Figure 6. Pelomyxa schiedti, after Schaeffer. b, bacterial rods characteristic of the genus Pelomyxa. c, v, contractile vacuole. g, glycogen bodies. n, nucleus. u, uroidal projections. At the left is shown a series of outlines of the animal during locomotion. Length, about 75 microns.
Pelomyxa schiedti moves in much the same way that Amoeba limicola does; that is, by eruptive waves of endoplasm which are usually deflected back along the side ([Figure 6], at the left). The endoplasm is likewise of very thin consistency. The thinness of the ectoplasm and the ease with which it may be ruptured, is very well shown by the fact that the large irregular glycogen bodies (Štolc, ’00) which fill it to capacity, lie so close to the surface that it is frequently impossible to see any protoplasm between them and the exterior. The contractile vacuoles which are numerous, also testify in their characteristics, to the ease with which the ectoplasm may be broken. The vacuoles never reach but a very small size (four microns in diameter) presumably because of the thin consistency of the endoplasm and because they can readily break through the ectoplasm. They burst on the surface of the ameba instantaneously, as a small air bubble might burst on pure water. But this ameba differs from limicola in that a cross section of the body is very nearly a circle.
Figure 7. Amoeba radiosa, after Penard. a, the rayed stage. b, the rayed stage in which some of the pseudopods are being withdrawn. One of them is thrown into a spiral as it is being withdrawn. c, the stage preceding the trophic stage shown at d.
Another very interesting feature of Pelomyxa schiedti is the uroid ([Figure 6], u), which in this species consists of a number of very thin projections resembling pseudopods extending from the posterior end. These projections are attached to the substratum and in some way aid in locomotion. These uroidal projections are of considerable length, and may persist for a considerable length of time. Thus while schiedti is unable to form pseudopods at its anterior end, it forms uroidal projections with great ease at its posterior end. But what the conditions are which are necessary for the formation of a uroid, a structure which it may be added, exists in many species of amebas (and perhaps also in Cercomonas), is quite unknown.
In contrast to the amebas thus far discussed from the point of view of the transformation of endoplasm into ectoplasm, there are a number of species in which two distinct methods of endoplasmic transformation occur typically. Among these species are the small Amoeba radiosa ([Figure 7]), A. bigemma ([Figure 8]) and a new species which for convenience will be referred to as bilzi.
Figure 8. Amoeba bigemma, after Schaeffer. a, usual form in locomotion, showing the numerous pseudopods, vacuoles, nucleus and food body. b, rayed stage frequently assumed when suspended in the water. The pseudopods in this stage are clear, slender, and more rigid than those in stage a. c, an excretion sphere attached to a twin-crystal characteristic of this ameba. d, the nucleus, consisting of a clear nuclear membrane and a mass of chromatin granules in the center. e, a small sphere attached to a crystal. f, a twin crystal unattached to a sphere. Length of a, 150 microns; of d, 12 microns; of f, 2 microns.