fig8

Figure 8. Blood islands begin as solid mesenchymal cell clusters aggregated within the yolk sac mesoderm. Structurally, they consist of flattened endothelial progenitor cells surrounding primitive hematopoietic progenitor cells. AM: Amnion; YS: yolk sac; CS: connecting stalk; YS.Endo: yolk sac endoderm; YS.Mes: yolk sac mesoderm. Image created by Adobe Illustrator.