experiments on some Lejndoptera . 147 



1887, by keeping the insect in all stages at a tempera- 

 ture of about 80°, I brought out four successive broods 

 of illunaria in ten months, all of the summer type. 



6. After larval growth is comijleted, no complete con- 

 version of the one type into the other can be effected ; 

 it seems clear that such a conversion cannot be made as 

 regards size, and but slightly, if at all, as regards shape ; 

 and it seems probable that it cannot be completely 

 made as regards colour or markings. This incapability 

 as to colour and markings certainly exists as respects 

 illustraria, also, according to the published experiments 

 before adverted to, as respects A. lev ana and P. ajax ; 

 and I gather that in the cases published as to P. rapce, 

 P. napi, P. pliaros, and P. inter rogationis the butter- 

 flies from the iced summer pup£e presented some diffe- 

 rences from the normal form proceeding from the winter 

 pupa. 



7. In the species experimented on by me (and in some 

 others) the capability of being turned during the pupal 

 period from the one type partially in the direction of 

 the other exists in both the summer and the winter type, 

 but is much greater in the former than in the latter. 



II. As to both double -brooded and single-brooded species. 



8. In those experimented on by me the temperature 

 to which the pupa is exposed modifies the colour and 

 markings of the imago, sometimes in a striking manner; 

 low temperature in these species tending to melanism. 



9. The difference between 65° and 80° in the tempera- 

 ture to which the pupa is exposed is sufficient in some 

 cases to make a very marked difference. In E. autum- 

 naria it is enough to make the whole difference in 

 appearance between the ordinary pale continental type 

 and the dark and spotted type. 



I do not see that the experiments in themselves lend 

 any support to the theory that illustraria, having 

 originally been a single-brooded species suited to a cold 

 climate, could, as it spread to a warmer region, or as a 

 glacial period receded, pass the winter in any other than 

 the pupal stage, and by that means adapt itself to 

 become regularly double-brooded ; for in no stage but 

 this have I been able to carry it alive through even a 

 short artificial winter, and the winters on the hypothesis 

 must have been very long ones. Nor do they appear to 



L 2 



