THE ZooLocist—Aveust, 1872. 3193 
tail was shaken, and the vibrations were extremely rapid. Even 
as long as the body retained its irritability, a tendency to this 
habitual movement was evident. This Trigonocephalus has, there- 
fore, in some respects, the structure of a viper, with the habits of 
a rattlesnake; the noise, however, being produced by a simpler 
device.” 
It was these remarks of Darwin that first suggested the problem 
of the rattlesnake’s tail to my mind, and, as I had thought con- 
siderably about the matter, of course I was deeply interested in the 
paper of Prof. Shaler; but I must acknowledge that, while many 
of his suggestions are correct and highly valuable, I was dis- 
appointed to find that the only advantageous use, in his estimation, 
of this tail appendage of the rattlesnake, is an 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 used 
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. 
Description of the Larva of Eupithecia pygmwata.—Long, very slender, 
extremely attenuated on the capital segments. Ground colour pale dull 
yellowish green. Central dorsal line pale olive, connecting a series of very 
distinct and well-defined urn-shaped blotches of the same colour, which 
become confluent on the anal and capital segments. Subdorsal and 
spiracular lines pale olive, sinuous, well-defined and rather broad. Belly 
without markings. Skin rough and rugose, freely studded with short 
whitish hairs. In form and general appearance comes nearest to the larva 
of Kupithecia pulchellata. Feeds on petals and anthers of Stellaria 
holostea. Full fed June 20th. I am indebted to the kindness of Mr. 
Hodgkinson, of Preston, and Mr. Hellins, of Exeter, for an opportunity of 
describing this interesting and almost unknown larva. The former gentle- 
man took a female moth on May 25th. She deposited three eggs on a 
daisy flower, which, together with the parent insect, he forwarded to 
Mr. Hellins. The eggs hatched June 2nd. Mr. Hellins kindly sent me 
a larva just previous to its last moult. I had no Stellaria holostea within 
easy reach, but found it feed greedily on the petals and stamens of 
Cerastium tomentosum. Mr. Buckler has taken several life-like portraits 
of the interesting little stranger —H. Harpur Crewe ; The Rectory, Drayton- 
Beauchamp, Tring, June 21, 1872. 
