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PRACTICAL INSTRUCTION

IX

ELEMENTARY BIOLOGY

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A COURSE

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PRACTICAL INSTRUCTION

IN

ELEMENTARY BIOLOGY

V.

BY \V-

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T. H. HUXLEY, LL.D., Si-c. R.S.,

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H. N. MARTIN, B.A., M.B., D.Sc.,

I'ROFKSSOR OF BIOLOGY IN JOHNS HOPKINS UNIVERSITY, I'.ALTlMoRK

I-F.LIO\Y OF CHRIST'S COLLEGE, CAMBRIDGE, AND OF

KNIVERSITY COLLEGE, LONDON.

SECOND EDITION, REVISED.

Donbon nub ICcu) york :
MACMILLAN AND CO

1876.

0i

COPYKIGHT, 1876,
BY

H. NEWELL MARTIN.

PREFACE,

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 scien-
tific 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.

M.

vi PREFACE.

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-
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 or-
ganization, 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 condi-
tions 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

PREFACE. vii

to Science Teachers on this occasion, I had the great ad-
vantage of being aided by my friends Dr Foster, F. R.S.,
Prof. Rutherford and Prof. Lankester, F.R.S., whose assist-
ance in getting the laboratory work into practical 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
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 de-
scription 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

Tin PREFACT.

descriptions of the several plants and animals, I am respon-
sible ; but I am indebted for many valuable suggestions and
criticisms from the botanical side to my friend Prof. Thisel-
ton Dyer.

LONDON,

September, 1875.

_.s*-, -Xv

'

T. H. H.

CONTENTS.

V

I.

YEAST.

General characters Fermentation Appearances of yeast under the
microscope Structure of yeast cells Chemical composition Mode of
multiplication Growth in Pasteur's fluid Physiology of yeast La-
boratory work. . . . . . . . p. i 10.

II.

PROTOCOCCUS.

Habitat Histological structure Modes of multiplication Depend-
ence on light Physiology of Protococcus Motile stage Laboratory
work. .......... p. u 16.

III.
PROTEUS ANIMALCULE. COLOURLESS BLOOD CORPUSCLES.

: Habitat Movements Structure Chemical composition
Effects of temperature and electric shocks Encystation COLOUR-
LESS BLOOD CORPUSCLES Movements Structure The influence of
various reagents on them Physiology of Amoeba. Laboratory work.

p. 1724.

IV.

BACTERIA.

Form and structure Movements Spirillum volutans Stationary
stage Zoogloea Growth in Pasteur's fluid Relation to putrefaction
Power of resisting desiccation Laboratory work. . . p. 25 29.

28916

x CONTENTS.

V.

MOULDS.

Fungi Their spores PENICILLIUM Habitat General characters
Form and structure Development MUCOR Habitat Form and
structure Development, asexual and sexual Alternation of generations
Mucor Torula Laboratory work. . . . . p. 30 41.

VI.

STONEWORTS.

Habitat and general characters Development Mode of growth and
microscopic structure Protoplasmic movements Organs of reproduc-
tion Physiology Laboratory work. . . . p. 42 54.

VII.
THE BRACKEN FERN.

Habit Structure, gross and microscopic The various tissues
Mode of growth Development Prothallus Sexual organs Alterna-
tion of generations Laboratory work. . . . . p. 55 69.

VIII.

THE BEAN PLANT.

Habit General structure Development and mode of growth
Sexual organs Homology with the reproductive organs of the Fern
Physiology Laboratory work. . . . . . p. 70 88.

IX.

THE BELL ANIMALCULE.

Habit and distribution Anatomy Movements Contractile vesicle
Ingestion Modes of multiplication Encystation Laboratory work.

p. 8997.

CONTEXTS. xi

X.

FRESH-WATER POLYPES.

Habit and form Naked-eye appearances Mode of feeding Mul-
tiplication Microscopic structure Relationships to simpler plants and
animals Laboratory work p. 98 106.

XL

THE FRESH-WATER MUSSEL.

General structure Respiratory organs Alimentary organs Circu-
latory system Excretory organs Reproductive organs Development
Laboratory work. ....... p. 107 126.

XII.

THE FRESH-WATER CRAYFISH AND THE LOBSTER.

Habitat General structure Appendages Segments Alimentary
canal Circulatory organs Respiratory organs The green glands
Nervous system Sense organs Reproductive organs Development
Laboratory work. ....... p. 127 158.

XIII.

THE FROG.

General characters Development Specific characters of Rana tem-
poraria and R. esculenta The pleuroperitoneal cavity and the alimen-
tary canal The neural canal and the cerebro-spinal axis Objects seen
on transverse sections at various points Comparison with lobster The
skeleton The digestive system The blood and lymph vascular systems
The ductless glands The respiratory organs The urinary organs
The generative organs The nervous system The sense organs La-
boratory work. ........ p. 159 267.

APPENDIX p. 268.

I.

YEAST (Torula or Saccharomyces Cerevisicz).

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
the filter allows the fluid part of the yeast to pass through
into the solution of sugar.

M. I

2 ELEMENTARY BIOLOGY. [CHAP.

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 Toruld] is seen to be a round, or oval,
transparent body, varying in diameter from Tj-gVo tn to
y^Voth of an inch (on the average about 80 1 00 th).

The Torultz 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
tough, but it may be easily burst, when it gives exit to its
contents, which readily diffuse themselves through the sur-

I.] YEAST. 3

rounding fluid. The whole structure is called a 'cell;' the
sac being the ' cell-wall ' and the contents the ' protoplasm.'

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 Torula, 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 Torulcz 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
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 Tortile?
are examined as this process of multiplication is going on, it

I 2

4 ELEMENTARY BIOLOGY. [CHAP.

will be found that they are giving rise to minute buds, which
rapidly grow, assume the size of the parent Torula, and
eventually become detached ; though, generally, not until
they have developed other buds, and these yet others. The
Torn/a thus produced by gemmation, one from the other,
are apt long to adhere together, and thus the heaps and
strings mentioned, as ordinarily occurring in yeast, are pro-
duced. No Torula arises except as the progeny of another;
but, under certain circumstances, multiplication may take
place in another way. The Torula does not throw out a bud,
but its protoplasm divides into (usually) four masses, termed
ascospores, 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. This is multiplication by endogenous
division.

As each of the many millions of Torulcz 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 Torulcz
thus generated, must have been produced in the course of
the operation. Now these products have been manufactured
by the Torulce out of the substances contained in the fluid
in which they float and which constitute 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.

Water (H 2 O).

Sugar (C 12 H 22 O n ).

Ammonium Tartrate (C 4 H 4 (NH 4 ) a O fa .).

Potassium Phosphate (KH 2 PO 4 ).

Calcium Phosphate (Ca 3 P 2 O 8 ).

Magnesium Sulphate (MgSO 4 ).

I.] YEAST. 5

In this fluid the Torula 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 Tonila 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.

The Tonila 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 Tonila is an indubitable plant, for two
reasons. In the first place, its protoplasm is invested by
a continuous cellulose coat, and thus has the distinctive
character of a vegetable cell. Secondly, it possesses the
power of constructing Protein out of such a compound as
Ammonium Tartrate, and this power of manufacturing
Protein is distinctively a vegetable peculiarity. Tonila
then is a plant, but it contains neither starch nor chlorophyll,
it absorbs oxygen and gives off carbonic anhydride, 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 Tonila 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
Tonila different from common yeast.

The fermentation of the sugar is in some way connected
with the living condition of the Torula, and is arrested by all
those conditions which destroy the life of the Tonila and

6 ELEMENTARY BIOLOGY. [CHAP.

prevent its growth and reproduction. The greater part of
the sugar is resolved into Carbonic anhydride and Alcohol,
the elements of which, taken together, 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 Torulce 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 Torula, it can
live in saccharine solutions which contain no free oxygen,
appearing, under these circumstances, to get its oxygen from
the sugar.

It has further been ascertained that Torulcz 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 Torul<z
approaches that of animals.

LABORATORY WORK.

Sow some fresh baker's yeast in Pasteur's fluid 1 with

1 Pasteur's fluid :

Potassium Phosph 20 parts.

Calcium Phosph 2 ,,

Magnesium Sulphate 2 ,,

Ammonium Tartrate 100 ,,

[Cane Sugar 1500 ]

Water 8576

j 0,000 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.

I.] YEAST. 7

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,
Hartnack, No. 4) 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 (-| objective. Hart-
nack, No. 7 or 8, Oc. 3 or 4).

a. Note the size (measure), shape, surface and mode
of union of the cells.

b. Their structure : sac, protoplasm, vacuole.
a. Sac; homogeneous, transparent.

ft. Protoplasm; less transparent; often with a few

clear shining dots in it.

y. Vacuole; sometimes absent ; size, position.
8. 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.

8 ELEMENTARY BIOLOGY. [CHAP.

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. [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.]

8. [Endogenous division : take some dry German yeast ;
suspend 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 asco-
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.

b. 10 per cent, solution of sugar in water.

c. Pasteur's fluid without the sugar.

I.] YEAST. 9

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, "" better,
*V better still, "d" well, and "e" best of all. Note that
bubbles of gas are plentifully evolved from both the so-
lutions which contain sugar.

That any growth at all takes place, in the case of
experiments a and , is due to the fact that the drop of
yeast added contains nutritious material sufficient to provide
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 "*/"; 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.

1 Mayer's solution (with pepsin) =

15 per cent, solution of sugar-candy 20 cc.

Dihydropotassic phosphate o' i grm.

Calcic phosphate o* r grm.

Magnesia sulphate o* i grm.

Pepsin o '23 grm.

io ELEMENTARY BIOLOGY. [CHAP. i.

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
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: redistil this after saturation with
potassic carbonate, and test the distillate for alcohol by
its odour and inflammability, and by the sulphuric acid
and potassic dichromate test.]

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.]

1 The object of the potash is to shield the baryta water from any
carbonic anhydride that may be in the atmosphere.

II.

PROTOCOCCUS (Protococcus pluvialis).

IF the mud w/hich accumulates in roof-gutters, water-
butts, and shallow pools, be collected, it will be found to
contain, among many other organisms, specimens of Pro-
tococcus. In one of the two conditions in which it occurs,
Protococcus is a spheroidal body -gi^- to 10 ^ 00 of an inch in
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 indications of starchy matter are
sometimes to be found in it. Either diffused through it, or
collected in granules, is a red or green colouring matter
(Chlorophyll). Individual Protococci may be either green
or red ; or half green and half red ; or the red and green
colours may coexist in any other proportion.

In addition to the single cells, others are found divided
by partitions, continuous with the cellulose wall, into two or
more portions, and the cells thus produced by fission become
separate, and grow to the size of that form from which they
started. In this manner Protococcus multiplies with very
great rapidity. Multiplication by gemmation in the mode
observed in Torula is said to occur, but is certainly of rare
occurrence.

12 ELEMENTARY BIOLOGY. [CHAP.

The influence of sunlight is an essential condition of the
growth and multiplication of Protococcus ; under that in-
fluence, it decomposes carbonic anhydride, appropriates the
carbon, and sets oxygen free. 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 Tomla and the other
Fungi.

As Protococcus flourishes in rain-water, and rain-water
contains 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 constructing
protein by rearrangement of the elements supplied to it by
their compounds. Torula, on the other hand, is unable to
construct protein matter put 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, which is in
some way related to the chlorophyll.

The still condition of Protococcus, just described, is not
the only state in which it exists. Under certain circum-
stances, a Protococcus becomes actively locomotive. The
protoplasm withdraws itself from the cell- wall at all but two

ii.] PROTOCOCCUS. 13

points, where it protrudes through the wall in the form of
long vibratile filaments or cilia, and by the lashing of these
cilia the cell is propelled with a rolling motion through the
water. The movement of the cilia is so rapid, and their
substance is so transparent and delicate, that they are invisi-
ble until they begin to move slowly, or are treated with
reagents, such as iodine, which colour them.

Not unfrequently the cell-wall eventually vanishes, and
the naked protoplasm of the cell swims about, and may
undergo division and multiplication in this state. Sooner
or later, the locomotive form draws in its cilia, becomes
globular, and, throwing out a cellulose coat, returns to the
resting state.

For reasons similar to those which prove the vegetable
nature of Tomla, Protococcus is a plant, although, in its
locomotive condition, it is 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 Protococcus belongs, give rise, under certain
circumstances, to locomotive bodies propelled by cilia, like
the locomotive Protococcus, so that there is nothing anomalous
in the case of Protococcus.

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 Proto cocci by winds.

i 4 ELEMENTARY BIOLOGY. [CHAP.

LABORATORY WORK.
A. MORPHOLOGY.

a. Resting or stationary Protococcus.

1. 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.

Size ; (measure) very variable.

Form ; more or less spheroidal, with individual
variations.

Structure ; sac protoplasm sometimes a vacuole
sometimes apparently a nucleus. (Compare
Torula, I. A. 2. &)

Colour; generally green sometimes red sometimes
half and half sometimes centre red, periphery
green the colouring matter always in the pro-
toplasm only most frequently diffused, but
sometimes in distinct granules, or oily looking
drops.

2. Note especially the following forms of cell
a. The primitive or normal form.

Roundish cells, with a cellulose sac, and unseg-
mented granular contents. Draw several carefully
to scale. Apply the methods of mechanical and
chemical analysis detailed for Torula. (I. A. 3. 4.
5. 6.) Note that iodine in some cells produces a
blue coloration by its action on the red matter
present. Treat a specimen with strong iodine
solution and then with sulphuric acid (75 per
cent.) : the sac will become stained blue.

n.] PROTOCOCCUS. 15

b. Cells multiplying by fission :

a. Simple fission. The cell elongates, and the
protoplasm divides into two across its longer
axis, and then a partition is formed sub-
dividing the sac; the halves either separate
at once, and each rounds itself off and be-
comes an independent cell ; or one or both
halves again divide, in a similar way, before
they separate, and so three or four new cells
are produced.
/?. Cells multiplying by budding, like Torula; rare.

b. Motile stage.

a. Mount a drop of water containing motile Proto-

coccus, and examine with a high power. Note
the actively locomotive green bodies, of which
two varieties can be distinguished.
a. Cells like the stationary ones in size, and
apparently directly formed from them. Each
possesses a structureless colourless sac, sur-
rounding the coloured protoplasm, but the
latter has shrunk away from the sac at most
points.

Note in various specimens The two cilia
prolonged from the protoplasm through aper-
tures in the sac ; their motionless part within
the sac ; their vibratile portion outside it.
The colourless thin external layer of the
protoplasm collected into a little heap at the
point from whence the cilia arise. The deli-
cate colourless processes radiating from the
outer protoplasmic layer to the interior of the
sac. The colour usually green, but frequently
one bright red spot is present.

1 6 ELEMENTAR Y BIOL OGY. [CHAP. n.

/?. Cells much like the above if the cellulose
sac were removed, and the radiating processes
extending to it from the protoplasm with-
drawn.

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.

[B. PHYSIOLOGY.

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.]

III.

THE PROTEUS ANIMALCULE (Amoeba).
COLOURLESS BLOOD CORPUSCLES.

Amcebcz are minute organisms of very variable size which
occur in stagnant water, in mud, and even in damp earth,
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 has the appearance of a particle of jeliy,
which is often 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 struc-
tureless sac, and in this encysted state they exhibit no
movements. More commonly, they present incessant and
frequently rapid changes of form, whence the name of
"Proteus Animalcule" given to them by the older ob-
servers; and these changes of form are usually accompanied
by a shifting of position, the Amoeba creeping about with
considerable activity, though with no constancy of direction.

The changes of form, and the movements, are effected by
the thrusting out of lobe-like prolongations of the peripheral
part of the body, which are termed pseudopodia, 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

M. 2

1 8 ELEMENTARY BIOLOGY. [CHAP.

it moves. Each pseudopodium is evidently, at first, an
extension of the denser clear substance (ectosarc] only;
but as it enlarges, the central, granular, more fluid sub-
stance flows into its interior, often with a sudden rush.

In some Anwbce a clear space makes its appearance, at
intervals, in a particular region of the ectosarc, and then
disappears by the rapid approach of its walls. After a
while, a small clear speck 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 vacuole,
and its rhythmical systole and diastole often succeed one
another with great regularity. Nothing is certainly known
respecting its function, nor even whether it does or does
not communicate with the exterior, and thus pump water
into and out of the body of the Amoeba, though there is
some reason to think that this may be the case.

Very frequently one part of the Amoeba exhibits a
rounded or oval body, which is termed the nucleus. This
structure sometimes has a distinctly vesicular character, and
contains a rounded granule called the nucleolus.

The gelatinous body of the Amoeba is not bounded by
anything that can be properly termed a membrane ; all
that can be said is, that its external or limitary layer is
of a somewhat 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 when the
animal is killed by raising the temperature to 45 C. Physic-
ally, the ectosarc might be compared to the wall of a
soap-bubble, which, though fluid, has a certain viscosity,
which not only enables its particles to hold together and

in.] THE PROTEUS ANIMALCULE. 19

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 Amoeba 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 Amcebtz take in the small, usually vegetable, organisms,
which serve them for food, and subsequently get rid of the
undigested solid parts.

The chemical composition of the bodies of the Amoeba
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 O
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.

Electric shocks of moderate strength cause Amoeba at
once to assume a spherical still form, but they recover after
a while. Strong shocks kill them.

Not unfrequently, an active Amoeba becomes still spon-
taneously, acquires a rounded form, and secretes a structure-
less case or cyst, in which it remains enclosed for a shorter
or longer period.

2 2

20 ELEMENTARY BIOLOGY. [CHAP.

If Amcebce are not to be found, their nature may be
understood by the examination of bodies, in many respects
very similar to them, which occur in the blood of all verte-
brate and most invertebrate animals, and are known as the
'colourless corpuscles! They are to be met with in abun-
dance in a fresh-drawn drop of human blood. In such a
drop, after the red corpuscles have run into rolls, irregular
bodies will be seen here and there in the meshes of the
rolls. If one of these bodies is carefully watched it will
be seen to undergo changes of form of the same character
as those exhibited by Amoeba, and these motions become
much more active if the drop is kept at the temperature of
the body by means of a hot stage. Each corpuscle is, in
fact, a mass of protoplasm containing a nucleus, and the
protoplasm sends out pseudopodia which are strictly com-
parable to those of Amoeba. The colourless corpuscles,
however, possess no contractile space.

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
Amoebae would. In the earliest condition of the embryo,
the whole body is composed of such nucleated cells as the
colourless corpuscles of the blood ; and the colourless cor-
puscles 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 Amceba is an animal, not because of its contractility
or power of locomotion, but because it never becomes en-
closed within a cellulose sac, and because it is devoid of

in.] THE PROTEUS ANIMALCULE. 11

the power of manufacturing protein from bodies of a com-
paratively simple chemical composition. The Amoeba has
to obtain its protein ready made, in which respect it re-
sembles all true animals, and therefore is, like them, in the
long run, dependent for its existence upon some form or
other of vegetable life.

LABORATORY WORK.

A. AMOEBA.

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, examine with a
higher power.

1. Size: differing considerably in different specimens.
Measure.

2. Outline: irregular, produced into a number of thick
rounded eminences (pseudopodid] which are con-
stantly undergoing changes : sketch it at intervals of
five seconds.

3. Structure:

a. Outer hyaline border (ectosarc}, tolerably sharply
marked off : granular layer (endosarc] inside this,
gradually passing into a more fluid central part.

b. Nucleus : (absent in some specimens) ; a round-
ish more solid-looking particle, which does not
change its form.

c. Contractile vesicle : in the ectosarc note a round-
ish clear space which disappears periodically,
and after a short time reappears ; its slow diastole
rapid systole. Not present in all specimens.

22 ELEMENTARY BIOLOGY. [CHAP.

d. Foreign bodies (swallowed) j Diatom cases. Des-
dice^ &c.

4. Movements :

a. Watch the process of formation of a pseudopo-

dium. A hyaline elevation at first ; then, as it
increases in size, currents carrying granules flow
into it.

b. Locomotion : watch the process, a pseudo-
podium is thrown out, then the rest of the
body appears to flow up to it, and the process
is repeated.

c. If the opportunity presents itself, watch the pro-
cess of the ingestion of solid matters.

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 as a rule produces no blue colora-
tion ; when blue specks become visible it is probable
that the starch which they indicate has been
swallowed.

7. [Look for encysted specimens: and for specimens which
are undergoing fission.]

in.] THE PROTEUS ANIMALCULE. 23

8. Another form of Amoeba is not unfrequently found
; which differs from that just described in being much

less coarsely granular, and in having no well-defined
ectosarc and endosarc, and also in having much
longer, more slender and pointed pseudopodia.
Another common form progresses rapidly with a
slug-like movement, only throwing out pseudopodia
at its anterior end.

B. WHITE BLOOD-CORFUSCLES, (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 oil. Neglect
the pale yellow homogeneous (red) corpuscles, and examine
the much less numerous, granular, colourless, ones.

Note their-

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 but
no distinct ectosarc, endosarc, and vacuole as in the
Amoeba. Nucleus rarely visible in the fresh state.
No contractile vesicle.

4. Treat with dilute acetic acid : the granules are
cleared up, and a nucleus is brought into view in a
more or less central position. If the acetic acid has
been too strong the nucleus will be constricted and
otherwise distorted.

5. Stain with magenta, and iodine; the whole becomes
coloured, the nucleus most intensely.

6. Place on the hot stage, and gradually warm up to
50 C. The movements are at first rendered more

24 ELEMENTARY BIOLOGY. [CHAP. in.

active, but ultimately cease, the pseudopodia-like
processes being all retracted and the whole forming
a motionless sphere.

Let the specimen cool again ; the movements are
not resumed ; the protoplasm having passed into a
state of permanent coagulation or rigidity.

7. Repeat the above observations on the white blood-
corpuscles of the frog or newt.

IV.
BACTERIA.

UNDER the general title of Bacterium 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 substance, devoid of
chlorophyll and multiplying by transverse division. The
smallest are not more than 30 o 00 th of an inch in diameter,
so that under the best microscopes they appear as little
more than mere specks, and even the largest have a thick-
ness of little more than 10 i 00 th of an inch, though they
may be very long in proportion. Many of them have, like
ProtococcuS) two conditions a still and an active state. In
their still condition, 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 oscillatory, and is readily distinguishable from the
rapid translation from place to place which is effected by
the really active Bacteria.

In one of the largest forms, Spirillum volutans, it has
been possible to observe the cilia by which the movement
is effected. In this there is a cilium at each end of the
spirally coiled body. No such structure, however, can be
made out in the straight Bacteria, and it remains doubtful
whether they possess cilia which are too fine to be rendered

26 ELEMENTARY BIOLOGY. [CHAP.

visible by our microscopes, or whether their movements are
due to some other cause. Many forms, such as the Vibriones,
so common in putrefying matters, appear obviously to have
a wriggling or serpentiform motion, but this is an optical
illusion. In this Bacterium, as in all others, the body does
not rapidly change its form ; but its joints are bent zig-zag-
wise, and the rotation of the zig-zag upon its axis, as it
moves, gives rise to the appearance of undulatory contrac-
tion. A cork-screw turned round, while its point rests
against the finger, gives rise to just the same appearance.

Bacteria, in the still state, very often become surrounded
by a gelatinous matter, which seems to be thrown out by
their protoplasmic bodies, and to answer to the cell-wall of
the resting Protococcus. This is termed the Zoogloea form of
Bacterium.

Bacteria grow and multiply in Pasteur's solution (with-
out 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. They thrive
best in a temperature of about 30 C. but, in most fluids,
they are killed by a temperature of 60 C. (140 F.).

In all these respects Bacteria closely resemble Torula ;
and a further point of resemblance lies in the circumstance
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,
u putrefaction is a concomitant not of death, but of life."

iv.] BACTERIA. 27

Bacteria, like Torulcz and Protococd, are not killed by
drying up, and from their excessive minuteness they must
be carried about still more easily than Torulce 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.

LABORATORY WORK.

1. 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.

2. 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.

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.

28 ELEMENTARY BIOLOGY. [CHAP,

c. Structure; an outer more transparent layer
enveloping 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.

d. Movements ; some vital, and some purely phy-
sical (Brownian). The former various but pro-
gressive: 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 protoplasm,
enveloped in nonprotoplasmic matter.

5. Resting Bacteria. (Zoogloea-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.

6. Mixed with the Bacteria proper, both in the pellicle
and the fluid beneath, may be found the following
forms of living beings.

a. Micrococcus. Bodies much like Bacteria, 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 Bacteria

iv.] BACTERIA. 29

but of a similar structure : they are always free-

swimming.

c. Vibrio. Like Bacillus, but with bent joints.

d. Spirillum. Elongated unjointed threads rolled
up into a more or less perfect spiral: frequently
two spirals intertwine. In some of the largest
forms a vibratile cilium can be made out on
each end of the thread.

<? Spirochaete. 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 fluids for Bacteria and
related organisms.

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.

b. 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.

V.

MOULDS (Penicillium 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 are simpler in
structure than Torula and Protococcus, and the only ani-
mals which are simpler than Amoeba, are essentially Amcebtz
devoid of a nucleus and contractile vesicle. Moreover, how-
ever complicated in structure one of the higher plants may
be in its adult state, when it commences its existence it is as
simple as Torula or Protococcus, or at most as Torula or Pro-
tococcus would be if it possessed a distinct nucleus ; and the
whole plant is built up by the fissive multiplication of the
simple cell in which it takes its origin, and by the subse-
quent growth and metamorphosis of the cells thus produced.
The like is true of all the higher animals. They commence
as nucleated cells, essentially similar to Amoebae and colour-
less blood-corpuscles, and their bodies are constructed by
aggregations of metamorphosed cells, produced by division
from the primary cell. It has been seen that Torula
and Protococcus, similar as they are in structure, are dis-
tinguished by certain important physiological peculiarities ;
and the more complicated plants are divisible into two
series, one produced by the growth and modification of cells
which have the physiological peculiarities of Torula and
contain no chlorophyll, while the other, and far larger, series

v.] MOULDS. 31

presents chlorophyll, 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 Tonilce. 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 Penidllium 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
clue, 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 hypha. 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 Penidllium 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
Torulci) and protoplasmic contents, which fill the tube

32 ELEMENTARY BIOLOGY. [CHAP.

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. The hyphae frequently
branch dichotomously ; and, in the crust, they are inex-
tricably entangled with one another ; but every hypha, with
its branches, is quite distinct from every other. Those
aerial hyphse 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 con-
strictions into a series of rounded spores arranged like a
row of beads. The spores formed in this manner are
termed conidia. At the free end of each filament of the
brush the conidia become very loosely adherent, and con-
stitute the green powdery matter to which reference has
been made. Examined separately, a conidium is seen to be
a spherical body, composed of a transparent sac, enclosing
a minute mass of protoplasm, 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 coni-
dium 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 Penidllium assumes the form of
a star, each ray being a hypha. The hyphse elongate, while
side branches 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,

v.] MOULDS. 33

their hyphse cross one another, interlace, and give rise
to a papyraceous crust. After the hyphae have attained a
certain length, the protoplasm 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. Not unfrequently Torulce make their appearance,
in abundance, among the hyphae and conidia of Penicillium,
and appear to be derived from them ; but it is still a disputed
point, whether they are so or not.

If some fresh horse-dung be placed in a jar and kept
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

M. -3

34 ELEMENTARY BIOLOGY. [CHAP.

they somewhat resemble long pins. The organism thus
produced is another of the Fungi the mould termed Mucor
mucedo*

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 horse-dung, and are the hyphce.
Each hypha is, as in Penicillium, a tube provided with a
tough thickish structureless wall, which is partly composed
of cellulose, and is filled by a vacuolated protoplasm. In
old specimens, transverse partitions, continuous with the
Avails of the hyphae, may divide them into chambers or cells.
The stalk of the sporangium is a hypha of the same structure
as the others. The wall of the sporangium is beset with
minute asperities composed of oxalate of lime, and it con-
tains a great number of minute oval bodies, the spores, held
together by a transparent intermediate 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 adheres to the stalk. The cavity of the stalk
does not communicate 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 pro-
jection. This is termed the columella and stands con-
spicuously above the collar, when the sporangium has burst
and the spores are evacuated.

The spores are oval and consist of a sac. having the
same composition as the wall of the hypha, which encloses
a mass of protoplasm. When they are sown in an appro-
priate medium, as for example in Pasteur's solution, they

v.] MOULDS. 3;

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 proceed from the spore
as a centre, their development gives rise, as in Penirillium,
to a delicate stellate mycelium. At first, no septa are deve-
loped in the hyphae, so that the whole mycelium may be
regarded as a single cell with long and ramified processes,
and the Mucor, at this stage, is an unicellular organism.
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
becomes 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
now readily bursts, and the spores are separated by the

32

36 ELEMENTARY BIOLOGY. [CHAP.

swelling and eventual dissolution of the gelatinous interme-
diate matter. Sporangia, in which spores are produced by
division of the protaplasm, are commonly termed asci, and
the spores receive the name of ascosporcs.

There appears to be no limit to the extent to which the
Mucor may be reproduced by this process of asexual deve-
lopment of spores, by the fission of the contents of the
sporangium; nor does any other mode of multiplication
become apparent, so long as the mould grows in a fluid
medium and is abundantly supplied with nourishment.

But when growing in nature, in such matters as horse-
dung, a method of reproduction is set up which represents
the sexual process in its simplest form. Adjacent hyphae,
or parts of the same hypha, give off short branches, which
become dilated at their free ends, and approach one ano-
ther, 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. This process of
conjugation evidently represents that of sexual impregnation
among higher organisms, but as there is no morphological
difference between the modified hyphae which enter into
relation with one another, it is impossible to say which
represents the male, and which the female, element. The
product of conjugation is termed a zygospore. Its cellulose
coat becomes separated into an outer layer of a dark black-
ish hue, the exosporium^ and an inner colourless layer, the
endosporiwn. The outer coat is raised into irregular eleva-
tions, to which corresponding elevations of the inner coat
correspond.

V.] MOULDS. 37

Placed in favourable circumstances, the zygospore does
not immediately germinate; but, after a longer or shorter
period of rest, the exosporium and the endosporium burst,
and a bud-like process is thrown out, which, usually, grows
only into a very short unbranched hypha. From this hypha
a vertical prolongation is developed, which becomes con-
verted into a sporangium, such as that already described,
whence spores are produced, w^hich give rise to the ordinary
stellate mycelium. Thus, Mticor presents what is termed an
"alternation of generations.'" The zygospore resulting from
a sexual process developes into a rudimentary mycelium,
with a single sporangium which constitutes the first gene-
ration (A], This gives rise, by the asexual development of
spores in its sporangium, to the second generation (B),
represented by as many separate Mncores as there are
spores. The second generation (B} may give rise sexually
to zygospores and so reproduce the generation (A); but,
more usually, an indefinite series of generations similar to
() are produced from one another asexually, before (A]
returns.

When Mucor is allowed to grow freely 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 hyphse 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 Torulis. Coincidentally with these changes, an active
fermentation is excited in the fluid, so that this " Mucor-
Torula" functionally as well as morphologically, deserves
the name of ' yeast.'

If the Mucor-Torula is filtered off from the saccharine
solution, washed, and left to itself in moist air, the ToruLs

38 ELEMENTARY BIOLOGY. [CHAP.

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
fortnight. Sometimes, however, the fluid will overrun with
Bacteria, to the exclusion of everything else. And very
frequently other moulds, such as Aspergillus, or Mucor >
may appear instead of or along with Penicillium.

i. 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. Hyphce. Note their diameter (measure)
form subdivisions (cells) dichotomous mode
of branching and structure : the external

v.] MOULDS. 59

homogeneous sac; the granular less trans-
parent protoplasm ; the small round vacuoles.
Draw.

(3. The intermixed Torulce. 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 down, from the under
surface of the mycelium : repeat the observations
2. a. a - a -

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 ; sac, protoplasm, vacuole.

b. Stain with magenta and iodine.

c. Treat another specimen with potash.

40 ELEMENTARY BIOLOGY. [CHAP.

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 hyphse ; 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 hyphce; the branching and
interlacement of the hyphas.]

B. MUCOR MUCEDO.

1. Place some fresh horse-dung under a bell-jar and
keep moist and warm ; in from 24 to 48 hours its
surface will nearly always be covered by a crop of
erect aerial mucor-hyphas, each ending in a minute
enlargement (sporangium] just visible with the un-
assisted eye: it is this first crop of hyphse and spor-
anges which is to be examined.

2. Snip off a few of the hyphaa with a pair of scissors,
mount in water, and examine with i inch obj.

a. Large unbranched hyphas, each ending in a
spherical enlargement (sporangium).

