A junior course of practical zoology online

aw







JUNIOE COUESE



OF




PEACTICAL ZOOLOGY



BY



A. MILNES MARSHALL, M.D., D.Sc., MA., F.R.S.

PROFESSOR IN THE VICTORIA UNIVERSITY : BEYER PROFESSOR OF

ZOOLOGY IN OWENS COLLEGE ; LATE FELLOW OF

ST JOHN'S COLLEGE, CAMBKIDGE

ASSISTED BY



C. HERBERT HURST

DEMONSTRATOR AND ASSISTANT LECTURER IN ZOOLOGY
IN OWKNS COLLEGE



LONDON
SMITH, ELDER, & CO., 15 WATERLOO PLACE

1887



[AH rights



BIOLOGY

LIBRARY

G




TO THE

STUDENTS OF OWENS' COLLEGE

THIS BOOK
IS DEDICATED

BY THEIR SINCERE WELL-WISHERS



THE AUTHORS



2Si



PEEFACB.



THIS BOOK has been written in the hope that it may meet the
wants of those who desire to obtain a practical acquaintance
with the elements of animal morphology, and who find the
existing manuals insufficient for their purpose.

The animals selected for description are those which are
generally accepted as suitable types for a junior laboratory
course. They are of convenient size, and can all be obtained
readily and at small cost : they include characteristic repre-
sentatives of the more important of the great groups of
animals ; and they give opportunity for very varied methods
of examination. A student who works conscientiously
through the book will thus acquire a good insight into the
leading facts of animal structure, and a technical knowledge
of the principal methods of research.

In the mode of treatment adopted the practical character
of the book has been made paramount. Directions for dis-
section have throughout been printed in italics, and a
system of indentation has been adopted to render the sub-
divisions more distinct,. In almost all cases the descriptions
are so arranged that the whole dissection can be performed
on a single specimen : if more than one can be obtained, the
order in which the several sections are taken may be varied,
but in every case each of the main systems vascular, nervous,
etc. should be dissected in its entirety, for in this way alone
can a proper idea of its relations be obtained.



1



viii PEEFACE

No attempt has been made to write exhaustive descrip-
tions of the several animals ; neither has strict uniformity of
treatment been specially aimed at. Portions of the subject
which experience has shown to present special difficulties
are treated at what may appear undue length ; while, 011
the other hand, the limits of time ordinarily available for
laboratory work have led to the almost entire omission of
systems, such as the muscular, which are of subordinate
educational value.

Although this is essentially and professedly a laboratory
text-book, yet morphological explanations have been freely
introduced; and this from a conviction that a student best
grasps the meaning of anatomical facts if the explanation
is given him while the facts are actually before his eyes.

Illustrations have been introduced somewhat sparingly,
for it is of the utmost importance that they should not be
allowed to replace the drawings which a student must make
from his own dissections. The maj ority of the figures here given
are new, and have been drawn expressly for the book by Mr.
Hurst or myself. The drawings on the wood were made by
Mr. P. Hundley, and the blocks engraved by Mr. G. Pearson :
both these gentlemen have taken great pains to render the
figures at once faithful and artistic.

Throughout the whole time of preparation of this volume
I have had the constant co-operation and assistance of my
friend Mr. C. H. Hurst. Several of the chapters were
originally drawn up by him, and in all I have had the ad-
vantage of his aid, but for which the publication of the book
might have been greatly delayed. Considerable pains have
been taken to avoid mistakes, but it is curiously difficult to
succeed in this, and corrections or suggestions from those who
use the book will be very gratefully received.

A. M. M.

OWENS COLLEGE : December 1886.



CONTENTS.



INTEODUCTION.

PAGE

On the observation of animals during life On drawing On the
methods of killing animals On dissection On injection On
the use of reagents On microscopical examination . . . xv



CHAPTEK I.

PROTOZOA.

Amoeba Paramecium Opalina Vorticella 1

CHAPTEE II.
HYDRA.

Examination of a living specimen Examination of transverse

sections . 13

CHAPTEE III.

THE LIVER-FLUKE OF THE SHEEP. Fasciola (Distomum)
hepatica.

The mature liver-fluke Life-history of the liver-fluke ... 25



X CONTENTS

CHAPTER IV.
THE LEECH. Hirudo medicinalis.

PA.GE

External characters Dissection Examination of transverse sec-
tions . 36



CHAPTER V.
THE EARTHWORM. Lumbricus terrestris.

