g embryo, one of them being devoted to an important duty,
that of conversion into the external and middle ear. Thus the opening
for hearing is an adaptation of what was once an opening for breathing.
Occasionally an ear-like outgrowth appears on the neck, indicative of
the attempt of a second slit to develop into an ear. The purpose of the
gill slits is made more apparent by the presence in the embryo of gill
arches of the blood-vessels, like those normal to the fish. These
disappear in common with the slits.

The temporary appearance of these gill slits is the strongest evidence
that could well be demanded that the human embryo passes through the
various stages which the adult has assumed in its long development in
past time, and that one of these stages was the fish. And these form
only one of the evidences of man's origin to be found in the embryo.
Another which may be mentioned is the wool-like hair which covers the
foetus, and whose presence is incomprehensible except on the theory of
descent. Its most probable explanation is that it appears as a passing
survival of the first permanent coat of hair of the lower mammals.

In the milk teeth of man we have another useless and often annoying
survival of an ancient state of the dental organs. We cannot well
imagine that in any direct creation a set of temporary teeth would have
been provided as preliminary to a permanent set--an utterly useless
provision. But when we find that in a lower stage of animal life the old
teeth are periodically succeeded by new ones, we can understand how a
trace of this condition has persisted in the mammalia.

Other evidences of man's origin in the lower animals could be drawn from
the phenomena of atavism, or arrest of development in parts or organs of
the body. Atavism is usually confined within the line of human descent,
conditions appearing in many of us which belonged to some of our human
ancestors a few generations, occasionally many generations, in the past.
But conditions now and then appear which are abnormal to man, but which
are normal to some of the lower animals. This tendency is exhibited by
all organisms. In an occasional horse the long-lost stripes of the
zebra-like ancestor reappear. Now and then a blue pigeon, like the
ancestral form, crops up in a pure breed of domesticated birds. Even in
the details of anatomy some long-vanished character suddenly appears.

Many instances of this in man might be cited, embracing variou