3. Examine with -| obj.

a. The hyphse.

a. Their size; they greatly exceed the hyphae of
Penicillium both in length and diameter.

/?. Their structure; homogeneous sac, granular
protoplasm, vacuoles : septa absent except
close to the sporange.

v.] MOULDS, 41

y. Treat with iodine and magenta; the proto-
plasm is stained.

8. Treat another specimen with Schulz's solu-
tion ; the wall is stained violet.

b. The sporangia or asci.

Examine with -| obj.

a. Their size and form.

b. Their structure.

a. The homogeneous enveloping sac covered b}"
irregular masses of calcic oxalate.

J3. The granular protoplasmic contents : un-
segmented in some ; divided into a great
number of distinct oval masses (ascospores) in
others.

y. The projection into the sporangial cavity of
the convex septum (columella} which separates
the hypha from the sporange.

8. The collar projecting around the base of the
columella of burst sporangia.

c. Stain some with iodine ; others with Schulz's
solution.

c. The ascospores.

a. Crush some ripe asci by gentle pressure upon
the cover-glass. Examine with ~ obj.

a. The size of the ascospores (measure).

(3. Their form ; cylindrical and elongated,

y. Their structure.

8. Stain with iodine and magenta.

VI.
STONE WORTS (Cham and Nitella).

\

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 stem, 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
structure is continued from the cortical layer, across the

vi .] STONE IVOR TS. 4 3

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 branches spring from the re-entering
angle between the stem and the leaf, which is termed the
axilla 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 sporangia
or spore-fruits, 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
constantly increases in length 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,
spore-fruits and antheridia are developed in their axillae.
Sometimes rounded cellular masses appear in the axillae of
the leaves, and, becoming detached, grow into new plants.
These are comparable to the bulbs of higher plants.

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,

44 ELEMENTARY BIOLOGY. [CHAP.

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 undergoing 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; and, while it lives, new nodes and internodes
are continually being added at its summit, or growing point.
The internodal cells which give rise to the centre of the
stem undergo no important change, except great increase
of size, after they are once formed. The nodal cells, on
the contrary, undergo division with comparatively little in-
crease in size. And out of them, the nodes, the cortical
layer, and all the appendages, are developed.

In all the young cells of Chara 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, containing cellulose. As the cell grows

vi.] STONE WORTS. 45

larger, the centre of the protoplasm becomes occupied by a
watery fluid, and its thick periphery, which remains applied
against the cell-wall, constitutes the wall of a sac, or pri-
mordial utricle, in which the nucleus is imbedded. 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.

Numerous small green bodies chlorophyll grains are
imbedded 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, w^hich 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 anthcridiiiin 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-
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

46 ELEMENTARY BIOLOGY. [CHAP.

40,000 chambers in each anthendium (8 x 6 x 4 x 100 or
x 200). The several pieces of which the wall of the an-
theridium is composed, the manubrium, 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 protoplasm 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 are burst, and the
antherozooids are set free, they are propelled rapidly, with
the small end forwards, by the vibration of the cilia. These
antherozooids answer to the spermatozoa of animals, and
represent the male element of the Cham.

The sporangia or spore-fruits are borne upon short stalks,
the end of which supports a large oval central cell; five
spirally-disposed sets of cells invest this, an aperture being
left between the investing cells at the apex of the sporan-
gium. When, the antheridia attain maturity they burst, the
antherozooids are set free, and swarm about in the water.
Some of them enter the aperture of the sporangium, 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 central cell become
full of starchy and oily matter; the spiral cells forming its
coat acquire a dark colour and hard texture, and the spo-
rangium, detaching itself, falls into the mud.

After a time it germinates; a tubular process, like a
hypha, protrudes from its open end, and almost immediately
gives off a branch, which is the first root (compare the ger-

vi.] STONEWORTS. 47

mination of the spore of a fern below). The hypha-like
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 termi-
nal bud of the adult Chara stem, and grows up into a new
Chara.

We have then, in C/iara, 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 mul-
tiplies sexually by means of the antherozooids (male ele-
ments) and central cells of the sporangia (female elements);
in which the first product of the germination of the impreg-
nated ovicell is a hypha-like body, from which the young
Chara is developed 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, so that its nutri-
tive 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 in the water; and
that, except so far as the reproductive organs are concerned,
there is a morphological differentiation of organs, unaccom-
panied by a corresponding physiological differentiation.

Nitella is a rarer plant than CJiara, and is simpler in
structure, its axis being devoid of the cortical layer. In

48 ELEMENTARY BIOLOGY. [CHAP.

other respects, however, it is very similar to C/iara, and its
structure is more easily made out.

[The Characecz, or plants belonging to the genera Char a and
Nitella,) are found in all parts of the world, and are in many
respects closely allied to the Algce, or water- weeds. But no
Algce are provided with an axis and appendages possessing a
similar structure, or following the same law of growth, nor
have any similar reproductive organs. The antherozooids of
the Characecc are, in fact, similar to those of the mosses, from
which however the Characece differ widely in all other respects.]

LABORATORY WORK.

A. NAKED-EYE CHARACTERS.

Note the slender elongated axis (stem] ; the whorled
appendages (leaves}} the nodes and internodes; 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 spore-fruits and anther idia; their position,
size, form, colour.

Draw a portion including two or three internodes.

B. HlSTOLOGICAL STRUCTURE.

a. The stem.

i. Examine the outside of a fresh interaode with a low
power, or pocket lens, to see the spirally-arranged
cortical cells.

vi.] STONE IVOR TS. 49

2. Hold a bit of fresh stem between two pieces of carrot,
or imbed 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
cell (medullary or internodal cell} in the internodes;
the cortical cells, round the medullary 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.

ft. The wall (sac), protoplasmic layer (primordial
utricle), nucleus, and vacuole of each cell. (The
nucleus is not always to be found in old cells.)

4. Examine sections from the fresh stem to make out
the points detailed in B. a. 3. ft. 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.

ft. 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 chlorophyll: collected into oval granules,
and arranged so as to leave an oblique

M. 4

ELEMENTARY BIOLOGY. [CHAP.

tmcoloured band round each cell; the position
of these granules, in the more superficial
layer of the protoplasm.

8. 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.

f3. 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 which are
successively segmented off from 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.

/3. 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.

vi.] STONEWORTS. 51

d. Their growth at the base, the terminal leaf-cell
soon attaining its full size and not dividing.

e. The development of branches; from nodal cells
in leaf-axils, which take on the character of ter-
minal cells.

d. The spore-fruits.

Examine fresh, under a low power.

a. Made up externally of five twisted cells, bearing
at their apices five smaller, not twisted cells.

/?. Cut sections from imbedded specimens, and
examine with a high power : make out the
large central nucleated cell; 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, /3).

3. Examine chromic acid specimens for young
spore-fruits, 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-

42

52 ELEMENTARY BIOLOGY. [CHAP.

larly from the inner surface of each; the
roundish cell (capituluni) on the inner end of
the manubrium; the six secondary capiiula
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 cuithero-
zooid.

b. The anther ozooids.

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.

p. The movements in water of ripe anthero-
zooids.

[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
examine it in water with a high power. Note

vi.] STONE WORTS. 53

the superficial layer of protoplasm in \vhich 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 usually
disappeared in cells in which currents have
commenced, but when present is passive and
carried along by them. Sometimes it is very
difficult, on account of the incrustation of the
leaf-cells of Chara, to make out the protoplasmic
movements in them; if this is found to be the
case, the manubrial cells from an antheridium
should be used instead.

I). 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 sac, protoplasm, nucleus, and vacuolar
spaces. Note the protoplasm; partly forming
a layer (primordial utricle] lining the sac 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.

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

54 ELEMENTARY BIOLOGY. [CHAP. vi.

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
35 C.

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.

VII.
THE BRACKEN FERN (Ptcris aquilinci).

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 rachis, from which transversely disposed offshoots
proceed, these ultimately subdividing into flattened leaflets,
the pinn ules. 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 attachments of the fronds are nodes, the spaces
between two such successive attachments, internodes. It

56 ELEMENTARY BIOLOGY. [CHAP.

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 fringed with numerous hair-like
processes which roof over the groove, enclosed by the
incurved edge. At the bottom of the groove, brown
granular bodies are aggregated, 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 sori.

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 of a protoplasmic 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 circumferential
zone of the same dark-brown colour as the external epi-
dermis, 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.

vii.] THE BRACKEN FERN. 57

The dark-brown dots are scattered irregularly, but the
major 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
traceable into mere streaks, which finally disappear alto-
gether in the semi-transparent gelatinous substance which
forms the growing end of the stem. Submitted to micro-
scopic examination, the white ground-substance, or paren-
chyma, is seen to consist of large polygonal cells, containing
numerous starch granules ; and the circumferential zone
is formed of somewhat elongated cells, the thick walls of
which have acquired a dark-brown colour, and contain
little or no starch. The dark-brown bands, on the other
hand, consist of cells which are so much elongated as
almost to deserve the name of fibres and constitute what
is termed sclerenchyma. Their walls are very thick, and of
a deep-brown colour; but the thickening has taken place
unequally, so as to leave short, obliquely directed, thin
places, which look like clefts. The yellow bands, lastly,
are vascular bundles. Each consists, externally, of thick-

58 ELEMENTARY BIOLOGY. [CHAP.

walled, elongated, parallel-sided cells, internal to which lie
elongated tubes devoid of protoplasm, and frequently con-
taining air. In the majority of these tubes, and in all
the widest, the walls are greatly thickened, the thickening
having taken place along equidistant transverse lines. The
tubes 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 scalariform 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.

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
invested superficially by an epidermis, composed of elon-
gated cells, with walls thickened in such a manner as to
leave thin circular spots here and there. Hence, those
walls of the cells, which are at right angles to the axis of
vision, appear dotted with clear spots ; while, in those
walls of which transverse sections are visible, the dots are
seen to be funnel-shaped depressions.

The pale bands are vascular bundles containing scalari-
form and spiral vessels. The outer layer investing each
is chiefly formed of long hollow fibres with very thick

vii.] THE BRACKEN FERX. 59

walls, and terminating in a point at each end. These
sclerenchymatousy^ra- have oblique cleft-like clear spaces,
produced by interruptions of the process of thickening in
their walls.

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 many of these 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 is sur-
mounted by two reniform 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 stomate ; and, as the stomata are present in
immense numbers, there is a free communication between
the outer air and the intercellular 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 through-
out the substance of the plant.

The vascular bundles break up in the pinnules, and

60 ELEMENTARY BIOLOGY. [CHAP.

follow the course of the so-called veins which are visible
upon its surface; ducts being continued into their ultimate
ramifications.

The rootlets present an outer coat of epidermis, enclosing
parenchyma traversed by a central vascular bundle. They
increase in length by the division and subdivision of the
cells at the growing point, but this point is not situated at
the very surface of the rootlet, as the growing point at the
extremity of the rhizome is, but is covered by a cap of cells.

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 gives rise to a tubular, hypha-like
prolongation, which developes a similar process, the primi-
tive rootlet, close to the spore. The hypha-like prolongation,
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 gradually assumes a
bilobed form, and becomes thickened, in some parts, by
division of its cells in a direction perpendicular to its
surface. The protoplasm of these cells developes chlorophyll
granules, whereby the bilobed disk acquires a green colour ;
while numerous simple radicle fibres are given off from
its under surface, and attach the little plant, which is
termed a prothallus or prothallium, 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 aspect. Some of
these are anther idia. The protoplasm of each of the cells
contained in their interior is converted into an antherozooid,

vii.] THE BRACKEN FERN. 61

somewhat similar to that of Chara, but provided with many
more cilia. The antheridium bursts, and the antherozooids,
set free from their containing cells, are propelled through
the moisture on the under surface of the prothallus by their
cilia.

The processes of the second kind acquire a more cylin-
drical form, and are called archegonia. Of the cells which
are situated in the axis of the cylinder, all disappear but
that which lies at the bottom of its cavity. This is the
embryo cell, and when the archegonium is fully formed, a
canal leads from its summit to this cell. The antherozooids
enter by this canal, and impregnate the embryo cell.

The embryo cell now begins to divide, and becomes
converted into four cells ; of these, the two which lie at the
deepest part of the cavity of the archegonium subdivide and
ultimately form a plug-like, cellular, mass, which imbeds
itself firmly in the substance of the prothallus. Of the re-
maining two cells, which also undergo subdivision, one gives
rise to the rhizome of the young fern, while the other becomes
its first rootlet. It appears probable that the plug-like mass
absorbs nutritive matter from the prothallus, and supplies
the rhizome of the young fern, until it is able to provide for
itself. As the rhizome grows, and developes its fronds, it
rapidly attains a size vastly superior to that of the prothalius,
which at length ceases to have any functional importance,
and disappears.

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 embryo cell by the antherozooid. 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

62 ELEMENTARY BIOLOGY. [CHAP.

free germinate ; the product of that germination is the incon-
spicuous 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 embryo cell produces only a single
* fern,' but each ' fern ' may give rise to innumerable pro-
thallia, seeing that every one of the numerous spores de-
veloped in the immense multitude of sporangia to which the
frond gives rise, may germinate.

LABORATORY WORK.

A. THE FERN-PLANT j 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 inter nodes.

b. The roots 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
pinnce; the ultimate divisions or pinnules.

(3. The son ; small brown patches along the
margin of the under surface of some of the
pinnules.

d. The nodes and internodes of the rhizome. The
absence of a terminal bud on it.

vii.] THE BRACKEN FERN. 63

b. The rhizome.

t. Cut it across and draw the section as seen with the
naked eye.

a. The outer brownish layer (epidermis and sub-
epidermis] ; the latter thins away somewhat,
opposite 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.

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 epidermic
cells.

b. The small opaque angular contours of the sub-
epidermic 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.

e. The great openings of the ducts and vessels in
the nbro-vascular bundles.

Draw the section.

64 ELEMENTARY BIOLOGY. [CHAP.

4. Examine with \ obj.

a. The epidermis : its thick-walled cells.

b. The parenchyma ; its large thin-walled cells : their
sac, protoplasm and nucleus : the great number
of starch granules in them.

c. The various patches of sderenchyma, made up of
thick-walled angular cells.

d. The vascular bundles. Note in each :

a. Outside, a single layer of cells containing no
starch granules (bundle sheath}. These really
belong to the parenchyma or ground tissue.

J3. Within the bundle sheath a layer of small
parenchymatous cells containing starch (inner
or bast s heath}.

y. Within the last layer comes the bast of the
bundle (phloem} consisting of externally, two
or more layers of small rectangular cells with
thickened walls (bast fibres} and then a single
row of large thin-walled cells (bast vessels]
between which lie smaller thin-walled cells
containing starch granules (bast parenchyma}.

8. Within the bast are seen the cross sections
of the vessels: note their greatly thickened
walls, and large central cavity containing no
protoplasm.

e. Scattered here and there, in the spaces between
the angles of the vessels, are small parenchy-
matous cells (ivood parenchyma} containing
starch granules.
The wood, or xylem, consists of 8 and e.

. Treat with iodine : the protoplasm stained
brown; the starch granules deep blue, render-

VIL] THE BRACKEN FERN. 65

ing some of the cells quite opaque and almost
black-looking.

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, subepidermis and parenchyma,
much as in the transverse section, except that
the subepidermic cells are longer.

b. The sclermchyma 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 much as in the
transverse section; the bast fibres ; elongated,
with thickened walls; the cells of the bast
parenchyma somewhat elongated ; the bast
vessels, elongated cells, presenting irregular
patches of pores (sieve-tubes]; the bast sheath
cells somewhat elongated.

/?. The vessels: elongated tubes presenting cross
partitions, dividing them into separate cells,
at long intervals. Two forms of vessel will
be seen, viz. scalariform vessels, with regular
transverse thickenings on their walls and
spiral vessels, less numerous than the last
form : with a continuous spiral thickening on
their walls.

y. The bast cells: seven or eight times as long as
they are broad, and terminating obliquely at
each end.

8. The elongated larger cells (4. d. S) : they have
very slightly thickened walls and no scalari-
form markings.

M. 5

ELEMENTARY BIOLOGY. [CHAP.

6. [Cut off half an inch of the growing end of the stem,
imbed it in paraffin upside down, and cut a series of
transverse sections : examine them with the microscope,
beginning with those farthest from the growing point.
At first the various tissues described in 3 and 4 will be
readily recognisable ; as the sections nearer the grow-
ing point are examined they will be less distinct, and
close to the growing point the whole section will be
found to be composed entirely of parenchymatous
closely-fitting cells.]

[c. The leaf. Imbed a leaf in paraffin and cut a thin
vertical section : examine with i inch obj. It will be
found to be constructed essentially on the same plan
as the leaf of the bean. (VI 1 1.)]

d. 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.

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.
]}. Their structure: composed of brownish cells, one

row of which has very thick walls, and forms a

marked ring (annulus] round the edge of the

sporange.
c. Their mode of dehiscence (look out for one that

has opened): by a cleft running towards the

centre of the sporange from a point where the

annulus has torn across.

3. Burst open some sporangia by pressing on the cover-
glass: examine, with \ obj., the spores which are set
free.

VIL] THE BRACKEN FERN. 67

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 a
glass slide, 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 r
inch obj. ^&

a. Its form: a thin kidney-sj^ed expansion from
which, especially towards its convex border, a
number of slender filaments (rootlets] 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.

P. The rootlets: composed of a series of cells
which contain no chlorophyll.

c. The anther idia and archegonia: the former can
just be seen with an inch objective as minute
eminences on the under surface of those parts of
the prothallus which consist of a single layer
of cells, especially among the root-hairs ; the
latter are partly imbedded in the cushion.

52

6S ELEMENTARY BIOLOGY. [CHAP.

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
rootlets*

a. Their form: small hemispherical eminences.

b. Their structure: made up of an outer layer of
cells containing a few chlorophyll-granules, and
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
antherozooids] resulting from its division : in the
latter cells, in ripe antheridia, spirally coiled
bodies (antherozooids] can be indistinctly seen.

2. The antherozooids.

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 antherozooid is often attached
a rounded mass containing colourless granules.

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; either by simply
chopping down it with a razor, or holding it between
two pieces of carrot and cutting. Note in the
archegonia

a. Their form: chimney-shaped eminences with a
small aperture at the apex.

vii.] THE BRACKEN FERN. 69

b. Their stnictttrt. 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 basal cell, with two or three
smaller granular cells (neck-cells] above it in the
narrow upper part of the cavity; in older speci-
mens this upper part is empty, forming a canal
leading down to the basal cell.

4. Examine young Fern in connection with its pro-
thallus.

VIII.
THE BEAN-PLANT (Vicia faba).

\

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 the flowers; each of which consists of a calyx, a
corolla, a staminal tube and a central pistil; the latter is ter-
minated by a style, the free end of which is the stigma.

The staminal tube ends in ten filaments, four of which
are rather shorter than the rest; and the filaments bear oval
bodies, the anthers, which, when ripe, give exit to a fine
powder, made up of minute pollen grains. 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 nucleus, invested by two coats, an outer and an inner.
Opposite the summit of the nucleus, these coats are per-
forated by a canal, the micropyle, which leads down to the

viii.] THE BEAN-PLANT. 71

nucleus. The nucleus contains a sac, the embryo sac, in
which certain cells, one of which is the embryo cell, and
the rest endosperm cells, are developed. A pollen grain
deposited on the stigma, sends out a hypha-like prolonga-
tion, the pollen tube, which elongates, passes down the style,
and eventually reaches the micropyle of an ovule. Travers-
ing the micropyle, the end of the pollen tube penetrates the
nucleus, and comes into close contact with the embryo sac.
This is the process of impregnation, and the result of it
is that the embryo cell divides and give 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
increase 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
nucleus 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.
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

72 ELEMENTARY BIOLOGY. [CHAP.

depends on the addition of new cells, takes place chiefly, if
not exclusively, in this part.

The apex of the root, on the other hand, gives rise to a
root-sheath, as in the Fern.

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.

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 epidermic cells, within
which, rounded or polygonal cells make up the ground-
substance, or parenchyma, of the plant, extending to its
very centre in the younger parts of the stem and in the root ;
while, in the older parts of the stem, the centre is occupied
by a more or less considerable 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. Nearer to the circumfer-
ence than to the centre, lies a ring of woody and vascular
tissue, which, in transverse sections, is seen to be broken up
into wedge-shaped bundles, by narrow bands of parenchy-
matous tissue, which extend from the parenchyma within
the circle of woody and vascular tissue (medulla or pith) to
that which lies outside it. Moreover, each bundle of woody
and vascular tissue is divided into two parts, an outer and
an inner, by a thin layer of small and very thin-walled cells,
termed the cambium layer. What lies outside this layer
belongs to the bark and epidermis ; what lies inside it, to
the wood &R& pith.

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

viii.] THE BEAN-PLANT. 73

their power of multiplication, and divide by septa parallel
with the length of the stem, or root, as well as transverse to
it. Thus new cells are 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
bark; and the axis of the plant continually increases in
diameter, so long as this process goes on. Plants in which
this constant addition to the outer face of the wood and the
inner face of the bark takes place, are termed exogens.

At the apex of the stem, and at that of the root, the
cambium layer is continuous with the cells, 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 cambium layer may be said to have the form of a double
cone. And it is the special peculiarity of an exogen 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 dotted
ducts and spiral vessels, the spiral vessels being particularly
abundant close to the pith. The bark contains elongated
liber or bast cells; but there are no scalariform vessels such
as are found in the Fern.

Stomates 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
intercellular passages, which are widest in the leaves, but
extend thence throughout the whole plant.

74 ELEMENTARY BIOLOGY. [CHAP.

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 sporan-
gium. The pollen grains answer to the male spores of those
flowerless plants in which the spores are of distinct sexes-
some spores giving rise to 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 cor-
responds with the first hypha-like 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 de-
tached fertilizing bodies or antherozooids, but exerts its
fertilizing influence without any such previous differentia-
tion. The connecting links between these two extreme
modifications are furnished, on the one hand, by the Coni-
fers, in which the protoplasm of the pollen tube becomes
divided into cells, from which, however, no antherozooids
are developed; and the Club-mosses, in which the proto-
plasm of the male spores (- pollen grains) divides into cells
which form no prothallus, but give rise directly to anthero-
zooids.

On the other hand, the embryo sac is the equivalent of a
female spore : the endosperm cells, which are produced from
part of its protoplasm, answer to the cells of a prothallus;
while the embryo cell of the flowering plant corresponds
with the embryo cell contained in the archegonium of the
prothallus. In the development of the female spore of the
flowering plant, therefore, the free prothallus and the arche-
gonia are suppressed. Here, again, the intermediate stages

VIIL] THE BEAN-PLANT. 75

are presented by the Conifers and the Club-mosses. 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 these the embryo cells arise; while, in some of the
Club-mosses, there are female spores distinct from the male
spores, and the prothallus which they develope does not
leave the cavity of the spore, but remains in it like an
endosperm.

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
Chara. 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 ex-
posed 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

76 ELEMENTARY BIOLOGY. [CHAP.

leaves. And it can be proved, experimentally, that fresh
green leaves possess this power to a remarkable extent.

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
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 carbon fixed 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 a material which
contains nitrogen and hydrogen, with oxygen and carbon,
in some other shape than that of carbonic anhydride. The
analogy of Torula suggests a fluid which contains in solu-
tion, either some ammoniacal salt comparable to ammonium
tartrate, or a more complex compound analogous to pepsin.
Thus, the higher plant combines within itself the two,
physiologically 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 shew that the ascent of fluid from the root to
the leaves takes place, to a great extent, through the elon-
gated ducts of the wood, which not unfrequently open into
one another by their applied ends, and, in that way, form
very fine capillary tubes of considerable length.

viii.] THE BEAN-PLANT. 77

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 surfa ceof the plant, and especially in theair-
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 stomates. The push from below is the absorptive action
which takes place at the extremities of the rootlets, and
which, for example, in a vine, before its leaves have grown
in the spring, 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 dots 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 compound containing
nitrogen and carbon, whatever it may be, which is formed
in the chlorophyll-bearing cells, probably takes place by
slow diffusion from cell to cell.

The supply of air, containing carbonic anhydride, to the
leaves and bark is effected by the abundant and large air-
passages which exist between the cells in those regions.
But it can hardly be doubted that all the living protoplasm
of the plant undergoes slow oxidation, with evolution of
carbonic anhydride; and that this process, alone, takes place
in the deeper-seated cells. The supply of oxygen needful
for this purpose is sufficiently provided for, on the one hand,
by the minute air-passages which are to be found between
the cells in all parenchymatous tissues ; and on the other, by
the spiral vessels, which appear always to contain air under
normal circumstances, in the woody bundles. The replace-

78 ELEMENTARY BIOLOGY. [CHAP.

*

ment of the oxygen of the air thus absorbed, and the re-
moval 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
contrary direction, from the surface exposed to the air,
through the air-passages and spiral vessels which extend
from the stomates 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 temperature, 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 stem}.

b. The branches: some, mere repetitions of the
main axis ; others, modified and bearing flowers.

c. The nodes and internodes.

d. The appendages*
a. Rootlets.

J3. Foliage leaves.
y. Floral leaves.

viii.] THE BEAN-PLANT. 79

b. The root.

a. Its main central portion (axis).

b. The irregularly arranged rootlets attached to the
axis.

c. The absence of chlorophyll in the root.

d. The root-sheath, 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.

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
cut than the rest : mount in water and examine with
i inch obj.: note

a. The medullary ox 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.

c. The epidermis: composed of a single layer of
somewhat squarish-looking cells, containing no
chlorophyll.

So ELEMENTARY BIOLOGY. [CHAP.

d. Beneath the epidermis several layers of large
rounded cells containing chlorophyll (parenchyma
of the bark}.

e. The medullary rays: radiating rows of paren-
chymatous cells uniting b and d : not quite con-
tinuous, being interrupted by the cambium zone

(/y).

f. The fibro-vascular bundles, lying between the
medullary rays; commencing at the side nearest
the pith, note

a. The large openings formed by the transverse
sections of the spiral vessels and ducts.

J3. The small thick-walled wood-cells, wedged in
between the vessels. These two (a and /?)
form the wood or xylem of the bundle. The
bast or phloem. It presents internally thin-
walled cells of various size, the bast paren-
chyma and bast vessels or sieve tubes. Ex-
ternally it appears in cross section to be com-
posed of rounded cells with thickened walls ;
the bast Jib res or liber.

y. The cambium zone: granular-looking, and
composed of small angular thin-walled cells.

S. The liber-layer: in cross section it seems
composed of rounded cells with much thick-
ened walls. Draw the section.

3. Cut a transverse section through a node, and compare
it with that through the intern ode.

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;

vin.] THE BEAN-PLANT. Si

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 sec-
tion.

b. The fibre-vascular bundles presenting-

a. The spiral vessels: elongated tubes with a spiral
thickening on their walls.

(3. The wood-cells: elongated and with much
thickened walls.

y. The dotted ducts: much like , but the thick-
ening not deposited in the form of a spiral.

8. The cambium zone: made up of cloudy-
looking, small, angular, thin-walled cells.

e. The bast parenchyma : thin-walled elongated

cells.
. The bast vessels: larger elongated cells with

oblique perforated septa (sieve-tubes].

77. The bast fibres, fusiform and thick-walled.

c. More parenchymatous cells.

d. Epidermis: composed apparently of cubical
colourless cells : here and there the opening of
a stomate (d. 2. d. (3) may be seen.

J )ra\v 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.

M. 6

ELEMENTARY BIOLOGY. [CHAP.

d. The leaves.

Their form and composition.

a. Each leaf consists of a number of different
parts, viz. :

a. The stalk or petiole.

/?. 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.

8. The rudimentary tendril terminating the pe-
tiole.

The histological structure of a leaflet.

a. Imbed a leaflet in paraffin or hold it between
two bits of carrot or turnip and cut a thin sec-
tion from it, perpendicular to its surfaces. Let
the section lie in water 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 epidermic layer consisting
of a single row of cells; the openings here
and there in it (stomatd).
Beneath the upper epidermis come elongated
chlorophyll-containing cells, set on perpendi-
cularly to the surface.

Then come irregularly branched (stellate) cells
forming the lower half of the leaf-substance ;
these also contain chlorophyll.

viii.] THE BEAN-PLANT. 83

S. The epidermic layer of the lower surface ;
like a.

e. The intercellular spaces, through the whole
thickness of the leaf: the direct communica-
tion 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. f.

Draw.

c. Treat with iodine : make out the sac, proto-
plasm (primordial utricle}, nucleus and vacuole
of the cells : the starch granules.

d. Peel off a strip of epidermis from a leaf and
examine with a low power : note

a. The large close-fitting cells, with irregularly
wavy margins and no chlorophyll, which
chiefly make up the epidermis.

/?. The openings here and there in it (stomata) ;
the two curved, chlorophyll-containing cells
bounding each stomate.

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
J or ^ objective : they will be found to consist
of partially unrolled spiral vessels.

e. The flower,
i. 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.

62

8 4 ELEMENTARY BIOLOGY, [CHAP.

/?. Inside the calyx the corolla : the most con-
spicuous part of the flower.

y. Inside the corolla the stamens.
8. Within the stamens the//V///.
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-
lum) expanded at its free end and folded over
the rest.

/?. On the sides, two oval pieces (alee), each
attached by a distinct narrowed stalk (unguis).

y. The inferior part of the corolla (carina), com-
posed of two oval pieces united along their
lower edge but readily tearing apart.

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 the filaments for three-fourths of
their length to form the stamen-tube : the sharp
bend of the filaments towards the upper side at
the point where they separate from one another.

c. Tease out an anther in water and examine with
\ obj. : there will be found numerous

vin.] THE BEAN-PLANT. Bj

a. Pollen-grains: small oval bodies, with pro-
jections on them 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 carrot,
cutting transverse sections, mounting in water
and examining with i inch obj.

a. It contains four chambers, two on each side
of the continuation of the filament, and in
each chamber lie numerous pollen-grains.

5. The pistil.

a. It is found by tearing open the stamen-tube : it
is a long green tapering body, somewhat flat-
tened laterally and ending in a point (the style)
which bears a tuft of strong hairs.

b. Slit it open carefully : in it lies a central cavity,
containing a number of small oval bodies, 1he
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 imbedded in a large quantity of paren-
chyma) and examining with i inch obj.

a. The central cellular portion of the ovule
(nucleus] made up of a large number of cells.

Its two coats, an inner (primine) and outer
(secundine).

36 ELEMENTARY BIOLOGY. [CHAP.

y. The small passage (micropyle) leading through
the coats down to the nucleus.

8. In some specimens, a large cavity (the
embryo-sac] will be seen in the nucleus just
opposite the micropyle. In the embryo-sac
may be seen some small granular cells (the
embryo-cell and endosperm 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 on one end of the bean,
marking where the stalk (funiculus] 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 : the two large fleshy cotyledons will be
laid bare.

d. 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 rudiments of
the stem and leaves (plumule] lying between
the cotyledons.

viii.] THE BEAN-PLANT. 87

g. The process of fertilization.

This is difficult to follow in the bean; but bv usini?

f O

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 ((Enothera 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. serpyUifolia - - often to be found
in shady places on lawns is well adapted for the
purpose. A flower should be taken from which the
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

88 ELEMENTARY BIOLOGY. [CHAP. vni.

that after some time the embryo-sac can be seen,
and the progress of the pollen-tube into the ovule
followed.

3. The young fruit of Campanula (especially the com-
mon Canterbury Bells of gardens, Campanula me-
dia) is convenient for examining the embryo-sac.
It is only necessary to cut thin transverse sections
of the fruit and examine in water. Some of the
ovules cut through will allow the embryo-sac to be
seen, and in fortunate sections the embryo-vesicle
and the end of the pollen-tube in contact with the
embryo-sac.

IX.
THE BELL-ANIMALCULE (Vorticella).

THE great majority of those animal organisms which are
more complex than Amoeba, begin their existence as simple
nucleated cells, having a general similarity to Amoeba; 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 metamorphosis of these primitively simi-
lar histological elements that the organs and tissues of the
body are built up. But in one group, 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 protoplasmic 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 make
their appearance in infusions of many animal and vegetable
substances, their germs either being contained in the sub-
stances infused, or being wafted through the air. Their
diffusion is greatly facilitated by the property which many
of them possess of being dried, and thus reduced to the
condition of an excessively light dust, without the destruc-

90 ELEMENTARY BIOLOGY. [CHAP.

tion of their vitality; 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. 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
peristome, 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 (Esophagus, 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 cutiatla. Immediately beneath the
cuticle it is tolerably firm and slightly granular, and this
part is distinguished as the cortical layer ; it passes into the
central substance, which is still softer and more fluid.

