another argument for the belief in common descent. In man, for example,
there exist over one hundred of these vestigial or rudimentary organs,
as the vermiform appendix, the pineal gland, and the like. Many of these
vestigal organs, which are now functionless in man, perform functions in
lower animals, and this is held to show that at some remote period in
the past they also functioned in man's ancestors.

(3) The facts of embryology seem to point to the descent of the higher
types of animals from the lower types. The embryo or fetus in its
development seems to recapitulate the various stages through which the
species has passed. Thus the human embryo at one stage of its
development resembles the fish; at another stage, the embryo of a dog;
and for a long time it is impossible to distinguish between the human
embryo and that of one of the larger apes. These embryological facts,
biologists say, indicate genetic relation between the various animal
forms which the embryo in its different stages simulates.

(4) The fossil remains of extinct species of animals are found in the
earth's crust which are evidently ancestors of existing species. Until
the doctrine of descent was accepted there was no way of explaining the
presence of these fossil remains of extinct animals in the earth's
crust. It was supposed by some that the earth had passed through a
series of cataclysms in which all forms of life upon the earth had been
many times destroyed and many times re-created. It is now demonstrated,
however, that these fossils are related to existing species, and
sometimes it is possible to trace back the evolution of existing forms
to very primitive forms in this way. For example, it is possible to
trace the horse, which is now an animal with a single hoof, walking on a
single toe, back to an animal that walked upon four toes and had four
hoofs and was not much larger than a fox. It is not so generally known