AMEBOID MOVEMENT 91 



would be rotational and irregular and no progression could take 

 place. The ectoplasm furnishes just that stiff tube against which 

 the backward action of the endoplasm can impinge so to speak 

 in order to enable it to flow forward. The ectoplasm is essential 

 for orderly movement forward, but it is not essential for 

 streaming. 



But this does not imply that the contractile power of the ecto- 

 plasm may not be used to aid in propelling the endoplasm in 

 streaming. It has been demonstrated by Miss Hyman ('17) that 

 the ectoplasm is actually contractile when the ameba is strongly 

 stimulated all over its exterior by a solution of potassium cyanide. 

 While this proves only the contractile powers of the ectoplasm 

 under exceptional conditions, and when at rest, it is not impossible 

 that under ordinary conditions of locomotion it may aid in stream- 

 ing. There is however one observation which may, upon further 

 investigation, negative this possibility. Frequently in a pseudo- 

 pod about to be retracted some of the endoplasm flows toward 

 the tip while the rest flows toward the base (Figure I, p. n). 



One more point needs mention in this connection, and that is 

 the small waves of clear protoplasm which are thrown out by 

 many amebas at their anterior ends during locomotion. They 

 are especially prominent in A. bigemma (Figure 7) and in radiosa 

 (Figure 8), but they are formed in perhaps all species. Observa- 

 tion does not indicate that they move in exactly the same way as 

 the main body of the endoplasm, even if the larger granules 

 could be left out of account. They behave more like the clear 

 pseudopods of Difflugia and Arcella and the foraminifera. 



Although these waves are frequently not to be seen during 

 locomotion in Amoeba proteus and other large amebas, particu- 

 larly in Pelomyxa palustris and P. belevskii, it is possible that 

 the wave forming process has become indistinguishably merged 

 with endoplasmic streaming. It is not impossible that the pro- 

 jection of these waves is the purest expression of ameboid move- 

 ment. But on account of their small size and transparency, it 

 is very much more difficult to investigate them than streaming 

 of the granular endoplasm, as it is observed in amebas, ciliates 

 and plant cells. It seems to be true however that streaming can 

 occur in the entire absence of these waves, so their importance 

 in ameboid movement is probably secondary. 



