The Animal Mind 



insects, as evidenced by a tendency to creep from horizontal 

 planes up vertical ones, was observed by Loeb (420). In 

 light the eyes of insects have probably much to do with 

 maintaining equilibrium. Certain aquatic insects, in ex- 

 periments where the light was made to strike them only 

 from below, as soon as they left the support on which they 

 were resting, turned themselves upside down (622). 



56. Orientation to Gravity: Vertebrates 



It has long been known that in vertebrates the static 

 function resides in the ear, and especially in the semicircular 

 canals (e.g. 103, 165, 229, 263). Various experimenters 

 have noted that operations on the ears of fishes disturb the 

 equilibrium of these animals. Sewall, indeed, found that 

 section of the semicircular canals in the shark had no effect 

 on its balancing powers, although operations on the vesti- 

 bule and ampullas did disturb movement (669) ; and 

 Steiner got no effect on equilibrium from removing the 

 contents of the labyrinth (692). Errors in method and 

 observation probably influenced these results. Loeb found 

 that severing the auditory nerve or removing the statolith 

 from the dogfish caused the fish to incline toward the 

 operated side and to roll the eyes in that direction (424). 

 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 (48) . 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 



