34 CHILDHOOD OF ANIMALS 



moults and changes to a pupa rather hke the adult in form, with 

 the appendages and rudimentary wings glued down to the body. 

 After a resting stage this pupa opens and the adult insect emerges. 



The eggs of other beetles may hatch out either as campodeiform 

 larvae, or as maggot-like larvae, which, after moulting, produce 

 pupae with rudimentary wings. The eggs of many other insects, 

 such as cockroaches and earwigs, hatch out as campodeiform larvae, 

 and then by a series of moults slowly acquire the adult form without 

 any true metamorphosis. 



Finally there are many insects, such as the locusts, in which the 

 earliest stages have been suppressed and there is no sudden meta- 

 morphosis, but the period of youth is occupied by a series of moults 

 (Fig. i8), in which the successive larvae slowly assume the 

 characters of the adult, the wings gradually growing longer. 



I do not wish to suggest that the examples I have chosen represent 

 actual stages in the evolution of insects. They have been selected 

 from insects that are by no means closely related, and they do no 

 more than give an idea how the extremely different modes in which 

 modern insects develop show a trace here and a trace there of 

 different parts of a common ancestral history, some parts of which 

 have been blurred and condensed in some insects, other parts in 

 others. The delicate and transparent pupal skins surrounding the 

 fly inside its puparium, with their rudimentary wings, and the pupal 

 cases themselves of moths and oil -beetles with their rudimentary 

 wings, plainly represent the active later larval stages of the locust. 

 The campodeiform larvae of the oil -beetle and of many other beetles, 

 cockroaches and earwigs represent the primitive insect, and may 

 pass by a series of moults into the adult, or these later stages may 

 have been condensed to a sudden metamorphosis. The caterpiUar- 

 like larva is a rather degenerate modification of the Campodea 

 larva, and the maggot -like larvae of many beetles and the legless 

 larvae of flies are still more degenerate interpolations in the life- 

 history, fitting the special conditions in which these larvae live. 



The stories of the youthful period in the crustaceans and insects 

 are, to a certain extent, alike. The hard nature of the skin has led 

 to a replacement of the more usual method of continuous growth, 

 by growth in little jumps, there being a moult at each jump. In both 

 there are many animals in which these successive moults separate a 

 set of larvae which are becoming more and more like the adult by 

 slow stages. In both the more continuous sets of larvae seem to be at 

 least a partial repetition of the ancestral history, but in both the 



