GROWTH AND TRANSFORMATION 169 



like jaws, there follows before the emergence of the winged 

 adult, a long period of quiescence. The nymph in its last 

 stage, with its front feet again developed, and displaying 

 prominent wing-rudiments, rests motionless in its earthen 

 burrow for several days or weeks, taking no food while it 

 awaits the time of its final moult. All immature insects 

 suspend their activities for a while when preparing to shed 

 the cuticle, and we have already noticed that the final moult, 

 as it precedes the full development of the wings, marks 

 always something of a crisis in the life-history ; the stage 

 leading up to this may therefore be regarded as naturally 

 suitable for prolongation into a definite resting stage. It 

 is noteworthy that such a quiescent interlude is to be seen 

 in the life-histories of insects of several families allied to the 

 cicads and classed in the same sub-order (Homoptera) as 

 they. Thus the Coccidae (mealy bugs and scale insects) 

 and the Aleyrodidae (Plate I, B) pass through a resting 

 stage which may indeed begin at a comparatively early 

 period of the development, before the last moult but one or 

 the last but two ; in these insects, however, though motion 

 ceases, feeding by suction may go on. Scale insects and 

 snowyflies exhibit a remarkable modification of the moulting 

 process in connection with these resting phases. The old 

 cuticle, after separation from the skin, is not cast off, but 

 becoming hard and firm serves as a protective case for the 

 creature in the comparatively thinly-coated condition that 

 characterises it during the next stage ; an emerging snowy- 

 fly may thus have to make its way to the outer world through 

 three successive discarded cuticles. A striking feature of 

 the life-history of many Coccidae is that the female scale 

 insect never emerges at all ; while the male develops wings 

 the female not only remains wingless when adult (like the 

 summer aphids already mentioned in this chapter), but 

 passes the rest of her life and lays her eggs under the 

 shehering '' scale," which consists of the last-shed cuticle 

 strengthened and enlarged by waxy secretions of the skin. 



In the insect life-histories so far sketched in this chapter 

 we have seen that the newly hatched young may resemble 



