28 SEXUAL SELECTION. [Part II. 



strongly-pronounced tints ; thus the black zigzag band on 

 the back of the male English viper is more distinctly de- 

 fined than in the female. The difference is much plainer 

 in the Rattlesnakes of North America, the male of which, 

 as the keeper in the Zoological Gardens showed me, can 

 instantly be distinguished from the female by having more 

 lurid yellow about its whole body. In South Africa the 

 Bucephalus capensis presents an analogous difference, for 

 the female " is never so fully variegated with yellow on 

 the sides, as the male." 49 The male of the Indian Dipsas 

 cynGdon, on the other hand, is blackish-brown, with the 

 belly partly black, while 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-colored. 60 

 No doubt the colors of some snakes serve as a protection, 

 as 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 colors of many kinds, for instance 

 of the common English snake or viper, serve to conceal 

 them ; and this is still more doubtful with the many for- 

 eign species which are colored with extreme elegance. 



During the breeding-season their anal scent-glands are 

 in active function ; 51 and so it is with the same glands in 

 lizards, and as we have seen with the submaxillary glands 

 of crocodiles. As' the males of most animals search for 

 the females, these odoriferous glands probably serve to 

 excite or charm the female, rather than to guide her to the 

 spot where the male maybe found. 62 Male snakes, though 



49 Sir Andrew Smith, 'Zoolog. of "South Africa: Reptilia,' 1849, pi. x. 



60 Dr. A. Gunther, 'Reptiles of British India,' Ray Soc. 18G4, pp. 304, 

 308. 



51 Owen, 'Anatomy of Vertebrates,' vol. i. 1866, p. 615. 



62 The celebrated botanist Schleiden incidentally remarks (' Uebei 

 den Darwinismus : Unsere Zeit,' 1869, s. 269), that Rattlesnakes use 



