so-called turban-eyes, so that the whole head is covered with seeing
surfaces. In these species the females are very greatly in the minority (1-
100), and it is easy to understand that a keen competition for them must
take place, and that, when the insects of both sexes are floating freely in
the air, an unusually wide range of vision will carry with it a decided
advantage. Here again the actual adaptations 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