Vestibular apparatus is present in the ear. It forms the labyrinth of the inner ear in association with the cochlea. This apparatus is responsible for balance and sense of orientation of the body in the air. It consists of 3 semi-circular canals, the base of which consist of the ampulla, and otolith organ, which consist of utricle and saccule which have a projecting ridge called macula. When the body is oriented in a different form in the darkness or absence of light, the apparatus helps to know about the orientation. Thus, the correct answer is option D.