78 MEDICAL ENTOMOLOGY 



squama. The last named is generally a distinct portion of the wing, 

 and is much thicker and coarser than the rest, and has often a fringe 

 of fine hairs around its border ; it is separated from the wing except 

 at one point, and is folded underneath in repose, so as to be in con- 

 tact with the antisquama, this being accomplished by a mechanism 

 such as that described when dealing with the anatomy of the thorax 

 of Tabanus. 



The wings may be simple, transparent, and more or less iridescent, in 

 which case it is usual to find a row or rows of short but stout spines 

 on the principal veins, or their surface may be mottled in various 

 ways, as in Haematopota. The veins may have no other coating 

 than the rows of spines, or they may bear scales of various sorts, as 

 in the Culicinae. The scales may be all of one colour, as in the 

 Culex group, or they may be variously coloured, and impart to the 

 wing the dappled appearance which is characteristic of the Anopheles 

 mosquitoes. In Phlebotomus they are covered with a dense layer of 

 fine hairs. 



The veins of the wing present great and important variations in 

 the different families, and the venation is, by common consent among 

 dipterologists, regarded as one of the most important 

 factors in deciding systematic position. As a general 

 rule the more primitive the form the more equally will the wing veins 

 be distributed over the surface, and the more advanced then the more 

 will they be concentrated towards the anterior border, the most ante- 

 rior veins of all becoming shorter and joining the anterior margin of 

 the wing at a more proximal point. The veins radiate from the nar- 

 row base, where they are continuous with the sclerites which control 

 the movements of the wing. The longitudinal veins are here and 

 there united by short cross-veins, and, with these and the margins of 

 the wing, the whole area is divided into a number of spaces called 

 cells. As the veins are crowded to the anterior border the more 

 anterior of these cells become reduced in a corresponding degree, the 

 posterior part of the wing being left clear. 



Several systems of nomenclature have been devised with regard to the 

 veins, two of which are in common use at the present time ; one of these 

 has the advantage of ease of application and has up to the present 

 time been the most used of any, while the other, that of Comstock 

 and Needham, has the greater scientific value in that it attempts to 

 bring the Diptera into line with other insects. It is probable that in 

 the future it will replace the older method. 



