Ultrastructural Studies on the Sporulation of Oocysts of Toxoplasma Gondii

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Abstract
The ultrastructural changes observed during T. gondii sporocyst formation and the structure of the sporocyst wall was examined in oocysts which had been allowed to sporulate for 12-48 h at 27.degree. C. As the spherical sporoblast developed into the sprorcyst the cytoplasmic mass became ellipsoidal in shape although no change was noted in the organelle compliment, which consisted of 2 nuclei plus a number of polysaccharide granules, lipid globules, mitochondria, Golgi bodies and some rough endoplasmic reticulum. The sporocyst wall consisted of a thin outer layer (15-20 nm) which was formed from 2 limiting membranes of the sporoblast and an inner layer (40-50 nm) which was comprised of 4 curved plates. This inner layer was formed under the outer layer and, although no specific cytoplasmic organelle disappeared with it formation, some unit membranes were observed close to the plasmalemma during its formation. Each curved plate has a marginal swelling and an interposing strip of material is present between the margins of adjacent plates. The plates are joined to the interposing strip by a thin band of osmiophilic material. In oblique and tangential sections through the plates 2 types of cross banding were observed which differed in periodicity.