External characters Dissection Examination of transverse sec-
tions . 55



CHAPTER VI.
THE FRESHWATER MUSSEL. Anodonta cygnea.

The shell Dissection of the mussel Examination of transverse

sections . . . .75

CHAPTER VII.
THE EDIBLE SNAIL. Helix pomatia.

External characters Dissection of the snail 102

CHAPTER VIII.
THE CRAYFISH. Astacus fluviatilis.

External characters Dissection The arteries as seen in an

injected specimen . . 124

CHAPTER IX.
THE COCKROACH. Periplanria americana.

Habits External characters Dissection 152



CONTENTS XI

CHAPTEK X.
THE LANCELET. Amphioxus lanceolatus.

PAGE

External characters Anatomy Examination of transverse sec-
tions ... 168

CHAPTEK XI.
THE DOG-FISH. Scyllium canicula.

External characters The skeleton The abdominal viscera Dis-
section of the digestive system Dissection of the respiratory
system Dissection of the circulatory system Dissection of
the urinary and reproductive systems Dissection of the nervous
system Dissection of the sense-organs 194

CHAPTER XII.
THE SKELETON OF THE RABBIT. Lepus cuniculus.

The axial skeleton The appendicular skeleton .... 257

CHAPTER XIII.
DISSECTION OF THE RABBIT. Lepus cuniculus.

External characters Dissection of the buccal cavity The ab-
dominal viscera Dissection of the digestive system The
thoracic viscera Dissection of the circulatory system Dissec-
tion of the urinary and reproductive systems Dissection of the
neck Dissection of the brain ....... 295

CHAPTER XIV.
THE SKELETON OF THE FOWL. Gallus barikiva.

The axial skeleton The appendicular skeleton .... 355



Xll CONTENTS

CHAPTER" XV.
DISSECTION OF THE PIGEON. Columba lima.

PAGE

External characters Dissection of the pectoral muscles Dissec-
tion of the air-sacs Dissection of the digestive system Dissec-
tion of the circulatory system Dissection of the respiratory
system Dissection of the secretory and reproductive systems
Examination of the brain The sense-organs . . . 383

APPENDIX.
ON THE PREPARATION OF REAGENTS. 417

INDEX . . 423



LIST OP WOODCUTS.



PAGE

1. Amceba > 2

2. Paramecium aurelia ......... 4

3. Vorticella ... 9

4. Hydra : Diagrammatic longitudinal section . . . . 14

5. Section of the body<-wall, highly magnified . 16

6. Fasciola hepatica : Diagrammatic figure of the digestive,

excretory, and nervous systems ... 27

7. The reproductive system 29

8-12. A series of stages in the life-history . . . 33

Fig. 8. The free-swimming embryo
>, 9. An adult sporocyst, containing rediae
10. A young redia
,,11. An adult redia, containing a daughter redia,

