HEXAPODA. 55 



plete metamorphosis; for in the case of other insects there 

 is no distinct pupa stage. When reference is made to the 

 young of an insect that undergoes an incomplete metamor- 



,m. 



Fig. 66. — A large cocoon within a rolled leaf. 



phosis it is called a nymph. This term is applied to all 

 stages of such an insect from the time they hatch from the 

 egg until they shed their skin for the last time. When a 

 nymph first hatches it has no signs of wings ; but after it 

 molts several times two projections appear on each side of 

 the thorax. These projections become larger and larger, 

 and more wing-like in form with each successive molt. 

 Usually the change in the size of these organs, between the 

 last nymph stage and the adult stage, is much greater than 

 that of any previous molt. With the nymphs of certain 

 families, dragon-flies, crickets, grasshoppers, and locusts, 

 the front pair of developing wings extend back beneath the 

 hind pair instead of covering them ; and by this inverted 

 position of the wings the nymphs may be distinguished from 

 the adults, even in those cases where the adults have only 

 rudimentary wings. 



The Adult. — This is the last stage or the mature form 

 of the insect. Almost all adult insects except Thysanura 

 have wings, although there are numerous exceptions to the 

 rule ; for there are many cases where wings have been lost 

 through disuse. An insect never grows after it reaches the 

 adult stage, and therefore never molts. There is a popular 

 belief that a small fly will grow into a large fly, but this is 

 not true, for after any insect gets its perfect wings it can 



