350 Animal Biology 



beat rhythmically and backward, thus propelling the animal forward. 

 The rhythmic strokes are diagonal; hence, the body is rotated on its long 

 axis. The greater rate of action of cilia in the oral groove tends to swerve 

 the Paramecium to the left. All these actions locomote the animal in a 

 spiral path, usually to the left. 



^Anterior 



Contmctilc-- 

 \/acuo\Q 



-C\\\a 



-PeJIJcle 



-Trichocyifc 



Macror)uc]eus 

 MicroriadiQi _. 



Tlad\at\r)q 



canals ^ 



Conbractile __ 

 vacuole 



^: . :. ',o ■^- ■'.[«:->i%3M- jiv- ^ 



• • .■ •■'.■'o - ."^l* '^'V. /.'•q •.-• 



*:o::.<!i^5-^:..-#;.;'.;;;'6:?.q fi 

 ■».'.-.-P. V xZxo • •. vo • -i^' j*. ; : o 



Oralcjroove 



Moabh 



„__gall<2fc 



^-.- Food vacuole 



£^ Anas 



Posterior 



Fig. 163. — Paramecium aurelia, a protozoan of the class Infusoria. 



Ingestion and Digestion. — A funnel-shaped oral groove extends from 

 the anterior end backward and obliquely toward the middle of the ani- 

 mal. The cell mouth or cytostome (si' to stom) (Gr. kystis, hollow; 

 stoma, mouth) is at the posterior end of the oral groove and opens into a 



