110 



PROTOZOOLOGY 



of a doad algal filament at the middle of its anterior surface (Fig. 

 46, a), the amoeboid movements proceeded on both sides of the 

 filament (b), but soon motion ceased on one side, while it contin- 

 ued on the other, and the organism avoided the obstacle by re- 

 versing a part of the current and flowing in another direction (c). 

 When an amoeba is stimulated mechanically by the tip of a glass 

 rod (d), it turns away from the side touched, by changing endo- 

 plasmic streaming and forming new pseudopodia (e). Positive re- 



FiG. 46. Reactions of amoebae to mechanical stimuli (Jennings), 

 a-c, an amoeba avoiding an obstacle; d, e, negative reaction to mechan- 

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



actions are also often noted, when a suspended amoeba (/) comes 

 in contact with a sohd surface with the tip of a pseudopodium, 

 the latter adheres to it by spreading out (g). Streaming of the 

 cytoplasm follows and it becomes a creeping form (h). Positive 

 reactions toward solid bodies account of course for the ingestion 

 of food particles. 



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 solid object, the response may be either negative 

 or positive. In the former case, avoiding movement (Fig. 47, c) 

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



