1 70 THE BIOLOGY OF INSECTS 



generally or differ markedly from its parent, as a rule, 

 according as its mode of life is the same or diverse, and that, 

 in either case, the process of development is largely concerned 

 with the acquisition of wings, while before the final perfect- 

 ing of these organs there may be a prolonged resting period. 

 We pass on now to consider some life-histories of another 

 type which prevails among the great majority of the insect 

 families. After comparison of the two types it should be 

 possible to appreciate the essential difference between them. 



It is a matter of common knowledge that most insects 

 during their life-histories pass through a marked trans- 

 formation (metamorphosis) ; the change of a caterpillar 

 into a butterfly, for example, is familiar to every one, and 

 hardly less familiar is the fact that maggots feeding in dead 

 flesh or carrion are the offspring of bluebottles, and that 

 into bluebottles they will in due course be changed. The 

 caterpillar displays many conspicuous features of divergence 

 from its parent butterfly, and the maggot is still more dis- 

 similar to the bluebottle. In the process of transition from 

 the one to the other there must evidently be a considerable 

 amount of reconstruction, and it is therefore not surprising 

 that in the stage preceding the adult, the insect is a quiescent 

 pupa, remaining usually motionless and taking no food. 

 We have already seen that in several groups of insects — 

 cicads, scales, thrips — whose growth exhibits far less marked 

 change of form than the growth of a butterfly or bluebottle, 

 there is partial or complete passivity during the penultimate 

 stage. The quiescence of the pupa, then, is not the essential 

 feature that distinguishes what is generally called '' com- 

 plete " from '' incomplete " metamorphosis ; it is necessary 

 to seek farther for the true distinction. 



The caterpillar hatched from the egg of a butterfly or 

 moth differs conspicuously from its parent, but the 

 differences are in details of structure, not in the funda- 

 mental plan of the body. A caterpillar (Fig. 45) has the 

 typical insectan head with all its appendages and organs 

 present, though several of them are simplified or speciaHsed 

 as compared with those of most adult insects ; thus the feelers 



