DIGESTIVE TISSUES 



297 



eosin, and are best demonstrated by the use of this stain in combina- 

 tion with others. 



Digestive tissues. The digestive tissues in Cerebratulus are not highly 



B 



FlG. 264. Portion of the digestive epithelium of Cerebratulus lactatus, showing a deep 

 mucous cell. . ., nucleus of mucous cell. X 1200. 



differentiated. In the oesophageal epithelium the same elements are rep- 

 resented as are found in the intestine. In this 

 region there are two types. The columnar, 

 ciliated cells have oval to rounded nuclei 

 lying in the basal third of the cell. There, is 

 an occasional vacuole bearing a secretion 

 substance found within these cells (Fig. 264). 

 The serous cells in this region are more than 

 twice as large as the ciliated cells. They 

 extend far below the basement membrane. 

 The nuclei are small and lie quite near the 

 base of the cells. The secretion bodies stain 

 black in iron haematoxylin. In the intestine 

 these elements become much taller, so that 

 the intestinal epithelium is very thick. The 

 ciliated cells here are as tall as the albumen 

 cells. Figure 265 shows but the lower third 

 of these cells. The ciliated, secreting cells 

 are most numerous in the dorsal region of 

 the intestine. Their cytoplasm contains many 

 spherical secretion particles. The elliptical 

 nuclei lie near the base of the cells (Fig. 265, 

 A}. The albumen cells in this region are 

 scattered and very slender. Their secretion 

 particles are small, round bodies (Fig. 265, 

 C). On the ventral side of the intestine the 

 albumen cells are the more numerous. In 



FIG. 265. The bases of three 

 long digestive cells from the en- 

 teron of Cerebratulus lactatus. 

 nu., nuclei; b.m., basement 

 membrane. Cells filled with 

 secretion granules. X 1 200. 



