower jaw. 

S. The external oblique; underlying and external to 
y8; forming an investment for the body wall 
laterally. Its fibres run obliquely upwards and 
forwards. 

e. The internal oblique ; seen on removing a portion 
of B. Its fibres pass obliquely downwards and 
backwards. 

. The trarisversalis ; seen on removing a portion of 
e. It forms the inner layer of the muscular 
constituent of the body-wall; its fibres run 
transversely, so as to encircle the trunk ventro- 
laterally. 

2. Raise the tissues of the body-wall with a pair of 
forceps and carefully divide them a little to the right 
of the median line, so as to open the underlying body- 
cavity without injuring its contents; prolong the 
incision from the pelvis to the posterior end of the 
breast-bone. Make a transverse incision close to the 
pelvis and throw back the flap on each side : on the 
under side of the left flap will be seen the anterior ab- 
dommalv&m (cf. i c. a). 

Seize the posterior border of the sternum with a 
pair of forceps and raise it up; then, with a strong pair 
of scissors, cut through the hard parts a little to one 
side of the middle line, being very careful not to 
injure the organs beneath them. Raise each half of 


I.] THE FROG. 39 

the shoulder girdle thus liberated and remove it, with 
care, together with the rest of the ventral portion 
of the body- wall. 

A spacious cavity (pleuro-peritoneal cavity] will be 
laid bare. Note the general characters and mutual 
relations of the undermentioned organs of the viscera 
which lie within it, as seen in the undisturbed state. 
They will be found severally connected with the body- 
wall and each other by a delicate membrane or 
mesentery. 

a. The liver: a great brown two-lobed mass, its left 
lobe the larger and subdivided into two, lying in 
the anterior end of the cavity. 

b. The lungs: the posterior ends of these may be seen 
as sacculated pouches, one on each side of the liver, 
but they are frequently not visible until the latter 
organ has been displaced. 

c. The stomach: a small portion of this is seen pro- 
jecting beyond the lower left border of the liver. 
Note that it lies exclusively to the left side. 

d. The intestine: a convoluted tube, continuous with 
the stomach, and occupying the middle third of the 
cavity. It can be resolved into- 

a. The small intestine; a yellowish-white tube, con- 
voluted and situated wholly to the right side. 

(3. The large intestine; a short straight greyish-green 
tube, of greater calibre than a, passing obliquely 
backwards in the middle line. 

e. The urinary bladder (urocyst], a thin-walled bilobed 
sac (which may or may not be distended) lying just 
in front of the pelvis, immediately above (ventral 
to)/?. 


40 ELEMENTARY BIOLOGY. [CHAP. 

In 7?. temporaria, the urinary bladder is larger 
proportionately and more deeply lobed than in R. 
esculenta. 

f. The spleen: a small red body lying in the middle 
line, immediately in front and to your right of the 
large intestine. 

g. The kidneys; two dark red lentil-shaped bodies, 
seen, on displacing the intestine, lying close to- 
gether in the middle line. 

//. The genital glands ; immediately adjacent (ventral 
and external) to g. 

a. In the male. The testes: a pair of yellowish 
bodies lying near the anterior ends of the 
kidneys. 

fi. In the female. The ovaries; a pair of blackish 
yellow bodies, coincident in position with, but 
much more extensive than, a. Each is folded, 
and seen to be composed of an immense number 
of spherical ova. 

i. The fat masses (corpora adiposd] ; long filiform 
deep-yellow processes attached to the anterior ends 
of the genital glands. They are much the larger in 
the male. 

;'. The genital ducts; obvious in the female as highly 
convoluted dead-white tubes (oviducts} lying imme- 
diately beneath (3. (Those of the male may be 
better studied later on.) 

k. The heart ; seen lying within a delicate sac (the 
pericardium] immediately in front of the liver. 

Slit open the pericardium. It will be found to 
contain a fluid (serous fluid] which bathes the en- 
closed viscus (heart). Examine the pleuro-peri- 


I.] THE FROG. 41 

toneal cavity; a similar fluid will be found to be 
present, but to a lesser degree, imparting a moist- 
ness to the organs therein contained. 

C. The study of transverse sections. Especially with a 
view to ascertaining the limits and mutual relationships 
of the larger cavities and the body-wall, together with 
the mode of suspension of the viscera. 

Obtain a frog (preferably one which has been for 
24 hours or longer in spirit) and make transverse 
sections across its body, as directed below. Examine 
under water. 

i. Across the mid region of the trunk; to pass through 
the kidneys, genital glands, and large intestine. 

a. The body-iuall ; especially its muscular constituent, 
which is thickened dorsally in the region of the 
back. 

I). The splanchnic (pleuro-peritoneal'] cavity ; ventral 
and spacious ; it lodges the organs of the viscera. 

c. The neural cavity; relatively small, situated in the 
dorsal middle line and enclosed on all sides by 
the bony vertebral column. It lodges the central 
nervous system, seen, in section, as a delicate white 
cord. 

d. The alimentary canal; cut across at various points. 
Remove those portions of it which do not happen 
to be connected by mesentery with the body-wall 
or other parts. The large intestine will be seen in 
section in the ventral middle line ; take note of its 
position and relationships. 

e. The kidneys ; lying close together, dorsally to all 
the other organs and obliquely disposed. 


42 ELEMENTARY BIOLOGY. [CHAP. 

f. The genital glands; immediately external and 
ventral to e. (cf. Sect. B. 2. h.) 

g. The plenro-peritoneal membrane. This will be most 
readily seen stretching from the dorsal border of 
the kidney to the upper angle of the body-wall; 
having found it, proceed as under. 

a. Start from one kidney and follow it upwards ; on 
reaching the body-wall it becomes closely applied 
thereto, lining it, in the form of a dense pig- 
mented membrane (parietal-layer or peritoneum). 

fi. Follow it downwards on the same side. It passes 
over the outer face of the kidney and then gives 
rise to a fold which suspends the genital gland 
(mesorchium ^, mesoarium ) ; the folds of 
opposite sides then meet in the middle line and 
pass down as a double membrane (mesentery) 
which suspends and enwraps the intestine. 

Little difficulty will be found with the above, if, 
starting from the i;idney, the membrane be care- 
fully torn away as followed. 

y. The cisterna magna (sub-vertebral lymph sinus) ; 
a spacious cavity into which the kidneys project, 
enclosed between the folds of the mesentery 
dorsal to the alimentary canal. The cut ends of 
a large blood-vessel (dorsal aorta) and of certain 
small nerves will be seen lying within it. 

2. Obliquely forwards, across the anterior end of the 
body cavity ; to pass through the heart, the anterior 
border of the liver and the roots of the lungs. Cf. 
generally with i. and note in addition. 


I.] THE FROG. 43 

a. The (esophagus; a thick walled tube lying at or near 
the middle of the whole section. 

b. The lungs; thin walled spongy sacs (tubular in. sec- 
tion) right and left of a. 

c. The liver; occupying the greater portion of the 
pleuro-peritoneal cavity and lying immediately below 
a. and b. 

d. The heart; situated in the middle ventral line. 

e. The neural canal and central nervous system; rela- 
tively much larger than in Sect. i. 

f. The body-wall; in part inflected, giving rise to a 
sheet of muscle (so-called diaphragm] which is 
attached, on opposite sides, to the oesophagus. 

g. The aorta; here paired (aortic arches). 

h. The pericardium; a double-walled sac enclosing 
the heart, and related to it as is the pleuro-peri- 
toneal membrane to the body-wall and its con- 
tained viscera. 

/. The pleuro-peritoneal membrane. (Cf. generally 
with previous section.) Note that having sus- 
pended the organs above-named, it passes round 
the pericardium, giving rise to a fold (falciform 
ligament) which is reflected on to the body-wall 
below, there being thus formed a septum which 
completely subdivides the pleuro-peritoneal cavity, 
in this region, into two. 
Its special folds are: 

a. The ligamentum latum; suspending the lung to 
the oesophagus. 

The lesser amentum; passing between the oeso- 
phagus and liver in the middle line. 


44 ELEMENTARY BIOLOGY. [CHAP. 

y. The falciform ligament (suspensory ligament of 
the liver). Cf. supra. If the section has passed 
through the anterior border of the liver, this will 
also be seen to pass between its outer edges and 
the body-wall. 

j. The sub-cutaneous lymph-spaces ; seen (in this and 
the preceding section) as a series of four spacious 
chambers, lying between the body-wall and in- 
tegument, and separated from each other by mem- 
branous partitions. 

k. The anterior abdominal vein; this will probably be 
seen, enclosed within the folds of the mesentery 
immediately below the liver. 

3 Across the head; to pass through the mouth-cavity 
and eyes. 

a. Note the absence of body-cavity and the relatively 
great size of the neural canal and central nervous 
system (brain\ 

b. The mouth cavity; spacious, and enclosed on all 
sides in a soft mucous membrane. 

c. The tongue;* a median up-growth of the floor of the 
mouth, supported at its base by a cartilaginous 
plate, the hyoid. 

d. The eyes ; spherical sacs with firmly resistant cap- 
sules, closely applied to the outer integument. 
Note, in connection with them, 

a. The eye-muscles ; passing backwards and down- 
wards, between the eye-ball and cranial wall. 

The eye-lids ; folds of integument above and 
below the eyes, continuous at their bases with 
a delicate fold of skin (conjunctiva] which invests 


I.] THE FROG. 45 

the outer face of the eye-ball. The upper lid is 
thick and fleshy; the lower (nictitating membrane] 
is thin and transparent. 

f-. The sub-cutaneous lymph spaces ; present only above 
and below. 

D. The alimentary system. 

i. Obtain a male frog, and pin down upon its back 
under water. Remove the whole of the ventral 
integument and body-wall and dissect away the 
heart. Next remove the dorso-lateral portion of the 
body-wall, between the back of the head and the 
level of the hinder third of the large intestine, and 
with it the kidneys and testes. Carefully dissect 
away the mesenteric folds which support the liver 
and bladder, and wash clean. 

a. The general disposition of the parts. Cf. Sect. B. 
2 a -f. 

b. The pancreas : a Y-shaped compact yellow mass 
lying in the mesentery between the stomach and 
head of the intestine. 

c. The gall-bladder : a small green sac, lying between 
the right lobe of the liver and the head of the 
pancreas. 

d. The small intestine; of uniform calibre through- 
out. It may be resolved into 

a. The duodenum; a short straight segment running 
parallel with the stomach and related to the 
pancreas. 

The ileum; the terminal coiled portion, desti- 
tute of connection with the pancreas. 


46 ELEMENTARY BIOLOGY. [CHAP. 

e. The large intestine; cf. Sect. B. 2. d. 

f. The lungs ; apparent as sac-like diverticula of the 
gullet, immediately in front of the liver (leave 
them in place). 

2. Lay open the interior of the stomach and duodenum. 
Wash carefully and examine in water under a hand 
lens. 

a. The stomach: its lining membrane (mucous mem- 
brane) is smooth and thrown (if the viscus be not 
distended with food) into a number of irregular 
longitudinal folds or ruga. 

Note the nature of its contents; consisting of 
worms or other small animals in a partially di- 
gested state. 

b. The duodenum. Note the shaggy nature of its 
lining membrane ; it is sharply marked off from 
that of the stomach at 

f. the pylorus; a valve-like fold, obvious as a con- 
striction at the point of junction between a. and b. 

d. The ileum; slit it open and examine under a hand 
lens. 

a. Its contents; food material in a highly emulsified 
assimilable condition. 

/?. Its lining membrane; beset by numerous semi- 
lunar folds (intestinal valves] arranged in parallel 
series. These may be ill denned. 

e. Open up, in like manner, the large intestine. 

a. Its contents; food material in a dry state, little 
assimilable and green (faces). Note that the 
colour of the same is identical with that of the 
bile seen in the gall-bladder. 


I.] THE FROG. 47 

yS. Its lining membrane; smooth and comparatively 
thin. 

3. The liver, bile and pancreatic ducts. Cf. Sect. B. 2. a. 
Gently squeeze the gall-bladder between the finger 
and thumb of the left hand, keeping your attention 
fixed on the duodenum and pancreas. The bile- 
duct will be thereby injected and the bile will be 
seen to enter the duodenum by a small orifice 
situated at about its middle. 

a. The common bile-duct; its terminal third is plainly 
visible, as a delicate tube (now injected green) 
emerging from the pancreas to enter the duode- 
num. Follow it up; it runs through the pancreas 
towards the gall-bladder. 

b. The hepatic ducts; variable in number. Seen, on 
moving the gall-bladder about, to pass from the 
liver and unite to form the main duct a. 

c. The gall bladder ; a blind sac, set on at the ex- 
treme end of the above system of ducts. Open it, 
and note that it communicates with the liver 
through the agency of the hepatic ducts alone. 

d. The pancreatic ducts; one or more in number; 
seen, on careful examination, to enter the bile- 
duct as it courses through the pancreas. 

4. The cloaca and bladder. Cut away the front of the 
pelvis with a stout pair of scissors, taking care not to 
injure the bladder: remove the front wall of the 
latter, together with a portion of that of the large 
intestine. Pin the bladder aside and examine under 
water. 

a. The cloaca; the terminal portion of the alimentary 


48 ELEMENTARY BIOLOGY. [CHAP. 

canal, at that point at which it receives the urine- - 
genital ducts. 

Examine its lining membrane ; it is for the most 
part identical with that of the large intestine ; that 
of its terminal third has the characters of the inte- 
gument. 

/>. The ureters (iirinogenital ducts . Cf. Sect. F. 3); 
their openings will be seen as two minute orifices, 
on the dorsal wall of a., situated close together and 
surrounded by tumid lips. 

c. The bladder ; a median ventral diverticulum of a., 
having no direct communication with the ureters. 

E. The cavity of the mouth and the respiratory organs. 

i. Use the specimen dissected above. Cut the ali- 
mentary canal across immediately in front of the 
liver, and retain the anterior portion. Pin down 
under water ventral surface uppermost; enlarge the 
mouth opening by cutting through the sides of the 
buccal cavity with a pair of scissors : pull down the 
lower jaw and pin it back. 

a. The two internal openings of the nasal cavities 
(posterior nares)\ near the anterior end of the roof 
of the mouth. 

I. The openings of the Eustachian recesses ; situated 
far back near the angles of the jaw. 

c. The teeth; confined to the upper jaw and roof of 
the mouth. 

a. The maxillary teeth; forming a parallel series, 
set along the inner face of the whole upper jaw. 


I.] THE FROG. 49 

/3. The vomerine teeth; two oval patches situated 
close together near the middle line, immediately 
internal to the posterior nares. 

d. The tongue; heart-shaped and projecting freely 
backwards; its free end is prolonged back into 
two fleshy cornua. Note its mode of attachment. 

Examine its surface under a hand lens; it is 
beset by a number of elevations (papilla?). 

e. The glottis ; a median longitudinal slit, situated im- 
mediately behind the tongue, on the summit of an 
elevation of the floor of the mouth (larynx]. Pass 
a probe down it and note that it enters the lungs. 

Occasionally, the mucous membrane at its an- 
terior end is prolonged into two short papillae, 
which project forwards and probably represent rudi- 
ments of the epiglottis. 

2. Close the mouth ; dissect away the mylohyoid muscle 
and examine from beneath. 

a. The larynx: forming a hard prominence in the 
middle line, between and in front of the lungs. 

b. A series of small muscles will be seen arising on 
all sides and converging immediately in front of a. 
Dissect them away on one side ; there will thus be 
laid bare the hyoid (cf. Sect. C. 3. c.\ Examine 
this, in relation to the larynx. 

a. Its body ; a plate of cartilage closely applied to 
the floor of the mouth, immediately in front of 
the larynx. 

J3. Its posterior cornua. That of the exposed side 
will be seen as a bony rod (thyro-hyal] in close 
apposition with the outer border of the larynx, 

M. 4 


50 ELEMENTARY BIOLOGY. [CHAP. 

immediately under cover of a small muscle (con- 
strictor laryngis). 

c. Examine the above-named muscles. 

a. The geniohyoid; a band of tissue arising from 
the body and cornu of the hyoid and passing 
forwards to be inserted into the lower jaw. 

/3. The hyoglossus ; arising from the posterior cornu 
and passing forwards in the middle line be- 
neath a. to enter the substance of the tongue. 

y. The sterno-hyoid ; its cut end will be seen passing 
up from behind to be attached along the outer 
border of the body and cornu of the hyoid. 

8. The omohyoid ; its cut end will probably be 
found attached to the outer anterior border of 
the body of the hyoid (it arises from the shoulder 
girdle). 

e. The petrohyoides ; a series of small slips lying 
immediately beneath 8. and passing between 
the hyoid and hind region of the skull. 

3. Remove the ventral face of the right lung, and ex- 
amine its interior under a hand lens. 

a. The lung sac ; thin-walled and distensible; highly 
vascular and thickened around the larger vessels 
which ramify within it. 

b. The bronchi ; short membranous tubes placing 
the lungs in communication with the laryngo- 
tracheal cavity. 

4. Remove the respiratory organs together with the 
floor of the mouth, and pin the whole down on its 
side, left lung uppermost. Dissect away the floor of 


I.] THE FROG. 51 

the mouth to the level of the larynx and examine the 
laryngeal cartilages. 

a. The laryngo-tracheal cartilage ; an annular tract, 
embracing the base of the larynx. It sends a spur 
down into the wall of each bronchus. 

b. The arytenoids. That of the left side will be seen 
as a hood-shaped mass, surmounting a. and lying 
within the wall of the larynx. 

Muscular fibres (constrictors} will be seen to pass 
between a, and b. 

5. Turn the specimen over and remove all that remains 
of the right half, cutting to the level of the middle 
line. 

a. The laryngo-tracheal cavity ; spacious above and 
lined by a soft mucous membrane. 

b. The vocal cords. That of the left side will be seen 
as a tense fold of the lining membrane, running 
antero-posteriorly. Note its intimate connection 
with the arytenoid cartilage. 

c. Examine the relations of the laryngeal cartilages, 
as seen by following their cut edges. 

d. Strip off the mucous membrane with care, so as 
fully to expose the cartilages for detailed ex- 
amination. 

These, and similar cartilaginous structures, may 
be isolated with ease by maceration in \ per cent, 
nitric acid solution, the excess of acid being after- 
wards removed by repeated washings in water. 

F. The Urinogenital organs. 

Dissect from the ventral aspect, proceeding as di- 
rected in Sect. B. Having laid bare the viscera, re- 

42 


52 ELEMENTARY BIOLOGY. [CHAP. 

move the alimentary canal between the base of the 
oesophagus and posterior third of the large intestine. 
Next open up the latter, as directed in Sect. D. 4 ; wash 
and examine under water. 

1. In both sexes. 

a. The kidneys ; symmetrically disposed on opposite 
sides ; relatively largest in the male. Each is 
convex dorsally (outer border), incompletely lobed 
on its inner border. 

b. The adrenal body ; a band of yellow tissue running 
along the ventral face of each kidney. 

c. The duct ureter (female) or genito-urinary canal 
(male) running from the outer side of the pos- 
terior part of each kidney to the cloaca. Open 
the cloaca and pass a bristle into one of their 
openings. 

In the male R. esculenta each duct is somewhat 
dilated after leaving the kidney : it then narrows 
again and opens on the dorsal wall of the cloaca 
by an oblique slit with sharply defined edges. 
In R. temporaria the duct does not dilate, or only 
very slightly ; but on its outer side lies a glandular 
mass (vesicula seminalis\ from the inner side of 
which a number of minute ducts open into the 
genito-urinary canal. The aperture of the latter 
in the cloaca is round and has tumid edges. In 
the female of both species the ureters are very 
slender. 

d. The bladder; (cf. Sect. D. 4. c.) 

2. In the female. 

a. The genital glands (ovaries] (cf. Sect. B. 2. //. /?.); 
varying much in size with the season of the year. 


I.] THE FROG. 53 

They overlie the kidneys as seen, each being 
suspended by a fold of mesentery (mesoarium). 

b. The genital ducts (oviducts) ; convoluted tubes, not 
continuous with the ovaries, and running back to 
open into the cloaca. Each can be resolved into 
three segments. 

a. A middle or glandular segment ; forming the 
conspicuous coiled portion of the tube. It will 
be found to swell rapidly under imbibition of 
water. 

jB. A terminal or uterine segment ; thin- walled and 
lying immediately below and external to the 
kidney. Examine it in relation to the cloaca ; 
it will be found to open on the apex of a pa- 
pilla, lying side by side with its fellow, im- 
mediately in front of the apertures of the 
ureters. 
Inflate it ; it is highly distensible. 

I f the Frog be killed during the breeding season, 
this segment will be seen to act as a receptacle 
for the eggs prior to oviposition. 

y. An anterior or thin-walled segment ; short and 
straight ; it passes behind (dorsal to) the lung 
and courses over the base of the same to open 
into the pleuro-peritoneal cavity antero-ventrally 
by a wide funnel-shaped mouth. 

3. In the male. 

a. The genital glands (testes], (cf. Sect. B. 2. h. a); 
varying in size with the season of the year, and 
each suspended by a fold of mesentery (inesor- 
chium\ 


54 ELEMENTARY BIOLOGY. [CHAP. 

b. The genital ducts (vasa efferentid}; delicate tubes 
lying within the mesorchium and placing each 
testis in communication with the inner border of 
the kidney of the same side. 

c. The genito-urinary canal (ureter). Cf. Sect. i. c. 

Examine the seminal vesicle (R. temporaria) 
under a hand lens ; it will appear to be continued 
forwards as an excessively delicate filament which 
can be traced, within the mesentery, as far as the 
base of the lung. Try to isolate this and follow it 
back ; it will be found to skirt the outer border of 
the vesicula seminalis, becoming lost in the base 
of the ureter. 

Not unfrequently one or more watery vesicles or 
cysts are set along the course of the above-named 
filament. More rarely it may be wholly or in part 
well defined and tubular, having the appearance of 
an immature oviduct, a vestige of which it really 
represents. 

d. The fat body (cf. Sect. B. 2. /.). This is, in the 
male, very large. Rarely its basal portion may be 
swollen and pigmented, giving rise to an organ 
(Bidder's organ) having much the appearance of 
the ovary of the female and confluent with the 
head of the testis. 

4. Remove a kidney and pin down under water, ventral 
face uppermost. Carefully dissect off the mesentery 
and examine under a lens ; its whole surface will be 
seen to be studded by an immense number of mi- 
nute orifices (nephrostomes\ placing the interior of 
the kidney in communication with the pleuro-peri- 
toneal cavity. 


I.] THE FROG. 55 

G. The skeleton. 

The skeleton of a Frog may be prepared for exami- 
nation by removing the viscera from the body, and 
roughly dissecting away the muscles and other soft 
parts. Then place the remainder in water and let 
it macerate for about a week; afterwards carefully 
pick away the soft parts, with forceps, from the bones 
and cartilages. 

Obtain two such skeletons; allow one to dry slowly; 
preserve the other in weak spirit. 

1. Its general arrangement. 

a. The axial skeleton; consisting of the vertebral 
column and skull, both of which lie in the same 
antero-posterior plane. 

b. The appendicular skeleton ; lateral parts (limbs and 
limb-girdles], supported, directly or indirectly, by 
the axis. 

a. The fore-limbs : their supporting shoulder-girdle 
or pectoral arch, not directly attached to the 
axial column; the limb proper ; its main di- 
visions, humerus, radius and ulna (the two 
latter ankylosed), carpus and digits. 

b. The hind-limbs: their supporting hip-girdle or 
pelvic arch, directly attached to the vertebral 
column ; the limb proper ; its main divisions, os 

femoris, tibia and fibula (ankylosed), tarsus, 
digits. 

2. The vertebral column; dried preparation. 

It consists of an anterior segmented portion (each 
segment being a vertebra] and of a posterior unseg- 
mented portion (the urostyle). 


56 ELEMENTARY BIOLOGY. [CHAP. 

a. Examine carefully and draw various aspects of a 
detached vertebra, say the third. 

a. Its solid flattened ventral part (centrum), with 
an anterior concave and a posterior convex 
surface (precocious). 

(3. The neural arch : an arch of bone arising from 
the centrum dorso-laterally. It furnishes the 
undermentioned. 

The transverse process : a bony bar arising on 
each side from the base of the arch and passing 
outwards and a little downwards. 

The articular processes (zygapophyses) ; an an- 
terior and posterior pair, springing from the 
sides of the arch ; the anterior (pre-zygapophyses] 
having their smooth articular surfaces directed 
upwards ; the posterior (post-zygapophyses] with 
similar surfaces directed downwards. 

The short spinous process ; springing from the 
dorsal aspect of the arch and directed back- 
wards. 

y. The neural canal ; bounded, above and at the 
sides by the arch, below by the centrum. 

b. Examine the remaining vertebrae. 

a. The first vertebra : its body, produced forwards 
into a wedge-shaped process (odontoid process] 
which lies between the occipital condyles of 
the skull : its arch, usually incompletely ossified 
in the region of the spinous process, which is 
rudimentary; posterior zygapophyses alone pre- 
sent : the large concave anterior facets (condylar 
facets], partly on the arch and partly on the 
centrum, for articulation with the skull. 


I.J THE FROG. 57 

/3. The 2nd, 4th, 5th, 6th and yth vertebrae : 
closely resembling the third, the chief differ- 
ences being found in the varying size and 
direction of the transverse processes, all of 
which are smaller than those of the third 
vertebra. 

y. The 8th vertebra : concave at each end of its 
centrum (amphiccelous). 

S. The gth vertebra (sacrum) : its centrum ; convex 
in front and with two convex tubercles behind : 
its powerful transverse processes directed up- 
wards and backwards and expanded for ar- 
ticulation of the hip-girdle. 

The characters of y. and 8. are liable to varia- 
tion. 

Occasionally the vertebrae may be 8 or 10 in 
number. 

c. Examine any two vertebrae from the side, in their 
natural positions. 

a. The zygapophyses ; cf. supra; note their modes 
of articulation. 

/?. The neural spines ; short and backwardly di- 
rected. 

y. The transverse processes ; sloping upwards and 
backwards. 

8. The inter-vertebral foramina (for exit of spinal 
nerves); interspaces left between each pair of 
neural arches, immediately below the zyga- 
pophyses. 

Note that there is no corresponding passage 
between the skull and first vertebra. 


58 ELEMENTARY BIOLOGY. [CHAP. 

d. The unsegmented portion of the column (tiro- 
style). 

a. Its anterior end, enlarged and bearing two ar- 
ticular concavities. 

This region is liable to variation. 

ft. Its posterior end; tubular in the dried skeleton, 
but in the fresh state filled with cartilage which 
projects beyond it. 

y. The prominent arch along its dorsal surface; 
getting ridge-like and disappearing posteriorly. 

8. The small neural canal, enclosed by y. 

e. The two minute foramina (for exit of the tenth 
pair of spinal nerves) at its extreme anterior 
end. 

3. The vertebral column, wet preparation. 

Cf. supra, and note in addition. 

a. The great mobility of the segments upon each 
other. Parts in articulation will be found to be 
united by sheets (capsules] or bands (ligaments] of 
glistening white fibrous tissue. 

/v Make a longitudinal vertical section of the entire 
vertebral column, and examine the cut surface. 

a. The vertebral bodies (centra]. Note the shapes 
and mode of articulation of their applied ends 
(articular surfaces}; each will be seen to be 
capped in cartilage, the apposed faces being 
kept moist during life. 

p. The intra-vertebral bodies; small gelatinous 
masses lying within the substance of a. They 
are most marked in young specimens. 


I.] THE FROG. 59 

y. The urostyle; its body is cylindrical in section 
and largely filled with a gristly core, identical 
with /?, which is continued back as a free termi- 
nation to the whole axial skeleton. 

8. The neural canal; note especially its termina- 
tion in a pointed extremity, lying within the 
arch of the urostyle. 

c. Isolate the third vertebra, and examine 

a. Its zygapophyses ; cf. Sect. 2. c. Each is capped 
in cartilage, in common with the other articular 
faces. 

ft. Its transverse processes ; each terminating in a 
backwardly prolonged cartilaginous expansion. 

4. The skull ; dried preparation. 

a. General. Examine from the dorsal aspect ; it 
embraces 

a. The cranium; median and enclosing the brain, 

sometimes termed the brain-case, 
ft. r \& facial apparatus ; the system of outstanding 

bars, conspicuous as the jaw-apparatus. 

y. The sense capsules. The auditory capsules, 
paired postero-lateral expansions ; the olfactory 
capsules, similar but less obvious antero-lateral 
expansions (they are better seen in the wet state. 
See infra}. 

b. Examine the posterior end of the skull. 

a. The large aperture (foramen magnum) in the 
middle line, leading into the cranial cavity. 

(3. The convex surface (occipital condyle) on each 
side of the foramen magnum, for articulation 


60 ELEMENTARY BIOLOGY. [CHAP. 

upon the corresponding concave facet on the 
front of the first vertebra. 

y. The exoccipitals ; bearing the condyle on each 
side, and bounding the foramen magnum 
laterally. 

8. The pro-otics ; lying immediately in front of y. 
and running outwards on each side, forming 
the roof and front wall of the auditory capsule. 

e. The sguamosal; a hammer-shaped bone, ex- 
tending from the outer edge of 8. downwards 
and backwards towards the articulation for the 
lower jaw. 

. The columella auris ; seen, at this stage, as a 
bony rod which underlies the pro-otic and 
stands out immediately behind the head of the 
squamosal. (It is best studied later on.) 

c. The roof of the skull. 

a. The exoccipitals^ pro-otics and squamosal. Cf. 
supra. 

f3. The fronto-parietals ; two long bones united 
by suture in the middle line, roofing in the 
cranium. 

y. The nasals ; two triangular bones immediately 
in front of {3. set transversely and a little ob- 
liquely. 

8. The pre-maxillce ; two small bones in front of y., 
meeting in the middle line and bounding the 
front of the gape. Each sends up an ascending 
process which is directed towards the inner end 
of the nasal bone. 


I.] THE FROG. 6 1 

. The maxilla; on either side a long bone 
bounding the greater part of the gape, and 
abutting against 3. in front. Each maxilla 
sends up an ascending process, which abuts 
against the outer end of the nasal. 

. The quadrato-jugal (JugalT)\ a delicate bone, on 
either side, bounding the hinder third of the gape 
and passing between the maxilla and squamosal. 

d. The base of the skull. 

a. The exocripitals, pro-otics, pre-maxilla, maxillce, 
and quadrato-jugals. Cf. supra. 

Note that each pre-maxilla sends back a short 
palatine-process. 

ft. T&z parasphenoid ; a dagger-shaped bone running 
along the greater part of the floor of the cranial 
cavity. 

y. The sphenethmoid or girdle-bone; a large bone 
underlying the anterior portion of ft. and en- 
closing the anterior third of the brain-case. 

3. The palatines ; slender bones, one on each side, 
passing out transversely from near the anterior 
end of the parasphenoid to the body of the 
maxilla. Each underlies the corresponding 
nasal bone. 

e. The vomers; two broad irregular shaped bones, 
immediately in front of S. These, in common 
with the maxillae and pre-maxillae, bear teeth. 
(Cf. Sect. E.) 

. The pterygoids ; large triradiate bones, one on 
either side. Each abuts against the antero- 
ventral border of the auditory-capsule internally; 


62 ELEMENTARY BIOLOGY. [CHAP. 

anteriorly it is prolonged forwards, flanking the 
maxilla, to meet the outer end of the palatine; 
posteriorly it runs downwards and backwards, 
parallel with the squamosal. 

e. The side of the skull. 

a. Compare generally with the foregoing; note 
especially the backward rotation of the squa- 
mosal, and the mutual relationships of the max- 
illo-jugal bones. 

/3. The mandible or lower jaw; it consists of two 
distinct halves, or rami t which meet in the 
middle line in front. 

In each ramns three pieces may be made out 
a main piece, which runs nearly to the middle 
line in front (angulo splcnial]; & thin scale- like 
piece (dentary) flanking the outer anterior face 
of the former; and a small nodular one (mento- 
Meckelian) meeting with its fellow in the sym- 
physial line. 

5. The skull; wet preparation. 

Remove the lower jaw and hyoid, and carefully 
dissect off from the rest of the skull, under water, 
the undermentioned bones. This may be done with 
comparative ease, if, holding the whole down with 
the left hand the bones of one side be removed, 
either by inserting the point of a scalpel beneath 
them or by the aid of forceps. 

The bones to be removed are dorsal series , fronto- 
parietals (one or both), nasal, squamosal, maxilla, 
pre-maxilla; ventral series, parasphenoid, vomer, pala- 
tine, pterygoid; care must be taken that none of the 
underlying cartilage is brought away with the latter. 


I.] THE FROG. 63 

There will thus be laid bare the chondro-cranium and 
its related bones. 

a. Dorsal aspect. 

a. The chondro-cranium ; a cartilaginous mass en- 
closing the brain and olfactory and auditory 
sense organs, and bearing, laterally, an out- 
standing cartilage which is flanked by the pala- 
tine and pterygoid bones (palato-quadrate car- 
tilage or sub-ocular arch}. 

j3. The sphenethmoid, pro-otics and exocdpitals ', seen 
to be formed as replacements of the chondro- 
cranium in bone; they are inseparable from it, 
being termed therefore cartilage bones, by way of 
distinction from those superadded ones which 
have been stripped off (membrane bones}. 

Examine in detail. 

y. The cranium ; its roof will be seen to be in- 
completely cartilaginous, bearing three mem- 
branous areas or fontanelles, all of which un- 
derlie the fronto-parietals. They are a larger 
median one in front, extending forwards to the 
posterior border of the sphenethmoid ; smaller 
paired ones behind, extending outwards to the 
inner border of the pro-otics. 

8. The sub-ocular arch; confluent, in front with 
the olfactory capsule, behind with the auditory 
capsule. Its palatine bar ; standing out at right 
angles to the long axis, and expanded ex- 
ternally to form a plate (orbital process] for sup- 
port of the maxilla (cf. opposite side). Its 
pterygoid bar ; produced backwards, outwards 


64 ELEMENTARY BIOLOGY. [CHAP. 

and downwards, into a stout rod or suspensorium, 
which lies between the pterygoid and squa- 
mosal and furnishes the articulation for the 
lower jaw. 

e. The olfactory capsules ; confluent with each other 
and the cranium, and incompletely separated 
above by a median longitudinal furrow. The 
dorsal wall of each will be seen to be scroll- 
shaped and produced in front, into a blunted 
pre-nasal process ) which abuts against the inner 
face of the maxilla (cf. opposite side) ; behind, 
into a laminate ali-nasal process, which encircles 
the outer and hinder margins of the anterior 
nostril. 

If the preparation be made with great care, the 
front wall of the narial passage will be seen to 
lodge a couple of minute labial cartilages, which 
overlie the base of the pre-nasal process. 

/>. Ventral aspect. 

a. The cranium; completely cartilaginous below 
and at the sides. Note the limits of the car- 
tilage bones. 

Certain apertures (exits for cranial nerves) 
will be seen ; they are best studied later. 

/3. The sub-ocular arch; in front, confluent with 
the expanded floor of the olfactory capsule; 
behind, in articulation with the ventral outer 
border of the auditory capsule. 

7. The rhinal processes. That of the dissected side 
will be seen as a small hammer-shaped cartilage 
lying near the middle-line in front, ventral to 


I.] THE FROG. 65 

the olfactory capsule. It projects freely for- 
wards and inwards. 

c. Lateral aspect. 

Compare generally with a. and b. and note es- 
pecially. 

a. The suspensorium ; its backward rotation ; its 
rounded free end, for articulation of the lower 
jaw. 

/?. The quadrate bone; represented by an insig- 
nificant nodule lying within the substance of a. 
near its articular end. It may or may not be 
confluent with the quadrato-jugal. 

d. Posterior aspect. 

a. The exocripitals ; separated above and below 
by cartilage (i.e. there are no median occipital 
bones). 

ft. The coliimella auris. Remove this on the dis- 
sected side ; and note that its inner end plugs a 
large aperture (fenestra ovalis] in the outer wall 
of the periotic capsule. 

y. The suspensorium ; now seen, on the same side, 
in its entirety. Note-; its pedicle, the main bar, 
prolonged down to give articulation to the lower 
jaw ; its dorsal cross, confluent with the outer 
wall of the auditory capsule, and expanded, to 
form a ledge (tcgme/i tympani] which overlies 
the columella; its ventral cross (cf. b. /?.) rounded, 
and in definite articulation with the antero- 
ventral border of the auditory capsule. 

e. Inner aspect. 

Remove all that remains of the chondro-cranium 
M. c 


66 ELEMENTARY BIOLOGY. [CHAP. 

on the side which has been dissected, cutting a 
little to one side of the middle line, thus reducing 
the whole to a condition of vertical longitudinal 
section. Examine from within. 

a. The cranial and nasal cavities ; note their limits 
and mutual relationships. 

J3. The septum nasi ; a median plate of cartilage, 
separating the two nasal chambers in the middle- 
line (examine from the front). 

y. The sphenethmoid. Seen to consist of a pos- 
terior cranial portion which embraces the an- 
terior third of the brain-case, and an anterior 
paired portion, which is similarly related to the 
bases of the olfactory capsules. 

8. The exoccipital and pro-otic. Examine these in 
relation, as seen from within (cf. 4 b.\ 

f. The fronto-parietal) nasal, vomer, and para- 
sphenoid (if in place). Examine, in relation to 
the chondro-cranium. 

. The rhinal process (cf. l>. y.); seen to form a 
support for the pre-maxilla, abutting against its 
inner face. 

17. The foramina for exit of the cranial nerves as 
under. 

i. The olfactory foramina (I. Cranial); a perfora- 
tion of the partition between the two portions 
of the sphenethmoid. 

ii. The optic foramen (II. Cranial); obvious as a 
perforation of an oval membraneous area of 
the side wall a short distance behind the 
sphenethmoid. 


I.] THE FROG. 6/ 

iii. The foramen of exit for V. VI. VII.; a large 
aperture, below and in front of the pro-otic. 

iv. The foramen for IX. and X.; perforating the 
body of the exoccipital. 

v. The auditory foramen (VIII.); a small per- 
foration of the cartilaginous wall of the audi- 
tory capsule just behind iii. 

vi. The foramen for III. ; small and situated im- 
mediately in front of iii. 

vii. The foramen for IV. (11. patheticus) very 
small, above and a little in front of the optic 
foramen. 

f. The mandible. See 4. e. j3. 

Strip off the dentary with care ; there will be 
found, in close apposition with the outer face of 
the angulo-splenial, 

a. Meeker s cartilage ; a gristly rod, forming a core 
for the lower jaw. Examine its posterior end ; 
it is alone concerned in articulation. 

ft. The mento-Meckdian bone ; a small nodule aris- 
ing as an ossification of the symphysial end 
of a. 

6. The hyoid. 

a. Its broad somewhat tetragonal central part (body], 
bearing a number of outstanding processes, for 
attachment of muscles (cf. Sect. E. 2. c.\ This 
is usually cartilaginous, being ossified only in old 
individuals. 

b. Its posterior cornua, or thyro-hyals ; short bony 
rods, sloping obliquely backwards and outwards. 


68 ELEMENTARY BIOLOGY. [CHAP. 

c. Its anterior cornua, slender cartilaginous rods, 
arising from the front of the body on either side : 
each is long and curved, running at first forwards, 
then backwards and outwards, and finally for- 
wards and upwards, to become attached to the 
periotic capsule below the fenestra ovalis. 

7. The limbs and limb-girdles. 

These are best studied in the wet state. In 
dealing with the carpus and tarsus, no difficulty will 
be found if treated as follows. Isolate sufficient of 
the limb-skeleton to embrace the carpus or tarsus 
and pick away any fragments of the soft parts which 
may remain; immerse in spirit for a few hours; 
transfer to absolute alcohol for i hour, thence into 
oil of cloves. The latter medium will thoroughly 
clarify the preparation, and it may be kept in it for 
an indefinite period. 

The shoulder-girdle and its related structures. 

a. Their general arrangement : they form an incom- 
plete ring round the fore part of the trunk, com- 
posed partly of bone, partly of cartilage. Note 
the cavity (glenoid fossa] with which the fore-limb 
articulates. 

Examine from the ventral aspect; the whole is 
seen to consist of 

a. Paired elements ; symmetrical on opposite sides 
and meeting each other in the mid-ventral 
line. 

Median elements; in corresponding relationship 
anteriorly and posteriorly with the applied ven- 
tral ends of a. 


I.] THE FROG. 69 

/'. The paired elements. Flatten out the whole on one 
side, so as to obtain a lateral view. In the region 
of the glenoid fossa there will be seen a sharp line 
of demarcation between a dorsal scapula segment ; 
and a ventral coracoid segment, the middle area of 
which is fenestrate (coracoid fontanelle). 

a. The scapula segment ; subdivided into a thin ex- 
panded partially ossified dorsal portion (supra 
scapula) and a stouter bony piece (the scapula] 
which furnishes the dorsal half of the glenoid 
fossa. 

/?. The coracoid segment ; largely ossified, and com- 
posed of a smaller anterior clavicle, and a 
stouter posterior coracoid, the latter furnishing 
the ventral half of the glenoid fossa. 

c. The median elements. 

a. The xiphisternum ; a median cartilage, en- 
sheathed in bone, abutting against the applied 
ends of the coracoids. It expands posteriorly 
to form a heart-shaped plate, notched from 
behind (xiphoid process). 

P. The omosternum, a slender cartilage ensheathed 
in bone, similarly related in front. It also ends 
in a cartilaginous expansion. 

It is doubtful if the above really represent 
sternal elements, especially in the case of the 
anterior one. 

The skeleton of the fore-limb. (Cf. Sect. A. 2. c.} 
a. The arm-bone (humerus), 

a. A somewhat cylindrical bone, composed of a 
middle shaft with an articular expansion at each 
end. 


70 ELEMENTARY BIOLOGY. [CHAR. 

/?. The great ridge (deltoid cresf] on its antero- 
internal surface, to which a muscle (deltoid) 
was attached. 

The development of this crest is greater in the 
male than in the female. 

b. The. bone of the forearm. 

a. Excavated above to receive the lower end of 
the humerus. 

/?. Shewing below two articular heads separated by 
a notch, which is the last trace of division be- 
tween the two bones of which it is made up; 
viz. the radius and the ulna. 

y. Pull the limb out straight, palmar surface down- 
wards, so that it comes to be situated at right 
angles to the long axis of the body. The radius 
and pollex lie on the anterior or pre-axial side, 
the ulna and little finger on the posterior or 
post-axial side, of a line drawn through the axis 
of the whole limb. 

c\ The digits. 

Five in number, the first (radial one) rudimentary: 
beginning at the outer or ulna side, we find- 

a. The fifth digit: it presents a cylindrical proximal 
bone (metacarpal} followed by three others 
(phalanges), each shorter than its predecessor. 

/3. The fourth digit: a metacarpal bone and three 

phalanges. 
y. The third digit: a metacarpal bone with t\vo 

phalanges. 
B. The second digit: a metacarpal bone with two 

phalanges. 


I.] THE FROG. 71 

e. The first digit (polleoc] supported only by a small 
met a car pa I bone. 

d. The carpus. Proceed as directed at the outset, 
and examine under a low power. Its elements 
can be resolved into three sets. 

a. Proximal elements ; two in number, articulating, 
side by side, upon the radius and ulna respec- 
tively. 

p. Distal elements; three in number. The outer 
one gives articulation to the three outermost 
digits ; and is mainly connected with the outer 
element of the proximal series. The two inner 
ones give articulation to the pollex and second 
metacarpal respectively. 

y. The central element (centrale]; pre-axial in posi- 
tion, and wedged in between the two innermost 
elements of the distal series and the correspond- 
v ing proximal piece. 

The hip girdle. 

a. Its general form : V-shaped, with the apex directed 
backwards. It consists of paired elements which 
unite in the middle line and are in direct articula- 
tion with the vertebral column (sacrum). 

b. The fossa (acetabuluni] on each side, for articula- 
tion of the hind-limb. 

c. Examine from the side. The whole will be seen 
to be subdivided, by a triradiate fissure running 
through the acetabulum, into three pieces, viz. 

a. The pubis; a small triangular wedge-shaped 
piece (cartilaginous except in old frogs) ; ventral 


72 ELEMENTARY BIOLOGY. [CHAP. 

in position and furnishing the middle third of 
the acetabulum. 

ft. An anterior elongated piece (ilium] -, subcylindri- 
cal in front, behind, laterally compressed (crista 
ilii) ; it furnishes rather more than the anterior 
third of the acetabulum. Its articulation with the 
sacrum is effected through the agency of a car- 
tilaginous supra-ilium; related to the ilium, as is 
the supra-scapula to the scapula in the shoulder- 
girdle (cf. p. 69). 

y. A posterior, laterally compressed piece (ischiutii) ; 
united with its fellow in the middle line. It 
meets the ilium above, below it is separated 
from it by the pubis ; it furnishes rather less 
than the posterior third of the acetabulum. 

The skeleton of the hind limb. 

a. The thigh-bone (os femoris) ; its cylindrical shaft 
and rounded articular ends. 

b. The leg-bone (os cruris). 

a. A long cylindrical bone, expanded at its articular 
extremities. Its upper end; excavated for ar- 
ticulation upon the femur. Its lower end; 
rounded and notched to give passage to the 
tendon of the tibialis posticus muscle (Sect. H. 
7 . a. ft.). 

ft. The longitudinal grooves on it ; indicating that 
it is really made up of two united bones, the 
tibia and \\\e fibula. 

y. The nutritive foramen (for passage of nerves and 
blood-vessels into its interior) ; a small slit-like 
perforation of the middle of the shaft. 


I.] THE FROG. 73 

Look for similar perforations in the other bones 
examined. 

3. Pull the limb out straight, plantar surface down- 
wards, as directed for the anterior appendage. 
The tibia and hallux are pre-axial ; the fibula 
and little-toe post-axial. 

c. The tarsus. 

Its proximal elements are seen as two elongated 
bones (separate in the middle but confluent at 
their cartilaginous extremities) in articulation with 
the ankylosed tibia and fibula; the pre-axial, or 
tibial, of these is the astragalus ; the post-axial or 
fibular, the calcaneum. 

d. The digits. Five in number ; the internal one the 
shortest, the fourth the longest. Their compo- 
sition 

a. The first, or hallnx (the most internal) ; a me- 
tatarsal bone, followed by two phalanges. 

/3. The second : same as a, but longer. 

y. The third : a metatarsal bone with three pha- 
langes. 

8. The fourth : a metatarsal bone and four pha- 
langes. 

. The fifth : like the third, but a little shorter. 

e. The tarsus and cakar. 

Remove the middle portion of the foot-skeleton, 
to include the apposed ends of the astragalus and 
calcaneum and the metatarsals ; treat with alcohol 
and oil of cloves as previously directed, and ex- 
amine under a low power. 


74 ELEMENTARY BIOLOGY. [CHAP. 

a. The distal tarsal series ; two in number in the 
adult and imperfectly ossified; viz. a larger 
compressed post-axial element, giving articu- 
lation to the second and third digits ; a smaller 
nodular pre-axial piece, giving articulation to 
the hallux and calcar. 

/?. The calcar (pre-hallux] ; seen to be composed, 
except in very old frogs, of three pieces, identical, 
in their characters and relationships, with the 
component parts of a digit. 

H. Myology; as illustrated in the hind limb. 

(For the following dissection it is desirable to have 
a frog which has been lying some time in spirit.) 

Pin the animal down on its back, and remove the 
skin from the hind limbs. 

i . General. 

In dissecting the muscles, separate them gently 
from one another, tearing through the connective 
tissue which unites them. 

a. Each is chiefly made up of a main mass, or belly , 
which is nearly white and readily tears into bundles 
in a muscle which has been in spirit ; but it is 
softer, redder, and does not so easily split up in a 
fresh muscle. 

b. At both ends, in most cases, the belly is replaced 
by dense shiny tissue forming a tendon. 

c. The tendons are fixed directly or indirectly to 
some of the neighbouring bones, the less move- 
able attachment is termed the origin of a given 
muscle; the more moveable its insertion. 


I.] THE FROG. 75 

2. The superficial muscles on the front of the thigh. 

a. The sartorius : a thin ribbon-like muscle running 
down the middle ; it arises from the symphysis 
pubis and is inserted into a tendinous expansion 
(aponeurosis] on the inner side of the knee-joint. 

b. The redus interims major: a large muscle running 
along the whole inner side of the thigh; arises 
from the symphysis pubis below the sartorius and 
is inserted into the same aponeurosis as that 
muscle. 

c. The rectus internus minor: a thin muscle lying in- 
side and rather behind the rectus internus major. 
It arises from the pelvis close to the anus and is 
inserted into the aponeurosis about the knee-joint. 

d. The triceps femoris : a powerful muscle on the outer 
side of the thigh (it may be best studied later). 

3. The deep muscles of the front of the thigh. Cut 

across the belly of the sartorius, and turn its ends 
out of the way; there will thus be laid bare 

a. The adductor magnus: a powerful muscle lying im- 
mediately above the rectus internus; it arises from 
the pelvis, between the origin of the sartorius and 
that of the rectus internus major. Its fibres are 
inserted directly (i.e. without the intervention of a 
specialised tendon) into the inner side of the distal 
half of the femur. 

b. The adductor longus: a thin band immediately in- 
ternal to the sartorius; it arises from the anterior 
border of the symphysis pubis and joins the ad- 
ductor magnus at its insertion. 


76 ELEMENTARY BIOLOGY. [CHAP. 

Force the adductors longus and magnus well apart 
(noting the insertion of the latter) and pin them back 
if needful; there will thus be exposed 

c. The pectineus: a small muscle, arising from the 
front of the pelvis, close to the symphysis, and 
inserted into the anterior surface of the distal half 
of the femur. 

$ d. The adductor brevis: a small muscle lying on the 

inner side of the pectineus, close to which it arises 
and is inserted. 

Sever the rectus internus major and r.i. minor and 
turn their cut ends back; thrust the adductor magnus 
forwards; there will thus be laid bare 

e. The semitendinosus: this is a long slender muscle 
bifurcated at its upper end: its two heads^ thus 
formed, arise, one (anterior head) from the pelvis 
between the ischial symphysis and the aceta- 
bulum; the other (posterior head) from the ischial 
symphysis: the muscle terminates below in a 
rounded tendon which is inserted along with the 
sartorius. * 

Its anterior head enters into a close relationship 
with the adductor magnus. 

4. The superficial muscles on the back of the thigh. 

Turn the frog over on to its belly, and remove the 
skin from the back of the limb. 

a. The triceps femoris: a very large muscle on the 
outer side, divided above into three heads, which 
are often regarded as separate muscles, viz. 

a. The vastus externus: its outer head; it arises 


I.] THE FROG. 77 

from the hinder edge of the iliac bone. Cut it 
across and reflect the two halves. 

J3. The vastus interims: its inner head; a very 
large muscle on the outer anterior aspect of the 
thigh, arising from the pelvis close to the hip- 
joint; it unites with a. to form a common 
tendon of insertion into the aponeurosis on the 
front of the os cruris. 

y. The rectus femoris anticus: its middle head; a 
small muscle arising from the postero-ventral 
border of the iliac bone and inserted along with 
the above. 

b. The biceps femoris: a long thin muscle, lying 
along the inner side of the vastus externus; it 
arises from the iliac bone above the acetabulum; 
below it divides into two slips, one of which is 
inserted into the middle of the shaft of the femur, 
while the other ends in a rounded tendon which is 
inserted into the back of the distal end of the same 
bone. 

c. The semimembranosus: a large muscle immediately 
below the biceps; it arises from the upper pos- 
terior part of the iliac symphysis and is inserted 
into the aponeurosis round the knee-joint. 

5. Tho deep muscles of the back of the thigh. 

Divide and reflect the biceps femoris and semi- 
membranosus ; there will thus be exposed :- 

a. The glutceus : a short thick muscle arising from 
the hinder two-thirds of the external border of 
the ilium ; it runs down between the vastus ex- 
ternus and the rectus anticus to be inserted, by a 


ELEMENTARY BIOLOGY. [CHAP. 

powerful tendon, into the back of the head of the 
femur. 

b. The ileo-psoas : it arises from the internal surface 
of the posterior end of the ilium and is inserted 
into the upper and outer border of the shaft of 
the femur, immediately above the lesser slip of 
the biceps. 

c. The pyriformis. This arises from the hinder end 
of the urostyle and, passing inside the vastus ex- 
ternus and biceps femoris, is inserted into the 
shaft of the femur. 

d. The adductor brevis (cf. 3. </.); a small muscle 
lying immediately beneath c. 

e. The adductor magmis (cf. 3. a.); a fleshy mass 
lying immediately beneath the semimembran- 
osus. 

6. The rotator muscles of the femur. 

Pin the whole down on one side, and remove all 
the muscles hitherto examined with the exception of 
the gluteus (5. a.), leaving their cut ends. Turn 
these well back, noting their relations; there will 
thus be laid bare : 

a. The gluteus (cf. supra); its whole course can now 
be followed. 

b. The quadratics fcmoris, arising from the postero- 
dorsal border of the ilium and inserted into the 
posterior upper border of the shaft of the femur, 
side by side with the pyriformis (5. c.). 

c. The obturatorius : this is best seen on reflection 
of b. It arises from the postero-ventral area of 
the hip-girdle to which it is closely applied; its 


I.] THE FROG. 79 

tendon of insertion passes obliquely forwards and 
downwards immediately beneath that of the glu- 
teus, to reach the head of the femur. 

7. The muscles of the leg. 

a. Turn the frog on its back, and remove the skin 
from the foot: fasten the same down, dorsal sur- 
face upwards. The os cruris will now be seen 
running down the middle of the leg. Lying on 
its inner side are two muscles, viz. : 

a. The gastrocnemius : a muscle with a great fleshy 
belly; it arises above by two tendons; one 
(much the larger) starts in the region of the 
knee-joint partly from the femur, partly from 
the os cruris ; the other arises from the apo- 
neurosis adjacent. Below, the muscle ends in 
a great tendon (tendo Achillis\ which termi- 
nates in an aponeurosis on the plantar surface 
of the foot. 

/3. The tibialis posticus : a slender muscle covered 
in the main by the gastrocnemius ; it arises 
from the posterior surface of the os cruris and, 
passing to the inner side of and through the 
ankle-joint (cf. p. 72, leg-bone), is inserted into 
the astragalus. 

b. a. and /?. act as flexors of the foot ; on the 
opposite side of the leg lie the following ex- 
tensors. 

a. The peroneus : the largest and most external ; 
it arises from the outer side of the distal ar- 
ticular end of the femur and, running across 
the ankle-joint, is inserted into the calcaneum. 


80 ELEMENTARY BIOLOGY. [CHAP. 

This muscle is best seen from the dorsal 
aspect. 

ft. The tibialis anticus : a small muscle beneath 
and dorsal to the peroneus ; it arises from the 
front of the lower end of the femur and from 
the capsule of the knee-joint; below it divides 
into two slips which are inserted into the dorsal 
surface of the astragalus and calcaneum re- 
spectively. 

y. The extensor cruris brevis : this lies internal to 
the upper part of the last muscle ; it arises 
from the front of the distal articular end of 
the femur and is inserted into the middle third 
of the os cruris. 

8. The flexor tarsi anterior; a small muscle, best 
seen on reflecting the tibialis anticus ; it arises 
where the extensor cruris ends, and is inserted 
into the dorsal face of the astragalus. 

I. The blood-vascular system. 

The dissection of the blood-vessels maybe facilitated by 
previous injection, as directed in the Appendix C. If 
a permanent preparation be desired gelatine or plaister 
of Paris may be preferably employed. For ordinary 
working purposes, there is nothing more convenient 
than a mixture of French blue, injected wherever de- 
sirable with a medicine dropper (see Appendix). 

i. The heart. 

Obtain a freshly-chloroformed Frog and pin down 
on its back ; slit up the ventral integument along 
the middle line as directed in Section B, and pin 
back the two flaps, avoiding stretching. Next raise 


I.] THE FROG. 8 1 

the xiphisternum with forceps, and remove the entire 
ventral portion of the shoulder-girdle, being very 
careful not to injure the underlying blood-vessels. 
Raise the pericardium In like manner and remove 
sufficient of it to expose the heart. 

a. External anatomy of the heart. 

a. Its posterior conical thick-walled portion (ven- 
tricle) with the apex directed backwards. 

ft. The truncus arteriosus ; a sub-cylindrical part, 
arising from the right side of the base of the 
ventricle and dividing anteriorly into two (aortic 
arches]. 

y. The atrium ; thin-walled, rounded, lies on the 
dorsal aspect of the truncus, in front of the 
ventricle. Its subdivision into the two auricles 
is not visible from this aspect. 

S. Carefully raise the ventricle : lying beneath it 
(that is, on its dorsal side) will be seen the sinus 
venosus ; an elongated thin-walled sac, seen to 
be in immediate relationship to the atrium and 
in connexion with the great veins, which enter 
it through the dorsal wall of the pericardium. 

b. The pulsation of the heart. 

a. Watch the movement carefully ; it is a regularly 
alternating series of contractions and dilatations. 

/3. It will be seen that the two auricles contract 
together ; immediately after them, the ventricle ; 
and then, instantly, the truncus arteriosus. 

y. Raise the ventricle so as to see the sinus ve- 
nosus ; it will be found to contract immediately 
before the auricles. 

M. 6 


82 ELEMENTARY BIOLOGY. [CHAP. 

2. The anterior abdominal vein. (Cf. Sect. B. i. c. a.) 

This is seen to receive a series of paired epigastric 
veins, which run in the tendinous intersections of 
the ventral muscles. 

Carefully dissect the body-wall away from it, until 
liberated for its whole course. Note 

a. Its origin ; by the fusion in the middle line of a 
couple of short veins (pelvic veins], lying at the 
base of the pleuro-peritoneal cavity and bringing 
back blood from the hind-limbs. 

b. Its distribution. Trace it forwards ; it runs be- 
neath (dorsal to) the ventricle : on raising the 
latter it will be found to divide into two branches, 
one of which goes to each lobe of the liver (afferent 
hepatic veins). 

c. Its lesser factors. 

a. The epigastric veins ; described above. 

(j. The vesical vein ; entering its base, and bringing 
in the blood from the urinary bladder and in- 
testinal wall immediately adjacent. 

y. The cystic vein ; a small vessel, usually entering 
the right afferent hepatic branch, bringing back 
the blood from the gall-bladder. 

8. The cardiac vein ; a minute vessel, seen, on 
displacing the ventricle, bound up in a special 
fold of the pericardium. It brings back the 
blood from the wall of the truncus arteriosus. 

3. The hepatic portal vein. 

Raise the left lobe of the liver ; the main trunk of 
the above will be seen running through the head of 
the pancreas to enter the same ; it communicates 


I.] THE FROG. 83 

with the anterior abdominal vein by a large vessel 
(systemico-portal anastomosis] . 

Note that it is formed by the union of those vessels 
bringing back the blood from the alimentary canal 
and its appended glands (its factors may be better 
studied in detail later on). 

Frequently, but not invariably, some of the veins 
(gastric veins] which carry back the blood from the 
stomach, enter the liver independently of the rest. 

4. The renal portal veins. 

Remove sufficient of the alimentary canal to fully 
expose the kidneys. The above-named veins will 
be seen skirting the outer borders of the same \ that 
of one side may be examined in detail. 

a. Its origin; when traced back it is seen to arise, 
side by side with the pelvic vein (i. a.} from the 
bifurcation of a vessel which skirts the outer 
border of the thigh (femoral vein}. 

b. Its distribution; on reaching the kidney it is seen 
to break up into a number of afferent renal veins, 
for distribution to that organ. 

c. Its remaining factors. 

a. The sciatic vein; a large vessel seen, on 
carefully dissecting away the hip-girdle, to bring 
in the blood from the deeper parts of the hind- 
limb. 

j3. The dorso-lumbar vein; a well-defined vessel 
joining it anteriorly on a level with the kidney; 
it brings back the blood from the body-wall 
adjacent. 

y. The oviducal veins ; two or three vessels entering 
it (in the female) immediately behind ft. 

62 


84 ELEMENTARY BIOLOGY. [CHAP. 

5. The inferior vena cava. 

Remove the stomach and intestine, being careful 
not to injure the liver. The above-named vein will 
be obvious as a large vessel lying between the 
kidneys ; follow it forwards ; it will be seen to pass 
behind (dorsal to) the liver, to enter the sinus 
venosus. Its factors are 

a. The efferent renal veins ; a series of vessels arising 
from the ventral faces of the kidneys. 

b. The genital veins; variable in number and detailed 
relationships, bringing in the blood from the 
genital glands. 

c. The hepatic veins (efferent hepatic vessels}; two or 
more in number, seen, on turning the liver over, 
to enter the vena cava just before it reaches the 
heart. 

6. The veins of the superior caval system. 

Little trouble will be found in following these if 
the ventral portion of the shoulder-girdle and its re- 
lated pectoral muscles be carefully removed. 

a. The superior vena cavce; short vessels seen to 
enter the sinus venosus on either side, im- 
mediately beneath the atrium. Each is formed 
by the union of the three following factors. 

a. The external jugular vein, running down the 
under side of the throat and bringing back 
blood from the superficial parts of the head. It 
is formed by the confluence of the lingual vein 
from the tongue, and the inferior maxillary vein 
which skirts the outer side of the lower jaw. 


I.] THE FROG. 85 

(3. The innominate vein; formed by the union of 
the internal jugular vein, seen just behind the 
angle of the jaw, and bringing back the blood 
from the brain, spinal cord, and deep-seated 
parts of the head, with the subscapular vein 
returning the blood from the muscles of the 
shoulder. 

y. The axillary vein; formed by the union of the 
subdavian vein which returns the blood from the 
arm, with a large vessel (great cutaneous] bring- 
ing back the blood from the integument. 

7. The pulmonary veins. 

These are exceedingly conspicuous in spite of 
their small size, on account of the black densely 
pigmented nature of their walls. On raising the 
ventricle they are seen arising along the inner faces 
of the lungs and uniting just before entering the left 
side of the atrium (1. auricle); the right one is, of 
necessity, the longer of the two. 

8. The system of the aortic arches. 

These may be dissected in the same animal; there 
are three sets of vessels on each side, arising from 
the truncus arteriosus. They may be readily distin- 
guished from the great veins by their pinkish colour, 
due to the presence of a small quantity of blood, and 
by the thickness of their walls, the latter being very 
obvious in the case of any one of the larger arteries 
as whitish contour lines. 

a. The anterior or carotid arch, concerned with the 
blood supply to the head; it arises on each side 
as a short trunk (common carotid) which early sub- 
divides into 


86 ELEMENTARY BIOLOGY. [CHAP. 

a. The external carotid (lingual artery] to the 
tongue and floor of the mouth; it and the com- 
mon carotid together accompany the external 
jugular vein. 

/?. The internal carotid; passing outwards and up- 
wards to reach the deep-seated parts of the 
head. Its branches accompany most of the 
. factors of the internal jugular vein. 

y. The carotid gland ; a pigmented enlargement at 
the base of fi. 

b. The middle or aortic arch: this is the largest of the 
three: it runs round the throat towards the verte- 
bral column, and unites with its fellow to form the 
dorsal aorta (this may best be followed in detail 
later). It gives off, on either side, at the level of 
the arm. 

a. The subclavian artery ; mainly distributed to the 
fore-limb. 

/?. The vertebral artery; arising immediately in the 
front of a, and distributed to the vertebral 
column and the back, together with the super- 
ficial parts of the head and face (occipital 
branch). 

c. The posterior or pulmonary arch ; it runs to the 
root of the lung, giving off on its way a cutaneous 
branch which passes out to the integument of the 
trunk, and supplies most of the blood which is 
carried back by the great cutaneous vein. 

9. The dorsal aorta and its branches. 

Follow the aorta back; it will be found to run along 
the middle line beneath the vertebral column giving 
off in order 


I.] THE FROG. 87 

a. The cxliaco-mesenteric artery, to the alimentary 
organs; the cut end of this will be seen arising 
either at the point of union of the two aortic 
arches or, more generally, from the base of the 
left arch. 

Very rarely this is represented by distinct cceliac 
and mesenteric trunks. 

/>. The renal arteries, to the kidneys; variable in 
number, arising from the aorta as it passes between 
the kidneys. 

c. The genital arteries, to the reproductive glands; 
usually arising from the anterior renal vessels. 

d. The inferior mesenteric artery; a small vessel 
arising far back and supplying the base of the 
large intestine. 

e. The common iliac arteries ; arising as an apparent 
bifurcation of the dorsal aorta. 

Very rarely, the aorta is continued back, beyond 
the point of origin of the above, as a delicate 
median sacral or caudal artery. 

a. The hypogastric arteries ; arising, one on each 
side, from the iliacs, just before they leave the 
body-cavity, and distributing branches to the 
urinary bladder and body-wall adjacent. 

i o. The hepatic-portal system in detail. 

Pin a newly-killed Frog down upon its left side, 
and remove the body-wall and arm of the right one. 
Reflect the skin of the back and remove the genera- 
tive organs; dissect off the pericardium and liberate 
the right lung. Displace the alimentary canal 
turning the stomach and liver forwards and the 
large intestine well back; and pin down under water. 


88 ELEMENTARY BIOLOGY. [CHAP. 

i. The hepatic- portal vein will now be seen emerging 
from the head of the pancreas to enter the left 
lobe of the liver (cf. 3); it is formed by the 
union of the following factors. 

a. The gastric vein ; bringing back the blood from 
the stomach. 

b. The superior mesenteric vein : a very short vessel 
running through the head of the pancreas and 
receiving 

a. The duodenal veins; bringing in the blood 
from the duodenum and pancreas. 

(B. The lieno-intestinal vein; formed by the union 
of the Heal from the ileum, the hcemorrhoidal 
from the large intestine, and the splenic or 
lienal from the spleen. 

ii. The cceliaco-mesenteric artery may now be traced to 
its ultimate distribution. Its origin has been 
described at 9*2; it breaks up near the head of 
the pancreas into a and b. 

a. The cceliac artery ; distributing branches to the 
stomach, liver and pancreas, 

b. The superior mesenteric artery ; supplying the 
intestine and spleen. The branches of this 
vessel accompany the factors of the superior 
mesenteric vein. 

c. The inferior mesenteric artery ; arising from the 
dorsal aorta far back and supplying the base of 
the large intestine (cf. 9 d). 

iii. Remove the hinder half of the hip-girdle and the 
head of the femur. Scrape away the liver to the 


I.] THE FROG. 89 

level of the vena cava Inferior, and dissect away 
the veins of the head. 

The dissection, as it now stands, presents a 
general view of the blood-vascular system; 
especially noticeable are the following. 

a. The renal portal system ( 4). The femoral and 
sciatic veins will be seen to be united by an 
anastomosing trunk, which encircles the outer 
side of the thigh and receives veins from the 
adjacent integument. 

b. The whole course of the vena cava inferior 

(5)- 

c. The aortic arches ( 8). Examine these with 
care; the middle one (aorta) may or may not 
be connected with the other two, one or both 
but most generally with the carotid arch, by a 
longitudinal cord-like ducius Botalli. 

That portion of the ductus which connects the 
aortic and pulmonary arches, and which is least 
constant in the Frog, is also known as the ductus 
arteriosus. 

ii. The anatomy of the heart. 

The examination of the heart requires a good 
deal of care and the use of a lens of low magnifying 
power, and it may be greatly facilitated by working 
as follows. In a chloroformed Frog the heart is dis- 
tended with blood when it ceases to beat. When all 
signs of contractility have disappeared, the distended 
heart should be removed from the body together 
with the lungs and sufficient of the adjacent parts to 
leave the terminations of the great veins and the 
origins of the aortic trunks intact. The whole should 


90 ELEMENTARY BIOLOGY. [CHAP. 

then be placed In tolerably strong spirit until tho- 
roughly set. 

i. When sufficiently hardened, remove the lungs and 
adjacent parts, so as to isolate the heart together 
with the cut ends of the great vessels. Examine as 
under. 

a. Ventral aspect. Work over the external charac- 
ters described in i. 

b. Dorsal aspect. Note especially- 

a. The sinus venosus - } spacious and elongated, 
receiving the three caval veins. 

/?. The atrium ; if the heart be well distended a 
slight constriction will be seen subdividing 
this into a larger right auricle and a smaller 
left auricle. 

y. The pulmonary veins (cf. 7) ; seen to con- 
verge immediately in front of the sinus ve- 
nosus, to enter the inner border of the left 
auricle. 

S. The sinu-auricular aperture seen on opening 
up the sinus venosus and removing its con- 
tents. It communicates with the cavity of 
the right auricle and is guarded by two mem- 
branous flaps (sinu-auricular valves}. 

i i . General dissection from tJie fron t. 

Pin down ventral surface uppermost, and dissect 
with great care, under water. Remove the front 
wall of the ventricle, atrium and truncus arteriosus, 
and lay open the bases of the aortic arches ; care- 
fully remove the coagulated blood which fills them 
and wash clean. 


I.] THE FROG. QI 

a. The ventricle ; its single ventricular cavity and 
thick spongy wall. 

b. The auriculo-ventricular aperture; situated to 
the extreme left (right of the preparation) of the 
ventricle, and bounded by two auriculo-ven- 
tricular valves. Raise the nearest of these, if 
not already removed, and dissect it away. 

c. The atrium ; its thin wall ; its spacious cavity 
completely subdivided into two chambers (r. and 
1. auricles) by a longitudinal inter-auricular sep- 
tum, lying well to the animal's left side. Ex- 
amine the relations of this to the auriculo-ven- 
tricular aperture ; it is prolonged down on to 
the valves which guard it, subdividing it into 
two. 

a. The sinu-auricular aperture ; large and situ- 
ated near the middle of the right auricle im- 
mediately adjacent to the inter-auricular sep- 
tum. Note its valvular margins. 

/?. The aperture of the pulmonary veins ; small 
and rounded, opening near the top of the 
left auricle, close to the septum. 

y. The auriculo-ventricular valve; note its cha- 
racters and mode of attachment. 

d. The truncus arteriosus ; arising from the ex- 
treme right-hand corner of the ventricle and 
largely subdivided into two by a longitudinal 
valve (cf. p. 18). Examine the aortic arches 
in relation, passing bristles into them; they 
arise as under 


92 ELEMENTARY BIOLOGY. [CHAP. 

a. The aortic and carotid arches ; from its an- 
terior end, immediately in front of the longi- 
tudinal septum, the calibre of the aortic arch 
being much the greater of the two. 

fi. The pulmonary arches ; the pair arise by a 
single aperture lying immediately to the 
animal's left of the anterior end of the longi- 
tudinal valve. 

iii. A companion dissection may be profitably made 
from the left side, for general comparison with the 
foregoing, especially with respect to the relations 
of the auriculo-ventricular valves and inter- auricular 
septum. 

12. The circulation of the blood in the web of the foot. 

i. Get a piece of thin board, about 5 inches long and 
2 J broad ; in the middle of one end of it cut a 
V-shaped notch about the size of the expanded 
web : place the frog on the board, belly down- 
wards, and fix it by passing round it two or three 
turns of tape : next tie threads round the toes of 
one foot, and by means of them spread out the 
web over the notch, taking great care that it is 
only very lightly stretched. The animal should be 
kept moist by spreading a piece of wet blotting- 
paper over its back. 

ii. Examine the web with i inch obj.: Note 

a. The black pigment-cells in the skin ; sometimes 
irregularly branched ; sometimes more compact. 

b. The close network of blood-vessels, lying deeper 
than the pigment-bearing layer. 


I.] THE FROG. 93 

a. The arteries, running mainly towards the free 
edge of the web, and constantly diminishing 
in size as they break up into branches ; the 
blood-flow, from larger to smaller branches. 

j3. The capillaries, in which the arterial branches 
end : small vessels forming a close network 
and frequently branching or anastomosing 
without much alteration in calibre. 

y. The veins, formed by the ultimate union of 
the capillaries, and increasing in size as they 
unite with one another ; the blood-flow, from 
smaller to larger factors. 

c. The nature of the blood-flow ; the current is 
marked by the solid bodies (corpuscles] carried 
along in the blood-fluid : it is most rapid in the 
arteries ; slowest, and most uniform, in the ca- 
pillaries. 

iii. Place a small drop of water on a bit of thin mica 
or of a thin cover-slip, and place the same, water 
downwards, gently on the web : then examine with 
J or \ obj. ; note 

a. The walls of arteries, capillaries, and veins, 

a. The arterial walls, tolerably thick, seen as a 
clear well-defined line on each side of the 
blood-stream. 

J3. The capillary walls ; difficult to see ; apparent 
as thin slightly transparent boundary lines. 

y. The venous walls ; much like the arterial. 

b. The blood-flow in the small arteries. 

a. The rapid stream in the middle, containing 
most of the red corpuscles. 


94 ELEMENTARY BIOLOGY. [CHAP. 

/?. The slower stream along the edge (inert 
layer), containing many granular-looking co- 
lourless corpuscles. 

c. ThQjfZow in the capillaries ; much slower than In 
the arteries ; the frequent distortion of the red 
corpuscles in the capillaries under pressure; 
the elasticity of the corpuscles, as indicated by 
the readiness with which they recover their 
shape when the cause of distortion is removed ; 
the manner in which the white corpuscles creep 
along, and their tendency to stick to the capil- 
lary wall. 

J. The lymphatic system. The full study of this system 
is beyond the scope of this work ; the undermentioned 
may however be made out with comparative ease. 

a. The sub-cutaneous lymph-spaces ; cf. Sect. C. 2./. 
l>. The dsterna magna ; cf. Sect. C. i. g. y. 

c. The circum-cesophageal lymph sinus ; a loose fold 
of mesentery embracing the base of the gullet, 
opalescent in appearance. It becomes exceed- 
ingly conspicuous if inflated, by introducing the 
point of a blow-pipe beneath the adjacent peri- 
toneum. 

d. The lymph-hearts ; small thin-walled sacs, paired 
and pulsatile ; to be sought for while still beat- 
ing, immediately on the death of the Frog. 
They are, on either side 

a. The posterior lymph-heart ; to be seen on re- 
moving the skin of the back, lying a short 
distance in advance of the cloacal aperture 


I.] THE FROG. 95 

and immediately in front of the pyriformis 
muscle (Sect. H. 5. c). 

(3. The anterior lymph-heart ; lying in an inter- 
space between the small muscles (intertrans- 
versi) which pass between the transverse pro- 
cesses of the third and fourth vertebras. Best 
seen on slitting open the body-wall ventro- 
laterally and cutting into the cisterna magna. 

The cartilaginous free end of the transverse 
process of the third vertebra is expanded (cf. 
Sect. G. 3<r) for protection of the above. 

K. The nervous system. 

i. The cerebro-spinal axis and neural canal. Take a 
recently-killed frog and divide the skin along the 
dorsal middle line and reflect it on each side ; re- 
move the muscles which overlie the arches of the 
vertebras, and open the neural canal as follows. Di- 
vide the membrane (vertebra-occipital ligament) which 
passes between the ist vertebra and occiput; then 
introduce one blade of a small, but strong, pair of 
scissors into the cranial cavity, and cut away bit by 
bit the bones which form the roof of the skull, 
taking care that the point of the scissors does not 
injure the brain. Next remove, in a similar manner, 
the tops of the vertebral arches and the head of the 
urostyle. In all probability a chalky fluid will be 
met with clouding the water and concealing the un- 
derlying organs (secretion of the periganglionic glands 
(cf. p. 32); if so, wash carefully until clean. There 
will thus be exposed 

a. The cerebro-spinal axis ; filling the greater part 
of the neural canal ; it can be resolved into 


96 ELEMENTARY BIOLOGY. [CHAP. 

a. The encephalon or brain ; that portion which 
lies within the cranium, its constituents in 
part paired. 

/3. The myelon or spinal cord ; axial and lying 
within the neural canal of the vertebral 
column. 

Its form : wide in front, but narrowing ra- 
pidly about the 5th or 6th vertebra, and 
thence continued back as a slender tapering 
filum terminate. 

The groove (dorsal fissure] running along 
its middle line. 

b. The investing membranes and the origin of the 

spinal nerves. 

a. The//<2 mater a delicate densely pigmented 
membrane, investing the whole nervous axis. 
It is thickened and highly vascular above the 
hind portion of the brain (choroid plexus). 

ft. The dura mater ; a similar but denser mem- 
brane lining the wall of the neural canal. 

y. The roots of the spinal nerves ; conspicuous in 
the case of the second and eighth and ninth 
pairs of nerves. The former are very stout, 
and pass out from the myelon at right angles 
to the axis, to reach the arm : the latter are 
long and delicate, passing back on opposite 
sides of the hinder half of the myelon. 

c. Obtain a second Frog (preferably one hardened 
in alcohol) and make a transverse section across 
the entire nervous axis and neural canal im- 


I.] THE FROG. 97 

mediately behind the above-named second spinal 
nerve. Examine in water, under a hand lens, 

a. The myclon ; subdivided, dorsally and vent- 
rally, by median longitudinal fissures ; en- 
closing a small central canaL 

{3. The nerve roofs ; arising dorsally and ventrally, 
and passing outwards and downwards through 
the inter-vertebral foramina to form, on each 
side, the trunk of the nerve. The dorsal 
root bears an enlargement or ganglion of the 
root, immediately on leaving the neural canal. 

y. The investing membranes (cf. supra) ; seen to 
merge into each other and the periosteum, in 
the vicinity of the iriter-vertebral foramina. 

2. The anatomy of the brain. 

i. Expose from the dorsal aspect, as directed in i, 
preferably in a frog which has been previously 
hardened in spirit. Examine in situ. 

The anterior half of the brain consists of two 
elongated masses, each marked off by a slight 
transverse depression into a smaller anterior and 
a larger posterior portion. 

a. The cerebral hemispheres (prosencephaloii); the 
posterior of the above-named, separated by a 
deep cleft. 

b. The olfactory lobes (rhinencephalori}; the anterior 
of the above-named, confluent with each other 
at their bases. Each passes into a rounded 
trunk (commonly termed the olfactory nerve], 
which leaves the skull, and ramifies in the 
lining membrane of the nose. 

M. 


98 ELEMENTARY BIOLOGY. [CHAP. 

c. The tlialamencephalon : a thickened mass imme- 
diately posterior to the cerebral hemispheres. 

Note, in connection with it, 

a. The thalami opt id ; its lateral walls, consti- 
tuting its main portion as here seen. 

/3. Its thin roof; transparent and very readily 
torn. 

y. The pineal gland ; represented by a small 
pinkish body, lying in the bay enclosed by 
the hinder ends of the hemispheres. 

d. The optic lobes (mesencephalon) : a pair of 
rounded eminences lying behind the thala- 
mencephalon. 

e. The cerebellum (inetencepJialon] : a narrow trans- 
verse band next in .order of succession. 

f. The medulla oblongata (myeloncephalon) : the por- 
tion of the brain lying behind the cerebellum 
and passing into the spinal cord. Its roof is 
covered by the choroid plexus (cf. i. b. a). 

ii. Divide the olfactory lobes, and raise the front end 
of the brain ; turning it back gradually, divide with 
a sharp scalpel any nerves that may be observed 
passing from it to the cranial walls : most of these, 
being small, will probably be torn across unob- 
served, but the large optic nerves will at any 
rate be seen. Remove the brain, together with 
a small portion of the spinal cord, and examine 
from the ventral aspect. 

<z. The hemispheres and olfactory lobes (cf. supra). 
The outer walls of the latter are thickened 


L] THE FROG. 99 

ventrally to form two cord-like tracts (ventral 
roots of the olf. lobes], 

b. The lamina terminalis ; a median bilobed emi- 
nence, interposed between the bases of the 
hemispheres. 

c. The optic lobes ; seen to project laterally, be- 
hind the hemispheres. 

d. The optic tracts; band-like masses arising in 
connection with c \ that of the left side giving 
off the optic nerve to the right eye and vice 
versa. The interlacing of the two at the point 
of decussation, to form the optic chiasma. 

c. Lying in the ventral middle line immediately 
behind the optic chiasma there will be seen, in 
the order named 

a. The tuber dnereum ; a large tongue-shaped 
mass, bilobed posteriorly. 

/?. The infundibulum ; a small stalk-like body 
giving attachment to 

y. the pituitary body ; a rounded pinkish mass 
(highly vascular in the fresh state). 

iii. Examine from one side (lateral aspect}, and com- 
pare generally with i. and ii. 

iv. Slice away, with a small scalpel, the dorsal walls 
of the cerebral hemispheres and olfactory and optic 
lobes, and remove in like manner the greater por- 
tion of the cerebellum and roof of the thalamen- 
cephalon. The central cavities or ventricles will 
thus be laid bare ; they can be resolved into two 
sets, as under : 

72 


IOO ELEMENTARY BIOLOGY. [CHAP. 

a. Median or axial (forward continuations of the 
central canal of the spinal cord); in order of 
succession from behind forwards 

a. The fourth ventricle; tongue-shaped and ex- 
panded in front ; enclosed by the medulla 
and cerebellum. 

ft. The iter or aqueduct of Sylvius ; between and 
below the optic lobes. 

y. The third ventricle ; lying within the thala- 
mencephalon and bounded in front by the 
lamina terminalis (front wall of the median 
portion of the cerebro-spinal axis). 

b. Paired. 

a. The optic ventricles ; lying within the optic 
lobes and derivative of the iter. 

(3. The lateral ventricles (central cavities of the 
hemispheres) in communication, on either 
side, with the third ventricle through a wide 
passage (foramen of Mbnro). Each is seen 
to lodge a thickened fold of pia-mater (cho- 
roid plexus] which enters it immediately in 
front of the above-named foramen. (Cf. p. 27.) 

y. The olfactory ventricles ; forward prolongations 
of j3, extending into the bases of the olfactory 
lobes. 

v. Longitudinal vertical section. Obtain the brain of 
the largest frog accessible, and, when fully hard- 
ened in spirit, remove one half cutting to the near 
side of the middle line. 

Examine in water under a hand lens, and note 
the following 


I.] THE FROG. 10 1 

a. The median ventricles ( iv. a) ; note their limits 
and their relationships to the several constituents 
of the brain. Take especial note of the third 
ventricle ; its walls are modified as follows 

CL Front wall ; greatly thickened to form the 
lamina terminalis (iv. a. y). 

(3. Roof; thin and delicate, prolonged upwards 
and forwards to give attachment to the "pineal 
- body." 

y. Its floor; for the most part thin prolonged 
downwards and backwards as the infundibu- 
him (ii. e. /3) to meet the pituitary body ; 
thickened at its middle around the optic 
chiasma (ii. d). 

8. The foramen of Monro ; lying immediately 
above the lamina terminalis and large enough 
to admit a good-sized bristle. 

b. The commissures ; small but definite tracts passing 

between the opposite halves of the brain ; rela- 
tively whitish in colour. Look for their cut 
edges with a powerful hand lens, as under 

a. The posterior commissure ; lying in the sub- 
stance of the roof, immediately in front of 
the optic lobe. 

/?. The corpus callosum ; represented by a well- 
defined tract traversing the head of the lamina 
terminalis, immediately below and behind 
the foramen of Monro. 


y. The anterior commissure; smaller than the 
above and runnin 
lamina terminalis. 


above and running through the middle of the 


102 ELEMENTARY BIOLOGY. [CHAP. 

3. The spinal nerves. 

Pin a frog down upon its back and remove the 
ventral integument and body-wall, together with one- 
half of the floor of the mouth. Carefully dissect 
away the viscera and dorsal aorta and remove the 
centra of the vertebras, cutting well down to the level 
of the roots of the spinal nerves. Wash, and exa- 
mine under water, 

a. The spinal cord ; in form cylindrical; enlarged 
at the points of origin of the nerves for the 
limbs (brachial and lumbo-sacral swellings}. 

b. The spinal nerves arising from it. Ten on each 
side ; the first one passing out between the 
first and second vertebrae, the last through the 
head of the urostyle (cf. Sect. G. 2. d. e). Each 
leaves the neural canal behind that vertebra 
with which it corresponds. 

a. Their origin ; each arising by two roots (an- 
terior and posterior] as is most easily seen in 
the yth, 8th and 9th nerves, in which they are 
much the longer. Sometimes the fibres of the 
anterior roots are bound up into two or more 
fasciculi. 

/?. The direction of their roots : outwards in the 
anterior nerves ; obliquely backwards in the 
4th, 5th and 6th; almost directly backwards, 
and running for a considerable distance in 
the neural canal, in the yth, 8th, 9th and 
loth. 

