AMEBOID MOVEMENT 55 



C 



Figure 20. Amoeba sphaeronucleosus. a, the under side of the ameba. 

 The part of the ameba attached to the substratum is stippled. Particles 

 attached to the surface film at x moved slowly forward. b t the 

 under side of the ameba, showing the attached parts stippled. The par- 

 ticles suspended in the water at x moved slowly forward with the ameba. 

 c, a cross section of an ameba of shape shown in b, showing the ridges on 

 the surface. Length of the ameba, about 100 microns. 



from that given by Jennings (1. c.) as we shall see further on. No 

 case of a similar rotation of larger particles which had sunk into 

 the ectoplasm, as described by Jennings ('04, p. 142), has come 

 under my observation. 



The movement of the surface layer in A. verrucosa is quite like 

 that of sphaeronucleosus. Figure 21 shows a group of three 

 .particles carried by a verrucosa while changing its direction of 

 locomotion. The particles changed position with regard to- each 

 other and they moved at different speeds. Particles a, b, c. 

 moved respectively 2.40, 3.26, 2.85 times as fast as the ameba 

 advanced. Other experiments indicate that the outer layer of 

 z'ernicosa moves at about the same speed, compared with the 

 speed of the ameba, as that of sphaeronucleosus. 



Amebas with so-called Umax-shaped bodies do not possess 

 surface layers that carry particles forward with the same Speed 

 as those amebas with broad bodies. It is only occasionally that 

 large amebas such as proteus are found in a limax or clavate 

 shape. One of the most favorable of the large amebas in this 

 respect is discoides. It is frequently found in clavate shape and 

 it possesses the further advantage in being nearly cylindrical in 



