rn the teachings of these several divisions by recalling
and putting together what we know already about the commonest animals, or
noting what can be observed in a visit to a zooelogical garden and
aquarium. On account of the present limitations of time, the subject of
classification will be combined with comparative anatomy; embryology will
be taken up together with these subjects; palaeontology will be the main
subject of the next discussion, which will include also a brief statement
of the meaning of distribution. Then we will be prepared to study nature
to see how evolution works.

II

THE STRUCTURE AND DEVELOPMENT OF ANIMALS AS EVIDENCE OF EVOLUTION

In order to become acquainted with the way the structures of animals
provide evidences of evolution, it is by no means necessary to review the
entire range of their forms, because research has discovered that the
principles of relationship are universal among animals, and that any group
of examples will demonstrate what is taught by comparative anatomy as a
whole. The commonest creatures may serve us best in order that we may come
to view evolution as a process that involves each and every living thing
that we know, and not as something which belongs only to the remote and
unknown past.

Let us begin with the common cat and the group of carnivora or
flesh-eating animals to which it belongs. As we pass along the streets of
the city, we will see many cats which differ in some details, though they
resemble one another closely. While they vary somewhat in form, the range
in this quality is not so noticeable as in the matter of color; some of
them will be gray, some maltese, while others will be yellowish or black,
and they will differ in the striped or spotted character of their
coloration. We readily classify them all as "cats" in spite of their
differences, because they are alike in so many ways that we have learned
to associate as the distinguishing characteristics of these animals, and
to label--"cat." The animals which we might see in a walk of several
blocks may reasonably be regarded as offspring of the same pair of
ancestors of a few years back, even though they are dissimilar. We all
know that the kittens of one and the same litter vary: no two of them are
ever exactly alike in color or disposition or voice or size, nor is any
one identical with either of its parents, although it may be necessary to
employ exact means of measuring them in order to demon