If the gametocytes, which are globular, or in the pernicious or malignant tertian parasite crescentic (fig. 81), gain access to the intestine of an Anopheline,[199] they mature. The macrogametocytes extrude a part of their nuclear substance (fig. 80, _13a_, _14a_) and thereby become females or macrogametes. The microgametocytes, on the other hand, undergo repeated nuclear division, preparation for this being made apparently whilst in the blood of man. This results in the formation of threadlike bodies which move like flagella and finally detach themselves from the residual body (fig. 80, _13b_, _14b_). These are the males or microgametes[200] (fig. 80, _15b_). [199] Schizonts ingested about the same time perish in the intestine of the mosquito. [200] If the microgametocytes are sufficiently mature the formation of microgametes occurs in the blood of man as soon as it is taken from the blood-vessel and has been cooled and diluted. Such a stage is called a _Polymitus_ form, and the process has been called “exflagellation.” Copulation takes place in the stomach of the Anopheline (fig. 80, _16_). A microgamete penetrates a macrogamete and coalesces with it. The fertilized females elongate very soon and are called oökinetes or “vermicules” (figs. 80, _17_; 82). They penetrate the walls of the stomach, pierce the epithelium (fig. 80, _18_, _19_), and remain lying between it and the superficial stratum (tunica elastico-muscularis). Then they become rounded and gradually develop into cysts which grow larger and are finally visible to the naked eye, being called oöcysts (figs. 80, _20_-_24_; 83). Their size at the beginning is about 5 µ, the maximum that they attain is 60 µ, only exceptionally are they larger. [Illustration: FIG. 83.--Section of the stomach of an _Anopheles_, with cysts (oöcysts) of the malignant tertian parasite. (After Grassi).] The sporulation (figs. 80, _21_-_25_; 84), which now follows, begins with repeated multiple fission of the nucleus. Long before the definitive number of nuclei, which varies with the individual, is attained the protoplasm, according to Grassi, begins to segment around the individual large nuclei but without separating completely into cell areas. According to Schaudinn, however, there is a condensation of the outstanding protoplasmic strands. It is certain that the number of nuclei increases with simultaneous decrease in size. They soon appear on the surface of the strands or sporoblasts, surround themselves with some cytoplasm and then elongate (fig. 84). In this manner the sporozoites are formed and break away from the unused remains of the cytoplasmic strands of the sporoblasts (fig. 80, _26_). The number of the sporozoites in an oöcyst varies from several hundreds to ten thousand.