HISTORY OF INSECTS. 5 



6. These transformations are in reality nothing 

 more than a continual casting of the outer skin ; 

 the larva often casts its skin four or five times 

 without any very remarkable change of form ; 

 every casting of the skin is a step towards arriv- 

 ing at ultimate perfection. In every insect the 

 skin must be cast a certain number of times, and 

 the last casting brings it to maturity. 



7- On account of their small size, it is difficult 

 to find common examples of the eggs of insects ; 

 those laid on meat by the blue-bottle fly must be 

 known to many ; the silk-worm's eggs again are 

 not unknown ; but the generality of insects' eggs 

 are so concealed and so little conspicuous, that 

 they are found with difficulty. 



8. Examples of larvae are numerous ; the 

 maggots found in wasps' nests, and used in fish- 

 ing ; the maggots in apples and in nuts ; the mag- 

 gots in cheese, and in decaying substances ; and the 

 caterpillars, which devour our cabbages, which spin 

 webs on our apple, pear, and plum trees, in the 

 spring, are familiar to us all : these are insects in 

 the larva state. 



9. The pupa state is more difficult to find, be- 

 cause insects generally crawl away into crevices 

 or underground, and hide themselves before chang- 

 ing to this state ; an angular pupa of a green 

 colour, with small black spots, which produces a 

 common white butterfly, may, however, be con- 

 tinually seen on palings and walls of gardens, and 



