BIRDS. 541 



into a mere circular red line in the adults of both sexes, or 

 quite disappears in the adult females.* 



Finally, with respect to our present class of cases, the 

 most probable view appears to be that successive variations 

 in brightness or in other ornamental characters occurring 

 in tlie males at a rather late period of life have alone been 

 preserved; and that most or all of these variations, owing 

 to the late period of life at which they appeared, 

 have been from the first transmitted only to the adult male 

 offspring. Any variations in brightness occurring in the 

 females or in the young would have been of no service to 

 them, and would not have been selected; and moreover, if 

 dangerous would have been eliminated. Thus the females 

 and the young will either have been left unmodified, or 

 (as is much more common) will have been partially modi- 

 fied by receiving through transference from the males some 

 of his successive variations. Both sexes have perhaps been 

 directly acted on by the conditions of life to which they 

 have long been exposed; but the females from not being 

 otherwise 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 acquired 

 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 colored 

 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 per- 

 forming the duties of incubation, lays great stress on this 



Audubon, "Omith, Biography," vol. i, p. 193. Macgillivray, 

 ** Hist. Brit. Birds," vol iii, p. 85. See also the case before given of 

 Indopicus carlotta. 



