Yolk plug 

Yolk plug is the remaining patch of endodermal cells that is created during the formation of the ventral lip of the blastopore. It is a patch of large endodermal cells which remains exposed on the vegetal surface of the amphibian blastula that will eventually be internalized by epiboly.

 This amphibian article is a stub. You can help Wikipedia by expanding it.
 This developmental biology article is a stub. You can help Wikipedia by expanding it.