The process in which a gastrula develops from a blastula by the inward migration of cells .
由于细胞向内移动囊胚形成胚囊或肠胚的过程。
Embryonic stem cells are cells extracted from the blastula , the very early embryo , that have an exceptional ability to duplicate in vitro , that is in a test tube , and to become cells of almost any tissue .
