_k_ shows one of these in the act of being fertilized by the entering spermatozooen.

The differentiation into male and female forms takes place in the blood, the further development of the sexual cycle within the mosquito.] If a mosquito of the species _anopheles_ bites the affected person, it obtains a large amount of blood which contains many parasites.

Within the mosquito the parasite undergoes a further development into male and female sexual forms, which may also form in the blood, termed respectively _microgametocyte_ and _macrogamete_.
From the microgametocyte small flagellate bodies, the male sexual elements _microgametes_ or _spermatozoa_, develop and fertilize the _macrogametes_; after fertilization this develops into a large body, the _ooecyst_ which is attached to the wall of the stomach of the mosquito.

Within the ooecyst, innumerable small bodies, the sporozoites, develop, make their way into the salivary glands and are injected into the individual who becomes the prey of the mosquito, and again the cycle of development begins.

The presence of the parasite within the mosquito does not constitute a disease.