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-

IX.] THE BELL- ANIMALCULE. 91

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. Whether it has any communication with
the exterior or not and what is its function, are still open
questions. If the Bell-animalcule is well fed, one or more
watery vesicles of a spheroidal form, each containing a cer-
tain 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 Vorticelliz 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, as a spheroidal drop,
henceforward free in the soft central substance. In some
Bell-animalcules, the food-vesicles thus formed undergo a
movement of circulation, passing up one side of the body,

9z ELEMENTARY BIOLOGY. [CHAP.

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 into the vestibule by
an aperture which exists only at the moment of extrusion of
the faeces, and is indistinguishable 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 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
endoplast, in which latter case the endoplast divides and one
or more of the rounded masses thus separated are set free
as locomotive germs.

Sometimes a rounded body, encircled by a ring 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 appears that they are independent individuals, 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. It is probable that this
" conjugation" has relation to a sexual process.

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, from
which, after remaining at rest for a longer or shorter time,
the Bell-animalcule may emerge and resume its former

Ix -] THE BELL-ANIMALCULE. 93

state of existence. In thus passing into a temporary condi-
tion of rest many of the other Infusoria resemble Vorticdla.

The two genera of Infusoria which most commonly occur
in the Frog are Nyctotherus and Ealantidium. 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.

LABORATORY WORK.

A. Examine duckweed roots, confervas, &c., with 1 inch
objective avoiding pressure ; having found a group of
Vorticella note the following points with a higher
power.

i. In the extended state of the animal.

a, The body.

<i. Its size (measure).

b. Form; broadly speaking, that of an inverted
bell : note

a. The prominent everted rim (peristome).

ft. The flattened central disc projecting above
the peristome.

7. The cilia fringing the disc.

o. The depression between the peristome and
disc.

The mouth of the chamber (vestibulum) into
which the oesophagus and anus open, in the
hollow between the peristome and disc.

e.

94 ELEMENTARY BIOLOGY. [CHAP.

c. Structure.

a. The thin, transparent, homogeneous external
layer (cuticle],

ft. The granular layer (cortical layer) inside the
cuticle.
[Its fine transverse striation.]

y. The central more fluid part, not sharply
marked off from ft.

The various clear spaces (alimentary va-
cuoles) in it, containing foreign (swallowed)
bodies (Diatoms, Protococcus, &c.).

3. 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 cortical layer; sometimes nearly homo-
geneous, sometimes more distinctly granular.
The nucleus is usually indistinguishable
until after treatment with iodine (4).

. The gullet ; sometimes seen in optical trans-
verse section as a clear round space; some-
times seen sidewise as a canal opening above
on the disc, and ending abruptly below in the
body-substance.

1). 77/6' stalk.

a. Its length and diameter (measure).

/?. Its structure ; the external homogeneous layer
(sheatJi) continuous with the cuticle; the highly
refractive centre (axis) generally surrounded
with granules, and continuous with the cor-
tical layer of the bell.

ix.] THE BELL-ANIMALCULE. 95

2. In the retracted state,
a. The body.

a. Its form; pear-shaped; rounded off above; no
disc or peristome visible.

ft. The clear transverse space near the top, indi-
cating the interval between the retracted disc
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. Compare especially
the regularity, definiteness and rapidity of some of
them with the slow and irregular movements of
Amoeba. (III.)

a. The ciliary movement.

a. Examine the cilia carefully; delicate homo-
geneous processes ; their length, diameter and
form; their position.

[/3. 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-ordination of these movements; they
work in a definite order; note the currents
produced in the neighbouring water (if ne-
cessary introduce a few particles of carmine
under the coverslip); the sweeping of small
bodies down the gullet.

b. The movements of the contractile vesicle (see III.
A. 3. c). Tolerably regular rhythmic distension
and collapse (diastole and systole).

ELEMENTARY BIOLOGY. [CHAP.

c. TJie currents in the central parts of the body car-
rying round the swallowed bodies. (Compare
VI. C.)

d. The movements of the animal as a whole. ( J inch
or \ inch obj.)

a. Its extreme irritability ; it contracts on the
slightest stimulation : often without any ap-
parent cause.

/?. The movements which occur in contraction;
the coiling up of the stalk ; the rolling in of
the disc. The rapidity of these movements.

y. The mode of re-expansion ; 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. Note the following points in various specimens

a. Multiplication by fission; a bell partially divided
into two by a vertical fissure starting from the
disc.

(3. 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.

ix.] THE BELL-ANIMALCULE. 97

[. Conjugation; the attachment of a small free
swimming bell to the side of a stalked one.]

[e. Encystation j 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 Vorticella which may be
met with, and which will do nearly as well for exami-
nation, are/-

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 re-
tracted.

[The activity of the movements of the free Infusoria inter-
feres 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 Para-
mcEciiun, Nyctotherus and Balantidium instantly, without de-
stroying the essential features of their organization.]

M.

\

X.

THE FRESHWATER POLYPES (Hydra viridis

and H. fusca).

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,
and are cylindrical or slightly conical in form. From the
free end numerous delicate filaments, which are often much
longer than the body, proceed and spread out with a more
or less downward curve, in the water. If touched, these
threads, which are the tentacles, 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 termed Hydra fusca, the green
to that called H. viridis. The polypes usually remain at-
tached 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.

When any small animal, such as a water-flea, swimming
through the water conies in contact with the tentacles, it is
grasped, and conveyed by their contraction to the aperture

CHAP, x.] THE FRESH-WATER POLYPES. 99

of the wide mouth, which is situated 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
irmutritious 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 is formed; 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 projections of the surface
appear at the bases of the tentacles or nearer the attached
end of the body. Within the former (testes] great numbers
of minute particles, each moved by a vibratile cilium, are
developed and are eventually set free. Functionally, these
answer to the antherozooids of plants, and they are termed
spermatozoa.

ioo ELEMENTARY BIOLOGY. [CHAP.

The enlargement formed near the attached end of the
polype may be single, as in Hydra firidis, or as many as
eight may be found in other species. It becomes much larger
than the testis, and is the ovary. Within it is developed
a single large egg, or ovum. This ovum, which is a huge
nucleated cell, is impregnated 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 becomes surrounded with a thick, usually
tuberculated or spinous, case ; and, detaching itself from
the body, forms the 'egg,' from which a new Hydra is de-
veloped.

Microscopic examination shews that the body of the
Hydra is a sac, the wall of which is composed of two
membranes, an outer (ectoderm), and an 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 those
of the ectoderm being prolonged into delicate fibres, which
run parallel with the long axis of the body on the inner face
of the ectoderm. The green colour of the Hydra viridis
results from the presence of chlorophyll grains imbedded in
the protoplasm of the cells.

In both the ectoderm and the endoderm the protoplasm
of the cells contains very singular bodies, the so-called
iirticatiug capsules, thread-cells, or nematocysts which are
oval bags, with thick and elastic walls, containing a spirally
coiled-up filament which is unrolled suddenly on the
slightest pressure, and then presents the appearance of a long
filament attached to the capsule, and often provided with
three recurved spines near its base. As similar capsules of

x] THE FRESH-WATER POLYPES. 101

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 their prey.

Thus, Hydra is essentially a cellular organism like one
of the lower plants, but differs from them morphologically
in the fact that its cells are not enclosed within cellulose
walls ; and physiologically, in the dependence of these cells
for their nutrition upon ready formed protein matter. The
function of the chlorophyll granules contained in the endo-
clerm of the green Hydra, and of the brown or orange-
coloured particles in the endoderm of the other species, is
wholly unknown.

The Hydra, again, may be compared to an aggregate of
Amcebce, which are arranged in the form of a double-walled
sac and have undergone a certain amount of metamorphosis.

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. No trace of a special
nervous system has yet been discovered, and the manner in
which the actions of the different parts of the Hydra are
combined to a common end, as in locomotion and the seizing
of prey, is not understood.

The Hydra has none of the special apparatuses which are
termed sense-organs, or glands. The cavity of the body
alone represents a stomach and intestine ; there are no
organs of circulation, respiration or urinary secretion; the
products of digestion being doubtless transmitted, by im-
bibition, from cell to cell, and those of the waste of the cells
exuded directly into the surrounding water.

102 ELEMENTAR Y BIOLOGY. [< n \r.

LABORATORY WORI

LV.

1. Put into a beaker some water containing bodies to
which Hydrse are attached, and place the beaker in a
window not exposed to direct sunlight : in the course
of some hours many Hydrse will be found attached
to that side of the glass which is turned towards the
light. Note their size, form, colour, mode of attach-
ment and movements.

2. Transfer a Hydra, by means of a pipette, on to a
slide; cover in plenty of water with a large coverslip,
and examine with i inch obj. Note-

a. Form.

a. The base (so called foot) : a flattened disc : nar-
rower or wider than the body according to the
state of extension of the latter.

/?. The body proper: cylindrical, varying much in
length and diameter with the state of extension
of the animal; its conical free end, with an open-
ing (mouth) in it. It is often difficult to see the
mouth in this way, especially in the green species.
It is readily seen however if a Hydra be placed
in a drop of water, without a coverslip, and be
watched with an inch objective until it turns its
anterior end up towards the observer.

y. The tentacles: ranged round the mouth; their
number and shape; their varying length and
diameter ; the knob-like eminences on them.

S. The testes: small conical colourless eminences be-
low the point of attachment of the tentacles.

x] THE FRESH-WATER POLYPES. 103

e. The ovary: a larger rounded colourless pro-
minence near the base : there may be more than
one.

. The buds: young Hydrae, of various sizes and
stages of development, attached to the sides of
the parent.

Either 8, e, or , or all of them, may be absent in
some specimens.

b. Structure.

a. The animal evidently composed of two layers,
an outer, ectoderm, and inner, endodcrm, the latter
alone containing chlorophyll in the green species :
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.

(3. The body -cavity: difficult to make out in the
green species, frequently visible in the brown
ones as a darker central patch with which the
mouth-opening is continuous ; the extension of
the body-cavity into the tentacles. Note cor-
puscles floating along inside them when they are
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.

{!. Its irritability ; slight pressure or other stimulus
immediately causes it to contract.

3. Examine with a high power: try to make out the
different cells of the ectoderm

104 ELEMENTARY BIOLOGY. [CHAP.

a. Large somewhat conical nucleated cells, with the
broader end turned outwards.

ft. Smaller rounded cells packed between the deep
ends of the larger ones.

y. The nematocysts: small oval capsules, with a fila-
ment coiled up inside them, which are dispersed
through the ectoderm in the interior of its com-
ponent cells.

4. Treat with magenta: note the staining of the cells,
the emission of the thread-cells, and the protrusion of
their threads : three chief forms of thread-cell-

a. An oval capsule with a filament many times its
own length attached to one end, and three short
processes radiating from the base of the thread.

(3. Smaller thread-cells, without the radiating pro-
cesses and with a short thread.

y. C ells like /3, but with a much longer thread.

5. Imbed in paraffin a Hydra which has been hardened
in chromic or osmic acid 1 and cut sections from it;
or lay a prepared Hydra on a glass slide and with
a razor cut off transverse slices ; having obtained by
either method a number of thin sections mount them
in glycerine and make out

a. The large and small cells of the ectoderm and its
thread-cells, their arrangement and relations. (3).

1 When a Hydra is placed in the above hardening fluids it nearly
always contracts so much as to make it difficult to cut sections. If it be
first killed, by placing it in a small quantity of water and when it has
expanded adding some boiling water, fairly extended specimens for
hardening can usually be obtained.

x.] 7 HE FRESH-WATER POLYPES. 105

/?. The cells of the endoderm : large, nucleated, with
a flattened base and a rounded free end : their
arrangement in a single layer.

7. The thin intermediate layer (muscular stratum}
between ectoderm and endoderm.

8. The body cavity.

6. Tease out in water a specimen which has been
treated with weak chromic acid (o. ig) or with osmic
acid : make out the various cells already described :
notice branched tails proceeding from the narrower
ends of the larger ectoderm cells.

Tease out a fresh Hydra in water and observe the
various cells. Note the amoeboid movements exhibited
by some, and the single cilium attached to other (endo-
derm) cells.]

8. Gently flatten out a testis in water by pressure on the
coverslip, and examine with a high power. Accord-
ing to its state of maturity the following contents will
be found in it

a. A collection of the smaller ectoderm cells.

/?. The same but having lost their nucleus and
become hyaline.

7. Cells otherwise like /?, but with a long filament
proceeding from them.

B. Ripe spermatozoa: bodies consisting of a very
small oval head to which a very delicate filament
is attached, and which, should they get free, swim
about in the water by the movements of this fila-
ment. They may frequently be seen in motion
within the unruptured testis.

1 06 ELEMENTAR Y B10L OGY. [CHAP. x.

9. Press out an ovary: according to its stage of develop-
ment there will be found in it

a. Simply ectoderm cells with an unusual prepon-
derance of the smaller form.

P. Imbedded among cells like a, one which has
become larger and clearer than the rest, and
possesses a distinct central clear spot in it.

y. Considerable aggregation of granular proto-
plasm round this cell, so as to form a body
consisting of a granular protoplasmic mass, in
which is imbedded a clear round vesicle, which
again contains a distinct rounded dot.

S. The ripe ovum. Consisting of a great irregu-
larly branched mass of protoplasm (vitettus),
in which is a clear space (germinal vesicle)
containing another body (the germinal spot}.

e. The segmented ovum : composed of a large
number of small cells. Its thick capsule,
rough on its external surface.

XL

THE FRESH-WATER MUSSEL
(A nodonta Cygncea) .

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 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 mantle, 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. If some finely dividing
colouring matter, such as indigo, is dropped into the water,

loS ELEMENTARY BIOLOGY. [CHAP.

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 'inhalant' and 'exhalent' currents go on, so long
as the animal is alive and the valves are open. Any disturb-
ance, however, causes the foot, if it was previously protruded,
to be retracted, while the edges of the mantle are drawn in
and the two valves shut with great force. On the other
hand, in a dead Anodonta the valves always gape, and if
they are forcibly shut spring open again. The reason of this
is the presence of an elastic band, which unites the dorsal
margins of the two valves, for some distance, and is put on
the stretch when the valves are forcibly brought together.
During life they are thus adducted by 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 %&& posterior adductors.

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 j the mouth is
median and situated between 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 vertically striated outer surfaces, are visible.
These are the gills or branchice. 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,

XL] THE FRESH-WATER MUSSEL. 109

and end, ventrally, in the thickened margins already men-
tioned. 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, before 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 is relatively small and shallow, and is termed the cloacal
chamber; while the gills, the foot, and the palps, hang down
into the relatively large branchial chamber which occupies
the space between the mantle-lobes for the rest of their
extent. It is the prolongation of the margins of the former
cavity which gives rise to the tubular anal siphon seen in so
many Lamellibranchs ; while the ventral or branchial siphon
is a similar prolongation of the margins of the branchial
chamber. The dorsal siphon is the channel through which
the exhalent currents pass ; the ventral, that for the inhalent
currents.

The currents are produced and kept up by the action of
the cilia which abound upon the gills. The latter are per-
forated by innumerable small apertures, and the chambers
contained between the two lamellae of which each gill 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 the current which sets
from the branchial to the cloacal chamber.

The current of water which is thus continually drawn into
the branchial chamber carries with it minute organisms, In-
fusoria^ Diatoms and the like, and many of these are swept
to the fore part of the branchial chamber, where they enter
the mouth, and are propelled by the cilia which line its cavity

no ELEMENTARY BIOLOGY. [CHAP.

into the alimentary canal. The latter presents a short and
wide gullet, a stomach surrounded by hepatic follicles, 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 finally ends in the
anus.

As the mouth is below and behind the anterior adductor
and the rectum passes in front of and above the posterior
adductor, it is clear that the alimentary canal, as a whole,
lies between the two adductor muscles.

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 5), 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
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.

XL] THE FRESH-WATER MUSSEL. in

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 ventricles contract, and is forced out,
either forwards or backwards, through the two aortse. 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.

The majority of the vessels which convey the blood from
the vena cava to the branchiae, traverse the walls of the
dark-coloured organs the organs of Bojanus which has
already been mentioned ; and it is probable that they here
part with their nitrogenous waste matters the organ of
Bojanus, in all probability, 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 which is situated close to the attach-
ment of the inner gill to the walls of the body. Thus the
cavity of the pericardium communicates directly with the
exterior, though by a roundabout way. But it also Com-
municates directly with the venous system, by sundry small
apertures placed in the anterior part of its floor. Hence
it must contain a mixture of blood and water.

if2 ELEMENTARY BIOLOGY. [CHAP.

The blood of the Anodoiita is colourless, and contains
colourless corpuscles, which resemble those of Man in struc-
ture and present the same Amcebiform movements.

The nervous system of the Anadonta consists of three
pairs of yellow ganglia ; the cephalic, situated at the sides of
the mouth ; the pedal, placed in the foot ; and the parieto-
splancJmic, on the under face of the posterior adductor mus-
cle. They are united by commissural cords which connect
the cephalic ganglia with one another, and with the pedal
and parieto-splanchnic ganglia, respectively. The only sense
organs which have been discovered, are a pair of auditory
vesicles, connected by nervous cords with the pedal ganglia.

The sexes are distinct. The testcs 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, and,
thrown off in enormous numbers, make their way out with
the exhalent currents.

The ova are spherical, and the vitelline membrane is pro-
duced at one point into a short open spout-like tube, with a
terminal aperture, the micropyle, through which, in all pro-
bability, the spermatozoon makes its entrance. When fully
formed, multitudes of these ova pass out of the oviducal
aperture and become lodged in the chambers of the gills,
particularly the external gill, which is frequently completely
distended by them. Here they are hatched, and give rise to
embryos, which are so wholly unlike the parent Anodonta,
that they were formerly thought to be parasites, and received
the name of Glochidhim. The embryo Anodonta is provided
with a bivalve shell. Each valve has the form of an equi-

XL] THE FRESH-WATER MUSSEL. 113

lateral 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 ap-
proach, 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. What appears to be 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.

After a time the larval Anodonta leave the body of the
parent, and attach themselves to floating bodies very com-
monly to the tails 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 undergo a metamorphosis; the gills are developed,
the foot grows, the auditory vesicles become conspicuous in
it, and the young Anodonta at length drops off and falls into
its ordinary habitation in the mud.

LABORATORY WORK.

. In the natural state of the animal only the shell or
exoskeleton is visible, or this may be slightly open,
and then the edge of the membrane lining it (the
mantle] may be visible. Raise one valve of the shell,
by separating the mantle from it with the handle of a
scalpel, and then cutting through two strong bodies

M. 8

1 i 4 ELEMENT A R Y BIOLOG Y. [CHAP.

(the adductor vmsdes}, one at each end of the animal,
which run from one valve of the shell to the other
and prevent their separation. The two valves will
now be united only by their ligament.

2. General form and structure.

a. In the animal now laid bare may be distin-

guished

a. A dorsal border turned towards the hinge of
the shell, and nearly straight.

/?. A curved ventral border, opposite the dorsal.

y. A wider anterior end.

8. A narrower posterior end.

e. A right and left side.

1. The mantle or pallium.

a. A bilobed semitransparent membrane, one lobe
linin each valve of the shell.

The continuity of the two lobes on the dorsal
side of the animal; their separation along
most of its ventral side, where each forms a
thick yellowish free border.

y. The union of the two pallial lobes, for a short
distance, towards the posterior part of their
ventral border.

3. The rudimentary dorsal and ventral siphons,
separated from one another at the point of
union y and each marked out by a part of
the mantle-edge covered by short hair-like
processes : the dorsal siphon completely closed
below and forming a narrow oval slit; the

XL] THE FRESH-WATER MUSSEL. 115

ventral siphon open below and continuous with
the cleft between the ventral edges of the
mantle-lobes.

e. The branchial or pallial chamber: turn back
the ventral edge of that mantle-lobe from which
the shell has been removed : a chamber is thus
exposed into which the ventral siphon, and the
cleft continuous with it, lead.

. The cloacal chamber: pass a probe through the
dorsal siphon; it will enter a small chamber,
separated from the pallial chamber by a par-
tition which unites the hinder part of the two
inner gills (c. /?).

c. The contents of the pallial chamber.

a. The foot: a large, yellowish, somewhat plough-
share-shaped mass, in the middle line; its apex
directed forwards and ventrally, towards the
front of the cleft between the mantle-lobes.

(3. The gills or branchite : two lamellar bodies
on each side of the foot, but reaching farther
back than it does : the outer gill on each side,
attached to the mantle-lobe; the inner, attached
to the foot in front, but farther back, separated
by a cleft from it ; and behind the foot, united
across the middle line with its fellow so as to
form a partition separating the cloacal from
the pallial chamber.

y. The labial palps : a pair of small triangular
processes on each side, in front of the gills
and on the dorsal end of the anterior edge of
the foot.

82

n6 ELEMENTARY BIOLOGY. [CHAP.

S. The mouth: each labial palp is continuous with
its fellow across the middle line, and between
the lip-like ridges thus formed, lies the wide
mouth-opening.

d. The anterior and posterior adductor muscles: if
the reflected mantle-lobe be turned down again,
the oval divided ends of the adductor muscles
can be seen. They appear to perforate the
mantle.

3. Now remove the animal completely from its shell, by
detaching the other mantle-lobe from the valve to
which it is fixed, and cutting through the attachments
of the adductor muscles to that valve. The thick
dorsal border of the animal and the continuity of
the mantle-lobes will now be more readily made out
than they could be previously (2. b.

The heart.

<?. On the dorsal border of the animal is a clear
space, where the mantle is very thin and covers-
in a cavity filled with fluid. This cavity is the
pericardium, and through its walls the heart can
be seen beating.

b. Pin the Anodon out in water between two pieces
of loaded cork, or paraffin, so that its dorsal
border is upwards, a mantle-lobe spread over
each bit of cork, and its foot and gills hanging
down between the two pieces: then carefully cut
away the dorsal side of the pericardium without
injuring the heart.

c. The heart will now be exposed; it is a yellow-
ish transparent sac, exhibiting regular contrac-

xr.] THE FRESH-WATER MUSSEL. 117

tions and composed of a median and two lateral

chambers.

a. The v entire, or median chamber; an oval sac,
from each end of which a large vessel (anterior
and posterior aorta) is continued ; running
through the middle of the ventricle is seen
part of the alimentary canal. All parts of
the wall of the ventricle do not contract to-
gether; but a sort of 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.

/5. 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.

5. The organs of Bojarms.

a. Divide the alimentary canal at the posterior part
of the pericardiac chamber and turn it and the
heart forwards, so as to lay bare the floor of the
pericardium. Running along the middle line
of this floor will be seen a large blood-sinus,
the great vena cava; on each side of this, the
floor is formed by the roof of a transparent sac
(the non-glandular part of the organ of Bojanus],
through which is seen a dark brown mass (the
glandular part of the orga?i of Bojanus).

b. At the extreme front end of the pericardiac floor,
immediately under the point at which the in-
testine enters the cavity, will be found a pair of
oval openings; pass into each a bristle, tipped

ji8 ELEMENTARY BIOLOGY. [CHAP.

with a small knob of sealing-wax to prevent it
from perforating a passage for itself : the open-
ing will be found to lead into a channel which
runs along the glandular part of the organ of
Bojanus.

c. Remove carefully the thin transparent roof of the
non-glandular part of the organ of Bojanus, on
one side, so as to lay bare the portion of the
glandular part which lies within the non-glandu-
lar: the bristle will be found to leave the passage
in the glandular portion by an aperture, which
puts it in communication with the non-glandular
part, and is situated on the upper side of the
glandular part, opposite the posterior end of the
pericardium. The glandular part extends back
some way beyond this point; but it is imbedded
closely in the neighbouring tissues, and is not
contained in the loose non-glandular sac, which
reaches back no farther than the posterior end
of the pericardium.

d. Examine the floor of the non-glandular part, at
its anterior end : in it will be found a small
aperture; gently push a guarded bristle through
this : then turn the animal over, and detach the
front end of the inner gill on the same side, from
the foot. The bristle will be found to have
passed out by an aperture (external opening of the
organ of Bojanus} which lies just above the attach-
ment of the gill to the body.

6. The gills or branchiae.

a. Cut out one of the gills and examine it; it will be
found to consist of two lamellae united by their

.] THE FRESH-WATER MUSSEL. it 9

ventral edges and enclosing a central cavity,
which opens into a chamber (epibranckial) above,
which is continued back to open into the cloacal
chamber. The cavity between the lamellae is
subdivided by irregular partitions, which pass
from one lamella to the other.

b. Carefully cut out a bit of the wall of the gill-sac
on one side; mount in water and examine with
i inch obj. The outer surface will be seen to be
formed by parallel vertical bars, containing pairs
of short rods; the inner face being formed by a
meshwork of large vessels, perforated by wide
apertures.

c. Examine with a higher power: the margins of
each cleft will be found covered with large active
cilia.

7. The nervous system.
a. The cerebral ganglia.

a. These will be found by carefully dissecting
away the bases of the labial palps and the
integument on the dorsal side of the mouth.
They are two in number, each about the size
of a pin's head, and somewhat triangular in
form.

/?. The commissures connected with the cerebral
ganglia are

A short cord uniting the two ganglia across
the middle line over the mouth.

A cord, the cerebro-pedal commissure, which
runs downwards and backwards from each and
becomes continuous with that which runs for-

ELEMENTARY BIOLOGY. [CHAP.

wards from the pedal ganglion of the same
side (b. /5).

A long slender cord which passes directly
backwards from each beneath the organ of
Bojanus and joins the parieto-splanchnic gan-
glia of the same side (c).

b. The pedal ganglia.

a. Lay the animal on one side and proceed gently
to scrape away the tissues of the foot at about
the junction of its anterior with its middle
third, where the muscular and the visceral
portions of the foot join. The pedal ganglia
will thus be brought into view. They are a
pair of deep-orange-coloured oval bodies, each
rather larger than a big pin's head; they are
applied to one another in the middle line.

/?. From each ganglion one commissural cord
(a. (3) passes forwards and upwards to the
cerebral ganglion of its side, and branches are
given off to the muscles of the foot and to the
auditory organ.

c. The parieto-splanchnic ganglia.

a. This pair are readily found by turning the
animal on its dorsal side, and dissecting away
the integument from the ventral surface of the
posterior adductor muscle.

(3. Trace forwards from each the cord (a. (3)
which runs to the cerebral ganglion of the
same side. It is easy to follow the commissure
so long as it lies in the region of the organ of
Bojanus difficult further on.

XL] THE FRESH-WATER MUSSEL. 121

8. 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 cord given oft" from the pedal
ganglion, to a branch of which it is attached.
There is usually an auditory vesicle connected
with each pedal ganglion.

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.

9. The alimentary canal.

a. This should be dissected out in another Anodon
w r hich has been \vell hardened in spirit. Care-
fully dissect away the thin layers of muscle which
cover the left side of the foot : as this is done
the dark-looking coil of the intestine will come
into view: the two coils lying parallel to one
another near the posterior border of the foot
being probably those first seen. Continue to
pick away the muscles and reproductive caeca
until as much as possible of the course of the
intestine is exposed. Make a small hole in it in
one of the hindermost coils, pass in the end of
a blow-pipe and inflate : then carefully lay open
the intestine throughout its whole length so as to
expose its inner surface; working towards the
stomach on the one hand and the rectum on the
other. Pass a guarded bristle into the mouth as
far as it will readily go, and then lay open the

1 Cyclas cornea a small fresh-water lamellibranchiate mollusk.

ELEMENTARY BIOLOGY. [CHAP.

alimentary canal along it, with a pair of scissors.
Then push the bristle gently a little farther on,
and follow it with the scissors, and so on, until
the part where the intestine has already been
laid open is reached.

I. The alimentary canal first runs towards the dorsal
side for a short way (oesophagus), lying on the
ventral side of the anterior adductor muscle : it
then dilates into an irregular sac (the stomach) ;
behind the stomach it continues as a long narrow
tube, the intestine; this turns abruptly down, be-
hind the stomach, into the foot, running at first
towards its postero-inferior border; then curves
up and forwards in the foot to near its dorsal
part; then bends abruptly down and backwards
again, parallel to its previous course, towards the
ventral part of the foot, where it makes another
turn and after running forwards some way turns
upwards and runs to the anterior part of the
pericardium, where it turns backwards and runs
as a straight tube (the rectum), first through the
ventricle of the heart, and then (passing on the
dorsal side of the posterior adductor muscle)
along the dorsal side of the cloacal chamber, in
which it ends in an opening, the anus, placed on
a prominent papilla.

c. On the sides of the stomach lies a brownish
glandular mass, the liver.

a. Tease out a bit of the liver in water, and
examine with \ obj. It is composed of
branched csecal tubes lined by a layer of
brownish epithelial cells.

XL] THE FRESH-WATER MUSSEL. 123

10. Reproductive organs.

a. The animals are dioecious, but the reproduc-
tive 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. Close to the external opening of the organ of
Bojanus will be found another small opening
on each side, this is the generative opening.

c. From the generative opening can be traced
back a duct, which divides into many csecal
branches which lie in the upper part of the
foot.

11. Muscular system.

a. This is most readily dissected out in a spe-
cimen which has been hardened in spirit. The
chief muscles are :

a. The anterior and posterior adductor muscles
which pass directly from one valve of the
shell to the other. These have already been
seen.

ft. The posterior retractor of the foot : this can
readily be found, on each side, running into
the foot from its attachment to the shell in
front of the posterior adductor muscle.

y. The anterior retractor of the foot : this runs
from its attachment to the shell behind the
anterior adductor muscle, into the front of
the foot.

B. The protractor of the foot arises from the
inner surface of the shell behind the organ

ELEMENTARY BIOLOGY. [CIIAIV

of the anterior adductor and below that of
the anterior retractor. Its fibres spread out in
a fan-like manner over the upper part of the
foot,, some of them extending over the sur-
face of the liver.

e. The lesser retractors. Several very small
muscles arising from the shell just in front
of the umbo and spreading over the surface
of the liver.

. The intrinsic foot-muscles: forming the
greater part of the ventral portion of that
organ.

77. Small muscles attached to each mantle-lobe,
at some little distance from its swollen free
edge and fixed to the shell along a linear
impression, which runs from one adductor to
the other and is termed the pallial line.

b. Tease out in glycerine a bit of one of the mus-
cles which has been treated with 0-5^ chromic
acid solution. Examine with |- inch obj. It
is composed of spindle-shaped flattened cells,
in each of which lies an elongated nucleus :
the substance surrounding the nucleus is clear,
but the rest of the cell is granular and con-
tains a great number of small particles arranged
pretty definitely in transverse rows. While these
muscular fibres agree in form with those of
smooth muscles, in minute structure they ap-
proach striped muscles,

12. The shell or exoskeleton.

a- Its two hardened lateral pieces or valves; each
with a straight dorsal and a curved ventral edge,

xr.] 7 'HE FRESH-WATER MUSSEL. 125

and an anterior larger and posterior smaller
end : note the soft uncalcified ventral edge of
each valve.

b. The umbo ; a small blunt eminence on the
dorsal border of each valve near its anterior
end.

c. The ligament: an elastic uncalcified part of the
exoskeleton behind the umbones, uniting the
two valves and tending to keep their ventral
edges slightly separated.

d. The markings on the shell.

a. External markings. The outside of the shell
is greenish brown, and on it are seen a num-
ber of concentric lines generally parallel to
the margin of the shell, and more numerous
towards the ventral edge.

(3. Internal markings. The interior of the valve
is white and iridescent : on it are seen, near
the dorsal border, two oval marks, the ante-
rior and posterior adductor impressions.

Joining the two adductor impressions is
a curved line, the pallial impression, which
marks where the muscles of the edge of the
mantle were fixed to the shell.

In front of the posterior adductor impres-
sion is seen a small mark, indicating where
the posterior retractor muscle was fixed.

Behind the anterior adductor impression
are two marks, one opposite its upper, the
other opposite its lower end : the former
indicates the point of attachment of the

ELEMENTARY BIOLOGY. [CHAP. xi.

anterior retractor, the latter of the protractor
pedis muscle.

Extending from each' adductor impression
towards the umbo is a fainter, gradually ta-
pering impression, which may be followed
into the cavity of the umbo, and indicates
the successive attachments of the adductor
muscles, as the animal has increased in size.

13. In the breeding season, examine the contents of the
testis for spermatozoa, and those of the ovary for
ova. Note the micropyle of the latter. If the outer
gill appear to be thick and distended, it will be found
full of the larvae of the Anodon^ Glochidium. Note
the characters of their shells and the entangled fila-
ments, or byssits, with which they are provided.

XII.

