168 ANIMAL BIOLOGY 



the animal usually moves with the blunt end (i.e. heel of the 

 slipper) in front, the Paramecium being propelled by the 

 strong backward strokes of the cilia and a slower recovery. 

 When it runs into an obstacle, the cilia are reversed in action 

 and thus the animal is enabled to move with the opposite end 

 (toe of slipper) in front. Most animals that swim {e.g. fishes 

 and frogs) have broad and flat appendages which are com- 

 paratively large. In Paramecium, on the other hand, the 

 organs of locomotion (cilia), while slender, are so numerous 

 that they perhaps accomplish the same results as the broad 

 swimming appendages of the frogs and fishes. 



121. Food, food getting, and digestion. — Paramecia feed 

 upon one-celled plants and animals. On one side of a Para- 

 mecium is a furrow or groove, which is lined with cilia. At the 

 lower end of the groove is an opening, the mouth, which leads 

 into a short, tubular gullet. The rapid motion of the cilia 

 in the groove draws the food toward the mouth opening and 

 other cilia lining the gullet push down the food particles. 

 Small collections of these food particles are made at the lower 

 end of the gullet, and these masses, food balls, are circulated 

 within the cell by the streaming movement of the proto- 

 plasm. Although the Paramecium is a single cell, it has cer- 

 tain parts specially developed for securing food, just as the 

 higher animals have special organs for this function. 



As the food balls circulate through the protoplasm, they 

 are gradually digested, and the food materials thus Uquefied 

 are used as in plants and other animals for the production 

 of more protoplasm or for the release of the energy needed 

 for locomotion and for food getting. The indigestible parts 

 of food are forced out through the side of the body. 



122. Respiration and the liberation of energy. — ^ The 

 Paramecium is surrounded by water that contains oxygen 



