1 74 Analysis of Scientific Books and Memoirs. 



a more limpid fluid, a jet of the colourtcl water will be seen 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 pro- 

 pels the insect in the opposite direction, by virtue of the resistance with 

 which it meets. Hence it appears that it is by means of its respiratory 

 system that the creature walks — a strange and anomalous 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, semitransparent : 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 dia- 

 meter, 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 va- 

 cuum, 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 scissors, and found it unoccupied with 

 solids. He watched when the jet of water was expelled in another, and as 

 soon as the body was darkened and lessened in diameter, he clipped it, and 

 found the cut portion occupied by solids. There is no doubt, then, that 

 the abdomen contains a moveable piston, and this piston is composed of the 

 air tubes. There are four of these longitudinal trunks. They terminate 

 in innumerable smaller ones, and, according to Reaumur, perform the 

 functions of respiration, as well as locomotion, in the ways detailed. 



" After the voracious creature has Iain in ambuscade devouring the 

 larvae of the gnat and other aquatic insects, till its appointed hour of change, 

 it leaves its natal element for the shore, to undergo its last metamorphosis : 

 for this purpose it usually fastens itself to some friendly plant, and begins 

 the important process which is. to convert an aquatic animal into an inha- 

 bitant of the air, 



" Any person who should at this period choose to seize a number of 

 them, and, taking them into his chamber, fix them to a bit of tapestry, 

 would be rewarded for his trouble by witnessing the conversion of an 

 aquatic into an aerial insect. 



" It may easily be seen by the eyes of the nymph whether it is about to 

 change its form ; for, instead of remaining tarnished and opaque, they sud- 

 denly become transparent and brilliant. This change is owing to the 

 visual organ of the perfect insect, which is amazingly lustrous, shining 

 through the mask of the nymph. If the eye of the nymph be removed, 

 that of the perfect insect may be seen beneath. As soon as the nymph has 

 fixed itself to any object by means of its claws, the first sign of the com- 

 mencing metamorphosis is a rent in the upper skin, extending along the 

 corslet to the head. When it approaches this latter part, another rent, 

 perpendicular to the first, runs across the face from eye to eye. These 



