ut a keen
analysis of the measurements of the various parts of their bodies will
show distinct differences. This is quite as true among lower animals.
A toad may lay a double string of four hundred eggs which may be
fertilized by the same male at the same time. These eggs may develop
into tadpoles in the same pool not over a foot square. Within a few
weeks these little toads may have gained their legs, lost their tails,
and all may have left the water and taken to the ground upon the same
day. Already the careful observer will notice differences among them.
Some are larger than others, having grown more rapidly even though
their surroundings were exactly the same; others are more skillful in
their peculiar method of throwing the tongue at an insect they wish to
catch. Still others will be differently colored. They might be
arranged to show a considerable gradation between the lightest and the
darkest of the group, though there may not be anywhere in the row a
considerable gap. It is variation in animals of the same parentage and
same surroundings which in the mind of Mr. Darwin made evolution
possible. He always favored the idea that it was the continuous
accumulation of these small variations that finally produced the
profound changes which mark the new species. He admitted the
possibility of the occasional appearance of those more distinct leaps
in variation on which the present school of mutationists so strongly
insists; but he believed them to be less influential, in the general
trend of evolution, than the slower but much more frequent variations.

One of the most complicated and perplexing problems in the biology of
to-day is the question of the origin of these variations. It is quite
as hard to understand as is the method by which animals produce their
own kind. No problem is being more earnestly studied. Suppositions we
have in considerable number, and two of these at least may reasonably
be mentioned. We will consider first the less certain theory. There is
nothing in the egg that in the remotest degree resembles its parent.
The old idea that every acorn had in it a miniature oak which only
needed to unfold itself, or that the hen's egg had within it a
miniature chick which only needed the warming process in order to make
it evident, could not possibly survive the invention of the
microscope. We may not, and we certainly do not, know everything that
is in one of these eggs, but we do know most certainly that wh