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SCIENCE 



[N. S. Vol. LIII. No. 1375 



of Selachians ai-e extremely favorable objects 

 for experiment because of the relatively large 

 size of their parts, their anatomical arrange- 

 ments which permit the stimulation or ex- 

 tirpation of single portions, the ease and 

 clearness with which operations can be per- 

 formed tlirough the cartilaginous skull, and 

 the machine-like definiteness with which com- 

 pensatory movements occur in these animals. 

 The compensatory movements of the eyes 

 and fins of the dogfish were first accurately 

 described by Loeb (1891). Lee (1893) made a 

 very detailed study of these movements in 

 response to rotation about the different body 

 axes, and laid emphasis on the precision with 

 which similar movements resulted from stim- 

 ulation of the ampullae of the different canals. 



I. THE SEMICIRCULAR CANALS 



(a) Stimulation Experiments 

 Lee's description of the results of stimula- 

 tion of the individual ampullae is very specific 

 and I (1910) could confirm it in every par- 

 ticular. In brief the results may be thus 

 stated: Stimulation of the ampulla of the 

 right horizontal canal causes both eyes to turn 

 to the left, the same movements as that which 

 occurs when the animal is rotated to the right 

 about its dorsoventral axis. Stimulation of 

 the ampulla of the right anterior vertical 

 canal causes the right eye to be elevated, the 

 left eye to be depressed, and both eyes to roll 

 backward on their axis; these movements are 

 similar to those which occur when the animal 

 is rotated head downward and to the right, 

 that is, in the plane of the canal stimulated. 

 When the ampulla of the posterior vertical 

 canal is stimulated the right eye is elevated, 

 the left eye is depressed and both eyes roll 

 forward on their axes. These movements are 

 identical with those which result from tilting 

 the head upward and to the right, that is, a 

 rotation in the plane of the posterior vertical 

 canal. Of course, the stimulation of the sym- 

 metrically placed canals of the other side 

 would merely transpose the use of the words 

 left^jind right in this description. Ampullae 

 are exceedingly sensitive to mechanical stim- 



ulation. The results are absolutely clear and 

 definite. 



(&) Extirpation 

 On the basis of the above experiments Lee 

 believed to have proof of tlie correctness of 

 the Mach-Breuer assumption that the semi- 

 circular canals constitute the organ for the 

 dynamic functions of the labyrinth. He at- 

 tempted to put them out of function by cut- 

 ting the ampullar nerves, or in some instances 

 by destroying the ampuUae. He states that 

 after cutting the nerves of all four vertical 

 canals compensatory movements are wanting 

 to all rotations in vertical planes, although 

 compensation may be retained to rotation in a 

 horizontal plane. Lyon (1899) on the other 

 hand reported compensatory motions in re- 

 sponse to all three rotations, after removal of 

 all six ampullae. I have develojjed a very 

 simple and certain method of removal of the 

 ampullae, and I have repeated these experi- 

 ments many times (1910, 1919) with the most 

 complete regularity of results. I found that 

 contrary to Lee's statement after removal of 

 the ampullae of the four vertical canals, or 

 indeed of all six ampullae, good compensatory 

 movements occur to rotations around the 

 longitudinal or transverse axis, but I have 

 never yet seen the compensatory movements 

 to rotation in the horizontal plane retained 

 after removal of the ampullae of tlie hori- 

 zontal canals. Anyone who will take the 

 trouble to repeat these experiments using my 

 method will be able to see for himself that 

 after loss of all the semicircular canals the 

 labyrinth retains all its static functions, and 

 all its dynamic functions except the response 

 to rotation in a horizontal plane. The 

 dynamic functions then are not confined to 

 the semicircular canals. 



II. THE OTOLITH ORGANS 



(a) Extirpation 



Experiments by removal of the otoliths 

 have been carried on by many observers. 

 Loeb (1891) found that scratching out the 

 otoliths completely from the vestibule had 

 much the same effect as section of the eighth 



