240 'Journal of Comparative Neurology and Psychology. 



ground plan, respectively. The subject, after being placed in the nest 

 box, A, by the experimenter, was permitted to pass into the entrance 

 chamber, B. Then a piece of cardboard, which was placed between 

 the animal and the opening into A, was slowly moved toward L, E, 

 of Figure 2. Thus the dancer was brought face to face with the tAvo 

 entrances, L and R, of this figure (B and W, i. e., black and white 

 of Figure 1). One of these it would soon attempt to Qnter in order 

 to escape to the nest box, and thus find space for dancing. If it 

 started to enter the black box (and this might be either the box on 

 the left, L, or the box on the right, R, for the white and black card- 

 boards, which were at the entrances and within the boxes, could be 

 transferred readily by the experimenter) it was immediately given 

 a weak electric shock by the closing of the key, K. This usually 

 caused it to retreat from the box and to try the other entrance. In 

 case it entered the black box in spite of the shock, it was not permitted 

 to escape by way of E and to the nest box, but instead was forced 

 to return to B and again make choice of an entrance. This was 

 continued until the white box was chosen, then the animal was allowed 

 to return to A. After an interval of one or two minutes it was given 

 another opportunity to select the right entrance. This was con- 

 tinued until the white box had been chosen ten times. Such a group 

 of ten trials constitutes what we shall refer to as a series. One series 

 was given each individual daily from the beginning of experimenta- 

 tion until the acquisition of a perfect habit of discrimination and 

 choice. 



The positions of the white and black cardboards were changed in 

 precisely the same way for each individual according to an order 

 which has already been described.* These shifts in the position of 

 the white box were made in order to prevent the mouse from acquir- 

 ing the habit of going regularly to the entrance at the left or at the 

 right. 



An experiment (test or trial) was recorded as yielding an error of 

 choice if the mouse entered the wrong box far enough to get a shock ; 

 as yielding a correct choice if, without first entering the black box, 



*Jour. of Comj). 'N cur. and Psy., vol. 18, p. 461, 1908. 



