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. 
Rhinocerophis ammodytoides, Leybold, 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 vertebree, firmly anchylosed to it and to each other, 
