264 ANIMAL COLOEATION. 



appendages of the birds of paradise, are among the more 

 striking effects which Darwin believed to have been produced' 

 by this selection on the part of the female birds. Obviously 

 this theory must be limited to such animals as have an acute 

 sight and an aesthetic appreciation ; accordingly, most inverte- 

 brate groups which show sexual differences, whether in colour 

 or in the form of special appendages, must be set aside. 

 The vision of these animals, as has been already remarked, 

 does not appear to come up to the requisite standard of 

 efficiency. 



/ 



On the other hand, it may be admitted that at least birds 

 and mammals do possess a sufficiently developed sense of sight.. 

 So far there is nothing to render the theory untenable. It is,. 

 however, a remarkable fact that the Mammalia show, relatively 

 speaking, very little sexual divergence. The stags have their 

 antlers ; blue and red patches are developed upon the skin in a 

 few monkeys ; and there are actual differences of colour in some 

 species, such as the red kangaroo. In the male of this animal 

 the colour is brown, and the throat is coloured pink by a sub- 

 stance of the colour of carmine which is secreted by the skin 

 in this region ; the female, on the contrary, is grey, and does 

 not show this peculiar efflorescence. On a priori grounds one 

 would expect the most intelligent of the Vertebrata to show 

 the most strongly marked differences of colour; particularly 

 since there are well-founded instances of preferences exhibited 

 by the female of certain mammals. Mr. Darwin, in a note- 

 prefixed to a paper by Prof. Van Dyck,* calls attention to> an, 

 instance of this kind exhibited by the dog. 



Among birds, it is remarkable that gorgeousness of colora- 

 tion is not always limited to the male sex ; very often both 

 sexes have an identical coloration, which is as brilliant as in, 



* Proc. Zool. .S'oc., 1882. 