THE FRESH-WATER CRAYFISH (Astaats 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 epi-
dermis, 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

128 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 telson. The anus is
situated on the ventral 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
belongs to the head or cephalon, from a posterior division
which covers the thorax ; and the thoracic division of the
carapace further presents a central region, which covers
the head, and wide lateral prolongations, which pass down-
wards and cover the sides of the thorax, their free ven-
tral edges being applied against the bases of the thoracic
limbs. These are the branchiostcgitcs. 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. 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 may be observed. There is no trace of any

xii.] THE FRESH-WATER CRAYFISH. 129

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 is formed
by the great claws or chelce. 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 maxilla.
The second, or outermost, is produced, externally, into the
scaphognathite, which will be seen to lie in a groove which
separates the head from the thorax laterally and is the
cervical groove.

Anterior to these maxillae lie the two very stout man-
dibles. Between their inner toothed ends is the wide aper-
ture of the mouth, bounded, in front, by a soft shield-shaped
plate, the labrum ; and behind, by another soft plate, divided
by a deep median fissure into two lobes, which is the meta-
stoma. Thus far, the surfaces of the somites to which the
appendages are attached look downwards, 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 is the cephalic flexure.
In correspondence with this change of position of the sur-
M. Q

130 ELEMENTARY BIOLOGY. [CHAP.

face to which they are attached, the three pairs of append-
ages 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 antennules ; and the most anterior
is formed by the short subcylindrical stalks (pphthalinites),
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 ;
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 appendages (two pairs
of maxillae, one pair of mandibles, one pair of antennae, one
puir of antennules, one pair of eyestalks), making in all twenty
pairs of appendages. In correspondence with the number of
appendages the body consists of twenty somites; of which six
remain moveable upon one another to form the abdomen,
while the other fourteen are united to form the cephalothorax.

The branchiostegite is an outgrowth of the dorsolateral
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
prseoral and post -oral somites.

Thus the whole skeleton in these animals may be con-
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-

xii.] THE FRESH-WATER CRAYFISH. 131

ducible to modifications of a fundamental form, consisting
of a basal joint (protopodite) with three terminal divisions
(endopodite, exopodite, epipodite).

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 sys-
tem, the muscles and the reproductive organs, being dis-
posed so as to be symmetrical in relation to the median
vertical plane of the body.

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-
fied 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 unite 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

92

j 3 2 ELEMENTARY BIOLOGY. [CHAP.

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; two small 'cardiac'
teeth are borne by the median process of the cardiac ossicle;
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. The dis-
position of all these parts is such that when these muscles
contract, the uro-cardiac tooth moves forwards and down-
wards, while the lateral teeth move inwards downwards and
backwards, and the three meet in the middle line. The
action 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
hepatic ducts open, one on each side, at the junction of the
pyloric division of the stomach with the intestine. The

XIL] THE FRESH-WATER CRAYFISH. 133

intestine is slender and delicate, smooth internally in the
Lobster, papillose in the Crayfish. Near its hinder end its
walls become thicker for a short distance, and this thick-
ened portion, with which, in the Lobster, a short dorsal
caecum is connected, may be regarded as the large intestine
or rectum.

The heart is a short, thick, somewhat hexagonal, symmetri-
cal 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, 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 abdominal
artery, which runs along the dorsal face of the intestine,
giving off transverse branches as it goes, in each somite ; and
the other, the sternal artery, which passes ventrally to the
interspace between the penultimate and antepenultimate

134 ELEMENTARY BIOLOGY. [CHAP.

thoracic ganglia, passes between their commissures and
divides into two branches, which run, backwards and for-
wards, 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
sinuses, 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 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, which is therefore, like the
heart of Anodon, a systemic and not a branchial heart. But
whether the whole of the venous blood takes the same

xii.] THE FRESH-WATER CRAYFISH. 135

course, or whether some of it returns from the dorsal sinuses
directly to the pericardium, is a question which is not de-
cided. 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 compartments in immediate communication with cer-
tain 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
irregularly 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. The place of the water thus thrown out is taken by
water which flows in by the inferior and posterior cleft be-
neath the free edge of the branchiostegite, and thus a constant
current over the gills is secured. Each branchia is somewhat
like a bottle-brush, having a stem beset with numerous fila-
ments; and the blood contained in the vessels of the latter

136 ELEMENTARY BIOLOGY. [CHAP,

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 attached partly to the epimera of the
thoracic somites, partly to the proximal ends of the thoracic
limbs. The epipodites 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 neces-
sarily 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 propor-
tion to the muscular contractions which give rise to the
movements of the limbs and the consequently increased
lormation of carbonic anhydride.

The mode and place of the excretion of nitrogenous
waste is not yet clearly made out, but it seems probable
that two large green glands which lie in the cephalon, close
to the bases of the antennae, are renal organs. Each gland
encircles the neck of a large thin-walled sac which opens by
a short canal upon the ventral face of the basal joint of the
antenna.

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 integuments; and of a
visceral nervous system, developed chiefly upon the stomach.

Of the thirteen ganglia, the most anterior lies in the
cephalon, close to the attachments of the three anterior pair
of appendages, and gives branches to them and to the vis-
ceral nervous system. It is usually termed the brain or the
supra&sophageal ganglion. It is connected by two commis-

XIL] THE FRESH-WATER CRAYFISH. 137

sural cords, which pass on each side of the gullet, with
a larger ganglionic mass, which is called the subccsophageal
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 maxillae and the three pair 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 between the abdominal
ganglia are single ; but, in the thorax, the commissures are
double, and the ganglia themselves shew more or less evi-
dent indications of being double. And there is reason to
believe that these thirteen apparent ganglia really represent
twenty pairs of primitive ganglia, one pair for each somite ;
the three pair of prseoral ganglia having coalesced into the
brain ; and the five 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.

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 eyes talk presents a
clear, smooth area of somewhat crescentic form, divided into
a great number of small four-sided facets. This area cor-
responds 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

138 ELEMENTARY BIOLOGY. [CHAP,

the striated spindle. The inner extremity of this again is
connected with the convex surface of the dilated cushion-
shaped ganglionic 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 per-
formed 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. Morphologi-
cally, the cones, connective rods and striated spindles, are
in many ways analogous to those elements of the retina of
the Vertebrata which make up the layers of rods and cones
and the granular layers. These structures are properly
modifications of the epidermis ; inasmuch as the cerebral
vesicle, of which the retinal vesicles are outgrowths, are in-
volutions of the epidermis of the embryo, and, morphologi-
cally speaking, the free ends of the rods and cones of the
vertebrate eye are, as in the crustacean, turned outwards.
It seems probable, therefore, that the crustacean eye is to be
compared to the retina alone of the vertebrate eye, and that
vision is performed as it would be by the retina deprived of
its refractive adjuncts.

The auditory organ of the Lobster and Crayfish is situated
in the basal joint of the antennule, on the dorsal surface of
which a small slit-like opening, protected by numerous
hairs, is to be seen. The chitinous layer of the integument
is invaginated at this opening, and thus gives rise to a small

xii.] THE FRESH-WATER CRAYFISH. 139

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 hairs. The auditory nerve enters the fold,
and its ultimate filaments reach the bases of these hairs.
The sac contains water in which minute particles of sand
are suspended.

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 the Laboratory
work.

The impregnated ova are attached in great numbers, by
a viscid secretion of the oviduct, to the hairs of the swim-
merets, where they undergo their development. A Lobster
with eggs thus attached, is said by the fishermen to be
* in berry.' In the Crayfish, the embryo 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 un-
like the parent, which undergo a series of metamorphoses in
order to attain their adult condition. The larvas may fre-
quently be obtained by opening the eggs of a ' hen-lobster '
in ' berry.' They have a rounded carapace, t\vo large eyes,
a jointed abdomen devoid of appendages ; and the thoracic
limbs are provided with long exopodites.

The ordinary growth, no less than the metamorphoses
of the Lobster and Crayfish, are accompanied by periodical
castings of the outer, chitinous, layer of the integument.
After each such ecdysis^ the body is soft and the animal
retires into shelter until the ' shell ' is reproduced.

i 4 o ELEMENTARY BIOLOGY. [CHAP.

LABORATORY WORK.

i. General external characters.

The animal is covered by a dense exoskeleton: in it
are readily recognised the following parts :

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 proper and thorax: the anterior pro-
longation of the carapace to form the frontal
spine.

ft. The posterior segmented portion (abdomen) :
its seven divisions ; the anterior six much like
one another; the most posterior (telson)
different from the rest.

b. The great number of 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 by separating the append-
ages beneath the head.

/?. The anus; a longitudinal slit beneath the
telson.

y. The paired genital openings: in the male, on
the first joints of the last pair of appendages
of the thorax: in the female, on the first joints
of the last thoracic appendages but two.

XIL] THE FRESH-WATER CRAYFISH. 141

[S. The openings of the auditory organs.
. The openings of the green glands.

These will be more readily found when the ap-
pendages on which they are situated have been
separated. See 21. f and gJ\

2. Examine carefully the third abdominal segment or
somite and its appendages.

a. The segment proper : arched above ; flattened
below.

a. Its dorsal part (tergum), with an anterior
smooth portion overlapped by the preceding
segment in extension of the abdomen, and a
posterior rougher part overlapping part of the
succeeding segment.

ft. The ventral surface of the segment : united
with the corresponding portions of the preced-
ing and succeeding segments by a flexible
membrane.

y. The point" of union of the appendages with
the somite.

8. The sternum: that portion of the ventral sur-
face of the somite which lies between the
points of attachment of the appendages.

e. The epimeron: the portion of the ventral sur-
face which lies on each side external to the
attachment of the appendage.
This region is very short and passes almost
directly into the inner walls of the pleuron.

. The downward extension (pleuron) of the
lateral walls of the somite formed by the pro-
longation of the tergum and epimeron: the

14* ELEMENTARY BIOLOGY. [CHAP.

smooth facet on the anterior half of the
pleuron where it is overlapped by the one in
front.

b. The appendages or swimmerets : one on each side:
the structure of each

a. The short two-jointed basal portion (protopo-
dite), consisting of a shorter proximal and a
longer distal piece.

/3. The antero-posteriorly flattened elongated
lamellae attached to the distal joint of the
protopodite, an inner (endopoditc] and outer
(exopodite).

3. The fourth and fifth abdominal segments : closely

resembling the third.

4. The sixth abdominal segment: its modified append-
ages.

a. The protopodite : represented by a single short
strong joint. (In the lobster there is an in-
complete basal joint.)

/?. The exopodite and endopodite : wide plates
fringed with setae : the exopodite divided into
two portions by a transverse joint.

5. The telson.

A flattened plate bearing no appendages : sub-
divided by a transverse joint (it is undivided in
the lobster) : the membranous character of the greater
part of the ventral surface of its anterior division.

The tail-Jin ; formed by the telson and the append-
ages of the sixth abdominal segment.

xii.] THE FRESH-WATER CRAYFISH. 143

6. The second abdominal segment.

Closely resembling the third in the female : in the
male its appendages are modified : the protopodite
and basal joint of endopodite much elongated, and
the latter produced into a plate rolled upon itself so
as to form a demicanal, concave inwards. (In the
lobster the endopodite is produced inwardly, into an
oval process.)

7. The first abdominal segment : its appendages ; rudi-
mentary in the female (it has only one instead of
two terminal divisions in the lobster) : in the male
consisting of a single plate rolled in upon itself. (In
the lobster the single terminal division has the form
of a flat scoop or a narrow spoon with its concave
side turned inwards.)

8. The structure of the cephalothorax.

a. Note again the carapace, with its frontal spine
and cervical suture.

/?. Turn the animal over and note the very
narrow sterna between the points of attach-
ment of the thoracic appendages.

The last thoracic somite is not completely
ankylosed with the one in front, on the verti-
cal side in the crayfish. In the lobster it is.

y. Raise with a pair of forceps the free edge of
the lateral part of the carapace which lies just
over the bases of the thoracic appendages, and
is termed the branchiostegite: note that it is
formed by the large united pleura of the
thoracic segments, and overlaps a chamber in
which the gills lie.

i 4 4 ELEMENTARY BIOLOGY. [CHAP.

'

9. Note the plane in which the sterna of the anterior
three somites of the animal (marked out by their
appendages) lie it is nearly at right angles to the
plane of the remaining sterna of the cephalothorax
so that their appendages are directed forwards in-
stead of downwards.

10. Cut a vertical section of a piece of the exoskeleton
which has been decalcified by lying in i{J- chromic
acid solution for a few days.

a. It will be seen to be composed of a large number
of parallel laminae which are thicker towards
the outer part. The laminae are marked by ill-
defined parallel lines which run perpendicular to
the surface, and which give their edges a striated
appearance. The outermost layer is more trans-
parent than the rest and wants this striation.

b. The epidermis lying beneath the innermost of the
above laminae is composed of ill-defined branched
nucleated granular cells : the outermost giving off
a large number of short processes which end in
clubbed ends and penetrate a short way into the
exoskeleton.

11. The respiratory organs. Remove now the branchio-

stegite on one side and examine the gills: they are
1 8 in number, arranged in two sets.
a. Six are attached to the epipodites of some of
the appendages (2nd and 3rd maxillipedes,
chelas, ist, 2nd, and 3rd pair of ambulatory
limbs).

/?. The remaining 12 are fixed to the sides of
the body, and each consists of a central stem
giving off a number of delicate filaments.

xii.] THE FRESH-WATER CRAYFISH. 145

y. Cut away the gills, noting the two large chan-
nels in the stem of each, and observe the
cervical groove at the front of the gill-chamber
with the scaphognathite (21. d. a.) lying in it.

[. In the lobster there are 20 gills on each side,
arranged as in the crayfish, except that there are
14 on the side of the body.]

12. Circulatory organs. Immerse the animal in water
with its ventral surface downwards: cut away care-
fully with a pair of scissors the dorsal part of the
carapace which lies behind the cervical suture and
that part of the wall of the thorax from which the
gills have been removed.

A chamber (the pericardia! sinus) is thus laid bare
in which lies a polygonal sac, the heart.

a. The six openings from the sinus into the heart ;
two superior, two inferior, and two lateral: pass
bristles into them. The arteries arising from the
heart; five anterior, one (ophthalmic) single m
the middle line, the others (antennary and hepatic}
in pairs; one, the sternal, the largest of all, given
off from the posterior end.

b. Cut away the terga of the abdominal somites and
follow back the superior abdominal branch of the
sternal artery, removing carefully the muscles
which lie over it in the abdominal region. It
will be seen as a transparent tube lying in the
middle line on the intestine (14. b.} y or in the
female lobster separated from it anteriorly by
the posterior ends of the two ovaries. It gives
off branches from its upper side to the muscles
over it, and also a pair of branches which run out

M. 10

146 ELEMENTARY BIOLOGY. [CHAP.

laterally in the intervals between each pair of
somites. In the sixth abdominal somite it termi-
nates by splitting up into three or four large
branches which pass in a radiating manner into
the telson. On account of the small size of the
crayfish this artery is difficult to dissect in it.

c. The sternal artery presents an enlargement at its
commencement just where the above branch
arises from it. It then passes vertically down-
wards towards the ventral surface, passing on
one side of the intestine. Its subsequent course
must be followed later (15).

13. Reproductive organs.

These differ considerably in the crayfish and the lob-
ster. They lie partly beneath the heart, which must
therefore be removed or pushed on one side in order
to see them. Both animals are unisexual.

a. Of the Crayfish.

a. The testis. A trilobed yellowish mass : two of
its lobes 'are larger than the third and pass
forwards side by side in the middle line: the
third lobe is directed backwards.

/?. The two vasa deferentia arise just where the
posterior lobe of the testis meets the two ante-
rior. Each is narrow near the gland, but
widens as it proceeds back from it, and be-
coming extremely convoluted, finally ends at
the genital opening on its own side (i. c. y.).
Trace the course of the vas deferens on that
side from which the thoracic wall has been
removed (12).

XIL] THE FRESH-WATER CRAYFISH. 147

y. Tease out a bit of the testis in water, and ex-
amine with ~ obj. : it will be seen to be com-
posed of sacculated tubes. In it or in the
vas deferens some of the spermatozoa may be
found : they are motionless and have the form
of nucleated cells provided with radiating pro-
cesses.

8. The ovary is a gland in shape and colour
very similar to the testis of the male. From
it two short oviducts arise and pass almost
directly downwards to the genital openings
(i. c. y.).

b. Of the Lobster.

a. The testcs are two long tubes which lie partly
in the thorax and partly in the abdomen.
Their posterior portions meet in the middle
line, but in front they diverge, and about one
fourth the length of each from its anterior end
a short transverse branch unites the two.

j3. The -cos deferens arises a little in front of the
middle of each testis and passes without con-
volutions towards the genital opening. Its
distal half is dilated.

y. Tease out a bit of the testis in water and ex-
amine with |- obj. for spermatozoa. They are
motionless, and consist of an elongated ceil
from one end of which three rigid pointed
processes radiate.

8. The ovaries of the lobster are also elongated
and lie partly in the thorax and partly in the
abdomen, above the alimentary canal (14).

10 2

1 4* ELEMENTARY BIOLOGY. [CHAP.

Each is a dark green mass, on the exterior of
which minute rounded eminences (indications
of the contained ova) can be seen. Near
their anterior ends they lie in contact in the
middle line, and for a short distance their
substance is continuous.

f. An oviduct arises from each ovary a little in
front of its middle, and passes directly to the
genital opening of its own side (i. c. y.).

14. Alimentary organs.

a. Remove the dorsal part of the carapace in front
of the cervical suture, and there will then be
laid bare, in front of the position of the heart,
a large sac the stomach ; pass a probe into it
along the gullet, through the mouth-opening
which lies between the mandibles.

b. Trace back the tubular intestine from the stomach
to the anus. It dilates near the latter in the
lobster. In the crayfish it presents a small ccecal
diverticulum close to the stomach, and in the
lobster one near the anus.

c. Examine the liver.

a. It is an elongated soft pale-yellow mass lying
in each side of the cephalo-thorax, and opening
by a duct on each side at the point where the
intestine joins the stomach.

P. Tease out a bit of the liver in water; it is
made up of branched ccecal tubes, which when
examined microscopically are seen to be lined
by a layer of cells (epithelium}.

xu.] THE FRESH-WATER CRAYFISH. 149

d. Carefully remove the alimentary canal, cutting
the gullet through close to the stomach.

a. Open the latter under water and make out in
it the constriction which divides it into an
anterior (cardiac] portion and a posterior
(pyloric).

/3. The supporting bars and the hairs in the
stomach, and the calcifications of its lining
membrane.

15. Now trace the sternal artery (removing the ali-
mentary canal and the genital organs), until it enters
a passage (sternal canal} formed by ingrowths of the
exoskeleton near the ventral surface of the animal.
Just before entering this the sternal artery gives
off the inferior abdominal branch, which runs back
along the middle line of the abdomen immediately
inside the sterna of the somites. Trace this branch
back removing the muscles which cover it. By this
proceeding the abdominal part of the nervous chain
will be exposed. It lies immediately above the blood-
vessel and is not to be injured.

1 6. The nervous system.

a. Find the suprao&sopkageal ganglion in front of
the gullet.

/3. The circumcesophageal commissures passing
back from it.

y. Follow back these commissures, cutting away
the hard parts (forming the roof of the sternal
canal) which come in the way j they lead to
a chain of six ganglia, lying along the floor of
the cephalothorax, and united by double cords

ELEMENTARY BIOLOGY. [CHAP.

(commissures}. Lying in the sternal canal be-
neath the ganglia may be seen the sternal
artery (15).

S. Follow back the single cord proceeding from
the last thoracic ganglion to the abdomen,
removing any muscles which come in the way :
it will lead to a chain of six ganglia, one for
each abdominal segment, united by single
cords.

17. The green gland. A soft greenish mass lying on
each side in the extreme front part of the cephalo-
thoracic cavity: pass a fine bristle into it from the
opening of its duct on the basal joint of the endo-
podite of the antenna (21. f.).

1 8. Tease out a bit of muscle in water and examine
it microscopically: note its structure; it is made up
of fibres, marked by regularly alternating transverse
lighter and darker bands.

19. Tease out a bit of perfectly fresh nerve-cord in water
and stain with magenta or riDematoxylin.

a. Composed of slender fibres of varying size, each
consisting of a structureless outer wall, on which
are nuclei at intervals, surrounding a clear or,
sometimes, finely granular or obscurely fibrillated
central axis.

20. Tease out in water a ganglion which has been treated
with osmic acid.

a. Composed of large oval branched cells, each con-
sisting of a granular mass in which lies a clear
round nucleus, containing a nucleolus.

xii.] THE FRESH- WATER CRAYFISH. 151

21. The appendages. Beginning with the sixth abdomi-
nal segment, remove with forceps the appendages of
the body and arrange them in order on a piece of
cardboard. The abdominal appendages have been
already described; note the following points in the
remainder, working from behind forwards.

a. The four posterior thoracic appendages (ambu-
latory appendages}.

a. The most posterior: elongated and seven-
jointed, the joints working in different planes
so that the limb as a whole can move in any
direction : the joints have the following names ;
the proximal, short and thick, coxopodite; the
next, small and conical, basipodite; next, cylin-
drical and marked by an annular constriction,
ischiopodite ; the next, longer, meropodite; then
successively, the carpopodite, propodite, and
dactylopodite. Probably the coxo- and basi-
podite together represent the protopodite of
the abdominal appendages : the remaining
joints the endopodite: the exo- and epipodite
are wanting.

/?. The next ambulatory leg: generally similar
to the preceding, but possessing, attached to
the coxopodite, a long membranous flattened
appendage (epipodite) which ascends into the
gill-chamber: it bears a gill.

y. The next anterior ambulatory leg: differing
from the last only in having its propodite
prolonged so as to be opposable to the dac-
tylopodite and form a pair of forceps (chelce).

152 ELEMENTARY BIOLOGY.

8. The most anterior ambulatory leg: resembling
y. closely and, like it, bearing a gill.

b. The great chelce: much larger and more powerful
than the last appendage: but resembling it in
structure, except that its ischio-podite and basi-
podite are ankylosed together; it carries a gill.

c. The three maxillipedes.

a. The most posterior: its short thick basal two-
jointed (/;'0/^>^'): the three prolongations
articulated to it ; the external {epipodite} a
curved elongated lamina lying in the branchial
chamber and bearing a gill ; the middle one
(exopodite) long, slender and many-jointed ;
the internal one (endopodite) several-jointed
and much resembling one of the ambulatory
limbs.

(3. The middle maxillipede : much like a. but
with the two joints of the protopodite fused
together and with a less stout endopodite.

y. The anterior maxillipede; protopodite, exopo-
dite and epipodite all present, but smaller
than those of f$. and the epipodite bearing no
gill ; the endopodite flattened and foliaceous.
The ambulatory limbs, great chelae, and
maxillipedes together constitute the append-
ages of the thorax ; we now come to those of
the head proper.

d. The two maxillcz.

a. The posterior: its protopodite and endopodite '
essentially like those of the anterior maxilli-
pede; the epipodite and exopodite united and

xii.] THE FRESH-WATER CRAYFISH. 153

forming a wide oval plate (scaphogncdhite)
which lies at the anterior end of the gill-
chamber (n. 7.).

/?. Anterior maxilla : epipodite and exopodite
undeveloped : the endopodite foliaceous.

e. The mandible. Its strong toothed basal joint
(j>rotopodite) bearing a small appendage (the palp}
which represents the endopodite ; the epipodite
and exopodite unrepresented.

/. The antenna. Its two-jointed basal portion (proto-
podite) bearing a flattened plate (the rudimentary
exopodite) 2C&& a long multiarticulate filament (the
endopodite]: the opening of the green gland (17)
on the oral side of the basal joint of the proto-
podite.

g. The antenmila. Its large trigonal basal joint
(protopodite) , bearing a pair of jointed filaments
(endopodite and exopodite)'. the opening of the
auditory organ (24) in the midst of a minute
hairy tuft on the basal joint.

h. The ophthalmites or eyestalks. Short two-jointed
appendages representing only the basipodite.

22. Now work back over the 20 pairs of appendages
and compare each with the third maxillipede : all
may be supposed to be derived from it by suppression,
coalescence or special change of form; it is what is
called a typical appendage.

23. Structure of the Eye.

a. Take the eye of a lobster which has lain four or
five days in 0-5 per cent, solution of chromic acid

ir4 ELEMENTARY BIOLOGY. [CHAP.

and then twenty-four hours or more in alcohol.
Examine its surface with one inch obj. with re-
flected light. It will be seen to be marked out
into a great number of minute square areas
or facets, each of which shews faint signs of
furrows crossing it diagonally from corner to
corner.

b. Imbed the eye and cut a number of sections from
it perpendicular to its surface : mount in glycerine
and examine with one inch objective.

a. If the section has passed through the middle
of the eye it will be seen to present a central
mass (optic ganglion} 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 pig-
mented layers) are indications of the striated
spindles, connective rods and crystalline cones.

c. Examine your thinnest section with a high power,
or tease out one of your thicker ones in gly-
cerine. Beginning at the exterior make out suc-
cessively

a. The cornea, answering to one of the superficial
facets. Its flat outer and slightly convex inner
surface. Immediately beneath the cornea
there will be seen (in good specimens) a
slightly granular layer.

/?. The crystalline cone, an angular transparent
body which is usually obscured by pigment.
If this is the case, another section must be
mounted in dilute caustic potash, which re-
moves the pigment.

xir. THE FRESH-WATER CRAYFISH. 155

y. Behind the crystalline cone comes the con-
nective rod. It 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.

B. The striated body is fusiform and presents
well-marked transverse striations. Besides
these coarse striations, however, much finer
ones can be seen by careful examination with
a high power. The outer ends of these
spindles correspond in position to the second
of the pigmented layers seen with the low
power (b, a.) : they are best seen in specimens
treated with dilute caustic potash.

c. Beneath the striated spindles is a perforated
membrane through which the spindles pass to
become continuous with the optic ganglion.
From their ends pass nerve-fibres which run
inwards in a converging manner and among
which nerve-cells are here and there scattered.
Within the ganglion are several concentric
pigmented bands.

. If the section has passed back along the optic
nerve two obliquely placed lenticular masses
will be seen among its fibres.

77. Passing back from the cornea to the optic
ganglion is a membrane investing each cone,
rod, and spindle. It is on this that most of
the pigment lies which causes the two outer
dark bands. Over the rods the pigment is

156 ELEMENTARY BIOLOGY. [CHAP.

wanting and there the membrane is seen to
possess oval nuclei.

24. 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 joins in front
at an angle a rounded anterior portion. It bears
several tufts of hairs: one of these is very small and
lies at the inner side of the flattened surface, just at
the angle where it meets the rounded part ; among
these hairs 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. A
chitinous transparent sac will readily be found in
it, among the muscles &c. ; 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 aperture to the exterior. 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 streaks : mount in sea-water or sodic
chloride solution and examine with one inch ob-
jective.

a. The white line will be seen to answer to a
ridge on the apex of which is a row of large
hairs, and both on the brown patch and on the
opposite side of the main row will be seen
scattered groups of smaller hairs.

xii.] THE FRESH-WATER CRAYFISH. 157

r. Examine with \ obj.

a. Each of the hairs seen with the lower power is
now seen to be covered over its whole surface
with innumerable very fine secondary hairs;
these are shortest near the base of the primary
hair. Towards its base each of the primary
hairs is constricted and then dilates into a
bulbous enlargement which is fixed to the
wall of the sac.

(3. The brown patch is seen to owe its colour to
a single layer of polygonal epithelial cells
containing pigment granules.

y. By focussing through this epithelial layer a
number of parallel slightly granular bands is
seen passing up, one to the base of each hair
in the main row on the top of the ridge. At
the base of the hair to which it runs, each
band is constricted and, entering the bulbous
enlargement of the hair, joins a small hemi-
spherical swelling within it.

B. If a fresh auditory sac be put in i per cent,
solution of osmic acid for half an hour, and
then laid for twenty-four hours in distilled
water and examined, each of the granular
bands mentioned above is seen to consist of
a bundle of fine fibres which swell out into
fusiform enlargements at intervals.

c. A great part of the whole interior of the audi-
tory sac of the lobster is covered with very
fine hairs which can only be seen with a high
power. Epithelium is absent except the pig-
mented patch above mentioned.

158 ELEMENTARY BIOLOGY. [CHAP. xn.

d. The auditory sac in the crayfish is very similar to
that in the lobster, and may be examined in a
similar way. It is however not so good, both
on account of its smaller size and because the
auditory hairs, although longer, are collected in
a close tuft, which makes it more difficult to see
the manner of their insertion.

XIII.

THE FROG (Rana temp or aria and Rana esculent a}.

THE only species of Arog indigenous in Britain is that termed
the 'common' or 'Grafes Frog' (Rana temporarid], 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 passing gradually into those of the body,
and the fore-limbs being situated immediately behind the
head. There are two pairs of limbs, one anterior and one
posterior. The whole body is invested by a smooth moist
integument, on which neither hairs, scales, nor other forms of
exoskeleton are visible; but hard parts, which constitute the
endoskckton, may readily be felt through the integument in
the head, trunk and limbs.

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,

1 60 ELEMENTAR Y BIOL OG Y. [CHAP.

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,
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; and, 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, antcbrachium 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,

xiii.] THE FROG. 161

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-
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, and 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,
which, 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 long iliac
bones 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
alternate pumping in and expulsion of the air needed for the
Frog's respiration is connected with these movements.

M. II

ir> 2 ELEMENTARY BIOLOGY. [CHAP.

The upper eyelid of the Frog is large and covered with
ordinary pigmented integument, and it has very little mobility.
What performs the function of the lower eyelid in Man,
is a fold of the integument of which very little is pigmented
and which is, for the most part, semi-transparent, so as to
resemble 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
descends 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 fecun-
dates them by a simultaneous out-pouring of the seminal
fluid. Shortly after the eggs pass into the water, the thin
layer of viscid albumen, 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 gelatinous
mass in which the eggs remain imbedded during the early
stages of their development.

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, which com-
mences within a few hours of impregnation, is readily ob-
served when the eggs are examined as opaque objects under
a low power of the microscope.

While still within the egg the embryo assumes the form

xiii.] THE FROG. 163

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 young acquires three pairs of
external branchia 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 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 abdominal cavity. A membranous lip,
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 abdomen,
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
branchics. 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-

II 2

164 ELEMENTARY BIOLOGY. [CHAP.

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 vomers ; the intestine becomes less and less coiled as,
not growing at the same rate as the body, it becomes rela-
tively 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 escuknta,
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
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 esculcnta, 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 temporaria, 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

xiii.] THE FROG. 165

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-
racter 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 abdomen be laid open, it will be found to inclose
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
those of the pleune and of the peritoneum in the higher
animals, it is termed the pleuroperitoneal cavity ; and the soft
smooth membrane which lines it and covers the contained
viscera is the 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 intestine. In the triangular interval left between
these two layers before they unite, a wide canal the sub-
vertebral lymph sinus the dorsal aorta, and the chain of
sympathetic ganglia, are situated.

The dorsal moiety of the anterior end of the pleuroperi-
toneal cavity is occupied by the gullet, which places the
mouth in communication with the stomach. Beneath the
gullet the peritoneal cavity is separated only by a thin parti-
tion from a chamber, the pericardium, which contains the
heart. The posterior face of the partition is constituted by

ELEMENTARY BIOLOGY. [CHAP.

the peritoneum, its anterior face by a membrane of similar
character, the pericardial membrane, which lines the peri-
cardium and is reflected on to the heart, in the same way as
the peritoneum lines the peritoneal cavity and is reflected on
to the intestine.

A layer of the muscular fibres which enter into the walls
of the abdomen 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 rudimentary diaphragm ; which, it will be observed,
is 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, one large posterior
pleuroperitoneal cavity, and one small, anterior to the fore-
going, the pericardial cavity, and neither of these communi-
cates directly with the exterior, though in the female there
is an indirect communication 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 vomcrs, are the vomerine teeth, while
the former, attached to the premaxillcR and maxilla, are
maxillary teeth. The lower jaw or mandible bears no teeth.

At the sides of the clusters of voraerine teeth are the
apertures termed 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

XIIL] THE FROG. 167

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 and nearly
opposite 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
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 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 abdominal 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 suddenly dilated short large intestine, and this opens into
a chamber with muscular walls, the cloaca, the external aper-
ture 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 alimentary canal.

Separated from the pleuroperitoneal and oral cavities by
the bodies of the vertebrae and the hard roof of the oral
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

1 68 ELEMENTARY BIOLOGY. [CHAP.

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.

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 abdomen will shew a dorsal
cavity containing the posterior part of the cerebro-spinal
axis, the spinal cord, separated by the solid floor of the ver-
tebral column from a ventral cavity containing the ali-
mentary canal and continuous with that of the mouth.
But the backward continuation of the alimentary canal is
embraced by the large pleuroperitoneal chamber, of which
there is no indication in the head.

