The amoeba has no exterior senses. It is an almost homogeneous mass, and yet it is sensible to almost the same sensorial impressions as the highest mammal. It feeds (smell and taste); it moves (sense of space, touch); it is sensible to light, at least to certain rays (sight); its environment being in perpetual movement, ceaselessly traversed by sonorous waves, it doubtless reacts to these vibrations (hearing). Perhaps, even, it possesses, without special organs, senses which we lack, and which we recover only by study and analysis, such as the chemical sense, which judges the composition of a body, declares it assimilable or counsels its rejection. The exercise of all these senses denotes, first of all, a very long heredity. They have, doubtless, been acquired successively only, unless, the absence of one of them being capable of causing death, their presence is the strict consequence of the life of this humble beast. But it is useless to construct any hypotheses on the subject. It is enough to keep to the fact, and this fact is the existence of a being without differentiated organs, that is to say, a being all of whose parts are equally adapted to react against every external excitation. Why these reactions? They are one of the conditions of life. But could not life be conceived without them? It is possible. It is a question of environment. If the amoeba's environment were homogeneous and calm, if it were of a constant temperature and luminosity, if it furnished an abundance of proper nourishment, if, in a word, the animal dwelt in an alimentary bath, no reactions would be necessary, and its only movement would be to open its pores for food, to reject the excess of this food, to divide itself, when swollen, into two amoebas. Why, then, does it possess all these senses which, though unorganized, are perfectly real? Because the environment obliges it to have them, because of its instability. The senses, whether differentiated, or spread over the entire surface of a living form, are the creation of the environment which--light, sound, material exteriority, odours, etc.--acts in accordance with different discontinuous manifestations. Constant or continuous, they would be without effect. Discontinuous, they make themselves felt. Discontinuous light has created the eye, just as the drop of water creates a hole in granite.