S, S. MAXWELL 355 



and I each found that in the dogfish the large otoUth of the sacculus 

 has nothing to do with equihbrium; and I have shown that an ear 

 from which the otolith of the sacculus as well as of all the ampullas has 

 been removed retains both static and dynamic functions. In this 

 case the only part remaining which can mediate these functions is the 

 small otolith organ in the recessus utriculi. 



The otolith of the recessus utriculi is, in the dogfish, an oval or 

 nearly circular mass, 3 or 4 mm. in diameter, shaped like a planoconvex 

 lens. Its convex surface rests upon the corresponding concave sur- 

 face of the macula in the bottom of the recessus. I have described 

 it as resting on the macula, but the relation of its edges to the mem- 

 branous walls suggests the idea that it is in reality partially suspended. 

 To one who is actually performing these experiments it is a remark- 

 ably striking fact that all the functions performed by the ampullae 

 of the vertical canals can also be performed by this one organ. In the 

 case of the ampullae each one has a highly specialized function, re- 

 sponding to rotation in a single plane. The otolith organ on the con- 

 trary responds to rotations in all planes except the horizontal. 



The approximation of the surfaces of the otolith and the macula, 

 each almost perfectly spherical, suggests a mechanical arrangement 

 by which any alteration of the position of the head would cause a 

 corresponding change of pressure relations between the two structures. 

 A pressure change of this sort could act as a stimulus to excite the 

 compensatory movement appropriate to any particular rotation. 

 Whether there is within the area of the macula a local differentiation 

 of function comparable to that of the different ampullae I have been 

 unable to determine. The small size of the area to be explored and 

 the difficulty of exact localization of an artificial stimulus have so 

 far prevented an answer to this question. 



