STATES OF INSECTS. 263 



exposed to a high temperature would sooner attain ma- 

 turity, even though larger in bulk, than others exposed 

 to a low one : — and this is the fact. The pupa of a large 

 moth, which has assumed that state in the early part of 

 summer, will often disclose the perfect insect in twelve or 

 fourteen days ; while that of an Ichneumon, not one hun- 

 dredth part of its size, that did not enter this state till 

 late in autumn, will not appear as a fly for seven or eight 

 months. But this is not the whole. The very same in- 

 sect, according as it has become a pupa at an earlier or 

 later period of the year, will at one time live but a few 

 weeks, at another several months, in that state. Thus, 

 if the caterpillar of Papilio Machaon, one of those which 

 has annually a double brood, becomes a pupa in July, 

 the butterfly will appear in thirteen days : if not until 

 September, it will not make its appearance until the June 

 following ; that is, not in less than nine or ten months : 

 and the case is the same with the pupae of Noctna Psi, 

 and of a vast number of other insects. To put beyond 

 all doubt the dependence of these remarkable variations 

 on temperature merely, it was only necessary that they 

 should be effected, as Lister long ago advised a , by arti- 

 ficial means. This Reaumur accomplished. In the 

 month of January he placed the chrysalises of several 

 moths and butterflies, which would not naturally have 

 been disclosed until the following May, in a hothouse : 

 the result was, that the perfect insects made their appear- 

 ance in less than a fortnight, in the very depth of winter ; 

 and by other numerous and varied experiments he ascer- 

 tained, that in this heated atmosphere five or six days 



3 Lister's GoeJarh 122. 



