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 atfected, 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 inlluence 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 tertile. The eggs and caterpillars 

 of the elm butterfly {Vanessa polijcliloros'?) perfectly 

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

 of the eggs of the blow-fly {Musca vomitoria) 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 piipae were produc- 

 tive at 104° and 106°, but not at 11 l°.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 vomUoria, 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 agndiron in the form of stakes, in 

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

 212°; and yet, instead of being hereby destroyed, we 



* See Insect Architecture, p. 24. 



t Spallanzani, Tracts by Dalyell, vol. i, p. 35. 



