NORTH AMERICAN DIPTERA. 



333 



inner side, and the pseudo-trachea are confined to the apical expan- 

 sion. The chitinous fragn)ents have been carried upward, and on 

 them the tracheate system rests. The structure of the palpi does not 

 differ very essentially from Strati omyia, as can be seen by a com- 

 parison of figures. Here, however, there is developed a sensory pit 

 in the palpus, and the palpifer is still further reduced. Perhaps it 

 may be in order to state that the apparent segmentation of the galea, 

 on the right of the figure, is really a fracture, and that the left side 

 illustrates the perfect condition. The labium is shown at a. There 

 is a broad, large, basal mentum, reminding of the Tabanidae, to which 

 the ligula and paraglossse, closely united, are attached. The lacinia, 

 not articulated to the mentum, but almost completely enveloping the 

 labium, is shown slightly separated from it. 



This is also one of the species in which the proboscis is not hinged. 

 The fulcrum does not show in my specimens, and I made no effort to 

 seek it, as I was not studying its development. The jiresence of the 

 distinct mentum would, however, indicate the absence of this organ. 

 Next comes Tipula sp., a form in which the maxillary palpi are 

 well developed. No effort was made to study any but the galear 



structure, though several 

 species were examined, as 

 nothing of special interest 

 was obvious. The galea is 

 here, in some respects, most 

 perfect. The chitinous 

 parts are flattened, and, 

 with the exception of the 

 terminal cap, are entirely 

 within the membraneous 

 envelope. The character 

 of the structure is best seen at b, figure 15, where the chitinous 

 structure is separated off and figured. The two sides here are 

 entirely separated, the joints are well marked, and a study of this 

 species alone leaves an overpowering conviction of the true homology 

 of the parts, which could not possibly be reconciled by any theory 

 of labial development. Within the sac enclosing this galea, is a 

 series of large trachese, uniting to a few trunks running into the 

 head. There seem to be no true pseudo-trachea, but there is a series 

 of transverse wrinkles covering the inner face. No dissections were 

 made to get at the other structures, since the galea was all I was 

 seeking for here. 



Fig. IS. Mouth parts of Tipulid. 



