118 INSECT TRANSFORMATIONS. 



The effect of heat upon the eggs of insects has been 

 carried much farther than in the experiments just 

 alluded to of R aumur and Bonnet.* Spallanzani 

 was desirous of ascertaining what degree of heat the 

 eggs of insects and other animals, as well as the seeds 

 of plants, would bear when compared with their larvae; 

 and he found that below 93 Fahr. silk-worms did 

 not appear affected, but at 95, and still more at 97 , 

 they became restless, while at 99 they ceased to move, 

 and all died at 108. The eggs of these, on the 

 other hand, long resisted the influence of heat. At 

 80 they were the most productive; at 99 many still 

 appeared, but with considerable diminution, and as 

 the heat was increased their fertility decreased, till at 

 144 not one was fertile. The eggs and caterpillars 

 of the elm butterfly (Vanessa polychlorosl) perfectly 

 corresponded with those of the silk-worm. In the case 

 of the eggs of the blow-fly (Musca vomitoina) a great 

 many produced maggots at 124; but at 135 and 

 138 very few, and all were sterile at 140. The 

 maggots produced from these eggs became restless at 

 88, and endeavoured to escape, and as this heat was 

 increased they became proportionably more agitated 

 till it arose to 108, when they all perished. Full- 

 grown maggots of the same kind all died at 108; 

 but when changed into flies they died when the heat 

 was so low as 99; though their pupae were produc- 

 tive at 104 and 106, but not at lll.t 



If these experiments may, as we believe they may, 

 be relied on, we have some reason to doubt that ' the 

 eggs of the musca vomiloria, our common blow-fly, 

 are often,' as Dr Good affirms, ' deposited in the 

 heat of summer upon putrescent meat, and broiled 

 with such meat over a gridiron in the form of stakes, in 

 a heat not merely of 212, but of three or four times 

 ; and yet, instead of being hereby destroyed, we 



* See Insect Architecture, p. 24. 



t Spallanzani, Tracts by Dalyell, vol. i, p. 85. 