On comparing the transverse section of the abdomen of
the Frog with a transverse section of the middle of the body
of the Lobster, 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, there is no solid and com-
plete partition between the nervous centre of the Lobster
and the alimentary canal. Moreover, the face of the body
on which the nervous centre lies, is that on which the Lobster
naturally rests, while in the Frog it is the reverse. The
limbs are turned towards the neural side in the Lobster and

XIIL] THE FROG. 169

away from it in the Frog, and the like difference obtains
between all Vcrtcbrata and all Arthropoda.

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 exoskeldon, 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
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 distinguished into an
axial and an appendicular portion.

The axial endoskeleton consists of the notochord, the spinal
column and the skull.

The appendicular endoskeleton occurs in the limbs and in
the pectoral and pelvic arches to which they are attached.

In the order of development, the endoskeleton is at first
represented by the notochord alone; secondly, nascent con-
nective tissue and cartilage are superadded to the notochord;
thirdly, these acquire their special characters; fourthly, they
become replaced by bone.

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; and the cartilage, of which the
greater part of the skeleton at one period of larval ex-
istence was composed, to a great extent persists.

Such cartilage is found forming the free surfaces of the

i;o EL EMENTAR Y BIOL OGY. [CH AP.

bodies of the vertebrae, the extremities of the caudal style
(urostyle) and the ends of the transverse processes; and it
enters largely into the sternum. In the skull, the para-
sphenoid 1 , vomers, parieto-frontals, nasals, premaxillae, max-
ilke, jugals, squamosals, and the bony elements of the man-
dible may be removed by maceration, leaving behind the
primitive 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 a large space (called & fontanelti) covered
in by membrane, which lies in the inter-orbital region under
the parieto-frontals, and by the foramina for the exit of the
cranial nerves. It consists entirely of cartilage, except where
the exoccipitals, the pro-otics, and the sphenethmoid invade
its substance. In front of the septum of the anterior cavity
of the sphenethmoid, it is continued forward between the
two nasal sacs, as the cartilaginous partition between the
nasal cavities (septum narhem), from which are given off,
dorsally and ventrally, transverse alee of cartilage which fur-
nish a roof and a floor, respectively, to the nasal chambers.
Of these, the floor is the wider. The dorsal and ventral alse
pass into one another where the chondro-cranium ends an-

A

teriorly and give rise to a truncated terminal face, which is
wide from side to side, narrow from above downwards, and
convex in the latter direction. The lateral angles of this
truncated face are produced outwards and forwards into two
flatten z& prce-nasal processes ; these widen externally and end
by free edges which support the adjacent portions of the
premaxillae and maxillae. From the ventral face, just behind
the truncated anterior end of the chondro-cranium, spring

1 See Laboratory work, D, c, for the structure of the bony skull
(osteocraninm), which should be thoroughly understood before any
attempt is made to study the cartilaginous skull or chondro-cranium.

XIIL] THE FROG. 171

two slender cartilages, the rhinal processes. Each of these
inclines towards the middle line and ends against the middle
of the posterior face of the ascending process of the pre-
maxilla by a vertically elongated extremity. An oval nodule
of cartilage is attached to the posterior face of the dorsal
end of the ascending process of the premaxilla, 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 aper-
tures are surrounded and supported by a curious curved
process of the cartilaginous ala the alinasal process. Where
the sphenoidal and the ethmoidal portions of the spheneth-
moid meet, a stout, transverse, partly osseous and partly
cartilaginous bar is given ofif, 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 cartilaginous pterygoid rod which bifurcates poste-
riorly. The outer division passes into the. ventral crus of
the suspensorium. The inner division is the pedicle of the
suspensorium; it articulates by a joint with the anterior face
of the broad lateral process of the hinder part of the chon-
dro-cranium, which contains the auditory labyrinth and is
termed the periotic capsule. The Suspensorium is a rod of
cartilage, which lies between the squamosal and the ptery-
goid bones and, at its distal end, articulates with Meckel's
cartilage which forms the core of the ramus of the mandible.
At its dorsal end it divides into two divergent processes or
crura, of which the ventral crus has already been said to be
continuous with the pterygoid. The dorsal crus, on the

i;2 ELEMENTARY BIOLOGY. [CHAP.

other hand, passes upwards and, curving backwards, becomes
attached to the dorsal part of the outer face of the periotic
capsule.

Meckel's cartilage, articulated to the free end of the sus-
pensorium, is unossified throughout the greater part of its
extent, no osseous articulare being developed; but, at its
symphysial end, each cartilage becomes ossified, and forms
the mento-Meckelian element of the mandible.

The slender, cartilaginous band (cornu of the hyo'uf] by
which the body of the hyoid is attached to the skull, is con-
nected with the periotic cartilage immediately in front of
I and below the fenestra ovalis.

The pectoral and pelvic arches (see Laboratory work
D. e. g.) are, in the young state, undivided cartilages on
each side, and the development of bone in and upon them
does not really destroy this continuity, the cartilage persist-
ing at the ends of the bones and between them, in the
glenoidal and acetabular cavities.

In like manner, the bones of the limbs consist origin-
ally of merely cartilaginous models of the perfect bone;
but, as development proceeds, the middle of the cartilagi-
nous model commonly becomes invested by a sheath of
true bone, while a calcareous deposit takes 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, the femur, consists of a median shaft of perfect bone,
and of two terminal cones of cartilage, containing calcified
epiphyses } inclosed within and more or less overlapping the
hollow ends of the shaft.

xni.] THE FROG. 173

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

Teeth are found attached only to the premaxillae, max-
illse and vomers. 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 be-
come ankylosed to processes of the subjacent bone.

The gullet passes without change of diameter into the
stomach, which lies on the left side of the abdominal cavity
and is nearly as long as it. The stomach narrows poste-
riorly and the almost tubular pyloric portion bends round
sharply and passes into the duodenum. A slight constric-
tion marks the pylorus. The duodenum runs forwards
parallel with the stomach, so that with the latter it forms a
sort of loop. At its anterior end it passes into the rest of
the small intestine (ileum), which is coiled up into a sort of
packet and lies on the right side of the abdominal cavity,
being held in its place by a mesenteric fold of the perito-
neum. From the comparatively narrow neck of the packet,
the small intestine proceeds backwards in the middle line
and opens into the anterior end of the dilated large intes-
tine or colon and rectum.

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.
Much more delicate continuations of these folds are conti-
nued into the small intestine and are there joined by trans-
verse folds.

The opening of the ileum into the colon is valvular, its
edges projecting backwards into the cavity of the colon.
On the dorsal aspect, this presents a slight forward dilata-
tion, which may be regarded as a rudiment of a caecum.

174 ELEMENTARY BIOLOGY. [CHAP.

The liver is very large, and is divided into two lobes
united by a mere bridge, dorsally and anteriorly. The left
lobe is further subdivided into two. The gall bladder is
attached to the posterior and dorsal face of the right lobe.
The biliary duct opens into the duodenum, at some distance
behind the pylorus, and its termination is embraced by the
base of the slender pancreas.

The rounded spleen lies in the mesentery, projecting
more to the left than to the right side, just above the point
at which the duodenum passes into the ileum.

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. There are four lymph-
hearts.

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
by communications between the anterior lymph-hearts and

xin.] THE FROG. 175

the innominate veins, and between the posterior lymph-
hearts and the iliac veins.

The heart is connected with the walls of the pericardium,
on which spots of pigment may be observed, 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 and dorsal wall of the pericardial chamber.

The heart consists of four readily distinguishable seg-
ments, (i) the sinus vcnosus, (2) the atrium, (3) the ven-
tricle, and (4) the truncus 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 me-
dian, ventral and posterior; and the truncus passes ob-
liquely forwards from the right side of the ventricle and is
ventral and anterior. The heart therefore may be com-
pared 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
into the right auricle. Into the left auricle, the common
pulmonary vein, a small trunk 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-

176 ELEMENTARY BIOLOGY. [CHAP.

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-ventricu lar 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,
clear cavity being left at the anterior end or base of the
ventricle. At the right extremity of this is the aperture
which leads into the truncus arteriosus. Three semilunar
valves, which open from the ventricle into the truncus, sur-
round 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
branches into which the truncus arteriosus divides, are, in
fact, each made up of three separate trunks, the pulmo-
cutancous 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

xiii.] THE FROG. 177

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
and less resistance is offered elsewhere, the next portion
of blood, consisting of the venous and arterial blood which
have 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 :

A. Arteries.

i. The system of the anterior aortic arch (carotid
trunk).

a. Lingual artery to the tongue.
M. 12

i;3 ELEMENTARY BIOLOGY. [CHAP.

b. Carotid artery to the interior of the skull and
the brain.

2. The system of the middle aortic arch (aortic trunks).

a. Vertebral and subclavian to the vertebral co-
lumn, and to the fore-limb. (Esophageal to the
gullet.

b. Cccliaco-mesentcric (given off from the left arch,
or from the dorsal aorta, at. or beyond, the junc-
tion of the two arches).

a. Cttliac to stomach and liver.

/?. Mcsenteric to intestine and spleen.

c. Branches of the dorsal aorta to the adrenal
and renal organs, to the genital organs and to
the muscles of the back.

d. The terminal branches of the dorsal aorta (com-
mon iliac] ; each of these gives off hypogastric
arteries to the bladder and walls of the abdomen
and is continued as the femoral artery into the
leg.

3. The system of the posterior aortic arch (puhno-
cutaneous trunk).

a. Pulmonary artery to the lungs.

b. Cutaneous artery to the dorsal integument.

P.. Veins.

i. The system of the superior cava formed on each
side by the union of the vena innominata, the sub-
clavian and the external jugular.

a. Internal jugular vein: leaves the skull by the
jugular foramen, and brings back blood from

xin.] THE FROG.

179

the brain, spinal cord and anterior vertebral
region.

b. Subscapular: returns the blood from the bra-
chium and shoulder. These two veins (a. and
b.) unite to form the vena innominate^

c. The musciilo-cutaneons vein, receiving the blood
of the surface of the head (except the mandi-
bular and hyoidean regions) and that of the
back of the trunk passes forwards between the
internal and external oblique muscles of the
abdomen.

d. The brachial vein receives blood from the ante-
brachium and manus.

These (c. and d.) unite to form the subdavian
vein.

<?. The veins of the mandibular region and those
of the tongue unite into the external jugular
vein.

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

a. The femoral vein from the front of the leg,
and

b. The sciatic vein from the back of the leg, pour
their blood into a trunk which lies in the lateral
wall of the pelvis and may be termed the pelvic
vein; the dorsal end of this becomes

c. The common iliac vein, which passes to the outer
edge of the kidney and is distributed to that
organ, whence the blood is carried to the vena
cava inferior by the renal veins.

12 2

i So ELEMENTARY BIOLOGY. [CHAP,

d. The dorso-lumbar vein, which lies along the
transverse processes of the vertebras and receives
blood from the walls of the abdomen and from
the interior of the spinal canal, opens into the
common iliac.

3. The system of the anterior abdominal vein, formed
by the union of the ventral ends of the pelvic veins
(2. b.). It receives blood from the urinary bladder
and the walls of the abdominal cavity, and at its
anterior end divides into two branches a right and
a left. These branches go to the corresponding
lobes of the liver, the left receiving a large commu-
nicating branch from the gastric division of the vena
portce.

4. The system of the vena port<z formed by the union
of two veins; one, gastric, which brings back the
blood from the stomach, the other, Heno-intestindl s
which returns that from the spleen and intestines.

[Hence the right lobe of the liver and part of the left
lobe are supplied with systemic venous blood, more
or less mixed with gastric venous blood, while only part
of the left lobe is supplied with intestinal venous blood.
Besides this venous blood, it must be recollected that
the liver receives arterial blood by the hepatic artery.]

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

In addition to the apparatus of the circulation of the
blood, the Frog possesses two pairs of lymph-hearts. These
are contractile muscular sacs, which are connected on the
one hand with the lymphatic vessels and on the other with
large veins in their neighbourhood; and which pump the

xni.] THE FROG. 18 1

lymph contained in the wide lymphatic vessels and in the
pleuro-peritoneal cavity of the Frog, into these veins.

The anterior lymph-hearts are situated close to the trans-
verse processes of the third vertebra, below the edge of the
scapula; the posterior pair lie one on each side of the uro-
style, and their pulsations may be observed by carefully
watching the integument in this region in a living Frog.

The Thymus gland is a small rounded body situated im-
mediately behind the suspensorium, in a position corre-
sponding to the dorsal ends of the obliterated branchial
arches.

The Thyroid gland appears to be represented by two or
more oval bodies, which are found attached to the lingual
vessels and between the aortic and pulmo-cutaneous trunks.

The Adrenal glands are yellow bodies imbedded in the
ventral face of the kidney.

The slit-like glottis of the Frog is formed by the apposi-
tion 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 produced.

Laterally the laryngo-tracheal chamber opens into the

ELEMENTARY BIOLOGY. [CHAP.

King of each side. The lung is a transparent oval sac,
somewhat pointed posteriorly, which lies at the side of the
oesophagus in the dorsal region of the abdominal 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 pro-
duced inwards so as to give rise to septa, which are much
more prominent and more numerous in the anterior than
in the posterior part of the lung and divide the periphery
of the cavity into numerous air-cells, on the walls of which
the ramifications of the pulmonary artery are distributed.

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

Inspiration is effected in the Frog 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 nostrils being then shut, the
hyoid, and with it the floor of the mouth, is raised, the
aperture of the gullet being at the same time closed. Thus
the air is forced through the glottis and distends the lungs.

In ordinary expiration, the elasticity of the lungs and
the pressure of the surrounding viscera probably suffice to
expel the air; but this operation may be powerfully aided,
firstly by the contraction of the intrinsic muscular fibres of
the lungs; secondly, by the contraction of the muscles of
the lateral and ventral regions of the abdominal wall; and,
thirdly, by the contraction of those muscular fibres which
enter into the diaphragm ; as all these actions tend, either
directly or indirectly, to diminish the capacity of the lungs.

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

xiii.] THE FROG. i $3

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 their places by the continuation of the peri-
toneum over their ventral faces. The ducts of the kidneys
pass from about the junction of the middle and posterior
thirds of the outer edge of each kidney and, approaching as
they pass backwards, open by two small closely approxi-
mated slit-like apertures in the posterior wall of the cloaca.

The urinary bladder is a large bilobed sac, opening pos-
teriorly, by a wide median aperture, into the anterior end
of the cloaca, on the ventral side of the rectum.

The testes are spheroidal yellowish bodies situated in
front of the kidneys and enveloped in peritoneum, a fold of
which, forming a sort of testicular mesentery or mesorchium^
passes into 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 ex-
cretion but as the vas defer ens.

The spermatozoa of Rana esculenta have thick and cylin-
drical heads, while those of Rana temporaria are linear.

The ovaria are broad lamellar organs, very large and
much folded and plaited in the breeding season. The in-

184 ELEMENTARY BIOLOGY. [CHAP.

ter'or of each is hollow, and is divided into several chambers.
Innumerable ovisacs, containing dark-coloured ova, are scat-
tered through the substance of the ovary and give rise to
projections upon the inner surface of the ovarian chamber
as they become fully developed.

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 diaphragm
and the lobe of the liver. The fold of peritoneum which
serves as a ligament, holding the lobe of the liver to the
diaphragm, oesophagus and posterior wall of the pericar-
dium, in fact constitutes the outer lip of the oviducal aper-
ture. For the greater part of their length their walls are
thick and glandular, and 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.

Each ovum, when ripe, consists of a structureless vitelline
membrane, inclosing a vitellus, within which is a germinal
vesicle, containing several ' germinal spots.' One half of
the vitellus is deeply coloured, the other pale.

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

Xiii.] THE FROG. 185

are found in the viscera and vessels. 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 cerebro-spinal and the sympathetic. The cerebro-
spinal nervous system again consists of the brain, or encepha-
lon, with its nerves, and the spinal cord, or myelon, with its
nerves.

The encephalon 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 thalamencephalon, the cerebral hemispheres, and the
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, on its dorsal aspect, a triangular
cavity, the apex of which is directed backwards. It is roofed
over by a thick and very vascular membrane (choroid plexus),
the inner surface of which presents transverse folds on either
side of a median longitudinal ridge. The cavity is the
fourth ventricle ; it communicates behind with the central
canal of the myelon, while, in front, it narrows into a pas-
sage which connects the fourth ventricle with the cavities
anterior to it. The thick lateral ridges of nervous substance
at the sides of the fourth ventricle, which represent the
rest if or m 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 long axes of which are
directed inwards and backwards. These are the optic lobes.
When laid open, each is seen to contain a cavity or ventricle

iS6 ELEMENTARY BIOLOGY. [CHAP,

with an opening on its inner face. These openings lead into
a short passage, which communicates with the iter a tertio ad
quartum ventriculum, as the canal which leads, through the
mesencephalon, from the fourth to the third ventricle is
termed. The floor of this canal is formed by the thick prin-
cipal mass of the cerebro-spinal axis. It exhibits a median
longitudinal depression or raphe, and in this region repre-
sents the cnira cerebri.

In front of the mid-brain comes the hinder division of
the fore-brain, or tkalammcephalon^ which is very distinct in
the Frog and contains a median cavity, the third ventricle.
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. Dorsally, the
walls of the third ventricle are very thin and easily torn
through, except behind, where there is a thick transverse
band of nervous substance, \h& posterior commissure.

From the fore part of the roof of the third ventricle, a
delicate process proceeds to the pineal gland an ovate body
lodged between the posterior parts of the cerebral hemi-
spheres. The front part of the floor of the ventricle, on the
other hand, is produced into a bilobed process directed
backwards, which is the infundibnlnm. This is connected
below with the pituitary body. In front of this is seen the
commissure of the optic nerves.

Anteriorly, the third ventricle is bounded by the thick
lamina terminalis which contains the anterior commissure.
On each side, between this and the peduncle of the pineal
gland, is a small aperture, the foramen of Munro, which
leads into a cavity in the interior of the cerebral hemisphere
the lateral ventricle.

The hemispheres are elongated bodies, broader behind
than in front, where they are marked off only by a slight

xiii.] THE FROG. 187

constriction from the olfactory lobes. The outer wall of
the ventricle, though relatively thick, presents nothing which
can be called a distinct corpus striatum. The inner wall
forms one or two convex projections into the ventricle.

In the bases of the olfactory lobes the forward continua-
tion of the ventricular cavity is very narrow and the 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 hemispheres are quite free and
separated by a cleft, the great fissure, but the inner faces of
the commencements of the olfactory lobes are closely united
together, giving rise to a kind of corpus callosum.

There are ten pairs of cranial nerves ordinarily so called,
though it is to be recollected that the first and second pairs
are proved, by their development, to be lobes of the brain.

1. O If actor il.

The olfactory lobes are what answer to the so-called
olfactory nerves of the higher Vertebrata. They are
distributed exclusively to the olfactory sacs.

2. Optici.

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.

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 capsules.

The Pr&auditory nerves are the following.

3. Mot ores oculorum

arise from the front part of the floor of the mid-brain
and are distributed to all the muscles of the eye

1 88 ELEMENTARY BIOLOGY. [CHAP.

except the external rectus, the superior oblique and
the retractor bulbi.

4. Pathctici

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 Gasscrian ganglion
which lies, in front of the auditory capsule, in the
foramen of the pro-otic bone 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, and some of the branches which appear to be
given off from it really belong to the sixth and the seventh
nerves. Beyond the ganglion, the nerve divides into three
main branches, the orbito-nasal^ the palatine and the maxitto-
mandibular.

i. The orbito-nasal (usually termed the first division of
the fifth nerve) is distributed :

a. To the external rectus.

b. To the retractor of the bulb.

(These branches (a. and b.) belong to the sixth nerve.)

c. A branch which anastomoses with the fourth
nerve.

d. A branch to the Harderian gland.

e. The principal trunk of the nerve passes through

xiii.] THE FROG. 189

the ant-orbital process of the skull into the
nasal chamber and is finally distributed to the
nasal mucous membrane and to the integu-
ment of the nose.

ii. The palatine is distributed :

a. To the roof of the oral cavity.

b. Its main trunk runs forward between the mucous
membrane of the roof of the mouth and the
skull, pierces the vomer and ends in the mucous
membrane of the anterior part of the palate.

(This nerve is chiefly, if not wholly, derived from
the seventh nerve.)

iii. The maxillo-mandibular divides into two trunks,
usually termed the second and third divisions of the
fifth nerve.

a. Maxillary, passes outside the eye and is distri-

buted to the integument of the upper jaw; an
anastomotic branch unites this nerve with the
palatine.

b. Mandibular, passes between the temporal and

pterygoid muscles, below the jugal, over the
articulation 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. Abdu antes

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

1 90 ELEMENTARY BIOLOGY. [CHAP.

of the fifth as to appear to be only a subdivision of
the latter (see 5. i. a. and

7. The Faciahs

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. The anterior passes into the palatine division
of the fifth ; the posterior passes between the dorsal
and ventral crura of the suspensorium, enters the
tympanic cavity, runs over the colnmella auris and
then, as it leaves the tympanum, receives a very
large branch from the glossopharyngeal. Finally it
divides into two branches, anterior and posterior.

a. The former, which answers to the chorda tym-
pani of the higher Vertebrata, runs along the
inner face of the ramus of the mandible parallel
with the mandibular branch of the fifth.

b. The posterior passes alongside the cornu of the
hyoid and supplies its muscles.

8. The Anditorii

arise in common with the foregoing. Each divides
into two branches which enter the auditory capsule.

The Post-auditory nerves are:

9. The Glossopharyngei.

These nerves arise, in common 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. From

xiii.] THE FROG. 19 r

this the trunk of the glossopharyngeal is given off.
It passes downwards and forwards to the root of the
tongue, which it enters and then supplies that organ.
Moreover, it gives off muscular branches and a large
anastomotic branch to the seventh.

i o. 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 (a.) runs on the inner side of
and above the cutaneous branch of the pulmo-cuta-
neous artery, the other (b.) lies below and diverges
from the first.

a. is the laryngeal nerve. It passes beneath the

first cervical nerve, then crosses over the third
aortic arch and, about its middle, turns sharply
round it to be distributed to the larynx. This
nerve corresponds with the recurrent laryngeal
of the higher animals.

b. is the splanchnic branch. It gives off (gastric)

branches to the gullet and stomach, and a fine
nerve (cardiac) which passes beneath the pul-
monary artery and along the root of the lung to
the heart, and ends in ganglia situated in the
septum of the auricles. The splanchnic branch
finally enlarges and is distributed to the lungs
and stomach.

The myelon 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-

192 ELEMENTARY BIOLOGY. [CHAP.

tinued back as a slender filament, \\\zfilum 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 and to be indented by
two longitudinal grooves, one dorsal and one ventral, which
leave but a small connecting bridge between its two halves.
In the centre of this is a canal, the canalis cent rails , 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 half. The dorsal root presents a
small ganglionic enlargement, beyond which it joins the
ventral root to form the common trunk of the spinal nerve.
The roots of the hinder spinal nerves are very long and lie,
side by side, for some distance, 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 suboccipital nerve in the Frog.
It gives a branch to the muscles which move the head upon
the atlas, but the main trunk of it descends behind the
mandible, along with the glossopharyngeal nerve, and is
distributed to the muscles of the tongue. It therefore
answers to the hypoglossal nerve in the higher Vertebrata.

The second and third spinal nerves, of which the second
is the larger, unite to form a ' brachial plexus] and are dis-
tributed 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

xni.] THE FROG. 193

given off to the posterior parietes of the body, and to the
hind-limb. The nerves of the latter are the crural to the
front part of the thigh, and the sciatic, which passes to the
back of the thigh and ultimately divides into the pcronaal
and tibial nerves which supply the leg and foot.

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

Sympathetic.

The sympathetic system consists of ten ganglia, connected
by longitudinal commissures, and situated on each side of
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 fila-
ment with one of the spinal nerves, and the most anterior
ganglia are united, in the same way, with the ganglion of
the ninth and tenth cerebral nerves. From this a delicate
cord, which must be regarded as the most anterior part of
the sympathetic, 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 of the
abdomen.

The Olfactory organs are two wide sacs which occupy all
the space between the mesethmoid cartilage, the antorbital
processes, and the premaxillse and maxillae, and open in
front and dorsally by the external nares, behind and ven-
trally by the posterior nares. The inner faces of these sacs
are lined by a very peculiar epithelium, and the olfactory
nerves, with some branches of the trigeminal, are distributed
to them.

M. 13

194 ELEMENTARY BIOLOGY. [CHAP.

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 sclerotic is cartilaginous but contains no ossifications,
and the lens is nearly spherical. There is no pecten.

The Ear consists of an essential part the membranous
labyrinth lodged in the periotic capsule, and accessory
parts, the cohimclla auris, the tympanic membrane and the
tympanum.

The former consists of the three ordinary semicircular
canals, with their vestibular dilatations, 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 contained in the partly
cartilaginous, partly osseous, periotic capsule into which it
fits but loosely; the interval is filled with a fluid, the peri-
/j mph. In the outer face of the periotic capsule is an oval

xm.j THE FROG. 195

opening, the fenestra ovalis, into which the end of the
columella auris fits. This columella is shaped like a pestlt- ,
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 lined externally by
the integument, internally by mucous membrane, continuous
with that of the mouth through the Eustachian recess.
The mucous membrane of the tympanic cavity covers
only the ventral face of the columella, over the dorsal fare
of which the posterior division of the facial nerve passes.

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 filifonnes 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 which open upon
its surface. In the swollen integument which covers the
base of the inner digit in the males, large papillae with inter-
posed glands are developed.

A singular body of unknown function, the brows 'pot or
inter-ocular gland, consisting of a spheroidal sac with minute

13 2

i</> ELEMENTARY BIOLOGY. [CHAP.

cells, occurs in the integument of the frontal region of the
head.

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.
A. GENERAL STRUCTURE.

r. Go over the specific characters given above (p. 164).

2. The divisions of the body: head, trunk, two pairs of
limbs (see p. 159).

a. The head.

Somewhat triangular, with the blunted apex
turned forwards and passing broadly, without
any neck-constriction, into the trunk ; notice
the prominent eyes with their lids ; the membrana
tympani, a part off the integument stretched over
a hard ring, placed on each side, behind and
somewhat below the eyes ; the two apertures of
the nostrils (anterior nares) between the eyes
and the end of the snout ; the mouth opening;
the hard parts felt through the skin on the
upper side of the head ; the soft flexible throat.

Pass a bristle into one of the anterior nares.
Make a small opening in one of the tympanic
membranes and pass another bristle into it.
Now open the mouth widely ; and, if the bristles
have been thrust far enough, the end of the
former will be seen traversing the posterior nasal
opening in the roof of the mouth : while the end
of the other will appear in the Eustachian recess

x-iii.] THE FROG. 197

which lies at the sides of the back of the oral
cavity. The fleshy tongue will be seen, with its
bifurcated free end turned backwards. Turn it
forwards to see the attachment of its base to the
floor of the mouth and to the front part of the
lower jaw. Notice the slit of the glottis in the
hinder part of the floor of the mouth, and above
this the opening of the oesophagus. Pass a
bristle into the former, and a probe into the
latter. Notice the fine teeth in the upper jaw
and on the palate.

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 ; rounded
and soft on the greater part of the sides and
belly; the doacal aperture near the dorsal surface
of the posterior end of the trunk.

c. The limbs.

a. The anterior pair ; their three subdivisions,
brachium, antebrachium, and man us ; the four
digits.

/?. The posterior pair; their length as compared
with that of the anterior; their subdivision
into femur, crus, and/^.- the five long digits :
the well-developed web ; the horny prominence
(see p. 161).

3. Raise the integument of the abdomen with forceps
and slit it open with scissors from the lower jaw to
the origin of the hind limbs, a little on one side of
the middle line. Observe the spacious lymph cavities

ELEMENTARY BIOLOGY. [CHAP.

between the skin and the subjacent muscular wall of
the abdomen ; also a vein which occupies the middle
line of the inner face of this wall and is usually
visible through it.

Raise the muscular wall of the abdomen and cut it
in the same way, a little on one side of the middle
line, sufficiently to lay open the abdominal cavity,
taking great care to avoid the bladder which lies at
the posterior end of the cavity. Note the con-
spicuous vein (anterior abdominal] which lies beneath
the muscles in the middle line of the belly. The
liver, stomach and intestines will be seen ; at the
sides, in the female, the ovaries and oviducts will be
very conspicuous in the breeding season. Insert a
small blow-pipe into the cloacal opening : air blown
in will distend the large bilobed urinary bladder. If
the lungs are distended with air, one will be visible
on each side of the anterior end of the abdominal
cavity, and the extremity of the bristle passed into
one of them, through the glottis, will be seen. Lay
open the stomach to see the end of the probe passed
into the oesophagus.

By turning the intestines on one side, the kidney, the
corpus adiposum and the testis (in the male) will be
exposed. Notice a number of small white patches
on each side of the vertebral column. They are
accumulations of calcareous crystals.

5. In front of the liver, the apex of the heart will be
seen through the pericardium. Lay the latter open
and observe the position of the heart.

6. Cut away the left fore-limb and the left hind-limb,
with so much of the left half of the vertebral column

XIIL] THE FROG. 199

and skull as is needful to lay open the cavity which
contains the cerebro-spinal nervous centres. Pin
the frog in a dissecting dish, on its right side, with
sufficient water to cover it, and study the position of
the various organs in relation to a median longitu-
dinal plane, making a careful diagram of the parts
displayed.

} 7. In a frog which has lain in bone-softening solution
(say i/ chromic acid) sufficiently long to soften
the bones, make transverse sections (i) through
the eyes, (2) through the centres of the tympanic
membranes, (3) through the shoulder-girdle, (4)
through the hinder half of the abdomen. Compare
them with the foregoing dissection.

>
B. DISSECTION OF THE VISCERA IN THE VENTRAL CAVITY.

i. Lay a frog, which has been killed with chloroform,
on its back and pin it out on a layer of paraffin or
beeswax, under water; divide the skin along the
abdominal median line from the pelvis to the
front of the lower jaw; next make a transverse
incision at each end of the longitudinal one, and
then throw outwards the two flaps of skin thus
marked out. The following points may now be
noted.

a. A great vein (imisculo-cutaneous] on the under-
surface of each flap of skin, about the level of
the shoulder.

b. Some of the muscles of the abdominal wall,
covered by a thin aponeurosis: through this
latter can be seen

a. The rectus abdominis running from pelvis to

:oo ELEMENTARY BIOLOGY. [CHAP.

sternum close to the middle line, and divided
into a number of bellies by transverse tendi-
nous intersections.

/?. Other muscles outside the rectus on each
side.

c. The pectoral region ; part of its hard parts in the
middle line, only covered by tendinous tissue:
external to this, muscles running towards the
shoulder-joint

d. The muscles of the throat ; small and with a
general direction from the lower jaw towards
the sternum and shoulder-girdle.

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 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
deep side of the left flap will be seen a large vein
(anterior abdominal}.

Seize the posterior border of the sternum with a
pair of forceps and raise it up : on looking beneath
it several fibrous bands will be seen running from it
and the hard parts in front of it to subjacent parts ;
carefully divide these : then, with a strong pair of
scissors, cut through the hard parts in the median
line, being very careful not to injure the organs
beneath them; turn each half outwards and pin it in
that position; stretch out each fore-limb to its fullest
extent and fasten it with pins.

XIIL] THE FROG. 201

3. Note the smooth moist membrane (plcuroperitoneum}
lining the inside of the body-cavity and covering the
outside of the contained viscera.

4. The liver will be readily recognized as a great
brownish mass covering a great part of the other
abdominal viscera: lying in a cleft in its anterior
border and partly concealed by it, will be seen a
delicate sac in which pulsations are going on; this
sac is the pericardium: if it be opened and removed
very carefully, the heart and some of the great
blood-vessels will be laid bare; clean carefully the
two great trunks (aortic arches) which diverge from
the anterior end of the heart, following each to the
point of its division into three vessels.

5. The heart.

a- Note the general form of the organ.

