132 Mr. F. Merrifield's systematic temperature 



Lepidoptera may hibernate in any of the 4 stages- 

 egg, larva, pupa, or imago ; and I wished to ascertain 

 whether those experimented on could be made to hiber- 

 nate in a stage normally passed in a warmer period of 

 the year. 



It is in one or other of the two inactive stages — those 

 of egg and pupa — that I believe the majority of the 

 Lepidoptera, in countries where there is a real winter, 

 pass the cold period of the year, during which for most 

 of them neither food is to be had for the larva nor 

 flowers for such perfect insects as are attracted by them ; 

 but the cases in which hibernation takes place in one 

 or other of the two active stages — those of larva and 

 imago — are common, and the capability of passing the 

 winter in a different stage from that in which it has 

 habitually been passed, especially if an insect has a 

 capacity for becoming double-brooded, would, it has 

 been suggested, be a means by which it could adapt 

 itself more readily to the great changes of climate to 

 which the species must have been subjected in past ages. 

 I began with the 



Egg Stage. — I believe it is a common opinion that 

 eggs which are usually exposed only to a summer tem- 

 perature will generally bear severe and protracted cold 

 without injury to their vitality. 



Referring to Tables I. and II. appended for details of 

 the experiments made on this point, I limit myself here 

 to a statement of results. In the case of illunaria 

 spring-laid eggs, iced in the central "red" stage, 28 

 days began to affect their vitality, and none hatched 

 after 60 days' icing. The case was worse with spring- 

 laid eggs oi illustrarJa, none of which survived 42 days' 

 icing ; and some illustrarid summer-laid eggs were no 

 better. In all the experiments up to 60 days' exposure, 

 and I think beyond that period, nearly all the eggs, after 

 being removed from the ice, matured so far as to admit 

 of the formation of the young larva, which could be seen 

 through the transparent shell ; the failure was a failure 

 to hatch. 



A curious result happened with some spring-laid 

 illiLstraria eggs iced before they had turned red ; two of 

 them became blackish while in the ice (where the eggs 

 were kept for 17 days), and hatched the day they were 

 taken out of the ice, or the next day, the rest remaining 



