Light and electron microscopy on the sporulation of the oocysts of Eimeria brunetti. II. Development into the sporocyst and formation of the sporozoite.

The later stages of sporulation in oocysts of Eimeria brunetti were examined in samples which had been allowed to sporulate at 27 degrees C for 24, 36 and 48 hours. It was observed that the sporoblasts became ellipsoidal and the nucleus underwent the final division. A nucleus with associated Golgi bodies was not observed at either end of the organism. The cytoplasm was limited by two unit membranes and contained rough endoplasmic reticulum, dense bodies, electron translucent vacuoles and mitochondria. The first evidence of sporozoite formation was the appearance of a dense plaque at either end of the organism. This appeared in the vicinity of the nuclei, and adjacent to the limiting membrane of the soroblast. At this stage the sporocyst wall was still unformed. Then the two sporozoites were formed from opposite ends of the organism by growth of the dense plaques and invaginations of the plasmalemma which thus formed the pellicles of the developing sporozoites. A conoid and subpellicular microtubules were observed at this stage as development continued, a number of vacuoles were found between the nucleus and the conoid. These vacuoles constituted the precursors of the rhoptries and micronemes. At the same stage a large dense body had appeared within the forming sporozoite. As the sporozoite developed, this body, anterior refractile body, is followed by the nucleus and another dense body which formed the posterior refractile body. During this period, the thin sporocyst wall was formed and Stieda and sub-Stieda bodies were now present at one end of the sporocyst. Each mature sporocyst contained two sporozoites.