Bui. 329, U. S. Dept of Agriculture. 



Plate IV. 



Heads and Rectal Gills of Simulium Larv/e. 



Fig. 1. — Head of larva of Simulium pictipes. Fig. 2. — Head of larva of Simulium vittatum. 

 Fig. 3. — Head of larva of Simulium jcnningsi. Fig. 4. — Head of larva of Simulium venus- 

 tum. Fig. 5: — Rectal gills of larva of Simulium fonningsi, typical form. Fig. 6. — Rectal 

 gills of larva of Simulium vittatum, variety with small lobes at base. Fig. 7. — Rectal 

 gills of larva of Simulium bracteatum, typical form. Fig. 8. — Rectal gills of larva of 

 Simulium pictipes, typical form. Fig. 9. — Rectal gills of larva of Simulium venustum, 

 typical form. All greatly enlarged. (Original.) 



