A crescent-shaped band of lightly pigmented cytoplasm visible on the surface of the fertilized eggs of certain amphibians, including frogs’ eggs. It develops opposite the point of entry of the sperm, due to rotation of the outer (cortical) layer of cytoplasm relative to the inner cytoplasm. The grey crescent contains cytoplasmic factors (e.g. catenins) that are essential for subsequent embryonic development, and certain cells in the grey crescent move inward to form the dorsal lip of the gastrula, the site of Spemann’s organizer.