4 Fa^iii.iks AM) Gexeka of 



wlicrc the same description under Osten Sacken's name he would 

 feel certain did not ai)i)ly. Doubt of tlie right generic location of a 

 specimen may often he surest dissipated l)v attempting to refer to 

 some species. In fact the only way that the ])resent writer was en- 

 abled to generically determine the larger part of his species in his 

 earlier studies was by first ascertaining the species. Until the stu- 

 dent has acquired a sort of intuitive ac<|uaintance with tiic different 

 families, the work will often be tedious, but, by perseverance, he 

 can not fail to overcome whatever obstacles families and genera 

 ma.v present. He will be very much aided, at the beginning, how- 

 ever, by having a tolerably large collection at his command — already 

 named b}' some one else if convenient — by which to make compar- 

 isons. Difficulties to the inexperienced will often disappear, with 

 positive evidence before him, where negative characters are puz- 

 zling. 



To determine his species the student will need a large scries of 

 papers, a list of which uj) to 1878, will be found in Osten Sacken's 

 Catalogue, and from that time to the present in the concluding 

 pages of this work. But, very much can be done with a much 

 snuiller and more accessible list. After he has become acquainted 

 with the order in general, he can select any particular group and 

 l)rocure the papers for systematic work in that group at compara- 

 tively small expense. Much the larger part of the descriptions, it 

 is true, will be found in foreign languages, but that need not deter 

 him ; descriptive phraseology is verj' simple, and it needs but a little 

 exertion to become sufficiently accjuainted with the four or five lan- 

 guages to read descriptions in them with ease or even to write them, 

 if need be. A tiiorough knowledge of the German, however, is ab- 

 solutely essential before much lieadway can be made. As in many 

 other branches of biology, German literature is by far the most im- 

 portant and abundant — indeed it is almost a matter of doubt whether 

 the balance between the bad and good in dipterological literature 

 by the French, English and Italian authors is not almost equal, 

 and this without intimating anything against the really good authors 

 these countries have jjroduced : Walker, Desvoidy and Lioy make 

 a combiiuition hard to match in any branch of science. 



The following works are to l)c connnended for the use of the be- 

 ginner 



OSTEX Sacken. Catalogue of Diptera, 2il edition, Smithsonian 

 Institution, 1878. 



