The Descent of Man

in the present class 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 were first acquired;
for, if the males had varied whilst quite
young, their characters would probably have
been transmitted to both sexes. (48. The following
additional cases may be mentioned; the
young males of Tanagra rubra can be distinguished
from the young females (Audubon,
'Ornith. Biography,' vol. iv. p. 392), and so it is
within 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 following
one of Eustephanus.)
In Aithurus polytmus, a humming-bird, the
male is splendidly coloured black and green,