HEX A POD A. 
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- 
Fig. 66 .—A large cocoon within a roiled 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 
