On Dissotrema papillatum. 5 



its inner lining, which may be as thick as 12^ in some places, ap- 

 pears as if composed of clear, small, polygonal prisms hard pressed 

 against one another and separated only by deeply staining 

 membranous partitions. In tangential sections of the prepharynx, 

 the prisms naturally appear as so many clear polygonal spaces with 

 deeply stained peripheries. Examination with high power objec- 

 tives shows that the clear prisms are nothing else than the openings 

 of the glands that surround the prepharynx along its whole length, 

 and that the deeply stained partitions are the substance of the 

 lining cuticle, which is the direct continution of that of the 

 oral sucker, but which has undergone a change in its physical 

 condition owing to the pressure to which it must be sub- 

 jected by the passage of so many glands through it. As a 

 proof of the correctness of this interpretation we see that the 

 cuticle is restored to its ordinary condition in those places where 

 the secretory activities of the gland cells appear to be in a resting 

 stage. In many places the free ends of the membranous partitions 

 above mentioned appear in sections like cilia, and where the 

 secretions are being poured into the prepharyngeal cavity, they 

 may be observed forming a column corresponding to each clear 

 prism and projecting inwards. 



The prepharynx is accompanied in its whole length by 

 numerous unicellular glands which invest it all around in cross 

 sections and which we think it appropriate to call the prepharyngeal 

 glands (fig. 3). They are arranged in more or less distinct groups of 

 some ten or more cells each, separated from one another by the 

 intervening parenchyma or pressed against one another in different 

 degrees according to the different phases of their secretory activity. 

 The cells are very deeply stained with haematoxylin when they 

 are small, i.e. in the intervals of their secretory activity and 

 more pale when they are large and contain much secretion in the 

 cytoplasm. In the latter state the nucleus is usually spherical 

 and vesicular and contains a single, well defined chromatin 

 spherule in the centre. The duct which leads from each of 

 these cells to the prepharyngeal lumen can be observed better 

 when they are deeply stained, since the filling of these ducts by 



