GEOTROPISM IN ANIMALS 189 



phenomena described under I are observed, only in a greater 

 degree. If both auditory nerves are cut the phenomena 

 described under II set in. 



V. If the otoliths are removed from one side and the 

 auditory nerve is cut upon the other, the animal behaves as 

 those described under II ; with this difference, however, that 

 the eyes of the animal are turned about the longitudinal 

 axis of the animal toward that side where the auditory nerve 

 is cut. 



Also, as regards the so-called forced movements which 

 are not considered in this paper the animal behaves as if 

 it had been operated upon only on one ear, namely, that whose 

 auditory nerve is cut. 



VI. A shark whose head has been cut off, and which, as 

 is well known, still swims, is no longer forced to assume a 

 definite orientation toward the center of the earth. When 

 laid upon its back it no longer attempts to reassume its 

 accustomed position with its ventral side downward. 



The disturbances in the geotropic orientation which fol- 

 low the cutting of the auditory nerve have thus far contin- 

 ued for a month. 



These observations, it seems to me, prove that the geo- 

 tropic phenomena observed in the shark are dependent upon 

 the inner ear, and support the assumption of Breuer and 

 Mach that they are called forth by the otoliths. 



But we can determine how the inner ear forces an ani- 

 mal to maintain a certain position with reference to the 

 horizontal as little as the botanists can explain how geotropic 

 curvatures are called forth in plants. We can only say, in 

 harmony with Goltz, 1 or Mach and Breuer, that the animal 

 comes to rest only under a certain arrangement of strain and 

 pressure in the peripheral ends of both auditory nerves. 

 This arrangement exists in the shark when the animal turns 



i GOLTZ, Pfliigers Archiv, Vol. III. 



