... the early embryo (blastos a bud); hence:— Blastoderm: skin (derma) or enclosing layer of the embryo. Blastosphere: the embryo in the hollow sphere stage. Blastula: same as preceding. Epiblast: the outer layer of the embryo (ectoderm). Hypoblast: the inner ... — The Evolution of Man, V.1. • Ernst Haeckel