150 DYNAMICS OF LIVING MATTER 



Knight's experiment can be made in these forms. When they are 

 put on a rotating disk and turned in a horizontal plane, the eyes are 

 displaced during the rotation in the plane of the rotation, but in the 

 opposite direction. 



In this case again a source of error has to be guarded against; 

 namely, the influence of the retinal image. The tendency to keep the 

 eyes and the head in the normal position to the horizontal when the 

 body is turned, may be determined by the influence of the visual impres- 

 sions. The apparent motion of the objects on the retina when the 

 animal turns may cause a motion of the eye and head in the opposite 

 direction. This suspicion is the more justified as in some insects 

 these compensatory motions cease when the eyes are blackened.* 

 Lyon has, however, shown that in sharks and flounders these compen- 

 satory motions are not diminished when the optic nerves are cut. 

 In these forms at least we seem to deal with really geotropic reactions. 



The next question must be, In which organs are these geotropic 

 reactions produced? The answer might be simple enough were this 

 field not in a hopeless state of confusion through the hypothesis con- 

 cerning the functions of the semicircular canals. Flourens had stated 

 that the sectioning of one of the semicircular canals causes the eyes and 

 head of the animal to move in the direction of the plane of the canal. 

 Goltz showed that destruction of the inner ear leads to disturbances 

 "of the maintenance of the equilibrium of the animal." This term, 

 "equilibrium," is not clear unless it be supplemented by the statement 

 "with reference to the horizon or to the center of the earth." Goltz 

 advanced the now famous hypothesis that semicircular canals are an. 

 organ where the equilibrium of the head, and indirectly of the whole 

 animal, is regulated. If the head is bent, according to Goltz, the flow 

 of the lymph in the canals causes a stimulation of the nerve endings 

 in the ampullae of these canals, and this calls forth a reflex motion, by 

 which the head is put back into its normal position. Mach showed 

 that physical reasons prevented a flow of lymph such as Goltz's hypothe- 

 sis demanded; but that the pressure of the lymph against the nerve 

 endings in the ampullae, caused by changes in the position of the head, 

 might suffice to bring about the effects which Goltz's hypothesis de- 

 manded. He showed, moreover, that this hypothesis also demanded 

 that any stimulation of one of three ampullae only called forth a motion 

 of the eyes and head in the direction of the canal, and no other. While 

 this hypothesis at first met with general opposition, it was later accepted, 

 and it has, among others, received some support from my own 

 laboratory. Nevertheless, the hypothesis is wrong. Lyon has shown 



* E. P. Lyon, loc. cit. Radl, Der Phototropismus der Thiere, Leipzig, 1903. 



