And of the simple elements two only, air and water, go to form sense organs (for the pupil is made of water, the organ of hearing is made of air, and the organ of smell of one or other of these two, while fire is found either in none or in all warmth being an essential condition of all sensibility and earth either in none or, if anywhere, specially mingled with the components of the organ of touch; hence it would remain that there can be no sense organ formed of anything except water and air); and these sense organs are actually found in certain animals.