The documentary Women in Boxes, spearheaded by Blaire Baron Larsen, is a springboard for pondering the deeper significance of magicians placing their assistants in boxes.  As performers, the duos likely have no idea what archetypal stories they're playing out.  But something profound is going on, in light of the renowned psychologist Erich Neumann, a trailblazer in feminine psychology and the Great Mother archetype of world mythology.  Applying Neumann's insights to stage magic, the prototypical female assistant symbolizes the anima -- that part of the psyche connected to the world of the subconscious -- the soul, if you will.  The anima can be human or animal (hence the great tradition of women magically transforming into tigers).  The prototypical male magician symbolizes the hero archetype on a quest toward individuality.  In order to be truly creative, the magician's masculine world of ego consciousness must make a link to the feminine assistant's world of the soul.  Through "sawing a lady in half," the magician tries to divide the anima, not so much to conquer her but to understand her like a scientist.  He tries to contain the anima in a box, not to imprison her but to accommodate, encompass, and give definite form to her curvaceous amorphousness.  Indeed, there's nothing inherently "sexist" about the roles of stage magician and assistant; the two form a single personality struggling to become integrated.  (Read more of Neumann's wisdom in his indispensable The Origins and History of Consciousness.  Here's a link to Camille Paglia's profile of Neumann).