Emboly Movement - Involution
It denotes turning in or rolling over. Involution of mesodermal blastomeres has been observed in Amphioxus, reptiles, monotremes, amphibians, buds, and even in some eutherian mammals. Throughout gastrulation in the amphibians the blastomeres situated on the margin of the lip of blastopore roll over the lip (involute) to turns into internal. In the bird embryo the cells situated on the posterior margin of the blastoderm roll over (involute) to from the lower layer termed as the hypoblast and the presumptive mesodermal and endodermal cells situated on the surface of the blastoderm reach the interior by turning in by the groove of the primitive streak.