NO. I 



THE INSECT HEAD — SNODGRASS 



17 



these margins are commonly reinforced by submarginal internal ridges 

 formed by a suhgenal sulcus on each side of the head (fig. 6 A, 

 B, sgs) . This sulcus is generally continuous from the epistomal sul- 

 cus in front to the postoccipital sulcus {pos) behind, and sets off a 



Fig. 6. — The common external sulci and defined areas of the adult insect head, 

 diagrammatic except C. 



A, B, The impressed lines, or sulci (generally called "sutures"). C, Anisolabis 

 maritima, Dermaptera, example of ecdysial cleavage line (,CL) retained on 

 adult head. D, E, F, The commonly defined areas of the head. 



Sulci on A, B : cas, circumantennal ; cos, circumocular ; es, epistomal ; mcs, 

 midcranial ; ocs, occipital ; pos, postoccipital ; sgs, subgenal ; sos, subocular; ts, 

 temporal. 



Head areas on D, E, F : Clp, clypeus ; Fr, frons ; Ge, gena ; Lm, labrum ; 

 Oc, occiput ; Poc, postocciput ; sge, subgena ; Vx, vertex. 



Other lettering as on figure 4. 



narrow marginal strip, the subgena (D, E, F, sge), from the main 

 genal area above it. The part of the subgena over the mandible is 

 distinguished as the pleurostoma, and that behind the mandible as the 

 hypostoma. The corresponding parts of the subgenal sulcus are cor- 

 respondingly termed pleurostomal and hypostomal. As will be seen 

 later this distinction is only one of convenience for descriptive pur- 

 poses. In some cases the subgena is obliterated by coincidence of 



