T30 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



The extension of the ventral surface of the cranial wall accommodates 

 the head to its horizontal position, and has involved a great elongation 

 in that part of the submentum which lies between the posterior ten- 

 torial pits {pt, pt) and extends forward to the articulations of the 

 cardines {e, c). This region of the submentum is known as the gula. 

 In Epicauta (fig. 49 C) the tentorial pits lie at about the middle of the 

 lateral margins of the gula, and the ventral ends of the postoccipital 

 suture {pos) are, consequently, turned anteriorly and lengthened in 

 the same direction behind the pits. The ventral parts of the post- 

 occipital suture, terminating in the tentorial pits, now become the so- 

 called " gular sutures." It is evident that the large gular region in the 

 adult meloid head (fig. 49 C) lying posterior to the tentorial pits 

 and continuous basally with the postoccipital rim of the cranium 

 (Poc) is produced from the small but corresponding area in the larval 

 silphid head (B, Gu) , and that this area, in turn, is merely the basal 

 strip of the submentum in the scarabaeid larva (A, Sint), attached to 

 the postocciput by its lateral extremities (/, /). 



In adult Coleoptera the distal end of the gula may be dififerentiated 

 as a " pregula " or " gular bar " (C, Pgu). It supports the terminal 

 part of the original submental plate (Suit), which lies between the 

 bases of the maxillae, and which, in a restricted sense, is usually called 

 " the submentum " by coleopterists. The pregular region may fuse 

 laterally with the " hypostomal " regions of the postgenae, and in 

 other ways the more primitive structure may become so obscured that 

 the relations of the parts are difficult to determine except by studying 

 them in a gradient series of simpler forms. The comparative studies 

 made by Crampton (1921, 1928) on the gula in various orders show 

 fully its numerous variations, and demonstrate its origin from the 

 proximal part of the primitive submental plate. Stickney (1923) also 

 has well illustrated the structure of the gula and associated parts in 

 a large number of coleopteran forms. Stickney fails to recognize, 

 however, that the " gular sutures " are direct continuations of the 

 ventral ends of the postoccipital suture, and that, therefore, the gular 

 plate between them must be the basal part of the submentum. He 

 would explain the gular bridge in the Coleoptera as a product of the 

 ventral fusion of the edges of the postgenae, and the gular sclerite 

 as a plate cut out of this newly-formed region by the anterior exten- 

 sion of the " gular sutures." As we have seen, the ventral bridge of 

 the cranial walls is formed in this manner in the Hymenoptera (fig. 

 48), as Stickney has pointed out, but in the Hymenoptera the ten- 

 torial pits have remained at the sides of the foramen magnum, and 

 the labium has lost its original connection with the postoccipital region. 



