(Redrawn after Soulsby 1968)
The morphological stages of Eimeria resemble those of Plasmodium, but occur within a single vertebrate host. The sporozoite is the infective stage and is specialized to infect the epithelial cells that line the intestinal tract. Within an epithelial cell the sporozoite transforms into a schizont that produces numerous merozites, which in turn reinfect new epithelial cells. There are a limited number of cycles of asexual reproduction. In a controlled infection it is possible to identify first, and second generation schizonts. The third round of infection produces gametocytes. Fertilization occurs within the vertebrate and an oocyst is produced. This oocyst differs from that of Plasmodium in that it secretes a resistant membrane around itself to provide protection when it is passed in the feces, but it still produces sporozoites within. The sporozoites, however, remain inside until the oocyst is ingested by a new host.