SEXUAL SELECTION. 26? 



life. The eared pheasant (Crossoptilon aurifum), however, 

 oilers a remarkable exception, for both sexes possess the 

 fine caudal plumes, the large ear- tufts and the crimson 

 velvet about the head; I rind that all these characters 

 appear very early in life in accordance with rule. The 

 adult male can, however, be distinguished from the adult 

 female by the presence of spurs; and, conformably with 

 our rule, these do not begin to be developed before the age 

 of six months, as I am assured by Mr. Bartlett, and even 

 at this age the two sexes can hardly be distinguished.* The 

 male and female peacock differ conspicuously from each 

 other in almost every part of their plumage, except in the 

 elegant head-crest, which is common to both sexes; and this 

 is developed very early in life, long before the other orna- 

 ments which are confined to the male. The wild duck 

 offers an analogous case, for the beautiful grexi speculum 

 on the wings is common to both sexes, though duller and 

 somewhat smaller in the female, and it is developed early 

 in life, while the curled tail-feathers and other ornaments 

 of the male are developed later, f Between such extreme 

 cases of close sexual resemblance and wide dissimilarity, as 

 those of the Crossoptilon and peacock, many intermediate 



* In the common peacock (Pavo cristatus) the male alone possesses 

 spurs, while both sexes of the Java Peacock (P. muticus) offer the 

 unusual case of being furnished with spurs. Hence I fully expected 

 that in the latter species they would have been developed earlier in 

 life than in the common peacock; but M. Hegt of Amsterdam informs 

 me, that with young birds of the previous year, of both species, 

 compared on April 23, 1869, there was no difference in the develop- 

 ment of the spurs. The spurs, however, were as yet represented 

 nierely by slight knobs or elevations. I presume that I should have 

 ii formed if any difference in the rate of development had been 



served subsequently. 



f In some other species of the Duck family the speculum differs in 

 a greater degree in the two sexes; but I have not been able to dis- 

 cover whether its full development occurs later in life in the males of 

 such species, than in the males of the common duck, as ought to be the 

 case according to our rule. With the allied Mergus cucuttatus we 

 have, however, a case of this kind: the two sexes differ conspicu- 

 ously in general plumage, and to a considerable degree in the specu- 

 lum, which is pure white in the male and grayish white in the 

 female. Now the young males at first entirely resemble the females, 

 and have a grayish-white speculum, which becomes pure white at an 

 earlier age than that at which the adult male acquires his other and 

 more strongly -marked sexual differences: see Audubon, " Ornitholo- 

 gical Biography," vol. iii, 1835, pp. 249-250. 



