The migration of the merozoites initiates a new attack of fever and two groups of tertian parasites in the blood, differing in development by about twenty-four hours, are the conditions for febris tertiana duplex. After a lengthy duration of fever the gametocytes (figs. 80, _9_--_12_) appear. They are uninucleate. The microgametocytes are about the size of fully developed schizonts, the macrogametocytes are somewhat larger. Their further development takes place in Anophelines. The chief distinctive characteristics of the simple tertian parasite, as seen in infected blood, are:--(1) The infected red-cell is usually enlarged; (2) the presence of fine red granules known as Schüffner’s dots in the red blood corpuscles, after Romanowsky staining; (3) the fragile appearance of the parasite compared with other species. Large forms are pigmented, irregular and “flimsy-looking,” sometimes appearing to consist of separate parts. Irregularity of contour is common. Ahmed Emin[203] (1914) has described a small variety of _P. vivax_. [203] _Bull. Soc. Path. Exot._, vii, p. 385. *Plasmodium malariæ*, Laveran. Syn.: _Oscillaria malariæ_, Laveran, p.p., 1883; _Hæmamœba malariæ_, Gr. et Fel., 1890; _Plasmodium malariæ_ var. _quartanæ_, Celli et Sanfel., 1891; _Hæmamœba laverani_ var. _quartana_, Labbé, 1894; _Hæmosporidium quartanæ_, Lewkowitz, 1897; _Plasmodium malariæ quartanum_, Labbé, 1899; _Plasmodium golgii_, Sambon, 1902; _Laverania malariæ_, Jancso, 1905 nec Grassi et Fel. 1890; _Hæmomœba malariæ_ var. _quartanæ_; Lav., 1901. _Plasmodium malariæ_ is the parasite of quartan malaria (fig. 86). The trophozoites of the quartan parasite differ from the corresponding stages of the tertian parasite in that their motility is less and soon ceases. They differ also in their slower growth, by the early disappearance of the food vacuole, by the more marked formation of the dark brown pigment, and by the fact that the red blood corpuscles attacked are not altered either in colour or size. [Illustration: FIG. 86.--Development of the quartan parasite in the red corpuscles of man--asexual stages. (After Manson.)] When the parasites have grown almost to the size of the erythrocytes schizogony occurs. The pigment granules arrange themselves in lines radiating towards the centre and the merozoites are also radially disposed in groups of 6, 8, 10 or even 12, but are often arranged less regularly. The whole development, growth and schizogony, occupies seventy-two hours. The appearance of quartana duplex or triplex is conditional on the presence in the blood of the patient of two or three groups of _Plasmodia_ differing in their development by twenty-four hours.