I 



ACKNOWLEDGMENTS 



The writer's heaviest obHgation is to Professor John B. Wat- 

 son, Director of the Psychological Laboratory of The Johns 

 Hopkins University, without whose unsparing suggestions and 

 criticisms, the work could not have been brought to a successful 

 conclusion. 



Dr. Knight Dunlap, Associate Professor of Psychology at 

 The Johns Hopkins University, offered much needed assistance 

 in the handling of the data. 



Dr. Gardner C. Basset, of Pittsburgh University, gave valu- 

 able suggestions regarding technique and method. 



Dr. Henry H. Donaldson of The Wistar Institute of Anatomy, 

 furnished practically all of the rats used for breeding purposes 

 as well as a few of those employed in the experiment, and was 

 most helpful in suggestions throughout the experiment. 



Dr. Shinkishi Hatai of The Wistar Institute of Anatomy, pre- 

 pared anatomical data for each rat used in the experiment, 

 which cannot be adequately handled in this discussion, and 

 which will probably be taken up in a separate publication to 

 appear later. 



