82 



TEXTBOOK OF ZOOLOGY 



to be digested in a vacuole within the endoplasm; this has been 

 called holozoic nutrition as typical of animals. E. viridis probably 

 does not possess this possibility. Others, like E. gracilis, are able to 

 assimilate dissolved nutriment by absorption through the general cell 

 surface (saprophytic nutrition). In fact, this species has been main- 

 tained for more than two years in a nutrient solution in darkness. 



-Fhgellum 



:0'». 



'Mouth 



-Stigma 



Contractile 

 Vacuole 



'§■ 



■)■■<■. 



■©. 



1^5 





^^ 



A\^ 



^Reservoir 



■ Ctirom at opt) ore 



-Nucleus 



Fig. 32. — Euglena viridis Ehrenberg. A chlorophyll-bearing flagellate. 



Those forms like E. viridis that are abundantly endowed with chloro- 

 phyll obtain their food largely by photosynthesis as does the green 

 plant. This process utilizes water, carbon dioxide, dissolved mineral 

 salts, and with the aid of light and chlorophyll builds up organic food 

 substances. The final stage of the carbohydrates formed by this 