and cercaris3
rt 12* A free cercaria

13. Hifudo medicinalis : The ventral surface . . . . . 39

14. Diagrammatic figure of the vascular, excretory,

reproductive^ and nervous systems ... 39

15. Diagrammatic transverse section through the

middle of the body . . . . . . . 60

16. Lumbricus terrestris ; Longitudinal vertical section through

the anterior part of the animal .... 59

17. Plan of the reproductive organs . . . . 65

18. Diagrammatic transverse section through the

middle of the body 71

19. Anodonta cygnea : Dissection from the right side, to show the

heart and gills. 84

20. Dissection from the right side, to show the diges-

tive, circulatory, and excretory systems . . 90

21. Diagrammatic transverse section through the

middle of the ventricle 99

22. Helix pomatia : Dissection from the right side, to show the

mantle-cavity 109



xiv LIST OF WOODCUTS

FIGURE PAGB

23. Helix pomatia : Dissection from the right side, to show the

digestive and reproductive systems . . . 112

24. Section along the axis of the shell, transverse to

the foot 122

25. Astacus fluviatilis : Transverse section through the abdomen 126
20. Diagrammatic transverse section through the

thorax 134

27. Dissection of a male from the right side . .138

28. Periplaneta americana : The head, front view . . . . 154

29. The head, from behind . . . . . .154

30. Dissection of a male from the right side . . . 160

31. Amphioxus lanceolatus : A young specimen, seen from the

right side 170

32. Transverse section through the anterior part of

the pharynx . . 185

33. Transverse section through the posterior part of

the pharynx 189

34. Transverse section through the atrial pore . . . 191

35. Transverse section through the anus . . . 192

36. Scyllium canicula : The skull and visceral skeleton from the

right side 202

37. Longitudinal and vertical section through the

head and anterior part of the body . ... 218

38. The venous system . 222

39. The branchial blood-vessels . . . . .227

40. Transverse section through the posterior dorsal fin . 231

41. Lepus cuniculus : The skull from the right side . ... 268

42. Dissection of a male from the left side . * . . 300

43. Longitudinal and vertical section of the brain . . 342

44. Transverse section of the brain, passing through

the third ventricle 350

45. Transverse section of the brain, passing through

the cerebellum 353

46. Gallus bankiva : The left half of the skeleton, from the right

side 356

47. The skull, from the right side 364

48. Columba lima : Dissection from the right side . . . 394



INTRODUCTION.



THE following pages contain a brief summary of the methods
ordinarily employed in the dissection and microscopical
examination of animals. They are not intended to form an
exhaustive account of anatomical technology ; and in many
cases they are repetitions of the practical directions given in
other parts of the book.

I. ON THE OBSERVATION OF ANIMALS CUBING LIFE.

All animals should be carefully observed alive before they
are dissected, for by this means alone is it possible to obtain
a clear idea of the uses and mode of action of many organs,
such as the tentacles of Hydra, the odontophore of a snail,
the scaphognathite of a crayfish, etc.

II. ON DBA WING.

Careful drawings must always be made, both of the living
animal and of all dissections and preparations. These draw-
ings should be made to scale, in a book kept for the purpose,
and on one side of the page only.

Correctness of outline is of more importance than minute
detail ; and the usefulness of the drawings is greatly increased
by the systematic use of diagrammatic colouring. A separate
colour should be employed for each system of organs, the
several parts of which may be indicated by gradations of tint.

As a rule, the more bulky organs, as the liver, should be
coloured with dull tints, and the brighter colours reserved for
the smaller and less conspicuous parts. Arteries are usually
coloured red, and veins blue.



xvi INTRODUCTION



III. ON THE METHODS OF KILLING ANIMALS.

The method of killing is of considerable importance, and
careful attention should be paid to the directions given at the
commencement of each chapter.

It is important in most cases that the animal should die
in an expanded or relaxed condition. This is most readily
secured in the case of very minute animals, as Hydra and
the Protozoa, by suddenly deluging them with osmic acid,
which kills them instantaneously, before contraction can
occur. With animals of larger size, chloroform affords the
most convenient means for attaining the same end.

Small animals, as the leech, earthworm, etc., may be
readily killed by dropping them into solutions of corrosive
sublimate, of chromic acid, or of picric acid, or into alcohol.
Crayfish may be killed by momentary immersion in boiling
water ; and snails should be drowned, when they die fully
expanded.

Many other methods are in everyday use, and the purpose
for which the animal is intended determines in many cases
the method of killing.

IV. ON DISSECTION.

, The object of dissection is to separate the several organs
from one another, so far as is necessary to define their boun-
daries, and display their relations to one another. It consists
mainly in the removal of the connective tissue which binds
the parts together and obscures their outlines.

The necessary instruments are the following :

1. Two or three scalpels, of different sizes.

2. Two pairs of forceps ; one large and one small. Both
pairs should be straight, and should have roughened tips to
secure a firmer hold.

8. Two pairs of scissors ; one pair large and strong for
general dissection, the other pair small for finer work. The
latter pair should have the blades either bent at an angle
elbow scissors or else curved. In selecting scissors, care



ON DISSECTION xvii

should be taken to see that they cut quite up to the points of
the blades.

4. A pair of bone-forceps or very stout scissors, for cutting
bone and other hard substances.

5. A pair of stout needles, firmly mounted in handles.

6. A pair of the finest sewing-needles, mounted in handles.
Only about a quarter of an inch of the needle should project.
They are used for teasing histological preparations.

7. A seeker, i.e. a blunt needle mounted in a handle, and
with the end bent at an angle.

8. A pocket-lens, containing two or three lenses mounted
in a handle, and giving when combined a magnifying power
of at least six diameters.

9. A razor, and some means for keeping it sharp.

For the dissection of the larger animals, as the dog-fish or
rabbit, an ordinary deal board, about two feet long by a foot
and a half wide, may be used : to this the animal should be
fastened by pins, those with large round heads being especially
convenient.

Smaller animals, and special parts of larger ones, should
be dissected under water, which supports the parts and greatly
facilitates the operation. For this purpose an ordinary white
pie-dish with sloping sides is very suitable, the bottom being
fitted with a soft deal board weighted with lead, or a sheet of
cork cemented in with marine glue. A similar but smaller
dish may be used for dissecting under spirit.

