PARAMECIUM OF CLASS INFUSORIA 



95 



endoplasm, is within. It contains food vacuoles, two contractile 

 vacuoles, macronucleus, and other granular masses. The numerous 

 food vacuoles are formed, one at a time, at the inner end of the gullet 

 by a mass of food material coming in with a droplet of water, a 

 process similar to that described in Amoeba. The vacuoles circulate 

 through the endoplasm in a rather definite course. This activity is 

 called cydosis. The contractile vacuoles are located near each end 

 of the animal. Each vacuole has several radiating canals entering it. 

 These vacuoles expand and contract alternately. The macronucleus 

 is located slightly posterior to the center and somewhat beside the 

 mouth. It is relatively large and rather bean-shaped. The micro- 

 nucleus is located in the curved surface of the macronucleus and is 

 much smaller. P. aurelia, another species, ordinarily has two micro- 

 nuclei instead of one. 



Metabolism 



The same general activities as described in Amoeba and others 

 occur, differing only in certain details. These same vital functions 

 must take place in all living things (organisms). 



Oral qroove 



J^l^ Nucleus 



^ Mouth 



% — Gullet 



if 



M Anus 



-Food vacuole 



Fig. 39. — Cydosis in Paramecium, showing the course of the food vacuoles through 

 the endoplasm while digestion is in progress. 



Food. — Smaller protozoans, bacteria, and particles of debris con- 

 stitute the principal items on the menu for Paramecia. 



Ingestion. — This animal hunts its food, and when it locates a re- 

 gion where food is abundant, it settles down and becomes relatively 