7. The ganglia of their dorsal roots (cf. i. c. /?); 
very conspicuous in the yth, 8th, and Qth; 
lying, for the most part, outside the spinal 


I.] THE FROG. 103 

canal and largely surrounded by the perigan- 
glionic glands (cf. p. 32). 

c. Distribution of the spinal nerves. Follow this 

on one side. 

a. The ist ; examine it on that side upon which 
the floor of the mouth is retained. It passes 
at first outwards and then forwards and in- 
wards, beneath the mylohyoid muscle, to be 
distributed to the muscles of the tongue 
(hypoglossal nerve). 

ft. The 2nd and 3rd; meeting, on a level with 
the end of the transverse process of the third 
vertebra, to form the brachial nerve. Follow 
it to the arm. 

y. The 4th, 5th, and 6th; each forming a long 
trunk which passes back for a considerable 
distance, for distribution to the body wall 
and integument. 

8. The yth, 8th, and gth ; running parallel with 
each other and the urostyle (lumbo-sacral 
plexus), and finally becoming bound together 
to form the iliac nerve for distribution mainly 
to the hind limb. Follow this to the leg. 
This plexus is liable to variation. 

. The loth, a small nerve lying immediately 
internal to 8 and close against the urostyle. 
It enters into connection with the lumbo- 
sacral plexus, and is distributed to some of 
the lesser muscles of the posterior extremity 
and parts adjacent. 

. Examine one of the middle spinal nerves 
with care, under a hand lens if necessarv. 

* j 


104 ELEMENTARY BIOLOGY. [CHAP. 

There will be found to arise immediately 
external to its ganglion a small dorsal ramus ; 
note that this is distributed to the muscles 
and other parts of the body dorsally, much as 
is the main trunk or ventral ramus ventrally. 

4. The cranial nerves. 

The study of these may be greatly facilitated by 
placing the animal when dead in -| per cent, chromic 
acid solution, the same to be frequently changed 
until decalcincation is complete. This done ; wash 
well under running water and preserve in methylated 
spirit, slightly dilute. 

i. Dissect from the ventral aspect as directed at 3, 
leaving the floor of the mouth intact. 

a. The qth or glossopharyngeal nerve. Its trunk ; 
seen, on removing the middle portion of the 
mylohyoid muscle (Sect. B. c. y) lying immedi- 
ately external to that of the hypoglossal nerve 
( 3. c. a) ; its branches, seen, on dissecting the 
genio-hyoid, to be distributed to the tongue and 
some of its muscles. 

ii. Remove the floor of the mouth together with the 
heart and gullet, leaving the mandible and a small 
portion of the mylohyoid muscle on one side. 
Raise the mucous membrane of the roof of the 
mouth with forceps and dissect it away with the 
utmost care, being especially cautious to avoid re- 
moving certain nerves which lie in close appo- 
sition with it. Next slice away the floor of the 
cranium and auditory capsules so as to expose 
their internal cavities ; wash clean and examine 
in water under a hand lens. 


I.] THE FROG. 105 

a. The \st or olfactory nerve ; passing forwards in 
front (cf. 2. />). Remove the vomer of one 
side and cut down to its level, following it out ; 
it will be seen to ramify on the base of the ol- 
factory sac. 

b. The 2nd or optic nerve ; arising from the optic 
chiasma ( 2. d] ; it runs forwards and upwards 
to enter the eye-ball from below. 

c. The yd or oculo-motor nerve (described, in com- 
mon with the 4th and 6th, in connection with 
the eye-muscles. Sect. L. 3. p. 116). 

//. The 5//J or trigeminal nerve. Remove the eye- 
ball on one side ; lying internally to it, deeply 
seated and in close apposition with the cranial 
wall, will be seen the ophthalmic or orbito-nasal 
nerve (ist division of the 5th) ; trace it back, it 
will be found to enter, immediately internal to 
the front end of the auditory capsule- 

a. the Gasserian ganglion ; a comparatively large 
oval pigmented body, seen to be in con- 
nection with other nerves also. 

p. The maxillo-mandibular nerve ; arising from 
a and passing outwards immediately be- 
hind the eye. It early subdivides into the 
two following ; the mandibular nerve (3rd 
division of the 5th) to the lower jaw and its 
integument (follow it on that side in which 
these still remain) ; the maxillary nerve (2nd 
division of the 5th) seen, on removing the 
hinder third of the upper jaw, to be somewhat 
similarly distributed to the maxillary region. 


106 ELEMENTARY BIOLOGY. [CHAP. 

y. The ophthalmic or orbito-nasal ; its distribu- 
tion may now be studied by turning the animal 
over and examining from the dorsal aspect. 
Remove the nasal and sphenethmoid bones 
to its level ; and note its branches to the 
antero-dorsal integument of the head. 

e. The *]th or facial ; intimately connected with 
the Gasserian ganglion and the trigeminal. Ex- 
amine it, from the ventral aspect, on that side 
at which the eye remains. 

a. Its root ; arising, side by side with that of the 
5th, from the side wall of the medulla; the 
two entering the Gasserian ganglion. 

j3. Its anterior branch (palatine nerve] ; leaving 
the Gasserian ganglion immediately external 
to the ophthalmic branch of the 5th, and 
passing forwards, perforating the vomer, to be 
distributed to the mucous membrane of the 
roof of the mouth. 

y. The maxillo-palatine commissure ; connecting 
the palatine and maxillary nerves; on a level 
with the front end of the eye-ball. 

3. The posterior branch of the yth; leaving the 
outer side of the Gasserian ganglion, im- 
mediately behind the maxillo-mandibular 
nerve, and passing outwards and backwards 
dorsal to the columella auris (beneath it as 
here seen). Its distribution may best be 
studied later. 


J. The Q/// and i vth (post-auditory nerves] ; arising 
close together from the medulla posteriorly to 


I.] THE FROG. I0; 

the 5th and yth, and passing behind the auditory 
capsule, much as do the 5th and yth in front of 

it. 

a. The loth or pneumogastric (vagus); its cut 
end will alone be seen. Soon after leaving the 
skull it bears a large ganglion (g. trunri vagi). 

(3. The qth or glossopharyngeal ; it arises im- 
mediately in front of a, and is largely con- 
fluent with the above-named ganglion. It 
is commissurally connected with the posterior 
branch of the 7th (commissura ad facialem). 
Its distribution has been studied ( i. a). 

g. The Sf/i or auditory ; arising from the medulla 
along with the yth, part of which it appears 
to be. Dissect to its level and trace it into the 
auditory capsule. 

5. The sympathetic system. 

Dissect from the ventral aspect as before, but 
leave the aorta, the cut end of the cceliaco-me- 
senteric artery and the base of the large intestine 
with the bladder, in place. On raising the aorta 
the sympathetic will be found immediately beneath 
(dorsal to) it. 

a. The mam trunk of the sympathetic ; paired and 
longitudinal, accompanying the arches and trunk 
of the aorta. 

b. The splanchnic nerve ; arising from a at the point 
of junction of the aortic arches and accompanying 
the coeliaco-mesenteric artery. 

c. The sympathetic ganglia; enlargements on a, vari- 
able in size and number; usually one for each 


I08 ELEMENTARY BIOLOGY. [CHAP. 

spinal nerve. Best seen on turning the aorta to 
one side. 

d. The ravri communicant.es; relatively long com- 
missures between c and the trunks of the spinal 
nerves. 

e. The distribution of the sympathetic ; best studied 
in the pelvic region, and rendered the more 
conspicuous if a little acetic acid be added to 
the water. Vaso-motor nerves ; arising from the 
ganglia and passing to the aorta. Viscero-motor 
nerves ; seen to arise from both sympathetic and 
lumbo-sacral plexus for distribution to the pelvic 
viscera. 

f. The cranial sympathetic. Remove the aortic arches 
with care and follow the sympathetic forwards, 
dissecting as at 4. ii. With a little care the above 
can be traced to the Gasserian ganglion ; passing 
internally to the auditory capsule and entering 
into connection, en route, with the post-auditory 
nerves. 

6. The further course of the facial and vagus nerves 
(yth and loth cranial). 

Pin a frog clown upon its side and remove the 
integument of the head, together with the arm and 
shoulder-girdle and body-wall adjacent. Pull down 
the stomach and pin it back, so as to put the me- 
sentery on the stretch and fully to expose the near 
lung and the heart. 

a. Note the course of the mandibular nerve ( 4. 
d. /?). It will be seen to run backwards and 
downwards immediately in front of the squamosal 


I.] THE FROG. 109 

and under the jugal, to reach the outer side of 
the mandible. 

/\ The facial nerve. Its hyoid branch ; seen on dis- 
secting away the membrana tympani and outer 
end of the columella auris. It leaves the skull 
immediately behind the squamosal and passes 
downwards and backwards, giving off 

a. A small branch to the integument of the cheek 
(in close apposition with the jugal bone). 

/?. A mandibulo-hyoid branch ; continued along the 
inner face of the mandible, and giving off nerves 
to the muscles and skin adjacent. (Be careful 
not to confuse these with the branches of the 
mandibular nerve.) 

c. The 9th and i2th (cf. 4); the former will be 
seen to pass internally, the latter externally, to 
the anterior cornu of the hyoid. Remove the 
hypoglossal with care, thus laying bare- 

d. The loth (vagus). Seen to pass downwards and 
backwards, externally to the posterior cornu of 
the hyoid. At the side of the gullet it breaks up 
into the under-mentioned 

a. The gastric rami ; two or more in number, dis- 
tributed to the stomach. They pass through 
the so-called diaphragm. 

/3. The pulmonary ramus, to the lung; accom- 
panying the pulmonary artery. 

y. The cardiac ramits, to the heart ; arising in 
front of ft and coursing along the dorsal wall 
of the atrium. (Sympathetic fibres are bound 
up with this, if not with a and (3.) 


I 10 ELEMENTARY BIOLOGY. [CHAP. 

S. The recurrent laryngeal ; a long nerve arising in 
front of and above a y and coursing round the 
base of the pulmonary aortic arch to reach the 
larynx. 

c. The dorsal ramus ; arising from the main trunk 
immediately after it leaves the skull, and dis- 
tributed to the adjacent dorsal integument. 

f. Incidental. 

a. The course of the 5th and yth (cf. 4. ii. d. e. 
et seq.). Remove the eye and the squamosal 
and quadrato-jugal bones and follow the course 
of the above nerves, as seen from the side. 

Note especially the relations of the 5th to the 
mouth-cavity and of the 7th to the tympano- 
Eustachian passage (Eustachian recess). See 
pp. 28, 29. 

fi. The sympathetic. Note especially the further 
course of the splanchnic nerve ( 5. /?). It 
bears a large ganglion in close proximity with 
the cceliaco-mesenteric artery; add a little acetic 
acid ; offshoots will be found to proceed from it 
to the alimentary canal, accompanying, at their 
outset, the branches of the artery. 

L. The anatomy of the sense organs. 
i. The gustatory organ. 

The shape and arrangement of the tongue have 
already been described (Sect. E. i d.). Snip off a 
bit of mucous membrane from the upper surface of 
the tongue of a recently killed frog, mount in salt 
solution and cover in plenty of the fluid with a large 
coverslip : examine with one inch obj. 


I.] THE FROG. Ill 

a. On the surface of the fragment and especially 
around its edges numerous minute elevations will 
be seen : these are the papilla : some (filiform 
papillcc] are pointed at the free end and others 
(fungiform papilla] are flattened. Note the loops 
which the blood capillaries make in many of them. 

b. Examine one of the thinner bits of the specimen 
with a high power : a flickering motion, due to 
the presence of cilia^ will be observed. Some of 
the papillae however will be seen to have no cilia 
except a narrow belt around the somewhat trun- 
cated apex : it is on these that the gustatory discs 
are placed, and in fortunate specimens nerve- 
fibres can be seen entering them. 

-. The olfactory organ. 

The general relations of this have already been 
described (Sects. A and E). 

a. Take a frog which has been preserved in spirit ; 
insert the point of a small pair of scissors into the 
external nostril of one side and cut away the roof 
of the nasal cavity. A chamber is thus exposed 
which has a somewhat triangular form, its apex 
being anterior. 

a. The walls of the cavity are slightly folded, and 
there is a well-marked hemispherical eminence 
on its floor which overlies the vomer. 

(3. The posterior nostril ; situated some distance in 
front of the hinder boundary of the nasal sac 
(i.e. the sac is prolonged back behind it). 

b. Open the other nasal cavity in a similar way : 

a. The septum narium; a median longitudinal par- 


112 ELEMENTARY BIOLOGY. [CHAP. 

tition separating the apposed sacs of opposite 

sides. 

fi. The boundaries of the olfactory organ. It lies 
within an area enclosed by the premaxilla and 
front end of the maxilla and the palatine bones, 
being wholly in front of the latter. 

c. Obtain a second frog, and lay open the olfactory 
sac from the side, cutting obliquely from the 
anterior nostril across the outer anterior border of 
the eyeball, in order that the line of section may 
pass through both anterior and posterior nares. 

a. General. Cf. supra. 

/?. The anterior nostril ; its upper lip, relatively 
small and constricted ; its lower lip, produced 
antero-laterally into a deep fold around the ali- 
nasal cartilage (cf. Sect. G. 5. a. e). 

3. The visual organ. 

i. General. 

Take an uninjured frog and examine its eye. It will 
be found to project considerably above the top of 
the head, but if touched it is withdrawn into a sort 
of socket. If the animal's mouth be opened, a de- 
pression, caused by the eye-ball, will be seen on its 
roof, and this is more prominent when the eye is re- 
tracted. When the eye is open observe from without. 

a. The eyelids ; folds of skin developed round the 
margin of the eye-ball. The upper lid is thick 
and swollen, the lower lid thin and transparent. 

Gently touch the eye and observe that it is 
closed, by the pulling over it of the lower eye- 
lid. The upper lid is hardly moveable. 


I.I THE FROG. 1 I 7 

_J *_/ 

b. When the eye is open, observe the following- 

a. The cornea ; the transparent covering for its 
exposed surface. 

/?. The iris, a membrane, seen through a, coloured 
by brown and golden pigment, the latter form- 
ing a very brilliant ring around its inner 
margin. Below it is interrupted by a faint 
dark line which can be traced downwards 
through the whole iris. 

y. The pupil ; elliptical and lying within the 
iris, its long axis directed antero-posteriorly. 

ii. The eye-muscles and their nerves. These can be 
most satisfactorily made out, notwithstanding their 
small size, in a frog preserved in chromic acid as 
directed in Sect. K. 4. Examine under a hand 
lens. 

a. Dorsal aspect. .Remove the head from the body, 
cutting well back so as to include the first two 
vertebrae, and pin down in as small a dish as 
may be convenient. Dissect off the integument 
of the top of the head together with the upper 
eyelids, but be very careful to leave the lower 
lids uninjured. 

a. The eyeball ; completely filling the orbit. 

p. The superior oblique muscle ; ribbon-shaped 
and passing obliquely forwards between the 
antero-dorsal face of a. and the orbit. 

y. The superior reef us ; a trifle larger than f3. 
and arising from the dorsal face of the eye- 
ball. It passes backwards and inwards, to be 
attached to the cranial wall. 

M. 8 


114 ELEMENTARY BIOLOGY. [CI1A1V 


8. The 4//z cranial nerve (n. patheticus) ; seen, on 
slightly pulling the eye-ball outwards, skirting 
the inner wall of the orbit to reach the su- 
perior oblique muscle. 

c. The $rd cranial nerve (oculomotor}. A branch 
of this may be seen breaking up in the 
superior rectus muscle, if that be cut across 
near its point of attachment to the eye-ball 
and turned back. 

. The lower eyelid ; follow it forwards, it will be 
found to be continuous with a strong tendon 
which passes through a loop immediately ex- 
ternal to the superior oblique muscle. 

b. Ventral aspect. Turn the head over and pin 
down ventral surface uppermost ; remove the 
entire lower jaw and floor of the mouth, and 
dissect off the mucous membrane of its roof 
with care. 

a. The levator bulbi muscle ; a sheet-like mass 
underlying (overlying as seen) the whole eye- 
ball ; its fibres pass obliquely outwards and 
backwards. 

Compare a transverse section such as is de- 
scribed at Sect. C. 3. The fibres will be found 
to pass between the upper jaw and the in- 
ternal dorsal wall of the orbit. 

P. The inferior oblique ; a small muscle passing 
upwards and inwards between the antero- 
internal face of the eye-ball and the orbit. 

7. The Harderian gland ; a nodular mass im- 
mediately behind /?, interposed between the 
eye-ball and orbit. 


I.] THE FROG. 115 

S. The recti muscles other than the superior 
one ; seen on removal of the levator bulbi, 
to converge postero-internally. The inferior 
rectus, arising from the ventral face of the eye- 
ball and passing obliquely backwards ; the 
external rectus, arising from its posterior face 
and passing inwards and upwards ; the in- 
ternal red us, arising in front under cover of 
the inferior oblique, and passing backwards 
along the inner face of the eye-ball. 

. The $rd (oculomotor} nerve ; seen to break up, 
immediately in front of the superior rectus, 
for distribution to (3. and 8. with the excep- 
tion of the external rectus. 

. The 6tk cranial nerve (n. ab due ens). A small 
muscle (pterygoid] will be seen lying in the 
posterior region of the orbit; remove this and 
lay bare the Gasserian ganglion (Sect. K. p. 105); 
the 6th nerve will be found passing from the 
outer face of the latter to the postero-ventral 
border of the external rectus. It is very 
short and may best be seen by gently drawing 
the muscle forwards. 

77. The retractor bulbi muscle; a considerable 
mass of tissue, seen, on removing {3. and 8. 
It surrounds the optic nerve. 

0. The tendon of the lower lid (Cf. a. .) ; shining 
and thread-like, passing round and intimately 
connected with the outer edge of 77. It is 
inserted behind into the adjacent integument. 


c. The origins of the $rd, tfh and 6t/i cranial nerves. 

82 


Il6 ELEMENTARY BIOLOGY. [CHAP. 

Lay bare the cerebro-spinal axis from the ventral 
aspect, as directed in Sect. K. 3, and expose 
the Gasserian ganglion with the utmost care. 

a. The $rd (oculomotor'] nerve ; arising, on each 
side, from the ventral surface of the brain on 
a level with the pituitary body. It passes up- 
wards and outwards to leave the skull in 
front of the 5th nerve (cf. p. 67, vi.). 

ft. The 6th nerves (n. abducentes) ; extremely 
delicate, arising close together in the middle 
line from the floor of the medulla, on a level 
with the gth and icth. Each passes upwards 
and outwards along with the trunk of the 
5th to enter the Gasserian ganglion. 

y. The 4/7* (n. patheticus) ; best seen on re- 
moving one optic nerve and turning the brain 
a little to one side. It leaves the dorsal sur- 
face of the brain in front of the cerebellum ; 
and passes upwards and forwards to leave the 
skull above and in front of the optic nerve 
(cf. p. 67, vii.). 

iii. The structure of the eye-ball. Obtain a freshly- 
killed frog and remove the head from the trunk ; 
bisect the former longitudinally and examine the 
eye-ball while still in position, as under. 

Make two sections ; that of one side (a.) to 
bisect the eye-ball transversely to the long axis of 
the body (to pass through the crystalline lens if 
possible) ; that of the other (b.) to bisect it equa- 
torially, at right angles to a. Examine under a 
hand-lens. 


I.] THE FROG. II/ 

Section a, 

i. Examine high and dry and note - 

a. The eye-ball ; firm and resistant, enclosing a 
central cavity. 

p. The crystalline lens ; a relatively large transparent 
body filling a considerable portion of a, globular, 
its outer face somewhat flattened. It is held 
firmly in position. 

y. The vitreous or inner chamber ; that portion of 
the cavity of the eye-ball internal to the lens. 
It is filled with a dense gelatinous viti'eous 
humour, which may be raised en masse with a 
forceps. 

8. The aqueous or outer chamber ; relatively much 
smaller than y. and external to the lens. It 
lodges a more fluid aqueous humour. 

ii. Dissect the inner portion, under water, to the level 
of the optic nerve, so as to get the same into 
longitudinal section. Examine the coats of the 
eye, following their cut edges. 

a. The sclerotic ; the outermost coat, dense and 
cartilaginous ; it serves to give consistency to 
the whole and to furnish attachment for the 
muscles. Externally it is continued over the 
outer face of the eye-ball as the thin and trans- 
parent cornea ; internally it forms the sheath of 
the optic nerve. 

/3. The choroid ; internal to a, vascular and spongy 
and blackened by pigment. It is prolonged 
forwards in front of the lens to form the ins 
(cf i. b). 


IlS ELEMENTARY BIOLOGY. [CHAP. 

y. The retina ; a thin filmy layer, greyish and 
transparent, internal to p. It stops short at 
the base of the iris (ora serratd] ; internally it 
passes into the optic nerve. 

If the vitreous humour be much disturbed this 
layer will be puckered and torn, or otherwise 
displaced. 

S. The conjunctiva and eyelids (cf. Sect. C. 3. <-/.). 
The former can only be distinguished from the 
cornea with difficulty. 

Section b. 

i. Examine the inner half from within, under water. 

a. The retina. Gently raise it ; it will be found to 
adhere firmly at the point of entrance of the 
optic nerve (blind spot}. Note the position of 
same. 

/?. The choroid ; strip off the whole retina and ex- 
amine this, noting its texture and great vas- 
cularity. 

y. The sclerotic; examine this in like manner, 
after having removed fi. 

ii. Examine the outer half from within, and note 
especially the relations of the lens and iris. 

4. The auditory organ. 

a. Examine the tympanic membrane from the outside 
(cf. Sect. A. a. (3.). Dissect off its outer or 'tegu- 
mentary layer'; there will thus be brought into 
view : 


a. The annul us tympanicus ; a cartilaginous rin 
supporting the edge of the membrane. 


I.] THE FROG. 119 

/?. The columella auris ; its head will be seen 
as an opaque white patch in the middle of the 
deeper layers of the tympanic membrane, now 
laid bare. Cut away the latter around it and 
note its relations to the Eustachian recess (Sect. 
E.). Follow the cut edge of the mucous mem- 
brane ; it will be found to wrap round the 
columella, suspending it much as the mesentery 
suspends the alimentary canal (i.e. the columella 
is outside it). 

/>. The internal ear. Remove the skin from the top 
of the head of a large frog which has been pre- 
served in alcohol, and scrape the roof of the 
auditory capsules quite clean. Isolate the capsule 
of one side and hold it between the finger and 
thumb of the left hand. If examined with care, a 
couple of greyish streaks will be seen on the inner 
side of its roof, diverging outwards. Carefully 
slice away the bone, being especially cautious to 
cut quite superficially along these streaks ; there 
will thus be laid bare : 

a. The cavity of the internal ear ; enclosed on all 
sides by the auditory capsule and filled with a 
fluid (perifyntph). 

/3. The membranous labyrinth ; a portion of this is 
now visible as two delicate pigmented canals, 
coincident in position with the divergent streaks 
afore-named. 

c. Still holding the capsule as before, slice away, 
bit by bit, its outer wall and the remainder of its 
roof. A third -membranous canal will be seen on 
the outer side; when this is liberated, transfer the 


120 ELEMENTARY BIOLOGY. [CHAP. 

whole to a watch-glass or small vessel filled with 
water (preferably one having a white bottom). The 
membranous labyrinth will probably float out ; if 
not, it may be liberated with a camel's hair brush. 
It consists of a greyish pigmented structure of the 
size of a small pea : Note 

u. The vestibule; sac-like and constricted into 
two an upper portion or utriculus, and a lower 
one or sacculus. It is largely filled during life 
by a milk-white otolithic mass. 

ft. The semicircular ca?ials ; three in number and 
connected with the utriculus. The anterior 
and posterior vertical canals, the two divergent 
ones referred to at b ; their inner ends unite 
before entering the utriculus. The horizontal 
canal ; situated externally, on a level with the 
bases of the other two. 

7. The ampulla ; enlargements of the bases of the 
canals. Those of the anterior and horizontal 
canals are situated close together at the anterior 
end of the utriculus. 

rt. The ultimate ramifications of the auditory nerve ; 
visible on the inner face of the labyrinth. 

d. General dissection of the whole auditory organ. 
Obtain the head of a frog which has been pre- 
served in spirit, and dissect from behind. 

Scrape the occipital region of the skull quite 
clean and then pin the whole down under water. 
Carefully remove the wall of the auditory capsule 

-externally, to the level of the columella auris- 
internally, to that of.the auditory nerve; cut away 


I.] THE FROG. 121 

the hinder half of the tympanic membrane, to the 
level of the head of the columella. 

Work over the mutual relations of the following, 
all of which have been previously described. 

a. The columella auris ; to the tympanic membrane 
and fenestra ovalis. 

fi. The membranous labyrinth ; to the periotic cap- 
sule and its enclosed cavity. 

y. The auditory nerve ; to the membranous laby- 
rinth and brain. 

& The Eustachian recess ; to the mouth cavity, 
and that of its lining membrane to the colu- 
mella. 

. The anmtlus tympanicus ; to the membrana 
tympani. 

M. Histology. 

In the undermentioned directions, the reagents which 
may preferably be employed in each case are alone 
enumerated; details as to preparation and methods 
of treatment will be found in the Appendix. 

i. The blood. 

a. Freshly drawn blood. Obtain a drop of the same 
from a freshly-killed frog, and examine with a 
low power, under a cover-glass. 

a. The plasma ; thin, watery and colourless. 

/?. The corpuscles; exceedingly numerous solid 
bodies, freely suspended in a. Two kinds will 
be seen : larger and more numerous red cor- 
puscles ; smaller and less numerous white cor- 
puscles ', irregular in shape, greyish in colour, and 


122 ELEMENTARY BIOLOGY. [CHAP. 

about ^ the size of the red ones. Examine 
under a high power. 

b. The red corpuscles. 

a. Their form ; oval when seen en face ; almost 
linear in profile but slightly swollen at the 
centre. 

ft. Their size ; their length, breadth, and thickness ; 
measure. 

y. Their colour ; pale yellow, when seen indivi- 
dually ; redder when seen in the aggregate. 

6. Their structure ; homogeneous for the most part, 
but possessed of acentral oval or rounded nucleus. 

(. Treat with water; they swell up and become 
more spherical; their colouring matter (hcemo- 
globiii] is gradually dissolved out, leaving be- 
hind a colourless protoplasm. The nucleus is 
rendered very evident, and ultimately all the 
rest of the corpuscle disappears. 

. Treat with dilute acetic acid ; results same as 
with water, but produced more rapidly. 

f). Treat with alcohol and borax-carmine suc- 
cessively. The nucleus stains with great in- 
tensity, the rest of the corpuscle remaining un- 
affected. 

c. The white corpuscles. 

Obtain a drop of fresh blood and examine as be- 
fore under your highest power. 

a. Their form ; very irregular, the surface being 
produced out into a number of blunted pro- 
cesses or pseudopodia. 


I.] THE FROG. 123 

/3. Their movements ; best seen if the slide be 
gently warmed, by contact with a lighted match 
or other heating agent They creep about in a 
sluggish manner through the agency of the 
above-named pseudopodia (amoeboid movement). 

y. Their size ; cf. generally with the red corpuscles. 

3. Their structure ; granular centrally, clear and 
transparent peripherally: usually lodging one 
or more clear round nuclei. 

e. Treat with acetic acid and magenta ; the nucleus 
alone will be stained. It will be found to lodge 
one or more small granular bodies (nucleoli). 

d. The microcytes. Very small bodies, for the most 
part colourless, freely suspended in the plasma : 
in shape variable; generally fusiform or ovoidal, 
more rarely irregular. 

c. Coagulating blood. Allow a drop of blood to 
coagulate upon a glass slide, taking care that it 
does not dry up. Examine under a high power, 
a. ^te plasma ; transformed into a colourless fluid 
(serum] which is permeated by well-defined and 
coagulate fibrin filament s. Note the course of 
the latter ; they radiate from numerous foci and 
anatomose irregularly. 

ft. The corpuscles; the red ones show a marked 
tendency to arrange themselves along the lines 
of coagulation ; the white ones are largely to be 
found, together with microcytes, in the foci of 
the fibrin filaments. 
2. Epithelia. 

An epithelium consists of a layer of cells which 
lines or invests a free surface : the epidermis cover- 


124 ELEMENTARY BIOLOGY. [CHAP. 

ing the skin and the epithelium of the alimentary 
canal, with which it is continuous at the buccal and 
cloacal orifices, may be cited as examples. There 
are several main types of epithelium, viz. 

a. Ciliated epithelium. Gently scrape the mucous 
membrane of the tongue or roof of the mouth of 
a recently-killed frog and transfer that which is 
obtained to a slide; mount in salt solution, avoiding 
pressure, and examine under a high power. 

u. The cells ; occurring singly or in aggregates. A 
shimmering appearance (ciliary action} will be 
seen along their free edges, produced by the 
rapidly moving cilia. 

As the cilia die their movements slacken. 
Watch an individual cilium as this happens ; it 
moves in a definite direction from a point of 
rest and does not oscillate. 

Place a freshly-killed frog upon its back and 
open the mouth to its utmost. If a fragment of 
pith or cork be placed on the roof of the mouth, 
it will be carried back to the gullet by the action 
of the cilia. 

/?. The cell protoplasm. Stain with eosin or ma- 
genta, and examine the individual cells. Shape ; 
flattened at the free surface, rounded or elongated 
at the base. Structure ; granular for the most 
part (endoplasm) ; clear and transparent peri- 
pherally (ectoplasm], especially so at the free 
border. Nucleus; usually central and rounded, 
containing one or more nucleoli. 

l>. Columnar epithelium. Scrape gently the inner 
surface of the mucous membrane of the intestine 


1.] THE FROG. 125 

of a frog, and mount the detached fragments in 
water. Examine with a high power. 

a. Numerous elongated cells will be seen, some- 
what resembling those of the ciliated epithelium 
in shape, but more uniform in size. Each is 
flat at one end and somewhat pointed at the 
other, and has a well-marked oval nucleus. 
Not unfrequently aggregates of them may be 
seen : look for such, and note that the cells 
are closely applied and arranged in a single 
layer. 

ft. Goblet cells ; scattered among a; characterised 
by the presence of a watery-looking globule 
(inucus drop} which distends the free end or 
greater part of the cell body. Note the position 
of the nucleus. 

c. Scaly or tesselated epithelium. Open the body 
cavity of a recently-killed frog ; carefully remove 
the viscera and lay bare the cisterna magna. Cut 
away its thin wall as carefully as possible, taking 
great care not to drag or pull it. Place the frag- 
ment in o - 5 solution of silver nitrate for three 
minutes or longer : then remove, wash well in 
distilled water, and finally leave the specimen in 
the same fully exposed to the sunlight. When it 
has assumed a well-marked brown colour stain 
with eosin or haematoxylin and examine with a 
high power. 

a. The matrix (intercellular cementing substance] ; 
rendered highly conspicuous as a network of 
black lines, irregularly disposed on the free 
surfaces of the mesentery. 


126 ELEMENTARY BIOLOGY. [CHAP. 

ft. The cells ; flattened and close fitting; irregular 
in outline, as may be seen on following a. 

y. The cell structure ; protoplasm differentiated into 
ecto- and endoplasm (cf. supra) ; nucleus central, 
oval or rounded. 

. Look for lymph stomata ; perforations of the 
membrane, each surrounded by small more 
deeply stained cells. 

d. Stratified epithelium ; see epidermis 15. iii. 

3. Connective tissue. 

Of these there are two main varieties, a. and b. 

a. White fibrous tissue. This occurs typically in 
tendons, but is widely distributed throughout the 
body, mixed with other tissues. Tease out a bit of 
fresh tendon in water : examine with a high power. 

a. It is chiefly made up of very fine wavy fibres 
which, in the aggregate, impart a glistening 
white colour to the tissue (white fibres) ; they 
run in bundles parallel to one another and do 
not branch. 

IB. Treat with dilute acetic acid. Most of the above 
disappear, but a few well-defined curled fibres 
(yellow clastic fibres) remain. Besides these 
some small elongated and granular proto- 
plasmic masses are brought into view (con- 
nective-tissue corpuscles) . 

b. Areolar tissue. Lay bare the muscles of the hind- 
limb ; sheets of areolar tissue will be seen passing 
between them and the integument. Remove one 
of these, being careful to avoid undue stretching 
and transfer to a slide: examine in water. 


I.] THE FROG. 12 


7 


a. White fibres ; more or less numerous and dis- 
posed in wavy bundles. 

p. The matrix ; a transparent imbedding mass, of 
sufficient density to resist the pressure of the 
cover-slip. 

y. ^\\^ yellow clastic fibres (a. /?.). Treat with acetic 
acid; the white fibres disappear, the yellow 
ones remaining. Note that they occur singly 
and anastomose, taking a very irregular course. 

S. Stain with magenta. The yellow fibres stain 
slowly but intensely ; their torn ends will fre- 
quently be seen rolled into a spiral or other- 
wise contorted, as the result of their elasticity. 

The connective-tissue corpuscles ; small nu- 
cleated cells, variable in size and shape, scat- 
tered throughout the whole. 


*0 J 


c. Submit a piece of areolar tissue to the action of 
silver nitrate solution as directed for the tesselated 
epithelium ( 2. c.}. When it has assumed a deep 
brown colour, examine in weak glycerine under a 
high power. 

a. The matrix ; stained a rich brown, having 
reduced the silver salt, as did the cementing sub- 
stance of the epithelium. 

/?. The connective-tissue corpuscles; little if at all 
stained, appearing as a series of irregular white 
patches (cell spaces). Examine these with care ; 
each is an irregular branching corpuscle, generally 
in organic continuity with one or more of its 
fellows (i.e. the whole tissue is permeated by 
protoplasmic matter). 


128 ELEMENTARY BIOLOGY. [CHAP. 

4. Hyaline cartilage. 

Dissect out the xiphisternal cartilage of a recently- 
killed frog and remove its membranous investment 
(perichondriuiii) ; mount in salt solution and examine 
under a high power. 

a. The matrix ; dense, structureless or finely granu- 
lated. 

b. The cartilage corpuscles ; large cells occurring singly, 
or in sets of two's to four's, their apposed faces 
being flattened. Examine the individual cells. 

a. Cell-protoplasm ; finely granulated and usually 
containing one or many minute refractive par- 
ticles (fat drops], 

/?. Nucleus ; round and sharply defined, containing 
a variable number of nucleoli. Two nuclei may 
not unfrequently be present. 

y. If the preparation be made and examined soon 
after death each cell will completely fill the 
cavity of the matrix in which it lies : but if it be 
kept some time or be treated with distilled water 
the cells contract ; thereupon the cavities (cell 
spaces) become obvious as transparent halos 
around the individual cells, or groups of cells if 
recently formed. 

c. Cell division. The initial phases in this process 
can be nowhere more favourably made out than 
here. The undermentioned may generally be 
found on carefully searching the field ; note that 
in all, division of the nucleus precedes that of the 
cell. 

a. Single cells (those filling an entire cell space) ; 


I.] THE FROG. 129 

one nucleus may be present (t'esting cell] or two 
(dividing cell}. 

J3. A two-celled nest ; one or both of the cells may 
lodge two nuclei. 

y. A three-celled nest. Usually one cell will be 
found to be the larger of the three ; its nucleus 
may or may not show traces of division. 

5. Bone. 

a. Cleave the femur of a recently-killed frog longi- 
tudinally in two, and examine while still fresh. 

a. The bone; its central cylindroidal shaft and 
terminal epiphyses (cf. p. 14). 

/?. The marrow ; a fatty vascular mass, filling the 
central cavity. 

y. The periosteum ; a tough vascular connective- 
tissue sheath, closely investing the shaft. 

8. The nutritive foramina. Carefully remove the 
marrow and examine from within ; the torn 
ends of the periosteum will be seen passing in 
through the above, for communication with the 
marrow. 

b. Decalcify the middle third of the femur of a freshly- 
killed frog in \ per cent, chromic acid solution, 
stain with borax-carmine and cut into transverse 
sections as directed in the Appendix. Mount in 
Canada balsam, and examine under a low power. 

a. The bony shaft ; seen to be divided, by a highly 
refractive middle lamella, into an outer more 
deeply stained portion and an inner thinner and 
less deeply stained one. 

M. o 


130 ELEMENTARY BIOLOGY. [CHAP. 

j3. The periosteum ; a thin layer closely applied to 
the outer face of a., and staining with great in- 
tensity. 

y. The marrow ; composed of larger vacuolated 
(fat-laden) cells, and smaller rounded deeply- 
stained ones (red marrow cells}. 

8 The nutrient vessels; in section as follows: a 
larger ovoidal and thin-walled vein, and a smaller 
cylindroidal and thick-walled artery, lying close 
together near the middle of the marrow. 

c. Search your sections for any which may have 
passed through a nutritive foramen ; if present, 
note the relations of the periosteum to the 
marrow. 

c. Examine your thinnest section under a high 

power. 

a. The bony shaft ; seen to consist of a number of 
concentric layers or lamella, rendered distinct 
under the action of the reagent. 

Find the middle lamella (b. a); it marks the 
boundary line between an inner, more lightly 
stained series (concentric or peri-medullary lamellce) 
and an outer, more deeply stained series (circum- 
ferential or sub-periosteal lamellce]. 

ft. The bone corpuscles ; minute fusiform or branch- 
ing cells, set along the lines of the above la- 
mellae. Each clear and little stained, with a 
deeply stained nucleus. (Cf. connective tissue 
corpuscle.) 

y. The periosteum ; if the section be a good one, 
its innermost layer will be seen to consist of a 
row of small flattened cells (osteoblasts]. 


I.] THE FROG. 131 

3. The marrow; note the aggregation of small 
cells on the inner face of the shaft. 

d. Make a transverse section of the dried shaft of the 
femur, by grinding it down upon a hone as di- 
rected in the Appendix (E.). Mount in Canada 
balsam and examine under a high power. 

a. The lamella : cf. supra. 

P. The lacuntz ; oval spots between the lamellae; 
black, as they become filled with dirt in grind- 
ing. Each originally lodged a bone-corpuscle. 

y. The canaliculi ; minute black lines radiating 
from the lacunae. Those of adjacent lacunae 
frequently anastomose. 

S. The Haver sian canals ; present only in the 
neighbourhood of the nutritive foramina. Ob- 
vious as spaces in the substance of the shaft, 
each surrounded with its own lamellae. 

c. Examine a longitudinal section of the dried 
femur, for comparison with the above. The 
Haversian canals are seen to be channels run- 
ning for the most part longitudinally, and com- 
municating with one another by cross branches. 
The lacuuce, and canaliculi appear much as in 
the transverse section. 

The study of the dried bone may advanta- 
geously be supplemented by that of the long 
bone of a mammal. 

6. Adipose tissue. 

Tease up portions of the corpus adiposum, as under. 

a. Fresh, in salt solution. Examine under a low 
power ; the following will be met with. 

92 


ELEMENTARY BIOLOGY. [CHAP. 

a. Connective tissue elements. 

ft. Ripe fat cells ; obvious as aggregates of large 
highly refractive globules (fat globules) of which 
the tissue is chiefly composed. 

Note their optical characters, under different 
levels of focus. 

y. Immature fat cells ; smaller irregular or rounded 
cells, each lodging one or more fat drops. 

b. Preserve in spirit ; stain with haematoxylin. Ex- 
amine the ripe cells under a high power; each 
consists of 

a. The fat globule ; apparent as a clear space, 
which may or may not contain crystals. 

ft. The cell membrane ; deeply stained and more or 
less granular, forming a thin envelope for a. 

y. The nucleus ; oval and compressed, buried up 
in the cell membrane and usually surrounded 
by granular protoplasm. 

8. Immature fat cells; look for those showing 
stages in the formation of the fat globule. 

7. Unstriped muscle. 

a. Place a small piece of the muscular coat of the 
intestine in Miiller's fluid for 2 3 days. Tease 
up in hasmatoxylin solution and examine under a 
high power. 

u. The muscle-cells ; elongated and fusiform, in 
close apposition with each other ; protoplasm 
granular. 

ft. Nucleus ; fusiform or ovoidal, generally situated 
near the middle of the cell. 


I.] THE FROG. 133 

b. Obtain a similar but thin piece from the intestine 
of a recently-killed frog. Treat with silver 
nitrate as directed at 2. c. 

a. The cementing substa?ice ; obvious as a series 
of dark lines which cross each other at long 
intervals. 

/3. Look for fragments showing two sets of lines 
which cross at right angles (i.e. cell-contours of 
longitudinal and circular layers). 

8. Striped muscle. 

a. Preserve the middle third of the belly of a limb- 
muscle (say the gastrocnemius) in spirit ; stain with 
borax-carmine and cut into transverse sections. 
Mount in Canada balsam and examine under a 
low power. 

a. The muscle; composed of a great number of 
large fibres, each oval, or angulated and irre- 
gular as the result of mutual compression. Note 
their transverse diameter, variable in proportion 
as the section passes through their middle 
or extremities. 


The perimysium (fascia) ; a deeply staining 
sheath for the whole muscle, carrying blood- 
vessels whose cut ends will be seen (cf. peri- 
osteum, 5.). It will be found to dip into the 
interior of the muscle as a delicate black pig- 
mented membrane, subdividing it into a number 
of muscle bundles or fasciculi. 

y. The muscular fibres. Examine the thinnest parts 
of your sections with a high power ; each fibre 
consists for the most part of a granular pro- 


134 ELEMENTARY BIOLOGY. [CHAP. 

toplasm lodging a number of fusiform deeply- 
staining nucleate bodies (muscle corpuscles}. 

b. The muscular fibre / structural analysis. 

i. Tease out gently a bit of muscle from a freshly- 
killed animal, and examine in salt solution with 
i inch obj. 

a. Composed of elongated fibres, which exhibit, 
unless the fibre be quite fresh, a tendency to 
split up into finer filaments (so-called fibrilla). 

ft. The sarcolemma; visible as a superficial clear 
layer of the fibre ; expansions of it may be 
seen at points where the continuity of the 
fibre has been interrupted by pressure, or 
other cause of rupture. 

ii. Examine with a high power. 

a. The alternate lighter and darker bands placed 

transversely to the long axis of the fibre 

(transverse striatioii). 
ft. The sarcolemma ; enveloping the fibre ; seen 

here and there as a delicate film, where the 

fibre is twisted or bruised. 

y. The muscle corpuscles ; visible as elongated 
and slightly refractive fusiform bodies, dis- 
posed longitudinally. 

iii. Treat with acetic acid ; the striation is rendered 
very indistinct, the sarcolemma and muscle cor- 
puscles becoming very conspicuous. Add a 
drop of magenta ; the nuclei stain deeply. 

iv. Transfer a fragment of fresh muscle fibre to a 
slide bearing a drop of salt solution, and tear it 
into small shreds with a couple of needles. 


I.] THE FROG. 135 

Examine the thinnest pieces under your highest 
power. 

a. The fibre is seen to be marked out into a 
close-set series of alternately light and dark 
transverse stria, the former being in all pro- 
bability the narrower. 

(3. Keep your eye steadily fixed on a given piece 
while you alter the focus parts which were 
originally dark now become light and vice 
versa. 

y. Examine a fragment in which the cross strise 
are very distinct, still more minutely. When 
in exact focus the following will be seen. 

The septal zones ; obvious as the afore- 
named clear striae. 

The inter septal zones ; alternating with and 
of greater thickness than a. Each is longi- 
tudinally striated. 

The septal lines ; dark lines of great deli- 
cacy, one in the middle of each septal zone; 
seen, on close examination, to appear as a 
parallel series of minute dots. 

Very generally the fibre is constricted at each 
septal line, having thus a beaded appearance. 

8. Repeat the operation described at (3. and note 
the different optical effects which are pro- 
duced at different levels of focus. 

v. Melland's method. Place some fragments of 
fresh muscle in i per cent, acetic acid solu. for 
10 seconds ; transfer to i per cent, gold chloride 
solu. for i hour and then to 25 per cent, formic 
acid solu. for 48 hours or longer (to be kept in 


136 ELEMENTARY BIOLOGY. [CHAP. 

the dark). Finally tear up with a couple of 
needles in glycerine. 

a. Longitudinal strict ; parallel lines, differentiated 
under the above treatment, which can be 
traced throughout the entire length of the 
fibre, traversing clear and dark zones alike. 

fi. Transverse networks ; seen, in the regions of 
the septal lines, traversing the fibre at right 
angles to a and thickened at their points of 
intersection with the same. When looked 
at en face they present a honeycomb-like 
appearance. 

iv. and v. may be profitably repeated upon 
the muscle fibre of an insect. 

9. Nerve. 

a. Preserve a portion of the iliac nerve in spirit of 
increasing strengths ; stain with hcematoxylin, 
imbed and cut transverse sections. Mount in 
Canada balsam and examine with a low power. 

a. The nerve trunk; composed of an immense 
number of small rounded nerve fibres. 

/?. The perineuriwn ; a deeply staining sheath, 
seen to carry blood-vessels (cf. perimysium and 
periosteum). It may be in part fat laden. 

y. The nerve bundles; lesser divisions of the trunk, 
each bound up in an ingrowth of the perineu- 
rium (cf. muscle bundles). 

l>. Examine the thinnest portion of a nerve bundle 
under a high power ; it will be found to contain- 

u. Medullatcd nerve fibres ; in section round, each 
with a central deep-stained portion (axis fibre] 


I.] THE FROG. 137 

and a peripheral clear portion (medullary sheath); 
the whole invested in a delicate primitive sheath, 
obvious as a darkly stained outline. 

ft. Non-medullated nerve fibres ; irregularly dispersed 
among a. ; each consisting of an axis-fibre alone. 

c. The medullated nerve-fibre ; structural analysis. 

i. Tease out a bit of a fresh spinal nerve in salt 
solution. Examine with a low power. 

a. Composed of well-defined fibres (niedullated 
nerve-fibres] mixed with white fibrous tissue. 

/3. The appearance of the nerve-fibres ; each has 
a double contour and a highly refractive 
border. Some fibres are regular in outline, 
others contorted and irregular. 

ii. Examine, under a high power, selecting the least 
contorted fibres. 


a. The primitive sheath ; look for it on bruised 
nerve-fibres or at the ends of torn ones. 

ft. The highly refractive border (medullary sheath} 
within the primitive sheath. 

y. The central homogeneous axis (axis fibre) ; 
look for it projecting beyond the medullary 
sheath of torn fibres. 

B. Treat with chloroform ; the medullary sheath 
will be dissolved out, and the axis fibre 
plainly seen. 

e. Ranvier's nodes; apparent breaks (constric- 
tions) in the medullary sheath, seen at com- 
paratively long intervals along the course of 
the individual fibre. 


138 ELEMENTARY BIOLOGY. [CHAP. 

t. Schmidt's nodes. Examine the medullary 
sheath of the least distorted fibres with great 
care ; the above will be found as interruptions 
of the same at short and fairly regular in- 
tervals, the sheath appearing to consist of a 
series of imbricated segments. 

?;. Compare a fibre with irregular contour. Note 
that the irregularity is due to shrinking of 
the medullary sheath under coagulation. The 
coagulate masses may often be seen to cor- 
respond with the above-named segments. 

iii. Tease up a piece of the trunk of a spinal nerve 
in a drop of i per cent, osmic acid solu. After 
3 4 hours immersion in the same, wash well 
and mount in weak glycerine. Examine under 
a high power. 

a. The medullary sheath ; rendered blackish and 
highly conspicuous by the above method. 
Examine it with care, noting especially the 
nodes of Ranvier and Schmidt. 

/?. The axis fibre ; greyish and well defined, 
seen on focussing through a. 

y. The nerve corpuscles ; apparent as thickenings 
of the sheath which bulge inwards, usually 
of a reddish brown colour under treatment 
with the above acid. They correspond in 
number with the nodes of Ranvier, and each 
consists of an oval refractive nucleus, em- 
bedded in a small amount of granular proto- 
plasm. 


I.] THE FROG. 139 

i o. Nerve-cells. 

a. Unipolar cells. 

i. Take a spinal ganglion from a recently-killed 
frog and tease up under a low power in eosin 
solution. Among the pigment cells and other 
small cells present, the above-named will be 
seen as large round or oval pale granular cells, 
each with a conspicuous large round nucleus. 
Examine under a high power. 

a. The cell-body; granular, and connected at its 
base with a single nerve-fibre (unipolar-cell). 

/?. The nucleus ; generally central in position ; 
invariably containing one large nucleolus. 

y. The cell capsule ; a delicate nucleated invest- 
ment which may or may not be torn away. 

ii. Tease up a second spinal ganglion, and treat 
with osmic acid and glycerine, as directed at 
9. iii. Examine under a high power. 

a. General. Cf. supra. 

P. The polar plate; consisting of two or more 
clear cells, situated at the base of the unipolar 
cell and in direct connection with the ulti- 
mate termination of the nerve fibre. 

b. Bipolar cells. 

Take a sympathetic ganglion from a recently- 
killed frog and tease it up in eosin as directed 
above. Examine under a low power. Among 
the pigment and other cells present, will be 
seen numerous large pale granular cells some- 
what like the unipolar ones. Examine under a 
high power. 


140 ELEMENTARY BIOLOGY. [CHAP. 

a. The cell-body; composed of granular proto- 
plasm, with a large round or oval nucleus. 
Cf. generally with that of the unipolar cell. 

(3. The cell capsule; like that of the unipolar cell 
but less conspicuously nucleated. 

y. The related nerve fibres, of these there are two 
(bipolar cell): one passes straight from the 
cell base like that of the unipolar cell; the 
other (processus spiralis) leaves the cell at a 
higher level, and, in passing downwards, winds 
round the base of the cell and the straight 
fibre. 

c. Multipolar cells. See infra 1 1 . 
1 1 . The spinal cord. 

Place some pieces of the fresh cord in potassium 
bichromate solution (2 to 3 weeks), wash well and 
afterwards harden in alcohol of increasing strengths. 
Stain with borax-carmine and mount in Canada 
balsam. 

i. Examine under a low power. 

a. The cord; bilaterally symmetrical; composed of 
a superficial lighter portion {white matter] and a 
deeper more deeply staining portion {grey 
matter}. 

b. Nerve roots ; seen as bundles of fibres running 
out dorsally and ventrally from prolongations 
(cornud) of the grey matter. 

c. The canalis centra I is ; oval, lined by a deep 
staining columnar epithelium. 

d. The fissures; median dorsal and ventral, cleaving 
the white matter only. 


I.] THE FROG. 141 

e. The//# mater ; obvious as a darkly stained in- 
vestment for the whole. It dips in, especially 
at the fissures, to form a supporting framework 
for the cord. Prolongations of it into the 
substance of the cord may be readily seen, in 
the vicinity of the ventral fissure. 

ii. Examine under a high power. 

a. The white matter ; chiefly composed of medul- 
lated fibres, cut across and lying within a sup- 
porting mesh work (iieuroglia). Non-medullated 
fibres may be detected here and there. 

b. The grey matter. 

a. Composed, for the most part, of non-medul- 
lated fibres lodged in a granular matrix. 

Note the course of the fibres, especially 
of those which pass from side to side. 

/8. Multipolar nerve-cells. A cluster of these will 
be seen in each ventral grey cornu, as large 
irregular cells, deeply staining and each with 
a round nucleus. Nerve fibres will be seen 
to enter them at several points. 

y. Ventral nerve root. Examine with care; con- 
tinuity may often be traced between its indi- 
vidual fibres and the multipolar nerve cells. 

12. The retina. 

Highly satisfactory preparations of this organ can 
be obtained as follows. Take perfectly fresh eyes 
from a frog ; remove a small portion of each, and lay 
the eyes for an hour in corrosive sublimate, or for 


142 ELEMENTARY BIOLOGY. [CHAP. 

3 to 4 hrs. in picric acid; wash and transfer them 
to alcohol of increasing strengths. 

Finally, stain with borax-carmine, imbed and cut 
into longitudinal vertical sections. Mount in Canada 
balsam. 

i. Examine with a low power, the whole eyeball will 
be seen in section. 

a. The sclerotic; a cartilaginous outer capsule. 

b. The choroid; recognizable by the straggling 
nature of its pigment cells, which form a sort 
of loose network. 

c. The retina; seen to be composed of a number 
of layers, differentiated under the action of the 
staining reagent. Note \h& pigment layer ; red- 
dish brown and regularly disposed, immediately 
internal to the choroid, one-third the thickness 
of the whole. 

il. Examine your thinnest section under a high power. 
AVork from within outwards; the following will be 
seen, in order of enumeration. 

a. The internal limiting membrane, a thin structure- 
less layer. 

b. The nerve-jibre layer ; thin and granular, with 
delicate fibres. 

[a. and /?. are sometimes difficult to make out.] 

c. The nerve-cell layer ; composed mainly of large 
irregular cells with round nuclei. From some, 
branches can be traced into the next layer. 

d. The inner molecular layer; this is thicker than 
any of the preceding, and has a finely 


I.] THE FROG. 143 

punctated appearance. It remajns unstained 
under the above method of treatment. 
c. The inner nuclear layer ; nearly as thick as d., 
and deeply stained. It is made up of a number 
of nuclei, around each of which is collected a 
very small amount of protoplasm ; and of fine 
fibres, some of which can be traced into the same. 

f. The outer molecular (fenestrated] layer. Narrow 
and unstained, somewhat resembling d. 

g. The outer nuclear layer. Much thinner than 
the inner nuclear layer and more closely packed. 
It is composed of distinct fibres (rod- and cone- 
fibres), each of which swells out and has a 
nucleus developed in the enlargement. 

h. The external lijniti?ig membrane. A thin homo- 
geneous layer like a, obvious as a hard line 
which not unfrequently overhangs the outer 
nuclear layer. 

/. The rod- and cone-layer. Usually stained a faint 
pink colour under the above treatment. 

a. The rods; parallel and ending in blunted free 
ends; each subdivided transversely into two 
segments. 

/}. The cones; few in number and shorter than 
the rods; each ending in a pointed free end. 
Look for them among the bases of the rods. 
k. 'The pigment layer; seen to consist of a close set 
series of elongated cells (pigment epithelium) 
forming a cap-like investment for the free ends 
of the rods and cones. 

a. The cell bases ; closely applied, each contain- 
ing a round or oval clear nucleus. 


144 ELEMENTARY BIOLOGY. [CHAP. 

/3. Their free ends ; fimbriated and prolonged 
down among the rods and cones. 

/. The fibres of Miillcr ; highly refractive sup- 
porting fibres, often traceable with ease from 
the internal limiting membrane to the fenes- 
trated layer. 

Hi. Obtain, if possible, similar sections which shall 
pass through the entrance of the optic nerve. 
Examine under a high power, and follow the 
course and relations of the nerve-fibres. 

iv. Take a fresh frog's eye : prick its cornea and col- 
lect the aqueous humour on a slide. Then open 
the eye, remove a bit of the retina and tease it 
out in the aqueous humour, mount and examine 
with a high power. 

a. Numerous rods will be seen floating about, 
many broken but some intact and showing the 
boundary line between their two segments very 
plainly. At first both segments are homoge- 
neous, but very soon they begin to alter; the 
outer layer frequently then gets transversely 
striated and shows a tendency to split up into 
several pieces : gradually these rods curl up, 
swell out, and entirely disintegrate. 

13. The olfactory epithelium. 

Open the nasal sac of a frog ; remove a portion of 
the epithelial lining and transfer to i p. c. osmic 
acid solution for 2 3 hours ; tease up in weak 
glycerine and examine with your highest power. 

Numerous mutilated cells will be found, and, 
among them, more or less perfect representatives 
of the following. 


I.] THE FROG. 145 

G. Epithelial cells; columnar and elongated, each 
with an oval nucleus, an unbranched peripheral 
process and a branched basal one. 

/>. Sensiferous cells ; more slender and often some- 
what shorter than a. : generally to be recognized 
by their swollen bases (enlarged around an en- 
closed nucleus). Each terminates at its free end 
in a cluster of delicate, hair-like, stiff processes, 
and receives at its base a thread-like nerve-fibre. 

14. The auditory epithelium. 

Place sufficient of the membranous labyrinth to 
embrace one of the ampullae (Sect. L. 4. c. y) in i. 
p. c. osmic acid solution for 3 4 hours ; transfer to 
weak glycerine and tease up its epithelium with a 
couple of fine needles. Examine under your highest 
power, and look for 

a. Hair cells (sensiferous cells of auditory epithelium). 
Each is pear-shaped and composed of a granular 
protoplasm with a large round or oval nucleus : 
from its flattened free end there stands out the 
auditory hair ; a long pointed structure (from 3 
to 4 times the length of the cell-body) seen, on 
careful examination, to consist of several delicate 
fibrils bound together. 

15. The skin. 

i. Cut out a piece of skin from the back of the thigh 
of a recently killed frog : spread it out in water, 
cover, and examine with a low power : note 

a. The pigment-cells; black irregular patches; 
some compact, others more or less branched. 

M. 10 


146 ELEMENTARY BIOLOGY. [CHAP. 

l>. The months of the cutaneous glands ; seen as 
clear round spots, although their openings are 
really triradiate : their number. 

ii. Preserve a piece of skin in alcohol of increasing 
strengths, and stain with borax-carmine ; imbed 
and cut sections perpendicular to its surface : 
mount in Canada balsam. Examine under a low 
power. 

a. The epidermis ; the superficial thinner and deep 
stained portion. 

l>. The dermis ; the deeper main mass, for the 
most part lightly stained. 

c. Pigment ; most marked as a conspicuous ir- 
regular black layer, in the superficial stratum 
of the dermis. 

(L Cutaneous glands ; seen in section as numerous 
large oval, rounded, or flask-shaped spaces, lying 
within the dermis. Many can be seen to open 
on the free surface by a narrow neck. 

iii. Examine under a high power. 

a. The epidermis (stratified epithelium}. Work 
from within outwards ; there will be found in 
order : 

a. The Malpigliian layer ; composed of a usu- 
ally single basal row of close-fitting columnar 
cells, each with an oval nucleus ; and of a 
superficial main mass, consisting of several 
rows of rounded or oval cells whose long 
axes are parallel with the free surface. Small 
pigment granules are frequently aggregated 
around the nuclei of the latter. 


I.] THE FROG. 147 

P. The horny layer; usually of a yellowish 
colour; made up of flattened cells whose 
boundary lines are rarely distinguishable. 
Nuclei for the most part absent; pigment 
granules present at intervals. 

l>. The dermis ; work inwards from the epidermis ; 
the following elements will be seen. 

a. Connective tissue ; forming the main mass, its 
cellular elements well marked, fibres for the 
most part in bundles. 

p. Unstriped muscle; most marked in the deeper 
portion where it forms a thick muscular stra- 
tum, lying beneath the cutaneous glands. 

y. Pigment ; deposited for the most part in two 
well-defined strata of irregular branching cells; 
rarely diffused throughout the connective- 
tissue mass. 

The above-named strata are : a superficial 
one lying beneath the epidermis (cf. ii. c.\ 
generally black and highly conspicuous ; a 
deeper one, immediately internal to the mus- 
cular stratum, of somewhat lighter colour 
than the other. 

o. fat; rarely present: when it is deposited, 
like the pigment, within individual cells of 
the connective-tissue mass. 

e. Blood vessels; inconspicuous in uninjected 
preparations. Their cut ends may however 
be seen among the cells of the inner pigment 
layer ; thence vessels may sometimes be traced 
passing up, in a pigmented sheath, towards 
the bases of the cutaneous glands. 


10- 


148 ELEMENTARY BIOLOGY. [CHAP. 

t : The cutaneous glands. Look for thin sections 
which pass through their necks. 

(.-. The gland ; lined by a single layer of flat- 
tened epithelial cells, occasionally surrounded 
by pigment. Its secretory product may often 
be seen within it, as a pale finely granular 
mass. 

p. The duct ; subdivided into two segments : an 
inner enlarged one, lined by a single layer of 
cells which graduate into the deeper layer of 
the epidermis ; an outer much constricted 
one, the epithelium of which graduates into 
the horny layer of the epidermis. 

y. Look for sections showing the glands en face. 
Note the boundaries and characters of their 
epithelial cells. 

1 6. Tho intestine. 

i. Preserve some pieces of the small intestine, first 
washing out the contents with care, in \ per cent, 
solution of chromic acid; transfer to alcohol of 
increasing strengths; stain with borax-carmine, 
imbed and cut transverse sections. Mount in 
Canada balsam and examine with a low power. 

a. The intestinal wall ; smooth externally, much 
folded internally. Its outer layer ; uniformly 
thick (muscular layer) : its inner layer ; much 
folded and more deeply stained (epithelium). 

I'. Examine the thinnest portion under a higher 
power. Work from without inwards ; there will 
be found in the order of enumeration 

a. Serous layer (peritoneum) ; obvious as a faint 


I.] THE FROG. 149 

contour line. Look for places where it may 
have been separated in preparation. 

/?. Longitudinal muscular layer ; thin and deeply 
stained ; seen to consist of the cut ends of 
close-set cells. 

y. Circular muscular layer; relatively thicker 
than /? ; cells close-set and parallel with the 
free surface (cf. 7. b. /3). 

3. Submucous layer ; faint and composed of vas- 
cular connective tissue. Large blood-vessels 
will be seen ramifying within it. 

e. Mucous membrane ; composed of three layers. 
A muscular layer, forming a thin stratum im- 
mediately internal to S; a lymphoidal layer, 
somewhat like the submucous layer, but con- 
taining numerous rounded or irregular cells 
(lymphoidal cells) ; the epithelium, composed 
of close-set columnar cells (cf. 2. b.} whose 
inner ends for the most part stain very deeply. 

c. Compare similar sections across an intestine the 
blood-vessels of which have been injected with 
gelatine (see Appendix C). Note the course 
of the vessels, and especially the relations of 
their ultimate ramifications. 

17. The pancreas. 

Preserve small portions in alcohol of increasing 
strengths ; stain with borax-carmine ; imbed and cut 
transverse sections ; mount in Canada balsam. 

a. Examine under a low power. 

a. The gland; composed of groups of cells (acini] 


150 ELEMENTARY BIOLOGY. [CHAP. 

diffused throughout a connective-tissue mesh- 
work (stroma). 

/>. Tlietitm'c; a dense connective-tissue investment 
for the whole, continuous with the stroma. Look 
for the cut ends of blood-vessels (cf. perimysium, 
perineurium, periosteum). 

b. Examine under a high power. 

a. The acini ; each composed of a single layer of 
large epithelial cells, set around a small ir- 
regular central cavity. 

P. The ducts ; packed among a, characterized by 
the large size and regularity of their central 
cavities ; in section rounded or oval, each lined 
by an epithelium of squarish cells. 

Look for portions showing the transition of 
gland into duct. 

1 8. The liver. 

Preserve some small pieces of fresh liver in alcohol, 
and prepare sections as directed for the pancreas. 

a. Examine under a low power. 

The gland cells will be found to be arranged in 
groups, around a ramifying system of clear spaces 
with granular-looking contents (blood- vessels). 

\,. 

/'. Examine under a high power. 

c. The gland cells ; for the most part squarish or 
hexagonal, each lodging a large round nucleus 
with one larger and several smaller nucleoli. 

P. Look for sections of longitudinal series cells ; 
note their arrangement in parallel rows. 

y. Blood capillaries ; cf. supra. The granular ap- 
pearance seen under the low power will be found 


I.] THE FROG. 151 

to be due to the presence of red corpuscles 
whose nuclei alone stain with great intensity, 
the bodies of the corpuscles remaining faint and 
yellow. 

3. Bile capillaries ; apparent as a system of minute 
inter-cellular passages. Look for them in your 
thinnest sections ; their cut ends appear some- 
times as round or oval spaces, at others as deeply 
stained dots, between applied cells, much smaller 
than the nuclei of the same. 

They may often be demonstrated if, prior to 
removal of the liver from the body, the bile-duct 
be ligatured and the bile injected into them by 
gently squeezing the gall-bladder. 

c. Compare sections of injected liver, prepared as 
directed for the intestine 16. c. 

d. Tease up a fragment of fresh liver in salt solution 
and examine with ~ objective. 

a. The hepatic cells; polygonal and granular, often 
containing oil-drops (cf. osmic acid reaction). 

/?. Treat with acetic acid : a nucleus, or sometimes 
two, will be rendered apparent in each of the 
cells. 

e. Tease up a similar fragment in iodine solution. 
Many of the cells will be seen to contain a product 
(glycogen} which stains a deep reddish brown. 

19. The kidney. 

Preserve a frog's kidney in alcohol of increasing 
strengths ; stain with haematoxylin or borax-carmine ; 
imbed it and cut into longitudinal sections parallel 
with its flat surface. Mount in Canada balsam. 


I $2 ELEMENTARY BIOLOGY. [CHAP. 

a. Examine with a low power. 

a. Note the numerous uriniferous tubuies of which 
the organ is mainly composed ; they twist about 
in several directions, and are consequently cut, 
some transversely, some obliquely, and others 
more or less longitudinally. The latter are most 
conspicuous at the outer (convex) border. 

ft. The clear round spaces, scattered about ; these 
are sections of Malpighian capsules. Some may 
be seen to lodge a granular mass (glomerulus). 

b. Examine with a higher power - 

a. The epithelium of the tubules ; composed for the 
most part of a single layer of large squarish 
cells, each with a large round deep-staining 
nucleus. 


The epithelium of the capsules ; flattened and 
squamous, its nuclei well denned, seen to be 
reflected over the glomeruli (i.e. the latter are 
outside it). Look for sections showing the con- 
nection of tubules with capsules. 

y. Blood capillaries ; scattered among the tubules, 
conspicuous in borax-carmine preparations by 
the refractive deep-staining nuclei cf the red 
corpuscles (cf. 18. b. y). 

c. Compare sections of the fresh kidney treated with 
silver nitrate, as directed at 2. c. Examine under 
a high power. 

a. The capsules. The boundary lines of their epi- 
thelial cells will be distinctly seen ; they are 
those of a tesselated epithelium. 


I] THE FROG. 153 

/3. The smaller blood-vessels. In those immediately 
related to the glomeruli, longitudinal and trans- 
verse striations are generally obvious under the 
above treatment. Examine with care; the longi- 
tudinal stride will be seen to be the deeper 
(boundary lines of epithelial cells); the trans- 
verse ones are more superficial (boundary lines 
of unstriped muscle cells). 

d. Compare sections of injected kidney. Examine 
under a low power ; two sets of capillary vessels 
will be seen- 
a. Around and among the tubules. 

/?. The glomeruli ; vascular tufts indenting the 
Malpighian capsules (cf. b. /3). Examine them 
in detail. 

20. The testis. 

Imbed a testis which has been hardened in alcohol 
of increasing strengths and stained with borax-car- 
mine. Cut into transverse sections and mount in 
Canada balsam. 

a. Examine with a low power. 

a. The organ is chiefly made up of large tubules, 
radially disposed at the periphery, more tortuous 
internally. 

Spermatozoa may or may not be present ; 
if so, they will probably be aggregated into 
bundles with their heads (deeply stained) in 
close relation with the walls of the tubules. 

b. Examine with a high power. 

a. Note the epithelium (germinal epithelium) lining 
the tubules : it varies with the season of the 


154 ELEMENTARY BIOLOGY. [CHAP. 

year, and may be one or more layers of cells 
deep. 

c. The spermatozoa. 

i. Tease up a small piece of the fresh testis in 
magenta solution. If spermatozoids are present, 
each will be seen to consist of 

a. Head; rod-like, generally straight, more rarely 
arched, mainly composed of a deep-staining 
body (nucleus]. 

ft. Tail ; elongated and flagelliform, stains but 
feebly, if at all. In favourable specimens it 
may be seen to be continuous with a small 
amount of clear protoplasm which surrounds 
the "head." 

ii. Compare the aggregates of spermatozoa seen in 
the prepared section. The applied heads of 
many of them will be seen to be capped by a 
large irregular nucleated ceil (last remnant of 
parent cells of the group). 

iii. Compare the living spermatozoa, if accessible, 
obtained from either the testis or vas deferens. 
Note the nature of their movements. 

21. The ovary. 

Prepare transverse sections of an ovary : alcohol, 
borax-carmine, Canada balsam. 

i. Examine under a low power. 

(7. The ova (ovisacs) ; variable in size : smaller 
ones, seen to consist of granular protoplasm 
with a large germinal vesicle (nucleus) : larger 
ones, pigmented peripherally; germinal vesicle 


I.] THE FROG. 155 

rarely seen, as it only occasionally lies in the 
plane of section. 

ii. Examine under a high power. 
n. The smaller ovisacs. 

a. The ovum ; the central large cell ; its proto- 
plasm, uniformly finely granular and deep- 
staining. 

P. Germinal vesicle; often irregular in outline; 
germinal spots diffused or arranged peri- 
pherally in a single row. 

y. Ovarian follicle ; a single-layered epithelial 
investment for the ovum. 

I). Compare the larger ovisacs. 

a.. Protoplasm of ovum. Peripherally, black and 
pigmented, otherwise converted, for the most 
part, into an immense aggregate of small ellip- 
soidal or irregular refractive yolk granules. 

P. Germinal vesicle. Look for specimens in 
which this is visible ; the germinal spots are 
mostly, if not wholly, aggregated in the middle 
of the same. 

y. Ovarian follicle ; still recognizable, but gene- 
rally flattened. 

S. Vitelline membrane; obvious as a thin faint 
line, interposed between the ovum and the 
follicle. Look for it in ova whose investing 
structures may have been ruptured. 

c. The germinal epithelium ; a cellular mass imme- 
diately beneath the investing membrane of the 
ovary. Look for young ovisacs still in connection 
with it. 


156 ELEMENTARY BIOLOGY. [CHAP. 

N. The physiological properties of muscle and nerve. 

Place a frog under a beaker, with a drop or two of 
chloroform : take it out immediately it becomes un- 
conscious, which will probably be in a few seconds. 
Now feel with a finger-nail for the depression beneath 
the skin at the back of the animal's head, which in- 
dicates the point of articulation of skull and spinal 
column : it lies in a line joining the posterior borders 
of the two tympanic membranes. Divide the skin 
and muscles at this point until the neural canal is 
laid open, and then pass a stout wire into the 
cranium and down the neural canal of the vertebral 
column. By this process (known as pithing] the frog 
is rendered totally incapable of further consciousness, 
though most of its tissues will retain their vitality for 
some time. 

a. Remove the skin from one leg, so as to lay bare the 
muscles : send an interrupted electric current through 
any one of them (or tap the muscle sharply with the 
back of a scalpel) : it will immediately contract, or 
alter its form in a definite way ; it becomes shorter 
and thicker, gaining in breadth just so much as it loses 
in length ; in so doing it moves the bones to which it 
i:3 attached. 

/>. Very carefully lay bare the sciatic nerve, taking care 
not to crush or drag it : divide it as high up as pos- 
sible, and, seizing it with a pair of forceps close to its 
cut end, lay it over the electrodes of an induction- 
coil. Probably when the nerve is cut the muscles of 
the limb will contract : whether or not, they will 
contract violently while the interrupted current is 
going through the nerve. 


I.] THE FROG. 


/ 


[If an induction-coil is not at hand a bit of clean 
copper wire twisted round a strip of zinc, with the 
points of contact moistened with dilute acetic acid, 
may be used to stimulate the nerve ; smart tapping or 
pinching with a pair of forceps will also excite it, but 
by such means the nerve is soon killed.] 

The above experiments show : 

i\ That the muscle is irritable and contractile: certain 
external agencies (stimuli) excite some change in it, 
the result of which is a muscular contraction. 

d. The nerve is irritable : certain external agencies ex- 
cite some change in it, which in this particular case 
manifests itself by a contraction of the muscles con- 
nected with the nerve. 

e. The nerve possesses conductivity : although it is stimu- 
lated at some distance from the muscles, the change 
excited by the stimulus travels along it to them. 

O. Development. 

Place some freshly-deposited frog's spawn (taken di- 
rectly after extrusion by the female) in a table aquarium 
or other glass vessel filled with water. Examine and 
preserve the eggs and embryos as directed below. 

It is necessary for both observation and preservation 
that the mucus investment which surrounds the egg 
should be removed \ this may best be done with a 
couple of fine needles, under water in a small saucer, or 
on any convenient white surface. When liberated, 
float the objects into a shallow watchmaker's glass, and 
examine under a low power as opaque objects, on a 
white ground unless otherwise directed. Preserve in 
Kleinenberg's picric acid solution, and transfer to 
alcohol of increasing strengths. 


3 ELEMENTARY BIOLOGY. [CHAP. 

i. Segmentation of the fertilized ovum (oosperm) and 

larval metamorphosis. 

The rate of both segmentation and development 
generally Is liable to vary, in accordance with cir- 
cumstances. The periods enumerated below are 
approximately those best suited for observation. 

The specimens should be examined both in the 
fresh state and when fully preserved. 

(7. One hour after fertilization. 

a. General characters ; shape and size ; the black 
pigmented upper pole ; the yellowish white non- 
pigmented lower pole. 

/?. Thejirst cleavage furrow ; an annular constric- 
tion passing right round the egg, longitudinally 
with respect to the afore-named poles. It con- 
stricts the whole into two equal halves (embryo 
cells or blastomeres}. 

l>. Two hours after fertilization. 

u. The second cleavage furrow ; longitudinal and at 
right angles to the first one, subdividing each 
blastomere into two. There are now four cells 
of equal size. 

c. T/ie same at 3 4 /tours. 

a. The third furrow ; at right angles to the two 
former and excentric, lying within the pig- 
mented pole. It subdivides the whole into four 
smaller pigmented upper layer cells, and four 
larger non-pigmented lower layer cells. Ex- 
amine from several aspects. 

d. The same at 6 8 hours. 

A mulberry-like mass conspicuous by the irregu- 
larity in size of the blastomeres. 


I] THE FROG. 159 

a. The lower layer cells ; forming the lower half of 
the whole ; their boundary lines regular. 

/?. The tipper layer cells ; forming the upper half, 

smaller and more numerous than those of the 

lower layer, their boundary lines in part irregular. 

i.e. the upper layer cells are dividing more 

rapidly than the lower ones. 

e. The same at 24 hours. 

Recognizable by the preponderance of the pig- 
mented area. 

a. The lower layer cells ; forming now the lower 
third or thereabouts ; their boundary lines can 
only be made out with difficulty. 

[j. The tipper layer cells ; forming the upper two- 
thirds at least ; their boundary lines no longer 
clearly definable under a low power, the pig- 
mented portion having a granulated appear- 
ance. 

i.e. the upper layer cells are growing round 
the lower ones. 

f. The same at 4 5 days. 

The lower layer cells apparent only as a small 
unite spot (blastopore or anus of Rusconi}. 

a. The blastomeres ; boundary lines no longer 
recognizable. 

The blastopore. Examine this with care ; its lip, 
horse-shoe shaped, well defined above and at 
the sides, ill-defined below. 

The same at 6 7 days. 

Signs of the embryo are now beginning to appear, 


1 60 ELEMENTARY BIOLOGY. [CHAP. 

the whole having undergone a slight increase in 
total capacity and lost its spherical shape. 

a. The blastopore ; still visible but small and 
excentric (displaced towards the flattened or 
dorsal surface). 

ft. The neural >plate ; obvious as a lyre-shaped flat- 
tening, in front of and in a line with the blasto- 
pore ; its edges thickened and raised up (neural 
folds], its mid region depressed (neural groove)* 

The neural folds will in all probability be seen 
to unite in front, and die away behind, at the sides 
of the blastopore. A more or less marked ap- 
proximation of their hinder halves will be obvious. 

/;. The same at 12 14 days. 

The embryo may now be definitely recognized as 
a pear-shaped body still enclosed within the mu- 
cus investment. Remove and examine it. 

a. The body ; head and trunk, very obvious if seen 
from the dorsal aspect. 

ft. The neural folds ; seen, if examined from the 
dorsal aspect, to be uniting in the middle line. 

y. The blastopore; recognizable as a minute pore 
behind and below ft. 

2. The suckers i two oval thick-lipped depressions 
on the under side of the head (mouth not yet 
recognizable). 

. The visceral arches ; generally to be seen at this 
stage, as a couple of oblique ridges on either 
side, above S. 

/. The embryo at 15 18 days. 

Still enclosed within the mucus mass ; recogniz- 


I.] THE FROG. l6l 

able by the presence of the tail, the lashing move- 
ments of which are very conspicuous (when at 
rest it is usually bent round to the right side). 
Liberate the embryo, and in doing so note that 
the mucus mass is undergoing disintegration. 

O CJ O 

a. The body ; now differentiated into distinct head, 
trunk and tail. 

Examine from the side. 

ft. The visceral arches ; four in number on each 
side, the two hindermost bearing papillate out- 
growths (external branchiae). 

y. The eye ; obvious as a rounded eminence above 
the interspace between the first t\vo visceral 
arches. 

S. The auditory organ ; obvious as a small pit 
(auditory pit) behind and above y. 

Examine from beneath. 

e. The suckers ; now at their maximum of de- 
velopment and probably confluent posteriorly. 

. The mouth ; a deep oval pit in the middle line 
immediately in front of e. 

?;. The olfactory organs ; apparent as two shallow 
pits (olfactory pits) in front of the mouth. 

0. The blastopore ; a minute pore at the base of 
the tail, persistent as the anus. 

k. The free swimming larva. Fish-like and bilaterally 
symmetrical, tail and external branchiae much 
elongated. Introduce some duck-weed or other 
small plant into the water, and note the move- 
ments and habits of the larvae. 

M. II 


162 ELEMENTARY BIOLOGY. [CHAP. 

Examine from the side. 

a. The Jiead ; well marked and possessed of func- 
tional sense organs. 

/j. The external branchice ; long and pectinated ; 
three in number on either side, a small third- 
pair having appeared. 

y. The tail ; elongated and marked out into a 
number of well-defined segments (myomeres). 

The median Jin ; a thin fold of integument en- 
circling the tail and continued forwards dor- 
sally to the middle of the back ventrally, for 
a short distance in front of the anus (cloacal 
orifice). 

Examine from beneath. 

c. The mouth ; transversely enlarged and sur- 
rounded by fleshy lips, within which can be seen 
the jaws, beset by small horny teeth. 

/. T/ic larva, at a later period. Look for larvae in 
which the external branchiae of the right side are 
no longer visible. Examine from beneath. 

a. Head, trunk and tail. Cf. generally with the 
foregoing stages, as to relative proportions. 

P. The external branchicz ; visible only on the left 
side, projecting out from beneath a fold of the 
cephalic integument (ope rail urn]. A similar fold 
is seen on the opposite side. 

y. The month ; transversely oval and very large ; 
the lips, now papillate ; horny tectJi, more 
marked. 

<$. The suckers ; disappearing, and reduced to the 
condition of a couple of small tubercles. 


I.] THE FROG. 163 

Examine from the side. 

c. The mouth; surrounded by a protractile bell- 
shaped suctorial tip, and utilized for purposes of 
adhesion, in place of the suckers which are now 
disappearing. 

Cf. the movements of the living larva. 

;//. The development of the operculum. Look for larva? 
intermediate between k and /. Examine from the 
side. 

The operculum will be seen arising, on either 
side, immediately in front of the external gills, as a 
backwardly-directed fold of the second (Jiyoid) 
visceral arch. 

n. The larva at a later stage than I ; conspicuous by 
the great length of its tail and the absence of 
external branchiae. Examine from beneath. 

a. The body generally ; clad in a thin transparent 
integument, elegantly pigmentcd in black and 
gold. 

(3. The mouth ; still increasing in size, the cir- 
cum-oral papilke becoming more marked. 

y. The suckers ; still further reduced and repre- 
sented by two small vestiges. 

8. The intestine; visible through the body-wall as 
a greyish coiled tube of large calibre. 

e. The amis (cloacal orifice); median and ventral, 
situated at the base of the tail on the summit of 
the pointed posterior extremity of the trunk 
(cf. side view). 

. The hind-limbs ; minute papillate outgrowths of 
the body- wall, at the sides and a little in front of e. 

I I 2 


1 64 ELEMENTARY BIOLOGY. [CHAP. 

rj. The branchial pore ; asymmetrical and situated 
on the left side (external branchiae are no longer 
present). Remove the ventral portion of the 
adjacent integument (coalesced opercula) ; a 
spacious branchial chamber will be exposed. 
Note its limits. 

0. The internal branchiiz ; paired vascular folds of 
the sides of the head, four sets on each side, 
lying within the branchial chamber. Try and 
make out their relations. They are borne upon 
outgrowths of the wall of the pharynx (branchial 
visceral arches], which alternate with perfora- 
tions of the same (visceral clefts] putting the 
pharyngeal cavity in communication with the 
branchial chamber. 

i. The lungs; seen, on opening up the body- 
cavity, as small diverticula of the alimentary 
canal not yet distended with air. 

c. The larva on the appearance of hind-limbs. 
Examine from beneath. 

a. The body generally ; note the proportions of its 
several constituents. 

/?. The month; its large size ; papillate lips and 
horny teeth well marked. 

y. The absence of suckers and branchial pores. 

8. The hi/id-limbs; small, but fully differentiated; 
one-third the length of the body and separated 
in the ventral middle line by the terminal por- 
tion of the alimentary canal. 

e. The fore limbs ; differentiated, but covered by 
(visible through) the opercular membrane. 


I.] THE FROG. 165 

The tail; in all probability beginning to shrink. 

/. The young frog shortly after the moult (shedding 
of the larval skin): characterized by the coex- 
istence of both pairs of limbs and the tail. 
Note its frog-like characters and especially- 

u. The month; gape-wide, sucking lips gone, horny 
teeth replaced by true teeth. 

/ The tail ; absolutely shorter than in the late 
tadpole. Note its relations to the trunk. 

y. The cloaca I orifice. Examine this with care ; 
although displaced, owing to the increase in 
size of the hind-limbs and their approximation 
in the ventral middle line, it still lies at the 
base of the tail (i.e. it is ventral in position. 
Cf. the adult). 

ii. The formation of the embryonic layers and certain 
of the more important organs. 

Imbed and cut sections of the preserved oosperm 
or larvae, as directed below. Staining is unnecessary; 
hsernatoxylin may be used, if desired. 

a. At the first cleavage ; longitudinal and at right 
angles to the cleavage furrow. 

a. The blastomeres ; equal in size and separated by 
the cleavage furrow. Protoplasm ; densely pig- 
mented above, little so below, for the most 
part laden with yolk granules. 

f3. Nuclei. These may or may not be visible; 
each is clear and transparent and generally sur- 
rounded by pigment. (If visible, look for indi- 
cations of division.) 


1 66 ELEMENTARY BIOLOGY. [CHAP. 


b. On the formation of the third furrow (cf. i. 

Median longitudinal, as at a. 

a. The blastomercs, four in number as seen in 
section; two smaller upper ones, densely pig- 
mented ; two larger lower ones, pigmented only 
at the periphery and yolk laden. 

P. The cleavage cavity (segmentation cavity); small 
and central, in a line with the transverse furrow. 

c. At 6 8 hours. (Cf. i. d.) Longitudinal vertical. 

a. The upper layer cells ; small and pigmented, 
a single layer deep, nuclei generally visible. 

ft. The lower layer cells ; large cells with little or 
no pigment, nuclei rarely visible. 

y. The yolk granules ; aggregated in and largely 
confined to the lower cells (vegetative pole of 
the oosperm). 

3. The cleavage cavity ; large and irregular, inter- 
posed between a and ft. 

d. At 30 38 hours. Longitudinal vertical, to pass 
through the first trace of the blastopore. 

a. The cleavage cavity ; large and excentric, inter- 
posed between the cells of the upper and lower 
layers. 

ft. The lower layer cells ; several rows deep, nu- 
cleated and yolk laden; forming the main mass. 

y. The upper layer cells ; now two or three rows 
deep (epiblast or outer germinal layer) and 
differentiated into two layers. 

Follow the course of the epiblast ; it largely 
encloses the lower layer cells and is probably 
invaginated at the blastopore. 


I.] THE FROG. 167 

e. At 4 5 days (typical blastopore stage. Cf. i. /). 
Longitudinal vertical, to pass through the blasto- 
pore. 

a. The lower layer cells ; now practically destitute 
of pigment and almost completely enclosed in 
epiblast; exposed only in the region of the 
blastopore. 

/>. The archenteroji (primitive alimentary canal); a 
spacious cavity occupying much the position of 
the cleavage cavity in Section d; in communi- 
cation with the exterior at the blastopore. 

y. The cleavage cavity ; small and irregular, situated 
below ft at the end opposite the blastopore. 

S. The hypoblast (inner germinal layer or digestive 
epithelium); a single layer of closely packed t 
cells forming the roof of the archenteron, con- 
tinuous with the epiblast at the upper lip of 
the blastopore (i. e. formed as the result of in- 
vagination of the latter layer). 

e. The mesoblast (middle germinal layer) ; obvious 
in median longitudinal section as two series of 
cells somewhat irregular and more loosely scat- 
tered than the rest ; an upper series lying in the 
interspace between the roof of the archenteron 
and adjacent epiblast; a lower series somewhat 
similarly interposed below between the lower 
layer cells and adjacent epiblast, and most 
numerous at the blastopore. 

f. The same at 12 14 days (cf. i. //). Transverse 
across the middle of the neural plate. Examine 
under a high power. 


