ing of the piano to sit by the player, and sometimes jumps into her lap or on the key-board of the instrument. I know of a dog, too, in a family in Berlin, which comes in in like manner when there is music, often from distant rooms, opening the door with his paw. I knew of another dog, usually thoroughly domestic, which occasionally played the vagabond for love of music. Whenever the semi-annual mass was celebrated in the city he could not be kept at the house. As soon as the so-called Bergknappen, which were accustomed to play at this time in the streets, appeared, he would run away and follow them from morning till evening.
Evidently neither cats nor dogs, nor other animals that listen to human music, were constituted for the appreciation of it, for it is not of the slightest use to them in the struggle for existence. Moreover, they and their organs of hearing were much older than man and his music. Their power of appreciating music is therefore an uncontemplated side-faculty of a hearing apparatus which has become on other grounds what we find it to be. So it is, I believe, with man. He has not acquired his musical hearing as such, but has received a highly developed organ of hearing by a process of selection, because it was necessary to him in the selective process; and this organ of hearing happens also to be adapted to listening to music.
It can not be said that this has been produced in man by natural breeding, or that it may not have been formed previous to the human period. We know nothing of our direct predecessors; and, even if their remains should be found, the bony parts of the organs of hearing in their skulls would furnish no clew to the microscopic particulars of the soft parts with which they were covered during life. It is, however, most probable that the precursors of man had nearly the same organs that he has now; for the living caricatures of men, the apes, have them in nearly the same perfection. We have a right to assume this, although we have not such detailed examinations of these organs as Hasse and Retzius have given us of similar organs in other mammals. We can not determine whether the compass of the scale audible to apes is quite as large as that of men; but we are authorized to presume that it is about the same. The power of perceiving the intervals between musical tones depends on a complicated apparatus in the coil of the ear. This apparatus, called, after its discoverer, the organ of Corti, includes thousands of nervous hair-cells, each of which is excitable only by a single tone of definite pitch. The delicacy of one's auditory apparatus—the correctness of Helmholtz's interpretation of the significance of these organs being presupposed—depends on the number of these hair-cells. According to the exact measurements and enumerations of Retzius, there are 15,500 of them in the ear of man, 12,500 in that of