CH. XII.] THE DRAGON-FLY. 215 



to issue from the anal extremity of the libellula, to 

 the extent sometimes of several inches ; at the same 

 time the force with which the column is ejected 

 propels the insect in the opposite direction, by vir- 

 tue of the resistance with which it meets. Hence 

 it appears that it is by means of its respiratory sys- 

 tem that the creature walks a strange and anoma- 

 lous combination of functions in one organ. 



If the insect be taken out of the water, held with 

 its head downwards, and a few drops of that fluid 

 poured on its tail, that which was a mere point will 

 immediately open and display a cavity ; at the same 



time the body of the insect, which was before flat, 

 will be observed to be enlarged and inflated, and if 

 held up to the light, semi-transparent: moreover, 

 something solid will appear to be displaced by the 

 water, and driven towards the head. This solid 

 mass will shortly descend, obscure the transparency 

 of the lower portion of the body of the insect, lessen 

 its diameter, and, when it does so, a jet of water 

 will issue from the vent. It is clear, then, that the 

 abdomen of the libellula is a syringe, the piston of 

 which being drawn up, of course the pressure of the 

 fluid fills up the vacuum, and, when pushed down, 

 expels the water. To ascertain the fact, Reaumur 

 held the insect in his hand, and when he saw its 

 body inflated, cut it immediately with a pair of scis- 

 sors, and found it unoccupied with solids. He 

 watched when the jet of water was expelled in an 

 other, and as soon as the body was darkened ana 

 lessoned in diameter, he clipped it., and found the cut 

 portion occupied by solids. There is no doubt, then. 



