And let's begin with the ectoderm. Now, the ectoderm is the outer layer. It's the external layer of that developing embryo, as we'll see in just a moment. And that ectoderm gives rise to the integumentary system of the human body and that includes the outer portion of the skin, the ears, the nails and the hair. Now because of an invagination process. As we'll see in just a moment, a portion of that ectoder makes its way into that developing embryo.