DISTINCTIVE CHARACTERS OF THE PROTOZOA 7 



seen to occur amongst them. Although their metabolism is in 

 general distinctly of a vegetative or saprophytic type, it often 

 exhibits peculiarities not found in any true plant.* 



In the second grade of the Protista, the organism possesses the 

 characteristics of a true cell, in that the body shows a differentia- 

 tion of the living substance into two quite distinct parts the 

 cytoplasm, or general body-protoplasm, in which is lodged at least 

 one nucleus, a body representing a concentration and organiza- 

 tion of the chromatin-substance. In some cases the nuclear sub- 

 stance or chroinatin niav be in the scattered, chromidial condition 



tj 





end-----, ^fa^ 



/////mi 



/ ,- : > f j f * 



FIG. 3. Actinosphcerium eichhornii. ect., Ectoplasm; end., endoplasm ; c.v. 1 , a 

 contractile vacuole at its full size ; c.v. 2 , a contractile vacuole which has just 

 burst ;f.v.,f.v., food vacuoles ; D., a large diatom engulfed in the protoplasm ; 

 ps., pseupopodia ; N., one of the numerous nuclei. After Leidy (226), magni- 

 fied 250 diameters. 



during certain phases of the life-history, but such a condition is 

 comparatively rare and probably always temporary. The body- 

 protoplasm may be limited by a firm envelope, or may, on the other 

 hand, be naked, in which case the body-form may be quite in- 

 definite. Organs of locomotion, when present, are of various kinds ; 

 and these organs may serve also for the capture and ingestion of 

 food. And, finally, the metabolism is always one of the four types 



* For a summary and review of different modes of metabolism among bacterial 

 organisms, see article " Fermentation " in Thorpe's " Dictionary of Applied 

 Chemistry " (Longmans). 



