198 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



(e.g., Chironomus, Cricotopus, Lasiodiamesa, and numerous others). 

 On the contrary, the species with a "bisegmented" mandible have no 

 hypochikim ; and there is a very clear progression in these primitive 

 forms, which Anthon describes. Thus the hypochilum is absent and 

 the mandible is "segmented" in Trichocera, Mycetohia, and Rhyphus, 

 while Ptychoptera shows only an immovable mandibular lobe corre- 

 sponding to the incisor part, and its hypochilum is only imperfectly 

 formed. The third example of this progression, Philosepedon, has 

 the mandible unsegmented and the hypochilum developed. 



The writer's indications are too summary to warrant a precise 

 statement about these correlations. But the relationships between 

 the mandibular functions, the axis of rotation, and the absence or 

 presence and structure of the hypochilum are too striking not to be 

 emphasized. 



These relationships might be summed up thus : The mandible is 

 only "bisegmented" in the forms where it moves in an oblique plane 

 and in which the hypochilum is absent. It is unsegmented when it 

 is opposed to a sclerotized hypochilum or also when it moves in a 

 horizontal plane, the two mandibles being opposite to each other ; in 

 this case, the hypochilum is often membranous. 



THE RELATIONSHIPS OF THE MAXILLA, THE LABIUM, AND THE 

 HYPOPHARYNX WITH THE HYPOCHILUM 



Between the maxilla and the hypochilum this "balancing" of the 

 organs is again to be noted. Generally in the Nematocera, the maxilla 

 is strongly reduced as compared with the orthopteran structure, and 

 includes only the following elements, which are not always differen- 

 tiated : The cardo with two bristles ; the palpigerous stipes identified 

 by the muscular insertions, besides being endowed with two seta! 

 and other cuticular processes ; the lacinial lobe furnished with an 

 extremely variable and differentiated armature ; a very reduced 

 skeleton. But the Mycetophilidae (Madwar) present a striking struc- 

 ture of the maxilla which in some types takes a mandibular form 

 and functions. 



The cellular and noncellular processes on the maxilla of the primi- 

 tive groups such as Trichocera, Mycetohia, and Rhyphus (Anthon) 

 are extremely abundant and various, evident signs of important 

 functions. In these forms, as we have already pointed out, the hypo- 

 chilum is absent, and the genus Philosepedon here again presents an 

 intermediate character, which has already been seen in the structure 

 of the mandible. In the Mycetophilidae (Madwar, 1937), the develop- 



