110 THE LIFE-STORY OF INSECTS [CH. 



process, adapted to its own particular mode of 

 larval life. 



The explanation of insect transformation is, in 

 brief, to be found in an increasing amount of di- 

 vergence between larva and imago. The most pro- 

 found metamorphosis is but a special type of growth, 

 accompanied by successive castings and renewings of 

 the chitinous cuticle, which envelopes all arthropods. 

 In the simplest type of insect life-story, there is no 

 marked difference in form between the newly -hatched 

 young and the adult, and in such cases we find that 

 the young insect lives in the same way as the adult, 

 has the same surroundings, eats the same food. This 

 is the rule (see Chapters n and in) with the Aptery- 

 gota, the Orthoptera, and most of the Hemiptera. 

 In the last-named order, however, we find in certain 

 families marked divergence between larva and imago, 

 for example in the cicads, whose larvae live under- 

 ground, while in the coccids, whose males are highly 

 specialised and females degraded, there succeeds 

 to the larva very like the young stage in allied 

 families a resting instar, which in the case of the 

 male, suggests comparison with the pupa of a moth 

 or beetle. 



Turning to the stone-flies, dragon-flies and may- 

 flies, whose life -stories have been sketched in 

 Chapter iv, we find that the early stages are passed 

 in water, whence before the final moult, the insects 



