Obder 3. 



ABPiAJ^CHIA. 



399 



The Leeches {Hirudo, Linn.) — 

 Have an oblong body, sometimes depressed, and wrinkled transversely ; the mouth encircled by a lip, 

 and the posterior extremity furnished with a flattened disk, both ends being adapted to fix upon bodies 

 by a kind of suction, by means 

 of which these animals move, 

 for. having fi.xed their anterior 

 extremity, they draw the other 

 up to it and fix that, and then 

 readvance the first, [besides 

 which, they swim with facility]. 



Several have a double series of Fig. 207.— Hlrudo officinalis ; e, its anterior extremity, shewing the sucker. 



pores underneath the body, which are the orifices of little internal pouches, considered by some natu- 

 ralists as organs of respiration, although they are generally filled with a mucous fluid. The intestinal 

 canal is straight and swoln at intervals, extending for two thirds the length of the body, where there 

 are true cceca. The blood they swallow continues red, and without alteration, for several weeks. The 

 ganglia of their nervous system are much more separated than those of the Earthworms. They are 

 hermaphrodite, and have a large penis about the anterior third of the body, and a vulva a little behind 

 it. Several accumulate their eggs into cocoons enveloped by a fibrous excretion. 



[On opening the Leech shortly after it has gorged itself with the blood of its prey, it will be found 

 that none of the blood has passed into the intestines. The operation of digestion is extremely slow, 

 notwithstanding the rapid and excessive manner in which the Leech fills its stomach : a single meal 

 of blood will suffice for many months, nay, more than a year will sometimes elapse before the blood 

 has passed through the intestines in the ordinary manner, during all which period so much of the 

 blood as remains undigested in the stomach continues in a fluid state, and as if just taken in, notwith- 

 standing the vast difference in the heat of the body of a mammiferous animal and that of a Leech.] 

 — Griffith, An. King., part 35, p. 129. 



They are subdivided upon characters derived principally from the organs of the mouth. In 



The Leeches, properly so called {San- 



guisuya, Sav.), — 

 The anterior sucker has the lip divided into 

 several segments ; its aperture is trans- 

 versal, and contains three jaws, each armed 

 with a double range of very fine trenchant 

 teeth, which enable them to pierce the 

 skin without inflicting a dangerous wound: 

 they have ten minute points, which have 

 been considered as eyes. 

 Every one is acquainted with the medicinal Leech (U. medicinalis, Linn.), so useful an iustrimient for local 



blood-letting. 



H^MOPis, Sav., — 



Differs by having the teeth less numerous and comparatively obtuse. 

 Such is the common Horse Leach, {H. sanguisorba, Sav.). 



Bdellia, Sav., — 

 Has only eight eyes, and no teeth whatever. 

 There is one in the Nile (Brf. nilotica, Egypt. Ann.) 



Nephelis, Sav., — 

 Has also but eight eyes, and the mouth with only three folds of the skin interiorly. 

 M. de Blaiuville terms tlieni Erpobdellis, and M. Oken Hellito. 



Numerous small species inhabit our fresh waters, among which should be distinguished 



Trochetia, Dutrochet, — 

 Which difl'er by having a bulge at the genitals. 

 A species {Geobdella trochetii, Blainv.), is often seen upon the ground, pursumg the Ear tliworms. 



Fig. 203. — Developeracut of Hirado medlciuulis. 



