Editing Invagination (section)

===Tunicate gastrulation===
In [[tunicates]], invagination is the first mechanism that takes place during gastrulation. The four largest [[endoderm]] cells induce the invagination process in the tunicates. Invagination consists of the internal movements of a sheet of cells (the endoderm) based on changes in their shape. The blastula of the tunicates is a little flattened in the [[vegetal pole]] making a change of shape from a columnar to a wedge shape. Once the endoderm cells were invaginated, the cells will keep moving beneath the ectoderm. Later, the blastopore will be formed and with this, the invagination process is complete. The blastopore will be surrounded by the [[mesoderm]] by all sides.<ref name="Sinauer Associates Inc">{{cite book |last1=Gilbert |first1=Scott |url=https://archive.org/details/embryologyconstr0000unse |title=Embryology, Constructing the Organism |last2=Rauno |first2=Anne |date=1997 |publisher=Sinauer Associates |isbn=0-87893-237-2 |location=Sunderland, Massachusetts |language=en |url-access=registration}}</ref>