ions are in accordance with the preliminary postulates of the
theory. We do not know the stages through which the eye has passed
to its present perfected state, but, since the number of simple eyes
(facets) has become very much greater in the male than in the female,
we may assume that their increase is due to a gradual duplication of
the determinants of the ommatidium in the germ-plasm, as I have already
indicated in regard to sense-organs in general. In this case, again,
the selection-value of the initial stages hardly admits of doubt; better
vision DIRECTLY secures reproduction.

In many cases THE ORGAN OF SMELL shows a similar improvement. Many lower
Crustaceans (Daphnidae) have better developed organs of smell in the
male sex. The difference is often slight and amounts only to one or two
olfactory filaments, but certain species show a difference of nearly
a hundred of these filaments (Leptodora). The same thing occurs among
insects.

We must briefly consider the clasping or grasping organs which have
developed in the males among many lower Crustaceans, but here natural
selection plays its part along with sexual selection, for the union
of the sexes is an indispensable condition for the maintenance of the
species, and as Darwin himself pointed out, in many cases the two forms
of selection merge into each other. This fact has always seemed to me to
be a proof of natural selection, for, in regard to sexual selection,
it is quite obvious that the victory of the best-equipped could have
brought about the improvement only of the organs concerned, the factors
in the struggle, such as the eye and the olfactory organ.

We come now to the EXCITANTS; that is, to the group of sexual characters
whose origin through processes of selection has been most frequently
called in question. We may cite the LOVE-CALLS produced by many male
insects, such as crickets and cicadas. These could only have arisen in
animal groups in which the female did not rapidly flee from the male,
but was inclined to accept his wooing from the first. Thus, notes like
the chirping of the male cricket serve to entice the females. At first
they were merely the signal which showed the presence of a male in the
neighbourhood, and the female was gradually enticed nearer and nearer
by the continued chirping. The male that could make himself heard to the
greatest distance would obtain the largest following, and would transmit
the beginnings, and, later, the impro