CHAETODERMA SQU.\MOSUM. 205 



the plate, or opening adjacent to it, are usually closely associated with nerve 

 fibres originating in the precerebral ganglia attached to the brain; but they 

 have not been definitely traced to any special set of cells. Several groups 

 of gland cells, of shrunken appearance probably owing to reagents, are imbedded 

 in the wall of the digestive tube in the neighborhood of the mouth. These 

 may be connected with the ductules in question, but on the other hand there 

 are signs that they are in reahty buccal glands opening by ill-defined passages 

 into the digestive tract. 



In common with other members of the genus, this species possesses a diges- 

 tive tract comparatively simple in its structural details. The mouth opens 

 into a well-defined buccal tube of average size and with sUghtly folded walls 

 in which the Uning epithelium consists of slender cells possibly ciliated and 

 without very distinct cell boundaries. Immediately anterior to the peg-Uke 

 tooth the ventral wall becomes modified to form a well-defined patch of slender, 

 ciUated cells — the subradular organ, judging by position and innervation. 

 Here and there, especially in the ventral half of the tract, gland cells are imbedded 

 in the muscular walls, and in some instances at least open into the digestive 

 tract by intercellular ductules. These glands become relatively abundant in 

 the neighborhood of the radula where they chiefly open on prominent folds of 

 the lateral walls of the gut. 



The radula (Plate 11, fig. 10) is, as usual, a slender conical structure 0.4 mm. 

 in length, and in its relations, muscular attachments, and matrix cells conforms 

 closely to other species of the genus. 



A very short distance posterior to the radula the digestive canal narrows 

 rapidly, becoming elliptical in cross section, whereupon it almost immediately 

 unites with a dilated portion whose walls have been largely stripped of their 

 hning epithelium due apparently to the reduction of pressure upon being brought 

 to the surface. Where it remains the cells agree in being relatively large 

 columnar elements in which the centrally placed nuclei are unusually conspicu- 

 ous. A darkly staining secretion covers their free surface, but its origin is 

 uncertain, though it may have been elaborated by these cells as they generally 

 show traces of glandular activity. This dilated section of the canal narrows 

 considerably in the posterior end of the prothorax (Plate 11, fig. 8), and as 

 an almost perfectly circular tube extends into the metathorax where it unites 

 in characteristic fashion with the stomach and Uver. In the abdomen a mass 

 of diatoms, sponge spicules, and inorganic debris prevented sectioning; in the 

 cloacal regions the position of the gut was typical. 



The coelomoducts are comparatively simple structures, holding the usual 



