218 PRONEOMENIA ACUMINATA. 



tudes of slender, lightly staining cells containing small quantities of yellowish 

 pigment. The contained cavity is extremely slender, preventing the entrance 

 of blood corpuscles but allowing the entrance of slender fibres from the under- 

 lying tissue. In certain species these fibres appear to be in part branches of 

 nerves and such may be the case here, but the contorted appearance of these 

 organs leads to the belief that contained muscle fibres are, at least in part, 

 responsible for their condition. 



Immediately behind the union of the atrial ridges the wall of the digestive 

 tract is smooth, but rapidly develops folds, as the pharynx is approached, of 

 irregular appearance and bounded by the cubical cells characteristic of the 

 pharyngeal epitheUum generally. The accompanying figure (Plate 5, fig. 1) 

 represents approximately the existing state of affairs, but the folds though 

 generally longitudinal are somewhat diagrammatically shown. 



In this species the dorsal saUvary gland (Plate 4, fig. 11, Plate 5, fig. 1) 

 is a marked feature, owing to its size and compactness. It comprises numerous 

 globular or pear-shaped lobules of various sizes bounded by a connective-tissue 

 sheath, and in every instance these are without central cavities. The compo- 

 nent cells are pyriform, and their ductules open by intercellular channels in the 

 epithelium of the prominent diverticulum on the dorsal wall of the pharynx. 

 Vacuoles are abundant in their cytoplasm, and in Ufe they are doubtless filled 

 with a secretion that in preserved material stains very faintly in haematoxyUn. 



From the outlet of the dorsal saUvary gland to the forward end of the 

 radula the pharynx is approximately circular in outline, and is reinforced by a 

 layer of circular muscles and more externally by a longitudinal set. Radiat- 

 ing bundles, acting as dilators, pass from this muscle sheath to the body wall. 



The ventral saUvary glands are tubular, paired organs about 3 mm. in 

 length, situated throughout the greater part of their coiu-se on the ventral side 

 of the body between the stomach-intestine and the body wall. The component 

 cells, all bordering on the narrow centrally placed lumen (Plate 5, fig. 2), are 

 without definite cell boundaries, and the secretion they elaborate occupies 

 numerous vacuoles in the cytoplasm except in the immediate vicinity of the 

 basal or subcentral nuclei. In close proximity to its outlet into the pharynx 

 this glandular portion passes abruptly into a much more slender, non-glandular 

 duct leading to the opening at the side of the exposed portion of the radula. 

 In this non-glandular section the lumen is eccentrically placed, the ventral cells 

 being three or four times longer than those of the dorsal side. 



The radula is a well-defined structure, normally placed, and is of the poly- 



