9! 

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The labrum-epipharynx (seen in cross-section in fig. I . fi-t, /!-< : from beneath 

 in fig. 1, lr-c) is composed of the labrum, which is a direct continuation of the 

 front walls of the head, and of the epipharynx, which is a direct continuation of 

 the upper chitinous lining of the pharynx. These two parts (fig. 1 , */, Ir and e) 

 are so combined that the upper convex surface of the epipharynx fits into the 

 under concave surface of the labrum, while the edges of the epipharynx are 

 connected to those of the labrum by a less strongly chitinized membrane, 

 whose infolding between the two can be distinctly seen on sections t-i. The 

 enclosed space between the labrum and epipharynx contains longitudinal muscles, 

 tracheae, and connective tissue. The muscles are at each side of the tube of the 

 epipharynx, and are represented in cross-section on fig. 1, >]-i. Below the muscles 

 on each side, near the fold between the labrum and epipharynx, is a tracheal 

 stem, seen in cross-section in sections -x. The combined labrum-epipharynx 

 tapers from base to tip, is shorter than the hypopharynx and labium, but longer 

 than the maxillae. Of its two component parts the labrum undergoes much 

 more change in form, from base to tip, than does the epipharynx. The epi- 

 pharynx forms a channel, open along the under side by a narrow slit; this slit 

 widens as it approaches the tip, and bears on its two sides hairs, pointing 

 inward and backward, to prevent the return of food (See fig. 1, lr-e); for it is' 

 through the epipharynx, as in all diptera which I have studied, that the food passes. 

 At its basis the labrum-epipharynx, by a sprt of reflexion of its margins, forms 

 chitin-plates, which serve to support it in the forward part of the head (see fig. 

 1, A'), and to contain the pharyngeal muscles (fig. 1, /.', ^m and fig. 3, pin), which 

 elevate the upper elastic wall of the pharynx, in the action of sucking. As will 

 be seen later, in the portion of this paper which I devote to the comparison of 

 the parts of the different species studied, this reflexed wall of the pharynx is 

 the homolog of the greater part of the so-called fulcrum of the Mmcidae. 



The hypopharynx of Bombylius is a flexible tube of thin chitinous membrane, 

 containing within itself a more rigid chitinous tube, which opens on the upper 

 side near the extremity of the hj^popharynx. The tip of the latter is thus of 

 the form of a pen, with its concave side upward. (See fig. J, A.) The inner 

 tube of the hypopharynx is continuous at its base with the salivary duct; the 

 outer flexible tube only serves to make the hypopharynx fit more closely to the 

 form of the surrounding mouth-parts. The upper surface of the hypopharynx is 

 naked ; its lower surface hairy. Its section (fig. I , >] and #, h) is variable in 

 form on account of the flexibility of its outer tube. Just before it reaches the 

 mouth, that is just before it unites with the epipharynx to form the mouth, the 

 hypopharynx joins, on each side, with folds from the united maxillae and maxillary 



