spatially Determined Reactions 191 



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 

 suppljdng 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 static equiUbrium ; that is, with the maintenance of 

 position while the fish is at rest, while the canals are con- 

 cerned with balance during motion (dynamic equilibrium) 

 (416). 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 assiuned even by 

 dead animals (251). 



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 

 which the nerves supplying both ears had been cut recovered 

 after two or three weeks and could swim quite normally 

 except when they were placed in a large body of water and 

 made to swim rapidly, when they showed no power of pre- 

 serving their balance (54). Their successful performance 

 of slower movements was very Ukely due to the use of 

 sight. 



Sensory impulses from the body muscles themselves un- 

 doubtedly cooperate with those from the semicircular canals 

 in the maintenance of balance. They are evidently in- 

 volved in the peculiar withdrawing movements by which 

 land animals, even puppies, kittens, and young rats whose 



