LARVAL HEAD OF SOME CHIRONOMIDAE GOUIN 185 



First of all, there is no premandible. Zavfel, it is true, identifies 

 the premandible with a very short ventral appendage, more or less 

 rodlike, inserted laterally on the labrum and somewhat proximal to 

 the tormal arch. Very strictly speaking we might say that it is situ- 

 ated close to the usual messorial insertion ; but has it the connections, 

 articulations, musculature, and innervation of this organ? The prepa- 

 rations in toto which Zavfel and I have examined do not allow us 

 to answer this question, which can only be solved by studies of the 

 living larva and histology. Whatever it is, this pretormal labral rod 

 has neither the form nor the usual functions of the premandible. 

 Therefore it is impossible to follow the Czech author on this point, 

 for, in order to homologize two organs, they must have a minimum 

 of structure to permit recognition of one connection at least (cf. 

 Gouin, 1955). 



The labral and epipharyngeal chaetae and setae have been very 

 well described by Zavfel. They are remarkable in their numbers, 

 dimensions, and disposition (fig. 6) ; the sensillae labri especially are 

 very long and articulated on very high socles. The centroepipharyn- 

 geal chaetae are strong, curved hooks ; the epipharyngeal comb is 

 represented in L. gracilis by a few rather tenuous bristles, set in 

 lines behind the tormal arch (this feature is rather variable in the 

 different genera, cf. Zavfel) ; there are, besides, numerous tenuous 

 chaetae disposed as in figure 6. This structure is characterized by 

 a clear tendency to multiplication, lengthening, and tenuity of the 

 labral and epipharyngeal hairlike processes ; analogous features are 

 also found on the lacinia. Finally, the multiplication of the mandibular 

 and hypochilan teeth is a new example of the very clear correlations 

 of these organs. 



There is another important fact to be noted: the presence of a 

 rudimentary tentorium. It has its origin on the internal phragma 

 close to the dorsal mandibular articulation and proceeds obliquely 

 nearly to the middle of the ventral wall where it ends, freely as it 

 seems, near an oval superficial scar. The antennal socles are also 

 supported by a parallelopipedic skeleton, and the whole preclypeal 

 area is uniformly sclerotized. This tentorial arm recalls the Ceratopo- 

 gonidae larval one (Gouin, 1955) ; the interantennal part might repre- 

 sent the dorsal tentorial arm. 



FUNDAMENTAL CHARACTERISTICS OF THE CHIRONOMIAN, 



ORTHOCLADIAN, AND PODONOMIAN CEPHALIC 



STRUCTURES 



After having studied the larval structures of Chironomus (Gouin, 

 1957) > of the Orthocladiinae and Podonominae, and, before de- 

 scribing the anatomy of Tanypinae, we will recapitulate these three 



