CHAPTER XIV 

 CONCLUSIONS 



One of the most important results of recent work on the move- 

 ments of ameba and of streaming endoplasm in plant cells is the 

 rapidly growing conviction that the streaming of protoplasm, 

 wherever it is found, is due to the same fundamental cause. The 

 value of this conception lies in the greatly widened front that 

 is presented for attacking the general problem of streaming. The 

 many special aspects of streaming, which in the past have been 

 thought to be essential or fundamental processes, may thus be 

 placed against each other, following what is known as the com- 

 parative method, and the main problem will thus be freed of 

 much that is not strictly relevant. In this way we come at once 

 to the heart of the problem. 



One of these special aspects of streaming in amebas is the 

 formation of ectoplasm. For ectoplasm formation is not essential 

 to streaming. But it is almost certainly essential to locomotion, 

 for locomotion- has not been observed in amebas where ectoplasm 

 was not formed. But, on the other hand, ectoplasm, as known in 

 the amebas, is not formed without streaming, although observa- 

 tions indicate that ectoplasm may suddenly and temporarily pass 

 into the gel state ( Vallisneria) . Streaming is therefore the funda- 

 mental process in ameboid locomotion. 



The surface layer of the ameba is physiologically distinct from 

 the ectoplasm, although it differs from ectoplasm chiefly, if not 

 wholly, by virtue of its position only. That is, the surface layer 

 is a true surface tension film. There are no observations recorded 

 which actually show that the surface film of the ameba is a semi- 

 permeable or plasma membrane ; but, on the other hand, there 

 are no observations which speak against such a supposition. On 

 theoretical grounds the conclusion is justifiable that the surface 

 film as demonstrated by the movements of attached particles is 

 the plasma membrane. 



The similarity of the movements of the surface film in ameba 



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