ill Pedigree Motli-hrecdinr/. 89 



sleeved originated in the pupal period, it would seem 

 to follow that the difference between about 66° and about 

 75° — 80° during an exposure of a very few weeks is 

 sufficient in this species for the purpose. It has been 

 suggested to me by Professor Weismann's remarks 

 (pp. 73 — 5) on the insufficiency of a difference of 14'9° E. 

 (33 "5° Fahr.) between the German winter and summer 

 temperatures to originate a climatic variety of P. j)oda- 

 lirius, while a difference of about 4° E. (= 9° Fahr.) be- 

 tween the summer temperatures of Germany and Sicily 

 is sufficient, and his inference that the cause is to be 

 found in the absolute temperature reached, that the 

 explanation of the difference between the forced and the 

 sleeved autumnaria is to be sought rather in the upper 

 than in the lower part of the thermometric range, i. c, 

 in the high temperature to which the forced were 

 exposed, a temperature which, as it happens, closely 

 approximates to the summer temperature of Palermo, 

 19'4° E. (75*6° Fahr.), rather than the low temperature 

 to which the sleeved were subjected.] 



EJfect of cold on impce of summer emergence. — The 

 observations made as to the effect of cold on the pupa 

 are as follows : — I begin with the effect of icing on pupte 

 that would in due course emerge in summer. I had 174 

 sleeved illustraria A pupee, which had spun up from 

 the 4th to the 15th July. All but 39 were forced from 

 the 17th. Nearly all of these emerged, and they did so 

 from the 20th to the 25th July. The 39 (23 males and 

 16 females), taken indiscriminately, except that large 

 ones were passed over so as not to prejudice the heredity 

 experiments, were on the 17th July exposed to a steady 

 temi3erature of 33"" — 34°, and so kept until 1st August, 

 i. e., for 15 days, when they were forced, and all emerged 

 in the 3 days from the 4th to the 7th, except one, Avhich 

 appeared on the 9th. As a whole they are noticeably, 

 but not strongly, darker in hue than the others ; in the 

 females especially there is a tendency to the contrast 

 between the dark inner and light outer portion of the 

 wings, which is so marked a feature in the spring 

 emergence. 



The effect of icing on the rate of development of pups 

 preparing for summer emergence appears, so far as my 

 observations have hitherto gone, to be to arrest [or 

 rather to retai'dj the development so long us the icing is 



