Studies on Giant Amoeboid Organisms: 2. Nuclear Division and Cyst Formation in Leptomyxa reticulata Goodey with Remarks on the Systematic Position of the Organism

Abstract

SUMMARY: Excellent cytological preparations may be made from growth of Leptomyxa reticulata on cover-slips on a film of agar. The organism is multinucleate. Each resting nucleus contains a deeply staining mass, the nucleolus, which is surrounded by a clear zone in which chromatin material is scattered. There is always a definite nuclear membrane. The nuclei divide simultaneously by intranuclear mitosis and the whole process is completed in a short time. At prophase the dispersed chromatin granules aggregate and later assume a thread-like structure and enter upon the metaphase. The formation of the spindle can be seen at the beginning of the metaphase. No centrosomes are seen at any stage. During anaphase the chromosomes begin to separate and it is difficult to count their numbers. The nuclear membrane disappears at late anaphase. At telophase the daughter chromosomes fuse together, the connecting threads break and the daughter nuclei are formed. Under suitable cultural conditions and on certain strains of bacterial food supply, multinucleate cysts are produced in clusters. The process of cyst formation is described.