LABEUM; HYPOPHAEYXX 39 



that in the male Culex, which does not possess — as does the female — a pumping 

 apparatus behind the oesophageal nerve-ring, these muscles are the ones that 

 must serve for suction. The section represented in fig. 9 was taken near the base 

 of the clypeus ; a few sections further on, posteriorly, the channel for the passage 

 of food turns upward and then backward again, passing in its course a place 

 (fig. 11, v) where its walls approximate dorsally and ventrally. This narrowing 

 of the walls is probably a valve to prevent the return of fluids to the mouth dur- 

 ing the pumping process. The pharynx with its surrounding muscles in Culex 

 is the equivalent of what has been termed the fulcrum in Musca. Macloskie * 

 Avrites of the fulcrum, ' It seems to be general in diptera ; even the mosquito 

 possesses it,' but he does not further describe it, in other diptera than Musca. 



"The tip of the labrum-epipharynx seems to turn upward (fig. 1, Ir-e), al- 

 though the opening is upon the ventral surface, as may be seen in fig. 6, b, which 

 represents the ventral view of the tip of this part. The tip of the labrum-epi- 

 pharynx is comparable to a quill-pen with three tips near each other, the middle 

 one of these three tips being slightly shorter than the other two. The two lateral 

 portions of the epipharynx, as seen in section, when they near the tip, lay them- 

 selves closely upon the sides of the tubular portion, passing upward upon it, as 

 seen in fig. 5, Ir-e; they thus serve to strengthen the two outer points of the tip 

 of the epipharynx, while the labrum continues to a sharp point at the tip, and, 

 united with the upper surface of the epipharynx tube, forms the middle point of 

 the tip. The channel, or slit, along the under side of the epipharynx, widens 

 toward the tip (fig. 6, 6), leaving thus an opening for the passage of fluids into 

 the tube of the epipharynx. 



" The labrum itself is a thin lanceolate lamella of chitin, concave along the 

 under side from the basal portion to the tip, and its conca^dty rests upon and 

 fits to the convexity of the tubular part of the epipharynx, to which it is so 

 lightly attached that they readily separate by application of caustic potash. The 

 outer edges of the labrum roll slightly inward toward the epipharynx along most 

 of its length. (See fig. 6, d.) At its base the labrum sends a chitinous support 

 beneath the clypeus, where it separates more from the epipharynx and has its 

 own muscles, indicating that the labrum has a degree of motion independent 

 of the epipharynx, a motion allowed, perhaps, by the elasticity of the connection 

 between the labrum and epipharynx. The muscles of the labrum (fig. 9, pm') 

 are inserted upon the upper side of its base and have their origin on the inner 

 surface of the roof of the clypeus. These muscles are, at least in the females of 

 Culex rufus, divided into three portions in their upper part, as shown in fig. 9. 



" The hypopharynx of the female of Culex is a linear, lanceolate, transparent 

 lamella of chitin, with a longitiudinal rod through the middle, the nature of 

 which will be discussed later. At its base the hypopharynx forms the continua- 

 tion of the under wall of the pharynx. (See fig. 11, h.) The hypopharynx is 

 closely pressed upon the under side of the epipharynx, completing the tube 

 nearly formed by the epipharynx. No muscles have their insertion on the base 

 of the hypopharynx. Its tip is simply lanceolate (fig. 5, li). In Culex pipiens 

 and C. rufus nothing further is visible (with a magnifying power of five hundred 

 diameters), in sections of the thicker middle portion of the hypopharynx, than 

 a simple rod of chitin ; but, in C. ciliatus, a North American species of which the 

 mouth-parts are larger, this rod appeared to be tubular. Is it a rod or is it a 

 tube? Menzbier f writes (p. 25) that in diptera 'neither the labrum nor the 

 hypopharynx possesses a completed tube, but only a channel ' which leads into 



• Macloskie, G. : The proboscis of the housefly. (Amer. Naturalist, March, 1880, v. 14, pp. 

 153-161, figs. 1-3.) 



t Menzbier, M. A. Ueber das Kopfskelet und die Mundwerkzeuge der Zweifliigler. (Bull. Soc. 

 lmp€r. natur. de Moscou, 1880, t. 55, no. 1, pp. 8-71, tabs. 2-3.) 



