C HAP. XVIII. 
SUMMARY. 
called sexual selection. This does not depend on any 
Sl -ipci'ioi'ity in the general struggle for life, hut on 
certain individuals of one sex, generally the male sex, 
having been successful in conquering other males, and 
° n their having left a larger number of offspring to 
mherit their superiority, than the less successful males. 
There is another and more peaceful kind of contest, 
hi which the males endeavour to excite or allure the 
females by various charms. This may be effected by 
■he powerful odours emitted, by the males during the 
hreeding-season ; the odoriferous glands having been 
ac quired through sexual selection. Whether the same 
v few can he extended to the voice is doubtful, for the 
v °cal organs of the males may have been strengthened 
hy use during maturity, under the powerful excitements 
°1 love, jealousy, or rage, and transmitted to the same 
s ex. Various crests, tufts, and mantles of hair, which 
ai 'e either confined to the male, or are more developed 
111 this sex than in the females, seem in most cases to 
he merely ornamental, though they sometimes serve as 
a defence against rival males. There is even reason to 
suspect that the branching horns of stags, and the 
e fegant horns of certain antelopes, though properly 
serving as weapons of offence or of defence, have been 
partly modified for the sake of ornament. 
When the male differs in colour from the female he 
generally exhibits darker and more strongly-contrasted 
^nts. We do not in this class meet with the splendid 
ly, l. blue, yellow, and green colours, so common with 
jaale birds and many other animals. The naked parts, 
however, of certain Quadrumana must be excepted ; for 
3Uc 'h parts, often oddly situated, are coloured in some 
s pecies in the most brilliant manner. The colours of 
the male in other cases may be due to simple variation, 
