CATALOGUE OF NORTH AMERICAN DIPTERA. 3 



along, inch by inch, until I am aware of having adopted most of the 

 changes which I at first opposed. In this I have been influenced by 

 the feeling that my catalogue must represent the actual condition of 

 the classification, not merely my own views. Within a family or 

 two, I would insist on the latter ; otherwise it has seemed best to con- 

 cede something to the opinions of others, only interposing a check 

 when some too revolutionary change is attempted (as in altering the 

 name of Rhamphomyia) . I am far from believing that the changes 

 of generic names now becoming common are in the interest of, or will 

 attain, subsequent permanence. Such a hope is illusive. There will 

 always be loop-holes which will allow further change. We are as 

 near to permanence now as we ever shall be. 



System. The sequence of families is substantially that of Osten 

 Sacken's later papers, influenced in minor points by Coquillett. 

 Brauer's system, although finding some favor in Europe at present, 

 appears less expressive of the relations. An abstract of the classifica- 

 tion will be found at the end of the introduction. 



Acknowledgments. First of all, I am indebted to Baron Osten 

 Sacken for his catalogue, the basis of my work. It is the best designed, 

 most accurate, most informing work of the kind that I have ever seen, 

 on any large order or group of animals. Hence it has been a great ad- 

 vantage to me to have such a guide to follow. While I do not claim 

 any such command of the subject as was possessed by Osten Sacken, 

 I am sure that my work has been benefited by the influence of his. 

 I also acknowledge the receipt of frequent encouraging and inspiring 

 letters from him during the progress of my work. He is not, however, 

 responsible for any of the details of my classification. 



To Professor S. W. Williston I am deeply indebted. His encour- 

 agement first induced me to undertake the preparation of this Cata- 

 logue. He gave me many unpublished notes, and looked over the 

 manuscript of the Asilidse. His published bibliographies I found in- 

 dispensable. In this connection I will add that his disinterested labors 

 in the cause during a long series of years, amid the arduous and exact- 

 ing duties of his more immediate specialties, call for our admiration 

 and our gratitude. These labors, considering also his success in adapt- 

 ing his writings to the needs of beginners in the science, entitle him to 

 rank with Osten Sacken as one of the founders of North American 

 dipterology. 



Mr. D. W. Coquillett several times furnished me with information 

 on obscure references, always responding promptly and courteously 

 with just what I wanted. 



Dr. L. O. Howard gave me a number of practical suggestions 

 which influenced the form of my work somewhat ; he also assisted me 

 very materially in getting it printed, and was, as usual, continually 

 giving me unexpected but gratefully appreciated lifts. 



