272 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
those of an air-breathing Vertebrate when its skull is directly connected with the 
source of sound. That this is to some extent true is borne out by experiment. In 
making their celebrated experiments on the transmission of sound in the water of Lake 
Geneva, Colladon and Sturm* found that sound vibrations, too feeble to produce 
any appreciable effect on the external surface of the skull when they passed through 
air could, nevertheless, strongly impress the ear when they were propagated in water 
and the head of the observer was completely immersed in the fluid. (2.) The same 
observers also remarked that while the vibrations passed with difliculty from water 
to air the converse was also true. For Fishes in general, therefore, we are unable to 
see that there is any need to assume, in the absence of any experimental proof to the 
contrary, that the essential conditions of subaqueous audition are very different from 
those in air, except in so far as the physical diflerences in the conductivities of the 
respective media are concerned. Sound waves produced by any sounding body in the 
water and impinging upon the surface of the Fish’s skull will readily be transmitted 
to the internal ear, and such sounds Avill in all probability be heard with greater 
rapidity and from greater distances than could possibly be the case under similar 
conditions in air. In the special case of those Fishes with a Weberian mechanism 
the question becomes much more complicated, and in dealing with it we shall conflne 
ourselves to the Siluridm more particularly, although, with slight and unimportant 
modifications, the same line of argument will be applicable to all other Ostariophysem. 
Weber himself not only regarded the ossicles which bear his name as homologous 
with the incus, malleus, and stapes of the Mammalian ear, but attributed to them an 
almost exactly similar function. He imagined that sound waves impinging on the 
surface of the body ultimately affected the air contained within the air-bladder, which 
organ then acted as a resonator, and by means of the Weberian ossicles transmitted 
the vibrations to the internal ear. Presumably, the only way in which sound waves 
can affect the Weberian ossicles and internal ear is by traversing the body wall of the 
animal and throwing into vibration the air in the air-bladder, which in turn may be 
conceived as impinging upon the only portions of the bladder at all likely to be 
capable of vibratory motion, viz., the lateral walls of the anterior chamber; the 
vibration of these walls might initiate corresponding vibrations in the series of 
ossicles considered as a rigid whole, and such vihiKitions through the movements of 
the scaphia may be siqjposed to affect the j^erilymph of the atrial cavities, and 
eventually the endolyrnjih of the internal ear itself If Weber’s theory be true the 
air-bladder must necessarily become an important accessory to audition in all Fishes 
in which this peculiar niechanism_ is present. In ordinary Fishes the only sound waves 
capable of acting as stimuli to the auditory nerves will be those that fall directly on 
the skull, but in those that possess Weber’s ossicles sound-waves impinging on the 
general surface of the body may, through the air-bladder, become convertible into 
auditory stimuli. 
* “ Memoire sur la nompression des liquides,” ‘ Mem. de I’Academic des Sciences,’ vol. 5 , p. 346. 
