And to see what we mean, let's take a look at the following diagram. So this is basically our blastula stage. So we have the trophy blast cells and we have these inner cell mass that are shown in blue. 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.