MANUAL OF ZOOLOGY. 



but the Leeches are nevertheless incapable of self-fertilisation. 

 Reproduction, also, is always effected by means of the sexes, 

 and never by fission or gemmation. 

 The generative products, instead of 

 being discharged into the perivisceral 

 cavity . (as in the Annelida generally), 

 reach the surface by special apertures. 

 The ova are deposited in delicate chi- 

 tinous capsules or " cocoons ; " and the 

 young, on being hatched, undergo no 

 metamorphosis, but are essentially simi- 

 lar to the adult in all except their size. 



The common Horse-leech, Hczmopsis, is only 

 provided with blunt teeth ; but the Medicinal 

 Leech (Sanguisiiga medicinalis, fig. 129) has its 

 mouth furnished with three crescentic jaws, the 

 convex surfaces of which are serrated with 

 minute teeth. This species is chiefly imported 

 from Germany, Bohemia, and Russia. In 

 Sanguisuga officinalis, the Hungarian Leech, 

 also used in medicine, the abdomen has numer- 

 ous black spots. In both species the oral and 

 caudal extremities are narrowed before dilating 

 into the suckers, and the body has from ninety 

 to one hundred rings. The anterior sucker is 

 small, with a lancet-shaped upper lip, carrying 

 ten ocelli on its superior surface. The posterior 

 sucker is round, obliquely placed, and separated 

 from the body by a distinct constriction. The 

 alimentary canal, usually termed the "stom- 

 ach" in its anterior portion, occupies the 



greater part of the body-cavity, and is furnished with eleven membranous 

 pouches or diverticula on each side. There are seventeen segmental organs 

 on each side, opening by minute stigmata on the lower surface of the body. 

 The opening of the male reproductive organs is in the anterior third of the 

 body, between the twenty-seventh and twenty-eighth rings ; that of the 

 female organs, in the form of a small fissure, five rings behind. Impregna- 

 tion of the hermaphrodite individuals is mutual, and the ova are deposited 

 in moist earth, within a cocoon, where they icmain until hatched. The 

 marine Pontobdellce have the body tuberculated, and attach themselves to 

 the bodies of fishes, especially skates. The anterior sucker is separated in 

 these from the body by a distinct constriction or neck. In the little fresh- 

 water Clepsines the anterior sucker is wanting, and there is a proboscidi- 

 form mouth. They are found attached to the stems of water-plants, or to 

 aquatic animals of different kinds. Branchiobdella lives upon the gills of 

 Crustaceans ; and Branchellion infests the gills of various Fishes, such as 

 the Turbot. A few Leeches inhabit damp situations on land. 



ORDER II. OLIGOCH^ETA (Terricola). The members of this 

 order, comprising the Earth-worms (Lumbricidce) and the 

 Water-worms (Ndidid&\ are distinguished by the fact that 

 their locomotive appendages are in the form of chitinous setce, or 



f. 129. Hirudinea. a The 

 ledicinal Leech (Sangui- 

 suga ojficinalis), natural size; 

 b Anterior extremity of the 

 same magnified, showing the 

 sucker and triradiate jaws ; 

 c One of the jaws detached, 

 showing the semicircular 

 toothed margin. 



