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Rh giving off a reduction nucleus, is ready for fertilization by the microgamete. The female cell (zygote) is capable of independent movement, and (now termed an oökinete) bores its way through the lining epithelium of the mosquito's stomach, there encysts between the epithelium and the limiting membrane, and becomes an oöcyst. The original nucleus now breaks up into sporoblasts, which in turn break up into sporozoites. The oöcyst then bursts, setting free the sporozoites, which contrive to pass into the salivary glands, whence, with the salivary secretion, they once more enter the blood on which the infected mosquito is feeding. In the avian red blood-corpuscle the young sporont of proteosoma displaces the nucleus of the cell to one side in its growth, and thus may be distinguished from a similar stage in Halteridium.

A form of pigment-producing plasmodium occurs in the blood of reptiles, and is known as Hæmocystidium (Fig. 250). These parasites are of large size, are very numerous in the blood, and do not exflagellate when the blood is drawn. Nothing further is known of their life-history.

Fig. 250.—Hæmocystidium simondi.

2. Members of the genus (also termed ) are parasitic in the blood of many widely different species of birds, and perhaps also of turtles. Within the red blood-corpuscle they grow into a characteristic halter-like shape, partially enveloping but not displacing the nucleus of the corpuscle. In the halteridium of the pigeon the sexual cycle is passed in a hippoboscid fly, Lynchia maura, and is similar to that described above, but differs in one respect, namely, that the melanin pigment is extruded by the oökinete, which becomes considerably larger than the sporont found in the blood of the bird, and in this stage is apparently re-inoculated by the lynchia into the pigeon. Possibly the further development of the oökinete takes place within a capillary endothelial cell of the pigeon, but it is afterwards found within a leucocyte in the lung capillaries. In this leucocyte the parasite grows and