has part has part has_part existence starts during existence ends during female germ cell nucleus zygote stage blastula stage embryonic structure blastodisc AAO:0000043 germinal disc BTO:0001504 gastrodisk TAO:0001175 ZFA:0001175 UBERON:0004749 BTO:0000494 germ disc Wikipedia:Germinal_disc embryonic disc NCIT:C34150 A small, circular, white spot (approximately 2-3 mm across) on the surface of the yellow yolk of an egg that has been laid. The nucleus of the egg is in the germinal disc.