DIPTERA 



811 



present; the antennas, as a rule, lack whorls of hairs (Fig. 1027) and 

 all the tibiae are furnished with spurs. 



At first sight considerable variation seems to exist in the venation 

 of the wings as shown in the three wnngs represented in Figure 1028; 

 but in realit}^ the variations are comparatively slight. The costa 

 extends along the margin of the wing to the end of the radial sector. 

 Radius preserves three branches in the more generalized forms (Fig. 

 1028, a); in some genera veins Ri and R2+3 coalesce from the apex of 

 the wing backward for a greater or less distance so that the basal part 

 of vein R2+3 appears like a cross-vein (Fig. 1028, b); in some genera 



^...^, 



/?.+= 



/M+, 



Fig. 1028. — Wings of fungus-gnats. (The drawings are after Winnertz; the 

 lettering is original.) 



radius is only two-branched, this condition may have been brought 

 about by the complete coalescence of veins Ri and R2-f3 or by the 

 coalescence of veins R2-1-3 and R4+5, whichever may be the case the 

 two branches are cornmonlv designated as Ri and Rg respectivelv 

 (Fig. 1028, c). ' . 



The fungus gnats are exceedingly numerous both in nimiber of 

 individuals and in number of species. They are often found in great 

 numbers on fungi and in damp places where there is decaying vege- 

 table matter. They are active and leap as well as fly. 



A monograph of the known species of the world, not including the 

 Sciarinse, was published by Professor Johannsen ('09a) ; and in a later 



