THE VERTEBRATES 



211 



With the exception of the coral- or bead-snake, a rather 

 small, jet-black snake, with seventeen broad, yellow-bor- 

 dered crimson rings, found in the Southern States, the 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 triangu- 

 lar head, and in the rat- 

 tlesnakes the posterior 

 tip of the body is provi- 

 ded with a "rattle, "com- 

 posed of a series of 

 partly overlapping, thin, 

 horny capsules, or cones, 

 of shape as shown in fig. 

 109. These horny pieces 



are simply the somewhat FIG. 109. The rattles of the rattle-snake; 



modified, successively the lower % ure shmvs a longitudinal 



r i i i section of the rattle. (Natural size.) 



tormed epidermal cover- 

 ings of the tip of the body, which instead of being entirely 

 moulted as the rest of the skin is, are, because of their pecu- 

 liar shape, loosely attached to one another, and by the basal 

 one to the bodv 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 es- 

 pecially 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- 



