ORNITHOLOGICAL NOTES FROM THE WEST. 263 
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 
tail was shaken ; and the vibrations were extremely rapid. Even 
habitual movement was evident. This Trigonocephalus has, there- 
, in some respects, the structure of a viper, with the habits of 
r rattlesnake; the noise, however, being produced by a simpler 
evice.” 
It was these remarks of Darwin that first suggested the problem 
of the rattlesnake’s tail to my mind, and, as I had thought consid- 
ably about the matter, of course I was deeply interested in the 
paper by Prof. Shaler ; but I must acknowledge that, while many of 
his suggestions are correct and highly valuable, I was disappointed 
to find that the only advantageous use, in his estimation, of this 
tail appendage of the rattlesnake, is am imitative call-note to 
allure birds within its reach, and that, otherwise, it is rather a 
disadvantage than an advantage to be preserved and perfected by 
natural selection. If it is useful for both purposes, then there is a 
double reason for the action of natural selection. If it is not 
wed as an imitative call-note, but is useful in the manner I have 
Pointed out, then I have shown that it is explained by natural 
Selection, 
ORNITHOLOGICAL NOTES FROM THE WEST. 
BY J. A. ALLEN. 
I. NOTES ON THE BIRDS OF KANSAS. 
iy the spring of 1871 an expedition to the Plains and the 
Rocky Mountains was sent out by the Museum of Comparative 
‘Zoilogy > under the charge of the writer. During the nine months 
oat m the field by the party in question, the department of 
Smnithology received a large share of attention. In the following 
Pages it is proposed to give a hasty résumé of such observations 
