part_of part of part of develops from develops from ends during starts during ectoderm mesoderm tail region tail bud UBERON:0002533 XAO:0000107 xenopus_anatomy tailbud Rapidly proliferating mass of cells at the caudal extremity of the embryo. Its formation is reflected in a caudal carving of the posterior portion of the archenteric canal at NF stage 22. With its further outgrowth, the postanal gut primordium becomes stretched. Its lumen is in broad communication with the hindgut at NF stage 25. multi-tissue structure NF stage 25 NF stage 66