Anatomical and SEM-studies of the brood-chambers (ovicells) in two bryozoans (Callopora dumerilii and C. lineata) were undertaken to resolve a long-term controversy existing in the literature about the origin of the ovicells. In contrast with the interpretation of Silén (1945), both species investigated possess hyperstomial ovicells with the ooecium formed by the distal (daughter) zooid. The ooecial coelomic cavity communicates with the zooidal coelom through a pore-like canal or canals remaining after the closure of an arch-shaped slit. The slit forms during ovicellogenesis. The communication canals are normally plugged by epithelial cells, however incompletely closed canals were also found in Callopora lineata. SEM-studies of noncleaned, air-dried specimens showed a relationship between membranous and calcified parts during early ovicellogenesis. It starts from a transverse wall as the calcification of the proximal part of the daughter zooid frontal wall, and has the shape of two flat rounded plates. There are no knobs or any other outgrowths. Conditions and phenomenology of hyperstomial ovicell formation are discussed.