In an ameba which has been brought to a standstill, as by a sudden flash of light, the first sign of recurring streaming is in the anterior half, whether the original direction of streaming is resumed or reversed. If the direction is reversed, the active pseudopods retract for a considerable distance before a new one is projected. The endoplasmic stream in a slender withdrawing pseudopod may not reach to the tip for from several seconds to a minute, if the tip is slightly positively stimulated. One may then observe ectoplasm streaming toward the tip and toward the base, in the respective regions, at the same time, with considerable fluctuation back and forth of the neutral zone separating the two streams. The fate of such a pseudopod depends on its size, on its position on the ameba, and the strength of the stimulus affecting it and the rest of the ameba. That is, if the pseudopod is small or on the posterior half of the ameba, or only slightly stimulated, it will be retracted; but if it is large, or on the anterior end of the ameba, or more strongly stimulated than the rest of the ameba, it may again become active. The fact that protoplasm is practically incompressible makes it clear that if streaming can be observed to begin after a pause at some point after it begins at others, the ectoplasmic walls of the ameba must give way in the region where streaming begins. Since it has been established by observation that the ectoplasm may give way at any point, it follows that one of the principal factors affecting streaming is the elasticity and liquefiability of the ectoplasm. The streaming in an ameba is coordinated. The direction in which the endoplasm flows in the several pseudopods, when there are no stimuli received externally that produce visible changes in behavior, gives one the impression that there is a “centre” controlling movement. The several pseudopods do not act at all capriciously. The ameba seems to move the pseudopods, not the pseudopods the ameba. If this impression of coordination is correct, it is of the first importance in a study of ameboid movement. Further on, this point will be taken up at length in connection with the character of the path an externally unstimulated ameba describes (p. 109); but there are certain observations which aid in the analysis of the problem of coördination from the point of view of the pseudopod, instead of that of the ameba as a whole, and to these observations we may now direct our attention. The mass of endoplasm within a pseudopod moves practically always in one direction. In any cross-section of a pseudopod that is more or less cylindrical in shape, the endoplasm in the center moves most rapidly, that near to it less rapidly, while that near the ectoplasm moves very slowly. One never observes a forward stream on one side of the pseudopod and a backward stream on the other. Nor does one observe parallel streams of endoplasm flowing in opposite directions within the same