[Illustration: Figure 1. Illustrating the various directions of endoplasmic streaming in growing and retracting pseudopods. _a_, two oppositely directed streams in a pseudopod, one directed toward the base and the other toward the tip of the pseudopod, with a neutral zone between. _b_, two streams flowing toward each other. Cases _c_ to _r_ are self explanatory. _s_, rotational currents observed occasionally in various species of amebas. _t_, “fountain currents,” sometimes observed in _Amoeba blattae_, and rarely in other forms. _u_ and _v_ represent cases of streaming which have not been observed and which probably do not occur. _w_, similar to _v_, but with a wide neutral zone between the streams, represents an actual observed case. _m_ and _r_ probably occur only very rarely; no such cases have been seen, but there seems to be no reason why they do not sometimes occur. Excepting _m_, _u_, _r_ and _v_, all these figures were drawn from observed cases of streaming.] ectoplasmic tube, in an ameba of several pseudopods, excepting where there is a wide zone of stationary endoplasm between the streams (Figure 1, _v_, _w_). But in “fountain currents,” such as Rhumbler (’98, p. 190) described and figured for _Amoeba blattae_ Bütschli, and which may readily be observed in most species of amebas if immersed in a solution of gelatin thick enough to keep the amebas from sinking, there is a central stream of endoplasm flowing forward, and a peripheral stream of ectoplasm flowing backward, with a thin neutral zone between (Figure 29, _d_). As we shall see further on, however, these fountain currents are in principle the same as the currents observed in ordinary locomotion, the apparent difference being due to the fact that there is no locomotion. It is true, then, that within the same pseudopod at any cross section the endoplasm always streams in one direction, and the streaming is unified. When new pseudopods are formed, or when old ones are retracted, and especially when both these phenomena occur at the same time and close together on a part of an older pseudopod, some of the details of coordination in streaming are readily made out. In Figure 1 are shown a number of observed cases of pseudopod formation and retraction, with the direction of endoplasmic streams indicated at a given instant. For the purpose of illustration, several (presumably) possible but unobserved cases, _m_ and _r_, are sketched, and also two cases, _u_ and _v_, which have not been observed and which probably do not occur. The general conclusion to be drawn from these observations is that, while the endoplasm in the body of an ameba as a whole may be streaming in several different directions at any given instant, that is almost never the case with an individual pseudopod, especially if the pseudopod is of small or medium size and not too flat or otherwise irregular in shape. The pseudopod is therefore the unit of coordinated protoplasmic streaming.