188 ANIMAL BEHAVIOUR 



general action, just as in animals in which a common centre 

 produces the action." As von Uexkiill puts it, when a dog 

 runs, the animal moves its legs; when a sea-urchin crawls, 

 the legs (spines) move the animal. 



The astounding fact is the unification of behaviour that 

 may occur in such a " republic of reflexes ". When a sea- 

 urchin is placed upside down, a continuation of all the usual 

 reactions would cause it to move on in an inverted position. 

 But as von Uexkiill has shown, the unusual physiological 

 state induces a thoroughgoing change in the behaviour of the 

 spines, they depart altogether from routine, and work adap- 

 tively to the needs of the organism as a whole, the animal 

 being turned right again. This warns us not to think of 

 reflexes woodenly; and if we need another warning we 

 may get it in the extraordinarily subtle reflex by which a 

 flatfish adjusts its coloration to that of the immediate en- 

 vironment of shingle. 



Reflex Responses are Affected by the Physiological Con- 

 dition of the Organism. In stinging animals, such as sea- 

 anemones and medusae, there are numerous reflex actions 

 of an adaptive kind, concerned, for instance, with feeding. 

 But it has been shown by Professor Jennings and others that 

 the reaction is not simply a question of predetermined struc- 

 ture and an external stimulus. The answer depends on the 

 relation of external conditions to internal processes. " We 

 cannot predict how an animal will react to a given condition 

 unless we know the state of its internal physiological proc- 

 esses " (Jennings, 1906, p. 231). Thus, to take a simple 

 case, a sea-anemone cheated several times with false food 

 ceases to exhibit the normal reflex. Many a sea-anemone, 

 e.g., the large Stoichactis helianthus, will remove food from 

 the oral disc if it is not hungry. A specimen of Metridium 



