54 AMEBOID MOVEMENT 



Figure 19. Illustrating the rapid movement of the upper surface of an 

 Amoeba sphaeronucleosus under the most favorable conditions. The par- 

 ticle moved 3.56 times as fast as the ameba. Length of the ameba, 130 

 microns. 



The movement of particles on the under side of an Amoeba 

 sphavronucleosiis depends upon what part of the ameba is attached 

 to the substratum. Where the ameba is attached there is of 

 course no movement of the surface layer and the particles remain 

 stationary. In an ameba attached as shown in figure 20, a, there 

 was a very slow movement of particles forward near the middle 

 of the attached region (x), but whether this was related to the 

 movement of the outer layer of the upper surface was not de- 

 termined. The movement of these particles was considerably 

 slower than the movement of the ameba. In another ameba at- 

 tached at the anterior and posterior ends (Figure 20, b) no 

 movement of particles on the under side could be discerned. The 

 small particles showing Brownian movement, with the surround- 

 ing water, are dragged along as a mass. This movement is purely 

 mechanical, and is what would be expected on purely physical 

 grounds, when a more or less cup-shaped object is moved along 

 in water in close contact with a flat surface. Such particles as 

 have become attached to the surface layer on the under side of the 

 ameba, because of their slower movement than that of the 

 ameba, eventually bring up at the sides near the posterior end, as 

 the ameba moves along. From here they are carried forward in 

 the manner already described. Thus there comes about a "rota- 

 tion" of particles adhering to an ameba as described by Jennings 

 ('04) and Bellinger ('06), though the explanation is different 