1 68 ELEMENTARY BIOLOGY. [CHAP. 

a. The neural plate ; a thickened medio-dorsal 
sheet of epiblast, partly invaginated and en- 
closing a deep neural groove; its raised edges 
(neural folds}. 

/]. The archenteron ; a wide cavity situated nearer 
the upper than the lower pole. 

y. The hypoblast; a single layer of cells forming 
the roof and side walls of/?: its cells, somewhat 
flattened above, graduating into the lower layer 
cells laterally. 

S. The notochord; a median oval mass of small 
cells, immediately beneath the neural plate, 
not yet completely constricted off from the 
hypoblast. 

e. The mesoblast ; interposed between the epiblast, 
and hypoblast with the lower layer cells; most 
marked dorso-laterally and symmetrical on op- 
posite sides. 

-. The same at 15 18 days (cf. i. /). Transverse 
across the middle of the trunk, for comparison 
with/ 

a. The epiblast; well-defined and pigmented. 
Examine under a high power, and note the 
order of succession and characters of its layers. 

/>. The hypoblast and lower layer cells. Cf. / y. 

y. The neural tube (cerebro-spinal axis) pigmented 
and medio-dorsal, enclosing a central canal; it 
no longer shows any trace of connection with 
epiblast. (Cf. i. //.) 

S. The notochord; immediately beneath y, large 
and rounded, composed of large vacuolated cells. 


L] THE FROG. 169 

c. The mesoblast; forming a denser mass (meso- 
blastic somite) on either side of the neural tube 
and notochord; below that point subdivided 
into two layers an outer one (somatic layer) 
which applies itself to the epiblast, and an inner 
one (splanchnic layer} which invests the hypo- 
blast and lower layer cells. 

. The body cavity ; the interspace between the 
somatic and splanchnic mesoblast; more or 
less obvious, in accordance with the degree of 
shrinkage of the preparation. 

77. The leading blood-vessels, as under. The dorsal 
aorta, median and cylindroidal underlying the 
sub-notochordal rod; the posterior cardinal 
veins, large vessels, ovoidal or irregular in 
section, right and left of the aorta. Blood 
corpuscles will in all probability be seen within 
them. 

Examine under a high power. The above 
vessels will be seen to be formed as excava- 
tions of the mesoblast, each bounded by a 
single layer of modified cells. 

0. The pro-renal (segment al) duct ; a conspicuous 
thick-walled tube seen, on either side, lying 
within the somatic mesoblast immediately be- 
neath the posterior cardinal vein. 

//. The larva at 12 14 days (cf. i. h\ Median lon- 
gitudinal vertical, to pass through the blastopore 
(anus). Examine under a low power. 

a. The body; elongated and enclosing two 
cavities: a ventral or archentcric canal, in 
communication with the exterior at the blasto- 


i;0 ELEMENTARY BIOLOGY. [CHAP. 

pore, and a dorsal or neural canal, at this period 
in communication posteriorly with the archen- 
teron and blastopore by a short narrow passage 
(iieurenteric canal}. 

fi. The notochord; a median rod of slightly vacuo- 
lated cells, lying in the interspace between the 
archenteric and neural tubes. 

y. The neural tube; enlarged in front (brain) and 
overhanging the notochord. 

8. The archenteron ; its extent; its roof, formed by 
the hypoblast cells; its floor, still bounded by 
undifTerentiated lower layer cells, now compara- 
tively few in number. 

e. The mesoblast ; composed of irregular scattered 
cells and more extensive than in the earlier 
stages examined. 

/. At 15 1 8 days (cf. i. /) ; transversely oblique, to 
pass through the visceral arches and external 
branchiae. 

a. The brain ; a large vesicle, situated at the an- 
terior end. 

/3. The mesenteron (archenteron) ; a large central 
cavity behind and in a line with u, wide in front, 
constricted behind. 

y. The visceral pouches ; paired diverticula of the 
hypoblast, 4 or 5 in number on either side, their 
blind ends abutting against the epidermis (if the 
section be much shrunk their walls may be in 
close apposition). 

& The visceral arches : mesoblastic aggregates 
alternating with y; each lying behind its cor- 


I.] THE FROG. i;i 

responding pouch, and usually lodging a large 
blood-vessel (aortic arch) seen in section. 

c. The external bran chics. These will be seen in 
some of the sections as filiform outgrowths (from 
i to 3 in number on either side) of the visceral 
arches. 

Each consists of a mesoblastic core invested in 
epiblast. If the five visceral pouches are seen, 
the first gill will be found to arise behind the 
second one (first branchial). 

k. Examine the lower sections of the above series 
and look for the formation of the mouth cavity. 

a. The mese nteron ; cf. supra; it ends blindly in 
front and is lined by a non-pigmented epithelium 
(yellow if prepared as directed and not stained). 

/?. The Stomatodteum ; a sac-like involution of the 
epidermis abutting against a, spacious, and well 
marked on account of its dense pigmentation. 
Its enclosed cavity is the mouth cavity. 

/. Compare similar sections through the head of an 
older larva, in which the internal branchiae are 
present. 

a. The visceral pouches ; those of the branchial 
series are now in open communication with the 
exterior (visceral clefts). 

ft. The internal branchicz ; vascular pectinations of 
the opposite faces of a. Note their number and 
arrangement. 

y. The operculum ; a backwardly-directed fold 
arising behind the first pouch (from the hyoid 
arch ; cf. i. ;;/). 


1/2 ELEMENTARY BIOLOGY. [CHAP. I. 

///. Across the head of /. (15 18 days); transversely 
to the long axis, to pass through the eyes. 

a. The epidermis ; forming a continuous investment 
for the whole ; thickened below and produced 
into two inverted cup-shaped folds (suckers}. 

ft. The brain ; dorsal and elongated, pigmented 
and enclosing a spacious central cavity (3rd 
ventricle). 

y. The notochord and archenteron ; occurring in 
order of succession below ft. 

o. The developing retina; on either side a cup- 
shaped outgrowth of the brain (optic cup}, con- 
nected with the same by a narrow neck (optic 
stalk) visible only in a few sections. Examine 
the cup and note its thick outer wall ; its thin 
inner wall ; its central cavity, continuous with 
that of the 3rd ventricle. 

(.. The lens ; visible either as a thickening or invo- 
lution of the epiblast, immediately external to 8. 

//. Compare similar sections through the eye of a 
more advanced larva. Examine under a high 
power. 

a. The optic cup ; its central cavity becoming ob- 
literated, its inner wall densely pigmented (pig- 
ment epithelium ; cf. Sect. M. 1 2 k}. 

ft. The lens ; completely constricted off from the 
epidermis and enclosing a central cavity ; its 
thin outer wall ; its thick inner wall. 

7. The remaining constituents of the eye ; seen, 
for the most part, in course of differentiation 
from the surrounding mesoblast. 


II. 


THE FRESH-WATER CRAYFISH (Astacus fluviatilis} 
AND THE LOBSTER (Homarus vulgaris). 

THE Crayfish and the Lobster are inhabitants of the water, 
the former occurring in many of our rivers and the latter 
abounding on the rocky parts of the coasts of the European 
seas. They are bilaterally symmetrical animals, provided 
with many pairs of limbs, among which the large prehensile 
'claws' are conspicuous. They are very active, walking 
and swimming with equal ease and sometimes propelling 
themselves backwards or_ forwards, with great swiftness, by 
strokes of the broad fin which terminates the body. They 
have conspicuous eyes, mounted upon moveable stalks, at 
the anterior end of the head ; and two pairs of feelers, one 
pair of which are as long as the body, while the other pair 
are much shorter. 

The body and limbs are invested by a strong jointed 
shell, or exoskeleton, which is a product of the subjacent 
epidermis, and consists of layers of membrane which remain 
soft and flexible in the interspaces between the segments of 
the body and limbs, but are rendered hard and dense else- 
where by the deposit of calcareous salts ; the exoskeleton 
is deeply tinged with a colouring matter which turns red 
when exposed to the action of boiling water. The body 
presents an anterior division the cephalothorax covered 


1 74 ELEMENTARY BIOLOGY. [CHAP. 

by a large continuous shield, or carapace ; and a posterior 
division the abdomen divided into a series of segments 
which are moveable upon one another in the direction of 
the vertical median plane, so that the abdomen can be 
straightened out, in extension ; or bent into a sharp curve, in 
flexion. Of these segments there are seven. The anterior 
six are the somites of the abdomen, and each of them has a 
pair of appendages attached to its ventral wall. The seventh 
bears no appendages and is termed the tclson it is sub- 
divided into two pieces in the Crayfish. The anus is 
situated on the v.entral aspect, beneath the telson and behind 
the last somite. 

A groove on the surface of the carapace, which is termed 
the cervical suture, separates an anterior division, which 
is termed the head or ccphalon, from a posterior division 
or thorax; and the thoracic division of the carapace fur- 
ther presents wide lateral prolongations, which pass down- 
wards and cover the sides of the thorax, their free ventral 
edges being applied against the bases of the thoracic 
limbs. These are the branckioslegites. Each roofs over a 
wide chamber in which the gills are contained and which 
communicates with the exterior, below and behind, by the 
narrow interval between the edge of the branchiostegite and 
the limbs. Anteriorly and inferiorly, the branchial chamber 
is prolonged into a canal, which opens in front and below 
at the junction of the head with the thorax, immediately 
behind the cervical suture. In this canal there lies a flat 
oval plate the scaphognathite which is attached to the 
second pair of maxillae and which plays a very important 
part in the performance of the function of respiration. Of 
the thoracic limbs themselves there are eight pairs, and, 
on the ventral face of the body, the lines of demarcation 
between the eight somites to which these limbs belong 


II.] THE CRAYFISH AND LOBSTER. 175 

may be observed. There is no trace of any corresponding 
divisions in the cephalothorax of the Lobster ; but, in the 
Crayfish, the last thoracic somite is incompletely united 
with those which precede it. The four posterior pairs of 
thoracic limbs are those by which the animal walks and are 
termed the ambulatory legs. The next pair in front is formed 
by the great claws or chela. The anterior three pairs are 
bent up alongside the mouth and are moved to and from 
the median line so as to play the part of jaws, whence they 
are termed foot-jaws or maxillipedes. The external or third 
pair of these maxillipedes are much stouter and more like 
the ambulatory limbs than the rest, and the inner edges of 
their principal joints are toothed. The innermost or first 
pair of maxillipedes are broad, foliaceous and soft. When 
these foot-jaws are taken away, two pairs of soft foliaceous 
appendages come into view. They are attached to the 
hinder part of the cephalon and are the jaws or maxillce. 
The second, or outermost, is produced, externally, into the 
scaphognathite, which will be seen to lie in a groove sepa- 
rating the head from the thorax laterally and known as 
the cervical groove. 

Anterior to these maxillae lie the two very stout mandibles. 
Between their inner toothed ends is the wide aperture of 
the mouth, bounded, in front, by a soft shield-shaped plate, 
the labntm ; and behind, by another soft plate, divided by a 
median fissure into two lobes which simulate appendages- 
it is termed the metastoma. Thus far, the surfaces of the 
somites to which the appendages are attached look down- 
wards, when the body is straightened out and the carapace 
is directed upwards. But, in front of the mouth, the wall of 
the body to which the appendages are attached is bent up, 
at right angles to its former direction, and consequently 
looks forwards. This bend of the ventral wall of the body 


i;6 ELEMENTARY BIOLOGY. [CHAP. 

is the cephalic flexure. In correspondence with this change of 
position of the surface to which they are attached, the three 
pairs of appendages of the somites which lie in front of the 
mouth are directed either forwards, or forwards and upwards. 
The posterior pair consists of the long feelers or antenna: the 
next, of the short feelers or antenmdes ; and the most anterior 
is formed by the short subcylindrical stalks (ophtJialmitcs], 
on the ends of which the eyes are situated. 

This enumeration shews that the Lobster and Crayfish 
have six pairs of abdominal appendages the swimmerets 
and " tail-fin"; eight pairs of thoracic appendages (four pairs 
of ambulatory limbs, one pair of chelate prehensile limbs, 
three pairs of maxillipeds), and six pairs of cephalic ap- 
pendages (two pairs of maxiike, one pair of mandibles, 
one pair of antennas, one pair of antennules, one pair of 
eyestalks), making in all twenty pairs of appendages. It 
may or may not be that the eyestalks are modified ap- 
pendages ; assuming however, as is most probable, that 
they are, the body in correspondence with the number of 
appendages consists of twenty somites (the telson excepted) : 
of these six remain moveable upon one another to form the 
abdomen, while the other fourteen are, with the exception 
of a portion of the last thoracic one in the Crayfish, com- 
pletely united to form the cephalothorax. 

The branchiostegite is an outgrowth of the dorso-lateral 
region of the confluent thoracic somites. The serrated 
rostrum which ends the carapace is a fixed median pro- 
longation of the dorsal wall of the anterior cephalic somites; 
while the telson is a moveable median prolongation of the 
dorsal wall of the sixth abdominal somite. The labrum and 
the metastoma are median growths of the sterna of the 
prse-oral and post-oral somites. 

Thus the whole skeleton in these animals may be con- 


II.] THE CRAYFISH AND LOBSTER. 177 

sidered as a twentyfold repetition of the ring-like somite 
with its pair of appendages, which is seen in its simplest 
form in one of the abdominal somites. Moreover, not- 
withstanding the great variety of functions allotted to the 
various appendages, the study of the details of their struc- 
ture (see Laboratory work) will shew that they are all re- 
ducible to modifications of a fundamental form, consisting 
of a basal-portion (protopodite) with two terminal divisions 
(endopodite and exopodite). A third division or epipodite is 
superadded to the appendages concerned in respiration. 

Of the twenty pairs of appendages, the three anterior 
are concerned with sensation and the six posterior with 
swimming; the mandibles, which bound the mouth, are 
most efficient in mastication. Of the ten pairs which re- 
main, five are modified to form foot-jaws, the others being 
functional for walking or climbing; three of the latter 
however, in that they are chelate and often used to capture 
prey or to tear up food material, combine the functions of 
locomotor feet and foot-jaws. 

Each of the larger appendages is composed of a number 
of segments, each movable upon its fellow in a single 
plane ; the various segments are so articulated that the 
limb, as a whole, is capable of considerable rotation. 

As has been already said, the Lobster and Crayfish are 
bilaterally symmetrical ; that is to say, a median vertical 
plane passing through the mouth and anus divides them into 
two similar halves. This symmetry is exhibited not merely 
by the exterior of the body and the correspondence of the 
paired limbs, but extends to the internal organs ; the alimen- 
tary canal and its appendages, the heart, the nervous system, 
the muscles and the reproductive organs, being disposed so 
as to be symmetrical in relation to the median vertical plane 
of the body. 

M. 12 


i;8 ELEMENTARY BIOLOGY. [CHAP. 

The wide gullet leads almost vertically into the spacious 
stomach, and both are lined by a chitinous continuation of 
the exoskeleton. The stomach is divided by a transverse 
constriction into a spacious cardiac, and a much smaller 
pyloric division, from which latter the intestine passes. The 
walls of the anterior half of the cardiac sac are thin and 
membranous, but, in the posterior half, they become calci- 
ned so as to give rise to a gastric skeleton of considerable 
complexity. The chief part of this skeleton consists of a 
median dorsal T-shaped ' cardiac ' ossicle, the cross-piece 
of which forms a transverse arch, while its long median 
process extends backwards in the middle line. The ends of 
the transverse arch are articulated obliquely with two small 
' antero-lateral' pieces, the extremities of which again are 
articulated with postero-lateral pieces, and these with a 
cross-piece, the ' pyloric ' ossicle, which arches over the 
roof of the pyloric division of the stomach. In this manner 
a sort of hexagonal frame with moveable joints is formed, 
and the median process projects backwards so far, as to end 
below the pyloric piece. It is connected with this, however, 
by a short ' pre-pyloric ' ossicle which ascends obliquely 
forwards and is articulated with the anterior edge of the 
pyloric piece. The lower extremity of this is produced into 
the strong median ' uro-cardiac ' tooth ; while the postero- 
lateral pieces are flanged inwards, and, becoming greatly 
thickened and ridged, form the large ' lateral cardiac ' teeth. 
Two powerful muscles are attached to the cardiac ossicle, 
and ascend obliquely forwards to be inserted into the 
under face of the carapace. Two other similar muscular 
bundles arise from the pyloric ossicle, and, passing obliquely 
upwards and backwards, are also inserted into the under 
face of the carapace, in the region of the cervical groove. 
The disposition of all these parts is such that when these 


II.] THE CRAYFISH AND LOBSTER. 1 79 

muscles contract, the dorsal ossicles are divaricated, the uro- 
cardiac tooth is thereby thrust forwards and downwards, while 
the lateral teeth move inwards downwards and backwards, 
and the three meet in the middle line. The working of these 
muscles can be readily imitated by seizing the anterior and 
posterior cross-pieces with forceps and pulling them in the 
direction in which the muscles act. The three teeth will 
then be seen to come together with a clash. Thus the 
food which has been torn by the jaws is submitted to 
further crushing in this gastric mill. The walls of the 
pyloric division of the stomach are thick, and project like 
cushions into its interior, thereby reducing its cavity to a 
narrow passage. The cushion-like surfaces of the pyloric 
walls are provided with long hairs which stretch across this 
narrow passage, and thus convert it into a strainer, which 
allows of the passage of only very finely divided matter 
from the gastric sac to the thin and delicate intestine. 
The intestine, in both Lobster and Crayfish, is made up of 
an anterior thin-walled segment whose roof is prolonged up 
into a ccecal process, and a posterior segment which, like 
the stomach, is lined by a chitinous continuation of the 
exoskeleton. The latter is spirally folded and papillose in 
the Crayfish. The anus is bounded by two valve-like 
thickenings of the exoskeleton, which are connected with 
the adjacent intestinal wall by a series of small muscles. 
The alimentary-canal is thus to be resolved into a straight 
tube of three segments ; an anterior fore-gut and a posterior 
hind-gut, each lined by an involution of the cuticular exo- 
skeleton, and a non-cuticular mid-gut which bears the above- 
named ccecal process and receives the ducts of the digestive 
gland. The digestive gland itself is the seat of the forma- 
tion of a combustible carbo-hydrate oily material which is 
as it were held in reserve in its constituent cells, as well as 

12 2 


180 ELEMENTARY BIOLOGY. [CHAP. 

of a digestive ferment ; as these physiological activities are 
frequently relegated respectively to separate liver and 
pancreas, the single gland which here performs the two 
functions has been appropriately termed the hepato-pancreas. 

The heart is a short, thick, somewhat hexagonal, symme- 
trical organ lodged in the pericardiac sinus, to the walls of 
which it is attached by fibrous bands. In its anterior half 
three pairs of apertures are visible, two being placed upon 
the upper face, two at the sides, and two on the under face. 
The lateral apertures are the most posterior, the dorsal, the 
most anterior in position. Each aperture begins in a funnel- 
shaped depression of the outer face of the organ, which leads 
obliquely inwards and terminates by a valvular slit in the 
cavity of the heart. This cavity is very much reduced by 
the encroachment of the muscular bands which constitute 
the walls of the heart, so that a transverse or longitudinal 
section shews only a small median cavity surrounded by a 
thick and spongy wall. 

During life, the heart beats vigorously, the whole of its 
parietes contracting together. From the dorsal part of its 
anterior extremity three arteries are given off, one median 
and two lateral, to the cephalon and its contents, and from 
the ventral aspect of this end of the heart an hepatic artery 
is given off, on each side, mainly to the liver. At its posterior 
end, the heart ends in a median dilatation from which two 
great arterial trunks are given off: one, the superior ab- 
dominal artery, runs along the dorsal face of the intes- 
tine, giving off transverse branches as it goes, in each 
somite; the other, the sternal artery, immediately on leaving 
the pericardial-sinus distributes branches to the genital 
gland; it then passes ventrally, to the interspace between 
the penultimate and antepenultimate thoracic ganglia, 
passes between their commissures and divides into two 


II.] THE CRAYFISH AND LOBSTER. iSl 

branches, which run, backwards and forwards, between the 
ganglionic chain and the exoskeleton. 

These arteries divide and subdivide and end in what, in 
some parts of the body at any rate, e.g. the liver, is a true 
capillary system. The veins are irregular channels, or 
sitmses, which lie between the several muscles and viscera. 
One of the largest of these is situated in the median ventral 
line, and can be readily laid open by piercing the soft inte- 
gument which lies between any two of the abdominal sterna. 
The blood flows out of the aperture with great rapidity, and 
the quantity shed shews the size of the sinus and its free 
communication with the rest of the vascular system. By 
cutting across any one of the limbs and inserting a blow- 
pipe into the place whence the blood wells forth, this ventral 
sinus can be readily injected with air. A large and irregular 
sinus is also to be found in the median dorsal region of the 
abdomen and is freely connected with the median ventral 
sinus. The stem of each branchia contains two canals, one 
running along its outer and the other along its inner face. 
The outer canal communicates, at its origin, with the thoracic 
portion of the median ventral sinus. The inner canal opens 
into a passage which ascends in the lateral wall of the 
thorax and opens, after meeting with other ' branchio-cardiac'' 
canals, opposite the lateral aperture of the heart. As the 
valvular lips of this and the other apertures of the heart 
open inwards, the blood, when the systole takes place, is 
driven out of the heart through the various arteries, and a 
considerable part of the blood thus propelled into the 
capillaries is collected by the median ventral sinus and 
thence, passing through the gills, eventually returns to the 
heart. It is customary to speak of a heart such as this, 
which propels aerated blood, as systemic, by way of dis- 
tinction from a branchial heart, which propels impure venous 


1 82 ELEMENTARY BIOLOGY. [CHAP. 

blood to the organs of respiration. But whether the whole 
of the venous blood takes the same course, or whether 
some of it returns from the dorsal sinuses directly to the 
pericardium, is a question which is not decided. Nor is it 
certain whether the so-called pericardium is to be regarded 
as one cavity, or whether the fibrous bands, which connect 
the heart with its walls, may not subdivide it into com- 
partments in immediate communication with certain of the 
cardiac apertures, and not with the rest. 

In the Lobster, from which the blood is readily obtained 
in quantity, it is a nearly colourless fluid, which usually has 
a faint neutral tint. It readily coagulates, a tolerably firm 
clot separating from the serum. It contains nucleated cor- 
puscles, devoid of any noticeable colour, which throw out 
very long pseudopodial prolongations, and thereby take an 
irregular stellate form. 

It has been seen that the respiratory organs, or branchiae, 
are lodged in a chamber situated between the branchiostegite 
externally, the lateral walls of the thoracic somites internally, 
and the bases of the thoracic limbs below; and that there 
is a narrow interspace between the free edge of the bran- 
chiostegite and the latter. At the anterior end of the cham- 
ber, a funnel-shaped passage leads to the anterior opening 
mentioned above, and, in this passage, the scaphognathite 
lies like a swing door. 

During life, the scaphognathite is in incessant movement 
forwards and backwards, scooping out the water in the bran- 
chial chamber through its anterior aperture at every forward 
motion. This bailing out of the water results in the in- 
ducing of a current which flows in by the inferior and 
posterior cleft beneath the free edge of the branchiostegite, 
and thus a constant circulation over the gills is secured. 


II.] THE CRAYFISH AND LOBSTER. 183 

Each branchia is somewhat like a bottle-brush, having a 
stem beset with numerous filaments; and the blood con- 
tained in the vessels of the latter, being separated by only a 
very thin membrane from the air contained in the water, 
loses carbonic anhydride and gains a corresponding amount 
of oxygen in its course through the branchiae. 

The branchiae are exclusively thoracic, being attached 
partly to the inter-articular membranes between the appen- 
dages and the body-wall and partly to the proximal ends of 
the limbs themselves. The last thoracic appendage is gill-less, 
and the branchia present in its vicinity in the Crayfish differs 
from the rest in being attached to the epimeral wall of the 
thorax; the Lobster has, in addition, three such gills on 
either side fully developed and functional : all or most of 
these are represented in the Crayfish by short filamentous 
rudiments, no longer functional as branchiae. The epipo- 
dites of the limbs ascend between the sets of branchiae which 
belong to each somite, and separate them. The branchiae 
which are attached to the limbs must necessarily be stirred by 
the movement of the latter, and hence the exchange of gases 
between the blood which they contain and the water must 
be, to a certain extent, increased, in proportion to the 
muscular contractions which give rise to the movements 
of the limbs and the consequently increased formation of 
carbonic anhydride. 

The excretion of nitrogenous waste goes on in the two 
large green glands which lie in the cephalon, close to the 
bases of the antennas. Each gland encircles the neck of a 
large thin-walled muscular sac which opens by a short 
canal upon the ventral face of the basal joint of the antenna. 
The gland itself consists of a coiled tube, lined by a 
large-celled epithelium and abundantly supplied with blood 
vessels. 


1 84 ELEMENTARY BIOLOGY. [CHAP. 

The nervous system consists of a chain of thirteen gan- 
glia united by longitudinal commissures lodged in the 
median line of the ventral aspect of the body, from which 
nerves are given to the organs of sense, to the muscles 
of the trunk and limbs, and to the integument; and of a 
visceral nervous system, developed chiefly upon the stomach 
and hinder segment of the intestine. 

The ganglia are centres of aggregation of the nerve 
cells ; of the thirteen seen in the adult the most an- 
terior lies in the cephalon, close to the attachments of 
the three anterior pair of appendages, and gives branches 
to them and to the visceral nervous system. It is usually 
termed the brain or the supraozsophageal ganglion. It is 
connected by two commissural cords, which pass on each 
side of the gullet, with a larger ganglionic mass, which is 
called the subcesophageal ganglion. This occupies the 
region of the hinder part of the cephalon and the anterior 
part of the thorax, and gives off nerves to the mandible, 
maxillae and the three pairs of maxillipeds. Five other 
ganglia lie in the five somites which bear the chelae and the 
ambulatory limbs, and there is one for each abdominal 
somite, the last of these being the largest of the six. 

The longitudinal commissures are double, and the 
ganglia themselves shew more or less evident indications 
of being double also. There is reason to believe that these 
thirteen apparent ganglia really represent twenty pairs of 
primitive ganglia, one pair for each somite ; the three an- 
terior pairs having coalesced preorally to form the brain; 
and the six which follow the mouth having united into the 
suboesophageal mass. 

The only organs of special sense which are recognizable 
in the Lobster and Crayfish are eyes and auditory organs, 
and a series of specially modified setose appendages which 


II.] THE CRAYFISH AND LOBSTER. 185 

fringe the exopodite of the antennule, and are thought to 
perform an olfactory function. 

The eyes are situated at the extremities of the eyestalks, 
or ophthalmites, which represent the first pair of appendages 
of the head. The rounded end of the eyestalk presents a 
clear smooth area of somewhat crescentic form, divided into 
a great number of small mostly four-sided facets. This area 
corresponds with the cornea, which is simply the ordinary 
chitinous layer of the integument become transparent. 
The inner face of each facet of the cornea corresponds with 
the outer end of an elongated transparent slightly conical 
body the crystalline cone the inner end of which passes into 
a relatively long and slender connective rod, by which it is 
united with a spindle-shaped transversely striated body- 
the striated spindle. The inner extremity of this again is 
connected by a nerve fibre with the optic bulb, the 
dilated gangliform termination of the optic nerve. The 
respective striated spindles, connective rods and crystalline 
cones, thus radiate from the outer surface of the terminal 
ganglion to the inner surface of the cornea, and each is 
separated from its neighbour by a nucleated sheath, parts 
of which are deeply pigmented. Nothing is accurately 
known as to the manner in which the function of vision is 
performed by the so-called compound eye which has just been 
described. The inner and outer faces of the corneal facets 
are flat and parallel. They therefore cannot play the part 
of lenses; and, if they could, there is no trace of nerve 
endings so disposed as to be affected by the points of light 
gathered together in the foci of such lenses. Morpho- 
logically, the striated spindles and their nerve fibres and 
probably the optic bulb itself wholly or in part, are in 
many ways analogous to those elements of the retina of 
the Vertebrata which make up the layers of rods and cones 


1 86 ELEMENTARY BIOLOGY. [CHAP. 

and the granular layers. These structures are properly 
modifications of the epidermis; inasmuch as the cerebral 
vesicle, of which the retinal elements are outgrowths, is an 
involution of the epidermis of the embryo, and, morpholo- 
gically speaking, the free ends of the rods and cones of the 
vertebrate eye are, as in the crustacean, turned outwards. 
There is good reason for believing the crystalline cones to 
be derivatives of the investing epidermis. 

The auditory organ of the Lobster and Crayfish is situated 
in the basal joint of the antennule, on the dorsal surface of 
which its small slit-like opening, protected by numerous setae, 
is to be seen. The chitinous layer of the integument is 
invaginated at the opening, and thus gives rise to a small 
flattened sac lodged in the interior of the antennule. One 
side of this sac is in-folded so as to produce a ridge, which 
projects into the cavity of the sac, and is beset with very fine 
and delicate hair-like setae. The auditory nerve enters the 
fold, and its ultimate filaments pass into the setae at their 
bases. The sac contains water in which minute particles of 
sand are suspended in the manner of otoliths. 

The sexes are distinct in the Lobster and Crayfish. The 
external characters of the males and females and the form 
of the reproductive organs are described in detail in the 
Laboratory work. 

The ovary is median and saccular, and its investing mem- 
brane is prolonged backwards to form a paired oviduct 
whose walls are glandular. Each ovicell is invested, during 
its maturation, in an epitheloid follicle of a single layer of 
cells; by the rupture of this the ripe ovum is liberated, and 
thrown off thus into the interior of the ovary it makes its 
way down the oviduct and so to the exterior. The impreg- 
nated ova are attached in great numbers, by a viscid secre- 
tion of the oviduct, to the hairs of the swimmerets, where 


II.] THE CRAYFISH AND LOBSTER. 

they undergo their development. A Lobster with eggs 
thus attached, is said by the fishermen to be ' in berry.' 

The segmenting egg of the Crayfish differs in some im- 
portant respects from that of the Frog. The yolk material 
is aggregated in the central protoplasm, and not at one pole 
as in the case of the latter animal, and segmentation is 
restricted to the superficial least yolk-laden protoplasm ; 
the egg is at no period completely cleft into two parts, 
segmentation is from first to last partial or meroblastic, a 
cellular investment being as it were formed around a central 
yolk-bearing mass. The investing cells become invaginated 
at one point to form a small sac, which remains for a time 
in open communication with the exterior. The embryo at 
this stage is to be resolved into a double-walled sac or gas- 
trula, the interspace between the two walls being filled with 
yolk. The outer layer or epiblast eventually gives rise to 
the epidermis and its derivatives the nervous system and 
sensiferous epithelia; the inner one or hypoblast forms the 
lining membrane of the mid-gut, and from it the digestive 
gland is formed later as a paired outgrowth it is from first 
to last the true digestive epithelium. The cavity enclosed 
by the hypoblast in its simple sac-like condition is the 
primitive alimentary canal or archenteron^ its aperture of 
invagination being termed the blastopore. The remaining 
constituents of the body are derived from cells which are 
budded off from one or both of the above layers. Early 
traces of the embryo are obvious in the development of the 
cephalo-thoracic appendages, which arise as paired out- 
growths of a relatively small area of the surface of the egg 
known as \h& germinal area - } there appear at the same time, 
at opposite ends of this, two median papillate outgrowths- 
an anterior one which gives rise to the labrum, and a pos- 
terior one which, by subsequent elongation and segmenta- 


1 88 ELEMENTARY BIOLOGY. [CHAP. 

tion is transformed into the abdomen, for which reason 
it is termed the abdominal papilla. The blastopore mean- 
while becomes closed, the archenteric sac being no longer 
in communication with the exterior; to meet this latter there 
are instituted, immediately under cover of the labrum and 
abdominal papilla, median ingrowths of the epidermis 
which give rise to the lining membranes of the fore and 
hind gut respectively, their apertures of invagination per- 
sisting as the adult mouth and anus. 

The yolk does not enter conspicuously into any of the 
above-mentioned outgrowths; it is enclosed within the ce- 
phalo-thoracic region, which becomes thereby much dis- 
tended. The gills and branchiostegites appear late; the 
former as simple outgrowths of the body-wall and appen- 
dages, the latter as lateral folds of the body wall. The 
embryo which results from these developmental processes 
passes through all the stages which are needed to bring it 
very near to the form of the adult before it leaves the egg : 
but, in the Lobster, the young, when hatched, are larvae 
extremely unlike the parent, which undergo a series of me- 
tamorphoses in order to attain their adult condition. The 
larvae may frequently be obtained by opening the eggs of a 
' hen-lobster ' in * berry.' They have when young a rounded 
carapace, two large eyes, a jointed abdomen devoid of appen- 
dages; and the thoracic limbs are all provided with long 
exopodites. During the later metamorphoses the abdominal 
appendages appear, as that region of the body elongates 
and increases in importance; the growth of the exopodites 
of the thoracic appendages is at the same time arrested, 
those of the chela and ambulatory legs vanishing entirely 
as these appendages become specialised for locomotion. 

The ordinary growth, no less than the metamorphoses of 
the Lobster and Crayfish, are accompanied by periodical 


II.] THE CRAYFISH AND LOBSTER. 189 

castings of the outer, chitinous, layer of the integument, or 
whole exoskeleton if calcified. The shedding of this is 
preceded by a process of disintegration along certain 
definite lines, such as the edge of the chela and the inter- 
articular membrane between the cephalo-thorax and abdo- 
men; these become, during the period at which the animal 
is freeing itself, so many points of least resistance and a 
consequent rupture of them ensues. After each ecdysis, the 
body is soft, being invested in a continuous chitinous cuticle, 
and the animal retires into shelter until, by calcification of 
this, the ' shell ' is reproduced. 

As the hard parts of the exoskeleton are the result of re- 
placement in earthy matter of portions of an originally con- 
tinuous chitinous cuticle, it follows that the uncalcified areas, 
which remain soft and flexible, are but persistent portions of 
the cuticular predecessor of the whole; they stand related 
to the calcified portions of the exoskeleton, as do the arti- 
cular surfaces of the long bones of the Frog's endoskeleton 
to their ossified shafts. Special thickenings or ingrowths 
of the exoskeleton take place at all points, for purposes 
of furnishing the surfaces requisite for the insertion of 
muscles: these ingrowths or tendons are, for the most part, 
mere tongue-shaped involutions, densest where resistance is 
greatest. The maximum of specialization is reached in the 
thoracic region where, from metameric ingrowths of the 
sternal and epimeral walls, a complicated endophragmal 
system is formed. This is fully described in the Laboratory 
work. 


I QO ELEMENTARY BIOLOGY. [CHAP. 


LABORATORY WORK. 

Crayfish are best killed under chloroform, proceeding as 
with the Frog. (p. 35). They may be best kept alive in a 
moist atmosphere near running water, fed upon sopped 
bread. A sink, covered with a sheet of glass, meets all 
requirements. 

A. General external characters. 

The animal is covered by a continuous exoskeleton which 
is for the most part calcified, the following parts are 
readily recognised :- 

a. The body proper : 

a. Its anterior unsegmented portion (cephalotho- 
rax}\ the great shield-like plate (carapace) 
covering the back and sides of the cephalotho- 
rax; the groove across the carapace (cervical 
suture) marking out the line of junction of head 
and thorax: the anterior prolongation of the 
carapace to form the rostrum or frontal spine. 

fi. Its posterior segmented portion (abdomen]: its 
seven divisions; the anterior six much like one 
another; the most posterior (telsoii) different 
from the rest (Cf. p. 174). 

b. The jointed limbs (appendages) attached to the 
ventral aspect of the body: their varying characters 
in different regions. 

c. The external apertures of the body. 


a. The mouth; seen on turning aside the append- 
ages beneath the head. 


II.] THE CRAYFISH AND LOBSTER. 191 

(3. The anus; a longitudinal slit beneath the 
telson. It is bounded by two flap-like folds of 
the adjacent integument (anal valves). 

y. ^te paired genital apertures : in the male, on the 
basal joints of the last pair of appendages of the 
thorax: in the female, on those of the ante- 
penultimate pair. 

The two sexes may be at once distinguished 
from each other, apart from these apertures, by 
the following characters. The transverse diameter 

of the abdomen of the J. exceeds, at its widest 
part, that of the cephalothorax ; it is the reverse 

for the <, The first two pairs of abdominal ap- 
pendages are especially modified for purposes 

accessory to reproduction, in the ; in the f the 
second pair are normal, the first are either very 
small or absent. 

8 The apertures of the excretory organs or green 
glands; each on the summit of a tubercle, borne 
upon the under surface of the basal joint of the 
antenna. 

. The auditory apertures; on the flattened upper 
surfaces of the basal joints of the antennules. 

These can be better examined when the ap- 
pendages on which they are situated have been 
removed. 

B. The exoskeleton and appendages. 

Note that the exoskeleton forms a continuous invest- 
ment for the whole body (axial portion] and its ap- 
pendages (appendicular portion}; it is for the most part 
calcified, but it remains soft and flexible where freedom 
of motion is required. 


1 92 ELEMENTARY BIOLOGY, [CHAP. 

i. The typical abdominal segment. 

Isolate, by carefully dissecting it away from its 
fellows, the third abdominal segment and its ap- 
pendages. Pick away its contents and examine 

a. The segment proper: arched above; flattened 
below. It may be subdivided into 

a. a dorsal tergum, the anterior smooth portion of 

which is overlapped by the preceding segment, 

in extension of the abdomen. 
ft. The sternum : that portion of the ventral surface 

which lies between the points of attachment of 

the appendages. 

y. The epimeron: the portion of the ventral surface 
which lies on each side immediately external to 
the attachment of the appendage. 
This region is very short and passes almost 
directly into the inner wall of 

8. fas pleuron; a free wing-like downgrowth of each 

lateral wall of the somite, seen, in section, to 
be formed by both tergum and epimeron. Note 
the smooth anterior half of the pleuron; it is 
overlapped by the one in front during flexion of 
the abdomen, much as is the tergum during 
extension. 

c. The articular facets; small tubercles developed, 
one on either side, from the anterior edge of the 
base of the tergum, immediately above the 
pleuron. They fit, during life, into correspond- 
ing recesses of the posterior border of the tergum 
in front. 

b. The appendages or swimmerets, one on each side: 
the structure of each 


II.] THE CRAYFISH AND LOBSTER. 193 

a. The short two- jointed basal portion (protopo- 
dite), consisting of a shorter proximal and a 
longer distal piece. 

(3. The flattened lamellae attached to the distal 
joint of the protopodite, an inner (endopodite) 
and outer (exopodite). 

2. The structure of the cephalothorax. 

a. Note again the carapace, with its frontal spine and 
cervical suture. 

b. Turn the animal over and note the narrow sterna 
of the thorax; they are laterally compressed, as the 
result of the great development of the basal joints 
of the appendages. 

The sternum of the last thoracic somite is not 
completely ankylosed with the one in front in the 
Crayfish. In the Lobster it is. 

c. Raise with a pair of forceps the free edge of the 
lateral expansion of the carapace which overlies the 
bases of the thoracic appendages: note that it is 
formed by the large united pleura of the thoracic 
segments, and overlaps a chamber in which the 
gills lie. It is termed the branchiostegite ac- 
cordingly; its ventral edge is smooth in the Cray- 
fish, it is notched metamerically in the Lobster. 

d. Make a transverse section across the thorax, im- 
mediately behind one of the larger appendages; 
boil for five minutes in weak solution of Caustic 
Potash and pick away the soft parts, until quite 
clean. Examine under water, and note, as com- 
pared with the corresponding section across the 
abdominal segment 

M. 13 


IQ4 ELEMENTARY BIOLOGY. [CHAP. 

a. The sternum; its middle portion is laterally 
compressed (cf. b.). It gives off (for each seg- 
ment) two ingrowths or endosternites, which arise 
close together, immediately internal to the bases 
of the appendages. 

ft. The tergum; arched above, prolonged down on 
either side to form the outer limb of the 
branchiostegite. 

If examined carefully, there will be seen 
arising from the cervical groove, close together 
near the middle line, two small tubercles or 
endotergites. They are most fully developed in 
the Lobster. 

y. The epimera. Each is vertically elongated 
pushed up as it were upon itself to form the 
inner wall of a great chamber (branchial 
chamber] lying under cover of the branchio- 
stegite. From it the inner limb of the branchio- 
stegite is derived. 

Note the endopleurites * ingrowths of the op- 
posite epimeral walls, which abut against the 
upper and outer borders of the endosternites. 
These, with the endosternites and endotergites 
above mentioned, are, one and all, ingrowths 
of the exoskeleton, developed in connection 
with muscular attachment. Cf. Sect. C. 2. 

8. The branchiostegite; its outer limb is dense and 
calcified, its inner one is very delicate, largely 
chitinous and hirsute. 

3. The telson. 

Its whole tergal area is densely calcified, its sternal 
one is largely chitinous. It bears, in "both Lobster 


II.] THE CRAYFISH AND LOBSTER. 195 

and Crayfish, two lateral spines; in the latter animal 
it is segmented, at the point of origin of these, into 
two portions an anterior one, the tergal surface of 
which remains largely chitinous, and a terminal post- 
anal one, which is completely calcified. 

The perianal area is calcified on opposite sides, to 
form a couple of anal plates ; they are most marked 
in the Lobster. 

Note the delicate setce, which fringe the free border 
of the telson. 

4. The appendages. 

Remove the entire set from one side of the body in 
the order enumerated below, cutting through the 
inter-articular membranes close to their poims of 
attachment to the axial skeleton. 

Examine under water, posterior face upper- 
most. 

a. The third abdominal appendage. Its general charac- 
ters have been described (i. &); examine in 
detail 

a. Its protopodite ; made up of two segments a 
shorter proximal hip-segment or coxopodite, and 
a long distal one (basipodite) which forms a base 
of articulation for the exopodite and endo- 
podite. 

J3. Its endopodite (the longer of the two terminal 
portions). It is subdivided into two segments 
of equal length the basal one is continuously 
calcified, the terminal one is multi-articulate. 

y. Its exopodite; relatively shorter than ft. It also 
is subdivided into a single basal and a terminal 

132 


196 ELEMENTARY BIOLOGY. [CHAP. 

multi-articulate segment; the former however is 
but a fourth the length of the whole. 

8. Examine under a low power, and note that the 
calcifications of the multi-articulate segments 
are incomplete; they are restricted to their 
outer borders. Both exopodite and endopodite 
will be found to be fringed with delicate setae. 

The above description applies equally to both 
Lobster and Crayfish, except that in the former 
animal the whole appendage is more foliaceous 
and paddle-like. 

b. The second maxillipede (second appendage in 
front of the great chela), as compared with a. 

a. Its protopodite; its two segments are short and 
equal in size. The distal one furnishes the base 
of articulation for both exopodite and endopo- 
dite; the proximal one is prolonged out into a 
delicate lamella or epipodite (not represented in 
a) which bears a well-defined gill. 

/?. Its endopodite. This now forms the main por- 
tion of the whole limb, it is subdivided into 
five segments; a basal ischiopodite ; an elongated 
laterally compressed meropodite; a small carpo- 
podite; an expanded propodite, and a short 
terminal dactylopodite. The inner edge of the 
dactylopodite is beset by a series of sharp 
spines; the rest of the endopodite is partly 
fringed in setae. 

y. Its exopodite, long and filamentous; its structu- 
ral features recall most nearly those of the 
endopodite of the abdominal appendage. 


II.] THE CRAYFISH AND LOBSTER. 197 

The above description applies equally to both 
Lobster and Crayfish, except that in the former 
animal the epipodite and gill are in no way con- 
fluent. 

c. The third maxillipede. Its protopodite ; much as in 
by except that its distal segment is ankylosed with 
the basal one (ischiopodite) of the endopodite. 
Its endopodite; greatly increased in size and im- 
portance, as compared with that of b. The five 
segments enumerated for b can be recognized ; the 
ischiopodite is the longer of the series, the others 
become relatively shorter in proportion as the free 
end of the appendage is approached. The inner 
edge of the ischiopodite is beset by a single series 
of crushing teeth, \\sexopodite; structurally identi- 
cal with that of , but considerably shortened up. 

Note the presence of a tuft of long setae (coxo- 
poditic seta) arising from the base of the epipodite. 

In the Lobster, the ischiopodite bears two rows of 
teeth and the meropodite one row. 

d. The great chela ; much larger and more powerful 
than the last appendage, but resembling it in 
general structure, and in the ankylosis of its ischio- 
podite and basipodite ; it also carries a gill. 

The exopodite is entirely suppressed. The 
ischiopodite is relatively short, the meropodite and 
propodite being, as in b, the longer of the series of 
segments. The propodite; greatly enlarged and 
prolonged outwardly to form, with the dactylopo- 
dite, an opposable forceps (chela). 

e. The four posterior thoracic appendages (ambulatory 
appendages). 


198 ELEMENTARY BIOLOGY. [CHAP. 

All are, like d, destitute of exopodite. All are 
elongated, the proportionate lengths of the several 
segments being identical with those of d. The first 
and second pairs are chelate, and the first three 
bear both a gill and an epipodite. 
The fourth; destitute of both gill and epipodite: 
when at rest it is backwardly directed. 

In the Lobster, the gill borne by each of the above 
appendages is, like that of b, distinct from the epi- 
podite. 

The genital orifices are borne upon these ap- 
pendages. They have been described at A. c. y. 

f. The abdominal appendages, other than the third pair 
(described at a). 

a. The fourth and fifth pairs : closely resembling 
the third, functional as swimmerets. 

(3. The sixth pair, modified to form, together with 
the telson, a tail-fin. The protopodite : repre- 
sented by a single short strong segment. (In 
the lobster there is a second incomplete basal 
segment.) The exopodite and endopodite : 
wide plates fringed with setae. The exopodite ; 
divided into two portions by a transverse joint : 
the free edges of its proximal portion are markedly 
serrated. The endopodite ; continuously calci- 
fied ; its proximal internal surface is beset, in 
the Crayfish, by a patch of short setae, which 
play, during life, upon a corresponding hirsute 
area of the under surface of the telson. 

y. The second pair. Cf. Sect. A. c. y. 

Closely resembling the third in the female. In 
the male the endopodite is much modified ; its 


II.] THE CRAYFISH AND LOBSTER. 199 

terminal multi-articulate segment being shortened 
up, in proportion as its basal one is elongated. 
The latter is here at its maximum for the whole 
abdominal series ; it is produced up into an 
accessory piece, which is segmented off and 
modified to form a plate, rolled upon itself so 
as to enclose a demicanal, concave inwardly. 

In the Lobster, this accessory process of the 
basal segment of the endopodite is still more 
marked. 

8. The first pair; in the female rudimentary, ex- 
ceedingly variable in size and not unfrequently 
absent altogether : except in very rare cases the 
exopodite is suppressed. In the male the exo- 
podite is invariably absent, the protopodite and 
endopodite become ankylosed and terminate in 
a plate rolled upon itself. In the Lobster the 
terminal division differs slightly from that of the 
Crayfish. 

g. The first maxillipede. Its protopodite, flattened 
and foliaceous, its two segments well defined; its 
exopodite, substantially identical with that of a; 
its endopodite, reduced to a small two-jointed 
structure, lying under cover of the basal joint of 
the exopodite ; its epipodite, fully developed but 
destitute of a gill. 

In the Lobster, the reduction of the endopodite is 
far less marked. 

//. The second maxilla. Its protopodite, foliaceous 
like that of g, but pectinated internally ; its endo- 
podite, elongated and filamentous, its free end is 
recurved to form a hook-shaped process which, 


200 ELEMENTARY BIOLOGY. [CHAP. 

during life, is received into a recess of the mandible. 
Its epipodite; well developed, and united in front 
with a lamina, which probably represents the exopo- 
dite, to form a wide oval plate (scaphognathite) which 
lies at the anterior end of the gill-chamber (Cf. 
Sect. H. c. and p. 182). 

If the above appendage be examined in the living 
animal, it will be found that with every movement 
of the scaphognathite there is a corresponding pull 
upon its filamentous endopodite. 

i. The first maxilla. Epipodite and exopodite un- 
developed. The endopodite is reduced to the 
condition of a small squame; its protopodite is 
foliaceous and two-jointed, the basal segment 
(coxopodite) being blade-like and recurved, with 
its free end inserted, during life, into the oral 
aperture. (Cf. Sect. E. 6 d.) 

In the Lobster, the endopodite is large and seg- 
mented. 

k. The mandible. Its strong toothed basal-joint (pro- 
topodite) bearing a small appendage (the pal f) which 
represents the endopodite; epipodite and exopo- 
dite unrepresented. 

/. The antenna. Its two-jointed basal portion (pro- 
topodite) bearing a flattened protective squame (the 
modified exopodite} and a long multi-articulate 
filament (the endopodite), the two basal segments of 
which are greatly enlarged and modified for pur- 
poses of articulation. Note the opening of the 
green gland (Cf. Sect. A. c. 8) on the under side of 
the basal joint of the protopodite. 


II.] THE CRAYFISH AND LOBSTER. 2OI 

The distal segment of the protopodite (basipo- 
dite) is subdivided into two ; the outer segment is 
squamous in the Lobster. 

m. The antennnle. Its large three-jointed basal seg- 
ment {protopodite)) bearing a pair of multi-articulate 
filaments (endopodite and exopodite) : the opening of 
the auditory organ, in the midst of a tuft of setae 
on the upper surface of the basal joint. The exo- 
podite, the longer of the two jointed filaments, is 
carried erect during life (it bears sensory setae. 
Cf. Sects. A. c. e. and K. 2). 

n. The ophthalmite or eyestalk. A short two-jointed 
structure which appears to represent the protopo- 
dite of an appendage. (Cf. Sect. K. 3 c.) 

5. Remove that half of the body from which the ap- 
pendages have been dissected, thus reducing the 
whole to the condition of longitudinal vertical section; 
boil for a few minutes in weak solution of Caustic 
Potash, pick away the soft parts and examine from 
within. 

a. The inter-articular membranes ; flexible, persistently 
uncalcified, portions of the exoskeleton. Note that 
(in the Crayfish) between the two last thoracic 
sterna. (Cf. Sect. B. 2 b.) 

fi: The endophragmal system. Each set of endoster- 
mites and endotergites of which it is composed (cf. 
Sect. B. 2 d.) are seen to arise in the same plane ; 
each endosternite slopes forwardly, carrying with it 
the anterior limb of its corresponding endotergite, 
the posterior limb of the one in front passing back to 
meet it. The points of apposition of the successive 
sets of elements alternate with those of their origin. 


202 ELEMENTARY BIOLOGY. [CHAP. 

c. The pro-cephalic process; a tongue-shaped ingrowth 
of the exoskeleton, at the base of the rostrum. 

d. The thoraco-abdominal link work; a somewhat com- 
plicated system of bars, passing between the last 
two thoracic sterna and a special process of that of 
the first abdominal segment. 

. The aperture of the mouth; bounded by the man- 
dible note the natural relations of the latter. The 
upper-lip or labrum and the lower-lip or metastoma 
will be seen, as uncalcified prolongations of the 
sternal skeleton, situated, respectively, in front of 
and behind the mouth. Compare the same as 
looked at from beneath, in an uninjured specimen- 
ex. The labrum ; a shield-shaped plate calcified mar- 
ginally. 

j3. The metastoma; composed of a median fold, pro- 
duced on either side into a blade-like process, 
which simulates the basal joint of the first maxilla. 

f. Note the limits of the several segments of the axial 
skeleton, and the mode of articulation of each upon 
its fellow and of the appendages upon each. 

6. The histology of the exoskeleton. 

a. Make a thin longitudinal-vertical section of any of 
the inter-articular membranes, and examine in water 
under a high power. It consists of a highly elastic 
membrane, traversed longitudinally by regularly 
disposed clear striae ; if pressure be applied to the 
cover-slip, the layers obvious as the above-named 
striae will be found to be denser and more resistant 
than the intervening ones, i.e. the whole is composed 


II.] THE CRAYFISH AND LOBSTER. 203 

of chitinous material, deposited in layers, alternately 
denser and less dense. 

b. Compare a similar section of any calcined portion 
of one of the appendages, ground down on a hone 
(see Appendix E.). A similar longitudinal striation 
is obvious. 

Examine the peripheral area; the striae but a 
tenth the diameter of those seen in the main mass 
are closely aggregated ; the free surface is invested 
in an uncalcified epiostracum. The whole is per- 
meated by a close set series of wavy pore-canals, 
usually filled with air in the process of manipula- 
tion, and rendered thereby highly refractive. 

Compare tangential sections, made in a similar 
manner. The pore-canals will be obvious as minute 
black-dots, closely (in places irregularly) aggregated 
together. 

An aggregation of the striae, identical with that 
described above, is frequently met with on the inner 
side also. 

c. Cut a longitudinal vertical section of a piece of the 
exoskeleton, together with the underlying in- 
tegument, which has been decalcified by treatment 
with i chromic acid solution. Note, in addition 
to the structural features already described 

a. The setce ; each is an uncalcified outgrowth, 
usually arising at the base of a shallow pit. 
They vary greatly in size and detailed structure in 
different parts of the body; the commoner forms 
end in a pointed extremity, fringed with lateral 
hairlike filaments. 


204 ELEMENTARY BIOLOGY. [CHAP. 

ft. The integument ; largely composed of branched 
nucleated granular cells : the outermost giving 
off a large number of short processes which pene- 
trate a short way into the exoskeleton. 

Prolongations of it extend into the setse and 
into all skeletal outgrowths. 

The ischiopodite of the third maxillipede may 
be preferably utilized, as, in it, all gradations from 
seta to spine and from spine to tooth can be 
readily followed. 

C. The muscular system. 

1. Detach one of the great chelae from the body and lay 
bare its interior. The enlarged base of the propodite 
will be found to lodge two muscles, which pass be- 
tween it and the dactylopodite ; they are 

a. A larger adductor, arising from the outer side. 

b. A smaller abductor, arising from the inner side. 

2. Remove the superficial portions of the two muscles ; 
there will be found lying within each a central tendon 
a plate-like ingrowth of the exoskeleton, towards which 
the muscular fasciculi converge. Remove all the soft 
parts and examine 

a. The tendons in relation to the dactylopodite; 
they are ingrowths of the opposite sides of its 
base. 

f3. The articular facets and interarticular membranes ; 
so arranged as only to admit of motion in one 
plane (abduction and adduction). 

3. Examine the remaining segments of the appendage. 
Note that 


II.] THE CRAYFISH AND LOBSTER. 20$ 

a. The relations between any two of them are identical 
with those described above, motion being possible 
in only one plane. 

b. The individual segments are incapable of rotation 
upon each other. The limb as a whole can be 
rotated; owing to the variation in the angles of 
inclination of its several joints. 

4. Make a median longitudinal section of the whole 
body, similar to that described in Sect. B. 5 ; pick 
away the viscera under water, wash and examine 

a. The flexor abdominis muscle ; a powerful mass, ex- 
tending from the anterior border of the thoracic 
epimeron and endophragmal system to the base of 
the telson. It arises by a series of slips, which 
wind round each other in a highly characteristic 
manner and are inserted into the abdominal sterna. 

b. The extensor abdominis ; a much less powerful 
muscle, arising immediately above a. Its fasciculi 
are inserted into the abdominal terga. 

c. The levator abdominis ; arising, immediately above 
the extensor, from the antero-dorsal border of the 
thoracic epimeron. It passes obliquely backwards, 
to be inserted, laterally, into the first abdominal 
segment. 

This muscle is continuous with a series of fibres 
which skirt the entire anterior border of the thoracic 
epimeron and attach it to the cervical groove. 

Note that the parts of the axis are, like those of 
the appendages, capable of motion only in one plane. 

d. The adductor muscle of the mandible ; a powerful 
fan-shaped mass, passing obliquely upwards from 


206 ELEMENTARY BIOLOGY. [CHAP. 

the hinder border of the mandible, to be attached 
to the cephalic shield, slightly in front of the cervical 
groove. Note its powerful tendon. 

Small muscles will be seen, passing from the man- 
dible and antennary organs to the adjacent exo- 
skeleton. 

e. Lay bare the basal portion of the great chela, and 
note the relations of its muscles. They arise from 
the endophragmal system, and are attached to 
tendinous ingrowths of the appendage itself similarly 
to those described in 2. 

D. The general disposition of the viscera. 

i. Place the animal on its ventral side and pin down 
under water, inserting the pins through the tail fin 
and bases of the chelae ; remove the whole tergal 
skeleton and with it the extensor abdominis muscle. 
Note in order 

a. The alimentary canal ; a straight tube, running the 
whole length of the body in the middle line. It is 
greatly enlarged in front to form the so-called 
stomach, which fills the greater portion of the 
cephalon. 

b. The heart ; a slightly yellowish pentagonal organ of 
delicate texture, lying above a in the middle thoracic 
region. 

c. The genital gland. In the female, a yellowish brown 
mass ; in the male, a whitish tongue-shaped mass ; 
lying immediately beneath b. 

It varies in size and character with the season of 
the year. (Cf. Sect. G.) 

d. ^L\\Z genital duct. In the male; a highly convoluted 


II.] THE CRAYFISH AND LOBSTER. 2O/ 

dead-white tube, immediately external to c. In the 
female ; a short membranous tube, only visible at 
this stage with difficulty. 

e. The digestive gland ; a yellow pulpy-looking mass, 
filling up the interspaces in the cephalothorax ; it 
is most obvious in front of the genital apparatus. 

f. The excretory organ (green-gland); a paired delicate 
green structure, lying, at a low level, in the extreme 
anterior end of the cephalic cavity. It can be at 
once seen on slightly displacing the stomach. 

g. Note, incidentally. 

a. The adductor mandibuli muscle; a large oval 
fleshy mass, lying immediately external to the 
stomach (cf. Sect. C. 4^.). 

/5. The extensor dbdominis muscle ; its cut ends will 
be found, attached to the thoracic epimera. 

y. The gastric muscles ; passing from the stomach to 
the adjacent exoskeleton (for details see Sect. E). 

3. The integument (hypodermis) ; a delicate dark red 
layer, lying immediately under cover of the 
exoskeleton. 

The body-cavity; obvious as an ill-defined chamber, 
within which the various organs of the viscera are 
contained. 

. The respiratory organs ; seen lying within the 
branchial chamber ; they are exclusively thoracic. 
Follow the cut edge of the branchiostegite. 

E. The alimentary organs. 

i. Dissect from the tergal aspect, as directed for Sect. D., 
and remove the heart and reproductive apparatus. 
Examine 


208 ELEMENTARY BIOLOGY. [CHAP. 

a. The stomach ; it is marked off by a transverse con- 
striction into a large cardiac chamber and a small, 
posterior, pyloric one. 

/;. The intestine^ a straight tube leading back to the 
anus ; its wall is thrown into a series of shallow 
folds, which take a longitudinal and slightly spiral 
course. 

c. The ccecum ; a median dorsal upgrowth, immediately 
behind the stomach. It is directed obliquely for- 
wards. 

In the Lobster, this is situated far back, near the 
anus. 

2. Some small muscles will be seen attached to the roof 
of the stomach. Remove these. In doing so, note 
that there comes away with them the soft cellular wall 
of the viscus, under cover of which there is seen a 
chitiuous lining. Examine the latter with care ; it will 
be found to be calcined to form a series of ossicles, 
related as under. 

a. The antero-dorsal (cardiac) ossicle ; a transverse bar, 
extending across the roof of the cardiac chamber. 

b. The postero-dorsal (pyloric) ; similarly related to the 
roof of the pyloric chamber as is a to that of the 
cardiac one. 

c. The antero-lateral (lateral-cardiac) ossicles; two 
small hammer-shaped pieces, abutting, one on either 
side, against a. 

d. The postero-lateral (lateral-pyloric) ; two long bars, 
similarly related on either side to b as are c to a. 

They extend forwards to meet the antero-lateral 

ossicles. 


II.] THE CRAYFISH AND LOBSTER. 2OQ 

e. The antero-median (urocardiac) ossicle ; a long 
tongue-shaped bar, passing back, from the antero- 
dorsal one, in the middle line of the roof of the 
cardiac chamber. 

f. The postero-median (prepyloric) ; a similar but 
shorter bar, arising from the postero-dorsal piece. 
When the parts are at rest, it passes obliquely down- 
wards and backwards, meeting the antero-median 
under cover of the postero-dorsal. 

It will be observed that the above-named parts 
form a repetitional series ; the roof and side walls 
of each chamber are calcified to form a dorsal trans- 
verse, a median, and a pair of lateral ossicles, the 
two latter sets articulating with each other. 

g. The digestive gland ; a paired mass, roughly trilobed, 
on either side. It is an aggregation of short 
cceca. 

Carefully dissect away its upper half on one side, 
until a spacious central duct is reached, around 
which the glandular coeca are seen to be arranged. 
Wash until quite clean, and look for their orifices. 

Follow the duct inwardly; it enters the head of 
the intestine by a wide aperture, immediately in 
front of the ccecum (i. c\ 

3. Place the animal on its side and remove the exposed 
half of the body and the digestive gland, so as fully 
to lay bare the entire alimentary canal. 

The cellular wall and certain muscles will be seen 
as before; remove these, and examine the chitinous 
lining and its associated structures. Note, in addition 
to the parts described above, the following. 

M. 1 4 


210 ELEMENTARY BIOLOGY. [CHAP. 

a. The gastrolith ; a discoidal stony-mass, interposed 
between the cellular and cuticular layers of the 
anterior cardiac wall. 

This is developed only in the summer season ; an 
underlying thickening of the chitinous cuticle is in- 
variably present to mark its position. 

b. The postero-ventral ossicles ; delicate vertically elon- 
gated bars in the hind wall of the cardiac sac. 

c. The accessory lateral ossicle ; a small bar, extending 
backwards and downwards from the point of junc- 
tion between the two main lateral ones. 

d. The intestine, the orifice of the digestive duct and 
the coecum. (Cf. supra.} 

4. Reduce the whole gut to the condition of median 
longitudinal section, by carefully removing the exposed 
half with scissors ; wash until quite clean and examine 
under water. 

a. line gullet; a spacious tube placing the stomach in 
communication with the exterior. Note its re- 
lations to the mouth. 

b. The median cardio-pyloric valve ; seen, in section, 
as an upgrowth constricting the passage from the 
cardiac to the pyloric chambers. 

c. Follow the cut edge of the chitinous lining of the 
stomach ; note 

a. That it is continuous at the oral aperture with 
the exoskeleton. 

/3. That it ends abruptly, in front of the orifice of 
the digestive duct; terminating in a series of 
valve-like processes, one of which can be very 


II.] THE CRAYFISH AND LOBSTER. 211 

readily seen to project backwards and down- 
wards immediately in front of the intestinal 
ccecum. 

d. Examine, in like manner, the cuticular lining of the 
intestine. 

a. It is continuous with the exoskeleton, at the anal 
orifice. 

/3. It terminates abruptly, in a thickened border, 
immediately posterior to the ccecum. 

y. Examine it under a lens ; it is folded longitudinally 
and slightly spirally and beset by a number of 
short papillae. 

e. Examine the middle segment of the alimentary canal 
(head of the intestine) : it is destitute of chitinous 
lining; it bears the ccecal appendage and receives 
the digestive ducts. 

f. Examine the interior of the stomach and note the 
characters and relations of the gastric teeth. 

a. The median tooth ; a. triangular red-brown struc- 
ture, set on at the point of apposition of the two 
median ossicles. 

It will probably be seen in section. 

J3. The lateral tooth ; larger but similar in character, 
and situated (when at rest) in front of and below 
a. It is carried by the postero-lateral ossicle. 

y. The accessory lateral tooth; a small denticle, borne 
upon the posterior end of the accessory lateral 
ossicle ( 3. c). 

g. The lateral cardio-pyloric valve; a thickening of 
the side wall of the stomach, immediately below 

14 2 


212 ELEMENTARY BIOLOGY. [CHAP. 

the lateral tooth. Examine it under a powerful 
hand lens ; it is beset by short stiff setae. 

5. Carefully remove the alimentary canal, cutting the 
gullet through close to the stomach; slit open longi- 
tudinally from beneath, and examine the interior under 
water. 

a. The crushing surfaces of the lateral teeth ; note that 
they approximate anteriorly, being obliquely set. 

b. Seize the opposite ends of the stomach between two 
pairs of forceps and pull them apart. Note that 
with the divarication of the cardiac and pyloric 
ossicles the median tooth is elevated (depressed in 
life) to meet the lateral ones, which are at the 
same time rotated inwardly and slightly backwardly. 

c. Examine the free border of the chitinous lining; 
the pyloric valves (4. c. (3) can be well seen from 
this aspect. 

6. Isolate the stomach of a fresh specimen, together with 
the adjacent mouth organs. Dissect from the front and 
remove the anterior half, cutting through the gullet 
below and the cardiac ossicle above. Wash out the 
food contents and examine under water. Note 

a. The median and lateral cardio-pyloric valves 
( 4. b and g) ; they form an efficient straining ap- 
paratus. 

b. The gastric teeth. Note that they meet, when in 
action, wholly in front of a. 

c. The lesser cardio-pyloric valves ; three small setose 
eminences, on either side, adjacent to the lateral 
teeth. 


II.] THE CRAYFISH AND LOBSTER. 213 

d. Note incidentally- 

a. The metastoma; its lateral lobes are seen to be 
outwardly directed. 

ft. The coxopodites of the first maxillae ; two blade- 
like structures, curving round the bases of a to 
reach the gullet (cf. Sect. B. 4. /). 

y. The relations of the gastrolith, if present. 

7. The Gastric muscles. All are paired, those of one 
side are alone described. Dissect the cephalo-thoracic 
region from the side, removing the exoskeleton and 
body-wall to the level of the pro-cephalic process 
(p. 202). Examine, in the order given, the extrinsic mus- 
cles. A spirit specimen may be used with advantage. 

a. The anterior and posterior gastric muscles (divari- 
cators of the gastric skeleton). Those of the ex- 
posed side will be seen the anterior ; arising from 
the roof of the cardiac chamber (cardiac ossicle) 
and inserted into the pro-cephalic process : the 
posterior ; arising similarly from the roof of the 
pyloric chamber (pyloric ossicle) and inserted into 
the carapace, immediately in front of the cervical 
groove. 

b. The lev at or muscles. 

a. A conical mass, arising from the roof of the py- 
loric chamber, immediately in front of the ccecum. 
It is attached to the cervical groove (endoiergite, 
Sect. B. 2. d. /3). 

ft. Two thin strips, arising from the side wall of the 
cardiac sac, and inserted above into the mid- 
cephalic region of the carapace. They cross 
each other on nearing their insertions. 


214 ELEMENTARY BIOLOGY. [CHAP. 

c. The depressor muscles. Three sets are obvious- 
ex. Two delicate strips, arising from the cardiac sac, 

immediately above the gullet. They pass ob- 
liquely forwards and downwards, converging as 
they do so, to be attached to the sternal skeleton 
immediately in front of the labrum. 

/?. A small slip, arising from the extreme posterior 
wall of the cardiac sac, and passing downwards 
and inwards to unite with its fellow of the oppo- 
site side, prior to its attachment to the anterior 
end of the endophragmal system. 

y. A long slip, arising from the ventral wall of 
the pyloric sac, and passing between (3 obliquely 
forwards and outwards. It is inserted close to 
the base of the gullet. 

d. The dilator muscles ; small fan-shaped tracts, arising 
from the gullet and attached 

a. the anterior ones, to the adjacent exoskeleton ; 
/?. the posterior, to the endophragmal system. 

The upper anterior one may receive a depressor 
slip. 

The intrinsic muscles. Carefully dissect off the le- 
vator and depressor fibres described above and ex- 
amine 

c. The great constrictor ; a large sheet investing the 
postero-ventral half of the cardiac sac (a seeker can 
be readily inserted beneath it). Its fibres are seen 
to be interrupted by the intervention of the postero- 
ventral ossicles (3. b) to which they are attached. 

f. The lesser constrictors ; of these there are two sets. 


II.] THE CRAYFISH AND LOBSTER. 215 

a. Two tracts of fibres, arising from the head of the 
postero-ventral ossicle and attached the slender 
ventral one to the base of the antero-lateral 
ossicle ; the fan-shaped dorsal one to the postero- 
lateral bar. 

j3. A sheet of fibres, investing the side wall of the 
pyloric chamber and usually broken up into three 
fasciculi. 

The above-named constrictor muscles exercise 
a direct control over the cardio-pyloric and other 
"valves" of the straining apparatus. 

y. The cardio-pyloric muscles ; two delicate sheets, 
seen, on carefully removing the cellular roof of the 
stomach, to pass obliquely forwards and inwards 
from the lateral-pyloric to the cardiac ossicles. 

g. The anal muscles ; extremely delicate tracts, passing 
between the anal valves and the immediately ad- 
jacent wall of the intestine. 

8. The digestive gland. Its general characters have 
been previously described. 

a. Tease out a bit in water; it is made up of ccecal 
tubes, which are seen to be lined by a large celled 
epithelium. 

b. Submit a small piece to the action of i 7 solution 
of Osmic Acid until well blackened. Examine in 
water under a high power; many of the cells will 
be found to contain a fatty product, deposited in 
globules, blackened under the action of the reagent. 

c. Prepare (as directed in the Appendix) transverse 
sections of the frozen gland ; transfer them, as cut, 


2l6 ELEMENTARY BIOLOGY. [CHAP. 

to a glass slide bearing a drop of Osmic Acid solu- 
tion ; wash, when sufficiently stained, and examine 
under a high power. 

Note that the cells are arranged in aggregates 
and flattened, as the result of mutual compression. 
Look for- 

a. Hepatic cells ; characterized by the presence of 
fatty globules, differentiated as at b. Their nuclei; 
rounded or oval, each frequently surrounded by 
a clear refractive halo. 

(3. Ferment cells ; each containing a single large 
secretory globule, which does not decompose the 
Osmic Acid. Their nuclei ; larger than those of 
a and oval, they usually contain a single nu- 
cleolus. 

The larger of these cells (the older of the series) 
will be found in or near the middle of each group. 

d. Compare similar sections of material, hardened in 
alcohol and stained with borax-carmine. The nuclei 
of the hepatic cells stain with great intensity. Look 
for stages in the elaboration and discharge of the 
secretory product of the ferment cell. 

F. The excretory-organ or green gland. 

i. Dissect from the left-side, and remove the greater part 
of the exposed cephalic shield. The entire organ lies 
in the extreme front part of the cephalo-thoracic 
cavity, immediately in front of the gullet (cf. Sect. D./). 
It consists of- 

a. The glandular 'segment; a soft greenish mass, po- 
sition as above. 

b. The muscular segment ; a distensible sac, overlying 


II.] THE CRAYFISH AND LOBSTER. 2 1/ 

a. It may be rendered the more obvious by in- 
flation from the excretory orifice (Sect. B. 4. /.). 

Having inflated in, lay open the basal joint of 
the antenna ; on entering this, the neck of the sac 
becomes constricted and duct-like. 

2. Tease up a small portion of the glandular segment in 
eosin solution ; examine under a high-power. It is 
largely composed of a coiled tube, lined by a square- 
celled epithelium. 

G. The reproductive organs. 

These differ in detail, in the Crayfish and the Lobster. 
They lie partly ventral to the heart ; their general re- 
lationships have been described (Sects. A. and D.). 
Dissect the cephalo-thoracic region from the tergal 
aspect, and remove the heart. Examine the genital 
apparatus in situ. 

i . The male organs. 

a. The testis. A median greyish-white mass, bilobed 
anteriorly. 

b. The two vasa deferentia, arising where the posterior 
lobe of the testis meets the two anterior. Each is 
narrow near the gland ; its calibre increases as it 
proceeds back from it, and, becoming extremely 
convoluted, it finally ends at the genital opening on 
its own side (Sect. A. c. y). 

These ducts generally contain a dense milk-white 
product, secreted by their glandular lining (sper- 
matophoral glands}. (Cf. Sect. L. i. 


In the Lobster, the testes are two long tubes which 
extend back into the abdomen. Their posterior 
portions meet in the middle line, but in front they 


218 ELEMENTARY BIOLOGY. [CHAP. 

diverge, and at about one fourth the length of each 
from its anterior end a short transverse branch unites 
the two. The vas deferens arises a little in front of 
the middle of each testis and passes without con- 
volution towards the genital opening. Its distal half 
is dilated. 

c. Tease out a bit of the testis in water, and examine 
with i obj. : it will be seen to be composed of 
glandular tubes terminating in grape-like saccula- 
tions. In it or in the vas deferens ripe spermatozoa 
may be found : they are motionless and have the 
form of discoidal cells provided with long radiating 
processes. Stain with eosin, each will be seen to 
contain 

a. The annulate corpuscle; a transparent ring, lying 
within the middle of cell body. 

fi. The oval corpuscle ; a granular mass, lying to one 
side of a. 

In the Lobster the spermatozoa are also motion- 
less ; each consists of an elongated cell, from one 
end of which three rigid pointed processes radiate. 

2. Tine female organs. 

a. The ovary ; in shape very similar to the testis of 
the male, being bilobed anteriorly. 

b. The oviducts ; two short ducts which, like the vasa 
deferentia of the male, are directly continuous with 
the genital gland. They pass directly downwards 
to the genital openings, and can be at once seen on 
displacing the anti-penultimate walking legs to one 
side (Sect. A. c. 7). 

The oviduct is, like the vas deferens, lined by a 
glandular epithelium (cf. Sect. L. a). 


II.] THE CRAYFISH AND LOBSTER. 2 19 

In the Lobster the ovaries are elongated and pro- 
longed into the abdomen. Each is a dark green 
mass, and near their anterior ends the two meet in 
the middle line and remain confluent for a short 
distance. An oviduct arises from each ovary a little 
in front of its middle, and passes directly to the 
genital opening of its own side. 

3. The genital organs, having been first examined /;/ 
situ as above directed, may be profitably compared 
side by side, after removal from the body, together 
with their related appendages and thoracic sterna. 

A highly instructive view of them may be obtained 
from the side, dissecting as directed for Sect. I. 3. 

4. Lay open the ovary from the dorsal aspect and wash 
carefully until quite clean. Examine under water 

a. Its wall ; directly continuous with that of the ovi- 
duct. 

b. Its central cavity ; similarly continuous with the 
lumen of the oviduct. 

c. The ovisacs ; spherical masses developed within the 
wall, they are sometimes irregular in shape owing 
to mutual compression. 

Examine under a hand-lens. They vary in size, 
the younger being very minute white bodies irregu- 
larly scattered in groups throughout the mass ; re- 
move a few of these, and transfer to a glass slide. 
Stain with magenta or eosin and examine under a 
low power, avoiding pressure. 

a. The ovum ; a single large cell, filling the entire 
ovisac. Note its highly granular vitellus ; its 
large round germinal vesicle containing a number 
of germinal spots. 


220 ELEMENTARY BIOLOGY. [CHAP. 

Examine the peripheral portion of the youngest 
ovisac under a high power. Look for 

/?. The vitelline membrane; transparent and well 
defined, closely investing the ovum. 

y. The follicular epithelium ; a single layer of small 
clear cells investing the whole ; they are slightly 
flattened. 

S. The membrana propria ; a delicate cuticle in- 
vesting y. 

Look for very young ovisacs. Note the rela- 
tively small size and simple structure of the 
ovum, as compared with the older egg-cell; 
there is greater uniformity in size between it and 
the cells of the follicular epithelium. 

H. The respiratory organs. Remove the branchiostegite 
of one side and examine the gills : the functional ones 
are 18 in number, arranged in three sets. 

1. Examine the branchial-chamber; it is bounded in front 
by the cervical-groove, foremost among its contents 
are- 

a. The epipodites of the thoracic appendages ; seven in 
number, all upwardly directed. The most anterior 
one (that of the first maxillipede) is gill-less; the 
others bear each a gill {podobranchid). 

b. The scaphognathite (Sect. B. 4. h) lying in the lower 
anterior region of the branchial chamber, immedi- 
ately in front of a. Examine its base of attach- 
ment ; compare the living animal. 

2. Cut each of the gill-bearing epipodites across at its 
base and remove thus the podobranchia as a set. Pin 
down under water and examine any one in detail. 


II.] THE CRAYFISH AND LOBSTER. 221 

a. The epipodite ; a delicate chitinous lamina, folded 
upon itself and pleated posteriorly. 

b. The podobranchia ; made up of a series of gill- 
filaments set upon a central stem. 

c. Examine the same in transverse section. The lamina 
of the epipodite and the stem of the gill are con- 
tinuous. 

Cf. the Lobster : the gill is free of the epipodite, 
and the gill-filaments, which are very numerous, are 
arranged in close set parallel series. 

3. Examine the remaining 12 branchiae in situ, each con- 
sists of a central stem giving off a number of delicate 
filaments. There is nothing answering to the epipodite. 
They are arranged in two sets 

a. The arthrobranchia ; attached to the inter-articular 
membranes of the thoracic appendages, with the 
exception of the first maxillipede and the last am- 
bulatory leg. There are eleven of them, the odd 
one being related to the second maxillipede. 

b. The pleurobranchioR 

a. Functional ; a solitary gill, attached to the inner 
wall of the branchial chamber, immediately above 
the last ambulatory appendage. 

(3. Vestigial ; two to four delicate filaments (best 
seen after removal of the arthrobranchise) at- 
attached anteriorly to and in a line with a. 

In the Lobster the above are all functional. 
There are, in that animal, 20 gills on each side ; 
six podobranchiae and four pleurobranchias at- 
tached as in the Crayfish, but only ten arthro- 
branchias there being no such gill related to the 
second maxillipede. 


222 ELEMENTARY BIOLOGY. [CHAP. 

I. The circulatory organs. 

1 . Dissect away the greater portion of one branchiostegite, 
so as to expose the branchial chamber and gills un- 
injured. Place the animal on its side and drill a 
small hole in the roof of the carapace near the heart ; 
insert the point of a cannula into the same, inject 
and examine under water. Upon displacing the 
branchiae there will be seen 

a. The branchio-cardiac canals ; six well-defined chan- 
nels, running parallel with each other immediately 
beneath the inner wall of the branchial chamber. 

b. Remove the podobranchias and turn back the gills 
remaining in situ. The stem of each will be seen 
to lodge a vessel (efferent branchial vessel] those of 
a given set of branchiae uniting to form one branchio- 
cardiac trunk. 

c. Cut all the gills short and follow the branchio- 
cardiac canals upwards. They converge towards the 
region of the heart, to enter the pericardial sinus a 
spacious chamber now largely filled with injection. 

As a rule, the trunks related to the ambulatory 
appendages 2, 3, and 4 enter the pericardium in- 
dependently : the last of them receives the posterior 
trunk of the series, which brings in the blood from 
the pleurobranchia alone ; the upper ends of the 
three are connected by short anastomoses. The an- 
terior trunk is formed by the union of those related 
to the second and third maxillipedes and the chela. 

2. Dissect a specimen which has been at least 24 hours 
in alcohol, under water, from the tergal aspect, cutting 
away carefully with a pair of scissors the mid-thoracic 
portion of the carapace. 


II.] THE CRAYFISH AND LOBSTER. 223 

A chamber (the pericardial sinus] is thus laid bare 
in which lies the heart (D. i. b}. 

a. The alary muscles ; delicate strands passing from 
the angles of the heart to the adjacent pericardial 
wall. 

l>. The two dorsal cardiac apertures ; oblique openings 
in the cardiac roof, guarded by valves. 

c. Carefully dissect off the roof of the heart, and 
note 

a. Its wall ; thick and spongy, the muscular fibres 
being arranged in irregular bundles. 

(3. Its cavity; central and single ; i.e. there are no 
auricles. 

y. The ventral apertures and valves ; identical in 
their characters with b ; they are situated at the 
anterior end, transversely to the long axis. 

o. The lateral apertures ; similar perforations of the 
middle region of the side walls. Dissect to the 
level of one and examine its valves ; they are 
pocket-shaped, and so arranged as only to admit 
of a passage of the blood from the pericardial 
sinus into the heart. 

d. Compare the heart of a similar specimen, after 
removal from the body. 

3. The great arteries. Obtain afresh uninjured specimen 
and pin down under water on its side; lay bare the 
pericardial sinus with extreme care, and inject from 
the lateral cardiac aperture. Work leisurely and 
apply a steady gentle pressure. 

Cut along the post-mandibular portion of the ex- 
oskeleton to the level of the middle line (with the 


224 ELEMENTARY BIOLOGY. [CHAP. 

exception of the ambulatory appendage bearing the 
genital orifice j leave that in sitii) and remove the 
skeleton together with its related muscles, being careful 
not to injure the digestive or reproductive organs. 

Cut along the dorsal middle line of the cephalic 
skeleton, and continue the incision downwards, clear 
of the green-gland. Remove the hard parts, but leave 
the adductor muscle of the mandible in situ. Dissect 
away any extraneous tissue and wash carefully. 

a. The superior abdominal artery ; a backward con- 
tinuation of the heart, immediately above the 
intestine. It distributes branches metamerically 
to the intestine (hind-gut) and adjacent parts. 

b. The ophthalmic artery; a similar forward continua- 
tion of the anterior end of the heart. It runs over 
the stomach and distributes branches to the eye 
stalks and parts immediately adjacent. 

c. The hepatic artery. Turn the exposed digestive 
gland downwards; branches of the above vessel 
will be seen ramifying in it. Cut its main trunk 
across and remove the gland, noting the branches 
to the mid-gut ; the main trunk can now be traced 
beneath the genital gland, to its origin, from the 
antero-ventral region of the heart. 

d. The sternal artery ; a large trunk, arising from the 
heart at the base of a. It runs vertically down- 
wards towards the ventral surface, passing to one 
side of the intestine, and perforating the nervous 
system (obvious as a delicate greyish median-ven- 
tral cord. Cf. Sect. J.). It subdivides into 

a. The antero-ventral artery ; a median trunk, ex- 
tending forwards to the mouth region, and dis- 


II.] THE CRAYFISH AND LOBSTER. 22$ 

tributing branches metamerically to the appen- 
dages, muscles and parts adjacent. 

(3. The postero-ventral (inferior-abdominal) artery ; 
a median trunk extending back to the telson. It 
also distributes branches metamerically to the 
adjacent parts. 

The above trunks furnish the main vessels to 
the reproductive organs. They are, on either 
side a dorsal one, arising from the sternal artery 
soon after it leaves the heart and distributed 
to the genital gland and duct; a ventral one, 
arising from the base of /?, and distributed to the 
terminal segment of the duct alone. 

The sternal trunk may pass to either side of the 
alimentary canal. If the injection be successful, 
it will be found that the vessels distributed to the 
ends of the intestine and genital ducts debouching 
on to the exterior, terminate in special capillary 
networks. 

e. The antennary artery ; arising from the antero- 
dorsal region of the heart, immediately external to 
b. Its main trunk runs downwards and forwards, 
passing round (external to) the adductor mandibuli 
muscle and immediately under the carapace, to 
terminate anteriorly in the antenna. It gives off 
on its course 

a. The gastric artery ; arising close behind the pos- 
terior gastric muscle, and distributed to the 
stomach (fore-gut). 

fi. Branches to the gastric muscles, several en route. 

y. A rostro-antennary branch ; arising from the main 
M. 15 


226 ELEMENTARY BIOLOGY. [CHAP. 

trunk at the base of eye-stalk, and distributed to 
the antennule and rostrum. 

8. The renal arteries ; two or more branches break- 
ing up on the anterior face of the green gland. 
. Other minor branches, which are variable. 

4. Puncture any one inter-sternal membrane of a freshly- 
killed animal ; blood will escape freely (a blood space 
has been entered). Treat the inter-articular mem- 
brane between the two last thoracic sterna similarly ; 
insert the point of a cannula and inject. 

a. Remove the branchiostegite and examine the 
branchiae. The injection will have filled some of 
the afferent branchial vessels ; large trunks running 
(one for each gill) along the outer face of the stem 
externally to the efferent vessel ( I. b.). 

b. Make a transverse section across the thoracic region. 
With a little care the afferent branchial vessels can 
be traced to a great ventral sinus (sternal sinus) 
now largely injected. It is in free communication 
with the adjacent blood-spaces. 

5. The blood. Obtain a drop of blood, from a freshly- 
killed Crayfish and examine under a high power. 

a. The plasma ; colourless. 

b. The corpuscles ; colourless and amoeboid, each with 
a large round nucleus. Their pseudopodia ; fili- 
form and frequently very numerous. 

Watch their movements ; they exhibit a great 
tendency to run together into aggregates prior to 
disintegration, upon exposure, after removal from 
the body. 


