20 HOW INSECTS TRANSFORM 
to a “chrysalis” or pupa. And finally, from the pupa emerges the 
winged butterfly, ready to begin the life round over again. This is 
an example of complete metamorphosis, including four distinct stages — 
egg, larva, pupa, and adult. 
With the squash bug we find the adult laying an egg, as before. 
But from this egg hatches, not a larva or worm, but a tiny, active bug, 
Fic. 17.— Illustrating incomplete metamorphosis. Eggs, nymphs, and adult 
of the Squash Bug, Anasa tristis De G. Original. 
similar to the parent insect except that it has no wings. This immature 
form grows, shedding its skin four or five times, and finally with the 
last moult acquires its wings and is now a typical adult. The imma- 
ture stage is known as a nymph, and this is an example of incomplete 
metamorphosis, including only three distinct. stages instead of four — 
egg, nymph, and adult. 
In all insects the larval or nymph stage is the period of growth. 
