EFFECTS OF DISLOCATION OF EYE UPON GOLDFISH. 67 



seen in such animals. He says that the unbalanced tonus and 

 innervation of the trunk, eye and fin muscles (Ewald) can explain 

 satisfactorily these forced motions. But he admits that this 

 tonus factor is also influenced by the geotropic function of the 

 labyrinth. 



Although different authors describe somewhat differently the 

 after-effects of labyrinth extirpation (this may be due to difference 

 in technique, injury of other cranial organs, etc.), all seem to 

 agree on the point that the geotropic function of the labyrinths is 

 responsible for normal orientation and equilibrium. 



No other factor has been considered to play an important part 

 in this behavior. Dogfish in which both labyrinths were removed 

 as observed by Maxwell (8), could hardly be seen to differ from 

 that of the normal fish except when greatly excited. The} 7 swim 

 quietly around or settle on the bottom in normal position. 

 Maxwell raised the question whether the orientation of labyrinth- 

 less fish is due to retinal stimuli, but his experimental results 

 showed to him that visual impulses did not play a role in the 

 orientation of his operated fish. When he covered each eye with 

 a large patch of heavy, black, rubber cloth, the animal swam 

 about w r ith good orientation and never came to rest on the bottom 

 in an abnormal position. This goes to show that in nature 

 chronic or permanent tilting of the body of the fish occurs only 

 from unilateral injury of the labyrinths and never from eye 

 injuries. When both labyrinths are removed there remains no 

 mechanism on which gravity can act in the way to induce orienta- 

 tion, according to Loeb. 



In our fish the labyrinths were normal and the otoliths should 

 have taken care of the normal position in swimming or at rest. 

 Nevertheless the tilting of the body took place, as described. 

 Evidently the influence of the labyrinth was modified by a new 

 factor of vision. This factor is probably the influence of the visual 

 field on the orientation mechanism. 



As long as the vision was impaired by the trauma of the oper- 

 ation, no tilting of the body was noticed. The question is, 

 whether this tilting is a phototropic reaction, a "forced" reaction 

 or due to attempts of the animal to keep its usual visual field. 

 Maxwell admits the possibility of such a mechanism, of course in 

 a different type of experiment: "When the dogfish is rotated 



