122 AMEBOID MOVEMENT 



Figure 42. Diagram illustrating the relation of the phenomenon of en- 

 circling to the wavy path of the ameba. The weakest point in the path, 

 i. e., where the wave may be broken most easily, is where one wave 

 merges into another, as indicated by the experiments with low tempera- 

 ture, a, b, c. The direction of movement of the ameba is the reverse of 

 what it would have been had there been no stimulus producing encircling. 

 The same stimulus at e, f, or g would not produce encircling because it is 

 more difficult for the ameba to move away from the concave side of the 

 wave. 



waves. (3) It must stimulate the ameba just strong enough 

 positively to break into the wave-forming process. Encircling 

 then is due to a "balance" between a positive stimulus and a ten- 

 dency to move in a curve. This explanation conforms with all 

 the data at hand and explains also the rarity of the phenomenon, 

 for the chances of encircling occurring on this view are rather 

 less than one-fifth as frequent as if encircling took place when- 

 ever a balance between a tendency to react positively and to move 

 straight ahead occurred. 



That the wavy path is broken up by the receipt of a stimulus, 

 that is, by a true sensation, rather than by direct effect of some 

 agency radiating from the particle, is indicated by the fact that 

 stimuli proceeding from various substances, such as keratin, glass, 

 carbon, light beams, etc., have all the same effect. 



In attempting to explain the characteristic nature of the path 

 of the ameba, one's attention centers first, perhaps, upon its 

 orderliness; a result undoubtedly of the general impression pro- 

 pagated through hastily written textbooks and general papers, 

 that an ameba's whole life is a direct response to its environment. 

 As the recorded facts of the life of this organism are accumulat- 

 ing, it is coming to be seen that the ameba possesses all the funda- 

 mental attributes of animals generally, in addition to many special 

 ones. So that as a matter of fact, if the ameba did not show 



