MODES OF EMERGING FROM PUP^. 



321 



breathing, by admitting a current of fresh water, 

 effected, no doubt, by the spiracles of the pupa ; and 

 he actually saw the grate-work in alternate motion 

 from convex to concave, as the water passed out 

 j and in, 



I Our motive, however, for introducing a notice of 

 'i these structures is for the purpose of explaining the 

 contrivance by which the pupa makes its exit through 

 the grating. To effect this, it is provided with a pair 

 of curved mandibles, which appear to be applied 

 to no other use, for they are thrown off upon its 

 transformation into a %, as was observed by Vallis- 

 nieri. These facts may be verified by searching for 

 caddis-worms during the early spring months, as 

 most of them are transformed in the first part of the 

 summer. 



a, Pupa of a case-fly (Phryganea). c, d, grate-wofks of tlie 

 same at the openings of the cases, greatly magnified, b, the 

 perfect insect. 



In the comm.on blow-fly {Musca carnaria), and 

 many of the same family, the exit of the perfect 

 insect from the pupa case is effected by a very dif- 

 ferent, b\it no less admirable contrivance. The head 

 of the perfect fly, it may be remarked, is hard and 

 unyieldmg ; but in the pupa it is soft, and capable 



