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 pu- 

 parium, and thus escapes from its prison. 1 



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 pupae, 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 pupae 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 in her 

 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 antennae and legs of this tribe of insects, when 

 they are pupae, 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 antennae, 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 Dytisci, is 

 fringed on one side with hairs, to enable the insects to use them as 

 swimming feet 2 , while those neither of the larva nor imago are so cir- 

 cumstanced. 



I am, &c. 



i Lyonet, Trait. Anat. 15. 3 De Geer, ii. 518. 



