an increasing resemblance to that of the fowl. A split occurs at one
point between outer layer and inner layer cells, and the space
resulting (Y in Figure 2) is filled by an increasing amount of fluid, and
rapidly enlarges, so that presently we have the state of affairs shown
in 3, in which the inner layer cells are gathered together at one point
on the surface of the ovum, and constitute the germinal area. If, with
Hubrecht, we regard the outer layer cells as an egg membrane, there
is a curious parallelism between this egg and the fowl's the fluid Y
representing the yolk; and the inner layer cells the cells of the fowl's
germinal area.
At any rate, the subsequent development goes far to justify such a
view. The inner cells split into epi-, meso-, and hypo-blast, like the
blastoderm in the fowl; there is a primitive streak and no blastopore;
an amnion arises; the yolk sac, small and full of serous fluid, is cut off
just as the enormous yolk of the fowl is cut off; and an allantois arises
in the same way. There is no need to give special diagrams-- Figures
3, 4b, 5, and 6 of the fowl will do in all respects, except proportion, for
the development of the rabbit. The differences are such as we may
account for, not on the supposition that the rabbit's ovum never had
any yolk, but that an abundant yolk has been withdrawn from it. The
nutrition of the embryo by yolk has been superseded by some better
method. The supposition that the rabbit is descended from ancestors
which, like the birds and reptiles, laid eggs with huge quantities of
yolk, meets every circumstance of the case.
Section 38. But the allantois and yolk sac of the rabbit, though they
correspond in development, differ entirely in function from the similar
organs of the fowl. The yolk sac is of the very smallest nutritive value;
instead of being the sole source of food, its contents scarcely avail
the young rabbit at all as nourishment. Its presence in development is
difficult to account for except on the supposition, that it was once of
far greater importance. At an early stage, the outgrowing allantois,
pushing in front of it the serous membrane, is closely applied to the
lining of the mother's uterus. The maternal uterus and the embryonic
allantois send out finger-like processes into each other which
interlock, and the tissue between the abundant bloodvessels in them
thins down to such an extent that nutritive material, peptones and
carbohydrates, and oxygen also, diffuse freely through it from
mother to foetus,* and carbon dioxide, water, and urea from the
foetus to the mother. The structure thus formed by the union of the
wall of the maternal uterus, allantois, and the intermediate structures
is called the placenta. Through its intermediation, the young rabbit
becomes, as it were, rooted and parasitic on the mother, and utilizes
her organs for its own alimentation, respiration, and excretion. It
gives off CO2, H2O, and urea, by the placenta, and it receives O and
elaborated food material through the same organ. This is the better
method that has superseded the yolk.
* The embryo.
Section 39. In its later development, the general facts already
enunciated with regard to the organs of frog and fowl hold, and where
frog and fowl are stated to differ, the rabbit follows the fowl. In the
circulation the left fourth vascular arch (second branchial) gives rise to
the aortic arch; in the right the corresponding arch disappears, except
so much of it as remains as the innominate artery. The azygos vein
(Chapter 3) -is a vestige of- [is derived from] the right posterior
cardinal sinus. Both pulmonary arteries in the rabbit are derived from
the left sixth vascular arch (= fourth branchial). Compare Section 32. The
allantois altogether disappears in the adult fowl; in the adult mammal
a portion of its hollow stalk remains as the urinary bladder, and the
point where it left the body is marked by the umbilicus or navel. The
umbilical arteries become the small hypogastric arteries on either side
of the urinary bladder. There is no trace of a pronephros at all in the
rabbit.
Section 40. We may note here the development of the eye. This is
shown in Figure 4, Sheet 24. A hollow cup-shaped vesicle from the
brain grows out towards an at first hollow cellular ingrowth from the
epidermis. The cavity within the wall of the cup derived from the brain
is obliterated, [and the stalk withers,] the cup becomes the retina, and
-its stalk- [thence fibres grow back to the brain to form] the optic
nerve. The cellular ingrowth is the lens. The remainder of the
eye-structures are of mesoblastic origin, except the superficial
epithelium of the cornea. The retinal cup is not complete at first
along the ventral line, so that the rim of the cup, viewed as in
Figure 1, r., is horseshoe shaped. -Hence the optic nerve differs from
other nerves in being primitively hollow.- In all other sense organs,
as, for instance, the olfactory sacs and the ears, the percipient
epithelium is derived, from the epiblast directly, and not indirectly
through the nervous system. These remarks apply to all vertebrate
types.
Section 41. The supposition, that the general characters of the
rabbit's ovum were stamped upon it as an heritage from a period when
the ancestors of the mammals were egg-laying reptiles, is
strengthened by the fact that the two lowest and most reptile-like of
all the mammalia, the duck-billed platypus and the echidna, have
been shown to depart from the distinctive mammalian character, and
to lay eggs. And, in further confirmation of this supposition, we find, in
tracing the mammals and reptiles back through the geological record,
that in the Permian and Triassic rocks there occur central forms
which combine, in a most remarkable way, reptilian and mammalian
characteristics.
Section 42. In conclusion, we would earnestly recommend the
student to see more of embryological fact than what is given him here.
It is seeing and thinking, much more than reading, which will enable
him to clothe the bare terms and phrases of embryology with coherent
knowledge. In Howes' Atlas of Biology there is a much fuller series of
figures of the frog's development than can be given here,
and they are drawn by an abler hand than mine can pretend to be.
There is also an Atlas d'Embryologie, by Mathias Duval, that makes
the study of the fowl's development entertaining and altogether
delightful. Such complete series as these are, from the nature of the
case, impossible with the rabbit. Many students who take up the
subject of biology do so only as an accessory to more extended work
in other departments of science. To such, practical work in
embryology is either altogether impossible, or only possibly to a very
limited extent. The time it will consume is much greater, and the
intellectual result is likely to be far less than the study of such plates
as we have named.
_The Theory of Evolution_
Section 43. We have now considered our types, both from the
standpoint of adult anatomy and from embryological data; and we
have seen through the vertebrate series a common structure
underlying wide diversity in external appearance and detailed
anatomy. We have seen a certain intermediateness of structure in the
frog, as compared with the rabbit and dog-fish, notably in the skull
and skeleton, in the circulation, in the ear, and in the reduced
myomeres; and we have seen that the rabbit passes in these
respects, and in others, through dog-fish- and frog-like stages in its
development, and this alone would be quite sufficient to suggest that
the similarities of structure are due to other causes than a primordial
adaptation to certain conditions of life.
Section 44. It has been suggested by very excellent people that these
resemblances are due to some unexplained necessity of adherence
to type, as though, the power that they assume created these
animals originally, as they are now, coupled creative ability with a
plentiful lack of ideas, and so perforce repeated itself with impotent
variations. On the other hand, we have the supposition that these are
"family likenesses," and the marks of a common ancestry. This is the
opinion now accepted by all zoologists of repute.
Section 45. It must not be for a moment imagined that it is implied
that rabbits are descended from frogs, or frogs from dog-fish, but that
these three forms are remote cousins, derived from some ancient
and far simpler progenitor. But since both rabbit and frog pass through
phases like the adult condition of the dog-fish, it seems probable that
the dog-fish has remained more like the primordial form than these
two, and similarly, the frog than the rabbit.
Section 46. Hence we may infer that the mammals were the last of
the three groups, of which we have taken types, to appear upon the
earth, and that the fishes preceded, the amphibia. Workers in an
entirely independent province, that of palaeontology, completely
endorse this supposition. The first Vertebrata to appear in the fossil
history of the world are fishes; fish spines and placoid scales
(compare dog-fish) appear in the Ordovician rocks. In the coal
measures come the amphibia; and in the Permo-triassic strata,
reptile-like mammals. In the Devonian rocks, which come between the
Silurian and the coal measures, we find very plentiful remains of
certain fish called the dipnoi, of which group three genera still survive;
they display, in numberless features of their anatomy, transitional
characters between true fish and amphibia. Similarly, in the Permian
come mammal-like reptiles, that point also downward to the amphibia.
We find, therefore, the story told by the ovum written also in the
rocks.
Section 47. Now, when this fact of a common ancestry is considered,
it becomes necessary to explain how this gradual change of animal
forms may have been brought about.
Section 48. Two subcontrary propositions hold of the young of any
animal. It resembles in many points its parent. It differs in many
points from its parent. The general scheme of structure and the
greater lines of feature are parental, inherited; there are also novel and
unique details that mark the individual. The first fact is the law of
inheritance; the second, of variation.
Section 49. Now the parent or parents, since they live and breed,
must be more or less, but sufficiently, adapted to their conditions of
living-- more or less fitted to the needs of life. The variation in the
young animal will be one of three kinds: it will fit the animal still
better to the conditions under which its kind live, or it will be a change
for the worse, or it is possible to imagine that the variation-- as in the
colour variations of domesticated cats-- will affect its prospects in life
very little. In the first case, the probability is that the new animal will
get on in life, and breed, and multiply above the average; in the
second, it is probable that, in the competition for food and other
amenities of life, the disadvantage, whatever it is, under which the
animal suffers will shorten its career, and abbreviate the tale of its
offspring; while, in the third case, an average career may be expected.
Hence, disregarding accidents, which may be eliminated from the
problem by taking many cases, there is a continual tendency among
the members of a species of animals in favour of the proportionate
increase of the individuals most completely adapted to the conditions
under which the species lives. That is, while the conditions remain
unchanged, the animals, considered as one group, are continually
more highly perfected to live under those conditions. And under
changed conditions the specific form will also change.
Section 50. The idea of this process of change may be perhaps
rendered more vivid by giving an imaginary concrete instance of its
working. In the jungles of India, which preserve a state of things which
has existed for immemorial years, we find the tiger, his stripes
simulating jungle reeds, his noiseless approach learnt from nature in
countless millions of lessons of success and failure, his perfectly
powerful claws and execution methods; and, living in the same jungle,
and with him as one of the conditions of life, are small deer, alert,
swift, light of build, inconspicuous of colour, sharp of hearing,
keen-eyed, keen-scented-- because any downward variation from
these attributes means swift and certain death. To capture the deer is
a condition, of the tiger's life, to escape the tiger a condition of the
deer's; and they play a great contest under these conditions, with life
as the stake. The most alert deer almost always escape; the least
so, perish.
