HEXAPODA : COCOONS. 



299 



rapidly. When the larva of an insect has attained its 

 full growth as a larva, it retires to some suitable place, 

 and in many cases it spins a silken covering called a 

 cocoon, then sheds its skin, and appears as a much short- 



FIG. 377. 



FIG 378. 



Coooou of Silk-worm Moth (Telea Polyphemus), 

 wi'apped in a leaf. 



Coeoou of Tent. Caterpillar, 

 Clisiocampa americana. 



ened, oblong, oval, or conical body, apparently lifeless ; 

 in this form it is called & pupa or chrysalis. In a major- 

 ity of species, however, no silken covering or cocoon is 

 made ; but in such cases the pupa is essentially of the same 

 form as those enclosed in a cocoon. At the end of the 

 pupa state, which varies greatly in duration in the differ- 

 ent species, the insect sheds its pupa skin and comes forth 

 fully grown, and in most species provided with wings; 

 and in this state it is called a perfect insect or imago. 



It is held by some that the imago and pupa skins are really already 

 formed under the skin of the larva. 



After insects enter upon the adult or imago state they 

 do not increase in size. They now provide for a con- 

 tinuation of their species, and then, in most cases, soon 

 perish. 



All insects which pass through the changes described 

 above are said to undergo a complete metamorphosis or 

 transformation. 



