THE WORLD OF LIVING ORGANISMS 127 



The actions directed by the animal towards the outer 

 world produce the third world, the world of action. 



World of action and world-as-sensed together make a 

 comprehensive whole, which I call the surrounding-world. 



The entire function-circle formed from inner world and 

 surrounding-world (the latter divisible into world of action 

 and world-as-sensed) constitutes a whole which is built in con- 

 formity with plan, for each part belongs to the others, and 

 nothing is left over to chance. 



If this circle is interrupted at any point whatsoever, the 

 existence of the animal is imperilled. 



It is not possible to write the biology of an animal unless 

 one has first studied its function-circle from every side. 

 However different they may be, all parts of it are equally 

 important. When we go on to study the various parts in 

 detail, this continuity of the complete whole must never be 

 lost sight of. 



THE FUNCTION-CIRCLES 



Just as we broke up the function-circle into sectors, so 

 we proceed to divide up the totality of function-circles into 

 separate circles or circle-groups, which, biologically con- 

 sidered, are absolutely distinct from one another. 



The first is the circle of the medium. This circle is charac- 

 terised by the fact that the medium itself exerts no stimulus 

 on the animal ; while on the other hand, if the animal forsakes 

 the medium, a stimulus is immediately released, which results 

 in the animal's being guided back into it. Accordingly, the 

 medium is so constituted that in itself it possesses no indica- 

 tions on which the animal can seize ; the water does not 

 influence the fish, but the air does as soon as the fish comes 

 to the surface. Conversely, for the animal living in the air, 

 the water is a stimulus, but the air is not. Animals are able 

 to live only in water or in air ; even when they live under- 



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