MEDICINAL LEECH. 223 



account of his observations on these points, and on the origin of the ova in various 

 Leeches, has not been accessible to me. Joseph has recently discovered in Clepsine 

 that the vasa deferentia and oviducts arise independently of the sexual glands. In 

 Branchiobdella, (which is probably an Oligochaete), both ovaries and testes are 

 proliferations of cells lining the coelome, and the generative products are carried 

 away by ducts with open mouths, which are, perhaps, modified nephridia. It is 

 quite possible that the glands and ducts have the same origin in the Hirudinea. 

 The extension of the vas deferens through several somites, and the presence of 

 nephridia in the same somites, creates a difficulty for this view, the same difficulty, 

 however, that recurs in the Earthworm. 



The Rhynchobddlidae possess neither the tubular intromittent organ nor the 

 muscular vagina. 



The nephridial funnel of Hirudo appears to be degenerate. It is imperforate 

 and multilobed. The lobed ciliated cells which compose it are set upon a vesi- 

 cular dilatation containing a debris of cells. The various lobes of the nephridium 

 are made up of nucleated cells, varying in size and character. These cells are 

 perforated by intracellular ductules with independent walls. The ductules pass 

 from one cell into another, and are branched, especially in the cells of the main 

 lobe, some of the branches remaining caecal. The main duct has cellular walls, its 

 lumen perforating the cell, as in part, at least, of the Earthworm's nephridium. The 

 vesicle has thin walls with muscular fibres, and is contractile. It is lined by a 

 ciliated epithelium. The cells of the gland are surrounded by a rich network of 

 capillary vessels connected with the lateral blood-vessel, and through the testicular 

 sinus with the main ventral blood sinus. The whole gland is invested with vaso- 

 fibrous tissue. 



Nephridial funnels appear to be present in all Leeches. They vary in com- 

 plexity. Among the Gnathobdellidae, they are perforate in Nephelis and Trochaeta, 

 and in these genera they open into special spaces developed in the botryoidal 

 tissue, termed by Gibbs Bourne ' metacoelome.' They are present and usually 

 perforate in Rhynchobdellidae. In Clepsine they open into the ventral blood sinus, 

 and in Pontobdella into a dorso-ventral sinus. In all Leeches the dilatation following 

 the funnel appears to be present. As to the gland, in Pontobdella, Branchellion, 

 and Piscicola, the tubules form a network continuous on both sides of the body and 

 across the ventral median line. The funnels and external openings, however, of 

 Pontobdella are metamerically arranged. Branchellion and Pisricola require further 

 examination. There is no terminal vesicle in Rhynchobdellidae. The Gnathobdel- 

 lidae in general appear to agree more or less closely with Hirudo. 



Gibbs Bourne has found in the ductules of the nephridium in the medicinal 

 Leech minute clear structureless bodies ; in the liquid of the vesicle, and sometimes 

 in the main duct, bunches of needle-shaped crystals, soluble in nitric acid. 



According to Leuckart, the embryo of Hirudo has four pairs of nephridia in 

 front of the first persistent pair of the adult, and three pairs behind the last per- 

 sistent (or seventeenth) pair. 



Genitalia. Leuckart, Die Parasiten, (ed. i.) i. p. 672. Ovary and ova of 

 Nephelis Aulostoma, Piscicola, Pontobdella. Schneider, Das Ei und seine Be- 

 fruchtung, Breslau, 1883. Egg-strings of Clepsine, Whitman, Q. J. M. xviii. 1878; 

 of Nephelis, Jijima, Q. J. M. xxii. 1882. 



