The ookinete produced after fertilization of the Plasmodium macrogamete penetrates the gut of the mosquito and transforms into an oocyst. Within the oocyst, thousands of sporozoites form. The sporozoites eventually burst free and migrate to the salivary glands, where they await inoculation into the vertebrate host.
This photo shows a section of the gut of an infected mosquito. The small cells above and below the lumen are epithelial cells while the larger spheres (arrows) are oocysts. At this stage of development, the oocysts are multinucleated but have not yet completed the development into sporozoites.