MOTIONS OF INSECTS. 443 
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 wili come under consideration 
hereafter. 
There are two descriptions of larvee of Hydrophilide, 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 respiration. Those of Wphemere, 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 /utaria), on the contrary, use their legs in 
swimming, and at the same time, by alternate inflexions, give to their 
bodies the undulations of serpents. But the larva of certain dragon- 
flies (Aeshna and Libellula) will afford you the most amusement by their 
motions. These larvee commonly 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 from the anus. When I treat upon the respira- 
tion of insects, 1 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 larvee 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 I may 
so speak, issues from it.4 
Il, I am next to say something upon the motions of insects in their 
pupa state. This is usually to our little favourites a state of perfect 
repose; but, as I long since observed, there are several that, even when 
become pupa, are as active and feed as rapaciously as they do when they 
are either larvee or perfect insects. The Dermaptera, Orthoptera, Hemi- 
plera, many of the Neuroptera, and the majority of the Apéera, are of this 
description. With respect to their motions, we may therefore consider 
pup as of two kinds —active pupe, and quiescent pupx. 
The motions of most insects whose pupz are active are so similar in all 
their states, except where the wings are concerned, as not to need any 
Separate account. I shall therefore request you to wait for what I have to 
Say upon them, till I enter upon those of the imago. One insect, however, 
1 Miger, Ann. du Mus. xiv, 441. 2 De Geer, ii. 621. 
5 Ibid. 725. ° 
4 Ibid, ii. 675. Compare Reaum. vi. 893. 
