Eimeria oocyst

The fertilized macrogamete of Eimeria leaves the epithelial layer and forms an impervious cyst wall. It is now called an oocyst. At this stage it is unsporulated. Once deposited in the feces of the host, it will sporulate in a few days and then be infective to another host.

This photo shows sections through about seven oocysts of Eimeria stiedae in the bile duct of a rabbit. A few gametocytes are also visible. The oocysts appear wrinkled, but this is a fixation artifact. The oocyst wall is so resistant that normal histological fixatives do not readily penetrate and the wall collapses. This property also helps the oocyst resist environmental stresses.