REPTILES 



235 



only by the shape of the head but also by the presence of a dark 

 zigzag stripe running down the back, and it is especially common 

 in dry localities, such as sandy heaths. 



The Common Rattle- Snake (fig. 147) is a representative of 

 the " Pit " Vipers, a group characteristic of South Asia and 

 the New World, and so called because they possess a deep pit 

 in front of each eye. This particular kind is a large species 



Fig. 147. — Common Rattle-Snake [Crotahis durissunus) 



(length up to 6 feet) which inhabits North America, and, like 

 five other allied American species, is distinguished by the peculiar 

 organ known as a " rattle ". This consists of a number of inter- 

 locked horny rings at the tip of the tail, generally supposed to 

 be the remains of successive cast skins, though this is denied 

 by some authorities. The rings are at any rate more numerous 

 in old forms, while to begin with, the rattle is only represented 

 by a button-like knob. 



6. Blind- Snakes are small animals adapted to a burrowing 

 life, and differing in many ways from other members of the 

 order. The small head merges insensibly into a worm -like 

 trunk, and that again into a very short tail. The body is 

 uniformly covered with rounded scales, the large ventral horny 



