478 MOTIONS OF INSECTS. 



The motions of these creatures in this state are various. Some walk 

 on the ground under water ; some move in mid-water, either by the same 

 motion of the legs as they use in walking, or by strokes, as in swimming; 

 others for this purpose employ certain laminae, which terminate their tails, 

 as oars ; others again swim like fish, with an equable motion ; some move 

 by the force of the water which they spirt from their anus ; others again 

 swim about in cases, or crawl over the submerged bottom ; and others 

 walk even on the surface of the water. I shall not now enlarge on all 

 these kinds of water-motion, since many will come under consideration 

 hereafter. 



There are two descriptions of larvae of Ilidrophilida, one furnished with 

 swimmers or anal appendages, by means of which they are enabled to swim ; 

 the other have them not, and hence are not able to rise from the bottom.^ 

 The larvae of Dytisci, by means of these natatory organs, will swim, though 

 slowly, and every now and then rise to the surface for the sake of respira- 

 tion. Those o{ Ephemera, when they swim, apply their legs to the body, 

 and swim with the swiftness and motions of fish.^ Those of the true May- 

 fly (Sialis lutaria), on the contrary, use their legs in swimming, and at 

 the same time, by alternate inflections, give to their bodies the undulations 

 of serpents."^ But the larvae of certain dragon-flies (Aeshna and Libelhda) 

 will afford you the most amusement by their motions. These larvae com- 

 monly swim very little, being generally found walking at the bottom on 

 aquatic plants : when necessary, however, they can swim well, though in 

 a singular manner. If you see one swimming, you will find that the body 

 is pushed forward by strokes, between 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 fiom 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 present 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 larva? 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 the 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 water, when a long thread of water, if 1 may 

 so speak, issues from it."* 



II. I am next to say something upon the motions of insects in their 

 pupa state. This is usually to our little favorites a state of perfect repose ; 

 but, as I long since observed, there are several that, even when become 

 pupae, are as active and feed as rapaciously as they do when they are 

 either larva? or perfect insects. The Dermaptera, Orthoytera, Hemiptera, 

 many of the Neuroptera, and the majority of the Aptera, are of this 

 description. With respect to their motions, we may therefore consider 

 pupae as of two kinds — active pupae, and quiescent pupae. 



' Miger, Ann. du Mm. xiv. 441. « De Geer, ii. 621. ^ Ibid. 725. 



* De Geer, ii. 675. Compare Reaum. vi. 393. 



