No. I.] THE VERTEBRATE EAR. 289 



Other means of introducing the undulations to the cochlear duct 

 — among which the diagonal penetration through Reissner's 

 membrane and the penetration through the round window are 

 the most important. 



The height of the undulations of the hairs is directly propor- 

 tional to the intensity of the disturbance in the endolymph. 

 The undulations equal in number the impulses of the endo- 

 lymph. 



The action of the intracellular fibrilli is probably intermediate 

 between that of the hairs and of the nerve fibres ; in other 

 words, they serve to transform the physical undulations of the 

 hairs into the physiological stimulation of the nerve fibrils. The 

 nerve fibrils which enter into connection with the cells are, as is 

 well known, non-medullated, varicose, and in some cases appar- 

 ently branched at their ends. The branching, however, I do 

 not consider to be of special or great physiological importance. 

 The normal, i.e. most common, mode of the nerve end in con- 

 nection with the cell seems to be the fusion of the nerve fibril 

 with the base of the cell, though the point of fusion often 

 appears to be placed high up on the side of the cell. Such a 

 transposition does not indicate that the fibre has entered the 

 cell on its lateral surface, as originally situated, but merely that, 

 in the process of the conversion of the papilla basilaris into the 

 cochlear organ, the cell has been distorted or changed in shape 

 to accommodate itself to its new surroundings, and that its base 

 is no longer directed squarely towards the basement membrane, 

 but at a greater or less angle to it. The inner or outer face, as 

 the case may be, in consequence, becomes in part the base of 

 the cell, but the nerve fibre retains its primitive connection 

 with the cell. 



When once the stimulus has been transmitted to the endo- 

 lymph, the propagation through this fluid produces a concomi- 

 tant propagation of the undulatory motion along the hair band 

 as a whole, just as a wind blowing across the free and open 

 prairie or a field of standing grain produces undulatory move- 

 ments of the surface as a whole. A considerable portion of this 

 undulatory motion is taken up by the individual stalks in the 

 case of the grass and by the individual hairs in the case of the 

 cochlea, and is transmitted to the fixed end of the slender struc- 

 ture. Now since physical analogies compel us to assume that all 



