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 with the movements of the superficial films of _Oscillatoria_ filaments, diatoms, crawling euglenas, and probably also Gregarinidas, indicates that the superficial films of all these organisms, including amebas, are all activated by surface tension changes. Thus instead of postulating several methods of locomotion which are fundamentally different from each other, for these respective organisms (excepting the ameba), one explanation serves the purpose; and it has the further merit of agreeing more nearly with observation than the various other theories proposed. From the point of view of ameboid movement, the discovery of the surface film and its activities narrows down the problem very considerably. It does not help _directly_ perhaps, in the solution of ameboid movement, but it shows clearly that the region where ectoplasm is most rapidly formed (at the anterior ends of pseudopods) is also the region where the superficial tension is increased. This therefore gives us somewhat of an insight into what must take place during the transformation of endoplasm into ectoplasm. Although the wavy path of the ameba does not at present relate itself to any other process in the ameba, it is bound to be of the greatest significance in investigating the intimate nature of protoplasm while in movement. In so far as the wavy path concerns the ameba, it effectively disproves the presence of that scientific monstrosity, random movement. The path of the ameba is orderly. The wavy path of the ameba represents a projection on a plane surface of a helical spiral. The path of the ameba is thus geometrically related to the spiral paths of free-swimming organisms such as ciliates, flagellates, rotifers, swarm spores, worm larvae, etc. But the paths are more closely related than merely geometrically. The effects produced by temperature on amebas and ciliates and flagellates indicate a relationship between the physical processes underlying the control of the direction of the paths traveled over in free movement. No causal distinction can yet be made between rotation on the long axis and the spiral swinging.