Answer:
In a frog embryo, gastrulation E) proceeds by involution as cells roll over the dorsal lip of the blastopore.
Step-by-step explanation:
Gastrulation is key because during it, cell movements result in a massive reorganization of the embryo from a simple spherical ball of cells, the blastula, into a multi-layered organism. Also many of the cells at or near the surface of the embryo move to a new, more interior location. It involves changes in cell motility, cell shape, and cell adhesion.