by a line for convenience of reference, were in the position indicated at 1 when the forward end of the ameba occupied the position indicated by outline 1. As the ameba moved forward the particle _c_ gained slightly on _a_ and _b_ for no ascertainable reason, unless it was on account of the projection of the large pseudopod on the opposite side. At stage 2 a new pseudopod was started on the right, which at stage 3 had grown to large size while streaming in the original pseudopod was arrested. At stage 3 particles _a_ and _b_ retained the same position they had in stage 2, except for a slight turning to the right. Particle _c_ however moved across the base of the original pseudopod and on to the middle of the new pseudopod. At stage 4 _a_ and _b_ had again only slightly moved to the right of the position they occupied in stages 2 and 3, while _c_ moved rapidly toward the tip of the new pseudopod. The new pseudopod was then retracted and at stage 5 the particles had begun to move back toward the main body of the ameba. Particles _a_ and _b_ now gained considerably on _c_ because they were located further away from the tip of the retracting pseudopod. Particles _a_ and _b_ were drawn to the middle of the retracting pseudopod because of the continuous enlargement of the large pseudopod on the right, below, through which the ameba moved on. The most important feature of this observation is the change in the position of the particle _c_ with respect to that of _a_ and _b_. The latter particles retained their relative positions with very slight, if any, change, while _c_ swung around _a_ and _b_ nearly 180°, and at the same time changed the distance very greatly between itself and the other particles. Moreover, _b_, at stage 5 led the procession of particles, while at stage 1, _a_ led. No further demonstration is necessary to show that the surface layer is distinctly fluid and dynamic, and not at all such a static structure as an elastic permanent skin, as Jennings (’04) and Rhumbler (’14) maintained. CHAPTER VIII ON THE NATURE OF THE SURFACE LAYER The observations in the preceding chapters on the general movements of the surface layer of amebas will afford a sufficient basis for an inquiry into the nature of this layer. The mere demonstration of the existence of this layer is, of course, interesting enough, for a number of contradictory statements by various students of the amebas are satisfactorily cleared up by these observations. But the problem of ameboid movement affects other organisms besides amebas, and since the movement of the surface layer is so intimately associated with ameboid movement, it becomes of more than ordinary interest to learn something of the nature and composition of this layer.