The Two-winged Flies 



3*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; /./>., lateral processes; t.g., tracheal gills; 

 s., sucker. (Natural length, f to i 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; I. p., lateral 

 process; v.c., ventral nerve-cord; r., rim of sucker; 5., stopper of sucker; nt.s.c., 

 muscles for retracting sucker and contracting body; /., 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- 



FlG. 432. Pupa, dorsal 

 aspect, of net-winged 

 midge, Bibiocephala 

 comstocki. Note re- 

 spiratory leaves on 

 dorsum of prothorax. 

 (Natural length, J inch.) 



