The shadow
Sex and the life instincts in general are, of course, represented in Jung's system. They are a part of an archetype called the shadow. It derives from our prehuman, animal past, when our concerns were limited to survival and reproduction, and when we weren't self-conscious.
It is the "dark side" of the ego, and the evil that we are capable of is often stored there. Actually, the shadow is amoral – neither good nor bad, just like animals. An animal is capable of tender care for its young and vicious killing for food, but it doesn't choose to do either. It just does what it does. It is "innocent." But from our human perspective, the animal world looks rather brutal, inhuman, so the shadow becomes something of a garbage can for the parts of ourselves that we can't quite admit to.
Symbols of the shadow include the snake (as in the garden of Eden), the dragon, monsters, and demons. It often guards the entrance to a cave or a pool of water, which is the collective unconscious. Next time you dream about wrestling with the devil, it may only be yourself you are wrestling with!