II.] THE CRAYFISH AND LOBSTER. 22/ 

J. The nervous system. 

i. Pin the animal down tergal surface uppermost and lay 
bare the whole body cavity. Remove the heart, 
reproductive and renal organs and the digestive gland; 
sever the alimentary canal across its middle and turn 
the two halves to one side; cut short the tendon of 
the adductor mandibuli muscle, and remove the flexor 
abdominis, together with the endophragmal system. 
The whole nervous axis will thus be laid bare. 

a. The supracesophageal ganglia ; two considerable 
masses, confluent in the middle line, situated at 
the base of the rostrum immediately behind the 
eye-stalks. 

b. The circumossophageal commissures passing back 
from a. 

c. The longitudinal ventral commissures; backward 
continuations of b, extending to the base of the 
telson. They are widely separated in the mid- 
thoracic region, where they enclose the sternal 
artery (seen in transverse section. Cf. Sect. I. 3 d.) ; 
elsewhere they are closely applied. 

d. The abdominal ganglia ; six paired masses, borne 
upon c in the abdominal region. They are equi- 
distant, there being one pair for each somite. The 
posterior pair are larger than the rest, and distribute 
fibres to the last somite and the telson. Note, in 
relation 

a. The ganglionic nerves ; paired trunks arising from 
the ganglia. 

y8. The inter- ganglionic nerves; arising from the 
longitudinal commissures, alternately with a. 


228 ELEMENTARY BIOLOGY. [CHAP. 

e. The suboesophageal ganglion ; a large oval mass, 
situated immediately behind the gullet. It dis- 
tributes nerves to the mandibular and five following 
somites. 

f. The thoracic ganglia; five pairs, each somewhat 
larger than the abdominal, distributing nerves to 
the five posterior thoracic somites. 

a. T\\.Q posterior pair ; situated in front of their cor- 
responding somite, and consequently far removed 
from the first abdominal pair. This is seen to 
be the result of approximation towards the pair 
in front, the two lying close together immediately 
behind the passage for the sternal artery. 

J3. The second and third pairs ; similarly but less 
conspicuously approximated, in front of the 
artery. 

y. The anterior pair ; equidistant between ft and 
the suboesophageal ganglion. 

2. The nerves of the supracesophageal ganglion. Carefully 
remove one half of the rostrum and lay open the 
eye-stalk of the same side. Note, passing into the 
latter 

a. The optic nerve ; a thick tract, arising from the 
anterior end of the ganglion and expanding within 
the eye-stalk to form the optic bulb. 

b. The antennulary nerve; a delicate trunk, arising 
from the outer border of the ganglion; it passes 
outwards and forwards to enter the base of the an- 
tennule. 

c. The antcnnary nerve ; a similar trunk, arising from 
the hinder region of the ganglion ; it passes back- 


II.] THE CRAYFISH AND LOBSTER. 22Q 

wards and downwards to reach the base of the 
antenna. 

3. Examine the circumcesophageal commissures under a 
lens ; they will be seen to be connected by 

a. The postoesophageal commissure ; a delicate trans- 
verse band, slightly in front of the suboesophageal 
ganglion. 

b. The antossophageal commissure ; a similar structure 
to a, arising at the sides and passing round the front 
of the gullet. 

c. The median-ventral commissure; a very delicate 
trunk, passing back from the supracesophageal 
ganglia in the middle line, to meet b. 

d. The anterior visceral nerve ; a median nerve arising 
from the point of union between b and c; it passes 
upwards and forwards to reach the roof of the 
stomach, upon which it subdivides for distribution 
to its walls. 

e. The posterior visceral nerves arising, one on either 
side, from the last abdominal ganglia. They pass 
slightly backwards to reach the base of the intes- 
tine, the side walls of which they skirt. 

4. A companion dissection may profitably be made, by 
bisecting the whole body a little to one side of the 
middle line. 

The real double nature of the entire nervous axis 
may best be appreciated by removing it and examin- 
ing it on a blackened surface, under water. 

5. a. Tease out a bit of perfectly fresh nerve-cord in 

water and stain with magenta or eosin. 


230 ELEMENTARY BIOLOGY. [CHAP. 

Composed of slender fibres of variable size, each 
consisting of a structureless outer wall, surrounding 
a finely granular or obscurely fibrillated central 
axis. Nuclei ; seen at intervals. 

b. Tease up in water, a ganglion which has been 
treated with osmic acid. 

Composed of large oval branched cells, each 
consisting of a granular mass in which lies a clear 
round nucleus, containing a nucleolus. 

K. The sense organs. 

i. The auditory organ. This lies in the basal joint of 
the antennule and is best examined in the Lobster. 
The upper surface of this basal joint is flat posteriorly 
and arched in front. It bears several tufts of setae : 
one of these is very small and lies at the inner side of 
the flattened surface, just at the angle where it meets 
the arched part ; among these setae is the opening into 
the auditory sac, through which a bristle can easily be 
passed. 

a. Take a fresh antennule from a Lobster and cut 
away the under surface of its basal joint, with a 
scalpel. A transparent chitinous sac will readily be 
found in it, among the muscles ; this is the auditory 
sac and is about \ of an inch long. Carefully dissect 
it out. 

b. If this sac be held up to the light a little patch of 
gritty matter will be seen on its under surface near 
the external aperture. Behind this can be seen a 
curved opaque line; behind this, and concentric 
with it, a shorter brownish streak. Cut out carefully 
the part of the sac which bears these marks : mount 


II.] THE CRAYFISH AND LOBSTER. 231 

in sea-water or salt solution and examine with one- 
inch objective. 

a. The gritty matter will be seen to consist of a 
number of irregular earthy particles, largely, if 
not wholly, foreign to the organism ; they are 
functional as otoliths. Carefully remove them 
with a camel-hair brush. 

/?. The white line will be seen to answer to a ridge, 
on the summit of which is a row of large setae 
(auditory setce. or hairs), and both on the brown 
patch and on the opposite side of the main row 
will be seen scattered groups of smaller setae. 

c. Examine with -| obj. 

a. Each auditory seta is now seen to be covered over 
its whole surface with numerous very delicate 
secondary setse ; these are shortest near the base 
of the primary one. Towards its base each of the 
primary setse is constricted and then dilates into 
a bulbous enlargement for articulation upon the 
wall of the sac. 

ft. The brown patch is seen to owe its colour to 
a single layer of polygonal epithelial cells con- 
taining pigment granules. 

y. By focussing through this epithelial layer a num- 
ber of parallel fibres will be seen passing up, one 
to the base of each seta of the main row. 

S. If a perfectly fresh auditory sac be put in i per 
cent, solution of osmic acid for half an hour, and 
be then well washed in distilled water and ex- 
amined, each of the fibres mentioned above (ul- 
timate ramifications of the auditory nerve) will be 


232 ELEMENTARY BIOLOGY. [CHAP. 

seen to terminate, near the free end of the seta, 
in an elongated end organ. 

The auditory sac in the Crayfish is very similar 
to that in the Lobster, and may be examined in a 
similar way. It is, on the whole, not so good, 
chiefly on account of its smaller size. 

2. Examine, in the Crayfish, the exopodite of the an- 
tennule; it exceeds the endopodite in calibre and 
length, and is carried, during life, upwardly directed. 
(Cf. Sect. B. 4 ;;/.) Remove it from the rest of the 
appendage and examine in water, under a low power. 

a. Its settz ; short filaments, developed from the an- 
terior borders of the several joints. 

b. Its sensory setce; developed in tufts, from the under 
face of the filament. There are usually two sets 
for each segment and they slope obliquely down- 
wards and forwards. 

c. Examine under \ or |- obj. Each seta is seen to be 
subdivided into two segments ; a shorter basal one 
and an elongated terminal one: in the ordinary 
setse the latter is pointed, in the sensory ones it 
is expanded and spatulate. 

More or fewer of the terminal segments of the 
sensory setae are, not unfrequently, globular and 
abnormal. 

3. The visual organ. Place the eye of a Crayfish for 
four or five days in 0*5 per cent, solution of chromic 
acid and then for twenty-four hours or more in 
alcohol. 

a. Strip off a portion of the cornea and examine under 
a \ obj. It is marked out into a great number of 


II.] THE CRAYFISH AND LOBSTER. 233 

minute facets; mostly square, more rarely hexagonal 
or irregular. 

b. Tease up in weak glycerine a portion of the con- 
tents which underlie the cornea. Look for 

a. Crystalline cones ; elongated angular transparent 
bodies, each of which may or may not be in con- 
tinuity with 

(3. A striated spindle ; fusiform and about a third 
the length of a. It is beset by blackish transverse 
striae. 

c. Imbed an eye similarly prepared and cut a number 
of longitudinal sections from it : mount in glycerine 
and examine under one inch objective. Look for 
the sections which have passed through its middle; 
they will be seen to present a central mass (optic 
bulb. Cf. Sect. J. 2 a.) from which a number of lines 
appear to radiate to the facets on the surface. 
These radiating lines (which are obscured here and 
there by concentric pigmented layers) are indica- 
tions of the striated spindles and crystalline cones. 

a. The exoskeleton ; calcified to form two segments, 
a smaller basal annular one and a larger terminal 
dome-shaped one, united by an inter-articular 
membrane (Cf. Sect. B. 4 ;z.). That of the ter- 
minal segment is thick and dense, except where 
it overlies the crystalline cones ; there it is thin 
and transparent, forming the cornea. 

(3. The muscles; seen on either side, immediately 
beneath a, they pass between the two segments, 
as between those of any one appendage. (Cf. 
Sect. C.) 


234 ELEMENTARY BIOLOGY. [CHAP. 

y. The intermediate mass ; a plug of vacuolated con- 
nective tissue, filling up the entire interspace be- 
tween the optic bulb and the muscles. 

d. Examine your thinnest section with a high power. 
Beginning at the exterior make out successively 

a. The corneal facet ; its flat outer and slightly ex- 
cavated inner surface. 

/3. The crystalline cones. Cf. supra. Each is in 
close apposition with the inner face of a corneal 
facet. 

y. The striated spindles ; cf. supra. They are dis- 
posed lineally with (3. 

8. The connective rod. Each is widest in front 
where it joins the cone, but narrows posteriorly 
where it is continuous with the striated spindle. 
If fresh eyes be treated with osmic acid and then 
teased out, each of these rods can be split up 
into four fibres. 

e. The sheath of the above ; a nucleated investment 
for each set of constituents. Pigment is de- 
posited therein, being densest around the outer 
ends of the cones and the greater portion of the 
spindles, whence the appearance of the two black 
zones seen under the low power. 

. The layer of nerve fibres ; passing between y 
and the optic bulb. Look for them in places 
where the pigment may have fallen away. 

17. The optic bulb; mainly composed of delicate 
fibres and small cells with large round nuclei, 
partly scattered, partly aggregated into two oval 


II.] THE CRAYFISH AND LOBSTER. 235 

central masses (gangliform bodies) which stain 
deeply. 

A zone of pigment is deposited at its outer 
border. 

L. Development. 

1. Examine the under surface of the body of a living 
female "in berry." 

a. The fertilized ova each is attached to the setae 
which fringe the swimmerets, by a delicate peduncle. 
Make an incision into one : the ovum will be 
liberated; the peduncle will be seen to be deriva- 
tive of an egg-capsule which remains behind (a secre- 
tory product of the oviduct, cf. Sect. G. 2 b.). 

b. Examine the thoracic sterna ; aggregates of sperma- 
tophores will in all probability be found adherent to 
the hinder ones, having been deposited by the 
male. 

Tease one up ; it consists of a bundle of sperma- 
tozoa, enclosed in a dense milk-white sperm- 
capsule (a secretory product of the vas deferens. 
Cf. Sect. G. i b.). 

Spermatophores may frequently be found project- 
ing from the reproductive orifices of the male, if 
killed during the breeding season. 

2. Remove the developing ova from time to time from 
the body of the parent, and dissect off their egg-cases 
with a couple of needles. Transfer to picric acid 
solution and harden in alcohol. Look for 

a. The segmenting ovum. Examined under a low 
power, its exterior appears slightly granulated. 
Imbed and cut sections ; stain with carmine. Note 

a. The food yolk ; aggregated centrally, and chiefly 


236 ELEMENTARY BIOLOGY. [CHAP. 

deposited In conical masses whose bases look 
outwardly. 

/?. The dear protoplasm; forming a superficial in- 
vestment for the whole. Nuclei are regularly ar- 
ranged within it. 

y. The blastomeres ; segmentations of /3, around the 
nuclei. The furrows which mark them off do not 
extend into the yolk-laden protoplasm. 

b. The same at the gastrula stage. Easily recognisable 
by the large horse-shoe shaped blastopore. 

Make sections of the area of invagination, 
through the long axis of the blastopore. Note 

a. The ectoderm; now established as a superficial 
layer investing the whole. 

/?. The endoderm; a small sac, derived from a by in- 
vagination, completely enclosing the archenteron. 

c. The same, at a slightly later stage. Look for speci- 
mens having on the surface a shoe- shaped white 
patch (blastoderm], immediately in front of the 
blastopore now greatly reduced in size. Preserve 
as before, stain and examine en face. 

a. The blastoderm; shoe-shaped or heart-shaped, 
thickened and expanded in front to form two 
rounded procephalic lobes. 

/?. The blastopore ; a small oval aperture, at the 
extreme hinder end of a. 

y. The abdominal papilla; a median outgrowth of 
a, immediately in front of the blastopore. 

d. The same, at a later stage. Look for specimens in 

which the blastopore has disappeared. Treat as atr. 


II.] THE CRAYFISH AND LOBSTER. 237 

a, The appendages; paired differentiations of the 
blastodermal area, separated by a median space 
(more or fewer will be seen). 

(3, The labrum; an oval median outgrowth, situated 
about on a level with the first pair of appendages. 

y. The abdominal papilla ; now elongating. 

If the specimen be a young one the involution 
to form the mouth may be seen immediately 
behind the labrum; that to form the anus, under 
cover of the abdominal papilla. If it be an 
advanced one, segmentation of the papilla will be 
very distinct. 

8. The optic pits ; two small round differentiations 
within the procephalic lobes (c. a.). 

e. The carapace; now appearing as a marginal thick- 
ening of the blastoderm, immediately external to 
the appendages. It is at first paired, the two 
folds meeting behind the abdominal papilla. 

t. The hatched embryos. To be found in numbers, 
fixed to the swimmerets of the mother. 

In general they resemble broadly the parent or- 
ganism. Examine 

a. The cephalo-thorax ; more arched than that of the 
adult, owing to distension by the food-yolk, not 
yet completely absorbed. The rostrum is bent 
downwards and the cervical groove is, at best, ill 
defined. 

fi. The cephalo-thoracic appendages ; differing but 
little from those of the adult. Remove and 
examine the free-end of the chela ; its pincers 


238 ELEMENTARY BIOLOGY. [CHAP. 

apparatus is spinous and recurved at the tips, 
for purposes of attachment to the parent. 

y. The abdomen ; fully segmented and terminating 
in the telson. Four pairs of appendages are 
alone free, the first and last pairs being buried 
beneath the larval integument. 

e. Look for and examine stages intermediate between 
c and d. 

f. The larval Lobster, when about half an inch in 
length. Obtain if possible a specimen in which 
the abdominal appendages are first appearing. 
Compare generally with the Crayfish larva and note 
especially 

a. The exoskeleton ; like that of the Crayfish larva, a 
continuous uncalcified cuticle. 

/?. The carapace; terminating in front in the ros- 
trum, which assumes the form of an immense 
protective spine. 

y. The abdomen; fully segmented and bearing several 
smaller protective spines. 

8. The eye; its great size at this stage. 

e. The antennary organs ; both are short and com- 
pletely under protection of the rostrum. 

. The thoracic appendages. The third maxillipede, 
great chela and ambulatory appendages, are more 
nearly uniform in size than in the adult ; they 
all bear well developed exopodites. 

i 

. Remove the second ambulatory appendage and 
the swimmeret of the third abdominal somite. 
Examine them side by side, and note in both- 


II.] THE CRAYFISH AND LOBSTER. 239 

a. The great relative size of the protopodite. 

(3. The increase in length of the endopodite over the 
exopodite ; little marked but obvious in the case 
of the abdominal appendage. (Cf. the cor- 
responding abdominal appendage of the adult 
Crayfish.) 


III. 

THE EARTHWORM (Lumbricus terrestris}. 

THE Earthworm is to be found wherever damp earth is 
accessible, no matter how hard or stony the surface; the 
presence of moisture is indispensable to its existence. Into 
this earth it burrows, excavating a tubular habitation to 
which it repairs during the day time, emerging at night to 
seek food and to work, or at early morning to reproduce its 
species. It remains within the burrow throughout both the 
winter and the dry summer seasons. 

The interior of the burrow is smooth and frequently lined 
with minute stones ; its mouth is often surrounded with 
"castings" and plugged with leaves drawn in by the animal 
itself, or covered, as with a lid, by stones sometimes of 
relatively great weight and size. 

The body of the worm is fairly uniform in dimensions 
throughout; it is bilaterally symmetrical, both mouth and 
anus being situated at opposite ends. The metameric 
symmetry such as was seen in the abdomen of the Crayfish, 
is here common to the whole body, which can no longer be 
subdivided into well-marked regions. It is constricted 
externally into a number of repetitional segments or somites, 
of which there may be, in a sexually mature animal, as few 
as 68 or considerably more than 200. For each of these 
somites there is a similar repetitional series of certain of the 
internal organs. Each somite is subdivided externally into 


III.] THE EARTHWORM. 241 

at least two lesser divisions or zonites, these however are but 
skin deep and in no way correlated with the internal parts. 
The body is invested in a continuous uncalcified exoskeleton 
in the form of a delicate iridescent cuticle. No limbs of 
any sort are present, and locomotion is effected by means of 
four longitudinal series of bristle-like setce, which project 
freely from all but some few of the anterior segments ; a 
powerful muscular apparatus is developed in connection 
with each of these, and the chitinous setae themselves are 
largely buried in tegumental sacs lined by cuticular invo- 
lutions. The setae are replaced when cast off. 

The posterior terminal segments of the body are, during 
life, flattened from above downwards, and when the animal 
on removal from its burrow is observed crawling, a charac- 
teristic spatulate appearance is imparted to that region, at 
the upturned end of which the anus is situated. Under 
ordinary circumstances the worm, on coming to the surface, 
retains its hold on its burrow by means of this expanded 
extremity. 

The Earthworm is omnivorous, living mainly upon leaves 
(for certain kinds of which it has a decided preference), and 
less conspicuously upon both animal and vegetable organ- 
isms ingested with the earth passed through its alimentary 
canal, in burrowing or otherwise. The alimentary canal is 
a straight tube, running the entire length of the body. The 
mouth leads into a thin-walled eversible buccal sac, which 
opens into a spacious muscular suctorial pharynx ; this, in 
turn, passes into a long tubular oesophagus, the terminal 
fifth of which is enlarged to form a distensible crop. The 
crop is, in the common earthworm, succeeded by a whitish 
thick-walled gizzard, so called as it performs a mechanical 
crushing action. This finally opens into a long sacculated 
intestine, which is continued on with but slight modification 

M. 1 6 


242 ELEMENTARY BIOLOGY. [CHAP. 

to the hind end of the body, where it communicates with 
the exterior by a valvular laterally compressed anus. The 
absorptive area of the intestine is increased by the develop- 
ment of a conspicuous intestinal-valve or typhlosole which 
lies along its whole roof, and not by a coiling of the whole 
viscus as in the case of the Frog. 

The intestinal wall is invested in a yellowish-brown 
mass sometimes termed a "liver." This tissue has no sort 
of connection with the lumen. of the gut; it is intimately 
associated with the walls of the great blood-vessels, many 
of which it completely surrounds, and there is reason for 
regarding it as functional in the formation of an excretory 
product which is discharged into the body-cavity, if not in 
that of some constituent of the blood also. 

The intestinal juice of the Earthworm contains a di- 
gestive ferment, and there open into the mouth-cavity a 
number of small so-called "salivary" glands. Digestion 
is nevertheless not wholly intra-intestinal, for the animal 
when feeding vomits a digestive fluid ; this is allowed to 
act upon the raw food material for some time, prior to its 


ingestion. 


Digestive glands other than those just named are un- 
known, and such diverticula of the alimentary canal as 
remain for consideration are somewhat remarkable, and 
little understood physiologically. There are usually three 
pairs of cesophageal pouches, lying midway between the 
crop and pharynx; they are smallest in winter, and it not 
unfrequently happens that one or more of them may be 
absent. Occasionally, their connections with the lumen of 
the oesophagus may become obliterated, and in rare cases 
no trace of them is to be found. These cesophageal diver- 
ticula are highly vascular, and contain a milk-white product 
consisting of carbonate of lime either in a finely divided 


III.] THE EARTHWORM. 243 

state or in concretionary masses sometimes reaching a 
diameter of i millim. Such being the case they are termed 
calciferols glands, but the purpose served by them is as yet 
not fully understood. 

The body-wall is invested in a single layer of elongated 
epidermal cells, many of which become converted into 
small unicellular cutaneotis glands. This investing epi- 
thelium of the body and the cuticle which it secretes (vide 
supra] are continuous respectively, at the mouth and anus, 
with the epithelial lining of the alimentary canal and its 
cuticular product. The greater mass of the body-wall is 
however composed of two sets of muscular fibres, an ex- 
ternal circular set and an internal longitudinal one; these 
also pass, at opposite ends of the body, into an internal 
circular and an external longitudinal series of fibres entering 
into the composition of the wall of the digestive tube. The 
two walls are widely separated by a spacious body-cavity, 
the alimentary canal being suspended by a series of trans- 
verse mesenteric septa, instead of by a median longitudinal 
fold as in the Frog. These septa are metamerically ar- 
ranged, one for each somitic constriction; circular muscular 
fibres are developed within them and radial ones pass across 
them from body-wall to wall of alimentary canal. The 
body-wall is lined internally by a peritoneum, clad in 
tessellated epithelium, which can be traced on to both the 
mesenteric septa and the free surfaces of the various organs 
contained within the body-cavity. It is from this layer that 
the yellow brown tissue aforenamed takes its origin. The 
walls of the body and alimentary canal are thus seen both 
to consist of at least three clearly defined layers; a pro- 
tective cuticular, an epitheloid, and a mechanical mus- 
cular one respectively. These layers are continuous at 
both mouth and anus, and the order of succession is the 

1 6 2 


244 ELEMENTARY BIOLOGY. [CHAP, 

same for each except that that which is external in the one 
wall is internal in the other and vice versa. 

The body-cavity is subdivided by the mesenteric septa 
into a series of somitic compartments, and the metameric 
symmetry thus established extends to the excretory organs, 
there being one pair of these attached to each septum, the 
first three somites excepted. These organs, being thus 
segmentally arranged, are termed segmental organs or 
nephridia. Each consists of a tortuous tube which can be 
resolved into three segments; a middle glandular one, 
abundantly supplied with blood-vessels, passing internally, 
into a delicate thin-walled loop, which perforates the 
mesentery and opens into the segment in front by means of 
a ciliated funnel or nephrostome externally, into a vesicular 
muscular segment, which communicates with the exterior in 
the vicinity of the ventral pair of setae. The lining mem- 
brane of these excretory tubules is profusely ciliated, and a 
current is thus induced from within outwardly. In addition 
to the indirect communication established, through the 
agency of the nephridia, between the body-cavity and the 
exterior, a direct one is instituted by means of a metameri- 
cally disposed series of median dorsal or peritoneal pores. 
The precise function of these is as yet not fully understood. 

The mesenteric septa themselves are incomplete ventrally; 
they do not subdivide the body-cavity into a series of closed 
chambers. As this is so, it follows that that cavity is a con- 
tinuous one in open communication with the surrounding 
medium. It contains during life a colourless perivisceral 
fluid, in which there are present immense numbers of 
nucleated amoeboid corpuscles. 

The true red-blood fluid circulates in a system of vessels, 
having, so far as is known, no direct communication with 
the body-cavity. The larger trunks of this circulatory 


III.] THE EARTHWORM. 245 

system are six in number; median longitudinal supra and 
subintestinal and supra and subneural vessels respectively, 
and two small lateral neural ones. These are connected 
metamerically in a manner described in the Laboratory 
work (p. 261), and highly efficient capillary systems are 
established in connection with them. In the segments 
numbering six to twelve, there exist two sets of vessels not 
met with elsewhere. These are, firstly, six pairs of enlarged 
rircumcesophageal vessels, connecting the supra-intestinal 
and supra-neural trunks and sometimes termed pseudo- 
hearts; secondly, a pair of lateral cesophageal trunks, which 
are connected with the supra-intestinal vessel in the twelfth 
segment alone. The latter vessels are specially concerned 
with the blood supply to the anterior portion of the ceso- 
phagus and its calciferous glands. A condition somewhat 
exceptional in the animal kingdom is met with in the blood 
vessels of the ditellum, and less conspicuously of the body- 
wall generally ; where the superficial capillaries pass up 
and ramify among the actual epidermal cells themselves, 
giving rise to an epidermal blood plexus. 

The exact seat of respiration in the Earthworm is not fully 
determined, but there can be little doubt that the red-blood 
fluid is directly concerned in the process. This fluid con- 
sists of a watery plasma in which are suspended exceedingly 
minute transparent non-nucleated corpuscles. These are 
somewhat variable in shape and size, being usually about 
the smooth of an mcn m length; their structural features 
agree closely with those of the nuclei of the epithelial lining 
of the vessels in which they circulate. 

The feature which most clearly distinguishes the red- 
blood fluid of the worm from that of the Frog, is that its 
colouring matter is diffused through the plasma and in no 
way related to the corpuscles. 


246 ELEMENTARY BIOLOGY. [CHAP. 

The nervous system is in an exceedingly simple and in- 
teresting condition. It consists of two pear-shaped supra- 
(Ksophageal ganglia which abut together in the middle line 
in front; from these there arise two commissures which, 
like those of the Crayfish, run longitudinally side by side 
for the whole ventral surface. These commissures are 
somewhat enlarged for each somite, and there arise from 
them a metamerically repeated series of nerve trunks. The 
supra-cesophageal ganglia distribute fibres to the buccal 
sac and to the anterior end of the body; the latter termi- 
nate in modified sensiferous cells borne upon the first seg- 
ment, which constitute all that the worm has in any way 
representative of sense organs. One of the most important 
facts concerning the nervous system of this animal, is the 
disposition of the nerve-cells. These, instead of being re- 
stricted to the ganglia, as they are in the Crayfish, are 
regularly diffused throughout the entire axis gangliform 
enlargements and longitudinal commissures alike. The 
sheath of the nervous axis is remarkable in being muscular, 
and especially as concerns the existence of a dorsal neuro- 
chord made up of three longitudinally disposed "tubular 
fibres." These fibres are highly elastic, and the muscular 
sheath forms a most efficient protective apparatus. 

The proper reproductive organs are restricted to seven of 
the anterior segments, and will be found described on p. 268. 
They are somewhat complicated, chiefly owing to the con- 
ditions of maturation of the seminal vesicles ; but the actual 
genital glands, though exceedingly small, are well defined. 
The ripe ovum consists of a round nucleated cell contain- 
ing a moderate food-yolk, and invested in a vitelline mem- 
brane. The sperm-producing cells undergo changes which 
result In the formation of a number of filiform spermatozoa, 
each with an elongated nucleus-bearing " head ;" and the 


III.] THE EARTHWORM. 247 

conditions are such as to render observation upon the ma- 
turation of these exceedingly easy and instructive. 

The worm is hermaphrodite but not self-impregnating. 
During copulation which usually takes place at early 
morning the bodies of two individuals are brought into 
apposition, and a transfer of ripe spermatozoa takes place. 
These are passed into definite seminal receptacles, there to 
await final deposition. During the interval which follows 
there is secreted by the clitellum an egg capsule or cocoon, 
within which functionally mature ova and spermatozoa are 
ultimately deposited. Segmentation of the fertilized ovum 
is holoblastic, and there result two layers of cells a more 
rapidly dividing one, which differs from that described for 
the Frog mainly in the absence of pigment, and a less 
rapidly dividing yolk-laden one. The smaller cells over- 
grow the larger ones very rapidly, and there results a simple 
two-layered sac or gastrula which becomes ciliated ex- 
ternally. The embryo early assumes a bilaterally sym- 
metrical form, and as the body elongates there are de- 
veloped, mainly if not entirely from the archenteric wall, 
a series of paired cellular masses which become metameri- 
cally arranged. The segmentation of the body receives its 
initiative in the appearance of these mesoblastic somites; from 
the central cavities ultimately developed within them the 
body-cavity is derived, while their walls, coming into apposi- 
tion antero-posteriorly, give rise to the mesenteric septa. 

The nervous system arises as a thickening of the investing 
epiblastic layer, and the supra-intestinal vessel when first 
formed is paired. The larva continues to elongate by the 
addition of fresh segments at its hinder end, but the sim- 
plicity and uniformity of structure so characteristic of it, is 
retained with but slight modifications by the adult animal. 

The clitellum, to which reference has been made, must 


248 ELEMENTARY BIOLOGY. [CHAP. 

not be regarded as in any way distinctive of the adult worm. 
It undergoes a periodic enlargement, and may be present in 
young worms but two inches in length or absent in fully 
formed ones of six or eight. 


LABORATORY WORK. 

The unnatural displacement of the organs of this animal, 
resultant upon contraction of the muscles during death 
under chloroform, may be entirely obviated by killing the 
worm in alcohol. Let it be immersed in methylated spirit 
for two minutes, and- allowed to remain in running water for 
half an hour. 

A. General external characters. 

1. Examine the living worm and note 

a. Its shape, elongated. Rounded and pigmented 
dorsally - - flattened and whitish ventro-laterally. 
Anteriorly it tapers off to a point, posteriorly it is 
flattened and spatulate. 

2. Compare the body of the dead animal, killed as 
above. Note 

a. Its subdivision by a number of constrictions into a 
recurring series of body segments or somites. Each 
of these is again subdivided by a lesser constriction 
into two zonites. 

The zonites of the genital segments (9 to 15) are 
frequently more numerous, though they never exceed 
four in number. 

b The ditellum or cingulum (if present, vide supra), 
a whitish saddle-shaped enlargement usually re- 


III.] THE EARTHWORM. 249 

stricted to segments 29 to 35 (rarely 30 36 or 
2936). 

This is best studied in a chloroformed specimen. 

The capacity of the whole body is greatest at this 
point. Posteriorly to the clitellum it is uniform in 
calibre, except for the postero-terminal region (cf. 
I. a), where its transverse diameter is greatest. An- 
teriorly, it is enlarged in the genital region (segments 
8 to 12) tapering off to a point in front. 

c. The locomotor organs or seta, four double rows 
(two lateral and two ventral) of bristle-like ap- 
pendages, which project freely from all but the 
extreme anterior and posterior segments. 

The body is flattened ventrally between the two 
sets of ventral setae, and laterally between the 
lateral and ventral ones. The setae project out 
at the angles formed by these flattened areas, the 
lateral ones arising within the limits of the pig- 
mented portion of the body-wall. 

d. The apertures. 

a. The mouth, antero-terminal. It perforates the 
first segment, which is subdivided into a dorsal 
prostomium which overhangs the mouth, and a 
circumoiail. jperisfomtum. Examine the latter with 
a lens ; its free edge is delicately serrated. 

Compare the living animal. The movements of 
the body clearly show that the first segment is 
highly sensitive. 

/:?. The anus, postero-terminal, and laterally com- 
pressed. It perforates the last segment. 
Note the valve-like nature of its lips. 


250 ELEMENTARY BIOLOGY. [CHAP. 

y. The dorsal or peritoneal pores ; small median per- 
forations of the body-wall, lying at the bases of 
the somitic constrictions between all but some 
few of the anterior segments. They are best 
seen in specimens which have been preserved 
in spirit. If examined in freshly killed worms, 
their presence can be made manifest by gently 
squeezing the body, whereupon there will exude 
from each a drop of perivisceral fluid. 

S. The sexual apertures. Examine the worm from 
beneath, and note the presence of two glandular 
enlargements immediately external to the ventral 
setae of the i5th segment. Each surrounds the 
slit-like orifice of the vas deferens of its own side. 
Opening, in a line with the above, on to the 
surface of the i4th segment, there are the smaller 
apertures of the oviducts. 

The ventral integument of segments 9 to n 
(more rarely 8 to 12) is generally swollen, like 
that of the lip of the vas deferens or the clitellum, 
owing to the presence of the so-called capsulo- 
genous glands. 

The exact function of these is at present un- 
known. 

Examine the somitic constrictions in this 
region from the side. There will be found, 
opening upon those which subdivide segments 
9 10 and ic n in a line with the lateral setae, 
the small apertures of the spermathecce. 

Not unfrequently one or other of these may 
open by two orifices, and their presence may 
easily be demonstrated by gently squeezing the 
body. 


III.] THE EARTHWORM. 251 

e. The orifices of the excretory or segmental organs, 
too minute to be examined here. They are best 
seen in section. (Cf. Sect. H. T. c.} 

B. The setae and exoskeleton. 

i. Remove one of the setae from a post-genital segment 
with a small pair of forceps, and examine in water 
under a low power. Note 

a. Its form, curved and needle-shaped, blunted inter- 
nally and terminating in a point. 

b. Its structure. Examine under a high power. It 
consists of a chitinous rod, a portion of the central 
axis of which is soft and granular. 

The setae vary somewhat in shape and calibre in 
different regions of the body, especially so in the 
clitellar and genital segments. 

c. The exoskeleton, a delicate iridescent cuticle, in- 
vesting the whole body. Take a freshly killed 
worm and strip off its cuticle under water; in doing 
so note that it passes in to line the alimentary 
canal at both mouth and anus. Transfer a small 
portion of it to a slide, mount in water and examine 
under a high power. Note 

a. It consists of a colourless transparent membrane, 
traversed by delicate lines or stria crossing each 
other at an angle of 45. 

Examine the same under a low power and note 
the cuticular sacs of the setce, finger-shaped pro- 
longations of the cuticle which occur in pairs. 
They embrace, during life, the middle of the setae. 

It not unfrequently happens that the setas are 
dragged away with the cuticle or it with them, upon 


252 ELEMENTARY BIOLOGY. [CHAP. 

removal from the body. Examination of a specimen 
in which this is the case shows that but one-third 
of the seta projects beyond the body-wall when at 
rest (Cf. Sect. H. 3). 

C. The body-cavity and general disposition of the viscera. 

Pin a large worm down under water dorsal side upper- 
most, and slit up the body-wall along the dorsal middle line. 
Pin back the two flaps and note 

a. The presence of a spacious body or perivisceral 
cavity. 

b. The alimentary canal, a straight tube running the 
whole length of the body. 

The yellowish-brown tissue investing its walls, ren- 
ders it especially conspicuous for all but the anterior 


20 segments. 


c. The mesenteric septa, a series of delicate transverse 
membranous partitions, coincident with the somitic 
constrictions (Cf. Sect. A. 2. a}. They attach 
the alimentary canal to the body-wall. 

d. The segmental organs or nephridia, whitish fluffy- 
looking appendages, one pair to each mesenteric 
septum. Examine under a lens, and note that each 
consists of a delicate convoluted tube, often of a 
dead-white colour owing to the presence of ex- 
cretory matter. 

e. The reproductive organs. Conspicuous among these 
will now be seen the seminal vesicles ; three pairs of 
large white bodies, overlying the alimentary canal 
in segments 9 to 12. 

The relative size of these is variable. (Cf. p. 
246.) The reproductive organs are restricted to this 


III.] THE EARTHWORM. 253 

region of the body, but further details concerning 
them may be left till later. 

/ The perivisceral fluid. Take a freshly killed worm 
and remove a small portion of the dorsal body- 
wall. Insert the point of a capillary tube and draw 
off a little of the perivisceral fluid. Examine at 
once under a high power, and note 

a. The watery serum, in which float colourless 
vacuolated amoeboid corpuscles. 

/3. Watch the corpuscles. Aggregates of them fre- 
quently fuse on exposure, prior to disintegration. 

y. Take a second drop of the fluid and treat with 
acetic acid and magenta. The nuclei of the 
corpuscles alone stain deeply. 

D. The alimentary organs. 

i. Pin the worm down as before and open it up dor- 
sally. Remove the seminal vesicles and work out in 
order- 

a. The buccal sac, a thin-walled sac lying within the 
first 2 3 segments. Muscular fibres pass from its 
anterior end to the body-wall. The aperture of 
the mouth can be seen through its transparent 
roof. 

b. The pharynx, a spacious thick- walled structure, ex- 
tending back to the sixth segment. It is tied 
down to the body-wall by a fan-shaped series of 
muscular fibres. 

The cut ends of those fibres which attach it to the 
dorsal surface of the body-wall (removed in dis- 
secting), give it a roughened appearance when 
viewed from above. 


254 ELEMENTARY BIOLOGY. [CHAP. 

The pharynx is marked off from the buccal sac 
by a deep recess, in which the pear-shaped supra- 
cesophageal ganglia are seen to lie. 

c. The oesophagus, a tube of relatively small calibre, 
continued back to the i5th segment, where it en- 
larges to form 

d. the crop, a spacious thin-walled sac, lying within 
segments 15 and 16. 

e. The cesophageal (caldferous] glands, three pairs of 
lateral cesophageal diverticula, conspicuous by their 
light yellow colour. The two anterior pairs arise 
in segment n and the posterior one in segment 
12. When fully formed, the anterior pair project 
into segment 10. 

Puncture one of the glands a milk-white fluid 
will escape. Examine this under a low power, and 
note the presence of carbonate of lime. (Cf. p. 243.) 

If any difficulty is experienced in following out the 
oesophagus, it can be overcome by starting from the 
crop and working forwards. 

f. The gizzard, a pearly-white thick-walled sac, follow- 
ing immediately upon the crop. It usually oc- 
cupies segments 17 to 19. 

g. The intestine, a spacious yellow thin-walled tube, 
extending back to the extreme end of the body. 
The sacculations of its walls become less con- 
spicuous as its hinder end is reached. 

h. Open up the crop, gizzard, and a small portion of 
the intestine from above, wash out the contents 
and note 

a. The crop. Its walls are thin and membranous. 


III.] THE EARTHWORM. 255 

There is sometimes present a well-marked lateral 
thickening of a highly vascular nature. 

(3. The gizzard. Note the great thickness of the 
muscular wall of its anterior half. The cuticular 
lining of the alimentary canal here attains its 
maximum of development. 

y. The intestine. Note the lateral ingrowths of its 
walls, developed metamerically at the points of 
attachment of the mesenteric septa. In trans- 
verse section they are seen to be refolded and 
complex. 

2. Take the body of a second worm killed as directed at 
the outset, but which has been subsequently pre- 
served for 1 8 24 hours in alcohol. Pin it down 
and dissect from the side. 

Make a median longitudinal section of the ali- 
mentary canal, wash out its contents and examine 

a. The buccal sac and pharynx. The floor of the 
former and roof and side walls of the latter are 
both thickened and muscular. 

(3. The oesophagus. Its metameric constrictions 
are plainly visible. Look for the orifices of the 
calciferous glands. (Cf. p. 242.) 

y. The intestine. Note the typhlosole, an immense 
median dorsal fold of the lining membrane of its 
roof; it is plicated laterally. 

Cf. the same in transverse section. 

Examine the lateral intestinal sacculations as 
seen from within (Cf. i. h. y). 

8. Work over the relations of the whole to the 


256 ELEMENTARY BIOLOGY. [CHAP. 

mesenteric septa. Those of the crop-gizzard 
region are liable to considerable variation. 

E. The excretory or segmental organs. 

T. Take the largest worm you can find and open up its 
anterior third along the dorsal middle line. Pin down 
the two flaps of the body-wall and remove the ali- 
mentary canal, being especially careful to avoid 
stretching the mesenteric septa more than is neces- 
sary. Wash until quite clean and examine in water 
under a lens. With a little care there will be seen 

a. The segmental organ or nephridium, a delicate tube, 
coiled upon itself and suspended to the mesenteric 
septum by a special fold or mesentery of its own. 

The whole organ is thrown into a series of loops. 
At its inner end, close to the nervous axis, a very 
conspicuous internal loop will be seen; it projects 
backwardly and outwardly. 

b. Examine the region of this internal loop with care. 
The nephridium will be seen to perforate the mes- 
enteric septum with which it is connected, and to 
open into the somite in front by an enlarged 
pendant extremity or nephrostome. 

2. Take a similar but freshly killed worm, and open up 
as before. Remove as much as possible of a mesen- 
teric septum (preferably from somite 15 or there- 
abouts, where the calibre of the alimentary tube is 
least and the reproductive organs do not overcrowd) 
with one of its related segmental organs. Examine 
under a low power, and restrict your attention to that 
portion of the tube in which ciliary action is going on. 
Follow it along until a point is reached at which it 


III.] THE EARTHWORM. 257 

undergoes a bending upon itself and a sudden in- 
crease in calibre ; substitute a high power and fix 
your attention on this last-named area. Note- 

a. The thick glandular walls of the tubule in which 
ciliary action is going on (glandular segment]. Care- 
ful examination will reveal the presence of large 
oval transparent nuclei. 

b. The thin-walled segment, a delicate transparent 
tube lying immediately adjacent to the lesser limb 
of a. It also is bent upon itself and ciliated. 

Its walls appear as mere hard outlines, and the 
transverse diameter of its two limbs collectively is 
about equal to that of the lesser one of a. 

c. The muscular segment. Examine under a low 
power. The position in which this segment will 
be found varies, as it is generally displaced in the 
process of manipulation. Like both a and b it is 
bent upon itself, and can be at once recognised by 
its great transverse diameter as compared with the 
rest of the organ. Follow it along it will be 
found to become suddenly constricted at the point 
at which the glandular segment enters it. 

Its aperture of communication with the exterior 
is best seen in section. (Cf. Sect. H. i c.) 

d. Look for the internal loop (i a). Note that both 
glandular and thin-walled segments enter into its 
composition. 

e. Look for the nephrostome (i b\ Having found it, 
examine under a high power. It is lined by a 
columnar ciliated epithelium, the individual cells of 
which are very large and clearly defined. Follow 

M. 17 


258 ELEMENTARY BIOLOGY. [CHAP. 

it back ; it is continuous with the thin-walled seg- 
ment. 

The actual course taken by the coils of the seg- 
mental organ can only be made out with very con- 
siderable trouble. Sufficient is here described to 
render it clear that three segments are present an 
internal thin-walled, a middle glandular and an 
external muscular one respectively ("internal" and 
"external" having reference to the fact that these 
segments communicate respectively with the body- 
cavity and the exterior). The only source of diffi- 
culty which will be found in attempting to unravel 
the whole, is the internal loop (d] formed by a 
secondary folding of both thin-walled and glandular 
segments. Eliminate that, and the whole resolves 
itself into a tube of three segments each bent upon 
itself. 

f. The nephridial blood-plexus. Remove, as directed 
above, the segmental organ of a worm which has 
been at least two days in alcohol. Examine in 
water under a high power. Its sheath carries a 
complicated series of blood-vessels, conspicuous 
by their yellow colour. Note 

a. The main nephridial vessels ; two thin-walled 
tubes running side by side, parallel with the long 
loop of the nephridium. They are connected 
by an excretory plexus, the smaller vessels of 
which form a bold series of loops on the surface 
of the organ. 

/?. The appendages of the excretory vessels ; a series 
of relatively large globular dilatations, filled with 
blood and generally crowded with minute colour- 
less non-nucleated corpuscles. 


III.] THE EARTHWORM. 259 

These structures are sometimes absent, and 
they are not confined exclusively to the nephridial 
plexus. 

F. The circulatory system. 

Examination of this system is materially facilitated by 
killing the animal as directed at the outset, and allowing it 
to remain undisturbed for six or eight hours, in order that 
the muscular walls of the larger vessels, no less than those 
of the body itself, may be rigid and well-set prior to dis- 
section. 

i. Pin down, at opposite ends, the body of a worm 
treated as above, and open it up along the dorsal 
middle line. Reflect the two flaps of the body wall, 
and note 

a. The supra-intestinal vessel ; a large median dorsal 
vessel, running along the whole length of the roof 
of the alimentary canal, to which it distributes 
branches. 


Large circumocsophageal vessels will be seen aris- 
ing from this in segments 6 12. Their detailed 
connections are described at 2 d. 

b. Dissect away some few of the mesenteric septa of 
one side, and displace a portion of the alimentary 
tube thus liberated. Note, overlying the nervous 
axis, the median longitudinal supra-neural vessel. 

The smaller lateral-neural vessels may sometimes 
be observed at this stage. (Cf. Sect. G. <?. y.) 

Take a second worm and pin it down on its side, 
being careful not to injure the anterior twenty seg- 
ments. Make an incision with the small scissors 
along its dorsal middle line, raising the body wall 

17-2 


260 ELEMENTARY BIOLOGY. [CHAP. 

with the instrument as you cut, in order to avoid the 
possibility of injuring the underlying vessels. Care- 
fully remove the lateral body wall of the above seg- 
ments to the level of the middle line, and without 
dissecting further, note 

a. The supra-intestinal and supra-neural vessels, to- 
gether with such of their branches as have been 
already mentioned. 

Look out for the lateral-neural vessels. 

b. The sub-neural vessel, a delicate median-ventral 
trunk, seen on raising the nervous axis, to which it 
is closely applied. 

c. The sub-intestinal vessel, a small median longi- 
tudinal trunk buried up in the ventral wall of the 
alimentary canal. It may best be seen on gently 
displacing the gizzard, the walls of which are 
white. Examine under a lens ; it will be found 
to be connected with the supra-neural trunk for 
each segment, by two or three delicate commissures. 

d. The so-called pseudo-hearts or circiimcesophageal ves- 
sels ; six in number and usually greatly distended. 
(Cf. T a.) They lie in segments 6 to n, and con- 
nect the supra-intestinal and supra-neural trunks. 

e. The lateral-cesophageal vessel, a conspicuous usually 
highly distended trunk, closely applied to the wall 
of the oesophagus on either side. Large branches 
of it are seen on the pharynx and oesophageal 
glands. It runs beneath the latter, and communi- 
cates with the supra-intestinal trunk in segment 12. 

d. and e. are the most conspicuous vessels in the 
whole system, and their general relations can be 
well seen if dissected from beneath. 


III.] THE EARTHWORM. 26 1 

3. Still working from the side, carefully cut (with scissors) 
into any three or four somitic constrictions of the 
intestinal region, and without dissecting further ma- 
nipulate the parts with forceps under water. Note 
the relations of the mesenteric septa and nephridia, 
as seen in the undisturbed condition (cf. Sect. E.) 
and next examine in order 

a. The circular commissural vessels; one on either side 
for each segment. They lie close under the body- 
wall (to which they give branches) midway between 
adjacent mesenteric septa, and connect the supra- 
intestinal and sub-neural trunks. 

b. The excretory plexus. The posterior of the two 
vessels from which this is derived springs from the 
sub-neural trunk immediately adjacent to the ne- 
phridium itself. The anterior one arises from the 
supra-neural in the segment in front, and perforates 
the mesenteric septum ventro-laterally. 

c. Remove a portion of the body-wall of this region, 
and gently scrape away as much as possible of the 
yellow-brown tunic of the intestine. There will 
thus be brought into view the lateral intestinal 
vessels ; two in number on either side in each seg- 
ment. They arise from the supra-intestinal trunk 
and break up into an alimentary plexus within the 
walls of the digestive canal. A series of small 
vessels will be seen to pass up towards these from 
the sub-intestinal trunk. 

The blood-vessels described above can all be made 
out by careful dissection. No mention has been 
made of the delicate lateral-neural commissures, or 
the smaller branches of the majority of the great 


262 ELEMENTARY BIOLOGY. [CHAP. 

vessels ; for the study of these recourse must be had 
to transverse sections. (Cf. Sect. G. y.) 

d. The blood fluid. Lay open, high and dry, the 
body cavity of a freshly-killed worm, and introduce 
a fine capillary tube into one of the larger vessels. 
Transfer the drop of red blood thus obtained to a 
slide, cover and examine at once under a high 
power. Note 

a. The blood serum, a watery yellowish-red fluid in 
which float 

/?. minute colourless corpuscles. In shape, they are 
somewhat irregular (rarely oval); each usually 
contains a central dark granule. 

If unsuccessful by the above method, remove 
a small portion of one of the larger vessels en 
masse between two pairs of forceps ; transfer to 
a slide and allow the fluid contents to escape. 

G. The nervous system. 

Dissect an entire worm from above, removing the dorsal 
portion of the body wall, and the alimentary canal from the 
pharynx backwards. Pin down, wash until quite clean, and 
dissect under water. Examine under a lens and note 

a. The supra-ossophageal ganglia; two pear-shaped 
masses lying in the third segment in a depression 
between the buccal-sac and pharynx. (Cf. Sect. 
D. i. b.} Fibres can be traced from them to the 
circum-oral integument. 

/'. The circumoesophageal commissures ; seen, on dis- 
placing the pharynx to one side, to arise from a. 
The nerves arising from them are distributed 
externally, to the first two segments internally, to 


III.] THE EARTHWORM. 263 

the pharynx (visceral nerves}. On reaching the 
ventral surface the commissures become firmly 
united and pass on, to the extreme end of the 
body, as longitudinal ventral commissures. Note 
the metameric gangliform enlargements formed upon 
the latter. 

c\ The ganglionic nerves ; two pairs for each somite. 
They arise from the ganglionic swellings trace 
them to the body wall. 

d. The interganglionic nemes ; one pair for each somite, 
arising from the longitudinal commissures at the 
bases of the mesenteric septa, to which they are 
largely distributed. 

e. The histology of the nervous axis and its associated 
structures (for method of preparation see Sect. H.). 

Examine transverse sections under a high power, 
note 

a. The sheath of the nervous system ; a deeply 
staining investment, mainly composed of the cut 
ends of muscular fibres. 

/?. The neurochord. It consists of three transparent 
thick-walled " tubular-fibres " (a larger central 
and two smaller lateral ones) buried up in the 
roof of a. 

y. The cut ends of the sub- and lateral neural blood- 
vessels, together with their anastomoses, all of 
which are buried up in a. 

S. The ventral nervous axis. Note the close appo- 
sition of the two commissures. Each is com- 
posed of a transparent matrix in which are seen 


264 ELEMENTARY BIOLOGY. [CHAP. 

the cut ends of delicate nen'e-fibres ; and of a 
denser peripheral ventro-lateral portion, in which 
large nerve-cells are lodged. 

Compare sections through the longitudinal 
commissures and ganglionic enlargements. 
Nerve-cells are present in both, and except 
so far as their relative proportions are con- 
cerned, there is no important structural differ- 
ence between them. In sections through the 
latter, look for the origins of the ganglionic 
nerves, and the small blood-vessels arising from 
the lateral neural trunks which accompany 
them. 

H. The study of transverse sections. 

i. Wash out the contents of the alimentary canal of a 
freshly killed worm with \ p. c. chromic acid solu- 
tion. When all the earthy matter has been removed, 
cut up into segments of an inch in length and trans- 
fer to solutions of chromic acid and alcohol of in- 
creasing strength (see appendix E). Stain with 
borax-carmine and mount in the usual manner in 
Canada balsam. 

Examine the thickest sections under a low power, 
and note 

a. The body wall. It is mainly composed of a thick 
muscular layer, external to which is a thin epidermis 
clad in a delicate cuticle. 

b. The intestinal wall ; its thick tunic of yellow- 
brown tissue. Internally to this there is a thin 
muscular layer, and the whole is lined by a well- 
defined epithelium. Examine the minute structure 
of the typhlosole. 


III.] THE EARTHWORM. 265 

c. The mcsenteric septum. A thin fibrous sheet pass- 
ing from a to b. Note its circular and radial 
muscular fibres. 

It is perforated ventrally (circum-neural arcade) 
to give passage to the nervous axis and its four 
accompanying blood-vessels. 

Look for the nephridia portions of them will 
certainly be visible in the thickest sections. Note 
especially their communication with the exterior, 
each by a narrow duct passing externally to the 
ventral setae. 

Look for the dorsal pore, for sections of the great 
blood-vessels and traces of their branches (see 
Sect. F). 

2. Examine a thin portion of the body-wall of the above, 
under a high power. Note - 

a. The epidermis ; composed of a layer of elongated 
cells. They stain very lightly, and their nuclei 
are very small. 

b. The unicellular cutaneous glands, large ovoidal 
structures buried up in a. Each opens on to 
the exterior by a short neck. They are rendered 
very conspicuous by the affinity of their granular 
contents for the staining reagent. 

c. The cuticular exoskeleton, a delicate investment for 
a. It is structureless, and stains uniformly and 
with moderate intensity. 

It is frequently puckered or otherwise displaced 
in the process of manipulation. 

d. The circular muscular layer. It lies immediately 
beneath, and is two or three times the transverse 
diameter of, a. 


256 ELEMENTARY BIOLOGY. [CHAP. 

Pigment granules will be found scattered among 
its fibres. 

e. The longitudinal muscular layer, somewhat thicker 
than d. Each of its several tracts is subdivided 
into a great number of fasciculi by uniformly 
arranged radial septa, within which small blood- 
vessels are carried. The muscular fibres are 
arranged in close set parallel lamellae, disposed 
at right angles to the septa. 

f. The peritoneum, a delicate membrane immediately 
internal to e. 

3. The setce, and their associated structures. When at 
rest they project inwardly to the level of the perito- 
neum. Examine in order 

a. The integumentary sheath of the seta. Trace its 
origin from the epidermis it can be followed to 
the inner end of the seta. 

b. The cuticular sheath, carried in with a. It can be 
traced some distance up the side of the seta. 
(Cf Sect. B.) 

c. The muscles of the setce. Examine any one pair 
of setae and note, passing obliquely downwards 
from their approximated inner ends, the fan-shaped 
(in section) protractor fibres. They pass into the 
circular layer of the body- wall. 

Two sets of retractor fibres will be seen arising 
from each seta at about its middle. By their 
union there are formed two ribbon-shaped bands 
which pass right and left of the setae, upwards 
and inwards, between the longitudinal fibres of the 
body-wall and the peritoneum. 


III.] THE EARTHWORM. 267 

d. The follicle of ike seta? ; a small granular proto- 
plasmic mass internal to each pair of functional 
setce. It lies close under the peritoneum, and 
usually bears two conical immature setce. 

4. The wall of the alimentary canal. This will be found 
to vary slightly in detail in different regions, the in- 
testine is here described. 

a. The epithelium, a single layer of elongated cells, 
lined internally by a delicate cuticular mem- 
brane. 

b. The muscular layer feebly developed. It consists 
of an internal circular and an external longitudinal 
series of fibres. 

The thickening of the wall of the gizzard is due to 
an excessive development of the circular fibres. 

c. The sub-epithelial tissue; a vascular layer interposed 
between a and b. Look for the cut ends of its 
small vessels. 

d. The yellow-brown tissue; a thick investment for the 
whole, immediately external to b (outside the wall 
of the whole viscus). Its component cells are 
elongated and club-shaped, each containing a 
single oval nucleus and crowded with minute 
highly refractive globules. 

Examine the muscular fibres of the mesenteric 
septum. An aggregation of circular fibres is fre- 
quently met with immediately external to the ali- 
mentary canal. Many of its radial fibres can be 
traced into the body-wall. 

5. The central nervous system, described in Sect. G. e. 


268 ELEMENTARY BIOLOGY. [CHAP. 

I. The reproductive organs. (Cf. Sect. C. e.) 

i. Obtain the body of a sexually immature worm (i.e. 
one in which there is no trace of clitellum) which has 
been well hardened in alcohol. Open up the an- 
terior twenty segments along the dorsal middle line 
and remove the alimentary canal with care, leaving 
the mesenteric septa undisturbed. Look for 

a. The spermatheccR^ two pairs of small yellowish- 
white globular bodies, attached to septa 9 10 
and 10 ii. 

They are developed within the substance of the 
septa referred to, and may project forwardly into 
segments 9 and 10 or backwardly into 10 11. 

Their points of exit are invariable, and they may 
conveniently be used as landmarks in dealing with 
the remaining organs of the reproductive system. 

l\ The seminal vesicles, three pairs of soft whitish organs 
attached in the sexually immature worm to septa 
9 10, 10 ii and n 12. They are internal to a. 

In the sexually mature animal they unite with each 
other and their fellows, below the alimentary canal, 
so as to form an anterior mass bilobed on either side, 
the body of which lies in segment 10, and a unilobed 
one for segment n. 

c. Remove the seminal vesicles of one side and ex- 
amine the mouths of the vasa deferentia (ciliated 
rosettes}. They are dead-white glairy structures, 
lying near the middle line in segments 10 and ii ; 
when fully formed exceedingly conspicuous and 
chalky looking. 

d. Trace back the ducts of c, on one side. Each per- 
forates the septum behind it and becomes im- 


III.] THE EARTHWORM. 269 

mediately convoluted, uniting in segment 12 with 
its fellow to form the vas deferens. Follow this 
back, it runs longitudinally midway between the 
nervous axis and the exterior, passing out on seg- 
ment 15. 

e. The icstcs (visible only in sexually immature speci- 
mens), two minute white bodies truncated pos- 
teriorly; attached, on either side, to septa 9 10 
and 10 ii close to the middle line. They pro- 
ject into segments 10 and n. 

In sexually mature worms these and the ciliated 
rosettes are both embraced by the enlarged seminal 
vesicles. 

f. The ovaries, two small conical bodies, attached by 
their bases to septum 12 13 in a line with e. 
Their free ends are not unfrequently recurved. 
They project into segment 13. 

g. The oviducts. Remove the segmental organs from 
septum 13 14, seize the latter with forceps and 
turn it backwards the mouths of the oviducts will 
be seen opening into segment 13 in a line with f. 
The ducts themselves are very short and closely 
bound down to the hinder face of the mesenteric 
septum. They pass outwards and backwards, 
opening on to the exterior in a line with d. 

h. The receptacula ovoritm ; tuft-like appendages of the 
hind-walls of the oviducts. They project freely 
into segment 15, and are rendered highly con- 
spicuous by their great vascularity. 

/". Remove the entire ovary and transfer it to a slide, 
stain with eosin and examine under a high power. 
Commence at its free end, and note 


2/0 ELEMENTARY BIOLOGY. [CHAP. 

a. The ripe ova, large round bodies completely 
filling the pointed extremity of the saccular 
ovary. A granular vitellus, a large round ger- 
minal vesicle and a vitclline membrane will be 
observed for each. 

fi. The immature ova. Work towards the base of 
the ovary the ova decrease in size and become 
more numerous. The younger of them are 
destitute of a vitelline membrane. Work back 
towards the attached end, and note graduating 
into fi as (3 does into a 

y. the germinal epithelium, a solid mass of small 
undifferentiated cells filling the base of the 
ovary. 

j. Remove a small portion of a testis of the youngest 
worm obtainable, crush and examine in eosin under 
a high power. Note the cells of the germinal epi- 
thelium, irregular in shape, each with a large central 
nucleus and a single nucleolus. 

/. Tease up in a similar manner a small portion of 
one of the seminal vesicles of an older animal. 
Treat with acetic acid and magenta spermatozoa 
in all stages of development will be seen. Look 
for the following 

a. Cells of the germinal epithelium identical with 
j. They are sometimes to be found only with 
difficulty. 

/3. The same during the early maturation stages- 
conspicuous as the predominant mulberry-like 
masses. Focus to the surface of one of these 
and work through it. It consists of a large pro- 
toplasmic body, differentiated peripherally into 


III.] THE EARTHWORM. 2/1 

a series of transparent nucleated protuberances- 

centrally into a large non-nucleated mass. 

y. The same during the later maturation stages. 
Nuclear division has gone on with rapidity, and 
the central mass is now surrounded by a great 
number of small nucleate bodies. Examine care- 
fully the protoplasmic investments of these each 
is prolonged out into a short filament. 

tx The ripe spermatozoa; aggregates of filiform struc- 
tures resulting from the nucleate bodies above 
described. Each is enlarged at its attached end 
to form a 'head,' within which the elongated 
nucleus is contained. Focus to the centre the 
non-nucleated mass has remained passive and 
unaltered. 

e. Look for free spermatozoa. 


IV. 


THE COMMON SNAIL (Helix aspersa). 

THE "Common Snail", 77! aspersa, and the "Garden 
Snail ", H. hortensis, are to be found in abundance in our 
gardens and hedgerows, and the descriptions here given 
apply equally to either with the exception of the shell. 
This, in the ' Garden Snail ', can be at once recognized by 
its delicate texture and predominant whitish-yellow colour, 
as compared with the rough-surfaced brown-banded shell of 
its ally. During the summer months the 'Common Snail' 
is to be met with, leading an active independent existence 
upon or in the immediate neighbourhood of fruit-bearing 
shrubs. It is very susceptible to cold, and retires during 
the later autumn to some recess in a wall or tree, where it 
usually remains dormant and hibernating until the following 
spring. It not unfrequently buries itself for the same pur- 
pose, and even in the warm season may be induced to 
hibernate temporarily if starved or submitted to a reduced 
temperature. During such a period, or during normal hi- 
bernation, the body is completely retracted within the shell, 
the mouth of the latter being sealed by a film of mucus 
secreted by the animal, which hardens on exposure to the 
atmosphere ; this is perforated to allow of the passage of 
air during respiration and is best termed for obvious reasons 
the hybernaculum. During the hibernating period the animals 
are frequently to be encountered huddled together in as- 


CHAP. IV.] THE COMMON SNAIL. 2/3 

semblages ; hence it is no uncommon thing to find, during 
the warm season, individuals, to the exterior of whose shells 
there adhere one or more (often a great number) of these 
hybernacula, cast off by their fellows on emerging from the 
dormant state. 

The body of the snail is soft and unsegmented, and, 
unlike that of any other animal dealt with in this work, 
asymmetrical inasmuch as the anal, respiratory, excretory 
and genital orifices all open to the right side, the latter 
beino; situated far forwards near the mouth. The ventral 

O 

surface of the body is thick and fleshy, giving rise to a 
locomotor foot, by the wave-like contractions of which the 
sluggish movements of the animal are performed. So deli- 
cately adjusted are these, that the creature can crawl with 
ease and comfort over a knife-edged surface. The anterior 
end of the body is differentiated into a well-marked head 
segment bearing two pairs of tentacles a shorter labial pair 
adjacent to the mouth and a longer ocular pair situated 
above and behind these. The integument covering the apex 
of each tentacle is especially modified in connection with a 
nerve supply derived from a large underlying ganglion, 
whence it follows that the eye-bearing tentacle performs a 
double function. It may be that the labial one is either 
tactile or olfactory, but the exact functions of these sensi- 
ferous areas have yet to be fully elucidated. 

Between the head-segment and the free anterior end of 
the pedal-disc there is a cleft, at the base of which opens a 
large mucus secreting pedal-gland which extends far back 
to the hind end of the body. 

The dorsal surface of the body is produced into a spirally 
coiled hump, within which the whole digestive gland and 
portions of the alimentary and reproductive viscera are 
lodged it is hence termed the visceral sac. This sac, to- 

M. 1 8 


2/4 ELEMENTARY BIOLOGY. [CHAP. 

gether with the wall of the pulmonary chamber which over- 
lies it in front, is invested in the spirally coiled shell, the 
apex of which lies altogether to the animal's right side. 
The mouth or per itr erne of the shell overlies the thickened 
anterior border of the pulmonary sac, from which a constant 
addition of shelly matter is secreted during the growth of 
the animal, as is also the hybernaculum during repose. 

The aperture of the mouth is bounded by soft fleshy lips, 
and it leads into a spacious buccal cavity the walls of which 
are excessively thick and muscular. A denticulate horny 
upper jaw or beak is present, and the floor of the mouth is 
raised up into a cushion-shaped odontophore or tongue, 
which is in turn surmounted by a dentigerous lingual-ribbon 
or radula. This is thrown into a licking rasp-like motion 
during feeding, by the activity of an underlying musculo- 
skeletal apparatus, the odontophoral cartilages connected 
with which are worthy of note as composing an eudoskeleton. 
The mouth itself leads into a long tubular oesophagus, 
which passes straight back and, on entering the visceral 
sac, opens into a small stomach which receives the secretion 
of the digestive gland. The stomach in turn gives origin 
to a coiled intestine which, on nearing the exterior, skirts 
the lower right-hand border of the pulmonary sac, termi- 
nating in an anus which lies to the right of the respiratory 
orifice. The middle segment of the cesophagus is enlarged 
to form a distensible crop, applied to which there are a 
pair of salivary glands, confluent above and pouring their 
secretion into the mouth by means of two elongated 
ducts. 

The digestive gland is a paired structure ; its lobes are 
asymmetrical the smaller right one lying altogether within 
the top whorls of the shell. Microchemical examination 
shows that it performs a complex function, serving both as a 


IV.] THE COMMON SNAIL. 2/5 

storehouse of combustible fatty carbo-hydrate material and 
as a centre for secretion of a digestive ferment 

The pulmonary sac or mantle arises as a fold of the 
body wall, in which pulmonary vessels appear during de- 
velopment. At the hinder end of the enclosed pulmonary 
chamber there are situated, side by side, the heart and 
kidney. The heart is enclosed in a definite pericardium, 
the floor of which is in open communication with the ex- 
cretory organ by means of a short ciliated reno-pericardial 
duct. The excretory organ itself lies altogether to the right 
side of the body and debouches on to the exterior by a 
long duct, running parallel with the rectum. 

The heart consists of a single auricle and ventricle, the 
valves between them being so disposed as only to admit of a 
current passing from the lung sac to the body. It therefore 
transmits only aerated blood, and as it is in no way con- 
cerned with the propulsion of the blood to the respiratory 
organs it is termed like that of the Crayfish already con- 
sidered a systemic heart. The ventricle gives origin to a 
single aorta which, on entering the body-cavity, subdivides 
into two branches. The anterior of these supplies all parts 
of the body which lie in front of the heart, and the posterior 
is restricted to the visceral sac and its contents. These 
arterial trunks break up into minute ramifications, which 
pass either into capillary systems or lacunar spaces, all of 
which converge, directly or indirectly, towards a great sinus 
which lies at the base of the pulmonary sac. From this, 
afferent pulmonary vessels arise on all sides ; the branches 
of these, reuniting in the substance of the lung-sac, form 
a system of efferent pulmonary vessels, which unite to 
form a large pulmonary vein which enters the heart. The 
efferent pulmonary vessels of the right side pass, on their 
way to the heart, through the excretory organ, in the sub- 


iG 2 


2/6 ELEMENTARY BIOLOGY. [CHAP. 

stance of which they break up into a second (i-enaf] 
capillary network. 

The blood contains amoeboid corpuscles, which float in 
an opalescent serum ; it assumes a bluish tinge on exposure 
to the atmosphere. 

The central nervous system is enclosed in a membranous 
circum-cesophageal sheath. It consists of three yellowish 
ganglionic masses ; the supra-oesophageal or cephalic lying 
above the gullet and giving off nerves to the head segment 
and related parts ; the pedal which supplies the foot and 
body-wall ; and the parieto-splanchnic which distributes 
fibres to the body-wall and viscera, and all parts lying behind 
its point of origin, irrespective of the foot. These ganglionic 
centres are connected together by lateral commissures ; and 
from the cerebral mass there arise a system of buccal nerves 
in relation with the buccal mass and its odontophore, and 
others distributed to the sense organs. The latter are, a 
pair of small auditory vesicles to be hereafter described (see 
Sect. J. 3) and visual and tegumental sense organs borne 
by the tentacles, to which reference has already been made. 

The snail is hermaphrodite and the sex-organs are highly 
complicated. With the exception of the hermaphrodite 
gland or ovotestis, a portion of the duct of the same and its 
appended albumen-secreting gland all of which are lodged 
in the visceral sac, they fill the greater part of the spacious 
body cavity and can be at once recognized by their dead- 
white colour. As the hermaphrodite duct approaches the 
exterior it suddenly divides into distinct oviduct and vas 
deferens ; the base of the latter is enlarged to form a swollen 
eversible intromittent organ or penis, which opens, side by 
side with the oviduct, into an integumental pit or genital 
cloaca. Appended to the whole apparatus there are several 
accessory glands and diverticula. Chief among these is a 


IV.] THE COMMON SNAIL. 2// 

coecal diverticulum of the base of the penis which secretes 
a mucilaginous investment for the spermatozoa ; the spcr- 
matophores or packets of spermatoza thus formed are trans- 
ferred, during copulation, to a corresponding ccecal diver- 
ticulum of the oviduct known as the receptaculum seminis. 
Fleshy valves are developed within the lips of the genital 
cloaca and at the orifices of the genital ducts which open 
into it, and the whole condition of the organs is such as to 
obviate the possibility of self-fertilization. 

In the spiculum amoris, an accessory to the female portion 
of the apparatus (see Sect. G. 3 f.) we have a structure, 
almost without parallel in the whole animal kingdom. It 
reaches maturity during the breeding season, and is forcibly 
ejected from individual to individual during the amorous 
overtures, which last for a period of some hours. 

The spermatozoa are long filiform bodies, each with 
an enlarged nucleus-bearing "head." The ova are chiefly 
noteworthy on account of the absence of a distinct vitelline 
membrane ; they are comparatively large and are provided 
with a nutritive food-yolk. 

The reproductive elements of opposite sexes ripen alter- 
nately, the maturation of a given batch of spermatozoa pre- 
ceding that of the ova they are destined to fertilize, and in 
view of the facts above related it follows that the sperma- 
tozoa must be transferred, during copulation, to the body of 
the second individual there to await the descent of the ova. 

Fertilization takes place as the ova leave the body, and 
there are to be found in the haunts of these animals during 
the summer months, usually beneath some stone or de- 
caying wood or more rarely buried in the earth itself, 
aggregates of 100 or more eggs, each invested in an albu- 
minous envelope, within which the early developmental 
phenomena are undergone. 


2/8 ELEMENTARY BIOLOGY. [CHAP. 

The conditions under which embryonic development is 
passed through in the " Pond Snail" (L,y.mnczus stagnalis) are 
much more favourable to observation than in the case of the 
"Common Snail," and they are accordingly here dealt with. 

The "Pond Snail" is a sluggish carnivorous animal which 
may be found in abundance during the summer months in 
ponds and stagnant waters ; it is moreover an indispensable 
acquisition to the aquarium. If confined in a hand-glass or 
table aquarium and well fed, the animals will very generally 
deposit their eggs upon the vessel, and they will be found 
in aggregates, firmly adherent to each other and to the sur- 
face by means of the albuminous secretion aforementioned. 
The important developmental changes are undergone while 
still in this investment. 

The transverse diameter of the fertilized ovum is about 
the o-^th of an inch. The segmentation is holoblastic and 
unequal, and the changes undergone during the early de- 
velopmental period are substantially such as have been 
already described for the Earthworm (cf. p. 247), resulting 
in the formation of a simple two-layered gastrula. 

During segmentation there appear on the surface of the 
dividing mass, some two or more minute protuberances, 
which finally become constricted off and lost. A portion of 
the nucleus of the cell whence each arises is carried away 
with it. Various interpretations have been put upon these 
polar bodies ; they are of fairly general occurrence in the 
animal kingdom, but further discussion concerning them is 
beyond the scope of this work. They are alluded to here, 
as the conditions of observation are exceedingly favourable. 

After the gastrula phase is passed, the embryo assumes a 
somewhat spherical shape, during which period the mouth 
is formed as a median involution of the epidermis. There 
now appears on the surface, immediately in front of the 


IV.] THE COMMON SNAIL. 2/9 

mouth, a thickened zone incomplete ventrally. The sur- 
face of the body becomes ciliated and especially so this 
zone, whereupon there results a rapid rotation of the embryo 
within its albuminous investment. This being so, the zone 
in question is termed the trochal ridge, the larva possessed 
of it being said to be in the trochosphere stage. This, in 
turn, gives place to a more advanced veliger stage, so called 
on account of the changes undergone by the trochal ridge, 
which now becomes more marked, being produced out into 
a hood-shaped pre-oral lobe or velum. During this stage 
the mantle arises as a fold of the body-wall, which, as age 
advances, takes on the characters of a lung sac. 

During the final stages of larval metamorphosis the left 
side of the body grows much more rapidly than the right 
one. Thus it is that the originally bilaterally symmetri- 
cal larva becomes converted into an asymmetrical adult, 
a fact which renders clear the displacement of the orifices 
(other than those of the mouth and pedal gland) and of 
the organs connected therewith, the suppression of the ex- 
cretory organ of one side, and the enormous increase in 
size of the left lobe of the digestive gland, as compared 
with the smaller right one. 

Very early in the history of the larva the locomotor foot 
arises, as a median ventral outgrowth between the mouth 
and anus; and as the importance of this structure becomes 
more marked, the cilia of the velum undergo a reduction. 
Consequent upon these changes the rotatory movements of 
the animal, so characteristic of the trochosphere, give place 
to a sluggish creeping motion. The velum itself does not 
entirely vanish in Lymnaeus, but persists throughout life 
as a couple of so-called subtentacular lobes which lie im- 
mediately above the mouth. These are wanting in the 
11 Common Snail." 


280 ELEMENTARY BIOLOGY. [CHAP. 


LABORATORY WORK. 

If the Snail be killed, by immersion in water heated to a 
temperature such as the hand can comfortably bear, the 
shell will readily part company with the muscles to which it 
gives attachment. This being the case, no difficulty will be 
experienced in removing the animal, if, holding it in the left 
hand, the shell be twisted off by the finger and thumb of 
the right. 

In dissecting the internal organs it is advisable to re- 
move the visceral sac in starting. This may best be 
done by cutting away its thickened edge with a pair of 
scissors, and tearing it off with a couple of pairs of strong 
forceps. 

A. General external characters. 

i. In the living animal observe : 

a. The body ; produced ventrally into an expanded 
locomotor disc or foot ; and dorsally into a spirally 
coiled visceral-sac, invested in the single coiled 
shell or cxoskelcton. 

b. The head segment ; a freely projecting anterior lobe 
of the body, which overhangs the foot. It bears 
two pairs of retractile tentacles; a smaller lower- 
most labial pair, situated at the sides of the mouth, 
and a longer dorsally placed ocular pair, at the 
summit of each of which there is borne, when fully 
extended, a minute black eye. 

c. The apertures. Examine the animal en face, and 
note : 


IV.] -THE COMMON SNAIL. 28 1 

a. The mouth ; surrounded by a thick circular lip y 
externally to which there is, on either side, a 
well-marked lateral lip. Observe that the mouth 
is bounded above by a denticulate horny beak, 
lying within the circular lip. 

/?. T\\& pedal gland ; opening by a wide aperture, at 
the base of a depression between the head seg- 
ment and the foot. Insert a seeker into it it 
can be readily introduced for a distance of more 
than an inch. 

y. With the animal still in this position, note that 
the shell (and visceral sac which underlies it) 
is carried altogether to the creature's right side. 

Place the snail right side uppermost, and examine : 

8. The genital orifice, situated a short distance be- 
hind the bases of the tentacles of the right side. 

e. Gently raise the shell, and note, underlying its 
free edge, the thickened glandular border of the 
pulmonary sac. Enclosed by valve-like folds of 
this there lies the large respiratory orifice. Situ- 
ated side by side with, and a little to the right 
of, this, is the anus. (The excretory orifice also 
opens at this point, but within the lip of the 
respiratory one. It is not visible without dis- 
section. Cf. Sect. C. i d.} 

. The genital furrow, a feebly defined integumental 
groove, extending from the base of the pulmonary 
sac to the genital orifice. 

B. The shell or exoskeletpn. 

a. It forms a continuous investment. Its free edge 
is produced into a whitish porcellanous reflected 


282 ELEMENTARY BIOLOGY. [CHAP. 

border or peritreme. It is thrown into a spiral of 
four whorls. 

I. Note its texture and colour (cf. p. 272). As the 
apex (first formed part) is approached, a smooth 
friable texture and a pearly lustre are assumed. 

c. The cohimella. If, with the peritreme directed to- 
wards you, the shell be carefully opened up with 
scissors, the columella will be seen as a central 
pillar or axis. Cut into this with care ; it will be 
found to be hollow, and closed in below by an 
overgrowth of the peritreme the shell is thus a 
spirally coiled tube. 

In young shells the columellar cavity opens freely 
below, by an aperture or umbilicus. 

d. The columellar muscles. Remnants of the glistening 
white tendons of these are often to be found, at- 
tached to the upper end of the shell axis. (Cf. 
Sect. E. i a.) 

e. The hybernaculum or epiphragm. Examine a dor- 
mant specimen, and note that the mouth of the 
shell is completely closed by this. Remove it and 
examine under a low power ; note the perforation 
of its central area. 

C. The pulmonary sac and its associated structures. 

i. Examine the pulmonary sac from above. It consists 
of a membranous expansion of the body-wall, which 
overlies the entire antero-dorsal region of the visceral 
hump. Large blood-vessels are developed within its 
walls; and there is visible through it, on the right 
side, the yellow excretory organ. Insert a scissors 


IV.] THE COMMON SNAIL. 283 

into the respiratory orifice and make an incision along 
the right-hand border of the sac, cutting clear of 
the excretory organ. Carry a second incision along 
the thickened base of the sac towards its left side, and 
reflect the whole. Note : 

a. The floor of the pulmonary chamber ; thin and 
transparent, there being seen through it the dead- 
white reproductive organs. 

I. The rectum, a thin walled tube coursing along the 
floor of the pulmonary chamber at its extreme right 
hand border. 

Follow it to the anus. It opens, at the base of 
a groove-like depression in the lip of the respira- 
tory sac, below and to the right of the respiratory 
orifice. 

c. The excretory gland, a considerable yellowish mass, 
lying in the posterior right hand end of the pul- 
monary sac. Make an incision into it and wash 
out its contents ; note the thickened spongy texture 
of its glandular lining, which is thrown into a series 
of folds by the underlying blood-vessels. 

d. The excretory duct, a yellow thin-walled tube, 
running to the right of and parallel with the rectum. 
Its orifice lies a little above and to the right of the 
anus. Insert a blowpipe into this and inflate the 
whole ; note that the duct is continued along the 
right hand border of the gland to its summit. 

If examined minutely, it will be seen that the 
excretory duct is continued on beyond the above- 
named orifice as a well marked excretory groove, 
whose walls are contractile. This courses over the 
base of the rectum dorsally to the anus, and, passing 


284 ELEMENTARY BIOLOGY. [CHAP. 

backwards and downwards, terminates to the left 
of the respiratory orifice. 

c. The pericardium^ a small sac lying in a recess of 
the left hand border of the excretory gland. Re- 
move its front wall and examine the heart ; it is 
subdivided into a single auricle and ventricle. 

2. Cut away the upper part of both the excretory organ 
and pericardium, and remove so much of them as 
remains, together with a portion of the adjacent 
visceral sac. Wash carefully until clear of sediment, 
and examine in water under a low power. 

A short ciliated duct will be found, passing from 
the base of the pericardium to the excretory gland, 
into which it opens by a reno-pericardial aperture. 

D. The alimentary organs. 

i. Place the animal on its left side, and pin it down 
through the muscular foot. Remove the lung-sac and 
liberate the rectum from its surroundings. Next dis- 
sect away the right half of the body wall and visceral 
sac. 

There will be seen filling up the greater part of the 
body cavity the dead-white generative organs ; re- 
move these en masse, whereupon there will be clearly 
visible 

a. The crop ; a large sac-like organ, filling a con- 
siderable portion of the body cavity. It is generally 
rendered the more conspicuous on account of the 
yellow colour of its contents. Its lining membrane 
is thrown into a series of longitudinal folds ; these 
are visible through its thin walls, giving it an 
apparent longitudinal striation. 


IV.] THE COMMON SNAIL. 285 

b. Follow the crop forwards, it will be found to arise 
from the roof of the thick-walled muscular buccal 
mass, as a simple cesophageal tube. 

c. The sac of the radula, a small backwardly directed 

diverticulum of the floor of the buccal mass. 

</. The salivary glands, two irregular whitish masses 
closely applied to the sides of the crop. They are 
confluent postero-dorsally, and each is connected 
with the roof of the mouth by an elongated 
salivary duct. Follow one of these forwards, its 
base becomes enlarged as it enters the mouth, at 
the re-entering angle between the oesophagus and 
buccal mass. 

e. Follow the crop backwards, it will be found to pass 
into the visceral sac under cover of the right lobe 
of the digestive gland (a yellowish brown mass, 
filling the apical whorls of the visceral hump). 
Turn this gland downwards and forwards, and 
note, lying beneath it, the small sac-like stomach, 
into the hinder end of which the oesophagus is seen 
to pass. 

f. The digestive gland. Buried up in its small right 
lobe will be found the white ovotestis (remove this 
with care). Its left lobe is much the larger of the 
two; it is subdivided into three lobules which adapt 
themselves to the coils of the intestine. Arising 
from these are seen well-defined ducts ; follow 
them and note that they unite to form a single 
short digestive duct. 

g. The stomach. Open this from the side, being 
careful not to injure the right lobe of the digestive 
gland, and wash out its contents. It is a simple 


286 ELEMENTARY BIOLOGY. [CHAP. 

sac, slightly subdivided into two by a longitudinal 
fold. Four apertures will be found in its walls; 
they are 
a. The oesophageal orifice, opening into its hinder 

end. 
/?. The origin of the intestine, lying below and to 

the right of a. 

y. The apertures of the digestive ducts ; opening- 
that of the left side just above the intestinal 
orifice that of the right into its apex (this duct 
skirts the free edge of its gland). 

//. The intestine. After leaving the stomach it passes 
upwards and forwards, altogether to the left side. 
It then makes two turns upon itself, approaching 
the right side as it does so, and finally courses 
along the right border of the pulmonary sac. (Cf. 
Sect. C. i b.) 

E. The buccal mass and odontophore, 

i. Examine the buccal mass from the side and make out 
its muscles. The constrictor fibres have already been 
referred to, as constituting the muscular wall of the 
whole structure. Of those which remain the more 
important are- 

a. The retractor ; a large sheet, arising from its floor 
and side walls below the sac of the radula, and 
passing back, side by side with the immense 
retractor pedis fibres arising from the foot, to be 
inserted into the columella or shell axis. (Cf. 
Sect. B. d.) 

l>. The protractors ; delicate muscles arising from its 
side walls, and passing downwards and forwards, 
to be inserted into the cephalic integument. 


IV.] THE COMMON SNAIL. 287 

c. The lev at or s ; delicate muscles arising just above 

the protractors, and passing upwards to be in- 
serted into the cephalic wall, near the bases of the 
smaller tentacles. 

d. The depressors, small muscles underlying the pro- 
tractors, and passing obliquely backwards. 

2. Carefully remove one half of the buccal mass, cutting 
to the near side of the middle line. Examine under 
water and note 

a. The odontophore, a cushion-shaped elevation of 
the floor of the mouth, completely covered in 
mucous membrane. There overlies it a yellowish 
ribbon-shaped band the lingual ribbon or radula; 
follow this back into its sac (see Sect. D. i. c] 
and note that as that is approached it assumes a 
whitish colour and membranous texture. 

b. The radula. Remove this bodily, with a pair of 
forceps ; transfer it to a glass slide, cover in water 
and examine under a low power. Note the 
presence of an immense number (between twelve 
and thirteen thousand) of chitinous teeth. Those 
which are functional can be readily distinguished 
by their yellow colour and sharp pointed cusps. 
Examine that portion of the radula which lay 
within the sac. Note the transparent immature 
teeth, becoming simpler and more papilla-like as 
the hindermost border is reached. Examine in 
like manner the front end. It is beset by teeth 
whose cusps are worn down, and reduced, in many 
cases, to the condition of mere functionless rudi- 
ments. 


288 ELEMENTARY BIOLOGY. [CHAP. 

c. Examine the functional region under a \ or i 
objective. Note that the bases of the two sets of 
lateral teeth (uncini\ by which the radula is for 
the most part beset, are concave externally. Follow 
those of one side inwardly a single median longi- 
tudinal row (rachis] will be reached, whose bases 
are concave on either side. 

The rasping surface of each median tooth is pro- 
duced into a pointed cusp. In the lateral teeth there 
appears, on the inner side of this, a second smaller 
one which increases in size relatively, as the free 
edge of the radula is approached. There appears, at 
the same time, a smaller external accessory cusp, 
which is not represented in the median teeth. 

d. The odo?itophoral cartilages ; two gristly masses to 
whose presence the elevation of the floor of the 
mouth is due. There are attached to their bases a 
series of small intrinsic muscles, arising from the 
side walls of the buccal mass. 

<?. The horny leak ; seen to be formed in relation with 
a special fold of the lining membrane of the roof of 
the mouth. It lies wholly within the circular lip, 
seen in section to be thick and fleshy. 

f. The salivary duel ; opening into the roof of the 
mouth by a minute orifice situated just above the 
odontophore. 

