132 THE PHILOSOPHY 



but not b2fore they have left the rudiments of a numerous 

 race of fuccelTors. As long as thefe infe£ls live in the water, 

 to inattentive obfervers, their general appearance is nearly 

 the fame. When they have paiTed, however, into nymphs, 

 the veftiges of wings may be perceived, which we look for 

 in vain during their firil: or worm ftate. In both ftates, the 

 infect which is to become an ephemcron fly has fix legs at- 

 tached 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 fubjecl is, 

 that, on each fide of the body, there are fix or {even protu- 

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

 thefe inftruments the animals defcrlbe arches in the water, 

 iirft on one fide, and then on the other, with afi:onifliing ra- 

 pidity. This circumftance led Clutius, and fome other 

 authors, to think that thefe protuberances were fins, or in- 

 ftruments of motion, and that the animals were fiflies. But 

 Reaumur remarked that they moved thefe fins with the 

 fame rapidity when the animals were at refi: as when they 

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

 by the microfcope, he difcovered them to be gills, through 

 \vhich the creatures refplre. Each gill confifts of a fliort 

 trunk, and two large branches, or tubes, which give off on 

 all fides a number of fmaller ramifications, and are perfeaiy 

 fimilar to the tracheae of other infers. At the origin of 

 every gill, two tracheae penetrate the trunk, and are difperf- 

 ed through the body of the animal. 



Though the ftigmata, or refpiratory organs, of caterpillars 

 and other infe(Sls, were long known to ferve the purpofe of 

 infpiration, yet it was uncertain whether the animals refpired 



