410 THE BODY AT WORK 



discrimination of tones of high frequency musical tones. 

 Their ears serve equally to inform them of the changes in 

 position of their heads and of the tremblings of the sea. The 

 shocks transmitted through the sea are near akin to the 

 slower vibrations of sound, if the fishermen of the Mediter- 

 ranean are justified in their practice of beating a wooden 

 clapper which rests upon the seat of the boat as they row 

 backwards and forwards in front of a curved net. They 

 believe that the fish are frightened by the noise ; but it matters 

 little whether we describe the fish as hearing a noise, or as 

 feeling the percussions of the clapper conducted through the 

 water. To the more rapid vibrations of the clapper, the fish 

 are probably insensitive. The cochlea, which we have every 

 reason for regarding as the organ by which sound is analysed, 

 is not possessed by fishes. It makes its first appearance in 

 reptiles. Birds, it is evident, are able to distinguish musical 

 tones. Their cochleae are very short, and are destitute of 

 " rods of Corti." For a moment this appears surprising, 

 but it must be remembered that the range of tones which any 

 bird discriminates is very short, however nicely it may value 

 the notes within its range. In mammals the ear is clearly 

 divided into three parts, to which the three functions which 

 have grown out of the specialization of the sense of touch are 

 allocated. (1) The semicircular canals are concerned with 

 the sense of orientation. (2) The utricle and saccule rever- 

 berate to noise the rumbling of trains, the boom of guns, 

 the beats of dissonant musical tones. We do not know how 

 to classify the agitations of the atmosphere which surrounds 

 us and of the earth on which we stand, nor can we point with 

 any certainty to the groups of stimuli which for us have 

 taken the place of the grinding of stones on the beach and 

 slapping of rocks by waves. (3) The organ of Corti in the 

 cochlea discriminates and analyses musical sounds. To these 

 three sense-organs, which are situate in the inner ear, certain 

 structures are accessory. 



The concha, which enables a horse or a cat to collect sound 

 and to localize its source, is in ourselves merely an ornament 

 to the side of the head. 



The external meatus is a curved tube, about an inch long. 

 Frequently a tuft of hairs guards its entrance. The wax 