F. The Pedal Gland. 

This is best examined at this stage, by removing the foot 
to one side of the middle line. It has the appearance of a 
white fluffy-looking mass, lying immediately above the 
pedal disc, and extending back for two-thirds the length of 
the same. Open it up with care it consists of a coecal 


IV.] THE COMMON SNAIL. 289 

diverticulum of the integument, opening below the mouth 
by an expanded orifice." (Cf. Sect. A. i. c. (3.) 

Compare the same, as seen in a transverse section across 
the foot. Note its thick glandular walls and central lumen. 
It is accompanied on either side by a well-defined lateral 
pedal blood sinus. 

G. The Reproductive Organs. 

1. Pin the animal down as directed in Sect. D., and re- 
move the right half of the body-wall posterior to the 
genital orifice, together with the rectum. Dissect off 
the visceral sac and examine in order- 

a. The ovotestis or hermaphrodite gland ; a small white 
mass, buried up in a fossa of the right lobe of the 
digestive gland. Remove sufficient of the latter 
to fully expose it. 

b. The duct of the ovotestis or hermaphrodite duct ; a 
short highly convoluted glistening white duct, 
passing upwards from the ovotestis towards the 
main mass of the reproductive apparatus. 

2. Remove sufficient of the right lobe of the digestive 
gland to liberate the ovotestis and hermaphrodite 
duct; note 

a. The albumen gland; a large greyish white structure 
lying, apex downwards, to the immediate left of the 
duct of the ovotestis. 

This gland swells up very rapidly under water, in 
the manner of the glandular segment of the Frog's 
oviduct already described (p. 53). Dissection may 
conveniently be carried on under weak alcohol. 

M. 19 


290 ELEMENTARY BIOLOGY. [CHAP. 

In the vicinity of the base of this gland, the 
genital organs come into close apposition with the 
intestine and aortic vessels. Carefully liberate 
them en masse from their surroundings and pin 
down under water the albumen gland with its 
flattened face uppermost. Now follow in order 

b. The further course of the hermaphrodite duct. On 
reaching the albumen gland it becomes suddenly 
constricted, to form an exceedingly delicate thread- 
like tube. As this is usually of a dead- white colour 
it can be seen through the more transparent albu- 
men gland, in the superficial portion of which it lies 
buried. It passes for a short distance towards the 
apex of this gland, and then, turning sharply upon 
itself, is continued straight back towards the base 
of the same ; it here becomes suddenly enlarged 
to form a convoluted duct with sacculated walls, 
which is continued on towards the genital orifice. 

The transition between the two segments of the 
hemaphrodite duct here described, is so sudden as 
to make it appear that they are distinct structures ; 
hence it is that the sacculated segment is sometimes 
spoken of as an oviduct. 

c. Its walls are beset externally by a continuously 
straight series of glandular follicles, making up an 
accessory gland (so-called prostate]. 

d. Open up the albumen gland and note its spacious 
central duct. It will be found to enter the enlarged 
"head" of the sacculated portion of the hermaphro- 
dite duct. Follow the hermaphrodite duct onwards 

-its sacculations gradually disappear, and it 
suddenly divides into two oviduct and vas deferens. 


IV.] THE COMMON SNAIL. 291 

e. The oviduct; a very short thick-walled tube, entering 
into immediate relationship with a large white sac 
the dart sac ( 3 c}. 

f. The i'as deferens; a thin-walled tube, arising side by 
side with g, but of lesser calibre than it. Its inner 
end is tied down to the female duct ; leaving this 
it passes under the retractor muscle of the right 
tentacles and becomes enlarged to form 

g. the penis, apparent now as the elongated swollen 
end of the vas deferens. It passes to the exterior 
side by side with the female duct. 

It is attached to the body-wall of the left side by 
a ribbon-shaped retractor muscle. Cut this across 
and displace the whole organ. 

//. The spermatophoral gland <ycflagellum; an elongated 
thread-like diverticulum of the base of the penis. 
It is much coiled. 

3. Remove the entire reproductive system from the body, 
together with a portion of the body-wall immediately 
adjacent to the sexual orifice. Pin the whole down 
carefully under water, and open up the larger ducts 
and their appendages, as they stand related to the 
exterior. Make out in order : 

a. The genital cloaca or vestibule; a shallow integu- 
mental pit, opening on to the exterior by the single 
genital orifice. 

b. The penis. Remove a portion of its enlarged 
eversible base. It opens into the front wall of the 
vestibule ; its lining membrane is produced into a 
fold or prepuce, above which there is usually an 
eminence. 

19 2 


2Q2 ELEMENTARY BIOLOGY. [CHAR 

c. The oviduct. Follow this down ; its first segment 
already described ( 2 c] is sometimes termed 
the vagina. This opens by a tumid lip into a thin- 
walled terminal segment, which enters the vesti- 
bule side by side with the penis. 

d. The spermatheca or receptaailiun seminis (receptacle 
of the spermatophores) ; an elongated diverticulum 
of the above-named terminal segment of the ovi- 
duct, bound down during life to the hermaphrodite 
duct ( 2 b\ Liberate it from this, and note that 
it arises by a short neck which subdivides into 
two ccecal diverticula a longer and stouter coiled 
one, and a shorter one which terminates in a globular 
enlargement (this lies, during life, tucked away in 
the bend of the first coil of the intestine. Cf. 


e. The dart-sac ; an immense melon-shaped diverti- 
culum of the base of the oviduct, in life backwardly 
directed. Open it up and note its powerful muscular 
walls ; lying within it will be seen 

f. the dart or spiculum amoris, a four-bladed calcareous 
projectile. Its head overlies a papillate ingrowth 
of the lining membrane of the sac. 

g. The accessory mucus or digitate glands; two 
branching masses opening side by side into the 
basal segment of the oviduct, immediately above e. 

H. The circulatory system. 

Examine an animal freshly removed from its shell, before 
it is in any way dissected. The pulmonary vein will be seen 
running in the wall of the lung-sac, in front of and in a line 
with the excretory organ. Make an incision in this and 


IV.] THE COMMON SNAIL. 293 

introduce a small syringe or medicine-dropper filled with 
injecting material. Seize the vessel and the inserted nozzle 
between the finger and thumb of the left hand, and inject. 
If this simple operation be carefully performed, all the 
leading vessels which carry aerated blood will be injected. 

1. Lay open the pulmonary-sac, and note : 

a. The efferent pulmonary vessels ; a uniformly arranged 
series of trunks bringing in the blood from the 
lung-sac ; they unite to form a large pulmonary 
vein which enters the auricle. 

b. The efferent renal vessels ; two or three small trunks 
conveying the blood from the excretory organ to 
the pulmonary vein. 

During the process of injecting these become very 
rapidly filled, and in the exercise of the pressure 
necessary to inject the whole arterial system their 
walls are not unfrequently ruptured. 

2. Open the heart (cf. Sect. C. i e). Note the thick 
muscular wall of the ventricle, and the auriculo-ven- 
tricular valves so disposed as only to admit of a 
passage of the blood from the auricle to the ventricle. 

3. The arterial system. Remove the right half of the 
body-wall and visceral sac, and together with them 
the rectum and greater portion of the genital ap- 
paratus -cutting the sacculated hermaphrodite-duct 
across at about its middle. 

There will thus be exposed the great arteries. Work 
them over in the following order : 

a. The aortic trunk, a very short vessel, arising from 
the base of the ventricle. It lies to the left of the 
head of the first coil of the intestine, immediately 


294 ELEMENTARY BIOLOGY. [CHAP. 

below which it suddenly subdivides into an ante- 
rior and a posterior branch. 

b. The anterior aorta; a well-defined vessel running 
parallel with the sacculated portion of the her- 
maphrodite-duct. On entering the body-cavity it 
passes beneath the first coil of the intestine and 
the adjacent globular head of the spermatheca 
(G. 3 d} ', it then travels to the right side of the 
body and runs on, beneath the crop, to the anterior 
extremity. Branches are given off along its course 
to the genital apparatus, foot, crop, salivary glands 
and tentacles, with the adjacent integument; it 
finally perforates the sheath of the nervous system, 
ending in relation with the floor of the buccal mass. 
Special branches accompany the rectum and pedal 
gland. 

c. The posterior aorta; a considerable vessel which ac- 
companies, at its outset, the first limb of the in- 
testine. It descends into the visceral sac, and is 
mainly distributed to those portions of the ali- 
mentary canal and its appended glands contained 
within the same. 

4. The venous system. With the exception of certain 
well-defined sinuses and vessels detailed below, the 
venous channels consist mainly of a series of lacunar 
spaces, in free communication with the body-cavity. 
Reference has already been made (Sect. F.) to the 
lateral pedal sinus, and if, in an uninjured Snail, the 
point of the injecting apparatus be carefully inserted 
into this, no difficulty will be found in demonstrating 
the existence of the vessels here described. 

Having injected the animal, reflect the lung-sac, 


IV.] THE COMMON SNAIL. 295 

cutting close alongside the rectum, in order that that 
portion of it bearing the smaller pulmonary vessels 
may be reflected intact. 

Note in order : 

a. The circulus venosus pulmonis ; a great sinus sur- 
rounding the base of the pulmonary sac. 

b. The marginal sinus of the visceral sac; a spacious 
channel continuous with a. posteriorly and running 
within the thickened edge of the visceral sac. 

On exposing the interior of the pedal sinus in an 
uninjected specimen, there will be seen opening 
into it the orifices of adjacent lacunae. During the 
process of injection from the above sinus the fluid 
introduced passes through these partly into the 
body-wall, partly into the body-cavity in either 
case finally reaching the pulmonary circulus, to- 
wards which all those channels in which venous 
blood circulates eventually converge. 

c. The afferent pulmonary vessels ; arising from the pul- 
monary circulus on all sides. They alternate with 
striking regularity with the efferent pulmonary 
vessels, the two sets of trunks being connected by 
a well-differentiated respiratory plexus. 

The afferent pulmonary vessels of the left side 
and front wall of the lung-sac are elongated. 
Those of its right side are very short, but in so far 
as their relations to the lung-sac are concerned 
they differ from their fellows in no other respect ; 
after leaving that to reach the heart however, they 
enter the excretory organ and break up within it 
into a renal plexus, from which the efferent renal 
vessels previously described (Sec. H. i b) arise. 


296 ELEMENTARY BIOLOGY. [CHAP. 

The walls of the vessels concerned in respiration 
are frequently pigmented. The entire pulmonary 
system can therefore be generally followed in an 
uninjured specimen, without the aid of injection, by 
examining with care the wall of the lung-sac from 
the outside. 

I. The nervous system. 

i. Pin the animal down right side uppermost and open 
up the lung-sac, cutting along the edge of the rectum ; 
divide the latter, together with the adjacent excretory- 
duct and lung-sac, across its middle transversely, and 
reflect the left hand half. Next remove the right 
half of the wall of the body and visceral-sac, together 
with the tentacles of the same side and the greater 
portion of the genital apparatus. Remove the foot 
to the level of the pedal gland, and with it the right 
half of the retractor pedis muscle. Follow in the 
order given : 

a. The central nervous system. It consists of a cir- 
cum-cesophageal mass, buried up in a loose con- 
nective-tissue sheath. Carefully dissect away the 
superficial portion of the sheath, until the nerve- 
ganglia are exposed (looked at thus from the side, 
but one set will be seen) ; they are- 

b. The supra- (zsophageal ganglia ; two considerable 
masses lying above the gullet, connected together 
by a short band-like commissure. 

c. The pedal ganglia ; two large masses lying im- 
mediately above the pedal-disc. They distribute a 
considerable series of fibres ventrally to the foot 
and pedal gland, and a smaller set laterally to the 
adjacent body-wall. Each pedal ganglion is united 


IV.] THE COMMON SNAIL. 297 

to the supra-cesophageal of its own side by a 
cerebro-pedal commissure. 

J. The parieto-splanchnic ganglia; a series of gangli- 
onic masses lying in close apposition, immediately 
behind and a little above c. They give off fibres 
(on the right side three sets and on the left two), 
which enter the body wall at the base of the 
visceral sac. 

The anterior fibres (pallial nerves) enter the 
thickened border of the lung sac, within which they 
anastomose. 

The ganglia of either side are connected with 
the supra-oesophageal by a cerebro-splanchnic com- 
missure^ which runs parallel with but is somewhat 
shorter than the cerebro-pedal one. 

e. The posterior-visceral nerve ; a single nerve arising 
from d. altogether to the left side. It passes back 
immediately beneath the anterior aorta (which it 
accompanies) to enter the visceral sac. On doing 
so, it gives off branches as under 

a. A main one, running on to reach the left side of 
the visceral sac. 

(3. A right one, whose fibres can be traced to the 
albumen-gland and duct of the ovotestis. 

y. A dorsal one, arising from the main trunk, in 
the immediate vicinity of the enlarged head of 
the spermatheca. It is distributed to the excre- 
tory-organ and heart. 

2. Remove sufficient of the cephalic wall of the right 
side to expose the whole buccal mass. Look for 


298 ELEMENTARY BIOLOGY. [CHAP. 

a. The buccal nerves. That of the right side will 
alone be seen ; it arises from the supra-oesophageal 
ganglion, and passes downwards and forwards to- 
wards the buccal mass. Trace it with care it 
passes beneath the dorsal protractor muscle (see 
Sect. E. i b\ and terminates in a small buccal 
ganglion, lying just behind the enlarged base of the 
salivary-duct. 

Just before it reaches the muscle referred to, it 
usually gives off two or three branches to the 
antero-lateral wall of the buccal-mass. 

b. The anterior visceral nerves ; a system of fibres 
arising from the above ganglion. The following 
can be seen with ease. 

a. A ventral branch, distributed to the oesophagus. 

(B. A dorsal one, to the salivary gland, the duct 
of which it accompanies. 

y. An anterior one, to the roof of the buccal- 
mass. 

3. Remove the whole nervous system, together with the 
buccal-mass and tentacle-bearing portion of the 
cephalic integument. Pin down under water with 
its posterior end uppermost, and dissect off as much 
as possible of the sheath of the nerve-collar. Note, 
in addition to the nerves already dissected- 

a. The buccal commissure; a delicate tract of nerve- 
fibres, seen, on raising the cut end of the oeso- 
phagus, to connect the buccal ganglia of opposite 
sides. It passes beneath the gullet. 


IV.] THE COMMON SNAIL. 299 

b. The anterior aorta. Its cut end is clearly visible 
at this stage. (Cf. Sect. H. 3 />.) It perforates 
the nerve-collar ventrally, running beneath the 
parieto-splanchnic and above the pedal ganglia. 

c. The tentacular nerves ; arising, together with the 
labial nerves, from the sides of the supra-ceso- 
phageal ganglia. The nerve to the optic tentacle 
is connected with a special ganglionic lobe. 

J. The Sense-Organs. 

i. Obtain a specimen in which the tentacles are fully 
extended. Remove the cephalic integument and 
tentacles, together with the nervous system, en masse; 
pin down very carefully under water and dissect 
under a lens. Open up the tentacles and note- 

a. The retractor muscles ; two ribbon-shaped bands 
arising from the extreme anterior ends of the 
tentacles ; they pass back to be inserted into the 
shell axis, side by side with the larger retractors 
already described (Sect. E. i a}. 

The muscles of the smaller pair of tentacles re- 
ceive slips from the adjacent cephalic integument. 

b. The labial tentacle. Note that the upper end of its 
retractor muscle is darkly pigmented. Trace up 
the tentacular nerve which accompanies the muscle; 
it ends in a large pear-shaped ganglion, from which 
fibres are distributed to the integument investing 
the free end of the tentacle. 

The nerve sends a branch to the adjacent cephalic 
integument. 

c. The ocular tentacle and eye. Its retractor muscle 
and nerve repeat the conditions described for b ; a 


300 ELEMENTARY BIOLOGY. [CHAP. 

large terminal ganglion is present, in relation to 
the integument investing its free end. 

The visual organ is perceptible as a minute 
black spot, lying to the outer side and a little in 
front of the ganglion. A delicate optic nerve can 
be traced back from it to the tentacular nerve, 
which it enters a short distance behind the above- 
named ganglion. 

2. Remove the eye together with a small portion of its 
related integument, and examine in water under a 
low power. Note 

a. The cJwroid; a pigmented investment for the eye, 
under cover of which the optic nerve passes to 
reach the retina. 

b. The crystalline lens ; seen to project freely beyond 
a. in front. It lies under cover of a delicate 
cornea. 

3. The auditory organ. Pin one half of the nerve-collar 
down under water, and, having dissected off the 
superficial stratum of its sheath, examine with a lens. 
Note- 

a. The auditory nerve ; a delicate undulating trunk, 
lying in the interspace between the cerebro-pedal 
and cerebro-splanchnic commissures. Follow it 
up it arises from the supra-cesophageal ganglion. 
Below, it enters the otic vesicle, now seen as 
a minute white speck, overlying the point of 
apposition of the pedal and parieto-splanchnic 
ganglia. 

b. The otic vesicle. Remove this, together with a 
small portion of its surrounding tissues, and 


IV.] THE COMMON SNAIL. 30 1 

transfer in toto to a glass slide. Cover and ex- 
amine in water under a low power. It appears as 
a conspicuous round vesicle, lodging a refractive 
black-looking granular contents. 

Examine under a high power. It is seen to 
consist of a small sac (otocyst} closed on all sides 
and in no way connected with the exterior. It is 
filled with a fluid contents, in which are suspended 
a large number of small oval calcareous corpuscles 
or otoliths. Trace the passage of the auditory 
nerve into the vesicle. 

K. The reproductive elements. 

Remove a small piece of the ovotestis, and mount in 
aqueous solution of Eosin. Examine under a low power 
and note 

a. The hermaphrodite follicles ; small ccecal diverticula 
of the ovotestis, from the epithelial lining of which 
the sexual products are derived. They are arranged 
in grape like aggregates. 

The appearances met with will be found to vary 
with the season of the year. If spermatogenesis is 
going on there will be found, floating in the central 
cavity of each follicle, spermatozoa in all stages of 
development. If the ova are undergoing maturation, 
they will be found, in all stages, still adherent to 
the germinal epithelium. 

Crush under the weight of a cover-glass and examine 
under a high power. 

a. The ripe spermatozoa. Each is an elongated fili- 
form body, bearing a small head-like enlargement 
at one end. They are commonly met with in 
aggregates. 


302 ELEMENTARY BIOLOGY. [CHAP. 

Immature spermatozoa are at times present in 
abundance. They can be recognised by the relatively 
large size of the 'head', which is oval and can be 
distinctly seen to lodge a small nucleus. (Cf. Luni- 
bricus and Rana.) 

b. The ripe ovum. Examine under a high power. 
a. Its shape; usually round, more rarely oval. 
ft. The absence of a distinct vitelline membrane, 
y. The protoplasm ; consisting of a central uniformly 

granular vitellus, which graduates peripherally 

into a superficial clear layer. 

8. The germinal vesicle ; a large round structure, 
usually containing one immense germinal spot. 

L. Development. (The Pond Snail, Lymnccus stagnalis.} 

See p. 278. 

Examine the developing eggs from time to time, and look 
especially for 

a. The fertilized ovum during segmentation. It divides 
up into two sets of cells a smaller rapidly dividing 
clearer set, and a larger slowly dividing yolk-laden 
set (the presence of the yolk gives these an 
opaque coarsely granular appearance). Look out 
for polar bodies (see p. 278). 

b. The same at the close of segmentation. Looked at 
from the outside the larger cells appear as a dark 
mass, lying within the smaller more transparent 
ones, which have now completely overgrown them. 

c. The gastrnla phase, immediately following upon b. 
Examine from beneath and note 

a. the blastopore; a small slit-like orifice on the 
flattened under surface. 


IV.] THE COMMON SNAIL. 303 

Examine from the side in optical section. 

fi. The archenteron; a sac-like pit opening externally 
by the blastopore, its walls are formed of the 
invaginate yolk-bearing endoderm cells. 

y. The ectoderm ; a single layer of investing cells, the 
product of the more transparent rapidly dividing 
ones referred to above. 

S. The cleavage-cavity or blastoccele ; a spacious cavity, 
enclosed between the investing and invaginate 
layers. 

d. The Trochosphere larva; recognizable by its egg- 
shaped contour and rotatory movements, 
a. The mouth; a small median orifice situated at the 
enlarged end. 

fi. The trochal ridge ; a saddle-like band encircling 
the dorso-lateral area pre-orally. Look for its 
cilia. 

Examine in optical section and note 

y. Thejfo?/ (it first appears at this stage); a median 
ventral outgrowth of the body wall just behind 
the mouth. 

8. The stomatodczum ; a blind sac-like involution of 
the integument, its aperture giving rise to the 
mouth. 

e. The archenteron; now partially surrounded by a 
conspicuous large-celled granular mass the 
digestive gland, arising as an outgrowth of its 
wall. 

Note the bilateral symmetry of the larva at this 
period. The blastopore appears shifted back, 
as the result of elongation of the embryo and 


304 ELEMENTARY BIOLOGY. [CHAP. IV. 

displacement, upon the development of the foot. 
An integumental pit known as the shell-gland, 
appears at the hind end of the body during this 


stage. 


e. The Veli^er larva. A head- segment is now be- 

o O 

coming differentiated, and the rotatory movements 
of the animal are less marked. Bilateral symmetry 
is becoming disturbed. Note especially 

a. The velum ; a ciliated pre-oral fold, occupying 
the position of the original trochal-ridge. 

ft. The foot i now greatly increased in size and 
utilized for purposes of locomotion. 

y. The eye-spots ; two black masses at the sides of 
the head segment. 


-& J 


f. The advanced larva. Tentacles are now appearing, 
as paired outgrowths of the cephalic wall (the eyes 
are not carried up by them as in Helix). The 
original bilateral symmetry no longer obtains. 
Note the beat of the heart ; the presence of the 
visceral sac and of its related shelL at this stage 
a transparent chitinous cap. The velum is under- 
going a marked reduction. 

If any difficulty is experienced in examining the 
embryos in the living state, they should be liberated 
from the surrounding albuminous investment by 
means of a couple of needles, and submitted, for 20 
minutes, to the action of ^ p.c. Osmic acid solution. 
They may then be transferred to alcohol of in- 
creasing strength, and preserved for future ex- 
amination. 


V. 

THE FRESH-WATER MUSSEL 
(Anodonta Cygtuza). 

UNDER the name of 'Fresh-water Mussel' two distinct kinds 
of animals, which are not unfrequently abundant in our ponds 
and rivers, are included; namely, the Anodonta and two or 
three kinds of Unio. The Anodonta is chosen for special 
study here, but what is said about it applies very well to 
nearly all parts of Unio except the shell. 

The animal is enclosed in a shell composed of two pieces 
or valves, which are lateral, or right and left, in relation to 
the median plane of the body. The more rounded and 
broader end is anterior, the more tapering, posterior. If 
placed in a vessel of water, at the bottom of which there is a 
tolerably thick layer of soft mud or sand, and left quite un- 
disturbed, the Anodonta will partially bury itself with its an- 
terior end directed obliquely downwards; and the valves will 
separate at their ventral edges for a short distance. At the 
edges of this 'gape' of the shell the thickened margins of a 
part of the contained body which is called the majitle, be- 
come visible, and between them a large, whitish, fleshy, 
tongue-shaped structure the foot not unfrequently pro- 
trudes, and is used to perform the sluggish movements of 
which the Anodonta is capable. Mud ' 'tracks' 1 are left 
behind the animal when in motion, as can be seen on ob- 
serving its natural habit in slow running or still shallow 

M. 2O 


306 ELEMENTARY BIOLOGY. [CHAP. 

waters. If some finely dividing colouring matter, such as 
indigo, is dropped into the water, so as to fall towards the 
gape, it will be seen to be sucked in; while, after a short 
time, a current of the same substance will flow out from an 
opening between the two edges of the mantle on the dorsal 
side of the posterior end of the body; and these 'inhalent' 
and 'exhalent' currents go on, so long as the animal is 
alive and the valves are open. Any disturbance, however, 
causes the foot, if it was previously protruded, to be re- 
tracted, while the edges of the mantle are drawn in and the 
two valves shut with great force. This adduction results 
from the contraction of two thick bundles of muscular 
fibres, which pass from the inner face of one valve to that 
of the other, one at the anterior and the other at the 
posterior end of the body, and are called the anterior and 
posterior adductors* The valves of the dead Anodonta 
always gape, and if they are forcibly shut they spring open 
again. The reason of this is the presence of an elastic 
band or ligament, which unites the dorsal margins of the 
two valves, for some distance, and is put upon the stretch 
when the valves are forcibly brought together. The natural 
tendency to divarication of the valves resulting from this, is 
held in check during life by the contractions of the afore- 
named adductor muscles. These respond to a nervous 
stimulus, and, on the death of the animal, that being with- 
drawn, the full force of the elasticity comes into play, the 
valves becoming divaricated to their utmost extent. 

The animal can be extracted from the shell without 
damage, only by cutting through these muscles close to their 
attachments. It is bilaterally symmetrical, the foot pro- 
ceeding from the middle of its ventral surface. There is a 
total absence of any distinct head segment such as is seen 
in the Snail. The mouth is median and situate between 


V.] THE FRESH-WATER MUSSEL. 307 

a projection, which answers to the under surface of the 
anterior adductor muscle, and the superior attachment of 
the foot. On each side of the mouth are two triangular 
flaps with free pointed ends the labial palpi and behind 
these, on each side, two broad plate-like organs, with ver- 
tically striated outer surfaces, are visible. These are the 
gills or branchiae. In the dorsal region, the integument is 
soft and smooth; on each side,, it is produced into large 
folds, the lobes of the mantle or pallium, which closely 
adhere to the inner surface of the valves of the shell, and 
end, ventrally, in the thickened muscular and glandular 
margins already mentioned. They pass into one another 
in front of the mouth; at the sides, they are united with 
the dorsal edges of the outer gill-plates ; and, behind, 
they extend upwards and on to the dorsal face of the 
body, finally passing into one another above and in front 
of the anus, which is small, tubular, prominent and 
median. Thus the anus is inclosed in a part of the cavity 
bounded by the two mantle-lobes which lies above the gills, 
it is relatively small and shallow, and is termed the supra- 
branchial or cloacal chamber ; while the gills, the foot, and 
the palps, hang down into the relatively large infra-branchial 
chamber which occupies the space between the mantle- 
lobes for the rest of their extent. During life the posterior 
margins of the mantle lobes are prolonged for a short dis- 
tance behind the free edge of the valves, and they come 
into apposition at the point of attachment of the gills 
in such a way as to give rise to two tubes or siphons a 
dorsal supra-branchial one which receives the anus, and a 
ventral one communicating with the infra-brancJiial chamber 
alone. The dorsal siphon is the channel through which 
the exhalent currents pass; the ventral, that for the inhalent 
currents. 

20 2 


308 ELEMENTARY BIOLOGY. [CHAP. 

The currents are produced and kept up by the action of 
the cilia, which abound upon the gills, labial palps and 
inner face of the mantle. The gills are perforated by in- 
numerable small apertures, and the cavities contained 
between the two lamellae of which each is formed, are 
in communication, above, with the cloacal chamber. The 
cilia work in such a way as to drive the water in which the 
animal lives 'from the outer surface of each gill towards its 
interior. Hence, to a large extent, the current which sets 
from the infra-branchial to the cloacal chamber. 

The current of water which is thus continually drawn into 
the infra- branchial chamber carries with it minute organ- 
isms, Infusoria, Diatoms and the like, and many of these 
are swept to the fore part of the chamber, where they enter 
the mouth, and are propelled by the cilia which line its 
cavity into the alimentary canal. The latter presents a 
short and wide gullet, a stomach surrounded by a digestive 
gland, a long intestine coiled upon itself, in a somewhat 
complicated manner, and, finally, a rectum, which lies in 
the middle line of the dorsal aspect of the body, traverses 
the pericardium and the heart which lies therein, and ends 
in the anus. 

The subdivision of the mantle-cavity into supra and 
infra branchial chambers is, in the long run, the result of 
confluence of adjacent gill-laminos with each other and 
with the pallial lobes. The gill-perforations, the groove en- 
closed by the labial palps and the aperture of the mouth 
towards which it leads, all open into the lower or inha- 
lent chamber; while the upper or exhalent one receives 
the anus, and both genital and excretory orifices. During 
life the thickened margins of the pallial lobes are in close 
apposition ; consequently, the infra-branchial chamber is 
closed below and in front, both it and the supra-branchial 


V.] THE FRESH-WATER MUSSEL. 309 

one communicating with the surrounding medium through 
the agency of the siphonal prolongations of the mantle 
border alone. The walls of the two chambers and the 
surfaces of all the organs contained within them, together 
with the whole lining membrane of the alimentary canal, 
are ciliated, and the currents thereby induced set in, as 
before stated, by the lower and out by the upper siphon. 
One of three courses is open to the inhalent current with its 
suspended food material it may pass either through the 
gills, through an interspace between the gills and the body 
wall, or into the mouth. Take whichever course it may, it 
finally reaches the supra-branchial chamber. It follows that 
the insetting current is both a nutritive and a respiratory 
one, while the outsetting one serves to carry away the 
waste products of respiration and digestion, together with 
the products of the excretory and genital organs. 

The clue to the real meaning of the more important 
structural features in the organization of this animal, is to 
be sought in an understanding of the above facts. 

Digestion, that is solution of the proteinaceous and other 
nutritive matters contained in food, is effected in the sto- 
mach and intestine; and the nutritious fluid, thus formed, 
transudes through the walls of the alimentary cavity and 
passes into the blood contained in the blood-vessels which 
surround it. This blood is thence carried into a large sinus, 
which occupies the middle line of the body under the peri- 
cardium and between the organs of Bojanus (see Laboratory 
Work E), and receives the greater part of the blood return- 
ing from all parts of the body. From this median vena cava, 
branches are given off to the gills and open into the exten- 
sive vascular network which those organs contain. From 
this, again, trunks lead towards the pericardium and open 
into one or other of the two auricles of the heart, which 


310 ELEMENTARY BIOLOGY. [CHAP. 

communicate by valvular apertures with the ventricle. The 
ventricle gives off two aortic trunks, one of which, the ante- 
rior, runs forwards in the middle line, above the rectum, 
while the other runs backwards, below the rectum. From 
these two aortae branches are given off which divide into 
smaller ramifications for the different regions of the body, 
and for the viscera, and finally terminate in channels which 
answer to the capillaries of the higher animals. 

The pericardial cavity, in which the heart is lodged, is 
situated in the posterior half of the dorsal region of the 
body. Through its thin dorsal wall, and, still better, when 
it is carefully laid open, the heart can be seen beating. The 
auricles contract, and, after them, the ventricle; the wave- 
like contraction of the latter being much the more easily 
visible. The lips of the auriculo-ventricular apertures are so 
disposed that the blood is impeded from flowing back into 
the auricles, when the ventricle contracts, and is forced out, 
either forwards or backwards, through the two aortae. From 
these it finds its way to the capillaries, and returns from them 
to the vena cava; whence it is carried, through the organs of 
Bojanus, to the branchiae. Here it becomes purified of car- 
bonic anhydride, and receives oxygen from the water in 
which the branchiae are plunged; and it is finally brought 
back in an arterialized condition to the heart. 

The heart is therefore systemic and propels aerated 
blood. As the heart, in most animals, first appears either 
in close proximity to, or in the substance of, the wall of the 
embryonic alimentary canal, there is no real anomaly in its 
position in the Anodonta. 

The blood of the Anodonta is colourless, and contains 
colourless corpuscles, which resemble those of Man in struc- 
ture and present the same Amcebiform movements. 

The majority of the vessels which convey the blood from 


V.] THE FRESH-WATER MUSSEL. 311 

the vena cava to the branchiae, traverse the walls of the 
dark-coloured organs the organs of Boj anus which have 
already been mentioned; and they here part with their 
nitrogenous waste matters the organ of Bojanus playing 
the part of a kidney. The cavity of the organ of Bojanus 
communicates, on the one hand, with the pericardium; and, 
on the other, with the exterior, by an aperture to which 
reference has already been made. Thus the cavity of the 
pericardium communicates directly with the exterior, though 
by a roundabout way. 

The organ of Bojanus consists of a pair of modified tubes, 
each of which can, like the nephridium of the worm, be 
resolved into three segments an internal non-glandular, a 
middle glandular, and a terminal muscular one. The rela- 
tions of the whole to the pericardium in this animal, are as 
those of any one pair of segmental organs to the body-cavity 
in the worm; and if so be that the pericardium of Anodonta 
is, like that of the Frog, a direct derivative of the body-cavity, 
the excretory organ is in no way anomalous in its rela- 
tionships. 

The digestive gland of this animal is mainly concerned 
in the elaboration of a digestive fluid. The production 
of combustible carbo-hydrate material a function by no 
means confined to the liver in other animals goes on to a 
considerable extent in other far removed parts of the body, 
glycogen being formed. The connective-tissues and espe- 
cially the mantle lobes are remarkable for its presence, it 
being elaborated in the form of large intra-cellular vesicles, 
as the product of activity of certain of the connective-tissue 
corpuscles 1 . 

The nervous system of the Anodonta consists mainly of 

1 Similar glycogenous cells are met with in the walls of the lacunar 
spaces and on the ' mesenteries ' of the Snail. 


312 ELEMENTARY BIOLOGY. [CHAP. 

three pairs of yellow ganglia; the cephalic, situated at the 
sides of the mouth; the pedal, placed in the foot; and the 
parieto-splanchnic, on the under face of the posterior adductor 
muscle. They are united by commissural cords which con- 
nect the cephalic ganglia with one another, and with the 
pedal and parieto-splanchnic ganglia, respectively. Traces 
of a small fourth pair of ganglia may be obvious on the 
cerebro-splanchnic commissures, near the anterior end of 
the pericardium. As the parieto-splanchnic ganglia are 
immediately connected with a patch of sensiferous epi- 
thelium in the roof of the inhalent siphon, they are sometimes 
regarded as olfactory. The only other sense organs which 
have been discovered, are a pair of auditory vesicles, con- 
nected by nervous cords with the pedal ganglia. 

The sexes are distinct. The tcstes and ovaria are similar 
in character, being racemose glands, which, in the breeding 
season, occupy a great part of the interior of the body. 
There is one gland on each side, opening by a minute aper- 
ture close to that of the organ of Bojanus. 

The spermatozoa have minute, short, rod-like bodies, to 
which a long, filamentous, active cilium is attached ; they 
are thrown off in enormous numbers, and make their way 
out with the exhalent currents. 

The ova are spherical, and the vitelline membrane is defi- 
cient at one point, leaving a terminal aperture or micropyle, 
through which, in all probability, the spermatozoon makes its 
entrance. When fully formed, multitudes of these ova pass 
out of the oviducal apertures and become lodged in the 
chambers of the gills, particularly the external ones, which 
during autumn and winter are completely distended by 
them and the embryos to which they give rise. 

Segmentation is holoblastic, and the early developmental 
phases resemble, in their main features, those already de- 


V.] THE FRESH-WATER MUSSEL. 313 

scribed for the Snail the original bilateral symmetry is 
however never disturbed. 

The embryos when hatched, are so wholly unlike the 
parent Anodonta, that they were formerly thought to be 
parasites, and received the name of Glochidium. Each is 
provided with a bivalve shell, and each valve has the form 
of an equilateral triangle united by its base with its fellow, 
by means of an elastic hinge, which tends to keep the two 
wide open. The apex of the triangle is sharply incurved, 
and is produced into a strong serrated tooth, so that when 
the valves approach, these teeth are directed towards one 
another. The mantle is very thin, and the inner surface of 
each of its lobes presents three papillae, terminated by fine 
pencils of hair-like filaments. The oral aperture is wide, 
and its margins are richly ciliated. There is a single ad- 
ductor muscle and a rudimentary foot, from which one or 
two long structureless filaments, representing the byssus of 
the sea-mussel, proceed. These byssal filaments become 
entangled with one another and tend to keep the ' Glochi- 
dia ' in their places. 

The gill-laminae of Anodonta will accommodate some 
three millions or more of these Glochidia. If the animal is 
living in company with fish it will eject them, whereupon 
they attach themselves to floating bodies very commonly 
to the tails, fins or gills, of fishes by digging the incurved 
points of their valves into the integument in the latter case, 
and holding on by them as if they were pincers. In this situa- 
tion they become encysted in an epidermal overgrowth of 
the host's body, within which they undergo a final metamor- 
phosis. 

The alimentary canal and foot become more marked with 
the increased development of the whole body ; the gills 
appear, in the form of filamentous outgrowths of the body- 


314 ELEMENTARY BIOLOGY. [CHAP. 

wall, which become plumose and subsequently unite to 
form the adult gill-lamellae; the byssus is thrown off, and 
the larval shell and adductor muscle are replaced by newly- 
formed valves provided with two adductors. The young 
Anodonta at length drops off and falls into its ordinary 
habitation in the mud, a bilaterally symmetrical animal, 
differing from its parent only in the absence of functional 
reproductive organs. 


LABORATORY WORK. 

The contraction of the foot and consequent displace- 
ment of the viscera, resultant upon death under chloroform, 
may be overcome by killing the animal in water sufficient to 
cover it heat slowly to about 40 C. 

In an animal freshly removed from the water only the 
shell or cxoskddon is visible, but if killed as above directed 
this will be slightly open, the foot will be protruded as 
in life and the edge of the membrane lining it (the mantle] 
will be visible. Raise one valve of the shell, by separating 
the mantle from it with the handle of a scalpel, and then 
cut through two strong bodies (the adductor muscles], one 
at each end of the animal, which pass from valve to valve 
and prevent their separation. The two valves will now be 
united only by their ligament, as the result of whose elas- 
ticity they gape ; cut through this, thus liberating one 
valve and work over 

A. General external characters. 

i. In the animal now laid bare may be distinguished 
a. A dorsal border turned towards the hinge of the 


V.] THE FRESH-WATER MUSSEL. 315 

shell, and nearly straight. A curved ventral border, 
opposite the dorsal. 

b. A wider anterior end. A narrower posterior end. 

c. A right and left side. 

2. Pin the animal down under water without removing 
its remaining valve (insert the pins obliquely, so that 
they embrace, and exercise a downward pressure 
upon, the edges of the valve). Examine in order- 

a. The mantle ox pallium ; a bilobed semitransparent 
membrane, one lobe lining each valve of the shell. 
Examine its ventral border, it is yellowish in colour 
and thickened to form a pallial muscle. 

b. The adductor muscles of the valves ; two immense 
masses whose cut edges are visible at opposite ends 
of the body. 

c. The retractor pedis muscles; smaller masses, one at 
the upper end of each adductor. The anterior one 
is posterior, and the posterior one anterior, to its 
corresponding adductor. 

d. The protractor pedis muscle; uniform in diameter 
with c. It lies a little below the anterior re- 
tractor. 

e. The lesser retractors ; insignificant bundles of fibres 
arising from the extreme dorsal surface of the body 
wall. 

3. Turn back the parallel lobe, and note under- 
lying it- 

a. The ventral portion of the body. It projects for- 
wards and downwards, immediately behind the 
anterior adductor muscle : it is thickened ventrally 


316 ELEMENTARY BIOLOGY. [CHAP. 

to form the locomotor foot ; a large, yellowish, 
somewhat ploughshare-shaped mass, whose apex 
projects freely between the mantle-lobes. 

b. The gills or branchm; two lamellar organs on each 
side of the body, extending to its posterior end. 

c. The labial palps ; a pair of membranous folds on 
each side, in front of the gills and immediately 
below the protractor pedis muscle. Note the 
structural similarity between them and the gills. 

B. The pallial-lobes, in relation to adjacent structures and 
the exterior. The branchial chambers and siphons. 

Remove the animal completely from its shell, by detach- 
ing the other mantle-lobe from the valve to which it is fixed 
and cutting through the attachments of the muscles to the 
same. 

Pin down under water (the pins should preferably be 
thrust through the adductor muscles). Raise the pallial 
lobe nearest you with forceps and remove it, cutting along 
its line of confluence with the underlying organs and the 
body wall. Examine carefully 

a. The infra-branchial chamber y bounded above and 
externally by the pallial lobe, a c of Section A. 3 
lie within it. 

Follow the cut edge of the mantle, working from 
behind forwards. It courses along the dorsal 
border of the external gill lamella, whence it passes 
downwards and backwards to reach the labial 
palps; it skirts these in a similar manner, and is 
continued on beneath the anterior adductor 
muscle. 


V.] THE FRESH-WATER MUSSEL. 317 

b. The mouth; a wide aperture, lying immediately 
behind and below the anterior adductor muscle. 
It is encircled by the labial palps. 

c. Examine the thickened posterior border of the 
pallial lobe. It is prolonged backwards for a 
short distance as a pigmented tentacle-bearing lip 

-the wall of the ventral siphon. Compare the 
living animal, as it lies with its anterior end buried 
in the sand, and note 

a. The projection of the ventral siphon beyond the 
free edges of the valves. 

ft. The close apposition of the thickened ventral 
margins of the pallial lobes. 

y. The siphonal tentacles. A series of small con- 
tractile finger-like lobes, the larger of which 
project freely across the siphonal passage in 
the path of the insetting current. 

Touch one of them with a bristle and note 
the immediate closure of the siphonal aperture 
-the tentacles are highly sensitive. Examine 
one of the longer ones under a lens ; its base is 
swollen and it terminates in a slightly expanded 
and flattened extremity. 

3. Examine the relations of the gill laminae. The 
outer one is confluent with the pallial lobe 
externally and with the inner lamina internally, 
for its whole length: the inner one is confluent 
with the body wall for a short distance in front 
and with its fellow of the opposite side behind ; 
there is a spacious cleft between it and the body 
wall. 


3l8 ELEMENTARY BIOLOGY. [CHAP. 

d. Insert the point of a scissors into the pallial lobe 
immediately above the gill laminae, and make an 
incision which shall pass under the posterior 
adductor muscle and immediately over the line of 
attachment of the outer gill-lamina. A large 
opening will be found in the dorsal middle line, in 
the region of the posterior adductor muscle; insert 
the scissors blade into this and cut obliquely 
backwards. There will now be laid bare the 
supra-branchial or cloacal chamber, 

a. Follow its boundaries. It ends blindly in front, 
immediately above the most anterior point of 
attachment of the gills. It opens posteriorly by 
two orifices; a dorsal median one referred to 
above, and a posterior one, whose lips are 
produced into a short smooth-walled dorsal 
siphon. It is walled in dorsally and externally 
by the pallial lobes and ventrally by the gill- 
laminae. 

(3. The suspensory ligament of the gills can now be 
seen; it is a membranous fold arising immediate- 
ly beneath the posterior adductor muscle. In- 
sert a seeker from below into the supra-branchial 
chamber, through the cleft between the body 
wall and inner gill-lamina. It passes internally 
to this ligament, which therefore subdivides the 
greater part of the supra-branchial chamber into 
two portions, each of which is in open commu- 
nication with one gill-cavity. 

y. Remove the anterior portion of fi and note, 
opening into the inner subdivision of the supra- 
branchial chamber, the genital and excretory 


V.] THE FRESH- WATER MUSSEL. 319 

orifices; two small apertures lying one above the 
other and embraced postero-ventrally by a 
common lip. (For further details see Sects. E. 
and L. a. .). 

S. The rectum; a yellowish thin-walled tube cours- 
ing over the hind face of the posterior adductor 
muscle. It opens by a terminal wide-mouthed 
anus. 

Introduce into the immediate vicinity of the 
ventral siphon of the living animal some finely 
divided colouring matter. It will be drawn into 
this with the inhalent current induced by the 
ciliary action at work, and ejected, a little later, 
through the dorsal siphon with the exhalent one. 
(Cf. pp. 308-9). 

e. Note the position and general relations of the 
pericardia I cavity. It lies in the middle line 
immediately above the supra-branchial chamber, 
wholly in front of the posterior adductor muscle. 
Examine in relation to it 

a.. the organ of Kcber (pcricardial gland] ; a red- 
brown thickening of the adjacent body-wall 
and pallial-lobe ; it is most conspicuous ante- 
riorly, above the gills. 

{3. Lay open the cavity of the pericardium and note 
the rectum; a yellowish tube, passing through it 
on its way to the supra-branchial chamber. It 
is surrounded at its middle by the yellow thick- 
walled ventricle. (For further details see Sects. 
F. and L.) 

Kebers organ can be advantageously seen 
at this stage, if looked at from within. 


320 ELEMENTARY BIOLOGY. [CHAP. 

C. The alimentary organs. 

1. Remove the valve, mantle-lobe, gills and labial-palps 
of the left side, and open up the pericardium. 

Pin down under water (preferably without remov- 
ing the right valve) and dissect away the body-wall; 
the coils of the intestine will come into view, two 
which lie parallel to one another at the posterior 
end of the body, being probably those first seen. 
Note, lying within the body 

a. The digestive gland ; a large greenish-brown mass, 
filling the interspace between the anterior adductor 
muscle and the pericardium. 

b. The reproductive gland ; a yellowish-white mass 
lying around the coils of the intestine, and filling 
the greater portion of the body-cavity. 

2. Remove one half of the digestive gland piecemeal 
and pick away the reproductive gland, until as much 
as possible of the course of the intestine is exposed. 
Work out the whole alimentary tube in detail, com- 
mencing at the mouth; examine in order 

a. The gullet; a spacious tube lying immediately 
behind the anterior adductor muscle; it runs 
upwards and backwards to enter 

b. the stomach, a large irregular sac lying immediately 
in front of the pericardium. 

Both a. and b. are buried up in the substance of 
the digestive gland ; the ducts of this will be seen 
opening into b. by a series of very large orifices. 
Examine the relationship of one or more of these 
to the lobes of the gland itself. Cf. Sec. L. d. 

c. The intestine. It arises by a wide aperture from 
the floor of the stomach; insert a scissors blade 


V.] THE FRESH- WATER MUSSEL. 321 

into it and lay bare its entire lumen its course 
is as follows. It first passes to the left side down- 
wards and backwards, and, on nearing the hinder 
end of the body, turns upwards towards the peri- 
cardium; it then bends sharply upon itself and 
passes downwards and backwards, in a line with 
the free posterior edge of the body-wall. On 
reaching the middle ventral region it is again bent 
sharply upon itself, passing upwards and back- 
wards altogether to the right side; at about the 
middle of the reproductive gland it becomes 
suddenly greatly enlarged, and passes (parallel 
with the first segment) upwards and forwards 
towards the anterior end of the pericardium. It 
enters this at its base, and, running upwards and 
backwards, leaves it postero-dorsally, finally pass- 
ing over the posterior adductor muscle. (Cf. 
Sect. B. d. 8.) 

d. Having laid bare the interior of the intestine, re- 
duce its walls to the condition of median longi- 
tudinal section and examine the intestinal valve or 
typhlosole; a thick rich yellow ingrowth of its lining 
membrane. It is very conspicuous in the first and 
the enlarged terminal segments. 

e. The labial-palps, in relation to the mouth. Obtain an 
undissected specimen, and, after removal from the 
shell, cut away the anterior end of the body, to 
the level of the labial-palps ; pin down and examine 
from beneath. The aperture of the mouth is oval. 
The labial-palps diminish in size as the mouth is 
reached and they embrace it in a lip-like fashion; 
they are confluent on either side and their free 

M. 21 


322 ELEMENTARY BIOLOGY. [CHAP. 

edges enclose a ciliated groove which leads directly 
to the oral aperture. 

f. Scrape off a little of the epithelium of the intestine ; 
mount in eosin and examine under a high power. 
Note the presence of cilia. 

Should difficulty be experienced in following the 
coils of the intestine, recourse may be had to injec- 
tion. Mix equal parts, by bulk, of plaster of Paris 
and water, stir well and strain through fine muslin ; 
inject with a small syringe per anum. 

D. The gills or branchiae. 

a. Cut out one of the gills and examine it under 
water; it will be found to consist of two lamellae 
united by their ventral edges and enclosing a 
central cavity, which opens into the epibranchial 
chamber above. The gill-cavity is subdivided by 
partitions, which pass from one lamella to the 
other, and carry the larger blood-vessels of the 
respiratory plexus. 

b. Carefully isolate a small piece of one lamella ; 
mount in water and examine with i inch obj. 
It will be seen to be traversed by a great number 
of small perforations, whose walls are supported 
laterally by short chitinous rods; the substance of 
the gill is permeated by a meshwork of large 
vessels. 

c. Examine under a higher power : the margins of 
each cleft are lined by a ciliated epithelium. 

E. The excretory organ (organ of Bojanus). 

Remove the animal from its shell and pin down 
through the adductor muscles. Dissect off the pallial 


V.] THE FRESH-WATER MUSSEL. 323 

lobe as directed for Sect. B. ; lay open the pericardial 
chamber and remove the auricle. The excretory organ 
will now be visible as a blackish mass underlying the 
floor of the pericardium; it becomes more marked 
posteriorly, and extends behind the pericardium, termi- 
nating immediately in front of the posterior adductor 
muscle. 

Remove the anterior two-thirds of the outer gill- 
lamina leaving its cut edge, and then dissect away 
carefully a portion of the anterior third of the outer 
wall of the inner lamina; there will thus be laid bare 

a. The excretory orifice (renal aperture); a small pore 
situated immediately below and behind the anterior 
end of the pericardium; it opens into the supra- 
branchial chamber, immediately above the genera- 
tive orifice. (Cf. Sect. B. d. y.) Insert a seeker 
into it and wash the whole under a gentle current 
until quite clean; the seeker will be found to 
project into 

b. the excretory vestibule (non-glandular portion of 
Bojanus); a thin-walled muscular sac, extending 
back to the hinder end of the pericardium. Open 
it up and gently raise its cut edge ; at its extreme 
anterior end it will be seen to be in communica- 
tion with its fellow of the opposite side, by an 
immense oval inter-renal aperture. 

c. Underlying b. and visible through its thin wall, 
there will now be seen the glandular segment of the 
organ. Open up the posterior portion of this, it is 
tubular and its walls are plicated. 

Examine the cut edges of the whole with care; 
note the transition from the glandular to the mus- 

21 2 


324 ELEMENTARY BIOLOGY. [CHAP. 


cular segments, as seen in the cut edge of the roof 
of the hinder portion of b. 

d. Follow the glandular segment forwards; it be- 
comes constricted anteriorly (in the region of the 
inter-renal aperture) to give rise to the thin-walled 
segment; a short whitish tube, which opens into 
the extreme anterior end of the pericardial 
chamber by a small reno-pericardial aperture. 
(Cf. Sect. F. 2. a.) 

F. The heart. 

i. Dissect an Anodonta from its shell, and remove the 
whole ventral portion of the body, well below the 
pericardium. Pin the upper portion down under 
water dorsal surface uppermost, and carefully lay 
bare the pericardial cavity. 

The heart will now be exposed; it is a yellowish 
transparent sac, probably exhibiting regular contrac- 
tions, composed of a median and two lateral chambers, 
these are 

a. the ventricle; a median pear-shaped body, its thick 
end directed backwards; it embraces the hind 
segment of the alimentary canal. All parts of the 
wall of the ventricle do not contract together; but 
a wave of contraction passes, from one end of it to 
the other, like the peristaltic contraction of the 
intestine in one of the higher animals. 

b. The auricles ; one of these will be seen on each 
side, if the ventricle be gently pushed out of the 
way: each is a somewhat pyramidal sac, continuous 
with the ventricle at the apex of the pyramid. 

c. Remove the dorsal wall of the ventricle and of a 
portion of one auricle. Note the thick spongy 


V.] THE FRESH-WATER MUSSEL. 325 

* 

nature of the former : at its point of communication 
with the auricle will be seen the auricula-ventricular 
valves; long pocket-shaped flaps, so disposed as to 
admit only of a flow of the blood from the auricle 
to the ventricle. 

2. Remove all but the bases of the auricles, and cut the 
rectum across at its extreme anterior end; turn it 
and the heart backwards, so as to lay bare the floor 
of the pericardium. Running along the middle line 
of this will be seen a large blood-sinus, the vena cava: 
it lies between the two excretory-organs. 

a. At the extreme front end of the pericardiac floor, 
immediately under the point at which the intestine 
enters the cavity, will be found the reno-pericardial 
apertures ; pass a bristle, or seeker, into one of 
them and open up the excretory vestibule of the 
same side. The glandular segment will now be 
seen the seeker projecting into it. Examine the 
general relations of the excretory organs, and 
their apertures of communication with the supra- 
branchial chamber. (Cf. Sect. E.) 

b. Examine the floor of one of the auricles under 
a lens, first having washed the specimen quite 
clean. Note the large orifices of the efferent bran- 
chial vessels which open into it. 

c. The organ of Keber. Follow its cut edge; it em- 
braces the antero-lateral region of the pericardium. 
(Cf. Sect. B. e. a.} 

G. The circulatory system. 

i. The arterial system. Lay bare the pericardial cavity 
and insert the point of a medicine-dropper, filled with 


326 ELEMENTARY BIOLOGY. [CHAP. 

injecting material, into the ventricle. Inject slowly, and dis- 
sect under water, right side uppermost. Remove the gills 
of the exposed side, together with the hinder three-fourths 
of the pallial-lobe ; leave the labial-palps, but remove the 
entire body-wall. Work from the ventricle and follow in 
order 

a. The anterior aorta; a spacious trunk embracing the 
rectum dorso-laterally. It runs across the digestive- 
gland to the right side, distributing branches to it 
as it does so, and enters the body immediately 
behind the anterior retractor muscle. Pick away 
the digestive and reproductive glands, and follow 
its course; it subdivides into visceral and pedal 
branches, asunder. 

a. The visceral artery. Its main branch accom- 
panies the first coil of the intestine; it distributes 
blood to the alimentary and reproductive organs. 

ft. The pedal artery. Follow its further course; its 
main trunk skirts the upper surface of the foot, 
and distributes a number of branches to the 
substance of the same. Soon after leaving the 
anterior aorta, it gives off a labial branch to the 
palps, and a pallial one to the anterior adductor 
muscle and pallial-lobe. 

b. The posterior aorta ; a much shorter trunk than a. 
It passes beneath the rectum and is mainly distri- 
buted to the posterior adductor muscle, the pallial 
lobes and body-wall. 

The two pallial arteries of either side anastomose 
within the substance of the thickened border of the 
mantle-lobe. 


V.] THE FRESH-WATER MUSSEL. 327 

2. Make a perforation in the roof of the ventricle, and 
pass the injecting apparatus through it into one of the 
auriculo-ventricular apertures; inject under a steady pres- 
sure, wash and examine the undissected animal under 
water. There will be seen 

a. The pallial sinuses ; a series of irregular channels 
permeating the substance of the pallial lobe. 

b. The efferent pallial vessel; a circular trunk, running 
along the upper surface of the thickened mantle- 
edge; it receives branches from the pallium at all 
points. 

Trace it upwards it follows the line of attachment 
of the pallial-lobe to the underlying organs (see 
Sect. B.); it is coincident, along the line of attach- 
ment of the gills, with the efferent-branchial sinus 


c. Remove the greater portion of the pallial-lobe, and 
examine the efferent-branchial vessels a series of 
short parallel trunks, lying in the walls of the gill- 
lamella:!; each is formed by the confluence of 
lesser vessels, coming in from the gill substance. 
They open into 

d. the efferent branchial sinus, a spacious chamber 
overlying the gills ; in the pericardial region it 
becomes expanded to form the auricle (Cf. Sect. 
F. 2. b.). 

3. Remove the rest of the mantle-lobe and open up the 
underlying external gill-lamina, along its line of junction 
with the same. There will be seen running along the top 
of the gill, at the base of the suspensory ligament (Sect. B. 
d. /?.), the afferent-branchial sinus a well-defined longitu- 
dinal blood-space; make a perforation in this and inject, 


328 ELEMENTARY BIOLOGY. [CHAP. 

backwardly and forwardly. Wash carefully, and remove a 
good portion of the outer wall of the external lamina; there 
will be seen 

a. the afferent branchial vessels, a series of short 
parallel trunks, conveying the blood from the 
above-named sinus to the gills. 

Examine the afferent branchial sinus and note that 
the injection has passed from it into the ventro- 
external portion of the excretory organ, having 
filled the efferent renal vessels. 

b. Open up the pericardium, and remove the auricle, 
thereupon exposed. Make a small hole in the 
middle of the vena cava (Sect. F. 2) and inject both 
backwardly and forwardly, exercising a gentle 
pressure. Wash carefully, and note that the ex- 
cretory organ is now completely injected, the 
colouring matter having passed from the vena cava 
into the afferent renal vessels. 

c. Remove the anterior half of the gill-laminae, and 
dissect to the level of the vena cava. Follow this 
into the body; it emerges immediately behind the 
rectum, and is seen to be formed by the confluence 
of a number of venous channels some of the more 
important of which accompany the intestinal coils. 
Follow it backwards ; it can be traced to the under 
surface of the posterior adductor muscle. 

The vena cava can be dissected from above, as 
directed in Sect. F, with comparative ease, in an 
uninjected specimen; its lumen will admit of the 
passage of a seeker. 

H. The pallial lobe. 

a. Tease up a portion of the substance of the pallial 


V.] THE FRESH-WATER MUSSEL. 329 

lobe of an animal which has been killed under 
chloroform. Conspicuous among the cells thus 
isolated there will be found large oval or rounded 
ones, each lodging a central refractive globule. 

b. Remove the mantle-lobe from a mussel which has 
been killed as above and subsequently preserved 
in alcohol, and split it into two. Transfer a 
portion of one half to a glass slide, torn surface 
upwards, and treat with iodine solution; the 
whole will be studded with small brown spots. 
Examine under a high power ; the spots are seen 
to be identical with the globules observed in 
a. (their chemical reactions are those of gly- 
cogen). 

I. The nervous system. 

i. Pin the animal down so as to get the body absolutely 
rigid ; remove the mantle-lobe and gills of one side 
and slit open the organ of Bojanus. 

Wash until quite clean and examine under water. 

a. Find the cerebro-splanchnic commissures; two parallel 
white cords traversing the excretory organ. Trace 
the near one backwards; it passes round the 
posterior retractor tendon towards the under side 
of the posterior adductor muscle. Turn this latter 
over, so as the better to display its under surface, 
and note 

l>. the parieto-splanchnic ganglia; two elongated yellow 
masses confluent in the middle line, seen on 
removing the membranous investment from the 
ventral surface of the above-named muscle. They 
distribute branches to the same, to the gills and 
pallial lobe. 


330 ELEMENTARY BIOLOGY. [CHAP. 

c. Carefully snip away the membranous tissue at the 
base of the labial palps ; there will thus be laid 
bare the cerebral ganglia. 

Each is about the size of a pin's head, and 
somewhat triangular in form; it lies immediately 
in front of the protractor pedis tendon, and dis- 
tributes fibres to the anterior adductor muscle, 
labial-palps and pallial lobe. Examine, in connec- 
tion with the one exposed 

a. the inter-cerebral commissure. 

A short cord uniting the two cerebral ganglia 
across the middle-line, above the gullet. 

P. The further course of the cerebro-splanchnic com- 
missure. 

Dissect off the fibrous tissue between the 
anterior retractor and protractor tendons, and 
remove the body-wall, between these and the 
anterior end of the pericardium. The commis- 
sure will be exposed, on carefully picking away 
the superficial portions of the digestive and 
reproductive glands along the same line. 

d. Remove a small portion of the body-wall along the 
point of origin of the muscular foot, and pick away 
the genital gland until \^Q pedal ganglia are reached; 
they are a pair of deep-orange-coloured oval 
bodies, each rather larger than a big pin's head, 
applied to one another in the middle line, near the 
point of junction between the body and the mus- 
cular foot. 

Branches are given off to the muscles of the 
foot and to the auditory organ. See infra. 

e. The cerebro-pedal commissure ; a cord which runs 


V.] THE FRESH-WATER MUSSEL. 331 

upwards and forwards, from the pedal to the cere- 
bral ganglion of either side. 
(Cf. Sect. L./) 

The cerebro-splanchnic commissures run close 
together and parallel with each other, in their 
course from behind forwards ; on leaving the peri- 
carclial area, they suddenly diverge and pass down- 
wards and forwards to meet the cerebral ganglia. 
If one of the commissures be removed and 
examined under a low power, there may occa- 
sionally be found, at the point of divergence, an 
enlargement (visceral ganglion). 

J. The auditory organ. 

a. This is rather difficult to dissect out in Anodon : 
it is a small sac which may be found by tracing 
back the posterior cords given off from the pedal 
ganglion, to a branch of one of which it is attached. 
There is a vesicle connected with each pedal 
ganglion. 

Failing the above, the otocyst can best be found 
by removing a portion of the reproductive gland 
lying immediately behind the pedal ganglion, and 
examining under a low power. 

b. If a fresh Cyclas 1 be obtained, and its foot re- 
moved, mounted in water, and examined with 
i inch obj., the auditory sac can readily be seen 
with a constantly- trembling particle, the otolith^ 
in it. 

K. The shell or exoskeleton. 

a. Its two hardened lateral pieces or valves ; each 
with a straight dorsal and a curved ventral edge, 

1 Cyclas cornea a small fresh-water lamellibranchiate mollusk. 


332 ELEMENTARY BIOLOGY. [CHAP. 

and an anterior larger and posterior smaller end, 
the latter compressed dorso-laterally note the soft 
chitinous ventral edge of each valve. 

b. The umbo; a small blunt eminence on the 
dorsal border of each valve near its anterior 
end; its apex is directed forwards. 

Note the delicate texture of this area. 

c. The ligament ; an elastic uncalcified part of the 
exoskeleton behind the umbones, uniting the two 
valves and tending to divaricate their ventral edges. 

d. External markings. The outside of the shell is 
greenish brown, and on it are seen a number of 
concentric lines of growth, running parallel to the 
margin of the shell and more numerous towards 
its ventral edge. 

e. Detach one valve by cutting through the ligament 
with a scissors; before removing the animal 
examine under water, and note the relations of the 
chitinous ventral edge (a.). It extends along the 
straight dorsal border of the valve in front of the 
ligament ; and from that point in front, as from 
the posterior edge of the ligament behind, it is 
sharply inflected passing inwardly to be reflected 
on to the free border of the pallium. (Cf. Sect. 
L. a. y.) 

f. Internal markings. The interior of the valve is 
white and iridescent : on it are seen, near the dorsal 
border, two oval scars, the anterior and posterior 
adductor impressions. 

Joining the two adductor impressions is a double 
curved line, the pallial impression, which marks the 
point of attachment of the pallial muscle. 


V.] THE FRESH-WATER MUSSEL. 333 

In front of the posterior adductor impression, is 
seen a small scar of attachment of \\\Q' posterior 
retractor muscle. 

Behind the anterior adductor impression are two 
others, one opposite its upper, the other opposite 
its lower end: the former indicates the point of 
attachment of anterior retractor, the latter of the 
protractor pedis muscle. 

The adductor and retractor scars are not unfre- 
quently confluent, and there extends from each 
into the umbo a fainter tapering impression, in- 
dicative of the growth of the muscles themselves 
as the animal has increased in size. 

g. Prepare (as directed for the Crayfish on p. 203) 
a dried section across the middle of one valve, cut 
at right angles to its long axis. Mount in Canada 
balsam and examine under a low power, note- 

a. The epiostracum ; a thin uncalcified superficial 
layer; it is greenish-yellow in colour, and very 
frequently torn away in the process of grinding. 

/?. The prismatic layer; composed of elongated 
columns of calcified substance running parallel 
with each other. 

y. The nacreous or pearly layer ; immediately in- 
ternal to /?. Its relative thickness is proportion- 
ate to the age of the animal from which the 
valve was taken. 

Examine under a high power it is finely 
granulated and traversed by delicate longi- 
tudinal striae. 

S. Make a tangential section across the prismatic 
layer and examine under a low power. The 


334 ELEMENTARY BIOLOGY. [CHAP. 

prisms are mostly hexagonal or pentagonal in 
contour; transverse diameter variable, often in 
proportion as the section passes through their 
inner ends. 

e. Dissolve out the earthy matter from a piece of 
a valve, by treatment with weak hydrochloric 
acid. An organic basis remains behind, conform- 
able in shape to the fully formed structure. 

L. The study of transverse sections. 

Remove one valve from an animal which has been dead 
some 6 8 hours, and make sections as directed below 
cutting through the soft parts with a razor or sharp scalpel 
and through the remaining valve with a bone-forceps. 
Examine under water, and if some of the more minute parts 
to which attention is directed do not fall in the plane of 
section, dissect until they are reached. 

Sections a, b, c, e, and f to be transverse to the long axis 
of the body, d to be oblique. 

a. Through the anterior pericardial region, immedi- 
ately behind the excretory and genital orifices. 
Work over 

a. The body ; median, laterally compressed below. 
Note the muscular nature of the body-wall; it is 
thickened ventrally to form the locomotor foot 
above the gills it is expanded dorso-laterally and 
modified to form the organ of Keber. 

ft. Thepallial lobes; membranous outgrowths of the 
thickened dorsal region of the body-wall; they 
are in close apposition with the valves. Note 
the thickening of their free borders to form the 
pa I Ha I muscles. 


V.] THE FRESH-WATER MUSSEL. 335 

y. The exoskeleton. Observe that this forms, during 
life, a continuous investment for all the exposed 
surfaces of the body, with the exception of the 
foot. It consists of a pair of calcareous valves, 
which pass dorsally into a cornified ligament 
ventrally into a chitinous free-border, which is in- 
flected on to the edges of the pallial muscles. 

8. The branchia; two pairs of lamellate organs, 
confluent with each other and the body-wall 
internally and with the pallial-lobes externally. 
Examine their central cavities and attachments, 
noting especially the subdivision of the supra- 
branchial chamber into two, by the suspensory 
ligament of the gills. (Cf. Sect. B. d, ft.) 

. The body-cavity. This is almost obliterated by 
the great development of the reproductive gland; 
note the large pericardial chamber, situated in the 
dorsal middle line. 

. The viscera. The cut edges of the intestine will 
be seen, lying within the body and traversing the 
pericardial chamber. 

The excretory organ; median and paired, lying 
immediately beneath the pericardial chamber. 
The glandular segments of opposite sides are 
seen to be approximated in the middle line; 
note the reno-pericardial apertures lying imme- 
diately above and internal to the attachments of 
the inner gill lamellae. The muscular segments 
are here confluent in the middle line, enclosing 
a spacious cavity ; dissect to the level of the 
excretory orifice of one side, and note that it is a 
perforation of the floor of this segment, opening 


336 ELEMENTARY BIOLOGY. [CHAP. 

into the supra-branchial chamber, internally to 
the suspensory ligament of the gills. 

The cerebro-splanchnic nerve commissures will be 
found, closely applied to the ventro-internal walls 
of the glandular segments of the above. The 
vena cava here lies in the middle line immediately 
below them. 

The reproductive gland; a yellowish mass, 
filling up all the available space in the infra- 
branchial portion of the body-cavity. 

Dissect it away on one side to near the level of 
the excretory orifice; there will thus be laid bare 
the genital duct. Insert a bristle into this and 
open it up; it communicates with the supra- 
branchial chamber immediately beneath and in- 
ternal to the excretory orifice (Cf. Sect. B. d, 
y). Follow the duct down and note the orifices 
of the smaller ducts which open into it, and by 
whose confluence it is formed. 

A good notion of the ramifying nature of this 
duct may be obtained by means of injection. 

r]. Pick away the reproductive gland and note the 
transverse muscles ; delicate tracts of tissue pass- 
ing between the body-wall of opposite sides. 

Examination of the above section will render it 
clear that the pallial lobes are paired, outgrowths 
of the dorso-lateral portion of the body-wall. The 
cavity which they bound during life, is sub- 
divided as the result of the confluence and 
attachments of the gills into infra and supra 
branchial chambers ; the latter being partitioned 
off into two portions, the inner of which receives 
the excretory and genital ducts. 


V.] THE FRESH-WATER MUSSEL. 337 

b. Through the middle pericardial region, across the 
heart and auriculo-ventricular valves. Compare 
generally with a, and work over, in addition. 

a. The gill-laminae. ; the inner one is free internally, 
the supra and infra-branchial chambers being 
thus in open communication. 

fi. The excretory organ. Note the increase in 
calibre of the glandular segment, as its posterior 
end is neared; the vena cava is here interposed 
between the muscular segments of opposite sides. 
The cerebro-splanchnic commissures lie close 
together beneath the vena cava. Cf. a. . 

y. The pericardial chamber and heart. The former 
is here at its maximum of development. Observe 
the fleshy wall of the ventricle and the thin auri- 
cles; the auriculo-ventricular valves are pocket- 
shaped in section, their mouths being directed 
towards the ventricle. 

Note the course of the rectum; it traverses 
the ventricle, but is in no way bound down to it. 

c. Through the middle of the posterior -adductor 
muscle. 

a. The attachments of the adductor muscle; it tra- 
verses the body and pallial lobes, and is inserted 
directly into the substance of the valves of oppo- 
site sides. 

ft. The rectum; lying in the dorsal middle line 
immediately above the adductor muscle. 

y. The supra-branchial chamber ; completely shut 
off, by the confluence and attachments of the 
gills, from communication with the infra-bran- 

M. 22 


338 ELEMENTARY BIOLOGY. [CHAP. 

chial one, except through the gill-slits. Its dorsal 
prolongation (cf. Sect. B. d\ seen, in section, as 
a small cavity overlying the rectum. 

8. The parieto- splanchnic ganglia; two yellow bo- 
dies confluent in the midddle line, buried up in 
a connective tissue sheath, immediately beneath 
the posterior adductor muscle. 

d. Obliquely backwards, through the stomach and 
first coil of the intestine. Examine from behind. 

a. The stomach; a spacious sac, passing into the 
intestine below. The orifice of the gullet is 
seen as a wide transverse aperture, situated near 
its roof. Immediately below this there is a cor- 
responding depression, which receives the main 
ducts of the digestive gland two enormous tubes 
admitting the seeker with ease; note the pre- 
sence of a series of lesser ducts. 

ft. The intestine; passing straight down in the middle 
line. Note the typhlosole; a median ingrowth of 
the lining membrane of its front wall. 

y. The labial palps. These, like the gills, are con- 
fluent externally with the pallial-lobes, inter- 
nally with each other and the body wall; thek 
free edges enclose a ventral ciliated groove. 

.. Through the anterior adductor muscle, immediately 
in front of the mouth. 

(i. The adductor muscle. Cf. c. a. 

ft. The mouth; median, transversely elongated. It 
lies immediately beneath the adductor muscle, 
and is embraced on all sides by the labial palps, 
which are confluent round it. Note that they 


V.] THE FRESH-WATER MUSSEL. 339 

are so disposed that the ciliated groove (cf. supra] 
leads directly to the mouth aperture. 

y. The foot; a fleshy mass, projecting fonvardly, 
immediately below the mouth. 

f. Dissect away the adductor muscle and labial palps 
on one side, and note the relations of the retractor 
and protractor pedis muscles. Their fibres are largely 
derived from the muscular layer of the body-wall; 
follow them to their attachments. (Cf. Sect. A.) 

Find the cerebral ganglion of the same side (see 
Sect. I. c] and trace the course of the inter- 
cerebral commissure; it runs over the gullet, in 
the substance of the labial-palps. Follow in like 
manner the cerebro-pedal commissures, until the 
pedal ganglia are reached ; note that these like 
the parieto- splanchnic ones are confluent in the 
middle line. 

M. The reproductive elements and the larva. 

a. The animals are dioecious, but the reproductive 
organs are similarly constructed in both sexes : 
they vary much in size with the season, being 
large in winter and spring, but small at other times. 

b. Tease up a small portion of the ovary in eosin 
solution, and examine under a high power. The 
ripe ova are large, rounded, rarely ovoidal bodies, 
and their special features are 

a. The vitelline membrane ; usually separated from 
the ovum by a cavity filled with a coagulate 
albuminous fluid. 

The micropyle ; a perforation, or frequently a 
short neck-shaped prolongation of a. 

22 2 


340 ELEMENTARY BIOLOGY. [CHAP. 

Look for specimens in which the ovum is pro- 
longed into a stalk passing through the above 
the remnant of an original pedicle of attach- 
ment to the germinal epithelium. 

y. The germinal vesicle; very large and transparent; 
it is rounded and usually contains two germinal 
spots a larger and a smaller one in close appo- 
sition. 

c. The Glochidium larva. If the outer gill appear to 
be thick and distended, it will be found full of the 
above. Note, while living, the characters of their 
shells, the entangled byssus filaments, with which 
they are provided, and the spasmodic contractions 
of the adductor muscle. 

Preserve a portion of the larva-laden gill (taken 
from an animal killed under chloroform) in spirit; 
when well hardened stain with magenta and exa- 
mine under a low power. Look for individuals 
whose valves gape, and note- 

a. The larval exoskeleton ; composed of two trans- 
parent valves, united dorsally by an elastic hinge. 

(3. The shell-teeth ; formed on either side as a spur- 
like inflection of a. Each terminates in a sharp 
upwardly directed spike, and its exposed surface 
is produced into a number of parallel serrated 
ridges. 

y. The adductor muscle ; a powerful transverse band 
passing between the upper parts of the two 
valves. 

8. The mantle. This consists, at this stage, of very 
large cells which project freely into the enclosed 


V.] THE FRESH-WATER MUSSEL. 34! 

cavity. Three sets of bristle-like appendages are 
developed in connection therewith; an upper 
one passing obliquely downwards immediately 
beneath the adductor muscle, and two shorter 
ones passing upwards, immediately above the 
shell-teeth. 

e. The byssus; an elongated, transparent, much- 
tangled filament, projecting beyond the free edges 
of the valves. 

d. Examine a similar larva from the side. The valves 
are quite transparent, and there can be seen through 
them 

a. the adductor muscle ; appearing as a median dark 
mass. 

(3. The visceral mass ; a somewhat less conspicuous 
mass lying in one of the top corners, altogether 
to one side. 

y. The byssus organ; a conspicuous transparent 
tube, arising from /?. and coiled upon itself. It is 
unpaired, being present on one side of the body 
only. 

8. Note the shape of the shelly valve; it tapers off 
below to form the shell-tooth. Focus to the 
level of this, and examine its serrations. The 
valve is seen to be dotted all over by minute 
perforations pore-canals. 


VI. 


THE FRESH-WATER POLYPES (Hydra viridis 

and H. fused]. 

IF a waterweed, such as duckweed, from a pond, is placed 
in a glass and allowed to remain undisturbed for a short time, 
minute gelatinous-looking bodies of a brownish or green 
colour may frequently be found attached to it, or to the sides 
of the glass. They have a length of from \ to \ of an inch, 
rarely more, and are cylindrical or slightly conical in form. 
From the free end delicate filaments, which are often much 
longer than the body, proceed and spread out with a more 
or less downward curve, in the water. These threads, which 
are the tentacles, may vary in number 1 : if touched they 
rapidly shorten and together with the body shrink into a 
rounded mass. After a while, the contracted body and the 
tentacles elongate and resume their previous form. These 
are Polypes, the brown ones belonging to the species usually 
termed Hydra fusca, the green to that called H. viridis. 
The polypes generally remain attached to one spot for a 
long time, but they are capable of crawling about by a 
motion similar to that of the looping caterpillar; and, 
sometimes, they detach themselves and float passively in 
the water. 

1 In //. Ilcxactinclhi) an Australian species, their number is in- 
variably six. 


CHAP. VI.] THE FRESH-WATER POLYPES. 343 

When any small animal, such as a water-flea, swimming 
through the water comes in contact with the tentacles, it is 
grasped, and conveyed by their contraction to the aperture 
of the wide mouth, which is situated on the summit of a 
cone (Jiypostome) in the middle of the circle formed by the 
bases of the tentacles. It is then taken into a cavity which 
occupies the whole interior of the body; the nutritive 
matters which it contains are dissolved out and absorbed 
by the substance of the Hydra; and the innutritious 
residuum is eventually cast out by the way it entered. 
Small pieces of meat, brought within reach of the tentacles, 
are seized, swallowed and digested in the same manner. 

If a Hydra is well fed, bud-like projections make their 
appearance upon the outer surface of the body. These 
gradually elongate and become pear-shaped. At the free 
end a mouth appears; and around it minute processes are 
developed and grow into tentacles ; and thus a young Hydra 
is formed by gemmation from the parent. This young Hydra 
becomes detached sooner or later, and leads an independent 
existence; but, not unfrequently, new buds are developed 
from other parts of the parent before the first is detached, 
and the progeny may themselves begin to bud before they 
attain independence. In this manner, temporarily compound 
organisms may be formed. Experiments have shewn that 
these animals may be cut into halves or quarters and that 
each portion will repair its losses, and grow up into a perfect 
Hydra; and there is reason to believe that this process 
of fission sometimes occurs naturally. 

The Hydra multiplies by budding through the greater 
part of the year; but in the summer sexual organs appear 
in the form of projections of the surface of the body. 
These, when ripe, may be resolved into a larger and a 
smaller set. The latter may appear on any part of the 


344 ELEMENTARY BIOLOGY. [CHAP. 

body, but they are not unfrequently restricted to the free 
end, at or near the bases of the tentacles. Within them 
(testes) great numbers of minute spermatozoa, each moved 
by a vibratile cilium, are developed and eventually set free. 

The former are large globular bodies, from one to eight 
in number, usually formed near the attached end of the 
polype. Each becomes much larger than the testis, and is 
the ovary. Within it is developed a single large egg-cell, or 
ovum. This ovum, which is a huge nucleated cell, is im- 
pregnated by the spermatozoa and undergoes division into 
two parts. Each of these again divides into two; and so 
on, until the ovum is broken up into a number of small 
embryo-cells. The mass of embryo-cells thus formed be- 
comes surrounded with a thick, usually tuberculated or 
spinous, case; and, detaching itself from the body, forms 
the 'egg/ from which a new Hydra is developed. 

Microscopic examination shews that the body of the 
Hydra is a sac, the wall of which is composed of two 
membranes, a transparent outer (ectoderm], and a coloured 
inner (endoderm}. The tentacles are tubular processes of 
the sac, and therefore are formed externally by the ectoderm 
and lined internally by the endoderm. Both the endoderm 
and the ectoderm are made up of nucleated cells; the inner 
ends of certain of these are prolonged into delicate fibres, 
those of the ectoderm, which are most marked, running 
parallel with the long axis of the body. The green colour 
of the Hydra viridis results from the presence of chloro- 
phyll grains imbedded in the protoplasm of the endoderm 
cells. 

The cells of the ectoderm, and especially that of the 
tentacles, contain very singular bodies, the so-called 
urticating capsules, thread cells, or nematocysts. These are 
oval bags, with thick and elastic walls, containing a spirally 


VI.] THE FRESH-WATER POLYPES. 345 

coiled or looped filament which can be unrolled, present- 
ing the appearance of a long filament attached to the 
capsule, and often provided with recurved spines near its 
base. As similar capsules of a larger size are the agents 
by which many of the jelly fishes sting severely, just as 
nettles do when they are handled, there is every reason to 
believe that the thread-cells of the Hydra exert a like 
noxious influence upon the small animals which serve as 
its prey. Very rarely, nematocysts are to be found in 
individual cells of the endoderm; there is reason to believe 
that they are introduced with the captured prey, but argu- 
ment from analogy to allied hydroids renders it probable 
that they may be developed in situ. 

The chlorophyll granules contained in the endoderm of 
the green Hydra are doubtless functional in the manner of 
those of the plant-cell, but none but faint traces of an 
'assimilation product' have yet been observed. The brown 
or orange-coloured particles predominant in the endoderm 
of the other species, and rarely present in that of H. 
viridis, are probably identical with the chlorophyll bodies 
(see Laboratory work) \ 

The larger endoderm cells of Hydra are throughout life 
amoeboid, and the like is partly true of the ectoderm in at 
least the young state of one variety (H. viridis var. Bakeri}. 
The Hydra, then, may be compared to an aggregate of 
Amcebtz, which are arranged in the form of a double-walled 
sac and have undergone a certain amount of metamor- 
phosis. 

The cavity of the body alone represents a stomach and 

1 It has been assumed, upon this, that the green and brown species 
are mere varieties of one and the same. On the other hand, structural 
differences in the nematocysts and their parent-cells have been claimed, 
as sufficient to justify a subdivision into three species. 


346 ELEMENTARY BIOLOGY. [CHAP. 

intestine; there are no organs of circulation, respiration or 
urinary secretion; the products of digestion are doubtless 
transmitted, by imbibition, from cell to cell, and those of 
the waste of the cells exuded directly into the surrounding 
water. While the Hydra has none of the special appara- 
tuses which are termed glands, definite secretory cells are 
nevertheless present. Among the more important of these 
are those developed in the ectoderm of the foot which are 
utilized for purposes of adhesion, and the secretory cells of 
the endoderm, most numerous in the hypostome, which is 
eversible. 

Nematocysts are generally, but not invariably, ejected, if 
any portion of the body which bears them be touched. 
Certain of the ectoderm cells, usually, if not always, lodging 
nematocysts, bear each a stiff filament or cnidocil such as 
can readily be seen in life projecting beyond the free surface 
of the tentacles. Continuity has been traced between these 
cells or cnidoblasts and certain small nerve-cells sparsely dif- 
fused in the deeper layer of the ectoderm; the whole con- 
stituting an elementary neuro-sensiferous apparatus, through 
the agency of which control of at least the cnidoblasts and 
their contained urticating capsules is exercised. 

The fully formed Hydra may further be compared to 
those animals previously dealt with, at that stage in their 
development when the body consists of a double-walled sac 
(cf. especially the gastrula stage of the Snail and its repre- 
sentative in the Crayfish). The inner layer gives origin, 
in the latter, to the digestive epithelium and its appended 
glands; in Hydra it forms the digestive layer. The ecto- 
derm is, in all, protective, and from it such neuro-sensifer- 
ous organs as are formed, exclusively arise. Between the 
applied surfaces of the ectoderm and endoderm there is 
interposed a gelatinous middle layer, which, under the 


VI.] THE FRESH-WATER POLYPES. 347 

action of reagents, appears as a structureless membrane. 
This furnishes attachment for the cells themselves and sup- 
port for the body generally; its optical characters in the 
prepared state are expressed in the term supporting lamella, 
its real nature more nearly in that of mesoglcea. 

It is possible that the longitudinal fibres connected with 
the cells of the ectoderm may be specially contractile, and 
represent muscles; but, however this may be, each cell has 
its own independent contractility. Similar fibres, disposed 
transversely, arise from the bases of the endoderm cells. 
These have been met with only in the body, and they ap- 
pear to be in connection with the fibres of the ectoderm 
cells, by means of delicate fibrils which perforate the above- 
named mesogloea. 


LABORATORY WORK. 

1. Put into a beaker some water containing bodies to 
which Hydras are attached, and place the beaker in a 
window not exposed to direct sunlight : in the course of 
some hours many Hydras will be found attached to that 
side of the glass which is turned towards the light. Note 
their size, form, colour, mode of attachment and move- 
ments. 

2. Transfer a Hydra, by means of a pipette, on to a 
slide with plenty of water. In order to avoid crushing, 
place the animal between two coverslips, so arranged as 
to support the edges of a third one which shall overlie it. 
Examine with a low power. 


348 ELEMENTARY BIOLOGY. [CHAP. 

a. Form. 

a. The body proper ; cylindrical, varying much in length 
and diameter with the state of extension of the 
animal; its conical free end (hypostome) with an 
opening (mouth} at its summit. 

It is often difficult to observe the mouth, especially 
in the green species. It may be readily seen however 
if a Hydra, placed in a drop of water without a 
coverslip, be watched under an inch objective, until 
it turns its anterior end up towards the observer. 
Occasionally, under these circumstances, the hypo- 
stome may be everted. 

J3. The tentacles: ranged round the mouth; their num- 
ber and shape ; their varying length and diameter ; 
the knob-like eminences on them. 

Look for developing tentacles, shorter and more 
rigid than the rest. Very rarely, one or more may 
branch. 

y. The base (so called foot] : a flattened disc ; narrower 
or wider than the body, according to the state of 
extension of the latter. It is functional as an organ 
of adhesion. If the animal be attached, its se- 
cretory product can often be seen, as a transparent 
laminated mass, interposed between the body and 
the surface of attachment ; if the animal be free, the 
disintegrating remains of the same are often to be 
found adherent to the 'foot'; if it be forcibly de- 
tached, rupture of the base of the polype may ensue, 
the animal appearing to possess that which has 
been erroneously termed an 'anus'. 

S. The buds ; young Hydrae, of various sizes and stages 
in development, attached to the sides of the parent. 
There may be one or more of them. 


