A.J. Kirchweger
Annulus Patonis (Aurea Catena Homeri)
1781; reprinted Berlin, 1921

'The One, the All', as in the Codex Marcianus, for instance, of the 2nd century A.D. It has also been explained as the union between the chthonian principle as represented by the serpent and the celestial principal as signified by the bird (a synthesis which can also be applied to the dragon). Ruland contends this proves that it is a variant of the symbol for Mercury - the duplex god. In some versions of the Ouroboros, the body is half light and half dark, alluding in this way to the successive counterbalancing of opposing principals as illustrated in the Chinese Yin-Yang  symbol for instance. Evola asserts that it represents the dissolution of the body, or the universal serpent which (to quote the Gnostic saying) 'passes through all things'. Poison, the viper and the universal solvent are all symbols of the undifferentiated-of the 'unchanging law' which moves through all things, linking them by a common bond. Both the dragon and the bull are symbolic antagonists of the solar hero. The Ouroboros biting its own tail is symbolic of self-fecundation, or the primitive idea of a self-sufficient Nature - a Nature, that is which, à la  Nietzsche, continually returns, within a cyclic pattern, to its own beginning. There is a Venetian manuscript on alchemy which depicts the Ouroboros with its body half-black (symbolizing earth and night) and half-white (denoting heaven and light).