220 SEXUAL selection: birds. Part II. 



edged with brown.*^ So that tlie very same feathers 

 wliich in the young blackbird assume their mature cha- 

 racter and become black after the others, in these two 

 species assume this character and become blue before 

 the others. The most probable view with reference to 

 these cases is that the males, differently from what 

 occurs in Class I., have transmitted their colours to 

 their male offspring at an earlier age than that at 

 which they themselves first acquired them ; for if they 

 had varied whilst quite young, they would probably 

 have transmitted all their characters to their offspring 

 of both sexes.*® 



In Aithurus polytmus (one of the humming-birds) 

 the male is splendidly coloured black and green, and 

 two of the tail-feathers are immensely lengthened ; the 

 female has an ordinary tail and inconspicuous colours ; 

 now the young males, instead of resembling the adult 

 female, in accordance with the common rule, begin 

 from the first to assume the colours proper to their 

 sex, and their tail-feathers soon become elongated. 

 I owe this information to Mr. Gould, who has given 

 me the following more striking and as yet unpub- 

 lished case. Two humming-birds belonging to the 

 genus Eustephauus, both beautifully coloured, inhabit 

 the small island of Juan Fernandez, and have always 

 been ranked as specifically distinct. But it has lately 

 been ascertained that the one, which is of a rich ches- 



ts Mr. C. A. Wright, in ' Ibis,' vol. vi, 18G4, p. 65. Jerclon, ' Birds 

 of India,' vol. i. p. 515. 



•*9 The following additional cases may be mentioned : tlie yoimg 

 males of Tanarjra ruhra can be distinguished from the young femaks 

 (Audubon, ' Ornith. Biography,' vol. iv. p. 392), and so it is with the 

 nestlings of a blue nuthatch, DendropliRa fronlaUs of India (Jerdon, 

 * Birds of India,' vol. i. p. 389). Mr. Blyth al.->o informs me that the 

 sexes of the stonechat, Saxicola ruhicola, are distinguishable at a very 

 early age. 



