Taking the amebas as a group and applying these principles of colloidal solutions, we find that we can arrange the amebas in a series of four or more grades representing differences of fluidity of the protoplasm. Among the most fluid are _Amoeba limicola_ and _Pelomyxa schiedti_; in the next group, with less fluid protoplasm is _Amoeba dubia_; in the third group is _A. proteus_ and _A. discoides_; in the fourth group, with the least fluid protoplasm, come _A. radiosa_ and _A. verrucosa_. These groups represent a progressive increase in the amount of ectoplasm in proportion to the endoplasm. There being less water present in the higher groups than in the lower, which follows from a stiffer endoplasm, it is possible for them to form endoplasm, that is, to change phase, more readily. And as a corollary to this we may add that more pseudopods are formed, since ectoplasm can be formed more readily. (The _verrucosa_ types possess very stiff ectoplasm, and they increase their surface by flattening out and by forming longitudinal ridges. They cannot for some unknown reason form pseudopods). Again with the increase in the consistency of the protoplasm, the pseudopods become more slender (and stiffer) and more contractile, the most slender pseudopods (_radiosa_, _flagellipodia_) being very much more contractile than the larger ones of _proteus_ or _discoides_, for example. An additional factor operates here, however, for some of the slender pseudopods as of _radiosa_ and _bilzi_ are static and for a great part of their existence practically incapable of contraction. The high development of contractility follows, of course, from the high degree of dispersion of the internal phase in ectoplasm, of which these pseudopods almost wholly consist. Thus, many, if not most, of the more generalized peculiarities of form of amebas may be traced to the amount of water in the protoplasm.