72 



THE BEHAVIOR OF PROTOZOA 



By the action of its cilia Paramcecium swims through the 

 water in a spiral course, rotating on its long axis to the left 

 and keeping the oral side facing the center of the spiral. 

 At times Paramoecium may swim backward, by reversing 

 the effective stroke of the cilia, although the direction of 

 rotation is unchanged. 



Paramoecium is a common organism in vegetable infu- 

 sions, where it subsists upon bac- 

 teria which are swept by cilia into 

 its gullet. There seems to be little 

 power of choice as to what sub- 

 stances are taken in; particles of 

 India ink and carmine are swept in 

 and swallowed in the same way as 

 its normal food, and the organism 

 selects its food only by swimming 

 elsewhere when the materials swept 

 in are unsuitable. Metalnikow, 

 however, states that when Par- 

 amoecia are fed with carmine for 

 fifteen days they gradually take 

 in less of this substance and finally 

 refuse it. Metalnikow's experiments 

 were repeated by Schaeffer who 

 failed to confirm these results when 



FIG. 8. Paramoecium cau- the carmine was kept in a condi- 

 datum. (After Kellogg.) . . , ,, , ., ., , r , 



tion such that it could be readily 



ingested. Occasional individuals, however, failed to take 

 in any of the substance, but examination showed that they 

 were deformed or had recently divided so that the oral ap- 

 paratus was not capable of sweeping in food. After thirty- 

 three days the Paramcecia failed to show any appreciable 

 diminution in the carmine ingested. 



