ANIMAL LIFE 



351 



cells we have studied they have no fixed form but have the 

 appearance of an irregular mass of protoplasm which 

 changes in form constantly as it moves about. 



There are no separate organs in these animals. The 

 one cell performs all the functions necessary to their 



FIG. 310. Amoeba Showing Division. 



life. Reproduction takes place by a division of the cell 

 into two cells (Figure 310). In the amoeba any part of 

 the cell seems to be able to perform all its functions, such 

 as absorbing food and oxygen and excreting waste material 

 (Figure 311). Slightly higher forms of single-celled 

 animals have a mouth through which food is taken. 



If a small bunch of hay is placed in a glass jar nearly 

 filled with water and allowed to stand for a few days in a 

 warm room, certain changes will be noticed in the con- 

 tents of the jar. An unpleasant odor indicates that the 



FIG. 311. The Way an Amoeba Gets its Food. 



hay is decaying ; a bacterial scum appears on the surface 

 of the water ; a little later small one-celled animals 

 appear in this scum in such quantities that the surface 

 of the water seems literally alive with them. These 



