264 BULLETIN OF THE 



The anatomy of Crotalus was studied by Tyson in 1683 (Philo- 

 sophical Transactions, No. 144). 



In regard to the use of the rattle there is not much to be said. 

 Mainly, it is used to warn off disturbers, and thus prevent useless ex- 

 penditure of venom. Success in capture of food depends on an ever ready 

 supply of poison. To secrete a new lot takes time. The rattle is used 

 also in breeding season, though it is doubtful if the dull-eared creatures 

 depend on sound, rather than scent, to find their mates. A theory ad- 

 vocated by some maintains that the organ is used in imitating insects, to 

 draw the birds. An objection to this is the fact that birds are somewhat 

 rarely found in stomachs of the Crotali. An observation appearing to 

 favor this theory was made on a Dakota snake, found braced up among 

 the branches of a sage bush in such a way that the head overlooked the 

 surrounding bushes, while the tail, within the mass of branchlets, was 

 free to keep up the rattling that attracted the attention of a party 

 more than fifty yards distant. But the approach of the troop may 

 have occasioned the creature's peculiar behavior. 



Origin of the Rattle. 



Many serpents besides those possessed of a crepitaculum are addicted 

 to making a rattling noise by vibrations of the end of the tail. It is 

 likely the modifications of the organ apparent in some or others of these 

 are consequences of this habit. In illustration of the extent to which 

 the tail has been modified in different cases, apparently for similar pur- 

 pose, attention is directed to Figures 9-14, from species allied to 

 the rattlesnakes. 



Rhinocero'phis ammodytoides, Ley bold, Figs. 9, 10, from the Argen 

 tine Confederation, has its most prominent distinguishing features in a 

 prominence on the top of the snout, and, of more importance in this 

 writing, a peculiar termination of the tail. Fig. 9 outlines the caudal 

 surface. The terminal piece is sub-crescentic in longitudinal vertical 

 section, and sub-round in transverse. Externally it is covered by the 

 horny skin, internally it is bony. On the top, two of the dorsal scales 

 reach back more than a third of the length, and near their tips fuse 

 with each other and the skin about them. Fig. 10 shows the arrange- 

 ment after the skin and muscles have been removed. The outside of 

 the bone is hard, the inside not solid. It is penetrated by the canals of 

 the vertebrae, — indications of its origin. Inferiorly, it extends forward 

 below three of the vertebrae, firinly anchylosed to it and to each other, 



