WHAT IS PHYSICAL LIFE 



single one of the sound apples which re- 

 main. But this difficulty about the eye 

 is not lessened by the fact that some of 

 the earliest and generally simpler animal 

 forms nevertheless had extraordinarily 

 complex eyes. Some creatures living in 

 the darkness of the ocean depths provide 

 themselves with what are virtually lan- 

 terns to help their eyes out. This means 

 that life has no limits in her ways for 

 helping functions. But where no seeing 

 is possible, life gives up the useless at- 

 tempt and bids the fishes in the under- 

 ground rivers of the Mammoth Cave to 

 go without eyes. This may be called a 

 negative adaptation, the opposite of that 

 of the eagle's eyes as he soars towards 

 the sun. 



However, we need not dwell longer 

 upon this instance of a living mechanism 

 which in a small space shows more ex- 

 amples of fitness in adaptation than the 

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