THE DEVELOPMENT OF INSECTS 31 



periods of feeding with molts, at which times growth and changes bringing 

 it nearer to the adult occur, the last molt completing the growth and adult 

 structure. In this life history we have a change, but as there was a 

 resemblance to the adult from the start, the change to it (metamorphosis) 

 is only an incomplete or partial one. 



In the Holometabola the insect hatches from the egg in a form totally 

 unhke the adult, and while feeding periods followed by molts and growth 

 give increase in size, no external evidence of any changes making the 

 insect more like the adult can be found. These changes are largely made 

 after the end of the feeding and growing periods during a pupa (generally 

 quiet) stage, in which the breaking down of the larval, and construction 

 of the adult structures is completed. The difference between the larva 

 on hatching and the adult is so great that an entire change (complete 

 metamorphosis) takes place. 



It should be evident from the foregoing that when the adult condition 

 is once reached, little if any growth is possible (except in rare cases) 

 and that the belief so common, that "big flies grow from little flies," 

 is without any basis of fact. 



The nymphs of the Hemimetabola appear not to have attracted 

 sufficient attention to have received any special common names. In 

 the Holometabola the larvae of various groups differ greatly in appear- 

 ance; many are large and noticeable and some of them have, as a result, 

 received special names. Larvae of butterflies and moths are commonly 

 called caterpillars; those of beetles are usually called grubs; those of 

 flies are called maggots. Larvae found boring in wood, however, whether 

 they will become moths, beetles or other insects, are uniformly called 

 borers. 



In the Hemimetabola then, the stages of life are: egg, nymph, adult; 

 in the Holometabola they are: egg, larva, pupa, adult. Whether or not 

 the pupa is enclosed by a cocoon depends upon circumstances. 



