io6 The Life Story of the Fish 



do fish hear? The concept is general that, except in the shal- 

 lows, sounds are rare beneath the surface. Sounds made in 

 the air do enter the water to some extent, but only with 

 difficulty. They tend to bounce back off its surface, and the 

 only fish which seem to pay much attention to them are 

 the group just mentioned in which hearing is reinforced by 

 the air-bladder — a group made up largely of shallow-water 

 dwellers. In the shallows, hearing can understandably be 

 useful to fish. But what about the fishes of the open sea, those 

 whose lives are passed in what we had been led to believe 

 was the all-pervading hush of the subsurface ocean, un- 

 troubled by the rush of winds, undisturbed by the roar of 

 waves, and beyond the reach of man-made noises? The truth 

 is that the all-pervading hush turns out to be a myth, and 

 that the subsurface ocean is a pretty noisy place. 



An emphatic and practical demonstration of this fact oc- 

 curred during the war. Our Navy developed a highly sensi- 

 tive instrument for detecting the noise of submarines under 

 water, and was about to put it triumphantly into service when 

 they found that it picked up so many other sounds that the 

 submarines could not be identified. Most of these noises 

 were made by submarine animals, and it was not until they 

 had learned to screen out these sounds that they were able 

 to use the instrument against submarine vessels. But that 

 there are plenty of noises for the oceanic fish to hear can no 

 longer be doubted. 



Our constant exceptions, the sharks and rays, have audi- 

 tory apparatus as complete as the other fish, but hear poorly. 

 This is to be expected, for their skulls are cartilage, not bone. 

 Bone is a good conductor of sound, cartilage is not. It would 

 be only with difficulty that sound-waves could make their 

 way through it to the inner ear. 



The sharks and rays have a spiracle, inherited from the 

 common Palaeozoic ancestor, but absent in most other present- 



