We can conclude from the passage that ………..

The ear in humans and most other mammals consists of three parts: the outer, middle, and inner portions. The outer ear, found in varying shapes in different species, is the structure commonly called the ear. The middle ear is an air-filled chamber containing the eardrum. The inner ear alone contains the sensory receptors for hearing, which are enclosed in a fluid-filled chamber called the cochlea. The middle and outer ears serve only to receive and amplify sound waves and occur only in amphibians and mammals, whereas the inner ear is present in all vertebrates.