STRUCTURE OF LARV^. 161 



saucer with water, with some of the dead leaves or sticks 

 it previously employed as a covering ; these will soon 

 be seen floating towards the tail, and afterwards re- 

 pelled, as a floating feather will be by a stick of sealing- 

 wax, or a bit of amber, when electrically excited. When 

 the insect has been kept out of the water for a short 

 time, the desire, or necessity, of respiration is increased, 

 and when again put into the water, the pumping is 

 repeated with unusual force and frequency. If it be 

 held in the hand, head downwards, and some drops 

 of water be let fall on its tail, it instantly sucks it in, 

 and the dimensions of its body become visibly aug- 

 mented ; but it collapses again when the water is ex- 

 pelled, which is effected by the same apparatus. 



While in the water, if a solution of cochineal, saf- 

 fron, indigo, or any other coloured fluid, be let down, 

 with great care, by means of a glass tube, just over 

 the tail of the insect, it will soon be seen to eject a 

 stream of tiie coloured solution to the distance of 

 several inches. Or the same may be seen by remov- 

 ing it suddenly out of a coloured fluid into limpid 

 water; when the coloured jet stream will be still more 

 conspicuous. The most extraordinary circumstance 

 respecting this jet is, that it propels the creature 

 through the water in consequence of its being resisted 

 by the stationary mass of the fluid behind it, and a 

 contrary current being thence produced by this singu 

 lar pumping. As the insect, between every stroke of 

 the internal piston, is obliged to draw in a fresh sup- 

 ply of water, an interval consequently occurs between 

 the strokes, during which it will sometimes elevate its 

 tail above water and squirt out a small stream like 

 that from a little syringe. 



This wonderful apparatus serves several purposes; 

 for, besides aiding the insect to move, the reverbe- 

 ratory current brings small water-insects within its 

 reach ; it is also, it would appear partly appropriated 



