296 MOTIONS OF INSECTS. 



tvveeii which an interval takes place. The legs are 

 not employed in producing this progressive motion, for 

 they are then applied close to the sides of the trunk, 

 in a state of perfect inaction. But it is effected by a 

 strong ejaculation of water from the anus. When I 

 treat upon the respiration of insects, I shall explain to 

 you the apparatus by which these animals separate 

 the air from the water for that purpose ; in the pre- 

 sent case it is subsidiary to their motions, since it is 

 by drawing in and then expelling the water that they 

 are enabled to swim. To see this, you have only to 

 put one of these larvae into a plate with a little water. 

 You will find that, while the animal moves forward, a 

 current of water is produced by this pumping, in a 

 contrary direction. As th.e larva, between every stroke 

 of its internal piston, has to draw in a fresh supply of 

 water, an interval must of course take place between 

 the strokes. Sometimes it will lift its anus out of the 

 w ater, when a long thread of water, if I may so speak, 

 issues from it^. 



II. I am next to say something upon the motions 

 of insects in their j^i^pa state. This is usually to our 

 little favourites a state of perfect repose ; but, as I 

 long since observed '', there are several that, even Avhen 

 become pupa?, are as active and feed as rapaciously as 

 they do when they are either larvEe or perfect insects. 

 The Dermaplera, Orthoptera, Iloniptera, many of the 

 JVeuroptera, and the majority of the ApUra, are of this 

 dei.cript{on. With respect to their motions, we may 



^ De Grer, ii. 675 — . Compare ilcaum. vi. 393 — • 

 ^ Vol. I. 2d Ed. 68. 



