Electron microscope studies on motile stages of malaria parasites VI. The oöknete of Plasmodium berghei yoelii and its transformation into the early oocyst

The oökinete and early oöcysts of Plasmodium berghei yoelii in Anopheles stephensi have been studied by electron microscopy. The oökinete resembles that previously described for other species of the genus. It contains a single nucleus, one or more crystalloids, mitochondria, a number of anterior elongated, convoluted rods or tubules, and it is bound by a pellicle of 2 unit membranes and a layer of subpellicular microtubules. The structure of the anterior end of the oökinete was revealed in more detail than hitherto. There is an annular thickening of the pellicle, the polar ring, from which the subpellicular microtubules appear to arise. In some specimens, the polar ring was on a narrow anterior protuberance; in others, it was retracted and, behind it, there was a cavity between the tubules and the pellicle apparently formed by a split in the plasmalemma.