Lyon, Functions of the Oiocyst. 243 



the otocyst. But the assumption that a sense of equiHbrium 

 exists in invertebrates — the assumption that they feel the direc- 

 tion of the vertical — seems unjustifiable. Indeed, when we 

 consider how perfectly in ourselves equilibrium is maintained 

 by purely reflex processes and how rarely we " feel " our posi- 

 tion in space, in the sense that we taste or smell or hear or rec- 

 ognize any external phenomenon whatsoever by means of a 

 sense organ, it seems extremely improbable that these low or- 

 ganisms have a recognition of the vertical. As Cyon facetiously 

 remarks it presupposes too high a degree of mathematical learn- 

 ing on the part of these low forms. 



Kreidl also tried removal of the otocysts from Palcemon 

 but, instead of cutting away the eyes as did Delage, he covered 

 them with black paint. The same lack of orientation followed 

 this treatment as did the more severe operation of Delage, and 

 of course every experiment which avoids removal of parts is 

 more satisfactory and convincing. 



IV. TJic Oiocyst and Equilbnuin. Clark, 1896, The Jour- 

 nal of Physiology, V. 19, P. 327. 



The chief interest in this paper lies in the author's claim 

 that the otocyst without the otolith is able to function as an 

 equilibrium organ. Clark worked upon the decapod crustaceans, 

 Gelasivms and Plathyotiichns, both of which have no otoliths in 

 the cyst but are very active and would seem to need an 

 equilibrium organ. He studied carefully the compensatory mo- 

 tions of the eyes accompanying passive rotation and bases his 

 conclusion largely on these. As is well known, when a verte- 

 brate (or a crustacean also, as Kreidl found), is rotated slowly 

 the animal's eyes turn in the opposite direction, or in other 

 words, tend to retain their positions in space. If the rotation 

 of the animal is such as to change its orientation with respect 

 to the vertical, the compensating eye positions are retained un- 

 til the original position of the body is restored. These motions 

 therefore seem closely connected with equilibrium. After re- 

 moval of the otocysts, Clark found that the geotropic compen- 

 sating motions of the eyes were lessened. When in addition 

 the eyes were blackened, the motions failed altogether ; or at 



