CHAPTER III 



THE GENERAL FEATURES OF ENDOPLASMIC 

 STREAMING 



The streaming of the endoplasm is the most conspicuous feature 

 of ameboid movement. It is even more noticeable than the move- 

 ment of the pseudopods themselves, because of its greater speed 

 and because it occurs in all parts of the ameba. Its importance 

 in movement is essential, for no continued locomotion can be ob- 

 served unless accompanied by streaming. It may be profitable 

 therefore to enquire into the general features of streaming, and to 

 observe some of the necessary consequences streaming imposes 

 upon such an animal as the ameba. 



Let us take as an example an Amoeba proteus (Pallas, '66, 

 emend. Leidy, '79, emend. Schaeffer, '16) in characteristic move- 

 ment (see Figure n, p. 37). The main streams of endoplasm 

 are in the same direction as that in which the ameba moves. In 

 the withdrawing pseudopods the current is, of course, toward the 

 main mass of the ameba. The endoplasmic stream is continuous 

 from the posterior end to the tips of the advancing pseudopods. 

 The retracting pseudopods flow into the main stream as tribu- 

 taries. If, as often happens, the ameba is without pseudopods, 

 there is then a single stream arising in the posterior end and 

 flowing to the anterior end. In such a case it is readily observed 

 how absolutely dependent locomotion is upon endoplasmic 

 streaming. 



It often happens, such as when the ameba is receiving a strong 

 stimulus, that streaming is arrested and brought to a stop for a 

 few seconds, more or less. Presently however the endoplasm 

 begins to flow as before. At what point, in such a case, is the 

 first movement of endoplasm detectible? Is it at the free end of 

 the pseudopod, at its middle region, at its base, or at the posterior 

 end of the ameba? Biitschli ('80, p. 116) observed that in a 

 withdrawing pseudopod the streaming begins at the free end of 

 the pseudopod; but his ('92, p. 201) later explanation of ameboid 



8 



