Development and Metamorphosis 41 



or months, to attain finally the parent structure and appearance. This 

 attainment is a matter of further development, of postembryonic develop- 

 ment, and the amount or degree of this development or change is obviously 

 determined by the remoteness or nearness of the young at the time of hatch- 

 ing to the adult or parental condition. The young of many of our most 

 familiar insects, as beetles, flies, moths and butterflies, and ants, bees, and 

 wasps, hatch out extremely unlike their parents in appearance: the well- 

 known worm-like caterpillars of butterflies and moths are striking examples 

 of this unlikeness. The changes necessarily undergone in the develop- 

 ment from caterpillar to butterfly are so great that there actually results 

 a very considerable degree of making over, or metamorphosis of the insect, 

 and for convenience of roughly classifying insects according to their develop- 

 ment, entomologists have adopted the terms complete metamorphosis, 

 incomplete metamorphosis, and no metamorphosis to indicate three not 

 very sharply distinguished kinds or degrees of postembryonic development. 



In the latter category are comparatively few species, because most insects 

 have wings, and no insect is winged at birth. But the members of the sim- 

 plest order (Aptera) are all primitively wingless, and their 

 young are, in practically all particulars except body size and 

 the maturity of the reproductive glands, like the adults 

 (Fig. 71) ; their development may fairly be said to take place 

 without metamorphosis. In addition to these primitively 

 simple insects there are certain degenerate wingless species 

 like the biting bird-lice, for example, whose young also 

 reach the parental stature and character without meta- 

 morphosis. 



In the next category, that of development with in- 

 complete metamorphosis, are included two large orders 



of insects and several smaller ones. All the sucking-bugs Fig. 71. Young 



(order Hemiptera) and all the locusts, katydids, crickets, =*"<! adult of Po- 

 and cockroaches (composing the order Orthoptera), as well th "simplest^ in- 

 as the May-flies, dragon-flies, white ants, and several other sects, showing 

 small groups of unfamiliar forms, agree in having their development 

 young hatched in a condition strongly resembling the morphosis. 

 parents, although lacking wings, and in some cases, particu- (Much enlarged.) 

 larly those in which the young live on different food and in a different hahutat 

 from the adults, differing rather markedly in several superficial characters. 

 Such is the case, for example, with the dragon-flies, whose young are aquatic 

 and breathe by means of tracheal gills, and are provided with specially con- 

 structed seizing and biting mouth-parts. But in such essential character- 

 istics as number of legs, character of eyes and antennae, and, usually, char- 

 acter of mouth-parts, the young and parent agree. During postembryonic 



