Editing Gastrulation (section)

===Overview===
In [[amniote]]s (reptiles, birds and mammals), gastrulation involves the creation of the blastopore, an opening into the [[archenteron]]. Note that the blastopore is not an opening into the [[blastocoel]], the space within the [[blastula]], but represents a new inpocketing that pushes the existing surfaces of the blastula together. In [[amniotes]], gastrulation occurs in the following sequence: (1) the [[embryo]] becomes [[asymmetry|asymmetric]]; (2) the [[primitive streak]] forms; (3) cells from the [[epiblast]] at the [[primitive streak]] undergo an [[Epithelial-mesenchymal transition|epithelial to mesenchymal transition]] and [[ingression (biology)|ingress]] at the [[primitive streak]] to form the [[germ layers]].<ref name=Arnold />