Section 51. But conditions may alter. For instance, while most of
these deer still live in the jungle with tigers, over a considerable area
of their habitat, some change may be at work that thins the jungle,
destroys the tigers in it, and brings in, let us say, wolves, as an
enemy to the deer, instead of tigers. Now, against the wolves, which
do not creep, but hunt noisily, and which do not spring suddenly upon
prey, but follow by scent, and run it down in packs, keen eyes, sharp
ears, acute perceptions, will be far less important than endurance in
running. The deer, under the new conditions, will need coarser and
more powerful limbs, and a larger chest; it will be an advantage to be
rough and big, instead, of frail and inconspicuous, and the ears and
eyes need not be so large. The old refinements will mean weakness
and death; any variation along the line of size and coarseness will be
advantageous. Slight and delicate deer will be continually being killed,
rougher and stronger deer continually escaping. And so gradually,
under the new circumstances, if they are not sufficient to exterminate
the species, the finer characteristics will be eliminated, and a new
variety of our old jungle deer will arise, and, if the separation and
contrast of the conditions is sufficiently great and permanent, we
may, at last, in the course of ages, get a new kind of deer specifically
different in its limbs, body, sense organs, colour, and instincts, from
the deer that live in the jungle. And these latter will, on their side, be
still continually more perfected to the jungle life they are leading.
Section 52. Take a wider range of time and vaster changes of
condition than this, and it becomes possible to imagine how the
social cattle-- with their united front against an enemy, fierce
onslaught, and their general adaptation to prairie life-- have
differentiated from the ancestors of the slight and timid deer; how the
patient camel, with his storage hump, water storage, and feet padded
against hot sand, has been moulded by the necessity of desert life
from the same ancestral form. And so we may work back, and link
these forms, and other purely vegetarian feeders, with remoter
cousins, the ancestral hogs. Working in this way, we presently get a
glimpse of a possible yet remoter connection of all these hoofed and
mainly vegetarian animals, with certain "central types" that carry us
across to the omnivorous, and, in some cases, almost entirely
vegetarian bears, and to the great and prosperous family of clawed,
meat-eaters. And thus we elucidate, at last, a thread of blood
relationship between the, at present, strongly contrasted and
antagonistic deer and tiger, and passing thence into still wider
generalizations, it would be possible to connect the rabbit playing in
the sunshine, with the frog in the ditch, the dog-fish in the sea-waters
and the lancelet in the sand. For the transition from dog-fish to rabbit
differs from the transition from one species of deer to another only in
magnitude: it is an affair of vast epochs instead merely of thousands
of years.
Section 53. It would, however, be beyond the design of this book to
carry our demonstration of the credibility of a common ancestry of
animals still further back. But we may point out here that it is not a
theory, based merely upon one set of facts, but one singularly rich in
confirmation. We can construct, on purely anatomical grounds, a
theoretical pedigree. Now the independent study of embryology
suggests exactly the same pedigree, and the entirely independent
testimony of palaeontology is precisely in harmony with the already
confirmed theory arrived at in this way.
Section 54. It is in the demonstration of this wonderful unity in life,
only the more confirmed the more exhaustive our analysis becomes,
that the educational value and human interest of biology chiefly lies. In
the place of disconnected species of animals, arbitrarily created, and
a belief in the settled inexplicable, the student finds an enlightening
realization of uniform and active causes beneath an apparent diversity.
And the world is not made and dead like a cardboard model or a
child's toy, but a living equilibrium; and every day and every hour,
every living thing is being weighed in the balance and found sufficient
or wanting.
Our little book is the merest beginning in zoology; we have stated one
or two groups of facts and made one or two suggestions. The great
things of the science of Darwin, Huxley, Wallace, and Balfour remain
mainly untold. In the book of nature there are written, for instance, the
triumphs of survival, the tragedy of death and extinction, the
tragi-comedy of degradation and inheritance, the gruesome lesson of
parasitism, and the political satire of colonial organisms. Zoology is,
indeed, a philosophy and a literature to those who can read its
symbols. In the contemplation of beauty of form and of mechanical
beauty, and in the intellectual delight of tracing and elucidating
relationships and criticising appearances, there is also for many a
great reward in zoological study. With an increasing knowledge of the
facts of the form of life, there gradually appears to the student the
realization of an entire unity shaped out by their countless, and often
beautiful, diversity. And at last, in the place of the manifoldness of a
fair or a marine store, the student of science perceives the infinite
variety of one consistent and comprehensive Being-- a realization to
which no other study leads him at present so surely.
To the student who feels inclined to amplify this brief outline of
Vertebrate Anatomy, we may mention the following books:
Wiedersheim's and Parker's Vertebrates, Huxley's Anatomy of the
Vertebrata, Flower's Osteology of the Mammalia, Wallace's
Distribution, Nicholson and Lyddeker's Palaeontology (Volume 2),
the summaries in Rolleston's Forms of Animal Life (where a
bibliography will be found), and Balfour's Embryology. But reading
without practical work is a dull and unprofitable method of study.
_Questions on Embryology_
[All these questions were actually set at London University
Examinations.]
{In Both Editions.}
1. Describe the changes in the egg-cell which precede fertilization;
describe the process of fertilization and the formation of the primary
cell-layers, as exhibited, in three of the animal types known to you.
What is the notochord, and how is it developed in the frog?
2. Describe the early stages in the development of the egg of the fowl
as far as the closure of the neural groove. How do you account for
the primitive streak?
3. Describe the cleavage and the surface appearances of the egg of
the frog and of the rabbit, up to the time when the first gill-slits
appear in the embryo. Give illustrative diagrams of what you
describe.
4. Describe the structure and cleavage of the ovum (a) of the frog, (b)
of the fowl, and (c) of the rabbit. (d) Explain as far as possible the
differences in the cleavage of these three eggs. (e) Point out how the
embryo is nourished in each case, and (f) describe the constitution of
the placenta in the rabbit.
5. (a) What are the protovertebrae? (b) How does the notochord
originate in the frog? (c) How are the vertebrae laid down in the
tadpole? (d) Describe the vertebral column of the adult frog. (e) In what
important respects do the centra of the vertebrae of the frog, the
dog-fish, and the rabbit differ from one another?
6. Give an account of the more important features in the development
of the frog.
7. What temporary organs are developed in the embryo frog which are
absent from the embryo bird and mammal, and what in the two latter
which are absent from the former?
8. Draw diagrams, with the parts named, of the heart and great
arteries of the frog, giving descriptions only in so far as is necessary
to explain your diagrams; trace the development of these structures in
the tadpole; point out particularly in which of the embryonic visceral
(branchial) arches the great arteries of the adult run.
9. Trace the history of the post-oral gill-slits and their accompanying
cartilaginous bars and vascular arches in the frog, fowl, and rabbit.
10. Give a short account, with illustrative figures, of the mode of
formation of the primary germinal layers in amphioxus and in the frog.
What explanation can you give of the differences between the two
cases?
11. Give a short account, with diagrammatic figures, of the principal
changes which occur in the circulatory and respiratory organs during
the metamorphosis of the tadpole into the frog.
12. How do protozoa differ from higher animals (metazoa) as regards
(a) structure, (b) reproduction? Compare the process of fission in an
amoeba with the segmentation of the ovum in amphioxus, pointing out
the resemblances and differences between the two cases.
-Miscellaneous Questions_
[Most of these questions were actually set at the Biological
Examinations of London University.] {In Both Editions.}
1. Describe (a) the digestive, (b) the circulatory, (c) the excretory, and
(d) the reproductive organs of the amphioxus.
2. Describe the stomach and intestines of the dog-fish and rabbit, and
point out in what way their differences are connected with diet.
3. Describe the mechanism of respiration in the adult frog, and
contrast it with that of the tadpole.
4. Give an account of the structure of the epidermis and its
outgrowths in the frog and the rabbit.
5. Describe the organs of circulation (heart and main arteries and
veins) and respiration in the frog in its mature and immature states.
6. Give a brief account of the physiology of respiration. Describe fully
the means by which respiration is effected in the following animals:--
frog, amphioxus, rabbit, and dog-fish.
7. Describe the minute structure of the blood of the rabbit, frog, and
amphioxus.
8. Describe and illustrate by means of sketches the chief points of
difference between the skeleton of the rabbit as a typical mammal,
and that of the common frog as a typical amphibian.
9. (a) Explain what is meant by the term "central nervous system."
(b) Describe the tissue elements which enter into its composition.
(c) Explain, as far as you can, the function of each structure
described. (d) How is the central nervous system developed in the
frog, and (e) in the rabbit? (f) What conclusions may be drawn from
the facts stated as to the origin of the central nervous system in
evolution?
10. Give an account of the structure (including histology) and of the
functions of the spinal cord and spinal nerves of the frog.
11. Give a description of the minute structure and chemical
characters of the following tissues as seen in the frog:-- cartilage,
bone, muscle. From which of the primary cell-layers of the embryo are
they respectively developed?
12. What substance is excreted by the renal organ of a frog, and what
relation does this substance bear to the general life of the organism?
Describe the parts by which similar excretion is believed to be
effected in amoeba, hydra, earthworm, mussel, and lobster.
13. Describe, with illustrative sketches, the structure of the connective
tissue, cartilage, and muscular tissue of a frog. Also describe the
structure of the muscular tissue of the lobster and snail.
14. Give in account of the more important features in the
development of the frog.
15. Describe and compare the structure of the renal organs in a frog
and a rabbit.
16. Give an account of the structure of the genito-urinary organs of the
frog. Compare these organs of the frog with those of the dog-fish and
of the rabbit. Distinguish in each case the conditions of the two
sexes, and describe briefly the microscopic structure and
development of the ova and of the spermatozoa.
17. Describe, with diagrams, the arrangement of the urinary and
generative organs in the male of (a) the rabbit, (b) the dog-fish, and
(c) the frog; (d) point out the most important differences between
them.
18. (a) Describe the structure of the ovarian egg of the rabbit, (b) and
of the pigeon, (c) and of the frog; (d) from what part of the embryo do
they originate? (e) What is the structure and origin of the ovarian
follicle in the rabbit, and (f) of the ovarian stroma? (g) What is the
"granulosa" and what the "zona pellucida"?
19. Describe the pre-segmentation changes, mode of impregnation,
and early stages of development in the ovum of the frog, as far as the
closure of the neural canal.
