56 THOUGHTS UPON THE MUSICAL SENSE [X. 



order that these animals might perceive music, for such an 

 experience confers absolutely no advantage in the struggle for 

 existence. Besides, the animals and their auditory organs are 

 far older than man and his music. The faculty of hearing 

 music possessed hy these animals must be an incidental ac- 

 cessory power possessed by an auditory apparatus which 

 assumed its present form under the operation of other causes. 



Now I believe that it is the same with man. Man, too, did 

 not acquire his power of hearing music as something by itself, 

 but he received, by processes of selection, a very delicate and 

 highly elaborate auditory organ ; for this organ has been 

 necessary in the struggle. And furthermore, it so happens 

 that this organ can also be used for hearing music. By the 

 assertion that the auditory organ of man was produced by 

 natural selection, I do not mean to imply that it was not 

 already formed in the pre-human period. We have never 

 found the direct ancestors of man, and even if we were fortunate 

 enough to meet with their remains it would be impossible to 

 make out the minute microscopic structure of the soft tissues 

 which, during life, covered the osseous parts of the auditory ap- 

 paratus deeply buried in one of the bones of the skull. But it is 

 most probable that our direct ancestors possessed an auditory 

 organ nearly similar to that which we possess to-day ; for in 

 the living caricatures of men, the apes, it reaches almost the 

 same degree of perfection. It must be admitted that there are 

 no researches into the minute details of the ape's ear hke those 

 of Hasse and Retzius on the auditory organ of certain other 

 Mammalia. Hence we cannot decide whether the length of the 

 scale which can be heard by an ape is as great as that heard by 

 a man ; but we may assume that it is nearly the same. 



The power of appreciating the interval between musical notes 

 depends, as we know, upon a wonderfully complex apparatus 

 placed in the so-called cochlea. This structure called after its 

 discoverer, Corti's Organ, consists of thousands of cells which 

 form the terminations of auditory nerve-fibres : each cell can 

 only be made to vibrate by a single note of a certain pitch. 

 This is brought about by the fact that each cell rests upon part 

 of an elastic membrane of microscopic delicacy which passes 

 across the cavity of the cochlea, just as upon a stretched string 

 which only vibrates with a particular note. If Helmholtz's in- 



