Caduceus.

n. The wand of Hermes, or Mercury, the messenger of the gods. A cosmic, sidereal, or astronomical symbol; its significance changing with its application. Originally a triple-headed serpent, it is now a rod with two serpents twined around it, and two wings at the top. As a medical insignia it may appear as a rod surmounted by a ball, representing the Solar orb, and a pine cone, representing the pineal gland. The entwined white and black serpents represent the struggle between good and evil – disease and cure. Another form is the Thyrus, often pictured in the hands of Bacchus. Astronomically, the head and tail represent the Nodes – the points on the ecliptic where Sun and Moon meet in an eclipse. v. Aaron’s Rod.

DeVore, Nicholas. Encyclopedia of Astrology. New York: Philosophical Library, 1947.