AMEBOID MOVEMENT 45 



highly characteristic nature of the pseudopods formed by the 

 amebas of any species, it is seen, is to be referred to the funda- 

 mental structure of the protoplasm, probably its stereochemical 

 structure. And what is of especial importance for this discussion, 

 the character of streaming concerned with pseudopod formation 

 and with movement in general, which is specific for each species, 

 is likewise found, to some extent at least, to be conditioned by 

 the specific structure of the protoplasm. 



That the specific character of the pseudopods, and the stream- 

 ing which of course lies back of it, is not wholly or perhaps 

 even largely, due to the specific structure of the protoplasm, is 

 evident from a consideration of streaming in some other organ- 

 isms, without a study of which, streaming in amebas can be only 

 imperfectly understood. 



The formation of pseudopods is not necessary to streaming. 

 Occasionally one sees internal currents unaccompanied by move- 

 ment or ectoplasm formation in amebas approximating spherical 

 shape, such as in Amoeba blattae (Rhumbler, '98) and rarely also 

 in protons or dubia. But especially well is such streaming seen 

 in a contracted Biomyxa, a naked foraminifer, and in numerous 

 plant cells. In paramecium and other ciliates the continuous cir- 

 culation of the endoplasm, a true streaming process, is an in- 

 voluntary act. But in Frontonia, another large ciliate, the cir- 

 culation of the endoplasm is under the control of the animal, that 

 is to say, voluntary, and is set in motion only when feeding, the 

 direction of streaming being away from the mouth so as to drag 

 in the food (see Figure 32, p. 99). If the food particle is a 

 long filament of Oscillatoria, for example, the endoplasm circu- 

 lates very much as it does in paramecium, only more rapidly, 

 until the whole filament is wound up into a coil. Then streaming 

 stops. In the second place streaming is not necessarily accom- 

 panied by the formation of ectoplasm as observed in ameba. In 

 plant cells the ectoplasm is practically stationary, while the endo- 

 plasm is in continual flux. The transformation of endoplasm 

 into ectoplasm and vice versa is therefore not an essential feature 

 of streaming, though it is of locomotion ; that is, ectoplasm is 

 always found between endoplasm and water, though it might be 

 possible under certain conditions for endoplasm to come into con- 



