preceded by blastula stage gastrula stage UBERON:0000109 gastrula XAO:1000005 Embryonic stage during which gastrulation takes place, with a proportion of cells migrating below the surface of the embryo to form two inner layers (endoderm and mesoderm) and the cells which remain outside spreading over the whole surface of the embryo to form the ectoderm; comprising Nieuwkoop and Faber stages 10 to 12.5. xenopus_developmental_stage embryonic stage