NO. 



THE INSECT CRANIUM — SNODGRASS 



II 



The frontal ganglion, therefore, always marks the dividing line 

 between the under surface of the preoral clypeus and the postoral part 



-,-OpL 

 P-..>iK''D RNv 



Stom 



FrGng; 

 IbrNv 



pt FrGng- Gng-I Gng^l Gngill Gng-l V 



Fig. 2. — Diagrams showing the relation of the facial muscles to the frontal 

 ganglion in the definitive structure, and in a theoretically primitive state. 



A, definitive structure of the head nervous system; first postoral ventral 

 ganglia (B, GngI) have become tritocerebral lobes of brain (T), the three 

 following ganglia united in the suboesophageal ganglion. B, primitive relations 

 of the same parts: the definitive tritocerebral ganglia {GngI) are postoral, the 

 frontal ganglion (FrGng) is a preoral ganglion of the ventral nerve cord. 

 C, theoretical facial musculature with primitive nervous system as at B. D, the 

 same muscles as at C, with definitive nervous system as at A. 



AntNv, antennal nerve ; Br, brain ; Cb, cibarium ; Clp, clypeus ; cprclp, com- 

 pressor muscles of clypeus, prospective dilators of cibarium ; D, deutocerebrum ; 

 dlcb, dilators of cibarium (compressors of clypeus) ; dlphy, dilator muscles of 

 phar3mx ; fm, food passage ; Fr, frons ; FrGng, frontal ganglion ; GngI, ganglia 

 of first postoral somite (definitive tritocerebral lobes of brain) ; Gngll, III, 

 IV, ganglia of second, third, and fourth postoral somites ; hphmcl, frontal 

 muscle of hypopharynx (same as C, rao) ; Hphy, hypopharynx; HS, hypo- 

 pharyngeal suspensorium ; I -IV, first four postoral somites; Ibrmcls, labral 

 muscles ; IbrNv, labral nerve ; Lm, labrum ; Mth, mouth ; OpL, optic lobe ; P, 

 protocerebrum ; rao, retractor muscle of mouth angle, frontal muscle of hypo- 

 pharynx (D, hphmcl); RNv, recurrent nerve; SoeGng, suboesophageal gan- 

 glion ; Stom, stomodaeum ; T, tritocerebrum ; y, oral arm of hypopharyrigeal 

 suspensorium. 



of the head (fig. 2 D), and it maintains its primitive oral association 

 regardless of whatever position the mouth may take by invagination 

 within the head. 



