THE DEVELOPMENT OF INSECTS 



29 



more and more prominent in each succeeding stage, but 

 are never used until the adult stage. The possession of 

 power of flight is a certain proof that any insect is an 

 adult. 



The different nymphal stages are separated or limited 

 by moults which occur at more or less definite intervals. 

 These moults consist 

 of the casting of the 

 skins. The skin of 

 a newly hatched or 

 freshly moulted in- 

 sect possesses a cer- 

 tain amount of elas- 

 ticity, but does not 

 grow. When the 

 growth of the insect 

 has about taken up 

 all the stretching 

 power of the skin, 

 a new skin forms 

 beneath the old one, 

 the old one bursts 

 and the insect makes 

 its way out. The cast skin is called the exuvia. The more 

 striking changes in the appearance which occur during the 

 course of development come with these moults. The final 

 moult liberates the adult form which does not moult and 

 does not grow. Many of the adults do not even feed 



25. Indirect Development. Where the development is 

 indirect there is a great difference in the process. The 

 form which is hatched from the egg bears, in most cases, 

 not the slightest resemblance to the parent form. There 

 would be no reason to suspect that the two belonged even 



FIG. 13. Metamorphosis of a Moth (Samia 

 cecropia), showing Larva, Pupa, Cocoon 

 and Adult. Much reduced. 



