270 
PROFESSOBS T. W. BRIDGE AND A. C. HADDON 
It is by no means obvious that DdfossE is correct in regarding all these examples 
of breathing noises as genuine instances of the production of voluntary sounds, still 
less is it clear that the emission of such sounds is in any way a part of the normal 
function of the air-bladder. In none of the Siluridae or Cyprinidae that DuFOSSlfe 
mentions is there any mechanism by which the expulsion of gas from the air-bladder 
through the ductus pneumaticus in sufficient volume or with sufficient rapidity to 
produce audible sounds could be effected. Any such expulsion of gas seems only 
to take place under the influence of a diminution in the pressure of the superin- 
cumbent water, in which case the expansion of the gas might lead to its forcible 
escape from the air-bladder and at the same time to the emission of a breathing noise. 
This certainly does occur in many Physostomi, and may be utilized by the Fish as a 
means of adjusting the volume of its air-bladder and the specific gravity of its body 
to varying external pressures, but there is certainly no clear evidence that this 
method is ever employed in the production of normal voluntary sounds in the 
Ostariophyseae, and even if it were the case the effect could only be produced at the 
expense of a considerable disturbance both of the normal equilibrium of the Fish in 
the water and of its locomotor activity. We are strongly inclined to the opinion 
that although sounds may indirectly have their origin in the air-bladder, they have 
no relation to it other than as accidental accompaniments in the exercise of its 
normal hydrostatic function.'"' In one example cited above [Clarias) it is almost 
certain that the grunting sound which tlie Fish is said to make could not be caused 
by the voluntary expulsion of gas from the air-bladder, inasmuch as this organ is not 
only rudimentary but almost completely encapsuled by bone. Eliminating such 
doubtful examples of the association of the air-bladder with phonation in a few 
Siluridae and Cyprinidae, it may be urged with regard to the rest that the compara- 
tive rarity of well authenticated instances of the production of voluntary sounds, the 
absence of extrinsic muscles in all biit a few genera (Pimelodinae), and the Avant of 
internal vibratory diaphragms, or other obviously vocal structures, are quite sufficient 
to prove that the air-bladder takes little or no part in this function, at all events, by 
any of the ordinary methods known in other Fishes. This conclusion seems to us to 
apply not only to the two families referred to above, but to all other Ostariophyseae 
about which reliable information can be obtained, and to warrant the exclusion of 
phonation from further consideration in connection with the Weberian mechanism. 
With regard to respiration the air-bladder in different Fishes is said to be related 
to this function in one of two ways, acting either as a lung subsidiary to the gills, or 
as an oxygen reservoir. 
There is no satisfactory evidence that respiration can be effected by the transit of 
* For these reasons, and in the absence of definite experimental evidence, we cannot at present accept 
Sorensen’s ingenious theory that the extrinsic muscles of the air-bladder in the Pimelodina9 and the 
“ elastic-spring ” apparatus of other Siluridae are solely subordinate to the voluntary production of 
sounds. 
