AMEBOID MOVEMENT 67 



the general results of the observations are as stated. It might be 

 added that in some cases the neutral zone for the particles at- 

 tached to the surface did not coincide exactly with the neutral 

 zone of the endoplasm, but was located a little further distally. 



From these observations it appears that a rough index of the 

 direction of movement of the surface film is the direction of the 

 streaming of the endoplasm; and that the surface layer moves 

 away from regions where ectoplasm is in the process of being 

 converted into endoplasm. Since a particle attached to the surface 

 may remain for some time at the tip of a retracting pseudopod, 

 while one that is attached to the sides of a pseudopod moves 

 toward its base, it appears that the speed of the moving surface 

 film is not directly correlated to the rate of transformation of 

 ectoplasm into endoplasm. The slower speed of particles near 

 the posterior end points also in this direction. The formation 

 of ectoplasm at the anterior end seems therefore to be much 

 more intimately connected with the movement of the surface 

 film than the destruction of the ectoplasm, though it is not yet 

 clear that the liquefaction of the ectoplasm is altogether without 

 effect. 



Now as to the speed with which the surface film moves. The 

 foregoing illustrations and figures show that the particles attached 

 to a sphaeronucleosus on the upper surface move from 2.5 to -3.6 

 times as fast as the ameba (Figure 19) while particles attached 

 to a discoides move only from 1.2 to 2 times as fast as the ameba 

 moves. In proteus the speed of the particles is still slower, be- 

 cause of the longitudinal ridge-like waves of protoplasm which 

 are continually being thrown out. In this species it frequently 

 happens that because of the numerous ridges, the ameba moves 

 faster than the particles attached to the outer surface; but this 

 is to be looked upon as a mechanical complication, not as indicat- 

 ing a difference in the nature of the surface layer. 



How is the difference in the speed of movement of the surface 

 layer between sphaeronucleosus and discoides to be explained? 

 There are no ridges to retard the movement of particles in 

 discoides, while there are ridges in sphaeronucleosus, where the 

 particles move on the average twice as fast as on discoides. In 

 the first place the advancing edge, the edge where ectoplasm is 



