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How does a blastula transform into a gastrula?

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embryos of different animals — Animal development The embryos of many animals appear similar to one another in the earliest stages of development and progress into their specialized forms in later stages.

The transformation of a blastula—a hollow, single-layered ball of cells—into a gastrula is a critical phase of animal development known as gastrulation. This process involves the dramatic reshuffling of cells to establish the three primary germinal layers: the ectoderm, mesoderm, and endoderm.12

In many species, this transformation occurs through invagination, where one side of the blastula pushes inward, similar to pressing a finger into a rubber ball. This movement converts the spherical embryo into a double-walled cup. The cells that move to the interior form the endoderm and mesoderm, while the cells remaining on the exterior become the ectoderm. This process creates a new internal cavity called the archenteron, or primitive gut, while reducing or eliminating the original blastocoel.12

Gastrulation methods vary across species due to factors like yolk content. For example, some embryos utilize epiboly (the spreading of cells) or the migration of individual cells into the interior. In mammals, gastrulation involves the migration of cells through a structure called the primitive streak.324