The purple cells are the cells that make up the trophy blast. And the trophy blast eventually forms the coriane as well as the placenta. Now, these are the three different germ layers. We have the green cells that make up the endoderm. We have these red cells that make up the mesoderm and we have these blue cells that make up our actoderm. Now, the endoderm is the germ layer that eventually forms the epithelial layer of our digestive tract as well as the lungs, our liver and our pancreas and other structures such as the thyroid and parathyroid glands and the thymus.