ON ANNELIDA. 121 



to another species. In our observations respecting the hiru- 

 dines in general, we shall take as a type, the medicinal leech, 

 which is by far the best known. 



The body of a leech, in a state of moderate extension, is 

 elongated, a little depressed, more convex above than un- 

 derneath, attenuating insensibly in front, and much less so 

 behind, where it is rounded. Therefore its greatest diameter 

 is towards its posterior third or fourth. It is formed of a 

 variable number of rings or articulations, very regular, very 

 equal, separated by interstices a little more narrowed, and sub- 

 linear. The anterior extremity is obtuse, although sub-angular. 

 In a state of inaction it presents a large orifice, oval, depressed, 

 and oblique, because the upper lip, composed of incomplete 

 rings, advances sensibly more than the lower, formed by the 

 edge of the first complete ring. Thus there is no distinct 

 sucker, or cupper, although these lips perform the functions of 

 one. On the first rings are observable some black points 

 which have been called eyes, but which, at most, are but 

 very imperfect rudiments of such. They are to the number 

 of five pairs, very regularly disposed like a horse-shoe. In 

 all the rest of the back, nothing is perceptible but some irre- 

 gular mucous pores. Finally, altogether backwards, is an 

 aperture much more evident, and perfectly medial, for the 

 anus. The ventral face of the body presents, towards the 

 first fourth of its length, two large medial orifices, at some 

 distance from each other, the anterior of which serves as we 

 shall see, for an issue to the male organ, and the posterior is 

 the female organ of generation. In its whole length, we see 

 on this inferior face of the body, some lateral pores pretty 

 much swelled or tuberculous, ranged by pairs, one at every 

 fifth ring. Finally, at the posterior extremity is a muscular 

 disk, perfectly circular, a little concave, forming a sort of 

 cupper. Sometimes we observe that each ring is provided 

 on each side with a small, not projecting, and retractile 



