THE FLOWERLESS PLANTS. 



45 



as we have seen, capable of moving independently. 

 Plants excrete water, carbon dioxide, and oxygen, but 

 have no special organ of excretion. 



Animals are characterized by the entire lack of cellu- 

 lose in their cell walls. Their nutrition is by the diges- 

 tion of somewhat complicated organic substances that are 

 taken into the animal through a mouth, which may be 

 only temporary, but is usually permanent. The waste 

 matters are removed from the organism through definite 

 organs of excretion, which also may be temporary, but are 

 usually permanent. Independent locomotion also charac- 

 terizes animals, though some live permanently attached to 

 fixed supports. 



The Protista. 



There are certain organisms in which these character- 

 istics that distinguish plants from animals are so com- 

 bined that the highest authorities do not undertake to 

 say whether the organism is a plant or an animal. To 

 these organisms the name Protista has been given. 

 To obtain an example of these organisms, allow water 

 weeds to go to decay in a vessel of water. Examine 

 some of the water from time to time under high power 

 until organisms resembling Fig. 22, e, are obtained. This 





FIG. 22. Euglena viridis. e, the normal form ; a, b, c, d, forms going through 

 the Euglenoid movements. The clear circular space seen in each figure is 

 a contractile vacuole; the dark spot between the contractile vacuole and 

 the anterior end is the eye spot. (X 480.) 



