60 THE LIFE OF AN INSECT. 



diately to consider the nature of the changes, it 

 may be mentioned as an interesting fact, that 

 although the eggs of insects are very quickly 

 sensible of a slight increase of heat, and in con- 

 sequence of its application to them very soon 

 begin to live, yet they will endure the most 

 severe degrees of cold almost without injury. As 

 an illustration of this point we may transcribe a 

 few sentences from a paper by the great Spallan- 

 zani upon this subject: 



"The year 1709, when the thermometer fell 

 to 1 Fahrenheit/' or thirty-one degrees below 

 freezing point, " is celebrated for its rigour and its 

 fatal effects on plants and animals. c Who can 

 believe/ exclaims Boerhaave, c that the severity 

 of this winter did riot destroy the eggs of insects, 

 especially those exposed to its influence in the 

 open fields, on the naked earth, or on the branches 

 of trees? Yet, when the spring had tempered 

 the air, these eggs produced as they usually did 

 after the mildest winters.' " He adds further on, " I 

 have exposed eggs to a more rigorous trial than 

 the winter of 1709 those of several insects, and 

 among others the silk-worm, moth, and elm-but- 

 terfly, were enclosed in a glass vessel, and buried 



