ei6 THE DESCENT OF MAN. 



young of both sexes. But as with some few birds it is the 

 female which is brigliter colored than the male, so with 

 the Rhesus monkey {Macacus rhesus), the female has a 

 large surface of naked skin round the tail, of a brilliant 

 carmine red, which, as I was assured by the keepers in the 

 Zoological Gardens, periodically becomes even yet more 

 vivid, and her face also is pale red. On the other hand, in 

 the adult male and in the young of both sexes (as I saw in 

 the gardens), neither tlie naked skin at the posterior end 

 of the body, nor the face, show a trace of red. It appears, 

 however, from some published accounts, that the male does 

 occasionall}^, or during certain seasons, exhibit 'some traces 

 of the red. Although he is thus less ornamented than the 

 female, yet in the larger size of his body, larger canine 

 teeth, more developed whiskers, more prominent super- 

 ciliary ridges, he follows the common rule of the male ex- 

 celling the female. 



I have now given all the cases known to me of a dif- 

 ference in color between the sexes of mammals. Some of 

 these may be the result of variations confined to one sex 

 and transmitted to the same sex, without any good being 

 gained, and therefore without the aid of selection. We 

 have instances of this with our domesticated animals, as in 

 the males of certain cats being rusty-red, while the females 

 are tortoise-shell colored. Analogous cases occur in nature: 

 Mr. Bartlett has seen many black varieties of the jaguar, 

 leopard, vulpine phalanger and wombat; and he is certain 

 that all, or nearly all these animals, were males. On the 

 other hand, with wolves, foxes, and apparently American 

 squirrels, both sexes are occasionally born black. Hence 

 it is quite possible that with some mammals a difference of 

 color between the sexes, especially when this is congenital, 

 may simply be the result, without the aid of selection, of 

 the occurrence of one or more variations, which from the 

 first were sexually limited in their transmission. Never- 

 theless it is improbable that the diversified, vivid, and con- 

 trasted colors of certain quadrupeds, for instance, of the 

 above monkeys and antelopes, can thus be accounted for. 

 We should bear in mind that these colors do not appear in 

 the male at birth, but only at or near maturity; and that, 

 unlike ordinary variations, they are lost if the male be 

 emasculated. It is on the whole probable that the strongly 



