CHAPTER XI I 



Habits and Adaptations 



ADAPTATIONS in the world of fish are numberless. Some 

 are insignificant. Some are important but unspectacular. And 

 some are so startling, so incredibly fantastic, that they leave 

 the imagination in a state of collapse, mumbling to itself the 

 hackneyed old line about truth being indeed stranger than 

 fiction. Could anyone be expected to believe in a fish which 

 renders itself blind by its own activities, but overcomes the 

 handicap by using those same activities in a radar-like ap- 

 paratus wherewith it finds its way about? And yet this is 

 just what the electric "eel" does. Its principal output is an 

 electric current so strong as not only to stun enemies and 

 prey, but also to cause cataracts on its own eyes. Its secondary 

 output is an almost continuous series of much weaker electrical 

 discharges. On its head are sensory pits which receive the 

 reflections of these weak currents from surrounding objects j 

 and so delicately are they adjusted that they orient the eel 

 after it has become blind and guide it wherever it wants to 



^°* . . . 



An adaptation, in the simplest possible words, is the modi- 

 fication of an organ, or of a whole animal, so that it is used 

 for a different purpose from the one which it originally 

 served, or so that it serves the same purpose in a different 

 way. When you use your hand to hold this book you are 

 benefiting from an adaptation, for hands were once front 

 paws and served only to walk on. Far below us in the scale a 

 somewhat similar adaptation has taken place, for the humble 



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