Let us now see what is the effect of ridge formation upon the movement of the surface layer. [Figure 25] shows a proteus and a narrow anterior end in proteus with two pseudopods and a particle attached to the side of the ameba at 1. Both pseudopods advanced until stage 4 was reached, but the particle was not appreciably deflected from an approximately straight path by the small pseudopod at the other side of the ameba. Reference to the figure shows that the particle travelled much faster while the pseudopod on the side was extending than after it began to retract. The particle moved 1.43 times as fast as the ameba from 1 to 4. But from 4 to 7 the particle moved only 1.06 times as fast as the ameba.
Figure 25. Amoeba proteus. Rate of movement of the surface layer as compared with the rate of movement of the ameba. The pseudopod on the right was extended to stage 5; from then on it was retracted, as indicated by the outlines. Length of the ameba, 400 microns.
In the earlier stages the outer layer was pulled toward the tip of both pseudopods, in the later stages only toward one, and in this lies the explanation for a more rapid movement of the particles in the earlier, and a slower movement in the later stages. This effect was also observed in discoides, but the fact that the particle in the later stages moved only very little faster than the ameba is due to a narrow anterior edge and to the formation of ectoplasm in the ridges over the surface of the ameba. The effect of ridge formation on the movement of particles attached to the surface film is well seen when an ameba has two forward moving regions opposite each other. Under such conditions particles located equidistant or nearly so between such regions, move only very slowly or not at all, the pull upon the film being nearly or quite equal. In a similar manner the ridges which are constantly forming on a proteus are continually competing with the anterior end in their pull upon the surface layer, thus preventing rapid forward movement.
Figure 26. Showing the comparative rate of movement of the surface film over the retracting parts of the ameba. In figures 2 to 8 only a part of the ameba is shown. Length of the ameba, 500 microns.
[Figure 26] shows that the surface layer flows away from the tip of a retracting pseudopod that is located near the anterior end. The particle moves slowly until the body of the ameba is reached, when movement becomes more rapid, 8, 9. This proves that the third layer moves away from the retracting parts of an ameba, no matter how large the total area of these parts may be in proportion to the area of new surface that is being made. But whether the speed of the moving third layer changes in correspondence with a larger or a smaller ratio between building and retracting ectoplasm has not been ascertained.
[Figure 27] shows that the relative positions of particles attached to the surface layer may readily change while the ameba deploys its psuedopods. Three particles marked a, b, c and connected