276 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
strength of the arguments against Weber’s theory which we have previously urged, 
and cannot but regard as fatal to it. 
{e.) Even if the admission be made that the air-bladder and its ossicles are 
accessory to hearing, the Fish could have no power of appreciating the direction of 
sounds conveyed to the internal ear by such means. Any cognizance of the varying- 
directions from which sounds may come is generally believed to be due in all 
vertebrated animals to the differential action of the two ears, but we have already 
shown* that no such action can possibly take place in response to impulses received 
through the Weberian mechanism in accordance with Weber’s theory. It would, 
therefore, seem that any increased acuteness of hearing that might be conferred on 
the Fish by the air-bladder in its presumptive function as an accessory to audition, 
would be counterbalanced by the fact that such increase of auditory capacity could 
not be associated with a corresponding increase in the power of appreciating the 
direction of sounds. Whatever may be the physiological importance of the sense of 
hearing in Fishes, whether associated with the pursuit of prey, or as an aid in 
escaping from enemies, or, as in the case of gregarious Fishes, as a means of keeping- 
together in shoals for breeding or other purposes, the power of appreciating the 
direction of sounds must be of primary importance in any modification of the auditory 
organ in the direction of giving to its possessor exceptional powers of hearing. 
(2.) Contrary to what might fairly be expected if so complicated a structure as the 
Weberian mechanism is an accessory to hearing, there is absolutely no evidence of the 
existence of exceptional powers of hearing either in the Siluridae or any other 
Ostariophyseae. 
(3.) Finally, it may be aflirmed that there is an alternative view of the function of 
the Weberian ossicles, which is in perfect harmony with the facts of structure, and is 
open to none of the objections which can be reasonably urged against Weber’s theory, 
and also, at the same time, has an important bearing- on the locomotor activities of 
the Fishes concerned. 
With the reservation which the entire absence of direct experimental evidence 
renders absolutely necessary, it may be affirmed that the arguments set forth in the 
preceding paragraphs aie distinctly adverse to the theory that the Weberian ossicles 
are in any way related to the function of audition, even to the subordinate and 
qualified extent tacitly suggested by Hasse and Ramsay Wright; and the solution 
of this difficult problem must be looked for in some other direction. 
Dismissing sound production, equilibration or orientation, respiration and audition 
from all physiological connection with the Weberian ossicles, we may now consider 
the sole remaining alternative view — that the ossicles are accessory to the hydrostatic 
function of the air-bladder. But before dealing with this aspect of the problem it 
will be advisable to state what is actually and experimentally known as to the hydro- 
static function of the air-bladder in Fishes in general. 
* See p. 268. 
