NO. I 



THE INSECT HEAD — SNODGRASS 



23 



Fig. 10. 



-Formation of a hypostomal bridge between the occipital foramen and 

 the labium. 



A, Pteronidea ribesii, Hymeiioptera, hypostomal lobes (HL) small. B, Dia- 

 gram of hypostomal lobes enlarged. C, Malacosoma americanus, larva, Lepidop- 

 tera with hypostomal lobes. D, Diagram, hypostomal lobes united in a bridge 

 (HB). E, Tabanus snlcijrons, Diptera, bridge narrow. F, Dcromyia discolor, 

 Diptcra, bridge enlarged. G, Calliphora sp., Diptera, bridge still larger. H, 

 Pelicinus sp., diagrammatic, Hymenoptera, bridge limited by the elongate pos- 

 terior tentorial pits. 



(G) it covers the whole ventral part of the head wall. Since the 

 hypostomal sulci (D, hs) are continuous with the postoccipital sulcus 

 {pos), the hypostomal bridge is continuous dorsally with the post- 

 occiput (Poc), and ventrally with the hypostomata. 



