THE SIMPLEST ANIMALS 309 



When the animal is actively moving, long arm-like pro- 

 jections, called pseudopods (false feet), are formed, and then 

 granules from the main body continue streaming in the 

 same direction. In fact, the motion reminds one of the flow- 

 ing of lifeless liquids, and we can imitate it by pouring some 

 thick liquid (molasses, melted gelatin, or mucilage) on a plate, 

 and then by tilting cause the liquid to flow in various direc- 

 tions. Notice that when a streamlet starts in one direction, 

 the liquid all tends to flow in the same direction. 



FIG. 92. Diagrams 1-6 show how an amoeba, or a similar white cell from 

 blood of higher animals, passes through very narrow openings. 



Sometimes a nucleus can be seen in a living amoeba, but 

 it is most evident in a stained preparation. 



In large specimens it is easy to see the one contractile vacuole, 

 which acts essentially like those seen in a paramecium, and 

 has the same function of excreting water containing nitroge- 

 nous waste. 



Food. The taking of food can sometimes be observed 

 when an amoeba is moving actively. If it comes in contact 

 with a small animal or plant, two .pseudopodia flow out and 

 gradually surround and inclose the food particle in the pro- 

 toplasm of the amoeba. A small amount of water surrounds 

 the food particle, just as in a paramecium. Sometimes an 

 amceba is seen so filled with food particles that the body 

 substance is opaque. The protoplasm of amcebas secretes 

 digestive enzymes which dissolve the proteins, etc., in the 

 animals and plants which are captured. The digested foods 

 are then absorbed by the surrounding particles of protoplasm, 



