HOW AN INSECT GROWS UP 33 



When greater changes of form than this occur in insects 

 they seem to require an additional stage devoted to the 

 making-over process. This is the pupal stage or chrysalis. 

 It is interpolated between the growth period and the adult 

 life. It is a period of relative inactivity that is spent in 

 retirement. The owlet moth shown in figure 13 will serve 

 for illustration. From the egg (a), there hatches a worm-like 

 caterpillar (c), which eats and grows, undergoing five molts, 

 with very little change of form (only the last instar is shown 

 in the figure). No wings appear externally, and the legs and 

 other appendages remain very minute indeed. This is called 

 a larva.* The grown larva goes into retirement and sheds its 

 skin, disclosing a pupa (d), in which the parts of the adult 

 insect plainly appear. Later, after the making-over is com- 

 pleted, out of the pupal skin the adult (e) emerges. 



These changes collectively we call metamorphosis. Of 

 metamorphosis there are many degrees and variants; but 

 for our purpose we may regard them all as falling into two 

 principal categories, as follows: 



Metamorphosis Stages 



1. Incomplete — egg, nymph and adult. 



2. Complete — egg, larva, pupa and adult. 



* The name larva is often used in a more general sense to cover all 

 immature stages, including nymphs. 



