COMPENSATORY MOTIONS AND THE SEMI- 

 CIRCULAR CANALS 



BY 



BENJ. C. GRUENBERG 



With Two Figures 



1 Reactions of the frog to movements of rotation 447 



2 Theories of the function of the semicircular canals 448 



3 Theoretical objections to the semicircular canal hypothesis 450 



4 Experimental objections to the hypothesis 452 



5 Analysis and new experiments 453 



6 Summary 461 



7 References and bibliography 463 



I REACTIONS OF THE FROG TO MOVEMENTS OF ROTATION 



When a frog is slowly turned in a horizontal plane by moving 

 or rotating the vessel in which the frog is at rest the animal turns 

 its head in a direction opposite to that of the rotation. When 

 the rotation has proceeded beyond a certain point, the frog will 

 jerk the head back into alinement with the body, and then again 

 turn it in the opposite direction, and so on, as long as the rotation 

 is continued. The existence of this back-jerk or "nystagmus" 

 is specifically denied by von Cyon ('97, pp. 45, J^) and by Lyon 

 (1899, p. 86), and has been overlooked by other observers. When 

 the frog is restless or active, it will frequently jump or walk in a 

 direction opposite to that of the rotation, bringing the head and 

 body into alinement; then turn the head again and follow this 

 movement with a jump, and so on, while the rotation is continued. 

 But when the frog is fairly quiet, there is always a back-jerk. 



When the vessel containing the frog is tilted on a transverse 

 horizontal axis, the animal nods its head up or down, according 

 as the rotation is upward or downward anteriorly. When the 

 base upon which the frog rests is tilted on the longitudinal (hori- 

 zontal) axis — too slowly to dislodge the animal — the movements 



The Journal of Experimental Zoology, vol. iv, no. 3. 



