446 MOTIONS OF INSECTS. 
short, and so escapes a fall that might destroy it. After some repose, in 
consequence of very violent efforts, it bursts through the front of the pus 
parium, and thus escapes from its prison.* > 
The insects of the Trichoptera order, or case-worm flies, are quiescent 
when they first assume the pupa, but become locomotive towards the close 
of their existence in that state. Since they inhabit the water when they 
become 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 
described to you the grates which shut up their cases when they become 
quiescent ; if they had no means of piercing these grates, they would perish 
in the waters. The head of these pupz is provided at first with a particular 
instrument, which enables them to effect this purpose ; its anterior part is 
armed with a pair of hooks in form resembling the beak of a bird ; and with 
this, previously to their last change, they make an opening in the grate, 
which, though it once defended, now confines them. But at this moment, 
perhaps, the insect has a considerable space of water to rise through before 
she can reach the surface. This is all wisely provided for; before she 
leaves the envelope which covers her body, she emerges from the water, 
and fixes herself upon some plant or other object, the summit of which is 
not overflowed. But you will here, perhaps, ask— How can a pupa inher 
envelope, with all her limbs set fast, do this? This affords another instance 
of the wise provision of the beneficent Father of the universe for the wel- 
fare of his creatures. The antenne and legs of this tribe of insects, when 
they are pupe, are not included, as is the case with most that are quiescent 
in that state, in the general envelope ; but each in a separate one, so as to 
allow it free motion. Thus the insect, when the time is come for its last 
change, can use them (except the hind-legs, which being partly covered by 
the wing-cases remain without motion) with ease. It then stretches out 
its antennee, and steering with its legs makes for the surface. De Geer saw 
one just escaped from its case run and swim with surprising agility over 
the bottom of a saucer, in which he had put some cases of these flies ; and 
at last when he held a piece of stick to it, it got upon it, and having emerged 
from the water, prepared to cast its envelope. It is remarkable, that the 
envelope of the intermediate tarsi, like the posterior ones of Dyftisci, is 
fringed on one side with hairs, to enable the insects to use them as 
swimming. feet*, while those neither of the larva nor imago are so cir- 
cumstanced. ( 
Tam, &c. 
1 Lyonet, Trait. Anat, 15 2 De Geer, ii, 518. 
