286 STATES OF INSECTS. 



skin till she was entirely extricated, when they left her 

 to recover her strength by herself. Probably the extreme 

 length of the two pair of hind-legs of these animals may 

 render such assistance necessary for their extrication. 



There remains yet to be explained under this head the 

 manner in which the perfect insect is excluded from cer- 

 tain aquatic pupae ; such as those of Phryganea, gnats, 

 and one of those Tipulidce that resemble gnats. These 

 pupae (perhaps that they may be safe from the attack of 

 birds) are destined to remain during the greater part of 

 their existence in this state at the bottom of the water. 

 But it is obvious that if the perfect insects were there to 

 be disclosed, their wings would be wetted, and they would 

 be drowned. It is the provision by which this result is 

 obviated that now calls for your attention. 



You have already been told that the larvae of Pliry- 

 ganea inclose themselves in cases of different materials, 

 open at each end a . You have also learned, that in be- 

 coming pupae, they secure each end of their cases with a 

 grating of silk b . When that change has occurred, they 

 remain motionless at the bottom of the water. Now how 

 are these pupae, encased in tubes of a greater specific 

 gravity than the surrounding fluid, to make their way to 

 the surface when the time has arrived for their becoming; 

 denizens of the air ? This they accomplish in the follow- 

 ing manner : — The pupa is furnished with two strong 

 exterior moveable mandibuliform processes, and has the 

 power of moving its four anterior legs and antennae while 

 in the pupa-case. With these temporary jaws it makes 

 an opening in one of the silken doors of its case, forces its 



a Vol. I. p, 4G7. b Vol. II. p. 264. 



