HEARING IN THE LOWER ANIMALS. 835 



which the spider returns to get the right direction. Further- 

 more, the extreme delicacy of the threads, the tension of which is 

 augmented by the weight of the spider, informs her of disturb- 

 ances of distant origin, which, are communicated only by the air 

 and arrested by this light screen. Boys's spider glided along the 

 thread toward the tuning-fork, as the spider did for Reclain's 

 violin solo, and came back when Boys touched a point of the web 

 with, the tuning-fork. This experiment sufficiently explains the 

 musical interest that led the Leipsic spider to the violin whose 

 vibrations reached it. But at the first tutti or concerted crash the 

 whole room trembled, including the web, and our spider ascended 

 precipitately. 



To a web-making spider, the regular trepidation or oscillatory 

 vibration, which is sound to us, means simply a struggling prey 

 to be taken ; a spider placed upon a table approaches the source 

 of a sound quite automatically. Sound, as we define it in the 

 sense of a continued sensation, is a dead letter to it. Forel has 

 remarked that insects continue insensible to the sound of the 

 voice if we interpose a screen before the mouth and cut them off 

 from the disturbance of the air. When animal nature acquires 

 the sense of sound as the extreme limit of its perceptions it is to 

 suffer itself to be fascinated, hypnotized, and charmed like the 

 serpent. That continued fixed sensation is to the serpent what 

 the fixity of its look will be to the bird which it will smite in its 

 turn. It is an extreme perception, exceedingly troubling, and 

 away at the extremity of physiological equilibrium, a source of 

 sensorial inhibition, extra-cerebral. 



Fishes, which have the power of orientation through the re- 

 markable development of the canals of the labyrinth and their 

 lateral organs directed to all points of their liquid horizon, with 

 such susceptibility to trepidation and disturbances that they per- 

 ceive the slightest, are only deaf-mutes. I have studied, in my 

 thesis on the Auricular Sense in Space, the transformation of the 

 sense of disturbance into a hearing sense, and the mechanism of 

 auricular orientation in the whole animal series. I only say that 

 all animals possessing the otolithic apparatus in any of its forms 

 perceive, of disturbances of the medium, the intensity, the direc- 

 tion, and the number only, but can not convert them into continu- 

 ous sensations like those we call sounds. All the experiments and 

 observations invoked as making manifest that invertebrates have 

 hearing only prove the perception of disturbances and tremors, 

 more or less rhythmical modifications of the ambient medium. 

 Of what use would be the perception of sounds in mediums where 

 hardly any sounds are produced ? The mollusk fastened to its 

 rock recognizes the approach of a prey or an enemy ; it feels the 

 waves breaking upon it; it usually lives on a well-conducting 



