Feb. '08] JOURNAL OF ECONOMIC ENTOMOLOGY 59 



quent experiments have proven to be true. This fall we placed sev- 

 eral lots in an icehouse and in cold storage for various lengths of 

 time during August and September, at the same time placing other 

 lots in glasshouses, where they never were subject to low temperatures. 

 Those which were placed in cold storage have hatched, in the case 

 of the tent caterpillar eggs in about two weeks, while those which 

 have not been subjected to cold have not hatched yet. Several lots 

 placed in storage and taken out at different times have proven this, 

 and our experiments are arranged to show how long they must be 

 subjected to low temperature and whether extreme low temperatures 

 have any more effect or will reduce the time of hibernation more than 

 those merely below the critical point. This fact had been previously 

 shown by Weismann in his paper, ''On the Seasonal Dimorphism of 

 Butterflies" nearly thirty years ago,^ when he described experiments 

 in which by subjecting pupee of the summer form of Pieris napi to 

 refrigeration for three months and then bringing them into a hothouse 

 he was able to secure the winter form by about October first, but in 

 which he was unable to secure the immediate transformation of pupae 

 of the fourth brood of Araschnia levaiva (prorsa) by placing them in 

 a hothouse as soon as the pupae formed, for invariably nearly all hiber- 

 nated over winter, even in the warm hothouse, and emerged in the 

 spring as the winter form. It is evident that subjecting these hiber- 

 nating forms to low temperatures has the effect of producing a more 

 complete rest than when hibernation goes on at higher temperatures, 

 and the time of hibernation may therefore be shortened in many in- 

 stances by subjecting to cold before heat. It is interesting to note 

 in this connection that the same effect as that normally sustained by 

 freezing has recently been secured with rhubarb, various bulbs, lilac 

 and other flowering plants, by anesthetizing them with ether. The 

 exact effect of the ether has not been definitely determined, as far as 

 I can ascertain from a cursory examination of the literature, but Dr. 

 Loeb^ has suggested that the effect is possibly related to the effect 

 of cold upon chrysalids as mentioned above. If the effect of the ether 

 is a drying process, as some claim, this seems possible. 



In the light of these facts, may it not be possible to account for the 

 fact that some insects have but a single generation in the South, while 

 others have several generations? Thus the tent caterpillar, peach 

 borer, plum curculio, canker worms, gypsy and brown-tail moths, and 

 others, mostly insects affecting native fruits and seemingly indigenous 



eAugust Weismann, Studies in the Theory of Descent, translated by Mel- 

 dola. Eng. Ed. London, 1882. 



fLoeb — The Dynamics of Living Matter. 1906, page 112. 



