222 



PRACTICAL ZOOLOGY 



cium with those of the other animals we have studied, we find that 

 they are similar in nature but are carried out by a single cell. 

 Paramecium moves about, protects itself, captures food, 

 digests food, circulates the digested food, assimilates it, pro- 

 duces secretions, excretes waste products, takes in oxygen, 

 gives off carbon dioxide, responds to stimuli, and reproduces 

 itself. The activities mentioned are all fundamental properties 



FIG. 133. Ameba. 



1, nucleus ; 2, contractile vacuole ; 3, pseudopodia ; 4, food vacuoles ; 5 grains 

 of sand. (After Gruber.) 



of the living substance, protoplasm. In Paramecium they are 

 performed by a single cell without organs of any kind. In Hydra 

 they are performed by many cells, and division of labor has taken 

 place ; that is, some cells are set aside for the performance of one 

 function and others for other functions. 



Ameba. Ameba is a representative of another type of one- 

 celled animals. It is only about -^ inch in diameter, and is 

 therefore invisible to the naked eye. Under the compound 



