Each Borg drone was assigned to a specific Borg alcove within the vessel they were assigned to, while specific alcoves could be interchanged with certain modifications, the central alcove however was meant only for the Queen. This chamber held the biological components of the Queens upper torso and head for regeneration while a mechanical lower half body was assembled and attached when the Borg Queen emerges. Typically however her emergence only occurred when the situation was deemed necessary. (Star Trek: First Contact; VOY: "Dark Frontier")