252 RECENT PROGRESS OF THE THEORY OF VISION. 



simple manner certain peculiarities which have been 

 observed in the perception of musical notes, peculiarities 

 as enigmatical as those we have been considering in 

 the eye. In the cochlea of the internal ear the ends 

 of the nerve fibres lie regularly spread out side by side, 

 and provided with minute elastic appendages (the rods 

 of Corti) arranged like the keys and hammers of a piano. 

 My hypothesis is, that here each separate nerve fibre is 

 constructed so as to take cognizance of a definite note, to 

 which its elastic fibre vibrates in perfect consonance. 

 This is not the place to describe the special characters of 

 our sensations of musical tones which led me to frame 

 this hypothesis. Its analogy with Young's theory of 

 colours is obvious, and it refers the origin of overtones, 

 the perception of the quality of sounds, the difference 

 between consonance and dissonance, the formation of the 

 musical scale and other acoustic phenomena to as sim- 

 ple a principle as that of Young. But in the case 

 of the ear, I could point to a much more distinct 

 anatomical foundation for such a hypothesis, and since 

 that time, I have been able actually to demonstrate the 

 relation supposed ; not, it is true, in man or any verte- 

 brate animals, whose labyrinth lies too deep for experi- 

 ment, but in some of the marine Crustacea. These animals 

 have external appendages to their organs of hearing 

 which may be observed in the living animal, jointed fila- 

 ments to which the fibres of the auditory nerve are dis- 

 tributed ; and Hensen, of Kiel, has satisfied himself that 

 some of these filaments are set in motion by certain notes, 

 and others by different ones. 



It remains to reply to an objection against Young's 

 theory of colour. I mentioned above that the outline of 

 the coloiu'-disc, which marks the position of the most 

 saturated colours (those of the spectrum), approaches to a 

 triangle in form ; but our conclusions upon the theory of 



