32 JLLISOIS BIOLOGICAL MOSOGRAPIIS [32 



between the occipital foramen and the submentum. Whether the force 

 exerted on the head was directed more towards the cephalization of the 

 submentum or towards the dorsalization of the occipital foramen it would 

 be hard to say. The condition resulting would be in either case approxi- 

 mately the same. For purposes of convenience and simplicity of language, 

 the expression "cephalic migration" is used in this discussion. 



This broad area between the occipital foramen and the submentum 

 is sometimes designated as the gula. Usually, though, the term gula is 

 used to indicate a sclerite, on the meson of the ventral aspect, separated 

 from the remainder of the head-capsule by distinct subparallel sutures, 

 the gular sutures. The term gula cannot satisfactorily be applied to both 

 an indefinite region and a distinct sclerite. The gula is considered in the 

 latter sense in this discussion. For the present the area between the oc- 

 cipital foramen and the submentum will simply be designated as the mesal 

 parts of the postgenae. 



The cephalic end of a postgena is usually modified into a rather flat 

 area sloping towards the meson, upon which is situated a paracoila and a 

 postcoila. This flat area is distinguished from the remainder of the post- 

 gena by a distinct ridge, which usually extends in a deep curve from near 

 the lateral margin of a postcoila to near the caudo-lateral margin of the 

 submentum. Sometimes this ridge is directed towards the occipital fora- 

 men, as in Leptinus (Fig. 165), Cantharis (Fig. 187), Macrosiagon (Fig. 

 197), Isorhipis (Fig. 210), Psephenus (Fig. 213), Helichus (Fig. 214), and 

 others. Attention has already been called to the fact that the cephalic 

 portion of this ridge represents the cephalic end of the occipital suture. 

 This modified part is reduced in size or indistinguishably fused with the 

 remainder of the head, in Photinus (Fig. 183), Eucinetus (Fig. 219), 

 Alobates (Fig. 248), Tenebrio (Fig. 249), Hyporphagus (Fig. 252), most of 

 the Scarabaeoidea, Sphenophorus (Fig. 293), Eupsalis (Fig. 284), and 

 Lixus (Fig. 291). 



There seems to be considerable confusion as to what constitutes the 

 gula. Some investigators consider it as simply the central portion of the 

 ventral surface of the head-capsule. Others restrict it to the distinct 

 sclerite appearing on the meson of the ventral surface of certain insects, 

 including the Coleoptera. Since this sclerite is distinctive and character- 

 istic it needs a name. The term gula is quite satisfactory to apply to it. 

 The origin of the gula also rests in considerable confusion. Comstock and 

 Kochi (1902) consider it the sternum of the cervical segment, and to 

 strengthen their argument they cite the situation in Corydalis, in which 

 they state that the sternellum of the cervical segment is retained back of 

 the gula, and they figure it as the small quadrangular sclerite immediately 

 caudad of the gula. The)- do not mention the very much larger rectangular 

 cervical sclerite caudad of their "sternellum." The larger sclerite is sug- 



