Pelomyxa palustris Greeff

Summary The Pelomyxa palustris amoebae used in this study were multinucleate, herbivorous protozoans. All nuclei within a single organism were similar, but several types of nuclei were seen in different amoeba. These nuclei might represent various stages of mitosis although metaphase and anaphase stages were never seen. Rod-shaped bacteria within vesicles characteristically surrounded the nuclei. Bacterial rods of this as well as another type also occurred within vesicles in the cytoplasm. The nuclear envelope contained annuli and it was covered externally by minute vesicles. Nucleoli and micronucleoli were most frequently located along the inner surface of the nuclear envelope. Clusters of electron-opaque spheroids were found within the nucleoli; sometimes, they existed free in the nucleoplasm. Intranuclear globules of lipidlike material were often seen.Mitochondria, Golgi bodies, contactile vacuoles, and crystal vacuoles were definitely absent in P. palustris. The cytoplasm contained many food vacuoles and clear vacuoles of various sizes. Vacuole-like aggregations, probably containing glycogen, were present.Work supported by the U. S. Atomic Energy Commission.