94 



Histology of the Digestive Gland 

 (PI. V, figs. 37, 38, 39). 



In sections the tubules are seen to be closely packed 

 together, generally being separated only by a very thin 

 layer of connective tissue (fig. 37, c. t.) or a small blood 

 sinus. Sometimes, however, the walls of the tubules are 

 not separated from each other by any tissue. The lumen 

 of the tubules has four angles in transverse section, and 

 the cells at the angles are much shorter than the others. 



The ducts are lined by a single layer of large 

 columnar and non-glandular cells. In the sections 

 stained with methyl-blue eosin these cells take the stain 

 more readily than the cells of the tubules. 



The tubules (fig. 37) have three kinds of cells. 



(1) Fat cells (fig 37, /.«,, fig. 38). These are 

 columnar cells from 70 f* to 120 /x in length and 

 15 /u wide. The contents of the cells are vacuolated, due 

 to the presence of fat globules (fig. 38, g. /".). The border 

 of each cell in contact with the lumen of the tubule is 

 striated (sb.). The nucleus (/?.) is generally situated in 

 the inner portion of the cell. 



(2) Ferment cells (fig. 37, fm. c, fig. 39). These are 

 not quite as long as the fat cells, but they are about four 

 times as broad. Each cell contains a large globular mass 

 (tig. 39, /. v.) which nearly fills the whole cell. These 

 masses are yellowish-brown and are responsible for the 

 characteristic colour of the digestive gland. According 

 to Frenzel each mass is enclosed in a bladder, and the 

 vesicles are more abundant during feeding time than 

 during the fasting periods. On the side of the cell in 

 contact with the lumen of the tubule there is a small 

 amount of vacuolated protoplasm which exhibits striation. 

 The border of the cell in contact with the lumen was 



