REPTILES 293 



ones covered t>y the basilar and middle ridges of the first. 

 In this manner are the rattles formed to the number of 

 twelve, or, if certain relations are to be credited, to the 

 number of twenty or even thirty cups. 



As the middle and terminal ridges of the last formed cup 

 are rather less in diameter than the grooves of the basilar 

 and middle ridges of the preceding one, in which they are 

 contained, a kind of ball and socket-joint is formed at each 

 division, admitting an imperfect degree of motion when the 

 body moves. 



Each cup, when covering the vertebra, appears to be 

 nourished in the same manner as the skin. When detach- 

 ed from the vertebra, however, though still connected with 

 the last formed one, it dries and becomes brittle and elastic. 

 When the serpent moves its body, the cups of the rattle, 

 likewise moving upon one another, make a noise not UIL- 

 like the folding of dried parchment. This noise is said to 

 be audible at the distance of twenty yards, and is thus use- 

 ful in giving warning of the approach of the destructive 

 reptile to which it is attached. As the cups of the rattle 

 consist merely of dried matter which, in the dry season, is 

 brought into a condition to make a noise when the animal 

 moves, so, in like manner, under the influence of external 

 circumstances, the rattle, in the wet season, is soft and 

 mute. 



It does not appear to be as yet determined, whether a 

 new cup is formed with each renewal of the skin, or whe- 

 ther the succession of the cups takes place in a different 

 order. The number of cups found in a rattle, can scarcely 

 be considered as the number which have actually been 

 formed, but merely as the number of those which have 

 outlived accidents. There are two nasal bags or crumciis, 

 ai d two scent bags at the vent, 



