274 THE ENTOMOLOGIST. 



In addition to the seasonal dimorphism of the above three 

 species of Pieris, another British butterfly has absorbed a good 

 deal of my attention. I refer to Va7iessa c-alhum. In ordinary 

 seasons the light form of this insect, which I have named 

 lutescens {ante, p. 257), appears in this country only as an 

 aberration of the type of the first brood. The number, however, 

 which appear each season in proportion to the type varies 

 entirely according to the temperature. In exceptionally wet, 

 cold seasons I have thus experienced considerable difficulty in 

 procuring a single specimen of the light form, although those of 

 the dark were not of uncommon occurrence. It is the males 

 w^iich seem to be more affected by the cold and wet, judging 

 from the relative proportions of the two sexes in the variety 

 lutescens whenever adverse climatic conditions prevail. The 

 males are similarly less affected by a higher temperature. This 

 season, which has been singularly fine and warm, has been the 

 means of producing the variety lutescens in abundance. I have, 

 in fact, taken over thirty of it, but not a single specimen of the 

 type, so that what is in the great majority of seasons only an 

 aberration of the first generation has occurred this year as the 

 type of that brood, as is the case upon the Continent — at least 

 in the centre and the south — every season. 



My hypothesis concerning this butterfly — and the facts seem 

 strongly to support it — is that what constitutes the second brood 

 of Vanessa c-alhum in Europe at the present day formerly 

 occurred as the only generation, perhaps shortly after the ter- 

 mination of the glacial period, but that more favourable climatic 

 conditions existing now enable the butterfly to perform its 

 metamorphoses in a shorter period, and thus to make two 

 appearances in the same year instead of only one. The first 

 brood existing now is therefore the most recent production, and 

 the light form of the butterfly in consequence the most highly 

 specialised of the two. 



Birmingham, August, 1896. 



SILK-PEODUCING LEPIDOPTERA. 



By Alfred Wailly. 

 (Membre Laureat de la Society Nationale d'Acclimatation de France.) 



(Continued from p. 239.) 



BoMBYx (Theoj)liila) sherwilli, Moore. The moth of this 

 species much resembles that of B. huttoni, but it is a little larger. 

 All that is known of it is that the perfect insect was found in the 

 collection of Major J. L. Sherwill ; it is not known whether it 

 was captured in the plains or at Darjeeling. 



BoMBYX {Ocinara) RELiGioSiE, Heifer.— '' Although bearing 



