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944 subtertian Plasmodium falciparum (formerly called Laverania malariæ) (Fig. 248). All these human parasites undergo sporogony in mosquitoes of the genus Anopheles. Similar parasites are found in monkeys (Fig. 249), antelopes, bats, and squirrels. In birds an analogous and pernicious parasite is known as Proteosoma (Proteosoma grassii, Labbé, 1894), but, in contradistinction to the human malaria parasite, it is transmitted by mosquitoes of the genus Culicinæ, and also by Stegomyia calopus.

The life cycle of these parasites (Fig. 247) is extremely well known and has already been described in detail (p. 28).

Fig. 248.—Plasmodium falciparum.

The sporozoites, minute slender organisms, are introduced by the proboscis of the mosquito, and enter red blood-corpuscles. The young trophozoite is characterized by its signet-ring appearance, there being a large space in the centre of the body. As the parasite grows this space disappears, and the pigment is deposited in its protoplasm. When full grown, multiplication by schizogony takes place. The nucleus, hitherto single, multiplies by repeated division, each daughter nucleus becoming the centre of a merozoite. A blood corpuscle containing a number of such merozoites represents the characteristic rosette of the malaria parasite. The host cell then



ruptures, setting free the merozoites; these penetrate other corpuscles and become trophozoites, which may either grow into schizonts or sporonts. These sporonts (gametocytes) are either male or female: the male forms have a large nucleus and a hyaline faintly-staining protoplasm; the female forms have a smaller nucleus and a deeply staining protoplasm. The sporonts are capable of further development only if taken up by the specific kind of mosquito. In the male the nucleus undergoes disintegration, and at the same time the fragments proceed to the periphery of the cell and become nuclei of a number of fine filaments or flagella, and two polar bodies are simultaneously extruded; these flagella are endowed with motile powers, and break free from the cell as microgametes. In the meantime the female sporont, after