S. S. MAXWELL 131 



side or back, but a vigorous specimen usually rights itself on the 

 bottom of the tank. In other words the geotropic reactions of the 

 animal are definitely and completely lost; the stereo tropic reaction 

 is retained. 



CONCLUSION. 



The results of my experiments show that the assumption of a 

 sharp differentiation of function between the otolith-bearing, vestib- 

 ular portions of the labyrinth and the semicircular canals is not 

 justified by the facts. Between the effects of extirpation of the one 

 and of the other set of sttuctures there is more resemblance than 

 contrast. They certainly reenfo^ce each other, for the reactions 

 produced by either one alone are always slower and less vigorous 

 than when both sets of organs are intact. It would not, however, 

 be safe to affirm that the functions are identical. In one respect a 

 difference is apparent; namely, in the response to rotation in a hori- 

 zontal plane. If the ampullae are uninjured, compensatory move- 

 ments occur when the animal is rotated around its dorsoventral 

 axis. I have never seen this reaction in the absence of the ampullae 

 of the horizontal canals. 



SUMMARY. 



1. A dogfish from which all six ampullae have been removed main- 

 tains its equifibrium; the righting reactions occur promptly; compen- 

 satory movements of the eyes occur in response to rotations in all 

 planes except the horizontal; the compensatory position of the eyes is 

 retained if the animal is held in an abnormal position. Both the 

 static and dynamic functions of equihbrium continue, therefore, after 

 complete removal of all the semicircular canals and all the ampullae. 



2. After complete removal of the otohths from the vestibules with- 

 out injury to the ampullae the animal maintains its equihbrium in 

 the water, rights itself promptly, and makes compensatory motions 

 to rotations in all planes. If held in an abnormal position the com- 

 pensatory position of the eyes is maintained. Both static and 

 dynamic functions of equihbrium continue. 



3. Destruction of both the semicircular canals and the otoHth organs 

 completely aboHshes all compensatory movements and equihbrium 

 reactions of labyrinthine origin. 



