The generally accepted view of the behavior of the contractile vesicular mechanism in Paramecium is that it is an osmotic system in which the fluid collected in the radial canals moves only forward into the central vesicle from which, on systole, it is wholly discharged outside. From an analysis of the total behavior of the mechanism by means of motion pictures, the following conclusions emerge: Diastole of the vesicle displays 2 periods, an earlier of rapid and irregular expansion, caused by the ejaculation of the replete canals into it, followed by a second of slow and steady increase of volume by diffusion. After the close of diastole of the vesicle, begins its systole, this also displaying two periods, an earlier, causing the sudden reflux of fluid into the canals, followed by a sudden contraction expelling the remaining fluid to the outside. That the expansion of the canals during slow systole of the vesicle is sudden calls for a mass inflow of fluid. This is undoubtedly followed by their further repletion by diffusion. They act during their diastole very much as the vesicle does during its diastole. If the latter is properly explained by inrush of fluid from the canals, so the former is explainable by inrush of fluid from the vesicle with equal propriety.