84 Mr. ^lerrifield's incuhnitdl i^hiicr vidians 



of my garden. During the very cold week at the 

 beginning of October, my sleeved larvae seemed to 

 make no growth at all. On the 6th October I brought all 

 indoors and forced them gently, and they had all spun 

 up by the 29th. I may here remark that I shut up 

 some illustraria larvae with birch leaves that were quite 

 sere and yellow, and they ate them ; the " frass " was 

 of a yellow-brown. 



While speaking of the coldness of the summer, I may 

 mention that Mr. Jenner of Lewes, to whom I gave 

 some illustraria eggs in the spring, had fifty or sixty 

 pupate in July, the first of them on the 5th, and the 

 others slowly through the month. Two moths, a male 

 and a female, appeared in July, the rest remaining over. 

 I shall have something more to say of these presently. 



One inference I should be inclined to draw from the 

 foregoing observations is that the temperature most 

 conducive to healthiness and large size in illunaria and 

 illustraria, is one a little higher than that of a warm 

 English summer. As to the cause of the usual 

 difference in size between the spring and the summer 

 emergence, I can at present suggest nothing beyond this, 

 — that the larva of the spring emergence is much longer 

 in feeding up than is the larva of the summer emer- 

 gence, and I think I have generally observed that where 

 there is no stunting or retarding from unhealthy 

 conditions, those larvae of a brood which are longest in 

 feeding up are the largest. 



As to the causes of variation in colour, markings, and 

 shape, the inquiry is a more complicated one, of course 

 embracing the pupal stage, though I am inclined to 

 think, for reasons I will give, that it should by no means 

 be confined to that stage. My experiments have been in 

 two directions, an artificially high temperature for larva 

 and pupa, and an artificially low one for the pupa, and 

 are concerned with three species, illunaria, illustraria, mid 

 Ennomos autuuinaria (the old abiiaria). [In connection 

 with this latter it should be remembered that it does not 

 hibernate as a pupa, and is, I believe, everywhere a 

 a single brooded species ; I have seen no indication to 

 the contrary after forcing it as larva and pupa, and then 

 forcing for several months the eggs laid by the forced 

 moths. J 



Dijfercnces in appearance between sprimj and summer 



