OF NATURAL HISTORY. 123 



files. But many of them live not one hour after their transforma- 

 tion. "When in the worm and nymph ftates, they generally live in 

 holes near the furface of the water ; and, under thefe two forms, 

 continue to grow till they are mature for paffing into the laft and 

 fhorteft period 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 nou- 

 rifhed and prepared for their laft and fatal change. Immediately 

 after the males have joined their mates, and the females have de- 

 pofited their eggs in the water, both perifh, but not before they have 

 left the rudiments of a numerous race of fucceflbrs. As long as 

 thefe infedis live in the water, to inattentive obfervers, their general 

 appearance is nearly the fame. When they have pafled, however, 

 into nymphs, the veftiges of wings may be perceived, which we look 

 for in vain during their firft or worm ftate. In both ftates, the in- 

 fe£t which is to become an ephemeron fly has fix legs attached to 

 the breaft. The head Is triangular, and from the bafe of each eye 

 proceeds an articulated feeler. The body is compofed of ten rings, 

 from the laft of which three tails, that probably perform the office 

 of tracheae, arife. Thefe tails, in fome fpecies, are as long as the 

 animal's body, and are fringed with hairs which have a refemblance 

 to feathers. But, what principally deferves our notice on this fub- 

 jefl: is, that, on each fide of the body, there are fix or feven protu- 

 berances, which have the appearance of fo many oars. With thefe 

 inftruments the animals defcribe arches in the water, firft on one 

 fide, and then on the other, with aftonifhing rapidity. This circum- 

 ftance led Clutius, and fome other authors, to think that thefe pro- 

 tuberances were fins, or inftruments of motion, and that the animals 

 were fifties. But Reaumur remarked that they moved thefe fins 

 with the fame rapidity when the animals were at reft as when they 

 were in motion ; and that, inftead of fins, when examined by the 

 microfcope, he difcovered them to be gills, through which the crea- 



0^2 turcs 



