328 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



membrane during the whole period of positive acceleration 

 of the inward movement of the stapes, tension being 

 greatest at the basal end. During the second portion of 

 the advance of the stapes (with a negative acceleration) 

 this first portion of the lower membrane will commence 

 to return to its position of rest, a longitudinal movement 

 of fluid in its neighbourhood being involved therein. This 

 movement of fluids will be forwards in the upper canal and 

 backwards in the lower canal but will extend through only a 

 small distance, and will affect chiefly the portion, of fluid 

 very near to the surfaces of the membrane, but not quite in 

 contact with them. The reverse or the return movement 

 of the stapes will produce a similar effect in the opposite 

 direction, the first portion of the return movement of the 

 stapes augmenting the fluid movements of the second part 

 of the advance. If we now consider the condition of the 

 parts near the base at the moment when the return 

 movement of the stapes is just completed we shall find 

 that they are such as are necessarily transmitted in the 

 form of a wave, though a wave very different from either 

 a sound wave or a wave in water or any wave which has 

 hitherto, so far as I know, been considered by physicists 

 or mathematicians. 



Let ABODE, in fig. 1 (PI. XX.), represent the middle 

 line of the displaced membrane, A being the basal end of 

 it. The portion AB is moving downwards to its position 

 of rest, the fluid displaced by it below being driven for- 

 wards (i.e., away from the basal end of the canal and 

 towards the apex) ; the fluid above moving downwards 

 with the membrane and somewhat backwards, its place 

 being filled by fluid from beyond B. 



The portion BC is moving upwards, being carried by 

 the moving fluid below which is driven forwards by the 

 downward movement of AB. The portion CD is returning 