Animals, such as the cockroach, which are difficult to fix
with pins may be cemented down with melted wax, or they
may be half imbedded in a plate of paraffin, and the plate
then fixed down with pins in the dissecting-dish.

For fine work a dissecting microscope affords great assist-
ance. The pocket-lens may readily be turned into one by
fitting one end of an ordinary wine-cork into the handle or
case of the lens, and passing a stout pin transversely through
the other end. The pin should be stuck upright into the
dissecting-board, with the lens over the part to be dissected :
focussing is effected by sliding the cork up and down the
pin.

a



xviii INTRODUCTION

The following rules for dissection should be carefully
observed.

1. Before commencing a dissection, fix the animal down
firmly to the dissecting-board or dish.

2. In fixing an animal with pins, stick them in obliquely,
so that their heads do not get in the way or obscure the
dissection.

3. Dissect under water, unless the animal is too large.
Change the water as soon as it gets dirty. A gentle stream of
water allowed to play upon the dissection is often a valuable aid.

4. Never cut away anything until you are quite certain
what it is you are removing.

5. Put the part you are dissecting slightly on the stretch.
This applies more particularly to blood-vessels, nerves, ducts,
and muscles.

6. In cleaning blood-vessels, nerves, etc., dissect along
them, and not across them ; and avoid laying hold of them
with the forceps.

7. The dissection is in many cases greatly facilitated by
placing the specimen in spirit for a day or so before dissecting
it. In some cases the dissection may with advantage be per-
formed under spirit.

8. Always keep your instruments clean and sharp. Be
careful not to blunt your fine scissors or scalpels by using
them for cutting hard parts.

9. If you get in a muddle, stop, and wash the dissection
thoroughly under the tap before proceeding further.

Successive slices cut off an animal, or part of an animal,
with a razor are often exceedingly instructive ; this is especially
the case with the mussel and snail, and with the brains of
the rabbit and pigeon. The specimens must be previously
hardened with spirit or other reagent, and the slices should
be examined in water or spirit.

V. ON INJECTION.

The injection of coloured fluids into the blood-vessels or
ducts of an animal renders them much easier to see, an,d to
follow to their distribution.



ON INJECTION xix

The colouring matter used must not be soluble in any of
the fluids in which the specimen is afterwards to be dissected,
hardened, or preserved. The most convenient are French
blue, Prussian blue, vermilion, and carmine.

In the case of the larger animals, freshly prepared plaster
of Paris forms, if coloured, a convenient substance for injec-
tion : it solidifies in the vessels, and so does not escape if a
vessel is accidentally cut during the dissection.

For smaller animals, thick gum- water or white of egg
may be injected cold, or a jelly made of gelatine and water
injected warm : the animal should afterwards be put into
alcohol to harden the injection. If the animal is not to be
dissected after injection, water coloured with any of the above
pigments may be used with advantage, and this method is
particularly useful for the alimentary and excretory systems
of the liver-fluke.

For injecting small animals, a suitable syringe consists of
a glass tube with an india-rubber cap fitted on one end, the
other end being drawn out to a point sufficiently fine to
enter the vessel to be injected. After the tube is drawn out
in the flame and cut off, its sharp edges must be slightly
rounded off by holding for a moment in the flame. Several
such cannulas of various sizes should be kept ready.

For injecting larger animals, such as a rabbit, with plaster
of Paris, the blood must first be washed out of the vessels
by injecting warm salt -solution. The following apparatus is
necessary, and must all be placed on the table ready for use
before the animal is killed ; for the blood coagulates after
death so rapidly as to allow no time to look for instruments.

1. Cannulae : glass ones are the most convenient; they
should be of various sizes, to fit the various vessels which it is
proposed, to inject, and each should have a slight constriction
near the tip, so that it may be firmly secured in the vessel by
a ligature. The largest cannula that will enter the vessel
should be used.

2. A glass syringe, capable of holding about an ounce of
fluid. A larger syringe is liable to get blocked up.

3. Several pieces of strong india-rubber tubing, about an



XX INTRODUCTION

inch long, to connect the nozzle of the syringe with the
cannula, both of which they must fit rather tightly.

4. Two or three glass plugs to fit the india-rubber tubing.

5. A dish of water or salt -solution, in which all the cannulas
and india-rubber connections are laid to displace the air from
them.

