AMEBOID MOVEMENT 53 



two rapidly growing regions on the anterior edge, leading in dif- 

 ferent directions, that particle is attracted to the edge less rapidly 

 than a particle lying immediately back of either advancing region. 

 As may readily be observed each change in speed or direction 

 of movement of the particle b finds its explanation in the amount 

 and location of ectoplasm formation at the time. Large particles 

 like a do not so readily reflect changes in the direction of pull 

 of the surface layer. 



The rapid rate of movement of particle a 3.5 times as fast 

 as the ameba finds its explanation in an actively advancing an- 

 terior edge that was unusually wide. Particle b moved at a 

 slower rate, 2.7 to i. It started from near the posterior edge 

 where it moved comparatively slowly for a short distance. 



Figure 18 shows more pronounced changes in the direction 

 taken by a particle attached to the back of an ameba. The 

 change in direction at stage 6 was caused by a wave of ectoplasm 

 thrown out at the left side, and cessation of movement at the 



Figure 18. Illustrating the effect on the path of a particle attached to 

 the surface film of an Amoeba sphaeronucleosus when the ameba changes 

 its direction of movement. From stages 3 to 5 the ameba veered to the 

 right, also the particle. From stages 6 to 9 the ameba turned sharply to 

 the left, and this change of direction was reflected in the movement of 

 the particle. Length of the ameba, about 120 microns. 



anterior edge. At 7 a small wave was thrown out at the anterior 

 edge and a large wave on the left. At stages 8 and 9 the direc- 

 tion of the particle was again a response to the waves of ecto- 

 plasm thrown out at the left anterior edge, which thus became the 

 anterior end. 



