So let's take a cross section of the gastrola stage of embryological development. We get the following diagram. So let's begin with these out of those cells known as the Trophy Blast cells. Now, these Trophy Blast cells eventually give rise to the coriane and the placenta while all these inside cells, inner cells, make up the three different germ layers. And all these germ layers eventually give rise to all the different structures and organs and tissues and systems found inside that adult human individual. So let's focus on the inner mass, on the inner portion of this gastrula.