330 Tlie Descent jf Man. Part It 



sometimes take pains to display their beautiful colours ; and we 

 cannot Delieve that they would act thus, unless the display was 

 :>f use to them in their courtship. 



When we treat of Birds, we shall see that they present in 

 their secondary sexual characters the closest analogy with 

 insects. Thus, many male birds are highly pugnacious, 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 diversified kinds, and are decorated with beautiful 

 colours, 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-coloured and uuoruamented. 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. We shall see that female birds, like female insects, 

 often possess more or less plain traces or rudiments of characters 

 which properly belong to the males and are of use only to them. 

 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 shew in further detail, is sexual 

 selection. 



CHAPTER XII. 



Secondary Sexual Characters of Fishes, Amphibians, 



and Reptiles. 



Fishes: Courtship and battles of the males — Larger size of the females 

 — Males, bright colours and ornamental appendages; other strange 

 characters — Colours and appendages acquired by the males during the 

 breeding-season alone — Fishes with both sexes brilliantly coloured 

 — Protective colours — The less conspicuous colours of the female cannot 

 be accounted for on the principle of protection — Male fishes building 

 nests, and taking charge of the ova and young. Amphibians : Dif- 

 ferences in structure and colour between the sexes — Vocal organs. 

 Reptiles: Che'onians — Crocodiles — Snakes, colours in some cases pro- 

 tective — Lizards, battles of — Ornamental appendages — Strange dif- 

 ferences in structure between the sexes — Colours — Sexual differences 

 almost as s;reat as with birds. 



>Ve have now arrived at the great sub-kingdom of the Vertebrata, 

 md will commence with the lowest class, that of Fishes. The 



