20 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



it. He thus assumes that these muscles are the retractors of the pre- 

 mentum. The premental retractors, when present, do arise on the 

 submentum, but they are always median in position. The muscles of 

 the mosquito larval labium are lateral muscles, and therefore should 



(J SIDcfc 



Hstm 



A 



FrCon 

 ^ Kb Hphy 



Anfc 



Hstm Hphy 



Hstm 



Fig. 7. — Labiohypopharyngeal complex of larvae, and associated structures. 



A, Tipula sp., section of larval head. B, Culex sp., posterior part of head, 

 anterior. C, Toxorhynchites rutilus, labiohypopharyngeal complex, dorsal. D, 

 Aedes aegypti, same, anterior. E, Culex sp., same, anterior 



a, posterior articulation of mandible ; Ant, antenna ; c, anterior articulation 

 of mandible ; Cb, cibarium ; Clp, clypeus ; dlcb, dilator muscles of cibarium ; 

 Fr, frons ; FrCon, brain connective of frontal ganglion ; FrGng, frontal ganglion ; 

 Jib, hypopharyngeal bar; Hphy, hypopharynx; Hstm, hypostomium ; Lb, labium; 

 Ibmcl, muscle of labium ; Ibrmcl, labral muscle ; Lm, labrum ; Md, mandible ; 

 Mth, mouth ; Mx, maxilla ; phmcls, pharyngeal muscles ; RNv, recurrent nerve ; 

 SIDct, salivary duct; Stom, stomodaeum. 



be one pair of the usual two pairs of cranial muscles of the prementum, 

 which in other insects commonly arise on the tentorium. The same 

 muscles in the tipulid larva (fig. 7 A, Ibmcl) certainly have their 

 origins on the head wall, since there is no sclerotization between the 

 postgenae (fig. 3 B). The labial muscles of the mosquito larva, there- 



