ONE-CELLED ANIMALS 313 



shows, under the microscope, a peculiar power of chang- 

 ing its shape, and of moving about. This is one of the 

 lowest animals; it is called an ameba (Fig. 253), from 

 a Greek word meaning "to change." 

 The jelly-like creature consists of a 

 cell of protoplasm (cf. 323). At its 

 center the cell is grainy; this region 

 is the nucleus. The ameba thus con- 

 sists of one cell, like protococcus ; but 

 it has no chlorophyll. It has no FlG ' 2 ma g nf fi n e^ meba ' 

 organs, either. It moves by extend- 

 ing the cell wall at any region into a projecting lobe; 

 the cell contents then flow into the lobe. These lobes 

 are called "false feet." The ameba has no mouth; it 

 feeds by extending two lobes around an article of food, 

 and then withdrawing the cell wall. The protoplasm 

 simply envelops the food. The ameba excretes (throws 

 out) waste parts of its food merely by moving away 

 from them. When food is thus passed through the cell 

 wall, no opening is left; just as there is no break in the 

 tough, though fragile, film of a soap bubble when a needle 

 is put through it. 



The reproduction of the ameba is also of the simplest 

 sort. The nucleus of the cell divides itself into two parts, 

 half of the protoplasm groups itself about each nucleus, 

 and at the line thus formed the cell divides; there are now 

 two amebas instead of one. 



A creature like the ameba forms a part of our own blood (cf. 378). 

 If you will examine a drop of blood, under the microscope, you will 

 see that it contains both red and colorless bodies. These are called 

 corpuscles, that is, " little bodies." The colorless ones, called white 



