When female Anopheles sucks the blood of an infected person, the gametocytes of Plasmodium are picked up by the mosquito. Now sexual reproduction of Plasmodium occurs inside mosquito. The outer envelope of gametocyte is dissolved and its contents are liberated into the cavity of gut. These contents then undergo gametogony, i.e., formation of microgametes and macroagamete. The nuclei of both fuse and a synkaryon or zygote is formed. This zygote is motionless and spherical for sometime but becomes motile, elongated and vermiform very soon. Now, it is called vermicule or ookinete. Ookinete pierces the stomach wall and forms a cyst (oocyst) on its outer surface which has about 10000 sporozoites. The latter pass into salivary glands of the mosquito.