Figure 22. Illustrating the movements of an Amoeba proteus, after Dellinger. At c in stage 2 a pseudopod is projected which fastens itself to the substratum as shown at c, 3, while a, 2, is pulled loose. In 4 another pseudopod is projected which fastens itself at d. The ameba is not in contact with the substratum at all points on its under side.
In figure 23 is shown a clavate discoides with a small particle attached to its side. The particle moved forward until it came to lie at the anterior edge, 10. The speed of the particle from 1 to 10 was 1.36 times as fast as that of the ameba, a much slower rate than was observed in sphaeronucleosus. At 6 a new pseudopod was projected for a short distance, thus increasing the amount of new ectoplasm forming in proportion to that of the whole ameba. This change was reflected in the increased speed of the particle, which moved 1.64 times as fast as the ameba from 5 to 6. At 10 the anterior end again spread out and again the particle moved faster—twice as fast as the ameba from 9 to 10. Stages 11, 12, 13 are added to show that the particles do not tend to go to the under surface but remain at or very near the tip. The slight irregularity of the waves of hyaloplasm pushed out at the anterior end accounts for the changing position of the particle after it has reached the anterior edge. The particle remained at the edge of the advancing ameba for several minutes after the stage drawn at 13.
Figure 23. Showing the movement of a particle on the surface layer of an Amoeba discoides. The particle remained on the anterior end of the ameba for several minutes after stage 13. The ameba was about 320 microns long.
In another observation the effect of a narrowing of the advancing tip of the ameba is shown very well. In figure 24 the ameba was advancing with a broad anterior end, as shown at 1 and 2. From 2 to 4, the region where new ectoplasm was made, narrowed down very considerably. These changes in the width of the anterior end are reflected, as in [Figure 17] by a decrease in the relative speed of the moving particle. Thus the particle moved 1.75 times as fast as the ameba from 1 to 2 while from 2 to 4 the particle moved only 1.27 times as fast as the ameba.
Figure 24. Showing the effect of a narrow anterior end on the rate of movement of the surface. Length of the ameba, about 320 microns.
The movement of the third layer in proteus is difficult to study owing to the formation continually of ridges, as explained on page 20. Even in clavate shaped amebas, waves of protoplasm are pushed out on the sides and on the tip with consequent formation of ectoplasm, so that the ameba grows in width slowly at the same time that it grows in length. A typical shape of a proteus in clavate form is slightly tapering toward the anterior end. This shape is maintained by gradual extension of the sides of the anterior half or two-thirds of the ameba as it moves along. These conditions are just the reverse of what was seen to be the case in sphaeronucleosus and verrucosa, where the anterior edge was wider than any other part of the body. But discoides, although free from the ridges and grooves characteristic of proteus, frequently has an anterior edge that is narrower than any part of the body, thus necessitating extension of the sides as the ameba moves forward.