352 'Journal of Comparative Neurology and Psychology. 



cm. bj 85 cm. which were fastened to the frame in the same way 

 as were the boards of the back. The floor, in one piece, Z, rested 

 on the frame at the bottom of the cage and could be taken out for 

 cleaning. In the lower ]3art of board F was a slide door, 8, 24 cm. 

 by 32 cm. whose lower edge was on a level with the floor. The 

 cage was mounted on ball-bearing castors so that it could be moved 

 about easily and quietly. 



The boards on the back, end, and top of the cage were half- 

 tongued so that no cracks appeared between them. They were re- 

 movable and other boards of corresponding dimensions could be 

 substituted. The mechanical devices which were presented to the 

 animals as i^roblems for manipulation were arranged in separate 

 boards. The cage was made ready for experimentation by remov- 

 ing one of the i^lain boards and substituting a board with a device. 

 This convenience made it possible to shift from one experiment 

 to another with facility. 



(c) Problems. — In the two cages eight problems were arranged. 

 These I shall describe in connection with the statements of results. 

 Here it will be sufficient to designate them by name, as follows : 



1. Chute Experiment A. In old cage. 



2. Chute Experiment B. In new cage. 



3. Rope Experiment. In new cage. 



4. Paper Experiment. In new cage. 



5. Screen Experiment. In new cage. 



6. Plug Experiment. In new cage. 



7. Button Experiment. In new cage. 



8. String Experiment. In new cage. 



3. Experime7ital Procedure. — For the most part, the experiments 

 were made between 7 :00 A. M. and 1 :00 P. M. when the animals 

 were in a normal state of hunger and when they were fresh from 

 the night's sleep. During some of the later experiments it was 

 necessary to continue the work until later in the afternoon. In 

 such cases, the feeding time was postponed for the animals so used. 

 The first experiment was made on successive afternoons between 

 two and three o'clock. 



The general plan of the experiments was as follows: First, 

 each animal was given a fair opportunity to learn to manipu- 



