Amphibian Gastrulation: Quick Overview
1.Gastrulation begins at the future dorsal side, below the equator (marginal zone) when prospective endodermal cells (bottle cells) invaginate and form a slit (blastopore). The bottle cells line the early archenteron.
2. The marginal zone cells undergo involution at the dorsal lip of the blastopore.
3. After the bottle cells, the next cells that enter the embryo form the prechordal plate (head mesoderm), and the mesoderm of the notochord.
4. Simultaneously, the animal cells undergo epiboly, completely surrounding the surface of the embryo until a ventral lip of the blastopore forms.
5. The last endodermal cells on the surface appear as the yolk plug.
6. The yolk plug is eventually covered by ectoderm.
*Image source: www.luc.edu/depts/biology/ dev/amphgut.jpg