5.3. Involution: Within embryo inward rolling of an epithelial sheet to form an underlying layer or cell sheet's inturning above the basal surface of the outer layer.

What is involution during gastrulation?

Involution. During involution, a tissue sheet rolls inward to form an underlying layer via bulk movement of tissue. ... As material moves in from the edges of the sheet, material originally at the sites of inward rolling (shown in blue here) is free to move further up underneath the exterior tissue.

What is invagination and involution?

Invagination; here, a fold is created in the epithelial cells by the mesoderm folding inwards to form the blastopore, which then takes the mesoderm further inwards as the fold deepens. ... Involution; here, the progenitor mesoderm and the endoderm cells cluster as a tissue around the blastopore.