And this is where that organism of the fetus will actually be found, as we'll see in just a moment. Now, we also have this extension of the Trophy Blast, this purple section that will develop into the coriane and ultimately into the placenta. Now, when we go from diagram three to diagram four, something important takes place. We form something called the mesoderm. So that's the middle layer of that developing embryo. And these are the retails, as shown in this diagram.