The Descent of Man

With Ruminants sexual differences of colour
occur more commonly than in any other order.
A difference of this kind is general in the Strepsicerene
antelopes; thus the male nilghau (Portax
picta) is bluish-grey and much darker than
the female, with the square white patch on the
throat, the white marks on the fetlocks, and the
black spots on the ears all much more distinct.
We have seen that in this species the crests and
tufts of hair are likewise more developed in the
male than in the hornless female. I am informed
by Mr. Blyth that the male, without shedding
his hair, periodically becomes darker during
the breeding-season. Young males cannot be
distinguished from young females until about
twelve months old; and if the male is emasculated
before this period, he never, according to
the same authority, changes colour. The importance
of this latter fact, as evidence that the colouring
of the Portax is of sexual origin, becomes
obvious, when we hear (24. Judge Caton,
in 'Transactions of the Ottawa Academy of Na-