1. The spores of Eimeria (not the oocysts) are the real infective agents and, as in other Sporozoa, they readily set free their sporozoites in the duodenum or in vitro under suitable conditions.

2. The protective oocyst has double walls: the ectocyst is thick and impervious to fluids but easily fractures by mechanical means, such as drying. Even though cracked, it may continue to protect the thin endocyst and spores until they reach the specially muscular regions of the alimentary canal. Free spores are probably also sometimes ingested.

3. The ectocyst is a continuous envelope without a persistent micropyle. It resembles keratin in many ways.