EXPERIMENTS ON INSECTS. 309 



hot-houses at Paris. His success was equal to his 

 expectations, for the insects appeared in the middle 

 of winter, some in ten or twelve days, and others in 

 from three to six weeks from the time of their removal 

 into a warmer atmosphere. Five or six days, indeed, 

 seemed to be equal to a month of natural temperature. 

 A week was even equal to a month for the chrysalides 

 which naturally required the temperature of mid- 

 summer to bring them to maturity ; because the arti- 

 ficial temperature was both high and more uniform, 

 particularly during the night. The butterflies and 

 moths thus forced into premature appearance, were 

 equally full grown, healthy and hvely, with those 

 produced in the usual way ; and the females deposited 

 their eggs and soon afterwards died, as they always 

 do in summer in the open fields. The life of these 

 insects was, therefore, shortened by some months. 



The following November, Ri^aumur tried a similar 

 experiment, which was consequently begun two 

 months earlier than the former ; and the insects were 

 also evolved proportionally sooner. Those, for ex- 

 ample, which ought naturally to have appeared in 

 May, he 'obtained in December. In butterflies which 

 have a double brood, such experiments become still 

 more interesting to the physiologist. The beautiful 

 swallow-tailed butterfly (Papilio Machaon) is one of 

 those which are double brooded, the first going into 

 chrysalis in July, and the butterfly appearing in 

 thirteen days ; — the second, in the autumn, and the 

 butterfly not appearing till the succeeding June. But 

 if placed in an artificial temperature of due warmth, 

 and properly regulated, the second brood will appear 

 in about the same time as the first. 



Reaumur tried some experiments, still more inge- 

 nious, with chrysalides, which were suggested by the 

 effects produced by birds sitting upon their eggs in 

 order to hatch them. He concluded, that if chry- 



