Evidence contributing to this conclusion is found in the circumstance that crawling euglenas, diatoms and Oscillatoria threads are much more refractory to galvanic currents than flagellate euglenas or other flagellates or ciliates: The electrical apparatus at my disposal was rather crude, but I was unable to find that I could influence the direction or character of movement of Oscillatoria filaments, diatoms or crawling euglenas without injuring the organisms. Currents which had produced a marked effect on ciliates or flagellates produced no effect whatever on amebas, diatoms, Oscillatoria or crawling euglenas. Diatoms are particularly resistant to the effect of electrical currents. The general conclusion regarding the source of energy of the moving surface films, whether found on amebas, diatoms, desmids, or crawling euglenas, is that all derive their motive power from the energy in the superficial films of these organisms; while ameboid streaming, if it is a surface tension phenomenon as seems to be the case, depends upon the surface energy of the interfaces of the emulsoid colloidal system in the endoplasm. It has already been seen that those cases of locomotion due in large measure to the power of contractility in the ectoplasm (Difflugia, Foraminifera) are also explained as being due to a change of phase in the colloidal system, which is in itself a surface tension effect. It appears therefore that all the lower organisms that move, excepting flagellated or ciliated organisms (of whose motor mechanism we have no detailed knowledge), depend upon surface energy as the source of the energy of movement. CHAPTER XII THE WAVY PATH OF THE AMEBA In the preceding chapters we discussed the various factors which characterize ameboid movement: the streaming of the endoplasm, the formation of ectoplasm, and the behavior of the surface film. The discussion has involved only momentary cross-sections of the life of an ameba, following the method of investigation in general use for the solving of problems connected with ameboid movement. It has been tacitly assumed that if one could explain ameboid movement at any particular cross-section in time, one understood the whole process of ameboid movement no matter how long it continued, excepting, of course, the action of various kinds of stimuli that produced changes in direction, speed, etc., of streaming. It was not assumed that time was an element in the practical sense in the explanation of locomotion. A few seconds’ or a few minutes’ comprehensive observation was supposed to furnish sufficient basis for an explanation.