The organ of hearing and balance - in real fish is represented only by the inner ear — a membranous labyrinth with pronounced three mutually perpendicular semicircular channels. There are no ear openings, outer ear, eardrum, and the cochlea is weakly expressed. The membranous labyrinth is enclosed in the cartilaginous or bony auditory capsule of the back of the skull. Its cavity is filled with endolymph, in which "auditory" stones float — otoliths, three on each side of the head. The upper part of the auditory organ with semicircular channels is the vestibular apparatus, while its lower part is associated with the reproduction and perception of sounds.