Chap. XI.] SUMMARY OX IXSECTS. 409 



been gained though the same means, namely, sexual selec- 

 tion. 



When we treat of Birds, we shall see that they pre- 

 sent in their secondary sexual characters the closest anal- 

 ogy with insects. Thus, many male birds are highly pug- 

 nacious, and some are furnished with special weapons for 

 fighting with their rivals. They possess organs which are 

 used during the breeding-season for producing vocal and 

 instrumental music. They are frequently ornamented 

 with combs, horns, wattles, and plumes, of the most diver- 

 sified kinds, and are decorated with beautiful colors, all 

 evidently for the sake of display. We shall find that, as 

 with insects, both sexes, in certain groups, are equally 

 beautiful, and are equally provided with ornaments which 

 are usually confined to the male sex. In other groups 

 both sexes are equally plain-colored and unornamented. 

 Lastly, in some few anomalous cases, the females are more 

 beautiful than the males. We shall often find, in the 

 same group of birds, every gradation from no difference 

 between the sexes to an extreme difference. In the latter 

 case we shall see that the females, like female insects, often 

 possess more or less plain traces of the characters which 

 properly belong to the males. The analogy, indeed, in all 

 these respects, between birds and insects, is curiously 

 close. Whatever explanation applies to the one class 

 probably applies to the other ; and this explanation, as we 

 shall hereafter attempt to show, is almost certainly sexual 

 selection. 



END OF VOL. I. 



