AMEBOID MOVEMENT 119 



Figure 39. The path of an Amoeba dubia in comparatively low tem- 

 perature (18 C). The large number of loops and deep waves in the 

 path are due to the low temperature. The experiment was performed 

 under light controlled conditions. Length of the ameba, 350 microns. 



become transformed into circles. As the temperature decreases, 

 the crests of the waves rise higher and higher, and the bases con- 

 tract more and more, until the two sides of the waves come to- 

 gether, resulting in the formation of circles (Figure 40). The 

 actual size of the wave also decreases at the same time from 

 about eight times the length until it is only two or three times the 

 length of the ameba. Temperature affects therefore the wave 

 mechanism independently of the mere viscosity of the endoplasm. 

 The speed of movement is not merely slowed down, but the 

 character of the waves themselves is changed. 



Amebas sometimes react to stimuli by moving around the source 

 of the stimulus at a more or less uniform distance through one or 

 more quadrants of a circle, instead of reacting positively, nega- 

 tively, or indifferently, in a definite manner, to the source of the 

 stimulus (Schaeffer '16, '17). See Figure 41. The explanation 

 that has been given by this investigator is that the encircling is 

 due to a balance between the tendency to move ahead in the 

 original direction ("Functional inertia") and a tendency to react 

 positively. But now that we know that amebas tend to form 



