The Descent of Man

snakes of N. America, the male of which, as the
keeper in the Zoological Gardens shewed me,
can at once be distinguished from the female by
having more lurid yellow about its whole body.
In S. Africa the Bucephalus capensis presents
an analogous difference, for the female "is never
so fully variegated with yellow on the sides
as the male." (56. Sir Andrew Smith, 'Zoology
of S. Africa: Reptilia,' 1849, pl. x.) The male of
the Indian Dipsas cynodon, on the other hand,
is blackish-brown, with the belly partly black,
whilst the female is reddish or yellowish-olive,
with the belly either uniform yellowish or marbled
with black. In the Tragops dispar of the
same country the male is bright green, and the
female bronze-coloured. (57. Dr. A. Gunther,
'Reptiles of British India,' Ray Soc., 1864, pp.
304, 308.) No doubt the colours of some snakes
are protective, as shewn by the green tints of
tree-snakes, and the various mottled shades of
the species which live in sandy places; but it is
doubtful whether the colours of many kinds,