NO. I 



THE INSECT HEAD SNODGRASS 



25 



Fig. II. — Formation of a postgenal bridge between the occipital foramen and 



the labium. 



A, Postgenal lobes (PgL) encroaching on the hypostomal bridge (HB), 

 diagrammatic. B, Apis mellifera. C, Vespula macitlata, postgenal lobes united 

 in a bridge (PgB). D, Postgenal bridge lengthened, diagrammatic. E, Pristo- 

 cera armifera, Hymenoptera. F, Olbiogaster sp., a primitive dipterous larva 

 with postgenital lobes not united (outline from Anthon, 1943). G, Chirononnis 

 plumosus, larva, Diptera, postgenal suture («u) partly suppressed. H, Noto- 

 necta variabilis, Homontera, postgenal bridge entire. I, Naucoris cimicoidcs, 

 Homoptera. 



almost (C) or entirely (D) suppressing the submentum (Smt) be- 

 tween them. In this case the head has been lengthened in both di- 

 rections relative to the pits. 



Finally, we may start again with a fairly generalized head struc- 



