Text: The ear is the organ of hearing, in other words, the organ for the appreciation of sound, i.e., of vibrations of the air or water. All that is necessary to form an ear is a nerve-mass capable of appreciating these vibrations. Its simplest actual expression is a sac, filled with fluids, containing "otoliths", and ear, and a stone, and supplied with a nerve, a condition best exemplified in the sub-kingdom of Mullusca, represented familiarly by the oysters, the mussels, snails both terrestrial and aquatic, and the octopus. The "otoliths" are masses of carbonate of lime, as may readily be seen by placing one of them dissected out from any of the above mentioned animals (e.g. a snail) on a glass slide, covering it with an object glass with sufficient water to fill the interspace between the two, and adding at the side of the covering glass a drop of any acid (acetic acid, or indeed ordinary vinegar will do very well) while the experimenter observes it through the microscope. Air bubbles ‹ really bubbles of carbonic gas ‹ will be seen to pour out from the otolith, and when these have ceased, that body will have entirely disappeared. It is true that we are suspicious of a specialized organ of hearing even in such animals as possess no specialized nerve system. This is somewhat apparently of a paradox, for it may be asked, How can an animal without nerves feel at all? and is it not highly improbable that if no nerve system exists, any special sense-organ can be developed? The answer to the first of these objections is very plain: all animals, even those who possess no specialized organs whatever manifest the simple phenomena of sensation; all, even the Infuroria and the Amoeba, of which we hear so much now-a-days, and which are very little more than simple masses of protoplasm, manifest this faculty. Any one who has observed these occupants of almost any drop of water, with a microscope of low power, will have seen enough to convince himself of this. As to the second objection, the fact remains that in some animals which have no undoubted nerves, in some medusa or jelly-fish, we find in the mass forming their body crystals of carbonate of lime, which substance must intensify the vibrations of the water in which they live, and must, when put into a state of motion as a whole, or into one which affects its particles inter se, cause by its relative density greater disturbance of the soft matter in which it lies, than would be the case if it were absent. But leaving this as somewhat problematical, and taking the hearing organ of molluscs as the type, we shall find this type essentially adhered to in the higher animals in spite of endless complications. Let us propound the bold paradox without fear of contradiction, that a man as well as a snail hears in water, and that the essential parts of his marvellous hearing apparatus are a sac containing fluid in which are otoliths, and around which are distributed the ultimate filaments of a nerve.

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