observed between the cells of the flowers of the oak and those of the
apple, but the cells of the one always produce oak trees, while those of
the other always produce apple trees. The same is true of the germs of
animals, there being not the slightest apparent difference. We are
unable to perceive how one cell should give origin to a dog, while
another exactly like it becomes a man. For aught we know, the ultimate
atoms of these cells are identical in physical character; at least we
have no means of detecting any difference.

SPECIES. The term species is generally used merely as a convenient name
to designate certain assemblages of individuals having various striking
points of resemblance. Scientific writers, as a rule, no longer hold
that what are usually called _species_ are constantly unvarying and
unchangeable quantities. Recent researches point to the conclusion that
_all species vary more or less_, and, in some instances, that the
variation is so great that the limits of general specific distinctness
are sometimes exceeded.

Our space will not permit us to do more than merely indicate the two
great fundamental ideas upon which the leading theories of the time
respecting the origin of species are based. These are usually termed the
doctrine of _Special Creation_ and the doctrine of _Evolution_.
According to the doctrine of Special Creation, it is thought that
species are practically immutable productions, each species having a
_specific centre_ where it was originally created, and from which it
spread over a certain area until its further progress was obstructed by
unfavorable conditions. The advocates of the doctrine of Evolution hold,
on the contrary, that species are not permanent and immutable, but that
they are subject to modification, and that "the existing forms of life
are descendants by true generation of pre-existing forms."[1] Most