PREFACE 



In the preparation of this paper the writer has been greatly bene- 

 fited by the advice and assistance of a number of eminent scientific 

 workers here in Washington. To Dr. Paul Bartsch I am conspicu- 

 ously indebted for cooperation and helpful advice in connection with 

 the preparation of this paper. The late Dr. B. H. Ransom, who was 

 chief of the Zoological Division of the Bureau of Animal Industry 

 of the Department of Agriculture for the greater part of the time 

 during which the paper was in preparation, made possible by his 

 constructive policy the carrying out of such a project by the present 

 writer. From Dr. Maurice C. Hall, his successor as chief of the 

 Zoological Division, I have received much valuable advice and, in 

 addition, I have used his study of the nematode parasites of rodents 

 as a model. To Dr. Albert Hassall I am indebted for aid in securing 

 the literature upon which much of this study is based. Dr. H. C. 

 Oberholser of the Biological Survey has revised the host names and 

 indicated the synomyns of these names which have been used in the 

 text; I am greatly indebted to him for this courtesy, involving as it 

 did in some cases a prolonged search for the identification of a re- 

 ported bird. To W. S. D. Haines is due much credit for copying the 

 illustrations. The National Geographic Society kindly aided me in 

 locating obscure places from which reports of collections had been 

 made. 



E. B. C. 



