Light and electron microscopy on the sporulation of the oocysts of Eimeria brunetti. I. Development of the zygote and formation of the sporoblasts.

The initial stages of sporulation in oocysts of Eimeria brunetti were examined in samples sporulated at 27 degrees C for 0, 12 and 24 hours. The initial zygote was found to be roughly spherical and to contain a number of polysaccharide granules which were congregated in one region of the organism. The cytoplasm also contained some strands of rough endoplasmic reticulum together with a number of mitochondria, some Golgi bodies, and some electron translucent vacuoles. The nucleus was large, with amorphous nucleoplasm and a nucleous. The cytoplasmic mass of the zygote was limited by a single unit membrane which possessed some micropores. After initiation of the sporulation, the metabolic activity of the organism appeared to increase as evidenced by the augmentation in the cytoplasm of the amounts of rough endoplasmic reticulum, number of Golgi bodies, and the appearance of polyribosomes. However, at this stage, the presence of large spherical bodies (anlagen of the refractile bodies of the sporozoites) constituted the most obvious change in the cytoplasm of the organism. After nuclear division the daughter nuclei were situated well separated in the cytoplasm and the polysaccharide granules were evenly distributed throughout the cytoplasm of the zygote. Eventually four sporoblasts were formed by invaginations of the limiting membrane. Each sporoblast was limited by a unit membrane and contained a nucleus, and the same cytoplasmic organelles as found in the zygote. The development of the sporoblast was initially accompanied by the appearance of a second limiting membrane.