I'm getting a vibe that this comes across as implausible. So I'd like to add that the skin, central nervous system, and interior layer of the gut are all fundam

I'm getting a vibe that this comes across as implausible. So I'd like to add that the skin, central nervous system, and interior layer of the gut are all fundamentally ectodermal epithelia. Both the gut and CNS arise in development through invagination and pinching off. First the gut, and later the neural tube, which becomes the spinal cord and brain. And amusingly, in deuterostomes (vertebrates and their kin), the invagination point (blastopore) becomes the anus :)