MOTIONS OF INSECTS. 



243 



particular instrument, which enables them to effect this pur- 

 pose ; 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 be- 

 neficent 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 qui- 

 escent 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 1 , while those neither of 

 the larva nor imago are so circumstanced. 



I am, &c. 



1 De Geer, ii. 518. 



R 2 



