The Sun (Male) on the left (Anima) as opposed to the moon (Female) on the right (Spiritus). The Hieros Gamos (Sacred Marriage) is the uniting (Coniunctionis) of the opposing elements, opposing thoughts, opposing doctrines, all opposites will become One. This is what is called "The Great Work." The two spheres on the inside of each of these, (the sun and moon) are the "Sulphur Philosophorum"
The sexual symbolism of the Toad can also be found outside alchemy, which strengthens our argument. On the great painting of Hieronymus Bosch The Garden of Earthly Delights, on its right wing, there is a figure of a woman with a toad on her breast which symbolizes the sin of debauchery.