THE METAMORPHOSIS OF INSECTS 



187 



chrysalids. The singular of the first form and the plural of the second 

 are those most often used. 



Active piipcB. — The pupae of mosquitoes and of certain midges are 

 remarkable for being active. Although the wings and legs are func- 

 tionless, as with other pupae, these creatures are able to swim by 

 means of movements of the caudal end of the body. 



In several genera of the Neuroptera (Chrysopa, Hemerobius, and 

 Raphidia) the pupa becomes active and crawls about just before 

 transforming to the adult state. 



Movements of a less striking character are made by many pups, 

 which work their way out of the ground, or from burrows in wood, 

 before transforming. In some cases, as in the pup« of the carpenter- 

 moths (Cossidce) the pupa is armed with rows of backward projecting 

 teeth on the abdominal segments, which facilitate the movements 

 within the burrow. 



The creniaster. — Many pupae, and especially those of most Lepidop- 

 tera, are provided with a variously shaped process of the posterior 

 end of the body, to which the term creniaster is applied. This process 

 is often provided with hooks which serve to suspend the pupa, as in 

 butterflies, or to hold it in place, after it has partly emerged from the 

 cocoon, and while the adult is emerging from the pupal skin, as in 

 cocoon-making moths. In its more simple form, where hooks are 

 lacking, it aids the pupa in working its way out of the earth, or from 

 other closed situations. 



The method of fixing the cremaster in the disk of silk from which 

 the pupa of a butterfly is suspended was well-illustrated by C. V. Riley 

 ('79). The full grown larva spins this disk and hangs from it during 



the prepupal stadium 

 by means of its anal 

 prolegs (Fig. 209, a). 

 When the last larval 

 skin is shed, it is 

 worked back to the 

 caudal end of the body 

 (Fig. 209, b); and is 

 then grasped between 

 two of the abdominal 

 segments (Fig. 209, c,) 

 while the caudal end of the body is removed from it ; and thus the 

 cremaster is freed, and is in a position from which it can be inserted 

 in the disk of silk. 



Fig. 209. — Transformations of the milkweed butter- 

 fly (From Riley). 



