MOTIONS OF INSECTS. 481 



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 cocoon. The pupa of the great 

 goat-moth (Cossus ligniperda) thus, by divers movements, keeps disen- 

 gaging 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, if 

 stops short, and so.escapes a fall that nnght destroy it. After some repose, 

 in consequence of very violent efforts, it bursts through the front of the 

 puparium, 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 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 ante- 

 rior 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 envelop 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 envelop, 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 welfare 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 envelop ; 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 envelop. 

 It is remarkable, that the envelop of the intermediate tarsi, like the poste- 

 rior ones of Dytisci, 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 circumstanced. 



I am, &c. 



• Lyonet, Trait. Anat. 15. « De Geer, ii. 518. 



41 



