SECRETION AND EXCRETION. 
123 
2. The gastric follicles are minute tubes in the walls of 
the stomach secreting gastric juice. They are found in 
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 
of an inch in diameter, and number mill¬ 
ions. 
3. The pancreas, or “ sweetbread,” so 
. . . „ ,. . Fig. 90.—Follicles from the 
important in the process ot digestion, stomach of a Dog, x 
exists in all but the lowest animals. In J^e^TViiniug'of col 
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 
Thus, in 
loricvalve;i,duodenum. Polyps it is represented 
by yellowish cells lining the stomach ; in Insects, by cells 
Fig. 91. —Pancreas of Man, o; g, gall-bladder; ^ nancreas. 
#, cystic duct; c, duct from the liver; p, py- r 
