The Beginnings of Intelligence 129 



affording a much wider and closer adjustment to 

 the environment. 



The studies which have been made of primitive 

 types of intelligence such as found in crustaceans, 

 fishes and amphibians have shown that associations 

 are formed by a gradual process of reinforcement 

 or inhibition of a particular reaction to a given stim- 

 ulus. The method followed is one which Lloyd 

 Morgan has designated as "trial and error." It 

 may be illustrated by the experiment of Yerkes on 

 the formation of associations In the crayfish. In 

 these experiments a box was employed into one 

 end of which the crayfish was admitted through a 

 narrow aperture. The other end of the box was 

 divided by a median partition which gave the cray- 

 fish a choice of two routes to a tank of water at 

 the other end into which the creature was naturally 

 desirous of getting. One of the two ways to the 

 water was closed by a glass plate at its farther end 

 so that the crayfish was afforded a choice of a right 

 and a wrong path to the water. Would the crayfish 

 after a numbei: of trials learn to choose the right 

 path and avoid the closed passage? In the first ten 

 experiments the crayfish went as often to the right 

 as it did to the left, but in the next ten trials the 

 percentage of correct choices was somewhat greater. 

 Finally after a large number of trials the animal 

 came to choose the right path to the water, mak- 

 ing but rarely any mistakes. 



Similar experiments with crabs, fishes and the 



