ancestors of all the life that exists on earth to-day after a period of evolution lasting hundreds of millions of years. This would account for the origin of life upon the Earth, but not of life in general. The germs, which travel as carriers of life from an older heavenly body to a younger one, must have sprung from parents, and however far back we trace their genealogical tree we are always finally faced by this dilemma: either life did, after all, originate at one time from something lifeless, and what has happened once must be able to happen again, now and always; or life never originated at all, but has always existed; it is eternal like matter, in forms whose variety we cannot even dimly grasp, its threads, having neither beginning nor end, wind through eternity. Of these two assumptions the latter is incomparably more in harmony with our present-day views on the universe. We believe the matter of which the universe is built up to be everlasting. It costs no great effort to believe life to be eternal too. True, the idea of eternity is inconceivable to us; it is a dim conception which has given rise to a word, a tone picture which portrays something indefinite, but within the bounds of the inconceivable there is room for both semi-obscurities, the everlastingness of matter and the everlastingness of life. But the most enigmatical point in the riddle of life is not life itself, which is a form of being, and is neither more nor less comprehensible than the existence of an inanimate object, of a stone, of water, of the air; it is consciousness. Descartes proves his own existence to himself by the fact that he thinks. Life must be accompanied by consciousness in order to convince the living being that it exists. The formula: "_cogito ergo sum_" has been admired for hundreds of years. It certainly is specious. But how many questions it leaves unanswered! Has it the right to deny life to an entity that does not conceive itself? Must it not be completed by the proof that life without thought, that is, without consciousness, does not exist, that consciousness is the necessary complement of life? And, above all, ought not Descartes to have given us an explanation of what thought and consciousness are?