Mechano- and Equilibrium-Reception 



521 



don does not take place, and drowning results. The other circumstance 

 is falling through air. A normal cat always lands on its feet regardless of 

 its position at the instant of falling, by executing a series of righting re- 

 actions while in the air. A bilaterally labyrinthectomized animal cannot 

 right itself during a fall.-^' ^'-^ Bilaterally labyrinthectomized pigeons-^" eventu- 

 ally regain some ability to fly, only, however, when there is no interference 

 with vision. These observations seem to indicate that higher animals can, 

 under most circumstances, compensate for the loss of both labyrinths. 



0. 



Fig. 191. The ampulla and semicircular canal photographed in the living state (pike) 

 before and during angular acceleration. B, oil droplet in canal before acceleration; C, oil 

 droplet during acceleration; h, position of cupula before acceleration; c, position of cupula 

 during acceleration. After Dohlman, from Fulton.™ 



The question naturally arises, "Where does the labyrinthectomized 

 animal obtain the sensory information necessary for orientation?" The 

 answer to this question has been supplied largely through the investigations 

 of Magnus"'^ and has been excellently reviewed by Evans.^^ Labyrinthec- 

 tomized dogs and cats orient their heads well when supported in air by the 

 pelvis, f^owever, if these animals are blindfolded under similar circum- 

 stances, no orientation of the head takes place. In rabbits and guinea 

 pigs, renowned for their lack of visual righting reflexes, no orientation 

 of the head takes place, even without blindfolding. These experiments 

 indicate that vision is an important adjunct to labyrinthine function in 

 orientation. If a labyrinthectomized rabbit is held in the air by the pelvis. 



