THE SONG OF FISHES. 
343 
has two hard prominences, one on each jaw, fulfilling the 
function of intermaxillary teeth. 
We now come to the second division, which comprises all 
kinds of blowing sounds, 66 bruits de souffle.” Many fishes pro- 
duce such sounds, among them being the carp tribe and the 
Silurus glanis; but the most remarkable effects have been 
noticed in the loach ( Cobitis ), the barbel, and the carp. All 
these fishes have an air-bladder provided with a duct, which com- 
municates with the gullet, and which is, moreover, divided, in the 
carp tribe, into two chambers, which, however, communicate, by 
a transverse constriction. In the loach this organ lies in front 
of and out of the abdomen, in a box formed for it by bony plates 
derived from the sides of the second and third vertebrae. Ac- 
cording to the researches of Weber, which have been confirmed 
by Brechet and others, the air-bladder in the barbel and loach 
is brought into relation with the organs of hearing through the 
medium of a chain of bones, so that the slightest vibrations of 
the wall of the bladder can be transmitted to them. Weber, 
in consequence, then, regarded the air-bladder as an organ for 
the reinforcement of the sounds transmitted to the body of the 
fish by the surrounding medium. From experiments made upon 
the barbel and “meunier” ( Cyprinus dobula ), M. Dufosse 
concludes — 
a. That the sounds emitted by these fish are voluntary, 
because the animal can open or close at pleasure little valves in 
the duct of the air-bladder, which control the escape of gas from 
this receptacle — an act essential to the production of sound. 
/3. That the function of the air-bladder and duct, in addition 
to any other which they may discharge in common with these 
organs in other fishes, is “ to produce a certain quantity of gas, 
and to expel the same with the speed necessary for the formation 
of sounds of expression ; ” and that the principal agent in the 
propulsion of this gas is, through its anatomical relations, the 
posterior lobe of the air-bladder. The sounds emitted by the 
loach have a greater intensity, and present greater varieties. 
We now come to the second and most important section of the 
second category. This includes sounds having the following 
character. Their timbre is more or less sweet and soft, and 
never excites such sensations as are produced by the grinding of 
teeth. It is, moreover, subject to an extraordinary degree of 
change, varying frequently, and even changing during the ex- 
tent of a sound. Such sounds can be appreciated musically ; 
are, in other words, u commensurable.” 
Let the reader place a finger in each ear, and then “ set his 
teeth” hard. Alter hearing a dull low murmur, like the 
