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Gastrulation refers to the integrated migration of cells and tissues of prospective endodermal and mesodermal areas to their definite positions inside the interior of the embryo. We can study gastrulation in amphibians by taking the example of frogs. In frogs, gastrulation involves the following three types of morphogenetic movements:

• Invagination- The marginal endodermal cells present at the future dorsal side of the embryo sinks into the embryo, thereby forming a slit-like blastopore. These cells then change their shape and become flask-shaped.
• Involution- The marginal cells turn inward and travel along the inner surface of the outer cells sheets when they reach the tip of the blastopore. The involuting cells compose blastophore lip.
• Epiboly- In this, the blastopore develops lateral lips and finally a ventral lip. The remaining patch of the endoderm called the yolk plug too is eventually internalized.

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