SEXUAL SELECTION 613 



is much more common) will have been partially modified by 

 receiving through transference from the male some of his 

 successive variations. Both sexes have, perhaps, been di- 

 rectly acted on by the conditions of life to which they have 

 long been exposed; but the females, from not being oth- 

 erwise much modified, will best exhibit any such effects. 

 These changes and all others will have been kept uniform 

 by the free intercrossing of many individuals. In some 

 cases, especially with ground birds, the females and the 

 young may possibly have been modified, independently of 

 the males, for the sake of protection, so as to have ac- 

 quired the same dull-colored plumage. 



Class II. When the adult female is more conspicuous 

 than the adult male, the young of both sexes in their first 

 plumage resemble the adult male. — This class is exactly the 

 reverse of the last, for the females are here brighter col- 

 ored or more conspicuous than the males; and the young, 

 as far as they are known, resemble the adult males instead 

 of the adult females. But the difference between the sexes 

 is never nearly so great as with many birds in the first class, 

 and the cases are comparatively rare. Mr. Wallace, who first 

 called attention to the singular relation which exists between 

 the less bright colors of the males and their performing the 

 duties of incubation, lays great stress on this point," as a 

 crucial test that obscure colors have been acquired for the 

 sake of protection during the period of nesting. A different 

 view seems to me more probable. As the cases are curious 

 and not numerous, I will briefly give all that I have beea 

 able to find. 



In one section of the genus Turnix, quail-like birds, the 

 female is invariably larger than the male (being nearly twice 

 as large in one of the Australian species), and this is an un- 

 usual circumstance with the Q-allinacese. In most of the 

 species the female is more distinctly colored and brighter 



i» "Westminster Eeview," July, 1867, and A. Murray, "Journal of Travel," 

 1868, p. 83. 



