Question

The infolding of the Xenopus dorsal blastopore lip, regression of Hensen's node in chickens, and the formation of the hypoblast in Zebrafish by the embryonic shield all use which mode of gastrulation?

Involution

Invagination

Epiboly

Ingression

Delamination

Answer 1

Ingression.

Ingression is the movement of individual cells from the outside of the embryo into the interior during gastrulation.

During the regression of primitive streak in chick, While mesodermal ingression continues, the primitive streak starts to regress, moving Hensen's node from near the center of the area pellucida to a more posterior position. As the node moves posteriorly, the notochord is laid down, starting at the level of the future midbrain. While the anterior portion of the notochord is formed by the ingression of cells through Hensen's node, the posterior notochord forms from the condensation of mesodermal tissue that has ingressed through the primitive streak.