The Two Contraries is an important concept in alchemy. It is much like the Western version of the Chinese Yin and Yang. Each Contrary exhibits characteristics opposite to the other.

One side, represented by the white, feathered dragon, is the bright, active (hence the open mouth), masculine side. It is associated with fire, the sun, and the element of Sophic Sulfur (the yellow background). The other side, represented by the black, scaly, legged dragon, is dark, passive, and feminine, and linked to water, the moon, and the element of Sophic Mercury (grey-blue background).
Although they are opposites, they are never one without the other, with the two dragons biting each other's tails, forming a ring, a constant dance that creates reality as we see it.