PREFACE. XXI 



n Tbe cases when the publication of detached species of 

 Diptera can be really useful in the present state of american 

 dipterology are rare, and will easily suggest themselves to the 

 good sense of the unprejudiced." 



,,Consciencious monographs are always useful." 



,,Let monographs be prepared of the families of diptera 

 on the same plan as the monograph of the Dolichopodidae by 

 Dr. Loew, or of the Ti-piiUdac by me. Let the series of these 

 monographs begin with the larger forms and the more numerous 

 families, as the Tabanidae*), the Asilidae, the Stratiomyidae, 

 the Bombylidae , the Empidae etc. Such a basis being laid 

 with those families, the study of which is comparatively easy, 

 the difficult ones, as the Chironomidae , the Culicidae and the 

 numerous groups of the Muscidae, will follow. The study of 

 these difficult families must be the work of specialists. Mr. 

 Winnertz, of Crefeld, Prussia, devoted more than twenty-five 

 years to the study of the genus Ceratopoyon , the genus Ceci- 

 domyia and the family Mycetophilidae. During that long period 

 of patient collecting, drawing and describing, he published only 

 four monographs of moderate size. And it is certain that, 

 without such patient collecting, drawing and describing for a 

 number of years, any monograph of such genera as Ccratopogon 

 or Sciara would have been worthless. Diptera are not like the 

 other orders of insects, where a superficial comparison of two 

 specimens enables one, in most cases, to decide, whether they 

 belong to the same species or not. Each family of diptera 

 requires a special study and a dipterologist may be very well 

 versed in some families, without being able to express any 

 opinion with regard to questions, concerning others." 



^Specialization is therefore the motto of dipterology. 

 Amateurs may collect and name diptera, but do not let them 

 publish anything, until they have chosen some single family and 

 nearly exhausted it by study and collecting. If they try such 

 a course, they will find that the exhaustive study of a single 



*) Since writing the above I have published a monographic essay on 

 the Tabauidae. 



