HAUNTS AND HABITATS 43 



sole representative of its genus) in Southern Mexico. On the 

 other hand the boas {Boincz) are mainly characteristic of tropical 

 America, the home of the gigantic anaconda. There are, in- 

 deed, certain Old World generic types (Eryx, Enygrus, and 

 Casarea), but the remarkable feature in the distribution of the 

 family is the occurrence of representatives of the American 

 genera Boa and Corallus in Madagascar ; — a peculiarity paral- 

 leled by the distribution of Podocnemis among the tortoises. 



As regards the distribution of the family Colubridce, which 

 includes the majority of snakes, a brief notice must suffice, as 

 many of the groups have a cosmopolitan range. Considerable 

 interest attaches, to the distribution of the poisonous sub- 

 family ElapincE (which includes the cobras of India and Africa). 

 This group ranges over the tropical and sub-tropical regions of 

 both hemispheres (exclusive of Madagascar), but is particularly 

 characteristic of Australia, where other snakes are represented 

 only by a few pythons and blind snakes (Typlilopidce) and a 

 small number of ColubrincB, or typical snakes. Nearly allied to 

 the Elapince are the sea-snakes (Hydrophitnce), which range 

 from the Persian Gulf to Central America. Noteworthy, too, 

 is the distribution of the AmblycephalidcB, a small family of 

 snakes allied to the Colubridce, of which some forms are found 

 in tropical America and the rest in the Oriental region. 



The vipers ( Viperidce) have a nearly cosmopolitan distribu- 

 tion, although absent from Madagascar and Australia ; but 

 whereas true vipers (subfamily Viperince) form an exclusively 

 Old World group, pit-vipers {Crotaluice) are represented in 

 tropical Asia as well as in both North and South America. 

 In this subfamily the rattlesnakes (Crotalus) form a characteris- 

 tic and widely distributed American group, although they have 

 near relatives in the Old World, which are however unprovided 

 with the distinctive rattle. 



As is evident from the statement already made as to their 

 absence from the high north, reptiles are extremely sensitive to 

 cold ; and in temperate climates the whole of the species hiber- 

 nate for a longer or shorter period in the cold season. With 

 the exception of those adapted to a life in the desert, reptiles, 

 and especially the sub-aquatic kinds, are intolerant of intense 

 dry heat, and certain kinds " aestivate," or become torpid, 

 during such periods. 



