220 
SEXUAL selection: bikes. 
Part IL 
edged with brown.^^ So that the yery same feathers 
which 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 Avhat 
occurs in Class I., have transmitted their colours to 
their male offspring at an earlier age than that at 
Avhich they themselves first acquired them ; for if they 
had varied whilst quite young, they Avould probably 
have transmitted all their characters to their offspring 
of both sexes.^^ 
In AUTiurus 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 Eustephanus, 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- 
Mr. C. A. Wright, in ‘ Ibis,’ vol. vi. 1864, p. 65. Jerdon, ^ Birds 
of India,’ vol. i. p. 515. 
The following additional cases may be mentioned : the young 
males of Tanagra ruhra 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 ruhicola, are distinguishable at a very 
early age. 
