Fine-Structural Aspects of Microgametogenesis of Eimeria magna in Rabbits and in Kidney Cell Cultures*

SYNOPSIS. The fine-structural aspects of development of microgamonts of Eimeria magna were studied in kidney cell cultures and in experimentally infected rabbits. Spheroidal masses of gamont-like cytoplasm containing ribosomes, polyribosomes, and amylopectin granules were found within the parasitophorous vacuole; these bodies were apparently pinched off the surface of the gamont. Nucleoli were present in the early stages of nuclear division but disappeared as development proceeded. Spindles were eccentric and the nuclear membrane always remained intact in dividing nuclei. Nuclei eventually became elongate in shape, compact, and electron dense at the end oriented toward the periphery and lucent centrally. Usually, only the dense portion was incorporated into the gamete as the gamete developed by protruding from the gamont surface. Fullyformed microgametes were biflagellate and contained a nucleus, a mitochondrion, and 8-10 microtubules. Multiple-membrane complexes, which apparently originated from the nuclear envelope or endoplasmic reticulum, were found within the gamont residual body. Occasionally, 2 or 3 micro- and/or macrogamonts were seen within the same cell. In some cells one or 2 micro- or macrogamonts as well as several merozoites were present in the same parasitophorous vacuole.