The monkey, unicorn and lion represent the three types of soul, mercury, or alchemical energy within the initiate:

Monkey - Nephesh - animal soul - Brute Mercury
Unicorn - Ruach - intellectual/emotional soul - Metallic Soul of the Sperm
Lion - Neshamah - spiritual soul - Mercury Fecundated by Fire: the Kundalini

Man and woman in Gemini represent the alchemical couple, or the couple working with the three types of mercury. This also represents how the perfect matrimony must conquer the three types of soul in order to become the androgynous being represented above, the superior two types of soul in Kabbalah: Yechida (Hebrew: "Unity") and Chaiah (Hebrew: "Life").

This is accomplished by working with the Heliogabalus Stone, upon which the monkey and around which the other two animals stand. This stone has nine sides, and within the center of the stone is the symbol of Gemini: the duality of the sexual force, Male-Female, Iod-Chavah, Adam-Eve, or Jupiter (IO-Patar): I (Ignis: fire, man), O (Origo: spirit, woman) and Patar: the stone of PTR, Peter. These two polarities, Od and Obd, Ida and Pingala, when combined through alchemy, form the unity of Christ above, the winged angel who conquers the infinite.

Man and woman establish the unity of Kether, אהיה אשר אהיה Eheieh Asher Eheieh, "I Am Become Who Becomes," through the proper performance of the sexual act. The Lord establishes His becoming, His initiation, His "life" (Chaiah) and "unity" (Yechida) within us through our cooperation in the magisterium of fire. By harmonizing sun (man) and moon (woman) we can give birth to the Chariot of Ezekiel, the Chariot of War of the Seventh Arcanum.

As for the origin of this piece of art, I do not know. It was definitely composed by an initiate who knew and practiced alchemy.