Reproduction of nuclei in Pelomyxa palustris.

Light and electron micrographs were made of nuclei in Pelomyxa palustris, a unicellular, multinucleated giant amoeboid organism. We analyzed 1019 pelomyxae and classified their nuclei according to their location in the nuclear cycle. The majority of organisms (56.3%) had interphase nuclei, some of which contained spores of mostly 1-3 microns in diameter. The nuclei had disintegrated in 1.3% of organisms that appeared to have no nuclei. The remainder (42.4%) had nuclei in the form of spores (1 to 10 microns spheroids) that were in various stages of development and growth. Mitotic figures were seen in some of them, with several chromosome pairs per nucleus. Interchromosomal fibers were seen at anaphase, and newly formed "young" interphase nuclei were observed.