CHAETODERMA VADORUM. 197 



In sections these are seen to occupy a position adjacent to the buccal tube, 

 and along the path traversed by the nerves destined to the buccal plate and 

 originating in the great precerebral nerve masses (buccal ganglia of Wiren). 

 In several other species of the genus ductules lead to cells in the same general 

 position, but the lack of a clearly defined secretion in these cells and owing to 

 their resemblance to ganglion cells it has never been possible heretofore to make 

 the identification certain. In the Ught of the state of affairs in the present 

 case it is altogether probable that gland cells are normally present and in the 

 position described above. 



These gland cells are usually arranged in the form of lobules, though sepa- 

 rate cells are occasionally met with in the neighborhood of the buccal plate. 

 Each, in a fully developed condition contains numbers of darkly staining gran- 

 ules, though not in sufficient numbers to mask th^ nucleus. This last named 

 body occupies a central position, and contains a well-defined though faintly 

 staining nucleolus. In a few instances the ductules perforate the margins of 

 the buccal plate; more generally they pass to the exterior without the borders 

 of the plate but in close proximity to it. 



As noted previously the mouth occupies a cleft in the buccal plate, and 

 sections show that it leads into a canal of average dimensions and with typical 

 relations. Generally speaking the epithelial lining rests upon a circular muscle 

 layer, but as this is pierced by numerous radial or diagonal fibres the Une of de- 

 marcation is by no means sharp, a state of affairs that is accentuated by the 

 presence of several glands. These last named organs (Plate 12, fig. 2), in the form 

 of lobules, encircle the tube and are in all stages of glandular activity. Those 

 in an inactive state bear a fairly close resemblance to the neighboring gangUon 

 cells, but in a fully developed condition they become distended with a vacuolated, 

 moderately staining secretion that escapes into the buccal tube or pharynx by 

 intercellular canals, though these are usually difficult to demonstrate. 



The radula of this genus, together with its supports and muscles, is a 

 remarkably constant structure, and this species is no exception to the rule 

 (Plate 12, fig. 1), there being no marked characteristics of diagnostic value. 



Immediately posterior to the radula the cUgestive tract narrows rapidly, 

 and becomes elliptical in outUne (Plate 12, figs. 9, 12). The cells of the lining 

 are greatly elongated and glandular, the secretion appearing as a finely granular, 

 moderately staining mass that may in rare instances become so abundant and 

 closely packed that it appears to be homogeneous. This state of affairs rapidly 

 changes as the canal is followed backward. The cells become lower, and in 

 most instances have been dislodged, evidently due to the decreased pressure 

 attendant upon coming to the surface. Where they have remained they are 



