40 NATURAL HISTORY. [CH. II, 



portion to the quickness with which the process of 

 evaporation is effected by the increase of heat, the 

 sooner the butterfly would be enabled to escape 

 from the chrysalis. Acting upon this idea, this cel- 

 ebrated author tried various experiments with chrys- 

 alides, the result of which fully justifies the conclu- 

 sion at which he had arrived, and thereby proved 

 that he was enabled to prolong or shorten the life 

 of an insect at pleasure. Thus, by placing various 

 kinds of chrysalides, which would not naturally 

 produce perfect insects until the spring or summer, 

 in one of the hothouses of the Jardin des Plantes, 

 in the month of January, 1734, he found that they 

 very shortly produced butterflies and moths, those 

 which would not have appeared until May escaping 

 from the chrysalis at the end of ten or twelve days, 

 others in three weeks, and others, which would not 

 have become perfect insects until August, in five or 

 six weeks. The insects thus produced differed in 

 no single respect from those reared in a state of na- 

 ture, and deposited their eggs even in the midst of 

 winter. In the month of November following, be- 

 ing two months earlier than before, he placed other 

 chrysalides in the hothouses, and these in like man- 

 ner produced perfect insects in the beginning of De- 

 cember, which would not otherwise have appeared 

 until May. Thus, by forcing the evolution of a but- 

 terfly in December, which ought not naturally to 

 take place until June or July, we are enabled to con- 

 vert a single-brooded species into one which pro- 

 duces two generations of caterpillars in the year, 

 the first brood appearing in June, from eggs depos- 

 ited in May, by butterflies recently disclosed ; this 

 brood of caterpillars being transformed into butter- 

 flies before the end of July, when they deposite eggs, 

 which are hatched in August or September ; and the 

 second brood of caterpillars entering into the chrys- 

 alis state before the winter, from which they are 

 excluded in the following May as butterflies. 



