Chap. VIII.] SEXUAL SELECTION. 281 



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

 velvet about the head ; and I find on inquiry in the Zo- 

 ological Gardens that all these characters, in accordance 

 with our rule, appear very early in life. The adult male 

 can, however, be distinguished from the adult female by 

 one character, namely, by the presence of spurs ; and 

 conformably with our rule, these do not begin to be de- 

 veloped, as I am assured by Mr. Bartlett, before the age 

 of six months, and even at this age, can hardly be dis- 

 tinguished in the two sexes. 28 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 de- 

 veloped 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 green 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 

 peculiar to the male are developed later. 29 Between such 



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

 spurs, while both sexes of the Java peacock (P. muticus) offer the unu- 

 sual 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, belonging to both species, com- 

 pared on April 23, 1869, there was no difference in the development of 

 the spurs. The spurs, however, were as yet represented merely by slight 

 knobs or elevations. I presume that I should have been informed if 

 any difference in the rate of development had subsequently been ob- 

 served. 



29 In some other species of the Duck Family the speculum in the two 

 sexes differs in a greater degree ; but I have not been able to discover 

 whether its full development occurs later in life in the males of such spe- 

 cies, than in the male of the common duck, as ought to be the case ac- 

 cording to our rule. With the allied Mergus cucullatus we have, however, 

 a case of this kind : the two sexes differ conspicuously in general plu- 



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