The symbol shown in the illustration is...

The Ouroboros is an ancient symbol depicting a serpent or dragon eating its own tail. Originating in ancient Egyptian iconography, the ouroboros entered western tradition via Greek magical tradition and was adopted as a symbol in Gnosticism and Hermeticism and most notably in alchemy. The genus of the armadillo girdled lizard, Ouroborus cataphractus, takes its name from the animal's defensive posture: curling into a ball and holding its own tail in its mouth.