[Illustration: FIG. 80.--Life-cycle of the tertian parasite (_Plasmodium vivax_). Figs. 1 to 17, × 1,200; figs. 18 to 27, × 600. (After Lühe, based on figures by Schaudinn and Grassi.) 1, sporozoite; 2, entrance of the sporozoite into a red blood corpuscle; 3, 4, growth of the parasite, now sometimes called a trophozoite; 5, 6, nuclear division in schizont; 7, free merozoites; 8, the merozoites which have developed making their way into blood corpuscles, (arrow pointing to the left) and increase by schizogony (3–7); after some duration of disease the sexual individuals appear; 9_a_-12_a_, macrogametocytes; 9_b_-12_b_, microgametocytes, both still in the blood-vessels of man. If macrogametocytes (12_a_) do not get into the intestine of _Anopheles_ they may perhaps increase parthenogenetically according to Schaudinn (12_a_; 13_c_-17_c_). The merozoites which have arisen (17_c_) become schizonts 3–7. The phases shown underneath the dotted line (13–17) proceed in the stomach of _Anopheles_. 13_b_ and 14_b_, formation of microgametes; 13_a_ and 14_a_, maturation of the macrogametes; 15_b_, microgamete; 16, fertilization; 17, oökinete; 18, oökinete in the walls of the stomach; 19, penetration of the epithelium of the stomach; 20–25, stages of sporogony on the outer surface of the intestinal wall; 26, migration of the sporozoites to the salivary gland; 27, salivary gland with sporozoites.] The growth and schizogony last different times, according to the species of the parasite, about forty-eight hours in the case of the parasite of febris tertiana or tropica, and seventy-two hours for the quartan parasite. The various intermittent forms produced by them depend on this specific difference in the malarial parasites.