Late Gastrulation
The blastocoel is obliterated and the embryo becomes surrounded by ectoderm. The endoderm has been internalized and the mesoderm has been positioned between the ectoderm and endoderm. While the mesodermal cells that enter through the dorsal lip of the blastopore give rise to the dorsal axial structures (notochord and somites), the remainder of the body mesoderm enter through the ventral and lateral blastopore lip (they form the heart, kidneys, blood, bones, etc.). A portion of the dorsal ectoderm is specified to become neural ectoderm. This region of the embryo is called the neural plate which will go on to form the neural tube through the process of neurulation.