20. Illustrate, with diagrams, from the structure of typical organisms,
the principle of repetition of similar parts.
-Note on Making Comparisons_
Students preparing for examinations are frequently troubled by
"comparison" questions. Tabulation is often recommended, but we are
inclined to favour a rather more flexible plan of marking off differences
and resemblances. In tabulation a considerable loss of time is
occasioned by writing down the features of both the things compared,
and this is a serious consideration for the examinee. We advise him
therefore, first, if he possibly can, to draw side by side and in
corresponding positions the two things under consideration, and then,
going over them in a methodical way, to state simply the difference
between each homologous part. We append as examples three test
answers actually submitted (with figures) in "Correspondence" work:--
1. Compare the brain of the frog with that of the rabbit.
In the frog's fore-brain--
The olfactory lobes are fused in the middle line.
There is no corpus callosum, nor is there a middle commissure to
the third ventricle.
The cerebral hemispheres are not convoluted, and, looked at from
the dorsal aspect, do not hide the thalamencephalon and mid-brain.
The pineal gland lies in the cranial wall and not deeply between
the hemispheres, and its stalk is longer and tilts forward.
In the mid-brain--
The optic lobes are two, instead of being corpora quadrigemina,
and hollow.
In the hind-brain--
The cerebellum is a very small transverse band, and has no
lateral parts.
The medulla is relatively larger.
There are no spinal accessory nor hypoglossal nerves to the
brain.
2. Compare the vertebrae of dog-fish, rabbit, and frog.
The centra of the dog-fish are -opistho- [amphi]-coelous
(i.e., hollow at either end).
The centra of the rabbit are flat-faced.
The centra of the frog are procoelous (hollow in front).
The notochord persists between the centra in the dog-fish and
rabbit, within the centra in frog.
The centra of the rabbit have epiphyses, absent in the dogfish
and frog.
The transverse processes of the rabbit typically bear ribs.
Short ribs occur in the dog-fish, but their homology with those
of the rabbit is doubtful. The frog has no ribs.
The interneural plates are peculiar to the dog-fish in this
comparison.
3. Compare the skull of the dog with that of the frog.
The Brain Case--
Of the frog is a cylindrical box, from which the otic capsules
project conspicuously on either side. It contains only two
ossifications in its cartilaginous substance (the sphen-ethmoid
and the ex-occipital), being protected by the membrane bones,
the parieto-frontals above and the parasphenoid below.
In the mammal it is enormously inflated, and the otic capsules
are imbedded in its wall. There are supra- and basi- as well as
ex-occipital bones; the para-sphenoid is (? entirely) gone, and
its place is taken by the basi- and pre-sphenoids, and the
lateral walls contain fresh paired ossifications, the ali- and
orbito-sphenoids-- all cartilage bones. The sphenethmoid is
perhaps represented in part by the ethmoid.
As a result of the inflation of the brain-case, the squamosal,
which slopes downward and outward in the frog, and overlies the
cartilaginous suspensorium (quadrate cartilage), has become a
constituent of the brain-case wall, and slopes downwardly and in.
Jaw Suspension--
The point of attachment of the jaw has shifted outward, and the
original suspensorial cartilage (the quadrate) has taken on a new
and minor function as the incus of the middle ear-- the squamosal
superseding it as the suspensory part.
Lower Jaw--
Distinct bones in the frog; one mass in the dog.
Otic Capsule--
Position as specified. One centre of ossification in the frog
forming pro-otic; several fuse together and form periotic of the
dog.
There is no bulla and no external ear in the frog.
Palate--
In the frog the posterior nares open into the front of the mouth.
In the dog the maxillae and palatines send plates down and in (the
palatine plates) to cut off a nasal passage from the rest of the
buccal chamber, and carry the posterior nares back to the pharynx,
thus cutting the vomers off from the mouth roof.
The pterygoids in the dog are much reduced, and do not reach back
to the suspensorium.
The frog has no lachrymal bone.
-Syllabus Of Practical Work_
We would impress upon the student at the outset the importance of
some preliminary reading before dissection is undertaken. No one
would dream of attempting to explore a deserted city without some
previous study of maps and guide-books, but we find again and again
students undertaking to explore the complicated anatomy of a
vertebrated animal without the slightest, or only the slightest,
preparatory reading. This is entirely a mistake. A student should be
familiar with the nomenclature of the structures he contemplates
examining, he should have some idea of their mutual relations and
functions, or his attention will inevitably be diverted by the difficulty
of new names and physiological questionings to the neglect of his
dissection, and that careful observation of form and mutual position
which is the essential object of dissection. On the other hand, it is
equally necessary-- perhaps more so-- to warn students against the
bookish fallacy, and to assure them of the absolute impossibility of
realizing biological facts from reading alone. Practical work can alone
confirm and complete the knowledge to which the text-book is the
guide. In scientific teaching it may sometimes be convenient for the
thought to precede the thing, but until the thing has been dealt with
the knowledge gained is an unsatisfactory and unstable possession.
For such dissection as the subject-matter of this book requires, the
following appliances will be needed:--
(a) Two or three scalpels of various sizes.
(b) Scissors, which must taper gradually, have straight blades, and
be pointed at the ends, and which must bite right up to the tips (or
they are useless). Two pairs, small and large, are advisable.
(c) Forceps, which must hold firmly, and meet truly at the points.
(d) Two needles set in wooden handles.
(e) An ordinary watchmaker's eye-glass is very helpful, but not
indispensable.
(f) A dissecting dish-- an ordinary pie dish will do-- into which
melted paraffin wax has been poured, to the depth of, say,
three-quarters of an inch, and allowed to solidify. (This wax may
be blackened by mixture with lampblack. If the wax floats up at any
time, it can, of course, be remelted. Or it may be loaded with
lead.)
(g) A rough table or board (for the rabbit and dog-fish).
(h) Blanket pins, and ordinary pins.
(i) A pickle or other wide-mouthed jar, and some common, methylated
spirit.
(j) A microscope, with low power of 1 inch or 1/2 inch, and high
power 1/6 inch or 1/4 inch. Glass slips and cover glasses, and a
bottle of very weak (1 per cent.) solution of salt.
Animals for dissection may be obtained from the recognised dealers,
who usually advertise in such scientific periodicals as Nature,
Natural Science, and Knowledge. Sinel (naturalist, Jersey) is the most
satisfactory dealer in dog-fish in our experience; Bolton (Malvern) will
supply Amphioxus through the post; frogs and rabbits may be
obtained anywhere. The tame variety of rabbit is quite satisfactory for
the purpose of dissection.
The following notes may possibly be of some use to the student; they
follow the lines of work arranged by the author for the evening classes
of the University Tutorial College, classes considerably restricted as
regards time, when compared with ordinary laboratory workers. Most
of the sections below occupied about three hours, but for a student
working alone they are more likely to take four or five, and even then it
is not probable that they will be so satisfactory as if performed under
skilled supervision. There are many points extremely difficult to
convey verbally which are elucidated at once by actual demonstration
upon a specimen. Each of these dissections should be repeated, and
it is well if a different condition of the type is selected for the
repetition-- an old one if the first specimen was immature, a female if
the first was a male.
-The Rabbit_
May be killed by chloroform, or potassium cyanide, or drowned. It
may also be readily suffocated with house-hold gas. It should be killed
immediately before use, as otherwise the gastric juice attacks the
wall of the stomach, and the dissection is, in consequence, rendered
extremely disagreeable. A very young rabbit is unsatisfactory as
regards the genitalia, but otherwise there is no objection to a little
one, and it has this advantage-- that it may be immersed more
conveniently under water, in a large pie dish, for purposes of fine
dissection. The external features of the animal should be examined:
eyelids, whiskers and teeth, toes, anus, perineal space on either side
of the same, urogenital opening, and position of the ribs, vertebral
column, and limb girdles beneath the skin should be made out. Then
the animal should be pinned out through the legs, the ventral surface
uppermost, the skin opened up along the middle line from pelvic girdle
to symphyses of jaw; separated from the body wall below by means
of the handle of a scalpel, and turned back; and then the abdominal
wall should be cut into and two flaps pinned back to expose its
contents. Note the xiphisternum. The caecum and colon will be
recognised (Section 16); the stomach, the right and left central, and
left lateral lobes of the liver will probably be apparent; and the urinary
bladder (especially if distended) in the middle line behind. Without any
further dissection, but simply by turning the parts over, all the
structures of the abdomen in Figure 1, Sheet 1, will be identified.
Seek especially for and note particularly, the gall bladder, bile duct,
and portal vein, pancreatic duct, sacculus rotundus, vermiform
appendix, ureters (by pulling urinary bladder forward), genital ducts
(looping over ureters), spleen, kidneys, and adrenals. The vena cava
inferior is seen dorsally. The genital duct guides the student to the
genital gland; if the subject is a male, the testes may be exposed by
dissection, or by pulling the vas deferens gently the scrotal sac will be
turned inside out, and the testes brought into view. The ovary lies
exposed without dissection posterior to the kidney. Examine all this
carefully, and make small sketches of points of interest-- the duodenal
loop and the pyloric end of the stomach, for instance; the meeting of
colon, caecum, and sacculus rotundus again; or the urinary bladder
and adjacent parts. Note the dorsal aorta and vena cava and their
connexions behind. (Compare figure of circulation.) Cut through pelvic
girdle, and remove one hind leg, to see bladder and genital ducts
better (compare Sheet 10). Wash away any blood that may flow. Turn
all the intestines over to the animal's right, and see the dorsal aorta
and vena cava inferior of the abdomen, the inferior mesenteric artery,
and the spermatic (or ovarian) artery (compare, of course, with figure
in book). In front, immediately dorsal to the spleen, is a variable
quantity of lymphoidal tissue, which must be very carefully cleared to
see the superior mesenteric and coeliac arteries. Separate Spigelian
lobe from stomach, and look for vagus nerve descending by
oesophagus, solar plexus around the superior mesenteric artery, and
thrown up very distinctly by the purple vena cava inferior beneath, and
the splanchnic nerve. To see the abdominal sympathetic behind,
gently remove the peritoneum that lies on either side of the aorta;
blood-vessels will be seen running in between the vertebral bodies,
and the sympathetic chain, with its ganglia, made out very distinctly,
as it runs across them longitudinally. Now cut oesophagus just in
front of stomach, and cut the rectum, cut through the mesentery
supporting the intestine, and remove and unravel alimentary canal; cut
open, wash out, and examine caecum and stomach. Bleeding to a
considerable extent is inevitable, chiefly from the portal vein. The liver
had better remain if the same rabbit is to serve for the second
dissection.
