48 THE SIMPLEST ANIMALS — PROTOZOA 



the rest of the body flows, by a rolling movement, in the 

 same direction. This creeping-rolling motion of the 

 protoplasm enables the amoeba to move through the water. 

 When the pseudopodium comes in contact with a minute 

 plant upon which the amoeba feeds, the protoplasm of the 

 pseudopodium surrounds the plant and takes it into the 

 cell. The microscopic plant thus eaten by the amoeba is in- 

 closed, with a small amount of water, in a tiny globe called 

 the food vacuole (vak'u-ol). The food vacuole is to be 

 thought of as a stomach in which digestion can take place, 

 for the plant is digested in it. The nutritious parts are 



absorbed into the proto- 

 plasm, the undigested 

 parts are cast from the 

 cell, and the food vacuole 

 disappears. 



There is no well- 

 defined cell wall ; there- 



Feelmg pseudopodium. 

 Ectoplasm 

 Endopldsm / \ 



£» 



Nucleus ; 



Walking pseudopodium 



Figure 46. — Diagram of an Amceba. f ore the amoeba IS an 



illustration of a living, 

 naked cell. Near the center of the cell is a spherical 

 mass of denser protoplasm called the nucleus. In many 

 amoebaB the nucleus is not easily seen except by means 

 of specially stained preparations. The rest of the proto- 

 plasm in the cell is called cytoplasm (si'to-plazm). This 

 does not appear the same in all parts of the amoeba. On 

 the outside, there is a thin, almost transparent layer, 

 called ectoplasm (ek'to-plazm : Greek, ecto, outside; 

 plasma, form). The larger part of the cytoplasm is filled 

 with numerous small granules and contains several 

 vacuoles. This inner mass of cytoplasm is called endo- 

 plasm (en'do-plazm: Greek, endo, within; plasma, form). 

 The vacuoles in the endoplasm may contain food, water, 

 or waste products. The food and water vacuoles are 



