58 



digestive gland, are numerous large spaces, crowded with 

 blood corpuscles, amongst wliich are large spindle-shaped 

 connective tissue cells, the ends of which are drawn out 

 into long fibres. 



The epithelial cells lining the cavity of the stomach 

 are very long and narrow, the length attained averaging 

 about 0"0T mm They have prominent elongated nuclei 

 situated at about the middle of their length. These, like 

 the epithelial cells throughout the whole length of the 

 alimentary canal, are richly ciliated. 



If sections be cut transversely across the grooved 

 epithelium it will be seen that the grooves and ridges are 

 due to the varying height of the epithelial cells ; those 

 which lie at the bottom of a groove are only one-quarter 

 of the height of those forming the ridge. The cell 

 contents are the same in the two cases, and the cells at the 

 bottom of the grooves bear just as well developed cilia, so 

 that the^^ apparently function as channels along which the 

 secretion of the digestive gland passes. Some of the cells 

 (but not chose of the grooved epitheliumj contain large 

 and small green granules, which are sometimes as wide 

 as the ceil, and lie in a distinct vacuole. 



THE DIGESTIVE GLAND. 



This large gland (tig. 1, Dg.), which is the only one 

 occurring in connection with the alimentary canal, has at 

 various times been known as the liver, the Hepato- 

 pancreas and the Gastric gland. The only function that 

 entitles it to the name " liver " is that of apparentl}^ 

 forming oi certainly of storing fat and pigment. After 

 much investigation, it now appears to be a " pancreas "" 

 with the additional function of storing pigment, and in 

 some Lamellibranchs [Ostrca) large quantities of fat. It 