Second Dissection.-- Skin front of thorax and neck. Note subclavian
veins running out to fore limbs-- avoid cutting these. Cut through ribs
and remove front of thorax, to expose its contents; cut up middle line
of neck, and clear off small muscle bands, to expose bloodvessels;
pick away carefully whatever is left of thymus gland; make out
structure of heart and blood-vessels, as described, in Chapter 3; note
larynx and trachea. Now proceed to the examination of the nerves of
this region. See phrenic nerve, by vena cava inferior, and between
heart and lungs, and sympathetic, running over the heads of the ribs.
By the common carotids will be found the large white vagus nerve, the
greyish sympathetic, and a small branch of X., the depressor. Make
out branches of X. named in text. The big white cervical spinal nerves
will be evident dorsally. Clear forward into the angle between the jaw
and the bulla tympani, to see XII. and XI.; IX. will be found, lying
deeper, dorsal to the carotid artery and body of the hyoid. Compare
with figure given of this. Skin the cheek, and see VII. running over it.
Cut through malar and remove it; cut through lower jaw-bone and turn
it back, to see the third branch of the fifth nerve on its inner side;
examine the muscles of eyeball, and remove it, to expose the first
and second branches of V.-- the latter is especially deep within orbit.
Remove, open, wash out, and examine the heart. Shave off the dorsal
wall of cranium, to expose hemispheres of brain, and then put the
head in strong spirit for a week or so. With a second rabbit, this
dissection may advantageously be varied by removing the lower jaw,
cutting -up- [through] soft palate, and observing openings of the
Eustachian tubes. [The tonsils (on the ventral side of the soft palate)
must not confused with these.] The heart should also be cut out,
washed out and examined (Compare Sections 38, 44.)
Third Dissection.-- (Before this is performed the mammalian skull
should have been studied and examined.) Take the head of a rabbit,
the brain of which has been hardened by spirit, and carefully remove
cranium; be particularly careful in picking away the periotic bone, on
account of the flocculi of cerebellum. It is difficult to avoid injury to
the pituitary body embedded in the basisphenoid bone. Examine with
the help of Sheet 8. Make the sections there indicated.
-The Frog_
May be killed by drowning in dilute methylated spirit, or by chloroform.
Take a recently-killed frog, and examine a drop of its blood, spread
out on a glass slip, under the microscope; compare it with your own.
Before using the high power, put a cover glass over the object, of
course. Scrape the roof of the mouth of the frog gently, to obtain
ciliated epithelium; and mount in very weak salt solution-- the cilia will
still be active. Squamous epithelium may be seen by the student
similarly scraping the interior of his own cheek. Take a piece of
muscle from one of the frog's limbs, tease out with needles upon a
glass slip, and examine. To see the striations clearly, the high power
will be needed. Compare a piece of muscle from the wall of the
alimentary canal. Similarly examine nerve and connective tissue.
First Dissection.-- Pin out the frog in a dissecting dish, ventral surface
uppermost, and cover with water. Open up the skin along the
mid-ventral line. Note the large sub-cutaneous lymph spaces, the
pelvic and pectoral girdles, and the anterior abdominal vein. Cut into
the body cavity on one side of this latter, cut across in front of where
the vein dips down to liver, and peel the body wall away from it. The
xiphisternum will probably be cut in this operation. In early spring the
females are greatly distended with ova, and the greater portion of the
ovary may, with advantage, be removed. The oviduct is dead white
then, and larger and much more in evidence than the (pinkish)
intestine even. Turn over the viscera, and compare with Sheet 11;
one lung is often found greatly inflated, and then projects back into
the body cavity; the stomach is, in some cases, pushed forward and
hidden behind the shoulder girdle. Observe the allantoic bladder, the
spleen, gall bladder, portal vein, and pancreas. By squeezing the gall
bladder gently, the bile duct will be injected with bile, and will be
apparent if the stomach is turned over. The oesophagus, just in front
of the stomach, should be cut through, and the rectum, and the
mesentery and alimentary canal supported by it, removed. This will
expose the urogenital organs. (Vide Figures given.) These vary
greatly, especially in the females, at different seasons. The condition
figured would be seen in late autumn, or winter. In spring females are
often found copulating with males, and then the ovary itself is
inconspicuous, while the lower part of the oviduct is enormously
distended with ova, so as to be mistaken sometimes for the ovary
by those who fail to note that the ova are enclosed by a thin
semi-transparent skin (wall of oviduct). The vena cava inferior is
seen between the kidneys and the renal portal vein beside the ureter.
Cutting through the mesentery supporting the kidney laterally, the
dorsal aorta is exposed, and on either side of it the sympathetic chain
and rami communicantes, often tinged with black pigment.
This black pigment is a frequent but variable feature of the frog's
anatomy, and usually dapples or blackens the testes, and also
sometimes darkens the otherwise pale pink arteries. Behind the
kidneys the sciatic plexus also becomes visible. Careful drawings
should be made. Cut off the head of the frog, shave off top of brain
case, and put the head in strong spirit.
Second Dissection.-- A fresh frog is required. Pin out under water as
before, and open up body cavity. Now carefully remove the muscle
from the ventral portion of the shoulder girdle, to expose the clavicles
and coracoids. Cut away xiphisternum, and then cut through clavicles
and coracoids on either side, and remove ventral part of shoulder
girdle, to expose the heart. Open out the cut portions of body wall and
pin. The veins going towards the heart should now, with a little
examination, be evident. Make out the external jugular, the
innominate, and its two branches, and the pulmo-cutaneous and vena
cava superior. Clear by carefully picking away any shreds of
semi-transparent tissue. Make out, by feeling, the position of the
hyoid body, and of its anterior cornua. Note the hypoglossal nerve
(first spinal) running ventral to this, and the ninth cranial nerve,
running parallel to it but dorsal to the hyoid-- hidden therefore by
the hyoid, and reappearing in front. The vagus may also be made out less
distinctly, running "postero-ventrally" towards the heart. By clearing
the muscle by the rumus of the jaw, VII. may be seen, and the third
branch of V., running across the jaw at about the middle of its length.
Pick off the thin transparent pericardium from the heart very carefully,
and proceed to cut away all the veins made out. The truncus
arteriosus may then be followed up as it branches. Note all the
branches shown in the figures in this book. The precise position of the
vessels will vary to a certain extent with the attitude in which the frog
is pinned. The cutaneous artery will prevent the student following up
the aortic arch until it is cut; then the arch may be followed round until
it meets its fellow to form the dorsal aorta. Note the sympathetic
again. Make careful drawings of all this. Cut off lower jaw, and note
posterior nares and Eustachian openings. If time allows, remove the
heart, and examine by cutting open and washing. (Compare, Section
44) Remove eyeball, to see the first and second branches of the fifth
nerve, and the Vidian (i.e. palatial) branch of the seventh.
Third Dissection.-- Read the account of the frog's skull carefully.
Take the head of a recently killed frog and drop into boiling water for
a minute. Then pick off, very carefully, muscle, connective tissue,
nerves, and etc., to clear the cranio-facial apparatus; examine the
bones, compare with figures given in this book, and draw. Take the
head, which has been in spirit a fortnight or so, pick away cranium,
and compare brain with figures given. Examine ventricles, by taking
sections, after drawings have been made.
-The Dog-Fish-
First Dissection.-- Examine external characters, nasal grooves-- no
internal nares-- fins, spiracle, scales passing over lips, and cloaca.
Cut off tail below the cloacal opening. The males are distinguished by
the large claspers along the inner edge of the pelvic fin. Open up body
cavity. Usually this is in a terrible mess in the fish supplied by
dealers, through the post-mortem digestion of the stomach. Wash out
all this under a stream of water from a tap or water-bottle. Frequently
the testes are washed out of the male in this operation and ova from
the loose ovaries in the female. Now compare with figure given in this
book, allowing for the collapse of the stomach, if it has occurred. Cut
through the oesophagus and rectum, and remove alimentary canal
from body; cut open and wash out the intestine, and examine spiral
valve. Now make a careful examination of the cloaca and its
apertures, and dissect away the peritoneum hiding the kidney. In the
female find the opening of the oviducts in front of the liver. Remove
liver, and cut off body now behind pectoral fin. Before throwing tail and
hinder part of body away, note the myotomes of body wall, the
notochord and vertebral body, neural canal, and, in the tail, the
haemal canal. [(See {Section 9 the Dog-fish})]
{Lines from First Edition only.}
-The relation of the vertebral bodies to the notochord may be very
well seen by taking successive slices, about one-tenth of an inch
thick, through the vertebral body. The cartilage is hard and
semi-transparent, the notochord jelly-like, least at the centres
of the centra, and at a maximum intervertebrally.-
[The notochord is a soft jelly.] Cut away the ventral part of the pectoral
girdle, to open pericardium. With a seeker, make out the pericardio
peritoneal opening. Cut into the sinus venous, and run seekers into
the Cuvierian and hepatic sinuses. [Cut open the Cuvierian and
posterior cardinal sinuses, and run seekers into their affluents.]
Dissect along the truncus arteriosus to afferent branchials. [Cut away
the heart and oesophagus; run a seeker up the dorsal aorta and cut
along it from the ventral side to subclavian and efferent branchial
arteries.] Skin the top of the head. Note, while doing this, the yellow,
jelly-like sense-tubuli beneath the skin. Shave off top of brain-case,
and leave the head in spirit for a week or so.
Second Dissection.-- Place the head with the ventral side downward,
skin all the dorsal surface as yet unskinned. Refer to book for
precise position of the anterior cardinal sinus, and then cut down
through body wall into this just over gill slits. The tenth nerve will
become visible, with its "slit" branches athwart the floor of the sinus.
Clear to make this more evident, and make out its lateral line and
visceral branches, and the ninth nerve.
{Lines from Second Edition only.}
[The pharyngo-branchials may be felt beneath the sinus. Run a
seeker from the dorsal aorta to the efferent branchials.]
