n] FEATURES OF ENVIRONMENT 27 



of mimicry. In reality it is a case of convergence, 

 brought about by identical environmental conditions. 

 One might almost say that tropical moist forests must 

 have tree-frogs, and that these are made out of what- 

 ever suitable material happens to be available. 



The same remark applies to tree-snakes, and it is 

 immaterial whether the available stock be boas or 

 pythons, harmless colubrines, cobras, vipers or even 

 pit-vipers. In India all these groups have con- 

 tributed. Typical tree-snakes invariably have a very 

 long, slender body with an excessively long whip-like 

 tail. Thus they can glide through the foliage from 

 tree to tree, their long body and tail always finding 

 some support. 



Boas and pythons have short and strong pre- 

 hensile tails, and the numerous chameleons of Africa 

 and Madagascar have grasping hands and feet as well. 

 This principle of prehensile organs is carried to an 

 extreme in various mammals, of which it is sufficient 

 to mention monkeys and lemurs, the pangolins and 

 sloths among edentates, palm-martins among carni- 

 vores, arboreal porcupines among rodents, and opos- 

 sums among marsupials. All have either specially 

 modified climbing hands and feet, or tails, or both. 



But the especial home of prehensile-tailed mam- 

 mals is in the tropical forests of America. There 

 alone live the prehensile-tailed monkeys. Nearly all 

 its marsupials are arboreal opossums. Even two 



