SECRETION AND EXCRETION 



331 



scope, the soft mucous membrane of the human stomach 

 presents a honeycomb appearance, caused by numerous 

 depressions or cells. At the bottom 

 of these depressions are clusters of 

 spots, which are the orifices of the 

 tubular follicles. The follicles are 

 about 2^0 f an mcn m diameter, 

 and number millions. 



3. The pancreas, or "sweetbread," 

 so important in the process of di- 

 gestion, exists in all but the lowest 

 animals. In its structure it closely 

 resembles the salivary glands. In the 

 cuttlefish, it is represented by a sac ; 

 in fishes, by a group of follicles. It is 

 proportionally largest in birds whose 

 salivary glands are deficient. The 

 pancreatic juice enters the duodenum. 



4. A so-called " liver " is found in 

 all animals having a distinct diges- 

 tive cavity. In the lower animals its function has 

 been shown to be that of a pancreas. Thus, in polyps 



it is represented by yellowish cells lining the 

 stomach ; in insects, by cells in the wall of 

 the stomach ; in mollusks, by a cluster of sacs, 

 or follicles, forming a loose compound gland. 

 In vertebrates, a true liver, the larg- 

 est gland in the body, is well defined, 

 and composed of a mul- 

 titude of lobules (which 

 give it a granular ap- 

 pearance) arranged on 

 the capillary veins, like 



FIG. 288. -Pancreas of Man; o, pancreas; g t grapCS On a Stem, and 

 gall bladder; s. cystic duct; c, duct from the . i J 



liver; A pyloric valve; e,f, duodenum. COn tainin g H UC leat ed 



FIG. 287. Follicles from the 

 Stomach of a Dog, X 150; 

 near the mouth, a, there 

 is a lining of columnar 

 epithelium. 



