SEASONAL DIMORPHISM OF LE^IDOPTERA. 107 



normal time of flight of the prorsa-iorm. Pupae of the second 

 brood of 1884, which had pupated at the end of August and 

 the beginning of September, were therefore hybernated in a 

 cold room, and then, at the beginning of the spring, on March 

 1st, brought into the refrigerator at + 5° C, and there left 

 until June 27th, when they were brought into a room. There 

 emerged : — 



On July 8th, 6 levana. 

 July 10th, 3 levana. 



Among these there were, however, two specimens, which by the 

 greater extent of the black on the upper side exhibited an 

 approach, though a slight one, to porima. The temperature of 

 the room during the development was generally a high summer 

 heat, 22-30° C. ; it was colder on July 2nd only, viz. 18-7° C. 



TJiird experiment ivith levana, 1886.— It was to be ascer- 

 tained, whether the second brood, which usually hybernates, 

 could be forced by warmth to emerge in a shorter time, and to 

 assume the prorsa-ioxm.. 



Eggs and young larvae of this brood, collected in the open on 

 July 29th, were reared in the incubator at 30-32° C. Many 

 pupated as soon as Aug. 8th, the others somewhat later. The 

 pupae remained in the incubator at 30-32° C. There emerged : — 



On Aug. 15th, 2 pure prorsa. 

 „ 16th, 2 „ „ 

 „ 17th, 2 „ 

 „ 18th, 2 „ 



8 pure prorsa. 



The majority of which, however, were hindered in unfolding their 

 wings by the great humidity, and thereby more or less crippled. 

 In addition, several larvae had come out of the incubator, and 

 had pupated about the room. These also produced : — 



On Aug. 19th, 5 pure prorsa. 

 „ 24th, 1 „ 

 „ 26th, 1 „ 



So that consequently 15 prorsa were reared altogether. 



Unfortunately the further question, whether by a high enough 

 temperature all individuals can be forced to assume the summer 

 form and to emerge forthwith, is not decided in this experiment, 

 as the remaining pupae (about 50) were dead. 



Fourth experiment with levana, 1886. — Eggs and young 

 larvae of the second brood, found in the open on July 29th, 

 were reared at an ordinary room temperature, and pupated at 

 21-22° C. between Aug. 17th and 22nd. Out of 241 pupae there 

 emerged in the same summer, between Aug. 25th and 28th, 

 5 prorsa. The remaining 236 pupae, as an emergence was no 



