446 HYBERNATION OF INSECTS. 



feet insects, are sheltered too slightly to be secure from 

 the frost. This they are either able to resist, remaining 

 unfrozen though exposed to the severest cold, or, which 

 is still more surprising, are uninjured by its intensest ac- 

 tion, recovering their vitality even after having been 

 frozen into lumps of ice. 



The eggs of insects are filled with a fluid matter, in- 

 cluded in a skin infinitely thinner than that of hens' eggs, 

 which John Hunter found to freeze at about 15° of 

 Fahrenheit. Yet on exposing several of the former, in- 

 cluding those of the silk-worm, for five hours to a freez- 

 ing mixture which made Fahrenheit's thermometer fall 



o 



to 38° below zero, Spallanzani found that they were not 

 frozen, nor their fertility in the slightest degree impaired. 

 Others were exposed even to 56° below zero, without 

 being injured ^. 



A less degree of cold suffices to freeze many pupae and 

 larvae, in both which states the consistency of the animal 

 is almost as fluid as in that of the egg. Their vitality 

 enables them to resist it to a certain extent, and it must 

 be considerably below the freezing point to affect them. 

 The winter of 1813-14 was one of the severest we have 

 had for many years, Fahrenheit's thermometer having 

 been more than once as low as 8° when the ground was 

 wholly free from snow ; yet almost the first objects which 

 I observed in my garden, in the commencement of spring, 

 were numbers of the caterpillars of the gooseberry-moth 

 [Abraxas grossulariata), which, though they had passed 

 the winter with no other shelter than the slightly pro- 

 jecting rim of some large garden-pots, were alive and 

 quite uninjured ; and these and many other larv£E never 

 • Tracts, ^2. 



