Yolk plug

The yolk plug is an important part of how some animals, like frogs, grow from tiny eggs into their early forms. It is made from special cells called endodermal cells. It appears during a key time when the embryo forms a structure called the dorsal lip of the blastopore. This happens in amphibians, like frogs, toads, and salamanders.

The yolk plug looks like a patch of large cells on the surface of the early embryo, called the blastula. These cells help shape the embryo as it grows. Over time, the yolk plug moves inward in a process called epiboly. This is one of the steps that help the embryo develop healthily. Learning about the yolk plug helps scientists understand how many living things grow and develop.