Proceed now to orbit, and, without any dissection beyond the removal
of skin, make out recti and oblique muscles of eyeball, and the optic,
third and fourth nerves. Cut through these structures carefully and
remove, exposing nerves seven, and five, as described and figured in
the text. Examine the otic capsule by taking successive slices
through it to show the labyrinth of the ear. -Remove the dorsal wall of
the skull to obtain a dorsal view of brain. If this is sufficiently hard,
examine it; if not, return it to spirit for a more convenient occasion.-
[Examine brain.]
-Amphioxus_
Two specimens of this type should be obtained. It should be
examined entire by the naked eye and with the low power of the
microscope. Immersion, in glycerine will render it more transparent; or
it may be cleared with oil of cloves, put up temporarily in that, or
permanently in Canada balsam. One specimen should then be pinned
out in the dissecting dish, ventral side uppermost, and the atrium
opened to expose liver and pharynx. A part of the pharynx may be
examined with the low power to see the form of the gill slits. The
second specimen should be soaked in turpentine for some time, and
then dropped into melted paraffin wax. Transverse sections may then
be cut with a razor, the paraffin wax removed from these by solution in
turpentine, the turpentine in its turn dissolved out by alcohol, and the
sections, after immersion in oil of cloves, may be transferred to
Canada balsam for examination and preservation. This work should
not be attempted until some practical histological work has been done
in botany, and it may be altogether avoided by the purchase of
stained and mounted sections.
-Development_
Laboratory work in this portion of the science is not usually
undertaken by elementary students of biology, but the reader will
probably find it helpful, in the realization of the facts given in this
book, to look out for frog spawn, in February and March, and to catch
and examine tadpoles of various sizes. A small dissecting dish may be
made by pouring melted paraffin wax into one of those shallow china
pots chemists use for cold-cream, and tadpoles may be pinned out
with entemologists' pins and dissected with needles. But this is a
work of supererogation. Partially incubated hen's eggs may be
obtained at a small cost almost anywhere, and the later stages
profitably examined and dissected under warm water. For a clear
understanding of the allantois and amnion, this last is almost
indispensable. A few microscopic slides of sections of embryonic
chicks should also be compared with our rough diagrams.
-{Key for Dissection Sheets, and Abbreviations.}_
Sheet 1
Figure 1. Main facts of the Rabbit's Anatomy (diagrammatic).
an., anus.
a.ao., arch of the aorta.
au., auricle.
a.r., ad-renal body.
br., brain.
b.d., bile duct.
brch., bronchus.
cd.st., cardiac end of stomach.
co., colon.
cae., caecum.
ddnm., duodenum.
d.ao., dorsal aorta.
dia., diaphragm.
ep., epiglottis.
g.d., genital duct (either sex).
il., ileum.
in.art., innominate artery.
k., kidney.
lg., lung.
lv., liver.
l., larynx.
l.s.c., [l.c.c.] left common carotid artery.
m., mouth.
na., nasal passage.
oes., oesophagus.
p.v., pyloric valve.
p.d., pancreatic duct.
pt., peritoneal cavity.
r., rectum.
st., stomach.
[stm., sternum.]
s.r., sacculus rotundus.
s.c., spinal cord.
tr., trachea.
ur., ureter.
ur.b., urinary bladder.
v.b., a vertebral body.
v.ap., vermiform appendix.
v.v., [v.p.] velum palatium.
v., ventricle of heart.
v.c.i., vena cava inferior.
Figure 2. The Liver (diagrammatic).
g.b., the gall bladder.
r.l., r.c., l.l.., l.c., right lateral and central, and left lateral and
central, lobes respectively.
sp., the Spigelian lobe (fits into angle of stomach and oesophagus).
{Illustration: Diagram Sheet 1.}
Sheet 2
Figure 1. The Rabbit's Circulation (see footnote to Section 45).
(Throughout l. indicates left, r. right. Vessels without r. or l. prefixed
are median.)
-[* The figure is inaccurate at one point; l.c.c. should spring from the
base of inn. See Sheet 9.]- {First Edition only text}
ao.a., aortic arch.
au., auricle.
az.v., (p.c. in Figure 2), azygos vein.
c.c., common carotid.
c.il.a., common iliac artery.
coe.a., coeliac artery.
d.ao., dorsal aorta.
e.il.v., external iliac vein.
e.ju., external jugular vein.
f., femoral artery.
h.v., hepatic vein.
inn., innominate artery.
in.j., internal jugular vein.
i.il.a., internal iliac artery.
i.il.v., internal iliac vein.
k., kidney.
lv., liver.
l.g.v., lienogastric vein (portal).
m.v., mesenteric (portal system).
p.m.a., posterior mesenteric artery.
p.v., main portal vein.
p.a. pulmonary artery.
r., rectum.
r.a., renal artery.
r.v., renal vein.
s.v., and a., spermatic (or ovarian) vein and artery (to genital
organ).
s.mes.a., superior mesenteric artery.
s.-cl.a., subclavian artery.
s.-cl.v., subclavian vein.
v.c.s., vena cava superior.
v.c.i., vena cava inferior.
v. or vn., ventricle.
Figure 2. Figure of Circulation (simplified) illustrating certain points in
development to be referred to later.
Figure 3. Respiration. See text, Section 41.
Figure 4. Blood. See text, Section 35.
{Illustration: Diagram Sheet 2.}
Sheet 3
Histological Figures, 1.
{No numbers I., or II.}
Figure III. An amoeba.--
n., nucleus.
ns., necleolus.
c.v., contractile vacuole.
Figure IV. Embryonic tissue from the blastoderm of a chick.
Figure V. Columnar epithelium.--
g.c.1, g.c.2, g.c.3, successive phases in the development of a goblet
cell.
Figure VI.
g.end., is geminating endothelium; the cells divide and apparently
drop off to become white corpuscles in the lymph current.
sq.end., squamous endothelium from the mesentery.
sq.ep., squamous epithelium (from the mucous membrane within the
cheek).
st., are opening (stomata) communicating between the lymphatics in
the mesentery and the peritoneal (coelomic) space.
Figure VII. Ciliated epithelium from the roof of the frog's mouth.
Figure VIII. Forms of glands.--
g.ep., is a gastric gland from the stomach; trs., below, is cross
section. This is one of the simplest types of gland.
s.g., a sweat gland, is also a simple tube, but convoluted below.
r.g., is a racemose gland, such as the pancreas, Brunner's or the
salivary glands.
The kidney, we shall see later, is simply an aggregate of branching
tubuli (Sheet 7).
Figure IX. A duodenal villus.--
lac., the lacteal.
v., the vein.
Figure X.a. Diagram of liver structure.--
b.d., the inter-lobular bile duct.
h.a., the hepatic artery, bringing blood to oxygenate and nourish the
liver tissue, and similarly distributed.
h.v., the hepatic vein taking blood from the liver to the heart, its twigs
commencing in the lobuli (intra-lobular).
lb. lb., lobuli.
p.v., the portal vein bringing blood, from which substances are to
be elaborated, into the liver, and breaking up between the lobuli
(inter-lobular).
Figure X.b. A diagram of the appearance of an injected liver lobule as
seen in section under the microscope.
{Illustration: Diagram Sheet 3.}
Sheet 4
Histological Diagrams, 2.
Figure XI. A blood capillary. White corpuscles are migrating through
the walls into the tissues (compare Section 66).
Figure XII. Hyaline cartilage (Section 64).
Figure XIII.
c.c., connective tissue corpuscle.
w.i.f., white inelastic fibres.
y.e.f., yellow elastic fibres.
Figure XIV. Botryoidal tissue (Section 66).
Figure XV. Development of a fat drop.--
f.d., fat drop, in a connective tissue corpuscle; c.c., in the formation of
adipose tissue (Section 67).
Figure XVI. Diagrammic cross section of a long bone.--
b.c., bone corpuscle in a lacuna.
H.v., Haversian vessel (in the Haversian canal) surrounded by
concentric lamellae of bone, c.l., and together with these and zones
of bone corpuscles, called a Haversian system.
i.l., inner lamellae.
m.c., medullary canal full of yellow marrow.
o.l., outer lamellae.
p.o., periosteum.
Figure XVII. To illustrate bone development (Section 71).
Figure XVIII. Dentition of rabbit, incisors 2/1, canine 0/0, premolar 3/2,
molar 3/3.
{Illustration: Diagram Sheet 4.}
Sheet 5.
Diagram of the Rabbit's Bones.
To be compared with the real things.
D and D' show the fore and hind limbs, to illustrate their homology.
D is in the embryonic position. The radius and tibia are, at an early
stage in development, on the anterior edge of their respective limbs;
the ulna and fibula, posterior; the former are spoken of as preaxial in
position, the latter as postaxial. But in the adult the humerus is
twisted so that the proximal end of the radius lies at the outer side of
the elbow, whence it crosses the ulna, so that its distal end is
inside, while the femur is also twisted round, so that the entire tibia
is internal.
Figures 1 and 2. -Limbs.--
a.c., acetabulum.
acr., acromion.
as., astragulus.
c., carpus.
ca., calcaneum.
co., coracoid.
[coty., cotyloid bone.]
fb., fibula.
fe., femur.
g., glenoid cavity (for head of humerus).
hd., head of femur.
hum., humerus.
i., ilium.
is., ischium.
m.c., meta-carpals.
na., navicular.
o., olecranon process of ulna.
o.f., olfactory fossa.
pb., pubis.
r., radius.
u., ulna.
Figure 3. -Sternum.--
Mb., manubrium.
r1., r2., and etc., sternal ribs.
st., sternebrae.
xi., Xiphisternum.
Figure 4. Vertebrae.--
At., Atlas.
Ax., axis.
c., [b.] centrum.
C.V., caudal vertebra.
c.v., [Cer.V.] cervical vertebra.
ep., epiphysis.
f.r., fused rib (in cervical vertebrae).
L.V., Lumbar vertebra.
m., metapophysis (of lumbar vertebra).
n.a., neural arch.
n.s., neural spine.
r., rib.
S.V., sacral vertebra.
[T.V., Thoracic.]
tr.p., transverse process.
v.a.c., vertebrarterial canal.
z., zygapophysis.
{Illustration: Diagram Sheet 5.}
Sheet 6.
