288 The Animal Mind 



species of flies that live on the seashore, feeding on dead 

 fish and the like, says that they will abandon the " head-on" 

 position which they regularly assume toward the wind, if 

 attracted by the odor of food (370). 



Wherever we find that one class of stimuli regularly 

 yields to another if the two act together, it is safe to assume 

 that the prepotent stimulus is more important to the organ- 

 ism's welfare than the vanquished one. And while we can- 

 not without more ado call such cases of the interference of 

 stimuli as are found in very simple animals cases of attention, 

 and ascribe to their psychic accompaniments all the character- 

 istics of attention as a feature of our own experience, yet we 

 may assert that they have in common with attention the sig- 

 nificance of being a device to secure reaction to the most vitally 

 important of several stimuli acting at once upon the organism. 



97. Methods of securing Prepotency of vitally Important 



Stimuli 



An inanimate object acted upon by several forces at once 

 is determined in its motion by their relative intensity. Con- 

 ceivably, an extremely simple form of animal life, when 

 subjected to two stimulations acting together, would also 

 respond in a way answering precisely to the relative strength 

 of the two. It is easy to see what would be the disadvantage 

 of such a state of affairs for the animal. The weaker of 

 the two stimuli might be of far greater significance for organic 

 welfare than the stronger. For example, it would often be im- 

 portant that an animal should be able to respond to a very 

 faint food stimulus rather than to any of the stronger forces 

 acting upon it. Evidently a prime need of animal life is 

 some arrangement whereby weak but important stimuli 

 shall be given the preference in determining reaction over 

 stronger but less vitally necessary ones. Sense organs are 



