VIII INTRODUCTION. 



perseverance he can not fail to overcome whatever obstacles 

 families and genera may present. He will be very much 

 aided at the beginning by having a tolerably large collection 

 at his command by which to make comparisons. Difficulties 

 will often disappear with positive evidence before him, where 

 negative characters are puzzling. With each genus in a fam- 

 ily positively determined the difficulties and uncertainties of 

 others will gradually disappear. S^^juji- 



To determine his species the w inter will need access to a 

 large number of papers, lists of which to the present time will 

 be found in the catalogue of Osten Sacken, and on page 

 xxxiii of the present work. There are a few masters of 

 dipterology, and the student wdll never err in consulting their 

 writings, no matter upon what subjects they may be. Of 

 these I would especially mention Meigen, Wiedemann, Schiner, 

 Winnertz, Loew, Osten Sacken, Brauer and Wulp. Other 

 writers whose works are indispensable, but who are not to be 

 trusted as guides, are Macquart, Walker, Rondani, Bigot, 

 Desvoidy, etc. Of the contemporary writers whose works will 

 be found useful, and in most cases valuable, may be mentioned 

 Verrall, Meade, Eaton and Austen of England ; Bergenstamm, 

 Mik, Strobl and Kowarz of Austria; Becker, Ruebsamen, 

 Girschner and Boeder of Germany ; Schnabl and Dziedzicki of 

 Poland; Giglio-Tos and Bezzi of Italy ; Bergroth of Finland ; 

 Skuse of Australia; the Lynchs of South America; Aldrich, 

 Banks, Coquillett, Johnson, Scudder, Snow, Townsend and 

 Wheeler of this country. Probably the most useful single 

 work that the student will find after Osten Sacken's Cata- 

 logue (Smithsonian Ins. 1878; is Schiner's Fauna Austriaca, 

 and the most useful foreign periodical the Wiener Ent. 

 Zeitung, of which the accomplished Mik is one of the editors. 

 The Zoological Record will be almost indispensable in ascer- 

 taining what has been done during the past thirty years. 

 For the beginner I would especially recommend Comstock's 

 Manual for use in conjunction with tliis work. 