The Skull of Canis.*--
1. Dorsal. 2. Ventral. 3. Right Lateral Aspect. 4. Section a little to the
left of the nasal septum. 5. Lower jaw (smaller) 6. Hyoid apparatus.
{Lines from First Edition only.}
-*A Fox in this case. The skull is quite like that of a Dog, but it has
the advantage of more distinct sutures between the bones.-
a.n., anterior nares.
a.s., ali-sphenoid.
b.h., body of the hyoid.
b.o., basi-occipital.
b.sp., basi-sphenoid.
c., condyle of the skull.
{c.1, c.4, canines.}
c.f., condylar foramen (for XII.).
c.h., cerato-hyal.
E.f., Eustachian foramen.
e.h., epihal.
-e.n., or a.n., the anterior nares.-
e.o., exoccipital.
eth., ethmoid.
e.t., ethmo-turbinal.
f., frontal.
f.l.a., foramen lacerum anterius.
f.l.m., foramen lacerum medium.
f.l.p., foramen lacerum posterius (for IX., X., XI.).
F.M., or f.m., foramen magnum.
f.o., foramen ovale.
f.r., foramen rotundum.
{i., incisors.}
ju., jugal.
m., molars.
m.t., maxillo-turbinal.
mx., maxilla.
na., nasal.
n.t., nasal turbinal.
o.f., optic foramen.
o.s., orbito-sphenoid.
p., or pal., palatine.
pa., parietal.
p.m., pre-maxilla.
p.m.1, p.m.4, premolars.
p.n., posterior nares.
p.sp., pre-sphenoid.
pt., pterygoid.
s.h., stylo-hyal.
s.m.f., stylo-mastoid foramen (for VII.).
s.o., supra-occipital.
sq., squamosal.
s.t., sectorial tooth.
t.h. thyro-hyal.
vo., -black line indicating position of- vomer.
z.p., zygomatic process of squamosal.
{Illustration: Diagram Sheet 6.}
Sheet 7
Figure 1. Striated muscle fibre (of the Rabbit), ruptured to show
sarcolemma.
e.p., its end plate.
K.m., membrane of Krause.
n., nucleus.
nv., nerve.
sc., sarcolemma.
s.e., sarcous elements.
Figure 2. Cardiac muscle.
Figure 3. Unstriated muscle fibres.
Figure 4. Diagram of the Skin.
b.v., blood vessel.
d., areolar tissue of the dermis (mesoblastic).
s.c., stratum corneum, and s.m., stratum mucosum of the
epidermis.
s.g., sweat gland.
t.c., tactile corpuscle.
Figure 5. To illustrate Kidney structure.--
a.b.v., and e.b.v., afferent and efferent blood-vessels, of which the
latter go to break up upon the tubli.
B.c., one of Bowman's capsules of the cortex;
ur.t., the uriniferous tubule running from it into the medulla, where
it loops and branches; around it branches a blood-vessel, of which the
latter go to break up upon the tubuli.
c., cortex.
g., glomerulus, a knot of blood-vessels in the capsule.
m., medulla.
p., pelvis.
ur., ureter.
The water of the urine is probably filtered off in the capsule, the urea
and other salts secreted by the tubuli.
{No Figure 6.}
Figure 7. The Auditory structures of the Rabbit (diagram). See text,
Section 115.
Figure 8. The Eye (diagram). See text, Section 111.
Figure 9. The Retina (diagram). See text, Section 112.
{Illustration: Diagram Sheet 7.}
Sheet 8
The Brain of the Rabbit.--
1. In median section. 2. From above, with the top of the right
hemisphere sliced off horizontally at the level of the corpus callosum.
3. A deeper section through the thalamencephalon, corresponding to
B in (1). 4. Under-view of the brain. 5. Diagram referred to in the text
and for comparison with Sheet 7, 3b., and Sheet 18, 2.
{Figures 1-5.}
ar., arrow in the iter.
a.c., the anterior commissure, a thickening of the anterior wall of the
third ventricle.
c.c., corpus callosum.
c. cb., crura cerebri.
c.h., cerebral hemispheres.
c.q., corpora quadrigemina.
f.cbm. (right), flocculus of the cerebellum.
l.h., left cerebral hemisphere (=ch.).
l.l., lateral lobe of cerebellum.
m.c., middle commissure.
m.o., medulla oblongata.
op., optic nerve.
o.l., olfactory lobe.
o.th., (right), optic thalamus.
p.c., posterior commissure (thickening of postero-dorsal wall of the
third ventricle).
p.g., pineal gland.
pt., pituitary body.
p.V., pons Varolii.
s.c., thin roof of the fourth ventricle.
v.cbm., vermis of cerebrum.
v.l., lateral ventricle.
{Figure 4.} Nerves.--
I., Olfactory.
II., Optic.
III., Oculo-motor.
IV., Patheticus.
V., Trigeminal.
VI., Abducens.
VII., Facial (portio dura).
VIII., Auditory (portio mollis).
IX., Gustatory (glossopharyngeal.
X., Pneumogastric or vagus.
XI., Spinal Accessory.
XII., Hygoglossal.
Figure 6. The Spinal Cord in section.--
c.c., the central canal.
d.f., the dorsal fissure.
d.n., the dorsal nerve root; g., its ganglion.
v.f., the ventral fissure.
v.n., the ventral nerve root.
Note that in Figure 1 the central canal is continuous with the fourth
ventricle.
Figure 7. Histological elements.--
g.c., multipolar ganglion cell.
n., nucleus of a medullated nerve.
a.c., its axis fibre.
s.S., (sheath of Schwann), medullary sheath interrupted at intervals by
n.R., the nodes of Ranvier.
n.m.f., a non-medullated fibre.
{Illustration: Diagram Sheet 8.}
Sheet 9.
-The Nerves of the Rabbit_.
Figure I. Rough sketch of dissection of the neck from the left ventral
aspect.-- The bands of muscle between hyoid, mandible, and
sternum, and the thymus gland carefully cleared.
lr., is the larynx, and b., the balla.
s.m.g., the right sub-maxillary gland (the left has been removed).
The nerves are numbered.
l.r.l.n., [r.r.l.n.] is the left recurrent laryngeal looping under that
solid connection between the pulmonary artery (p.a.) and ao., the aortic
arch, which was an open tube in the embryo, the ductus arteriosus.
hy., is the hyoid with its posterior cornua.
ph.n., is the phrenic nerve.
r.r.l.n., [l.r.l.n.] is the right recurrent looping under the sub-clavian.
s.c.g., is the super or cervical ganglion of the sympathetic (sym.);
s.l.n., is the left superior laryngeal, and g. the left depressor
branch of x.
z., is the ramus descendens noni of the twelfth nerve.
In early development the heart lay just beneath the pharynx in the
position of the larynx (compare Dog-fish and Frog); as the neck
elongated, the heart shifted back with its vessels, and so the long
loop of the recurrent laryngeal comes to be drawn out in this singular
way.
Figure II. Diagram of orbit to show V.1 orbit-nasal, V.2 the maxillary,
and V.3 the mandibular branch of V. In order to show these in
dissection, the malar must be cut away, and the eye and glands of
the orbit removed.
s.r., e.r. [p.r.], i.r., and a.r., cut ends of the superior, external (or
posterior), inferior, and anterior (or internal) recti muscles.
s.o., and i.o., the superior and inferior obliques.
Figure III. General diagram of the Rabbit's cranial nerves.
Figure IV. Rough sketch of dissection of the nerves and
blood-vessels dorsal to stomach.--
The stomach turned over to the animal's right, the Spigelian liver lobe
cleared from the oesophagus, the mesentery supporting spleen and
hiding solar plexus picked off, and the mesentery hiding sympathetic
cleared.
coe.art., coeliac artery, and s.m.a., superior mesenteric artery.
coe.g. coeliac, and s.m.g., superior mesenteric ganglion. The two
together form the solar plexus.
l.abd.sym., left abdominal sympathetic (in the actual dissection, the
right would also be visible).
l.a.r., left adrenal.
l.sp.n., left splanchnic nerve.
r.art., renal artery.
r.v., renal vein.
st., the stomach, and sp., the spleen.
x., the vagus on oes., the oesophagus.
{Illustration: Diagram Sheet 9.}
Sheet 10.
-Reproductive Organs of the Rabbit_.
Figure 1. The Male.
Figure 2. The Female Organs. (The symbols below the figures
indicate the sex.)
pb., is the pubic symphysis [which has been] cut through.
R., the rectum, with r.g., the rectal gland, and a., the anus.
t., the tail.
r.ur., the right ureter.
l.ur., the left ureter.
ur.b., the urinary bladder.
In the Male
ep., the epididymis.
P., the penis.
pp., the prepuce.
scr., the scrotal sac, containing these;
r.v.d., the right vas deferens.
T., is the testis.
u.m., the uterus masculinus.
In the Female
c.ut, the left cornu uteri.
F.t., the left Fallopian tube.
ov., is the ovary, with a Graafian follicle, G.F.
V., the vagina.
v.b., the vestibule.
Figure 3. Diagram of ovary with stages in the development of a
Graafian follicle 1, 2, 3, 4, 5, see text, Section 137. The arrow
indicates the changes in position of the developing follicles.
{Illustration: Diagram Sheet 10.}
Sheet 11.
Figure 1. General dissection of Frog (male).
Figure 2. The heart and great vessels laid open.
Figure 3. The circulatory system from the side.
Figure 4. Blood.
{n., nucleus.}
r.c., red corpuscle (oval and nucleated).
w.c., white corpuscle
Small figure of Frog in left-hand corner is to show position
of heel, h.
Reference Letters.
all.b., allantoic bladder (= urinary bladder).
c.ad., corpus adiposum.
cl.c., cut end of the right clavicle.
d., duodenum.
g.b., gall bladder.
il., ileum.
k., kidney.
l.au., left auricle.
l.g., lung.
l.int., large intestine.
l.s.v., longitudino-spiral valve.
L.v., Liv., liver.
pan., pancreas.
r.au., right auricle.
sp., spleen.
st., stomach.
T., testis.
t.a., truncus arteriosus.
ur., urogenital duct.
v., ventricle of heart.
Arteries (white).
ao., aorta.
c.a., carotid arch.
c.g. [c.gl.], carotid gland.
coe., coeliac.
cu., -and pa.",- cutaneous.
d.ao., dorsal aorta.
e.c., lingual artery.
