LARVAL HEAD OF SOME CHIRONOMIDAE — GOUIN 



191 



What Zavfel calls "Hypopharyngealgeriist" is principally a sclero- 

 tized ring surrounding the complex and supported by the prementum 

 (fig. 8) ; the dorsal (hypopharyngeal) arch is fringed with steellike 

 teeth. 



.MTo 



J3gl Fr 

 .Ph 

 'MTo 



-M Ph dia 



MPh 



Sp*Prm 

 PIMx 



01 Lab 



CS Mrao MSLo MPhl 

 Fig. 9. — Macropelopta cf. ncbulosa Mg. 



^-MabMd 



\i 1 1 1 1 1 1 1 1 1 1 1 



Part of a cross section situated on the level of the frontal ganglion, the origins 

 of the internal tormal fiber groups {MTo) and distally from the glossal teeth. 

 A double membrane separates the antennal muscle and imaginal disc from the 

 set of the pharyngeal muscles ; the cavity included by that double membrane 

 widens toward the front into a broad cleft communicating with the pharynx 

 and embracing the antennae. The external tormal muscle origins are situated 

 a few sections farther back laterally on the cranium; the two fiber groups are 

 inserted forward on the membrane itself, constituting the roof of the preoral 

 cavity; there is here no sclerotized differentiation. The blood, very abundant, 

 is not figured. 



The musculature of these organs comprises only two muscles, of 

 which one is not found in the generalized orthocladian structure 

 (figs. 9, 10) ; they are: (i) the true labial or premental muscle 

 {M Prm), the mi of figure 18 of Zavfel; (2) the retractor angu- 

 lorum oris {Mrao), opposite to the premental muscle, directed 

 dorsally, posteriorly, and diagonally. Zavfel designates it by wj 

 (fig. 18) and mh (fig. 47). Its tendon is inserted on the basis of 

 the toothed fringe of the dorsal hypopharyngeal arch ; this muscle, 

 which bifurcates into two powerful fiber groups surrounding the 

 antennal muscle, takes its origin on the posterior part of the cranium. 



