THE HERRING, 437 



up from some depth, by means of this arrangement. For under these 

 circumstances the air which the air-bladder contains expands to such a 

 degree, on being relieved from the pressure of the water, that deep-sea 

 fishes with a closed air-bladder which are brought to the surface rap- 

 idly are sometimes fairly turned inside out by the immense distention, 

 or even bursting, of the air-bladder. If the same thing should hap- 

 pen to the herring, the like misfortune would not befall it, for the air 

 would be forced out of the opening in question, and might readily 

 enough produce the squeak which is reported. The common loach* is 

 said to produce a piping sound by expelling the air which this fish 

 takes into its intestine for respiratory purposes. 



At the opposite end of the air-bladder there is an even more curious 

 arrangement. The silvery coat of the air-bladder ends in front just 

 behind the head. But the air-bladder itself does not terminate here. 

 Two very fine canals, each of which is not more than a two-hundredth 

 of an inch in diameter, though it is surrounded by a relatively thick 

 wall of cartilage, pass forward, one on each side, from the air-bladder 

 to the back of the skull. The canals enter the walls of the skull, and 

 then each divides into two branches. Finally, each of these two 

 dilates into a bag which lies in a spheroidal chamber .of corresponding 

 size and form ; and, in consequence of the air which they contain, 

 these bags may be seen readily enough shining through the side-walls 

 of the skull, the bone of which has a peculiar structure where it sur- 

 rounds them. Now, these two bags, which constitute the termination 

 of the air-bladder on each side, are in close relation with the organ of 

 hearing. Indeed, a process of that organ projects into the front cham- 

 ber on each side, and is separated by only a very delicate partition 

 from the terminal sac of the air-bladder. Any vibrations of the air 

 in these sacs, or any change in the pressure of the air in them, must 

 thus tell upon the hearing apparatus. 



There is no doubt about the existence of these structures, which, 

 together with the posterior opening of the air-bladder, were most accu- 

 rately described, more than sixty years ago, by the eminent anatomist 

 Weber ; but I am afraid we are not much wiser regarding their mean- 

 ing than we were when they were first made known. In fishes in gen- 

 eral, there can be little doubt that the chief use of the air-bladder is to 

 diminish the specific gravity of the fish, and, by rendering its body of 

 nearly the same weight as so much water, to render the business of 

 swimming easier. In those fishes in which the passage of communi- 

 cation between the air-bladder and the alimentary canal is closed, the 

 air is no doubt secreted into the air-bladder by its vessels, which are 

 often very abundant. In the herring the vessels of the air-bladder are 

 very scanty ; and it seems probable that the air is swallowed and 

 forced into the air-bladder just as the loach swallows air and drives it 



* See Muller, " Ueber Fische welche Tone von sich geben (" Archiv f iir Physiologie," 

 1857, p. 267). The herring is not mentioned in Miillcr's list of yocal fishes. 



