24 A ROOK OF INSECTS 



epitome of its ancestral history, we are justified in the 

 belief that complete metamorphosis became established 

 through an evolutionary process such as the above facts 

 suggest — a process which has culminated in the aston- 

 ishing transformations of the higher insects. Let us 

 recapitulate the points of the case. The function of nutri- 

 tion is relegated to the young insect, that of reproduction 

 to the adult. In the course of ages the gap between the 

 two life-stages has increased, the young insect and its 

 perfect form becoming adapted to very different environ- 

 ments. Finally, the gap has grown so wide that the 

 revolutionary changes which must be effected to bridge 

 it over necessitate an intermediate period of quiescence — 

 the pupal state. 



The term pupa — a Latin word signifying a doll or 

 mummy — is reserved strictly to describe the resting stage 

 of those insects which undergo complete metamorphosis, 

 the alternative term chrysalis (from the Greek chrysos, 

 gold) being often applied to the pupa? of butterflies on 

 account of the shining, metal-like areas for which many of 

 them are remarkable. The pupae of most butterflies and 

 moths, and of some two-winged flies, are obtect, or 

 covered, the appendages of the body being compactly 

 united. But among beetles, caddis-flies, ants, bees, wasps, 

 and other insects, the pupa reveals many of the characters 

 of the perfect insect. The legs, though pressed closely to 

 the body, are not intimately fused with it, while the wing 

 rudiments hang like flaps from the segments of the thorax. 

 Such pupae are said to be " free." Finally, in the case of 

 most two-winged flies, the last larval skin, instead of 

 being worked off by the usual process, is retained. It 

 contracts and hardens to form a kind of protective case, 

 called the puparium, within which the pupa lies. 



Although the pupa state is typically one of quiescence, 





