STANDARD WORKS FOR STUDENTS. 35 



exotiques," Zetterstedt's " Diptera Scandinaviae," Walker's " List 

 of the dipterous insects in the British Museum," and " Insecta 

 Saundersiana," Bigot's " Dipteres nouveaux, etc.," Schiner's " Eeise 

 der Novara " and the " Biologia Centrali-Americana." Everything 

 written by at least Loew, Osten Sacken, Schiner, Williston and 

 Van der Wulp should be obtained, whilst the works of Eondani 

 and Bobineau-Desvoidy, though less reliable, are always in 

 requisition. All the writings of living dipterologists should also 

 be consulted. 



7. ESTIMATED NUMBER OF KNOWN SPECIES. 



The DIPTERA, or two-wiuged insects, may be regarded as 

 represented by about 35,000 described species. Of these some 

 portion will, of course, be ultimately relegated to synonymy, but, 

 even after deleting these, the remainder in all probability 

 represent but a tithe of those actually existing throughout the 

 world. 



Many regions have been practically unexplored by the collector. 

 Such parts are the bulk of the South American Continent, where 

 many thousands must remain to be discovered in the immensely 

 fertile valleys of the Amazon, Orinoco, La Plata and other large 

 rivers, and in the teeming tropical districts of the northern part 

 of the Continent. Africa is at present almost unworked, save for 

 the Mediterranean shores, Egypt, Italian East Africa and the 

 Cape ; none of these, moreover, having been treated to a tenth 

 part of the study that has been given to the Diptera of Western 

 Europe. Australia, judging from what I possess of unnamed 

 material in my own collection, must eventually yield a rich 

 quota ; Skuse, the only writer in that country, gave 10,000 as a 

 reasonable estimate of the species probably existent there. Besides 

 these, there are large areas in Asia and even iu Eastern Europe 

 which have hardly been touched by the collector. A very large 

 number of species must still remain to be discovered in the vast 

 North American continent, whilst lesser worked regions of the 

 New World, Mexico, Central America and the West Indies 

 will certainly double or treble their present lists of species, if 

 the enormous increase during the past three or four years in the 

 known forms of the Oriental Region in such groups as have been 

 more thoroughly worked, is any criterion. 



For instance, no family has ever been so systematically or 

 assiduously collected in such a number of varied districts through- 

 out the world as have the CULICID^E during the past ten years or 

 thereabout, and the enormous increase in the recorded species in 

 this family (even allowing for a large proportion of synonyms or 

 varieties only, as was suggested by me a few years ago),* seems 

 to foretell a grand total throughout the whole order of incredible 



; Catal. Orient. Culicida" Rec. Ind. Mus. i, p. 297. 



D2 



