338 CLASS REPTILIA. 



move with a rattling sound as soon as the animal agitates its 

 tail. These various pieces receive no nourishment from the 

 animal's body and therefore do not grow. The first which is 

 formed is always closed and smaller than the rest ; the size of 

 the last piece of the bells or rattles, depends on the growth 

 of the last caudal vertebrae, for those pieces are primitively 

 moulded upon them. M. Bosc thinks that one is produced 

 every year, " and if their number should be found to vary 

 in the same species and at the same age, it is," adds this 

 observer, " that they are subject to separate accidentally, and 

 we can always, by means of calculation, find the number that 

 is wanting, since they all grow in a regular proportion." 



All these species are entirely similar to each other, not 

 only in form, but also frequently in size. They are all of a 

 fragile, elastic, semi-transparent matter, and of the same 

 nature as that of the scales. Their numbers vary from one 

 to thirty and upwards ; it is for the most part between five 

 and thirteen. 



The noise which these rattles produce, when they are 

 shaken, resembles that made by rumpled parchment, or that 

 of two quills of a goose rubbed smartly against one another. 

 It is reported that this noise can be heard at the distance of 

 more than one hundred feet ; but in the species which M. 

 Bosc has observed in the living state, he says that it could 

 not be heard farther ofi" than twelve or fifteen paces ; and 

 when the animal was moving in its usual gait, it was neces- 

 sary to be close to it, and even listen very attentively, to 

 perceive the sound. 



The crotali spread far around them a very foetid odour. 

 For a long time it was believed, and many naturalists still 

 believe, that this odour has the power of stupifying, or even 

 of fascinating the animal on which the venomous reptile is 

 desirous of preying. When the rattle-snakes are dead, they 



