Figure 20. Amoeba sphaeronucleosus. a, the under side of the ameba. The part of the ameba attached to the substratum is stippled. Particles attached to the surface film at x moved slowly forward. b, the under side of the ameba, showing the attached parts stippled. The particles suspended in the water at x moved slowly forward with the ameba. c, a cross section of an ameba of shape shown in b, showing the ridges on the surface. Length of the ameba, about 100 microns.
The movement of the surface layer in A. verrucosa is quite like that of sphaeronucleosus. [Figure 21] shows a group of three particles carried by a verrucosa while changing its direction of locomotion. The particles changed position with regard to each other and they moved at different speeds. Particles a, b, c, moved respectively 2.40, 3.26, 2.85 times as fast as the ameba advanced. Other experiments indicate that the outer layer of verrucosa moves at about the same speed, compared with the speed of the ameba, as that of sphaeronucleosus.
Amebas with so-called limax-shaped bodies do not possess surface layers that carry particles forward with the same speed as those amebas with broad bodies. It is only occasionally that large amebas such as proteus are found in a limax or clavate shape. One of the most favorable of the large amebas in this respect is discoides. It is frequently found in clavate shape and it possesses the further advantage in being nearly cylindrical in cross section. It is also more in the habit of loping along the surface in the manner described by Dellinger (’06, p. 57) so that what is observed to take place in discoides in the clavate shape, holds likewise for free pseudopods extended into the water out of contact with a solid support ([Figure 22]).
Figure 21. Illustrating the similarity of the movement of the surface layer of Amoeba verrucosa with that of A. sphaeronucleosus. A group of three particles, connected by dotted lines for reference, change their relative positions as the ameba (verrucosa) changes its direction of movement. Length of the ameba, 150 microns.
