THE CANADIAN ENTOMOLOGIST. 229 



two factors from which such an influence might be expected, temperature 

 and length of development, i. e., the duration of the pupi period. The 

 duration of the larva period may be neglected, as this is very little shorter 

 with the winter generation (at least with the species used for experiment). 

 Starting at this point, experiments were made with levana. From the eggs 

 of the winter generation, which had emerged as butterflies in April, the 

 author bred larvae, which, immediately after they turned to chrysalids, were 

 put into an ice box, in which the temperature was but 8° to io° R. (5 2° 

 Fahr.) It appeared that this temperature was not low enough to have 

 much effect, for when after 34 days the box was taken out of the ice 

 chest, all the butterflies (about 40) had emerged. The experiment 

 succeeded in so far that instead of the prorsa form to be expected under 

 ordinary circumstances, most of the butterflies emerged as the so-called 

 porima, i. e., as one of the intermediate forms between prorsa and levana, 

 sometimes taken out of doors, and which more or less resembles prorsa 

 in design, but has much yellow like levana. In the succeeding experiment 

 the author placed the pupae directly in the ice house, where the tempera- 

 ture was o to 1, R. (33 Fahr.), and left them there four weeks. Of twenty 

 butterflies fifteen emerged porima, and among these were three which 

 looked exactly like levana, except that the narrow blue border line was 

 wanting. Five butterflies of the lot were unchanged, but came out 

 prorsa, and therefore were uninfluenced by the cold. From this it 

 appeared that by four weeks of cold down to 0-1 R., a greater part of the 

 butterflies inclined toward the levana form, and single individuals arrived 

 at the same almost completely. Should it now not be possible to make 

 the change complete, so that every one should have the levana form ? 

 But the author never succeeded in bringing this about. There were 

 always some individuals which kept the summer form, others were inter- 

 mediate, and but a few so changed that they looked like genuine levanas. 

 Experiments succeeded better with some of the Pierides, many of 

 which show the phenomena of seasonal-dimorphism. In P. napi the 

 summer and winter forms differ strikingly. Numerous individuals of the 

 summer generation were set in the ice house immediately after becoming 

 chrysalids, the cold being 0-1 R., and were left for three months, then 

 brought (nth Sept.) into the green-house. Between 26th Sept. and 3rd 

 Oct. there emerged 60 butterflies, which, without an exception, bore the 

 characters of the winter form, most even in an uncommonly strong 

 degree. But all did not emerge in the green-house, a part going over the 

 winter, and emerging the winter form the next spring. 



