MOTIONS OF INSECTS. or 
segments. By this simple contrivance, aided by new- 
born vigour, when the time for its great change is ar- 
rived, the included prisoner of hope, if under ground, 
pushes itself gradually upwards, till reaching the sur- 
face its head and trunk emerge, when an opening in the 
latter being effected by its efforts, it escapes from its 
confinement, and once more tastes the sweets of liberty 
and the joys of life. Those that are inclosed in trees 
and spin a cocoon, are furnished with points on the head, 
with which they make an opening in the former. The 
pupa of the great goat-moth (Bombyx Cossus, ¥.) thus, 
by divers movements, keeps disengaging itself from this 
envelope, till it arrives at a hole in the tree which it had 
made when a caterpillar ; when its anterior part having 
emerged, it stops short, and so escapes a fall that might 
destroy it. After some repose, in consequence of very 
violent efforts, the puparium opens, and it escapes from 
its prison?. 
The insects of the Trichoptera order (Phryganea, L.) 
are quiescent when they first assume the pupa, but be- 
come locomotive towards the close of their existence in 
that state. Since they inhabit the water when they be- 
come pup, Providence has furnished them with the 
means of quitting that fluid without injury, when they 
are to exchange it for the air; which in their winged 
state is their proper sphere of action. I have before de- 
scribed to you the grates which shut up their cases when 
they became quiescent®; if they had no means of pierc- 
ing these grates, they would perish in the waters. The 
@ Lyonet, Trait. Anat. 15— b See above, p. 264. 
