stor, we may recall,
is also reflected for a time in the gill-slits and arches, with their
corresponding fish-like heart and blood-vessels, during man's embryonic
development, as we saw in a former chapter.

These are only a few of the more conspicuous instances of vestigial
structures in man. Metchnikoff describes about a hundred of them. Even
if there were no remains of primitive man pointing in the direction of
a common ancestry with the ape, no lower types of men in existence with
the same tendency, no apes found in nature to-day with a structure so
strikingly similar to that of man, and no fossil records telling of the
divergence of forms from primitive groups in past time, we should be
forced to postulate the evolution of man in order to explain his actual
features. The vestigial structures must be interpreted as we interpret
the buttons on the back of a man's coat. They are useless reminiscences
of an age in which they were useful. When their witness to the past
is supported by so many converging lines of evidence it becomes
irresistible. I will add only one further testimony which has been
brought into court in recent years.

The blood consists of cells, or minute disk-shaped corpuscles, floating
in a watery fluid, or serum. It was found a few years ago, in the course
of certain experiments in mixing the blood of animals, that the serum of
one animal's blood sometimes destroyed the cells of the other animal's
blood, and at other times did not. When the experiments were multiplied,
it was found that the amount of destructive action exercised by one
specimen of blood upon another depended on the nearness or remoteness of
relationship between the animals. If the two are closely related, there
is no disturbance when their blood is mixed; when they are not closely
related, the serum of one destroys the cells of the other, and the
intensity of the action is in proportion to their remoteness from each
other. Another and more elaborate form of the experiment was devised,
and the law was confirmed. On both tests it was found by experiment that
the blood of man and of the anthropoid ape behaved in such a way as to
prove that they were closely related. The blood of the monkey showed a
less close relationship--a little more remote in the New World than in
the Old World monkeys; and the blood of the femur showed a faint and
distant relationship.

The FACT of the evolution of man and the apes from a common ancestor is,
the