HISTORY OF INSECTS. 5 



6. Tliese 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 tovcards 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 larva; 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 



