338 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



and below represent the direction in which the first and 

 second waves are travelling along the upper and lower 

 membranes respectively. The smaller arrows of figures 

 1 and 2 are omitted. The line XY which is the same in 

 all three figures marks the level at which the two waves 

 pass each other in corresponding (not "like") phases. 

 The first wave, in passing the helicotrema has of course 

 been turned over so that its first phase is one of upward 

 displacement, while that of the second wave which has 

 not been reversed is one of downward displacement. Let 

 points in the waves be called ABCD and E as in fig. 1, 

 and phases M, N and as in fig. 2 — it is more convenient 

 to divide the wave into these three phases than in the more 

 usual way. In fig. 3 at the level XY both waves have 

 just reached the end of the first phase (M), i.e., the point 

 D of each wave is just passing the line XY. This means 

 that fluid has just been forced into region of XY from 

 both before and behind, and in the neighbourhoods of both 

 upper and lower membranes. The two points B of upper 

 and lower membranes are now separated to the utmost 

 extent and by virtue of their elasticity have just brought 

 the fluid in contact with them to rest. From this moment 

 onwards the two membranes by virtue of that same 

 elasticity will approach each other, with increasing velocity 

 till at the level XY the stage shown in fig. 4 is reached. 

 The points C (fig. 1) of the two waves are now passing 

 each other at the level XY. At this moment the two 

 membranes are approaching each other with maximum 

 velocity, being forced towards each other by the fluids in 

 the upper and lower canals, and the fluid between the 

 two membranes, that is in the middle canal (scala media, 

 canalis cochleae) is being forced out from this region, now 

 with maximum velocity, both forwards and backwards. 

 A moment later the stage shown in fig. 5 is reached. 



