In the West, the Ouroboros originated in Egypt  around 1600 B.C.,  but many other cultures have this same symbol that predates its Egyptian counterpart.  The name Ouroboros is Greek, meaning "devouring its tail."  In the broadest sense, the Ouroboros represents the continuity of life,  and it symbolizes the primeval, anarchic dynamism preceding creation of the cosmos and emergence of order. 
The continuous destruction of life, and the continuity of life, and its cyclical nature connect in the Ouroboros. In this way, it encapsulates the complexities of life into a singular fact: Life eats life and sheds away the generations.
The Ouroboros is a dragon biting or swallowing its own tail.  The individual Ouroboros might have the description of another Dragon Type, such as Lindorm or Wyvern, but its depiction with its tail in its mouth is what separates it as an Ouroboros.
Figure 1. Ouroboros woodcutting.
History of the Ouroboros
The Ouroboros appears all over the world in many different cultures. With its origins in Africa, specifically in Egypt,  the Ouroboros became introduced to Greece, and later Northern Europe, likely through trade.  Norse Mythology absorbed the Ouroboros as Jormungand, the Midgard Serpent, whose symbolism is counter to that of the Ouroboros. 
Perhaps the most notorious usage of the Ouroboros remains that of the Alchemists. The most famous depiction of the Ouroboros comes from the Alchemist Cleopatra's Chrysopoeia ('Gold-making').  Other Alchemists use the Ouroboros to represent mutable matter. 
Alchemy and the Ourobors
The Codex Marcianus is one of the oldest alchemical texts created in Hellenistic Egypt, cited to exist in the eleventh century A.D. but sometimes indicated to be dated back to the second century A.D. because it is a collection of the earliest surviving Greek alchemical texts.
The Ouroboros in the Codex Marcianus is depicted as half-white and half-black. Other alchemical manuscripts, including a Venetian manuscript, depict the Ouroborus in this same way.  The coloration alludes to successive counterbalancing of opposites, similar to the meaning of the Yin Yang. 
The Alchemist Cleopatra uses this particular depiction to symbolize day and night.  The black half symbolizes the Night, the Earth, the destructive forces of nature, and yin.  The light half represents Day, Heaven, the creative/generating forces of nature, and yang. 
The Cross is the antithesis of the Ouroboros, which represents the primeval, anarchic dynamism preceding creation of the cosmos and emergence of order.  Thus, the close relationship between the cross and the sword, as both of them are wielded against the primordial monster. 
Ouroboros the Symbol
The particular expression of the black/white Ouroboros evokes layered symbolism, the union between the chthonian (beneath the earth) and the celestial (above the earth) principles.  The serpent and the darkness represent the chthonian principle; the bird and the light represent the celestial principle. The winged dragon also represents this combination, this balance, between what lies below and what lies above.
In some depictions, the Ouroboros is marked with the caption HEN TO PAN, meaning 'The One, The All.' 
The Gnostics say that the universal serpent passes through all things and represents the unchanging law, which moves through all things, linking them with a common thread or bond. 
The Ouroboros represents a truly self-sufficient Nature in a primitive sense; it symbolizes the possibility of parthenogenesis or self-fertilization. 
As a circular depiction of an already potent symbol, the Ourboros represents time,  particularly eternity,  and is a symbol of infinity.  As a symbol of the cycle-like nature of the universe, which begins and ends with chaos, but presents with some element of order and peace in between. 
Another vantage point is that the Ouroboros is a symbol of eternal return, the descent of the spirit into the physical world and its return.  Nature continually returns with its cyclical patterns of the seasons back to its own beginning;  thus, each ending carries the seed of the next beginning.  In this way, the Ouroboros embraces all cyclical systems: unity, multiplicity, and return to unity; evolution and involution; birth, growth, decrease, death, etc. 
- Rose [Dragons] 282
- Ouroboros Connections. Link Defunct: <http://abacus.best.vwh.net/oro/ouroboros.html>
- What is Ouroboros?
- Spira Solaris and the Universal Ouroborus
- Cirlot 246
- Cirlot 247
- Herder 207
- Herder 208
- Cirlot 15
- Cirlot 48
- Cirlot 71
For more information on footnotes and references, please see the bibliography.