177 
[Garman. 
in the prevention of useless expenditure of venom upon objects 
unfit for prey. As I take it, the snake does not have a great num- 
ber of chances to feed in the course of the summer, and if one or 
more of these were lost, through lack of the venom recklessly thrown 
away on anything that came along, the consequence might be a long 
period of fasting before another opportunity of getting food pre- 
sented itself. After having thrown himself into coil, on the defen- 
sive, if the snake is not molested for a time he will start to escape. 
As he goes he often looks back over his shoulder, to be sure of not 
being pursued, sounding the rattle at the same time. Satisfied 
that attack is not intended he moves off more rapidly and quietly. 
The sound made by a rattle of half a dozen rings can be heard a 
distance of eight rods. Dampness modifies the sound. It has 
been suggested that the rattling serves as a call for the sexes. I 
have not found the snakes to be quick of hearing. There is much 
resemblance between the sound and the shrilling of certain insects, 
and it is possible, as has been remarked by Professor N. S. Shaler, 
that it may serve to bring animals that prey on the insects within 
reach of the rattler. Some specimens met with have never had rat- 
tles, through deformity, and through accident some have lost all ex- 
cept the button, yet those so deprived were in as good condition as 
others provided with long series. Thinness and brittleness in the 
rings cause such frequent losses that a perfect series of more than 
nine is something of a rarity.. 
The rattle of the rattlesnake is a series of the sloughs of the end 
of the tail, mechanically and loosely held together by reason of their 
shapes. This being the character of the organ, of course it can- 
not exist before the sloughing processes begin. The animal is not 
born with it, but acquires it some time after birth. Consequently, 
though we may not say exactly that the creature inherited the rat- 
tle, we can say that he has inherited the form of cap that induces 
it, that makes it both possible and unavoidable. It follows that in 
order to answer the inquiry as to how the snake got its rattle we 
shall have to trace the history of the cap. 
The testimony of the embryo is to the effect that the cap on the 
tip of the tail of the progenitor of the rattlesnake was essentially 
similar to that of the snakes which have no rattle, but it tells noth- 
ing of the causes of the later modification. For these we shall have 
to interrogate forms, in the various groups of serpents more or less 
PROCEEDINGS B. S. N. H. VOL. XXIV. 12 JULY, 1889 . 
