1.S 



in the base of the head and serve to control the motions of the lahium. (See 

 figs. 8 and 9, ml.) At the sides of the tip of the labium are attached two 

 lobiform appendages, the labellae, which are seen at II in fig. 3 with the true 

 tip of the labium proper between them. These terminal lobes are jointed to the 

 labium, a little distance behind its tip, as can be seen in fig. 7, which is a 

 cross-section of the labium a trifle anterior to the actual centre of motion of 

 these joints. The section of that portion of the labium which extends forward to 

 form its tip is seen in the middle of the figure, just below the section of the 

 maxillae (<,/). Outside the section of each lobe is seen the section of the exterior 

 edge of the labium itself, which here forms a double socket, or pair of acetabula, 

 into which the heads of the two labellae are set. The reason why this exterior 

 edge of the labium does not appear, in the section, as entirely surrounding the 

 sections of the labellae, is that the labium extends forward further on the dorsal 

 and ventral sides than at other points. Each of the lobes of the labium, 

 the labellae, is provided with an extensor and flexor muscle. (See fig. 7, me., 

 and mf.) The extensor muscles (me) are toward the outer side of the cavity of 

 each lobe, and serve, when simultaneously contracted, to separate the tips of the 

 labellae ; the flexors (mf) are upon the inner sides of the cavity of each lobe, 

 and serve to approximate the tips of the labellae. Near each flexor is -to be seen 

 (fig. 7) the section of the thickening of the chitin-walls, which, continued as a 

 chitinous rod, extends a distance back into the labium, and serves as attachment 

 for the flexor. In Cidex, then, the labellae are attached to the labium by true joints. 

 The labium has for function, for the most part, the protection of the fine 

 setae which form the true piercing organ of Cnles. In the females of Cidex 

 proper, the protective sheath is formed by the labium alone. When the mosquito 

 has found a place which suits its taste for piercing for it often tries different 

 places on our skin with its labellae, probing right and left, before finding a 

 place where it decides to remain. - it plants its labellae firmly upon the spot, 

 and a moment later the labium is seen to be flexing backward in its middle, the 

 setae, firmly grouped together, remain straight and enter the skin, while the two 

 labellae guide them, much as a carpenter guides his bit with his fingers, while 

 boring a piece of plank. When the setae of Culex have entered the skin to 

 nearly their full length the labium is bent double beneath the body of the insect, 

 the labellae still holding the base of the setae at the point where they enter the 

 skin. When the mosquito wishes to withdraw the setae it probably first with- 

 draws the two barbed maxillae beyond the other setae, that is, so that their 

 barbs, or papillae, will be kept out of action by the mandibles and hypopharynx; 

 then it readily withdraws the setae, perhaps aiding their withdrawal by the 



