Organisms and Their Origin 107 



goes on for weeks and months, and, if it gets big 

 rests, for years. When its energies flag, it feeds, 

 and recuperates itself. When danger threatens, 

 it seeks its hiding-place. Its life is full of effective 

 responses, and not the least important or marvel- 

 lous is the power of taking a rest. 



{d) Unified Behavior. This naturally leads on 

 to a recognition of the general fact that the living 

 creature has a unified activity, which is usually 

 worthy of being called behavior. In his ** Cray- 

 fish" — one of the best introductions to the study of 

 zoology — Huxley compared the organism to a 

 whirlpool, such as one may see below the Niagara 

 Falls, which is always changing and yet always re- 

 maining the same. Amid ceaseless flux it retains 

 a remarkable sameness. And truly, the living 

 organism is like a whirlpool — a system within a 

 system; streams of matter and energy are continu- 

 ally passing in and as continually passing out; and 

 yet the unity persists. But the comparison does 

 not sufficiently bring out what is so essentially 

 characteristic of the organism, that all its changes 

 are correlated in such a way that persistent unified 

 behavior is in most cases possible. 



Our familiarity with plant organisms may raise 

 a diflSculty, for their whole life seems rounded with 

 a sleep. Plants are continually converting the 

 kinetic energy of the sunlight into the potential 

 energy of complex stored products, while animals 



