ELEMENTARY VITAL PHENOMENA 



145 



the digested food (Fig. 45, A). In the higher animals, such as man 

 and other mammals, however, the intestinal cells are somewhat 

 modified. They are cylindrical cells that possess upon their free 

 surface, turned toward the lumen of 

 the intestine, a striated border. As 

 Thanhoffer (74) has shown, this stri- 

 ated border represents really nothing 

 more or less than fine, pseudopodium- 

 like, protoplasmic processes, which can 

 be extended and retracted, and with 

 which the cells, exactly like Amoeba, 

 flow around the fat-droplet and draw 

 it into its body (Fig. 45, ). 



The phenomena are wholly dif- 

 ferent in the second type of food- 

 ingestion, where the cell has a firmer 

 superficial layer of a fixed form, and 

 only a small opening, the cell -mouth, 

 which. leads directly into the liquid 

 endoplasm. Here the movement of 

 the cilia and flagella of the cell 

 exclusively mediates the ingestion of 

 solid substances. The delicate Vor- 

 ticella may serve as an example, a 



ciliate infusorian whose bell-shaped cell-body sits upon a contractile 

 stalk and bears at its broad end a spiral-like circlet of cilia (Fig. 46). 



a b c 



FIG. 44. Leucocyte from the frog de- 

 vouring a bacterium. Three suc- 

 cessive stages in the ingestion of 

 food. (After Metschnikoff.) 



FIG. 45. A. Intestinal epithelium-cells from the liver-fluke, possessing pseudopodium-like proto- 

 plasmic processes for the ingestion of blood-corpuscles,a, &,and drops of chyle, c. (After Sommer.) 

 B. Intestinal epithelium-cells from the vertebrate, ingesting fat. In the interior of the cells 

 single microscopic fat -droplets are found. (After Thanhoffer.) 



At the bottom of this spiral-like ciliated funnel is a cell-mouth, 

 which is prolonged a short distance into the protoplasm as the cell- 

 pharynx, and then gradually disappears into the liquid endoplasm. 



