352 Animal Biology 



suspended foods) of various sizes and in \arious stages of food digestion 

 can usually be seen. Food vacuoles are formed at the posterior end of 

 the gullet. When filled, the food vacuole is pinched off by the cytoplasm 

 and it moves away in the flowing cytoplasm. Digestion occurs within 



Fig. 165. — The "avoiding reaction" of a Paramecium. A, Solid object a source 

 of stimulation; 1-6, successive positions occupied by the Paramecium in attempting 

 to avoid the object; rotation on its long axis also occurs but is not shown in the 

 diagram. (From Jennings: Behavior of the Lower Organisms, published by 

 Columbia University Press.) 





I I 



:•/.'.' -^-^'--^ ' - 



. I - / 

 ^ / 



I ■ 





• \ "■ 



B. 



Fig. 166. — Reaction of Paramecium to salt solution. A, Method of introducing 

 a drop of 0.5 per cent of NaCl solution; B, four minutes later. (From Jennings: 

 Behavior of the Lower Organisms, published by Columbia University Press.) 



