part of ends during starts during embryo primary germ layer A layer of cells produced during the process of gastrulation during the early development of the embryo, which is distinct from other such layers of cells, as an early step of cell differentiation. The types of germ layers are the endoderm, ectoderm, and mesoderm. XAO:0003011 germ layer embryonic germ layer xenopus_anatomy UBERON:0000923 tissue NF stage 10 NF stage 66