- 42 







not further describe it, in other diptera than Musca. Menzbier 8 writes (p. 64) 

 of the fulcrum, without attempting further to homologize it, that, " it is chitinized 

 processes of the walls of the throat." * It is probably the fact that the fulcrum 

 is only a modified form of chitinization of the walls of the pharynx, which are 

 turned upward at the sides, and fastened, more or less firmly, to the under side 

 of the clypeus; in cases where independent motion of the entire pharynx takes 

 place in the extension and retraction of the proboscis, the lateral upward con- 

 tinuations of the pharyngeal walls may unite again above, to a greater or less extent, 

 so as to form a cylinder for the firm attachment above of the pharyngeal muscles, 

 which thus act with equal ease to whatever extent the proboscis may be withdrawn 

 or stretched out. The whole plan of structure of an independently movable fulcrum 

 is well shown in the section of the fulcrum of Musca figured on pi. 4, fig. 4. 

 The fulcrum is, then, an internal skeletal piece, the chitinized expanded portion 

 of the walls of the pharynx, and not a mouth-part in the strict sense of the 

 term. The reason will now be more apparent, why, in an earlier part of this 

 paper (p. 26), I objected to laying too much stress on the division of the 

 proboscis into basal, middle, and terminal portions. While applying the term 

 proboscis, in its ordinary sense, to the whole organ, I agree with Macloskie that 

 the so-called middle portion of the proboscis is the true basal segment of the 

 fly's proboscis. I may, perhaps, add, at this point, that my reasons for using 

 the somewhat clumsy term labrum-epipharynx, in place of the name operculurn, 

 applied by Lowne to the same part in Musca, are that, first, the name operculurn 

 is inappropiate in some diptera, and that, secondly, the name labrum-epipharynx 

 saves all confusion of parts by indicating, at first sight, what mouth-parts are 

 meant. 



If one considers, in order, the different mouth-parts of diptera, they are as 

 follows : 



The labrum-epipharynx is composed of the labrum above and the epipharynx 

 beneath, united at their margins by a delicate membrane, which is often infolded 

 (Bombylius). The labrum and epipharynx may be separable in caustic potash 

 (Mused) or inseparable (Empis according to Menzbier). The epipharynx may be 

 absent, according to Menzbier (Sargus). At its base the labrum-epipharynx may 

 be united to the apical end of the fulcrum by a true joint (Musca), or without 

 joint (Culex); the labrum is always continuous with the clypeus at the' base, the 

 epipharynx always continuous with the upper wall of the pharynx. The labrum- 



* " . .es chitinizirte Fortsatze der Schlundwand siud. 



