part of female reproductive gland embryo hatching gland A transversely oriented set of cells located deep to the enveloping layer on the pericardial membrane, especially prominent during pharyngula period because of the brightly refractile cytoplasmic granules (containing hatching enzymes) of the principal cells of the gland; The fish hatching gland is a unicellular holocrine gland. Although it has recently been found that the precursors or immature forms of the gland cells considerably migrate in the embryonic body during development (see later), the final location of the hatching gland cells in fish is generally restricted to anterior and/or dorsal regions of a well-grown prehatching embryo. In medaka, the final location is somewhat unique: The giant gland cells are mostly localized in the inner surface of the buccal (or pharyngeal) cavity. BTO:0000558 BrendaTissueOBO pharynx