experiments on some Lcpidoptera. 139 



actually reached, and whether the markings also would 

 change ; and, if so, it struck me that it would be inter- 

 esting to let the insect record, as it were for itself, in the 

 markings of the preserved specimens, the steps by 

 which the change in the markings was effected. Accord- 

 ingly I brought up a brood from a single pair, from which 



I obtained 87 pupse between 17th June and 3rd July. 

 Fourteen were not iced, and previous experiments having 

 led me to observe that there is often some difference in 

 general colouring between the first and last parts of a 

 brood, 8 of these 14 were taken from among those 

 which pupated earliest, and 6 when about two-thirds 

 had spun up. The whole of the 14 emerged in good 

 condition, showing that I had fallen on a healthy 

 brood ; and showing also that it was a naturally dark 

 coloured one, and therefore, perhaps, not so well 

 adapted to show any darkening of colour as a lighter 

 coloured set would have been. I had rather gathered, 

 from experiments by others previously published, that 

 about 28 days might be expected to produce full results ; 

 and therefore at first I was rather extravagant in the 

 use of my materials, so that the numbers taken from 

 time to time out of the ice had to be greatly reduced 

 when experience showed that a much longer time was 

 necessary to produce full efi'ects in the case of this 

 insect. The fortnightly withdrawals were as follows : — 

 10 pupae in 2 weeks, 12 in 4 weeks, 4 each in periods of 

 6, 8, 10, 12, 14 and 16 weeks, and 2 each in periods of 



II and 20 weeks ; and I have 14 pupae remaining, which 

 I hope to spread, if necessar}^ over another 12 weeks, 

 as this will make up the period of 71- months, which is 

 the full duration of the usual winter pupational period ; 

 this, however, does not seem necessary, as previous 

 experiments lead me to believe that about 5 months is 

 sufficient to produce the full colouring of the spring 

 form under natural conditions, with an average tem- 

 perature much higher than 33°. 



((/) Summer pupa of illustraria ; effect of icing on 

 vigour. — Great as is the dift'erence between exposure for 

 two or three weeks to a temperature of 60^ — 70°, which 

 is what this summer pupa in its natural state would 

 sustain, and exposure of it, as in the experiments last 

 described, to a temperature of 33° for 20 weeks, no 

 injury seems to have been inflicted by this severe trial. 



