32 SEXUAL SELECTION. Part II. 



thought dangerous by tlieir enemies. The cause, how- 

 ever, of the bright colours of the venomous Elaps 

 remains to be explained, and this may perhaps be 

 sexual selection. 



Lacertilia. — The males of some, probably of many 

 kinds of lizards fight together from rivalry. Thus the 

 arboreal Aiiolis cristatellus of S. America is extremely 

 pugnacious : " During the spring and early part of the 

 " suDimer, two adult males rarely meet without a con- 

 " test. On first seeing one another, they nod their heads 

 " up and down three or four times, at the same time 

 '•' expanding the frill or pouch beneath the throat ; their 

 " eyes glisten with rage, and after waving their tails 

 " from side to side for a few seconds, as if to gather 

 '' energy, they dart at each other furiously, rolling over 

 " and over, and holding firmly with their teeth. The 

 " conflict irenerallv ends in one of the combatants losinoj 

 " his tail, which is often devoured by the victor." The 

 male of this species is considerably larger than the fe- 

 male ;^'^ and this, as far as Dr. Giinther has been able to 

 ascertain, is the general rule with lizards of all kinds. 



The sexes often differ greatly in various external 

 characters. The male of the above-mentioned Anolis 

 is furnished with a crest, which runs along the back and 

 tail, and can be erected at pleasure ; but of this crest 

 the female does not exhibit a trace. In the Indian 

 Coj>hotis ceylanica, the female possesses a dorsal crest, 

 though much less developed than in the male ; and 

 so it is, as Dr. Giinther informs me, with the females 

 of many Iguanas, Chameleons and other lizards. In 

 some species, however, the crest is equally developed in 

 both sexes, as in the Iguana tuherculata. In the genus 



^^ Mr. N. L. Austen kept these animals alive for a considerable time ; 

 see ' Land and Water,' July, 18G7, p. 9. 



