CHAPTER X 

 STREAMING, CONTRACTILITY AND AMEBOID MOVEMENT 



The nearest relatives of the amebas are the shelled rhizopods, 

 the Difflugias and the Arcellas and their congeners. The move- 

 ment of these organisms is quite different from that of the 

 amebas in that the whole body of the endoplasm does not stream 

 into the pseudopods, but only a small portion of it. There is 

 consequently no regular transformation of ectoplasm into endo- 

 plasm at the posterior end, that is, the protoplasmic mass within 

 the shell. The method of movement in Difflugia was described 

 by Bellinger ('06). A pseudopod is thrown out to a considerable 

 distance. It fastens itself to the substrate at the tip. It then 

 contracts, pulling the Difflugia forwards. While this pseudopod is 

 contracting, another one is extended in the same direction. When 

 it has arrived at the maximum length, it fastens itself at the tip 

 and then contracts, pulling the Difflugia along. Continued loco- 

 motion consists of a repetition of this process. The pseudopods 

 are slender and consist nearly always of clear protoplasm. Only 

 occasionally does one see conspicuous endoplasmic granules flow 

 into a pseudopod, and then only at the base. 



The transparency of the pseudopods in Difflugia and the ab- 

 sence of granules in the protoplasm composing them, prevents 

 one from seeing clearly how the pseudopods are formed, that is, 

 whether or not there is a regular transformation of endoplasm 

 into ectoplasm at the anterior end. The fact that one occasion- 

 ally sees the endoplasm stream into the base of a pseudopod in 

 the same way as was described for ameban pseudopods, indicates 

 that the method of formation of pseudopods in Difflugia is in 

 general similar to that in ameba. But the process is not exactly 

 the same, for the surface layer on the pseudopods of Difflugia 

 does not move as fast as the tips of the pseudopods advance, while 

 in amebas the surface layer moves faster than the pseudopods. 

 What this difference indicates has not yet been ascertained. 



The protoplasm of the pseudopods of Difflugia is thick and 



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