THE PROBLEM OF LEARNING 



l8l 



away. The animal was usually given five trials 

 on a single day. From October 12, 191 1, to 



Figure 55. Perspective of T apparatus for study of habit 

 formation in the earthworm; Ai, plate-glass base for parts of 

 apparatus; A2, layers of white blotting paper covering ap- 

 proximately two-thirds of Ai ; w, w, w, w, plate-glass walls of 

 T-shaped passage-way; En. T., wooden entrance tube, lined 

 with moistened blotting paper, from which worm enters pas- 

 sage-way, as indicated by arrow (the cover of the tube is 

 shown removed; Ex. T., wooden exit tube in position for re- 

 ception of worm as it emerges from open arm of glass T (in 

 this case, the cover is in position) ; P, strip of sandpaper resting 

 on A2 and extending across passage-way; E, pieces of copper 

 wire serving as electrodes, insulated and kept at fixed distances 

 from one another by the corrugations of the strip of rubber, R; 

 I, inductorium, wires from the secondary coil of which termi- 

 nate in the electrodes at E; K, key in primary circuit of in- 

 ductorium; B, dry cell. From Yerkes, Intelligence of Earth- 

 worms, Jour. Animal Behavior, vol. 2, p. 332, 1912. 



April 30, 19 1 2, a single worm was given 850 les- 

 sons (trials) in passing through the labyrinth. 

 In the latter part of the experiments, the worm 



