In fact, modern psychology can only advance by means of observation and experiment, which constitute it one of the natural sciences; and this is abundantly proved by the modern English schools, and the experimental school in Germany. Yet observation of the states of consciousness taken alone is defective, unless it is enlarged by the comparative examination of a greater number of subjects; nor must ethnical peculiarities be passed over, and it is precisely these which are included in the comparative psychology of peoples. The large amount of results, their infinite variety, and at the same time a certain uniformity in their modes of beginning, of their development, and of their place in the universe, give a splendid illustration of the innate exercise of human thought; the likenesses as well as the contrasts are instructive as to its real nature. The comparative psychology of peoples, studied from this point of view, certainly does not include the whole of psychological science, which requires other instruments and other modes of experience, but it is a great help as a foundation. We believe that the study of myth, which throws so much light on comparative psychology, is likewise of use for the special psychology of man, since this can only arise from individual and ethnical observation, and from experiment, dissociated from every hindrance, and from metaphysical prejudice. And if by our humble essay we can throw any light on this noble science, we shall be abundantly rewarded. CHAPTER II. ANIMAL SENSATION AND PERCEPTION. All animals communicate with each other and with the external world through their senses, and by means of their perception, both internal and external, they possess knowledge and apprehension of one another. In the vast organic series of the animal kingdom, some are better provided than others with methods, instruments, and apparatus fit for effecting such communication. The senses of relation are not found in the same degree in all animals, nor when such senses are the same in number are they endowed with equal intensity, acuteness, and precision. But the fundamental fact remains the same in all cases; they communicate with themselves and with the external world through their senses.