Now, when we go from our blastula to our gastula, what begins to happen is these blue cells that are part of the inner cell mass not only undergo cell differentiation, they don't only form two different types of cells, but they also begin to move away from one another. And to move away from one another, they have to detach from one another. And to detach from one another, what must happen is these morphogens must bind onto the cell membrane, causing the breakdown of these special types of cell membrane molecules known as cell adhesion molecules. And by decreasing the amount of cell adhesion molecules between these cells, these cells are able to actually detach from one another and they can move away from one another once they actually detach. And so, by decreasing the amount of cell adhesion molecules, we can eventually form these two structures. So remember, this eventually forms the Umbilical vesicle, also known as our yolksack.