It lies in the nature of this mechanism that the subjective image is not identical with the objective original, but is modified and even distorted by the panes through which it penetrates to the inner being of the organism. What the subject perceives is never anything but a symbol of the object, never the object itself; but this symbol suffices to enable the consciousness to form an idea of the object, just as letters enable the reader to take in words and thoughts. We must conceive the development of consciousness to go hand in hand with that of the senses. The more windows the organism can open to the outer world the more easily and the more clearly does its image penetrate. The number of objects which the subject can take in is the measure of the perfection of its consciousness. The protista, lacking specific sense organs and possessing only the general sensitiveness of protoplasm, can form only to a very limited extent and with very little variety an inner realization of the stimuli of the outer world. Its consciousness is necessarily very restricted and exceedingly dim. Consciousness is enlarged and grows clearer as the organism develops and its general sensitiveness is differentiated into specific senses, until we reach the level of man whose consciousness embraces far more of the outer world than does that of any other living creature; because, lacking new senses, he has succeeded in amplifying and enlarging those he possesses, and has by artificial means made himself capable of perceiving stimuli to which he is not directly susceptible and which therefore would have remained unknown to him; to a certain extent he has translated them into a form which his senses can perceive.