FISHES, BATR/iCHIANS, AND REPTILES 



227 



Fig. 186. — The rattles of the rattlesnake; 

 the lower figure shows a longitudinal sec- 

 tion of the rattle. 



only poisonous snakes of the United States are the rattle- 

 snakes and their immediate relatives, the copperhead and 

 water-moccasin. These snakes all have a large triangular 

 head, and in the rattlesnakes the posterior tip of the body 

 is provided with a 

 "rattle," composed 

 of a series of partly 

 overlapping, thin, 

 horny capsules, or 

 cones, of shape as 

 shown in fig. 186. 

 These horny pieces 

 are simply the some- 

 what modified, succes- 

 sively formed epider- 

 mal coverings of the 

 tip of the body, which 

 instead of being entirely moulted as the rest of the skin is, 

 are, because of their peculiar shape, loosely attached to one 

 another, and by the basal one to the body of the snake. 

 The number of rattles does not correspond to the snake's 

 years for several reasons, partly because more than one 

 rattle can be added in a year, and especially because 

 rattles are easily and often broken off. As many as 

 thirty rattles have been found on one snake. There are 

 two species of ground-rattlesnakes, or massasaugas, in 

 the United States, and ten species of the true rattlesnakes. 

 The center of distribution of the rattlesnakes is the dry 

 tablelands of the Southwest in New Mexico, Arizona, and 

 Texas. But there are few localities in the United States 

 outside the high mountains in which ' ' rattlers ' ' do not 

 occur, or did not occur before they were exterminated by 

 man. The copperhead is light chestnut in color, with 

 inverted Y-shaped darker blotches on the sides, and 

 seldom exceeds three feet in length. It occurs in the 



