ON THE ANATOMY OF FISHES. 
269 
attributed to the air-bladder by different writers may be mentioned (l) plionation ; 
(2) respiration ; (3) an accessory to audition ; or (4) its function may be purely 
hydrostatic. 
Certain of these functions can at once be eliminated from any discussion as to the 
physiological significance of the Weberian ossicles. 
Equilibration is one of these. No conceivable changes are likely to take place in 
the condition of the gaseous contents of the air-bladder as the result of any movement 
of rotation or oscillation on the part of the Fish, and without such changes of a 
degree and kind calculated to produce movements of the lateral walls of the anterior 
chamber, no motion of the Weberian ossicles could take place, neither would any 
change occur in the endolymph of the semicircular canals, either in the form of intra- 
lab}^rinthic pressure, as Goltz himself proposed, or by an actual flow, as maintained 
by Mach, Breur, and Crum-Brown. But even supposing that movements of 
oscillation or rotation were competent to so alter the internal condition of the air- 
bladder that increased pressure or a flow would be produced in the fluids of the atrial 
cavities, and secondarily, in the sinus and ductus endolymphaticus and the two 
sacculi, the presence of an oblique valve in the ductus sacculi-utricularis wouM 
certainly tend to hamper, even if it did not entirel}^ prevent, the extension of such 
disturbances into the semicircular canals, where the function of equilibration is 
specially located. And, finally, it may be mentioned that even if no other difficulty 
existed, the fact that no differential action of the two membranous labyrinths could 
take place as the result of stimuli received from the air-bladder through the Weberian 
ossicles, must be fatal to the existence of any functional relations between equilibration 
and the Weberian mechanism. 
In addition to the various other methods by which voluntary sounds are produced 
in different Fishes, the air-bladder not infrequently shares in the function of phonation. 
Such sounds are either produced by the vibration of the internal annular diaphragm,* 
or by the vibration of certain extrinsic muscles,t the air-bladder in the latter case 
intensifying the sound produced by acting as a resonator. Dufoss^: {loc. cit.) is also 
of opinion that some Ostariophyseae {e.g., some Cyprinidse and one or two Siluridte) 
produce breathing noises (“ les bruits de souffle ”) by the expulsion of gas from the 
air-bladder through the ductus pneumaticus, and it has been suggested that the 
grunting sounds emitted by Clarias\ have a similar origin. 
The possibility that the Weberian ossicles have anything whatever to do with 
phonation, either in the Siluridae, or in other Ostariophyseae, is very remote and need 
be but briefly considered. 
auditory organs of many aquatic Invertebrata may perform singly or conjointly the functions of 
equilibration and audition. 
* Moreao (27a). 
t DoFOSsfi (11 b). 
t Quoted by Day in “ Instincts and Emotions in Fish,” ‘ Linn. Soc. Trans.’ (Zool.), vol. 15, 1880. 
