The Two-winged Flies 
3 1 5 
larvae squirm slowly around, feeding on diatoms and other microscopic water 
Fig. 430. Fig. 431. 
Fig. 430.—Larva of net-winged midge, Bibiocephala comstocki. At left, dorsal view; 
at right, ventral view, ant., antennae; l.p., lateral processes; t.g., tracheal gills; 
s., sucker. (Natural length, § to b inch.) 
Fig. 431.—Cross-section of body of larva of net-winged midge, showing anatomical 
details of sucker and other parts, h., heart; al.c., alimentary canal; l.p., lateral 
process; v.c., ventral nerve-cord; r., rim of sucker; s., stopper of sucker; m.s.c., 
muscles for retracting sucker and contracting body; t., tendon at end of muscles. 
(Much enlarged.) 
organisms, and never suffering themselves to get into slow water, 
planted from the highly aerated swift water of the 
stream’s center to the slow water of eddies or pools 
along the bank, they die very soon. When ready 
to pupate they gather in small patches, still keeping 
in the swift water, and each changes into a curious 
flattened, turtle-shaped, motionless, non-feeding pupa 
(Fig. 432) which is safely glued to the rock face by 
its under surface. The dorsal wall is thick and black, 
and projecting from it at the broad front head end 
is a pair of breathing-organs, each composed of three 
or four thin plate-like gills. When the fly is ready 
to emerge the pupal skin splits longitudinally along the 
back, and the delicate body pushes up through this 
slit, and through the shallow swift water until the 
wings can be outspread. All this is quickly done, 
the fly being enchained by its long legs, which cling 
to the pupal shell until it can fly away. But the 
Trans- 
Fig. 432.—Pupa, dorsal 
aspect, of net-winged 
midge, Bibiocephala 
comstocki. Note re¬ 
spiratory leaves on 
dorsum of prothorax. 
(Natural length, | inch.) 
