The Air-Bladder 129 



sometimes lies on bottom at a thousand feet, sometimes feeds 

 at the surface. It has no air-bladder. The chub mackerel has 

 an air-bladder, the common mackerel has not. They are not 

 only almost indistinguishable in appearance, but they fre- 

 quently live side by side and school together. It is difficult to 

 believe in the indispensability of an instrument which one of 

 them gets along perfectly without. 



At this point we have to stop and consider the connection 

 which the air-bladder makes with the ear in some fishes. 

 Controversy has gone on for years about this apparatus, one 

 school of thought holding that it serves to keep the fish 

 more completely informed as to the state of its air-bladder, 

 the other, that it is a hearing mechanism. 



In the cod and some other fishes, the connection takes 

 place merely through forked lobes of the forward end of 

 the air-bladder which rest against the auditory capsules. Much 

 more complicated is the system found in a great group of 

 fresh-water fishes which includes not only such familiar forms 

 as the catfish, the carp, and the sucker, but also the characins 

 so abundant in South America and in fish-fanciers' aquaria. 

 Here there are four small bones linked together with mov- 

 able hinges (see Figure 16). These are called, after their 

 discoverer, the Weberian ossicles, but they are not to be 

 confused with the ossicles in our ears, the hammer, anvil, 

 and stirrup. The latter derive, as we have seen, from three 

 bones in the fish's jaw, and the carp is still using them to eat 

 with, whereas his Weberian ossicles he has improvised out 

 of the forward end of his backbone. But, however different 

 their origin, there is a similarity in their present action, for 

 our ossicles form a bony linkage between our membranous 

 ear-drum and our auditory capsule, and the carp's Weberian 

 ossicles form a bony linkage between the membrane of his 

 air-bladder and his auditory capsule. It is this similarity 

 which first suggested that the Weberian ossicles might be 



