268 ADA W. YERKES 



forms of behavior of these rats, which had then reached the 

 twelfth generation of inbreeding. The scope of the work was 

 more limited than that of Doctor Basset because of lack of time, 

 and the number of animals tested was smaller. My thanks are 

 due Doctor Donaldson of the Wistar Institute for supplying us 

 with our original stock of rats, and to Doctor Hatai for the 

 examinations which supplied the anatomical data. I wish, also, 

 to express my thanks to Mr. Pedrick and Mr. Dine for assist- 

 ance with some of the experiments. 



The inbred rats which were sent to us in October, 1913, were 

 of the thirteenth generation. In January some belonging to 

 the twelfth and also to the fourteenth generation were obtained. 

 Our normal control rats were secured partly from the Wistar 

 Institute and partly from Miss Lathrop, Granby, Massachusetts. 

 They were kept in a special room in the laboratory on the fourth 

 floor of Emerson Hall, in clean wire cages, with sawdust on the 

 floor and shredded tissue paper for nests. They were fed bread 

 soaked in milk, cracked corn, oats, and occasionally green stuff, 

 such as lettuce and celery tops. For some reason still unknown 

 to us, although they appeared for the most part to be in excel- 

 lent physical condition, they bred very slowly, and the work 

 was occasionally delayed for lack of material of the right age. 

 The rats with which the later experiments were made were 

 also considerably underweight for their age, as shown in the 

 anatomical data of table 11 (p. 293). It was found imprac- 

 ticable to forward to Philadelphia for examination the rats used 

 in the earlier tests, so that the relative brain weights are given 

 for only the last lot of seven rats. 



Two methods were employed in the comparative study of 

 the behavior of stock and inbred animals: the maze and the 

 brightness discrimination methods. Time, distance, and error 

 data were obtained for the maze experiments; and time and 

 error data for the discrimination experiments. 



1. MAZE EXPERIMENTS 



The type of maze used in these experiments was the circular 

 one devised by Watson. 3 The method of recording the path 



3 Watson, J. B. A circular maze with camera lucida attachment. Jour. An. 

 Behavior, 1914, 4, 56-59. 