VI.] THE FRESH-WATER POLYPES. 349 

e. The sex-organs, if present ; colourless prominences, 
variable in number and position (cf. Sect. 8). 

d, may be one or more absent, or all may coexist, 
in individual specimens. 

b. Structure. 

a. The animal evidently composed of two layers, an 
outer transparent, ectoderm, and inner, endoderm; the 
latter alone containing chlorophyll in the green 
species, or such colouring matter as is present in 
the brown one. The ectoderm is marked out into 
areas, and may with care be seen to be composed 
of distinct cells, though this is a little difficult to 
make out in fresh specimens. 

j3. The body-cavity ; least obvious in the green species, 
frequently visible in the brown ones as a darker 
central area with which the mouth-opening is con- 
tinuous. Note that it extends into the tentacles ; 
corpuscles can, with care, be seen floating within 
these, when extended. 

c. Movements. 

a. The general contractility of the animal ; it is con- 
stantly either extending or shortening its body and 
tentacles, and so altering its form and place. 

P. Its irritability ; slight pressure or other stimulus im- 
mediately causes it to contract. 

3. The tentacles and nematocysts. Attention has al- 
ready been called to the knob-like eminences of the former. 
Note that these are widely separated in extension ; closely 
applied in contraction. Examine one of them under a high 
power, with the tentacle fully extended. 


35O ELEMENTARY BIOLOGY. [CHAP. 

a. The cnidocils ; well defined stiff processes, each 
pointed and standing out from the free surface. 

b. The nematocysts or thread-cells; highly refractive 
bodies embedded in the common mass. They can 
be resolved into 

a. Smaller and more numerous ones ; ovoidal, and 
situated almost invariably at the bases of the 
longer cnidocils. 

/?. Larger and less numerous ones (very often one 
only) lying near the middle of the mass ; globular 
when seen en face, flask-shaped when looked at 
from the side. 

c. Run in a drop of magenta solution and watch, under 
a low power, the ejection of the threads of the ne- 
matocysts. Note from what parts of the body they 
are thrown out. Examine, under a high power, a 
portion of a tentacle beset by them. There will be- 
found : 

a. Short, deeply staining, stout threads, usually thrown 
into a spiral. Note that these are related to the 
smaller nematocysts. 

ft. Delicate whip-lash filaments, from 8 to 10 times 
the length of a. Trace them to their origin from 
the larger nematocysts. 

d. Should opportunity offer, examine any small or- 
ganism or other prey that may have been seized 
by the tentacles. When about to be swallowed it 
will be found to be studded by nematocysts, espe- 
cially of the smaller kind. 

4. The asexual buds. (Cf. Sect. 3 a. B) Examine in 
relation to the parent, under a high power. 


VI.] THE FRESH-WATER POLYPES. 351 

(7. The body-cavity ; in young buds continuous with that 
of the parent ; in buds ripe for dehiscence com- 
pletely constricted off therefrom. Note that the 
month is formed as a secondary perforation. 

b. The tentacles ; variable in number. A solitary one 
may appear first, the second and third being sym- 
metrical with respect to each other. Compare the 
fully-formed animal. 

The rate of development of the tentacles, indi- 
vidually or collectively, varies under change of tem- 
perature, and their order of appearance is somewhat 
inconstant. There are usually in the fully-formed 
animal (8 12 hrs.), 6 for H. fusca, 8 for H. m- 
ridis. 

5. The study of prepared sections. Place one or more 
Hydras, preferably in full diet, in Kleinenberg's picric 
acid solution; after two hours' immersion therein, transfer to 
alcohol of increasing strengths. When fully hardened, stain 
with borax-carmine, imbed in paraffin and cut into trans- 
verse sections. Mount in Canada balsam and examine 
under a low power. 

a. The ectoderm; of uniform thickness and composed, 
for the most part, of squarish-looking cells which stain 
lightly. 

/;. The endoderm ; composing the inner two-thirds or 
more of the body-wall, extremely variable in thick- 
ness. Its component cells are highly vacuolated. 

c. The body-cavity (enteron) ; enclosed by b. Variable 
in capacity in different sections, in accordance with 
the state of contraction of the body-wall. 

i. 

d. a and b will be seen to be separated by a hard line, 


352 ELEMENTARY BIOLOGY. [CHAP. 

which stains deeply. Examine this under a high 
power and look for 

a. the mesogla'a or supporting lamella; visible as the 
above-named line. 

/3. Kleinenbergs fibres (contractile-processes of the 
ectoderm-cells) ; obvious, if the section be a good 
one, as a parallel series of deeply-stained dots 'im- 
mediately external to a. 

t. Examine the ectoderm under a high power, selecting 
your thinnest sections. Look for 

a. The larger ectoderm cells ; conical, their bases being 
external, and fairly uniform in contour. Each is 
composed of a lightly staining protoplasm, nu- 
cleated and at times vacuolated. Note the strong 
granulation of their free outer borders. 

/?. The interstitial tissue ; composed of aggregates of 
smaller cells, at the bases of a\ rendered con- 
spicuous by its affinity for the stain and by the 
great development of nematocysts. 

Cf. sections across a tentacle. The knob-like pro- 
tuberances previously seen (Sect. 2 a. ft) will be found 
to consist of aggregates of these cells which have 
reached the surface. Similar eminences, less regu- 
larly disposed, will be found in the body-wall. 

f. Examine, in like manner, the endoderm. Its larger 
cells will show 

a. Shape, irregular ; size and contour, variable. 

The cell-protoplasm; largely replaced in one or 
more clear vacuoles. It forms peripherally a cell 
membrane, and is generally densest at the base, 
where it is aggregated to form the so-called 'foot'. 


VI.] THE FRESH-WATER POLYPES. 353 

Occasionally some of the vacuoles may be seen to 
contain groups of minute needle-shaped crystals. 

y. The secretory cells of the endoderm ; smaller deeply- 
staining pear-shaped cells, interposed between the 
bases of the larger ones. Numerous and well-de- 
fined in sections across the hypostome, fewer in 
those across the body. They may be recognized 
by their tapering inner ends, the highly-granular 
nature of their cell-protoplasm, and by their small 
deep-staining nucleus. 

g. Place a Hydra in i per cent, osmic acid solution for 
24 hours, and then tease up a portion of the en- 
doderm in weak glycerine, under a low power. Ex- 
amine, under your highest objective, and look for the 
flagella ; long whip-lash filaments, one to six being 
borne upon a single cell. 

As these structures are capable of withdrawal, cells 
will be present which do not bear them. Look for 
specimens showing stages in their elongation. 

6. Structural analysis of the individual cells. Pre- 
serve some Hydras in Miiller's fluid (2 3 days). Transfer 
to alcohol of increasing strengths, and finally tease up under 
a low power in eosin or hsematoxylin solution. Alter- 
natively, preserve for a similar period in i per cent, solu- 
tion of ammonia bichromate, transfer to alcohol and tease 
up in carmine solution. Select the best preserved cells and 
examine, under your highest power, in order 

a. The larger ectoderm cells ; nucleated, with a flattened 
base and a rounded free end (cf. Sect. 5. e). Their 
nuclei ; frequently containing two nucleoli. Their pro- 
toplasm ; often differentiated into a superficial cuticle- 
like product. Look especially for Kleinenbergs fibres 

M. 23 


354 ELEMENTARY BIOLOGY. [CHAP. 

(Sect. 5. d. /3) ; one or more of these may be con- 
nected with an individual cell. They arise as out- 
growths of the constricted cell-base, the whole fre- 
quently having the appearance of an inverted T with 
a thick stem (cell-body) and greatly elongated arms 
(the fibres). 

I. The cells of the interstitial tissue (cf. Sect. 5. e. /3) much 
smaller than a, and often separable from one another 
only with difficulty. Numbers of them will be found 
to contain two nuclei (evidence of active division). 

c. The nematocysts ; highly refractive bodies to be found 
in both a and b in the latter in abundance and in 
all stages of development. Look for the under- 
mentioned (cf. Sect. 3). 

a. The larger nematocysts ; each consists of a My, 
ovoidal and truncated, with a strongly- marked 
double contour due to the thickness of its wall ; a 
neck, inverted and beset by three or four powerful 
spines ; a filament, lying within the base of the 
body, coiled into a spiral the edges of which may 
occasionally be seen (cf. Sect. 3). 

Compare a large nematocyst in the everted state ; 
the summit of the neck is beset by a series of ex- 
cessively delicate spines. 

/3. The smaller nematocysts ; rarely present In the larger 
cells. Each is ovoidal and much smaller than <?, 
having a similar double contour. The filament ; 
but \ to T V the length of, and very much stouter 
than, that of a ; at rest looped, in eversion fre- 
quently spiral (cf. Sect. 3). 


VI.] THE FRESH-WATER POLYPES. 355 

y. Examine, in detail, a nematocyst In relation to its 
parent-cell. The cell-protoplasm will be seen to 
form a delicate envelope, thickened only around 
the nucleus, which stains deeply and is to be found 
in close apposition with the nematocyst. 

S. The cnidoblasts ; recognizable by the presence of a 
stiff spinous process or ciiidoril, usually projecting 
from one corner of the cell-body. 

Note the variable size of the cnidocils (cf. Sect. 
3). Nematocysts may or may not be present; 
where they are it will generally be found that the 
longer cnidocils are associated with the smaller 
thread-cells and vice-versa. 

e. Look for nerve-cells; small, stellate, and with a 
deeply-staining round nucleus. They are rare and 
only to be found with difficulty. 

. Immature nematocysts ; occasionally to be met with 
in the isolated state. Bottle-shaped and bearing a 
short blunted filament, which subsequently becomes 
invaginated (be careful not to confound this with 
the cnidocil). 

d. The larger cells of the endoderm. Examine cells freshly 
isolated from specimens killed with osmic acid vapour. 
Note, in addition to the characters already observed 
(Sect. 5). 

a. The cell-base ; not unfrequently expanded and pro- 
longed out to form contractile processes, identical 
with, but shorter and less marked than, those of 
the ectoderm cells. 

/?. The nucleus ; variable in position with the state of 
distension of the cell generally marginal. 

232 


356 ELEMENTARY BIOLOGY. [CHAP. 

y. Superadded to the cell-protoplasm. In H. viridis 
the chloroplastids ; small round bodies fairly uniform 
in size, for the most part aggregated at the cell- 
base. They stain very feebly, and may or may 
not contain chlorophyll : note the manner of its 
deposition. 

In H. fusca. The sooty corpuscles ; irregular and 
transparent, rarely rounded ; sooty particles may or 
may not be present. Look for the presence of 
chlorophyll ; occasionally to be found in individual 
cells. 

3. Compare the living cells, as obtained by crushing a 
Hydra. They are highly amoeboid. Watch the 
nature of their movements. 

<?. The mesoglcea. Search under a low power for stray 
pieces of this ; obvious as transparent shreds of mem- 
brane with parallel striae. There will be found in 
connection therewith 

a. Nuclei and fragments of cells, mostly of the in- 
terstitial tissue. 

/3. Contractile processes ; firmly adherent to the meso- 
glcea, the above-named striation being due to their 
presence. 

Look for fragments in which the two sets of 
striae cross each other (cf. p. 347). 

y. Compare a piece of the same, obtained from the 
freshly-killed animal. If forthcoming, press gently 
upon the cover-glass with the point of a needle; 
it will be found to be gelatinous and compressible. 

7. Food material and digestion. Work through all your 
sections under a low power, and look for ingested prey. 


VI.] THE FRESH-WATER POLYPES. 357 

a. Small organisms; especially Entomostraca and other 
small Crustacea. When present one such will gene- 
rally be found, tightly embraced by the endoderm. 

Examine under a high power and look for evidences 
of digestion (infra-enteric) and assimilation. 

b. Smaller organisms ; especially Infusoria, Diatoms, and 
the like. Frequently to be met with in the central 
cavity; they may however be found, unchanged or in 
process of digestion (intra-cellnlar\ within the indivi- 
dual cells of the endoderm. 

8. The reproductive organs. (Cf. Sect. 2. a. e). 

a. The testes; small conical colourless eminences below 
the point of attachment of the tentacles, more rarely 
irregularly scattered over the whole body. 

Gently flatten out a testis in eosin or magenta by 
pressure on the coverslip, and examine with a high 
power. According to its state of maturity the follow- 
ing contents will be found in it 

a. A collection of the smaller ectoderm (interstitial) 

cells of variable shape. 
j3. The same, but having become ovoidal and hyaline. 

y. Cells otherwise like /?, but with a long filament 
proceeding from them. 

S. Ripe spermatozoa; bodies consisting of a very small 
oval nucleated head to which a very delicate 
flagellum is attached, by the movements of which 
they swim about in the water. They may fre- 
quently be seen in motion within the unruptured 
testis. 

b. The ovaries; one or more in number, larger than a, 
and situated near the base of the polype. 


358 ELEMENTARY BIOLOGY. [CHAP. VI. 

When young, each appears as a hill-shaped enlarge- 
ment of the ectoderm; when ripe, it becomes rounded 
and very prominent. 

c. Press out an ovary: according to its stage of develop- 
ment there will be found in it 

a. Ectoderm cells with a marked preponderance of 
the smaller form (interstitial tissue). 

(3. Imbedded among a, one (pvicelt) which has become 
larger and clearer than the rest, and possesses a 
distinct central germinal vesicle. 

d. The ripe ovum. Conspicuous in H. viridis by its 
green colour. It consists of a great irregularly 
branched (amoeboid) mass of protoplasm (vitellus), in 
which is a clear space (germinal vesicle] containing one 
larger and a number of smaller germinal spots. 

Examine under a high power, and note 

a. The absence of a vitelline membrane. 

f3. The yolk granules; exceedingly large and modified to 
form the so-called 'pseudo-cells'. Each is rounded 
or oval, thickened on one side to form a plug- 
shaped ingrowth and filled with a fluid contents. 

y. The chloroplastids ; present in H. viridis; identical 
with those found in the endoderm (Sect. 6. d. y). 

e. The segmented ovum : composed of a large number of 
small cells. Its thick horny capsule, rough on its ex- 
ternal surface. 


VII. 

THE BELL-ANIMALCULE (Vorticella}. 

THE bell-animalcule is one of a very large group of animals 
called the Infusoria, on account of the fact that many mem- 
bers thereof make their appearance in infusions of certain 
animal and vegetable substances. 

The higher multicellular animals begin their existence as 
simple nucleated cells, and the single nucleated cell which 
constitutes the whole animal in its primitive condition 
divides and subdivides until an aggregation of similar cells 
is formed. And it is by the differentiation and metamor- 
phosis of these primitively similar histological elements that 
the organs and tissues of the body are built up. In the 
Infusoria, the protoplasmic mass which constitutes the germ 
does not undergo this process of preliminary subdivision, 
but such structure as the adult animal possesses is the 
result of the direct metamorphosis of parts of its proto- 
plasmic substance. Hence, morphologically, the bodies of 
these animals are the equivalents of a single cell; while, 
physiologically, they may attain a considerable amount of 
complexity. 

The Infusoria abound in fresh and salt waters, and many 
make their appearance, as before stated, in organic in- 
fusions, their germs either being contained in the substances 
infused, or being wafted through the air. Their diffusion is 
greatly facilitated by the fact that many of them retain their 


360 ELEMENTARY BIOLOGY. [CHAP. 

vitality when dried, and reduced to the condition of an ex- 
cessively light dust; while their rapid propagation is, in 
the main, due to their power of multiplying by division, 
with extraordinary rapidity, when duly supplied with nou- 
rishment. The majority are free and provided with nu- 
merous cilia by which they are incessantly and actively pro- 
pelled through the medium in which they live; but some 
attach themselves to stones, plants, or even the bodies of 
other animals. A few are parasitic, and the bladder and 
intestines of the Frog are usually inhabited by several spe- 
cies of large size. 

The Bell-animalcules are Infusoria which are fixed, usu- 
ally by long stalks, to water plants, or, not unfrequently, 
to the limbs of aquatic Crustacea. They are barely visible 
to the unaided vision. The body has the shape of a wine- 
glass with a very long and slender stem, provided with a 
flattened disc-like cover. What answers to the rim of the 
wine-glass is thickened, somewhat everted, and richly 
ciliated, and the edges of the disc are similarly thickened 
and ciliated. Between the thickened edge of the cover, or 
pertsfome, and the edge of the disc, is a groove, which, at 
one point, deepens and passes into a wide depression, the 
vestibulum. From this a narrow tube, the oesophagus, leads 
into the central substance of the body, and terminates ab- 
ruptly therein; and when faecal matters are discharged, they 
make their way out by an aperture which is temporarily 
formed in the floor of this vestibule. The outermost layer 
of the substance of the body is denser and more transparent 
than the rest, forming a cuticula. Immediately beneath the 
cuticle it is tolerably firm and slightly granular, and this 
part is distinguished as the cortical layer or ectosarc; it 
passes into the central substance or endosarc, which is still 
softer and more fluid. 


VII.] THE BELL-ANIMALCULE. 361 

In the undisturbed condition of the Bell-animalcule, 
the stem is completely straightened out; the peristome is 
everted, and the edges of the disc separated from the peri- 
stome; the vestibule gaping widely and the cilia working 
vigorously. But the least shock causes the disc to be re- 
tracted, and the edge of the peristome to be curved in and 
shut against it, so as to give the body a more globular form. 
At the same time, the stem is thrown into a spiral, and the 
body is thus drawn back towards the point of attachment. 
If the disturbing influence be continued, this state of retrac- 
tion persists; but if it be withdrawn, the spirally coiled stem 
slowly straightens, the peristome expands, and the cilia 
resume their activity. 

In the interior of the body, immediately below the disc, 
a space, occupied by a clear watery fluid, is seen to make 
its appearance at regular intervals slowly enlarging until 
it attains its full size and then suddenly and rapidly dis- 
appearing by the approximation of its walls. This is the 
contractile vesicle or vacuole. It communicates with the ex- 
terior at the moment of contraction, and in all probability 
performs an excretory function. If the Bell-animalcule is 
well fed, one or more watery vesicles of a spheroidal form, 
each containing a certain portion of the ingested food, will 
be seen in the soft central mass of the body. And by 
mixing a small quantity of finely divided carmine or indigo 
with the water in which the Vorticellce live, the manner in 
which these food-vesicles are formed may be observed. 
The coloured particles are driven into the vestibule by the 
action of the cilia of the peristome and the adjacent parts, 
and gradually accumulate at the inner end of the gullet. 
After a time the mass here heaped together projects into the 
central substance of the body, surrounded by an envelope 
of the accompanying water; and then suddenly breaks off, 


362 ELEMENTARY BIOLOGY. [CHAP. 

as a spheroidal drop, henceforward free in the soft central 
substance. Such being the mode of formation of the vesicles, 
they have been termed vesicles of ingestion; in some Bell- 
animalcules, they are carried round with the deeper layer of 
protoplasm or endosarc in a movement of circulation, 
passing up one side of the body, then crossing over below 
the disc and descending on the other side. Sooner or later 
the contents of these vesicles are digested, and the refuse is 
thrown out of the body, surrounded as a rule by a watery 
vacuole or vesicle of egestion. This process takes place by 
an aperture leading into the vestibule, which exists only at 
the moment of extrusion of the faeces, and is indistinguish- 
able at any other time. 

A portion of the substance of the body, which is slightly 
different in transparency and in its reactions to colouring 
substances from the rest, is called the nucleus or endoplast. 
It is elongated and bent upon itself into a crescentic or 
horseshoe shape. 

The numerous species and varieties of bell-animalcules 
are, for the most part, colourless. Green varieties are how- 
ever occasionally to be met with, the green colour being 
due to a deposit of chlorophyll within the endosarc, com- 
parable to that seen within the endoderm of the green- 
hydra. This colouring matter may be restricted to small 
bodies or chloroplastids identical with those of the polype 
referred to, or diffused throughout the cell-protoplasm (en- 
dosarc) in a manner such as, there is good reason to believe, 
is never the case in the vegetable organism. 

The Bell-animalcules multiply in two ways ; partly by 
longitudinal fission, when a bell becomes cloven down the 
middle, each half acquiring the structure previously pos- 
sessed by the whole ; and partly by gemmation from the 
t) in which latter case the endoplast divides into a 


VII.] THE BELL-ANIMALCULE. 363 

number of rounded spore-like masses, which are ultimately 
set free as locomotive germs. 

Sometimes a rounded body, encircled by a basal circlet 
of cilia but having otherwise the characters of a Vorticella 
bell, is seen to be attached to the base of the bell of an 
ordinary Vorticella. It was formerly supposed that these 
were buds, but it is now known that they are independent 
individuals, formed as the result of repeated longitudinal 
fission, which have attached themselves to that to which 
they adhere and are gradually becoming fused with it, so 
that the two will form one indistinguishable whole. There 
is here a process of "conjugation" sexual in nature, and it 
is, moreover, preliminary to the budding of the endoplast 
and the subsequent formation of germs. 

Under certain circumstances a Vorticella may become 
encysted. The peristome closes and the bell becomes con- 
verted into a spheroidal body, in which only the nucleus 
and the contractile vesicle remain distinguishable. This 
surrounds itself with a structureless envelope or cyst, the 
whole process sometimes following that of conjugation and 
preceding that of germ formation. It does not appear 
however that this encystment is invariably associated with 
reproduction ; for the encysted animal after remaining for 
a longer or shorter time in a temporary condition of rest, 
may emerge and resume its former state of existence. 

The two genera of Infusoria which most commonly occur 
in the Frog are Nyctotherus and Balantidium. Both are 
free and actively locomotive, and the former is particularly 
remarkable for its relatively large size and semilunar con- 
tour, and for the length and distinctness of its curved oeso- 
phagus. Balantidium is pyriform, and has a very short 
cesophageal depression. 


364 ELEMENTARY BIOLOGY. [CHAP. 


LABORATORY WORK. 

A. Examine duckweed roots, confervas, c., with J inch 
objective avoiding pressure ; having found a group of 
Vorticetlce note the following points with a higher 
power. 

i. In the extended state of the animal. 

a. The body. 

a. Its size (measure). 

b. Form ; broadly speaking, that of an inverted 
bell : note 

a. The prominent everted rim (peristome). 

p. The flattened central disc projecting above 
the peristome. 

y. The cilia fringing the disc. 

8. The depression between the peristome and 
disc. 

e. The vestibulum; a chamber in the hollow 
between the peristome and disc. 

c. Structure. 

a. The thin, transparent, homogeneous external 
layer (cuticle]. 

The granular layer (ectosare) inside the cuticle, 
longitudinally striate at the base of the bell 
(myophan layer}. 

The central more fluid part (endosarc) not 
sharply marked off from /?. 


VII.] THE BELL-ANIMALCULE. 365 

The various clear spaces (food vacuoles] in 
it, containing foreign (ingested) bodies (Dia- 
toms, Protococcus, &c.). 

8. The contractile vesicle; its position, in the 
cortical layer just beneath the disc ; its systole 
and diastole. 

e. The nucleus ; an elongated curved body in 
the deeper layer ; sometimes nearly homo- 
geneous, sometimes more distinctly granular. 
The nucleus is usually indistinguishable until 
after treatment with iodine, or acetic acid and 
magenta (cf. 5). 

. The gullet ; sometimes seen in optical trans- 
verse section as a clear round space ; some- 
times seen sideways as a canal opening above 
into the vestibulum, and ending abruptly be- 

9 

low in the body-substance. 

77. The anus ; look for the egestion of solid par- 
ticles. 

b. The stalk. 

a. Its length and diameter (measure). 

J3. Its structure ; the external homogeneous layer 
(sheath] continuous with the cuticle; the highly 
refractive centre (axis or contractile filament} 
continuous with the cortical layer of the bell. 

2. In the retracted state, 
a. The body. 

a. Its form ; pear-shaped ; rounded off above ; 
neither disc nor peristome visible. 

/?. The clear transverse space near the top, indi- 
cating the interval between the retracted disc 


366 ELEMENTARY BIOLOGY. [CHAP. 

and the rolled-In peristome. In this space the 
cilia can frequently be seen moving. 

y. Structure; as in i. a. c. 
b. The stalk ; thrown into corkscrew-like folds. 

3. The movements of Vorticella. 

a. The ciliary movement. 

a. Examine the cilia carefully; delicate homo- 
geneous processes; their length, diameter and 
form ; their position. 

/?. The continuity of the cilia with the cortical 
layer. 

y. The function of the cilia ; their rapid move- 
ments, alternately bending and straightening : 
the co-oi'dinatioii of these movements ; they 
work in a definite order ; note the currents 
produced in the neighbouring water (if neces- 
sary introduce a few particles of carmine under 
the coverslip) ; the sweeping of small bodies 
down the gullet. 

b. The movements of the contractile vesicle. Tolerably 
regular rhythmic distension and collapse (diastole 
and systole). 

c. The currents in the endosarc carrying round the in- 
gested bodies. 

d. The movements of the animal as a whole. (Ex- 
amine under \ inch or \ inch obj.) 

a. Its extreme irritability ; it contracts on the 
slightest stimulation, often without any appa- 
rent cause. 

/?. The movements which occur in contraction; 


VII.] THE BELL-ANIMALCULE. 367 

the coiling up of the stalk ; the rolling in of the 
disc. The rapidity of these movements. 

y. The mode of re-expansiori ; the stalk straightens 
first; then the peristome is everted; finally the 
disc and its cilia are protruded. 

4. Stain with iodine or magenta; the cuticle uncoloured 

-the rest stained; the nucleus especially becomes 
deeply coloured. 

5. Treat with acetic acid; the contents soon disappear 
(except perhaps some swallowed bodies) the cuticle 
later or not at all. 

6. Look for the following in various specimens 

a. Multiplication by fission, early stage ; a bell par- 
tially divided into two by a vertical fissure start- 
ing from the disc. 

/3. The same, late stage ; two complete bells on one 
stalk ; the result of completion of the fission. 
The development of a basal circlet of cilia by 
one or both of these bells. 

y. Free swimming unstalked bells (detached bells 
from /3). 

8. Conjugation; the attachment of a small free 
swimming bell to the side of a stalked one. 

e. Ency station ; the body contracted into a ball 
and surrounded by a thickened structureless 
layer, the contractile vesicle being persistently 
dilated. 

B. Other forms closely allied to Vorticdla which may be 
met with, and which will do nearly as well for exami- 
nation, are ; 


368 ELEMENTARY BIOLOGY. [CHAP. VII. 

a. Epistylis. Bell-shaped animals growing on a 
branched non-contractile stalk. 

b. Carchesium. A form very like Vorticella but 
borne on a branched contractile stalk. 

c. Cothurnia. An almost sessile form, provided 
with a cup or envelope into which the bell can 
be retracted. 

[The activity of the movements of the free Infusoria interferes 
with the complete examination of the living animal. It is well 
therefore to add a little osmic acid solution to the drop of water 
under examination. This kills such Infusoria as ParamcEcium^ 
Nyctotherus and Balantidium instantly, without destroying the 
essential features of their organization.] 


VIII. 

THE PROTEUS ANIMALCULE (Amabd) AND THE 
COLOURLESS BLOOD CORPUSCLE. 

Amabce are minute organisms of very variable size which 
occur in stagnant water, in mud, in damp earth and else- 
where, and are frequently to be obtained by infusing any 
animal matter in water and allowing it to evaporate while 
exposed to direct sunlight. An Amoeba 1 has also been 
found living, apparently as a parasite, in the diseased skin 
of the sheep. 

The Amoeba has the appearance of a particle of jelly, 
which is more or less granular and fluid in its central 
parts, but usually becomes clear and transparent, and of 
a firmer consistency, towards its periphery. Sometimes 
Amoeba are found having a spherical form and encased 
in a structureless sac, and in this encysted state they ex- 
hibit no movements. More commonly, they present in- 
cessant and frequently rapid changes of form, whence the 
name of "Proteus Animalcule" given to them by the older 
observers ; and these changes of form are usually accom- 
panied by a shifting of position, the Amoeba creeping about 
with considerable activity and, in most cases, with no con- 
stancy of direction. 

The changes of form, and the movements, are effected 

1 A. parasitica. New S. Wales. 
M. 24 


370 ELEMENTARY BIOLOGY. [CHAP. 

by the thrusting out of lobe-like prolongations of the 
peripheral part of the body, which are termed pseudo- 
podia, sometimes from one region and sometimes from 
another. Occasionally, a particular region of the body is 
constantly free from pseudopodia, and therefore forms its 
hindmost part when it moves. Each pseudopodium is evi- 
dently, at first, an extension of the denser clear substance 
(ectosarc] only; but as it enlarges, the central, granular, 
more fluid endosarc flows into its interior, often with a 
sudden rush. 

The protoplasm is in some Amoeba crowded with small 
watery vacuoles. In most there is present a clear space 
which makes its appearance at intervals, in a particular 
region of the ectosarc, and then disappears by the rapid 
approximation of its walls. After a while, a small clear 
speck or a line appears at the same spot and slowly dilates 
until it attains its full size, when it again rapidly disappears 
as before. Sometimes two or three small clear spots arise 
close together, and run into one another to form the single 
large cavity. The structure thus described is termed the 
contractile vesicle or vaciwle, and its rhythmical systole and 
diastole often succeed one another with great regularity. 
Nothing is certainly known respecting its function ; but 
there is reason to think that it may be excretory like the 
corresponding structure in Vorticella. 

Very generally one part of the Amoeba exhibits a rounded 
or oval nucleus. This structure is liable to considerable 
variation, and not unfrequently more than one nucleus may 
be present. 

The gelatinous body of the Amoeba is not as a rule 
bounded by anything that can be properly termed a 
cuticular membrane; all that can be said is, that its ex- 
ternal or limitary layer is, in most cases, of a somewhat 


VIII.] THE PROTEUS ANIMALCULE. 371 

different constitution from the rest, so that it acquires a 
certain appearance of distinctness when it is acted upon 
by such reagents as acetic acid or iodine, or when the 
animal is killed by raising the temperature to 45 C. 
Physically, the ectosarc might be compared to the wall 
of a soap-bubble, which, though fluid, has a certain vis- 
cosity, which not only enables its particles to hold together 
and form a continuous sheet, but permits a rod to be passed 
into or through the bubble without bursting it ; the walls 
closing together, and recovering their continuity, as soon as 
the rod is drawn away. 

It is this property of the ectosarc of the Amabci which 
enables us to understand the way in which these animals 
take in and throw out again solid matter, though they have 
neither mouth, anus, nor alimentary canal. The solid body 
passes through the ectosarc, which immediately closes up 
and repairs the rent formed by its passage. In this manner, 
the Amatbtz take in the small, usually vegetable, organisms, 
which serve them for food, and subsequently get rid of the 
undigested solid parts. 

Ingested matter is invariably taken in, in conjunction 
with a watery vacuole of ingestion such as has been de- 
scribed for Vorticella (pp. 361 2). If the matters thus 
introduced be nutritive and digestible the vacuole persists, 
during at any rate the earlier stages of digestion ; later, the 
unassimilable innutritions portions of the same are cast out 
surrounded by a vacuole of egestion. Experiment has led 
to the belief that Ainotbce, will not digest fat globules or 
starch grains. In the case of the latter the grains have 
been seen to be thrown out 6 7 days after ingestion, 
unchanged in their optical characters and in their behaviour 
towards certain reagents and unaccompanied by the vesicle 


of egestion. 


24 2 


5/2 ELEMENTARY BIOLOGY. [CHAP. 

It is of interest to note that in the case of small vege- 
table organisms the cellulose coats have been at times 
observed to be thrown out in a distorted, if not a digested 
and disintegrating condition. 

The chemical composition of the bodies of the Amcebce 
has not been accurately ascertained, but they undoubtedly 
consist, in great measure, of water containing a protein com- 
pound, and are similar to other forms of protoplasm. They 
absorb oxygen and give out carbonic acid, and the presence 
of free oxygen is necessary to their existence. When the 
medium in which they live is cooled down to the freezing 
point their movements are arrested, but they recover when 
the temperature is raised. At a temperature of about 35 C. 
their movements are arrested, and they pass into a condition 
of "heat-stiffening," from which they recover if that tem- 
perature is not continued too long; at 40 to 45 C. they 
are killed. 

Crystals are generally to be met with in the cell proto- 
plasm, but of their origin and significance nothing is at 
present known. 

Electric shocks of moderate strength cause Amcebce at 
once to assume a spherical still form, but they recover after 
a while. Strong shocks kill them and, at the same time, 
bring the nucleus distinctly into view. 

If Amoeba are not to be found, their nature may be 
understood by the examination of the colourless corpuscles of 
the blood. (Cf. ch. I. pp. 121- -123.) 

The colourless corpuscles of the blood of some of the 
cold-blooded vertebrates, such as Frogs and Newts, may be 
kept alive for many weeks in serum properly protected from 
evaporation; and if finely divided colouring matter, such 
as indigo, is supplied to them, either in the body or out of 
it, they take it into their interior in the same way as true 


VIII.] THE PROTEUS ANIMALCULE. 373 

Amoebce would. In the earliest condition of the embryo, 
the whole body is largely composed of such nucleated cells 
as the colourless corpuscles of the blood; and the colourless 
corpuscles must be regarded as simply the progeny of such 
cells, which have not become metamorphosed, and have 
retained the characteristics of the lowest and most rudi- 
mentary forms of animal life. 

The Amoeba is an animal, not because of its contractility 
or power of locomotion, but chiefly because it is devoid 
of the power of manufacturing protein from bodies of a 
comparatively simple chemical composition. The Amoeba 
has to obtain its protein ready made, in which respect 
it resembles all true animals, and therefore is, like them, 
in the long run, dependent for its existence upon some 
form or other of vegetable life. 

Am&bcz multiply by fission in a manner similar to that 
described for the bell-animalcule; the nucleus first divides, 
the cell becoming subsequently cleft in two. Occasionally 
an Amoeba has been seen to engulph another of smaller size 
than itself; and there is reason to believe that this process, 
originally thought to have been one of cannibalism, may 
probably be one of conjugation of dissimilar individuals, 
for reproduction, such as is seen in the bell-animalcule. 


LABORATORY WORK. 

A. Place a drop of water containing Amoeba on a slide, 
cover with a cover glass, avoiding pressure, and search 
over with \ inch obj. : having found an Amoeba, ex- 
amine with a higher power. 


3/4 ELEMENTARY BIOLOGY. [CHAP. 

1. Size; differing considerably in different specimens. 
Measure. 

2. Outline; irregular, produced into a number of thick 
rounded eminences (pseudopodia) which are con- 
stantly undergoing changes: sketch it at intervals of 
five seconds. 

3. Structure. 

tie. Outer hyaline layer (ectosarc\ tolerably sharply 
marked off: inner granular layer (endosarc] be- 
coming more fluid centrally. 

I'. Nucleus (indistinguishable in some specimens); 
a roundish more solid-looking body, often highly 
granular. There may be one, two, or many. 

i. Contractile vesicle; (if present) a roundish clear 
space in the ectosarc which disappears peri- 
odically, and after a short time reappears; its slow 
diastole rapid systole. 

d. Ingested foreign bodies; Diatom cases, Des- 
midice, c. 

4. Movements. 

a. Watch the process of formation of a pseudopo- 
diurn. A hyaline ectosarcal lobe first appears; 
then, as it increases in size, the granular endosarc 
flows into it. 

I. Locomotion ; watch the process, a pseudopodium 
is thrown out, then the rest of the body is drawn 
up to it, and the process is repeated. 

c. If the opportunity presents itself, watch the pro- 
cesses of the ingestion and egestion of solid 
matters. 


VIII.] THE PROTEUS ANIMALCULE. 375 

d. Observe the movements on the hot stage; warmth 
at first accelerates the movements, but as the tem- 
perature approaches 40 C. they cease, and the 
whole mass remains as a motionless sphere. 

e. Effects of electrical shocks on the movements. 

5. Mechanical Analysis ; crush. The whole collapses, 
except sometimes the nucleus, and even that after a 
time disappears: there is no trace of a distinct 
resisting outer sac. 

6. Chemical Analysis ; Treat with magenta and iodine. 
The whole stains, and there is no unstained envelop- 
ing sac. Iodine produces no blue colouration unless 
starch has been swallowed; if so, blue specks become 
visible. 

7. Look for encysted specimens; and for specimens 
which are undergoing fission. 

8. Another form of Amoeba is not unfrequently found 
which differs from that just described in being much 
less coarsely granular, and. in having ill-defined 
ectosarc and endosarc, together with much longer, 
more slender and pointed pseudopodia. Another 
common form progresses rapidly with a slug-like 
movement, only throwing out pseudopodia at its an- 
terior end. 

B. White Blood- Corpuscles (human). 

Prick your finger and press out a drop of blood: 
spread out on a slide under a coverslip,, avoiding 
pressure, and surround the margin of the coverglass 
with vaseline or oil. Neglect the red corpuscles,, and 
examine the larger and much less numerous colourless 
ones. 


;;6 ELEMENTARY BIOLOGY. [CHAP. VIII. 

Note 

1. Size; (measure). 

2. Form ; changing much like that of the Amoeba, but 
less actively. Draw at intervals of ten seconds. 

3. Structure; Some more and some less granular; 
ectosarc and endosarc less distinct than in the 
Amoeba. Nucleus rarely visible in the fresh state. 
No contractile vesicle. 

4. Treat with dilute acetic acid: the whole is clarified 
and a nucleus is brought into view in a more or less 
central position. Occasionally two nuclei may be 
seen. 

5. Stain with magenta; the whole becomes coloured, 
the nucleus most intensely. 

6. Place a fresh preparation on the hot stage, and 
gradually warm up to 50 C. The movements are 
at first rendered more active, but ultimately cease, 
the pseudopodia-like processes being all retracted 
and the whole forming a motionless sphere. 


IX. 

YEAST (Torula or Saccharomyces Cercvisice}. 

YEAST Is a substance which has been long known on ac- 
count of the power which it possesses of exciting the process 
termed fermentation in substances which contain sugar. 

If strained through a coarse filter, it appears to the naked 
eye as a brownish fluid in which no solid particles can be 
discerned. When some of this fluid is added to a solution 
of sugar and kept warm, the mixture soon begins to dis- 
engage bubbles of gas and become frothy ; its sweetness 
gradually disappears ; it acquires a spirituous flavour and 
intoxicating qualities ; and it yields by distillation a light 
fluid alcohol (or spirits of wine) which readily burns. 

When dried slowly and at a low temperature, yeast is 
reduced to a powdery mass, which retains its power of 
exciting fermentation in a saccharine fluid for a considerable 
period. If yeast is heated to the temperature of boiling- 
water, before it is added to the saccharine fluid, no ferment- 
ation takes place ; and fermentation which has commenced 
is stopped by boiling the saccharine liquid. 

A saccharine solution will not ferment spontaneously. If 
it begins to ferment, yeast has undoubtedly got into it in 
some way or other. 

If the yeast is not added directly to the saccharine fluid, 
but is separated from it by a very fine filter, such as porous 
earthenware, the saccharine fluid will not ferment, although 


378 ELEMENTARY BIOLOGY. [CHAP. 

the filter allows the fluid part of the yeast to pass through 
into the solution of sugar. 

If the saccharine fluid is boiled, so as to destroy the 
efficiency of any yeast it may accidentally contain, and then 
allowed to come in contact only with such air as has been 
passed through cotton wool, it will never ferment. But if 
it is exposed freely to the air, it is almost sure to ferment 
sooner or later, and the probability of its so doing is greatly 
increased if there is yeast anywhere in the vicinity. 

These experiments afford evidence (i) that there is some- 
thing in yeast which provokes fermentation, (2) that this 
something may have its efficiency destroyed by a high tem- 
perature, (3) that this something consists of particles which 
may be separated from the fluid which contains them by a 
fine filter, (4) that these particles may be contained in the 
air ; and that they may be strained off from the air by 
causing it to pass through cotton wool. 

Microscopic examination of a drop of yeast shews what 
the particles in question are. 

Even with a hand-glass, the drop no longer appears 
homogeneous, as it does to the naked eye, but looks as if 
fine grains of sand were scattered through it ; but a con- 
siderable magnifying power (5 600 diameters) is necessary 
to shew the form and structure of the little granules which 
are thus made visible. Under this power, each granule 
(which is termed a Torula) is seen to be a round, or oval, 
transparent body, varying in diameter from -^y-y-th to 
TuVy-tn of an inch (on the average about g^y-th). 

The Torulce are either single, or associated in heaps or 
strings. Each consists of a thin-walled sac, or bag, contain- 
ing a semi-fluid matter, in the centre of which there is often 
a space full of a more clear and watery fluid than the rest, 
which is termed a ' vacuole.' The sac is comparatively 


IX.] YEAST. 379 

tough, but it may be easily burst, when it gives exit to its 
contents, which readily diffuse themselves through the sur- 
rounding fluid. The whole structure is called a 'cell;' the 
sac being the ' cell-wall,' and the more solid portion of the 
contents the 'protoplasm.' It appears that a nucleus is 
also present, but on this point there is still some difference 
of opinion. 

When yeast is dried and burned in the open air it gives 
rise to the same kind of smell as burning animal matter, 
and a certain quantity of mineral ash is left behind. Ana- 
lysed into its chemical elements, yeast is found to contain 
Carbon, Hydrogen, Oxygen, Nitrogen, Sulphur, Phosphorus, 
Potassium, Magnesium and Calcium ; the last four in very 
small quantities. 

These elements are combined in different ways, so as to 
form the chief proximate constituents of the Toritla, which 
are (i) a Protein compound, analogous to Casein, (2) Cellu- 
lose, (3) Fat, and (4) Water. The cell-wall contains all the 
Cellulose and a small proportion of the mineral matters. 
The protoplasm contains the Protein compound and the Fat 
with the larger proportion of the mineral salts. 

These Torulce are the 'particles' in the yeast which have 
the power of provoking fermentation in sugar; it is they 
which are filtered off from the yeast when it loses its effi- 
ciency by being strained through porous earthenware ; it 
is they which form the fine powder to which yeast is reduced 
by drying, and which, from their extreme minuteness, are 
readily diffused through the air in the form of invisible 
dust. 

That the Torulce, are living bodies is proved by the manner 
in which they grow and multiply. If a small quantity of 
yeast is added to a large quantity of clear saccharine fluid, 
so as hardly to disturb its transparency, and the whole is 


3 80 ELEMENTARY BIOLOGY. [CHAP. 

kept in a warm place, it will gradually become more and 
more turbid, and, after a time, a scum of yeast will collect, 
which may be many thousand, or million, times greater in 
weight than that which was originally added. If the Torultz 
are examined as this process of multiplication is going on, it 
will be found that they are giving rise to minute buds, which 
rapidly grow, assume the size of the parent Tonila, and 
eventually become detached ; though, generally, not until 
they have developed other buds, and these yet others. The 
Torultz thus produced by gemmation, one from the other, 
are apt long to adhe-re together, and thus the heaps and 
strings mentioned, as ordinarily occurring in yeast, are pro- 
duced. No Tontla arises except as the progeny of another; 
but, under certain circumstances, multiplication may take 
place in another way. The Tonila does not throw out a bud, 
but its protoplasm divides into (usually) four masses, each 
of which surrounds itself with a cell-wall, and the whole are 
set free by the dissolution of the cell-wall of the parent. 
These endogenous reproductive bodies are termed spores, 
and retain their power of germination for a long time. 

As each of the many millions of Torulcc which may thus 
be produced from one Torula has the same composition as 
the original progenitor, it follows that a quantity of Protein, 
Cellulose and Fat proportional to the number of Torulte 
thus generated, must have been produced in the course of 
the operation. Now these products have been manu- 
factured by the Torulcc. out of the substances contained in 
the fluid in which they float and which constitutes their 
food. 

To prove this it is necessary that this fluid should have 
a definite composition. Several fluids will answer the pur- 
pose, but one of the simplest (Pasteur's solution) is the 
following : 


IX.] YEAST. 381 

Water (H O). 

Sugar (C> 22 n )- 

Ammonium Tartrate (C.H^NH^OJ. 

Potassium Phosphate (KHJPOJ. 

Calcium Phosphate (Ca 3 P 2 O 8 ). 

Magnesium Sulphate (MgSOJ. 

In this fluid the Torulcz will grow and multiply, But it 
will be observed that the fluid contains neither Protein nor 
Cellulose, nor Fat, though it does contain the elements of 
these bodies arranged in a different manner. It follows that 
the Torula must absorb the various substances contained in 
the water and arrange their elements anew, building them 
up into the complex molecules of its own body. This is a 
property peculiar to living things. 

If, on the other hand, some Tonila cells be added to a 
quantity of pure distilled water, it will be found not only 
that no growth or multiplication of the cells takes place, but 
that the amount of their protoplasm actually undergoes a 
perceptible diminution. Hence we see that there are 
processes going on in the cells which tend to diminish their 
substance. 

The chemical changes going on in a living cell, such as 
that of yeast, may conveniently be spoken of collectively as 
its metabolism. Among these changes those which result in 
the building up of more complex chemical bodies, and thus 
in an increase of the organic substance of the cell, constitute 
its constructive metabolism or anabolism^ while to those 
which bring about a diminution of organic substance, with 
evolution of simpler compounds, such as carbonic anhydride, 
the term destructive metabolism or catdboHsm has been 
applied. 

It must be pointed out that the anabolic processes of the 


382 ELEMENTARY BIOLOGY. [CHAP. 

organism not only result in the building up of its organic 
substances, but also involve an accumulation of potential 
energy. If a quantity of dried yeast is burned a definite 
amount of heat is given off, due to the conversion of this 
potential energy into the kinetic form. Conversely, the 
catabolic processes involve a change of potential into kinetic 
energy. The evolution of heat by actively growing yeast is 
due to changes connected with its destructive metabolism. 

The Torula being alive, the question arises whether it is 
an animal or a plant. Although no sharp line of demarca- 
tion can be drawn between the lowest form of animal and of 
vegetable life, yet Torula is an indubitable plant, for two 
reasons. In the first place, its protoplasm is invested by a 
cellulose coat, and thus has the distinctive character of a 
vegetable cell. Secondly, it possesses the power of con- 
structing Protein out of such a compound as Ammonium 
Tartrate, and this power of manufacturing Protein is dis- 
tinctively a vegetable peculiarity. Torula then is a plant, 
but it contains neither starch nor chlorophyll, and it cannot 
obtain the whole of its food from inorganic compounds, thus 
differing widely from the green plants. On the other hand, 
it is, in these respects, at one with the great group of Fungi. 
Like many of the latter, its life is wholly independent of 
light, and in this respect, again, it differs from the green 
plants. 

Whether Torula is connected with any other form of 
Fungi is a question which must be left open for the present. 
It is sufficient to mention the fact that under certain circum- 
stances some Fungi (e.g. Mucor] may give rise to a kind of 
Torula different from common yeast. 

The fermentation of the sugar is in some way connected 
with the living condition of the Tonila, and is arrested by all 
those conditions which destroy its life. At the same time 


IX.] YEAST. 383 

it appears that the conditions which are most favourable to 
the growth and multiplication of the Tonda are unfavourable 
to the process of fermentation. Thus the latter goes on 
most vigorously in the absence of free oxygen, while its 
presence is favourable to the increase of the yeast-cells. 
The greater part of the sugar is resolved into Carbonic 
anhydride and Alcohol, the elements of which, taken to- 
gether, equal in weight those of the sugar. A small part 
breaks up into Glycerine and Succinic acid, and one or two 
per cent, is not yet accounted for, but is perhaps assimilated 
by the Torulce. 

This is the more probable as Tor nice will grow and multiply 
actively in a solution in which sugar and Ammonium Nitrate 
replace the Ammonium Tartrate of the former solution, in 
which case the carbon of the Protein, Cellulose and Fat 
manufactured must be obtained from the sugar. Moreover, 
though oxygen is essential to the life of the Tonda, it can, 
as already mentioned, live in saccharine solutions which 
contain no free oxygen, appearing, under these circum- 
stances, to carry on its life by the substitution of the ab- 
normal catabolic process of fermentation for the normal 
respiration. 

It has further been ascertained that Tondce flourish re- 
markably in solutions in which sugar and pepsin replace 
the Ammonium Tartrate. In this case, the nitrogen of their 
protein compounds must be derived from the pepsin; and 
it would seem that the mode of nutrition of such Tondce 
approaches that of animals. 


ELEMENTARY BIOLOGY. [CHAP. 


LABORATORY WORK. 

Sow some fresh baker's yeast in Pasteur's fluid 1 with 
sugar and keep it in a warm place : as soon as the mixture 
begins to froth up, and the yeast is manifestly increasing in 
quantity, it is ready for examination. 

A. Morphology. 

1. Spread a little out, on a slide, in a drop of the fluid, 
and examine it with a low power (- inch objective) 
without a cover-glass. Note the varying size of the 
cells, and their union into groups. 

2. Cover a similar specimen with a thin glass and 
examine it under a high power (1 objective). 

a. Note the size (measure), shape, surface and mode 
of union of the cells. 

b. Their structure: sac, protoplasm, vacuole. 
a. Sac; homogeneous, transparent. 

(3. Protoplasm; less transparent; often with a few 

clear shining dots in it. 
y. Vacuole; sometimes absent; size, position. 

1 Pasteur's fluid : 

Potassium Phosph 20 parts. 

Calcium Phosph 2 ,, 

Magnesium vSulphate 2 ,, 

Ammonium Tartrate 100 ,, 

[Cane Sugar 1500 ,,] 

Water , ^57*3 ,, 

10,000 parts. 

The sugar is to be omitted when Pasteur's fluid "without sugar" is 
ordered. Pasteur himself used actual yeast ash; the above constituents 
give an imitation ash, which, with the ammonium salt and sugar, 
answers all practical purposes. 


IX.] YEAST. 385 

5. The relative proportion of sac, protoplasm, and 
vacuole in various cells. 

Draw a few cells carefully to scale. 

3 . Run in magenta solution under the cover-glass. (This 
is readily done by placing a drop of magenta so- 
lution in contact with one side of the cover-glass, 
and a small strip of blotting-paper at the opposite 
side.) 

a. Note what cells stain soonest and most deeply, 
and what part of each cell it is that stains : the sac 
is unaffected; the protoplasm stained; the vacuole 
unstained, though it frequently appears pinkish, 
being seen through a coloured layer of protoplasm. 

4. Burst the stained cells by placing a few folds of 
blotting-paper on the surface of the cover-glass and 
pressing smartly with the handle of a mounted 
needle : note the torn empty and colourless, but 
solid and uncrushed transparent sacs ; the soft 
crushed stained protoplasm. 

5. Repeat observation 3, running in iodine solution 
instead of magenta. The protoplasm stains brown ; 
the rest of the cell remains unstained. Note the 
absence of any blue coloration; starch is therefore 
not present. 

6. Treat another specimen with potash solution, running 
it in as before : this reagent dissolves out the proto- 
plasm, leaving the sac unaltered. 

7. [On staining with Haematoxylin-ammonia, one or more 
bodies may be distinguished by their deeper colour, 
which are probably of a nuclear nature.] 

M. 25 


386 ELEMENTARY BIOLOGY. [CHAP. 

8. [Sow a few yeast-cells in Pasteur's solution in a moist 
chamber and keep them under observation from day to 
day ; watch their growth and multiplication.] 

9. [Spore-formation : take some dry German yeast ; sus- 
pend it in water and shake so as to wash it. Let the 
mixture stand for half-an-hour : pour off the super- 
natant fluid, and, with a camel's hair pencil, spread out 
the creamy deposit in a thin layer on fresh cut potato 
slices or on a plate of plaster of Paris, and place with 
wet blotting-paper under a bell-jar : examine from day 
to day with a very high power (800 diam.) for spores, 
which will probably be found on the eighth or ninth 
day.] 

B. PHYSIOLOGY. 

(Conditions and results of the vital activity of Torula.} 
i. Sow a fair-sized drop of yeast in - 
a. Distilled water. 
I. 10 per cent, solution of sugar in water. 

c. Pasteur's fluid without the sugar. 

d. Pasteur's fluid with sugar. 
[e. Mayer's pepsin solution 1 .] 

Keep all at about 35 C., and compare the growth of the 
yeast, as measured by the increase of the turbidity of the 
fluid, in each case, "a" will hardly grow at all, "b" better, 
"<:" better still, "^" well, and "e" best of all. Note that 
bubbles of gas are plentifully evolved from both the so- 
lutions which contain sugar. 

1 Mayer's solution (with pepsin) = 

15 per cent, solution of sugar-candy 20 cc. 

Dihydropotassic phosphate o* i grm. 

Calcic phosphate o' i grm. 

"Magnesic sulphate o' i grm. 

Pepsin 0-23 grm. 


IX.] YEAST. 387 

That any growth at all takes place, in the case of 
experiments a and b, is due to the fact that the drop of 
yeast added contains nutritious material sufficient to pro- 
vide for that amount of growth. 

2. Prepare two more specimens of "d" and keep one 
in a cold the other in a warm (35 C.) place, but 
otherwise under like conditions. Compare the growth 
of the yeast in the two cases ; it is much greater in 
the specimen kept warm. 

3. Prepare two more specimens of "d"-, keep both 
warm, but one in darkness, the other exposed to the 
light : that in the dark will grow as well as the other ; 
sunlight is therefore not essential to the growth of 
Torula. 

4. Sow some yeast-cells in Pasteur's solution in a flask, 
the neck of which is closed by a plug of cotton 
wool, and boil for five minutes ; then set it aside ; 
no signs of vitality will afterwards be manifested by 
the yeast in the flask ; it is killed by exposure to this 
temperature. 

5. [Take two test tubes ; in one place some yeast, with 
Pasteur's solution containing sugar; in the other place 
baryta water, and then connect the two test tubes by 
tightly fitting perforated corks and a bent tube passing 
from above the surface of the fluid in the first tube to 
the bottom of the baryta water in the second; pass a 
narrow bent tube, open at both ends, through the cork 
of the baryta water tube, so that its outer end dips just 
below the surface of some solution of potash 1 . All gas 
formed in the first tube will now bubble through the 
baryta water in the second, and, from thence, any that 

1 The object of the potash is to shield the baryta water from any 
carbonic anhydride that may be in the atmosphere. 

^1 252 


388 ELEMENTARY BIOLOGY. [CHAP. IX. 

is not absorbed will pass out through the potash into 
the air. An abundant precipitate of barytic carbonate 
will be formed which can be collected and tested. The 
fermenting fluid, therefore, evolves carbonic anhydride.] 

6. [Grow some yeast in Pasteur's solution (with sugar), in a 
nearly closed vessel (say a bottle with a cork through 
which a long narrow open tube passes) : as soon as the 
evolution of gas seems to have ceased, distil the fluid in 
a water bath and condense and collect the first fifth 
that comes over: redistill this after saturation with 
potassic carbonate, and test the distillate for alcohol by 
its odour and inflammability.] 

7. [Determine that heat is evolved by a fluid in which 
active alcoholic fermentation is going on. Place 200 cc. 
of fresh yeast in a flask, and add i litre of Pasteur's 
fluid with sugar : put another litre of the fluid alone in 
a similar flask, cover each flask with a cloth and place 
the two side by side in a place protected from draughts. 
When gas begins to be actively evolved from the yeast- 
containing solution, take the temperature of the fluid in 
each flask with a good thermometer ; the temperature of 
the one in which fermentation is going on will be found 
the higher.] 


X. 
PROTOCOCCUS (Protococcus pluvialis '). 

IF the mud which accumulates in roof-gutters, water-butts, 
and shallow pools be collected, it will be found to contain, 
among many other organisms, specimens of Protococcus. 
In its vegetative condition Protococcus is a spheroidal body 
TITO to ^oVo f an mcn m diameter, composed, like Torula, 
of a structureless tough transparent wall, inclosing viscid and 
granular protoplasm. The chief solid constituent of the 
cell-wall is cellulose. The protoplasm contains a nitrogenous 
substance, doubtless of a proteinaceous nature, though its 
exact composition has not been determined, and some 
small starch-grains are sometimes to be found in it. Certain 
definite portions of the protoplasm, termed chromatophores, 
contain a red or green colouring matter. The latter is 
called clilorophylL These chromatophores occupy a large 
part of the cavity of the cell, so that under a low power the 
whole contents appear to be coloured. 

Individual Protococci may be either green or red ; or half 
green and half red ; or the red and green colours may co- 
exist in any other proportion. 

In the middle of the cell is a distinct nucleus, containing 
a nucleolus. 

1 The names Hsematococcus, and Chlamydococcus pluvialis have 
also been applied to this form, but it must not be confused with the 
more abundant Pleurococcus which everywhere forms a green powdery 
layer on trees, palings, &c. 


3QO ELEMENTARY BIOLOGY. [CHAP. 

The influence of sunlight is an essential condition of the 
growth and multiplication of Protococcus ; under that influ- 
ence, it decomposes carbonic anhydride, appropriates the 
carbon, and sets oxygen free. The energy thus derived 
from the sun's rays is stored up in the potential form, to be 
again partly expended in the growth of the plant, and in the 
movements of its spores. It is this power of obtaining the 
carbon which it needs from carbonic anhydride, which is 
the most important distinction of Protococcus, as of all 
plants which contain chlorophyll, from Torula and the 
other Fungi. 

As Protococcus flourishes in rain-water, and rain-water con- 
tains nothing but carbonic anhydride, which it absorbs 
along with other constituents of the atmosphere, ammonium 
salts (usually ammonium nitrate, also derived from the air) 
and minute portions of earthy salts which drift into it as 
dust, it follows that it must possess the power of con- 
structing protein by rearrangement of the elements supplied 
to it by their compounds. Torula, on the other hand, is 
unable to construct protein matter out of such materials as 
these. 

Another difference between Torula and Protococcus is 
only apparent : Torula absorbs oxygen and gives out car- 
bonic anhydride; while Protococcus, on the contrary, absorbs 
carbonic anhydride and gives out oxygen. But this is true 
only so long as the Protococcus is exposed to sunlight. In 
the dark, Protococcus, like all other living things, undergoes 
oxidation and gives off carbonic anhydride ; and there is 
every reason to believe that the same process of oxidation 
and evolution of carbonic anhydride goes on in the light, 
but that the loss of oxygen is far more than covered by the 
quantity set free by the carbon-fixing apparatus, of which 
the chlorophyll forms an essential part. 


X.] PROTOCOCCUS. 391 

The multiplication of Protococcus takes place by means of 
actively locomotive spores, termed zoospores. These are of 
two kinds. The larger, or macrozoospores, are produced by 
the division of the contents of one of the ordinary cells into 
two or four portions. These portions assume a pear-like 
shape and become free by the resorption of the wall of the 
mother-cell. When they first escape the zoospores are 
naked protoplasmic bodies (primordial cells) destitute of any 
cell-wall. They swim actively through the w r ater by means 
of two delicate processes of the protoplasm, termed cilia , 
which are inserted at the pointed end of the zoospore. The 
movement is of a double kind, the progressive motion, in 
which the pointed ciliated end goes foremost, being accom- 
panied by a rotation of the zoospore about its long axis. 
The macrozoospore soon acquires a thin cell-wall, through 
which the cilia protrude. The wall does not remain in 
immediate contact with the protoplasm of the primordial 
cell, but becomes separated from it by a space containing 
clear cell-sap. This space is however traversed by fine 
radiating protoplasmic threads. The internal structure is 
similar to that of the vegetative cell, each zoospore contain- 
ing a nucleus and chromatophores. The ciliated end con- 
sists of colourless protoplasm only. The movement of the 
cilia is so rapid, and their substance is so transparent and 
delicate, that they are invisible until they begin to move 
slowly, or are treated with reagents, such as iodine, which 
colour them, and arrest their movements. 

The smaller, or microzoospores, are-produced by the division 
of the vegetative mother-cell into a larger number of por- 
tions, the number being always some power of two. They 
differ from the macrozoospores, apart from their size, in 
never acquiring a cell-wall so long as their movement con- 
tinues. In other respects the two kinds of zoospores agree. 


392 ELEMENTARY BIOLOGY. [CHAP. 

Both eventually come to rest, assume a globular shape, 
lose their cilia and form a thick cell-wall around their pro- 
toplasm, thus reproducing the vegetative condition of the 
plant. 

Both kinds of zoospores are sensitive to light, swimming 
towards the source of light, when its intensity is moderate, 
and away from it when its intensity is increased. 

For reasons similar to those which prove the vegetable 
nature of Torula, Proiococcus is a plant, although its zoo- 
spores are curiously similar to the Monads among the lowest 
forms of animal life. But it is now known that many of the 
lower plants, especially in the group of Alga, to which Pro- 
tococcus belongs, also give rise to locomotive spores propelled 
by cilia, like those of Protococcus, so that there is nothing 
anomalous in the case of the latter. 

Like the yeast-plant, Protococcus retains its vitality after it 
has been dried. It has been preserved for as long as two 
years in the dry condition, and at the end of that time has 
resumed its full activity when placed in water. The wide 
distribution of Protococcus on the tops of houses and else- 
where, is thus readily accounted for by the transport of the 
dry Protococd by winds. 


LABORATORY WORK. 

A. Morphology. 

a. Vegetative stage. 

i. Spread out in water some mud from a gutter or 
similar locality, and put on a cover-glass. Look for 
the red or green Protococcus cells with a low power. 
Having found some, put on a high power and make 
out the following points. 


x.] PROTOCOCCUS. 393 

Size; (measure) very variable. 

Form ; more or less spheroidal, with individual 
variations. 

Strudtire; cell-wall, protoplasm, chromatophores, some- 
times a vacuole, always a nucleus containing a 
nucleolus. 

Colour ; generally green sometimes red sometimes 
half and half sometimes centre red, periphery 
green the colouring matter always in the proto- 
plasm of the chromatophores only. 

Draw carefully to scale. 

2. Apply the methods of mechanical and chemical 
analysis detailed for Tonila. (I. A. 3. 4. 5. 6.) The 
application of iodine is especially useful for bringing 
out the limits of the chromatophores, and also the 
nucleus and nucleolus. The same reagent will also 
often show the presence of some small starch-grains. 
Treat a specimen with strong iodine solution and 
then with sulphuric acid (75 per cent.): the cell-wall 
will become stained blue. 

3. Look out for cells the contents of which are dividing 
up to form zoospores. 

b. Zoospores. 

a. Mount a drop of water containing zoospores of 
Protococcus, and examine with a high power. 
Note the actively locomotive green bodies, of 
which two varieties can be distinguished. 

a. Cells of relatively large size derived from 
the vegetative cells by division of their con- 
tents into 2 or 4 portions. These are the 
macrozoospores. Observe the thin colour- 


394 ELEMENTARY BIOLOGY. [CHAP. 

less cell-wall, surrounding the protoplasm, 
but separated from it by a clear space. 
Note in various specimens The two cilia 
prolonged from the protoplasm through aper- 
tures in the cell-wall ; their motionless part 
within the wall ; their vibratile portion out- 
side it. The colourless thin external layer 
of the protoplasm collected into a little heap 
at the point from whence the cilia arise. 
The delicate colourless processes radiating 
from the outer protoplasmic layer to the in- 
terior of the cell-wall. The colour usually 
green, but frequently one bright red spot is 
present. 

Here, as in the vegetative stage, the colour- 
ing matter is limited to the relatively large 
chromatophores, and here also a nucleus is 
present. 

/?. Cells of smaller size but much like the above 
if the cellulose sac were removed, and the 
radiating processes extending to it from the 
protoplasm withdrawn. These are the micro- 
zoospores. 

b. Try to find specimens in which the movements 
are becoming sluggish, and see the cilia in 
motion. 

c. Stain with iodine ; this kills the cells, and stops 
their movements, and frequently renders the 
cilia very distinct. 

//. Try to find zoospores which have come to rest, 
and are beginning to form a new cell-wall. 


x.] PROTOCOCCUS. 395 

[B. PHYSIOLOGY. 

1. Get some water that is quite green from containing a 
large quantity of Protococcus; introduce some of it 
into two tubes filled with and inverted over mercury, 
and pass a small quantity of carbonic anhydride into 
each : keep one tube in the dark and place the other 
in bright sunlight for some hours. Then measure the 
gas in each tube and afterwards introduce a fragment 
of caustic potash into each ; the gas from the specimen 
kept in the dark will be more or less completely ab- 
sorbed (= carbonic anhydride), that from the other 
will not be absorbed by the potash alone, but will be 
absorbed on the further introduction of a few drops of 
solution of pyrogallic acid (= oxygen). Protococcus, 
therefore, in the sunlight, takes up carbonic anhydride 
and evolves oxygen. A comparative experiment may 
be made with a third tube containing water but no 
Protococcus. 

2. Place some water containing numerous zoospores of 
Protococcus near a window, exposed to bright sun- 
light. Observe that the majority of the zoospores 
accumulate on the side away from the source of 
light. 

Next remove them to some distance from the window, 
or otherwise diminish the intensity of the light acting 
on them. Observe that now the zoospores accumulate 
on the side towards the light. 

The zoospores of Protococcus are thus seen to be 
photometric, i.e. they seek or avoid the light according 
to the degree of its intensity.] 


XI. 
SPIROGYRA. 

IN ponds and tanks, the water of which is tolerably pure, 
we constantly find in summer floating masses, of a light 
green colour, which feel slippery when handled. A very 
superficial examination is sufficient to show that these 
masses consist of a vast number of very long and fine green 
threads. The organisms in question may belong to various 
genera of a group of plants called the Confervoid Algae : 
one of the genera, representatives of which are most com- 
monly found, is Spirogyra. 

On microscopical examination we find that each thread 
of Spirogyra consists of a single, unbranched, row of 
cylindrical cells, of very variable length, but of constant 
diameter throughout the filament. There is no distinction 
of apex and base ; both ends of the filament are quite 
alike, and neither is attached to any substratum. We have 
to clo here with a plant which is morphologically multi- 
cellular, for each thread consists of many cells. All these 
cells, however, are uniform in structure, and each performs 
for itself, so far as can be ascertained, all the functions of 
the plant. Hence Spirogyra may be spoken of as phy- 
siologically a unicellular plant. In each of the cells there 
are one or more (sometimes as many as 10) bright green 
spiral bands, and by these the genus may at once be 
recognized. Their number varies according to the species, 
which are very numerous, and in many cases hard to 


CHAP. XL] SPIROGYRA. 397 

distinguish. The most favourable for investigation are of 
course the larger ones, and among these the most con- 
venient forms are those in which the spiral bands have 
somewhat lax windings, so that they do not interfere with 
the view into the interior of the cell. 

Each cell of Spirogyra is bounded on the outside by a 
cellulose wall. This consists of a number of layers, which 
however can only be made out distinctly by the use of 
reagents such as potash. Immediately inside the cell-wall 
and closely applied to it is a layer of protoplasm, to which 
the name primordial utricle is applied. In Spirogyra this 
is so thin that it is difficult to make out under natural con- 
ditions except with a very high power. It can however be 
easily demonstrated by the use of what are termed plas- 
molysing re-agents, such as solution of common salt, which 
withdraw water from the interior of the cell, and thus cause 
its contents to contract. The contracted mass will then be 
seen to be bounded on all sides by a thin membrane, which 
is the primordial utricle. The latter is of precisely the 
same nature as the protoplasm in the cells of Yeast or Pro- 
tococcus. Its occurrence in the form of a relatively thin 
parietal layer, while the greater part of the cavity of the cell 
is occupied by a large vacuole, is characteristic of most 
vegetable cells in their mature condition. 

The green spiral bands correspond to the chromatophores 
in Protococcus, and bear the same name, each band being 
spoken of as a single chromatophore. Each cell may there- 
fore contain one chromatophore, or several, according to 
the species. In these bodies all the chlorophyll of the 
plant is contained. They themselves consist of protoplasm 
and retain their form unaltered when the chlorophyll is 
extracted by alcohol or other solvents, and they are in im- 
mediate contact with the primordial utricle throughout their 


398 ELEMENTARY BIOLOGY. [CHAP. 

whole course. At Intervals along each chromatophore 
round bodies will be observed which appear green like 
the rest of the band, but on careful examination are 
each found to contain a small colourless mass of proteid 
substance, termed the pyrenoid. This pyrenoid is of a 
crystalline form, usually appearing hexagonal in optical 
section, and can be brought out more clearly by the use of 
staining reagents. Bodies of this nature are of very general 
occurrence in the chromatophores of the Algse. It is only 
around the pyrenoids that starch is formed, and if the plant 
has been exposed to the light before examination, the 
pyrenoid will be found to be surrounded by a layer of small 
starch-grains often present in so great a mass that the band 
is distinctly swollen at the places where they occur. 

As already mentioned the greater part of the interior of 
the cell is occupied by a single large vacuole, containing 
cell-sap, i.e. water in which certain inorganic salts, and 
certain organic substances, such as sugar and acids, are 
dissolved. 

In addition to the structures already described each cell of 
Spirogyra contains a conspicuous nucleus. Its position varies 
somewhat in different species, for in some cases it is placed 
in the middle of the cell, while in others it is nearer to 
the external wall. Forms with a central nucleus are more 
convenient for observation. The shape of the nucleus also 
shows certain specific differences. A very common form is 
that of a biconvex lens, the edge of the lens being turned 
towards the lateral walls of the cell, and the circular faces 
towards its ends. The nucleus is surrounded by a layer of 
protoplasm, from which long processes radiate which 
traverse the vacuole and are attached at their further ends 
to those parts of the chromatophores in which the pyrenoids 
are situated. 


XL] SPIROGYRA. 399 

The nucleus contains a relatively large nudcolus, the 
substance of which seems to be homogeneous, and some- 
what resembles that of the pyrenoids in its reactions. The 
nucleus itself usually appears to be finely granular. Its real 
structure is however fibrous, but for the study of these 
details the nucleus of Spirogyra is not favourable. 

The growth of Spirogyra in length is accompanied by the 
increase in number of its cells. This increase takes place 
by the repeated division of each cell into two equal parts, 
by means of a transverse wall; the process is not localized 
in any special region of the filament; all its cells are alike 
capable of division. In this fact Spirogyra differs from all 
the more perfect plants to be subsequently considered, and 
here also we have an indication of the physiological equiva- 
lence of the constituent cells of Spirogyra. 

The process of cell-division takes place, under normal 
conditions, in the night, the products of assimilation which 
have been accumulated in the daytime being used up during 
the darkness to form new cell-wall and protoplasm. The 
division is however dependent on temperature, and by keep- 
ing the plants cold during the night it is possible to make 
them postpone their cell-division till the morning, when it 
can be conveniently observed. The nucleus divides into 
two, the daughter nuclei being at first connected by fine 
protoplasmic threads. In the meantime a transverse ring of 
cellulose is formed by the protoplasm around the cell, mid- 
way between its two ends. This ring is continuous, at its 
outer edge, with the lateral wall on which it abuts. By 
further additions from the protoplasm it gradually grows in- 
wards until its inner edges meet, so that a complete disc of 
cellulose is formed across the cavity of the cell. The con- 
tents necessarily become constricted by the inward growth 
of the new cell-wall, and are eventually severed into two 


400 ELEMENTARY BIOLOGY. [CHAP. 

distinct halves, each containing one of the daughter nuclei. 
The whole process, especially as regards the division of the 
nucleus, is a complicated one, but it is not necessary to enter 
into the details here. Cell-division, of which this may be 
taken as a type, is the general mode of formation of cells 
throughout the vegetable kingdom. In the higher plants 
however it is usual for the new wall to be formed simul- 
taneously over its whole area, instead of by progressive 
growth from without inwards. 

The Reproduction of Spirogyra takes place in quite a 
different way from that of the plants hitherto considered, 
and affords one of the simplest examples of a sexual process. 
In the form in which it here occurs this process is termed 
conjugation, which may be denned as the union of two ex- 
ternally similar cells to form a single reproductive cell. 
Conjugating specimens can usually be distinguished from 
vegetative ones by their more tangled filaments, and duller 
colour, and by feeling rougher when handled. When under 
cultivation Spirogyra can usually be induced to conjugate 
by allowing the water in which it is growing to evaporate 
very gradually. In the ordinary form of conjugation two 
filaments lying side by side send out short lateral protrusions, 
one from each cell. The protrusions from the one filament 
grow to meet those from the other, their contiguous walls 
become absorbed, and in this way the two filaments become 
connected by a number of transverse tubes, arranged like the 
rungs of a ladder. Changes now begin to take place in the 
contents of the cells, and it is at this stage that a difference 
first shows itself in the behaviour of the two filaments. In 
the one filament the contents of each cell contract away 
from the wall, so as to lie freely in the cavity of the cell, 
as a distinct sac bounded by the primordial utricle. In 
the other filament these changes take place somewhat later. 


XL] SPIROGYRA. 401 

After a time the contents of the cells which first under- 
went contraction begin to move into the connecting tube. 
The entire contents pass over and fuse completely with 
those of the cell which receives them. Recent researches 
have shown that the corresponding constituents of the 
contents of each cell unite one with another, primordial 
utricle fusing with primordial utricle, chromatophore with 
chromatophore, and, which is the most important point, 
nucleus with nucleus. 

The cell formed by conjugation is termed the zygospore, 
It is at first spherical in shape and destitute of any cell-wall 
of its own. It soon increases in size, by taking up water, 
assumes an elliptical outline, and becomes surrounded by a 
cell-wall. The latter consists, in its mature condition, of 
three layers, the middle one of which is of a brown colour, 
while those on either side of it are colourless. The wall is 
cuticularized) that is to say, it has undergone a chemical 
change which renders it almost wholly impermeable to 
water. Meanwhile changes go on in the contents of the 
zygospore, the most important being the appearance of oil 
in place of starch. In this condition the zygospore passes 
through a long stage of rest, during which it can withstand 
great extremes of temperature, and is not injured by periods 
of drought. On germination each zygospore bursts its cuti- 
cularized wall and grows out directly into a new plant. 

We have seen that in the normal case of conjugation just 
described a distinct differentiation of the filaments into 
male and female individuals is shown, as all the cells of 
each of the conjugating filaments behave in the same way, 
either giving up their own contents or receiving those of the 
other thread. This sexual difference however has not yet 
become completely fixed, for in certain cases adjoining cells 
of one and the same filament conjugate with each other. 

M. 26 


402 ELEMENTARY BIOLOGY. [CHAP. 

This process, to which the name of moncscious conjugation 
may be applied, occurs in the same species which are usually 
reproduced by the normal ladder-like or dioecious con- 
jugation. 

Some allies of Spirogyra show no demonstrable difference 
of sex between the conjugating cells, for the zygospore is 
formed in the connecting passage, each cell thus appearing 
to take an exactly equal part in the process. 

The mode of reproduction in Spirogyra and its allies, simple 
as it is, may serve as the type of all sexual reproduction. 
Among the innumerable modifications under which the 
sexual process takes place, the one point which is found to 
be constant is the fusion of the nuclei of two distinct cells. 

A few words. on the Physiology of Spirogyra may be added. 
Its nutrition takes place in all important respects in the 
same way as that of Protococcus. The carbonaceous food 
of the plant is obtained by decomposition of the carbon 
dioxide dissolved in the water, and this of course only goes 
on under the influence of light Starch is the first easily 
demonstrable product of this process, though it is certainly 
not the first product actually formed. It is easy to show 
that the formation of the starch-grains is dependent on the 
action of light. If the plant be kept for some hours in the 
dark all the starch will be found to have disappeared. A 
very short exposure to daylight is sufficient to induce its 
renewed formation. Under the action of direct sunlight a 
demonstrable amount of starch may be developed within so 
short a time as five minutes. It will be remembered that 
the starch-grains are formed around the pyrenoids. As re- 
gards the part played by the latter in the process we have 
no definite knowledge at present, but similar proteid crys- 
talloids are found elsewhere in connection with starch- 
forming corpuscles. 


XI.] SPIROGYRA. 403 

Spirogyra will not of course grow in distilled water any 
more than will Yeast or Protococcus. If the water be sup- 
plied with the following salts the Spirogyra will be able to 
obtain all the food it requires : Potassium Nitrate, Calcium 
Sulphate, Magnesium Sulphate, Calcium Phosphate, Sodium 
Chloride, and Ferric Chloride. The sodium chloride is only 
of indirect service as neither of its elements is essential as a 
food-constituent. As regards the other elements required 
by the plant, we already know that Carbon, Hydrogen, 
and Oxygen are the elements of starch and cellulose, while 
the protoplasm and nucleus are built up of these elements 
with the addition of Nitrogen, Sulphur and Phosphorus. 
Iron is necessary for the formation of chlorophyll, while 
potassium plays an essential, though obscure, part in the 
process of assimilation. Calcium and Magnesium have 
been shown by experiment to be necessary for the nutrition 
of green plants, but their exact function is still doubtful. 


LABORATORY AVORK. 

A. Morphology. 

I. Vegetative condition. 

1. Naked-eye characters. 

Observe that the masses of Spirogyra consist of 
long, delicate, bright green, unbranched filaments, 
which in the vegetative condition are quite smooth 
and glossy. 

2. Microscopical characters. 

Mount one or two filaments of Spirogyra in water 
and observe first with the low, and then with the 
high power. 

26 2 


404 ELEMENTARY BIOLOGY. [CHAP. 

a. Note that each filament is composed of a series 
of cylindrical cells, that it is unbranched, and that 
all its cells are alike (apart from slight differences 
of length). Observe especially that there is no 
difference of structure between the two ends of 
the filaments. 

b. In each cell observe 

a. The cell-wall, completely surrounding the cell. 
It consists of cellulose and gives the same re- 
actions as the cell-wall of Protococcus (p. 393). 
On treatment with Potash solution, the stratifi- 
cation of the cell-wall can be made out with a 
high power. 

J3. The protoplasmic primordial utricle, completely 
lining the cell-wall on the inside. This is 
colourless and appears finely granular under 
a very high power. In order to see the 
primordial utricle better, plasmolyse the cell by 
running in 10 p. c. salt solution. The prim- 
ordial utricle will now contract away from the 
cell-wall and be easily seen. 

y. The bright green spiral chromatophores. These 
are from i to 10 in number, according to 
the species. Observe the round bodies oc- 
curring at intervals in each chromatophore. 
These are the pyrenoids, each of which is 
surrounded by a layer of starch-grains if the 
plant has been exposed to light. Run in Iodine 
solution to demonstrate the presence of starch. 

8. The large vacuole occupying the greater part of 
the interior of the cell. 

e. The nucleus in the middle of the cell. In most 


XL] SPIROGYRA. 405 

species its form is that of a biconvex lens, as 
described in the text. Inside it is the nucleolus. 
The nucleus is surrounded by a layer of pro- 
toplasm. Observe that strands of protoplasm 
radiate from the latter, crossing the cavity of 
the cell, and attached at their outer ends to 
those parts of the chromatophores where the 
pyrenoids occur. 

. The minute structure will be better made out by 
means of staining. Place some Spirogyra in satu- 
rated solution of Picric acid 1 for not less than 
12 hours. Then wash thoroughly in distilled 
water. The chlorophyll will now have entirely 
disappeared. Stain the filaments thus prepared 
with Borax carmine solution 2 for an hour or more. 
Then mount in dilute glycerine 3 and examine with 
the highest power available. The cell-wall will 
be unstained. The protoplasm of the primordial 
utricle, chromatophores, and radial strands will 
have taken the stain very lightly. On the other 
hand the nucleus will be decidedly, and the nu- 
cleolus very deeply, coloured. The pyrenoids 
stain deeply, and their crystalline form can now 
be clearly made out. The layer of starch-grains 
surrounding each pyrenoid remains quite colour- 
less. It is especially in material prepared in this 
way that the relation of the radial protoplasmic 
strands to the pyrenoids can be traced. 

77. The process of cell-division, as described in the 
text, can be best observed by keeping the Spiro- 
gyra at a low temperature during the night, and 

1 Appendix, E. 

2 Appendix, E. 

3 The best plan is to mount in water and gradually run in glycerine 
under the cover-slip. 


406 ELEMENTARY BIOLOGY. [CHAP. 

examining in a warm room the following morning. 
In cold weather it is sufficient to put the vessel 
containing the Spirogyra out-of-doors ; in summer 
it may be surrounded with ice. 

In mounting the filaments to observe the di- 
vision it is necessary to support the cover-slip by 
means of two bristles or fragments of thin glass, so 
that it may not press on the object. The higher 
the power used the better. 

II. Reproduction. 

1. Look out for masses of Spirogyra in which the fila- 
ments are tangled, and of a dull-green colour, as 
described in the text. These will generally be found 
late in the summer, or at any time when the water 
in which the plant is growing is getting low. 

2. Examine such filaments first with a low power, in 
order to find the various stages of conjugation. 
The details at each stage are then to be made out 
with the high power. Observe 

a. Pairs of parallel filaments which have begun to 
produce the lateral protrusion. Note that the 
protrusions in the filaments are formed opposite 
one another. 

b. Similar pairs in which the protrusions have al- 
ready become continuous by absorption of their 
walls at the point of contact, so that they now 
form transverse tubes connecting the filaments. 
Note that at this stage the cells of the one fila- 
ment show a contraction of their contents, while 
those of the other are unaltered. 

c. Stages in which the cell-contents of the one fila- 
ment are passing over through the connecting 
tubes into the cells of the other. 


XI.] SPIROGYRA. 407 

The details of the fusion of the contents are best 
made out in material prepared and stained as de- 
scribed above (I. 2. b. .). Without some such 
treatment the nuclei cannot be seen at this stage 
at all. 

d. Stages of development of the Zygospore, formed 
from the united contents of the two cells. Ob- 
serve its for lit) at first spherical, then oval, and the 
gradual thickening of its wall, which ultimately 
consists of 3 layers. Treat a ripe zygospore with 
Sulphuric acid. Observe that its wall is not dis- 
solved, showing that it has become cuticularized. 
Observe the abundant oil-drops in the contents of 
the Zygospore. 

B. Physiology. 

1. Keep some filaments of Spirogyra in distilled water. 
Observe that although they may remain alive for some 
time, growth soon ceases entirely. 

Place other filaments in a food-solution 1 containing 
the salts enumerated in the text. Under proper con- 
ditions of light and temperature active growth of the 
filaments and division of their cells will now take place. 

2. Place a vessel containing Spirogyra in the dark for 
12 hours. Then mount some filaments, test with 
Iodine, and observe that the starch has entirely dis- 
appeared. 

Expose some of the filaments to as bright a light as 
possible. Observe again after a short interval (varying 
from 5 minutes to an hour or more according to the 
intensity of the illumination). Test with Iodine as 
before, and observe that starch-grains have again made 
their appearance around the pyrenoids. 

1 Appendix, E. For Spirogyra the solution should be considerably 
diluted. 


XII. 
BACTERIA (Schizomycetes}. 

UNDER these names a considerable variety of organisms, 
for the most part of extreme minuteness, are included. 

They may be defined as globular, oblong, rod-like or 
spirally coiled masses of protoplasmic matter enclosed in a 
more or less distinct structureless membrane, in most cases 
devoid of chlorophyll and multiplying by transverse division. 
The smallest are not more than ao ^ 00 th of an inch in dia- 
meter, so that under the best microscopes they appear as 
little more than mere specks, and even the largest have a 
thickness of little more than -roiroo'th f an inch, though they 
may be very long in proportion. Many of them have two 
conditions a still and an active state. In their still condi- 
tion, however, they very generally exhibit that Brownian 
movement which is common to almost all very finely divided 
solids suspended in a fluid. But this motion is merely oscil- 
latory, and is readily distinguishable from the rapid transla- 
tion from place to place which is effected by the really active 
Bacteria. 

In a large number of forms the presence of cilia has been 
detected. In Spirillum volutans, for example, one of the 
largest species, there is a cilium at each end of the spirally 
coiled body. In this case and in some others there can 
scarcely be a doubt that these cilia consist of protoplasm, 
and are really the organs by which the movement is effected. 


CHAP. XII.] BACTERIA. 409 

In other cases again, however, there is some reason to 
believe that the so-called cilia are simply prolongations of 
the cell-membrane, and destitute of any power of inde- 
pendent movement. In the latter case the movement of 
the organism must be due to some other cause, such as the 
contractility of the protoplasmic body as a whole. Many 
forms, such as the Vibriones^ so common in putrefying 
matters, appear obviously to have a wriggling or serpenti- 
form motion, but this is an optical illusion. In this Bac- 
terium the body does not rapidly change its form ; but its 
joints are bent zigzag-wise, and the rotation of the zig-zag 
upon its axis, as it moves, gives rise to the appearance of 
undulatory contraction. A cork-screw turned round, while 
its point rests against the finger, gives rise to just the same 
appearance. 

In other forms, however, such as Spirillum, true contrac- 
tile curvatures have been observed. 

A nucleus has not yet been detected in any of these 
plants. The delicate membrane of the Bacteria is in all 
cases surrounded on the outside by a gelatinous layer, often 
difficult of detection. In the still state, however, this gela- 
tinous substance is often developed to a very large extent, 
forming a continuous mass of considerable size, in which 
the individual cells appear embedded. This is termed the 
Zoogloea form of the Bacteria. The membrane of the Bac- 
teria, with its gelatinous layers, corresponds to the cell-wall 
of Protococcus or yeast. Its reactions, however, vary in 
different cases, sometimes agreeing with those of cellulose, 
and sometimes indicating an albuminous composition. 

