DESIGN FOR A BRAIN 12/8 



later numbers of organisms after two initial states that differed 

 only in the concentrations of chemical. 



To test whether a state-determined system is dependent on a 

 parameter, i.e. to test whether the parameter is ' effective ', the 

 observer records the system's behaviour on two occasions when 

 the parameter has different values. Thus, to test whether a 

 thermostat is really affected by its regulator he sets the regulator 

 at some value, checks that the temperature is at its usual value, 

 and records the subsequent behaviour of the temperature; then 

 he returns the temperature to its previous value, changes the 

 position of the regulator, and observes again. A change of 

 behaviour implies an effective regulator. 



Finally, an example from animal behaviour. Parker tested the 

 sea-anemone to see whether the behaviour of a tentacle was 

 independent of its connexion with the body. 



4 When small fragments of meat are placed on the tentacles 

 of a sea-anemone, these organs wind around the bits of food 

 and, by bending in the appropriate direction, deliver them 

 to the mouth.' 



(He has established that the behaviour is regular, and that the 

 system of tentacle-position and food-position is approximately 

 state-determined. He has described the line of behaviour follow- 

 ing the initial state: tentacle extended, food on tentacle.) 



'If, now, a distending tentacle on a quiet and expanded 

 sea-anemone is suddenly seized at its base by forceps, cut 

 off and held in position so that its original relations to the 

 animal as a whole can be kept clearly in mind, the tentacle 

 will still be found to respond to food brought in contact 

 with it and will eventually turn toward that side which was 

 originally toward the mouth.' 



(He has now described the line of behaviour that follows an initial 

 state identical with the first except that the parameter ' con- 

 nexion with the body ' has a different value. He observed that 

 the two behaviours of the variable ' tentacle-position ' are identi- 

 cal.) He draws the deduction that the tentacle-system is, in this 

 aspect, independent of the body-system: 



' Thus the tentacle has within itself a complete neuro- 

 muscular mechanism for its own responses.' 



The definition, then, agrees with what is usually accepted* 

 Though clumsy in simple cases, it has the advantage in complex 



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