The names of these three all-important layers are derived from their position: the outer layer is called ectoderm, the inner layer endoderm, and the middle layer mesoderm. Ectodermformsmuch of the outer part of the body (the skin) and the nervous system. Endoderm, the inside layer, forms many of the inner structures of the body, including our digestive tract and numerous glands associated with it. The middle layer, the mesoderm, forms tissue in between the guts and skin, including much of our skeleton and our muscles. Whether the body belongs to a salmon, a chicken, a frog, or a mouse, all of
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