XXXIII 

 CONVERGENCE IN EVOLUTION 



IN the darkness of the Deep Sea there are 

 certain fishes whose eyes have dwindled to 

 a vanishing-point. By means of delicate tactile 

 organs they feel their way about on the sea floor. 

 There are other abyssal fishes with enormously 

 enlarged eyes, and it is reasonably supposed that 

 they are able to profit by the faint illumination 

 due to " phosphorescent " deep-sea animals. Yet a 

 third condition is seen in a number of fishes from 

 great depths in which the eyes are elongated into 

 cylinders, projecting like opera-glasses on the top 

 of the head. These have been called " telescope 

 eyes," and they are adapted to make the most of 

 faint light. The lens is relatively large, and the 

 distance between it and the surface of the retina, on 

 which the image is formed, is much greater than 

 usual. Something of the same sort is seen in the 

 eyes of owls, though they do not project in the same 

 way. For the sake of simplicity let us leave the 

 owls and two or three similar instances out of 

 account, and focus attention on the fact that the 

 " telescope eyes " of some deep-sea fishes are 

 closely paralleled by "telescope eyes" in some 

 deep-sea cuttlefishes, which, of course, are mollusks. 



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