Answer
On the 8th day after fertilization , the embryoblast( inner cell mass) differentiates into two layers--the epiblast (facing the endometrium), and the hypoblast( facing the blastocoel). The hypoblast gives rise to the primitive endoderm; the primitive ectoderm develops from the epiblast.
Work Step by Step
Together, primitive endoderm and primitive ectoderm form the bilaminar embryonic disc. Later in development, a cavity --the amnionic cavity--opens up between the layers of the bilaminar embryonic disc.
