ENTOMOLOGY. 95 



af Dipterous insects have the power of introducing 

 lir into their pupa-case for the purpose of forcing a 

 passage out of it. The air is said to be introduced 

 jnder the middle part of the head, which becomes 

 nflated into a membranous vesicle, and thus acts 

 ipon the end or lid of the pupa-case, and, in time, 

 brces it open. This singular lever is necessary in 

 he case of the flies alluded to, in consequence of the 

 >ubstance of the puparium being so hard as to offer 

 nore than usual resistance. 



Many subterraneous pupae assume the perfect form 

 Beneath the ground, and others make their way to 

 he surface before undergoing that change. In the 

 brmer case, the insect remains where it was disclosed 

 ill it acquires sufficient strength and hardness to 

 'ender it safe to force a passage upwards ; the rose- 

 jhafer (Cetonia aurata,) continues about fifteen days, 

 ,he cockchafer (Melolontha vulgaris,*) and Oryctes 

 lasicornis, nearly a month. This, however, would 

 >bviously be impracticable for soft winged insects, 

 such as moths, two-winged flies, &c.) and it is, 

 >herefore, necessary that they should reach the sur- 

 ace (whether it be of the ground or the rotten trunk 

 of a tree,) while yet pupae. We have mentioned 

 ;he means by which the pupa of the goat-moth effects 

 ;his, and a similar plan is followed by most others so 

 nrcumstanced. Such pupae as are enclosed in co- 

 xxms are provided with means for forcing a passage 



ough this additional obstacle of which an account 

 :ias been given when treating of the insects by which 

 socoons ars usually constructed. Other peculiarities 



