SECRETION AND EXCRETION. 



123 



2. The gastric follicles are minute tubes in the walls of 

 the stomach secreting gastric juice. They are found io 

 all Vertebrates, and in the higher Mol- 



lusks and Arthropods. In the lower 

 forms, a simple membrane lined with 

 cells serves the same purpose. Under 

 the microscope, the soft mucous mem- 

 brane of the human stomach presents a 

 honey-comb appearance, caused by nu- 

 merous depressions or cells. At the bot- 

 tom of these depressions are clusters of 

 spots, which are the orifices of the tubu- 

 lar follicles. The follicles are about -5-^5- 

 of an inch in diameter, and number mill- 

 ions. 



3. The pancreas, or " sweetbread," so 

 important in the process of digestion, 

 exists in all but the lowest animals. In 



its structure it closely resembles the sal- lumnar epithelium, 

 ivary glands. In the Cuttle-fish, it is represented by a 

 sac ; in Fishes, by a group of follicles. It is proportion- 

 ally largest in Birds whose 

 salivary glands are defi- 

 cient. The pancreatic 

 juice enters the duode- 

 num. 



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 



FIG. 91. Pancreas of Man, o; g, ea 11 -bladder? f nanrrpA<5 TVino in 

 8, cystic duct; c, duct from the liver ; p, py- U 118 > 1] 



loric valve ; ,i, duodenum. Polyps it is represented 



by yellowish cells lining the stomach ; in Insects, by cells 



