The orderliness of the paths of these organisms when moving under such conditions as described above, is itself orderly; that is, the path of all these organisms is a spiral of one kind or another: (1) a helical spiral, as in the free-swimming unicellulars; (2) a true spiral in one plane, as in man; (3) a helical spiral projected on a plane surface, as in ameba. These facts point inevitably to the hypothesis that the movements of these and all other moving organisms are controlled by an automatic regulating mechanism, which is of essentially similar nature in all organisms, as is indicated by the tendency to spiralize the path. This mechanism, being automatic, absolutely controls the direction of the path so long as outside interferences permit; but when sensory stimulation occurs, or when changes in temperature, etc. occur, the mechanism is no longer able to operate automatically or smoothly. The direction of the path then depends upon the nature and direction from which stimulation was received, and upon the degree and direction of change of temperature, etc. The importance of this conception of movement lies in the fact that it enables us to look at a large mass of otherwise unrelated data from a single point of view. Secondly, it permits of a mathematical treatment of the whole subject of movement in organisms. And third, it replaces a teleological explanation of spiral movement in unicellulars, swarm spores, rotifers, etc., with a purely mechanistic explanation. CHAPTER XIV CONCLUSIONS One of the most important results of recent work on the movements of ameba and of streaming endoplasm in plant cells is the rapidly growing conviction that the streaming of protoplasm, wherever it is found, is due to the same fundamental cause. The value of this conception lies in the greatly widened front that is presented for attacking the general problem of streaming. The many special aspects of streaming, which in the past have been thought to be essential or fundamental processes, may thus be placed against each other, following what is known as the comparative method, and the main problem will thus be freed of much that is not strictly relevant. In this way we come at once to the heart of the problem. One of these special aspects of streaming in amebas is the formation of ectoplasm. For ectoplasm formation is not essential to streaming. But it is almost certainly essential to locomotion, for locomotion has not been observed in amebas where ectoplasm was not formed. But, on the other hand, ectoplasm, as known in the amebas, is not formed without streaming, although observations indicate that ectoplasm may suddenly and temporarily pass into the gel state (_Vallisneria_). Streaming is therefore the fundamental process in ameboid locomotion.