PRIMITIVE TYPES OF INTELLIGENCE 185 



periments with both passages open to determine if they had 

 any tendency to go toward the right or the left, and after 

 it was shown that either path was chosen with equal readi- 

 ness, the glass plate was inserted and the animals put again 

 into the box. In the first experiment the crayfish took the 

 correct path in 50 per cent, of the trials, and during the 

 subsequent trials the percentage of correct choices gradually 

 rose until in the final ten trials it reached 90 per cent. The 

 improvement was very gradual, as is indicated by the follow- 

 ing series of percentages of successful trials for each set of 

 ten trips: 50, 60, 75.8, 83.3, 76.6, 90. Although slowly 

 acquired, the habit of following the right path was not 

 forgotten after an interval of two weeks. 



Further experiments in which the box was thoroughly 

 washed out after each trip to eliminate any guiding influence 

 of odor or moisture gave similar results. If after a cray- 

 fish had learned to turn to the right, the right pathway was 

 closed, the animal, after a number of trials, would turn to the 

 left. One specimen which had come to turn to the left in 

 the first fifty trials, turned to the left uniformly thereafter 

 in the following fifty trips. The left side was then blocked 

 by the glass and in the next fifty trips forty were successful. 

 Finally the crayfish made but one error in fifty trials. 

 Further changes in the position of the glass plate were made, 

 but the crayfish after a number of trials adjusted itself to 

 the new condition. 



The docility of the crayfish is shown also by some experi- 

 ments of the writer in which the animals were trained to come 

 for food. To quote from a previous paper: "At first I 

 would very slowly bring a piece of meat held in a fine forceps 

 near the antennules. After the movements of the antennules 

 and mouth parts, the grasping movements of the chelipeds 

 would result in securing the meat. After some trials I would 



