The principal stages of the avian plasmodium closely resemble those of the malarial parasites of man. In its earliest stage _P. relictum_ is unpigmented, but soon the trophozoite grows and becomes pigmented, meanwhile displacing the nucleus of the avian red-blood corpuscle, a characteristic feature, distinguishing it from _Halteridium_. Schizonts are formed, each of which gives rise to about nine merozoites in the circulating blood. Sexual forms or gametocytes also occur in the blood. These develop in _Culex fatigans_, _C. pipiens_ and _C. nemorosus_. Oökinetes or vermicules are formed in twelve to fifteen hours in the stomach of the mosquito, and in one to two days well-developed round oöcysts may be seen. In three to four days sporoblasts have formed within the oöcysts and young sporozoites begin to develop. In nine to ten days the oöcysts are mature, being filled with sporozoites. The oöcysts then burst and the sporozoites travel through the thoracic muscles to the salivary glands of the Culicine. Neumann, experimenting with canaries, found that _Stegomyia fasciata_ could transmit the infection, but less efficiently than species of _Culex_. THE CULTIVATION OF MALARIAL PARASITES. The successful cultivation of malarial parasites _in vitro_ was first recorded by C. C. Bass and by Bass and Johns (1912).[206] Since then, J. G. and D. Thomson,[207] and McLellan (1912–13), Ziemann[208] and others have repeated the experiments. [206] _Journ. Exptl. Med._, xvi, p. 567. [207] _Annals Trop. Med. and Parasitol._, vi, p. 449; vii, pp. 153, 509. [208] _Trans. Soc. Trop. Med. and Hyg._, vi, p. 220. DIFFERENTIAL CHARACTERS OF THE HUMAN MALARIAL PARASITES.