I do not overlook any of the difficulties which my attempt to explain consciousness leaves untouched. On all sides the most urgent and disquieting questions arise. Above all, the fundamental question, the most enigmatic of all: how is an external stimulus, that is a movement, a vibration, converted into a sensation, a perception? Further: must we in the consciousness distinguish between the frame and its contents, the conceptual mechanism and the concept? Or do the two coincide? Is there no consciousness without a conceptual content? And is it the movement entering into the organism, the inner realization of the outer world which, transmuting itself in an incomprehensible manner into a concept, creates consciousness, becomes consciousness? Is the consciousness of the man standing upon the highest plane of intellectuality the greatest consciousness possible? Does there exist anywhere in the universe a more abundant, perhaps an infinitely more abundant consciousness than that of human beings on the Earth, and will the latter ever rise to this height? It is obvious that a development is in progress. There was a time when the most comprehensive, the clearest consciousness on earth was that of the trilobite or the cephalopod. Evolution has gone as far as man. Does it stop at that or will it continue? According to Herbert Spencer evolution is progress from the simple to the complicated. Let us accept this definition. Have we the right to set up a scale of values and place the complicated above the simple? Is the latter not the more perfect because it has more power of resistance, greater durability, and can hold its own triumphantly against all destructive influences? Is not evolution, then, a retrogression from the perfect, because simple, to the more complicated, and therefore more fragile, more easily upset and less capable of resistance to harm? Is it not sheer egocentrism if we appraise the value of living beings according to their greater or less resemblance to ourselves, and judge them to be less or more worthy in proportion to their disparity with us? Are the fish which, living in the sea wherein we cannot exist, can inhabit the greater part of the globe, are wild duck which fly, swim and walk, not more perfect than we, who have had to conquer the air and the water by artificial means? Is not the mouse's hearing sharper than ours? The eagle's sight keener? The dog's scent incomparably more delicate? Has not the carrier pigeon an infinitely better sense of locality than we have? Are not many beasts physically stronger, more nimble and agile than man? His only claim to superiority rests on the greater perfection of his consciousness. Why do not all living creatures participate equally in the evolution to which this superiority is due? Why does it not take place in every organism and lead the unicellular living being in an unbroken ascent to the level of Goethe or Napoleon, or to a still