The NERVOUS SYSTEM exhibits the typical structure of other segmented worms; the sensory organs consist of the previously mentioned goblet-shaped cutaneous sensory organs, of the organs of taste, and of eyes, the latter frequently being present in large numbers.
The EXCRETORY or segmental organs exhibit many peculiarities, which cannot, however, be detailed here. They commence with funnels in the lacunes of the body cavity, and usually discharge on the ventral surface.
Almost all the Hirudinea are hermaphrodite and copulate reciprocally. The two ovaries are very small, and the oviducts that proceed from them soon unite into a common duct, which then passes into the uterus and discharges through the short vagina in the median line of the ventral surface behind the male organs into the so-called clitellar region. The male sexual apparatus consists of symmetrically arranged testicles, varying in number according to the species, the short vasa efferentia of which, one by one, run into the vas deferens, passing towards the front on each side. In front, at about the level, or a little in front, of the female genitalia, the two vessels pass into a convoluted mass of tubes to the so-called epididymis, and then discharge into the single protractile penis (fig. 348D).
All leeches deposit so-called COCOONS. These are small barrel-shaped or pouch-like bodies, which are surrounded by a thicker shell and contain a number of eggs in a large mass of albumen; the albumen originates from glands of the generative organs, the shell substance from cutaneous glands of the clitellar region.
Family. Gnathobdellidæ (Leeches with Jaws).
These are distinguished by the possession of usually three jaws in the pharynx; the body consists of twenty-six segments. The posterior sucker is large and flat; the anterior sucker is smaller. The Hirudinea have five pairs of eyes, the Nephelinæ have four pairs.
Genus. Hirudo, L., 1758.
The entire body consists of 102 annulations, five appearing on one segment in the central region of the body. The pharynx has three semicircular jaws, the arched border of which is beset with numerous teeth (50 to 100). The male sexual orifice lies between the thirtieth and thirty-first rings, the female orifice between the thirty-fifth and thirty-sixth. There are numerous species, some of which are utilized for medicinal purposes.