44 The Selection Theory 
the struggle for the possession of the female, we might name many 
kinds of means, but it would be difficult to suggest any which is not 
actually employed in some animal group or other. I begin with the 
mere difference in strength, through which the male of many animals 
is so sharply distinguished from the female, as, for instance, the lion, 
walrus, “sea-elephant,” and others. Among these the. males_fight 
violently for the possession of.the female, who falls to the victor in 
the.eembat. In this simple case no one can doubt the operation of 
selection, and there is just as little room for doubt as to the selection- 
value of the initial stages of the variation. Differences in bodily 
strength are apparent even among human beings, although in their 
case the struggle for the possession of the female is no longer decided 
by bodily strength alone. 
Combats between male animals are often violent and obstinate, 
and the employment of the natural weapons of the species in this 
way has led to perfecting of these, eg. the tusks of the boar, the 
antlers of the stag, and the enormous, antler-like jaws of the stag- 
beetle. Here again it is impossible to doubt that variations in 
these organs presented themselves, and that these were considerable 
enough to be decisive in combat, and so to lead to the improvement 
of the weapon. 
Among many animals, however, the females at first withdraw from 
the males; they are coy, and have to be sought out, and sometimes 
eld by force. This tracking and grasping of the females by the 
ales has given rise to many different characters in the latter, as, 
or instance, the larger eyes of the male bee, and especially of the 
males of the Ephemerids (May-flies), some species of which show, in 
jaddition to the usual compound eyes, large, 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 pre- 
liminary 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_re- 
production, ae 
In many cases the organ of smell shows a similar improvement. 
