Final answer:
The vestibular, tympanic, and cochlear ducts of the mammalian inner ear are filled with perilymph.
Step-by-step explanation:
True. The vestibular, tympanic, and cochlear ducts of the mammalian inner ear are filled with a substance called perilymph. Perilymph is a clear fluid that helps transmit vibrations and pressure waves within the ear. It is similar in composition to cerebrospinal fluid.