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KARL T. WAl'CH 



forth in the box. A scale is marked off on the floor of the box, 

 extending from the point X at the end of the passageway to the 

 opening into the nest. 



Method: The animals are started from the enclosure A 

 through the box toward the nest. Mice, owing to a stereotactic 

 instinct, tend to linger in the passage and then dash quickly forth 



Fig. 7 Apparatus for the study of perception of depth (third dimension). 

 A, triangular entrance chamber; X, passageway; B, C, moveable board partitions; 



N, nest-box. 



across the open space toward the nest. In the experiment, there- 

 fore, the animal must observe from the point A' which of the two 

 partitions, B or C, is the nearer. If the partition on the left is 

 nearer the animal, it is evident that, in order to pass through, 

 he must swerve to the right as he rims forward, and then turn 

 sharply to the left. If the partition on the right is the nearer, a 

 manoeuvre of the opposite sort is necessary. The mice should 

 turn correctly in case they have perceived from X the true rela- 

 tive positions of the two partitions. 



In the experiments food was scattered in the enclosure and the 

 animals were allowed to run back and forth between it and the 

 nest a few times, then while an animal was in A, the partitions 

 were changed and a sharp clap of the hands sent him toward the 

 nest. His behavior at the point X and at B or C was noted with 

 care. 



Thirteen mice were used. 