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

b. The truimis arteriosus: a sub- cylindrical part,
arising from the right side of the base of the
ventricle and dividing anteriorly into the two
aortic arches.

c. The atrium : thin-walled, rounded, lies on the
dorsal aspect of the truncus and ventricle. The
separation between the two auricles is not visi-
ble externally.

d. Carefully raise the ventricle : lying beneath it
(that is, on its dorsal side) will be seen another
division of the heart, the sinus venosus ; it lies
between the atrium and the great systemic

ELEMENTARY BIOLOGY. [CHAP.

veins, which enter it through the dorsal and
posterior walls of the pericardium.

f. The further examination of the structure of the
Frog's heart requires a good deal of care and
the use of a lens of low magnifying power. In
a chloroformed Frog the heart is distended
with blood when it ceases to beat. When all
signs of contractility have disappeared, the dis-
tended heart should be removed from the body
by cutting through the adjacent parts in such a
manner as to leave the terminations of the
veins and the origins of the aortic trunks
intact. The organ should next be transferred
to a shallow dissecting dish and covered with
weak spirit. The right and left walls of the
atrium being now carefully slit and the blood
which they contain washed away, the delicate
septum of the auricles will become visible. By
cautiously removing the ventral face of the
ventricle, its cavity will be laid open and the
auriculo-ventricular opening will be displayed.
If the ventral wall of the truncus arteriosus is
laid open longitudinally with fine scissors, the
valves in its interior will become visible. The
pulmonary vein runs along the dorsal aspect of
the sinus venosus, between the right and left
superior venae cavae, to the left auricle, into
which it opens close to the dorsal attachment
of the septum.

The natural relations of the different divi-
sions of the heart should be carefully studied in
such a dissection as is described in A. 6.

xiii.] THE FROG. 203

b. The pulsation of the heart. This should be stu-
died in a Frog rendered insensible by chloroform
or by being pithed; though the latter operation
causes such dilatation of the vessels that little or
no blood may afterwards flow through the heart,
yet the organ goes on beating.

a. Watch the movement carefully; it is a regu-
larly alternating series of contractions and dila-
tations.

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

c. Raise the ventricle so as to see the venous
sinus; note that it contracts immediately before
the auricles.

6. The parts exposed by the preceding dissections
(B. i. 2).

Draw them carefully without disturbing them.

a. The throat-muscles: through the broad thin mus-
cle in front (inylo-hyoid} is seen the hypoglossal
nerve.

b. The larynx: forming a hard prominence in the
middle line, just in front of the aortic arches.

c. The heart and aortic arches (see B. 5. i.) : the
three terminal branches of the latter, viz.

a. The carotid trunk; the anterior division; end-
in a small reddish body (the carotid gland}.

(3. The systemic aortic arch.

y. The pulmo-cutaneous artery: the hindmost
branch.

704 ELEMENTARY BIOLOGY. [CHAT.

d. The liver: a great brown two-lobed mass; its
left lobe the larger and subdivided into two.

e. 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 removed.

f. The stomach: a small portion of this is seen pro-
jecting beyond the lower left border of the
liver.

g. The mtestifie: a convoluted tube, continuous with
the stomach, and slung by a delicate membrane,
the mesentery : posteriorly the intestine ends in a
dilated portion (rectum) which runs into the
pelvis.

h. The urinary bladder: a thin-walled bilobed sac
(which may or may not be distended) appear-
ing just in front of the pelvis.

i. The fat masses: long slender yellow processes
appearing on each side of the liver.

In R. temporaria, the urinary bladder is much
more deeply lobed and also much larger propor-
tionately, than in R. esculenta.

7. The liver.

a. Study its form more closely. (6. d.)

b. Raise its lower border; between its two lobes
will be seen a small greenish sac, the gall-bladder.

c. Carefully cut away the liver, except its deepest
part, close to the venous sinus.

d. Tease out a bit of liver in o'7^.sodic chloride

* j \j

solution and examine with |- obj.

xni.] THE FROG. 205

a. Numbers of polygonal granular cells (h'patic
cells), with oil-drops in them, will be seen.

/?. Treat with acetic acid : a nucleus, or sometimes
two, will be rendered apparent in each of the
cells.

S. The stomach, intestine, pancreas and spleen.

a. Cut away the front of the pelvis with a stout
pair of scissors, taking care not to injure the
urinary bladder: pass a probe from the anus,
through the cloaca, into the rectum: uncoil the
intestine and spread out the mesentery, so far as
is possible without cutting the latter.

a. The spleen: a small red body lying in the
mesentery, near its attachment to the back of
the abdomen.

/?. The stomach: an elongated sac on the left
side of the abdominal cavity: the narrower
tube (oesophagus] opening into its anterior end.

y. The intestine: its length and varying diame-
ter; especially the great width of its rectal
portion : its posterior termination in the cloaca.

6. The pancreas: a pale-coloured compact mass
lying in the mesentery near the commence-
ment of the intestine.

e. The bile-duct. Slit open the duodenum where
the right end of the pancreas is attached to
it: a small aperture will be seen on the
mucous membrane of the intestine at this
point: this is the opening of the bile-duct:
pass a bristle into it.

The mesentery: its width; mode of attach-

ao(5 ELEMENTARY BIOLOGY. [CHAP.

ment to the intestine; the blood-vessels run-

mg in it.

b. Divide the oesophagus close to the stomach and
the rectum near the cloaca: remove all the por-
tion of alimentary canal between these two
points, cutting through the mesentery.

a. Pass a probe up the oesophagus into the mouth.

/3. Open the upper end of the intestine and snip
off a bit of its internal layer (mucous mem-
brane) and mount in normal saline solution :
examine with |- obj.; on the fragment will be
found minute prominences (representing the
villi of the higher animals) covered by a closely-
set layer of cells (epithelium}.

9. The kidneys. These organs are now exposed as two
elongated deep red bodies lying in the posterior
part of the perivisceral space close to the verte-
bral column; clear away any bits of mesentery, &c.
which may cover them; note

a. 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 the opening of
one of the ureters.

b. In the male R. esculenta each duct is somewhat
dilated after leaving the kidney : it then narrows
again and opens on the posterior surface 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 (vcsicula seminal is],

XIIL] THE FROG. 207

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.

c. The vein (renal portal] entering the kidney at
its posterior outer border.

d. The great vein (vena cava inferior") lying between
the kidneys and chiefly formed by their efferent
(renal] veins.

Now that the cloaca is open, trace the open-
ing of the urinary bladder (B. 6. h) into it.

i o. The generative organs.

a. In the male.

a. The testes: a pair of yellowish bodies lying
in front of the anterior ends of the kidneys;
their form.

The ducts of each testicle (vasa efferent ia}
entering the inner border of the kidney of the
same side in order to communicate with the
genito-urinary canal (9. a).

Remove the testes : open one and press out
some of its contents upon a slide and mount
in common water: examine with i objective.

The spermatozoa: bodies provided with a
small oval head and a long vibratile tail in R.
esculenta : in R. temporaries the oval head is
absent : their movements.

b. In the female.

a. The ovary : an organ varying much in size

ELEMENTARY BIOLOGY. [CHAP.

with the season of the year. The numerous
ova in it.

The oviduct: a convoluted tube, not con-
tinuous with the ovary, and running back to
open into the cloaca. The greater part of
the oviduct is opaque and glandular; the
part near the cloaca however is dilated, thin-
walled and transparent. The oviducts open
on the posterior wall of the cloaca a little
anterior to the openings of the ureters.

ii. The mouth, oesophagus, and respiratory organs.

a. Open the mouth : note on its roof near the front
the two hinder openings of the nasal cavities
(posterior nares); farther back, the two larger
openings of the Enstachian recesses ; the long
tongue in the floor of the mouth ; fixed by its
front end to the lower jaw ; its free bifid end
turned towards the throat.

b. Enlarge the mouth-opening by cutting through
the sides of the buccal cavity with a pair of
scissors : pull down the lower jaw so as to see
the chamber (pharynx] behind the mouth.

c. On the floor of the pharynx is a narrow opening
(the glottis] : pass a probe down it through the
larynx and very short trachea into the lungs.

d. Remove the lungs ; open one ; it is a thin-walled
cavity with a sacculated inner surface.

e. Trace the oesophagus up to the pharynx.

C. THE CIRCULATION OF THE BLOOD IN THE FROG'S WEB.

i. Get a piece of thin board, about 5 inches long
. and 2- broad; in the middle of one end of it cut

XIIL] THE FROG. 209

a V-shaped notch about the size of a spread-out
frog's 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
hind-foot, and by means of them spread out the web
over the notch in the board, taking great care that it
is only very lightly stretched. The animal should be
kept moist by a bit of wet blotting-paper spread over
its back.

2. 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-cell layer.

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

(3. The capillaries, in which the arterial branches
end : small vessels forming a close network
and frequently branching or anastomosing
without much altering their size.

y. The reins, formed by the ultimate union of
the capillaries, and increasing in size by union
with one another; the blood-flow in them
from smaller to larger trunks.

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

M. 14

210 ELEMENTARY BIOLOGY. [CHAP.

3. Place a small drop of water on a bit of a thin cover-
glass, and place the bit, with the water downwards,
gently on the web: then examine the following points
with \ or ~ obj. ; note

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

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

/?. The capillary walls : difficult to see ; merely
a thin somewhat more transparent boundary
line.

y. The venous walls ; much like the arterial.

b. The blood-flow in the small arteries of the web.

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

ft. The slower stream along the edge (inert
layer), containing many colourless corpuscles.

c. The flow in the capillaries : much slower than in
the arteries ; the frequent distortion of the red
corpuscles in the capillaries from pressure, &c. ;
their elasticity as indicated by the readiness with
which they recover their shape when the cause
of distortion is removed ; the way the white
corpuscles creep along, with a tendency to stick
to the capillary wall.

4. Examine a drop of frog's blood with the microscope
(j:0r-| obj.). Sufficient blood to supply a whole class
for this purpose can be obtained by killing one frog
and opening its heart.

It consists of solid bodies (corpuscles] floating in
fluid (plasma).

xin.] THE FROG. 211

a. The red corpuscles.

a. Their form : oval when seen in front face ;
almost linear in profile but slightly swollen at
the centre.

/?. Their size: their length, breadth, and thick-
ness ; measure.

y. Their colour : pale yellow, when seen indivi-
dually ; redder if a thick mass of them is
looked at.

8. Their structure: they are homogeneous for
the most part, but possess a round granular
central nucleus.

c. Treat with water; they swell up and become
more spherical ; their colouring matter is gra-
dually discharged ; 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.

b. The white corpuscles.

Less numerous than the red : their colour, size,
granular character, nucleus, and changes of form
(amoeboid movements]: see III. B.

D. THE EXAMINATION OF A PREPARED SKELETON.

The skeleton of a Frog may be prepared for ex-
amination by removing the viscera from the body,
and roughly dissecting away the muscles, &c. 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 carti-

lages.

14-

212 ELEMENTARY BIOLOGY. [CHAP.

a. Its general arrangement.

1. The central axis, consisting of the vcrtdral or spinal
column and of the central farts of the skull which
lie, in front of the spinal column, in the same antero-
posterior line.

2. Lateral parts, supported, directly or indirectly, by
the axis.

a. The appendages proper. (Limbs vxd. limb-arches.)

a . 'The fore-limbs : their su pporting 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.

p. The hind-limbs : their supporting arch (pelvic
girdle), carried directly by bony processes
proceeding from the vertebral column ; the
limb proper ; its main divisions, os feinoris,
tibia 33\& fibula (ankylosed), tarsus, digits.

b. The facial and lateral cranial bones.

1). The vertebral column.

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

i. Examine carefully and draw various aspects of a de-
tached vertebra, say the third.

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

b. The neural arch : an arch of bone springing
from the sides of the dorsal aspect of the cen-

THE FROG. 213

trum of the vertebra and not quite so wide as
the centrum in its antero-posterior diameter.

The transverse process : a bony bar on each
side, arising from the arch and passing out-
wards and a little downwards.

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

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

c. The neural canal enclosed between the arch and
the body.

2. Examine the remaining vertebrae.

a. The first vertebra (at/as) : its body produced
forwards into a wedge-shaped process which lies
between the occipital condyles : its arch, some-
times incompletely ossified in the region of the
spinous process, which is rudimentary; posterior
zygapophyses only present : the large concave
anterior facets, partly on the arch and partly on
the centrum, with which the skull articulates.

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

2i 4 ELEMENTARY BIOLOGY. [CHAP.

c. The 8th vertebra: the concave facet at each end
of its centrum.

d. The 9th vertebra (sacrum): its centrum; convex
in front and with two convex tubercles behind :
its large strong transverse processes (sacral ribs]
directed somewhat backwards and expanded at
their ends.

3. The posterior unsegmented portion of the vertebral
column (urostyle).

a. An elongated rod-like bone, rather thicker to-
wards its anterior end, which bears two con-
cavities.

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

c. The prominent ridge along its dorsal surface ;
wider and higher in front ; getting thinner and
gradually disappearing towards the posterior end.

d. The small canal contained in the forepart of
the ridge.

e. The two minute passages leading from the canal
to the outside of the ridge on each side.

4. The vertebral column as a whole.

a. Its composition.

a. Its anterior segmented part formed of the nine
vertebrae.

/3. Its posterior unsegmented part formed by the
urostyle and nearly as long as the segmented
part.

XIIL] THE FROG. 215

b. Its ventral surface.

a. The solid bony axis formed by the bodies
of the vertebrae in front and continued pos-
teriorly by the ventral rounded part of the
urostyle.

ft. The transverse processes : their size and direc-
tion : those of the second vertebra, slender
and directed nearly straight outwards ; those
of the third and fourth, largest of all and with
a distinct inclination backwards : those of
the fifth, sixth, seventh and eighth vertebras
smaller than the rest and directed nearly out-
wards ; those of the ninth, very stout, directed
outwards upwards and backwards, and having
the iliac bones attached to their distal ends.
The transverse processes arise from their
arches closer to the centrum in the second,
third and fourth vertebrae than in the others.

y. The inter-vertebral foramina : the interspaces
left between each pair of neural arches, below
the level of the zygapophyses.

c. T/ie dorsal surface of the spinal column.

a. The ridge down its middle formed by the row
of spinous processes, and continued behind
by the dorsal ridge of the urostyle.

J3. The lateral prominences caused by the ar-
ticular processes : the articulations between
the anterior articular processes of one verte-
bra, and the corresponding posterior processes
of its predecessor.

7. The spaces left between the dorsal part of

216 ELEMENTARY BIOLOGY. [CHAP.

each neural arch and its successor : between
the atlas and the second vertebra and be-
tween the eighth and ninth vertebrae ; these
are almost obliterated by the approach of the
respective arches.

d. The neural canal.

a. Closed by the centra of the vertebrae beneath,
and incompletely by the neural arches on the
sides and above : its backward continuation
as the canal in the front part of the ridge of
the urostyle.

(3. The communication with it, of the inter-
vertebral foramina (4. b. y), and the dorsal
intervals between the neural arches (4. c. y) :
also of the openings in the urostyle (3. e).

c. The skull. The prepared bony skull of the frog
is difficult to understand, for two reasons ;
firstly, on account of the dried-up condition of
the cartilages of which, in the fresh state, it is in
part composed ; and, secondly, on account of
the tendency of many of its constituent bones
to become ankylosed together in the adult : the
following points can however be made out with
tolerable ease. Drawings should be made of
each aspect of the skull.

i. Examine the posterior end of the skull.

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

b. The convex surface (occipital condyle), on each
side of the foramen magnum, which articulates

XIIL] THE FROG. 217

with the corresponding concave facet on the
front of the atlas.

c. The bone bearing the condyle on each side
and, with its fellow, enclosing the foramen mag-
num, is the exoccipital.

d. The thick bone running outwards in front of
the exoccipital, on each side, protects the front
part of the internal ear, and is the pro-otic bone.

e. Between these two bones, on the outer side of
the chamber which contains the organ of hear-
ing (periotic capsule], is a cartilaginous inter-
space containing an oval aperture, thefenestra
ovalis. In this is fixed the inner end of a partly
cartilaginous and partly osseous rod, the colu-
mclla aitris.

f. Attached to the outer end of the pro-otic bone
is a hammer-shaped bone the squamosal, which
extends from the pro-otic bone to the articu-
lation of the lower jaw.

2. T/ic roof of the skull.

a. Passing forwards from the exoccipitals are two
long flat bones, the par ieto-f rentals^ one on each
side of a median suture which answers to the
sagittal and frontal sutures in man.

I. In front of these come two triangular bones-
tkc nasals.

c. In front of the nasals are two other bones, which
belong rather to the ventral than to the dorsal
face of the skull. They form the extreme front
of the snout, and each sends a process towards
the nasals; these are \ke_premaxillary bones.

2i8 ELEMENTARY BIOLOGY. [CHAP.

3. The base of the skull.

a. Running along the greater part of the floor of
the cranial cavity, from the occipital foramen
to the vomers, is a bone shaped like a dagger
with a short handle and a strong guard. The
latter spreads out under the pro-otics. This is
the parasphenoid bone.

b. Appearing at the base of the skull, at the front
end of the parasphenoid, is the girdle-bone or
sphenethmoid (which represents several bones
joined together); this bone closes in the floor
and sides of the forepart of the cranial cavity and
also its roof, being concealed in the latter place
by the anterior ends of the parieto-frontals. The
sphenethmoid has a single cavity behind, which
enters into the formation of the cephalic chamber,
and two cavities in front, one for each nasal
chamber, separated by a septum.

c. Running out transversely from the girdle-bone
and the anterior end of the blade of the para-
sphenoid on each side, is the &QH&QT palatine.

d. In front of the end of the blade of the para-
sphenoid and of the palatines are two broad
irregularly shaped bones, each bearing an oblique
row of teeth on its posterior part : these are the
vomers.

e. The middle anterior boundary of the contour o
the skull, in this view, is formed by the denti-
gerous parts of the pre-maxillae ; and, behind
them, by the maxillae and the quadrato-jugal
bones (4. a. b). Running backwards from the

xni.] THE FROG. 219

outer end of the palatine, and closely applied to
the maxilla, is a bone, which soon separates
from the maxilla, and becoming broad and
stout, bifurcates; the inner process nearly joins
the para sphenoid and is moveably articulated
with the skull; the outer runs along the inner
face of a cartilage (the suspensorium), on the
outer face of which the squamosal rests: this is
the pterygoid bone.

At the outer edge of each vomer, immediately
in front of the palatine, is an aperture which
leads into the nasal cavity. These two apertures
are the posterior nares.

4. The side of the skull.

a. Running back from that part of the pre-maxilla
winch bounds the gape is a long bone, forming
almost the whole of the rest of the upper edge
of the gape; this is the Manilla.

b. Joined to the posterior end of the maxilla is a
small bone, which at its posterior end is attached
to the distal portion of the squamosal. This is
the quadrato-jugal.

c. The under jaw or mandible consists of two dis-
tinct portions, or ratni, which meet in the middle
line in front, and which, behind, articulate with
the extremities of the suspensorial cartilages.
In the articular end of each suspensorial cartilage
there is an ossification which represents the
quadrate bone in other Vertebrata, and is united
with the jugal to form the quadrato-jugal.

In each ramus three pieces may be made out-

ELEMENTARY BIOLOGY. [CHAP.

a. A central axis formed of cartilage (MeckeFs
cartilage), which enlarges at its posterior end
in order to articulate with the suspensorial
cartilage, while at the opposite or symphysial
end it is ossified to form the mento-Meckdian
bone.

J3. A posterior inferior piece, which runs nearly to
the middle line in front (angulo-spleniaT) and
partly ensheaths the foregoing.

y. A small anterior superior piece (dentary).

d. The liyoid bone or cartilage.

a. Its broad somewhat tetragonal central part
(body\ bearing a number of processes, viz.

/?. The anterior cornuct, proceeding from the
front of the body on each side : each is a
long slender curved cartilage running at first
forwards, then backwards and outwards, and
finally forwards and upwards, to become at-
tached to the periotic capsule beneath the
fenestra ovalis.

y. The posterior cormta, or thyro-hyals ; bony,
and shorter and thicker than the anterior
cornua: attached to the posterior border of
the body near the middle line and diverging
as they run backwards.

S. Two pairs of smaller processes formed by the
elongation of the anterior and posterior an-
gles of the body of the hyoid.

e. The sternum and shoulder-girdle.

i. Their general arrangement : they form an incomplete
ring round the fore-part of the trunk : this ring is

xiii.] THE FROG. 121

composed partly of bone, partly of cartilage. Note
the hollow (glenoid fossa) with which the fore-limb
articulates.

a. The sternum : situate in the ventral median line
and made up of several parts: beginning behind
we find

a. The xiphistern um ; a thin cartilage, wide
behind, narrow in front, where it passes
into

(3. A median cartilage ensheathed in bone, the
sternum proper. The anterior end of the
sternum unites with the posterior and inter-
nal angles of the coracoids (b. y), the inner
edges of which meeting in the middle line
separate the sternum from

y. The omostcnntm, consisting of a slender, flat-
tened bone, terminated in front by an ex-
panded cartilage. The posterior end arti-
culates with the praecoracoids and the clavi-
cles.

b. The shoulder-girdle: beginning dorsally, it ex-
hibits on each side

a. A thin expanded dorsal portion, partly car-
tilaginous, partly ossified : the supra-scapula.

ft. Next a bony segment the scapula, the pos-
terior inferior edge of which is excavated by
the glenoidal fossa.

The ventral parts of the shoulder-girdle, which
lie between the two scapulae, meet in the mid-
dle line; the part on each side is subdivided

222 ELEMENTARY BIOLOGY. [CHAP.

into an anterior and a posterior portion by a
large foramen.

y. The bony piece running behind the foramen,
from the scapula almost to the middle line,
is the coracoid. Where the coracoid unites
with the scapula it contributes to the forma-
tion of the glenoidal cavity.

8. The adjacent margins of the two coracoids
are fringed with cartilage (epicoracoid\ which
passes in front of the foramen into a bar of
cartilage the pr&coracoid which, externally,
is continuous with the cartilage which lies
tween the scapula and coracoid and helps to
bound the glenoidal cavity.

e. Closely attached to the fore-part of the prae-
coracoid lies a bone, the clavicle, the outer
end of which articulates with the coracoid
and scapula, the inner with the omosternum.

Draw the whole pectoral arch carefully, shading
differently the bones and cartilages.

f. The bones of the fore-limb.
a. The arm-bone (Jiumerus).

a. A somewhat cylindrical bone, with an arti-
cular expansion at each end and a shaft unit-
ing them.

j3. The great ridge (deltoid crest] on its antero-
internal surface, to which a muscle was at-
tached.

The development of this crest is greater in
the males than in the females.

xiii.] THE FROG. 223

/;. The bone of the forearm.

a. Hollowed out above to fit the lower end of
the humerus.

/3. Shewing below a tendency to divide into the
two bones of which it is made up; viz. the
radius and the ulna. When the limb is
stretched out at right angles to the body
with the pollex forwards, the radius is on the
anterior, and the ulna on the posterior side
of the axis of the limb.

c. The carpus. Two bones (a, b) articulate with
the ankylosed radius and ulna. A third bone
(c\ on the radial side of the carpus, articulates
only with the carpal bones on the proximal and
distal sides of it. A large bone (d) occupies
two-thirds of the ulnar side of the carpus, and
articulates with a, b and c on one side, and
with the third, fourth and fifth metacarpals on
the other. Two small ossicles articulate with
the distal face of c and bear the first and second
metacarpals.

d. The digits.

Five in number, the first (radial one) being,
however, rudimentary: beginning at the ulnar
side, we find

a. The fifth digit (that on the outer or ulnar
side of the limb) : it presents a cylindrical
proximal bone (metacarpat] followed by three
others (phalanges), each shorter than its pre-
decessor.

p. The fourth digit : a metacarpal bone and three
phalanges.

224 ELEMENTARY BIOLOGY. [CHAP.

y. The third digit: a mctacarpal bone with two

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

phalanges.
c. The first digit (pollex) consists only of a

small metacarpal bone.

g. The pelvic girdle.

a. Its general form : V-shaped, with the apex
turned backwards.

b. The concavity (acetabulum) on each side with
which the thigh-bone articulates.

c. The triradiate fissure running through the aceta-
bulum and dividing each half of the pelvis into
three pieces, viz.-

a. ' An anterior elongated piece (ilium)] subcy-
lindrical in front, where it articulates with
the sacrum ; bearing behind, on its dorsal
aspect, a laterally compressed ridge of bone
(crista ////); it forms almost half of the aceta-
bulum.

f3. A posterior, irregularly rounded piece (ts-
chiuni); closely united posteriorly with its
fellow, in the middle line.

y. A small triangular piece (os pubis\ (calcified
cartilage except in old frogs), wedged in
between ilium and ischium, and meeting its
fellow in the median ventral line, thus form-
ing the symphysis pubis.

h.' The bones of the lower limb.

a. The thigh-bone (os femoris); its long cylindrical
shaft and expanded articular extremities.

b. The leg-bone (os cntris).

XIIL] THE FROG. 225

a. A very long cylindrical bone, expanded at
each end.

/?. The grooves on it; one running along the
whole ventral surface, but most marked near
the ends; other grooves on the dorsal sur-
face, one at the upper, another at the lower
extremity: these indicate that the os cruris
is really made up of two united bones, the
fibula and the tibia. When the limb is
stretched out at right angles to the body, the
tibia is anterior, corresponding with the
radius; and the fibula, posterior, correspond-
ing with the ulna.

c. The tarsus.

a. Two elongated bones (separate in the middle
but united by confluence of their cartilagin-
ous extremities) articulate with the ankylosed
tibia and fibula; the anterior, or tibial, of
these is the astragalus; the posterior, or
fibular, the calcaneum.

P. With the distal ends of these, two partially
ossified cartilages, one on the calcaneal and
the other on the astragalar side, articulate.
The latter is connected by ligamentous
fibres, within which a nodule of cartilage
may be found, with the first and second meta-
tarsals, and supports the calcar (d. ).

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

a. The first, or hallux (the most internal) ; a

mdatarsal bone, followed by two phalanges.
M. i^

226 ELEMENTARY BIOLOGY. [CHAP.

/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
phalanges.

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

. On the anterior or tibial edge of the foot there
are two, small, more or less cartilaginous,
ossicles, articulated with the tarsus (c. (3) in
such a manner as to resemble an extra digit.
This calcar, or spur, supports the horny pro-
minence referred to above.

E. DISSECTION OF THE FROG'S HIND-LIMB TO ILLUSTRATE

ITS MYOLOGY.

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

1. Lay the animal on its back, and make an incision
through the skin on the front of the limb from the
symphysis pubis to the ankle ; then reflect the skin
to each side so as to lay bare the parts beneath it;
in turning it back note the loose bands and fibres
(subcutaneous areolar tissue] with large lymph-spaces
between them, which unite the skin to subjacent
parts, and which have to be cut through.

A number of muscles will now be exposed on the
front of the thigh and leg.

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

Separate these gently from one another, tearing
through the connective tissue which unites them.

xiii.] THE FROG.

a. Each is chiefly made up of a mass, the belly
of the muscle, which is nearly white and readily
tears into bundles in a muscle which has been in
spirit; but 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 being the origin of the muscles :
the point of attachment to the more moveable
bone, its insertion.

d. The names of the muscles laid bare on the front
of the thigh, are

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

ft. The adductor magnus: it becomes superficial
along the upper two- thirds of the inner border
of the sartorius.

y. The adductor brevis: a little bit of it is seen
on the inner side of the adductor magnus,
close to the symphysis pubis.

B. The rectus 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.

e. The rectus interims minor: a thin muscle lying

22S ELEMENTARY BIOLOGY. [CHAP.

inside 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.

. The adductor longus: it is partly superficial
along the outer edge of the sartorius.

77. The vastus internus: a very large muscle on
the outer anterior aspect of the thigh; arising
from the pelvis close to the hip-joint, it joins,
below, two muscles on the back of the thigh
(4. a. ft. y), and all end in a tendon which is
inserted into the aponeurosis over the front of
the os cruris.

c. Cut across the belly of the sartorius, and turn its
ends out of the way; dissect out the origin and
insertion of the adductor longus and the adductor
magnus (d. . and (3).

a. The adductor longus arises from the anterior
inferior part of the symphysis of the iliac
bones ; by its lower end it joins the adductor
magnus.

(3. The adductor magnus 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.

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

a. Divide and reflect the adductor longus, rectus
internus major and rectus internus minor. The
following muscles will be displayed :

xni.] THE FROG. 2:9

a. The pectineus: it lies at the upper part of the
thigh immediately internal to the vastus inter-
ims: it arises from the front of the pelvis,
close to the symphysis, and is inserted into
the anterior surface of the distal half of the
femur.

/?. The adductor brans (2. d. y): it lies along the
inner side of the pectineus and arises and
is inserted close to it.

y. The semitendinosiis : this is a long slender
muscle lying beneath the rectus internus major
and bifurcated at its upper end : its two //<<///>.
thus formed, arise, one (anterior head] from
the pelvis between the ischial symphysis and
the acetabulum; the other (posterior head}
from the ischial symphysis : the muscle termi-
nates below in a rounded tendon which is
inserted along with the sartorius.

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

The muscles on the back of the thigh. These are :-

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 internus: the anterior division,
which has been already seen on the front of
the thigh. (2. d. rj.)

/?. The vastus externus : the posterior division ;
it arises from the hinder edge of the iliac
bone.

ELEMENTARY BIOLOGY, [CHAP.

y. The rcctus fcmoris anticus: the middle divi-
sion of the triceps ; it arises from the pos-
terior part of the ventral border of the iliac
bone. For the insertion of the triceps femo-
ris, see 2. d. 77.

b. The ghitccus : this muscle arises from the hinder
two-thirds of the external surface of the ilium ;
it runs down between the vastus externus and
the rectus anticus to be inserted into the back
of the head of the femur.

c. The pyriformis. This arises from the posterior
part of the urostyle and, passing inside the
vastus externus, is inserted into the shaft of the
femur.

d. 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 pieces, 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.

e. The semimembranosus : a large muscle inside the
biceps ; it arises from the upper posterior part
of the iliac symphysis and is inserted into the
aponeurosis round the knee-joint.

Lying deep in the thigh, between the biceps
and semimembranosus muscles, will be seen the
femoral vessels and the sciatic nerve.

f. Divide and reflect the vastus externus and the
biceps : beneath them will be laid bare

xni.] THE FROG. 1*1

The ileo-psoas : it arises from the internal
surface of the posterior part of the ilium and is
inserted into the posterior aspect of the shaft of
the femur.

g. Remove the pyriformis, cut through the semi-
membranosus close to its origin and throw it
downwards ; this brings into view a small tri-
angular muscle

The quadratns femoris, which arises from the
ilium behind the acetabulum and is inserted into
the middle of the shaft of the ventral surface of
the femur.

h. The obtiiratorius : this is a small muscle lying
on the dorsal surface of the hip-joint.

5. The muscles of the leg.

a. Turn the frog on its back, and remove the skin
from the foot : fix the dorsal surface of the foot
upwards. The os cruris will now be seen run-
ning down the middle of the leg. Lying on its
present inner (proper dorsal) side are two mus-
cles, viz.

a. The gastroenemius : a muscle with a great
fleshy belly; it arises above by two tendons ;
one (much the larger) is inserted behind the
knee-joint partly into the femur, partly into
the os cruris ; the other joins the aponeurosis
on the outer side of the knee-joint. Be-
low, the muscle ends in a great tendon (tendo
Achillis], which terminates in an aponeurosis
on the plantar surface of the foot.

232 ELEMENTARY BIOLOGY. [CHAP.

/?. The tibialis posticus : a slender muscle co-
vered in great part by the gastrocnemius ; it
arises from the greater part of the posterior
surface of the os cruris and, passing along the
inner side of the ankle-joint, is inserted into
the astragalus.

b. On the opposite side of the bone lie four mus-
cles : viz.

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

P. The tibialis anticus : a small muscle inside
and beneath the peroneus ; it arises from the
front of the lower end of the femur and from
the capsule of the knee-joint ; below it di-
vides into two parts, one inserted into the
dorsal side of the astragalus, the other into
the calcaneum.

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 : this arises where
the last muscle ends, and is inserted into the
dorsal side of the astragalus.

6. The nerves of the hind-limb.

These are now to be dissected out in that leg which
has not been used for the muscles.

xiii.] THE FROG. 233

a. The sciatic nerve.

a. Find it on the dorsal side of the thigh by
separating the biceps and semimembranosus
muscles ; it appears as a slender white cord.

/?. Dissect it out carefully in the middle of the
thigh, noting the branches it gives off to the
various muscles.

y. Follow it up to the abdominal cavity, cutting
away the tissues lying between the ilium and
urostyle, which cover it in.

8. Follow it down towards the knee : a little
way above the joint it divides into two
branches; one (posterior tibia!} runs inside
the large head of the gastrocnemius muscle,
the other (peroneal) between its two heads.

b. The posterior tibial nerve.

a. Note especially the branch which it gives off
opposite the knee-joint, and which, after run-
ning for some way along the deep surface of

the gastrocnemius, enters that muscle.

