26 



lines. Their cell substance is coarsely granular, with 

 many round clear spaces ; the nuclei are placed at their 

 lower extremities. Only four to six cells are found in 

 each group. The groups are delimited by the arms of the 

 cross-shaped lumen, which extend nearly to the walls of 

 the tubule, and here at the thinnest portion of the wall 

 the cells composing it are small and irregular, and have 

 relatively large nuclei. If the section has been stained 

 with Heidenhain's haematoxylin a very distinct basement 

 membrane, staining dense black, can be seen investing 

 each alveolus. The whole mass of the gland is bound 

 together by fibrous connective tissue, in the interspaces of 

 which are crowded corpuscles of various kinds. 



The lining epithelium at the animal's mouth consists of 

 elongated columnar cells bearing cilia, and supported on a 

 rather distinct basement membrane. Passing inwards this 

 epithelium is thrown into a close series of longitudinal 

 folds, and the height of the cells diminishes. The cells 

 have distinct striated free borders, the nuclei are situated 

 about their middle, the lower ends are rather loose and 

 seem separated from each other ; rounded faintly granular 

 eosinophilous cells are found here and there wedged in 

 between the columnar cells. 



As the oesophagus widens out to form the stomach 

 these cells gradually elongate to form the epithelium 

 lining the cavity of the latter. This gastric epithelium 

 (fig. 18, PI. III.) is of variable thickness, but the cells are 

 always longer than in the oesophagus. A gelatinous 

 looking substance — the " fleche tricuspide " (F.trL, 

 fig. 18) — lines a large portion of the stomach-wall, and 

 underneath this the epithelium becomes much thicker, 

 consisting of long spindle-shaped cells, the long oval nuclei 

 of which occupy any position within a rather wide zone 

 about their middle. The lower ends of these cells are 



