EGGS RESIST THE SEVEREST COLD. 61 



five hours in a mixture of ice and rock-salt, the 

 thermometer falling 6 below zero. In the middle 

 of the following spring, however, caterpillars 

 came from all the eggs, and at the same time as 

 from those which had suffered no cold. In the 

 following year, I submitted them to an experiment 

 still more hazardous. A mixture of ice and rock- 

 salt, with the burning spirit of nitre, reduced the 

 thermometer 22 below zero, that is, 23 lower 

 than the cold of 1709, or 52 lower than the 

 point at which water freezes. They were not 

 injured, as I had evident proof by their being 

 hatched." 



When it is known that many seeds will not 

 endure these degrees of cold without injury, and 

 those even of some tolerably hardy plants, it is the 

 more surprising to find such apparently delicate 

 and readily damaged objects as the eggs of these 

 members of the insect tribe thus resisting an in- 

 tensity of cold to which, in a state of nature, they 

 are scarcely ever exposed. It is impossible to 

 assign any rational explanation of these singular 

 facts. It is undoubtedly owing to this power of 

 resisting the generally deadly influence of extreme 

 cold that we find insects reappear in spring, even 



