OF NATURAL HISTORY. 131 



Btlt the nymphs or the llbella receive and ejeCt water by an 

 aperture at the termination of their bodies. Thefe nymphs 

 fometimes throw out the water, at certain intervals, with 

 fuch force, that the ftream is perceptible at the diftance of 

 two or three inches from their bodies. "When kept fome 

 time out of water, the defire or neceffity of refpiration is 

 augmented ; and, accordingly, when replaced in a vefTel fil- 

 led with water, infpirations and refpirations are repeated 

 with unufual force and frequency. If you hold one of thefe 

 nymphs in your hand, and apply drops of water to the pofte- 

 rior end of its body, it inftantly, by an apparatus fimilar to 

 the pifton of a pump, fucks in the water, and the dimenfions 

 of its body are vifibly augmented. This water is again 

 quickly thrown out by the fame inftrument. But, though 

 this infefl refpires water, air feems to be not the lefs necef<» 

 fary to its exiftence ; for, like other infefls, the whole inte- 

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

 voluted tracheae ; and, externally, there are feveral ftigmata 

 deftined for the introdudtion of air*. 



The worms, or nymphs, of the ephemeron flies merit at* 

 tention. They have received the denomination o£ ephemeron, 

 becaufe almoft none of them furvive the day in which they 

 are transformed into flies. But many of them Uve not one 

 hour after their transformation. When in the worm and 

 nymph fhates, they generally live in holes near the fur face of 

 the water ; and, under thefe two forms, continue to grow 

 till they are mature for pafllng into the lafl: and fliortefl: pe- 

 tiod of their exiftence. Swammerdam informs us, that fome 

 of them remain three years under water, others two, and 

 others one only. During their abode in this element, they 

 are nouriflied and prepared for their laft and fatal change. 

 Immediately after the males have joined their mates, and the 

 females have depoflted their eggs in the water, both periib, 

 * Reaumur, torn. xa. page 187. i^mo edition. 



