The Descent of Man

which were born pure white. These young
birds were not albinos, as shewn by the colour
of their beaks and legs, which nearly resembled
the same parts in the adults. (32. 'Bulletin de la
Soc. Vaudoise des Sc. Nat.' vol. x. 1869, p. 132.
The young of the Polish swan, Cygnus immutabilis
of Yarrell, are always white; but this species,
as Mr. Sclater informs me, is believed to be
nothing more than a variety of the domestic
swan (Cygnus olor).)
It may be worth while to illustrate the above
three modes by which, in the present class, the
two sexes and the young may have come to
resemble each other, by the curious case of the
genus Passer. (33. I am indebted to Mr. Blyth
for information in regard to this genus. The
sparrow of Palestine belongs to the sub-genus
Petronia.) In the house-sparrow (P. domesticus)
the male differs much from the female and
from the young. The young and the females are
alike, and resemble to a large extent both sexes