52 ILLINOIS BIOLOGICAL MONOGRAPHS [222 



under the heading labrum. The epipharynx in a number of generalized 

 Diptera, such as Tabanus (Pig. 494), Simulium (Fig. 497), Dixa (Fig. 

 501), Limnobia (Fig. 507), and Sciara (Fig. 513), resembles the hypo- 

 thetical type. In the majority of the Diptera it differs from the hypo- 

 thetical type in that it is completely separated from the basipharynx 

 by a constriction or a secondary suture. This hinge in the epipharynx 

 permits the proboscis to bend at this point when it is withdrawn into 

 the oral cavity. The lance-like portion of the epipharynx in the Calyp- 

 tratae and some other forms is completely separated from the basiphar- 

 ynx by the development of a special piece which is commonly called 

 the hyoid (hy). The lance-like portion of the hypopharynx also articu- 

 lates against the hyoid. The hyoid is a secondary sclerite which origi- 

 nated from the epipharynx or the hypopharynx and serves the purpose 

 of keeping open the alimentary canal, which passes thru it. A structure 

 similar to the hyoid of Musca (Fig. 600) is found in Stomoxys (Fig. 

 599), where a large and strong trachea-like tube extends between the 

 dorsal ends of the lance-like portions of the epipharynx, the hypophar- 

 ynx, and the basipharynx. 



In size and shape the epipharynx agrees more or less closely with 

 the labrum. The epipharynx in sucking Diptera is, as a rule, long and 

 needle-like, while in other forms it is usually short and blunt. In many 

 genera of the Acalyptratae it has a secondary transverse suture near its 

 distal end, as shown in Sepsis (Fig. 583) and Eristalis (Fig. 588). 



A few genera show special modifications of the epipharynx. This 

 is particularly true of Dolichopus (Fig. 524 and 528). In this genus 

 the epipharynx closely resembles the hypothetical type in the presence 

 of a distinct membrane between the labrum (1) and the epipharynx 

 (ep). The specialization of the epipharynx consists in the bifurcation 

 of its distal end and in the presence of a long club-shaped piece which 

 projects from its meson dorsad into the cavity formed by the basiphar- 

 ynx, the tormae, and the fronto-clypeus. These modifications are 

 peculiar to species of the Dolichopodidae. The bifurcations at the distal 

 end are of particular interest, since they have been interpreted as man- 

 dibles by Langhoffer (1888). They are much longer in some of the 

 genera of the family than in others. The lateral and caudal views of 

 the epipharynx and the hypopharynx of Dolichopus show clearly the 

 relation these projections have to the other parts, and justify the inter- 

 pretation here given. 



The single, median, distal, lance-like portion of the hj'popharynx 

 is present in all but a few of the genera studied. The cephalic portion 

 of the labium usually connects with the lance-like portion of the hy- 

 popharynx just ventrad of the point of entrance of the salivary duct. 



