es, and on this investigation Darwin
founded a new theory, that of sexual selection. With astonishing
patience he gathered together an immense mass of material, and showed,
in regard to Arthropods and Vertebrates, the wide distribution of
secondary characters, which develop almost exclusively in the male, and
which enable him, on the one hand, to get the better of his rivals in
the struggle for the female by the greater perfection of his weapons,
and on the other hand, to offer greater allurements to the female
through the higher development of decorative characters, of song, or of
scent-producing glands. The best equipped males will thus crowd out the
less well-equipped in the matter of reproduction, and thus the relevant
characters will be increased and perfected through sexual selection.
It is, of course, a necessary assumption that these secondary sexual
characters may be transmitted to the female, although perhaps in
rudimentary form.

As we have said, this theory of sexual selection takes up a great deal
of space in Darwin's book, and it need only be considered here in so far
as Darwin applied it to the descent of man. To this latter problem the
whole of Part I is devoted, while Part III contains a discussion of
sexual selection in relation to man, and a general summary. Part II
treats of sexual selection in general, and may be disregarded in our
present study. Moreover, many interesting details must necessarily be
passed over in what follows, for want of space.

The first part of the "Descent of Man" begins with an enumeration of
the proofs of the animal descent of man taken from the structure of
the human body. Darwin chiefly emphasises the fact that the human body
consists of the same organs and of the same tissues as those of the
other mammals; he shows also that man is subject to the same diseases
and tormented by the same parasites as the apes. He further dwells
on the general agreement exhibited by young, embryonic forms, and
he illustrates this by two figures placed one above the other, one
representing a human embryo, after Eaker, the other a dog embryo, after
Bischoff. ("Descent of Man" (Popular Edition, 1901), fig. 1, page 14.)

Darwin finds further proofs of the animal origin of man in the
reduced structures, in themselves extremely variable, which are either
absolutely useless to their possessors, or of so little use that they
could never have developed under existing conditions. Of such vestiges
h