96 RESPIRATION. 



discovered, that these horns, which pierced the hard exterioT 

 covering, terminate in as many tracheae in the body of the 

 animal. This fact affords a strong example of the necessity 

 of air for sustaining the principle of life, even in its lowest 

 condition. After these animals pass from the chrysalis state 

 to that of flies, they are deprived both of their tails arid horns. 

 But Nature, in this last stage of their existence, has not left 

 them without proper resources for the introduction of air into 

 their bodies. Instead of protuberant tracheae in the form of 

 tails or horns, they now, like other flies, receive air by means 

 of stigmata, or holes, variously disposed over different parts of 

 the body 



The nymphs of the libella, or dragon-fly, respire water by 

 an aperture at the termination of their bodies. These nymphs 

 sometimes throw out the water, at certain intervals, with such 

 force, that the stream is perceptible at the distance of two or 

 three inches from their bodies. When kept some time out of 

 the water, the desire or necessity of respiration is augmented , 

 and, accordingly, when replaced in it, inspirations and ex- 

 pirations are repeated with unusual force and frequency. If 

 you hold one of these nymphs in your hand, and apply drops 

 of water to the posterior end of its body, it instantly, by an 

 apparatus similar to the piston of a pump, sucks it in, and 

 the dimensions of its body are visibly augmented. This water 

 is again quickly thrown out by the same instrument. But 

 though this insect respires water, air seems to be not the less 

 necessary to its existence ; for, like other insects, the whole 

 interior part of its body is amply provided with large and con- 

 voluted tracheae ; and, externally, there are several stigmata 

 destined for the introduction of air. 



The worms, or nymphs, of the ephemeron flies merit atten- 

 tion. They have received the denomination of ephemeron, 

 because very few of tnem survive the day in which they are 

 transformed into flies. Many of them live not one hour after 

 their transformation. When in the worm and nymph states, 

 they generally live in holes near the surface of the water ; and 

 under these two forms, continue to grow till they are mature 

 for passing into the last and shortest period of their existence. 

 Swammerdam informs us, that some of them remain three 

 years under water, others two, and others one only. 



On each side of their bodies, there are six or seven protu- 

 berances, which have the appearance of so many oars. With 

 these instruments the animals describe arches in the water, 

 first on one side, and then on the other, with astonishing ra 



