viii Acknowledgments 



The pen-and-ink drawings at the chapter endings are by William 

 Montagna of Cornell University. 



To W. L. McAtee of the U. S. Fish and Wildlife Service, I am most 

 grateful for careful editing of the whole work. 



I have left for the last my deepest obligation. I want to thank 

 Dr. Arthur A. Allen of Cornell University for his wise and kindly 

 guidance in my chosen field for many, many years, and for his help-, 

 ful suggestions on the organization and writing of this book. 



