328 



PRACTICAL ZOOLOGY 



habiting the southern part of the United States that are prac- 

 tically harmless. 



The rattlesnakes (Fig. 206) occur almost all over the United 

 States, but are particularly abundant in the deserts of the south- 

 west. The largest species, the diamond-back rattlesnake, occurs 

 in the Southeastern States, and reaches a length of over eight 

 feet. The banded rattlesnake is a resident of the Eastern States; 

 the massasauga inhabits the Central States; and the horned 

 rattlesnake is common in the deserts of the Southwest. 



The rattles of these snakes are strings of bell-shaped pieces 

 of exoskeleton, each piece representing what was once the end 

 of the tail. The skin is shed several times a year, but the bell- 

 shaped " button " at the end of the body does not come off, being 

 added to the rattles already present. Rattles are often lost so 

 that the age of the snake cannot be determined by counting 



them. The rat- 

 tles are used to 

 warn other ani- 

 mals of the pres- 

 ence of the snake ; 

 when vibrated, 

 they produce a 

 buzzing sound. 



The poison ap- 

 paratus of the rat- 

 tlesnake (Fig. 207) 

 consists of a pair 

 of poison glands 

 lying above the 

 roof of the mouth, 

 which are con- 

 nected by ducts 

 with a pair of 

 long, hollow teeth, the fangs, situated near the outer end of the 

 upper jaw. When the snake strikes, the jaws are opened very 



FK;. 207. Poison apparatus of rattlesnake. 

 (Photo, furnished by American Museum of Natural 

 History.) 



