3192 TuE Zootocist—Avcust, 1872. 
size and strength. Nor does its deadly poison act quickly enough 
to secure its own safety when it is attacked, but, in most cases, the 
victim, after the deadly stroke is given, may still revenge itself by 
the destruction of the snake. But the certainty of the effect of 
the poison serves as a warning and is advantageous, not in defence 
after the attack is made, but in preventing an attack from being 
made. If, then, the colour of the rattlesnake were different from 
all harmless snakes, so much so as to render it conspicuous, this 
would be beneficial to it, by the readiness with which all animals 
would recognize it, and thus protect the snake by this notice of the 
deadly character of its weapons. If, then, a conspicuous colour 
would be of advantage, it seems to me that any other means which 
it may be able to use in making knownits character to any animal 
that may come near it, would be advantageous, and would be 
increased and preserved by natural selection, and that the whirring 
noise which it produces, in this view of the matter, admirably 
serves its purpose. In effect it amounts to this, and by experience 
its enemies learn to understands its language, “‘ I am a rattlesnake, 
armed with what will be death to you if you come too near; give 
me a wide berth!” 
Prof. Shaler remarks that it is a fact well known doubtless to 
those who have observed serpents, that many when in a state of 
excitement vibrate the end of their tail just as the rattlesnake does. 
This statement reminded me of a South-American species described 
by Darwin in his ‘ Voyage of a Naturalist’ (vol. i., p. 123, Harper’s 
ed.), where he says :-— 
“Of reptiles there are many kinds: one snake (a Trigono- 
cephalus, or Cophias), from the size of the poison-channel in 
its fangs, must be very deadly. Cuvier, in opposition to some 
other naturalists, makes this a sub-genus of the rattlesnake, and 
intermediate between it and the viper. In confirmation of this 
opinion I observed a fact, which appears to me very curious and 
instructive, as showing how every character, even though it may 
be in some degree independent of structure, has a tendency to 
vary by slow degrees. The extremity of the tail of this snake is 
terminated by a point, which is very slightly enlarged, and as the 
animal glides along, it constantly vibrates the last inch; and this 
part, striking against the dry grass and brushwood, produces a 
rattling noise, which can be distinctly heard at the distance of 
six feet. As often as the animal was irritated or surprised, its 
