The amoeboid and flagellate phases of Naegleria grüberi were examined by phase-contrast microscopy, cytochemical techniques, and conventional staining methods. Some electron micrographs were taken. Results showed that lipid was confined to the cytoplasmic globules, cell membrane, and mitochondria. Glycogen was absent, but a polysaccharide, probably a protein-carbohydrate complex, was generally distributed throughout the cytoplasm and was particularly abundant in the food vacuoles. Particular attention was paid to the mitotic figure, with the result that stage I of mitosis, in which RNA-protein and DNA-protein particles were dispersed throughout the nuclear area, is claimed as being a constant and essential occurrence in the initiation of mitosis. After stage I, the RNA and DNA took up and remained in sharply demarcated areas of the mitotic figure. No lipid or carbohydrate was present in the mitotic figure.

During the transformation from amoeba to flagellate, some of the mitochondria concentrated at the point on the periphery of the organism where the flagella later emerged, and in the fully formed flagellate appeared as a dense cap at the bases of the flagella. Electron micrographs showed that the mitochondria had a double limiting membrane and an internal system of tubules similar to those described in Acanthamoeba.

As the flagellate reverted to the amoeboid stage the flagella were resorbed by the endoplasm.

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