OK THE MOUTH I'AUTS OF ( KlilAIX IXSKCTS. 195 



has written, see any reason why the rudimentary striietures at tlie tip of the lal)ral 

 extension in Simuliwit ai'c not mandibles. 



If we refer back again for an instant to tlie Panorj)ids we note (PI. Ill, Fig. 4") 

 that in Bittacus sln(josiis the origin of tlic mandibles form an extension of a lateral 

 head sclerite, with the labrnm-epipharynx between them. In I'uaorpa the mouth 

 structures are much shorter, set on an immensely elongated stipes, and at the tip of 

 the frontal extension of the head we again have the mandibles, much reduced, with a 

 small, lai)pet-like labrum-e[)i[)haryn\ between them. Now the situation of the rudi- 

 ments in Simuliurn corresponds almost exactly with that of the undoubted mandil)les 

 in I'anorpd rufescens (PL III, Fig. 4'); but in the Umpidre we find a yet more closely 

 allied structure. I have already called attention to the peculiar elongation of the Iront 

 of the head in this family, and now if we examine this at tip, in Einpis spectahilis 

 (PL II, Fig. 13') its very close resemblance to I'anoipa is at once evident. We fnid 

 a central lappet-likc; structure with a sensitive surface, which looks like and logically 

 should be the epi[)harynx, and moving below it is a pair of appendages which, in my 

 opinion, represent mandiljles. They are membranous and probably not functional; but 

 this is no argument against their charactci'. I believe that the similarity in the appear- 

 ance between PL III, Fig. 4', and PL II, Fig. 13", is the expression of a true homol- 

 ogy, and that mandibles in the Dii)tera exist in no other form or situation. It is likely 

 that other species, showing them much more perfectly, will yet be discovered ; but so 

 indeed do I believe that labial palpi, pioperly connected with the mentum, will yet be 

 found, so distinct in chai'aeter that, even if not functional, thuir homology cannot be 

 mistaken. 



Labrum and epipiiaiynx have l)een freipiently referretl to in the courst' of this 

 paper, and in the introduction tlie general relation of these two parts has been ex- 

 plained. Both structures occur in many families of the Diptera. As in the case of 

 the hypo[)harynx, the epipharynx lias always connected with it a salivary duct. In its 

 intimate connection with the lahrum it is shown on PL I. Fig. 10', illustrating the 

 epipharynx of Libelhila. Here the chitinous tube giving passage to the duct is fully 

 shown. As an exanii)le of a highly developed structure, the eiiipharynx of '' 'oitris 

 Carolina is shown (PL I, Fig. 4), and here the salivary duet opens among the dense 

 central mass of spinous processes. The epipharynx of I'olistes w^as relerrcd to in the 

 description ot the labium, as w^as that of ^n(//'e»a in the connection. In the liemip- 

 tera the labrum and epipharynx are usually well developed and the salivary duct is in 

 many cases very well marked. 



Among the Diptera some of the lai-gir S)/i/ /ihln have the labium cpiite distinct, 

 and on the under surface is a sensitive surface into which an obvious duct, with chit- 