[i.c., internal carotid.]
l.a.a., left aortic arch.
pa., and p., pulmonary.
p.c. [p.cu.], pulmo-cutaneous.
r.a.a., right aortic arch.
[s.cl., sub-clavian.]
t.a., truncus arteriosus.
Veins of the Caval System -(black)-.
b.v., brachial (from fore limb).
e.j., external jugular.
h.v., hepatic vein.
i.j., internal jugular.
[in.v., innominate vein.]
l.v.c.s., left vena cava superior.
p.v., cutaneous vein.
[s.cl.v., sub-clavian vein]
s.s.r., sub-scapular vein.
v.c.i., vena cava inferior.
Veins of the Portal and Renal Portal Systems -(shaded)-.
a.ad., and a.ab.v., anterior abdominal vein.
b.v., and p.v., united are called the sub-clavian vein.
l.fm., left femoral.
l.p., left pelvic.
l.r.p., (and r.p.) left renal portal.
l.sc., left sciatic.
p.v., portal vein.
-(The anterior abdominal is coloured black in Figure 1.)-
The cutaneous artery in the above figures is turned back. In dissection
it will be found to lie over and hide the dorsal-ward sweep of the aortic
arch.
{Illustration: Diagram Sheet 11.}
Sheet 12.
Figure 1. Upper view of the Frog's brain.
Figure 2. Under view of the same.
Figure 3. The same-- median section.
Figure 4. The distribution of the Frog's nerves. Compare Sheet 9,
Figure III.
The shaded part in 4 is the -otic capsule- [tympanum]. The hyoid
apparatus is roughly represented in black to show its relation to IX.
(dorsal to it) and sp. 1 (ventral). Compare {nerves} IX and XII in Sheet
9. The nerves are numbered.
cb., the cerebellum.
c.h., cerebral hemispheres.
f.t., filum terminale.
g.tr., ganglion on the fifth nerve.
l.t., lamina terminalis.
mb., mid-brain.
md., medulla oblongata.
o.l., optic lobes.
pin., pineal gland.
pit., pituitary body.
r.h., olfactory lobes (rhinencephalon).
th.c., thalamencephalon.
sp.1, first spinal nerve.
sp.2, 3, brachial plexus to fore limb.
Figure 5. The spinal column (and pelvic girdle) of the Frog.
Figure 5b. Vertebrae.
Figure 6. The pectoral girdle and limb, dorsal view.
Figure 7. The pelvic girdle and right limb from the side.
(l.h. shows the position of the right lymph hearts-- they are
paired.)
as., astragalus.
b., body.
c., calcar (?= a sixth digit).
cal., calcaneum.
cl., clavicle overlying a procoracoid cartilage.
co., coracoid.
f., fibula.
[FE., femur.]
h., humerus.
il., ilium.
is., ischium.
o.st., omosternum.
pu., pubis.
r., radius.
sc., scapula.
s.sc., supra-scapula.
s.v., sacral vertebra.
t., tibia.
t.p., transverse process.
ul., ulna.
ur., urostyle.
x., xiphisternum.
z., zygapophysis.
1, 2, and etc., first, second, and etc., digits.
D. and D'. are simplified diagrams of the limbs for comparison with the
similar ones of the Rabbit. In each girdle we have a dorsal ossification
(scapula, ilium) and two ventral parts (pubis and procoracoid cartilage,
ischium and coracoid), and at the meeting-place of the three in each
case the proximal bone of the limb (humerus, femur) articulates.
{Illustration: Diagram Sheet 12.}
Sheet 13.
-Urogenital Organs of the Frog_.
Figure 1. The Male.
Figure 2. The Female. The oviduct removed on the animal's left, and
the ovary on its right.
Organs common to both sexes.--
al.b., allantoic bladder.
c.ad., corpus adiposum.
cl., cloaca.
int., intestine.
K., kidney.
lg., (dotted outline of) lung.
oes., oesophagus.
r.p.v., renal portal vein.
st., stomach.
In the Male.--
T., testis.
v.e., vasa efferentia.
u.g.d., urogenital duct.
p., prostate gland.
In the Female.--
adr., adrenal.
f.t., fallopian tube (anterior part of oviduct). * its opening.
o.d., oviduct (letters on [the opening] -uterine portion-).
ov., ovary.
ur., ureter.
(This would be the condition about midwinter.) In March o.d. will be
either enormously distended with eggs, or large, flabby, and empty,
and ov. will be small and brownish, without any large eggs; the ovary
gradually recovers its size through the summer.
Figure 3. Spermatozoa attached to the parent cell (g.e.) from the
lining epithelium of the testis, and one free.
fl., the flagellum.
{Illustration: Diagram Sheet 13.}
Sheet 14
-Skull Structure and Development of the Frog_.
Figure 1. I., II., early and late stages of the Tadpole's chindrocranium.
Diagrammatic.
Figure 2. Dorsal view of a young Frog's cranium-- the membrane
bones removed. Diagrammatic.
Figures 3 and 4. Dorsal and ventral views, respectively, of the Frog's
skull-- the lower jaw removed.
Figure 5. Side view of the Frog's skull.
Figure 6. Median section of the brain case.
Figure 7. The hyoid apparatus.
Figure 8. I., II., III., progressive stages of the Tadpole's skull from the
side. After W. K. Parker.
Figure 9. F., side and hind views of the Frog's skull. D., the same of
the Dog. Roughly diagrammatic.
N.B.--
In all cartilage is dotted, cartilage bone cross-barred, and membrane
bone, white. In Figure 4, pt., should be cross-barred;
and in 5, th.h. plain.
a.c., anterior cornu of hyoid [(= CH.)] -not lettered, in {Figure} 5-.
a.o., antorbital cartilage.
ar., angulo-splenial -(On Frog Section 34, for Articulare read
-Angulo-Splenial_)-.
-b., parachordal part of brain box-.
b.c., brain case.
b.h., body of hyoid.
b.r., branchial arches.
CH = a.c.
c.t., cornua trabeculi.
d., dentary.
e., eye.
E.N., external nares.
e.o., exoccipital bone.
f., fenestra (membranous part of cranial wall).
-f.p., fronto-parietal.-
h.m., hyomandibular cleft = Eustachian tube and ear drum.
mb., mandible.
[M.C., Meckel's Cartilage.]
m.mk., mento-Meckelian bone.
m.p., mouth passage.
mx., maxilla.
n.c., notochord.
n.o., nasal organ.
n.p., nasal passage.
ot., or o.c., otic (auditory) capsule.
pal., palatine bone.
PAL., hard palate of Mammal.
p.c., parachordal.
p.f., [parieto-frontal] -see f.p.-
p.m., premaxilla.
P.N., internal nares.
p.o., prootic bone.
p.p., palato-pterygoid cartilage.
psph., parasphenoid bone.
pt., pterygoid bone.
q., quadrate cartilage.
q.j., quadrato-jugal.
s.e., sphenethmoid bone.
sq., squamosal.
t., trabecular part of brain box.
t.c., trabecula.
th.h., thyrohyal.
{Illustration: Diagram Sheet 14.}
Sheet 15
Figure 1. Dissection of -Male- [Female] Dog-Fish to show alimentary
canal, the pericardium also being opened and the cloaca slit up.
[Above is also seen the dorsal view of the head.]
Figure 2. The pelvic girdle and fin skeleton [of a male].
{No Figure 3, in First Edition.}
Figure 4. The spiral valve in the colon. {Figure 3, in Second Edition.}
a.p., abdominal pore.
aur., -auricle- [atrium] of heart.
b.d., bile duct.
b.pt., basi-pterygium.
-cl., clasper.-
cl.c., -its- [the] supporting cartilage [of the clasper].
co., colon.
d'dnm., duodenum.
e., the eye.
g.bl., gall bladder.
g.s., gill slits.
L.Lv., left lobe of liver.
M.Lv., middle lobe of liver.
olf., olfactory opening.
[pan., pancreas.]
pcd., pericardial wall.
pel.g., the pelvic girdle.
p.p., arrow through pericardio-peritoneal canal.
r.g., rectal gland.
[R.Liv., right lobe.]
sp., spiracle.
spl., spleen.
st., the stomach.
s.v., sinus venosus.
u.g.p., uro-genital pore.
v., ventricle.
{Illustration: Diagram Sheet 15.}
Sheet 16.
Figure 1. Circulation of the Dog-Fish.
Figure 2. Simplified and more typical fish circulation, in which the
posterior cardinals have not coalesced in the median line. The
Cuvierian veins = the vena cava superior of the higher type; the
posterior cardinal is represented by the azygos vein in the Rabbit.
Compare Sheet 24, Figure 7, and Sheet 2, Figure 2.
Figure 3. Side view of the pericardium.
a.br., afferent branchial artery.
a.c.s., anterior cardinal sinus (= internal jugular vein).
au., atrium (auricle) (= the two auricles of higher forms).
b.a., bulbus arteriosus.
c.a., conus arterious.
cd. a., caudal artery.
cd.v., caudal vein.
c.s., Cuvierian sinus.
d.a., dorsal aorta.
E., eye.
e.br., efferent branchial arteries.
g.s., in position of gill slits.
h.br.a., hypobranchial artery.
H.S., hepatic sinus.
[i.j.s., inferior jugular sinus (= external jugular vein).]
K., kidney.
L.V., lateral vein.
[oe.s., ventral wall of oesophagus.]
P.C.C., pericardial cavity.
P.C.S., posterior cardinal sinus.
p.p.c., pericardio-peritoneal canal.
P.V., portal vein.
r.p.v., reno-portal vein.
s.c.v., subclavian vein.
Vn., ventricle.
-v.s.v., inferior (= external) jugular vein-.
Figure 4. Skeleton of pectoral limb, and girdle.--
g., the girdle (also in Figure 3).
m.p., meso-pterygium.
mt.p., meta-pterygium.
p.p., pro-pterygium.
sc., its dorsal portion.
{Illustration: Diagram Sheet 16.}
Sheet 17
-The Uro-genital Organs of the Dog-Fish_.
Figure 1. The Female, the oviduct of the left side cut away, -and an
egg case in the oviduct.-
Figure 2. The Male.
The rectum is removed in both cases, and the silvery peritoneum
dissected off from the kidneys.
Figure 3. A generalized diagram of the uro-genital organs.--
All references in text.
