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 
