SEASONAL DIMORPHISM OF LEPIDOPTERA. 79 



to whether the butterfly assumes the summer or the winter form, 

 with this species, at least, is determined by the temperature, 

 which influences it immediately after pupation. All the pupae of 

 this lot produced the winter form not so sharply defined, when, 

 after 25 days' cooling in the refrigerator, they were then forced 

 in the incubator, as when they remained until the autumn in the 

 lower temperature and then hybernated in the cold. 



Experiments with Pieris napi var. hryonice. 

 First experiment tvitJi hryonice. — The excellent entomologist, 

 Pastor Hauri, at Davos, in Les Grisons, had the goodness to 

 send me by post, at Freiburg i. Br., a number of captured 

 females of hryonice.^ Several arrived still alive on June 27th, 

 1887, and were placed under a gauze net on a flowering plant of 

 rape, on which they soon laid numerous eggs. These developed 

 rapidly at 26° C. in the room, and the young larvae, which were 

 not to be distinguished from ordinary nayi, fed greedily on rape, 

 and later on on ordinary cabbage. Pupation took place between 

 July 16th and 25th. 



As is well known, only one brood of hryonice flies in the Alps, 

 and it was first to be ascertained, whether in any way the tem- 

 perature of the lowlands would develope some of the butterflies. 

 Although great heat prevailed during the whole of July and 

 August, and the temperature of the room was generally over 

 20° C, yet none of the 24 pupae emerged that summer. They 

 were all hybernated in a cold room, and produced 24 butterflies 

 in the spring of 1888, between April 26th and June 7th, 12 males 

 and 12 females, all completely normal hryonice. 



Second experiment ivith hryonice. — On July 17th, 25 individuals 

 of the same brood as the first experiment, some shortly before, 

 others shortly after, their pupation, were brought into the in- 

 cubator, the temperature of which fluctuated about 29° C, and 

 never rose above 31*6° C. A male emerged as early as July 

 17th, coming from the pupae first brought into the incubator, 

 consequently after only 7 days' rest as a pupa. This butterfly 

 bore the characters of the summer form of napi ; the green 

 powdering of the veins on the under side of the hind wings is 

 very slight, and so is the black powdering of the bases of the 

 wings above ; on the other hand, the apices of the fore wings 

 above are dull and of a washed-out grey, therefore similar to the 

 winter form, and also to the var. hryonice. The black powdering 

 of the veins towards the margin of the wings, so characteristic 

 of the males of bryonies, is completely absent. The butterfly is 

 in gi-eat contrast to the male hryonice. As it was the only one of 



''' I should not neglect to here express my most grateful thanks to the 

 above-named gentleman for the repeated consignments of living females of 

 hryonice, by which alone I was enabled to set on foot the following breeding 

 experiments. 