6. Fine plaster of Paris.

7. A mortar and pestle.

8. Colouring matter, such as carmine previously rubbed
up with water : it must be well shaken before use.

9. A piece of muslin to strain the injection through. It
must be well wetted before use.

10. A jar into which to strain the injection.

11. Ajar containing about half a pint of salt-solution ('75
per cent.), at a temperature of 100 F.

12. Dissecting-board, pins, scalpels, scissors, two pairs of
forceps, seeker, thin string or thread, and two or three pairs
of 'bull-dogs.' These last are very short spring-forceps, the
spring being so arranged as to close the forceps. They are
convenient to stop the escape of blood or injection from any
vessel that may have been cut.

The injection should be performed close to a large sink,
over which is a water-tap with a foot or two of wide india-
rubber tubing attached.

When everything is ready, kill the animal, and as soon as
it is dead, lay it open, cutting as few blood-vessels as possible.
Expose the root of the aorta or other vessel from which it is
intended to inject the animal ; choose a cannula of the right
size ; fit it with an india-rubber connection ; fill it with salt-
solution, and stop the end of the connection with a glass plug.
Pass a ligature around the vessel : make a longitudinal slit in
the vessel ; insert the cannula ; tighten the ligature upon it,
and tie it with a bow. If the ligature be too tight it will cut
the vessel. Fill the syringe with the warm salt-solution :
remove the plug from the cannula : press the body of the
animal slightly, to remove some of the blood from its vessels,
and to get rid of any clot that may have formed close to the
cannula-. Inject the salt- solution, to force the remaining blood
om the vessels before it can coagulate ; and wash or sponge



ON REAGENTS xxi

the blood away. If the arteries are being injected, the vena
cava and portal veins should be cut open to allow free escape
of the blood, and vice versa.

Mix the plaster of Paris in the mortar, stirring in the
colour, and making the plaster thin. Strain it rapidly through
the muslin, and inject immediately with the syringe. When
the vessels appear to be well injected, remove the syringe and
insert the glass plug, and wash the animal to get rid of blood
and any injection that may have escaped.

Allow the animal to remain two or three hours before
dissecting it or putting it' into spirit.

VI. ON THE USE OF EEAGENTS.

Eeagents are used for hardening, staining, and preserving
specimens. Those required for general use are but few in
number, and directions for their preparation will be found in
the appendix.

1. Hardening is necessary in the case of soft animals or
tissues of which it is proposed to cut slices. For the mussel
a \ per cent, solution of chromic acid in water serves well.
For the brain of a rabbit or pigeon ordinary methylated spirit
is very convenient and effective. The specimen must be left
in the hardening fluid two or three days, and a large bulk of
the fluid must be used, or else it must be frequently changed.

Other methods are used when the specimen is to be cut
into microscopical sections.

2. Staining with some colouring fluid renders the various
parts much more distinct, and is especially useful when the
object is to be examined microscopically, and especially when
it has to be cut into sections.

Magenta is useful for staining fresh specimens, but the
stain is not permanent.

Carmine is perhaps the most useful of all stains. It
affects different cells and parts of cells differently, and the
stain is permanent. The most useful preparation of it is
Grenacher's borax-carmine : this should be used warm, and
the specimens after removal from it should be placed in acid-
alcohol for a few minutes or hours, according to their size.



xxii INTRODUCTION

Pier o- carmine has the advantage of being an aqueous
stain, and may therefore be used either for fresh or hardened
tissues. Immersion of the specimen in acid-alcohol for some
time after staining improves the effect.

Hsematoxylin (Kleinenberg's solution) gives excellent
results if used with due care, but a trace of chromic or other
acid may completely destroy the colour after the specimen is
mounted.

Osmic acid, of which a 1 per cent, or ^ per cent, aqueous
solution is used, is both a hardening and a staining reagent.
It is only used with fresh tissues, and only with small speci-
mens. It kills Protozoa instantly, and after a time stains
their nuclei, though only faintly. Objects hardened with
osmic acid may be stained with picro- carmine. A mixture of
chromic and osmic acids forms a useful hardening reagent.

Acetic acid, 1 per cent, solution, is useful for render-
ing the nuclei of cells more distinct : it is used with fresh
specimens.

VII. ON MICROSCOPICAL EXAMINATION.

The microscope affords the means of investigating the
structure of minute animals, and the finer details of those
of larger size. The microscopical examination of the special
organs of the larger animals is of great importance, and must
on no account be neglected.

The microscope consists of a body and a stand. The body