EVOLUTION OF THE COLORS OF BIRDS. 89 



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arrived at these opposite conclusions from consulting in 

 the main the same works that have been referred to in 

 the preceding discussion, it may be profitable to notice 

 the grounds for their decisions. 



Prof. Beddard, in his chapter on Sexual Coloration,* 

 first enumerates instances of sexual dimorphism and 

 dichromatism among forms where sexual selection is ob- 

 viously precluded by the nature of the case, as, for ex- 

 ample, among some species of Echinoderms. He states 

 that even among birds when the sexes are different in 

 color the female is sometimes as beautifully marked as 

 the male, as in certain species of curassows, parrots, 

 and the upland goose. He contends with Wallace that 

 these brilliant colors are most common and striking 

 in butterflies and birds where the nature of the expanded 

 surface would facilitate their development. He points 

 to the very slight exhibition of sexual dichromatism in 

 mammals, and cites instances showing the .dependence 

 of sexual dichromatism in birds upon the sexual organs. 



What is to be said of those objections to sexual 

 selection? His first objection is, indeed, a valid one so 

 far as it goes, viz., in showing that there can be sexual 

 diversity in color and form without any selection, but 

 this by no means disproves sexual selection in forms 

 where it might be possible. As regards certain isolated 

 instances of birds in which the female, although differ- 

 ently colored from the male is equally beautiful, there is 

 much room for argument. In the first place it would 

 be necessary to know in each specific instance in what 

 the degree of difference consisted. Certain colors in 

 birds have complementary colors which are more prim- 

 ative but not necessarily less beautiful. Thus many 

 scarlet male birds when kept in captivity become yellow, 

 which color is often characteristic of the female of the 



*pp. 253-282. 



