In the life cycle of the coccidium E. stiedai in the epithelial cells of the bile ducts of rabbits, uni- and multinucleate merozoites were seen undergoing endodyogeny. Results confirm that endodyogeny is a primary and fundamental process of asexual reproduction in the Coccidia, and that schizogomy is a secondary process which has developed from endodyogeny. This theory is important with regard to the taxonomy of the Sporozoa.