PREFACE 



A great number of my friends have helped materially to make this 

 book possible, by criticizing portions of the manuscript relating to their 

 specialties, by furnishing specimens, information, or technical assistance; 

 and in other ways. I could not omit to mention some of them by name : 

 Ermine C. Case, Alfred Cowan, Elizabeth Crosby, Brian Curtis, Walter 

 F. Grether, Parker Heath, Selig Hecht, Arlington C. Krause, George 

 E. Lathrop, Wade H, Marshall, George A. Moore, Kevin J. O'Day, 

 Erich Sachs, John F. Shepard, Alec Skolnick, Gabriel Steiner, Francis 

 B. Sumner, Samuel A. Talbot, and Burton D, Thuma. During the 

 writing, generous financial support was forthcoming from the Wayne 

 University College of Medicine and from the Jennie Grogan Mendelson 

 Memorial Fund for Ophthalmology. During the actual making of the 

 book, the expert and sympathetic guidance of William L. Wood, 

 director of the Cranbrook Press, has been invaluable. 



I am particularly obligated to the curators of the Museum of Zoology 

 of the University of Michigan and the Cranbrook Institute of Science 

 who read the entire text and straightened my kinks in their especial 

 realms: Carl L. Hubbs (fishes), Helen T, Gaige (amphibians and 

 reptiles) , Josselyn Van Tyne (birds) , and Robert T, Hatt (mammals) . 



Finally, I am most deeply indebted of all to Director Hatt and the 

 Trustees of the Institute for their invitation to write the book as one of 

 their series of Bulletins, and for their generosity in the allowance of 

 space and illustrations. As is so usual with such books, the problem has 

 been to know how much to leave out. My trepidations in this connection 

 have led, during the writing, to several upward revisions of the expected 

 size of the work. I have felt as though I were behaving rather like the 

 camel which at first asked only to warm his nose within the Arab's tent, 

 and finished by crowding out the owner. My conscience will be easier 

 if most of my readers are glad that the book was not smaller. 



G. L. W. 

 Detroit, Michigan 

 May, 1942 



