ACKNOWLEDGMENTS 



The experiments herein reported were carried out under the 

 direction of Dr. Harvey A. Carr of The University of Chicago 

 who has been unsparing in suggestion, supervision, and criticism. 

 To him I wish to express my sincerest gratitude for his un- 

 wearying kindness and interest. 



My thanks are due Professor James R. Angell, Dr. W. S. 

 Hunter, and Dr. Clarence S. Yoakum for their thorough and 

 stimulating instruction. My initial interest in Animal Psychol- 

 ogy is due to my contact with the enthusiasm and scientific 

 ability of Dr. Hunter. 



For helpful suggestions I am indebted in particular to the 

 work of Wylie; in general, to those other investigators whose 

 work is cited in this report. 



Acknowledgment is also due Mr. J. Hall Sheppard, a graduate 

 student in the University of Texas, for assistance in the early 

 training of some of the animals, and to Mrs. Yarbrough for 

 assistance in preparing the manuscript. 



Jos. U. YARBROUGH. 



University of Chicago, 

 Feb. 25, 1920. 



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