30 



ELEMENTARY LESSONS ON INSECTS 



quarters of the egg shell, stretches itself, and expands. 



Its skin hardens. Chitin is formed and it becomes, 



as we have seen (page 4) 

 like a coat of mail; for it 

 will not stretch very 

 much. Therefore, with 

 growth, it becomes too 

 small and has to be cast 

 off. The process is called 

 molting. The chitinous 

 outer layer of armor 

 loosens from the under- 

 lying new skin. Then it 

 splits down the back, and 

 the soft, limp, pale, but 

 lusty and growing insect 

 creeps out of it. Head 

 and thorax first come up 

 through the rent then 

 the legs and abdomen are 

 withdrawn. After each 

 molt a sudden expansion 

 and increase of size oc- 

 curs, while the skin is new 



and stretchable. Then it hardens again. 



The number of molts undergone by different kinds of 



insects in their growing up varies, but is rather constant 



for each kind. One common stonefly, (Nemoura) moults 



Fig. 11. — The developmental stages of a plant 

 bug, Tropidosleptes cardinalis (after Leonard). 

 Figures 1 to 5 are the successive nymphal ins tars; 

 6 is the adult. 



