THE ANALYSIS OF BEHAVIOUR 151 



its shell, and for a time it is almost unprotected against many 

 natural enemies. In such cases it seeks shelter in a crevice among 

 the stones or weed on the sea floor, and so conceals itself. These 

 are examples of responses involving the activity of the sensori- 

 motor system, but they are fixed, " mechanical " ones that have 

 become part of the organisation of the animals displaying them ; 

 they are transmissible by heredity, and they do not have to be 

 acquired individually. It is true that they must have been 

 acquired some time or other, but in a different way from the 

 cases which we are aljput to mention. 



Young chicks learn to distinguish between small stones and 

 grains of corn. Collie dogs find that they ought to leave sheep 

 alone, and soon do so. Retrievers pick up, and bring back, game 

 without crushing or eating it. Cats and dogs learn to open 

 latches, to beg for food, and to recognise people who take notice 

 of them. A man puts on an overcoat when the weather becomes 

 cold, and the master of a ship alters his course when a sudden fall 

 of the barometer in certain latitudes suggests that a cyclonic 

 storm is approaching. These are all true adaptations, and each 

 of them ends in the animal obtaining advantage to itself of some 

 kind or other. They all involve intelligent acting of the sensori- 

 motor system, and they are based upon experience. Some time 

 in the past similar external changes have occurred, and the 

 responses made have been successful or not that is, they have 

 or have not been advantageous. The stimulus is remembered, 

 and also the nature of the responses made, so that when the 

 same external event, or change, recurs the unsuccessful response 

 is avoided and the successful one is made. It does not matter 

 that the master of a ship which is approaching a cyclonic storm 

 may not himself ever have had this experience; he has acquired 

 the experience of others, and knows what response is the advan- 

 tageous one. 



Behaviour, in the sense that we employ the term, is therefore 

 the functioning of the sensori-motor system which is based upon 

 experience. By " experience " we mean individual acquirements, 

 and not something that is inherited. When experience becomes 

 a factor in the determination of the particular response that is 

 being made to a stimulus, something new that is, something 

 that we have not yet considered is included in the activities of 

 the animal organism, and our conception of mechanistic responses 

 must be re-examined, 



