The Theory of Sexual Selection. 387 
take into consideration the following facts. Namely, 
(a) secondary sexual characters of the embellishing 
kind are, as a rule, developed only at maturity; and 
most frequently during only a part of the year, which 
is zzvariably the breeding season : (8) they are always 
more or less seriously affected by emasculation: (c) 
they are always, and only, displayed in perfection 
during the act of courtship : (¢) then, however, they are 
displayed with the most elaborate pains; yet always, 
and only, before the females: (e) they appear, at all 
events in many cases, to have the effect of charming | 
the females into a performance of the sexual act; 
while it is certain that in many cases, both among 
quadrupeds and birds, individuals of the one sex are 
capable of feeling a strong antipathy against, or a strong 
preference for, certain individuals of the opposite sex. 
Such are the main lines of evidence in favour of the 
theory of sexual selection. And although it is enough 
that some of them should be merely stated as above 
in order that their immense significance should be- 
come apparent, in the case of others a bare statement 
is not sufficient for this purpose. More especially is 
this the case as regards the enormous profusion, variety, 
and elaboration of sexually-embellishing characters 
which occur in birds and mammals—not to mention 
several divisions of Arthropoda; together with the 
extraordinary amount of trouble which, in a no less 
extraordinary number of different ways, is taken by 
the male animals to display their embellishments 
before the females. And even in many cases where 
to our eyes there is no particular embellishment to 
display, the process of courtship consists in such an 
elaborate performance of dancings, struttings, and 
Ce2 
