164 The Animal Mind 



observation probably influenced these results. Loeb found 

 that severing the auditory nerve or removing the statoliths 

 from the dogfish caused the fish to incline toward the operated 

 side and to roll the eyes in that direction (238). Total 

 extirpation of one labyrinth in the perch was observed by 

 Bethe to make the fish curve toward the affected side. The 

 fish Scardinius showed a tendency to curve toward the 

 opposite side (27). Lee's experiments on the dogfish showed 

 a very definite relation between the position of the canal 

 operated upon and rolling movements of the fish. Cutting 

 the front canals caused the fish to dive forward, cutting the 

 rear canals made it dive backward, and cutting the canal 

 on either side made it roll over toward that side. A natural 

 explanation of this behavior is to suppose that the absence 

 of stimulus from the cut canal produces the same effect that 

 rolling the fish in the opposite direction, and thus diminish- 

 ing the pressure of the fluid in the canal, would produce. 

 The fish " feels as if" it were being rolled over, and makes 

 movements to regain its equilibrium. When the nerves 

 supplying the ears on both sides were cut, the fish became 

 perfectly indifferent to its position and would float upside 

 down without any effort to right itself. The vestibule and 

 otoliths of the fish ear are thought by Lee to be concerned 

 with statical equilibrium; that is, with the maintenance of 

 position while the fish is at rest, while the canals are concerned 

 with balance during motion (dynamic equilibrium) (230). 

 It may be added that experiments on the sea horse indicate 

 that destruction of the labyrinths in this animal has no effect 

 on equilibrium: the upright attitude is due to the position 

 of the air bladder and is assumed even by dead animals (139). 

 That vision may materially aid in maintaining equilibrium 

 in vertebrates is indicated by evidence from various sources, 

 among others, the observation of Bigelow that goldfish in 



