LARVAL HEAD OF SOME CHIRONOMIDAE — GOUIN 1 99 



ment of this appendage is likewise related to the reduced hypochilum. 

 In the Tanypinae (p. 189) of which the hypochilum is membranous 

 and relatively narrow, the maxillae are very much developed ; and 

 there would be numerous other examples. 



As to the labiohypopharyngeal complex, it shows relationships 

 with the hypochilum that may be compared with those of the maxilla ; 

 therefore, we find again a parallel progression. In the forms nearer 

 to the fundamental structure studied by Anthon, the labium and 

 hypopharynx (passing the labium forward) are well constituted and 

 abundantly furnished with setae, chaetae, and other various cuticular 

 processes ; they then have complex and important functions. 



Moreover, the formation of a sclerotized hypochilum goes with 

 the structural and functional reduction of the labium and hypo- 

 pharynx. Philosepedon (Anthon) shows again an intermediate point 

 of this progression, in which reduction reaches its highest degree in 

 the other Nematocera: Culicidae (Schremmer), Simuliidae (Gre- 

 nier) ; Ceratopogonidae (Lawson; Gouin, 1955a), Chironomidae, and 

 others. In the last named, the Tanypinae (cf. supra, p. 189) in a way 

 furnish the proof a contrario : the hypochilum is rather reduced and 

 membranous, the labiohypopharyngeal complex is more developed 

 than in the other Chironomidae. 



There are therefore assured and precise relationships between the 

 hypochilum on one side and the maxilla and the labiohypopharyngeal 

 complex on the other; the development of the former is in a way 

 contrary to the latter. 



It has been possible only to sketch the correlations between the 

 gnathal appendages and the conformation of the anterior ventral 

 cranial wall. In fact, only an exhaustive morphological study will let 

 us draw our conclusions with certainty. It is clear, after the preceding 

 report, that for such a study the morphology, as Snodgrass claims, 

 "must be intimate with function." 



ABBREVIATIONS USED ON THE FIGURES 



A, antenna ; antennal. Co, connective. 



ad Md, dorsal mandibular articulation. CS, salivary duct or pump. 



arc d, dorsal arch of the hypopharyn- DJA, antennal imaginal disc. 



geal skeleton. DJLab, labial imaginal disc. 



av Md, ventral mandibular articulation. DJMx, maxillary imaginal disc. 



ch, labral "chaeta" (Zavfel). Ep, epithelium. 



ch b, posterior centroepipharyngeal Ggl fr, frontal ganglion. 



chaeta ("chaetula basalis," Zavfel). Hch, hypochilum. 



ch I, lateral centroepipharyngeal chaeta HPh, hypopharynx. 



("chaetula lateralis," Zavfel). /, intima. 



