Editing Ontogeny (section)

=== Gastrulation ===
After blastulation, the single-layered blastula expands and reorganizes into multiple layers, a gastrula (seen in the figure to the right). [[Reptile]]s, [[bird]]s and [[mammal]]s are triploblastic organisms, meaning the gastrula comprises three [[germ layer]]s; the endoderm (inner layer), mesoderm (middle layer), and ectoderm (outer layer).<ref name="Muhr-2022" /> As seen in the figure below, each germ layer will become [[Cell potency|multi-potent stem cells]] that can become a specific tissue depending on the germ layer and is what happens in humans. This [[Cellular differentiation|differentiation]] of germ layers differs slightly, because not all of the organs and tissues below are in all organisms, but corresponding body systems can be substituted in place of these.<ref>{{Cite journal |last=Leptin |first=Maria |date=2005-03-01 |title=Gastrulation Movements: the Logic and the Nuts and Bolts |journal=Developmental Cell |language=English |volume=8 |issue=3 |pages=305–320 |doi=10.1016/j.devcel.2005.02.007 |issn=1534-5807 |pmid=15737927|doi-access=free }}</ref>