PHYSIOLOGY 



115 



In Paramecium, according to Jennings, the anterior end is more 

 sensitive than any other parts, and while swimming, if it comes in 

 contact with a soHd object, the response may be either negative or 

 positive. In the former case, avoiding movement (Fig. 49, c) follows 

 and in the latter case, the organism rests with its anterior end 

 or the whole side in direct contact with the object, in which position 

 it ingests food particles through the cytostome. 



Fig. 48. Reactions of amoebae to mechanical stimuli (Jennings), a-c, 

 an amoeba avoiding an obstacle; d, e, negative reaction to mechanical 

 stimulation; f-h, positive reaction of a floating amoeba. 



Reaction to gravity. The reaction to gravity varies among dif- 

 ferent Protozoa, according to body organization, locomotor organ- 

 ellae, etc. Amoebae, Testacea and others which are usually found 

 attached to the bottom of the container, react as a rule positively 

 toward gravity, while others manifest negative reaction as in the 

 case of Paramecium (Jensen; Jennings), which explains in part why 

 Paramecium in a culture jar are found just below the surface film in 

 mass, although the vertical movement of P. caudatum is undoubt- 

 edl.y influenced by various factors, as was pointed out by Dem- 

 bowski (1929). 



Reaction to current. Free-swimming Protozoa appear to move 

 or orientate themselves against the current of water. In the case of 

 Paramecium, Jennings observed the majority place themselves in 

 line with the current, with anterior end upstream. The mycetozoan 

 is said to exhibit also a well-marked positive reaction. 



