584 SCIENCE PROGRESS 



it will be found that invariably the process has been of a 

 similar character. 



Provision is always made by means of an open and definite 

 perilymph cavity for a direct and unimpeded passage for 

 vibrations between an opening in the outer skull wall {fenestra 

 ovalis) and a similar opening elsewhere in the wall of the otic 

 capsule. This perilymph passage at a certain definite spot 

 or spots is separated from the cavity of the endolymph labyrinth 

 by tense drum-like thinnings of the labyrinth walls and near or 

 on these thinnings there is a nerve-ending which becomes very 

 highly specialised in the higher though simple in the lower 

 groups. 



Thus in the simplest and most direct way provision is made 

 for unimpeded movements of the fluid around the endolymph 

 labyrinth and for the transference of these movements from the 

 perilymph to the endolymph at certain definite spots. 



In the labyrinth of a fish, except for a thickening beneath the 

 sensory areas, the walls of each particular region are of fairly 

 uniform thickness or at least there is no sudden change from 

 thick to thin. 



In the amphibia this is not so. 1 Among them, except in the 

 lowest purely aquatic Urodeles, certain restricted areas of the 

 endolymph labyrinth wall are thinned down to the lining 

 epithelium, whilst around them the walls are suddenly thickened 

 like a frame. 



These framed thinnings in the wall of the endolymph 

 labyrinth are the first sign of an auditory organ. 



In amphibia where they first appear, there are three of them 

 which almost might be spoken of as tentative experiments in the 

 manufacture of an auditory instrument, for one of them only has 

 apparently stood the test of experience, the one namely that 

 is situated in a special dilatation between the saccule and 

 the lagena. 



This dilatation {pars basilaris lagena;), with its thin area 

 stretched like a drum-head in its frame, at its first appearance 

 is inconspicuous enough but though so insignificant for the 

 moment, it is potentially of the very highest importance, for 

 it is from this paltry rudiment that the human cochlea with its 

 intricate powers of hearing has been evolved. 



There is at first sight little in the structure of the pars 

 1 Harrison, Internat, Monthly Jour. Anat. 19, 1902, p. 221, 



