| Gastrulation in its broadest sense is the reorganization of the cells of the blastula to form a multilayered embryo, the gastrula. |
| A lot of research has gone into answering that, and determining the earliest stage at which the blastula breaks symmetry. |
| They migrate along the inner face of the blastula wall to form a ring in the vegetal region and lay down calcareous skeletal rods. |
| At blastula stage 8, cells forming the blastocoelic roof were cultured in isolation as explants. |
| At this stage, the blastula is in the form of a hollow sphere with radial symmetry. |
| The nucleus must be taken from the blastula and gastrula stages of frog embryos. |
