Yolk plug

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

The yolk plug looks like a patch of large cells on the surface of the early embryo, known as the blastula. These cells are important because they help shape the embryo as it grows. Over time, the yolk plug gets pulled inward in a process called epiboly, which is part of the careful steps that let the embryo develop healthily. Understanding the yolk plug helps scientists learn about the growth and development of many living things.