170 THE ENTOMOLOGIST. 



average measure of Polj/cldows in expanse of wings, being about 

 the usual size of Urticcc (two inches). The insect is the only 

 individual of the brood known to have varied, even in the 

 slightest degree. Although I did not see every member of the 

 brood, I can vouch for at least forty or fifty specimens, which I 

 examined carefully, and found not a trace of variation in any 

 single case. No larvae of any other species of Vancssidce were 

 reared contemporaneously with the brood. 



I have examined the antennse of this specimen under the 

 microscope, and find that they present the special characters 

 found in Polycliloros. 



From these facts I make four deductions, all of which turn 

 upon points of interest. It is from such instances of divergence 

 as the present that we are enabled to gain some clue respecting 

 the affinity of species known to be closely related, and for this 

 reason I ofl'er the following observations : — 



1. As Polycliloros lives upon elm and other trees, and Urticce 

 upon nettle and low plants, the instance is valuable as affording 

 further evidence of the fact that neither a particular food nor a 

 change in diet affects in any way the colouring and markings of 

 the perfect insect, so as to offer j^er se a means of originating 

 "varieties." This conclusion is valid whether the specimen 

 under consideration be really a Polycldoros or Urticce. Many 

 experiments upon different species of insects agree, I believe 

 without exception, in so deciding this question. 



2. On the supposition that the specimen is the product of 

 Polycliloros parents, it is easy to infer either that the ovum was 

 dropped whilst the female was on the wing, or else that the 

 young caterpillar fell from a neighbouring tree soon after 

 emergence from the egg ; in either case the accident must have 

 occurred immediately over the Urticce web. As the broods of the 

 two species rarely appear synchronously, the conjecture is scarcely 

 to be entertained, even if the accident were probable. On such a 

 supposition, however, it is to be deduced that (if Polycliloros) the 

 society of an allied species does not affect the development of the 

 individual, but such individuals are treated as friends. It is to be 

 remembered, at the same time, that the larva of Urticce bears a 

 much closer resemblance to Pyrameis Cardni than to Polycliloros 



ispecimens of larvee (preserved) were exhibited for the sake of 

 comparison.] 



