EUGLENA, AMOEBA, AND PARAMECIUM 295 



the gullet are fused together into a sheet, forming the undulating 

 membrane. 



The cell is divided into the outer, tough, nongranular ectosarc 

 which is composed of ectoplasm. The outer surface of it is a thin, 

 elastic cuticle or pellicle which is marked in hexagonal areas by the 

 distribution of the cilia. The cilia are direct outgrowths of the ecto- 

 sarc. There are a great many spindle-shaped cavities located in the 

 ectosarc with their long axes perpendicular to the surface. These 

 structures, trichocysts, are filled mth a semifluid substance and each 

 opens to the outside through the pellicle. The endosarc, composed 

 of 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 cyclosis. 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 outline of 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). 



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 

 quiet. The food is swept through the oral groove by the beating 

 action of the cilia, and carried back through the mouth into the 

 gullet. Finally it passes by means of the action of the undulating 

 membrane into the endoplasm in the form of one food vacuole after 

 another. These food vacuoles move in a definite course through the 

 endoplasm. Since this course is in the form of a cycle, the circula- 

 tion is known as cyclosis. 



