432 ALFRED GIBBS BOUENE. 



within the clitellar region and behind, it there are numerous 

 deep-lying glands — clitellar glands. They are absent in 

 Clepsine alone, this leech laying its eggs without any 

 cocoon.^ 



In the Gnathobdellidse they are very numerous in the clitellar 

 region, and are placed in groups of four or five in the connec- 

 tive tissue between the bundles of muscular fibres (figs. 13 and 

 61,^^. c). Their ducts are radially arranged, and open upon 

 the surface of the clitellum. 



In Piscicola, Pontobdella, and Branchellion they are 

 very extensively developed ; they occur in masses within the 

 longitudinal muscles of the body wall, and the region of their 

 occurrence extends from the clitellum backwards almost to the 

 posterior end of the body. They attain relatively, and in 

 Pontobdella and Branchellion, actually huge dimensions 

 (figs. 9 and 63, ffl. c). 



Their ducts which, as in the case of the mucous glands, 

 are mere prolongations of the cell membrane, are arranged 

 in bundles, and run forwards to open at the clitellum. In 

 Pontobdella (figs. 9 and 63, gl. c. d.) there are some twelve 

 bundles, each containing as it approaches the clitellum some 200 

 to 400 ductules. Some of these ductules and gland-cells take 

 up a very deep staining; others do not, the difi'erence 

 depending here, doubtless, upon their state of activity. In 

 teazed preparation from the fresh animal it is easy to cause the 

 granular contents to flow along the ductules by pressing upon 

 the coverglass. 



X. Prostomial Glands. — A third variety of these deep- 

 lying unicellular glands exists in Hirudo, Aulostoma, and 

 Nephelis, doubtless in all the Gnathobdellidse. They are 

 situated in the prostomium and the region around the mouth. 

 They form a very distinct group, and send their ducts forwards 

 to open all round the edge of the buccal cavity. They are 

 perfectly distinct Irom the salivary glands, there being a con- 

 siderable space between the most posterior of these and the 

 most anterior of the salivary glands. Their contents, moreover, 



' C. 0. Whitman, ' Quart. Journ. Micr. Sci./ 1878, p. 224. 