All forms of Bacteria, of which the life-history has been 
fully investigated, are found to produce resting spores. 
These bodies make their appearance when the supply of 
food has become exhausted or the conditions have otherwise 


410 ELEMENTARY BIOLOGY. [CHAP. 

grown unfavourable. Either the spore may arise as a small 
cell in the interior of certain of the vegetative cells, or the 
latter may themselves become directly converted into 
spores. In either case the spore is characterized by its 
more granular protoplasm and firmer cell-wall. On germi- 
nation, which may be delayed until after a long period 
of rest, the hard membrane is thrown off, and the pro- 
toplasm of the spore resumes the ordinary vegetative deve- 
lopment. 

Bacteria grow and multiply in Pasteur's solution (without 
sugar) with extreme rapidity, and, as they increase in 
number, they render the fluid milky and opaque. Their 
vital actions are arrested at the freezing point, but no tem- 
perature has yet been reached low enough to kill them. 
They thrive best in a temperature of about 30 C. but, in 
most fluids, they are 'killed by a temperature of 60 C. 
(140 K). This, however, only applies to the vegetative 
condition, for the spores can in many cases resist a tempera- 
ture very considerably over the boiling point of water. 

In many points of their physiology Bacteria closely re- 
semble Tondce; and a further resemblance lies in the cir- 
cumstance that many of them excite specific fermentative 
changes in substances contained in the fluid in which they 
live, just as yeast excites such changes in sugar. 

All the forms of putrefaction which are undergone by 
animal and vegetable matters are fermentations set up by 
Bacteria of different kinds. Organic matters freely exposed 
to the air are, in themselves, nowise unstable bodies, and 
if due precautions have been taken to exclude Bacteria 
they do not putrefy, so that, as has been well remarked, 
" putrefaction is a concomitant not of death, but of life." 

Bacteria, like Tondce and Protococci, are not killed by 
drying up, and from their excessive minuteness they must 


XII.] BACTERIA. 41 1 

be carried about still more easily than Tondce are. In 
fact there is reason to believe that they are very widely 
diffused through the air, and that they exist in abundance 
in all ordinary water and on the surface of all vessels that 
are not chemically clean. They may be readily filtered off 
from the air, however, by causing it to pass through cotton- 
wool. 

The Bacteria have no near relationship to any of the 
other plants described in this book, and are introduced 
chiefly on account of the great importance of the various 
fermentative changes which they produce. 

The life-history of the Bacteria is only completely known 
in comparatively few species. Some of them have been 
found to be highly pleomorphic, that is to say, the same species 
may appear under very different forms at different periods 
of its development. In other cases the life-history is com- 
paratively simple. Hence the various forms mentioned in 
the Laboratory work must not be regarded as necessarily 
representing so many distinct species. 


LABORATORY WORK. 

Infuse some hay in warm water for half-an-hour 
filter, and set aside the filtrate : note the changes 
which go on in it at first clear, in 24 or 36 hours it 
becomes turbid ; later on, a scum forms on the sur- 
face and the infusion acquires a putrefactive odour. 

Rub some gamboge down in water and examine a 
drop of the mixture with a high power: avoid all 
currents in the fluid and watch the Brownian move- 
ments; note that they are simply oscillatory not 
translative. 


412 ELEMENTARY BIOLOGY. [CHAR 

3. Take a drop of fluid from a turbid hay infusion 
and examine it, using the highest power you have; 
in it will be found multitudes of 

Moving Bacteria. Note their 

a. Form; elliptic or rodlike sometimes forming 
short (2 8) jointed rows. 

b. Size; breadth, very small but pretty constant; 
length, varying, but several times greater than 
their breadth : measure. 

c. Structure; an outer more transparent layer en- 
veloping less transparent matter: in the com- 
pound forms the envelope appears only where 
two joints come in contact, so that the rod looks 
as if made up of alternating transparent and more 
opaque substances. 

tL Movements ; some vital, and some purely physical 
(Browniari). The former various but progressive : 
the latter a rotatory movement round a stationary 
centre ; study it in a drop of boiled infusion in 
which the Bacteria are all dead. 

4. Treat with iodine only the more opaque parts 

stain; probably then we have to do with proto- 
plasm, enveloped in nonprotoplasmic matter. 

5. Resting Bacteria. (Zooglcsa-stage.) 

a. Examine the scum from the surface of a hay 
infusion; it exhibits myriads of motionless Bac- 
teria, embedded in gelatinous material. 

b. Treat with iodine ; the Bacteria stain as before : 
the gelatinous uniting material remains un- 
stained. 


XII.] BACTERIA. 413 

6. Besides the form hitherto described, which would 
be known as Arthrobacterium, many other Schi- 
zomycetes will certainly be found, both in the 
pellicle and the fluid beneath. The following may 
be especially mentioned : 

a. Micrococcus. Bodies much like Arthrobacterium 
but short and rounded, and occurring singly, or 
in bead-like rows. They may be found free or 
in a Zoogloea stage. 

b. Bacillus. Threads composed of straight cylin- 
drical joints much longer than those of Arthro- 
bacterium, but of similar structure: they are al- 
ways free-swimming. 

c. Vibrio. Like Bacillus, but with bent joints. 

d. Spirillum. Elongated un jointed threads rolled 
up into a more or less perfect spiral : frequently 
two spirals interwine. In some of the largest 
forms a vibratile cilium can be made out on 
each end of the thread. 

e. Spirochsete. Much like Spirillum, but longer 
and with a much more closely rolled spiral. A 
very actively motile but not common form. 

7. Examine various putrefying substances for different 
forms of Bacteria. Successful cultures may be 
made on hard-boiled white of egg, or slices of 
potato, kept moist under a bell-glass. Various 
brilliantly coloured micrococci including the blood- 
red " Micrococcus prodigiosus " will make their 
appearance on such cultures. An infusion of pea- 
flour, filtered, is especially favourable for Spiro- 
chsete. 


414 ELEMENTARY BIOLOGY. [CHAP. XII. 

8. Place some fresh-made hay infusion in three flasks ; 
boil two of them for three or four minutes, and while 
one is boiling briskly stop its neck with a plug of 
cotton-wool and continue to boil for a minute or 
two: leave the necks of the other two flasks un- 
closed, and put all three away in a warm place. 

a. In a day or two abundant Bacteria will be found 
in the unboiled flask. 

/>. In the boiled but unclosed flask Bacteria will 
also appear, but perhaps not quite so soon as 
in a. 

c. In the flask which has been boiled and kept 
closed Bacteria will not appear, if the experi- 
ment has been properly performed, even if it be 
kept for many months. 


XIII. 
MOULDS (Penicittium, Eurotium and Mucor). 

Torula, Protococcus and Amoeba are extremely simple con- 
ditions of the two great kinds of living matter which are 
known as Plants and Animals. No plants, except perhaps 
the Bacteria, are simpler in structure than Torula and Pro- 
tococcus, and the only animals which are simpler than Amoeba, 
are essentially Amoeba devoid of a nucleus and contractile 
vesicle. Moreover, however complicated in structure one 
of the higher plants may be in its adult state, when it com- 
mences its existence it is as simple as Torula or Protococcus : 
and the whole plant is built up by the fissive multiplication 
of the simple cell in which it takes its origin, and by the 
subsequent growth and metamorphosis of the cells thus 
produced. We have already seen that the like is true of all 
the higher animals. They commence as nucleated cells, 
essentially similar to Amoeba and colourless blood-corpuscles, 
and their bodies are constructed by aggregations of meta- 
morphosed cells, produced by division from the primary 
cell. It has been seen that Torula and Protococcus, similar 
as they are in structure, are distinguished by certain im- 
portant physiological peculiarities ; and the more compli- 
cated plants are divisible into two series, one produced by 
the growth and modification of cells which have the physio- 
logical peculiarities of Torula and contain no chlorophyll, 
while the other, and far larger, series contains chlorophyll, 


416 ELEMENTARY BIOLOGY. [CHAP. 

and has the physiological peculiarities of Protococcus. The 
former series comprises the fungi, the latter all other plants, 
only a few parasitic forms among these being devoid of 
chlorophyll. 

The Fungi take their origin in spores, a kind of cells, 
which, however much they may vary in the details of their 
structure, are essentially similar to Torulcz. Indirectly or 
directly, the spore gives rise to a long tubular filament, 
which is termed a hypha, and out of these hyphae the 
Fungus is built up. 

One of the commonest Moulds, the Penicillium glaucum, 
which is familiar to every one from its forming sage-green 
crusts upon bread, jam, old boots, &c. affords an excellent 
and easily studied example of a Fungus. When examined 
with a magnifying glass, the green appearance is seen to be 
due, in great measure, to a very fine powder which is de- 
tached from the surface of the mould by the slightest touch. 
Beneath this lies a felt-work of delicate tubular filaments, 
the hyphae, forming a crust like so much blotting-paper, 
which is the mycelium. From the free surface of the crust 
innumerable hyphae project into the air and bear the green 
powder. These are the aerial hyphce. On the other hand, 
the attached surface gives rise to a like multitude of longer 
branched hyphae, which project into the fluid in which the 
crust is growing, like so many roots, and may be called the 
submerged hyphce. If the patch of Penicillium has but a 
small extent relatively to the surface on which it lies, mul- 
titudes of silvery hyphae will be seen radiating from its 
periphery and giving off many submerged, but few or no 
vertical, or subaerial branches. Submitted to microscopic 
examination, a hypha is seen to be composed of a transpa- 
rent wall (which has the same characters as the cell- wall of 
Torula) and protoplasmic contents, which fill the tube 


XIII.] MOULDS. 417 

formed by the wall, and present large central clear spaces, 
or vacuoles. At intervals, transverse partitions, continuous 
with the walls of the tube, divide it into elongated cells, 
each of which contains a correspondingly elongated proto- 
plasmic sac, or primordial utricle. Each cell contains a 
number of small nuclei, the presence of which can only be 
detected by the use of staining reagents. Thus in Peni- 
cillium we have our first example in the vegetable kingdom 
of multimideate cells. The hyphae frequently branch, and, 
in the crust, they are inextricably entangled with one 
another ; but every hypha, with its branches, is quite dis- 
tinct from every other. Those aerial hyphae which are 
nearest the periphery of the crust end in simple rounded 
extremities ; but the others terminate in brushes of short 
branches, and each of these- branches, as it grows and 
elongates, becomes divided by transverse constrictions into 
a series of rounded spores arranged like a row of beads. 
The spores formed in this manner are termed conidia, and 
the hyphae bearing them are termed conidiophores. At the 
free end of each filament of the brush the conidia become 
very loosely adherent, and constitute the green powdery 
matter to which reference has been made. Examined 
separately, a conidium is seen to be a spherical body, com- 
posed of a transparent sac, enclosing a minute mass of pro- 
toplasm and a nucleus, in all essential respects similar to a 
Torula. If sown in an appropriate medium, as for example 
Pasteur's solution, with or without sugar, the conidium 
germinates. Upon from one to four points of its surface an 
elevation or bulging of the cell-wall and of its contained 
protoplasm appears. This rapidly increases in length, and, 
continually growing at its free end, gives rise to a hypha, so 
that the young Penicillium assumes the form of a star, each 
ray being a hypha. The hyphae elongate, while side branches 

M. 27 


41 8 ELEMENTARY BIOLOGY. [CHAP. 

are developed from them by outgrowths of their walls ; and 
this process is repeated by the branches, until the hyphse 
proceeding from a single conidium may cover a wide circular 
area, as a patch of mycelium. When, as is usually the case, 
many conidia germinate close together, their hyphae cross 
one another, interlace, and give rise to a papyraceous crust. 
After the hyphae have attained a certain length, the pro- 
toplasm divides at intervals, and transverse septa are formed 
between the masses thus divided off from one another. But 
neither in this, nor in any other Fungus, are septa formed in 
the direction of the length of the hypha. 

Very early in the course of the development of the 
mycelium, branches of the hyphae extend downwards into 
the medium on which the mycelium grows ; while, as soon 
as the patch has attained a certain size, the hyphae in its 
centre give off vertical aerial branches, and the develop- 
ment of these goes on, extending from the centre to the 
periphery. The outgrowth of pencil-like bunches of branches 
at the end of these takes place in the same order ; and 
these branches, becoming transversely constricted as fast as 
they are formed, break up into conidia, which are ready to 
go through the same course of development. 

The conidia may be kept for a very long time in the dry 
state, without their readiness to germinate being in any way 
impaired, and their extreme minuteness and levity enable 
them to be dispersed and carried about by the slightest 
currents of air. The persistence of their vitality is subject 
to nearly the same conditions of temperature as that of 
yeast. Pullulating cells, resembling Torulae, are not un- 
frequently derived from the conidia of Penicillium and many 
other of the lower Fungi, but they must not be confounded 
with true Yeast. 

In Penicillium we have for the first time a differentiation 


XIII.] MOULDS. 419 

of the body of the plant into distinct organs. On the one 
hand we have the hyphas, constituting the vegetative part of 
the organism, on the other the conidia, the function of 
which is purely reproductive. 

The hyphse again, are either submerged or aerial. The 
former may be described from a purely physiological point 
of view as the root, being characterized by the two func- 
tions of attaching the plant to the substratum, and of taking 
up food-material from it. The aerial hyphae, on the other 
hand, in so far as they absorb oxygen from the air, and 
bear the reproductive organs, may be compared to the 
shoot, or leafy stem of the higher plants. 

Besides the purely asexual organs of reproduction above 
described, Penicillium also occasionally produces structures 
which appear to represent sexual organs, though their func- 
tional activity is in this case more than doubtful. A com- 
plex truffle-like fruit is produced from them, but these 
phenomena will be more easily studied in another mould, 
the Euro Hum Aspergillus glaucus. Though less abundant 
than Penicillium, this plant is of very common occurrence, 
especially on such substances as preserved fruits. Apricot 
jam, for example, may be used for growing the Eurotium 
upon. In the vegetative structure and the asexual repro- 
duction there is little difference from Penicillium. All the 
hyphae are stouter, and the conidiophores are unbranched. 
Each head of conidia can be distinguished separately with 
the naked eye, which is not the case with the more minute 
Penicillium. After the fungus has been growing for some 
weeks the sexual fruits will begin to make their appear- 
ance. They may be recognized as small round yellow 
bodies, easily distinguished from the heads of conidia by 
their colour and their sessile position. The development 
of these fruits is somewhat complicated. A branch grows 

27 2 


420 ELEMENTARY BIOLOGY. [CHAP. 

out from one of the hyphse, and becomes spirally coiled, 
like a cork-screw. This branch is called the ascogoniiim. 
A second branch (termed the pollinodiuni] is formed in the 
immediate neighbourhood of the first. This applies itself 
closely to the ascogonium, and it is alleged that fusion 
takes place at the point of contact. Subsequently the as- 
cogonium increases greatly in size, and produces a number 
of clavate branches called asci, in the interior of each of 
which eight spores are formed. In the meantime closely 
interwoven hyphse, arising from below the ascogonium, 
form the dense envelope of the fruit. The production of 
spores in asci is characteristic of a very large group of 
Fungi, but it is only in exceptional cases that the asci owe 
their origin to an act of fertilization. The spores formed in 
the asci are termed ascospores, and reproduce the ordinary 
form of the Fungus. 

If some bread be placed in a jar and kept very wet and 
moderately warm, its surface will, in two or three days, be 
covered with white cottony filaments, many of which rise 
vertically into the air, and end in rounded heads, so that 
they somewhat resemble long pins. The organism thus 
produced is another of the Fungi the mould termed Mucor 
stolonifer. 

Each rounded head is a sporangium ; the stalk on which 
It is supported rises from one of the filaments which ramify 
in the substance of the bread, and are the hyphce. In this 
species the hyphse send out branches (the so-called " sto- 
lons ") which grow out from the bread, and on reaching 
any substratum, such as the plate on which the bread rests, 
may produce a new crop of sporangia. Each hypha is, 
as in Penicillium, a tube provided with a tough thickish 
structureless wall, which is composed of a form of cellulose, 


XIII.] MOULDS. 421 

and is filled by a vacuolated protoplasm. In old speci- 
mens, transverse partitions, continuous with the walls of 
the hyphae, may divide them into chambers or cells, but 
the plant is as a rule unicellular, or rather non-cellular, 
as regards its vegetative organs. The hyphae contain very 
numerous nuclei. The stalk of the sporangium is a hypha 
of the same structure as the others. The wall of the 
sporangium is beset w r ith minute asperities composed of 
oxalate of lime, and it contains a great number of minute 
oval bodies, the spores, held together by a transparent in- 
termediate substance. When the sporangium is ripe, the 
slightest pressure causes its thin and brittle coat to give 
way, and the spores are separated by the expansion of 
the intermediate substance, which readily swells up and 
finally dissolves, in water. The greater part of the wall 
of the sporangium then disappears, but a little collar, 
representing the remains of its basal part, frequently ad- 
heres to the stalk. The cavity of the stalk does not com- 
municate with that of the sporangium, but is separated 
from it by a partition, which bulges into the cavity of 
the sporangium, forming a central pillar or projection. 
This is termed the columella and stands conspicuously 
above the collar, when the sporangium has burst and the 
spores are evacuated, 

The spores are oval and consist of a sac, having nearly 
the same composition as the wall of the hypha, which 
encloses a mass of protoplasm and a nucleus. When they 
are sown in an appropriate medium, as for example in 
Pasteur's solution, they enlarge, become spheroidal, and 
then send out several thick prolongations. Each of these 
elongates, by constant growth at its free end, and becomes 
a hypha, from which branches are given off, which grow 
and ramify in the same way. As all the ramifying hyphae 


422 ELEMENTARY BIOLOGY. [CHAP. 

proceed from the spore as a centre, their development 
gives rise, as in Penicillium^ to a delicate stellate mycelium. 
At first, no septa are developed in the hyphae, so that the 
whole mycelium may be regarded as a single cell with 
long and ramified processes, or as an organism which does 
not show a cellular structure at all. The distinction be- 
tween this condition and the multicellular structure of 
Penicillium is not so sharp as it appears at first sight, for 
it has been shown that even in plants which consist of 
many cells the protoplasm is very generally continuous, 
through minute perforations in their walls. From near 
the centre of the mycelium a branch is given off from a 
hypha, rises vertically, and after attaining a certain length 
ceases to elongate. Its free end dilates into a rounded 
head, which gradually increases in size, until it attains 
the dimensions of a full-grown sporangium ; and, at the 
same time, the protoplasm contained in this head be- 
comes separated from that in the stalk by a septum, 
which is curved towards the cavity of the sporangium, and 
constitutes the columella. The wall of the sporangium, 
thus formed, becomes covered externally with a coat of 
oxalate of lime spines. As the sporangium increases in 
size, its protoplasmic contents become marked out into a 
large number of small oval masses, which are close together, 
but not in actual contact. Each of these masses next 
becomes completely separate from the rest, surrounds itself 
with a cellulose coat, and becomes a spore ; while the 
protoplasm not thus used up in the formation of spores, 
appears to give rise to the gelatinous intermediate sub- 
stance, which swells up in water, referred to above. The 
walls of the spores become coloured, and that of the spo- 
rangium gradually thins, until it is reduced to little more 
than the outer crust of oxalate of lime. The sporangium 


XIII.] MOULDS. 423 

now readily bursts, and the spores are separated by the 
swelling and eventual dissolution of the gelatinous inter- 
mediate matter. 

There appears to be no limit to the extent to which the 
Mucor may be reproduced by this process of asexual de- 
velopment of spores, by the fission of the contents of the 
sporangium ; nor does any other mode of multiplication 
become apparent, if the mould be grown in a fluid medium 
and abundantly supplied with nourishment. 

But when growing in nature, a method of reproduction 
is set up which represents the sexual process in its simplest 
form, such as we have already seen in Spirogyra. Adjacent 
hyphos, or parts of the same hypha, give off short branches, 
which become dilated at their free ends, and approach one 
another, until these ends are applied together. The proto- 
plasm in each of the dilated ends becomes separated by a 
septum from that of the rest of the branch ; the two cells 
thus formed open into one another by their applied faces, 
and their protoplasmic contents becoming mixed together, 
form one spheroidal mass, to the shape of which the coa- 
lesced cell-membranes adapt themselves. Here, as in Spi- 
rogyra, the product of conjugation is termed a zygospore. 
Its cellulose coat becomes separated into an outer layer 
of a dark blackish hue and an inner colourless layer. 
The outer coat is raised into irregular elevations, to 
which corresponding elevations of the inner coat cor- 
respond. 

Placed in suitable circumstances, the zygospore does not 
immediately germinate ; but, after a longer or shorter period 
of rest, the walls burst, and a bud-like process is thrown 
out, which grows out into a mycelium. Under favourable 
conditions this may at once assume the normal develop- 
ment, but if the supply of food be scanty, the mycelium 


424 ELEMENTARY BIOLOGY. [CHAP. 

remains rudimentary, and immediately gives rise to a 
sporangium, in which the asexual conidia are produced. 

When Mucor is allowed to grow freely on such a sub- 
stratum as bread, or at the surface of a saccharine liquid, it- 
takes on no other form than that described; but, if it be 
submerged in the same liquid, the mode of development of 
the younger hyphae becomes changed. They break up, by 
a process of constriction, into short lengths, which separate, 
acquire rounded forms, and at the same time multiply by 
budding after the manner of Torulce. Coincidentally with 
these changes, an active fermentation is excited in the 
fluid, so that this " Mucor-Torula" functionally as well as 
morphologically, bears a resemblance to the yeast-plant, 
from which however its life-history shows it to be quite 
distinct. 

If the Miicor-Torula is filtered off from the saccharine 
solution, washed, and left to itself in moist air, the " Torulee" 
give off very short aerial hyphae, which terminate in minute 
sporangia. In these a very small number of ordinary 
mucor spores is developed, but, in essential structure, both 
the sporangia and the spores resemble those of normal 
Mucor. 


LABORATORY WORK. 

A. PENICILLIUM. 

Prepare some Pasteur's fluid, and leave it exposed to 
the air in saucers in a warm place; if Penicillium spores are 
at hand add a few to the fluid in each saucer: if spores 
cannot be obtained, the fluid, if simply left to itself, will 
probably be covered with Penicillium in ten days or a 


XIII.] MOULDS. 425 

fortnight. Sometimes, however, the fluid will overrun with 
Bacteria, to the exclusion of everything else. And very 
frequently other moulds, such as Eurotium, or Mucor, 
may appear instead of or along with Penidllium. 

1. NAKED-EYE CHARACTERS. Note the powdery-looking 
upper surface, white in young specimens, pale 
greenish in older, and later still becoming dark sage- 
green : the smooth pale under surface : the dense 
tough character of the mycelium. 

2. HlSTOLOGICAL STRUCTURE. 

a. The mycelium. 

a. Tease a bit out in water, and examine first with 
low, and then with a high power : it is chiefly 
made up of interlaced threads or tubes the 

a. Hypha. Note their diameter (measure)- 
form subdivisions (cells) - - mode of branch- 
ing and structure : the external homogeneous 
sac; the granular less transparent protoplasm; 
the small round vacuoles, the nuclei (only to be 
seen on treatment with alcohol, and staining 
with haematoxylin). Draw. 

J3. The intermixed " Tcndce." Note their size and 
number. 

b. Hold a bit of the mycelium between two pieces 
of carrot, and cut a thin vertical section with a 
sharp razor: mount in water and examine with 
low and high power. 

b. The submerged hyphse. 

Small branched threads hanging dow r n from the under 
surface of the mycelium: repeat the observations 
2. a. (i. a. 


426 ELEMENTARY BIOLOGY. [CHAP. 

c. The aerial hyphse and conidiophores. 

Tease out in water a bit from the surface of one of 
the greenish patches; observe the difficulty with 
which water wets it. Examine with low and high 
power. 

Note;- 

a. The primary erect hypha. 

/?. Its division into a number of branches. 

y. The division of the terminal branches by con- 
strictions into a chain of conidia. Draw. 

d. The conidia. 

a. Their Size (measure). 

Form; spherical. 

Structure; cell-wall, protoplasm, vacuole, 
and nucleus. 

b. Stain different specimens with magenta or hae- 
matoxylin and iodine. 

c. Treat another specimen with potash. 

e. The germination of the Conidia, and building up 

of the Mycelium. 

a. Sow some conidia in Pasteur's fluid in a watch-glass; 
protect from evaporation, and watch the development 
of the mycelium (examine the surface with a low 
power) ; then the formation of aerial hyphae ; finally 
the production of new conidia. 

b. [Sow Conidia in Pasteur's fluid in a moist chamber, and 
watch from day to day; note the formation of eminences 
at one or more points on a conidium ; the elongation of 
these eminences to form hyphae; the branching and 
interlacement of the hyphns.] 


XIII.] MOULDS. 427 

B. EUROTIUM ASPERGILLUS-GLAUCUS. 

1. Place some apricot jam under a bell-jar and keep 
moist and warm. In a few days the Eurotium will 
probably make its appearance. A crop of conidia 
will first be produced. Neglect these, and look out, 
after some weeks, for the sexual fruits, as described 
in the text. 

2. Mount some of the mycelium and fruits in water, 
and observe first with a low and then with a high 
power. Examine 

a. The mature fruits. These are approximately 
spherical in form. Observe the outside of the 
fruit formed of dense cellular tissue. Burst some 
of the fruits by pressure on the coverslip. Observe 
the asci in the interior, each containing eight asco- 
spores. 

b. The development of the fruit. Make out the 
spirally coiled branch forming the ascogonium, 
and the pollinodium in contact with it. Observe 
the outgrowth of hyphae from below the asco- 
gonium, to form the envelope of the fruit. 

C. MUCOR STOLONIFER. 

1. Place some bread under a bell-jar and keep very 
moist and warm; in from 24 to 48 hoars its surface 
will nearly always be covered by a crop of erect 
aerial mucor-hyphse, each ending in a minute en- 
largement (sporangium} just visible with the unas- 
sisted eye. 

2. Snip off a few of the hyphae with a pair of scissors, 
mount in water, and examine with i inch obj. 


428 ELEMENTARY BIOLOGY. [CHAP. 

a. Large unbranched hyphae, each ending in a 
spherical enlargement (sporangium}. 

3. Examine with \ obj. 

a. The hyphae. 

a. Their size; they greatly exceed the hyphaa of 
Penicillium both in length and diameter. 

/?. Their structure ; homogeneous sac, granular 
protoplasm, vacuoles : septa absent except 
close to the sporangium. 

y. Treat with iodine and magenta or hnsma- 
toxylin; the protoplasm is stained and nuclei 
may be made out. 

S. Treat another specimen with Schulze's solu- 
tion; the cell- wall is stained violet. 

b. The sporangia. 

Examine with ~ obj. 

a. Their size and form. 

b. Their structure. 

a. The homogeneous enveloping sac covered by 
irregular masses of calcic oxalate. 

ft. The granular protoplasmic contents : un- 
segmented in some ; divided into a great 
number of distinct oval masses (spores) in 
others. 

y. The projection into the sporangial cavity of 
the convex septum (columelld) which separates 
the hypha from the sporangium. 

3. The collar projecting around the base of the 
columella of burst sporangia. 


XIII.] MOULDS. 429 

c. Stain some with iodine; others with Schulze's 
solution. 

c. The spores or conidia. 

a. Crush some ripe sporangia by gentle pressure 
upon the cover-glass. Examine with -J- obj. 

a. The size of the spores (measure). 
(3. Their form; cylindrical and elongated, 
y. Their structure. 

8. Stain with iodine and magenta or hcema- 
toxylin. 


XIV. 
STONEWORTS (Char a and Nitelld). 

THESE water-weeds are not uncommonly found in ponds 
and rivers, growing in tangled masses of a dull green colour. 
Each plant is hardly thicker than a stout needle, but may 
attain a length of three or four feet. One end of the stem 
is fixed in the mud at the bottom, by slender thread-like 
roots, the other floats at the surface. At intervals, append- 
ages, consisting of leaves, branches, root-filaments, and repro- 
ductive organs, are disposed in circles, or whorls. In the 
middle and lower parts of the plant these whorls are dis- 
posed at considerable and nearly equal distances ; but, 
towards the free upper end, the intervals between the whorls 
diminish, and the whorled appendages themselves become 
shorter, until, at the very summit, they are all crowded 
together into a terminal bud, which requires the aid of the 
microscope for its analysis. 

The parts of the stern, or axis, from which the append- 
ages spring are termed nodes ; the intervening parts being 
internodes. When viewed with a hand-magnifier the inter- 
nodes exhibit a spiral striation. 

In Chara, each internode consists of a single, much- 
elongated cell, which extends throughout its whole length, 
invested by a cortical layer, composed of many cells, the 
spiral arrangement of which gives rise to the superficial 
marking which has been noted. And this multicellular 


CHAP. XIV.] STONEWORTS. 43 r 

structure is continued from the cortical layer, across the 
stem, at each node. The stem therefore consists of a series 
of long, axial cells, contained in as many closed chambers 
formed by the small cortical cells. The nodes are the mul- 
ticellular partitions between these chambers. The branches 
are altogether similar in structure to the main stem. The 
leaves are also similar to the stem, so far as they consist of 
axial and cortical cells, but they differ in the form and 
proportions of these cells, as well as in the fact that the 
summit, or free end, of the leaf is always a much-elongated 
pointed cell The most important distinction, however, 
consists in the fact that the growth of the leaves is limited 
while that of the axis is unlimited. The branches spring 
from the re-entering angle between the stem and the leaf, 
which is termed the axil of the leaf; and, in the same 
position, at the fruiting season of the plant are found the 
reproductive organs. These are of two kinds, the one large 
and oval, the oogonia, the other smaller and globular, the 
antheridia. Both, when ripe, have an orange-red colour, 
and are seated upon a short stalk. 

If a growing plant be watched, it will be found that it con- 
stantly increases in length in two ways. New nodes, inter- 
nodes, and whorls of appendages are constantly becoming 
obvious at the base of the terminal bud; and these append- 
ages increase in size and become more and more widely 
separated, until they are as large and as far apart as in the 
oldest parts of the plant. The appendages at first consist 
exclusively of leaves and root-filaments (rhizoids\ and it is 
only when these have attained their full size, that branches, 
oogonia and antheridia are developed in their axils. 
Sometimes rounded cellular masses appear in the axils of 
the leaves, and, becoming detached, grow into new plants. 
These are comparable to the bulbs of higher plants. 


432 ELEMENTARY BIOLOGY. [CHAP. 

If the innermost part of the terminal bud, which con- 
stitutes the free end of the axis, or stem, be examined, it 
will be found to be formed by a single nucleated cell, 
separated by a transverse septum from another. Beneath 
this last follows another cell, which has already undergone 
division into several smaller cells by the development of 
longitudinal septa. This is the most newly-formed node. 
Below this again is a single cell, which is both longer and 
broader than those at the apex, and is an internodal cell. 
Below it follows another node, composed of more numerous 
small cells than in the first. Some of the peripheral cells 
of this node are undergrowing growth and division, and thus 
give rise to cellular prominences, which are rudiments of 
the first whorl of leaves. In the still lower parts of the 
stem the internodal cells get longer and longer, but they 
never divide. The nodal cells, on the other hand, multiply 
by division, but do not greatly elongate. From the first, 
the nodal cells overlap the internodal cell, so as to meet 
round its equator, and thus completely invest it externally. 
And, as the internodal cell grows and elongates, the overlap- 
ping parts of the nodes increase in length and become divided 
into internodal and nodal cells, which take on a spiral 
arrangement, and thus give rise to the cortical layer. 

Thus the whole plant is composed of an aggregation of 
simple cells, just as is the case with Hydra among animals; 
and, while it lives, new nodes and internodes are continually 
being added at its summit, or growing point. The inter- 
nodal cells which give rise to the middle of the stem un- 
dergo no important change, except great increase of size, 
after they are once formed. The nodal cells, on the con- 
trary, undergo division with comparatively little increase in 
size. And out of them, the nodes, the cortical layer, and 
all the appendages, are developed. 


XIV.] STONEWORTS. 433 

In all the young cells of Char a a. nucleus of relatively 
large size is to be seen imbedded in the centre of the pro- 
toplasm, which is motionless, and is enclosed in a structure- 
less cell-wall, composed of cellulose. As the cell grows 
larger, the centre of the protoplasm becomes occupied by a 
watery fluid, and its thick periphery, which remains applied 
against the cell- wall, constitutes a sac, or primordial utricle, 
in which the nucleus is embedded. In the larger cells the 
primordial utricle is readily detached and made to shrivel 
up into the middle of the cell by treatment with strong 
alcohol. In the older cells the nucleus breaks up into a 
number of portions. 

Numerous small green bodies chlorophyll grains are 
embedded in the outer, or superficial, part of the primordial 
utricle, and they increase in number by division, as the 
cell enlarges. These chlorophyll grains are composed of 
protoplasmic matter, which frequently contains starch gra- 
nules, and is impregnated with the green colouring sub- 
stance. 

During life, the layer of the primordial utricle which 
lies next to the watery contents of all the larger cells is in 
a state of incessant rotatory motion, while the outermost 
layer which contains the chlorophyll grains is quite still. 
In the large cells, so long as the nucleus is discernible, it is 
carried round with the rotating stream. 

The antheridium is a globular spheroidal body with a 
thick wall, made up of eight pieces, which are united by 
interlocking edges. The four pieces which make up the 
hemisphere to which the stalk of the antheridium is at- 
tached, are foursided, the other four are triangular. From 
the centre of the inner, concave face of each piece a sort of 
short process, the handle or manubrium, projects into the 
cavity of the hollow sphere. At the free end of the manu- 

M. 28 


434 ELEMENTARY BIOLOCxY. [CHAP. 

brium is a rounded body, the capitulum, which bears six 
smaller secondary capitula; and each secondary capitulum 
gives attachment to four long filaments divided by trans- 
verse partitions into a multitude (100 to 200) of small 
chambers. Thus, there may be as many as 20,000 to 
40,000 chambers in each anlheridium (8 x 6 x 4 x 100 or 
x 200). The several pieces of which the wall of the an- 
theridium is composed, the manubria, the capitula, the 
secondary capitula and the chambers of the filaments are 
all more or less modified cells, as may be proved by tracing 
the antheridia from their earliest condition, as small pro- 
cesses of the nodal region, to their complete form. The 
cells of the filaments are, at first, like any other cells ; but, 
by degrees, the nucleus of each becomes changed into a 
thread-like body, thicker at one end than at the other, and 
coiled spirally like a corkscrew. From the thin end two 
long cilia proceed ; and, when the cells have burst, and the 
spermatozoids are set free, they are propelled rapidly, with 
the small end forwards, by the vibration of the cilia. These 
spermatozoids answer to the spermatozoa of animals, and 
represent the male element of Chara. 

The oogonia are borne upon short stalks, the end of 
which supports a large oval central cell or ovum; five 
spirally-disposed sets of cells invest this, an aperture being 
left between the investing cells at the apex of the oogonium. 
When the antheridia attain maturity they burst, the sper- 
matozoids are set free, and swarm about in the water. Some 
of them enter the aperture of the oogonium, and, in all 
probability, pierce the free summit of the oval central cell, 
and enter its protoplasm ; but all the steps of this process 
of impregnation have not been worked out. The result, 
however, is, that the contents of the impregnated central 
cell now called the oospore become full of starchy and oily 


XIV.] STONEWORTS, 435 

matter ; the spiral cells forming its coat acquire a dark 
colour and hard texture, and the oogonium, detaching itself, 
falls into the mud. 

After a time the oospore germinates ; a tubular process, 
like a hypha, protrudes from it through the aperture between 
the investing cells and almost immediately gives off a branch, 
which is the first root. The tube elongates, and becomes 
divided transversely into cells, the protoplasm of which 
developes chlorophyll. Very soon, the further growth of 
this pro-embryo is arrested. But one of the cells, which lies 
at some distance below the free end of the pro-embryo, 
undergoes budding, and gives rise to a set of leaves (which 
are not arranged in a whorl), amidst which a bud appears, 
which has the structure of the terminal bud of the adult 
Chara stem, and grows up into a new Cfiara-pla.nt, 

We have then, in Chara, a plant which is acrogenous (or 
grows at its summit), and which becomes segmented by the 
development of appendages, at intervals, along an axis ; 
which multiplies, asexually by bulb-like buds, and also 
multiplies sexually by means of the spermatozoids (male 
elements) and central cells of the oogonia (female elements); 
in which the first product of the germination of the oospore 
is a simple filament, from which the young Chara is de- 
veloped by the germination and growth of one cell ; so that 
there is a sort of alternation of generations, though the 
alternating forms are not absolutely distinct from one 
another. 

Chara flourishes in pond-water under the influence of 
sunlight, and by the aid of its chlorophyll CO 2 is decom- 
posed, so that its nutritive processes must be the same as 
those of Protococcus, From its complete immersion, and the 
absence of any duct-like, or vascular tissues, it is probable 
that all parts absorb and assimilate the nutriment contained 

282 


436 ELEMENTARY BIOLOGY. [CHAP. 

in the water; and that, except so far as the reproductive 
organs are concerned, there is a morphological differentia- 
tion of organs, unaccompanied by a corresponding phy- 
siological differentiation. 

Nitella is a rarer plant than C/iara, and is simpler in 
structure, its axis being devoid of the cortical layer. In 
other respects, however, it is very similar to C/iara, and its 
structure is more easily made out. 

[The Ckaracea, or plants belonging to the genera Chara and 
Nitella^ are found in all parts of the world, and belong to the 
class of Alga, which also includes the sea-weeds.] 


LABORATORY WORK. 

A. NAKED-EYE CHARACTERS. 

Note the slender elongated axis (stem] ; the whorled 
appendages (leaves]; the nodes and inter nodes ; the shortening 
of the latter towards the apex of the stem ; the rhizoids. 

a. The roots ; small; serving chiefly for attachment, 
the plant getting most of its nutrition, through 
other parts, from matters dissolved in the water. 

b. The leaves ; their sub-divisions (leaflets] ; their 
form, size, &c. 

c. The oogonia and autheridia ; their position, 
size, form, colour. 

Draw a portion including two or three internodes. 

B. HlSTOLOGlCAL STRUCTURE. 

a. The stem. 

i. Examine the outside of a fresh internode with a low 
power, or pocket lens, to see the spirally-arranged 
cortical cells. 


XIV.] STONEWORTS. 437 

2. Hold a bit of fresh stem between two pieces of elder- 
pith or embed it in paraffin, and, with a sharp razor, 
cut thin transverse and longitudinal slices through 
nodes and internodes. Note the cavity of the large 
central internodal cell ; the cortical cells, round the 
internodal cell ; the nodal cells, and the interruption 
of the central cavity at the nodes. 

3. Examine similar sections in specimens treated with 
spirit, and also preparations made by teasing or press- 
ing out in glycerine bits of stem from chromic acid 
(0*2 per cent.) preparations: make out in these, 

a. The nodal, internodal, and cortical cells. 

/?. The wall, protoplasmic layer (primordial 
utricle), nucleus, and vacuole of each cell. 
(The nucleus will have undergone fragmenta- 
tion in the older cells.) 

4. Examine sections from the fresh stem to make out 
the points detailed in B. a. 3. /?. The protoplasm 
and nucleus are difficult to see. Note the chloro- 
phyll-granules. (See B. b. y.) 

5. Stain sections of the fresh stem with iodine, and 
magenta: note the results. 

b. The leaves. 

Examine fresh and chromic acid specimens. 

a. The large uncovered terminal cell. 

/?. Then a series of internodal cells, separated 
from one another, and covered-in, by nodal 
cells: the sac, protoplasm, nucleus, and vacuole 
of each. 

y. The oval chlorophyll-granules, arranged so as 
to leave an oblique uncoloured band round 


438 ELEMENTARY BIOLOGY. [CHAP. 

each cell; the position of these granules, in 
the more superficial layer of the protoplasm. 

<$. The protoplasmic movements (see C. a.). 

c. The terminal bud. 

Dissect out chromic acid specimens as far as pos- 
sible with needles, and then press gently out in 
glycerine. Note in different specimens 

a. The terminal or apical cell : 

a. Its form: hemispherical, the rounded surface 
free; the flat surface attached to the cell 
below it. 

fi. Structure : sac, protoplasm, nucleus; no vacuole- 
present. 

y. Sometimes two nuclei, preliminary to division. 

8. Its mode of division; across the long axis of 
the stem, giving rise to two superimposed 
nucleated cells. 

b. The further fate of the new cells derived from 
the segments of the terminal cell; work back in 
your specimens from the terminal cell 

a. The new cells are successively nodal and inter- 
nodal ; the latter enlarge, develope a large 
vacuole, and ultimately form the medullary 
cells of the internodes; they never divide. 

ft. The nodal cells divide freely, and do not 
increase much in size ; they give origin to the 
nodes and the cortical cells. 

c. The development of leaves: by the multiplication 

and outgrowth of nodal cells. 


XIV.] STONEWORTS. 439 

<L Their growth at the base, the terminal leaf-cell 
soon attaining its full size and not dividing. 

f. The development of branches ; from nodal cells 
in leaf-axils, which take on the character of ter- 
minal cells. 

d. The oogonia. 

Examine fresh, under a low power. 

a. Made up externally of five twisted cells, bearing 
at their apices five smaller, not twisted cells. 

ft. Cut sections from embedded specimens, and 
examine with a high power : make out the 
large central nucleated cell or ovum ; the fatty 
and starchy matters contained in it ; stain 
with iodine. 

y. Press out chromic acid specimens in glycerine; 
make out the above points (d. a, ft). 

8. Examine chromic acid specimens for young 
oogonia, and press them out in glycerine: 
make out in the youngest the five roundish 
cells surrounding a central one; then in older 
specimens the elongation, and twisting of the 
external cells, and the separation of their apices 
as five distinct cells. 

e. The antheridia. 

a. Examine, with a low power, a ripe (orange- 
coloured) one. 

a. Make out its external dentated cells. 

Tease out a ripe antheridium in water; and 
examine with a high power ; note the flat, 
dentated, nucleated external cells ; the cylin- 
drical cell (manubrium) springing perpendicu- 


440 ELEMENTARY BIOLOGY. [CHAP. 

larly from the inner surface of each ; the 
roundish cell (capituluni] on the inner end of 
the manubrium ; the six secondary capitula 
attached to the capitulum ; the thread-like 
filaments (usually four) proceeding from each 
of the secondary capitula. 

y. The structure of these threads; each consists 
of a single row of cells, containing in unripe 
specimens nucleated protoplasm ; in older 
specimens each contains a coiled-up spermato- 
zoid. 

!>. The spermatozoids (or antherozoids). 

a. Their form and structure ; thickened at one 
end and granular ; tapering off gradually to- 
wards the other end, which is hyaline and 
has two long cilia attached to it. 

/?. The movements in water of ripe spermato- 
zoids. 

[Sometimes Chara cannot be obtained, when Ni- 
tella, another genus of the same Natural Order, and 
of similar habit and structure, can. Nearly all the 
points above described for Chara can be made out 
in Nitella, with the following differences : the cortical 
cells of the stem and leaves are absent, and, in the 
commoner species, the plant is not hardened by cal- 
careous deposit ; the branches arise, not one from a 
whorl of leaves, but two; and the five twisted cells of 
the spore-fruit are each capped by two small cells, 
instead of one.] 

C. PROTOPLASMIC MOVEMENTS IN VEGETABLE CELLS. 

a. Chara. Take a vigorous -looking fresh Chara or 
Nitella cell (say the terminal cell of a leaf), and 


XIV.] STONEWORTS. 441 

examine it in water with a high power. Note 
the superficial layer of protoplasm in which the 
chlorophyll lies ; it is stationary : focus through 
this layer and examine the deeper one ; note 
the currents in it, marked by the granules they 
carry along : their direction ; in the long axis 
of the cell, up one side and down the other, 
the boundary of the two currents being marked 
by the colourless band, in which no movements 
occur. Try to find the nucleus ; it has usu- 
ally undergone fragmentation in cells in which 
currents have commenced. The original nu- 
cleus or the products of its division are passively 
carried along by the currents. Sometimes it 
is very difficult, on account of the incrustation 
of the leaf-cells of Chara, to make out the proto- 
plasmic movements in them; if this is found to 
be the case, the manubrial cells from an anthe- 
ridium should be used instead. 

/;. Tradescantia. Examine in water, with a high 
power, the hairs which grow upon the stamens: 
they consist of a row of large roundish cells, each 
with cell-wall, protoplasm, nucleus, and vacuolar 
spaces. Note the protoplasm; partly forming 
a layer (primordial utricle] lining the wall and 
heaped up round the nucleus, and partly form- 
ing bridles running across the cell in various 
directions from the neighbourhood of the nu- 
cleus, and from one part of the protoplasm to 
another; observe the currents in these bridles; 
from the nucleus in some, towards it in 
others. 


442 ELEMENTARY BIOLOGY. [CHAP. XIV. 

c. Vallisneria. Take a leaf beginning to look old; 
split it into two layers with a sharp knife and 
mount a bit in water ; examine with a high 
power. Note the larger rectangular cells, be- 
longing to the deeper layers, with well-marked 
currents in them, which carry the chlorophyll 
granules round and round inside the cell-wall. 

If no currents are seen at first, gently warm 
the leaf by immersing it for a short time in 
water heated to a temperature between 30" and 

zcT 

o5 ^- 

d. Anacharis*. Take a yellowish-looking leaf: 
mount in water and examine with a high power; 
the phenomena observed are like those in Val- 
lisneria. They are best observed in the single 
layer of cells at the margin of the leaf. 

e. Nettle-hair. Mount an uninjured hair in water 
with the bit of leaf to which it is attached 
(it is essential that the terminal recurved part 
of the large cell forming the hair be not broken 
off); examine with the highest available power: 
currents carrying along very fine granules will 
be seen in the cell, their general direction being 
that of its long axis. 

* Also called Elodca. 


XV. 

THE BRACKEN EERN (Pteris aquilina}. 

THE conspicuous parts of this plant are the large green 
leaves, or fronds, which rise above the ground, sometimes 
to the height of five or six feet, and consist of a stem-like 
axis or rctchis^ from which transversely disposed offshoots 
proceed, these ultimately subdividing into flattened leaflets, 
ft& pinnules. The rachis of each frond may be followed for 
some distance into the ground. Its imbedded portion ac- 
quires a brown colour, and eventually passes into an irre- 
gularly branched body, also of a dark-brown colour, which 
is commonly called the root of the fern, but is, in reality, a 
creeping underground stem, or rhizome. From the surface 
of this, numerous filamentous true roots are given off. 
Traced in one direction from the attachment of the frond, 
the rhizome exhibits the withered bases of fronds, developed 
in former years, which have died down ; while, in the 
opposite direction, it ends, sooner or later, by a rounded 
extremity beset with numerous fine hairs, which is the apex, 
or growing extremity, of the stem. Between the free end 
and the fully formed frond one or more processes, the rudi- 
ments of fronds, which will attain their full development in 
following years, are usually found. 

The stem branches in two ways; ist by apparent dicho- 
tomy of the terminal growing point, and 2nd by the forma- 


444 ELEMENTARY BIOLOGY. [CHAP. 

tion of adventitious buds. The latter are produced singly 
on the dorsal side of the leaf-stalks, near the base. 

The attachments of the fronds are nodes, the spaces 
between two such successive attachments, internodes. It 
will be observed that the internodes do not become crowded 
towards the free end, and there is nothing comparable to 
the terminal bud of Chara with its numerous rudimentary 
appendages. 

When the fronds have attained their full size, the edges 
of the pinnules will be observed to be turned in towards 
the underside, and to be bordered by a fringed membrane 
called the indusium, which roofs over the groove enclosed 
by the incurved edge. At the bottom of the groove brown 
granules are aggregated in large numbers, so as to form a 
streak along each side of the pinnule. The granules are the 
sporangia, and the streaks formed by their aggregation, the 
son. 

Examined with a magnifying glass, each sporangium is 
seen to be pouch-shaped, like two watch-glasses united by 
a thick rim. When ripe, it has a brown colour, readily 
bursts, and gives exit to a number of minute bodies which 
are the spores. 

The plant now described is made up of a multitude of 
cells, having the same morphological value as those of 
Chara, and each consisting, at least when young, of a pro- 
toplasmic mass, a nucleus and a cellulose wall. These cells, 
however, become very much modified in form and structure 
in different regions of the body of the plant, and give rise 
to groups of structures called tissues, in each of which the 
cells have undergone special modifications. These tissues 
are, to a certain extent, recognizable by the naked eye. 
Thus, a transverse section of the rhizome shews a circum- 
ferential zone of the same dark-brown colour as the external 


XV.] THE BRACKEN FERN. 445 

epidermis, enclosing a white ground-substance^ interrupted by 
variously disposed bands, patches, and dots, some of which 
are of the same dark-brown hue as the external zone, while 
others are of a pale yellowish-brown. 

The dark-brown dots are scattered irregularly, but the 
greater part of the dark-brown colour is gathered into two 
narrow bands, which lie midway between the centre and 
the circumference. Sometimes the ends of these bands are 
united. Enclosed between these narrow, dark-brown bands 
are, usually, two elongated, oval, yellowish-brown bands; 
and, outside them, lie a number of similarly coloured 
patches, one of which is usually considerably longer than 
the others. 

A longitudinal section shews that each of these patches 
of colour answers to the transverse section of a band of 
similar substance, which extends throughout the whole 
length of the stem ; sometimes remaining distinct, some- 
times giving off branches which run into adjacent bands, 
and sometimes uniting altogether with them. 

At a short distance below the apex of the stem, however, 
the colour of all the bands fades away, and they are trace- 
able into mere streaks, which finally disappear altogether in 
the semi-transparent soft tissue which forms the growing 
end of the stem. Submitted to microscopic examination, 
the white ground-substance is seen to consist of large poly- 
gonal cells, containing numerous starch granules ; this tissue 
is called the ground-parenchyma. The circumferential zone 
is formed of somewhat elongated cells, containing little or 
no starch, the thick walls of which have acquired a dark- 
brown colour. These cells constitute the hypoderma. The 
dark-brown bands, on the other hand, consist of cells which 
are so much elongated as almost to deserve the name of 
fibres. Their walls are very thick, and of a deep-brown 


446 ELEMENTARY BIOLOGY. [CHAP. 

colour ; but the thickening has taken place unequally, so as 
to leave short, obliquely directed, thin places, which look 
like clefts and are called pits. This tissue is termed scleren- 
chyma. The yellow bands, lastly, are vascular bundles. 
Each bundle is surrounded on the outside by a layer of 
rather thick-walled, elongated, parallel-sided cells, con- 
stituting the bundle-sheath. The bundle itself consists of 
two main parts ; a central portion, constituting the xylem or 
wood, and a peripheral portion which is the phloem or bast. 
Bundles of this structure, in which the xylem is surrounded 
by the phloem, are termed concentric. The xylem consists 
chiefly of vessels, many of them of relatively large size. They 
are derived from cells, the transverse walls between which 
have been partially broken down. In the mature vessels 
the protoplasmic contents have entirely disappeared ; they 
only contain water or air. Their walls are greatly thickened, 
the thickening having taken place along equidistant trans- 
verse lines, the thin spaces left between them being the 
pits. The vessels have become flattened against one another, 
by mutual pressure, so that they are five- or six-sided ; and, 
as the markings of their flattened walls simulate the rounds 
of a ladder, they have been termed scalar if or m ducts or 
vessels. The cavities of these scalariform ducts are divided 
at intervals, in correspondence with the lengths of the cells 
of which they are made up, by oblique, often perforated, 
partitions. Among the smaller vessels, a few will be found, 
in which the thickening forms a closely wound spiral. 
These are spiral vessels. They usually occur in two groups, 
and as they are the first elements of the xylem to be differ- 
entiated, they are said to constitute the protoxylem of the 
bundle. Among the vessels a few parenchymatous cells 
containing starch are scattered. The phloem is at once dis- 
tinguished from the xylem by the smaller average size of its 


XV.] THE BRACKEN FERN. 447 

cells, and their thinner walls. The most conspicuous elements 
of the phloem are the sieve-tubes^ which consist of long cells, 
the lateral walls of which show groups of minute perforations. 
The outer layer of the phloem is formed of long narrow cells, 
with comparatively thick walls. These cells are developed 
before the rest, and are hence termed the protophloem. Be- 
tween the phloem and the bundle-sheath is a layer of paren- 
chymatous cells containing starch, termed the phloem- 
si ic at h. 

The rachis of a frond, so far as it projects above the 
surface of the ground, is of a bright green colour ; and, in 
transverse section, it presents a green ground-substance, 
interrupted by irregular paler markings, which are the trans- 
verse sections of longitudinal bands of a similar colour. 
There are no brown spots or bands. Examined micro- 
scopically, the ground-substance is found to be composed 
of polygonal cells containing chlorophyll. These are in- 
vested superficially by an epidermis, composed of elongated 
cells. The pale bands are vascular bundles, of similar 
structure to those in the stem, with which they are con- 
tinuous. 

The vascular bundles, the green parenchyma, and the 
epidermis are continued into each pinnule of the frond. 
The epidermis retains its ordinary character on the upper 
side of the pinnule, except that the contours of its com- 
ponent cells become somewhat more irregular. On the 
under side, many hairs are developed from it, and the 
cells become singularly modified in form, their walls being 
thrown out into lobes, which interlock with those of adja- 
cent cells. 

Between certain epidermal cells an oval space is left, 
forming a channel of communication between the interior 
of the frond and the exterior. The opening of this space 


448 ELEMENTARY BIOLOGY. [CHAP. 

is surrounded by two kidney-shaped cells, the concavities of 
which are turned towards one another, while their ends are 
in contact. The opening left between the applied concave 
faces is a stoina, and the two cells are the guard-cells, and, 
as the stomata are present in immense numbers, there is a 
free communication between the outer air and the inter- 
cellular passages which exist in the substance of the frond. 
Those cells of the green parenchyma of the frond which 
form the inferior half of its thickness, in fact, are irregularly 
elongated, and frequently produced into several processes, 
or stellate. They come into contact with adjacent cells 
only by comparatively small parts of their surfaces, or by 
the ends of these processes. They thus bound passages 
between the cells, intercellular passages, which are full of 
air, and are in communication with similar, but narrower, 
passages, which extend throughout the substance of the plant. 

The vascular bundles break up in the pinnules, and 
follow the course of the so-called reins, which are visible 
upon its surface : ducts being continued into their ultimate 
ramifications. 

The growing point of the stem terminates in a single 
apical cell, by the divisions and subdivisions of which all the 
tissues of the stem and leaves are formed. 

Each root presents an outer coat of epidermis, bearing a 
number of unicellular root-hairs, and enclosing parenchy- 
matous and sclerenchymatous tissues traversed by a central 
vascular bundle. The latter contains the same elements as 
are found in the bundles of the stem, but the xylem and 
phloem have a different arrangement. The roots, like the 
stem, develop by means of an apical cell at the growing 
point, but this is not situated at the extreme end of the 
organ, as the growing point of the rhizome is, but is covered 
by a root-cap of protective cells. 


XV.] THE BRACKEN FERN. 449 

The nutrition of the Fern takes place essentially as in 
the other chlorophyll-containing plants previously con- 
sidered. The root-hairs constitute the organs for the ab- 
sorption of water and dissolved salts. As regards the 
vascular bundles, the xylem has been found to be the tissue 
in which the water is conducted to the leaves, while the 
phloem serves for the transference of assimilated food, 
especially proteids, from the leaves to all parts of the plant. 

Passing on to the reproductive organs, the sporangia have 
first to be considered. The study of their development has 
shown that each sporangium arises from the growth and 
subdivision of a single epidermal cell of the leaf. The 
sporangium consists of the pouch-shaped head above de- 
scribed, which is borne on a short stalk. The interior of 
the former part is occupied by the spores, usually 64 in 
number, which are formed by the division into four of six- 
teen mother-cells. The thick rim of the sporangium (called 
the annulus] ccnsists of a row of thick-walled cells ex- 
tending from the stalk over the top of the sporangium. The 
annulus contracts in dry weather and thus tears the spo- 
rangium open, setting the spores free. Each of the latter is 
a single cell, and the outer layer of its wall is strongly cuti- 
cularized. 

When the spores are sown upon damp earth, or a tile, or 
a slip of glass, and kept thoroughly moist and warm, they 
germinate. Each spore bursts its outer wall and gives rise 
to a tubular filamentous prolongation, the protoplasm of 
which contains chlorophyll-grains. At the base of this a 
similar but colourless process, the first root-hair^ is de- 
veloped. The green filament at first undergoes transverse 
division, so that it becomes converted into a series of cells. 
Then, the cells at its free end divide longitudinally, as well 
as transversely, and thus give rise to a flat expansion, which. 

M. 29 


450 ELEMENTARY BIOLOGY. [CHAP. 

gradually assumes a bilobed form, and becomes thickened 
in its middle part by division of its cells in a direction 
parallel to its surface. The thickened portion is termed 
the cushion. Numerous colourless, unicellular root-hairs 
are given off from the under surface of the little plant, 
which is called a prothallus or prothallium, and attach it to 
the surface on which it grows. 

The prothallus attains no higher development than this, 
and does not directly grow into a fern such as that in which 
the spores took their origin but, after a time, rounded or 
ovoidal elevations are developed, by the outgrowth and 
division of the cells which form its under surface. These 
bodies are of two kinds, the antheridia and archegonia. In 
the former, which may be developed on any part of the 
under side of the prothallus, the nucleus of each of the 
cells contained in their interior is converted into a sperma- 
tozoid somewhat similar to that of Chara, but provided 
with many more cilia. The antheridium bursts, and the 
spermatozoids set free from their containing cells are pro- 
pelled through the moisture on the under surface of the 
prothallus by their cilia. 

The processes of the second kind, the archegonia, acquire 
a more cylindrical form. The outside of the organ is formed 
of a single layer of cells, which are persistent, but those 
which are situated in the axis of the archegonium all dis- 
appear with the exception of that which lies at the bottom 
of its cavity. This is the ovum or oosphere, and when the 
archegonium is fully formed, a canal leads from its summit 
to this cell. The spermatozoids enter by this canal, and 
impregnate the ovum. 

The ovum now begins to divide, and becomes converted 
into eight cells, which give rise to the stem, leaf, root and 
foot, of the fern-plant, the foot being the organ by which 


XV.] THE BRACKEN FERN. 451 

the embryo is attached to the prothallus and derives food- 
supplies from it. 

As the rhizome grows, and developes its fronds, it rapidly 
attains a size vastly superior to that of the prothallus, which 
at length ceases to have any functional importance, and dis- 
appears. 

Thus Pteris presents a remarkable case of the alternation 
of generations. The large and complicated organism com- 
monly known as the ' Fern ' is the product of the impreg- 
nation of the ovum by the spermatozoid. This 'Fern,' 
when it attains its adult condition, developes sporangia; 
and the inner cells of these sporangia give rise, by a perfectly 
asexual fissive process, to the spores. The spores when set 
free germinate; the product of that germination is the in- 
conspicuous and simply cellular prothallus ; an independent 
organism, which nourishes itself and grows, and on which, 
eventually, the essential organs of the sexual process the 
archegonia and antheridia are developed. 

Each impregnated ovum produces only a single ' fern/ 
but each 'fern' may give rise to innumerable prothalli, 
seeing that every one of the numerous spores developed in 
the immense multitude of sporangia to which the frond gives 
rise, may germinate. 


LABORATORY WORK. 

A. THE FERN-PLANT ; ASEXUAL GENERATION. 

a. External characters. 

a. The brown underground stem or rhizome, with 
a lighter band (the lateral line) running along 
each side of it : its nodes and internodes. 

29 2 


452 ELEMENTARY BIOLOGY. [CHAP. 

b. The roofs springing from the rhizome. 

c. The leaves or fronds arising from the rhizome at 
intervals, along the lateral lines. 

a. The great amount of subdivision of the frond : 
its main axis (rachis); the primary divisions or 
pinna ; the ultimate divisions OK pinnules. 

ft. The sort; small brown patches along the 
margin of the under surface of some of the 
pinnules. 

y. The indusium or membrane covering the 
sorus. 

d. The nodes and internodes of the rhizome. The 
naked growing point at its extremity. 

b. The rhizome. 

1. Cut it across and draw the section as seen with the 
naked eye. 

a. The outer brownish layer (epidermis and hypo- 
derma) ; the latter thins aways somewhat oppo- 
site the lateral lines. 

b. The yellowish-white substance (ground-substance 
or parenchyma) forming most of the thickness of 
the section. 

c. The internal incomplete brown ring (sclerenchyma) 
imbedded in the parenchyma. 

d. The small patches of sclerenchyma scattered 
about in the parenchyma outside the main 
sclerenchymatous ring. 

e. The yellowish tissue (vascular bundles) lying in- 
side and outside the ring of sclerenchyma. 

2. Cut a longitudinal section of the rhizome ; make out 
on the cut surface b. i. a, b, c, d, e. 


XV.] THE BRACKEN FERN. 453 

3. Cut a thin transverse section of the rhizome, mount 
in water and examine with i inch obj. 

a. The single layer of much thickened epidermal 
cells. 

b. The small opaque angular contours of the 
hypodermal cells (external sclerenchyma). 

c. The large polyhedral more transparent paren- 
chymatous cells. 

d. The small opaque angular contours of the cells 
of the internal sclerenchyma. 

c. The great openings of the vessels in the fibro- 
vascular bundles. 
Draw the section. 

4. Examine with -| obj. 

a. The epidermis: its thick-walled cells. 

b. The parenchyma : its large thin-walled cells : their 
wall, protoplasm and nucleus : the great number 
of starch granules in them. 

c. The various patches of sclerenchyma^ made up of 
thick-walled angular cells. 

d. The vascular bundles. Note in each :- 

a. Outside, a single layer of cells with brownish 
walls, containing no starch granules (bundle 
sheath). 

(3. Within the bundle sheath a layer of small 
parenchymatous cells containing starch (inner 
QI phloem sheath}. 

y. Within the last layer comes the bast of the 
bundle (phloem) consisting of externally, two 
or more layers of small rectangular cells with 


454 ELEMENTARY BIOLOGY. [CHAP. 

thickened walls (protophloem) and then a 
single row of large thin-walled cells (sieve- 
tubes or bast vessels) between which lie smaller 
thin-walled cells containing starch granules 
(past parenchyma}* 

8. The whole of the space within the phloem 
is occupied by the xylem or wood. Note the 
greatly thickened walls of its large vessels, and 
their central cavity containing no protoplasm ; 
the groups (usually two in number) of much 
smaller vessels (protoxylem) ; scattered here 
and there, in the spaces between the angles 
of the vessels, note the small parenchymatous 
cells (wood parenchyma) containing starch 
granules. 

e. Treat with iodine : observe the protoplasm 
stained brown ; the starch granules deep blue, 
rendering some of the cells quite opaque and 
almost black-looking; the cell-walls of the 
xylem light brown. 

5. Cut a thin longitudinal section of the stem and 
examine with i inch and then with ~ obj. Make 
out the various tissues described in 3 and 4. 

a. The epidermis, hypoderma and parenchyma, much 
as in the transverse section, except that the 
hypodermal cells are longer. 

b. The sclerenchyma is seen to be made up of greatly 
elongated cells, tapering towards each end. 

c. The vascular bundles ; note in them- 

a. The cells of the bundle sheath and of the 
phloem sheath much as in the transverse 


XV.] THE BRACKEN FERN. 455 

section but longer; the protophloem cells, 
elongated, with thickened walls ; the cells of 
the bast parenchyma somewhat elongated; 
the relatively large sieve tubes, of great length 
with oblique ends ; their lateral walls marked 
by irregular groups of minute pores. 

/3. The vessels of the xylem: elongated tubes 
presenting oblique perforated partitions, at 
long intervals. Two forms of vessels will be 
seen, viz. scalariform vessels, with regular 
transverse thickenings on their walls and 
smaller spiral vessels (protoxylem), less nume- 
rous than the last form, with a continuous 
spiral thickening on their walls. Among the 
vessels the square-ended cells of the xylem- 
parenchyma will be recognised. 

6. By macerating in Schulze's mixture (see Appendix E) 
the various cells and vessels may be isolated one from 
another, and their form better observed. 

7. By making a series of transverse sections from the 
growing end of a stem the gradual development of the 
various forms of t ; ssue from the originally uniform 
parenchyma (merisiem) of the growing point, may be 
traced. If a section through the actual apex be obtained 
it will be possible to make out the relatively large, 
wedge-shaped apical cell. 

c. The leaf. 

i. Hold a small piece of a barren leaflet in pith or imbed 
it in paraffin and cut a thin vertical section at right 
angles to one of the veins. 
Observe with low and high power 

a. The epidermis of the upper and lower surface. 


456 ELEMENTARY BIOLOGY. [CHAP. 

b. The mesophyll, the cells of which contain chloro- 
phyll-grains in large numbers. 

c. The transverse sections of the vascular bundles. 

2. Slice off the epidermis from the under side of a leaflet. 
Mount in water and observe with a high power 

a. the ordinary epidermal cells of irregular form, 

b. the hairs, 

c. the stomata, each stoma with its two kidney-shaped 
guard-cells. 

d. The root. 

1. Examine the tip of an uninjured root with a lens ; note 
the relatively large root-cap covering the end of the 
root. 

2. Make a transverse section of a mature root held in 
elder-pith, or imbedded in paraffin. Note, under a low 
power, 

a. the epidermis with its root-hairs, 

b. the cortex consisting of parenchyma towards the 
outside, and of very thick-walled sclerenchyma 
nearer the centre, 

c. the central vascular bundle. 

e. The reproductive organs. 

1. Examine a sorus with a low power without a cover- 
glass. It is composed of a great number of minute 
oval bodies, the sporangia, roofed in by the indusiitm. 

2. Scrape off some sporangia and mount in water : ex- 
amine with i inch obj. 

a. Their form : they are oval biconvex bodies 
borne on a short stalk. 

b. Their structure: composed of brownish cells, one 
row of which has very thick walls, and forms a 


XV.] THE BRACKEN FERX. 457 

marked ring (cumulus] round the edge of the 
sporangium. 

c. Their mode of dehiscence (look out for one that 
has opened) : by a cleft running transversely 
across the sporangium. 

3. Burst open some sporangia by pressing on the cover- 
glass : examine, with ^ obj., the spores which are set 
free. 

a. Their size : measure. 

b. Their form : somewhat triangular. 

[c. Their structure : a thick outer coat, a thin inner 
coat, protoplasm, and a nucleus : crush some by 
pressure on the cover-glass.] 

B. THE PROTHALLUS ; SEXUAL GENERATION. 

Prothalli may be obtained by sowing some spores on 
peat and keeping them warm and very moist for about three 
months. They are small deep green leaf-like bodies. 

a. The Prothallus. 

i. Transfer a prothallus to a slide, and mount it in water 
with its under surface uppermost. Examine with i 
inch obj. 

a. Its form : a thin kidney-shaped expansion from 
which, especially towards its convex border, a 
number of slender filaments (root-hairs] arise. 

b. Its structure. 

a. The leafy expansion : it consists throughout 
most of its extent of a single layer of polyhe- 
dral chlorophyll-containing cells, but at a part 
(the cushion} a little behind the depression 
marking the growing point it is several cells 
thick. 


458 ELEMENTARY BIOLOGY. [CHAP. 

/?. The root-hairs : each composed of a single 
cell which contains no chlorophyll. 

c. The antheridia and archegonia : the former can 
just be seen with an inch objective as minute 
eminences on the under surface of the older 
parts of the prothallus especially among the 
root-hairs; the latter are partly imbedded in 
the cushion. 

b. The reproductive organs. 

These are to be found by examining the under surface of 
the prothallus with |- obj. 

1. The antheridia. Most numerous near and among the 
root-hairs. 

a. Their form : small hemispherical eminences. 

b. Their structitre : made up of an outer layer 
of cells containing a few chlorophyll-granules, 
through which can be seen, according to the 
stage of development, either a single central cell, 
or a number of smaller cells (mother-cells of 
spcrmatozoids] resulting from its division : in the 
latter cells, in ripe antheridia, spirally coiled 
bodies (spermatozoids) can be indistinctly seen. 

2. The spermatozoids. 

Some of these are sure to be found swimming about 
in the water if a number of ripe prothalli are examined. 

a. Small bodies, coiled like a corkscrew, thick at 
one end, and tapering towards the other, which 
has a number of cilia attached to it. To the 
thicker end of the spermatozoid is often attached 
a rounded mass containing colourless granules. 


XV.] THE BRACKEN FERN. 459 

b. Treat with Iodine ; this stains them and stops 
their movements, so that their form can be more 
distinctly seen. 

3. The archegonia. Make vertical sections of the pro- 
thallus passing through the cushion ; this is best 
done while holding it between two pieces of pith. 
Note in the archegonia 

a. Their form: chimney-shaped eminences with a 
small aperture at the apex. 

b. Their structure. Each is composed of a layer 
of transparent cells containing no chlorophyll, 
arranged in four rows, and surrounding a central 
cavity which extends into the cushion formed by 
the thickened part of the prothallus (a. i. b. a). 
In this cavity lies, in young specimens, a large 
nucleated granular central cell, with two or three 
smaller granular cells (neck canal-cells] above it 
in the narrow upper part of the cavity ; in older 
specimens this upper part is empty, forming a 
canal leading down to the central cell. The 
latter has now divided into two ; the upper 
smaller cell resulting from its division forming 
the ventral canal-cell , which becomes disorganized, 
while the larger lower cell is the ovum or oosphere. 

4. Examine a young fern-plant in connection with its 
prothallus, to the lower side of which it is attached 
by means of \htfoot. 


XVI. 
THE BEAN-PLANT (Vida Fabd). 

IN this, which is selected as a convenient example of a 
Flowering Plant, the same parts are to be distinguished as 
in the Fern; but the axis is erect and consists of a root im- 
bedded in the earth and a stem which rises into the air. The 
appendages of the stem are leaves, developed from the op- 
posite sides of successive nodes; and the internodes become 
shorter and shorter towards the summit of the stem, which 
ends in a terminal bud. Buds are also developed in the 
axils of the leaves, and some of them grow into branches, 
which repeat the characters of the stem; but others, when 
the plant attains its full development, grow into stalks which 
support i\\o. flowers ; each of which consists of a calyx, a 
corolla, ten stamens and a central pistil '; the latter is ter- 
minated by a style, the free end of which is the stigma. 

The flower-stalks are modified branches, and the flower 
itself consists of several whorls of modified leaves. 

The stamens form a tube which ends in ten filaments, 
four of which are rather shorter than the rest ; and the fila- 
ments bear oval bodies, the anthers, which, when ripe, give 
exit to a fine powder, made up of minute pollen grains, each 
of which is a single cell. The pistil is hollow; and, attached 
by short stalks along the ventral side of it, or that turned 
towards the axis, is a longitudinal series of minute bodies, 
the ovules. Each ovule consists of a central conical nucellus, 


CHAP. XVI.] THE BEAN PLANT. 461 

invested by two coats, an outer and an inner. Opposite 
the summit of the nucellus, these coats are perforated by 
a canal, the micropyle, which leads down to the nucellus. 
One of the cells of the nucellus is very much larger than 
the rest ; this is called the embryo-sac. In its interior several 
smaller cells are developed, the most important of which 
is the ovum or oosphere, which lies at the end of the embryo- 
sac towards the micropyle. When the pollen is deposited 
on the stigma the grains germinate. Each sends out a long 
filament, the pollen-tube, which elongates, passes down the 
style, and eventually reaches the micropyle of an ovule. 
Traversing the micropyle, the end of the pollen tube pene- 
trates the nucellus, and comes into close contact with the 
embryo sac. The original nucleus of the pollen-grain has 
in the mean time divided into two, and one of the daughter 
nuclei passes down the tube, reaches the embryo-sac, and 
then fuses with the nucleus of the ovum. This is the 
process of impregnation, and the result of it is that the 
ovum divides and gives rise to a cellular embryo. This 
becomes a minute Bean-plant, consisting of a radicle or 
primary root ; of two, relatively large, primary leaves, the 
cotyledons ; and of a short stem, the plumule, on which 
rudimentary leaves soon appear. The cotyledons now in- 
crease in size, out of all proportion to the rest of the em- 
bryonic plant ; and the cells of which they are composed 
become filled with starch and other nutritious matter. The 
nucellus and coats of the ovule grow to accommodate the 
enlarging embryo, but, at the same time, become merged 
into an envelope which constitutes the coat of the seed. 
The pistil enlarges and becomes the pod; this, when it has 
attained its full size, dries and readily bursts along its edges, 
or decays, setting the seeds free. Each seed, when placed 
in proper conditions of warmth and moisture, then germinates. 


462 THE BEAN PLANT. [CHAP. 

The cotyledons of the contained embryo swell, burst the 
seed coat, and, becoming green, emerge as the fleshy seed 
leaves. The nutritious matters which they contain are ab- 
sorbed by the plumule and radicle, the latter of which de- 
scends into the earth and becomes the root, while the former 
ascends and becomes the stem of the young Bean-plant. 
The apex of the stem retains, throughout life, the simply 
cellular structure which is, at first, characteristic of the whole 
embryo; and the growth in length of the stem, so far as it 
depends on the addition of new cells, takes place chiefly, if 
not exclusively, in this part. The growing point does not 
terminate in a single apical cell, as in the Fern, but con- 
sists of a number of small, actively dividing cells, termed 
collectively the apical meristem. The root likewise develops 
its tissues from an apical meristem, but this, as in the Fern, 
is protected by a root-cap. 

The leaves cease to grow by cell multiplication at their 
apices, when these are once formed, the addition of new 
cells taking place at their bases. Each leaf is compound, 
the common petiole bearing from four to six leaflets. 

The tissues which compose the body of the Bean-plant 
are similar, in their general characters, to those found in the 
Fern, but they differ in the manner of their arrangement. 
The surface is bounded by a layer of epidermal cells, among 
which are stomata similar to those described in the Fern. 
Within the epidermis is a broad zone of tissue, termed 
the cortex. The greater part of this zone consists of paren- 
chymatous cells of the usual structure. At the four pro- 
jecting corners of the stem however, the cortical tissue 
has a somewhat different structure, consisting of cells which 
have their walls much thickened at the points of junction. 
Within the cortex comes a ring of vascular bundles, and 
within this is the parenchymatous pith extending to the very 


XVI.] THE BEAN PLANT. 463 

centre in the younger parts of the stem, while, in the older 
parts, the centre is occupied by a more or less consider- 
able cavity, full of air. This cavity results from the central 
parenchyma becoming torn asunder, after it has ceased to 
grow, by the enlargement of the peripheral parts of the 
stem. 

The arrangement of the vascular bundles in the Bean is 
not quite regular. Most of them, as already stated, form 
a ring between cortex and pith, but besides these there are 
two bundles, which are situated outside the ring. Each 
of these occurs opposite one of the projecting corners of the 
stem. Each vascular bundle consists of two halves; the 
xylem or wood, which is turned towards the centre of the 
stem, and the phloem or bast, which is turned towards its 
periphery. Bundles with this arrangement of xylem and 
phloem are termed collateral. The wedge-shaped bundles 
of the ring are separated from one another by narrow bands 
of parenchymatous tissue, which extend from the paren- 
chyma within the circle of woody and vascular tissue 
(medulla or pith) to that which lies outside it. These are 
the medullary rays. In each of the bundles the xylem 
and phloem are separated by a thin layer of small, and very 
thin-walled cells, termed the cambium layer. In the older 
parts of the stem this layer extends across the medullary 
rays between the bundles so as to form a continuous ring 
all round the stem. The tissues inside this layer are the 
wood and pith, while those outside it are the bast, cortex, 
and epidermis. 

The great morphological distinction between the axis of 
the Bean and that of the Fern lies in the presence of this 
cambium layer. The cells composing it, in fact, retain 
their power of multiplication, and divide by septa parallel 
with the length of the stem, or root. Thus new cells are 


464 THE BEAN PLANT. [CHAP. 

continually being added, on the inner side of the cambium 
layer, to the thickness of the wood, and on the outer side 
of it, to the thickness of the bast ; and the axis of the plant 
continually increases in diameter, so long as this process 
goes on. This constant addition to the outer face of the 
wood and the inner face of the bast is characteristic of the 
Dicotyledons and Gymnosperms, to which two groups all our 
forest trees belong. In the Bean this process of secondary 
thickening only goes on to a comparatively small extent. 

At the apex of the stem, and at that of the root, the 
cambium layer is continuous with the cells of the apical 
meristem which retain the capacity of dividing in these 
localities. As the plant is thickest at the junction of the 
stem and root, and diminishes thence to the free ends, or 
apices, of these two structures, the layer of cambium and 
meristem may be said to have the form of a double cone. 
And it is the special peculiarity of the groups of plants 
above-mentioned to possess this doubly conical layer of 
constantly dividing cells, the upper end of which is free, 
at the growing point of the terminal bud of the stem, 
while its lower end is covered by the root-cap of the ultimate 
termination of the principal root. 

The most characteristic tissues of the wood are pitted and 
spiral vessels, the spiral vessels being particularly abundant 
close to the pith. They are the first elements of the xylem 
to be formed. The outer part of the bast consists of elon- 
gated bast fibres, while the inner, or soft bast, contains 
sieve-tubes, the transverse walls of which are perforated. 

Stomata are absent in the epidermis of the root : they 
are to be found, here and there, in the epidermis of all the 
green parts of the stem and its appendages, but, as in the 
Fern, they are most abundant in the epidermis of the under 
side of the leaves. As in the Fern, they communicate with 


XVI.] THE BEAN PLANT. 465 

intercellular passages, which are widest in the leaves, but 
extend thence throughout the whole plant. 

The blade of the leaf is traversed by the branched vascular 
bundles, the xylem being turned towards the upper, and the 
phloem towards the lower surface. The parenchyma of the 
leaf, or mesophyll, is of two kinds; towards the upper surface 
the cells are closely packed, and elongated at right angles 
to the surface, forming the palisade parenchyma. Towards 
the lower surface the cells are of more irregular shape and 
very loosely arranged, and are termed the spongy paren- 
chyma. Both kinds of cells contain chlorophyll-grains, but 
they are most abundant in the palisade cells. 

The root has an epidermis, bearing unicellular root-hairs. 
Within this is a wide cortex of parenchyma, while the centre 
of the root is traversed by a single vascular bundle, of 
radial structure, usually containing four groups of xylem, 
and four of phloem, which alternate one with another. The 
lateral roots arise endogenously , immediately outside the vas- 
cular bundle, opposite the xylem groups. They thus have 
to force their way through the whole of the cortex before 
reaching the surface. There are in typical cases four rows 
of lateral roots, corresponding to the four xylem-groups 
opposite which they originate. 

The difference between a flowering plant, such as the 
Bean, and a flowerless plant, such as the Fern, at first sight 
appears very striking, but it has been proved that the two 
are but the extreme terms of one series of modifications. 
The anther, for example, is strictly comparable to a leaf 
bearing sporangia, the sacs in which the pollen is contained 
answering to the sporangia themselves. The pollen grains 
exactly resemble spores in their mode of development and 
answer to the small spores of those flowerless plants in which 
the spores are of two kinds some spores giving rise to 

M. 30 


466 THE BEAN PLANT. [CHAP. 

prothallia which develope only antheridia, and others to 
prothallia which develope only archegonia; instead of the 
same prothallia producing the organs of both sexes, as in 
Pteris, And the pollen tube may be compared to the first fila- 
mentous process of the spore. But, in the flowering plants, 
the protoplasm of the pollen tube does not undergo division 
and conversion into a prothallus, from which antheridia are 
developed, giving rise to detached fertilizing bodies or 
spermatozoids, but exerts its fertilizing influence without 
any such previous differentiation, other than the division of 
its nucleus. The connecting links between these two ex- 
treme modifications are furnished, on the one hand, by the 
Conifers, in which the protoplasm of the pollen tube be- 
comes divided into cells, from which, however, no sperma- 
tozoids are developed ; and by Selaginella, in which the 
protoplasm of the smaller spores ( = pollen grains) divides 
into cells which form no prothallus, but give rise directly to 
spermatozoids. 

On the other hand the embryo-sac is the equivalent of 
the large spore which gives rise to a prothallus bearing 
female organs. The ovum of the flowering plant cor- 
responds to the ovum contained in the archegonium of the 
prothallus. There are other cells produced from the pro- 
toplasm of the embryo-sac, which probably answer to the 
cells of a prothallus. Here again the intermediate stages 
are presented by the Conifers and Selaginella. For, in 
the Conifers, the protoplasm of the embryo-sac gives rise 
to a solid prothallus-like endosperm, in which bodies called 
corpuscula, which answer to the archegonia, are formed, 
and in each of these an ovum is produced; while, in Selagi- 
nella the prothallus developed in the large spores does not 
leave the cavity of the spore, but remains in it like an 
endosperm. 


XVI.] THE BEAN PLANT. 467 

The physiological processes which go on in the higher 
green plants, such as the Fern and the Bean, resemble, 
in the gross, those which take place in Protococcus and 
Cham. For such plants grow and flourish if their roots 
are immersed in water containing a due proportion of 
certain saline matters, while their stem and leaves are 
exposed to the air, and receive the influence of the sun's 
rays. 

A Bean-plant, for instance, may be grown, if supplied 
through its roots with a dilute watery solution of potassium 
and calcium nitrate, potassium and iron sulphate, and mag- 
nesium sulphate. While growing it absorbs the solution, 
the greater part of the water of which evaporates from the 
extensive surface of the plant. In sunshine, it rapidly 
decomposes carbonic anhydride, fixing the carbon, and 
setting free the oxygen ; at night, it slowly absorbs oxygen, 
and gives off carbonic acid j and it manufactures a large 
quantity of protein compounds, cellulose, starch, sugar and 
the like, from the raw materials supplied to it. 

It is further clear that, as the decomposition of carbonic 
anhydride can take place only under the combined in- 
fluences of chlorophyll and sunlight, that operation must 
be confined, in all ordinary plants, to the tissue imme- 
diately beneath the epidermis in the stem, and to the 
leaves. And it can be proved, experimentally, that fresh 
green leaves possess this power to a remarkable extent. 
The decomposition of carbonic anhydride and of water 
appears to go on simultaneously, and as the result of the 
process, various carbohydrates, such as grape-sugar, make 
their appearance. 

On the other hand, it is clear that, when a plant is grown 
under the conditions described, the nitrogenous and mineral 
constituents of its food can reach the leaves only by passing 

30 2 


468 THE BEAN PLANT. [CHAP. 

from the roots, where they are absorbed, through the stem 
to the leaves. And, at whatever parts of the plant the nitro- 
genous and mineral constituents derived from the roots 
are combined with the carbohydrates produced in the leaves, 
the resulting compound must be diffused thence, in order to 
reach the deep-seated cells, such for instance as those of 
the cambium layer and those of the roots, which are 
growing and multiplying, and yet have no power of ex- 
tracting carbon directly from carbonic anhydride. In fact, 
those cells which contain no chlorophyll, and are out of 
the reach of light, must live after the fashion of Torula ; 
and manufacture their protein out of the nitrates and salts 
of ammonia taken up by the root, in combination with such 
bodies as grape-sugar, already formed in the leaves. Thus, 
the higher plant combines within itself the two, physiologi- 
cally distinct, lower types of the Fungus and the Alga. 

That some sort of circulation of fluids must take place 
in the body of a plant, therefore, appears to be certain, but 
the details of the process are by no means clear. There is 
evidence to show that the ascent of fluid from the root to 
the leaves takes place, to a great extent, through the vessels 
of the wood, which in the higher plants have their transverse 
walls broken down so as to form very fine capillary tubes 
traversing both stem and root. 

The mechanism by which this ascent is effected is of two 
kinds ; there is a pull from above, and there is a push from 
below. The pull from above is the evaporation which takes 
place at the surface of the plant, and especially in the air- 
passages of the leaves, where the thin-walled cells of the 
parenchyma are surrounded, on almost all sides, with air, 
which communicates directly with the atmosphere through 
the stomata. The push from below is due in the first 
instance to the absorptive action of the root hairs. The 


XVI.] THE BEAN PLANT. 469 

water they take up passes to the parenchymatous cells of 
the cortex of the root, and is thence pressed into the vessels. 
In a vine, for example, before its leaves have grown in the 
spring, this process, called "root-pressure," causes a rapid 
ascent of fluid (sap} absorbed from the soil. A certain 
portion of the fluid thus pumped up from the roots to the 
surface of the plant doubtless exudes, laterally, through the 
walls of the vessels (the thin places which give rise to the 
pits on the walls of these structures especially favouring this 
process), and passing from cell to cell, eventually reaches 
those which contain chlorophyll. The distribution of the 
carbohydrates formed in the chlorophyll-bearing cells, pro- 
bably takes place by slow diffusion from cell to cell. The 
proteid compounds are in all probability conveyed through 
the sieve-tubes of the vascular bundles. 

