CONTRIBUTIONS TO THE ANATOMY OF THE HIRUDINEA. 431 



very thin layer only of protoplasm, the remainder of the cell 

 being filled with the secreted substance. 



In Piscicola (fig. 11, gl. in.) these mucous glands are 

 very numerous, but they never extend below the level of the 

 other epidermic cells; they lie in the same series, and are 

 only distinguishable by their greater breadth, the position 

 of the nucleus and their contents. 



In Hsemadipsa the majority remain small and retain their 

 position among the epidermic cells. 



In other genera they become so large as to be completely 

 forced out of the epidermic series, and lie in the sub-epidermic 

 layer. They obtain a larger size in the Rhyncobdellidae than 

 in the Gnathobdellidse. 



When seen in sections some appear to have almost clear or 

 very finely granular contents, and generally remain almost 

 unstained. This difference may be due to the state of activity, 

 and be comparable to the difference observable in glandular 

 cells of the pancreas or gastric glands at different periods ; but 

 I am inclined to think that there is some difference in the 

 nature of the secretion, and that the clearer cells are always 

 smaller and more superficial (figs. 9 — 14, gl. m.). 



ii. Glands which have taken up a deep position present at 

 least three well-marked varieties, depending upon the nature 

 of the secretion. 



a. Salivary Glands. — These occur in all the genera in the 

 region of the pharynx, whether that be protrusible or not; 

 they occur almost as far back as the generative organs. They 

 are exceedingly numerous and large, with coarsely granular con- 

 tents; they possess very long ductules which open, in the 

 Gnathobdellidse, on the surface of the ridges which bear the 

 teeth, and, in the Rhyncobdellidse, in the walls of the pharynx. 

 When the pharynx is protruded they are stretched, and when 

 it is withdrawn they are thrown into convolutions. 



Figs. 16—24 show salivary ducts {gl. s. d.). Also woodcut, 

 p. 437. For salivary glands in Hirudo see this Journal, voL 

 XX, 1880, fig. 13, PI. XXV. 



/3. Clitellar Glands. — Behind the *' salivary "region, both 



VOL. XXIV. NEW SER. G G 



