The Descent of Man

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yet unpublished case.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
chestnut-brown colour with a golden-red head,
is the male, whilst the other which is elegantly
variegated with green and white with a metallic
green head is the female. Now the young
from the first somewhat resemble the adults of
the corresponding sex, the resemblance gradually
becoming more and more complete.