AMEBOID MOVEMENT 79 



The stationary properties of the ectoplasm are however not 

 properly a matter for discussion ; for five minutes' observation of 

 a proteus, discoidcs, annulata, particularly a laureata, under 300 

 diameters magnification, will convince anyone that the ectoplasm 

 is stationary while the. surf ace film, with attached particles, moves 

 over it. No one can possibly come to any other conclusion. Jen- 

 nings' conclusion was due undoubtedly to an error of observation. 



Jennings' statement that the rate of movement of the outer 

 surface is the same as that of the endoplasm (p. 142) when taken 

 in connection with his other statement that the ectoplasm is a 

 more or less permanent skin, presents a mechanical impossibility ; 

 for unless the outer surface moves twice* as fast as the endoplasm, 

 no rolling movement would be possible. Several of Jennings' 

 figures (especially Figures 38, 39, and 41) indicate in fact that he 

 conceived of the outer surface as moving faster than the ameba 

 advances, or that the upper surface moves over the ameba as the 

 ameba moves over the substrate. Jennings' theory requires that 

 the surface layer move twice as fast as the ameba advances. 

 Hyman ('17) also makes a similar mistake in referring to the 

 rate of movement of the outer surface (p. 85). 



Lest the discussion of this point be suspected of being merely 

 verbalistic, it should be recalled that the surface layer of proteus 

 often moves at about the same rate as the ameba ; that the surface 

 layer of discoides moves about twice as fast as the ameba; that 

 the surface layer of verrucosa and sphaeronucleosus moves about 

 three times as fast as the ameba ; and that the ectoplasm does not 

 move at all. It is of course incumbent on one to discuss what is 

 stated ; one is not at liberty to select one of several possible inter- 

 pretations. 



To illustrate this point graphically so as to avoid as far as 

 possible future confusion Figure 29 is appended. In a is shown a 

 particle traveling on an ameba at the same rate of speed as the 

 ameba; at b is shown a particle that moves twice as fast as the 

 ameba; at c the attached heavy particle does not move at all. 

 For the sake of completeness d, Figure 29, is added here. If 

 illustrates the backward moving ectoplasm in .an ameba that is 

 suspended in a jelly medium that prevents the ameba from sink- 

 ing to the bottom. It must be admitted that in thus considering 



