TROPISMS AND RELATED PHENOMENA 151 



conclusively in my laboratory that the stimulation of the horizontal 

 canals in sharks and flounders calls forth motions of the eyes in the 

 plane of the canal, as the hypothesis demands, but that the two 

 other canals, or their ampullae, are either nonsensitive to stimula- 

 tion, or give no motion of the eyes or the head in the plane of the 

 stimulated canal. I will confess that I .did not at first credit Lyon's 

 statements, but I have convinced myself that he is unquestionably 

 right. It seems that all the authors who had stated that stimulation 

 of one of the semicircular canals caused motions of the eyes or head 

 in the plane of the canal, based their statements only on the effects 

 of the stimulation of one of the three canals; namely, the horizontal. 

 The negative or questionable results they obtained in the case of the 

 two vertical canals they did not dare to accept in the face of the strik- 

 ingly clear results the horizontal canal yielded.* Suggestion does not 

 play a r61e in ordinary matters only, but occasionally also in science. 



It is, however, possible that the compensatory motions and reactions 

 are after all produced in the inner ear, although the semicircular canals 

 have little or nothing to do with it. This follows from the fact that 

 when the auditory nerve in a shark is cut, all the compensatory motions 

 cease, t It may be that the otoliths in the inner ear are responsible for 

 this effect. Mach % was the first to point out this possibility, and De- 

 lage § made a number of experiments which seemed to speak in favor 

 of this view. The most striking experiment was made by Kreidl on 

 PalcEfnon. The otolith organs of this Crustacean are found in the 

 basal part of the small antennae. Palcemon loses its otoliths during the 

 process of moulting, and after moulting it repairs the loss by putting 

 small granules of sand into the ear. Kreidl kept such Crustaceans in 

 vessels which were free from sand, but which contained instead very 

 finely powdered iron. After moulting the animals put this iron powder 

 into their ears. It was possible to test in such animals the otolith- 

 hypothesis of the geotropic reaction. The otohth rests on cells in which 

 the sense nerves end. They are therefore supposed to press upon the 

 nerve endings. When the animal is laid on one side, the otolith, instead 

 of pressing, will pull at the cell, and this causes a change in the nerve 

 endings which results in a righting motion (compensatory motion) of 

 the eyes, or, if possible, of the whole body. If this view were correct, 

 it should be expected that a magnet could produce effects similar to 



* It is much easier to ascertain motions of the eyeball from right to left or vice versa 

 than up and down. This is due to the fact that we estimate the motion from the displace- 

 ment of the sclerotic. In the upward and downward motions, however, the sclerotic is, as 

 a rule, not visible. 



t Loeb, Pfiiiger's Archiv, Vol. 49, p. 179, 1891 ; and Vol. 50, p. 66, 1891. 



X Mach, Grundlinien der Lehre von den BewegungsemMndungen, Leipzig, 1875. 



§ Delage, Archiv. de Zoologie experimentale. Vol. 5, 1887. 