%
/?. Follow the nerve down the leg : it runs along

the tibialis posticus muscle, giving off branches
here and there.

y. Near the foot it turns to the back of the
ankle-joint and enters the plantar surface
of the foot, where it ends in a number of
branches.

c. The peroneal nerve.

a. This runs down the leg close to the peroneus
muscle, giving off branches on its way.

s;U ELEMENTARY BIOLOGY. [CHAP.

/3. Towards the bottom of the leg it comes to
the front of the ankle-joint, and divides into
branches which are distributed on the dorsum
of the foot.

[F. DISSECTION OF THE VASCULAR SYSTEM.

The dissection of the blood-vessels is much facilitated by
previous injection: this maybe done as follows: Dissolve
some gelatine, with the aid of heat, in a coloured fluid
(solution of carmine or of Berlin blue) ; the gelatine ought
to be added in such quantity that the fluid just sets when
cold : kill a frog with chloroform ; lay bare its heart, taking
care not to injure the anterior abdominal vein ; prick a
small hole in the venous sinus and sop up any blood that
flows out; pass a ligature round the truncus arteriosus j
make a small aperture in the ventricle and pass a glass
tube, drawn out to a fine point, through the ventricle into
the arterial bulb, and tie it in ; fill this tube with normal
salt solution and connect it, by a bit of gutta percha tubing,
with a syringe filled with the injecting fluid, which should
not be warmer than 35 C. ; inject very slowly and with
slight pressure. The venous system may also be readily
injected by dividing the anterior abdominal vein and
passing the syringe into its posterior end. When the in-
jection is finished, put the animal in alcohol for some
hours.]

i. The anterior abdominal vein.

a. Carefully dissect the belly-walls away from the
anterior abdominal vein : at its posterior end
this vessel will be found to get a small branch
from the front of each thigh and then to divide
into two large trunks (pelvic veins) which run,
one on each side, towards the back of the thigh.

xni.j THE FROG. 235

b. Turn the animal over and follow one of these

trunks back : it will be found to be continuous

with the sciatic vem, which ends in the pelvis

by dividing into this and another (renal portal]

vessel.

c. Trace the anterior abdominal vein forwards : it
divides into two branches, one of which goes to
the right and the other to the left lobe of the
liver.

2. Raise the liver, and note the vena portse which enters
its lower surface; it is formed by the union of a vein
(gastric] from the stomach with one (lieno-intestinal)
from the spleen and intestines. The gastric division
of the vena portse communicates by a large branch
with the left division of the anterior abdominal vein.

3- The veins of the head and neck and fore-limbs.

a. Remove the liver, being careful not to injure
the inferior vena cava beneath it.

b. Pass a bit of glass tube down the frog's gullet
(in order to stretch out the neighbouring parts)
and clean the aortic arches : passing in front
of each aortic arch, near its point of division is

c. The external jugular vein, running up the side of
the throat towards the angle of the lower jaw
and receiving the veins of the mandibular and
lingual regions.

d. Follow this vein down towards the heart : a
little way below the aortic arch it is joined by
another large vein

e. The subclavian : follow this outwards ; it will
be found to be formed mainly by the union

236 ELEMENTARY BIOLOGY. [CHAP,

of two large branches : one (axillary or brachial
vein) coming from the antebrachium and manus ;
the other (musGulo-futane&us) from the back and
head.

f. The innominate vein is formed by the union of
the internal jugular vein, which brings back the
blood from the brain and spinal cord, with the
subscapular vein returning the blood from the
brachium and shoulder.

g. The superior vena cava (right and Jeff): this
is formed by the union of the subclavian, ex-
ternal jugular and innominate veins on each
side : follow it to the heart, where it ends by
entering the sinus venosus.

4- The inferior vena cava and renal portal veins.

a. Divide the alimentary canal above the stomach
and also close to the cloaca, and remove the
intermediate portion : dissect out the veins con-
nected with the kidneys.

b. The renal portal vein : running from the bifur-
cation of the pelvic vein to enter the lower-
outer border of the kidney.

c. The inferior vena cava: the large vein lying
between the kidneys and chiefly formed of
branches from them, but also getting branches
from the generative organs and the liver.

d. Follow it up to its anterior ending in the sinus
venosus.

5. The aortic arches and their branches.

a. Dissect out the branches of the aortic arches:
three on each side.

xin.] THE FROG, -237

a. The anterior division (carotid trunk] : it, after
giving off a branch (lingual artery] which runs
up the throat, ends in a small red body, the
carotid gland, from which other arteries pro-
ceed.

/?. The systemic aortic arch: this is the middle
and largest division : it runs round the throat
towards the vertebral column, giving off on
its way the subclavian artery which runs to
the fore-limb.

y. The pulmo-cittancous artery, or posterior di-
vision of the aortic arch : it runs to the root
of the lung, giving off on its way a cutaneous
branch which runs out to the integument
about the shoulder.

b. Imbed in paraffin an aortic arch which has been
hardened in spirit and cut transverse sections
of it : examine with i inch obj. Note the two
partitions subdividing it into three channels.

6. The dorsal aorta and its branches.

a. Remove the kidneys with vena cava inferior and
the generative organs : the dorsal aorta is then
laid bare lying on the bodies of the vertebrae.

b. Follow the systemic aortce (5. a. /?) round the
neck; they will be found to unite beneath the
vertebral column to form the dorsal aorta.

c. Follow the aorta backwards: it gives off many
branches on its course; note the large one (cos- J
liaco-mesenteric artery] arising from it just below
its point of formation.

ELEMENTARY BIOLOGY. [CHAP.

d. Small branches to the renal and generative
organs (only the cut ends of these branches can
now be found) and to the muscles of the back.

e. Near the pelvis it ends by dividing into two
trunks (the iliac arteries) which run behind the
pelvic bones, giving off hypogastric branches to
the bladder and the walls of the abdomen.

f. Turn the animal over on to its belly and trace
the iliac arteries backwards: they are mainly
continued down the thigh as the femoral arte-
ries.

7- The pulmonary veins.

a. Trace them from the left auricle to the lungs.
Examine the left auricle carefully and find the
opening of the common pulmonary vein into it.

G. THE NERVOUS SYSTEM OF THE FROG.

i. The method of exposing the brain and spinal cord.-
Take a frog which has been a day or two in spirit;
divide the skin along the middle of the dorsal sur-
face from the snout to the anus and reflect it to
each side, noting the small nerves running into it
on each side of the middle line; remove the muscles
lying on the arches of the vertebra; open the neural
canal by dividing the membrane between the atlas
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
the upper part of the arches of the vertebrae in a
similar manner. A delicate pigmented membrane
(the pia-mater) is now laid bare, covering the brain ;

xiii.] THE FROG. 739

over the spinal cord it is usually concealed by a
quantity of soft material ; gently remove this with a
pair of forceps or wash it away with a syringe.

2. The brain.

On the dorsal aspect of the brain, which is now ex
posed, the following parts will be seen;

a. In front, two elongated masses forming about
the anterior half of the brain: a slight trans-
verse depression divides each into an anterior
smaller and a posterior larger portion. The
inner faces of the anterior portions are closely
united together; those of the posterior portions
are separated by a cleft. The posterior por-
tions are the cerebral hemispheres {prosencepha-
lo?i); the anterior, the bases of the olfactory
lobes (rhinenceplialoii).

a. The olfactory lobes become narrowed into two
rounded trunks (commonly termed the olfactory
nerves), which leave the skull, and applying
themselves to the outer face of the lining mem-
brane of the nasal chamber, give off a number
of branches which are distributed on that mem-
brane.

b. The thalamencephalon : lying between the pos-
terior ends of the cerebral hemispheres : on it
are to be noticed

a. The pineal gland ': a very small mass in front;
not composed of nervous tissue.

J3. The thalami optici: the nervous masses seen
below the pineal gland : between them lies a
narrow cavity, the third ventricle.

ELEMENTARY BIOLOGY. [CHAP.

c. The of tic lobes (mesencephalon) : a pair of
rounded eminences lying behind the thalamen-
cephalon.

d. The cerebellum (metencephalon): a narrow trans-
verse band lying behind the optic lobes.

c. The medulla oblongata (myeloncephaloji) : the por-
tion of the brain lying behind the cerebellum.

a. Lying on the medulla oblongata is a trian-
gular depression (4th ventricle] with its apex
turned backwards.

3- The spinal cord.

a. Its form: wide in front, but narrowing rapidly
about the 5th or 6th vertebra, and thence con-
tinued along the neural canal as a slender
tapering* filament.

b. The groove {posterior fissure) running along its
middle line.

c. The spinal nerves arising from it.
a. Ten on each side.

/?. Each arising by two roots (anterior and poste-
rior}-, these are most easily seen in the yth,
8th and 9th nerves, where they are much
longer than in the others. Sometimes the
anterior root is double.

y. The direction of the roots: directly outwards
in anterior nerves; obliquely backwards in
the 4th, 5th and 6th; almost directly back-
wards for a considerable distance in the neu-
ral canal in the 7th, 8th, 9th and loth.

xin.] THE FROG. 241

8. The point of union of the roots to form a
nerve trunk, in the intervertebral foramina.

Draw the exposed parts of the brain and spinal
cord.

4. Divide the olfactory lobes, and raise the front end
of the brain; turning it back gradually, divide with
a sharp scalpel any nerves that are seen running
from it to the cranial walls: most of the nerves
being small, they will probably be torn across unob-
served, but the large optic nerves will at any rate be
seen : next divide the nerve-roots of the spinal cord ;
remove it and the brain together and place them
with the ventral side upwards.

a. On the under surface (base) of the brain will be
seen

a. The optic commissure or chiasma opposite the
posterior end of the cerebral hemispheres;
with the optic nerves diverging from its ante-
rior end and the optic tracts entering it poste-
riorly.

(3. Lying behind the optic commissure, between
the optic tracts, is a small eminence the
pituitary body.

y. On each side of the two last-mentioned struc-
tures and arched over in front by the optic
tracts, are the crura cerebri.

b. Divide the cerebral hemispheres horizontally with
a sharp scalpel : in each will be found a cavity
the lateral ventricle. Each lateral ventricle com-
municates with the third ventricle. The optic
lobes, divided in the same way, will be seen to

M. 1 6

? ELEMENTARY BIOLOGY. [CHAP.

roof over a cavity which communicates with the
third ventricle in front, and with the fourth
ventricle behind.

c. The spinal cord.

a. The anterior fissure running along its ventral
surface.

/?. Its form: subcylindrical ; wider from side to
side (especially opposite the second pair of
nerves) than dorso-ventrally.

y. Imbed it in paraffin and cut a transverse sec-
tion : mount in glycerine, and examine with i
inch obj.; note its peripheral portion (white
matter) different in appearance from the cen-
tral parts (grey matter} : the canal (canalis
centralis] running up its centre.

5. Turn the frog over on to its back, lay open its abdo-
minal cavity and remove all the alimentary canal
from the gullet to the rectum, along with the liver,
kidneys and generative organs.

6. The sciatic plexus.

a. This is now seen as a number of large nerve-
cords on each side of the dorsal aorta; note
the communications between the different cords
of the same side.

b. Follow down the plexus on one side : it ends
below in a large trunk which is continuous with
the sciatic nerve.

c. Trace the nerve-trunks forming the plexus up to
the spinal column. They are continuous with
the yth, 8th, and pth spinal nerves.

XIIL] THE FROG. 243

7. In front of the sciatic plexus lying on the muscles
bounding posteriorly the abdominal cavity are three
nerves running obliquely downwards and outwards on
each side: they are continuous with the 4th, 5th and
6th spinal roots.

8. Some nerves of the neck.

a. Pass a piece of tubing down the gullet so as to
distend it : and then carefully remove the mylo-
hyoid muscle (B. 6. a).

b. Find the posterior cornu of the hyoid bone on
one side : from it a slip of muscle (fetrohyoid)
will be seen passing up towards the occipital
region of the skull. Lying along the posterior
border of this muscle is the pneumogastric nerve;
follow its branch to the heart.

c. Lying on the petrohyoid and in front of the
pneumogastric, from which it arises, is the laryn-
geal nerve.

d. Some way in front of the laryngeal nerve is seen
the glossopkaryngeal nerve, turning up towards
the front of the jaw.

e. Superficial to the glossopharyngeal, but with a
generally similar direction, is the hypoglossal
nerve (B. 6. a).

9. The brachial nerve.

Lay it bare in the arm-pit and follow it back to the
spinal cord : it is formed by the union of the 2nd and
3rd spinal nerves.

10. The sympathetic system.

a. Gently raise the aorta: along each side of it will
be found the main sympathetic trunk. A slender

16 2

244 ELEMENTARY BIOLOGY. [CHAP.

cord, with enlargements (ganglia) on it at in-
tervals.

b. Note the branches passing between its ganglia
and the nerves of the sciatic plexus.

c. Carefully dissect out the gangliated cord for its
whole length : ten ganglia, each provided with
communicating branches to other (spinal] nerves,
will be found on it.

H. THE ORGANS OF SPECIAL SENSE.

The complete examination of these, especially as re-
gards their histology, is difficult, and necessitates the
employment of niceties in manipulation which it would
be beyond the scope of this work to describe, so that in
the following account attention is mainly given to those
points which can be made out without the microscope.
A brief account of the microscopic structure of the re-
tina will however be found below (J. h).

a. The Eye.

i. Take an uninjured frog and examine its eye. It will
normally 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,
an elevation, caused by the eye-ball, will be seen on
its roof, and this is more prominent when the eye-ball
is retracted.

a. Gently touch the eye and observe how it is closed,
by the pulling over it of the lower transparent -
eye-lid. The upper eye-lid is very small and
hardly moveable.

XIIL] THE FROG. 245

b. When the eye is open, observe the parts ex-
posed.

a. The transparent cornea covering all its exposed
surface.

/?. Through the cornea is seen the iris, a mem-
brane coloured by brown and golden pigment,
the latter forming a very brilliant ring around
the inner margin of the iris. The lower mar-
gin of this ring is interrupted at one point,
the yellow pigment being there absent, and
from the break a faint dark line can be traced
downwards through the rest of the lower part
of the iris.

y. The elliptical opening or pupil in the middle
of the iris with its long axis directed antero-
posteriorly.

2. Kill the frog (by chloroform or by pithing), and care-
fully dissect away the parts from around the eye-ball,
cutting away, with the rest, the part of the upper jaw-
bone which forms the lower boundary of the socket
of the eye-ball, or the orbital cavity.

a. As the surrounding tissues are cleared away
from the eye-ball, notice the small muscles
which are inserted into it.

/?. At the back of the eye-ball and passing into it
will be found the optic nerve.

3. Divide the optic nerve and, having thus detached the
eye, pin it to a piece of loaded cork, with the corneal
surface upwards.

a. Notice the more opaque coat (sclerotic], with \
which the margin of the cornea is continuous.

ELEMENTARY BIOLOGY. [CHAP.

and which forms the outer envelope of the eye-
ball on its sides and back. In some parts the
sclerotic is semi-transparent and allows the pig-
mented choroid coat (3. g) to be more or less
distinctly seen through it.

b. Prick the cornea with the point of a sharp scalpel,
taking care not to injure the iris ; note the clear
aqueous humour which spirts out, the cornea at
the same time collapsing.

c. Seize the cut edge of the cornea with a fine pair
of forceps and, with sharp scissors, carefully cut
through it all round at the line of junction with
the sclerotic. The convex anterior surface of the
transparent crystalline lens will now be seen pro-
jecting through the pupil.

d. Place the cork in a vessel of convenient size
and add enough water to cover the eye. Then,
with sharp scissors, cut away the iris, and so
expose all the anterior surface of the lens.
Passing the point of a scalpel under one edge of
the lens, gently tilt it out and examine it.

a. The crystalline lens of the frog is nearly sphe-
rical but somewhat thicker from side to side
than antero-posteriorly. Its anterior surface
(that which projects into the pupil) is also less
convex than its posterior surface.

e. The cavity of the posterior chamber of the eye
is now exposed. It is filled with a gelatinous
transparent mass, the vitreous humour, which
can be seen if the water, in which the eye is
being dissected, be poured away.

xiii.] THE FROG. a 4 7

f. Lining the posterior chamber of the eye is the
retina, which, from the action of the water, will
probably now be somewhat cloudy : in the un-
altered state it is perfectly transparent, allow-
ing the choroid (3. g) to be seen through it.
With the point of a microscope needle gently
raise the retina from the black membrane (cho-
roid) beneath it. It will be found that this can
be readily done except at one point (answering to
the blind spot of our own eyes), which, by turning
the eye-ball over will be seen to be opposite the
point of entrance of the optic nerve (2.

g. The ckoroid coat of the eye-ball is now exposed.
It is a dark pigmented membrane, of loose floccu-
lent texture, which can be readily detached, by
needles, from the sclerotic which lies outside it.

b. The Ear.

i. The frog has no external ear, its tympanic membrane,
as already mentioned (A. 2. a), being exposed on each
side of the head.

a. Note the arrangement of the tympanic mem-
brane : it is smoothly stretched over a hard ring.

b. Dissect away the outer or integumentary layer
of the tympanic membrane. Beneath it will be
found a transparent membrane, formed by the
fibrous and mucous layers, with an opaque white
patch abput its middle.

c. Cut through these layers of the tympanic mem-
brane along their margins : the tympanic cavity
will then be laid open.

ELEMENTARY BIOLOGY. [CHAP.

a. The tympanum of the frog is a funnel-shaped
cavity with its wider end turned outwards.
Its sides are bounded by a smooth slightly pig-
mented mucous membrane, continuous with
that of the mouth through the Eustachian
recess.

/?. In its roof lies a rod, ossified in the middle,
cartilaginous at each end, which is the columella
auris. The columella is attached, by its inner
end, to the upper and anterior part of the
inner wall of the tympanum and, by its outer
end, to the middle layer of the tympanic
membrane, in the region of the opaque patch
mentioned above (i. b).

y. Close to the inner attachment of the columella
there is a comparatively large oval opening in
the wall of the tympanic cavity ; this is the
outer end of the Eustachian recess, the inner
end of which has been already (B. n. a) seen
on the posterior part of the roof of the mouth.
Pass a probe through the opening now ex-
posed, and open the frog's mouth to see its
passage into that cavity.

2. The internal ear.

a. Carefully dissect away the columella auris from
its inner attachment. An aperture into which it
was inserted will thus be exposed : this is the
fenestra ovalis.

b. Take a pair of scissors and cut through the
bones of the side of the skull in a line joining
the fenestra ovalis and the " guard " of the para-

xiir.] THE FROG. 249

sphenoid bone (D. c. 3.^); the chamber in the
pro-otic bone (D. c. \.d) which is thus exposed
contains part of the internal ear.

c. The dissection of the internal ear of the frog
is difficult, on account of its minuteness. But
by carefully removing the bony and cartilagi-
nous walls of the periotic capsule, piecemeal,
the semicircular canals will be exposed and the
whole membranous labyrinth may be extracted.
It should be placed in a watch-glass containing
salt solution or spirit, and its form studied under
the simple microscope.

c. The olfactory organs.

i. These consist of two chambers which open externally,
near the end of the snout, by the anterior nares, and
posteriorly into the mouth, just behind the vomerine
teeth by the posterior nares. Make out these open-

ings.

a. Take a frog which has been preserved in spirit
and pass 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 ex-
posed which has a somewhat triangular form, the
apex of the triangle being at the external nostril
and the posterior nostril being at another angle
and farther from the middle line.

b. The walls of the cavity are slightly folded, and
there is a well-marked hemispherical eminence
on its floor.

c. Open the other nasal cavity in a similar way:
notice the boundary wall (septum narium) which

250 ELEMENTARY BIOLOGY. [CHAI-.

lies between the two and completely separates
them.

d. Open the nasal cavity of a frog which has been pre-
served in Miiller's fluid ; gently scrape away a little
of the epithelium lining the chamber, mount in
water : examine with your highest power.

a. Among numerous mutilated cells, a certain num-
ber of more or less perfect ones will be found :
these are of two kinds, viz. large columnar epi-
thelial cells (J. i. b\ each with an oval nucleus,
an unbranched peripheral process and a branched
deeper one ; and smaller cells, with less proto-
plasm around the nucleus and finer peripheral
and central processes.

d. The gustatory organ.

i. The shape and arrangement of the frog's tongue have
already been described (B. n. a).

a. Snip off a bit of mucous membrane from the
upper surface of the tongue of a recently killed
frog, mount in normal saline solution and cover
in plenty of the fluid with a large coverslip : ex-
amine with one inch obj.

a. On the surface of the fragment and especially
around its edges numerous minute elevations
of the surface will be seen : these are the pa-
pilla : some (filiform papilla;} are pointed at
the free end and others (fungiform papillce)
flattened. Note the loops which the blood
capillaries make in some of the papillae.

/3. Examine one of the thinner bits of the speci-
men with a higher power : the papillae will be
seen to be covered by epithelium, which is for

xiii.] THE FROG. 251

the most part ciliated (J. i. c] ; some of the
papillae however will be seen to have no cilia
except a narrow belt around the somewhat
truncated apex ; it is on these latter papillae
that the gustatory disks are placed, and in
fortunate specimens nerve-fibres can be seen
entering them.

J. SOME OF THE MORE IMPORTANT POINTS IN THE HISTO-
LOGY OF THE FROG.

a. Epithelium.

i. This consists of cells which line free surfaces within
the body : the epidermis covering the skin is a simi-
lar structure, and is continuous with epithelium at
the apertures of the body. There are several main
types of epithelium, viz.

a. Scaly epithelium. Open the abdomen of a re-
cently killed frog, carefully remove the viscera
and lay bare the lymph sinus at the back of the
body-cavity. Cut away its thin wall as care-
fully as possible, taking great care not to drag or
pull it. Place the fragment in 0^5^ solution of
silver nitrate for about three minutes : then
remove, wash well in distilled water, and finally
leave the specimen in distilled water and ex-
posed to the sunlight. So soon as the bit of
pleuroperitoneum has become of a well-marked
brown colour, mount it in glycerine and exa-
mine with a high power.

a. It will be seen to be covered on both sides
with flat closely fitting cells, the boundary
lines of which are stained black by the sil-

ELEMENTARY BIOLOGY. [CHAP.

ver ; according to the amount of staining a
nucleus may or may not be rendered conspi-
cuous in each cell.

Here and there in good specimens, rings
of smaller and more deeply stained cells will
be seen surrounding minute apertures (sto-
mata\

b. Columnar epithelium. Scrape gently the inner
surface of the mucous membrane of the intes-
tine of a frog which has been preserved in
Miiller's fluid ; mount the detached fragments
in water and examine with a high power.

a. Numerous elongated cells, flat at one end
and somewhat pointed at the other, will be
seen. Each has a well-marked oval nucleus.

^. These cells may be seen in situ if a thin sec-
tion of the hardened mucous membrane of
the intestine or stomach be examined. Thev

,/

are closely applied and arranged in a single
layer.

, Ciliated epithelium. Snip off a bit of the mucous
membrane from the tongue of a recently killed
frog with a sharp pair of scissors : mount the
bit in 07 5 sol. of sodic chloride, avoiding
pressure, and examine with a high microscopic
power.

a. Note the shimmering appearance along its
free edge, produced by the rapidly moving
cilia; as the cilia begin to die and their
movement slackens, individual ones can be
seen.

xiii.] THE FROG. 153

P. Scrape gently, with a scalpel, one of the pro-
minences in the roof of the frog's mouth be-
neath the eye-balls: mount the scrapings in
075 salt solution and examine with -| objec-
tive for individual ciliated cells ; note their
roundish form, granular protoplasm and nu-
cleus, and the group of cilia borne on one
end ; stain with iodine.

b. Cartilage.

i. Dissect out carefully the omosternal or xiphisternal
cartilage of a recently killed frog; mount in 075 J
sodic chloride solution and examine with ^ or -| obj.

a. Large roundish granular cartilage-cells will
be seen imbedded in a structureless or very
finely granular matrix, which is more refrac-
tive next the cells than elsewhere, and causes
the appearance of a sort of halo round each.

/?. In each cell lies a distinct granular round
nucleus or sometimes two nuclei, containing
large highly refractive molecules.

y. If the preparation be carefully made, each
cell will at first 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 and so leave a transparent
ring between their surface and the inside of
the cavity in which each lies.

c. Bone.

a. Examine a prepared transverse section of hard'
bone (say a bit of the shaft of the humerus or
femur) with i inch obj. A bit of mammalian

2 54 ELEMENTARY BIOLOGY. [CHAP.

bone is the best for seeing the essential struc-
ture.

a. The Haver sian canals : round or oval spaces,
usually filled with dirt in grinding down the
bone, and therefore black and opaque, but
sometimes clear and empty.

/?. The lamella: a series of concentric layers
round each Haversian canal.

*

y. The lacuna: oval black spots between the
lamellae.

8. The canaliculi : minute black lines seen radi-
ating from the lacunae.

e. Besides the lamellae above mentioned others
will be seen which belong to no Haversian
system, but either fit in the angles between
the systems, or run around the outer surface
of the bone.

b. Examine with \ obj. Observe the lacunas and
canaliculi more accurately.

c. Examine in water or glycerine a thin transverse
section of a long bone which has been softened
by dilute acid.

a. The Haversian canals empty or containing a
granular mass.

J3. The lamella: very indistinct.

y. The lacuna seen as transparent oval spaces.

S. The canaliculi transparent and almost invisible.

d. Examine sections of softened bone which have
been stained with carmine: in each lacuna will
be found a stained mass of protoplasm.

xni.] THE FROG. 255

e. Examine longitudinal sections of the femur or
humerus : the Haversian canals are seen to be
channels running for the most part in the long
axis of the bone, but communicating with one
another frequently by cross branches. The
lacuna, &c. appear much as in the transverse
section.

d. Connective tissue,
i. Of this there are two main varieties, viz.

a. White fibrous tissue. This occurs nearly pure 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 run in bundles parallel to one another;
they have an ill-defined outline and do not
branch.

/?. Treat with dilute acetic acid. Most of the
fibres disappear, but a few well-defined curled
fibres (yellow elastic fibres , see b] remain. Be-
sides these some elongated granular proto-
plasmic masses are brought into view (con-
nective-tissue corpuscles] .

b. Yellow elastic tissue. This does not occur in large
collections, in the pure form, in the frog; although
mixed with white fibrous and other tissues, it is
very widely distributed.

a. Tease out in acetic acid some of the bands of
tissue beneath the frog's skin; examine with
a high power. Numerous fine well-defined

256 ELEMENTARY BIOLOGY. [CHAP.

branched fibres, running in bold curves, will be
seen: these are yellow elastic fibres, as the
acetic acid (a. ft) destroys the white fibrous
tissue.

e. Striped muscle.

a. Tease out gently a bit of muscle which has been
kept in alcohol, and examine with i inch obj.

a. Composed of elongated fibres, which exhibit
a tendency to split up into finer filaments
(Jibrillcz).

b. Examine with high power.

a. The alternate lighter and darker bands placed
transversely to the long axis of the fibre
(transverse striatioii).

P. The fine structureless membrane (sarcolemma)
enveloping the fibre: seen here and there as
a delicate film where the fibre is twisted or
bruised.

y. The tendency to split up into fibrillae.

c. Tease out a bit of fresh muscle in 075^ so die
chloride solution.

a. The transverse striation of the fibres: less
distinct than in the muscle from alcohol.

ft. The absence of a tendency to split up into
fibrillse.

y. The sarcolemma, which may be seen at

points where the continuity of its contents

has been interrupted by pressure, twisting,
&c.

THE FROG. -257

S. Treat with acetic acid : the striation rendered
very indistinct; oval nuclei made apparent
here and there in the fibre.

f. Nerve-fibres.

i. Tease out a bit of fresh nerve in 07 5 sodic chlo-
ride. Examine with a high power.

a. Composed of well-defined fibres (white nerve
fibres] mixed with white fibrous tissue (d. i. a}.

b. The appearance of the nerve-fibres: each has
a double contour, marked out by a curdled-
looking highly refractive border on each side.

c. The structure of the nerve-fibres.

a. The delicate structureless investing mem-
brane (primitive sheath); look for it on
bruised nerve-fibres or at the ends of torn
fibres.

ft. The highly refractive border (medullary
sheath) within the primitive sheath.

y. The central homogeneous axis (axis cylinder);
look for it projecting beyond the medullary
sheath of torn fibres.

d. Treat a fresh bit of teased-out nerve with chlo-
roform : the medullary sheath will be dissolved
out, and the axis cylinder plainly seen.

g. Nerve-cells.

i. Take a sympathetic ganglion from a recently killed
frog: dissect out in normal saline solution and ex-
amine with -- obj.

a. Among the pigment-cells, which are clustered
around the ganglion, will be seen numerous

M. 17

258 ELEMENTARY BIOLOGY. [CHAP.

large pale granular cells, each possessing a
conspicuous clear round nucleus with a dis-
tinct nucleolus.

/?. Tease out in glycerine a Gasserian ganglion
from a frog's head which has been preserved
in Miiller's fluid or chromic acid. Cells like
those described above will be found.

y. Examine sections of spinal cord which have
been stained with carmine or haematoxylin,
and note the large branched nucleated cells
in the grey matter especially towards the ven-
tral side of the cord.

h. The retina.

i. Sufficiently satisfactory specimens of this organ can
be obtained as follows. Take perfectly fresh eyes
from a frog, prick the corneas in two or three places,
and lay the eyes aside for three or four days in 0*25^
-chromic acid solution: then transfer them to alcohol
and keep them in it until wanted.

a. Carefully cut open an eye preserved in the
above method and expose the retina: transfer
the latter to a glass slide, and with a razor chop
down on it so as to cut off a number of slices :
add glycerine, put on a cover, and examine
with a low power. Some of the bits will be
found thin enough for further examination.

b. With the low power little can be seen but that
the retina is composed of a number of different
layers, some of which appear less opaque than
the others.

xiii.] THE FROG. 259

c. Put on a high power and examine, make out

the following points

a. The internal limiting membrane, a thin struc-
tureless layer.

/?. The nerve-fibre layer: thin and granular.

[Both a and /3 are often difficult to make out in
retinas prepared as above.]

y. The nerve-cell layer: composed mainly of cells
like those described above (g. i. a), 'but rather
smaller than those from the sympathetic
ganglia. From some, branches can be traced
into the next layer.

nt,t.^Z^* J-rCLt^

S. The molecular layer: this is thicker than any
of the preceding, and has a finely punctated
appearance : running through it the fibres of
Miiller (h. i. t ) are very plainly seen.

e. The inner granular layer: this is the layer
which usually looks clearest in sections, its
elements being less closely packed than those
of the other layers. It is made up of a num-
ber of nuclei (which in chromic-acid speci-
mens look granular), around which is col-
lected a very small amount of protoplasm,
and of fine fibres, some of which can be
traced joining the nuclei or granules.

. The inter-granular (fenestrated] layer. A nar-
row cloudy layer in which no definite struc-
tural elements are. visible.

f]. The outer granular layer. Much thinner than
the inner granular layer and more closely
packed. It is composed of distinct fibres

172

ELEMENTARY BIOLOGY. [CHAP.

(rod- and cone-fibres], each of which swells out
and has a nucleus (the granule) developed in
the enlargement.

6. The external limiting membrane. A thin
homogeneous layer like a.

t. The fibres of Mutter. These are highly re-
fracting fibres which can be traced with ease
from the internal limiting membrane to the
fenestrated layer. They probably run beyond
the latter and end on the external limiting
membrane, but are difficult to trace through
the outer granular layer.

K. The rod- and cone-layer. The main thing
which will be noted here is the huge rods for
the most part distorted by the treatment
to which the retina has been exposed. In
favourable bits it can be seen that each rod
is divided transversely into an inner and an
outer segment. The cones are few and small,
and generally completely concealed by the
rods.

d. Take a fresh frog's eye : prick its cornea and
collect 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 shewing the
boundary line between their two segments very
plainly. At first both segments are homoge-
neous, but very soon they begin to alter ; the

XIIL] THE FROG. 161

outer layer frequently then getting a trans-
versely striated appearance and shewing a
tendency to split up into corresponding pieces :
gradually these rods entirely disintegrate, first
curling up, swelling out, &c.

i. The skin.

1. 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 ; seen as black irregularly
shaped patches; some compact, others more or
less branched.

I. The mouths of the cutaneous glands; seen as
clear round spots, although their openings are
really triradiate : their number.

2. Take a piece of skin that has lain for a day or two in
solution of ammonia bichromate and then in alcohol:
imbed it, and cut sections perpendicular to its sur-
faces : mount in glycerine. Examine with a low
power; note

a. The two layers of the skin, dermis and epidermis,
the former being much the thicker : note in the
dermis its deeper connective-tissue layer, and
its more superficial granular layer immediately
beneath the epidermis.

