MORPHOLOGY AND PHYSIOLOGY 



35 



in distinguishing between animals and plants. The Protozoa 

 nourish themselves by various methods as follows: 



1. Holozoic (zootrophic, heterotrophic) nutrition. This is 

 the animal-like nutrition. The organism obtains nourishment by 

 taking in other animals or plants and digesting them as does a 

 typical metazoan. 



2. Holophytic (autotrophic, phytotrophic) nutrition. The 

 Protozoa possessing chlorophyll or allied substances are capable 

 of obtaining necessary nourishment by using water, carbon 

 dioxide and other inorganic substances. This nutrition is truly 

 plant-like and is common among the Phytomastigina. In a 



Fig. 14 Outline sketches showing the defecation process in Spirostomum 

 ambiguum. (After Blattner). 



number of cases, the organism itself is without chromatophores, 

 but is apparently not holozoic because of the presence of chloro- 

 phyll-bearing foreign organisms. For example, in Paulinella 

 (Fig. 96) in which occur no food particles, chromatophores of 

 peculiar shape are always present. They appear to be a species 

 of Alga which holds a symbiotic relationship with this testacean. 

 Perhaps they act as the true chromatophores of Euglenidae. 



3. Saprozoic (saprophytic) nutrition. Certain Protozoa are 

 able to derive materials necessary for building up their body 

 from dissolved organic substances in water. The actual ac- 

 quisition is done by osmosis through the body surface. 



4. Parasitic nutrition. Many Protozoa living in other ani- 

 mals absorb by osmosis the body fluid, digested food material or 

 cell-substances of the host. This is somewhat similar to the 

 saprozoic nutrition, but substances used here are those which 

 have been produced in the host body. Other parasites, for exam- 



