30 SEXUAL SELECTION. [Part IL 



the world except in South America, and here no less than 

 four genera occur. One of these, Elaps, is venomous ; a 

 second and widely-distinct genus is doubtfully venomous, 

 and the two -others are quite harmless. The species be- 

 longing to these distinct genera inhabit the same districts, 

 and are so like each other, that no one " but a naturalist 

 would distinguish the harmless from the poisonous kinds." 

 Hence, as Mr. Wallace believes, the innocuous kinds have 

 probably acquired their colors as a protection, on the 

 principle of imitation; for they would naturally be 

 thought dangerous by their enemies. The cause, how- 

 ever, of the bright colors 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 Anolis cristatellus of South America is extremely 

 pugnacious: "During the spring and early part of the 

 summer, two adult males rarely meet without a contest. 

 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 generally ends in one of the 

 combatants losing his tail, which is often devoured by the 

 victor." The male of this species is considerably larger 

 than the female ; 5B 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 char- 

 acters. The male of the above-mentioned Anolis is fur- 



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

 see ' Land and Water,' Ju 1 ?, 1867, p. 9. 



