Blastopore

Blastopore, the opening by which the central cavity of an embryo, when in the blastosphere (q.v.) stage, communicates with the exterior. This may persist either as the mouth in most worms and molluscs, or as the anus in Serpula (q.v.) and the limpet; or as both mouth and anus in some sea anemones (e.y. Peachia); or it may be closed entirely, and the permanent openings formed elsewhere; or, as in the case of insects, it may never be formed at all.