Ms., the mesonephros, is the epididymis in the male, and is reduced
in the female; Ms.d., its duct, is the vas deferens in the male, and
persists only as the urinary receptacle in the female.
Mt. and Mt.d., the metanephros and metanephric duct, become the
functional kidney and ureter in both sexes. G. is the gonad
(reproductive gland), and M.L. the animal's middle line (median
plane).
-Ps.-, [Pr.,] the pronephros, is never developed in the Dog-fish;
P.d., its supposed duct, is the oviduct of the female, and is
suppressed in the male.
{Illustration: Diagram Sheet 17.}
Sheet 18.
Figure 1. The Dog-Fish Brain, dorsal view.
Figure 2. Median section of the same. To the right a more
diagrammatic figure. The nerves are numbered:--
[BR1, BR2, BR3, BR4 branches of X forking over the second to the
fifth gillslit.]
cb., cerebellum.
h.s.c., horizontal semi-circular canal of ear, exposed by the slicing
down of the otic mass.
[LAT., lateral-line branch of X.]
m.o., medulla oblongata.
oph., ophthalmic nerve (V.1+VII.1).
op.l., optic lobe.
pit., pituitary body.
pr.c., prosencephalon (cerebral hemisphere).
rh., olfactory lobe (rhinencephalon).
r.t., -its- restiform tracts [of medulla].
-st-. [S.P.G.], stalk of the pineal gland.
th., thalamencephalon.
th.c., thalamencephalon.
-ut., the utriculus, seen through the semi-transparent cartilage-.
Vid., the Vidian branch of VII.
[Visc., visceral branch of X.]
Figure 3. Diagram of the ear of a fish.
The structure of this is easily made out by clearing otic capsule and
cutting slices of the cartilage in the Dog-Fish (e.g., Figure 1, h.s.c.).
amp., their ampullae.
a.v.c., p.v.c., h.c., anterior, posterior, horizontal canal respectively.
[amp., the ampullae.]
d.e., the ductus endo-lymphaticus.
-sac., the sacculus; c., a small outgrowth of the latter, corresponding
to the rabbit's cochlea-.
-ut., the utriculus-.
Figure 4. The cranium and branchial bars of a Dog-Fish.
The groove in the otic capsule connects the orbital and anterior
cardinal sinuses.
A.C.S., position of the anterior cardinal sinus (dotted outline).
c., the vertebral centra.
c.b., the cerato-branchial.
c.h., the cerato-hyal.
e.b., epi-branchial.
ex.b., extra-branchial.
h.M., the hyo-mandibular.
i.n.p., inter-neural plate.
M.C., Meckel's (lower jaw) bar.
Na.C., the nasal capsule.
n.p., neural plate.
n.s., neural spine.
Ot.C., the otic capsule.
ph.b., the pharyngo-branchial.
P.pt., the palato-pterygoid bar (upper jaw bar).
p.s., pre-spiracular ligament, containing a cartilaginous nodule.
r., rib.
sp., the position of the spiracle.
Figure 5. Diagrams of a vertebral centrum.-- For reference letters,
see text (Section 9).
{No Figure 6, in First Edition.}
[Figure 6. Diagram for comparison with Figure III., Sheet 9.]
{Illustration: Diagram Sheet 18.}
Sheet 19.
Figure 1. Amphioxus, seen from the right side. a----b shows the
natural size. The animal is supposed to be clarified, and mounted in
some highly refracting medium, so that it is practically transparent; I.,
II., III., and etc., refer to the section figured on Sheet 20.
Figure 2. Amphioxus, General Dissection. (Slightly altered from a
figure by Professor E. R. Lankester.) The ventral atrial wall is
removed. The pharynx cut away from the dorsal body-wall, and with
the true ventral body-wall turned over to the (animal's) right. The arrow
a., a., passes through anus to intestine; b., b., is thrust through the
atrial pore to the atrial cavity. Note coe., the body cavity.
References to the two figures.
an., anus.
at., atrial cavity.
at.w., atrial wall.
at.p., atrial pore.
a.d., anterior dilatata of nervous system.
b.w., body-wall.
b.t.L., brown tubes of Lankester.
c.f., ciliated funnel.
coe., coelome.
c.ao., cardiac aorta.
d.ao., dorsal aorta (paired).
d.ao'., dorsal aorta median.
g., gonads (male or female genital gland).
hep., hepatic vein.
in., intestine.
i.w., intestine wall.
lv., liver.
m.f., median fin.
n.c., notochord.
p.v., portal vein.
ph., pharynx.
-p.s.-, [e.s.] pigment spot ("eye spot").
s.c., spinal cord.
{Illustration: Diagram Sheet 19.}
Sheet 20
-Sections of Amphioxus_.
The Roman numerals indicate the corresponding region in Figure 1,
Sheet 19. The lettering is identical; but note, in addition;
br.c., branchial canal.
c.f., ciliated funnel.
d.c.c., dorsal coelomic canal.
end., endostyle.
ep., epipleur.
e.s., eye spot.
h.p., hypopharyngeal grove.
h.vn., for hepatic vein.
o.c., oral cavity (or hood).
{Illustration: Diagram Sheet 20.}
Sheet 21.
-Phases in the Development of Amphioxus_.
Figures 1, 2, 3, 4. Phases in segmentation.
Figure 5. The blastosphere.
Figure 6. The gastrula in section, anterior end to the right.
Figure 7. i. Dorsal view post gastrula stage.
Figure 7. ii. Diagrammatic section of the same in the position
indicated by the transverse line in 7, i.
Figure 8. Diagrammatic section of a later stage.
coe.p., the coelomic pouches.
n.c., the notochord.
n.p., the neural plate.
Figure 9.i. Still later section.
Figure 9. ii. Diagrammatic view of late embryo.
Figures 10, 11, 12 illustrate the formation of the atrium as a median
ventral invagination, at.
{Illustration: Diagram Sheet 21.}
Sheet 22.
-The Development of the Frog_.
These diagrams must be studied with the text. They should be
compared with the corresponding ones of Amphioxus as indicated
below.
Figures 1, 2, 3. Stages in segmentation (compare 1, 2 ,3 of {Sheet
21} Amphioxus).
Figure 4. Blastosphere stage (compare 5, Amphioxus). This, on a
smaller scale. The cells on the ventral side are so much larger
because distended with yolk.
Figure 5. Gastrula stage in section (compare 6, Amphioxus). The
Frog on a smaller scale than Amphioxus.
Figure 6. Dorsal view of gastrula (compare 7, Amphioxus).
Figure 7. Part of a transverse section of developing tadpole,
corresponding to Figure 8 of Amphioxus.
Figures 8 and 9. Diagrammatic longitudinal sections of tadpoles
(compare 9. ii. of Amphioxus). Y. represents a mass of
yolk cells.
Figure 10. Side view of young tadpole, showing external gills (e.g.)
and suckers (s.). Note the ventral bulging due to the yolk.
Figure 11. Ventral view of a later tadpole.
op., the operculum.
int., coiling intestine.
Figure 12. Head of still later tadpole in horizontal section to show
atrial chamber formed by operculum.
int.g., internal gills.
L., developing lungs.
Figure 13. Diagrammatic cross-section of the mid-dorsal part of an
embryonic vertebrate.
ao., aorta.
B.C., Bowman's capsule.
coe., coelom.
d.g., ganglion on dorsal root of spinal nerve.
gl., -its branch- [arteriole] to form glomerulus.
g.r., genital ridge.
I., intestine.
M.D., Mullerian duct.
ns. [nst.], nephrostome.
n.c., notochord; -n.s.-, [n.sh.] its sheath.
s.c., neural canal.
W.D., Wolffian duct.
{Illustration: Diagram Sheet 22.}
Sheet 23.
-The Development of the Fowl_.
Figure 1. Diagram of the early ovum. The section below is a small
portion of the blastodermic area.
b.d., blastoderm.
y., the undivided yolk.
s.c., the segmentation between the blastoderm and yolk. Compare
s.c. in {Sheet} 22, {Figure} 4.
Figure 2. Area pellucida about the sixteenth hour. The figure below is
the central part of the section indicated by the transverse line, and
showing the primitive streak (p.s.).
Figure 3. Area pellucida about the twenty-first hour. Two sections
through a and b below.
Figure 4. About the twenty-fifth hour; surface view; longitudinal section
to right and transverse above.
Figure 4b. Diagrammatic rendering of same stage (compare Figure 9
of Frog and 9.ii. Amphioxus). This will be most clearly understood if
the reader look at Sheet 22, {Figure} 9, and imagine Y. enormously
increased, and the embryo sinking into it. Epiblast, ep., -line of
dashes- [black line]. Mesoblast, dotted. Hypoblast, -black- [line of
dashes]. pp., the pleuro-peritoneal cavity.
Figure 5 and 6 illustrate formation of amnion (a.) and allantois (all.).
6 is about the fourth day.
{Illustration: Diagram Sheet 23.}
Sheet 24.
-The Development of the Fowl_.
Figure 1. Chick about the -fifth- [third] day. At this stage the chick lies
on its left side in the yolk. [For lettering of blood vessels, see (7)
below.]
i., the intestine.
u.v., the yolk sac.
v.v., the vitelline veins.
al., the allantois.
Figure 2. Chick about sixth day.
Figure 3. Development of heart.
Figure 4. Development of the eye.
Figure 5. Chick about the sixteenth day.
A.M. is the amnion surrounding the embryo. Note particularly how the
allantois (al.) has spread over surface of shell and how the yolk sac is
shrivelled.
Figure 6. Figures to illustrate the relative function and importance of
allantois and yolk sac in bird and mammal. In the fowl, however, the
blood-vessels of the allantois also probably absorb the albumen of the
egg, and may excrete urea into the egg-space.
Figure 7. Simplified figure of the embryonic circulation, for comparison
with the similar figures annexed to Dog-Fish and Rabbit.
{Lines from Second Edition only.}
[A.C., anterior cardinal.
Ao., Aorta.
Br4, sixth aortis arch (fourth branchial).
C.S. Cuvierian sinus.
H., the heart.
I.C., inferior cava.
P.C., posterior cardinal vein.
Tr.A., truncus arteriosus.
v.v., vitelline vein.]
Figure 8. Chick on the nineteenth day.
{Illustration: Diagram Sheet 24.}