106 THE ENTOMOLOGIST. 



by more exhaustive and, where possible, more accurate experi- 

 ments. After the conclusion of these I first came to regard the 

 seasonal dimorphism of many butterflies, and so also, hypotheti- 

 cally at least, that of prorsa-levaiia, not (as hitherto) as the 

 direct effect of the differences of temperature, but as adaptive- 

 dimorphism, the two schemes of development of which are only 

 connected with different temperatures as the excitants which set 

 them free (Auslosungsreize). If the experiments afford con- 

 firmation of this view, they may be regarded as unbiased testi- 

 mony for the accuracy of it. 



First experiment with levana, 1883-84. — Numerous (far over 

 100) eggs and young larvae of the second brood were collected 

 on Aug. 8th, and reared at the ordinary temperature. Pupation 

 took place at the beginning of September. The pupae were kept 

 in a heated room, and one prorsa emerged there. 



From Jan. 10th, 1884, onwards, the pupae were kept in the 

 incubator over water at 27-30° C. The regulation of the in- 

 cubator was, however, not quite suitable, and the temperature 

 occasionally rose too high. Many pupae therefore died, and 

 many butterflies emerged crippled. I bred : — 



On Jan 



18th, 5 levana i 







19th, 6 









20th, 2 









21st, 3 

 22nd, 2 

 23rd, 3 

 24th, 1 





All are without the blue 





porima 



marginal lines of the 

 hind wings. 





25th, 10 levana 





j> 



26th, 1 



a 







29th, 1 



»» 







34 butterfli 



es. 



Out of these 34 specimens only 15 were developed quite perfectly; 

 19 had more or less crumpled and crippled wings, but so that 

 the colour and marking can be recognised. The frequent 

 crippling is doubtless to be referred to the very damp air of the 

 incubator, which moistens the pupal integuments and makes 

 them soft, and thus renders emergence difficult. In order to 

 prevent this, the pupae were taken out of the incubator on 

 March 1st, and placed in a warm room, which was unheated 

 later on. However, only one more emerged, viz. : — 



On May 24th, 1 pure levana female. 



Second experiment with levana, 1884-85. — It should be de- 

 .cided, whether hybernated pupae can be forced to assume the 

 prorsa-ioim instead of the levana-ioxm by artificially with- 

 holding their development until the summer, i. e. until the 



