[Illustration: FIG. 84.--Four different sporulation stages of malarial parasites from _Anopheles maculipennis_, much magnified. _a_-_c_, of the malignant tertian parasite; _a_, four to four and a half days after sucking; _b_ and _c_, five to six days after sucking; _d_, of the tertian parasite, eight days after sucking. (After Grassi.)] The sporulation is influenced in its duration by the external temperature (Grassi, Jansci, Schoo). In the tertian parasite it takes place quickest at a temperature of 25° to 30° C. and takes eight to nine days. A temperature a few degrees lower has a retarding effect (eighteen to nineteen days at 18° to 20° C). A still lower one has a restraining or even destructive effect. Temperatures over 35° C. also exercise a harmful effect. The malignant tertian parasite seems to need a somewhat higher temperature and the quartan parasite a lower one. The sporozoites of the various malarial parasites show no specific differences. They were stated by Schaudinn to occur in three forms, and these were described as indifferent (neuter), female and male. There is, however, little or no evidence for this hypothetical differentiation. The last were said to perish prematurely, that is, in the oöcyst. The others after the rupture of the oöcysts enter the body cavity of the Anophelines, whence they are carried along in the course of the blood. Finally they penetrate the salivary glands (fig. 80, _27_) probably by their own activity, break through their epithelia and accumulate in the salivary duct (fig. 80, _27_). At the next bite by the mosquito they are transmitted to the blood-vessels of man. THE SPECIES OF MALARIAL PARASITES OF MAN. In view of the differences in opinion regarding “species” and “varieties,” the dispute whether the malarial parasites of man represent one species with several varieties, or several species is almost superfluous. If necessary two genera may be distinguished. The parasites of the tertian and quartan fever are alike in that their gametocytes have a rounded shape (figs. 80, _12_, _13_), whilst the corresponding stages of the pernicious or malignant tertian parasites are crescentic (figs. 81, 88). These differences are used by some writers as the distinguishing characteristic of two genera: _Plasmodium_, Marchiafava and Celli, 1885, for the first mentioned species; _Laverania_, Grassi and Feletti, 1889, for the pernicious or malignant tertian parasite. Whether there is a genuine quotidian fever and accordingly a special quotidian parasite is still disputed. These parasites are treated in practical detail in Stephens and Christophers’ “Practical Study of Malaria,” 3rd edition, 1908. *Plasmodium vivax*, Grassi and Feletti, 1890.