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BLIND CAVE-FISH AND ITS NORMAL RELATIVE 



Above is a fish from the Mammoth Cave of Kentucky, wliicli has no eyes but merely a sHght 

 discoloration of the skin at the point where the ej-es ought to be. To take the place of sight, 

 the fish depends on the sense of touch even more than blind people do — it is said in this way 

 to be able to determine whether a certain object with which it comes in contact is or is not 

 edible. If a fish is going to live in cave-darkness, eyes would obviousty be of little use to it; 

 but the exact nature of the process by which the eyes disappeared has long been a bone of 

 contention among students of evolution. Below is a minnow, probably distantly related to 

 the blind cave-fish. It may, therefore, give some idea of what the cave-fish looked like 

 before it lost its eyes and became modified in other ways to meet the conditions of life 

 in underground waters. Photographs (much enlarged) by John Howard Paine. (Fig. 4.) 



in detecting certain kinds of vibrations 

 is due to the papillae. Experiments 

 have proved that the ears are poorly 

 developed, and the fish is unable to 

 perceive most sounds, but the papillae 

 are so sensitive that any slight disturb- 

 ance of the water is instantly noted, 

 and since the fish are confined almost 

 entirely to pools, any such disturbance 



is sufficient to warn them that the 

 vibrations are the result of something 

 unusual. The fish is entirely scaleless, 

 these papillae evidently replacing the 

 scales. The ear itself is apparently 

 normal, and while it is evidently not 

 used to detect sound, it probably serves 

 to maintain equilibrium. 



The fish is believed to breathe through 



449 



