In a certain sense, the true science of man, rational anthropology, takes precedence of every other science. The saying of the ancient sage, "Man, know thyself," and that other famous maxim, "Man is the measure of all things," have been accepted and applied from all time. And yet this science--taking it in its widest sense--has languished longer than all other sciences in the fetters of tradition and superstition. We saw in the first section how slowly and how late the science of the human organism was developed. One of its chief branches--embryology--was not firmly established until 1828 (by Baer), and another, of equal importance--the cellular theory--until 1838 (by Schwann). And it was even later still when the answer was given to the "question of all questions," the great riddle of the origin of man. Although Lamarck had pointed out the only path to a correct solution of it in 1809, and had affirmed the descent of man from the ape, it fell to Darwin to establish the affirmation securely fifty years afterwards, and to Huxley to collect the most important proofs of it in 1863, in his _Place of Man in Nature_. I have myself made the first attempt, in my _Anthropogeny_ (1874), to present in their historical connection the entire series of ancestors through which our race has been slowly evolved from the animal kingdom in the course of many millions of years. CONCLUSION The number of world-riddles has been continually diminishing in the course of the nineteenth century through the aforesaid progress of a true knowledge of nature. Only one comprehensive riddle of the universe now remains--the problem of substance. What is the real character of this mighty world-wonder that the realistic scientist calls Nature or the Universe, the idealist philosopher calls Substance or the Cosmos, the pious believer calls Creator or God? Can we affirm to-day that the marvellous progress of modern cosmology has solved this "problem of substance," or at least that it has brought us nearer to the solution?