Editing Ontogeny (section)

=== Blastulation ===
After the zygote has become an embryo, it continues dividing into a hollow sphere of cells, which is a [[Blastulation|blastula]]. These outer cells form a single epithelial layer, the blastoderm, that essentially encases the fluid-filled inside that is the blastocoel. The figure to the right shows the basic process that is modified in different species. Blastulation differs slightly in different species, but in mammals, the eight-cell stage embryo forms into a slightly different type of blastula, called a blastocyst.<ref>{{Cite web |title=blastula {{!}} biology {{!}} Britannica |url=https://www.britannica.com/science/blastula |access-date=2022-04-08 |website=www.britannica.com |language=en}}</ref> Other species such as [[Starfish|sea stars]], [[frog]]s, [[Chicken|chicks]], and [[Mouse|mice]] have all the same structures in this stage, yet the orientation of these features differs, plus these species have additional types of cells in this stage.<ref>{{Cite web |title=Blastulation {{!}} Cleavage and Early Development {{!}} Principles of Development {{!}} Continuity and Evolution of Animal Life |url=https://biocyclopedia.com/index/general_zoology/blastulation.php |access-date=2022-04-08 |website=biocyclopedia.com}}</ref>
[[File:Blastula.png|thumb|457x457px|Blastula to gastrula more detailed]]