If the form of _sphaeronucleosus_ were more regular than it is, the amount of ectoplasm in the process of forming at any given moment could be compared with a similar relation existing in _discoides_, to see whether these respective ratios were proportional to the speed of the moving surface films in the two amebas. As it is, the irregularity of form of _sphaeronucleosus_ makes such computation subject to the possibility of considerable error. In _discoides_ however the problem is comparatively simple. I therefore did not go into this matter extensively, but merely worked out the relations mentioned in one case, and I mention it here to illustrate the method rather than to record the result, which is not to be taken as very exact. [Illustration: Figure 28. A clavate _Amoeba discoides_, showing the amount of ectoplasm that is constantly being made at the anterior end. Length of the ameba, 310 microns. ] Since the movement of the surface film is obviously a surface phenomenon, only the surfaces of the amebas need to be taken into account. In Figure 28 is illustrated a _discoides_ of such a shape as to allow a fairly accurate computation of its surface. Three outlines of the anterior end only are given; the rear portion of the ameba remained approximately the same size and shape in the three outlines. The cross lines at the anterior end divide the forming ectoplasm of the ameba from the formed. As will be noticed the cross lines are drawn through the intersections of two successive outlines. Computing the areas on both sides of the cross lines for the two outlines and averaging them, there is found a ratio of 1 to 10; one-eleventh of the total surface represents forming ectoplasm, and ten-elevenths formed ectoplasm. (One-twenty-second of the total surface was deducted for surface attached to the substratum.) _Sphaeronucleosus_ stands in contrast with _discoides_ for it is attached to the substratum over a much greater area and in consequence only a slight amount of surface is drawn from the under side. This ameba may therefore be regarded in this connection as of only one surface, the upper. That part of outline 1 in Figure 14 cut by outline 2 indicates, as in _discoides_, the region of forming ectoplasm, and the space between outlines 1 and 2 may be used as a basis of computation. New ectoplasm is formed in this zone and far enough back to include the tips of the longitudinal ridges, of which we have already spoken (Figure 13). The zone of forming ectoplasm would therefore be about twice as wide as the average width of the three zones between the successive outlines in the figure, and of approximately the same shape. On this basis, the surface occupied by forming ectoplasm is 1/5.8 of the total surface, and the ratio of formed to forming ectoplasm is 4.8 to 1.