develops from start stage end stage hatching gland hgg A transversely oriented set of cells located deep to the EVL 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. zebrafish_anatomy ZFA:0000026 TAO:0000026 polster embryonic structure segmentation:10-13 somites hatching:pec-fin