SEXUAL SELECTION 629 



the nestling males of both species have their main wing 

 and tail-feathers edged with blue, while those of the female 

 are edged with brown." In the young blackbird the wing- 

 feathers assume their mature character and become black 

 after the others; on the other hand, in the two species just 

 named the wing-feathers become blue before the others. 

 The most probable view with reference to the cases in the 

 present class is that the males, differently from what occurs 

 in Class I., have transmitted their colors to their male off- 

 spring at an earlier age than that at which they were first 

 acquired; for, if the males had varied while quite young, 

 their characters would probably have been transmitted to 

 both sexes." 



In A'ithurus polytmus, a humming-bird, the male is splen- 

 didly colored black and green, and two of the tail-feathers 

 are immensely lengthened; the female has an ordinary tail 

 and inconspicuous colors; now the young males, instead of 

 resembling the adult female, in accordance with the common 

 rule, begin from the first to assume the colors proper to their 

 sex, and their tail-feathers soon become elongated. I owe 

 this information to Mr. Gould, who has given me the fol- 

 lowing more striking and as yet unpublished case. Two 

 humming-birds belonging to the genus Eustephanus, both 

 beautifully colored, inhabit the small island of Juan Fer- 

 nandez, and have always been ranked as specifically distinct. 

 But it has lately been ascertained that the one, which is of 

 a rich chestnut brown color with a golden-red head, is the 

 male, while the other, which is elegantly variegated with 

 green and white, with a metallic-green head, is the female. 

 JNow the young from the first somewhat resemble the adults 

 of the corresponding sex, the resemblance gradually becom- 

 ing more and more complete. 



In considering this last case, if, as before, we take the 

 plumage of the young as our guide, it would appear that 



« Mr. C. A. Wright, in "Ibis," vol. vi., 1864, p. 65. Jerdon, "Birds of 

 India," vol. i. p. 515. See, also, on the blackbird, Blyth, in Charlesworth's 

 "Mag. of Nat. History," vol. i., 1837, p. 113. 



^ The following additional cases may be mentioned : the young males of 

 Umagra rubra can be distinguished from the young females (Audubon, "Ornith. 

 Biography," vol. iv. p. 392), and so it is with the nestlings of a blue nuthatch, 

 Dendrophila frontalis of India (Jerdon, "Birds of India," vol. i. p. 389). Mr. 

 Blyth also informs me that the sexes of the stonechat, Saxicola rubicola, are 

 distinguishable at a very early age. Mr. Salvin gives ("Proc. Zoolog. Soc," 

 1870, p. 206) the case of a humming-bird, like the above one of Eustephanui. 



