14 SEXUAL SELECTION. [Part II. 



ticulatus), of the United States, especially of the male, 

 become, during the breeding-season, exceedingly intense, 

 brilliant, and iridescent. 22 Another striking instance out 

 of many is afforded by the male stickleback ( Gasterosteus 

 leiumis), which is described by Mr. Warington, 23 as being 

 then " beautiful beyond description." The back and eyes 

 of the female are simply brown, and the belly white. The 

 eyes of the male, on the other hand, are " of the most 

 splendid green, having a metallic lustre like the green 

 feathers of some humming-birds. The throat and belly 

 are of a bright crimson, the back of an ashy-green, and 

 the whole fisii appears as though it were somewhat trans- 

 lucent, and glowed with an internal incandescence." 

 After the breeding-season these colors all change, the 

 throat and belly become of a paler red, the back more 

 green, and the glowing tints subside. 



That with fishes there exists some close relation be- 

 tween their colors and their sexual functions we can clearly 

 see — firstly, from the adult males of certain species being 

 differently colored from the females, and often much more 

 brilliantly; secondly, from the same males, while im- 

 mature, resembling the mature females ; and, lastly, from 

 the males, even of those species which at all other times 

 of the year are identical in color with the females, often 

 acquiring brilliant tints during the spawning-season. We 

 know that the males are ardent in their courtship, and 

 sometimes fight desperately together. If we„ may assume 

 that the females have the power of exerting a choice and 

 of selecting the more highly-ornamented males, all the 

 above facts become intelligible through the principle of 

 sexual selection. On the other hand, if the females ha- 

 bitually deposited and left their ova to be fertilized by the 

 first male which chanced to approach, this fact would be 



22 'The American Agriculturist,' 1868, p. 100. 

 ,3 ' Annals and Mag. of Nat. Hist.' Oct. 1852. 



