128 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



plate called the " gula." The nature of the gula has long been a 

 puzzle to entomologists, but Crampton (1921, 1928) has given reasons 

 for believing that it is a differentiation of the base of the labium, 

 and a few examples taken from the Coleoptera will amply substanti- 

 ate this view. 



In a scolytid or scarabaeid beetle larva the structure of the head 

 does not differ essentially from that of the grasshopper. The face 

 is directed forward, the mouth parts hang downward, and the under 

 surface of the head is short. In the scarabaeid larva (fig. 49 A) the 

 occipital and postgenal regions terminate in a postoccipital suture 

 ipos), in the ventral ends of which are situated the large invagina- 

 tions (pf, pt) of the posterior arms of the tentorium. Beyond the 

 suture is a narrow postoccipital rim of the cranium (Poc), best de- 

 veloped ventrally, where the lateral cervical sclerites (ci') are articu- 

 lated to it. The postoccipital ridge is developed on each side of the 

 foramen magnum into a broad apodemal plate (PoR), the two plates 

 constricting the foramen laterally, and uniting ventrally in the broad 

 tentorial bridge, which is concealed in the figure by the ventral part 

 of the neck membrane (NMb). The labium, the maxillae, and the 

 mandibles of the scarabaeid larva are suspended from the ventral 

 edges of the cranium exactly as in the grasshopper (fig. 36 C), but 

 the two forms differ by the elongation in the beetle (fig. 49 A) of the 

 postgenal margins of the head between the articulations of the car- 

 dines (e) and the posterior articulations of the mandibles (a). 



The basal part of the submental region of the labium in the scara- 

 baeid larva, Popillia japonica (fig. 49 A), is chitinized to form a 

 triangular plate (Smt). This plate is attached to the mesal points of 

 the postgenae (Pge), and has its extreme basal angles prolonged be- 

 hind the tentorial pits to points (/, /) corresponding with the basal 

 articulations of the submentum with the postocciput in an orthopteron 

 (fig. 36 C, /). There can be no doubt that this; plate in the beetle head 

 is the submentum, or a chitinized basal part of the submentum. It is 

 marked by a transverse groove between the tentorial pits ( pt, pf). 



In a silphid larva (fig. 49 B) the general structure of the head is 

 similar to that in the scarabaeid larva, but the ventral postgenal mar- 

 gins between the articulations of the cardines (c, c) and the mandibles 

 (a) are much longer, and the posterior tentorial pits (pt, pt) are 

 approximated in the mesally prolonged basal angles of the postgenae. 

 The submentum (Smt) is large; its base is narrowly constricted be- 

 tween the tentorial pits, which here almost cut off a small but distinct 

 proximal area (Gu). The lateral angles of this extreme basal area of 

 the submentum are prolonged behind the tentorial pits and become con- 



