■ S. S. MAXWELL 127 



"July 14, 1919. Dogfish 5. 10.00 a.m. All six ampullae removed. Com- 

 pensatory movements prompt on rotation around longitudinal and transverse 

 axes; none on rotation in horizontal plane. Animal rights itself perfectly in 

 water. Eyelids sewed together to exclude retinal stimuli, and animal put into 

 deep tank; righting perfect. 



2.00 p.m. Animal rather weak but rights itself promptly when turned over 

 in water; swims rather wobbly; turned completely over once when excited by 

 other dogfish; I have seen a normal dogfish do this under similar circumstances. 



July 15, 9.00 a.m. Animal very weak; rests on bottom of tank in normal 

 position. Rights itself but may swim one or two turns belly up before getting 

 over. Opened stitches in eyelids. No compensatory movements of eyes. 



July 16, 9.30 a.m. Animal moribund. Killed for autopsy. Considerable 

 blood clot in each vestibule." 



The above experiment shows a possible source of the confusion 

 in the reports of previous investigators. Had I assumed that on 

 account of shock effects observations made on the day of operation 

 would be unreUable, and had I waited until the following day to 

 make my observations, it would have appeared that loss of the ampul- 

 las aboKshes compensatory movements, which is manifestly not true. 

 When immediately following the destruction of an organ a function 

 is clearly retained it is indisputable proof that at least that organ is 

 not the only one which can perform the function. Observations 

 made on July 15, on Dogfish 5, might have favored the statement 

 that destruction of the ampullae of the semicircular canals aboHshes 

 compensatory movements of the eyes, but the observations of July 

 14 clearly show such a conclusion to be wrong. 



In the attempts to determine the role of the various sense organs 

 in the geotropic reactions of the dogfish, it has long been recognized 

 that retinal stimuh play a part. Lyon^ and Parker^ excluded visual 

 stimuh by section of the optic nerve. I have accompHshed the same 

 result by the less radical operation of sewing the eyelids together, 

 when equilibrium and the righting reactions were under consideration, 

 and by placing a black, opaque disk on the cornea over the region of 

 the pupil when eye movements were to be studied. Other methods 

 of blinding were also used. I can affirm with complete assurance 



^ Parker, G. H., Influence of the eyes, ears, and other allied sense organs on the 

 movements of the dogfish, Mustelus canis (Mitchill), Bull. Bureau of Fisheries, 

 1909, xxix, 43. 



