Angioblasts are embryonic cells from which the endothelium of blood vessels arises. They are derived from embryonic mesoderm. Blood vessels first make their appearance in several scattered vascular areas that are developed simultaneously between the endoderm and the mesoderm of the yolk-sac, i. e., outside the body of the embryo. Here a new type of cell, the angioblast, is differentiated from the mesoderm.