STATES OF INSECTS. (Pupa.) 285 
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 Phry- 
ganee inclose themselves in cases of different materials, 
open at each end?. You have also learned, that in be- 
coming pupe, they secure each end of their cases with a 
grating of silk®. When that change has occurred, they 
remain motionless at the bottom of the water. Now how 
are these pupae, incased 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 mannner:—The pupa is furnished with two strong 
exterior movable mandibuliform processes, and has the 
power of moving its four anterior legs and antennz 
while in the pupa-case. With these temporary jaws it 
makes an opening in one of the silken doors of its case, 
forces its way out at that end, and then by moving its 
legs, the cases of which in some species are ciliated for 
this very purpose, swims to the surface, where its skin 
splits, and discloses the included insect. That these 
jaws are given for the express and exclusive purpose 
of being thus applied, seems undeniable. The pupa 
eats nothing—they are therefore in every other point of 
view superfluous. ‘They are given to it alone of all 
other similar pup, because unnecessary to all others ; 
and they are cast off along with the rest of the puparium, 
the perfect insect having no vestige of jaws°. 
* Vou. J. p. 465. » Vor. TI. p. 261. * De Geer, ii. 519. 
&e 
