HEARING. 437 



slender nervous filaments, like the clapper of a 

 bell, and probably performing an office ana- 

 logous to that instrument; for, being thrown into 

 a tremulous motion by every undulation of the 

 surrounding fluid, they will strike against the 

 membrane, and communicate similar and still 

 stronger impulses to the nerves by which they are 

 suspended, thus increasing the impression made 

 on those nerves. The mechanical effect of an 

 apparatus of this kind is shown by the simple 

 experiment, mentioned by Camper, of enclosing 

 a marble in a bladder full of water, and held in 

 the hand ; when the slightest shaking of the 

 bladder will be found instantly to communicate 

 motion to the marble, the reaction of which on 

 the bladder gives an unexpected concussion to 

 the hand. 



The ear of Fishes contains, in addition to the 

 vestibule, the three semicircular canals, which 

 are in general greatly developed.* An enlarged 

 view of the membranous labyrinth of the Lophius 

 piscatorius is given in Fig. 403, showing the form 

 and complication of its parts, which are repre- 

 sented of twice the natural size. x, y, z, are 

 the semicircular canals, with their respective 

 ampullae (a, a, a). m is the Sinus mediamis^ or 

 principal vestibular sac, with its anterior ex- 



* In the lamprey, these canals exist only in a rudimental state, 

 appearing as folds of the membrane of the vestibule; and there 

 are also no cretaceous bodies in the vestibular sac. 



