Introduction 



Acknowledgments 



It is impossible to express fully my appreciation of the generous 

 cooperation of all those who have assisted in the preparation of this 

 Avork. It is most fitting that I should mention first the generosity of 

 Mrs. S. W. Williston for not only permitting me to use the illustrations 

 from Williston 's "Manual of North American Diptera", but for her 

 offer to furnish the cuts themselves. Needless to say this offer was ac- 

 cepted and many of the illustrations are reproduced from cuts used in 

 the ]\Ianual. Unfortunately, due to a rearrangement of many genera 

 and their transfer to different families, it has not been possible to use all 

 of the cuts. Further, in this connection, I owe much to ]\Irs. George 

 Shor, a daughter of Dr. and Mrs. Williston, for her assistance in this 

 matter, and for her sympathy in the work. It might not be out of place 

 to mention here that, according to Mrs. Shor, her father, upon the com- 

 pletion of the manuscript of the third edition of his Manual, dropped it 

 upon his desk and remarked: "Well, that's finished. When it is re- 

 vised again, it will be by someone else. ' ' 



Every request for the loan of specimens and for the review of 

 keys met with a wholehearted response and as a result the value of this 

 book has been greatly enhanced. Dr. C. P. Alexander is deserving of 

 especial thanks for the preparation of the manuscript dealing with the 

 Tipuloidea and the preparation of the illustrations for that superfamily. 

 Drs. Jos. Bequaert, C. T. Brues, 0. A. Johannscn, Roljert IMatheson, F. 

 ]\I. Root and ]\Ir. IMarston Bates liave assisted very materially in clieck- 

 ing over keys and suggesting changes. Dr. E. P. Felt suggested the use 

 of illustrations from his papers published in the Bulletins of the New 

 York State Museum on the Ceeidomyid» (Itonidida^) and Dr. C. C. 

 Adams very generouslj^ furnished the cuts. Drs. J. M. Aldrich, F. H. 

 Benjamin and Mr. Marston Bates, and others have loaned specimens not 

 found in the American I\Iuseum collection and Dr. ]\Iatheson has given 

 permission to use illustrations from his "Handbook of the Mosquitoes". 

 I wish also to express my a])preciation to all those Dipterologists of the 

 past and present whose works have been so freely drawn upon. 



The preparation of a work of this kind entails a large amount of 

 stenographic and routine work and for the careful typing of the manu- 

 script I am indebted to ]\Iiss Ethel Olsen. j\Ir. Adolph Klein has con- 

 tributed the excellent colored plate of several typical forms, while my 

 wife has assisted with the illustrations and in many other ways. 



