112 L. W. COLE 



their investigation, as given in their paper, -are relative as are 

 those of the present paper. 



The chicks. In the experiments sixty-eight barred Plymouth 

 Rock chicks were used, six in preliminary tests and sixty-two 

 under the established conditions of the experiments. The eggs 

 from which the chicks were hatched were all obtained from a 

 single poultry breeder and were guaranteed to be of pure stock. 

 It was necessary, however, to purchase six young chicks of 

 another breeder, but these also were warranted to be pure 

 barred Plymouth Rock chicks and they were kept until it was 

 certain that they presented no marks of difference from the 

 rest of our chicks. Six chicks were used in every series of tests 

 except three. Under the medium condition of discrimination 

 with the weakest stimulus which was employed four chicks were 

 used, while in each of two other groups a chick became sick 

 during the progress of the experiments. 



When the chicks were eight days old they were given two 

 days of preliminary training (twenty trials) in order that they 

 might learn the way through the experiment box. This was 

 followed by twenty trials in order to ascertain whether the 

 chick had a preference for either the lighter or the darker screen, 

 thus the training series began in every case on the twelfth day after 

 hatching. The training continued until the chick had made 

 twenty consecutive choices of the darker screen. Thus the order 

 of tests, for each chick, was (i) preliminary series, (2) prefer- 

 ence series, (3) training series. 



Apparatus. Figure i represents in its essential details the 

 apparatus w^hich was used in the investigation. The electrical 

 connections are omitted and the electric key, K, was somewhat 

 further to the right than appears in the figure. For convenience 

 of description we may consider the apparatus as composed of 

 three divisions or boxes, (i) The hover box, O; (2) the illumina- 

 tion box which contains the electric lamps and has for its nearer 

 end the two opal glass screens N-, and N3, and their frame or 

 holder; (3) the experiment box which has the screens and holder 

 for its remote end and consists of tw^o compartments, A. and C. 



The hover box, O, had dimensions of 100 x 27.5 x 21 cm.* 

 Its floor w^as covered with sand and midway of its length was 



* All dimensions are given in the order length, width, and depth, and are inside 

 measurements. 



