62 AMEBOID MOVEMENT 



while streaming in the original pseudopod was arrested. At stage 

 3 particles a and b retained the same position they had in stage 2, 

 except for a slight turning to the right. Particle c however 

 moved across the base of the original pseudopod and on to the 

 middle of the new pseudopod. At stage 4 a and b had again only 

 slightly moved to the right of the position they occupied in stages 

 2 and 3, while c moved rapidly toward the tip of the new pseudo- 

 pod. The new pseudopod was then retracted and at stage 5 the 

 particles had begun to move back toward the main body of the 

 ameba. Particles a and b now gained considerably on c because 

 they were located further away from the tip of the retracting 

 pseudopod. Particles a and b were drawn to the middle of the 

 retracting pseudopod because of the continuous enlargement of 

 the large pseudopod on the right, below, through which the 

 ameba moved on. 



The most important feature of this observation is the change 

 in the position of the particle c with respect to that of a and b. 

 The latter particles retained their relative positions with very 

 slight, if any, change, while c swung around a and b nearly 180, 

 and at the same time changed the distance very greatly between 

 itself and the other particles. Moreover, b, at stage 5 led the 

 procession of particles, while at stage i, a led. No further demon- 

 stration is necessary to show that the surface layer is distinctly 

 fluid and dynamic, and not at all such a static structure as an 

 elastic permanent skin, as Jennings ('04) and Rhumbler ('14) 

 maintained. 



