THE LIFE CYCLE 



91 



a few easily perceived changes in its post-embryonic devel- 

 opment, of an insect with an "incomplete metamorpho- 

 sis." The eggs of grasshoppers are laid in little packets 

 of several score half an inch below the surface of the 

 ground. When the young grasshopper hatches from the 

 egg it is of course very small, but it is plainly recognizable 

 as a grasshopper. But in one important character it dif- 

 fers from the adult, and that is in its lack of wings. The 

 adult grasshopper has two pairs of wings ; the just hatched 

 young or larval grasshopper has no wings at all. The 

 young grasshopper feeds voraciously and grows rapidly. 



FIG. 42. Post-embryonic development (incomplete metamorphosis) of the Rockj" 

 Mountain locust (Melanoplus spretus). a, b, c, d, e, and /, successive develop- 

 mental stages from just hatched to adult individual. After EMERTON. 



In a few days it molts, or casts its outer skin (not the 

 true skin, but a thin, firm covering or outer body wall com- 

 posed of a substance called chitin, which is secreted by the 

 cells of the true skin). In this second larval stage there 

 can be seen the rudiments of four wings, in the condition 

 of tiny wing pads on the back of the middle part of the 

 body (the thorax). Soon the chitinous body covering is 

 shed again, and after this molt the wing pads are mark- 

 edly larger than before. Still another molt occurs, with 

 another increase in size of the developing wings, and after 

 a fifth and last molt the wings are fully developed, and 



