542 PHILOSOPHY OF ZOOLOGY. 



In the aphides, or plant lice, as they are called, the fe- 

 male retains the eggs internally at one time until they are 

 hatched, and at another, lays them like other insects. 



When the eggs are hatched, the young ones, among the 

 Crustacea and arachnida, are perfectly formed, and resem- 

 ble the parent. It is otherwise with insects. When they 

 are hatched, the young are termed grubs, maggots, cater- 

 pillars, or technically, larva. In this state, they are pro- 

 verbially voracious, and their digestive organs are of much 

 greater dimensions than when arrived at maturity. In the 

 condition of larvae, insects possess a variety of members, as 

 legs, suckers, hairs, and even stigmata, which they do not 

 possess in their maturity. They are all, however, desti- 

 tute of wings. Some of them live constantly in the water, 

 instead of the land, their future residence, swimming in 

 youth, and flying in maturity. The food of the larvae is 

 often solid, requiring powerful jaws to gnaw it, while the 

 food of the perfect insect is fluid, and sucked up. When 

 the larva has attained a certain size, and acquired the re- 

 quisite quantity of fat, having been nourished either by the 

 food which it has acquired by its own industry, as the ca- 

 terpillars, or by that which has been brought to its cell, as 

 in the grub of the bee, it prepares to assume the forms of 

 maturity, by passing through the third stage of existence 

 as a pupa. In this state, the parts, which were suitable 

 only in the larva condition, either become obliterated, or 

 are changed into organs fit for maturity. The following 

 conditions of the pupa state are recognised by naturalists : 



1. Some insects of the apterous tribes, merely by repeat- 

 ed castings of the skin, arrive at the perfect state, without 

 undergoing any sudden or remarkable change of form or 

 structure. These are termed Pupa complete. They move 

 and eat like the perfect insect. 