There is no doubt that all the living protoplasm of the 
plant undergoes slow oxidation, with evolution of carbonic 
anhydride. In the green parts, and in daylight, this process 
of respiration is disguised by the more conspicuous one of 
assimilation, in which carbonic anhydride is decomposed 
and oxygen given off. In the deeper seated cells, and in 
all parts of the plant when light is absent, respiration alone 
goes on. The supply of oxygen needful for this purpose 
is sufficiently provided for, by the air-passages which are to 
be found between the cells in all parenchymatous tissues. 
The replacement of the oxygen of the air thus absorbed, 
and the removal of the carbonic anhydride formed, will be 
sufficiently provided for by gaseous diffusion. 

From what has been said, it results that, in an ordinary 
plant, growing in damp earth and exposed to the sunshine, 
a current of fluid is setting from the root towards the surface 
exposed to the air, where its watery part is for the most 
part evaporated ; while gaseous diffusion takes place, in the 


470 THE BEAN PLANT. [CHAP. 

contrary direction, from the surface exposed to the air, 
through the air-passages which extend from the stomata 
to the radicles ; the balance of exchange being in favour 
of oxygen, in all the chlorophyll-bearing parts of the plant 
which are reached by the sunlight, and in favour of carbonic 
anhydride, in its colourless and hidden regions. At night, 
the evaporation diminishing with the lowering of the tem- 
perature, the ascent of liquid becomes very slow, or stops, 
and the balance of exchange in the air-passages is entirely 
in favour of carbonic anhydride ; even the chlorophyll- 
bearing parts oxydizing, while no carbonic anhydride is 
decomposed. 


LABORATORY WORK. 

a. General characters. 

a. The erect central main axis (root and steni). 

b. The branches of the stem; some, mere repetitions 
of the main axis; others, modified and bearing 
flowers. 

c. The nodes and internodes. 

d. The appendages. 
a. Foliage leaves. 
/?. Floral leaves. 

b. The root. 

a. Its main central portion (axis). 

b. The rootlets attached to the axis in four rows. 

c. The root-hairs, only found on the younger parts 
of the root. 


XVI.] THE BEAN PLANT. 4/1 

d. The root-cap, covering the tip of each rootlet : 
this is difficult to get whole out of the ground in 
the bean, but is readily seen by examining the 
roots of duckweed (Lemna) with i inch obj. In 
the latter plant it consists of several layers of 
cells forming a cap on the end of the root, and 
ending abruptly with a prominent rim some way 
up it. In the bean the root-cap can be well 
seen by making a longitudinal section of the 
radicle of the seed. See below, f. i. c. 

. Make a transverse section of the main root of 
a seedling about an inch below its junction with 
the stem. Note that the whole root is destitute 
of chlorophyll. Observe with a low power 

a. The epidermis. 
/?. The wide cortex. 

y. The central vascular bundle. Note the four 
xylem - groups alternating with the same 
number of phloem groups. 

&. In a section passing through the insertion of 
a lateral root, observe that this arises endo- 
genously and immediately outside one of the 
groups of xylem. 

c. The stem. 

1. Erect, green, four-cornered, with a ridge at each 
angle; not woody; the gradual shortening of the 
internodes towards its apex. 

2. Cut a thin transverse section of the stem through an 
internode; note its central cavity, and the whitish ring 
of fibro-vascular bundles in it, which is harder to 


4/2 THE BEAN PLANT. [CHAP. 

cut than the rest : mount in water and examine with 
i inch obj.: note 

a. The medullary or pith-cavity in the centre of the 
section. 

b. The pith-cells, around the central cavity : large 
and more or less rounded (parenchyma) : some- 
times with dotted walls from spots of local thin- 
ness on them (pits). 

c. The fibro-vasculQt bundles arranged in a ring im- 
mediately outside the pith. Two of them how- 
ever will be found separate from the ring in two 
opposite corners of the stem. Commencing at 
the side nearest the pith, note in each bundle 

a. The small openings formed by the transverse 
sections of the spiral vessels (protoxylem). 

J3. The larger cavities of the pitted vessels. 

y. The small thick-walled wood-cells, wedged in 
between the vessels. These three (a, ft and y) 
form the wood or xylem of the bundle. 

8. The cambium zone : granular-looking, and com- 
posed of small angular thin-walled cells, ranged 
in regular radial rows. 

c. The bast or phloem. It presents internally 
thin-walled cells of various sizes, the bast 
parenchyma and bast vessels or sieve tubes. 
Externally it appears in cross section to be 
composed of rounded cells with thickened walls; 
the bast fibres or sclerenchyma. Draw the section. 

d. The cortex, consisting of several layers of large 
rounded cells containing chlorophyll. Note that 
at the four corners of the stem the walls of these 


XVI.] THE BEAN PLANT. 473 

cells are much thickened at the angles (collen- 
chymatous], 

e. The medullary rays: radiating rows of paren- 
chymatous cells passing between the bundles and 
uniting b and d : not quite continuous, being in- 
terrupted by the cambium zone (c. 8.). 

f. The epidermis: composed of a single layer of 
somewhat squarish looking cells, containing no 
chlorophyll. Note the stomata, their two small 
guard-cells being seen in section. 

3. Cut a transverse section through a node, and com- 
pare it with that through the internode. Observe 
the bundles passing out from the stem into the leaf. 

4. Cut a thin longitudinal section through part of an 
internode (if necessary the bit of stem may be im- 
bedded in paraffin first), and mount it in water ; 
working from the medullary cavity outwards, note 
the following layers, using at first a low power : 

a. The pith-cells : much as in the transverse section. 

b. The fibro-vascular bundles presenting 

a. The spiral vessels : elongated tubes with a spiral 
thickening on their walls. 

/?. The wood-cells: elongated and with much 

thickened walls. 
y. The pitted vessels : much like a, but with their 

walls pitted instead of spirally thickened. 

8. The cambium zone : made up of small, angular, 
thin-walled cells, containing abundant proto- 
plasm. 

e. The bast parenchyma: thin-walled elongated 
cells. 


474 THE BEAN PLANT. [CHAP. 

. The bast vessels: larger elongated cells with 
oblique perforated septa (sieve-tubes], 

if]. The bast fibres, fusiform and thick-walled. 

c. More parenchymatous cells, constituting the cortex. 

d. Epidermis: composed apparently of cubical colour- 
less cells : here and there the opening of a stoma 
(d. 2. d. (3.) may be seen. 

Draw the section. 

5. Compare the transverse and longitudinal sections 
together, making out the corresponding parts in each. 

6. Put on a high power, and examine each of the 
above-mentioned tissues carefully. 

7. Stain with iodine: note the cell-walls; the protoplasm 

-its presence or absence, and relative quantity in 
the various tissues ; the nuclei of the cells ; starch 
granules in some, stained deep blue by the iodine. 

d. The leaves. 

1 . Their form and composition. 

a. Each leaf consists of a number of different parts, 
viz. : 

a. The stalk or petiole. 

(3. The four to six oval leaflets attached laterally to 
the stalk. 

y. The pair of small leaf-like expansions (stipules] 
at the base of the petiole. 

S. The rudimentary tendril terminating the petiole. 

2. The histological structure of a leaflet. 

a. Imbed a leaflet in paraffin or hold it between two 
bits of elder pith and cut a thin section from it, 


XVI.] THE BEAN PLANT. 475 

perpendicular to its surfaces. Let the section lie 
in alcohol l a few minutes to drive the air out of its 
intercellular spaces, and then mount it in water, 
and examine with i inch objective. 

b. Begin at the upper surface (marked out by its 
more closely packed cells), and work through to 
the lower. Note 

a. The colourless epidermal layer consisting of a 
single row of cells ; the openings here and there 
in it (stbmatd). 

(3. Beneath the upper epidermis come elongated 
chlorophyll-containing cells, set on perpendicu- 
larly to the surface, forming the palisade paren- 
chyma. 

y. Then come irregularly branched cells forming 
the lower half of the leaf-substance ; these also 
contain chlorophyll. They constitute the spongy 
parenchyma. 

S. The epidermal layer of the lower surface ; like a. 

e. The intercellular spaces, through the whole thick- 
ness of the leaf: the direct communication of 
some of them with stomata. 

. Here and there sections of ribs or veins : make 

out in them the same elements as in c. 2. c. 
Draw. 

c. Treat with iodine : make out the wall, protoplasm 
(primordial utricle), nucleus and vacuole of the 
cells : the chlorophyll grains, the starch granules. 

d. Peel off a strip of epidermis from a leaf and ex- 
amine with a low power : note- 

1 This will discolour the chlorophyll grains. 


476 THE BEAN PLANT. [CHAP. 

a. The large close-fitting cells, with irregularly 
wavy margins and no chlorophyll, which chiefly 
make up the epidermis. 

ft. The openings here and there in it (stomata) ; 
the two curved, chlorophyll-containing guard- 
cells bounding each stoma. 

e. Gently pull a midrib in two across its long axis ; 
note the fine threads uniting the two broken ends; 
cut them off with a sharp pair of scissors, mount 
in water and examine with \ or \ objective : they 
will be found to consist of partially unrolled spiral 
vessels. 

e. The flower. 

1. Its general structure. 

a. Borne on a short stalk (peduncle). 

b. Composed of four rows or whorls of organs, 
a. The external green cup-like calyx. 

J3. Inside the calyx the corolla: the most con- 
spicuous part of the flower. 

y. Inside the corolla the stamens. 
8. Within the stamens the pistil. 

2 . The calyx. 

A cup terminated at its free edge by five prominent 
points, two dorsal, and three ventral : the five small 
midribs running along it (one to the end of each of 
the points) represent the free ends of five sepals, 
which are united below. 

3. The corolla. 

a. Composed of five pieces or petals. 

a. On the dorsal side, a single large piece (vexil- 


XVI.] THE BEAN PLANT. 477 

lum] expanded at its free end and folded over 
the rest. 

/?. On the sides, two oval pieces (ala], each 
attached by a distinct narrowed stalk (ungttis). 

y. The inferior part of the corolla (farina), com- 
posed of two oval pieces united along their 
lower edge but readily tearing apart. 

4. The stamens. 

a. Ten in number, each consisting of a stalk-like 
part, the filament, terminated by a small knob, 
the anther. 

b. The union of nine of the filaments for three-fourths 
of their length to form the stamen-tube, the tenth 
being free : the sharp bend of the filaments to- 
wards the upper side at the point where they sepa- 
rate from one another. 

c. Tease out an anther in water and examine with 
-| obj. : there will be found numerous 

a. Pollen-grains : small oval cells, with projections 
on the cell-wall in the equatorial region. 

d. The anther of a bean is so small that sections 
cannot be made of it without considerable skill: 
the structure of an anther can however be easily 
made out by imbedding one from a tiger-lily in 
paraffin or holding it between two bits of elder- 
pith, cutting transverse sections, mounting in water 
and examining with i inch. obj. 

a. It contains four chambers, the pollen-sacs, two 
on each side of the continuation of the fila- 
ment, and in each chamber lie numerous pollen- 
grains. 


478 THE BEAN PLANT. [CHAP. 

P. By making careful transverse sections of young 
flower buds the stages of development of the anther 
and pollen may be made out. Observe especially 
the origin of the pollen-grains by the successive 
division of each of the numerous mother-cells, into 
two and then into four. Each of the four daughter- 
cells forms a wall of its own and becomes a 
pollen-grain. 

5. The pistil. 

a. It is found by tearing open the stamen-tube : it 
is a long green tapering body, somewhat flattened 
laterally and ending in a point (the style] which 
bears a tuft of strong hairs. 

b. Slit it open carefully: its central cavity contains 
a number of small oval bodies, the ovules, attached 
along its ventral side by short pedicles. 

c. It is difficult to get a section of a bean-ovule, 
but its essential structure may be readily made 
out by making thin transverse sections of the 
ovary of a large lily (where the ovules are closely 
surrounded by the tissue of the pistil) and examin- 
ing with i inch obj. 

a. The central cellular portion of the ovule (nucel- 
lus] made up of a large number of cells. 

J3. Its two coats, an inner (J>rimine] and outer 
(secundine]. 

y. The small passage (micropyle] leading through 
the coats down to the nucellus. 

8. In median sections of the ovule, a very large 
cell (the embryo-sac] will be seen in the nucellus 
just opposite the micropyle. 


XVI.] THE BEAN PLANT. 479 

e. The contents of the embryo-sac are best studied 
in material which has been preserved, when quite 
fresh, in absolute alcohol, and then transferred to 
a mixture of alcohol and glycerine. The alcohol 
is allowed to evaporate, and the sections are then 
made, and mounted in glycerine. With a high 
power the following structures may be made out 
in the embryo- sac : 

aa. At the micropylar end three cells forming collec- 
tively the " egg-apparatus" The most deeply in- 
serted of the three is the ovum itself, the other 
two are the synergidae and undergo no further 
development. 

ft/3. About the middle of the sac the large nucleus. After 
fertilization this divides, repeatedly, to form the 
nuclei of the endosperm-cells. 

yy. At the end opposite the micropyle the three " anti- 
podal cells." 

f. The seeds. 

i. Soak some dried beans in water for twenty-four 
hours; they will slightly swell up and be more readily 
examined than when dry. 

a. Note the black patch (the hiluni) on one end of 
the bean, marking where the stalk (Juniculus) which 
fixed it in the pod was attached to it. 

b. Having wiped all moisture off the bean gently 
press it while observing that part of the black 
patch which is next its broader end : close to 
the patch a minute drop of fluid will be observed 
to be pressed out through a small opening, the 
micropyle. 

c. Carefully peel off the outer coat (testa] of the seed : 


480 THE BEAN PLANT. [CHAR 

the two large fleshy cotyledons of the embryo will 
be laid bare. Joining the cotyledons together 
will be found the rest of the embryo : it consists 
of a conical part (the radicle] lying outside the 
cotyledons, with its apex directed towards the 
point where the micropyle was : and of the rudi- 
ments of the stem and leaves (plumule) lying 
between the cotyledons. 

g. The process of fertilization. 

This is difficult to follow in the bean; but by using 
different plants for the observation of its various stages 
it is fairly easy to observe all its more important steps. 

1. A plant well adapted for seeing the penetration of 
the pollen tube into the stigma and style is the 
Evening Primrose (GELnothera biennis). 

Detach the style from the flower and hold the 
club-shaped stigma between the finger and thumb 
of the left hand. Moisten it with a drop of water 
and then make with a wetted razor several successive 
cuts through it. This will divide the stigma into 
several slices. Spread these out on a glass slide 
with a needle in water and examine the thinnest, 
after putting on a covering-glass. 

The triangular grains of pollen will be seen send- 
ing out from one angle a tube into the stigmatic 
tissue, which is easily seen from its slight difference 
in colour. 

2. The entrance of the pollen-tube into the micropyle 
can be readily made out in some species of Veronica. 
The common V. serpyllifolia often to be found 
in shady places on lawns is well adapted for the 
purpose. A flower should be taken from which the 


XVI.] THE BEAN PLANT. 481 

corolla has just dropped. Dissect out the minute 
ovary and, using the dissecting microscope, open 
with a needle one of its two cells in a drop of water ; 
remove the mass of ovules and gently tease them 
apart. Then put on a covering-glass and examine 
with a low power till an ovule is found which shews 
the entry of the pollen-tube. The addition of dilute 
glycerine will make the ovule more transparent, so 
that after some time the embryo-sac can be seen, 
and the progress of the pollen-tube into the ovule 
followed. 

3. In favourable median sections of the ovule of the lily 
prepared as directed in e. 5. c. e., the pollen-tube may be 
traced through the micropyle and between the cells 
of the nucellus to the embryo-sac. 

4. Among other plants favourable for the study of the 
details of fertilization may be mentioned Caltha (marsh- 
marigold), Helleborus, and Campanula (Canterbury 
Bells). In each case thin transverse sections of the 
fruit are to be made, and the material is best prepared 
as above described. 


M. 31 


APPENDIX. 


A. GENERAL. 

The animals and plants employed in this work should be 
obtained alive, and if possible by the student himself. Direc- 
tions for killing and preserving them will be found under each 
head. Living specimens should be kept ready at hand, in order 
that their habits and movements may be studied side by side 
with their structure. 

Apparatus required. 

i. Dissecting instruments, as under 

Two or three scalpels of variable sizes, with straight 
blades. 

Two pairs of scissors with straight points (one large and 
one small). 

Two pairs of forceps (one large and one small) with 
straight points, the inner faces of which shall be ground 
or notched. 

A seeker with a tapering point. 
A German-silver blow-pipe. 
Two razors (for section-cutting). 

A section-lifter. This may most readily be made by 
beating out the terminal jth of a piece of copper-wire, 
4 inches in length. 

3 or 4 camel's hair brushes. 

6 needles mounted in long wooden handles. 


APPENDIX. 483 

2. Dissecting dishes. 

A small pie-dish 6 or 8 inches in length, and an ordinary 
salve-pot will meet all requirements. They should be 
half filled with a mixture of paraffin and lamp-black, put 
in hot, and weighted down with a piece of sheet lead. 

3. Injecting apparatus. 

Two or three |-oz. medicine-droppers, with their points 
drawn out to varying degrees of fineness. 

A 1-oz. syringe, preferably of metal, for histological 
work. 

4. A compound microscope, preferably with a short body ; 
fitted with low power (i inch) and high power (|-th inch) 
objectives. A shallow eye-piece of low magnifying power 
will suffice, but a higher one may conveniently be to 
hand. 

5. A hand-lens : preferably of the pocket or watchmaker's 
type. 

A simple dissecting microscope may conveniently be 
added. 

6. Sundries. 

Drawing material. Unlined paper ; pencils H and 
HB, and a box of moist-colours. Paints may be em- 
ployed in preference to chalks, and it is advisable to 
use corresponding colours in representing corresponding 
organs of different organisms, or corresponding parts of 
organs themselves. 

In drawing, accurate representation in outline should 
be aimed at, and it will generally suffice to colour in light 
flat washes. 

Microscopic slides and cover-slips. 

Of the former, 2 oz., with rough or ground edges at will. 
Of the latter, ^ a gross, preferably square thin. 

Glass dipping-tubes of various calibres and lengths ; 
two or three to be drawn out to a point. 

312 


484 APPENDIX. 

Three or four small thin glass beakers. 

Half a dozen watch-glasses. 

Three or four glass salve-pots with lids. 


B. ON DISSECTING. 

Unless otherwise directed, all the dissections embraced by 
this work should be performed under water. 

The undermentioned precautions are indispensable to success. 

1. The animal or organ under dissection should be firmly 
pinned down, the pins being thrust through those more 
solid parts of the same, furthest removed from the point 
of operation. 

2. Displacement of parts of organs, prior to removal or 
otherwise, should be effected by means of forceps, the 
larger ones being employed wherever possible (in order 
that the smaller ones may be the more fit for delicate 
work) ; the direct use of the fingers should be dis- 
couraged. 

3. Never dissect under dirty water. Should the water be- 
come clouded, as it may do from numerous causes, 
change it at once and, in doing so, wash the dissection 
clean under a gentle stream. 

4. In dissecting a given system remove nothing unneces- 
sarily. Dissect away only such parts as may interfere 
with the immediate purpose of inquiry, and do this only 
after full deliberation. 

5. Dissecting instruments should always be wiped perfectly 
clean and dry after use. The hinges should be occa- 
sionally oiled by means of a camel's hair-brush ; and if 
put away for a lengthy period after use, all parts subject 
to immersion in water should be similarly treated. 


APPENDIX. 485 


C. ON INJECTING. 

i. Precautions, indispensable to success under all circum- 
stances. 

a. Injection should always be performed as soon after 
death as possible ; and, in the case of the Frog, 
it is advisable to first remove the apex of the ven- 
tricle, in order to allow of the escape of as much 
blood as possible. 

In filling the syringe (or its equivalent) with injecting 
material care should be taken to first expel the con- 
tained air : when fully charged it should be held 
nozzle uppermost, while, by displacement of the 
piston, all trace of air is dispelled. 

c. In opening a blood-vessel prior to injection the 
exposed wall should be slit longitudinally with small 
scissors. Escape of as much blood as possible 
should be permitted. Before inserting the cannula 
or its equivalent, the whole should be well washed 
and the incision examined to make sure of the ab- 
sence of a blood-clot or other obstructive agent. 

To this end the introduction of the cannula may 
be advantageously preceded by that of the seeker. 

d. If the cannula is to be tied in place (as must always 
be the case when injecting for histological purposes) 
the thread (preferably one of surgical silk) should be 
passed round the vessel and loosely knotted, prior to 
making the incision in its wall. The incision should 
be made a short distance from the thread, in a 
direction away from that in which it is intended to 
inject. 

Under such circumstances the knotted thread will 
be found to serve as a landmark, which experience 
will show to be occasionally necessitated, in the 
course of the work. 


486 APPENDIX. 

e. Upon removal of the injecting apparatus the cut end 
of the blood-vessel or other organ through which it 
was inserted should be immediately ligatured or 
clamped, in order to guard against reflux. 

2. Coarse injection, for anatomical purposes. 

Complete satisfaction may be obtained by using a mix- 
ture of French blue and water in the proportion of a tea- 
spoonful to half a tumbler. The mixture should be well 
stirred immediately before use, and it may be introduced 
under water or otherwise as occasion demands. Most 
satisfactory results are to be obtained with this mixture 
by injecting piecemeal from such of the larger vessels as 
may be desirable. 

For permanent anatomical preparations plaster of Paris 
may be preferably employed. Mix with two-thirds its 
bulk in water and colour with French blue or vermilion ; 
stir thoroughly and strain through two thicknesses of 
fine muslin. The mixture thus prepared will remain for 
8 10 minutes sufficiently fluid for all practical purposes. 

3. Fine injection, for histological purposes. 

Allow a given quantity of gelatine to stand for 3 4 hours 
in twice its bulk of cold water; heat slowly until quite 
fluid and colour to taste with Berlin blue or carmine. 
Inject when lukewarm, the animal being immersed in 
water at the same temperature. 

In the above process the following precautions should 
be taken. 

a. The point of the cannula should bear a slight con- 
tusion near its tip, round which the thread may bite 
when ligatured. 

b. The cannula should be as short as possible, and 
there should be attached to its base an inch or so of 
india-rubber tubing to receive the nozzle of the 
syringe. 

c. The cannula should not be inserted until all bleed- 
ing has ceased. 


APPENDIX. 487 

d. While injecting, a steady pressure should be main- 
tained. Should resistance to this be offered, the 
operation must be interrupted until the cause of 
obstruction shall have been ascertained and, if pos- 
sible, removed. 

Obstruction generally arises from one or more of 
the undermentioned causes. 

i. The presence of clotted blood in the smaller 
vessels. This source of difficulty is usually 
fatal to success. 

ii. Resistance offered in the capillary systems, 
often resulting from the forcing back of the 
blood upon the great vessels. This may ge- 
nerally be overcome by puncturing a large 
vessel as far removed from the point of opera- 
tion as possible (i. e. if injecting the arteries 
puncture one of the larger veins, or vice versa}. 

iii. A too rapid cooling of the gelatine within the 
smaller vessels and capillary systems. To over- 
come this, increase the temperature of the water 
in which the animal is immersed. 

e. Complete injection of a given capillary system ul- 
timately results in visible distension of the organ 
concerned ; should enlargement such as this become 
suddenly obvious the operation must be terminated, 
otherwise rupture and extravasation will ensue. 

f. On withdrawal of the syringe the end of the india- 
rubber tube attached to the cannula should be either 
plugged with a glass-rod or other convenient stopper, 
or clamped ; and the whole should be placed in cold 
water until the gelatine shall have set. 

g. Animals or tissues thus injected should never be 
placed at once into strong alcohol, but into spirit 
of increasing strength, from 50 per cent, upwards as 
directed at Appendix E. 


488 APPENDIX. 

D. MICROSCOPE AND MICROSCOPIC 
EXAMINATION. 

i. In using the microscope the first thing to be considered 
is the illumination. A position facing a window should 
be selected, and if the window be a north one there will 
be an advantage in the absence of direct sunlight, which 
should never be employed for microscopic work. The 
light from a south window is however equally good, if a 
white blind be used to exclude bright sunshine. 

The mirror must be so placed that the field of the 
microscope appears quite bright. The admission of 
light from the mirror to the object is regulated by the 
diaphragms. The size of the opening to be used should 
depend on the magnifying power. With a low power a 
large opening is necessary, or the whole field will not be 
illuminated ; with a high power a smaller opening gives 
a better definition., though it diminishes the intensity of 
the illumination. Most modern microscopes are pro- 
vided with a double mirror : the flat one should be used 
low down in illuminating with a low power ; with a high 
power on the other hand, the concave one should be 
used obliquely and high up. 

2. The microscope has two adjustments of focus. The 
coarse adjustment is effected by sliding the body of the 
microscope up and down in its tube, or in the larger in- 
struments by a rack and pinion movement. The fine 
adjustment is worked by a screw. In all observations 
the low power should be used first, and then the high, if 
necessary. The focal distance of the low power is of 
course relatively long, usually either an inch or half an 
inch. Hence there is no difficulty in focussing and no 
danger of crushing the object. With the high power, 
which may have a focal distance of -J in., ^ in., or 
less, great care is necessary, lest the objective should 
touch the cover-slip. It is best to slide the body of the 


APPENDIX. 489 

microscope very carefully down, until the object is just 
visible, and then to focus accurately with the fine ad- 
justment. 

3. Never observe with a high power until the object is 
covered with a cover-slip. If the object appears in- 
distinct, this may be due to dirt or condensed vapour, 
on the cover-slip, the objective, or the eye-piece. If the 
first is in fault the distinctness will vary as the slide is 
moved. The presence of any foreign particles on the 
eye-piece can be easily detected by turning it round. A 
general indistinctness, which is not affected either by 
moving the slide, or by rotating the eye-piece, must be 
due to the objective having become dirty, or injured. 

4. Should the objective be dirty, it must be cleaned with a 
soft linen rag, or with a piece of wash-leather, never 
with a coarse cloth. The greatest care must be taken 
that the objective does not become dirty, for even the 
most careful cleaning is likely to injure the lens. In 
order to keep the objective clean, it is essential that no 
more fluid should be used in mounting, whether tem- 
porarily or permanently, than will exactly fill the space 
under the cover-slip. 

5. During observation the focussing should constantly be 
slightly varied, by means of the fine adjustment, as this 
greatly aids in getting a clear idea of the object. 

6. It is best to cultivate a habit of using the microscope in 
the vertical position, so that the stage is horizontal. An 
inclined position of the instrument is only admissible in 
examining permanent preparations. 

7. The body of the microscope should always fit accurately, 
but not tightly, in its tube. It should be oiled if it does 
not work up and down quite smoothly. 

8. A micrometer of some kind is indispensable, and the 
purpose to be aimed at in its use is the knowledge of the 
size of objects under examination. An eye-piece mi- 


4QO APPENDIX. 

crometer ruled into squares answers most purposes and 
the squares and objects delineated should be drawn to 
the proportions observed. Having thus a record of ob- 
jects, drawn in proportion relative to the said squares, 
it remains but to ascertain the value of the latter. This 
is best done by using, in conjunction with the eye-piece 
micrometer above named, a stage micrometer ruled to 
intervals of known value ; there will thus be superposed 
lines of absolute and relative measurement. The actual 
value of the squares of the eye-piece micrometer may by 
this means be once for all calculated, and a record of the 
same should be kept for each lens combination. 


E. PREPARATION AND USE OF REAGENTS 
AND CULTURE SOLUTIONS. 

The reagents employed in microscope work are best put up 
for use in ^ oz. bottles. Those marked thus * should be kept in 
glass bottles with ground necks and stoppers, their contents 
being removed by means of clean capillary tubes. The re- 
ceptacles of the remaining ones should be corked, each cork to 
carry a thin glass rod long enough to reach near the bottom of 
the bottle. 

1. Acetic acid, Dilute. 

Mix i cub. centimetre of glacial acetic acid with 99 cub. 
cent, of distilled water. 

2. Alcohol. 

Methylated spirit should be kept ready to hand in stock 
bottles, diluted with water to various strengths, viz. 
50 per cent., 75 per cent., 90 per cent. Upon placing 
any specimen, organ, or tissue in the same, at least 3 4 
times its bulk in fluid should be employed. Immersion 
in the weaker solutions should not exceed 6 8 hours in 
the case of whole organs, or 2 3 hours in those of 
tissues in course of hardening for histological work. 


APPENDIX. 491 

The stronger solutions employed in the final stages of 
hardening or preservation should be replaced at intervals. 
In the case of preparations which have been transferred 
from acid solutions, the spirit must be repeatedly changed, 
until all excess of acid is removed. 

Preparations of nervous tissues or sense-organs, if 
treated with alcohol, should be put at once, when quite 
fresh, into strong spirit. 

3. Ammonic bichromate, Solution of. 

Dissolve 10 grammes of crystallized ammonic bichro- 
mate in a litre of distilled water. 

4. Canada balsam*. 

A chloroform or turpentine solution of fairly fluid con- 
sistency should be employed. It must be kept in a well- 
stopped bottle with a wide neck. 

5. Carmine, Solution of. 

Carmine 2 grammes. 

Strong solution of ammonia 4 cub. cent. 

Distilled water 48 cub. cent. 

Dissolve the carmine in the ammonia and water ; leave 
in an unstoppered bottle until nearly all smell of ammo- 
nia has gone. Afterwards keep in a well-closed bottle. 
Dilute a small quantity with fifteen or twenty times its 
bulk of water, when required for use. 

6. Carmine, Borax, Solution of. 

Carmine I gramme. 

Borax 4 grammes. 

Distilled water 56 cub. cent. 

To this solution add twice its volume of absolute alcohol. 
Filter. 

7. Chromic acid, Solution of. 

Dissolve 10 grammes of crystals of chromic acid in one 
litre of water. This gives a i per cent, solution, from 


492 APPENDIX. 

which weaker ones can readily be prepared when re- 
quired. 

Preparations should be placed in 'i per cent, solution 
for the first 24 hours, that being ultimately replaced for a 
similar period by one of '5 per cent, which should be 
changed if necessary. When well hardened they should 
be transferred to 75 per cent, alcohol. 

When used for purposes of decalcification the maxi- 
mum quantity should be employed, and to it a few drops 
of nitric acid may be added. 

8. Corrosive sublimate, Solution of. 

To a saturated aqueous solution add a few drops of 
acetic acid. 

A relatively large quantity of the above must be em- 
ployed, and the preparation, after at most an hour's 
immersion therein, should be well washed under running 
water before being transferred to alcohol. 

9. Eosin, Solution of. 

Aqueous and alcoholic solutions should be prepared ;- 
the former for use with fresh material, the latter with 
that which has been previously hardened. 

10. Glycerine. 

By 'weak glycerine,' referred to in the text, is meant a 
solution composed of equal parts in bulk of glycerine 
and distilled water. 

1 1 . Gold chloride, Solution of. * 

A i per cent, solution is customarily employed. 

Tissues submitted to the action of this reagent should 
be kept free of contact with metal. 

12. Hsematoxylin, Solution of. 

a. Prepare a saturated solution of crystallized calcic 
chloride in 70 per cent, alcohol ; then add alum to 
saturation. 


APPENDIX. 493 

b. Prepare a saturated solution of alum in 70 per cent, 
alcohol. Add i volume of a to 8 of b. 

c. To the mixture of a and b add a few drops of a 
saturated solution of pure haematoxylin in absolute 
alcohol. 

d. Filter. 

This reagent stains with great intensity. Overstain- 
ed preparations may be clarified by immersion for 
a longer or shorter period in acidulated alcohol 
(70 per cent, solution plus '25 per cent, solution of 
nitric acid). 

13. Haematoxylin-ammonia, Solution of. 

Expose some crystals of Haematoxylin under a bell-glass 
to the action of the Ammonia gas given off from a strong 
solution. The crystals can then be dissolved in distilled 
water. This reagent must be prepared fresh when re- 
quired. 

14. Iodine, Solution of. 

Prepare a saturated solution of potassic iodide in dis- 
tilled water; saturate this solution with iodine. Filter. 
Dilute to a brown sherry colour. 

It sometimes happens that the iodine and sulphuric 
acid tests for starch and cellulose fail, when dealing with 
fresh material. Under such circumstances a check ex- 
periment should be performed, as follows, viz. : preserve 
in alcohol, transfer to weak solution of caustic potash 
for 6 8 hours, neutralize with dilute acetic acid and 
finally stain, as in ordinary, with iodine and strong sul- 
phuric acid. 

The presence of starch or cellulose should never be 
denied before both the above-named tests have failed. 

1 5. Magenta, Solution of. 

Dissolve i decigr. of crystallized magenta (roseine) in 
160 cubic centimetres of distilled water: add i cub. cent, 
of absolute alcohol. Keep in a well-closed bottle. 


494 APPENDIX. 

1 6. Mayer's Solution. 

See note, p. 386. 

17. Miiller's Fluid. 

Bichromate of potash 25 grammes. 

Sodi c sulphate I o grammes. 

Distilled water i litre. 

1 8. Osmic Acid, Solution of. 

Best bought ready made in the form of i per cent, solu- 
tion. 

The crystals are supplied in small tubes each containing 
i gramme. Such a tube should be broken up in 100 c. c. 
of distilled water, great care being taken to avoid contact 
with the resulting vapour. 

This reagent should be kept in a blank stoppered 
bottle, perfectly in the dark. 

19. Paraffin. 

See Appendix F. 

20. Pasteur's Solution. 

See note, p. 384. The amount of water should be 8376 
parts. 

21. Picric Acid, Solution of. 

Make a saturated solution in distilled water. 

22. Picric Acid, Kleinenberg's solution of. 

To a cold saturated solution of the acid add 2 parts of 
nitric or concentrated sulphuric acid. 

Filter, and add to the filtrate three times its bulk of 
water. 

Immersion of from 3 5 hours will suffice for most 
preparations. 


23- 


Potash Solution .* 

Dissolve 5 grammes of potassic hydrate in 100 cubic 
cent, of water. 


APPENDIX. 495 

24. Sachs's Food-solution for green plants. 

Distilled water 1000 cub. cent. 

Potassium nitrate i gramme. 

Sodium chloride 0-5 gramme. 

Calcium sulphate 0*5 gramme. 

Magnesium sulphate 0-5 gramme. 

Calcium phosphate 0-5 gramme. 

To this solution add a trace of a weak solution of ferric 
chloride. The calcium phosphate is only slightly 
soluble in water. 

25. Schulze's Macerating mixture. 

Dissolve i gramme of potassium chlorate in 50 cub. cent. 
of nitric acid. Immerse the tissue in this solution, and 
heat it. The tissue will then readily break up into its 
constituent cells, their middle lamellae being dissolved. 

Cold maceration often gives better results, but takes 
longer. 

Take care that the gases given off from the mixture 
do not injure the microscope. 

26. Schulze's Solution. 

Dissolve some zinc in hydrochloric acid; permit the 
solution to evaporate, in contact with metallic zinc, until 
it has attained a syrupy consistence. Saturate the syrup 
with potassic iodide, and then add enough iodine to 
make a dark sherry-coloured solution. The object to be 
stained must be placed in a little water, and then some 
of the above solution added. 

27. Silver Nitrate, Solution of.* 

Dissolve o - 5 grammes of silver nitrate in 100 cubic cent, 
of distilled water. Keep in an opaque stoppered bottle. 

28. Sodic Chloride, Solution of. (Normal saline Solution. 
Salt solution.} 

Dissolve 7'5 grammes of sodic chloride in i litre of 
distilled water. 


496 APPENDIX. 


F. SECTIONS AND SECTION CUTTING. 

Directions for preparing sections of the vegetable tissues will 
be found incorporated in the text; those which follow apply to 
the animal series alone. 

1. Imbedding. 

All tissues or embryos about to be imbedded, whether 
stained or unstained, should have been first well hardened 
in 90 p. c. alcohol. 

For imbedding, a mixture of hard and soft paraffins is 
most serviceable, such as shall melt at from 50 to 60. 

The preparation to be imbedded, if stained, should be 
first soaked in turpentine to saturation ; if unstained, it 
may be transferred direct from the alcohol. In either 
case it must be placed in melted paraffin (the temperature 
of which must not exceed that of its melting point) until 
thoroughly permeated thereby. When ready for imbed- 
ding, take of the solid paraffin a piece of about the 
calibre of a candle and excavate at one end a pit, large 
enough to fully accommodate the preparation ; then 
transfer the latter and fill the pit with melted paraffin. 
Put the whole aside, until quite cool and firmly set. 

2. Cutting. 

For this purpose an ordinary razor will suffice, so far as 
the requirements of this volume are concerned. The 
edge should be kept permanently sharp. 

Before cutting, pare away the imbedding material, so 
as to reduce that which surrounds the preparation to the 
minimum. 

3. Mounting. 

Transfer the sections as cut, paraffin and all, to micro- 
scopic slides previously prepared by one of the two 
undermentioned methods, and proceed as directed in 
either case. 


APPENDIX. 497 

a. White of egg method. 

Smear the surface of the slide with a thin but uniform 
film of freshly drawn white of egg and deposit the 
sections in order of cutting. Gently heat the slide 
until the paraffin begins to melt and then put it aside. 
When set, put the whole bodily into turpentine and 
leave it until all the paraffin is dissolved out ; upon ex- 
amination the sections will be found to be firmly at- 
tached to the glass slide by means of the coagulated 
albumen. 

Immersion in turpentine for an indefinite period 
will do no harm. 

b. Kreasote and shellac method. 

Smear the surface of the slide with a heated solution 
of white shellac in Kreasote. Submit the whole to 
the temperature of the melting point of the paraffin 
until the kreasote is evaporated, whereupon the 
sections will become firmly adherent to the glass by 
means of the shellac. Next immerse the whole in 
turpentine, and leave it at rest until the excess of im- 
bedding material is dissolved out. 

This method is best applicable to preparations 
which have been previously stained and clarified. The 
white of egg process is not only the simpler of the two, 
but the more advantageous, as the sections may be cut 
and mounted unstained, that process and the sub- 
sequent clarifying being permissible after fixture to the 
slide. 

4. Final mounting. 

Allow sufficient of the canada balsam to drop upon the 
sections to fully cover them. When thoroughly diffused 
among them, smear the under face of a cover-slip with 
balsam and place one edge of it upon the slide support- 
ing its body upon the point of a needle ; by gradually 

M. 32 


498 APPENDIX. 

withdrawing the latter the cover-slip will descend ob- 
liquely expelling the enclosed air. 

Finished preparations should be examined from time 
to time, in order that loss of the mounting medium by 
evaporation may be made good. 

5. To prepare ground sections of shells, bones, or other 
hard parts. 

A small piece of the structure to be manipulated should 
be first isolated and then cemented in the desired posi- 
tion to a piece of plate glass, by means of canada balsam. 
When firmly set it should be ground down upon a hone 
or rough surface to the required thinness, and finally dis- 
lodged for mounting, by immersing the whole in benzole 
or chloroform. It may then be put up in Canada balsam 
in the manner described above. 

6. Frozen sections. 

Material for this purpose should be preserved in weak 
glycerine. For the preparation of these sections an ether- 
spray freezing microtome is desirable ; good preparations 
may however be made as follows. 

Obtain a metal rod of the calibre of a candle and 2 3 
inches in length : place the preparation (which, unless 
quite fresh, should be previously soaked in gum-water) 
on one end of it and add 6 8 times its bulk in ordinary 
fluid gum. Freeze with pounded ice and salt. Cut. 

Mount in weak glycerine. 


INDEX. 


A. 

ABDOMEN, 174, 190, 192, 238 
Abdominal appendages, 195, 198; 

papilla, 188, 236 
Acetabulum, 71 

Adipose tissue, histology of, 131 
Adrenal, 24, 52 
Adventitious buds, 444. 
Afferent branchial vessels, Cray- 

fish, 226 ; Mussel, 328 
Abe, 477 

Albumen gland, 289; duct of, 290 
Alcoholic fermentation, 377, 383, 

388 


Alimentary canal, Crayfish, 178, 

10-; Earthworm, 241, 253,267; 

Frog, 10, 15, 45; Mussel, 308, 

320 ; Snail, 274, 284 
Alinasal process, 13, 64 
Alternation of generations, Chara, 

435 ; Fern, 451 

Ambulatory appendages, 175, 197 
Ama'ba, 369 376 
Amoeboid movement, 123 
Anabolism, 381 
Anacharis, 442 
Angulo-splenial, 62 
Annulus, Fern, 449, 457 ; tym- 

panicus, 118 

Anodonta cygnea, 305 341 
Antenna, 176, 200 
Antennule, 176, 201 
Anther, 460, 465, 477 
Antheridium, Chara, 431, 433, 

439 5 Fern > 45> 458 5 466 


Antherozoid (see Spermatozoid) 

Antipodal cells, 4 79 

Anus, Crayfish, 1 79 ; Earthworm, 
241, -249 ; Mussel, 307 ; Snail, 
281, 283 

Aorta, Frog, 19, 20, 86; Snail, 
293; anterior, Mussel, 326; 
Snail, 294, 299; posterior, 
Mussel, 326; Snail, 294 

Aortic arches, 20, 85, 89, 92 

Apical cell, Chara, 432, 438; 
Fern, 448, 455 

Appendages, Chara, 430 ; Cray- 
fish and Lobster, 174, 176, 177, 
l 9-i J 95 5 development of, 237, 
238 

Aqueduct of Sylvius (see Iter) 

Aqueous humour, 117 

Arachnoid, 10 

Archegonium, 450, 459, 466 

Archenteron, Crayfish, 187, 236; 
Frog, 167, 170; Snail, 303 " 

Artery, antennary, 225; antero- 
ventral, 224; carotid, 18, 20, 
85 ; creliac, 88 ; ccelicao-mesen- 
teric, 87, 88 ; common iliac, 87; 
gastric, 225; genital, 87; he- 
patic, 180, 224; hypogastric, 
87 ; inferior abdominal (see pos- 
tero-ventral) ; inferior mesen- 
teric, 87, 88 ; ophthalmic, 224; 
pedal, Mussel, 326 ; postero- 
ventral, 225; pulmo-cutaneous, 
19, 20, 86; renal, Crayfish, 2 26; 
Frog, 87 ; rostro-antennary, 225; 
splenic, 88; sternal, 180, 224; 
subclavian, 86 ; superior ab- 

322 


5<DO 


INDEX. 


dominal, 180, 224; superior me- 

senteric, 88 ; vertebral, 86 ; 

visceral, Mussel, 326 
A rthrobactcrhun, 413 
Arthrobranchice, 221 
Arytenoid, 21,51 
Ascent of sap, 468 
Ascogonium, 420, 427 
Ascospore, 420, 427 
Ascus, 420, 427 
Asexual generation: Fern, 451 
Astaats fluviatilus, 173 2 39 
Astragalus, 73 
Atrium, 17, 81, 90 
Auditory epithelium, Frog, 145 ; 

Lobster, 232 
Auditory capsule, 59 ; organ : 

Crayfish, T86, 230; Cyclas, 331 ; 

Frog, 33, 118 ; development 

of, 161 ; Mussel, 331 ; Snail, 

276, 300 
Auricle, Frog, 17, 90; Mussel, 

324; Snail, 275, 284 
Auricular septum, 17, 91 
Axil, Bean, 460 ; Chara, 431 


B. 


Bacillus, 413 

BACTERIA, 408 414 

Balan tidin in, 363 

Basipodite, 195 

Bast, Bean, 464, 472 ; Fern, 446, 

453 
Bast fibres, 464, 474 

Bast parenchyma, 454, 473 

Bast vessels, 454, 473 

BEAN-PLANT, 460 481 

BELL-ANIMALCULE, 359 368 

Bidder's organ, 54 

Bile ducts, 47 

Bipolar nerve-cell, 139 

Blastoderm, 236 

Blastopore, Crayfish, 187, 236 ; 
Frog, 159, 160, 161; Snail, 302 

Blood, Crayfish, 226; Earthworm, 
245, 262; Frog, 16, 121 ; Lob- 
ster, 182; Mussel, 310; Snail, 
276 


Body - cavity, Earthworm, 247, 
252; Frog, dev. of, 169; Hydra, 
349' 35i 5 Mussel, 335 

Body-wall, Earthworm, 243, his- 
tology of, 264; Frog, 41, 43; 
Hydra, 344, 349 

Bone, histology of, 129 

Brachial plexus, 103 

BRACKEN FERN, 443 459 

Brain, n, 24, 96, 170 

Branch, 430, 443, 460 

Branchiae, Crayfish, 182, 220; 
Mussel, 307, 316, 3F7, 322, 
335> 33 6 ; suspensory ligament 
of' 3 l8 ' 335 Tadpole, 5, 6, 161, 
162, 164, 171 

Branchial clefts, 5 

Branchio-cardiac canals, 181, 222 

Branchiostegite, 174, 176, 193, 
194 

Bronchi, 50 

Brownian movement, 408, 411 

Brow-spot, 35, 36 

Buccal-mass, 285, 286; sac, 241, 

^53' 2 55 
Bud, Bean, 460 ; Chara, 432, 438 ; 

Hydra, 350 

Bundle-sheath, 446, 453 
Byssus, 313, 341 ; organ, 341 


C. 


C/ECUM, Crayfish, 208; Frog, 16 ; 

Lobster, 208 
Calcaneum, 73 
Calcar, 3, 73 

Calciferous glands, 243, 254 
Calcium, 379, 403 
Caltha, 481 
Calyx, 460, 476 
Cambium, 463, 473 
Cauipamila, 481 
Canal cells, 459 
Canalis centralis, 31 
Capillaries, 93 
Capitulum, 434 
Capsulogenous glands, 250 
Carapace, 174, 190; development 

of, 237 


INDEX. 


501 


Carbo-hydrate, 467 

Carbon, 379, 390, 403 

Carbonic anhydride, 38 r, 390, 402, 
467 

Carchesium, 368 

Carina, 477 

Carotid gland, 86 

Carpopodite, 196 

Carpus, 71 

Cartilage, histology of, 129; re- 
placement in bone, 14 

Cartilage bones, 63 

Catabolism, 381 

Cell-division, hyaline cartilage, 
128; Spirogyra, 399, 405; wall, 

379 

Cellulose, 379 

Centrum, 56, 58 

Cephalon, 174 

Cephalothorax, 173, 190, 193, 237 

Cerebellum, 25, 98 

Cerebral hemisphere, 97 

Cerebro-spinal axis, 10, 95 ; de- 
velopment of, 1 60, 1 68 ; nerves, 
10 

Cervical groove, 174, 175 

Chara, 430 441 

Chela, 175, 197, 237 

Chlamydococctts, 389 

Chlorophyll, Bean, 465, 467 ; 
Chara, 433 ; Fern, 447 ; Hy- 
dra, 344, 345, 356 ; Protococ- 
cus, 389 ; Spirogyra, 397 ; Vor- 
ticella, 362 

Chloroplastid, Hydra, 356 (see 
also Chromatophore) 

Chondro-cranium, 12, 63 

Choroid, coat, 33, 117, 300; 
plexus, 27, 100 

Chromatophore, Protococus, 389, 
391, 393; Spirogyra, 397, 404 

Cilia, Bacteria, 408; Chara, 434.; 
Fern, 450; Protococcus, 391, 

394 
Ciliary action, Frog, 124; Vorti- 

cella, 366 

Ciliated groove, 322, 338 
Circulation, Crayfish, 182 ; Frog, 

19, 92 


Circulatory system, Crayfish, 180, 
222; Earthworm, 244, 259; 
Frog, 16, 80 ; Mussel, 309, 325; 
Snail, 275, 292 

Circulus venosus pulmonis, 295 

Circum-neural arcade, 265 

Circum-cesophageal vessels, 245, 
259, 260 

Clavicle, 69 

Clitellum, 245, 248 

Cloaca, Frog, 2, 10, 47 ; orifice of 
in Tadpole, 163, 165 

Cnidoblast, 346, 355 

Cnidocil, 346, 355 

Cocoon, 247 

Cochlea, 33 

Collateral bundle, 463 

COLOURLESS BLOOD CORPUSCLE, 
122, 369, 372, 375 

Columella, Mucor, 42 r ; Snail, 
282 ; auris, 33, 34, 60, 65, 119 

Commissures, ant, oesophageal, 
229; buccal, 298; cerebro- 
pedal, Mussel, 330, 339; Snail, 
297 ; cerebro-splanchnic, Mus- 
sel, 329, 330, 336; Snail, 297; 
circum -oesophageal, Crayfish, 
227; Earthworm, 262 ; of brain, 
Frog, 26, 101 ; inter-cerebral, 
Mussel, 330, 339 ; lateral neural, 
261 ; longitudinal ventral, Cray- 
fish, 184, 227 ; Earthworm, 
263 ; maxillo - palatine, 106 ; 
median ventral, 229 ; post-ceso- 
phageal, 229 

Concentric bundle, 446 

Condylar facet, 56 

Confervoid algce, 396 

Conidium, 417, 419, 426 

Conidiophore, 417, 419, 426 

Conifers, 466 

Conjugation, Amoeba, 373 ; Mu- 
cor, 423 ; Spirogyra, 400, 406 ; 
Vorticella, 363 

Conjunctiva, 44 

Connective rod, 185, 234 

Connective tissue, histology of, 
126 

Coracoid, 69 


502 INDEX. 

Cornea, 117, 185, 300; facets of, 


Corolla, 460, 476 

Corpora adiposa, 40, 54 

Corpus callosum, 26, 101 

Corpuscula, 466 

Cortex, 462, 465, 472 

Cortical layer, Chara, 430, 432 

Cotlntrnia, 368 

Cotyledon, 461, 480 

Coxopodite, 195 

Cranium, 63 

CRAYFISH, 173 239 

Crop, Earthworm, 241, 254; 
Snail, 274, 284 

Crystalline cone, 185, 233, 234, 
lens, 117; Snail, 300, develop- 
ment of, in Frog, 1 72 

Crystals, Amceba, 372, Hydra, 353 

Cutaneous glands, 34, 146, 14-8; 
Earthworm, 243, 265 

Cuticle, Crayfish, 189 ; Earth- 
worm, 241, 251 ; Hydra, 353 ; 
Vorticella, 360, 364 

Cuticularized cell- wall, 401, 407 

Cyclas, 331 

D. 

DACTYLOPODITE, 196 

Dart, 277, 292 ; sac, 291, 292 

Dentary, 62 

Dennis, 146, 147 

Development, Crayfish, 187, 235 ; 

Earthworm, 247 ; Frog, 5, 157; 

Hydra, 344 ; Lobster, 238 ; 

Mussel, 312, 340; Snail, 278, 

302 

Diaphragm, 43 
Dicotyledons, 464 
Digestion, Amosba, 371 : Cray- 
fish, 179; Earthworm, 242; 

Hydra, 343, 357 
Digestive gland, Crayfish, 179, 

207, 209, 215; Earthworm, 242 ; 

Mussel, 311, 320; Snail, 285; 

development of, 303 
Digitate gland, 292 
Disc, 364 


Ductus arteriosus, 89; Botalli, 89 
Duodenum, 45, 46 
Dura Mater, 96 

E. 

EAR (see Auditory organ) 
EARTHWORM, 240271 
Ecdysis, 189 

Ectoderm, 236, 303; Hydra, 344; 
^ histology of, 351, 352, 353 
Ectoplasm, 124 

Ectosarc, Amceba, 370, 374; Vor- 
ticella, 360, 364 

Efferent branchial vessels, Cray- 
fish, 222; Mussel, 327 
Egg- apparatus, 479 
Egg-capsule, 235 
Elodea, 442 
Embryo, Bean, 461, 480; Fern, 

45i 
Embryo-cells, 5, 158 

Embryonic layers, 165 

Embryo-sac, 461, 466, 478 

Encephalon, (see Brain) 

Encystment, Amceba, 369 ; Vorti- 
cella, 363 

Endoderm, 236, 303; Hydra, 344 
histology of, 351, 352, 353, 355 

Endolymph, 33 

Endophragmal system, 189, 201 

Endoplasm, 124 

Endoplast (see Nucleus) 

Endopleurite, 194 

Endopodite, 177, 193, 239 

Endosarc, Amoeba, 370, 374; 
Vorticella, 360, 364 

Endoskeleton, Frog, n, 55 ; Snail, 
274 

Endosperm, 466, 479 

Endosternite, 194 

Endotergite, 194 

Epiblast, 166, 187 

F.pidermis, Bean, 462, 473 ; Earth- 
worm, 245, 265; blood plexus 
of, 245; Fern, 445, 447, 453; 
Frog, 121, 146 

Epiglottis, 49 

Epimeron, 192, 194 


INDEX. 


503 


Epiostracum, 203, 333 

Kpiphragm (see Hybernaculum) 

Epipodite, 177, 183, 221 

Epistylis, 368 

Epithelium, 124 

friirotinm, 419 

Eustachian recess, 9, 48 

Excretory organ, Crayfish, 183; 

Earthworm, 244 ; Frog (see 

Kidney); Mussel (see Organ of 

Bojanus); Snail, 275, 283; ori- 

^ fice, Mussel, 323, 335 

Exoccipital, 60, 63, 65 

Exopodite, 177, 193, 238 

Exoskeleton, Crayfish, 173, 189, 
191; Earthworm (see Cuticle); 
Frog, ii ; Mussel, 331, 335; 
Snail, 274, 281; histology of, 
Crayfish, 202; Mussel, 333 

External characters, Crayfish, 173, 
190; Earthworm, 240, 248; 
Frog, i, 6, 35; Hydra, 342, 
348; Mussel, 305, 314; Snail, 
272, 280 

Eye, Crayfish, 184, 233; Frog, 2, 
36, 44, 112; Snail, 273, 299 

Eyelids, 2, 3, 36, 44, 112 

Eyespot, 304 

Eye-stalk (see Ophthalmite) 


F. 


FALCIFORM ligament, 43, 44 

Fa t 379 

Fat bodies (see Corpora adiposa) 

Fenestra ovalis, 34, 65 
Fermentation, Bacteria, 410; Mu- 

cor, 424; Yeast, 377, 382, 388 
Fern, 443459 
Fertilization, Bean, 480; Chara, 

Fern (see Impregnation) ; Frog, 

4; Mussel, 312; Snail, 277 
Fibula, 72 
Filament, 460, 477 
Filum terminale, 30, 96 
Flagellum (see Spermatophoral 

gland) 

Flower, 460, 476 
Flowering plant, 460 481. 


Follicular epithelium, Crayfish, 

220, Frog, 155 
Fontanelles, 12 63 
Food yolk, Crayfish and Frog, 187, 

235 
Foot, Fern, 450, 459; Hydra, 348; 

histology of, 346 ; Mussel, 334 ; 

Snail, 273, 280; development 

of, 304 
Foramen magnum, 59 ; of Munro, 

26, 100, 101 
Foramina for exit of cranial nerves, 

66 

Fourth ventricle, 100 
Fragmentation of nucleus, 437 
FRESHWATER POLYPES, 342 358 
FROG, i 172 
Fronto-parietal, 60 
Fungi, 382, 416 
Funiculus, 479 

G. 

GALL bladder, 45, 47 

Ganglion, abdominal, 227; cere- 
bral, Mussel, 330, 339; Gas- 
serian, 28, 105; parieto-splanch- 
nic, Mussel, 312, 329, 338; Snail, 
276, 297; pedal, Mussel, 312, 
339; Snail, 276, 296; spinal, 
102; suboesophageal, Crayfish, 
184, 228; supra oesophageal, 
Crayfish, 184, 227; Earthworm, 
246, 262; Snail, 276, 296; 
sympathetic, 107; thoracic, 228; 
visceral, 331 

Gastrolith, 210 

Gastrula, 187, 236, 247, 278, 302 

Gemmation, 362, 380 

Genital cloaca, 276, 291 

Genital duct, Crayfish, 206; 250; 
Frog, 40, 53; Mussel, 336; 
Snail, 276 

Genital furrow, 281 

Genital gland, Crayfish, 206; Frog, 
4 o, 42, 53; Mussel, 336; Snail, 
276, 301 

Germinal epithelium, Frog, 155; 
Earthworm, 270; spots, Cray- 


504 


INDEX. 


fish, 219; Mussel, 340; vesicle, 

Crayfish, 219; Earthworm, 270; 

Frog, 24, 155; Mussel, 340; 

Snail, 302 
Germination, Bean, 461 ; Chara, 

435 1 F ? rn > 4495 Mucor, 423; 

Penicillium, 41 7, 426; Spirogyra, 

401 

Gills (see Branchice) 
Girdle-bone (see Sphenethmoid) 
Gizzard, 241, 255 
Glenoid fossa, 68 
Glochidiuin, 313, 340 
Glottis, 9, 21, 49 
Glycerine, 383 
Glycogen, 151, 311, 329 
Green gland, 183, 207, 216 
Ground parenchyma, 445 
Growing point, Bean, 462; Chara, 

432; Fern, 448 
Guard-cells, 448, 473 
Gullet, Crayfish, 210; Mussel, 320 
Gustatory organ, 110 
GymnosperniS) 464 


H. 

H&matococcuSi 389 

Harderian gland, 33, 114 

Head segment, 273 

Heart, Crayfish, 180, 181, 206, 

223; Frog, 17, 40, 43, 80, 89; 

Mussel, 310, 324, 337; Snail, 

275, 284 
Hehx aspersa, II. hortensis, 272 

304 

Helleborus, 481 
Hepato-pancreas, 180 
Hermaphrodite duct, 276, 289; 

gland (see Ovotestis) 
Hilum, 479 
Hip-girdle, 71 

J-fomants vulgaris, 173 239 
Humerus, 69 
Hybernaculum, 272, 282 
Hydra fusca, viridis^ 342 358, 

liexactinella, 342 
Hydrogen, 379, 403 


Hyoid, 9, 14, 49, 67 

Hyphoe, 416, 419, 420 

Hypoblast, 167, 187 

Hypoderma, 445 

Hypodermis, Worm, (see Epider- 

mis) 
Hypostome, 343, 348 ; histology 


353 


I. 


ILEUM, 45, 46 

Ilium, 72 

Impregnation, Bean, 461; Chara, 
434 ; Crayfish, 235 ; Earth- 
worm, 247; Fern, 450; Hydra, 

344 

Indusium, 444, 456 
Infra-branchial chamber, 316 
Infundibulum, 26, 99, 101 

Infusoria, 359 

Integument, Crayfish, 204; Frog, 
34 (see also Skin) 

Inter-articular membrane, 201 

Intercellular passages, 448, 475 

Internal ear, 119 

Internodal cell, Chara, 432 

Internode, Bean, 460; Chara, 430; 
Fern, 444 

Inter-ocular gland (see Brow- 
spot) 

Interstitial tissue, 352; histology 

of, 354 

Inter- vertebral foramina, 57 
Intestinal valve, Earthworm, 242, 

255; Mussel, 321; Frog, 15, 46 
Intestine, Crayfish, 179, 208; 

Earthworm, 242, 254; Frog, 39; 

Mussel, 320; Snail, 274, 286; 

Tadpole, 163 ; histology of, 

Earthworm, 264; Frog, 148 
Intra- vertebral bodies, 12, 58 
Iris, 113 
Iron, 403 
Ischiopodite, 196 
Ischium, 72 
Iter, 100 


INDEX. 


505 


K. 

KEBER'S organ, 319, 334 
Kidney, 22, 40, 41 ; histology of, 

151 
Kleinenberg's fibres, 352, 353 

L. 

LABIAL cartilages, 64 
Labial palpi, 307, 316, 321, 338 
Labrum, 175, 176, 202; develop- 
ment of, 237 

Lamina terminalis, 99, 100 
Large intestine, 10, 15, 39, 41 
Laryngo-tracheal cartilage, 21, 51 
Larynx, 21, 49, 51 
Lateral intestinal vessels, 261 
Lateral neural vessels, 259 
Lateral cesophageal trunks, 245, 

260 

Lateral roots, 465, 471 
Lateral ventricle, 100 
Leaf, Bean, 460, 462, 465, 474; 
Chara, 430, 431, 437; Fern, 

443> 455 
Leaflets, Bean, 462, 474; Chara, 

436; Fern, 443 
Lenin a, 471 
Lesser omentum, 43 
Ligament, of shell, 306, 332, 335 
Ligamentum la turn, 43 
Lily, 477, 478, 481 
Limb-girdle, 14, 55, 68 
Limbs, Frog, 2, 36; development 

of 163, 164; Crayfish, 175 
Lingual ribbon (see Radula) 
Liver, 16, 39, 43, 47 ; histology of, 

150 

LOBSTER, 173 239 

Lower layer cells, 158, 159, 166 
Lumbo-sacral plexus, 103 
Lutnbricus terrestris, 240 271 
Lungs, 21, 39, 43, 46, 50; deve- 
lopment of, 164 
Lymph, 16 
Lymph-cavities, subcutaneous, 37, 

44' 45 

Lymph-hearts, 17, 94 


Lymph sinus, circum -cesophageal, 

94; sub-vertebral, 8, 16, 42 
Lymph stomata, j 26 

M. 

MACROZOOSPORE, 391, 393 

Magnesium, 379, 403 

Mandible, Frog, 9, 62 ; Crayfish, 
200 

Mantle, 305, 307, 316, 328, 334; 
development of, 340 

Manubrium, 433 

Manus, 2 

Marginal sinus, 295 

Maxilla, Crayfish, 175, 199, 213; 
Frog, 9, 6 1 

Maxillipede, 175, 196, 197, 199 

Mayer's solution, 386 

Meckel's cartilage, 13, 67 

Medulla oblongata, 98 

Medullary rays, 463, 473 

Membrana propria, 220 

Membrane bones, 63 

Membranous labyrinth, 33, 119, 
1 20 

Mento-Meckelian bone, 62, 67 

Meristem, 455, 462, 464 

Meropodite, 196 

Mesencephalon, 98 

Mesenteric septa, 243, 252, 265 

Mesenteron (see Archenteron) 

Mesentery, 8, 39, 42 

Mesoarium, 42 

Mesoblast, Earthworm, 247; Frog, 
167, 169, 170 

Mesoglcea, 347, 352, 356 

Mesophyll, 456, 465 

Mesorchium, 42 

Metabolism, 381 

Metacarpals, 70 

Metastoma, 175, 176, 202, 213 

Metatarsals, 73 

Metencephalon, 98 

Micrococcus, 413 

Micropyle, Bean, 461, 478; Mus- 
sel, 312, 339 

Microzoospore, 391, 394 

Moncecious conjugation, 401 


5o6 


INDEX. 


MOULDS, 415 429 

Mouth, Crayfish, 175, 202; Earth- 
worm, 249; Frog, 9, 44, 48; 
Hydra, 343, 348; Mussel, 306, 
3 T 7> 3 2 i> 33 8 ; Snail, 274, 281; 
Tadpole, 161, 163. 

Mttcor, 420; Torula of, 424 

Multinucleate cells, 417 

Multipolar nerve-cell, 141 

Muscles, abdominal, Crayfish, 205, 
207 ; adductor, Mussel, 306, 
315, 337; anal, 215; of body 
wall, Earthworm, 265 ; of buc- 
cal mass, 286 : columellar, 282 ; 
constrictor laryngis, 50 ; of eye, 
33, 113; of eyestalk, 233; of 
hind limb, Frog, 74 80 ; of 
hyoid, 50 ; limb, Crayfish, 204 ; 
mandibular, 205, 207; mylo- 
hyoid, 37; oblique of trunk, 38; 
pallial, 315; pectoral, 37; pe- 
dal, Mussel, 315, 339; of seta, 
Earthworm, 266; of stomach, 
Crayfish, 178, 213; transver- 
salis, 38 

Muscle, histology, striped, 133; 
unstriped, 132; physiology, 156 

Muscular system, Crayfish, 204; 
Frog, 24 

MUSSEL. 305 341 

Mycelium, 416, 422, 425 

Myelon (see Spinal cord) 

Myophan layer, 364 


N. 

NARES, 2, 9, 48, in 

Nasal, 60 

Nematocysts, 344, 346, 350 ; his- 
tology and development of, 354 

Nephridium (see Segmental organ), 
blood plexus of, 258 

Nephrostome, Earthworm, 244, 
256, 257 ; Frog, 54 

Nerve, histology of, Crayfish, 229 ; 
Earthworm, 264; Frog, 136; 
physiology, 156 

Nerve-cells, Crayfish, 230; Earth- 


worm, 246, 264, Frog, 139; 
Hydra, 346, 355 

Nerves, ist Cranial (olfactory) 27, 
105; 2nd Cranial (optic) 27, 
105 ; 3rd Cranial (oculomotor) 
27, 105, 114, 116; 4th Cranial 
(pathetic), 28, 114, 116; 5th 
Cranial (trigeminal), 28, 105 ; 
6th Cranial (abducent) 29, 115, 
116; 7th Cranial (facial), 29, 106, 
109; 8th Cranial (auditory), 29, 

107 ; 9th Cranial (glossopharyn- 
geal), 30, 104, 106; loth Cranial 
( vagus or pneumogastric), 30, 106, 
108 ; antennary, 228; anten- 
nulary, 228; buccal, 276, 298; 
ganglionic, Earthworm, 263, 
Crayfish, 227; hypoglossal, 31, 
103; interganglionic, Earth- 
worm, 263 ; Crayfish, 227; la- 
bial, Snail, 299 ; maxillo-man- 
dibular, 105; ophthalmic, 105; 
optic, Crayfish, 228 ; Snail, 300; 
pallial, Mussel, 329 ; Snail, 297 ; 
palatine, 106; recurrent laryn- 
geal, no; spinal, 31, 96, 102; 
splanchnic, 107, no; sympa- 
thetic, 32, 107 ; tentacular, 
299 ; vaso-motor, 108 ; visceral, 
Crayfish, 229; Earthworm, 263 ; 
Snail, 297, 298 ; viscero-motor, 

1 08 

Nervous system, Crayfish, 184, 
227; Earthworm, 246, 262; 
Frog, 10, 24, 95 ; Mussel, 312; 
Snail, 276, 296; sheath of, 
Earthworm, 263; Snail, 296 

Nettle, 442 

Neural arch, 56; canal, 56, 59; 
cavity, 10, 41 ; folds and plate, 
160, 168 

Neurochord, 246, 263 

Neurosensiferous apparatus, Hy- 
dra, 346 

Nitella, 436, 440 

Nitrogen, 379, 403 

Nodal cell, 432 

Node, Bean, 460, 473 ; Chara, 
430 ; Fern, 444 


INDEX. 


SO/ 


Ts T otochord, 12, 168, 170 

Nucellus, 460, 478 

Nucleolus, 123, 389, 393, 399 

Nucleus, 122 ; Amceba, 370; Bean, 
461 ; Chara, 433, 434 ; Fern, 
444; Mucor, 421; Penicillium, 
417; Protococcus, 389, 391, 
393 ; Spirogyra, 398, 404 ; Vor- 
ticella, 362, 365; Yeast, 379 

Nyciothcrus, 368 

O. 

OCCIPITAL condyle, 59 

Odontoid process, 56 

Odontophore, 274, 287, 288 

(Enothera, 480 

(Esophageal glands (see Calcifer- 
ous glands) 

(Esophagus, Earthworm, 254, 255; 
Frog, 43; Snail, 274, 285 (see 
also Gullet) 

Oil, 407 

Olfactory capsule, 64 ; epithelium, 
144; lobe, 97; organ, Crayfish, 
184, 232, Frog, 32, in ; ven- 
tricle, 100 

Omosternum, 69 

Oogonium, Chara, 431, 434, 439 

Oosphere, 450, 461 (see also 
Ovum) 

Oospore, 434 

Opercular membrane, 6, 162; de- 
velopment of, 163, 171 

Ophthalmite, 176, 201 

Optic bulb, 233, 234 ; chiasma, 
99; cup, 172; lobes, 25, 98; 
pit, 237; stalk, 172; thalami, 
26, 98 ; tract, 99; ventricle, 100 

Organ of Bojanus, 311, 322, 335, 

337 
Os cruris, 72 

Ossicles, Crayfish stomach, 178, 
208, 210 

Otocyst, 300, 331 

Otolith, Crayfish, 231; Cyclas, 
331 ; Frog, 120; Snail, 300 

Ovary, Crayfish, 186, 218; Earth- 
worm, 269 ; Flowering plant, 


478; Frog, 23, 40, 52, 154; 
Hydra, 344, 357; Lobster, 219 

Oviduct, Crayfish, 218; Earth- 
worm, 269; Frog, 23, 40, 53, 
54; Snail, 290, 292 

Ovisac, 219 

Ovotestis, 276, 285, 289 

Ovule, 460, 478 

Ovum, Bean, 46 r, 466, 4795 
Chara, 434; Crayfish, 2 19; Earth- 
worm, 246, 270 ; Fern, 450, 
459; Frog, 5, 24, 154; Hydra, 
344, 357! Mussel, 312, 339; 
Snail, 277, 302 

Oxygen, 379, 390, 403 


P. 


PALATINE, 61 

Palato-quadrate cartilage, 63 

Palisade parenchyma, 465, 475 

Pallium (see Mantle) 

Pancreas, 45 ; ducts of, 47 ; his- 
tology of, 149 

Papilla?, of tongue, 34, ITI 

Parasphenoid, 61 

Parenchyma, 453, 454 

Pasteur's solution, 380, 384 

Pectoral arch (see Shoulder girdle) 

Pedal gland, 273, 281, 288; sinus, 
289, 294 

Peduncle, 476 

Pelvic arch (see Hip girdle) 

Penicillium, 416 

Pericardium, Crayfish, 182, 222 ; 
Frog, 8, 40, 43; Mussel; 310, 
3i9> 335> 3375 Snail, 275, 284 

Periganglionic glands, 32, 103 

Peri lymph, 34, 119 

Periotic capsule (see Auditory 
capsule) 

Peristome, 360, 364 

Peristomium, 249 

Peritoneal pores, 244, 250 

Peritoneum, Frog, 4 2 ; Earth- 
worm, 243, 266 

Peritreme, 282 

Perivisceral fluid, 244, 253 

Pes, 3 


508 


INDEX. 


Petal, 476 

Petiole, 462, 474 

Phalanges, manus, 70; pes, 73 

Pharynx, Earthworm, 241, 253, 

255; Frog, 5 
Phloem, Bean, 463, 472; Fern, 

446, 448, 449, 453 
Phloem-sheath. 447, 453 
Phosphorus, 379, 403 
Photometric Zoospores, 395 
Pia mater, 27, 96 
Pineal gland, 26 
Pinnule, 443, 447 
Pistil, 460, 478 
Pith, 462, 472 
Pits, 446, 472 
Pitted vessels, 464, 473 
Pituitary body, 26, 99 
Plasmolysis, 397 
Pleomorphic Bacteria, 411 
Pleurobranchire, 221 
PLEUROCOCCUS, 389 
Pleuron, 192 
Pleuroperitoneal cavity, 7, 39, 41; 

membrane, 8, 42, 43 
Plexus, brachial, 31 ; epidermal, 

245; excretory, 261; lumbo- 

sacral, 31, 103 
Plumule, 461, 480 
Pod, 461 

Podobranchire, 220 
Polar plate, 1 39 
Pollen, 460, 465, 477 
Pollen-sac, 465, 477; tube, 461, 

480 

Pollinodium, 420 
Pore-canals, Crayfish, 203 ; Mus- 
sel, 341 

Posterior commissure, 101 
Potassium, 379 
Pre-hallux (see Calcar) 
Pre-maxilla, 9, 60 
Pre-nasal process, 13, 64 
Primine, 478 
Primordial cell, 391 
Primordial utricle, 397, 404, 417, 

433 
Procephalic process, 202 

Processus spiralis, 140 


Pro-embryo, 435 

Pro-otic, 60 

Propodite, 196 

Pro-renal duct (see Segmcntal 
duct) 

Prosencephalon, 97 

Prostate, 290 

Prostomium, 249 

Protein, 379, 390, 467 

Proteus animalcule, 369 376 

Prothallus, 450, 457, 466 

PROTOCOCCUS, 389 395 

Protophloem, 447, 454 

Protoplasm, 379 

Protoplasmic movement, Anacha- 
ris, 442 ; Chara, 440 ; Nettle- 
hair, 442; Tradescantia, 441; 
Vallisneria, 442 

Protopodite, 177, 193, 239 

Protoxylem, 446, 454, 472 

Pseudo-hearts (see Circum-ceso- 
phageal vessels) 

Pseudopodia, 122, 370, 374 

Pteris, 443459 
Pterygoid, 61 
Pubis, 71 

Pulmonary sac, 274, 282 
Putrefaction, 410 
Pylangium, 18 
Pylorus, 15, 46 
Pyrenoid, 398, 404 

Q- 

QUADRATE, 65 
Quadrato-jugal, 61 

R. 

RACHIS, 288 

Radial bundle, 465 

Radicle, 461, 480 

Radius, 70 

Radula, 287 ; sac of, 285 

Rana esculenta temporaria, i- 

172 

Receptaculum ovorum, 269 
Receptaculum seminis, 292 
Rectum, Mussel, 337 ; Snail, 283 


INDEX. 


509 


Renal organs (see Excretory organ 
and Kidney) 

Renal vessels, Snail, 295 

Reno-pericardial aperture ; Mus- 
sel, 324, 335; duct, Snail, 275, 
281 

Reproduction, Amoeba, 373 ; Cray- 
fish, 187; Earthworm, 2 47 ; Frog, 
5 ; Hydra, 343 ; Mucor, 423 ; 
Mussel, 312 ; Snail, 277; Spiro- 
gyra, 400, 406 ; Vorticella, 362 

Reproductive organs, Bean, 465 ; 
Chara, 433 ; Crayfish, 186, 217 ; 
Earthworm, 246, 268; Eurotium, 
419 ; Fern, 449, 456, 458 ; Frog, 
23,51; Hydra, 349, 357; Mu- 
cor, 421, 423 ; Mussel, 312, 320 ; 
Penicillium, 419 ; Snail, 276, 289 

Respiration, Bean, 469 ; Crayfish, 
183 ; Earthworm; 245 ; Frog, 3, 
22; Mussel, 308; Snail, 275; 
Yeast, 383 

Respiratory organs, Crayfish, 182, 
207, 221; Frog, 21, 48; Mussel, 
307, 322 ; Snail, 275, 282 

Restiform body, 25 

Retina, 33, 118; development of, 
172 ; histology of, 141 

Rhinal process, 13, 64 

Rhinencephalon, 97 

Rhizoid, 431 

Rhizome, 443 

Root, Bean, 460, 465, 470 ; Fern, 
448, 452, 456 

Root-cap, 448, 462, 471 

Root-filaments, Chara, 430 

Root-hairs, 448, 449, 458, 465 

Root-pressure, 469 

Rostrum, 190, 238 


S. 


SAC (see Cell-wall) 

Saccharomyces, 377 388 

Sacculus, 33, 1 20 

Sacrum, 57 

Salivary duct, Snail, 285, 288 ; 

gland, Earthworm, 242 ; Snail, 

285 


Scalariform vessels, 446, 455 

vScaphognathite, 174, 182 

Scapula, 69 

Sch izomycetes, 408 4 1 4 

Sclerenchyma, 446, 453, 454, 472 

Sclerotic, 33, 117 

Secondary thickening, 464 

Secundine, 478 

Seed, 479 

Segmental duct, 169; organ, 244, 

5 r 2 5 2 > 2 56 

Segmentation, cavity, 166 ; of 
ovum, Crayfish, 187, 235 ; 
Earthworm, 247; Frog, 5, 158, 
165; Mussel, 312; Snail, 278, 


Selaginella, 466 

Seminal receptacle (see Sperma- 

theca) ; vesicle, 246, 268 
Sense-organs, Earthworm, 246 ; 

Hydra (see Cnidocil) 
Sepal, 476 

Septum narium, 13, 66, nr 
Seta, Crayfish, 203 ; Earthworm, 

241, 249, 251, 266; sac of, 251, 

266 
Sex-organs (see Reproductive 

organs) 

vSexual generation, Fern, 457 
Sexual reproduction, 400, 402, 

4!9 4' 2 3 

Shell (see Exoskeleton) 

Shell-teeth, 340 

Shoulder-girdle, 68 

Sieve-tubes, Bean, 464, 469, 473 ; 

Fern, 447, 454, 455 
Sinus venosus, 17, 81, 90 
Siphonal tentacles, 317 
Siphons, 307, 317 
Skeleton, Crayfish, 173, 189; Frog, 

JI > 55 

Skin, Frog, histology of, 145 
Skull, 12 

Small intestine, 10, 15, 39, 45 
SNAIL, 272 304 
Somite, 174, 177, 240, 248 
Sooty corpuscles, 356 
Sorus, 444 
Spermatheca, 250, 268, 292 


5io 


INDEX. 


Spermatophoral gland, 217, 291 
Spermatophore, Crayfish, 235 ; 

Snail, 277 

Spermatozoid, Chara, 434, 440 ; 
Crayfish, 218; Earthworm, 246, 
Fern, 450, 458; Frog, 23, 154; 
Hydra, 344, 357; Mussel, 312; 
Snail, 277, 301 ; development 
of, 270 

Sperm -capsule, 235 
Sphenethmoid, 61, 63, 66 
Spiculum amoris (see Dart) 
Spinal cord, n, 25, 30, 96 ; histo- 

logy of, 140 
Spinous process, 56 
Spiral vessel, 446, 455, 464, 473 
Spirillum, 408, 413 
Spirochcete, 413 
SPIROGYKA, 396 407 
Splanchnic cavity (see Pleuro- 

peritoneal cavity) 
Spleen, 16, 40 

Spongy parenchyma, 465, 475 
Sporangium, Fern, 444, 449, 456; 

Mucor, 420, 427 

Spore, Bacteria, 409 ; Fern, 444, 
449, 457; Mucor, 421, 428; 
Penicillium, 417; Yeast, 380, 
386 

Squamosal, 60 
Stamen, 460, 477 
Starch, 389, 398, 402, 433, 445 
Stem, Bean, 460, 47 i ; Chara, 430, 

436; Fern, 443 
Sternal sinus, 226 
Sternum, 192, 194 
Stigma, 460 
Stipule, 474 
Stoma, Bean, 462, 464, 473 ; Fern, 

448, 456 

Stomach, Crayfish, 178, 208; 
Fl "og, 15. 39' 46; Mussel, 320, 
_ 338 ; Snail, 285 
Stomatodaeum, 171, 303 
STONEWORTS, 430 441 
Stratification, 404 
Striated spindle, 185, 233, 234 
Style, 460, 478 
Sub-intestinal vessel, 245, 260 


Sub-neural vessel, 245, 260 

Sub-ocular arch, 63, 64 

Sub-tentacular lobe, 279 

Succinic acid, 383 

Suckers, 160, 162 

Sulphur, 379, 403 

Supporting lamella (see Meso- 

gloea) 
Supra-branchial chamber, 307,318, 

337 
Supra-ilium, 72 

Supra-intestinal vessel, 245, 259, 

260 

Supra-neural vessel, 245, 259 
Supra-scapula, 69 
Suspensorium, 13, 64, 65 
Swimmerets, 192 
Synangium, 18 
Synergidte, 479 

T, 

TADPOLE, 5, 162 

Tail, 162, 165 

Tail fin, 162 

Tarsus, 73 

Teeth, Cray fish stomach, 178, 211, 
2 [2; Frog, 9, 15, 48 

Telson, 174, 190, 194 

Tendon, 74, 189 

Tendril, 474 

Tentacles, Hydra, 342, 348; de- 
velopment of, 351 ; histology of, 
349, 352 ; Snail, 273, 280, 299 

Terguin, 192, 194 

Testa, 479 

Testis, Crayfish, 217 ; Earthworm, 
269 ; Frog, 23, 40, 53 ; histology, 
153; Hydra, 357; Mussel, 312 

Thalamencephalon, 25, 98 

Thoraco-abdominal linkwork, 202 

Thorax, 174 

Thread cells (see Nematocysts) 

Thymus, 24 

Thyroid, 24 

Tibia, 72 

Tongue, 9, 34, 44, 49 

Torula, 377388 

Tradescantidi 44 1 


INDEX. 


Transverse process, 56 
Trochal ridge, 279, 303 
Trochosphere, -279, 303 
Truncus arteriosus, 17, 19, Si, 91 
Tuber cinereum, 99 
Tubular fibres (see Neurochord) 
Tympanic cavity, 9, 33 ; mem- 
brane, 2, 9, 33 
Typhlosole (see Intestinal valve) 

U. 

ULNA, 70 

Umbilicus, 282 

Umbo, 332 

Uncini, 288 

Unguis, 477 

Unio, 305 

Unipolar nerve-cell, 139 

Upper layer cells, 158, 159, 166 

Ureter, 48 

Urinary bladder (see Urocyst) 

Urino-genital duct, 48, 52, 54; 

organs, 51 
Urocyst, 23, 39 
[Jrostyle, 12, 55, 58, 59 
Utriculus, 33, 120 

V. 

VACUOLE, Chara, 437,438 ; Mucor, 
421, 428 ; Penicillium, 417, 425, 
426 ; Protococcus, 393 ; Spiro- 

gyra, 397' 3Q8> 44 ; Trades- 

cantia, 441 ; Yeast, 378, 384 
Vallisneria, 442 
Valves, of heart, Crayfish, 223; 

Frog, 18; Mussel, 325, 337; 

Snail, 293 
Valves, of stomach, Crayfish, 211, 

212 ; of shell (see Exoskeleton) 
Vasa efferentia, 23, 54 
Vascular bundle, Bean, 463 ; Fern, 

446 453 

Vasdeferens, Crayfish, 217; Earth- 
worm, 268; Frog, 23 ; Snail, 291 

Vein, afferent hepatic, 82 ; afferent 
renal, 20, 83 ; anterior abdo- 
minal, 20, 37, 38, 44, 82 ; ax- 


illary, 85 ; cystic, 82 ; dorso- 
lumbar, 83 ; duodenal, 88 ; 
efferent hepatic, 20, 84 ; effer- 
ent renal, 20, 84 ; epigastric, 82 ; 
external jugular, 84; femoral, 
83 ; gastric, 88; genital, 20, 84; 
great cutaneous, 20, 37, 85 ; 
hasmorrhoidal, 88 ; hepatic-por- 
tal, 20, 82, 87 ; inferior cava, 

17, 20; innominate, 85; in- 
ternal jugular, 85 ; lieno-intesti- 
nal, 88 ; lingual, 84 ; oviducal, 
83 ; pelvic, 82 ; posterior car- 
dinal, 169; pulmonary, Frog, 

18, 21, 85; Snail, 292; renal 
portal, 20, 83, 89 ; sciatic, 83 ; 
subclavian, 85 : superior cava, 
17, 20; superior mesenteric, 88; 
vesical, 82 

Veliger, 279, 304 

Velum, 279, 304 

Venous system, Crayfish, 181 ; 
Frog, 20; Mussel, 328; Snail. 
294 

Ventricle, Frog, 17, 81, 91 ; Mus- 
sel, 324 ; Snail, 275 

Ventricles of brain, 26, 100 

Veronica, 480 

Vertebral body (see Centrum) 

Vertebral column, u, 55 

Vesicle, contractile, Arnceba, 370, 
374 ; Vorticella, 361, 365 ; of 
egestion, Amoeba, 371 ; Vorti- 
cella, 362; ofingestion, Amoeba, 
371 ; Vorticella, 362 

Vesicula seminalis, 52 

Vessel, Bean, 464 ; Fern, 446, 455 

Vestibulum, 360, 364 

Vexillum, 476 

Vibrio, 409, 413 

Vicia, 460 481 

Visceral arch, 160, 161, 164, 170; 
cleft, 164, 171; pouch, 170, 171; 
sac, 273 

Visual organ (see Eye) 

Vitellus, 24, 270 

Vitelline membrane, 155, 220, 270, 

339 

Vitreous humour, 117 


512 INDEX. 

Vocal sac, 9, 51 ; ligament, 21 
Vorticdla, 359, 368 

W. 

WOOD, 446, 454, 463, 472 
Wood-cells, 473 

X. 


Y. 


YEAST, 377388 
Yellow-brown tissue, 242, 243, 2^ 

Z. 

ZONITES, 241, 248 

Zooglcea, 409, 412 
Zoospores, 391, 393 


XlPHISTERNUM, 69 

Xylem, Bean, 463, 464, 473; Zygapophyses, 56 

Fern, 446, 448, 449, 454 Zygospore, Mucor, 423 ; Spiro- 

Xylem-parenchyma, 455 gyra, 401, 407 


<:A.\IHKIL>GE : PRINTED HV c. j. CLAY, M.A. AND SONS, AT THE UNIVERSITY PRESS.