• S. S, MAXWELL 129 



Removal of the Otoliths. 



In the dogfish the otoliths are of soft, friable, calcareous material. 

 In the sacculus there is a large otolith spread over the main macula 

 acustica and a smaller mass on the lagena. These are so situated 

 that their removal can be accompHshed with Httle injury and the 

 operation is relatively easy. For the otohth of the utriculus the 

 case is very different. This otohth lies in the recessus utriculi so 

 close to the openings of the ampullae of the anterior vertical and the 

 horizontal canals that it requires some skill and much practice to 

 remove it without injury to the ampullae. If, however, after opening 

 the vestibule by removing a portion of the cartilaginous roof, the 

 utricular wall is sHt open with a very sharp microdissection knife, 

 the otohth material may be washed out by the careful use of a fine 

 pointed pipette. In a similar way the saccule may be sHt open and 

 its otoliths removed. No operation was considered successful unless 

 it was found at postmortem examination that no otolith material 

 remained. For reasons to be stated in another paper it was considered 

 important not only to avoid injury of the ampullas but also to reduce 

 the injury of the utriculus to a minimum. 



After removal of all the otohths from both ears in successful cases- 

 the following results are seen. (1) Compensatory movements of the 

 eyes are made in the regular way to rotations about all three body 

 axes, longitudinal, transverse, and dorsoventral. If the animal i& 

 rotated around a longitudinal or transverse axis and held in the 

 abnormal position the compensatory position of the eyes is retained, 

 but when the rotation is around the dorsoventral axis the eyes make 

 the compensatory movement and then return to the primary position. 

 These movements appear to differ from those in the normal animal only 

 in being sHghtly slower. (2) The animal swims in normal orienta- 

 tion and maintains its equihbrium in the water, but its swimming, hke 

 that of the fish without ampullae, is likely to be accompanied by a 

 rocking movement; this rocking or swaying is less apparent in vigor- 

 ous specimens. (3) If turned belly up in the water, the fish rights 

 itself promptly; in doing so, however, it sometimes overcompensates 

 and turns almost or completely over. 



It will be seen that these results are strikingly similar to those 