I). Examine with a higher power.

a. The epidermis is seen to be made up of nume-
rous closely packed cells, arranged in several
layers.

/?. The deepest epidermic cells are granular, nu-

262 ELEMENTARY BIOLOGY. [CHAP.

cleated, and somewhat oval, with their long
axes at right angles to the surface.

y. Then come several rows of cells, also granular
and nucleated, but becoming smaller and
rounder as they become more superficial.

5. The most superficial three or four layers of
cells are flattened parallel to the surface,
are not granular, and possess no apparent
nucleus.

c. Here and there a pigment-cell is seen among
the epidermic cells, and some of the latter
contain a few pigment-granules.

. The dermiS) consisting fundamentally of white
fibrous and elastic tissues : its glandular and
non-glandular layers.

-q. Immediately beneath the epidermis is a thin
stratum of connective tissue in which lie
many large pigment-cells, sometimes forming
an almost continuous layer.

6. Then come a large number of round cavities,
the cutaneous glands, lined by large, pale,
slightly granular, nucleated cells, which are
columnar when seen sidewise, but polygonal
when seen from the base or apex. Some-
times the duct of the gland can be traced
running from it through the epidermis. Sepa-
rating the glands and supporting the epi-
thelium are bundles of connective tissue,
consisting mainly of fibres running perpen-
dicularly to the surface.

. The deepest layer of the dermis is made up

XIIL] THE FROG. 263

of connective-tissue bundles, running for the
most part parallel to the surface.

j. The kidney.

i. Take a frog's kidney which has been for a week
in solution of bichromate of potash, and then for a
day or two in spirit. Imbed it, cut sections parallel
to its flatter surfaces, and mount in glycerine.

a. Examine with a low power.

a. Note the numerous tubules of which the organ
is mainly composed and which twist about in
all directions, and are consequently cut, some
transversely, some obliquely, and others more
or less longitudinally. The absence of any
marked division into cortex and medulla.

/3. The clear round holes, scattered about; these
are sections of glomeruli from which the con-
tained vessels have fallen out. Some may be
seen in which a granular mass still lies.

b. Examine with a higher power

a. The epithelium lining the tubules, composed
in some of granular and ill-defined cells, in
other (usually larger) tubules of clearer and
better-defined cells ; both varieties are nu-
cleated.

c. Examine specimens of injected kidney with a
low power. Note the vascular tufts of the glo-
meruli.

k. The testis.

i. Imbed a testis which has been hardened in alcohol :
cut sections and mount in'glycerine.

264 ELEMENTARY BIOLOGY. [CHAP.

a. Examine with a low power.

a. The organ is chiefly made up of tortuous
tubules, which are seen cut in various direc-
tions.

b. Examine with a high power.

a. Note the epithelium lining the tubules : it
varies with the season of the year (whether
before or after the breeding-time), and is usu-
ally extremely granular and ill-defined. The
cells are arranged in two or three rows, and
at the time of breeding the most superficial
layer of cells is transformed into spermatozoa,
each cell giving rise to several. These lie
side by side at right angles to the lumen of
the tubule, which accordingly appears to be
lined by them.

c. The spermatozoa (B. 10. a. y).

1. The ovary.

1. The structure of this organ is easiest made out
shortly after the breeding-time. Remove one of the
ovaries, place it in water, and make an incision into
it : it will be seen to contain a cavity, and projecting
upon the walls of this cavity and also upon the outer
surface of the ovary are numerous round eminences
of various sizes : these are ova in different stages of
development, and the large ones will be seen to have
become more or less pigmented.

2. Tease out a bit of ovary in normal saline solution :
cover, and examine with a low power.

a. Note the ova, many much smaller than those
which were seen (i) with the naked eye : they

xiii.] THE FROG. 265

appear as granular spherical masses with a clearer
central patch.

b. Examine with a high power a portion of your
specimen containing some of the younger and
more transparent ova. Note

a. The thin structureless membrane, vitelline
membrane, enveloping each.

/?. The granular matter (yelk, vitellus) forming
most of the ovum. It sometimes appears to
be composed of an outer granular and an
inner clearer layer.

y. The clearer central mass (germinal vesicle) im-
bedded in the vitellus. The large number of
highly refracting masses (germinal spots) within
the germinal vesicle.

K. 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
unconscious, which will probably be in a few se-
conds. Now feel with a finger-nail for the depression
beneath the skin at the back of the animal's head,
which indicates 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 ver-
tebral column. By this process (known as pithing)
the frog is rendered totally incapable of further con-
sciousness, though most of its tissues will retain their
vitality for some time.

ELEMENTARY BIOLOGY. [CHAP.

a. Remove the skin from one leg, so as to lay bare
the muscles : send an interrupted electric cur-
rent through any one of them (or tap the muscle
sharply with the back of a scalpel) : it will im-
mediately contract, or alter its form in a definite
way ; it becomes shorter and thicker, and in so
doing moves the bones to which it is attached.

b. Very carefully lay bare the sciatic nerve, taking
care not to crush or drag it : divide it as high
up as possible and, seizing it with a pair of for-
ceps close to its cut end, lay it over the elec-
trodes of an induction-coil. Probably when the
nerve is cut the muscles of the limb will con-
tract : whether or not, however, they will con-
tract violently while the interrupted current is
going through the nerve.

[If an induction-coil is not at hand a bit ot
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 shew:

c. 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
excite some change in it, which in this par-
ticular case manifests itself by a contraction of
the muscles connected with the nerve.

XIIL] THE FROG. 267

e. The nerve possesses conductivity : although it is
stimulated at some distance from the muscles,
yet the change excited by the stimulus travels
along it to them.

APPENDIX.

The various re-agents, mentioned in the " Laboratory work"
in the preceding pages, are prepared as follows :

1. Acetic acid, Dilute.

Mix i cub. centimetre of glacial acetic acid with 99 cub.
cent, of distilled water.

2. Ammonic bichromate, Solution of.

Dissolve 10 grammes of crystallized ammonic bichro-
mate in a litre of distilled water.

3. 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.

4. 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
which weaker ones can readily be prepared when re-
quired.

APPENDIX. 269

5. Haematoxylin, Solution of.

a. Prepare a saturated solution of crystallized calcic
chloride in 70 per cent, alcohol; then add alum to
saturation.

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. Filter.

6. 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.

7- 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.

8. Mayer's Solution.
See note p. 8.

9. Miiller's Solution.

Bichromate of potash 25 grammes.

Sodic sulphate 10 grammes.

Distilled water I litre.

10. Osmic Acid, Solution of.

Best bought ready made in the form of i per cent, solu-
tion.

11. Paraffin.

Melt together one part of solid paraffin (paraffin candles
will do), one part of paraffin oil and one part of pig's
lard. A mixture in the above proportions gives, when it
has cooled, a mass of the most generally useful con-
sistency.

270 APPENDIX.

To imbed an object, scoop a hole in a bit of the paraffin,
place the object (the surface of which must be dry) in
this hole and fill up the latter with some melted paraffin.

12. Pasteur's Solution.

See note, p. 6.

1 3. Potash Solution.

Dissolve 5 grammes of potassic hydrate in 100 cubic
cent, of water.

14. Schultz'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.

1 5. Silver Nitrate, Solution of.

Dissolve 0*5 grammes of silver nitrate in 100 cubic
cent, of distilled water. Keep in an opaque stoppered
bottle.

1 6. Sodic Chloride, Solution of. (Normal saline solution.
Salt solution?)

Dissolve 7-5 grammes of sodic chloride in i litre of dis-
tilled water.

'

;

INDEX.

LJ

A.

ABDUCENTES, nervi, 189

Acetabulum, 224

Acrogenous growth, 47

Adductor muscles, 108, 116, 123

Alse, 84

Alcoholic fermentation, 5, 9, 10

Algce, 48

Alimentary canal, of Anodonta,
no, 12 1 ; of Crayfish, 131, 148;
of Frog, 167, 173, 205; of Lob-
ster, 131, 148; of Tadpole, 163

Alinasal process, 171

Alternation of generations, 37, 47,
61

Ambulatory limbs, 129, 151

Amoeba, 17 ; Laboratory work, 21

Amoeboid movements, 20, 105

Anacharis, protoplasmic move-
ments in, 54

Angulo-splenial, 220

Annulus, 66

Anodonta cygncza, 107; Laboratory
work, 113

Antennae, 130, 153

Antennules, 130, 153

Anterior commissure, 186

Anterior abdominal vein, 180,
200, 234

Anther, 70, 84

Antheridium, 43, 45, 51, 60, 68

Antherozooids, 46, 52, 61, 68

Aortic arches, 176, 203, 236

Appendages, of Bean, 70, 78; of
Chara, 42, 48; of Crayfish, 128,
142, 151; of Frog, 160, 197,
212; of Lobster, 128, 140, 151

Aqueous humor, 246

Arachnoid membrane, 168

Archegonia, 61, 68

Arterial system, of Anodonta, in;
of Crayfish, 133, 145, 149; of
Fr g> I 77> 2 37; of Lobster, 133,

Artery, cceliac, 178, cceliaco-me-
senteric, 178, 237; cutaneous,
178; femoral, 178, 238; hypo-
gastric, 178, 238; iliac, 178, 238;
lingual, 177, 237; mesenteric,
178; cesophageal, 178; pulmo-
c.utaneous, 178, 203, 237; pul-
monary, 176, 178; subclavian,
178; vertebral, 178

Articular process, 213

Arytenoid cartilages, 181

Asci, 36

Ascospores, 8, 36, 41

Astacus fluviatilis, 127; Labora-
tory work, 140

Astragalus, 225

Atlas vertebra, 213

Atrium, 175, 201

Auditorii, nervi, 190

Auditory organs, of Anodonta, 113,
121 ; of Crayfish, 138, 156; of
Frog, 194, 247 ; of Lobster, 138,

156

Axillary vein, 236
Axis cylinder, 257

B.

Bacillus, 28

Bacteria, 25 ; Laboratory work, 27

Balantidium, 93

Bark, 72

Basipodite, 151

272

INDEX.

Bast cells, 65, 73

Bean plant, 70; Laboratory work,

78
Bell- Animalcule, 89; Laboratory

work, 93
Blood, of Anodonta, 112; of

Frog, 174, 210; of Lobster, 155
Blood corpuscles, coloured, 211;

colourless, 20, 23, 112, 135, 174,

211

Body cavity, of Hydra, 101, 105
Bojanus, organs of, 117
Brachial, plexus, 192; vein, 179,

236 ; nerve, 243 "
Bracken Fern, 55 ; Laboratory

work, 62
Brain, 185, 239
Branchio-cardiac veins, 134
Branchiostegite, 130, 143
Browspot, 195

Bud, terminal, of Chara, 42, 50
Buds, 70
Byssus, 113, 126

C.

CALCANEUM, 225
Calcar, 169, 225
Calyx, 70, 83
Cambium, 72, 80, 81
Campanula media, 88
Canalis centralis, 192, 242
Carapace, 128, 139
Carchesiuni) 97
Carina, 84

Carotid, artery, 177, 178, 203,
^237; gland, 237
Capitulum, 45
Carpopodite, 151
Carpus, 223

Cartilage, 169, 171, 253
Cerebellum, 185, 240
Cerebral hemispheres, 185, 239
Cerebro- spinal, axis, 168; nervous

system, 185
Cephalic flexure, 129
Cephalic ganglia, 112, 119
Cephalothorax, 127, 140, 143
Cervical groove, 129

Cervical suture, 128, 140
Chara, 42 ; Laboratory work, 48
Chelse, 129, 152
Chiasma, optic, 241

Chlorophyll, n, 45, 49, 75, 100,
103

Chondro- cranium, 1 70

Choroid, coat, 247 ; plexus, 185

Cilia, of Anodonta, 1 19; of anthero-
zooids, 46, 52, 61, 68; of Bell-
animalcule, 91, 95 ; of the Frog,
252 ; of Hydra, 99, 105; of
Protococcus, 13, 15; of Spiril-
lum volutans, 25

Circulatory organs, of Anodonta,
in, 116; of Crayfish, 133, 145;
of Frog, 174, 201, 234; of Lob-
^ster, 133, 145

Clavicle, 222

Cloaca, of Anodonta, 109, 115; of
Frog, 167, 206

Clubmosses, 74, 75

Cochlea, 194

Cceliac artery, 178

Cceliaco-mesenteric artery, 178,
237

Colon, 173

Columella, 34

Columella auris, 194, 217

Colourless blood-corpuscles, 20,
23* us, 135, 174, 211

Cotyledon, 71, 86

Conidia, 32, 39

Conidiophores, 39

Conifers, 74

Conjugation, 36, 92, 97

Connective rod, 137, 154

Connective tissue, 169, 255

Contractile vesicle, 18, 21, 91, 94

Coracoid, 222

Cornea, 137, 245

Corolla, 70, 84

Corpus adiposum, 198, 204

Corpuscula, 75

Cortical layer, of Chara, 42 ; of
Bell-animalcule, 94

Cothiirnia, 97

Coxopodite, 151

Cranial nerves, 187

IXDEX.

273

Crura cerebri, 186, 241

Crural nerve, 193

Crystalline lens, 137, 154, 246

Cutaneous glands, 262 ; artery,

178

D.

DACTYLOPODITE, 151

Dentary bone, 220

Dermis, 261

Development, of Anodonta, 112 ;

of Bean, 71 ; of Chara, 46, 50 ;

of Crayfish, 139; of Fern, 60;

of Frog, 162; of Lobster, 139;

of Mucor, 34, 37; of Penicil-

lium, 32, 40
Diaphragm, 166
Dorsal aorta, 178, 237
Dorso-lumbar vein, 180
Dotted ducts, Si
Duodenum, 173

E.

EAR, see Auditory organ

Ecdysis, 139

Ectoderm, 100, 103

Ectosarc, 18, 2 r

Embryo, of Anodonta, 112, 126;

of Bean, 71, 86; of Chara, 47 ;

of Fern, 61 ; of Frog, 16.2 ; of

Lobster, 139
Embryo, cell, 61, 71, 86; sac, 71,

86, 88

Encephalon, 185, 239
Encystation, of Amceba, 19; of

Vorticella, 92, 97
Endoderm, 100, 103
Endogenous cell division, 4
Endoplast, 92
Endopodite, 131, 142, 153
Endosarc, 21
Endoskeleton, 169, 21 1
Endosperm, 71, 86
Endosporium, 36
Epicoracoicl, 222
Epidermis, of Bean, 72, 79, Si ;

of Fern, 56, 58, 63; of Frog,

261

M.

Epithelium, 251

EpistyliS) 97

Eustachian recesses, 166, 196, 248

Evening Primrose, 87

Exoccipital, 217

Exogens, 73

Exopodite, 131, 142, 153

Exoskeleton, of Anodonta, 113,
124; of Crayfish, 127, 140; of
Frog, 169; of Lobster, 137, 139

Exosporium, 36

Eye, of Crayfish, 137, 153; of
Frog, 194, 244; of Lobster,

J 37> '53
Eyestalks, 130, 153

F.

FACIALIS, nervus, 190

Femoral artery, 178, 238; vein,

'79

Fenestra ovalis, 195, 217, 248

Fermentation, alcoholic, i, 5, 9,
10; putrefactive, 26

Fertilization, process of, in Ano-
donta, 112; in Bean, 71 ; in Cha-
ra, 46; in Fern, 61 ; in Frog,
162; in Hydra, 100

Fibro-vascular bundles, 57, 63,
^ 64, 72, 80

Fibula, 225

Filament, 84

Filum terminale, 192

Fission, 92, 96, 99

Flower, of Bean, 70, 83

Fontanelle, 170

Foot, of Anodonta, 107, 115

Foramen of Munro, 1 86

Foramen magnum, 216

Fourth ventricle, 185, 240

Fresh water, Crayfish, 127; La-
boratory work, 140 ; Mussel,
107; Laboratory work, 113;
Polypes, 98; Laboratory work,
102

Frog, 159; Laboratory work, 196

Fronds, 55, 58, 67

Fungi, 31

Fuuiculus, 86

18

'74

INDEX.

G.

GASTRIC skeleton of Crayfish,

or-

ve-

i3 r > i49
Gastric vein, 180, 235

Gasserian ganglion, 188, 258
Gemmation, 4, u, 15, 92, 99
Generative organs, see Sexual
^gans

Genito-urinary canal, 206
Germinal, spot, 106, 184, 265;

sicle, 1 06, 184, 265
Gills, of Crayfish, 136, 144; of

Lobster, 136, 144; of Tadpole,

',163

Girdle bone, 218
Glenoid fossa, 221
GlocMdium, 112
Glossopharyngeus, nervus, 1 90,

243

Glottis, 167, 181, 197, 208
Green gland, 136, 150
Gustatory disks, 251 ; organ, 195,

250

H.

HARDERTAN gland, 194

Hay infusion, 28

Heat stiffening, 19, 22, 23

Heart, of Anodonta, in, 116; of
Crayfish, 133, 145; of Frog,
175, 201; of Lobster, 133, 145

Histology, of Anodonta, 118, 122,
124; of Bean, 72, 79, 82; of
Blood, 23, 210; of Bracken
Fern, 56, 63; of Chara, 43, 48;
of Crayfish, 144, 148, 150, 153,

155 ; of Frog, 204, 206, 250,

251; of Hydra, 100, 104; of

Lobster, 136, 148, 150, 153,

155; of Mucor, 33, 40; of Pe-

nicillium, 31, 38
Homanis vidgaris, 127; Labora-

tory work, 140
Humerus, 222
Humour, aqueous, 246; vitreous,

246
Hydra fusca and H. viridis^ 98 j

Laboratory work, 102

Hyoid bone, 166, 220
Hyphas, 31, 34, 3840
Hypogastric artery, 178, 238
Hypoglossal nerve, 203, 243

I.

TLEUM, 173

Iliac arteries, 178, 238; vein, 179

Ilium, 224

Inert layer, 210

Infundibulum, 186

Infusoria, 89

Innominate vein, 179, 236

Integument, of Frog, 195, 261

Inspiration, 182

Intercellular passages, 59, 83

Internal ear, 194, 248

Internodes, 42, 48, 55, 62, 70

Inter-ocular gland, 195

Inter- vertebral foramina, 215

Intestine, of Anodonta, no, 122;
of Crayfish, 132, 148; of Frog,
167, 173, 204, 205 ; of Lob-
ster, 132, 148; of Tadpole, 163

Iris, 245

Irritability, muscular, 266

Ischiopodite, 151

Ischium, 224

J-

JUGULAR vein, external, 178,235;
internal, 178, 236

K.

KIDNEYS, 183, 206, 263

L.

LABIAL palpi, 108, 115

Laboratory work, Amoeba, 21;
Anodonta, 113; Bacteria, 27;
Bean, 78 ; Bell-animalcule, 93 ;
Bracken Fern, 62 ; Chara, 48 ;
Crayfish, 140; Frog, 196; Hy-
dra, 102; Lobster, 140; Mucor,
40; Penicillium, 38; Protococ-
cus, 14; Yeast, 6

INDEX.

275

Labrum, 129
Labyrinth, 194, 249
Lamina terminalis, 186
Laryngeal nerve, 191, 243
Laryngo-tracheal cartilages, 181
Larynx, 181, 203, 208
Lateral ventricle, 186, 241
Leaf, of Bean, 70, 82 ; of Chara,

49; of Fern, 55, 58, 66
Lens, crystalline, 246
Liber, 73, 80, 81
Lieno-intestinal vein, 180, 235
Limbs, of Crayfish, 128, 142, 151;

of Frog, 159, 197; of Lobster,

128, 142, 151
Lingual artery, 177, 237
Liver, of Anodonta, no, 122; of

Crayfish, 132, 148; of Frog,

174, 201; of Lobster, 132, 148
Lobster, 127; Laboratory work,

140

Lumbosacral plexus, 192, 242
Lung, 182, 208
Lymph, 174
Lymph-hearts, 174, 180
Lymph sinus, subvertebral, 165,

174

M.

MANDIBLE, 129, 153, 219

Mantle, 107, 114

Manubrium, 45

Manus, 160, 223

Maxilla, of Crayfish, 129, 152; of

Frog, 219

Maxillipede, 129, 152
Maxillo-mandibular nerve, 188
Meckel's cartilage, 171, 220
Medulla, 72, 79; oblongata, 185,

240
Medullary cavity, 79; rays, 80;

sheath, 257
Membrana tympani, 194, 196,

247

Mento-Meckelian bone, 220
Meropodite, 151
Mesencephalon, 185, 240
Mesenteric artery, 1 78

Mesentery, 165, 204, 205
Metacarpal bones, 223
Metamorphosis, 113
Metastoma, 129
Metatarsal bones, 225
Metencephalon, 185, 240
Micrococciis, 28
Micropyle, 71, 86, 112
Midbrain, 185, 240
Motor oculi, nervus, 187
Moulds, 30
Mitcor, 30, 34 ; Laboratory work,

40
Muscle, histology of, 124, 150,

256; physiology of, 265
Muscular system, of Anodonta,

123; of Hydra, 101, 105; of

Frog, 226
Musculo-cutaneous vein, 179, 199,

236

Mycelium, 31, 35, 38
Myelon, 191, 240
Myology, of the Frog, 226

N.

NARES, 166, 196, 208, 249
Nasal bones, 217
Nematocysts, 100, 104
Nerve, cells, 150, 257; fibres, 150,

257

Nerve, physiology of, 265
Nervous system, of Anodonta, 109,
112; of Crayfish, 136, 149; of
Frog, 185, 2 38; of Lobster, 136,
149

Nerve, auditory, 239; brachiaL.
243; crural, 193; facial, 190;
glossopharyngeal, 190, 243 ;
hypoglossal, 203, 243; laryn-
geal, 191, 243; maxillo-mandi-
bular, 188, motor oculi, 187;
olfactory, 187, 239 ; orbito-nasal,
188; palatine, 188; pathetic,
1 88; sciatic, 193, 233 ; trigemi-
nal, i88;tibial, 193
Nettle hair, protopl. movt. in, 54
Neural, arch, 212; canal, 216;
cavity, 168

276

INDEX.

Ni 'fella, 42, 52

Node, 42, 48, 55, 62, 70, 78

Notochord, 169

Nucleolus, 1 8

Nucleus, of Amoeba, 18, 21; of

ovule, 70, 85; of Vorticella, 92,

94

O.

OBLIQUE muscles, 194
Occipital condyle, 216
CEnothcra biennis, 87
(Esophageal artery, r 7
CEsophagus, of Bell-animalcule,

90, 93; of Anodonta, 109, 122;

of Crayfish, 131, 148; of Frog,

173, 208
Olfactory, lobes, 187, 239; nerves,

iS/> '-239; organs, 193, 249
Omosternum, 221
Opercular membrane, 163
Ophthalmites, 130, 153
Optic, commissure, 241 ; lobes,

185, 24o;nerves, [87, 241, 245;

thalami, 186, 239; tracts, 241
Orbito-nasal nerve, 188
Organ of Boj anus, no, 117
Os, cruris, 224; femoris, 224; pu-

bis, 224

Otolith, 121, 194
Ovary, of Anodonta, 112, 123; of

Crayfish, 147; of Frog, 183,

264; of Hydra, 100, 106; of

Lobster, 147

Oviduct, 147, 148, 184, 208
Ovules, 70, 85
Ovum, of Anodonta, 112, 123 ; of

Crayfish, 139; of Frog, 184,

264 ; of Hydra, 100, 106 ; of

Lobster, 139

P.

PALATINE, bone, 218; nerve, iSS

Pallium, 1 08, 114

Pancreas, 174, 205

Papillre, filiformes, 195, 250; fun-

giformes, 195, 250
Parasphenoid bone, 218
Parenchyma, 57, 63,64, 72, 79, 80

Parieto-frontal bone, 217
Parieto-splanchnic ganglion, 112,

120

Pasteur's fluid, 6
Patheticus, nervus, iSS
Pectoral arch, 172, 221
Pedal ganglion, 112, 120
Peduncle, 83
Pelvic arch, 172, 224
Pelvic vein, 179, 234
Penicillium, 30; Laboratory work,

3 8
Pericardium, of Anodonta, in,

116; of Crayfish, 133, 145; of
Frog, 165, 201; of Lobster,

133, 145
Perilymph, 194

Peristome, 90, 93

Periotic capsule, 171, 217

Peroneal nerve, 193, 233

Pes, 160, 225

Petal, 84

Petiole, 82

Phalanges, 223, 225

Pia mater, 238

Pigment-cells, 196, 261

Pineal gland, 186, 239

Pinnule, 55

Pistil, 70, 84, 85

Pith, 72, 79

Pituitary body, 186, 241

Pleuroperitoneal cavity, 165 ;

membrane, 165, 201
Plumule, 71, 86
Pneumogastric nerve, 191, 243
Pollen, 70, 85
Posterior commissure, 186
Posterior tibial nerve, 233
Pnecoracoid, 222
Praenasal process, 1 70
Premaxillary bone, 217
Primine, 85
Primitive sheath, 257
Primordial utricle, 32, 45, 83
Pro-embryo of Chara, 47
Pro-otic, 217
Propodite, 151
Prosencephalon, 186, 239
Proteus Animalcule, 17

INDEX.

Prothallus, 60, 67

Protococcus phivialis, n; Labora-
tory work, 14

Protoplasmic movements in vege-
table cells, 45, 52

Protopodite, 131, 142

Pseudopoclia, 17, 21

/tew agnilina, 55; Laboratory
work, 62

Pterygoid bone, 219

Pterygoid rod, 171

Pulmocutaneous artery, 176, 203,

237
Pulmonary, artery, 176, 178 ; vein,

175, 180,238
Putrefaction, 26
Pylangium, 176

Q-

QUADRATE bone, 219
Quadrato-jugal bone, 219

R.

RACHIS, 55

Radicle, 71, 86

Radius, 223

J\ana temporaria and R. esculenta,
159; Laboratory work, 196

Recti muscles, 194

Rectum, of Anodonta, no, 122;
of Crayfish, 133, 148; of Frog,
173, 204 ; of Lobster, 133, 148

Renal veins, 1 79

Renal portal veins, 235, 236

Respiratory organs, of Anodonta,
118; of Crayfish, 135, 144; of
Lobster, 135, 144; of Frog, 181

Restiform bodies, 185

Retina, 247, 258

Retractor bulbi, 194

Rhinal processes, 171

Rhinencephalon, 239

Rhizome, 55, 62

Roots, of the spinal nerves, 192,
240

Rootsheath, 72, 79

S.

Saccharomyces cerevisiiT, I ; Labo-
ratory work, 6

Sacculus, 194

Sacrum, 214

Scalariform ducts, 58, 65

Scaphognathite, 128, 153

Scapular vein, 179

Sciatic, nerve, 193; vein, 179,

235
Sclerenchyma, 57, 03, 64, 65

Sclerotic, 194, 245

Secondary capitula, 45

Secundine, 85

Seed, 71, 86

Seed-leaves, 71, 86

Sense organs, of Anodonta, 112,
121 ; of Crayfish, 137, 153; of
Frog, 193, 244; of Lobster,

137, 153

Sepals, 84

Septum narium, 170, 249

Sexual organs, of Anodonta, 112,
123; of Bean, 70, 84; of Chara,
45, 51; of Crayfish, 139, 146;
of Fern, 59, 66; of Frog, 175,
198; of Hydra, 96, 102; of
Lobster, 139, 146

Shell, of Anodonta, 124

Sinus venosus, 175, 201

Siphons, of Lamellibranchiata,
109, 115

Skeleton, of Anodonta, 107, 124;
of Crayfish, 127, 139; of Frog,
169, 211 ; of Lobster, 127, 139

Skull, 216

Somite, 128, 141

Sorus, 56, 66

Spermatozoa, of Anodonta, 112;
of Crayfish, 147; of Frog, 183,
207; of Lobster, 147

Spinal, column, 212; cord, 191,
240, 242 ; nerves, 244

Spinous process, 213

Spiral vessels, 58, 65, 73, 80, 83

Spirillum volutans, 25, 29

Spirochccte, 29

Splanchnic nerve, 191

Spleen, 174, 205

Sporangium, of Chara, 43, 46 ; of
Bracken, 56, 66; of Mucor, 34,

4*

278

INDEX.

Spore, of Moulds, 31, 34; of

Fern, 56, 66
Spore fruit, 43, 46, 5 1
Squamosal bone, 217
Stamens, 70, 84
Starch, 45, 57, 64, Si
Stellate cells, 82
Stem, of Chara, 42, 48, 79 ; of

Bracken (rhizome), 55, 63
Sternal artery, 133, 149
Stigma, 70, 87
Stipule, 82
Stomach, of Anodonta, no, 122;

of Crayfish, 131, 148; of Frog,

l6 7 !73> 20 5; of Lobster, 131,

148

Stomata, 59, 73, 82, 83
Stone worts, 42
Striated spindle, 138, 155
Style, 70, 85
Subclavian artery, 178; vein, 179,

^
Suboesophageal ganglion, 137

Sub-vertebral lymph sinus, 165
Supraoesophageal ganglion, 136,

149

Suspensorium, 171
Sympathetic system, 185, 193, 243
Synangium, 176

T.

TADPOLE, 163

Tarsus, 225

Teeth, of Frog, 164, 173; gastric,

of Crayfish, 132
Telson, 140, 142
Tendo Achillis, 231
Tendril, 82
Tentacles, 98, 102
Terminal bud, of Chara, 43, 50 ;

of Bean, 70, 73
Terminal cell, 43, 49, ^o
Testa, 86
Testis, of Anodonta, 112 ; of Cray-

fish, 146; of Frog, 183, 207,

263; of Hydra, 99, 105; of

Lobster, 147
Thalamencephalon, 186, 239

Thalami optici, 186, 239

Third ventricle, 186, 239

Thread cells, 100, 104

Thymus gland, 181

Thyro-hyal, 220

Thyroid gland, 181

Tibia, 225

Tibial nerve, 193

Tongue, 167, 195, 197

Tornla cerevisi<z, i ; Laboratory

woi'k, 6

Torula, of Mucor, 37
Tmdescantia, protopl. movts. in,

53

Transverse process, 213
Trigeminal nerve, 188
Trachea, 181, 208
Truncus arteriosus, 175, 176, 201
Tympanic membrane, 194, 247
Tympanum, 194, 247, 248

U.

ULNA, 223
Umbo, 125
Unguis, 84
Unio, 107
Ureter, 183, 206
Urinary bladder, 183, 204
Urostyle, 170, 214
Urticating capsules, 100
Utriculus, 194

V.

VACUOLE, alimentary, 94; con-
tractile, 18; in vegetable cells,

2 , 7, 32, 34, 39, 49
Vagus nerve, 191, 243
Vallisneria, protopl. movts. in,

54

Vas deferens, of Crayfish, 146; of

Frog, 183, 207; of Lobster, 147
Vascular bundles, 57, 63, 72, 79
Vascular system, see Circulatory

organs
Vein, axillary, 236; brachial, 179,

236; branchio-cardiac, 134;

dorsolumbar, 180 ; femoral, 179;

gastric, 180, 235; iliac, 179;

INDEX.

79

innominate, 179, 236 ; jugular,
external, 179, -235; jugular, in-
ternal, 178, 236; lienointesti-
nal, 1 80, 235 ; musculo-cuta-
neous, 179, 199, 236; pelvic,

179, 234; pulmonary, 175, 180;
scapular, 179; sciatic, 179, 235;
subclavian, 179, 235 ; renal, 179;
renal portal, 235, 236 ; portal,

180, 235

Vena, cava, of Anodonta, 1 1 r, 117;
of Frog, infr., 178, 236; of
Frog, supr., 178, 236; innomi-
nata, 178, 236; portee, 180, 235

Venous system of Frog, 178

Ventricles of the brain, 185

Vertebra, 212

Vertebral artery, 178

Vertebral column, 2 1 2

Veronica serpyllifolia, 87

Vesicula seminalis, 206

Vestibulum, 90, 93

Vexillum, 84

Vibr tones, 26, 29

Vicia faba, 70 ; Laboratory work,
78"

Vitelline membrane, 184, 265

Vitellus, 106, 184, 265

Vitreous humour, 246
Visceral nervous system, of Cray-
fish, 136

Vocal, sacs, 167; ligaments, 181
Vomer, 218
Vorticella, 89; Laboratory work,

93

W.

WHITE fibrous tissue, 255
Wood, 72, 80

X.

XlPHISTERNUM, 221

Y.

YEAST, i ; Laboratory work, 6
Yelk division, Hydra, 100; Frog,
162

Z.

ZOOGLOEA, l6, 28

Zygapophysis, 213
Zygospore, 36

.

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PRINTED BY C. J. CLAY, M.A.
AT THE UNIVERSITY PRESS.

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