172 THEORETICAL BIOLOGY 



Not until we have completely worked out all the function- 

 circles of an animal, do we get some idea of the closed sur- 

 rounding-world, which on all sides shuts off each individual 

 subject from the rest of the world, and forms the only outer 

 world it knows. 



It is especially instructive to know the medium thoroughly. 

 If we place before us, as our indicator, some human tool, 

 its counter-framework is built up from our indications con- 

 nected together into a unity by our rule of use. If we try 

 to do the same thing for other animals, we find ourselves 

 unable to set up any adequate rule of the kind. (Not even 

 in the case of our domestic animals, trained as they are for 

 our service.) Instead, we are always seeking rules of action 

 by which we may connect up animals into living unities. 

 A dog, for instance, is not merely a tool that we use for hunt- 

 ing ; but — quite apart from its services to us — it embodies 

 for us human beings a whole number of action-rules, when 

 it barks, eats, runs, etc., and these combine together into one 

 extremely complex action-rule for the whole. 



In this way the indicator " dog " becomes for us the 

 epitome of a rule assigned to it for the totality of its actions ; 

 and this rule distinguishes it from all other indicators. 



If now we confront one animal with another as indicator, 

 it is obvious that the indicator must change according to the 

 nature of the animal receiving the indication. If the latter 

 has not the power to receive its own action-rules in its mark- 

 organ, the former does not constitute a unity for it. It is 

 only we, as observers, who are in a position to see the indicator 

 as a unity, in virtue of our own action-rules, which we trans- 

 fer to it. 



Nevertheless, we know that the indicator may form a 

 special unity in the senses of the receiver of the indication, as 

 bearer of function-rules, even if not as bearer of action-rules. 



If we take a star-fish as indicator for a sea-urchin, the 



