Ouroboros, ancient Egyptian symbol. The black lower part symbolized the destructive force of nature, Night, Earth, or yin whereas the white upper half represents the generative and creative force, Day, Heaven, or yang. It is symbolic of the cyclic nature of the universe where creation begins after destruction and life springs from death. In a way, the serpent eating its own tail is symbolic of renewal. As an alchemical glyph, it represented purification.