On the Study of Zoology | Page 4

general application throughout both the
animal and the vegetable worlds, but the ground common to these
kingdoms of nature is not of very wide extent, and the multiplicity of
details is so great, that the student of living beings finds himself

obliged to devote his attention exclusively either to the one or the other.
If he elects to study plants, under any aspect, we know at once what to
call him. He is a botanist, and his science is botany. But if the
investigation of animal life be his choice, the name generally applied to
him will vary according to the kind of animals he studies, or the
particular phenomena of animal life to which he confines his attention.
If the study of man is his object, he is called an anatomist, or a
physiologist, or an ethnologist; but if he dissects animals, or examines
into the mode in which their functions are performed, he is a
comparative anatomist or comparative physiologist. If he turns his
attention to fossil animals, he is a palaeontologist. If his mind is more
particularly directed to the specific description, discrimination,
classification, and distribution of animals, he is termed a zoologist.
For the purpose of the present discourse, however, I shall recognise
none of these titles save the last, which I shall employ as the equivalent
of botanist, and I shall use the term zoology as denoting the whole
doctrine of animal life, in contradistinction to botany, which signifies
the whole doctrine of vegetable life.
Employed in this sense, zoology, like botany, is divisible into three
great but subordinate sciences, morphology, physiology, and
distribution, each of which may, to a very great extent, be studied
independently of the other.
Zoological morphology is the doctrine of animal form or structure.
Anatomy is one of its branches; development is another; while
classification is the expression of the relations which different animals
bear to one another, in respect of their anatomy and their development.
Zoological distribution is the study of animals in relation to the
terrestrial conditions which obtain now, or have obtained at any
previous epoch of the earth's history.
Zoological physiology, lastly, is the doctrine of the functions or actions
of animals. It regards animal bodies as machines impelled by certain
forces, and performing an amount of work which can be expressed in
terms of the ordinary forces of nature. The final object of physiology is
to deduce the facts of morphology, on the one hand, and those of
distribution on the other, from the laws of the molecular forces of
matter.
Such is the scope of zoology. But if I were to content myself with the

enunciation of these dry definitions, I should ill exemplify that method
of teaching this branch of physical science, which it is my chief
business to-night to recommend. Let us turn away then from abstract
definitions. Let us take some concrete living thing, some animal, the
commoner the better, and let us see how the application of common
sense and common logic to the obvious facts it presents, inevitably
leads us into all these branches of zoological science.
I have before me a lobster. When I examine it, what appears to be the
most striking character it presents? Why, I observe that this part which
we call the tail of the lobster, is made up of six distinct hard rings and a
seventh terminal piece. If I separate one of the middle rings, say the
third, I find it carries upon its under surface a pair of limbs or
appendages, each of which consists of a stalk and two terminal pieces.
So that I can represent a transverse section of the ring and its
appendages upon the diagram board in this way.
If I now take the fourth ring, I find it has the same structure, and so
have the fifth and the second; so that, in each of these divisions of the
tail, I find parts which correspond with one another, a ring and two
appendages; and in each appendage a stalk and two end pieces. These
corresponding parts are called, in the technical language of anatomy,
"homologous parts." The ring of the third division is the "homologue"
of the ring of the fifth, the appendage of the former is the homologue of
the appendage of the latter. And, as each division exhibits
corresponding parts in corresponding places, we say that all the
divisions are constructed upon the same plan. But now let us consider
the sixth division. It is similar to, and yet different from, the others. The
ring is essentially the same as in the other divisions; but the appendages
look at first as if they were very different; and yet when we regard them
closely, what do we find? A stalk and two terminal divisions, exactly as
in