 He enlists Tarzan, and a fabulous airship is constructed to penetrate Pellucidar via the natural polar opening connecting the outer and inner worlds.The airship is crewed primarily by Germans, with Tarzan's Waziri warriors under their chief Muviro also along for the expedition.In Pellucidar Tarzan and Gridley are each separated from the main force of the expedition and must struggle for survival against the prehistoric creatures and peoples of the inner world.